bluuebunny/crossref_metadata_2025 huggingface dataset:
A solvable many-body problem, its equilibria, and a second-order ordinary differential equation whose general solution is polynomial
Authors: Calogero Francesco
Published: January 2013

Some properties of a solvable N-body problem featuring several free parameters (“coupling constants”) are investigated. Restrictions on its parameters are reported which guarantee that all its solutions are completely periodic with a fixed period independent of the initial data (isochrony). The restrictions on its parameters which guarantee the existence of equilibria are also identified. In this connection a remarkable second-order ODE—generally not of hypergeometric type, hence not reducible to those characterizing the classical polynomials—is studied: if its parameters satisfy a Diophantine condition, its general solution is a polynomial of degree N, the N zeros of which identify the equilibria of the N-body system.
Ejecta source model based on the nonlinear Richtmyer-Meshkov instability
Authors: Dimonte Guy , Terrones Guillermo , Cherne F. J. , Ramaprabhu P.
Published: January 2013

We describe a simple algebraic model for the particulate spray that is ejected from a shocked metal surface based on the nonlinear evolution of the Richtmyer-Meshkov instability (RMI). The RMI is a shock-driven hydrodynamic instability at a material interface in which the dense and tenuous fluids penetrate each other as spikes and bubbles, respectively. In our model, the ejecta areal density is determined by the product of the post-shock metal density and the saturated bubble amplitude, which depends on both the amplitude and wavelength of the initial surface imperfections of the metal. The maximum ejecta velocity is determined by the ever-growing spikes, which are accelerated relative to the RMI growth rate by the spatial harmonics that sharpen them. The model is formulated to fit new hydrodynamics and molecular dynamics simulations of the RMI and validated by existing ejecta experiments over a wide range of material properties, shock strengths, and surface perturbations. The results are also contrasted with existing ejecta source models.
Fuzzy based frequency control in an isolated network employing parallel operated fuel cell/ultra-capacitor systems
Authors: Taghizadeh Mahdi , Mardaneh Mohammad , Sha Sadeghi Mokhtar
Published: January 2013

This paper proposes a fuzzy logic controller for power management of hybrid wind turbine (WT), photovoltaic (PV), fuel cell (FC), and ultra-capacitor (UC) for stand-alone applications. WT and PV are the primary power sources of the system, and an FC is expected to provide long-term energy balance, whereas the UC is employed as buffer storage for the short-term compensation. The improvement in fuzzy logic strategies enhances dynamic response of the FC/UC power system under various load conditions by suitable rule base design for fuzzy controller. The combined use of FC and UC has the potential for better energy efficiency and lifetime increment of FC technology. These rules are designed such that charging and discharging the UC voltage is controlled automatically. The fuzzy controller creates a balance between production and consumption with determination of the exact reference values for WT, PV, and FC. This causes a good frequency controlled in the hybrid generation power system. The fuzzy logic strategies performance under different condition has been verified by using real weather data practical load demand profile. To demonstrate the effectiveness of the proposed fuzzy logic strategies, comparison with improved frequency control method was performed using matlab/simulink by integrating the detailed mathematical and electrical models of the hybrid generation power system.
Characterisation and representation of non-dissipative electromagnetic medium with two Lorentz null cones
Authors: Dahl Matias F.
Published: January 2013

We study Maxwell's equations on a 4-manifold N with a medium that is non-dissipative and has a linear and pointwise response. In this setting, the medium can be represented by a suitable $\scriptsize{\big({\begin{array}{l}{2}\\ {2}\end{array}}\big)}$22-tensor on the 4-manifold N. Moreover, in each cotangent space on N, the medium defines a Fresnel surface. Essentially, the Fresnel surface is a tensorial analogue of the dispersion equation that describes the response of the medium for signals in the geometric optics limit. For example, in an isotropic medium the Fresnel surface is at each point a Lorentz null cone. In a recent paper, Lindell, Favaro, and Bergamin introduced a condition that constrains the polarisation for plane waves. In this paper we show (under suitable assumptions) that a slight strengthening of this condition gives a complete pointwise characterisation of all medium tensors for which the Fresnel surface is the union of two distinct Lorentz null cones. This is, for example, the behaviour in uniaxial media such as calcite. Moreover, using the representation formulas from Lindell et al. we obtain a closed form representation formula that pointwise parameterises all medium tensors for which the Fresnel surface is the union of two distinct Lorentz null cones. Both the characterisation and the representation formula are tensorial and do not depend on local coordinates.
Strong coupling at room temperature in ultracompact flexible metallic microcavities
Authors: Grossmann C. , Christmann G. , Baumberg J. J. , Farrer I. , Beere H. , Ritchie D. A.
Published: January 2013

Strong coupling between metallic microcavity modes and inorganic quantum well (QW) excitons at room temperature is observed in an ultracompact flexible sample design less than 100 nm thick. Four GaAs QWs embedded in a 65 nm AlGaAs/GaAs cavity are sandwiched between gold mirrors. The strong electromagnetic confinement and metallic phase shifts provide substantial local field enhancement and angular-resolved reflectivity spectra clearly show the anti-crossing in the dispersion relation resolving a Rabi splitting of 21 meV at room temperature, in good agreement with calculations. Flex-tuning metal thin foil microcavities demonstrate new possibilities for tunable optoelectronics and the study of polaritonic micromechanical effects.
Single molecule probe reports of dynamic heterogeneity in supercooled ortho-terphenyl
Authors: Leone Lindsay M. , Kaufman Laura J.
Published: January 2013

