bluuebunny/crossref_metadata_2025 huggingface dataset:
Stability of very-high pressure arc discharges against perturbations of the electron temperature
Authors: Benilov M. S. , Hechtfischer U.
Published: April 2012

We study the stability of the energy balance of the electron gas in very high–pressure plasmas against longitudinal perturbations, using a local dispersion analysis. After deriving a dispersion equation, we apply the model to a very high–pressure (100 bar) xenon plasma and find instability for electron temperatures, Te, in a window between 2400 K and 5500-7000 K, depending on the current density (106–108 A/m2). The instability can be traced back to the Joule heating of the electron gas being a growing function of Te, which is due to a rising dependence of the electron-atom collision frequency on Te. We then analyze the Te range occurring in very high–pressure xenon lamps and conclude that only the near-anode region exhibits Te sufficiently low for this instability to occur. Indeed, previous experiments have revealed that such lamps develop, under certain conditions, voltage oscillations accompanied by electromagnetic interference, and this instability has been pinned down to the plasma-anode interaction. A relation between the mechanisms of the considered instability and multiple anodic attachments of high-pressure arcs is discussed.
Relativistic explicit correlation: Coalescence conditions and practical suggestions
Authors: Li Zhendong , Shao Sihong , Liu Wenjian
Published: April 2012

To set up the general framework for relativistic explicitly correlated wave function methods, the electron-electron coalescence conditions are derived for the wave functions of the Dirac-Coulomb (DC), Dirac-Coulomb-Gaunt (DCG), Dirac-Coulomb-Breit (DCB), modified Dirac-Coulomb (MDC), and zeroth-order regularly approximated (ZORA) Hamiltonians. The manipulations make full use of the internal symmetries of the reduced two-electron Hamiltonians such that the asymptotic behaviors of the wave functions emerge naturally. The results show that, at the coalescence point of two electrons, the wave functions of the DCG Hamiltonian are regular, while those of the DC and DCB Hamiltonians have weak singularities of the type \documentclass[12pt]{minimal}\begin{document}$r_{12}^{\nu }$\end{document}r12ν with ν being negative and of \documentclass[12pt]{minimal}\begin{document}$\mathcal {O}(\alpha ^2)$\end{document}O(α2). The behaviors of the MDC wave functions are related to the original ones in a simple manner, while the spin-free counterparts are somewhat different due to the complicated electron-electron interaction. The behaviors of the ZORA wave functions depend on the chosen potential in the kinetic energy operator. In the case of the nuclear attraction, the behaviors of the ZORA wave functions are very similar to those of the nonrelativistic ones, just with an additional correction of \documentclass[12pt]{minimal}\begin{document}$\mathcal {O}(\alpha ^2)$\end{document}O(α2) to the nonrelativistic cusp condition. However, if the Coulomb interaction is also included, the ZORA wave functions become close to the large-large components of the DC wave functions. Note that such asymptotic expansions of the relativistic wave functions are only valid within an extremely small convergence radius Rc of \documentclass[12pt]{minimal}\begin{document}$\mathcal {O}(\alpha ^2)$\end{document}O(α2). Beyond this radius, the behaviors of the relativistic wave functions are still dominated by the nonrelativistic limit, as can be seen in terms of direct perturbation theory (DPT) of relativity. However, as the two limits α → 0 and r12 → 0 do not commute, DPT is doomed to fail due to incorrect descriptions of the small-small component ΨSS of the DC wave function for r12 < Rc. Another deduction from the possible divergence of ΨSS at r12 = Rc is that the DC Hamiltonian has no bound electronic states, although the last word cannot be said. These findings enrich our understandings of relativistic wave functions. On the practical side, it is shown that, under the no-pair approximation, relativistic explicitly correlated wave function methods can be made completely parallel to the nonrelativistic counterparts, as demonstrated explicitly for MP2-F12. Yet, this can only be achieved by using an extended no-pair projector.
Configurational effects on shock wave propagation in Ni-Al multilayer composites
Authors: Specht Paul E. , Thadhani Naresh N. , Weihs Timothy P.
Published: April 2012

The shock compression response of cold-rolled Ni and Al multilayered composites at various angles of inclination are investigated by employing meso-scale simulations. The orientation of the laminate layers in the multilayered composite is varied at 0°, 45°, and 90° to the direction of shock front propagation to determine and understand the resulting changes in the shock compression response. Real, heterogeneous microstructures, obtained from optical micrographs of the multilayered composite cross-section, are incorporated into the Eulerian, finite volume code, CTH. The simulations are performed to establish the role that the orientation of material interfaces plays in the dispersion and dissipation of the shock wave as well as the US-UP relationship for each configuration. Noticeable differences are observed at the meso-scale in the pressure, temperature, and strain response, as a function of the underlying microstructure. Geometric dispersion is seen to alter the shape of the resulting pressure pulse and inhibit the development of a steady-state shock wave in the laminate geometry. This effect is heightened by the extensive non-uniformities of the layering caused by cold-rolling. Additionally, two-dimensional effects of strain are seen to increase the dissipation of the shock wave through interfacial heating and shearing, resulting in high levels of viscosity and attenuation. While the effects of dispersion are minimal on the bulk response of the multilayered composite, the high rate of dissipation is seen to change the dependence of the shock velocity on the particle velocity, making dissipation a major contributor to the bulk response of these composites under shock compression.
A highly coarse-grained model to simulate entangled polymer melts
Authors: Zhu You-Liang , Liu Hong , Lu Zhong-Yuan
Published: April 2012

