bluuebunny/crossref_metadata_2025 huggingface dataset:
Oxygen Consumption and Blood Flow Coupling in Human Motor Cortex during Intense Finger Tapping: Implication for a Role of Lactate
Authors: Vafaee Manouchehr S , Vang Kim , Bergersen Linda H , Gjedde Albert
Published: July 2012

Rates of cerebral blood flow (CBF) and glucose consumption (CMRglc) rise in cerebral cortex during continuous stimulation, while the oxygen-glucose index (OGI) declines as an index of mismatched coupling of oxygen consumption (cerebral metabolic rate of oxygen—CMRO2) to CBF and CMRglc. To test whether the mismatch reflects a specific role of aerobic glycolysis during functional brain activation, we determined CBF and CMRO2 with positron emission tomography (PET) when 12 healthy volunteers executed finger-to-thumb apposition of the right hand. Movements began 1, 10, or 20 minutes before administration of the radiotracers. In primary and supplementary motor cortices and cerebellum, CBF had increased at 1 minute of exercise and remained elevated for the duration of the 20-minute session. In contrast, the CMRO2 numerically had increased insignificantly in left M1 and supplementary motor area at 1 minute, but had declined significantly at 10 minutes, returning to baseline at 20 minutes. As measures of CMRglc are impossible during short-term activations, we used measurements of CBF as indices of CMRglc. The decline of CMRO2 at 10 minutes paralleled a calculated decrease of OGI at this time. The implied generation of lactate in the tissue suggested an important hypothetical role of the metabolite as regulator of CBF during activation.
Effects of Therapeutic Hypothermia on Inflammasome Signaling after Traumatic Brain Injury
Authors: Tomura Satoshi , de Rivero Vaccari Juan Pablo , Keane Robert W , Bramlett Helen M , Dietrich W Dalton
Published: July 2012

Traumatic brain injury (TBI) activates the NALP1/NLRP1 inflammasome, which is an important component of the early innate inflammatory response to injury. We investigated the influence of therapeutic hypothermia on inflammasome activation after TBI. Adult male Sprague–Dawley rats were subjected to moderate fluid percussion brain injury. Temperature manipulation (33°C or 37°C) was initiated 30 minutes after TBI and maintained for 4 hours. At 4 or 24 hours after TBI, traumatized cortex and hippocampus were prepared for immunoblot or immunohistochemical analysis. In the normothermic groups, caspase-1, caspase-11 and expression of the purinergic receptor P2X7 increased at 24 hours after TBI. Posttraumatic hypothermia lead to decreased expression of these proteins at 24 hours compared with normothermic levels. Immunocytochemical studies showed that posttraumatic hypothermia also decreased caspase-1 staining in cerebral cortical neurons compared with normothermic TBI. Cultured cortical neurons subjected to stretch injury demonstrated significant secretion of caspase-1 into the culture medium and caspase-3 activation, both results reduced by hypothermic treatment. Posttraumatic hypothermia decreases inflammasome signaling in neurons and reduces the innate immune response to TBI at 24 hours after injury. Therapeutic hypothermia may protect the injured central nervous system by targeting the detrimental consequences of the innate immune response to injury.
Effects of dust particles in plasma kinetics: Ion dynamics time scales
Authors: de Angelis U. , Tolias P. , Ratynskaia S.
Published: July 2012

The self-consistent kinetic theory of dusty plasmas [V. N. Tsytovich and U. de Angelis, Phys. Plasmas 6, 1093 (1999)] is extended to frequency regimes relevant for ion dynamics, accounting for both constant and fluctuating plasma sources. In contrast to earlier models, binary plasma collisions are no longer neglected with respect to collisions with dust; hence, the model developed here is also valid for low dust densities. Expressions are found for the system’s permittivity, the ion collision integral, and the spectral densities of ion density fluctuations. The structure of the ion kinetic equation is analyzed, and applications of the model for both astrophysical and laboratory environments are discussed.
A high power ion thruster for deep space missions
Authors: Polk James E. , Goebel Dan M. , Snyder John S. , Schneider Analyn C. , Johnson Lee K. , Sengupta Anita
Published: July 2012

The Nuclear Electric Xenon Ion System ion thruster was developed for potential outer planet robotic missions using nuclear electric propulsion (NEP). This engine was designed to operate at power levels ranging from 13 to 28 kW at specific impulses of 6000–8500 s and for burn times of up to 10 years. State-of-the-art performance and life assessment tools were used to design the thruster, which featured 57-cm-diameter carbon-carbon composite grids operating at voltages of 3.5–6.5 kV. Preliminary validation of the thruster performance was accomplished with a laboratory model thruster, while in parallel, a flight-like development model (DM) thruster was completed and two DM thrusters fabricated. The first thruster completed full performance testing and a 2000-h wear test. The second successfully completed vibration tests at the full protoflight levels defined for this NEP program and then passed performance validation testing. The thruster design, performance, and the experimental validation of the design tools are discussed in this paper.
Monitoring microbial population dynamics at low densities
Authors: Julou Thomas , Desprat Nicolas , Bensimon David , Croquette Vincent
Published: July 2012

