bluuebunny/crossref_metadata_2025 huggingface dataset:
Local structural effects on orientational relaxation of OH-bond in liquid water over short to intermediate timescales
Authors: Lin S. R. , Tang Ping-Han , Wu Ten-Ming
Published: December 2014

By simulating the rigid simple point charge extended model at temperature T = 300 K, the orientational relaxation of the OH-bond in water was investigated over short to intermediate timescales, within which molecules undergo inertial rotation and libration and then enter the rotational diffusion regime. According to the second-cumulant approximation, the orientational time correlation function (TCF) of each axis that is parallel or perpendicular to an OH-bond is related to an effective rotational density of states (DOS), which is determined using the power spectra of angular velocity autocorrelation functions (AVAFs) of the other two axes. In addition, the AVAF power spectrum of an axis was approximated as the rotational stable instantaneous normal mode (INM) spectrum of the axis. As described in a previous study [S. L. Chang, T. M. Wu, and C. Y. Mou, J. Chem. Phys. 121, 3605 (2004)], simulated molecules were classified into subensembles, according to either the local structures or the H-bond configurations of the molecules. For global molecules and the classified subensembles, the simulation results for the first- and second-rank orientational TCFs were compared with the second-cumulant predictions obtained using the effective rotational DOSs and the rotational stable-INM spectra. On short timescales, the OH-bond in water behaves similar to an inertial rotor and its anisotropy is lower than that of a water molecule. For molecules with three or more H-bonds, the OH-bond orientational TCFs are characterized by a recurrence, which is an indication for libration of the OH-bond. The recurrence can generally be described by the second-cumulant prediction obtained using the rotational stable-INM spectra; however, the orientational TCFs after the recurrence switch to a behavior similar to that predicted using the AVAF power spectra. By contrast, the OH-bond orientational TCFs of molecules initially connected with one or two H-bonds decay monotonically or exhibit a weak recurrence, indicating rapid relaxation into the rotational diffusion regime after the initial Gaussian decay. In addition to accurately describing the Gaussian decay, the second-cumulant predictions formulated using the rotational stable-INM spectra and the AVAF power spectra serve as the upper and lower limits, respectively, for the OH-bond orientational TCFs of these molecules after the Gaussian decay.
Non-geometric fluxes, quasi-Hopf twist deformations, and nonassociative quantum mechanics
Authors: Mylonas Dionysios , Schupp Peter , Szabo Richard J.
Published: December 2014

We analyse the symmetries underlying nonassociative deformations of geometry in non-geometric R-flux compactifications which arise via T-duality from closed strings with constant geometric fluxes. Starting from the non-abelian Lie algebra of translations and Bopp shifts in phase space, together with a suitable cochain twist, we construct the quasi-Hopf algebra of symmetries that deforms the algebra of functions and the exterior differential calculus in the phase space description of nonassociative R-space. In this setting, nonassociativity is characterised by the associator 3-cocycle which controls non-coassociativity of the quasi-Hopf algebra. We use abelian 2-cocycle twists to construct maps between the dynamical nonassociative star product and a family of associative star products parametrized by constant momentum surfaces in phase space. We define a suitable integration on these nonassociative spaces and find that the usual cyclicity of associative noncommutative deformations is replaced by weaker notions of 2-cyclicity and 3-cyclicity. Using this star product quantization on phase space together with 3-cyclicity, we formulate a consistent version of nonassociative quantum mechanics, in which we calculate the expectation values of area and volume operators, and find coarse-graining of the string background due to the R-flux.
Temperature effects on prevalent structures of hydrated Fe+ complexes: Infrared spectroscopy and DFT calculations of Fe+(H2O)n (n = 3–8)
Authors: Ohashi Kazuhiko , Sasaki Jun , Yamamoto Gun , Judai Ken , Nishi Nobuyuki , Sekiya Hiroshi
Published: December 2014

Hydrated Fe+ ions are produced in a laser-vaporization cluster source of a triple quadrupole mass spectrometer. The Fe+(H2O)n (n = 3–8) complexes are mass-selected and probed with infrared (IR) photodissociation spectroscopy in the OH-stretch region. Density functional theory (DFT) calculations are also carried out for analyzing the experimental IR spectra and for evaluating thermodynamic quantities of low-lying isomers. Solvation through H-bonding instead of direct coordination to Fe+ is observed already at n = 3, indicating the completion of the first hydration shell with two H2O molecules. Size dependent variations in the spectra for n = 5–7 provide evidence for the second-shell completion at n = 6, where a linearly coordinated Fe+(H2O)2 subunit is solvated with four H2O molecules. Overall spectral features for n = 3–8 agree well with those predicted for 2-coordinated structures. DFT calculations predict that such 2-coordinated structures are lowest in energy for smaller n. However, 4-coordinated isomers are predicted to be more stable for n = 7 and 8; the energy ordering is in conflict with the IR spectroscopic observation. Examination of free energy as a function of temperature suggests that the ordering of the isomers at warmer temperatures can be different from the ordering near 0 K. For n = 7 and 8, the 4-coordinated isomers should be observed at low temperatures because they are lowest in enthalpy. Meanwhile, outer-shell waters in the 2-coordinated structures are bound less rigidly; their contribution to entropy is rather large. The 2-coordinated structures become abundant at warmer temperatures, owing to the entropy effect.
The impact of anisotropy and interaction range on the self-assembly of Janus ellipsoids
Authors: Ruth D. P. , Gunton J. D. , Rickman J. M. , Li Wei
Published: December 2014