We introduce a highly coarse-grained model to simulate the entangled polymer melts. In this model, a polymer chain is taken as a single coarse-grained particle, and the creation and annihilation of entanglements are regarded as stochastic events in proper time intervals according to certain rules and possibilities. We build the relationship between the probability of appearance of an entanglement between any pair of neighboring chains at a given time interval and the rate of variation of entanglements which describes the concurrence of birth and death of entanglements. The probability of disappearance of entanglements is tuned to keep the total entanglement number around the target value. This useful model can reflect many characteristics of entanglements and macroscopic properties of polymer melts. As an illustration, we apply this model to simulate the polyethylene melt of C1000H2002 at 450 K and further validate this model by comparing to experimental data and other simulation results.
Utility of reactively sputtered CuNx films in spintronics devices
Authors: Fang Yeyu , Persson J. , Zha C. , Willman J. , Miller Casey W. , Åkerman Johan
Published: April 2012

We have studied nitrified copper (CuNx) thin films grown by reactive sputtering in the context of spintronic devices. The Ar-to-N2 flow ratio enables tunability of the electrical resistivity and surface roughness of the CuNx films, with the former increasing to nearly 20 times that of Cu, and the latter reduced to the atomic scale. Incorporating this into a Ta/CuNx/Ta seed stack for spin valves improves the current-in-plane (CIP) magnetoresistance; maximum magnetoresistance results with CuNx seed layer and Cu interlayer. Finally, finite element modeling results are presented that suggest the use of CuNx in nanocontact spin torque oscillators can enhance current densities by limiting the current spread through the device. This may positively impact threshold currents, power requirements, and device reliability.
Interface-controlled thermal transport properties in nano-clustered phase change materials
Authors: Lee Dongbok , Kang Stephen Dongmin , Kim Hyun-Mi , Kang Dae-Hwan , Lyeo Ho-Ki , Kim Ki-Bum
Published: April 2012

We measured the thermal conductivity of nano-clustered Ge2Sb2Te5(GST)–TiOx films in situ upon annealing from room temperature to 200 °C by the time-domain thermoreflectance method. The nano-clustered structure was found to significantly reduce the thermal conductivity of the crystallized GST–TiOx films. The reduction is attributed to the thermal resistance provided by the TiOx boundaries, of which the impact is identified by estimating the apparent interfacial thermal conductance of the embedded GST/TiOx interfaces. We suggest how to deal with the electronic contribution to thermal transport for this procedure. The apparent interfacial thermal conductance of the embedded GST/TiOx interfaces was found to tune closer to the intrinsic value 30 MW/m2 K as the microstructure of the films evolved into a distinctly clustered structure.
High voltage ultrawide band pulse generator using Blumlein pulse forming line
Authors: Jin Y. S. , Lim S. W. , Cho C. H. , Kim J. S. , Kim Y. B. , Lee S. H. , Roh Y.
Published: April 2012

A high voltage ultrawide band pulse generation system has been developed to radiate intense and ultrawide band electric fields for the examination of effects of the electric fields on the operation of electronic devices. As major components of the system, a helical strip/wire type of air-cored pulse transformer and a triaxial type of Blumlein pulse forming line have been designed and fabricated to amplify and shape the output pulse, respectively. For the construction of a compact system, the pulse transformer and the Blumlein line are installed in a single cylindrical container. An ultrawide band TEM horn antenna has been fabricated to radiate the Blumlein output pulses to electronic devices. A number of experimental results demonstrate that the system is capable of providing an output pulse whose voltage is greater than 300 kV, pulse duration is ∼5 ns, and rise time is ∼500 ps with repetition rate of 10 Hz. The peak-to-peak value of electric field intensity of a radiated pulse is also measured to be approximately 42 kV/m at a distance of 10 m away from the antenna.
Franck-Condon simulation of vibrationally resolved optical spectra for zinc complexes of phthalocyanine and tetrabenzoporphyrin including the Duschinsky and Herzberg-Teller effects
Authors: Guo Meiyuan , He Rongxing , Dai Yulan , Shen Wei , Li Ming , Zhu Chaoyuan , Lin Sheng Hsien
Published: April 2012

High resolved absorption and fluorescence spectra of zinc complexes of phthalocyanine (ZnPc) and tetrabenzoporphyrin (ZnTBP) in the region of Q states were reported. Few theoretical investigations were performed to simulate the well-resolved spectra and assigned the vibrational bands of the large molecules, especially for high symmetrical characteristic molecules, on account of the difficulties to optimize the excited states and analyze a large number of final vibrational-normal modes. In the present work, the S0 ↔ S1 absorption and fluorescence spectra (that is, the Q band) of ZnPc and ZnTBP were simulated using time-dependent density functional theory with the inclusions of Duschinsky and Herzberg-Teller contributions to the electronic transition dipole moments. The theoretical results provide a good description of the optical spectra and are proved to be in excellent agreement with experimental spectra in inert-gas matrices or in supersonic expansion. This study focused attentions on the optical spectral similarities and contrasts between ZnPc and ZnTBP, in particular the noticeable Duschinsky and Herzberg-Teller effects on the high-resolved absorption and fluorescence spectra were considered. Substitution of meso-tetraaza on the porphyrin macrocycle framework could affect the ground state geometry and alter the electron density distributions, the orbital energies that accessible in the Q band region of the spectrum. The results were used to help interpret both the nature of the electronic transitions in Q band region, and the spectral discrepancies between phthalocyanine and porphyrin systems.
Magnetic reconnection and stochastic plasmoid chains in high-Lundquist-number plasmas
Authors: Loureiro N. F. , Samtaney R. , Schekochihin A. A. , Uzdensky D. A.
Published: April 2012

