bluuebunny/crossref_metadata_2025 huggingface dataset:
Extensive epistasis for olfactory behaviour, sleep and waking activity inDrosophila melanogaster
Authors: SWARUP SHILPA , HARBISON SUSAN T. , HAHN LAUREN E. , MOROZOVA TATIANA V. , YAMAMOTO AKIHIKO , MACKAY TRUDY F. C. , ANHOLT ROBERT R. H.
Published: February 2012

Epistasis is an important feature of the genetic architecture of quantitative traits, but the dynamics of epistatic interactions in natural populations and the relationship between epistasis and pleiotropy remain poorly understood. Here, we studied the effects of epistatic modifiers that segregate in a wild-derivedDrosophila melanogasterpopulation on the mutational effects ofP-element insertions inSemaphorin-5C(Sema-5c) andCalreticulin(Crc), pleiotropic genes that affect olfactory behaviour and startle behaviour and, in the case ofCrc, sleep phenotypes. We introducedCanton-S B(CSB) third chromosomes with or without aP-element insertion at theCrcorSema-5clocus in multiple wild-derived inbred lines of theDrosophila melanogasterGenetic Reference Panel (DGRP) and assessed the effects of epistasis on the olfactory response to benzaldehyde and, forCrc, also on sleep. In each case, we found substantial epistasis and significant variation in the magnitude of epistasis. The predominant direction of epistatic effects was to suppress the mutant phenotype. These observations support a previous study on startle behaviour using the sameD. melanogasterchromosome substitution lines, which concluded that suppressing epistasis may buffer the effects of new mutations. However, epistatic effects are not correlated among the different phenotypes. Thus, suppressing epistasis appears to be a pervasive general feature of natural populations to protect against the effects of new mutations, but different epistatic interactions modulate different phenotypes affected by mutations at the same pleiotropic gene.
Abundant genetic variability inDrosophila simulansfor hybrid female lethality in interspecific crosses toDrosophila melanogaster
Authors: GÉRARD PIERRE R. , PRESGRAVES DAVEN C.
Published: February 2012

Intrinsic postzygotic reproductive isolation is thought to result from the substitution of multiple harmless or beneficial genetic differences between species that are incidentally deleterious when combined in species hybrids, causing hybrid sterility or inviability. Genetic variability for hybrid sterility or inviability phenotypes is, however, rarely assessed in natural populations. Here, we assess variation forDrosophila simulans-encoded maternal factor(s) that cause lethality inD. simulans–Drosophila melanogaster F1hybrid females. First, we survey genetic variability in the strength ofD. simulans-mediated maternal effect hybrid lethality among 37 geographic and laboratory isolates. We find abundant variability in the strength of maternal effect hybrid lethality, ranging from complete lethality to none. Second, we assess maternal effect hybrid lethality for a subset of wild isolates made heterozygous with two so-called hybrid rescue strains. The results suggest that theD. simulansmaternal effect hybrid lethality involves a diversity of alleles and/or multiple loci.
Review of the state of the art: discovering and associating semantics to tags in folksonomies
Authors: García-Silva Andrés , Corcho Oscar , Alani Harith , Gómez-Pérez Asunción
Published: February 2012

This paper describes and compares the most relevant approaches for associating tags with semantics in order to make explicit the meaning of those tags. We identify a common set of steps that are usually considered across all these approaches and frame our descriptions according to them, providing a unified view of how each approach tackles the different problems that appear during the semantic association process. Furthermore, we provide some recommendations on (a) how and when to use each of the approaches according to the characteristics of the data source, and (b) how to improve results by leveraging the strengths of the different approaches.
Independent reinforcement learners in cooperative Markov games: a survey regarding coordination problems
Authors: Matignon Laetitia , Laurent Guillaume J. , Le Fort-Piat Nadine
Published: February 2012

In the framework of fully cooperative multi-agent systems, independent (non-communicative) agents that learn by reinforcement must overcome several difficulties to manage to coordinate. This paper identifies several challenges responsible for the non-coordination of independent agents: Pareto-selection, non-stationarity, stochasticity, alter-exploration and shadowed equilibria. A selection of multi-agent domains is classified according to those challenges: matrix games, Boutilier's coordination game, predators pursuit domains and a special multi-state game. Moreover, the performance of a range of algorithms for independent reinforcement learners is evaluated empirically. Those algorithms are Q-learning variants: decentralized Q-learning, distributed Q-learning, hysteretic Q-learning, recursive frequency maximum Q-value and win-or-learn fast policy hill climbing. An overview of the learning algorithms’ strengths and weaknesses against each challenge concludes the paper and can serve as a basis for choosing the appropriate algorithm for a new domain. Furthermore, the distilled challenges may assist in the design of new learning algorithms that overcome these problems and achieve higher performance in multi-agent applications.
Auroral electrojets variations caused by recurrent high‐speed solar wind streams during the extreme solar minimum of 2008
Authors: Guo Jianpeng , Feng Xueshang , Pulkkinen T. I. , Tanskanen E. I. , Xu Wenyao , Lei Jiuhou , Emery Barbara A.
Published: February 2012