The rotational dynamics of three perylene diimide dyes are studied on the single molecule (SM) level in ortho-terphenyl (OTP) near the glass transition temperature (Tg). At all temperatures probed, spanning 1.03–1.06 Tg, each of the three probes exhibits rotational correlation times, τc, that span more than a decade, consistent with the presence of spatially heterogeneous dynamics in OTP. No trend is found as a function of temperature, but a trend as a function of probe is observed: Average probe rotational correlation time scales inversely with breadth of SM τc distribution, with faster probes exhibiting broader τc distributions. This implies that dynamic exchange occurs on and below time scales associated with probe rotation. Extrapolating FWHM of rotational relaxation times to the structural relaxation time of the host shows that the τc distribution would span nearly two decades in the limit of no probe temporal averaging. Comparison with SM measurements in glycerol suggests that OTP demonstrates a greater degree of spatially heterogeneous dynamics in this temperature range than does glycerol.
Electronic spectroscopy of 9,10-dichloroanthracene inside helium droplets
Authors: Pentlehner D. , Slenczka A.
Published: January 2013

The spectroscopy of molecules doped into superfluid helium droplets provides information on both, the dopant molecule and the helium environment. Electronic spectra of 9,10-dichloroanthracene in helium droplets are presented and compared with corresponding gas phase spectra to unravel the influence of the helium environment. The combined investigation of fluorescence excitation and dispersed emission provides information on dynamic processes in addition to energetic conditions. For vibronic states, the helium induced decay channels dominate over all intramolecular channels that contribute to the gas phase behavior. In addition to the triplet splitting caused by the Cl isotopes, a fine structure resolved for all transitions in the fluorescence excitation spectrum was found, which is the signature of microsolvation of this compound in helium droplets. This fine structure is identified as a single pure molecular transition accompanied by a sharply structured phonon wing. The corresponding fine structure measured for bare anthracene shows remarkable differences.
Preparation of Fe2Ni2N/SiO2 nanocomposite via a two-step route and investigation of its electromagnetic properties
Authors: Pan Haoshuai , Cheng Xiaoqiang , Zhang Chunhui , Gong Chunhong , Yu Laigui , Zhang Jingwei , Zhang Zhijun
Published: January 2013

Fe2Ni2N/SiO2 nanocomposite was fabricated by thermal reduction in association with nitridation in flowing ammonia gas at elevated temperature. The electromagnetic parameters of as-prepared Fe2Ni2N/SiO2 nanocomposite were measured in a frequency range of 2–18 GHz. Furthermore, its magnetic properties were investigated with a superconducting quantum interference device. Findings reveal that as-prepared Fe2Ni2N/SiO2 nanocomposite possesses a larger magnetic loss than soft magnetic metal-based magnetic/dielectric nanocomposites, which is attributed to its strong multi-resonance peaks in the high frequencies. Besides, as-prepared Fe2Ni2N/SiO2 nanocomposite exhibits typical superparamagnetic characteristics, showing promising potential as an alternative microwave absorbent.
Application of a bi-stable chain model for the analysis of jerky twin boundary motion in NiMnGa
Authors: Benichou Itamar , Faran Eilon , Shilo Doron , Givli Sefi
Published: January 2013

The “jerky” motion of a twin boundary in the ferromagnetic shape memory alloy NiMnGa is studied experimentally and theoretically. We employ a bi-stable chain model in order to interpret macroscopic stress-strain experiments and extract important micro-level properties. The analysis reveals the existence of a periodic barrier for type I twin boundary motion with an average distance of 19 μm and amplitude of 0.16 J/m2. Further, we show that the macroscopic mechanical response depends on the length of the crystal and predict a significant decrease of the hysteresis in sub-mm length specimens.
A study of resonance progressions in the F + HCl → Cl + HF reaction: A lifetime matrix analysis of pre-reactive and post-reactive collision complexes
Authors: Takahashi Kaito , Hayes Michael Y. , Skodje Rex T.
Published: January 2013

Quantum scattering calculations were performed for the F + HCl → Cl + HF reaction for total angular momentum J = 0–6 using an ab initio potential energy surface. Employing a time-independent algorithm on a very fine energy grid allowed the resolution of hundreds of narrow resonances with lifetimes in the picosecond range. The resonances were assigned to rotationally excited van der Waals complexes lying in the entrance and exit channels. Resonance peaks observed in the J = 0 calculation broke into multiplets for J > 0 corresponding to the range of allowed helicity states. The Smith lifetime matrix, Q(E), was used to efficiently extract the resonance properties. The largest eigenvalue of Q(E) was used for the position and total width, while the corresponding eigenvector was used to obtain the partial widths. A simple model based on the conventional treatment of rotationally excited van der Waals triatomics was used to predict the resonance spectrum to an accuracy of ∼0.02 kcal/mol. The model predicts the density of resonance states in good agreement with the exact scattering results.
Investigation of the humidity-dependent conductance of single-walled carbon nanotube networks
Authors: Ling Yunfeng , Gu Guiru , Liu Runyu , Lu Xuejun , Kayastha Vijaya , Jones Carissa S. , Shih Wu-Sheng , Janzen Daniel C.
Published: January 2013

