From prismx@scienceweek.com Sat Oct 14 22:40:12 2000 Date: Sat, 14 Oct 2000 02:25:34 -0600 From: Science-Week To: prismx@scienceweek.com Subject: SCIENCE-WEEK October 13, 2000 -------------- Enclosure number 1 ---------------- SCIENCE-WEEK A Weekly Email Digest of the News of Science A journal devoted to the improvement of communication between the scientific disciplines, and between scientists, science educators, and science policy-makers. October 13, 2000 -- Vol. 4 Number 41 ----------------------------------------------- Experimenters are the shocktroops of science. -- Max Planck (1858-1947) ----------------------------------------------- Please Note: Beginning with the issue of 13 October, ScienceWeek will be transmitted on Saturdays, the day following the date of the issue. ----------------------------------------------- =-=-=-=-=-=-=-=-= Section 1 =-=-=-=-=-=-=-=-= Contents of this Issue (Full reports in Section 2): 1. NEUROBIOLOGY: DIFFERENTIATED NEUROGLIAL CELLS REPROGRAMMED TO BECOME MULTI- POTENTIAL CNS STEM CELLS Exposure to certain factors in culture causes oligodendrocyte precursor cells to revert to a state that resembles that of multipotential central nervous system stem cells: the reverted cells can self-renew and give rise to neurons and astrocytes, as well as to oligodendrocytes. The authors suggest these unexpected findings indicate that extracellular signals can reverse glial cell specification and can convert specified precursor cells into multipotential stem cells. If methods can be found to reprogram adult mammalian and human tissue cells into multipotential stem cells, the ramifications in research in developmental and cell biology will be profound. (Science 8 Sep 00 289:1754) 2. EPIDEMIOLOGY: ON THE GLOBAL SPREAD OF MALARIA IN A FUTURE WARMER WORLD Since malaria is a serious disease common in tropical and semi- tropical regions, with annual deaths in excess of 1 million people, mostly among children, there is concern that one of the consequences of near-future global warming will be a substantially increased incidence of malaria in regions now free of the disease. A new quantitative model of malaria epidemiology contradicts prevailing forecasts of global malaria expansion, with model malaria distributions exhibiting remarkably few changes from the present distribution, even under the most extreme scenarios. (Science 8 Sep 00 289:1763) 3. MEDICAL BIOLOGY: ON THE GENOMICS OF THE CHOLERA PATHOGEN Cholera continues to be a scourge throughout much of the world, with 7 global epidemics ("pandemics") recorded since 1817. In 1991, for the first time in 100 years, cholera arrived in the Western Hemisphere from its focal center in Asia. Cases were first reported in Peru, and epidemics throughout South and Central America rapidly followed. The recent completion of the genome sequence of the bacterium Vibrio cholerae reveals that slightly more than 50 percent of the organism's apparent genes encode proteins homologous to proteins of known function; the remainder encode proteins without ascribed functions or that are not homologous to any known protein. (Science 1 Sep 00 289:1486) 4. BIOPHYSICS: MEASUREMENT OF THE CRAWLING FORCE GENERATED BY AMOEBOID CELLS An analysis of the crawling force generated by social amoeba undergoing amoeboid locomotion indicates that the inability of the amoeba to maintain directional locomotion against a centrifugal field depends on the very high local density of its leading pseudopod rather than on the apparent weight felt by the whole amoeba. The authors postulate that the directional locomotion of an amoeboid cell requires the contractile cortical framework to provide the turgidity needed for the leading pseudopod to direct the locomotion in that direction. (Proc. Natl. Acad. Sci. US 29 Aug 00 97:10020) 5. CHEMISTRY: SYNTHESIS OF THE SMALLEST FULLERENE In general, fullerene graphite cage structures incorporate exactly 12 pentagons, and the smallest possible fullerene is thus C(sub20), which consists solely of pentagons. But the extreme curvature and reactivity of this structure have led to doubts about its existence and stability. Researchers now report a demonstration that the cage-structured fullerene C(sub20) can be produced from its perhydrogenated form [dodecahedrane C(sub20)H(sub20)] by replacing the hydrogen atoms with relatively weakly bound bromine atoms, followed by gas-phase debromination. Until now, fullerenes have been produced primarily by carbon condensation processes, and this is apparently the first production of fullerenes which makes use of a precursor with a rationally designed carbon core. (Nature 7 Sep 00 407:60) 6. EXPERIMENTAL PHYSICS: ON ULTRACOLD MOLECULES During the past few decades, the cooling of atoms to lower and lower temperatures has produced exciting and sometimes unforeseen results in atomic interferometry, precision spectroscopy, Bose- Einstein condensates, and atomic lasers. Experimenters are now exploring the domain of ultracold molecules, and a number of groups are pointed toward the goal of bringing molecules to submillikelvin temperatures, at which temperatures molecules are slow enough to be trapped or otherwise manipulated. (Physics Today September 2000) 7. IN FOCUS: ON STATISTICAL NEURODYNAMICS 8. FROM THE SCIENCEWEEK ARCHIVE: ON THE SOKAL HOAX AND PHILOSOPHICAL EXTRAPOLATIONS IN PHYSICS 9. CORRECTION: ISSUE OF 1 SEP 00 FIRST ELECTROSTATIC TRAPPING OF AMMONIA MOLECULES =-=-=-=-=-=-=-=-= Section 2 =-=-=-=-=-=-=-=-= 1. NEUROBIOLOGY: DIFFERENTIATED NEUROGLIAL CELLS REPROGRAMMED TO BECOME MULTI- POTENTIAL CNS STEM CELLS In this context, the term "differentiation" refers to developmental cell specialization (morphology and biochemistry) resulting from activation of specific parts of the cell genome, and the term "stem cells" refers to undifferentiated cells that upon differentiation can give rise to various specialized cell lines such as blood cells, skin cells, nerve cells, etc. Adult bone marrow, for example, contains stem cells that are the precursors of the various specialized types of blood cells. In the middle of the 19th century, the anatomist Rudolf Virchow (1821-1902) recognized that cells in the brain could be categorized into two distinct groups: a) neurons (nerve cells), and b) a far more numerous group of cells that appear to surround the neurons and fill the spaces between them. Virchow called this second category of cell the "neuroglia", or "nerve glue", the idea being that one of the functions of these cells is to hold the neurons in place ("stutzfunktion"). Although this gluing function of neuroglia (glia; glial cells) was long ago abandoned for lack of evidence, the name of these cells has survived. Glial cells are in turn subdivided into several classes based on their appearance in the microscope. In the central nervous system, the two main types of glial cells are the "astrocytes" and the "oligodendrocytes" (oligodendroglia). Astrocytes have a star-like appearance, with numerous long processes radiating out from a central cell body; the oligodendrocytes also have a central cell body, but with radial arms that tend to be shorter and more branched than those of the astrocytes. ... ... T. Kondo and M. Raff (University College London, UK) now report a study of reprogramming of oligodendrocyte precursor cells, the authors making the following points: 1) During animal development, cells become progressively more restricted in the cell types to which they can give rise. In the central nervous system, for example, multipotential stem cells produce various kinds of specified precursors that divide a limited number of times before they terminally differentiate into either neurons or glial cells. 2) Oligodendrocyte precursor cells can be considered the best-characterized precursors in the mammalian central nervous system. These cells arise from multipotential cells in spatially restricted germinal zones and then migrate widely through the developing central nervous system. After a number of cell divisions, most oligodendrocyte precursor cells terminally differentiate into oligodendrocytes, although some precursor cells persist in the adult central nervous system. Fetal calf serum and certain *cytokines induce oligodendrocyte precursor cells in culture to differentiate into a particular type of astrocyte (type-2), but there is no convincing evidence that oligodendrocyte precursor cells normally become astrocytes in vivo. 3) The authors report that a 3-day exposure to the signals that induce the differentiation of oligodendrocyte precursor cells into type-2 astrocytes, followed by culture in basic *fibroblast growth factor, causes oligodendrocyte precursor cells to revert to a state that resembles that of multipotential central nervous system stem cells: the reverted cells can self- renew and give rise to neurons and type-1 astrocytes, as well as to oligodendrocytes. The authors suggest these unexpected findings indicate that extracellular signals can reverse glial cell specification and can convert specified precursor cells into multipotential stem cells. 