bluuebunny/crossref_metadata_2025 huggingface dataset:
Sulfide passivation of III–V semiconductors: Kinetics of the photoelectrochemical reaction*
Authors: Bessolov V. N. , Lebedev M. V. , Novikov E. B. , Tsarenkov B. V.
Published: July 2002

A phenomenological model is proposed to describe sulfide passivation of the surfaces of III–V semiconductors as a process of charge transfer between a semiconductor and a passivation solution. The model assumes that formation of the passivation sulfide coat occurs as a result of oxidation of the semiconductor in a photoelectrochemical reaction. The growth rate of the passivating coat is determined by the rate at which electrons are transferred from the semiconductor into the solution, as well as by the energy which binds atoms in the surface layer of the semiconductor and the heat evolving in the process. It is found that the growth rate of the coat is dependent upon conductivity type and doping level of the semiconductor, hydrogen ion exponent, and concentration of the solution and, as well, the intensity of light incident upon the electrolyte/semiconductor interface. In terms of the model, passivation of different III–V semiconductors is considered.
Significance of nitrogen mass transfer mechanism on the nitriding behavior of austenitic stainless steel
Authors: Samandi M. , Shedden B. A. , Bell T. , Collins G. A. , Hutchings R. , Tendys J.
Published: July 2002

Plasma immersion ion implantation (PIII), although originally developed as an alternative non-line-of-sight ion implantation technique, is also capable of producing structures typical of thermochemical processing. In this work, the structure and properties of PIII and plasma nitrided AISI 316 austenitic stainless steel were characterized in order to establish the similarities and differences between PIII and plasma nitriding. A distinct difference between PIII and plasma nitriding has been identified with respect to the degree of nitrogen supersaturation of the austenite that can be achieved. It is proposed that the extent of supersaturation and the resultant microstructure are primarily controlled by the nitrogen mass transfer mechanism. For plasma nitrided stainless steel, a surface iron nitride layer is formed and limits the nitrogen content to less than 20 at. %. For PIII, where nitrogen is also directly implanted below the surface, nitrogen contents near the theoretical limit of 50 at. % can be achieved.
Micromachining applications of a high resolution ultrathick photoresist
Authors: Lee K. Y. , LaBianca N. , Rishton S. A. , Zolgharnain S. , Gelorme J. D. , Shaw J. , Chang T. H.-P.
Published: July 2002

This article describes a new negative-tone photoresist, SU-8, for ultrathick layer applications. An aspect ratio of 10:1 has been achieved using near-ultraviolet lithography in a 200-μm-thick layer. The use of this resist for building tall micromechanical structures by deep silicon reactive-ion etching and electroplating is demonstrated. Using SU-8 stencils, etched depths of ≳200 μm in Si and electroplated 130-μm-thick Au structures with near-vertical sidewalls have been achieved.
Surface metal contamination during ion implantation: Comparison of measurements by secondary ion mass spectroscopy, total reflection x-ray fluorescence spectrometry, and vapor phase decomposition used in conjunction with graphite furnace atomic absorption spectrometry and inductively coupled plasma mass spectrometry
Authors: Frost Michael R. , Harrington William L. , Downey Daniel F. , Walther Steven R.
Published: July 2002

Among the many challenges being addressed by manufacturers and users of ion implanters is the reduction of contamination of wafers during implantation by metals such as Al, Fe, Cr, Na, Cu, Mo, and W. Reproducible and accurate measurement of this near-surface contamination is equally challenging for analytical techniques and analysts. For this study As+ and BF+2 implants were made into Si wafers to study sources of metals contamination and to provide samples to be analyzed by a variety of techniques for comparison of their analytical strengths and weaknesses. Analytical techniques chosen for evaluation were quadrupole and magnetic sector secondary ion mass spectrometry, total reflection x-ray fluorescence spectrometry, and vapor phase decomposition used in conjunction with both graphite furnace atomic absorption spectrometry and inductively coupled plasma mass spectrometry.
Scanning tunneling microscope study of defect structures on As-terminated Si(001) surfaces
Authors: Jackson M. D. , Leibsle F. M. , Cole R. J. , Gregory D. A. C. , Woolf D. A. , Weightman P.
Published: July 2002

As-terminated Si surfaces are model semiconductor interface systems with a wide range of technological applications. We have studied As-terminated Si (001) surfaces with scanning tunneling microscopy which reveals that it is possible to produce a well ordered surface. Some characteristic types of defects do occur on this surface, however, which are found to be of particular interest. These include antiphase domain boundaries, step edges, and long, atomically straight trenches running perpendicular to the dimer rows across the surface. The nature and origin of these defects are discussed.
Substrate temperature measurement by absorption-edge spectroscopy during molecular beam epitaxy of narrow-band gap semiconductor films
Authors: de Lyon T. J. , Roth J. A. , Chow D. H.
Published: July 2002

A novel method is described for utilization of absorption-edge spectroscopy (ABES) to monitor the temperature of a semiconducting substrate during molecular beam epitaxy (MBE) of a film with a band gap narrower than that of the substrate. Conventional ABES cannot be used for substrate temperature determination with narrow-band gap epilayers that are sufficiently thick so as to be opaque in the wavelength range corresponding to the substrate band gap. However, we show that by inserting a reflecting layer (or layers) between the substrate and overlying narrow-band gap epilayer, ABES temperature measurements can be carried out in reflection from the backside of the substrate, even in the presence of arbitrarily thick narrow-band gap epilayers. This approach is demonstrated for MBE growth of InAs on GaAs substrates and also for HgCdTe on CdZnTe substrates, and is shown to be accurate to ±2 °C over temperature spans of 300 and 120 °C, respectively, for these two material systems in the vicinity of the typical MBE growth temperatures.
Process development of sub-0.5 μm nonvolatile magnetoresistive random access memory arrays
Authors: Nordquist K. , Pendharkar S. , Durlam M. , Resnick D. , Tehrani S. , Mancini D. , Zhu T. , Shi J.
Published: July 2002

