bluuebunny/crossref_metadata_2025 huggingface dataset:
Proliferating Progenitor Cells: A Required Cellular Element for Induction of Ischemic Tolerance in the Brain
Authors: Maysami Samaneh , Lan Jin Quan , Minami Manabu , Simon Roger P
Published: March 2008

Permanent cerebral blood flow reduction results in brain injury (stroke), whereas transient ischemic stress results in preconditioning, which can ameliorate the extent of irreversible brain injury from subsequent ischemia—the phenomena of ischemic tolerance. Neurogenesis in the brain occurs after both ischemic injury and the brief ischemia resulting in preconditioning. As neurogenesis is regarded as having an intrinsic neuroprotective role in the brain, we investigated the possible role of these endogenous progenitor cells in the induction of ischemic tolerance. Methylazoxymethanol acetate (MAM) was injected in wild-type mice to attenuate precursor cell proliferation and ganciclovir was used to diminish newly generated cells in GFAP/HSV-TK mice. Both MAM and ganciclovir significantly attenuated ischemia-induced progenitor cell proliferation in the subventricular zone, dentate gyrus, penumbra, and corpus callosum as quantified by 5-bromo-2′-deoxyuridine- or Ki-67-positive cells. Attenuation of ischemia-induced progenitor cell proliferation in the brain blocked the induction of ischemic tolerance. Further the number of TUNEL (TdT-mediated dUTP nick end labeling)-positive cells was considerably increased in MAM-treated animals, whereas MAM did not cause cell death in sham-operated controls. The results of this study suggest a role for endogenous progenitors in the protective effect of ischemic tolerance.
X-ray analysis of the magnetic influence of oxygen in Pt∕Co∕AlOx trilayers
Authors: Manchon A. , Pizzini S. , Vogel J. , Uhlîr V. , Lombard L. , Ducruet C. , Auffret S. , Rodmacq B. , Dieny B. , Hochstrasser M. , Panaccione G.
Published: March 2008

X-ray spectroscopy measurements have been performed on a series of Pt∕Co∕AlOx trilayers to investigate the role of Co oxidation in the perpendicular magnetic anisotropy at the Co∕AlOx interface. It is observed that varying the degree of oxidation modifies the magnetic properties of the Co layer, inducing a magnetic anisotropy crossover from in plane to out of plane. The microscopic structural properties are analyzed via x-ray photoelectron spectroscopy measurements. It is shown that increasing the oxidation time enhances the amount of interfacial oxide, which may be at the origin of perpendicular magnetic anisotropy.
X-ray structural investigation of Co∕Cu granular multilayers with giant magnetoresistance
Authors: Spizzo F. , Ferrero C. , Mazuelas A. , Albertini F. , Casoli F. , Nasi L. , Metzger T. H.
Published: March 2008

The effect of the reduction of the magnetic layer thickness on sample correlated roughness in Co∕Cu granular samples produced via the incomplete layer method has been investigated. When Co layer thickness is smaller than 3Å, they undergo a fragmentation process that modifies the expected sample magnetic and magnetoresistive properties. This behavior has been studied with anomalous x-ray diffuse intensity data collected in grazing incidence configuration by evaluating both roughness correlation lengths and the dynamic roughness exponent. The fragmentation process is found to promote conformal nanoscale roughness and to lower the giant magnetoresistance response of the system.
Synthesis and magnetic properties of monodisperse magnetite nanocubes
Authors: Yang Haitao , Ogawa Tomoyuki , Hasegawa Daiji , Takahashi Migaku
Published: March 2008

The monodisperse Fe3O4 nanocubes with controllable sizes from 6.5to30.0nm have been synthesized in one pot. The shape-induced texture of the self-assembled nanocube superlattices has been deposited onto substrates by a convective assembly technique. The cubelike shapes affect the crystalline orientation of individual particles within the self-assembled superlattices compared with the nanoparticles with an isotropic spherical shape. The nanocubes with a size less than 25nm show a typical superparamagnetic behavior at room temperature. Comparison of the hysteresis loop at 5K of cubes with different sizes reveals a size-dependent behavior of saturation magnetization and coercivity.
Barrier scattering with complex-valued quantum trajectories: Taxonomy and analysis of isochrones
Authors: David Julianne K. , Wyatt Robert E.
Published: March 2008

To facilitate the search for isochrones when using complex-valued trajectory methods for quantum barrier scattering calculations, the structure and shape of isochrones in the complex plane were studied. Isochrone segments were categorized based on their distinguishing features, which are shared by each situation studied: High and low energy wave packets, scattering from both thick and thin Gaussian and Eckart barriers of varying height. The characteristic shape of the isochrone is a trifurcated system: Trajectories that transmit the barrier are launched from the lower branch (T), while the middle and upper branches form the segments for reflected trajectories (F and B). In addition, a model is presented for the curved section of the lower branch (from which transmitted trajectories are launched), and important features of the complex extension of the initial wave packet are identified.
Effect of applied magnetic field on the rectifying characteristics in self-doped La0.9MnO3∕0.8wt%Nb–SrTiO3 heteroepitaxial junctions
Authors: Wang Z. H. , Yu G. L. , Nie Y. , Wu Z. F. , Qiu L. , Luo Z. , Gao J.
Published: March 2008

