bluuebunny/crossref_metadata_2025 huggingface dataset:
Anisotropic dispersion and attenuation due to wave‐induced fluid flow: Quasi‐static finite element modeling in poroelastic solids
Authors: Wenzlau F. , Altmann J. B. , Müller T. M.
Published: July 2010

Heterogeneous porous media such as hydrocarbon reservoir rocks are effectively described as anisotropic viscoelastic solids. They show characteristic velocity dispersion and attenuation of seismic waves within a broad frequency band, and an explanation for this observation is the mechanism of wave‐induced pore fluid flow. Various theoretical models quantify dispersion and attenuation of normal incident compressional waves in finely layered porous media. Similar models of shear wave attenuation are not known, nor do general theories exist to predict wave‐induced fluid flow effects in media with a more complex distribution of medium heterogeneities. By using finite element simulations of poroelastic relaxation, the total frequency‐dependent complex stiffness tensor can be computed for a porous medium with arbitrary internal heterogeneity. From the stiffness tensor, velocity dispersion and frequency‐dependent attenuation are derived for compressional and shear waves as a function of the angle of incidence. We apply our approach to the case of layered media and to that of an ellipsoidal poroelastic inclusion. In the case of the ellipsoidal inclusion, compressional and shear wave modes show significant attenuation, and the characteristic frequency dependence of the effect is governed by the spatiotemporal scale of the pore fluid pressure relaxation. In our anisotropic examples, the angle dependence of the attenuation is stronger than that of the velocity dispersion. It becomes clear that the spatial attenuation patterns show specific characteristics of wave‐induced fluid flow, implying that anisotropic attenuation measurements may contribute to the inversion of fluid transport properties in heterogeneous porous media.
The photochemistry of carbon monoxide in the stratosphere and mesosphere evaluated from observations by the Microwave Limb Sounder on the Aura satellite
Authors: Minschwaner K. , Manney G. L. , Livesey N. J. , Pumphrey H. C. , Pickett H. M. , Froidevaux L. , Lambert A. , Schwartz M. J. , Bernath P. F. , Walker K. A. , Boone C. D.
Published: July 2010

The photochemical production and loss rates for carbon monoxide (CO) in the stratosphere and mesosphere are evaluated using measurements from the Aura Microwave Limb Sounder (MLS) and the Atmospheric Chemistry Experiment‐Fourier Transform Spectrometer (ACE‐FTS). The distributions of reactive trace gases involved in the photochemistry of CO, including OH, CH4, O(1D), Cl, as well as temperatures for calculating reaction rates, are either directly observed or constrained from observations. We map the CO net production and loss as a function of pressure (10–0.02 hPa, about 30–75 km altitude), latitude (approximately ±70°), and season. The results indicate that photochemical loss dominates over production for nearly all conditions considered here. A minimum photochemical loss lifetime of about 10 days occurs near the 2 hPa pressure level, and it follows the region of maximum sunlight exposure. At high latitudes during winter, the CO lifetime is generally longer than 30 days. Time scales become much shorter in spring, however, when CO lifetimes can be 15–20 days poleward of 60° latitude in the upper stratosphere. On the basis of these results, CO is a suitable tracer during autumn to spring above the 0.1 hPa pressure level but not in the upper stratosphere near 1 hPa.
Vertical velocity structure of nonprecipitating continental boundary layer stratocumulus clouds
Authors: Ghate Virendra P. , Albrecht Bruce A. , Kollias Pavlos
Published: July 2010

Continental boundary layer (BL) stratocumulus clouds affect the local weather by modulating the surface energy and moisture budgets and are also intimately tied to the diurnal cycle of the turbulence in the BL. Vertical velocity structure of these clouds is studied using data from the Atmospheric Radiation Measurement Program's Southern Great Plains observing facility located near Lamont, Oklahoma. Data from vertically pointing cloud radar from eleven cases of nonprecipitating BL stratocumulus clouds are used to obtain half‐hourly values of in‐cloud vertical velocity variance, skewness, updraft fraction, downdraft fraction, and mass flux. The variance showed a general decrease with height, while the skewness was weakly positive in the cloud layer and negative near cloud top on half‐hourly time scales. Vertically coherent structures spanning through the entire cloud layer were responsible for ∼40% of the observed vertical velocity variance, while horizontally (temporally) coherent structures lasting at least 20 s were responsible for ∼77% of the vertical velocity variance. The half‐hour periods were then classified on the basis of the surface buoyancy flux (B) as small B periods (B < 10 Wm−2) and large B periods (B > 60Wm−2). Small B periods exhibited lower variance near cloud base compared to large B periods with the differences being reversed near cloud top. The skewness was positive in the cloud layer during large B periods and negative during small B periods, while the skewness was negative near cloud top in both scenarios. The small B periods had about ten times more updrafts greater than 1 m s−1 near cloud top compared to large B periods.
Coupling of mass transfer and reactive transport for nonlinear reactions in heterogeneous media
Authors: Willmann M. , Carrera J. , Sanchez‐Vila X. , Silva O. , Dentz M.
Published: July 2010

