bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion beam deposition of permanent magnet layers for liftoff processes
Authors: Hegde Hari , Wang Jinsong , Devasahayam Adrian J. , Kanarov Viktor , Hayes Alan , Yevtukhov Rustam , Bozeman Steve , Anderson Paul , Tabat Ned , Ryan Patrick
Published: July 2002

Thin film permanent magnet layers of Cr/CoCrPt were prepared by ion beam deposition in a Veeco IBD-350 tool. The magnetic properties were measured as a function of deposition angle, deposition energy, assist energy, and the underlayer and permanent magnet thicknesses. It was found that higher deposition energies and angles (from normal) resulted in larger coercivities. Increasing the assist energy also helped increase the coercivity. The coercivities were in the range of 1400–2100 Oe depending on the deposition conditions, for a Cr-50 Å/CoCrPt-250 Å film. The squareness, S (the ratio of remnant magnetization to saturation magnetization) and Mrt (remnant magnetization and film thickness product) for these films were about 0.85 and 1.3 memu/cm2, respectively. It was found that underlayers of Cr as thin as 25 Å could be used, without significant degradation of magnetic properties. The coercivity had a broad peak between 100 and 200 Å of CoCrPt, above which the coercivity gradually decreased. θ–2θ x-ray diffraction measurements showed the presence of in-plane textures of (101̄0) and (112̄0) with the largest coercivity being obtained when a strong (101̄0) peak is observed. The side-wall profile of the permanent magnet, measured after a liftoff process, was found to depend on the deposition angle. As the angle got larger (further away from normal incidence), the side wall showed greater tapering. This is due to the increased effect of shadowing by the photoresist structure. The directional, collimated, nature of the deposition beam was found to aid the liftoff process, by avoiding step coverage of the liftoff structures. This significantly increased the ease of lifting off. By adjusting the deposition angle, it is possible to tailor the process to provide optimum magnetic properties, coupled with good electrical contact. Thus, it was found that ion beam deposition is an attractive alternative to sputter deposition (physical vapor deposition), providing some important advantages over it.
Extreme ultraviolet lithography mask patterning and printability studies with a Ta-based absorber
Authors: Mangat P. J. S. , Hector S. D. , Thompson M. A. , Dauksher W. J. , Cobb J. , Cummings K. D. , Mancini D. P. , Resnick D. J. , Cardinale G. , Henderson C. , Kearney P. , Wedowski M.
Published: July 2002

Extreme ultraviolet (EUV) lithography masks were fabricated using a stack of TaSi or TaSiN (absorber), SiON (repair buffer), and Cr (conductive etch stop) on a Mo/Si multilayer mirror deposited on a Si wafer. High-resolution structures were exposed using a commercial i-line resist, and the pattern was transferred using both electron cyclotron resonance and reactive ion etching with halogen-based gases. Process temperatures to fabricate these reticles were always maintained below 150 °C. EUV properties after patterning were measured using a synchrotron source reflectometer. Completed masks exhibited a negligible shift in the peak wavelength and less than 2% loss in reflectivity due to processing. Qualified masks were exposed with a 10× EUV exposure system. The exposures were made in 80-nm-thick DUV resist and with numerical apertures (NA) of 0.08, 0.088, and 0.1. Resolution down to 70 nm equal lines and spaces was achieved at a NA of 0.1. Line edge roughness in the resist features was 5.5 nm (3σ, one side), and the depth of focus for ±10% CD control was ±1 μm for 100 nm equal lines and spaces.
Development of tungsten nitride film as barrier layer for copper metallization
Authors: Ganguli Seshadri , Chen Ling , Levine Timothy , Zheng Bo , Chang Mei
Published: July 2002

A process has been developed to deposit tungsten nitride (WxN) film below 350 °C to be used as a barrier layer in copper metallization. The film is deposited using tungsten hexa-fluoride (WF6) as a precursor in a hydrogen (H2)–nitrogen (N2)–argon (Ar) radio-frequency plasma. The tungsten-to-nitrogen ratio (x) in the tungsten nitride film determines its effectiveness as a barrier film. The process described in this article allows one to vary x from 1.2 to 3.7 by a single parameter: H2/N2 ratio. The article describes the characteristics of the film such as resistivity, stress, and deposition rate for different processing conditions. Film properties and surface conditions that cause WxN film to fail adhesion on oxide are indicated, and methods to improve adhesion are also discussed. Thickness measurements by alpha-step and scanning electron microscopy were correlated with measurements by the Rudolph Metapulse™ equipment to develop a methodology of nondestructively measuring film thickness, uniformity, and obtaining a first-order approximation of the W/N ratio of the film.
Ba losses due to oxygen adsorption on Ba-dispenser carthodes
Authors: Raasch D. , Geittner P. , Gärtner G.
Published: July 2002

The emission stability against ion bombardment and oxygen adsorption was investigated on thermionic Ba-dispenser cathodes with different top layers (W, Os/Ru, Re, Ir, and Re+Sc2O3) as a function of temperature and oxygen partial pressure. From these data, Ba and BaO reactivation energies and oxygen desorption energies were derived. During ion bombardment, two degradation/regeneration channels were observed due to the sequential carrying off of the emitting dipole and the corresponding resupply of Ba and BaO. Also two degradation/regeneration channels were detected during oxygen poisoning due to adsorption of oxygen and oxygen induced desorption of the emitting dipole or parts thereof and corresponding oxygen desorption and regeneration of the BaO dipole. The different top layers showed Ba and BaO reactivation energies of 1.5–2.6 and 2.0–2.93 eV, respectively. The values determined from the poisoning measurements were 0.3–0.7 eV larger that those from ion bombardment measurements. The oxygen desorption energies were between 1.5 (Sc/Re) and 2.91 eV (W).
X-ray rocking curve analysis of tetragonally distorted ternary semiconductors on mismatched (001) substrates
Authors: Zhang X. G. , Parent D. W. , Li P. , Rodriguez A. , Zhao G. , Ayers J. E. , Jain F. C.
Published: July 2002