4) The authors conclude: "Taken together, our findings indicate that oligodendrocyte precursor cells are not irreversibly committed to forming oligodendrocytes, type-2 astrocytes, or adult oligodendrocytes... There is increasing evidence that stem cells generally have a broader developmental potential than previous thought, and that local environmental cues normally restrict this potential in tissues... The use of extracellular signal molecules to reprogram specified precursor cells in culture to become multipotential stem cells may prove useful for cell therapy, as specified precursors are generally more abundant and easier to purify than multipotential stem cells." ----------- [Editor's note: The authors of this study emphasize the application of their results to cell therapy, but the implications are more general: If methods can be found to reprogram adult mammalian and human tissue cells into multipotential stem cells, the ramifications in research in developmental and cell biology will be profound.] ----------- T. Kondo and M. Raff: Oligodendrocyte precursor cells reprogrammed to become multipotential CNS stem cells. (Science 8 Sep 00 289:1754) QY: Toru Kondo: t.kondo@ucl.ac.uk ----------- Text Notes: ... ... *cytokines: A cytokine is any substance that promotes cell growth and cell division. As a promoter of cell growth and division, a cytokine acts as a messenger to cells, and the transmission of the message requires a binding of the cytokine molecule to a cytokine-specific receptor on the cell surface. ... ... *fibroblast growth factor: This is a protein known to stimulate proliferation of neural stem cells. ------------------- Summary & Notes by SCIENCE-WEEK http://scienceweek.com 13Oct00 For more information: http://scienceweek.com/swfr.htm ------------------- Related Background: MEDICAL BIOLOGY: PROSPECTS FOR NEURAL STEM CELL REPAIR OF INJURED SPINAL CORD What has happened in vertebrate evolution is that the brain has evolved from a mere head cluster of nerve cells (a head ganglion) of the spinal array of ganglia (the spinal cord) to a burgeoned structure that dominates the spinal cord almost completely. In terms of both function and anatomy, the human spinal cord can thus be viewed as a "service" extension of the commanding brain, the two together constituting the "central nervous system", and like in the brain, traumatic injury to the spinal cord is usually irreversible: brain and spinal nerve cells and nerve fibers usually do not regenerate when damaged. Since many nerve cells and nerve fibers in the spinal cord are essential to the control of various voluntary and involuntary muscles of the body below the head, traumatic injury to the spinal cord can be devastating in its consequences. An acceleration of research into possible mechanisms of neuronal regeneration has occurred during the past several decades, and there is now some hope for applications of this research to the treatment and repair of spinal cord injuries. ... ... S.S.W. Han and I. Fischer (Hahnemann University School of Medicine, US) present a review of current research in this field, the authors making the following points: 1) Recent observations that several regions of the mammalian central nervous system do continue to produce neurons throughout life suggests there are prospects for repairing an injured spinal cord. Researchers have developed efficient methods for culturing the neural *stem cells of rodents, genetically modifying these cells to produce therapeutic genes, and then transplanting these cells into animal models of brain diseases. These same gene therapy and grafting techniques are being explored as possible methods for restoring function following traumatic spinal cord injury. 2) In the developing embryo, *epithelial cells of the *neural tube generate a variety of precursor cells that migrate and *differentiate into neurons, *astrocytes, and *oligodendrocytes. Central nervous system stem cells have now been discovered in the human central nervous system and appear to behave similarly to their rodent counterparts, and these stem cells could potentially be used to promote the generation of new nerve cells (neurogenesis) following injury and disease. 3) Transplantation studies have demonstrated that neural stem cells have the capacity to differentiate in response to the environment into which they are reintroduced and to integrate appropriately with the host tissue. Neural stem cells can be isolated from different areas and propagated for long periods in culture without losing their ability for varied differentiations (their "multipotentiality"). When transplanted back into the central nervous system, these stem cells have the capacity to migrate, to integrate with the host tissue, and to respond to local cues for differentiation. 4) The authors conclude: "Transplantation of neural stem cells and precursor cells together with gene therapy offers great promise for spinal cord repair. Specific research goals include improving neuronal survival, promoting functional recovery through *axonal regeneration, compensating for *demyelination, and replacing lost cells. Many issues will need to be resolved before stem cells can be considered for use in human subjects, but continued basic research on the properties of these cells and development of appropriate animal models of repair will pave the way for successful clinical applications." ----------- S.S.W. Han and I. Fischer: Neural stem cells and gene therapy: Prospects for repairing the injured spinal cord. (J. Amer. Med. Assoc. 3 May 20 283:2300) QY: S.S.W. Han, MCP Hahnemann University School of Medicine, Philadelphia, PA US. ----------- Text Notes: ... ... *stem cells: In general, a stem cell is any precursor cell, a form prior to cell differentiation. E.g., stem cells in bone marrow that give rise to blood cells. ... ... *epithelial cells: In animals, "epithelial cells" compose the cell layers that form the interface between a tissue and the external environment, for example, the cells of the skin, the lining of the intestinal tract, and the lung airway passages. ... ... *neural tube: The term "neural tube" refers to the early embryonic structure (an actual hollow tube of cells formed by the infolding and closing of a long sheet of cells) that subsequently gives rise to the entire brain and spinal cord. ... ... *differentiate: In this context, the term "differentiation" refers to developmental cell specialization (morphology and biochemistry) resulting from activation of specific parts of the cell genome. E.g., the differentiation of a stem cell into a nerve cell. ... ... *astrocytes: (astroglial cell) Neuroglia are non-neuronal cellular elements of the central and peripheral nervous systems, and astroglia (astrocytes) are a type of neuroglia. In general, neuroglia are thought to have important metabolic functions. ... ... *oligodendrocytes: (oligodendroglia) Glial cells characterized by sheet-like processes that are wrapped around individual neuron axons to form the myelin sheath of nerve fibers in the central nervous system. (The myelin sheath of a nerve fiber is effectively a periodically interrupted insulation which increases the propagation velocity of nerve impulses. See note on "demyelination" below.) ... ... *axonal regeneration: In general, nerve cells have a single long extension (the "axon") that propagates the electrical output (the action potential) of the cell. In some types of nerve cells, axons are extensively branched into a multitude of fine fibers that make contact (synapses) with other nerve cells. ... ... *demyelination: (demyelinization) A number of neurodegenerative diseases involve progressive demyelination of various myelinated nerve fibers. High signal propagation velocities in motor and sensory neurons in vertebrates are achieved by association of the nerve fiber with an enfolding sheath called myelin. The myelin sheath consists of concentric layers of electrically insulating lipid material, but the sheath is periodically interrupted, and at the points where the sheath is interrupted so is the electrical insulation interrupted. The result, predictable from the classical physics of electrical transmission lines and the electrical parameters of nerve fibers, is that the propagation of an electrical pulse along such nerve fibers occurs at a velocity much higher than that found in unmyelinated fibers. ------------------- Summary & Notes by SCIENCE-WEEK http://scienceweek.com 2Jun00 For more information: http://scienceweek.com/swfr.htm ------------------- Related Background: CONVERSION OF NEURAL STEM CELLS INTO BLOOD CELLS In a multicellular living organism such as a human or a mouse, what differentiates one cell type from another is apparently not the genome, since the genome is the same in every cell, but which parts of the genome are operational. In other words, each cell type, skin cell, muscle cell, etc., has a particular gene profile characteristic of that cell type. Cells of a particular cell type are said to be "differentiated". Stem cells are undifferentiated cells that in response to appropriate signals differentiate and give rise to a variety of cell types. Stem cells are common in embryos, but they have also been identified in adult tissues that undergo