bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular beam epitaxy of CdS self-assembled quantum dots on ZnSe
Authors: Kobayashi M. , Nakamura S. , Wakao K. , Yoshikawa A. , Takahashi K.
Published: July 2002

CdS quantum dot (QD) structures were grown by molecular beam epitaxy on (001) ZnSe. Circular QDs were observed from the sample grown at 220 °C, whereas rectangular QDs were observed from the sample grown at 280 °C. The difference of the dot shape may be related to the metastable nature of CdS since CdS thin films grown at 220 °C show zincblende structures and thin films grown at 280 °C show wurtzite structures. The PL peak position and linewidth were strongly affected by the growth condition of QDs; QD samples with a thicker CdS deposition showed redshifts of the peak position along with the narrowing of the linewidth.
Dissolution characteristics of chemically amplified 193 nm resists
Authors: Itani Toshiro , Yoshino Hiroshi , Hashimoto Shuichi , Yamana Mitsuharu , Miyasaka Mami , Tanabe Hiroyoshi
Published: July 2002

The dissolution kinetics of two types of chemically amplified positive 193 nm resists were investigated; a ter-polymer resist consisting of poly(tricyclodecylacrylate-co-tetrahydrodpyranyl-methacrylate-co-methacrylic acid) and triphenylsulfonium triflate as a photoacid generator, and a copolymer resist consisting of poly(carboxytetracyclododecylmethacrylate-co-tetrahydro-pyranyloxy-carbonyl-tetracyclododecylmethacrylate) and triphenylsulfonium triflate as a photoacid generator. The dissolution rate contrast was higher and the slope of dissolution rate curve was steeper for the ter-polymer resist than those for the copolymer resist. However, the Arrhenius plots of the dissolution rates were straight lines for both resists irrespective of the exposure doses. This indicates that only one mechanism determines the dissolution of both resists, and it is believed that the dominant rate-determining step in both resists is the tetramethylammoniumhydroxide penetration into the resist films. The resolution capability of the ter-polymer resist was very high, 0.14 μm lines and spaces pattern. The resolution capability of the copolymer resist was moderate, 0.16 μm lines and spaces in spite of its lower dissolution contrast and smaller slope value. In addition, the dry-etch resistance of both resists was close to that of a conventional polyhydroxystyrene base KrF resist. These results indicate that both the ter-polymer and the copolymer resists are candidates for practical use.
Ion projection lithography: International development program
Authors: Kaesmaier Rainer , Löschner Hans , Stengl Gerhard , Wolfe John C. , Ruchhoeft Paul
Published: July 2002

Ion projection lithography (IPL) has demonstrated not only the resolution required for next-generation lithography (50 nm resolution at >4:1 aspect ratio) [Bruenger et al., Microelectron Eng. 46, 477 (1999)] but also cost advantages with respect to other competing technologies [Gross et al., J. Vac. Sci. Technol. B 16, 3150 (1998)]. This article reports on the progress of a worldwide development program, with the target to manufacture a process development tool and create the necessary mask infrastructure to demonstrate that IPL is a viable industrial lithography technology for the future. An overview of papers, reporting on the progress in critical areas, is given and new, experimentally validated, simulations of complementary mask stitching are shown for the first time. Longitudinal and lateral offsets of up to 32 nm for 100 nm critical dimensions are possible with linewidth variations less than 11 nm. Our concept for beta tools, based on a powerful new stitcher strategy, is described. This will lead to a high-throughput tool for manufacturing integrated-circuit generations with minimum feature sizes of 50 nm and, possibly, below.
Lithography for sub-60 nm resist nanostructures
Authors: Ocola L. E. , Tennant D. , Timp G. , Novembre A.
Published: July 2002

As the semiconductor community continues to follow the Semiconductor Industry Association Roadmap, resist structures are being printed further into the nanometer domain. However, a persistent issue for successful sub-60 nm resist patterning is mechanical stability at high aspect ratios. The objective of this article is to understand what processing conditions facilitate processing resist nanostructures with useful aspect ratios for the fabrication of sub-60 nm transistors. We have found that, in aqueous based development and rinse, if the resist thickness is reduced, then the aspect ratio is sacrificed for the sake of resolution. The implication is that there is a resolution limit at which resist structures will have aspect ratios that are useful for device fabrication. We have also found that there are development effects that occur in the thick film regime that are not reproducible with thin films. The best resolution structures we have been able to print are lines of 28 nm in width using direct write electron-beam lithography on negative chemically amplified resists NEB-22 and NEB-31 (Sumitomo Chemical Inc.) with an aspect ratio of about 3. To put this result in perspective, this is about 40 molecules wide.
Lateral pn-junctions as a novel electron detector for microcolumn systems
Authors: Fritz G. S. , Fresser H. S. , Prins F. E. , Kern D. P.
Published: July 2002

A lateral pn-junction detector (l-pn detector) for low energy backscattered electrons has been designed, fabricated, and characterized. General design rules for l-pn detectors have been established. The detector assembly consists of a n-type finger structure diffused in p-type silicon. It was fabricated using standard clean room technologies and tested in a conventional scanning electron microscope under conditions similar to those in electron beam microcolumns. With this setup, images of Au/Si alignment marks were obtained with primary beam currents around 1 nA at 1 keV electron energy. The gain was measured for 1 and 2 keV primary beam energy. Signal to noise ratio and bandwidth were determined from image data. It is demonstrated that l-pn detectors are well suited for imaging in microcolumns.
Design of field emission based magnetic sensors
Authors: Marqués M. I. , Serena P. A. , Nicolaescu D. , Correia A.
Published: July 2002