For ternary heteroepitaxial layers, the independent determination of the composition and state of strain requires x-ray rocking curve measurements for at least two different hkl reflections because the relaxed lattice constant is a function of the composition. The usual approach involves the use of one symmetric reflection and one asymmetric reflection. Two rocking curves are measured at opposing azimuths for each hkl reflection. Thus, it is possible to account for tilting of the hkl planes in the epitaxial layer with respect to the hkl planes in the substrate, by averaging the peak separations obtained at the opposing azimuths. This procedure presents a practical problem in the case of asymmetric reflections, for which the tilting can only be canceled if the rocking curve for one azimuth is obtained using θ−φ incidence. A preferable approach, which provides sharper, more intense rocking curves and greater experimental accuracy, is to measure both asymmetric rocking curves at θ+φ incidence. This approach requires that the data be corrected for the tilting of the asymmetric planes introduced by tetragonal distortion. Here we have presented a new analytic procedure that incorporates the tilting of asymmetric diffracting planes due to tetragonal distortion. The new procedure allows the measurement of all rocking curves at θ+φ incidence. We have applied this new method to the case of ZnSySe1−y grown heteroepitaxially on GaAs (001), using 004 and 044 x-ray rocking curves. We have shown that neglect of the tilting in asymmetric planes results in gross errors in the calculated values of composition (as much as 35 times) and in-plane strain (as much as 2.6 times) for this material.
Group III nitride–arsenide long wavelength lasers grown by elemental source molecular beam epitaxy
Authors: Coldren C. W. , Spruytte S. G. , Harris J. S. , Larson M. C.
Published: July 2002

Elemental source molecular beam epitaxy was used to grow InGaNAs quantum well samples, edge-emitting laser diodes, and vertical-cavity laser diodes on GaAs substrates. The quantum well samples exhibited an as-grown room temperature photoluminescence peak beyond 1310 nm which both increased dramatically in intensity and blueshifted with thermal annealing. Edge emitting laser diodes had threshold current densities as low as 450 and 750 A/cm2 for single and triple quantum well active regions, respectively, and emitted light at 1220–1250 nm. The vertical cavity laser diodes emitted light at 1200 nm and had threshold current densities of 3 kA/cm2 and efficiencies of 0.066 W/A.
Molecular beam epitaxy of PbSrSe and PbSe/PbSrSe multiple quantum well structures for use in midinfrared light emitting devices
Authors: Fang X. M. , Namjou K. , Chao I-Na , McCann P. J. , Dai N. , Tor G.
Published: July 2002

PbSrSe layers and PbSe/PbSrSe multiple quantum well (MQW) structures have been grown on BaF2 (111) substrates by molecular beam epitaxy. The lattice constant of the PbSrSe alloy was determined by x-ray diffraction, and both the refractive index and absorption edge of the PbSrSe alloy with Sr composition up to 0.23 were obtained from Fourier transform infrared transmission spectra at room temperature. MQW structures exhibit strong photoluminescence (PL) in the 3–5 μm wavelength range at room temperature. The PL intensity decreases monotonically with increasing temperature below 230 K.
Role of Rab9 GTPase in Facilitating Receptor Recruitment by TIP47
Authors: Carroll Kate S. , Hanna John , Simon Iris , Krise Jeff , Barbero Pierre , Pfeffer Suzanne R.
Published: July 2002

Mannose 6-phosphate receptors (MPRs) deliver lysosomal hydrolases from the Golgi to endosomes and then return to the Golgi complex. TIP47 recognizes the cytoplasmic domains of MPRs and is required for endosome-to-Golgi transport. Here we show that TIP47 also bound directly to the Rab9 guanosine triphosphatase (GTPase) in its active, GTP-bound conformation. Moreover, Rab9 increased the affinity of TIP47 for its cargo. A functional Rab9 binding site was required for TIP47 stimulation of MPR transport in vivo. Thus, a cytosolic cargo selection device may be selectively recruited onto a specific organelle, and vesicle budding might be coupled to the presence of an active Rab GTPase.
Synchronous Tropical South China Sea SST Change and Greenland Warming During Deglaciation
Authors: Kienast M. , Steinke S. , Stattegger K. , Calvert S. E.
Published: July 2002

The tropical ocean plays a major role in global climate. It is therefore crucial to establish the precise phase between tropical and high-latitude climate variability during past abrupt climate events in order to gain insight into the mechanisms of global climate change. Here we present alkenone sea surface temperature (SST) records from the tropical South China Sea that show an abrupt temperature increase of at least 1°C at the end of the last glacial period. Within the recognized dating uncertainties, this SST increase is synchronous with the Bølling warming observed at 14.6 thousand years ago in the Greenland Ice Sheet Project 2 ice core.
Construction Principles of "Hyparenes": Families of Molecules with Planar Pentacoordinate Carbons
Authors: Wang Zhi-Xiang , Schleyer Paul von Ragué
Published: July 2002