extensive cell replacement due to physiological turnover or injury, e.g., the *hematopoietic, intestinal, and *epidermal systems. Stem cells have also been found in the central nervous system, a tissue believed to be capable of only extremely limited self-repair. Central nervous system stem cells can generate the 3 major cell types found in the adult brain: *astrocytes, *oligodendrocytes, and neurons. This is consistent with the view that the developmental potential of stem cells is restricted to the differentiated elements of the tissue in which they reside. But some developmental peculiarities suggest certain cells may be able to differentiate into cell types that are not of the same origin. ... ... C.R.R. Bjornson et al (5 authors at 4 installations, CA IT) now report an investigation to determine whether stem cells are restricted to produce specific cell types, namely, those from the tissue in which they reside. The authors report that after transplantation into *irradiated host mice, genetically labelled mouse neural stem cells were found to produce a variety of blood cell types, including *myeloid and *lymphoid cells, as well as early hematopoietic cells. The authors suggest that neural stem cells appear to have a wider differentiation potential than previously thought, and that if they behave similarly to their mouse counterparts, human neuronal stem cells may provide a renewable and characterized source of cells that could be used in approaches aimed at hematopoietic reconstitution in various blood diseases and disorders. ----------- C.R.R. Bjornson et al: Turning brain into blood: A hematopoietic fate adopted by adult neural stem cells in vivo. (Science 22 Jan 99 283:534) QY: Christopher R.R. Bjornson: adanac@u.washington.edu ----------- Text Notes: ... ... *hematopoietic: From hematopoiesis (hemopoiesis, hematogenesis) Refers to the formation and development of the various types of blood cells. ... ... *epidermal: The term "epidermal" refers to the superficial epithelial portion of the skin. In animals, epithelial cells compose the cell layers that form the interface between a tissue and the external environment, for example, the cells of the skin, the lining of the intestinal tract, and the lung airway passages. ... ... *astrocytes: (astroglia, macroglia) Glial cells are more numerous than neurons in the brain, but their function has been generally characterized as "metabolic" or "supportive", without much discussion of details. Astrocytes are the largest glial cells, with many extensions radiating outward like a starburst, and at least one of their functions is apparently to maintain the so-called "blood-brain barrier" effectively separating neural tissue from blood. ... ... *oligodendrocytes: (oligodendroglia) Glial cells characterized by sheet-like processes that are wrapped around individual neuron axons to form the myelin sheath of nerve fibers in the central nervous system. (The myelin sheath of a nerve fiber is effectively a periodically interrupted insulation which increases the propagation velocity of nerve impulses.) ... ... *irradiated host mice: In this investigation, host animals were radiated before transplantation in order to reduce the population of immune system blood cells, this reduction apparently intensifying the signals resulting in donor stem cell differentiation. ... ... *myeloid: Refers to bone marrow cells or cells derived from bone marrow cells. ... ... *lymphoid cells: Refers to cells of the lymphatic system. The lymphatic system is a complex network for the distribution of lymph fluid (which is similar to blood plasma -- blood without red cells). ------------------- Summary & Notes by SCIENCE-WEEK http://scienceweek.com 2Apr99 For more information: http://scienceweek.com/swfr.htm =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= 2. EPIDEMIOLOGY: ON THE GLOBAL SPREAD OF MALARIA IN A FUTURE WARMER WORLD The disease malaria is caused by a protozoan parasite of the genus Plasmodium, and it is one of the most dangerous diseases infecting human populations. Approximately 300 million to 500 million people are infected annually, and 1.5 million to 2.7 million lives are lost to malaria each year, with most deaths occurring among children in sub-Saharan Africa. Of the 4 species that cause malaria in humans, P. falciparum is the greatest cause of *morbidity and mortality. The resistance of the malaria parasite to drugs and the resistance of mosquitoes to insecticides have resulted in a resurgence of malaria in many parts of the world and a pressing need for vaccines and new drugs. Malaria is endemic in Africa, much of South and Southeast Asia, Central America, and northern South America. The disease was once endemic in the US, but it has been virtually eliminated from North America. Since malaria is a serious disease common in tropical and semi-tropical regions, there is concern that one of the consequences of near-future global warming will be a substantially increased incidence of malaria in regions now free of the disease. ... ... D.J. Rogers and S.E. Randolph (University of Oxford, UK) present a study on the effect of future global warming on the spread of malaria, the authors making the following points: 1) The authors point out that predictions of global climate change have stimulated forecasts that *vector-borne diseases will spread into regions that are at present too cool for their persistence. For example, life-threatening cerebral malaria, caused by P. falciparum transmitted by anopheline mosquitoes, is predicted to reach the central or northern regions of Europe and large parts of North America. Despite the high incidence and large number of deaths each year caused by malaria, like many other vector-borne diseases, the epidemiology of malaria remains inadequately understood. Only the most general of maps for its worldwide distribution are available, and its global transmission patterns cannot be modeled satisfactorily because crucial parameters and their relations with environmental factors have not yet been quantified. Most importantly, absolute mosquito abundance has not yet been related to multivariate climate. 2) The authors point out that the frequent warnings that global climate change will allow falciparum malaria to spread into northern latitudes, including Europe and large parts of the US, are based on biological transmission models driven principally by temperature. The authors report they have assessed these models for their value in predicting present, and therefore future, malaria distribution. In the alternative statistical approach of the authors, the recorded present-day global distribution of falciparum malaria was used to establish the current multivariate climate constraints. The authors report that when these results were applied to future climate scenarios to predict future distributions, model malaria distributions exhibited remarkably few changes from the present distribution, even under the most extreme scenarios. 3) The authors conclude: "The quantitative model presented here contradicts prevailing forecasts of global malaria expansion. It highlights the use of multivariate rather than univariate constraints in such applications, and the advantage of statistical rather than biological approaches in situations where biological knowledge is incomplete. Whatever the method adopted, the usefulness of global circulation models as a basis for making predictions about the future of biological systems needs further clarification. The current low spatial resolution of such models hides considerable local variation and represents mean conditions across large geographical areas, conditions that may not occur in many places within them. Furthermore, the accuracy of global circulation models in predicting covariation of climate variables, to which biological systems are very sensitive, is unknown." ----------- D.J. Rogers and S.E. Randolph: The global spread of malaria in a future, warmer world. (Science 8 Sep 00 289:1763) QY: David J. Rogers: david.rogers@zoology.ox.ac.uk ----------- Text Notes: ... ... *morbidity and mortality: In general, "morbidity" refers to a diseased state; in particular, the term refers to the ratio of the diseased population to the well population in a community. The term "mortality", in contrast, refers to the number of deaths from the disease. ... ... *vector-borne diseases: In this context, the term "vector-borne" refers to a disease or infection transmitted by an invertebrate carrier (vector). ------------------- Summary & Notes by SCIENCE-WEEK http://scienceweek.com 13Oct00 For more information: http://scienceweek.com/swfr.htm ------------------- Related Background: IDENTIFICATION OF THE INDUCER OF MOSQUITO MALARIA DEVELOPMENT The disease malaria is caused by a type of protozoan with the general name Plasmodium, an organism characterized by a sequence of life cycles involving different organismic forms. The asexual cycle occurs in the liver and red blood cells of vertebrates (including humans), and the sexual cycle occurs in mosquitoes. Essentially, the asexual form is ingested by blood-sucking mosquitoes, and in the mosquito the asexual form is