bluuebunny/crossref_metadata_2025 huggingface dataset:
Interaction of traveling current filaments and its relation to a nontrivial thermal breakdown scenario in avalanching bipolar transistor
Authors: Mamanee W. , Johnsson D. , Rodin P. , Bychikhin S. , Dubec V. , Stecher M. , Gornik E. , Pogany D.
Published: April 2009

Traveling multiple current filaments (CFs) are investigated by transient interferometric mapping method in avalanching bipolar n-p-n transistors. The number of CFs can vary for identical current pulses and their averaged number increases with the total current. The CF movement is driven by a temperature gradient in it, caused by the self-heating effect. For pulses of 500 ns duration, the existence of two CFs appears dangerous as it causes a nontrivial premature thermal breakdown (TB), which does not occur when only one CF exists at the same current level. TB occurs due to redistribution of current between the two CFs. The current components flowing through each CF depend on CF temperature and are globally coupled by a fixed device current. When a first CF reaches the device end, it heats up and disappears due to vanishing impact ionization rate in it. When a second traveling CF, taking consequently the whole current, reaches the already preheated device end, a TB event occurs. The transition from two to one filament mode is accompanied by a voltage step of 1 V, which is related to a finite resistance of CF access region.
Self-organized regular arrays of carbon nanocones induced by ultrashort laser pulses and their field emission properties
Authors: Zhao Q. Z. , Ciobanu F. , Wang L. J.
Published: April 2009

Periodic, self-organized carbon nanocone structures with a spatial period of up to 170 nm (less than 1/5 laser wavelength) are induced by exposing a graphite surface to a single beam 800 nm ultrashort pulsed laser. When a linearly polarized laser beam is used, the nanocones are aligned perpendicularly to the direction of polarization. This paper also demonstrates the fabrication of large-area carbon nanocone structures. The resulting carbon nanocones show a field emission performance with a turn-on electric field of as low as 3.2 V/μm.
A phenomenological heat transfer model for the molecular gas lubrication system in hard disk drives
Authors: Chen Du , Liu Nan , Bogy David B.
Published: April 2009

A reliable model of the heat transfer at the air bearing surface of a flying head slider is important for treating thermomechanical aspects of the molecular gas lubrication system in today’s hard disk drives. This article proposes a new model for heat transfer in the head disk interface, which considers both the heat conduction and viscous dissipation. The conduction heat flux based on this model shows better agreement with the numerical results of the linearized Boltzmann equation than existing models derived from the temperature jump theory. The viscous dissipation of plane Couette flow as well as that of plane Poiseuille flow in the gas film is analyzed using the energy conservation equation instead of the linearized Boltzmann equation, which is incapable of calculating the viscous dissipation at the boundaries. The new model gives simple analytical expressions for the heat flux contributed by heat conduction and viscous dissipation, and it is applicable to numerical thermomechanical simulations of the slider’s performance.
Control of the switching behavior of ferromagnetic nanowires using magnetostatic interactions
Authors: Basu S. , Fry P. W. , Gibbs M. R. J. , Schrefl T. , Allwood D. A.
Published: April 2009

Magnetostatic interactions between two end-to-end Permalloy (Ni80Fe20) nanowires have been studied as a function of their separation, end shape, and width. The change in switching field increases as the wires become closer, with deviations from the switching field of an isolated wire of up to 40% observed. The sign of the change depends on the relative magnetization orientation of the two wires, with higher fields for parallel magnetization and lower fields for antiparallel magnetization. A wire end shape has a strong influence, with larger field variations being seen for flat-ended wires than wires with tapered ends. The micromagnetic modeling and experiments performed here were in good qualitative agreement. The experimental control of switching behavior of one nanowire with another was also demonstrated using magnetostatic interactions.
Design and optimization of one-dimensional ferrite-film based magnonic crystals
Authors: Chumak A. V. , Serga A. A. , Wolff S. , Hillebrands B. , Kostylev M. P.
Published: April 2009

One-dimensional magnonic crystals have been implemented as gratings of shallow grooves chemically etched into the surface of yttrium-iron-garnet films. Scattering of backward volume magnetostatic spin waves from such structures is investigated experimentally and theoretically. Well-defined rejection frequency bands are observed in transmission characteristics of the magnonic crystals. The loss inserted by the gratings and the rejection band bandwidths are studied as a function of the film thickness, the groove depth, the number of grooves, and the groove width. The experimental data are well described by a theoretical model based on the analogy of a spin-wave film waveguide with a microwave transmission line. Our study shows that magnonic crystals with required operational characteristics can be engineered by adjusting these geometrical parameters.
Interfacial tension of nonassociating pure substances and binary mixtures by density functional theory combined with Peng–Robinson equation of state
Authors: Li Zhidong , Firoozabadi Abbas
Published: April 2009

We develop a density functional theory and investigate the interfacial tension of several pure substances N2, CO2, H2S, normal alkanes from C1 to nC10, and binary mixtures C1/C3, C1/nC5, C1/nC7, C1/nC10, CO2/nC4, N2/nC5, N2/nC6, N2/nC8, N2/nC10, nC6/nC7, nC6/nC8, and nC6/nC10. The theory is combined with the semiempirical Peng–Robinson equation of state (PR-EOS). The weighted density approximation (WDA) is adopted to extend the bulk excess Helmholtz free energy to the inhomogeneous interface. Besides, a supplementary term, quadratic density expansion (QDE), is introduced to account for the long-range characteristic of intermolecular dispersion attractions, which cannot be accurately described by the WDA. In the bulk limit, the QDE vanishes and the theory is reduced to the PR-EOS. For pure substances, the potential expansion parameter is the only adjustable parameter in the QDE and determined by using a single measured interfacial tension at the lowest temperature examined. Then without any parameter adjustment, we faithfully predict the interfacial tensions of pure substances and mixtures over a wide range of conditions.
Mixing effects in glass-forming Lennard-Jones mixtures
Authors: Valdes L.-C. , Affouard F. , Descamps M. , Habasaki J.
Published: April 2009

