bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of the lithographic properties of positive resists upon exposure to deep- and extreme-ultraviolet radiation
Authors: Brainard Robert L. , Henderson Craig , Cobb Jonathan , Rao Veena , Mackevich Joseph F. , Okoroanyanwu Uzodinma , Gunn Scott , Chambers Janet , Connolly Susan
Published: July 2002

Nineteen chemically amplified ultrathin resists were imaged using exposure to extreme-ultraviolet (EUV) (13.4 nm) and deep-ultraviolet (DUV) (248 nm) radiation. Direct comparisons were made of photospeed, resolution, and line edge roughness (LER). The photospeed of these resists at 248 nm shows a good correlation with photospeed at EUV for three polymer types, but appears independent of photoacid generator type. This result underscores the importance of the polymer in photoacid generation at EUV. Resolution showed poor correlation between DUV and EUV. Correlations were made between the line edge roughness of EUV-imaged features and unexposed film thickness loss, resist contrast, image log slope (ILS), and LER of resists exposed at DUV. Both contrast and image log slope play important roles in defining LER performance—where the best LER is achieved at high contrast and high ILS.
Ion-assisted etching and profile development of silicon in molecular and atomic chlorine
Authors: Levinson Joshua A. , Shaqfeh Eric S. G. , Balooch Mehdi , Hamza Alex V.
Published: July 2002

An ion beam etching study, designed to characterize the important kinetic and transport processes involved in the ion-assisted etching of silicon in both molecular and atomic chlorine, was performed. Monoenergetic argon ions were directed normal to a silicon wafer that was simultaneously exposed to a neutral molecular and/or atomic chlorine beam. Dissociation of the beam was induced by thermally heating the graphite tip of an effusive source via electron impact. Beam composition was characterized using a quadrupole mass spectrometer and was found to be in excellent agreement with a thermodynamic equilibrium model at the source pressure and tip temperature. Unpatterned polysilicon wafers were etched to determine the ion-induced etching yields as a function of ion energy, ion to neutral flux ratio, and neutral flux composition. A physically based kinetic model was developed to represent the yield data, incorporating chlorine adsorption, atomic to molecular chlorine surface recombination, and the ion-induced desorption of adsorbed chlorine and silicon chloride products. Feature profile etching experiments using patterned silicon wafers were also performed under ion and neutral-limited conditions of varying neutral composition. Resulting profiles were examined for aspect ratio dependent etching effects, where traditional lag was observed for features etched using an isotropically distributed background chlorine flux and inverse lag was observed for features etched with a molecular and atomic chlorine flux arriving directly from the effusive source. Microtrenching was also present in the etched features. Computer simulations of the etching process and profile development were performed using the kinetic model and a line-of-sight re-emission model for the chlorine transport. The dependence of the yield on the ion angle of incidence was also incorporated into a simulation for an isotropically distributed molecular chlorine flux and was found to have a significant impact on profile evolution as a function of the ion to neutral flux ratio. Using the simulation, atomic to molecular chlorine recombination effects were also explored as a function of the surface recombination coefficient. Predictions of the simulations were compared to experimentally derived profiles and were found to be in good agreement.
Forecasting Agriculturally Driven Global Environmental Change
Authors: Tilman David , Fargione Joseph , Wolff Brian , D'Antonio Carla , Dobson Andrew , Howarth Robert , Schindler David , Schlesinger William H. , Simberloff Daniel , Swackhamer Deborah
Published: July 2002

During the next 50 years, which is likely to be the final period of rapid agricultural expansion, demand for food by a wealthier and 50% larger global population will be a major driver of global environmental change. Should past dependences of the global environmental impacts of agriculture on human population and consumption continue, 10
9
hectares of natural ecosystems would be converted to agriculture by 2050. This would be accompanied by 2.4- to 2.7-fold increases in nitrogen- and phosphorus-driven eutrophication of terrestrial, freshwater, and near-shore marine ecosystems, and comparable increases in pesticide use. This eutrophication and habitat destruction would cause unprecedented ecosystem simplification, loss of ecosystem services, and species extinctions. Significant scientific advances and regulatory, technological, and policy changes are needed to control the environmental impacts of agricultural expansion.
Allosteric Control of RNA Polymerase by a Site That Contacts Nascent RNA Hairpins
Authors: Toulokhonov Innokenti , Artsimovitch Irina , Landick Robert
Published: July 2002

DNA, RNA, and regulatory molecules control gene expression through interactions with RNA polymerase (RNAP). We show that a short α helix at the tip of the flaplike domain that covers the RNA exit channel of RNAP contacts a nascent RNA stem-loop structure (hairpin) that inhibits transcription, and that this flap-tip helix is required for activity of the regulatory protein NusA. Protein-RNA cross-linking, molecular modeling, and effects of alterations in RNAP and RNA all suggest that a tripartite interaction of RNAP, NusA, and the hairpin inhibits nucleotide addition in the active site, which is located 65 angstroms away. These findings favor an allosteric model for regulation of transcript elongation.
Spin Chirality, Berry Phase, and Anomalous Hall Effect in a Frustrated Ferromagnet
Authors: Taguchi Y. , Oohara Y. , Yoshizawa H. , Nagaosa N. , Tokura Y.
Published: July 2002

