bluuebunny/crossref_metadata_2025 huggingface dataset:
Q-band ferromagnetic resonance for CoPt-based stacked perpendicular recording media with interlayer exchange coupling
Authors: Hinata Shintaro , Saito Shin , Hasegawa Daiji , Takahashi Migaku
Published: April 2011

The ferromagnetic interlayer exchange coupling Jinter for stacked perpendicular recording media with a granular layer (GL)/interlayer (IL)/alloy capping layer (CL) structure was quantitatively evaluated by Q-band ferromagnetic resonance (FMR). Two resonances with acoustic and optical precession modes were observed in the FMR signals from the stacked media. Fitting using the Landau–Lifshitz–Gilbert (LLG) equation indicated that Jinter increased from 0.55 to 1.83 erg/cm2 when the Pt IL thickness was reduced from 2.0 to 1.0 nm for media based on Co82Cr10Pt8-CL (4 nm) and Co74Pt16Cr10-8 mol (SiO2)-GL (16 nm). The optimum Pt IL thickness at which the switching field distribution was minimized due to a large reduction in the saturation field of the stacked media was found to correspond to the boundary condition between antiparallel and parallel precession of the magnetic moments of the GL and CL in FMR.
The suspension balance model revisited
Authors: Nott Prabhu R. , Guazzelli Elisabeth , Pouliquen Olivier
Published: April 2011

This paper addresses a fundamental discrepancy between the suspension balance model and other two-phase flow formulations. The former was proposed to capture the shear-induced migration of particles in Stokesian suspensions, and hinges on the presence of a particle phase stress to drive particle migration. This stress is taken to be the “particle stress,” defined as the particle contribution to the suspension stress. On the other hand, the two-phase flow equations derived in several studies show only a force acting on the particle phase, but no stress. We show that the identification of the particle phase stress with the particle contribution to the suspension stress in the suspension balance model is incorrect, but there exists a well-defined particle phase stress. Following the rigorous method of volume averaging, we show that the force on the particle phase may be written as the sum of an interphase drag and the divergence of the particle phase stress. We derive exact micromechanical relations for these quantities. We also comment on the interpretations and results of previous studies that are based on the identification of the particle phase stress with the particle contribution to the suspension stress.
Anomalous temperature-dependency of phonon line widths probed by Raman scattering from β-FeSi2 thin films
Authors: Liu H. F. , Huang A. , Chi D. Z.
Published: April 2011

Micro-Raman scattering and its temperature dependencies have been used to investigate lattice dynamic properties of β-FeSi2 thin films epitaxially grown on Si (111) substrates by sputtering at elevated temperatures. A linear correlation between the blueshift in phonon energies and the lattice expansions in the growth direction of β-FeSi2 is observed. The shifting rate of the Raman mode at 248 cm−1 (13.6 cm−1/%) is much larger than that of the mode at 194 cm−1 (8.4 cm−1/%) due to the involvement of radial bonding vibrations between Fe and Si atoms. Temperature-dependent Raman scattering, which is hitherto unknown for β-FeSi2, reveals an extremely small phonon line width broadening in the range of 80-480 K. It is revealed that the broadening in the phonon line widths contributed by phonon-phonon scattering is weaker and is masked by phonon-hole couplings in β-FeSi2, while the effect of phonon-hole coupling on phonon line width broadening is saturated at the studied temperatures due to the high impurity densities.
The driving frequency effects on the atmospheric pressure corona jet plasmas from low frequency to radio frequency
Authors: Kim Dan Bee , Jung H. , Gweon B. , Moon S. Y. , Rhee J. K. , Choe W.
Published: April 2011

Lately, the atmospheric pressure jet type corona plasma, which has been typically driven by dc to low frequency (LF: several tens of kHz), is often generated by using radio frequency of 13.56 MHz. Yet, the relationship between the plasma and its driving frequency has seldom been investigated. Hence, in this study, dependence of the atmospheric pressure corona plasma characteristics on the driving frequency was explored experimentally from LF to rf (5 kHz–13.56 MHz). The plasmas generated by the driving frequency under 2 MHz were cylindrical shape of several tens of millimeters long while the 13.56 MHz plasma is spherical and a few millimeters long. As the driving frequency was increased, the plasma length became shortened. At the lower driving frequencies (below 2 MHz), the plasmas existed as positive streamer and negative glow for each half period of the applied voltage, but the discharge was more continuous in time for the 13.56 MHz plasma. It was inferred from the measured I–V curves that the higher driving frequency induced higher discharge currents, and the gas temperature was increased as the driving frequency was increased.
Evolution of nonlinear waves in compressing plasma
Authors: Schmit P. F. , Dodin I. Y. , Fisch N. J.
Published: April 2011

Through particle-in-cell simulations, the evolution of nonlinear plasma waves is examined in one-dimensional collisionless plasma undergoing mechanical compression. Unlike linear waves, whose wavelength decreases proportionally to the system length L(t), nonlinear waves, such as solitary electron holes, conserve their characteristic size Δ during slow compression. This leads to a substantially stronger adiabatic amplification as well as rapid collisionless damping when L approaches Δ. On the other hand, cessation of compression halts the wave evolution, yielding a stable mode.
Three-dimensional particle-in-cell simulations of laser channeling in fast ignition
Authors: Li G. , Yan R. , Ren C. , Tonge J. , Mori W. B.
Published: April 2011

