bluuebunny/crossref_metadata_2025 huggingface dataset:
Observations and analysis of magnetic fluctuations in the Maryland centrifugal experiment
Authors: Choi S. , Guzdar P. N. , Case A. , Ellis R. , Hassam A. B. , Lunsford R. , Teodorescu C. , Uzun-Kaymak I.
Published: April 2008

Initial results from magnetic probes on the Maryland Centrifugal eXperiment (MCX) [R. F. Ellis et al., Phys. Plasmas 8, 2057 (2001)] provide details of the propagation and azimuthal mode structure of magnetic fluctuations in the edge region. Magnetic coils placed azimuthally along the edge measure changes in the axial magnetic field during the time history of the plasma discharge. The eight evenly spaced coils can resolve azimuthal modes up to m=3. The plasma rotates azimuthally in MCX due to an applied radial electric field. Using a variety of different analysis of the data, it is inferred that the magnetic fluctuations are dominantly convected by the plasma rotation for several rotation periods before significant decorrelation. These findings help to identify the modes at the edge and indicate that there are a few low mode numbers that are dominant during the discharge. Also, the speed of rotation of the modes is found to change dramatically from the High Rotation (HR) state to a low rotation ordinary (O) state, consistent with a corresponding change in the plasma load voltage. The fluctuation spectrum becomes dominated by a single mode after the transition.
Spectroscopic ellipsometry studies of GaN films deposited by reactive rf sputtering of GaAs target
Authors: Biswas A. , Bhattacharyya D. , Sahoo N. K. , Yadav Brajesh S. , Major S. S. , Srinivasa R. S.
Published: April 2008

GaN films have been deposited by reactive rf sputtering of GaAs target in 100% nitrogen ambient on quartz substrates at different substrate temperatures ranging from room temperature to 700°C. A series of films, from arsenic-rich amorphous to nearly arsenic-free polycrystalline hexagonal GaN, has been obtained. The films have been characterized by phase modulated spectroscopic ellipsometry to obtain the optical parameters, viz., fundamental band gap, refractive index, and extinction coefficient, and to understand their dependence on composition and microstructure. A generalized optical dispersion model has been used to carry out the ellipsometric analysis for amorphous and polycrystalline GaN films and the variation of the optical parameters of the films has been studied as a function of substrate temperature. The refractive index values of polycrystalline films with preferred orientation of crystallites are slightly higher (2.2) compared to those for amorphous and randomly oriented films. The dominantly amorphous GaN film shows a band gap of 3.47eV, which decreases to 3.37eV for the strongly c-axis oriented polycrystalline film due to the reduction in amorphous phase content with increase in substrate temperature.
Preparation and electrical properties of fine-scale 1–3 lead zirconic titanate∕epoxy composite thick films for high-frequency ultrasonic transducers
Authors: Zhen Yuhua , Li Jing-Feng
Published: April 2008

1–3 connectivity lead zirconic titanate (PZT)∕epoxy composite thick films containing fine-scale and high aspect ratio PZT pillars (40μm sectional width, 40μm spacing, and 5.5 aspect ratio) were obtained by a modified dice and fill method. The composite thick film works at a high frequency >7MHz with a clear and uncoupled thickness mode, together with a relatively high electromechanical coupling coefficient (kt=56.4%), low acoustic impedance (Z=7.8 Mrayls), and low mechanical Qm (3.3). High piezoelectric coefficient (d33=332pCN−1) along with reduced dielectric constant (εr=105) endowed the composite films an enhanced piezoelectric voltage coefficient g33 value of 357×10−3m2∕C, which is required to increase the receiving voltage sensitivity. The present piezocomposite thick film with microscale ordered structure is promising for high-frequency ultrasonic transducers.
Semiquantal analysis of adiabatic hydrogen transfer rate
Authors: Sakumichi Naoyuki , Ando Koji
Published: April 2008

The reaction rate of adiabatic proton/hydrogen/hydride (H) transfers in condensed phase is examined by combining the semiquantal time-dependent Hartree theory and the multidimensional transition state theory, which takes into account the zero-point effect and the dynamical modulation of the wavepacket width in the adiabatic transfer regime. By applying the theory to a model potential consisting of a quartic double well coupled linearly and quadratically (symmetrically) to external degrees of freedom, a set of compact analytical formulas was derived for the adiabatic H transfer rate. The analysis suggests that the kinetic isotope effect on the H transfer rate may exhibit a maximum as a function of the coupling strength to the external degrees of freedom measured by the reorganization energy.
Lower hybrid current drive experiments on Alcator C-Mod: Comparison with theory and simulation
Authors: Bonoli P. T. , Ko J. , Parker R. , Schmidt A. E. , Wallace G. , Wright J. C. , Fiore C. L. , Hubbard A. E. , Irby J. , Marmar E. , Porkolab M. , Terry D. , Wolfe S. M. , Wukitch S. J. ,   the Alcator C-Mod Team, Wilson J. R. , Scott S. , Valeo E. , Phillips C. K. , Harvey R. W.
Published: April 2008