An electron hopping on non-coplanar spin sites with spin chirality obtains a complex phase factor (Berry phase) in its quantum mechanical amplitude that acts as an internal magnetic field, and is predicted to manifest itself in the Hall effect when it is not cancelled. The present combined work of transport measurement, neutron scattering, and theoretical calculation provides evidence that the gigantic anomalous Hall effect observed in Nd
2
Mo
2
O
7
, a pyrochlore ferromagnet with geometrically frustrated lattice structure, is mostly due to the spin chirality and the associated Berry phase originating from the Mo spin tilting.
Population Biology of Multihost Pathogens
Authors: Woolhouse Mark E. J. , Taylor Louise H. , Haydon Daniel T.
Published: July 2002

The majority of pathogens, including many of medical and veterinary importance, can infect more than one species of host. Population biology has yet to explain why perceived evolutionary advantages of pathogen specialization are, in practice, outweighed by those of generalization. Factors that predispose pathogens to generalism include high levels of genetic diversity and abundant opportunities for cross-species transmission, and the taxonomic distributions of generalists and specialists appear to reflect these factors. Generalism also has consequences for the evolution of virulence and for pathogen epidemiology, making both much less predictable. The evolutionary advantages and disadvantages of generalism are so finely balanced that even closely related pathogens can have very different host range sizes.
Quinones as the Redox Signal for the Arc Two-Component System of Bacteria
Authors: Georgellis Dimitris , Kwon Ohsuk , Lin Edmund C. C.
Published: July 2002

The Arc two-component signal transduction system mediates adaptive responses of
Escherichia coli
to changing respiratory conditions of growth. Under anaerobic conditions, the ArcB sensor kinase autophosphorylates and then transphosphorylates ArcA, a global transcriptional regulator that controls the expression of numerous operons involved in respiratory or fermentative metabolism. We show that oxidized forms of quinone electron carriers act as direct negative signals that inhibit autophosphorylation of ArcB during aerobiosis. Thus, the Arc signal transduction system provides a link between the electron transport chain and gene expression.
Afterimage of Perceptually Filled-in Surface
Authors: Shimojo Shinsuke , Kamitani Yukiyasu , Nishida Shin'ya
Published: July 2002

An afterimage induced by prior adaptation to a visual stimulus is believed to be due to bleaching of photochemical pigments or neural adaptation in the retina. We report a type of afterimage that appears to require cortical adaptation. Fixating a neon-color spreading configuration led not only to negative afterimages corresponding to the inducers (local afterimages), but also to one corresponding to the perceptually filled-in surface during adaptation (global afterimage). These afterimages were mutually exclusive, undergoing monocular rivalry. The strength of the global afterimage correlated to a greater extent with perceptual filling-in during adaptation than with the strength of the local afterimages. Thus, global afterimages are not merely by-products of local afterimages, but involve adaptation at a cortical representation of surface.
Formation of Neurofibrillary Tangles in P301L Tau Transgenic Mice Induced by Aβ42 Fibrils
Authors: Götz J. , Chen F. , van Dorpe J. , Nitsch R. M.
Published: July 2002

β-Amyloid plaques and neurofibrillary tangles (NFTs) are the defining neuropathological hallmarks of Alzheimer's disease, but their pathophysiological relation is unclear. Injection of β-amyloid Aβ
42
fibrils into the brains of P301L mutant tau transgenic mice caused fivefold increases in the numbers of NFTs in cell bodies within the amygdala from where neurons project to the injection sites. Gallyas silver impregnation identified NFTs that contained tau phosphorylated at serine 212/threonine 214 and serine 422. NFTs were composed of twisted filaments and occurred in 6-month-old mice as early as 18 days after Aβ
42
injections. Our data support the hypothesis that Aβ
42
fibrils can accelerate NFT formation in vivo.
Ascent of Dinosaurs Linked to an Iridium Anomaly at the Triassic-Jurassic Boundary
Authors: Olsen P. E. , Kent D. V. , Sues H.-D. , Koeberl C. , Huber H. , Montanari A. , Rainforth E. C. , Fowell S. J. , Szajna M. J. , Hartline B. W.
Published: July 2002

Analysis of tetrapod footprints and skeletal material from more than 70 localities in eastern North America shows that large theropod dinosaurs appeared less than 10,000 years after the Triassic-Jurassic boundary and less than 30,000 years after the last Triassic taxa, synchronous with a terrestrial mass extinction. This extraordinary turnover is associated with an iridium anomaly (up to 285 parts per trillion, with an average maximum of 141 parts per trillion) and a fern spore spike, suggesting that a bolide impact was the cause. Eastern North American dinosaurian diversity reached a stable maximum less than 100,000 years after the boundary, marking the establishment of dinosaur-dominated communities that prevailed for the next 135 million years.
Oscillating Rows of Vortices in Superconductors
Authors: Matsuda T. , Kamimura O. , Kasai H. , Harada K. , Yoshida T. , Akashi T. , Tonomura A. , Nakayama Y. , Shimoyama J. , Kishio K. , Hanaguri T. , Kitazawa K.
Published: July 2002

Superconductors can be used as dissipation-free electrical conductors as long as vortices are pinned. Vortices in high-temperature superconductors, however, behave anomalously, reflecting the anisotropic layered structure, and can move readily, thus preventing their practical use. Specifically, in a magnetic field tilted toward the layer plane, a special vortex arrangement (chain-lattice state) is formed. Real-time observation of vortices using high-resolution Lorentz microscopy revealed that the images of chain vortices begin to disappear at a much lower temperature,
T
d
, than the superconducting transition temperature,
T
c
. We attribute this image disappearance to the longitudinal oscillation of vortices along the chains.
Photoinduced Conversion of Silver Nanospheres to Nanoprisms
Authors: Jin Rongchao , Cao YunWei , Mirkin Chad A. , Kelly K. L. , Schatz George C. , Zheng J. G.
Published: July 2002

