bluuebunny/crossref_metadata_2025 huggingface dataset:
Dry development in an O2/SO2 plasma for sub-0.18 μm top layer imaging processes
Authors: Goethals A. M. , Van Roey F. , Sugihara T. , Van den hove L. , Vertommen J. , Klippert W.
Published: July 2002

Dry development using thin layer imaging (TLI) in either a bilayer approach or top surface imaging are currently investigated as viable alternatives to extend optical lithography to 0.13 μm and below. This article describes a systematic study of dry development in a LAM TCP9400SE inductively coupled plasma etcher for both a single layer TLI resist process and for a bilayer resist process using O2 and SO2/O2 chemistries. The effect of the important machine parameters such as TCP power, bias power, O2 and SO2 gas flows, on the process characteristics (etch rate, selectivity, uniformity, anisotropy) and on the lithographic performance (resolution, profile control, proximity) of a TSI process at 248 has been investigated by means of statistically designed experiments. As line edge roughness (LER) is a critical issue for TSI, the effect of the dry development conditions on LER have been quantified. The effect of temperature on profile control is also presented. In a second part of this article, these trends have been applied to the process optimization for a bilayer resist process at 193 nm. With an optimized dry development process, good profile control is demonstrated down to 0.12 μm L/S resolution.
Low-dose exposure technique for 100-nm-diam hole replication in x-ray lithography
Authors: Fujii K. , Tanaka Y. , Taguchi T. , Yamabe M. , Suzuki K. , Gomei Y. , Hisatsugu T.
Published: July 2002

In this article, we describe a new exposure technique for printing hole patterns with diameters of 100 nm or below in x-ray lithography. By using mask patterns approximately twice the size of the required resist patterns, 100-nm-diam holes can be replicated with doses less than those required to clear a large exposed area (D0) with a 20–30 μm gap. A 540-nm-thick UVII-HS resist was used for the exposure experiment. With a proximity gap of 20 μm, a 100-nm-diam hole was replicated with a 200-nm-diam mask pattern by exposing it with 0.56 D0 dose. Both the experimental and the simulation results indicated that this technique provides a higher resolution and a larger exposure latitude compared to normal-dose exposure. In terms of mask biasing, this technique corresponds to the mask bias optimization at doses below D0.
Subvolt turn-on voltage self-align gate diamond emitter fabricated by self-align-gate-sharpened molding technique
Authors: Kang W. P. , Wisitsora-at A. , Davidson J. L. , Howell M. , Kerns D. V. , Li Q. , Xu F.
Published: July 2002

A diamond field emitter diode array with subvolt turn-on voltage and high emission current is reported. The diamond field emitter diode array with self-align anode was fabricated using a new self-align technique, “self-align-gate-sharpened molding.” The emission current vs anode voltage of the self-align diamond emitter diode shows an extremely low turn-on voltage of 0.7 V, one of the lowest values reported in the field emission literatures. A high emission current of 4 μA at an anode voltage of less than 5 V can be obtained from a 2×2 array of diamond tips. The turn-on voltage is comparable to conventional p-n junction diode.
Arrays of ungated GaAs field emitters fabricated by wet or dry etching
Authors: Ducroquet F. , Kropfeld P. , Yaradou O. , Vanoverschelde A.
Published: July 2002

Dry and wet etching methods are used to fabricate arrays of ungated GaAs field emitters. Comparisons were made among tips, wedges, pillars and walls. Effects of the etching technique and subsequent deoxidation procedure on the GaAs surface are evaluated in terms of emitter geometry, uniformity, heating and integration. Moreover, the current emission capability of field emitter arrays is investigated. In particular, the influence of a thin surface oxide layer on the emission stability is observed. An extraction of geometrical parameters is attempted on the basis of a statistical examination of the emission characteristics and the validity of this approach is discussed.
Properties of nanometer-sized metal–semiconductor interfaces of GaAs and InP formed by an in situ electrochemical process
Authors: Hasegawa Hideki , Sato Taketomo , Kaneshiro Chinami
Published: July 2002

The properties of GaAs and InP Schottky diodes having nanometer-sized metal dots were investigated in order to clarify whether or not strong Fermi level pinning is an intrinsic property of the metal–semiconductor interface. Macroscopic Schottky diode samples having many nanometer-sized metal dots as well as single-dot Schottky diode samples were prepared by an in situ electrochemical process which consisted of pulsed anodic etching of the semiconductors followed by subsequent dc or pulsed cathodic deposition of the metal. Strong Fermi level pinning was not seen in the GaAs and InP macroscopic samples. The Schottky barrier height SBH values were strongly dependent on the metal work function and on the electrochemical processing conditions. Of particular interest, the difference in the dot size changed the SBH almost 340 meV in Pt/InP macroscopic Schottky diodes, indicating that Fermi level pinning disappears as the dot size is sufficiently reduced. X-ray photoelectron spectroscopy and Raman measurements indicated that these interfaces are oxide and stress free. Use of an atomic force microscope with a conductive probe allowed direct I–V measurements on single-dot samples. The metal work function and dot size dependencies of the SBHs in these samples were similar to those in macroscopic samples. Large ideality factors observed in the single-dot sample were explained in terms of environmental Fermi level pinning which produces a saddle point potential. The metal work function dependence of the SBHs measured as well as the relationship between the SBH and the ideality factor were both far from what was found in recent predictions based on the metal-induced gap state model. All the experimental results were consistently explained by the disorder-induced gap state model which asserts that strong Fermi level pinning is an extrinsic property of the metal–semiconductor interface.
Direct measurement of x-ray mask sidewall roughness and its contribution to the overall sidewall roughness of chemically amplified resist features
Authors: Reynolds Geoffrey W. , Taylor James W. , Brooks Cameron J.
Published: July 2002

