bluuebunny/crossref_metadata_2025 huggingface dataset:
Type Ia Supernovae from Sub-Chandrasekhar Mass White Dwarfs
Authors: Sim Stuart A. , Röpke Friedrich K. , Kromer Markus , Fink Michael , Ruiter Ashley J. , Seitenzahl Ivo R. , Pakmor Rüdiger , Hillebrandt Wolfgang
Published: January 2013

We argue that detonations of sub-Chandrasekhar mass white dwarfs can lead to bright explosions with light curves and spectra similar to those of observed Type Ia supernovae. Given that binary systems containing accreting sub-Chandrasekhar mass white dwarfs should be common, this suggests that a non-negligible fraction of the observed Type Ia supernova rate may arise from sub-Chandrasekhar mass explosions, if they can be ignited. We discuss aspects of how such explosions might be realized in nature and both merits and challenges associated with invoking sub-Chandrasekhar mass explosion models to account for observed Type Ia supernovae.
Hydrostatic 12C Burning in CO WDs: the Simmering Phase of SNe Ia Progenitors
Authors: Förster Francisco , Lesaffre Pierre , Podsiadlowski Philipp
Published: January 2013

Among the possible progenitor scenarios considered for Type Ia supernovae, those that involve a carbon–oxygen white dwarf (CO WD) accreting stably towards the Chandrasekhar mass should undergo a phase of hydrostatic carbon burning under high densities and strong convection: the simmering or carbon–flash phase, which can extend for a few hundred years before explosion. During this phase the progenitor CO WD can burn a small fraction of its carbon hydrostatically, releasing energy and ashes that make the star convective and able to capture electrons from the degenerate plasma. In this work we present simplified pre–supernova evolution models of CO WDs growing towards the Chandrasekhar mass accreting matter stably and evolving through the simmering phase towards ignition in order to explore the effects of different initial masses and cooling times in the final chemical composition of the WD before explosion. Preliminary results show that, as expected, denser systems at the start of the simmering phase undergo stronger neutronization. The amount of neutronization is less than what is found in the one–zone models of Chamulak et al. (2008), about a third, and can vary by about a factor of two depending on the exact path to explosion.
Optical Studies of the Low Velocity Gradient Type Ia Supernovae 2009an and 2009ig
Authors: Sahu D. K. , Anupama G. C. , Anto P. , Gurugubelli U. K.
Published: January 2013

UBVRI photometry and medium resolution spectroscopy of two Type Ia supernovae, SN 2009an and SN 2009ig, are presented. Their Δm15(B) indicate these two SNe marginally deviate from “normal” Type Ia events. Spectroscopically, both SNe belong to the low velocity gradient group. The estimated mass of 56Ni ejected is almost a factor of two different for these two objects, with the estimates being ~0.4M⊙ for SN 2009an and ~0.8 M⊙ for SN 2009ig.
Late-Phase Observations of a Super-Chandrasekhar SN Ia
Authors: Yamanaka M. , Kawabata K. S. , Maeda K. , Tanaka M. , Yoshida M. , Hattori T. , Nomoto K. , Komatsu T. , Okushima T.
Published: January 2013

A super-Chandrasekhar (SC) supernova (SN) has an extremely high luminosity and a slow decline rate of the light curve in the early-phase. We present late-phase observations of the SC SN 2009dc. We find that the optical luminosity a year after maximum is much fainter than that expected from its early luminosity. We attempt to fit the analytic light curve model to the observations using Arnett's rule. The model successfully explains the light curves until 120 days. This suggests that the extremely high luminosity originates from the 56Ni decay. We suggest that the late-phase decline would be caused by dust formation. The existence of strong carbon features in early-phase spectra would support this scenario. We also find a blend of [Ca ii] and [Ni ii] in its late-phase spectrum. This indicates that the calcium is distributed in the inner layer along with nickel and iron. We conclude that the mixing may occur in the inner parts of the ejecta.
Type Ia Progenitor Hunt in Ancient Remnants
Authors: Kerzendorf Wolfgang E.
Published: January 2013

There is broad agreement that the stars which explode as Type Ia supernovae are white dwarfs. They have accreted material in a binary system until they are near the Chandrasekhar mass and detonate/deflagrate. The two main scenarios for this accretion process are merging with a companion white dwarf (double degenerate scenario), or accretion from a main-sequence to red giant donor (single degenerate scenario). The donor star survives post-explosion and would provide substantial evidence for the single degenerate scenario, if found. Our team is analyzing stars in close proximity to Galactic Type Ia remnants to find surviving donor stars. In my talk I will introduce the different progenitor systems and the expected state for a donor star today. I will outline our search using high resolution spectroscopy and will present updated results.
On the Progenitor of SNR 0509-67.5
Authors: Pagnotta Ashley , Schaefer Bradley E.
Published: January 2013