A photoinduced method for converting large quantities of silver nanospheres into triangular nanoprisms is reported. The photo-process has been characterized by time-dependent ultraviolet-visible spectroscopy and transmission electron microscopy, allowing for the observation of several key intermediates in and characteristics of the conversion process. This light-driven process results in a colloid with distinctive optical properties that directly relate to the nanoprism shape of the particles. Theoretical calculations coupled with experimental observations allow for the assignment of the nanoprism plasmon bands and for the first identification of two distinct quadrupole plasmon resonances for a nanoparticle. Unlike the spherical particles they are derived from that Rayleigh light-scatter in the blue, these nanoprisms exhibit scattering in the red, which could be useful in developing multicolor diagnostic labels on the basis not only of nanoparticle composition and size but also of shape.
Micro/Nano Encapsulation via Electrified Coaxial Liquid Jets
Authors: Loscertales I. G. , Barrero A. , Guerrero I. , Cortijo R. , Marquez M. , Gañán-Calvo A. M.
Published: July 2002

We report a method to generate steady coaxial jets of immiscible liquids with diameters in the range of micrometer/nanometer size. This compound jet is generated by the action of electro-hydrodynamic (EHD) forces with a diameter that ranges from tens of nanometers to tens of micrometers. The eventual jet breakup results in an aerosol of monodisperse compound droplets with the outer liquid surrounding or encapsulating the inner one. Following this approach, we have produced monodisperse capsules with diameters varying between 10 and 0.15 micrometers, depending on the running parameters.
Marine Biodiversity Hotspots and Conservation Priorities for Tropical Reefs
Authors: Roberts Callum M. , McClean Colin J. , Veron John E. N. , Hawkins Julie P. , Allen Gerald R. , McAllister Don E. , Mittermeier Cristina G. , Schueler Frederick W. , Spalding Mark , Wells Fred , Vynne Carly , Werner Timothy B.
Published: July 2002

Coral reefs are the most biologically diverse of shallow water marine ecosystems but are being degraded worldwide by human activities and climate warming. Analyses of the geographic ranges of 3235 species of reef fish, corals, snails, and lobsters revealed that between 7.2% and 53.6% of each taxon have highly restricted ranges, rendering them vulnerable to extinction. Restricted-range species are clustered into centers of endemism, like those described for terrestrial taxa. The 10 richest centers of endemism cover 15.8% of the world's coral reefs (0.012% of the oceans) but include between 44.8 and 54.2% of the restricted-range species. Many occur in regions where reefs are being severely affected by people, potentially leading to numerous extinctions. Threatened centers of endemism are major biodiversity hotspots, and conservation efforts targeted toward them could help avert the loss of tropical reef biodiversity.
An αβ T Cell Receptor Structure at 2.5 Å and Its Orientation in the TCR-MHC Complex
Authors: Garcia K. Christopher , Degano Massimo , Stanfield Robyn L. , Brunmark Anders , Jackson Michael R. , Peterson Per A. , Teyton Luc , Wilson Ian A.
Published: July 2002

The central event in the cellular immune response to invading microorganisms is the specific recognition of foreign peptides bound to major histocompatibility complex (MHC) molecules by the αβ T cell receptor (TCR). The x-ray structure of the complete extracellular fragment of a glycosylated αβ TCR was determined at 2.5 angstroms, and its orientation bound to a class I MHC-peptide (pMHC) complex was elucidated from crystals of the TCR-pMHC complex. The TCR resembles an antibody in the variable Vα and Vβ domains but deviates in the constant Cα domain and in the interdomain pairing of Cα with Cβ. Four of seven possible asparagine-linked glycosylation sites have ordered carbohydrate moieties, one of which lies in the Cα-Cβ interface. The TCR combining site is relatively flat except for a deep hydrophobic cavity between the hypervariable CDR3s (complementarity-determining regions) of the α and β chains. The 2C TCR covers the class I MHC H-2K
b
binding groove so that the Vα CDRs 1 and 2 are positioned over the amino-terminal region of the bound dEV8 peptide, the Vβ chain CDRs 1 and 2 are over the carboxyl-terminal region of the peptide, and the Vα and Vβ CDR3s straddle the peptide between the helices around the central position of the peptide.
Enhanced Dissociation of HLA-DR-Bound Peptides in the Presence of HLA-DM
Authors: Weber Dominique A. , Evavold Brian D. , Jensen Peter E.
Published: July 2002

Human leukocyte antigen (HLA)-DM is a critical participant in antigen presentation that catalyzes the release of class II-associated invariant chain-derived peptides (CLIP) from newly synthesized class II histocompatibility molecules, freeing the peptide-binding site for acquisition of antigenic peptides. The mechanism for the selective release of CLIP but not other peptides is unknown. DM was found to enhance the rate of peptide dissociation to an extent directly proportional to the intrinsic rate of peptide dissociation from HLA-DR, regardless of peptide sequence. Thus, CLIP is rapidly released in the presence of DM, because its intrinsic rate of dissociation is relatively high. In antigen presentation, DM has the potential to markedly enhance the rate of peptide exchange, favoring the presentation of peptides with slower intrinsic rates of dissociation.
Effects of Monomer Structure on Their Organization and Polymerization in a Smectic Liquid Crystal
Authors: Guymon C. Allan , Hoggan Erik N. , Clark Noel A. , Rieker Thomas P. , Walba David M. , Bowman Christopher N.
Published: July 2002

