bluuebunny/crossref_metadata_2025 huggingface dataset:
Nuclear spin dependence of the reaction of ${\rm H}_3^+$H3+ with H2. II. Experimental measurements
Authors: Crabtree Kyle N. , Kauffman Carrie A. , Tom Brian A. , Beçka Eftalda , McGuire Brett A. , McCall Benjamin J.
Published: May 2011

The nuclear spin dependence of the chemical reaction \documentclass[12pt]{minimal}\begin{document}${\rm H}_3^+ +$\end{document}H3++ H2 → H2 + \documentclass[12pt]{minimal}\begin{document}${\rm H}_3^+$\end{document}H3+ has been studied in a hollow cathode plasma cell. Multipass infrared direct absorption spectroscopy has been employed to monitor the populations of several low-energy rotational levels of ortho- and para-\documentclass[12pt]{minimal}\begin{document}${\rm H}_3^+$\end{document}H3+ (o-\documentclass[12pt]{minimal}\begin{document}${\rm H}_3^+$\end{document}H3+ and p-\documentclass[12pt]{minimal}\begin{document}${\rm H}_3^+$\end{document}H3+) in hydrogenic plasmas of varying para-H2 (p-H2) enrichment. The ratio of the rates of the proton hop (kH) and hydrogen exchange (kE) reactions α ≡ kH/kE is inferred from the observed p-\documentclass[12pt]{minimal}\begin{document}${\rm H}_3^+$\end{document}H3+ fraction as a function of p-H2 fraction using steady-state chemical models. Measurements have been performed both in uncooled (Tkin ∼ 350 K) and in liquid-nitrogen-cooled (Tkin ∼ 135 K) plasmas, marking the first time this reaction has been studied at low temperature. The value of α has been found to decrease from 1.6 ± 0.1 at 350 K to 0.5 ± 0.1 at 135 K.
Photolysis of pure solid O3 and O2 films at 193 nm
Authors: Raut U. , Loeffler M. J. , Famá M. , Baragiola R. A.
Published: May 2011

We studied quantitatively the photochemistry of solid O3 and O2 films at 193 nm and 22 K with infrared spectroscopy and microgravimetry. Photolysis of pure ozone destroyed O3, but a small amount of ozone remained in the film at high fluence. Photolysis of pure O2 produced O3 in an amount that increased with photon fluence to a stationary level. For both O2 and O3 films, the O3:O2 ratio at large fluences is ∼0.07, about two orders of magnitude larger than those obtained in gas phase photolysis. This enhancement is attributed to the increased photodissociation of O2 due to photoabsorption by O2 dimers, a process significant at solid-state densities. We obtain initial quantum yield for ozone synthesis from solid oxygen, Φ(O3) = 0.24 ± 0.06, and quantum yields for destruction of O3 and O2 in their parent solids, Φ(−O3) = 1.0 ± 0.2 and Φ(−O2) = 0.36 ± 0.1. Combined with known photoabsorption cross sections, we estimate probabilities for geminate recombination of 0.5 ± 0.1 for O3 fragments and 0.88 ± 0.03 for oxygen atoms from O2 dissociation. Using a single parameter kinetic model, we deduce the ratio of reaction cross sections for an O atom with O2 vs. O3 to be 0.1–0.2. The general good agreement of the model with the data suggests the validity of the central assumption of efficient energy and spin relaxation of photofragments in the solid prior to their reactions with other species.
Dynamics of laser-produced Sn microplasma for a high-brightness extreme ultraviolet light source
Authors: Yuspeh S. , Tao Y. , Burdt R. A. , Tillack M. S. , Ueno Y. , Najmabadi F.
Published: May 2011

The effect of laser focal spot diameters of 26 and 150 μm on 13.5 nm extreme ultraviolet (EUV) radiation is investigated. Simulations show that the smaller spot size has a shorter electron plasma density scale length and deeper and denser laser energy deposition region. This results in additional time required for plasma expansion and radiation transport to efficiently emit EUV light. This is experimentally observed as an increase in the delay between the EUV emission and the laser pulse. The shorter scale length plasma reabsorbs less EUV light, resulting in a higher conversion efficiency, smaller and slightly brighter light source.
Exploring the top and bottom of the quantum control landscape
Authors: Beltrani Vincent , Dominy Jason , Ho Tak-San , Rabitz Herschel
Published: May 2011

A controlled quantum system possesses a search landscape defined by the target physical objective as a function of the controls. This paper focuses on the landscape for the transition probability Pi → f between the states of a finite level quantum system. Traditionally, the controls are applied fields; here, we extend the notion of control to also include the Hamiltonian structure, in the form of time independent matrix elements. Level sets of controls that produce the same transition probability value are shown to exist at the bottom Pi → f = 0.0 and top Pi → f = 1.0 of the landscape with the field and/or Hamiltonian structure as controls. We present an algorithm to continuously explore these level sets starting from an initial point residing at either extreme value of Pi → f. The technique can also identify control solutions that exhibit the desirable properties of (a) robustness at the top and (b) the ability to rapidly rise towards an optimal control from the bottom. Numerical simulations are presented to illustrate the varied control behavior at the top and bottom of the landscape for several simple model systems.
Fast ambipolar integrated circuits with poly(diketopyrrolopyrrole- terthiophene)
Authors: Roelofs W. S. C. , Mathijssen S. G. J. , Bijleveld J. C. , Raiteri D. , Geuns T. C. T. , Kemerink M. , Cantatore E. , Janssen R. A. J. , de Leeuw D. M.
Published: May 2011