We have used three independent methods to determine an accurate and precise geometric center of SNR 0509-67.5, at RA=05:09:31.208, DEC=−67:31:17.48 (J2000). This supernova, which occurred approximately 400 years ago in the Large Magellanic Cloud, was confirmed to be a Type Ia by Rest et al. (2005), Rest et al. (2008) based on spectra of a light echo from the eruption. If this supernova had a single-degenerate progenitor system, we would see the “leftover” companion star within a certain distance of the remnant's center. Accounting for an offset due to enhanced ISM in the west-southwest quadrant of the remnant, we find the eruption position to be at RA=05:09:30.976, DEC=−67:31:17.90; the error circle which should contain any possible ex-companion star has a radius of 1.60″ for 99.73% (3-sigma) containment. This accounts for the proper motion of the stars, the possibility of kicks from the supernova, and asymmetries in the explosion and remnant expansion. We find no possible ex-companion stars within this ellipse, to a limiting magnitude of V=26.9: there are no red giants, which precludes symbiotic progenitors, no subgiants, which when combined with the lack of red giants precludes recurrent nova progenitors, and no main sequence stars with mass greater than 1.16 solar masses (V brighter than 22.7 mag), which precludes persistent supersoft X-ray source progenitors. Indeed, all published SD models are eliminated, so we conclude that this particular Type Ia supernova had a double-degenerate progenitor.
Binary Paths to Type Ia Supernovae Explosions: the Highlights
Authors: Ferrario Lilia
Published: January 2013

This symposium was focused on the hunt for the progenitors of Type Ia supernovae (SNe Ia). Is there a main channel for the production of SNe Ia? If so, are these elusive progenitors single degenerate or double degenerate systems? Although most participants seemed to favor the single degenerate channel, there was no general agreement on the type of binary system at play. An observational puzzle that was highlighted was the apparent paucity of supersoft sources in our Galaxy and also in external galaxies. The single degenerate channel (and as it was pointed out, quite possibly also the double degenerate channel) requires the binary system to pass through a phase of steady nuclear burning. However, the observed number of supersoft sources falls short by a factor of up to 100 in explaining the estimated birth rates of SNe Ia. Thus, are these supersoft sources somehow hidden away and radiating at different wavelengths, or are we missing some important pieces of this puzzle that may lead to the elimination of a certain class of progenitor? Another unanswered question concerns the dependence of SNe Ia luminosities on the age of their host galaxy. Several hypotheses were put forward, but none was singled out as the most likely explanation.

It is fair to say that at the end of the symposium the definitive answer to the vexed progenitor question remained well and truly wide open.
Remarkable drag reduction in non-affine viscoelastic turbulent flows
Authors: Horiuti Kiyosi , Matsumoto Kazuma , Fujiwara Kosuke
Published: January 2013

We carry out a direct numerical simulation (DNS) study which aims to reveal the mechanism of turbulence drag reduction (DR) in polymer diluted flows. The polymer chains are modeled as elastic dumbbells. This paper focuses on elucidation of effect of introduction of non-affinity to describe the motions of the dumbbells on DR. We consider the cases in which the motions do not precisely correspond to macroscopically-imposed deformation. The Johnson-Segalman (JS) model is adopted to express the polymer stress. Assessment is done in forced homogeneous isotropic turbulence and pipe flow. In both flows, DR exhibits non-monotonous dependence on the strength of non-affinity. DR is maximal when non-affinity is either minimum (slip parameter α = 0.0) or maximum (α = 1.0) and almost no DR is obtained when α = 0.5. Remarkable enhancement of DR is achieved when α = 1.0 in both flows. In pipe flow, the mean velocity profile surpasses the Virk's maximum DR limit and nearly complete relaminarization occurs. This marked DR is not established when α ≠ 1.0. Mechanism of DR applied commonly to both flows is identified. A method to evaluate the normal-stress difference (NSD) and elongation viscosity is proposed using new eigenvector basis which span the isosurface of vortex tube and sheet. It is shown that the first NSD is predominantly positive, while the second NSD is negative along the sheets and tubes in both α = 0.0 and 1.0, implying that the polymer molecules exhibit alignment in a preferential direction in both cases. Mechanism in α = 1.0, however, is distinctively different from that in α = 0.0. When α = 0.0, the connector vector of dumbbell is convected as a contravariant vector representing material line element and elasticity is incurred primarily on filament-like element or the vortex tube. As shown in previous studies, the force exerted by the polymer stress such as the torque force reduces the vortex strength by opposing the vortical motions. When α = 1.0, the connector vector is convected as a covariant vector representing material surface element, and directs outward perpendicularly on the vortex sheet and exert an extra tension on the sheet. Creation of tubes due to rolling-up of the sheet is attenuated by this tensile force and energy cascade is annihilated. In high-DR cases, the elongation viscosity increases and stretching of the sheet and tube is hindered. Consistency of the results obtained in the DNS data with those predicted using an explicit expression of the polymer stress in the JS model is shown. Analogy of DR in α = 1.0 with DR occurring in the fluid diluted with high-concentration cationic surfactant and the fibers is presented. Limitation of the JS model in the intermediate range of 0.0 < α < 1.0 is discussed.
Hydrodynamic interaction of oblique sheets in tandem arrangement
Authors: Yin Bo , Luo Haoxiang
Published: January 2013