We assess the roles of anisotropy and interaction range on the self-assembly of Janus colloidal particles. In particular, Monte Carlo simulation is employed to investigate the propensity for the formation of aggregates in a spheroidal model of a colloid having a relatively short-ranged interaction that is consistent with experimentally realizable systems. By monitoring the equilibrium distribution of aggregates as a function of temperature and density, we identify a “micelle” transition temperature and discuss its dependence on particle shape. We find that, unlike systems with longer ranged interactions, this system does not form micelles below a transition temperature at low density. Rather, larger clusters comprising 20–40 particles characterize the transition. We then examine the dependence of the second virial coefficient on particle shape and well width to determine how these important system parameters affect aggregation. Finally, we discuss possible strategies suggested by this work to promote self-assembly for the encapsulation of particles.
The fabrication of polyfluorene and polycarbazole-based photovoltaic devices using an air-stable process route
Authors: Bovill E. , Yi H. , Iraqi A. , Lidzey D. G.
Published: December 2014

We report a comparative study based on the fabrication of polymer:fullerene photovoltaic (PV) devices incorporating carbazole, fluorene, and a PTB based co-polymer. We have explored the efficiency and performance of such devices when the active polymer:fullerene layer is deposited by spin-casting either under nitrogen or ambient conditions. We show that PV devices based on carbazole and fluorene based materials have very similar power conversion efficiencies when processed under both air and nitrogen, with other photobleaching measurements suggesting that such materials have comparatively enhanced photostability. Devices based on the PTB co-polymer, however, have reduced efficiency when processed in air.
Communication: Active space decomposition with multiple sites: Density matrix renormalization group algorithm
Authors: Parker Shane M. , Shiozaki Toru
Published: December 2014

We extend the active space decomposition method, recently developed by us, to more than two active sites using the density matrix renormalization group algorithm. The fragment wave functions are described by complete or restricted active-space wave functions. Numerical results are shown on a benzene pentamer and a perylene diimide trimer. It is found that the truncation errors in our method decrease almost exponentially with respect to the number of renormalization states M, allowing for numerically exact calculations (to a few μEh or less) with M = 128 in both cases. This rapid convergence is because the renormalization steps are used only for the interfragment electron correlation.
Local formation of nitrogen-vacancy centers in diamond by swift heavy ions
Authors: Schwartz J. , Aloni S. , Ogletree D. F. , Tomut M. , Bender M. , Severin D. , Trautmann C. , Rangelow I. W. , Schenkel T.
Published: December 2014

We exposed nitrogen-implanted diamonds to beams of swift heavy ions (∼1 GeV, ∼4 MeV/u) and find that these irradiations lead directly to the formation of nitrogen vacancy (NV) centers, without thermal annealing. We compare the photoluminescence intensities of swift heavy ion activated NV− centers to those formed by irradiation with low-energy electrons and by thermal annealing. NV− yields from irradiations with swift heavy ions are 0.1 of yields from low energy electrons and 0.02 of yields from thermal annealing. We discuss possible mechanisms of NV center formation by swift heavy ions such as electronic excitations and thermal spikes. While forming NV centers with low efficiency, swift heavy ions could enable the formation of three dimensional NV− assemblies over relatively large distances of tens of micrometers. Further, our results show that NV center formation is a local probe of (partial) lattice damage relaxation induced by electronic excitations from swift heavy ions in diamond.
Quantitative estimation of the spin-wave features supported by a spin-torque-driven magnetic waveguide
Authors: Consolo Giancarlo , Currò Carmela , Valenti Giovanna
Published: December 2014

The main features of the spin-waves excited at the threshold via spin-polarized currents in a one-dimensional normally-to-plane magnetized waveguide are quantitatively determined both analytically and numerically. In particular, the dependence of the threshold current, frequency, wavenumber, and decay length is investigated as a function of the size of the nanocontact area through which the electric current is injected. From the analytical viewpoint, such a goal has required to solve the linearized Landau-Lifshitz-Gilbert-Slonczewski equation together with boundary and matching conditions associated with the waveguide geometry. Owing to the complexity of the resulting transcendent system, particular solutions have been obtained in the cases of elongated and contracted nanocontacts. These results have been successfully compared with those arising from numerical integration of the abovementioned transcendent system and with micromagnetic simulations. This quantitative agreement has been achieved thanks to the model here considered which takes explicitly into account the diagonal demagnetizing factors of a rectangular prism as well as the dependence of the relaxation rate on the wavenumber. Our analysis confirmed that the spin-wave features supported by such a waveguide geometry are significantly different from the ones observed in classical two-dimensional nanocontact devices. Moreover, it has been proved that the characteristic parameters depend strongly on the material properties and on the modulus of external field, but they could be independent of the nanocontact length. Finally, it is shown that spin-transfer oscillators based on contracted nanocontacts have a better capability to transmit spin-waves over large distances.
Gallium hole traps in irradiated KTiOPO4:Ga crystals
Authors: Grachev V. , Meyer M. , Hunt A. W. , Malovichko G.
Published: December 2014