Fast chemical reactions are driven by mixing‐induced chemical disequilibrium. Mixing is poorly represented by the advection‐dispersion equation. Instead, effective dynamics models, such as multirate mass transfer (MRMT), have been successful in reproducing observed field‐scale transport, notably, breakthrough curves (BTCs) of conservative solutes. The objective of this work is to test whether such effective models, derived from conservative transport observations, can be used to describe effective multicomponent reactive transport in heterogeneous media. We use a localized formulation of the MRMT model that allows us to solve general reactive transport problems. We test this formulation on a simple three‐species mineral precipitation problem at equilibrium. We first simulate the spatial and temporal distribution of mineral precipitation rates in synthetic hydraulically heterogeneous aquifers. We then compare these reaction rates to those corresponding to an equivalent (i.e., same conservative BTC) homogenized medium with transport characterized by a nonlocal in time equation involving a memory function. We find an excellent agreement between the two models in terms of cumulative precipitated mass for a broad range of generally stationary heterogeneity structures. These results indicate that mass transfer models can be considered to represent quite accurately the large‐scale effective dynamics of mixing controlled reactive transport at least for the cases tested here, where individual transport paths sample the full range of heterogeneities represented by the BTC.
Solute transport across an interface: A Fickian theory for skewness in breakthrough curves
Authors: Appuhamillage T. A. , Bokil V. A. , Thomann E. , Waymire E. , Wood B. D.
Published: July 2010

This paper provides a mathematical treatment of solute transport when the mean velocity is perpendicular to a sharp interface. For this case, the resident and flux‐averaged concentrations can be derived from Fickian laws of convection‐dispersion. In a recently reported approach to (deterministic) Fickian convection‐dispersion equations it was shown that the concentration field describing solute transport parallel to a sharp interface could be equivalently expressed in terms of the distribution of a particular skew Brownian motion. The present paper is an extension of this theory to the case of Fickian convection‐dispersion for solute transport in the direction of flow orthogonal to a sharp interface. Just as in the case of parallel interface, this is significant in that it leads to an explicit formula for the concentration field as well as providing some guidance to the further development of particle tracking methods for representing solute transport in discontinuous media. As an application of this theory we obtain specific results to explain the interesting types of symmetries and asymmetries in the breakthrough curves of a conservative tracer across an sharp interface recently reported by Berkowitz et al. (2009).
Impact of atmospheric CO2 levels on continental silicate weathering
Authors: Beaulieu E. , Goddéris Y. , Labat D. , Roelandt C. , Oliva P. , Guerrero B.
Published: July 2010

Anthropogenic sources are widely accepted as the dominant cause for the increase in atmospheric CO2 concentrations since the beginning of the industrial revolution. Here we use the B‐WITCH model to quantify the impact of increased CO2 concentrations on CO2 consumption by weathering of continental surfaces. B‐WITCH couples a dynamic biogeochemistry model (LPJ) and a process‐based numerical model of continental weathering (WITCH). It allows simultaneous calculations of the different components of continental weathering fluxes, terrestrial vegetation dynamics, and carbon and water fluxes. The CO2 consumption rates are estimated at four different atmospheric CO2 concentrations, from 280 up to 1120 ppmv, for 22 sites characterized by silicate lithologies (basalt, granite, or sandstones). The sensitivity to atmospheric CO2 variations is explored, while temperature and rainfall are held constant. First, we show that under 355 ppmv of atmospheric CO2, B‐WITCH is able to reproduce the global pattern of weathering rates as a function of annual runoff, mean annual temperature, or latitude for silicate lithologies. When atmospheric CO2 increases, evapotranspiration generally decreases due to progressive stomatal closure, and the soil CO2 pressure increases due to enhanced biospheric productivity. As a result, vertical drainage and soil acidity increase, promoting CO2 consumption by mineral weathering. We calculate an increase of about 3% of the CO2 consumption through silicate weathering (mol ha−1 yr−1) for 100 ppmv rise in CO2. Importantly, the sensitivity of the weathering system to the CO2 rise is not uniform and heavily depends on the climatic, lithologic, pedologic, and biospheric settings.
Stratification of east‐west plasma flow channels observed in the ionospheric cusp in response to IMF BY polarity changes
Authors: Rinne Y. , Moen J. , Carlson H. C. , Hairston M. R.
Published: July 2010

During a period of predominantly north‐westward flow for IMF BZ negative and IMF BY positive, a sequence of three distinct negative excursions of IMF BY resulted in a train of three eastward directed flow channels, interleaved by westward flow enhancements propagating into the polar cap. The high resolution of the EISCAT Svalbard radar data enables us to track formation and movement of the flow channels, which are interpreted as a sequence of intermittent reconnection alternating between different reconnection sites. Our observations are consistent with the view that a new region of reconnected flux manifests as development of a distinct flow channel near the polar cap boundary, and that successive events stay separated while pushing each other into the polar cap. Each flow channel will remain separated from neighboring channels mapping to different reconnection sites as long as the magnetic tension force with its associated field aligned current systems is maintained.
Search for a glacial‐age 14C‐depleted ocean reservoir
Authors: Broecker Wally , Clark Elizabeth
Published: July 2010

Measurements of the radiocarbon age difference between mixed benthic foraminifera and several coexisting planktic entities were made in hopes of finding evidence for the existence of an isolated glacial‐age abyssal ocean reservoir whose demise would explain the large drops in the 14C to C ratio in atmosphere and surface ocean carbon which occurred during the period of deglaciation. Forty‐six new radiocarbon results were obtained at seven depths covering the full range of glacial time (i.e., ∼27 to 15 14C kyrs) from an equatorial Pacific sediment core at 4.4‐km water depth. Even though age reversals for foraminifera (but not for coccoliths) at two of the eight depths and large age differences between G. sacculifer and three submixed‐layer planktic species mar this data set, there remains little likelihood that such a reservoir existed.
Stromal cells’ B7‐1 is a key stimulatory molecule for interleukin‐10 production by HOZOT, a multifunctional regulatory T‐cell line
Authors: Otani Takeshi , Tsuji‐Takayama Kazue , Okochi Ayumi , Yamamoto Mayuko , Takeuchi Makoto , Yamasaki Fumiyuki , Nakamura Shuji , Kibata Masayoshi
Published: July 2010