Vortex-induced vibration of thin structures attached with piezoelectric materials has recently been explored for its potential application in energy harvesting from a flow. In this work, we numerically simulate the hydrodynamic interaction of two elastic sheets in tandem arrangement, and we study the mechanism of system resonance, at which both sheets are excited and experience greatly increased oscillations as compared to the single sheet with identical properties. The sheets are mounted obliquely to the flow to facilitate vortex shedding. The separation distance between the sheets is systematically varied, and the resonance is found within a range that depends on the mass ratio of the sheets. In contrast with two elastically mounted cylinders oscillating in the transverse direction and experiencing a similar group behavior, the resonance occurs in the present study even when the free stream does not directly impinge on the rear sheet. Further study shows that the resonance is caused by the vortex-vortex and vortex-sheet interactions that adjust the oscillation frequency and modify the magnitude/phase-shift of the hydrodynamic force on the sheets. Implication of the study on multiple sheets in tandem arrangement is also discussed.
Molecular organization in organic semiconductor thin films observed in real time
Authors: Evans D. A. , Roberts O. R. , Vearey-Roberts A. R. , Williams G. T. , Brieva A. C. , Langstaff D. P.
Published: January 2013

Post-deposition molecular rearrangement in thin organic films is revealed by in situ real-time photoelectron spectroscopy during organic molecular beam deposition. Agreement between real time spectroscopy and Monte Carlo modeling confirms the role of nearest-neighbor molecular attraction in driving a time-dependent morphology for oriented films of tin phthalocyanine (SnPc) on a range of substrates. The time-dependent molecular self-organization occurs over timescales comparable to the growth rates and is therefore an important factor in the degradation of thin films of organic semiconductors typically considered for the fabrication of multilayer semiconductor devices.
New proofs for the two Barnes lemmas and an additional lemma
Authors: Jantzen Bernd
Published: January 2013

Mellin–Barnes (MB) representations have become a widely used tool for the evaluation of Feynman loop integrals appearing in perturbative calculations of quantum field theory. Some of the MB integrals may be solved analytically in closed form with the help of the two Barnes lemmas which have been known in mathematics already for one century. The original proofs of these lemmas solve the integrals by taking infinite series of residues and summing these up via hypergeometric functions. This paper presents new, elegant proofs for the Barnes lemmas which only rely on the well-known basic identity of MB representations, avoiding any series summations. They are particularly useful for presenting and proving the Barnes lemmas to students of quantum field theory without requiring knowledge on hypergeometric functions. The paper also introduces and proves an additional lemma for a MB integral ∫dz involving a phase factor exp (±iπz).
Localized Si enrichment in coherent self-assembled Ge islands grown by molecular beam epitaxy on (001)Si single crystal
Authors: Valvo M. , Bongiorno C. , Giannazzo F. , Terrasi A.
Published: January 2013

Transmission electron microscopy (TEM), atomic force microscopy, and Rutherford backscattering spectrometry (RBS) have been used to investigate the morphology, structure, and composition of self-assembled Ge islands grown on Si (001) substrates by molecular beam epitaxy (MBE) at different temperatures. Increasing the temperature from 550 °C to 700 °C causes progressive size and shape uniformity, accompanied by enhanced Si-Ge intermixing within the islands and their wetting layer. Elemental maps obtained by energy filtered-TEM (EF-TEM) clearly show pronounced Si concentration not only in correspondence of island base perimeters, but also along their curved surface boundaries. This phenomenon is strengthened by an increase of the growth temperature, being practically negligible at 550 °C, while very remarkable already at 650 °C. The resulting island shape is affected, since this localized Si enrichment not only provides strain relief near their highly stressed base perimeters but it also influences the cluster surface energy by effective alloying, so as to form Si-enriched SiGe interfaces. Further increase to 700 °C causes a shape transition where more homogenous Si-Ge concentration profiles are observed. The crucial role played by local “flattened” alloyed clusters, similar to truncated pyramids with larger bases and enhanced Si enrichment at coherently stressed interfaces, has been further clarified by EF-TEM analysis of a multi-layered Ge/Si structure containing stacked Ge islands grown at 650 °C. Sharp accumulation of Si has been here observed not only in proximity of the uncapped island surface in the topmost layer but also at the buried Ge/Si interfaces and even in the core of such capped Ge islands.
Nanoparticle agglomeration in an evaporating levitated droplet for different acoustic amplitudes
Authors: Tijerino Erick , Basu Saptarshi , Kumar Ranganathan
Published: January 2013

Radiatively heated levitated functional droplets with nanosilica suspensions exhibit three distinct stages namely pure evaporation, agglomeration, and finally structure formation. The temporal history of the droplet surface temperature shows two inflection points. One inflection point corresponds to a local maximum and demarcates the end of transient heating of the droplet and domination of vaporization. The second inflection point is a local minimum and indicates slowing down of the evaporation rate due to surface accumulation of nanoparticles. Morphology and final precipitation structures of levitated droplets are due to competing mechanisms of particle agglomeration, evaporation, and shape deformation. In this work, we provide a detailed analysis for each process and propose two important timescales for evaporation and agglomeration that determine the final diameter of the structure formed. It is seen that both agglomeration and evaporation timescales are similar functions of acoustic amplitude (sound pressure level), droplet size, viscosity, and density. However, we show that while the agglomeration timescale decreases with initial particle concentration, the evaporation timescale shows the opposite trend. The final normalized diameter can be shown to be dependent solely on the ratio of agglomeration to evaporation timescales for all concentrations and acoustic amplitudes. The structures also exhibit various aspect ratios (bowls, rings, spheroids) which depend on the ratio of the deformation timescale (tdef) and the agglomeration timescale (tg). For tdef<tg, a sharp peak in aspect ratio is seen at low concentrations of nanosilica which separates high aspect ratio structures like rings from the low aspect ratio structures like bowls and spheroids.
Depth-resolved magnetization reversal in nanoporous perpendicular anisotropy multilayers
Authors: Kirby B. J. , Rahman M. T. , Dumas R. K. , Davies J. E. , Lai C. H. , Liu Kai
Published: January 2013

