bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Barrier Coatings for Gas-Turbine Engine Applications
Authors: Padture Nitin P. , Gell Maurice , Jordan Eric H.
Published: July 2002

Hundreds of different types of coatings are used to protect a variety of structural engineering materials from corrosion, wear, and erosion, and to provide lubrication and thermal insulation. Of all these, thermal barrier coatings (TBCs) have the most complex structure and must operate in the most demanding high-temperature environment of aircraft and industrial gas-turbine engines. TBCs, which comprise metal and ceramic multilayers, insulate turbine and combustor engine components from the hot gas stream, and improve the durability and energy efficiency of these engines. Improvements in TBCs will require a better understanding of the complex changes in their structure and properties that occur under operating conditions that lead to their failure. The structure, properties, and failure mechanisms of TBCs are herein reviewed, together with a discussion of current limitations and future opportunities.
Mammal Population Losses and the Extinction Crisis
Authors: Ceballos Gerardo , Ehrlich Paul R.
Published: July 2002

The disappearance of populations is a prelude to species extinction. No geographically explicit estimates have been made of current population losses of major indicator taxa. Here we compare historic and present distributions of 173 declining mammal species from six continents. These species have collectively lost over 50% of their historic range area, mostly where human activities are intensive. This implies a serious loss of ecosystem services and goods. It also signals a substantial threat to species diversity.
A Genomic Regulatory Network for Development
Authors: Davidson Eric H. , Rast Jonathan P. , Oliveri Paola , Ransick Andrew , Calestani Cristina , Yuh Chiou-Hwa , Minokawa Takuya , Amore Gabriele , Hinman Veronica , Arenas-Mena César , Otim Ochan , Brown C. Titus , Livi Carolina B. , Lee Pei Yun , Revilla Roger , Rust Alistair G. , Pan Zheng jun , Schilstra Maria J. , Clarke Peter J. C. , Arnone Maria I. , Rowen Lee , Cameron R. Andrew , McClay David R. , Hood Leroy , Bolouri Hamid
Published: July 2002

Development of the body plan is controlled by large networks of regulatory genes. A gene regulatory network that controls the specification of endoderm and mesoderm in the sea urchin embryo is summarized here. The network was derived from large-scale perturbation analyses, in combination with computational methodologies, genomic data, cis-regulatory analysis, and molecular embryology. The network contains over 40 genes at present, and each node can be directly verified at the DNA sequence level by cis-regulatory analysis. Its architecture reveals specific and general aspects of development, such as how given cells generate their ordained fates in the embryo and why the process moves inexorably forward in developmental time.
Unpredictable Evolution in a 30-Year Study of Darwin's Finches
Authors: Grant Peter R. , Grant B. Rosemary
Published: July 2002

Evolution can be predicted in the short term from a knowledge of selection and inheritance. However, in the long term evolution is unpredictable because environments, which determine the directions and magnitudes of selection coefficients, fluctuate unpredictably. These two features of evolution, the predictable and unpredictable, are demonstrated in a study of two populations of Darwin's finches on the Galápagos island of Daphne Major. From 1972 to 2001,
Geospiza fortis
(medium ground finch) and
Geospiza scandens
(cactus finch) changed several times in body size and two beak traits. Natural selection occurred frequently in both species and varied from unidirectional to oscillating, episodic to gradual. Hybridization occurred repeatedly though rarely, resulting in elevated phenotypic variances in
G. scandens
and a change in beak shape. The phenotypic states of both species at the end of the 30-year study could not have been predicted at the beginning. Continuous, long-term studies are needed to detect and interpret rare but important events and nonuniform evolutionary change.
Dynamic Imaging of T Cell-Dendritic Cell Interactions in Lymph Nodes
Authors: Stoll Sabine , Delon Jérôme , Brotz Tilmann M. , Germain Ronald N.
Published: July 2002

T cell immune responses begin within organized lymphoid tissues. The pace, topology, and outcomes of the cellular interactions that underlie these responses have, so far, been inferred from static imaging of sectioned tissue or from studies of cultured cells. Here we report dynamic visualization of antigen-specific T cells interacting with dendritic cells within intact explanted lymph nodes. We observed immunological synapse formation and prolonged interactions between these two cell types, followed by the activation, dissociation, and rapid migration of T cells away from the antigenic stimulus. This high-resolution spatiotemporal analysis provides insight into the nature of cell interactions critical to early immune responses within lymphoid structures.
Reorganization of North Atlantic Marine Copepod Biodiversity and Climate
Authors: Beaugrand Grégory , Reid Philip C. , Ibañez Frédéric , Lindley J. Alistair , Edwards Martin
Published: July 2002

We provide evidence of large-scale changes in the biogeography of calanoid copepod crustaceans in the eastern North Atlantic Ocean and European shelf seas. We demonstrate that strong biogeographical shifts in all copepod assemblages have occurred with a northward extension of more than 10° latitude of warm-water species associated with a decrease in the number of colder-water species. These biogeographical shifts are in agreement with recent changes in the spatial distribution and phenology detected for many taxonomic groups in terrestrial European ecosystems and are related to both the increasing trend in Northern Hemisphere temperature and the North Atlantic Oscillation.
TNF-R1 Signaling: A Beautiful Pathway
Authors: Chen Guoqing , Goeddel David V.
Published: July 2002

