bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Impermeable Boundaries on the Propagation of Rayleigh Waves in an Unsaturated Poroelastic Half-Space
Authors: Chen Y.-S. , Lo W.-C. , Leu J.-M. , Cheng Alexander H.-D.
Published: October 2011

This study presents an analytical model for describing propagation of Rayleigh waves along the impermeable surface of an unsaturated poroelastic half-space. This model is based on the existence of the three modes of dilatational waves which employ the poroelastic equations developed for a porous medium containing two immiscible viscous compressible fluids (Lo, Sposito and Majer, [13]). In a two-fluid saturated medium, the three Rayleigh waves induced by the three dilatational waves can be expressed as R1, R2, and R3 waves in descending order of phase speed magnitude. As the excitation frequency and water saturation are given, the dispersion equation of a cubic polynomial can be solved numerically to obtain the phase speeds and attenuation coefficients of the R1, R2, and R3 waves. The numerical results show the phase speed of the R1 wave is frequency independent (non-dispersive). Comparatively, the R1 wave speed is 93 ∼ 95% of the shear wave speed, and 28% to 49% of the first dilatational wave speed for selected frequencies between 50Hz & 200Hz and relative water saturation ranging from 0.01 to 0.99. However, the R2 and R3 waves are dispersive at the frequencies examined. The ratios of R2 and R3 wave phase speeds to the second and third dilatational wave speeds fall between 56% and 90%. The R1 wave attenuates the least while the R3 wave has the highest attenuation coefficient. Furthermore, the phase speed of the R1 wave under an impermeable surface approaches 1.01 ∼ 1.37 times of the R1 wave under a permeable boundary. Impermeability has significant influence on the phase speeds and attenuation coefficients of the R1 and R2 waves at high water saturation due to the existence of confined fluids.
Magnetohydrodynamic Poiseuille-Couette Flow and Heat Transfer in an Inclined Channel
Authors: Umavathi J. C. , Liu I-C. , Kumar J. Prathap
Published: October 2011

An analysis of the Poiseuille-Couette flow of two immiscible fluids between inclined parallel plates is investigated. One of the fluids is assumed to be electrically conducting while the other fluid and channel walls are assumed to be electrically insulating. The viscous and Ohmic dissipation terms are taken into account in the energy equation. The coupled nonlinear equations are solved both analytically valid for small values of the product of Prandtl number and Eckert number (= ε) and numerically valid for all ε. Solutions for large ε reveal a marked change on the flow and rate of heat transfer. The effects of various parameters such as Hartmann number, Grashof number, angle of inclination, ratios of viscosities, widths and thermal conductivities are presented and discussed in detail.
Modern mermaids: New floats image the deep Earth
Authors: Hello Yann , Ogé Anthony , Sukhovich Alexey , Nolet Guust
Published: October 2011

Scientists get a window into deep Earth structures by using a method called seismic tomography. Similar to computed tomography (CT) scans of the brain, seismic tomography uses delays in the arrival times of seismic P waves to make scans and three‐dimensional images of the variations in seismic wave speed in the Earth's interior. Patterns in the delays indicate thermal or compositional anomalies in the Earth's mantle and core, such as those caused by sinking cold oceanic lithosphere or rising hot thermal plumes. A large number of observations of such delays are available for continental regions; the number of observations for the United States is especially high due to a dense deployment of stations currently being installed temporarily and moved across a large area as part of the USArray project, a branch of the U.S. National Science Foundation's EarthScope program. In contrast, no comparable sensor density has been available in the oceans
International Year of Deltas 2013: A proposal
Authors: Foufoula‐Georgiou Efi , Syvitski James , Paola Chris , Hoanh Chu Thai , Tuong Phuc , Vörösmarty Charles , Kremer Hartwig , Brondizio Eduardo , Saito Yoshiki , Twilley Robert
Published: October 2011

Marine and lacustrine deltas around the world are economic and environmental hot spots. They occupy approximately 1% of the Earth's land area but are home to more than 500 million people—a population density more than 10 times the world average [Ericson et al., 2006]—all within 5 meters of sea level [Overeem and Syvitski, 2009]. This high density is supported by high productivity, rich biodiversity, and transport along a network of waterways. Yet deltaic systems are some of the world's most delicate and vulnerable natural systems, residing at the boundary between land and water, and are subject to upstream human control, local resource exploration, and climatic impacts.
Effect of a single Dialysis session on plasma Lp(a) levels in patients on Maintenance haemodialysis
Authors: Seshadri Reddy Varikasuvu , Suchitra MM , Reddy Prabhakar , Bitla Aparna , Kumar Siva , Srinivasa Rao PVLN
Published: October 2011

Background:

Cardiovascular disease (CVD) is a major cause of mortality in End stage renal disease (ESRD) patients on Maintenance haemodialysis (MHD). Lp (a), is a specialized form of glycoprotein-LDL-cholesterol complex and is an independent risk factor for myocardial infarction. The risk is related to its atherogenic and thrombogenic properties. The present study was taken up to evaluate changes in Lp(a) and Lipid profile in patients undergoing hemodialysis session.Methodology:Twenty seven patients with end stage renal disease who were on maintenance hemodialysis were included. Plasma samples were collected hourly during a dialysis session with polysulfone membrane using bicarbonate dialysate. Plasma cholesterol, triglycerides, and Lp(a) were estimated on Beckmann CX9 Fully Automated Analyzer using commercial kits. Statistical analysis was performed using SPSS for windows version 11.5.

