bluuebunny/crossref_metadata_2025 huggingface dataset:
Total depletion of Hg° in the upper troposphere–lower stratosphere
Authors: Talbot R. , Mao H. , Scheuer E. , Dibb J. , Avery M.
Published: December 2007

Our current understanding of atmospheric mercury lacks fundamental details. Gas phase elemental mercury (Hg°) was measured aboard the NASA DC‐8 research aircraft during the Intercontinental Chemical Transport Experiment‐Phase B (INTEX‐B) conducted in spring 2006 over the North Pacific. Our data confirm efficient chemical cycling of Hg° in the tropopause region and show that it is strongly anti‐correlated with O3 there, yielding a tropospheric‐stratospheric mixing curve of ∼−0.20 ppqv Hg°/ppbv O3. In addition, we found frequent total depletion of Hg° in upper tropospheric (8–12 km) air masses impacted by stratospheric influence. When O3 mixing ratios were >300 ppbv, Hg° was rarely detected. It appears that in the tropopause and stratosphere Hg° is oxidized on the order of days followed by heterogeneous transformation to particulate mercury. These processes constitute an effective chemical sink for Hg° at the top of the troposphere, which may recycle mercury back to the gas phase as stratospheric aerosols are eventually dispersed into the troposphere.
High‐latitude forcing of regional aridification along the subtropical west coast of South America
Authors: Vuille Mathias , Milana Juan‐Pablo
Published: December 2007

Precipitation in north‐central (subtropical) Chile has been declining over the last 130 years. This is of concern in a region where precipitation is already low and which hosts considerable economic activity and a large population. Interannual variability of precipitation is primarily controlled by ENSO, but the reasons for the increasing aridity have remained elusive. Here we show that the negative trend in precipitation is not related to tropical Pacific forcing and that recent El Niño activity instead helped to alleviate the worst drought conditions. Based on data from 1979–2004 we further show that sea surface temperatures and sea‐ice concentration in the Amundsen Sea and associated blocking activity in the Bellingshausen Sea are related to winter precipitation in subtropical Chile, independently of ENSO. High latitude forcing from the Amundsen Sea region may provide an alternative explanation for the observed secular drying trend.
Energetic particle precipitation into the middle atmosphere triggered by a coronal mass ejection
Authors: Clilverd Mark A. , Rodger Craig J. , Millan Robyn M. , Sample John G. , Kokorowski Michael , McCarthy Michael P. , Ulich Thomas , Raita Tero , Kavanagh Andrew J. , Spanswick Emma
Published: December 2007

Precipitation of relativistic electrons into the atmosphere has been suggested as the primary loss mechanism for radiation belt electrons during large geomagnetic storms. Here we investigate the geographical spread of precipitation as a result of the arrival of a coronal mass ejection (CME) on 21 January 2005. In contrast to previous statistical studies we provide one of the first attempts to describe the geographic and temporal variability of energetic particle precipitation on a global scale using an array of instruments. We combine data from subionospheric VLF radio wave receivers, the high‐altitude Miniature Spectrometer (MINIS) balloons, riometers, and pulsation magnetometers during the first hour of the event. There were three distinct types of energetic electron precipitation observed, one globally, one on the dayside, and one on the nightside. The most extensively observed form of precipitation was a large burst starting when the CME arrived at the Earth, where electrons from the outer radiation belt were lost to the atmosphere over a large region of the Earth. On the dayside of the Earth (10–15 MLT) the CME produced a further series of precipitation bursts, while on the nightside dusk sector (∼20 MLT) a continuous precipitation event lasting ∼50 min was observed at 2.5 < L < 3.7 along with Pc 1–2 pulsations observed with a ground‐based magnetometer. These observations suggest that the generation of energetic electron precipitation at the inner edge of the outer radiation belt from electromagnetic ion cyclotron (EMIC) wave scattering into the loss cone is the most direct evidence to date connecting EMIC activity and energetic precipitation.
Reconstructing twentieth‐century sea surface temperature variability in the southwest Pacific: A replication study using multiple coral Sr/Ca records from New Caledonia
Authors: DeLong Kristine L. , Quinn Terrence M. , Taylor Frederick W.
Published: December 2007

Coral‐based climate reconstructions typically have not used multiple cores from a region to capture and replicate a climate signal largely because of concerns of coral conservation, analytical expense, and time constraints. Coral Sr/Ca reproducibility through the twentieth century was investigated using three intracolony and three intercolony coral records from the reefs offshore of Amédée Island, New Caledonia. Different sampling resolutions were examined in coral Sr/Ca (fortnightly and monthly) and δ18O (fortnightly, monthly, and seasonally) as well as similar scale subsampling of the daily in situ sea surface temperature (SST) record. The mean coral Sr/Ca, δ18O, and SST values do not change as a function of sampling resolution. The coral Sr/Ca signal is highly reproducible; the average absolute offset between coeval monthly Sr/Ca determinations between any two coral time series is 0.035 ± 0.026 mmol/mol (1σ) (∼0.65°C), which is less than twice the analytical precision of the coral Sr/Ca measurements. The stack average of the monthly coral Sr/Ca variations and monthly anomalies are significantly correlated with monthly in situ SST (1967–1992; r = −0.96 and −0.64, respectively; p < 0.05; and n = 302) and 1° grid monthly SST data product (1900–1999; r = −0.95 and −0.56, respectively; p < 0.05; and n = 1198). The coral Sr/Ca–SST reconstruction exhibits interannual and decadal‐ timescale fluctuations that exceed those observed in the gridded SST record, which may reflect true differences between SST at a shallow reef site and those averaged over a 1° grid box or inadequacies in the methodology used to create the gridded SST product when few observations are available. A warming trend of ∼0.6°C is observed in the twentieth century coral Sr/Ca–SST record.
Linear and nonlinear optical properties of some organoxenon derivatives
Authors: Avramopoulos Aggelos , Serrano-Andrés Luis , Li Jiabo , Reis Heribert , Papadopoulos Manthos G.
Published: December 2007

