bluuebunny/crossref_metadata_2025 huggingface dataset:
A novel approach for identifying the true temperature sensitivity from soil respiration measurements
Authors: Gu Lianhong , Hanson Paul J. , Mac Post W. , Liu Qing
Published: November 2008

We propose a novel approach, called the “localized ratio fitting” (LRF), to estimating the true temperature sensitivity from soil respiration measurements, a task crucial to modeling terrestrial carbon cycle and climate but so far hindered by the inadequate conventional regression approach. LRF takes advantage of the different timescales of the pool dynamics–induced and environmental variation–induced changes in soil CO2 efflux. It first transforms the expression for soil respiration into a form suppressing the influence of soil carbon pool dynamics and then uses the transformed expression to infer the parameters of environmental sensitivities. LRF works best for high‐frequency soil respiration measurements and thus is particularly suitable for analyzing time series produced by automated soil chambers and from soil incubation experiments. We evaluated the validity of LRF with both simulated (with a multipool soil organic carbon model driven by realistic plant litter input scenarios) and measured (with automated soil chambers) time series of soil respiration. LRF accurately retrieved the true temperature sensitivity from the simulated heterotrophic soil respiration while the conventional approach failed to do so. The simulation also revealed that LRF performed better than the conventional approach when a direct photosynthetic signal existed in the time series of soil respiration although even LRF could not completely eliminate the interference of photosynthetic contribution for estimating the true temperature sensitivity. Importantly, the simulation on the photosynthetic influence reproduced a typical seasonal pattern of apparent temperature sensitivity reported in the literature: higher sensitivity in winter (dormant season) and lower sensitivity in summer (growing season). Such pattern has been interpreted as an indication of temperature acclimation of soil respiration by previous studies. Our simulation now indicated that that interpretation may be incorrect. The validation with actual soil chamber data showed that the use of LRF led to more consistent estimates of temperature and moisture sensitivities from observations, indicating its better robustness against compounding effects of parallel processes on soil respiration. It was demonstrated that once the true environmental controls were properly accounted for, soil respiration measurements could be used to infer effects of biological processes on soil respiration.
Air compression as a mechanism for the underdamped slug test response in fractured glacier ice
Authors: Meierbachtol Toby W. , Harper Joel T. , Humphrey Neil F. , Shaha Jeremy , Bradford John H.
Published: November 2008

Artificial perturbations of borehole water levels, known as slug tests, are a useful means of characterizing the glacier hydrologic system. Slug tests were performed on Bench Glacier, Alaska, in 21 boreholes over three field seasons during the transition from a winter to a summer drainage mode. Fifty‐four slug tests were conducted, with water level monitoring in up to five boreholes adjacent to the slugged borehole. Seven of the slug tests were performed in conjunction with dye dispersion tests to identify water pathways within the slugged borehole following perturbation. Nearly 60% of monitored adjacent boreholes showed a hydraulic connection to the slugged borehole via the glacier bed. The nature and degree of connectivity was temporally variable, suggesting that the drainage network at the bed was highly dynamic on a daily timescale and spatial scale of tens of meters. The variability of slug test responses over time and space limit the feasibility of six alternative explanations for the oscillatory water level behavior characteristic of the underdamped response. We propose a seventh, that is, that coherent air packages are a reasonable means of producing the compliance needed to generate the underdamped slug test responses on Bench Glacier, and that these air packages may exist within the glacier at the tips of subglacially propagated fractures.
Atmospheric impact on beryllium isotopes as solar activity proxy
Authors: Aldahan A. , Hedfors J. , Possnert G. , Kulan A. , Berggren A.‐M. , Söderström C.
Published: November 2008

Reconstructing solar activity variability beyond the time scale of actual measurements provides invaluable data for modeling of past and future climate change. The 10Be isotope has been a primary proxy archive of past solar activity and cosmic ray intensity, particularly for the last millennium. There is, however, a lack of direct high‐resolution atmospheric time series on 10Be that enable estimating atmospheric modulation on the production signal. Here we report quasi‐weekly data on 10Be and 7Be isotopes covering the periods 1983–2000 and 1975–2006 respectively, that show, for the first time, coherent variations reflecting both atmospheric and production effects. Our data indicate intrusion of stratosphere/upper troposphere air masses that can modulate the isotopes production signal, and may induce relative peaks in the natural 10Be archives (i.e., ice and sediment). The atmospheric impact on the Be‐isotopes can disturb the production signals and consequently the estimate of past solar activity magnitude.
A laboratory seismoelectric measurement for the permafrost model with a frozen–unfrozen interface
Authors: Liu Zhengping , Yuan Lei , Zhang Xin , Liu Zhihui , Wu Haiyan
Published: November 2008

In this study, a laboratory seismoelectric measurement for the permafrost model with a frozen–unfrozen interface is presented. The measurements obtained experimentally confirms that an electric double‐layer can be formed at the interface due to the electric and mechanical differences of the frozen and unfrozen media, and seismoelectric conversion EM waves originted from the relative motion of the charges in the electric double‐layer can be observed at n × 10 kHz frequency band. This suggests a potential application for non‐destructive detection of the frost depth.
Periodic modulations in thermospheric composition by solar wind high speed streams
Authors: Crowley G. , Reynolds A. , Thayer J. P. , Lei J. , Paxton L. J. , Christensen A. B. , Zhang Y. , Meier R. R. , Strickland D. J.
Published: November 2008