Three-dimensional particle-in-cell simulations with an underdense plasma length up to 540  μm are presented to show that laser channeling in 3D is qualitatively similar to that shown in previous 2D simulations [Li et al., Phys. Rev. Lett. 100, 125002 (2008)], but quantitative differences exist. Due to a larger laser ponderomotive force resulting from self-focusing and easier channel formation in 3D, the channeling speed in 3D is larger compared to 2D. Laser hosing and channel bending are also observed in 3D. Decoupling of the laser and plasma is observed when the electrons are heated to relativistic temperatures during the channeling process.
Integrated optical model for organic light-emitting devices
Authors: Mladenovski Saso , Hofmann Simone , Reineke Sebastian , Penninck Lieven , Verschueren Thomas , Neyts Kristiaan
Published: April 2011

One of the most important parameters of organic light-emitting devices (OLEDs) in their application for illumination or displays is their efficiency. In order to maximize the efficiency, one needs to understand all loss mechanisms and effects present in these devices and properly model them. For that purpose, we introduce an integrated model for light emission from OLEDs. The model takes into account the exciton decay time change and light outcoupling. Furthermore, it shows how to calculate the external quantum efficiency, the spectral radiance and the luminous current efficacy of OLEDs. The overall theory is experimentally verified through a range of measurements done on a set of green OLED samples with an Ir-based phosphorescent emitter. From the analysis of simulations and experiments one can estimate the charge balance in the OLED stack and the radiative efficiency of the emitter.
Optical properties of SnCl2 phosphor
Authors: Nara Jun-ichi , Adachi Sadao
Published: April 2011

A white SnCl2 phosphor is synthesized by the chemical etching of Sn shots in an aqueous HCl solution. The optical properties of this phosphor are investigated using diffuse reflectance, photoluminescence (PL) analysis, PL excitation spectroscopy, and PL lifetime measurements. The SnCl2 phosphor exhibits PL in the blue (∼460 nm) and red spectral regions (∼600 nm) under ultraviolet excitation (≥4.1 eV). The differences in the PL features observed using Nd:YAG (λ = 266 nm) and He-Cd (λ = 325 nm) lasers as excitation light sources are interpreted using the configurational-coordinate model, taking into account the band-gap energy (∼3.8 eV) of SnCl2 and the excited-state energies of the Sn2+ ions. A reliable energy level diagram for Sn2+ ions in the SnCl2 host is also proposed.
Dielectric structure pyrotechnic initiator realized by integrating Ti/CuO-based reactive multilayer films
Authors: Zhu Peng , Shen Ruiqi , Fiadosenka N. N. , Ye Yinghua , Hu Yan
Published: April 2011

A dielectric structure pyrotechnic initiator was proposed and the initiator samples were designed and realized by integrating Ti/CuO-based reactive multilayer films on ceramic substrate. The dielectric structure consists of essentially two titanium films separated by a copper oxide (CuO) film, which is just like as a capacitor guaranteeing the initiator will not be discharged until the external voltage has exceeded the breakdown strength of the CuO film. Results of the electrical explosion experiment show that the breakdown strength of 1-μm-thick CuO film is 60 V, and the initiator has “late time discharge” characteristics, which will improve the conversion ratio of the electricity greatly, and there is a nanoscale exothermic reaction in the electrical explosion process. A systematic temperature measurement model based on the “double-line atomic emission spectroscopy of copper element” was presented and used to test the explosion temperature and duration. The ejected explosion flame was seen clearly with a potential temperature exceeding 4500 K for 0.1 ms, 4250 K for 0.35 ms, and 4000 K for 0.5 ms. Besides, electric energy and exothermic reaction create high-temperature products, which discharge to a distance of 1 cm or more. The high temperature and ejected products may be able to ignite the attached energetic materials even if the initiator makes no physical contact. These characteristics of the initiator may open a door to the preparation of the highly efficient and insensitive initiating explosive device.
Richtmyer–Meshkov turbulent mixing arising from an inclined material interface with realistic surface perturbations and reshocked flow
Authors: Hahn M. , Drikakis D. , Youngs D. L. , Williams R. J. R.
Published: April 2011

This paper presents a numerical study of turbulent mixing due to the interaction of a shock wave with an inclined material interface. The interface between the two gases is modeled by geometrical random multimode perturbations represented by different surface perturbation power spectra with the same standard deviation. Simulations of the Richtmyer–Meshkov instability and associated turbulent mixing have been performed using high-resolution implicit large eddy simulations. Qualitative comparisons with experimental flow visualizations are presented. The key integral properties have been examined for different interface perturbations. It is shown that turbulent mixing is reduced when the initial perturbations are concentrated at short wavelengths. The form of the initial perturbation has strong effects on the development of small-scale flow structures, but this effect is diminished at late times.
An ultrafast quantum random number generator with provably bounded output bias based on photon arrival time measurements
Authors: Wahl Michael , Leifgen Matthias , Berlin Michael , Röhlicke Tino , Rahn Hans-Jürgen , Benson Oliver
Published: April 2011

We report the implementation of a quantum random number generator based on photon arrival times. Due to fast and high resolution timing we are able to generate the highest bitrate of any current generator based on photon arrival times. Bias in the raw data due to the exponential distribution of the arrival times is removed by postprocessing which is directly integrated in the field programmable logic of the timing electronics.
Comparing nanowire, multijunction, and single junction solar cells in the presence of light trapping
Authors: Catchpole K. R. , Mokkapati S. , Beck F. J.
Published: April 2011

