bluuebunny/crossref_metadata_2025 huggingface dataset:
Detection of temperatures conducive to Arctic polar stratospheric clouds using CHAMP and SAC‐C radio occultation data
Authors: de la Torre Juárez M. , Marcus S. , Dörnbrack A. , Schrøder T. M. , Kivi R. , Iijima B. A. , Hajj G. A. , Mannucci A. J.
Published: April 2009

We use global positioning system radio occultation (GPSRO) data from the Challenging Mini‐Satellite Payload for Geophysical Research and Application (CHAMP) and Satélite de Applicaciones Científicas‐C (SAC‐C) low Earth orbiting satellites to investigate the occurrence of air with temperatures cold enough to allow the formation of polar stratospheric clouds (PSCs) during four successive Arctic winters spanning 2001 to 2005. The GPSRO data are validated and compared with analysis data from the European Centre for Medium‐Range Weather Forecasts using a series of criteria designed to eliminate faulty soundings but retain profiles which do not differ too strongly from the model data. We find that GPSRO is able to detect more PSC‐prone temperature profiles during winters with disturbed conditions (in particular during December 2001 and 2003) than the analysis, but that the model fully captures the extent of PSC‐prone air in winters with strong, cold vortices (in particular December 2002 and January 2005). Examination of detailed profiles for December 2001 shows that this difference is due to the ability of GPSRO to detect short‐vertical wavelength features which may represent either localized gravity or global‐scale planetary waves. Since the GPSRO data are now being directly assimilated into operational analysis systems, the benefits of the higher vertical resolution retrievals it provides should become evident in future observational studies of PSC formation and ozone loss, particularly under the disturbed conditions noted in several recent winters.
Ice nuclei emissions from biomass burning
Authors: Petters Markus D. , Parsons Matthew T. , Prenni Anthony J. , DeMott Paul J. , Kreidenweis Sonia M. , Carrico Christian M. , Sullivan Amy P. , McMeeking Gavin R. , Levin Ezra , Wold Cyle E. , Collett Jeffrey L. , Moosmüller Hans
Published: April 2009

Biomass burning is a significant source of carbonaceous aerosol in many regions of the world. When present, biomass burning particles may affect the microphysical properties of clouds through their ability to function as cloud condensation nuclei or ice nuclei. We report on measurements of the ice nucleation ability of biomass burning particles performed on laboratory‐generated aerosols at the second Fire Lab at Missoula Experiment. During the experiment we generated smoke through controlled burns of 21 biomass fuels from the United States and Asia. Using a Colorado State University continuous flow diffusion chamber, we measured the condensation/immersion freezing potential at temperatures relevant to cold cumulus clouds (−30°C). Smokes from 9 of the 21 fuels acted as ice nuclei at fractions of 1:10,000 to 1:100 particles in at least one burn of each fuel; emissions from the remaining fuels were below the ice nuclei detection limit for all burns of each fuel. Using a bottom‐up emission model, we estimate that smokes that emit ice nuclei fractions exceeding 1:10,000 particles can perturb ice nuclei concentrations on a regional scale.
Aerosol optical and hygroscopic properties during TexAQS‐GoMACCS 2006 and their impact on aerosol direct radiative forcing
Authors: Massoli P. , Bates T. S. , Quinn P. K. , Lack D. A. , Baynard T. , Lerner B. M. , Tucker S. C. , Brioude J. , Stohl A. , Williams E. J.
Published: April 2009

In situ measurements of aerosol optical and hygroscopic properties were made on board the National Oceanic and Atmospheric Administration R/V Ronald H. Brown during the Texas Air Quality Study–Gulf of Mexico Atmospheric Composition and Climate Study (TexAQS‐GoMACCS). The aerosol light extinction coefficient (σep) was measured at 355, 532, and 1064 nm at 25%, 60%, and 85% relative humidity (RH) for both sub‐1‐ and sub‐10‐μm‐diameter particles with a cavity ring–down aerosol extinction spectrometer. The 532‐nm σep was coupled with the 532‐nm light absorption coefficient (σap) measured with a photoacoustic absorption spectrometer to calculate the aerosol single scattering albedo (ω) with absolute uncertainty <0.01. The σep dependence on RH was expressed in terms of gamma (γ). The sampled aerosols covered a broad spectrum of γ and ω values; aerosols from traffic emissions were hydrophobic and highly light‐absorbing with γ ∼ 0.4 and ω ∼ 0.6, whereas the regional aerosols exhibited variable values of both γ and ω. Aerosols with the highest sulfate content also had the highest γ and ω values (>0.65 and >0.9, respectively). The optical data were used to estimate local, top of atmosphere aerosol‐induced climate forcing (ΔFR). The ΔFR calculations were performed using both ω values measured at 25% RH and ω values converted to ambient RH. The calculated ambient ΔFR ranged from −7 to −40 W/m2 with absolute uncertainty between 0.7 and 2.5 W/m2. The results show that including aerosol hygroscopic properties in climate calculations is critical for improving estimates of aerosol forcing on climate.
A fundamental parameters approach to calibration of the Mars Exploration Rover Alpha Particle X‐ray Spectrometer
Authors: Campbell J. L. , Lee M. , Jones B. N. , Andrushenko S. M. , Holmes N. G. , Maxwell J. A. , Taylor S. M.
Published: April 2009