ΣO/N2 ratios in the Earth's thermosphere are measured by the Global Ultraviolet Imager (GUVI) on the TIMED satellite, and demonstrate strong 9 and 7 day oscillations in 2005 and 2006, respectively, that are well correlated with the solar wind speed and Kp index. This work builds on the recently discovered connection between rotating solar coronal holes and thermospheric mass density variations. The work described here is the first description of geomagnetically forced periodicities in neutral composition. Furthermore, these observations provide the first definitive proof that the processes creating neutral composition changes during geomagnetic storms occur continuously at all activity levels and all over the world. The ΣO/N2 response versus the mass density response indicates the important role of vertical winds at high latitudes while thermal expansion dominates at lower latitudes.
Deep subduction and rapid exhumation: Role of crustal strength and strain weakening in continental subduction and ultrahigh‐pressure rock exhumation
Authors: Warren Clare J. , Beaumont Christopher , Jamieson Rebecca A.
Published: November 2008

The exhumation of crustal ultra‐high‐pressure (UHP) material depends on temporal and spatial variations in its detachment within the subduction channel. This dependence is investigated using numerical models with variable initial crustal strengths, representing a range of initial crustal compositions, and parameterized strain weakening, representing a range of processes that reduce effective crustal viscosity during deformation. Competition between down‐channel shear traction, favoring subduction, and up‐channel buoyancy, favoring exhumation, is expressed as the exhumation number, E, which can vary with time and position along the channel. Exhumed lower strength crust, which resists subduction owing to weak down‐channel traction, records peak conditions <35 kbar and exhumation rates <30 km Ma−1. Higher strength crust is efficiently subducted to UHP depths (E < 1), recording peak pressures >38 kbar. Given sufficient strain weakening, exhumation proceeds at >60 km Ma−1, indicating that buoyancy (E ≫ 1) drives exhumation in these models. In all models, exhuming UHP material forms a deforming ductile plume, with a range of possible structural relationships predicted between exhumed UHP and HP materials.
Adenovirus‐mediated ICOSIg gene transfer alleviates cardiac remodeling in experimental autoimmune myocarditis
Authors: Liu Wei , Feng Weiwei , Wang Fang , Li Weimin , Zhou Baoguo , Gao Cheng , Li Yue , Kong Yihui , Ma Manling , Fu Songbin
Published: November 2008

To explore the therapeutic effects of adenovirus vector mediated transfer of the ICOSIg gene on immuno‐inflammation‐mediated cardiac remodeling in an experimental autoimmune myocarditis (EAM) model, pAdeno‐ICOSIg was constructed and transfected into HEK 293 cells to produce the ICOSIg adenovirus. Ad‐CMV‐GFP was used as a control. EAM was induced in Lewis rats by injection of porcine cardiac myosin. The immunized rats were divided into two groups. The inducible co‐stimulatory molecule (ICOS) group received the adenovirus containing ICOSIg on day 14; the green fluorescent protein (GFP) group received the adenovirus containing GFP as the control adenovirus and 15 normal rats (Control group) consisted of the normal controls that were not immunized. On day 28, all rats were euthanized after echocardiography and histopathologically examined for cardiac fibrosis. Western blotting was performed to detect ICOS, ICOS ligand (ICOSL), matrix metalloproteinase (MMP)‐2, MMP‐9, tissue inhibitors of metalloproteinase (TIMP)‐1 and TIMP‐2 and real‐time RT‐PCR was performed to detect B7‐1, B7‐2 and interleukin (IL)‐17 expression. ELISPOT was applied to detect Th1 and Th2 cytokine production. Collagen concentration and collagen cross‐linking were determined as markers of cardiac fibrosis. It was found that blockade with ICOSIg exerted antifibrotic effects on cardiac remodeling in EAM. On day 28, cardiac function and inflammatory myocardial fibrosis improved significantly in the ICOS group compared to the GFP group. The expression of ICOS, the ICOSL, B7‐1 and IL‐17 was statistically significantly lower in the ICOS and Control groups compared to the GFP group. ICOSIg significantly augmented Th2 cytokine production and diminished Th1 and Th17 cytokine production. This blockade of the ICOS co‐stimulatory pathway with ICOSIg alleviated autoimmune inflammation‐mediated cardiac remodeling and improved cardiac function. Regulation of the Th1/Th2/Th17 balance may be one of the underlying mechanisms responsible for this effect.
Selective progressive response of soil microbial community to wild oat roots
Authors: DeAngelis Kristen M , Brodie Eoin L , DeSantis Todd Z , Andersen Gary L , Lindow Steven E , Firestone Mary K
Published: November 2008

Roots moving through soil induce physical and chemical changes that differentiate rhizosphere from bulk soil, and the effects of these changes on soil microorganisms have long been a topic of interest. The use of a high-density 16S rRNA microarray (PhyloChip) for bacterial and archaeal community analysis has allowed definition of the populations that respond to the root within the complex grassland soil community; this research accompanies compositional changes reported earlier, including increases in chitinase- and protease-specific activity, cell numbers and quorum sensing signal. PhyloChip results showed a significant change compared with bulk soil in relative abundance for 7% of the total rhizosphere microbial community (147 of 1917 taxa); the 7% response value was confirmed by16S rRNA terminal restriction fragment length polymorphism analysis. This PhyloChip-defined dynamic subset was comprised of taxa in 17 of the 44 phyla detected in all soil samples. Expected rhizosphere-competent phyla, such as Proteobacteria and Firmicutes, were well represented, as were less-well-documented rhizosphere colonizers including Actinobacteria, Verrucomicrobia and Nitrospira. Richness of Bacteroidetes and Actinobacteria decreased in soil near the root tip compared with bulk soil, but then increased in older root zones. Quantitative PCR revealed rhizosphere abundance of β-Proteobacteria and Actinobacteria at about 108 copies of 16S rRNA genes per g soil, with Nitrospira having about 105 copies per g soil. This report demonstrates that changes in a relatively small subset of the soil microbial community are sufficient to produce substantial changes in functions observed earlier in progressively more mature rhizosphere zones.
Weight Loss Surgery Eligibility According to Various BMI Criteria Among Adolescents
Authors: Lenders Carine M. , Wright Julie A. , Apovian Caroline M. , Hess Donald T. , Shukla Rishi R. , Adams William G. , Lee Kayoung
Published: November 2008