In this study we analyze a new vacuum microelectronics (VM) magnetic field sensor based on a simple configuration with a single-gated wedge emitter with a split anode current as detection system. The actuation of such a device has been simulated using different numerical approaches including a full determination of electrostatic potentials with an accurate description of the fields at the wedge-like emitter, the propagation of electrons inside the device, and the evaluation of the current density distributions at the anode detector screen. This device presents sensor sensitivities higher than those of conventional magnetic field sensors, and similar to other VM double-gated sensors. The dependence of the sensitivity on the geometric parameters and control voltages is discussed.
Geomicrobiology: How Molecular-Scale Interactions Underpin Biogeochemical Systems
Authors: Newman Dianne K. , Banfield Jillian F.
Published: July 2002

Microorganisms populate every habitable environment on Earth and, through their metabolic activity, affect the chemistry and physical properties of their surroundings. They have done this for billions of years. Over the past decade, genetic, biochemical, and genomic approaches have allowed us to document the diversity of microbial life in geologic systems without cultivation, as well as to begin to elucidate their function. With expansion of culture-independent analyses of microbial communities, it will be possible to quantify gene activity at the species level. Genome-enabled biogeochemical modeling may provide an opportunity to determine how communities function, and how they shape and are shaped by their environments.
Contribution of Receptor Editing to the Antibody Repertoire
Authors: Casellas Rafael , Shih Tien-An Yang , Kleinewietfeld Markus , Rakonjac Jasna , Nemazee David , Rajewsky Klaus , Nussenzweig Michel C.
Published: July 2002

Receptor editing, clonal deletion, and anergy are the mechanisms by which B cells maintain tolerance to self antigens. To determine the extent to which receptor editing shapes the normal antibody repertoire, we generated an immunoglobulin κ polymorphism that facilitates the detection of editing of immunoglobulin light chains in vivo. We found that B cells are targeted for editing during a 2-hour delay in development at the pre-BII cell stage, and that about 25% of all antibody molecules are produced by gene replacement. These results suggest that receptor editing represents a major force in shaping the antibody repertoire.
Regulation of Vegetative Phase Change in
Arabidopsis thaliana
by Cyclophilin 40
Authors: Berardini Tanya Z. , Bollman Krista , Sun Hui , Scott Poethig R.
Published: July 2002

During its development, a plant shoot progresses from a juvenile to an adult phase of vegetative growth and from a reproductively incompetent to a reproductively competent state. In
Arabidopsis
, loss-of-function mutations in
SQUINT
(
SQN
) reduced the number of juvenile leaves and had subtle effects on inflorescence morphology but had no effect on flowering time or on reproductive competence.
SQN
encodes the
Arabidopsis
homolog of cyclophilin 40 (CyP40), a protein found in association with the Hsp90 chaperone complex in yeast, mammals, and plants. Thus, in
Arabidopsis
, CyP40 is specifically required for the vegetative but not the reproductive maturation of the shoot.
Dynamics of the Vocal Imitation Process: How a Zebra Finch Learns Its Song
Authors: Tchernichovski Ofer , Mitra Partha P. , Lints Thierry , Nottebohm Fernando
Published: July 2002

Song imitation in birds provides good material for studying the basic biology of vocal learning. Techniques were developed for inducing the rapid onset of song imitation in young zebra finches and for tracking trajectories of vocal change over a 7-week period until a match to a model song was achieved. Exposure to a model song induced the prompt generation of repeated structured sounds (prototypes) followed by a slow transition from repetitive to serial delivery of syllables. Tracking this transition revealed two phenomena: (i) Imitations of dissimilar sounds can emerge from successive renditions of the same prototype, and (ii) developmental trajectories for some sounds followed paths of increasing acoustic mismatch until an abrupt correction occurred by period doubling. These dynamics are likely to reflect underlying neural and articulatory constraints on the production and imitation of sounds.
Ordering Genes in a Flagella Pathway by Analysis of Expression Kinetics from Living Bacteria
Authors: Kalir S. , McClure J. , Pabbaraju K. , Southward C. , Ronen M. , Leibler S. , Surette M. G. , Alon U.
Published: July 2002

The recent advances in large-scale monitoring of gene expression raise the challenge of mapping systems on the basis of kinetic expression data in living cells. To address this, we measured promoter activity in the flagellar system of
Escherichia coli
at high accuracy and temporal resolution by means of reporter plasmids. The genes in the pathway were ordered by analysis algorithms without dependence on mutant strains. The observed temporal program of transcription was much more detailed than was previously thought and was associated with multiple steps of flagella assembly.
Climate Change as the Dominant Control on Glacial-Interglacial Variations in C
3
and C
4
Plant Abundance
Authors: Huang Y. , Street-Perrott F. A. , Metcalfe S. E. , Brenner M. , Moreland M. , Freeman K. H.
Published: July 2002

Although C
4
plant expansions have been recognized in the late Miocene, identification of the underlying causes is complicated by the uncertainties associated with estimates of ancient precipitation, temperature, and partial pressure of atmospheric carbon dioxide (
P
co
2
). Here we report the carbon isotopic compositions of leaf wax
n
-alkanes in lake sediment cores from two sites in Mesoamerica that have experienced contrasting moisture variations since the last glacial maximum. Opposite isotopic trends obtained from these two sites indicate that regional climate exerts a strong control on the relative abundance of C
3
and C
4
plants and that in the absence of favorable moisture and temperature conditions, low
P
co
2
alone is insufficient to drive an expansion of C
4
plants.
Genetic Analysis of Digestive Physiology Using Fluorescent Phospholipid Reporters
Authors: Farber Steven A. , Pack Michael , Ho Shiu-Ying , Johnson Iain D. , Wagner Daniel S. , Dosch Roland , Mullins Mary C. , Hendrickson H. Stewart , Hendrickson Elizabeth K. , Halpern Marnie E.
Published: July 2002