Tumor necrosis factor (TNF) is a major mediator of apoptosis as well as inflammation and immunity, and it has been implicated in the pathogenesis of a wide spectrum of human diseases, including sepsis, diabetes, cancer, osteoporosis, multiple sclerosis, rheumatoid arthritis, and inflammatory bowel diseases. The interaction of TNF with TNF receptor–1 (TNF-R1) activates several signal transduction pathways. A common feature of each pathway is the TNF-induced formation of a multiprotein signaling complex at the cell membrane. Over the past decade, many of the components and mechanisms of these signaling pathways have been elucidated. We provide an overview of current knowledge of TNF signaling and introduce an STKE Connections Map that depicts a canonical view of this process.
Structure of an HIF-1α-pVHL Complex: Hydroxyproline Recognition in Signaling
Authors: Min Jung-Hyun , Yang Haifeng , Ivan Mircea , Gertler Frank , Kaelin William G. , Pavletich Nikola P.
Published: July 2002

The ubiquitination of the hypoxia-inducible factor (HIF) by the von Hippel–Lindau tumor suppressor (pVHL) plays a central role in the cellular response to changes in oxygen availability. pVHL binds to HIF only when a conserved proline in HIF is hydroxylated, a modification that is oxygen-dependent. The 1.85 angstrom structure of a 20-residue HIF-1α peptide–pVHL–ElonginB–ElonginC complex shows that HIF-1α binds to pVHL in an extended β strand–like conformation. The hydroxyproline inserts into a gap in the pVHL hydrophobic core, at a site that is a hotspot for tumorigenic mutations, with its 4-hydroxyl group recognized by buried serine and histidine residues. Although the β sheet–like interactions contribute to the stability of the complex, the hydroxyproline contacts are central to the strict specificity characteristic of signaling.
Partially Molten Middle Crust Beneath Southern Tibet: Synthesis of Project INDEPTH Results
Authors: Nelson K. D. , Zhao Wenjin , Brown L. D. , Kuo J. , Che Jinkai , Liu Xianwen , Klemperer S. L. , Makovsky Y. , Meissner R. , Mechie J. , Kind R. , Wenzel F. , Ni J. , Nabelek J. , Leshou Chen , Tan Handong , Wei Wenbo , Jones A. G. , Booker J. , Unsworth M. , Kidd W. S. F. , Hauck M. , Alsdorf D. , Ross A. , Cogan M. , Wu Changde , Sandvol E. , Edwards M.
Published: July 2002

INDEPTH geophysical and geological observations imply that a partially molten midcrustal layer exists beneath southern Tibet. This partially molten layer has been produced by crustal thickening and behaves as a fluid on the time scale of Himalayan deformation. It is confined on the south by the structurally imbricated Indian crust underlying the Tethyan and High Himalaya and is underlain, apparently, by a stiff Indian mantle lid. The results suggest that during Neogene time the underthrusting Indian crust has acted as a plunger, displacing the molten middle crust to the north while at the same time contributing to this layer by melting and ductile flow. Viewed broadly, the Neogene evolution of the Himalaya is essentially a record of the southward extrusion of the partially molten middle crust underlying southern Tibet.
Evidence from Earthquake Data for a Partially Molten Crustal Layer in Southern Tibet
Authors: Kind Rainer , Ni James , Zhao Wenjin , Wu Jianxin , Yuan Xiaohui , Zhao Lianshe , Sandvol Eric , Reese Chris , Nabelek John , Hearn Thomas
Published: July 2002

Earthquake data collected by the INDEPTH-II Passive-Source Experiment show that there is a substantial south to north variation in the velocity structure of the crust beneath southern Tibet. North of the Zangbo suture, beneath the southern Lhasa block, a midcrustal low-velocity zone is revealed by inversion of receiver functions, Rayleigh-wave phase velocities, and modeling of the radial component of teleseismic
P
-waveforms. Conversely, to the south beneath the Tethyan Himalaya, no low-velocity zone was observed. The presence of the midcrustal low-velocity zone in the north implies that a partially molten layer is in the middle crust beneath the northern Yadong-Gulu rift and possibly much of southern Tibet.
How Thiamine Diphosphate Is Activated in Enzymes
Authors: Kern Dorothee , Kern Gunther , Neef Holger , Tittmann Kai , Killenberg-Jabs Margrit , Wikner Christer , Schneider Gunter , Hübner Gerhard
Published: July 2002

The controversial question of how thiamine diphosphate, the biologically active form of vitamin B
1
, is activated in different enzymes has been addressed. Activation of the coenzyme was studied by measuring thermodynamics and kinetics of deprotonation at the carbon in the 2-position (C2) of thiamine diphosphate in the enzymes pyruvate decarboxylase and transketolase by use of nuclear magnetic resonance spectroscopy, proton/deuterium exchange, coenzyme analogs, and site-specific mutant enzymes. Interaction of a glutamate with the nitrogen in the 1′-position in the pyrimidine ring activated the 4′-amino group to act as an efficient proton acceptor for the C2 proton. The protein component accelerated the deprotonation of the C2 atom by several orders of magnitude, beyond the rate of the overall enzyme reaction. Therefore, the earlier proposed concerted mechanism or stabilization of a C2 carbanion can be excluded.
Measuring Serotonin Distribution in Live Cells with Three-Photon Excitation
Authors: Maiti S. , Shear Jason B. , Williams R. M. , Zipfel W. R. , Webb Watt W.
Published: July 2002

Tryptophan and serotonin were imaged with infrared illumination by three-photon excitation (3PE) of their native ultraviolet (UV) fluorescence. This technique, established by 3PE cross section measurements of tryptophan and the monoamines serotonin and dopamine, circumvents the limitations imposed by photodamage, scattering, and indiscriminate background encountered in other UV microscopies. Three-dimensionally resolved images are presented along with measurements of the serotonin concentration (∼50 mM) and content (up to ∼5 × 10
8
molecules) of individual secretory granules.
A General Model for the Origin of Allometric Scaling Laws in Biology
Authors: West Geoffrey B. , Brown James H. , Enquist Brian J.
Published: July 2002

