bluuebunny/crossref_metadata_2025 huggingface dataset:
Vacuum properties of a new panel structure for field emission displays
Authors: Cho Y. R. , Kim H. S. , Mun J. D. , Oh J. Y. , Jeong H. S. , Ahn S.
Published: July 2002

A new field emission display (FED) panel structure with an auxiliary space was developed in order to increase the conductance of the system for evacuation and help evacuate the cavity inside the FED more effectively. Gas molecules in the main space of the panel can move easily into the auxiliary space through the multiple openings in the base plate and can then be pumped out through the exhaust tube at the auxiliary tank. For the very thin panel, in which the space between the face plate and base plate is 58 μm, pressure drop characteristics during evacuation are very sensitive to the number of openings in the base plate. The main purpose of multiple openings in shortening evacuation time is to reduce pressure gradient inside the cavity. Additionally, the auxiliary space makes it easy to place various getters inside the FED panel and to maintain high vacuum for a prolonged lifetime of the FED.
Use of a spreadsheet for Fowler–Nordheim equation calculations
Authors: Forbes Richard G.
Published: July 2002

Cold field emission of electrons is governed by the Fowler-Nordheim (FN) equation, and when the tunneling barrier includes the image potential the calculation of emission current density involves evaluation of elliptic integrals. Results are expressed as correction factors, sometimes called Nordheim functions and often denoted by v(y), s(y) and t(y). Values were tabulated long ago, but the calculation procedure is not well documented. Some new Nordheim functions have recently been introduced as part of a revised procedure for extracting emission area from the intercept of a Fowler-Nordheim plot. One of these, the emission-area extraction function needs to be known as a function of work function and emission-current density; this requires inversion of the FN equation to give values of the parameter y as a function of work function and emission-current density. All necessary mathematical formulas and numerical algorithms, both for direct calculation of the Nordheim functions and FN characteristics, and for inversion of the FN equation are given in this article. A modern notation and the rmks equation system are employed. Modern portable personal computers are sufficiently powerful that these calculations are easily carried out using the spreadsheet facility of a wordprocessing package. Organization of the calculation is described, the computational performance is discussed, and the convenience of using spreadsheets for such calculations is noted.
Field emission spectroscopy from discharge activated chemical vapor deposition diamond
Authors: Gröning O. , Küttel O. M. , Gröning P. , Schlapbach L.
Published: July 2002

Electron field emission from vacuum-arc discharge activated chemical vapor deposition diamond films has been investigated by measuring the current–voltage characteristics and the field emitted electron energy distribution. The crater region created by the discharge has been investigated by atomic force microscopy with simultaneous conductivity mapping. Comparison of the morphology and local conductivity in the activated zone with that of a good emitting, nonactivated chemical vapor deposition diamond film, shows common features. Specifically these are a large surface roughness in the submicrometer range and a drastically enhanced local conductivity. Both the activated and nonactivated diamond emitters are characterized by strong “G” and “D” lines centered at 1590 and 1350 cm−1 wave numbers in the Raman spectrum. By the combined measurement of the field emission energy distribution and of the current–voltage characteristics we determined the field enhancement factor and the work function of the emitters independently. For the nonactivated diamond emitter we found a work function of 5.6 eV and for the activated diamond emitter 5.3 eV. These values correspond well with the 5 eV work function measured for nanotubes around.
X-ray photoelectron spectroscopy analyses of oxide-masked organic polymers etched in high density plasmas using SO2/O2 gas mixtures
Authors: Monget C. , Joubert O.
Published: July 2002

Top surface imaging processes are considered as attractive schemes for future lithographic processes. A major issue associated with these schemes is the dry development step which implies the obtention of anisotropic resist profiles. This anisotropy is achieve by adding SO2 to O2 gas mixtures. In this work, oxide-masked organic resist features are etched in high density plasma sources using SO2/O2 gas mixtures. The chemical constituents present on the tops, sidewalls, and bottoms of the etched features are determined by quasi in situ x-ray photoelectron spectroscopy (XPS). XPS analyses show that when using SO2/O2 gas mixtures, a thin passivation layer is formed on the sidewalls of the polymer features. This layer is mainly formed by sulfur atoms present on the polymer surface in elemental state or bonded to carbon atoms. This film is thick enough to minimize the spontaneous etching reaction of oxygen atoms with the organic resist. Samples are also analyzed after air exposure in order to determine the air-induced modification of the reactive layers formed during the dry development step. XPS analyses show that the sulfur-based passivation layer formed during the etch process interact with water moisture to form sulfur-based acids.
Carbon-nanotube probe equipped magnetic force microscope
Authors: Arie Takayuki , Nishijima Hidehiro , Akita Seiji , Nakayama Yoshikazu
Published: July 2002

Metal capped carbon nanotubes, prepared by catalytic decomposition of benzene, have been applied as a magnetic force microscope tip. The particles at the end of nanotubes were about 35 nm in diameter, which were found to be Ni3C from the electron diffraction pattern. The other end of the nanotubes was attached on the tip of conventional Si probes. The magnetization of the particles was carried out parallel to the nanotube axis by applying a pulsed magnetic field of 12.5 T. We demonstrate the performance of these carbon nanotube probes by imaging the stored signal in magnetic recording media with magnetic force microscopy.
Atomic fluorine beam etching of silicon and related materials
Authors: Larson P. R. , Copeland K. A. , Dharmasena G. , Lasell R. A. , Keil M. , Johnson M. B.
Published: July 2002