The fabrication of magnetoresistive random access memory (MRAM) devices requires full characterization of the giant magnetoresistive ratio (GMR) permalloy films at the sub-0.5 μm feature dimensions. Future memory arrays of the 1 and 4 Gb density require GMR bit cells of a 0.25 μm and below in configurations which will require close proximity of cells. Since the cells are magnetic and act like tiny magnets, the switching field of a cell may be influenced by the polarization direction of the neighboring cell. This article describes the development of sub-0.5 μm MRAM devices using current e-beam microfabrication techniques and the implementation of the latest chemically amplified deep ultraviolet resists. Etch processing is also discussed as well as the testing results for the 0.25 μm arrays. Testing the GMR material at these dimensions consists of evaluating the single magnetic domain behavior and observing the effect of cell size on the magnetoresistance ratio. Array testing will consist of measuring switching field variations on a 0.25 μm 5×5 array to determine if there is field coupling with neighboring cells.
Analysis of twin defects in GaAs(111)B molecular beam epitaxy growth
Authors: Park Yeonjoon , Cich Michael J. , Zhao Rian , Specht Petra , Weber Eicke R. , Stach Eric , Nozaki Shinji
Published: July 2002

The formation of twin is common during GaAs(111) and GaN(0001) molecular beam epitaxy (MBE) metalorganic chemical vapor deposition growth. A stacking fault in the zinc-blende (ZB)(111) direction can be described as an insertion of one monolayer of wurtzite structure, sandwiched between two ZB structures that have been rotated 60° along the growth direction. GaAs(111)A/B MBE growth within typical growth temperature regimes is complicated by the formation of pyramidal structures and 60° rotated twins, which are caused by faceting and stacking fault formation. Although previous studies have revealed much about the structure of these twins, a well-established simple nondestructive characterization method which allows the measurement of total aerial density of the twins does not exist at present. In this article, the twin density of AlGaAs layers grown on 1° miscut GaAs(111)B substrates has been measured using high resolution x-ray diffraction, and characterized with a combination of Nomarski microscopy, atomic force microscopy, and transmission electron microscopy. These comparisons permit the relationship between the aerial twin density and the growth condition to be determined quantitatively.
Influence of Carbonic Anhydrase Activity in Terrestrial Vegetation on the
18
O Content of Atmospheric CO
2
Authors: Gillon Jim , Yakir Dan
Published: July 2002

The oxygen-18 (
18
O) content of atmospheric carbon dioxide (CO
2
) is an important indicator of CO
2
uptake on land. It has generally been assumed that during photosynthesis, oxygen in CO
2
reaches isotopic equilibrium with oxygen in
18
O-enriched water in leaves. We show, however, large differences in the activity of carbonic anhydrase (which catalyzes CO
2
hydration and
18
O exchange in leaves) among major plant groups that cause variations in the extent of
18
O equilibrium (θ
eq
). A clear distinction in θ
eq
between C
3
trees and shrubs, and C
4
grasses makes atmospheric C
18
OO a potentially sensitive indicator to changes in C
3
and C
4
productivity. We estimate a global mean θ
eq
value of ∼0.8, which reasonably reconciles inconsistencies between
18
O budgets of atmospheric O
2
(Dole effect) and CO
2
.
Birth of Two Chimeric Genes in the
Hominidae
Lineage
Authors: Courseaux Anouk , Nahon Jean-Louis
Published: July 2002

How genes with newly characterized functions originate remains a fundamental question.
PMCHL1
and
PMCHL2
, two chimeric genes derived from the melanin-concentrating hormone (
MCH
) gene, offer an opportunity to examine such an issue in the human lineage. Detailed structural, expression, and phylogenetic analysis showed that the
PMCHL1
gene was created near 25 million years ago (Ma) by a complex mechanism of exon shuffling through retrotransposition of an antisense
MCH
messenger RNA coupled to de novo creation of splice sites.
PMCHL2
arose 5 to 10 Ma by an event of duplication involving a large chromosomal region encompassing the
PMCHL1
locus. The RNA expression patterns of those chimeric genes suggest that they have been submitted to strong regulatory constraints during primate evolution.
A Decoherence-Free Quantum Memory Using Trapped Ions
Authors: Kielpinski D. , Meyer V. , Rowe M. A. , Sackett C. A. , Itano W. M. , Monroe C. , Wineland D. J.
Published: July 2002

We demonstrate a decoherence-free quantum memory of one qubit. By encoding the qubit into the decoherence-free subspace (DFS) of a pair of trapped
9
Be
+
ions, we protect the qubit from environment-induced dephasing that limits the storage time of a qubit composed of a single ion. We measured the storage time under ambient conditions and under interaction with an engineered noisy environment and observed that encoding into the DFS increases the storage time by up to an order of magnitude. The encoding reversibly transfers an arbitrary qubit stored in a single ion to the DFS of two ions.
Virus Maturation Involving Large Subunit Rotations and Local Refolding
Authors: Conway J. F. , Wikoff W. R. , Cheng N. , Duda R. L. , Hendrix R. W. , Johnson J. E. , Steven A. C.
Published: July 2002