Allometric scaling relations, including the 3/4 power law for metabolic rates, are characteristic of all organisms and are here derived from a general model that describes how essential materials are transported through space-filling fractal networks of branching tubes. The model assumes that the energy dissipated is minimized and that the terminal tubes do not vary with body size. It provides a complete analysis of scaling relations for mammalian circulatory systems that are in agreement with data. More generally, the model predicts structural and functional properties of vertebrate cardiovascular and respiratory systems, plant vascular systems, insect tracheal tubes, and other distribution networks.
Multiple and Ancient Origins of the Domestic Dog
Authors: Vilà Carles , Savolainen Peter , Maldonado Jesús E. , Amorim Isabel R. , Rice John E. , Honeycutt Rodney L. , Crandall Keith A. , Lundeberg Joakim , Wayne Robert K.
Published: July 2002

Mitochondrial DNA control region sequences were analyzed from 162 wolves at 27 localities worldwide and from 140 domestic dogs representing 67 breeds. Sequences from both dogs and wolves showed considerable diversity and supported the hypothesis that wolves were the ancestors of dogs. Most dog sequences belonged to a divergent monophyletic clade sharing no sequences with wolves. The sequence divergence within this clade suggested that dogs originated more than 100,000 years before the present. Associations of dog haplotypes with other wolf lineages indicated episodes of admixture between wolves and dogs. Repeated genetic exchange between dog and wolf populations may have been an important source of variation for artificial selection.
Tropical Climate Instability: The Last Glacial Cycle from a Qinghai-Tibetan Ice Core
Authors: Thompson L. G. , Yao T. , Davis M. E. , Henderson K. A. , Mosley-Thompson E. , Lin P.-N. , Beer J. , Synal H.-A. , Cole-Dai J. , Bolzan J. F.
Published: July 2002

An ice core record from the Guliya ice cap on the Qinghai-Tibetan Plateau provides evidence of regional climatic conditions over the last glacial cycle.
36
Cl data suggest that the deepest 20 meters of the core may be more than 500,000 years old. The δ
18
O change across Termination I is ∼5.4 per mil, similar to that in the Huascarán (Peru) and polar ice cores. Three Guliya interstadials (Stages 3, 5a, and 5c) are marked by increases in δ
18
O values similar to that of the Holocene and Eemian (∼124,000 years ago). The similarity of this pattern to that of CH
4
records from polar ice cores indicates that global CH
4
levels and the tropical hydrological cycle are linked. The Late Glacial Stage record contains numerous 200-year oscillations in δ
18
O values and in dust, NH
4
+
, and NO
3
−
levels.
ARF1, a Transcription Factor That Binds to Auxin Response Elements
Authors: Ulmasov Tim , Hagen Gretchen , Guilfoyle Tom J.
Published: July 2002

The plant hormone auxin regulates plant physiology by modulating the interaction of transcription factors with auxin response elements (AuxREs) of the affected genes. A transcription factor, Auxin Response Factor 1 (ARF1), that binds to the sequence TGTCTC in AuxREs was cloned from
Arabidopsis
by using a yeast one-hybrid system. ARF1 has an amino-terminal DNA-binding domain related to the carboxyl terminus of the maize transactivator Viviparous-1. Sequence requirements for ARF1 binding in vitro are identical to those that confer auxin responsiveness in vivo. The carboxyl terminus of ARF1 contains two motifs found in the Aux/IAA class of proteins and appears to mediate protein-protein interactions.
Influence of Food Web Structure on Carbon Exchange Between Lakes and the Atmosphere
Authors: Schindler Daniel E. , Carpenter Stephen R. , Cole Jonathan J. , Kitchell James F. , Pace Michael L.
Published: July 2002

Top predators and nutrient loading in lakes were manipulated to assess the influence of food web structure on carbon flux between lakes and the atmosphere. Nutrient enrichment increased primary production, causing lakes to become net sinks for atmospheric carbon (C
atm
). Changes in top predators caused shifts in grazers. At identical nutrient loading, C
atm
invasion was greater to a lake with low grazing than to one with high grazing. Carbon stable-isotope distributions corroborated the drawdown of lake carbon dioxide and traced C
atm
transfer from algae to top predators. Thus, top predators altered ecosystem carbon fixation and linkages to the atmosphere.
Agricultural Intensification and Ecosystem Properties
Authors: Matson P. A. , Parton W. J. , Power A. G. , Swift M. J.
Published: July 2002

Expansion and intensification of cultivation are among the predominant global changes of this century. Intensification of agriculture by use of high-yielding crop varieties, fertilization, irrigation, and pesticides has contributed substantially to the tremendous increases in food production over the past 50 years. Land conversion and intensification, however, also alter the biotic interactions and patterns of resource availability in ecosystems and can have serious local, regional, and global environmental consequences. The use of ecologically based management strategies can increase the sustainability of agricultural production while reducing off-site consequences.
Neural Correlates of Motor Memory Consolidation
Authors: Shadmehr Reza , Holcomb Henry H.
Published: July 2002