Density-functional theory calculations predict that three borocarbon units with planar pentacoordinate carbons −C
3
B
3
−, −C
2
B
4
−, and −CB
5
−, can replace the −(CH)
3
− subunits in aromatic or even in antiaromatic hydrocarbons to construct “hyparenes” (families of molecules with planar pentacoordinate carbons). These borocarbon units contribute two, one, and zero electrons, respectively, to the parent pi system. Depending on the choice of these units, the hyparenes (judging from computed proton and nucleus-independent chemical shifts), can maintain or can interconvert the aromatic or antiaromatic character of the parent compounds. The hyparenes are low-lying local minima with normal carbon-boron, boron-boron, and carbon-carbon bond lengths. The multicenter bonding in the hyparenes involves contributions of partial sigma and partial pi bonds to the planar pentacoordinate carbons; the octet rule is not violated. Borocarbon species, for which there is some mass spectrometric evidence, might be observed and identified, for example, in matrix isolation by vibrational spectroscopy.
Nitrogen Fixation by Symbiotic and Free-Living Spirochetes
Authors: Lilburn T. G. , Kim K. S. , Ostrom N. E. , Byzek K. R. , Leadbetter J. R. , Breznak J. A.
Published: July 2002

Spirochetes from termite hindguts and freshwater sediments possessed homologs of a nitrogenase gene (
nifH
) and exhibited nitrogenase activity, a previously unrecognized metabolic capability in spirochetes. Fixation of 15-dinitrogen was demonstrated with termite gut
Treponema
ZAS-9 and free-living
Spirochaeta aurantia
. Homologs of
nifH
were also present in human oral and bovine ruminal treponemes. Results implicate spirochetes in the nitrogen nutrition of termites, whose food is typically low in nitrogen, and in global nitrogen cycling. These results also proffer spirochetes as a likely origin of certain
nifH
s observed in termite guts and other environments that were not previously attributable to known microbes.
A Neural Correlate of Working Memory in the Monkey Primary Visual Cortex
Authors: Supèr Hans , Spekreijse Henk , Lamme Victor A. F.
Published: July 2002

The brain frequently needs to store information for short periods. In vision, this means that the perceptual correlate of a stimulus has to be maintained temporally once the stimulus has been removed from the visual scene. However, it is not known how the visual system transfers sensory information into a memory component. Here, we identify a neural correlate of working memory in the monkey primary visual cortex (V1). We propose that this component may link sensory activity with memory activity.
Compartmentalized and Binary Behavior of Terminal Dendrites in Hippocampal Pyramidal Neurons
Authors: Wei Dong-Sheng , Mei Yan-Ai , Bagal Ashish , Kao Joseph P. Y. , Thompson Scott M. , Tang Cha-Min
Published: July 2002

The dendritic arbor of pyramidal neurons is not a monolithic structure. We show here that the excitability of terminal apical dendrites differs from that of the apical trunk. In response to fluorescence-guided focal photolysis of caged glutamate, individual terminal apical dendrites generated cadmium-sensitive all-or-none responses that were subthreshold for somatic action potentials. Calcium transients produced by all-or-none responses were not restricted to the sites of photolysis, but occurred throughout individual distal dendritic compartments, indicating that electrogenesis is mediated primarily by voltage-gated calcium channels. Compartmentalized and binary behavior of parallel-connected terminal dendrites can greatly expand the computational power of a single neuron.
Thickness of a Europan Ice Shell from Impact Crater Simulations
Authors: Turtle E. P. , Pierazzo E.
Published: July 2002

Several impact craters on Jupiter's satellite Europa exhibit central peaks. On the terrestrial planets, central peaks consist of fractured but competent rock uplifted during cratering. Therefore, the observation of central peaks on Europa indicates that an ice layer must be sufficiently thick that the impact events did not completely penetrate it. We conducted numerical simulations of vapor and melt production during cratering of water ice layers overlying liquid water to estimate the thickness of Europa's icy crust. Because impacts disrupt material well beyond the zone of partial melting, our simulations put a lower limit on ice thickness at the locations and times of impact. We conclude that the ice must be more than 3 to 4 kilometers thick.
Late Holocene Climate and Cultural Changes in the Southwestern United States
Authors: Polyak Victor J. , Asmerom Yemane
Published: July 2002

Columnar stalagmites in caves of the Guadalupe Mountains during the late Holocene record a 4000-year annually resolved climate history for the southwestern United States. Annual banding, hiatuses, and high-precision uranium-series dating show a present day–like climate from 4000 to 3000 years ago, following a drier middle Holocene. A distinctly wetter and cooler period from 3000 to 800 years ago was followed by a period of present day–like conditions, with the exception of a slightly wetter interval from 440 to 290 years before the present. The stalagmite record correlates well with the archaeological record of changes in cultural activities of indigenous people. Such climate change may help to explain evidence of dwelling abandonment and population redistribution.
Hydrogen Produced from Hydrohalic Acid Solutions by a Two-Electron Mixed-Valence Photocatalyst
Authors: Heyduk Alan F. , Nocera Daniel G.
Published: July 2002

Energy conversion cycles are aimed at driving unfavorable, small-molecule activation reactions with a photon harnessed by a transition metal complex. A challenge that has occupied researchers for several decades is to create molecular photocatalysts to promote the production of hydrogen from homogeneous solution. We now report the use of a two-electron mixed-valence dirhodium compound to photocatalyze the reduction of hydrohalic acid to hydrogen. In this cycle, photons break two Rh
II
–X bonds of a LRh
0
–Rh
II
X
2
core in the presence of a halogen trap to regenerate the active LRh
0
–Rh
0
catalyst, which reacts with hydrohalic acid to produce hydrogen.
Regulation of the Immune Response by Antigen
Authors: Zinkernagel Rolf M. , Hengartner Hans
Published: July 2002