We propose a new and simple method for the measurement of microbial concentrations in highly diluted cultures. This method is based on an analysis of the intensity fluctuations of light scattered by microbial cells under laser illumination. Two possible measurement strategies are identified and compared using simulations and measurements of the concentration of gold nanoparticles. Based on this comparison, we show that the concentration of Escherichia coli and Saccharomyces cerevisiae cultures can be easily measured in situ across a concentration range that spans five orders of magnitude. The lowest measurable concentration is three orders of magnitude (1000×) smaller than in current optical density measurements. We show further that this method can also be used to measure the concentration of fluorescent microbial cells. In practice, this new method is well suited to monitor the dynamics of population growth at early colonization of a liquid culture medium. The dynamic data thus obtained are particularly relevant for microbial ecology studies.
Influence of the winding number on field- and current driven dynamics of magnetic vortices and antivortices
Authors: Martens Michael , Kamionka Thomas , Drews André , Krüger Benjamin , Meier Guido
Published: July 2012

The excitation of magnetic singularities in ferromagnetic thin films by radio frequency currents and fields is of high technological interest. Theoretical and experimental work often focuses on the dynamics of vortices and not on antivortices as their topological counterparts with inverted winding number of the domain structure. A comprehensive analytical description is presented for vortices and antivortices excited by spatial homogeneous two-dimensional in-plane currents and fields. In particular, the case of rotational excitation is investigated that is known to exhibit an efficient and selective coupling to the intrinsic gyrotropic eigenmode but here shows a crucial dependence on the winding number. The analytical model is compared with numerical results obtained by micromagnetic simulations.
Correlation of spectral features of photoluminescence with residual native defects of ZnO thin films annealed at different temperatures
Authors: Kukreja L. M. , Misra P. , Fallert J. , Phase D. M. , Kalt H.
Published: July 2012

We investigated the effects of post-growth annealing in the temperature range of 873 to 1273 K on the spectral features of photoluminescence (PL) vis-à-vis the crystalline and compositional native defects of ZnO thin films grown at 773 K by pulsed laser deposition (PLD) on sapphire substrates. It is found in the PL spectra at 10 K that the deep level emission (DLE) shifted from red-orange spectral region of ∼1.8–2.4 eV to yellow–green region of ∼2.4–2.9 eV with the increasing temperature of annealing. We propose that the PL in red-orange region originating from the singly ionized oxygen vacancies diminished due to increased replenishment of oxygen with increasing annealing temperature and that in the yellow–green region originating from the oxygen interstitials and/or zinc vacancies increased due to enhanced concentration of these point defects. As the annealing temperature was increased, the overall intensity of PL in the DLE region increased slightly up to 973 K but beyond that it increased steeply and made a quantum leap at 1073 K. In contrast to that, intensity of PL due to the near band-edge emission (NBE) in UV region of ∼3.15 to 3.45 eV increased very steeply up to the annealing temperature of 973 K, which is found to be due to improvement in the crystalline and compositional qualities of the films and beyond that it dropped drastically due to deteriorations of these qualities. The high resolution PL spectra at 10 K in the NBE region mainly consisted of peaks due to the recombinations of neutral donor bound excitons’ complexes (D0X) at ∼3.36 eV, free excitons (FXA) at ∼3.38 eV with their conspicuous LO phonon replicas and some other features such as exciton complexes bound to surface states or transitions of conduction band electrons to acceptor levels located in stacking faults and recombination of neutral acceptor bound excitons. The relative intensities of these individual features were strongly dependent on the annealing temperature of the films and the ensuing crystalline and compositional qualities. The 10 K PL spectra from the interfacial region of the annealed ZnO films and the sapphire substrates observed from the backside of the samples showed that the annealing temperature affected the crystalline and compositional qualities at the interface in a complex manner. Particularly, the features corresponding to the interface deteriorations resulting from the diffusion of Al into the ZnO films and the crystalline defects at the interface caused by the sputtering due to the PLD plume were prominently present in these PL spectra. These studies provide deeper insight into the fundamental PL processes in ZnO thin films annealed at different temperatures.
Short-term prediction of dynamical behavior of flame front instability induced by radiative heat loss
Authors: Gotoda Hiroshi , Ikawa Takuya , Maki Koshiro , Miyano Takaya
Published: July 2012

We apply nonlinear forecasting to the time series of the flame front instability induced by radiative heat loss to test for the short-term predictability and long-term unpredictability characteristic of deterministic chaos in flame front instability. Our results indicate that the flame front instability represents high-dimensional chaos generated via the period-doubling cascade process reported in our previous study [H. Gotoda, K. Michigami, K. Ikeda, and T. Miyano, Combust Theory Modell. 14, 479 (2010)], while its short-term behavior is predictable using a local nonlinear predictor based on the Sugihara-May method [H. Gotoda, H. Nikimoto, T. Miyano, and S. Tachibana, Chaos 20, 013124 (2011); G. Sugihara and R. M. May, Nature 344, 734 (1990)] as well as a generalized radial basis function network as a global nonlinear predictor. The feasibility of a new approach based on short-term prediction is also discussed in this work from the practical viewpoint of combustion systems.
Fuchsian Riemann-Hilbert problem for “real doubles” of Hurwitz Frobenius manifolds
Authors: Khreibani H. , Shramchenko V.
Published: July 2012