We have used polarized neutron reflectometry to study the field-dependent magnetizations of Co/Pt mulitlayers patterned via deposition onto nanoporous alumina hosts with varying pore aspect ratio. Despite the porosity and lack of long-range order, robust spin-dependent reflectivities are observed, allowing us to distinguish the magnetization of the surface multilayer from that of material in the pores. We find that as the pores become wider and shallower, the surface Co/Pt multilayers have progressively smaller high field magnetization and exhibit softer magnetic reversal—consistent with increased magnetic disorder and a reduction of the perpendicular anisotropy near the pore rims. These results reveal complexities of magnetic order in nanoporous heterostructures, and help pave the way for depth-resolved studies of complex magnetic heterostructures grown on prepatterned substrates.
Magnetic shielding of walls from the unmagnetized ion beam in a Hall thruster
Authors: Mikellides Ioannis G. , Katz Ira , Hofer Richard R. , Goebel Dan M.
Published: January 2013

We demonstrate by numerical simulations and experiments that the unmagnetized ion beam formed in a Hall thruster can be controlled by an applied magnetic field in a manner that reduces by 2–3 orders of magnitude deleterious ion bombardment of the containing walls. The suppression of wall erosion in Hall thrusters to such low levels has remained elusive for decades.
Static solitons, Lorentz invariance, and a new perspective on the integrability of the sine Gordon equation in (1+2) dimensions
Authors: Zarmi Yair
Published: January 2013

Contrary to the common understanding, the sine-Gordon equation in (1+2) dimensions does have N-soliton solutions for any N. The Hirota algorithm allows for the construction of static N-soliton solutions (i.e., solutions that do not depend on time) of that equation for any N. Lorentz transforming the static solutions yields N-soliton solutions in any moving frame. They are scalar functions under Lorentz transformations. In an N-soliton solution in a moving frame, (N-2) of the (1+2)-dimensional momentum vectors of the solitons are linear combinations of the two remaining vectors.
Pressure-induced series of phase transitions in sodium azide
Authors: Zhu Hongyang , Zhang Fuxiang , Ji Cheng , Hou Dongbin , Wu Jianzhe , Hannon Trevor , Ma Yangzhang
Published: January 2013

The phase analysis of sodium azide (NaN3) has been investigated by in situ synchrotron X-ray diffraction measurements in a diamond anvil cell up to 52.0 GPa at room temperature. Three pressure-induced phase transitions were observed. The phase transition pressures were determined to be 0.3, 17.3, and 28.7 GPa verified by three different pressure transmitting media. The first high pressure phase, α-NaN3 (0.3 ∼ 17.3 GPa), was identified to be monoclinic with a C2/m space group. The β-NaN3 to α-NaN3 transition is a second-order phase transition, accompanied by the shearing of the Na-layers and the tilting of the azide chains. The second high pressure phase, γ-NaN3 (18.4 ∼ 28.7 GPa), has a lower symmetry than the α-NaN3. A further phase transition of γ-NaN3 to δ-NaN3 at 28.7 GPa was observed.
Deep levels generated by thermal oxidation in p-type 4H-SiC
Authors: Kawahara Koutarou , Suda Jun , Kimoto Tsunenobu
Published: January 2013

Thermal oxidation is an effective method to reduce deep levels, especially the Z1∕2-center (EC−0.67 eV), which strongly suppresses carrier lifetimes in n-type 4H-SiC epilayers. The oxidation, however, simultaneously generates other deep levels, HK0 (EV+0.79 eV) and HK2 (EV+0.98 eV) centers, within the lower half of the bandgap of SiC, where the HK0 center is a dominant deep level with a concentration of about 1×1013 cm−3 after oxidation. By comparing deep levels observed in three sets of p-type 4H-SiC: oxidized, electron-irradiated, and C+- or Si+-implanted samples, we find that the HK0 and HK2 centers are complexes including carbon interstitials such as the di-carbon interstitial or di-carbon antisite. Other defects observed in p-type 4H-SiC after electron irradiation or after C+/Si+ implantation are also studied.
Surface plasmon enhanced photoluminescence and Raman scattering of ultra thin ZnO-Au hybrid nanoparticles
Authors: Saravanan K. , Panigrahi B. K. , Krishnan R. , Nair K. G. M.
Published: January 2013