A numerical study of magnetic reconnection in the large-Lundquist-number (S), plasmoid-dominated regime is carried out for S up to 107. The theoretical model of Uzdensky et al. [Phys. Rev. Lett. 105, 235002 (2010)] is confirmed and partially amended. The normalized reconnection rate is Ẽeff∼0.02 independently of S for S≫104. The plasmoid flux (Ψ) and half-width (wx) distribution functions scale as f(Ψ)∼Ψ-2 and f(wx)∼wx-2. The joint distribution of Ψ and wx shows that plasmoids populate a triangular region wx≳Ψ/B0, where B0 is the reconnecting field. It is argued that this feature is due to plasmoid coalescence. Macroscopic “monster” plasmoids with wx∼10% of the system size are shown to emerge in just a few Alfvén times, independently of S, suggesting that large disruptive events are an inevitable feature of large-S reconnection.
Support effects on the atomic structure of ultrathin silica films on metals
Authors: Yu Xin , Yang Bing , Anibal Boscoboinik Jorge , Shaikhutdinov Shamil , Freund Hans-Joachim
Published: April 2012

We studied the atomic structure of ultrathin silica films on Pt(111) in comparison with the previously studied films on Mo(112) and Ru(0001). The results obtained by scanning tunneling microscopy, photoelectron spectroscopy, and infrared reflection absorption spectroscopy suggest that the metal-oxygen bond strength plays the decisive role in the atomic structure of the silica overlayers on metal substrates. Metals with high oxygen adsorption energy favor the formation of the crystalline monolayer SiO2.5 films, whereas noble metals form primarily vitreous SiO2 bilayer films. The metals with intermediate energies may form either of the structures or both coexisting. In the systems studied, the lattice mismatch plays only a minor role.
Nonreciprocal optical Bloch-Zener oscillations in ternary parity-time-symmetric waveguide lattices
Authors: Ding Shulin , Ping Wang Guo
Published: April 2012

We demonstrate a kind of ternary parity-time (PT)-symmetric complex waveguide arrays to observe nonreciprocal optical Bloch-Zener oscillations (OBZOs) at the PT thresholds. The waveguide arrays are periodically constructed with a unit of a dielectric waveguide sandwiched by a loss and a gain waveguides. The nonreciprocal optical Bloch-Zener oscillations are attributed to the unidirectional Bragg scattering behaviors of light in the systems, which can be controlled by the propagation constant mismatch between dielectric waveguides and loss or gain waveguides through independently tuning the propagation constants of the dielectric waveguides of the units.
Mn2PtIn: A tetragonal Heusler compound with exchange bias behavior
Authors: Nayak Ajaya K. , Shekhar Chandra , Winterlik Jürgen , Gupta Arunava , Felser Claudia
Published: April 2012

The structural and magnetic properties of a tetragonal Heusler compound Mn2PtIn are reported. Low temperature (5 K) magnetic measurements of the material show a hard magnetic behavior with relatively low saturation magnetization of 1.6 μB/f.u., suggesting ferrimagnetic ordering in the system. Moreover, observance of shifted field-cooled hysteresis loops indicates the presence of unidirectional exchange anisotropy resulting from nano-scale interaction between ferromagnetic/antiferromagnetic clusters. An exchange bias (EB) field of 16 mT is measured at 5 K, with the value steadily decreasing with increasing temperature to zero at temperatures around 200 K. The EB behavior likely originates from the glassy nature of the low temperature magnetic state, as indicated by ac susceptibility and zero-field-cooled relaxation measurements.
Strong light confinement in a photonic amorphous diamond structure
Authors: Imagawa Shigeki , Edagawa Keiichi , Notomi Masaya
Published: April 2012

Formation of cavity modes in a recently found unique photonic structure “photonic amorphous diamond (PAD)” has been investigated by finite-difference time domain calculations. A well-confined monopole mode has been found to form when a rod is removed from the structure. The quality (Q) factor and mode volume (Vm) of such a cavity mode in PAD have been evaluated and compared with those in a conventional photonic crystal with a crystalline diamond structure. The two structures have shown nealy the same Q-factor and Vm, leading to the conclusion that strong light confinement is realizable in PAD as well as conventional photonic crystals.
Rolled-up nanotechnology for the fabrication of three-dimensional fishnet-type GaAs-metal metamaterials with negative refractive index at near-infrared frequencies
Authors: Rottler Andreas , Harland Malte , Bröll Markus , Schwaiger Stephan , Stickler Daniel , Stemmann Andrea , Heyn Christian , Heitmann Detlef , Mendach Stefan
Published: April 2012

We propose and demonstrate the fabrication of a three-dimensional fishnet metamaterial by utilizing rolled-up nanotechnology. It consists of 6 alternating layers of silver and (In)GaAs with an array of subwavelength holes “drilled” by focused ion beams. By means of finite-integration technique simulations, we show that the fabricated structure is a single-negative material possessing a negative real part of the refractive index in the near-infrared regime. We show that the fabricated material can be made double negative by slightly changing the size of the holes.
High resolution heterodyne interferometer based on time-to-digital converter
Authors: Wang Fei , Long Zhangcai , Zhang Bin , Zhao Meirong
Published: April 2012