The IMAGE network magnetic measurements are used to investigate the response of the auroral electrojets to the recurrent high‐speed solar wind streams (HSSs) during the extreme solar minimum period of 2008. We first compare the global AU/AL indices with the corresponding IU/IL indices determined from the IMAGE magnetometer chain and find that the local IMAGE chain can better monitor the activity in MLT sectors 1230–2230 for IU and 2230–0630 for IL during 2008. In the optimal MLT sectors, the eastward and westward electrojets and their central latitude reveal clear 9‐day periodic variations associated with the recurrent HSSs. For the 9‐day perturbations, both the eastward and westward electrojet currents are better correlated with parallel electric field (EPAR) and electron hemispheric power (HPe) than with other forcing parameters. Interestingly, the eastward electrojet shows good correlations (r > 0.6) with EPAR and HPe only in part of its optimal MLT‐sector, roughly 1200–1800, while the westward electrojet shows good correlations (r < −0.6) with EPAR and HPe in its whole optimal MLT sector. The poor correlations between the eastward electrojet and EPAR and HPe in the MLT sector 1800–2200 might be attributed to the impact of other magnetosphere‐ionosphere coupling processes. The sensitivities of the eastward and westward electrojet currents to EPAR are close to 0.06 MA/(mV/m) and −0.12 MA/(mV/m), respectively, and the sensitivities of their central latitudes to EPAR are close to −2.83 Deg/(mV/m) and −2.14 Deg/(mV/m), respectively. The observed auroral electrojet response to the recurrent solar wind forcing provides new opportunities to study the physical processes governing the eastward and westward auroral electrojets.
Biogenic sedimentation in the equatorial Pacific: Carbon cycling and paleoproduction, 12–24 Ma
Authors: Piela Christine , Lyle Mitchell , Marcantonio Franco , Baldauf Jack , Olivarez Lyle Annette
Published: February 2012

The equatorial Pacific is an important part of the global carbon cycle and has been affected by climate change through the Cenozoic (65 Ma to present). We present a Miocene (12–24 Ma) biogenic sediment record from Deep Sea Drilling Project (DSDP) Site 574 and show that a CaCO3 minimum at 17 Ma was caused by elevated CaCO3 dissolution. When Pacific Plate motion carried Site 574 under the equator at about 16.2 Ma, there is a minor increase in biogenic deposition associated with passing under the equatorial upwelling zone. The burial rates of the primary productivity proxies biogenic silica (bio‐SiO2) and biogenic barium (bio‐Ba) increase, but biogenic CaCO3 decreases. The carbonate minimum is at ∼17 Ma coincident with the beginning of the Miocene climate optimum; the transient lasts from 18 to 15 Ma. Bio‐SiO2 and bio‐Ba are positively correlated and increase as the equator was approached. Corg is poorly preserved, and is strongly affected by changing carbonate burial. Terrestrial 232Th deposition, a proxy for aeolian dust, increases only after the Site 574 equator crossing. Since surface production of bio‐SiO2, bio‐Ba, and CaCO3 correlate in the modern equatorial Pacific, the decreased CaCO3 burial rate during the Site 574 equator crossing is driven by elevated CaCO3 dissolution, representing elevated ocean carbon storage and elevated atmospheric CO2. The length of the 17 Ma CaCO3 dissolution transient requires interaction with a ‘slow’ part of the carbon cycle, perhaps elevated mantle degassing associated with the early stages of Columbia River Basalt emplacement.
Ostracodes reveal the sea‐bed origin of tsunami deposits
Authors: Tanaka Gengo , Naruse Hajime , Yamashita Shota , Arai Kazuno
Published: February 2012

In Rikuzentakata City, Ostracode assemblages in sediment deposited by the Tohoku‐Oki earthquake and tsunami of 11 March 2011 revealed that the sediment was derived from the seafloor from at least 9 m water depth, and was transported inland more than 1 km. The tsunami wave height at this location was higher than 10 m. Four hundred fifty seven modern ostracode assemblages were used in the modern analogue technique to estimate the depth source of the tsunami deposited assemblages. The application of this method to paleo‐tsunami deposits may provide insight into past tsunami wave height and potentially earthquake slip and magnitude.
Magnetic phase competition in Dy1−xYxMnO3
Authors: Vajk O. P. , Wang Y. , Gunasekera J. , Tarwater K. , Heitmann T.
Published: February 2012

The magnetic phase diagram of Dy1−xYxMnO3 is investigated with neutron diffraction measurements for concentrations ranging from x = 0.6−1. The onset of a transition from YMnO3-like order to DyMnO3-like order of the Mn3+ moments is observed at temperatures as high as 25 K. This transition approaches from low temperatures, as in Er1−xYxMnO3, rather than from high temperatures, as in Ho1−xYxMnO3, but the Y-like phase persists over a broad compositional range, as in Ho1−xYxMnO3 and in contrast to Er1−xYxMnO3. Inelastic scattering measurements in the Y-like phase reveal quasielastic scattering at positions for scattering from the Dy-like phase. These results suggest significant complexity in the magnetic phase competition in RMnO3.
Magnetization modeling of silicon steel using a simplified domain structure model
Authors: Sudo M. , Matsuo T.
Published: February 2012

A simplified domain structure model with shape anisotropy and cubic crystalline anisotropy is applied to the analysis of the mesoscopic magnetization of silicon steel sheets. Alternating magnetization is analytically described by the transition among several magnetization states, such as the single-domain, 180∘ domain-wall-motion, and magnetization-rotation types. The magnetic field vector is calculated from a given average magnetization vector under the rotational magnetization condition. The loci of the magnetic field vector qualitatively reconstruct the rotational magnetization properties of non-oriented and grain-oriented silicon steel sheets.
Magnetic hardening of Ce2Fe14B
Authors: Herbst J. F. , Meyer M. S. , Pinkerton F. E.
Published: February 2012