As critical dimensions of resist features shrink, the sidewall roughness in resists may adversely affect the uniformity of the critical dimensions. Because x-ray lithography uses 1:1 size mapping of the mask pattern to the resist, it is plausible that any roughness or defects in the mask would transfer into the resist, contributing to the overall sidewall roughness of the resist feature. This article will report on our efforts to ascertain the contribution of mask sidewall roughness to the overall sidewall roughness in chemically amplified resists exposed by x-ray lithography by comparing the directly measured sidewall roughness of x-ray mask features to that of resist sidewall roughness patterned with the x-ray mask. For instance, Shipley UV5 exposed with a gold-absorber mask has a sidewall roughness on the order of 2.8 nm rms while resist exposed with a TaSi mask has a sidewall roughness on the order of 3.0 nm rms. Preliminary atomic force microscopy measurements to determine directly the mask sidewall roughness have been on engineering masks and not optimized production-quality masks. Preliminary sidewall roughness measurements performed on mask membranes with ∼0.5-μm-thick TaSi patterned with reactive ion etching indicate that sidewall roughness is on the order of 2.7 nm rms but may be dependent on the particular x-ray mask. Images show that the mask sidewall surface is comprised of ridges and grooves that span the depth of the absorber feature. Much of the higher frequency roughness that has been observed on resist sidewall surfaces is not as prevalent on the mask sidewall surface. The measured mask sidewall roughness of 2.7 nm rms is on the order of the sidewall roughness of UV5 exposed by x-ray lithography. The initial conclusion is that sidewall roughness of the resist used to pattern the mask may be the determining factor in the mask roughness unless improvements in the etching or fabrication process of the mask can reduce this figure.
Determination of the possible magnitude of the charging effect in a SCALPEL mask membrane
Authors: Mkrtchyan M. M. , Gasparyan A. S. , Mkhoyan K. A. , Liddle J. A. , Novembre A. E.
Published: July 2002

Previously, we theoretically investigated the charging of free standing dielectric thin films irradiated by 100 keV electrons and formulated kinetic equations describing the dynamic process [M. Mkrtchyan et al., Microelectron. Eng. 46, 233 (1999)]. It was shown that in the currently used SCALPEL® masks comprising a 1000-Å-thick amorphous SiNx film supported by a grillage of Si struts, the membrane charging could be significant and might have an adverse effect on the system performance. The membrane charging, sensitive to both the conductivity and the geometry of conductive path, can be regulated in a straightforward manner by tailoring both of them; for instance, by applying a top surface conductive layer (TSCL) with an appropriate thickness and doping level. Here we discuss the results obtained on the basis of our charging model modified to be applicable to the case of a SiNx membrane with a TSCL (e.g., a 10-nm-thick amorphous Si or poly-Si film doped by boron). The results presented demonstrate that this modification of the membrane is sufficient to avoid the adverse effect of the mask-membrane charging. The required structure can be generated simply by regulating the gas flows in the low-pressure chemical vapor deposition process to produce a thin final layer of a:Si or poly-Si which can be doped during or after deposition.
Depth-resolved electron-excited nanoscale-luminescence spectroscopy studies of defects near GaN/InGaN/GaN quantum wells
Authors: Levin T. M. , Jessen G. H. , Ponce F. A. , Brillson L. J.
Published: July 2002

We have measured the energies, relative intensities, and spatial distribution of deep level defect transitions near GaN/InGaN/GaN quantum well structures using low-energy electron-excited nanoscale-luminescence (LEEN) spectroscopy. Results obtained with electron excitation energies as low as 100 eV provide evidence on an incremental, 10–20 nm scale for defects within the GaN confinement layer, their variation with distance from the quantum well, and their electronic quality relative to the GaN substrate. The InGaN quantum well and GaN near-band-edge luminescence intensities exhibit strong variations as a function of excitation depth. Combined with a model of energy-dependent penetration, diffusion, and recombination, these variations indicate a value of 25–28 nm for the minority carrier diffusion length within the GaN confinement layer. Depth-dependent spectra also reveal the presence of cubic GaN phase formation at the InGaN/GaN substrate interface of a relatively In-rich quantum well structure. The contrast in LEEN features between structures of two different InGaN quantum well compositions demonstrates the effect of growth composition on local state formation.
Characterization of WF6/N2/H2 plasma enhanced chemical vapor deposited WxN films as barriers for Cu metallization
Authors: Li Hua , Jin Sing , Bender Hugo , Lanckmans Filip , Heyvaert Ilse , Maex Karen , Froyen Ludo
Published: July 2002