How, why, and when specific T and B lymphocytes respond against infection follow explicit rules, but how this can be assessed experimentally depends crucially on the methodology used. In this Viewpoint, we discuss the parameters of receptor specificity and antigen that determine whether an immune response can be accurately measured against model antigens and how this relates to protection against a given pathogen. We suggest that antigen structure, localization, dose, and time during which antigen is available are all decisive factors in regulating an immune response.
The Mitotic Spindle: A Self-Made Machine
Authors: Karsenti E. , Vernos I.
Published: July 2002

The mitotic spindle is a highly dynamic molecular machine composed of tubulin, motors, and other molecules. It assembles around the chromosomes and distributes the duplicated genome to the daughter cells during mitosis. The biochemical and physical principles that govern the assembly of this machine are still unclear. However, accumulated discoveries indicate that chromosomes play a key role. Apparently, they generate a local cytoplasmic state that supports the nucleation and growth of microtubules. Then soluble and chromosome-associated molecular motors sort them into a bipolar array. The emerging picture is that spindle assembly is governed by a combination of modular principles and that their relative contribution may vary in different cell types and in various organisms.
T Cell Responses Modulated Through Interaction Between CD8αα and the Nonclassical MHC Class I Molecule, TL
Authors: Leishman Andrew J. , Naidenko Olga V. , Attinger Antoine , Koning Frits , Lena Christopher J. , Xiong Yi , Chang Hsiu-Ching , Reinherz Ellis , Kronenberg Mitchell , Cheroutre Hilde
Published: July 2002

The thymus leukemia antigen (TL) is a nonclassical class I molecule, expressed abundantly on intestinal epithelial cells. We show that, in contrast to other major histocompatibility complex (MHC) class I molecules that bind CD8αβ, TL preferentially binds the homotypic form of CD8α (CD8αα). Thus, TL tetramers react specifically to CD8αα-expressing cells, including most intestinal intraepithelial lymphocytes. Compared with CD8αβ, which recognizes the same MHC as the T cell receptor (TCR) and thus acts as a TCR coreceptor, high-affinity binding of CD8αα to TL modifies responses mediated by TCR recognition of antigen presented by distinct MHC molecules. These findings define a novel mechanism of lymphocyte regulation through CD8αα and MHC class I.
Organogenesis--Heart and Blood Formation from the Zebrafish Point of View
Authors: Thisse Christine , Zon Leonard I.
Published: July 2002

Organs are specialized tissues used for enhanced physiology and environmental adaptation. The cells of the embryo are genetically programmed to establish organ form and function through conserved developmental modules. The zebrafish is a powerful model system that is poised to contribute to our basic understanding of vertebrate organogenesis. This review develops the theme of modules and illustrates how zebrafish have been particularly useful for understanding heart and blood formation.
Structural Basis for Recognition of the Intron Branch Site RNA by Splicing Factor 1
Authors: Liu Zhihong , Luyten Ingrid , Bottomley Matthew J. , Messias Ana C. , Houngninou-Molango Sophie , Sprangers Remco , Zanier Katia , Krämer Angela , Sattler Michael
Published: July 2002

During spliceosome assembly, splicing factor 1 (SF1) specifically recognizes the intron branch point sequence (BPS) UACUAAC in the pre-mRNA transcripts. We show that the KH-QUA2 region of SF1 defines an enlarged KH (hn RNP K) fold which is necessary and sufficient for BPS binding. The 3′ part of the BPS (UA
A
C), including the conserved branch point adenosine (underlined), is specifically recognized in a hydrophobic cleft formed by the Gly-Pro-Arg-Gly motif and the variable loop of the KH domain. The QUA2 region recognizes the 5′ nucleotides of the BPS (ACU). The branch point adenosine acting as the nucleophile in the first biochemical step of splicing is deeply buried. BPS RNA recognition suggests how SF1 may facilitate subsequent formation of the prespliceosomal complex A.
Dynamical Spreading of Asteroid Families by the Yarkovsky Effect
Authors: Bottke William F. , Vokrouhlický David , Broz̆ Miroslav , Nesvorný David , Morbidelli Alessandro
Published: July 2002

The orbital distributions of prominent asteroid families are thought to be direct by-products of catastrophic disruption events among diameter
D
≳ 100 kilometer bodies. Ejection velocities derived from studying observed families, however, are surprisingly high compared with results from impact experiments and simulations. One way to resolve this apparent contradiction is by assuming that
D
≲ 20 kilometer family members, since their formation, have undergone semimajor axis drift by the thermal force called the Yarkovsky effect. Interactions between drifting family members and resonances can also produce unique eccentricity and/or inclination changes. Together, these outcomes help explain (i) why families are sharply bounded by nearby Kirkwood gaps, (ii) why some families have asymmetric shapes, and (iii) the curious presence of family members on short-lived orbits.
Exosome-Mediated Recognition and Degradation of mRNAs Lacking a Termination Codon
Authors: van Hoof Ambro , Frischmeyer Pamela A. , Dietz Harry C. , Parker Roy
Published: July 2002

One role of messenger RNA (mRNA) degradation is to maintain the fidelity of gene expression by degrading aberrant transcripts. Recent results show that mRNAs without translation termination codons are unstable in eukaryotic cells. We used yeast mutants to demonstrate that these “nonstop” mRNAs are degraded by the exosome in a 3′-to-5′ direction. The degradation of nonstop transcripts requires the exosome-associated protein Ski7p. Ski7p is closely related to the translation elongation factor EF1A and the translation termination factor eRF3. This suggests that the recognition of nonstop mRNAs involves the binding of Ski7p to an empty aminoacyl-(RNA-binding) site (A site) on the ribosome, thereby bringing the exosome to a mRNA with a ribosome stalled near the 3′ end. This system efficiently degrades mRNAs that are prematurely polyadenylated within the coding region and prevents their expression.
Germline Stem Cells Anchored by Adherens Junctions in the
Drosophila
Ovary Niches
Authors: Song Xiaoqing , Zhu Chun-Hong , Doan Chuong , Xie Ting
Published: July 2002

