bluuebunny/crossref_metadata_2025 huggingface dataset:
SEGUE, and the future of large scale surveys of the Galaxy
Authors: Beers Timothy C. , Lee Young Sun , Carollo Daniela
Published: March 2009

The Sloan Extension for Galactic Exploration and Understanding (SEGUE) has now been completed. This is one of three surveys that were executed as part of the first extension of the Sloan Digital Sky Survey (SDSS-II), which consist of LEGACY, SUPERNOVA SURVEY, and SEGUE. The SEGUE program has obtained over 3600 square degrees of ugriz imaging of the sky outside the original SDSS-I footprint. The regions of sky targeted for SEGUE imaging were primarily at lower Galactic latitudes (|b| < 35°), in order to better sample the disk/halo interface of the Milky Way. SEGUE also obtained medium-resolution (R = 2000) spectroscopy, over the wavelength range 3800-9200 Å, for over 200,000 stars in 200 selected areas over the sky available from Apache Point, New Mexico. We discuss the determination of stellar atmospheric parameters (Teff, log g, and [Fe/H]) for these stars, and highlight several of the scientific results obtained to date. The proposed second extension of SDSS, known as SDSS-III, will include SEGUE-2, a program to roughly double the numbers of stars with available spectroscopy, as well as APOGEE, a program to obtain high-resolution (R = 20000) near-IR spectroscopy for over 100,000 stars in the disk, bulge and halo populations of the Galaxy. Other massive spectroscopic surveys of interest to Galactic science are also briefly discussed.
Desmosterol can replace cholesterol in sustaining cell proliferation and regulating the SREBP pathway in a sterol-Δ24-reductase-deficient cell line
Authors: Rodríguez-Acebes Sara , de la Cueva Paloma , Fernández-Hernando Carlos , Ferruelo Antonio J. , Lasunción Miguel A. , Rawson Robert B. , Martínez-Botas Javier , Gómez-Coronado Diego
Published: March 2009

Cholesterol homoeostasis is critical for cell viability and proliferation. The SREBP (sterol regulatory element-binding protein) pathway is crucial for the maintenance of cholesterol homoeostasis. This pathway is controlled by cholesterol and cholesterol-derived oxysterols. J774 cells cannot convert desmosterol into cholesterol, a defect resulting from the absence of mRNA for sterol-Δ24-reductase. Using J774 cells, we addressed the capacity of desmosterol to replace cholesterol in sustaining cell proliferation and regulating the SREBP pathway. J774 cells were able to grow indefinitely after the virtually total replacement of cholesterol by desmosterol (J774-D cells). Inhibition of sterol biosynthesis with lovastatin suppressed J774-D cell proliferation. Desmosterol prevented this effect, but its analogue, cholest-5,22-trans-dien-3β-ol, did not. Addition of desmosterol inhibited processing of SREBP-1 and -2 and also reduced the expression of SREBP-targeted genes. As occurs in cholesterol-containing cells, 25-hydroxycholesterol was more potent than desmosterol or cholesterol in suppressing these processes. Moreover, desmosterol addition enhanced the expression of Abca1 and Srebf1c, two LXR (liver X receptor)-targeted genes. To test the ability of endogenously produced desmosterol to regulate gene expression, J774-D cells were pretreated with lovastatin to inhibit sterol biosynthesis. After removal of the inhibitor the expression of SREBP-targeted genes decreased and that of an LXR-targeted gene increased, reaching control levels. Our results demonstrate that the virtually complete replacement of cholesterol by desmosterol is compatible with cell growth and the functioning of the SREBP pathway. In these cells, desmosterol suppresses SREBP processing and targeted gene expression, and it is especially effective activating LXR-targeted genes.
Inferencing Processes After Right Hemisphere Brain Damage: Maintenance of Inferences
Authors: Blake Margaret Lehman
Published: February 2009

Purpose

This study was designed to replicate and extend a previous study of inferencing in which some adults with right hemisphere damage (RHD) generated but did not maintain predictive inferences over time (M. Lehman-Blake & C. Tompkins, 2001). Two hypotheses were tested: (a) inferences were deactivated, and (b) selection of previously generated inferences was slowed and not measurable with the original stimuli. Existing literature did not support one hypothesis over the other.

Method

Fourteen adults with RHD and 14 with no brain damage (NBD) participated in this mixed-design study. Participants read short narratives that suggested a predictive inference. Reading times were obtained to assess inference generation, maintenance, and integration.

Results

The majority of participants evidenced generation and maintenance of inferences. For the few who did not maintain inferences, participants with NBD always deactivated the inferences, whereas those with RHD demonstrated either deactivation or slowed selection. Adults with RHD were more likely to exhibit slowing in inference generation and integration.

Conclusions

The results for inference maintenance differ from the original study in that most participants with RHD maintained inferences. Deactivation appeared in both groups, whereas slowed selection appeared to be an aberrant process related to RHD. Future work is needed to tease out the relationships between comprehension, working memory, and inferencing processes.
Adult and Child Semantic Neighbors of the Kroll and Potter (1984) Nonobjects
Authors: Storkel Holly L. , Adlof Suzanne M.
Published: February 2009

Purpose

The purpose was to determine the number of semantic neighbors, namely,
semantic set size,
for 88 nonobjects (J. F. Kroll & M. C. Potter, 1984) and determine how semantic set size related to other measures and age.