The epitaxial self-doped La0.9MnO3 thin film was deposited on a 0.8wt%Nb-doped SrTiO3 substrate by pulse laser deposition method to form a bilayer p-n junction with an area of 8mm2. The isothermal current-voltage loops measured from 10to380K with an interval of 10K in applied magnetic fields up to 7T show typical temperature-dependent rectifying characteristic and asymmetrical hysteresis. The effect of magnetic field on the rectifying property is very small for the temperature above 150K and a strong asymmetrical effect on the rectifying property below 150K. In the low temperature region, although the diffusive voltage Vd is not affected by the applied magnetic field, the breakdown voltage Vb decreases with the increasing of magnetic field. At 10K, the relative ratio of voltage [Vb(0)−Vb(7T)]∕Vb(0) is about 14%, showing a magnetically tunable property. These results reveal the great potential of the manganites in configuring artificial devices.
The short-time self-diffusion coefficient of a sphere in a suspension of rigid rods
Authors: Guzowski J. , Cichocki B. , Wajnryb E. , Abade G. C.
Published: March 2008

The short-time self-diffusion coefficient of a sphere in a suspension of rigid rods is calculated in first order in the rod volume fraction ϕ. For low rod concentrations, the correction to the Einstein diffusion constant of the sphere due to the presence of rods is a linear function of ϕ with the slope α proportional to the equilibrium averaged mobility diminution trace of the sphere interacting with a single freely translating and rotating rod. The two-body hydrodynamic interactions are calculated using the so-called bead model in which the rod of aspect ratio p is replaced by a stiff linear chain of touching spheres. The interactions between spheres are calculated using the multipole method with the accuracy controlled by a multipole truncation order and limited only by the computational power. A remarkable accuracy is obtained already for the lowest truncation order, which enables calculations for very long rods, up to p=1000. Additionally, the bead model is checked by filling the rod with smaller spheres. This procedure shows that for longer rods the basic model provides reasonable results varying less than 5% from the model with filling. An analytical expression for α as a function of p is derived in the limit of very long rods. The higher order corrections depending on the applied model are computed numerically. An approximate expression is provided, valid for a wide range of aspect ratios.
Density-functional study of small neutral and cationic bismuth clusters Bin and Bin+(n=2–24)
Authors: Yuan H. K. , Chen H. , Kuang A. L. , Miao Y. , Xiong Z. H.
Published: March 2008

Density-functional theory with scalar-relativistic pseudopotential and a generalized gradient correction is used to calculate the neutral and cationic Bin clusters (2⩽n⩽24), with the aim to elucidate their structural evolution, relative stability, and magnetic property. The structures of neutral Bi clusters are found to be similar to that of other group-V elemental clusters, with the extensively studied sizes of n=4 and 8 having a tetrahedron and wedgelike structure, respectively. Generally, larger Bi clusters consist of a combination of several stable units of Bi4, Bi6, and Bi8, and they have a tendency to form an amorphous structure with the increase of cluster sizes. The curves of second order energy difference exhibit strong odd-even alternations for both neutral and cationic Bi clusters, indicating that even-atom (odd-atom) sizes are relatively stable in neutral clusters (cationic clusters). The calculated magnetic moments are 1μB for odd-atom clusters and zero for even-atom clusters. We propose that the difference in magnetism between experiment and theory can be greatly improved by considering the orbital contribution. The calculated fragmentation behavior agrees well with the experiment, and for each cationic cluster the dissociation into Bi4 or Bi7+ subclusters confirms the special stability of Bi4 and Bi7+. Moreover, the bond orders and the gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital show that small Bi clusters would prefer semiconductor characters to metallicity.
Global uniform semiclassical approximation for Clebsch-Gordan coefficients
Authors: Engel Hamutal , Kay Kenneth G.
Published: March 2008

Semiclassical integral representations, analogous to initial value expressions for the propagator, are presented for the Clebsch-Gordan angular momentum coupling coefficients. Two forms (L and R types) of the approximation are presented. For each form, new non-Gaussian expressions, which are specifically adapted to the nature of angular momentum variables, are proposed in place of the familiar Gaussian coherent state functions. With these non-Gaussian kernels, it is found that the present treatments are capable of accuracy similar to that obtained from a uniform Airy approximation. Although the present semiclassical approximations involve only real-valued angle variables, associated with sets of angular momenta that are related by ordinary, real, classical transformations, the treatments produce accurate results not only for classically allowed choices of quantum numbers but also for very strongly classically forbidden values.
Multipolar surface plasmon peaks on gold nanotriangles
Authors: Félidj N. , Grand J. , Laurent G. , Aubard J. , Lévi G. , Hohenau A. , Galler N. , Aussenegg F. R. , Krenn J. R.
Published: March 2008

In this paper, we report on the observation of multipolar surface plasmon excitation in lithographically designed gold nanotriangles, investigated by means of far-field extinction microspectroscopy in the wavelength range of 400–1000nm. Several bands are observed in the visible and near infrared regions when increasing the side length of the triangles. The assignment of these peaks to successive in-plane multipolar plasmon modes is supported by calculations using the discrete dipole approximation method. We show that the lowest three multipolar excitations are clearly resolved in the visible and near infrared range. These new spectral features could be very promising in nanooptics or for chemosensing and biosensing applications.
A quantitative account of electron energy transport in a National Spherical Tokamak Experiment plasma
Authors: Wong K. L. , Kaye S. , Mikkelsen D. R. , Krommes J. A. , Hill K. , Bell R. , LeBlanc B.
Published: March 2008