Ambipolar integrated circuits were prepared with poly(diketopyrrolopyrrole-terthiophene) as the semiconductor. The field-effect mobility of around 0.02 cm2/V s for both electrons and holes allowed for fabrication of functional integrated complementary metal-oxide semiconductor (CMOS)-like inverters and ring oscillators. The oscillation frequency was found to have a near quadratic dependence on the supply bias. The maximum oscillation frequency was determined to be 42 kHz, which makes this ring oscillator the fastest CMOS-like organic circuit reported to date.
The potential energy landscape contribution to the dynamic heat capacity
Authors: Brown Jonathan R. , McCoy John D.
Published: May 2011

The dynamic heat capacity of a simple polymeric, model glassformer was computed using molecular dynamics simulations by sinusoidally driving the temperature and recording the resultant energy. The underlying potential energy landscape of the system was probed by taking a time series of particle positions and quenching them. The resulting dynamic heat capacity demonstrates that the long time relaxation is the direct result of dynamics resulting from the potential energy landscape. Moreover, the equilibrium (low frequency) portion of the potential energy landscape contribution to the heat capacity is found to increase rapidly at low temperatures and at high packing fractions. This increase in the heat capacity is explained by a statistical mechanical model based on the distribution of minima in the potential energy landscape.
Combined electron beam imaging and ab initio modeling of T1 precipitates in Al–Li–Cu alloys
Authors: Dwyer C. , Weyland M. , Chang L. Y. , Muddle B. C.
Published: May 2011

Among the many considerable challenges faced in developing a rational basis for advanced alloy design, establishing accurate atomistic models is one of the most fundamental. Here we demonstrate how advanced imaging techniques in a double-aberration-corrected transmission electron microscope, combined with ab initio modeling, have been used to determine the atomic structure of embedded 1 nm thick T1 precipitates in precipitation-hardened Al–Li–Cu aerospace alloys. The results provide an accurate determination of the controversial T1 structure, and demonstrate how next-generation techniques permit the characterization of embedded nanostructures in alloys and other nanostructured materials.
Shrinking an arbitrary object as one desires using metamaterials
Authors: Jiang Wei Xiang , Cui Tie Jun , Yang Xin Mi , Ma Hui Feng , Cheng Qiang
Published: May 2011

Based on transformation optics, we present a shrinking device, which can transform an arbitrary object virtually into a small-size object with different material parameters as one desires. Such an illusion device will confuse the detectors or the viewers, and hence the real size and material parameters of the enclosed object cannot be perceived. We fabricated and measured a shrinking device by using metamaterials, which works at the nonresonant frequency and has low loss. The device has been validated by both numerical simulations and experiments on circular and square objects. Good shrinking performance has been demonstrated.
Hydrodynamic sorting of microparticles by size in ridged microchannels
Authors: Mao Wenbin , Alexeev Alexander
Published: May 2011

Sorting and separation are key elements in many microfluidic processes. Here, we use computational modeling to design a hydrodynamic method for high-throughput separation of solid microparticles by size in microchannels. The rapid and high-resolution separation occurs due to a combination of two hydrodynamic effects: cross-stream inertial migration of particles and circulatory fluid flows created by periodic diagonal ridges protruding from opposite channel walls. This new continuous separation method operates in a wide range of Reynolds numbers, is insensitive to the magnitude of channel flow rate, and features simple design that can be readily integrated into microfluidic devices for massive sample analysis.
Photovoltaic properties of Bi2FeCrO6 epitaxial thin films
Authors: Nechache R. , Harnagea C. , Licoccia S. , Traversa E. , Ruediger A. , Pignolet A. , Rosei F.
Published: May 2011

We report a large photovoltaic (PV) effect in multiferroic Bi2FeCrO6 (BFCO) films under monochromatic illumination at 635 nm with an intensity of 1.5 mW cm−2. These multiferroic films exhibit a large photocurrent at zero bias voltage and an open-circuit voltage of about 0.6 V. A high PV power conversion efficiency of about 6% for red light is achieved and attributed to a high degree of B-site cationic ordering between Fe and Cr sublattices, the tuning of which is likely to play a key role in further improvements of the PV properties in BFCO.
Properties of copper (fluoro-)phthalocyanine layers deposited on epitaxial graphene
Authors: Ren Jun , Meng Sheng , Wang Yi-Lin , Ma Xu-Cun , Xue Qi-Kun , Kaxiras Efthimios
Published: May 2011

We investigate the atomic structure and electronic properties of monolayers of copper phthalocyanines (CuPc) deposited on epitaxial graphene substrate. We focus in particular on hexadecafluorophthalocyanine (F16CuPc), using both theoretical and experimental (scanning tunneling microscopy – STM) studies. For the individual CuPc and F16CuPc molecules, we calculated the electronic and optical properties using density functional theory (DFT) and time-dependent DFT and found a red-shift in the absorption peaks of F16CuPc relative to those of CuPc. In F16CuPc, the electronic wavefunctions are more polarized toward the electronegative fluorine atoms and away from the Cu atom at the center of the molecule. When adsorbed on graphene, the molecules lie flat and form closely packed patterns: F16CuPc forms a hexagonal pattern with two well-ordered alternating α and β stripes while CuPc arranges into a square lattice. The competition between molecule-substrate and intermolecular van der Waals interactions plays a crucial role in establishing the molecular patterns leading to tunableelectron transfer from graphene to the molecules. This transfer is controlled by the layer thickness of, or the applied voltage on, epitaxial graphene resulting in selective F16CuPc adsorption, as observed in STM experiments. In addition, phthalocyanine adsorption modifies the electronic structure of the underlying graphene substrate introducing intensity smoothing in the range of 2–3 eV below the Dirac point (ED) and a small peak in the density of states at ∼0.4 eV above ED.
Local orbitals by minimizing powers of the orbital variance
Authors: Jansík Branislav , Høst Stinne , Kristensen Kasper , Jørgensen Poul
Published: May 2011

