bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultra-Low Velocity Zones Near the Core-Mantle Boundary from Broadband PKP Precursors
Authors: Wen Lianxing , Helmberger Donald V.
Published: July 2002

Short- and long-period precursors of the PKP phase were used to study an ultra-low velocity zone (ULVZ) near the core-mantle boundary beneath the Western Pacific. Synthetic seismograms were computed from a hybrid method, which handles seismic wave propagation through two-dimensional complex structures. Long-period precursors were explained by Gaussian-shaped ULVZs of 60 to 80 kilometers height with
P
velocity drops of at least 7 percent over 100 to 300 kilometers. Short-period precursors suggest the presence of smaller scale anomalies accompanying these larger Gaussian-shaped structures. These fine structures may be areas of partial melt caused by vigorous small-scale convection or the instability of a thermal boundary layer at the mantle's base, or both.
Competition in Retinogeniculate Patterning Driven by Spontaneous Activity
Authors: Penn Anna A. , Riquelme Patricio A. , Feller Marla B. , Shatz Carla J.
Published: July 2002

When contacts are first forming in the developing nervous system, many neurons generate spontaneous activity that has been hypothesized to shape appropriately patterned connections. In
Mustela putorius furo
, monocular intraocular blockade of spontaneous retinal waves of action potentials by cholinergic agents altered the subsequent eye-specific lamination pattern of the lateral geniculate nucleus (LGN). The projection from the active retina was greatly expanded into territory normally belonging to the other eye, and the projection from the inactive retina was substantially reduced. Thus, interocular competition driven by endogenous retinal activity determines the pattern of eye-specific connections from retina to LGN, demonstrating that spontaneous activity can produce highly stereotyped patterns of connections before the onset of visual experience.
Self-Trapping of Dark Incoherent Light Beams
Authors: Chen Zhigang , Mitchell Matthew , Segev Mordechai , Coskun Tamer H. , Christodoulides Demetrios N.
Published: July 2002

“Dark beams” are nonuniform optical beams that contain either a one-dimensional (1D) dark stripe or a two-dimensional (2D) dark hole resulting from a phase singularity or an amplitude depression in their optical field. Thus far, self-trapped dark beams (dark solitons) have been observed using coherent light only. Here, self-trapped dark incoherent light beams (self-trapped dark incoherent wavepackets) were observed. Both dark stripes and dark holes nested in a broad partially spatially incoherent wavefront were self-trapped to form dark solitons in a host photorefractive medium. These self-trapped 1D and 2D dark beams induced refractive-index changes akin to planar and circular dielectric waveguides. The experiments introduce the possibility of controlling high-power coherent laser beams with low-power incoherent light sources such as light emitting diodes.
High-Power Directional Emission from Microlasers with Chaotic Resonators
Authors: Gmachl Claire , Capasso Federico , Narimanov E. E. , Nöckel Jens U. , Stone A. Douglas , Faist Jérôme , Sivco Deborah L. , Cho Alfred Y.
Published: July 2002

High-power and highly directional semiconductor microcylinder lasers based on an optical resonator with deformed cross section are reported. In the favorable directions of the far-field, a power increase of up to three orders of magnitude over the conventional circularly symmetric lasers was obtained. A “bow-tie”–shaped resonance is responsible for the improved performance of the lasers in the higher range of deformations, in contrast to “whispering-gallery”–type modes of circular and weakly deformed lasers. This resonator design, although demonstrated here in midinfrared quantum-cascade lasers, should be applicable to any laser based on semiconductors or other high–refractive index materials.
Close Contacts with the Endoplasmic Reticulum as Determinants of Mitochondrial Ca
2+
Responses
Authors: Rizzuto Rosario , Pinton Paolo , Carrington Walter , Fay Frederic S. , Fogarty Kevin E. , Lifshitz Lawrence M. , Tuft Richard A. , Pozzan Tullio
Published: July 2002

The spatial relation between mitochondria and endoplasmic reticulum (ER) in living HeLa cells was analyzed at high resolution in three dimensions with two differently colored, specifically targeted green fluorescent proteins. Numerous close contacts were observed between these organelles, and mitochondria in situ formed a largely interconnected, dynamic network. A Ca
2+
-sensitive photoprotein targeted to the outer face of the inner mitochondrial membrane showed that, upon opening of the inositol 1,4,5-triphosphate (IP
3
)–gated channels of the ER, the mitochondrial surface was exposed to a higher concentration of Ca
2+
than was the bulk cytosol. These results emphasize the importance of cell architecture and the distribution of organelles in regulation of Ca
2+
signaling.
Design and Fabrication of Topologically Complex, Three-Dimensional Microstructures
Authors: Jackman Rebecca J. , Brittain Scott T. , Adams Allan , Prentiss Mara G. , Whitesides George M.
Published: July 2002

Two concepts for use in the fabrication of three-dimensional (3D) microstructures with complex topologies are described. Both routes begin with a two-dimensional (2D) pattern and transform it into a 3D microstructure. The concepts are illustrated by use of soft lithographic techniques to transfer 2D patterns to cylindrical (pseudo-3D) substrates. Subsequent steps—application of uniaxial strain, connection of patterns on intersecting surfaces—transform these patterns into free-standing, 3D, noncylindrically symmetrical microstructures. Microelectrodeposition provides an additive method that strengthens thin metal designs produced by patterning, welds nonconnected structures, and enables the high-strain deformations required in one method to be carried out successfully.
Effects of Water on the α-β Transformation Kinetics in San Carlos Olivine
Authors: Kubo Tomoaki , Ohtani Eiji , Kato Takumi , Shinmei Toru , Fujino Kiyoshi
Published: July 2002

