bluuebunny/crossref_metadata_2025 huggingface dataset:
Two charges on a plane in a magnetic field: Special trajectories
Authors: Escobar-Ruiz M. A. , Turbiner A. V.
Published: February 2013

The classical mechanics of two Coulomb charges on a plane (e1, m1) and (e2, m2) subject to a constant magnetic field perpendicular to the plane is considered. Special “superintegrable” trajectories (circular and linear) for which the distance between charges remains unchanged are indicated and their constants of motion are presented. The number of the independent constants of motion for the special trajectory is larger than for generic ones and hence they can be called “superintegrable.” A classification of pairs of charges for which special trajectories occur is given. The special trajectories are analyzed for three particular cases, namely that of two electrons, an electron-positron pair, and an electron-α-particle pair.
Identification of electron and hole trap based on isothermal surface potential decay model
Authors: Shen Wen-Wei , Mu Hai-Bao , Zhang Guan-Jun , Deng Jun-Bo , Tu De-Min
Published: February 2013

For identifying electron and hole traps in polymeric materials, we combine the isothermal relaxation current theory and surface potential decay together and present a model called isothermal surface potential decay (ISPD). A non-contact measurement setup is specially designed, which features that energy distribution of electron or hole-type traps can be discriminated with negative or positive corona charging, respectively. By measuring the ISPD characteristics of low-density polyethylene and polypropylene films, their trap distributions are obtained, revealing the different semi-crystalline morphology of these two materials. The results we obtained may imply the essentially distinct nature of electron/hole traps: inter-chain for electron-type traps and intra-chain for hole-type traps, which is in agreement with other researchers' molecular modeling results.
Effects of external magnetic field on the morphology and magnetic property of BiFeO3 particles prepared by hydrothermal synthesis
Authors: Hou L. , Zuo K. H. , Sun Q. B. , Ren Z. M. , Zeng Y. P. , Li X.
Published: February 2013

The perovskite multiferroic bismuth ferrite (BiFeO3) particles were synthesized by hydrothermal method under external magnetic fields with respective intensities of 0 T, 4 T, 8 T, and 12 T. High magnetic field greatly affected the growth behavior and magnetic property of BiFeO3. The morphology of BiFeO3 changed from regular cube to irregular sphere, and finally became a chain-like structure. Meanwhile, the magnetization of the as-prepared BiFeO3 particles measured under a 1.8 T magnetic field was enhanced from 0.1003 emu/g (0 T) to 0.2067 emu/g (12 T). The possible mechanisms of crystal growth and magnetic property were also discussed.
Derivation and assessment of phase-shifted, disordered vector field models for frustrated solvent interactions
Authors: Weber Jeffrey K. , Pande Vijay S.
Published: February 2013

The structure and properties of water at biological interfaces differ drastically from bulk due to effects including confinement and the presence of complicated charge distributions. This non-bulk-like behavior generally arises from water frustration, wherein all favorable interactions among water molecules cannot be simultaneously satisfied. While the frustration of interfacial water is ubiquitous in the cell, the role this frustration plays in mediating biophysical processes like protein folding is not well understood. To investigate the impact of frustration at interfaces, we here derive a general field theoretic model for the interaction of bulk and disordered vector fields at an embedded surface. We calculate thermodynamic and correlation functions for the model in two and three dimensions, and we compare our results to Monte Carlo simulations of lattice system analogs. In our analysis, we see that field-field cross correlations near the interface in the model give rise to a loss in entropy like that seen in glassy systems. We conclude by assessing our theory's utility as a coarse-grained model for water at polar biological interfaces.
Anomalies in a waterlike model confined between plates
Authors: Krott Leandro B. , Barbosa Marcia C.
Published: February 2013

Using molecular dynamic simulations we study a waterlike model confined between two fixed hydrophobic plates. The system is tested for density, diffusion, and structural anomalous behavior and compared with the bulk results. Within the range of confining distances we had explored and observed that in the pressure-temperature phase diagram the temperature of maximum density (TMD line) and the temperature of maximum and minimum diffusion occur at lower temperatures when compared with the bulk values. For distances between the two layers below a certain threshold, d ⩽ dc, only two layers of particles are formed, for d ⩾ dc three or more layers are formed. In the case of three layers the central layer stays liquid while the contact layers crystallize. This result is in agreement with simulations for atomistic models.
Representing elements of the Weyl algebra by labeled trees
Authors: Asakly Walaa , Mansour Toufik , Schork Matthias
Published: February 2013

It is shown how arbitrary elements of the Weyl algebra can be represented by labeled plane trees using normal ordering. Several examples are treated and combinatorial aspects are discussed. Also, possible avenues for future research are described.
Magnetoelectric effects in functionally graded multiferroic bilayers
Authors: Zhang C. L. , Chen W. Q. , Zhang Ch.
Published: February 2013

We present an analytical model to evaluate the magnetoelectric (ME) effects in functionally graded multiferroic laminated plates. The static and frequency-dependant ME effects in functionally graded piezoelectric and piezomagnetic (FGPP) bilayers with different gradations of the material property along the thickness are analyzed. The results show that the FGPP bilayers with special gradation have a stronger ME coupling effect than that in the homogeneous structure. The magnetic energy-harvesters made of FGPP bilayers achieve a larger output power as well.
Photoacoustic absorption spectrometer for highly transparent dielectrics with parts-per-million sensitivity
Authors: Waasem Niklas , Fieberg Stephan , Hauser Janosch , Gomes Gregory , Haertle Daniel , Kühnemann Frank , Buse Karsten
Published: February 2013