W x N is a promising candidate as a barrier material for Cu metallization. In this work, we report the characterization of WxN films deposited by plasma enhanced chemical vapor deposition using WF6/N2/H2 gas mixtures. The films are analyzed by Rutherford backscattering spectrometry, Auger electron spectroscopy, atomic force microscopy, x-ray diffraction, transmission electron microscopy, differential scanning calorimetry, and sheet resistance combined with thickness measurements. The diffusion barrier properties are studied by using Cu-gate metal–oxide–semiconductor capacitors and subjecting to either bias-temperature stress (BTS) of 2 MV/cm at 250 °C or thermal anneal up to 700 °C, and evaluated by capacitance–voltage measurement. It is found that the as-deposited films with W/N ratios from 2–19 have an “amorphous-like” nature. Study of the initial growth shows that the WxN films form by nucleation and grow through coalescence, and the films exhibit a granular structure. The transformation from the amorphous-like structure to crystalline phase(s) depends on the film stoichiometry. For the W/N∼2 films, there are two transformations starting at 497 and 578 °C (at a heating rate of 10 °C/min), corresponding to the formation of the W2N phase and to the further growth of the phase together with the formation of a small amount of α-W, respectively. The corresponding activation energies are 2.20 and 2.98 eV. For the W/N∼3 films, there is only one transformation (to the W2N+α-W) starting at 601 °C and with an activation energy of 2.94 eV. The resistivity is found to be insensitive to the film stoichiometry when the film has an amorphous-like nature, but shows a larger decrease for W richer films upon annealing at 500 °C. Moreover, for W/N∼2 and 3 films, the resistivities are largely determined by the film thickness, from about 200 μΩ cm for the 120 nm films to 310–350 μΩ cm for the 10 nm films. BTS results reveal that 10 nm of the W/N∼3 barrier shows no sign of degradation at least up to 105 h. By contrast, it is found that the initial barrier degradation occurs by annealing at 600 °C and above. This is probably due to the formation of α-W grains in the WxN barrier at these temperatures.
Real time resistometric depth monitoring in the focused ion beam
Authors: Latif A. , Booij W. E. , Durrell J. H. , Blamire M. G.
Published: July 2002

We have developed an in situ focused ion beam measurement technique, which has applications for the accurate, controlled, and reproducible removal of material for high aspect ratio nanometer scale cuts in tracks. This technique uses the resistance change of a track, as it is milled by ions, to monitor in real time the thickness and the end point. We have compared this technique with the thickness measurements by atomic force microscope for 1 μm wide cuts. The technique has an accuracy of a few nanometers.
Calculations of field emission from AlxGa1−xN as a function of stoichiometry
Authors: Chung M. S. , Cutler P. H. , Miskovsky N. M. , Kumar N.
Published: July 2002

The field emission current densities from AlxGa1−xN are theoretically calculated as a function of stoichiometry. The material parameters of AlxGa1−xN are obtained as weighted averages of those of AlN and GaN. The Poisson equation is first solved to obtain the energy band diagrams as a function of the composition x. The transmission coefficient through the tunneling barrier is numerically calculated using the fact that the Airy function is the exact solution of Schrödinger’s equation for a linear potential. By evaluating the energy-dependent integral on the band structure-dependent surface that is given by projecting the energy ellipsoid on the emission surface, we obtained the field electron energy distribution j(E). The calculated emission current j shows a strong dependence of the field emission on the stoichiometric composition x. The obtained Fowler–Nordheim plots exhibit different field dependent structures in the low and high field regimes. It is also found that the carrier concentration dependence of j is not pronounced for low fields but becomes significant for high fields.
Synthesis of high density arrays of nanoscaled gridded field emitters based on anodic alumina
Authors: Li Y. , Holland E. R. , Wilshaw P. R.
Published: July 2002

A technique for the fabrication of thin porous films of anodic alumina on a rigid glass substrate is reported. This nanoporous material is the starting point for the development of high density (108 cm−2) field emitter arrays (FEAs) that have already been proven using fragile alumina membranes. A merging of these two technologies is proposed, to facilitate the production of robust, high density, large area FEAs without recourse to step and repeat lithography at the micron scale.
Analysis of a pressure sensor using n-Si/nitrogen doped diamond cathodes
Authors: Nicolaescu Dan , Filip Valeriu , Itoh Junji , Okuyama Fumio
Published: July 2002

The purpose of this article is to analyze the operation of a pressure sensor in a diode configuration based on field emission from n-Si/nitrogen doped diamond cathodes. The device comprises a silicon membrane, which is the pressure sensing element. When the device emission current is kept constant, the membrane bending under external pressure modifies its operating voltage in a linear way. A new model has been developed to characterize field emission from n-Si/nitrogen doped diamond cathodes, showing good agreement with experimental data. The device sensitivity has been computed as function of both the silicon membrane and diamond layer parameters. Better sensor sensitivity is obtained for membranes with smaller dimensions and thinner, but the opposite trend allows to increase the measurable pressure range. The obtained modeling results can be further used for sensor design improvement.
Narrow photoluminescence linewidths from ensembles of self-assembled InGaAs quantum dots
Authors: Mirin R. P. , Silverman K. L. , Christensen D. H. , Roshko A.
Published: July 2002

Self-assembled InGaAs quantum dots have been grown using alternating molecular beams of In, Ga, and As2. The size distribution changes from bimodal to monodisperse as the quantum dots grow larger. Room-temperature photoluminescence experiments on ensembles of these quantum dots show that the emitted intensity remains high as the center wavelength changes from about 1130 to 1345 nm. The linewidths are less than 30 meV for all samples studied, with the narrowest measured linewidth being 18 meV at a peak emission energy of 930.1 meV (1333 nm).
Quantitative Measurement of Short-Range Chemical Bonding Forces
Authors: Lantz M. A. , Hug H. J. , Hoffmann R. , van Schendel P. J. A. , Kappenberger P. , Martin S. , Baratoff A. , Güntherodt H.-J.
Published: July 2002