Lower hybrid (LH) current drive experiments have been carried out on the Alcator C-Mod tokamak [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] using a radio-frequency system at 4.6GHz. Up to 900kW of LH power has been coupled and driven LH currents have been inferred from magnetic measurements by extrapolating to zero loop voltage, yielding an efficiency of neILHR0∕PLH≈2.5±0.2×1019(A∕W∕m2). We have simulated the LH current drive in these discharges using the combined ray tracing/three-dimensional (r,v⊥,v∥) Fokker–Planck code GENRAY-CQL3D (R. W. Harvey and M. McCoy, in Proceedings of the IAEA Technical Committee Meeting on Simulation and Modeling of Thermonuclear Plasmas, Montreal, Canada, 1992) and found similar current drive efficiencies. The simulated profiles of current density from CQL3D, including both ohmic plus LH drive have been found to be in good agreement with the measured current density from a motional Stark effect diagnostic. Measurements of nonthermal x-ray emission confirm the presence of a significant fast electron population and the three-dimensional (r,v⊥,v∥) electron distribution function from CQL3D has been used in a synthetic diagnostic code to simulate the measured hard x-ray data.
Large scale rotating motions in a multiple jets combustor
Authors: Duwig Christophe , Gutmark Ephraim
Published: April 2008

The flow dynamics of a multiple jet combustor is investigated using large eddy simulation. This particular combustor geometry is designed to mix hot combustion products from a central recirculation zone into the surrounding fuel/air jets. Using proper orthogonal decomposition, a large scale rotation of the central recirculation zone around the combustor axis was identified, though the averaged flow field does not exhibit any azimuthal motion. The rotating mode was found to have a relatively low frequency and to contain about 10% of the total turbulent kinetic energy. The occurrence of this mode was explained using the nonlinear delay saturation model.
Low frequency electrostatic waves in weakly inhomogeneous magnetoplasma modeled by Lorentzian (kappa) distributions
Authors: Basu B.
Published: April 2008

Linear dispersion relations for electrostatic waves in spatially inhomogeneous, current-carrying anisotropic plasma, where the equilibrium particle velocity distributions are modeled by various Lorentzian (kappa) distributions and by well-known bi-Maxwellian distribution, are presented. Spatial inhomogeneities, assumed to be weak, include density gradients, temperature gradients, and gradients (shear) in the parallel (to the ambient magnetic field) flow velocities associated with the current. In order to illustrate the distinguishing features of the kappa distributions, stability properties of the low frequency (lower than ion cyclotron frequency) and long perpendicular wavelength (longer than ion gyroradius) modes are studied in detail, and the results are contrasted with those for the bi-Maxwellian distribution. Specific attention is given to the drift waves, the current-driven ion-acoustic waves in the presence of velocity shear, the velocity shear-driven ion-acoustic modes, and the ion temperature-gradient driven modes. Growth rates of the drift wave instability and the current-driven ion-acoustic instability are reduced from their values for bi-Maxwellian distribution due to larger ion Landau damping rates associated with the kappa distributions. For the same reason, excitation conditions for these two instabilities are more stringent in the case of the kappa distributions. Growth rates of the velocity shear-driven ion-acoustic instability and the ion temperature-gradient driven instability are reduced from their values for bi-Maxwellian distribution as a consequence of the reduced adiabatic response of the electrons to the electrostatic potential perturbation. Frequencies of the drift waves and the ion-acoustic waves are also reduced in kappa-distribution plasmas due to the reduced adiabatic response of the electrons.
Kolmogorov 4∕5 law, nonlocality, and sweeping decorrelation hypothesis
Authors: Kholmyansky M. , Tsinober A.
Published: April 2008

We report results of experiments at large Reynolds numbers, confirming the equivalent form of the Kolmogorov 4∕5 law obtained recently by Hosokawa [Prog. Theor. Phys. 118, 169 (2007)]. This, as well as purely kinematic exact relations, demonstrates one of the important aspects of nonlocality of turbulent flows in the inertial range and stands in contradiction with the sweeping decorrelation hypothesis understood as statistical independence between large and small scales.
Comment on “Anharmonic properties of the vibrational quantum computer” [J. Chem. Phys. 126, 204102 (2007)]
Authors: Gollub C. , de Vivie-Riedle R.
Published: April 2008

Suitable molecules for quantum computing cannot be discussed in terms of anharmonicity and CNOT gates alone. The validity of the approximate approach [M. Zhao and D. Babikov, J. Chem. Phys.126, 204102 (2007)] is limited. Frequencies and anharmonicities cannot be used independent from the molecule. Hermite polynomials with the linear approximation for the dipole moment lead to oversimplified gates with potentially low intensities.
Response to “Comment on ‘Anharmonic properties of the vibrational quantum computer’ ” [J. Chem. Phys. 128, 167101 (2008)]
Authors: Babikov Dmitri , Zhao Meiyu
Published: April 2008

A benchmark study of the approximate approach to the optimal control of vibrational qubits, which was used in the original paper [J. Chem. Phys.126, 204102 (2007)], is presented. Two simplified assumptions are used in this method: A linear approximation for the dipole moment function and a harmonic approximation for the vibrational wave functions. Both assumptions are often used in spectroscopy and are known to work well for many molecules when the vibrational excitation is low. Here, we show that our method works well for the OH molecule, which exhibits a very anharmonic spectrum of vibrational eigenstates and a complicated dipole moment function.
Plasma properties of laser-ablated strontium target
Authors: Hafeez S. , Shaikh Nek M. , Rashid Baber , Baig M. A.
Published: April 2008

Optical emission spectroscopy is used to characterize the laser-produced strontium plasma by using the fundamental, second, and third harmonics of a Nd:YAG laser. Variations in the electron temperature (Te) and number density (Ne) as a function of distance, laser irradiance, and ambient gas pressure have been studied by using the emission lines of neutral strontium. In addition, absorption mechanisms responsible for the variation of the electron temperature and number density and the dependence of the spectral line intensities on the ambient gas pressure and laser irradiance are discussed.
Laser ablation of preheated copper samples
Authors: Tavassoli S. H. , Khalaji M.
Published: April 2008

