bluuebunny/crossref_metadata_2025 huggingface dataset:
A Trans-Acting Factor that Binds to a GT-motif in a Phytochrome Gene Promoter
Authors: Dehesh Katayoon , Bruce Wesley B. , Quail Peter H.
Published: October 2006

The regulatory photoreceptor, phytochrome, controls the expression of numerous genes, including its own
phyA
genes, which are transcriptionally repressed in response to light. Functional analysis of a rice
phyA
gene promoter, by means of microprojectile-mediated gene transfer, indicates that a GT motif, GCGGTAATT, closely related to elements in the promoters of a number of other light-regulated genes, is critical for expression. Partial complementary DNA clones have been obtained for a rice nuclear protein, designated GT-2, that binds in a highly sequence-specific fashion to this motif. Mutational analysis shows that the paired G's are most crucial to binding. GT-2 has domains related to certain other transcription factors. Northern blot analysis shows that GT-2 messenger RNA levels decline in white light although red and far red light pulses are ineffective.
Florida Current Volume Transports from Voltage Measurements
Authors: Larsen Jimmy C. , Sanford Thomas B.
Published: October 2006

The volume transport of the Florida Current is determined from the motionally induced voltage difference between Florida and Grand Bahama Island. Simultaneous measurements of potential differences and of volume transport by velocity profiling have a correlation of 0.97. The calibration factor is 25 ± 0.7 sverdrups per volt, and the root-mean-square discrepancy is 0.7 sverdrup. The induced voltage is about one-half the open-circuit value, implying that the conductance of the sediments and lithosphere is about equal to that of the water column.
Sea Level Variation as an Indicator of Florida Current Volume Transport: Comparisons with Direct Measurements
Authors: Maul George A. , Chew Frank , Bushnell Mark , Mayer Dennis A.
Published: October 2006

Sea level measurements from tide gauges at Miami, Florida, and Cat Cay, Bahamas, and bottom pressure measurements from a water depth of 50 meters off Jupiter, Florida, and a water depth of 10 meters off Memory Rock, Bahamas, were correlated with 81 concurrent direct volume transport observations in the Straits of Florida. Daily-averaged sea level from either gauge on the Bahamian side of the Straits was poorly correlated with transport. Bottom pressure off Jupiter had a linear coefficient of determination of
r
2
= 0.93, and Miami sea level, when adjusted for weather effects, had
r
2
= 0.74; the standard errors of estimating transports were ± 1.2 × 10
6
and ± 1.9 × 10
6
cubic meters per second, respectively. A linear multivariate regression, which combined bottom pressure, weather, and the submarine cable observations between Jupiter and the Bahamas, had
r
2
= 0.94 with a standard error of estimating transport of ± 1.1 × 10
6
cubic meters per second. These results suggest that a combination of easily obtained observations is sufficient to adequately monitor the daily volume transport fluctuations of the Florida Current.
Understanding Molecular Dynamics Quantum-State by Quantum-State
Authors: Lawrance Warren D. , Moore C. Bradley , Petek Hrvoje
Published: October 2006

It is now possible to resolve completely the initial and final quantum states in chemical processes. Spectra of reactive intermediates, of highly vibrationally excited molecules, and even of molecules in the process of falling apart have been recorded. This information has led to greater understanding of the molecular structure and dynamics of small gas-phase molecules. Many of the concepts and spectroscopic techniques that have been developed will be valuable throughout chemistry.
Indian-Atlantic Transfer of Thermocline Water at the Agulhas Retroflection
Authors: Gordon Arnold L.
Published: October 2006

During November and December 1983, two anticyclonic eddies were observed west of the Agulhas Retroflection, apparently spawned at the retroflection. The western eddy, centered 300 kilometers southwest of Cape Town, has a winter cooled core encircled by warm Indian Ocean water. Between Cape Town and the "Cape Town Eddy" is a net geostrophic transport of Indian Ocean thermocline water (14 × 10
6
cubic meters per second) into the South Atlantic Ocean. This circulation configuration, similar to that observed by earlier researchers, suggests that Indian-Atlantic thermocline exchange is a common occurrence. Such a warmwater link between the Atlantic and Indian oceans would strongly influence global climate patterns. The Indian Ocean water is warmer than the adjacent South Atlantic water and thus represents a heat input of 2.3 × 10
13
to 47 × 10
13
watts into the Atlantic. The large uncertainty arises from the unknown partition between two possible routes for the return flow from the Atlantic to the Indian Ocean: cooler South Atlantic thermocline water or much colder North Atlantic Deep Water. In either case, interocean mass and heat exchange of thermocline water at the Agulhas Retroflection is a distinct likelihood.
Sex Ratio Adjustment in Fig Wasps
Authors: Herre Edward Allen
Published: October 2006

The effects of inbreeding and local mate competition have often been confounded in theoretical and empirical studies of sex ratio. A general model considering the interplay of their influences on sex ratio evolution is presented, and its predictions are compared with data collected from three fig wasp species. The results indicate that female fig wasps adjust the sex ratio of their offspring in response to both the intensity of proximate local mate competition and the level of inbreeding in the population.
Free Radicals in the Stratosphere: A New Observational Technique
Authors: Anderson J. G. , Hazen N. L. , McLaren B. E. , Rowe S. P. , Schiller C. M. , Schwab M. J. , Solomon L. , Thompson E. E. , Weinstock E. M.
Published: October 2006