Photopolymerizable diacrylate monomers dissolved in fluid-layer smectic A and smectic C liquid crystal (LC) hosts exhibited significant spatial segregation and orientation that depend strongly on monomer structure. Small, flexible monomers such as 1,6-hexanediol diacrylate (HDDA) oriented parallel to the smectic layers and intercalated, whereas rod-shaped mesogen-like monomers such as 1,4-di-(4-(6-acryloyloxyhexyloxy)benzoyloxy)-2-methylbenzene (C6M) oriented normal to the smectic layers and collected within them. Such spatial segregation caused by the smectic layering dramatically enhanced photopolymerization rates; for HDDA, termination rates were reduced, whereas for C6M, both the termination and propagation rates were increased. These polymerization precursor structures suggest novel materials-design paradigms for gel LCs and nanophase-separated polymer systems.
Superoxides Relay Ras Protein's Oncogenic Message
Authors: Pennisi Elizabeth
Published: July 2002

Health-conscious consumers may now have another reason for thinking that antioxidants might help protect against cancer. On page
1649
, researchers report new results suggesting that superoxide-—a free radical consisting of an oxygen molecule with an extra electron—helps a protein called Ras transmit its growth-stimulating signals to the nucleus. Because overactivity of this pathway is thought to contribute to the development of a wide variety of cancers, the work provides further support for the idea that reactive oxygen species such as superoxide are good targets for anticancer drugs. George Bush, eat your broccoli!
Initial Genetic Characterization of the 1918 “Spanish” Influenza Virus
Authors: Taubenberger Jeffery K. , Reid Ann H. , Krafft Amy E. , Bijwaard Karen E. , Fanning Thomas G.
Published: July 2002

The “Spanish” influenza pandemic killed at least 20 million people in 1918–1919, making it the worst infectious pandemic in history. Understanding the origins of the 1918 virus and the basis for its exceptional virulence may aid in the prediction of future influenza pandemics. RNA from a victim of the 1918 pandemic was isolated from a formalin-fixed, paraffin-embedded, lung tissue sample. Nine fragments of viral RNA were sequenced from the coding regions of hemagglutinin, neuraminidase, nucleoprotein, matrix protein 1, and matrix protein 2. The sequences are consistent with a novel H1N1 influenza A virus that belongs to the subgroup of strains that infect humans and swine, not the avian subgroup.
Evolution of the Outgassing of Comet Hale-Bopp (C/1995 O1) from Radio Observations
Authors: Biver Nicolas , Bockelée-Morvan Dominique , Colom Pierre , Crovisier Jacques , Davies John K. , Dent William R. F. , Despois Didier , Gérard Eric , Lellouch Emmanuel , Rauer Heike , Moreno Raphael , Paubert Gabriel
Published: July 2002

Spectra obtained from ground-based radio telescopes show the progressive release of CO, CH3OH, HCN, H2O (from OH), H2S, CS, H2CO, CH3CN, and HNC as comet Hale-Bopp (C/1995 O1) approached the sun from 6.9 to 1.4 astronomical units (AU). The more volatile species were relatively more abundant in the coma far from the sun, but there was no direct correlation between overabundance and volatility. Evidence for H2O sublimation from icy grains was seen beyond 3.5 AU from the sun. The change from a CO-driven coma to an H2O-driven coma occurred at about 3 AU. The gas outflow velocity and temperature increased as Hale-Bopp approached the sun.
Wound Healing--Aiming for Perfect Skin Regeneration
Authors: Martin Paul
Published: July 2002

The healing of an adult skin wound is a complex process requiring the collaborative efforts of many different tissues and cell lineages. The behavior of each of the contributing cell types during the phases of proliferation, migration, matrix synthesis, and contraction, as well as the growth factor and matrix signals present at a wound site, are now roughly understood. Details of how these signals control wound cell activities are beginning to emerge, and studies of healing in embryos have begun to show how the normal adult repair process might be readjusted to make it less like patching up and more like regeneration.
Surface Deformation and Lower Crustal Flow in Eastern Tibet
Authors: Royden Leigh H. , Burchfiel B. Clark , King Robert W. , Wang Erchie , Chen Zhiliang , Shen Feng , Liu Yuping
Published: July 2002

Field observations and satellite geodesy indicate that little crustal shortening has occurred along the central to southern margin of the eastern Tibetan plateau since about 4 million years ago. Instead, central eastern Tibet has been nearly stationary relative to southeastern China, southeastern Tibet has rotated clockwise without major crustal shortening, and the crust along portions of the eastern plateau margin has been extended. Modeling suggests that these phenomena are the result of continental convergence where the lower crust is so weak that upper crustal deformation is decoupled from the motion of the underlying mantle. This model also predicts east-west extension on the high plateau without convective removal of Tibetan lithosphere and without eastward movement of the crust east of the plateau.
Thermodynamics and Kinetics of a Brownian Motor
Authors: Astumian R. Dean
Published: July 2002

Nonequilibrium fluctuations, whether generated externally or by a chemical reaction far from equilibrium, can bias the Brownian motion of a particle in an anisotropic medium without thermal gradients, a net force such as gravity, or a macroscopic electric field. Fluctuation-driven transport is one mechanism by which chemical energy can directly drive the motion of particles and macromolecules and may find application in a wide variety of fields, including particle separation and the design of molecular motors and pumps.
Functionalized Monolayers on Ordered Mesoporous Supports
Authors: Feng X. , Fryxell G. E. , Wang L.-Q. , Kim A. Y. , Liu J. , Kemner K. M.
Published: July 2002