We have previously shown that xenogeneic stromal cell stimulation of naïve T cells resulted in the generation of a new type of regulatory T (Treg) cell termed HOZOT, which has multifunctional properties and a CD4/CD8 double‐positive phenotype. Even after the establishment of HOZOT, stromal cells can function as an antigen‐presenting cell (APC) by inducing these cells to produce interleukin (IL)‐10. When compared with other stimuli, stromal cells showed an IL‐10‐producing ability comparable to anti‐CD3 antibody (Ab) stimulation, and much greater than dendritic cell (DC) stimulation. Distinct from professional APCs, stromal cells express only major histocompatibility complex (MHC) class I and B7‐1 costimulatory molecules, and not MHC class II or other costimulatory molecules, such as ICOSL (CD275), PD‐L1 (CD274), PD‐L2 (CD273), CD40, OX40L (CD252) and 4‐1BBL (CD137L) in the absence of stimulation. Blocking experiments revealed that, in addition to anti‐H‐2Kd Ab and anti‐human CD8 Ab, anti‐mouse B7‐1 Ab could effectively block IL‐10 production, indicating a key role of the B7‐1/CD28 pathway. Using stromal cells expressing different levels of B7‐1, IL‐10 production correlated with the levels of B7‐1 expression. Distinct from ICOSL or PD‐L1 expressed on DCs (which are regarded as IL‐10‐inducing costimulatory molecules), this study showed that B7‐1 on stromal cells is a key molecule regulating IL‐10 production by multifunctional Treg cells, HOZOT.
CD40‐activated B cells contribute to mesothelioma tumor regression
Authors: Jackaman Connie , Cornwall Scott , Graham Peter Thomas , Nelson Delia Jane
Published: July 2010

Targeting CD40, a member of the tumor necrosis factor superfamily, using agonist antibodies (Abs) produces dramatic antitumor effects. Indeed, high‐dose intravenous anti‐CD40 Ab ‘licenses’ dendritic cells (DCs) that instruct activated CD8+ cytotoxic T cells to leave lymph nodes (LNs) and penetrate the mesothelioma tumor microenvironment. However, toxic side effects and the potential of an ‘overwhelmed’ immune response warrant an alternative approach. In this study, we show that injecting lower doses of anti‐CD40 Ab directly into the tumor bed avoided toxic side effects and prolonged survival in 60% of mice, with most cured. Unexpectedly, DCs in tumors and LNs ‘disappeared’, CD8+ tumor‐specific T‐cell numbers and function were not enhanced, and T cells did not infiltrate regressing tumors. CD4+ or CD8+ depletion only marginally hindered anti‐CD40 Ab efficacy implying another effector mechanism. B‐cell numbers significantly increased in tumors, draining LNs and spleens during intratumoral anti‐CD40 Ab treatment. CD40 targeting had no effect on splenic B‐1 cells, obliterated marginal zone B cells and promoted follicular (FO) B‐cell activity. Adoptive transfer of tumor antigen‐experienced, CD40‐activated B cells, or their immunoglobulin products, which recognized autoantigens on mesothelioma cells, protected against tumor challenge. Finally, studies using B‐cell knockout mice showed that successful treatment of established tumors required the presence of B cells. Thus, these data suggest that CD40‐activated FO B cells can become an important component of an effective antitumor immune response.
Bifurcation phenomena in two-dimensional piecewise smooth discontinuous maps
Authors: Rakshit Biswambhar , Apratim Manjul , Banerjee Soumitro
Published: July 2010

In recent years the theory of border collision bifurcations has been developed for piecewise smooth maps that are continuous across the border and has been successfully applied to explain nonsmooth bifurcation phenomena in physical systems. However, there exist a large number of switching dynamical systems that have been found to yield two-dimensional piecewise smooth maps that are discontinuous across the border. In this paper we present a systematic approach to the problem of analyzing the bifurcation phenomena in two-dimensional discontinuous maps, based on a piecewise linear approximation in the neighborhood of the border. We first motivate the analysis by considering the bifurcations occurring in a familiar physical system—the static VAR compensator used in electrical power systems—and then proceed to formulate the theory needed to explain the bifurcation behavior of such systems. We then integrate the observed bifurcation phenomenology of the compensator with the theory developed in this paper. This theory may be applied similarly to other systems that yield two-dimensional discontinuous maps.
Effect of Nb-donor and Fe-acceptor dopants in (Bi1/2Na1/2)TiO3–BaTiO3–(K0.5Na0.5)NbO3 lead-free piezoceramics
Authors: Jo Wook , Erdem Emre , Eichel Rüdiger-A. , Glaum Julia , Granzow Torsten , Damjanovic Dragan , Rödel Jürgen
Published: July 2010

The role of Fe as an acceptor and Nb as a donor in [0.94−x](Bi1/2Na1/2)TiO3–0.06BaTiO3−x (K0.5Na0.5)NbO3 (100xKNN) (x=0.02 and 0.03) lead-free piezoceramics was investigated. X-ray diffraction analyses show that all the profiles are best-fitted with a cubic symmetry where Fe doping tends to induce a lattice expansion, while Nb doping does the opposite. The strain and polarization characteristics are enhanced and suppressed by the acceptor and donor dopants, respectively. The improvement in the electrical properties with acceptor doping is accompanied by the stabilization of a ferroelectric order. Electron paramagnetic resonance spectroscopic analysis suggests that the stabilization of the ferroelectric order by the Fe dopant originates from the formation of (FeTi′–VO••)• defect dipoles.
On the impact of germanium doping on the vacancy formation energy in Czochralski-grown silicon
Authors: Vanhellemont Jan , Suezawa Masashi , Yonenaga Ichiro
Published: July 2010