A new approach to in situ observations of trace reactive species in the stratosphere is described. A balloon-borne system, floating 40 kilometers above the earth's surface, successfully lowered and then retracted a cluster of instruments a distance of 12 kilometers on a filament of Kevlar. This instrument cluster is capable of detecting gas-phase free radicals at the part-per-trillion level. The suspended instrument array has excellent stability and has been used to measure atomic oxygen concentrations in the stratosphere.
Speciation and Symbiotic Dinoflagellates
Authors: Blank Rudolf J. , Trench Robert K.
Published: October 2006

Morphometric analyses based on three-dimensional reconstruction of the nuclei of four different strains of the symbiotic dinoflagellate
Symbiodinium microadriaticum
, the algae that inhabit corals, giant clams, and other marine invertebrates, revealed marked differences in chromosome numbers and chromosome volumes. The differences are not consistent with different ploidy states within the same species, but can most easily be interpreted as indicating different species.
Enhancement of SIV Infection with Soluble Receptor Molecules
Authors: Allan Jonathan S. , Strauss Janet , Buck David W.
Published: October 2006

The CD4 receptor on human T cells has been shown to play an integral part in the human immunodeficiency virus type 1 (HIV-1) infection process. Recombinant soluble human CD4 (rCD4) was tested for its ability to inhibit SIVagm, an HIV-like virus that naturally infects African green monkeys, in order to define T cell surface receptors critical for SIVagm infection. The rCD4 was found to enhance SIVagm infection of a human T cell line by as much as 18-fold, whereas HIV-1 infection was blocked by rCD4. Induction of syncytium formation and de novo protein synthesis were observed within the first 24 hours after SIVagm infection, whereas this process took 4 to 6 days in the absence of rCD4. This enhancing effect could be inhibited by monoclonal antibodies directed to rCD4. The enhancing effect could be abrogated with antibodies from naturally infected African green monkeys with inhibitory titers of from 1:2,000 to 1:10,000; these antibodies did not neutralize SIVagm infection in the absence of rCD4. Viral enhancement of SIVagm infection by rCD4 may result from the modulation of the viral membrane through gp120-CD4 binding, thus facilitating secondary events involved in viral fusion and penetration.
Life History of Symbiont-Bearing Giant Clams from Stable Isotope Profiles
Authors: Jones Douglas S. , Williams Douglas F. , Romanek Christopher S.
Published: October 2006

Stable isotopic and shell-growth banding studies of the symbiont-bearing giant clam
Tridacna maxima
reveal the existence of two growth phases related to sexual maturity that can be discerned in the shells of extinct and extant mollusks. The changeover from the first to second growth phase at an age of approximately 10 years is accompanied by a decrease in rate of calcification and suggests a reordering of energy priorities between biomineralization and reproduction. The carbon-13 to carbon-12 ratio of
Tridacna maxima
is systematically depleted relative to symbiont-barren mollusks, making it possible to determine the importance of algal-molluscan symbiosis to the functional morphology and paleoecology of mollusks in the geologic record.
Parallel Supercomputing Today and the Cedar Approach
Authors: Kuck David J. , Davidson Edward S. , Lawrie Duncan H. , Sameh Ahmed H.
Published: October 2006

More and more scientists and engineers are becoming interested in using supercomputers. Earlier barriers to using these machines are disappearing as software for their use improves. Meanwhile, new parallel supercomputer architectures are emerging that may provide rapid growth in performance. These systems may use a large number of processors with an intricate memory system that is both parallel and hierarchical; they will require even more advanced software. Compilers that restructure user programs to exploit the machine organization seem to be essential. A wide range of algorithms and applications is being developed in an effort to provide high parallel processing performance in many fields. The Cedar supercomputer, presently operating with eight processors in parallel, uses advanced system and applications software developed at the University of Illinois during the past 12 years. This software should allow the number of processors in Cedar to be doubled annually, providing rapid performance advances in the next decade.
VEGA Balloon System and Instrumentation
Authors: Kremnev R. S. , Linkin V. M. , Lipatov A. N. , Pichkadze K. M. , Shurupov A. A. , Terterashvili A. V. , Bakitko R. V. , Blamont J. E. , Malique C. , Ragent B. , Preston R. A. , Elson L. S. , Crisp D.
Published: October 2006

The VEGA Venus balloon radio transmissions received on Earth were used to measure the motion of the balloons and to obtain the data recorded by onboard sensors measuring atmospheric characteristics. Thus the balloons themselves, the gondolas, the onboard sensors, and the radio transmission system were all components of the experiment. A description of these elements is given, and a few details of data sampling and formatting are discussed.
VEGA Balloon Dynamics and Vertical Winds in the Venus Middle Cloud Region
Authors: Linkin V. M. , Kerzhanovich V. V. , Lipatov A. N. , Pichkadze K. M. , Shurupov A. A. , Terterashvili A. V. , Ingersoll A. P. , Crisp D. , Grossman A. W. , Young R. E. , Seiff A. , Ragent B. , Blamont J. E. , Elson L. S. , Preston R. A.
Published: October 2006

The VEGA balloons provided a long-term record of vertical wind fluctuations in a planetary atmosphere other than Earth's. The vertical winds were calculated from the observed displacement of the balloon relative to its equilibrium float altitude. The winds were intermittent; a large burst lasted several hours, and the peak velocity was 3 meters per second.
Two-Dimensional Rare Gas Solids
Authors: Birgeneau Robert J. , Horn Paul M.
Published: October 2006