Mixing effects have been investigated from molecular dynamics simulations at constant number of particles, volume, and temperature on the Kob–Andersen glass-forming Lennard-Jones atomic mixture AxB1−x for 0≤x≤1 compositions. Upon cooling, crystallization is observed for x≤0.5 and x≥0.9 compositions. The crystalline states can be described by a quite complex coexistence of voids (x≤0.5), point defects, and one or two crystal structures which were characterized and found identical to those reported by Fernandez and Harrowell [Phys. Rev. E 67, 011403 (2003)] from energy minimization. Amorphization is also seen at 0.6≤x≤0.8 compositions and it is suggested that both crystal structures, CsCl and fcc-hcp, do not compete at these compositions since only one type of crystalline seed is found in the liquid, either fcc/hcp or CsCl. A significant decrease in the diffusion constants for both A and B particles is also seen above xA≃0.5. The problem of the extraordinary stability of the model against crystallization is discussed.
Synchrotron photoionization mass spectrometry study of intermediates in fuel-rich 1,2-dimethoxyethane flame
Authors: Lin Z. K. , Han D. L. , Li S. F. , Li Y. Y. , Yuan T.
Published: April 2009

Intermediates in a fuel-rich premixed laminar 1,2-dimethoxyethane (DME) flame are studied by molecular beam mass spectrometry combined with tunable synchrotron vacuum ultraviolet photoionization. About 30 intermediate species are identified in the present work, and their mole fraction profiles are evaluated. The experimental results show that the formations of intermediates, both hydrocarbons and oxygenated hydrocarbons, are closely linked to the structure of fuel, which is consistent with the previous reports. Species produced from H atom abstraction and beta scission of DME usually have much higher concentrations than others. The oxygen atoms in DME are considered to act as partitions of the primary intermediates; therefore farther reactions among these primary intermediates are difficult to occur, resulting in absence of most large intermediate species.
Dendrimers as synthetic gene vectors: Cell membrane attachment
Authors: Voulgarakis N. K. , Rasmussen K. Ø. , Welch P. M.
Published: April 2009

We present molecular-level simulations of dendrimer/DNA complexes in the presence of a model cell membrane. We determine the required conditions for the complex to arrive intact at the membrane, and the lifetime of the complex as it resides attached to the membrane. Our simulations directly pertain to critical issues arising in emerging gene delivery therapeutic applications, where a molecular carrier is required to deliver DNA segments to the interior of living cells.
Dielectric constant and leakage of BaZrO3 films
Authors: Łupina G. , Dąbrowski J. , Dudek P. , Kozłowski G. , Zaumseil P. , Lippert G. , Fursenko O. , Bauer J. , Baristiran C. , Costina I. , Müssig H.-J. , Oberbeck L. , Schröder U.
Published: April 2009

Dielectric properties of thin (<30 nm) BaZrO3 perovskite layers deposited onto TiN were investigated. Polycrystalline films show a dielectric constant of ∼40 and an optical band gap of ∼5.4 eV. Leakage currents of the polycrystalline BaZrO3 films are significantly higher than that of the corresponding amorphous layers. As evidenced by conductive atomic force microscopy, secondary ion mass spectrometry, and ab initio calculations, these currents may be due to hot spots and point defects related to Ti contamination of the dielectrics.
The water-benzene interaction: Insight from electronic structure theories
Authors: Ma Jie , Alfè Dario , Michaelides Angelos , Wang Enge
Published: April 2009

Weak noncovalent interactions such as van der Waals and hydrogen bonding are ubiquitous in nature, yet their accurate description with electronic structure theories is challenging. Here we assess the ability of a variety of theories to describe a water-benzene binding energy curve. Specifically, we test Hartree–Fock, second-order Møller–Plesset perturbation theory, coupled cluster, density functional theory with several exchange-correlation functionals with and without empirical vdW corrections, and quantum Monte Carlo (QMC). Given the relative paucity of QMC reports for noncovalent interactions, it is interesting to see that QMC and coupled cluster with single, double, and perturbative triple excitations [CCSD(T)] are in very good agreement for most of the binding energy curve, although at short distances there are small deviations on the order of 20 meV.
Ultrafast electron dynamics following outer-valence ionization: The impact of low-lying relaxation satellite states
Authors: Lünnemann Siegfried , Kuleff Alexander I. , Cederbaum Lorenz S.
Published: April 2009

