bluuebunny/crossref_metadata_2025 huggingface dataset:
Intermittent ventilation in the hypoxic zone of western Long Island Sound during the summer of 2004
Authors: O'Donnell James , Dam Hans G. , Bohlen W. Frank , Fitzgerald William , Gay Peter S. , Houk Adam E. , Cohen David C. , Howard‐Strobel Mary M.
Published: September 2008

Observations of dissolved oxygen (DO) concentration, salinity, and temperature, during summer of 2004, at three levels on two moorings in the area of western Long Island Sound that is prone to seasonal hypoxia are described. Ship surveys in the area reveal that the DO concentration below the pycnocline decreases at approximately 2.4 mM m−3 d−1 throughout the summer. We show that this is the net result of oscillations in the rate of change of the DO concentration with periods of 3 to 7 days. During intervals of declining DO concentration, the rate of change is consistent with previous estimates of the rate of community respiration. Since there is insufficient light for photosynthesis below the pycnocline, increasing DO concentration (ventilation) must be a consequence of either vertical mixing or horizontal advection from regions of higher concentration. Analysis of the covariation of DO, salinity, and temperature and knowledge of the mean property distributions allow us to associate most (∼80%) of the ventilation intervals with increased vertical mixing. Comparison of DO and wind stress measurements suggest that it is the component in the along‐sound direction that controls the occurrence of ventilation, perhaps through modification of the rate of stratification by the density‐driven circulation. We conclude that the spatial and temporal variability of vertical mixing is crucial to understanding the duration and extent of hypoxia in the Long Island Sound estuary.
Three‐dimensional CFD modeling of morphological bed changes in the Danube River
Authors: Fischer‐Antze Tim , Olsen Nils Reidar B. , Gutknecht Dieter
Published: September 2008

The bed changes in a section of the river Danube were computed using a 3‐D computational fluid dynamics model. A time series of discharges during the flood in 2002 was used. The results compared reasonably well with regular bed level surveys before and after the flood. The Danube River section was 6 km long and located between Vienna and the Austrian‐Slovakian border. The fully three‐dimensional numerical model solved the Navier‐Stokes equations using the k‐epsilon turbulence closure. Nonuniform sediment transport was computed using the formulas of Wu et al. (2000b), considering hiding‐exposure algorithms. Both bed deformation and sorting processes were calculated. A number of parameter sensitivity tests were carried out on roughness values, parameters in the sediment transport capacity formula, parameters in the hiding‐exposure formulas, critical Shields number, and variations in the formulas for the effect of a sloping bed. Additionally, the sediment inflow to the section was varied together with investigations of physical parameters such as vegetation and groyne structures. The results were most sensitive to the Shields number for critical movement of the sediments. An error analysis was performed to give a quantitative assessment of the parameter sensitivity tests.
Spatial moments analysis of kinetically sorbing solutes in aquifer with bimodal permeability distribution
Authors: Massabó M. , Bellin A. , Valocchi A. J.
Published: September 2008

We analyze the influence of the formation structure upon transport of nonreactive and kinetically sorbing solutes in heterogeneous porous formations. Formation structure is represented through a bimodal distribution of hydraulic conductivity with two scales of spatial variability, which is a simplified, yet realistic, model of spatial variability. Kinetic sorption is modeled using a linear reversible rate expression. We derive new closed‐form solutions of the second ergodic spatial moments of a kinetically sorbing solute. Although these solutions are obtained through a perturbation expansion in term of logconductivity variance, they are not limited to any particular model of spatial variability. We show that the formation structure, as described by the bimodal model, has a significant impact on plume moments of a non‐reactive tracer at moderate contrast between mean hydraulic conductivity of the two hydrofacies, when the two scales of variability have comparable weight. On the contrary, the impact diminishes when bimodality weakens at both low and high contrast. As expected, the large time asymptotic longitudinal macrodispersion coefficient is influenced by the structure only through the variance and integral scale of log‐conductivity, and thus the result for the bimodal model is identical to that of a unimodal Gaussian field sharing the same second‐order statistics. The impact of kinetic sorption depends upon the plume travel time since injection. At early times, sorption kinetics tends to accentuate the difference between the longitudinal macrodispersivity in bimodal and unimodal fields, while at later times the difference is minimal because overall macrodispersivity is dominated by the spreading caused by nonequilibrium sorption. In a bimodal formation transverse macrodispersivity peaks later and declines to zero slower than in a Gaussian unimodal field with the same second‐order statistics. These results demonstrate that even a very simplified facies model, such as the bimodal model relying on a statistical distribution of high‐ and low‐conductivity zones, has important impacts upon global parameters describing the migration of nonreactive and reactive tracers. Consequently, larger effects are expected for quantities such as early arrival times and BTC tailing which are more directly influenced by the spatial patterns of high hydraulic conductivity than global parameters, such as macrodispersivity. Furthermore, these solutions contribute to bridge the gap between stochastic modeling and applications, since bimodal fields can be obtained to honor soft data typically available in applications, for example through conditional simulations using stratigraphic information from well logs.
Radial gradients of phase space density of the outer radiation belt electrons prior to sudden solar wind pressure enhancements
Authors: Turner Drew L. , Li Xinlin
Published: September 2008