Monolayers of rare gas atoms adsorbed onto the basal planes of graphite play the same prototype role in two dimensions that rare gas liquids and solids do in three dimensions. In recent experiments such novel phenomena as continuous melting, the lack of true crystallinity in two dimensions, orientationally ordered fluid phases, and melting from a solid to a reentrant fluid with decreasing temperature have been observed. Because the forces in these rare gas monolayers are simple and well understood, by studying them the investigator can examine a direct interface between experiment and first principles. In order to understand the phases and phase transitions that occur in such materials, it is necessary to consider the geometrical matching of the rare gas overlayer to the graphite substrate. It turns out that in two dimensions both the local and the long-distance behavior are important. These two-dimensional rare gas solids may be effectively probed with synchrotron x-ray techniques, and the results of a series of synchrotron x-ray scattering studies of these solids are presented.
Soft X-Ray Lasers and Their Applications
Authors: Suckewer S. , Skinner C. H.
Published: October 2006

The emerging technology of soft x-ray lasers has novel applications to microscopy, lithography, and other fields. This article describes the status of soft x-ray laser research with the aim of bringing the rapid developments in this field to the attention of potential users in other disciplines. The different techniques for generating a population inversion and producing a soft x-ray laser are reviewed. The status of current research in the field and the near-term prospects are described. It is expected that the range of potential applications of soft x-ray lasers will increase as their performance improves. Work aimed at increasing the output power and progressing to shorter wavelengths with these devices is also reviewed.
Limit of T Cell Tolerance to Self Proteins by Peptide Presentation
Authors: Schild Hansjörg , Rötzschke Olaf , Kalbacher Hubert , Rammensee Hans-Georg
Published: October 2006

Cytotoxic T lymphocytes (CTLs) recognize foreign peptides bound to major histocompatibility complex (MHC) class I molecules. MHC molecules can also bind endogenous self peptides, to which T cells are tolerant. Normal mice contained CTLs specific for self peptides that were from proteins of ubiquitous or tissue-restricted expression. In vivo, these endogenous self peptides are not naturally presented in sufficient density by somatic cells expressing MHC class I molecules. They can, however, be presented if added exogenously. Thus, our data imply that CTLs are only tolerant of those endogenous self peptide sequences that are presented by MHC class I-positive cells in a physiological manner.
Mechanical Stress and Reactivity in Organic Solids
Authors: McBride J. Michael , Segmuller Brigitte E. , Hollingsworth Mark D. , Mills David E. , Weber Bruce A.
Published: October 2006

Organic single crystals provide an ideal model for studying the factors that influence chemical processes in structured media. Reaction trajectories are well defined and reveal the influence of spontaneous mechanical stresses equivalent to tens of thousands of atmospheres. Analysis of molecular and crystal structures helps to explain both local mechanical properties, which influence reactions, and bulk properties such as melting point, compressibility, and surface energy.
Optical Experiments and Weak Interactions
Authors: Bouchiat Marie-Anne , Pottier Lionel
Published: October 2006

Recent optical experiments have demonstrated cases in which mirror symmetry in stable atoms is broken during absorption of light. These results, which are in contradiction with quantum electrodynamics, support the theory of unification of the electromagnetic and weak forces. The interpretation of these experimental results is based on exchanges of weak neutral Z
0
bosons between the electrons and the nucleus of the atom. The information obtained from low-energy experiments is different from, but complementary to, the results of high-energy experiments. Sensitive measurements in a simple, reliably computable atom are in quantitative agreement with the standard electroweak theory and put stringent constraints on alternative models. Attaining sufficient accuracy in the experiments and the computations for the electroweak radiative corrections to manifest themselves is now the challenge for experimenters and theorists.
Randomly Exact Methods
Authors: Doll J. D. , Freeman D. L.
Published: October 2006

Important advances in the understanding of "random" processes have produced a variety of stochastic algorithms that offer unprecedented scope and utility in the study of physical systems. These algorithms represent a departure from the usual philosophy inherent in the study of many-body problems and have a number of significant features. Chief among these features are simplicity, weak dependence on dimensionality, and ease of transition between classical and quantum-mechanical descriptions. These methods are also readily adapted for use on massively parallel computer architectures. These new stochastic methods represent a valuable addition to the tools available for the analysis of both equilibrium and time-dependent many-body problems.
Artificially Structured Thin-Film Materials and Interfaces
Authors: Narayanamurti V.
Published: October 2006

The ability to artificially structure new materials on an atomic scale by using advanced crystal growth methods such as molecular beam epitaxy and metal-organic chemical vapor deposition has recently led to the observation of unexpected new physical phenomena and to the creation of entirely new classes of devices. In particular, the growth of materials of variable band gap in technologically important semiconductors such as GaAs, InP, and silicon will be reviewed. Recent results of studies of multilayered structures and interfaces based on the use of advanced characterization techniques such as high-resolution transmission electron microscopy and scanning tunneling microscopy will be presented.
The 1986 Lake Nyos Gas Disaster in Cameroon, West Africa
Authors: Kling George W. , Clark Michael A. , Wagner Glen N. , Compton Harry R. , Humphrey Alan M. , Devine Joseph D. , Evans William C. , Lockwood John P. , Tuttle Michele L. , Koenigsberg Edward J.
Published: October 2006