We report an effort to optimize the room-temperature permanent magnet properties of Ce-Fe-B materials rapidly solidified by melt spinning. Starting alloy compositions in the ternary phase diagram were selected systematically. Ribbons were melt spun from them at a quench wheel velocity of 35 m/s, corresponding to a solidification rate high enough to yield mostly amorphous or nanocrystalline material. Heat treatment above 450 °C crystallizes Ce2Fe14B, as x-ray diffraction clearly indicates, with the concomitant development of hard magnetic properties. The anneal temperature yielding optimum remanence Br, intrinsic coercivity Hci, and energy product (BH)max was determined in each case. For the ingot composition Ce17Fe78B6, we obtain Br = 4.9 kG, Hci = 6.2 kOe, and energy product (BH)max = 4.1 MGOe in ribbons comprised principally of Ce2Fe14B. This composition differs substantially from the optimum Nd13Fe82B5 stoichiometry for melt-spun magnets based on Nd2Fe14B and can be understood from a comparison of the distinct Ce-Fe-B and Nd-Fe-B phase diagrams.
Thermoelectric properties of Zn-doped GaSb
Authors: Kim Chang-eun , Kurosaki Ken , Muta Hiroaki , Ohishi Yuji , Yamanaka Shinsuke
Published: February 2012

III-V compounds with the zinc blende structure have good power factors due to their high carrier mobility. In the present study, Zn-doped GaSb (Ga1−xZnxSb, x = 0.001, 0.002, 0.005, and 0.01) samples were fabricated and the thermoelectric (TE) properties of the samples were measured. Hall measurements were conducted to investigate the carrier transport properties and the results revealed a highest power factor of 2.02 W/m K2 for the sample with x = 0.002 at 573 K, of which the largest weighted mobility was also obtained. However, Zn-doped GaSb also exhibits high thermal conductivity (24.3 W/m K for the sample with x = 0.002 at room temperature). The maximum TE efficiency of 0.23 was obtained at 873 K for the sample with x = 0.01.
Overcoming the bandgap limitation on solar cell materials
Authors: Niv A. , Abrams Z. R. , Gharghi M. , Gladden C. , Zhang X.
Published: February 2012

The thermodynamic efficiency of a single junction solar cell is bounded by the Shockley-Queisser detailed balance limit at ∼30% [W. Shockley and H. J. Queisser, J. Appl. Phys. 32, 510 (1961)]. This maximal efficiency is considered achievable using a semiconductor within a restricted bandgap range of 1.1-1.5 eV. This work upends this assumption by demonstrating that the optimal material bandgap can be shifted to lower energies by placing selective reflectors around the solar cell. This technique opens new possibilities for lower bandgap materials to achieve the thermodynamic limit and to be effective in high efficiency solar cells.
Multi-agent system for the operation of an integrated microgrid
Authors: Logenthiran Thillainathan , Srinivasan Dipti
Published: February 2012

Operation of modern power system has become a complex problem, as its focus has shifted to implementing smart grid techniques and integrating distributed renewable energy sources. Integrated microgrid is an innovative control and management architecture at distribution network level, where several microgrids are electrically interconnected with each other. This paper presents a multi-agent system (MAS) for the operation of an integrated microgrid. A hierarchical control scheme is used for maximizing the power production output of local distributed generators, and optimizing power exchanges among the microgrids as well as power exchange between the main distribution system and the integrated microgrid. This scheme was implemented on the multi-agent system. Simulation studies carried out on the developed system demonstrate the effectiveness of the proposed multi-agent system for the operation of an integrated microgrid.
Design, fabrication and measurement of a broadband polarization-insensitive metamaterial absorber based on lumped elements
Authors: Zhi Cheng Yong , Wang Ying , Nie Yan , Zhou Gong Rong , Xiong Xuan , Wang Xian
Published: February 2012

A broadband metamaterial absorber (MA) based on lumped elements is presented, which is composed of the dielectric substrate sandwiched with metal split-coin resonators (SCR) welded with lumped elements and continuous metal film. We simulated, fabricated, and measured the lumped elements MA. Compared with the single SCR structure MA, the composite MA loaded with lumped elements has a wider absorptivity and works in a lower frequency. The experiment results show that the bandwidth of absorption of 90% is about 1.5 GHz and the full width at half maximum (FWHM) can be up to 50%, the absorptivity is also nearly unchanged for different polarizations. The further simulations of the absorptivity of composite MA with different lumped resistances and capacitances indicate that there exist optimal values for lumped resistances and capacitances, where the absorptivity is the highest and the bandwidth is the widest.
On the structure of positive maps: Finite-dimensional case
Authors: Majewski Władysław A.
Published: February 2012

A natural and intrinsic characterization of the structure of the set \documentclass[12pt]{minimal}\begin{document}$\mathfrak {C}$\end{document}C of positive unital maps is given, i.e., it is shown that \documentclass[12pt]{minimal}\begin{document}$\mathfrak {C}$\end{document}C is isometrically isomorphic to the subset \documentclass[12pt]{minimal}\begin{document}${\mathfrak D}$\end{document}D of bp-positive density matrices endowed with the geometry given by the norm α dual to the Grothendieck projective norm π, the structure of \documentclass[12pt]{minimal}\begin{document}${\mathfrak D}$\end{document}D is determined by the set of its exposed points, and finally a characterization of exposed points of \documentclass[12pt]{minimal}\begin{document}${\mathfrak D}$\end{document}D in terms of convex analysis is presented. This seems to be an answer to an old open problem, characterization of the structure of the set of positive maps, studied both in quantum information and operator algebras. Our arguments are based on the concept of exposed points and links between tensor products and mapping spaces. It should be emphasized that the concept of exposed point depends strongly on the geometry; hence, the role of the norm α is crucial.
Scaling of linear microtearing stability for a high collisionality National Spherical Torus Experiment discharge
Authors: Guttenfelder W. , Candy J. , Kaye S. M. , Nevins W. M. , Bell R. E. , Hammett G. W. , LeBlanc B. P. , Yuh H.
Published: February 2012