In this paper we quantify the constraints and opportunities for radial junction nanowire solar cells, compared to single junction and multijunction solar cells, when light trapping is included. Both nanowire and multijunction designs are reliant on a very low level of traps in the junction region, and without this, single junction designs are optimal. If low trap density at the junction can be achieved, multijunction cells lead to higher efficiencies than nanowire cells for a given diffusion length, except in the case of submicron diffusion lengths. Thus the radial junction structure is not in itself an advantage in general, though if nanowires allow faster deposition or better light trapping than other structures they could still prove advantageous.
Sound generation due to unsteady motion of a cylinder
Authors: Sharma Arjun , Lele Sanjiva K.
Published: April 2011

A two-dimensional model problem of sound generation due to prescribed unsteady starting and stopping motion of a circular cylinder is studied by the numerical solution of two-dimensional compressible Navier–Stokes equations. The unsteady flow near the cylinder surface and the sound generation and propagation are analyzed with respect to three parameters: the time scale of the startup and stopping motion, the peak Mach number (based on peak velocity and ambient speed of sound), and the Reynolds number (based on peak velocity, cylinder diameter, ambient density, and dynamic viscosity). The flow behavior is studied for fast (time scale of unsteady motion similar to acoustic time scale) or very slow startup motion. The Mach number is varied between 0.1 and 0.4 and the Reynolds number between 150 and 9500. The accuracy of unsteady flow solution is demonstrated by comparison to the experimental data. For fast startup motion, a sharp peak is observed in the drag curve during the acceleration phase of motion. We find that the dominant contribution to total drag comes from the pressure drag and the peak drag force scales with peak velocity. The startup process introduces weak shock waves in the flow, which contributes to the far-field noise. For slow startup motion, the drag curve is smoother and the drag force scales with the square of the peak velocity. For fast startup motion, the acoustic energy that propagates to the far-field scales with the square of the peak velocity, whereas for slow startup, it scales with the fourth power of the peak velocity. The amount of sound energy radiated to the far-field is found to be a small percentage of the total energy input to set up the entire motion of cylinder. An interpretation for the observed scaling relations in the numerical data is presented using different asymptotically valid reduced forms of the governing equations.
Laser-nucleated acoustic cavitation in focused ultrasound
Authors: Gerold Bjoern , Kotopoulis Spiros , McDougall Craig , McGloin David , Postema Michiel , Prentice Paul
Published: April 2011

Acoustic cavitation can occur in therapeutic applications of high-amplitude focused ultrasound. Studying acoustic cavitation has been challenging, because the onset of nucleation is unpredictable. We hypothesized that acoustic cavitation can be forced to occur at a specific location using a laser to nucleate a microcavity in a pre-established ultrasound field. In this paper we describe a scientific instrument that is dedicated to this outcome, combining a focused ultrasound transducer with a pulsed laser. We present high-speed photographic observations of laser-induced cavitation and laser-nucleated acoustic cavitation, at frame rates of 0.5×106 frames per second, from laser pulses of energy above and below the optical breakdown threshold, respectively. Acoustic recordings demonstrated inertial cavitation can be controllably introduced to the ultrasound focus. This technique will contribute to the understanding of cavitation evolution in focused ultrasound including for potential therapeutic applications.
Enhancement of current injection in organic light emitting diodes with sputter treated molybdenum oxides as hole injection layers
Authors: Wang Po-Sheng , Wu I-Wen , Tseng Wei-Hsuan , Chen Mei-Hsin , Wu Chih-I
Published: April 2011

The enhancement of current density and luminance in organic light emitting diodes is achieved by treating molybdenum oxide (MoO3) hole-injection-layers with slight argon ion sputtering. The sputter treated MoO3 layers provide improvement in current injection efficiency, resulting in better current density which is about ten times higher than that of the reference devices. Photoemission spectroscopy shows that molybdenum in MoO3 is reduced to lower oxidation states after sputter treatment due to the removal of oxygen. As a result, gap states are formed to enhance metallic characteristics of the sputter treated MoO3 surface and facilitate better hole injection efficiency.
Tuning Fano-type resonances in coupled quantum point contacts by applying asymmetric voltages
Authors: Villarreal Rubén C. , Mireles Francisco , Marinero Ernesto E. , Gurney Bruce A.
Published: April 2011

We study the ballistic magnetotransport in a double quantum point contact (QPC) device consisting of a quasi-one-dimensional quantum wire with an embedded islandlike impurity-etched nanohole as in a recently published experiment {J. C. Chen et al., [Appl. Phys. Lett. 94, 012105 (2009)]}. We reproduce the zero field quantized conductance, the interference phenomenon induced by the coupled QPCs, as well as the Ramsauer-like resonances observed in the experiments. At finite magnetic fields Fano-type resonances arises in the conductance due to the formation of localized states at the impurity periphery and to an interedge state resonant coupling effect. It is predicted that the Fano-type resonances can be controlled by an asymmetric confinement of the QPCs.
Self-assembling of 1C4Sn and 4C10Sn clusters in Ge:(C, Sn)
Authors: Elyukhin V. A.
Published: April 2011

