bluuebunny/crossref_metadata_2025 huggingface dataset:
Outcomes of Conservative Treatment of 134 Cases of Umbilical Pilonidal Sinus
Authors: Kareem Tayeb
Published: October 2012

Background

There are different opinions about the treatment of umbilical pilonidal sinus. The aim of the present study was to evaluate the outcome of conservative treatment of this disease.

Methods

All patients with umbilical pilonidal sinus who attended our private surgical clinic in Erbil, Kurdistan, from January 1997 to August 2011, were treated by conservative treatment. Umbilectomy was performed for those who did not respond to the conservative treatment after three sessions.

Results

A total of 134 patients were seen; 121 (90.3 %) were men. Only 105 (78.35 %) patients came back for the second visit. Eighty of them (76.19 %) responded to the treatment. The other 25 (23.8 %) patients were retreated by a second session of conservative treatment. Of these 25 patients, 19 (76 %) came back for the third visit and only three (15.78 %) patients did not respond to the treatment. One patient insisted on umbilectomy. The other two patients were treated but did not respond to the third session treatment. Umbilectomy was performed for them. Hair was found in the sinus after excision in these three patients. The follow‐up period ranged from 9 months to 6.5 years for 46 (34.32 %) patients and revealed no recurrence.

Conclusions

Conservative treatment should be regarded as the first choice and the main method of treatment in the management of umbilical pilonidal sinus. Improper extraction of hair is the main cause of failure of conservative treatment. Recurrence can be prevented by giving the patients instructions on preventive measures.
The mechanism of the fecundity reduction in Callosobruchus maculatus caused by Callosobruchus chinensis males
Authors: Kyogoku Daisuke , Nishida Takayoshi
Published: October 2012

Male promiscuity sometimes results in interspecific reproductive interaction, also known as reproductive interference. Reproductive interference entails costs for the individuals involved and affects the community structure by reducing the population growth rate. However, our understanding of the mechanisms generating reproductive interference is still insufficient. Two congeneric bean weevils, Callosobruchus chinensis and C. maculatus, show asymmetric reproductive interference; only C. chinensis males reduce the fecundity of the other species. Here we investigated the mechanism of reproductive interference by C. chinensis males on C. maculatus females in terms of lifetime fecundity. Callosobruchus chinensis males with ablated genitals, which could harass C. maculatus females but not copulate with them, did not reduce the C. maculatus fecundity, suggesting that interspecific copulation was necessary. However, a single interspecific copulation did not affect C. maculatus fecundity as long as the females also copulated with a conspecific male. Exposure to C. chinensis males for 24 h prior to oviposition significantly reduced C. maculatus fecundity, and fecundity was negatively correlated with the number of C. chinensis males the females were exposed to. Additionally, C. maculatus females experienced more interspecific copulations when they were housed with more C. chinensis males. Together these findings suggest that multiple interspecific copulations by C. chinensis males reduce the fecundity of C. maculatus females. Thus in general, even if a single interspecific copulation is apparently harmless, repeated interspecific copulations can be costly for the individuals involved. Furthermore, only by quantifying reproductive success were we able to identify the precise mechanism of reproductive interference.
Renormalization for piecewise smooth homeomorphisms on the circle
Authors: Cunha Kleyber , Smania Daniel
Published: October 2012

In this work we study the renormalization operator acting on piecewise smooth homeomorphisms on the circle, that turns out to be essentially the study of Rauzy–Veech renormalizations of generalized interval exchange maps with genus one. In particular we show that renormalizations of such maps with zero mean nonlinearity and satisfying certain smoothness and combinatorial assumptions converge to the set of piecewise affine interval exchange maps.
Dynamic collision risk modeling under uncertainty
Authors: Belkhouche F. , Bendjilali B.
Published: October 2012

This paper introduces a probabilistic model for collision risk assessment between moving vehicles. The uncertainties in the states and the geometric variables obtained from the sensory system are characterized by probability density functions. Given the states and their uncertainties, the goal is to determine the probability of collision in a dynamic environment. Two approaches are discussed: (1) The virtual configuration space (VCS), and (2) the rates of change of the visibility angles. The VCS is a transformation of observer that reduces collision detection with a moving object to collision detection with a stationary object. This approach allows to create simple geometric collision cones. Error propagation models are used to solve the problem when going from the VCS to the configuration space. The second approach derives the collision conditions in terms of the rate of change of the limit visibility angles. The probability of collision is then calculated. A comparison between the two methods is carried out. Results are illustrated using simulation, including Monte Carlo simulation.
Total and fractionation metal contents obtained with sequential extraction procedures in a sediment core from Terra Nova Bay, West Antarctica
Authors: Casalino Claudia E. , Malandrino Mery , Giacomino Agnese , Abollino Ornella
Published: October 2012