It is demonstrated that a set of local orthonormal Hartree–Fock (HF) molecular orbitals can be obtained for both the occupied and virtual orbital spaces by minimizing powers of the orbital variance using the trust-region algorithm. For a power exponent equal to one, the Boys localization function is obtained. For increasing power exponents, the penalty for delocalized orbitals is increased and smaller maximum orbital spreads are encountered. Calculations on superbenzene, C60, and a fragment of the titin protein show that for a power exponent equal to one, delocalized outlier orbitals may be encountered. These disappear when the exponent is larger than one. For a small penalty, the occupied orbitals are more local than the virtual ones. When the penalty is increased, the locality of the occupied and virtual orbitals becomes similar. In fact, when increasing the cardinal number for Dunning's correlation consistent basis sets, it is seen that for larger penalties, the virtual orbitals become more localthan the occupied ones. We also show that the local virtual HF orbitals are significantly more local than the redundant projected atomic orbitals, which often have been used to span the virtual orbital space in local correlated wave function calculations. Our local molecular orbitals thus appear to be a good candidate for local correlation methods.
Zero-field splittings from density functional calculations: Analysis and improvement of known methods
Authors: Schmitt Sebastian , Jost Patrick , van Wüllen Christoph
Published: May 2011

Several different approaches have been proposed to calculate the zero-field splitting tensor with density functional methods. In this work, our own derivation is presented in some detail, to allow a theoretical analysis and a comparison with other methods [M. R. Pederson and S. N. Khanna, Phys. Rev. B 60, 9566 (1999)10.1103/PhysRevB.60.9566; F. Neese, J. Am. Chem. Soc. 128, 10213 (2006)10.1021/ja061798a; J. Chem. Phys. 127, 164112 (2007)10.1063/1.2772857]. Pederson's method can be improved by properly taking into account the quantum nature of spin when extracting the zero field splitting tensor from the magnetic anisotropy. A closed-shell molecule at large distance from an open shell complex will have a spurious contribution to the zero-field splitting tensor calculated with Neese's methods. We thus have analyzed his approach in some detail and found that it can be corrected if one properly transforms the equations used in wave function based theory to a sum-over-states type expression before one interprets it as an energy derivative. If improved along these lines, Neese's and Pederson's methods become identical down to the working equations. The theoretical analysis is illustrated by sample calculations on the well-studied Mn(III)-tris-acetylacetonato complex Mn(acac)3, both as an isolated molecule and with a Pd(II) dichloro diammine complex at large distance as an innocent spectator.
Calculating solvation energies by means of a fluctuating charge model combined with continuum solvent model
Authors: Zhao Dong-Xia , Yu Ling , Gong Li-Dong , Liu Cui , Yang Zhong-Zhi
Published: May 2011

Continuum solvent models have shown to be very efficient for calculating solvation energy of biomolecules in solution. However, in order to produce accurate results, besides atomic radii or volumes, an appropriate set of partial charges of the molecule is needed. Here, a set of partial charges produced by a fluctuating charge model—the atom-bond electronegativity equalization method model (ABEEMσπ) fused into molecular mechanics is used to fit for the analytical continuum electrostatics model of generalized-Born calculations. Because the partial atomic charges provided by the ABEEMσπ model can well reflect the polarization effect of the solute induced by the continuum solvent in solution, accurate and rapid calculations of the solvation energies have been performed for series of compounds involving 105 small neutral molecules, twenty kinds of dipeptides and several protein fragments. The solvation energies of small neutral molecules computed with the combination of the GB model with the fluctuating charge protocol (ABEEMσπ/GB) show remarkable agreement with the experimental results, with a correlation coefficient of 0.97, a slope of 0.95, and a bias of 0.34 kcal/mol. Furthermore, for twenty kinds of dipeptides and several protein fragments, the results obtained from the analytical ABEEMσπ/GB model calculations correlate well with those from ab initio and Poisson-Boltzmann calculations. The remarkable agreement between the solvation energies computed with the ABEEMσπ/GB model and PB model provides strong motivation for the use of ABEEMσπ/GB solvent model in the simulation of biochemical systems.
Comparison between beryllium and diamond-backing plates in diamond-anvil cells: Application to single-crystal x-ray diffraction high-pressure data
Authors: Periotto Benedetta , Nestola Fabrizio , Balic-Zunic Tonci , Angel Ross J. , Miletich Ronald , Olsen Lars A.
Published: May 2011