A sensitive photoacoustic absorption spectrometer for highly transparent solids has been built and tested. As the light source an optical parametrical oscillator pumped by a nanosecond pulse laser with 10 Hz repetition rate is employed, covering the complete wavelength range from 407 to 2600 nm. A second-harmonic-generation unit extends the range of accessible wavelengths down to 212 nm. A lead-zirconate-titanate piezo transducer, directly coupled to the sample, detects the photoacoustically generated sound waves. Absorption spectra of lithium triborate, lithium niobate, and alpha barium borate crystals with absorption coefficients down to 10−5 cm−1 are presented.
Low-frequency noise properties of beryllium δ-doped GaAs/AlAs quantum wells near the Mott transition
Authors: Palenskis V. , Matukas J. , Pralgauskaitė S. , Seliuta D. , Kašalynas I. , Subačius L. , Valušis G. , Khanna S. P. , Linfield E. H.
Published: February 2013

Noise properties of beryllium delta-doped GaAs/AlAs multiple quantum wells, doped both above and below the Mott transition, are studied within the frequency range of 10 Hz−20 kHz and at temperature from 77 K to 350 K. It is shown that the generation-recombination noise in structures close to the Mott transition exhibits two peaks—a frequency and temperature-dependent peak between 120 and 180 K and a broadband, frequency- and temperature- nearly independent peak around 270 K. Activation energies are estimated; origin of the broadband maximum is attributed to holes tunnelling into defect trap states located in the AlAs barrier/GaAs quantum well interface.
Ambipolar organic light-emitting electrochemical transistor based on a heteroleptic charged iridium(III) complex
Authors: Zhou Ye , Han Suting , Zhou Guijiang , Wong Wai-Yeung , Roy V. A. L.
Published: February 2013

High performance organic light-emitting electrochemical transistor (OLECT) based on a phosphorescent heteroleptic charged iridium(III) complex has been developed with low-cost solution processing technique. The new OLECT showed good ambipolar behavior with balanced hole and electron mobilities of 0.20 cm2 V–1 s–1 and 0.22 cm2 V–1 s–1, respectively. Furthermore, light emission has been observed from the OLECT device and modulated by the gate. All these results suggest that charged iridium(III) complexes could be a promising candidate for single-component multifunctional organic light-emitting field-effect transistor.
Controlled polarity of sputter-deposited aluminum nitride on metals observed by aberration corrected scanning transmission electron microscopy
Authors: Harumoto T. , Sannomiya T. , Matsukawa Y. , Muraishi S. , Shi J. , Nakamura Y. , Sawada H. , Tanaka T. , Tanishiro Y. , Takayanagi K.
Published: February 2013

The polarity determination process of sputter-deposited aluminum nitride (AlN) on metals has been analyzed using aberration corrected atomic resolution scanning transmission electron microscope. Direct growth of c-axis orientated AlN on face centered cubic metals (fcc) (111) with the local epitaxy has been observed, and the polarity was determined at the AlN/metal interface. We found that the AlN polarity can be controlled by the base metal layer: N-polarity AlN grows on Pt(111) while Al-polarity AlN forms on Al(111). Based on these results, the growth mechanism of AlN on metals is discussed.
Electrically small, complementary electric-field-coupled resonator antennas
Authors: Odabasi H. , Teixeira F. L. , Guney D. O.
Published: February 2013

We study the radiation properties of electrically small resonant antennas (ka<1) composed of electric-field-coupled (ELC) and complementary electric-field-coupled (CELC) resonators and a monopole antenna. We use such parasitic ELC and CELC “metaresonators” to design various electrically small antennas. In particular, monopole-excited and bent-monopole-excited CELC resonator antennas are proposed that provide very low profiles on the order of λ0/20. We compare the performance of the proposed ELC and CELC antennas against more conventional designs based upon split-ring resonators.
Electro-caloric effect in 0.45BaZr0.2Ti0.8O3-0.55Ba0.7Ca0.3TiO3 single crystal
Authors: Singh Gurvinderjit , Bhaumik Indranil , Ganesamoorthy S. , Bhatt R. , Karnal A. K. , Tiwari V. S. , Gupta P. K.
Published: February 2013

Electro-caloric effect in 0.45BaZr0.2Ti0.8O3-0.55Ba0.7Ca0.3TiO3 single crystal has been investigated and electro-caloric coefficient of ∼0.38 K mm/kV has been obtained near the tetragonal-to-cubic phase transition. The value obtained is significantly higher than that for the lead-free ferroelectric materials reported so far.
Ligand exchange leads to efficient triplet energy transfer to CdSe/ZnS Q-dots in a poly(N-vinylcarbazole) matrix nanocomposite
Authors: Khetubol Adis , Van Snick Sven , Hassinen Antti , Fron Eduard , Firdaus Yuliar , Pandey Lesley , David Charlotte C. , Duerinckx Karel , Dehaen Wim , Hens Zeger , Van der Auweraer Mark
Published: February 2013

