bluuebunny/crossref_metadata_2025 huggingface dataset:
Reduced damage reactive ion etching process for fabrication of InGaAsP/InGaAs multiple quantum well ridge waveguide lasers
Authors: Qiu B. C. , Ooi B. S. , Bryce A. C. , Hicks S. E. , Wilkinson C. D. W. , De La Rue R. M. , Marsh J. H.
Published: July 2002

The damage introduced into an InGaAs/InGaAsP quantum well structure during CH4/H2 reactive ion etching (RIE) processes was measured, for plasma powers from 20 to 100 W, using low temperature photoluminescence. The damage depth profile is estimated to be around 12–70 nm after annealing at 500 °C for 60 s using a rapid thermal annealer. A reduced damage RIE process has been developed to fabricate InGaAs/InGaAsP multiquantum well ridge waveguide lasers. The performance of these lasers has been compared to that of lasers fabricated from the same epilayer using wet etching to form the ridge. The resultant threshold currents were essentially indistinguishable, being 44.5 and 43 mA, respectively, for dry and wet etched lasers with 500 μm long laser cavities.
Application of dichromated gelatin for dry developed lithographic techniques on GaAs
Authors: Villalvilla J. M. , Vallés-Abarca J. A. , Quintana J. A. , Crespo J.
Published: July 2002

Dichromated gelatin developed in an O2 plasma is used as a negative resist to transfer patterns onto GaAs. After reactive ion etching, the results show a 10:1 aspect ratio with no gelatin residue when 1 μm period structures are transferred.
Low-stress W/Cr films for SCALPEL® mask scattering layers
Authors: Windt David L.
Published: July 2002

I describe the development of low-stress W/Cr bilayer films, for use as SCALPEL® mask scattering layers. These films are produced by dc magnetron sputtering in argon, and consist of 25–50-nm-thick W layers deposited onto 5–10-nm-thick Cr layers. X-ray reflectance analysis is used to measure the thicknesses of the individual W and Cr layers with subangstrom precision; surface and interface roughnesses, film densities, and also the thickness of the tungsten–oxide overlayer which forms after exposure to air are determined by this technique as well. Film stress, which is measured using the wafer curvature technique, is controlled by adjusting the deposition conditions such that the Cr layers are in tension while the W layers are in compression (and thus have high density and low surface roughness), so that the net stress in the bilayer is balanced near zero. I present data that illustrates how the net stress in these films varies with argon pressure, background pressure (i.e., partial pressure of residual gases present in the vacuum chamber), and Cr layer thickness. I also show how the stress depends on the composition of the substrate: i.e., stresses measured in films deposited onto Si wafers are systematically higher (by several hundred MPa) than the stresses measured for the same films deposited onto silicon–nitride-coated Si wafers. I discuss the implication of these results with regard to the production of high-quality SCALPEL® mask blanks for sub 0.12 μm lithography.
Mesoscopic hemisphere arrays for use as resist in solid state structure fabrication
Authors: Green Mino , Tsuchiya Shin
Published: July 2002

The kinetics of formation of disordered arrays of hemispherically shaped islands of cesium chloride on an oxidized silicon wafer, starting from a deposited thin film of CsCl, has been investigated. The essential process step is the exposure of the CsCl thin film to water vapor. Transport of dissolved material in the adsorbed water layer occurs, driven by the size dependent solubility of CsCl. Growth rate is dominated by the kinetics of dissolution and deposition at the solid/solution boundary, rather than by interisland diffusion. The equipment and procedure are arranged so that constant humidity conditions prevail at every moment of hemisphere development. The process variables were: the effective thickness of the CsCl film, the relative humidity and the exposure time. The nature of the solid surface was found to be important and it was monitored using contact angle measurements of the water/solid interface: hydrophilic surfaces were used. The resulting arrays of hemispheres are characterized by a mean diameter, 〈d〉, a standard deviation, and a fractional surface coverage, F. Arrays from 〈d〉=450±145 Å at F=0.4 and 2050±330 Å at F=0.09, are reported.
Synthesis and modification of red oxide phosphors for low voltage excitation
Authors: Gwak J.-H. , Park S. H. , Jang J. E. , Lee S. J. , Jung J. E. , Kim J. M. , Jin Y. W. , Lee N. S. , Yi W. K. , Vorobyov V. A.
Published: July 2002

New red oxide phosphors Y2O3:Eu3+,Si4+ and (Y,Gd)2O3:Eu3+,Si4+,Bi3+ are synthesized by a coprecipitation method. Relative cathodoluminescence (CL) brightness at low voltages (⩽1 kV) is analyzed. At the low voltage excitation, luminance of the synthesized phosphors is higher than that of other commercially available red phosphors Y2O2S:Eu3+ and Y2O3:Eu3+. In particular, the difference of relative brightness between the commercially available phosphors and the synthesized Y2O3:Eu3+,Si4+ is larger at low voltages (⩽500 V) than at higher voltages. The synthesized (Y,Gd)2O3:Eu3+,Si4+,Bi3+ phosphor gives the same level of brightness as that of Y2O3:Eu3+,Si4+ at voltages greater than 500 V. (Y,Gd)2O3:Eu3+,Si4+,Bi3+ is coated with a conductive material SnO2:Eu3+. The coating of SnO2:Eu3+ shows a considerable improvement in brightness without a color shift. The excellent luminescence characteristics of (Y,Gd)2O3:Eu3+,Si4+,Bi3+ coated with SnO2:Eu3+, studied using field emitter arrays, suggests that our synthesized phosphor is practically applicable to field emission display devices.
High Geomagnetic Intensity During the Mid-Cretaceous from Thellier Analyses of Single Plagioclase Crystals
Authors: Tarduno John A. , Cottrell Rory D. , Smirnov Alexei V.
Published: July 2002