A direct comparison between two complete intensity datasets, collected on the same sample loaded in two identical diamond-anvil pressure cells equipped, respectively, with beryllium and diamond-backing plates was performed. The results clearly demonstrate that the use of diamond-backing plates significantly improves the quality of crystal structure data. There is a decrease in the internal R factor for averaging, structure refinement agreement factors, and in the errors and uncertainties of the atomic coordinates, atomic displacement parameters, and individual bond lengths.
Optical modulation of persistent photoconductivity in ZnO nanowires
Authors: Wang Yao , Liao Zhaoliang , She Guangwei , Mu Lixuan , Chen Dongmin , Shi Wensheng
Published: May 2011

In this study, ZnO nanowires (ZNWs)-based optoelectric devices are found to exhibit strong persistent photoconductivity (PPC) effect. An optical modulation on the PPC effect of the ZNWs with 980 nm infrared (IR) laser has been investigated. It was found that the decay time for the PPC can be significantly shortened by IR irradiation. The modulation mechanism related with the oxygen vacancies and the subband gap excitation is proposed. Based on this mechanism, the modulation behavior of the IR can be well explained. The present optical modulation on the PPC is suggested to have potential applications in enhancing the performance of ZnO-based photodetectors.
Calibration system with cryogenically-cooled loads for cosmic microwave background polarization detectors
Authors: Hasegawa M. , Tajima O. , Chinone Y. , Hazumi M. , Ishidoshiro K. , Nagai M.
Published: May 2011

We present a novel system to calibrate millimeter-wave polarimeters for cosmic microwave background (CMB) polarization measurements. This technique is an extension of the conventional metal mirror rotation approach, however, it employs cryogenically-cooled blackbody absorbers. The primary advantage of this system is that it can generate a slightly polarized signal (∼100 mK) in the laboratory; this is at a similar level to that measured by ground-based CMB polarization experiments observing a ∼10 K sky. It is important to reproduce the observing condition in the laboratory for reliable characterization of polarimeters before deployment. In this paper, we present the design and principle of the system and demonstrate its use with a coherent-type polarimeter used for an actual CMB polarization experiment. This technique can also be applied to incoherent-type polarimeters and it is very promising for the next-generation CMB polarization experiments.
Room-temperature emission at telecom wavelengths from silicon photonic crystal nanocavities
Authors: Lo Savio R. , Portalupi S. L. , Gerace D. , Shakoor A. , Krauss T. F. , O’Faolain L. , Andreani L. C. , Galli M.
Published: May 2011

Strongly enhanced light emission at wavelengths between 1.3 and 1.6 μm is reported at room temperature in silicon photonic crystal (PhC) nanocavities with optimized out-coupling efficiency. Sharp peaks corresponding to the resonant modes of PhC nanocavities dominate the broad sub-bandgap emission from optically active defects in the crystalline Si membrane. We measure a 300-fold enhancement of the emission from the PhC nanocavity due to a combination of far-field enhancement and the Purcell effect. The cavity enhanced emission has a very weak temperature dependence, namely less than a factor of 2 reduction between 10 K and room temperature, which makes this approach suitable for the realization of efficient light sources as well as providing a quick and easy tool for the broadband optical characterization of silicon-on-insulator nanostructures.
Low temperature phenomena in ferroic BiMO3–PbTiO3 (M: Mn and Sc)
Authors: Algueró M. , Jiménez R. , Amorín H. , Vila E. , Castro A.
Published: May 2011

Low temperature, reversible mechanical effects in BiMnO3–PbTiO3 are shown to be analogous to those reported in multiferroic BiFeO3. The same stiffening (on cooling) has been found in ferroelectric BiScO3–PbTiO3 that shows negligible conduction. This has allowed permittivity and polarization studies, not possible in BiMnO3–PbTiO3, to be accomplished. Results indicate mechanical effects to be associated with a phase transition, most probably governed by an order parameter other than electric polarization, but to which it is coupled. The possibility of a common origin for the effects in the three Bi-containing perovskites is discussed, along with implications on the multiferroicity of BiMnO3–PbTiO3.
Photodissociation dynamics of 3-bromo-1,1,1-trifluoro-2-propanol and 2-(bromomethyl) hexafluoro-2-propanol at 234 nm: Resonance-enhanced multiphoton ionization detection of Br (2P
j)
Authors: Indulkar Yogesh N. , Saha Ankur , Upadhyaya Hari P. , Kumar Awadhesh , Waghmode Suresh B. , Naik Prakash D. , Bajaj Parma Nand
Published: May 2011

The photodissociation dynamics of 3-bromo-1,1,1-trifluoro-2-propanol (BTFP) and 2-(bromomethyl) hexafluoro-2-propanol (BMHFP) have been studied at 234 nm, and the C–Br bond dissociation investigated using resonance-enhanced multiphoton ionization coupled with time-of-flight mass spectrometer (REMPI-TOFMS). Br formation is a primary process and occurs on a repulsive surface involving the C–Br bond of BTFP and BMHFP. Polarization dependent time-of-flight profiles were measured, and the translational energy distributions and recoil anisotropy parameters extracted using forward convolution fits. A strong polarization dependence of time-of-flight profiles suggest anisotropic distributions of the Br(2P3/2) and Br(2P1/2) fragments with anisotropy parameter, β, of respectively 0.5 ± 0.2 and 1.2 ± 0.2 for BTFP, and 0.4 ± 0.1 and 1.0 ± 0.3 for BMHFP. The measured velocity distributions consist of a single velocity component. The average translational energies for the Br(2P3/2) and Br(2P1/2) channels are 9.2 ± 1.0 and 7.4 ± 0.9 kcal/mol for BTFP, and 15.4 ± 1.8 and 15.1 ± 2.0 kcal/mol for BMHFP. The relative quantum yields of Br(2P3/2) and Br(2P1/2), which are 0.70 ± 0.14 and 0.30 ± 0.06 in BTFP and 0.81 ± 0.16 and 0.19 ± 0.04 in BMHFP, indicate that the yield of the former is predominant. The measured anisotropy parameters for the Br(2P3/2) and Br(2P1/2) channels suggest that the former channel has almost equal contributions from both the parallel and the perpendicular transitions, whereas the latter channel has a significant contribution from a parallel transition. Non-adiabatic curve crossing plays an important role in the C–Br bond dissociation of both BTFP and BMHFP. The estimated curve crossing probabilities suggest a greater value in BTFP, which explains a greater observed value of the relative quantum yield of Br(2P1/2) in this case.
Refinement of the experimental energy levels of higher 2D Rydberg states of the lithium atom with very accurate quantum mechanical calculations
Authors: Sharkey Keeper L. , Bubin Sergiy , Adamowicz Ludwik
Published: May 2011