Nominally pure and gallium doped single crystals of potassium titanyl phosphate (KTiOPO4) have been studied by Electron Paramagnetic Resonance at low temperatures before and after irradiation. Irradiation with 20 MeV electrons performed at room temperature and liquid nitrogen temperature caused an appearance of electrons and holes. Gallium impurities act as hole traps in KTiOPO4 creating Ga4+ centers. Two different Ga4+ centers were observed, Ga1 and Ga2. The Ga1 centers are dominant in Ga-doped samples. For the Ga1 center, a superhyperfine structure with one nucleus with nuclear spin ½ was registered and attributed to the interaction of gallium electrons with a phosphorus nucleus or proton in its surrounding. In both Ga1 and Ga2 centers, Ga4+ ions substitute for Ti4+ ions, but with a preference to one of two electrically distinct crystallographic positions (site selective substitution). The Ga doping eliminates one of the shortcomings of KTP crystals—ionic conductivity of bulk crystals. However, this does not improve significantly the resistance of the crystals to electron and γ-radiation.
Viscoelastic modeling and experimental characterization of thermo-electromechanical response of 1–3 piezocomposites
Authors: Jayendiran R. , Arockiarajan A.
Published: December 2014

The viscoelastic behaviour of 1–3 piezocomposites with different volume fractions and bulk piezoceramics is studied under thermal environment subjected to electrical loading. Experiments are conducted to measure the temperature dependent effective properties based on IEEE standards and time dependent thermo-electromechanical response of 1–3 piezocomposites and piezoceramic subjected to high cyclic electrical loading under elevated thermal environment. The temperature dependent effective properties are predicted using the proposed numerical model based on unit cell approach and implemented into the viscoelastic model to predict the time dependent thermo-electro-elastic effective properties. The predicted effective properties are incorporated in a finite element based 3-D micromechanical model to predict the time dependent thermo-electro-mechanical performance behaviour of 1–3 piezocomposites. Comparison between the experiments and simulations shows that this model can reproduce the characteristics of time dependent non-linear electromechanical response under thermal environment. It is observed that the variation in fiber volume fraction and elevated operating temperature has a significant influence on the response of the 1–3 piezocomposites.
Numerical simulation of the sign switching of the electrostatic force between charged conducting particles from repulsive to attractive
Authors: Murovec T. , Brosseau C.
Published: December 2014

Coulombic interaction remains the framework for understanding a variety of features in the physical world. Through ab initio three-dimensional numerical simulations of the electrostatic forces (EFs) between vacuum-separated charged particles, at least one of them having doughnut geometry, we analyze their size, gap distance, orientation, and shape dependence. This analysis predicts a gap distance-induced transition in the sign of the EF, from repulsive to attractive occurring as the particles come closer, which is consistent with the two-sphere and two-ellipsoid cases. This transition is manifested via a static charge compensation mechanism that is the non-uniform redistribution of charges at the surfaces of the two particles. To be specific, we focus on a variety of examples of the close proximity attraction. We observe and quantitatively analyze the charge distribution as we operate a lateral displacement of one particle with respect to the other. We show that a pair of metal spheres, ellipsoids, and doughnut-shaped particles held at unequal voltages share the same universal scaling law when they are in close proximity. In light of our findings, we also point out that the calculated EF is singular as the separation distance vanishes and scales as the inverse of the gap distance between the two particles. Additionally, the work highlights the changes in the capacitance coefficients which are strongly affected by proximity effect of the two particles.
[N(CH3)3H]2ZnCl4: Ferroelectric properties and characterization of phase transitions by Raman spectroscopy
Authors: Ben Bechir M. , Karoui K. , Bulou A. , Tabellout M. , Guidara K. , Ben Rhaiem A.
Published: December 2014

The X-ray powder diffraction pattern shows that at room temperature, [N(CH3)3H]2ZnCl4 is crystallized in the orthorhombic system with Pnma space group. The phase transitions at T1 = 255 K, T2 = 282 K, T3 = 302 K, T4 = 320 K, and T5 = 346 K have been confirmed by the differential scanning calorimetry. The electrical technique was measured in the 10−1–107 Hz frequency range and 233–363 K temperature intervals. The temperature dependence of the dielectric constant at different temperatures proved that this compound is ferroelectric below 282 K. Besides, [N(CH3)3 H]2ZnCl4 shows classical ferroelectric behaviour near curie temperature. In order to characterize the phase transitions, Raman spectra have been recorded in the temperature range of 233–383 K and the frequency range related to the internal and external vibrations of the cations and anions (90–4000 cm−1). The temperature dependence of the Raman line shifts ν and the half-width Δν detects all phase transitions and confirms their nature, especially at 282 K that corresponds to the ferroelectric-paraelectric phase transition.
Incorporation model of N into GaInNAs alloys grown by radio-frequency plasma-assisted molecular beam epitaxy
Authors: Aho A. , Korpijärvi V.-M. , Tukiainen A. , Puustinen J. , Guina M.
Published: December 2014

