bluuebunny/crossref_metadata_2025 huggingface dataset:
Structures, magnetic properties, and electronic counting rule of metals‐encapsulated cage‐like M2 Si18 (M = Ti‐Zn) clusters
Authors: Ji Weixiao , Luo Chenglin
Published: November 2011

The geometries, magnetic properties and stabilities of the transition metal (TM) atoms encapsulated M2Si18 (M = Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) clusters have been systematically calculated by using the density function theory with generalized gradient approximation. Only when the doping metal atom has no more than half‐full d electronic shell, a double hexagonal prism cage‐like M2Si18 structure could form. The total moments of M2Si18 are either 0 or 2μB. Co2Si18 is the most stable cluster among all 3d doped M2Si18 clusters. The model of shell closure at the TM atom may be helpful to understand the stability of M2Si18 clusters. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011
How to Avoid Postoperative Liver Failure: A Novel Method
Authors: de Santibañes Eduardo , Alvarez Fernando A. , Ardiles Victoria
Published: November 2011

Background

Postoperative liver failure (PLF) is the most feared and severe complication after extensive liver resections.

Methods

We present an innovative surgical technique that has been employed for the treatment of three patients (two with multiple colorectal liver metastases and one with hilar cholangiocarcinoma) whose livers were previously considered locally unresectable because of an insufficient future liver remnant (FLR). In‐situ liver transection with right portal vein ligation was implemented.

Results

Six days after surgery a volumetric computed tomography (CT)‐scan showed 40–80% hypertrophy of the FLR. The patients then underwent a completion surgery with right hepatectomy or right trisectionectomy. None of the patients developed PLF during a mean hospital stay of 16 days. After a mean follow‐up of two months, the three of them are free of disease.

Conclusions

This technique induced rapid growth of the FLR, greater than that reported with portal vein occlusion alone. It represents a promising advance in oncological liver surgery that readdresses the current management of patients with primarily unresectable liver disease. Such a revolutionary strategy allows a two‐stage surgical approach during a single hospital stay and without PLF. However, further research is needed to determine the long‐term outcomes of this technique and to explain the occurrence of such enhanced liver regeneration.
Effects of inbreeding on life history and thermal performance in the tropical butterfly Bicyclus anynana
Authors: Dierks Anneke , Hoffmann Bianca , Bauerfeind Stephanie S. , Fischer Klaus
Published: November 2011

Human‐induced loss and fragmentation of natural habitats reduces population size and thereby presumably genetic diversity through inbreeding or genetic drift. Additionally, many species are confronted with increased temperature stress due to climate change, with reduced genetic diversity potentially interfering with a species’ ability to cope with such conditions. While in general the detrimental impact of inbreeding has often been documented, its consequences for the ability to cope with temperature stress are still poorly understood. Against this background we here investigate the effects of inbreeding on egg hatching success, development and temperature stress tolerance in the tropical butterfly Bicyclus anynana. Specifically we test for an increased sensitivity to environmental stress in inbred individuals. Our results revealed that even comparatively low levels of inbreeding yield negative consequences for reproduction and development under beneficial conditions. Inbreeding also reduced cold tolerance in adult butterflies, while heat tolerance remained unaffected. We therefore conclude that acute stress tolerance may not be generally impaired by inbreeding.
Regeneration of native vascular plants facilitated by Ischaemum aristatum var. glaucum tussocks: an experimental demonstration
Authors: Wang Zhe , Nishihiro Jun , Washitani Izumi
Published: November 2011

Facilitation of a perennial tussock grass, Ischaemum aristatum var. glaucum, was hypothesized to be the provision of germination safe sites against inundation. We conducted field census and seed addition experiments to test this hypothesis. Facilitation effects of I. aristatum var. glaucum tussocks were obvious; in contrast to 280 seedlings/m2 of ten native species observed on tussocks, seedlings hardly emerged on bare ground, even after seed addition. Although effects of moss occurrence at tussocks were not significant on the total number or species richness of emerged seedlings, significantly positive effects were observed on the seedling survival of some species, including endangered species. Conservation of facilitators will efficiently ensure the regeneration success of native vascular plants.
Tissue Distribution of α‐ and γ‐Tocotrienol and γ‐Tocopherol in Rats and Interference with Their Accumulation by α‐Tocopherol
Authors: Uchida Tomono , Abe Chisato , Nomura Saki , Ichikawa Tomio , Ikeda Saiko
Published: November 2011