The sudden, catastrophic release of gas from Lake Nyos on 21 August 1986 caused the deaths of at least 1700 people in the northwest area of Cameroon, West Africa. Chemical, isotopic, geologic, and medical evidence support the hypotheses that (i) the bulk of gas released was carbon dioxide that had been stored in the lake's hypolimnion, (ii) the victims exposed to the gas cloud died of carbon dioxide asphyxiation, (iii) the carbon dioxide was derived from magmatic sources, and (iv) there was no significant, direct volcanic activity involved. The limnological nature of the gas release suggests that hazardous lakes may be identified and monitored and that the danger of future incidents can be reduced.
Evidence for Chain Molecules Enriched in Carbon, Hydrogen, and Oxygen in Comet Halley
Authors: Mitchell D. L. , Lin R. P. , Anderson K. A. , Carlson C. W. , Curtis D. W. , Korth A. , Rème H. , Sauvaud J. A. , d'Uston C. , Mendis D. A.
Published: October 2006

In situ measurements of the composition and spatial distribution of heavy thermal positive ions in the coma of comet Halley were made with the heavy-ion analyzer RPA2-PICCA aboard the Giotto spacecraft. Above 50 atomic mass units an ordered series of mass peaks centered at 61, 75, 91, and 105 atomic mass units were observed. Each peak appears to be composed of three or more closely spaced masses. The abundances decrease and the dissociation rates increase smoothly with increasing mass. These observations suggest the presence of chain molecules that are enriched in carbon, oxygen, and hydrogen, such as polyoxymethylene (polymerized formaldehyde), in comet Halley.
First Polymer in Space Identified in Comet Halley
Authors: Huebner W. F.
Published: October 2006

The heavy-ion mass spectrum obtained in the inner coma of comet Halley with the PICCA instrument on the Giotto spacecraft has been examined. Short polymer chains of polyoxymethylene and their decay products are identified as the source for the spectrum with six mass peaks between about 45 and 120 atomic mass units. The properties of polyoxymethylene are consistent with many of the unexpected observations in the coma.
Picosecond Holographic-Grating Spectroscopy
Authors: Wiersma D. A. , Duppen K.
Published: October 2006

Interfering light waves produce an optical interference pattern in any medium that interacts with light. This modulation of some physical parameter of the system acts as a classical holographic grating for optical radiation. When such a grating is produced through interaction of pulsed light waves with an optical transition, a transient grating is formed whose decay is a measure of the relaxation time of the excited state. Transient gratings can be formed in real space or in frequency space depending on the time ordering of the interfering light waves. The two gratings are related by a space-time transformation and contain complementary information on the optical dynamics of a system. The status of a grating can be probed by a delayed third pulse, which diffracts off this grating in a direction determined by the wave vector difference of the interfering light beams. This generalized concept of a transient grating can be used to interpret many picosecond-pulse optical experiments on condensed-phase systems. Examples of some low-temperature experiments will be presented. In principle, many of these experiments could also be performed by using stochastic broad-band excitation. In these nonlinear photon-interference experiments the time resolution is determined by the correlation time of the light source rather than its pulse width.
Design of DNA-Binding Peptides Based on the Leucine Zipper Motif
Authors: O'Neil Karyn T. , Hoess Ronald H. , DeGrado William F.
Published: October 2006

A class of transcriptional regulator proteins bind to DNA at dyad-symmetric sites through a motif consisting of (i) a "leucine zipper" sequence that associates into noncovalent, parallel, α-helical dimers and (ii) a covalently connected basic region necessary for binding DNA. The basic regions are predicted to be disordered in the absence of DNA and to form α helices when bound to DNA. These helices bind in the major groove forming multiple hydrogen-bonded and van der Waals contacts with the nucleotide bases. To test this model, two peptides were designed that were identical to natural leucine zipper proteins only at positions hypothesized to be critical for dimerization and DNA recognition. The peptides form dimers that bind specifically to DNA with their basic regions in α-helical conformations.
Capture of Atmospheric Ammonium by Grassland Canopies
Authors: Heil G. W. , Werger M. J. A. , de Mol W. , van Dam D. , Heijne B.
Published: October 2006

Air pollution can cause a decline in species through acidification of the habitat. New data suggest that the decline may be due to eutrophication rather than acidification. In Western Europe, eutrophication largely results from atmospheric ammonium deposition. The amount deposited on vegetation is a function of its canopy structure. Deposition on grasslands has been underestimated, and a significant amount of the deposited ammonium appears to be assimilated by the plant canopy. These quantities are sufficient to initiate changes in the competitive relations among the plant species.
Xotch
, the
Xenopus
Homolog of
Drosophila Notch
Authors: Coffman Clark , Harris William , Kintner Chris
Published: October 2006

During the development of a vertebrate embryo, cell fate is determined by inductive signals passing between neighboring tissues. Such determinative interactions have been difficult to characterize fully without knowledge of the molecular mechanisms involved. Mutations of
Drosophila
and the nematode
Caenorhabditis elegans
have been isolated that define a family of related gene products involved in similar types of cellular inductions. One of these genes, the
Notch
gene from
Drosophila
, is involved with cell fate choices in the neurogenic region of the blastoderm, in the developing nervous system, and in the eye-antennal imaginal disc. Complementary DNA clones were isolated from
Xenopus
embryos with
Notch
DNA in order to investigate whether cell-cell interactions in vertebrate embryos also depend on
Notch
-like molecules. This approach identified a
Xenopus
molecule,
Xotch
, which is remarkably similar to
Drosophila
Notch
in both structure and developmental expression.
Technology and Competitiveness: A Key to the Economic Future of the United States
Authors: Young John A.
Published: October 2006