Linear gyrokinetic simulations are performed based on a high collisionality NSTX discharge that is part of dimensionless confinement scaling studies. In this discharge, the microtearing mode is predicted to be unstable over a significant region of the plasma (r/a = 0.5–0.8), motivating comprehensive tests to verify the nature of the mode and how it scales with physical parameters. The mode is found to be destabilized with sufficient electron temperature gradient, collisionality, and beta, consistent with previous findings and simple theoretical expectations. Consistent with early slab theories, growth rates peak at a finite ratio of electron-ion collision frequency over mode frequency, νe/i/ω ∼ 1–6. Below this peak, the mode growth rate decreases with reduced collisionality, qualitatively consistent with global confinement observations. Also, in this region, increased effective ionic charge (Zeff) is found to be destabilizing. Experimental electron beta and temperature gradients are two to three times larger than the inferred linear thresholds. Increasing magnetic shear (s) and decreasing safety factor (q) are both destabilizing for ratios around the experimental values s/q = 0.6–1.3. Both the Zeff and s/q scaling are opposite to those expected for the ETG instability offering an opportunity to experimentally distinguish the two modes. Finally, we note that the kinetic ballooning mode is found to compete with the microtearing mode at outer locations r/a ≥ 0.8.
Kinetic equilibrium for an asymmetric tangential layer
Authors: Belmont G. , Aunai N. , Smets R.
Published: February 2012

Finding kinetic (Vlasov) equilibria for tangential current layers is a long standing problem, especially in the context of reconnection studies, when the magnetic field reverses. Its solution is of pivotal interest for both theoretical and technical reasons when such layers must be used for initializing kinetic simulations. The famous Harris equilibrium is known to be limited to symmetric layers surrounded by vacuum, with constant ion and electron flow velocities, and with current variation purely dependent on density variation. It is clearly not suited for the “magnetopause-like” layers, which separate two plasmas of different densities and temperatures, and for which the localization of the current density j=nδv is due to the localization of the electron-to-ion velocity difference δv and not of the density n. We present here a practical method for constructing a Vlasov stationary solution in the asymmetric case, extending the standard theoretical methods based on the particle motion invariants. We show that, in the case investigated of a coplanar reversal of the magnetic field without electrostatic field, the distribution function must necessarily be a multi-valued function of the invariants to get asymmetric profiles for the plasma parameters together with a symmetric current profile. We show also how the concept of “accessibility” makes these multi-valued functions possible, due to the particle excursion inside the layer being limited by the Larmor radius. In the presented method, the current profile across the layer is chosen as an input, while the ion density and temperature profiles in between the two asymptotic imposed values are a result of the calculation. It is shown that, assuming the distribution is continuous along the layer normal, these profiles have always a more complex profile than the profile of the current density and extends on a larger thickness. The different components of the pressure tensor are also outputs of the calculation and some conclusions concerning the symmetries of this tensor are pointed out.
Self-propelled motion of a fluid droplet under chemical reaction
Authors: Yabunaka S. , Ohta T. , Yoshinaga N.
Published: February 2012

We study self-propelled dynamics of a droplet due to a Marangoni effect and chemical reactions in a binary fluid with a dilute third component of chemical product which affects the interfacial energy of a droplet. The equation for the migration velocity of the center of mass of a droplet is derived in the limit of an infinitesimally thin interface. We found that there is a bifurcation from a motionless state to a propagating state of droplet by changing the strength of the Marangoni effect.
Experimental evidence for excess entropy discontinuities in glass-forming solutions
Authors: Lienhard Daniel M. , Zobrist Bernhard , Zuend Andreas , Krieger Ulrich K. , Peter Thomas
Published: February 2012

Glass transition temperatures Tg are investigated in aqueous binary and multi-component solutions consisting of citric acid, calcium nitrate (Ca(NO3)2), malonic acid, raffinose, and ammonium bisulfate (NH4HSO4) using a differential scanning calorimeter. Based on measured glass transition temperatures of binary aqueous mixtures and fitted binary coefficients, the Tg of multi-component systems can be predicted using mixing rules. However, the experimentally observed Tg in multi-component solutions show considerable deviations from two theoretical approaches considered. The deviations from these predictions are explained in terms of the molar excess mixing entropy difference between the supercooled liquid and glassy state at Tg. The multi-component mixtures involve contributions to these excess mixing entropies that the mixing rules do not take into account.
First-principles study on electronic structures and magnetic properties of AlN nanosheets and nanoribbons
Authors: Zhang Chang-wen
Published: February 2012