Carbon and Sn co-doping transforms Ge into Ge-rich CxSnyGe1−x−y alloy. Self-assembling of 1C4Sn and 4C10Sn clusters decreases the strain energy. These cluster formation processes are competing. The self-assembling conditions of 1C4Sn and 4C10Sn clusters are represented from 0 °C to 800 °C and at 5 × 10−5 ≤ x ≤ 0.015 and 1 × 10−4 ≤ y ≤ 0.015. The conditions demonstrate that only 1C4Sn clusters form if carbon is a minority impurity. Both types of clusters with the preferential formation of 4C10Sn clusters over 1C4Sn occur if the impurity concentrations are nearly equal or if Sn is a minority impurity.
Light extraction efficiency improvement and strain relaxation in InGaN/GaN multiple quantum well nanopillars
Authors: Zhu Jihong , Wang Liangji , Zhang Shuming , Wang Hui , Zhao Degang , Zhu Jianjun , Liu Zongshun , Jiang Desheng , Yang Hui
Published: April 2011

Light extraction efficiency improvement and strain relaxation were observed in InGaN/GaN multiple quantum well (MQW) nanopillars. InGaN/GaN MQW-based LED nanopillar arrays with different diameters varying from about 120 to 250 nm were fabricated via inductively coupled plasma etching using Ni self-assembled nanodots as etching mask. The ray trace method and TiberCAD were used to calculate the light extraction efficiency and strain relaxation in the nanopillars. Remarkably improved light extraction efficiency and strain relaxation were obtained from the calculation results in the nanopillar structures.
A high-pressure atomic force microscope for imaging in supercritical carbon dioxide
Authors: Lea A. S. , Higgins S. R. , Knauss K. G. , Rosso K. M.
Published: April 2011

A high-pressure atomic force microscope (AFM) that enables in situ, atomic scale measurements of topography of solid surfaces in contact with supercritical CO2 (scCO2) fluids has been developed. This apparatus overcomes the pressure limitations of the hydrothermal AFM and is designed to handle pressures up to 100 atm at temperatures up to ∼350 K. A standard optically-based cantilever deflection detection system was chosen. When imaging in compressible supercritical fluids such as scCO2, precise control of pressure and temperature in the fluid cell is the primary technical challenge. Noise levels and imaging resolution depend on minimization of fluid density fluctuations that change the fluid refractive index and hence the laser path. We demonstrate with our apparatus in situ atomic scale imaging of a calcite (CaCO3) mineral surface in scCO2; both single, monatomic steps and dynamic processes occurring on the (${\rm 10\bar 14}$101¯4) surface are presented. This new AFM provides unprecedented in situ access to interfacial phenomena at solid–fluid interfaces under pressure.
[Co/Pd]–NiFe exchange springs with tunable magnetization tilt angle
Authors: Nguyen T. N. Anh , Fang Y. , Fallahi V. , Benatmane N. , Mohseni S. M. , Dumas R. K. , Åkerman Johan
Published: April 2011

We investigate exchange coupled [Co/Pd]5–NiFe thin films. Due to competition between the in-plane shape anisotropy of the NiFe and strong perpendicular magnetic anisotropy of the [Co/Pd]5 multilayer, unique magnetic configurations are achievable. In particular, we explore the out-of-plane magnetization tilt angle of the NiFe layer. Experimental results, based on conventional magnetometry, ferromagnetic resonance, and magnetic force microscopy, agree well with one-dimensional micromagnetic simulations. We find that the tilt angle is highly tunable (0°–60°) over a small range of NiFe thicknesses (4.8–8 nm). Potential applications for high power, zero-field operation spin torque oscillators are discussed.
An analysis of head-on droplet collision with large deformation in gaseous medium
Authors: Zhang Peng , Law Chung K.
Published: April 2011

A theoretical analysis was performed for the head-on collision of two identical droplets in a gaseous environment, with the attendant bouncing and coalescence outcomes, for situations in which the extent of droplet deformation upon collision is comparable to the original droplet radius, corresponding to O(1)–O(10) of the droplet Weber number. The model embodies the essential physics that describes the substantial amount of droplet deformation, the viscous loss through droplet internal motion induced by the deformation, the dynamics and rarefied nature of the gas film between the interfaces of the colliding droplets, and the potential destruction and thereby merging of these interfaces due to the van der Waals attraction force. The theoretical model was applied to investigate collisions involving hydrocarbon and water droplets at sub- and superatmospheric pressures. The results agree well with previous experimental observations in that as the Weber number increases in the range of O(1)–O(10), collision of hydrocarbon droplets at one atmospheric pressure results in the nonmonotonic coalescence-bouncing-coalescence transition, that while bouncing is absent for water droplets at atmospheric pressure, it occurs at higher pressures, and that while bouncing is observed for hydrocarbon droplets at atmospheric pressure, it is absent at lower pressures.
Frequency-addressed tunable transmission in optically thin metallic nanohole arrays with dual-frequency liquid crystals
Authors: Hao Qingzhen , Zhao Yanhui , Juluri Bala Krishna , Kiraly Brian , Liou Justin , Khoo Iam Choon , Huang Tony Jun
Published: April 2011

Frequency-addressed tunable transmission is demonstrated in optically thin metallic nanohole arrays embedded in dual-frequency liquid crystals (DFLCs). The optical properties of the composite system are characterized by the transmission spectra of the nanoholes, and a prominent transmission peak is shown to originate from the resonance of localized surface plasmons at the edges of the nanoholes. An ∼17 nm shift in the transmission peak is observed between the two alignment configurations of the liquid crystals. This DFLC-based active plasmonic system demonstrates excellent frequency-dependent switching behavior and could be useful in future nanophotonic applications.
Stationary residual layers in buoyant Newtonian displacement flows
Authors: Taghavi S. M. , Séon T. , Wielage-Burchard K. , Martinez D. M. , Frigaard I. A.
Published: April 2011