Very accurate variational non-relativistic calculations are performed for four higher Rydberg 2D states (1s2nd1, n = 8, …, 11) of the lithium atom (7Li). The wave functions of the states are expanded in terms of all-electron explicitly correlated Gaussian functions and finite nuclear mass is used. The exponential parameters of the Gaussians are optimized using the variational method with the aid of the analytical energy gradient determined with respect to those parameters. The results of the calculations allow for refining the experimental energy levels determined with respect to the 2S 1s22s1 ground state.
Charge transport in solution processable polycrystalline dual-gate organic field effect transistors
Authors: Tripathi A. K. , Smits E. C. P. , Loth M. , Anthony J. E. , Gelinck G. H.
Published: May 2011

Dual gate organic thin film transistors based on solution processable fluorinated 5,11 bis(triethylsilylethynyl) anthradithiophene semiconductor were fabricated. Top (Teflon™, εr=2.1) and bottom (SiO2, εr=3.9) gate dielectrics with different dielectric constants were chosen. Top gate mobilities >1 cm2/Vs and bottom gate mobilities >0.1 cm2/V s were achieved. Temperature dependent mobility measurements show thermally activated charge transport and a comparative analysis is performed in the framework of two models representing polaron hopping as well as hopping in Gaussian density of states (DOS), respectively.
Tunability of the critical-current density in superconductor-ferromagnet hybrids
Authors: Del-Valle Nuria , Navau Carles , Sanchez Alvaro , Chen Du-Xing
Published: May 2011

Important modifications on the magnetization loops of the superconductor have been observed in superconductor-ferromagnet hybrids due to the effects of the ferromagnetic components, which can be used for tuning the superconductor critical-current density Jc to desirable values. Here, a model based on an energy minimization procedure is presented to analyze the complex interaction between the superconductor and the ferromagnets. We show how the geometry and orientation of the ferromagnets can be chosen for shifting the position of the peaks appearing in the magnetization to positive or negative applied fields, and, consequently, to tune Jc in superconductor-ferromagnet hybrids.
High quantum efficiency InGaN/GaN multiple quantum well solar cells with spectral response extending out to 520 nm
Authors: Farrell R. M. , Neufeld C. J. , Cruz S. C. , Lang J. R. , Iza M. , Keller S. , Nakamura S. , DenBaars S. P. , Mishra U. K. , Speck J. S.
Published: May 2011

We demonstrate high quantum efficiency InGaN/GaN multiple quantum well (QW) solar cells with spectral response extending out to 520 nm. Increasing the number of QWs in the active region did not reduce the carrier collection efficiency for devices with 10, 20, and 30 QWs. Solar cells with 30 QWs and an intentionally roughened p-GaN surface exhibited a peak external quantum efficiency (EQE) of 70.9% at 390 nm, an EQE of 39.0% at 450 nm, an open circuit voltage of 1.93 V, and a short circuit current density of 2.53 mA/cm2 under 1.2 suns AM1.5G equivalent illumination.
Microwave characterization of vertically aligned multiwalled carbon nanotube arrays
Authors: Katsounaros Anestis , Rajab Khalid Z. , Hao Yang , Mann Mark , Milne William I.
Published: May 2011

Vertically aligned multiwalled carbon nanotube (VACNT) films have been characterized by rectangular waveguide measurements. The complex scattering parameters (S-parameters) are measured by a vector network analyzer at X-band frequencies. The effective complex permittivity and permeability of the VACNT films have been extracted. The extracted parameters are verified by full wave simulations and very good agreement has been obtained. The results of the systematic error analysis are presented and the errors are within the acceptable range. The performance of VACNT films as an absorber is examined, and comparison with the conventional carbon loaded materials shows that a 90% size reduction is possible while maintaining the same absorption level.
Interaction between metamaterial resonators and intersubband transitions in semiconductor quantum wells
Authors: Gabbay Alon , Reno John , Wendt Joel R. , Gin Aaron , Wanke Michael C. , Sinclair Michael B. , Shaner Eric , Brener Igal
Published: May 2011

We report on the coupling and interaction between the fundamental resonances of planar metamaterials (split ring resonators) and intersubband transitions in GaAs/AlGaAs quantum wells structures in the mid-infrared. An incident field polarized parallel to the sample surface is converted by the metamaterial resonators into a field with a finite component polarized normal to the surface and interacts strongly with the large dipole moment associated with quantum well intersubband transitions.
Continuous measurement of the arrival times of x-ray photon sequence
Authors: Yan Qiurong , Zhao Baosheng , Sheng Lizhi , Liu Yong'an
Published: May 2011