A 1 eV neutral atomic fluorine beam has been shown to produce etch rates in silicon as high as 1 μm/min. Using a CaF2 resist layer we fabricated 120 μm deep by 1 μm wide trenches (aspect ratio 120:1) in silicon with little sidewall taper (slopes of about 1000:1) or aspect-ratio dependent etching effects. Achieving such anisotropic etching suggests that the scattered species do not contribute significantly to sidewall etching under the conditions of this experiment. We estimate that the ultimate depth attainable for a 1 μm wide trench is about 250 μm and that the critical parameter for attaining a trench of a certain depth is the aspect ratio. Our observations and analysis suggest that this etching technique can be used to fabricate trenches on a nanoscale level while maintaining high aspect ratios of 100 or greater.
AlGaN-based ultraviolet light detectors with integrated optical filters
Authors: Karrer Uwe , Dobner Armin , Ambacher Oliver , Stutzmann Martin
Published: July 2002

AlGaN-based ultraviolet light detectors with high responsivities in a narrow range of photon energy (≈0.3 eV) were grown by plasma induced molecular beam epitaxy on sapphire substrates. A thin Al0.4Ga0.6N film acting as an optical filter blocking high energy light was separated by an insulating AlGaN barrier from a third light sensitive Al0.3Ga0.7N layer. By optimizing the alloy compositions in the heterostructure and thickness of the filter layer, a peak responsivity of up to 35 A/W was achieved over a narrow range of wavelength with a peak position at 305 nm. The rejection of visible light response with respect to the peak responsivity was 5 orders of magnitude for a photoconductor device with a filter thickness of 1.4 μm. Decay times of the photoresponse after excimer laser exposure were determined to be between 40 and 330 ns.
Molecular and Morphological Supertrees for Eutherian (Placental) Mammals
Authors: Liu Fu-Guo Robert , Miyamoto Michael M. , Freire Nicole P. , Ong Phong Q. , Tennant Michele R. , Young Timothy S. , Gugel Kikumi F.
Published: July 2002

A large body of diverse comparative data now exists for a major phylogenetic synthesis of the higher-level relationships among eutherian (placental) mammals. We present such a phylogenetic synthesis using the composite trees or supertrees from the combined and separate analyses of their published molecular and morphological source phylogenies. Our combined and separate supertrees largely support the same suprafamilial taxa and orders, but different interordinal clades. These similarities and differences reinforce the continuing contributions of morphological studies, while highlighting the growing influence of molecular information on the field. As current summaries of past research, our supertrees emphasize opportunities for future work, while providing a step toward the eventual integration of the data and characters themselves.
Dyslexia: Cultural Diversity and Biological Unity
Authors: Paulesu E. , Démonet J.-F. , Fazio F. , McCrory E. , Chanoine V. , Brunswick N. , Cappa S. F. , Cossu G. , Habib M. , Frith C. D. , Frith U.
Published: July 2002

The recognition of dyslexia as a neurodevelopmental disorder has been hampered by the belief that it is not a specific diagnostic entity because it has variable and culture-specific manifestations. In line with this belief, we found that Italian dyslexics, using a shallow orthography which facilitates reading, performed better on reading tasks than did English and French dyslexics. However, all dyslexics were equally impaired relative to their controls on reading and phonological tasks. Positron emission tomography scans during explicit and implicit reading showed the same reduced activity in a region of the left hemisphere in dyslexics from all three countries, with the maximum peak in the middle temporal gyrus and additional peaks in the inferior and superior temporal gyri and middle occipital gyrus. We conclude that there is a universal neurocognitive basis for dyslexia and that differences in reading performance among dyslexics of different countries are due to different orthographies.
14
C-Dead Living Biomass: Evidence for Microbial Assimilation of Ancient Organic Carbon During Shale Weathering
Authors: Petsch S. T. , Eglinton T. I. , Edwards K. J.
Published: July 2002

Prokaryotes have been cultured from a modern weathering profile developed on a ∼365-million-year-old black shale that use macromolecular shale organic matter as their sole organic carbon source. Using natural-abundance carbon-14 analysis of membrane lipids, we show that 74 to 94% of lipid carbon in these cultures derives from assimilation of carbon-14–free organic carbon from the shale. These results reveal that microorganisms enriched from shale weathering profiles are able to use a macromolecular and putatively refractory pool of ancient organic matter. This activity may facilitate the oxidation of sedimentary organic matter to inorganic carbon when sedimentary rocks are exposed by erosion. Thus, microorganisms may play a more active role in the geochemical carbon cycle than previously recognized, with profound implications for controls on the abundance of oxygen and carbon dioxide in Earth's atmosphere over geologic time.
Amphibians as Indicators of Early Tertiary "Out-of-India" Dispersal of Vertebrates
Authors: Bossuyt Franky , Milinkovitch Michel C.
Published: July 2002

Sixty-five million years ago, massive volcanism produced on the India-Seychelles landmass the largest continental lava deposit (Deccan Traps) of the past 200 million years. Using a molecular clock–independent approach for inferring dating information from molecular phylogenies, we show that multiple lineages of frogs survived Deccan Traps volcanism after millions of years of isolation on drifting India. The collision between the Indian and Eurasian plates was followed by wide dispersal of several of these lineages. This “out-of-India” scenario reveals a zoogeographical pattern that might reconcile paleontological and molecular data in other vertebrate groups.
Conditional Restoration of Hippocampal Synaptic Potentiation in GluR-A-Deficient Mice
Authors: Mack Volker , Burnashev Nail , Kaiser Katharina M. M. , Rozov Andrei , Jensen Vidar , Hvalby Øvind , Seeburg Peter H. , Sakmann Bert , Sprengel Rolf
Published: July 2002