A suite of 21 elements, namely Al, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, La, Mg, Mn, Na, Ni, P, Pb, Sr, Ti, V and Zn, was investigated in a sediment core from the Ross Sea, Antarctica. The experimental results were treated by chemometric techniques. The elemental composition of core H2 was found to be mainly dominated by terrigenous elements, but it is also influenced by biological factors, such as the presence of corals. No evidence of anthropogenic contamination was observed, even in the top layer of the sediment. Furthermore, the modified Community Bureau of Reference (BCR) three-step sequential extraction procedure was applied to evaluate metal mobility and availability. The results confirmed the separation between higher and lower sections of the core and showed the presence of Fe as amorphous and crystalline oxide and of Mn mostly as nodules. The high percentages of metals extracted into the fourth fraction indicate their strong binding with the sediment matrix. Finally, BCR procedure was compared to Tessier's protocol which made it possible to distinguish between mobile and mobilizable fraction. Therefore, in general partitioning procedure must be chosen taking into account the nature of the sample and the aim of the research.
Mobile Decontamination Units—Room for Improvement?
Authors: Ribordy Pascale , Rocksén David , Dellgar Uno , Persson Sven-Åke , Arnoldsson Kristina , Ekåsen Hans , Häggbom Sune , Nerf Ola , Ljungqvist Åsa , Gryth Dan , Claesson Ola
Published: October 2012

Introduction

Mobile decontamination units are intended to be used at the accident site to decontaminate persons contaminated by toxic substances. A test program was carried out to evaluate the efficacy of mobile decontamination units.

Objective

The tests included functionality, methodology, inside environment, effects of wind direction, and decontamination efficacy.

Methods

Three different types of units were tested during summer and winter conditions. Up to 15 test-persons per trial were contaminated with the imitation substances Purasolve ethyl lactate (PEL) and methyl salicylate (MES). Decontamination was carried out according to standardized procedures. During the decontamination trials, the concentrations of the substances inside the units were measured. After decontamination, substances evaporating from test-persons and blankets as well as remaining amounts in the units were measured.

Results

The air concentrations of PEL and MES inside the units during decontamination in some cases exceeded short-term exposure limits for most toxic industrial chemicals. This was a problem, especially during harmful wind conditions, i.e., wind blowing in the same direction as persons moving through the decontamination units. Although decontamination removed a greater part of the substances from the skin, the concentrations evaporating from some test-persons occasionally were high and potentially harmful if the substances had been toxic. The study also showed that blankets placed in the units absorbed chemicals and that the units still were contaminated five hours after the end of operations.

Conclusions

After decontamination, the imitation substances still were present and evaporating from the contaminated persons, blankets, and units. These results indicate a need for improvements in technical solutions, procedures, and training.

RibordyP, RocksénD, DellgarU, PerssonS, ArnoldssonK, EkåsenH, HäggbomS, NerfO, LjungqvistA, GrythD, ClaessonO. Mobile decontamination units—room for improvement?. Prehosp Disaster Med.2012;27(4):1–7.
The relationship of breakfast skipping and type of breakfast consumed with overweight/obesity, abdominal obesity, other cardiometabolic risk factors and the metabolic syndrome in young adults. The National Health and Nutrition Examination Survey (NHANES): 1999–2006
Authors: Deshmukh-Taskar Priya , Nicklas Theresa A , Radcliffe John D , O'Neil Carol E , Liu Yan
Published: October 2012

Objective

To examine the association between breakfast skipping and type of breakfast consumed with overweight/obesity, abdominal obesity, other cardiometabolic risk factors and the metabolic syndrome (MetS).

Design

Cross-sectional. Three breakfast groups were identified, breakfast skippers (BS), ready-to-eat-cereal (RTEC) consumers and other breakfast (OB) consumers, using a 24 h dietary recall. Risk factors were compared between the breakfast groups using covariate-adjusted statistical procedures.

Setting

The 1999–2006 National Health and Nutrition Examination Survey, USA.

Subjects

Young adults (20–39 years of age).

Results

Among these young adults (n 5316), 23·8 % were BS, 16·5 % were RTEC consumers and 59·7 % were OB consumers. Relative to the BS, the RTEC consumers were 31 %, 39 %, 37 %, 28 %, 23 %, 40 % and 42 % less likely to be overweight/obese or have abdominal obesity, elevated blood pressure, elevated serum total cholesterol, elevated serum LDL-cholesterol, reduced serum HDL-cholesterol or elevated serum insulin, respectively. Relative to the OB consumers, the BS were 1·24, 1·26 and 1·44 times more likely to have elevated serum total cholesterol, elevated serum LDL-cholesterol or reduced serum HDL-cholesterol, respectively. Relative to the OB consumers, the RTEC consumers were 22 %, 31 % and 24 % less likely to be overweight/obese or have abdominal obesity or elevated blood pressure, respectively. No difference was seen in the prevalence of the MetS by breakfast skipping or type of breakfast consumed.

Conclusions

Results suggest that consumption of breakfast, especially that included an RTEC, was associated with an improved cardiometabolic risk profile in US young adults. Additional studies are needed to determine the nature of these relationships.
GRADATIONAL ACCURACY AND NONCLASSICAL SEMANTICS
Authors: WILLIAMS J. ROBERT G.
Published: October 2012

This paper gives a generalization of Jim Joyce’s 1998 argument for probabilism, dropping his background assumption that logic and semantics are classical. Given a wide variety of nonclassical truth-value assignments, Joyce-style arguments go through, allowing us to identify in each case a class of “nonclassically coherent” belief states. To give a local characterization of coherence, we need to identify a notion of logical consequence to use in an axiomatization. There is a very general, ‘no drop in truth-value’ characterization that will do the job. The result complements Paris’s 2001discussion of generalized forms of Dutch books appropriate to nonclassical settings.
Tracing mantle sources and Samoan influence in the northwestern Lau back‐arc basin
Authors: Lytle Marion L. , Kelley Katherine A. , Hauri Erik H. , Gill James B. , Papia Dominic , Arculus Richard J.
Published: October 2012