In order to record x-ray pulse profile for x-ray pulsar-based navigation and timing, this paper presents a continuous, high-precision method for measuring arrival times of photon sequence with a common starting point. In this method, a high stability atomic clock is counted to measure the coarse time of arrival photon. A high resolution time-to-digital converter is used to measure the fine time of arrival photon. The coarse times and the fine times are recorded continuously and then transferred to computer memory by way of memory switch. The pulse profile is obtained by a special data processing method. A special circuit was developed and a low-level x-ray pulse profile measurement experiment system was setup. The arrival times of x-ray photon sequence can be consecutively recorded with a time resolution of 500 ps and the profile of x-ray pulse was constructed. The data also can be used for analysis by many other methods, such as statistical distribution of photon events per time interval, statistical distribution of time interval between two photon events, photon counting histogram, autocorrelation and higher order autocorrelation.
Analysis of frequency band structure in one-dimensional sonic crystal using Webster horn equation
Authors: Gupta A. , Lim K. M. , Chew C. H.
Published: May 2011

Sound propagation through periodic arrangement of scatterers lead to formation of bands of frequencies, known as band gaps, where sound cannot propagate though the structure. We propose a method based on Webster horn equation, along with Floquet theorem, to predict the band gap of a one-dimensional periodic structure made of hard sound-scatterers. The method is further modified to obtain the complex wave numbers, which give the decay constants. The decay constant is used to predict the sound attenuation of the evanescent wave in the finite sonic crystal. The theoretical prediction is verified with experimental measurements.
Band gap of InxGa1−xN: A first principles analysis
Authors: César Mathieu , Ke Youqi , Ji Wei , Guo Hong , Mi Zetian
Published: May 2011

We report first principles analysis of the band gap Eg of ternary group-III nitride InxGa1−xN in both the wurtzite and zincblende form, within the linear muffin-tin orbital (LMTO) density functional theory method. We have implemented the semilocal modified Becke–Johnson (MBJ) exchange potential to accurately determine the band gap. The doping of In atoms into the GaN crystal is handled by the InxGa1−xN alloy model within the coherent potential approximation (CPA). The LMTO-CPA-MBJ approach allows us to predict Eg as a function of arbitrary In concentration x. Quantitative comparison to the experimental data is made.
Low activation energy, high-quality oxidation of Si and Ge using neutral beam
Authors: Wada Akira , Endo Kazuhiko , Masahara Meishoku , Huang Chi-Hsien , Samukawa Seiji
Published: May 2011

In this letter, we investigated the mechanism that forms thin silicon and germanium oxide films with a high-quality interface using a low-temperature neutral beam oxidation (NBO) process. Because NBO has high reactivity due to bombardment by energetic oxygen-neutral beams even at low substrate temperatures, we found that an extremely low activation energy for the atomic layer oxidation reaction could be achieved during the process itself. As a result, there was little suboxide at the interface between the oxide films and the semiconductor, and device characteristics with a high performance were observed.
Resonant excitation of coherent Cerenkov radiation in dielectric lined waveguides
Authors: Andonian G. , Williams O. , Wei X. , Niknejadi P. , Hemsing E. , Rosenzweig J. B. , Muggli P. , Babzien M. , Fedurin M. , Kusche K. , Malone R. , Yakimenko V.
Published: May 2011

We report the observation of coherent Cerenkov radiation in the terahertz regime emitted by a relativistic electron pulse train passing through a dielectric lined cylindrical waveguide. We describe the beam manipulations and measurements involved in repetitive pulse train creation including comb collimation and nonlinear optics corrections. With this technique, modes beyond the fundamental are selectively excited by use of the appropriate frequency train. The spectral characterization of the structure shows preferential excitation of the fundamental and of a higher longitudinal mode.
Collection method for extra aligned nanofibers deposited by electrospinning
Authors: Pokorny M. , Velebny V.
Published: May 2011

Electrospinning is a very promising nanotechnology method, mostly thanks to industrial scale up ability, relatively low purchase cost, and huge variability. Nevertheless, its principal disadvantage is the way in which the individual nanofibers are randomly deposited while being collected onto a collector after passing through the chaotic whipping phase. Present and future applications of nanomaterials will need their precise, ordered intrinsic structures, or may even require accurately determined anisotropic properties because of significant improvement of material properties such as mechanical, electronic, optical, etc. This work demonstrates a novel and advanced collector including a sliding board mechanism. The resulting nanofibrous materials obtain extremely high orientation order parameter (S > 97%). Other important advantages of this technological method are discussed here in more detail.
Plasma resonances in a gated semiconductor slab of arbitrary thickness
Authors: Marinchio H. , Millithaler J.-F. , Palermo C. , Varani L. , Reggiani L. , Shiktorov P. , Starikov E. , Gružinskis V.
Published: May 2011

We present an analytical model suitable for the study of the plasma modes in gated semiconductor slabs of arbitrary thickness. A pseudo-two-dimensional Poisson equation allows us to consider both transverse and longitudinal electric field variations. We calculate the dispersion relation demonstrating the dispersive nature of the slab. We express the frequencies of the plasma modes appearing in a cavity. A transition from a two-dimensional to a three-dimensional behavior is revealed when the transverse dimension of the device or the order of modes grow. These analytical results show a good agreement with Monte Carlo calculations of the voltage noise spectrum.
Semiconductor nanoring lasers
Authors: Kim Min W. , Ku P.-C.
Published: May 2011