A new heterodyne interferometer is presented, which adopts time-to-digital converter (TDC) measuring the time intervals of zero crossings of heterodyne signal for phase demodulation. Thanks to the 0.1 ns time resolution of TDC and linear phase demodulation, it can achieve high resolution and avoids nonlinear measuring distortion in other indirect high precise phase demodulation methods, such as pulse width modulation (PWM) and in-phase/quadrature (I/Q) method.
The microwave sensing of DNA hybridization using carbon nanotubes decorated with gold nanoislands
Authors: Cismaru Alina , Dragoman Mircea , Radoi Antonio , Dinescu A. , Dragoman Daniela
Published: April 2012

The hybridization of the deoxyribonucleic acid (DNA) is detected with the help of electromagnetic band gap resonator. The resonance frequency of the unloaded resonator f0=16.07 GHz is shifted to the left at 11.49 GHz when the resonator is loaded with single-stranded DNA anchored to gold nanoislands decorating bamboo-shaped carbon nanotubes deposited on the resonator. Further, single stranded DNA is hybridized and the resonator frequency is shifted to 14.16 GHz for double-stranded DNA. So, the frequency span of the two DNA states are separated by a span of 2.6 GHz in the band 11.5-16.07 GHz due to the very different electrical permittivity values of single- and double-stranded DNA. Thus, the hybridization of DNA is detected unambiguously.
Microstripes for transport and separation of magnetic particles
Authors: Donolato Marco , Dalslet Bjarke Thomas , Hansen Mikkel Fougt
Published: April 2012

We present a simple technique for creating an on-chip magnetic particle conveyor based on exchange-biased permalloy microstripes. The particle transportation relies on an array of stripes with a spacing smaller than their width in conjunction with a periodic sequence of four different externally applied magnetic fields. We demonstrate the controlled transportation of a large population of particles over several millimeters of distance as well as the spatial separation of two populations of magnetic particles with different magnetophoretic mobilities. The technique can be used for the controlled selective manipulation and separation of magnetically labelled species.
Predator transitory spillover induces trophic cascades in ecological sinks
Authors: Casini Michele , Blenckner Thorsten , Möllmann Christian , Gårdmark Anna , Lindegren Martin , Llope Marcos , Kornilovs Georgs , Plikshs Maris , Stenseth Nils Christian
Published: April 2012

Understanding the effects of cross-system fluxes is fundamental in ecosystem ecology and biological conservation. Source-sink dynamics and spillover processes may link adjacent ecosystems by movement of organisms across system boundaries. However, effects of temporal variability in these cross-system fluxes on a whole marine ecosystem structure have not yet been presented. Here we show, using 35 y of multitrophic data series from the Baltic Sea, that transitory spillover of the top-predator cod from its main distribution area produces cascading effects in the whole food web of an adjacent and semi-isolated ecosystem. At varying population size, cod expand/contract their distribution range and invade/retreat from the neighboring Gulf of Riga, thereby affecting the local prey population of herring and, indirectly, zooplankton and phytoplankton via top-down control. The Gulf of Riga can be considered for cod a “true sink” habitat, where in the absence of immigration from the source areas of the central Baltic Sea the cod population goes extinct due to the absence of suitable spawning grounds. Our results add a metaecosystem perspective to the ongoing intense scientific debate on the key role of top predators in structuring natural systems. The integration of regional and local processes is central to predict species and ecosystem responses to future climate changes and ongoing anthropogenic disturbances.
Epigenetic regulation of
Kiss1
gene expression mediating estrogen-positive feedback action in the mouse brain
Authors: Tomikawa Junko , Uenoyama Yoshihisa , Ozawa Makiko , Fukanuma Tatsuya , Takase Kenji , Goto Teppei , Abe Hitomi , Ieda Nahoko , Minabe Shiori , Deura Chikaya , Inoue Naoko , Sanbo Makoto , Tomita Koichi , Hirabayashi Masumi , Tanaka Satoshi , Imamura Takuya , Okamura Hiroaki , Maeda Kei-ichiro , Tsukamura Hiroko
Published: April 2012

This study aims to determine the epigenetic mechanism regulating
Kiss1
gene expression in the anteroventral periventricular nucleus (AVPV) to understand the mechanism underlying estrogen-positive feedback action on gonadotropin-releasing hormone/gonadotropin surge. We investigated estrogen regulation of the epigenetic status of the mouse AVPV
Kiss1
gene locus in comparison with the arcuate nucleus (ARC), in which
Kiss1
expression is down-regulated by estrogen. Histone of AVPV
Kiss1
promoter region was highly acetylated, and estrogen receptor α was highly recruited at the region by estrogen. In contrast, the histone of ARC
Kiss1
promoter region was deacetylated by estrogen. Inhibition of histone deacetylation up-regulated in vitro
Kiss1
expression in a hypothalamic non–
Kiss1
-expressing cell line. Gene conformation analysis indicated that estrogen induced formation of a chromatin loop between
Kiss1
promoter and the 3′ intergenic region, suggesting that the intergenic region serves to enhance estrogen-dependent
Kiss1
expression in the AVPV. This notion was proved, because transgenic reporter mice with a complete
Kiss1
locus sequence showed kisspeptin neuron-specific GFP expression in both the AVPV and ARC, but the deletion of the 3′ region resulted in greatly reduced GFP expression only in the AVPV. Taken together, these results demonstrate that estrogen induces recruitment of estrogen receptor α and histone acetylation in the
Kiss1
promoter region of the AVPV and consequently enhances chromatin loop formation of
Kiss1
promoter and
Kiss1
gene enhancer, resulting in an increase in AVPV-specific
Kiss1
gene expression. These results indicate that epigenetic regulation of the
Kiss1
gene is involved in estrogen-positive feedback to generate the gonadotropin-releasing hormone/gonadotropin surge.
Ecological and evolutionary determinants for the adaptive radiation of the Madagascan vangas
Authors: Jønsson Knud A. , Fabre Pierre-Henri , Fritz Susanne A. , Etienne Rampal S. , Ricklefs Robert E. , Jørgensen Tobias B. , Fjeldså Jon , Rahbek Carsten , Ericson Per G. P. , Woog Friederike , Pasquet Eric , Irestedt Martin
Published: April 2012