A study of the effect of initial sample temperature on laser ablation of a copper sample at ambient air pressure by a 1064nm, 10ns laser pulse with energies of 11 and 15mJ (2.7–3.2GW∕cm2) is carried out. The sample is uniformly heated by a heating element up to 600K. Spectral emission of plasma is measured at different initial sample temperatures and delay times. Plasma temperatures are determined from the method of line pair ratio. The temperature profile inside the preheated target, ablation depth, thickness of dielectric, and melting layer are numerically computed by the finite difference method based on the phase explosion mechanism. Results show that an increase in the initial sample temperature leads to an increase in the spectral emission of plasma up to 90% which is attributed to both the plasma temperature and the ablated volume. Initial sample temperatures have no effects on background intensity of plasma emission. Thus, for spectroscopic purposes, the signal to noise ratio can be improved with initial sample temperature.
1
∕
f
noise in patterned La2∕3Sr1∕3MnO3 thin films in the 300–400K range
Authors: Méchin Laurence , Routoure Jean-Marc , Mercone Silvana , Yang Fan , Flament Stéphane , Chakalov Radoslav A.
Published: April 2008

Detailed investigations of 1∕f electrical noise were performed in bridges of various widths and lengths patterned in La2∕3Sr1∕3MnO3 (LSMO) thin films deposited on SrTiO3 (001) substrates. The measurements were analyzed in the framework of the semiempirical Hooge relation, which routinely enables the evaluation of noise level in materials of different compositions, sizes and in different bias conditions. A review of published data on noise in manganites is first given. Our measurement setup is briefly described, pointing out the possible parasitic external noise sources. As expected, the quadratic dependence of the noise power voltage spectral density versus applied voltage was verified in all the measured bridges. However, the normalized Hooge parameter (αH∕n) has been surprisingly found width dependent, and this dependence remained in all the investigated temperature range of 300–400K. Open questions arise to determine whether the use of the semiempirical Hooge relation is valid in these LSMO thin films, especially in a temperature range close to their phase transition. The effective volume might be different from the geometrical volume indeed. We finally measured αH∕n of 8×10−31m3 at 300K, which is among the lowest values reported for LSMO thin films and of the order of noise level in conventional metals.
Subnanosecond electron transport in a gas in the presence of polarized electromagnetic waves
Authors: Dey Indranuj , Mathew Jose V. , Bhattacharjee Sudeep , Jain Sachin
Published: April 2008

An ensemble of free electrons in a classical Boltzmann gas under equilibrium condition follow a square law for the number of collisions suffered during random walk, in the elastic limit [N∝(Λ∕λ)2]. This study reveals for the first time that in the same limit the dependence is considerably modified in the presence of linearly polarized electromagnetic waves. The phenomenon happens at time scales shorter (∼10−10s) than the characteristic discharge initiation time and the wave period. Considering the actual dependence of collision cross-sections on electron energy, a new relation is obtained, which tends to the classical result for the zero field case. The random walk parameter ⟨χ2⟩ characterizes a true versus constrained random process. The implications of the new relation describing the phenomena are discussed in the light of applications.
Burns, Néel, and structural phase transitions in multiferoic Pb(Fe2∕3W1∕3)O3–xPbTiO3 detected by an acoustic emission
Authors: Dul’kin E. , Mojaev E. , Roth M. , Kamba S. , Vilarinho P. M.
Published: April 2008

We investigated the ceramics samples of multiferoic solid solution of relaxor ferroelectric Pb(Fe2∕3W1∕3)O3 with ferroelectric PbTiO3 (abbreviated as PFW-xPT; x=0, 0.25, and 0.37) by means of acoustic emission (AE) method and simultaneously using the dielectric measurement below 700K. A distinct AE response has been detected at Burns temperature Td≈640–650K, where the dynamic polar clusters start to appear, at intermediate temperature of 510–520K, where the polar clusters become probably static, at ferroelectric phase transition temperatures Tc, and at Néel antiferromagnetic phase transitions. The Néel temperatures TN in ceramics were observed to be lower than in the crystals; the origin is discussed. Based on detected AE responses, we have corrected previously obtained phase diagram for PFW-xPT system.
Quantum electric circuits analogous to ballistic conductors
Authors: Dragoman D.
Published: April 2008

The conductance steps in a constricted two-dimensional electron gas (2DEG) and the minimum conductivity in graphene are related to a new uncertainty relation between the electric charge and conductance in a quantized electric circuit that mimics the electric transport in mesoscopic systems. This uncertainty relation makes specific use of the discreteness of the electric charge. Quantum electric circuits analogous to both constricted a 2DEG and graphene are introduced. In the latter case, a new insight into the origin of the minimum conductivity is obtained.
Field effect on spin-polarized transport in graphene nanoribbons
Authors: Guo Jing , Gunlycke D. , White C. T.
Published: April 2008

An efficient method is presented for simulating spin polarization and transport through zigzag-edge graphene nanoribbons in the presence of transverse fields. The approach is used to examine two graphene nanoribbon spintronic devices. One device operates as a spin filter whle the other operates as a spin field-effect transistor without requiring spin-polarized contacts.
Enhancing the quantum efficiency of InGaN green light-emitting diodes by trimethylindium treatment
Authors: Lin Hung-Cheng , Lin Ruo-Syuan , Chyi Jen-Inn
Published: April 2008