Helium isotopes are commonly used as a diagnostic fingerprint of Samoan mantle in the northern Lau Basin, but the extent of input from Samoan sources can only be clearly resolved by coupling 3He/4He with other geochemical tracers such as trace elements and other isotope systems. We present new major element, dissolved volatile (H2O, CO2, S, Cl, F), trace element, and Sr‐Nd‐Pb‐Hf isotope data for new samples from the NW Lau Basin from five distinct regions (Rochambeau Rifts (RR), Northwest Lau Spreading Center (NWLSC), Peggy Ridge (PR), Lau Extensional Transform Zone (LETZ), and Central Lau Spreading Center (CLSC)) that range from distinctively elevated to normal mid‐ocean ridge basalt3He/4He. Helium isotopes variations are not correlated with radiogenic isotopes or trace element abundances. Our new data suggest two‐component mixing of MORB‐like mantle with an enriched mantle source, similar to Samoa, although consideration of a complete regional data set suggests there may be other sources of heterogeneity in the mantle beneath NW Lau. Models of mantle potential temperature (Tp) and primary melt equilibration temperatures indicate similar Tp of ∼1400°C for NW Lau, suggesting no strong temperature gradient. The pressure of melt equilibration deepens toward the north (∼1.1–1.2 GPa at PR, LETZ, CLSC; ∼1.3–1.4 GPa at RR, NWLSC), consistent with melting mantle of a constant Tp but variable H2O content. Samoan and MORB‐like sources are clearly present beneath the NW Lau basin, but geochemical diversity among the existing data suggest that more than two mantle sources may contribute to mantle enrichment beneath NW Lau.
Perpendicular magnetic anisotropy of cobalt films intercalated under graphene
Authors: Rougemaille N. , N'Diaye A. T. , Coraux J. , Vo-Van C. , Fruchart O. , Schmid A. K.
Published: October 2012

Magnetic properties of nanometer-thick Co films intercalated at the graphene/Ir(111) interface are investigated using spin-polarized low-energy electron microscopy and Auger electron spectroscopy. We show that the graphene top layer promotes perpendicular magnetic anisotropy in the Co film underneath, even for relatively thick intercalated deposits. The magnetic anisotropy energy is significantly larger for the graphene/Co interface than for the free Co surface. Hybridization of the graphene and Co electron orbitals is believed to be at the origin of the observed perpendicular magnetic anisotropy.
Stability analysis of ion motion in asymmetric planar ion traps
Authors: Shaikh Fayaz A. , Ozakin Arkadas
Published: October 2012

Motivated by recent developments in ion trap design and fabrication, we investigate the stability of the motion of an ion in asymmetrical, planar versions of the linear Paul trap. The equations of motion of an ion in such a trap are generally coupled due to a nonzero relative angle θ between the principal axes of RF and DC fields, invalidating the assumptions behind the standard stability analysis for symmetric Paul traps. Using numerical methods, we obtain stability diagrams for the coupled system for various values of θ, generalizing the standard q-a stability diagrams. We then use multi-scale perturbation theory to obtain approximate formulas for the boundaries of the primary stability region and check our formulas against results from numerical analysis. Our results show that while the primary stability region is quite robust to changes in θ, a secondary stability region is highly variable, joining the primary stability region at the special case of θ=45°, which results in a significantly enlarged stability region for this particular angle. We conclude that while the standard stability diagrams for classical, symmetric Paul traps are not entirely accurate for asymmetric surface traps (or for other types of traps with a relative angle between the RF and DC axes), they are “safe” in the sense that operating conditions deemed stable according to standard stability plots are in fact stable for asymmetric traps, as well. By ignoring the coupling in the equations, one only underestimates the size of the primary stability region.
Geometric descriptions of entangled states by auxiliary varieties
Authors: Holweck Frédéric , Luque Jean-Gabriel , Thibon Jean-Yves
Published: October 2012

The aim of the paper is to propose geometric descriptions of multipartite entangled states using algebraic geometry. In the context of this paper, geometric means each stratum of the Hilbert space, corresponding to an entangled state, is an open subset of an algebraic variety built by classical geometric constructions (tangent lines, secant lines) from the set of separable states. In this setting, we describe well-known classifications of multipartite entanglement such as 2 × 2 × (n + 1), for n ⩾ 1, quantum systems and a new description with the 2 × 3 × 3 quantum system. Our results complete the approach of Miyake and make stronger connections with recent work of algebraic geometers. Moreover, for the quantum systems detailed in this paper, we propose an algorithm, based on the classical theory of invariants, to decide to which subvariety of the Hilbert space a given state belongs.
Al6H18: A baby crystal of γ-AlH3
Authors: Kiran B. , Kandalam Anil K. , Xu Jing , Ding Y. H. , Sierka M. , Bowen K. H. , Schnöckel H.
Published: October 2012