The detection sensitivities of the Alpha Particle X‐ray Spectrometer (APXS) instruments on the Mars Exploration Rovers for a wide range of elements were experimentally determined in 2002 using spectra of geochemical reference materials. A flight spare instrument was similarly calibrated, and the calibration exercise was then continued for this unit with an extended set of geochemical reference materials together with pure elements and simple chemical compounds. The flight spare instrument data are examined in detail here using a newly developed fundamental parameters approach which takes precise account of all the physics inherent in the two X‐ray generation techniques involved, namely, X‐ray fluorescence and particle‐induced X‐ray emission. The objectives are to characterize the instrument as fully as possible, to test this new approach, and to determine the accuracy of calibration for major, minor, and trace elements. For some of the lightest elements the resulting calibration exhibits a dependence upon the mineral assemblage of the geological reference material; explanations are suggested for these observations. The results will assist in designing the overall calibration approach for the APXS on the Mars Science Laboratory mission.
Solar energetic particle flux enhancement as a predictor of geomagnetic activity in a neural network‐based model
Authors: Valach F. , Revallo M. , Bochníček J. , Hejda P.
Published: April 2009

Coronal mass ejections (CMEs) are believed to be the principal cause of increased geomagnetic activity. They are regarded as being in context of a series of related solar energetic events, such as X‐ray flares (XRAs) accompanied by solar radio bursts (RSPs) and also by solar energetic particle (SEP) flux. Two types of the RSP events are known to be geoeffective, namely, the RSP of type II, interpreted as the signature of shock initiation in the solar corona, and type IV, representing material moving upward in the corona. The SEP events causing geomagnetic response are known to be produced by CME‐driven shocks. In this paper, we use the method of the artificial neural network in order to quantify the geomagnetic response of particular solar events. The data concerning XRAs and RSPs II and/or IV together with their heliographic positions are taken as the input for the neural network. There is a key question posed in our study: can the successfulness of the neural network prediction scheme based solely on the solar disc observations (XRA and RSP) be improved by additional information concerning the SEP flux? To resolve this problem, we chose the SEP events possessing significant enhancement in the 10‐h window, commencing 12 h after the generation of XRAs. In particular, we consider the flux of high‐energy protons with energies over 10 MeV. We have used a chi‐square test to demonstrate that supplying such extra input data improves the neural network prediction scheme.
Parameter estimation from flowing fluid temperature logging data in unsaturated fractured rock using multiphase inverse modeling
Authors: Mukhopadhyay Sumit , Tsang Yvonne W. , Finsterle Stefan
Published: April 2009

A simple conceptual model has been recently developed for analyzing pressure and temperature data from flowing fluid temperature logging (FFTL) in unsaturated fractured rock. Using this conceptual model, we developed an analytical solution for FFTL pressure response, and a semianalytical solution for FFTL temperature response. We also proposed a method for estimating fracture permeability from FFTL temperature data. The conceptual model was based on some simplifying assumptions, particularly that a single‐phase airflow model was used. In this paper, we develop a more comprehensive numerical model of multiphase flow and heat transfer associated with FFTL. Using this numerical model, we perform a number of forward simulations to determine the parameters that have the strongest influence on the pressure and temperature response from FFTL. We then use the iTOUGH2 optimization code to estimate these most sensitive parameters through inverse modeling and to quantify the uncertainties associated with these estimated parameters. We conclude that FFTL can be utilized to determine permeability, porosity, and thermal conductivity of the fracture rock. Two other parameters, which are not properties of the fractured rock, have strong influence on FFTL response. These are pressure and temperature in the borehole that were at equilibrium with the fractured rock formation at the beginning of FFTL. We illustrate how these parameters can also be estimated from FFTL data.
Why short‐term crustal shortening leads to mountain building in the Andes, but not in Cascadia?
Authors: Luo Gang , Liu Mian
Published: April 2009

Subduction‐induced crustal shortening, now measured by the GPS across many subduction zones, has led to mountain building in the Andes but not in Cascadia and some other Andean‐type convergent plate boundaries. Here we use a two‐dimensional viscoelastoplastic finite element model to explore how the GPS‐measured short‐term strain relates to long‐term mountain building. We show that previously proposed causative factors of mountain building can be represented by two model parameters: the strength of mechanical coupling on the plate interface, and the yield strength of the overriding plate. The critical condition for producing permanent (plastic) crustal shortening, hence mountain building, is for the plastic yield strength of the plate interface to be higher than that of the overriding plate. Strong trench coupling and a weak lithosphere explain the Andean mountain building, whereas weak trench coupling in Cascadia allows short‐term crustal shortening to be restored periodically by trench earthquakes and aseismic slips.
A low‐velocity conduit throughout the mantle in the robust component of a tomography model
Authors: Takeuchi N.
Published: April 2009

Detecting the roots of mantle plumes and constraining their connections to the Large Low Shear Velocity Provinces (LLSVPs) in the CMB region are critical problems for understanding mantle dynamics. Among the low‐velocity conduits observed in the previous tomography models, the conduit beneath the Samoa/Tahiti region appears to be the most reliable because many models suggest it has a deep root. However, it is not clear whether the models are sufficiently accurate to confirm the reliability of this feature. In this study, we apply the singular value decomposition to confirm that this feature is well constrained by the data. The results indicate the plume beneath the Samoa/Tahiti region rising from the upper surface of the Pacific LLSVP. It might be a plume rising from a chemically distinct dome in the thermo‐chemical convection.
Statistical and fragmentation properties of the micrometeoroid flux observed at Arecibo
Authors: Briczinski S. J. , Mathews J. D. , Meisel D. D.
Published: April 2009