Zebrafish are a valuable model for mammalian lipid metabolism; larvae process lipids similarly through the intestine and hepatobiliary system and respond to drugs that block cholesterol synthesis in humans. After ingestion of fluorescently quenched phospholipids, endogenous lipase activity and rapid transport of cleavage products results in intense gall bladder fluorescence. Genetic screening identifies zebrafish mutants, such as
fat free
, that show normal digestive organ morphology but severely reduced phospholipid and cholesterol processing. Thus, fluorescent lipids provide a sensitive readout of lipid metabolism and are a powerful tool for identifying genes that mediate vertebrate digestive physiology.
Television Viewing and Aggressive Behavior During Adolescence and Adulthood
Authors: Johnson Jeffrey G. , Cohen Patricia , Smailes Elizabeth M. , Kasen Stephanie , Brook Judith S.
Published: July 2002

Television viewing and aggressive behavior were assessed over a 17-year interval in a community sample of 707 individuals. There was a significant association between the amount of time spent watching television during adolescence and early adulthood and the likelihood of subsequent aggressive acts against others. This association remained significant after previous aggressive behavior, childhood neglect, family income, neighborhood violence, parental education, and psychiatric disorders were controlled statistically.
Seismic Observations of Splitting of the Mid-Transition Zone Discontinuity in Earth's Mantle
Authors: Deuss Arwen , Woodhouse John
Published: July 2002

The transition zone of Earth's mantle is delineated by globally observed discontinuities in seismic properties at depths of about 410 and 660 kilometers. Here, we investigate the detailed structure between 410 and 660 kilometers depth, by making use of regional stacks of precursors to the SS phase. The previously observed discontinuity at about 520 kilometers depth is confirmed in many regions, but is found to be absent in others. There are a number of regions in which we find two discontinuities at about 500 and 560 kilometers depth, an effect which can be interpreted as a “splitting” of the 520 kilometer discontinuity. These observations provide seismic constraints on the sharpness and observability of mineralogical phase transitions in the mantle transition zone.
Control of Stem Cell Self-Renewal in
Drosophila
Spermatogenesis by JAK-STAT Signaling
Authors: Tulina Natalia , Matunis Erika
Published: July 2002

Stem cells, which regenerate tissue by producing differentiating cells, also produce cells that renew the stem cell population. Signals from regulatory microenvironments (niches) are thought to cause stem cells to retain self-renewing potential. However, the molecular characterization of niches remains an important goal. In
Drosophila
testes, germ line and somatic stem cells attach to a cluster of support cells called the hub. The hub specifically expresses Unpaired, a ligand activating the JAK-STAT (Janus kinase–signal transducer and activator of transcription) signaling cascade. Without JAK-STAT signaling, germ line stem cells differentiate but do not self-renew. Conversely, ectopic JAK-STAT signaling greatly expands both stem cell populations. We conclude that the support cells of the hub signal to adjacent stem cells by activation of the JAK-STAT pathway, thereby defining a niche for stem cell self-renewal.
Isolated Star Formation: From Cloud Formation to Core Collapse
Authors: Ward-Thompson Derek
Published: July 2002

The formation of stars is one of the most fundamental problems in astrophysics, as it underlies many other questions, on scales from the formation of galaxies to the formation of the solar system. The physical processes involve the turbulent behavior of a partially ionized medium containing a non-uniform magnetic field. Current debate centers around the time taken for turbulence to decay and the relative importance of the roles played by magnetic fields and turbulence. Technological advances such as millimeter-wave cameras have made possible observations of the temperature and density profiles, and statistical calculations of the lifetimes, of objects collapsing under their own self-gravity and those on the verge of collapse. Increased computing power allows more complex models to be made that include magnetic and turbulent effects. No current model can reproduce all of the observations.
Will Retinal Implants Restore Vision?
Authors: Zrenner Eberhart
Published: July 2002

A number of research groups are developing electrical implants that can be attached directly to the retina in an attempt to restore vision to patients suffering from retinal degeneration. However, despite promising results in animal experiments, there are still several major obstacles to overcome before retinal prostheses can be used clinically.
Subnuclear Compartmentalization of Immunoglobulin Loci During Lymphocyte Development
Authors: Kosak Steven T. , Skok Jane A. , Medina Kay L. , Riblet Roy , Le Beau Michelle M. , Fisher Amanda G. , Singh Harinder
Published: July 2002

Immunoglobulin (Ig) loci are selectively activated for transcription and rearrangement during B lymphocyte development. Using fluorescence in situ hybridization, we show that Ig heavy (H) and Igκ loci are preferentially positioned at the nuclear periphery in hematopoietic progenitors and pro-T cells but are centrally configured in pro-B nuclei. The inactive loci at the periphery do not associate with centromeric heterochromatin. Upon localization away from the nuclear periphery in pro-B cells, the IgH locus appears to undergo large-scale compaction. We suggest that subnuclear positioning represents a novel means of regulating transcription and recombination of IgH and Igκ loci during lymphocyte development.
Single-Molecule Optomechanical Cycle
Authors: Hugel Thorsten , Holland Nolan B. , Cattani Anna , Moroder Luis , Seitz Markus , Gaub Hermann E.
Published: July 2002