We report direct force measurements of the formation of a chemical bond. The experiments were performed using a low-temperature atomic force microscope, a silicon tip, and a silicon (111) 7×7 surface. The measured site-dependent attractive short-range force, which attains a maximum value of 2.1 nanonewtons, is in good agreement with first-principles calculations of an incipient covalent bond in an analogous model system. The resolution was sufficient to distinguish differences in the interaction potential between inequivalent adatoms, demonstrating the ability of atomic force microscopy to provide quantitative, atomic-scale information on surface chemical reactivity.
Climate Response to Orbital Forcing Across the Oligocene-Miocene Boundary
Authors: Zachos James C. , Shackleton Nicholas J. , Revenaugh Justin S. , Pälike Heiko , Flower Benjamin P.
Published: July 2002

Spectral analyses of an uninterrupted 5.5-million-year (My)–long chronology of late Oligocene–early Miocene climate and ocean carbon chemistry from two deep-sea cores recovered in the western equatorial Atlantic reveal variance concentrated at all Milankovitch frequencies. Exceptional spectral power in climate is recorded at the 406-thousand-year (ky) period eccentricity band over a 3.4-million-year period [20 to 23.4 My ago (Ma)] as well as in the 125- and 95-ky bands over a 1.3-million-year period (21.7 to 23.0 Ma) of suspected low greenhouse gas levels. Moreover, a major transient glaciation at the epoch boundary (∼23 Ma), Mi-1, corresponds with a rare orbital congruence involving obliquity and eccentricity. The anomaly, which consists of low-amplitude variance in obliquity (a node) and a minimum in eccentricity, results in an extended period (∼200 ky) of low seasonality orbits favorable to ice-sheet expansion on Antarctica.
The Role of Atomic Ensembles in the Reactivity of Bimetallic Electrocatalysts
Authors: Maroun F. , Ozanam F. , Magnussen O. M. , Behm R. J.
Published: July 2002

Bimetallic electrodes are used in a number of electrochemical processes, but the role of particular arrangements of surface metal atoms (ensembles) has not been studied directly. We have evaluated the electrochemical/catalytic properties of defined atomic ensembles in atomically flat PdAu(111) electrodes with variable surface stoichiometry that were prepared by controlled electrodeposition on Au(111). These properties are derived from infrared spectroscopic and voltammetric data obtained for electrode surfaces for which the concentration and distribution of the respective metal atoms are determined in situ by atomic resolution scanning tunneling microscopy with chemical contrast. Palladium monomers are identified as the smallest ensemble (“critical ensemble”) for carbon monoxide adsorption and oxidation, whereas hydrogen adsorption requires at least palladium dimers.
Structure of Arp2/3 Complex in Its Activated State and in Actin Filament Branch Junctions
Authors: Volkmann Niels , Amann Kurt J. , Stoilova-McPhie Svetla , Egile Coumaran , Winter Dirk C. , Hazelwood Larnele , Heuser John E. , Li Rong , Pollard Thomas D. , Hanein Dorit
Published: July 2002

The seven-subunit Arp2/3 complex choreographs the formation of branched actin networks at the leading edge of migrating cells. When activated by Wiskott-Aldrich Syndrome protein (WASp), the Arp2/3 complex initiates actin filament branches from the sides of existing filaments. Electron cryomicroscopy and three-dimensional reconstruction of
Acanthamoeba castellanii
and
Saccharomyces cerevisiae
Arp2/3 complexes bound to the WASp carboxy-terminal domain reveal asymmetric, oblate ellipsoids. Image analysis of actin branches indicates that the complex binds the side of the mother filament, and Arp2 and Arp3 (for actin-related protein) are the first two subunits of the daughter filament. Comparison to the actin-free, WASp-activated complexes suggests that branch initiation involves large-scale structural rearrangements within Arp2/3.
Real-Time Single-Molecule Imaging of the Infection Pathway of an Adeno-Associated Virus
Authors: Seisenberger Georg , Ried Martin U. , Endreß Thomas , Büning Hildegard , Hallek Michael , Bräuchle Christoph
Published: July 2002

We describe a method, based on single-molecule imaging, that allows the real-time visualization of the infection pathway of single viruses in living cells, each labeled with only one fluorescent dye molecule. The tracking of single viruses removes ensemble averaging. Diffusion trajectories with high spatial and time resolution show various modes of motion of adeno-associated viruses (AAV) during their infection pathway into living HeLa cells: (i) consecutive virus touching at the cell surface and fast endocytosis; (ii) free and anomalous diffusion of the endosome and the virus in the cytoplasm and the nucleus; and (iii) directed motion by motor proteins in the cytoplasm and in nuclear tubular structures. The real-time visualization of the infection pathway of single AAVs shows a much faster infection than was generally observed so far.
Chromosome Dynamics in the Yeast Interphase Nucleus
Authors: Heun Patrick , Laroche Thierry , Shimada Kenji , Furrer Patrick , Gasser Susan M.
Published: July 2002

Little is known about the dynamics of chromosomes in interphase nuclei. By tagging four chromosomal regions with a green fluorescent protein fusion to
lac
repressor, we monitored the movement and subnuclear position of specific sites in the yeast genome, sampling at short time intervals. We found that early and late origins of replication are highly mobile in G
1
phase, frequently moving at or faster than 0.5 micrometers/10 seconds, in an energy-dependent fashion. The rapid diffusive movement of chromatin detected in G
1
becomes constrained in S phase through a mechanism dependent on active DNA replication. In contrast, telomeres and centromeres provide replication-independent constraint on chromatin movement in both G
1
and S phases.
Structural Basis for Selective Recognition of Oligosaccharides by DC-SIGN and DC-SIGNR
Authors: Feinberg Hadar , Mitchell Daniel A. , Drickamer Kurt , Weis William I.
Published: July 2002