Low-lying relaxation satellites give rise to ultrafast electron dynamics following outer-valence ionization of a molecular system. To demonstrate the impact of such satellites, the evolution of the electronic cloud after sudden removal of an electron from the highest occupied molecular orbital (HOMO) of the organic unsaturated nitroso compound 2-nitroso[1,3]oxazolo[5,4-d][1,3]oxazole is traced in real time and space using ab initio methods only. Our results show that the initially created hole charge remains stationary but on top of it the system reacts by an ultrafast π-π∗ excitation followed by a cyclic excitation-de-excitation process which leads to a redistribution of the charge. The π-π∗ excitation following the removal of the HOMO electron takes place on a subfemtosecond time scale and the period of the excitation-de-excitation alternations is about 1.4 fs. In real space the processes of excitation and de-excitation represent ultrafast delocalization and localization of the charge. The results are analyzed by simple two- and three-state models.
A time-resolved laser induced fluorescence study on the ion velocity distribution function in a Hall thruster after a fast current disruption
Authors: Mazouffre S. , Gawron D. , Sadeghi N.
Published: April 2009

The temporal characteristics of the Xe+ ion axial velocity distribution function (VDF) were recorded in the course of low-frequency discharge current oscillations (∼14 kHz) of the 5 kW class PPS®X000 Hall thruster. The evolution in time of the ion axial velocity component is monitored by means of a laser induced fluorescence diagnostic tool with a time resolution of 100 ns. As the number of fluorescence photons is very low during such a short time period, a homemade pulse-counting lock-in system was used to perform real-time discrimination between background photons and fluorescence photons. The evolution in time of the ion VDF was observed at three locations along the thruster channel axis after a fast shutdown of the thruster power. The anode discharge current is switched off at 2 kHz during 5 μs without any synchronization with the current oscillation cycle. This approach allows to examine the temporal behavior of the ion VDF during decay and ignition of the discharge as well as during forced and natural plasma oscillations. Measurements show that the distribution function of the axial component of the Xe+ ion does change periodically in time with a frequency close to the current oscillation frequency in both forced and natural cases. The ion density and the mean velocity are found to oscillate, whereas the velocity dispersion stays constant, which indicates that ionization and acceleration layers have identical dynamics. Finally, variations over time in the electric field are for the first time experimentally evidenced in a crossed-field discharge.
Density effects on collimation of energetic electron beams driven by two intense laser pulses
Authors: Wu Sizhong , Liu Zhanjun , Zhou Cangtao , Zhu Shaoping
Published: April 2009

When an intense laser pulse irradiates solid targets, the light energy is deposited at the relativistic critical density and relativistic electrons are produced. However, these fast electrons are generally divergent. In this paper, a scheme to reduce the divergence of laser-driven energetic electron beams in solid-density plasmas is investigated by two-dimensional particle-in-cell simulation. In the scheme, two intense laser pulses and a plasma target consisting of two parts with different densities are employed. The first laser pulse induces a strong interface magnetic field by generating fast electron flow along the density interface. The magnetic field collimates the electrons generated by the second laser pulse. The simulation results show that the strong interface magnetic field can change the direction of the energetic beam electrons and considerably reduce their divergence.
Ion-acoustic vortices in inhomogeneous and dissipative electron-positron-ion quantum magnetoplasmas
Authors: Masood W. , Mirza Arshad M. , Nargis Shahida , Ayub M.
Published: April 2009

Linear and nonlinear properties of quantum ion-acoustic waves are studied in a nonuniform, dissipative quantum plasma (composed of electrons, positrons, and ions) with sheared ion flow parallel to the ambient magnetic field, using the quantum hydrodynamic model. It is shown that the shear ion flow parallel to the external magnetic field can drive the quantum ion-acoustic wave unstable provided ∣S∣ky>kz. Stationary solutions of the nonlinear equations that govern the quantum ion-acoustic waves are also obtained. It is found that electrostatic monopolar, dipolar, and vortex street-type solutions can appear in such a plasma. It is observed that the inclusion of positron, quantum statistical, and Bohm potential terms significantly modifies the scale lengths of these nonlinear structures. The relevance of the present investigation with regard to the dense astrophysical environments is also pointed out.
Detailed flow physics of the supersonic jet interaction flow field
Authors: Viti Valerio , Neel Reece , Schetz Joseph A.
Published: April 2009

The supersonic jet interaction flow field generated by a sonic circular jet with a pressure ratio of 532 exhausting into a turbulent MACH 4.0 cross flow over a flat plate was investigated using numerical simulations. The simulations made use of the three-dimensional Reynolds-averaged Navier–Stokes (RANS) equations coupled with Wilcox’s 1998 k-ω turbulence model. The numerical solution was validated with experimental data that include the pressure distribution on the flat plate, with an empirical formula for the height of the barrel shock, and with the Schlieren pictures showing the location and shape of the main shock formations. The simulations correctly captured the location and shape of the main flow features and compared favorably with the experimental pressure distribution on the flat plate. The validated numerical simulation was used to investigate in detail the flow physics. The flow field was found to be dominated by the shock formations and their coupling with the strong vortical structures. Three primary shock formations were observed: a barrel shock, a bow shock, and a separation-induced shock wave. While the general structure of the barrel shock was found to be similar to that of the underexpanded jet exhausting into a quiescent medium, two unique features distinguished the flow field: the concave indentation in the leeside of the recompression (barrel) shock and the folding of the windward side of the barrel shock due to an inner reflection line. The presence of the steep pressure gradients associated with the shocks creates strong vortical motions in the fluid. Six primary vortices were identified: (i) the well-known horseshoe vortex, (ii) an upper trailing vortex, (iii) two trailing vortices formed in the separation region and, aft of the bow shock wave, (iv) two more trailing vortices that eventually merge together into one single rotational motion. The low-pressure region aft of the injector was found to be generated by the combined effect of the concave indentation in the leeside of the barrel shock and the lower trailing vortices. The trailing vortices were found to be the main mechanism responsible for the mixing of the injectant with the freestream fluid.
Absolute spin calibration of an electron spin polarimeter by spin-resolved photoemission from the Au(111) surface states
Authors: Cacho Céphise M. , Vlaic Sergio , Malvestuto Marco , Ressel Barbara , Seddon Elaine A. , Parmigiani Fulvio
Published: April 2009