Computational studies suggest that acquisition of a motor skill involves learning an internal model of the dynamics of the task, which enables the brain to predict and compensate for mechanical behavior. During the hours that follow completion of practice, representation of the internal model gradually changes, becoming less fragile with respect to behavioral interference. Here, functional imaging of the brain demonstrates that within 6 hours after completion of practice, while performance remains unchanged, the brain engages new regions to perform the task; there is a shift from prefrontal regions of the cortex to the premotor, posterior parietal, and cerebellar cortex structures. This shift is specific to recall of an established motor skill and suggests that with the passage of time, there is a change in the neural representation of the internal model and that this change may underlie its increased functional stability.
Realization of a Functional Cell for Quantum-Dot Cellular Automata
Authors: Orlov A. O. , Amlani I. , Bernstein G. H. , Lent C. S. , Snider G. L.
Published: July 2002

This paper presents an experimental demonstration of a basic cell of the quantum-dot cellular automata, a transistorless approach to computation that addresses the issues of device density, interconnection, and power dissipation. The device under study was composed of four metal dots, connected with tunnel junctions and capacitors, and operated at <50 mK. Operation was evidenced by switching of a single electron between output dots controlled by a single electron switching in input dots, demonstrating a nonlinear, bistable response.
40
Ar/
39
Ar Dating into the Historical Realm: Calibration Against Pliny the Younger
Authors: Renne P. R. , Sharp W. D. , Deino A. L. , Orsi G. , Civetta L.
Published: July 2002

Laser incremental heating of sanidine from the pumice deposited by the Plinian eruption of Vesuvius in 79 A.D. yielded a
40
Ar/
39
Ar isochron age of 1925 ± 94 years ago. Close agreement with the Gregorian calendar–based age of 1918 years ago demonstrates that the
40
Ar/
39
Ar method can be reliably extended into the temporal range of recorded history. Excess
40
Ar is present in the sanidine in concentrations that would cause significant errors if ignored in dating Holocene samples.
IKK-1 and IKK-2: Cytokine-Activated IκB Kinases Essential for NF-κB Activation
Authors: Mercurio Frank , Zhu Hengyi , Murray Brion W. , Shevchenko Andrej , Bennett Brydon L. , Li Jian wu , Young David B. , Barbosa Miguel , Mann Matthias , Manning Anthony , Rao Anjana
Published: July 2002

Activation of the transcription factor nuclear factor kappa B (NF-κB) is controlled by sequential phosphorylation, ubiquitination, and degradation of its inhibitory subunit IκB. A large multiprotein complex, the IκB kinase (IKK) signalsome, was purified from HeLa cells and found to contain a cytokine-inducible IκB kinase activity that phosphorylates IκB-α and IκB-β. Two components of the IKK signalsome, IKK-1 and IKK-2, were identified as closely related protein serine kinases containing leucine zipper and helix-loop-helix protein interaction motifs. Mutant versions of IKK-2 had pronounced effects on RelA nuclear translocation and NF-κB–dependent reporter activity, consistent with a critical role for the IKK kinases in the NF-κB signaling pathway.
Triblock Copolymer Syntheses of Mesoporous Silica with Periodic 50 to 300 Angstrom Pores
Authors: Zhao Dongyuan , Feng Jianglin , Huo Qisheng , Melosh Nicholas , Fredrickson Glenn H. , Chmelka Bradley F. , Stucky Galen D.
Published: July 2002

Use of amphiphilic triblock copolymers to direct the organization of polymerizing silica species has resulted in the preparation of well-ordered hexagonal mesoporous silica structures (SBA-15) with uniform pore sizes up to approximately 300 angstroms. The SBA-15 materials are synthesized in acidic media to produce highly ordered, two-dimensional hexagonal (space group
p
6
mm
) silica-block copolymer mesophases. Calcination at 500°C gives porous structures with unusually large interlattice
d
spacings of 74.5 to 320 angstroms between the (100) planes, pore sizes from 46 to 300 angstroms, pore volume fractions up to 0.85, and silica wall thicknesses of 31 to 64 angstroms. SBA-15 can be readily prepared over a wide range of uniform pore sizes and pore wall thicknesses at low temperature (35° to 80°C), using a variety of poly(alkylene oxide) triblock copolymers and by the addition of cosolvent organic molecules. The block copolymer species can be recovered for reuse by solvent extraction with ethanol or removed by heating at 140°C for 3 hours, in both cases, yielding a product that is thermally stable in boiling water.
Interband Electronic Excitation-Assisted Atomic-Scale Restructuring of Metal Surfaces by Nanosecond Pulsed Laser Light
Authors: Ernst Hans-Joachim , Charra Fabrice , Douillard Ludovic
Published: July 2002

Interaction of high-power laser light with materials often causes irreversible damage of the near-surface region. It is shown that copper single-crystal surfaces can be patterned by laser light. Irradiation with green light produced adatoms and vacancies, which self-organized into nanoscale pyramids. This restructuring can be removed by annealing. In contrast to green light, infrared laser irradiation at equivalent absorbed energy density did not produce any structural change. This, for metallic systems, unforeseen spectral difference in laser light action points to a concerted process as the source for structural modification, which involves long-lived primary excitation of localized d-electrons through interband transition together with phonon excitation.
Changes in the West Antarctic Ice Sheet Since 1963 from Declassified Satellite Photography
Authors: Bindschadler Robert , Vornberger Patricia
Published: July 2002

Comparison of declassified satellite photography taken in 1963 with more recent satellite imagery reveals that large changes have occurred in the region where an active ice stream enters the Ross Ice Shelf. Ice stream B has widened by 4 kilometers, at a rate much faster than suggested by models, and has decreased in speed by 50 percent. The ice ridge between ice streams B and C has eroded 14 kilometers. These changes, along with changes in the crevassing around Crary Ice Rise, imply that this region's velocity field shifted during this century.
Phosphorylation and Activation of p70
s6k
by PDK1
Authors: Pullen Nicholas , Dennis Patrick B. , Andjelkovic Mirjana , Dufner Almut , Kozma Sara C. , Hemmings Brian A. , Thomas George
Published: July 2002