Dendritic cell specific intracellular adhesion molecule–3 (ICAM-3) grabbing nonintegrin (DC-SIGN), a C-type lectin present on the surface of dendritic cells, mediates the initial interaction of dendritic cells with T cells by binding to ICAM-3. DC-SIGN and DC-SIGNR, a related receptor found on the endothelium of liver sinusoids, placental capillaries, and lymph nodes, bind to oligosaccharides that are present on the envelope of human immunodeficiency virus (HIV), an interaction that strongly promotes viral infection of T cells. Crystal structures of carbohydrate-recognition domains of DC-SIGN and of DC-SIGNR bound to oligosaccharide, in combination with binding studies, reveal that these receptors selectively recognize endogenous high-mannose oligosaccharides and may represent a new avenue for developing HIV prophylactics.
Divergent Regulation of Dihydrofolate Reductase Between Malaria Parasite and Human Host
Authors: Zhang Kai , Rathod Pradipsinh K.
Published: July 2002

For half a century, successful antifolate therapy against
Plasmodium falciparum
malaria has been attributed to host-parasite differences in drug binding to dihydrofolate reductase–thymidylate synthase (DHFR-TS). Selectivity may also arise through previously unappreciated differences in regulation of this drug target. The DHFR-TS of
Plasmodium
binds its cognate messenger RNA (mRNA) and inhibits its own translation. However, unlike translational regulation of DHFR or TS in humans, DHFR-TS mRNA binding is not coupled to enzyme active sites. Thus, antifolate treatment does not relieve translational inhibition and parasites cannot replenish dead enzyme.
Nonresonant Spectral Hole Burning in the Slow Dielectric Response of Supercooled Liquids
Authors: Schiener B. , Böhmer R. , Loidl A. , Chamberlin R. V.
Published: July 2002

Large-amplitude, low-frequency electric fields can be used to burn spectral holes in the dielectric response of supercooled propylene carbonate and glycerol. This ability to selectively modify the dielectric response establishes that the non-Debye behavior results from a distribution of relaxation times. Refilling of the spectral hole was consistent with a single recovery time that coincided with the peak in the distribution. Moreover, refilling occurred without significant broadening, which indicates negligible direct exchange between the degrees of freedom that responded to the field. Nonresonant spectral hole burning facilitates direct investigation of the intrinsic response of systems that exhibit nonexponential relaxation.
Association of Anxiety-Related Traits with a Polymorphism in the Serotonin Transporter Gene Regulatory Region
Authors: Lesch Klaus-Peter , Bengel Dietmar , Heils Armin , Sabol Sue Z. , Greenberg Benjamin D. , Petri Susanne , Benjamin Jonathan , Müller Clemens R. , Hamer Dean H. , Murphy Dennis L.
Published: July 2002

Transporter-facilitated uptake of serotonin (5-hydroxytryptamine or 5-HT) has been implicated in anxiety in humans and animal models and is the site of action of widely used uptake-inhibiting antidepressant and antianxiety drugs. Human 5-HT transporter (5-HTT) gene transcription is modulated by a common polymorphism in its upstream regulatory region. The short variant of the polymorphism reduces the transcriptional efficiency of the 5-HTT gene promoter, resulting in decreased 5-HTT expression and 5-HT uptake in lymphoblasts. Association studies in two independent samples totaling 505 individuals revealed that the 5-HTT polymorphism accounts for 3 to 4 percent of total variation and 7 to 9 percent of inherited variance in anxiety-related personality traits in individuals as well as sibships.
Abrupt Early to Mid-Holocene Climatic Transition Registered at the Equator and the Poles
Authors: Stager J. C. , Mayewski P. A.
Published: July 2002

Paleoclimatic records from equatorial East Africa, Antarctica, and Greenland reveal that atmospheric circulation changed abruptly at the early to mid-Holocene transition to full postglacial conditions. A climatic reorganization occurred at all three sites between 8200 and 7800 years ago that lasted 200 years or less and appears to have been related to abrupt transitions in both marine and terrestrial records around the world.
Pain Affect Encoded in Human Anterior Cingulate But Not Somatosensory Cortex
Authors: Rainville Pierre , Duncan Gary H. , Price Donald D. , Carrier Benoı̂t , Bushnell M. Catherine
Published: July 2002

Recent evidence demonstrating multiple regions of human cerebral cortex activated by pain has prompted speculation about their individual contributions to this complex experience. To differentiate cortical areas involved in pain affect, hypnotic suggestions were used to alter selectively the unpleasantness of noxious stimuli, without changing the perceived intensity. Positron emission tomography revealed significant changes in pain-evoked activity within anterior cingulate cortex, consistent with the encoding of perceived unpleasantness, whereas primary somatosensory cortex activation was unaltered. These findings provide direct experimental evidence in humans linking frontal-lobe limbic activity with pain affect, as originally suggested by early clinical lesion studies.
Abnormal Hippocampal Spatial Representations in αCaMKII
T286A
and CREB
αΔ−
Mice
Authors: Cho Yoon H. , Giese Karl P. , Tanila Heikki , Silva Alcino J. , Eichenbaum Howard
Published: July 2002

Hippocampal “place cells” fire selectively when an animal is in a specific location. The fine-tuning and stability of place cell firing was compared in two types of mutant mice with different long-term potentiation (LTP) and place learning impairments. Place cells from both mutants showed decreased spatial selectivity. Place cell stability was also deficient in both mutants and, consistent with the severities in their LTP and spatial learning deficits, was more affected in mice with a point mutation [threonine (T) at position 286 mutated to alanine (A)] in the α calmodulin kinase II (αCaMKII
T286A
) than in mice deficient for the α and Δ isoforms of adenosine 3′5′-monophosphate–responsive element binding proteins (CREB
αΔ
−
). Thus, LTP appears to be important for the fine tuning and stabilization of place cells, and these place cell properties may be necessary for spatial learning.
Detection of Atomic Deuterium in the Upper Atmosphere of Mars
Authors: Krasnopolsky Vladimir A. , Mumma Michael J. , Gladstone G. Randall
Published: July 2002

