bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrogen bond effects in the vibrational spectra of 1,3-propanediol in acetonitrile:Ab initioand experimental study
Authors: Muniz-Miranda Francesco , Pagliai Marco , Cardini Gianni , Righini Roberto
Published: December 2012

Hydrogen bond interactions strongly affect vibrational properties and frequencies, the most common consequence being a redshift of the stretching vibration involved; there are, however, few exceptions to this general trend. In previous works, we have proved the effectiveness of ab initiosimulations combined with wavelet analysis to investigate these effects and put them into relation to structural environment. In this work, we investigate the hydrogen bond effects on the structural and vibrational properties of 1,3-propanediol in acetonitrile by a combined experimental and computational approach. We explain the appearance of two spectral components in the O−H stretching band on the basis of intra- and intermolecular hydrogen bond interactions. We also elucidate the blueshift of the C≡N stretching band as due to a hydrogen bond interaction between the glycol and acetonitrile that modify the electron density distribution inside the CN group. This effect is well reproduced by ab initio molecular dynamics simulations and density functional calculations reported in this work.
Central metal dependence of conformation and self-assembly of porphyrins on Ag(110)
Authors: Yokoyama Takashi , Tomita Yuuki
Published: December 2012

The conformation and self-assembly of tertiary-butylphenyl substituted free-base and metal porphyrins (M-TBPP) on Ag(110) have been investigated as a function of the central metals (M = 2H, Cu, Pt, Ni, Zn, and Co) using scanning tunneling microscopy and low-energy electron diffraction. In the case of M = Cu, Pt, Ni, and Zn, a metastable adsorption structure is formed by the deposition below about 270 K and irreversibly transformed into a stable one after thermal annealing above 280 K. Nevertheless, we find that 2H- and Co-TBPP molecules do not exhibit structural transformation even after thermal annealing. The distinct adsorption behaviors should be related mainly to the porphyrin-substrate interactions depending on the central metal in M-TBPP.
Spectroscopic investigation of the A and 3 1Σ+ states of 39K85Rb
Authors: Kim Jin-Tae , Lee Yonghoon , Kim Bongsoo , Wang Dajun , Gould Phillip L. , Eyler Edward E. , Stwalley William C.
Published: December 2012

By using a combination of molecular beam (MB) excitation spectra and two distinct ultracold molecule excitation spectra (UM+ and UM−), we have assigned high vibrational levels of the A and 3 1Σ+ states from absorption spectra of the mutually strongly perturbed A 1Σ+ − 3 1Σ+ − 1 1Π − 2 3Σ+ − b 3Π states of ultracold 39K85Rb molecules in the energy region between 15 116 and 16 225 cm−1 above the minimum of the ground X 1Σ+ state. The ultracold molecules (UM+ and UM−) are formed by radiative decay following photoassociation (PA) to a specific level of the 3(0+) state (UM+) or to a specific level of the 3(0−) state (UM−). We observe that the A and 3 1Σ+ states are observable in the UM+ spectra, but absent from the UM− spectra. This is explained by considering Hund's case (c) selection rules and transition dipole moments between the upper excited A 1Σ+ (2(0+)) state and the three Ω components (0+, 0−, and 1) at the ground-state dissociation limit. We propose further investigations of the extended potential wells of the A and 3 1Σ+ states by combining short-range MB excitation spectra in a narrow Franck-Condon (FC) window near Re of the X 1Σ+ state, and long-range UM (and PA) excitation spectra, which have much larger FC windows.
Partial synchronization in diffusively time-delay coupled oscillator networks
Authors: Steur Erik , Oguchi Toshiki , van Leeuwen Cees , Nijmeijer Henk
Published: December 2012

We study networks of diffusively time-delay coupled oscillatory units and we show that networks with certain symmetries can exhibit a form of incomplete synchronization called partial synchronization. We present conditions for the existence and stability of partial synchronization modes in networks of oscillatory units that satisfy a semipassivity property and have convergent internal dynamics.
Characterizing the excess electron of Li(NH3)4
Authors: Sommerfeld Thomas , Dreux Katelyn M.
Published: December 2012

