bluuebunny/crossref_metadata_2025 huggingface dataset:
Rotational spectroscopy of pyridazine and its isotopologs from 235–360 GHz: Equilibrium structure and vibrational satellites
Authors: Esselman Brian J. , Amberger Brent K. , Shutter Joshua D. , Daane Mitchell A. , Stanton John F. , Woods R. Claude , McMahon Robert J.
Published: December 2013

The rotational spectrum of pyridazine (o-C4H4N2), the ortho disubstituted nitrogen analog of benzene, has been measured and analyzed in the gas phase. For the ground vibrational state of the normal isotopolog, over 2000 individual rotational transitions have been identified between 238 and 360 GHz and have been fit to 13 parameters of a 6th-order centrifugal distortion Hamiltonian. All transitions in this frequency region can now be predicted from this model to near experimental accuracy, i.e., well enough for the purpose of any future radio-astronomical search for this species. Three isotopologs, [3-13C]-C4H4N2, [4-13C]-C4H4N2, and [1-15N]-C4H4N2, have been detected in natural abundance, and several hundred lines have been measured for each of these species and fit to 6th-order Hamiltonians. Ten additional isotopologs were synthesized with enhanced deuterium substitution and analyzed to allow for a complete structure determination. The equilibrium structure (Re) of pyridazine was obtained by correcting the experimental rotational constants for the effects of vibration-rotation coupling using interaction constants predicted from CCSD(T) calculations with an ANO0 basis set and further correcting for the effect of electron mass. The final Re structural parameters are determined with excellent accuracy, as evidenced by their ability to predict 28 independent moments of inertia (Ia and Ib for 14 isotopologs) very well from 9 structural parameters. The rotational spectra of the six lowest-energy fundamental vibrational satellites of the main isotopolog have been detected. The rotational spectra of the five lowest-energy vibrational satellites have been assigned and fit to yield accurate rotational and distortion constants, while the fit and assignment for the sixth is less complete. The resultant vibration-rotation interaction (α) constants are found to be in excellent agreement with ones predicted from coupled-cluster calculations, which proved to be the key to unambiguous assignment of the satellite spectra to specific vibration modes.
Creation of mixed beam from alloy target and couple of pure targets with laser
Authors: Ikeda Shunsuke , Romanelli Mark , Cinquegrani David , Sekine Megumi , Kumaki Masafumi , Fuwa Yasuhiro , Munemoto Naoya , Kanesue Takeshi , Jin Qianyu , Okamura Masahiro , Horioka Kazuhiko
Published: December 2013

To create mixed species ion beam with laser pulses, we investigated charge state distributions of plasma formed from both Al-Fe alloy targets and pure Al and Fe targets placed close together. With two targets, we observed that the two kinds of atoms were mixed when the interval of two laser pulses was large enough (40 μs). On the other hand, when the interval was 0.0 μs, we observed fewer Fe ions and they did not mix well with the Al ions. The two species were mixed well in the plasma from the alloy target. Furthermore, we observed that specific charge states of Fe ions increased. From the results, it was determined that we can use two pure targets to mix two species whose difference of the drift velocity is large. On the other hand, we must use an alloy target when the drift velocities of the species are close.
Numerical simulation of ion charge breeding in electron beam ion source
Authors: Zhao L. , Kim Jin-Soo
Published: December 2013

The Electron Beam Ion Source particle-in-cell code (EBIS-PIC) tracks ions in an EBIS electron beam while updating electric potential self-consistently and atomic processes by the Monte Carlo method. Recent improvements to the code are reported in this paper. The ionization module has been improved by using experimental ionization energies and shell effects. The acceptance of injected ions and the emittance of extracted ion beam are calculated by extending EBIS-PIC to the beam line transport region. An EBIS-PIC simulation is performed for a Cs charge-breeding experiment at BNL. The charge state distribution agrees well with experiments, and additional simulation results of radial profiles and velocity space distributions of the trapped ions are presented.
A room temperature electron cyclotron resonance ion source for the DC-110 cyclotron
Authors: Efremov A. , Bogomolov S. , Lebedev A. , Loginov V. , Yazvitsky N.
Published: December 2013

The project of the DC-110 cyclotron facility to provide applied research in the nanotechnologies (track pore membranes, surface modification of materials, etc.) has been designed by the Flerov Laboratory of Nuclear Reactions of the Joint Institute for Nuclear Research (Dubna). The facility includes the isochronous cyclotron DC-110 for accelerating the intensive Ar, Kr, Xe ion beams with 2.5 MeV/nucleon fixed energy. The cyclotron is equipped with system of axial injection and ECR ion source DECRIS-5, operating at the frequency of 18 GHz. This article reviews the design and construction of DECRIS-5 ion source along with some initial commissioning results.
Ion source developments for the production of radioactive isotope beams at TRIUMF
Authors: Ames F. , Bricault P. , Heggen H. , Kunz P. , Lassen J. , Mjøs A. , Raeder S. , Teigelhöfer A.
Published: December 2013