We present a Maxwell-Boltzmann electron energy distribution based model for the incorporation rate of nitrogen into GaInNAs grown by molecular beam epitaxy (MBE) using a radio frequency plasma source. Nitrogen concentration is predicted as a function of radio-frequency system primary resistance, N flow, and RF power, and group III growth rate. The semi-empirical model is shown to be repeatable with a maximum error of 6%. The model was validated for two different MBE systems by growing GaInNAs on GaAs(100) with variable nitrogen composition of 0%–6%.
One-dimensional particle simulations of Knudsen-layer effects on D-T fusion
Authors: Cohen Bruce I. , Dimits Andris M. , Zimmerman George B. , Wilks Scott C.
Published: December 2014

Particle simulations are used to solve the fully nonlinear, collisional kinetic equation describing the interaction of a high-temperature, high-density, deuterium-tritium plasma with absorbing boundaries, a plasma source, and the influence of kinetic effects on fusion reaction rates. Both hydrodynamic and kinetic effects influence the end losses, and the simulations show departures of the ion velocity distributions from Maxwellian due to the reduction of the population of the highest energy ions (Knudsen-layer effects). The particle simulations show that the interplay between sources, plasma dynamics, and end losses results in temperature anisotropy, plasma cooling, and concomitant reductions in the fusion reaction rates. However, for the model problems and parameters considered, particle simulations show that Knudsen-layer modifications do not significantly affect the velocity distribution function for velocities most important in determining the fusion reaction rates, i.e., the thermal fusion reaction rates using the local densities and bulk temperatures give good estimates of the kinetic fusion reaction rates.
Generation of quasi-monoenergetic carbon ions accelerated parallel to the plane of a sandwich target
Authors: Wang J. W. , Murakami M. , Weng S. M. , Xu H. , Ju J. J. , Luan S. X. , Yu W.
Published: December 2014

A new ion acceleration scheme, namely, target parallel Coulomb acceleration, is proposed in which a carbon plate sandwiched between gold layers is irradiated with intense linearly polarized laser pulses. The high electrostatic field generated by the gold ions efficiently accelerates the embedded carbon ions parallel to the plane of the target. The ion beam is found to be collimated by the concave-shaped Coulomb potential. As a result, a quasi-monoenergetic and collimated C6+-ion beam with an energy exceeding 10 MeV/nucleon is produced at a laser intensity of 5 × 1019 W/cm2.
Dielectric stress tests and capacitance-voltage analysis to evaluate the effect of post deposition annealing on Al2O3 films deposited on GaN
Authors: Yeluri Ramya , Liu Xiang , Guidry Matthew , Koksaldi Onur S. , Lal Shalini , Kim Jeonghee , Lu Jing , Keller Stacia , Mishra Umesh K.
Published: December 2014

Systematic stress tests that help to evaluate the stability and dielectric performance of Al2O3 films under DC bias conditions are reported. Capacitance-voltage (C-V) curves were monitored for changes after subjecting the dielectric film to constant forward and reverse bias stress. Stress tests, along with C-V analysis, are used to evaluate the effect of post deposition annealing on Metal-Organic Chemical Vapor Deposition) Al2O3 films deposited on GaN. The individual benefits and drawbacks of each film and anneal condition were identified. These suggest that the anneals can be tailored to the unannealed film characteristics to achieve desired improvements in performance. It is found that post deposition annealing in forming gas improves performance under reverse bias stress by reducing the fixed charge and the field in the oxide but does not improve performance under forward bias.
Effect of copper surface pre-treatment on the properties of CVD grown graphene
Authors: Kim Min-Sik , Woo Jeong-Min , Geum Dae-Myeong , Rani J. R. , Jang Jae-Hyung
Published: December 2014

Here, we report the synthesis of high quality monolayer graphene on the pre-treated copper (Cu) foil by chemical vapor deposition method. The pre-treatment process, which consists of pre-annealing in a hydrogen ambient, followed by diluted nitric acid etching of Cu foil, helps in removing impurities. These impurities include native copper oxide and rolling lines that act as a nucleation center for multilayer graphene. Raman mapping of our graphene grown on pre-treated Cu foil primarily consisted of ∼98% a monolayer graphene with as compared to 75 % for the graphene grown on untreated Cu foil. A high hydrogen flow rate during the pre-annealing process resulted in an increased I2D/IG ratio of graphene up to 3.55. Uniform monolayer graphene was obtained with a I2D/IG ratio and sheet resistance varying from 1.84 – 3.39 and 1110 – 1290 Ω/□, respectively.
Understanding density functional theory (DFT) and completing it in practice
Authors: Bagayoko Diola
Published: December 2014