We study buoyant displacement flows with two miscible fluids of equal viscosity in ducts that are inclined at angles close to horizontal (β≈90°). As the imposed velocity (V̂0) is increased from zero, we change from an exchange flow dominated regime to a regime in which the front velocity (V̂f) increases linearly with V̂0. During this transition, we observed an interesting phenomenon in which the layer of displaced fluid remained at the top of the pipe (diameter D̂) during the entire duration of the experiment, apparently stationary for times t̂≳103D̂/V̂0 (the stationary residual layer). Our investigation revealed that this flow marks the transition between flows with a back flow, counter to the imposed flow, and those that displace instantaneously. The same phenomena are observed in pipes (experiments) and in plane channels (two-dimensional numerical computations). A lubrication/thin-film model of the flows also shows the transition from back flow to instantaneous displacement. At long times, this model has a stationary residual layer solution of the type observed, which is found at a unique ratio χ of the axial viscous velocity to the imposed velocity. The prediction of the stationary residual layer from the lubrication model is compared with the transition in observed behavior in our pipe flow experiments and our 2D numerical displacements in the channel. Reasonable agreement is found for the pipe and excellent agreement for the channel. Physically, in either geometry at transition, the upper layer of the fluid is in a countercurrent motion with zero net volumetric flux; the velocity at the interface is positive, but the velocity of the interface is zero. This results from a delicate balance between buoyancy forces against the mean flow and viscous forces in the direction of the mean flow.
Magnetic reconnection in a compressible MHD plasma
Authors: Hesse Michael , Birn Joachim , Zenitani Seiji
Published: April 2011

Using steady-state resistive MHD, magnetic reconnection is reinvestigated for conditions of high resistivity/low magnetic Reynolds number, when the thickness of the diffusion region is no longer small compared to its length. Implicit expressions for the reconnection rate and other reconnection parameters are derived based on the requirements of mass, momentum, and energy conservation. These expressions are solved via simple iterative procedures. Implications specifically for low Reynolds number/high resistivity are being discussed.
Design and development of repetitive capacitor charging power supply based on series-parallel resonant converter topology
Authors: Patel Ankur , Nagesh K. V. , Kolge Tanmay , Chakravarthy D. P.
Published: April 2011

LCL resonant converter based repetitive capacitor charging power supply (CCPS) is designed and developed in the division. The LCL converter acts as a constant current source when switching frequency is equal to the resonant frequency. When both resonant inductors’ values of LCL converter are same, it results in inherent zero current switching (ZCS) in switches. In this paper, ac analysis with fundamental frequency approximation of LCL resonant tank circuit, frequency dependent of current gain converter followed by design, development, simulation, and practical result is described. Effect of change in switching frequency and resonant frequency and change in resonant inductors ratio on CCPS will be discussed. An efficient CCPS of average output power of 1.2 kJ/s, output voltage 3 kV, and 300 Hz repetition rate is developed in the division. The performance of this CCPS has been evaluated in the laboratory by charging several values of load capacitance at various repetition rates. These results indicate that this design is very feasible for use in capacitor-charging applications.
Calibration of ac and dc magnetometers with a Dy2O3 standard
Authors: Chen D.-X. , Skumryev V. , Bozzo B.
Published: April 2011

The ac susceptibility and magnetization curves of a glued Dy2O3 powder sample are measured by an ac susceptometer and a dc superconducting quantum interference device magnetometer, both of which have been calibrated previously. It is shown that the magnetic moment of the paramagnetic sample as a function of field and temperature may be accurately expressed by a combination of the Curie–Weiss law and the Langevin function at T > 45 K with three adjusting parameters, so that the dc magnetization curves and the magnitude and phase of ac susceptibility at different values of dc bias field measured by any magnetometer can be calibrated by using Dy2O3 as a standard. The expressions are empirical and cannot be justified in the entire field and temperature range by existing theories of paramagnetism. Below 10 K, indication of approaching a possible phase transition is found. It is shown that pure Dy2O3 powder may be used as a primary standard, with susceptibility [13.28(T + 17)]−1 emu/Oe/g at T > 50 K and H < 10 kOe, in consistency with the Curie–Weiss law and the quantum mechanical theory of paramagnetism.
Design and characterization of optical heads for interferometric ballistic velocity measurements
Authors: Berkovic Garry , Horovitz Yossef , Moshe Ella , Sadi Yair , Shafir Ehud
Published: April 2011

The design of optical fiber based heads offering high accuracy and bandwidth for use in VISAR (velocity interferometer system for any reflector) experiments measuring ballistic velocities is described. A new, expanded, model for predicting the distance-dependent collection efficiency of the heads is presented. The model is shown to agree very well with experimental results, both within and outside the “depth of field”. Various optical heads are demonstrated, to suit different experimental setups and conditions. Designs offering options for high bandwidths, accurate prealignment, and large stand-off distances are discussed. Results from a typical VISAR experiment are presented, verifying that our designs yield high-quality data.
Physical mechanism of quantum dot to quantum ring transformation upon capping process
Authors: Cao Y. Y. , Li X. L. , Yang G. W.
Published: April 2011