Results:

Results of analysis of variance for repeated measures after correction for hemoconcentration where necessary revealed a decrease in Lp(a) (p=0.022) and triglycerides (p=0.001) levels and no change in cholesterol (p=0.48) levels.Conclusion:Maintenance dialysis program is known to produce Dyslipidemia. Study of Lp(a) in dialysis patients is important as this is an independent risk marker. However there are very few reports on changes in Lp(a) due to the dialysis session. Our findings will be discussed in comparison with other reports.
Effect Of A Dialysis Session On Plasma Branched Chain Aminio Acids In Hemodialysis Patients
Authors: Seshadri Reddy Varikasuvu , Srinivasa Rao PVLN , Bitla Aparna , Kumar Siva , Suchitra MM , Reddy Prabhakar
Published: October 2011

Protein and amino acid (AA) metabolism is abnormal in End stage renal disease (ESRD). Hemodialysis (HD) procedure is a strong catabolic stimulus. Branched chain amino acids (BCAAs) can affect other AA levels by reducing AA efflux from muscle due to inhibition of muscle protein degradation. Essential amino acids and keto acid supplements including BCAA and branched-chain keto acid (BCKA) are proposed to decrease protein intake while maintaining protein status. This study was taken up to evaluate the effect of a dialysis session on plasma BCAA’s for which fifteen patients of ESRD on Maintenance HD, thrice a week were recruited into the study. Analysis was done on samples drawn at the beginning (pre-HD) and after the end of each dialysis session (post-HD). Plasma BCAA’s were estimated by Reverse phase High performance liquid chromatography using pre column derivatization with O-pthalaldehyde-Mercaptoethanol. A significant decrease in plasma concentration of Valine and Isoleucine were observed post-HD compared to the pre-HD levels (p<0.05). After correcting the data by creatinine, the decrease in plasma concentrations of Valine and Isoleucine were still found to be statistically significant. The percentage losses after the completion of HD were –24.45, –23.19, and –6.22% respectively for valine, isoleucine, and leucine. The lower reduction in leucine could be due to its appearance from muscle catabolism during the dialysis session. In conclusion, hemodialysis itself may influence dialysate amino acid losses and may have an effect on muscle protein breakdown and this negative protein can be reversed with nutritional supplementation.
Local entropy and structure in a two-dimensional frustrated system
Authors: Robinson Matthew D. , Feldman David P. , McKay Susan R.
Published: October 2011

We calculate the local contributions to the Shannon entropy and excess entropy and use these information theoretic measures as quantitative probes of the order arising from quenched disorder in the diluted Ising antiferromagnet on a triangular lattice. When one sublattice is sufficiently diluted, the system undergoes a temperature-driven phase transition, with the other two sublattices developing magnetizations of equal magnitude and opposite sign as the system is cooled.1 The diluted sublattice has no net magnetization but exhibits spin glass ordering. The distribution of local entropies shows a dramatic broadening at low temperatures; this indicates that the system’s total entropy is not shared equally across the lattice. The entropy contributions from some regions exhibit local reentrance, although the entropy of the system decreases monotonically as expected. The average excess entropy shows a sharp peak at the critical temperature, showing that the excess entropy is sensitive to the structural changes that occur as a result of the spin glass ordering.
High temperature dielectric properties of YMnO3 ceramics
Authors: Tomczyk Monika , Maria Vilarinho Paula , Moreira Agostinho , Almeida Abílio
Published: October 2011

The temperature dependence of the dielectric properties and ac conduction of YMnO3 ceramics annealed under different atmospheres is investigated from 25 to 700 °C. The origin of the dielectric anomalies is clarified. Two dielectric peaks in the permittivity accompanied by a single anomaly in the dielectric losses characterize the dielectric response. Simultaneously, three different regions can be distinguished in the temperature dependence of ac conductivity. Oxygen vacancies with an activation energy for the conduction of 1.13 eV are suggested to be responsible for the dielectric anomaly observed at < 400 °C. For temperatures > 400 °C, the dielectric data are influenced by conductivity and no ferroelectric anomaly is obvious.
Correction factors for boundary diffusion in reaction-diffusion master equations
Authors: Leier Andre , Marquez-Lago Tatiana T.
Published: October 2011

