bluuebunny/crossref_metadata_2025 huggingface dataset:
Regulation of Jumonji-domain-containing histone demethylases by hypoxia-inducible factor (HIF)-1α
Authors: Pollard Patrick J. , Loenarz Christoph , Mole David R. , McDonough Michael A. , Gleadle Jonathan M. , Schofield Christopher J. , Ratcliffe Peter J.
Published: August 2008

The transcription factor HIF (hypoxia-inducible factor) mediates a highly pleiotrophic response to hypoxia. Many recent studies have focused on defining the extent of this transcriptional response. In the present study we have analysed regulation by hypoxia among transcripts encoding human Fe(II)- and 2-oxoglutarate-dependent oxygenases. Our results show that many of these genes are regulated by hypoxia and define two groups of histone demethylases as new classes of hypoxia-regulated genes. Patterns of induction were consistent across a range of cell lines with JMJD1A (where JMJD is Jumonji-domain containing) and JMJD2B demonstrating robust, and JMJD2C more modest, up-regulation by hypoxia. Functional genetic and chromatin immunoprecipitation studies demonstrated the importance of HIF-1α in mediating these responses. Given the importance of histone methylation status in defining patterns of gene expression under different physiological and pathophysiological conditions, these findings predict a role for the HIF system in epigenetic regulation.
Temperature dependence of the magnetic-field-induced strain of NiMnGa in the presence of an acoustic drive
Authors: Peterson Bradley W. , Allen Samuel M. , O’Handley Robert C.
Published: August 2008

A small amplitude acoustic signal was applied to a Ni-Mn-Ga single crystal. The effect of the acoustic signal in enhancing the magnetic-field-induced strain was measured as a function of temperature over the range of 1-35°C below the austenite-start temperature. Strain output was found to decrease with decreasing temperature as a result of lowered twin-boundary mobility. The combination of a piezoelectric drive with the magnetic drive yields an improvement in strain response for all temperatures investigated; however, the piezoenhanced, field-induced strain is maximized at 12.5°C, where ∂ϵ∕∂T is maximum.
Experimental study of the Hall effect and electron diffusion region during magnetic reconnection in a laboratory plasma
Authors: Ren Yang , Yamada Masaaki , Ji Hantao , Dorfman Seth , Gerhardt Stefan P. , Kulsrud Russel
Published: August 2008

The Hall effect during magnetic reconnection without an external guide field has been extensively studied in the laboratory plasma of the Magnetic Reconnection Experiment [M. Yamada et al., Phys. Plasmas 4, 1936 (1997)] by measuring its key signature, an out-of-plane quadrupole magnetic field, with magnetic probe arrays whose spatial resolution is on the order of the electron skin depth. The in-plane electron flow is deduced from out-of-plane magnetic field measurements. The measured in-plane electron flow and numerical results are in good agreement. The electron diffusion region is identified by measuring the electron outflow channel. The width of the electron diffusion region scales with the electron skin depth (∼5.5–7.5c∕ωpe) and the peak electron outflow velocity scales with the electron Alfvén velocity (∼0.12–0.16VeA), independent of ion mass. The measured width of the electron diffusion region is much wider and the observed electron outflow is much slower than those obtained in 2D numerical simulations. It is found that the classical and anomalous dissipation present in the experiment can broaden the electron diffusion region and slow the electron outflow. As a consequence, the electron outflow flux remains consistent with numerical simulations. The ions, as measured by a Mach probe, have a much wider outflow channel than the electrons, and their outflow is much slower than the electron outflow everywhere in the electron diffusion region.
Restoring the size consistency of multireference configuration interactions through class dressings: Applications to ground and excited states
Authors: Ben Amor Nadia , Maynau Daniel , Malrieu Jean-Paul , Monari Antonio
Published: August 2008

The present paper presents a revised version of a size-consistency correction to the multireference configuration interaction techniques previously proposed by Szalay et al. [J. Phys. Chem. 100, 6288 (1996)]. The method assumes a complete active space reference space and separates the nonreference determinants in several classes according to their number of inactive holes and particles. The correction is formulated as a dressing of the diagonal energies of these determinants, which depends on their class, as originally proposed by Ruttink et al. [J. Chem. Phys. 94, 7212 (1991)]. The exclusion principle violating corrections are evaluated through a simple counting of the various excitation processes which remain possible on each class. The efficiency of the method has been tested on a series of multireference problems for which full configuration interaction results are available (OH2 bond breaking, Be insertion in H2, excited states of CH2). The dressing of a given state not only provides excellent results for this state but also provides accurate excited roots. The efficiency of state-specific dressings is dramatic. The adaptation of this proposal to difference-dedicated configuration interactions can be extremely fruitful, as illustrated in the calculation of the 1Ag1-1Bu1(π−>π*) transition energy of the trans-butadiene molecule.
Mass flow-rate control through time periodic electro-osmotic flows in circular microchannels
Authors: Chakraborty Suman , Ray Subhashis
Published: August 2008