A quantitative thermodynamic model has been established to investigate the evolution mechanism from quantum dot (QD) to quantum ring (QR) during the capping process. Taking the Ge/Si system as an example, we found that there is a critical concentration of Ge required in QDs in order for Si absorption by QDs to take place. When the Ge concentration of QDs decreases to that critical concentration during the Si capping process, Si atoms deposited on the surface of the QDs cannot be absorbed by the QDs and prefer to diffuse to the base side of the QDs. The accumulation of Si atoms on the base side of the QDs results in a great gradient of Ge composition on the surface of the QDs, which leads to the migration of Ge atoms from the top region of the QDs to the base side of the QDs. As a result, the QDs finally evolve into ringlike structures. Importantly, these theoretical results are in good agreement with experiments, which implies that our investigations not only offer general insight into the basic physics involved in QR formation during the capping process, but also provide useful information for experimenters.
Simplified two-layer models of precipitating atmosphere and their properties
Authors: Lambaerts J. , Lapeyre G. , Zeitlin V. , Bouchut F.
Published: April 2011

We derive a two-layer rotating shallow-water model for a moist atmosphere with water vapor condensation and related diabatic heating. Moist convection is represented by additional mass exchanges between the layers, which are determined from the moist enthalpy conservation principle, and related to the precipitation. Various boundary conditions at the lower and upper boundaries may be used. We show that the model reproduces in appropriate limits the main simplified models used previously in the literature for description of the large-scale moist-convective dynamics and precipitation fronts, namely the linear two-layer baroclinic models, the nonlinear two-layer quasigeostrophic model, and the nonlinear one-layer moist-convective rotating shallow-water model. We study the properties of the equations of the model, with special attention to the hyperbolicity loss, which is inherent to multilayer shallow-water models, and to the front propagation. Numerical illustrations of these properties are given with the help of a recently proposed high-resolution finite-volume numerical scheme with precipitation sources/sinks.
Multiple scaling in the ultimate regime of thermal convection
Authors: Grossmann Siegfried , Lohse Detlef
Published: April 2011

Very different types of scaling of the Nusselt number Nu with the Rayleigh number Ra have experimentally been found in the very large Ra regime beyond 1011. We understand and interpret these results by extending the unifying theory of thermal convection [Grossmann and Lohse, Phys. Rev. Lett. 86, 3316 (2001)] to the very large Ra regime where the kinetic boundary-layer is turbulent. The central idea is that the spatial extension of this turbulent boundary-layer with a logarithmic velocity profile is comparable to the size of the cell. Depending on whether the thermal transport is plume dominated, dominated by the background thermal fluctuations, or whether also the thermal boundary-layer is fully turbulent (leading to a logarithmic temperature profile), we obtain effective scaling laws of about Nu∝Ra0.14, Nu∝Ra0.22, and Nu∝Ra0.38, respectively. Depending on the initial conditions or random fluctuations, one or the other of these states may be realized. Since the theory is for both the heat flux Nu and the velocity amplitude Re, we can also give the scaling of the latter, namely, Re∝Ra0.42, Re∝Ra0.45, and Re∝Ra0.50 in the respective ranges.
Economical design of gate-commutated inverters for the grid-tied distributed generators
Authors: Islam Mujahidul , Omole Adedamola , Islam Arif , Domijan Alexander
Published: April 2011

The cost-effectiveness of small distributed generating resources is vital to the success of the high penetration of distributed generators within the microgrid concept. A common mechanism is the use of highly efficient inverters following the electrical storage systems. In this paper, the design of a basic inverter deploying a switching power amplifier is discussed. The amplifier acts like a power booster that taps the grid current as its frequency reference. The inverter transfer function was examined against voltage droop characteristics and was found to be in compliance with the IEEE 1547 standard for microgrid. The basic design simply utilizes the linear rise of voltage for the small triggering angle where the sinus of angle can be approximated as the angle in radians. This inherently performs a similar action such as a pulse width modulator for a narrow band. This inherent feature saves cost because it precludes the need for an extra power controller.
Three-dimensional surface profiling and optical characterization of liquid microlens using a Shack–Hartmann wave front sensor
Authors: Li Chenhui , Hall Gunnsteinn , Zeng Xuefeng , Zhu Difeng , Eliceiri Kevin , Jiang Hongrui
Published: April 2011

We demonstrate three-dimensional (3D) surface profiling of the water–oil interface in a tunable liquid microlens using a Shack–Hartmann wave front sensor. The principles and the optical setup for achieving 3D surface measurements are presented and a hydrogel-actuated liquid lens was measured at different focal lengths. The 3D surface profiles are then used to study the optical properties of the liquid lens. Our method of 3D surface profiling could foster the improvement of liquid lens design and fabrication, including surface treatment and aberration reduction.
Strain balanced quantum posts
Authors: Alonso-Álvarez D. , Alén B. , Ripalda J. M. , Llorens J. M. , Taboada A. G. , Briones F. , Roldán M. A. , Hernández-Saz J. , Hernández-Maldonado D. , Herrera M. , Molina S. I.
Published: April 2011