This work demonstrates the effectiveness of using trimethylindium (TMIn) treatment to improve the luminescence efficiency of InGaN∕GaN quantum wells grown by metal-organic vapor-phase epitaxy. Photoluminescence, x-ray diffraction, atomic force microscopy, and high-resolution transmission electron microscopy indicate that the treatment leads to a smoother InGaN surface and InGaN∕GaN interface with substantial decrease in V-shape defects density, compared to the samples without treatment. Green light-emitting diodes prepared by this method exhibit higher output power than the control device. These improvements are attributed to the surface smoothing process in TMIn ambient, resulting in an abrupt InGaN∕GaN interface.
Direct numerical simulation of transitions towards structural vacillation in an air-filled, rotating, baroclinic annulus
Authors: Read Peter L. , Maubert Pierre , Randriamampianina Anthony , Früh Wolf-Gerrit
Published: April 2008

The route to chaos of baroclinic waves in a rotating, stratified fluid subjected to lateral heating can occur via several possible routes, involving either low-dimensional, quasiperiodic states or via a series of secondary small-scale instabilities. In a recent paper, we have discussed direct numerical simulations (DNS) of the low-dimensional route to chaos in a baroclinic annulus filled with air as the working fluid and compared results to those obtained in the laboratory for high Prandtl number liquids. In the present paper, we consider further DNS in the air-filled annulus at higher rotation rates. A transition in the flow structure is observed, where the centrifugal acceleration exceeds gravity and the dominant physical process changes from baroclinic instability to convection due to radial buoyancy. The transition of this convection to chaotic behavior is fundamentally different from that observed in the transition to the chaotic flow observed at lower rotation rates. Rather than via a sequence of low-dimensional, quasiperiodic states, the large-scale convection developed small-scale instabilities, which has been previously suggested as the origin of structural vacillation on the transition to geostrophic turbulence.
Gravitational and harmonic oscillator potentials on surfaces of revolution
Authors: Santoprete Manuele
Published: April 2008

In this paper, we consider the motion of a particle on a surface of revolution under the influence of a central force field. We prove that there are at most two analytic central potentials for which all the bounded, nonsingular orbits are closed and that there are exactly two on some surfaces with constant Gaussian curvature. The two potentials leading to closed orbits are suitable generalizations of the gravitational and harmonic oscillator potential. We also show that there could be surfaces admitting only one potential that leads to closed orbits. In this case, the potential is a generalized harmonic oscillator. In the special case of surfaces of revolution with constant Gaussian curvature, we prove a generalization of the well-known Bertrand theorem.
(
In
,
Sn
)
2
O
3
∕
Ti
O
2
∕
Pt
Schottky-type diode switch for the TiO2 resistive switching memory array
Authors: Shin Yong Cheol , Song Jaewon , Kim Kyung Min , Choi Byung Joon , Choi Seol , Lee Hyun Ju , Kim Gun Hwan , Eom Taeyong , Hwang Cheol Seong
Published: April 2008

A Schottky-type diode switch consisting of a Pt∕(In,Sn)2O3∕TiO2∕Pt stack was fabricated for applications to cross-bar type resistive-switching memory arrays. The high (0.55eV) and low potential barrier at the TiO2∕Pt and TiO2∕(In,Sn)2O3 junctions, respectively, constitute the rectifying properties of the stacked structure. The forward/reverse current ratio was as high as ∼1.6×104 at an applied voltage of ∼1V. When Pt∕TiO2∕Pt memory was connected to this diode in series, there was an insignificant interference on the memory function from the diode under the forward bias and virtually no resistive switching under a reverse bias.
Ultrafast optical modulation of exchange coupling in FePt∕CoFe composite structure
Authors: Ren Yang , Zhao Hui , Zhang Zongzhi , Jin Q. Y.
Published: April 2008

Photoinduced magnetization dynamics in FePt∕CoFe bilayer is investigated by optical pump-probe measurements. The transient Kerr loops exhibit an instantaneous separated switching behavior due to exchange decoupling between FePt and CoFe layers induced by photoexcitation, which subsequently recover to the original uniform switching at a certain delay time of 10–20ps. By analyzing the temporal dependence of magnetization ratio of FePt to CoFe and coercivity of FePt phase, we infer that the decoupling and slow magnetization recovery phenomena are ascribed to the laser-created spin disordering mainly in FePt layer, while the following onset of interfacial coupling results from spin/lattice cooling process.
Generation of hard x rays by femtosecond laser pulse interaction with Cu in laminar helium flow in ambient air
Authors: Hou Bixue , Easter James , Krushelnick Karl , Nees John A.
Published: April 2008

Hard x rays are generated in laminar helium flow in atmosphere (without a vacuum vessel) through the interaction of tightly focused 35fs laser pulses of varying energy with a Cu target. The energy conversion efficiency from laser to Kα x rays is measured to be 5.4×10−6, giving a flux of 5.9×109photons∕s into 2π sr from a source measuring approximately 9×12μm2 in size (vertical×horizontal). Results are compared to those measured in vacuum and in static helium environments.
Ultramultiple-level storage in TiN∕SbTeN double-layer cell for high-density nonvolatile memory
Authors: Yin You , Higano Naoya , Sone Hayato , Hosaka Sumio
Published: April 2008