The reaction-diffusion master equation (RDME) has been widely used to model stochastic chemical kinetics in space and time. In recent years, RDME-based trajectorial approaches have become increasingly popular. They have been shown to capture spatial detail at moderate computational costs, as compared to fully resolved particle-based methods. However, finding an appropriate choice for the discretization length scale is essential for building a reasonable RDME model. Moreover, it has been recently shown [R. Erban and S. J. Chapman, Phys. Biol. 4, 16 (2007)10.1088/1478-3975/4/1/003; R. Erban and S. J. Chapman, Phys. Biol. 6, 46001 (2009)10.1088/1478-3975/6/4/046001; D. Fange, O. G. Berg, P. Sjöberg, and J. Elf, Proc. Natl. Acad. Sci. U.S.A. 107, 46 (2010)] that the reaction rates commonly used in RDMEs have to be carefully reassessed when considering reactive boundary conditions or binary reactions, in order to avoid inaccurate – and possibly unphysical – results. In this paper, we present an alternative approach for deriving correction factors in RDME models with reactive or semi-permeable boundaries. Such a correction factor is obtained by solving a closed set of equations based on the moments at steady state, as opposed to modifying probabilities for absorption or reflection. Lastly, we briefly discuss existing correction mechanisms for bimolecular reaction rates both in the limit of fast and slow diffusion, and argue why our method could also be applied for such purpose.
Dynamic properties of water around a protein–DNA complex from molecular dynamics simulations
Authors: Sinha Sudipta Kumar , Bandyopadhyay Sanjoy
Published: October 2011

Formation of protein–DNA complex is an important step in regulation of genes in living organisms. One important issue in this problem is the role played by water in mediating the protein–DNA interactions. In this work, we have carried out atomistic molecular dynamics simulations to explore the heterogeneous dynamics of water molecules present in different regions around a complex formed between the DNA binding domain of human TRF1 protein and a telomeric DNA. It is demonstrated that such heterogeneous water motions around the complex are correlated with the relaxation time scales of hydrogen bonds formed by those water molecules with the protein and DNA. The calculations reveal the existence of a fraction of extraordinarily restricted water molecules forming a highly rigid thin layer in between the binding motifs of the protein and DNA. It is further proved that higher rigidity of water layers around the complex originates from more frequent reformations of broken water–water hydrogen bonds. Importantly, it is found that the formation of the complex affects the transverse and longitudinal degrees of freedom of surrounding water molecules in a nonuniform manner.
Micromechanical testing with microstrain resolution
Authors: Dunstan D. J. , Gallé J. U. , Ehrler B. , Schmitt N. J. , Zhu T. T. , Hou X. D. , P’ng K. M. Y. , Gannaway G. , Bushby A. J.
Published: October 2011

Simple test equipment has been developed for studying the elastic limit and plastic deformation of thin metal wires and thin foils (down to 10 μm) under torsion, tension, and bending. Using load-unload methods and gauge lengths up to 1 m, plastic strain as low as 10−6 can be measured accurately.
Anatomy of a bit: Information in a time series observation
Authors: James Ryan G. , Ellison Christopher J. , Crutchfield James P.
Published: October 2011

Appealing to several multivariate information measures—some familiar, some new here—we analyze the information embedded in discrete-valued stochastic time series. We dissect the uncertainty of a single observation to demonstrate how the measures’ asymptotic behavior sheds structural and semantic light on the generating process’s internal information dynamics. The measures scale with the length of time window, which captures both intensive (rates of growth) and subextensive components. We provide interpretations for the components, developing explicit relationships between them. We also identify the informational component shared between the past and the future that is not contained in a single observation. The existence of this component directly motivates the notion of a process’s effective (internal) states and indicates why one must build models.
Torsional vibrational structure of the propene radical cation studied by high-resolution photoelectron spectroscopy
Authors: Vasilatou K. , Merkt F.
Published: October 2011

The pulsed-field-ionization zero-kinetic-energy photoelectron spectra of the \documentclass[12pt]{minimal}\begin{document}$\widetilde{\mathrm{X}}^{+}\,^{2}\rm {A}^{\prime \prime }\leftarrow \widetilde{\rm {X}}\,^{1}$\end{document}X̃+2A″←X̃1A′ transition of \documentclass[12pt]{minimal}\begin{document}${\rm CH}_{\sf 3}$\end{document} CH 3\documentclass[12pt]{minimal}\begin{document}${\rm CHCH}_{\sf 2}$\end{document} CHCH 2 (propene), \documentclass[12pt]{minimal}\begin{document}${\rm CD}_{\sf 3}$\end{document} CD 3\documentclass[12pt]{minimal}\begin{document}${\rm CDCD}_{\sf 2}$\end{document} CDCD 2, and several partially deuterated isotopomers have been recorded in the region of their adiabatic ionization thresholds and up to 2000 cm−1 of internal energy of the cations. The vibrational structure has been assigned on the basis of the frequency shifts resulting from deuteration of selected sites of the propene molecule. Two highly anharmonic progressions have been identified and assigned to the two torsional modes of the propene cation, the methyl and methylene torsions. The positions of the torsional levels could be approximately reproduced using one-dimensional models, allowing a semi-quantitative description of the potential energy surface along each torsional coordinate. The observation of forbidden vibrational bands and the analysis of their partially resolved rotational contours reveal the importance of the vibronic coupling between the \documentclass[12pt]{minimal}\begin{document}$\widetilde{\mathrm{X}}^{+}\,^{2}\rm {A}^{\prime \prime }$\end{document}X̃+2A″ and the \documentclass[12pt]{minimal}\begin{document}$\widetilde{\mathrm{A}}^{+}\,^{2}\rm {A}^{\prime }$\end{document}Ã+2A′ states mediated by the methylene (ν20) and methyl (ν21) torsional modes.
A geometric approach to complexity
Authors: Ay Nihat , Olbrich Eckehard , Bertschinger Nils , Jost Jürgen
Published: October 2011