We employ a series of state-of-the-art computational techniques to study the effect of inserting one or more Xe atoms in HC2H and HC4H, on the linear and nonlinear optical (L&NLO) properties of the resulting compounds. It has been found that the inserted Xe has a great effect on the L&NLO properties of the organoxenon derivatives. We analyze the bonding in HXeC2H, and the change of the electronic structure, which is induced by inserting Xe, in order to rationalize the observed extraordinary L&NLO properties. The derivatives, which are of interest in this work, have been synthesized in a Xe matrix. Thus the effect of the local field (LF), due to the Xe environment, on the properties of HXeC2H, has also been computed. It has been found that the LF effect on some properties is significant. The calculations have been performed by employing a hierarchy of basis sets and the techniques MP2 and CCSD(T) for taking into account correlation. For the interpretation of the results we have employed the complete active space valence bond and CASSCF/CASPT2 methods.
Lattice relaxation mechanism of ZnO thin films grown on c-Al2O3 substrates by plasma-assisted molecular-beam epitaxy
Authors: Park S. H. , Hanada T. , Oh D. C. , Minegishi T. , Goto H. , Fujimoto G. , Park J. S. , Im I. H. , Chang J. H. , Cho M. W. , Yao T. , Inaba K.
Published: December 2007

We report on the lattice relaxation mechanism of ZnO films grown on c-Al2O3 substrates by plasma-assisted molecular-beam epitaxy. The lattice relaxation of ZnO films with various thicknesses up to 2000nm is investigated by using both in situ time-resolved reflection high energy electron diffraction observation during the initial growth and absolute lattice constant measurements (Bond method) for grown films. The residual strain in the films is explained in terms of lattice misfit relaxation (compression) at the growth temperature and thermal stress (tension) due to the difference of growth and measurement temperatures. In thick films (>1μm), the residual tensile strain begins to relax by bending and microcrack formation.
High-geometrical-resolution imaging of dislocations in SiC using monochromatic synchrotron topography
Authors: Huang X. R. , Black D. R. , Macrander A. T. , Maj J. , Chen Y. , Dudley M.
Published: December 2007

We demonstrate high-geometrical-resolution imaging of dislocations in 4H-SiC by monochromatic synchrotron topography (but still under the “integrated wave” condition). In back-reflection topographs, 1c screw dislocation images are “magnified” to appear as well-defined circular white spots, while basal plane dislocations with opposite edge Burgers vector components exhibit two distinct kinds of contrast features. All the dislocation images are precisely described by ray-tracing simulations. This imaging technique provides an accurate, comprehensive, and nondestructive characterization tool, which is needed by current SiC researchers is used for industrial applications. It also provides a simple picture for understanding the mechanisms underlying synchrotron diffraction imaging of defects.
Nanoscale imaging of permittivity in giant-κ CaCu3Ti4O12 grains
Authors: Fiorenza Patrick , Lo Nigro Raffaella , Raineri Vito , Toro Roberta G. , Catalano Maria Rita
Published: December 2007

The possibility to image the local permittivity in giant-κ dielectrics by scanning probe microscopy was demonstrated. In particular, the microstructure and the dielectric properties of CaCu3Ti4O12 (CCTO) films grown on (001) LaAlO3 substrates were studied. CCTO amorphous layers obtained by metal-organic chemical vapor deposition have been crystallized by subsequent rapid thermal treatments at 1100 °C. X-ray diffraction measurements demonstrated the growth of CCTO and CaTiO3 phases. As a novelty, large square CCTO grains (a few microns) were formed with a very high permittivity. The local impedance modulus, phase, and morphology were simultaneously acquired, and the local permittivity (around 8000 at 90 kHz) of each isolated CCTO grain was calculated.
Coupled phase transformation, chemical decomposition, and deformation in plastic-bonded explosive: Models
Authors: Levitas Valery I. , Henson Bryan F. , Smilowitz Laura B. , Zerkle David K. , Asay Blaine W.
Published: December 2007