A solution to the matrix Fuchsian Riemann-Hilbert problem (inverse monodromy problem) corresponding to “real doubles” of Dubrovin's Frobenius structures on Hurwitz spaces is constructed. The solution is given in terms of certain meromorphic differentials integrated over a basis of an appropriate relative homology space of the Riemann surface. The relationship with the solution of Fuchsian Riemann-Hilbert problem for Dubrovin's Hurwitz Frobenius manifolds is established. A solution of the Riemann-Hilbert problem corresponding to deformations of the “real doubles” is also given.
Calibration and analysis of spatially resolved x-ray absorption spectra from a nonuniform plasma
Authors: Knapp P. F. , Hansen S. B. , Pikuz S. A. , Shelkovenko T. A. , Hammer D. A.
Published: July 2012

We report here the calibration and analysis techniques used to obtain spatially resolved density and temperature measurements of a pair of imploding aluminum wires from x-ray absorption spectra. A step wedge is used to measure backlighter fluence at the film, allowing transmission through the sample to be measured with an accuracy of ±14% or better. A genetic algorithm is used to search the allowed plasma parameter space and fit synthetic spectra with 20 μm spatial resolution to the measured spectra, taking into account that the object plasma nonuniformity must be physically reasonable. The inferred plasma conditions must be allowed to vary along the absorption path in order to obtain a fit to the spectral data. The temperature is estimated to be accurate to within ±25% and the density to within a factor of two. This information is used to construct two-dimensional maps of the density and temperature of the object plasma.
Effect of nonthermality of electrons on the speed and shape of ion-acoustic solitary waves in a warm plasma
Authors: Abdelwahed H. G. , El-Shewy E. K.
Published: July 2012

Nonlinear ion-acoustic solitary waves in a warm collisionless plasma with nonthermal electrons are investigated by a direct analysis of the field equations. The Sagdeev’s potential is obtained in terms of ion acoustic speed by simply solving an algebraic equation. It is found that the amplitude and width of the ion-acoustic solitons as well as the parametric regime where the solitons can exist are sensitive to the population of energetic non-thermal electrons. The soliton and double layer solutions are obtained as a small amplitude approximation.
Influence of heat and particle fluxes nonlocality on spatial distribution of plasma density in two-chamber inductively coupled plasma sources
Authors: Kudryavtsev A. A. , Serditov K. Yu.
Published: July 2012

This study presents 2D simulations of the two-chamber inductively coupled plasma source where power is supplied in the small discharge chamber and extends by electron thermal conductivity mechanism to the big diffusion chamber. Depending on pressure, two main scenarios of plasma density and its spatial distribution behavior were identified. One case is characterized by the localization of plasma in the small driver chamber where power is deposed. Another case describes when the diffusion chamber becomes the main source of plasma with maximum of the electron density. The differences in spatial distribution are caused by local or non-local behavior of electron energy transport in the discharge volume due to different characteristic scale of heat transfer with electronic conductivity.
Measuring optical phonon dynamics in a bismuth thin film through a surface plasmon resonance
Authors: Chen Zhiyuan , DeCamp Matthew F.
Published: July 2012

Surface plasmon resonances have become a useful tool for measuring coherent motion in solids, ranging from nanoparticle dynamics to acoustic vibrations in thin films. The non-linear electronic response near the surface plasmon resonance can significantly enhance transient optical measurements, making efficient detection of the coherent motion possible. In this work, we measure coherent optical phonon dynamics in a thin bismuth film through a surface plasmon resonance. We observe distinct changes in the measured amplitude and phase of the fully symmetric A1g optical phonon mode that are not explained through the standard model of displacive excitation of coherent phonons. In particular, near the surface plasmon resonance, we observe a strong polarization dependence on the amplitude and phase of the optical phonon. These results are explained through the rapid change of the optical reflectivity as a function of the complex dielectric constant near the surface plasmon resonance.
Far-infrared polarimetry diagnostic for measurement of internal magnetic field dynamics and fluctuations in the C-MOD Tokamak (invited)
Authors: Bergerson W. F. , Xu P. , Irby J. H. , Brower D. L. , Ding W. X. , Marmar E. S.
Published: July 2012

A laser-based (2.55 THz) mulitchord polarimeter is now operational on Alcator C-Mod and is used to make measurements of the internal magnetic field structure as well as plasma fluctuations. The polarimeter is designed to measure the Faraday effect for high-field (up to 8.3 T) and high-density (up to 5 × 1020 m−3) ITER relevant plasma conditions. Initial 3 chord tests are consistent with magnetic equilibrium reconstructions and indicate no measurable contamination from the toroidal magnetic field due to the Cotton-Mouton effect or misalignment. Time response of <1 μs enables the measurement of fast equilibrium temporal dynamics as well as high-frequency fluctuations.
Development of a mirror-based endoscope for divertor spectroscopy on JET with the new ITER-like wall (invited)
Authors: Huber A. , Brezinsek S. , Mertens Ph. , Schweer B. , Sergienko G. , Terra A. , Arnoux G. , Balshaw N. , Clever M. , Edlingdon T. , Egner S. , Farthing J. , Hartl M. , Horton L. , Kampf D. , Klammer J. , Lambertz H. T. , Matthews G. F. , Morlock C. , Murari A. , Reindl M. , Riccardo V. , Samm U. , Sanders S. , Stamp M. , Williams J. , Zastrow K. D. , Zauner C. ,   JET-EFDA Contributors
Published: July 2012