Adaptive radiation is the rapid diversification of a single lineage into many species that inhabit a variety of environments or use a variety of resources and differ in traits required to exploit these. Why some lineages undergo adaptive radiation is not well-understood, but filling unoccupied ecological space appears to be a common feature. We construct a complete, dated, species-level phylogeny of the endemic Vangidae of Madagascar. This passerine bird radiation represents a classic, but poorly known, avian adaptive radiation. Our results reveal an initial rapid increase in evolutionary lineages and diversification in morphospace after colonizing Madagascar in the late Oligocene some 25 Mya. A subsequent key innovation involving unique bill morphology was associated with a second increase in diversification rates about 10 Mya. The volume of morphospace occupied by contemporary Madagascan vangas is in many aspects as large (shape variation)—or even larger (size variation)—as that of other better-known avian adaptive radiations, including the much younger Galapagos Darwin's finches and Hawaiian honeycreepers. Morphological space bears a close relationship to diet, substrate use, and foraging movements, and thus our results demonstrate the great extent of the evolutionary diversification of the Madagascan vangas.
Near attack conformers dominate β-phosphoglucomutase complexes where geometry and charge distribution reflect those of substrate
Authors: Griffin Joanna L. , Bowler Matthew W. , Baxter Nicola J. , Leigh Katherine N. , Dannatt Hugh R. W. , Hounslow Andrea M. , Blackburn G. Michael , Webster Charles Edwin , Cliff Matthew J. , Waltho Jonathan P.
Published: April 2012

Experimental observations of fluoromagnesate and fluoroaluminate complexes of β-phosphoglucomutase (β-PGM) have demonstrated the importance of charge balance in transition-state stabilization for phosphoryl transfer enzymes. Here, direct observations of ground-state analog complexes of β-PGM involving trifluoroberyllate establish that when the geometry and charge distribution closely match those of the substrate, the distribution of conformers in solution and in the crystal predominantly places the reacting centers in van der Waals proximity. Importantly, two variants are found, both of which satisfy the criteria for near attack conformers. In one variant, the aspartate general base for the reaction is remote from the nucleophile. The nucleophile remains protonated and forms a nonproductive hydrogen bond to the phosphate surrogate. In the other variant, the general base forms a hydrogen bond to the nucleophile that is now correctly orientated for the chemical transfer step. By contrast, in the absence of substrate, the solvent surrounding the phosphate surrogate is arranged to disfavor nucleophilic attack by water. Taken together, the trifluoroberyllate complexes of β-PGM provide a picture of how the enzyme is able to organize itself for the chemical step in catalysis through the population of intermediates that respond to increasing proximity of the nucleophile. These experimental observations show how the enzyme is capable of stabilizing the reaction pathway toward the transition state and also of minimizing unproductive catalysis of aspartyl phosphate hydrolysis.
β-Catenin signaling initiates the activation of astrocytes and its dysregulation contributes to the pathogenesis of astrocytomas
Authors: Yang Chunzhang , Iyer Rajiv R. , Yu Albert C. H. , Yong Raymund L. , Park Deric M. , Weil Robert J. , Ikejiri Barbara , Brady Roscoe O. , Lonser Russell R. , Zhuang Zhengping
Published: April 2012

Astrocytes are the most abundant cell of the CNS and demonstrate contact inhibition in which a nonproliferative, nonmotile cellular state is achieved once stable intercellular contacts are formed between mature cells. Cellular injury disrupts these intercellular contacts, causing a loss of contact inhibition and the rapid initiation of healing. Dysregulation of the molecular pathways involved in this process is thought to lead to an aggressive cellular state associated with neoplasia. We investigated whether a comparable correlation exists between the response of astrocytes to injury and the malignant phenotype of astrocytomas. We discovered that the loss of contact inhibition plays a critical role in the initiation and regulation of reactive astrocytes in the healing of wounds. In particular, injury of the astrocytes interrupts and destabilizes the cadherin-catenin complexes at the cell membrane leading to nuclear translocation of β-catenin and characteristic changes associated with the activation of astrocytes. Similar signaling pathways are found to be active—but dysregulated—in astrocytomas. Inhibition of β-catenin signaling diminished both the response of astrocytes to injury and induction of the malignant phenotype of astrocytomas. The findings shed light on a unique mechanism associated with the pathogenesis of astrocytomas and provide a model for the loss of contact inhibition that may broadly apply to understanding the mechanisms of tissue repair and tumorigenesis in the brain.
Biologically relevant mechanism for catalytic superoxide removal by simple manganese compounds
Authors: Barnese Kevin , Gralla Edith Butler , Valentine Joan Selverstone , Cabelli Diane E.
Published: April 2012