In experiments at 13.5 gigapascals and 1030°C, the growth rate of wadsleyite, which forms from transformation of olivine, was substantially enhanced by the presence of water. Wadsleyite had a low dislocation density and subgrain boundaries in wet runs. Water enhanced the dislocation recovery in wadsleyite and therefore caused inelastic relaxation of the localized pressure drop associated with the transformation, resulting in an increase of the growth rate in wet runs. These results imply that even a small amount of water of 0.05 weight percent can weaken wadsleyite in the mantle.
Evidence of Soft-Mode Quantum Phase Transitions in Electron Double Layers
Authors: Pellegrini Vittorio , Pinczuk Aron , Dennis Brian S. , Plaut Annette S. , Pfeiffer Loren N. , West Ken W.
Published: July 2002

Inelastic light scattering by low-energy spin-excitations reveals three distinct configurations of spin of electron double layers in gallium arsenide quantum wells at even-integer quantum Hall states. The transformations among these spin states appear as quantum phase transitions driven by the interplay between Coulomb interactions and Zeeman splittings. One of the transformations correlates with the emergence of a spin-flip intersubband excitation at vanishingly low energy and provides direct evidence of a link between quantum phase transitions and soft collective excitations in a two-dimensional electron system.
Defects in Semiconductors: Some Fatal, Some Vital
Authors: Queisser Hans J. , Haller Eugene E.
Published: July 2002

REVIEW

The role of defects as essential entities in semiconductor materials is reviewed. Early experiments with semiconductors were hampered by the extreme sensitivity of the electronic properties to minute concentrations of impurities. Semiconductors were viewed as a family of solids with irreproducible properties. Scientific efforts overcame this idiosyncrasy and turned the art of impurity doping into today's exceedingly useful and reproducible technology that is used to control precisely electrical conductivity, composition, and minority-carrier lifetimes over wide ranges. Native defects such as vacancies and self-interstitials control basic processes, foremost self- and dopant diffusion. The structural properties of dislocations and higher dimensional defects have been studied with atomic resolution, but a thorough theoretical understanding of their electronic properties is incomplete. Reactions between defects within the host lattices are increasingly better understood and are used for gettering and electrical passivation of unwanted impurities. Metastable defects such as DX centers and the EL2-related arsenic antisite are briefly discussed. The recent development of isotopically controlled semiconductors has created new research opportunities in this field.
MP1: A MEK Binding Partner That Enhances Enzymatic Activation of the MAP Kinase Cascade
Authors: Schaeffer Hans J. , Catling Andrew D. , Eblen Scott T. , Collier Lara S. , Krauss Anke , Weber Michael J.
Published: July 2002

Signal transduction is controlled both by regulation of enzyme activation and by organization of enzymatic complexes with nonenzymatic adapters, scaffolds, and anchor proteins. The extracellular signal–regulated kinase (ERK) cascade is one of several evolutionarily conserved mitogen-activated protein (MAP) kinase cascades important in the regulation of growth, apoptosis, and differentiation. A two-hybrid screen was conducted to identify nonenzymatic components of this signaling cascade that might be important in regulating its activity. A protein called MP1 (MEK Partner 1) was identified that bound specifically to MEK1 and ERK1 and facilitated their activation. When overexpressed in cultured cells, MP1 enhanced activation of ERK1 and activation of a reporter driven by the transcription factor Elk-1. Expression of MP1 in cells increased binding of ERK1 to MEK1. MP1 apparently functions as an adapter to enhance the efficiency of the MAP kinase cascade.
Inhibition of Toxic Epidermal Necrolysis by Blockade of CD95 with Human Intravenous Immunoglobulin
Authors: Viard Isabelle , Wehrli Philippe , Bullani Roberto , Schneider Pascal , Holler Nils , Salomon Denis , Hunziker Thomas , Saurat Jean-Hilaire , Tschopp Jürg , French Lars E.
Published: July 2002

Toxic epidermal necrolysis (TEN, Lyell's syndrome) is a severe adverse drug reaction in which keratinocytes die and large sections of epidermis separate from the dermis. Keratinocytes normally express the death receptor Fas (CD95); those from TEN patients were found to express lytically active Fas ligand (FasL). Antibodies present in pooled human intravenous immunoglobulins (IVIG) blocked Fas-mediated keratinocyte death in vitro. In a pilot study, 10 consecutive individuals with clinically and histologically confirmed TEN were treated with IVIG; disease progression was rapidly reversed and the outcome was favorable in all cases. Thus, Fas-FasL interactions are directly involved in the epidermal necrolysis of TEN, and IVIG may be an effective treatment.
Plant Comparative Genetics after 10 Years
Authors: Gale M. D. , Devos K. M.
Published: July 2002

The past 10 years have seen the discovery of unexpected levels of conservation of gene content and gene orders over millions of years of evolution within grasses, crucifers, legumes, some trees, and
Solanaceae
crops. Within the grasses, which include the three 500-million-ton-plus-per-year crops (wheat, maize, and rice), and the crucifers, which include all the
Brassica
crops, colinearity looks good enough to do most map-based cloning only in the small genome model species, rice and
Arabidopsis
. Elsewhere, knowledge gained in a few major crops is being pooled and applied across the board. The extrapolation of information from the well-studied species to orphan crops, which include many tropical species, is providing a solid base for their improvement. Genome rearrangements are giving new insights into evolution. In fact, comparative genetics is the key that will unlock the secrets of crop plants with genomes larger than that of humans.
Chromosome 2 Sequence of the Human Malaria ParasitePlasmodium falciparum
Authors: Gardner Malcolm J. , Tettelin Hervé , Carucci Daniel J. , Cummings Leda M. , Aravind L. , Koonin Eugene V. , Shallom Shamira , Mason Tanya , Yu Kelly , Fujii Claire , Pederson James , Shen Kun , Jing Junping , Aston Christopher , Lai Zhongwu , Schwartz David C. , Pertea Mihaela , Salzberg Steven , Zhou Lixin , Sutton Granger G. , Clayton Rebecca , White Owen , Smith Hamilton O. , Fraser Claire M. , Adams Mark D. , Venter J. Craig , Hoffman Stephen L.
Published: July 2002