Plasticity of mature hippocampal CA1 synapses is dependent on
l
-α-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptors containing the glutamate receptor A (GluR-A) subunit
.
In GluR-A–deficient mice, plasticity could be restored by controlled expression of green fluorescent protein (GFP)–tagged GluR-A, which contributes to channel formation and displayed the developmental redistribution of AMPA receptors in CA1 pyramidal neurons. Long-term potentiation (LTP) induced by pairing or tetanic stimulation was rescued in adult GluR-A
–/–
mice when
GFP
GluR-A expression was constitutive or induced in already fully developed pyramidal cells. This shows that GluR-A–independent forms of synaptic plasticity can mediate the establishment of mature hippocampal circuits that are prebuilt to express GluR-A–dependent LTP.
Methylation of Histone H4 at Arginine 3 Facilitating Transcriptional Activation by Nuclear Hormone Receptor
Authors: Wang Hengbin , Huang Zhi-Qing , Xia Li , Feng Qin , Erdjument-Bromage Hediye , Strahl Brian D. , Briggs Scott D. , Allis C. David , Wong Jiemin , Tempst Paul , Zhang Yi
Published: July 2002

Acetylation of core histone tails plays a fundamental role in transcription regulation. In addition to acetylation, other posttranslational modifications, such as phosphorylation and methylation, occur in core histone tails. Here, we report the purification, molecular identification, and functional characterization of a histone H4–specific methyltransferase PRMT1, a protein arginine methyltransferase. PRMT1 specifically methylates arginine 3
(
Arg 3
)
of H4 in vitro and in vivo. Methylation of Arg 3 by PRMT1 facilitates subsequent acetylation of H4 tails by p300. However, acetylation of H4 inhibits its methylation by PRMT1. Most important, a mutation in the
S
-adenosyl-
l
-methionine–binding site of PRMT1 substantially crippled its nuclear receptor coactivator activity. Our finding reveals Arg 3 of H4 as a novel methylation site by PRMT1 and indicates that Arg 3 methylation plays an important role in transcriptional regulation.
Visible-Light Photocatalysis in Nitrogen-Doped Titanium Oxides
Authors: Asahi R. , Morikawa T. , Ohwaki T. , Aoki K. , Taga Y.
Published: July 2002

To use solar irradiation or interior lighting efficiently, we sought a photocatalyst with high reactivity under visible light. Films and powders of TiO

2-
x

N

x

have revealed an improvement over titanium dioxide (TiO
2
) under visible light (wavelength < 500 nanometers) in optical absorption and photocatalytic activity such as photodegradations of methylene blue and gaseous acetaldehyde and hydrophilicity of the film surface. Nitrogen doped into substitutional sites of TiO
2
has proven to be indispensable for band-gap narrowing and photocatalytic activity, as assessed by first-principles calculations and x-ray photoemission spectroscopy.
Mantle Flow Beneath a Continental Strike-Slip Fault: Postseismic Deformation After the 1999 Hector Mine Earthquake
Authors: Pollitz Fred F. , Wicks Chuck , Thatcher Wayne
Published: July 2002

Two recent large earthquakes in the Mojave Desert, California—the magnitude 7.3 1992 Landers and magnitude 7.1 1999 Hector Mine earthquakes—have each been followed by elevated crustal strain rates over periods of months and years. Geodetic data collected after the Hector Mine earthquake exhibit a temporally decaying horizontal velocity field and a quadrant uplift pattern opposite to that expected for localized shear beneath the earthquake rupture. We interpret the origin of this accelerated crustal deformation to be vigorous flow in the upper mantle in response to the stress changes generated by the earthquake. Our results suggest that transient flow in the upper mantle is a fundamental component of the earthquake cycle and that the lower crust is a coherent stress guide coupling the upper crust with the upper mantle.
Crystal Structure of a Carbon Monoxide Dehydrogenase Reveals a [Ni-4Fe-5S] Cluster
Authors: Dobbek Holger , Svetlitchnyi Vitali , Gremer Lothar , Huber Robert , Meyer Ortwin
Published: July 2002

The homodimeric nickel-containing CO dehydrogenase from the anaerobic bacterium
Carboxydothermus hydrogenoformans
catalyzes the oxidation of CO to CO
2
. A crystal structure of the reduced enzyme has been solved at 1.6 angstrom resolution. This structure represents the prototype for Ni-containing CO dehydrogenases from anaerobic bacteria and archaea. It contains five metal clusters of which clusters B, B′, and a subunit-bridging, surface-exposed cluster D are cubane-type [4Fe-4S] clusters. The active-site clusters C and C′ are novel, asymmetric [Ni-4Fe-5S] clusters. Their integral Ni ion, which is the likely site of CO oxidation, is coordinated by four sulfur ligands with square planar geometry.
Crystal Structure of a Neutralizing Human IgG Against HIV-1: A Template for Vaccine Design
Authors: Saphire Erica Ollmann , Parren Paul W. H. I. , Pantophlet Ralph , Zwick Michael B. , Morris Garrett M. , Rudd Pauline M. , Dwek Raymond A. , Stanfield Robyn L. , Burton Dennis R. , Wilson Ian A.
Published: July 2002

We present the crystal structure at 2.7 angstrom resolution of the human antibody IgG1 b12. Antibody b12 recognizes the CD4-binding site of human immunodeficiency virus–1 (HIV-1) gp120 and is one of only two known antibodies against gp120 capable of broad and potent neutralization of primary HIV-1 isolates. A key feature of the antibody-combining site is the protruding, finger-like long CDR H3 that can penetrate the recessed CD4-binding site of gp120. A docking model of b12 and gp120 reveals severe structural constraints that explain the extraordinary challenge in eliciting effective neutralizing antibodies similar to b12. The structure, together with mutagenesis studies, provides a rationale for the extensive cross-reactivity of b12 and a valuable framework for the design of HIV-1 vaccines capable of eliciting b12-like activity.
The Guanine Nucleotide-Binding Switch in Three Dimensions
Authors: Vetter Ingrid R. , Wittinghofer Alfred
Published: July 2002