Recent numerical simulations have yielded the most efficient geodynamo, having the largest dipole intensity when reversal frequency is low. Reliable paleointensity data are limited but heretofore have suggested that reversal frequency and paleointensity are decoupled. We report data from 56 Thellier-Thellier experiments on plagioclase crystals separated from basalts of the Rajmahal Traps (113 to 116 million years old) of India that formed during the Cretaceous Normal Polarity Superchron. These data suggest a time-averaged paleomagnetic dipole moment of 12.5 ± 1.4 × 10
22
amperes per square meter, three times greater than mean Cenozoic and Early Cretaceous–Late Jurassic dipole moments when geomagnetic reversals were frequent. This result supports a correlation between intervals of low reversal frequency and high geomagnetic field strength.
Energy Gaps in "Metallic" Single-Walled Carbon Nanotubes
Authors: Ouyang Min , Huang Jin-Lin , Cheung Chin Li , Lieber Charles M.
Published: July 2002

Metallic single-walled carbon nanotubes have been proposed to be good one-dimensional conductors. However, the finite curvature of the graphene sheet that forms the nanotubes and the broken symmetry due to the local environment may modify their electronic properties. We used low-temperature atomically resolved scanning tunneling microscopy to investigate zigzag and armchair nanotubes, both thought to be metallic. “Metallic” zigzag nanotubes were found to have energy gaps with magnitudes that depend inversely on the square of the tube radius, whereas isolated armchair tubes do not have energy gaps. Additionally, armchair nanotubes packed in bundles have pseudogaps, which exhibit an inverse dependence on tube radius. These observed energy gaps suggest that most “metallic” single-walled nanotubes are not true metals, and they have implications for our understanding of the electronic properties and potential applications of carbon nanotubes.
Pot1, the Putative Telomere End-Binding Protein in Fission Yeast and Humans
Authors: Baumann Peter , Cech Thomas R.
Published: July 2002

Telomere proteins from ciliated protozoa bind to the single-stranded G-rich DNA extensions at the ends of macronuclear chromosomes. We have now identified homologous proteins in fission yeast and in humans. These Pot1 (
p
rotection
o
f
t
elomeres) proteins each bind the G-rich strand of their own telomeric repeat sequence, consistent with a direct role in protecting chromosome ends. Deletion of the fission yeast
pot1
+
gene has an immediate effect on chromosome stability, causing rapid loss of telomeric DNA and chromosome circularization. It now appears that the protein that caps the ends of chromosomes is widely dispersed throughout the eukaryotic kingdom.
Molecular Evolution of Protein Atomic Composition
Authors: Baudouin-Cornu Peggy , Surdin-Kerjan Yolande , Marlière Philippe , Thomas Dominique
Published: July 2002

Living organisms encounter various growth conditions in their habitats, raising the question of whether ecological fluctuations could alter biological macromolecules. The advent of complete genome sequences and the characterization of whole metabolic pathways allowed us to search for such ecological imprints. Significant correlations between atomic composition and metabolic function were found in sulfur- and carbon-assimilatory enzymes, which appear depleted in sulfur and carbon, respectively, in both the bacterium
Escherichia coli
and the eukaryote
Saccharomyces cerevisiae
. In addition to genetic instructions, genomic data thus also provide paleontological records of environmental nutrient availability and of metabolic costs.
Sexual Recombination and the Power of Natural Selection
Authors: Rice William R. , Chippindale Adam K.
Published: July 2002

Theory predicts that recombination will increase the effectiveness of natural selection. A
Drosophila melanogaster
model system was developed that increased experimental power with the use of high experimental replication, explicit tracking of individual genes, and high but natural levels of background selection. Each of 34 independent experiments traced the fate of a newly arisen mutation located within genome-wide, synthetic chromosomes that were propagated with or without recombination. An intrinsic advantage to recombination was demonstrated by the finding that the realized strength of selection on new mutations was markedly increased when recombination was present.
Rap1 GTPase Regulation of Adherens Junction Positioning and Cell Adhesion
Authors: Knox Andrea L. , Brown Nicholas H.
Published: July 2002

Cell-cell junctions are distributed evenly around the lateral circumference of cells within an epithelium. We find that the even distribution of adherens junctions is an active process that requires the small guanosine triphosphatase Rap1. Cells mutant for
Rap1
condensed their adherens junctions to one side of the cell. This disrupted normal epithelial cell behavior, and mutant cell clones dispersed into the surrounding wild-type tissue. Rap1 is enriched at adherens junctions, particularly between newly divided sister cells where it may reseal the adherens junction ring. The regulation of adherens junction positioning could play a role in cell mobility and cell division.
Functional MRI of Macaque Monkeys Performing a Cognitive Set-Shifting Task
Authors: Nakahara Kiyoshi , Hayashi Toshihiro , Konishi Seiki , Miyashita Yasushi
Published: July 2002

Functional brain organization of macaque monkeys and humans was directly compared by functional magnetic resonance imaging. Subjects of both species performed a modified Wisconsin Card Sorting Test that required behavioral flexibility in the form of cognitive set shifting. Equivalent visual stimuli and task sequence were used for the two species. We found transient activation related to cognitive set shifting in focal regions of prefrontal cortex in both monkeys and humans. These functional homologs were located in cytoarchitectonically equivalent regions in the posterior part of ventrolateral prefrontal cortex. This comparative imaging provides insights into the evolution of cognition in primates.
Hybridization and the Evolution of Reef Coral Diversity
Authors: Vollmer Steven V. , Palumbi Stephen R.
Published: July 2002