Light-powered molecular machines are conjectured to be essential constituents of future nanoscale devices. As a model for such systems, we have synthesized a polymer of bistable photosensitive azobenzenes. Individual polymers were investigated by single-molecule force spectroscopy in combination with optical excitation in total internal reflection. We were able to optically lengthen and contract individual polymers by switching the azo groups between their trans and cis configurations. The polymer was found to contract against an external force acting along the polymer backbone, thus delivering mechanical work. As a proof of principle, the polymer was operated in a periodic mode, demonstrating for the first time optomechanical energy conversion in a single-molecule device.
A Synaptically Controlled, Associative Signal for Hebbian Plasticity in Hippocampal Neurons
Authors: Magee Jeffrey C. , Johnston Daniel
Published: July 2002

The role of back-propagating dendritic action potentials in the induction of long-term potentiation (LTP) was investigated in CA1 neurons by means of dendritic patch recordings and simultaneous calcium imaging. Pairing of subthreshold excitatory postsynaptic potentials (EPSPs) with back-propagating action potentials resulted in an amplification of dendritic action potentials and evoked calcium influx near the site of synaptic input. This pairing also induced a robust LTP, which was reduced when EPSPs were paired with non-back-propagating action potentials or when stimuli were unpaired. Action potentials thus provide a synaptically controlled, associative signal to the dendrites for Hebbian modifications of synaptic strength.
Photochemically Driven Collapse of Titan's Atmosphere
Authors: Lorenz Ralph D. , McKay Christopher P. , Lunine Jonathan I.
Published: July 2002

Saturn's giant moon Titan has a thick (1.5 bar) nitrogen atmosphere, which has a temperature structure that is controlled by the absorption of solar and thermal radiation by methane, hydrogen, and organic aerosols into which methane is irreversibly converted by photolysis. Previous studies of Titan's climate evolution have been done with the assumption that the methane abundance was maintained against photolytic depletion throughout Titan's history, either by continuous supply from the interior or by buffering by a surface or near surface reservoir. Radiative-convective and radiative-saturated equilibrium models of Titan's atmosphere show that methane depletion may have allowed Titan's atmosphere to cool so that nitrogen, its main constituent, condenses onto the surface, collapsing Titan into a Triton-like frozen state with a thin atmosphere.
Structure of Bcl-x
L
-Bak Peptide Complex: Recognition Between Regulators of Apoptosis
Authors: Sattler Michael , Liang Heng , Nettesheim David , Meadows Robert P. , Harlan John E. , Eberstadt Matthias , Yoon Ho Sup , Shuker Suzanne B. , Chang Brian S. , Minn Andy J. , Thompson Craig B. , Fesik Stephen W.
Published: July 2002

Heterodimerization between members of the Bcl-2 family of proteins is a key event in the regulation of programmed cell death. The molecular basis for heterodimer formation was investigated by determination of the solution structure of a complex between the survival protein Bcl-x
L
and the death-promoting region of the Bcl-2-related protein Bak. The structure and binding affinities of mutant Bak peptides indicate that the Bak peptide adopts an amphipathic α helix that interacts with Bcl-x
L
through hydrophobic and electrostatic interactions. Mutations in full-length Bak that disrupt either type of interaction inhibit the ability of Bak to heterodimerize with Bcl-x
L
.
Single Molecule Force Spectroscopy on Polysaccharides by Atomic Force Microscopy
Authors: Rief Matthias , Oesterhelt Filipp , Heymann Berthold , Gaub Hermann E.
Published: July 2002

Recent developments in piconewton instrumentation allow the manipulation of single molecules and measurements of intermolecular as well as intramolecular forces. Dextran filaments linked to a gold surface were probed with the atomic force microscope tip by vertical stretching. At low forces the deformation of dextran was found to be dominated by entropic forces and can be described by the Langevin function with a 6 angstrom Kuhn length. At elevated forces the strand elongation was governed by a twist of bond angles. At higher forces the dextran filaments underwent a distinct conformational change. The polymer stiffened and the segment elasticity was dominated by the bending of bond angles. The conformational change was found to be reversible and was corroborated by molecular dynamics calculations.
Formation of Actin Stress Fibers and Focal Adhesions Enhanced by Rho-Kinase
Authors: Amano Mutsuki , Chihara Kazuyasu , Kimura Kazushi , Fukata Yuko , Nakamura Nao , Matsuura Yoshiharu , Kaibuchi Kozo
Published: July 2002

The small guanosine triphosphatase (GTPase) Rho is implicated in the formation of stress fibers and focal adhesions in fibroblasts stimulated by extracellular signals such as lysophosphatidic acid (LPA). Rho-kinase is activated by Rho and may mediate some biological effects of Rho. Microinjection of the catalytic domain of Rho-kinase into serum-starved Swiss 3T3 cells induced the formation of stress fibers and focal adhesions, whereas microinjection of the inactive catalytic domain, the Rho-binding domain, or the pleckstrin-homology domain inhibited the LPA-induced formation of stress fibers and focal adhesions. Thus, Rho-kinase appears to mediate signals from Rho and to induce the formation of stress fibers and focal adhesions.
Isolation of a Common Receptor for Coxsackie B Viruses and Adenoviruses 2 and 5
Authors: Bergelson Jeffrey M. , Cunningham Jennifer A. , Droguett Gustavo , Kurt-Jones Evelyn A. , Krithivas Anita , Hong Jeong S. , Horwitz Marshall S. , Crowell Richard L. , Finberg Robert W.
Published: July 2002