Method

Data were collected from 82 adults and 92 preschool children in a discrete association task. The nonobjects were presented via computer, and participants reported the first word that came to mind that was meaningfully related to the nonobject. Words reported by 2 or more participants were considered semantic neighbors. The strength of each neighbor was computed as the proportion of participants who reported the neighbor. All data are provided online in a Microsoft Excel file accompanying this article (the data file can be found accompanying this article online at
http://jslhr.asha.org
).

Results

Results showed that semantic set size was not significantly correlated with objectlikeness ratings or object decision reaction times from J. F. Kroll and M. C. Potter (1984). However, semantic set size was significantly negatively correlated with the strength of the strongest neighbor(s). In terms of age effects, adult and child semantic set sizes were significantly positively correlated and the majority of numeric differences were on the order of 0–3 neighbors. Comparison of actual neighbors showed greater discrepancies; however, this varied by neighbor strength.

Conclusions

Semantic set size can be determined for nonobjects. Specific guidelines are suggested for using these nonobjects in future research.

Supplemental Material

https://doi.org/10.23641/asha.6170342
The Effect of Semantic Set Size on Word Learning by Preschool Children
Authors: Storkel Holly L. , Adlof Suzanne M.
Published: February 2009

Purpose

The purpose was to determine whether semantic set size, a measure of the number of semantic neighbors, influenced word learning, and whether the influence of semantic set size was broad, showing effects on multiple measures both during and after learning.

Method

Thirty-six preschool children were exposed to 10 nonobjects, varying in semantic set size, paired with 10 nonwords, controlling phonotactic probability and neighborhood density. Nonobject–nonword pairs were presented in a game format. Learning was measured in naming and referent identification tasks administered before, during, and 1 week after training.

Results

Results showed no differences in naming or identifying the referents of the nonobject–nonword pairs with small versus large semantic set sizes before and during training. However, 1 week after training, children named and identified the referents of nonobject–nonword pairs with small set sizes more accurately than those with large set sizes.

Conclusions

Similarity to known representations appears to influence word learning, regardless of whether the similarity involves lexical or semantic representations. However, the direction of the effect of similarity to known representations on word learning varies depending on the specific type of representation involved. Specifically, lexical similarity speeds learning, whereas semantic similarity slows learning.
Effects of carrier mobility and morphology in organic semiconductor spin valves
Authors: Liu Yaohua , Lee Taegweon , Katz Howard E. , Reich Daniel H.
Published: February 2009

We studied spin transport in four organic semiconductors (OSCs) with different electronic properties. Magnetoresistance (MR) effects were observed up to room temperature in junctions based on an electron-carrying OSC, tris(8-hyroxyquinoline) aluminum (Alq3) and a hole-carrying OSC, copper phthalocyanine (CuPc). The MR shows similar temperature dependence for these two OSCs. We also investigated junctions based on two high lateral mobility electron-carrying OSCs, 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) and N,N′-bis(4-trifluoromethylbenzyl)-1,4,5,8-naphthalenetetracarboxylic diimide (CF3-NTCDI). However, these junctions showed much weaker spin transport effects. Morphological studies suggest that these high mobility OSC films have much rougher surfaces than either Alq3 or CuPc, therefore the degradation of spin transport may originate from enhanced scattering due to the rougher FM/OSC interfaces. Our study shows that FM/OSC interfaces play an important role for spin transport in organic devices and need further exploration.
Dot arrays of L11 type Co–Pt ordered alloy perpendicular films
Authors: Shimatsu T. , Sato H. , Mitsuzuka K. , Kataoka H. , Aoi H. , Okamoto S. , Kitakami O.
Published: February 2009

Magnetic properties of dot arrays of L11 type Co–Pt ordered alloy perpendicular films were studied. L11-Co–Pt films with a large uniaxial magnetic anisotropy Ku of the order of 107 erg/cm3 were fabricated at a substrate temperature of 360 °C using ultrahigh vacuum sputter film deposition. Dot patterns with dot diameters of 70–200 nm were made using high resolution e-beam lithography and reactive ion etching (RIE). The values of Ku were measured by the GST method using the Anomalous Hall Effect; we observed the averaged signals of 6000 dots. The values of Ku for dot arrays of 10-nm-thick L11-Co50Pt50 films deposited on MgO(111) substrates (single crystal films) and glass disks (polycrystalline films) were nearly the same as those of the original films independent of D, indicating no significant etching damage by the RIE process. Magnetic force microscopy images revealed that all dots were single domains in the present D region. The coercivity Hc of the dot arrays was 25.0 kOe [MgO(111) substrate, D=70 nm] and 14.3 kOe (glass disks, D=80 nm). The switching field distribution σ/Hc was relatively small, σ/Hc=0.15, even for dot arrays fabricated on glass disks, indicating the homogeneous formation of a L11 type ordered structure in the Co50Pt50 layers.
Low frequency magnetization excitations in magnetic nanopillars induced by a dc spin-polarized current
Authors: Theodoropoulou N. , Sharma A. , Pratt W. P. , Bass J.
Published: February 2009