Hundreds of coral species coexist sympatrically on reefs, reproducing in mass-spawning events where hybridization appears common. In the Caribbean, DNA sequence data from all three sympatric
Acropora
corals show that mass spawning does not erode species barriers. Species
A. cervicornis
and
A. palmata
are distinct at two nuclear loci or share ancestral alleles. Morphotypes historically given the name
Acropora prolifera
are entirely F
1
hybrids of these two species, showing morphologies that depend on which species provides the egg for hybridization. Although selection limits the evolutionary potential of hybrids, F
1
individuals can reproduce asexually and form long-lived, potentially immortal hybrids with unique morphologies.
Genomic Sequence Information Should Be Released Immediately and Freely in the Public Domain
Authors: Bentley David R.
Published: July 2002

The author endorses the early release into the public domain of all genomic sequence data produced by sequencing centers. Such informal prerelease of data before the finishing stage would have many advantages for both research and commercial exploitation. The data would be of sufficiently high quality to be useful in biological and genetic studies, and restrictions on their early release would impede scientific progress. Free release of raw genomic sequence would lead to unimpeded competition among academic and commercial interests to create new therapeutic agents.
Laser Capture Microdissection
Authors: Emmert-Buck Michael R. , Bonner Robert F. , Smith Paul D. , Chuaqui Rodrigo F. , Zhuang Zhengping , Goldstein Seth R. , Weiss Rhonda A. , Liotta Lance A.
Published: July 2002

Laser capture microdissection (LCM) under direct microscopic visualization permits rapid one-step procurement of selected human cell populations from a section of complex, heterogeneous tissue. In this technique, a transparent thermoplastic film (ethylene vinyl acetate polymer) is applied to the surface of the tissue section on a standard glass histopathology slide; a carbon dioxide laser pulse then specifically activates the film above the cells of interest. Strong focal adhesion allows selective procurement of the targeted cells. Multiple examples of LCM transfer and tissue analysis, including polymerase chain reaction amplification of DNA and RNA, and enzyme recovery from transferred tissue are demonstrated.
An Internet Review: The Compleat Neuroscientist Scours the World Wide Web
Authors: Bloom Floyd E.
Published: July 2002

The World Wide Web provides a graphical interface that allows users to explore the multiple databases of information that are accessible on the Internet. In the field of neuroscience, several hundred sites contain potentially pertinent information. This article takes a critical look at those sites and offers recommendations to those seeking broad neuroscience resources as well as those desiring sites specialized for the developmental neurosciences.
Melanoma Cell Expression of Fas(Apo-1/CD95) Ligand: Implications for Tumor Immune Escape
Authors: Hahne M. , Rimoldi D. , Schröter M. , Romero P. , Schreier M. , French L. E. , Schneider P. , Bornand T. , Fontana A. , Lienard D. , Cerottini J.-C. , Tschopp J.
Published: July 2002

Malignant melanoma accounts for most of the increasing mortality from skin cancer. Melanoma cells were found to express Fas (also called Apo-1 or CD95) ligand (FasL). In metastatic lesions, Fas-expressing T cell infiltrates were proximal to FasL
+
tumor cells. In vitro, apoptosis of Fas-sensitive target cells occurred upon incubation with melanoma tumor cells; and in vivo, injection of FasL
+
mouse melanoma cells in mice led to rapid tumor formation. In contrast, tumorigenesis was delayed in Fas-deficient
lpr
mutant mice in which immune effector cells cannot be killed by FasL. Thus, FasL may contribute to the immune privilege of tumors.
Immunologic NO Synthase: Elevation in Severe AIDS Dementia and Induction by HIV-1 gp41
Authors: Adamson D. Cory , Wildemann Brigitte , Sasaki Masayuki , Glass Jonathan D. , McArthur Justin C. , Christov Vesselin I. , Dawson Ted M. , Dawson Valina L.
Published: July 2002

Indirect mechanisms are implicated in the pathogenesis of the dementia associated with human immunodeficiency virus-type 1 (HIV-1) infection. Proinflammatory molecules such as tumor necrosis factor α and eicosanoids are elevated in the central nervous system of patients with HIV-1-related dementia. Nitric oxide (NO) is a potential mediator of neuronal injury, because cytokines may activate the immunologic (type II) isoform of NO synthase (iNOS). The levels of iNOS in severe HIV-1-associated dementia coincided with increased expression of the HIV-1 coat protein gp41. Furthermore, gp41 induced iNOS in primary cultures of mixed rat neuronal and glial cells and killed neurons through a NO-dependent mechanism. Thus, gp41-induced NO formation may contribute to the severe cognitive dysfunction associated with HIV-1 infection.
Two Modulatory Effects of Attention That Mediate Object Categorization in Human Cortex
Authors: Rees Geraint , Frackowiak Richard , Frith Chris
Published: July 2002

Attentional modulation of cortical activity was examined by varying the rate of visual stimuli in object categorization tasks according to single and conjoined features. Activation of dorsolateral frontal cortex was independent of the stimulus presentation rate and elicited by the participant's attention to conjoined compared with single features. Several cortical regions showed attentionally modulated activity. In inferior temporal cortex, modulation was due to an additional bias signal underlying normal rate-correlated activity. In two other regions (premotor cortex and cerebellum), attention modified the correlation of activity and the stimulus presentation rate. Attentional effects in the human cortex are expressed by at least two physiologically distinct mechanisms acting on spatially distributed areas.
Optimality: From Neural Networks to Universal Grammar
Authors: Prince Alan , Smolensky Paul
Published: July 2002