The micrometeor observations performed using the 430 MHz Arecibo Observatory radar have proven to be crucial for the understanding of meteoric effects on the aeronomy of the upper atmosphere. Meteors observed during the February 2001, 2006, and 2007 campaigns have been analyzed with a fast Fourier transform periodic search algorithm that automatically and uniformly detects meteor events between altitudes of 80 and 142 km. We present a description of the new technique used to detect meteors as well as the meteoroid parameters: altitude profiles, radial speeds, and decelerations. We also note the expected correlation between the radar transmitted power and the observed meteor event rate. The large number of events has enabled us to statistically estimate the average mass density of the observed population indicating that our detected events are generally cometary (1 g/cm3) and not asteroidal (3 g/cm3) in origin. Additionally, many meteor events are observed in which the radar meteor disappears from one radar pulse to the next (i.e., in 1 ms). We interpret this as indicative of the catastrophic destruction of the meteoroid. Until destruction, these events appear to undergo only minor ablation of their volatile components over the observed trajectory. As with a major fraction of all events recorded, the meteoroids that disappear in a terminal event show linear decelerations before their abrupt disappearance. This apparently low ablative mass deposition process may play an important role in the composition (aeronomy) of the upper atmosphere, as it likely produces submicron‐sized particles rather than the atom level products of ablation. First results on the altitude, speed, and mass distributions of terminal event meteoroids are given yielding some clues on the physics of the terminal event. Finally, the statistics of those events that yield no deceleration are compared statistically with those that exhibit deceleration with the conclusion that both groups are statistically the same. We further conclude that along with low signal‐to‐noise ratio and short echo duration, fragmentation of this group of particles is a primary cause of the inability to determine deceleration.
Newborn- and Adult-Derived Brain Microvascular Endothelial Cells Show Age-Related Differences in Phenotype and Glutamate-Evoked Protease Release
Authors: Legros Hélène , Launay Séverine , Roussel Benoit Denis , Marcou-Labarre Aurélie , Calbo Sébastien , Catteau Julie , Leroux Philippe , Boyer Olivier , Ali Carine , Marret Stéphane , Vivien Denis , Laudenbach Vincent
Published: April 2009

Few data are available on the involvement of brain microvascular endothelial cells (BMECs) in excitotoxic neonatal brain lesions. Therefore, we developed an original approach for investigating mouse-derived BMECs in vitro. We hypothesized that newborn and adult BMEC cultures would show age-related differences in phenotype and sensitivity to glutamate. Expression of the monocarboxylate transporter, MCT1, was higher in neonatal than in adult BMECs, whereas expression of the glucose transporter, GLUT1, was higher in adult than in neonatal BMECs that overexpressed the N-methyl-D-aspartate receptor NR1 subunit (NMDAR1) compared with adult BMECs. The ability of neonatal and adult BMECs to be activated by glutamate was confirmed through intracellular calcium ([Ca2+]i) recording. The glutamate-induced [Ca2+]iincrease was blocked by the selective NMDAR antagonist, MK-801. Significant glutamate-evoked concentration-dependent release of tissue-type plasminogen activator (t-PA) and matrix metalloproteinases (MMPs) activities was found in supernatants of neonatal, but not in adult BMECs. The glutamate-mediated release of t-PA, MMP-2, and MMP-9 proteolytic activities in neonatal BMECs was blocked by MK-801. Conceivably, this protease release from neonatal BMECs may participate in neonatal brain lesions.
The presence of monoglucosylated N196-glycan is important for the structural stability of storage protein, arylphorin
Authors: Ryu Kyoung-Seok , Lee Jie-Oh , Kwon Taek Hun , Choi Han-Ho , Park Hong-Seog , Hwang Soo Kyung , Lee Zee-Won , Lee Kyung-Bok , Han Young Hyun , Choi Yun-Seok , Jeon Young Ho , Cheong Chaejoon , Kim Soohyun
Published: April 2009

Although N-glycosylation has been known to increase the stability of glycoproteins, it is difficult to assess the structural importance of glycans in the stabilization of glycoproteins. APA (Antheraea pernyi arylphorin) is an insect hexamerin that has two N-glycosylations at Asn196 and Asn344 respectively. The glycosylation of Asn344 is critical for the folding process; however, glycosylation of Asn196 is not. Interestingly, the N196-glycan (glycosylation of Asn196) remains in an immature form (Glc1Man9GlcNAc2). The mutation of Asn196 to glutamine does not change the ecdysone-binding activity relative to that of the wild-type. In the present study, we determined the crystal structure of APA, and all sugar moieties of the N196-glycan were clearly observed in the electron-density map. Although the sugar moieties of the glycan generally have high structural flexibility, most sugar moieties of the N196-glycan were well organized in the deep cleft of the subunit interface and mediated many inter- and intrasubunit hydrogen bonds. Analytical ultracentrifugation and GdmCl (guanidinium chloride) unfolding experiments revealed that the presence of the N196-glycan was important for stabilizing the hexameric state and overall stability of APA respectively. Our results could provide a structural basis for studying not only other glycoproteins that carry an immature N-glycan, but also the structural role of N-glycans that are located in the deep cleft of a protein.
Diabetic cardiomyopathy
Authors: Asghar Omar , Al-Sunni Ahmed , Khavandi Kaivan , Khavandi Ali , Withers Sarah , Greenstein Adam , Heagerty Anthony M. , Malik Rayaz A.
Published: April 2009