Here we report the absolute characterization of a spin polarimeter by measuring the Sherman function with high precision. These results have been obtained from the analysis of the spin and angle-resolved photoemission spectra of Au(111) surface states. The measurements have been performed with a 250 kHz repetition rate Ti:sapphire amplified laser system combined with a high energy-, angle-, and spin-resolving time-of-flight electron spectrometer.
Dynamic equations for three different qudits in a magnetic field
Authors: Ivanchenko E. A.
Published: April 2009

A closed system of equations for the local Bloch vectors and spin correlation functions of three magnetic qudits, which are in an arbitrary, time-dependent, external magnetic field, is obtained using decomplexification of the Liouville–von Neumann equation. The algorithm of the derivation of the dynamic equations is presented. In the basis convenient for the important physical applications, structure constants of algebra su(2S+1) are calculated.
High bandwidth force estimation for optical tweezers
Authors: Sehgal Hullas , Aggarwal Tanuj , Salapaka Murti V.
Published: April 2009

A prevalent mode of optical tweezers involves position clamping that regulates a constant position of a trapped bead. Traditional schemes employ the measured bead position in the open loop or the control signal in the position-clamp mode as an estimate of external force on the trapped bead. This article shows that traditional methods introduce fundamental limitations on bandwidth of the external force estimation. A method is presented that leads to an order of magnitude increase in the bandwidth of the external force estimation. Furthermore, a comprehensive modeling paradigm is introduced that facilitates estimation of forces on the bead.
Thermal transport in composites of self-assembled nickel nanoparticles embedded in yttria stabilized zirconia
Authors: Shukla Nitin C. , Liao Hao-Hsiang , Abiade Jeremiah T. , Murayama Mitsuhiro , Kumar Dhananjay , Huxtable Scott T.
Published: April 2009

We investigate the effect of nickel nanoparticle size on thermal transport in multilayer nanocomposites consisting of alternating layers of nickel nanoparticles and yttria stabilized zirconia (YSZ) spacer layers that are grown with pulsed laser deposition. Using time-domain thermoreflectance, we measure thermal conductivities of k=1.8, 2.4, 2.3, and 3.0 W m−1 K−1 for nanocomposites with nickel nanoparticle diameters of 7, 21, 24, and 38 nm, respectively, and k=2.5 W m−1 K−1 for a single 80 nm thick layer of YSZ. We use an effective medium theory to estimate the lower limits for interface thermal conductance G between the nickel nanoparticles and the YSZ matrix (G>170 MW m−2 K−1), and nickel nanoparticle thermal conductivity.
Valence-bond description of chemical reactions on Born–Oppenheimer molecular dynamics trajectories
Authors: Noguchi Nao , Nakano Haruyuki
Published: April 2009

The nature of chemical bonds on dynamic paths was investigated using the complete active space valence-bond (CASVB) method and the Born–Oppenheimer dynamics. To extract the chemical bond picture during reactions, a scheme to collect contributions from several VB (resonance) structures into a small numbers of indices was introduced. In this scheme, a tree diagram for the VB structures is constructed with the numbers of the ionic bonds treated as generation. A pair of VB structures is related to each other if one VB structure is transferred into the other by changing a covalent bond to an ionic bond. The former and latter VB structures are named parent and child structures, respectively. The weights of the bond pictures are computed as the sum of the CASVB occupation numbers running from the top generation to the bottom along the descent of the VB structures. Thus, a number of CASVB occupation numbers are collected into a small number of indices, and a clear bond picture may be obtained from the CASVB wave function. The scheme was applied to the hydrogen exchange reaction H2+F→H+HF and the Diels–Alder reaction C5H6(cyclopentadiene)+CH2=CH2(ethylene)→C7H10(norbornene). In both the reactions, the scheme gave a clear picture for the Born–Oppenheimer dynamics trajectories. The reconstruction of the bonds during reactions was well described by following the temporal changes in weight.
Nuclear dynamics during the resonant Auger decay of water molecules
Authors: Eroms Matthis , Vendrell Oriol , Jungen Martin , Meyer Hans-Dieter , Cederbaum Lorenz S.
Published: April 2009

The resonant Auger decay of water molecules is investigated. Here, the excitation process, the motion of the nuclei, and the decay of the resonantly excited state take place on the same (femtosecond) time scale. Therefore, a multistep picture is not suitable. Instead, the nuclear wave packet at each instant of time is a result of several competing and interfering contributions. The resonant Auger decay of water is simulated and its dynamics is studied in detail. An analysis of the final vibrational distribution is given. The multiconfiguration time-dependent Hartree method is used to study the intricate multidimensional dynamics. The potential energy surfaces have been calculated using a multireference configuration interaction method.
Wrinkled surface topographies of electrospun polymer fibers
Authors: Wang Lifeng , Pai Chia-Ling , Boyce Mary C. , Rutledge Gregory C.
Published: April 2009