When Earth's magnetosphere is impacted by a sudden solar wind pressure enhancement, dayside trapped electrons are transported radially inwards, conserving their first and second adiabatic invariants (μ and K). Thus, with magnetic field and particle flux measurements at geosynchronous orbit (GEO) before and after the impact, the phase space density (PSD) radial gradients of the particles prior to the impact can be reconstructed. We show two examples, in which the PSD of low‐μ electrons, which correspond to energies less than ∼100 keV, increases slightly with increasing radial distance for one event and remains unchanged for the other, while that of high‐μ electrons decreases significantly with increasing radial distance from GEO for both events. These results suggest that the PSD radial gradients are μ dependent, and a significant heating, which violates μ and K, occurs inside GEO for the high energy electrons for the two cases examined.
Freshwater flows to the sea: Spatial variability, statistics and scale dependence along coastlines
Authors: Destouni Georgia , Shibuo Yoshihiro , Jarsjö Jerker
Published: September 2008

Beyond the monitoring of main river flows, the discharges of freshwater from land to the sea are typically left unmonitored along long coastline stretches. This study uses uniquely fine‐resolved data and determines the spatial variability and statistics of the freshwater fluxes to the sea along two Swedish coastlines. The flux statistics depend greatly on subjective investigation choices of the support (or aggregation) scale of flux measurement, H, and the coastline length resolution, G. For common H and G values and relations, the flux coefficient of variation ranges from 1.5 to 22.5 and there is around 90–95% probability that locally measured or modelled fluxes miss the high‐end fluxes that are greater than the arithmetic mean flux and carry most of the total freshwater discharge across the coastline. Quantification of the inland hydrological balance and its distribution over the whole coastal catchment area is needed for objective guidance of coastal discharge interpretations.
On the relationship between thin Birkeland current arcs and reversed flow channels in the winter cusp/cleft ionosphere
Authors: Moen J. , Rinne Y. , Carlson H. C. , Oksavik K. , Fujii R. , Opgenoorth H.
Published: September 2008

In this paper we study reversed flow events (RFEs) that seem regulated by Birkeland current arcs in the winter cusp ionosphere above Svalbard. An RFE is a longitudinally elongated, 100–200 km wide channel, in which the flow direction is opposite to the background convection, persisting for 10–20 min. The RFE onset occurs with the brightening of a discrete arc near the open‐closed boundary. The auroral arc is situated exactly at a sharp clockwise flow reversal, consistent with a converging electric field and an upward field‐aligned current. One category of RFEs propagates into the polar cap in tandem with poleward moving auroral forms, while another category of RFEs moves with the cusp/cleft boundary. The RFE phenomenon is addressed to a region void of electron precipitation, and in lack of direct sunlight the E‐region conductivity will be very low. We propose two possible explanations: (1) the RFE channel may be a region where two MI current loops, forced by independent voltage generators, couple through a poorly conducting ionosphere and (2) the reversed flow channel may be the ionospheric footprint of an inverted V‐type coupling region. Electron beams of <1 keV will not give rise to significant conductivity gradients, and the form of a discontinuity in the magnetospheric electric field will be conserved when mapped down to the ionosphere, although reduced in amplitude. These two explanations may be related in the sense that the boundary discontinuity in the magnetospheric electric field in (1) may be the driver for the inverted V in (2).
Analysis of a crater‐forming meteorite impact in Peru
Authors: Brown P. , ReVelle D. O. , Silber E. A. , Edwards W. N. , Arrowsmith S. , Jackson L. E. , Tancredi G. , Eaton D.
Published: September 2008

The fireball producing a crater‐forming meteorite fall near Carancas, Peru, on 15 September 2007 has been analyzed using eyewitness, seismic, and infrasound records. The meteorite impact, which produced a crater of 13.5 m diameter, is found to have released of order 1010 J of energy, equivalent to ∼2–3 tons of TNT high explosives based on infrasonic measurements. Our best fit trajectory solution places the fireball radiant at an azimuth of 82° relative to the crater, with an entry angle from the horizontal of 63°. From entry modeling and infrasonic energetics constraints, we find an initial energy for the fireball to be in the 0.06–0.32 kton TNT equivalent. The initial velocity for the meteoroid is restricted to be below 17 km/s from orbit considerations alone, while modeling suggests an even lower best fit velocity close to 12 km/s. The initial mass of the meteoroid is in the range of 3–9 tons. At impact, modeling suggests a final end mass of order a few metric tons and impact velocity in the 1.5–4 km/s range. We suggest that the formation of such a substantial crater from a chondritic mass was the result of the unusually high strength (and corresponding low degree of fragmentation in the atmosphere) of the meteoritic body. Additionally, the high altitude of the impact site (3800 m.a.s.l) resulted in an almost one order of magnitude higher impact speed than would have been the case for the same body impacting close to sea level.
Colon cancer cells maintain low levels of pyruvate to avoid cell death caused by inhibition of HDAC1/HDAC3
Authors: Thangaraju Muthusamy , Carswell Kristina N. , Prasad Puttur D. , Ganapathy Vadivel
Published: September 2008