Small lithium ammonia clusters are model systems for the dissociation of metals into solvated cations and electrons in ammonia. Metal–ammonia solutions display a complex behavior with increasing metal concentration including a phase change from a paramagnetic to a metallic diamagnetic phase, and small clusters should be useful models in the low concentration regime, where one may expect the ammoniated electron to show a behavior similar to that of the hydrated electron. Yet, even in the low concentration regime the nature of the ammoniated electron is still controversial with cavity models supported by optical and density measurements whereas localized radical models have been invoked to explain magnetic measurements. Small clusters can shed light on these open questions, and in particular the Li–NH3 tetramer represents the smallest cluster with a complete solvation shell for the Li+ cation. In view of the controversies about the character of the excess electron, the first question investigated is whether different theoretical characterizations of the “excess electron” lead to different conclusions about it. Only small differences are found between orbital-based and spin density-based and between self-consistent-field and coupled-cluster-based methods. Natural orbitals from equation-of-motion coupled-cluster calculations are then used to analyze the excess electron's distribution of Li(NH3)4 with particular emphasis on the portion of the excess electron's density that is closely associated with the N atoms. Three different comparisons show that only about 6% of the excess electron's density are closely associated with the atoms, with about 1% being closely associated with any N atom, and that the electron is best characterized as a Rydberg-like electron of the whole cluster. Finally, it is shown that in spite of the small amount of density close to the N atoms, the spin-density at the N nuclei is substantial, and that the magnetic observations can plausibly be explained within the cavity model.
Freak waves in white dwarfs and magnetars
Authors: Sabry R. , Moslem W. M. , Shukla P. K.
Published: December 2012

We report properties of ion acoustic freak waves that propagate in a plasma composed of warm ions and ultrarelativistic electrons and positrons. The dynamics of the nonlinear freak waves is governed by the nonlinear Schrödinger equation. The possible region for the freak waves to exist is defined precisely for typical parameters of white dwarfs and magnetars corona. It is found that for low wave number, the nonlinear ion-acoustic wave packets are structurally stable in magnetars corona than in white dwarfs. However, for large wave numbers the situation is opposite. The critical wave number threshold (kc), which indicates where the modulational instability sets in, is defined for both applications. It is seen that near to kc the freak wave amplitude becomes high, but it decreases whenever we stepped away from kc. For the wave numbers close to kc, the increase of the unperturbed density ratio of positrons-to-electrons (β) would lead to increase the freak wave amplitude, but for larger wave numbers the amplitude decreases with the increase of β.
A novel time stamping technique for distributed data acquisition systems
Authors: Subramaniam E. T.
Published: December 2012

In this paper, we discuss the design and implementation of a synchronizing technique for data acquisition systems, which can effectively use the normal, standard local area network cables to provide a time stamp, with a range up to 32 days, resolution of 10 ns, and synchronization within ± 5 ns. This system may be used to synchronize data being collected by independent heterogeneous data acquisition modules, that acquire events independently. Such distributed systems are generally designed with a tree-like structure or independent self-triggered acquisition boxes. These leaf edges are connected through branches to the root node, via non-bus based inter-connecting links. The present system has been tested with a set of self-triggered digital signal processing based data acquisition engines, having a 100 MHz analog to digital converter front end.
Slow photoelectron velocity-map imaging spectroscopy of cold negative ions
Authors: Hock Christian , Kim Jongjin B. , Weichman Marissa L. , Yacovitch Tara I. , Neumark Daniel M.
Published: December 2012

Anion slow photoelectron velocity-map imaging (SEVI) spectroscopy is a high-resolution variant of photoelectron spectroscopy used to study the electronic and geometric structure of atoms, molecules, and clusters. To benefit from the high resolution of SEVI when it is applied to molecular species, it is essential to reduce the internal temperature of the ions as much as possible. Here, we describe an experimental setup that combines a radio-frequency ion trap to store and cool ions with the high-resolution SEVI spectrometer. For C5–, we demonstrate ion temperatures down to 10 ± 2 K after extraction from the trap, as measured by the relative populations of the two anion spin-orbit states. Vibrational hot bands and sequence bands are completely suppressed, and peak widths as narrow as 4 cm−1 are seen due to cooling of the rotational degrees of freedom.
Effects of surface functional groups on the formation of nanoparticle-protein corona
Authors: Podila R. , Chen R. , Ke P. C. , Brown J. M. , Rao A. M.
Published: December 2012

Herein, we examined the dependence of protein adsorption on the nanoparticle surface in the presence of functional groups. Our UV-visible spectrophotometry, transmission electron microscopy, infrared spectroscopy, and dynamic light scattering measurements evidently suggested that the functional groups play an important role in the formation of nanoparticle-protein corona. We found that uncoated and surfactant-free silver nanoparticles derived from a laser ablation process promoted a maximum protein (bovine serum albumin) coating due to increased changes in entropy. On the other hand, bovine serum albumin displayed a relatively lower affinity for electrostatically stabilized nanoparticles due to the constrained entropy changes.
Dissipative transport in rough edge graphene nanoribbon tunnel transistors
Authors: Yoon Youngki , Salahuddin Sayeef
Published: December 2012