We develop a geometric approach to complexity based on the principle that complexity requires interactions at different scales of description. Complex systems are more than the sum of their parts of any size and not just more than the sum of their elements. Using information geometry, we therefore analyze the decomposition of a system in terms of an interaction hierarchy. In mathematical terms, we present a theory of complexity measures for finite random fields using the geometric framework of hierarchies of exponential families. Within our framework, previously proposed complexity measures find their natural place and gain a new interpretation.
Examination of Au, Cu, and Al contacts in organic field-effect transistors via displacement current measurements
Authors: Liang Yan , Chang Hsiu-Chuang , Paul Ruden P. , Daniel Frisbie C.
Published: October 2011

Displacement current measurements (DCM) on long-channel capacitors (LCCs) were used to examine carrier injection and extraction processes in organic field-effect transistors (OFETs). An LCC can be seen as an OFET with one channel contact removed and the conducting channel elongated to millimeter range. While carrier injection and extraction processes occur simultaneously in OFETs during traditional DC measurements, these two processes can be examined separately with LCCs and DCMs. In addition, the numbers of injected, extracted, and trapped carriers can be determined by integrating the displacement current with respect to time. Pentacene LCCs with Au, Cu, and Al contacts were fabricated. Surprisingly, it was found that more carriers were trapped in the Au devices than in the Cu devices even though the pentacene film and dielectric layers were essentially identical. We propose that carrier trapping in the long channel of the Au devices is indirectly caused by the deep trap states at the pentacene-dielectric interface in the contact region generated by Au penetration. In addition, ambipolar injection and transport were observed in an LCC with an Al contact and a PMMA buffer layer between pentacene and SiO2.
Nano epitaxial growth of GaAs on Si (001)
Authors: Hsu Chao-Wei , Chen Yung-Feng , Su Yan-Kuin
Published: October 2011

Nano epitaxial growth (NEG) is used to develop GaAs monolithic hetero-epitaxy onto Si (001). For the GaAs grown in a nanopatterned trench with an aspect ratio of 5, the dislocations originally generated at the GaAs/Si interface are mostly isolated by the SiO2 sidewall. Compared with the conventional-planar Si substrate, implementing the NEG technique is able to decrease the dislocation density from about 109 cm−2 to almost zero. It is also confirmed that NEG is capable of confining the dislocations within the GaAs initial epitaxial layer (<100 nm), which meets the requirement of relatively less complicated epitaxial processes.
A photonic-plasmonic structure for enhancing light absorption in thin film solar cells
Authors: Bhattacharya Joydeep , Chakravarty Nayan , Pattnaik Sambit , Dennis Slafer W. , Biswas Rana , Dalal Vikram L.
Published: October 2011

We describe a photonic-plasmonic nanostructure, for significantly enhancing the absorption of long-wavelength photons in thin-film silicon solar cells, with the promise of exceeding the classical 4n2 limit for enhancement. We compare identical solar cells deposited on the photonic-plasmonic structure, randomly textured back reflectors and silver-coated flat reflectors. The state-of-the-art back reflectors, using annealed Ag or etched ZnO, had high diffuse and total reflectance. For nano-crystalline Si absorbers with comparable thickness, the highest absorption and photo-current of 21.5 mA/cm2 was obtained for photonic-plasmonic back-reflectors. The periodic photonic plasmonic structures scatter and reradiate light more effectively than a randomly roughened surface.
Integration of perovskite oxide dielectrics into complementary metal–oxide–semiconductor capacitor structures using amorphous TaSiN as oxygen diffusion barrier
Authors: Mešić Biljana , Schroeder Herbert
Published: October 2011

The high permittivity perovskite oxides have been intensively investigated for their possible application as dielectric materials for stacked capacitors in dynamic random access memory circuits. For the integration of such oxide materials into the CMOS world, a conductive diffusion barrier is indispensable. An optimized stack p++-Si/Pt/Ta21Si57N21/Ir was developed and used as the bottom electrode for the oxide dielectric. The amorphous TaSiN film as oxygen diffusion barrier showed excellent conductive properties and a good thermal stability up to 700 °C in oxygen ambient. The additional protective iridium layer improved the surface roughness after annealing. A 100-nm-thick (Ba,Sr)TiO3 film was deposited using pulsed laser deposition at 550 °C, showing very promising properties for application; the maximum relative dielectric constant at zero field is κ ≈ 470, and the leakage current density is below 10–6 A/cm2 for fields lower then ± 200 kV/cm, corresponding to an applied voltage of ± 2 V.
Nitrogen [N]-incorporated ZnO piezoelectric thin films and their application for ultra-small film bulk acoustic wave resonator device fabrication
Authors: Lee Eunju , Zhang Ruirui , Yoon Giwan
Published: October 2011