We report a phase-change nonvolatile memory (NVM) concept based on a TiN∕SbTeN (N-doped Sb2Te3) double-layer structure, which can be used for ultramultiple-level storage (UMLS). SbTeN shows a gradual resistivity drop and good phase stability with increasing annealing temperature, a characteristic which makes it suitable for UMLS applications. We demonstrate that the number of distinguishable resistance levels can readily reach 16 and even higher. These levels in this study result from the initial threshold switching and the subsequent current-controlled crystallization induced by Joule heating. The latter allows the creation of many distinct levels, thus, enabling the low-cost ultrahigh-density NVM.
Magnetostriction in Mn3CuN
Authors: Asano K. , Koyama K. , Takenaka K.
Published: April 2008

Discovery of large magnetostriction in an antiperovskite Mn3CuN is reported. Mn3CuN undergoes the first-order transition from high-temperature (high-T) paramagnetic to low-temperature ferromagnetic (FM) phase at the Curie temperature TC=143K, accompanied by cubic-to-tetragonal structural deformation. In the tetragonally distorted FM phase, Mn3CuN, even in a polycrystalline form, expands 0.2% and shrinks 0.1% in the direction parallel and perpendicular to the external field of 90kOe, respectively. This magnetostriction is possibly due to rearrangement of thermoelastic martensite variants by magnetic field, similar to FM Heusler alloys such as Ni2MnGa.
Experimental probe of adsorbate binding energies at internal crystalline/amorphous interfaces in Gd-doped Si3N4
Authors: van Benthem Klaus , Painter Gayle S. , Averill Frank W. , Pennycook Stephen J. , Becher Paul F.
Published: April 2008

Electron beam irradiation during scanning transmission electron microscopy has been used to probe the relative abundance and stabilities of gadolinium adsorption sites in polycrystalline silicon nitride ceramics. Site-specific binding strengths in the interface plane between β-Si3N4 grains and the adjacent amorphous triple pockets were found to be consistent with theoretical predictions. Decreasing stability was found for Gd within partially ordered planes further from the interface. Atomic level characterization such as that reported here provides detailed insights that will allow one to tailor new functional ceramic microstructures with improved macroscopic mechanical properties.
Microwave spectral analysis by means of nonresonant parametric recovery of spin-wave signals in a thin magnetic film
Authors: Schäfer S. , Chumak A. V. , Serga A. A. , Melkov G. A. , Hillebrands B.
Published: April 2008

We report on the storage and nonresonant parametric recovery of microwave signals carried by a dipolar surface spin-wave pulse in a thin ferrimagnetic film. The information about the intensity of the spectral components of the signal within a narrow frequency band is saved due to the excitation of a dipolar-exchange standing spin-wave mode across the film thickness and is afterward restored by means of parametric amplification of this mode. The intensity of the restored signal measured for varying shifts between the signal carrier frequency and half of the pumping frequency, which is equal to the frequency of the standing mode, reveals information about the entire frequency spectrum of the input microwave signal.
Analytical energy loss distribution for accurate high resolution depth profiling using medium energy ion scattering
Authors: Pezzi R. P. , Krug C. , Grande P. L. , da Rosa E. B. O. , Schiwietz G. , Baumvol I. J. R.
Published: April 2008

An analytical approach to ion energy loss distributions capable of simplifying medium energy ion scattering (MEIS) spectral analysis is presented. This analytical approach preserves the accuracy of recent numerical models that evaluate energy loss effects overlooked by standard calculations based on the Gaussian approximation. Results are compared to first principle calculations and experimental MEIS spectra from 0.2-to1.5-nm-thick HfO2 films on Si, supporting the application of this analytical model for proton scattering in the kinetic energy range from 100to200keV.
Interaction between the intrinsic second- and third-order optical fields in an Al0.53Ga0.47N∕GaN heterostructure
Authors: Chen P. , Zuo Y. H. , Tu X. G. , Cai D. J. , Li S. P. , Kang J. Y. , Yu Y. D. , Yu J. Z. , Wang Q. M.
Published: April 2008

We present an experimental demonstration of the interaction between the intrinsic second- and third-order optical fields in an Al0.53Ga0.47N∕GaN heterostructure. The sample was deposited by metal-organic chemical vapor deposition on (0001) sapphire. The nonlinear optical coefficients of the sample, which were measured with a Mach–Zehnder interferometer system, quadratically increase with the applied modulating voltage, indicating the existence of the third-order optical field. The third-order signal was then detected by the Z-scan method and we calculated the built-in dc field on the AlGaN∕GaN interface to confirm the strong interaction between the intrinsic second- and third-order optical fields.
Indoleamine 2,3-dioxygenase in lung dendritic cells promotes Th2 responses and allergic inflammation
Authors: Xu Hui , Oriss Timothy B. , Fei Mingjian , Henry Adam C. , Melgert Barbro N. , Chen Li , Mellor Andrew L. , Munn David H. , Irvin Charles G. , Ray Prabir , Ray Anuradha
Published: April 2008