The United States still is a leader in technology and innovation, but American industry has been slow to translate that advantage into commercial success. A major contributing factor is the low status accorded manufacturing in this country and a lack of teamwork among scientists, engineers, and managers. However, there are encouraging signs that these key players in the innovation cycle are recognizing the need to work together to improve products and manufacturing processes and to restore the competitive position of the United States.
Naturally Occurring Auxin Transport Regulators
Authors: Jacobs Mark , Rubery Philip H.
Published: October 2006

The process of polar auxin transport, central to a plant's auxin relations, can be inhibited by a group of synthetic compounds that apparently act by binding to a plasma membrane protein known as the naphthylphthalamic acid (NPA) receptor. No endogenous ligand to the NPA receptor, capable of affecting polar auxin transport in plants, has yet been found. It is now shown that a group of flavonoids-including quercetin, apigenin, and kaempferol—can specifically compete with [
3
H]NPA for binding to its receptor and can perturb auxin transport in a variety of plant tissues and transport systems in a manner closely paralleling the action of synthetic transport inhibitors. Because the active flavonoids are widely distributed in the plant kingdom and exert their effects at micromolar concentrations approximating likely endogenous levels, they may act as natural auxin transport regulators in plants.
Hepatitis B virus DNA Sequences in Lymphoid Cells from Patients with AIDS and AIDS-Related Complex
Authors: Laure F. , Zagury D. , Saimot A. G. , Gallo R. C. , Hahn B. H. , Brechot C.
Published: October 2006

A lymphotropic virus HTLV-III/LAV was recently identified as the etiologic agent of the acquired immune deficiency syndrome (AIDS). In a study of concomitant hepatitis B infections in patients with AIDS or the AIDS-related complex, DNA sequences of hepatitis B virus (HBV) were found in fresh and cultured lymphocytes from patients with AIDS even in the absence of conventional HBV serological markers. Furthermore, the restriction DNA pattern was consistent with the integration of the viral DNA. These results should prompt additional studies to reevaluate a possible role of HBV as a cofactor in AIDS in addition to the HTLV-III/LAV causal agent.
Circumsporozoite Protein of
Plasmodium vivax
: Gene Cloning and Characterization of the Immunodominant Epitope
Authors: Arnot David E. , Barnwell John W. , Tam James P. , Nussenzweig Victor , Nussenzweig Ruth S. , Enea Vincenzo
Published: October 2006

The gene encoding the circumsporozoite (CS) protein of the human malaria parasite
Plasmodium vivax
has been cloned. The deduced sequence of the protein consists of 373 amino acids with a central region of 19 tandem repeats of the nonapeptide Asp-Arg-Ala-Asp/Ala-Gly-Gln-Pro-Ala-Gly. A synthetic 18-amino acid peptide containing two tandem repeats binds to a monoclonal antibody directed to the CS protein of
Plasmodium vivax
and inhibits the interaction of this antibody with the native protein in sporozoite extracts. The portions of the CS gene that do not contain repeats are closely related to the corresponding regions of the CS genes of two simian malarias,
Plasmodium cynomolgi
and
Plasmodium knowlesi
. In contrast, the homology between the CS genes of
Plasmodium vivax
and
Plasmodium falciparum
, another malaria parasite of humans, is very limited.
Elasticity of MgSiO
3
in the Perovskite Structure
Authors: Yeganeh-Haeri A. , Weidner D. J. , Ito E.
Published: October 2006

The single-crystal elastic moduli of MgSiO
3
in the perovskite structure, the high-pressure polymorph of MgSiO
3
pyroxene, have been determined. The data indicate that a mantle with either pyrolite or pyroxene stoichiometry is compatible with the seismic models appropriate to the earth's lower mantle, provided that the shear modulus of MgSiO
3
perovskite exhibits a strong negative temperature derivative. Such a temperature derivative falls outside of the range expected for a well-behaved refractory ceramic and could result if the pressure-temperature regime of the earth's lower mantle is near that required for a ferroelastic phase transformation of the perovskite phase.
Restriction Fragment Length Polymorphisms Associated with Water Use Efficiency in Tomato
Authors: Martin Bjorn , Nienhuis James , King Gretchen , Schaefer Alison
Published: October 2006

Improvement of crop water use efficiency (WUE) has not been successful because evaluation for this component of drought resistance is unreliable in field-grown plants. The composition of stable isotopes of plant carbon (δ
13
C) was earlier shown to be an excellent indicator of WUE in tomato and other species. It is now reported that δ
13
C can be satisfactorily predicted from three restriction fragment length polymorphisms (RFLPs), which are genetic markers for discrete DNA sequences within the genome. An additive type of gene action was observed for all three RFLP markers, and for one of them there also was a significant nonadditive component. Combining the δ
13
C and RFLP technologies may aid in identifying genes associated with WUE and in studying mechanisms contributing to WUE. These technologies will also be useful for crop improvement.
Epitopes of the CD4 Antigen and HIV Infection
Authors: Sattentau Quentin J. , Dalgleish Angus G. , Weiss Robin A. , Beverley Peter C. L.
Published: October 2006