Electrospun polymer fibers are shown to have wrinkled surface topographies that result from buckling instabilities during processing. A glassy shell forms on the surface of the gel-like core during solvent evaporation; continued evaporation leads to a contraction mismatch between the core and shell that triggers buckling of the shell. The wrinkled topographies are quantified in terms of the critical buckling wave number and wavelength. The results explain the observed wrinkled topographies and provide a framework for designing fibers with high specific surface areas and textured/patterned surface topographies to enhance surface dominated properties in fibers and fibrous mats.
The growth of metallic nanofilaments in resistive switching memory devices based on solid electrolytes
Authors: Guo H. X. , Gao L. G. , Xia Y. D. , Jiang K. , Xu B. , Liu Z. G. , Yin J.
Published: April 2009

Memory cells with sandwich structure based on solid electrolytes Ag30S2P14O42, called ASP, were fabricated on Pt/Ti/Si(001) wafers by using pulsed laser deposition and focused ion beam nanofabrication technique. The current-voltage characteristic of the ASP memory units shows satisfactory switching behaviors. The switching of the devices was explained by the formation and rupture of Ag nanofilaments with the help of bipolar electrical pulses. A simplified model was proposed to describe the growth of the Ag nanofilaments. It was shown that the effective cross section area of the Ag nanofilaments increased at initial stage, then decreased after reaching a maximum until the top and bottom electrodes were connected.
Improvement of structural, electronic, and magnetic properties of Co2MnSi thin films by He+ irradiation
Authors: Gaier O. , Hamrle J. , Hillebrands B. , Kallmayer M. , Pörsch P. , Schönhense G. , Elmers H. J. , Fassbender J. , Gloskovskii A. , Jenkins C. A. , Felser C. , Ikenaga E. , Sakuraba Y. , Tsunegi S. , Oogane M. , Ando Y.
Published: April 2009

The influence of 30 keV He+ ion irradiation on structural, electronic, and magnetic properties of Co2MnSi thin films with a partial B2 order was investigated. It was found that room temperature irradiation with light ions can improve the local chemical order. This provokes changes of the electronic structure and element-specific magnetization toward the bulk properties of a well-ordered Co2MnSi Heusler compound.
Optimum condition for spin-current generation from magnetization precession in thin film systems
Authors: Ando K. , Yoshino T. , Saitoh E.
Published: April 2009

The generation efficiency of spin currents induced by a magnetization-precession motion in a thin film system has been investigated in terms of a magnetization-precession trajectory. By using the Landau–Lifshitz–Gilbert equation combined with the phenomenological model of the spin pumping, the generation efficiency is calculated to be equal to the elliptical orbit area of magnetization precession, which is maximized when the precession trajectory is distorted. This calculation well reproduces experimental results on the magnetization-angle dependence of the inverse spin-Hall signal induced by the spin pumping in a Ni81Fe19/Pt bilayer film.
Anisotropic carrier transport properties in layered cobaltate epitaxial films grown by reactive solid-phase epitaxy
Authors: Sugiura Kenji , Ohta Hiromichi , Nakagawa Shin-ichi , Huang Rong , Ikuhara Yuichi , Nomura Kenji , Hosono Hideo , Koumoto Kunihito
Published: April 2009

Herein we report the anisotropic carrier transport properties of a layered cobaltate, NaxCoO2 epitaxial film grown on the m-plane of an α-Al2O3 substrate using reactive solid-phase epitaxy. Scanning and transmission electron microscopy analyses revealed that NaxCoO2 was heteroepitaxially grown with the CoO2 conducting planes inclined by ∼43° against the α-Al2O3 substrate surface. The electrical resistivity parallel to the CoO2 planes was ∼1/5 of the perpendicular one, but the parallel Seebeck coefficient was about twice as large as the perpendicular one. Hence, a higher thermoelectric efficiency in the cobaltates can be obtained within the CoO2 planes.
Anomalous strength anisotropy of γ′-Fe4N identified by first-principles calculations
Authors: Yang Jun , Sun Hong , Chen Changfeng
Published: April 2009

γ ′ -phase Fe4N holds great promise for applications in magnetic recording devices and its (001) plane shows the highest stiffness according to elastic constant calculations. Here we demonstrate by first-principles stress-strain calculations that, contrary to the prevailing view, γ′-Fe4N exhibits the greatest strength and strongest wear resistance in its (011) plane. This unusual behavior stems from the nonlinear stress response at large strains which cannot be derived from elastic parameters. We analyze the underlying deformation mechanism and discuss implications of the present results on the design of hard coating materials in general.
Model of interface states at III-V oxide interfaces
Authors: Robertson John
Published: April 2009

We present a generalized model of the density of interface states at III-V oxide interfaces. The states are based on the native defects such as dangling bonds on the Ga and As sites or As–As bonds created by oxidation. The model explains the difficulty of n-type operation for GaAs field effect transistors (FETs) compared to GaAs pFETs or to InGaAs nFETs.
Carrier-mediated ferromagnetism in single crystalline (Co, Ga)-codoped ZnO films
Authors: Lu Zhonglin , Hsu Hua-Shu , Tzeng Yonhua , Huang Jung-Chun-Andrew
Published: April 2009

Metallic (Co, Ga)-codoped ZnO single crystalline films have been grown by molecular beam epitaxy. Besides room temperature ferromagnetism, the anomalous hall effect (AHE) due to spin-orbit interaction was also found. The small AHE signals match quantitatively with the magnetic hysteresis and can be correspondent to the intrinsic ferromagnetism in a true diluted magnetic oxide with charge carrier spin polarization. Both the saturation magnetization and AHE can be significantly enhanced by additional carrier doping, revealing that the ferromagnetism is carrier mediated in (Co, Ga)-codoped ZnO films.
Enhanced exciton diffusion in an organic photovoltaic cell by energy transfer using a phosphorescent sensitizer
Authors: Luhman Wade A. , Holmes Russell J.
Published: April 2009