We report substantially enhanced photoluminescence (PL) and Raman signal from ZnO nanoparticles (NPs) deposited on Si with Au NPs. The resonant excitation of surface plasmon of Au NPs is responsible for the enhanced PL intensity and Raman signal from the ZnO-Au hybrid NPs. Low temperature PL measurements exhibit 14 fold enhancements in the PL intensity of ZnO-Au sample in comparison with ZnO/Si sample. It is found that, at low temperature, the donor bound exciton (DX) has dominant contribution in the PL emission of ZnO-Au hybrid NPs. At high temperature, the free exciton (FX) has dominant contribution in PL emission of these NPs. The thermal activation energies of DX and FX are found to be 5 meV and 50 meV, respectively. The defect related visible PL emission of ZnO is completely suppressed in the ZnO-Au hybrid NPs.
Raman spectroscopic study of plasma-treated salmon DNA
Authors: Joon Lee Geon , Kwon Young-Wan , Hee Kim Yong , Ha Choi Eun
Published: January 2013

In this research, we studied the effect of plasma treatment on the optical/structural properties of the deoxyribonucleic acid (DNA) extracted from salmon sperm. DNA-cetyltrimethylammonium (CTMA) films were obtained by complexation of DNA with CTMA. Circular dichroism (CD) and Raman spectra indicated that DNA retained its double helical structure in the solid film. The Raman spectra exhibited several vibration modes corresponding to the nuclear bases and the deoxyribose-phosphate backbones of the DNA, as well as the alkylchains of CTMA. Dielectric-barrier-discharge (DBD) plasma treatment induced structural modification and damage to the DNA, as observed by changes in the ultraviolet-visible absorption, CD, and Raman spectra. The optical emission spectra of the DBD plasma confirmed that DNA modification was induced by plasma ions such as reactive oxygen species and reactive nitrogen species.
Modulational instability of a Langmuir wave in plasmas with energetic tails of superthermal electrons
Authors: Timofeev I. V.
Published: January 2013

The impact of superthermal electrons on dispersion properties of isotropic plasmas and on the modulational instability of a monochromatic Langmuir wave is studied for the case when the power-law tail of the electron distribution function extends to relativistic velocities and contains most of the plasma kinetic energy. Such an energetic tail of electrons is shown to increase the thermal correction to the Langmuir wave frequency, which is equivalent to the increase of the effective electron temperature in the fluid approach, and has almost no impact on the dispersion of ion-acoustic waves, in which the role of temperature is played by the thermal spread of low-energy core electrons. It is also found that the spectrum of modulational instability in the non-maxwellian plasma narrows significantly, as compared to the equilibrium case, without change of the maximum growth rate and the corresponding wavenumber.
Quantitative analysis of annealed scanning probe tips using energy dispersive x-ray spectroscopy
Authors: Cobley R. J. , Brown R. A. , Barnett C. J. , Maffeis T. G. G. , Penny M. W.
Published: January 2013

A quantitative method to measure the reduction in oxide species on the surface of electrochemically etched tungsten tips during direct current annealing is developed using energy dispersive x-ray spectroscopy. Oxide species are found to decrease with annealing current, with the trend repeatable over many tips and along the length of the tip apex. A linear resistivity approximation finds significant oxide sublimation occurs at 1714 K, but surface melting and tip broadening at 2215 K. This method can be applied to calibrate any similar annealing stage, and to identify the tradeoff regime between required morphological and chemical properties.
Improved accuracy thin film permeability extraction for a microstrip permeameter
Authors: Sebastian Tom , Clavijo Sergio A. , Diaz Rodolfo E.
Published: January 2013

It is shown using full-wave simulations that several of the conventional assumptions made for extracting permeability data from a microstrip permeameter are not justified. In particular, the proportionality between the measured effective permeability in the device and the true permeability of the film is not a constant. It is a function of the permeability of the film, its geometry and the dimensions of the microstrip permeameter. A model exploiting the analyticity of the function relating effective to true permeability is used to derive this proportionality function for our device and the results are confirmed using full-wave simulations. The error incurred by not using this method and employing a reference sample for calibration or by using saturation magnetization “Ms” and anisotropy field “Ha” is shown to be anywhere between 5% and 40% and possibly even more. Our measurement set up is capable of measuring films as thin as 300 nm with a relative permeability as low as 10.
High power radio frequency oscillation by spin transfer torque in a Co2MnSi layer: Experiment and macrospin simulation
Authors: Seki Takeshi , Sakuraba Yuya , Okura Ryo , Takanashi Koki
Published: January 2013

We experimentally and numerically investigated rf oscillation induced by spin transfer torque in a current-perpendicular-to-plane giant magnetoresistance (GMR) device with full-Heusler Co2MnSi (CMS) layers. High output power (Prf) of 1 nW was experimentally achieved owing to the large GMR effect resulting from the half-metallic feature of the CMS layers. However, the high power rf oscillation was observed only in the narrow dc current (Idc) region. Macrospin simulation suggested that the high spin polarization of CMS layers led to narrowing the optimum Idc region for the rf oscillation.
Origin of InGaN light-emitting diode efficiency improvements using chirped AlGaN multi-quantum barriers
Authors: Piprek Joachim , Simon Li Z. M.
Published: January 2013

We analyze efficiency droop reductions in InGaN/GaN light-emitting diodes caused by a chirped AlGaN/GaN multi-quantum barrier (MQB). Such electron barriers are expected to create an additional forbidden energy range above the natural conduction band edge, which reduces the electron leakage current. Advanced numerical device simulations reveal that energy band bending practically eliminates this MQB effect. Instead, we find that the measured efficiency improvement has its origin in enhanced hole injection, which can be more easily accomplished using a single thin AlGaN layer.
Enhanced dielectric properties of BaTiO3/poly(vinylidene fluoride) nanocomposites for energy storage applications
Authors: Yu Ke , Wang Hong , Zhou Yongcun , Bai Yuanyuan , Niu Yujuan
Published: January 2013