Guanine nucleotide–binding proteins regulate a variety of processes, including sensual perception, protein synthesis, various transport processes, and cell growth and differentiation. They act as molecular switches and timers that cycle between inactive guanosine diphosphate (GDP)–bound and active guanosine triphosphate (GTP)–bound states. Recent structural studies show that the switch apparatus itself is a conserved fundamental module but that its regulators and effectors are quite diverse in their structures and modes of interaction. Here we will try to define some underlying principles.
Myotonic Dystrophy Type 2 Caused by a CCTG Expansion in Intron 1 of
ZNF9
Authors: Liquori Christina L. , Ricker Kenneth , Moseley Melinda L. , Jacobsen Jennifer F. , Kress Wolfram , Naylor Susan L. , Day John W. , Ranum Laura P. W.
Published: July 2002

Myotonic dystrophy (DM), the most common form of muscular dystrophy in adults, can be caused by a mutation on either chromosome 19q13 (DM1) or 3q21 (DM2/PROMM). DM1 is caused by a CTG expansion in the 3′ untranslated region of the dystrophia myotonica–protein kinase gene (
DMPK
). Several mechanisms have been invoked to explain how this mutation, which does not alter the protein-coding portion of a gene, causes the specific constellation of clinical features characteristic of DM. We now report that DM2 is caused by a CCTG expansion (mean ∼5000 repeats) located in intron 1 of the zinc finger protein 9 (
ZNF9
) gene. Parallels between these mutations indicate that microsatellite expansions in RNA can be pathogenic and cause the multisystemic features of DM1 and DM2.
Resistance to an Herbivore Through Engineered Cyanogenic Glucoside Synthesis
Authors: Tattersall David B. , Bak Søren , Jones Patrik R. , Olsen Carl Erik , Nielsen Jens K. , Hansen Mads L. , Høj Peter B. , Møller Birger Lindberg
Published: July 2002

The entire pathway for synthesis of the tyrosine-derived cyanogenic glucoside dhurrin has been transferred from
Sorghum bicolor
to
Arabidopsis thaliana
. Here, we document that genetically engineered plants are able to synthesize and store large amounts of new natural products. The presence of dhurrin in the transgenic
A. thaliana
plants confers resistance to the flea beetle
Phyllotreta nemorum
, which is a natural pest of other members of the crucifer group, demonstrating the potential utility of cyanogenic glucosides in plant defense.
Oxygen Isotopes and the Moon-Forming Giant Impact
Authors: Wiechert U. , Halliday A. N. , Lee D.-C. , Snyder G. A. , Taylor L. A. , Rumble D.
Published: July 2002

We have determined the abundances of
16
O,
17
O, and
18
O in 31 lunar samples from Apollo missions 11, 12, 15, 16, and 17 using a high-precision laser fluorination technique. All oxygen isotope compositions plot within ±0.016 per mil (2 standard deviations) on a single mass-dependent fractionation line that is identical to the terrestrial fractionation line within uncertainties. This observation is consistent with the Giant Impact model, provided that the proto-Earth and the smaller impactor planet (named Theia) formed from an identical mix of components. The similarity between the proto-Earth and Theia is consistent with formation at about the same heliocentric distance. The three oxygen isotopes (Δ
17
O) provide no evidence that isotopic heterogeneity on the Moon was created by lunar impacts.
Sleep, Learning, and Dreams: Off-line Memory Reprocessing
Authors: Stickgold R. , Hobson J. A. , Fosse R. , Fosse M.
Published: July 2002

Converging evidence and new research methodologies from across the neurosciences permit the neuroscientific study of the role of sleep in off-line memory reprocessing, as well as the nature and function of dreaming. Evidence supports a role for sleep in the consolidation of an array of learning and memory tasks. In addition, new methodologies allow the experimental manipulation of dream content at sleep onset, permitting an objective and scientific study of this dream formation and a renewed search for the possible functions of dreaming and the biological processes subserving it.
Physiological Migration of Hematopoietic Stem and Progenitor Cells
Authors: Wright Douglas E. , Wagers Amy J. , Gulati Anjali Pathak , Johnson Frances L. , Weissman Irving L.
Published: July 2002

Hematopoietic stem cells (HSCs) reside predominantly in bone marrow, but low numbers of HSCs are also found in peripheral blood. We examined the fate of blood-borne HSCs using genetically marked parabiotic mice, which are surgically conjoined and share a common circulation. Parabionts rapidly established stable, functional cross engraftment of partner-derived HSCs and maintained partner-derived hematopoiesis after surgical separation. Determination of the residence time of injected blood-borne progenitor cells suggests that circulating HSCs/progenitors are cleared quickly from the blood. These data demonstrate that HSCs rapidly and constitutively migrate through the blood and play a physiological role in, at least, the functional reengraftment of unconditioned bone marrow.
Sitosterol-β-glucoside as Primer for Cellulose Synthesis in Plants
Authors: Peng Liangcai , Kawagoe Yasushi , Hogan Pat , Delmer Deborah
Published: July 2002

Cellulose synthesis in plants requires β-1,4-glucan chain initiation, elongation, and termination. The process of chain elongation is likely to be distinct from the process of chain initiation. We demonstrate that a CesA glucosyltransferase initiates glucan polymerization by using sitosterol-β-glucoside (SG) as primer. Cotton fiber membranes synthesize sitosterol-cellodextrins (SCDs) from SG and uridine 5′-diphosphate–glucose (UDP-Glc) under conditions that also favor cellulose synthesis. The cellulase encoded by the
Korrigan
(
Kor
) gene, required for cellulose synthesis in plants, may function to cleave SG from the growing polymer chain.
Steep-Dip Seismic Imaging of the Shallow San Andreas Fault Near Parkfield
Authors: Hole J. A. , Catchings R. D. , Clair K. C. St. , Rymer M. J. , Okaya D. A. , Carney B. J.
Published: July 2002