We review some salient points in the derivation of density functional theory (DFT) and of the local density approximation (LDA) of it. We then articulate an understanding of DFT and LDA that seems to be ignored in the literature. We note the well-established failures of many DFT and LDA calculations to reproduce the measured energy gaps of finite systems and band gaps of semiconductors and insulators. We then illustrate significant differences between the results from self consistent calculations using single trial basis sets and those from computations following the Bagayoko, Zhao, and Williams (BZW) method, as enhanced by Ekuma and Franklin (BZW-EF). Unlike the former, the latter calculations verifiably attain the absolute minima of the occupied energies, as required by DFT. These minima are one of the reasons for the agreement between their results and corresponding, experimental ones for the band gap and a host of other properties. Further, we note predictions of DFT BZW-EF calculations that have been confirmed by experiment. Our subsequent description of the BZW-EF method ends with the application of the Rayleigh theorem in the selection, among the several calculations the method requires, of the one whose results have a full, physics content ascribed to DFT. This application of the Rayleigh theorem adds to or completes DFT, in practice, to preserve the physical content of unoccupied, low energy levels. Discussions, including implications of the method, and a short conclusion follow the description of the method. The successive augmentation of the basis set in the BZW-EF method, needed for the application of the Rayleigh theorem, is also necessary in the search for the absolute minima of the occupied energies, in practice.
Fundamental limitations of the local approximation for electron distribution function and fluid model in bounded plasmas
Authors: Krasilnikov M. B. , Kapustin K. D. , Kudryavtsev A. A.
Published: December 2014

It is shown that the local approximation for computing the electron distribution function depends both on the ratio between the energy relaxation length and a characteristic plasma length and on the ratio between heating and ambipolar electric fields. In particular, the local approximation is not valid at the discharge periphery even at high pressure due to the fact that the ambipolar electric field practically always is larger than the heating electric field.
Intraspecific variation in leaf growth of wheat (Triticum aestivum) under Australian Grain Free Air CO2 Enrichment (AGFACE): is it regulated through carbon and/or nitrogen supply?
Authors: Thilakarathne Chamindathee L. , Tausz-Posch Sabine , Cane Karen , Norton Robert M. , Fitzgerald Glenn J. , Tausz Michael , Seneweera Saman
Published: December 2014

Underlying physiological mechanisms of intraspecific variation in growth response to elevated CO2 concentration [CO2] were investigated using two spring wheat (Triticum aestivum L.) cultivars: Yitpi and H45. Leaf blade elongation rate (LER), leaf carbon (C), nitrogen (N) in the expanding leaf blade (ELB, sink) and photosynthesis (A) and C and N status in the last fully expanded leaf blade (LFELB, source) were measured. Plants were grown at ambient [CO2] (~384µmolmol–1) and elevated [CO2] (~550µmolmol–1) in the Australian Grains Free Air CO2 Enrichment facility. Elevated [CO2] increased leaf area and total dry mass production, respectively, by 42 and 53% for Yitpi compared with 2 and 13% for H45. Elevated [CO2] also stimulated the LER by 36% for Yitpi compared with 5% for H45. Yitpi showed a 99% increase in A at elevated [CO2] but no A stimulation was found for H45. There was a strong correlation (r2=0.807) between LER of the ELB and soluble carbohydrate concentration in LFELB. In ELB, the highest spatial N concentration was observed in the cell division zone, where N concentrations were 67.3 and 60.6mg g–1 for Yitpi compared with 51.1 and 39.2mg g–1 for H45 at ambient and elevated [CO2]. In contrast, C concentration increased only in the cell division and cell expansion zone of the ELB of Yitpi. These findings suggest that C supply from the source (LFELB) is cultivar dependent and well correlated with LER, leaf area expansion and whole-plant growth response to elevated [CO2].
Cryotolerance of porcine in vitro-produced blastocysts relies on blastocyst stage and length of in vitro culture prior to vitrification
Authors: Morató Roser , Castillo-Martín Míriam , Yeste Marc , Bonet Sergi
Published: December 2014

The aim of our study was to assess whether the cryotolerance of in vitro-produced embryos could be influenced by the length of in vitro culture and size of blastocoel cavity before vitrification, using the pig as a model. For this purpose we analysed the cryoresistance and apoptosis rate of blastocysts at different stages of development as derived on Day 5 and 6 of in vitro culture. Blastocysts were subsequently vitrified, warmed and cultured for 24 h. Re-expansion rates were recorded at 3 and 24 h and total cell number and apoptotic cells were determined at 24 h. Day-6 blastocysts showed the highest rates of survival after warming, which indicates higher quality compared with Day-5 blastocysts. Higher re-expansion rates were observed for expanded blastocysts and those in the process of hatching when compared with early blastocysts. Total cell number and apoptotic cells were affected by blastocyst stage, vitrification–warming procedures and length of in vitro culture, as expanding and hatching–hatched blastocysts from Day 6 presented higher percentages of apoptotic cells than fresh blastocysts and blastocysts vitrified at Day 5. Our findings suggest that the cryotop vitrification method is useful for the cryopreservation of porcine blastocysts presenting a high degree of expansion, particularly when vitrification is performed after 6 days of in vitro culture. Furthermore, these results show that faster embryo development underlies higher blastocyst cryotolerance and provide evidence that blastocoel cavity expansion before vitrification is a reliable index of in vitro-produced embryo quality and developmental potential.
Genetic variation in resistance of the preimplantation bovine embryo to heat shock
Authors: Hansen Peter J.
Published: December 2014