We have studied quantum transport in graphene nanoribbon tunnel field-effect transistors. Unlike other studies on similar structures, we have included dissipative processes induced by inelastic electron-phonon scattering and edge roughness in the nanoribbon self-consistently within a non-equilibrium transport simulation. Our results show that the dissipative scattering imposes a limit to the minimum OFF current and a minimum subthreshold swing that can be obtained even for long channel lengths where direct source-drain tunneling is inhibited. The edge roughness, in the presence of dissipative scattering, somewhat surprisingly, shows a classical behavior where it mostly reduces the maximum ON current achievable in this structure.
Structural and thermodynamical properties of charged hard spheres in a mixture with core-softened model solvent
Authors: Lukšič Miha , Hribar-Lee Barbara , Vlachy Vojko , Pizio O.
Published: December 2012

The canonical Monte Carlo computer simulations and integral equation theory were applied to examine the structural and thermodynamic properties of a mixture of ions and a core-softened fluid molecules. The positive and negative ions forming a +1:−1 salt were modeled as charged hard spheres, immersed in the dielectric medium. It was shown previously that the core-softened fluid under study is characterized by a set of structural, thermodynamic, and dynamic anomalies. The principal objective of this work was to elucidate how the presence of ions alters this behavior. The structural properties of the mixtures are discussed in terms of the pair distribution functions; in addition, the pair contribution to the excess entropy was calculated. Thermodynamic properties are investigated by using the dependencies of energy and compressibility factor on density, composition of the mixture, and reduced temperature. The heat capacity was also evaluated. Our principal findings concern the description of structural anomalies in the mixture, the dependence of the temperature of maximum density on the ionic concentration, and establishing the regions delimiting the structural and thermodynamic anomalies of the model mixture.
Threshold conditions for lasing of a free electron laser oscillator with longitudinal electrostatic wiggler
Authors: Sepehri Javan N.
Published: December 2012

The system of the nonlinear non-stationary equations describing spatial-temporal dynamics of the amplitudes of an ondulator radiation and a space-charge wave of a relativistic electron beam in the resonator is obtained. A free electron laser resonator with longitudinal electrostatic wiggler is considered. In the linear approximation, the threshold conditions of lasing for Raman and Compton regimes under excitation of forward and backward electromagnetic wave are achieved. In the various physical situations, the variation of the minimum length of the resonator with the amplitude of wiggler, density of electron beam, and with the reflection coefficients of resonator's mirrors is investigated.
Ultrahigh conductivity of large area suspended few layer graphene films
Authors: Rouhi Nima , Wang Yung Yu , Burke Peter J.
Published: December 2012

Room-temperature (atmospheric-pressure) electrical conductivity measurements of wafer-scale, large-area suspended (few layer) graphene membranes with areas up to 1000 μm2 (30 μm × 30 μm) are presented. Multiple devices on one wafer can be fabricated with high yield from the same chemical vapor deposition grown graphene sheet, transferred from a nickel growth substrate to large opening in a suspended silicon nitride support membrane. This represents areas two to orders of magnitude larger than prior transport studies on any suspended graphene device (single or few layer). We find a sheet conductivity of ∼2500 e2/h (or about 10 Ω/sq) of the suspended graphene, which is an order of magnitude higher than any previously reported sheet conductance of few layer graphene.
Experimental techniques for imaging and measuring transient vapor
nanobubbles
Authors: Lukianova-Hleb E. Y. , Lapotko D. O.
Published: December 2012

Imaging and measuring transient vapor bubbles at nanoscale pose certain experimental challenges due to their reduced dimensions and lifetimes, especially in a single event experiment. Here, we analyze three techniques that employ optical scattering and acoustic detection in identifying and quantifying individual photothermally induced vapor nanobubbles (NBs) at a wide range of excitation energies. In optically transparent media, the best quantitative detection can be achieved by measuring the duration of the optical scattering time-response, while in an opaque media, the amplitude of the acoustic time-response well describes NBs in the absence of stress waves.