Upon exchanging long chain alkylamine ligands with a carbazole terminated fatty acid as 6-(N-carbazolyl)-hexanoic acid (C6) and 11-(N-carbazolyl) undecanoic acid (C11), efficient photoluminescence (PL) of CdSe/ZnS colloidal quantum dots (QDs) was observed upon excitation in the absorption band of the carbazole moiety at 330 nm. This effect, which occurred both in solution and in a poly(N-vinylcarbazole) (PVK) matrix doped with the QDs, is attributed to sensitization of the QDs by PVK and the ligands. More efficient energy transfer was observed in solution for the shorter ligand (C6) capped QDs, due to a shorter average distance between the donor (carbazole) and the acceptor (QD). The binding of C6 and C11 to the QDs was confirmed by 1H solution nuclear magnetic resonance, which showed line broadening of the carbazole signal due to a decrease of the mobility of the carbazoles upon binding to the QDs compared with the sharp lines observed for the free molecules in solution. In doped PVK films, the significant enhancement of the energy transfer to the QD core could also be related to a better miscibility between the QDs and the PVK as confirmed by optical transmission and confocal microscopy images. In contrast to the experiment in solution, the overall energy transfer in the doped films was found more efficient for QDs capped with C11. To study in more detail the energy transfer between the carbazole moieties and the QDs, time-resolved fluorescence measurements were performed for solutions of C6 and C11, capped QDs and PVK films doped with the QDs. In contrast to the large enhancement of the QD emission indicated by steady-state PL spectra, the latter experiments suggested only a relatively low efficiency (19.6% and 10.8%) for singlet transfer from the carbazole ligands to the QDs. This suggests that the enhancement of the QD emission must be largely due to triplet transfer.
Experimental study on impact-initiated characters of multifunctional energetic structural materials
Authors: Zhang X. F. , Shi A. S. , Qiao L. , Zhang J. , Zhang Y. G. , Guan Z. W.
Published: February 2013

Multifunctional energetic structural materials (MESMs) are a new class of energetic materials, which release energy due to exothermic chemical reactions initiated under shock loading conditions. In order to analyze the impact-initiated process of MESMs, a quasi-sealed test chamber, which was originally developed by Ames [“Vented chamber calorimetry for impact-initiated energetic materials,” in AIAA (American Institute of Aeronautics and Astronautics, 2005), p. 279], is used to study on shock-induced chemical reaction characters at various impact velocities. The impact initiated experiments are involving two typical MESMs, Al/PTFE (polytetrafluoroethylene), W/Zr and inert 2024 Al fragment. The video frames recorded from reactive and inert material impact events have shown the process of late-time after burn phenomena. The total pressure and shock wave reflection at the wall of the test chamber are measured using high frequency gauges. The quasi-pressures inside the test chamber, which is fitting from the total pressure curves, are used to determine the impact initiated reaction efficiencies of MESMs at different impact velocities. A thermochemical model for shock-induced reactions, in which the reaction efficiency is considered, is validated against the experimental data from impact initiation. The results show that the impact velocity plays a significant role in chemical reaction and the energy release characteristics of MESMs. The theoretical calculations correlate reasonably well to the corresponding experimental results, which can be used to predict the reaction results of MESMs over a wide range of pressure satisfactorily.
Improved light extraction efficiency of cerium-doped lutetium-yttrium oxyorthosilicate scintillator by monolayers of periodic arrays of polystyrene spheres
Authors: Zhu Zhichao , Liu Bo , Cheng Chuanwei , Yi Yasha , Chen Hong , Gu Mu
Published: February 2013

In this Letter, monolayers of arrays of periodic polystyrene (PS) spheres are designed to couple onto the surface of cerium-doped lutetium-yttrium oxyorthosilicate scintillator to improve the light extraction efficiency. The enhancement of extraction efficiency up to 38% relative to the reference case without polystyrene spheres is achieved. Combining with the simulation for the transmission as well as its dispersion relation, detailed analysis of the effect of whispering gallery modes and diffraction on the extraction mechanism are given. As a result, the optimal diameter of 414 nm is obtained based on a trade-off between the transmission loss and the diffraction enhancement.
Efficiency limits of rectenna solar cells: Theory of broadband photon-assisted tunneling
Authors: Joshi Saumil , Moddel Garret
Published: February 2013

Because rectifiers can convert a wide range of frequencies to dc it was thought that rectenna solar cells–antennas coupled to ultra-high speed diodes–could efficiently harvest the entire solar spectrum and exceed the Shockley-Queisser limit. We show that there are efficiency limits to broadband optical conversion and provide a quantitative analysis using the theory of photon-assisted tunneling. This quantum-based approach differs from classical rectification in lower frequency rectennas. The conversion efficiency approaches 100% for monochromatic illumination. For broadband illumination at terrestrial solar intensities, the diode operating voltage plays the role that bandgap plays in conventional solar cells.
Thomson parabola spectrometry for gold laser-generated plasmas
Authors: Torrisi L. , Cutroneo M. , Andò L. , Ullschmied J.
Published: February 2013

The plasma generated from thin gold films irradiated in high vacuum at high intensity (∼1015 W/cm2) laser shot is characterized in terms of ion generation through time-of-flight techniques and Thomson parabola spectrometry. Gold ions and protons, accelerated in forward direction by the electric field developed in non-equilibrium plasma, have been investigated. Measurements, performed at PALS laboratory, give information about the gold charge states distributions, the ion energy distributions and the proton acceleration driven as a function of film thickness, laser parameters, and angular emission. The ion diagnostics of produced plasma in forward direction permits to understand some mechanisms developed during its expansion kinetics. The role of the focal position of a laser beam with respect to the target surface, plasma properties, and the possibility to accelerate protons up to energies above 3 MeV has been presented and discussed.
Quantitative Kelvin probe force microscopy of current-carrying devices
Authors: Fuller Elliot J. , Pan Deng , Corso Brad L. , Tolga Gul O. , Gomez Jose R. , Collins Philip G.
Published: February 2013