In this work, homogeneous ceramics-polymer nanocomposites consisting of surface treated BaTiO3 (BT) particles as fillers and poly(vinylidene fluoride) polymer as matrix have been prepared using a solution casting process. The nanocomposites exhibit enhanced dielectric permittivity and reduced loss tangent. The frequency and temperature dependencies of the dielectric permittivity and loss tangent of the nanocomposites suggest that the introduced BT phase and interface areas contribute to the improvement of the dielectric responses. Meanwhile, the X-ray diffraction patterns and Differential Scanning Calorimetry (DSC) curves indicate that the incorporation of ceramic particles contributes to the decrease of the crystallite size, the increase of the crystallinity, and the shift of the crystallization temperature of the polymer matrix. Furthermore, the dielectric displacement and energy density of the nanocomposites are significantly enhanced and an energy density of 3.54 J/cm3 was obtained under an electric field of 200 MV/m with the BT concentration of 20 vol. %. The results indicate that the introduced ceramic fillers and interface areas have positive influences on the structure of the polymer matrix and contribute to the enhancement of the dielectric responses and energy storage properties of the nanocomposites.
Optically detected magnetic resonance studies of point defects in quaternary GaNAsP epilayers grown by vapor phase epitaxy
Authors: Dagnelund D. , Stehr Jan , Yu. Egorov A. , Chen W. M. , Buyanova I. A.
Published: January 2013

Defect properties of quaternary GaNAsP/GaP epilayers grown by vapor phase epitaxy (VPE) are studied by photoluminescence and optically detected magnetic resonance techniques. Incorporation of more than 0.6% of nitrogen is found to facilitate formation of several paramagnetic defects which act as competing carrier recombination centers. One of the defects (labeled as Gai-D) is identified as a complex defect that has a Ga interstitial (Gai) atom residing inside a Ga tetrahedron as its core. A comparison of Gai-D with other Gai-related defects known in ternary GaNP and GaNAs alloys suggests that this defect configuration is specific to VPE-grown dilute nitrides.
Estimating the time since fire of long-unburnt Eucalyptus salubris (Myrtaceae) stands in the Great Western Woodlands
Authors: Gosper Carl R. , Prober Suzanne M. , Yates Colin J. , Wiehl Georg
Published: January 2013

Establishing the time since fire in infrequently burnt, yet fire-prone, communities is a significant challenge. Until this can be resolved for >50-year timeframes, our capacity to understand important ecological processes, such as the periods required for development of habitat features, will remain limited. We characterised the relationship between observable tree growth rings, plant age and plant size in Eucalyptus salubris F.Muell. in the globally significant Great Western Woodlands in south-western Australia. In the context of recent concerns regarding high woodland fire occurrence, we then used this approach to estimate the age of long-unburnt E. salubris stands, and the age-class distribution of Eucalyptus woodlands across the region. Time since fire was strongly predicted by trunk growth rings and plant size predicted growth rings with reasonable accuracy. The best model estimating growth rings contained parameters for trunk diameter, plant height and plot location, although simple models including either trunk diameter or plant height were nearly as good. Using growth ring–size relationships to date long-unburnt stands represents a significant advance over the current approach based on satellite imagery, which substantially truncates post-fire age. However, there was significant uncertainty over the best model form for estimating the time since fire of stands last burnt over 200 years ago. The management implications of predicted age-class distributions were highly dependent on both the choice of what, if any, transformation was applied to growth rings, and the theoretical age-class distribution to which the actual age-class distribution was compared.
Reductions in the number of mid-sized antral follicles are associated with markers of premature ovarian senescence in dairy cows
Authors: Modina Silvia C. , Tessaro Irene , Lodde Valentina , Franciosi Federica , Corbani Davide , Luciano Alberto M.
Published: January 2013

High-producing dairy cows are subfertile; however, the mechanisms responsible for the decreased fertility are unknown. The aim of the present study was to test the hypothesis that culled dairy cows (4–8 years old) characterised by ‘Lo’ ovaries (i.e. those with <10 mid-antral follicles) are affected by premature ovarian senescence. Cows in which both ovaries were ‘Lo’ ovaries represented 5% of the total population analysed, and exhibited reduced ovarian size (P < 0.001) and increased perifollicular stroma (P < 0.05) compared with age-matched controls (i.e. cows in which both ovaries had >10 mid-antral follicles; ‘Hi’ ovaries). The total number of follicles, including healthy and atretic primordial, primary, secondary and small antral follicles, was lower in Lo ovaries (P < 0.01). Interestingly, the primordial follicle population in Lo ovaries was lower (P < 0.05) than in the control. Finally, the follicular fluid of mid-antral follicles from Lo ovaries had reduced oestradiol and anti-Müllerian hormone levels (P < 0.05), but increased progesterone concentrations (P < 0.05). Together, these data account for the reduced fertility of cows with Lo ovaries and are in agreement with previous observations that oocytes isolated from Lo ovaries have reduced embryonic developmental competence. Cows with a specific Lo ovary condition may represent a suitable model to address the causes of low fertility in high-yielding dairy cows, as well as the condition of premature ovarian aging in single-ovulating species.
Engineering a BCR-ABL–activated caspase for the selective elimination of leukemic cells
Authors: Kurokawa Manabu , Ito Takahiro , Yang Chih-Sheng , Zhao Chen , Macintyre Andrew N. , Rizzieri David A. , Rathmell Jeffrey C. , Deininger Michael W. , Reya Tannishtha , Kornbluth Sally
Published: January 2013