Nitrogen [N]-incorporated ZnO films with columnar grains of a preferred c-axis orientation were deposited on p-Si (100) wafers, using an RF magnetron sputter deposition technique. For the N incorporation into the ZnO films, an N2O gas was used as a doping source and also various process conditions such as N2O gas fraction and RF power were applied. Besides, some of the ZnO films were treated with the post annealing process. And then, the micro-structural characteristics of the N-incorporated ZnO films were investigated by a scanning electron microscope, an X-ray diffractometer, and an atomic force microscope techniques. Finally, employing the N-incorporated ZnO films, the solidly mounted resonator-type film bulk acoustic wave resonator devices were fabricated and their resonance characteristics were extracted. As a result, an excellent return loss (S11) of− 63 dB was observed at∼ 0.6 GHz, better than ever reported.
Influence of the critical point on the electrocaloric response of relaxor ferroelectrics
Authors: Rožič Brigita , Kosec Marija , Uršič Hana , Holc Janez , Malič Barbara , Zhang Q. M. , Blinc Robert , Pirc Raša , Kutnjak Zdravko
Published: October 2011

The electrocaloric effect (ECE), i.e., the conversion of electric energy into heat, is of great importance for application in new generation cooling or heating devices that would be friendlier to the environment. Here, utilizing direct measurements of the ECE change of the temperature ΔT via a high resolution calorimeter, we study the ECE as a function of the magnitude of the electric-field step E in the vicinity of the critical point in several bulk relaxor ferroelectric ceramic systems. Relatively large ΔT of ∼2 to 3 K were obtained at modest fields of 90 kV/cm, even in the case of ceramic materials. The effective responsivity ΔT/E as a function of the electric field shows a characteristic peak near the critical point, which demonstrates the importance of proximity to the critical point for the enhancement of the electrocaloric effect. Experimental results are in good agreement with the theoretical calculations based on the spherical random-bond random-field model.
Equilibrium velocity distributions in parallel propagating low-frequency Alfvénic turbulence
Authors: Nariyuki Y.
Published: October 2011

The equilibrium velocity distributions in parallel propagating, circularly polarized low-frequency Alfvénic turbulence are presented. The equilibrium solutions of the monochromatic Alfvén waves are extended to those of incompressible Alfvénic turbulence with the broadband spectrum in low beta plasmas. It is shown that the “apparent temperature” due to the nonresonant ion heating is explained on the basis of the equilibrium velocity distribution. The anisotropic equilibrium velocity distribution corresponding to Alfvénic turbulence in the Chew-Goldberger-Low system is also demonstrated. It is suggested that the distribution can be the back ground structure in the asymmetric velocity distributions observed in the solar wind.
Eigenfunctions decay for magnetic pseudodifferential operators
Authors: Iftimie Viorel , Purice Radu
Published: October 2011

We prove rapid decay (even exponential decay under some stronger assumptions) of the eigenfunctions associated with discrete eigenvalues, for a class of self-adjoint operators in \documentclass[12pt]{minimal}\begin{document}$L^2(\mathbb {R}^d)$\end{document}L2(Rd) defined by “magnetic” pseudodifferential operators (studied by Iftimie et al. [Publ. Res. Inst. Math. Sci. 43, 585–623 (2007)]10.2977/prims/1201012035). This class contains the relativistic Schrödinger operator with magnetic field.
Nitrogen-doped rice grain-shaped titanium dioxide nanostructures by electrospinning: Frequency and temperature dependent conductivity
Authors: Babu Veluru Jagadeesh , Rao Rayavarapu Prasada , Nair A. Sreekumaran , Ramakrishna Seeram
Published: October 2011

Rice grain-shaped, nitrogen-doped titanium dioxide (N-TiO2) nanostructures are synthesized using sol-gel method and followed by electrospinning. The as-spun composite fibers are sintered at 500 °C for 1 h in air. SEM images of the sintered samples showed rice grain-shaped nanostructures. The nanostructures were made up of spherical nanoparticles with average diameters of ∼ 20 nm, and the average diameter decreased with increase of N doping level. The temperature and frequency dependent electrical characterization has carried on nanostructures using impedance spectroscopy in the range of 298 K to 498 K and 30 Hz to 7 MHz, respectively. The magnitude of the ac conductivity is obtained from Nyquist plots and is proved that the ac conductivity is strongly dependent on temperature. The activation energy (Ea) is obtained from Arrhenius plots, and it is lowered from 0.31 to 0.22 eV with increasing N content. Therefore, the rice-grain shaped nanostructures can be employed in the low temperature gas sensor applications.
Fragile magnetic ground state and metal-insulator transitions in CaCrO3: The first-principles calculations
Authors: Liu H. M. , Zhu C. , Ma C. Y. , Dong S. , Liu J.-M.
Published: October 2011

So far available experimental data on the magnetic ground state and transport behaviors of CaCrO3 are conflicting, suggesting that the electronic structure may be fragile against intrinsic or external perturbations. In this work we perform full-scale first principles calculations on the magnetic ground state and electronic structure of CaCrO3. It is revealed that the electronic structure and spin order are sensitive to the on-site Coulomb interaction and lattice distortion. The magnetic ground state is of the marginal stability, close to the boundary between various antiferromagnetically ordered phases. A crossing over the magnetic boundaries and associated metal-insulator transitions can be allowed by even weak lattice distortion (compressive strain) on the ab plane. The numerical results suggest that the on-site Coulomb interaction and lattice distortion represent two major ingredients of physics to determine the magnetic ground state, thus reasonably interpreting the scattered experimental data on the spin order and transport behaviors for CaCrO3.
C/CrC nanocomposite coating deposited by magnetron sputtering at high ion irradiation conditions
Authors: Zhou Z. , Rainforth W. M. , Gass M. H. , Bleloch A. , Ehiassarian A. P. , Hovsepian P. Eh.
Published: October 2011