High-resolution spectroscopy of Mars' atmosphere with the Hubble Space Telescope revealed the deuterium Lyman α line at an intensity of 23 ± 6 rayleighs. This measured intensity corresponds to HD/H
2
= 1.5 ± 0.6 × 10
–4
, which is smaller by a factor of 11 than HDO/H
2
O. This indicates that fractionation of HD/H
2
relative to that of HDO/H
2
O is not kinetically controlled by the rates of formation and destruction of H
2
and HD but is thermodynamically controlled by the isotope exchange HD + H
2
O ↔ HDO + H
2
. Molecular hydrogen is strongly depleted in deuterium relative to water on Mars because of the very long lifetime of H
2
(1200 years). The derived isotope fractionation corresponds to an estimate of a planetwide reservoir of water ice about 5 meters thick that is exchangeable with the atmosphere.
Congenital Heart Disease Caused by Mutations in the Transcription Factor
NKX2-5
Authors: Schott Jean-Jacques , Benson D. Woodrow , Basson Craig T. , Pease William , Silberbach G. Michael , Moak Jeffrey P. , Maron Barry J. , Seidman Christine E. , Seidman J. G.
Published: July 2002

Mutations in the gene encoding the homeobox transcription factor NKX2-5 were found to cause nonsyndromic, human congenital heart disease. A dominant disease locus associated with cardiac malformations and atrioventricular conduction abnormalities was mapped to chromosome 5q35, where
NKX2-5
, a
Drosophila tinman
homolog, is located. Three different
NKX2-5
mutations were identified. Two are predicted to impair binding of NKX2-5 to target DNA, resulting in haploinsufficiency, and a third potentially augments target-DNA binding. These data indicate that NKX2-5 is important for regulation of septation during cardiac morphogenesis and for maturation and maintenance of atrioventricular node function throughout life.
High-Temperature Silicate Volcanism on Jupiter's Moon Io
Authors: McEwen A. S. , Keszthelyi L. , Spencer J. R. , Schubert G. , Matson D. L. , Lopes-Gautier R. , Klaasen K. P. , Johnson T. V. , Head J. W. , Geissler P. , Fagents S. , Davies A. G. , Carr M. H. , Breneman H. H. , Belton M. J. S.
Published: July 2002

Infrared wavelength observations of Io by the Galileo spacecraft show that at least 12 different vents are erupting lavas that are probably hotter than the highest temperature basaltic eruptions on Earth today. In at least one case, the eruption near Pillan Patera, two independent instruments on Galileo show that the lava temperature must have exceeded 1700 kelvin and may have reached 2000 kelvin. The most likely explanation is that these lavas are ultramafic (magnesium-rich) silicates, and this idea is supported by the tentative identification of magnesium-rich orthopyroxene in lava flows associated with these high-temperature hot spots.
A "Green" Route to Adipic Acid: Direct Oxidation of Cyclohexenes with 30 Percent Hydrogen Peroxide
Authors: Sato Kazuhiko , Aoki Masao , Noyori Ryoji
Published: July 2002

Currently, the industrial production of adipic acid uses nitric acid oxidation of cyclohexanol or a cyclohexanol/cyclohexanone mixture. The nitrous oxide emission from this process measurably contributes to global warming and ozone depletion. Therefore, the development of an adipic acid production process that is less damaging to the environment is an important subject in chemical research. Cyclohexene can now be oxidized directly to colorless crystalline adipic acid with aqueous 30 percent hydrogen peroxide under organic solvent- and halide-free conditions, which could provide an ideal solution to this serious problem.
The Effect of Alumina on the Electrical Conductivity of Silicate Perovskite
Authors: Xu Yousheng , McCammon Catherine , Poe Brent T.
Published: July 2002

Measurements of the electrical conductivity of silicate perovskite at 25 gigapascals and 1400° to 1600°C show that the conductivity of (Mg,Fe)SiO
3
perovskite containing 2.89 weight percent Al
2
O
3
is about 3.5 times greater than that of aluminum-free (Mg
0.915
Fe
0.085
)SiO
3
perovskite. The conduction mechanism in perovskite between 1400° and 1600°C is most likely by polarons, because Mössbauer studies show that the aluminum-bearing perovskite has about 3.5 times the amount of Fe
3+
as the aluminum-free sample. A conductivity-depth profile from 660 to 2900 kilometers based on aluminum-bearing perovskite is consistent with geophysical models.
Role for Cingulate Motor Area Cells in Voluntary Movement Selection Based on Reward
Authors: Shima Keisetsu , Tanji Jun
Published: July 2002

Most natural actions are chosen voluntarily from many possible choices. An action is often chosen based on the reward that it is expected to produce. What kind of cellular activity in which area of the cerebral cortex is involved in selecting an action according to the expected reward value? Results of an analysis in monkeys of cellular activity during the performance of reward-based motor selection and the effects of chemical inactivation are presented. We suggest that cells in the rostral cingulate motor area, one of the higher order motor areas in the cortex, play a part in processing the reward information for motor selection.
Pb Isotopic Variability in Melt Inclusions from Oceanic Island Basalts, Polynesia
Authors: Saal A. E. , Hart S. R. , Shimizu N. , Hauri E. H. , Layne G. D.
Published: July 2002