Large-scale conformational changes transform viral precursors into infectious virions. The structure of bacteriophage HK97 capsid, Head-II, was recently solved by crystallography, revealing a catenated cross-linked topology. We have visualized its precursor, Prohead-II, by cryoelectron microscopy and modeled the conformational change by appropriately adapting Head-II. Rigid-body rotations (∼40 degrees) cause switching to an entirely different set of interactions; in addition, two motifs undergo refolding. These changes stabilize the capsid by increasing the surface area buried at interfaces and bringing the cross-link–forming residues, initially ∼40 angstroms apart, close together. The inner surface of Prohead-II is negatively charged, suggesting that the transition is triggered electrostatically by DNA packaging.
Combined Functional Genomic Maps of the
C. elegans
DNA Damage Response
Authors: Boulton Simon J. , Gartner Anton , Reboul Jérôme , Vaglio Philippe , Dyson Nick , Hill David E. , Vidal Marc
Published: July 2002

Many human cancers originate from defects in the DNA damage response (DDR). Although much is known about this process, it is likely that additional DDR genes remain to be discovered. To identify such genes, we used a strategy that combines protein-protein interaction mapping and large-scale phenotypic analysis in
Caenorhabditis elegans
. Together, these approaches identified 12 worm DDR orthologs and 11 novel DDR genes. One of these is the putative ortholog of hBCL3, a gene frequently altered in chronic lymphocytic leukemia. Thus, the combination of functional genomic mapping approaches in model organisms may facilitate the identification and characterization of genes involved in cancer and, perhaps, other human diseases.
Neuronal Calcium Sensor 1 and Activity-Dependent Facilitation of P/Q-Type Calcium Currents at Presynaptic Nerve Terminals
Authors: Tsujimoto Tetsuhiro , Jeromin Andreas , Saitoh Naoto , Roder John C. , Takahashi Tomoyuki
Published: July 2002

P/Q-type presynaptic calcium currents (
I
pCa
) undergo activity-dependent facilitation during repetitive activation at the calyx of the Held synapse. We investigated whether neuronal calcium sensor 1 (NCS-1) may underlie this phenomenon. Direct loading of NCS-1 into the nerve terminal mimicked activity-dependent
I
pCa
facilitation by accelerating the activation time of
I
pCa
in a Ca
2+
-dependent manner. A presynaptically loaded carboxyl-terminal peptide of NCS-1 abolished
I
pCa
facilitation. These results suggest that residual Ca
2+
activates endogenous NCS-1, thereby facilitating
I
pCa
. Because both P/Q-type Ca
2+
channels and NCS-1 are widely expressed in mammalian nerve terminals, NCS-1 may contribute to the activity-dependent synaptic facilitation at many synapses.
Coherent Temporal Oscillations of Macroscopic Quantum States in a Josephson Junction
Authors: Yu Yang , Han Siyuan , Chu Xi , Chu Shih-I , Wang Zhen
Published: July 2002

We report the generation and observation of coherent temporal oscillations between the macroscopic quantum states of a Josephson tunnel junction by applying microwaves with frequencies close to the level separation. Coherent temporal oscillations of excited state populations were observed by monitoring the junction's tunneling probability as a function of time. From the data, the lower limit of phase decoherence time was estimated to be about 5 microseconds.
Time-Domain Observations of a Slow Precursor to the 1994 Romanche Transform Earthquake
Authors: McGuire Jeffrey J. , Ihmlé Pierre F. , Jordan Thomas H.
Published: July 2002

Low-frequency spectral anomalies have indicated that some large earthquakes are preceded by extended episodes of smooth moment release, but the reality of these slow precursors has been debated because they have not been directly observed in the time domain. High-gain seismograms from the 14 March 1994 Romanche Transform event (moment magnitude
M
w
7.0) show a precursory ramp with a moment of 7 × 10
18
newton meters beginning about 100 seconds before the arrival of the high-frequency
P
waves. This precursor was the initial phase of a slow component of slip that released nearly half of the total moment of the earthquake. Such behavior may be typical for large earthquakes on the oceanic ridge-transform system.
Femtosecond X-ray Pulses at 0.4 Å Generated by 90° Thomson Scattering: A Tool for Probing the Structural Dynamics of Materials
Authors: Schoenlein R. W. , Leemans W. P. , Chin A. H. , Volfbeyn P. , Glover T. E. , Balling P. , Zolotorev M. , Kim K.-J. , Chattopadhyay S. , Shank C. V.
Published: July 2002

Pulses of x-rays 300 femtoseconds in duration at a wavelength of 0.4 angstroms (30,000 electron volts) have been generated by 90° Thomson scattering between infrared terawatt laser pulses and highly relativistic electrons from an accelerator. In the right-angle scattering geometry, the duration of the x-ray burst is determined by the transit time of the laser pulse across the ∼90-micrometer waist of the focused electron beam. The x-rays are highly directed (∼0.6° divergence) and can be tuned in energy. This source of femtosecond x-rays will make it possible to combine x-ray techniques with ultrafast time resolution to investigate structural dynamics in condensed matter.
Io's Interaction with the Plasma Torus: Galileo Magnetometer Report
Authors: Kivelson M. G. , Khurana K. K. , Walker R. J. , Warnecke J. , Russell C. T. , Linker J. A. , Southwood D. J. , Polanskey C.
Published: July 2002

Galileo magnetometer data at 0.22-second resolution reveal a complex interaction between Io and the flowing plasma of the Io torus. The highly structured magnetic field depression across the downstream wake, although consistent with a magnetized Io, is modified by sources of currents within the plasma that introduce ambiguity into the interpretation of the signature. Highly monochromatic ion cyclotron waves appear to be correlated with the local neutral particle density. The power peaks in the range of molecular ion gyrofrequencies, suggesting that molecules from Io can remain undissociated over a region of more than 15 Io radii around Io.
Molar Tooth Diversity, Disparity, and Ecology in Cenozoic Ungulate Radiations
Authors: Jernvall Jukka , Hunter John P. , Fortelius Mikael
Published: July 2002