A continuum thermomechanochemical model of the behavior of a plastic-bonded explosive (PBX) 9501 formulation consisting of the energetic crystal octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) embedded in a polymeric binder is developed. Our main focus is on the study of the β↔δ phase transformations (PTs) in crystalline HMX under a complex pressure-temperature path. To reproduce the pressure-temperature path, in particular during heating of PBX inside of a rigid cylinder, the β↔δ PTs in HMX are coupled to chemical decomposition of the HMX and binder leading to gas formation, gas leaking from the cylinder, elastic, thermal, and transformational straining as well as straining due to mass loss. A fully physically based thermodynamic and kinetic model of the β↔δ PT in HMX crystal is developed. It is based on a suggested nucleation mechanism via melt mediated nanocluster transformation and the recently revealed growth mechanism via internal stress-induced virtual melting. During the nucleation, nanosize clusters of the β phase dissolve in a molten binder and transform diffusionally into δ phase clusters. During the interface propagation, internal stresses induced by transformation strain cause the melting of the stressed δ phase much below (120 K) the melting temperature and its immediate resolidification into the unstressed δ phase. These mechanisms explain numerous puzzles of HMX polymorphism and result in overall transformation kinetics that is in good agreement with experiments. Simple phenomenological equations for kinetics of chemical decomposition of the HMX and the binder are in good correspondence with experiments as well. A continuum deformation model is developed in two steps. The geometrically linear (small strain) theory is used to prove that the internal stresses and macroscopic shear stresses are negligible. Then a large strain theory is developed under hydrostatic loading. The developed continuum thermomechanochemical model is applied in the accompanying paper [V. I. Levitas, B. F. Henson, L. B. Smilowitz, D. K. Zerkle, and B. W. Asay, J. Appl. Phys. (submitted)] to modeling the heating of PBX inside of a rigid cylinder.
Thermodynamic properties of Cu3(CO3)2(OH)2 and the spin-1/2 distorted diamond Heisenberg chain
Authors: Li Yan-Chao
Published: December 2007

The thermodynamic properties of the spin-1/2 diamond quantum Heisenberg chain model have been investigated by means of the transfer matrix renormalization group (TMRG) method. Considering different crystal structures, by changing the interactions among different spins and the external magnetic fields, we first investigate the magnetic susceptibility, magnetization, and specific heat of the distorted diamond chain as a model of ferrimagnetic spin systems. The susceptibility and the specific heat show different features for different ferromagnetic (F) and antiferromagnetic (AF) interactions and different magnetic fields. A 1/3 magnetization plateau is observed at low temperature in a magnetization curve. Then, we discuss the theoretical mechanism of the double-peak structure of the magnetic susceptibility and the three-peak structure of the specific heat of the compound Cu3(CO3)2(OH)2, on which an elegant measurement was performed by Kikuchi et al. [Phys. Rev. Lett. 94, 227201 (2005)]. Our computed results are consistent with the main characteristics of the experimental data. Meanwhile, we find that the double-peak structure of susceptibility can be found in several different kinds of spin interactions in the diamond chain. Moreover, a three-peak behavior is observed in the TMRG results of magnetic susceptibility. In addition, we perform calculations relevant for some experiments and explain the characteristics of these materials.
High power impulse magnetron sputtering: Current-voltage-time characteristics indicate the onset of sustained self-sputtering
Authors: Anders André , Andersson Joakim , Ehiasarian Arutiun
Published: December 2007

The commonly used current-voltage characteristics are found inadequate for describing the pulsed nature of the high power impulse magnetron sputtering (HIPIMS) discharge; rather, the description needs to be expanded to current-voltage-time characteristics for each initial gas pressure. Using different target materials (Cu, Ti, Nb, C, W, Al, and Cr) and a pulsed constant-voltage supply, it is shown that the HIPIMS discharges typically exhibit an initial pressure dependent current peak followed by a second phase that is power and material dependent. This suggests that the initial phase of a HIPIMS discharge pulse is dominated by gas ions, whereas the later phase has a strong contribution from self-sputtering. For some materials, the discharge switches into a mode of sustained self-sputtering. The very large differences between materials cannot be ascribed to the different sputter yields but they indicate that generation and trapping of secondary electrons play a major role for current-voltage-time characteristics. In particular, it is argued that the sustained self-sputtering phase is associated with the generation of multiply charged ions because only they can cause potential emission of secondary electrons, whereas the yield caused by singly charged metal ions is negligibly small.
Fourier transform photoabsorption spectroscopy based on scanning tunneling microscopy
Authors: Naruse Nobuyasu , Mera Yutaka , Fukuzawa Yo , Nakamura Yoshiaki , Ichikawa Masakazu , Maeda Koji
Published: December 2007

A scheme of photoabsorption spectroscopy (PAS) based on scanning tunneling microscopy (STM) applicable to semiconductors has been devised to circumvent experimental difficulties inherent in STM-PAS measurements so far conducted in the conventional lock-in detection scheme. The present scheme uses multiplexed lights from an interferometer for spectroscopic lights and the modulated current flowing through the STM tip for the signal from which the photoabsorption spectrum is deduced by Fourier transformation. The technique under an optimized condition has been applied to Si samples deposited with epitaxially grown Ge1−xSnx nanodots, which proved the spatial resolution of a few nanometers.
Model calculation for enhancement factor of a gated field emission nanotube
Authors: Lei D. , Zeng L. Y. , Wang W. B. , Liang J. Q.
Published: December 2007