The present study is directed towards devising a scientific strategy for obtaining controlled time-periodic mass flow-rate characteristics through the employment of pulsating electric fields in circular microchannels by exploiting certain intrinsic characteristics of periodic electro-osmosis phenomenon. Within the assumption of thin electrical double layers, the governing equations for potential distribution and fluid flow are derived, corresponding to a steady base state and a time-varying perturbed state, by assuming periodic forms of the imposed electrical fields and the resultant velocity fields. For sinusoidal pulsations of the electric field superimposed over its mean, a signature map depicting the amplitudes of the mass flow rate and the electrical field as well as their phase differences is obtained from the theoretical analysis as a function of a nondimensional frequency parameter for different ratios of the characteristic electric double layer thickness relative to the microchannel radius. Distinctive characteristics in the signature profiles are obtained for lower and higher frequencies, primarily attributed to the finite time scale for momentum propagation away from the walls. The signature characteristics, obtained from the solution of the prescribed sinusoidal electric field, are subsequently used to solve the “inverse” problem, where the mass flow rate is prescribed in the form of sinusoidal pulsations and the desired electric fields that would produce the required mass flow-rate variations are obtained. The analysis is subsequently extended for controlled triangular and trapezoidal pulsations in the mass flow rate and the required electric fields are successfully obtained. It is observed that the higher the double layer thickness is in comparison to the channel radius, the more prominent is the deviation of the shape of the required electric field pulsation from the desired transience in the mass flow-rate characteristics. Possible extensions of the analysis to more complicated pulsation profiles are also outlined.
Effect of nonsuperconducting particles on the effective magnetostriction of bulk superconductors
Authors: Yong Hua-Dong , Zhou You-He
Published: August 2008

In this article, the dependence of effective magnetostriction of the bulk superconductors on the parameters including the elastic moduli and volume fraction is investigated. For a bulk superconductor of nonsuperconducting particles dispersed in a superconducting matrix, a simple and approximate model for effective magnetostriction is described. Based on the plane strain approach, the two-dimensional magnetostriction is obtained by implementing the continuity conditions of displacement and stress at the interface between the particle and the matrix. The results obtained show that the elastic moduli and volume fraction have obvious effects on the magnetostriction of bulk superconductors, which may explain why the experimental and the theoretical results have small differences.
O
2
evolution on a clean partially reduced rutile TiO2(110) surface and on the same surface precovered with Au1 and Au2: The importance of spin conservation
Authors: Chrétien Steeve , Metiu Horia
Published: August 2008

We have used spin-polarized density functional theory (DFT) to study O2 evolution on a clean partially reduced rutile TiO2(110) surface (i.e., a surface having oxygen vacancies) and its interaction with Au1 or Au2 cluster adsorbed on it. We assume that the total spin of the electronic wave function is related to the number of unpaired spins (Ns) and calculate the binding and the activation energies involved in O2 evolution for fixed values of Ns. In addition to keeping Ns constant, we assume that reactions in which the Ns of the reactants differs from that of the products are very slow. The potential energy surfaces obtained in this way depend strongly on Ns. For example, O2 dissociation at the vacancy site on a clean partially reduced TiO2(110) surface is exothermic by 0.85 eV in the triplet state and the highest activation energy in the chain of reactions leading to the O2 dissociation is 0.67 eV. In the singlet state, O2 dissociation is endothermic by 0.11 eV and the activation energy leading to dissociation is 1.30 eV. These observations are in qualitative agreement with scanning tunneling microscopy experiment in which O2 dissociation on a partially reduced rutile TiO2(110) surface is observed at temperature as low as 120 K. In contrast, O2 dissociation is predicted to be endothermic and is prevented by an activation barrier larger than 1 eV in all the previous DFT calculations, in which the DFT program varies Ns to get the lowest energy state. We find that on a partially reduced rutile TiO2(110) with Au1 and Au2 preadsorbed on its surface, O2 dissociates at the vacancy site: One oxygen atom fills the oxygen vacancy and the other becomes available for oxidation chemistry. This means that Au1 and Au2 supported on a partially reduced TiO2(110) surface is not an oxidation catalyst since the presence of oxygen turns it into a stoichiometric Aun/TiO2(110) surface. Finally, we find that the evolution of oxygen on Au1 and Au2 in the gas phase is very different from the evolution on the same clusters supported on the partially reduced TiO2(110) surface. For example, the molecular adsorption of O2 is favored in the gas phase (except on Au1− and Au2− in the quartet state), while the dissociative adsorption is favored by more than 1 eV when Au1 and Au2 are supported on the partially reduced TiO2(110). Furthermore, the activation energies associated with O2 dissociation in the gas phase (ΔEact>2.4 eV) are reduced by at least a factor of 2 when the clusters are supported on TiO2(110).
Tunable magnetic order of Co nanoparticles and magnetotransport in Co∕ZnO nanocomposites
Authors: Hsu C. Y. , Huang J. C. A. , Chen S. F. , Liu C. P. , Sun S. J. , Tzeng Yonhua
Published: August 2008

We demonstrate tunable magnetic order of cobalt nanoparticles in Co∕ZnO nanocomposites. High-density electronic states in ZnO formed during high vacuum annealing help generate bound and free charge carriers, which in turn enable the stable magnetic ordering of Co nanoparticles in the Co∕ZnO nanocomposites in a tunable manner. This is demonstrated by the following experimental observations: (i) enhanced spontaneous magnetization and coercivity, (ii) transition from semiconducting to metallic electrical-transport, and (iii) transverse magnetotransport transition from negative magnetoresistance to the anomalous Hall effect. The work explores a route to manipulate the magnetic order of magnetic nanoparticles by means of intentionally generated defects in oxides.
Electron microscopy analysis of crystalline silicon islands formed on screen-printed aluminum-doped p-type silicon surfaces
Authors: Bock Robert , Schmidt Jan , Brendel Rolf , Schuhmann Henning , Seibt Michael
Published: August 2008