We demonstrate enhanced exciton diffusion in an organic photovoltaic cell through the incorporation of a phosphorescent sensitizer. The increase in exciton diffusion length (LD) is realized using a composite electron donor layer consisting of a N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine (NPD) host doped with the phosphorescent guest fac-tris(2-phenylpyridine) iridium [Ir(ppy)3]. The presence of the phosphor at low concentration allows for the population of the long-lived NPD triplet state and an increase in LD. An increase in the NPD LD from 6.5±0.3 to 11.8±0.6 nm is extracted from measurements of the external quantum efficiency for donor layers containing 5 wt % Ir(ppy)3. This enhancement leads to a ∼80% improvement in the power conversion efficiency relative to devices containing an undoped donor layer.
Electrical responses in high permittivity dielectric (Li, Fe)-doped NiO ceramics
Authors: Thongbai Prasit , Yamwong Teerapon , Maensiri Santi
Published: April 2009

Electrical properties of giant-permittivity core/shell structured Li0.05FexNi0.95−xO (LFNO) are studied as functions of frequency, temperature, and dc bias. Three electrical responses of depletion surface (DS), grain boundary (GB), and bulk grain are detected in the LFNO ceramics. The DS and GB effects can be separated by removing the surface samples, whereas the grain effect is extracted by applying dc bias. It is found that the interfacial polarizations at the DSs and GBs are suppressed by applied voltages. Our results suggest that the polarization relaxation in the LFNO ceramics is closely related to the electrical response inside the grains.
Vertical organic inverter with stacked pentacene thin film transistors
Authors: Baek Changhoon , Seo Soon-min
Published: April 2009

A vertical organic inverter is introduced that consists of two p-channel transistors. The concept of stacking transistors vertically is utilized with the resulting circuit structure is which one pentacene transistor is stacked on top of another pentacene transistor. The two transistors have different polymer dielectrics. Utilization of two different dielectrics enables each of the two transistors to behave as a drive and load transistor for the inverter. The fabrication is simple and allows for a larger scale of integration. The performance of this all p-channel inverter is comparable to that of complementary organic inverters that operate at high voltage.
Buffer layer-induced unusual rectifying behavior in La0.67Ca0.33MnO3/LaMnO3/SrTiO3:Nb junctions
Authors: Lü W. M. , Sun J. R. , Chen Y. Z. , Shen B. G.
Published: April 2009

Rectifying behavior has been studied for the La0.67Ca0.33MnO3/LaMnO3/SrTiO3:Nb junctions with a LaMnO3 layer between 0 and 12 nm. Different from the single-process behavior in the junction with a thin intermediate layer, the junction buffered by the LaMnO3 layer of 6 or 8 nm shows two distinctive processes with the character of thermionic emission. Based on the analyses of current-voltage characteristics, a spikelike and notchlike band structures in the two sides of the junctions are derived, with respectively, the interfacial barriers of ∼0.75 and ∼0.57 eV. The complex band structure is believed to be responsible for the two-process feature observed.
Cryopreservation affects bovine sperm intracellular parameters associated with capacitation and acrosome exocytosis
Authors: Pons-Rejraji Hanae , Bailey Janice L. , Leclerc Pierre
Published: April 2009

Although semen cryopreservation is widely and commonly used in the bovine breeding industry, half the spermatozoa do not survive and most of those that do survive undergo numerous physiological changes that affect their fertilising ability. The aim of the present study was to determine how cryopreservation affects the intracellular events involved in sperm capacitation and acrosome reaction. Immediately after thawing and washing, almost 50% of spermatozoa were capacitated and more than 20% had lost their acrosome. The sperm cAMP concentration was lower than that in freshly ejaculated spermatozoa, but the cytosolic pH (pHcyt) was in the expected range. The free cytosolic Ca2+ concentration ([Ca2+]cyt) was higher than in fresh spermatozoa and cryopreserved spermatozoa had internally stored Ca2+. Phenylarsine oxide increased pHcyt and both cytosolic and stored Ca2+ concentrations, whereas orthovanadate enhanced acrosome loss and protein tyrosine phosphorylation (P-Tyr). Heparin increased the percentage of spermatozoa expressing the B (capacitated) chlortetracycline binding pattern, pHcyt, P-Tyr and Ca2+ storage. Moreover, positive correlations exist between capacitation, cAMP, P-Tyr and stored Ca2+, whereas the acrosome reaction is positively correlated with pHcyt and [Ca2+]cyt. These results demonstrate that sperm regulatory mechanisms may be affected by the cryopreservation procedure, but frozen–thawed sperm can still regulate their capacitation and acrosome reaction signalling pathways.
Upstream open reading frames cause widespread reduction of protein expression and are polymorphic among humans
Authors: Calvo Sarah E. , Pagliarini David J. , Mootha Vamsi K.
Published: April 2009