The first successful quantitative account of the electron thermal conductivity χe in a tokamak experiment due to imperfect magnetic surfaces is presented. The unstable spectrum of microtearing instabilities is calculated with the GS2 code for a well-behaved H-mode plasma in the National Spherical Tokamak Experiment [M. Ono et al., Nucl. Fusion 40, 557 (2000)], with 6 MW deuterium neutral beam heating at Ip=0.75MA, Bt=0.5T. The application of existing nonlinear theory shows that the unstable modes can produce overlapping magnetic islands leading to global stochastic magnetic fields. The calculated χe based on the present theory is in reasonable agreement with the values from transport analysis of the experimental data over the entire region (0.4<r∕a<0.75) where the electron temperature gradient is strong enough to make microtearing the most unstable mode. There is no adjustable parameter in this comparison. This instability can be avoided by reversed magnetic shear or by heating the electrons to lower the electron-ion collision frequency.
Terahertz emission mediated by surface plasmon polaritons in doped semiconductors with surface grating
Authors: Kong B. D. , Sokolov V. N. , Kim K. W. , Trew R. J.
Published: March 2008

Doped semiconductors with one-dimensional surface gratings are studied theoretically for application to terahertz emission. The presence of free carriers supports thermally excited surface plasmon polaritons at the semiconductor-vacuum interface whose resonance frequency can be controlled by doping. The calculation based on the fluctuational electrodynamics shows that the near-field spectral energy density of this surface excitation can be many orders of magnitude larger than those in the blackbody radiation. At the same time, a rigorous coupled-wave analysis with a properly designed surface microstructure clearly indicates narrow angular lobes in the directional emissivity at the targeted frequencies, illustrating strong coupling between surface plasmon polaritons and propagating waves. Thus, doped semiconductors with engineered radiation may provide an efficient terahertz source with spatial and spectral control.
Polarization selection with stacked hole array metamaterial
Authors: Beruete M. , Navarro-Cía M. , Sorolla M. , Campillo I.
Published: March 2008

Polarization rotation or selection appears in materials with optical activity, or those with Faraday effect, or in liquid crystals. In this letter we present a structure, with an analogous response, using stacked extraordinary transmission subwavelength hole arrays modified to be nearly self-complementary. This produces a polarization selector because of the negative index of refraction for one of its linearly polarized eigenwaves. Simulation results and experiments at millimeter wavelengths confirm these features. Applications in miniaturized devices are envisioned as well as the possibility to scale to optical wavelengths.
FePt films on self-assembled SiO2 particle arrays
Authors: Makarov D. , Brombacher C. , Liscio F. , Maret M. , Parlinska M. , Meier S. , Kappenberger P. , Albrecht M.
Published: March 2008

Chemically L10 ordered (001) textured FePt thin films with perpendicular magnetic anisotropy can be grown on amorphous planar SiO2 substrate with an underlayer stack of [Pt (3nm)∕Cr (50nm)] adopting a [002] orientation when deposited at 350°C. This knowledge of optimum layer stack was transferred to self-assembled SiO2 particle arrays. While 330nm SiO2 particle arrays reveal perpendicular magnetic anisotropy with a remanence of almost one and a coercivity of 370mT, on 160nm particles, the FePt caps show a (111) texturing, leading to the random orientation of the easy axis of the magnetization.
Scaling the final deposits of dry cohesive granular columns after collapse and quasi-static fall
Authors: Mériaux Catherine , Triantafillou Trent
Published: March 2008

This paper reports on laboratory experiments that were designed to investigate the collapse and quasi-static fall of dry cohesive granular columns. These experiments were compared with similar experiments that were performed with non-cohesive dry sand columns. A powder of gypsum (calcium sulphate dihydrate) was used to represent cohesive granular material. In all the experiments, the cohesive granular columns fractured and flowed in coherent blocks but, while faults remained steep in the quasi-static fall experiments, they flattened in the collapse experiments as the initial aspect ratio of the columns increased. Dilation was seen in the quasi-static fall experiments, while some air entrapment within the columns occurred in the collapse experiments. The final deposits of the cohesive granular columns were found to satisfy power law relationships as a function of the initial aspect ratio of the columns. Two asymptotes were found for the lower and higher range of initial aspect ratios, which varied between 0.5 and 8, respectively. When compared with the power law relationships found for dry noncohesive columns, the power dependence of the ratio of initial to final height and final runout to initial length with the aspect ratio of the columns was found to be similar. The prefactors of the power laws were found to slightly decrease with the increase of the cohesion or, equivalently, the decrease in grain size. Similar to the dry noncohesive case, the prefactors for the runout length were found to increase by a factor 2 with the increase of flow rate. When the collapse experiments were compared with the quasi-static fall experiments, a shift towards higher aspect ratios of the transition between the two asymptotic power laws was found.
Phonon properties in narrow gap FeSi and FeSb2 single crystals
Authors: Racu A.-M. , Menzel D. , Schoenes J. , Marutzky M. , Johnsen S. , Iversen B. B.
Published: March 2008