Mesoporous silica materials containing functionalized organic monolayers have been synthesized. Solid-state nuclear magnetic resonance suggests that a cross-linked monolayer of mercaptopropylsilane was covalently bound to mesoporous silica and closely packed on the surface. The relative surface coverage of the monolayers can be systematically varied up to 76 percent. These materials are extremely efficient in removing mercury and other heavy metals from both aqueous and nonaqueous waste streams, with distribution coefficients up to 340,000. The stability of these materials and the potential to regenerate and reuse them have also been demonstrated. The surface modification scheme reported here enables rational design of the surface properties of tailored porous materials and may lead to the synthesis of more sophisticated functionalized composites for environmental and industrial applications.
The Motion and Boundary Between the Capricorn and Australian Plates
Authors: Royer Jean-Yves , Gordon Richard G.
Published: July 2002

The motions between the Somalian, Antarctic, and Australian plates—the three plates believed to meet at the Rodrigues triple junction in the Indian Ocean—are inconsistent with the assumption that all three plates are rigid. The discrepancy is best explained if the Australian plate contains two component plates. Thus, the traditionally defined Indo-Australian plate consists of three component plates and multiple diffuse plate boundaries. The pattern of present deformation indicates that the boundaries between the three component plates are two unconnected zones accommodating divergence and a larger zone, which we interpret as three diffuse convergent plate boundaries and a diffuse triple junction.
Three-Dimensional Dynamic Simulation of the 1992 Landers Earthquake
Authors: Olsen K. B. , Madariaga R. , Archuleta R. J.
Published: July 2002

The 1992 Landers, California, earthquake (magnitude 7.3) was modeled as the propagation of a spontaneous rupture controlled by a realistic prestress distribution with the use of a three-dimensional finite-difference method. The dynamic rupture reproduces the general slip pattern used to compute the initial stress distribution and generates near-fault ground motions at the surface similar to observations. The simulated rupture propagates on the fault along a complex path with highly variable speed and rise time, changing the magnitude and pattern of the stress significantly. The method provides the framework to estimate earthquake rupture parameters from recorded seismic and geodetic data.
Imaging of Intermittency in Ripple-Wave Turbulence
Authors: Wright William B. , Budakian R. , Pine D. J. , Putterman S. J.
Published: July 2002

The dynamics of a fluid surface filled with high-amplitude ripples were studied with a technique (diffusing light photography) that resolves the height at all locations instantaneously. Even when nonlinearities are strong enough to generate a (Kolmogorov) cascade from long wavelength (where energy is input) to shorter wavelength, the resulting turbulent state contains large coherent spatial structures. The appearance of these structures in a thermal equilibrium state (with the same average energy) would be highly improbable.
Organically Modified Aluminosilicate Mesostructures from Block Copolymer Phases
Authors: Templin Markus , Franck Achim , Du Chesne Alexander , Leist Heike , Zhang Yuanming , Ulrich Ralph , Schädler Volker , Wiesner Ulrich
Published: July 2002

Organically modified aluminosilicate mesostructures were synthesized from two metal alkoxides with the use of poly(isoprene-
b
-ethyleneoxide) block copolymers (PI-b-PEO) as the structure-directing molecules. By increasing the fraction of the inorganic precursors with respect to the polymer, morphologies expected from the phase diagrams of diblock copolymers were obtained. The length scale of the microstructures and the state of alignment were varied using concepts known from the study of block copolymers. These results suggest that the use of higher molecular weight block copolymer mesophases instead of conventional low–molecular weight surfactants may provide a simple, easily controlled pathway for the preparation of various silica-type mesostructures that extends the accessible length scale of these structures by about an order of magnitude.
Transcription Factor-Specific Requirements for Coactivators and Their Acetyltransferase Functions
Authors: Korzus Edward , Torchia Joseph , Rose David W. , Xu Lan , Kurokawa Riki , McInerney Eileen M. , Mullen Tina-Marie , Glass Christopher K. , Rosenfeld Michael G.
Published: July 2002

Different classes of mammalian transcription factors—nuclear receptors, cyclic adenosine 3′,5′-monophosphate–regulated enhancer binding protein (CREB), and signal transducer and activator of transcription-1 (STAT-1)—functionally require distinct components of the coactivator complex, including CREB-binding protein (CBP/p300), nuclear receptor coactivators (NCoAs), and p300/CBP-associated factor (p/CAF), based on their platform or assembly properties. Retinoic acid receptor, CREB, and STAT-1 also require different histone acetyltransferase (HAT) activities to activate transcription. Thus, transcription factor–specific differences in configuration and content of the coactivator complex dictate requirements for specific acetyltransferase activities, providing an explanation, at least in part, for the presence of multiple HAT components of the complex.
Autophosphorylation at Thr
286
of the α Calcium-Calmodulin Kinase II in LTP and Learning
Authors: Giese Karl Peter , Fedorov Nikolai B. , Filipkowski Robert K. , Silva Alcino J.
Published: July 2002