induced to produce the sexual form necessary to complete the total life cycle. The details of the process are as follows: Plasmodium cells called "gametocytes" (precursors of gametes) in human blood are ingested by the mosquito, and in the mosquito, apparently within seconds, gametocytes are induced into "gametogenesis", producing gametes. These gametes produce a cell-type called "sporozoites", which accumulate in the salivary gland of the mosquito, from where they are injected into the vertebrate blood stream when the mosquito feeds on vertebrate blood. The sporozoites accumulate in the vertebrate liver, where they multiply and produce a form (merozoites) that invades red blood cells, replicates, destroys red blood cells, and so on, with an eventual decline in this asexual replication. However, after invasion of red blood cells, some merozoites produce gametocytes, which have the genomic potential for restarting the total life cycle. These gametocytes cannot self-replicate, and they die unless ingested by a mosquito, but once in the mosquito, the total life cycle begins again. There are apparently 2 inducers of gametogenesis in vivo (i.e., in the mosquito): one inducer is a pH of 7.5 to 7.6, and the other inducer has been thought to be an unknown mosquito-derived gametocyte-activating factor. ... ... Now Billker et al (9 authors at 2 installations, UK US) report that the second inducer in vivo of gametocyte induction in the mosquito is apparently xanthurenic acid, and that low concentrations of xanthurenic acid can act together with pH to induce gametogenesis in vitro. The authors suggest these data could form the basis of the rational development of new drugs to interrupt the transmission of malaria, or for the development of methods producing the selection of new mosquito genotypes (species variants) resistant to infection. ----------- QY: R.E. Sinden, Imperial College London, SW7 2BB UK. (Nature 19 Mar 98) (Science-Week 3 Apr 98) For more information: http://scienceweek.com/swfr.htm =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= 3. MEDICAL BIOLOGY: ON THE GENOMICS OF THE CHOLERA PATHOGEN Cholera is an ancient disease, an acute infection by the bacterium Vibrio cholerae involving the entire small bowel, the infection characterized by profuse watery diarrhea, vomiting, muscular cramps, dehydration, and collapse. Death may follow in a few hours after the first bacterial invasion. The disease is endemic in portions of Asia, the Middle East, Africa, South and Central America, and the Gulf Coast of the US. The group of bacteria known as the "vibrios" are found in marine and surface waters, and are among the most common bacteria in surface waters worldwide. The organisms are curved aerobic rods possessing a polar flagellum, the rod 2 to 4 microns long and approximately 1 micron in diameter. V. cholerae and related vibrios produce a heat-labile protein *enterotoxin (mol. wt. 84,000) consisting of 2 subunits. One of the subunits enters cells, yields increased levels of *cyclic adenosine monophosphate (cAMP), and results in prolonged hypersecretion of water and electrolytes. ... ... Victor J. DiRita (University of Michigan, US) presents a commentary on the recent sequencing of the genome of V. cholerae, the author making the following points: 1) The author points out that modern epidemiology originated in the work of John Snow (1813-1858), whose careful study of cholera victims led him to discover the waterborne nature of this disease [*Note #1]. Cholera also played a part in the foundation of modern bacteriology: 40 years after Snow's seminal discovery, Robert Koch (1843-1910) developed the germ theory of disease subsequent to his identification of V. cholerae as the pathogen responsible for cholera [*Note #2]. 2) The complete genome sequence of the 2 circular chromosomes of V. cholerae was recently reported by J. Heidelberg et al (Nature 406:477 2000). This team discovered a total of 3885 lengths of DNA that encode proteins ("open reading frames"): 2770 open reading frames (2.9 million nucleotide base pairs) on the larger chromosome-1, and 1115 open reading frames (1.1 million nucleotide base pairs) on the smaller chromosome-2. Slightly more than 50 percent of these open reading frames encode proteins homologous to proteins of known function; the remainder encode proteins without ascribed functions or that are not homologous to any known protein. In addition to factors of potential importance for pathogenicity, the V. cholerae genome apparently contains genes encoding metabolic proteins, *transporters, and regulatory proteins appropriate for a free-living organism adapted to niches outside of the human intestine. 3) The V. cholerae that normally inhabits aquatic environments is not pathogenic. However, acquisition of virulence factors enables this microbe to colonize the intestinal *mucosa of human hosts, where the microbe releases cholera toxin (enterotoxin), which causes rapid release of water and electrolytes from intestinal epithelium, and which results in severe and often fatal diarrhea. Cholera continues to be a scourge throughout much of the world, with 7 global epidemics ("pandemics") recorded since 1817. In 1991, for the first time in 100 years, cholera arrived in the Western Hemisphere from its focal center in Asia. Cases were first reported in Peru, and epidemics throughout South and Central America rapidly followed. 4) The author (DiRita) concludes: "The postgenomic era of V. cholerae research has begun, and the challenge for investigators will be to use the genomic sequence information to probe more deeply into all aspects of the life-style of this fascinating, frightening, and often frustrating microbe." ----------- Victor J. DiRita: Genomics happens. (Science 1 Sep 00 289:1486) QY: Victor J. DiRita: Univ. of Michigan 313-764-7433. ----------- Text Notes: ... ... *enterotoxin: In general, any toxin specific for cells of the intestinal mucosa (see below). ... ... *cyclic adenosine monophosphate (cAMP): An important intracellular "messenger" substance involved in various aspects of cell regulation and protein synthesis. ... ... *Note #1: In 1854, John Snow demonstrated the transmission of cholera from contaminated water by analyzing disease rates among citizens served by the Broad Street Pump in London's Golden Square. Snow stopped the further spread of the disease by removing the pump handle from the polluted well. ... ... *Note #2: Koch devised techniques for culturing bacteria outside the body, and formulated the rules for demonstrating whether or not a bacterium is the cause of a disease. He identified the bacteria responsible for tuberculosis, cholera, and other diseases. He demonstrated that rats are vectors of bubonic plague and that sleeping sickness is transmitted by the tsetse fly. He received the Nobel Prize for Physiology or Medicine in 1905. He began his scientific life as a country doctor in a rural village. ... ... *transporters: (transport proteins) Proteins (or enzymes) instrumental in transporting materials across biological membranes or within a biological fluid (e.g., blood). ... ... *mucosa: In general, a multilayer tissue lining various tubular structures in the body (e.g., the intestine). ------------------- Summary & Notes by SCIENCE-WEEK http://scienceweek.com 13Oct00 For more information: http://scienceweek.com/swfr.htm =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= 4. BIOPHYSICS: MEASUREMENT OF THE CRAWLING FORCE GENERATED BY AMOEBOID CELLS The term "amoeba" (ameba) refers to a genus of single-celled protozoa characterized by the ability to continuously change shape by localized extension (pseudopod formation) and retraction, with shape-change used for both locomotion and engulfment of food. In contrast, the term "amoeboid movement" ("amoeboid cells"; "amoeba-like movement") refers to the movements of any cell of any genus, where the movement is effected by means of pseudopods and the shape of the cell is subject to constant change. The organism Dictyostelium discoideum is a special case of a simple organism occurring in two basic forms: free individual cells and the same cells in an organized colony. Although often called a "cellular slime mold", D. discoideum is not a mold, nor is it consistently slimy. The term "social amoeba" is more accurate. When the organism is individualized, the entities are called "myxamoebae". When they aggregate into a slug, the organism is called a "pseudoplasmodium" or termed the "grex". The aggregation into a unitary grex may involve tens of thousands of individual amoebae. Experiments have demonstrated that the directional locomotion of myxamoebae is dependent on ambient gradients of cyclic adenosine-3',5'-monophosphate (cAMP). "Motor proteins" are mechanico-chemical enzymes involved in locomotion of cells or transport of materials in cells, and there are three families of such proteins: kinesins, dyneins, and myosins. Kinesins and dyneins are microtubule-based motor proteins, while myosin is a microfilament-based motor protein. The microtubules are hollow cylinders approximately 24 nanometers in diameter, many microns in length, and consist of heterodimers of alpha- and beta-tubulin proteins plus a variable set of other proteins. Microfilaments are 4 to 6 nanometers in diameter, highly variable in length, and are found in all cells with internal membrane-bound organelles (eukaryotic cells). In general, as mechanico-chemical enzymes, motor proteins convert energy from hydrolysis of nucleotides to mechanical force, and since they are involved in many important cellular events, the molecular details are currently the focus of intensive research. ... ... Y. Fukui et al (4 authors at 3 installations, US JP) present an analysis of the crawling force generated by cells undergoing amoeboid locomotion, the authors making the following points: 1) Generation of mechanical forces is essential for cell locomotion, cell division, embryonic development, and morphogenesis. Although the forces involved in some of these biological activities have been measured as mechanical properties in local regions of living cells, few measurements have been made of the maximum ability of an entire cell to propel itself. An example is the measurement of the maximum propulsive force of 7 x 10^(3) piconewtons generated by a swimming ciliated protozoan, Paramecium caudatum, measured using a centrifuge microscope. In contrast, little is known of the propulsive forces that can be generated by any cell undergoing amoeboid movement. 