We review the phonon analysis of FeSi and present a new study of the Raman and infrared (IR) active phonons of the related compound FeSb2. The measurements are supplemented by a factor group analysis, enabling the full mode assignment. While in FeSi, all nine Raman active modes predicted by the theory are visible in our spectra, in FeSb2, three of the six predicted modes have been observed. The unusual temperature dependence of the Raman linewidth of FeSi has been interpreted in terms of electron-phonon interactions. In FeSb2, a Fano-like IR absorption is reported at 300K, indicating electron-phonon coupling. The asymmetry vanishes and the damping constant decreases drastically by cooling, in correspondence with the depletion of the charge carrier concentration.
A combined theoretical treatment of T1→S intersystem crossing and intramolecular vibrational redistribution in thiophosgene
Authors: Rashev Svetoslav , Moule David C.
Published: March 2008

We combine our two recent theoretical approaches for electronic relaxation T1→S0 and vibrational relaxation processes in thiophosgene (SCCl2) to provide a more detailed picture of the intersystem crossing (ISC) and phosphorescence from the first triplet T1. Our analysis shows that ISC is not a true irreversible decay and should lead to violent phosphorescence quantum beats that could be observed experimentally.
Self-assembly of multiwalled carbon nanotubes from quench-condensed CNi3 films
Authors: Young D. P. , Karki A. B. , Adams P. W. , Ngunjiri Johnpeter N. , Garno Jayne C. , Zhu Hongwei , Wei Bingqing , Moldovan D.
Published: March 2008

Freestanding, vertical, multiwalled carbon nanotubes (MWCNTs) are formed during the vacuum deposition of thin films of the metastable carbides CT3 (T=Ni, Co) onto fire-polished glass substrates. In contrast to widely used chemical and laser vapor deposition techniques, we utilize direct e-beam evaporation of arc-melted CT3 targets to produce MWCNTs that are self-assembled out of the CT3-film matrix. The depositions are made in an ambient vapor pressure that is at least six orders of magnitude lower than the 1−100 Torr typically used in chemical vapor techniques. Furthermore, the substrates need not be heated, and, in fact, we observe a robust nanotube growth on liquid nitrogen cooled glass and sapphire substrates. High-resolution atomic force microscopy reveals that MWCNTs of heights 1−40 nm are formed in films with nominal thicknesses in the range of 5−60 nm. We show that the growth parameters of the nanotubes are very sensitive to the grain structure of the films. This is consistent with a precipitation mediated root-growth mechanism.
Variability of electronics and spintronics nanoscale devices
Authors: Ovchinnikov Igor V. , Wang Kang L.
Published: March 2008

We address the problem of how the quantum (and the temperature) fluctuations will affect the magnetoelectronic circuits’ operation, and if there are any advantages, or possibly drawbacks, in the switching from the charge for uncorrelated electronics to the spin for spintronics. Within the framework of “minimal” ferromagnetic Hamiltonian, we consider the fluctuations in the total number of the electrons on the gate, the total spin, and the spin vector projection on the easy axis. It is expected that spintronics devices will improve variability compared with today’s electronics devices.
Negative electron binding energies observed in a triply charged anion: Photoelectron spectroscopy of 1-hydroxy-3,6,8-pyrene-trisulfonate
Authors: Yang Jie , Xing Xiao-Peng , Wang Xue-Bin , Wang Lai-Sheng , Sergeeva Alina P. , Boldyrev Alexander I.
Published: March 2008

We report the observation of negative electron binding energies (BEs) in a triply charged anion, 1-hydroxy-3,6,8-pyrene-trisulfonate (HPTS3−). Low-temperature photoelectron spectra were obtained for HPTS3− at several photon energies, revealing three detachment features below 0 electron BE. The HPTS3− trianion was measured to possess a negative BE of −0.66eV. Despite the relatively high excess energy stored in HPTS3−, it was observed to be a long-lived anion due to its high repulsive Coulomb barrier (RCB) (∼3.3eV), which prevents spontaneous electron emission. Theoretical calculations were carried out, which confirmed the negative electron BEs observed. The calculations further showed that the highest occupied molecular orbital in HPTS3− is an antibonding π orbital on the pyrene rings, followed by lone pair electrons in the peripheral –SO3− groups. Negative electron BE is a unique feature of multiply charged anions due to the presence of the RCB. Such metastable species may be good models to study electron-electron and vibronic interactions in complex molecules.
Stability and bonding properties of finite single-walled carbon nanotubes adsorbed on Si(001)
Authors: Orellana Walter
Published: March 2008

The stability and bonding properties of capped single-walled carbon nanotubes (CNTs) adsorbed on the Si(001) surface are addressed by density-functional theory calculations. We study the armchair (5,5) and the zigzag (9,0) CNTs with a similar length of about 24Å, which are adsorbed parallel and perpendicular to the dimer direction of the reconstructed Si(001) surface. At the equilibrium geometries, both CNTs form covalent bonds with the substrates with binding energies ranging from 0.40to0.62eV per C–Si bond. These bonds only form when neighboring C and Si atoms are closer than 2.13Å. We find a preferential direction for the CNT adsorptions along the dimers where the zigzag CNT is found to be the most stable. Changes in the Si(001) band structures after the CNT adsorption are also discussed.
Continuous-wave room temperature operated 3.0μm type I GaSb-based lasers with quinternary AlInGaAsSb barriers
Authors: Hosoda T. , Belenky G. , Shterengas L. , Kipshidze G. , Kisin M. V.
Published: March 2008