The calcium-calmodulin–dependent kinase II (CaMKII) is required for hippocampal long-term potentiation (LTP) and spatial learning. In addition to its calcium-calmodulin (CaM)–dependent activity, CaMKII can undergo autophosphorylation, resulting in CaM-independent activity. A point mutation was introduced into the αCaMKII gene that blocked the autophosphorylation of threonine at position 286 (Thr
286
) of this kinase without affecting its CaM-dependent activity. The mutant mice had no
N
-methyl-
d
-aspartate receptor–dependent LTP in the hippocampal CA1 area and showed no spatial learning in the Morris water maze. Thus, the autophosphorylation of αCaMKII at Thr
286
appears to be required for LTP and learning.
The Involvement of Cell-to-Cell Signals in the Development of a Bacterial Biofilm
Authors: Davies David G. , Parsek Matthew R. , Pearson James P. , Iglewski Barbara H. , Costerton J. W. , Greenberg E. P.
Published: July 2002

Bacteria in nature often exist as sessile communities called biofilms. These communities develop structures that are morphologically and physiologically differentiated from free-living bacteria. A cell-to-cell signal is involved in the development of
Pseudomonas aeruginosa
biofilms. A specific signaling mutant, a
lasI
mutant, forms flat, undifferentiated biofilms that unlike wild-type biofilms are sensitive to the biocide sodium dodecyl sulfate. Mutant biofilms appeared normal when grown in the presence of a synthetic signal molecule. The involvement of an intercellular signal molecule in the development of
P. aeruginosa
biofilms suggests possible targets to control biofilm growth on catheters, in cystic fibrosis, and in other environments where
P. aeruginosa
biofilms are a persistent problem.
Impacts of Rising Atmospheric Carbon Dioxide on Model Terrestrial Ecosystems
Authors: Jones T. H. , Thompson L. J. , Lawton J. H. , Bezemer T. M. , Bardgett R. D. , Blackburn T. M. , Bruce K. D. , Cannon P. F. , Hall G. S. , Hartley S. E. , Howson G. , Jones C. G. , Kampichler C. , Kandeler E. , Ritchie D. A.
Published: July 2002

In model terrestrial ecosystems maintained for three plant generations at elevated concentrations of atmospheric carbon dioxide, increases in photosynthetically fixed carbon were allocated below ground, raising concentrations of dissolved organic carbon in soil. These effects were then transmitted up the decomposer food chain. Soil microbial biomass was unaffected, but the composition of soil fungal species changed, with increases in rates of cellulose decomposition. There were also changes in the abundance and species composition of Collembola, fungal-feeding arthropods. These results have implications for long-term feedback processes in soil ecosystems that are subject to rising global atmospheric carbon dioxide concentrations.
Ferromagnetism in LaFeO
3
-LaCrO
3
Superlattices
Authors: Ueda Kenji , Tabata Hitoshi , Kawai Tomoji
Published: July 2002

Ferromagnetic spin order has been realized in the LaCrO
3
-LaFeO
3
superlattices. Ferromagnetic coupling between Fe
3+
and Cr
3+
through oxygen has long been expected on the basis of Anderson, Goodenough, and Kanamori rules. Despite many studies of Fe-O-Cr–based compounds, random positioning of Fe
3+
and Cr
3+
ions has frustrated the observation of ferromagnetic properties. By creating artificial superlattices of Fe
3+
and Cr
3+
layer along the [111] direction, ferromagnetic ordering has been achieved.
Hormone-Dependent Coactivator Binding to a Hydrophobic Cleft on Nuclear Receptors
Authors: Feng Weijun , Ribeiro Ralff C. J. , Wagner Richard L. , Nguyen Hoa , Apriletti James W. , Fletterick Robert J. , Baxter John D. , Kushner Peter J. , West Brian L.
Published: July 2002

The ligand-binding domain of nuclear receptors contains a transcriptional activation function (AF-2) that mediates hormone-dependent binding of coactivator proteins. Scanning surface mutagenesis on the human thyroid hormone receptor was performed to define the site that binds the coactivators, glucocorticoid receptor–interacting protein 1 (GRIP1) and steroid receptor coactivator 1 (SRC-1). The residues involved encircle a small surface that contains a hydrophobic cleft. Ligand activation of transcription involves formation of this surface by folding the carboxyl-terminal α helix against a scaffold of three other helices. These features may represent general ones for nuclear receptors.
Primary Production of the Biosphere: Integrating Terrestrial and Oceanic Components
Authors: Field Christopher B. , Behrenfeld Michael J. , Randerson James T. , Falkowski Paul
Published: July 2002

Integrating conceptually similar models of the growth of marine and terrestrial primary producers yielded an estimated global net primary production (NPP) of 104.9 petagrams of carbon per year, with roughly equal contributions from land and oceans. Approaches based on satellite indices of absorbed solar radiation indicate marked heterogeneity in NPP for both land and oceans, reflecting the influence of physical and ecological processes. The spatial and temporal distributions of ocean NPP are consistent with primary limitation by light, nutrients, and temperature. On land, water limitation imposes additional constraints. On land and ocean, progressive changes in NPP can result in altered carbon storage, although contrasts in mechanisms of carbon storage and rates of organic matter turnover result in a range of relations between carbon storage and changes in NPP.
The Roles of Structural Imperfections in InGaN-Based Blue Light-Emitting Diodes and Laser Diodes
Authors: Nakamura Shuji
Published: July 2002