We present observations of low frequency, (fundamentals ≤1 GHz) current-driven magnetization dynamics at 293 K in partially patterned Py (24 nm)/Cu(10)/Py(6), elliptical, nanopillars, with the top Py(6) magnetic layer and part of the Cu layer shaped into an ∼70×140 nm2 nanopillar and the rest left extended. The magnetoresistance curves for applied current I≈2 mA, and the spin-transfer-torque curves for applied magnetic field H≈0, both behave as expected for simple, uncoupled magnetic layers. We describe several behaviors similar to those previously seen and associated with excitation and dynamics of vortices: sharp, low frequency (f) peaks at H=0, with df/dI∼40 MHz/mA; hysteretic behavior with the direction of sweep of current I; disappearance of the peaks for parallel field larger than 10 mT and for perpendicular field larger than 400 mT; nonmonotonic power production as a function of I. Two new behaviors are the “simultaneous” presence of such peaks for both I>0 and I<0, and strong asymmetry of the I<0 peaks when H is reversed.
The angular dependence of Néel wall resistance by magnetotransport in the centipedelike Permalloy structures
Authors: Chung T. Y. , Hsu S. Y.
Published: February 2009

The angular dependence of Néel wall resistance has been studied by measuring the in-plane magnetoresistances (MRs) of the centipedelike Permalloy (Py) structure, which consists of a central wire with numerous orthogonally bisecting finger wires. All Py wires were designed to have a single domain structure at remanence and high anisotropy by the geometric control. The remanent domain at the junction between the central and finger wires is determined by the anisotropy constants of both wires and hence, variable angles of Néel wall can be achieved. Using a simple resistance-in-series model in corporation with the anisotropic MR effect, the analyses of the longitudinal and transverse MRs of the centipedelike structure give the domain wall resistance. Our results show that the Néel wall resistance is about milliohm and decreases with decreasing the relative angle between two domains.
Fast acquisition of high-resolution NMR spectra in inhomogeneous fields via intermolecular double-quantum coherences
Authors: Chen Zhong , Cai Shuhui , Chen Zhiwei , Zhong Jianhui
Published: February 2009

A pulse sequence, IDEAL-II, is proposed based on the concept of intermolecular dipolar-interaction enhanced all lines [Z. Chen et al., J. Am. Chem. Soc. 126, 446 (2004)] for obtaining one-dimensional (1D) high-resolution liquid NMR spectra in inhomogeneous fields via two-dimensional acquisitions. With the new acquisition scheme, the range of magnetic field inhomogeneity rather than chemical shift is sampled in the indirect dimension. This enables a great reduction in acquisition time and amount of data, much improved over the original IDEAL implementation. It is applicable to both isolated and J-coupled spin systems in liquid. For the latter, apparent J coupling constants are magnified threefold in spectra obtained with this sequence. This allows a more accurate measurement of J coupling constants in the cases of small J coupling constants or large inhomogeneous fields. Analytical expression was derived based on intermolecular multiple-quantum coherence treatments. Solution samples that were purposely deshimmed and biological samples with intrinsic field inhomogeneities were tested. Experimental results demonstrate that this sequence retains useful structural information including chemical shifts, relative peak areas, and multiplet patterns of J coupling even when the field inhomogeneity is severe enough to almost erase all spectroscopic information with conventional 1D single-quantum coherence techniques. This sequence is more applicable to weakly coupled and uncoupled spin systems, potentially useful for studying metabolites in in vivo NMR spectroscopy and for characterizing technologically important new materials in combinatorial chemistry.
Orbital representation of kinetic energy pressure
Authors: Fakhraee S. , Azami S. M.
Published: February 2009

The kinetic energy pressure (KEP) is quantified in terms of displaced charges and their orbital representations. Two deformation density matrices are introduced to separate reorganization of the electron density due to Pauli antisymmetrization from that of orbital relaxation. The formalism is applied to interaction of carbon nanotubes with hydrogen molecule and the results confirmed that KEP has the main contribution to such interaction. Also, it was found that the contribution of KEP can be easily traced in the complex formation.
Full-solution-processed blue organic light emitting device based on a fluorescent 1,3,5-tristyrylbenzene stilbenoid small molecule
Authors: Coya C. , de Andrés A. , Zaldo C. , Álvarez A. L. , Arredondo B. , Gómez R. , Segura J. L. , Seoane C.
Published: February 2009

A full-solution-processed blue organic light emitting diode display based on a small molecule built on a fluorescent stilbenoid core has been fabricated and characterized. The structure of the blue device is ITO/PEDOT:PSS/active layer/Al. The optical characterization of the 1,3,5-tristyrylbenzene endowed with alkoxy (OC6H13) chain active layer reveals a change in the excited molecular level configuration due to the molecular packing in the thin film that gives as a result a large Stokes shift in the solid state. The electroluminescence in the deep-blue region of the single layer device corresponds well with the photoluminescence emission of the thin films (438nm) and is independent of the applied voltage. Raman analysis confirms the stability of the compound through the fabrication process. From the I-V study, an effective hole mobility of 9.3×10−6cm2∕Vs for the active layer has been obtained.
Cryogenic-target performance and implosion physics studies on OMEGA
Authors: Smalyuk V. A. , Betti R. , Boehly T. R. , Craxton R. S. , Delettrez J. A. , Edgell D. H. , Glebov V. Yu. , Goncharov V. N. , Harding D. R. , Hu S. X. , Knauer J. P. , Marshall F. J. , McCrory R. L. , McKenty P. W. , Meyerhofer D. D. , Radha P. B. , Regan S. P. , Sangster T. C. , Seka W. , Short R. W. , Shvarts D. , Skupsky S. , Soures J. M. , Stoeckl C. , Yaakobi B. , Frenje J. A. , Li C. K. , Petrasso R. D. , Séguin F. H.
Published: February 2009