The field enhancement factor of gated nanotube with opened top was analytically calculated by the electrostatic method. The effect of geometrical parameters of the device on their field enhancement factor was investigated, including the gate-hole radius, gate-anode distance, and nanotube radius. The theoretical analysis shows that the enhancement factor increases greatly with the decrease of gate-hole radius. However, if the gate voltage is zero, the factor increases with the increase of gate-hole radius, and finally reaches a constant, which increases with the increase of nanotube length L. The enhancement factor β gets larger when the nanotube radius gets smaller. As the gate-anode distance d2 is finite, the β will decrease with the increase of d2. If the d2 is infinite, the effect of gate-anode distance on β can be ignored. All the results of theoretical calculation can provide useful information in the fabrication and design of the gated nanotube cold cathode for field emission display panels and other nanoscale triode devices.
High-contrast readout of superconducting qubits beyond the single-shot resolution limit
Authors: Lisenfeld J. , Lukashenko A. , Ustinov A. V.
Published: December 2007

The states of superconducting quantum bits, as the Josephson phase qubits and flux qubits, are distinguished by magnetic flux generated by a persistent current in a superconducting loop. As the readout circuit contributes decoherence, its coupling to the qubit should be made as weak as possible. We demonstrate a method to maximize the measurement contrast of the two qubit states, thus allowing to significantly decrease the coupling to the readout. This technique is promising for multiqubit circuits since it allows to read out the states of several qubits by using a single readout circuit.
Spatially resolved pump-probe second harmonic generation study of multilayer semiconductor heterostructures
Authors: Glinka Y. D. , Tolk N. H. , Liu X. , Sasaki Y. , Furdyna J. K.
Published: December 2007

The transient electric-field-induced second harmonic generation change (TEFISHGC) signals from GaAs∕GaSb∕InAs heterostructures measured in pump-probe configuration have been applied to monitor the interfacial electric fields arising from the charge separation of pump-induced carriers at the interfaces. The total intensity of the TEFISHGC signal is determined by the interference of contributions from both of the heterointerfaces. By changing the photon energy of the laser light over the GaAs absorption edge, the depth spatial resolution can be achieved allowing the ultrafast dynamics of interfacial electric field at each of the interfaces to be monitored separately.
Templated fabrication of large area subwavelength antireflection gratings on silicon
Authors: Sun Chih-Hung , Min Wei-Lun , Linn Nicholas C. , Jiang Peng , Jiang Bin
Published: December 2007

We report a cheap and scalable bottom-up technique for fabricating wafer-scale, subwavelength-structured antireflection coatings on single-crystalline silicon substrates. Spin-coated monolayer colloidal crystals are utilized as shadow masks to generate metallic nanohole arrays. Inverted pyramid arrays in silicon can then be templated against nanoholes by anisotropic wet etching. The resulting subwavelength gratings greatly suppress specular reflection at normal incidence. The reflection spectra for flat silicon and the templated gratings at long wavelengths agree well with the simulated results using a rigorous coupled wave analysis model. These subwavelength gratings are of great technological importance in crystalline silicon solar cells.
Effects of chemical stability of platinum/lead zirconate titanate and iridium oxide/lead zirconate titanate interfaces on ferroelectric thin film switching reliability
Authors: Chen Ye , McIntyre Paul C.
Published: December 2007

We report a comparative study focusing on characterization of the ferroelectric film/top electrode interface and electrical measurements, for nominally identical Pb(Zr,Ti)O3 (PZT) films with either Pt or IrO2 top electrodes. We find that the superior reliability and polarization switching behavior of capacitors with IrO2 top electrodes are associated with the inert nature of lead present near the PZT film surface during top electrode processing. In contrast, lead near the PZT surface reacted with the Pt at the film/Pt-top-electrode interface, possibly creating a stable PbxPt1−x phase, and this reaction appeared to cause thickening of a nonferroelectric layer at the PZT/electrode interface.
Substrate engineering for high-performance surface-channel III-V metal-oxide-semiconductor field-effect transistors
Authors: Xuan Yi , Ye Peide D. , Shen Tian
Published: December 2007

High-performance inversion-type enhancement-mode n-channel In0.65Ga0.35As metal-oxide-semiconductor field-effect transistors (MOSFETs) with atomic-layer-deposited Al2O3 as gate dielectric are demonstrated. A 0.5μm gate-length MOSFET with an Al2O3 gate oxide thickness of 10nm shows a gate leakage current less than 5×10−6A∕cm2 at 4V gate bias, a threshold voltage of 0.40V, a maximum drain current of 670mA∕mm, and transconductance of 230mS∕mm at drain voltage of 2V. More importantly, a model is proposed to ascribe this 80% improvement of device performance from In0.53Ga0.47As MOSFETs mainly to lowering the energy level difference between the charge neutrality level and conduction band minimum for In0.65Ga0.35As. The right substrate or channel engineering is the main reason for the high performance of the devices besides the high-quality oxide-semiconductor interface.
The Relationship between Search Efficiency and Crowding
Authors: Gheri Carolina , Morgan Michael J , Solomon Joshua A
Published: December 2007