Diode lasers emitting at 3.0μm were designed and fabricated. Device active region contained two compressively strained InGaAsSb quantum wells incorporated in quinternary AlInGaAsSb barriers. Laser output power at room temperature was 130mW in continuous wave regime and more than 1W in pulse.
Application of frustrated total internal reflection of millimeter waves for detection and evaluation of disbonds in dielectric joints
Authors: Kharkovsky Sergey , Nanni Emilio , Zoughi Reza
Published: March 2008

Millimeter waves penetrate inside of low loss dielectric materials and they are sensitive to the presence of internal interfaces and nonuniformities. This allows millimeter wave nondestructive inspection techniques to be utilized for inspecting dielectric composite structures. A disbond (a thin and extended airgap) in structures possessing adhesively bonded joints with complex geometries is commonly difficult to inspect. In this letter, we demonstrate the operational principle and the useful features of a millimeter wave technique, employing a frustrated total internal reflection of signals transmitted and received by dielectric waveguide probes for detecting and evaluating disbonds in such joints.
Electron-phonon interaction in disordered semiconductors
Authors: Yu X. Z. , Yang Y. , Pan W. , Shen W. Z.
Published: March 2008

We have presented a detailed experimental investigation of the effects of disorder on the electron-phonon interaction in semiconducting InN system. Both the temperature (T) and disorder (electron mean free path l) dependences of the electron-phonon scattering time τe-ph have been determined from the weak localization analysis. It is found that τe-ph−1 exhibits a tendency to change gradually from the characteristic dependence τe-ph−1∝T3l0 in the pure limit to the form of T2l−1 as the films become disordered. Our observation gives clear evidence for the substantial enhancement of the electron-phonon coupling in semiconductor structures due to elastic electron scattering.
Dipole model explaining high-k/metal gate field effect transistor threshold voltage tuning
Authors: Kirsch P. D. , Sivasubramani P. , Huang J. , Young C. D. , Quevedo-Lopez M. A. , Wen H. C. , Alshareef H. , Choi K. , Park C. S. , Freeman K. , Hussain M. M. , Bersuker G. , Harris H. R. , Majhi P. , Choi R. , Lysaght P. , Lee B. H. , Tseng H.-H. , Jammy R. , Böscke T. S. , Lichtenwalner D. J. , Jur J. S. , Kingon A. I.
Published: March 2008

An interface dipole model explaining threshold voltage (Vt) tuning in HfSiON gated n-channel field effect transistors (nFETs) is proposed. Vt tuning depends on rare earth (RE) type and diffusion in Si∕SiOx∕HfSiON∕REOx/metal gated nFETs as follows: Sr<Er<Sc+Er<La<Sc<none. This Vt ordering is very similar to the trends in dopant electronegativity (EN) (dipole charge transfer) and ionic radius (r) (dipole separation) expected for a interfacial dipole mechanism. The resulting Vt dependence on RE dopant allows distinction between a dipole model (dependent on EN and r) and an oxygen vacancy model (dependent on valence).
La and Nb codoped BiFeO3 multiferroic thin films on LaNiO3∕Si and IrO2∕Si substrates
Authors: Cheng Z. X. , Wang X. L. , Kimura H. , Ozawa K. , Dou S. X.
Published: March 2008

Nb and La codoped BiFeO3 thin films were fabricated on oxide bottom electrodes, LaNiO3∕Si and IrO2∕Si, by pulsed laser deposition method. The doped BiFeO3 thin film capacitor on LaNiO3 showed a remnant polarization of more than 75μC∕cm2 in a saturated hysteresis loop. The same La and Nb codoped BiFeO3 thin film capacitors on IrO2 showed a larger remnant polarization, while with a significant contribution from the leakage current. Furthermore, the doped BiFeO3 capacitor on the LaNiO3 bottom electrode showed worse fatigue resistance than the film on IrO2. All the doped BiFeO3 thin films showed weak ferromagnetism at room temperature.
Electrically driven high-Q quantum dot-micropillar cavities
Authors: Böckler C. , Reitzenstein S. , Kistner C. , Debusmann R. , Löffler A. , Kida T. , Höfling S. , Forchel A. , Grenouillet L. , Claudon J. , Gérard J. M.
Published: March 2008

We report on electrically pumped high-Q quantum dot-micropillar cavities with quality factors of up to 16.000. A special current injection scheme using a ring-shaped upper contact is presented which ensures an efficient light out-coupling through the uncapped upper surface of the micropillar. The devices feature excellent single-quantum dot cavity quantum electrodynamic effects with a Purcell enhancement of about 10 for a micropillar with a diameter of 2.5μm.
Improving the operation temperature of semiconductor-based terahertz photodetectors: A multiphoton design
Authors: Castellano Fabrizio , Iotti Rita C. , Rossi Fausto
Published: March 2008

We propose and theoretically investigate a semiconductor-based terahertz-detector design exploiting a multiphoton absorption strategy through a bound-to-bound-to-continuum scheme. Our results demonstrate that such a multisubband architecture may access values of the background-limited infrared photodetection temperature, significantly higher than those of conventional quantum well infrared photodetectors operating at the same frequency, and therefore could represent a better alternative to the latter in the terahertz spectral region.
Spectrally resolved femtosecond Maker fringes technique
Authors: Heisler Ismael André , Misoguti Lino , Zílio Sérgio Carlos , Rodriguez Ernesto V. , Bartolomeu de Araújo Cid
Published: March 2008