A classic example of adaptive radiation is the diversification of Cenozoic ungulates into herbivore adaptive zones. Their taxonomic diversification has been associated with changes in molar tooth morphology. Analysis of molar crown types of the Artiodactyla, Perissodactyla, and archaic ungulates (“Condylarthra”) shows that the diversity of genera and crown types was high in the Eocene. Post-Eocene molars of intermediate crown types are rare, and thus the ungulate fauna contained more taxa having fewer but more disparate crown types. Taxonomic diversity trends alone give incomplete descriptions of adaptive radiations.
Parallel Synthesis and Screening of a Solid Phase Carbohydrate Library
Authors: Liang Rui , Yan Lin , Loebach Jennifer , Ge Min , Uozumi Yasuhiro , Sekanina Klara , Horan Nina , Gildersleeve Jeff , Thompson Chris , Smith Andri , Biswas Kaustav , Still W. Clark , Kahne Daniel
Published: July 2002

A solid phase carbohydrate library was synthesized and screened against
Bauhinia purpurea
lectin. The library, which contains approximately 1300 di- and trisaccharides, was synthesized with chemical encoding on TentaGel resin so that each bead contained a single carbohydrate. Two ligands that bind more tightly to the lectin than Gal-β-1,3-GalNAc (the known ligand) have been identified. The strategy outlined can be used to identify carbohydrate-based ligands for any receptor; however, because the derivatized beads mimic the polyvalent presentation of cell surface carbohydrates, the screen may prove especially valuable for discovering new compounds that bind to proteins participating in cell adhesion.
NF-AT-Driven Interleukin-4 Transcription Potentiated by NIP45
Authors: Hodge Martin R. , Chun Hyung J. , Rengarajan Jyothi , Alt Aya , Lieberson Rebecca , Glimcher Laurie H.
Published: July 2002

The induction of cytokine gene transcription is mediated in part by the nuclear factor of activated T cells (NF-AT). Factors involved in the mechanisms of NF-AT-mediated transcription are not well understood. A nuclear factor that interacted with the Rel homology domain (RHD) of NF-ATp was identified with the use of a two-hybrid interaction trap. Designated NIP45 (NF-AT interacting protein), it has minimal similarity to any known genes. Transcripts encoding this factor were enriched in lymphoid tissues and testes. NIP45 synergized with NF-ATp and the proto-oncogene c-Maf to activate the interleukin-4 (IL-4) cytokine promoter; transient overexpression of NIP45 with NF-ATp and c-
maf
in B lymphoma cells induced measurable endogenous IL-4 protein production. The identification of NIP45 advances our understanding of gene activation of cytokines, critical mediators of the immune response.
Interaction of the Thiol-Dependent Reductase ERp57 with Nascent Glycoproteins
Authors: Oliver Jason D. , van der Wal Fimme J. , Bulleid Neil J. , High Stephen
Published: July 2002

Calnexin and calreticulin interact specifically with newly synthesized glycoproteins in the endoplasmic reticulum (ER) and function as molecular chaperones. The carbohydrate-specific interactions between ER components and glycoproteins synthesized in isolated canine pancreatic microsomes were analyzed using a cross-linking approach. A carbohydrate-dependent interaction between newly synthesized glycoproteins, the thiol-dependent reductase ERp57, and either calnexin or calreticulin was identified. The interaction between ERp57 and the newly synthesized glycoproteins required trimming of the N-linked oligosaccharide side chain. Thus, it is likely that ERp57 functions as part of the glycoprotein-specific quality control machinery operating in the lumen of the ER.
Thyroid Disease—A Case of Cell Suicide?
Authors: Williams Nigel
Published: July 2002

In autoimmune diseases, such as diabetes and rheumatoid arthritis, the immune system goes awry and turns on the body's own tissues. But researchers do not know which of the immune system's several types of killer T cells carries out the attack, nor why killer cells are scarce at the site of tissue destruction in many autoimmune diseases. New results published in this issue (
p. 960
) suggest that in at least one autoimmune disease, the immune system itself may not carry out the final act: Instead, the target cells commit suicide through a process called apoptosis.
Control of Vertebrate Left-Right Asymmetry by a
Snail
-Related Zinc Finger Gene
Authors: Isaac Alison , Sargent Michael G. , Cooke Jonathan
Published: July 2002

A gene encoding a zinc finger protein of the
Snail
family,
cSnR
, is expressed in the right-hand lateral mesoderm during normal chick development. Antisense disruption of
cSnR
function during the hours immediately preceding heart formation randomized the normally reliable direction of heart looping and subsequent embryo torsion. Implanted ectopic sources of intercellular signal proteins that are involved in establishing normal left-right information randomized the handedness of heart development and also altered the asymmetry of
cSnR
expression.
cSnR
thus appears to act downstream of these signals, or perhaps in parallel with the latest expressed of them, the Nodal protein, in controlling the anatomical asymmetry.
North and Northeast Greenland Ice Discharge from Satellite Radar Interferometry
Authors: Rignot E. J. , Gogineni S. P. , Krabill W. B. , Ekholm S.
Published: July 2002

Ice discharge from north and northeast Greenland calculated from satellite radar interferometry data of 14 outlet glaciers is 3.5 times that estimated from iceberg production. The satellite estimates, obtained at the grounding line of the outlet glaciers, differ from those obtained at the glacier front, because basal melting is extensive at the underside of the floating glacier sections. The results suggest that the north and northeast parts of the Greenland ice sheet may be thinning and contributing positively to sea-level rise.
Europa's Magnetic Signature: Report from Galileo's Pass on 19 December 1996
Authors: Kivelson M. G. , Khurana K. K. , Joy S. , Russell C. T. , Southwood D. J. , Walker R. J. , Polanskey C.
Published: July 2002