Activation of the protein p70
s6k
by mitogens leads to increased translation of a family of messenger RNAs that encode essential components of the protein synthetic apparatus. Activation of the kinase requires hierarchical phosphorylation at multiple sites, culminating in the phosphorylation of the threonine in position 229 (Thr
229
), in the catalytic domain. The homologous site in protein kinase B (PKB), Thr
308
, has been shown to be phosphorylated by the phosphoinositide-dependent protein kinase PDK1. A regulatory link between p70
s6k
and PKB was demonstrated, as PDK1 was found to selectively phosphorylate p70
s6k
at Thr
229
. More importantly, PDK1 activated p70
s6k
in vitro and in vivo, whereas the catalytically inactive PDK1 blocked insulin-induced activation of p70
s6k
.
Call Duration as an Indicator of Genetic Quality in Male Gray Tree Frogs
Authors: Welch Allison M. , Semlitsch Raymond D. , Gerhardt H. Carl
Published: July 2002

The “good genes” hypothesis predicts that mating preferences enable females to select mates of superior genetic quality. The genetic consequences of the preference shown by female gray tree frogs for long-duration calls were evaluated by comparing the performance of maternal half-siblings sired by males with different call durations. Offspring of male gray tree frogs that produced long calls showed better performance during larval and juvenile stages than did offspring of males that produced short calls. These data suggest that call duration can function as a reliable indicator of heritable genetic quality.
Abolition of Long-Term Stability of New Hippocampal Place Cell Maps by NMDA Receptor Blockade
Authors: Kentros Clifford , Hargreaves Eric , Hawkins Robert D. , Kandel Eric R. , Shapiro Matthew , Muller Robert V.
Published: July 2002

Hippocampal pyramidal cells are called place cells because each cell tends to fire only when the animal is in a particular part of the environment—the cell's firing field. Acute pharmacological blockade of
N
-methyl-
d
-aspartate (NMDA) glutamate receptors was used to investigate how NMDA-based synaptic plasticity participates in the formation and maintenance of the firing fields. The results suggest that the formation and short-term stability of firing fields in a new environment involve plasticity that is independent of NMDA receptor activation. By contrast, the long-term stabilization of newly established firing fields required normal NMDA receptor function and, therefore, may be related to other NMDA-dependent processes such as long-term potentiation and spatial learning.
Nutrient Biogeochemistry of the Coastal Zone
Authors: Jickells T. D.
Published: July 2002

REVIEW

The coastal seas are one of the most valuable and vulnerable of Earth's habitats. Significant inputs of nutrients to the coastal zone arrive via rivers, groundwater, and the atmosphere. Nutrient fluxes through these routes have been increased by human activity. In addition, the N:P:Si ratios of these inputs have been perturbed, and many coastal management practices exacerbate these perturbations. There is evidence of impacts arising from these changes (in phytoplankton numbers and relative species abundance, and deep-water oxygen declines) in areas of restricted water exchange. Elsewhere, the nutrient fluxes through the coastal zone appear to be still dominated by large inputs from the open ocean, and there is little evidence of anthropogenic perturbations.
Magnetoelectronics
Authors: Prinz Gary A.
Published: July 2002

An approach to electronics is emerging that is based on the up or down spin of the carriers rather than on electrons or holes as in traditional semiconductor electronics. The physical basis for the observed effects is presented, and the initial successful applications of this technology for information storage are reviewed. Additional opportunities for the exploitation of this technology, which are currently under study, are described.
Thymidine Phosphorylase Gene Mutations in MNGIE, a Human Mitochondrial Disorder
Authors: Nishino Ichizo , Spinazzola Antonella , Hirano Michio
Published: July 2002

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an autosomal recessive human disease associated with multiple deletions of skeletal muscle mitochondrial DNA (mtDNA), which have been ascribed to a defect in communication between the nuclear and mitochondrial genomes. Examination of 12 MNGIE probands revealed homozygous or compound-heterozygous mutations in the gene specifying thymidine phosphorylase (TP), located on chromosome 22q13.32-qter. TP activity in leukocytes from MNGIE patients was less than 5 percent of controls, indicating that loss-of-function mutations in
TP
cause the disease. The pathogenic mechanism may be related to aberrant thymidine metabolism, leading to impaired replication or maintenance of mtDNA, or both.
Signaling of Cell Fate Decisions by
CLAVATA3
in
Arabidopsis
Shoot Meristems
Authors: Fletcher Jennifer C. , Brand Ulrike , Running Mark P. , Simon Rüdiger , Meyerowitz Elliot M.
Published: July 2002

In higher plants, organogenesis occurs continuously from self-renewing apical meristems.
Arabidopsis thaliana
plants with loss-of-function mutations in the
CLAVATA (CLV1
,
2
, and
3)
genes have enlarged meristems and generate extra floral organs. Genetic analysis indicates that
CLV1
, which encodes a receptor kinase, acts with
CLV3
to control the balance between meristem cell proliferation and differentiation.
CLV3
encodes a small, predicted extracellular protein.
CLV3
acts nonautonomously in meristems and is expressed at the meristem surface overlying the
CLV1
domain. These proteins may act as a ligand-receptor pair in a signal transduction pathway, coordinating growth between adjacent meristematic regions.
Complexity and the Economy
Authors: Arthur W. Brian
Published: July 2002