Nonenzymatic manganese was first shown to provide protection against superoxide toxicity in vivo in 1981, but the chemical mechanism responsible for this protection subsequently became controversial due to conflicting reports concerning the ability of Mn to catalyze superoxide disproportionation in vitro. In a recent communication, we reported that low concentrations of a simple Mn phosphate salt under physiologically relevant conditions will indeed catalyze superoxide disproportionation in vitro. We report now that two of the four Mn complexes that are expected to be most abundant in vivo, Mn phosphate and Mn carbonate, can catalyze superoxide disproportionation at physiologically relevant concentrations and pH, whereas Mn pyrophosphate and citrate complexes cannot. Additionally, the chemical mechanisms of these reactions have been studied in detail, and the rates of reactions of the catalytic removal of superoxide by Mn phosphate and carbonate have been modeled. Physiologically relevant concentrations of these compounds were found to be sufficient to mimic an effective concentration of enzymatic superoxide dismutase found in vivo. This mechanism provides a likely explanation as to how Mn combats superoxide stress in cellular systems.
Reassessment of the 2010–2011 Haiti cholera outbreak and rainfall-driven multiseason projections
Authors: Rinaldo Andrea , Bertuzzo Enrico , Mari Lorenzo , Righetto Lorenzo , Blokesch Melanie , Gatto Marino , Casagrandi Renato , Murray Megan , Vesenbeckh Silvan M. , Rodriguez-Iturbe Ignacio
Published: April 2012

Mathematical models can provide key insights into the course of an ongoing epidemic, potentially aiding real-time emergency management in allocating health care resources and by anticipating the impact of alternative interventions. We study the ex post reliability of predictions of the 2010–2011 Haiti cholera outbreak from four independent modeling studies that appeared almost simultaneously during the unfolding epidemic. We consider the impact of different approaches to the modeling of spatial spread of
Vibrio cholerae
and mechanisms of cholera transmission, accounting for the dynamics of susceptible and infected individuals within different local human communities. To explain resurgences of the epidemic, we go on to include waning immunity and a mechanism explicitly accounting for rainfall as a driver of enhanced disease transmission. The formal comparative analysis is carried out via the Akaike information criterion (AIC) to measure the added information provided by each process modeled, discounting for the added parameters. A generalized model for Haitian epidemic cholera and the related uncertainty is thus proposed and applied to the year-long dataset of reported cases now available. The model allows us to draw predictions on longer-term epidemic cholera in Haiti from multiseason Monte Carlo runs, carried out up to January 2014 by using suitable rainfall fields forecasts. Lessons learned and open issues are discussed and placed in perspective. We conclude that, despite differences in methods that can be tested through model-guided field validation, mathematical modeling of large-scale outbreaks emerges as an essential component of future cholera epidemic control.
The inner-mitochondrial distribution of Oxa1 depends on the growth conditions and on the availability of substrates
Authors: Stoldt Stefan , Wenzel Dirk , Hildenbeutel Markus , Wurm Christian A. , Herrmann Johannes M. , Jakobs Stefan
Published: April 2012

The Oxa1 protein is a well-conserved integral protein of the inner membrane of mitochondria. It mediates the insertion of both mitochondrial- and nuclear-encoded proteins from the matrix into the inner membrane. We investigated the distribution of budding yeast Oxa1 between the two subdomains of the contiguous inner membrane—the cristae membrane (CM) and the inner boundary membrane (IBM)—under different physiological conditions. We found that under fermentable growth conditions, Oxa1 is enriched in the IBM, whereas under nonfermentable (respiratory) growth conditions, it is predominantly localized in the CM. The enrichment of Oxa1 in the CM requires mitochondrial translation; similarly, deletion of the ribosome-binding domain of Oxa1 prevents an enrichment of Oxa1 in the CM. The predominant localization in the IBM under fermentable growth conditions is prevented by inhibiting mitochondrial protein import. Furthermore, overexpression of the nuclear-encoded Oxa1 substrate Mdl1 shifts the distribution of Oxa1 toward the IBM. Apparently, the availability of nuclear- and mitochondrial-encoded substrates influences the inner-membrane distribution of Oxa1. Our findings show that the distribution of Oxa1 within the inner membrane is dynamic and adapts to different physiological needs.
Health for some: global health and social development since Alma
Ata
Authors: Carpenter Mick
Published: April 2012

This article assesses the impact of the World Health Organization's strategy of Health For All by the Year 2000 (HFA2000) as a global strategy initiated from above, shaped by the 1970s world-wide challenge from below. While having been partially successful, the grand aims of Alma Ata have not been realized. Pressing new problems such as AIDS have emerged, health inequalities widened, and economic globalization has impacted negatively on health policy. The article concludes by suggesting that HFA2000 remains a relevant vision, and draws hope from the fact that a new global strategy for healthy development is emerging from below out of the campaigns of Global Social Movements (GSMs) against the neoliberal system of global governance.
Timing of Vote Decision in First and Second Order Dutch Elections 1978–1995: Evidence from Artificial Neural Networks
Authors: Eisinga Rob , Franses Philip Hans , van Dijk Dick
Published: April 2012

A time series (t= 921) of weekly survey data on vote intentions in the Netherlands for the period 1978–1995 shows that the percentage of undecided voters follows a cyclical pattern over the election calendar. The otherwise substantial percentage of undecided voters decreases sharply in weeks leading up to an election and gradually increases afterwards. This article models the dynamics of this asymmetric electoral cycle using artificial neural networks, with the purpose of estimating when the undecided voters start making up their minds. We find that they begin to decide which party to vote for nine weeks before a first order national parliamentary election and one to four weeks before a second order election, depending on the type of election (European Parliament, Provincial States, City-councils). The effect of political campaigns and the implications for political analysis are discussed.
Structure in Mathematics and Logic: A Categorical Perspective
Authors: AWODEY S.
Published: April 2012