Based on first-principles calculations, the effects of the intrinsic defects and edge states on electronic structures and magnetic properties of AlN nanosheets (NSs) and nanoribbons (NRs) are investigated. In comparison to Al-defective AlN NS, N-defective systems can be easily achieved in experiments, and show a ferromagnetic (FM) property with Curie temperatures above room temperature. For quasi one-dimensional (1D) single-layer zigzag (ZZ) and armchair (AC) AlNNRs with and without edge atoms passivated by hydrogen, the bare and H-passivated AC and ZZNRs are found to be nonmagnetic (NM) semiconductors, whereas a FM character occurs in bare ZZNRs. We also find that the bandgap in H-passivated NRs decreases with the increase of the width of NRs, while bandgap in bare ACNRs increases with increasing the ribbon width. More interesting, in the case of multilayer ZZNRs, when the number of Al-N layers are even, they show NM semiconducting characters, while the odd-layer ZZNRs exhibit magnetic behaviors. Our predicted diverse and tunable electronic and magnetic properties endow AlN nanostructures potential applications in electronics and spintronics.
Interface charge transfer in polypyrrole coated perovskite manganite magnetic nanoparticles
Authors: Pana O. , Soran M. L. , Leostean C. , Macavei S. , Gautron E. , Teodorescu C. M. , Gheorghe N. , Chauvet O.
Published: February 2012

Different hybrid structures were obtained by coating magnetic nanoparticles of perovskite type manganite at optimal doping (La0.67Sr0.33MnO3,LSMO) with different quantities of polypyrrole (PPy). The amorphous layer of polypyrrole surrounding the crystalline magnetic core was observed by high resolution transmission electron microscopy (HRTEM) and analyzed by using X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) measurements in near edge structure (XANES) techniques. By analyzing the magnetic behavior of the samples one can observe that the surface modification of magnetic nanoparticles by PPy results in an increase in the saturation magnetization of the composites. The process is ascribed to paired electrons transferred from the delocalized π states of the PPy into the outer disordered layers of the manganite. The analysis of pre-edge peak of the Mn K-edge XANES spectra in the case of PPy coated LSMO nanoparticles indicates that the charge transfer between polymer and nanoparticles is (directed) going to missing or distorted oxygen positions, hence increasing the 3d electrons’ mobility and orbital hybridization between the neighboring manganese ion. As a consequence, within the surface layers of LSMO nanoparticles, both energy bands disrupted the structure, and the double exchange process between Mn ions was reestablished determining the saturation magnetizations and pre-edge features increase, respectively.
Near-resonant two-photon absorption in luminescent CdTe quantum dots
Authors: Khatei Jayakrishna , Suchand Sandeep C. S. , Philip Reji , Koteswara Rao K. S. R.
Published: February 2012

We report the nonlinear optical absorption studies in two differently sized water-soluble cadmium telluride quantum dot (QD) samples, exhibiting first excitonic absorption peaks at 493 nm and 551 nm, respectively. An optical limiting behavior is observed for near-resonant excitation at 532 nm using nanosecond laser pulses, originating from the effective two-photon absorption (TPA) mechanism. The effective TPA coefficient (βeff) is measured to be in the range of 10−12 m/W. This is one order of magnitude higher than the TPA coefficient (β) reported for off-resonant excitation. At this excitation wavelength, the smaller QD shows a relatively weaker photoluminescence and stronger nonlinear absorption.
Sub-nanosecond switching of vortex cores using a resonant perpendicular magnetic field
Authors: Wang Ruifang , Dong Xinwei
Published: February 2012

We performed micromagnetic numerical studies on ultrafast switching of magnetic vortex cores (VCs) using a perpendicular magnetic field that oscillates at the eigenfrequency of a permalloy nanodisk. Our calculations show that a resonant magnetic field with amplitude of 30 mT stimulates strong axially symmetric magnetization oscillation and forces the vortex core to stay at the center of the nanodisk. The compression of the vortex core by spin wave leads to core reversal at 602 ps. This switching process is mediated by the propagation of a Neel wall across the sample thickness.
The optimum tilt angle for flat-plate solar collectors in Iran
Authors: Jafarkazemi Farzad , Ali Saadabadi S. , Pasdarshahri Hadi
Published: February 2012

This paper aims at determining the optimum tilt angle for south facing flat-plate solar collectors in Iran. Solar radiation on a horizontal surface was estimated by applying an empirical method and employing meteorological data from 80 selected cities. A mathematical model was used for estimating the solar radiation at different tilt angles. Daily, monthly, seasonally, bi-annually, and yearly optimum tilt angles and solar radiations were determined for 80 selected cities. Recommendations were made on the optimum tilt angle adjustment for different places in the country in order to benefit the best solar radiation available. The averaged benefits of annual solar radiation for 80 cities were 21.3% for daily, 21% for monthly, 19.6% for seasonal, 19.3% for bi-annual, and 13.3% for yearly adjustments compared with the radiation on the horizontal collector. Based on these results, adjusting tilt angles, at least twice a year, is recommended. Optimum tilt angles for cloudy sky cities with a low clearness index are lower than those for cities at the same latitude angle having a higher clearness index. In addition to latitude angle, the climate conditions are also important for determining the optimum tilt angle.
Electronic structures of silicene fluoride and hydride
Authors: Ding Yi , Wang Yanli
Published: February 2012