The origin of a not yet understood concentration peak, which is generally measured at the surface of aluminum-doped p+ regions produced in a conventional screen-printing process is investigated. Our findings provide clear experimental evidence that the concentration peak is due to the microscopic structures formed at the silicon surface during the firing process. To characterize the microscopic nature of the islands (lateral dimensions of 1–3 μm) and line networks of self-assembled nanostructures (lateral dimension of ≤50 nm), transmission electron microscopy, scanning electron microscopy, scanning transmission electron microscopy, and energy dispersive x-ray analysis are combined. Aluminum inclusions are detected 50 nm below the surface of the islands and crystalline aluminum precipitates of ≤7 nm in diameter are found within the bulk of the islands. In addition, aluminum inclusions (lateral dimension of ∼30 nm) are found within the bulk of the self-assembled line networks.
Anomalous bubble propagation in elastic tubes
Authors: Heap Alexandra , Juel Anne
Published: August 2008

Airway reopening is an important physiological event, as exemplified by the first breath of an infant that inflates highly collapsed airways by driving a finger of air through its fluid-filled lungs. Whereas fundamental models of airway reopening predict the steady propagation of only one type of bubble with a characteristic rounded tip, our experiments reveal a surprising selection of novel bubbles with counterintuitive shapes that reopen strongly collapsed, liquid-filled elastic tubes. Our multiple bubbles are associated with a discontinuous relationship between bubble pressure and speed that sets exciting challenges for modelers.
Relaxation rate and scaling function of the critical system 3-methylpentane-nitroethane-cyclohexane
Authors: Iwanowski I. , Mirzaev S. Z. , Kaatze U.
Published: August 2008

The critical system 3-methylpentane-nitroethane-cyclohexane (3-MP-NE-CH) has been investigated and compared to the limiting binary systems 3-MP-NE as well as NE-CH in order to study the degree of renormalization in the critical exponents of the ternary system. The solubility curves of the 3-MP-NE-CH system have been determined at various molar ratios of the nonpolar constituents in order to obtain the plait points as a function of mixture composition. At the col point (the mixture with the lowest transition temperature) and two further plait point compositions shear viscosity, dynamic light scattering, and frequency-dependent ultrasonic attenuation coefficient measurements have been performed as a function of temperature near the critical temperatures. The fluctuation correlation length and the relaxation rate of fluctuations display power law behavior as a function of reduced temperature, with universal critical exponents ν̃=0.63 and ν̃Z0=1.928, respectively, as characteristic for binary critical mixtures. In conformity with the 3-MP-NE and NE-CH critical mixtures the scaling function in the ultrasonic spectra nicely agrees with the empirical scaling function of the Bhattacharjee–Ferrell dynamic scaling theory. Hence with respect to power laws and scaling the 3-MP-NE-CH system behaves like a quasibinary mixture. The individual amplitudes of the relaxation rate show a minimum at the col point composition, corresponding with a maximum in the background viscosity of the liquids. The amount of the adiabatic coupling constant g, derived from the amplitudes in the ultrasonic spectra, increases monotonously when going from NE-CH (∣g∣=0.1) to 3-MP-NE (∣g∣=0.26).
Dual descriptors within the framework of spin-polarized density functional theory
Authors: Chamorro E. , Pérez P. , Duque M. , De Proft F. , Geerlings P.
Published: August 2008

Spin-polarized density functional theory (SP-DFT) allows both the analysis of charge-transfer (e.g., electrophilic and nucleophilic reactivity) and of spin-polarization processes (e.g., photophysical changes arising from electron transitions). In analogy with the dual descriptor introduced by Morell et al. [J. Phys. Chem. A 109, 205 (2005)], we introduce new dual descriptors intended to simultaneously give information of the molecular regions where the spin-polarization process linking states of different multiplicity will drive electron density and spin density changes. The electronic charge and spin rearrangement in the spin forbidden radiative transitions S0→T(n,π*) and S0→T(π,π*) in formaldehyde and ethylene, respectively, have been used as benchmark examples illustrating the usefulness of the new spin-polarization dual descriptors. These quantities indicate those regions where spin-orbit coupling effects are at work in such processes. Additionally, the qualitative relationship between the topology of the spin-polarization dual descriptors and the vertical singlet triplet energy gap in simple substituted carbene series has been also discussed. It is shown that the electron density and spin density rearrangements arise in agreement with spectroscopic experimental evidence and other theoretical results on the selected target systems.
Preparation and characterization of epitaxial Fe2−xTixO3 films with various Ti concentrations (0.5<x<1.0)
Authors: Takada Y. , Nakanishi M. , Fujii T. , Takada J. , Muraoka Y.
Published: August 2008