Chromosome 2 ofPlasmodium falciparumwas sequenced; this sequence contains 947,103 base pairs and encodes 210 predicted genes. In comparison with theSaccharomyces cerevisiaegenome, chromosome 2 has a lower gene density, introns are more frequent, and proteins are markedly enriched in nonglobular domains. A family of surface proteins, rifins, that may play a role in antigenic variation was identified. The complete sequencing of chromosome 2 has shown that sequencing of the A+T-richP. falciparumgenome is technically feasible.
Direct Demonstration of Milk as an Element of Archaeological Economies
Authors: Dudd Stephanie N. , Evershed Richard P.
Published: July 2002

The stable carbon isotope (δ
13
C) compositions of individual fatty acid components of remnant fats preserved in archaeological pottery vessels show that dairying was a component of archaeological economies. Characteristic δ
13
C values arise from biases in the biosynthetic origins of the C
18:0
fatty acids in milk and adipose fat. Milk and adipose fat from animals raised on similar pastures and fodders have distinct isotopic signatures.
Synaptic Segregation at the Developing Neuromuscular Junction
Authors: Gan Wen-Biao , Lichtman Jeff W.
Published: July 2002

Throughout the developing nervous system, competition between axons causes the permanent removal of some synaptic connections. In mouse neuromuscular junctions at birth, terminal branches of different axons are intermingled. However, during the several weeks after birth, these branches progressively segregated into nonoverlapping compartments before the complete withdrawal of all but one axon. Segregation was caused by selective branch atrophy, detachment, and withdrawal; the axon branches that were nearest to the competitor's branches were removed before the more distant branches were removed. This progression suggests that the signals that mediate the competitive removal of synapses must decrease in potency over short distances.
Regulation of Polar Auxin Transport by AtPIN1 in
Arabidopsis
Vascular Tissue
Authors: Gälweiler Leo , Guan Changhui , Müller Andreas , Wisman Ellen , Mendgen Kurt , Yephremov Alexander , Palme Klaus
Published: July 2002

Polar auxin transport controls multiple developmental processes in plants, including the formation of vascular tissue. Mutations affecting the
PIN-FORMED (PIN1)
gene diminish polar auxin transport in
Arabidopsis thaliana
inflorescence axes. The
AtPIN1
gene was found to encode a 67-kilodalton protein with similarity to bacterial and eukaryotic carrier proteins, and the AtPIN1 protein was detected at the basal end of auxin transport–competent cells in vascular tissue. AtPIN1 may act as a transmembrane component of the auxin efflux carrier.
Transduction of Human CD34
+
Cells That Mediate Long-Term Engraftment of NOD/SCID Mice by HIV Vectors
Authors: Miyoshi Hiroyuki , Smith Kent A. , Mosier Donald E. , Verma Inder M. , Torbett Bruce E.
Published: July 2002

Efficient gene transfer into human hematopoietic stem cells (HSCs) is an important goal in the study of the hematopoietic system as well as for gene therapy of hematopoietic disorders. A lentiviral vector based on the human immunodeficiency virus (HIV) was able to transduce human CD34
+
cells capable of stable, long-term reconstitution of nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice. High-efficiency transduction occurred in the absence of cytokine stimulation and resulted in transgene expression in multiple lineages of human hematopoietic cells for up to 22 weeks after transplantation.
A Copper Cofactor for the Ethylene Receptor ETR1 from
Arabidopsis
Authors: Rodrı́guez Fernando I. , Esch Jeffrey J. , Hall Anne E. , Binder Brad M. , Schaller G. Eric , Bleecker Anthony B.
Published: July 2002

The ETR1 receptor from
Arabidopsis
binds the gaseous hormone ethylene. A copper ion associated with the ethylene-binding domain is required for high-affinity ethylene-binding activity. A missense mutation in the domain that renders the plant insensitive to ethylene eliminates both ethylene binding and the interaction of copper with the receptor. A sequence from the genome of the cyanobacterium
Synechocystis
sp. strain 6803 that shows homology to the ethylene-binding domain of ETR1 encodes a functional ethylene-binding protein. On the basis of sequence conservation between the
Arabidopsis
and the cyanobacterial ethylene-binding domains and on in vitro mutagenesis of ETR1, a structural model for this copper-based ethylene sensor domain is presented.
HLAand HIV-1: Heterozygote Advantage andB*35-Cw*04Disadvantage
Authors: Carrington Mary , Nelson George W. , Martin Maureen P. , Kissner Teri , Vlahov David , Goedert James J. , Kaslow Richard , Buchbinder Susan , Hoots Keith , O'Brien Stephen J.
Published: July 2002