Upstream ORFs (uORFs) are mRNA elements defined by a start codon in the 5′ UTR that is out-of-frame with the main coding sequence. Although uORFs are present in approximately half of human and mouse transcripts, no study has investigated their global impact on protein expression. Here, we report that uORFs correlate with significantly reduced protein expression of the downstream ORF, based on analysis of 11,649 matched mRNA and protein measurements from 4 published mammalian studies. Using reporter constructs to test 25 selected uORFs, we estimate that uORFs typically reduce protein expression by 30–80%, with a modest impact on mRNA levels. We additionally identify polymorphisms that alter uORF presence in 509 human genes. Finally, we report that 5 uORF-altering mutations, detected within genes previously linked to human diseases, dramatically silence expression of the downstream protein. Together, our results suggest that uORFs influence the protein expression of thousands of mammalian genes and that variation in these elements can influence human phenotype and disease.
Bmi1
lineage tracing identifies a self-renewing pancreatic acinar cell subpopulation capable of maintaining pancreatic organ homeostasis
Authors: Sangiorgi Eugenio , Capecchi Mario R.
Published: April 2009

A central question in stem cell biology is whether organ homeostasis is maintained in adult organs through undifferentiated stem cells or self-duplication of specialized cell populations. To address this issue in the exocrine pancreas we analyzed the Bmi1-labeled cell lineage of pancreatic acinar cells. Previously, we had shown that inducible linage tracing with Bmi1-Cre-estrogen receptor (ER) in the small intestine specifically, labels “classical” undifferentiated intestinal stem cells. In this article we demonstrate that the Bmi1-Cre-ER system labels a subpopulation of differentiated acinar cells in the exocrine pancreas whose derivatives are still present, at a steady-state level, 1 year after a single TM pulse. This study suggests that Bmi1 is a marker for a subpopulation of self-renewing acinar cells, indicating that self-renewal is not an exclusive feature of adult undifferentiated stem cells. Further, the extended period that Bmi1-labeled acinar cells retain a pulse of BrdU suggests that some of this subpopulation of cells are not continuously replicating, but rather are set aside until needed. This cellular behavior is again reminiscent of behavior normally associated with more classical adult stem cells. Setting aside cells capable of self-renewal until needed retains the advantage of protecting this subpopulation of cells from DNA damage induced during replication.
Molecular dissection of Alzheimer's disease neuropathology by depletion of serum amyloid P component
Authors: Kolstoe Simon E. , Ridha Basil H. , Bellotti Vittorio , Wang Nan , Robinson Carol V. , Crutch Sebastian J. , Keir Geoffrey , Kukkastenvehmas Riitta , Gallimore J. Ruth , Hutchinson Winston L. , Hawkins Philip N. , Wood Stephen P. , Rossor Martin N. , Pepys Mark B.
Published: April 2009

New therapeutic approaches in Alzheimer's disease are urgently needed. The normal plasma protein, serum amyloid P component (SAP), is always present in cerebrospinal fluid (CSF) and in the pathognomonic lesions of Alzheimer's disease, cerebrovascular and intracerebral Aβ amyloid plaques and neurofibrillary tangles, as a result of its binding to amyloid fibrils and to paired helical filaments, respectively. SAP itself may also be directly neurocytotoxic. Here, in this unique study in Alzheimer's disease of the bis(d-proline) compound, (R)-1-[6-[(R)-2-carboxy-pyrrolidin-1-yl]-6-oxo-hexanoyl]pyrrolidine-2-carboxylic acid (CPHPC), we observed depletion of circulating SAP and also remarkable, almost complete, disappearance of SAP from the CSF. We demonstrate that SAP depletion in vivo is caused by CPHPC cross-linking pairs of SAP molecules in solution to form complexes that are immediately cleared from the plasma. We have also solved the structure of SAP complexed with phosphothreonine, its likely ligand on hyperphosphorylated τ protein. These results support further clinical study of SAP depletion in Alzheimer's disease and potentially other neurodegenerative diseases.
Humanized immunotoxins: A new generation of immunotoxins for targeted cancer therapy
Authors: Mathew Mrudula , Verma Rama S.
Published: April 2009

Chemotherapy, radiation, and surgery are the conventional treatment modalities for cancer. The success achieved with these approaches has been limited due to several factors like chemoresistance to drugs, non‐specificity leading to peripheral toxicity, and non‐resectable tumors. To combat these problems, the concept of targeted therapy using immunotoxins was developed. Immunotoxins are chimeric proteins with a cell‐selective ligand chemically linked or genetically fused to a toxin moiety and can target cancer cells overexpressing tumor‐associated antigens, membrane receptors, or carbohydrate antigens. Ligands for these receptors or monoclonal antibodies or single chain variable fragments directed against these antigens are fused with bacterial or plant toxins and are made use of as immunotoxins. Pseudomonas exotoxin, anthrax toxin, and diphtheria toxin are the commonly used bacterial toxins. Ricin, saporin, gelonin, and poke weed antiviral protein are the plant toxins utilized in immunotoxin constructs. Several such fusion proteins are in clinical trials, and denileukin difitox is a FDA‐approved fusion protein. In spite of the promise shown by bacterial‐ and plant toxin‐based chimeric proteins, their clinical application is hampered by several factors like immunogenicity of the toxin moiety and non‐specific toxicity leading to vascular leak syndrome. In order to overcome these problems, a novel generation of immunotoxins in which the cytotoxic moiety is an endogenous protein of human origin like proapoptotic protein or RNase has been developed. This review summarizes the advances in this new class of fusion protein and the future directions to be explored. (Cancer Sci 2009)
Endostar, a recombined humanized endostatin, enhances the radioresponse for human nasopharyngeal carcinoma and human lung adenocarcinoma xenografts in mice
Authors: Wen Qing‐Lian , Meng Mao‐Bin , Yang Bo , Tu Ling‐Li , Jia Li , Zhou Lin , Xu Yong , Lu You
Published: April 2009