Kelvin probe force microscopy (KPFM) should be a key tool for characterizing the device physics of nanoscale electronics because it can directly image electrostatic potentials. In practice, though, distant connective electrodes interfere with accurate KPFM potential measurements and compromise its applicability. A parameterized KPFM technique described here determines these influences empirically during imaging, so that accurate potential profiles can be deduced from arbitrary device geometries without additional modeling. The technique is demonstrated on current-carrying single-walled carbon nanotubes (SWNTs), directly resolving average resistances per unit length of 70 kΩ/μm in semimetallic SWNTs and 200 kΩ/μm in semiconducting SWNTs.
Bulk interface engineering for enhanced magnetization in multiferroic BiFeO3 compounds
Authors: Pillai Shreeja , Bhuwal Deepika , Banerjee Alok , Shelke Vilas
Published: February 2013

We investigated composites of two antiferromagnetic perovskite oxides BiFeO3 and LaMnO3 to study change in bulk magnetic behavior. Composites with nominal compositions (1−x)BiFeO3-xLaMnO3 (x = 0, 5, 10, 20 wt. %) were synthesized by solid state reaction route. The structural analysis performed using X-ray diffraction and Raman spectroscopy indicated presence of phase separated compounds. Significant enhancement in magnetic moment is observed in composite samples, which was attributed to the uncompensated spins at the interface of two distinct antiferromagnetic phases.
Theoretical study of elastic properties and phase stability of M0.5Al0.5N1−xOx (M = Sc, Ti, V, Cr)
Authors: Jin Rotert Soo , Music Denis , to Baben Moritz , Schneider Jochen M.
Published: February 2013

The influence of oxygen content and transition metal valence electron concentration on the phase stability and elastic properties of cubic M0.5Al0.5N1−xOx (M = Sc, Ti, V, Cr; x = 0 – 0.5) was studied using ab initio calculations. The negative value of enthalpy of mixing was observed for all phases indicating full miscibility of M0.5Al0.5N with the hypothetical M0.5Al0.5O. Bulk moduli are decreased as x in M0.5Al0.5N1−xOx is increased. This can be understood based on the electronic structure. As N is substituted by O, there are no noticeable changes in the chemical bonding nature. However, O is more electronegative than N, giving rise to an increase in the ionic character of the overall bonding. In spite of that, the M – O bond in M0.5Al0.5N1−xOx is longer than the corresponding M–N bond, which implies that this bond becomes weaker. Hence, we propose that the decrease of bulk moduli upon O incorporation into M0.5Al0.5N1−xOx is caused by weaker M–O bonds.
Room-temperature detection of spin accumulation in silicon across Schottky tunnel barriers using a metal–oxide–semiconductor field effect transistor structure (invited)
Authors: Hamaya K. , Ando Y. , Masaki K. , Maeda Y. , Fujita Y. , Yamada S. , Sawano K. , Miyao M.
Published: February 2013

Using a metal-oxide-semiconductor field effect transistor structure with a high-quality CoFe/n+-Si contact, we systematically study spin injection and spin accumulation in a nondegenerated Si channel with a doping density of ∼4.5 × 1015 cm−3 at room temperature. By applying the gate voltage (VG) to the channel, we obtain sufficient bias currents (IBias) for creating spin accumulation in the channel and observe clear spin-accumulation signals even at room temperature. Whereas the magnitude of the spin signals is enhanced by increasing IBias, it is reduced by increasing VG interestingly. These features can be understood within the framework of the conventional spin diffusion model. As a result, a room-temperature spin injection technique for the nondegenerated Si channel without using insulating tunnel barriers is established, which indicates a technological progress for Si-based spintronic applications with gate electrodes.
Lithium implantation at low temperature in silicon for sharp buried amorphous layer formation and defect engineering
Authors: Oliviero E. , David M. L. , Fichtner P. F. P. , Beaufort M. F. , Barbot J. F.
Published: February 2013

The crystalline-to-amorphous transformation induced by lithium ion implantation at low temperature has been investigated. The resulting damage structure and its thermal evolution have been studied by a combination of Rutherford backscattering spectroscopy channelling (RBS/C) and cross sectional transmission electron microscopy (XTEM). Lithium low-fluence implantation at liquid nitrogen temperature is shown to produce a three layers structure: an amorphous layer surrounded by two highly damaged layers. A thermal treatment at 400 °C leads to the formation of a sharp amorphous/crystalline interfacial transition and defect annihilation of the front heavily damaged layer. After 600 °C annealing, complete recrystallization takes place and no extended defects are left. Anomalous recrystallization rate is observed with different motion velocities of the a/c interfaces and is ascribed to lithium acting as a surfactant. Moreover, the sharp buried amorphous layer is shown to be an efficient sink for interstitials impeding interstitial supersaturation and {311} defect formation in case of subsequent neon implantation. This study shows that lithium implantation at liquid nitrogen temperature can be suitable to form a sharp buried amorphous layer with a well-defined crystalline front layer, thus having potential applications for defects engineering in the improvement of post-implantation layers quality and for shallow junction formation.
Anomalous electronic and magnetic properties of the Eu2Ru2O7 pyrochlore
Authors: Muñoz Pérez S. , Cobas R. , Cadogan J. M. , Albino Aguiar J. , Frontera C. , Puig T. , Long G. , DeMarco M. , Coffey D. , Obradors X.
Published: February 2013