Recent progress in direct-drive cryogenic implosions on the OMEGA Laser Facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] is reviewed. Ignition-relevant areal densities of ∼200 mg/cm2 in cryogenic D2 implosions with peak laser-drive intensities of ∼5×1014 W/cm2 were previously reported [T. C. Sangster et al., Phys. Rev. Lett. 100, 185006 (2008)]. The laser intensity is increased to ∼1015 W/cm2 to demonstrate ignition-relevant implosion velocities of 3–4×107 cm/s, providing an understanding of the relevant target physics. Planar-target acceleration experiments show the importance of the nonlocal electron-thermal-transport effects for modeling the laser drive. Nonlocal and hot-electron preheat is observed to stabilize the Rayleigh–Taylor growth at a peak drive intensity of ∼1015 W/cm2. The shell preheat caused by hot electrons generated by two-plasmon-decay instability was reduced by using Si-doped ablators. The measured compressibility of planar plastic targets driven with high-compression shaped pulses agrees well with one-dimensional simulations at these intensities. Shock mistiming has contributed to compression degradation of recent cryogenic implosions driven with continuous pulses. Multiple-picket (shock-wave) target designs make it possible for a more robust tuning of the shock-wave arrival times. Cryogenic implosions driven with double-picket pulses demonstrate somewhat improved compression performance at a peak drive intensity of ∼1015 W/cm2.
Phase diagrams in compressible weakly interacting all-polymer nanocomposites
Authors: Ruiz de Luzuriaga Alaitz , Grande Hans J. , Pomposo José A.
Published: February 2009

A compressible regular solution free energy model for describing the phase behavior of weakly interacting binary blends comprising nonrigid polymer nanoparticles and linear-polymer chains (i.e., all-polymer nanocomposites) has been developed by incorporating specific nanoparticle-nanoparticle and nanoparticle-polymer contributions into the original free volume theory for binary polymer blends of Ruzette et al. [J. Chem. Phys. 114, 8205 (2001)]. The extended model allows predicting phase behavior for weakly interacting polymer-nanoparticle/linear-polymer nanocomposites using only pure component properties (nanoparticle and polymer sizes, mass densities, coefficients of thermal expansion, and solubility parameters). The effect of polymer and nanoparticle size, as well as those arising from nanoparticle rigidity, exchange interaction energy and composition on the phase behavior of all-polymer nanocomposites have been systematically investigated. A rich variety of phase diagrams (including upper critical solution temperature-type, lower critical solution temperature-type, and hour-glass shape) are illustrated. Predicted phase diagrams for nonrigid poly(styrene)-nanoparticle (PS-np)/linear-poly(styrene) (l-PS), and branched poly(ethylene)-nanoparticle (PE-np)/l-PS nanocomposites were in excellent agreement with available experimental data.
Crystallization kinetics of polydisperse hard-sphere-like microgel colloids: Ripening dominated crystal growth above melting
Authors: Iacopini Sara , Palberg Thomas , Schöpe Hans Joachim
Published: February 2009

Highly cross-linked polystyrene microgel colloids dispersed in an index and density matching solvent provide a system with hard-sphere-like interactions, where gravity effects are effectively minimized. They are a suitable target for time-resolved observations of solidification in purely repulsive systems. We have investigated the crystallization kinetics at increasing undercooling using time resolved light scattering. Crystallization starts always with the formation of compressed, structurally heterogeneous precursor domains. In the coexistence region the precursors, after being converted into true crystallites, start growing fast by assimilating particles from the melt. The resulting polycrystalline material consists of high quality crystals and seems not to undergo long time-scale rearrangements. As the particle concentration grows, the higher undercooling and reduced particle mobility increasingly compromise the conversion-growth process. The growth of crystallites relies then on much slower ripeninglike processes, while refining of the crystal structure is detected up to the longest observed times.
Structure and short-time dynamics in suspensions of charged silica spheres in the entire fluid regime
Authors: Gapinski J. , Patkowski A. , Banchio A. J. , Buitenhuis J. , Holmqvist P. , Lettinga M. P. , Meier G. , Nägele G.
Published: February 2009

We present an experimental study of short-time diffusion properties in fluidlike suspensions of monodisperse charge-stabilized silica spheres suspended in dimethylformamide. The static structure factor S(q), the short-time diffusion function D(q), and the hydrodynamic function H(q) have been probed by combining x-ray photon correlation spectroscopy experiments with static small-angle x-ray scattering. Our experiments cover the full liquid-state part of the phase diagram, including de-ionized systems right at the liquid-solid phase boundary. We show that the dynamic data can be consistently described by the renormalized density fluctuation expansion theory of Beenakker and Mazur over a wide range of concentrations and ionic strengths. In accordance with this theory and Stokesian dynamics computer simulations, the measured short-time properties cross over monotonically, with increasing salt content, from the bounding values of salt-free suspensions to those of neutral hard spheres. Moreover, we discuss an upper bound for the hydrodynamic function peak height of fluid systems based on the Hansen–Verlet freezing criterion.
Demonstration of the shock-timing technique for ignition targets on the National Ignition Facility
Authors: Boehly T. R. , Munro D. , Celliers P. M. , Olson R. E. , Hicks D. G. , Goncharov V. N. , Collins G. W. , Robey H. F. , Hu S. X. , Morozas J. A. , Sangster T. C. , Landen O. L. , Meyerhofer D. D.
Published: February 2009