On 19 December 1996 as Galileo passed close to Jupiter’s moon, Europa, the magnetometer measured substantial departures from the slowly varying background field of Jupiter’s magnetosphere. Currents coupling Europa to Jupiter’s magnetospheric plasma could produce perturbations of the observed size. However, the trend of the field perturbations is here modeled as the signature of a Europa-centered dipole moment whose maximum surface magnitude is ∼240 nanotesla, giving a rough upper limit to the internal field. The dipole orientation is oblique to Europa’s spin axis. This orientation may not be probable for a field generated by a core dynamo, but higher order multipoles may be important as they are at Uranus and Neptune. Although the data can be modeled as contributions of an internal field of Europa, they do not confirm its existence. The dipole orientation is also oblique to the imposed field of Jupiter and thus not directly produced as a response to that field. Close to Europa, plasma currents appear to produce perturbations with scale sizes that are small compared with a Europa radius.
Transcription Regulation by Initiating NTP Concentration: rRNA Synthesis in Bacteria
Authors: Gaal Tamas , Bartlett Michael S. , Ross Wilma , Turnbough Charles L. , Gourse Richard L.
Published: July 2002

The sequence of a promoter determines not only the efficiency with which it forms a complex with RNA polymerase, but also the concentration of nucleoside triphosphate (NTP) required for initiating transcription.
Escherichia coli
ribosomal RNA (
rrn
P1) promoters require high initiating NTP concentrations for efficient transcription because they form unusually short-lived complexes with RNA polymerase; high initiating NTP concentrations [adenosine or guanosine triphosphate (ATP or GTP), depending on the
rrn
P1 promoter] are needed to bind to and stabilize the open complex. ATP and GTP concentrations, and therefore
rrn
P1 promoter activity, increase with growth rate. Because ribosomal RNA transcription determines the rate of ribosome synthesis, the control of ribosomal RNA transcription by NTP concentration provides a molecular explanation for the growth rate–dependent control and homeostatic regulation of ribosome synthesis.
Distinct Cellular Interactions of Secreted and Transmembrane Ebola Virus Glycoproteins
Authors: Yang Zhi-yong , Delgado Rafael , Xu Ling , Todd Robert F. , Nabel Elizabeth G. , Sanchez Anthony , Nabel Gary J.
Published: July 2002

The mechanisms by which Ebola virus evades detection and infects cells to cause hemorrhagic fever have not been defined, though its glycoprotein, synthesized in either a secreted or transmembrane form, is likely involved. Here the secreted glycoprotein was found to interact with neutrophils through CD16b, the neutrophil-specific form of the Fc γ receptor III, whereas the transmembrane glycoprotein was found to interact with endothelial cells but not neutrophils. A murine retroviral vector pseudotyped with the transmembrane glycoprotein preferentially infected endothelial cells. Thus, the secreted glycoprotein inhibits early neutrophil activation, which likely affects the host response to infection, whereas binding of the transmembrane glycoprotein to endothelial cells may contribute to the hemorrhagic symptoms of this disease.
Deuterium in Comet C/1995 O1 (Hale-Bopp): Detection of DCN
Authors: Meier Roland , Owen Tobias C. , Jewitt David C. , Matthews Henry E. , Senay Matthew , Biver Nicolas , Bockelée-Morvan Dominique , Crovisier Jacques , Gautier Daniel
Published: July 2002

Deuterated hydrogen cyanide (DCN) was detected in a comet, C/1995 O1 (Hale-Bopp), with the use of the James Clerk Maxwell Telescope on Mauna Kea, Hawaii. The inferred deuterium/hydrogen (D/H) ratio in hydrogen cyanide (HCN) is (D/H)
HCN
= (2.3 ± 0.4) × 10
−3
. This ratio is higher than the D/H ratio found in cometary water and supports the interstellar origin of cometary ices. The observed values of D/H in water and HCN imply a kinetic temperature ≥30 ± 10 K in the fragment of interstellar cloud that formed the solar system.
Genomic Cis-Regulatory Logic: Experimental and Computational Analysis of a Sea Urchin Gene
Authors: Yuh Chiou-Hwa , Bolouri Hamid , Davidson Eric H.
Published: July 2002

The genomic regulatory network that controls gene expression ultimately determines form and function in each species. The operational nature of the regulatory programming specified in cis-regulatory DNA sequence was determined from a detailed functional analysis of a sea urchin control element that directs the expression of a gene in the endoderm during development. Spatial expression and repression, and the changing rate of transcription of this gene, are mediated by a complex and extended cis-regulatory system. The system may be typical of developmental cis-regulatory apparatus. All of its activities are integrated in the proximal element, which contains seven target sites for DNA binding proteins. A quantitative computational model of this regulatory element was constructed that explicitly reveals the logical interrelations hard-wired into the DNA.
Docking Phospholipase A
2
on Membranes Using Electrostatic Potential-Modulated Spin Relaxation Magnetic Resonance
Authors: Lin Ying , Nielsen Robert , Murray Diana , Hubbell Wayne L. , Mailer Colin , Robinson Bruce H. , Gelb Michael H.
Published: July 2002