At the ISAC facility at TRIUMF radioactive ions are produced by bombarding solid targets with up to 100 μA of 500 MeV protons. The reaction products have to diffuse out of the hot target into an ion source. Normally, singly charged ions are extracted. They can be transported either directly to experiments or via an ECR charge state breeder to a post accelerator. Several different types of ion sources have to be used in order to deliver a large variety of rare isotope beams. At ISAC those are surface ion sources, forced electron beam arc discharge (FEBIAD) ion sources and resonant laser ionization sources. Recent development activities concentrated on increasing the selectivity for the ionization to suppress isobaric contamination in the beam. Therefore, a surface ion rejecting resonant laser ionization source (SIRLIS) has been developed to suppress ions from surface ionization. For the FEBIAD ion source a cold transfer line has been introduced to prevent less volatile components from reaching the ion source.
Double, Rydberg and charge transfer excitations from pairing matrix fluctuation and particle-particle random phase approximation
Authors: Yang Yang , van Aggelen Helen , Yang Weitao
Published: December 2013

Double, Rydberg, and charge transfer (CT) excitations have been great challenges for time-dependent density functional theory (TDDFT). Starting from an (N ± 2)-electron single-determinant reference, we investigate excitations for the N-electron system through the pairing matrix fluctuation, which contains information on two-electron addition/removal processes. We adopt the particle-particle random phase approximation (pp-RPA) and the particle-particle Tamm-Dancoff approximation (pp-TDA) to approximate the pairing matrix fluctuation and then determine excitation energies by the differences of two-electron addition/removal energies. This approach captures all types of interesting excitations: single and double excitations are described accurately, Rydberg excitations are in good agreement with experimental data and CT excitations display correct 1/R dependence. Furthermore, the pp-RPA and the pp-TDA have a computational cost similar to TDDFT and consequently are promising for practical calculations.
Domain of validity of the perturbative approach to femtosecond optical spectroscopy
Authors: Gelin Maxim F. , Rao B. Jayachander , Nest Mathias , Domcke Wolfgang
Published: December 2013

We have performed numerical nonperturbative simulations of transient absorption pump-probe responses for a series of molecular model systems. The resulting signals as a function of the laser field strength and the pump-probe delay time are compared with those obtained in the perturbative response function formalism. The simulations and their theoretical analysis indicate that the perturbative description remains valid up to moderately strong laser pulses, corresponding to a rather substantial depopulation (population) of the initial (final) electronic states.
On the diagonal susceptibility of the two-dimensional Ising model
Authors: Tracy Craig A. , Widom Harold
Published: December 2013

We consider the diagonal susceptibility of the isotropic 2D Ising model for temperatures below the critical temperature. For a parameter k related to temperature and the interaction constant, we extend the diagonal susceptibility to complex k inside the unit disc, and prove the conjecture that the unit circle is a natural boundary.
Dynamics of a polyelectrolyte in simple shear flow
Authors: Jayasree Kandiledath , Kumar Manna Raj , Banerjee Debapriya , Kumar P. B. Sunil
Published: December 2013

The configurational dynamics of a polyelectrolyte (PE), subjected to a simple shear flow, is studied using Brownian dynamics (BD) and Dissipative Particle Dynamics (DPD) simulations of a bead-spring model with explicit counterions. We explore the effect of counterion condensation on the tumbling and extension of PEs by varying the shear rates for a range of values of the electrostatic coupling parameter A (which is defined as the ratio of the Bjerrum length to the size of the monomer). In all cases, the power spectrum of Rs(t) (which characterizes the projected length of the PE in the flow direction as a function of time) exhibits a power law decay at high frequencies, similar to that for a dumbbell in shear flow. For lower values of A (A ∼ 2), the tumbling of the PE is periodic and is always associated with folding and stretching, which is in contrast to the oscillatory transition between the extended and globular states seen at higher values of A (A ∼ 15). We observe that for A ∼ 2 the tumbling frequency decreases and the average tumbling time increases with hydrodynamic interaction (HI). For A > 15, we observe a critical shear rate \documentclass[12pt]{minimal}\begin{document}${\dot{\gamma }}_c$\end{document}γ̇c below which there is considerable counterion condensation and the PE remains in the globular state with a structure akin to that of a neutral polymer in poor solvent. The \documentclass[12pt]{minimal}\begin{document}${\dot{\gamma }}_c$\end{document}γ̇c and the behavior of the PE above the critical shear rate are dependent on the HI. For a given shear rate, when there is considerable condensed counterion fluctuation, the PE extends as a whole and then collapses by the formation of folds with no observable periodicity in tumbling. When the condensed counterion fluctuations are suppressed, the polymer exhibits periodic tumbling. Simulation artifacts resulting from the implicit nature of the solvent and that due to boundary conditions are discussed by comparing the BD results with that obtained from the DPD simulations incorporating Ewald summation for electrostatics.
Ionic liquids from the bottom up: Local assembly motifs in [EMIM][BF4] through cryogenic ion spectroscopy
Authors: Johnson Christopher J. , Fournier Joseph A. , Wolke Conrad T. , Johnson Mark A.
Published: December 2013

To clarify the intramolecular distortions exhibited by the complementary ions in the archetypal ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate [EMIM][BF4], we report the vibrational spectra of the isolated ionic constituents and small aggregates cooled to about 10 K. Deuteration of bare EMIM+ at the C(2) position, the putative hydrogen bond donating group, establishes that the observed bulk red shift is too small (<10 cm−1) for hydrogen bonding to be a dominant structural feature. We then analyze how the vibrational patterns evolve with increasing size to identify the spectral signatures of well-defined structural motifs in the growing assembly. Surprisingly, the main features of the bulk spectrum are already developed in the cluster with a single BF4− anion sandwiched between just two EMIM+ cations. We suggest that this local motif, while not strongly hydrogen bonded, nonetheless induces considerable intensity in the C(2)H stretches and is a robust feature in the local molecular structure of the liquid.
Bioorganic nanodots for non-volatile memory devices
Authors: Amdursky Nadav , Shalev Gil , Handelman Amir , Litsyn Simon , Natan Amir , Roizin Yakov , Rosenwaks Yossi , Szwarcman Daniel , Rosenman Gil
Published: December 2013