Using global-minima search methods based on the density functional theory calculations of (AlH3)n (n = 1–8) clusters, we show that the growth pattern of alanes for n ≥ 4 is dominated by structures containing hexa-coordinated Al atoms. This is in contrast to the earlier studies where either linear or ring structures of AlH3 were predicted to be the preferred structures in which the Al atoms can have a maximum of five-fold coordination. Our calculations also reveal that the Al6H18 cluster, with its hexa-coordination of the Al atoms, resembles the unit-cell of γ-AlH3, thus Al6H18 is designated as the “baby crystal.” The fragmentation energies of the (AlH3)n (n = 2–8) along with the dimerization energies for even n clusters indicate an enhanced stability of the Al6H18 cluster. Both covalent (hybridization) and ionic (charge) contribution to the bonding are the driving factors in stabilizing the isomers containing hexa-coordinated Al atoms.
Stoichiometric controlling of boron carbide thin films by using boron-carbon dual-targets
Authors: Zhang Song , Lu Wenzhong , Wang Chuanbin , Shen Qiang , Zhang Lianmeng
Published: October 2012

The stoichiometry of boron carbide thin films was controlled in the range of 0.1–8.9 via pulsed laser deposition by using boron-carbon dual-targets. The amorphous films sized 50 nm in thickness. The reaction rate of boron and carbon atoms increased with the increasing of target rotating speed. Carbon atoms preferentially substituted boron atoms within the chain site as sp2 hybridization at lower carbon concentrations and then within the icosahedrons site as sp3 hybridization at higher carbon concentrations.
A periodic charge-dipole electrostatic model: Parametrization for silver slabs
Authors: Bodrenko I. V. , Sierka M. , Fabiano E. , Sala F. Della
Published: October 2012

We present an extension of the charge-dipole model for the description of periodic systems. This periodic charge-dipole electrostatic model (PCDEM) allows one to describe the linear response of periodic structures in terms of charge- and dipole-type Gaussian basis functions. The long-range electrostatic interaction is efficiently described by means of the continuous fast multipole method. As a first application, the PCDEM method is applied to describe the polarizability of silver slabs. We find that for a correct description of the polarizability of the slabs both charges and dipoles are required. However a continuum set of parametrizations, i.e., different values of the width of charge- and dipole-type Gaussians, leads to an equivalent and accurate description of the slabs polarizability but a completely unphysical description of induced charge-density inside the slab. We introduced the integral squared density measure which allows one to obtain a unique parametrization which accurately describes both the polarizability and the induced density profile inside the slab. Finally the limits of the electrostatic approximations are also pointed out.
Spin dynamics of (Pr0.5-xCex)Ca0.5MnO3 (x = 0.05, 0.10, and 0.20) system studied by muon spin relaxation
Authors: Mavani K. R. , Hillier A. D. , Paulose P. L. , Kockelmann W. A. , Adroja D. T.
Published: October 2012

Muon spin relaxation (μSR) measurements were performed on the (Pr0.5-xCex)Ca0.5MnO3 (x = 0.05, 0.10, and 0.20) manganite system to study the influence of Ce substitution on the spin dynamics. A long-range antiferromagnetic state at low Ce substitution levels (x = 0.05) transforms to a spin-glass state by a marginal increase in x to 0.10. The manganite with x = 0.05 shows simple exponential relaxation down to low temperatures, whereas the manganites with x = 0.10 and 0.20 show a coexistence of two distinct relaxation mechanisms below spin glass-like transition temperature (TG). The μSR data for x = 0.10 and 0.20 provide evidence for the existence of a component with a root-exponential relaxation below TG, suggesting a nondiffusive relaxation mechanism similar to that in a magnetic glass. Above TG, the relaxation follows a stretched exponential function with distributed time-scales up to ∼150 K. Although similar types of relaxation dynamics exist in these two manganites (x = 0.10 and 0.20), the temperature dependent behavior slightly differ. In the light of the present results, we construct the phase-diagram of the (Pr0.5-xCex)Ca0.5MnO3 manganite system which encompasses different structural and magnetic correlations evolving as a function of Ce substitution.
Tunable nonlinear optical absorption in semiconductor nanocrystals doped with transition metal ions
Authors: Peng Xiao-Niu , Li Jian-Bo , Yang Yue-Zhou , Gong Hong-Mei , Nan Fan , Zhou Li , Yu Xue-Feng , Hao Zhong-Hua , Wang Qu-Quan
Published: October 2012

Semiconductor nanocrystals (SNCs) doped with Mn2+ and Cu2+ ions (ZnSe:Mn, ZnSe:Mn/CdSe, and ZnSe:Cu) were synthesized and their nonlinear absorption properties were investigated using the typical open-aperture Z-scan technique. A reversal from reverse saturable absorption (RSA) to saturable absorption (SA) was observed in the ZnSe:Mn SNCs. In contrast, the SA signals were largely suppressed and only RSA signals were measured in the ZnSe:Mn/CdSe and ZnSe:Cu SNCs. These different nonlinear absorption properties implied strong interactions between the excited excitons and impurity ions, which agreed well with the analysis performed by the theory model of the exciton transition in the energy structures. The nonlinearities of the doped SNCs could be controllably tuned by the integration of different doped ions and host SNCs. This strategy shows promise for extensive potential applications in optical limiting and switching.
Small polaronic hole hopping mechanism and Maxwell-Wagner relaxation in NdFeO3
Authors: Ahmad I. , Akhtar M. J. , Younas M. , Siddique M. , Hasan M. M.
Published: October 2012