2) The authors report measurement of the maximum "apparent weight" centrifugal force against which ordinary (wild-type) and myosin mutants of D. discoideum amoebae were able to crawl "upward". The small mass of the amoebae required the use of a recently developed centrifuge polarizing microscope capable of generating fields of greater than 11,465 g (where g = Earth's gravitational acceleration), with image resolution of better than 1 micron. 3) The authors report that D. discoideum mutant amoeba lacking myosin ("myosin knockout mutants") stall or cease to be able to crawl up against the imposed apparent weight at characteristic centrifugal accelerations, so they are least able to overcome that much external force. Those lacking the muscle type myosin (myosin II) stall at very much lower centrifugal acceleration. 4) The authors suggest that the mechanism of stalling, or inability of the amoeba to maintain directional locomotion against the centrifugal field, depends on the very high local density of its leading pseudopod rather than on the apparent weight felt by the whole amoeba. Even in media whose density is greater than that of the whole amoeba, amoebae lacking myosin II are unable to sustain the forward protrusion of the high-density pseudopod that is apparently needed for directional amoeboid locomotion against the external field. 5) The authors conclude: "We believe that the forward protrusion of the leading pseudopod is not simply a phenomenon observed in Dictyostelium and other amoebae, but that it is an essential feature for the directional migration of cells undergoing amoeboid locomotion in general. Once the direction of propagation is defined by some cue (e.g., cyclic adenosine-3',5'-monophosphate gradient for Dictyostelium amoebae) and a pseudopod starts forming in that direction, we suggest that the contractile force generated by the trailing cell cortex must provide adequate support for the pseudopod to penetrate into that direction without collapsing against the external force, whether gravitational or a barrier presented (e.g., against leukocytes, parasitic *protista, or migrating embryonic cells) by a tissue layer... We postulate that the directional locomotion of an amoeboid cell requires the contractile cortical framework to provide the turgidity needed for the leading pseudopod to direct the locomotion in that direction." ----------- Y. Fukui et al: How well can an amoeba climb? (Proc. Natl. Acad. Sci. US 29 Aug 00 97:10020) QY: Yoshio Fukui: y-fukui@northwestern.edu ----------- Text Notes: ... ... *protista: (Protoctista; protists) The term "protista" refers to one of the phylogenetic kingdoms, this category defined mostly by exclusion and containing all the eukaryotic nucleated organisms that cannot be classified as animal, plant, or fungus. Protists include protozoans, algae, kelps, slime molds, and many obscure eukaryotes. ------------------- Summary & Notes by SCIENCE-WEEK http://scienceweek.com 13Oct00 For more information: http://scienceweek.com/swfr.htm =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= 5. CHEMISTRY: SYNTHESIS OF THE SMALLEST FULLERENE Fullerenes are large molecules composed entirely of carbon, with the chemical formula C(n), where n is any even number 20 or greater. They apparently have the structure of a hollow spheroidal cage (and certain other forms) with a surface network of carbon atoms connected in hexagonal and pentagonal rings. They were discovered by Richard E. Smalley, who in 1996 received the Nobel Prize in Chemistry for the discovery. In general, fullerene graphite cage structures incorporate exactly 12 pentagons, and the smallest possible fullerene is thus C(sub20), which consists solely of pentagons. But the extreme curvature and reactivity of this structure have led to doubts about its existence and stability. Although theoretical calculations have identified, besides this cage, a bowl and a monocyclic ring isomer as low-energy members of the C(sub20) cluster family, only ring isomers of C(sub20) have been observed. ... ... H. Prinzbach et al (9 authors at 2 installations, DE US) now report the production of C(sub20) fullerene, the authors making the following points: 1) The authors report a demonstration that the cage- structured fullerene C(sub20) can be produced from its perhydrogenated form [dodecahedrane C(sub20)H(sub20)] by replacing the hydrogen atoms with relatively weakly bound bromine atoms, followed by gas-phase debromination. For comparison, the authors have also produced the bowl isomer of C(sub20) using the same procedure. 2) The authors characterized the generated C(sub20) clusters using *mass-selective anion photoelectron spectroscopy. The observed electron affinities and vibrational structures of these two C(sub20) isomers (sphere and bowl) differ significantly from each other, as well as from those of the known monocyclic isomer. 3) The authors conclude: "The photoelectron spectrum of the unique C(sub20) species derived from dodecahedrane... stands as a benchmark test for [analysis of vibrational energies of this system by] quantum-mechanical methods. It is hoped that the experimental results reported here will stimulate further theoretical activities. Until now, fullerenes have been produced primarily by carbon condensation processes. The route to cage 1 [the spherical isomer] that we report here is, to our knowledge, the first which makes use of a precursor with a rationally designed carbon core." ----------- H. Prinzbach et al: Gas-phase production and photoelectron spectroscopy of the smallest fullerene, C(sub20). (Nature 7 Sep 00 407:60) QY: Horst Prinzbach: horst.prinzbach@orgmail.chemie.uni-freiburg.de ----------- Text Notes: ... ... *mass-selective anion photoelectron spectroscopy: In the technique used here, C(sub20)(-) anions are irradiated with a pulsed laser that detaches some of the extra electrons. The kinetic energy of the photo-detached electrons is then determined by precisely clocking their travel time over a predetermined distance. The difference between the photon energy and the energy of the fastest-moving electrons provides a measure of how strongly the extra electron is held by the anion. If the geometries of the initial anion and the resulting neutral C(sub20) are slightly different, removing the electron leaves the neutral C(20) vibrationally excited. The vibrational frequencies can then be deduced from oscillations in the photoelectron signal. (cf. Martin F. Jerrold: Nature 407:26 2000). ------------------- Summary & Notes by SCIENCE-WEEK http://scienceweek.com 13Oct00 For more information: http://scienceweek.com/swfr.htm ------------------- Related Background: FIRST SYNTHESIS OF A LOW-MASS FULLERENE Under appropriate non-equilibrium growth conditions, carbon atoms form relatively stable hollow clusters of well-defined mass number, collectively known as "fullerenes". The mass production, purification, and condensation of such clusters into a molecular solid is generally essential to full experimental characterization. The initial discovery of C(sub60) in 1985, for example, had to await a bulk synthesis method 6 years later before detailed characterization of the molecule was possible. Gas-phase experiments have indicated the existence of a wide range of possible fullerene clusters, but beyond C(sub60) only a few pure fullerene solids have been obtained, most notably C(sub70). Low-mass fullerenes are of particular interest because their high curvature and increased strain energy owing to adjacent pentagonal rings could lead to solids with unusual intermolecular bonding and electronic properties. ... ... Piskoti et al (3 authors at 3 installations, US) now report the synthesis of the solid form of C(sub36) by the *arc-discharge method. They report the development of purification methods