Previous studies have suggested that melting processes are responsible for the trace element variability observed in olivine-hosted basaltic melt inclusions. Melt inclusions from three individual lava samples (two from Mangaia, Cook Islands, and one from Tahaa, Society Islands) have heterogeneous Pb isotopic compositions, even though the erupted lavas are isotopically homogeneous. The range of Pb isotopic compositions from individual melt inclusions spans 50 percent of the worldwide range observed for ocean island basalts. The melt inclusion data can be explained by two-component mixing for each island. Our data imply that magmas with different isotopic compositions existed in the volcanic plumbing system before or during melt aggregation.
Oxidative Phosphorylation at the
fin de siècle
Authors: Saraste Matti
Published: July 2002

Mitochondria produce most of the energy in animal cells by a process called oxidative phosphorylation. Electrons are passed along a series of respiratory enzyme complexes located in the inner mitochondrial membrane, and the energy released by this electron transfer is used to pump protons across the membrane. The resultant electrochemical gradient enables another complex, adenosine 5′-triphosphate (ATP) synthase, to synthesize the energy carrier ATP. Important new mechanistic insights into oxidative phosphorylation have emerged from recent three-dimensional structural analyses of ATP synthase and two of the respiratory enzyme complexes, cytochrome bc
1
and cytochrome c oxidase. This work, and new enzymological studies of ATP synthase's unusual catalytic mechanism, are reviewed here.
Revisiting the Commons: Local Lessons, Global Challenges
Authors: Ostrom Elinor , Burger Joanna , Field Christopher B. , Norgaard Richard B. , Policansky David
Published: July 2002

In a seminal paper, Garrett Hardin argued in 1968 that users of a commons are caught in an inevitable process that leads to the destruction of the resources on which they depend. This article discusses new insights about such problems and the conditions most likely to favor sustainable uses of common-pool resources. Some of the most difficult challenges concern the management of large-scale resources that depend on international cooperation, such as fresh water in international basins or large marine ecosystems. Institutional diversity may be as important as biological diversity for our long-term survival.
Direct Experiments on the Ocean Disposal of Fossil Fuel CO
2
Authors: Brewer Peter G. , Friederich Gernot , Peltzer Edward T. , Orr Franklin M.
Published: July 2002

Field experiments were conducted to test ideas for fossil fuel carbon dioxide ocean disposal as a solid hydrate at depths ranging from 349 to 3627 meters and from 8° to 1.6°C. Hydrate formed instantly from the gas phase at 349 meters but then decomposed rapidly in ambient seawater. At 3627 meters, the seawater–carbon dioxide interface rose rapidly because of massive hydrate formation, forcing spillover of the liquid carbon dioxide from the container. A strong barrier between the liquid carbon dioxide and interaction with the sediments was observed. A pool of liquid carbon dioxide on the sea floor would expand in volume more than four times, forming hydrate, which will dissolve.
Identification of Both Shared and Distinct Proteins in the Major and Minor Spliceosomes
Authors: Will Cindy L. , Schneider Claudia , Reed Robin , Lührmann Reinhard
Published: July 2002

In metazoans, two distinct spliceosomes catalyzing pre–messenger RNA splicing have been identified. Here, the human U11/U12 small nuclear ribonucleoprotein (snRNP), a subunit of the minor (U12-dependent) spliceosome, was isolated. Twenty U11/U12 proteins were identified, including subsets unique to the minor spliceosome or common to both spliceosomes. Common proteins include four U2 snRNP polypeptides that constitute the essential splicing factor SF3b. A 35-kilodalton U11-associated protein homologous to the U1 snRNP 70K protein was also identified. These data provide fundamental information about proteins of the minor spliceosome and shed light on its evolutionary relationship to the major spliceosome.
On the Weakening Relationship Between the Indian Monsoon and ENSO
Authors: Kumar K. Krishna , Rajagopalan Balaji , Cane Mark A.
Published: July 2002

Analysis of the 140-year historical record suggests that the inverse relationship between the El Niño–Southern Oscillation (ENSO) and the Indian summer monsoon (weak monsoon arising from warm ENSO event) has broken down in recent decades. Two possible reasons emerge from the analyses. A southeastward shift in the Walker circulation anomalies associated with ENSO events may lead to a reduced subsidence over the Indian region, thus favoring normal monsoon conditions. Additionally, increased surface temperatures over Eurasia in winter and spring, which are a part of the midlatitude continental warming trend, may favor the enhanced land-ocean thermal gradient conducive to a strong monsoon. These observations raise the possibility that the Eurasian warming in recent decades helps to sustain the monsoon rainfall at a normal level despite strong ENSO events.
The Immunological Synapse: A Molecular Machine Controlling T Cell Activation
Authors: Grakoui Arash , Bromley Shannon K. , Sumen Cenk , Davis Mark M. , Shaw Andrey S. , Allen Paul M. , Dustin Michael L.
Published: July 2002

The specialized junction between a T lymphocyte and an antigen-presenting cell, the immunological synapse, consists of a central cluster of T cell receptors surrounded by a ring of adhesion molecules. Immunological synapse formation is now shown to be an active and dynamic mechanism that allows T cells to distinguish potential antigenic ligands. Initially, T cell receptor ligands were engaged in an outermost ring of the nascent synapse. Transport of these complexes into the central cluster was dependent on T cell receptor–ligand interaction kinetics. Finally, formation of a stable central cluster at the heart of the synapse was a determinative event for T cell proliferation.
Proteinaceous Pheromone Affecting Female Receptivity in a Terrestrial Salamander
Authors: Rollmann Stephanie M. , Houck Lynne D. , Feldhoff Richard C.
Published: July 2002