At the request of the authors, this article is being retracted effective 20 March 2017.
Electrically controlled absorption in a slab waveguide formed by the implantation of protons in a potassium lithium tantalate niobate substrate
Authors: Ilan Har'el , Agranat Aharon J.
Published: December 2012

Electrically controlled absorption was observed in a slab waveguide, fabricated in a potassium lithium tantalate niobate substrate by proton implantation, at an energy of E=1.15 MeV and a fluence of 6.1×1016ions/cm2. The implantation created an amorphous layer which acted as the cladding with an adjacent proton doped layer at its bottom. It is suggested that a n-i junction is formed at the interface between the proton layer and the substrate, which is the core of the waveguide. The electrically controlled absorption is attributed to changes in the width of the depletion area of the n-i junction induced by the applied field.
Enhanced photocurrent in crystalline silicon solar cells by hybrid plasmonic antireflection coatings
Authors: Fahim Narges F. , Ouyang Zi , Jia Baohua , Zhang Yinan , Shi Zhengrong , Gu Min
Published: December 2012

Photocurrent enhancement induced by plasmonic light trapping is of great interest for photovoltaics. We design and demonstrate hybrid plasmonic antireflection coatings as an efficient light trapping strategy for broadband absorption and photocurrent enhancement in crystalline silicon solar cells. Gold nanoparticles of size ranging from 15 to 150 nm are embedded in standard SiNx antireflection coatings with a thickness of 90 nm. Through optimizing the location of tailored nanoparticles within the SiNx layer, both light scattering enhancement and near-field light concentration can be harnessed. A maximum increase of 6.3% in photocurrent is achieved for textured multi-crystalline Si solar cells with the optimum configuration.
Radial behavior of the pulsed dielectric-barrier discharge in atmospheric helium
Authors: Zhang Dingzong , Wang Yanhui , Wang Dezhen
Published: December 2012

The radial behavior of the pulsed dielectric-barrier discharge in atmospheric helium is studied by a two-dimensional, self-consistent fluid model. It is found that the two discharges ignited during one voltage pulse can possess different radial behaviors, and the discharge behavior is determined by the electron density distribution right before this discharge is ignited. The electron density distributions before the two discharges start depend on the time intervals between two discharges and their previous discharge processes. If the electron density distribution is radially uniform at the end of the previous discharge, the shorter the time interval between two discharges is, the more uniform the electron density distribution before the next discharge is, and thus the more homogenous the subsequent discharge becomes. In pulsed discharge, the time intervals between two discharges are mainly determined by the duration and repetition frequency of applied voltage pulse. These results are further supported by the investigation of the discharge behaviors under different pulse durations and repetition frequencies.
Characteristics of implosion and radiation for aluminum planar wire array z-pinch at 1.5 MA
Authors: Liangping Wang , Jian Wu , Mo Li , Juanjuan Han , Ning Guo , Gang Wu , Aici Qiu
Published: December 2012

Planar wire arrays Z pinches were carried out on Qiangguang generator (1.5 MA, 100 ns). Loads with varied row widths (6–24 mm) and wire numbers (10–34) were employed in the experiments. The implosion dynamics of planar wire arrays has been studied. Meanwhile, the changes of the implosion time, radiation yield and power with array mass, inter-wire gap, and array width were investigated. The images of a soft X-ray camera exhibit that the trailing mass, precursor column, and R-T instability exist during the implosion phase, and when m = 0 maybe accompanied with m = 1, instability will rapidly develop after stagnation. The implosion trajectories show that loads will implode by the snowplow mode and about 50% of total initial array mass will participate in the final implosion. The maximum total X-ray energy is 22 kJ with a power of 630 GW, while the maximum K-shell yield is 3.9 kJ with a power of 158 GW. Experiments with different planar wire arrays show that the value of mPD02 (the product of line mass and squared width) is the critical factor which affects the implosion time and the X-ray products of the wire arrays. The optimum value of mPD02 should be in the range of 200–400 μgcm and the inter-wire gap should be less than 1 mm.
Thermally assisted spin-transfer torque magnetization reversal in uniaxial nanomagnets
Authors: Pinna D. , Mitra Aditi , Stein D. L. , Kent A. D.
Published: December 2012