A high-performance inertial confinement fusion capsule is compressed by multiple shock waves before it implodes. To minimize the entropy acquired by the fuel, the strength and timing of those shock waves must be accurately controlled. Ignition experiments at the National Ignition Facility (NIF) will employ surrogate targets designed to mimic ignition targets while making it possible to measure the shock velocities inside the capsule. A series of experiments on the OMEGA laser facility [Boehly et al., Opt. Commun. 133, 495 (1997)] validated those targets and the diagnostic techniques proposed. Quartz was selected for the diagnostic window and shock-velocity measurements were demonstrated in Hohlraum targets heated to 180 eV. Cryogenic experiments using targets filled with liquid deuterium further demonstrated the entire timing technique in a Hohlraum environment. Direct-drive cryogenic targets with multiple spherical shocks were used to further validate this technique, including convergence effects at relevant pressures (velocities) and sizes. These results provide confidence that shock velocity and timing can be measured in NIF ignition targets, allowing these critical parameters to be optimized.
Chromatic-free spatially resolved optical emission spectroscopy diagnostics for microplasma
Authors: Zhu Li-Guo , Chen Wen-Cong , Zhu Xi-Ming , Pu Yi-Kang , Li Ze-Ren
Published: February 2009

A chromatic-free spatially resolved diagnostic system for microplasma measurement is proposed and demonstrated, which consists of an optical chromatic-free microscope mirror system, an electron multiplying charge coupled device (EMCCD), and bandpass filters. The diagnostic system free of chromatic aberrations with a spatial resolution of about 6 μm is achieved. The factors that limit the resolution of this diagnostic system have been analyzed, which are optical diffraction, the pixel size of the EMCCD, and the thickness of the microplasma. In this paper, the optimal condition for achieving a maximum resolution power has been analyzed. With this diagnostic system, we revealed the spatial nonuniformity of a microwave atmospheric-pressure argon microplasma. Furthermore, the spatial distribution of the time-averaged effective electron temperature has been estimated from the intensity distributions of 750.4 and 415.8 nm emissions.
A rigorous and nonsingular two dimensional cloaking coordinate transformation
Authors: Cummer Steven A. , Liu Ruopeng , Cui Tie Jun
Published: March 2009

We derive an approximate but rigorous two dimensional electromagnetic cloaking shell in which no parameters are singular. The simplicity of the material parameters makes it potentially easier to realize in practice than other cloaking solutions. The analytical formulation of this shell also provides a simple and explicit analytical trade-off between its scatter reduction performance, its thickness relative to the interior size, and the complexity and realization difficulty of the required permittivity and permeability.
Influence of a dielectric layer on photon emission induced by a scanning tunneling microscope
Authors: Tao X. , Dong Z. C. , Yang J. L. , Luo Y. , Hou J. G. , Aizpurua J.
Published: February 2009

We investigate theoretically the influence of a dielectric layer on light emission induced by a scanning tunneling microscope through a combined approach of classical electrodynamics and first-principles calculations. The modification of the junction geometry upon the insertion of a dielectric layer is treated first by using the density functional theory to calculate the effective potential along the surface normal and then by solving a one-dimensional Schrödinger equation to obtain the exact distance between the tip and the substrate for a given current and bias voltage. The modified external field with the inclusion of a dielectric layer is evaluated by using the Fresnel formula. The local-field enhancement factor and radiated power are calculated by the boundary element method for two typical systems, W-tip/C60/Au(111) and W-tip/Al2O3/NiAl(110). The calculated results indicate that the insertion of a dielectric layer tends to reduce the light emission intensity considerably but hardly changes the spectral profile with no substantial peak shifts with respect to the layer-free situation, in agreement with experimental observations. The suppression of the radiated power is mainly due to the increase in the tip-metal separation and the resultant reduction in the electromagnetic coupling between the tip and metal substrate.
Near-wall similarity between velocity and scalar fluctuations in a turbulent channel flow
Authors: Abe Hiroyuki , Antonia Robert Anthony
Published: February 2009

The degree of near-wall similarity between velocity and scalar fields is examined with the use of direct numerical simulation databases for a smooth wall turbulent channel flow with passive scalar transport. Particular attention is given to correlations between velocity and scalar fluctuations as well as those between their derivatives. In the vicinity of the wall, the largest correlation is between the wall-normal vorticity fluctuation and the spanwise scalar derivative, mainly due to the significantly reduced effect of the fluctuating pressure gradient. Other correlations peak at locations where the effect of the pressure fluctuation is smallest. The near-wall similarity between momentum and thermal streaks is not perfect because momentum streaks are often intensified or weakened by the fluctuating pressure gradient.
The exponential decay of homogeneous turbulence
Authors: George William K. , Wang Honglu
Published: February 2009

Similarity equations of the spectral equations for decaying homogeneous turbulence are considered for which the similarity length scale is not allowed to grow. Two types of solutions are found: an inviscid solution and one involving viscosity. For the former, the energy decays asymptotically as t−2, while for the latter the energy decays exponentially and the ratio of integral scale to Taylor microscale is constant. For both the spectra for fixed initial conditions collapse during decay with simply the energy and a single length scale. The exponentially decaying solution appears to provide an excellent description of the turbulence generated in recent space-filling fractal grid experiments.
Vortex filament simulation of the turbulent coflowing jet
Authors: Bernard Peter S.
Published: February 2009