Structural, 99Ru Mössbauer, dc and ac susceptibility magnetization, and magneto-transport properties of the polycrystalline Eu2Ru2O7 pyrochlore are reported in this paper. From the experimental data, we deduce that the ruthenium cations Ru4+ (S = 1) are surrounded by an unusual electronic environment, involving conduction electron polarization and extrinsic Eu3+ ions at low temperature. This situation leads to an anomalous spin-glass transition at 23 K.
Atomic scale structure and chemistry of Bi2Te3/GaAs interfaces grown by metallorganic van der Waals epitaxy
Authors: Houston Dycus J. , White Ryan M. , Pierce Jonathan M. , Venkatasubramanian Rama , LeBeau James M.
Published: February 2013

Here, we report the atomic scale structure and chemistry of epitaxial Bi2Te3 thin films grown via metallorganic chemical vapor deposition on (001) GaAs substrates. Using aberration corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM), we report an atomically abrupt interface spanned by a second phase. Further, we demonstrate that interpretation of HAADF STEM image intensities does not provide an unambiguous interface structure. Combining atomic resolution imaging and spectroscopy, we determine the identity of the interfacial species is found to be consistent with that of a bilayer of Ga–Te that terminates GaAs dangling bonds.
Communication: Influence of graphene interlayers on the interaction between cobalt phthalocyanine and Ni(111)
Authors: Uihlein Johannes , Peisert Heiko , Glaser Mathias , Polek Małgorzata , Adler Hilmar , Petraki Fotini , Ovsyannikov Ruslan , Bauer Maximilian , Chassé Thomas
Published: February 2013

The influence of graphene interlayers on electronic interface properties of cobalt phthalocyanine on Ni(111) is studied using both photoemission and X-ray absorption spectroscopy. A charge transfer associated with a redistribution of the d-electrons at the Co-atom of the phthalocyanine occurs at the interface to Ni(111). Even a graphene buffer layer cannot prevent the charge transfer at the interface to Ni(111); however, the detailed electronic situation is different.
Modulation of persistent photoconductivity by electric-field-controlled strain in thin films of La0.39Pr0.24Ca0.37MnO3
Authors: Wang J. F. , Jiang Y. C. , Wu Z. P. , Gao J.
Published: February 2013

Thin films of La0.39Pr0.24Ca0.37MnO3 (LPCMO) were epitaxially grown on 0.7PbMg1/3Nb2/3O3-0.3PbTiO3 (PMN-PT) substrates. These LPCMO films exhibited low-temperature persistent photoconductivity (PPC) when illuminated by a visible light of 532 nm. Not only the resistance but also PPC were modulated by electric fields across PMN-PT. Detailed analysis and in situ x-ray diffraction indicate that such modulations were mainly due to the change of lattice deformation by applied electric fields via converse piezoelectric effect. It was also found that light and strain influence the phase competition in different ways.
Brillouin light scattering spectra as local temperature sensors for thermal magnons and acoustic phonons
Authors: Birt Daniel R. , An Kyongmo , Weathers Annie , Shi Li , Tsoi Maxim , Li Xiaoqin
Published: February 2013

We demonstrate the use of the micro-Brillouin light scattering (micro-BLS) technique as a local temperature sensor for magnons in a permalloy (Py) thin film and phonons in the glass substrate. When the Py film is uniformly heated, we observe a systematic shift in the frequencies of two thermally excited perpendicular standing spin wave modes. Fitting the temperature dependent magnon spectra allows us to achieve a temperature resolution better than 2.5 K. In addition, we demonstrate that the micro-BLS spectra can be used to measure the local temperature of magnons and the relative temperature shift of phonons across a thermal gradient. Such local temperature sensors are useful for investigating spin caloritronic and thermal transport phenomena in general.
Hall thruster with grooved walls
Authors: Li Hong , Ning Zhongxi , Yu Daren
Published: February 2013

Axial-oriented and azimuthal-distributed grooves are formed on channel walls of a Hall thruster after the engine undergoes a long-term operation. Existing studies have demonstrated the relation between the grooves and the near-wall physics, such as sheath and electron near-wall transport. The idea to optimize the thruster performance with such grooves was also proposed. Therefore, this paper is devoted to explore the effects of wall grooves on the discharge characteristics of a Hall thruster. With experimental measurements, the variations on electron conductivity, ionization distribution, and integrated performance are obtained. The involved physical mechanisms are then analyzed and discussed. The findings help to not only better understand the working principle of Hall thruster discharge but also establish a physical fundamental for the subsequent optimization with artificial grooves.
Suppression of shear banding in amorphous ZrCuAl nanopillars by irradiation
Authors: Xiao Qiran , Huang Liping , Shi Yunfeng
Published: February 2013