After two centuries of studying equilibria—static patterns that call for no further behavioral adjustments—economists are beginning to study the general emergence of structures and the unfolding of patterns in the economy. When viewed in out-of-equilibrium formation, economic patterns sometimes simplify into the simple static equilibria of standard economics. More often they are ever changing, showing perpetually novel behavior and emergent phenomena. Complexity portrays the economy not as deterministic, predictable, and mechanistic, but as process dependent, organic, and always evolving.
Complexity, Pattern, and Evolutionary Trade-Offs in Animal Aggregation
Authors: Parrish Julia K. , Edelstein-Keshet Leah
Published: July 2002

One of the most striking patterns in biology is the formation of animal aggregations. Classically, aggregation has been viewed as an evolutionarily advantageous state, in which members derive the benefits of protection, mate choice, and centralized information, balanced by the costs of limiting resources. Consisting of individual members, aggregations nevertheless function as an integrated whole, displaying a complex set of behaviors not possible at the level of the individual organism. Complexity theory indicates that large populations of units can self-organize into aggregations that generate pattern, store information, and engage in collective decision-making. This begs the question, are all emergent properties of animal aggregations functional or are some simply pattern? Solutions to this dilemma will necessitate a closer marriage of theoretical and modeling studies linked to empirical work addressing the choices, and trajectories, of individuals constrained by membership in the group.
Paracellin-1, a Renal Tight Junction Protein Required for Paracellular Mg
2+
Resorption
Authors: Simon David B. , Lu Yin , Choate Keith A. , Velazquez Heino , Al-Sabban Essam , Praga Manuel , Casari Giorgio , Bettinelli Alberto , Colussi Giacomo , Rodriguez-Soriano Juan , McCredie David , Milford David , Sanjad Sami , Lifton Richard P.
Published: July 2002

Epithelia permit selective and regulated flux from apical to basolateral surfaces by transcellular passage through cells or paracellular flux between cells. Tight junctions constitute the barrier to paracellular conductance; however, little is known about the specific molecules that mediate paracellular permeabilities. Renal magnesium ion (Mg
2+
) resorption occurs predominantly through a paracellular conductance in the thick ascending limb of Henle (TAL). Here, positional cloning has identified a human gene,
paracellin-1
(
PCLN-1
), mutations in which cause renal Mg
2+
wasting. PCLN-1 is located in tight junctions of the TAL and is related to the claudin family of tight junction proteins. These findings provide insight into Mg
2+
homeostasis, demonstrate the role of a tight junction protein in human disease, and identify an essential component of a selective paracellular conductance.
Replication of Subgenomic Hepatitis C Virus RNAs in a Hepatoma Cell Line
Authors: Lohmann V. , Körner F. , Koch J.-O. , Herian U. , Theilmann L. , Bartenschlager R.
Published: July 2002

An estimated 170 million persons worldwide are infected with hepatitis C virus (HCV), a major cause of chronic liver disease. Despite increasing knowledge of genome structure and individual viral proteins, studies on virus replication and pathogenesis have been hampered by the lack of reliable and efficient cell culture systems. A full-length consensus genome was cloned from viral RNA isolated from an infected human liver and used to construct subgenomic selectable replicons. Upon transfection into a human hepatoma cell line, these RNAs were found to replicate to high levels, permitting metabolic radiolabeling of viral RNA and proteins. This work defines the structure of HCV replicons functional in cell culture and provides the basis for a long-sought cellular system that should allow detailed molecular studies of HCV and the development of antiviral drugs.
Pigment Epithelium-Derived Factor: A Potent Inhibitor of Angiogenesis
Authors: Dawson D. W. , Volpert O. V. , Gillis P. , Crawford S. E. , Xu H.-J. , Benedict W. , Bouck N. P.
Published: July 2002

In the absence of disease, the vasculature of the mammalian eye is quiescent, in part because of the action of angiogenic inhibitors that prevent vessels from invading the cornea and vitreous. Here, an inhibitor responsible for the avascularity of these ocular compartments is identified as pigment epithelium–derived factor (PEDF), a protein previously shown to have neurotrophic activity. The amount of inhibitory PEDF produced by retinal cells was positively correlated with oxygen concentrations, suggesting that its loss plays a permissive role in ischemia-driven retinal neovascularization. These results suggest that PEDF may be of therapeutic use, especially in retinopathies where pathological neovascularization compromises vision and leads to blindness.
Photovoltaic Technology: The Case for Thin-Film Solar Cells
Authors: Shah A. , Torres P. , Tscharner R. , Wyrsch N. , Keppner H.
Published: July 2002

The advantages and limitations of photovoltaic solar modules for energy generation are reviewed with their operation principles and physical efficiency limits. Although the main materials currently used or investigated and the associated fabrication technologies are individually described, emphasis is on silicon-based solar cells. Wafer-based crystalline silicon solar modules dominate in terms of production, but amorphous silicon solar cells have the potential to undercut costs owing, for example, to the roll-to-roll production possibilities for modules. Recent developments suggest that thin-film crystalline silicon (especially microcrystalline silicon) is becoming a prime candidate for future photovoltaics.
TRACE Observation of Damped Coronal Loop Oscillations: Implications for Coronal Heating
Authors: Nakariakov V. M. , Ofman L. , DeLuca E. E. , Roberts B. , Davila J. M.
Published: July 2002