In this paper, we investigate the conductance of single walled carbon nanotube (SWCNT) networks at different humidity levels and various device temperatures. The carrier transport processes are analyzed by performing a temperature-dependent conductance study. It is found that the conductance of the SWCNT networks is dominated by the thermal activation carrier hopping over the barriers between CNTs. The average separation between the SWCNTs is found to vary linearly with the humidity levels. The humidity-dependent conductance of the SWCNT network is modeled and compared with the experimental data. The model agrees well with the experimental data.
Relationship between neighbor number and vibrational spectra in disordered colloidal clusters with attractive interactions
Authors: Yunker Peter J. , Zhang Zexin , Gratale Matthew , Chen Ke , Yodh A. G.
Published: January 2013

We study connections between vibrational spectra and average nearest neighbor number in disordered clusters of colloidal particles with attractive interactions. Measurements of displacement covariances between particles in each cluster permit calculation of the stiffness matrix, which contains effective spring constants linking pairs of particles. From the cluster stiffness matrix, we derive vibrational properties of corresponding “shadow” glassy clusters, with the same geometric configuration and interactions as the “source” cluster but without damping. Here, we investigate the stiffness matrix to elucidate the origin of the correlations between the median frequency of cluster vibrational modes and average number of nearest neighbors in the cluster. We find that the mean confining stiffness of particles in a cluster, i.e., the ensemble-averaged sum of nearest neighbor spring constants, correlates strongly with average nearest neighbor number, and even more strongly with median frequency. Further, we find that the average oscillation frequency of an individual particle is set by the total stiffness of its nearest neighbor bonds; this average frequency increases as the square root of the nearest neighbor bond stiffness, in a manner similar to the simple harmonic oscillator.
Direct measurements of collisionally broadened Raman linewidths of CO2 S-branch transitions
Authors: Roy Sukesh , Hsu Paul S. , Jiang Naibo , Gord Joseph R. , Kulatilaka Waruna D. , Stauffer Hans U. , Gord James R.
Published: January 2013

We report direct measurements of S-branch Raman-coherence lifetimes of CO2 resulting from CO2–CO2 and CO2–N2 collisions by employing time-resolved picosecond coherent anti-Stokes Raman scattering spectroscopy. The S-branch (ΔJ = +2) transitions of CO2 with rotational quantum number J = 0–52 were simultaneously excited using a broadband (∼5 nm) laser pulse with a full-width-at-half-maximum duration of ∼115 ps. The coherence lifetimes of CO2 for a pressure range of 0.05–1 atm were measured directly by probing the rotational coherence with a nearly transform-limited, 90-ps-long laser pulse. These directly measured Raman-coherence lifetimes, when converted to collisional linewidth broadening coefficients, differ from the previously reported broadening coefficients extracted from frequency-domain rotational Raman and infrared-absorption spectra and from theoretical calculations by 7%–25%.
New multiferroics based on EuxSr1−xTiO3 nanotubes and nanowires
Authors: Eliseev Eugene A. , Glinchuk Maya D. , Khist Victoria V. , Lee Chan-Woo , Deo Chaitanya S. , Behera Rakesh K. , Morozovska Anna N.
Published: January 2013

Using Landau-Ginzburg-Devonshire theory, we have addressed the complex interplay between structural antiferrodistortive order parameter (oxygen octahedron rotations), polarization and magnetization in EuxSr1−xTiO3 nanosystems. We have calculated the phase diagrams of EuxSr1−xTiO3 bulk, nanotubes and nanowires, which include the antiferrodistortive, ferroelectric, ferromagnetic, and antiferromagnetic phases. For EuxSr1−xTiO3 nanosystems, our calculations show the presence of antiferrodistortive-ferroelectric-ferromagnetic phase or the triple phase at low temperatures (≤10 K). The polarization and magnetization values in the triple phase are calculated to be relatively high (∼50 μC/cm2 and ∼0.5 MA/m). Therefore, the strong coupling between structural distortions, polarization, and magnetization suggests the EuxSr1−xTiO3 nanosystems as strong candidates for possible multiferroic applications.
Incoherent twin boundary migration induced by ion irradiation in Cu
Authors: Li N. , Wang J. , Wang Y. Q. , Serruys Y. , Nastasi M. , Misra A.
Published: January 2013

Grain boundaries can act as sinks for radiation-induced point defects. The sink capability is dependent on the atomic structures and varies with the type of point defects. Using high-resolution transmission electron microscopy, we observed that Σ3{112} incoherent twin boundary (ITB) in Cu films migrates under Cu3+ ion irradiation. Using atomistic modeling, we found that Σ3{112} ITB has the preferred sites for adsorbing interstitials and the preferential diffusion channels along the Shockley partial dislocations. Coupling with the high mobility of grain boundary Shockley dislocations within Σ3{112} ITB, we infer that Σ3{112} ITB migrates through the collective glide of grain boundary Shockley dislocations, driven by a concurrent reduction in the density of radiation-induced defects, which is demonstrated by the distribution of nearby radiation-induced defects.
Experimental investigations on the relations between configurations and radiation patterns of a relativistic magnetron with diffraction output
Authors: Li Wei , Liu Yong-gui , Zhang Jun , Shi Di-fu , Zhang Wei-qi
Published: January 2013