The formation energy and thermal equilibrium concentration of vacancies in Ge doped Czochralski-grown Si are studied by quenching of samples annealed at temperatures between 1200 and 1350 °C for 1 h under hydrogen atmosphere. After quenching, the majority of the formed vacancy and hydrogen containing point defect clusters are transformed into VH4 defects by a 1 h anneal at 450 °C. Measuring the amplitude of the vibrational band of VH4 at 2223 cm−1 as function of the quenching temperature allows estimating the vacancy formation energy. An apparent formation energy of about 2 eV is obtained for Ge doping between 7×1017 and 6.5×1020 cm−3 which is significantly lower than the 4 eV obtained for high purity Si. In the whole quenching temperature window, the vacancy thermal equilibrium concentration is significantly higher than in Si without Ge doping. It is shown that this lower apparent formation energy can be explained by the presence of vacancy traps.
Polyethyleneoxide/sodium dodecyl sulfate as hole-blocking/electron-transporting layer for high-performance blue polymer light-emitting diode with oxygen- and moisture-stable aluminum cathode
Authors: Wu Jiun-Shian , Lu Hsin-Hung , Hung Wei-Chun , Lin Guan-Hong , Chen Show-An
Published: July 2010

We present the case of the blend of polyethyleneoxide (PEO) with sodium dodecyl sulfate (SDS) as a hole-blocking (HB)/electron-transporting (ET) layer to allow the use of oxygen- and moisture-stable aluminum (Al) as the cathode for achieving high-performance polymer light-emitting diode. With inserting the PEO-SDS layer (at the weight ratio 1:1.25), the blue-emitting device with poly(9,9-di-n-octylfluorene) exhibits the maximum brightness 12 300 cd/m2 and current efficiency 2.8 cd/A, much higher than the device without this layer (0.3 cd/m2 and 0.005 cd/A) and that using CsF/Al as the cathode (5835 cd/m2 and 1.06 cd/A). This HB-ET layer can also improve the performances of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene vinylene]-based device with Al as the cathode.
Single crystalline CoFe/MgO tunnel contact on nondegenerate Ge with a proper resistance-area product for efficient spin injection and detection
Authors: Jeon Kun-Rok , Min Byoung-Chul , Lee Hun-Sung , Shin Il-Jae , Park Chang-Yup , Shin Sung-Chul
Published: July 2010

We report the proper resistance-area products in the single crystalline bcc CoFe/MgO tunnel contact on nondegenerate n-Ge desirable for efficient spin injection and detection at room temperature. The electric properties of the single crystalline CoFe(5.0 nm)/MgO/n-Ge(001) tunnel contacts with an ultrathin MgO thickness of 1.5, 2.0, and 2.5 nm have been investigated by the I-V-T and C-V measurements. Interestingly, the crystalline tunnel contact with the 2.0-nm MgO exhibits the Ohmic behavior with the RA products of 5.20×10−6/1.04×10−5 Ω m2 at ±0.25 V, satisfying the theoretical conditions required for significant spin injection and detection. We believe that the results are ascribed to the presence of MgO layer between CoFe and n-Ge, enhancing the Schottky pinning parameter as well as shifting the charge neutrality level.
Communications: On the relation between the scalar and tensor exchange-correlation kernels of the time-dependent density-functional theory
Authors: Nazarov V. U. , Vignale G. , Chang Y.-C.
Published: July 2010

The scalar fxc and tensor f̂xc exchange-correlation (xc) kernels are key ingredients of the time-dependent density functional theory and the time-dependent current density functional theory, respectively. We derive a comparatively simple relation between these two kernels under the assumption that the dynamic xc can be considered “weak.” A calculation of the frequency-dependent dielectric function of silicon using this relation in conjunction with Vignale–Kohn f̂xc demonstrates a potential of our method to account for the dynamic many-body effects within the rigorous scheme of time-dependent density functional theory. Our formula provides a bridge between the scalar fxc, which directly enters many applications, and the tensor f̂xc which, due to its locality in space, is much easier to approximate.
Magneto-phonon polaritons of antiferromagnetic/ion-crystal superlattices
Authors: Ta Jin-Xing , Song Yu-Ling , Wang Xuan-Zhang
Published: July 2010

Magnetophonon polaritons in the superlattices composed of alternating antiferromagnetic and ion-crystal components are investigated with the transfer matrix method. Numerical simulations based on FeF2/TlBr superlattices show that there are four different bulk polariton bands, with negative refraction and positive refraction. Many surface polariton modes with various features arise around the bulk bands with negative refraction.
Lumped elements circuit of terahertz fishnet-like arrays with composite dispersion
Authors: Carbonell Jorge , Croënne Charles , Garet Frédéric , Lheurette Eric , Coutaz Jean Louis , Lippens Didier
Published: July 2010

We have analyzed and characterized a terahertz stacked holes array over a broad transmission bandwidth. In this context, we identify the key contributions of the surface plasmon modes related to the periodicity of array, and of the subcut off transmission through the holes responsible of a ground left-handed dispersion branch. The experimental verification of a multimode electromagnetic behavior is performed by time domain spectroscopy, with a complementary assessment by full-wave analysis. A circuitlike approach appears suitable for the understanding of a zero-gap transition between the left- and right-handed characteristics, opening the way of nonvanishing group velocity in a near-zero index propagation medium. Such a balanced composite operation, pointed out over the past in the dual element transmission line approaches, is thus generalized for a stacked subwavelength holes array, whose operation can be compared to the one of the so-called fishnet structures.
Determination of band gap energy (Eg) of Cu2ZnSnSe4 thin films: On the discrepancies of reported band gap values
Authors: Ahn SeJin , Jung Sunghun , Gwak Jihye , Cho Ara , Shin Keeshik , Yoon Kyunghoon , Park Doyoung , Cheong Hyeonsik , Yun Jae Ho
Published: July 2010