An ilmenite-hematite solid solution (Fe2–xTixO3) is one of the candidates for practical magnetic semiconductors with a high Curie temperature. We have prepared well-crystallized epitaxial Fe2–xTixO3 films with a wide range of Ti concentrations—x=0.50, 0.60, 0.65, 0.76, 0.87, and 0.94—on α-Al2O3(001) substrates. The films are prepared by a reactive helicon plasma sputtering technique to evaporate Fe and TiO targets simultaneously under optimized oxygen pressure conditions. The structural characterizations of the films reveal that all films have a single phase of the ordered structure with R3¯ symmetry, where Ti-rich and Fe-rich layers are stacked alternately along the c axis. All films have large ferrimagnetic moments at low temperature, and room temperature magnetization is clearly observed at x<0.7. The inverse temperature dependence of the resistivities of the films indicates their semiconducting behavior. The film resistivities decrease with decreasing Ti concentration.
On the formation of cyclones and anticyclones in a rotating fluid
Authors: Sreenivasan Binod , Davidson P. A.
Published: August 2008

It is commonly observed that the columnar vortices that dominate the large scales in homogeneous, rapidly rotating turbulence are predominantly cyclonic. This has prompted us to ask how this asymmetry arises. To provide a partial answer to this we look at the process of columnar vortex formation in a rotating fluid and, in particular, we examine how a localized region of swirl (an eddy) can convert itself into a columnar structure by inertial wave propagation. We show that, when the Rossby number (Ro) is small, the vortices evolve into columnar eddies through the radiation of linear inertial waves. When the Rossby number is large, on the other hand, no such column is formed. Rather, the eddy bursts radially outward under the action of the centrifugal force. There is no asymmetry between cyclonic and anticyclonic eddies for these two regimes. However, cyclones and anticyclones behave differently in the intermediate regime of Ro∼1. Here we find that the transition from columnar vortex formation to radial bursting occurs at lower values of Ro for anticyclones, with the transition for anticyclones occurring at Ro∼0.5, and that for cyclones at Ro∼2. Thus, in a homogeneous turbulence experiment conducted at, say, Ro=1, we would expect to see more cyclones than anticyclones. The reason for this asymmetry at Ro∼1 is explained.
Influence of absorbed water components on SiOCH low-k reliability
Authors: Li Yunlong , Ciofi Ivan , Carbonell Laureen , Heylen Nancy , Van Aelst Joke , Baklanov Mikhaïl R. , Groeseneken Guido , Maex Karen , Tőkei Zsolt
Published: August 2008

We investigated plasma treatment induced water absorption in a SiOCH low-k dielectric and the influence of the absorbed water components on the low-k dielectric reliability. By using thermal desorption spectroscopy (TDS), water absorption in SiOCH was evidenced for N2/H2 plasma treatments. Based on these TDS results, two anneal temperatures were selected to separate and quantify the respective contributions of two absorbed water components, physisorbed (α) and chemisorbed (β) water, to low-k dielectric reliability. With the physisorbed water desorbed by an anneal at 190 °C, the low-k dielectric shows reduced leakage currents and slightly improved time-dependent dielectric breakdown (TDDB) lifetimes. However, the observed failure mechanism represented by the TDDB thermal activation energy (Ea) does not change until the chemisorbed water component was desorbed by an anneal at 400 °C. The close similarity between Ea and the bond energy associated with the β water component demonstrates that the β bond is among the weakest links for the SiOCH low-k dielectric breakdown.
Magnetization reversal in epitaxial MnAs thin films
Authors: Fraser E. D. , Kim C. H. , Hegde S. , Zeng H. , Luo H. , Wei P. K.
Published: August 2008

The magnetization reversal process of MnAs epitaxial films grown on semiconductor substrates was investigated by magneto-optical Kerr effect (MOKE) microscopy, magnetic hysteresis, and magnetoresistance measurements. While the stripe patterns with opposite magnetization in the α-phase of MnAs have been observed previously, we have observed domain dynamics on a vastly different length scale. MOKE images revealed domain nucleation and avalanche domain reversal, which are a collective behavior resulting from interactions among a large number of α-phase regions. The observed reversal processes are reflected in the magnetic hysteresis and magnetotransport measurements. These effects are strongly film thickness dependent.
Explicitly correlated coupled-cluster singles and doubles method based on complete diagrammatic equations
Authors: Shiozaki Toru , Kamiya Muneaki , Hirata So , Valeev Edward F.
Published: August 2008

The explicitly correlated coupled-cluster singles and doubles (CCSD-R12) and related methods—its linearized approximation CCSD(R12) and explicitly correlated second-order Møller–Plesset perturbation method—have been implemented into efficient computer codes that take into account point-group symmetry. The implementation has been largely automated by the computerized symbolic algebra SMITH that can handle complex index permutation symmetry of intermediate tensors that occur in the explicitly correlated methods. Unlike prior implementations that invoke the standard approximation or the generalized or extended Brillouin condition, our CCSD-R12 implementation is based on the nontruncated formalisms [T. Shiozaki et al., Phys. Chem. Chem. Phys. 10, 3358 (2008)] in which every diagrammatic term that arises from the modified Ansatz 2 is evaluated either analytically or by the resolution-of-the-identity insertion with the complementary auxiliary basis set. The CCSD-R12 correlation energies presented here for selected systems using the Slater-type correlation function can, therefore, serve as benchmarks for rigorous assessment of other approximate CC-R12 methods. Two recently introduced methods, CCSD(R12) and CCSD(2)R12¯, are shown to be remarkably accurate approximations to CCSD-R12.
Ultralow-power all-optical wavelength conversion in a silicon-on-insulator waveguide based on a heterogeneously integrated III-V microdisk laser
Authors: Liu Liu , Van Campenhout Joris , Roelkens Günther , Van Thourhout Dries , Rojo-Romeo Pedro , Regreny Philippe , Seassal Christian , Fédéli Jean-Marc , Baets Roel
Published: August 2008