In the modern micro-electronics, transition metal oxides due to their colossal values of dielectric permittivity possess huge potential for the development of capacitive energy storage devices. In the present work, the dielectric permittivity and the effects of temperature and frequency on the electrical transport properties of polycrystalline NdFeO3, prepared by solid state reaction method, are discussed. Room temperature Mossbauer spectrum confirms the phase purity, octahedral environment for Fe ion, and high spin state of Fe3+ ion. From the impedance spectroscopic measurements, three relaxation processes are observed, which are related to grains, grain boundaries (gbs), and electrode-semiconductor contact in the measured temperature and frequency ranges. Decrease in resistances and relaxation times of the grains and grain boundaries with temperature confirms the involvement of thermally activated conduction mechanisms. Same type of charge carriers (i.e., small polaron hole hopping) have been found responsible for conduction and relaxation processes through the grain and grain boundaries. The huge value of the dielectric constant (∼8 × 103) at high temperature and low frequency is correlated to the Maxwell-Wagner relaxation due to electrode-sample contact.
Structural stability of proteins in aqueous and nonpolar environments
Authors: Yasuda Satoshi , Oshima Hiraku , Kinoshita Masahiro
Published: October 2012

A protein folds into its native structure with the α-helix and/or β-sheet in aqueous solution under the physiological condition. The relative content of these secondary structures largely varies from protein to protein. However, such structural variability is not exhibited in nonaqueous environment. For example, there is a strong trend that alcohol induces a protein to form α-helices, and many of the membrane proteins within the lipid bilayer consists of α-helices. Here we investigate the structural stability of proteins in aqueous and nonpolar environments using our recently developed free-energy function F = (Λ − TS)/(kBT0) = Λ/(kBT0) − S/kB (T0 = 298 K and the absolute temperature T is set at T0) which is based on statistical thermodynamics. Λ/(kBT0) and S/kB are the energetic and entropic components, respectively, and kB is Boltzmann's constant. A smaller value of the positive quantity, −S, represents higher efficiency of the backbone and side-chain packing promoted by the entropic effect arising from the translational displacement of solvent molecules or the CH2, CH3, and CH groups which constitute nonpolar chains of lipid molecules. As for Λ, in aqueous solution, a transition to a more compact structure of a protein accompanies the break of protein-solvent hydrogen bonds: As the number of donors and acceptors buried without protein intramolecular hydrogen bonding increases, Λ becomes higher. In nonpolar solvent, lower Λ simply implies more intramolecular hydrogen bonds formed. We find the following. The α-helix and β-sheet are advantageous with respect to −S as well as Λ and to be formed as much as possible. In aqueous solution, the solvent-entropy effect on the structural stability is so strong that the close packing of side chains is dominantly important, and the α-helix and β-sheet contents are judiciously adjusted to accomplish it. In nonpolar solvent, the solvent-entropy effect is substantially weaker than in aqueous solution. Λ is crucial and the α-helix is more stable than the β-sheet in terms of Λ, which develops a tendency that α-helices are exclusively chosen. For a membrane protein, α-helices are stabilized as fundamental structural units for the same reason, but their arrangement is performed through the entropic effect mentioned above.
Light trapping enhancements of inverted pyramidal structures with the tips for silicon solar cells
Authors: Cheng Hsin-Hung , Chang Ying-Yu , Chu Jen-You , Lin Ding-Zheng , Chen Yi-Ping , Li Jia-Han
Published: October 2012

The anti-reflection properties of the inverted pyramidal structures with the tips for crystalline silicon solar cells are studied numerically and experimentally, and the comparisons with inverted pyramidal structures without the tips are given. Because the light has more multiple reflection between different surfaces of the inverted pyramidal structures with the tips and more light energies are trapped and absorbed by the solar cell materials, the structures with the tips can have smaller reflection. This study can be useful for the designs of textured structures for the solar cells or other anti-reflection applications.
Enhanced carrier-carrier interaction in optically pumped hydrogenated nanocrystalline silicon
Authors: Roger Thomas W. , He Wei , Yurkevich Igor V. , Kaplan Andrey
Published: October 2012

A femtosecond pump-probe setup was used to measure the time resolved reflectivity of hydrogenated amorphous silicon containing crystalline silicon nanoparticles at eight different incidence angles. Results fitted with the Drude model found a scattering rate of Γ=2−1+1.2×1015 s−1 at a corresponding carrier concentration of ∼1020 cm−3. The observed scattering rate is attributed to enhanced carrier-carrier interaction in optically pumped nanocrystals.
Sign-inversion of charging-induced variation of electrical resistance of nanoporous platinum
Authors: Steyskal Eva-Maria , Besenhard Maximilian , Landgraf Stephan , Zhong Yi , Weissmüller Jörg , Pölt Peter , Albu Mihaela , Würschum Roland
Published: October 2012

The electrical resistance (R) of nanoporous platinum prepared by dealloying reversibly changes by 4% upon electrochemical surface charging in a regime where oxygen adsorption/desorption and surface oxidation/reduction occur. The variation of R with charging shows a sign inversion. Besides the usual behavior of increasing R with positive charging, a decrease of R occurs at higher potentials. Following recent studies of the sign inversion of the surface stress-charge response of porous nanophase Pt, the sign-inversion of the resistance with charging may be related to the electronic structure of the surface oxide. In addition, a charge-induced variation of the charge-carrier scattering rate at the metal–electrolyte interface is taken into account.
Increasing the applicability of density functional theory. III. Do consistent Kohn-Sham density functional methods exist?
Authors: Verma Prakash , Bartlett Rodney J.
Published: October 2012