A new endoscope with optimised divertor view has been developed in order to survey and monitor the emission of specific impurities such as tungsten and the remaining carbon as well as beryllium in the tungsten divertor of JET after the implementation of the ITER-like wall in 2011. The endoscope is a prototype for testing an ITER relevant design concept based on reflective optics only. It may be subject to high neutron fluxes as expected in ITER. The operating wavelength range, from 390 nm to 2500 nm, allows the measurements of the emission of all expected impurities (W I, Be II, C I, C II, C III) with high optical transmittance (≥30% in the designed wavelength range) as well as high spatial resolution that is ≤2 mm at the object plane and ≤3 mm for the full depth of field (±0.7 m). The new optical design includes options for in situ calibration of the endoscope transmittance during the experimental campaign, which allows the continuous tracing of possible transmittance degradation with time due to impurity deposition and erosion by fast neutral particles. In parallel to the new optical design, a new type of possibly ITER relevant shutter system based on pneumatic techniques has been developed and integrated into the endoscope head. The endoscope is equipped with four digital CCD cameras, each combined with two filter wheels for narrow band interference and neutral density filters. Additionally, two protection cameras in the λ > 0.95 μm range have been integrated in the optical design for the real time wall protection during the plasma operation of JET.
Stereolithography based method of creating custom gas density profile targets for high intensity laser-plasma experiments
Authors: Jolly S. W. , He Z. , McGuffey C. , Schumaker W. , Krushelnick K. , Thomas A. G. R.
Published: July 2012

Laser based stereolithography methods are shown to be useful for production of gas targets for high intensity laser-plasma interaction experiments. A cylindrically symmetric nozzle with an opening of approximately 100 μm and a periodic attachment of variable periodicity are outlined in detail with associated density profile characterization. Both components are durable within the limits of relevant experiments.
Correlation between oxygen vacancies and magnetism in Mn-doped Y2O3 nanocrystals investigated by defect engineering techniques
Authors: Wu T. S. , Chen Y. C. , Shiu Y. F. , Peng H. J. , Chang S. L. , Lee H. Y. , Chu P. P. , Hsu C. W. , Chou L. J. , Pao C. W. , Lee J. F. , Kwo J. , Hong M. , Soo Y. L.
Published: July 2012

Defect engineering techniques have been employed to generate and remove oxygen vacancy defects in nanoparticles of Y2O3:Mn diluted magnetic oxide (DMO). These samples were prepared by thermal decomposition method followed by a series of thermal annealing in oxygen and forming gas. The x-ray absorption analysis reveals that O vacancies surrounding Mn and Y atoms were appreciably increased by forming-gas-annealing and decreased by oxygen-annealing, accompanied by enhanced and reduced saturation magnetization as demonstrated by magnetic measurements, respectively. Our results demonstrate strong correlation between magnetism and O vacancies and therefore strongly support the bound magnetic polaron model for these high-k DMOs.
Charge transfer in semi-insulating Fe-doped GaN
Authors: Dashdorj J. , Zvanut M. E. , Harrison J. G. , Udwary K. , Paskova T.
Published: July 2012

Charge transfer kinetics is studied in free-standing Fe-doped GaN using photo-induced electron paramagnetic resonance (EPR). Samples with Fe concentrations of 1017 cm−3 reveal an increase in Fe3+ during exposure with photon energy greater than 0.8 eV, while samples with higher Fe concentrations exhibit a decrease in the Fe3+ under the same conditions. Steady-state photo-EPR measurements of the most lightly doped sample imply the existence of an Fe2+/3+ defect level within 0.8 eV of the conduction band edge consistent with earlier work, but time-dependent measurements of more heavily doped crystals indicate a multi-step charge transfer process. Analysis of time-dependent photo-EPR data reveals that charge exchange may be separated into two processes, one that is temperature independent and one that depends monotonically on temperature. While a physical model for the charge transfer is not apparent, likely scenarios involve charge trapping at extended defects and phonon interactions.
Linear instability of the Darcy–Hadley flow in an inclined porous layer
Authors: Barletta A. , Rees D. A. S.
Published: July 2012

The buoyant flow in a saturated porous layer inclined to the horizontal is studied under the assumption that the plane impermeable boundaries are subject to linear temperature distributions up the layer. The basic solution is stationary and such that the temperature gradient is inclined to the boundary walls. Two parameters govern the thermal boundary conditions: the Rayleigh number, associated with the component of the basic temperature gradient orthogonal to the boundaries, the Hadley-Rayleigh number, associated with the component of the basic temperature gradient parallel to the boundaries. The linear stability of the basic solution with respect to the longitudinal normal modes is studied by employing two different numerical methods: a collocation method of weighted residuals, and a Runge–Kutta solver. Different regimes are considered: the upward–cooling condition, the upward–heating condition, and the buoyancy–balanced condition. The latter regime implies a vanishing velocity distribution and a vertical temperature gradient in the basic state. In the upward–cooling regime, for a fixed Hadley–Rayleigh number, the increasing inclination to the horizontal leads to a destabilising effect. When the inclination exceeds a threshold angle that depends on the Hadley–Rayleigh number, the basic solution becomes unstable for every Rayleigh number. The reverse holds true in the upward–heating regime, where the increasing inclination to the horizontal stabilises the basic flow. The general oblique normal modes are finally considered. It is shown that the longitudinal modes are selected at the onset of convection, except for the case of the Darcy–Bénard limiting case where all the oblique modes are equivalent.
Novel mono-static arrangement of the ASDEX Upgrade high field side reflectometers compatible with electron cyclotron resonance heating stray radiation
Authors: Silva A. , Varela P. , Meneses L. , Manso M. ,   ASDEX Upgrade Team
Published: July 2012