Increased understanding of the precise molecular mechanisms involved in cell survival and cell death signaling pathways offers the promise of harnessing these molecules to eliminate cancer cells without damaging normal cells. Tyrosine kinase oncoproteins promote the genesis of leukemias through both increased cell proliferation and inhibition of apoptotic cell death. Although tyrosine kinase inhibitors, such as the BCR-ABL inhibitor imatinib, have demonstrated remarkable efficacy in the clinic, drug-resistant leukemias emerge in some patients because of either the acquisition of point mutations or amplification of the tyrosine kinase, resulting in a poor long-term prognosis. Here, we exploit the molecular mechanisms of caspase activation and tyrosine kinase/adaptor protein signaling to forge a unique approach for selectively killing leukemic cells through the forcible induction of apoptosis. We have engineered caspase variants that can directly be activated in response to BCR-ABL. Because we harness, rather than inhibit, the activity of leukemogenic kinases to kill transformed cells, this approach selectively eliminates leukemic cells regardless of drug-resistant mutations.
Zeros of varying Laguerre–Krall orthogonal polynomials
Authors: Castaño–García Laura , Moreno–Balcázar Juan
Published: January 2013

In this paper we introduce a sequence of varying orthogonal polynomials related to a Laguerre weight where this absolutely continuous measure is perturbed by a sequence of nonnegative masses located at the origin. The main objective is to obtain asymptotic relations between the zeros of these polynomials and the zeros of the Bessel functions of the first kind (or linear combinations of them). This is done through Mehler–Heine type formulas. With these relations we can easily compute asymptotically the zeros of these polynomials. We show some numerical experiments.
Short geodesic loops on complete Riemannian manifolds with a finite volume
Authors: Rotman Regina
Published: January 2013

In this paper we will show that on any complete noncompact Riemannian manifold with a finite volume there exist uncountably many geodesic loops of arbitrarily small length.
CRAVAT: cancer-related analysis of variants toolkit
Authors: Douville Christopher , Carter Hannah , Kim Rick , Niknafs Noushin , Diekhans Mark , Stenson Peter D. , Cooper David N. , Ryan Michael , Karchin Rachel
Published: January 2013

Summary: Advances in sequencing technology have greatly reduced the costs incurred in collecting raw sequencing data. Academic laboratories and researchers therefore now have access to very large datasets of genomic alterations but limited time and computational resources to analyse their potential biological importance. Here, we provide a web-based application, Cancer-Related Analysis of Variants Toolkit, designed with an easy-to-use interface to facilitate the high-throughput assessment and prioritization of genes and missense alterations important for cancer tumorigenesis. Cancer-Related Analysis of Variants Toolkit provides predictive scores for germline variants, somatic mutations and relative gene importance, as well as annotations from published literature and databases. Results are emailed to users as MS Excel spreadsheets and/or tab-separated text files.

Availability:  http://www.cravat.us/

Contact:  karchin@jhu.edu

Supplementary information:  Supplementary data are available at Bioinformatics online.
DSK: k-mer counting with very low memory usage
Authors: Rizk Guillaume , Lavenier Dominique , Chikhi Rayan
Published: January 2013

Summary: Counting all the k-mers (substrings of length k) in DNA/RNA sequencing reads is the preliminary step of many bioinformatics applications. However, state of the art k-mer counting methods require that a large data structure resides in memory. Such structure typically grows with the number of distinct k-mers to count. We present a new streaming algorithm for k-mer counting, called DSK (disk streaming of k-mers), which only requires a fixed user-defined amount of memory and disk space. This approach realizes a memory, time and disk trade-off. The multi-set of all k-mers present in the reads is partitioned, and partitions are saved to disk. Then, each partition is separately loaded in memory in a temporary hash table. The k-mer counts are returned by traversing each hash table. Low-abundance k-mers are optionally filtered. DSK is the first approach that is able to count all the 27-mers of a human genome dataset using only 4.0 GB of memory and moderate disk space (160 GB), in 17.9 h. DSK can replace a popular k-mer counting software (Jellyfish) on small-memory servers.