Ultralow-power all-optical wavelength conversion is presented for a silicon-on-insulator wire waveguide with a heterogeneously integrated III-V microdisk laser. The principle relies on the suppression of natural lasing from the microdisk laser by an external injection. No probe beam is needed in this configuration. Static wavelength conversion with a control power of 6.4 μW or even lower is achieved. The resonance and gain provided by the microdisk cavity are at the origin of such low control power. Dynamically, wavelength conversion using a 5 Gbps non-return-to-zero bit sequence is demonstrated in the proposed device.
Influence of surface anisotropy on magnetization distribution in a single-domain particle
Authors: Usov N. A. , Grebenshchikov Yu. B.
Published: August 2008

The magnetization distribution in a single domain particle with appreciable surface anisotropy energy contribution is investigated for particles of cylindrical, spherical, and rectangular shapes. It is shown that the behavior of the particle in applied magnetic field can be described using effective energy functional. The latter determines the direction of average particle magnetization in external magnetic field, as well as the particle coercive force, at least for the case when the uniform rotation mode is the easiest one. The nonuniform correction to average particle magnetization is found to be proportional to a small parameter KsL/C⪡1, where Ks is the surface anisotropy constant, L is the characteristic particle size, and C is the exchange constant.
Self-consistent performance modeling for dualband detectors
Authors: Matsik S. G. , Perera A. G. U.
Published: August 2008

Dualband and multiband detectors have generated interest for their ability to measure two very different wavelength bands simultaneously. The dualband detection is achieved by using two different mechanisms to cover the two separate response bands: an interband process for the shorter wavelengths, and free carrier absorption followed by internal photoemission for the longer wavelengths. Previously the two processes have been modeled separately, and a reasonable agreement has been obtained on the spectral shape, although the entire wavelength range has not been covered in a single model. Also, the previous modeling efforts did not give an absolute scale for the response, instead using an experimentally determined gained factor to fix the absolute response. Here a model is presented (which does not use any fitting parameters) which can provide absolute responsivity values and detector performance parameters. By using a Monte Carlo approach including various scattering mechanisms, the carrier transport is modeled giving an absolute value for the dark current and photocurrent. The results are used to predict the spectral response for a GaN∕AlGaN UV-IR dual band heterojunction detector.
Variable range hopping in A2MnReO6 (A=Ca, Sr, Ba)
Authors: Fisher B. , Genossar J. , Chashka K. B. , Knizhnik A. , Patlagan L. , Reisner G. M.
Published: August 2008

We report on transport measurements on polycrystalline samples of A2MnReO6 (A=Ca, Sr, Ba), CMRO, SMRO, and BMRO, in the Ohmic and non-Ohmic regimes. The resistivity follows, over wide ranges of temperatures, the relation derived for variable range hopping of carriers localized in a parabolic gap, ρ=ρo exp(To/T)1/2. The values of To are unusually high for the Efros Shklovskii Coulomb gap interpretation. The thermopower is large and positive for SMRO and BMRO and even larger and negative for CMRO. The magnitude of the thermopower and its temperature dependence indicate that it may be unrelated to the hopping conductivity. The theoretical relations for hopping in the intermediate electric field regime provide reasonable approximations for the measured nonlinear conductivity of most samples (and for one sample also for the high-field regime). However, localization lengths derived from the non-Ohmic regime are much larger than those estimated from To. Clues to settle these inconsistencies are suggested.
Magnetic polarization effects of temperature sensors and heaters in LISA Pathfinder
Authors: Sanjuán J. , Lobo A. , Nofrarias M. , Mateos N. , Xirgu X. , Cañizares P. , Ramos-Castro J.
Published: August 2008

Temperature sensors and heaters belong in the diagnostics subsystem of the LISA Technology Package (LTP) on board LISA Pathfinder, the technology demonstrator for LISA. A number of these diagnostics items are placed at short distances from the LTP proof masses and are negative temperature coefficient (NTC) thermistors. By design, these devices have tiny amounts of ferromagnetic materials, which therefore constitute a potential source of disturbance to the performance of the LTP. In this paper we report on detailed magnetic characterization of the NTCs and use the data to evaluate their impact on the acceleration noise budget of the LTP. The effect is seen to be small if the NTCs are submitted to a demagnetization process before they are attached. Remagnetization is unlikely, as rather strong fields (approximately millitesla) are required to produce enough NTC magnetic polarization.
Optical delay line for high time resolution measurement: W-type delay line
Authors: Hashimoto Kyohei , Kano Satoru S. , Wada Akihide
Published: August 2008

We propose and demonstrate a newly designed optical delay line (W-type delay line) that improves the resolution of optical path length, namely, time resolution, by an order of more than 3 in comparison to the spatial resolution of a conventionally used translational stage. Using a conventional mechanical translational stage having a spatial resolution of 1μm, the performance of the W-type delay line was evaluated by interferometric measurements with a diode laser, and the time resolution of 16as was confirmed.
Assessment of quantum dot infrared photodetectors for high temperature operation
Authors: Martyniuk P. , Krishna S. , Rogalski A.
Published: August 2008