Human colon cancer cells and primary colon cancer silence the gene coding for LDH (lactate dehydrogenase)-B and up-regulate the gene coding for LDH-A, resulting in effective conversion of pyruvate into lactate. This is associated with markedly reduced levels of pyruvate in cancer cells compared with non-malignant cells. The silencing of LDH-B in cancer cells occurs via DNA methylation, with involvement of the DNMTs (DNA methyltransferases) DNMT1 and DNMT3b. Colon cancer is also associated with the expression of pyruvate kinase M2, a splice variant with low catalytic activity. We have shown recently that pyruvate is an inhibitor of HDACs (histone deacetylases). Here we show that pyruvate is a specific inhibitor of HDAC1 and HDAC3. Lactate has no effect on any of the HDACs examined. Colon cancer cells exhibit increased HDAC activity compared with non-malignant cells. HDAC1 and HDAC3 are up-regulated in colon cancer cells and in primary colon cancer, and siRNA (small interfering RNA)-mediated silencing of HDAC1 and HDAC3 in colon cancer cells induces apoptosis. Colon cancer cells silence SLC5A8, the gene coding for a Na+-coupled pyruvate transporter. Heterologous expression of SLC5A8 in the human colon cancer cell line SW480 leads to inhibition of HDAC activity when cultured in the presence of pyruvate. This process is associated with an increase in intracellular levels of pyruvate, increase in the acetylation status of histone H4, and enhanced cell death. These studies show that cancer cells effectively maintain low levels of pyruvate to prevent inhibition of HDAC1/HDAC3 and thereby to evade cell death.
Dielectric, ferroelectric, and piezoelectric properties of the lead-free (1−x)(Na0.5Bi0.5)TiO3-xBiAlO3 solid solution
Authors: Yu Huichun , Ye Zuo-Guang
Published: September 2008

Lead-free piezoelectric ceramics derived from the solid solution of (1−x)(Na0.5Bi0.5)TiO3–xBiAlO3 (NBT-BA) (x=0–0.10) have been synthesized by solid state reactions. A pure perovskite phase was formed for x≤0.08. The temperature dependence of dielectric constant indicates an increased broadness of the dielectric peak as the amount of BA increases. The large dielectric loss of NBT ceramics at low frequency and high temperature has been significantly reduced by the substitution of BA. The high coercive field is decreased and ferroelectric hysteresis loops were displayed at room temperature. The NBT-BA ceramics exhibit improved ferroelectric and piezoelectric properties compared to pure NBT ceramics, with Pr=52 μC/cm2, Ec=44 kV/cm, d33=130 pC/N, and kp=0.23 for 0.92NBT–0.08BA.
Effects of annealing on local composition and electrical transport correlations in MgO-based magnetic tunnel junctions
Authors: Chiaramonti A. N. , Schreiber D. K. , Egelhoff W. F. , Seidman David N. , Petford-Long A. K.
Published: September 2008

The effects of annealing on the electrical transport behavior of CoFe/MgO/CoFe magnetic tunnel junctions have been studied using a combination of site-specific in situ transmission electron microscopy and three-dimensional atom-probe tomography. Annealing leads to an increase in the resistance of the junctions. A shift in the conductance curve (dI/dV) minimum from 0 V for the as-grown specimen correlates with a sharply defined layer of CoFe oxide at the lower ferromagnetic interface. Annealing decreases the asymmetry in the conductance by making the interfaces more diffuse and the tunnel barrier more chemically homogeneous.
Beneficial effect of La on band offsets in Ge/high-κ insulator structures with GeO2 and La2O3 interlayers
Authors: Afanas’ev V. V. , Stesmans A. , Mavrou G. , Dimoulas A.
Published: September 2008

The electron energy band alignment between (100)Ge and high-κ oxide insulators (ZrO2,Gd2O3,La2Hf2O7) grown by the atomic beam deposition method is analyzed using photoemission of electrons from the Ge valence band. Formation of a thin GeO2 passivation layer before the high-κ deposition is found to significantly reduce the barrier for electrons. However, when La2O3 is deposited as an interlayer, it strongly reacts with the Ge substrate to form a La–Ge–O germanate at the interface, which is found to retain a high barrier for the carriers in Ge.
Effects of plasma shaping on nonlinear gyrokinetic turbulence
Authors: Belli E. A. , Hammett G. W. , Dorland W.
Published: September 2008

The effects of flux surface shape on the gyrokinetic stability and transport of tokamak plasmas are studied using the GS2 code [M. Kotschenreuther, G. Rewoldt, and W. M. Tang, Comput. Phys. Commun. 88, 128 (1995); W. Dorland, F. Jenko, M. Kotschenreuther, and B. N. Rogers, Phys. Rev. Lett. 85, 5579 (2000)]. Studies of the scaling of nonlinear turbulence with shaping parameters are performed using analytic equilibria based on interpolations of representative shapes of the Joint European Torus [P. H. Rebut and B. E. Keen, Fusion Technol. 11, 13 (1987)]. High shaping is found to be a stabilizing influence on both the linear ion-temperature-gradient (ITG) instability and the nonlinear ITG turbulence. For the parameter regime studied here, a scaling of the heat flux with elongation of χ∼κ−1.5 or κ−2.0, depending on the triangularity, is observed at fixed average temperature gradient. While this is not as strong as empirical elongation scalings, it is also found that high shaping results in a larger Dimits upshift of the nonlinear critical temperature gradient due to an enhancement of the Rosenbluth-Hinton residual zonal flows.
Ferroelectric properties of spin-coated ultrathin (down to 10 nm) copolymer films
Authors: Müller Klaus , Mandal Dipankar , Henkel Karsten , Paloumpa Ioanna , Schmeisser Dieter
Published: September 2008