We demonstrate experimental data to elucidate the reason for the discrepancies of reported band gap energy (Eg) of Cu2ZnSnSe4 (CZTSe) thin films, i.e., 1.0 or 1.5 eV. Eg of the coevaporated CZTSe film synthesized at substrate temperature (Tsub) of 370 °C, which was apparently phase pure CZTSe confirmed by x-ray diffraction (XRD) and Raman spectroscopy, is found to be around 1 eV regardless of the measurement techniques. However, depth profile of the same sample reveals the formation of ZnSe at CZTSe/Mo interface. On the other hand, Eg of the coevaporated films increases with Tsub due to the ZnSe formation, from which we suggest that the existence of ZnSe, which is hardly distinguishable from CZTSe by XRD, is the possible reason for the overestimation of overall Eg.
Minimal resonator loss for circuit quantum electrodynamics
Authors: Barends R. , Vercruyssen N. , Endo A. , de Visser P. J. , Zijlstra T. , Klapwijk T. M. , Diener P. , Yates S. J. C. , Baselmans J. J. A.
Published: July 2010

We report quality factors of up to 500×103 in superconducting resonators at the single photon levels needed for circuit quantum electrodynamics. This result is achieved by using NbTiN and removing the dielectric from regions with high electric fields. As demonstrated by a comparison with Ta, the crucial sources of intensity-dependent loss are dielectrics on the surface of the metal and substrate.
The noise of the needle: Avalanches of a single progressing needle domain in LaAlO3
Authors: Harrison Richard J. , Salje Ekhard K. H.
Published: July 2010

The propagation of a single ferroelastic needle domain under weak elastic stress consists of two parts: a continuous front propagation and jerky avalanches. Optical observation and themodynamic analysis show that the continuous behavior is thermally activated. The avalanches follow power law behavior with an energy exponent ε=−1.8±0.2 in agreement with self-similar avalanches close to the depinning threshold. Our experiments on ferroelastic LaAlO3 exclude nucleation of secondary domains, so that the observed behavior is related exclusively to the statistical behavior of one single needle domain.
Air stable, ambipolar organic transistors and inverters based upon a heterojunction structure of pentacene on N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic di-imide
Authors: An Min-Jun , Seo Hoon-Seok , Zhang Ying , Oh Jeong-Do , Choi Jong-Ho
Published: July 2010

In this paper, we report on the fabrication and electrical characterization of top-contact, ambipolar organic field-effect transistors (OFETs) and inverters based upon a heterostructure of p-type pentacene on n-type N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic di-imide (P13), using the neutral cluster beam deposition (NCBD) method. The device characteristics measured as a function of both P13 and pentacene layer thicknesses revealed that OFETs with thicknesses of P13 (300 Å) and pentacene (200 Å) showed high air-stability and well-balanced ambipolarity with hole and electron mobilities of 0.12 and 0.08 cm2/V s. The complementary inverters, comprising two identical ambipolar OFETs, were found to operate both in the first and third quadrants of the transfer curves and exhibited a high voltage inversion gain of 13, good noise margins, and little hysteresis under ambient conditions. The results presented demonstrate that the NCBD-based ambipolar transistors and inverters qualify them as promising potential candidates for the construction of high-performance, organic thin film-based integrated circuits.
Spin polarization of currents in Co/Pt multilayer and Co–Pt alloy thin films
Authors: Rajanikanth A. , Kasai S. , Ohshima N. , Hono K.
Published: July 2010

The point contact Andreev reflection technique was employed to estimate the spin polarization of currents in Co/Pt multilayered thin film and Co–Pt alloy film with perpendicular anisotropy. The spin polarization of currents in the Co–Pt alloy film was estimated to be 0.48, while that in Co/Pt multilayered film was 0.56. These results suggest that the spin-polarization of currents in multilayered film is enhanced compared to that in alloy film.
Citrate-stabilized palladium nanoparticles as catalysts for sub-20 nm epitaxial silicon nanowires
Authors: Wittemann J. V. , Kipke A. , Pippel E. , Senz S. , Vogel A. T. , de Boor J. , Kim D. S. , Hyeon T. , Schmidt V.
Published: July 2010

Citrate-stabilized palladium nanoparticles with a mean diameter of 13 nm were synthesized in aqueous solution. These particles were utilized as catalysts to grow epitaxial silicon nanowires by chemical vapor deposition at temperatures below 500 °C. The resulting nanowires have a mean diameter of 15 nm. It is found that during the growth process the palladium particles transform into dipalladium silicide.
Strong enhancement of terahertz response in GaAs/AlGaAs quantum well photodetector by magnetic field
Authors: Yu C. H. , Zhang B. , Lu W. , Shen S. C. , Liu H. C. , Fang Y.-Y. , Dai J. N. , Chen C. Q.
Published: July 2010