Can concepts from the theory of neural computation contribute to formal theories of the mind? Recent research has explored the implications of one principle of neural computation, optimization, for the theory of grammar. Optimization over symbolic linguistic structures provides the core of a new grammatical architecture, optimality theory. The proposition that grammaticality equals optimality sheds light on a wide range of phenomena, from the gulf between production and comprehension in child language, to language learnability, to the fundamental questions of linguistic theory: What is it that the grammars of all languages share, and how may they differ?
Kaposi's Sarcoma-Associated Herpesvirus Infection of Bone Marrow Dendritic Cells from Multiple Myeloma Patients
Authors: Rettig M. B. , Ma H. J. , Vescio R. A. , Põld M. , Schiller G. , Belson D. , Savage A. , Nishikubo C. , Wu C. , Fraser J. , Said J. W. , Berenson J. R.
Published: July 2002

Kaposi's sarcoma–associated herpesvirus (KSHV) was found in the bone marrow dendritic cells of multiple myeloma patients but not in malignant plasma cells or bone marrow dendritic cells from normal individuals or patients with other malignancies. In addition the virus was detected in the bone marrow dendritic cells from two out of eight patients with monoclonal gammopathy of undetermined significance (MGUS), a precursor to myeloma. Viral interleukin-6, the human homolog of which is a growth factor for myeloma, was found to be transcribed in the myeloma bone marrow dendritic cells. KSHV may be required for transformation from MGUS to myeloma and perpetuate the growth of malignant plasma cells.
Simulated Increase of Hurricane Intensities in a CO
2
-Warmed Climate
Authors: Knutson Thomas R. , Tuleya Robert E. , Kurihara Yoshio
Published: July 2002

Hurricanes can inflict catastrophic property damage and loss of human life. Thus, it is important to determine how the character of these powerful storms could change in response to greenhouse gas–induced global warming. The impact of climate warming on hurricane intensities was investigated with a regional, high-resolution, hurricane prediction model. In a case study, 51 western Pacific storm cases under present-day climate conditions were compared with 51 storm cases under high-CO
2
conditions. More idealized experiments were also performed. The large-scale initial conditions were derived from a global climate model. For a sea surface temperature warming of about 2.2°C, the simulations yielded hurricanes that were more intense by 3 to 7 meters per second (5 to 12 percent) for wind speed and 7 to 20 millibars for central surface pressure.
Partial Hormone Resistance in Mice with Disruption of the Steroid Receptor Coactivator-1 (SRC-1) Gene
Authors: Xu Jianming , Qiu Yuhong , DeMayo Francesco J. , Tsai Sophia Y. , Tsai Ming-Jer , O'Malley Bert W.
Published: July 2002

The in vivo biological function of a steroid receptor coactivator was assessed in mice in which the SRC-1 gene was inactivated by gene targeting. Although in both sexes the homozygous mutants were viable and fertile, target organs such as uterus, prostate, testis, and mammary gland exhibited decreased growth and development in response to steroid hormones. Expression of RNA encoding TIF2, a member of the SRC-1 family, was increased in the SRC-1 null mutant, perhaps compensating partially for the loss of SRC-1 function in target tissues. The results indicate that SRC-1 mediates steroid hormone responses in vivo and that loss of its coactivator function results in partial resistance to hormone.
Structural Conservation in Prokaryotic and Eukaryotic Potassium Channels
Authors: MacKinnon Roderick , Cohen Steven L. , Kuo Anling , Lee Alice , Chait Brian T.
Published: July 2002

Toxins from scorpion venom interact with potassium channels. Resin-attached, mutant K
+
channels from
Streptomyces lividans
were used to screen venom from
Leiurus quinquestriatus hebraeus
, and the toxins that interacted with the channel were rapidly identified by mass spectrometry. One of the toxins, agitoxin2, was further studied by mutagenesis and radioligand binding. The results show that a prokaryotic K
+
channel has the same pore structure as eukaryotic K
+
channels. This structural conservation, through application of techniques presented here, offers a new approach for K
+
channel pharmacology.
Geochemical Evidence for a Comet Shower in the Late Eocene
Authors: Farley K. A. , Montanari A. , Shoemaker E. M. , Shoemaker C. S.
Published: July 2002

Analyses of pelagic limestones indicate that the flux of extraterrestrial helium-3 to Earth was increased for a 2.5-million year (My) period in the late Eocene. The enhancement began ∼1 My before and ended ∼1.5 My after the major impact events that produced the large Popigai and Chesapeake Bay craters ∼36 million years ago. The correlation between increased concentrations of helium-3, a tracer of fine-grained interplanetary dust, and large impacts indicates that the abundance of Earth-crossing objects and dustiness in the inner solar system were simultaneously but only briefly enhanced. These observations provide evidence for a comet shower triggered by an impulsive perturbation of the Oort cloud.
Helical Superstructures from Charged Poly(styrene)-Poly(isocyanodipeptide) Block Copolymers
Authors: Cornelissen Jeroen J. L. M. , Fischer Matthias , Sommerdijk Nico A. J. M. , Nolte Roeland J. M.
Published: July 2002