We present a femtosecond third-harmonic generation Maker fringes technique capable of simultaneously providing the magnitude of the cubic nonlinearity and the refractive index dispersion of optical materials. This technique takes advantage of the high intensity and broad spectral band of femtosecond pulses, but requires the use of a spectrometer to deconvolute the information contained in Maker fringes produced by the broad band light.
Reduction of dislocations in GaN films on AlN/sapphire templates using CrN nanoislands
Authors: Ha Jun-Seok , Lee Hyo-Jong , Lee Seog Woo , Lee Hyun Jae , Lee Sang Hyun , Goto Hiroki , Cho Meoung Whan , Yao Takafumi , Hong Soon-Ku , Toba Ryuichi , Lee Jae Wook , Lee Jeong Yong
Published: March 2008

We report significant reduction of threading dislocations in GaN films grown by hydride vapor phase epitaxy on AlN/sapphire templates by employing CrN nanoislands on the AlN. High quality GaN films with very small twist mosaic as well as small tilt mosaic have been grown on the AlN/sapphire templates, which had small tilt but very large twist mosaic. The CrN nanoislands were formed by nitridation of a thin Cr film deposited by sputtering on the AlN/sapphire template, where the AlN/sapphire template was prepared by metal organic vapor phase epitaxy. The full width at half maximum values of x-ray rocking curves from the GaN film with the CrN were 114, 209, and 243arcsec for (0002), (10−12), and (11−20) reflections, respectively, while those of the GaN film without the CrN were 129, 1130, and 1364arcsec, respectively. Evaluation of total dislocation density of the GaN films by plan view transmission electron microscopy revealed that the dislocation density was reduced to 2.7×108 from 6.4×109cm−2 by employing the CrN nanoislands. The CrN nanoislands play a key role in reducing the threading dislocations by masking the propagation of dislocations as well as by bending the dislocations.
White-light light-emitting device based on surface plasmon-enhanced CdSe∕ZnS nanocrystal wavelength conversion on a blue/green two-color light-emitting diode
Authors: Yeh Dong-Ming , Huang Chi-Feng , Lu Yen-Cheng , Yang C. C.
Published: March 2008

The authors demonstrate the implementation of a white-light device by spin-coating CdSe∕ZnS nanocrystals (NCs) on the top of a blue/green two-color InGaN∕GaN quantum-well light-emitting diode for converting blue and green emissions into red light through the absorption/reemission process. Meanwhile, Au nanoparticles are mixed with CdSe∕ZnS NCs for generating localized surface plasmon (LSP) modes to couple with the CdSe∕ZnS NCs. The LSP modes can absorb green emission and effectively transfer the energy into the CdSe∕ZnS NCs through the coupling process for enhancing red emission. With the LSP coupling process, the conversion efficiency from the blue/green range into red light can be increased by around 30%. The conversion quantum efficiency can reach 52.8%.
A write time of 6ns for quantum dot–based memory structures
Authors: Geller M. , Marent A. , Nowozin T. , Bimberg D. , Akçay N. , Öncan N.
Published: March 2008

The concept of a memory device based on self-organized quantum dots (QDs) is presented, enabling extremely fast write times, limited only by the charge carrier relaxation time being in the picosecond range. For a first device structure with embedded InAs∕GaAs QDs, a write time of 6ns is demonstrated. A similar structure containing GaSb∕GaAs QDs shows a write time of 14ns. These write times are independent of the localization energy (e.g., storage time) of the charge carriers and at the moment are limited only by the experimental setup and the parasitic cutoff frequency of the RC low pass of the device.
Micro- and nanoparticles self-assembly for virtually defect-free, adjustable monolayers
Authors: Aubry N. , Singh P. , Janjua M. , Nudurupati S.
Published: March 2008

As chips further shrink toward smaller scales, fabrication processes based on the self-assembly of individual particles into patterns or structures are often sought. One of the most popular techniques for two-dimensional assembly (self-assembled monolayers) is based on capillary forces acting on particles placed at a liquid interface. Capillarity-induced clustering, however, has several limitations: it applies to relatively large (radius > ≈10 μm) particles only, the clustering is usually non-defect-free and lacks long-range order, and the lattice spacing cannot be adjusted. The goal of the present article is to show that these shortcomings can be addressed by using an external electric field normal to the interface. The resulting self-assembly is capable of controlling the lattice spacing statically or dynamically, forming virtually defect-free monolayers, and manipulating a broad range of particle sizes and types including nanoparticles and electrically neutral particles.
Opening and closing of the periplasmic gate in lactose permease
Authors: Zhou Yonggang , Guan Lan , Freites J. Alfredo , Kaback H. Ronald
Published: March 2008

X-ray crystal structures of lactose permease (LacY) reveal pseudosymmetrically arranged N- and C-terminal six-transmembrane helix bundles surrounding a deep internal cavity open on the cytoplasmic side and completely closed on the periplasmic side. The residues essential for sugar recognition and H
+
translocation are located at the apex of the cavity and are inaccessible from the outside. On the periplasmic side, helices I/II and VII from the N- and C- six helix bundles, respectively, participate in sealing the cavity from the outside. Three paired double-Cys mutants—Ile-40 → Cys/Asn-245 → Cys, Thr-45 → Cys/Asn-245 → Cys, and Ile-32 → Cys/Asn-245 → Cys—located in the interface between helices I/II and VII on the periplasmic side of LacY were constructed. After cross-linking with homobifunctional reagents less than ≈15 Å in length, all three mutants lose the ability to catalyze lactose transport. Strikingly, however, full or partial activity is observed when cross-linking is mediated by flexible reagents greater than ≈15 Å in length. The results provide direct support for the argument that transport via LacY involves opening and closing of a large periplasmic cavity.
Aurora A Regulates the Activity of HURP by Controlling the Accessibility of Its Microtubule-binding Domain
Authors: Wong Jim , Lerrigo Robert , Jang Chang-Young , Fang Guowei
Published: March 2008