Lasing in a subwavelength metal-clad nanoring resonator has been demonstrated with a tunable emission wavelength, controlled by the width of the ring. The emission wavelength is shown to be tunable within a 10 nm wavelength range by changing the ring width between 240 and 340 nm. This property is expected to mitigate a common nanolaser problem of fine-tuning the emission wavelength without significantly changing the laser dimensions.
Exploiting long-ranged order in quasiperiodic structures for broadband plasmonic excitation
Authors: le Feber B. , Cesario J. , Zeijlemaker H. , Rotenberg N. , Kuipers L.
Published: May 2011

A comparison of transmission spectra from periodic, quasiperiodic, and randomly spaced slit arrays in thick gold films reveals resonant plasmonic excitations that arise solely due to the long-range order of the quasiperiodic structures. Specifically, first-order plasmonic resonances at the air-gold interface of the quasiperiodic arrays are identified at a broader range of wavelengths than those observed from periodic structures with the same average slit distance. Thus, a quasiperiodic plasmonic coupler that couples both visible and near-infrared light to surface plasmon polaritons is designed and demonstrated.
Interfacial energy level bending in a crystalline p/p-type organic heterostructure
Authors: Zhu Feng , Grobosch Mandy , Treske Uwe , Knupfer Martin , Huang Lizhen , Ji Shiliang , Yan Donghang
Published: May 2011

A conduction channel was observed at the heterointerface of the crystalline p-type organic films copper phthalocyanine (CuPc) and 2,5-bis(4-biphenylyl) bithiophene (BP2T). Energy level bending at the interface is confirmed by photoemission spectroscopy, which verifies a charge transfer between CuPc and BP2T. This provides a further route to utilize interfacial electronic properties in functional devices and also documents the importance of reconsidering the interfacial electronic structure of organic heterostructures.
High electron mobility transistors on plastic flexible substrates
Authors: Chen Wayne , Alford T. L. , Kuech T. F. , Lau S. S.
Published: May 2011

The double-flip transfer of indium phosphide (InP) based transistors onto plastic flexible substrates was demonstrated. Modulation doped field effect transistor layers, epitaxially grown on InP bulk substrates, were transferred onto sapphire using a masked ion-cutting process. Following layer transfer, transistors were fabricated at low temperatures (≤150 °C). The device structure was then bonded to flexible substrate, and laser ablation was used to separate the initial bond. The transferred transistors were characterized and exhibited high field-effect mobility (μaverage∼2800 cm2 V−1 s−1).
Structural and vibrational properties of amorphous GeO2 from first-principles
Authors: Scalise E. , Houssa M. , Pourtois G. , Afanas’ev V. V. , Stesmans A.
Published: May 2011

The structural and vibrational properties of amorphous germanium oxide (a-GeO2) are investigated using first-principles calculations based on density functional theory. We first generate an a-GeO2 structure by first-principles molecular dynamics and analyze its structural properties. The vibrational spectra is then calculated within a density-functional approach. Both static and dynamic properties are in good agreement with experimental data. We next generate defects in our structure (oxygen vacancies with several density and charge states) and consider the most stable atomic configurations, focusing on the vibrational features of threefold coordinated O and divalent Ge centers.
Phonons of the anomalous element cerium
Authors: Krisch Michael , Farber D. L. , Xu R. , Antonangeli Daniele , Aracne C. M. , Beraud Alexandre , Chiang Tai-Chang , Zarestky J. , Kim Duck Young , Isaev Eyvaz I. , Ahuja Rajeev , Johansson Börje
Published: May 2011

Many physical and chemical properties of the light rare-earths and actinides are governed by the active role of
f
electrons, and despite intensive efforts the details of the mechanisms of phase stability and transformation are not fully understood. A prominent example which has attracted a lot of interest, both experimentally and theoretically over the years is the isostructural
γ
 - 
α
transition in cerium. We have determined by inelastic X-ray scattering, the complete phonon dispersion scheme of elemental cerium across the
γ
 → 
α
transition, and compared it with theoretical results using
ab initio
lattice dynamics. Several phonon branches show strong changes in the dispersion shape, indicating large modifications in the interactions between phonons and conduction electrons. This is reflected as well by the lattice Grüneisen parameters, particularly around the X point. We derive a vibrational entropy change

, illustrating the importance of the lattice contribution to the transition. Additionally, we compare first principles calculations with the experiments to shed light on the mechanism underlying the isostructural volume collapse in cerium under pressure.
Using silver nanowire antennas to enhance the conversion efficiency of photoresponsive DNA nanomotors
Authors: Yuan Quan , Zhang Yunfei , Chen Yan , Wang Ruowen , Du Chaoling , Yasun Emir , Tan Weihong
Published: May 2011