In recent years we are witnessing an intensive integration of bio-organic nanomaterials in electronic devices. Here we show that the diphenylalanine bio-molecule can self-assemble into tiny peptide nanodots (PNDs) of ∼2 nm size, and can be embedded into metal-oxide-semiconductor devices as charge storage nanounits in non-volatile memory. For that purpose, we first directly observe the crystallinity of a single PND by electron microscopy. We use these nanocrystalline PNDs units for the formation of a dense monolayer on SiO2 surface, and study the electron/hole trapping mechanisms and charge retention ability of the monolayer, followed by fabrication of PND-based memory cell device.
Electrical conduction mechanism in La3Ta0.5Ga5.3Al0.2O14 single crystals
Authors: Yaokawa Ritsuko , Aota Katsumi , Uda Satoshi
Published: December 2013

The electrical conduction mechanism in La3Ta0.5Ga5.3Al0.2O14 (LTGA) single crystals was studied by nonstoichiometric defect formation during crystal growth. Since stoichiometric LTGA is not congruent, the single crystal grown from the stoichiometric melt was Ta-poor and Al-rich, where Al atoms were substituted not only in Ga sites but also in Ta sites. The population of the substitutional Al in Ta sites increased with increasing oxygen partial pressure during growth (growth-pO2) in the range from 0.01 to 1 atm. Below 600 °C, substitutional Al atoms in Ta sites were ionized to yield holes, and thus the electrical conductivity of the LTGA crystal depended on temperature and the growth-pO2. The dependence of the electrical conductivity on the growth-pO2 decreased as temperature increased. The temperature rise increases ionic conductivity, for which the dominant carriers are oxygen defects formed by the anion Frenkel reaction.
A percolation-based model for the conductivity of nanofiber composites
Authors: Chatterjee Avik P.
Published: December 2013

A model is presented that integrates the critical path approximation with percolation theory to describe the dependence of electrical conductivity upon volume fraction in nanofiber-based composites. The theory accounts for clustering and correlation effects that reflect non-randomness in the spatial distribution of the particles. Results from this formalism are compared to experimental measurements performed upon carbon nanotube-based conductive nanocomposites.
Electrical and microstructure analysis of nickel-based low-resistance ohmic contacts to n-GaSb
Authors: Rahimi Nassim , Aragon Andrew A. , Romero Orlando S. , Shima Darryl M. , Rotter Thomas J. , Mukherjee Sayan D. , Balakrishnan Ganesh , Lester Luke F.
Published: December 2013

Ultra low resistance ohmic contacts are fabricated on n-GaSb grown by molecular beam epitaxy. Different doping concentrations and n-GaSb thicknesses are studied to understand the tunneling transport mechanism between the metal contacts and the semiconductor. Different contact metallization and anneal process windows are investigated to achieve optimal penetration depth of Au in GaSb for low resistances. The fabrication, electrical characterization, and microstructure analysis of the metal-semiconductor interfaces created during ohmic contact formation are discussed. The characterization techniques include cross-sectional transmission electron microscopy and energy dispersive spectroscopy. Specific transfer resistances down to 0.1 Ω mm and specific contact resistances of 1 × 10−6 Ω cm2 are observed.
First-principles study of quantum confinement and surface effects on the electronic properties of InAs nanowires
Authors: Ning Feng , Tang Li-Ming , Zhang Yong , Chen Ke-Qiu
Published: December 2013

We have used first principles methods to systematically investigate the quantum confinement effect on the electronic properties of zinc-blende (ZB) and wurtzite (WZ) InAs nanowires (NWs) with different orientations and diameters, and compared their electronic properties before and after pseudo-hydrogen passivation. The results show that the calculated carrier effective masses are dependent on the NW diameter, except for [110] ZB NWs, and the hole effective masses of [111] ZB NWs are larger than the electron effective masses when the NW diameter is ≥26 Å. The band alignments of [111] ZB and [0001] WZ NWs reveal that the effect of quantum confinement on the conduction bands is greater than on the valence bands, and the position of the valence band maximum level changes little with increasing NW diameter. The pseudo-hydrogen passivated NWs have larger band gaps than the corresponding unpassivated NWs. The carrier effective masses and mobilities can be adjusted by passivating the surface dangling bonds.
Enhanced thermoelectric power factor in Yb1−xScxAl2 alloys using chemical pressure tuning of the Yb valence
Authors: Lehr Gloria J. , Morelli Donald T. , Jin Hyungyu , Heremans Joseph P.
Published: December 2013