Investigation of the performance of quantum dot infrared photodetectors (QDIPs) in comparison to other types of infrared photodetectors operated near room temperature is presented. The model is based on fundamental performance limitations enabling a direct comparison between different infrared material technologies. It is assumed that the performance is due to thermal generation in the active region. Theoretical estimations provide evidence that the QDIP is suitable for noncryogenic operation especially in long-wavelength infrared region, where conventional HgCdTe photodiodes are not viable. Hence it is expected that improvement in technology and design of QDIP detectors will make it useful for practical application. The higher operating speed of QDIP and multispectral capability are considerable advantages in comparison with thermal detectors. Comparison of theoretically predicted and experimental data indicates that, as so far, the QDIP devices have not demonstrated their potential advantages and are expected to posses the fundamental ability to achieve higher detector performance. Poor QDIP performance is generally linked to nonoptimal band structure and control over the QDs size and density.
Ultrafast E1(LO) phonon and plasma dynamics in a-plane wurtzite InN
Authors: Chang Y.-M. , Lin H.-W. , Hong Y.-L. , Gwo S.
Published: August 2008

Coherent phonon spectroscopy of an a-plane wurtzite InN epitaxial thin film is demonstrated with time-resolved second-harmonic generation technique. Coherent E1(LO) phonons are launched via a transient electric field screening process in the near surface region of the a-plane wurtzite InN. Because of the macroscopic electric dipole interaction between coherent E1(LO) phonons and photoexcited plasmons, two hybridized vibration modes, phononlike (L−) and plasmonlike (L+) E1(LO) phonon-plasmon coupling modes, are identified. The investigation of these coupling modes allows us to understand the ultrafast carrier and phonon dynamics in a-plane wurtzite InN.
Femtosecond time-resolved x-ray diffraction from optical coherent phonons in CdTe(111) crystal
Authors: Nakamura Kazutaka G. , Ishii Satoshi , Ishitsu Shusei , Shiokawa Masato , Takahashi Hiroshi , Dharmalingam Kurunthu , Irisawa Jun , Hironaka Yoichiro , Ishioka Kunie , Kitajima Masahiro
Published: August 2008

Coherent phonons excited in a CdTe(111) crystal by 70fs laser irradiation have been investigated by femtosecond time-resolved x-ray diffraction. The longitudinal optical phonon with a frequency of approximately 5THz near the Brillouin zone center has been detected as modulation in intensities of x-ray diffraction. Atomic displacement in the [111] direction in the coherent longitudinal optical phonon has been estimated.
Study on interfacial properties of InGaAs and GaAs integrated with chemical-vapor-deposited high-k gate dielectrics using x-ray photoelectron spectroscopy
Authors: Oh H. J. , Lin J. Q. , Lee S. J. , Dalapati G. K. , Sridhara A. , Chi D. Z. , Chua S. J. , Lo G. Q. , Kwong D. L.
Published: August 2008

Interfacial reaction study using x-ray photoelectron spectroscopy was carried out for metal-organic chemical-vapor-deposited HfO2 and HfAlO gate dielectrics on p-In0.53Ga0.47As layer as compared to the cases of p-GaAs substrate. The results show that the alloying of GaAs with InAs (In0.53Ga0.47As) in the III-V channel layer and the alloying HfO2 with Al2O3 in the high-k dielectric can be an effective way to improve the interface quality due to their significant suppression effects on native oxides formation, especially arsenic oxide which causes Fermi level pinning on the high-k/III-V channel interface during the fabrication processes. Transmission electron microscopy result and the electrical characteristics of HfAlO∕p-In0.53Ga0.47As capacitors further validate the x-ray photoelectron spectroscopy observations.
In situ GaN decomposition analysis by quadrupole mass spectrometry and reflection high-energy electron diffraction
Authors: Fernández-Garrido S. , Koblmüller G. , Calleja E. , Speck J. S.
Published: August 2008

Thermal decomposition of wurtzite (0001)-oriented GaN was analyzed: in vacuum, under active N exposure, and during growth by rf plasma-assisted molecular beam epitaxy. The GaN decomposition rate was determined by measurements of the Ga desorption using in situ quadrupole mass spectrometry, which showed Arrhenius behavior with an apparent activation energy of 3.1 eV. Clear signatures of intensity oscillations during reflection high-energy electron diffraction measurements facilitated complementary evaluation of the decomposition rate and highlighted a layer-by-layer decomposition mode in vacuum. Exposure to active nitrogen, either under vacuum or during growth under N-rich growth conditions, strongly reduced the GaN losses due to GaN decomposition.
A silicon metal-oxide-semiconductor field-effect transistor Hall bar for scanning Hall probe microscopy
Authors: Yamaguchi Akinobu , Saito Hiromasa , Shimizu Masayoshi , Miyajima Hideki , Matsumoto Satoru , Nakamura Yoshiharu , Hirohata Atsufumi
Published: August 2008