A strong enhancement of terahertz (THz) response in a GaAs/AlGaAs quantum well photodetector (QWP) is observed under perpendicular magnetic field. Photocurrent spectra show that besides partial contribution from an increase in the detector differential resistance, improvement of photoconductive gain induced by electron localization and Landau quantization of the in-plane electron motion in quantum wells is the predominant underlying mechanism. This study sheds light on the transport mechanism in THz QWPs and provides a possible means for enhancing THz QWP’s response.
Maskless fabrication of large scale Si nanohole array via laser annealed metal nanoparticles catalytic etching for photovoltaic application
Authors: Wang Fei , Yu Hong Yu , Wang Xincai , Li Junshuai , Sun Xiaowei , Yang Mingfei , Wong She Mein , Zheng Hongyu
Published: July 2010

In this paper, laser annealing is used to produce metal (Ag) nanoparticles as etching catalyst on a silicon surface, which enables controllable fabrication of large-scale nanohole array surface texturing without using a mask. Semispherical Ag nanoparticles with variable size and distribution are achievable by manipulating the laser annealing parameters and metal film thickness, and the underlying physics is clarified. The nanoholes array in silicon can then be realized by selective etching of silicon under Ag pattern. The optical characteristics suggest that the surface reflection can be significantly suppressed owing to the nanohole texturing, which is promising for thin film photovoltaic applications.
Asymmetric heterostructure for photovoltaic InAs quantum dot infrared photodetector
Authors: Nevou L. , Liverini V. , Castellano F. , Bismuto A. , Faist J.
Published: July 2010

A photovoltaic InAs quantum dot-under-a-well photodetector is reported with a peak responsivity at 7 μm wavelength. In this structure, we implement an improved injection scheme, which allows a controlled feeding of the quantum dots through a modulation-doped InGaAs quantum well injector. A thin Al0.3Ga0.7As barrier significantly reduces the dark current and, at the same time, is responsible for the photovoltaic behavior. At 4 K and no applied bias, a responsivity of 2.5 mA/W and a detectivity of D∗=2.3×1010 cm Hz1/2/W in the dark is measured. The TBLIP of the device is 60 K and the D∗ at this temperature is 2×109 cm Hz1/2/W.
Development of a dye with broadband absorbance in visible spectrum for an efficient dye-sensitized solar cell
Authors: Rani Seema , Shishodia P. K. , Mehra R. M.
Published: July 2010

A blended dye composed of five organic dyes, namely, Rose Bengal, Eosin-Y, Rhodamine-B, Fast Green, and Acridine Orange, was developed and tested for various solar cell parameters of ZnO based dye-sensitized solar cell (DSSC). A comparison of the absorption spectra of dyes adsorbed on ZnO electrode revealed that the blended dye efficiently absorbs light in the entire visible region as compared with the individual dye. Six DSSCs were fabricated using the five individual dyes and one developed blended dye. The photovoltaic performance of the cells was examined by determining the various parameters such as open-circuit voltage, short-circuit current, energy conversion efficiency, fill factor, series resistance, and shunt resistance. Incident photon to current conversion efficiency was also measured to correlate the effect of the blended dye on the significant improvement of the solar cell parameters. The sensitization of ZnO electrode with blended dye has resulted in a maximum energy conversion efficiency of 7.9% of the solar cell.
Terahertz electroluminescence from Be δ-doped GaAs/AlAs quantum well
Authors: Li Su Mei , Zheng Wei Min , Wu Ai Ling , Cong Wei Yan , Liu Jing , Chu Ning Ning , Song Ying Xin
Published: July 2010

A Be δ-doped GaAs/AlAs three quantum wells emitter in the terahertz range is fabricated and electroluminescence is investigated. An electroluminescence peak centered at 23.4 meV with a full width at half maximum of 4.2 meV is observed under a bias of 2 V at low temperature (T=4.5 K). The emission peak is attributed to the 2p to 1s internal transitions of the Be acceptors in the center of δ-doped GaAs quantum well. The current-voltage characteristics of the device measured at different temperatures demonstrate a strong negative differential resistance and temperature dependence.
Visible-blind ultraviolet sensitive photodiode with high responsivity and long term stability
Authors: Wu Shuang-hong , Li Wen-lian , Chu Bei , Lee C. S. , Su Zi-sheng , Wang Jun-bo , Ren Qing-jiang , Hu Zhi-zhi , Zhang Zhi-qiang
Published: July 2010

A high responsivity organic visible-blind ultraviolet photodiode is achieved using aluminum (III) bis(2-methyl-8-quinolinato)4-phenylphenolate (BAlq) and 4,4′,4″-tri-(2-methylphenyl phenylamino) triphenylaine (m-MTDATA) as the electron acceptor and donor, respectively. Under 365 nm illumination with an intensity of 1.2 mW/cm2, the photodiode behaves a maximum photoresponse of 514 mA/W at −7 V, which is markedly higher than previous reports in our group by Su et al. [Appl. Phys. Lett. 93, 103309 (2008)] and inorganic counterparts based on GaN (150 mA/W) and Si (120 mA/W), respectively. The operational time of the unsealed photodiode is larger than 1000 min when the photocurrent decreases to 67% of its original intensity in air environment. Harvest of so high performance photodiode is mainly attributed to the larger band offsets at m-MTDATA/BAlq heterojunction and skillful device design, etc. The improvement mechanisms are also augured in detail.
Effects of spin structures on phonons in BaFe2As2
Authors: Wang Y. , Shang S. L. , Hui X. D. , Chen L. Q. , Liu Z. K.
Published: July 2010