Plasmonic near-field coupling can induce the enhancement of photoresponsive processes by metal nanoparticles. Advances in nanostructured metal synthesis and theoretical modeling have kept surface plasmons in the spotlight. Previous efforts have resulted in significant intensity enhancement of organic dyes and quantum dots and increased absorption efficiency of optical materials used in solar cells. Here, we report that silver nanostructures can enhance the conversion efficiency of an interesting type of photosensitive DNA nanomotor through coupling with incorporated azobenzene moieties. Spectral overlap between the azobenzene absorption band and plasmonic resonances of silver nanowires increases light absorption of photon-sensitive DNA motor molecules, leading to 85% close-open conversion efficiency. The experimental results are consistent with our theoretical calculations of the electric field distribution. This enhanced conversion of DNA nanomotors holds promise for the development of new types of molecular nanodevices for light manipulative processes and solar energy harvesting.
Solution structure of the ESCRT-I complex by small-angle X-ray scattering, EPR, and FRET spectroscopy
Authors: Boura Evzen , Różycki Bartosz , Herrick Dawn Z. , Chung Hoi Sung , Vecer Jaroslav , Eaton William A. , Cafiso David S. , Hummer Gerhard , Hurley James H.
Published: May 2011

ESCRT-I is required for the sorting of integral membrane proteins to the lysosome, or vacuole in yeast, for cytokinesis in animal cells, and for the budding of HIV-1 from human macrophages and T lymphocytes. ESCRT-I is a heterotetramer of Vps23, Vps28, Vps37, and Mvb12. The crystal structures of the core complex and the ubiquitin E2 variant and Vps28 C-terminal domains have been determined, but internal flexibility has prevented crystallization of intact ESCRT-I. Here we have characterized the structure of ESCRT-I in solution by simultaneous structural refinement against small-angle X-ray scattering and double electron–electron resonance spectroscopy of spin-labeled complexes. An ensemble of at least six structures, comprising an equally populated mixture of closed and open conformations, was necessary to fit all of the data. This structural ensemble was cross-validated against single-molecule FRET spectroscopy, which suggested the presence of a continuum of open states. ESCRT-I in solution thus appears to consist of an approximately 50% population of one or a few related closed conformations, with the other 50% populating a continuum of open conformations. These conformations provide reference points for the structural pathway by which ESCRT-I induces membrane buds.
Psychological adaptation of Moroccan and Ecuadorean immigrant adolescents in Spain
Authors: Briones Elena , Verkuyten Maykel , Cosano Juan , Tabernero Carmen
Published: May 2011

In adapting to the host society, immigrant adolescents may have problems negotiating the challenges of acculturation. The factors that promote and those that hamper psychological adaptation may not play the same role in all ethnic groups. Our study focuses on psychological adaptation of two main immigrant groups in Spain that differ in cultural distance to the host society and level of societal acceptance: adolescents of Moroccan and Ecuadorean origin. Our findings show, first, that mainstream cultural orientation is positively related to psychological adaptation, whereas perceived ethnic discrimination is negatively associated with adaptation. Second, the relationship between ethnic cultural orientation and psychological adaptation and between length of residence in Spain and adaptation is stronger for the Moroccan youth than for their Ecuadorean peers. Theoretical and practical implications of these results are discussed.
Recognition Memory Strength is Predicted by Pupillary Responses at Encoding While Fixation Patterns Distinguish Recollection from Familiarity
Authors: Kafkas Alexandros , Montaldi Daniela
Published: May 2011

Thirty-five healthy participants incidentally encoded a set of man-made and natural object pictures, while their pupil response and eye movements were recorded. At retrieval, studied and new stimuli were rated as novel, familiar (strong, moderate, or weak), or recollected. We found that both pupil response and fixation patterns at encoding predict later recognition memory strength. The extent of pupillary response accompanying incidental encoding was found to be predictive of subsequent memory. In addition, the number of fixations was also predictive of later recognition memory strength, suggesting that the accumulation of greater visual detail, even for single objects, is critical for the creation of a strong memory. Moreover, fixation patterns at encoding distinguished between recollection and familiarity at retrieval, with more dispersed fixations predicting familiarity and more clustered fixations predicting recollection. These data reveal close links between the autonomic control of pupil responses and eye movement patterns on the one hand and memory encoding on the other. Moreover, the data illustrate quantitative as well as qualitative differences in the incidental visual processing of stimuli, which are differentially predictive of the strength and the kind of memory experienced at recognition.
Some effort for some: Further evidence that scalar implicatures are effortful
Authors: Dieussaert Kristien , Verkerk Suzanne , Gillard Ellen , Schaeken Walter
Published: May 2011

Under the assumption of the principle of cooperation (Grice, 1989), a statement such as “some eels are fish” is thought to be false since it contains less information than is considered sufficient. However, the statement is logically sound since the meaning of “some” is compatible with “all”. Currently, the primary interpretation of such underinformative statements remains subject to debate. According to Levinson (2000), the pragmatic “some but not all” interpretation is the default interpretation, while others (e.g., Sperber & Wilson, 1995) argue that this pragmatic interpretation only comes to the fore when relevant within the context and is thus considered secondary to the logical “some and perhaps all” interpretation. In this study, three factors that may influence the answer pattern are studied: task load, working memory capacity, and repetition of the statements. In Experiment 1, we used a secondary task paradigm to manipulate the cognitive load under which a number of underinformative statements had to be judged. We observed that for participants with a rather limited working memory span it is harder to reach a pragmatic interpretation under cognitive load. In Experiment 2, we manipulated the repetition of the statements. We observed that with a higher number of filler statements, participants produced fewer consistent answer patterns. This study provides further evidence against the automaticity of the pragmatic interpretation: It shows that the pragmatic interpretation requires more cognitive effort than the logical interpretation and that increasing the number of filler statements inhibits the development of a response strategy.