We have investigated the influence of Sc substitution on the transport and magnetic properties of YbAl2, a well-known intermediate valence compound. Sc substitution provides a chemical pressure that decreases the lattice constant and thereby alters the Yb valence as a function of composition and temperature. We observe a strong correlation between the Seebeck coefficient and the ratio of trivalent to divalent Yb in these compounds, as determined from magnetic susceptibility measurements. This correlation indicates that the largest absolute value of the Seebeck coefficient is achieved when the average Yb valence is near 2.5 (the ratio of divalent to trivalent Yb is 1:1). It is shown that Sc concentration can be used as a means to tune both the magnitude of the maximum of the Seebeck coefficient and the temperature at which this absolute maximum occurs, improving the prospects of the use of these materials in cryogenic Peltier coolers.
Role of polaron hopping in leakage current behavior of a SrTiO3 single crystal
Authors: Cao Y. , Bhattacharya S. , Shen J. , Randall C. A. , Chen L. Q.
Published: December 2013

We studied the ionic/electronic transport and resistance degradation behavior of dielectric oxides by solving the electrochemical transport equations. Here, we took into account the non-periodical boundary conditions for the transport equations using the Chebyshev collocation algorithm. A sandwiched Ni|SrTiO3|Ni capacitor is considered as an example under the condition of 1.0 V, 1.0 μm thickness for SrTiO3 layer, and a temperature of 150 °C. The applied voltage resulted in the migration of ionic defects (oxygen vacancies) from anode towards cathode. The simulated electric potential profile at steady state is in good agreement with the recent experimental observation. We introduced the possibility of polaron-hopping between Ti3+ and Ti4+ at the electrode interface. It is shown that both the oxygen vacancy transport and the polaron-hopping contribute to the resistance degradation of single crystal SrTiO3, which is consistent with the experimental observations.
Spin-flip relaxation via optical phonon scattering in quantum dots
Authors: Wang Zi-Wu , Liu Lei , Li Shu-Shen
Published: December 2013

Based on the spin-orbit coupling admixture mechanism, we theoretically investigate the spin-flip relaxation via optical phonon scattering in quantum dots by considering the effect of lattice relaxation due to the electron-acoustic phonon deformation potential coupling. The relaxation rate displays a cusp-like structure (or a spin hot spot) that becomes more clearly with increasing temperature. We also calculate the relaxation rate of the spin-conserving process, which follows a Gaussian form and is several orders of magnitude larger than that of spin-flip process. Moreover, we find that the relaxation rate displays the oscillatory behavior due to the interplay effects between the magnetic and spatial confinement for the spin-flip process not for the spin-conserving process. The trends of increasing and decreasing temperature dependence of the relaxation rates for two relaxation processes are obtained in the present model.
Communication: Angular momentum alignment and fluorescence polarization of alkali atoms photodetached from helium nanodroplets
Authors: Hernando Alberto , Beswick J. Alberto , Halberstadt Nadine
Published: December 2013

The theory of photofragments angular momentum polarization is applied to the photodetachment of an electronically excited alkali atom from a helium nanocluster (N = 200). The alignment of the electronic angular momentum of the bare excited alkali atoms produced is calculated quantum mechanically by solving the excited states coupled equations with potentials determined by density functional theory (DFT). Pronounced oscillations as a function of excitation energy are predicted for the case of Na@(He)200, in marked contrast with the absorption cross-section and angular distribution of the ejected atoms which are smooth functions of the energy. These oscillations are due to quantum interference between different coherently excited photodetachment pathways. Experimentally, these oscillations should be reflected in the fluorescence polarization and polarization-resolved photoelectron yield of the ejected atoms, which are proportional to the electronic angular momentum alignment. In addition, this result is much more general than the test case of NaHe200 studied here. It should be observable for larger droplets, for higher excited electronic states, and for other alkali as well as for alkali-earth atoms. Detection of these oscillations would show that the widely used pseudo-diatomic model can be valid beyond the prediction of absorption spectra and could help in interpreting parts of the dynamics, as already hinted by some experimental results on angular anisotropy of bare alkali fragments.
NaLaF4:Pr3+,Yb3+, an efficient blue to near infra-red quantum cutter
Authors: Guille A. , Pereira A. , Moine B.
Published: December 2013

In order to reduce the thermalization losses in solar cells, down-conversion of blue photons into near infra-red photons is a promising solution. In the present paper, we analyse the energy transfer processes between Pr3+ and Yb3+ in NaLaF4 and we show that an efficient quantum-cutting process occurs. Nevertheless, we also show that a back transfer from Yb3+ toward the 1G4 level of Pr3+ ion leading to emission beyond 1 μm reduces the potentiality of this material as a quantum cutter for Si solar cells.
The reversal of the laser-beam-induced-current contrast with varying illumination density in a Cu2ZnSnSe4 thin-film solar cell
Authors: Chen Qiong , Zhang Yong
Published: December 2013

We apply an array of correlated spatially-resolved techniques, including μ-Raman/photoluminescence/reflectance/laser-beam-induced-current in conjunction with scanning electron microscopy and atomic force microscopy, to study the impact of the microscopic-scale thickness inhomogeneity of CdS layer in a Cu2ZnSnSe4 thin-film solar cell. Thicker CdS regions are found to cause more light reflecting loss thus yield lower external quantum efficiencies and energy conversion efficiencies than the general area. However, these regions show much less efficiency degradation at high illumination intensity, leading to an inversion of laser-beam-induced-current contrast in the area mapping. While improving the CdS layer uniformity can boost the device performance, the finding further points out the possibility of operating thin-film photovoltaic devices based on the similar materials (such as CuInGaSe2, CdTe, Cu2ZnSn(S,Se)4) under a substantially higher illumination density for concentrated photovoltaic and photo-detection.
Effect of intentional p-GaN surface roughening on the performance of InGaN/GaN solar cells
Authors: Farrell R. M. , Al-Heji A. A. , Neufeld C. J. , Chen X. , Iza M. , Cruz S. C. , Keller S. , Nakamura S. , DenBaars S. P. , Mishra U. K. , Speck J. S.
Published: December 2013