The CD4 (or T4) surface antigen of human T lymphocytes is an important part of the receptor for the human immunodeficiency virus (HIV). After binding to the receptor, the HIV may enter the T cell and induce the formation of syncytia. In an attempt to identify the receptor site more closely, monoclonal antibodies (Mab's) to CD4 were tested for their ability to block HIV infection in a syncytium formation assay, and the CD4 epitopes so identified were mapped by antibody cross-blocking. The antibodies that showed strong inhibition of HIV fell into two main families while a third group of Mab's blocked syncytia formation weakly or not at all. Several different isolates of HIV as well as the laboratory strain CBL1 grown in CEM cells were used to induce the syncytia. The data indicate that only some epitopes of CD4 are important for virus binding and imply that the virus-binding site for CD4 is conserved in different isolates of HIV with substantially divergent
env
gene sequences. Preliminary studies of patients suggest that polymorphism of these epitopes does not play a role in determining susceptibility to infection.
Kestel: An Early Bronze Age Source of Tin Ore in the Taurus Mountains, Turkey
Authors: Yener K. Aslihan , Özbal Hadi , Kaptan Ergun , Pehlivan A. Necip , Goodway Martha
Published: October 2006

An ancient mine located at Kestel on the outskirts of Nigde, in the Taurus Mountains of south central Turkey, has been dated by radiocarbon and pottery type to the third millennium B.C. Archeological soundings in the mine located cassiterite (tin oxide) in the detritus of ancient mining activity. Cassiterite is also present in veins and, as placer deposits, in streams nearby. Since tin is used with copper in order to form bronze but is thinly distributed in the earth's crust, the presence of tin ore at Kestel offers a source for the much sought after tin of the Bronze Age. The discovery of an ancient mine containing cassiterite sheds light on this question, but also greatly complicates the accepted picture of regional economic patterns in the highland resource areas of Anatolia and of interregional metal exchange in the formative periods of urbanization and metal use in the eastern Mediterranean.
Some Developments in Nuclear Magnetic Resonance of Solids
Authors: Chmelka B. F. , Pines A.
Published: October 2006

Nuclear magnetic resonance (NMR) spectroscopy continues to evolve as a primary technique in the study of solids. This review briefly describes some developments in modern NMR that demonstrate its exciting potential as an analytical tool in fields as diverse as physics, chemistry, biology, geology, and materials science. Topics covered include motional narrowing by sample reorientation, multiple-quantum and overtone spectroscopy, probing porous solids with guest atoms and molecules, two-dimensional NMR studies of chemical exchange and spin diffusion, experiments at extreme temperatures, NMR imaging of solid materials, and low-frequency and zero-field magnetic resonance. These developments permit increasingly complex structural and dynamical behavior to be probed at a molecular level and thus add to our understanding of macroscopic properties of materials.
Carbon Dioxide Transport by Ocean Currents at 25°N Latitude in the Atlantic Ocean
Authors: Brewer Peter G. , Goyet Catherine , Dyrssen David
Published: October 2006

Measured concentrations of CO
2
, O
2
, and related chemical species in a section across the Florida Straits and in the open Atlantic Ocean at approximately 25°N, have been combined with estimates of oceanic mass transport to estimate both the gross transport of CO
2
by the ocean at this latitude and the net CO
2
flux from exchange with the atmosphere. The northward flux was 63.9 × 10
6
moles per second (mol/s); the southward flux was 64.6 × 10
6
mol/s. These values yield a net CO
2
flux of 0.7 × 10
6
mol/s (0.26 ± 0.03 gigaton of C per year) southward. The North Atlantic Ocean has been considered to be a strong sink for atmospheric CO
2
, yet these results show that the net flux in 1988 across 25°N was small. For O
2
the equivalent signal is 4.89 × 10
6
mol/s northward and 6.97 × 10
6
mol/s southward, and the net transport is 2.08 × 10
6
mol/s or three times the net CO
2
flux. These data suggest that the North Atlantic Ocean is today a relatively small sink for atmospheric CO
2
, in spite of its large heat loss, but a larger sink for O
2
because of the additive effects of chemical and thermal pumping on the CO
2
cycle but their near equal and opposite effects on the CO
2
cycle.
On the Fringes of Conquest: Maya-Spanish Contact in Colonial Belize
Authors: Graham Elizabeth , Pendergast David M. , Jones Grant D.
Published: October 2006

The defeat of the Aztecs of Mexico by Hernán Cortés in 1521 was but the beginning of a long and torturous conquest of Central America that did not always result in the mastery of people and production for which the Spanish had hoped. The Maya of the resource-poor Yucatán peninsula were spared the heavy colonial hand that held fast to central Mexico and its riches. In addition, the dense forests of the peninsula served as a haven for refugees fleeing oppressive conditions in colonial towns. Despite the paucity of documentary information on Maya communities of the frontier, knowledge of Maya-Spanish relations in the 16th and 17th centuries has advanced in recent years through archeological and ethnohistorical research. Work in one region of the Maya lowlands has brought us closer to an understanding of the early interaction of the rulers and the ruled.
Ultraviolet Spectrometer Observations of Neptune and Triton
Authors: Broadfoot A. L. , Atreya S. K. , Bertaux J. L. , Blamont J. E. , Dessler A. J. , Donahue T. M. , Forrester W. T. , Hall D. T. , Herbert F. , Holberg J. B. , Hunter D. M. , Krasnopolsky V. A. , Linick S. , Lunine J. I. , McConnell J. C. , Moos H. W. , Sandel B. R. , Schneider N. M. , Shemansky D. E. , Smith G. R. , Strobel D. F. , Yelle R. V.
Published: October 2006