Amphiphilic block copolymers containing a poly(styrene) tail and a charged helical poly(isocyanide) headgroup derived from isocyano-
l
-alanine-
l
-alanine and isocyano-
l
-alanine-
l
-histidine were prepared. Analogous to low–molecular mass surfactants, these block copolymers self-assembled in aqueous systems to form micelles, vesicles, and bilayer aggregates. The morphology of these aggregates can be controlled by variation of the length of the poly(isocyanide) block, the pH, and the anion-headgroup interactions. The chirality of the macromolecules results in the formation of helical superstructures that have a helical sense opposite to that of the constituent block copolymers. The great variety of morphologies displayed by these block copolymers and the fact that they are easily accessible from poly(styrene) and different types of peptides open new opportunities for applications in the fields of life and materials sciences.
Compatibility of Rhenium in Garnet During Mantle Melting and Magma Genesis
Authors: Righter Kevin , Hauri Erik H.
Published: July 2002

Measurements of the partitioning of rhenium (Re) between garnet and silicate liquid from 1.5 to 2.0 gigapascals and 1250° to 1350°C show that Re is compatible in garnet. Oceanic island basalts (OIBs) have lower Re contents than mid-ocean ridge basalt, because garnet-bearing residues of deeper OIB melting will retain Re. Deep-mantle garnetite or eclogite may harbor the missing Re identified in crust-mantle mass balance calculations. Oceanic crust recycled into the upper mantle at subduction zones will retain high Re/Os (osmium) ratios and become enriched in radiogenic
187
Os. Recycled eclogite in a mantle source should be easily traced using Re abundances and Os isotopes.
Mixer
, a Homeobox Gene Required for Endoderm Development
Authors: Henry Gilbert L. , Melton Douglas A.
Published: July 2002

An expression cloning strategy in
Xenopus laevis
was used to isolate a homeobox-containing gene,
Mixer
, that can cause embryonic cells to form endoderm.
Mixer
transcripts are found specifically in the prospective endoderm of gastrula, which coincides with the time and place that endodermal cells become histologically distinct and irreversibly determined. Loss-of-function studies with a dominant inhibitory mutant demonstrate that
Mixer
activity is required for endoderm development. In particular, the expression of
Sox17
α and
Sox17
β, two previously identified endodermal determinants, require
Mixer
function. Together, these data suggest that
Mixer
is an embryonic transcription factor involved in specifying the endodermal germ layer.
"Inordinate Fondness" Explained: Why Are There So Many Beetles?
Authors: Farrell Brian D.
Published: July 2002

The phylogeny of the Phytophaga, the largest and oldest radiation of herbivorous beetles, was reconstructed from 115 complete DNA sequences for the 18
S
nuclear ribosomal subunit and from 212 morphological characters. The results of these analyses were used to interpret the role of angiosperms in beetle diversification. Jurassic fossils represent basal lineages that are still associated with conifers and cycads. Repeated origins of angiosperm-feeding beetle lineages are associated with enhanced rates of beetle diversification, indicating a series of adaptive radiations. Collectively, these radiations represent nearly half of the species in the order Coleoptera and a similar proportion of herbivorous insect species.
Fusion-Competent Vaccines: Broad Neutralization of Primary Isolates of HIV
Authors: LaCasse Rachel A. , Follis Kathryn E. , Trahey Meg , Scarborough John D. , Littman Dan R. , Nunberg Jack H.
Published: July 2002

Current recombinant human immunodeficiency virus (HIV) gp120 protein vaccine candidates are unable to elicit antibodies capable of neutralizing infectivity of primary isolates from patients. Here, “fusion-competent” HIV vaccine immunogens were generated that capture the transient envelope-CD4-coreceptor structures that arise during HIV binding and fusion. In a transgenic mouse immunization model, these formaldehyde-fixed whole-cell vaccines elicited antibodies capable of neutralizing infectivity of 23 of 24 primary HIV isolates from diverse geographic locations and genetic clades A to E. Development of these fusion-dependent immunogens may lead to a broadly effective HIV vaccine.
Nonproteolytic Neuroprotection by Human Recombinant Tissue Plasminogen Activator
Authors: Kim Yang-Hee , Park June-Hee , Hong Seung Hwan , Koh Jae-Young
Published: July 2002

Human recombinant tissue plasminogen activator (tPA) may benefit ischemic stroke patients by dissolving clots. However, independent of thrombolysis, tPA may also have deleterious effects on neurons by promoting excitotoxicity. Zinc neurotoxicity has been shown to be an additional key mechanism in brain injuries. Hence, if tPA affects zinc neurotoxicity, this may provide additional insights into its effect on neuronal death. Independent of its proteolytic action, tPA markedly attenuated zinc-induced cell death in cortical culture, and, when injected into cerebrospinal fluid, also reduced kainate seizure–induced hippocampal neuronal death in adult rats.
The Formation of Jupiter's Faint Rings
Authors: Burns Joseph A. , Showalter Mark R. , Hamilton Douglas P. , Nicholson Philip D. , Pater Imke de , Ockert-Bell Maureen E. , Thomas Peter C.
Published: July 2002

Observations by the Galileo spacecraft and the Keck telescope showed that Jupiter's outermost (gossamer) ring is actually two rings circumscribed by the orbits of the small satellites Amalthea and Thebe. The gossamer rings' unique morphology—especially the rectangular end profiles at the satellite's orbit and the enhanced intensities along the top and bottom edges of the rings—can be explained by collisional ejecta lost from the inclined satellites. The ejecta evolves inward under Poynting-Robertson drag. This mechanism may also explain the origin of Jupiter's main ring and suggests that faint rings may accompany all small inner satellites of the other jovian planets.
Helicobacter pylori
Virulence and Genetic Geography
Authors: Covacci Antonello , Telford John L. , Giudice Giuseppe Del , Parsonnet Julie , Rappuoli Rino
Published: July 2002