The effect of intentional p-GaN surface roughening on the performance of c-plane InGaN/GaN solar cells was investigated. Surface roughness was introduced by growing the p-GaN at a relatively high rate and low temperature which resulted in a faceted surface with a high density of V-defects. Increasing the surface roughness led to a 69.4% increase in short circuit current density. Similar surface roughening techniques should also be applicable for increasing the extraction efficiency of InGaN/GaN light-emitting diodes.
Sensitivity of laboratory based implementations of edge illumination X-ray phase-contrast imaging
Authors: Diemoz P. C. , Hagen C. K. , Endrizzi M. , Olivo A.
Published: December 2013

We present a theoretical and experimental analysis of the angular sensitivity of edge illumination X-ray phase-contrast imaging in its implementation with conventional X-ray sources (sometimes referred to as the “coded-aperture” method). We study how the polychromaticity and finite source dimensions encountered in laboratory-based setups affect the detected signal. We also show that the sensitivity is independent of the period of the masks. Experimental images are presented and analyzed, proving that, despite the simple setup, high angular resolutions of a few hundred nanoradians can be obtained.
Thermal creation of electron spin polarization in n-type silicon
Authors: Dankert André , Dash Saroj P.
Published: December 2013

Conversion of heat into a spin-current in electron doped silicon can offer a promising path for spin-caloritronics. Here, we create an electron spin polarization in the conduction band of n-type silicon by producing a temperature gradient across a ferromagnetic tunnel contact. The substrate heating experiments induce a large spin signal of 95 μV, corresponding to 0.54 meV spin-splitting in the conduction band of n-type silicon by Seebeck spin tunneling mechanism. The thermal origin of the spin injection has been confirmed by the quadratic scaling of the spin signal with the Joule heating current and linear dependence with the heating power.
L1-FePd nanocluster wires by template-directed thermal decomposition and subsequent hydrogen reduction
Authors: Cui B. Z. , Marinescu M. , Liu J. F.
Published: December 2013

This paper reports the nanostructure, formation mechanism, and magnetic properties of tetragonal L10-type Fe55Pd45 (at. %) nanocluster wires (NCWs) fabricated by thermal decomposition of metal nitrates and subsequent hydrogen reduction in nanoporous anodized aluminum oxide templates. The as-synthesized NCWs have diameters in the range of 80–300 nm, and lengths in the range of 0.5–10 μm. The NCWs are composed of roughly round-shaped nanoclusters in the range of 3–30 nm in size and a weighted average size of 10 nm with a mixture of single-crystal and poly-crystalline structures. The obtained intrinsic coercivity iHc of 3.32 kOe at room temperature for the tetragonal Fe55Pd45 NCWs is higher than those of electrodeposited Fe-Pd solid nanowires while among the highest values reported so far for L10-type FePd nanoparticles.
Dynamics of thermalization in GaInN/GaN quantum wells grown on ammonothermal GaN
Authors: Binder J. , Korona K. P. , Wysmołek A. , Kamińska M. , Köhler K. , Kirste L. , Ambacher O. , Zając M. , Dwiliński R.
Published: December 2013

In this work, we present measurements of the dynamics of photoexcited carriers in GaInN/GaN quantum wells (QWs) grown on ammonothermal GaN, especially thermalization and recombination rates. Emission properties were measured by time-resolved photoluminescence (PL) and electroluminescence spectroscopy. Due to the use of high quality homoepitaxial material, we were able to obtain very valuable data on carrier thermalization. The temperature dependence of the QW energy observed in PL shows characteristic S-shape with a step of about 10 meV. Such a behavior (related to thermalization and localization at potential fluctuations) is often reported for QWs; but in our samples, the effect is smaller than in heteroepitaxial InGaN/GaN QWs due to lower potential fluctuation in our material. Absorption properties were studied by photocurrent spectroscopy measurements. A comparison of emission and absorption spectra revealed a shift in energy of about 60 meV. Contrary to PL, the QW energy observed in absorption decreases monotonically with temperature, which can be described by a Bose-like dependence E(T) = E(0) − λ/(exp(θ/T) − 1), with parameters λ = (0.11 ± 0.01) eV, θ = (355 ± 20) K, or by a Varshni dependence with coefficients α = (10 ± 3) × 10−4 eV/K and β = (1500 ± 500) K. Taking into account absorption and emission, the fluctuation amplitude (according to Eliseev theory) was σ = 14 meV. The time resolved PL revealed that in a short period (<1 ns) after excitation, the PL peaks were broadened because of the thermal distribution of carriers. We interpreted this distribution in terms of quasi-temperature (Tq) of the carriers. The initial Tq was of the order of 500 K. The thermalization led to a fast decrease of Tq. The obtained cooling time in the QW was τC = 0.3 ns, which was faster than the observed recombination time τR = 2.2 ns (at 4 K).
Silicon-oxide-assisted wear of a diamond-containing composite
Authors: Xiao Huaping , Sinyukov Alexander M. , He Xingliang , Lin Chih , Liang Hong
Published: December 2013