HURP is a spindle-associated protein that mediates Ran-GTP-dependent assembly of the bipolar spindle and promotes chromosome congression and interkinetochore tension during mitosis. We report here a biochemical mechanism of HURP regulation by Aurora A, a key mitotic kinase that controls the assembly and function of the spindle. We found that HURP binds to microtubules through its N-terminal domain that hyperstabilizes spindle microtubules. Ectopic expression of this domain generates defects in spindle morphology and function that reduce the level of tension across sister kinetochores and activate the spindle checkpoint. Interestingly, the microtubule binding activity of this N-terminal domain is regulated by the C-terminal region of HURP: in its hypophosphorylated state, C-terminal HURP associates with the microtubule-binding domain, abrogating its affinity for microtubules. However, when the C-terminal domain is phosphorylated by Aurora A, it no longer binds to N-terminal HURP, thereby releasing the inhibition on its microtubule binding and stabilizing activity. In fact, ectopic expression of this C-terminal domain depletes endogenous HURP from the mitotic spindle in HeLa cells in trans, suggesting the physiological importance for this mode of regulation. We concluded that phosphorylation of HURP by Aurora A provides a regulatory mechanism for the control of spindle assembly and function.
Polyubiquitin Promoter-Based Binary Vectors for Overexpression and Gene Silencing in Lotus japonicus
Authors: Maekawa Takaki , Kusakabe Mitsumasa , Shimoda Yoshikazu , Sato Shusei , Tabata Satoshi , Murooka Yoshikatsu , Hayashi Makoto
Published: March 2008

In this study, we compared the transcriptional activities between Cauliflower mosaic virus (CaMV)35S promoter and polyubiquitin (Ljubq1) promoter from Lotus japonicus using β-glucuronidase (gus) reporter gene in transgenic plants of L. japonicus. The promoter analysis demonstrated that the Ljubq1 promoter possessed higher activity than the CaMV35S promoter in leaves, stems, roots, nodules, and pollen. Finally, we created GATEWAY conversion technology-compatible binary vectors for over-expression and RNA interference under the Ljubq1 promoter. These materials could provide alternative choice for studies in L. japonicus.
Pathogenicity of Pseudomonas syringae pv. tomato on Tomato Seedlings: Phenotypic and Gene Expression Analyses of the Virulence Function of Coronatine
Authors: Uppalapati Srinivasa Rao , Ishiga Yasuhiro , Wangdi Tamding , Urbanczyk-Wochniak Ewa , Ishiga Takako , Mysore Kirankumar S. , Bender Carol L.
Published: March 2008

Bacterial speck disease, which is caused by Pseudomonas syringae pv. tomato, is an economically important disease on tomato. In the present study, we show that P. syringae pv. tomato DC3000 is a pathogen of tomato seedlings, an aspect of pathogen biology that has not been previously investigated. This resulted in the development of a virulence assay on tomato seedlings that has several advantages over labor-intensive foliar assays, including a shorter growth and incubation period, ease of inoculation and handling, and rapid generation of larger sample sizes per experiment. The utility of this assay was investigated by exploring the virulence function of coronatine (COR) on tomato seedlings. Using the COR– mutant DB29 and a MAPMAN display of transcript data from TOM1 microarrays, COR-dependent expression of genes involved in secondary metabolism, polyamine biosynthesis, reactive oxygen species homeostasis, and the novel transcription factor SlNAC2 were identified. Furthermore, during pathogenesis, genes involved in photosynthetic light reactions and the Calvin-Benson cycle were strongly repressed by COR. In conclusion, we show that P. syringae pv. tomato infects tomato seedlings and that COR is required for virulence in seedlings. The seedling assay can be used in high-throughput screens for the identification of molecular targets for COR and for the identification of genes involved in pathogenesis.
The rsmA-like Gene rsmAXcc of Xanthomonas campestris pv. campestris Is Involved in the Control of Various Cellular Processes, Including Pathogenesis
Authors: Chao Nai-Xia , Wei Ke , Chen Qi , Meng Qing-Lin , Tang Dong-Jie , He Yong-Qiang , Lu Guang-Tao , Jiang Bo-Le , Liang Xiao-Xia , Feng Jia-Xun , Chen Baoshan , Tang Ji-Liang
Published: March 2008