Isolated for the first time in 1982 from human gastric biopsy,
Helicobacter pylori
is responsible for gastritis, peptic ulcer, and gastric cancer. A pathogenicity island acquired by horizontal transfer, coding for a type IV secretion system, is a major determinant of virulence. The infection is now treated with antibiotics, and vaccines are in preparation. The geographic distribution suggests coevolution of man and
Helicobacter pylori
.
Enhanced Cortical Dopamine Output and Antipsychotic-like Effects of Raclopride by α
2
Adrenoceptor Blockade
Authors: Hertel Peter , Fagerquist Maria V. , Svensson Torgny H.
Published: July 2002

Clozapine exerts superior clinical efficacy and markedly enhances cortical dopamine output compared with classical antipsychotic drugs. Here the α
2
adrenoceptor antagonist idazoxan was administered to rats alone or in combination with the D
2/3
dopamine receptor antagonist raclopride. Dopamine efflux in the medial prefrontal cortex and conditioned avoidance responding were analyzed. Idazoxan selectively potentiated the cortical output of dopamine and augmented the suppression of conditioned avoidance responding induced by raclopride. These results challenge basic assumptions underlying the dopamine hypothesis of schizophrenia and provide insight into clozapine's mode of action.
A Biochemical Genomics Approach for Identifying Genes by the Activity of Their Products
Authors: Martzen Mark R. , McCraith Stephen M. , Spinelli Sherry L. , Torres Francy M. , Fields Stanley , Grayhack Elizabeth J. , Phizicky Eric M.
Published: July 2002

For the identification of yeast genes specifying biochemical activities, a genomic strategy that is rapid, sensitive, and widely applicable was developed with an array of 6144 individual yeast strains, each containing a different yeast open reading frame (ORF) fused to glutathione
S
-transferase (GST). For the identification of ORF-associated activities, strains were grown in defined pools, and GST-ORFs were purified. Then, pools were assayed for activities, and active pools were deconvoluted to identify the source strains. Three previously unknown ORF-associated activities were identified with this strategy: a cyclic phosphodiesterase that acts on adenosine diphosphate–ribose 1"-2" cyclic phosphate (Appr>p), an Appr-1"-p–processing activity, and a cytochrome c methyltransferase.
Specific Lipopolysaccharide Found in Cystic Fibrosis Airway
Pseudomonas aeruginosa
Authors: Ernst Robert K. , Yi Eugene C. , Guo Lin , Lim Kheng B. , Burns Jane L. , Hackett Murray , Miller Samuel I.
Published: July 2002

Cystic fibrosis (CF) patients develop chronic airway infections with
Pseudomonas aeruginosa
(PA).
Pseudomonas aeruginosa
synthesized lipopolysaccharide (LPS) with a variety of penta- and hexa-acylated lipid A structures under different environmental conditions. CF patient PA synthesized LPS with specific lipid A structures indicating unique recognition of the CF airway environment. CF-specific lipid A forms containing palmitate and aminoarabinose were associated with resistance to cationic antimicrobial peptides and increased inflammatory responses, indicating that they are likely to be involved in airway disease.
van der Waals Interactions in the Cl + HD Reaction
Authors: Skouteris Dimitris , Manolopoulos David E. , Bian Wensheng , Werner Hans-Joachim , Lai Lih-Huey , Liu Kopin
Published: July 2002

The van der Waals forces in the entrance valley of the Cl + HD reaction are shown here to play a decisive role in the reaction's dynamics. Exact quantum mechanical calculations of reactive scattering on a potential energy surface without Cl–HD van der Waals forces predict that the HCl and DCl products will be produced almost equally, whereas the same calculations on a new ab initio potential energy surface with van der Waals forces show a strong preference for the production of DCl. This preference is also seen in crossed molecular beam experiments on the reaction. The study of chemical reaction dynamics has now advanced to the stage where even comparatively weak van der Waals interactions can no longer be neglected in calculations of the potential energy surfaces of chemical reactions.
Modulation of Brain Reward Circuitry by Leptin
Authors: Fulton Stephanie , Woodside Barbara , Shizgal Peter
Published: July 2002

Leptin, a hormone secreted by fat cells, suppresses food intake and promotes weight loss. To assess the action of this hormone on brain reward circuitry, changes in the rewarding effect of lateral hypothalamic stimulation were measured after leptin administration. At five stimulation sites near the fornix, the effectiveness of the rewarding electrical stimulation was enhanced by chronic food restriction and attenuated by intracerebroventricular infusion of leptin. In contrast, the rewarding effect of stimulating neighboring sites was insensitive to chronic food restriction and was enhanced by leptin in three of four cases. These opposing effects of leptin may mirror complementary changes in the rewarding effects of feeding and of competing behaviors.
A Population of Murine γδ T Cells That Recognize an Inducible MHC Class Ib Molecule
Authors: Crowley Michael P. , Fahrer Aude M. , Baumgarth Nicole , Hampl Johannes , Gutgemann Ines , Teyton Luc , Chien Yueh-hsiu
Published: July 2002