Diabetic cardiomyopathy is a distinct primary disease process, independent of coronary artery disease, which leads to heart failure in diabetic patients. Epidemiological and clinical trial data have confirmed the greater incidence and prevalence of heart failure in diabetes. Novel echocardiographic and MR (magnetic resonance) techniques have enabled a more accurate means of phenotyping diabetic cardiomyopathy. Experimental models of diabetes have provided a range of novel molecular targets for this condition, but none have been substantiated in humans. Similarly, although ultrastructural pathology of the microvessels and cardiomyocytes is well described in animal models, studies in humans are small and limited to light microscopy. With regard to treatment, recent data with thiazoledinediones has generated much controversy in terms of the cardiac safety of both these and other drugs currently in use and under development. Clinical trials are urgently required to establish the efficacy of currently available agents for heart failure, as well as novel therapies in patients specifically with diabetic cardiomyopathy.
Resonances and spectral shift function for a magnetic Schrödinger operator
Authors: Khochman Abdallah
Published: April 2009

We consider the three-dimensional Schrödinger operator H0 with a constant magnetic field and subject to an electric potential v0 depending only on the variable along the magnetic field x3. The operator H0 has infinitely many eigenvalues of infinite multiplicity embedded in its continuous spectrum. We perturb H0 by smooth scalar potentials V=O(⟨(x1,x2)⟩−δ⊥⟨x3⟩−δ∥), δ⊥>2, δ∥>1. We assume also that V and v0 have an analytic continuation, in the magnetic field direction, in a complex sector outside a compact set. We define the resonances of H=H0+V as the eigenvalues of the nonself-adjoint operator obtained from H by analytic distortions of Rx3. We study their distribution near any fixed real eigenvalue of H0, 2bq+λ for q∊N. In a ring centered at 2bq+λ with radii (r,2r), we establish an upper bound, as r tends to 0, of the number of resonances. This upper bound depends on the decay of V at infinity only in the directions (x1,x2). Finally, we deduce a representation of the derivative of the spectral shift function for the operator pair (H0,H) in terms of resonances. This representation justifies the Breit–Wigner approximation and implies a local trace formula.
Tube dislocations in gravity
Authors: de Berredo-Peixoto G. , Katanaev M. O.
Published: April 2009

We consider static massive thin cylindrical shells (tubes) as the sources in Einstein’s equations. They correspond to δ- and δ′-function-type energy-momentum tensors. The corresponding metric components are found explicitly. They are not continuous functions, in general, and lead to ambiguous curvature tensor components. Nevertheless all ambiguous terms in Einstein’s equations safely cancel. The interplay between elasticity theory, geometric theory of defects, and general relativity is analyzed. The elasticity theory provides a simple picture for defect creation and a new look on general relativity.
Comment on “Generation of cold low divergent atomic beam of indium by laser ablation” [Rev. Sci. Instrum. 76, 113302 (2005)]
Authors: Denning A. , Booth A. , Lee S. , Amonson M. , Bergeson S. D.
Published: April 2009

We present measurements of the velocity distribution of calcium atoms in an atomic beam generated using a dual-stage laser back-ablation apparatus. Distributions are measured using a velocity selective Doppler time-of-flight technique. They are Boltzmann-like with rms velocities corresponding to temperatures above the melting point for calcium. Contrary to a recent report in the literature, this method does not generate a subthermal atomic beam.
Structural study of the Eu3+ environments in fluorozirconate glasses: Role of the temperature-induced and the pressure-induced phase transition processes in the development of a rare earth’s local structure model
Authors: Muñoz-Santiuste Juan E. , Rodríguez-Mendoza Ulises R. , González-Platas Javier , Lavín Víctor
Published: April 2009

The correlation between the optical properties of the Eu3+ ions and their local structures in fluorozirconate glasses and glass-ceramics have been analyzed by means of steady-state and time-resolved site-selective laser spectroscopies. Changes in the crystal-field interaction, ranging from weak to medium strength values, are observed monitoring the luminescence and the lifetime of the Eu3+ ions in different local environments in the glass. As key roles in this study, the Eu3+ luminescence in the thermally-induced crystallization of the glass and the pressure-induced amorphization of the crystalline phase of the glass-ceramic experimentally states the existence of a parent local structure for the Eu3+ ions in the glass, identified as the EuZrF7 crystalline phase. Starting from the ab initio single overlap model, crystal-field calculations have been performed in the glass and the glass-ceramic. From the site-selective measurements, the crystal-field parameters sets are obtained, giving a suitable simulation of the F7J (J=0–6) Stark energy level diagram for the Eu3+ ions in the different environments present in the fluorozirconate glass. A simple geometrical model based on a continuous distortion of the parent structure is proposed for the distribution of local environments of the Eu3+ ions in the fluorozirconate glass.
Tearing modes with pressure gradient effect in pair plasmas
Authors: Cai Huishan , Li Ding , Zheng Jian
Published: April 2009