A BMI cutoff point at the 99th percentile for age and gender or at 40 kg/m2 has been suggested for more aggressive treatment of adolescent obesity. The main objective of this study was to determine the proportion of adolescents eligible for weight loss surgery (WLS) based on various BMI cutoff points. Data was extracted from the electronic medical record database of an urban pediatric ambulatory care center over 4 years. National data were used to calculate BMI percentiles (Centers for Disease Control and Prevention (CDC), 2000). Eligibility for WLS was based on a BMI percentile criterion (≥99th percentile) or the adult WLS cutoff point (≥40 kg/m2). The sample consisted of 3,220 adolescents aged 12–17.9 years, of which 53% were female, 55% were of black race, and 17% of Hispanic ethnicity. Overall, 88 (3%) adolescents had a BMI ≥40 kg/m2 and 236 (7%) had a BMI ≥99th percentile (P < 0.001). All adolescents with BMI ≥40 kg/m2 had a BMI ≥99th percentile. A total of 159/2,007 (8%) of 12–14.9‐year olds had a BMI ≥99th percentile compared with 77/1,213 (6%) 15–17.9‐year olds (P = 0.10), whereas 43/2,007 (2%) of 12–14.9‐year olds had a BMI ≥40 kg/m2 compared with 45/1,213 (4%) 15–17.9‐year olds (P = 0.003). In summary, a relatively large proportion of adolescents from a diverse urban population would qualify for WLS based on the percentile criterion. Fewer adolescents would be eligible based on the adult WLS criterion, and younger adolescents would be less likely to be eligible for WLS than older adolescents.
Proinflammatory Markers, Insulin Sensitivity, and Cardiometabolic Risk Factors in Treated HIV Infection
Authors: Samaras Katherine , Gan Seng K. , Peake Phillip W. , Carr Andrew , Campbell Lesley V.
Published: November 2008

Treated HIV infection and HIV‐lipoatrophy increases risk of cardiovascular disease (CVD) and type 2 diabetes mellitus (T2DM). Circulating inflammatory molecules may, in part, explain this increased risk. This study examined circulating inflammatory molecules in treated HIV infection in relation to insulin sensitivity, lipids total body, and intramyocellular fat, compared to insulin‐resistant obesity (an index group at high risk of diabetes). Detailed metabolic phenotypes were measured in 20 treated HIV‐infected men (with and without subcutaneous lipoatrophy) vs. 26 insulin‐resistant obese men (IR‐O, n = 26), including inflammatory molecules, insulin sensitivity, total body fat (TBF), visceral fat (visceral adipose tissue (VAT)), and intramyocellular lipid (IMCL). C‐reactive protein (CRP) levels in treated HIV were similar to those in IR‐O, despite lower TBF and greater insulin sensitivity in treated HIV. In HIV‐lipoatrophy, CRP was higher than that found in IR‐O. Adiponectin was similar between treated HIV and IR‐O, but significantly lower in those with HIV‐lipoatrophy. In treated HIV, subjects with higher CRP had significantly higher total cholesterol, VAT, and IMCL. In treated HIV, subjects with lower adiponectin had significantly lower HDL and higher triglycerides, glucose, VAT, and IMCL. In conclusion, a proinflammatory milieu equivalent to that of insulin‐resistant obesity characterizes lean men with treated HIV infection, worse in those with subcutaneous lipoatrophy. These factors may contribute to the accelerated diabetogenesis and cardiac risk observed in treated HIV infection.
A small component of the endoplasmic reticulum is required for store-operated Ca2+ channel activation in liver cells: evidence from studies using TRPV1 and taurodeoxycholic acid
Authors: Castro Joel , Aromataris Edoardo C. , Rychkov Grigori Y. , Barritt Greg J.
Published: November 2008

The question of whether the activation of SOCs (store-operated Ca2+ channels) requires the whole or part of the ER (endoplasmic reticulum) has not been fully resolved. The role of a putative sub-compartment of the ER in SOC activation in liver cells was investigated using ectopically expressed TRPV1 (transient receptor potential vanilloid 1), a non-selective cation channel, and TDCA (taurodeoxycholic acid), an activator of SOCs, to release Ca2+ from different regions of the ER. TRPV1 was expressed in the ER and in the plasma membrane. The amount of Ca2+ released from the ER by a TRPV1 agonist, measured using fura-2, was the same as that released by a SERCA (sarcoplasmic/endoplasmic reticulum Ca2+-ATPase) inhibitor, indicating that TRPV1 agonist-sensitive stores substantially overlap with SERCA inhibitor-sensitive stores. In contrast with SERCA inhibitors, TRPV1 agonists did not activate store-operated Ca2+ entry. These findings were confirmed by patch-clamp recording. Using FFP-18, it was shown that SERCA inhibitors release Ca2+ from the ER located closer to the plasma membrane than the region from which TRPV1 agonists release Ca2+. In contrast with SERCA inhibitors, TRPV1 agonists did not induce a redistribution of STIM1 (stromal interaction molecule 1). TDCA caused the release of Ca2+ from the ER, which was detected by FFP-18 but not by fura-2, and a redistribution of STIM1 to puncta similar to that caused by SERCA inhibitors. It is concluded that in liver cells, Ca2+ release from a small component of the ER located near the plasma membrane is required to induce STIM1 redistribution and SOC activation.
High capacitance carbon-based xerogel film produced without critical drying
Authors: Tao Yousheng , Endo Morinobu , Ohsawa Risa , Kanoh Hirofumi , Kaneko Katsumi
Published: November 2008