The aim of this study was to evaluate tissue distribution of vitamin E isoforms such as α‐ and γ‐tocotrienol and γ‐tocopherol and interference with their tissue accumulation by α‐tocopherol. Rats were fed a diet containing a tocotrienol mixture or γ‐tocopherol with or without α‐tocopherol, or were administered by gavage an emulsion containing tocotrienol mixture or γ‐tocopherol with or without α‐tocopherol. There were high levels of α‐tocotrienol in the adipose tissue and adrenal gland, γ‐tocotrienol in the adipose tissue, and γ‐tocopherol in the adrenal gland of rats fed tocotrienol mixture or γ‐tocopherol for 7 weeks. Dietary α‐tocopherol decreased the α‐tocotrienol and γ‐tocopherol but not γ‐tocotrienol concentrations in tissues. In the oral administration study, both tocopherol and tocotrienol quickly accumulated in the adrenal gland; however, their accumulation in adipose tissue was slow. In contrast to the dietary intake, α‐tocopherol, which has the highest affinity for α‐tocopherol transfer protein (αTTP), inhibited uptake of γ‐tocotrienol to tissues including adipose tissue after oral administration, suggesting that the affinities of tocopherol and tocotrienol for αTTP in the liver were the critical determinants of their uptake to peripheral tissues. Vitamin E deficiency for 4 weeks depleted tocopherol and tocotrienol stores in the liver but not in adipose tissue. These results indicate that dietary vitamin E slowly accumulates in adipose tissue but the levels are kept without degradation. The property of adipose tissue as vitamin E store causes adipose tissue‐specific accumulation of dietary tocotrienol.
Physicochemical Properties of Red Salmon Oil (Oncorhynchus nerka) and Microencapsulated Red Salmon Oil Added to Baby Food
Authors: Wan Yuting , Li Juan , Solval Kevin Mis , Stine Jesse J. , Bechtel Peter J. , Sathivel Subramaniam
Published: November 2011

Unpurified red salmon oil (UPSO) was processed to obtain purified salmon oil (PSO) by chitosan adsorption. Both unpurified and purified oils were evaluated for peroxide value (PV), free fatty acids (FFA), fatty acid methyl esters (FAME), moisture, and color. An emulsion system containing PSO (EPSO) was prepared; the system was analyzed for color, rheological properties and microstructure before spray drying to produce microencapsulated PSO (MPSO). MPSO was analyzed for moisture, water activity, bulk density, color and FAME composition. PSO or MPSO was added to a commercial baby‐food product (CB) and all baby‐food samples were compared for PV, FFAs, FAME, and color. Experiments were completed in triplicate and data statistically analyzed (α = 0.05). PSO had higher percentages of total omega‐3, total monounsaturated DHA, and EPA than MPSO. EPSO exhibited viscoelastic characteristic and the droplet size of EPSO was 1–9 μm. Total omega‐3 and total monounsaturated contents of the MPSO were lower than PSO. All baby‐food samples with added fish oils had similar color. DHA and EPA contents of baby food were increased over three fold by the addition of PSO and/or MPSO. MPSO can be added to CB resulting in increasing total percent omega‐3 fatty acids while maintaining desirable attributes of the CB.
On Coding the Position of Letters in Words
Authors: Whitney Carol , Bertrand Daisy , Grainger Jonathan
Published: November 2011

Open-bigram and spatial-coding schemes provide different accounts of how letter position is encoded by the brain during visual word recognition. Open-bigram coding involves an explicit representation of order based on letter pairs, while spatial coding involves a comparison function operating over representations of individual letters. We identify a set of priming conditions (subset primes and reversed interior primes) for which the two types of coding schemes give opposing predictions, hence providing the opportunity for strong scientific inference. Experimental results are consistent with the open-bigram account, and inconsistent with the spatial-coding scheme.
Twenty-Four Hours of Total Sleep Deprivation Selectively Impairs Attentional Networks
Authors: Jugovac Davide , Cavallero Corrado
Published: November 2011

Performance decrements after sleep loss have been extensively studied and are usually attributed to generic attentional deficits. This claim, however, is based on the view of attention as a unitary construct, despite evidence that it should be considered a multidimensional cognitive ability. The aim of the present study was to evaluate the impact of one night of sleep deprivation on the efficiency of three attentional networks, defined by Posner and Raichle (1994) in anatomical and functional terms, as alerting, orienting, and executive control. Thirty participants performed the Attention Network Test at 9:00 a.m. following two different sleep conditions: baseline (a normal night of sleep) and deprivation (24 hrs of wakefulness). Results showed an overall slowing in reaction times and a significant decrease in accuracy after sleep deprivation. Sleep deprivation selectively affected the three attentional networks, given that only executive control efficacy significantly decreased after sleep deprivation. By contrast, phasic alerting and orienting showed no differences in the two sleep conditions. Thus, performance deficits following sleep deprivation do not reflect global attentional deficits.
Measurement and inference of profile soil‐water dynamics at different hillslope positions in a semiarid agricultural watershed
Authors: Green Timothy R. , Erskine Robert H.
Published: November 2011

Dynamics of profile soil water vary with terrain, soil, and plant characteristics. The objectives addressed here are to quantify dynamic soil water content over a range of slope positions, infer soil profile water fluxes, and identify locations most likely influenced by multidimensional flow. The instrumented 56 ha watershed lies mostly within a dryland (rainfed) wheat field in semiarid eastern Colorado. Dielectric capacitance sensors were used to infer hourly soil water content for approximately 8 years (minus missing data) at 18 hillslope positions and four or more depths. Based on previous research and a new algorithm, sensor measurements (resonant frequency) were rescaled to estimate soil permittivity, then corrected for temperature effects on bulk electrical conductivity before inferring soil water content. Using a mass‐conservation method, we analyzed multitemporal changes in soil water content at each sensor to infer the dynamics of water flux at different depths and landscape positions. At summit positions vertical processes appear to control profile soil water dynamics. At downslope positions infrequent overland flow and unsaturated subsurface lateral flow appear to influence soil water dynamics. Crop water use accounts for much of the variability in soil water between transects that are either cropped or fallow in alternating years, while soil hydraulic properties and near‐surface hydrology affect soil water variability across landscape positions within each management zone. The observed spatiotemporal patterns exhibit the joint effects of short‐term hydrology and long‐term soil development. Quantitative methods of analyzing soil water patterns in space and time improve our understanding of dominant soil hydrological processes and provide alternative measures of model performance.
Hydrological parameter estimations from a conservative tracer test with variable‐density effects at the Boise Hydrogeophysical Research Site
Authors: Dafflon B. , Barrash W. , Cardiff M. , Johnson T. C.
Published: November 2011