The general dispersion relation of tearing mode with pressure gradient effect in pair plasmas is derived analytically. If the pressure gradients of positron and electron are not identical in pair plasmas, the pressure gradient has significant influence at tearing mode in both collisionless and collisional regimes. In collisionless regime, the effects of pressure gradient depend on its magnitude. For small pressure gradient, the growth rate of tearing mode is enhanced by pressure gradient. For large pressure gradient, the growth rate is reduced by pressure gradient. The tearing mode can even be stabilized if pressure gradient is large enough. In collisional regime, the growth rate of tearing mode is reduced by the pressure gradient. While the positron and electron have equal pressure gradient, tearing mode is not affected by pressure gradient in pair plasmas.
Electric and dielectric properties of Bi-doped CaCu3Ti4O12 ceramics
Authors: Luo Fengchao , He Jinliang , Hu Jun , Lin Yuan-Hua
Published: April 2009

Pure and Bi-doped BixCaCu3Ti4O12+1.5x (BCCTO, x=0, 0.15, 0.25, and 0.3) ceramics were fabricated by the solid-state sintering method. The results indicate that the additional bismuth has a great influence on both the microstructures and the electric properties. A new phase (Bi4Ti3O12) can be observed in the doped samples from the x-ray diffraction patterns. Additionally, the CCTO gain size can be controlled by bismuth content. All of the BCCTO samples show high dielectric permittivity (∼104 at 103 Hz) and varistor effect, and the relaxation peak shifts to higher frequency. The resistance rises with the increase in bismuth, and the activation energy at the grain boundary is reduced from 0.65 to 0.47 eV.
Effects of bonding structure from niobium carbide buffer layer on the field electric emission properties of a-C films
Authors: Xu L. , Wang C. , Hu C. Q. , Zhao Z. D. , Yu W. X. , Zheng W. T.
Published: April 2009

We investigate the field electron emission for amorphous carbon (a-C) films deposited on Si (100) substrates through a niobium carbide buffer layer at different flow rate ratios of CH4/(CH4+Ar) in a CH4/Ar mixture discharge, and find that the composition and chemical bonding of the buffer layer can substantially affect the electron field emission properties of a-C films. The high ratio of Nb–C/Nb–Nb bonds in the buffer layer promotes the electron emission of a-C film. The first-principles calculated results show that the work function of NbC is lower than that of Nb, which is the reason why the high ratio of Nb–C/Nb–Nb bonds in the buffer layer favors the field emission of a-C film.
Enhanced thermoelectric performance of AgSbTe2 synthesized by high pressure and high temperature
Authors: Su Taichao , Jia Xiaopeng , Ma Hongan , Yu Fengrong , Tian Yongjun , Zuo Guihong , Zheng Youjin , Jiang Yiping , Dong Dan , Deng Le , Qin Bingke , Zheng Shizhao
Published: April 2009

Near single phase ternary bulk thermoelectric material AgSbTe2 was synthesized by high pressure and high temperature (HPHT) method. The temperature-dependent thermoelectric properties including Seebeck coefficient, electrical conductivity, and thermal conductivity were studied. The HPHT synthesized AgSbTe2 sample has higher thermoelectric performance in the measured temperature range than that of the same sample prepared at normal pressure. The enhanced thermoelectric properties should be attributed to the HPHT quenching which keeps partially the high electrical conductivity of AgSbTe2 under high pressure.
Modification of alpha-particle emission spectrum in beam-injected deuterium-tritium plasmas
Authors: Matsuura H. , Nakao Y.
Published: April 2009

The alpha (α)-particle and neutron emission spectra in a deuterium-tritium plasma accompanied with neutral-beam-injection (NBI) heating are evaluated in a consistent way by solving the Boltzmann–Fokker–Planck equations for deuteron, triton, and α-particle simultaneously. It is shown that owing to the existence of non-Maxwellian tail component in fuel-ion distribution function due to NBI and/or nuclear elastic scattering, the generation rate of the energetic (≥4 MeV) α-particle increases significantly. When 20 MW intense deuterium beam with 1 MeV beam-injection energy is injected into an 800 m3 plasma (Te=10 keV, ne=6.2×1019 m−3), the enhancement of the fraction of the power carried by α-particles with energy above 4 (3.9) MeV to total α-particle power is almost twice (1.5 times) as much from the value for Gaussian distribution. A verification scenario for the modification of the emission spectrum by using the gamma (γ)-ray-generating B9e(α,nγ)C12 reaction is also presented.
Modulated photonic-crystal structures as broadband back reflectors in thin-film solar cells
Authors: Krc J. , Zeman M. , Luxembourg S. L. , Topic M.
Published: April 2009

A concept of a modulated one-dimensional photonic-crystal (PC) structure is introduced as a back reflector for thin-film solar cells. The structure comprises two PC parts, each consisting of layers of different thicknesses. Using layers of amorphous silicon and amorphous silicon nitride a reflectance close to 100% is achieved over a broad wavelength region (700–1300 nm). Based on this concept, a back reflector was designed for thin-film microcrystalline silicon solar cells, using n-doped amorphous silicon and ZnO:Al. Simulations show that the short-circuit current of the cell with a modulated PC back reflector closely resembles that of a cell with an ideal reflector.
Decrease of nonlinearity and linewidth narrowing in spin-transfer oscillators under the external field applied near the hard axis
Authors: Mizushima K. , Nagasawa T. , Kudo K. , Saito Y. , Sato R.
Published: April 2009