REVIEW

High-efficiency light-emitting diodes emitting amber, green, blue, and ultraviolet light have been obtained through the use of an InGaN active layer instead of a GaN active layer. The localized energy states caused by In composition fluctuation in the InGaN active layer are related to the high efficiency of the InGaN-based emitting devices. The blue and green InGaN quantum-well structure light-emitting diodes with luminous efficiencies of 5 and 30 lumens per watt, respectively, can be made despite the large number of threading dislocations (1 × 10
8
to 1 × 10
12
cm
−2
). Epitaxially laterally overgrown GaN on sapphire reduces the number of threading dislocations originating from the interface of the GaN epilayer with the sapphire substrate. InGaN multi-quantum-well structure laser diodes formed on the GaN layer above the SiO
2
mask area can have a lifetime of more than 10,000 hours. Dislocations increase the threshold current density of the laser diodes.
Coaxial Nanocable: Silicon Carbide and Silicon Oxide Sheathed with Boron Nitride and Carbon
Authors: Zhang Y. , Suenaga K. , Colliex C. , Iijima S.
Published: July 2002

Multielement nanotubes comprising multiple phases, with diameters of a few tens of nanometers and lengths up to 50 micrometers, were successfully synthesized by means of reactive laser ablation. The experimentally determined structure consists of a β-phase silicon carbide core, an amorphous silicon oxide intermediate layer, and graphitic outer shells made of boron nitride and carbon layers separated in the radial direction. The structure resembles a coaxial nanocable with a semiconductor-insulator-metal (or semiconductor-insulator-semiconductor) geometry and suggests applications in nanoscale electronic devices that take advantage of this self-organization mechanism for multielement nanotube formation.
The Bcl-2 Protein Family: Arbiters of Cell Survival
Authors: Adams Jerry M. , Cory Suzanne
Published: July 2002

REVIEW

Bcl-2 and related cytoplasmic proteins are key regulators of apoptosis, the cell suicide program critical for development, tissue homeostasis, and protection against pathogens. Those most similar to Bcl-2 promote cell survival by inhibiting adapters needed for activation of the proteases (caspases) that dismantle the cell. More distant relatives instead promote apoptosis, apparently through mechanisms that include displacing the adapters from the pro-survival proteins. Thus, for many but not all apoptotic signals, the balance between these competing activities determines cell fate. Bcl-2 family members are essential for maintenance of major organ systems, and mutations affecting them are implicated in cancer.
Regulation of Cell Death Protease Caspase-9 by Phosphorylation
Authors: Cardone Michael H. , Roy Natalie , Stennicke Henning R. , Salvesen Guy S. , Franke Thomas F. , Stanbridge Eric , Frisch Steven , Reed John C.
Published: July 2002

Caspases are intracellular proteases that function as initiators and effectors of apoptosis. The kinase Akt and p21-Ras, an Akt activator, induced phosphorylation of pro–caspase-9 (pro-Casp9) in cells. Cytochrome c–induced proteolytic processing of pro-Casp9 was defective in cytosolic extracts from cells expressing either active Ras or Akt. Akt phosphorylated recombinant Casp9 in vitro on serine-196 and inhibited its protease activity. Mutant pro-Casp9(Ser196Ala) was resistant to Akt-mediated phosphorylation and inhibition in vitro and in cells, resulting in Akt-resistant induction of apoptosis. Thus, caspases can be directly regulated by protein phosphorylation.
Carbon in the Universe
Authors: Henning Th. , Salama F.
Published: July 2002

Carbon is a major player in the evolutionary scheme of the universe because of its abundance and its ability to form complex species. It is also a key element in the evolution of prebiotic molecules. The different forms of cosmic carbon are reviewed ranging from carbon atoms and carbon-bearing molecules to complex, solid-state, carbonaceous structures. The current state of knowledge is assessed on the observational and laboratory fronts. Fundamental astrophysical implications are examined as well as the impact of these studies on the hitherto poorly understood physical and chemical properties of carbon materials in space.
A Processive Single-Headed Motor: Kinesin Superfamily Protein KIF1A
Authors: Okada Yasushi , Hirokawa Nobutaka
Published: July 2002

A single kinesin molecule can move “processively” along a microtubule for more than 1 micrometer before detaching from it. The prevailing explanation for this processive movement is the “walking model,” which envisions that each of two motor domains (heads) of the kinesin molecule binds coordinately to the microtubule. This implies that each kinesin molecule must have two heads to “walk” and that a single-headed kinesin could not move processively. Here, a motor-domain construct of KIF1A, a single-headed kinesin superfamily protein, was shown to move processively along the microtubule for more than 1 micrometer. The movement along the microtubules was stochastic and fitted a biased Brownian-movement model.
"Debye-Scherrer Ellipses" from 3D Fullerene Polymers: An Anisotropic Pressure Memory Signature
Authors: Marques L. , Mezouar M. , Hodeau J.-L. , Núñez-Regueiro M. , Serebryanaya N. R. , Ivdenko V. A. , Blank V. D. , Dubitsky G. A.
Published: July 2002

High-pressure studies on fullerenes have previously shown the existence of one- and two-dimensional (2D) polymerized C
60
structures. Synchrotron radiation measurements, performed on C
60
samples quenched from 13 gigapascals and 820 kelvin, yield unambiguous proof for the existence of a three-dimensional (3D) polymerized C
60
derivative. Moreover, unusual ellipsoidal Debye-Scherrer diffraction patterns are observed, which shows that the giant anisotropic deformation induced by the nonhydrostatic compression is retained in the quenched samples. The multiple bonding possibilities of the highly symmetrical C
60
allow the retention (down to ambient pressure) of the deformation, a phenomenon reported previously only under high pressure.
Structural Maturation of Neural Pathways in Children and Adolescents: In Vivo Study
Authors: Paus Tomáš , Zijdenbos Alex , Worsley Keith , Collins D. Louis , Blumenthal Jonathan , Giedd Jay N. , Rapoport Judith L. , Evans Alan C.
Published: July 2002