A high resolution grid-free vortex filament scheme is applied to the prediction and simulation of coflowing round jets with a view to acquiring a new perspective on their physics and establishing the validity of the numerical technique. Vortex loop removal at inertial range scales provides a nondiffusive model of local dissipation that remains compatible with the presence of backscatter. Consistency with the Kolmogorov −5/3 inertial range spectrum is used to estimate the effective dissipation rate and subsequently the local and global Reynolds numbers associated with the turbulent vortex field. New insights into the accuracy of the scheme are presented including dependencies on numerical parameters. Comparisons of the computed statistics and structural features of the coflowing jet versus experiments show the method to provide an accurate rendering of the flow. Some consideration is also given to the dispersion of a scalar contaminant in the jet and its comparison to data.
Current-driven ferromagnetic resonance in magnetic trilayers with a tilted spin polarizer
Authors: He Peng-Bin , Li Zai-Dong , Pan An-Lian , Zhang Qing-Lin , Wan Qiang , Wang Ri-Xing , Wang Yan-Guo , Liu Wu-Ming , Zou Bing-Suo
Published: February 2009

We theoretically investigate the current-excited and adjusted ferromagnetic resonance in magnetic trilayers with a tilted spin polarizer. The current- and frequency-swept resonant spectra are obtained by the linearization method. We find that the precessional frequency, the equilibrium position, the energy pumping and damping, and the resonant linewidth and location can be adjusted by changing the current and the magnetization in the pinned layer. By optimizing the current density and the direction of the pinned magnetization, the energy pumping will be more efficient.
Deep level investigation of p-type GaN using a simple photocurrent technique
Authors: Armstrong A. , Thaler G. , Koleske D. D.
Published: February 2009

The deep level spectrum of p-type GaN was investigated using time-resolved photocurrent spectroscopy. The spectral dependence of the optical cross section for hole photoemission from a deep level was determined from the initial value of the photocurrent transient. Unlike other implementations of photocurrent, the present method does not require multiple excitation sources or determination of the optical emission rate. A deep level was observed at Ev+1.84 eV, where Ev is the valence band maximum, with a Franck-Condon shift of 0.25 eV. A bias-dependent component of the photocurrent, possibly due to metal-semiconductor interface states, complicated the steady-state response but did not affect the measured spectrum for the Ev+1.84 eV deep level. This photocurrent method is expected to be readily extended to materials with very deep dopants, such as p-type AlGaN, for which many other deep level spectroscopy techniques are unsuited.
Nonlinear dislocation dynamics at ultrasonic frequencies
Authors: Cantrell John H.
Published: February 2009

An analytical model of the effects of the Peierls–Nabarro barrier stress on the nonlinear dynamics of dislocation motion in crystalline solids resulting from a perturbative ultrasonic wave is derived. The nonlinearity is quantified by a material nonlinearity parameter β extracted from measurements of the amplitudes of the fundamental and harmonically generated ultrasonic waveforms. The β parameter is found to be functionally dependent on the magnitude of the Peierls–Nabarro barrier stress, the dislocation loop length, the shear modulus, and the Burgers vector of the crystal. The parameter is shown to exhibit a Bessel function oscillatory dependence on the stress amplitude of the fundamental ultrasonic wave resulting directly from the Peierls–Nabarro barrier stress. A sharp increase in the magnitude of β is shown to occur at low ultrasonic amplitudes where the dislocation motion is confined between adjacent lattice planes bounding the unperturbed dislocation. The generalization of the model to polycrystalline solids predicts a significant reduction in the β oscillations that results in a dramatic hooklike shape of the β versus stress amplitude curve at small values of the ultrasonic stress amplitude. Experimental observations of the hooklike shape (known as the Buck hook) have been reported in literature but the phenomenon has been previously unexplained. The present model shows that the Buck hook is a consequence of dislocation dynamics at low ultrasonic drive amplitudes.
Scanning tunneling microscopy imaging of Au coated microcantilevers
Authors: Lacey J. , Stevens R. , Beaulieu L. Y.
Published: February 2009

Scanning tunneling microscopy (STM) imaging was performed on Au coated cantilevers. Attempts to image the cantilevers directly in air or in viscous fluids were not possible beyond one third of the lever’s length despite the fact that the cantilevers were critically damped as determined by calculations. These results indicate the presences of a non-negligible force between the STM tip and the cantilever. Cantilevers were therefore detached from the chip and held on a rigid sample holder and imaged by STM. Statistical analysis of the STM images shows that the roughness and the peak-to-valley value of the thin Au film increases by approximately up to 200% and 300%, respectively, near the lever’s free end as compared to the Au surface on the chip. This change in morphology is significant since cantilever sensor measurements have been shown to be dependent on the morphology of the thin film used to attach the sensing layer on the cantilever.
Suppression of efficiency roll off in blue phosphorescent organic light-emitting devices using double emission layers with additional carrier-transporting material
Authors: Lee Meng-Ting , Lin Jin-Sheng , Chu Miao-Tsai , Tseng Mei-Rurng
Published: February 2009

By employing double emission layers (DELs) into blue phosphorescent organic light-emitting device (PHOLED), the device shows improved current efficiency by a factor of 1.8 as compared with that of device using single emission layer. Furthermore, by doping additional carrier-transporting material into DELs, the device shows only a slight efficiency roll off of 24% from low (1 mA/cm2 and 400 cd/m2) to high current density (40 mA/cm2 and 10 000 cd/m2). The dramatic improvement in device performances can be attributed to the formation of a broader carrier recombination zone and the elimination of carrier accumulation at the interface. A blue PHOLED with a current efficiency of 29.5 cd/A, a power efficiency of 21 lm/W, and a low driving voltage of 4.4 V with a Commission Internationale deL’Eclairage (CIEx,y) of (0.16, 0.35) at a practical brightness of 1000 cd/m2 can be achieved.
Comment on “A new integrable equation with cuspons and W/M-shape-peaks solitons” [J. Math. Phys. 47, 112701 (2006)]
Authors: Marinakis Vangelis
Published: February 2009