Angular dependence of power spectra is measured for tunnel-type spin-transfer oscillators by changing the direction of the external field in the plane. The oscillation frequency shows the red shift with increasing the current in the case that the field directions are away from the hard axis of the free layer. The frequency shift changes from red to blue at a specific direction near the hard axis, where the linewidth is much reduced. These results are explained by taking into account the nonlinearity arising from the in-plane anisotropy as well as that arising from the demagnetizing effect.
Structural and dielectric study of parylene C thin films
Authors: Kahouli A. , Sylvestre A. , Ortega L. , Jomni F. , Yangui B. , Maillard M. , Berge B. , Robert J.-C. , Legrand J.
Published: April 2009

α , β, and γ relaxation mechanisms have been identified in semicrystalline (45% of crystallinity) parylene-C (–H2C–C6H3Cl–CH2–)n films. C–Cl bonds induce the β-relaxation and explain increase in the dielectric constant as the frequency decreases in usual temperatures of operation for devices incorporating parylene-C. At cryogenic temperature (<−20 °C), γ-relaxation is assigned to the local motions of phenyl groups. Both β and γ relaxation processes obey an Arrhenius law with activation energy Ea(β)=91.7 kJ/mole and Ea(γ)=8.68 kJ/mole. α-relaxation associated with cooperative segmental motions of the (–H2C–∅–CH2–)n chains is observed with a peak at 10−2 Hz for T=80 °C and follows a Vogel–Fulcher–Tamman–Hesse law.
Finite de Finetti theorem for conditional probability distributions describing physical theories
Authors: Christandl Matthias , Toner Ben
Published: April 2009

We work in a general framework where the state of a physical system is defined by its behavior under measurement and the global state is constrained by no-signaling conditions. We show that the marginals of symmetric states in such theories can be approximated by convex combinations of independent and identical conditional probability distributions, generalizing the classical finite de Finetti theorem of Diaconis and Freedman. Our results apply to correlations obtained from quantum states even when there is no bound on the local dimension, so that known quantum de Finetti theorems cannot be used.
Blow up of the nonclassical diffusion equation
Authors: Song Haitao , Zhong Chengkui
Published: April 2009

In this paper, we consider the blow up phenomenon of the nonclassical diffusion equation. Under suitable conditions on the initial data, we prove a finite time blow up result.
Friction models incorporating thermal effects in highly precision actuators
Authors: Li J. W. , Chen X. B. , An Q. , Tu S. D. , Zhang W. J.
Published: April 2009

This paper presents two models based on the LuGre model for friction with consideration of thermal effects. In Model I, parameters in the LuGre model are considered as temperature dependent. In Model II, parameters in the LuGre model are considered as temperature independent; while a temperature-dependent function is added to the temperature-independent LuGre model. Both models are experimentally evaluated, which shows that both can effectively incorporate thermal effects but Model II has better accuracy. Since these models are developed in the context of the motion system, they should be readily incorporated in motion control algorithms for effective control of motion systems with friction if temperature rise is significant in these systems.
On integrability of the Yang–Baxter σ-model
Authors: Klimčík Ctirad
Published: April 2009

We prove that the recently introduced Yang–Baxter σ-model can be considered as an integrable deformation of the principal chiral model. We find also an explicit one-to-one map transforming every solution of the principal chiral model into a solution of the deformed model. With the help of this map, the standard procedure of the dressing of the principal chiral solutions can be directly transferred into the deformed Yang–Baxter context.
Linear stability analysis and numerical simulation of miscible two-layer channel flow
Authors: Sahu K. C. , Ding H. , Valluri P. , Matar O. K.
Published: April 2009

The stability of miscible two-fluid flow in a horizontal channel is examined. The flow dynamics are governed by the continuity and Navier–Stokes equations coupled to a convective-diffusion equation for the concentration of the more viscous fluid through a concentration-dependent viscosity. Our analysis of the flow in the linear regime delineates the presence of convective and absolute instabilities and identifies the vertical gradients of viscosity perturbations as the main destabilizing influence in agreement with previous work. Our transient numerical simulations demonstrate the development of complex dynamics in the nonlinear regime, characterized by roll-up phenomena and intense convective mixing; these become pronounced with increasing flow rate and viscosity ratio, as well as weak diffusion.
A 2.8 K cryogen-free cryostat with compact optical geometry for multiple photon counting
Authors: Verdier M.-A. , Di Stefano P. C. F. , Bonte F. , Bret B. , De Jésus M. , Marot G. , Trollier T. , Vanzetto S.
Published: April 2009

Interest in solid scintillators down to liquid helium temperature and below has grown recently, fuelled by searches for exotic processes in particle physics. We describe a closed-cycle optical cryostat with a 2.8 K base temperature and a compact optical geometry for multiple photon counting. The large numerical aperture achieved, of the order of 0.79 from the optical center to each of the two windows and amounting to 40% of the total solid angle, allows a significant gain in the efficiency of photon collection. This and the relatively big sample size that can be used facilitate the study of scintillators under γ irradiation. These features should be an asset for multiple photon counting techniques at low temperatures.
Diagnostic development in precise opacity measurement of radiatively heated Al plasma on Shenguang II laser facility
Authors: Zhao Yang , Yang Jiamin , Zhang Jiyan , Liu Jinsong , Yuan Xiao , Jin Fengtao
Published: April 2009