The ASDEX Upgrade frequency modulated continuous wave broadband reflectometer system uses a mono-static antenna configuration with in-vessel hog-horns and 3 dB directional couplers. The operation of the new electron cyclotron resonance heating (ECRH) launcher and the start of collective Thomson scattering experiments caused several events where the fragile dummy loads inside the high field side directional couplers were damaged, due to excessive power resulting from the ECRH stray fields. In this paper, we present a non-conventional application of the existing three-port directional coupler that hardens the system to the ECRH stray fields and at the same time generates the necessary reference signal. Electromagnetic simulations and laboratory tests were performed to validate the proposed solution and are compared with the in-vessel calibration tests.
A dark-line two-dimensional magneto-optical trap of 85Rb atoms with high optical depth
Authors: Zhang Shanchao , Chen J. F. , Liu Chang , Zhou Shuyu , Loy M. M. T. , Wong G. K. L. , Du Shengwang
Published: July 2012

We describe the apparatus of a dark-line two-dimensional (2D) magneto-optical trap (MOT) of 85Rb cold atoms with high optical depth (OD). Different from the conventional configuration, two (of three) pairs of trapping laser beams in our 2D MOT setup do not follow the symmetry axes of the quadrupole magnetic field: they are aligned with 45° angles to the longitudinal axis. Two orthogonal repumping laser beams have a dark-line volume in the longitudinal axis at their cross over. With a total trapping laser power of 40 mW and repumping laser power of 18 mW, we obtain an atomic OD up to 160 in an electromagnetically induced transparency (EIT) scheme, which corresponds to an atomic-density-length product NL = 2.05 × 1015 m−2. In a closed two-state system, the OD can become as large as more than 600. Our 2D MOT configuration allows full optical access of the atoms in its longitudinal direction without interfering with the trapping and repumping laser beams spatially. Moreover, the zero magnetic field along the longitudinal axis allows the cold atoms maintain a long ground-state coherence time without switching off the MOT magnetic field, which makes it possible to operate the MOT at a high repetition rate and a high duty cycle. Our 2D MOT is ideal for atomic-ensemble-based quantum optics applications, such as EIT, entangled photon pair generation, optical quantum memory, and quantum information processing.
Computational analysis of responses of a wedge-shaped-tip optical fiber probe in bubble measurement
Authors: Sakamoto A. , Saito T.
Published: July 2012

Optical-fiber probing is widely employed in bubble/droplet measurement in gas-liquid two-phase flows. Several types of optical fiber probes with a very high S/N ratio and high performance have been developed, but further improvement in the probes’ measurement accuracy and reliability for industrial applications is desired. We tried to eliminate optical noise in the probe measurements, and we found that the signals include some peak signs that have potential for advanced measurement with optical-fiber probing. We developed a ray-tracing numerical simulator and identified the mechanisms underlying the generation of the signals. In order to numerically simulate the optical probing signals, the simulator must use 3D frameworks composed of incident beams, the reflection and refraction on the surfaces of the optical elements (i.e., an optical fiber, a sensing tip, an air phase, and a water phase), and beams returning from the sensing tip to the other tip through the fiber. We used all of these in a simple rendering framework based on a ray-tracing algorithm with Fresnel's law, and we observed the mechanism of some promising signals that may be useful for extracting the hidden potential of optical-fiber probing. To verify the simulator's performance, we carried out three comparative experiments with fundamental setups using a wedge-shaped single-tip optical fiber probe, examining: (1) the beam trajectories and energy leaking out from the sensing tip into the surrounding air phase or water phase, (2) the probing signals throughout penetration of the sensing tip at the air-water free interface in light of the three-dimensional deformation, and (3) the probing signals throughout penetration of the sensing tip into a bubble in light of the three-dimensional bubble shape. As a result, (a) we found that an optical fiber probe with a wedge-shaped tip has particular characteristics of beam emissions from the tip, and the emitting angles switched depending on the phases covering the tip. This phenomenon is very effective for further advanced measurement. (b) We observed numerically that the cutting angle of the sensing tip maximizing the air signal level was approximately 30°, and therefore this angle is the best for obtaining the highest S/N ratio. (c) We found that the meniscus shape clearly affected the probing signal optically. (d) We observed the mechanism of a pre-signal caused by the reflection at the frontal and rear interfaces of a bubble. The pre-signal is very useful for practical measurement because it appears only when the probe penetrates the center region of a bubble. We compared the above numerical results with the results of the three experiments, and there was satisfactory correspondence between the numerical and experimental results.
3 MV hypervelocity dust accelerator at the Colorado Center for Lunar Dust and Atmospheric Studies
Authors: Shu Anthony , Collette Andrew , Drake Keith , Grün Eberhard , Horányi Mihály , Kempf Sascha , Mocker Anna , Munsat Tobin , Northway Paige , Srama Ralf , Sternovsky Zoltán , Thomas Evan
Published: July 2012