A method involving electron paramagnetic resonance spectroscopy of a site-selectively spin-labeled peripheral membrane protein in the presence and absence of membranes and of a water-soluble spin relaxant (chromium oxalate) has been developed to determine how bee venom phospholipase A
2
sits on the membrane. Theory based on the Poisson-Boltzmann equation shows that the rate of spin relaxation of a protein-bound nitroxide by a membrane-impermeant spin relaxant depends on the distance (up to tens of angstroms) from the spin probe to the membrane. The measurements define the interfacial binding surface of this secreted phospholipase A
2
.
Association of the AP-3 Adaptor Complex with Clathrin
Authors: Dell'Angelica Esteban C. , Klumperman Judith , Stoorvogel Willem , Bonifacino Juan S.
Published: July 2002

A heterotetrameric complex termed AP-3 is involved in signal-mediated protein sorting to endosomal-lysosomal organelles. AP-3 has been proposed to be a component of a nonclathrin coat. In vitro binding assays showed that mammalian AP-3 did associate with clathrin by interaction of the appendage domain of its β3 subunit with the amino-terminal domain of the clathrin heavy chain. The β3 appendage domain contained a conserved consensus motif for clathrin binding. AP-3 colocalized with clathrin in cells as observed by immunofluorescence and immunoelectron microscopy. Thus, AP-3 function in protein sorting may depend on clathrin.
Antarctic Elevation Change from 1992 to 1996
Authors: Wingham Duncan J. , Ridout Andrew J. , Scharroo Remko , Arthern Robert J. , Shum C. K.
Published: July 2002

Satellite radar altimeter measurements show that the average elevation of the Antarctic Ice Sheet interior fell by 0.9 ± 0.5 centimeters per year from 1992 to 1996. If the variability of snowfall observed in Antarctic ice cores is allowed for, the mass imbalance of the interior this century is only −0.06 ± 0.08 of the mean mass accumulation rate.
Rapid Identification of Subtype-Selective Agonists of the Somatostatin Receptor Through Combinatorial Chemistry
Authors: Rohrer Susan P. , Birzin Elizabeth T. , Mosley Ralph T. , Berk Scott C. , Hutchins Steven M. , Shen Dong-Ming , Xiong Yusheng , Hayes Edward C. , Parmar Rupa M. , Foor Forrest , Mitra Sudha W. , Degrado Sylvia J. , Shu Min , Klopp John M. , Cai Sheng-Jian , Blake Allan , Chan Wanda W. S. , Pasternak Alex , Yang Lihu , Patchett Arthur A. , Smith Roy G. , Chapman Kevin T. , Schaeffer James M.
Published: July 2002

Nonpeptide agonists of each of the five somatostatin receptors were identified in combinatorial libraries constructed on the basis of molecular modeling of known peptide agonists. In vitro experiments using these selective compounds demonstrated the role of the somatostatin subtype-2 receptor in inhibition of glucagon release from mouse pancreatic alpha cells and the somatostatin subtype-5 receptor as a mediator of insulin secretion from pancreatic beta cells. Both receptors regulated growth hormone release from the rat anterior pituitary gland. The availability of high-affinity, subtype-selective agonists for each of the somatostatin receptors provides a direct approach to defining their physiological functions.
Reconstructing Past Ocean pH-Depth Profiles
Authors: Palmer M. R. , Pearson P. N. , Cobb S. J.
Published: July 2002

Measurement of boron isotope compositions in species of planktonic foraminifera that calcified their tests at different depths in the water column are used to reconstruct the pH profile of the upper water column of the tropical ocean. Results for five time windows from the middle Miocene to the late Pleistocene indicate pH-depth profiles similar to that of the modern ocean in this area, which suggests that this method may greatly aid in our understanding of the global carbon cycle.
Action of DNA Repair Endonuclease ERCC1/XPF in Living Cells
Authors: Houtsmuller Adriaan B. , Rademakers Suzanne , Nigg Alex L. , Hoogstraten Deborah , J. Jan H. , Hoeijmakers  , Vermeulen Wim
Published: July 2002

To study the nuclear organization and dynamics of nucleotide excision repair (NER), the endonuclease ERCC1/XPF (for excision repair cross complementation group 1/xeroderma pigmentosum group F) was tagged with green fluorescent protein and its mobility was monitored in living Chinese hamster ovary cells. In the absence of DNA damage, the complex moved freely through the nucleus, with a diffusion coefficient (15 ± 5 square micrometers per second) consistent with its molecular size. Ultraviolet light–induced DNA damage caused a transient dose-dependent immobilization of ERCC1/XPF, likely due to engagement of the complex in a single repair event. After 4 minutes, the complex regained mobility. These results suggest (i) that NER operates by assembly of individual NER factors at sites of DNA damage rather than by preassembly of holocomplexes and (ii) that ERCC1/XPF participates in repair of DNA damage in a distributive fashion rather than by processive scanning of large genome segments.
Arabidopsis
Galactolipid Biosynthesis and Lipid Trafficking Mediated by DGD1
Authors: Dörmann Peter , Balbo Ilse , Benning Christoph
Published: July 2002

The photosynthetic apparatus in plant cells is associated with membranes of the thylakoids within the chloroplast and is embedded into a highly specialized lipid matrix. Diacylglycerol galactolipids are common in thylakoid membranes but are excluded from all others. Isolation of the gene
DGD1
, encoding a galactosyltransferase-like protein, now provides insights into assembly of the thylakoid lipid matrix and subcellular lipid trafficking in
Arabidopsis thaliana
.
Structural Basis of Chaperone Function and Pilus Biogenesis
Authors: Sauer Frederic G. , Fütterer Klaus , Pinkner Jerome S. , Dodson Karen W. , Hultgren Scott J. , Waksman Gabriel
Published: July 2002