Simultaneous measurements of the self-emission spectrum, the backlighting source spectrum, and the transmission spectrum in one shot, which reduce the experimental uncertainties from shot-to-shot fluctuation, are essential for precise opacity experiments. In order to achieve precise absorption spectrum of Al plasmas, a special half sample sandwich target was designed and short backlighter was used to provide time- and space-resolving diagnostics on the Shenguang II high power laser facility. In the measurement, a cylindrical cavity with CH foam baffles was used to provide a clean x-ray radiation environment for sample heating. The x-ray source spectrum, the transmission spectrum, and the self-emission spectrum of the soft x-ray heated Al sample were recorded in one shot with a penta-erythritol tetrakis (hydroxymethy) methane C(CH2OH)4 (PET) crystal spectrometer by using the point-projection method. Experimental results have been compared with the calculation results of a detailed level accounting opacity code.
Low temperature magnetism in the perovskite substrate DyScO3
Authors: Ke X. , Adamo C. , Schlom D. G. , Bernhagen M. , Uecker R. , Schiffer P.
Published: April 2009

We investigate the low temperature magnetic properties of crystalline DyScO3, a material that has seen increasing importance as a substrate for the growth of strained perovskite films. The compound exhibits strong magnetic anisotropy with an easy axis along the [100] direction and a hard axis along the [001] direction, respectively, attributable to magnetocrystalline anisotropy. We find that DyScO3 undergoes a magnetic phase transition at 3.1 K, presumably from paramagnetism to antiferromagnetic long range order. The presence of such a transition and the magnetic anisotropy suggests the possibility of significant substrate impact on studies of the magnetism of the epitaxial thin films grown on this material.
Evidence of nonplanar field emission via secondary electron detection in near field emission scanning electron microscopy
Authors: Kirk T. L. , Scholder O. , De Pietro L. G. , Ramsperger U. , Pescia D.
Published: April 2009

Nonplanar field emission from electrochemically etched tungsten field emitters has been observed using near field emission scanning electron microscopy. Close-proximity field emission in adequate ultrahigh vacuum conditions was implemented to attain Fowler–Nordheim plots using typical imaging parameters. The emission radii deduced via a detailed, spherical surface field emission theory, by [Edgcombe and de Jonge, J. Phys. D 40, 4123 (2007)], reveal that our sharpest tip asperities are less than a nanometer. This yields a spatial resolution on the order of one nanometer.
High-performance injectorless quantum cascade lasers emitting below 6 μm
Authors: Katz Simeon , Vizbaras Augustinas , Boehm Gerhard , Amann Markus-Christian
Published: April 2009

An injectorless quantum cascade laser emitting around 5.7 μm with more than 1 W of output power and a wall-plug efficiency of 3.6% at room temperature in pulsed operation is presented. The active region of the device is a design that picked up the idea of the four-alloy structure, which has already lead to very low threshold current densities. The pulsed threshold current densities were measured as low as 1.1 kA/cm2 at room temperature for an as-cleaved 3.6 mm long device, and 0.93 kA/cm2 for a high-reflection-coated 4 mm long device.
Experimental verification of Boltzmann equilibrium for negative ions in weakly collisional electronegative plasmas
Authors: Ghim(Kim) Young-chul , Hershkowitz Noah
Published: April 2009

Weakly collisional Ar–O2 electronegative plasmas are investigated in a dc multidipole chamber. An electronegative core and an electropositive halo are observed. The density ratio of negative ions to electrons (α) in the nondrifting bulk is found to be 0.43. The profile of α is found using both the phase velocity of ion acoustic waves and the drift velocity of positive ions determined by laser-induced fluorescence. The experiment shows that negative ions are in Boltzmann equilibrium with a temperature of 0.06±0.02 eV. Double layers are not found separating the electronegative core and the electropositive halo.
Spontaneous charge transfer from indium tin oxide to organic molecules for effective hole injection
Authors: Koo Young-Mo , Song Ok-Keun
Published: April 2009

Naphthalene tetracaboxylic dianhydride (NTCDA) shows strong chemical interaction with metal atoms in an indium tin oxide (ITO) substrate to form charge transfer (CT) complexes. The CT complex at the ITO/NTCDA interface can lower the energy barrier height for hole injection from ITO into the hole transporting layer of N,N′-diphenyl-N, N′-bis(1-naphthyl)(1,1′-biphenyl)-4,4′ diamine (NPB). The operational voltage of an emissive device at a current density of 100 mA/cm2 was significantly reduced from 12.2 to 9.2 V by simply inserting a thin layer of NTCDA between the ITO and NPB. The results enable the achievement of organic light-emitting diodes that consume relatively less power.
Generation and transport of photoexcited electrons in single-crystal diamond
Authors: Heremans F. J. , Fuchs G. D. , Wang C. F. , Hanson R. , Awschalom D. D.
Published: April 2009

We report time-dependent photocurrent and transport measurements of sub-bandgap photoexcited carriers in nitrogen-rich (type Ib), single-crystal diamond. Transient carrier dynamics are characteristic of trapping conduction with long charge storage lifetimes of ∼3 hours. By measuring the photoexcited Hall effect, we confirm that the charge carriers are electrons and by varying the excitation energy we observe a strong turn-on in the photoconduction at ∼1.9 eV. These findings shed light on sub-bandgap states in nitrogen-doped single-crystal diamond.
Determinants of establishment success for introduced exotic mammals
Authors: Bomford Mary , Darbyshire Rebecca O. , Randall Lucy
Published: April 2009