Silicene is the graphene-like silicon nanosheet, which has been synthesized very recently [B. Lalmi, H. Oughaddou, H. Enriquez, A. Kara, S. Vizzini, B. Ealet, and B. Aufray, Appl. Phys. Lett. 97, 223109 (2010)]. Using first-principles calculations, we systematically investigate the structures and properties of fluorinated and hydrogenated silicene, the silicon analogues of graphane. Different from the carbon-counterpart, the fluorination prefers the conformation with a zigzag-line buckling, while the hydrogenation keeps the chair conformation similar to graphane. A direct band gap is opened in the silicene fluoride, and the gap values can be continuously modulated by the strain. While for the hydride, a strain-induced indirect-to-direct band gap transition is found.
Global bioenergy potential from high-lignin agricultural residue
Authors: Mendu Venugopal , Shearin Tom , Campbell J. Elliott , Stork Jozsef , Jae Jungho , Crocker Mark , Huber George , DeBolt Seth
Published: February 2012

Almost one-quarter of the world's population has basic energy needs that are not being met. Efforts to increase renewable energy resources in developing countries where per capita energy availability is low are needed. Herein, we examine integrated dual use farming for sustained food security and agro-bioenergy development. Many nonedible crop residues are used for animal feed or reincorporated into the soil to maintain fertility. By contrast, drupe endocarp biomass represents a high-lignin feedstock that is a waste stream from food crops, such as coconut (
Cocos nucifera
) shell, which is nonedible, not of use for livestock feed, and not reintegrated into soil in an agricultural setting. Because of high-lignin content, endocarp biomass has optimal energy-to-weight returns, applicable to small-scale gasification for bioelectricity. Using spatial datasets for 12 principal drupe commodity groups that have notable endocarp byproduct, we examine both their potential energy contribution by decentralized gasification and relationship to regions of energy poverty. Globally, between 24 million and 31 million tons of drupe endocarp biomass is available per year, primarily driven by coconut production. Endocarp biomass used in small-scale decentralized gasification systems (15–40% efficiency) could contribute to the total energy requirement of several countries, the highest being Sri Lanka (8–30%) followed by Philippines (7–25%), Indonesia (4–13%), and India (1–3%). While representing a modest gain in global energy resources, mitigating energy poverty via decentralized renewable energy sources is proposed for rural communities in developing countries, where the greatest disparity between societal allowances exist.
Musical rhythm spectra from Bach to Joplin obey a 1/
f
power law
Authors: Levitin Daniel J. , Chordia Parag , Menon Vinod
Published: February 2012

Much of our enjoyment of music comes from its balance of predictability and surprise. Musical pitch fluctuations follow a 1/
f
power law that precisely achieves this balance. Musical rhythms, especially those of Western classical music, are considered highly regular and predictable, and this predictability has been hypothesized to underlie rhythm's contribution to our enjoyment of music. Are musical rhythms indeed entirely predictable and how do they vary with genre and composer? To answer this question, we analyzed the rhythm spectra of 1,788 movements from 558 compositions of Western classical music. We found that an overwhelming majority of rhythms obeyed a 1/
f
β
power law across 16 subgenres and 40 composers, with β ranging from ∼0.5–1. Notably, classical composers, whose compositions are known to exhibit nearly identical 1/
f
pitch spectra, demonstrated distinctive 1/
f
rhythm spectra: Beethoven's rhythms were among the most predictable, and Mozart's among the least. Our finding of the ubiquity of 1/
f
rhythm spectra in compositions spanning nearly four centuries demonstrates that, as with musical pitch, musical rhythms also exhibit a balance of predictability and surprise that could contribute in a fundamental way to our aesthetic experience of music. Although music compositions are intended to be performed, the fact that the notated rhythms follow a 1/
f
spectrum indicates that such structure is no mere artifact of performance or perception, but rather, exists within the written composition before the music is performed. Furthermore, composers systematically manipulate (consciously or otherwise) the predictability in 1/
f
rhythms to give their compositions unique identities.
Intact function of Lgr5 receptor-expressing intestinal stem cells in the absence of Paneth cells
Authors: Kim Tae-Hee , Escudero Silvia , Shivdasani Ramesh A.
Published: February 2012

Lifelong self-renewal of the adult intestinal epithelium requires the activity of stem cells located in mucosal crypts. Lgr5 and Bmi1 are two molecular markers of crypt-cell populations that replenish all lineages over time and hence function as stem cells. Intestinal stem cells require Wnt signaling, but the understanding of their cellular niche is incomplete. Lgr5-expressing crypt base columnar cells (CBCs) reside deep in the crypt, mingled among mature Paneth cells that are well positioned for short-range signaling. Partial lineage ablation previously had implied that Paneth cells are nonessential constituents of the stem-cell niche, but recently their absence was reported to interfere with Lgr5
+
CBCs, resurrecting an appealing idea. However, previous mouse models failed to remove Paneth cells completely or permanently; defining the intestinal stem-cell niche requires clarity with respect to the Paneth cell role. We find that Lgr5
+
cells with stem-cell activity cluster in future crypts early in life, before Paneth cells develop. We also crossed conditional
Atoh1

−
/
−

mice, which lack Paneth cells entirely, with

Lgr5
GFP

mice to visualize Lgr5
+
CBCs and to track their stem-cell function. In the sustained absence of Paneth cells, Lgr5
+
CBCs occupied the full crypt base, proliferated briskly, and generated differentiated progeny over many months. Gene expression in fluorescence-sorted Lgr5
+
CBCs reflected intact Wnt signaling despite the loss of Paneth cells. Thus, Paneth cells are dispensable for survival, proliferation, and stem-cell activity of CBCs, and direct contact with Lgr5-nonexpressing cells is not essential for CBC function.
Bacterial chemoreceptor arrays are hexagonally packed trimers of receptor dimers networked by rings of kinase and coupling proteins
Authors: Briegel Ariane , Li Xiaoxiao , Bilwes Alexandrine M. , Hughes Kelly T. , Jensen Grant J. , Crane Brian R.
Published: February 2012