Seismic reflection and refraction images illuminate the San Andreas Fault to a depth of 1 kilometer. The prestack depth-migrated reflection image contains near-vertical reflections aligned with the active fault trace. The fault is vertical in the upper 0.5 kilometer, then dips about 70° to the southwest to at least 1 kilometer subsurface. This dip reconciles the difference between the computed locations of earthquakes and the surface fault trace. The seismic velocity cross section shows strong lateral variations. Relatively low velocity (10 to 30%), high electrical conductivity, and low density indicate a 1-kilometer-wide vertical wedge of porous sediment or fractured rock immediately southwest of the active fault trace.
Evidence for Large Decadal Variability in the Tropical Mean Radiative Energy Budget
Authors: Wielicki Bruce A. , Wong Takmeng , Allan Richard P. , Slingo Anthony , Kiehl Jeffrey T. , Soden Brian J. , Gordon C. T. , Miller Alvin J. , Yang Shi-Keng , Randall David A. , Robertson Franklin , Susskind Joel , Jacobowitz Herbert
Published: July 2002

It is widely assumed that variations in Earth's radiative energy budget at large time and space scales are small. We present new evidence from a compilation of over two decades of accurate satellite data that the top-of-atmosphere (TOA) tropical radiative energy budget is much more dynamic and variable than previously thought. Results indicate that the radiation budget changes are caused by changes in tropical mean cloudiness. The results of several current climate model simulations fail to predict this large observed variation in tropical energy budget. The missing variability in the models highlights the critical need to improve cloud modeling in the tropics so that prediction of tropical climate on interannual and decadal time scales can be improved.
Chemically Induced Electronic Excitations at Metal Surfaces
Authors: Gergen Brian , Nienhaus Hermann , Weinberg W. Henry , McFarland Eric W.
Published: July 2002

The energy released in low-energy chemisorption or physisorption of molecules on metal surfaces is usually expected to be dissipated by surface vibrations (phonons). Theoretical descriptions of competing electronic excitations are incomplete, and experimental observation of excited charge carriers has been difficult except at energies high enough to eject electrons from the surface. We observed reaction-induced electron excitations during gas interactions with polycrystalline silver for a variety of species with adsorption energies between 0.2 and 3.5 electron volts. The probability of exciting a detectable electron increases with increasing adsorption energy, and the measured time dependence of the electron current can be understood in terms of the strength and mechanism of adsorption.
Crystal Structure of the Free Radical Intermediate of Pyruvate:Ferredoxin Oxidoreductase
Authors: Chabrière Eric , Vernède Xavier , Guigliarelli Bruno , Charon Marie-Hélène , Hatchikian E. Claude , Fontecilla-Camps Juan C.
Published: July 2002

In anaerobic organisms, the decarboxylation of pyruvate, a crucial component of intermediary metabolism, is catalyzed by the metalloenzyme pyruvate: ferredoxin oxidoreductase (PFOR) resulting in the generation of low potential electrons and the subsequent acetylation of coenzyme A (CoA). PFOR is the only enzyme for which a stable acetyl thiamine diphosphate (ThDP)–based free radical reaction intermediate has been identified. The 1.87 Å–resolution structure of the radical form of PFOR from
Desulfovibrio africanus
shows that, despite currently accepted ideas, the thiazole ring of the ThDP cofactor is markedly bent, indicating a drastic reduction of its aromaticity. In addition, the bond connecting the acetyl group to ThDP is unusually long, probably of the one-electron type already described for several cation radicals but not yet found in a biological system. Taken together, our data, along with evidence from the literature, suggest that acetyl-CoA synthesis by PFOR proceeds via a condensation mechanism involving acetyl (PFOR-based) and thiyl (CoA-based) radicals.
A Transgenic Model of Visceral Obesity and the Metabolic Syndrome
Authors: Masuzaki Hiroaki , Paterson Janice , Shinyama Hiroshi , Morton Nicholas M. , Mullins John J. , Seckl Jonathan R. , Flier Jeffrey S.
Published: July 2002

The adverse metabolic consequences of obesity are best predicted by the quantity of visceral fat. Excess glucocorticoids produce visceral obesity and diabetes, but circulating glucocorticoid levels are normal in typical obesity. Glucocorticoids can be produced locally from inactive 11-keto forms through the enzyme 11β hydroxysteroid dehydrogenase type 1 (11β HSD-1). We created transgenic mice overexpressing 11β HSD-1 selectively in adipose tissue to an extent similar to that found in adipose tissue from obese humans. These mice had increased adipose levels of corticosterone and developed visceral obesity that was exaggerated by a high-fat diet. The mice also exhibited pronounced insulin-resistant diabetes, hyperlipidemia, and, surprisingly, hyperphagia despite hyperleptinemia. Increased adipocyte 11β HSD-1 activity may be a common molecular etiology for visceral obesity and the metabolic syndrome.
Spontaneous Air-Driven Separation in Vertically Vibrated Fine Granular Mixtures
Authors: Burtally N. , King P. J. , Swift Michael R.
Published: July 2002