The imaging telescope on board the Transition Region and Coronal Explorer (TRACE) spacecraft observed the decaying transversal oscillations of a long [(130 ± 6) × 10
6
meters], thin [diameter (2.0 ± 0.36) × 10
6
meters], bright coronal loop in the 171 angstrom Fe
IX
emission line. The oscillations were excited by a solar flare in the adjacent active region. The decay time of the oscillations is 14.5 ± 2.7 minutes for an oscillation with a frequency 3.90 ± 0.13 millihertz. The coronal dissipation coefficient is estimated to be eight to nine orders of magnitude larger than the theoretically predicted classical value. The larger dissipation coefficient may solve existing difficulties with wave heating and reconnection theories.
β-Secretase Cleavage of Alzheimer's Amyloid Precursor Protein by the Transmembrane Aspartic Protease BACE
Authors: Vassar Robert , Bennett Brian D. , Babu-Khan Safura , Kahn Steve , Mendiaz Elizabeth A. , Denis Paul , Teplow David B. , Ross Sandra , Amarante Patricia , Loeloff Richard , Luo Yi , Fisher Seth , Fuller Janis , Edenson Steven , Lile Jackson , Jarosinski Mark A. , Biere Anja Leona , Curran Eileen , Burgess Teresa , Louis Jean-Claude , Collins Frank , Treanor James , Rogers Gary , Citron Martin
Published: July 2002

Cerebral deposition of amyloid β peptide (Aβ) is an early and critical feature of Alzheimer's disease. Aβ generation depends on proteolytic cleavage of the amyloid precursor protein (APP) by two unknown proteases: β-secretase and γ-secretase. These proteases are prime therapeutic targets. A transmembrane aspartic protease with all the known characteristics of β-secretase was cloned and characterized. Overexpression of this protease, termed BACE (for beta-site APP-cleaving enzyme) increased the amount of β-secretase cleavage products, and these were cleaved exactly and only at known β-secretase positions. Antisense inhibition of endogenous BACE messenger RNA decreased the amount of β-secretase cleavage products, and purified BACE protein cleaved APP-derived substrates with the same sequence specificity as β-secretase. Finally, the expression pattern and subcellular localization of BACE were consistent with that expected for β-secretase. Future development of BACE inhibitors may prove beneficial for the treatment of Alzheimer's disease.
A Laboratory Model for Convection in Earth's Core Driven by a Thermally Heterogeneous Mantle
Authors: Sumita Ikuro , Olson Peter
Published: July 2002

Thermal convection experiments in a rapidly rotating hemispherical shell suggest a model in which the convection in Earth's liquid outer core is controlled by a thermally heterogeneous mantle. Experiments show that heterogeneous boundary heating induces an eastward flow in the core, which, at a sufficiently large magnitude, develops into a large-scale spiral with a sharp front. The front separates the warm and cold regions in the core and includes a narrow jet flowing from the core-mantle boundary to the inner-core boundary. The existence of this front in the core may explain the Pacific quiet zone in the secular variation of the geomagnetic field and the longitudinally heterogeneous structure of the solid inner core.
Structure of a Transcribing T7 RNA Polymerase Initiation Complex
Authors: Cheetham Graham M. T. , Steitz and Thomas A.
Published: July 2002

The structure of a T7 RNA polymerase (T7 RNAP) initiation complex captured transcribing a trinucleotide of RNA from a 17–base pair promoter DNA containing a 5-nucleotide single-strand template extension was determined at a resolution of 2.4 angstroms. Binding of the upstream duplex portion of the promoter occurs in the same manner as that in the open promoter complex, but the single-stranded template is repositioned to place the +4 base at the catalytic active site. Thus, synthesis of RNA in the initiation phase leads to accumulation or “scrunching” of the template in the enclosed active site pocket of T7 RNAP. Only three base pairs of heteroduplex are formed before the RNA peels off the template.
Postnatal Sex Reversal of the Ovaries in Mice Lacking Estrogen Receptors α and β
Authors: Couse J. F. , Hewitt S. Curtis , Bunch D. O. , Sar M. , Walker V. R. , Davis B. J. , Korach K. S.
Published: July 2002

Mice lacking estrogen receptors α and β were generated to clarify the roles of each receptor in the physiology of estrogen target tissues. Both sexes of αβ estrogen receptor knockout (αβERKO) mutants exhibit normal reproductive tract development but are infertile. Ovaries of adult αβERKO females exhibit follicle transdifferentiation to structures resembling seminiferous tubules of the testis, including Sertoli-like cells and expression of Müllerian inhibiting substance, sulfated glycoprotein-2, andSox9. Therefore, loss of both receptors leads to an ovarian phenotype that is distinct from that of the individual ERKO mutants, which indicates that both receptors are required for the maintenance of germ and somatic cells in the postnatal ovary.
Detection of Molecular Alignment in Confined Films
Authors: Eisert F. , Gurka M. , Legant A. , Buck M. , Grunze M.
Published: July 2002

Optical second harmonic generation was used to study the in-plane alignment of self-assembled silane monolayers attached to a glass surface under mechanical loading. The measurements allow correlation of the macroscopic forces acting on the monolayer with the average orientation and the azimuthal molecular alignment of the terminal molecular entity. Compression and shear forces lead to an alignment of the initially randomly oriented molecules on a macroscopic length scale. The change in azimuthal alignment of molecules under mechanical stress was found to be irreversible on the time scale of 12 hours, whereas changes of the molecular tilt angle were reversible.
On the Presence of Liquid in Earth's Inner Core
Authors: Singh S. C. , Taylor M. A. J. , Montagner J. P.
Published: July 2002