Using molecular dynamics simulations, model Zr50Cu40Al10 metallic glass (MG) nanopillars were subjected to simulated irradiation processes followed by uniaxial compression tests. As the intensity or dosage of irradiation increases, the plastic deformation mode of the MG nanopillars transits from localized shear banding to homogeneous shear flow. The suppression of shear banding in MG nanopillars is due to irradiation-induced structural disordering. Furthermore, a correlation is found between the average potential energy of MG nanopillars and their deformation modes, common to both irradiation processing and thermal processing. Our results imply that the homogeneous shear flow observed in experimental MG nanopillars carved by focused ion beam may be due to irradiation damage instead of size effect.
Gate-tunable selective operation of single electron/hole transistor modes in a silicon single quantum dot at room temperature
Authors: Lee Sejoon , Lee Youngmin , Song Emil B. , Wang Kang L. , Hiramoto Toshiro
Published: February 2013

We demonstrate a gate-tunable selective operation of single-electron-transistor (SET) and single-hole-transistor (SHT) in a unit silicon (Si) quantum dot (QD) system at room temperature. The small sized Si-QD (∼7 nm) with well-defined tunnel barriers, which are formed along the p+-i-n+ Si nanowire in both the conduction band and the valence band, permits the alternative use of quantum states for electrons or holes to be selected by the polarity of the gate bias. The device shows clear Coulomb blockade and negative differential-conductance oscillations on both gate-tunable SET and SHT modes as a result of quantum transport in the p+-i-n+ Si QD system.
Bandstructure measurement in nonlinear optical waveguide arrays
Authors: Setzpfandt F. , Falkner M. , Pertsch T. , Sohler W. , Schiek R.
Published: February 2013

We demonstrate a technique for measuring the linear bandstructure of periodic systems with quadratic nonlinearity. The phase-matching constraints of parametric optical frequency mixing are employed to probe the longitudinal wavevectors of the eigenmodes. The method is verified experimentally by measuring the diffraction relation of eigenmodes in periodically poled titanium-indiffused lithium niobate waveguide arrays with second-harmonic generation.
Measurement of coupled cavities' optomechanical coupling coefficient using a nanoelectromechanical actuator
Authors: Tian Feng , Zhou Guangya , Siong Chau Fook , Deng Jie , Akkipeddi Ramam
Published: February 2013

In this Letter, we report an approach to experimentally determine the optomechanical coupling coefficient of coupled cavities, taking advantage of the ultra-fine cavity positioning capability of a nanoelectromechanical system (NEMS) actuator design. The approach is simple and flexible and can measure the optomechanical coupling coefficient as a function of the coupled cavities' slot gap. In addition, the ratio of mechanical detunings of the odd and even resonance modes can make the existing approach to the decoupling of thermo-optic and optomechanical effects more precise and applicable to more types of cavities.
Continuous-film vs. device-level ferromagnetic resonance in magnetic tunnel junction thin films
Authors: Evarts Eric R. , Pufall Matthew R. , Rippard William H.
Published: February 2013

We quantitatively compared film-level ferromagnetic resonance (FMR) measurements using standard vector network analyzer (VNA) techniques with device-level FMR measurements for both thermal FMR (T-FMR) and field-swept spin-torque FMR (FS-ST-FMR) techniques on magnetic tunnel junction (MTJ) thin films with in-plane magnetization. The film and FS-ST-FMR device determination of damping α are in agreement; however, α cannot be reliably determined by use of T-FMR device measurements due to bandwidth limitations. The device-level intercept of Hres vs. f is lower than film-level measurements of the effective magnetization (Meff) due to the demagnetizing field and exchange coupling of the patterned free layer. The intercept shows device-to-device variations due to a combination of size variation and local film variations. At the device level, the inhomogeneous broadening (ΔH0) is nearly zero, while in film-level measurements, μ0ΔH0 > 10 mT due to averaging of the local film variations detected explicitly in the intercept of Hres vs. f at the device level. These results suggest that continuous-film and FS-ST-FMR measurements on multiple devices can provide comparable information about thin-film Meff, α, and ΔH0 with minimal interpretation, but caution is necessary when using T-FMR to determine α or ΔH0.
Note: Auto-relock system for a bow-tie cavity for second harmonic generation
Authors: Haze Shinsuke , Hata Sousuke , Fujinaga Munekazu , Mukaiyama Takashi
Published: February 2013

This Note reports on the implementation of an automatic relocking system for a bow-tie cavity for second harmonic generation to produce an ultra-violet laser source. The system is based on a sample-and-hold technique for controlling the cavity length using simple servo electronics. Long-term stabilization of the cavity output power is successfully achieved, which makes this system suitable for designing stable atomic physics experiments.
A pH sensor with a double-gate silicon nanowire field-effect transistor
Authors: Ahn Jae-Hyuk , Kim Jee-Yeon , Seol Myeong-Lok , Baek David J. , Guo Zheng , Kim Chang-Hoon , Choi Sung-Jin , Choi Yang-Kyu
Published: February 2013

A pH sensor composed of a double-gate silicon nanowire field-effect transistor (DG Si-NW FET) is demonstrated. The proposed DG Si-NW FET allows the independent addressing of the gate voltage and hence improves the sensing capability through an application of asymmetric gate voltage between the two gates. One gate is a driving gate which controls the current flow, and the other is a supporting gate which amplifies the shift of the threshold voltage, which is a sensing metric, and which arises from changes in the pH. The pH signal is also amplified through modulation of the gate oxide thickness.
Influence of magnetic interactions between phases on the magnetocaloric effect of composites
Authors: Romero-Muñiz C. , Franco V. , Conde A.
Published: February 2013