The relations between configurations of a relativistic magnetron with diffraction output (MDO) and radiation patterns obtained by experimental investigations are presented in this paper. A fluorescent lamps array is used to snap microwave patterns radiated from an A6 type MDO. Experimental results are well in agreement with computer simulations. Conclusions obtained from experiments are that (1) when an MDO operates at 2π mode, with all cavities tapered onto the output port, the MDO can directly radiate TE01 mode. (2) TEn1 (n > 0, n is integer) modes can be radiated from a π mode operating MDO with 2n azimuthally symmetric cavities tapered onto the output port. (3) By inserting optimal transition sections into tapered cavities, a pure TE11 microwave can be obtained.
Mechanical properties and scaling laws of nanoporous gold
Authors: Sun Xiao-Yu , Xu Guang-Kui , Li Xiaoyan , Feng Xi-Qiao , Gao Huajian
Published: January 2013

Nanoporous metals are a class of novel nanomaterials with potential applications in many fields such as sensing, catalysis, and fuel cells. The present paper is aimed to investigate atomic mechanisms associated with the uniaxial tensile deformation behavior of nanoporous gold. A phase field method is adopted to generate the bicontinuous open-cell porous microstructure of the material. Molecular dynamics simulations then reveal that the uniaxial tensile deformation in such porous materials is accompanied by an accumulation of stacking faults in ligaments along the loading direction and their junctions with neighboring ligaments, as well as the formation of Lomer–Cottrell locks at such junctions. The tensile strain leads to progressive necking and rupture of some ligaments, ultimately resulting in failure of the material. The simulation results also suggest scaling laws for the effective Young's modulus, yield stress, and ultimate strength as functions of the relative mass density and average ligament size in the material.
Empirical chemosensitivity testing in a spheroid model of ovarian cancer using a microfluidics-based multiplex platform
Authors: Das Tamal , Meunier Liliane , Barbe Laurent , Provencher Diane , Guenat Olivier , Gervais Thomas , Mes-Masson Anne-Marie
Published: January 2013

The use of biomarkers to infer drug response in patients is being actively pursued, yet significant challenges with this approach, including the complicated interconnection of pathways, have limited its application. Direct empirical testing of tumor sensitivity would arguably provide a more reliable predictive value, although it has garnered little attention largely due to the technical difficulties associated with this approach. We hypothesize that the application of recently developed microtechnologies, coupled to more complex 3-dimensional cell cultures, could provide a model to address some of these issues. As a proof of concept, we developed a microfluidic device where spheroids of the serous epithelial ovarian cancer cell line TOV112D are entrapped and assayed for their chemoresponse to carboplatin and paclitaxel, two therapeutic agents routinely used for the treatment of ovarian cancer. In order to index the chemoresponse, we analyzed the spatiotemporal evolution of the mortality fraction, as judged by vital dyes and confocal microscopy, within spheroids subjected to different drug concentrations and treatment durations inside the microfluidic device. To reflect microenvironment effects, we tested the effect of exogenous extracellular matrix and serum supplementation during spheroid formation on their chemotherapeutic response. Spheroids displayed augmented chemoresistance in comparison to monolayer culturing. This resistance was further increased by the simultaneous presence of both extracellular matrix and high serum concentration during spheroid formation. Following exposure to chemotherapeutics, cell death profiles were not uniform throughout the spheroid. The highest cell death fraction was found at the center of the spheroid and the lowest at the periphery. Collectively, the results demonstrate the validity of the approach, and provide the basis for further investigation of chemotherapeutic responses in ovarian cancer using microfluidics technology. In the future, such microdevices could provide the framework to assay drug sensitivity in a timeframe suitable for clinical decision making.
Bipolar resistive switching characteristics of low temperature grown ZnO thin films by plasma-enhanced atomic layer deposition
Authors: Zhang Jian , Yang Hui , Zhang Qi-long , Dong Shurong , Luo J. K.
Published: January 2013

ZnO films deposited by plasma-enhanced atomic layer deposition (PEALD) have been used to investigate resistive memory behavior. The bipolar resistance switching properties were observed in the Al/PEALD-ZnO/Pt devices. The resistance ratio for the high and low resistance states (HRS/LRS) is more than 103, better than ZnO devices deposited by other methods. The dominant conduction mechanisms of HRS and LRS are trap-controlled space charge limited current and Ohmic behavior, respectively. The resistive switching behavior is induced upon the formation/disruption of conducting filaments. This study demonstrated that the PEALD-ZnO films have better properties for the application in 3D resistance random access memory.
Spontaneous three-dimensional magnetic reconnection in merging toroidal plasma experiment
Authors: Ii Toru , Ono Yasushi
Published: January 2013

We investigated a new phenomenon of three-dimensional (3D) magnetic reconnection in TS-4 torus plasma merging experiments by directly measuring the 3D structures of the current sheet. Removal of all toroidal asymmetry of the device reveals that a strong external drive of reconnection inflow increases the toroidal asymmetry of the current sheet only during the reconnection. This spontaneous 3D deformation of the current sheet increases the reconnection outflow as well as the reconnection electric field, probably because local compression of the current sheet to a thickness less than the ion gyroradius triggers its strong dissipation of the current sheet, responsible for the onset of 3D reconnection. These mechanisms indicate that the 3D reconnection is a newly observed spontaneous process of fast reconnection.
Properties of magnetic vortices at elevated temperatures
Authors: Lebecki Kristof M. , Nowak Ulrich
Published: January 2013