Many Gram-negative pathogens assemble architecturally and functionally diverse adhesive pili on their surfaces by the chaperone-usher pathway. Immunoglobulin-like periplasmic chaperones escort pilus subunits to the usher, a large protein complex that facilitates the translocation and assembly of subunits across the outer membrane. The crystal structure of the PapD-PapK chaperone-subunit complex, determined at 2.4 angstrom resolution, reveals that the chaperone functions by donating its G
1
β strand to complete the immunoglobulin-like fold of the subunit via a mechanism termed donor strand complementation. The structure of the PapD-PapK complex also suggests that during pilus biogenesis, every subunit completes the immunoglobulin-like fold of its neighboring subunit via a mechanism termed donor strand exchange.
Origin of Graphitic Carbon and Pentlandite in Matrix Olivines in the Allende Meteorite
Authors: Brearley Adrian J.
Published: July 2002

Matrix olivines in the Allende carbonaceous chondrite are believed to have formed by condensation processes in the primitive solar nebula. However, transmission electron microscope observations of numerous matrix olivines show that they contain abundant, previously unrecognized, nanometer-sized inclusions of pentlandite and poorly graphitized carbon. Neither of these phases would have been stable at the high-temperature conditions required to condense iron-rich olivine in the solar nebula. The presence of these inclusions is consistent with formation of the olivines by parent body processes that involved overgrowth of fine-grained organic materials and sulfides in the precursor matrix materials.
Clonal Interference and the Evolution of RNA Viruses
Authors: Miralles Rosario , Gerrish Philip J. , Moya Andrés , Elena Santiago F.
Published: July 2002

In asexual populations, beneficial mutations that occur in different lineages compete with one another. This phenomenon, known as clonal interference, ensures that those beneficial mutations that do achieve fixation are of large effect. Clonal interference also increases the time between fixations, thereby slowing the adaptation of asexual populations. The effects of clonal interference were measured in the asexual RNA virus vesicular stomatitis virus; rates and average effects of beneficial mutations were quantified.
Climate Change as a Regulator of Tectonics on Venus
Authors: Solomon Sean C. , Bullock Mark A. , Grinspoon David H.
Published: July 2002

Tectonics, volcanism, and climate on Venus may be strongly coupled. Large excursions in surface temperature predicted to follow a global or near-global volcanic event diffuse into the interior and introduce thermal stresses of a magnitude sufficient to influence widespread tectonic deformation. This sequence of events accounts for the timing and many of the characteristics of deformation in the ridged plains of Venus, the most widely preserved volcanic terrain on the planet.
Imaging Magma Transport During the 1997 Seismic Swarm off the Izu Peninsula, Japan
Authors: Aoki Yosuke , Segall Paul , Kato Teruyuki , Cervelli Peter , Shimada Seiichi
Published: July 2002

The spatio-temporal evolution of a propagating magma-filled crack was estimated from inversion of Global Positioning System (GPS) data, tiltmeters, and leveling. The dike opened at a maximum rate of 50 millimeters per day and had a peak magma flux of 2 × 10
6
cubic meters per day. Although the spatial resolution was limited, slow upward propagation was resolved during the 9-day-long intrusion. In contrast, the earthquakes migrated rapidly upward during the first 12 hours of the swarm, and nearly all of the seismic energy was released in the first 2 days. Comparison of inversion results with accurate hypocenter locations will lead to improved understanding of magma transport through the brittle crust and of the causes of volcanic seismicity.
Similarity of the
C. elegans
Developmental Timing Protein LIN-42 to Circadian Rhythm Proteins
Authors: Jeon Mili , Gardner Heather F. , Miller Eric A. , Deshler Jodie , Rougvie Ann E.
Published: July 2002

The
Caenorhabditis elegans
heterochronic genes control the relative timing and sequence of many events during postembryonic development, including the terminal differentiation of the lateral hypodermis, which occurs during the final (fourth) molt. Inactivation of the heterochronic gene
lin-42
causes hypodermal terminal differentiation to occur precociously, during the third molt. LIN-42 most closely resembles the Period family of proteins from
Drosophila
and other organisms, proteins that function in another type of biological timing mechanism: the timing of circadian rhythms.
Per
mRNA levels oscillate with an approximately 24-hour periodicity.
lin-42
mRNA levels also oscillate, but with a faster rhythm; the oscillation occurs relative to the approximately 6-hour molting cycles of postembryonic development.
More Than 200 Meters of Lake Ice Above Subglacial Lake Vostok, Antarctica
Authors: Jouzel J. , Petit J. R. , Souchez R. , Barkov N. I. , Lipenkov V. Ya. , Raynaud D. , Stievenard M. , Vassiliev N. I. , Verbeke V. , Vimeux F.
Published: July 2002

Isotope studies show that the Vostok ice core consists of ice refrozen from Lake Vostok water, from 3539 meters below the surface of the Antarctic ice sheet to its bottom at about 3750 meters. Additional evidence comes from the total gas content, crystal size, and electrical conductivity of the ice. The Vostok site is a likely place for water freezing at the lake-ice interface, because this interface occurs at a higher level here than anywhere else above the lake. Isotopic data suggest that subglacial Lake Vostok is an open system with an efficient circulation of water that was formed during periods that were slightly warmer than those of the past 420,000 years. Lake ice recovered by deep drilling is of interest for preliminary investigations of lake chemistry and bedrock properties and for the search for indigenous lake microorganisms. This latter aspect is of potential importance for the exploration of icy planets and moons.
Stat3-Mediated Transformation of NIH-3T3 Cells by the Constitutively Active Q205L Gα
o
Protein
Authors: Ram Prahlad T. , Horvath Curt M. , Iyengar Ravi
Published: July 2002