Magnetocaloric materials with coexisting magnetic phases appear either due to the phase coexistence in first order phase transitions, or due to the development of composites, which are known to enhance the refrigerant capacity and produce table-like magnetocaloric effect. However, interactions between phases are rarely considered. We have modeled the influence of interactions on the magnetocaloric effect of a biphasic composite by implementing a mean field model. Interactions shift the peak magnetic entropy change to higher temperatures than those of the pure phases and enhance the table-like character of the curves. Although there is no qualitative change of the magnetocaloric response of the composites due to interactions, the optimal fraction of phases which produces the largest enhancement of the refrigerant capacity is shifted to compositions richer in the low Curie temperature phase. This shift can be used to estimate the magnitude of the interactions in composites measured experimentally.
Dust-acoustic solitary waves in dusty plasmas with non-thermal ions
Authors: Asgari H. , Muniandy S. V. , Wong C. S.
Published: February 2013

Most studies on dusty plasmas have assumed that electrons and ions follow Maxwellian distributions. However, in the presence of energetic ions, the distribution of ions tends to be non-Maxwellian. It is shown here that the existence of non-thermal ions would increase the phase velocity of a dust-acoustic wave. It is also found that the change in the phase velocity profoundly affects the characteristics of a dust-acoustic solitary wave.
Observation of a possible superconducting gap in silicene on Ag(111) surface
Authors: Chen Lan , Feng Baojie , Wu Kehui
Published: February 2013

A possible superconducting gap, about 35 meV, was observed in silicene on Ag(111) substrate by scanning tunneling spectroscopy. The temperature-dependence measurement reveals a superconductor-metal transition in silicene and gives a critical temperature of 35–40 K. The possible mechanism of superconductivity in silicene is discussed.
The effect of ground and first excited state transitions on transistor laser relative intensity noise
Authors: Tan F. , Xu W. , Huang X. , Feng M. , Holonyak N.
Published: February 2013

We report the results of relative intensity noise (RIN) measurement on the ground and first excited state transitions of a single quantum-well (QW) transistor laser (TL). Because of higher differential gain and faster recombination lifetime on the first excited state transition, a lower laser RIN is measured as compared with ground state laser operation. The minority carrier density in the base of QWTL extracted from the laser RIN shows a carrier density of 2.6–3.5 × 1016 cm−3, a more than 40× reduction from that of a conventional diode laser.
Transformation of diphenylarsinic acid and related compounds in groundwater: production of thiol-containing arsenicals
Authors: Nakamiya Kunichika , Yoshikane Mitsuha , Tomoko Hosoya , Shibata Yasuyuki
Published: February 2013

Environmental context
Contamination of groundwater by arsenic compounds used in chemical warfare research is a recently discovered environmental problem in Japan. We report evidence that the arsenic compounds originally present in the groundwater are transforming to thio-arsenic compounds of currently unknown environmental fate.

Abstract
During routine analyses of groundwater samples contaminated with diphenylarsinic acid (DPAA) at Kamisu, Ibaraki Prefecture, Japan, we obtained data indicating that unknown arsenic compounds accounted for up to 75% of the total arsenic in some of the samples. Results from using liquid chromatography in combination with elemental mass spectrometry and tandem molecular mass spectrometry suggested that two of the main unknown peaks were diphenyldithioarsinic acid and methylphenyldithioarsinic acid. These assignments were later confirmed by comparison with chemically synthesised compounds. A potential transformation scheme for DPAA in the environment is proposed based on the derivatives identified in the environmental samples.
Time-varying functional network information extracted from brief instances of spontaneous brain activity
Authors: Liu Xiao , Duyn Jeff H.
Published: February 2013

Recent functional magnetic resonance imaging studies have shown that the brain is remarkably active even in the absence of overt behavior, and this activity occurs in spatial patterns that are reproducible across subjects and follow the brain’s established functional subdivision. Investigating the distribution of these spatial patterns is an active area of research with the goal of obtaining a better understanding of the neural networks underlying brain function. One intriguing aspect of spontaneous activity is an apparent nonstationarity, or variability of interaction between brain regions. It was recently proposed that spontaneous brain activity may be dominated by brief traces of activity, possibly originating from a neuronal avalanching phenomenon. Such traces may involve different subregions in a network at different times, potentially reflecting functionally relevant relationships that are not captured with conventional data analysis. To investigate this, we examined publicly available functional magnetic resonance imaging data with a dedicated analysis method and found indications that functional networks inferred from conventional correlation analysis may indeed be driven by activity at only a few critical time points. Subsequent analysis of the activity at these critical time points revealed multiple spatial patterns, each distinctly different from the established functional networks. The spatial distribution of these patterns suggests a potential functional relevance.
Effects of insufficient sleep on circadian rhythmicity and expression amplitude of the human blood transcriptome
Authors: Möller-Levet Carla S. , Archer Simon N. , Bucca Giselda , Laing Emma E. , Slak Ana , Kabiljo Renata , Lo June C. Y. , Santhi Nayantara , von Schantz Malcolm , Smith Colin P. , Dijk Derk-Jan
Published: February 2013