Indoleamine 2,3 dioxygenase (IDO) has emerged as an important mediator of immune tolerance via inhibition of Th1 responses. However, the role of IDO in antigen-induced tolerance or allergic inflammation in the airways that is regulated by Th2 responses has not been elucidated. By using IDO
−/−
mice, we found no impairment of airway tolerance, but, surprisingly, absence of IDO provided significant relief from establishment of allergic airways disease, as evident from attenuated Th2 cytokine production, airway inflammation, mucus secretion, airway hyperresponsiveness, and serum ovalbumin-specific IgE. Myeloid dendritic cells isolated from lung-draining lymph nodes of mice immunized for either Th1 or Th2 response revealed fewer mature dendritic cells in the lymph nodes of IDO
−/−
mice. However, the net functional impact of IDO deficiency on antigen-induced responses was more remarkable in the Th2 model than in the Th1 model. Collectively, these data suggest that IDO is not required for the induction of immune tolerance in the airways but plays a role in promoting Th2-mediated allergic airway inflammation via unique effects on lung dendritic cells.
Targeted deletion of the murine
corneodesmosin
gene delineates its essential role in skin and hair physiology
Authors: Matsumoto Mitsuru , Zhou Yiqing , Matsuo Shinji , Nakanishi Hideki , Hirose Kenji , Oura Hajimu , Arase Seiji , Ishida-Yamamoto Akemi , Bando Yoshimi , Izumi Keisuke , Kiyonari Hiroshi , Oshima Naoko , Nakayama Rika , Matsushima Akemi , Hirota Fumiko , Mouri Yasuhiro , Kuroda Noriyuki , Sano Shigetoshi , Chaplin David D.
Published: April 2008

Controlled proteolytic degradation of specialized junctional structures, corneodesmosomes, by epidermal proteases is an essential process for physiological desquamation of the skin. Corneodesmosin (CDSN) is an extracellular component of corneodesmosomes and, although considerable debate still exists, genetic studies have suggested that the
CDSN
gene in the major psoriasis-susceptibility locus (
PSORS1
) may be responsible for susceptibility to psoriasis, a human skin disorder characterized by excessive growth and aberrant differentiation of keratinocytes. CDSN is also expressed in the inner root sheath of hair follicles, and a heterozygous nonsense mutation of the
CDSN
gene in humans is associated with scalp-specific hair loss of poorly defined etiology. Here, we have investigated the pathogenetic roles of CDSN loss of function in the development of skin diseases by generating a mouse strain with targeted deletion of the
Cdsn
gene.
Cdsn
-deficient mouse skin showed detachment of the stratum corneum from the underlying granular layer and/or detachment within the upper granular layers due to the disrupted integrity of the corneodesmosomes. When grafted onto immunodeficient mice,
Cdsn
-deficient skin showed rapid hair loss together with epidermal abnormalities resembling psoriasis. These results underscore the essential roles of CDSN in hair physiology and suggest functional relevance of
CDSN
gene polymorphisms to psoriasis susceptibility.
Cell water dynamics on multiple time scales
Authors: Persson Erik , Halle Bertil
Published: April 2008

Water–biomolecule interactions have been extensively studied in dilute solutions, crystals, and rehydrated powders, but none of these model systems may capture the behavior of water in the highly organized intracellular milieu. Because of the experimental difficulty of selectively probing the structure and dynamics of water in intact cells, radically different views about the properties of cell water have proliferated. To resolve this long-standing controversy, we have measured the
2
H spin relaxation rate in living bacteria cultured in D
2
O. The relaxation data, acquired in a wide magnetic field range (0.2 mT–12 T) and analyzed in a model-independent way, reveal water dynamics on a wide range of time scales. Contradicting the view that a substantial fraction of cell water is strongly perturbed, we find that ≈85% of cell water in
Escherichia coli
and in the extreme halophile
Haloarcula marismortui
has bulk-like dynamics. The remaining ≈15% of cell water interacts directly with biomolecular surfaces and is motionally retarded by a factor 15 ± 3 on average, corresponding to a rotational correlation time of 27 ps. This dynamic perturbation is three times larger than for small monomeric proteins in solution, a difference we attribute to secluded surface hydration sites in supramolecular assemblies. The relaxation data also show that a small fraction (≈0.1%) of cell water exchanges from buried hydration sites on the microsecond time scale, consistent with the current understanding of protein hydration in solutions and crystals.
Cyclic distension of fibrin-based tissue constructs: Evidence of adaptation during growth of engineered connective tissue
Authors: Syedain Zeeshan H. , Weinberg Justin S. , Tranquillo Robert T.
Published: April 2008

Tissue engineering provides a means to create functional living tissue replacements. Here, we examine the effects of 3 weeks of cyclic distension (CD) on fibrin-based tubular tissue constructs seeded with porcine valve interstitial cells. CD with circumferential strain amplitude ranging from 2.5% to 20% was applied to evaluate the effects of CD on fibrin remodeling into tissue. We hypothesized that during long-term CD cells adapt to cyclic strain of constant strain amplitude (constant CD), diminishing tissue growth. We thus also subjected constructs to CD with strain amplitude that was incremented from 5% to 15% over the 3 weeks of CD [incremental CD (ICD)]. For constant CD, improvement occurred in construct mechanical properties and composition, peaking at 15% strain: ultimate tensile strength (UTS) and tensile modulus increased 47% and 45%, respectively, over statically incubated controls (to 1.1 and 4.7 MPa, respectively); collagen density increased 29% compared with controls (to 27 mg/ml). ICD further improved outcomes. UTS increased 98% and modulus increased 62% compared with the largest values with constant CD, and collagen density increased 34%. Only in the case of ICD was the ratio of collagen content to cell number greater (70%) than controls, consistent with increased collagen deposition per cell. Studies with human dermal fibroblasts showed similar improvements, generalizing the findings, and revealed a 255% increase in extracellular signal-regulated kinase signaling for ICD vs. constant CD. These results suggest cell adaptation may limit conventional strategies of stretching with constant strain amplitude and that new approaches might optimize bioreactor operation.
Molecular conformation and dynamics of the Y145Stop variant of human prion protein in amyloid fibrils
Authors: Helmus Jonathan J. , Surewicz Krystyna , Nadaud Philippe S. , Surewicz Witold K. , Jaroniec Christopher P.
Published: April 2008