Results from the occultation of the sun by Neptune imply a temperature of 750 ± 150 kelvins in the upper levels of the atmosphere (composed mostly of atomic and molecular hydrogen) and define the distributions of methane, acetylene, and ethane at lower levels. The ultraviolet spectrum of the sunlit atmosphere of Neptune resembles the spectra of the Jupiter, Saturn, and Uranus atmospheres in that it is dominated by the emissions of H Lyman α (340 ± 20 rayleighs) and molecular hydrogen. The extreme ultraviolet emissions in the range from 800 to 1100 angstroms at the four planets visited by Voyager scale approximately as the inverse square of their heliocentric distances. Weak auroral emissions have been tentatively identified on the night side of Neptune. Airglow and occultation observations of Triton's atmosphere show that it is composed mainly of molecular nitrogen, with a trace of methane near the surface. The temperature of Triton's upper atmosphere is 95 ± 5 kelvins, and the surface pressure is roughly 14 microbars.
Plasma Observations Near Neptune: Initial Results from Voyager 2
Authors: Belcher J. W. , Bridge H. S. , Bagenal F. , Coppi B. , Divers O. , Eviatar A. , Gordon G. S. , Lazarus A. J. , McNutt R. L. , Ogilvie K. W. , Richardson J. D. , Siscoe G. L. , Sittler E. C. , Steinberg J. T. , Sullivan J. D. , Szabo A. , Villanueva L. , Vasyliunas V. M. , Zhang M.
Published: October 2006

The plasma science experiment on Voyager 2 made observations of the plasma environment in Neptune's magnetosphere and in the surrounding solar wind. Because of the large tilt of the magnetic dipole and fortuitous timing, Voyager entered Neptune's magnetosphere through the cusp region, the first cusp observations at an outer planet. Thus the transition from the magnetosheath to the magnetosphere observed by Voyager 2 was not sharp but rather appeared as a gradual decrease in plasma density and temperature. The maximum plasma density observed in the magnetosphere is inferred to be 1.4 per cubic centimeter (the exact value depends on the composition), the smallest observed by Voyager in any magnetosphere. The plasma has at least two components; light ions (mass, 1 to 5) and heavy ions (mass, 10 to 40), but more precise species identification is not yet available. Most of the plasma is concentrated in a plasma sheet or plasma torus and near closest approach to the planet. A likely source of the heavy ions is Triton's atmosphere or ionosphere, whereas the light ions probably escape from Neptune. The large tilt of Neptune's magnetic dipole produces a dynamic magnetosphere that changes configuration every 16 hours as the planet rotates.
A Mechanosensitive Ion Channel in the Yeast Plasma Membrane
Authors: Gustin Michael C. , Zhou Xin-Liang , Martinac Boris , Kung Ching
Published: October 2006

Mechanosensitive ion channels use mechanical energy to gate the dissipation of electrochemical gradients across cell membranes. This function is fundamental to physiological processes such as hearing and touch. In electrophysiological studies of ion channels in the plasma membrane of the yeast
Saccharomyces cerevisiae
, channels were observed that were activated by, and adapted to, stretching of the membrane. Adaptation of channel activity to mechanical stimuli was voltage-dependent. Because these mechanosensitive channels pass both cations and anions, they may play a role in turgor regulation in this walled organism.
Atrial Natriuretic Peptide Inhibits a Cation Channel in Renal Inner Medullary Collecting Duct Cells
Authors: Light Douglas B. , Schwiebert Erik M. , Karlson Katherine H. , Stanton Bruce A.
Published: October 2006

The patch-clamp technique was used to examine the effects of atrial natriuretic peptide (ANP) and its second messenger guanosine 3′,5′-monophosphate (cGMP) on an amiloride-sensitive cation channel in the apical membrane of renal inner medullary collecting duct cells. Both ANP (10
-11
M
) and dibutyryl guanosine 3′,5′-monophosphate (10
-4
M
) inhibited the channel in cell-attached patches, and cGMP (10
-5
M
) inhibited the channel in inside-out patches. The inner medullary collecting duct is the first tissue in which ANP, via its second messenger cGMP, has been shown to regulate single ion channels. The results suggest that the natriuretic action of ANP is related in part to cGMP-mediated inhibition of electrogenic Na
+
absorption by the inner medullary collecting duct.
Immune Response to Cholera Toxin Epitope Inserted in
Salmonella
Flagellin
Authors: Newton Salete M. C. , Jacob Chaim O. , Stocker Bruce A. D.
Published: October 2006

Bacterial flagella are potent immunogens and aromatic-dependent (
aro
)
Salmonella
as live vaccines evoke humoral and cellular immune responses. Such strains expressing epitopes of protective antigens as inserts in flagellin would provide a novel way to vaccinate against diseases caused by unrelated pathogens. A synthetic oligonucleotide specifying an epitope of cholera toxin subunit B was inserted in a
Salmonella
flagellin gene. The chimeric flagellin functioned normally and the epitope was expressed at the flagellar surface. Parenteral administration to mice of an
aroA
flagellin-negative strain of
S. dublin
expressing the chimeric flagellin gene evoked antibody to cholera toxin.
Stratospheric Hydroperoxyl Measurements
Authors: Traub Wesley A. , Johnson David G. , Chance Kelly V.
Published: October 2006