The purpose of this paper is to determine the efficacy of combining radiation therapy with endostar, a recombined humanized endostatin, in human nasopharyngeal carcinoma and human lung adenocarcinoma xenografts. Tumor xenografts were established in the hind limb of male athymic nude mice (BALB/c‐nu) by subcutaneous transplantation. The tumor‐bearing mice were assigned into four treatment groups: sham therapy (control), endostar (20 mg/kg, once daily for 10 days), radiation therapy (6 Gray per day to 30 Gray, once a day for 1 week), and endostar plus radiation therapy (combination). The experiment was repeated and mice were killed at days 3, 6, and 10 after initiation therapy, and the tumor tissues and blood samples were collected to analyze the kinetics of antitumor, antiangiogenesis, and antivascularization responses of different therapies. In human nasopharyngeal carcinoma and human lung adenocarcinoma xenografts, endostar significantly enhanced the effects of tumor growth inhibition, endothelial cell and tumor cell apoptosis induction, and improved tumor cell hypoxia of radiation therapy. Histological analyses demonstrated that endostar plus radiation also induced a significant reduction in microvascular density, microvascular area, and vascular endothelial growth factor and matrix metalloproteinase‐2 expression compared with radiation and endostar alone respectively. We concluded that endostar significantly sensitized the function of radiation in antitumor and antiangiogenesis in human nasopharyngeal carcinoma and human lung adenocarcinoma xenografts by increasing the apoptosis of the endothelial cell and tumor cell, improving the hypoxia of the tumor cell, and changing the proangiogenic factors. These data provided a rational basis for clinical practice of this multimodality therapy. (Cancer Sci 2009)
Epidermoid anal cancer prognosis comparison among HIV+ and HIV− patients
Authors: ABRAMOWITZ L. , MATHIEU N. , ROUDOT‐THORAVAL F. , LEMARCHAND N. , BAUER P. , HENNEQUIN C. , MITRY E. , ROMELAER C. , APARICIO T. , SOBHANI I.
Published: April 2009

Background  Previous studies suggest a poor prognosis of epidermoid anal cancer in HIV+ patients.

Aim  To investigate the long‐term outcome of epidermoid anal cancer in HIV+ and HIV− patients in the highly active antiretroviral treatment (HAART) era.

Methods  We included all patients with epidermoid anal cancer referred to six hospitals from 1998 to 2004.

Results  In all, 151 patients (44 HIV+, 107 HIV−) were reviewed retrospectively for 27 (median of 16–44) months. HIV+ patients were male (100% vs. 27%, P < 0.001) and younger (45 vs. 62 years old, P < 0.001) than HIV− patients. No significant differences were observed in the tumour stage, pelvic radiotherapy dose or concomitant chemotherapy, according to the HIV status. After chemoradiotherapy, similar numbers of HIV+ and HIV− patients had grade III‐IV toxicity. A complete response was obtained in 82% and 75% (N.S.) of cases, respectively. The disease‐free survival rates were 77% and 67% (N.S.) and the overall survival rates were 85% and 84% (N.S.), respectively, after 3 years of follow‐up. Duration of HIV infection, viral load and CD4 count had no effect on the survival rate of HIV+ patients with EAC.

Conclusions  The clinical outcome of HIV+ patients with epidermoid anal cancer is similar to that of HIV− patients. Therefore, the same therapeutic guidelines should be applied to both populations.
Predicting the outcome of oral food challenges with hen's egg through skin test end‐point titration
Authors: Tripodi S. , Di Rienzo Businco A. , Alessandri C. , Panetta V. , Restani P. , Matricardi P. M.
Published: April 2009

Background
Oral food challenge (OFC) is the diagnostic ‘gold standard’ of food allergies but it is laborious and time consuming. Attempts to predict a positive OFC through specific IgE assays or conventional skin tests so far gave suboptimal results.

Objective
To test whether skin test with titration curves predict with enough confidence the outcome of an oral food challenge.

Methods
Children (n=47; mean age 6.2 ± 4.2 years) with suspected and diagnosed allergic reactions to hen's egg (HE) were examined through clinical history, physical examination, oral food challenge, conventional and end‐point titrated skin tests with HE white extract and determination of serum specific IgE against HE white. Predictive decision points for a positive outcome of food challenges were calculated through receiver operating characteristic (ROC) analysis for HE white using IgE concentration, weal size and end‐point titration (EPT).

Results
OFC was positive (Sampson's score 3) in 20/47 children (42.5%). The area under the ROC curve obtained with the EPT method was significantly bigger than the one obtained by measuring IgE‐specific antibodies (0.99 vs. 0.83, P<0.05) and weal size (0.99 vs. 0.88, P<0.05). The extract's dilution that successfully discriminated a positive from a negative OFC (sensitivity 95%, specificity 100%) was 1 : 256, corresponding to a concentration of 5.9 μg/mL of ovotransferrin, 22.2 μg/mL of ovalbumin, and 1.4 μg/mL of lysozyme.

Conclusion
EPT is a promising approach to optimize the use of skin prick tests and to predict the outcome of OFC with HE in children. Further studies are needed to test whether this encouraging finding can be extended to other populations and food allergens.