The dependences of phonons on the spin structures of BaFe2As2 were studied using first-principles supercell approach. We considered the nonmagnetic, checkerboard, stripe, and spin-density-wave structures as well as a spin structure labeled as STR17. We find that STR17 is lower in energy than the stripe. It is seen the ∼20 meV missing peak at the generalized phonon density-of-states and the measured specific heat are well reproduced when the magnetic effects are accounted. We see phonon energy gaps for all the four magnetic structures but not for the nonmagnetic structure.
Band structure engineering of ZnO1−xSex alloys
Authors: Mayer Marie A. , Speaks Derrick T. , Yu Kin Man , Mao Samuel S. , Haller Eugene E. , Walukiewicz Wladek
Published: July 2010

ZnO 1 − x Se x alloys with Se substitutional composition x<0.12 were synthesized using pulsed laser deposition. Incorporation of small concentrations of Se results in a greater than 1 eV red shift in the ZnO optical absorption edge which is quantitatively explained in the framework of the band anticrossing model. The Se defect level is found to be located at 0.9 eV above the ZnO valence band and the band anticrossing coupling constant is determined to be 1.2 eV. These parameters allow prediction of the composition dependence of the band gap as well as the conduction and the valence band offsets in the full composition range of ZnO1−xSex alloys.
Maturation of the olfactory sensory neurons by Apaf-1/caspase-9–mediated caspase activity
Authors: Ohsawa Shizue , Hamada Shun , Kuida Keisuke , Yoshida Hiroki , Igaki Tatsushi , Miura Masayuki
Published: July 2010

Although the apoptotic role of caspases has been largely understood, accumulating evidence in
Drosophila
suggests that caspases also control other processes than apoptotic cell death. However, how caspases contribute to the development of the mammalian nervous system remains obscure. Here, we provide unique evidence that Apaf-1/caspase-9–mediated caspase signaling regulates the development of olfactory sensory neurons (OSNs), which includes axonal projection, synapse formation, and maturation of these neurons. This caspase signaling leads to a cleavage of Semaphorin 7A, a membrane-anchored semaphorin that is required for the proper axonal projection. Mutant mice deficient for
apaf-1
or
caspase-9
exhibit misrouted axons, impaired synaptic formation, and defects in the maturation of OSNs without affecting the number of these cells. Our findings suggest that Apaf-1/caspase-9–mediated nonapoptotic caspase signaling is required for the proper neural network formation during olfactory development.
Tissue kallikrein permits early renal adaptation to potassium load
Authors: El Moghrabi Soumaya , Houillier Pascal , Picard Nicolas , Sohet Fabien , Wootla Bharath , Bloch-Faure May , Leviel Françoise , Cheval Lydie , Frische Sebastian , Meneton Pierre , Eladari Dominique , Chambrey Régine
Published: July 2010

Tissue kallikrein (TK) is a serine protease synthetized in renal tubular cells located upstream from the collecting duct where renal potassium balance is regulated. Because secretion of TK is promoted by K
+
intake, we hypothesized that this enzyme might regulate plasma K
+
concentration ([K
+
]). We showed in wild-type mice that renal K
+
and TK excretion increase in parallel after a single meal, representing an acute K
+
load, whereas aldosterone secretion is not modified. Using aldosterone synthase-deficient mice, we confirmed that the control of TK secretion is aldosterone-independent. Mice with
TK
gene disruption (

TK
−/−

) were used to assess the impact of the enzyme on plasma [K
+
]. A single large feeding did not lead to any significant change in plasma [K
+
] in
TK
+/+
, whereas
TK
−/−
mice became hyperkalemic. We next examined the impact of
TK
disruption on K
+
transport in isolated cortical collecting ducts (CCDs) microperfused in vitro. We found that CCDs isolated from
TK
−/−
mice exhibit net transepithelial K
+
absorption because of abnormal activation of the colonic H
+
,K
+
-ATPase in the intercalated cells. Finally, in CCDs isolated from
TK
−/−
mice and microperfused in vitro, the addition of TK to the perfusate but not to the peritubular bath caused a 70% inhibition of H
+
,K
+
-ATPase activity. In conclusion, we have identified the serine protease TK as a unique kalliuretic factor that protects against hyperkalemia after a dietary K
+
load.
E3 ubiquitin ligase Mule ubiquitinates Miz1 and is required for TNFα-induced JNK activation
Authors: Yang Yi , Do HanhChi , Tian Xuejun , Zhang Chaozheng , Liu Xinyuan , Dada Laura A. , Sznajder Jacob I. , Liu Jing
Published: July 2010

The zinc finger transcription factor Miz1 is a negative regulator of TNFα-induced JNK activation and cell death through inhibition of TRAF2 K63-polyubiquitination in a transcription-independent manner. Upon TNFα stimulation, Miz1 undergoes K48-linked polyubiquitination and proteasomal degradation, thereby relieving its inhibition. However, the underling regulatory mechanism is not known. Here, we report that HECT-domain-containing Mule is the E3 ligase that catalyzes TNFα-induced Miz1 polyubiquitination. Mule is a Miz1-associated protein and catalyzes its K48-linked polyubiquitination. TNFα-induced polyubiquitination and degradation of Miz1 were inhibited by silencing of Mule and were promoted by ectopic expression of Mule. The interaction between Mule and Miz1 was promoted by TNFα independently of the pox virus and zinc finger domain of Miz1. Silencing of Mule stabilized Miz1, thereby suppressing TNFα-induced JNK activation and cell death. Thus, our study reveals a molecular mechanism by which Mule regulates TNFα-induced JNK activation and apoptosis by catalyzing the polyubiquitination of Miz1.
Surprising gene expression patterns within and between PDF-containing circadian neurons in
Drosophila
Authors: Kula-Eversole Elzbieta , Nagoshi Emi , Shang Yuhua , Rodriguez Joseph , Allada Ravi , Rosbash Michael
Published: July 2010