A hypervelocity dust accelerator for studying micrometeorite impacts has been constructed at the Colorado Center for Lunar Dust and Atmospheric Studies (CCLDAS) at the University of Colorado. Based on the Max-Planck-Institüt für Kernphysik (MPI-K) accelerator, this accelerator is capable of emitting single particles of a specific mass and velocity selected by the user. The accelerator consists of a 3 MV Pelletron generator with a dust source, four image charge pickup detectors, and two interchangeable target chambers: a large high-vacuum test bed and an ultra-high vacuum impact study chamber. The large test bed is a 1.2 m diameter, 1.5 m long cylindrical vacuum chamber capable of pressures as low as 10−7 torr while the ultra-high vacuum chamber is a 0.75 m diameter, 1.1 m long chamber capable of pressures as low as 10−10 torr. Using iron dust of up to 2 microns in diameter, final velocities have been measured up to 52 km/s. The spread of the dust particles and the effect of electrostatic focusing have been measured using a long exposure CCD and a quartz target. Furthermore, a new technique of particle selection is being developed using real time digital filtering techniques. Signals are digitized and then cross-correlated with a shaped filter, resulting in a suppressed noise floor. Improvements over the MPI-K design, which include a higher operating voltage and digital filtering for detection, increase the available parameter space of dust emitted by the accelerator. The CCLDAS dust facility is a user facility open to the scientific community to assist with instrument calibrations and experiments.
2-ω and 3-ω temperature measurement of a heated microcantilever
Authors: Lee Byeonghee , King William P.
Published: July 2012

This article describes temperature measurement of a heated atomic force microscope cantilever using the 2ω and 3ω harmonics of the cantilever temperature signal. When the cantilever is periodically heated, large temperature oscillations lead to large changes in the cantilever electrical resistance and also lead to nonconstant temperature coefficient of resistance. We model the cantilever heating to account for these sources of nonlinearity, and compare models with experiment. When the heating voltage amplitude is 17.9 V over the driving frequency range 10 Hz–34 kHz, the cantilever temperature oscillation is between 5 °C and 200 °C. Over this range, the corrected 2ω method predicts cantilever temperature to within 16% and the corrected 3ω method predicts the cantilever temperature within 3%. We show a general method for predicting the periodic cantilever temperature, sources of errors, and corrections for these errors.
Simulated thermal conductivity of silicon-based random multilayer thin films
Authors: Frachioni Anthony , White B. E.
Published: July 2012

Reverse nonequilibrium molecular dynamics simulations have been used to quantify the impact of randomly placed mass-altered atomic planes, such as those produced in pseudomorphically grown heterostructures, on the thermal conductivity of silicon. The results indicate that the room temperature thermal conductivity of these silicon-based structures can be reduced to values below 0.050 W/m-K. These values are significantly less than those found in random alloy or superlattice structures containing the same percentage of mass-altered atoms and are attributed to Anderson localization of phonons. Such low lattice thermal conductivity in these silicon-based structures could dramatically improve the thermoelectric efficiency of this earth abundant material.
P-type doping of lithium peroxide with carbon sheets
Authors: Zhao Yufeng , Ban Chunmei , Kang Joongoo , Santhanagopalan Shriram , Kim Gi-Heon , Wei Su-Huai , Dillon Anne C.
Published: July 2012

The interaction of lithium peroxide (Li2O2) with carbon electrodes in Li-air batteries is studied with model systems of graphene-intercalated Li2O2, using density functional theory (DFT) methods. Although both the Li2O2 bulk and its stoichiometric surface structures (without single O atoms) are insulating, the incorporation of graphene sheets into the Li2O2 introduces hole states in the oxygen orbitals due to the electron transfer from the anti-bonding O2 orbitals to the graphene sheets. This indicates that carbon sheets not only provide conducting channels by themselves, but they also open new channels in Li2O2.
Semiconductor lasers driven by self-sustained chaotic electronic oscillators and applications to optical chaos cryptography
Authors: Takougang Kingni Sifeu , Hervé Talla Mbé Jimmi , Woafo Paul
Published: July 2012

In this work, we numerically study the dynamics of vertical cavity surface emitting laser (VCSEL) firstly when it is driven by Chua’s oscillator, secondly in case where it is driven by a broad frequency spectral bandwidth chaotic oscillator developed by Nana et al. [Commun. Nonlinear Sci. Numer. Simul. 14, 2266 (2009)]. We demonstrated that the VCSEL generated robust chaotic dynamics compared to the ones found in VCSEL subject to a sinusoidally modulated current and therefore it is more suitable for chaos encryption techniques. The synchronization characteristics and the communication performances of unidirectional coupled VCSEL driven by the broad frequency spectral bandwidth chaotic oscillators are investigated numerically. The results show that high-quality synchronization and transmission of messages can be realized for suitable system parameters. Chaos shift keying method is successfully applied to encrypt a message at a high bitrate.
Metal-to-insulator transition in anatase TiO2 thin films induced by growth rate modulation
Authors: Tachikawa T. , Minohara M. , Nakanishi Y. , Hikita Y. , Yoshita M. , Akiyama H. , Bell C. , Hwang H. Y.
Published: July 2012

We demonstrate control of the carrier density of single phase anatase TiO2 thin films by nearly two orders of magnitude by modulating the growth kinetics during pulsed laser deposition, under fixed thermodynamic conditions. The resistivity and the intensity of the photoluminescence spectra of these TiO2 samples, both of which correlate with the number of oxygen vacancies, are shown to depend strongly on the growth rate. A quantitative model is used to explain the carrier density changes.
Giant enhancement in ferromagnetic properties of Pd nanoparticle induced by intentionally created defects
Authors: Kulriya P. K. , Mehta B. R. , Agarwal D. C. , Kumar Praveen , Shivaprasad S. M. , Pivin J. C. , Avasthi D. K.
Published: July 2012