How stem cells are recruited to and maintained in their niches is crucial to understanding their regulation and use in regenerative medicine. Here, we demonstrate that DE-cadherin–mediated cell adhesion is required for anchoring germline stem cells (GSCs) in their niches in the
Drosophila
ovary. Two major components of this adhesion process, DE-cadherin and Armadillo/β-catenin, accumulate at high levels in the junctions between GSCs and cap cells, one of the niche components. Removal of these proteins from GSCs results in stem cell loss. Furthermore, DE-cadherin is required for recruiting GSCs to their niche. Our study demonstrates that anchorage of GSCs in their niche by DE-cadherin–mediated adhesion is important for stem cell maintenance and function.
Emerging Coherence in a Population of Chemical Oscillators
Authors: Kiss István Z. , Zhai Yumei , Hudson John L.
Published: July 2002

Coherence of interacting oscillating entities has importance in biological, chemical, and physical systems. We report experiments on populations of chemical oscillators and verify a 25-year-old theory of Kuramoto that predicts that global coupling in a set of smooth limit-cycle oscillators with different frequencies produces a phase transition in which some of the elements synchronize. Both the critical point and the predicted dependence of order on coupling are seen in the experiments. We extend the studies both to relaxation and to chaotic oscillators and characterize the quantitative similarities and differences among the types of systems.
The Jasmonate Pathway
Authors: Liechti Robin , Farmer Edward E.
Published: July 2002

Plants are faced with many of the same problems as animals—a need for regulation of metabolic processes and reproduction and for defense against enemies. Jasmonates in plants serve key roles in gene and metabolic regulation, defense, responses to trauma, reproduction, and possibly communication. Some remarkable features of plant responses, such as production of repellent volatiles as a defense against herbivorous insects, or the massive transcriptional reprogramming that occurs in response to wounding, are under the control of the jasmonate pathway. Details of the jasmonate signaling pathway are currently at the center of active research that is generating exciting results. The Jasmonate Biochemical Pathway at the STKE Connections Maps is designed to present and keep pace with these developments.
Requirement for Invariant Chain in B Cell Maturation and Function
Authors: Shachar Idit , Flavell Richard A.
Published: July 2002

Previously the role of invariant chain (Ii) had been described only as a chaperone that facilitates folding and transport of major histocompatability complex class II molecules; here it is shown that Ii is required for B cell development. B cells from mice lacking Ii were found to have a low response to T-independent type II antigen and could not proliferate after the mice were injected with antigen. Study of cell surface markers revealed a developmental arrest that prevented immature virgin B cells from becoming mature B cells in the periphery. This block was independent of major histocompatability complex class II expression and was an intrinsic feature of B cells that correlated with the amount of Ii. Thus, Ii participates by an unknown mechanism in B cell maturation.
Decreased Resistance to Bacterial Infection and Granulocyte Defects in IAP-Deficient Mice
Authors: Lindberg Frederik P. , Bullard Daniel C. , Caver Tony E. , Gresham Hattie D. , Beaudet Arthur L. , Brown Eric J.
Published: July 2002

Granulocyte [polymorphonuclear leucocyte (PMN)] migration to sites of infection and subsequent activation is essential for host defense. Gene-targeted mice deficient for integrin-associated protein (IAP, also termed CD47) succumbed to
Escherichia coli
peritonitis at inoccula survived by heterozygous littermates. In vivo, they had an early defect in PMN accumulation at the site of infection. In vitro, IAP
−/−
PMNs were deficient in β
3
integrin-dependent ligand binding, activation of an oxidative burst, and Fc receptor-mediated phagocytosis. Thus, IAP plays a key role in host defense by participating both in PMN migration in response to bacterial infection and in PMN activation at extravascular sites.
Anisotropy in the Inner Core: Could It Be Due To Low-Order Convection?
Authors: Romanowicz Barbara , Li Xiang-Dong , Durek Joseph
Published: July 2002

A recently assembled data set of inner core-sensitive free oscillation splitting measurements and body wave differential travel times provides constraints on the patterns of anisotropy in the Earth's inner core. Applying a formalism that allows departures from radial symmetry and cylindrical anisotropy results in models with
P
-wave velocity distributions whose strength and pattern are incompatible with frozen-in anisotropy, but rather suggest a simple large-scale convection regime in the inner core.
Major Susceptibility Locus for Prostate Cancer on Chromosome 1 Suggested by a Genome-Wide Search
Authors: Smith Jeffrey R. , Freije Diha , Carpten John D. , Grönberg Henrik , Xu Jianfeng , Isaacs Sarah D. , Brownstein Michael J. , Bova G. Steven , Guo Hong , Bujnovszky Piroska , Nusskern Deborah R. , Damber Jan-Erik , Bergh Anders , Emanuelsson Monika , Kallioniemi Olli P. , Walker-Daniels Jennifer , Bailey-Wilson Joan E. , Beaty Terri H. , Meyers Deborah A. , Walsh Patrick C. , Collins Francis S. , Trent Jeffrey M. , Isaacs William B.
Published: July 2002