Spin-cast films of the ferroelectric copolymer poly(vinylidene fluoride-trifluoroethylene) are attractive for various applications. For such films the question arises whether there exists a ferroelectric functionality depending on film thickness. We characterize the ferroelectric properties of ultrathin films down to a layer thickness of 10 nm with spectroscopic and electrical methods (capacitance-voltage). The measurements indicate an extrinsic switching mechanism with a much lower operation voltage than that for a collective intrinsic switching. Both independent methods agree that there is no critical thickness for spin-coated copolymer films down to 10 nm if an adapted system of electrodes is used.
Conceptual design of spin wave logic gates based on a Mach–Zehnder-type spin wave interferometer for universal logic functions
Authors: Lee Ki-Suk , Kim Sang-Koog
Published: September 2008

We present conceptual designs of an emerging class of logic gates, including NOT, NOR, and NAND, that use traveling spin waves (SWs) in the gigahertz range and that are based on a Mach–Zehnder-type SW (MZSW) interferometer. In this MZSW interferometer, logical input and output signals are achievable by the application of currents in order to control the phases that are accumulated by propagating SWs and by either destructive or constructive SW interference, respectively. In this article, the operation mechanism underlying a NOT gate function using a single MZSW interferometer is described and demonstrated numerically. The MZSW interferometer can itself become a NOT gate and be combined in its parallel and serial configurations to form NAND and NOR gates, respectively, which represent emerging classes of universal logic functions for microwave information signal processing.
Microstructuration induced differences in the thermo-optical and luminescence properties of Nd:YAG fine grain ceramics and crystals
Authors: Jacinto C. , Benayas A. , Catunda T. , García-Solé J. , Kaminskii A. A. , Jaque D.
Published: September 2008

The temperature and compositional dependences of thermo-optical properties of neodymium doped yttrium aluminum garnet (YAG) crystals and fine grain ceramics have been systematically investigated by means of time-resolved thermal lens spectrometry. We have found that Nd:YAG ceramics show a reduced thermal diffusivity compared to Nd:YAG single crystals in the complete temperature range investigated (80–300K). The analysis of the time-resolved luminescent properties of Nd3+ has revealed that the reduction in the phonon mean free path taking place in Nd:YAG ceramics cannot be associated with an increment in the density of lattice defects, indicating that phonon scattering at grain boundaries is the origin of the observed reduction in the thermal diffusivity of Nd:YAG ceramics. Finally, our results showed the ability of the time-resolved thermal lens to determine and optimize the thermo-optical properties of Nd:YAG ceramic based lasers.
Photoemission, resonant photoemission, and x-ray absorption of a Ru(II) complex adsorbed on rutile TiO2(110) prepared by in situ electrospray deposition
Authors: Mayor Louise C. , Ben Taylor J. , Magnano Graziano , Rienzo Anna , Satterley Christopher J. , O’Shea James N. , Schnadt Joachim
Published: September 2008

An experimental study of the bonding geometry and electronic coupling of cis-bis(isothiocyanato)bis(2,2′-bipyridyl-4,4′-dicarboxylato)-ruthenium(II) (N3) adsorbed on rutile TiO2(110) is presented, along with supporting theoretical calculations of the bonding geometry. Samples were prepared in situ using ultrahigh vacuum electrospray deposition. Core-level photoemission spectroscopy was used to characterize the system and to deduce the nature of the molecule-surface bonding. Valence band photoemission and N 1s x-ray absorption spectra were aligned in a common binding energy scale to enable a quantitative analysis of the bandgap region. A consideration of the energetics in relation to optical absorption is used to identify the photoexcitation channel between the highest occupied and lowest unoccupied molecular orbitals in this system, and also to quantify the relative binding energies of core and valence excitons. The core-hole clock implementation of resonant photoemission spectroscopy is used to reveal that electron delocalization from N3 occurs within 16fs.
Electrical spectroscopy of high resistivity ion-implanted layers by current-voltage measurements
Authors: Cesca Tiziana , Gasparotto Andrea , Fraboni Beatrice
Published: September 2008

We report on a spectroscopic characterization of electrically compensated high resistivity Fe-implanted InP and GaInP by room temperature space-charge-limited-current measurements. This method results to be a reliable and powerful tool to obtain a quantification of the degree of compensation and the free carrier concentration in the samples, together with the activation energy and density of states distribution of the dominant majority carrier traps. Moreover, by correlating these results with temperature dependent electrical spectroscopy analyses, it is possible to obtain information on material parameters, such as the carrier mobility, not always easily accessible by direct measurements.
A liquid metal flume for free surface magnetohydrodynamic experiments
Authors: Nornberg M. D. , Ji H. , Peterson J. L. , Rhoads J. R.
Published: September 2008

We present an experiment designed to study magnetohydrodynamic effects in free surface channel flow. The wide aspect ratio channel (the width to height ratio is about 15) is completely enclosed in an inert atmosphere to prevent oxidization of the liquid metal. A custom-designed pump reduces entrainment of oxygen, which was found to be a problem with standard centrifugal and gear pumps. Laser Doppler velocimetry experiments characterize velocity profiles of the flow. Various flow constraints mitigate secondary circulation and end effects on the flow. Measurements of the wave propagation characteristics in the liquid metal demonstrate the surfactant effect of surface oxides and the damping of fluctuations by a cross-channel magnetic field.
Application of mixed interface in white-electrophosphorescent devices: An efficient approach to adjust the distributions of carriers
Authors: Wang Yu , Hua Yulin , Wu Xiaoming , Zhang Lijuan , Hou Qingchuan , Zhang Nan , Ma Liang , Cheng Xiaoman , Yin Shougen
Published: September 2008