that separate C(sub36) from amorphous carbon and other fullerenes to yield saturated solutions, thin films, and polycrystalline powders of the pure solid form. The authors report observation of large increases in the electrical conductivity of the solid on doping with alkali metals, and they suggest that if C(sub36) could be made sufficiently conducting -- either by doping or by structural rearrangement (e.g., induced by pressure) -- one might expect high-temperature superconductivity to be manifested. QY: A. Zettl (Nature 25 Jun 98 393:771) (Science-Week 24 Jul 98) ------------------- Related Background: ... ... *arc-discharge method: In the present instance, the method involves an originally designed helium-environment arc- discharge chamber, with an arc between two 0.25 inch-diameter graphite electrodes, using a DC current of 100 amperes while maintaining a 1 millimeter gap between the electrodes. Arcing is maintained for several minutes, until a uniform carbon film of approximately 10 microns thickness coats a removable metal substrate 10 centimeters from the discharge region. ------------------- Summary & Notes by SCIENCE-WEEK http://scienceweek.com 24Jul98 For more information: http://scienceweek.com/swfr.htm =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= 6. EXPERIMENTAL PHYSICS: ON ULTRACOLD MOLECULES At room temperature, a gas of atoms moves with speeds estimated at 0.6 x 10^(3) meters per second, and slowing an atom down is equivalent to cooling it. One way to cool atoms is to force a head-on collision with a laser beam: if the photons of the beam have the appropriate energy to be absorbed, then conservation of momentum implies that the atom slows. In 1985, Stephen Chu devised a successful method based on this idea, the method involving 3 pairs of lasers aligned along the three optical axes, with each pair of lasers antiparallel, the consequence a cooling of essentially trapped atoms. The resulting electromagnetic field in which the atoms move has been described as "optical molasses". Atoms that are trapped at low temperatures can be used for a variety of purposes. For example, trapped atoms can be allowed to fall freely, and their excitations can be measured as they are subsequently hit with a series of short laser pulses of different frequencies. These excitations vary with the motion of the atoms, due to a *Doppler shift determined by their speed. The result is that the weakening of gravity due to a rise of as little as 3 centimeters has been measured. At present, a number of laboratories have focused on the cooling and trapping of molecules, a more formidable challenge. ... ... Barbara Goss Levi (American Institute of Physics, US) presents a review of current research on ultracold molecules, the author making the following points: 1) During the past few decades, the cooling of atoms to lower and lower temperatures has produced exciting and sometimes unforeseen results in atomic interferometry, precision spectroscopy, Bose-Einstein condensates, and atomic lasers. Experimenters are now exploring the domain of ultracold molecules, and a number of groups are pointed toward the goal of bringing molecules to submillikelvin temperatures, at which temperatures molecules are slow enough to be trapped or otherwise manipulated. 2) The latest achievement in this endeavor was recently announced by H.L. Bethlem et al (Nature 406:491 2000), who have demonstrated a promising new method for obtaining ultracold molecules, the method involving cooling and trapping molecules in a single quantum level with a density of 10^(6) per cubic centimeter, and at temperatures estimated to be well below 350 millikelvin. 3) The author points out that with trapped molecules, one would ideally like to achieve three things: a) reduce translational temperatures to submillikelvin levels; b) cool a large number of molecules; and c) put the molecules in a single, and preferably the lowest, rotational-vibrational state. In addition, it would be important to find a method for achieving these constraints for any type of molecule. Impressive progress toward some of these goals has been made during the past few years using several different methods, with each method possessing its particular strengths and weaknesses. 4) In general, the research agenda for ultracold molecules is probably not too different from the agenda for their atomic counterparts, with the following possibilities: a) precision spectroscopy, because the spectral lines will be much narrower in the absence of motional effects; b) the study of the collisions of ultracold molecules, which should involve a reduced number of angular momentum states; c) the availability of ultracold molecules might also facilitate searches for electric dipole moments of elementary particles; d) the manipulation of molecules by various types of electromagnetic fields; e) the formation of a Bose-Einstein condensate of molecules. But perhaps the most compelling interest is the lure of the unknown. ----------- Barbara Goss Levi: Hot prospects for ultracold molecules. (Physics Today September 2000) QY: Barbara Goss Levi: pt@aip.org ... ... *Doppler shift: In general, the term "Doppler shift" refers to the change in wavelength of electromagnetic radiation as a result of relative movement between the source and the observer. ------------------- Summary & Notes by SCIENCE-WEEK http://scienceweek.com 13Oct00 For more information: http://scienceweek.com/swfr.htm ------------------- Related Background: CHEMICAL PHYSICS: FIRST ELECTROSTATIC TRAPPING OF AMMONIA MOLECULES The ability to cool and slow atoms with light for subsequent trapping allows investigations of the properties and interactions of the trapped atoms in unprecedented detail. Although in general the complex structure of molecules prohibits this type of manipulation, magnetic trapping of calcium hydride molecules *thermalized in ultra-cold buffer gas, and optical trapping of cesium dimers generated from ultra-cold cesium atoms have been reported. These methods, however, depend on the target molecules being paramagnetic (e.g., calcium hydride) or able to form through the association of atoms amenable to laser cooling (e.g., cesium dimers), thus restricting the range of molecular species that can be studied. ... ... H.L. Bethlem et al (6 authors at 2 installations, NL) now report the slowing of an *adiabatically cooled beam of deuterated ammonia molecules by time-varying inhomogeneous electric fields, and subsequent loading into an electrostatic trap. The authors report they are able to trap ammonia molecules with a density of 10^(6) per cubic centimeter in a volume of 0.25 cubic centimeters at temperatures below 0.35 degrees kelvin. The authors report they observe pronounced density oscillations caused by the rapid switching of the electric fields during loading of the trap. The authors suggest their results illustrate that polar molecules can be efficiently cooled and trapped, thus providing an opportunity to study collisions and collective quantum effects in a wide range of ultra-cold molecular systems. ----------- H.L. Bethlem et al: Electrostatic trapping of ammonia molecules. (Nature 3 Aug 00 406:491) QY: Gerard Meijer gerardm@rijnh.nl ----------- Text Notes: ... ... *thermalized: In general, to bring entities into thermal equilibrium with their surroundings. ... ... *adiabatically cooled: In general, an adiabatic process is any thermodynamic process, reversible or irreversible, that takes place in a system without exchange of heat with the surroundings of the system. All real processes are nonadiabatic in the sense that some heat exchange always occurs. But close approximation to an adiabatic ideal can be realized in practice. ------------------- Summary & Notes by SCIENCE-WEEK http://scienceweek.com 1Sep00 For more information: http://scienceweek.com/swfr.htm ------------------- Related Background: PHYSICS: FIRST MOLECULES IN A BOSE-EINSTEIN CONDENSATE In 1997, Steven Chu, Claude Cohen-Tannoudji, and William D. Philips shared the Nobel Prize in Physics for their work in the 1980s involving laser-cooled atoms, work that ultimately led to the cooling of atoms to extremes close to absolute zero degrees kelvin, and finally to the creation by Anderson et al (Science 269:198 1995) of a Bose-Einstein condensation in a dilute gas of rubidium atoms. The essential idea behind these techniques involves a reduction in the momentum of an atom when it absorbs a photon. Bose-Einstein statistics is the statistical mechanics of a system of indistinguishable particles for which there is no restriction on the number of particles that may simultaneously exist in the same quantum energy state. Bosons are particles that obey Bose-Einstein statistics, and they include photons, pi mesons, all nuclei having an even number of particles, and all particles with integer spin. In low temperature physics, the Bose-Einstein condensation is a phenomenon that occurs in the study of systems of bosons: below a critical temperature, the quantum ground state becomes highly populated, individual wave equations merging into a single wave equation, the particles indistinguishable, and the condensate