A composite containing diamond in silicon carbide substrate was studied for revealing wear mechanisms. Due to the low production cost, this material is being evaluated as an alternative economical solution in industry. Tribochemical examination was conducted using a pin-on-disk configuration in both aqueous and dry environments. Characterization was conducted on worn disks and wear debris. Phase transformation from diamond carbon (sp3) to graphite, tetrahedral carbon, or amorphous carbon (sp2) in friction was confirmed by Raman spectroscopy. In addition, the Raman peak of wear debris identified a shift from crystalline Si (521 cm−1) to the mixture of amorphous silicon and silicon oxide at 510 cm−1. The surface roughness of the diamond particles was found to be greatly reduced due to wear. The smoothening of the edges was due to polishing by silicon oxide as abrasives promoting removal of weaker sp2 bonded carbon. This research proposes a tribochemical wear mechanism of diamond that has significant benefits in the applications of automotive, aerospace, and energy industries.
Vibrationally induced center reconfiguration in co-doped GaN:Eu, Mg epitaxial layers: Local hydrogen migration vs. activation of non-radiative channels
Authors: Mitchell B. , Lee D. , Lee D. , Fujiwara Y. , Dierolf V.
Published: December 2013

Europium doped gallium nitride (GaN:Eu) is a promising candidate as a material for red light emitting diodes. When Mg was co-doped into GaN:Eu, additional incorporation environments were discovered that show high excitation efficiency at room temperature and have been attributed to the coupling of Mg-H complexes to the majority Eu site. Electron beam irradiation, indirect and resonant (direct) laser excitation were found to modify these complexes, indicating that vibrational energy alone can trigger the migration of the H while the presence of additional charges and excess energy controls the type of reconfiguration and the activation of non-radiative decay channels.
Evidence for topological band inversion of the phase change material Ge2Sb2Te5
Authors: Pauly Christian , Liebmann Marcus , Giussani Alessandro , Kellner Jens , Just Sven , Sánchez-Barriga Jaime , Rienks Emile , Rader Oliver , Calarco Raffaella , Bihlmayer Gustav , Morgenstern Markus
Published: December 2013

We present an angle-resolved photoemission study of a ternary phase change material, namely Ge2Sb2Te5, epitaxially grown on Si(111) in the metastable cubic phase. The observed upper bulk valence band shows a minimum at Γ¯ being 0.3 eV below the Fermi level EF and a circular Fermi contour around Γ¯ with a dispersing diameter of 0.27–0.36 Å−1. This is in agreement with density functional theory calculations of the Petrov stacking sequence in the cubic phase which exhibits a topological surface state. The topologically trivial cubic Kooi-De Hosson stacking shows a valence band maximum at Γ in line with all previous calculations of the hexagonal stable phase exhibiting the valence band maximum at Γ for a trivial Z2 topological invariant ν0 and away from Γ for non-trivial ν0. Scanning tunneling spectroscopy exhibits a band gap of 0.4 eV around EF.
Layered insulator hexagonal boron nitride for surface passivation in quantum dot solar cell
Authors: Shanmugam Mariyappan , Jain Nikhil , Jacobs-Gedrim Robin , Xu Yang , Yu Bin
Published: December 2013

Single crystalline, two dimensional (2D) layered insulator hexagonal boron nitride (h-BN), is demonstrated as an emerging material candidate for surface passivation on mesoporous TiO2. Cadmium selenide (CdSe) quantum dot based bulk heterojunction (BHJ) solar cell employed h-BN passivated TiO2 as an electron acceptor exhibits photoconversion efficiency ∼46% more than BHJ employed unpassivated TiO2. Dominant interfacial recombination pathways such as electron capture by TiO2 surface states and recombination with hole at valence band of CdSe are efficiently controlled by h-BN enabled surface passivation, leading to improved photovoltaic performance. Highly crystalline, confirmed by transmission electron microscopy, dangling bond-free 2D layered h-BN with self-terminated atomic planes, achieved by chemical exfoliation, enables efficient passivation on TiO2, allowing electronic transport at TiO2/h-BN/CdSe interface with much lower recombination rate compared to an unpassivated TiO2/CdSe interface.
Electrical spin injection using GaCrN in a GaN based spin light emitting diode
Authors: Banerjee D. , Adari R. , Sankaranarayan S. , Kumar A. , Ganguly S. , Aldhaheri R. W. , Hussain M. A. , Balamesh A. S. , Saha D.
Published: December 2013

We have demonstrated electrical spin-injection from GaCrN dilute magnetic semiconductor (DMS) in a GaN-based spin light emitting diode (spin-LED). The remanent in-plane magnetization of the thin-film semiconducting ferromagnet has been used for introducing the spin polarized electrons into the non-magnetic InGaN quantum well. The output circular polarization obtained from the spin-LED closely follows the normalized in-plane magnetization curve of the DMS. A saturation circular polarization of ∼2.5% is obtained at 200 K.
Effect of dietary ellagic acid supplementation on semen quality parameters in chickens
Authors: Shanmugam M. , Rao S. V. Rama
Published: December 2013