We report the production of carbon-based xerogel film without the need for supercritical drying. Xerogel samples were characterized with field emission scanning electron microscopy, nitrogen adsorption/desorption at 77 K, Raman spectroscopy, thermogravimetric analysis, and electrical conductivity and cyclic voltammetry measurements. Experimental results reveal that the film is largely crack free and homogeneous in thickness, and, importantly, has high surface area, large nanopore volume, and an excellent performance for electrical charge storage—both per unit mass and unit volume. These results indicate that the film has potential applications for electrical energy storage devices.
Bulk dense fine-grain (1−x)BiScO3–xPbTiO3 ceramics with high piezoelectric coefficient
Authors: Zou Tingting , Wang Xiaohui , Wang Han , Zhong Caifu , Li Longtu , Chen I-Wei
Published: November 2008

High density fine grain (1−x)BiScO3–xPbTiO3 ceramics were successfully prepared by two-step sintering and their ferroelectric properties were investigated. Experimental evidence indicates the existence of a morphotropic phase boundary at the composition x=0.635, which exhibits a piezoelectric coefficient d33 of 700 pC/N at room temperature, significantly higher than the reported values to date. Furthermore, a higher electromechanical coupling factor Kp=0.632 and a larger remnant polarization Pr=47.3 μC/cm2 were obtained. The paraelectric-to-ferroelectric phase transition occurs at 446 °C, slightly lower than in the coarse grain ceramics with a similar composition, suggesting a grain size effect. The local effective piezoelectric coefficient d33∗ was estimated to be 795 pC/N at 2.29 V, measured by scanning probe microscopy. Further atomic force microscope observation revealed the existence of 90° domains of about 60–70 nm in width, confirming the previous results that small domain structure enhances the piezoelectric properties.
Directional adhesion of gecko-inspired angled microfiber arrays
Authors: Lee Jongho , Fearing Ronald S. , Komvopoulos Kyriakos
Published: November 2008

Arrays of angled microfibers with a gecko-inspired structure were fabricated from a stiff thermoplastic polymer (polypropylene) with elastic properties similar to those of β-keratin of natural setae. Friction experiments demonstrated that this fibrillar polymer surface exhibits directional adhesion. Sliding of clean glass surfaces against and along the microfiber direction without applying an external normal force produced an apparent shear stress of 0.1 and 4.5 N/cm2, respectively. This directional adhesion is interpreted in the context of a nonlinear elastic bending model of an angled beam. Shearing and normal contact experiments yielded further evidence of the anisotropic adhesion of the fibrillar polymer and revealed the occurrence of a pull-off (adhesive) force at the instant of surface detachment, unlike vertically aligned microfiber arrays of the same material that exhibited a zero pull-off force. The results of this study provide impetus for the design of gecko-inspired adhesives with angled structures that demonstrate directional adhesion against different material surfaces.
Trace gas measurements using optically resonant cavities and quantum cascade lasers operating at room temperature
Authors: Welzel S. , Lombardi G. , Davies P. B. , Engeln R. , Schram D. C. , Röpcke J.
Published: November 2008

Achieving the high sensitivity necessary for trace gas detection in the midinfrared molecular fingerprint region generally requires long absorption path lengths. In addition, for wider application, especially for field measurements, compact and cryogen free spectrometers are definitely preferable. An alternative approach to conventional linear absorption spectroscopy employing multiple pass cells for achieving high sensitivity is to combine a high finesse cavity with thermoelectrically (TE) cooled quantum cascade lasers (QCLs) and detectors. We have investigated the sensitivity limits of an entirely TE cooled system equipped with an ∼0.5 m long cavity having a small sample volume of 0.3 l. With this spectrometer cavity enhanced absorption spectroscopy employing a continuous wave QCL emitting at 7.66 μm yielded path lengths of 1080 m and a noise equivalent absorption of 2×10−7 cm−1 Hz−1/2. The molecular concentration detection limit with a 20 s integration time was found to be 6×108 molecules/cm3 for N2O and 2×109 molecules/cm3 for CH4, which is good enough for the selective measurement of trace atmospheric constituents at 2.2 mbar. The main limiting factor for achieving even higher sensitivity, such as that found for larger volume multi pass cell spectrometers, is the residual mode noise of the cavity. On the other hand the application of TE cooled pulsed QCLs for integrated cavity output spectroscopy and cavity ring-down spectroscopy (CRDS) was found to be limited by the intrinsic frequency chirp of the laser. Consequently the accuracy and advantage of an absolute internal absorption calibration, in theory inherent for CRDS experiments, are not achievable.
Magnetoelastic effects in terbium ferroborate
Authors: Zvyagina G. A. , Zhekov K. R. , Bezmaternykh L. N. , Gudim I. A. , Bilych I. V. , Zvyagin A. A.
Published: November 2008