We demonstrate successful operation of a scanning Hall probe microscope with a few micron-size resolution by using a silicon metal-oxide semiconductor field-effect transistor (Si-MOSFET) Hall bar, which is designed to improve not only the mechanical strength but also the temperature stability. The Si-MOSFET micro-Hall probe is cheaper than the current micro-Hall probes and is found to be as sensitive as a micro-Hall probe with GaAs/AlGaAs heterostructure or an epitaxial InSb two-dimensional electron gas. This was used to magnetically image the surface of a Sm2Co17 permanent magnet during the magnetization reversal process as a function of an external magnetic field below 1.5 T. This revealed firm evidence of the presence of the inverse magnetic seed as theoretically predicted earlier. Magnetically pinned centers, with a typical size 80 μm, are observed to persist even under a high magnetic field, clearly indicating the robustness of the Si Hall probe against the field application as well as the repetition of the measurement.
SiGe quantum dot molecules grown on patterned Si (001) substrates
Authors: Yang Hongbin , Zhang Xiang-jiu , Jiang Zuiming , Yang Xinju , Fan Yongliang
Published: August 2008

SiGe quantum dot molecules (QDMs) grown on patterned Si (001) substrates by molecular beam epitaxy were studied. Experimental results showed that the density, the dimension, and the dimension distribution of the SiGe QDMs grown in the windows were dependent on the window size. When the thickness of the Si0.8Ge0.2 film was 40 nm, QDMs only appeared in the unpatterned areas of the Si substrate and none could be found inside the windows of 6×6 μm2 on the same substrate. However, when the thickness of Si0.8Ge0.2 film was increased to 80 nm, QDMs appeared both inside the windows and in the unpatterned areas, and the density of QDMs was reduced with the decrease in the window size. We attribute these results to the different strain relaxations in different size windows, which are caused by the edge effect of the epitaxial film in the window. Based on these experimental results we discuss the formation and the size stability of the QDMs and conclude that the formation of the SiGe QDM originates from an intrinsic cause of the strain relief mechanism. This work also shows that by means of the edge induced strain relaxation of the epitaxial film in the window, it is possible to reveal the influence of the strain on some physical properties of the SiGe film without changing its Ge atomic fraction.
Luminescence behavior of Er3+ doped glass ceramics containing Sr2RF7 (R=Y,Gd,La) nanocrystals
Authors: Qiao Xvsheng , Fan Xianping , Wang Minquan , Yang Hui , Zhang Xianghua
Published: August 2008

The luminescence behaviors of Er3+ doped glass ceramics containing Sr2RF7 (R=Y,Gd,La) nanocrystals were investigated. The formation of Sr2RF7 nanocrystals in the glass ceramics was confirmed by x-ray diffraction and high resolution transmission electron microscopy. Energy dispersive x-ray spectroscopy analysis showed that the Er3+ ions were efficiently incorporated in Sr2GdF7 nanocrystals. The efficient upconversion luminescence of the Er3+ in the glass ceramics can be observed. The lifetime of the Er3+ in the glass ceramics was found to be much longer than that in the glass due to the lower phonon energy of fluoride crystals when Er3+ entered efficiently fluoride crystals in the glass ceramics.
Fabrication of periodic complex photonic crystals constructed with a portion of photonic quasicrystals by interference lithography
Authors: Yang Yi , Li Qiuze , Wang Guo Ping
Published: August 2008

By using a single-beam optical interference lithography we fabricated a kind of periodic complex photonic crystals constructed with a portion of photonic quasicrystals. The periodic photonic crystals show the photonic bandgap properties of the original photonic quasicrystals but maintain the periodicity in long range so that their photonic band structures can exactly be calculated in theory. Diverse structures were fabricated by real time modulating the phase relation of the interference beams. The complex photonic crystal materials presented here may provide an example for creating diverse photonic structures for effectively manipulating electromagnetic properties.
A simple readout electronics for automatic power controlled self-mixing laser diode systems
Authors: Cattini Stefano , Rovati Luigi
Published: August 2008

The paper describes a simple electronic circuit to drive a laser diode for self-mixing interferometry. The network integrates a stable commercial automatic power controller and a current mirror based readout of the interferometric signal. The first prototype version of the circuit has been realized and characterized. The system allows easily performing precise interferometric measurements with no thermostatic circuitry to stabilize the laser diode temperature and an automatic control gain network to compensate emitted optical power fluctuations. To achieve this result, in the paper a specific calibration procedure to be performed is described.
Stabilized porous silicon optical superlattices with controlled surface passivation
Authors: Ghulinyan M. , Gelloz B. , Ohta T. , Pavesi L. , Lockwood D. J. , Koshida N.
Published: August 2008

We report on very effective stabilization of porous silicon optical devices through a chemical surface modification technique. Such a chemical treatment proves to alter the growth of native silicon oxide on pore surfaces and thus prevents the optical device from chemical aging. As an example, we apply this technique to one-dimensional freestanding optical superlattices made of five coupled microcavities. We demonstrate how the transmission resonances of the superlattice stabilize after treatment, which implies that refractive indices in the multilayer structure remain constant. The effectiveness of the chemical surface modification technique guarantees a long-life functionality of porous silicon-based optical devices.
Absolute calibration of an electron spectrometer using high energy electrons produced by the laser-plasma interaction
Authors: Masuda S. , Miura E. , Koyama K. , Kato S.
Published: August 2008