Although γδ T cells are implicated in regulating immune responses, γδ T cell–ligand pairs that could mediate such regulatory functions have not been identified. Here, the expression of the major histocompatibility complex (MHC) class Ib T22 and the closely related T10 molecules is shown to be activation-induced, and they confer specificity to about 0.4% of the γδ T cells in normal mice. Thus, the increased expression of T22 and/or T10 might trigger immunoregulatory γδ T cells during immune responses. Furthermore, the fast on-rates and slow off-rates that characterize this receptor/ligand interaction would compensate for the low ligand stability and suggest a high threshold for γδ T cell activation.
Ambipolar Pentacene Field-Effect Transistors and Inverters
Authors: Schön J. H. , Berg S. , Kloc Ch. , Batlogg B.
Published: July 2002

Organic field-effect transistors based on pentacene single crystals, prepared with an amorphous aluminum oxide gate insulator, are capable of ambipolar operation and can be used for the preparation of complementary inverter circuits. The field-effect mobilities of carriers in these transistors increase from 2.7 and 1.7 square centimeters per volt per second at room temperature up to 1200 and 320 square centimeters per volt per second at low temperatures for hole and electron transport, respectively, following a power-law dependence. The possible simplification of the fabrication process of complementary logic circuits with these transistors, together with the high carrier mobilities, may be seen as another step toward applications of plastic electronics.
gridlock
, an HLH Gene Required for Assembly of the Aorta in Zebrafish
Authors: Zhong Tao P. , Rosenberg Michael , Mohideen Manzoor-Ali P. K. , Weinstein Brant , Fishman Mark C.
Published: July 2002

The first artery and vein of the vertebrate embryo assemble in the trunk by migration and coalescence of angioblasts to form endothelial tubes. The
gridlock
(
grl
) mutation in zebrafish selectively perturbs assembly of the artery (the aorta). Here it is shown that
grl
encodes a basic helix-loop-helix (bHLH) protein belonging to the Hairy/Enhancer of the split family of bHLH proteins. The
grl
gene is expressed in lateral plate mesoderm before vessel formation, and thereafter in the aorta and not in the vein. These results suggest that the arterial endothelial identity is established even before the onset of blood flow and implicate the
grl
gene in assignment of vessel-specific cell fate.
Sink or Swim: Strategies for Cost-Efficient Diving by Marine Mammals
Authors: Williams Terrie M. , Davis R. W. , Fuiman L. A. , Francis J. , Le B. J. , Boeuf  , Horning M. , Calambokidis J. , Croll D. A.
Published: July 2002

Locomotor activity by diving marine mammals is accomplished while breath-holding and often exceeds predicted aerobic capacities. Video sequences of freely diving seals and whales wearing submersible cameras reveal a behavioral strategy that improves energetic efficiency in these animals. Prolonged gliding (greater than 78% descent duration) occurred during dives exceeding 80 meters in depth. Gliding was attributed to buoyancy changes with lung compression at depth. By modifying locomotor patterns to take advantage of these physical changes, Weddell seals realized a 9.2 to 59.6% reduction in diving energetic costs. This energy-conserving strategy allows marine mammals to increase aerobic dive duration and achieve remarkable depths despite limited oxygen availability when submerged.
A Superconducting Field-Effect Switch
Authors: Schön J. H. , Kloc Ch. , Haddon R. C. , Batlogg B.
Published: July 2002

We report here on a novel realization of a field-effect device that allows switching between insulating and superconducting states, which is the widest possible variation of electrical properties of a material. We chose C
60
as the active material because of its low surface state density and observed superconductivity in alkali metal–doped C
60
. We induced three electrons per C
60
molecule in the topmost molecular layer of a crystal with the field-effect device, creating a superconducting switch operating up to 11 kelvin. An insulator was thereby transformed into a superconductor. This technique offers new opportunities for the study of superconductivity as a function of carrier concentration.
Alteration of Stimulus-Specific Guard Cell Calcium Oscillations and Stomatal Closing in
Arabidopsis det3
Mutant
Authors: Allen Gethyn J. , Chu Sarah P. , Schumacher Karin , Shimazaki Chad T. , Vafeados Dionne , Kemper Andrea , Hawke Scott D. , Tallman Gary , Tsien Roger Y. , Harper Jeffrey F. , Chory Joanne , Schroeder Julian I.
Published: July 2002

Cytosolic calcium oscillations control signaling in animal cells, whereas in plants their importance remains largely unknown. In wild-type
Arabidopsis
guard cells abscisic acid, oxidative stress, cold, and external calcium elicited cytosolic calcium oscillations of differing amplitudes and frequencies and induced stomatal closure. In guard cells of the V-ATPase mutant
det3
, external calcium and oxidative stress elicited prolonged calcium increases, which did not oscillate, and stomatal closure was abolished. Conversely, cold and abscisic acid elicited calcium oscillations in
det3
, and stomatal closure occurred normally
.
Moreover, in
det3
guard cells, experimentally imposing external calcium-induced oscillations rescued stomatal closure. These data provide genetic evidence that stimulus-specific calcium oscillations are necessary for stomatal closure.
Evidence for Coherent Proton Tunneling in a Hydrogen Bond Network
Authors: Horsewill Anthony J. , Jones Nicholas H. , Caciuffo Roberto
Published: July 2002