The role of target salience in crowding has remained controversial largely because salience usually escapes objective measurement. Here we address this problem using search efficiency as a measure of target salience. In separate experiments observers determined whether parafoveal arrays of vertical Gabor patterns contained targets having a unique colour, a unique direction of motion, and a unique temporal frequency. We analysed search efficiency in the conventional manner using reaction-time gradients (in seconds per item). We also considered accuracy gradients (in percent-correct per item). Crowding is typically quantified by comparing the acuity for a target within an array to the acuity for a target presented alone. We measured orientation acuity for determining whether a slightly tilted target was clockwise or anticlockwise of vertical. Targets with a unique colour or direction of motion were found to pop out, ie (with one exception) reaction-time and accuracy gradients were insignificantly different from zero. Acuity for these targets was significantly greater than acuity for targets whose neighbours had the same colour and direction of motion. Manipulation of temporal frequency produced a wide range of search efficiencies. For three of four observers we found a linear relationship between acuity and the accuracy gradient, shallow gradients being associated with high acuity. In general, we find that crowding is weakened when observers can find a parafoveally presented target quickly and accurately.
Seeing beyond the Target: Environmental Context Affects Distance Perception
Authors: Witt Jessica K , Stefanucci Jeanine K , Riener Cedar R , Proffitt Dennis R
Published: December 2007

It is commonly assumed that perceived distance in full-cue, ecologically valid environments is redundantly specified and approximately veridical. However, recent research has called this assumption into question by demonstrating that distance perception varies in different types of environments even under full-cue viewing conditions. We report five experiments that demonstrate an effect of environmental context on perceived distance. We measured perceived distance in two types of environments (indoors and outdoors) with two types of measures (perceptual matching and blindwalking). We found effects of environmental context for both egocentric and exocentric distances. Across conditions, within individual experiments, all viewer-to-target depth-related variables were kept constant. The differences in perceived distance must therefore be explained by variations in the space beyond the target.
dsAAV type 2-mediated gene transfer of MORS196A-EGFP into spinal cord as a pain management paradigm
Authors: Chen S. L. , Ma H. I. , Han J. M. , Tao P. L. , Law P. Y. , Loh H. H.
Published: December 2007

We previously reported that mutations in the μ-opioid receptor (MOR), S196L or S196A, rendered MOR responsive to the opioid antagonist naloxone without altering the agonist phenotype. Subsequently, a mouse strain carrying the S196A mutation exhibited
in vivo
naloxone antinociceptive activity without the development of tolerance. In this study we investigated the possibility of combining the
in vivo
site-directed delivery of MORS196A and systemic naloxone administration as a paradigm for pain management. Double-stranded adenoassociated virus type 2 (dsAAV2) was used to deliver MORS196A-EGFP by injecting the virus into the spinal cord (S2/S3) dorsal horn region of ICR mice. MORS196A-EGFP fluorescence colocalized with some calcitonin gene-related peptide and neuron-specific protein immunoreactivity in the superficial layers of the dorsal horn 1 week after injection and lasted for at least 6 months. In mice injected with the mutant receptor, morphine induced similar antinociceptive responses and tolerance development or precipitated withdrawal symptoms and reward effects, similar to those in the control mice (saline injected into the spinal cord). Conversely, in the dsAAV2-injected mice, naloxone produced antinociceptive effects at the spinal level but not at the supraspinal level, whereas naloxone had no measurable effect on the control mice. Furthermore, the chronic administration of naloxone to mice injected with dsAAV2-MORS196A-EGFP did not induce tolerance, dependence, or reward responses. Thus, our current approach to activate a mutant receptor, but not the endogenous receptor, with an opioid antagonist represents an alternative to the use of traditional opioid agonists for pain management.
The hidden structure of overimitation
Authors: Lyons Derek E. , Young Andrew G. , Keil Frank C.
Published: December 2007

Young children are surprisingly judicious imitators, but there are also times when their reproduction of others' actions appears strikingly illogical. For example, children who observe an adult inefficiently operating a novel object frequently engage in what we termoverimitation, persistently reproducing the adult's unnecessary actions. Although children readily overimitate irrelevant actions that even chimpanzees ignore, this curious effect has previously attracted little interest; it has been assumed that children overimitate not for theoretically significant reasons, but rather as a purely social exercise. In this paper, however, we challenge this view, presenting evidence that overimitation reflects a more fundamental cognitive process. We show that children who observe an adult intentionally manipulating a novel object have a strong tendency to encode all of the adult's actions as causally meaningful, implicitly revising their causal understanding of the object accordingly. This automatic causal encoding process allows children to rapidly calibrate their causal beliefs about even the most opaque physical systems, but it also carries a cost. When some of the adult's purposeful actions are unnecessary—even transparently so—children are highly prone to mis-encoding them as causally significant. The resulting distortions in children's causal beliefs are the true cause of overimitation, a fact that makes the effect remarkably resistant to extinction. Despite countervailing task demands, time pressure, and even direct warnings, children are frequently unable to avoid reproducing the adult's irrelevant actions because they have already incorporated them into their representation of the target object's causal structure.
Dramatic increase in naïve T cell turnover is linked to loss of naïve T cells from old primates
Authors: Čičin-Šain Luka , Messaoudi Ilhem , Park Byung , Currier Noreen , Planer Shannon , Fischer Miranda , Tackitt Shane , Nikolich-Žugich Dragana , Legasse Alfred , Axthelm Michael K. , Picker Louis J. , Mori Motomi , Nikolich-Žugich Janko
Published: December 2007