A selective advantage against infectious disease associated with increased heterozygosity at the human major histocompatibility complex [human leukocyte antigen (HLA) class I and class II] is believed to play a major role in maintaining the extraordinary allelic diversity of these genes. MaximumHLAheterozygosity of class I loci (A,B, andC) delayed acquired immunodeficiency syndrome (AIDS) onset among patients infected with human immunodeficiency virus–type 1 (HIV-1), whereas individuals who were homozygous for one or more loci progressed rapidly to AIDS and death. TheHLAclass I allelesB*35andCw*04were consistently associated with rapid development of AIDS-defining conditions in Caucasians. The extended survival of 28 to 40 percent of HIV-1–infected Caucasian patients who avoided AIDS for ten or more years can be attributed to their being fully heterozygous atHLAclass I loci, to their lacking the AIDS-associated allelesB*35andCw*04, or to both.
Multilineage Potential of Adult Human Mesenchymal Stem Cells
Authors: Pittenger Mark F. , Mackay Alastair M. , Beck Stephen C. , Jaiswal Rama K. , Douglas Robin , Mosca Joseph D. , Moorman Mark A. , Simonetti Donald W. , Craig Stewart , Marshak Daniel R.
Published: July 2002

Human mesenchymal stem cells are thought to be multipotent cells, which are present in adult marrow, that can replicate as undifferentiated cells and that have the potential to differentiate to lineages of mesenchymal tissues, including bone, cartilage, fat, tendon, muscle, and marrow stroma. Cells that have the characteristics of human mesenchymal stem cells were isolated from marrow aspirates of volunteer donors. These cells displayed a stable phenotype and remained as a monolayer in vitro. These adult stem cells could be induced to differentiate exclusively into the adipocytic, chondrocytic, or osteocytic lineages. Individual stem cells were identified that, when expanded to colonies, retained their multilineage potential.
Dissecting and Exploiting Intermodular Communication in Polyketide Synthases
Authors: Gokhale Rajesh S. , Tsuji Stuart Y. , Cane David E. , Khosla Chaitan
Published: July 2002

Modular polyketide synthases catalyze the biosynthesis of medicinally important natural products through an assembly-line mechanism. Although these megasynthases display very precise overall selectivity, we show that their constituent modules are remarkably tolerant toward diverse incoming acyl chains. By appropriate engineering of linkers, which exist within and between polypeptides, it is possible to exploit this tolerance to facilitate the transfer of biosynthetic intermediates between unnaturally linked modules. This protein engineering strategy also provides insights into the evolution of modular polyketide synthases.
Functional Arteries Grown in Vitro
Authors: Niklason L. E. , Gao J. , Abbott W. M. , Hirschi K. K. , Houser S. , Marini R. , Langer R.
Published: July 2002

A tissue engineering approach was developed to produce arbitrary lengths of vascular graft material from smooth muscle and endothelial cells that were derived from a biopsy of vascular tissue. Bovine vessels cultured under pulsatile conditions had rupture strengths greater than 2000 millimeters of mercury, suture retention strengths of up to 90 grams, and collagen contents of up to 50 percent. Cultured vessels also showed contractile responses to pharmacological agents and contained smooth muscle cells that displayed markers of differentiation such as calponin and myosin heavy chains. Tissue-engineered arteries were implanted in miniature swine, with patency documented up to 24 days by digital angiography.
Transcriptional Coregulators in Development
Authors: Mannervik Mattias , Nibu Yutaka , Zhang Hailan , Levine Michael
Published: July 2002

Small differences in the levels of an extracellular signaling molecule can specify cell fate during development. Threshold responses are often determined at the level of transcription. Cell-specific and spatially localized patterns of gene expression depend on combinations of sequence-specific activators and repressors that bind to extensive cis-regulatory regions. Different mechanisms for integrating this complex regulatory information are discussed, particularly the role of coregulatory proteins, which are recruited to the DNA template by sequence-specific transcription factors. Recent studies suggest that a growing set of coactivators and corepressors mediate communication between diverse upstream regulatory proteins and the core RNA polymerase II transcription complex.
Large Magnetoresistance of Electrodeposited Single-Crystal Bismuth Thin Films
Authors: Yang F. Y. , Liu Kai , Hong Kimin , Reich D. H. , Searson P. C. , Chien C. L.
Published: July 2002

Single-crystal bismuth thin films 1 to 20 micrometers thick were fabricated by electrodeposition and suitable annealing. Magnetoresistance up to 250 percent at 300 kelvin and 380,000 percent at 5 kelvin as well as clean Shubnikov–de Haas oscillations were observed, indicative of the high quality of these films. A hybrid structure was also made that showed a large magnetoresistive effect of 30 percent at 200 oersted and a field sensitivity of 0.2 percent magnetoresistance per oersted at room temperature.
26Al in Eucrite Piplia Kalan: Plausible Heat Source and Formation Chronology
Authors: Srinivasan G. , Goswami J. N. , Bhandari N.
Published: July 2002

Aluminum-magnesium isotopic analysis of plagioclase in the eucrite Piplia Kalan, with27Al/24Mg ratio between 2000 to 7000, reveals the presence of excess magnesium-26 resulting from in situ decay of the short-lived nuclide aluminum-26. This observation confirms aluminum-26 as a plausible heat source for melting and differentiation of the eucrite parent body in particular and for planetesimals in general. The inferred initial abundance of26Al/27Al of (7.5 ± 0.9) × 10−7indicates that melting, differentiation, and crust formation in the parent body of Piplia Kalan was complete within 5 million years of the formation of the solar system.
The Organization of Replication and Transcription
Authors: Cook Peter R.
Published: July 2002