A precise notion of ‘mathematical structure’ other than that given by model theory may prove fruitful in the philosophy of mathematics. It is shown how the language and methods of category theory provide such a notion, having developed out of a structural approach in modern mathematical practice. As an example, it is then shown how the categorical notion of a topos provides a characterization of ‘logical structure’, and an alternative to the Pregean approach to logic which is continuous with the modern structural approach in mathematics.
The Impact of Trade on Organization and Productivity*
Authors: Caliendo Lorenzo , Rossi-Hansberg Esteban
Published: April 2012

A firm's productivity depends on how production is organized. To understand this relationship we develop a theory of an economy where firms with heterogeneous demands use labor and knowledge to produce. Entrepreneurs decide the number of layers of management and the knowledge and span of control of each agent. As a result, in the theory, heterogeneity in demand leads to heterogeneity in productivity and other firms' outcomes. We use the theory to analyze the impact of international trade on organization and calibrate the model to the U.S. economy. Our results indicate that, as a result of a bilateral trade liberalization, firms that export will increase the number of layers of management. The new organization of the average exporter results in higher productivity, although the responses of productivity are heterogeneous across these firms. Liberalizing trade from autarky to the level of openness in 2002 results in a 1% increase in productivity for the marginal exporter and a 1.8% increase in its revenue productivity. Endogenous organization increases the gains from trade by 41% relative to standard models.
Liquidity and Asset Returns Under Asymmetric Information and Imperfect Competition
Authors: Vayanos Dimitri , Wang Jiang
Published: April 2012

We analyze how asymmetric information and imperfect competition affect liquidity and asset prices. Our model has three periods: Agents are identical in the first, become heterogeneous and trade in the second, and consume asset payoffs in the third. We show that asymmetric information in the second period raises ex ante expected asset returns in the first, comparing both to the case where all private signals are made public and to that where private signals are not observed. Imperfect competition can instead lower expected returns. Each imperfection can move common measures of illiquidity in opposite directions.
Flavitalea gansuensis sp. nov., isolated from soil from an arid area, and emended descriptions of the genus

Flavitalea

and

Flavitalea populi
Authors: Zhang Lei , Qin Baofu , Jia Zhihua , Wei Gehong
Published: April 2012

A Gram-reaction-negative, rod-shaped, gliding and bright-yellow-pigmented bacterial strain, designated JCN-23T, was isolated from a soil sample collected from an arid area in Gansu Province in north-west China, and characterized by using a polyphasic taxonomic approach. This isolate grew optimally at 30 °C and in the absence of NaCl. The only respiratory quinone was menaquinone-7 and the major cellular fatty acids were iso-C15 : 0, iso-C17 : 0 3-OH, summed feature 9 (iso-C17 : 1ω9c and/or C16 : 0 10-methyl) and summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c). The only polyamine was homospermidine and the major polar lipid was phosphatidylethanolamine. The DNA G+C content was 47.1 mol%. Comparative 16S rRNA gene sequence analysis showed that strain JCN-23T was a member of the phylum

Bacteroidetes

, exhibiting the highest 16S rRNA gene sequence similarity to

Flavitalea populi

CCTCC AB 208255T (97.6 %). No other recognized bacterial species showed more than 93.4 % 16S rRNA gene sequence similarity to the novel isolate. DNA–DNA hybridization experiments showed a low level (26 %) of DNA–DNA relatedness between strain JCN-23T and

F. populi

CCTCC AB 208255T. On the basis of the phenotypic and genotypic data and phylogenetic inference, strain JCN-23T is considered to represent a novel species of the genus

Flavitalea

, for which the name Flavitalea gansuensis sp. nov. is proposed. The type strain is JCN-23T ( = ACCC 05418T = KCTC 23071T). Emended descriptions of the genus

Flavitalea

and

Flavitalea populi

are also proposed.
Aspergillus baeticus sp. nov. and Aspergillus thesauricus sp. nov., two species in section Usti from Spanish caves
Authors: Nováková Alena , Hubka Vit , Saiz-Jimenez Cesareo , Kolarik Miroslav
Published: April 2012

Two novel species ofAspergillusthat are clearly distinct from all known species in sectionUstiwere revealed during a study of microfungal communities in Spanish caves. The novel species identified in this study and additional species ofAspergillussectionUstiare associated with places and substrates related to human activities in caves. Novel species are described using data from four loci (ITS,benA,caMandrpb2), morphology and basic chemical and physiological analyses. Members of the speciesAspergillus thesauricussp. nov. were isolated from various substrates, including decaying organic matter, cave air and cave sediment of the Cueva del Tesoro Cave (the Treasure cave); the species is represented by twelve isolates and is most closely related to the recently describedAspergillusgermanicus. Members of the speciesAspergillus baeticussp. nov. were isolated from cave sediment in the Gruta de las Maravillas Cave (the Grotto of the Marvels); the species is represented by two isolates. An additional isolate was found in the Cueva del Tesoro Cave and in the Demänovská Peace Cave (Slovakia), suggesting a potentially wide distribution of this micro-organism. The species is related toAspergillusustusandAspergilluspseudoustus. Both species were unable to grow at 37 °C, and a weakly positive, light greenish yellow Ehrlich reaction was observed inA.thesauricus. Unique morphological features alone are sufficient to distinguish both species from related taxa.
The Effect of Admission Creatinine Levels on One-Year Mortality in Acute Myocardial Infarction
Authors: Cakar Mehmet Akif , Gunduz Huseyin , Vatan Mehmet Bulent , Kocayigit Ibrahim , Akdemir Ramazan
Published: April 2012