We report the observation of the spontaneous separation of vertically vibrated mixtures of fine bronze and glass spheres of similar diameters. At low frequencies and at sufficient vibrational amplitudes, a sharp boundary forms between a lower region of glass and an upper region of the heavier bronze. The boundary undergoes various oscillations, including periodic tilting motion, but remains extremely sharp. At higher frequencies, the bronze separates as a mid-height layer between upper and lower glass regions, and the oscillations are largely absent. The mechanism responsible for the separation can be traced to the effect of air on the granular motion.
X-ray Microdiffraction Images of Antiferromagnetic Domain Evolution in Chromium
Authors: Evans P. G. , Isaacs E. D. , Aeppli G. , Cai Z. , Lai B.
Published: July 2002

Magnetic x-ray diffraction combined with x-ray focusing optics was used to image individual antiferromagnetic spin density wave domains in a chromium single crystal at the micron scale. The cross section for nonresonant magnetic x-ray scattering depends on the antiferromagnetic modulation vector and spin polarization direction and allows these quantities to be extracted independently. The technique was used to show that the broadening of the nominally first-order “spin-flip” transition at 123 kelvin, at which the spins rotate by 90°, originates at the walls between domains with orthogonal modulation vectors. During cooling, the transition begins at these walls and progresses inward. The modulation vector domains are themselves unchanged.
Remarkably Selective Iridium Catalysts for the Elaboration of Aromatic C-H Bonds
Authors: Cho Jian-Yang , Tse Man Kin , Holmes Daniel , Maleczka Robert E. , Smith Milton R.
Published: July 2002

Arylboron compounds have intriguing properties and are important building blocks for chemical synthesis. A family of Ir catalysts now enables the direct synthesis of arylboron compounds from aromatic hydrocarbons and boranes under “solventless” conditions. The Ir catalysts are highly selective for C–H activation and do not interfere with subsequent in situ transformations, including Pd-mediated cross-couplings with aryl halides. By virtue of their favorable activities and exceptional selectivities, these Ir catalysts impart the synthetic versatility of arylboron reagents to C–H bonds in aromatic and heteroaromatic hydrocarbons.
Evolution and Biogeography of Deep-Sea Vent and Seep Invertebrates
Authors: Van Dover C. L. , German C. R. , Speer K. G. , Parson L. M. , Vrijenhoek R. C.
Published: July 2002

Deep-sea hydrothermal vents and cold seeps are submarine springs where nutrient-rich fluids emanate from the sea floor. Vent and seep ecosystems occur in a variety of geological settings throughout the global ocean and support food webs based on chemoautotrophic primary production. Most vent and seep invertebrates arrive at suitable habitats as larvae dispersed by deep-ocean currents. The recent evolution of many vent and seep invertebrate species (<100 million years ago) suggests that Cenozoic tectonic history and oceanic circulation patterns have been important in defining contemporary biogeographic patterns.
Emerging Roles of Ubiquitin in Transcription Regulation
Authors: Conaway Ronald C. , Brower Christopher S. , Conaway Joan Weliky
Published: July 2002

Ubiquitin is a small protein that was initially found to function as a tag that can be covalently attached to proteins to mark them for destruction by a multisubunit, adenosine 5′-triphosphate–dependent protease called the proteasome. Ubiquitin is now emerging as a key regulator of eukaryotic messenger RNA synthesis, a process that depends on the RNA synthetic enzyme RNA polymerase II and the transcription factors that control its activity. Ubiquitin controls messenger RNA synthesis not only by mechanisms involving ubiquitin-dependent destruction of transcription factors by the proteasome, but also by an intriguing collection of previously unknown and unanticipated mechanisms that appear to be independent of the proteasome.
Control of Synaptic Strength by Glial TNFα
Authors: Beattie Eric C. , Stellwagen David , Morishita Wade , Bresnahan Jacqueline C. , Ha Byeong Keun , Von Zastrow Mark , Beattie Michael S. , Malenka Robert C.
Published: July 2002

Activity-dependent modulation of synaptic efficacy in the brain contributes to neural circuit development and experience-dependent plasticity. Although glia are affected by activity and ensheathe synapses, their influence on synaptic strength has largely been ignored. Here, we show that a protein produced by glia, tumor necrosis factor α (TNFα), enhances synaptic efficacy by increasing surface expression of AMPA receptors. Preventing the actions of endogenous TNFα has the opposite effects. Thus, the continual presence of TNFα is required for preservation of synaptic strength at excitatory synapses. Through its effects on AMPA receptor trafficking, TNFα may play roles in synaptic plasticity and modulating responses to neural injury.
A MADS-Box Gene Necessary for Fruit Ripening at the Tomato
Ripening-Inhibitor
(
Rin
) Locus
Authors: Vrebalov Julia , Ruezinsky Diane , Padmanabhan Veeraragavan , White Ruth , Medrano Diana , Drake Rachel , Schuch Wolfgang , Giovannoni Jim
Published: July 2002

Tomato plants harboring the
ripening
-
inhibitor
(
rin
) mutation yield fruits that fail to ripen. Additionally,
rin
plants display enlarged sepals and loss of inflorescence determinacy. Positional cloning of the
rin
locus revealed two tandem MADS-box genes (
LeMADS
-
RIN
and
LeMADS
-
MC
), whose expression patterns suggested roles in fruit ripening and sepal development, respectively. The
rin
mutation alters expression of both genes. Gene repression and mutant complementation demonstrate that
LeMADS
-
RIN
regulates ripening, whereas
LeMADS
-
MC
affects sepal development and inflorescence determinacy.
LeMADS
-
RIN
demonstrates an agriculturally important function of plant MADS-box genes and provides molecular insight into nonhormonal (developmental) regulation of ripening.
Antarctic Krill Under Sea Ice: Elevated Abundance in a Narrow Band Just South of Ice Edge
Authors: Brierley Andrew S. , Fernandes Paul G. , Brandon Mark A. , Armstrong Frederick , Millard Nicholas W. , McPhail Steven D. , Stevenson Peter , Pebody Miles , Perrett James , Squires Mark , Bone Douglas G. , Griffiths Gwyn
Published: July 2002