The hydroperoxyl radical (HO
2
) plays a key role in stratospheric chemistry through the HO

x

catalytic cycle of ozone destruction. Earlier measurements of stratospheric HO
2
have given mixed results; some measured mixing ratios greatly exceed theoretical predictions. Measurements of HO
2
have now been made with a balloon-borne far-infrared spectrometer. The measured daytime profile is in excellent agreement with theory up to 40 kilometers; above this level the measurements exceed theory by 30 percent, perhaps because of underprediction of ozone at these altitudes. The nighttime HO
2
profile is strongly depressed with respect to the daytime profile, in general agreement with theory.
Experiments on the Structure of an Individual Elementary Particle
Authors: Dehmelt Hans
Published: October 2006

Research begun in the early 1970s on geonium is reviewed. Genoium is a man-made atom, created at liquid-helium temperature in ultrahigh vacuum from an individual electron in magnetic and electric trapping fields. For this atom the electron gyromagnetic ratio
g
= 2. 000 000 000 110(60) has been measured in microwave spectroscopy experiments after subtraction of quantum electrodynamics shifts. The
g
-
g
Dirac
= 11 × 10
-11
excess over the value
g
Dirac
= 2 for the theoretical Dirac point electron suggests for the electron of nature a corresponding excess radius
R
e
-
R
Dirac
over the Dirac radius
R
Dirac
= 0 and a spatial structure. From a plot of measured
g
and
R
values for the near-Dirac particles electron, proton, triton, and helium-3, an electron radius
R
e
≈ 10
-20
centimeter is extrapolated. In a speculation, the triton-proton-quark model has been extended to the electron, to a succession of subquarks, and finally to the "cosmon." Rapid decay of a cosmon-anticosmon pair created from the "nothing" state in a spontaneous quantum jump initiated the Big Bang.
Structural Chemistry and the Local Charge Picture of Copper Oxide Superconductors
Authors: Cava R. J.
Published: October 2006

The crystal structures of the known copper oxide superconductors are described, with particular emphasis on the manner in which they fall into structural families. The local charge picture, a framework for understanding the influence of chemical composition, stoichiometry, and doping on the electrical properties of complex structures, is also described.
"Dead Quasars" in Nearby Galaxies?
Authors: Rees Martin J.
Published: October 2006

The nuclei of some galaxies undergo violent activity, quasars being the most extreme instances of this phenomenon. Such activity is probably short-lived compared to galactic lifetimes, and was most prevalent when the universe was only about one-fifth of its present age. A massive black hole seems the inevitable end point of such activity, and dead quasars should greatly outnumber active ones. In recent years, studies of stellar motions in the cores of several nearby galaxies indicate the presence of central dark masses which could be black holes. This article discusses how such evidence might be corroborated, and the potential implications for our understanding of active galaxies and black holes.
Mars: Change in Axial Tilt Due to Climate?
Authors: Rubincam David Parry
Published: October 2006

The average tilt of Mars' equator with respect to its orbital plane may have increased significantly over the age of the solar system. Obliquity oscillations might have induced changes in the climate, which altered the mass distribution and hence the solar torque on the planet. Viscous deformation attributable to loading by the large polar caps expected at low obliquity may have induced secular changes in the axial tilt. Earth-like effective viscosities can account for virtually the entire present obliquity of 24.4 degrees. Thus the present average tilt of Mars may not be primordial.
Chiral Metal Complexes as Discriminating Molecular Catalysts
Authors: Noyori Ryoji
Published: October 2006

As molecular recognition continues to gain importance in the biological and physical sciences as well as in the technologies of molecular electronics and optics, so has the need for efficient syntheses of chiral molecules. Chemists are fulfilling this need through use of chiral organometallic molecules. These chiral metal complexes precisely discriminate between enantiotopic atoms, groups, or faces in achiral molecules and catalyze production of a broad array of natural or unnatural substances of excellent enantiomeric purity. Because of their ability to efficiently multiply chirality, even on an industrial level, these catalysts promise to exert a general impact on molecular science and engineering.
Strong Association Between West African Rainfall and U.S. Landfall of Intense Hurricanes
Authors: Gray William M.
Published: October 2006

Intense hurricanes occurred much more frequently during the period spanning the late 1940s through the late 1960s than during the 1970s and 1980s, except for 1988 and 1989. Seasonal and multidecadal variations of intense hurricane activity are closely linked to seasonal and multidecadal variations of summer rainfall amounts in the Western Sahel region of West Africa. The multidecadal nature of West African precipitation variations and their association with variations of intense Atlantic hurricane activity can be observed in data going back nearly a century. The apparent recent breaking of the 18-year Sahel drought during 1988 and 1989 suggests that the incidence of intense hurricanes making landfall on the U.S. coast and in the Caribbean basin will likely increase during the 1990s and early years of the 21st century to levels of activity notably greater than were observed during the 1970s and 1980s.
How Old Is the Genetic Code? Statistical Geometry of tRNA Provides an Answer
Authors: Eigen Manfred , Lindemann Björn F. , Tietze Manfred , Winkler-Oswatitsch Ruthild , Dress Andreas , von Haeseler Arndt
Published: October 2006

The age of the molecular organization of life as expressed in the genetic code can be estimated from experimental data. Comparative sequence analysis of transfer RNA by the method of statistical geometry in sequence space suggests that about one-third of the present transfer RNA sequence divergence was present at the urkingdom level about the time when archaebacteria separated from eubacteria. It is concluded that the genetic code is not older than, but almost as old as our planet. While this result may not be unexpected, it was not clear until now that interpretable data exist that permit inferences about such early stages of life as the establishment of the genetic code.