Chemoreceptor arrays are supramolecular transmembrane machines of unknown structure that allow bacteria to sense their surroundings and respond by chemotaxis. We have combined X-ray crystallography of purified proteins with electron cryotomography of native arrays inside cells to reveal the arrangement of the component transmembrane receptors, histidine kinases (CheA) and CheW coupling proteins. Trimers of receptor dimers lie at the vertices of a hexagonal lattice in a “two-facing-two” configuration surrounding a ring of alternating CheA regulatory domains (P5) and CheW couplers. Whereas the CheA kinase domains (P4) project downward below the ring, the CheA dimerization domains (P3) link neighboring rings to form an extended, stable array. This highly interconnected protein architecture underlies the remarkable sensitivity and cooperative nature of transmembrane signaling in bacterial chemotaxis.
Pathogenesis and transmission of swine origin A(H3N2)v influenza viruses in ferrets
Authors: Pearce Melissa B. , Jayaraman Akila , Pappas Claudia , Belser Jessica A. , Zeng Hui , Gustin Kortney M. , Maines Taronna R. , Sun Xiangjie , Raman Rahul , Cox Nancy J. , Sasisekharan Ram , Katz Jaqueline M. , Tumpey Terrence M.
Published: February 2012

Recent isolation of a novel swine-origin influenza A H3N2 variant virus [A(H3N2)v] from humans in the United States has raised concern over the pandemic potential of these viruses. Here, we analyzed the virulence, transmissibility, and receptor-binding preference of four A(H3N2)v influenza viruses isolated from humans in 2009, 2010, and 2011. High titers of infectious virus were detected in nasal turbinates and nasal wash samples of A(H3N2)v-inoculated ferrets. All four A(H3N2)v viruses possessed the capacity to spread efficiently between cohoused ferrets, and the 2010 and 2011 A(H3N2)v isolates transmitted efficiently to naïve ferrets by respiratory droplets. A dose-dependent glycan array analysis of A(H3N2)v showed a predominant binding to α2-6–sialylated glycans, similar to human-adapted influenza A viruses. We further tested the viral replication efficiency of A(H3N2)v viruses in a relevant cell line, Calu-3, derived from human bronchial epithelium. The A(H3N2)v viruses replicated in Calu-3 cells to significantly higher titers compared with five common seasonal H3N2 influenza viruses. These findings suggest that A(H3N2)v viruses have the capacity for efficient replication and transmission in mammals and underscore the need for continued public health surveillance.
Graph fission in an evolving voter model
Authors: Durrett Richard , Gleeson James P. , Lloyd Alun L. , Mucha Peter J. , Shi Feng , Sivakoff David , Socolar Joshua E. S. , Varghese Chris
Published: February 2012

We consider a simplified model of a social network in which individuals have one of two opinions (called 0 and 1) and their opinions and the network connections coevolve. Edges are picked at random. If the two connected individuals hold different opinions then, with probability 1 - 
α
, one imitates the opinion of the other; otherwise (i.e., with probability
α
), the link between them is broken and one of them makes a new connection to an individual chosen at random (
i
) from those with the same opinion or (
ii
) from the network as a whole. The evolution of the system stops when there are no longer any discordant edges connecting individuals with different opinions. Letting
ρ
be the fraction of voters holding the minority opinion after the evolution stops, we are interested in how
ρ
depends on
α
and the initial fraction
u
of voters with opinion 1. In case (
i
), there is a critical value
α

c

which does not depend on
u
, with
ρ
 ≈ 
u
for
α
 > 
α

c

and
ρ
 ≈ 0 for
α
 < 
α

c

. In case (
ii
), the transition point
α

c

(
u
) depends on the initial density
u
. For
α
 > 
α

c

(
u
),
ρ
 ≈ 
u
, but for
α
 < 
α

c

(
u
), we have
ρ
(
α
,
u
) = 
ρ
(
α
,1/2). Using simulations and approximate calculations, we explain why these two nearly identical models have such dramatically different phase transitions.
Musicians' Working Memory for Tones, Words, and Pseudowords
Authors: Benassi-Werke Mariana E. , Queiroz Marcelo , Araújo Rúben S. , Bueno Orlando F. A. , Oliveira Maria Gabriela M.
Published: February 2012

Studies investigating factors that influence tone recognition generally use recognition tests, whereas the majority of the studies on verbal material use self-generated responses in the form of serial recall tests. In the present study we intended to investigate whether tonal and verbal materials share the same cognitive mechanisms, by presenting an experimental instrument that evaluates short-term and working memories for tones, using self-generated sung responses that may be compared to verbal tests. This paradigm was designed according to the same structure of the forward and backward digit span tests, but using digits, pseudowords, and tones as stimuli. The profile of amateur singers and professional singers in these tests was compared in forward and backward digit, pseudoword, tone, and contour spans. In addition, an absolute pitch experimental group was included, in order to observe the possible use of verbal labels in tone memorization tasks. In general, we observed that musical schooling has a slight positive influence on the recall of tones, as opposed to verbal material, which is not influenced by musical schooling. Furthermore, the ability to reproduce melodic contours (up and down patterns) is generally higher than the ability to reproduce exact tone sequences. However, backward spans were lower than forward spans for all stimuli (digits, pseudowords, tones, contour). Curiously, backward spans were disproportionately lower for tones than for verbal material—that is, the requirement to recall sequences in backward rather than forward order seems to differentially affect tonal stimuli. This difference does not vary according to musical expertise.
Association between Anesthesiologist Age and Litigation
Authors: Tessler Michael J. , Shrier Ian , Steele Russell J.
Published: February 2012

Background

: The threat of being sued is a concern for many anesthesiologists. This paper asks whether litigation brought against anesthesiologists is associated with the age of the anesthesiologist.