We surveyed Antarctic krill (
Euphausia superba
) under sea ice using the autonomous underwater vehicle
Autosub-2
. Krill were concentrated within a band under ice between 1 and 13 kilometers south of the ice edge. Within this band, krill densities were fivefold greater than that of open water. The under-ice environment has long been considered an important habitat for krill, but sampling difficulties have previously prevented direct observations under ice over the scale necessary for robust krill density estimation.
Autosub-2
enabled us to make continuous high-resolution measurements of krill density under ice reaching 27 kilometers beyond the ice edge.
Theory of Quantum Annealing of an Ising Spin Glass
Authors: Santoro Giuseppe E. , Martoňák Roman , Tosatti Erio , Car Roberto
Published: July 2002

Probing the lowest energy configuration of a complex system by quantum annealing was recently found to be more effective than its classical, thermal counterpart. By comparing classical and quantum Monte Carlo annealing protocols on the two-dimensional random Ising model (a prototype spin glass), we confirm the superiority of quantum annealing relative to classical annealing. We also propose a theory of quantum annealing based on a cascade of Landau-Zener tunneling events. For both classical and quantum annealing, the residual energy after annealing is inversely proportional to a power of the logarithm of the annealing time, but the quantum case has a larger power that makes it faster.
Decoding the Patterns of Self and Nonself by the Innate Immune System
Authors: Medzhitov Ruslan , Janeway Charles A.
Published: July 2002

The innate immune system evolved several strategies of self/nonself discrimination that are based on the recognition of molecular patterns demarcating infectious nonself, as well as normal and abnormal self. These patterns are deciphered by receptors that either induce or inhibit an immune response, depending on the meaning of these signals.
Purkinje cell degeneration
(
pcd
) Phenotypes Caused by Mutations in the Axotomy-Induced Gene,
Nna1
Authors: Fernandez-Gonzalez Angeles , Spada Albert R. La , Treadaway Jason , Higdon Jason C. , Harris Belinda S. , Sidman Richard L. , Morgan James I. , Zuo Jian
Published: July 2002

The classical recessive mouse mutant,
Purkinje cell degeneration
(
pcd
), exhibits adult-onset degeneration of cerebellar Purkinje neurons, retinal photoreceptors, olfactory bulb mitral neurons, and selected thalamic neurons, and has defective spermatogenesis. Here we identify
Nna1
as the gene mutated in the original
pcd
and two additional
pcd
alleles (
pcd
2J
and
pcd
3J
).
Nna1
encodes a putative nuclear protein containing a zinc carboxypeptidase domain initially identified by its induction in spinal motor neurons during axonal regeneration. The present study suggests an unexpected molecular link between neuronal degeneration and regeneration, and its results have potential implications for neurodegenerative diseases and male infertility.
Between the Ivory Tower and the Market
Authors: Owen-Smith Jason
Published: July 2002

Who Owns Academic Work?
Battling for Control of Intellectual Property. Corynne McSherry. Harvard University Press, Cambridge, MA, 2001. 287 pp. $29.95, £20.50, €34.40. ISBN 0-674-00629-1.

McSherry marshals legal, historical, and qualitative social analysis to argue that intellectual property threatens the ideals of the research university and, reciprocally, that scientific research troubles the principles of intellectual property.
Requirement for a Peptidoglycan Recognition Protein (PGRP) in Relish Activation and Antibacterial Immune Responses in
Drosophila
Authors: Choe Kwang-Min , Werner Thomas , Stöven Svenja , Hultmark Dan , Anderson Kathryn V.
Published: July 2002

Components of microbial cell walls are potent activators of innate immune responses in animals. For example, the mammalian TLR4 signaling pathway is activated by bacterial lipopolysaccharide and is required for resistance to infection by Gram-negative bacteria. Other components of microbial surfaces, such as peptidoglycan, are also potent activators of innate immune responses, but less is known about how those components activate host defense. Here we show that a peptidoglycan recognition protein, PGRP-LC, is absolutely required for the induction of antibacterial peptide genes in response to infection in
Drosophila
and acts by controlling activation of the NF-κB family transcription factor Relish.
Making the University of California
Authors: Geiger Roger L.
Published: July 2002

The Gold and the Blue
A Personal Memoir of the University of California, 1949-1967. Volume 1, Academic Triumphs. Clark Kerr. University of California Press, Berkeley, 2001. 574 pp. $35, £24.95. ISBN 0-520-22367-5.

Kerr offers his perspective on academic and administrative affairs during the explosive growth of the University of California system under his leadership.
Nota Bene: Enticing and Informative Tales
Authors: Lavine Marc
Published: July 2002

The Genie in the Bottle
64 All New Commentaries on the Fascinating Chemistry of Everyday Life. Joe Schwarcz. W. H. Freeman (Henry Holt), New York, 2001. 311 pp. $23.95. ISBN 0-7167-4601-8.

These short, often humorous popular science essays discuss the chemistry of substances ranging from licorice and chocolate to foot odors and drain cleaners.
Toward a New Human Species?
Authors: Spier R. E.
Published: July 2002

Redesigning Humans
Our Inevitable Genetic Future. Gregory Stock. Houghton Mifflin Company, Boston, 2002. 287 pp. $24. ISBN 0-618-06026-X.

Our Posthuman Future
Consequences of the Biotechnology Revolution. Francis Fukuyama. Farrar, Straus and Giroux, New York, 2002. 270 pp. $25, C$39.95. ISBN 0-374-23643-7.