Reproduction is among the physiological functions in mammals most susceptible to disruption by hyperthermia. Many of the effects of heat stress on function of the oocyte and embryo involve direct effects of elevated temperature (i.e. heat shock) on cellular function. Mammals limit the effects of heat shock by tightly regulating body temperature. This ability is genetically controlled: lines of domestic animals have been developed with superior ability to regulate body temperature during heat stress. Through experimentation in cattle, it is also evident that there is genetic variation in the resistance of cells to the deleterious effects of elevated temperature. Several breeds that were developed in hot climates, including Bos indicus (Brahman, Gir, Nelore and Sahiwal) and Bos taurus (Romosinuano and Senepol) are more resistant to the effects of elevated temperature on cellular function than breeds that evolved in cooler climates (Angus, Holstein and Jersey). Genetic differences are expressed in the preimplantation embryo by Day 4–5 of development (after embryonic genome activation). It is not clear whether genetic differences are expressed in cells in which transcription is repressed (oocytes >100 µm in diameter or embryos at stages before embryonic genome activation). The molecular basis for cellular thermotolerance has also not been established, although there is some suggestion for involvement of heat shock protein 90 and the insulin-like growth factor 1 system. Given the availability of genomic tools for genetic selection, identification of genes controlling cellular resistance to elevated temperature could be followed by progress in selection for those genes within the populations in which they exist. It could also be possible to introduce genes from thermotolerant breeds into thermally sensitive breeds. The ability to edit the genome makes it possible to design new genes that confer protection of cells from stresses like heat shock.
Physical basis of spindle self-organization
Authors: Brugués Jan , Needleman Daniel
Published: December 2014

Significance

The spindle segregates chromosomes during cell division and is composed of microtubules and hundreds of other proteins, but the manner in which these molecular constituents self-organize to form the spindle remains unclear. Here we use a holistic approach, based on quantitative measurements in spindles of the spatiotemporal correlation functions of microtubule density, orientation, and stresses, to identify the key processes responsible for spindle self-organization. We show that microtubule turnover and the collective effects of local microtubule interactions, mediated via motor proteins and cross-linkers, can quantitatively account for the dynamics and the structure of the spindle. We thus reveal the physical basis of spindle self-organization and provide a framework that may be useful for understanding cytoskeletal function in vivo.
Regulatory modulation of the T-box gene
Tbx5
links development, evolution, and adaptation of the sternum
Authors: Bickley Sorrel R. B. , Logan Malcolm P. O.
Published: December 2014

Significance

The fin-to-limb transition and acquisition of sterna were critical steps in the evolution of tetrapods, but despite the importance of the sternum in enabling quadrupedal locomotion and avian flight, the mechanisms controlling acquisition and evolutionary adaptation of sterna are not understood. Furthermore, the mechanisms that underlie sternum development and sternal defects are not known. We describe T-box transcription factor gene
Tbx5
function in sternum formation, how disruption of
TBX5
causes human sternum defects, and how modulation of
Tbx5
was key to acquisition and adaptation of sterna in vertebrates. We also demonstrate a quantitative correlation between sternum dimensions and forelimb use in avian species.
The charged linker of the molecular chaperone Hsp90 modulates domain contacts and biological function
Authors: Jahn Markus , Rehn Alexandra , Pelz Benjamin , Hellenkamp Björn , Richter Klaus , Rief Matthias , Buchner Johannes , Hugel Thorsten
Published: December 2014

Significance

Many proteins consist of domains that are connected by flexible linkers. Because of their flexibility they are usually unresolved in crystal structures. Using single-molecule force spectroscopy we were able to measure free energy changes around the thermal energy and obtained for the first time, to our knowledge, structural information on the linker connecting the N-domain and M-domain in Hsp90. We show a sequence-dependent rapid equilibrium between the docked and undocked state of these two domains. This is facilitated by transient binding of the linker to the N-domain. Single-molecule FRET, analytical ultracentrifugation, and cell viability assays show that the equilibrium between these two states affects intermolecular domain movement, client activation, cell viability, and stress tolerance.
Observation of ice-like water layers at an aqueous protein surface
Authors: Meister Konrad , Strazdaite Simona , DeVries Arthur L. , Lotze Stephan , Olijve Luuk L. C. , Voets Ilja K. , Bakker Huib J.
Published: December 2014

Significance

Antifreeze proteins (AFPs) enable the survival of various organisms in freezing or subfreezing habitats by preventing the macroscopic growth of ice crystals. Understanding how AFPs recognize and bind ice crystals is the most important step to unravel their working mechanism. Using surface-specific sum frequency generation spectroscopy, we were able to directly probe the ice-binding site of the protein and discovered that, already at room temperature and in an aqueous solution, the antifreeze proteins arrange water molecules into an ice-like array, which they then use to bind to ice crystals.
Type IV pili interactions promote intercellular association and moderate swarming of
Pseudomonas aeruginosa
Authors: Anyan Morgen E. , Amiri Aboutaleb , Harvey Cameron W. , Tierra Giordano , Morales-Soto Nydia , Driscoll Callan M. , Alber Mark S. , Shrout Joshua D.
Published: December 2014

Significance

The opportunistic pathogen
Pseudomonas aeruginosa
utilizes both its flagellum and type IV pili (TFP) to facilitate motility, attachment, and colonization. Surface motility such as swarming is thought to precede biofilm formation during infection. We combined laboratory and computational methods to probe the physical interactions of TFP during flagellar-mediated swarming and found that TFP of one cell strongly interact with TFP of other cells, which limits swarming expansion rate. Hence, wild-type
P. aeruginosa
use cell−cell physical interactions via their TFP to control self-organization within motile swarms. This collective mechanism of cell−cell coordination using TFP allows for moderation of swarming direction of individual cells and avoidance of a toxic environment.
RADIAL VELOCITIES OF SOUTHERN VISUAL MULTIPLE STARS*
Authors: Tokovinin Andrei , Pribulla Theodor , Fischer Debra
Published: December 2014