Methods

: Institutional research ethics approval was granted. We obtained billing data for all procedures performed by specialist anesthesiologists stratified into three age groups (less than 51, 51-64, and 65 and older) from British Columbia, Quebec, and Ontario for the 10-yr period from Jan. 1, 1993 to Dec. 31, 2002. We also obtained all litigations (including disability weighted claims) handled by the Canadian Medical Protective Association during the same time period in which the Canadian Medical Protective Association experts considered the anesthesiologist cited to be at least partially responsible for the adverse event leading to the complaint.

Results

: In univariate analysis with the less than 51 age group as the reference category, the litigation rate ratio for the 51-64 age group was 1.14 (95% CI: 0.99-1.32) and for the 65 and older age group was 1.50 (95% CI: 1.14-1.97). Our analyses using disability weighted claims showed the 51-64 group to have 1.31 (95% CI: 0.95-1.80) and 65 and older group to have 1.94 (95% CI: 1.41-2.67) relative increase in disability compared to the less than 51 age group.

Conclusions

: We found a higher frequency of litigation and a greater severity of injury in patients treated by anesthesiologists in the 65 and older group. The reasons for these findings should become an active field of research.
Exertional Rhabdomyolysis
Authors: Landau Mark E. , Kenney Kimbra , Deuster Patricia , Campbell William
Published: February 2012

In this review, the clinical and laboratory features of exertional rhabdomyolysis (ER) are discussed in detail, emphasizing the full clinical spectrum from physiological elevations of serum creatine kinase after exertion to life-threatening rhabdomyolysis with acute kidney injury and associated systemic complications. Laboratory markers used to diagnose both ER and rhabdomyolysis are very sensitive, but not very specific, and imperfectly distinguish “subclinical” or asymptomatic from severe, life-threatening illness. However, genetic factors, both recognized and yet to be discovered, likely influence this diverse clinical spectrum of disease and response to exercise. Genetic mutations causative for McArdle disease, carnitine palmitoyl transferase deficiency 2, myoadenylate deaminase deficiency, and malignant hyperthermia have all been associated with ER. Polymorphic variations in the myosin light chain kinase, α-actin 3, creatine kinase–muscle isoform, angiotensin I-converting enzyme, heat shock protein, and interleukin-6 genes have also been associated with either ER or exercise-induced serum creatine kinase elevations typical of ER. The prognosis for ER is significantly better than that for other etiologies of rhabdomyolysis, but the risk of recurrence after an initial episode is unknown. Guidelines for management are provided.
Fish and robots swimming together: attraction towards the robot demands biomimetic locomotion
Authors: Marras Stefano , Porfiri Maurizio
Published: February 2012

The integration of biomimetic robots in a fish school may enable a better understanding of collective behaviour, offering a new experimental method to test group feedback in response to behavioural modulations of its ‘engineered’ member. Here, we analyse a robotic fish and individual golden shiners (Notemigonus crysoleucas) swimming together in a water tunnel at different flow velocities. We determine the positional preference of fish with respect to the robot, and we study the flow structure using a digital particle image velocimetry system. We find that biomimetic locomotion is a determinant of fish preference as fish are more attracted towards the robot when its tail is beating rather than when it is statically immersed in the water as a ‘dummy’. At specific conditions, the fish hold station behind the robot, which may be due to the hydrodynamic advantage obtained by swimming in the robot's wake. This work makes a compelling case for the need of biomimetic locomotion in promoting robot–animal interactions and it strengthens the hypothesis that biomimetic robots can be used to study and modulate collective animal behaviour.
Drug treatment of malaria infections can reduce levels of protection transferred to offspring via maternal immunity
Authors: Staszewski Vincent , Reece Sarah E. , O'Donnell Aidan J. , Cunningham Emma J. A.
Published: February 2012

Maternally transferred immunity can have a fundamental effect on the ability of offspring to deal with infection. However, levels of antibodies in adults can vary both quantitatively and qualitatively between individuals and during the course of infection. How infection dynamics and their modification by drug treatment might affect the protection transferred to offspring remains poorly understood. Using the rodent malaria parasitePlasmodium chabaudi,we demonstrate that curing dams part way through infection prior to pregnancy can alter their immune response, with major consequences for offspring health and survival. In untreated maternal infections, maternally transferred protection suppressed parasitaemia and reduced pup mortality by 75 per cent compared with pups from naïve dams. However, when dams were treated with anti-malarial drugs, pups received fewer maternal antibodies, parasitaemia was only marginally suppressed, and mortality risk was 25 per cent higher than for pups from dams with full infections. We observed the same qualitative patterns across three different host strains and two parasite genotypes. This study reveals the role that within-host infection dynamics play in the fitness consequences of maternally transferred immunity. Furthermore, it highlights a potential trade-off between the health of mothers and offspring suggesting that anti-parasite treatment may significantly affect the outcome of infection in newborns.