Quantum posts are assembled by epitaxial growth of closely spaced quantum dot layers, modulating the composition of a semiconductor alloy, typically InGaAs. In contrast with most self-assembled nanostructures, the height of quantum posts can be controlled with nanometer precision, up to a maximum value limited by the accumulated stress due to the lattice mismatch. Here, we present a strain compensation technique based on the controlled incorporation of phosphorous, which substantially increases the maximum attainable quantum post height. The luminescence from the resulting nanostructures presents giant linear polarization anisotropy.
Saturable absorbing dynamics of GaInN multiquantum well structures
Authors: Miyajima Takao , Kono Shunsuke , Watanabe Hideki , Oki Tomoyuki , Koda Rintaro , Kuramoto Masaru , Ikeda Masao , Yokoyama Hiroyuki
Published: April 2011

We evaluated saturation energies and absorption recovery time dependent on reverse-bias voltage for a waveguide-coupled GaInN multiquantum well saturable absorber in a bisectional laser structure. When the applied reverse-bias was increased from 5 to 20 V, the saturation energy at 405 nm monotonically increased from 5 to 14 pJ; the linear absorption coefficient at 405 nm showed the same dependence. These dependences are different from those observed in an AlGaAs multiquantum well. The absorption recovery time was shortened to 3 ps when a highly reverse-bias voltage of 20 V was applied.
Impact of ultrathin Al2O3 diffusion barriers on defects in high-k LaLuO3 on Si
Authors: Shen S. , Liu Y. , Gordon R. G. , Brillson L. J.
Published: April 2011

We used depth-resolved cathodoluminescence spectroscopy (DRCLS) to measure trap energies and relative densities in metal/high-κ dielectric LaLuO3/Si stacks, defects produced by LaLuO3–Si interdiffusion, and suppression of these defects by monolayer-thick Al2O3 interlayers. DRCLS reveals deep levels at 3.8, 4.2, and 4.7 eV above the valence band, consistent with LaLuO3 oxygen vacancies predicted by theory and a 5.5 eV band gap. Oxygen annealing produces LaLuO3/Si interdiffusion that increases 3.8 eV defect density and which a 0.4 nm Al2O3 completely removes. Transmission electron microscopy and current leakage results shows that Al2O3 prevent LaLuO3/Si silicate layer formation and dramatically lower defects with oxygen annealing.
A photovoltaic system with three solar cells and a band-stop optical filter
Authors: Mokri A. , Emziane M.
Published: April 2011

One approach for designing high-efficiency photovoltaic systems is to use several solar cells. One technique is to stack several solar cells with different energy band gaps on each other and concentrate sunlight on them, but the technical challenges and the manufacturing cost increase as the number of cells increases. Another technique is to keep the cells apart and split the sunlight into different sub-beams and direct the sub-beams toward separate cells, which are made of semiconductors with specific energy band gaps. In this study, we are proposing a novel photovoltaic system that combines both approaches for the sake of reducing the manufacturing cost of the system and increasing the efficiency. The system involves three solar cells: two cells are made of GaAs (1.42 eV) and Ge (0.66 eV), which are almost lattice matched, and the other cell is made of Si (1.12 eV), which is kept apart because it is not lattice matched to the two other cells. Different from the systems reported in literature, the proposed system involves a band-stop optical filter instead of a low-pass optical filter. This approach demonstrates the use of double-junction cells made of lattice matched materials, while the top cell has a high energy band gap (GaAs) and the bottom cell has a low energy band gap (Ge). In this paper, we describe the architecture of the proposed system, its features, the modeling approach adopted, and the system performance under the standard conditions.
Observation of slow-light in a metamaterials waveguide at microwave frequencies
Authors: Savo Salvatore , Casse B. D. F. , Lu Wentao , Sridhar Srinivas
Published: April 2011

We report an experimental observation of slow-light in the GHz microwave regime utilizing the mechanism of the degeneracy of forward and backward waves in a planar waveguide consisting of a dielectric core cladded by single-negative metamaterial. The metamaterial cladding consists of periodic arrays of metallic split-ring resonators, exhibiting an effective negative permeability. Group delay dispersions obtained from pulsed measurements are in complete agreement with theoretical predictions.
In search of energy landscape for network glasses
Authors: Golovchak Roman , Kovalskiy Andriy , Shpotyuk Oleh , Jain Himanshu
Published: April 2011

Quick scanning extended x-ray absorption fine-structure spectroscopy is used to obtain in situ structural information on the real-time response of network glasses at the nanoscale level of atomic organization to the temperature ramp through the glass transition range. The results testify nonlinear, real-time temperature response indicative of nanoscale dynamic heterogeneity in disordered systems with intermediate fragility, related to the intermetabasin transitions within potential energy/enthalpy landscape.
In situ and noncontact measurement of silicon membrane thermal conductivity
Authors: Liu Xi , Wu Xiaoming , Ren Tianling
Published: April 2011

An in situ and noncontact method using micro-Raman spectroscopy for silicon membrane thermal conductivity measurement was proposed. The considerations of temperature dependence of thermal conductivity and nonuniform temperature distribution in the laser spot improved the measurement accuracy. The thermal conductivity was obtained by solving two-dimensional nonlinear Fourier heat transfer equation and reconstruction of the Raman spectrum of specimen in laser spot. At room temperature, the thermal conductivities of two silicon membranes in the thickness of ∼495 nm and ∼699 nm were measured as 118±6 W/(m K) and 123±10 W/(m K), respectively, which are consistent with theoretic values from Boltzmann transfer equation.
High-temperature thermoelectric properties of Cu2Ga4Te7 with defect zinc-blende structure
Authors: Plirdpring Theerayuth , Kurosaki Ken , Kosuga Atsuko , Ishimaru Manabu , Harnwunggmoung Adul , Sugahara Tohru , Ohishi Yuji , Muta Hiroaki , Yamanaka Shinsuke
Published: April 2011