Models for replication and transcription often display polymerases that track like locomotives along their DNA templates. However, recent evidence supports an alternative model in which DNA and RNA polymerases are immobilized by attachment to larger structures, where they reel in their templates and extrude newly made nucleic acids. These polymerases do not act independently; they are concentrated in discrete “factories,” where they work together on many different templates. Evidence for models involving tracking and immobile polymerases is reviewed.
Homeotic Transformation of Rhombomere Identity After Localized
Hoxb1
Misexpression
Authors: Bell Esther , Wingate Richard J. T. , Lumsden Andrew
Published: July 2002

Segmentation of the hindbrain and branchial region is a conserved feature of head development, involving the nested expression of
Hox
genes. Although it is presumed that vertebrate
Hox
genes function as segment identifiers, responsible for mediating registration between elements of diverse embryonic origin, this assumption has remained untested. To assess this, retroviral misexpression was combined with orthotopic grafting in chick embryos to generate a mismatch in
Hox
coding between a specific rhombomere and its corresponding branchial arch. Rhombomere-restricted misexpression of a single gene,
Hoxb1
, resulted in the homeotic transformation of the rhombomere, revealed by reorganization of motor axon projections.
Late Miocene Atmospheric CO
2
Concentrations and the Expansion of C
4
Grasses
Authors: Pagani Mark , Freeman Katherine H. , Arthur Michael A.
Published: July 2002

The global expansion of C
4
grasslands in the late Miocene has been attributed to a large-scale decrease in atmospheric carbon dioxide (CO
2
) concentrations. This triggering mechanism is controversial, in part because of a lack of direct evidence for change in the partial pressure of CO
2
(
p
CO
2
) and because other factors are also important determinants in controlling plant-type distributions. Alkenone-based
p
CO
2
estimates for the late Miocene indicate that
p
CO
2
increased from 14 to 9 million years ago and stabilized at preindustrial values by 9 million years ago. The estimates presented here provide no evidence for major changes in
p
CO
2
during the late Miocene. Thus, C
4
plant expansion was likely driven by additional factors, possibly a tectonically related episode of enhanced low-latitude aridity or changes in seasonal precipitation patterns on a global scale (or both).
A Chemical Inhibitor of p53 That Protects Mice from the Side Effects of Cancer Therapy
Authors: Komarov Pavel G. , Komarova Elena A. , Kondratov Roman V. , Christov-Tselkov Konstantin , Coon John S. , Chernov Mikhail V. , Gudkov Andrei V.
Published: July 2002

Chemotherapy and radiation therapy for cancer often have severe side effects that limit their efficacy. Because these effects are in part determined by p53-mediated apoptosis, temporary suppression of p53 has been suggested as a therapeutic strategy to prevent damage of normal tissues during treatment of p53-deficient tumors. To test this possibility, a small molecule was isolated for its ability to reversibly block p53-dependent transcriptional activation and apoptosis. This compound, pifithrin-α, protected mice from the lethal genotoxic stress associated with anticancer treatment without promoting the formation of tumors. Thus, inhibitors of p53 may be useful drugs for reducing the side effects of cancer therapy and other types of stress associated with p53 induction.
Instability of Magma Flow from Volatile-Dependent Viscosity
Authors: Wylie Jonathan J. , Voight Barry , Whitehead J. A.
Published: July 2002

Volatiles dissolved in silicic magma at depth exsolve as the magma nears the surface and cause an increase in viscosity of the magma. A model of a volcanic conduit within an elastic medium and a viscosity dependent on the volatile content of the magma produces oscillatory magma flow for a critical range of steady input flow rates. Oscillatory flow is recognized as a fundamental mode of behavior at silicic volcanoes, and understanding it allows improved short-term forecasting of timing and eruption style.
Water Vapor Absorption in Arthropods by Accumulation of Myoinositol and Glucose
Authors: Bayley Mark , Holmstrup Martin
Published: July 2002

Hydrophilic soil arthropods have been thought to respond to soil desiccation exclusively by migrating to deeper soil layers. Numerous studies have shown that their survival below 90 percent relative humidity dry weight, is limited to hours. However, little attention has been paid to physiological adaptations to more realistic desiccation regimes, such as at the permanent wilting point of plants (98.9 percent relative humidity). A water vapor absorption mechanism is described that allows a common soil collembolan,Folsomia candida, to remain active down to below the permanent wilting point. A reevaluation of the water physiology of this widespread and diverse animal group is required.
Mimicry of CD40 Signals by Epstein-Barr Virus LMP1 in B Lymphocyte Responses
Authors: Uchida Junji , Yasui Teruhito , Takaoka-Shichijo Yuko , Muraoka Masaaki , Kulwichit Wanla , Raab-Traub Nancy , Kikutani Hitoshi
Published: July 2002

The effect of the Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1) on the activation and differentiation of normal B cells was investigated. B cells of transgenic mice expressing LMP1 under the control of immunoglobulin promoter/enhancer displayed enhanced expression of activation antigens and spontaneously proliferated and produced antibody. Humoral immune responses of LMP1 transgenic mice in CD40-deficient or normal backgrounds revealed that LMP1 mimics CD40 signals to induce extrafollicular B cell differentiation but, unlike CD40, blocks germinal center formation. Thus, these specific properties of LMP1 may determine the site of primary B cell infection and the state of infection in the natural course of EBV infection, whereas subsequent loss of LMP1 expression may affect the site of persistent latent infection.
Polycationic Peptides from Diatom Biosilica That Direct Silica Nanosphere Formation
Authors: Kröger Nils , Deutzmann Rainer , Sumper Manfred
Published: July 2002