The concept of a “consistent,” Kohn-Sham (KS) density functional theory (DFT) is discussed, where the functional is able to provide good total energies and its self-consistent potential is such that the KS eigenvalues correspond to accurate approximations to the principal ionization potentials for the molecule. Today, none of the vast number of DFT approximations show this property. The one exception is the ab initio dft method built upon the optimized effective potential strategy for exchange and correlation. This qualifies as a DFT method because it represents the correlated density as a single determinant and by imposing that condition, generates local exchange and correlation operators which are used in self-consistent solutions of the orbitals and eigenvalues. Such a “consistent” DFT shares many of the properties of the Dyson equation, but without its frequency dependence and associated complications. The relationship between ab initio dft based on MBPT2 functional and GW method is discussed. Ab initio dft provides a self-consistent, frequency independent, effective independent particle alternative with a local correlation potential.
Morphology and dynamics of three interacting kink-unstable flux ropes in a laboratory magnetoplasma
Authors: Van Compernolle B. , Gekelman W.
Published: October 2012

Flux ropes are ubiquitous in space and solar plasmas. Multiple adjacent flux ropes are commonly observed both in the solar corona and in the earth's magnetotail. The interaction of adjacent flux ropes is often dynamic and can lead to magnetic reconnection. In this paper, the interaction of three flux ropes is studied in a low β background laboratory magnetoplasma. The magnetic structure of the flux rope is produced by the poloidal field of a field-aligned finite sized current which adds to the guide magnetic field and creates the typical helical field line structure. Each rope produces magnetic fields on the order of a few percent of the guide field. Volumetric magnetic field data were acquired and the magnetic field structure and dynamics of the flux ropes can thus be reconstructed. The flux ropes are found to propagate at the Alfvén speed. Merging and bouncing of the flux ropes have been observed. The ropes twist and writhe as they propagate through the plasma. They are line tied and clearly separate at the cathode end but further away they merge into one extended rope. The steady state of the flux ropes is characterized by a rotation of the three flux ropes as a whole. At the same time, the flux ropes are twisting around each other. Time resolved density and temperature measurements from Langmuir probe data exhibit the same dynamics as the magnetic field data.
Energy conserving, linear scaling Born-Oppenheimer molecular dynamics
Authors: Cawkwell M. J. , Niklasson Anders M. N.
Published: October 2012

Born-Oppenheimer molecular dynamics simulations with long-term conservation of the total energy and a computational cost that scales linearly with system size have been obtained simultaneously. Linear scaling with a low pre-factor is achieved using density matrix purification with sparse matrix algebra and a numerical threshold on matrix elements. The extended Lagrangian Born-Oppenheimer molecular dynamics formalism [A. M. N. Niklasson, Phys. Rev. Lett. 100, 123004 (2008)10.1103/PhysRevLett.100.123004] yields microcanonical trajectories with the approximate forces obtained from the linear scaling method that exhibit no systematic drift over hundreds of picoseconds and which are indistinguishable from trajectories computed using exact forces.
Structural optimization of molecular clusters with density functional theory combined with basin hopping
Authors: Do Hainam , Besley Nicholas A.
Published: October 2012

Identifying the energy minima of molecular clusters is a challenging problem. Traditionally, search algorithms such as simulated annealing, genetic algorithms, or basin hopping are usually used in conjunction with empirical force fields. We have implemented a basin hopping search algorithm combined with density functional theory to enable the optimization of molecular clusters without the need for empirical force fields. This approach can be applied to systems where empirical potentials are not available or may not be sufficiently accurate. We illustrate the effectiveness of the method with studies on water, methanol, and water + methanol clusters as well as protonated water and methanol clusters at the B3LYP+D/6-31+G* level of theory. A new lowest energy structure for H+(H2O)7 is predicted at the B3LYP+D/6-31+G* level. In all of the protonated mixed water and methanol clusters, we find that H+ prefers to combine with methanol rather than water in the lowest-energy structures.
A high resolution ultraviolet Brillouin scattering set-up
Authors: Bencivenga F. , Battistoni A. , Fioretto D. , Gessini A. , Sandercock J. R. , Masciovecchio C.
Published: October 2012

We report on a high resolution inelastic UV scattering table-top setup conceived for Brillouin measurements. The system is based on a tandem 1+1 pass scanning Fabry-Perot interferometer of Sandercock type. Special optics were used in order to adapt such an interferometric device, nowadays only used at visible or IR wavelength, to the UV range. The advantages with respect to other UV Brillouin scattering instruments are the larger resolving power and the improved contrast in the low frequency spectral region. To corroborate these features we provide a comparison between data obtained using the described system and those from existing UV Brillouin scattering instruments.
Leakage current mechanisms in high performance alumina-silicone nanolaminate dielectrics
Authors: Sahoo S. K. , Patel R. P. , Wolden C. A.
Published: October 2012