RsmA is an RNA-binding protein functioning as a global post-transcriptional regulator of various cellular processes in bacteria and has been demonstrated to be an important virulence regulator in many animal bacterial pathogens. However, its function in other phytopathogenic bacteria is unclear, except for the Erwinia carotovora RsmA, which acts as a negative virulence regulator. In this work, we investigated the function of the rsmA-like gene, named rsmAXcc, of the phytopathogen Xanthomonas campestris pv. campestris. Deletion of rsmAXcc resulted in complete loss of virulence on the host plant Chinese radish, hypersensitive response on the nonhost plant pepper ECW-10R, and motility on the surface of an agar plate. The rsmAXcc mutant displayed a significant reduction in the production of extracellular amylase, endoglucanase, and polysaccharide, but a significant increase in intracellular glycogen accumulation and an enhanced bacterial aggregation and cell adhesion. Microarray hybridization and semiquantitative reverse-transcription polymerase chain reaction analysis showed that deletion of rsmAXcc led to significantly reduced expression of genes encoding the type III secretion system (T3SS), T3SS-effectors, and the bacterial aggregate dispersing enzyme endo-β-1,4-mannanase. These results suggest that rsmAXcc is involved in the control of various cellular processes, including pathogenesis of X. campestris pv. campestris.
Cyst Nematode Parasitism of Arabidopsis thaliana Is Inhibited by Salicylic Acid (SA) and Elicits Uncoupled SA-Independent Pathogenesis-Related Gene Expression in Roots
Authors: Wubben Martin John Evers , Jin Jing , Baum Thomas Josef
Published: March 2008

Compatible plant–nematode interactions involve the formation of an elaborate feeding site within the host root that requires the evasion of plant defense mechanisms by the parasite. Little is known regarding plant defense signaling pathways that limit nematode parasitism during a compatible interaction. Therefore, we utilized Arabidopsis thaliana mutants perturbed in salicylic acid (SA) biosynthesis or signal transduction to investigate the role of SA in inhibiting parasitism by the beet cyst nematode Heterodera schachtii. We determined that SA-deficient mutants (sid2-1, pad4-1, and NahG) exhibited increased susceptibility to H. schachtii. In contrast, SA-treated wild-type plants showed decreased H. schachtii susceptibility. The npr1-2 and npr1-3 mutants, which are impaired in SA signaling, also showed increased susceptibility to H. schachtii, whereas the npr1-suppressor mutation sni1 showed decreased susceptibility. Constitutive pathogenesis-related (PR) gene-expressing mutants (cpr1 and cpr6) did not show altered susceptibility to H. schachtii; however, constitutive PR gene expression was restricted to cpr1 shoots with wild-type levels of PR-1 transcript present in cpr1 roots. Furthermore, we determined that H. schachtii infection elicits SA-independent PR-2 and PR-5 induction in wild-type roots, while PR-1 transcript and total SA levels remained unaltered. This was in contrast to shoots of infected plants where PR-1 transcript abundance and total SA levels were elevated. We conclude that SA acts via NPR1 to inhibit nematode parasitism which, in turn, is negatively regulated by SNI1. Our results show an inverse correlation between root basal PR-1 expression and plant susceptibility to H. schachtii and suggest that successful cyst nematode parasitism may involve a local suppression of SA signaling in roots.
Two Receptor-Like Genes, Vfa1 and Vfa2, Confer Resistance to the Fungal Pathogen Venturia inaequalis Inciting Apple Scab Disease
Authors: Malnoy Mickael , Xu Mingliang , Borejsza-Wysocka Ewa , Korban Schuyler S. , Aldwinckle Herb S.
Published: March 2008

The Vf locus, originating from the crabapple species Malus floribunda 821, confers resistance to five races of the fungal pathogen Venturia inaequalis, the causal agent of apple scab disease. Previously, a cluster of four receptor-like genes, Vfa1, Vfa2, Vfa3, and Vfa4, was identified within the Vf locus. Because the amino-acid sequence of Vfa3 is truncated, it was deemed nonfunctional. In this study, each of the three full-length Vfa genes was introduced into a plant cloning vector, pCAMBIA2301, and used for Agrobacterium-mediated transformation of two apple cultivars, Galaxy and McIntosh, to assess functionality of these genes and to characterize their roles in resistance to V. inaequalis. Transformed apple lines carrying each of Vfa1, Vfa2, or Vfa4 were developed, analyzed for the presence of the transgene using polymerase chain reaction and Southern blotting, and assayed for resistance to apple scab following inoculation with V. inaequalis. Transformed lines expressing Vfa4 were found to be susceptible to apple scab, whereas those expressing either Vfa1 or Vfa2 exhibited partial resistance to apple scab. Based on Western blot analysis as well as microscopic analysis of plant resistance reactions, the roles of Vfa1 and Vfa2 in apple scab disease resistance response are discussed.
Interacting dipole pairs on a rotating sphere
Authors: Newton Paul K , Shokraneh Houman
Published: March 2008

The evolution, interaction and scattering of 2Npoint vortices grouped into equal and opposite pairs (N-dipoles) on a rotating unit sphere are studied. A new coordinate system made up of centres of vorticity and centroids associated with each dipole is introduced. With these coordinates, the nonlinear equations for an isolated dipole diagonalize and one directly obtains the equation for geodesic motion on the sphere for the dipole centroid. When two or more dipoles interact, the equations are viewed as an interacting billiard system on the sphere—charged billiards—with long-range interactions causing the centroid trajectories to deviate from their geodesic paths. Canonical interactions are studied both with and without rotation. For two dipoles, the four basic interactions are described asexchange-scattering,non-exchange-scattering,loop-scattering(head on) and loop-scattering (chasing) interactions. For three or more dipoles, one obtains a richer variety of interactions, although the interactions identified in the two-dipole case remain fundamental.