Despite its high prevalence, very little is known regarding genetic predisposition to prostate cancer. A genome-wide scan performed in 66 high-risk prostate cancer families has provided evidence of linkage to the long arm of chromosome 1 (1q24-25). Analysis of an additional set of 25 North American and Swedish families with markers in this region resulted in significant evidence of linkage in the combined set of 91 families. The data provide strong evidence of a major prostate cancer susceptibility locus on chromosome 1.
How Proteolysis Drives the Cell Cycle
Authors: King Randall W. , Deshaies Raymond J. , Peters Jan-Michael , Kirschner Marc W.
Published: July 2002

Oscillations in the activity of cyclin-dependent kinases (CDKs) promote progression through the eukaryotic cell cycle. This review examines how proteolysis regulates CDK activity—by degrading CDK activators or inhibitors—and also how proteolysis may directly trigger the transition from metaphase to anaphase. Proteolysis during the cell cycle is mediated by two distinct ubiquitin-conjugation pathways. One pathway, requiring CDC34, initiates DNA replication by degrading a CDK inhibitor. The second pathway, involving a large protein complex called the anaphase-promoting complex or cyclosome, initiates chromosome segregation and exit from mitosis by degrading anaphase inhibitors and mitotic cyclins. Proteolysis therefore drives cell cycle progression not only by regulating CDK activity, but by directly influencing chromosome and spindle dynamics.
A Legume Ethylene-Insensitive Mutant Hyperinfected by Its Rhizobial Symbiont
Authors: Penmetsa R. Varma , Cook Douglas R.
Published: July 2002

Development of the
Rhizobium
-legume symbiosis is controlled by the host plant, although the underlying mechanisms have remained obscure. A mutant in the annual legume
Medicago truncatula
exhibits an increase of more than an order of magnitude in the number of persistent rhizobial infections. Physiological and genetic analyses indicate that this same mutation confers insensitivity to the plant hormone ethylene for multiple aspects of plant development, including nodulation. These data support the hypothesis that ethylene is a component of the signaling pathway controlling rhizobial infection of legumes.
Akt Signaling--Linking Membrane Events to Life and Death Decisions
Authors: Hemmings Brian A.
Published: July 2002

Many growth factors exert their effects on cells by simulating intracellular kinases, which add phosphate groups to proteins. Two reports on
p. 661
and
p. 665
of this week's issue implicate the oncogenic kinase Akt in IGF-1-mediated neuronal survival (Dudek
et al
.) and show how lipids can regulate the activity of Akt (Franke
et al
.). In his Perspective, Hemmings discusses these results and several other recent reports about Akt and its unique mode of activation by phospholipids.
A Silicon Single-Electron Transistor Memory Operating at Room Temperature
Authors: Guo Lingjie , Leobandung Effendi , Chou Stephen Y.
Published: July 2002

A single-electron memory, in which a bit of information is stored by one electron, is demonstrated at room temperature. The memory is a floating gate metal-oxide-semiconductor transistor in silicon with a channel width (∼10 nanometers) smaller than the Debye screening length of a single electron and a nanoscale polysilicon dot (∼7 nanometers by 7 nanometers) as the floating gate embedded between the channel and the control gate. Storing one electron on the floating gate screens the entire channel from the potential on the control gate and leads to (i) a discrete shift in the threshold voltage, (ii) a staircase relation between the charging voltage and the shift, and (iii) a self-limiting charging process. The structure and fabrication of the memory should be compatible with future ultralarge-scale integrated circuits.
Low-Temperature Carbonate Concretions in the Martian Meteorite ALH84001: Evidence from Stable Isotopes and Mineralogy
Authors: Valley John W. , Eiler John M. , Graham Colin M. , Gibson Everett K. , Romanek Christopher S. , Stolper Edward M.
Published: July 2002

The martian meteorite ALH84001 contains small, disk-shaped concretions of carbonate with concentric chemical and mineralogical zonation. Oxygen isotope compositions of these concretions, measured by ion microprobe, range from δ
18
O = +9.5 to +20.5‰. Most of the core of one concretion is homogeneous (16.7 ± 1.2‰) and over 5‰ higher in δ
18
O than a second concretion. Orthopyroxene that hosts the secondary carbonates is isotopically homogeneous (δ
18
O = 4.6 ± 1.2‰). Secondary SiO
2
has δ
18
O = 20.4‰. Carbon isotope ratios measured from the core of one concretion average δ
13
C = 46 ± 8‰, consistent with formation on Mars. The isotopic variations and mineral compositions offer no evidence for high temperature (>650°C) carbonate precipitation and suggest non-equilibrium processes at low temperatures (<∼300°C).
Climatic Limits on Landscape Development in the Northwestern Himalaya
Authors: Brozović Nicholas , Burbank Douglas W. , Meigs Andrew J.
Published: July 2002

The interaction between tectonism and erosion produces rugged landscapes in actively deforming regions. In the northwestern Himalaya, the form of the landscape was found to be largely independent of exhumation rates, but regional trends in mean and modal elevations, hypsometry (frequency distribution of altitude), and slope distributions were correlated with the extent of glaciation. These observations imply that in mountain belts that intersect the snowline, glacial and periglacial processes place an upper limit on altitude, relief, and the development of topography irrespective of the rate of tectonic processes operating.
Identification of α-Fodrin as a Candidate Autoantigen in Primary Sjögren's Syndrome
Authors: Haneji Norio , Nakamura Takanori , Takio Koji , Yanagi Kumiko , Higashiyama Hiroyuki , Saito Ichiro , Noji Sumihare , Sugino Hiromu , Hayashi Yoshio
Published: July 2002