Stock and Fukuyama offer dramatically different perspectives on how humans may be changed by the application of recent and forthcoming developments in biotechnology. Fukuyama focuses on social and political outcomes and argues against severe restrictions on genetic engineering. Stock believes that public pressures are likely to continue the trend toward choosing the embryo's genes.
We Don't Think the Way We Think We Think
Authors: Kennedy James
Published: July 2002

The Illusion of Conscious Will
. Daniel M. Wegner. MIT Press, Cambridge, MA, 2002. 419 pp. $34.95. ISBN 0-262-23222-7.

Capping his several decades of research into understanding how people come to feel that they have control over their own behavior, Wegner argues that our sense of conscious agency is always imaginary.
Correlative Memory Deficits, Aβ Elevation, and Amyloid Plaques in Transgenic Mice
Authors: Hsiao Karen , Chapman Paul , Nilsen Steven , Eckman Chris , Harigaya Yasuo , Younkin Steven , Yang Fusheng , Cole Greg
Published: July 2002

Transgenic mice overexpressing the 695-amino acid isoform of human Alzheimer β-amyloid (Aβ) precursor protein containing a Lys
670
→ Asn, Met
671
→ Leu mutation had normal learning and memory in spatial reference and alternation tasks at 3 months of age but showed impairment by 9 to 10 months of age. A fivefold increase in Aβ(1-40) and a 14-fold increase in Aβ(1-42/43) accompanied the appearance of these behavioral deficits. Numerous Aβ plaques that stained with Congo red dye were present in cortical and limbic structures of mice with elevated amounts of Aβ. The correlative appearance of behavioral, biochemical, and pathological abnormalities reminiscent of Alzheimer's disease in these transgenic mice suggests new opportunities for exploring the pathophysiology and neurobiology of this disease.
Subpicosecond X-ray Pulses
Authors: Eisenberger P. , Suckewer S.
Published: July 2002

Short pulses of x-rays with a time duration comparable to the dynamics of molecules would make a variety of new structural studies possible. In their Perspective, Eisenberger and Suckewer discuss results reported by Schoenlein
et al
. (
p. 236
) in the same issue on a new source of subpicosecond x-rays. A short-pulse infrared laser beam is scattered from a beam of high-energy electrons. The radiation scattered from the electrons is in the form of subpicosecond pulses at a wavelength of 0.4 angstrom.
Crustal Root Beneath the Urals: Wide-Angle Seismic Evidence
Authors: Carbonell R. , Pérez-Estaún A. , Gallart J. , Diaz J. , Kashubin S. , Mechie J. , Stadtlander R. , Schulze A. , Knapp J. H. , Morozov A.
Published: July 2002

Wide-angle reflection and refraction data acquired as part of the URSEIS '95 geophysical experiment across the southern Uralide orogen provide evidence for a 12- to 15-kilometer-thick crustal root, yielding a total crustal thickness of 55 to 58 kilometers. Strong reflections from the Mohorovičić discontinuity (Moho) at relatively small precritical distances suggest that the crust-mantle transition beneath the crustal root is a sharp feature. The derived
P
- and
S
-wave velocity models constrain key physical properties of the crust, including the depth of the mafic rocks of the Magnitogorsk volcanic arc and the existence of a lower crustal zone of possible basic rock enrichment beneath the East Uralian zone.
Suppression of TNF-α-Induced Apoptosis by NF-κB
Authors: Van Antwerp Daniel J. , Martin Seamus J. , Kafri Tal , Green Douglas R. , Verma Inder M.
Published: July 2002

Tumor necrosis factor α (TNF-α) signaling gives rise to a number of events, including activation of transcription factor NF-κB and programmed cell death (apoptosis). Previous studies of TNF-α signaling have suggested that these two events occur independently. The sensitivity and kinetics of TNF-α-induced apoptosis are shown to be enhanced in a number of cell types expressing a dominant-negative IκBα (IκBαM). These findings suggest that a negative feedback mechanism results from TNF-α signaling in which NF-κB activation suppresses the signals for cell death.
Ultraviolet Light and Osmotic Stress: Activation of the JNK Cascade Through Multiple Growth Factor and Cytokine Receptors
Authors: Rosette Caridad , Karin Michael
Published: July 2002

Exposure of mammalian cells to ultraviolet (UV) light or high osmolarity strongly activates the c-Jun amino-terminal protein kinase (JNK) cascade, causing induction of many target genes. Exposure to UV light or osmotic shock induced clustering and internalization of cell surface receptors for epidermal growth factor (EGF), tumor necrosis factor (TNF), and interleukin-1 (IL-1). Activation of the EGF and TNF receptors was also detected biochemically. Whereas activation of each receptor alone resulted in modest activation of JNK, coadministration of EGF, IL-1, and TNF resulted in a strong synergistic response equal to that caused by exposure to osmotic shock or UV light. Inhibition of clustering or receptor down-regulation attenuated both the osmotic shock and UV responses. Physical stresses may perturb the cell surface or alter receptor conformation, thereby subverting signaling pathways normally used by growth factors and cytokines.
Tomography of the Source Area of the 1995 Kobe Earthquake: Evidence for Fluids at the Hypocenter?
Authors: Zhao Dapeng , Kanamori Hiroo , Negishi Hiroaki , Wiens Douglas
Published: July 2002

Seismic tomography revealed a low seismic velocity (−5%) and high Poisson's ratio (+6%) anomaly covering about 300 square kilometers at the hypocenter of the 17 January 1995, magnitude 7.2, Kobe earthquake in Japan. This anomaly may be due to an overpressurized, fluid-filled, fractured rock matrix that contributed to the initiation of the Kobe earthquake.