A 22-kilodalton protein was isolated from the submandibular (mental) gland of the male terrestrial salamander,
Plethodon jordani
(family: Plethodontidae). This proteinaceous pheromone, termed plethodontid receptivity factor (PRF), was experimentally delivered to the female during courtship and shown to increase female receptivity. In most plethodontid salamanders, ovulation occurs weeks or months after insemination, so the pheromone-induced change in receptivity is the only known function of PRF. The messenger RNAs corresponding to isoforms of PRF were transcribed into complementary DNA, cloned, sequenced, and shown to have homology with cytokines of the interleukin-6 family. Pheromone activity would represent a previously unrecognized function for cytokines.
Fault Slip Rates in the Modern New Madrid Seismic Zone
Authors: Mueller Karl , Champion Jocasta , Guccione Margaret , Kelson Keith
Published: July 2002

Structural and geomorphic analysis of late Holocene sediments in the Lake County region of the New Madrid seismic zone indicates that they are deformed by fault-related folding above the blind Reelfoot thrust fault. The widths of narrow kink bands exposed in trenches were used to model the Reelfoot scarp as a forelimb on a fault-bend fold; this, coupled with the age of folded sediment, yields a slip rate on the blind thrust of 6.1 ± 0.7 mm/year for the past 2300 ± 100 years. An alternative method used structural relief across the scarp and the estimated dip of the underlying blind thrust to calculate a slip rate of 4.8 ± 0.2 mm/year. Geometric relations suggest that the right lateral slip rate on the New Madrid seismic zone is 1.8 to 2.0 mm/year.
Regulation of Myosin Phosphatase by a Specific Interaction with cGMP- Dependent Protein Kinase Iα
Authors: Surks Howard K. , Mochizuki Naoki , Kasai Yasuyo , Georgescu Serban P. , Tang K. Mary , Ito Masaaki , Lincoln Thomas M. , Mendelsohn Michael E.
Published: July 2002

Contraction and relaxation of smooth muscle are regulated by myosin light-chain kinase and myosin phosphatase through phosphorylation and dephosphorylation of myosin light chains. Cyclic guanosine monophosphate (cGMP)–dependent protein kinase Iα (cGKIα) mediates physiologic relaxation of vascular smooth muscle in response to nitric oxide and cGMP. It is shown here that cGKIα is targeted to the smooth muscle cell contractile apparatus by a leucine zipper interaction with the myosin-binding subunit (MBS) of myosin phosphatase. Uncoupling of the cGKIα-MBS interaction prevents cGMP-dependent dephosphorylation of myosin light chain, demonstrating that this interaction is essential to the regulation of vascular smooth muscle cell tone.
Quality Control by DNA Repair
Authors: Lindahl Tomas , Wood Richard D.
Published: July 2002

Faithful maintenance of the genome is crucial to the individual and to species. DNA damage arises from both endogenous sources such as water and oxygen and exogenous sources such as sunlight and tobacco smoke. In human cells, base alterations are generally removed by excision repair pathways that counteract the mutagenic effects of DNA lesions. This serves to maintain the integrity of the genetic information, although not all of the pathways are absolutely error-free. In some cases, DNA damage is not repaired but is instead bypassed by specialized DNA polymerases.
Emerging Infectious Diseases of Wildlife-- Threats to Biodiversity and Human Health
Authors: Daszak Peter , Cunningham Andrew A. , Hyatt Alex D.
Published: July 2002

Emerging infectious diseases (EIDs) of free-living wild animals can be classified into three major groups on the basis of key epizootiological criteria: (i) EIDs associated with “spill-over” from domestic animals to wildlife populations living in proximity; (ii) EIDs related directly to human intervention, via host or parasite translocations; and (iii) EIDs with no overt human or domestic animal involvement. These phenomena have two major biological implications: first, many wildlife species are reservoirs of pathogens that threaten domestic animal and human health; second, wildlife EIDs pose a substantial threat to the conservation of global biodiversity.
CsBi
4
Te
6
: A High-Performance Thermoelectric Material for Low-Temperature Applications
Authors: Chung Duck-Young , Hogan Tim , Brazis Paul , Rocci-Lane Melissa , Kannewurf Carl , Bastea Marina , Uher Ctirad , Kanatzidis Mercouri G.
Published: July 2002

Thermoelectric (Peltier) heat pumps are capable of refrigerating solid or fluid objects, and unlike conventional vapor compressor systems, they can be miniaturized without loss of efficiency. More efficient thermoelectric materials need to be identified, especially for low-temperature applications in electronics and devices. The material CsBi
4
Te
6
has been synthesized and its properties have been studied. When doped appropriately, it exhibits a high thermoelectric figure of merit below room temperature (ZT
max
∼0.8 at 225 kelvin). At cryogenic temperatures, the thermoelectric properties of CsBi
4
Te
6
appear to match or exceed those of Bi
2–

x

Sb

x

Te
3–

y

Se

y

alloys.
Dispersive Multiplexing in Multimode Optical Fiber
Authors: Stuart Howard R.
Published: July 2002

Recently developed ideas in the field of wireless communications suggest that the presence of scattering can be used to enhance, rather than degrade, the total information capacity of a transmission system. This concept is applied to data transmission over multimode optical fiber, and the result is an optical multiplexing that can increase the capacity of such fiber. Experimental results demonstrate the feasibility of this approach. The technique may play an important role in future high-bandwidth local area networking applications.