We simulate the stochastic Landau-Lifshitz-Gilbert dynamics of a uniaxial nanomagnet out to sub-millisecond timescales using a graphical processing unit based micromagnetic code and determine the effect of geometrical tilts between the spin-current and uniaxial anisotropy axes on the thermally assisted reversal dynamics. The asymptotic behavior of the switching time (I→0, 〈τ〉∝exp(−ξ(1−I)2)) is approached gradually, indicating a broad crossover regime between the ballistic and thermally assisted spin transfer reversal. Interestingly, the functional form of the mean switching time is shown to be independent of the angle between the spin current and magnet's uniaxial axes. These results have important implications for modeling the energetics of thermally assisted magnetization reversal of spin transfer magnetic random access memory bit cells.
Yoke-shaped MgO-barrier magnetic tunnel junction sensors
Authors: Chen J. Y. , Carroll N. , Feng J. F. , Coey J. M. D.
Published: December 2012

Yoke-shaped sensors based on MgO-barrier magnetic tunnel junctions have been designed, fabricated, and studied; they show a good linear tunneling magnetoresistance (TMR) response. A nearly-perpendicular configuration of two ferromagnetic electrodes was set by two-step annealing together with shape anisotropy. The low-frequency noise characterization shows these yoke-shaped TMR sensors have relatively low magnetic 1/f noise. The field sensitivity is up to 27%/mT, while the field detectivity reaches 4.6 nT/Hz at 10 Hz and 460 pT/Hz at 1 kHz. These TMR sensors may be useful for applications such as biomagnetic detection.
Study of radiation effects on the cell structure and evaluation of the dose delivered by x-ray and α-particles microscopy
Authors: Kosior Ewelina , Cloetens Peter , Devès Guillaume , Ortega Richard , Bohic Sylvain
Published: December 2012

Hard X-ray fluorescence microscopy and magnified phase contrast imaging are combined to study radiation effects on cells. Experiments were performed on freeze-dried cells at the nano-imaging station ID22NI of the European synchrotron radiation facility. Quantitative phase contrast imaging provides maps of the projected mass and is used to evaluate the structural changes due to irradiation during X-ray fluorescence experiments. Complementary to phase contrast imaging, scanning transmission ion microscopy is performed and doses of all the experiments are compared. We demonstrate the sensitivity of the proposed approach to study radiation-induced damage at the sub-cellular level.
Scaling the dynamic response and energy harvesting potential of piezoelectric beams
Authors: Tolga Akcabay Deniz , Lu Young Yin
Published: December 2012

This work presents dynamic scaling relations for the fluid-structure interaction (FSI) response and energy harvesting potential of fluttering piezoelectric beams. The results show that it is difficult to find a model-sized material to satisfy all the scaling relations using Reynolds scaling. Mach scaling, which does not imply that flow compressibility is important, but simply requires the same inflow speed and operating fluid, allows the same material as full-scale to be used; this enables the model to emulate similar FSI response, energy harvesting potential, and material failure mechanisms, if both the model and full-scale operate at sufficiently high Reynolds numbers (≥1000).
The stability and the growth rate of the electron acoustic traveling wave under transverse perturbations in a magnetized quantum plasma
Authors: Gao Dong-Ning , Wang Cang-Long , Yang Xue , Duan Wen-Shan , Yang Lei
Published: December 2012

Theoretical and numerical studies are carried out for the stability of the electron acoustic waves under the transverse perturbation in a magnetized quantum plasma. The Zakharov-Kuznetsov (ZK) equation of the electron-acoustic waves (EAWs) is given by using the reductive perturbation technique. The cut-off frequency is obtained by applying a transverse sinusoidal perturbation to the plane soliton solution of the ZK equation. The propagation velocity of solitary waves, the real cut-off frequency, as well as the growth rate of the higher order perturbation to the traveling solitary wave are obtained.
Effect of spatial coherence on determining the topological charge of a vortex beam
Authors: Zhao Chengliang , Wang Fei , Dong Yuan , Han Yujing , Cai Yangjian
Published: December 2012

It is known that one can determine the topological charge of a vortex beam based on the Fourier transform of its intensity. We demonstrate both theoretically and experimentally that this method will be invalid for determining the topological charge of a vortex beam with low coherence. Furthermore, we propose a method to determine the topological charge of a vortex beam with low coherence based on its complex degree of coherence.
Spatial resolution of synchrotron x-ray microtomography in high energy range: Effect of x-ray energy and sample-to-detector distance
Authors: Seo D. , Tomizato F. , Toda H. , Uesugi K. , Takeuchi A. , Suzuki Y. , Kobayashi M.
Published: December 2012