The behavior of the elastic moduli and sound absorption in a terbium orthoborate single crystal at low temperatures is studied. The components of the tensor of the elastic moduli of this system are determined. A structural phase transition and a transition of the magnetic subsystem into an antiferromagnetically ordered state appear in the temperature dependences of the sound velocities and absorption. The magnetic field dependences of the velocities of transverse sound exhibit singularities in the form of jumps at a magnetic field equal to the field of the spin-flop transition of the antiferromagnetic subsystem. Theoretical analysis shows that the observed behavior of the acoustic characteristics are associated not with the rare-earth subsystem of ferroborate but rather with the renormalization of the exchange interaction between iron ions as a result of the magnetoelastic coupling.
Electronic structure and ferromagnetic behavior of the alloys Mn1−xAxAs1−yBy
Authors: Golovchan A. V. , Gribanov I. F.
Published: November 2008

A systematic, first-principles investigation is made of the influence of cationic and anionic substitutions on the electronic structure and local magnetic characteristics of ferromagnetic MnAs. It is shown that most dopants considered as potentially suitable for modifying MnAs as a working material for magnetic refrigerators decrease the ferromagnetic moment. But there are variants of anionic substitution (for example, S and Se for As) for which the magnetic moment increases.
Influence of a single defect on the conductance of a tunnel point contact between a normal metal and a superconductor
Authors: Avotina Ye. S. , Kolesnichenko Yu. A. , van Ruitenbeek J. M.
Published: November 2008

We have investigated theoretically the conductance of a normal-superconductor point contact in the tunnel limit and analyzed the quantum interference effects originating from the scattering of quasi-particles by point-like defects. Analytical expressions for the oscillatory dependence of the conductance on the position of the defect are obtained for a defect situated either in the normal metal or in the superconductor. It is found that the amplitude of oscillations increases significantly when the applied bias approaches the gap energy of the superconductor. The spatial distribution of the order parameter near the surface in the presence of a defect is also obtained.
Mechanical properties of ultrafine-grain zirconium in the temperature range 4.2–300K
Authors: Tabachnikova E. D. , Podol’skiĭ A. V. , Bengus V. Z. , Smirnov S. N. , Natsik V. D. , Azhazha V. M. , Tikhonovskiĭ M. A. , Velikodnyĭ A. N. , Andrievskaya N. F. , Storozhilov G. E. , Tikhonovskaya T. M.
Published: November 2008

The mechanical properties under uniaxial compression of cylindrical samples of ultrafine-grain (UFG) zirconium (grain size ∼0.4μm) obtained by intense plastic strain (IPS)—a combination of extrusion, annealing, and drawing—have been studied in the temperature range 4.2–300K. The mechanical characteristics of UFG zirconium have been studied in two structural states and the results are compared with each other as well as with the characteristics of coarse-grain polycrystals of this material (state 1—samples after IPS, state 2—samples after IPS and annealing). It has been established that grain-size reduction under IPS substantially increases the yield stress of polycrystals (by a factor of 6 at 300K and by a factor of 4 at 77K) while maintaining a large reserve of plasticity up to 15%. Two stages of strain hardening and a decrease of the plastic-flow activation volume with increasing strain has been recorded in the strain diagrams of UFG zirconium. It is concluded that the main mechanisms determining the yield stress and strain hardening are the same for ultrafine- and coarse-grain zirconium: intragrain dislocation slip and twinning occur in parallel and interact with one another.
A revised electronic Hessian for approximate time-dependent density functional theory
Authors: Ziegler Tom , Seth Michael , Krykunov Mykhaylo , Autschbach Jochen
Published: November 2008

Time-dependent density functional theory (TD-DFT) at the generalized gradient level of approximation (GGA) has shown systematic errors in the calculated excitation energies. This is especially the case for energies representing electron transitions between two separated regions of space or between orbitals of different spatial extents. It will be shown that these limitations can be attributed to the electronic ground state Hessian GGGA. Specifically, we shall demonstrate that the Hessian GGGA can be used to describe changes in energy due to small perturbations of the electron density (Δρ), but it should not be applied to one-electron excitations involving the density rearrangement (Δρ) of a full electron charge. This is in contrast to Hartree–Fock theory where GHF has a trust region that is accurate for both small perturbations and one-electron excitations. The large trust radius of GHF can be traced back to the complete cancellation of Coulomb and exchange terms in Hartree–Fock (HF) theory representing self-interaction (complete self-interaction cancellation, CSIC). On the other hand, it is shown that the small trust radius for GGGA can be attributed to the fact that CSIC is assumed for GGA in the derivation of GGGA although GGA (and many other approximate DFT schemes) exhibits incomplete self-interaction cancellation (ISIC). It is further shown that one can derive a new matrix GR-DFT with the same trust region as GHF by taking terms due to ISIC properly into account. Further, with TD-DFT based on GR-DFT, energies for state-to-state transitions represented by a one-electron excitation (ψi→ψa) are approximately calculated as ΔEai. Here ΔEai is the energy difference between the ground state Kohn–Sham Slater determinant and the energy of a Kohn–Sham Slater determinant where ψi has been replaced by ψa. We make use of the new Hessian in two numerical applications involving charge-transfer excitations. It is concluded that higher than second order response theory (involving ISIC terms) must be used in approximate TD-DFT, in order to describe charge-transfer excitations.
Core-excitation energy calculations with a long-range corrected hybrid exchange-correlation functional including a short-range Gaussian attenuation (LCgau-BOP)
Authors: Song Jong-Won , Watson Mark A. , Nakata Ayako , Hirao Kimihiko
Published: November 2008