Structural maturation of fiber tracts in the human brain, including an increase in the diameter and myelination of axons, may play a role in cognitive development during childhood and adolescence. A computational analysis of structural magnetic resonance images obtained in 111 children and adolescents revealed age-related increases in white matter density in fiber tracts constituting putative corticospinal and frontotemporal pathways. The maturation of the corticospinal tract was bilateral, whereas that of the frontotemporal pathway was found predominantly in the left (speech-dominant) hemisphere. These findings provide evidence for a gradual maturation, during late childhood and adolescence, of fiber pathways presumably supporting motor and speech functions.
The Search for Unrecognized Pathogens
Authors: Relman David A.
Published: July 2002

The distribution and diversity of microorganisms in the world are far greater than have been previously appreciated. Molecular, cultivation-independent methods have played a key role in this insight. To what extent do humans remain ignorant of microbial diversity within the human body and the settings in which microorganisms cause human disease? In addition to implicating microbial agents in nontraditional infectious diseases, the use of methods such as broad-range polymerase chain reaction, representational difference analysis, expression library screening, and host gene expression profiling may force a reassessment of the concepts of microbial disease causation.
Bacterial Biofilms: A Common Cause of Persistent Infections
Authors: Costerton J. W. , Stewart Philip S. , Greenberg E. P.
Published: July 2002

Bacteria that attach to surfaces aggregate in a hydrated polymeric matrix of their own synthesis to form biofilms. Formation of these sessile communities and their inherent resistance to antimicrobial agents are at the root of many persistent and chronic bacterial infections. Studies of biofilms have revealed differentiated, structured groups of cells with community properties. Recent advances in our understanding of the genetic and molecular basis of bacterial community behavior point to therapeutic targets that may provide a means for the control of biofilm infections.
Cracks Faster than the Shear Wave Speed
Authors: Rosakis A. J. , Samudrala O. , Coker D.
Published: July 2002

Classical dynamic fracture theories predict the surface wave speed to be the limiting speed for propagation of in-plane cracks in homogeneous, linear elastic materials subjected to remote loading. This report presents experimental evidence to the contrary. Intersonic shear-dominated crack growth featuring shear shock waves was observed along weak planes in a brittle polyester resin under far-field asymmetric loading. When steady-state conditions were attained, the shear cracks propagated at speeds close to

2

times the material shear wave speed. These observations have similarities to shallow earthquake events where intersonic shear rupture speeds have been surmised.
BLyS: Member of the Tumor Necrosis Factor Family and B Lymphocyte Stimulator
Authors: Moore Paul A. , Belvedere Ornella , Orr Amy , Pieri Krystyna , LaFleur David W. , Feng Ping , Soppet Daniel , Charters Meghan , Gentz Reiner , Parmelee David , Li Yuling , Galperina Olga , Giri Judith , Roschke Viktor , Nardelli Bernardetta , Carrell Jeffrey , Sosnovtseva Svetlana , Greenfield Wilbert , Ruben Steven M. , Olsen Henrik S. , Fikes James , Hilbert David M.
Published: July 2002

The tumor necrosis factor (TNF) superfamily of cytokines includes both soluble and membrane-bound proteins that regulate immune responses. A member of the human TNF family, BLyS (B lymphocyte stimulator), was identified that induced B cell proliferation and immunoglobulin secretion. BLyS expression on human monocytes could be up-regulated by interferon-γ. Soluble BLyS functioned as a potent B cell growth factor in costimulation assays. Administration of soluble recombinant BLyS to mice disrupted splenic B and T cell zones and resulted in elevated serum immunoglobulin concentrations. The B cell tropism of BLyS is consistent with its receptor expression on B-lineage cells. The biological profile of BLyS suggests it is involved in monocyte-driven B cell activation.
Conservatism of Ecological Niches in Evolutionary Time
Authors: Peterson A. T. , Soberón J. , Sánchez-Cordero V.
Published: July 2002

Theory predicts low niche differentiation between species over evolutionary time scales, but little empirical evidence is available. Reciprocal geographic predictions based on ecological niche models of sister taxon pairs of birds, mammals, and butterflies in southern Mexico indicate niche conservatism over several million years of independent evolution (between putative sister taxon pairs) but little conservatism at the level of families. Niche conservatism over such time scales indicates that speciation takes place in geographic, not ecological, dimensions and that ecological differences evolve later.
Emerging Marine Diseases--Climate Links and Anthropogenic Factors
Authors: Harvell C. D. , Kim K. , Burkholder J. M. , Colwell R. R. , Epstein P. R. , Grimes D. J. , Hofmann E. E. , Lipp E. K. , Osterhaus A. D. M. E. , Overstreet R. M. , Porter J. W. , Smith G. W. , Vasta G. R.
Published: July 2002

Mass mortalities due to disease outbreaks have recently affected major taxa in the oceans. For closely monitored groups like corals and marine mammals, reports of the frequency of epidemics and the number of new diseases have increased recently. A dramatic global increase in the severity of coral bleaching in 1997–98 is coincident with high El Niño temperatures. Such climate-mediated, physiological stresses may compromise host resistance and increase frequency of opportunistic diseases. Where documented, new diseases typically have emerged through host or range shifts of known pathogens. Both climate and human activities may have also accelerated global transport of species, bringing together pathogens and previously unexposed host populations.