Diatom cell walls are regarded as a paradigm for controlled production of nanostructured silica, but the mechanisms allowing biosilicification to proceed at ambient temperature at high rates have remained enigmatic. A set of polycationic peptides (called silaffins) isolated from diatom cell walls were shown to generate networks of silica nanospheres within seconds when added to a solution of silicic acid. Silaffins contain covalently modified lysine-lysine elements. The first lysine bears a polyamine consisting of 6 to 11 repeats of the
N
-methyl-propylamine unit. The second lysine was identified as
ɛ
-
N,N
-dimethyl- lysine. These modifications drastically influence the silica-precipitating activity of silaffins.
Evidence for a Ubiquitous Seismic Discontinuity at the Base of the Mantle
Authors: Sidorin Igor , Gurnis Michael , Helmberger Don V.
Published: July 2002

A sharp discontinuity at the base of Earth's mantle has been suggested from seismic waveform studies; the observed travel time and amplitude variations have been interpreted as changes in the depth of a spatially intermittent discontinuity. Most of the observed variations in travel times and the spatial intermittance of the seismic triplication can be reproduced by a ubiquitous first-order discontinuity superimposed on global seismic velocity structure derived from tomography. The observations can be modeled by a solid-solid phase transition that has a 200-kilometer elevation above the core-mantle boundary under adiabatic temperatures and a Clapeyron slope of about 6 megapascal per kelvin.
Nonlinear Optics for High-Speed Digital Information Processing
Authors: Cotter D. , Manning R. J. , Blow K. J. , Ellis A. D. , Kelly A. E. , Nesset D. , Phillips I. D. , Poustie A. J. , Rogers D. C.
Published: July 2002

Recent advances in developing nonlinear optical techniques for processing serial digital information at high speed are reviewed. The field has been transformed by the advent of semiconductor nonlinear devices capable of operation at 100 gigabits per second and higher, well beyond the current speed limits of commercial electronics. These devices are expected to become important in future high-capacity communications networks by allowing digital regeneration and other processing functions to be performed on data signals “on the fly” in the optical domain.
Differentiation Stage-Specific Inhibition of the Raf-MEK-ERK Pathway by Akt
Authors: Rommel Christian , Clarke Brian A. , Zimmermann Sven , Nuñez Lorna , Rossman Roni , Reid Kristina , Moelling Karin , Yancopoulos George D. , Glass David J.
Published: July 2002

Extracellular signals often result in simultaneous activation of both the Raf-MEK-ERK and PI3K-Akt pathways (where ERK is extracellular-regulated kinase, MEK is mitogen-activated protein kinase or ERK kinase, and PI3K is phosphatidylinositol 3-kinase). However, these two signaling pathways were shown to exert opposing effects on muscle cell hypertrophy. Furthermore, the PI3K-Akt pathway was shown to inhibit the Raf-MEK-ERK pathway; this cross-regulation depended on the differentiation state of the cell: Akt activation inhibited the Raf-MEK-ERK pathway in differentiated myotubes, but not in their myoblast precursors. The stage-specific inhibitory action of Akt correlated with its stage-specific ability to form a complex with Raf, suggesting the existence of differentially expressed mediators of an inhibitory Akt-Raf complex.
Microorganisms in the Accreted Ice of Lake Vostok, Antarctica
Authors: Karl D. M. , Bird D. F. , Björkman K. , Houlihan T. , Shackelford R. , Tupas L.
Published: July 2002

Analysis of a portion of Vostok ice core number 5G, which is thought to contain frozen water derived from Lake Vostok, Antarctica (a body of liquid water located beneath about 4 kilometers of glacial ice), revealed between 2 × 102and 3 × 102bacterial cells per milliliter and low concentrations of potential growth nutrients. Lipopolysaccharide (a Gram-negative bacterial cell biomarker) was also detected at concentrations consistent with the cell enumeration data, which suggests a predominance of Gram-negative bacteria. At least a portion of the microbial assemblage was viable, as determined by the respiration of carbon-14–labeled acetate and glucose substrates during incubations at 3°C and 1 atmosphere. These accreted ice data suggest that Lake Vostok may contain viable microorganisms.
Memory--a Century of Consolidation
Authors: McGaugh James L.
Published: July 2002

The memory consolidation hypothesis proposed 100 years ago by Müller and Pilzecker continues to guide memory research. The hypothesis that new memories consolidate slowly over time has stimulated studies revealing the hormonal and neural influences regulating memory consolidation, as well as molecular and cellular mechanisms. This review examines the progress made over the century in understanding the time-dependent processes that create our lasting memories.
Cenozoic Deep-Sea Temperatures and Global Ice Volumes from Mg/Ca in Benthic Foraminiferal Calcite
Authors: Lear C. H. , Elderfield H. , Wilson P. A.
Published: July 2002

A deep-sea temperature record for the past 50 million years has been produced from the magnesium/calcium ratio (Mg/Ca) in benthic foraminiferal calcite. The record is strikingly similar in form to the corresponding benthic oxygen isotope (δ18O) record and defines an overall cooling of about 12°C in the deep oceans with four main cooling periods. Used in conjunction with the benthic δ18O record, the magnesium temperature record indicates that the first major accumulation of Antarctic ice occurred rapidly in the earliest Oligocene (34 million years ago) and was not accompanied by a decrease in deep-sea temperatures.
Transmission of Vesicular Stomatitis Virus from Infected to Noninfected Black Flies Co-Feeding on Nonviremic Deer Mice
Authors: Mead Daniel G. , Ramberg Frank B. , Besselsen David G. , Maré C. John
Published: July 2002