Reliable predictions of groundwater flow and solute transport require an estimation of the detailed distribution of the parameters (e.g., hydraulic conductivity, effective porosity) controlling these processes. However, such parameters are difficult to estimate because of the inaccessibility and complexity of the subsurface. In this regard, developments in parameter estimation techniques and investigations of field experiments are still challenging and necessary to improve our understanding and the prediction of hydrological processes. Here we analyze a conservative tracer test conducted at the Boise Hydrogeophysical Research Site in 2001 in a heterogeneous unconfined fluvial aquifer. Some relevant characteristics of this test include: variable‐density (sinking) effects because of the injection concentration of the bromide tracer, the relatively small size of the experiment, and the availability of various sources of geophysical and hydrological information. The information contained in this experiment is evaluated through several parameter estimation approaches, including a grid‐search‐based strategy, stochastic simulation of hydrological property distributions, and deterministic inversion using regularization and pilot‐point techniques. Doing this allows us to investigate hydraulic conductivity and effective porosity distributions and to compare the effects of assumptions from several methods and parameterizations. Our results provide new insights into the understanding of variable‐density transport processes and the hydrological relevance of incorporating various sources of information in parameter estimation approaches. Among others, the variable‐density effect and the effective porosity distribution, as well as their coupling with the hydraulic conductivity structure, are seen to be significant in the transport process. The results also show that assumed prior information can strongly influence the estimated distributions of hydrological properties.
The Roles of Cerebral Blood Flow, Capillary Transit Time Heterogeneity, and Oxygen Tension in Brain Oxygenation and Metabolism
Authors: Jespersen Sune N , Østergaard Leif
Published: November 2011

Normal brain function depends critically on moment-to-moment regulation of oxygen supply by the bloodstream to meet changing metabolic needs. Neurovascular coupling, a range of mechanisms that converge on arterioles to adjust local cerebral blood flow ( CBF), represents our current framework for understanding this regulation. We modeled the combined effects of CBF and capillary transit time heterogeneity (CTTH) on the maximum oxygen extraction fraction ( OEFmax) and metabolic rate of oxygen that can biophysically be supported, for a given tissue oxygen tension. Red blood cell velocity recordings in rat brain support close hemodynamic—metabolic coupling by means of CBF and CTTH across a range of physiological conditions. The CTTH reduction improves tissue oxygenation by counteracting inherent reductions in OEFmax as CBF increases, and seemingly secures sufficient oxygenation during episodes of hyperemia resulting from cortical activation or hypoxemia. In hypoperfusion and states of blocked CBF, both lower oxygen tension and CTTH may secure tissue oxygenation. Our model predicts that disturbed capillary flows may cause a condition of malignant CTTH, in which states of higher CBF display lower oxygen availability. We propose that conditions with altered capillary morphology, such as amyloid, diabetic or hypertensive microangiopathy, and ischemia—reperfusion, may disturb CTTH and thereby flow-metabolism coupling and cerebral oxygen metabolism.
Resolving the contributions of the membrane-bound and periplasmic nitrate reductase systems to nitric oxide and nitrous oxide production in Salmonella enterica serovar Typhimurium
Authors: Rowley Gary , Hensen Daniela , Felgate Heather , Arkenberg Anke , Appia-Ayme Corinne , Prior Karen , Harrington Carl , Field Sarah J. , Butt Julea N. , Baggs Elizabeth , Richardson David J.
Published: November 2011

The production of cytotoxic nitric oxide (NO) and conversion into the neuropharmacological agent and potent greenhouse gas nitrous oxide (N2O) is linked with anoxic nitrate catabolism by Salmonella enterica serovar Typhimurium. Salmonella can synthesize two types of nitrate reductase: a membrane-bound form (Nar) and a periplasmic form (Nap). Nitrate catabolism was studied under nitrate-rich and nitrate-limited conditions in chemostat cultures following transition from oxic to anoxic conditions. Intracellular NO production was reported qualitatively by assessing transcription of the NO-regulated genes encoding flavohaemoglobin (Hmp), flavorubredoxin (NorV) and hybrid cluster protein (Hcp). A more quantitative analysis of the extent of NO formation was gained by measuring production of N2O, the end-product of anoxic NO-detoxification. Under nitrate-rich conditions, the nar, nap, hmp, norV and hcp genes were all induced following transition from the oxic to anoxic state, and 20% of nitrate consumed in steady-state was released as N2O when nitrite had accumulated to millimolar levels. The kinetics of nitrate consumption, nitrite accumulation and N2O production were similar to those of wild-type in nitrate-sufficient cultures of a nap mutant. In contrast, in a narG mutant, the steady-state rate of N2O production was ~30-fold lower than that of the wild-type. Under nitrate-limited conditions, nap, but not nar, was up-regulated following transition from oxic to anoxic metabolism and very little N2O production was observed. Thus a combination of nitrate-sufficiency, nitrite accumulation and an active Nar-type nitrate reductase leads to NO and thence N2O production, and this can account for up to 20% of the nitrate catabolized.
Sb2O3 anode buffer induced morphology improvement in small molecule organic solar cells
Authors: Zuo Lijian , Jiang Xiaoxia , Yang Ligong , Xu Mingsheng , Nan Yaxiong , Yan Quanxiang , Chen Hongzheng
Published: November 2011