To compare circadian gene expression within highly discrete neuronal populations, we separately purified and characterized two adjacent but distinct groups of
Drosophila
adult circadian neurons: the 8 small and 10 large PDF-expressing ventral lateral neurons (s-LNvs and l-LNvs, respectively). The s-LNvs are the principal circadian pacemaker cells, whereas recent evidence indicates that the l-LNvs are involved in sleep and light-mediated arousal. Although half of the l-LNv–enriched mRNA population, including core clock mRNAs, is shared between the l-LNvs and s-LNvs, the other half is l-LNv– and s-LNv–specific. The distribution of four specific mRNAs is consistent with prior characterization of the four encoded proteins, and therefore indicates successful purification of the two neuronal types. Moreover, an octopamine receptor mRNA is selectively enriched in l-LNvs, and only these neurons respond to in vitro application of octopamine. Dissection and purification of l-LNvs from flies collected at different times indicate that these neurons contain cycling clock mRNAs with higher circadian amplitudes as well as at least a 10-fold higher fraction of oscillating mRNAs than all previous analyses of head RNA. Many of these cycling l-LNv mRNAs are well expressed but do not cycle or cycle much less well elsewhere in heads. The results suggest that RNA cycling is much more prominent in circadian neurons than elsewhere in heads and may be particularly important for the functioning of these neurons.
Structural organization of the functional domains of
Clostridium difficile
toxins A and B
Authors: Pruitt Rory N. , Chambers Melissa G. , Ng Kenneth K.-S. , Ohi Melanie D. , Lacy D. Borden
Published: July 2010

Clostridium difficile
toxins A and B are members of an important class of virulence factors known as large clostridial toxins (LCTs). Toxin action involves four major steps: receptor-mediated endocytosis, translocation of a catalytic glucosyltransferase domain across the membrane, release of the enzymatic moiety by autoproteolytic processing, and a glucosyltransferase-dependent inactivation of Rho family proteins. We have imaged toxin A (TcdA) and toxin B (TcdB) holotoxins by negative stain electron microscopy to show that these molecules are similar in structure. We then determined a 3D structure for TcdA and mapped the organization of its functional domains. The molecule has a “pincher-like” head corresponding to the delivery domain and two tails, long and short, corresponding to the receptor-binding and glucosyltransferase domains, respectively. A second structure, obtained at the acidic pH of an endosome, reveals a significant structural change in the delivery and glucosyltransferase domains, and thus provides a framework for understanding the molecular mechanism of LCT cellular intoxication.
Notch2 is required for progression of pancreatic intraepithelial neoplasia and development of pancreatic ductal adenocarcinoma
Authors: Mazur Pawel K. , Einwächter Henrik , Lee Marcel , Sipos Bence , Nakhai Hassan , Rad Roland , Zimber-Strobl Ursula , Strobl Lothar J. , Radtke Freddy , Klöppel Günter , Schmid Roland M. , Siveke Jens T.
Published: July 2010

Pancreatic cancer is one of the most fatal malignancies lacking effective therapies. Notch signaling is a key regulator of cell fate specification and pancreatic cancer development; however, the role of individual Notch receptors and downstream signaling is largely unknown. Here, we show that Notch2 is predominantly expressed in ductal cells and pancreatic intraepithelial neoplasia (PanIN) lesions. Using genetically engineered mice, we demonstrate the effect of conditional Notch receptor ablation in

Kras
G12D

-driven pancreatic carcinogenesis. Deficiency of
Notch2
but not
Notch1
stops PanIN progression, prolongs survival, and leads to a phenotypical switch toward anaplastic pancreatic cancer with epithelial–mesenchymal transition. By expression profiling, we identified increased Myc signaling regulated by Notch2 during tumor development, placing Notch2 as a central regulator of PanIN progression and malignant transformation. Our study supports the concept of distinctive roles of individual Notch receptors in cancer development.
Magnetic nanoparticle-based isolation of endocytic vesicles reveals a role of the heat shock protein GRP75 in macromolecular delivery
Authors: Wittrup Anders , Zhang Si-He , Svensson Katrin J. , Kucharzewska Paulina , Johansson Maria C. , Mörgelin Matthias , Belting Mattias
Published: July 2010

An increased understanding of cellular uptake mechanisms of macromolecules remains an important challenge in cell biology with implications for viral infection and macromolecular drug delivery. Here, we report a strategy based on antibody-conjugated magnetic nanoparticles for the isolation of endocytic vesicles induced by heparan sulfate proteoglycans (HSPGs), key cell-surface receptors of macromolecular delivery. We provide evidence for a role of the glucose-regulated protein (GRP)75/PBP74/mtHSP70/mortalin (hereafter termed “GRP75”) in HSPG-mediated endocytosis of macromolecules. GRP75 was found to be a functional constituent of intracellular vesicles of a nonclathrin-, noncaveolin- dependent pathway that was sensitive to membrane cholesterol depletion and that showed colocalization with the membrane raft marker cholera toxin subunit B. We further demonstrate a functional role of the RhoA GTPase family member CDC42 in this transport pathway; however, the small GTPase dynamin appeared not to be involved. Interestingly, we provide evidence of a functional role of GRP75 using RNAi-mediated down-regulation of GRP75 and GRP75-blocking antibodies, both of which inhibited macromolecular endocytosis. We conclude that GRP75, a chaperone protein classically found in the endoplasmic reticulum and mitochondria, is a functional constituent of noncaveolar, membrane raft-associated endocytic vesicles. Our data provide proof of principle of a strategy that should be generally applicable in the molecular characterization of selected endocytic pathways involved in macromolecular uptake by mammalian cells.