Alumina-silicone nanolaminates deposited by plasma-enhanced chemical vapor deposition were explored as dielectrics in metal-insulator-metal capacitors. Temperature-dependent current versus voltage (I-V) measurements were used to investigate the conduction mechanisms contributing to the leakage current in these structures. It is observed that space charge limited current mechanism is the dominant conduction process in the high field region. The estimated shallow trap level energies (Et) are 0.16 eV and 0.33 eV for 50% and 83.3% Al2O3 nanolaminates, respectively.
Reversible ferromagnetism in rutile TiO2 single crystals induced by nickel impurities
Authors: Zhao Y. L. , Motapothula M. , Yakovlev N. L. , Liu Z. Q. , Dhar S. , Rusydi A. , Ariando  , Breese M. B. H. , Wang Q. , Venkatesan T.
Published: October 2012

We report a Ni impurity induced reversible ferromagnetism and surface conduction in rutile TiO2 crystals subjected to specific thermal annealing. For annealing in vacuum at 800 °C, a growing ferromagnetic signal is seen with time while for a similar annealing in air, the magnetism vanishes. The magnetism is concomitant with a surface conductivity which at low temperatures shows tunneling characteristics. Here, we show that Ni magnetic impurity (in TiO2 crystals at <100 ppm) under vacuum annealing segregates to the surface over a 50 nm layer where the Ni concentration exceeds 10%–20% and drops with subsequent air annealing.
Dynamic control of directional asymmetry observed in ultrafast laser direct writing
Authors: Salter P. S. , Booth M. J.
Published: October 2012

A liquid crystal spatial light modulator (SLM) is used to control the focal symmetry and the associated directional “quill” effect encountered when using a femtosecond laser for direct laser writing of fused silica. Applying a blazed grating to the SLM effectively introduces pulse front tilt to the fabrication beam and a spatiotemporal asymmetry at the focus. As a result different fabricated features are generated when moving the substrate in opposite directions relative to the tilt. It is additionally shown that inhomogeneous pupil illumination can cause similar directionality in the fabrication via a spatial asymmetry in the focus.
Polarization-insensitive and wide-angle plasmonically induced transparency by planar metamaterials
Authors: Duan Xiaoyang , Chen Shuqi , Yang Haifang , Cheng Hua , Li Junjie , Liu Wenwei , Gu Changzhi , Tian Jianguo
Published: October 2012

We present the design, characterization, and experimental demonstration of a polarization-insensitive wide-angle plasmonically induced transparency (PIT) planar metamaterial (MM) in the near-infrared regime. A four-level plasmonic system is proposed to explain and analyze the forming mechanisms of the PIT planar MM, whose results agree closely with the simulated and experimental results. This shows that the local asymmetrical nanostructure leading to the plasmon-assisted interaction is the key to producing PIT, but it does not mean that PIT cannot be achieved by the whole symmetrical nanostructure. This work offers a further step in developing optical modulation.
Direct observation of anti-phase boundaries in heteroepitaxy of GaSb thin films grown on Si(001) by transmission electron microscopy
Authors: Woo S. Y. , Hosseini Vajargah S. , Ghanad-Tavakoli S. , Kleiman R. N. , Botton G. A.
Published: October 2012

Unambiguous identification of anti-phase boundaries (APBs) in heteroepitaxial films of GaSb grown on Si has been so far elusive. In this work, we present conventional transmission electron microscopy (TEM) diffraction contrast imaging using superlattice reflections, in conjunction with convergent beam electron diffraction analysis, to determine a change in polarity across APBs in order to confirm the presence of anti-phase disorder. In-depth analysis of anti-phase disorder is further supported with atomic resolution high-angle annular dark-field scanning transmission electron microscopy. The nature of APBs in GaSb is further elucidated by a comparison to previous results for GaAs epilayers grown on Si.
Influence of flexoelectric effects on multiferroic nanocomposite thin bilayer films
Authors: Chen H. T. , Soh A. K.
Published: October 2012

The flexoelectric effect, which describes the induction of polarization from strain gradient, is negligible in bulk but not nanometer scale ferroelectrics. The influence of flexoelectric effects on magnetic field induced electric polarizations in multiferroic nanocomposite thin bilayer films has been investigated. It has been found that with flexoelectric effects taken into consideration, the polarization would not be reduced to zero even if the film was ultra-thin. Under an applied magnetic field, polarizations were induced from two effects, i.e., the conventional electrostrictive and flexoelectric effects. In the case where the film thickness was relatively large, the former factor was the main one influencing the magnetic field induced polarization. By decreasing the film thickness, the flexoelectric induced polarization became more and more dominant and it finally overcame the electrostrictive induced polarization and changed the value of magnetic field induced polarization from negative to positive.
Band-gap tuning and nonlinear optical characterization of Ag:TiO2 nanocomposites
Authors: Hari Misha , Ani Joseph Santhi , Mathew S. , Radhakrishnan P. , Nampoori V. P. N.
Published: October 2012

Silver/titanium dioxide nanoparticles with varied concentration of silver have been synthesized by a simple laser light induced chemical reaction, where bulk titanium dioxide powder is used as the starting material. The particle size, morphology, crystal structure, and optical properties were characterized by transmission electron microscopy, x-ray diffraction, UV-Vis absorption spectroscopy, fluorescence spectroscopy, and Fourier transform infrared spectroscopy. The x-ray diffraction pattern revealed that the TiO2 nanoparticles obtained are in pure rutile phase. The important observation from transmission electron microscopic images is that the Ag particles are distributed over the surface of titanium dioxide nanoparticles. The band gap of the TiO2 nanoparticles was tuned between 1.75 and 2.75 eV by varying Ag concentration. The nonlinear optical absorption and optical limiting performance of Ag:TiO2 nanocomposites were investigated by open aperture z-scan using nanosecond Nd:YAG laser pulses operating at 532 nm. The best optical limiting threshold obtained was 113MW/cm2.
Optoelectronic and magnetic properties of Mn-doped indium tin oxide: A first-principles study
Authors: Nath Tripathi Madhvendra , Saeed Bahramy Mohammad , Shida Kazuhito , Sahara Ryoji , Mizuseki Hiroshi , Kawazoe Yoshiyuki
Published: October 2012