We report that a very thin n-type Sb2O3 anode buffer layer in copper phthalocyanine (CuPc)/fullerene (C60) organic solar cells (OSCs) increases the power conversion efficiency by a factor of ∼34%. The enhancement is mostly attributed to the preferred orientation of CuPc layer and the increased contact area of CuPc/C60 interface, induced by the Sb2O3 layer rather than commonly regarded energy level alignment achieved by other metal oxides such as MoO3. Our study provides an insight to understand effect of the metal oxide buffer layers on the morphological influence in organic solar cells.
Generation mechanism of dislocations and their clusters in multicrystalline silicon during two-dimensional growth
Authors: Kutsukake Kentaro , Abe Takuro , Usami Noritaka , Fujiwara Kozo , Yonenaga Ichiro , Morishita Kohei , Nakajima Kazuo
Published: November 2011

The generation mechanism of dislocations and their clusters during the two-dimensional growth of multicrystalline Si was studied by in situ observation of a growing interface and subsequent analysis of dislocations. Dislocations were frequently generated at impingement points of the growth of crystal grains where Si melt was enclosed by crystal grains when it solidified. The generation of dislocations was accompanied by the formation of a new twin boundary. On the other hand, no dislocations were observed at impingement points of the growth of crystal grains where Si melt was open when it solidified. We herein present a scheme for dislocation generation with the formation of a new twin boundary on the basis of the results of our former study on dislocation generation in the unidirectional growth of multicrystalline Si ingots.
Non-equilibrium phonon generation and detection in microstructure devices
Authors: Hertzberg J. B. , Otelaja O. O. , Yoshida N. J. , Robinson R. D.
Published: November 2011

We demonstrate a method to excite locally a controllable, non-thermal distribution of acoustic phonon modes ranging from 0 to ∼200 GHz in a silicon microstructure, by decay of excited quasiparticle states in an attached superconducting tunnel junction (STJ). The phonons transiting the structure ballistically are detected by a second STJ, allowing comparison of direct with indirect transport pathways. This method may be applied to study how different phonon modes contribute to the thermal conductivity of nanostructures.
Dispersion, static correlation, and delocalisation errors in density functional theory: An electrostatic theorem perspective
Authors: Dwyer Austin D. , Tozer David J.
Published: November 2011

Dispersion, static correlation, and delocalisation errors in density functional theory are considered from the unconventional perspective of the force on a nucleus in a stretched diatomic molecule. The electrostatic theorem of Feynman is used to relate errors in the forces to errors in the electron density distortions, which in turn are related to erroneous terms in the Kohn-Sham equations. For H2, the exact dispersion force arises from a subtle density distortion; the static correlation error leads to an overestimated force due to an exaggerated distortion. For \documentclass[12pt]{minimal}\begin{document}${\rm H}_2^+$\end{document}H2+, the exact force arises from a delicate balance between attractive and repulsive components; the delocalisation error leads to an underestimated force due to an underestimated distortion. The net force in \documentclass[12pt]{minimal}\begin{document}${\rm H}_2^+$\end{document}H2+ can become repulsive, giving the characteristic barrier in the potential energy curve. Increasing the fraction of long-range exact orbital exchange increases the distortion, reducing delocalisation error but increasing static correlation error.
Elastic scattering and rotational excitation of nitrogen molecules by sodium atoms
Authors: Loreau Jérôme , Zhang Peng , Dalgarno Alexander
Published: November 2011

A quantal study of the rotational excitation of nitrogen molecules by sodium atoms is carried out. We present the two-dimensional potential energy surface of the NaN2 complex, with the N2 molecule treated as a rigid rotor. The interaction potential is computed using the spin unrestricted coupled-cluster method with single, double, and perturbative triple excitations (UCCSD(T)). The long-range part of the potential is constructed from the dynamic electric dipole polarizabilities of Na and N2. The total, differential, and momentum transfer cross sections for rotationally elastic and inelastic transitions are calculated using the close-coupling approach for energies between 5 cm−1 and 1500 cm−1. The collisional and momentum transfer rate coefficients are calculated for temperatures between 100 K and 300 K, corresponding to the conditions under which Na–N2 collisions occur in the mesosphere.
Structurally dictated anisotropic “designer surface plasmons”
Authors: Rance Helen J. , Hooper Ian R. , Hibbins Alastair P. , Roy Sambles J.
Published: November 2011

The concept of pseudo-plasmonic surfaces at microwave frequencies is extended to include structures with a high degree of surface anisotropy. The experimental sample is fabricated by patterning a metal with a rectangular array of rectangular holes and is found to support structurally dictated surface plasmon-like modes; the anisotropic dispersion of which results from an ellipsoid of limiting frequencies. By exploiting the anisotropy of the unit cell, the family of higher order surface waves associated with the quantization of the electromagnetic fields within the holes is also explored.
Electronic level alignment at a metal-molecule interface from a short-range hybrid functional
Authors: Biller Ariel , Tamblyn Isaac , Neaton Jeffrey B. , Kronik Leeor
Published: November 2011