In a recent paper [J. Math. Phys. 47, 112701 (2006)] Qiao proposed a new completely integrable wave equation. The equation was derived from the two dimensional Euler equations and was proven to posses Lax pair, bi-Hamiltonian structure, and new types of soliton solutions. In this Comment we show that Qiao’s equation is a subcase of an integrable equation, derived by a method that was proposed by Fuchssteiner and Fokas [Physica D 4, 47 (1981)] in the early 1980s. We also discuss the existence of the new types of soliton solutions.
Freestanding AlN single crystals enabled by self-organization of 2H-SiC pyramids on 4H-SiC substrates
Authors: Yazdi G. R. , Beckers M. , Giuliani F. , Syväjärvi M. , Hultman L. , Yakimova R.
Published: February 2009

A sublimation-recondensation process is presented for high quality AlN (0001) crystals at a high growth rate by employing 4H-SiC substrates with a predeposited epilayer. It is based on the coalescence of well oriented AlN microrods, which evolve from the apex of 2H-SiC pyramids grown out of hexagonal pits formed by thermal etching of the substrate during a temperature ramp up. This process yields stress-free 120-μm-thick AlN single crystals with a dislocation density as low as 2×106cm−2.
Comparison of balloon-carried atmospheric motion sensors with Doppler lidar turbulence measurements
Authors: Harrison R. G. , Heath A. M. , Hogan R. J. , Rogers G. W.
Published: February 2009

Magnetic sensors have been added to a standard weather balloon radiosonde package to detect motion in turbulent air. These measure the terrestrial magnetic field and return data over the standard uhf radio telemetry. Variability in the magnetic sensor data is caused by motion of the instrument package. A series of radiosonde ascents carrying these sensors has been made near a Doppler lidar measuring atmospheric properties. Lidar-retrieved quantities include vertical velocity (w) profile and its standard deviation (σw). σw determined over 1 h is compared with the radiosonde motion variability at the same heights. Vertical motion in the radiosonde is found to be robustly increased when σw>0.75 m s−1 and is linearly proportional to σw.
Structural analyses of strained SiGe wires formed by hydrogen thermal etching and Ge-condensation processes
Authors: Tezuka Tsutomu , Toyoda Eiji , Irisawa Toshifumi , Hirashita Norio , Moriyama Yoshihiko , Sugiyama Naoharu , Usuda Koji , Takagi Shin-ichi
Published: February 2009

Strained SiGe-wire structures formed by a thermal oxidation of SiGe-on-insulator (SGOI) fins after an anisotropic gas etching in atmospheric hydrogen are investigated in terms of morphology, strain, and crystalline defects. It is found that vertical and smooth {110} sidewalls emerged on the SGOI fins after the hydrogen etching and that the SiGe wires consisted of a Si-rich core region and a surrounding Ge-rich layer formed by the Ge-condensation mechanism through the oxidation. Detailed strain analyses reveal that uniaxial and compressive strain accumulated in the Ge-rich layer via an elastic lattice deformation without generating dislocations.
Gas detection using low-temperature reduced graphene oxide sheets
Authors: Lu Ganhua , Ocola Leonidas E. , Chen Junhong
Published: February 2009

We demonstrate a high-performance gas sensor using partially reduced graphene oxide (GO) sheets obtained through low-temperature step annealing (300 °C at maximum) in argon flow at atmospheric pressure. The electrical conductance of GO was measured after each heating cycle to interpret the level of reduction. The thermally reduced GO showed p-type semiconducting behavior in ambient conditions and were responsive to low-concentration NO2 diluted in air at room temperature. The sensitivity is attributed to the electron transfer from the reduced GO to adsorbed NO2, which leads to enriched hole concentration and enhanced electrical conduction in the reduced GO sheet.
Two-dimensional nanohybridization of gold nanorods and polystyrene colloids
Authors: Yi Dong Kee , Lee Jin-Hyon , Rogers John A. , Paik Ungyu
Published: February 2009

Zero-dimensional (0D) and one-dimensional (1D) nanomaterials can be coarrayed in a cocontinuous manner using convective force driven self-assembly to obtain hybrid nanomaterials. The process is demonstrated using 0D polystyrene colloids and 1D Au nanorods. The flexural properties of the spherical colloidal templates and the concentration of the nanosized building-blocks are crucial parameters that determine the dominant rod-colloid hybrid nanoarrays that are obtained. Plasmon resonance phenomena in the resulting hybrid systems are examined by ultraviolet-visible transmission/absorbance spectroscopy. The resulting coarrayed nanostructures show variable optical stop bands dependent on the angle of the incident light relative to the plane of the coarrayed film.
Flexible low voltage nonvolatile memory transistors with pentacene channel and ferroelectric polymer
Authors: Lee Kwang H. , Lee Gyubaek , Lee Kimoon , Oh Min Suk , Im Seongil
Published: March 2009

We report on the fabrication of pentacene-based nonvolatile memory thin-film transistors (NVM-TFTs) with thin poly(vinylidene fluoride/trifluoroethylene) ferroelectric gate insulators. Our NVM-TFT adopts flexible polyethersulfone substrate and operates under the low voltage write-erase (WR-ER) pulses of ±13∼±20 V with field effect mobilities of 0.1–0.18 cm2/V s, depending on the ferroelectric polymer thickness. Our NVM-TFT displays good memory window (ΔV) of 2.5–8 V and also exhibits WR-ER current ratio of 20–40. The retention properties persist over ∼10 000 s and the dynamic response for WR-ER pulses demonstrates clear distinction of WR-ER states under the short switching pulse of 50 ms.
500 nm electrically driven InGaN based laser diodes
Authors: Queren Désirée , Avramescu Adrian , Brüderl Georg , Breidenassel Andreas , Schillgalies Marc , Lutgen Stephan , Strauß Uwe
Published: February 2009