We observed coherent proton tunneling in the cyclic network of four hydrogen bonds in calix[4]arene. The tunneling frequency of 35 megahertz was revealed by a peak in the magnetic field dependence of the proton spin-lattice relaxation rate measured with field-cycling nuclear magnetic resonance in the solid state at temperatures below 80 kelvin. The amplitude of the coherent tunneling peak grows with temperature according to a Boltzmann law with energy
D
/
k
B
= (125 ± 10) kelvin (where

k
B

is Boltzmann's constant). The tunneling peak can be interpreted in the context of level crossings in the region where the tunneling frequency matches the proton Larmor frequency. The tunneling spectrum reveals fine structure that we attribute to coupling between the hydrogen bonds in the network. The characteristics of the tunneling peak are interpreted in the context of the potential energy surface experienced by the hydrogen atoms in the network.
Substitution of the Thioredoxin System for Glutathione Reductase in
Drosophila melanogaster
Authors: Kanzok Stefan M. , Fechner Anke , Bauer Holger , Ulschmid Julia K. , Müller Hans-Michael , Botella-Munoz José , Schneuwly Stephan , Schirmer R. Heiner , Becker Katja
Published: July 2002

The disulfide reducing enzymes glutathione reductase and thioredoxin reductase are highly conserved among bacteria, fungi, worms, and mammals. These proteins maintain intracellular redox homeostasis to protect the organism from oxidative damage. Here we demonstrate the absence of glutathione reductase in
Drosophila melanogaster
, identify a new type of thioredoxin reductase, and provide evidence that a thioredoxin system supports GSSG reduction. Our data suggest that antioxidant defense in
Drosophila
, and probably in related insects, differs fundamentally from that in other organisms.
Submicrometer Metallic Barcodes
Authors: Nicewarner-Peña Sheila R. , Freeman R. Griffith , Reiss Brian D. , He Lin , Peña David J. , Walton Ian D. , Cromer Remy , Keating Christine D. , Natan Michael J.
Published: July 2002

We synthesized multimetal microrods intrinsically encoded with submicrometer stripes. Complex striping patterns are readily prepared by sequential electrochemical deposition of metal ions into templates with uniformly sized pores. The differential reflectivity of adjacent stripes enables identification of the striping patterns by conventional light microscopy. This readout mechanism does not interfere with the use of fluorescence for detection of analytes bound to particles by affinity capture, as demonstrated by DNA and protein bioassays.
Pharmacokinetics of Tobramycin in Adults with Cystic Fibrosis: Implications for Once-Daily Administration
Authors: Beringer P. M. , Vinks A. A. T. M. M. , Jelliffe R. W. , Shapiro B. J.
Published: July 2002

Once-daily administration of aminoglycosides is routinely used in many institutions. However, comparative efficacy data for patients with cystic fibrosis (CF) are lacking. The purpose of the present study was to compare the predicted pharmacodynamic activity of tobramycin at 10 mg/kg of body weight/day administered every 24 h (q24h), q12h, and q8h. Pharmacokinetic (PK) data were derived from analysis of data on the drug concentration in sera from 60 adult CF patients. Individual maximum a posteriori probability Bayesian PK parameter values were used to construct serum concentration-versus-time curves and to determine various indices (peak concentration/MIC ratio [peak/MIC], area under the concentration-time curve/MIC ratio [AUC/MIC], and time that the concentration was less than the MIC [T<MIC]) for the three regimens described above. MICs of 1, 2, and 4 μg/ml forPseudomonas aeruginosawere assumed in the simulations. Irrespective of the MIC, significantly lower peak/MIC but shorterT<MIC were noted when regimens of q8h versus q12h (P< 0.001), q8h versus q24h (P< 0.001), and q12h versus q24h (P< 0.001) were compared. This analysis suggests that the potential benefit of achieving a greater peak/MIC with once-daily aminoglycoside administration may be offset by the significantly greaterT<MIC in CF patients compared with that achieved with multiple-daily-dosing regimens. Clinical trials are necessary to determine if once daily aminoglycoside administration is efficacious in the CF population before its routine use can be recommended.
Macrolide Resistance Genes in
Enterococcus
spp
Authors: Portillo Aránzazu , Ruiz-Larrea Fernanda , Zarazaga Myriam , Alonso Ana , Martinez Jose Luis , Torres Carmen
Published: July 2002

Seventy-eight isolates of different
Enterococcus
species (
E. faecalis
,
n
= 27;
E. faecium
,
n
= 23;
E. durans
,
n
= 8;
E. avium
,
n
= 6;
E. hirae
,
n
= 9;
E. gallinarum
,
n
= 3; and
E. casseliflavus
,
n
= 2) with a variety of erythromycin resistance phenotypes were examined for the presence of macrolide resistance genes (
ermA
,
ermB
,
ermC
,
ermTR
,
mefA/E
, and
msrA
). Positive PCR amplifications of
ermB
were obtained for 39 of 40 highly erythromycin-resistant
Enterococcus
isolates (MICs, >128 μg/ml) of different species; the remaining highly resistant
E. faecium
isolate was positive for PCR amplification of
ermA
but was negative for PCR amplification of the
ermB
and
ermC
genes. For all enterococcal strains for which erythromycin MICs were ≤32 μg/ml PCRs were negative for
erm
methylase genes. For all
E. faecium
isolates PCR amplified products of the expected size of 400 bp were obtained when
msrA
primers were used, with the results being independent of the erythromycin resistance phenotype. All the other enterococcal species gave negative results by
msrA
PCRs. Sequencing of the
msrA
PCR products from either erythromycin-susceptible, low-level-resistant, or highly resistant
E. faecium
strains showed that the amplicons did not correspond to the
msrA
gene described for
Staphylococcus epidermidis
but corresponded to a new putative efflux determinant, which showed 62% identity with the
msrA
gene at the DNA level and 72% similarity at the amino acid level. This new gene was named
msrC
.