It is unclear whether organ-specific autoantigens are critical for the development of primary Sjögren’s syndrome (SS). A 120-kilodalton organ-specific autoantigen was purified from salivary gland tissues of an NFS/
sld
mouse model of human SS. The amino-terminal residues were identical to those of the human cytoskeletal protein α-fodrin. The purified antigen induced proliferative T cell responses and production of interleukin-2 and interferon-γ in vitro. Neonatal immunization with the 120-kilodalton antigen prevented the disease in mice. Sera from patients with SS reacted positively with purified antigen and recombinant human α-fodrin protein, whereas those from patients with systemic lupus erythematosus and rheumatoid arthritis did not. Thus, the immune response to 120-kilodalton α-fodrin could be important in the initial development of primary SS.
Trace Gas Emissions and Smoke-Induced Seed Germination
Authors: Keeley Jon E. , Fotheringham C. J.
Published: July 2002

Dormant seeds of a California chaparral annual were induced to germinate by smoke or vapors emitted from smoke-treated sand or paper. Nitrogen oxides induced 100 percent germination in a manner similar to smoke. Smoke-treated water samples inducing germination were comparable in acidity and concentration of nitrate and nitrite to nitrogen dioxide (NO
2
)–treated samples. Vapors from smoke-treated and NO
2
-treated filter paper had comparable NO
2
flux rates. Chaparral wildfires generate sufficient nitrogen oxides from combustion of organic matter or from postfire biogenic nitrification to trigger germination of
Emmenanthe penduliflora
. Nitrogen oxide–triggered germination is not the result of changes in imbibition, as is the case with heat-stimulated seeds.
Discrete Determinants in Transfer RNA for Editing and Aminoacylation
Authors: Hale Stephen P. , Auld Douglas S. , Schmidt Eric , Schimmel Paul
Published: July 2002

During translation errors of aminoacylation are corrected in editing reactions which ensure that an amino acid is stably attached to its corresponding transfer RNA (tRNA). Previous studies have not shown whether the tRNA nucleotides needed for effecting translational editing are the same as or distinct from those required for aminoacylation, but several considerations have suggested that they are the same. Here, designed tRNAs that are highly active for aminoacylation but are not active in translational editing are presented. The editing reaction can be controlled by manipulation of nucleotides at the corner of the L-shaped tRNA. In contrast, these manipulations do not affect aminoacylation. These results demonstrate the segregation of nucleotide determinants for the editing and aminoacylation functions of tRNA.
Young Stars and Their Surroundings
Authors: O’Dell C. Robert , Beckwith Steven V. W.
Published: July 2002

As stars are created by the gravitational contraction of knots in giant interstellar clouds, they shed angular momentum and magnetic and gravitational energy in an interplay of complex circumstellar structures: swirling disks, fast collimated jets, and shock waves in the surrounding cloud. Many of these structures were inferred a decade ago from ground-based telescope observations. The high resolution of the Hubble Space Telescope and other instruments has now revealed these circumstellar regions in great detail, showing features never before imagined. In the Orion Nebula alone, examples of all types of interactions between young stars and their environment can be seen simultaneously, highlighting circumstellar dynamics in sharp relief in one of astronomy’s most famous objects.
Bacterial Interference Caused by Autoinducing Peptide Variants
Authors: Ji Guangyong , Beavis Ronald , Novick Richard P.
Published: July 2002

The synthesis of virulence factors and other extracellular proteins by
Staphylococcus aureus
is globally controlled by the
agr
locus, which encodes a two-component signaling pathway whose activating ligand is an
agr
-encoded autoinducing peptide. The cognate peptides produced by some strains inhibit the expression of
agr
in other strains, and the amino acid sequences of peptide and receptor are markedly different between such strains, suggesting a hypervariability-generating mechanism. Cross-inhibition of gene expression represents a type of bacterial interference that could be correlated with the ability of one strain to exclude others from infection or colonization sites, or both.
Drosophila
Mitotic Domain Boundaries as Cell Fate Boundaries
Authors: Cambridge Sidney B. , Davis Robert L. , Minden Jonathan S.
Published: July 2002

Fate determination in
Drosophila
embryos is evidenced by the appearance of mitotic domains. To identify fate or fates of cells, individual cells in mitotic domains 2, 8, and 15 were marked and monitored through development. Comparison of the different fates indicated that domain boundaries are cell fate boundaries. Cells were marked by expression of GAL4-dependent transgenes after photoactivation of a caged GAL4VP16 analog that had its DNA binding activity inhibited with a photolabile blocking reagent. Caged GAL4VP16 was also used to induce gene expression in
Xenopus
embryos. Thus, photoactivated gene expression is a versatile tool for spatiotemporal control of gene expression.
Infants' Memory for Spoken Words
Authors: Jusczyk Peter W. , Hohne Elizabeth A.
Published: July 2002

Infants' long-term retention of the sound patterns of words was explored by exposing them to recordings of three children's stories for 10 days during a 2-week period when they were 8 months old. After an interval of 2 weeks, the infants heard lists of words that either occurred frequently or did not occur in the stories. The infants listened significantly longer to the lists of story words. By comparison, a control group of infants who had not been exposed to the stories showed no such preference. The findings suggest that 8-month-olds are beginning to engage in long-term storage of words that occur frequently in speech, which is an important prerequisite for learning language.
Molecular and Cellular Basis of Addiction
Authors: Nestler Eric J. , Aghajanian George K.
Published: July 2002