Based on recent improvements of growth of In-rich InGaN quantum wells with low defect density, we demonstrate current driven InGaN laser diodes at wavelengths as long as 500 nm. The laser structures are grown on c-plane GaN substrate and are processed as broad oxide-insulated stripe laser diodes. We discuss the impact of the piezoelectric field on the emission energy of long wavelength laser diodes for this growth orientation. The combination of low threshold current density of 8.2 kA/cm2 with high slope efficiency of 650 mW/A enables high output powers up to several tens of milliwatts.
Comment on “On electromechanical stability of dielectric elastomers” [Appl. Phys. Lett. 93, 101902 (2008)]
Authors: Liu Yanju , Liu Liwu , Sun Shouhua , Shi Liang , Leng Jinsong
Published: March 2009

We would like to thank Díaz-Calleja et al. [Appl. Phys. Lett. 93, 101902 (2008)] for their insight and help on “On electromechanical stability of dielectric elastomers;” unstable domain of electromechanical coupling system of neo-Hookean-type silicone was analyzed by Díaz-Calleja et al. Different from that given in the paper of Díaz-Calleja, in the current work, the elastic strain energy function with two material constants was used to analyze the stable domain of electromechanical coupling system of Mooney–Rivlin-type silicone, and the results seem to support the theory of Díaz-Calleja.
Observation of frequency band gaps in a one-dimensional nanostructured magnonic crystal
Authors: Wang Z. K. , Zhang V. L. , Lim H. S. , Ng S. C. , Kuok M. H. , Jain S. , Adeyeye A. O.
Published: February 2009

We report the experimental observation of band gaps in a synthetic nanostructured magnonic crystal composed of two different magnetic materials. The sample, in the form of a one-dimensional periodic array comprising alternating Permalloy and cobalt nanostripes, has been fabricated using advanced lithographic techniques. Dispersion relations of spin waves in the magnonic crystal have been mapped by Brillouin spectroscopy. The center frequency and width of the band gaps observed are tunable by an applied magnetic field. Dispersion relations calculated based on the finite element method accord with the measured data.
Optically pumped intersubband emission of short-wave infrared radiation with GaN/AlN quantum wells
Authors: Driscoll Kristina , Liao Yitao , Bhattacharyya Anirban , Zhou Lin , Smith David J. , Moustakas Theodore D. , Paiella Roberto
Published: February 2009

Optically pumped pulsed emission of short-wave infrared radiation based on intersubband transitions in GaN/AlN quantum wells is demonstrated. Nanosecond-scale pump pulses are used to resonantly excite electrons from the ground states to the second-excited subbands, followed by radiative relaxation into the first-excited subbands. The measured room-temperature output spectra are peaked near 2 μm with integrated powers of a few hundred nanowatts. The intersubband origin of the measured luminescence is confirmed via an extensive study of its polarization properties and pump wavelength dependence, as well as simulations of the quantum well subband structure.
Asymmetric parametric amplification in nonlinear left-handed transmission lines
Authors: Powell David A. , Shadrivov Ilya V. , Kivshar Yuri S.
Published: February 2009

We study parametric amplification in nonlinear left-handed transmission lines, which serve as model systems for nonlinear negative-index metamaterials. We experimentally demonstrate the amplification of a weak signal in the three following regimes: with the signal in the left-handed band, with the signal in the stop band, and with the signal at a defect frequency. In particular, we demonstrate the amplification of the incident wave by up to 15 dB in the left-handed regime.
Removing dust particles from a large area discharge
Authors: Li Yang-fang , Konopka U. , Jiang K. , Shimizu T. , Höfner H. , Thomas H. M. , Morfill G. E.
Published: February 2009

Introducing a striped electrode in a large area discharge allows us to transport microparticles in the discharge in a user defined way. A directed and continuous dust transport is established by modulating the voltage signals on all individual electrodes to cause a traveling plasma sheath distortion. Particles, trapped in the potential wells and thus following the distortions, are finally removed from the central discharge region. Transport efficiency and velocity can be controlled by changing amplitude and traveling velocity of the plasma distortions.
Optical properties of GaSb/GaAs type-ІІ quantum dots grown by droplet epitaxy
Authors: Kawazu Takuya , Mano Takaaki , Noda Takeshi , Sakaki Hiroyuki
Published: February 2009

We study the optical properties of GaSb/GaAs type-ІІ quantum dots (QDs) on a GaAs substrate grown by droplet epitaxy. Ga droplets are formed on GaAs and then exposed to Sb flux to be clad by large granular crystals of Sb. Then the sample was annealed at 380 °C to enhance the reaction of Ga droplets with Sb and to evaporate the excess granular layer. In photoluminescence (PL) measurements, the peaks of the QDs and wetting layer (WL) are observed. The PL intensity of the QDs is much stronger than that of the WL, where the ratio IQD/IWL of the integral intensities is about 13.3. The PL peaks shift toward higher energies with increasing excitation energy, suggesting that the band lineups exhibit a type-ІІ staggered alignment. In addition, we investigate the temperature dependences of the PL peak energy and intensity.