The distributions of carriers in white organic light-emitting devices can be tuned effectively by incorporating a mixed interface layer, consisting of 4,7-diphenyl-1,10-phenanthroline doped in N,N′-dicarbazolyl-4-4′-biphenyl. By adjusting the thickness and the BPhen concentration of the mixed interface, the optimal devices exhibit maximum current and power efficiencies of 20.9 cd/A and 19.9 lm/W, respectively, and slightly modified Commission Internationale De L’Eclairage coordinates, from (0.3174 0.3276) to (0.3141 0.3218). This is attributed to the good distributions of carriers between two emissive layers by inserting the mixed interface, thereby improving both the exciton formation probability and the charge transport balance.
Current-voltage characteristics for lead zirconate titanate bulk ceramics
Authors: Balke Nina , Granzow Torsten , Rödel Jürgen
Published: September 2008

Current-voltage characteristics have been obtained on lead zirconate titanate bulk ceramics using robust measurement techniques separating polarization effects from actual charge transport. Measurement of the electrical conduction upon both increase and decrease in the electric field shows that long settling times are required to suppress polarization currents and obtain reliable data. The influence of additional field cycles and different electrode materials is also studied. The analysis reveals that an Ohmic conduction is dominant at low fields, while at high fields charge transport is most likely governed by space charge limited currents.
AlGaAs/InGaAs metal-oxide-semiconductor pseudomorphic high-electron-mobility transistor with low temperature liquid phase deposited Al2O3 gate insulator
Authors: Basu Sarbani , Singh Pramod K. , Sze Po-Wen , Wang Yeong-Her
Published: September 2008

AlGaAs/InGaAs/GaAs metal-oxide-semiconductor–pseudomorphic high electron mobility transistors (MOS-PHEMTs) with Al2O3 as a gate dielectric oxide prepared in low-temperature liquid phase deposition (LPD) are presented in this study. The Al2O3 films on the GaAs substrates are characterized by means of x-ray photoelectron spectroscopy, Auger electron spectroscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, and atomic force microscopy. The applications to depletion mode n-channel GaAs MOS-PHEMTs showed larger gate swing voltage, lower gate leakage current, higher breakdown voltage, higher drain current density, and maximum extrinsic transconductance compared to conventional AlGaAs/InGaAs PHEMTs. This demonstrates that LPD Al2O3 could be a suitable candidate for future gate insulator applications.
Effects of ozone oxidation on interfacial and dielectric properties of thin HfO2 films
Authors: Wang L. , Chu Paul K. , Anders Andre , Cheung Nathan W.
Published: September 2008

The effects of high concentration ozone oxidation at different temperatures on the interfacial and dielectric properties of thin HfO2 films are examined. Analysis of the chemical shifts of the Hf 4f, Si 2p and O 1s core-level spectra acquired by x-ray photoelectron spectroscopy clearly indicates that the introduction of ozone can significantly improve the bonding characteristics between hafnium and oxygen even at low temperature. High-resolution cross-sectional transmission electron microscopy study shows that when the oxidation temperature is increased, film densification and crystallization occur at high temperature. The change in the dielectric properties of high temperature oxidation is analyzed and the results show that a negligible hysteresis and low fixed charge density can be achieved by medium temperature oxidation. When the oxidation temperature is increased to over 800 °C, the dielectric properties degrade due to regrowth of the interfacial layer and change in the film morphology. Our results also reveal that the leakage current can be reduced by high temperature ozone oxidation.
Slipping friction of an optically and magnetically manipulated microsphere rolling at a glass-water interface
Authors: Agayan Rodney Ray , Smith Ron Gordon , Kopelman Raoul
Published: September 2008

The motion of submerged magnetic microspheres rolling at a glass-water interface has been studied using magnetic rotation and optical tweezers combined with bright field microscopy particle tracking techniques. Individual microspheres of varying surface roughness were magnetically rotated both in and out of an optical trap to induce rolling along either plain glass cover slides or glass cover slides functionalized with polyethylene glycol. It has been observed that the manipulated microspheres exhibited nonlinear dynamic rolling-while-slipping motion characterized by two motional regimes: At low rotational frequencies, the speed of microspheres free rolling along the surface increased proportionately with magnetic rotation rate; however, a further increase in the rotation frequency beyond a certain threshold revealed a sharp transition to a motion in which the microspheres slipped with respect to the external magnetic field, resulting in decreased rolling speeds. The effects of surface-microsphere interactions on the position of this threshold frequency are posed and investigated. Similar experiments with microspheres rolling while slipping in an optical trap showed congruent results.
Strain enhanced spin polarization in Nd0.43Sr0.57MnO3/YBa2Cu3O7 bilayers
Authors: Mani Awadhesh , Kumary T. Geetha , Hsu Daniel , Lin J. G.
Published: September 2008