Significance

Insufficient sleep and circadian rhythm disruption are associated with negative health outcomes, but the mechanisms involved remain largely unexplored. We show that one wk of insufficient sleep alters gene expression in human blood cells, reduces the amplitude of circadian rhythms in gene expression, and intensifies the effects of subsequent acute total sleep loss on gene expression. The affected genes are involved in chromatin remodeling, regulation of gene expression, and immune and stress responses. The data imply molecular mechanisms mediating the effects of sleep loss on health and highlight the interrelationships between sleep homeostasis, circadian rhythmicity, and metabolism.
PML mediates glioblastoma resistance to mammalian target of rapamycin (mTOR)-targeted therapies
Authors: Iwanami Akio , Gini Beatrice , Zanca Ciro , Matsutani Tomoo , Assuncao Alvaro , Nael Ali , Dang Julie , Yang Huijun , Zhu Shaojun , Kohyama Jun , Kitabayashi Issay , Cavenee Webster K. , Cloughesy Timothy F. , Furnari Frank B. , Nakamura Masaya , Toyama Yoshiaki , Okano Hideyuki , Mischel Paul S.
Published: February 2013

Despite their nearly universal activation of mammalian target of rapamycin (mTOR) signaling, glioblastomas (GBMs) are strikingly resistant to mTOR-targeted therapy. We analyzed GBM cell lines, patient-derived tumor cell cultures, and clinical samples from patients in phase 1 clinical trials, and find that the promyelocytic leukemia (PML) gene mediates resistance to mTOR-targeted therapies. Direct mTOR inhibitors and EGF receptor (EGFR) inhibitors that block downstream mTOR signaling promote nuclear PML expression in GBMs, and genetic overexpression and knockdown approaches demonstrate that PML prevents mTOR and EGFR inhibitor-dependent cell death. Low doses of the PML inhibitor, arsenic trioxide, abrogate PML expression and reverse mTOR kinase inhibitor resistance in vivo, thus markedly inhibiting tumor growth and promoting tumor cell death in mice. These results identify a unique role for PML in mTOR and EGFR inhibitor resistance and provide a strong rationale for a combination therapeutic strategy to overcome it.
Metal ions control product specificity of isoprenyl diphosphate synthases in the insect terpenoid pathway
Authors: Frick Sindy , Nagel Raimund , Schmidt Axel , Bodemann René R. , Rahfeld Peter , Pauls Gerhard , Brandt Wolfgang , Gershenzon Jonathan , Boland Wilhelm , Burse Antje
Published: February 2013

Isoprenyl diphosphate synthases (IDSs) produce the ubiquitous branched-chain diphosphates of different lengths that are precursors of all major classes of terpenes. Typically, individual short-chain IDSs (scIDSs) make the C
10
, C
15
, and C
20
isoprenyl diphosphates separately. Here, we report that the product length synthesized by a single scIDS shifts depending on the divalent metal cofactor present. This previously undescribed mechanism of carbon chain-length determination was discovered for a scIDS from juvenile horseradish leaf beetles,
Phaedon cochleariae
. The recombinant enzyme
P. cochleariae
isoprenyl diphosphate synthase 1 (
Pc
IDS1) yields 96% C
10
-geranyl diphosphate (GDP) and only 4% C
15
-farnesyl diphosphate (FDP) in the presence of Co
2+
or Mn
2+
as a cofactor, whereas it yields only 18% C
10
GDP but 82% C
15
FDP in the presence of Mg
2+
. In reaction with Co
2+
,
Pc
IDS1 has a
K
m
of 11.6 μM for dimethylallyl diphosphate as a cosubstrate and 24.3 μM for GDP. However, with Mg
2+
,
Pc
IDS1 has a
K
m
of 1.18 μM for GDP, suggesting that this substrate is favored by the enzyme under such conditions. RNAi targeting
Pc
IDS1 revealed the participation of this enzyme in the de novo synthesis of defensive monoterpenoids in the beetle larvae. As an FDP synthase,
Pc
IDS1 could be associated with the formation of sesquiterpenes, such as juvenile hormones. Detection of Co
2+
, Mn
2+
, or Mg
2+
in the beetle larvae suggests flux control into C
10
vs. C
15
isoprenoids could be accomplished by these ions in vivo. The dependence of product chain length of scIDSs on metal cofactor identity introduces an additional regulation for these branch point enzymes of terpene metabolism.
Identification of parameters through which surface chemistry determines the lifetimes of hot electrons in small Au nanoparticles
Authors: Aruda Kenneth O. , Tagliazucchi Mario , Sweeney Christina M. , Hannah Daniel C. , Schatz George C. , Weiss Emily A.
Published: February 2013

This paper describes measurements of the dynamics of hot electron cooling in photoexcited gold nanoparticles (Au NPs) with diameters of ∼3.5 nm, and passivated with either a hexadecylamine or hexadecanethiolate adlayer, using ultrafast transient absorption spectroscopy. Fits of these dynamics with temperature-dependent Mie theory reveal that both the electronic heat capacity and the electron–phonon coupling constant are larger for the thiolated NPs than for the aminated NPs, by 40% and 30%, respectively. Density functional theory calculations on ligand-functionalized Au slabs show that the increase in these quantities is due to an increased electronic density of states near the Fermi level upon ligand exchange from amines to thiolates. The lifetime of hot electrons, which have thermalized from the initial plasmon excitation, increases with increasing electronic heat capacity, but decreases with increasing electron–phonon coupling, so the effects of changing surface chemistry on these two quantities partially cancel to yield a hot electron lifetime of thiolated NPs that is only 20% longer than that of aminated NPs. This analysis also reveals that incorporation of a temperature-dependent electron–phonon coupling constant is necessary to adequately fit the dynamics of electron cooling.