Hybrid functionals often exhibit a marked improvement over semi-local functionals in the description of the electronic structure of organic materials. Because short-range hybrid functionals, notably the Heyd-Scuseria-Ernzerhof (HSE) functional, can also describe the electronic structure of metals reasonably well, it is interesting to examine to which extent they can correctly describe the electronic structure at metal-organic interfaces. Here, we address this question by comparing HSE calculations with many-body perturbation theory calculations in the GW approximation, or with experimental photoemission data, for two prototypical systems: benzene on graphite and benzene diamine on gold. For both cases, we find that while HSE yields results that are somewhat closer to experiment than those of semi-local functionals, the HSE prediction is still lacking quantitatively by ∼1 eV. We show that this quantitative failure arises because HSE does not correctly capture the fundamental gap of the organic or its renormalization by the metal. These discrepancies are traced back to missing long-range exchange and correlation components, an explanation which applies to any conventional or short-range hybrid functional.
Folding dynamics of Trp-cage in the presence of chemical interference and macromolecular crowding. I
Authors: Samiotakis Antonios , Cheung Margaret S.
Published: November 2011

Proteins fold and function in the crowded environment of the cell's interior. In the recent years it has been well established that the so-called “macromolecular crowding” effect enhances the folding stability of proteins by destabilizing their unfolded states for selected proteins. On the other hand, chemical and thermal denaturation is often used in experiments as a tool to destabilize a protein by populating the unfolded states when probing its folding landscape and thermodynamic properties. However, little is known about the complicated effects of these synergistic perturbations acting on the kinetic properties of proteins, particularly when large structural fluctuations, such as protein folding, have been involved. In this study, we have first investigated the folding mechanism of Trp-cage dependent on urea concentration by coarse-grained molecular simulations where the impact of urea is implemented into an energy function of the side chain and/or backbone interactions derived from the all-atomistic molecular dynamics simulations with urea through a Boltzmann inversion method. In urea solution, the folding rates of a model miniprotein Trp-cage decrease and the folded state slightly swells due to a lack of contact formation between side chains at the terminal regions. In addition, the equilibrium m-values of Trp-cage from the computer simulations are in agreement with experimental measurements. We have further investigated the combined effects of urea denaturation and macromolecular crowding on Trp-cage's folding mechanism where crowding agents are modeled as hard-spheres. The enhancement of folding rates of Trp-cage is most pronounced by macromolecular crowding effect when the extended conformations of Trp-cast dominate at high urea concentration. Our study makes quantitatively testable predictions on protein folding dynamics in a complex environment involving both chemical denaturation and macromolecular crowding effects.
Debye to non-Debye scaling of the Boson peak dynamics: Critical behavior and local disorder in vitreous germania
Authors: Zanatta M. , Baldi G. , Caponi S. , Fontana A. , Petrillo C. , Rossi F. , Sacchetti F.
Published: November 2011

We report on the observation of a significant softening of the Boson peak (BP) frequency of vitreous GeO2 above the glass transition temperature. The softening reminds a critical trend, with a transition temperature intermediate between the glass transition temperature, Tg, and the melting point. The softening of the BP frequency corresponds to a transition from a region dominated by Debye scaling to a non-Debye one. Below Tg the density of vibrational states varies according to the modification of the elastic continuum medium. Above Tg the relevant softening of the BP modes can be explained by a broadening of the distribution of elastic constants between neighboring atoms, induced by the structural rearrangement. These findings are discussed together with recent experimental and theoretical results on the low frequency vibrations in glasses.
Optical detection of deep electron traps in poly(p-phenylene vinylene) light-emitting diodes
Authors: Kuik Martijn , Vandenbergh Joke , Goris Ludwig , Begemann Eline J. , Lutsen Laurence , Vanderzande Dirk J. M. , Manca Jean V. , Blom Paul W. M.
Published: November 2011

The trap-limited electron currents in poly(p-phenylene vinylene) (PPV) derivatives can be modeled using a Gaussian trap distribution that is positioned approximately 0.75 eV below the lowest unoccupied molecular orbital (LUMO) of PPV. Photothermal deflection spectroscopy measurements and internal photo-emission spectroscopy measurements confirm the claim of a Gaussian shaped trap distribution centered at 0.75 eV below the LUMO of PPV. Additionally, two PPV derivatives that differ in the number of conformational defects incorporated during synthesis exhibit identical electron trapping behavior, showing that the traps do not originate from extrinsic impurities of the synthesis or defects in the polymer chains.
Scanning electro-optic microscopy of ferroelectric domain structure with a near-field fiber probe
Authors: Tikhomirov O. , Labardi M. , Ascoli C. , Allegrini M.
Published: November 2011

Ferroelectric domain structure of barium titanate single crystals has been visualized using a fiber probe near-field microscope, combined with temporal modulation of optical signal provided by a sinusoidal electric field applied to the sample. We find that electro-optic contrast between the adjacent domains depends on the polarization of incident light not as strongly as in case of confocal microscopy. This fact is ascribed to presence of additional optical aberrations caused by the near-field arrangement confirmed by complicated approaching curve observed for the electro-optic signal. Surprising improvement in spatial resolution of the near-field electro-optic image comparing to the optical one has been observed in some cases, supporting the idea of surface-confined electro-optic modulation in qualitative agreement with the observed phenomenon.
Electronic and optical properties of potential solar absorber Cu3PSe4
Authors: Foster D. H. , Jieratum V. , Kykyneshi R. , Keszler D. A. , Schneider G.
Published: November 2011