We report the calculations of core-excitation energies of first-row atoms using the time-dependent density functional theory (DFT) and the long-range correction (LC) scheme for exchange-correlation functionals, including LC-BOP, Coulomb-attenuated method BLYP, and our recently developed LCgau-BOP method, which includes a flexible portion of short-range Hartree–Fock (HF) exchange through the inclusion of a Gaussian function in the LC scheme. We show that the LC scheme completely fails to improve the poor accuracy of conventional generalized gradient approximation functionals, while the LCgau scheme gives an accuracy which is an order of magnitude better than BLYP and significantly better than B3LYP. A reoptimization of the two parameters controlling the inclusion of short-range HF exchange in the LCgau method enables the errors to be reduced to the order of 0.1 eV which is competitive with the best DFT methods we are aware of. This reparametrization does not affect the LC scheme and therefore maintains the high accuracy of predicted reaction barrier heights. Moreover, while there is some loss in accuracy in thermochemical predictions compared to the previously optimized LCgau-BOP, rms errors in the atomization energies over the G2 test set are found to be comparable to B3LYP. Finally, we attempt to rationalize the success of the LC and LCgau schemes in terms of the well-known self-interaction error (SIE) of conventional functionals. To estimate the role of the SIE, we examine the total energy calculations for systems with a fractional number of electrons, not only in the highest occupied molecular orbital but also in the 1s-characterized core orbital. Our conclusion is that the inclusion of short-range HF exchange in LC-type functionals can significantly alleviate the problems of the SIE in the core region. In particular, we confirm that the absence of the SIE diagnostics in the core orbital energies correlates with the accurate prediction of core-excitation energies using the newly optimized LCgau approach.
Effects of anharmonicity on diffusive-controlled symmetric electron transfer rates: From the weak to the strong electronic coupling regions
Authors: Zhu Wenjuan , Zhao Yi
Published: November 2008

The approach for the diffusive-controlled electron transfer rates [W. Zhu and Y. Zhao, J. Chem. Phys. 126, 184105 (2007)], which is modeled after the Sumi–Marcus theory, is applied to symmetric electron-transfer reactions in a solvent environment with anharmonic potential functions. The electron-transfer rates are evaluated using the quantum R-matrix theory for dealing with the intramolecular vibrational motions and imaginary-time split operator technique for solving the diffusive equations, thereby taking explicit account of the weak-to-strong electronic couplings. The effect of anharmonicity for both the solvent and intramolecular vibrational degrees of freedom are investigated. It is found that the anharmonicity of the intramolecular modes always enhances the rate while the solvent anharmonicity decreases the rate, compared with the harmonic modes. The possible mechanisms have been clarified.
Mechanisms and scalings of energetic ion transport via tokamak microturbulence
Authors: Hauff T. , Jenko F.
Published: November 2008

The turbulent E×B advection of energetic ions in three-dimensional tokamak geometry is investigated both analytically and numerically. It is shown that orbit averaging (leading to a significant reduction of the diffusivity) is only valid for low magnetic shear. At moderate or high magnetic shear, a rather slow decrease of the diffusivity is found, proportional to (E∕Te)−1 or (E∕Te)−1.5 for particles with a large or small parallel velocity component, respectively. The decorrelation mechanisms responsible for this behavior are studied and explained in detail. Moreover, it is found that resonances between the toroidal drift of the particles and the diamagnetic drift of the turbulence can lead to an enhancement of the fast ion transport.
Synchronization of a class of chaotic systems with fully unknown parameters using adaptive sliding mode approach
Authors: Roopaei M. , Zolghadri Jahromi M.
Published: November 2008

In this paper, an adaptive sliding mode control method for synchronization of a class of chaotic systems with fully unknown parameters is introduced. In this method, no knowledge of the bounds of parameters is required in advance and the parameters are updated through an adaptive control process. We use our proposed method to synchronize two chaotic gyros, which has been the subject of intense study during the recent years for its application in the navigational, aeronautical, and space engineering domains. The effectiveness of our method is demonstrated in simulation environment and the results are compared with some recent schemes proposed in the literature for the same task.
Pitch angle scattering and synchrotron radiation of relativistic runaway electrons in tokamak stochastic magnetic fields
Authors: Martín-Solís J. R. , Sánchez R.
Published: November 2008

In a recent work [J. R. Martín-Solís and R. Sánchez, Phys. Plasmas 13, 012508 (2006)], the increase that the presence of stochastic magnetic fields causes on the synchrotron radiation losses of relativistic runaway electrons was quantified using a guiding-center approximation. Here, we complete those studies by considering instead the mechanism which dominates the interaction at the gyromotion level. It is shown that, under typical tokamak conditions, the resonant cyclotron interaction with high enough parallel (to the magnetic field) wave numbers (k∥) modes can create, even for moderate magnetic fluctuation levels, an upper bound on the runaway energy. Implications for disruption-generated runaway electrons will be also discussed.
Electrical properties of high energy ion irradiated 4H-SiC Schottky diodes
Authors: Izzo G. , Litrico G. , Calcagno L. , Foti G. , La Via F.
Published: November 2008

The changes in the electrical properties of 4H-SiC epitaxial layer induced by irradiation with 7.0 MeV C+ ions were investigated by current-voltage measurements and deep level transient spectroscopy (DLTS). Current-voltage characteristics of the diodes fabricated from epilayers doped with different nitrogen concentrations were monitored before and after irradiation in the fluence range of 109–1010 cm−2. The leakage current was not changed after irradiation, while the forward current-voltage characteristics of the diodes showed an increase in the series resistance, which is mainly related to the high degree of compensation occurring near the end of the ion implant depth.