The loss of naïve T cells is a hallmark of immune aging. Although thymic involution is a primary driver of this naïve T cell loss, less is known about the contribution of other mechanisms to the depletion of naïve T cells in aging primates. We examined the role of homeostatic cycling and proliferative expansion in different T cell subsets of aging rhesus macaques (RM). BrdU incorporation and the expression of the G1-M marker Ki-67 were elevated in peripheral naïve CD4 and even more markedly in the naïve CD8 T cells of old, but not young adult, RM. Proliferating naïve cells did not accumulate in old animals. Rather, the relative size of the naïve CD8 T cell compartment correlated inversely to its proliferation rate. Likewise, T cell receptor diversity decreased in individuals with elevated naïve CD8 T cell proliferation. This apparent contradiction was explained by a significant increase in turnover concomitant with the naïve pool loss. The turnover increased exponentially when the naïve CD8 T cell pool decreased below 4% of total blood CD8 cells. These results link the shrinking naïve T cell pool with a dramatic increase in homeostatic turnover, which has the potential to exacerbate the progressive exhaustion of the naïve pool and constrict the T cell repertoire. Thus, homeostatic T cell proliferation exhibits temporal antagonistic pleiotropy, being beneficial to T cell maintenance in adulthood but detrimental to the long-term T cell maintenance in aging individuals.
Comparison of a Semipermeable Dressing Bonded to an Absorbent Pad and a Semipermeable Dressing Over a Separate Gauze Pad for Containment of Vaccinia Virus at the Vaccination Site
Authors: Savona Michael R. , Cruz Wilfred P. Dela , Thornton Jennifer A. , Danaher Patrick J.
Published: December 2007

Objective.

To compare the ability of 2 types of dressings to contain vaccinia virus after smallpox vaccination.

Design.

Prospective, nonrandomized trial.

Setting.

The smallpox vaccination clinic in a medium-sized military hospital.

Participants.

Ninety-seven active-duty military members who received smallpox vaccination in accordance with US Department of Defense and Centers for Disease Control and Prevention guidelines.

Methods.

The first 40 participants enrolled were instructed to cover their vaccination sites with a semipermeable membrane placed over a separate gauze pad, and the subsequent 57 participants were given a semipermeable membrane bonded to an absorbent pad. Swab samples of the external surface of the dressing were collected 7 and 21 days after vaccination. Real-time quantitative polymerase chain reaction was used to detect vaccinia DNA in the samples.

Results.

The rate of vaccinia DNA detection was significantly higher for samples obtained from vaccinees who were using the separate gauze and semipermeable membrane, compared with the vacinees who were using the gauze-impregnated semipermeable membrane (22% vs 2.2%;P= .008; odds ratio, 12.3 [95% confidence interval, 1.4-567.4]).

Conclusion.

A gauze-impregnated semipermeable membrane more effectively reduced viral passage to the external surface of the dressing than did a semipermeable membrane placed over a separate gauze pad. Routine use of such dressings following smallpox vaccination might reduce the incidence of autoinoculation and secondary transmission.
Staphylococcus aureusColonization Among Healthcare Workers at a Tertiary Care Hospital
Authors: Johnston Cecilia P. , Stokes Amy K. , Ross Tracy , Cai Mian , Carroll Karen C. , Cosgrove Sara E. , Perl Trish M.
Published: December 2007

We describe the epidemiology ofStaphylococcus aureuscolonization among 200 healthcare workers. The prevalence ofS. aureuswas 28%, and the prevalence of methicillin-resistantS. aureus(MRSA) was 2%. The incidence of MRSA colonization was extremely low. This study suggests that the risk of MRSA transmission to healthcare workers is low in a hospital where MRSA is endemic.
Prospective Study of Nosocomial Transmission of Hepatitis C in a Swedish Gastroenterology Unit
Authors: Verbaan Hans , Molnegren Vilma , Pentmo Inez , Rubin Lena , Widell Anders
Published: December 2007

A prospective study of incident hepatitis C in 515 gastroenterology patients was conducted by follow-up sampling at 3-6 months after admission to the gastroenterology unit to test for antibodies to hepatitis C virus and for hepatitis C virus RNA. Universal precautions were implemented, and the use of multidose vials had been banned in this unit. Despite 5,964 exposure–days for several risk factors associated with nosocomial hepatitis C virus transmission, no incident case of hepatitis C occurred.
Rfold: an exact algorithm for computing local base pairing probabilities
Authors: Kiryu Hisanori , Kin Taishin , Asai Kiyoshi
Published: December 2007

Motivation: Base pairing probability matrices have been frequently used for the analyses of structural RNA sequences. Recently, there has been a growing need for computing these probabilities for long DNA sequences by constraining the maximal span of base pairs to a limited value. However, none of the existing programs can exactly compute the base pairing probabilities associated with the energy model of secondary structures under such a constraint.

Results: We present an algorithm that exactly computes the base pairing probabilities associated with the energy model under the constraint on the maximal span W of base pairs. The complexity of our algorithm is given by in time and in memory, where N is the sequence length. We show that our algorithm has a higher sensitivity to the true base pairs as compared to that of RNAplfold. We also present an algorithm that predicts a mutually consistent set of local secondary structures by maximizing the expected accuracy function. The comparison of the local secondary structure predictions with those of RNALfold indicates that our algorithm is more accurate. Our algorithms are implemented in the software named ‘Rfold.’