We theoretically investigate the electronic and optical properties of semiconductor Cu3PSe4. We also report diffuse reflectance spectroscopy measurements for Cu3PSe4 and Cu3PS4, which indicate a band gap of 1.40 eV for the former. Ab initio density functional theory (DFT) calculations based on hybrid functionals agree well with this value and reveal that the band gap is direct. Calculations yield an optical absorption spectrum similar to GaAs in the visible region, with α > 5 × 104 cm−1 for λ < 630 nm. We conclude that the optical properties of Cu3PSe4 are within the desired range for a photovoltaic solar absorber material.
Ag-nanowire films coated with ZnO nanoparticles as a transparent electrode for solar cells
Authors: Morgenstern Frederik S. F. , Kabra Dinesh , Massip Sylvain , Brenner Thomas J. K. , Lyons Philip E. , Coleman Jonathan N. , Friend Richard H.
Published: November 2011

We demonstrate that solution-processible silver-nanowire films coated with zinc-oxide-nanoparticles (ZnO-NPs) can be used as transparent electrodes in organic photovoltaic devices. The ZnO-NP coating acts as electron extraction layer and as encapsulating agent, protecting the wires from oxidation and improving their mechanical stability. Scanning photocurrent microscopy showed photocurrent generation to be more efficient at the active material surrounding the wires. Ultra-violet illumination as present in the solar spectrum was found to enhance photocurrent by improving the ZnO in-layer conductivity through the photoconductive effect. Inverted polythiophene:fullerene devices using ZnO-NP coated silver-nanowires or indium-tin-oxide as transparent electrode reached power conversion efficiencies of 2.4%.
A study of thermal counterflow using particle tracking velocimetry
Authors: Chagovets T. V. , Van Sciver S. W.
Published: November 2011

The motion of solid hydrogen particles in He II thermal counterflow has been measured using the particle tracking velocimetry technique. The tracers can move with the velocity comparable to the velocity of the normal fluid. However, below some transition velocity, the particles can be trapped on individual vortex lines and towed by the vortex tangle in the direction of superfluid flow. Above this transition velocity, the Stokes drag with the normal fluid dislodges the trapped particles from vortex cores and such particles move in the same direction as the normal fluid, albeit with lower average velocity. We discuss the measurement of the transition velocity and the mechanism by which tracers may be trapped by or dislodged from quantized vortices.
Spatiotemporal persistence of spectral fluxes in two-dimensional weak turbulence
Authors: Kelley Douglas H. , Ouellette Nicholas T.
Published: November 2011

Using a recently developed filtering technique, we study the spatiotemporal properties of the scale-to-scale fluxes of energy and enstrophy in a weakly turbulent experimental quasi-two-dimensional flow. Although these spectral properties vary in time and space, we show that they persist along the Lagrangian trajectories of fluid elements for times that can be nearly as long as the correlation time of the velocity field itself. Additionally, we show that at small scales, the spectral energy flux persists longest for fluid elements in strongly hyperbolic regions of the flow, whereas at large scales it persists in strongly elliptic regions.
High-resolution spatial mapping of the temperature distribution of a Joule self-heated graphene nanoribbon
Authors: Yu Young-Jun , Han Melinda Y. , Berciaud Stéphane , Georgescu Alexandru B. , Heinz Tony F. , Brus Louis E. , Kim Kwang S. , Kim Philip
Published: November 2011

We investigate the temperature distributions of Joule self-heated graphene nanoribbons (GNRs) with a spatial resolution finer than 100 nm by scanning thermal microscopy (SThM). The SThM probe is calibrated using the Raman G mode Stokes/anti-Stokes intensity ratio as a function of electric power applied to the GNR devices. From a spatial map of the temperature distribution, heat dissipation and transport pathways are investigated. By combining SThM and scanning gate microscopy data from a defected GNR, we observe hot spot formation at well-defined, localized sites.
Dilute-nitride GaInAsN/GaAs site-controlled pyramidal quantum dots
Authors: Carron R. , Gallo P. , Dwir B. , Rudra A. , Kapon E.
Published: November 2011

GaInAsN quantum dots (QDs) were grown in inverted pyramids on a patterned (111)B GaAs surface. Incorporation of N in the active structure is attested to by a significant (∼80 meV) redshift of the photoluminescence spectrum of the QDs. Influence of the capillarity effect on the N incorporation is evidenced by comparing the redshift in the QD emission to that of its quantum wire (QWR) barriers. The significant increase in the inhomogeneous broadening of the InGaAsN QD arrays as compared to similar InGaAs QDs is explained by the large influence of a small number of N atoms and their configuration within the QD on its effective bandgap and confinement energy.
Doping of GaN1−xAsx with high As content
Authors: Levander A. X. , Novikov S. V. , Liliental-Weber Z. , dos Reis R. , Dubon O. D. , Wu J. , Foxon C. T. , Yu K. M. , Walukiewicz W.
Published: November 2011