of particles behaving as a singe entity. ... ... R. Wynar et al (5 authors at University of Texas Austin, US) now report the production of rubidium-87 dimers that are essentially at rest by assembling them from ultracold rubidium atoms in an atomic Bose-Einstein condensate. In a commentary in the same journal, C.J. Williams and P.S. Julienne (National Institute of Standards and Technology, US) point out that this work is the first observation of molecule formation in a Bose- Einstein condensate, that a method for the ultraprecise measurement of molecular binding energies has now been introduced, and that the work is the first measurement of the interaction energy between a condensate and a molecule. ----------- R. Wynar et al: Molecules in a Bose-Einstein Condensate. (Science 11 Feb 00 287:1016) QY: D.J. Heinzen [heinzen@physics.utexas.edu] ----------- C.J. Williams and P.S. Julienne: Molecules at rest. (Science 11 Feb 00 287:986) QY: paul.julienne@nist.gov ------------------- Summary by SCIENCE-WEEK http://scienceweek.com 3Mar00 For more information: http://scienceweek.com/swfr.htm ------------------- Related Background: FERMI DEGENERACY IN A TRAPPED ATOMIC GAS In quantum mechanics, electrons, protons, and neutrons have an intrinsic angular momentum known as "spin", and a *magnetic moment parallel or antiparallel to that angular momentum. When electrons are combined together to form an atom or ion, there is a resultant angular momentum which is a combination of the intrinsic spin of the electrons and the angular momentum due to their motion about the nucleus, and this is the "spin" of the atom or ion. Atoms or ions with non-zero spin are magnetic atoms or ions [*Note #1]. Elementary particle spin involves a virtual rotation about the axis of the particle, which means only two spin states are possible, one clockwise and one counterclockwise. According to quantum theory, spin is quantized and restricted to multiples of h/2ã, where (h) is the Planck constant. Only integer or half-integer multiples are allowed. The multiple factor is the "spin number" or "spin state": e.g., for spin number of + 1/2, the actual spin is + 1/2 x h/2ã. Elementary particles (e.g., electrons, protons, neutrons) that have half-integer spin are called fermions, and such particles obey the Pauli exclusion principle: i.e., no two fermions of the same kind can occupy the same quantum state in a system. Because of their quantized energy constraints, fermions obey a special statistics (Fermi-Dirac statistics). In general, an atomic or molecular system is said to exhibit "quantum degeneracy" when the system has a number of possible quantized states and two or more distinct states of the set of possible states have the same energy. A "degenerate gas" is a gas in which the concentration of particles is sufficiently high for classical distribution statistics (Maxwell-Boltzmann statistics) not to hold, with the behavior of the gas controlled by quantum statistics (e.g., Fermi statistics). In a Fermi-Dirac system, the "Fermi level" is the energy level at which there is an 0.5 probability of finding an electron, and the "Fermi temperature" is defined by T(subF) = E(subF)/k, where E(subF) is the Fermi level energy and k is the Boltzmann constant. In general, Fermi-Dirac systems (Fermi systems) are dense and strongly interacting. Until now the only realization of a low- density Fermi system has been a dilute solution of liquid (sup3)He dissolved in superfluid (sup4)He. ... ... B. DeMarco and D.S. Jin (University of Colorado, US) now report the creation of a nearly ideal Fermi gas composed of atoms [(sup40)K] cooled to the regime where the effects of quantum statistics can be observed. The authors used an evaporative cooling strategy in which a two-component Fermi gas was used to cool a magnetically trapped gas of 7 x 10^(5) (sup40)K atoms to 0.5 of the Fermi temperature. The authors report that in this temperature regime quantum degeneracy was observed as a barrier to evaporative cooling and as a modification of the thermodynamics, and that measurements of the momentum distribution and the total energy of the confined Fermi gas directly revealed the quantum statistics. The authors conclude: "Reaching this quantum regime in the dilute Fermi gas extends the field of quantum degenerate gases and sets the stage for further experimental probes of a Fermi sea of atoms." ----------- B. DeMarco and D.S. Jin: Onset of Fermi degeneracy in a trapped atomic gas. (Science 10 Sep 99 285:1703) QY: D.S. Jin [jin@jilau1.colorado.edu] ----------- Text Notes: ... ... *magnetic moment: (magnetic dipole moment) The intrinsic spins of the electrons in an atom, together with the motion of the electrons around the nucleus, give rise to a magnetic field around the atom, and the magnitude of this field is related to the magnetic dipole moment of the atom or ion. ... ... *Note #1: The idea of electron spin was first proposed by Goudsmit and Uhlenbeck in 1925 to explain the splitting of atomic spectroscopic emission lines in the presence of a magnetic field. ------------------- Summary & Notes by SCIENCE-WEEK http://scienceweek.com 29Oct99 For more information: http://scienceweek.com/swfr.htm ------------------- Related Background: GRAVITO-OPTICAL SURFACE TRAP FOR SUPER-COOLED ATOMS Most physical systems have several forces simultaneously active upon the system, and if means can be found to isolate the interaction of two or more of these forces some interesting effects can be obtained, particularly configurations of the system that allow observations of parameters and relationships that are ordinarily masked. Rudolf Grimm et al (Max Planck Institute for Atomic Physics Heidelberg, DE) have developed a gravito-optical surface trap. The essential idea is to confine a small cloud of atoms (in this case, cesium atoms) at extremely low temperatures (approximately 0.003 degrees Kelvin). The cloud of atoms is confined in a vertical chamber whose bottom surface is a prism. At such low temperatures, atoms will fall to the bottom surface under the gravitational force. A laser beam is directed under the prism to strike the underside of the prism surface, which is the lowest surface of the confining chamber. The falling cesium atoms are now subjected to two forces: the downward gravitational force, and the upward electromagnetic force that spreads to the surface from the sub-incident laser beam. The end result is that the atoms eventually form an approximate two-dimensional cloud at the lower end of the confining chamber, and since one can produce such two-dimensional clouds with populations of only about 100 thousand atoms, this is a system that can be used to study a variety of subtle quantum phenomena. The actual experiment by Grimm et al has some additional refinements to further constrain the geometry of the atomic cloud. ----------- (Physical Review Letters 22 Sep 97) (Science-Week 17 Oct 97) For more information: http://scienceweek.com/swfr.htm =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= 7. IN FOCUS: ON STATISTICAL NEURODYNAMICS "It is clear that for our brains at least, there are two natural levels of description. One talks about detailed knowledge of connections, internal potentials, etc., in the constituent nerve cells. To specify the present state of nervous activity at this level requires at least 10^(10) numbers, probably more. The other level is that of the psychologist, with gross definitions of stimulus or response, or of introspection, the results of which can often be approximated with ordinary language. Furthermore, although we wish to explain the latter level in terms of the former, our real interest lies in the latter and if, for example, there are features of cellular activity irrelevant to behavior then they are also of relatively little interest to us. The situation is therefore superficially very similar to that which obtains in statistical mechanics, as it applies to the relation between macroscopic thermodynamic quantities and the underlying microscopic description in terms of the complete specification of the states of all the individual atoms or molecules, and the prime requirements for a statistical theory are present. These are first that we could not, even if we knew all the necessary parameters, actually solve in detail the 10^(10) or more coupled neuronal "equations of motion" necessary to follow the state of the system in detail as a function of time. Second, that there exists a simpler "macroscopic" level of description which is really our main ultimate object of interest, so that we do not wish, even if we could, to follow the "microscopic" state in detail, but merely wish to use it to understand the time development of the macroscopic state. One most important aspect of this is that we only wish to specify at the macroscopic level the initial conditions of any calculation we may make. This leads immediately to the problem of whether the fundamental assumptions of equal a priori probabilities and random a priori phases hold for nerve cell aggregates, and, if not, whether we can find anything to replace them. It is important to realize that normal statistical mechanics