Availability: The C++ source code of the Rfold software and the test dataset used in this study are available at http://www.ncrna.org/software/Rfold/

Contact:  kiryu-h@aist.go.jp

Supplementary information: Supplementary data are available at Bioinformatics online.
Characterization of Natural and Induced Variation in the LOV1 Gene, a CC-NB-LRR Gene Conferring Victorin Sensitivity and Disease Susceptibility in Arabidopsis
Authors: Sweat Teresa A. , Lorang Jennifer M. , Bakker Erica G. , Wolpert Thomas J.
Published: December 2007

The fungus Cochliobolus victoriae, the causal agent of Victoria blight, produces a compound called victorin that is required for pathogenicity of the fungus. Victorin alone reproduces disease symptoms on sensitive plants. Victorin sensitivity and susceptibility to C. victoriae were originally described on oats but have since been identified on Arabidopsis thaliana. Victorin sensitivity and disease susceptibility in Arabidopsis are conferred by LOV1, a coiled-coil-nucleotide-binding-leucine-rich repeat (CC-NB-LRR) protein. We sequenced the LOV1 gene from 59 victorin-insensitive mutants and found that the spectrum of mutations causing LOV1 loss of function was similar to that found to cause loss of function of RPM1, a CC-NB-LRR resistance protein. Also, many of the mutated residues in LOV1 are in conserved motifs required for resistance protein function. These data indicate that LOV1 may have a mechanism of action similar to resistance proteins. Victorin sensitivity was found to be the prevalent phenotype in a survey of 30 Arabidopsis ecotypes, and we found very little genetic variation among LOV1 alleles. As selection would not be expected to preserve a functional LOV1 gene to confer victorin sensitivity and disease susceptibility, we propose that LOV1 may function as a resistance gene to a naturally-occurring pathogen of Arabidopsis.
The Arabidopsis Gain-of-Function Mutant ssi4 Requires RAR1 and SGT1b Differentially for Defense Activation and Morphological Alterations
Authors: Zhou Fasong , Mosher Stephen , Tian Miaoying , Sassi Giovanna , Parker Jane , Klessig Daniel F.
Published: December 2007

A gain-of-function mutation in resistance (R) gene SSI4 causes constitutive activation of defense responses, spontaneous necrotic lesion formation, enhanced resistance against virulent pathogens, and a severe dwarf phenotype. Genetic analysis revealed that ssi4-induced H2O2 accumulation and spontaneous cell death require RAR1, whereas ssi4-mediated stunting is dependent on SGT1b. By contrast, both RAR1 and SGT1b are required in a genetically additive manner for ssi4-induced disease resistance, SA accumulation, and lesion formation after pathogen infection. These data point to cooperative yet distinct functions of RAR1 and SGT1b in responses conditioned by a deregulated nucleotide-binding leucine-rich repeat protein. We also found that RAR1 and SGT1b together contribute to basal resistance because an ssi4 rar1 sgt1b triple mutant exhibited enhanced susceptibility to virulent pathogen infection compared with wild-type SSI4 plants. All ssi4-induced phenotypes were suppressed when plants were grown at 22°C under high relative humidity. However, low temperature (16°C) triggered ssi4-mediated cell death via an RAR1-dependent pathway even in the presence of high humidity. Thus, multiple environmental factors impact on ssi4 signaling, as has been observed for other constitutive defense mutants and R gene-triggered pathways.
Distinct Mechanisms Govern the Dosage-Dependent and Developmentally Regulated Resistance Conferred by the Maize Hm2 Gene
Authors: Chintamanani Satya , Multani Dilbag S. , Ruess Holly , Johal Gurmukh S.
Published: December 2007

The maize Hm2 gene provides protection against the leaf spot and ear mold disease caused by Cochliobolus carbonum race 1 (CCR1). In this regard, it is similar to Hm1, the better-known disease resistance gene of the maize–CCR1 pathosystem. However, in contrast to Hm1, which provides completely dominant resistance at all stages of plant development, Hm2-conferred resistance is only partially dominant and becomes fully effective only at maturity. To investigate why Hm2 behaves in this manner, we cloned it on the basis of its homology to Hm1. As expected, Hm2 is a duplicate of Hm1, although the protein it encodes is grossly truncated compared with HM1. The efficacy of Hm2 in conferring resistance improves gradually over time, changing from having little or no impact in seedling tissues to providing complete immunity at anthesis. The developmentally specified phenotype of Hm2 is not dictated transcriptionally, because the expression level of the gene, whether occurring constitutively or undergoing substantial and transient induction in response to infection, does not change with plant age. In contrast, however, the Hm2 transcript is much more abundant in plants homozygous for this gene compared with plants that contain only one copy of the gene, suggesting a transcriptional basis for the dosage-dependent nature of Hm2. Thus, different mechanisms seem to underlie the developmentally programmed versus the partially dominant resistance phenotype of Hm2.
African elephants have expectations about the locations of out-of-sight family members
Authors: Bates Lucy A , Sayialel Katito N , Njiraini Norah W , Poole Joyce H , Moss Cynthia J , Byrne Richard W
Published: December 2007

Monitoring the location of conspecifics may be important to social mammals. Here, we use an expectancy-violation paradigm to test the ability of African elephants (Loxodonta africana) to keep track of their social companions from olfactory cues. We presented elephants with samples of earth mixed with urine from female conspecifics that were either kin or unrelated to them, and either unexpected or highly predictable at that location. From behavioural measurements of the elephants' reactions, we show that African elephants can recognize up to 17 females and possibly up to 30 family members from cues present in the urine–earth mix, and that they keep track of the location of these individuals in relation to themselves.
Marrying women 15 years younger maximized men's evolutionary fitness in historical Sami
Authors: Helle Samuli , Lummaa Virpi , Jokela Jukka
Published: December 2007