CrC with the fcc NaCl (B1) structure is a metastable phase that can be obtained under the non-equilibrium conditions of high ion irradiation. A nano-composite coating consisting of amorphous carbon embedded in a CrC matrix was prepared via the unbalanced magnetron sputtering of graphite and Cr metal targets in Ar gas with a high ionized flux (ion-to-neutral ratio Ji/Jn = 6). The nanoscale amorphous carbon clusters self-assembled into layers alternated by CrC, giving the composite a multilayer structure. The phase, microstructure, and composition of the coating were characterized using x-ray diffraction, transmission electron microscopy, and aberration corrected scanning transmission electron microscopy coupled with electron energy loss spectroscopy. The interpretation of the true coating structure, in particular the carbide type, is discussed.
The significance of in situ conditions in the characterization of GaSb nanopatterned surfaces via ion beam sputtering
Authors: El-Atwani Osman , Allain J. P. , Cimaroli Alex , Suslova Anastassiya , Ortoleva Sami
Published: October 2011

A systematic study is conducted in order to elucidate the underlying mechanism(s) for nanopatterning with low-energy irradiation of GaSb (100) under normal incidence. Ion energies between 50 and 1000 eV of Ar+ and ion fluences of up to 1018 cm−2 were employed. Characterization of the shallow (e.g., 1 to 6 nm) amorphous phase region induced by irradiation and the sub-surface crystalline phase region is accomplished with low-energy ion scattering spectroscopy and x-ray photoelectron spectroscopy, respectively. In situ studies are conducted due to the strong chemical affinity for oxygen of GaSb. The studies conclude that at energies below 200 eV, the native oxide layer hampers nanopatterning until it becomes removed at a fluence of approximately 5 × 1016 cm−2. At this energy and threshold fluence, the surface is enriched with Ga atoms during irradiation. At energies above 200 eV, the native oxide layer is efficiently removed in the early irradiation stages, and thus the detrimental effects from the oxide on nanopatterning are negligible. In situ surface concentration quantification indicates that the surface enrichment with Sb atoms in the amorphous phase layer increases with the incident ion energy. Post-air exposure characterization reveals that the measured enrichment of the surface with gallium is due to oxygen reduction by Ga atoms segregated from both the amorphous and the crystalline phase regions as a result of air exposure.
Darwinian demons, evolutionary complexity, and information maximization
Authors: Krakauer David C.
Published: October 2011

Natural selection is shown to be an extended instance of a Maxwell’s demon device. A demonic selection principle is introduced that states that organisms cannot exceed the complexity of their selective environment. Thermodynamic constraints on error repair impose a fundamental limit to the rate that information can be transferred from the environment (via the selective demon) to the genome. Evolved mechanisms of learning and inference can overcome this limitation, but remain subject to the same fundamental constraint, such that plastic behaviors cannot exceed the complexity of reward signals. A natural measure of evolutionary complexity is provided by mutual information, and niche construction activity—the organismal contribution to the construction of selection pressures—might in principle lead to its increase, bounded by thermodynamic free energy required for error correction.
Sensitizing solid state nuclear magnetic resonance of dilute nuclei by spin-diffusion assisted polarization transfers
Authors: Lupulescu Adonis , Frydman Lucio
Published: October 2011

Recent years have witnessed efforts geared at increasing the sensitivity of NMR experiments, by relying on the suitable tailoring and exploitation of relaxation phenomena. These efforts have included the use of paramagnetic agents, enhanced 1H–1H incoherent and coherent transfers processes in 2D liquid state spectroscopy, and homonuclear 13C–13C spin diffusion effects in labeled solids. The present study examines some of the opportunities that could open when exploiting spontaneous 1H–1H spin-diffusion processes, to enhance relaxation and to improve the sensitivity of dilute nuclei in solid state NMR measurements. It is shown that polarization transfer experiments executed under sufficiently fast magic-angle-spinning conditions, enable a selective polarization of the dilute low-γ spins by their immediate neighboring protons. Repolarization of the latter can then occur during the time involved in monitoring the signal emitted by the low-γ nuclei. The basic features involved in the resulting approach, and its potential to improve the effective sensitivity of solid state NMR measurements on dilute nuclei, are analyzed. Experimental tests witness the advantages that could reside from utilizing this kind of approach over conventional cross-polarization processes. These measurements also highlight a number of limitations that will have to be overcome for transforming selective polarization transfers of this kind into analytical methods of choice.
Analytical modeling of organic solar cells and photodiodes
Authors: Altazin S. , Clerc R. , Gwoziecki R. , Pananakakis G. , Ghibaudo G. , Serbutoviez C.
Published: October 2011

An analytical and physically based expression of organic solar cell I-V characteristic under dark and illuminated conditions has been derived. This model has been found in very good agreement with both experimental data and drift-diffusion numerical simulations accounting for the coupling with Poisson equation and optical propagation.
String formation and demixing in monolayers of dipolar colloidal mixtures
Authors: Luo Liang , Klapp Sabine H. L. , Chen Xiaosong
Published: October 2011