A complementary DNA clone has been isolated that encodes a coxsackievirus and adenovirus receptor (CAR). When transfected with CAR complementary DNA, nonpermissive hamster cells became susceptible to coxsackie B virus attachment and infection. Furthermore, consistent with previous studies demonstrating that adenovirus infection depends on attachment of a viral fiber to the target cell, CAR-transfected hamster cells bound adenovirus in a fiber-dependent fashion and showed a 100-fold increase in susceptibility to virus-mediated gene transfer. Identification of CAR as a receptor for these two unrelated and structurally distinct viral pathogens is important for understanding viral pathogenesis and has implications for therapeutic gene delivery with adenovirus vectors.
Crystal Structure of Protein Farnesyltransferase at 2.25 Angstrom Resolution
Authors: Park Hee-Won , Boduluri Sobha R. , Moomaw John F. , Casey Patrick J. , Beese Lorena S.
Published: July 2002

Protein farnesyltransferase (FTase) catalyzes the carboxyl-terminal lipidation of Ras and several other cellular signal transduction proteins. The essential nature of this modification for proper function of these proteins has led to the emergence of FTase as a target for the development of new anticancer therapy. Inhibition of this enzyme suppresses the transformed phenotype in cultured cells and causes tumor regression in animal models. The crystal structure of heterodimeric mammalian FTase was determined at 2.25 angstrom resolution. The structure shows a combination of two unusual domains: a crescent-shaped seven-helical hairpin domain and an α-α barrel domain. The active site is formed by two clefts that intersect at a bound zinc ion. One cleft contains a nine-residue peptide that may mimic the binding of the Ras substrate; the other cleft is lined with highly conserved aromatic residues appropriate for binding the farnesyl isoprenoid with required specificity.
Synaptic Vesicle Endocytosis Impaired by Disruption of Dynamin-SH3 Domain Interactions
Authors: Shupliakov Oleg , Löw Peter , Grabs Detlev , Gad Helge , Chen Hong , David Carol , Takei Kohji , De Camilli Pietro , Brodin Lennart
Published: July 2002

The proline-rich COOH-terminal region of dynamin binds various Src homology 3 (SH3) domain–containing proteins, but the physiological role of these interactions is unknown. In living nerve terminals, the function of the interaction with SH3 domains was examined. Amphiphysin contains an SH3 domain and is a major dynamin binding partner at the synapse. Microinjection of amphiphysin’s SH3 domain or of a dynamin peptide containing the SH3 binding site inhibited synaptic vesicle endocytosis at the stage of invaginated clathrin-coated pits, which resulted in an activity-dependent distortion of the synaptic architecture and a depression of transmitter release. These findings demonstrate that SH3-mediated interactions are required for dynamin function and support an essential role of clathrin-mediated endocytosis in synaptic vesicle recycling.
Trafficking of Matrix Collagens Through Bone-Resorbing Osteoclasts
Authors: Nesbitt Stephen A. , Horton Michael A.
Published: July 2002

An intracellular pathway for proteins liberated from mineralized matrix during resorption was identified in osteoclasts. Analysis by confocal microscopy of sites of active bone resorption showed that released matrix proteins, including degraded type I collagen, were endocytosed along the ruffled border within the resorption compartment and transcytosed through the osteoclast to the basolateral membrane. Intracellular trafficking of degraded collagen, as typified by the resorbing osteoclast, may provide the cell with a regulatory mechanism for the control of tissue degradation.
AI as Sport
Authors: McCarthy John
Published: July 2002

Kasparov versus Deep Blue.
Computer Chess Comes of Age. MONTY NEWBORN. Springer-Verlag, New York, 1996. xiv, 322 pp., illus. $29.95 or DM 49.90. ISBN 0-387-94820-1.
Inhibition of Ran Guanosine Triphosphatase-Dependent Nuclear Transport by the Matrix Protein of Vesicular Stomatitis Virus
Authors: Her Lu-Shiun , Lund Elsebet , Dahlberg James E.
Published: July 2002

Transport of macromolecules into and out of nuclei, essential steps in gene expression, are potential points of control. The matrix protein (M protein) of vesicular stomatitis virus (VSV) was shown to block transport of RNAs and proteins between the nucleus and cytoplasm of
Xenopus laevis
oocytes. The pattern of inhibition indicated that M protein interfered with transport that is dependent on the
ra
s-like
n
uclear guanosine triphosphatase (GTPase) Ran-TC4 and its associated factors. This inhibition of nuclear transport by M protein explains several observations about the effects of VSV infection on host cell gene expression and suggests that RNA export is closely coupled to protein import.
The Effect of Pressure on Deuterium-Hydrogen Fractionation in High-Temperature Water
Authors: Driesner T.
Published: July 2002

The pressure dependence of deuterium-hydrogen (D-H) fractionation in water to 500°C and 200 megapascals has been calculated from high-temperature, high-pressure spectroscopic data. Pressure effects have a maximum at the critical temperature of water (20 per mil between 22 and 200 megapascals). Even larger effects are predicted for vaporlike densities from molecular dynamics simulations and molecular orbital calculations. Pressure effects explain many of the large discrepancies in published mineral-water D-H fractionation curves. Possible applications to natural examples include mineral-water isotope geobarometry.
The Effects of Plant Composition and Diversity on Ecosystem Processes
Authors: Hooper David U. , Vitousek Peter M.
Published: July 2002

The relative effects of plant richness (the number of plant functional groups) and composition (the identity of the plant functional groups) on primary productivity and soil nitrogen pools were tested experimentally. Differences in plant composition explained more of the variation in production and nitrogen dynamics than did the number of functional groups present. Thus, it is possible to identify and differentiate among potential mechanisms underlying patterns of ecosystem response to variation in plant diversity, with implications for resource management.
Exploring the Metabolic and Genetic Control of Gene Expression on a Genomic Scale
Authors: DeRisi Joseph L. , Iyer Vishwanath R. , Brown Patrick O.
Published: July 2002