Vesicular stomatitis is an economically important arboviral disease of livestock. Viremia is absent in infected mammalian hosts, and the mechanism by which insects become infected with the causative agents, vesicular stomatitis viruses, remains unknown. Because infected and noninfected insects potentially feed on the same host in nature, infected and noninfected black flies were allowed to feed on the same host. Viremia was not detected in the host after infection by a black fly bite, but because noninfected black flies acquired the virus while co-feeding on the same host with infected black flies, it is concluded that a viremic host is not necessary for an insect to be infected with the virus. Thus co-feeding is a mechanism of infection for an insect-transmitted virus.
Coupling of Stress in the ER to Activation of JNK Protein Kinases by Transmembrane Protein Kinase IRE1
Authors: Urano Fumihiko , Wang XiaoZhong , Bertolotti Anne , Zhang Yuhong , Chung Peter , Harding Heather P. , Ron David
Published: July 2002

Malfolded proteins in the endoplasmic reticulum (ER) induce cellular stress and activate c-Jun amino-terminal kinases (JNKs or SAPKs). Mammalian homologs of yeast IRE1, which activate chaperone genes in response to ER stress, also activated JNK, and
IRE1
α
−/−
fibroblasts were impaired in JNK activation by ER stress. The cytoplasmic part of IRE1 bound TRAF2, an adaptor protein that couples plasma membrane receptors to JNK activation. Dominant-negative TRAF2 inhibited activation of JNK by IRE1. Activation of JNK by endogenous signals initiated in the ER proceeds by a pathway similar to that initiated by cell surface receptors in response to extracellular signals.
Widespread Complex Flow in the Interior of the Antarctic Ice Sheet
Authors: Bamber Jonathan L. , Vaughan David G. , Joughin Ian
Published: July 2002

It has been suggested that as much as 90% of the discharge from the Antarctic Ice Sheet is drained through a small number of fast-moving ice streams and outlet glaciers fed by relatively stable and inactive catchment areas. Here, evidence obtained from balance velocity estimates suggests that each major drainage basin is fed by complex systems of tributaries that penetrate up to 1000 kilometers from the grounding line into the interior of the ice sheet. This finding has important consequences for the modeled or estimated dynamic response time of past and present ice sheets to climate forcing.
Efficient Activation of Aromatic C-H Bonds for Addition to C-C Multiple Bonds
Authors: Jia Chengguo , Piao Dongguo , Oyamada Juzo , Lu Wenjun , Kitamura Tsugio , Fujiwara Yuzo
Published: July 2002

Efficient electrophilic metalation of aromatic C–H bonds leading to new C–C bond formation through regio- and stereoselective addition to alkynes and alkenes has been realized by a catalytic amount (0.02 to 5 mole percent) of palladium(II) or platinum(II) compounds in a mixed solvent containing trifluoroacetic acid at room temperature. Various arenes undergo unexpected selective trans hydroarylation to terminal or internal C≡C bonds inter- and intramolecularly with high efficiency (up to a turnover number of 4500 for palladium), especially for electron-rich arenes, giving thermodynamically unfavorablecis-alkenes, and the oxygen- and nitrogen-containing heterocycles. The simplicity, generality, and efficiency of this process should be very attractive to the possible industrial application for the functionalization of arenes.
Accretion of Primitive Planetesimals: Hf-W Isotopic Evidence from Enstatite Chondrites
Authors: Lee Der-Chuen , Halliday Alex N.
Published: July 2002

Enstatite chondrites have often been considered to be closely related to the material from which Earth accreted. However, tungsten isotopic data reveal clear differences. Moreover, the silicate and metal fractions define distinct initial
182
Hf/
180
Hf corresponding to a 13.8 ± 5.3 million year apparent age difference. Internal reequilibration does not provide a ready explanation for this result. Larger scale redistribution of tungsten is more likely, such as may have occurred during collisions between planetesimals.
Psychological and Neural Mechanisms of the Affective Dimension of Pain
Authors: Price Donald D.
Published: July 2002

The affective dimension of pain is made up of feelings of unpleasantness and emotions associated with future implications, termed secondary affect. Experimental and clinical studies show serial interactions between pain sensation intensity, pain unpleasantness, and secondary affect. These pain dimensions and their interactions relate to a central network of brain structures that processes nociceptive information both in parallel and in series. Spinal pathways to limbic structures and medial thalamic nuclei provide direct inputs to brain areas involved in affect. Another source is from spinal pathways to somatosensory thalamic and cortical areas and then through a cortico-limbic pathway. The latter integrates nociceptive input with contextual information and memory to provide cognitive mediation of pain affect. Both direct and cortico-limbic pathways converge on the same anterior cingulate cortical and subcortical structures whose function may be to establish emotional valence and response priorities.
Reduced Food Intake and Body Weight in Mice Treated with Fatty Acid Synthase Inhibitors
Authors: Loftus Thomas M. , Jaworsky Donna E. , Frehywot Gojeb L. , Townsend Craig A. , Ronnett Gabriele V. , Lane M. Daniel , Kuhajda Francis P.
Published: July 2002

With the escalation of obesity-related disease, there is great interest in defining the mechanisms that control appetite and body weight. We have identified a link between anabolic energy metabolism and appetite control. Both systemic and intracerebroventricular treatment of mice with fatty acid synthase (FAS) inhibitors (cerulenin and a synthetic compound C75) led to inhibition of feeding and dramatic weight loss. C75 inhibited expression of the prophagic signal neuropeptide Y in the hypothalamus and acted in a leptin-independent manner that appears to be mediated by malonyl–coenzyme A. Thus, FAS may represent an important link in feeding regulation and may be a potential therapeutic target.
Topographic Mapping of the Quantum Hall Liquid Using a Few-Electron Bubble
Authors: Finkelstein G. , Glicofridis P. I. , Ashoori R. C. , Shayegan M.
Published: July 2002