Employing hypernetted chain (HNC) integral equations and a stability analysis we investigate the structure and phase behavior of bidisperse mixtures of dipolar hard spheres with different size ratios \documentclass[12pt]{minimal}\begin{document}$s=\sigma _{\text{S}}/\sigma _{\text{L}}$\end{document}s=σS/σL confined to a plane. The dipole moments of the particles are perfectly ordered along an in-plane direction, yielding anisotropic interactions favoring chain formation. Exploring a range of size ratios and compositions, our study predicts a complex interplay between aggregation phenomena, on the one hand, and volume phase transitions, on the other hand. In dilute, strongly asymmetric systems (s = 0.5), our HNC analysis indicates chain formation of the large particles, while the small particles act as a weakly correlated background. According to our fluctuation analysis, this aggregation behavior results in combined condensation-demixing transitions, with a trend towards pure demixing when the concentration of the large particles, \documentclass[12pt]{minimal}\begin{document}$c_{\text{L}}$\end{document}cL, becomes small. In dense systems, the most interesting results are found for intermediate size ratios, s ∼ 0.7–0.8. Here we find signatures of a concentration-driven transition from pure chains of large particles (large \documentclass[12pt]{minimal}\begin{document}$c_{\text{L}}$\end{document}cL) to mixed chains with alternating order of large and small particles (small \documentclass[12pt]{minimal}\begin{document}$c_{\text{L}}$\end{document}cL). The two regimes are separated by a characteristic “jump” in the HNC non-solution line.
A discrete interaction model/quantum mechanical method to describe the interaction of metal nanoparticles and molecular absorption
Authors: Morton Seth Michael , Jensen Lasse
Published: October 2011

A frequency-dependent quantum mechanics/molecular mechanics method for the calculation of response properties of molecules adsorbed on metal nanoparticles is presented. This discrete interaction model/quantum mechanics (DIM/QM) method represents the nanoparticle atomistically, thus accounting for the local environment of the nanoparticle surface on the optical properties of the adsorbed molecule. Using the DIM/QM method, we investigate the coupling between the absorption of a silver nanoparticle and of a substituted naphthoquinone. This system is chosen since it shows strong coupling due to a molecular absorption peak that overlaps with the plasmon excitation in the metal nanoparticle. We show that there is a strong dependence not only on the distance of the molecule from the metal nanoparticle but also on its orientation relative to the nanoparticle. We find that when the transition dipole moment of an excitation is oriented towards the nanoparticle there is a significant increase in the molecular absorption as a result of coupling to the metal nanoparticle. In contrast, we find that the molecular absorption is decreased when the transition dipole moment is oriented parallel to the metal nanoparticle. The coupling between the molecule and the metal nanoparticle is found to be surprisingly long range and important on a length scale comparable to the size of the metal nanoparticle. A simple analytical model that describes the molecule and the metal nanoparticle as two interacting point objects is found to be in excellent agreement with the full DIM/QM calculations over the entire range studied. The results presented here are important for understanding plasmon–exciton hybridization, plasmon enhanced photochemistry, and single-molecule surface-enhanced Raman scattering.
Morphology effects on charge generation and recombination dynamics at ZnPc:C60 bulk hetero-junctions using time-resolved terahertz spectroscopy
Authors: Bartelt Andreas F. , Strothkämper Christian , Schindler Wolfram , Fostiropoulos Konstantinos , Eichberger Rainer
Published: October 2011

The influence of growth temperature induced phase segregation and crystallinity in ZnPc:C60 blend films on the charge generation and recombination dynamics is investigated with optical-pump terahertz-probe spectroscopy. While an ultrafast photo-induced charge generation process is observed for all morphologies, a subsequent sub-nanosecond photoconductivity rise depends on crystallinity and phase segregation. For higher intensities, the signal is dominated by a morphology-dependent bimolecular recombination process. High local mobilities of minimal μ ∼ 0.3 cm2/Vs are found. The increase of photoconductivity with film growth temperature correlates with formerly observed device photocurrent improvements.
Vibrational resonance in excitable neuronal systems
Authors: Yu Haitao , Wang Jiang , Liu Chen , Deng Bin , Wei Xile
Published: October 2011

In this paper, we investigate the effect of a high-frequency driving on the dynamical response of excitable neuronal systems to a subthreshold low-frequency signal by numerical simulation. We demonstrate the occurrence of vibrational resonance in spatially extended neuronal networks. Different network topologies from single small-world networks to modular networks of small-world subnetworks are considered. It is shown that an optimal amplitude of high-frequency driving enhances the response of neuron populations to a low-frequency signal. This effect of vibrational resonance of neuronal systems depends extensively on the network structure and parameters, such as the coupling strength between neurons, network size, and rewiring probability of single small-world networks, as well as the number of links between different subnetworks and the number of subnetworks in the modular networks. All these parameters play a key role in determining the ability of the network to enhance the outreach of the localized subthreshold low-frequency signal. Considering that two-frequency signals are ubiquity in brain dynamics, we expect the presented results could have important implications for the weak signal detection and information propagation across neuronal systems.
Effect of organic bulk heterojunction as charge generation layer on the performance of tandem organic light-emitting diodes
Authors: Chen Yonghua , Chen Jiangshan , Ma Dongge , Yan Donghang , Wang Lixiang
Published: October 2011