DNA microarrays containing virtually every gene of
Saccharomyces cerevisiae
were used to carry out a comprehensive investigation of the temporal program of gene expression accompanying the metabolic shift from fermentation to respiration. The expression profiles observed for genes with known metabolic functions pointed to features of the metabolic reprogramming that occur during the diauxic shift, and the expression patterns of many previously uncharacterized genes provided clues to their possible functions. The same DNA microarrays were also used to identify genes whose expression was affected by deletion of the transcriptional co-repressor
TUP1
or overexpression of the transcriptional activator
YAP1
. These results demonstrate the feasibility and utility of this approach to genomewide exploration of gene expression patterns.
Transgenic Knockout Mice with Exclusively Human Sickle Hemoglobin and Sickle Cell Disease
Authors: Pászty Chris , Brion Catherine M. , Manci Elizabeth , Witkowska H. Ewa , Stevens Mary E. , Mohandas Narla , Rubin Edward M.
Published: July 2002

To create mice expressing exclusively human sickle hemoglobin (HbS), transgenic mice expressing human α-, γ-, and β
S
-globin were generated and bred with knockout mice that had deletions of the murine α- and β-globin genes. These sickle cell mice have the major features (irreversibly sickled red cells, anemia, multiorgan pathology) found in humans with sickle cell disease and, as such, represent a useful in vivo system to accelerate the development of improved therapies for this common genetic disease.
Tunneling into a Single Magnetic Atom: Spectroscopic Evidence of the Kondo Resonance
Authors: Madhavan V. , Chen W. , Jamneala T. , Crommie M. F. , Wingreen N. S.
Published: July 2002

The Kondo effect arises from the quantum mechanical interplay between the electrons of a host metal and a magnetic impurity and is predicted to result in local charge and spin variations around the magnetic impurity. A cryogenic scanning tunneling microscope was used to spatially resolve the electronic properties of individual magnetic atoms displaying the Kondo effect. Spectroscopic measurements performed on individual cobalt atoms on the surface of gold show an energetically narrow feature that is identified as the Kondo resonance—the predicted response of a Kondo impurity. Unexpected structure in the Kondo resonance is shown to arise from quantum mechanical interference between the
d
orbital and conduction electron channels for an electron tunneling into a magnetic atom in a metallic host.
Can Patents Deter Innovation? The Anticommons in Biomedical Research
Authors: Heller Michael A. , Eisenberg Rebecca S.
Published: July 2002

The “tragedy of the commons” metaphor helps explain why people overuse shared resources. However, the recent proliferation of intellectual property rights in biomedical research suggests a different tragedy, an “anticommons” in which people underuse scarce resources because too many owners can block each other. Privatization of biomedical research must be more carefully deployed to sustain both upstream research and downstream product development. Otherwise, more intellectual property rights may lead paradoxically to fewer useful products for improving human health.
Disruption of Splicing Regulated by a CUG-Binding Protein in Myotonic Dystrophy
Authors: Philips Anne V. , Timchenko Lubov T. , Cooper Thomas A.
Published: July 2002

Myotonic dystrophy (DM) is caused by a CTG expansion in the 3′ untranslated region of the
DM
gene. One model of DM pathogenesis suggests that RNAs from the expanded allele create a gain-of-function mutation by the inappropriate binding of proteins to the CUG repeats. Data presented here indicate that the conserved heterogeneous nuclear ribonucleoprotein, CUG-binding protein (CUG-BP), may mediate the trans-dominant effect of the RNA. CUG-BP was found to bind to the human cardiac troponin T (cTNT) pre–messenger RNA and regulate its alternative splicing. Splicing of cTNT was disrupted in DM striated muscle and in normal cells expressing transcripts that contain CUG repeats. Altered expression of genes regulated posttranscriptionally by CUG-BP therefore may contribute to DM pathogenesis.
Extracting Primordial Density Fluctuations
Authors: Gawiser Eric , Silk Joseph
Published: July 2002

The combination of detections of anisotropy in cosmic microwave background radiation and observations of the large-scale distribution of galaxies probes the primordial density fluctuations of the universe on spatial scales varying by three orders of magnitude. These data are found to be inconsistent with the predictions of several popular cosmological models. Agreement between the data and the cold + hot dark matter model, however, suggests that a significant fraction of the matter in the universe may consist of massive neutrinos.
Evidence for Large Earthquakes in Metropolitan Los Angeles
Authors: Rubin Charles M. , Lindvall Scott C. , Rockwell Thomas K.
Published: July 2002

The Sierra Madre fault, along the southern flank of the San Gabriel Mountains in the Los Angeles region, has failed in magnitude 7.2 to 7.6 events at least twice in the past 15,000 years. Restoration of slip on the fault indicated a minimum of about 4.0 meters of slip from the most recent earthquake and suggests a total cumulative slip of about 10.5 meters for the past two prehistoric earthquakes. Large surface displacements and strong ground motions resulting from greater than magnitude 7 earthquakes within the Los Angeles region are not yet considered in most seismic hazard and risk assessments.
Visualization of Three-Dimensional Chaos
Authors: Fountain G. O. , Khakhar D. V. , Ottino J. M.
Published: July 2002