Thermal properties of steady-state magnetic vortices in soft materials are numerically evaluated using the recently proposed Landau-Lifshitz-Bloch approach. Circular samples with permalloy-like parameters are simulated. Relevant properties of the vortex core, as its radius, the magnetization drop in its center, and the radius of this magnetization drop are extracted. The dependence of the vortex core radius on temperature agrees well with the theoretical predictions, if only temperature-dependent parameters are taken into account. A new effect is found, which we call magnetization squeezing, resulting from the thermodynamic nature of the Landau-Lifshitz-Bloch approach. Our results show, however, that this squeezing in vortices is a rather weak effect in permalloy.
Evaluation of Sr2MMoO6 (M = Mg, Mn) as anode materials in solid-oxide fuel cells: A neutron diffraction study
Authors: Troncoso L. , Martínez-Lope M. J. , Alonso J. A. , Fernández-Díaz M. T.
Published: January 2013

Sr2MMoO6 (M = Mg, Mn) double perovskites have recently been proposed as anode materials in solid-oxide fuel cells (SOFC). The evolution of their crystal structures has been followed by “in situ” temperature-dependent neutron powder diffraction from 25 °C room temperature (RT) to 930 °C by heating in ultrahigh vacuum (PO2 ≈ 10−6 Torr) in order to simulate the reducing atmosphere corresponding to the working conditions of an anode in a SOFC. At RT, the samples are described as tetragonal (I4/m space group) and monoclinic (P21/n) for M = Mg, Mn, respectively. Sr2MgMoO6 undergoes a structural phase transition from tetragonal to cubic (Fm-3m) below 300 °C; Sr2MnMoO6 experiences two consecutive phase transitions to tetragonal (I4/m) and finally cubic (Fm-3m) at 600 °C and above. In the cubic phases, the absence of octahedral tilting accounts for a good overlap between the oxygen and transition-metal orbitals, resulting in a good electronic conductivity; a high mobility of the oxygen atoms is derived from the elevated displacement parameters, for instance 3.0 Å2 and 4.6 Å2 at 930 °C for M = Mg, Mn, respectively. Both factors contribute to the excellent performance described for these mixed ionic and electronic conductor oxides as anodes in single fuel cells. From dilatometric measurements, the thermal expansion coefficients (TEC) in the cubic region are 12.7 × 10−6 K−1 and 13.0 × 10−6 K−1 for M = Mg and Mn, respectively. These figures are comparable to those obtained from the mentioned structural analysis; moreover, the TECs for the cubic phases perfectly match those of the usual electrolytes in a SOFC.
Hollow cylindrical plasma filament waveguide with discontinuous finite thickness cladding
Authors: Alshershby Mostafa , Hao Zuoqiang , Lin Jingquan
Published: January 2013

We have explored here a hollow cylindrical laser plasma multifilament waveguide with discontinuous finite thickness cladding, in which the separation between individual filaments is in the range of several millimeters and the waveguide cladding thickness is in the order of the microwave penetration depth. Such parameters give a closer representation of a realistic laser filament waveguide sustained by a long stable propagation of femtosecond (fs) laser pulses. We report how the waveguide losses depend on structural parameters like normalized plasma filament spacing, filament to filament distance or pitch, normal spatial frequency, and radius of the plasma filament. We found that for typical plasma parameters, the proposed waveguide can support guided modes of microwaves in extremely high frequency even with a cladding consisting of only one ring of plasma filaments. The loss of the microwave radiation is mainly caused by tunneling through the discontinuous finite cladding, i.e., confinement loss, and is weakly dependent on the plasma absorption. In addition, the analysis indicates that the propagation loss is fairly large compared with the loss of a plasma waveguide with a continuous infinite thickness cladding, while they are comparable when using a cladding contains more than one ring. Compared to free space propagation, this waveguide still presents a superior microwave transmission to some distance in the order of the filamentation length; thus, the laser plasma filaments waveguide may be a potential channel for transporting pulsed-modulated microwaves if ensuring a long and stable propagation of fs laser pulses.
Communication: How to generate and measure anomalous diffusion in simple systems
Authors: Fuliński A.
Published: January 2013

It is shown that in systems with time-dependent and/or spatially nonuniform temperature T(t, r), the diffusion (Brownian motion) is anomalous (AD). A few examples of simple arrangements, easy for experimental realization, are discussed in detail. Proposed measurements will enable also the observation of transitions from normal to anomalous diffusion. New effects are predicted: (i) zero-mean oscillations of T(t) accelerate AD (pumping effect), (ii) the combination of temporal and spatial variations of temperature may lead to superballistic AD, (iii) various forms of T(t, r) may result in non-algebraic AD including exponential diffusion. One can expect similar effects in inflationary systems with time-dependent metric and in expanding/contracting gases.
Enhanced reliability of drift-diffusion approximation for electrons in fluid models for nonthermal plasmas
Authors: Becker M. M. , Loffhagen D.
Published: January 2013