Most men marry younger women. This has been attributed to men selecting young women due to their high reproductive value and women preferring older men due to their wealth and high social status. Such mate preferences have been suggested to be adaptive, but despite a flourishing number of studies on the mate selection patterns themselves, little is still known of their actual fitness consequences. We examined how the age difference between spouses who married only once affected their lifetime reproductive success in historical monogamous Sami populations. We found that men maximized their fitness by marrying women approximately 15 years younger and vice versa. However, most couples failed to marry optimally. Only 10% of marriages fell within the optimal parental age difference, suggesting that cultural and ecological constraints for maximizing fitness were considerable. Those who succeeded in marrying optimally were the most preferred partners: young women and old men. Our findings indicate that, in Sami, parental age difference was under natural and sexual selection, as suggested by evolutionary theory.
The effect of stimuli that isolate S-cones on early saccades and the gap effect
Authors: Anderson A.J , Carpenter R.H.S
Published: December 2007

Disappearance of the fixation spot before the appearance of a peripheral target typically reduces average saccadic reaction times (the gap effect) and may also produce a separate population of early or express saccades. The superior colliculus (SC) is generally believed to be critically involved in generating both effects. As the direct sensory input to the SC does not encode colour information, to determine whether this input was critical in generating the gap effect or express saccades we used coloured targets which this pathway cannot distinguish. Our observers still made early saccades to colour-defined targets, but these were anticipations in response to the offset of the non-coloured fixation target. We also show that a gap effect still occurs when either the fixation target or the peripheral target is colour defined, suggesting that direct sensory input to the SC is not required and that information about the location of colour-defined targets is abstracted prior to processing within the SC.
Smeared-Property Models for Shock-Impact Reliability of Area-Array Packages
Authors: Lall Pradeep , Panchagade Dhananjay , Liu Yueli , Johnson Wayne , Suhling Jeff
Published: December 2007

Portable electronics is subjected to extreme accelerations in shock and drop impact. Product development cycle times and the cost constraints often restrict the number of design variations tested for drop robustness prior to identification of the final configuration. Simulation models capable of predicting transient dynamics can provide valuable insight into the design reliability under shock environments. In this study, explicit finite-element models have been used to study the transient dynamics of printed circuit boards during drop from 6ft. Methodologies for modeling components using smeared-property formulations have been investigated. Reduced integration element formulations examined include shell and solid elements. Model predictions have been validated with experimental data. Results show that models with smeared properties can predict transient-dynamic response of board assemblies in drop impact fairly accurately. High-speed data acquisition system has been used to capture in situ strain, continuity, and acceleration data in excess of 1×106samples∕s. Ultra-high-speed video at 40,000fps has been used to capture the deformation kinematics. Component types examined include plastic ball-grid arrays, tape-array ball-grid array, quad-flat-no-lead package, and conduction-cooled ball-grid array. Model predictions have been correlated with experimental data. Impact of experimental error sources on model correlation with experiments has been also investigated
A Heterogeneous Array of Off-Chip Interconnects for Optimum Mechanical and Electrical Performance
Authors: Kacker Karan , Sokol Thomas , Yun Wansuk , Swaminathan Madhavan , Sitaraman Suresh K.
Published: December 2007

Demand for off-chip bandwidth has continued to increase. It is projected by the Semiconductor Industry Association in their International Technology Roadmap for Semiconductors that by the year 2015, the chip-to-substrate area-array input-output interconnects will require a pitch of 80 μm. Compliant off-chip interconnects show great potential to address these needs. G-Helix is a lithography-based electroplated compliant interconnect that can be fabricated at the wafer level. G-Helix interconnects exhibit excellent compliance in all three orthogonal directions, and can accommodate the coefficient of thermal expansion (CTE) mismatch between the silicon die and the organic substrate without requiring an underfill. Also, these compliant interconnects are less likely to crack or delaminate the low-k dielectric material in current and future integrated circuits. The interconnects are potentially cost effective because they can be fabricated in batch at the wafer level and using conventional wafer fabrication infrastructure. In this paper, we present an integrative approach, which uses interconnects with varying compliance and thus varying electrical performance from the center to the edge of the die. Using such a varying geometry from the center to the edge of the die, the system performance can be tailored by balancing electrical requirements against thermomechanical reliability concerns. The test vehicle design to assess the reliability and electrical performance of the interconnects is also presented. Preliminary fabrication results for the integrative approach are presented and show the viability of the fabrication procedure. The results from reliability experiments of helix interconnects assembled on an organic substrate are also presented. Initial results from the thermal cycling experiments are promising. Results from mechanical characterization experiments are also presented and show that the out-of-plane compliance exceeds target values recommended by industry experts. Finally, through finite element analysis simulations, it is demonstrated that the die stresses induced by the compliant interconnects are an order of magnitude lower than the die stresses in flip chip on board (FCOB) assemblies, and hence the compliant interconnects are not likely to crack or delaminate low-k dielectric material.