The temperature dependence of the carrier mobility determined from the I-V measurements in the temperature range of 100–700 K shows a T−3 dependence of mobility as determined from the nonirradiated as well as the irradiated diodes. DLTS measurements of the irradiated diodes reveal the presence of two deep levels located at 0.98 and 1.4 eV below the conduction band edge.
Spin-orbit coupling in bulk ZnO and GaN
Authors: Fu J. Y. , Wu M. W.
Published: November 2008

Using group theory and Kane-type k⋅p model together with the Löwdin partition method, we derive the expressions for the spin-orbit coupling of electrons and holes, including the linear-k Rashba term due to the intrinsic structure inversion asymmetry and the cubic-k Dresselhaus term due to the bulk inversion asymmetry in wurtzite semiconductors. The coefficients of the electron and hole Dresselhaus terms of ZnO and GaN in wurtzite structure and GaN in zinc-blende structure are calculated using the nearest-neighbor sp3 and sp3s∗ tight-binding models, respectively.
Stacked white organic light emitting devices consisting of separate red, green, and blue elements
Authors: Qi Xiangfei , Slootsky Michael , Forrest Stephen
Published: November 2008

We demonstrate a white organic light-emitting device where individual red, green, and blue (R, G, and B) phosphorescent organic light-emitting devices are vertically stacked and electrically interconnected by a compound MoO3/Li-doped charge generation layer. For the order of B, G, and R cells positioned relative to the indium tin oxide anode, the device yields a peak total external quantum efficiency (EQE) and power efficiency (PE) of ηext=(36±2)% at a current density of J=82 μA/cm2 and ηp=21±1 lm/W at J=17 μA/cm2, respectively. The EQE and PE of the device roll off to (32±2)% and 13±1 lm/W at 1000 cd/m2, corresponding to J=2 mA/cm2. At this luminance, the device shows Commission Internationale de L’Eclairage chromaticity coordinates of (0.45, 0.36) and a color rendering index of 63.
High-speed operation of GaN/AlGaN quantum cascade detectors at λ≈1.55 μm
Authors: Vardi A. , Kheirodin N. , Nevou L. , Machhadani H. , Vivien L. , Crozat P. , Tchernycheva M. , Colombelli R. , Julien F. H. , Guillot F. , Bougerol C. , Monroy E. , Schacham S. , Bahir G.
Published: November 2008

We demonstrate room-temperature, high-speed operation of GaN/AlGaN quantum cascade detectors. The devices are processed as square mesas with 50 Ω coplanar access lines. Frequency response measurements were performed under illumination by a modulated laser diode emitting at λ=1.55 μm. The electrical response exhibits a first-order filter frequency response. For 17×17 μm2 (25×25 μm2) detectors the −3 dB cutoff frequency is 11.4 GHz (6.5 GHz). S-parameter analysis confirms that the cutoff frequency is extrinsically limited and that the speed of the device can be further increased by reducing the device size.
Arsenic-dominated chemistry in the acid cleaning of InGaAs and InAlAs surfaces
Authors: Sun Yun , Pianetta Piero , Chen Po-Ta , Kobayashi Masaharu , Nishi Yoshio , Goel Niti , Garner Michael , Tsai Wilman
Published: November 2008

The surface cleaning of InGaAs and InAlAs is studied using synchrotron radiation photoelectron spectroscopy. Thermal annealing at 400°C cannot completely remove the native oxides from those surfaces. Elemental arsenic buildup is observed on both surfaces after acid treatment using HCl, HF, or H2SO4 solution, which is similar to acid-cleaned GaAs surface. Cleaned InGaAs surface is oxide-free but small amount of aluminum oxide remains on cleaned InAlAs surface. The common chemical reactions between III-As semiconductors and acid solutions are identified and are found to be dominated by arsenic chemistry.
Comparison of nanoscale measurements of strain and stress using electron back scattered diffraction and confocal Raman microscopy
Authors: Vaudin Mark D. , Gerbig Yvonne B. , Stranick Stephan J. , Cook Robert F.
Published: November 2008

Stresses in Si as small as 10 MPa have been measured using electron backscattered diffraction (EBSD) and confocal Raman microscopy (CRM) with spatial resolutions of 10 nm and 100 nm, respectively. In both techniques, data were collected across wedge indentations in (001) Si. EBSD measured the stress and strain tensors and CRM measured the uniaxial stress. The results agreed very well except close to the indentation, where the surface-sensitive EBSD results indicated larger stresses. Results converged when the CRM laser excitation wavelength was reduced, probing smaller depths. The stress profiles are consistent with the inverse-square power law predicted by Eshelby analysis.
Performance improvement of inverted polymer solar cells with different top electrodes by introducing a MoO3 buffer layer
Authors: Tao Chen , Ruan Shengping , Zhang Xindong , Xie Guohua , Shen Liang , Kong Xiangzi , Dong Wei , Liu Caixia , Chen Weiyou
Published: November 2008