A C-terminally truncated Y145Stop variant of the human prion protein (huPrP23–144) is associated with a hereditary amyloid disease known as PrP cerebral amyloid angiopathy. Previous studies have shown that recombinant huPrP23–144 can be efficiently converted
in vitro
to the fibrillar amyloid state, and that residues 138 and 139 play a critical role in the amyloidogenic properties of this protein. Here, we have used magic-angle spinning solid-state NMR spectroscopy to provide high-resolution insight into the protein backbone conformation and dynamics in fibrils formed by
13
C,
15
N-labeled huPrP23–144. Surprisingly, we find that signals from ≈100 residues (i.e., ≈80% of the sequence) are not detected above approximately −20°C in conventional solid-state NMR spectra. Sequential resonance assignments revealed that signals, which are observed, arise exclusively from residues in the region 112–141. These resonances are remarkably narrow, exhibiting average
13
C and
15
N linewidths of ≈0.6 and 1 ppm, respectively. Altogether, the present findings indicate the existence of a compact, highly ordered core of huPrP23–144 amyloid encompassing residues 112–141. Analysis of
13
C secondary chemical shifts identified likely β-strand segments within this core region, including β-strand 130–139 containing critical residues 138 and 139. In contrast to this relatively rigid, β-sheet-rich amyloid core, the remaining residues in huPrP23–144 amyloid fibrils under physiologically relevant conditions are largely unordered, displaying significant conformational dynamics.
DNA barcodes and cryptic species of skipper butterflies in the genus
Perichares
in Area de Conservación Guanacaste, Costa Rica
Authors: Burns John M. , Janzen Daniel H. , Hajibabaei Mehrdad , Hallwachs Winnie , Hebert Paul D. N.
Published: April 2008

DNA barcodes can be used to identify cryptic species of skipper butterflies previously detected by classic taxonomic methods and to provide first clues to the existence of yet other cryptic species. A striking case is the common geographically and ecologically widespread neotropical skipper butterfly
Perichares philetes
(Lepidoptera, Hesperiidae), described in 1775, which barcoding splits into a complex of four species in Area de Conservación Guanacaste (ACG) in northwestern Costa Rica. Three of the species are new, and all four are described. Caterpillars, pupae, and foodplants offer better distinguishing characters than do adults, whose differences are mostly average, subtle, and blurred by intraspecific variation. The caterpillars of two species are generalist grass-eaters; of the other two, specialist palm-eaters, each of which feeds on different genera. But all of these cryptic species are more specialized in their diet than was the morphospecies that held them. The four ACG taxa discovered to date belong to a panneotropical complex of at least eight species. This complex likely includes still more species, whose exposure may require barcoding. Barcoding ACG hesperiid morphospecies has increased their number by nearly 10%, an unexpectedly high figure for such relatively well known insects.
Functional specialization among insect chitinase family genes revealed by RNA interference
Authors: Zhu Qingsong , Arakane Yasuyuki , Beeman Richard W. , Kramer Karl J. , Muthukrishnan Subbaratnam
Published: April 2008

The biological functions of individual members of the large family of chitinase-like proteins from the red flour beetle,
Tribolium castaneum
(Tc), were examined by using gene-specific RNAi. One chitinase, TcCHT5, was found to be required for pupal–adult molting only. A lethal phenotype was observed when the transcript level of
TcCHT5
was down-regulated by injection of
TcCHT5
-specific dsRNA into larvae. The larvae had metamorphosed into pupae and then to pharate adults but did not complete adult eclosion. Specific knockdown of transcripts for another chitinase, TcCHT10, which has multiple catalytic domains, prevented embryo hatch, larval molting, pupation, and adult metamorphosis, indicating a vital role for TcCHT10 during each of these processes. A third chitinase-like protein, TcCHT7, was required for abdominal contraction and wing/elytra extension immediately after pupation but was dispensable for larval–larval molting, pupation, and adult eclosion. The wing/elytra abnormalities found in
TcCHT7
-silenced pupae were also manifest in the ensuing adults. A fourth chitinase-like protein, TcIDGF4, exhibited no chitinolytic activity but contributed to adult eclosion. No phenotypic effects were observed after knockdown of transcripts for several other chitinase-like proteins, including imaginal disk growth factor IDGF2. These data indicate functional specialization among insect chitinase family genes, primarily during the molting process, and provide a biological rationale for the presence of a large assortment of chitinase-like proteins.
Genetic approaches identify adult pituitary stem cells
Authors: Gleiberman Anatoli S. , Michurina Tatyana , Encinas Juan M. , Roig Jose L. , Krasnov Peter , Balordi Francesca , Fishell Gord , Rosenfeld Michael G. , Enikolopov Grigori
Published: April 2008