Common fluid models used for the description of electron transport in nonthermal discharge plasmas are subject to substantial restrictions if the electron energy transport significantly influences the discharge behaviour. A drift-diffusion approach is presented which is based on a multiterm approximation of the electron velocity distribution function and overcomes some of these restrictions. It is validated using a benchmark model and applied for the analysis of argon discharge plasmas at low and atmospheric pressure. The results are compared to those of common drift-diffusion models as well as to experimental data. It is pointed out that fluid models are able to describe nonlocal phenomena caused by electron energy transport, if the energy transport is consistently described. Numerical difficulties that frequently occur when the conventional drift-diffusion model is consistently applied are avoided by the proposed method.
Communication: A simple analytical formula for the free energy of ligand–receptor-mediated interactions
Authors: Angioletti-Uberti Stefano , Varilly Patrick , Mognetti Bortolo M. , Tkachenko Alexei V. , Frenkel Daan
Published: January 2013

Recently [P. Varilly, S. Angioletti-Uberti, B. M. Mognetti, and D. Frenkel, “A general theory of DNA-mediated and other valence-limited colloidal interactions,” J. Chem. Phys. 137, 094108 (2012)10.1063/1.4748100], we presented a general theory for calculating the strength and properties of colloidal interactions mediated by ligand–receptor bonds (such as those that bind DNA-coated colloids). In this Communication, we derive a surprisingly simple analytical form for the interaction free energy, which was previously obtainable only via a costly numerical thermodynamic integration. As a result, the computational effort to obtain potentials of interaction is significantly reduced. Moreover, we can gain insight from this analytic expression for the free energy in limiting cases. In particular, the connection of our general theory to other previous specialised approaches is now made transparent. This important simplification will significantly broaden the scope of our theory.
Effects of defoliation intensity at the first grazing of forage rape (Brassica napus L.) by dairy cattle on subsequent regrowth potential, total DM consumed, nutritive characteristics and nutrient selection
Authors: Ward G. N. , Jacobs J. L.
Published: January 2013

The use of summer brassica forage crops in dryland dairy systems in southern Victoria is considered a key component of the feed base as they provide home-grown forage with high nutritive characteristics during a period where perennial ryegrass growth is limited due to high summer temperatures and low soil water content. Current knowledge on the use of single-grazing brassica crops such as turnips (Brassica rapa L.) is well defined; however, information on the management of regrowth brassica species that can provide multiple grazings is more limited. The present experiment determined the effect of different grazing regimes (high, medium and low defoliation intensity) at the first grazing on subsequent regrowth capability and nutritive characteristics of Winfred (Brassica napus L.) over the summer growing period across 2 years. We hypothesised that intensive defoliation of a summer regrowth brassica at the first grazing will result in lower total DM yields and harvested estimated metabolisable energy (ME) and crude protein per hectare for the growing season than do more lax grazing options that results in less DM removal at the first grazing. Total DM and estimated ME consumed over the growing period varied between years. In Year 1, more (P < 0.05) DM was consumed at the first grazing and less (P < 0.05) at the subsequent grazing for the high-intensity treatment. However, both total DM and estimated ME consumed were higher (P < 0.05) for the high-intensity treatment than for the low-intensity treatment, while in Year 2, there were no differences between the treatments. Nutritive characteristics and mineral concentrations were relatively unaffected by grazing regimes. The results of the present experiment indicated that the optimum grazing management to maximise total DM yields and consumption of spring-sown Winfred will vary depending on the seasonal growing conditions. In years where moisture stress will be limiting crop growth, a high defoliation-intensity first grazing that consumes a high proportion of DM on offer, including some of the main stem, will maximise the total DM grown and consumed from the crop. Care, however, should be taken not to remove all axillary buds from the remaining stems. In summers where moisture stress is not likely to seriously restrict crop growth, a medium defoliation-intensity grazing where the leaf and petiole, but little of the stem, are removed will maximise DM regrowth, leading to maximum total DM grown for the season. A high defoliation-intensity first grazing that removes at least half the stem is, under these conditions, likely to remove too many axillary buds and reduce water-soluble carbohydrate reserves required for DM regrowth, while a lax first grazing will result in a lower DM regrowth.
Effect of high altitude on nutrient digestibility, rumen fermentation and basal metabolism rate in Chinese Holstein cows on the Tibetan plateau
Authors: Qiao G. H. , Yu C. Q. , Li J. H. , Yang X. , Zhu X. Q. , Zhou X. H.
Published: January 2013

Two experiments were conducted to investigate the effect of two altitudes (3600 and 1600 m) on nutrient digestibility, rumen fermentation and basal metabolism rate in Chinese Holstein cows. Experiment 1 was conducted to investigate the effect of high altitude (3600 m) on rumen fermentation, in vitro dry matter degradability, and nitrogen metabolism compared with low altitude (1600 m) in Chinese Holstein cows. Results indicated that total volatile fatty acids concentration, total gas production and gas coefficient a, b and c, efficiency of microbial protein synthesis and in vitro dry matter degradability were lower at 3600 m than 1600 m (P < 0.05). The number of protozoa and ammonia nitrogen concentration was higher at 3600 m than 1600 m (P < 0.05). We concluded that carbohydrate fermentation in the rumen was impaired, and ammonia nitrogen used for microbial nitrogen synthesis was also decreased at high altitude of 3600 m compared with 1600 m. Experiment 2 was conducted in vivo to investigate the effect of high altitude on apparent nutrient digestibility and basal metabolism rate in Chinese Holstein cows. Results indicated that the apparent digestibility of the diet’s dry matter, organic matter, neutral detergent fibre and acid detergent fibre was lower at 3600 m than those at 1600 m, respectively (P < 0.05). In Chinese Holstein cows, basal metabolism rate was increased with increasing level of altitude (P < 0.05). The results indicated that the high altitude of the Tibetan plateau impaired rumen fermentation and elevated the basal metabolism rate of Chinese Holstein cows.
Consequences of Corymbia (Myrtaceae) hybridisation on leaf-oil profiles
Authors: Hayes R. Andrew , Nahrung Helen F. , Lee David J.
Published: January 2013