Ellagic acid (EA), a polyphenoloic constituent in fruits and nuts, has been shown to have antioxidant and antiapoptotic properties. The aim of this study was to investigate the effect of dietary EA supplementation on semen quality parameters in chickens. Forty roosters (Dahlem Red breed), 28 weeks of age, were randomly assigned to four groups and fed diets containing EA at 0, 25, 50, or 75 mg/kg for 8 weeks. Semen was evaluated for volume, appearance, individual motility, sperm concentration, 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) dye reduction test, and live, dead and abnormal sperm counts. The seminal plasma was separated and evaluated for protein, alkaline phosphatase, and lipid peroxidation. At the end of the experiment, blood from individual birds was collected, and serum was separated and evaluated for superoxide dismutase activity, lipid peroxidation, and ferric-reducing ability of plasma. Supplementation with EA had no effect (P > 0.05) on gross semen parameters. Seminal plasma protein and lipid peroxidation were different (P < 0.01) between the treatment groups. The group fed EA at 75 mg/kg had high (P < 0.01) seminal plasma lipid peroxidation and lower (P < 0.05) serum superoxide dismutase activity. In conclusion, dietary supplementation of EA in chickens had no effect on the gross semen qualities and increased lipid peroxidation in seminal plasma.
Hatching success of rainbowfish eggs following exposure to air
Authors: Oulton Lois , Carbia Penelope , Brown Culum
Published: December 2013

Translocation of fishes within and between drainage basins is widely recognised as a threatening process to Australian native fishes. While many translocations are deliberate, for example for fisheries enhancement, it is possible that translocation can occur naturally. In the Wet Tropic region of Australia, the widespread eastern rainbowfish, Melanotaenia splendida, has begun to colonise the Atherton tablelands. This is of particular concern because the area is home to several endangered endemic species such as the Lake Eacham rainbowfish, M. eachamensis, and its allies. It is likely that some of the translocations have occurred through the use of this species as bait, but the recent invasion of Lake Eacham may have occurred naturally via the movement of eggs between nearby streams running into Lake Tinaroo. Here we determine whether rainbowfish eggs could be transported over land by examining their desiccation tolerance. In the first experiment we plucked eggs from spawning media and exposed them to air for varying amounts of time. The results show almost 100% mortality after just 15 min. Rainbowfish eggs have a web-like projection that enables them to adhere to aquatic vegetation. In the second experiment, therefore, eggs were exposed to air attached to simulated weed (wet acrylic wool). Around 20% of eggs on the simulated weed where still viable after an hour. The results show that rainbowfish eggs could readily be transported between catchments by aquatic birds or human leisure activities such as kayaking or swimming. The implications for conservation management of Australian freshwater species is discussed.
Recent advances in graphene-based planar micro-supercapacitors for on-chip energy storage
Authors: Wu Zhong-Shuai , Feng Xinliang , Cheng Hui-Ming
Published: December 2013

The current development trend towards miniaturized portable electronic devices has significantly increased the demand for ultrathin, flexible and sustainable on-chip micro-supercapacitors that have enormous potential to complement, or even to replace, micro-batteries and electrolytic capacitors. In this regard, graphene-based micro-supercapacitors with a planar geometry are promising micro-electrochemical energy-storage devices that can take full advantage of planar configuration and unique features of graphene. This review summarizes the latest advances in on-chip graphene-based planar interdigital micro-supercapacitors, from the history of their development, representative graphene-based materials (graphene sheets, graphene quantum dots and graphene hybrids) for their manufacture, typical microfabrication strategies (photolithography techniques, electrochemical methods, laser writing, etc.), electrolyte (aqueous, organic, ionic and gel), to device configuration (symmetric and asymmetric). Finally, the perspectives and possible development directions of future graphene-based micro-supercapacitors are briefly discussed.
First Report of the NA2 Lineage of Phytophthora ramorum from an Ornamental Rhododendron in the Interior of California
Authors: Garbelotto M. , Barbosa D. , Mehl H. , Rizzo D. M.
Published: December 2013

In July 2012, we collected a rhododendron var. Trilby with twig dieback symptoms in the lower canopy, consistent with the disease “ramorum blight” caused by Phytophthora ramorum. The symptomatic plant had been planted a year earlier to replace a dead rhododendron in a landscape setting in Placer County, California (Lat: 39.036216°; Long: –120.999274°), Sierra Nevada foothills at ~600 m elevation. Isolations yielded a culture with a fast growth rate and overall morphology resembling the P. ramorum NA2 lineage described by Ivors et al. (4). DNA was extracted from the culture as described previously (4) and six SSR loci: MS18, MS39, MS43, MS45, MS64, MS145, were amplified (2,4). Allelic patterns were compared with those of three testers from each of the three lineages NA1, NA2, and EU1 known to be present in ornamental plants in North America, and they unambiguously confirmed the isolate belongs to the NA2 lineage of the pathogen. Although the symptomatic plant was confined to a landscape setting, it had been planted in that location for a year, providing a possible source of inoculum for the surrounding area. This is the first report of P. ramorum from the Sierra Nevada eco-region in the interior of California. It is also the first report of a NA2 isolate from a plant outside of commercial nurseries in California. The mating type of the isolate was not determined, but NA2 isolates are normally A2, the same mating type of NA1 isolates. The only other report of a NA2 isolate found outside of a nursery is from Washington State (1). Although there is no evidence the pathogen may have infected other plants, the infected rhododendron was found at a location situated over 100 km east of the closest known infestation (www.sodmap.org). Additionally, this is the first report of the pathogen outside the coast mountain range of California. Because the three lineages are genetically and phenotypically distinct (3), the escape of NA2 or EU1 isolates, both still absent from plants in natural settings, could have significant implications for California ecosystems. This finding highlights that introductions of P. ramorum via ornamental plants are still possible, in spite of current regulations.