Adult tissues undergo continuous cell turnover in response to stress, damage, or physiological demand. New differentiated cells are generated from dedicated or facultative stem cells or from self-renewing differentiated cells. Here we describe a different stem cell strategy for tissue maintenance, distinct from that observed for dedicated or facultative stem cells. We report the presence of nestin-expressing adult stem cells in the perilumenal region of the mature anterior pituitary and, using genetic inducible fate mapping, demonstrate that they serve to generate subsets of all six terminally differentiated endocrine cell types of the pituitary gland. These stem cells, while not playing a significant role in organogenesis, undergo postnatal expansion and start producing differentiated progeny, which colonize the organ that initially entirely consisted of differentiated cells derived from embryonic precursors. This generates a mosaic organ with two phenotypically similar subsets of endocrine cells that have different origins and different life histories. These parallel but distinct lineages of differentiated cells in the gland may help the maturing organism adapt to changes in the metabolic regulatory landscape.
Requirement of Nanog dimerization for stem cell self-renewal and pluripotency
Authors: Wang Jianlong , Levasseur Dana N. , Orkin Stuart H.
Published: April 2008

Pluripotency of embryonic stem (ES) cells is maintained by transcription factors that form a highly interconnected protein interaction network surrounding the homeobox protein Nanog. Enforced expression of Nanog in mouse ES (mES) cells promotes self-renewal and alleviates their requirement for leukemia inhibitory factor (LIF). Understanding molecular mechanisms by which Nanog functions should illuminate fundamental properties of stem cells and the process of cellular reprogramming. Previously, we showed that Nanog forms multiple protein complexes in mES cells. Here, we demonstrate that Nanog dimerizes through its C-terminal domain rather than the homeodomain. Dimerization is required for interaction with other pluripotency network proteins. We also show that enforced expression of the Nanog dimer, but not the monomer, functionally replaces wild-type Nanog to sustain LIF-independent self-renewal of ES cells. Our results demonstrate that Nanog–Nanog homodimerization is a critical aspect of its function promoting stem cell pluripotency.
Missing stitches
Authors: Morris Ruth
Published: April 2008

Along a continuum of interlingual interpreting which begins with police investigations and may end in a supreme court, consistent quality must be assured in order to comply with the standards of justice to which enlightened countries aspire and lay claim. With the advent of the global village, the quantity of cases requiring language mediation has exploded exponentially. The issues involved are not new, and simply put involve arranging for the provision of competent interpreters throughout the criminal justice system. However, the actual provision of quality interlingual interpreting in a criminal justice system is not a straightforward enterprise. The mere existence of legislation requiring the provision of interpreters in courts is not the key element. Nor are insightful comments made by appellate judges in cases brought because of an absence of satisfactory language arrangements. The article shows the problematic nature of interpreting arrangements in the criminal justice system for which the government and its players — even judges — assume no responsibility. The resultant “missing stitches” are likely to deprive those who do not speak the language of the proceedings of their fundamental rights.
Interpreting at the Tokyo War Crimes Tribunal
Authors: Takeda Kayoko
Published: April 2008

This paper gives an overview of the interpreting arrangements at the Tokyo War Crimes Tribunal (1946–1948), focusing on some sociopolitical aspects of the interpreting phenomena, and discusses the behavior of the interpreters and monitors during the testimony of Hideki Tojo, Japan’s wartime Prime Minister. It provides a contextualized examination of court interpreting rather than a microlinguistic analysis of interpreted texts. The study demonstrates how political and social aspects of the trial and wartime world affairs affected the interpreting arrangements, especially the hierarchical set-up in which three ethnically and socially different groups of “linguists” (language specialists) performed three different functions in the interpreting process. An examination of the linguists’ behavior during Tojo’s testimony points to a link between their relative positions in the power constellation of the trial and their choices, strategies and behavior in interpreting and monitoring. These findings reinforce the view that interpreting is a social practice conditioned by the social, political and cultural contexts of the setting in which interpreters operate.
Norms, ethics and roles among military court interpreters
Authors: Lipkin Shira L.
Published: April 2008

This study examined the activities of military court interpreters at the Yehuda Military Court near Jerusalem over a period of one year. The aim of the study was to examine the norms and ethical rules that guide the interpreters’ work. In-depth interviews were carried out with eleven interpreters and officers, and court sessions were observed. The questions asked related to the interpreters’ powers and duties, the nature of their work, their personal preferences, the rules that guide their work, and the training they receive. The findings show that the interpreters’ powers and duties cover a range of areas over and above interpreting per se, and include translating documents, acting as ushers in the courtroom, and handling logistical matters. The study also pointed to the lack of a clear set of rules in relation to the interpreters’ work, and revealed that training is provided only after they have begun working. The study suggests the need for a code of ethics defining and providing a framework for the interpreters’ powers and duties, which should be limited to interpreting, and should not encompass administrative tasks, as the current situation causes confusion over the ethical boundaries of the interpreters’ work.
Judges’ deviations from norm-based direct speech in court
Authors: Christensen Tina Paulsen
Published: April 2008

This article presents a small-scale empirical study of legal discourse which focuses on the use of direct and indirect speech in Danish interpreter-mediated court proceedings. The study analyses the practices of three Danish judges in three different interpreted proceedings. The primary objective of the paper is to study the potential correlation between the use of direct and indirect speech styles and certain stages of court proceedings. These stages are defined and classified in terms of explicit prescriptive legal norms ascribable to the participants in Danish court proceedings, acting in accordance with a predefined style of interaction (direct speech). In addition, the study investigates whether what the judges say about their speech style corresponds with their actual language use in court. The techniques combined in the study are survey research, participant observation and descriptive analysis based on transcriptions of authentic data from three audio-recorded criminal cases conducted by district courts in Denmark.