Molybdenum trioxide (MoO3) was inserted between the active layer and top electrode in inverted polymer solar cells (PSCs) with nanocrystalline titanium dioxide as an electron selective layer. The performances of structurally identical PSCs with different top electrodes (Au, Ag, and Al) were investigated and compared. The interface between MoO3 and different metals was studied by x-ray photoelectron spectroscopy. The results showed that the performances of devices with different metals are greatly improved due to the incorporation of MoO3 and the open-circuit voltage of devices is relatively insensitive to the choice of the anode metal when MoO3 is introduced.
N
2
O
-grown oxides/4H-SiC (0001), (033¯8), and (112¯) interface properties characterized by using p-type gate-controlled diodes
Authors: Noborio Masato , Suda Jun , Kimoto Tsunenobu
Published: November 2008

The N2O-grown SiO2/4H-SiC (0001), (033¯8), and (112¯0) interface properties in p-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) have been characterized by using gate-controlled diodes. Although the inversion layer is not formed in simple SiC MOS capacitors at room temperature due to its large bandgap, a standard low frequency capacitance-voltage (C-V) curve can be obtained for the gate-controlled diodes, owing to the supply of minority carriers from the source region. From the quasistatic C-V curves measured by using gate-controlled diodes, the interface state density has been evaluated by an original method proposed in this study. The interface state density near the valence band edge evaluated by the method is the lowest at the oxides/4H-SiC (033¯8) interface. Comparison with the channel mobility is also discussed.
The magnetic resonance shutter speed discriminates vascular properties of malignant and benign breast tumors in vivo
Authors: Huang Wei , Li Xin , Morris Elizabeth A. , Tudorica Luminita A. , Seshan Venkatraman E. , Rooney William D. , Tagge Ian , Wang Ya , Xu Jingang , Springer Charles S.
Published: November 2008

The pharmacokinetic analysis of dynamic-contrast-enhanced (DCE) MRI data yields
K
trans
and
k
ep
, two parameters independently measuring the capillary wall contrast reagent transfer rate. The almost universally used standard model (SM) embeds the implicit assumption that equilibrium transcytolemmal water exchange is effectively infinitely fast. In analyses of routine DCE-MRI data from 22 patients with suspicious breast lesions initially ruled positive by institutional screening protocols, the SM
K
trans
values for benign and malignant lesions exhibit considerable overlap. A form of the shutter-speed model (SSM), which allows for finite exchange kinetics, agrees with the SM
K
trans
value for each of the 15 benign lesions. However, it reveals that the SM underestimates
K
trans
for each of the seven malignant tumors in this population. The fact that this phenomenon is unique to malignant tumors allows their complete discrimination from the benign lesions, as validated by comparison with gold-standard pathology analyses of subsequent biopsy tissue samples. Likewise, the SM overestimates
k
ep
, particularly for the benign tumors. Thus, incorporation of the SSM into the screening protocols would have precluded all 68% of the biopsy/pathology procedures that yielded benign findings. The SM/SSM difference is well understood from molecular first principles.
microRNA-138 modulates cardiac patterning during embryonic development
Authors: Morton Sarah U. , Scherz Paul J. , Cordes Kimberly R. , Ivey Kathryn N. , Stainier Didier Y. R. , Srivastava Deepak
Published: November 2008

Organ patterning during embryonic development requires precise temporal and spatial regulation of protein activity. microRNAs (miRNAs), small noncoding RNAs that typically inhibit protein expression, are broadly important for proper development, but their individual functions during organogenesis are largely unknown. We report that miR-138 is expressed in specific domains in the zebrafish heart and is required to establish appropriate chamber-specific gene expression patterns. Disruption of miR-138 function led to ventricular expansion of gene expression normally restricted to the atrio-ventricular valve region and, ultimately, to disrupted ventricular cardiomyocyte morphology and cardiac function. Temporal-specific knockdown of miR-138 by antagomiRs showed miR-138 function was required during a discrete developmental window, 24–34 h post-fertilization (hpf). miR-138 functioned partially by repressing the retinoic acid synthesis enzyme, aldehyde dehydrogenase-1a2, in the ventricle. This activity was complemented by miR-138-mediated ventricular repression of the gene encoding versican (
cspg2
), which was positively regulated by retinoic-acid signaling. Our findings demonstrate that miR-138 helps establish discrete domains of gene expression during cardiac morphogenesis by targeting multiple members of a common pathway, and also establish the use of antagomiRs in fish for temporal knockdown of miRNA function.
Profiling antibody responses by multiparametric analysis of primary B cells
Authors: Story Craig M. , Papa Eliseo , Hu Chih-Chi Andrew , Ronan Jehnna L. , Herlihy Kara , Ploegh Hidde L. , Love J. Christopher
Published: November 2008

Determining the efficacy of a vaccine generally relies on measuring neutralizing antibodies in sera. This measure cannot elucidate the mechanisms responsible for the development of immunological memory at the cellular level, however. Quantitative profiles that detail the cellular origin, extent, and diversity of the humoral (antibody-based) immune response would improve both the assessment and development of vaccines. Here, we describe a novel approach to collect multiparametric datasets that describe the specificity, isotype, and apparent affinity of the antibodies secreted from large numbers of individual primary B cells (≈103-104). The antibody/antigen binding curves obtained by this approach can be used to classify closely related populations of cells using algorithms for data clustering, and the relationships among populations can be visualized graphically using affinity heatmaps. The technique described was used to evaluate the diversity of antigen-specific antibody-secreting cells generated during anin vivohumoral response to a series of immunizations designed to mimic a multipart vaccination. Profiles correlating primary antibody-producing cells with the molecular characteristics of their secreted antibodies should facilitate both the evaluation of candidate vaccines and, broadly, studies on the repertoires of antibodies generated in response to infectious or autoimmune diseases.