The important central question related to origin of ferromagnetic properties in the non-magnetic materials at nano-dimensions has been investigated by a novel approach of studying the evolution of magnetic properties by intentionally creating defects. The ferromagnetic response of Pd is found to increase by 20 times for nanoparticle (NP) dispersed in carbon matrix and increase by about 3.5 times in case of Pd nanoparticles dispersed in SiO2 matrix on exposure to swift heavy ion irradiation. Ferromagnetic response is found to increase by about 9.3 times on subjecting the Pd nanoparticles to hydrogen loading-deloading cycle. Ferromagnetic properties of Pd nanoparticles dispersed in carbon and SiO2 matrices, despite having same size and concentration, are observed to be vastly different due to matrix effect. These changes in ferromagnetic properties are correlated to the change in the electronic structure due to matrix, nanoparticle size, and creation of defects in the nanoparticle core and at NP-matrix interface during post deposition treatments. Giant enhancement in the magnetic properties and change in electronic properties point toward a core and surface magnetic structure in metal nanoparticle.
Study of the photoluminescence emission line at 3.33 eV in ZnO films
Authors: Yalishev V. Sh. , Kim Y. S. , Deng X. L. , Park B. H. , Yuldashev Sh. U.
Published: July 2012

We study properties of the line at 3.33 eV observed in photoluminescence (PL) emission spectra of various ZnO films prepared using pulsed laser deposition method. The influence of deposition parameters, such as oxygen pressure, laser fluence, post-annealing, and electric field exposure on intensity of this luminescence band has been investigated. The recombination characteristics are probed by temperature and excitation dependent PL spectroscopy. The obtained experimental data suggest that the 3.33 eV luminescence line in ZnO depends strongly on surface band bending and originates from recombination of bound excitons (BEs) complex located near the surface and grain boundaries. The anomalously small thermal activation energy of BE in comparison with the localization energy is explained by decreasing of the interface barrier. Possible nature of defects that bind free excitons and cause the 3.33 eV emission line in ZnO is proposed.
In-plane mapping of buried InGaAs quantum rings and hybridization effects on the electronic structure
Authors: Teodoro M. D. , Malachias A. , Lopes-Oliveira V. , Cesar D. F. , Lopez-Richard V. , Marques G. E. , Marega E. , Benamara M. , Mazur Yu. I. , Salamo G. J.
Published: July 2012

This work reports the investigation on the structural differences between InAs quantum rings and their precursor quantum dots species as well as on the presence of piezoelectric fields and asymmetries in these nanostructures. The experimental results show significant reduction in the ring dimensions when the sizes of capped and uncapped ring and dot samples are compared. The iso-lattice parameter mapped by grazing-incidence x-ray diffraction has revealed the lateral extent of strained regions in the buried rings. A comparison between strain and composition of dot and ring structures allows inferring on how the ring formation and its final configuration may affect optical response parameters. Based on the experimental observations, a discussion has been introduced on the effective potential profile to emulate theoretically the ring-shape confinement. The effects of confinement and strain field modulation on electron and hole band structures are simulated by a multiband k.p calculation.
Remarkable optical red shift and extremely high optical absorption coefficient of V-Ga co-doped TiO2
Authors: Deng Quanrong , Han Xiaoping , Gao Yun , Shao Guosheng
Published: July 2012

A first attempt has been made to study the effect of codoping of transition metal and sp metal on the electronic structure and associated optical properties of TiO2, through V-Ga codoped thin films. V-Ga codoped rutile TiO2 films were fabricated on fused quartz substrates using pulsed laser ablation, followed by heat treatment at high temperatures. Gigantic redshift in the optical absorption edge was observed in V-Ga co-doped TiO2 materials, from UV to infrared region with high absorption coefficient. Through combined structural characterization and theoretical modeling, this is attributed to the p-d hybridization between the two metals. This leads to additional energy bands to overlap with the minimum of the conduction band, leading to remarkably narrowed band gap free of mid-gap states. The direct-gap of the co-doped phase is key to the remarkably high optical absorption coefficient of the coped titania.
Photonic effect in a hyper-swollen lyotropic lamellar phase
Authors: Kobayashi Chikashi , Yamamoto Jun , Takanishi Yoichi
Published: July 2012

We studied the photonic effect in a hyper-swollen lyotropic lamellar phase. This system is composed of only a small percentage of amphiphilic molecules and more than 98% of water by weight; however, it shows clear Bragg reflection because of the periodicity in the order of the visible wavelength. By mixing a laser dye into the lamellar phase, we confirmed the emission enhancement near the higher energy side of the Bragg reflection band, although the effect is weak. We also discuss whether such a structure can exhibit the photonic effect using Berreman’s 4 × 4 matrix method.
The influence of the atomic interactions in out-of-plane on surface energy and its applications in nanostructures
Authors: Li Xinlei
Published: July 2012

Considering the influence of atomic interactions in out-of-plane on surface energy between the layers of nanostructures underneath surface, we establish a thermodynamic model to elucidate its applications in various nanostructures, e.g., nanocrystals with positive curvature, nanocavities with negative curvature, etc. It has been found that the size and surface morphology of nanostructures play the key role in the surface energy, which results in the surface energy that decreases with decreasing size of nanoparticles, nanowires, and nanofilms, but increases with decreasing size of the nanopipes and nanocavities. The theoretical predictions are well consistent with other existing theoretical models, implying that the model could be expected to be a general approach to understand surface energy in nanomaterials.
Epitaxial graphene on single domain 3C-SiC(100) thin films grown on off-axis Si(100)
Authors: Ouerghi A. , Balan A. , Castelli C. , Picher M. , Belkhou R. , Eddrief M. , Silly M. G. , Marangolo M. , Shukla A. , Sirotti F.
Published: July 2012