The manganese doped indium tin oxide (ITO) has integrated magnetics, electronics, and optical properties for next generation multifunctional devices. Our first-principles density functional theory (DFT) calculations show that the manganese atom replaces b-site indium atom, located at the second coordination shell of the interstitial oxygen in ITO. It is also found that both anti-ferromagnetic and ferromagnetic behaviors are realizable. The calculated magnetic moment of 3.95μB/Mn as well as the high transmittance of ∼80% for a 150 nm thin film of Mn doped ITO is in good agreement with the experimental data. The inclusion of on-site Coulomb repulsion corrections via DFT + U methods turns out to improve the optical behavior of the system. The optical behaviors of this system reveal its suitability for the magneto-opto-electronic applications.
On the heterogeneous character of the heartbeat instability in complex (dusty) plasmas
Authors: Pustylnik M. Y. , Ivlev A. V. , Sadeghi N. , Heidemann R. , Mitic S. , Thomas H. M. , Morfill G. E.
Published: October 2012

A hypothesis on the physical mechanism generating the heartbeat instability in complex (dusty) plasmas is presented. It is suggested that the instability occurs due to the periodically repeated critical transformation on the boundary between the microparticle-free area (void) and the complex plasma. The critical transformation is supposed to be analogous to the formation of the sheath in the vicinity of an electrode. The origin of the transformation is the loss of the electrons and ions on microparticles surrounding the void. We have shown that this hypothesis is consistent with the experimentally measured stability parameter range, with the evolution of the plasma glow intensity and microparticle dynamics during the instability, as well as with the observed excitation of the heartbeat instability by an intensity-modulated laser beam (inducing the modulation of plasma density).
Thickness dependent effects of an intermediate molecular blocking layer on the optoelectronic characteristics of organic bilayer photovoltaic cells
Authors: Steindamm A. , Brendel M. , Topczak A. K. , Pflaum J.
Published: October 2012

In this work, we address the microscopic effects related to the implementation of a bathophenanthroline (BPhen) exciton blocking layer (EBL) sandwiched between Ag cathode and molecular diindenoperylene (DIP)/C60 bilayer of a photovoltaic cell. Complementary studies of current density, external quantum efficiency, and photoluminescence quenching for EBL thicknesses up to 50 nm indicate that Ag atoms are able to penetrate through the whole 35 nm thick C60 film into the polycrystalline DIP layer underneath, thereby enhancing exciton quenching if no blocking layer is applied. In contrast, an optimal trade-off between exciton blocking, suppression of metal penetration, and electron transport is achieved for a 5 nm thick BPhen layer yielding an improvement of power conversion efficiency by more than a factor of 2.
Optimization of in-line phase contrast particle image velocimetry using a laboratory x-ray source
Authors: Ng I. , Paganin D. M. , Fouras A.
Published: October 2012

Phase contrast particle image velocimetry (PIV) using a laboratory x-ray microfocus source is investigated using a numerical model. Phase contrast images of 75 μm air bubbles, embedded within water exhibiting steady-state vortical flow, are generated under the paraxial approximation using a tungsten x-ray spectrum at 30 kVp. Propagation-based x-ray phase-contrast speckle images at a range of source–object and object–detector distances are generated, and used as input into a simulated PIV measurement. The effects of source-size-induced penumbral blurring, together with the finite dynamic range of the detector, are accounted for in the simulation. The PIV measurement procedure involves using the cross-correlation between temporally sequential speckle images to estimate the transverse displacement field for the fluid. The global error in the PIV reconstruction, for the set of simulations that was performed, suggests that geometric magnification is the key parameter for designing a laboratory-based x-ray phase-contrast PIV system. For the modeled system, x-ray phase-contrast PIV data measurement can be optimized to obtain low error (<0.2 effective pixel of the detector) in the system with magnification lying in the range between 1.5 and 3. For large effective pixel size (>15 μm) of the detector, high geometric magnification (>2.5) is desired, while for large source size system (FWHM > 30 μm), low magnification (<1.5) would be suggested instead. The methods developed in this paper can be applied to optimizing phase-contrast velocimetry using a variety of laboratory x-ray sources.
Impact of gate resistance in graphene radio frequency transistors
Authors: Farmer Damon B. , Valdes-Garcia Alberto , Dimitrakopoulos Christos , Avouris Phaedon
Published: October 2012

The effect of gate resistance on the high frequency device properties of graphene transistors is explored. Decreasing this resistance does not alter the current gain cutoff frequency (fT), but it does allow for the power gain cutoff frequency (fmax) to be increased. Analysis of this effect reveals that the relative rate of change between fT and fmax is most sensitive to the relationship between the parasitic resistance in the device channel and the output conductance, a manifestation of device scaling in the triode regime. This result underlies the importance of a small output conductance in the scaling of graphene transistors.