Organic bulk heterojunction comprising a pentacene and C60 blend can be used as the charge generation layer (CGL) in tandem organic light-emitting diodes (OLEDs) for significantly improved power efficiency. Herein, we systematically study the effects of the ratio and thickness of the CGL on the performance of tandem OLEDs. We have found that the efficiency of tandem OLEDs not only is related to the thickness of the CGL but also strongly depends on the ratio of pentacene to C60 in the CGL. Investigations regarding the capacitance-voltage and atomic force microscopy measurements clearly indicate that different thicknesses of the CGL lead to different behaviors of the charge distributions, and different ratios of pentacene to C60 in the CGL result in different probabilities of charge transfer from pentacene to C60 and imbalanced charge transport, thereby leading to completely different device performance.
Two electric-field components measurement using a 2-port pigtailed electro-optic sensor
Authors: Gaeremynck Yann , Gaborit Gwenaël , Duvillaret Lionel , Ruaro Mickaël , Lecoche Frédéric
Published: October 2011

Based on an isotropic electro-optic crystal, a two-port pigtailed electro-optic sensor has been built. The probe allows to measure two orthogonal components of the ambient electric field. The sensor intrinsically presents a temperature-dependent free response. The two measured electric field components are orthogonal to the sensor revolution axis, leading to a transverse electro-optic probe. Magnitude and orientation of the electric field are measured simultaneously with an accuracy of 0.5 dB and 2°, respectively. The rejection of orthogonal components to the electric field vector reaches 30 dB.
A belt of magnetically trapped antiprotons girdles Earth
Authors: Schwarzschild Bertram M.
Published: October 2011

An orbiting spectrometer has revealed the greatest concentration of antimatter yet seen—and it’s only a few hundred kilometers away.
US mulls the next steps in human spaceflight
Authors: Kramer David
Published: October 2011

NASA gives its space-station transport contractors wide latitude in developing spacecraft. After a long delay, the White House unveils its plan for a heavy-lift rocket.
Communicating the science of climate change
Authors: Somerville Richard C. J. , Hassol Susan Joy
Published: October 2011

It is urgent that climate scientists improve the ways they convey their findings to a poorly informed and often indifferent public.
The echo of a dying quasar
Authors: Gay Pamela L.
Published: October 2011

In space, no one can hear you scream. But if you are a dying quasar, you can call attention to your death with a brilliant light show.
Publicly Funded Prestart Support for New Firms: Who Demands it and How it Affects Their Employment Growth
Authors: Capelleras Joan-Lluis , Contín-Pilart Ignacio , Larraza-Kintana Martin
Published: October 2011

We examine prestart determinants of the demand for publicly funded external support to new ventures. We also investigate the effects of different types of such support on subsequent firm growth. Adopting resource-based and information asymmetry approaches, we argue that the entrepreneurs who ask for publicly funded prestart support are more likely to face information asymmetries with regard to resource providers, which in turn depend on their level of human and social capital. We also suggest that intangible support oriented towards knowledge generation would be the most beneficial. A series of two-stage treatment effects models applied to a representative sample of new firms in Navarra (Spain) offer considerable support to our predictions. Implications for research and policy are discussed.
The Question of Clusters in Lagging Regions: Do They Really Make the Difference? A Case Study in Romania
Authors: Constantin Daniela-Luminita , Pauna Carmen Beatrice , Dragusin Mariana , Goschin Zizi , Bodea Constanta
Published: October 2011

We propose an empirical analysis of the clustering phenomenon in the Eastern part of Romania as a relevant example to support the idea that the question of clusters in lagging regions, usually with economic structures dominated by mid-tech and low-tech industries, could become an interesting niche for cluster-devoted research in forthcoming years. The specific features in two lagging Romanian regions have been investigated by means of geographic information systems, followed by an interview-based qualitative inquiry. The findings indicate that, despite its great potential, the clustering process has not yet reached an upper-level stage; it is still in a ‘start-up’ phase with a series of ‘economic agglomerations’ that could be mostly considered of a static-cluster type. Subsequent reflections on support policies suggest that local production systems of industrial-district type are an appropriate organisational form for cluster development in the two analysed regions, with a special emphasis on ‘soft’ measures that are able to strengthen the local networks and to ensure cluster identity.
University Technology Business Incubators: Helping New Entrepreneurial Firms to Learn to Grow
Authors: Patton Dean , Marlow Susan
Published: October 2011

With this paper we explore how differing forms of entrepreneurial learning are facilitated within the context of business incubation. To support new technology venturing, university business incubators offer their tenants professional support and advice plus exposure to entrepreneurial networks with the objective of assisting them to address associated liabilities of newness. Accordingly, new venture founders are offered access to a range of resources to assist them in learning how to commercialize technological ideas. Entrepreneurial learning can be deemed explorative or exploitative; we explore how business incubation assists entrepreneurs to leverage these differing learning approaches to generate a secure resource base within the firm. From case-study evidence we suggest business incubation is effective in aligning a balance of learning approaches which support future growth prospects and add competitive advantage to young, fragile firms. We conclude by suggesting that incubator managers are critical actors in facilitating appropriate learning environments for new technology entrepreneurs.