Electrical and magnetic properties of antiferromagnetic/superconducting bilayers Nd0.43Sr0.57MnO3/YBa2Cu3O7 (NSMO/YBCO) are investigated as functions of NSMO thickness (d) and current density (J). The superconducting transition temperatures (Tc) of bilayers decrease monotonically with decreasing d, and the suppression rate of Tc with J (dTc/dJ) is enhanced by three orders of magnitude in NSMO(d)/YBCO compared with that in pure YBCO. Based on the analysis on the d dependencies of Tc and dTc/dJ, it is suggested that the strain enhanced spin polarization is responsible for the great suppression of superconductivity in NSMO(d)/YBCO with d=40 and 80 nm.
Synthesis and characterizations of silver-fullerene C70 nanocomposite
Authors: Singhal R. , Agarwal D. C. , Mohapatra S. , Mishra Y. K. , Kabiraj D. , Singh F. , Avasthi D. K. , Chawla A. K. , Chandra R. , Mattei G. , Pivin J. C.
Published: September 2008

Films of C70 fullerene containing silver nanoparticles were synthesized by thermal codeposition. Optical absorption studies revealed that surface plasmon resonance of Ag nanoparticles occurs at unusually large wavelength, which showed a regular redshift from 521 to 581 nm with increase in metal content from 4.5% to 28%. It is explained by the Maxwell–Garnett theory considering the absorbing nature of fullerene matrix. Rutherford backscattering and transmission electron microscopy were performed to quantify metal content and the particle size, respectively. A better detection of low intensity vibrational modes of C70 in Raman scattering is observed due to surface enhanced Raman scattering.
The roles of the various plasma agents in the inactivation of bacteria
Authors: Lu XinPei , Ye Tao , Cao YingGuang , Sun ZiYong , Xiong Qing , Tang ZhiYuan , Xiong ZhiLan , Hu Jing , Jiang ZhongHe , Pan Yuan
Published: September 2008

The roles of various plasma agents in the inactivation of bacteria have recently been investigated. However, up to now, the effect of the charged particles on the inactivation of bacteria is not well understood. In this paper, an atmospheric pressure plasma jet device, which generates a cold plasma plume carrying a peak current of 300 mA, is used to investigate the role of the charged particles in the inactivation process. It is found that the charged particles play a minor role in the inactivation process when He/N2(3%) is used as working gas. On the other hand, when He/O2(3%) is used, the charged particles are expected to play an important role in the inactivation of bacteria. Further analysis shows that the negative ions O2− might be the charged particles that are playing the role. Besides, it is found that the active species, including O, O3, and metastable state O2∗, can play a crucial role in the inactivation of the bacteria. However, the excited He∗, N2 C Π3u, and N2+ B Σ2u+ have no significant direct effect on the inactivation of bacteria. It is also concluded that heat and UV play no or minor role in the inactivation process.
An amplifier concept for spintronics
Authors: Acremann Y. , Yu X. W. , Tulapurkar A. A. , Scherz A. , Chembrolu V. , Katine J. A. , Carey M. J. , Siegmann H. C. , Stöhr J.
Published: September 2008

Typical spin-dependent devices proposed for information processing lack one of the most important features provided by charge based logic: they do not provide gain. In this letter we show the basic concept of a spin amplifier and propose ways to amplify a spin current at room temperature.
Coherent control of gigahertz surface acoustic and bulk phonons using ultrafast optical pulses
Authors: Hurley D. H. , Lewis R. , Wright O. B. , Matsuda O.
Published: September 2008

We demonstrate the coherent generation and control of gigahertz acoustic phonons with ultrafast optical pulses. Two distinct acoustic phonon modes, a surface acoustic phonon mode and a longitudinal acoustic phonon mode, are generated simultaneously by irradiating nanolithographic absorption gratings on semiconductor substrates. Two material systems are examined: suboptical wavelength aluminum absorption gratings on Si and GaAs substrates. Constructive and complete destructive interference conditions are demonstrated using two pump pulses derived from a single Michelson interferometer.
Acceleration and suppression of photoemission of GaAs quantum dots embedded in photonic crystal microcavities
Authors: Kuroda Takashi , Ikeda Naoki , Mano Takaaki , Sugimoto Yoshimasa , Ochiai Tetsuyuki , Kuroda Keiji , Ohkouchi Shunsuke , Koguchi Nobuyuki , Sakoda Kazuaki , Asakawa Kiyoshi
Published: September 2008

We fabricated optical microcavities in a photonic crystal slab embedded with GaAs quantum dots by electron beam lithography and droplet epitaxy. The Purcell effect of exciton emission of GaAs quantum dots was confirmed for the first time by microphotoluminescence and lifetime measurements.
A containerless levitation setup for liquid processing in a superconducting magnet
Authors: Lu Hui-Meng , Yin Da-Chuan , Li Hai-Sheng , Geng Li-Qiang , Zhang Chen-Yan , Lu Qin-Qin , Guo Yun-Zhu , Guo Wei-Hong , Shang Peng , Wakayama Nobuko I.
Published: September 2008

Containerless processing of materials is considered beneficial for obtaining high quality products due to the elimination of the detrimental effects coming from the contact with container walls. Many containerless processing methods are realized by levitation techniques. This paper describes a containerless levitation setup that utilized the magnetization force generated in a gradient magnetic field. It comprises a levitation unit, a temperature control unit, and a real-time observation unit. Known volume of liquid diamagnetic samples can be levitated in the levitation chamber, the temperature of which is controlled using the temperature control unit. The evolution of the levitated sample is observed in real time using the observation unit. With this setup, containerless processing of liquid such as crystal growth from solution can be realized in a well-controlled manner. Since the levitation is achieved using a superconducting magnet, experiments requiring long duration time such as protein crystallization and simulation of space environment for living system can be easily succeeded.
Gas-temperature-dependent generation of cryoplasma jet under atmospheric pressure
Authors: Noma Yuri , Choi Jai Hyuk , Tomai Takaaki , Terashima Kazuo
Published: September 2008