We conducted comparisons for exotic mammal species introduced to New Zealand (28 successful, 4 failed), Australia (24, 17) and Britain (15, 16). Modelling of variables associated with establishment success was constrained by small sample sizes and phylogenetic dependence, so our results should be interpreted with caution. Successful species were subject to more release events, had higher climate matches between their overseas geographic range and their country of introduction, had larger overseas geographic range sizes and were more likely to have established an exotic population elsewhere than was the case for failed species. Of the mammals introduced to New Zealand, successful species also had larger areas of suitable habitat than did failed species. Our findings may guide risk assessments for the import of live mammals to reduce the rate new species establish in the wild.
Selective piglet feeders improve age-related bait specificity and uptake rate in overabundant Eurasian wild boar populations
Authors: Ballesteros Cristina , Carrasco-García Ricardo , Vicente Joaquín , Carrasco Jesús , Lasagna Angelo , de la Fuente José , Gortázar Christian
Published: April 2009

The Eurasian wild boar (Sus scrofa) is a reservoir for pathogens that affect both humans and domestic animals. The control of these diseases requires the development of strategies such as oral vaccination of the reservoir species. The aim of the present study was to determine the species-specific visitation and removal rates of cereal-based baits under field conditions in an overabundant wild boar population. Two different field trials were conducted at a hunting estate. In one trial, baits were placed at track stations set up either randomly in the undeveloped portions of the estate or close to permanent wild boar feeding places. In the second trial, baits were placed in feeders that were selective for use by wild boar piglets. Both trials were conducted in summer 2007 and repeated in spring 2008. No evidence of attractant effect by the bait was found when comparing baited against control stations. A close proximity to the feeders was associated with an increased probability of being visited by wild boar, and piglet feeders were shown to be highly selective for young wild boar. Baits disappeared faster in summer than in spring (i.e. ~70% consumption after the first day in selective feeders in summer, and 40% in spring). Therefore, a combination of a summer season and selective feeders was found to be a potentially reliable bait-deployment strategy for wild boar juveniles under Mediterranean conditions. These results support the use of selective feeders for oral delivery of baits to 2–4-month-old wild boar piglets, which is the preferred age for vaccination. Our delivery technique based on selective piglet feeders also has potential for other uses in the Eurasian wild boar and wild pigs under different management conditions.
Structural and dynamic aspects related to oligomerization of apo SOD1 and its mutants
Authors: Banci Lucia , Bertini Ivano , Boca Mirela , Calderone Vito , Cantini Francesca , Girotto Stefania , Vieru Miguela
Published: April 2009

The structural and dynamical properties of the metal-free form of WT human superoxide dismutase 1 (SOD1) and its familial amyotrophic lateral sclerosis (fALS)-related mutants, T54R and I113T, were characterized both in solution, through NMR, and in the crystal, through X-ray diffraction. We found that all 3 X-ray structures show significant structural disorder in 2 loop regions that are, at variance, well defined in the fully-metalated structures. Interestingly, the apo state crystallizes only at low temperatures, whereas all 3 proteins in the metalated form crystallize at any temperature, suggesting that crystallization selects one of the most stable conformations among the manifold adopted by the apo form in solution. Indeed, NMR experiments show that the protein in solution is highly disordered, sampling a large range of conformations. The large conformational variability of the apo state allows the free reduced cysteine Cys-6 to become highly solvent accessible in solution, whereas it is essentially buried in the metalated state and the crystal structures. Such solvent accessibility, together with that of Cys-111, accounts for the tendency to oligomerization of the metal-free state. The present results suggest that the investigation of the solution state coupled with that of the crystal state can provide major insights into SOD1 pathway toward oligomerization in relation to fALS.
Cognitive gains in 7-month-old bilingual infants
Authors: Kovács Ágnes Melinda , Mehler Jacques
Published: April 2009

Children exposed to bilingual input typically learn 2 languages without obvious difficulties. However, it is unclear how preverbal infants cope with the inconsistent input and how bilingualism affects early development. In 3 eye-tracking studies we show that 7-month-old infants, raised with 2 languages from birth, display improved cognitive control abilities compared with matched monolinguals. Whereas both monolinguals and bilinguals learned to respond to a speech or visual cue to anticipate a reward on one side of a screen, only bilinguals succeeded in redirecting their anticipatory looks when the cue began signaling the reward on the opposite side. Bilingual infants rapidly suppressed their looks to the first location and learned the new response. These findings show that processing representations from 2 languages leads to a domain-general enhancement of the cognitive control system well before the onset of speech.
Oligosaccharyltransferase directly binds to ribosome at a location near the translocon-binding site
Authors: Harada Yoichiro , Li Hua , Li Huilin , Lennarz William J.
Published: April 2009

Oligosaccharyltransferase (OT) transfers high mannose-type glycans to the nascent polypeptides that are translated by the membrane-bound ribosome and translocated into the lumen of the endoplasmic reticulum through the Sec61 translocon complex. In this article, we show that purified ribosomes and OT can form a binary complex with a stoichiometry of ≈1 to 1 in the presence of detergent. We present evidence that OT may bind to the large ribosomal subunit near the site where nascent polypeptides exit. We further show that OT and the Sec61 complex can simultaneously bind to ribosomes in vitro. Based on existing data and our findings, we propose that cotranslational translocation and N-glycosylation of nascent polypeptides are mediated by a ternary supramolecular complex consisting of OT, the Sec61 complex, and ribosomes.