Most chaotic mixing experiments have been restricted to two-dimensional, time-periodic flows, and this has shaped advances in theory as well. A prototypical, bounded, three-dimensional flow with a moderate Reynolds number is presented; this system lends itself to detailed experimental observation and allows for high-precision computational inspection. The flow structure, captured by means of cuts with a laser sheet (experimental Poincaré section), was visualized with the use of continuously injected fluorescent dye streams and revealed detailed chaotic structures with high-period islands.
Essential Role of CED-4 Oligomerization in CED-3 Activation and Apoptosis
Authors: Yang Xiaolu , Chang Howard Y. , Baltimore David
Published: July 2002

Control of the activation of apoptosis is important both in development and in protection against cancer. In the classic genetic model
Caenorhabditis elegans
, the pro-apoptotic protein CED-4 activates the CED-3 caspase and is inhibited by the Bcl-2–like protein CED-9. Both processes are mediated by protein-protein interaction. Facilitating the proximity of CED-3 zymogen molecules was found to induce caspase activation and cell death. CED-4 protein oligomerized in cells and in vitro. This oligomerization induced CED-3 proximity and competed with CED-4:CED-9 interaction. Mutations that abolished CED-4 oligomerization inactivated its ability to activate CED-3. Thus, the mechanism of control is that CED-3 in CED-3:CED-4 complexes is activated by CED-4 oligomerization, which is inhibited by binding of CED-9 to CED-4.
Improved Gravity Field of the Moon from Lunar Prospector
Authors: Konopliv A. S. , Binder A. B. , Hood L. L. , Kucinskas A. B. , Sjogren W. L. , Williams J. G.
Published: July 2002

An improved gravity model from Doppler tracking of the Lunar Prospector (LP) spacecraft reveals three new large mass concentrations (mascons) on the nearside of the moon beneath the impact basins Mare Humboltianum, Mendel-Ryberg, and Schiller-Zucchius, where the latter basin has no visible mare fill. Although there is no direct measurement of the lunar farside gravity, LP partially resolves four mascons in the large farside basins of Hertzsprung, Coulomb-Sarton, Freundlich-Sharonov, and Mare Moscoviense. The center of each of these basins contains a gravity maximum relative to the surrounding basin. The improved normalized polar moment of inertia (0.3932 ± 0.0002) is consistent with an iron core with a radius of 220 to 450 kilometers.
Enhanced Phosphorylation of p53 by ATM in Response to DNA Damage
Authors: Banin S. , Moyal L. , Shieh S.-Y. , Taya Y. , Anderson C. W. , Chessa L. , Smorodinsky N. I. , Prives C. , Reiss Y. , Shiloh Y. , Ziv Y.
Published: July 2002

The ATM protein, encoded by the gene responsible for the human genetic disorder ataxia telangiectasia (A-T), regulates several cellular responses to DNA breaks. ATM shares a phosphoinositide 3-kinase–related domain with several proteins, some of them protein kinases. A wortmannin-sensitive protein kinase activity was associated with endogenous or recombinant ATM and was abolished by structural ATM mutations. In vitro substrates included the translation repressor PHAS-I and the p53 protein. ATM phosphorylated p53 in vitro on a single residue, serine-15, which is phosphorylated in vivo in response to DNA damage. This activity was markedly enhanced within minutes after treatment of cells with a radiomimetic drug; the total amount of ATM remained unchanged. Various damage-induced responses may be activated by enhancement of the protein kinase activity of ATM.
A Preorganized Active Site in the Crystal Structure of the
Tetrahymena
Ribozyme
Authors: Golden Barbara L. , Gooding Anne R. , Podell Elaine R. , Cech Thomas R.
Published: July 2002

Group I introns possess a single active site that catalyzes the two sequential reactions of self-splicing. An RNA comprising the two domains of the
Tetrahymena thermophila
group I intron catalytic core retains activity, and the 5.0 angstrom crystal structure of this 247-nucleotide ribozyme is now described. Close packing of the two domains forms a shallow cleft capable of binding the short helix that contains the 5′ splice site. The helix that provides the binding site for the guanosine substrate deviates significantly from A-form geometry, providing a tight binding pocket. The binding pockets for both the 5′ splice site helix and guanosine are formed and oriented in the absence of these substrates. Thus, this large ribozyme is largely preorganized for catalysis, much like a globular protein enzyme.
A Large Terrestrial Carbon Sink in North America Implied by Atmospheric and Oceanic Carbon Dioxide Data and Models
Authors: Fan S. , Gloor M. , Mahlman J. , Pacala S. , Sarmiento J. , Takahashi T. , Tans P.
Published: July 2002

Atmospheric carbon dioxide increased at a rate of 2.8 petagrams of carbon per year (Pg C year
−1
) during 1988 to 1992 (1 Pg = 10
15
grams). Given estimates of fossil carbon dioxide emissions, and net oceanic uptake, this implies a global terrestrial uptake of 1.0 to 2.2 Pg C year
−1
. The spatial distribution of the terrestrial carbon dioxide uptake is estimated by means of the observed spatial patterns of the greatly increased atmospheric carbon dioxide data set available from 1988 onward, together with two atmospheric transport models, two estimates of the sea-air flux, and an estimate of the spatial distribution of fossil carbon dioxide emissions. North America is the best constrained continent, with a mean uptake of 1.7 ± 0.5 Pg C year
−1
, mostly south of 51 degrees north. Eurasia–North Africa is relatively weakly constrained, with a mean uptake of 0.1 ± 0.6 Pg C year
−1
. The rest of the world's land surface is poorly constrained, with a mean source of 0.2 ± 0.9 Pg C year
−1
.
Novel Endotheliotropic Herpesviruses Fatal for Asian and African Elephants
Authors: Richman Laura K. , Montali Richard J. , Garber Richard L. , Kennedy Melissa A. , Lehnhardt John , Hildebrandt Thomas , Schmitt Dennis , Hardy Douglas , Alcendor Donald J. , Hayward Gary S.
Published: July 2002