High-resolution spectra of visual multiple stars were taken in 2008–2009 to detect or confirm spectroscopic subsystems and to determine their orbits. Radial velocities of 93 late-type stars belonging to visual multiple systems were measured by numerical cross-correlation. We provide the individual velocities, the width, and the amplitude of the Gaussians that approximate the correlations. The new information on the multiple systems resulting from these data is discussed. We discovered double-lined binaries in HD 41742B, HD 56593C, and HD 122613AB, confirmed several other known subsystems, and constrained the existence of subsystems in some visual binaries where both components turned out to have similar velocities. The orbits of double-lined subsystems with periods of 148 and 13 days are computed for HD 104471 Aa,Ab and HD 210349 Aa,Ab, respectively. We estimate individual magnitudes and masses of the components in these triple systems and update the outer orbit of HD 104471 AB.
The Daugavet property in rearrangement invariant spaces
Authors: Acosta M. , Kamińska A. , Mastyło M.
Published: December 2014

We study rearrangement invariant spaces with the Daugavet property. The main result of this paper states that under mild assumptions the only nonseparable rearrangement invariant space

X
X

over an atomless finite measure space with the Daugavet property is

L

∞

L_{\infty }

endowed with its canonical norm. We also prove that a uniformly monotone rearrangement invariant space over an infinite atomless measure space with the Daugavet property is isometric to

L
1

L_1

. As an application we obtain that an Orlicz space over an atomless measure space has the Daugavet property if and only if it is isometrically isomorphic to

L
1

L_1

.
Limits of positive flat bivariate moment matrices
Authors: Fialkow Lawrence
Published: December 2014

The bivariate moment problem for a sequence

β
≡

β

(
6
)

\beta \equiv \beta ^{(6)}

of degree

6
6

remains unsolved, but we prove that if the associated

10
×
10

10 \times 10

moment matrix

M

3

(
β
)

M_{3}(\beta )

satisfies

M

3

⪰
0

M_{3}\succeq 0

and

r
a
n
k
 

M

3

≤
6

rank~M_{3}\le 6

, then

β
\beta

admits a sequence of approximate representing measures, and

β

(
5
)

\beta ^{(5)}

has a representing measure. More generally, let

F

d

¯

\overline {\mathcal {F}_{d}}

denote the closure of the positive flat moment matrices of degree

2
d

2d

in

n
n

variables. Each matrix in

F

d

¯

\overline {\mathcal {F}_{d}}

admits computable approximate representing measures, and in 2013, Jiawang Nie and the author began to study concrete conditions for membership in this class. Let
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="beta identical-to beta Superscript left-parenthesis 2 d right-parenthesis Baseline equals left-brace beta Subscript i Baseline right-brace Subscript i element-of double-struck upper Z Sub Subscript plus Sub Superscript n Subscript comma StartAbsoluteValue i EndAbsoluteValue less-than-or-equal-to 2 d">

β
≡

β

(
2
d
)

=
{

β

i

}

i
∈

Z

+

n

,

|

i

|

≤
2
d

\beta \equiv \beta ^{(2d)}=\{\beta _{i}\}_{ i\in \mathbb {Z}_{+}^{n},|i| \leq 2d }

,

β

0

>
0

\beta _{0}>0

, denote a real

n
n

-dimensional sequence of degree

2
d

2d

. If the corresponding moment matrix

M

d

≡

M

d

(
β
)

M_{d}\equiv M_{d}(\beta )

is the limit of a sequence of positive flat moment matrices

{

M

d

(
k
)

}

\{M_{d}^{(k)}\}

, i.e.,

M

d

(
k
)

⪰
0

M_{d}^{(k)}\succeq 0

and

r
a
n
k
 

M

d

(
k
)

=
r
a
n
k
 

M

d
−
1

(
k
)

rank~M_{d}^{(k)} = rank~M_{d-1}^{(k)}

, then i)

M

d

⪰
0

M_{d}\succeq 0

, ii)
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="r a n k upper M Subscript d Baseline less-than-or-equal-to rho Subscript d minus 1 Baseline identical-to d i m double-struck upper R left-bracket x 1 comma ellipsis comma x Subscript n Baseline right-bracket Subscript d minus 1 Baseline">

r
a
n
k
 

M

d

≤

ρ

d
−
1

≡
d
i
m
 

R

[

x

1

,
…
,

x

n

]

d
−
1

rank~M_{d} \le \rho _{d-1} \equiv dim~\mathbb {R}[x_{1},\ldots ,x_{n}]_{d-1}

, and iii)

β

(
2
d
−
1
)

\beta ^{(2d-1)}

admits a representing measure. We extend our earlier results by proving, conversely, that for

n
=
2

n=2

, if

M

d

M_{d}

satisfies certain positivity and rank conditions related to i)-iii), then

M

d

M_{d}

is the limit of positive flat moment matrices.
Untreated Masked Hypertension and Subclinical Cardiac Damage: A Systematic Review and Meta-analysis
Authors: Cuspidi Cesare , Sala Carla , Tadic Marijana , Rescaldani Marta , Grassi Guido , Mancia Giuseppe
Published: December 2014

AIM

Data on the association of masked hypertension (MH) (i.e., normal office and elevated out-of-office blood pressure (BP)) with cardiac damage are scanty. We performed a meta-analysis in order to provide a comprehensive information on subclinical cardiac alterations in subjects with MH.