Expression of Q205L Gα
o
(Gα
o
*), an alpha subunit of heterotrimeric guanine nucleotide–binding proteins (G proteins) that lacks guanosine triphosphatase (GTPase) activity in NIH-3T3 cells, results in transformation. Expression of Gα
o
* in NIH-3T3 cells activated signal transducer and activator of transcription 3 (Stat3) but not mitogen-activated protein (MAP) kinases 1 or 2. Coexpression of dominant negative Stat3 inhibited Gα
o
*-induced transformation of NIH-3T3 cells and activation of endogenous Stat3. Furthermore, Gα
o
* expression increased activity of the tyrosine kinase c-Src, and the Gα
o
*-induced activation of Stat3 was blocked by expression of Csk (carboxyl-terminal Src kinase), which inactivates c-Src. The results indicate that Stat3 can function as a downstream effector for Gα
o
* and mediate its biological effects.
Evidence for a High Frequency of Simultaneous Double-Nucleotide Substitutions
Authors: Averof Michalis , Rokas Antonis , Wolfe Kenneth H. , Sharp Paul M.
Published: July 2002

Point mutations are generally assumed to involve changes of single nucleotides. Nevertheless, the nature and known mechanisms of mutation do not exclude the possibility that several adjacent nucleotides may change simultaneously in a single mutational event. Two independent approaches are used here to estimate the frequency of simultaneous double-nucleotide substitutions. The first examines switches between TCN and AGY (where N is any nucleotide and Y is a pyrimidine) codons encoding absolutely conserved serine residues in a number of proteins from diverse organisms. The second reveals double-nucleotide substitutions in primate noncoding sequences. These two complementary approaches provide similar high estimates for the rate of doublet substitutions, on the order of 0.1 per site per billion years.
Detection of SO in Io's Exosphere
Authors: Russell C. T. , Kivelson M. G.
Published: July 2002

The Galileo orbiter's close pass by Io in 1995 produced evidence for extensive mass loading of the plasma torus through the ionization of SO
2
. On 11 October 1999, Galileo passed even closer to Io, this time across the upstream side relative to the flow of magnetospheric plasma that corotates with Jupiter. On the first flyby, ion cyclotron waves gave direct evidence for the production of SO
2
+
ions. On the second flyby, ion cyclotron waves associated with SO
+
were stronger and more persistent. Moreover, SO
+
emissions were seen closer to Io than SO
2
+
emissions, suggesting that the exosphere was spatially inhomogeneous. The location of the waves suggests a fan-shaped region of ion pickup extending in the anti-Jupiter direction. Because the wave spectra were different even where the 1995 and 1999 trajectories crossed, we infer that Io's exosphere is temporally variable.
Start Sites of Bidirectional DNA Synthesis at the Human Lamin B2 Origin
Authors: Abdurashidova Gulnara , Deganuto Marta , Klima Raffaella , Riva Silvano , Biamonti Giuseppe , Giacca Mauro , Falaschi Arturo
Published: July 2002

The initiation sites of bidirectional synthesis at the DNA replication origin located at the 3′ end of the human lamin B2 gene were investigated. RNA-primed nascent DNA molecules were subjected to second-strand synthesis with appropriate primers, amplified by ligation-mediated polymerase chain reaction, and size fractionated. Evidence for precise start sites was obtained. Exploration of close to 1 kilobase, coupled to inhibition of Okazaki fragment synthesis, demonstrates that the leading strands initiate at precise nucleotides on either helix, overlapping by three base pairs, within the area bound to a protein complex possibly analogous to the prereplicative complex of yeast.
Rapid Extinction of the Moas (Aves: Dinornithiformes): Model, Test, and Implications
Authors: Holdaway R. N. , Jacomb C.
Published: July 2002

A Leslie matrix population model supported by carbon-14 dating of early occupation layers lacking moa remains suggests that human hunting and habitat destruction drove the 11 species of moa to extinction less than 100 years after Polynesian settlement of New Zealand. The rapid extinction contrasts with models that envisage several centuries of exploitation.
Structure of the S15,S6,S18-rRNA Complex: Assembly of the 30
S
Ribosome Central Domain
Authors: Agalarov Sultan C. , Sridhar G. , Prasad  , Funke Peter M. , Stout C. David , Williamson James R.
Published: July 2002

The crystal structure of a 70-kilodalton ribonucleoprotein complex from the central domain of the
Thermus thermophilus
30
S
ribosomal subunit was solved at 2.6 angstrom resolution. The complex consists of a 104-nucleotide RNA fragment composed of two three-helix junctions that lie at the end of a central helix, and the ribosomal proteins S15, S6, and S18. S15 binds the ribosomal RNA early in the assembly of the 30
S
ribosomal subunit, stabilizing a conformational reorganization of the two three-helix junctions that creates the RNA fold necessary for subsequent binding of S6 and S18. The structure of the complex demonstrates the central role of S15-induced reorganization of central domain RNA for the subsequent steps of ribosome assembly.
Micropatterning of Organic Electronic Devices by Cold-Welding
Authors: Kim Changsoon , Burrows Paul E. , Forrest Stephen R.
Published: July 2002

A simple and general postdeposition electrode patterning technique for active organic electronic devices is demonstrated and is applied to patterning the metal cathodes of organic light-emitting devices. Selective lift-off of the metal cathode layer is achieved by pressing a prepatterned, metal-coated silicon stamp on the unpatterned device layers. Under pressure, the metal coating on the stamp cold-welds to the metal cathode coating the underlying organic films. Subsequent separation of the stamp from the substrate results in removal of the cathode metal in the regions contacted by the stamp, resulting in submicrometer feature definition. A 17×17 passive matrix display, with a pixel size of 440 micrometers by 320 micrometers, was fabricated with this process. Cold-welding followed by lift-off of the cathode metal allows simple, cost-effective, and high-throughput large-area fabrication of organic electronic devices.