The present study examines patterns of heritability of plant secondary metabolites following hybridisation among three genetically homogeneous taxa of spotted gum (Corymbia henryi (S.T.Blake) K.D.Hill & L.A.S.Johnson, C. citriodora subsp. variegata (F.Muell.) K.D.Hill & L.A.S.Johnson and C. citriodora (Hook.) K.D.Hill & L.A.S.Johnson subsp. citriodora (section Maculatae), and their congener C. torelliana (F.Muell.) K.D. Hill & L.A.S.Johnson (section Torellianae)). Hexane extracts of leaves of all four parent taxa were statistically distinguishable (ANOSIM: global R = 0.976, P = 0.008). Hybridisation patterns varied among the taxa studied, with the hybrid formed with C. citriodora subsp. variegata showing an intermediate extractive profile between its parents, whereas the profiles of the other two hybrids were dominated by that of C. torelliana. These different patterns in plant secondary-metabolite inheritance may have implications for a range of plant–insect interactions.
Experimental warming and long-term vegetation dynamics in an alpine heathland
Authors: Wahren C.-H. , Camac J. S. , Jarrad F. C. , Williams R. J. , Papst W. A. , Hoffmann A. A.
Published: January 2013

High mountain ecosystems are vulnerable to the effects of climate warming and Australia’s alpine vegetation has been identified as particularly vulnerable. Between 2004 and 2010, we monitored vegetation changes in a warming experiment within alpine open grassy-heathland on the Bogong High Plains, Victoria, Australia. The study was part of the International Tundra Experiment (ITEX Network) and used open-topped chambers (OTC) to raise ambient growing-season temperatures by ~1°C at two sites. We assessed the effects of experimental warming on vegetation composition, diversity and cover using ordination, linear models and hierarchical partitioning. Results were compared with vegetation changes at four long-term (non-ITEX) monitoring sites in similar vegetation sampled from 1979 to 2010. The warming experiment coincided with the driest 13-year period (1996–2009) since the late 1880s. At the ITEX sites, between 2004 and 2010, graminoid cover decreased by 25%, whereas forb and shrub cover increased by 9% and 20%, respectively. Mean canopy height increased from 7 cm to 10 cm and diversity increased as a result of changes in relative abundance, rather than an influx of new species. These vegetation changes were similar to those at the four non-ITEX sites for the same period and well within the range of changes observed over the 31-year sampling period. Changes at the non-ITEX sites were correlated with a decrease in annual precipitation, increase in mean minimum temperatures during spring and increase in mean maximum temperature during autumn. Vegetation changes induced by the warming experiment were small rather than transformational and broadly similar to changes at the long-term monitoring sites. This suggests that Australian alpine vegetation has a degree of resilience to climate change in the short to medium term (20–30 years). In the long term (>30 years), drought may be as important a determinant of environmental change in alpine vegetation as rising temperatures. Long-term vegetation and climate data are invaluable in interpreting results from short-term (≤10 years) experiments.
The waterlogging/salinity interaction in higher plants revisited – focusing on the hypoxia-induced disturbance to K+ homeostasis
Authors: Barrett-Lennard Edward G. , Shabala Sergey N.
Published: January 2013

Salinity and waterlogging (root-zone hypoxia) are abiotic stresses that often occur together on saltland. It is widely recognised that these two factors interact to increase Na+ and/or Cl– concentrations in shoots, which can have adverse effects on plant growth and survival. This review expands on this understanding, providing evidence that the adverse effects of the interaction are also associated with a disturbance to plant K+ homeostasis. This conclusion is based on a comparative analysis of changes in ion concentrations and growth reported in the literature between species (glycophytes vs halophytes) and within a single species (Hordeum marinum L.). Comparisons between species show that hypoxia under saline conditions causes simultaneous increases in Na+ and Cl– concentrations and decreases in K+ concentrations in shoots and that these changes can all be related to changes in shoot dry mass. Comparisons between accessions of a single species (Hordeum maritima L.) strengthen the argument, with increases in Na+ and decreases in K+ being related to decreases in shoot relative growth rate.
Structural basis for C-ribosylation in the alnumycin A biosynthetic pathway
Authors: Oja Terhi , Niiranen Laila , Sandalova Tatyana , Klika Karel D. , Niemi Jarmo , Mäntsälä Pekka , Schneider Gunter , Metsä-Ketelä Mikko
Published: January 2013