Drug addiction results from adaptations in specific brain neurons caused by repeated exposure to a drug of abuse. These adaptations combine to produce the complex behaviors that define an addicted state. Progress is being made in identifying such time-dependent, drug-induced adaptations and relating them to specific behavioral features of addiction. Current research needs to understand the types of adaptations that underlie the particularly long-lived aspects of addiction, such as drug craving and relapse, and to identify specific genes that contribute to individual differences in vulnerability to addiction. Understanding the molecular and cellular basis of addictive states will lead to major changes in how addiction is viewed and ultimately treated.
The Impact of Aerosols on Solar Ultraviolet Radiation and Photochemical Smog
Authors: Dickerson R. R. , Kondragunta S. , Stenchikov G. , Civerolo K. L. , Doddridge B. G. , Holben B. N.
Published: July 2002

Photochemical smog, or ground-level ozone, has been the most recalcitrant of air pollution problems, but reductions in emissions of sulfur and hydrocarbons may yield unanticipated benefits in air quality. While sulfate and some organic aerosol particles scatter solar radiation back into space and can cool Earth's surface, they also change the actinic flux of ultraviolet (UV) radiation. Observations and numerical models show that UV-scattering particles in the boundary layer accelerate photochemical reactions and smog production, but UV-absorbing aerosols such as mineral dust and soot inhibit smog production. Results could have major implications for the control of air pollution.
Direct Measurement of the Current-Phase Relation of a Superfluid
3
He-B Weak Link
Authors: Backhaus S. , Pereverzev S. V. , Loshak A. , Davis J. C. , Packard R. E.
Published: July 2002

Direct measurements of the current-phase relation,
I
versus Δφ, for a weak link coupling two reservoirs of B-phase superfluid helium-3 (
3
He-B) were made over a wide range of temperatures. The weak link consists of a square array of 100-nanometer-diameter apertures. For temperatures
T
such that
T
/
T
c
≥ 0.6 (where
T
c
is the superfluid transition temperature),
I
∝ sin(Δφ). At lower temperatures,
I
(Δφ) approaches a straight line. Several remarkable phenomena heretofore inaccessible to superconducting Josephson junctions, including direct observation of quantum oscillations and continuous knowledge of Δφ, were also observed.
Hyaluronan Synthase of Chlorella Virus PBCV-1
Authors: DeAngelis Paul L. , Jing Wei , Graves Michael V. , Burbank Dwight E. , Van Etten James L.
Published: July 2002

Sequence analysis of the 330-kilobase genome of the virus PBCV-1 that infects a chlorella-like green algae revealed an open reading frame, A98R, with similarity to several hyaluronan synthases. Hyaluronan is an essential polysaccharide found in higher animals as well as in a few pathogenic bacteria. Expression of the
A98R
gene product in
Escherichia coli
indicated that the recombinant protein is an authentic hyaluronan synthase.
A98R
is expressed early in PBCV-1 infection and hyaluronan is produced in infected algae. These results demonstrate that a virus can encode an enzyme capable of synthesizing a carbohydrate polymer and that hyaluronan exists outside of animals and their pathogens.
Spike Synchronization and Rate Modulation Differentially Involved in Motor Cortical Function
Authors: Riehle Alexa , Grün Sonja , Diesmann Markus , Aertsen Ad
Published: July 2002

It is now commonly accepted that planning and execution of movements are based on distributed processing by neuronal populations in motor cortical areas. It is less clear, though, how these populations organize dynamically to cope with the momentary computational demands. Simultaneously recorded activities of neurons in the primary motor cortex of monkeys during performance of a delayed-pointing task exhibited context-dependent, rapid changes in the patterns of coincident action potentials. Accurate spike synchronization occurred in relation to external events (stimuli, movements) and was commonly accompanied by discharge rate modulations but without precise time locking of the spikes to these external events. Spike synchronization also occurred in relation to purely internal events (stimulus expectancy), where firing rate modulations were distinctly absent. These findings indicate that internally generated synchronization of individual spike discharges may subserve the cortical organization of cognitive motor processes.
NDR1
, a Pathogen-Induced Component Required for
Arabidopsis
Disease Resistance
Authors: Century Karen S. , Shapiro Allan D. , Repetti Peter P. , Dahlbeck Douglas , Holub Eric , Staskawicz Brian J.
Published: July 2002

Plant disease resistance (
R
) genes confer an ability to resist infection by pathogens expressing specific corresponding avirulence genes. In
Arabidopsis thaliana
, resistance to both bacterial and fungal pathogens, mediated by several
R
gene products, requires the
NDR1
gene. Positional cloning was used to isolate
NDR1
, which encodes a 660–base pair open reading frame. The predicted 219–amino acid sequence suggests that NDR1 may be associated with a membrane.
NDR1
expression is induced in response to pathogen challenge and may function to integrate various pathogen recognition signals.
Optical Amplification of Ligand-Receptor Binding Using Liquid Crystals
Authors: Gupta Vinay K. , Skaife Justin J. , Dubrovsky Timothy B. , Abbott Nicholas L.
Published: July 2002

Liquid crystals (LCs) were used to amplify and transduce receptor-mediated binding of proteins at surfaces into optical outputs. Spontaneously organized surfaces were designed so that protein molecules, upon binding to ligands hosted on these surfaces, triggered changes in the orientations of 1- to 20-micrometer-thick films of supported LCs, thus corresponding to a reorientation of ∼10
5
to 10
6
mesogens per protein. Binding-induced changes in the intensity of light transmitted through the LC were easily seen with the naked eye and could be further amplified by using surfaces designed so that protein-ligand recognition causes twisted nematic LCs to untwist. This approach to the detection of ligand-receptor binding does not require labeling of the analyte, does not require the use of electroanalytical apparatus, provides a spatial resolution of micrometers, and is sufficiently simple that it may find use in biochemical assays and imaging of spatially resolved chemical libraries.