Background.We have known that patients with renal insufficiency (creatinine level) have increased mortality for coronary artery disease. In this study, the relationship between admission creatinine level and one year mortality are evaluated in patients with acute myocardial infarction (AMI).Method. 160 AMI patients (127 men and 33 women with a mean age of 59 ± 13) were enrolled in the study. Serum creatinine levels were measured within 12 hours of AMI. The patients were divided into two groups according to admission serum creatinine level. (1) elevated group (serum creatinine > 1.3 mg/dL) and (2) normal group (≤1.3 mg/dL). One year mortality rates were evaluated.Results. Elevated serum creatinine is observed in the 27 patients (16.9%). The mean creatinine level is 1.78 ± 7 mg/dL in the elevated group and 0.9 ± 0.18 mg/dL in the normal group (P<0.0001). The mortality rate of the elevated group (n=7, 25.9%) is higher than that of the normal group (n=9, 6.8%). A significant increase in one year mortality is also observed (P=002) 60.Conclusion. The mildly elevated admission serum creatinine levels are markedly increased to one year mortality in patients with AMI.
Antioxidants for Preventing Preeclampsia: A Systematic Review
Authors: Salles Adriana Magalhaes Ribeiro , Galvao Tais Freire , Silva Marcus Tolentino , Motta Lucilia Casulari Domingues , Pereira Mauricio Gomes
Published: April 2012

Objective. To investigate the efficacy of antioxidants for preventing preeclampsia and other maternal and fetal complications among pregnant women with low, moderate, or high risk of preeclampsia.Methods. We searched MEDLINE, Embase, CENTRAL, mRCT, and other databases, with no language or publication restrictions. Two independent reviewers selected randomized controlled trials that evaluated the use of antioxidants versus placebo and extracted the relevant data. Relative risks (RRs) and 95% confidence intervals (95% CIs) were calculated. The data were compiled through the random effects model.Main Results. Fifteen studies were included (21,012 women and 21,647 fetuses). No statistically significant difference was found between women who received antioxidant treatment and women who received placebo for preeclampsia (RR =0.92; 95% CI: 0.82–1.04), severe preeclampsia (RR =1.03; 95% CI: 0.87–1.22), preterm birth (RR =1.03; 95% CI: 0.94–1.14), and small for gestational age <10th centile (RR =0.92; 95% CI: 0.80–1.05). Side effects were numerically more frequent in the antioxidants group compared to placebo, but without significant statistical difference (RR =1.24; 95% CI: 0.85–1.80).Conclusions. The available evidence reviewed does not support the use of antioxidants during pregnancy for the prevention of preeclampsia and other outcomes.
Isolation of a New Mexican Strain ofBacillus subtiliswith Antifungal and Antibacterial Activities
Authors: Basurto-Cadena M. G. L. , Vázquez-Arista M. , García-Jiménez J. , Salcedo-Hernández R. , Bideshi D. K. , Barboza-Corona J. E.
Published: April 2012

Although several strains ofB. subtiliswith antifungal activity have been isolated worldwide, to date there are no published reports regarding the isolation of a nativeB. subtilisstrain from strawberry plants in Mexico. A native bacterium (Bacillus subtilis21) demonstratedin vitroantagonistic activity against different plant pathogenic fungi. Under greenhouse conditions, it was shown that plants infected withRhizoctonia solaniandFusarium verticillioidesand treated withB. subtilis21 produced augment in the number of leaves per plant and an increment in the length of healthy leaves in comparison with untreated plants. In addition,B. subtilis21 showed activity against pathogenic bacteria. Secreted proteins byB. subtilis21 were studied, detecting the presence of proteases and bacteriocin-like inhibitor substances that could be implicated in its antagonistic activity. Chitinases and zwittermicin production could not be detected. Then,B. subtilis21 could potentially be used to control phytopathogenic fungi that infect strawberry plants.
Modeling Rare Species Distribution at the Edge: The Case for the Vulnerable Endemic Pyrenean Desman in France
Authors: Williams-Tripp M. , D'Amico F. J. N. , Pagé C. , Bertrand A. , Némoz M. , Brown J. A.
Published: April 2012

The endemic Pyrenean Desman (Galemys pyrenaicus) is an elusive, rare, and vulnerable species declining over its entire and narrow range (Spain, Portugal, France, and Andorra). The principal set of conservation measures in France is a 5-years National Action Plan based on 25 conservation actions. Priority is given to update its present distribution and develop tools for predictive distribution models. We aim at building the first species distribution model and map for the northern edge of the range of the Desman and confronting the outputs of the model to target conservation efforts in the context of environmental change. Contrasting to former comparable studies, we derive a simpler model emphasizing the importance of factors linked to precipitation and not to the temperature. If temperature is one of the climate change key factors, depicted shrinkage in Desman distribution could be lower or null at the northern (French) edge suggesting thus a major role for this northern population in terms of conservation of the species. Finally, we question the applied issue of temporal and spatial transferability for such environmental favourability models when it is made at the edge of the distribution range.