Here we show the high-temperature thermoelectric (TE) properties of Cu2Ga4Te7 with the defect zinc-blende structure in which one-seventh of the cation sites are structural vacancies. Cu2Ga4Te7 exhibited relatively low electrical resistivity (ρ) and thermal conductivity (κ) and moderate positive Seebeck coefficient (S) at high temperatures, making this compound a promising high-performance p-type TE material. At 940 K, the S, ρ, and κ were +215 μV K−1, 10.1×10−5 Ω m, and 0.67 Wm−1 K−1, respectively, which resulted in the maximum dimensionless figure of merit ZT (=S2T/ρ/κ, where T is the absolute temperature) of 0.64.
Manipulation of multidimensional plasmonic spectra for information storage
Authors: Chen Wei Ting , Wu Pin Chieh , Chen Chen Jung , Weng Chun-Jen , Lee Hsin-Chen , Yen Ta-Jen , Kuan Chieh-Hsiung , Mansuripur Masud , Tsai Din Ping
Published: April 2011

We demonstrate a concept of optical data storage through plasmonic resonances of metallic nanostructures. Metallic nanostructures exhibit strong variations in their reflectance and/or transmittance spectra due to surface plasmon polariton resonances. We study the variations in spectra through 50×50 arrays of repeated unit cells covering a total area of ∼50×50 μm2. Each cell contains ten different nanofeatures, such as an ellipse, a ring, a circle, a triangle, a square, etc. The size of each unit-cell is 500×500 nm2, and the periodicity is 1.0 μm. The variations in spectra are obvious enough to be distinguished and then retrieved.
Light-induced structural changes in Eu-doped (Pb,La)(Zr,Ti)O3 ceramics
Authors: Myint Thandar , Gunawidjaja Ray , Eilers Hergen
Published: April 2011

Fluorescence spectra of poled and unpoled Eu-doped (Pb,La)(Zr,Ti)O3 ceramics with various compositions were measured using 580 nm excitation. The ratio of the intensities of the Eu3+ D50→F72/D50→F71 fluorescence transitions was used as an indicator for the symmetry of the Eu3+ site. As the symmetry decreases, the ratio increases. Increasing the Zr content in (Pb,La)(Zr,Ti)O3 increases the ratio, indicating that the symmetry of the Eu3+ site decreases. Exposure of the Eu-doped (Pb,La)(Zr,Ti)O3 samples to UV light also increases the intensity ratio, indicating that UV light exposure leads to structural distortions in Eu-doped (Pb,La)(Zr,Ti)O3 samples, lowering the Eu3+ site symmetry.
Photoacoustic detection of CO2 based on LABVIEW at 10.303 μm
Authors: Zhao Junjuan , Zhao Zhan , Du Lidong , Geng Daoqu , Wu Shaohua
Published: April 2011

A detailed study on a photoacoustic carbon dioxide detection system, through sound card based on virtual instrument, is presented in this paper. In this system, the CO2 concentration was measured with the non-resonant photoacoustic cell technique through measuring the photoacoustic signal caused by the CO2. In order to obtain small photoacoustic signals buried in noise, a measurement software was designed with LABVIEW. It has functions of Lock-in Amplifier, digital filter, and signal generator; can also be used to achieve spectrum analysis and signal recovery; has been provided with powerful function for data processing and communication with other measuring instrument. The test results show that the entire system has an outstanding measuring performance with the sensitivity of 10μv between 10–44 KHz. The non-resonance test of the trace gas analyte CO2 conducted at 100 Hz demonstrated large signals (15.89 mV) for CO2 concentrations at 600 ppm and high signal-to-noise values (∼ 85:1).
Studying single nanocrystals under high pressure using an x-ray nanoprobe
Authors: Wang Lin , Ding Yang , Patel Umesh , Yang Wenge , Xiao Zhili , Cai Zhonghou , Mao Wendy L. , Mao Ho-kwang
Published: April 2011

In this report, we demonstrate the feasibility of applying a 250-nm focused x-ray beam to study a single crystalline NbSe3 nanobelt under high-pressure conditions in a diamond anvil cell. With such a small probe, we not only resolved the distribution and morphology of each individual nanobelt in the x-ray fluorescence maps but also obtained the diffraction patterns from individual crystalline nanobelts with thicknesses of less than 50 nm. Single crystalline diffraction measurements on NbSe3 nanobelts were performed at pressures up to 20 GPa.
A formula for the *-core of an ideal
Authors: Fouli Louiza , Vassilev Janet , Vraciu Adela
Published: April 2011

Expanding on the 2010 work of Fouli and Vassilev, we determine a formula for the

∗

-

core

*\textrm {-}\textrm {core}

of an ideal in two different settings: (1) in a Cohen–Macaulay local ring of characteristic

p
>
0

p>0

, with perfect residue field and test ideal of depth at least two, where the ideal has a minimal

∗
*

-reduction that is a parameter ideal, and (2) in a normal local domain of characteristic

p
>
0

p>0

, with perfect residue field and

m

\mathfrak {m}

-primary test ideal, where the ideal is a sufficiently high Frobenius power of an ideal. We also exhibit some examples where our formula fails if our hypotheses are not met.