A highly fatal hemorrhagic disease has been identified in 10 young Asian and African elephants at North American zoos. In the affected animals there was ultrastructural evidence for herpesvirus-like particles in endothelial cells of the heart, liver, and tongue. Consensus primer polymerase chain reaction combined with sequencing yielded molecular evidence that confirmed the presence of two novel but related herpesviruses associated with the disease, one in Asian elephants and another in African elephants. Otherwise healthy African elephants with external herpetic lesions yielded herpesvirus sequences identical to that found in Asian elephants with endothelial disease. This finding suggests that the Asian elephant deaths were caused by cross-species infection with a herpesvirus that is naturally latent in, but normally not lethal to, African elephants. A reciprocal relationship may exist for the African elephant disease.
Pseudogaps and Extrinsic Losses in Photoemission Experiments on Poorly Conducting Solids
Authors: Joynt Robert
Published: July 2002

A photoelectron emitted from a conducting solid may suffer a substantial energy change through ohmic losses that can drastically alter the line shape on the millielectron volt scale that is now observable through improved resolution. Almost all of this energy loss occurs after the electron leaves the solid. These losses are expected to be important in isotropic materials with relatively low conductivity, such as certain colossal magnetoresistance manganates, and in very electrically anisotropic materials, such as one-dimensional conductors, and may also affect interpretation of photoemission in superconductors with high transition temperatures. The electric field of the photoelectron can penetrate the solid, and extrinsic losses of this type can mimic pseudogap effects and other peculiar features of photoemission in cubic manganates, as illustrated for La
0.67
Ca
0.33
MnO
3
.
Requirement for Type 2 NO Synthase for IL-12 Signaling in Innate Immunity
Authors: Diefenbach Andreas , Schindler Heike , Röllinghoff Martin , Yokoyama Wayne M. , Bogdan Christian
Published: July 2002

Interleukin-12 (IL-12) and type 2 NO synthase (NOS2) are crucial for defense against bacterial and parasitic pathogens, but their relationship in innate immunity is unknown. In the absence of NOS2 activity, IL-12 was unable to prevent spreading of
Leishmania
parasites, did not stimulate natural killer (NK) cells for cytotoxicity or interferon-γ (IFN-γ) release, and failed to activate Tyk2 kinase and to tyrosine phosphorylate Stat4 (the central signal transducer of IL-12) in NK cells. Activation of Tyk2 in NK cells by IFN-α/β also required NOS2. Thus, NOS2-derived NO is a prerequisite for cytokine signaling and function in innate immunity.
The Cosmic Triangle: Revealing the State of the Universe
Authors: Bahcall Neta A. , Ostriker Jeremiah P. , Perlmutter Saul , Steinhardt Paul J.
Published: July 2002

The cosmic triangle is introduced as a way of representing the past, present, and future status of the universe. Our current location within the cosmic triangle is determined by the answers to three questions: How much matter is in the universe? Is the expansion rate slowing down or speeding up? And, is the universe flat? A review of recent observations suggests a universe that is lightweight (matter density about one-third the critical value), is accelerating, and is flat. The acceleration implies the existence of cosmic dark energy that overcomes the gravitational self-attraction of matter and causes the expansion to speed up.
Imaging of Asteroid 433 Eros During NEAR's Flyby Reconnaissance
Authors: Veverka J. , Thomas P. C. , Bell J. F. , Bell M. , Carcich B. , Clark B. , Harch A. , Joseph J. , Martin P. , Robinson M. , Murchie S. , Izenberg N. , Hawkins E. , Warren J. , Farquhar R. , Cheng A. , Dunham D. , Chapman C. , Merline W. J. , McFadden L. , Wellnitz D. , Malin M. , Owen W. M. , Miller J. K. , Williams B. G. , Yeomans D. K.
Published: July 2002

During the 23 December 1998 flyby of asteroid 433 Eros, the Near-Earth Asteroid Rendezvous (NEAR) spacecraft obtained 222 images of Eros, as well as supporting spectral observations. The images cover slightly more than two-thirds of Eros (best resolution is ∼400 meters per pixel) and reveal an elongated, cratered body with a linear feature extending for at least 20 kilometers. Our observations show that Eros has dimensions of 33 × 13 × 13 kilometers. The volume, combined with the mass determined by the NEAR radio science experiment, leads to a density of 2.5 ± 0.8 grams per cubic centimeter. This relatively high density, and the presence of an extensive linear feature, suggest that Eros may be a structurally coherent body.
Two-Metal-Ion Catalysis in Adenylyl Cyclase
Authors: Tesmer John J. G. , Sunahara Roger K. , Johnson Roger A. , Gosselin Gilles , Gilman Alfred G. , Sprang Stephen R.
Published: July 2002

Adenylyl cyclase (AC) converts adenosine triphosphate (ATP) to cyclic adenosine monophosphate, a ubiquitous second messenger that regulates many cellular functions. Recent structural studies have revealed much about the structure and function of mammalian AC but have not fully defined its active site or catalytic mechanism. Four crystal structures were determined of the catalytic domains of AC in complex with two different ATP analogs and various divalent metal ions. These structures provide a model for the enzyme-substrate complex and conclusively demonstrate that two metal ions bind in the active site. The similarity of the active site of AC to those of DNA polymerases suggests that the enzymes catalyze phosphoryl transfer by the same two-metal-ion mechanism and likely have evolved from a common ancestor.