depends absolutely crucially on these assumptions and the laws of mechanics which may be used to justify them. If they are not true, we still can and should be trying to formulate a statistical neurodynamics, but we must then expect that, unless we are remarkably lucky, it will be much more difficult and differ enormously in structure from the statistical mechanics of physicists." ----------- J.S. Griffith: _Mathematical Neurobiology_ (Academic Press, London 1971, p.138.) ------------------- SCIENCE-WEEK http://scienceweek.com 13Oct00 For more information: http://scienceweek.com/swfr.htm =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= 8. FROM THE SCIENCEWEEK ARCHIVE: ON THE SOKAL HOAX AND PHILOSOPHICAL EXTRAPOLATIONS IN PHYSICS In the last quarter of this century, many fields outside of physical science are apparently in the throes of epistemological crises that are seen as originating in similar crises in physics during the first quarter of the century. *Complementarity, uncertainty, relativity, observer interactions -- the perceived philosophical implications of these ideas have been imported into the humanities and social sciences where they have rocked foundations and produced what many critics view as an intellectual babble. In 1996, theoretical physicist Alan Sokal concocted an article consisting mostly of the ideations of so- called "*postmodern" cultural studies of science, the article concerned with "a transformative hermeneutics of quantum gravity" and purporting to be an application of theoretical physics to affirm the thrust of postmodern cultural studies of science in the humanities and social sciences. The article was accepted and *published by the journal *Social Text*, and shortly afterward, in the journal *Lingua Franca*, Sokal revealed that his article was a complete hoax and designed as a parody of contemporary postmodern thought. In the academic furor that followed, Sokal's article was characterized as "an ingenious exposure of the decline of intellectual standards in contemporary academia," and "a brilliant parody of the postmodern nonsense rampant among the cultural studies of science." ... ... Writing in a physics journal, M. Beller now outlines an argument that theoretical physicists both past and present have had much responsibility for what appear to be the nonsensical applications of theoretical physics to the humanities and social sciences. The author makes the following points: 1) The philosophical pronouncements (several of which are quoted at length by Beller) of theoretical physicists *Niels Bohr, *Max Born, *Werner Heisenberg, *Wolfgang Pauli, and *Pascual Jordan deserve some of the blame for the excesses of the postmodern critique of science. 2) Like the deconstructionist *Jacques Derrida, Bohr was notorious for the obscurity of his writing. Yet physicists relate to the obscurities of Derrida and Bohr in fundamentally different ways: Derrida is treated with contempt and Bohr is treated with awe, his obscurity attributed to "depth and subtlety". 3) The author points out that in a widely used compendium of papers in theoretical physics published in 1983, there is an often cited reprinted paper by Bohr whose pages are out of order, and yet no complaints are heard and the mistake, which occurs in both hardcover and softcover editions, is apparently rarely noticed. 3) The author points out that Bohr intended his philosophy of complementarity to be an overarching epistemological principle applicable to physics, biology, psychology, and anthropology. Pauli argued for application of the quantum concept of reality to unify science, religion, Jungian archetypes, and extrasensory perception. Born stated that quantum philosophy would help humanity cope with the postwar era. Heisenberg expressed the hope that the results of quantum physics would transform cultural life by producing a renaissance of ideas. Jordan explored the "formal" parallels between quantum physics and Freudian psychoanalysis. 4) Beller points out that the philosophical pronouncements of Bohr and other founders of quantum physics are not just an anachronistic curiosity, since contemporary popular writings by physicists and science writers continue to proclaim the victory of Bohr's conception of reality, even though the Copenhagen "orthodox" interpretation of quantum physics -- the abandonment of causality and the ordinary conception of reality -- is not the only possible interpretation of quantum physics, and ultimately it might not even be the surviving one. 5) Beller concludes: "The opponents of the postmodernist cultural studies of science conclude confidently from the Sokal affair that 'the emperors have no clothes.' But who, exactly, are all these naked emperors? At whom should we be laughing?" ----------- M. Beller (Hebrew University Jerusalem, IL): The Sokal hoax: at whom are we laughing? (Physics Today September 1998) QY: Mara Beller, Hebrew University, Jerusalem IL. ----------- Text Notes: ... ... *Complementarity: The idea that a fundamental particle is neither a wave nor a particle, because these are complementary modes of description (see below, Report #6). ... ... *postmodern: The term here refers to studies of how contemporary concepts and methods are determined by historical or ideological context. So, for example, one set of postmodern questions concerning science involves the influences of Western socio-political ideology on the structure and methods of Western science. The general idea is the consideration of science as a product of the culture from which it arises. But the term "postmodern" has a loose usage, with one meaning in literature, another in art, and a third in the social sciences. ... ... *published: Sokal's paper was published in *Social Text* (Spring/Summer 1996, p.216), and then exposed immediately by himself in *Lingua Franca* (May/June 1996, p.62). ... ... *Niels Bohr (1885-1962): Nobel Prize in Physics 1922. He worked in the fields of atomic structure and nuclear fission, and he proposed the doctrine of complementarity. As director of the Institute of Theoretical Physics in Copenhagen from 1920 on, Bohr was the head of what came to be called the Copenhagen School of Quantum Mechanics, which produced what came to be called the "Copenhagen orthodoxy" view of the implications of quantum mechanics as applied in general to theoretical physics. ... ... *Max Born (1882-1970): Nobel Prize in Physics 1954. Did fundamental work in quantum theory, particularly work linking the wave function of the electron to electron distribution probability. It was Born who apparently coined the term "quantum mechanics". Born worked with Werner Heisenberg, one of his students, in the development of the mathematical techniques of matrix mechanics, an alternative to the Schroedinger wave equation for calculation of the position and momentum of the electron in the atom. From Born: "I am now convinced that theoretical physics is actual philosophy." ... ... *Werner Heisenberg (1901-1976): Nobel Prize in Physics 1932. Developed quantum theory and formulated the uncertainty principle, which concerns matter, radiation, and their reaction, and which places absolute limits on the achievable accuracy of measurement of physical phenomena in the quantum domain. ... ... *Wolfgang Pauli (1900-1958): Nobel Prize in Physics 1945. Originated the exclusion principle, which states that in a given system no two fermions (electrons, protons, neutrons, or other elementary particles of half-integral spin) can be characterized by the same set of quantum numbers. He also predicted the existence of neutrinos. ... ... *Pascual Jordan (1902-1980): Worked with Born and Heisenberg in the development of matrix mechanics. Also worked in the relativistic quantum field theory of electromagnetism (quantum electrodynamics). ... ... *Jacques Derrida (1930- ): A philosopher whose work spans literary criticism, psychoanalysis, linguistics, and philosophy, with an emphasis on the primacy of written text, the referentiality of language, and the objectivity of conceptual structures. Founded the school of criticism known as "deconstruction". ------------------- Summary & Notes by SCIENCE-WEEK 25Sep98 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= 9. CORRECTION: ISSUE OF 1 SEP 00 FIRST ELECTROSTATIC TRAPPING OF AMMONIA MOLECULES In the ScienceWeek issue of 1 Sep 00 (vol.4, #35), report #4, the major citation should (Nature 3 Aug 00 406:491) =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= NOTICES =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= CHANGE OF EMAIL ADDRESS: If at any time you need to change the Email address at which you receive SW, please send the information to: request@scienceweek.com =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= SCIENCE-WEEK SUBSCRIPTIONS: Subscriptions to ScienceWeek cost as little as US$15 a year. Complete subscription information is available at: http://scienceweek.com/subinfo.htm =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= The first issue of SCIENCE-WEEK appeared May 1, 1997, and it has been published regularly each week since that date. 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