An in situ observation system has been developed to observe the absolute electron energy spectra of electron beams generated by laser-plasma interaction. A phosphor screen (DRZ) coupled with a charge coupled device camera is used to detect the electrons. A new method is proposed to calibrate the absolute sensitivity of the detection system for a wide energy range with a single shot by using an electron beam generated by laser-plasma interaction. The sensitivity of the system is found to be high, which is comparable to that of an imaging plate.
Investigations on multimagnetron sputtered Zn1−xMgxO thin films through metal-ferroelectric-semiconductor configuration
Authors: Dhananjay  , Nagaraju J. , Krupanidh S. B.
Published: August 2008

The effect of Mg doping in ZnO is investigated through structural, electrical, and optical properties. Zn1−xMgxO (0<×<0.3) thin films were deposited on Si (100) and corning glass substrates using multimagnetron sputtering. Investigations on the structural properties of the films revealed that the increase in Mg concentration resulted in phase evolution from hexagonal to cubic phase. The temperature dependent study of dielectric constant at different frequencies exhibited a dielectric anomaly at 110 °C. The Zn0.7Mg0.3O thin films exhibited a well-defined polarization hysteresis loop with a remnant polarization of 0.2 μC/cm2 and coercive field of 8 kV/cm at room temperature. An increase in the band gap with an increase in Mg content was observed in the range of 3.3–3.8 eV for x=0–0.3. The average transmittance of the films was higher than 90% in the wavelength region λ=400–900 nm.
The evolution of fast reconnection in a three-dimensional current sheet system
Authors: Ugai M.
Published: August 2008

By showing the details of the numerical procedure, global dynamics of the current sheet system is systematically studied by three-dimensional magnetohydrodynamic simulations in the parameter range where the numerical resistivity is much smaller than the physical resistivity. In the absence of resistivity, initiated by a reconnection disturbance, current sheet thinning drastically occurs because of the sheet pinch, leading to extreme increase in current density around the X neutral point. For the uniform resistivity model, the drastic current increase is suppressed by the magnetic diffusion (reconnection), but the reconnection jet cannot be accelerated effectively, so that any fast reconnection mechanism cannot evolve; for the smaller resistivity, the current density at the X point becomes larger. Once current-driven anomalous resistivities build up, both the reconnection flow and the anomalous resistivity simultaneously grow to enhance each other, eventually giving rise to the Alfvénic fast reconnection jet. However, if the current sheet width is smaller than three times its thickness, the fast reconnection mechanism cannot be realized even in the presence of anomalous resistivity. Hence, only when a thin current sheet of sufficiently large scale is formed in space plasmas, the fast reconnection mechanism is likely to evolve drastically, leading to distinct plasma processes responsible for flares and substorms.
The evolution of the structure and mechanical properties of fullerenelike hydrogenated amorphous carbon films upon annealing
Authors: Wang Qi , He Deyan , Wang Chengbing , Wang Zhou , Zhang Junyan
Published: August 2008

Hydrogenated amorphous carbon films were deposited on Si (100) substrates using dc-pulse plasma chemical vapor deposition. Structurally, the as-deposited carbon films could be considered as nanocomposite thin films with fullerenelike microstructure in diamondlike carbon matrix based on our previous result [Q. Wang et al., Appl. Phys. Lett. 91, 141902 (2007)]. In this paper, the evolution of the structure and the mechanical properties of hydrogenated carbon films with fullerenelike microstructure on the annealing in vacuum was investigated. The fullerenelike hydrogenated carbon films annealed at 500 °C showed higher hardness (16.9% harder) and higher elastic recovery (11.2% higher) than the as-deposited films. The friction coefficient of fullerenelike hydrogenated carbon films in air with 40% relative humidity remained constant at about 0.037 when annealed at 600 °C. The wear rate of the films decreased sharply when annealed at 200 or 300 °C. Structural analysis shows that annealing at 300 °C improved tribological properties originated from the volume increase in the fullerenelike microstructure, and further annealing at 600 °C improved mechanical properties originated from the transformation of nanosized curved sp2 to sp3 clusters.
Size-dependent “malleable-to-brittle” transition in a bulk metallic glass
Authors: Wu W. F. , Han Z. , Li Y.
Published: August 2008

We report a size-dependent malleability in a Zr-based bulk metallic glass (BMG) under both as-cast and annealed states. A “malleable-to-brittle” transition occurred at a critical sample size of 3 mm in diameter, below which the sample yielded with a consistent strength and above which the sample fractured in a brittle manner with decreasing strength. With minimization of the free volume effect by annealing, it was ascertained that this transition was due to the geometrical size effect rather than the free volume effect. The sharp decrease in strength for BMG within the brittle region was explained in terms of flaw sensitivity.
100% internal quantum efficiency and stable efficiency roll-off in phosphorescent light-emitting diodes using a high triplet energy hole transport material
Authors: Jeon Soon-Ok , Yook Kyoung Soo , Joo Chul Woong , Lee Jun Yeob , Ko Kwang-Youn , Park Jong-Yek , Baek Yong Gu
Published: August 2008

Highly efficient green phosphorescent organic light-emitting diodes were developed by using high triplet energy hole transport materials. The quantum efficiency of green devices could be improved from 12% to 20% at 1000cd∕m2 by using a phenylcarbazole based hole transport material. In addition, the high quantum efficiency could be stably maintained up to a high luminance of 10000cd∕m2.