Recent work has shown that GaN1−xAsx can be grown across the entire composition range by low temperature molecular beam epitaxy with intermediate compositions being amorphous, but control of the electrical properties through doping is critical for functionalizing this material. Here we report the bipolar doping of GaN1−xAsx with high As content to conductivities above 4 S/cm at room temperature using Mg or Te. The carrier type was confirmed by thermopower measurements. Doping requires an increase in Ga flux during growth resulting in a mixed phase material of polycrystalline GaAs:N embedded in amorphous GaN1−xAsx.
Complete energy transfer due to rare-earth phase segregation in optical fiber preform glasses
Authors: Lahoz F. , Pérez-Rodríguez C. , Halder A. , Das S. , Paul M. C. , Pal M. , Bhadra S. K. , Vasconcelos H. C.
Published: November 2011

An Yb3+ to Tm3+ energy-transfer quantum yield close to one has been found in phase-separated yttrium–alumina silicate optical fiber preform glasses. Optical absorption, luminescence, lifetime measurements, and rare-earth concentration dependence have been performed to investigate the feasibility of efficient blue upconversion fiber lasers through convenient Yb3+ sensitation. Luminescence decay measurements have demonstrated the co-existence of two phases. One of the phases is characterized by an yttrium-rich composition. Most of the RE ions partition into the yttrium-rich phase and produce the intense upconversion emission.
Microscale pH regulation by splitting water
Authors: Cheng Li-Jing , Chang Hsueh-Chia
Published: November 2011

We present a simple, flexible approach for pH regulation in micro-chambers by injecting controllable amounts of protons and hydroxide ions via field-enhanced dissociation of water molecules. Under a DC voltage bias, the polymeric bipolar membranes integrated in microfluidics devices generate and separate H+ and OH− ions without gas production or contaminant generation resulting from electron-transfer reactions. Robust local on-chip pH and pH gradients are sustained with no need of additional acidic/basic solutions that dilute analyte concentrations. The method could provide a better strategy for pH control in microfluidics.
Monte Carlo simulation on polymer translocation in crowded environment
Authors: Cao Wei-Ping , Sun Li-Zhen , Wang Chao , Luo Meng-Bo
Published: November 2011

The effect of crowded environment with static obstacles on the translocation of a three-dimensional self-avoiding polymer through a small pore is studied using dynamic Monte Carlo simulation. The translocation time τ is dependent on polymer-obstacle interaction and obstacle concentration. The influence of obstacles on the polymer translocation is explained qualitatively by the free energy landscape. There exists a special polymer-obstacle interaction at which the translocation time is roughly independent of the obstacle concentration at low obstacle concentration, and the strength of the special interaction is roughly independent of chain length N. Scaling relation τ ∼ N1.25 is observed for strong driving translocations. The diffusion property of polymer chain is also influenced by obstacles. Normal diffusion is only observed in dilute solution without obstacles or in a crowded environment with weak polymer-obstacle attraction. Otherwise, subdiffusion behavior of polymer is observed.
A displacement sensor combining cavity tuning of a laser with a piezoelectric transducer's subdivision technique for a bidirectional sampling on the rising and falling flanks
Authors: Zhao Zhengqi , Zhang Shulian , Zhang Song , Tan Yidong , Li Yan
Published: November 2011

A displacement sensor combining cavity tuning of a laser with a piezoelectric transducer's subdivision technique is presented. Because of the low gain, the measuring range of the displacement sensor based on the orthogonally polarized dual-frequency He–Ne laser at 633 nm is limited. The gain coefficient is proportional to the cube of the wavelength, so the He–Ne laser at 1.15 μm is adopted in research. A subdivision technique using a piezoelectric transducer enhances the resolution and the bidirectional sampling of the actuated voltage on its rising and falling flanks effectively amends the hysteresis and nonlinearity effect. The displacement sensor achieves the resolution of 10 nm in the range of 100 mm.
Selective pair luminescence in the 1.4-eV band of CdTe:In
Authors: Procházka J. , Hlídek P. , Franc J. , Grill R. , Belas E. , Bugár M. , Babentsov V. , James R. B.
Published: November 2011

We investigated the photoluminescence (PL) of CdTe doped with indium using above- and below-bandgap excitation at temperatures of 4.5−20 K. We recorded and measured the selectively excited PL arising from the recombination of donor-acceptor (D–A) pairs with the A-center acceptor in the spectral region of the 1.4-eV PL band for different excitation photon energies, ℏωEXC. Sharp, strong PL lines that shifted with ℏωEXC over the total contour of the D–A pair band represented the selective pair luminescence (SPL). The energy difference of ∼125 meV between the excited- and ground-state of the charged D–A pair is very close to the 6-longitudinal-optical phonon energy in CdTe. This multiplicity favors the relaxation of an excited hole to the ground state of an acceptor, and increases the probability of recombination in the D–A pair. The SPL line quenches with temperature, characteristically with energy of 6–14 meV for D–A pairs with different D-A distances. The temperature shift of the 1.4-eV band supposedly is caused by the redistribution of occupied- and empty-shallow donors neighboring the A-center.
Properties of defected one-dimensional terahertz plasmonic crystal films in a metal air-gap waveguide
Authors: Lee Sun-Goo , Su Lee Eui , Jeon Tae-In , Kee Chul-Sik
Published: November 2011