Alnumycin A is an exceptional aromatic polyketide that contains a carbohydrate-like 4′-hydroxy-5′-hydroxymethyl-2′,7′-dioxane moiety attached to the aglycone via a carbon−carbon bond. Recently, we have identified the
D
-ribose-5-phosphate origin of the dioxane unit and demonstrated that AlnA and AlnB are responsible for the overall C-ribosylation reaction. Here, we provide direct evidence that AlnA is a natural C-glycosynthase, which catalyzes the attachment of
D
-ribose-5-phosphate to prealnumycin by formation of the C
8
−C
1′
bond as demonstrated by the structure of the intermediate alnumycin P. This compound is subsequently dephosphorylated by AlnB, an enzyme of the haloacid dehalogenase superfamily. Structure determination of the native trimeric AlnA to 2.1-Å resolution revealed a highly globular fold encompassing an α/β/α sandwich. The crystal structure of the complex with
D
-ribose-5-phosphate indicated that the phosphosugar is bound in the open-chain configuration. Identification of residues E29, K86, and K159 near the C-1 carbonyl of the ligand led us to propose that the carbon−carbon bond formation proceeds through a Michael-type addition. Determination of the crystal structure of the monomeric AlnB in the open conformation to 1.25-Å resolution showed that the protein consists of core and cap domains. Modeling of alnumycin P inside the cap domain positioned the phosphate group next to a Mg
2+
ion present at the junction of the domains. Mutagenesis data were consistent with the canonical reaction mechanism for this enzyme family revealing the importance of residues D15 and D17 for catalysis. The characterization of the prealnumycin C-ribosylation illustrates an alternative means for attachment of carbohydrates to natural products.
Larvae of the parasitoid wasp
Ampulex compressa
sanitize their host, the American cockroach, with a blend of antimicrobials
Authors: Herzner Gudrun , Schlecht Anja , Dollhofer Veronika , Parzefall Christopher , Harrar Klaus , Kreuzer Andreas , Pilsl Ludwig , Ruther Joachim
Published: January 2013

Food resources contaminated with spoilage or pathogenic microorganisms pose severe problems to all higher organisms. Here, we describe a food-hygienic strategy of the emerald cockroach wasp
Ampulex compressa
. The wasp larvae develop on and inside the American cockroach
Periplaneta americana
, a host that can harbor various putrefactive microbes, as well as human and insect pathogens. From
P. americana
, we isolated the Gram-negative bacterium
Serratia marcescens
, which is a potent entomopathogen that can rapidly kill insect larvae. It is also known as a food contaminant and as an opportunistic human pathogen. Using behavioral observations and chemical analyses, we demonstrated that
A. compressa
larvae impregnate their cockroach hosts from inside with large amounts of an oral secretion containing a blend of γ-lactones and isocoumarins with (
R
)-(-)-mellein [(
R
)-(-)-3,4-diydro-8-hydroxy-3-methylisocoumarin] and micromolide [(4
R
,9
Z
)-octadec-9-en-4-olide] as dominant components. We fractionated hexane extracts of the secretion and investigated the antimicrobial properties of the fraction containing the lactones and isocoumarins, as well as of synthetic (
R
)-(-)-mellein and micromolide, against
S. marcescens
and a Gram-positive bacterium,
Staphylococcus hyicus
, in broth microdilution assays. The test fraction inhibited growth of both tested bacteria. The activity of the fraction against
S. marcescens
was explained by (
R
)-(-)-mellein alone, and the activity against
S. hyicus
was explained by the combined action of (
R
)-(-)-mellein and micromolide. Our data suggest that the specific combination of antimicrobials in the larval secretion provides an effective frontline defense against the unpredictable spectrum of microbes that
A. compressa
larvae may encounter during their development inside their cockroach hosts.
Incoherent feed-forward regulatory logic underpinning glucocorticoid receptor action
Authors: Chen Sheng-hong , Masuno Kiriko , Cooper Samantha B. , Yamamoto Keith R.
Published: January 2013

The complexity and specificity of metazoan transcription are determined by combinatorial control of the composition and activity of regulatory complexes. To investigate the basis of this specificity, we focused on the glucocorticoid receptor (GR), a single regulatory factor that integrates multiple signals to give rise to many distinct patterns of expression. We measured the expression of a set of genes, each directly GR-regulated, but by different mechanisms in two cell lines. We varied ligand (dose, chemistry, and duration of treatment), GR (expression level and functionality), and a non-GR regulatory factor that commonly interacts with GR. Our study revealed distinct expression patterns within this set of genes, but all could be modeled by an incoherent feed-forward regulatory logic. Cellular signals, operating on GR and other factors within regulatory complexes, may define and modulate the kinetics and strength of the activating or inhibitory paths of the regulatory logic. Thus, characterizing systems behavior by perturbing single or multiple signals can reveal general principles of regulation, providing an approach to the dissection and deconvolution of combinatorial control.
Structural uniformity of neocortex, revisited
Authors: Carlo C. Nikoosh , Stevens Charles F.
Published: January 2013

The number of neurons under a square millimeter of cortical surface has been reported to be the same across five cortical areas and five species [Rockel et al. (1980)
Brain
103(2):221–244] despite differences in cortical thickness between the areas. Although the accuracy of this result has been the subject of sharp debate since its publication approximately 30 y ago, the experiments of Rockel et al. have never been directly replicated with modern stereological methods. We have replicated these experiments and confirm the accuracy of the original report. In addition, we have observed that the number of glial cells under a square millimeter of cortical surface depends on cortical thickness, but not on cortical area or species.