Seismological studies indicate that the inner core of Earth is anisotropic for compressional waves (
P
waves), and has low shear wave (
S
wave) velocity, and high seismic attenuation. Using an effective medium theory for composite materials, we show that the presence of a volume fraction of 3 to 10% liquid in the form of oblate spheroidal inclusions aligned in the equatorial plane between iron crystals is sufficient to explain the aforementioned seismic phenomena. Variation of
S
-wave velocity between the polar axis and equatorial plane is more sensitive to the addition of liquid than that of
P
waves. The liquid could arise from the presence of dendrites or a mixture of elements other than iron that exist in liquid form under inner-core conditions.
Insect Population Control Using a Dominant, Repressible, Lethal Genetic System
Authors: Thomas Dean D. , Donnelly Christl A. , Wood Roger J. , Alphey Luke S.
Published: July 2002

A major modification to the sterile insect technique is described, in which transgenic insects homozygous for a dominant, repressible, female-specific lethal gene system are used. We demonstrate two methods that give the required genetic characteristics in an otherwise wild-type genetic background. The first system uses a sex-specific promoter or enhancer to drive the expression of a repressible transcription factor, which in turn controls the expression of a toxic gene product. The second system uses non–sex-specific expression of the repressible transcription factor to regulate a selectively lethal gene product. Both methods work efficiently in
Drosophila melanogaster
, and we expect these principles to be widely applicable to more economically important organisms
.
Requirement of JNK for Stress- Induced Activation of the Cytochrome c-Mediated Death Pathway
Authors: Tournier Cathy , Hess Patricia , Yang Derek D. , Xu Jie , Turner Tod K. , Nimnual Anjaruwee , Bar-Sagi Dafna , Jones Stephen N. , Flavell Richard A. , Davis Roger J.
Published: July 2002

The c-Jun NH
2
-terminal kinase (JNK) is activated when cells are exposed to ultraviolet (UV) radiation. However, the functional consequence of JNK activation in UV-irradiated cells has not been established. It is shown here that JNK is required for UV-induced apoptosis in primary murine embryonic fibroblasts. Fibroblasts with simultaneous targeted disruptions of all the functional
Jnk
genes were protected against UV-stimulated apoptosis. The absence of JNK caused a defect in the mitochondrial death signaling pathway, including the failure to release cytochrome c. These data indicate that mitochondria are influenced by proapoptotic signal transduction through the JNK pathway.
Requirement for RORγ in Thymocyte Survival and Lymphoid Organ Development
Authors: Sun Zuoming , Unutmaz Derya , Zou Yong-Rui , Sunshine Mary Jean , Pierani Alessandra , Brenner-Morton Susan , Mebius Reina E. , Littman Dan R.
Published: July 2002

Most developing thymocytes undergo apoptosis because they cannot interact productively with molecules encoded by the major histocompatibility complex. Here, we show that mice lacking the orphan nuclear hormone receptor RORγ lose thymic expression of the anti-apoptotic factor Bcl-xL. RORγ thus regulates the survival of CD4
+
8
+
thymocytes and may control the temporal window during which thymocytes can undergo positive selection. RORγ was also required for development of lymph nodes and Peyer's patches, but not splenic follicles. In its absence, there was loss of a population of CD3
–
CD4
+
CD45
+
cells that normally express RORγ and that are likely early progenitors of lymphoid organs. Hence, RORγ has critical functions in T cell repertoire selection and lymphoid organogenesis.
Cytochrome c Release and Apoptosis Induced by Mitochondrial Targeting of Nuclear Orphan Receptor TR3
Authors: Li Hui , Kolluri Siva Kumar , Gu Jian , Dawson Marcia I. , Cao Xihua , Hobbs Peter D. , Lin Bingzhen , Chen Guo-quen , Lu Jiang-song , Lin Feng , Xie Zhihua , Fontana Joseph A. , Reed John C. , Zhang Xiao-kun
Published: July 2002

TR3, an immediate-early response gene and an orphan member of the steroid-thyroid hormone-retinoid receptor superfamily of transcription factors, regulates apoptosis through an unknown mechanism. In response to apoptotic stimuli, TR3 translocates from the nucleus to mitochondria to induce cytochrome c release and apoptosis. Mitochondrial targeting of TR3, but not its DNA binding and transactivation, is essential for its proapoptotic effect. Our results reveal a mechanism by which a nuclear transcription factor translocates to mitochondria to initiate apoptosis.
Bone Resorption by Osteoclasts
Authors: Teitelbaum Steven L.
Published: July 2002

Osteoporosis, a disease endemic in Western society, typically reflects an imbalance in skeletal turnover so that bone resorption exceeds bone formation. Bone resorption is the unique function of the osteoclast, and anti-osteoporosis therapy to date has targeted this cell. The osteoclast is a specialized macrophage polykaryon whose differentiation is principally regulated by macrophage colony-stimulating factor, RANK ligand, and osteoprotegerin. Reflecting integrin-mediated signals, the osteoclast develops a specialized cytoskeleton that permits it to establish an isolated microenvironment between itself and bone, wherein matrix degradation occurs by a process involving proton transport. Osteopetrotic mutants have provided a wealth of information about the genes that regulate the differentiation of osteoclasts and their capacity to resorb bone.
Sedimentary Rocks of Early Mars
Authors: Malin Michael C. , Edgett Kenneth S.
Published: July 2002

Layered and massive outcrops on Mars, some as thick as 4 kilometers, display the geomorphic attributes and stratigraphic relations of sedimentary rock. Repeated beds in some locations imply a dynamic depositional environment during early martian history. Subaerial (such as eolian, impact, and volcaniclastic) and subaqueous processes may have contributed to the formation of the layers. Affinity for impact craters suggests dominance of lacustrine deposition; alternatively, the materials were deposited in a dry, subaerial setting in which atmospheric density, and variations thereof mimic a subaqueous depositional environment. The source regions and transport paths for the materials are not preserved.