Plasma with a gas temperature below room temperature is not yet fully understood although it is expected to be an attractive tool for applications to material processing. In the present work, gas-temperature-dependent generation of a cryoplasma jet was studied. So far, we have generated a helium cryoplasma jet (296–5K) under atmospheric pressure. At gas temperatures below 20K, the helium excimer, He2, was observed clearly from by optical emission spectroscopy.
Waveguiding and nonlinear optical properties of three-dimensional waveguides in LiTaO3 written by high-repetition rate ultrafast laser
Authors: McMillen Ben , Chen Kevin P. , An Honglin , Fleming Simon , Hartwell Vincent , Snoke David
Published: September 2008

We report the fabrication of waveguides in lithium tantalate using a 250kHz high-repetition rate ultrafast laser at 771nm and the characterization of the resulting laser induced structure with second harmonic microscopy. Waveguides operating at the 1.5μm telecommunication wavelength were formed above and below the focal volume using pulse energies ranging from 100to1.6J and translation speeds from 100μm∕sto5mm∕s. The second harmonic microscopy reveals no degradation of the electro-optic coefficient in the guiding region above the focal volume.
Reversibility of magnetostructural transition and associated magnetocaloric effect in Ni–Mn–In–Co
Authors: Liu Jian , Scheerbaum Nils , Lyubina Julia , Gutfleisch Oliver
Published: September 2008

By analyzing isothermal magnetization curves under magnetic field cycling, the reversibility of the magnetostructural transition was investigated in Ni–Mn–In–Co in form of bulk sample and melt-spun ribbons. The hysteresis of thermally/magnetically induced martensitic transformation plays an important role in the reversibility of the magnetostructural transition. In ribbons with a large hysteresis of 18K, residual field-induced austenite is present after removing the magnetic field, while, in the bulk sample, the magnetostructural transition is reversible at moderate temperatures due to a relatively smaller hysteresis of 8K. Additionally, the magnetocaloric effect strongly depends on the sample history due to the occurrence of the irreversible magnetostructural transition, especially for the ribbons.
Nanosecond laser induced ignition thresholds and reaction velocities of energetic bimetallic nanolaminates
Authors: Picard Yoosuf N. , McDonald Joel P. , Friedmann Thomas A. , Yalisove Steven M. , Adams David P.
Published: September 2008

Thresholds for optically igniting self-propagating reactions are quantified for energetic Ni/Ti, Co/Al, and Al/Pt nanolaminates, where smaller enthalpy material pairs required larger laser ignition fluences. The threshold fluences (J/cm2) for ignition by 30 ns laser pulses focused to ∼8 μm spot size varied from 720 to 15 000 J/cm2 for Ni/Ti, 8.6 to 380 J/cm2 for Co/Al, and 3.2 to 27 J/cm2 for Al/Pt. Conversely, smaller enthalpy nanolaminates exhibited reduced steady-state propagation speeds ranging from 0.05 to 0.9 m/s for Ni/Ti, 0.6 to 8.5 m/s for Co/Al, and 24 to 73 m/s for Al/Pt. Increasing the laser spot diameter tenfold reduced the ignition threshold fluence by as much as two orders of magnitude.
Deep level optical and thermal spectroscopy of traps in n-GaN grown by ammonia molecular beam epitaxy
Authors: Arehart A. R. , Corrion A. , Poblenz C. , Speck J. S. , Mishra U. K. , Ringel S. A.
Published: September 2008

The incorporation of deep level defects in n-type GaN grown by ammonia-based molecular beam epitaxy (MBE) is studied via systematic adjustment of the NH3/Ga flux ratio. Deep level optical and transient spectroscopies, which together enable deep level detection throughout the GaN bandgap, reveal defect states whose individual concentrations vary with the NH3/Ga flux ratio. A general trend of lower concentration for deep levels at EC−3.28, EC−1.28, EC−0.62, and EC−0.25 eV with higher NH3/Ga flux ratio was observed, with the strongest reduction at the EC−0.25 eV level, consistent with expectations for a VN-related defect. The known CN impurity state at EC−3.28 eV and suspected CI-related state at EC−1.28 eV also showed a moderate decrease in concentration at the higher NH3/Ga flux ratio. In contrast, the VGa-related defect at EC−2.62 eV was insensitive to the NH3/Ga flux ratio over the range studied here. Taken together, ammonia-MBE GaN has deep level defects with different sensitivities in flux ratios suggestive of independent physical sources. However, the total trap concentrations were significantly reduced for higher NH3/Ga flux ratios in n-type GaN grown by ammonia-MBE under the range of growth conditions used in this study, suggesting that higher NH3/Ga flux ratios will generate higher electronic quality GaN material when using ammonia-based MBE for device applications.
Bubble nucleation on hydrophobic islands provides evidence to anomalously high contact angles of nanobubbles
Authors: Nam Youngsuk , Ju Y. Sungtaek
Published: September 2008