DESIGN

Studies were identified by the following search terms: “masked hypertension,” “white coat normotension,” “isolated ambulatory hypertension,” “left ventricular mass,” “left ventricular hypertrophy,” “cardiac damage,” and “echocardiography.” Full articles published in English language providing data on left ventricular (LV) mass and/or prevalence of LV hypertrophy in MH, as assessed by ambulatory BP monitoring, were considered.

RESULTS

Overall, 4,884 untreated subjects (2,467 normotensive, 776 MH, and 1,641 sustained hypertensive individuals) of both genders included in 12 studies were analyzed. LV mass index showed a progressive increase from normotensive (79.2±0.35g/m2) to MH (91.6±4.0g/m2) (standard difference in means (SDM): 0.50±0.11, confidence interval (CI): 0.28–0.73, P < 0.01) and to hypertensive subjects (102.9±3.3g/m2) (SDM: 0.22±0.07, CI: 0.09–0.35, P < 0.01). After assessing data for publication bias, the difference between groups was still significant.

CONCLUSIONS

Our findings support an association between MH and increased risk of LV structural alterations compared to true normotensive individuals. Due to the worse cardiovascular prognosis associated with subclinical cardiac damage, subjects with MH should be carefully screened in order to detect hypertensive organ damage and provide appropriate therapeutic interventions.
Effects of a Dual‐Frequency Frequency‐Sweeping Ultrasound Treatment on the Properties and Structure of the Zein Protein
Authors: Ren Xiaofeng , Wei Xun , Ma Haile , Zhou Huiji , Guo Jingjing , Mao Shuyun , Hu An
Published: December 2014

We investigated the effects of a dual‐frequency frequency‐sweeping ultrasound (DFFSU) treatment on the functional properties and structure of zein. The solubility of ultrasound‐treated zein proteins increased slightly but significantly as the treatment time increased. The results showed that the DFFSU treatment had an obvious influence on the mean particle size and the size distribution. A significant (P < 0.05) increase in the size of the particles with respect to time was observed after a sonication time of more than 20 min in zein solutions. Differential scanning calorimetry results showed that sonication alters the thermal behavior of zein. Circular dichroism spectra showed a small increase in the percentage of ordered structure elements within the protein molecule. After 60 min of ultrasonication, the percentage of α‐helix structures increased by 0.9%, whereas the percentage of β‐sheets and β‐turns decreased by 0.5%. Microstructural analyses by scanning electron microscopy showed that several microholes appeared in the zein following ultrasonic pretreatment. Under the conditions investigated in this study, DFFSU treatment was found to affect the studied functional properties of the zein protein. This technology could be used to obtain improved functional properties in some protein samples.
Changes in Cytokines, Sensory Tests, and Self-reported Pain Levels After Manual Treatment of Low Back Pain
Authors: Degenhardt Brian F. , Johnson Jane C. , Fossum Christian , Andicochea Chad T. , Stuart Melissa K.
Published: December 2014

Study Design:

Unbalanced 3-factor design with repeated measures on 1 factor.

Objective:

To determine the effect of manual treatment (MT) on cytokine and pain sensations in those with and without low back pain (LBP).

Summary of Background Data:

Evidence suggests that MT reduces LBP but by unknown mechanisms. Certain cytokines have been elevated in patients with LBP and may be affected by MT.

Methods:

Participants aged 20–60 years with chronic LBP or without LBP were recruited and randomly assigned to MT, sham ultrasound treatment, or no treatment groups. Venous blood samples were collected and pain levels assessed at baseline, 1 hour later, and 24 hours later. Blood was analyzed for interleukin (IL)-1β, IL-6, tumor necrosis factor-α, and C-reactive protein. Pain levels were measured by pressure pain threshold (PPT), mechanical detection threshold (MDT), dynamic mechanical allodynia, and self-report.

Results:

Forty (30 women, age 36±11 y) participants completed the study, 33 with LBP (13 MT, 13 sham ultrasound treatment, and 7 no treatment) and 7 without LBP. Participants with or without LBP could not be differentiated on the basis of serum cytokine levels, PPT, or MDT (P≥0.08). There were no significant differences between the groups at 1 hour or 24 hours on serum cytokines, PPT, or MDT (P≥0.07). There was a significant decrease from baseline in IL-6 for the no treatment (LBP) group (P=0.04), in C-reactive protein for the sham ultrasound treatment group (P=0.03), in MDT for all 3 LBP groups (P≤0.02), and in self-reported pain for the MT and sham ultrasound treatment groups (P=0.03 and 0.01).

Conclusions:

Self-reported pain was reduced with MT and sham ultrasound treatment 24 hours after treatment, but inflammatory markers within venous circulation and quantitative sensory tests were unable to differentiate between study groups. Therefore, we were unable to characterize mechanisms underlying chronic LBP.