References: (1) G. Chastagner et al. Phytopathology 101:S32, 2011. (2) P. P. Croucher et al. Biol. Invasions 15:2281, 2013. (3) N. J. Grünwald et al. Trends Microbiol. 20:131, 2012. (4) K. Ivors et al. Mol. Ecol. 15:1493, 2006.
Surgical Treatment for Thoracic Myelopathy Due to Simultaneous Ossification of the Posterior Longitudinal Ligament and Ligamentum Flavum at the Same Level
Authors: Onishi Eijiro , Sano Hirokazu , Matsushita Mutsumi
Published: December 2013

Study Design:

Retrospective review.

Objective:

The aim of this study was to assess the clinical outcomes of surgery in patients with simultaneous ossification of the posterior longitudinal ligament (OPLL) and ossification of the ligamentum flavum (OLF) at the same thoracic spine level and identify the risk factors for poor outcomes.

Summary of Background Data:

OPLL complicated with OLF in the thoracic spine is a rare condition. The optimal treatment option for thoracic myelopathy due to OPLL and OLF remains controversial, and high risk of postoperative paralysis remains a major complication.

Methods:

We conducted a retrospective review of clinical and radiographic records of 15 patients who underwent surgery for simultaneous OPLL and OLF at the same level.

Results:

Simultaneous OPLL and OLF occurred in the upper thoracic spine in 3 patients (20%), mid-thoracic spine in 10 patients (67%), and lower thoracic spine in 2 patients (13%). Six, 4, 2, and 3 patients underwent posterior decompression, posterior decompression and fusion, posterior decompression and circumferential decompression through a posterior approach, and circumferential decompression and posterior fusion, respectively. The mean Japanese Orthopaedic Association score before surgery and at the final follow-up was 5.7±1.9 and 7.0±2.1 points, respectively, yielding a mean recovery rate of 16.5%. However, no significant difference was observed between preoperative and postoperative Japanese Orthopaedic Association scores. Two patients with mid-thoracic lesions reported postoperative lower extremity weakness. Mid-thoracic lesions and considerable blood loss were risk factors for poor surgical outcome.

Conclusions:

Simultaneous OPLL and OLF in the mid-thoracic spine was observed in two thirds of the patients. We suggest that simultaneous OPLL and OLF in this area has a relatively poor recovery and may be very challenging and risky to treat, regardless of the surgical method selected, and recommend early surgery for OPLL and OLF in the mid-thoracic spine.
Evolutionary inevitability of sexual antagonism
Authors: Connallon Tim , Clark Andrew G.
Published: December 2013

Sexual antagonism, whereby mutations are favourable in one sex and disfavourable in the other, is common in natural populations, yet the root causes of sexual antagonism are rarely considered in evolutionary theories of adaptation. Here, we explore the evolutionary consequences of sex-differential selection and genotype-by-sex interactions for adaptation in species with separate sexes. We show that sexual antagonism emerges naturally from sex differences in the direction of selection on phenotypes expressed by both sexes
or
from sex-by-genotype interactions affecting the expression of such phenotypes. Moreover, modest sex differences in selection or genotype-by-sex effects profoundly influence the long-term evolutionary trajectories of populations with separate sexes, as these conditions trigger the evolution of strong sexual antagonism as a by-product of adaptively driven evolutionary change. The theory demonstrates that sexual antagonism is an inescapable by-product of adaptation in species with separate sexes, whether or not selection favours evolutionary divergence between males and females.
Decay of interspecific avian flock networks along a disturbance gradient in Amazonia
Authors: Mokross Karl , Ryder Thomas B. , Côrtes Marina Corrêa , Wolfe Jared D. , Stouffer Philip C
Published: December 2013

Our understanding of how anthropogenic habitat change shapes species interactions is in its infancy. This is in large part because analytical approaches such as network theory have only recently been applied to characterize complex community dynamics. Network models are a powerful tool for quantifying how ecological interactions are affected by habitat modification because they provide metrics that quantify community structure and function. Here, we examine how large-scale habitat alteration has affected ecological interactions among mixed-species flocking birds in Amazonian rainforest. These flocks provide a model system for investigating how habitat heterogeneity influences non-trophic interactions and the subsequent social structure of forest-dependent mixed-species bird flocks. We analyse 21 flock interaction networks throughout a mosaic of primary forest, fragments of varying sizes and secondary forest (SF) at the Biological Dynamics of Forest Fragments Project in central Amazonian Brazil. Habitat type had a strong effect on network structure at the levels of both species and flock. Frequency of associations among species, as summarized by weighted degree, declined with increasing levels of forest fragmentation and SF. At the flock level, clustering coefficients and overall attendance positively correlated with mean vegetation height, indicating a strong effect of habitat structure on flock cohesion and stability. Prior research has shown that trophic interactions are often resilient to large-scale changes in habitat structure because species are ecologically redundant. By contrast, our results suggest that behavioural interactions and the structure of non-trophic networks are highly sensitive to environmental change. Thus, a more nuanced, system-by-system approach may be needed when thinking about the resiliency of ecological networks.