We observe stable steady-periodic vapor bubble nucleation on islands of nanoscopically smooth hydrophobic materials microfabricated on a silicon substrate. The minimum surface superheat required for the onset of bubble nucleation is very low (∼9 °C), which cannot be explained by the established models of heterogeneous bubble nucleation. A modified bubble nucleation model indicates that the observed minimum superheat can be explained when one assumes the existence of a nanoscale interfacial gas phase with anomalously high contact angles (>160°). Our data therefore provide independent evidence that supports previous atomic force microscopy and infrared spectroscopy studies of the topography of nanobubbles.
Wavelength tuning and emission width widening of ultrabroad quantum dash interband laser
Authors: Tan C. L. , Djie H. S. , Wang Y. , Dimas C. E. , Hongpinyo V. , Ding Y. H. , Ooi B. S.
Published: September 2008

The authors report the demonstration of the bandgap-tuned InAs quantum dash broadband laser with widened laser emission linewidth at room temperature using postgrowth intermixing technique. The 100 nm wavelength blueshifted, as-cleaved laser exhibits ultrabroad lasing spectral coverage of ∼85 nm at a center wavelength of 1.54 μm with a total emission power of ∼1 W per device. Compared to the as-grown laser, this laser shows broader lasing bandwidth (∼41 nm) with improved spectral ripple (<1 dB).
Polarization-dependent coupling to plasmon modes on submicron gold wire in photonic crystal fiber
Authors: Lee H. W. , Schmidt M. A. , Tyagi H. K. , Sempere L. Prill , Russell P. St. J.
Published: September 2008

We present experimental results on coupling to surface plasmon modes on gold nanowires selectively introduced into polarization-maintaining photonic crystal fibers. Highly polarization- and wavelength-dependent transmission is observed. In one sample 24.5 mm long, the transmission on and off resonance differs by as much as 45 dB. Near-field optical images of the light emerging from such a gold-filled fiber show light guided on the wire at surface plasmon resonances. Finite element simulations are in good agreement with the experimental results. These gold-filled fibers can be potentially used as in-fiber wavelength-dependent filters and polarizers and as near-field tips for sub-wavelength-scale imaging.
Spatial modulation instability driven by light-enhanced nonlinearities in semiconductor CdZnTe:V crystals
Authors: Shwartz Sharon , Segev Mordechai , Zolotoyabko Emil , El-Hanany Uri
Published: September 2008

We present the experimental observation of spatial modulation instability in photorefractive semiconductor crystals (CdZnTe:V), where the optical nonlinear effects are enhanced by light. We find that the total refractive index change can be expressed as sum of a uniform index change, which can exceed the value of 0.003, and a local index change which is limited to ≈1.6×10−4. However, only the later, arising from the intensity-enhanced photorefractive effect, contributes to the formation of the modulation instability. Finally, we find that the refractive index change experiences large temporal fluctuations induced by the combination of uniform cw illumination and applied electric field.
Dielectric response and tunability of a dielectric-paraelectric composite
Authors: Zhou K. , Boggs S. A. , Ramprasad R. , Aindow M. , Erkey C. , Alpay S. P.
Published: September 2008

A theoretical study was carried out to determine the dielectric response and tunability of a composite consisting of a linear, low-loss dielectric matrix with uniformly sized, randomly distributed paraelectric Ba0.60Sr0.40TiO3 (BST 60/40) particles as functions of the volume fraction and size of the particles. The field dependence of the polarization and the dielectric response of the inclusions are specified through a nonlinear thermodynamic model and then incorporated into a two-dimensional finite element analysis. Near the percolation threshold for BST particles (∼27% to 45% depending on the particle size), high dielectric tunabilities with a lower effective permittivity than monolithic BST can be realized.
Graphene segregated on Ni surfaces and transferred to insulators
Authors: Yu Qingkai , Lian Jie , Siriponglert Sujitra , Li Hao , Chen Yong P. , Pei Shin-Shem
Published: September 2008

We report an approach to synthesize high quality graphene by surface segregation and substrate transfer. Graphene was segregated from Ni surface under the ambient pressure by dissolving carbon in Ni at high temperatures followed by cooling down with various rates. Different cooling rates led to different segregation behaviors, strongly affecting the thickness and quality of the graphene films. Electron microscopy and Raman spectroscopy indicated that the graphene films synthesized with medium cooling rates have high quality crystalline structure and well-controlled thicknesses. The graphene films were transferred to insulating substrates by wet etching and found to maintain their high quality.
Environmental correlates of coastal heathland and allied vegetation
Authors: Griffith S. J. , Bale C. , Adam P.
Published: September 2008

The east Australian coastline supports regionally distinct heathlands and allied structural formations, and of particular interest is the vegetation on Quaternary dunefields and beach ridge plains containing aquifers. Groundwater is abstracted from these aquifers for domestic, industrial and agricultural consumption, and this abstraction proceeds without a sound understanding of plant–water relations. This study examined relationships between the vegetation and a range of simple and complex environmental variables. Aspects of intra-habitat and micro-site environmental heterogeneity were also explored. Watertable depth varied spatially and temporally relative to vegetation type, although differences were not consistently significant. Differences in watertable depth were significant for vegetation samples grouped by topographic position. Plant roots were invariably present at the upper boundary of the aquifer and these were observed at depths of up to 10.5 m. Groundwater was found to have the chemical composition of dilute seawater. Soil properties for the A1 horizon (total phosphorus, total nitrogen and organic matter content) varied with vegetation type and topography, and although mean values were generally higher in wetter habitats, differences were not consistently significant. Ordination identified topography as the more important determinant of vegetation pattern. Intra-habitat and micro-site differences in soil and groundwater properties were detected, and the likely causes of this variation are discussed.