A scanning probe technique was used to obtain a high-resolution map of the random electrostatic potential inside the quantum Hall liquid. A sharp metal tip, scanned above a semiconductor surface, sensed charges in an embedded two-dimensional (2D) electron gas. Under quantum Hall effect conditions, applying a positive voltage to the tip locally enhanced the 2D electron density and created a “bubble” of electrons in an otherwise unoccupied Landau level. As the tip scanned along the sample surface, the bubble followed underneath. The tip sensed the motions of single electrons entering or leaving the bubble in response to changes in the local 2D electrostatic potential.
Evidence for Ecological Causation of Sexual Dimorphism in a Hummingbird
Authors: Temeles Ethan J. , Pan Irvin L. , Brennan Jillian L. , Horwitt Jedediah N.
Published: July 2002

Unambiguous examples of ecological causes of animal sexual dimorphism are rare. Here we present evidence for ecological causation of sexual dimorphism in the bill morphology of a hummingbird, the purple-throated carib. This hummingbird is the sole pollinator of two
Heliconia
species whose flowers correspond to the bills of either males or females. Each sex feeds most quickly at the flower species approximating its bill dimensions, which supports the hypothesis that floral specialization has driven the evolution of bill dimorphism. Further evidence for ecological causation of sexual dimorphism was provided by a geographic replacement of one
Heliconia
species by the other and the subsequent development of a floral dimorphism, with one floral morph matching the bills of males and the other of females.
Treatment of Murine Colitis by
Lactococcus lactis
Secreting Interleukin-10
Authors: Steidler Lothar , Hans Wolfgang , Schotte Lieven , Neirynck Sabine , Obermeier Florian , Falk Werner , Fiers Walter , Remaut Erik
Published: July 2002

The cytokine interleukin-10 (IL-10) has shown promise in clinical trials for treatment of inflammatory bowel disease (IBD). Using two mouse models, we show that the therapeutic dose of IL-10 can be reduced by localized delivery of a bacterium genetically engineered to secrete the cytokine. Intragastric administration of IL-10–secreting
Lactococcus lactis
caused a 50% reduction in colitis in mice treated with dextran sulfate sodium and prevented the onset of colitis in IL-10
−/−
mice. This approach may lead to better methods for cost-effective and long-term management of IBD in humans.
Immune Inhibitory Receptors
Authors: Ravetch Jeffrey V. , Lanier Lewis L.
Published: July 2002

With the detailed description and analysis of several inhibitory receptor systems on lymphoid and myeloid cells, a central paradigm has emerged in which the pairing of activation and inhibition is necessary to initiate, amplify, and then terminate immune responses. In some cases, the activating and inhibitory receptors recognize similar ligands, and the net outcome is determined by the relative strength of these opposing signals. The importance of this modulation is demonstrated by the sometimes fatal autoimmune disorders observed in mice with targeted disruption of inhibitory receptors. The significance of these receptors is further evidenced by the conservation of immunoreceptor tyrosine-based inhibitory motifs during their evolution.
Graphite Polyhedral Crystals
Authors: Gogotsi Yury , Libera Joseph A. , Kalashnikov Nikolay , Yoshimura Masahiro
Published: July 2002

Polyhedral nano- and microstructures with shapes of faceted needles, rods, rings, barrels, and double-tipped pyramids, which we call graphite polyhedral crystals (GPCs), have been discovered. They were found in pores of glassy carbon. They have nanotube cores and graphite faces, and they can exhibit unusual sevenfold, ninefold, or more complex axial symmetry. Although some are giant radially extended nanotubes, Raman spectroscopy and transmission electron microscopy suggest GPCs have a degree of perfection higher than in multiwall nanotubes of similar size. The crystals are up to 1 micrometer in cross section and 5 micrometers in length, and they can probably be grown in much larger sizes. Preliminary results suggest a high electrical conductivity, strength, and chemical stability of GPC.
Acute Sensitivity of Landslide Rates to Initial Soil Porosity
Authors: Iverson R. M. , Reid M. E. , Iverson N. R. , LaHusen R. G. , Logan M. , Mann J. E. , Brien D. L.
Published: July 2002

Some landslides move imperceptibly downslope, whereas others accelerate catastrophically. Experimental landslides triggered by rising pore water pressure moved at sharply contrasting rates due to small differences in initial porosity. Wet sandy soil with porosity of about 0.5 contracted during slope failure, partially liquefied, and accelerated within 1 second to speeds over 1 meter per second. The same soil with porosity of about 0.4 dilated during failure and slipped episodically at rates averaging 0.002 meter per second. Repeated slip episodes were induced by gradually rising pore water pressure and were arrested by pore dilation and attendant pore pressure decline.
Invasive Plants Versus Their New and Old Neighbors: A Mechanism for Exotic Invasion
Authors: Callaway Ragan M. , Aschehoug Erik T.
Published: July 2002

Invading exotic plants are thought to succeed primarily because they have escaped their natural enemies, not because of novel interactions with their new neighbors. However, we find that
Centaurea diffusa
, a noxious weed in North America, has much stronger negative effects on grass species from North America than on closely related grass species from communities to which
Centaurea
is native.
Centaurea
's advantage against North American species appears to be due to differences in the effects of its root exudates and how these root exudates affect competition for resources. Our results may help to explain why some exotic species so successfully invade natural plant communities.