We investigated properties of localized modes of one-dimensional terahertz plasmonic crystal films with defects in a metal air-gap waveguide by terahertz time-domain spectroscopy experiments and finite-difference time-domain simulations. A defect was created by varying the width of an air slit at the center of the plasmonic crystal film. The donor (accept)-like defect modes were observed when the width of the defect air slit increases (decreases) from an initial width. The quality factor increases abruptly as the air-gap size decreases, while the defect mode frequency slightly decreases. The high quality-defect mode was examined for terahertz sensor applications.
Interface sharpening in miscible Ni/Cu multilayers studied by atom probe tomography
Authors: Balogh Zoltán , Reda Chellali Mohammed , Greiwe Gerd-Hendrik , Schmitz Guido , Erdélyi Zoltán
Published: November 2011

Interfaces of Ni/Cu multilayers were studied by atom probe tomography. To this aim, specimens with sharp or artificially smeared interfaces were prepared and investigated before and after annealing at 773 K. Owing to three-dimensional subnanometer resolution of the atom probe, local chemical analysis of layer interfaces becomes possible without interferences of grain boundaries or geometric roughness. In contrast to the classical expectation for a miscible system, but in agreement with more recent theoretical considerations, diffusion reduces the chemical width of the interfaces by up to 50%.
Contribution of surface plasmon decay to secondary electron emission from an Al surface
Authors: Werner Wolfgang S. M. , Salvat-Pujol Francesc , Smekal Werner , Khalid Rahila , Aumayr Friedrich , Störi Herbert , Ruocco Alessandro , Stefani Giovanni
Published: November 2011

Spectra of secondary electrons (SE) emitted from a polycrystalline Al surface have been measured in coincidence with 500 eV-electrons for energy losses between 10 and 155 eV. The spectra for a given energy loss are qualitatively similar, consisting of surface and volume plasmon decay and a contribution attributable to direct electron–electron scattering. The similarity of the contribution of surface and volume plasmon decay in the SE spectra proves directly that electron multiple scattering is governed by a Markov-type process. The average value of the surface plasmon decay contribution to the SE spectrum amounts to ∼25%.
Graded-size Si quantum dot ensembles for efficient light-emitting diodes
Authors: Anopchenko A. , Marconi A. , Wang M. , Pucker G. , Bellutti P. , Pavesi L.
Published: November 2011

We propose a simple way to engineer the energy band gap of an ensemble of silicon nanocrystal (Si-NC) embedded in SiO2 via thickness/composition profiling of Si-NC multilayers. By means of a complementary metal-oxide-semiconductor compatible process, light emitting diodes (LEDs) which incorporate graded energy gap Si-NC multilayers in the active region have been grown. Electrical and optical properties of these graded Si-NC LEDs demonstrate the ability of the proposed method to tailor the optoelectronic properties of Si-NC devices.
Competing influence of an in-plane electric field on the Stark shifts in a semiconductor quantum dot
Authors: Nakaoka T. , Tamura Y. , Saito T. , Miyazawa T. , Watanabe K. , Ota Y. , Iwamoto S. , Arakawa Y.
Published: November 2011

We report on the fabrication of a side-gate structure which enables a purely lateral electric field to be applied onto a self-assembled quantum dot. The lateral field produces an unconventional “M’-shaped exciton energy shift—a blueshift followed by a redshift. The unconventional energy shift is reproduced by calculation. The calculation shows that only the positively charged exciton shows the unconventional shift. The origin is attributed to the field-induced hole-concentration in the bottom-corner of the dot, which strongly enhances the repulsive direct Coulomb interaction and reduces the exciton binding energy.
Electronic structures in single self-assembled InAs quantum dashes detected by nanogap metal electrodes
Authors: Shibata K. , Seki K. , Luukko P. J. J. , Räsänen E. , Cha K. M. , Horiuchi I. , Hirakawa K.
Published: November 2011

We have investigated electronic structures in single self-assembled InAs quantum dashes (QDHs) coupled to metal nanogap electrodes. The fabricated QDH samples operate as single electron transistors, exhibiting high differential conductances as well as small charging/orbital quantization energies for large electron numbers. In the few electron regimes, the conductance and addition energies strongly depend on the number of the electrons. Calculation of electronic properties by spin-density-functional theory reveals that electron transport is affected by a drastic change in the electronic orbital shape. These transport properties are intrinsic to InAs QDH structures with a highly anisotropic wire-like shape.
Comment on “Indications of energetic consequences of decoherence at short times for scattering from open quantum systems” [AIP Advances 1, 022118 (2011)]
Authors: Mayers J. , Reiter G.
Published: November 2011

The paper by Chatzidimitriou-Dreismann, Gray and Blach in the title reports measurements on gaseous hydrogen, performed on the VESUVIO electron volt neutron spectrometer at the ISIS neutron source. It was claimed in this paper that the VESUVIO measurements show that, if the energy transfer is sufficiently large that the bond in the H2 molecule is broken, then a larger energy transfer than that predicted by conventional neutron scattering theory occurs. It was also claimed that this is the first evidence for an increase in the energies of the proton and its environment due to quantum disentanglement. It is shown here that this evidence is almost certainly a spurious consequence of errors in the data analysis of Chatzidimitriou-Dreismann et al. When the standard VESUVIO instrument programs are used to analyse the same data on gaseous hydrogen the results obtained are in very good agreement with conventional theory.