Availability:  http://minia.genouest.org/dsk

Contact:  rayan.chikhi@ens-cachan.org
Swarming, swirling and stasis in sequestered bristle-bots
Authors: Giomi L. , Hawley-Weld N. , Mahadevan L.
Published: January 2013

The collective ability of organisms to move coherently in space and time is ubiquitous in any group of autonomous agents that can move and sense each other and the environment. Here, we investigate the origin of collective motion and its loss using macroscopic self-propelled bristle-bots, simple automata made from a toothbrush and powered by an onboard cell phone vibrator-motor, that can sense each other through shape-dependent local interactions, and can also sense the environment non-locally via the effects of confinement and substrate topography. We show that when bristle-bots are confined to a limited arena with a soft boundary, increasing the density drives a transition from a disordered and uncoordinated motion to organized collective motion either as a swirling cluster or a collective dynamical stasis. This transition is regulated by a single parameter, the relative magnitude of spinning and walking in a single automaton. We explain this using quantitative experiments and simulations that emphasize the role of the agent shape, environment and confinement via boundaries. Our study shows how the behavioural repertoire of these physically interacting automatons controlled by one parameter translates into the mechanical intelligence of swarms.
Epigenetic marking and repression of porcine endogenous retroviruses
Authors: Wolf Gernot , Nielsen Anders Lade , Mikkelsen Jacob Giehm , Pedersen Finn Skou
Published: January 2013

Endogenous retroviruses (ERVs) are remnants of retroviral germ line infections and have been identified in all mammals investigated so far. Although the majority of ERVs are degenerated, some mammalian species, such as mice and pigs, carry replication-competent ERVs capable of forming infectious viral particles. In mice, ERVs are silenced by DNA methylation and histone modifications and some exogenous retroviruses were shown to be transcriptionally repressed after integration by a primer-binding site (PBS) targeting mechanism. However, epigenetic repression of porcine ERVs (PERVs) has remained largely unexplored so far. In this study, we screened the pig genome for PERVs using LTRharvest, a tool for de novo detection of ERVs, and investigated various aspects of epigenetic repression of three unrelated PERV families. We found that these PERV families are differentially up- or downregulated upon chemical inhibition of DNA methylation and histone deacetylation in cultured porcine cells. Furthermore, chromatin immunoprecipitation analysis revealed repressive histone methylation marks at PERV loci in primary porcine embryonic germ cells and immortalized embryonic kidney cells. PERV elements belonging to the PERV-γ1 family, which is the only known PERV family that has remained active up to the present, were marked by significantly higher levels of histone methylations than PERV-γ2 and PERV-β3 proviruses. Finally, we tested three PERV-associated PBS sequences for repression activity in murine and porcine cells using retroviral transduction experiments and showed that none of these PBS sequences induced immediate transcriptional silencing in the tested primary porcine cells.
The impact of corporate social responsibility in food industry in product‐harm crises
Authors: Assiouras Ioannis , Ozgen Ozge , Skourtis George
Published: January 2013

Purpose

The first purpose of this study is to analyse the impact of prior CSR information on the perceived degree of danger, attribution of blame, brand evaluation and buying intentions after a product‐harm crisis in the food industry. The second purpose is to examine the moderation effect of CSR importance ascribed by the consumers on the above mentioned relations.

Design/methodology/approach

An experimental design consisting of three between‐subjects conditions was applied and three CSR initiative conditions were selected (positive, negative CSR and no CSR information as a control condition). In this framework, three different scenarios were designed and tested under the condition of a product‐harm crisis related to margarine.

Findings

This study highlights that CSR has an impact on attribution of blame, brand evaluation and buying intention but not on the perceived degree of danger. CSR importance has a moderation effect on the relationship between CSR and blame attribution, brand evaluation and buying intention.

Practical implications

Companies in the food industry should generate CSR strategies and should develop favourable CSR history not only because CSR has an impact on brand evaluation and buying intention in routine situations but because it is a part of crisis management and response strategy as well.

Originality/value

There is lack of research directly emphasizing the role of CSR in product‐harm crises, in the food industry. Besides, the assessment of CSR as an antecedent assurance factor in crisis situations has significant meaning due to the high vulnerability of food industry.
Consumers' awareness of CSR in the German pork industry
Authors: Hartmann Monika , Heinen Sarah , Melis Sabrina , Simons Johannes
Published: January 2013

Purpose

All food sectors, especially meat production and processing, has been in the dock over the last decades. CSR is considered as a way for an enterprise to increase its reputation and safeguard against risks, e.g. food safety, environmental or social incidence. Thus, it is not surprising that CSR has gained importance for meat companies. However, the question arises whether consumers are indeed aware and appreciative of this involvement. This paper seeks to address these issues.

Design/methodology/approach

A convenient sample of 123 consumers was interviewed with a standardized questionnaire. The data were analyzed using descriptive as well as uni‐ and multivariate methods.

Findings

The results show that CSR is hardly known by German consumers and only plays a moderate role in their present purchase behavior. However, consumers are interested in CSR and the survey results reveal a potential for CSR to become an important determinant in consumers' purchase decision of meat.

Research limitations/implications

Concerning the interpretation of the results, there exist potential limitations that arise from the small sample size, the method of data collection and a social desirability bias in responses. Future research may analyze the role of CSR in consumers' purchase decisions using non‐hypothetical choice experiments.

Practical implications

There is scope for companies to gain competitive advantage by responsible conduct and by spreading information about that in a thoughtful and authentic manner. This holds especially for the area of animal welfare.

Originality/value

There exists little research that analyzes consumers' attitudes towards and perception of CSR for the food sector and no study so far has concentrated on the meat industry. This study provides information for decision makers in food companies and researchers interested in the impact of CSR on consumers' attitudes and behavior.