The current process of growing graphene by thermal decomposition of 3C-SiC(100) on silicon is technologically attractive. Here, we study epitaxial graphene on single domain 3C-SiC films on off-axis Si(100). The structural and electronic properties of such graphene layers are explored by atomic force microscopy, x-ray photoelectron spectroscopy, and Raman spectroscopy. Using low energy electron diffraction, we show that graphene exhibits single planar domains. Near-edge x-ray absorption fine structure is used to characterize the sample, which confirms that the graphene layers present sp2 hybridization and are homogeneously parallel to the substrate surface.
Multi-pulse enhanced laser ion acceleration using plasma half cavity targets
Authors: Scott G. G. , Green J. S. , Bagnoud V. , Brabetz C. , Brenner C. M. , Carroll D. C. , MacLellan D. A. , Robinson A. P. L. , Roth M. , Spindloe C. , Wagner F. , Zielbauer B. , McKenna P. , Neely D.
Published: July 2012

We report on a plasma half cavity target design for laser driven ion acceleration that enhances the laser to proton energy conversion efficiency and has been found to modify the low energy region of the proton spectrum. The target design utilizes the high fraction of laser energy reflected from an ionized surface and refocuses it such that a double pulse interaction is attained. We report on numerical simulations and experimental results demonstrating that conversion efficiencies can be doubled, compared to planar foil interactions, when the secondary pulse is delivered within picoseconds of the primary pulse.
Magneto-electric tuning of the phase of propagating spin waves
Authors: Bao Mingqiang , Zhu Guodong , Wong Kin L. , Hockel Joshua L. , Lewis Mark , Zhao Jing , Wu Tao , Khalili Amiri Pedram , Wang Kang L.
Published: July 2012

The utilization of a magnetoelectric film composite to control, by an electric field, the phase of magnetostatic surface spin waves propagating along thin films is reported. Laminates of ferromagnetic films of Ni and NiFe are deposited on a ferroelectric substrate, lead magnesium niobate-lead titanate. The phase of propagating spinwaves is shown to be modulated by an electric field while traveling a finite distance along the surface. The observed phase change in the spinwaves is in agreement with the anisotropy field changes measured with magneto optical Kerr effect hysteresis loops. A quantitative agreement is demonstrated.
A structural viscosity model for magnetorheology
Authors: Berli Claudio L. A. , de Vicente Juan
Published: July 2012

A structural viscosity model is proposed, which describes the shear viscosity from the balance between build up (magnetic field-induced clustering) and breakdown (shear-induced breakup) of particle aggregates. The model accounts for typical deviations from Bingham model predictions that are extensively reported in the MR literature. More precisely, the model (i) provides a physical ground for the observed Casson-like shear flow behaviour, (ii) predicts the existence of a low shear plateau in weak MR fluids, and (iii) asymptotically recovers the typical Bingham-like behavior that is observed in (strong) conventional MR fluids at experimentally accessible times.
Efficient and broadband polarization rotator using horizontal slot waveguide for silicon photonics
Authors: Zhang Huijuan , Das Suchandrima , Zhang Jing , Huang Ying , Li Chao , Chen Shiyi , Zhou Haifeng , Yu Mingbin , Guo-Qiang Lo Patrick , Thong John T. L.
Published: July 2012

We report an efficient and low-loss polarization rotator based on mode evolution using horizontal slot waveguide. The device is fabricated using complementary metal–oxide–semiconductor compatible processes, which allows monolithic integration with active drive electronics and other photonic components. A rotator fabricated with 100 μm transition length provides a high extinction ratio >14 dB for both transverse-magnetic (TM)-transverse-electric (TE) and TE-TM rotation. The excess loss of the device is <1 dB for both rotations as etching of the bottom Si waveguide is prevented. The device also exhibits a uniform rotation response over C+L band wavelength range of 1530-1600 nm.
Determination of graphene work function and graphene-insulator-semiconductor band alignment by internal photoemission spectroscopy
Authors: Yan Rusen , Zhang Qin , Li Wei , Calizo Irene , Shen Tian , Richter Curt A. , Hight-Walker Angela R. , Liang Xuelei , Seabaugh Alan , Jena Debdeep , Grace Xing Huili , Gundlach David J. , Nguyen N. V.
Published: July 2012

We determined the band alignment of a graphene-insulator-semiconductor structure using internal photoemission spectroscopy. From the flatband voltage and Dirac voltage, we infer a 4.6× 1011cm−2 negative extrinsic charge present on the graphene surface. Also, we extract the graphene work function to be 4.56 eV, in excellent agreement with theoretical and experimental values in literature. Electron and hole injection from heavily doped p-type silicon (Si) are both observed. The barrier height from the top of the valence band of Si to the bottom of the conduction band of silicon dioxide (SiO2) is found to be 4.3 eV. The small optical absorption in graphene makes it a good transparent contact to enable the direct observation of hole injection from Si to graphene. The barrier height for holes escaping from the bottom of Si conduction band to the top of SiO2 valence band is found to be 4.6 eV.