Spatial resolution of three-dimensional images obtained by synchrotron X-ray microtomography technique is evaluated using cyclic bar patterns machined on a steel wire. Influences of X-ray energy and the sample-to-detector distance on spatial resolution were investigated. High X-ray energies of 33-78 keV are applied due to the high X-ray absorption of transition metals. Best spatial resolution of about 1.2 μm pitch was observed at the sample-to-detector distance range of 20-110 mm and at the energy range of 68-78 keV. Several factors such as X-ray scattering and diffraction phenomena affecting the degradation of spatial resolution are also discussed.
Broadband and tunable mid-infrared laser source based on a transversal array of chirped filaments
Authors: Daigle J.-F. , Théberge F. , Roy G. , Châteauneuf M. , Dubois J.
Published: December 2012

A scheme for the generation of broadband and tunable mid-infrared pulses based on two-color filamentation in air is presented. The mid-infrared pulses, spanning the spectral region between 4 and 6.5 μm, result from a third-order nonlinear interaction between two short pulses, one at 800 nm and the other at 437 nm. The latter was created by frequency doubling a Raman-shifted pulse at 873 nm amplified in a chirped-pulse Raman amplifier. Tunability of this mid-infrared laser source was provided by introducing spatial chirp across the fundamental pulse profile which created a transversal array of chirped filaments.
Superconducting nanowire single photon detectors on-fiber
Authors: Bachar Gil , Baskin Ilya , Shtempluck Oleg , Buks Eyal
Published: December 2012

We present a design of a superconducting nanowire single photon detector fabricated on a core of a single mode optical fiber. The proposed design allows high overlap between the fiber light mode and the detector, and consequently, our fabricated devices can remain small in dimension and maintain speed of operation, without sacrificing the detection efficiency. The on-fiber fabrication method is detailed, together with experimental results. The proposed method can be exploited in the future for the fabrication of other fiber coupled devices.
Dielectric function spectra at 40 K and critical-point energies for CuIn0.7Ga0.3Se2
Authors: Choi S. G. , Chen R. , Persson C. , Kim T. J. , Hwang S. Y. , Kim Y. D. , Mansfield L. M.
Published: December 2012

We report ellipsometrically determined dielectric function ε spectra for CuIn0.7Ga0.3Se2 thin film at 40 and 300 K. The data exhibit numerous spectral features associated with interband critical points (CPs) in the spectral range from 0.74 to 6.43 eV. The second-energy-derivatives of ε further reveal a total of twelve above-bandgap CP features, whose energies are obtained accurately by a standard lineshape analysis. The ε spectra determined by ellipsometry show a good agreement with the results of full-potential linearized augmented plane wave calculations. Probable electronic origins of the CP features observed are discussed.
Anisotropy of effective masses in CuInSe2
Authors: Yakushev M. V. , Luckert F. , Rodina A. V. , Faugeras C. , Karotki A. V. , Mudryi A. V. , Martin R. W.
Published: December 2012

Anisotropy of the valence band is experimentally demonstrated in CuInSe2, a key component of the absorber layer in one of the leading thin-film solar cell technology. By changing the orientation of applied magnetic fields with respect to the crystal lattice, we measure considerable differences in the diamagnetic shifts and effective g-factors for the A and B free excitons. The resulting free exciton reduced masses are combined with a perturbation model for non-degenerate independent excitons and theoretical dielectric constants to provide the anisotropic effective hole masses, revealing anisotropies of 5.5 (4.2) for the A (B) valence bands.
Broadband asymmetric acoustic transmission in a gradient-index structure
Authors: Li Rui-Qi , Liang Bin , Li Yong , Kan Wei-Wei , Zou Xin-Ye , Cheng Jian-Chun
Published: December 2012

We propose a scheme of realizing broadband asymmetric acoustic transmission using gradient-index structure, and demonstrate an implementation utilizing phononic-crystal-based metamaterials which can realize an idealized model with desired parameters. The asymmetric transmission is valid within a remarkably broad frequency range. This phenomenon stems from the break of the geometric symmetry of wave trajectories along two opposite directions, essentially different from the mechanisms of previous designs. The numerical results agree well with the analytical predictions using acoustic ray theory. Our design may have potential applications in many fields such as ultrasonic therapy and noise control.
Effect of dislocations on electron mobility in AlGaN/GaN and AlGaN/AlN/GaN heterostructures
Authors: Kaun Stephen W. , Burke Peter G. , Hoi Wong Man , Kyle Erin C. H. , Mishra Umesh K. , Speck James S.
Published: December 2012

AlxGa1−xN/GaN (x = 0.06, 0.12, 0.24) and AlGaN/AlN/GaN heterostructures were grown on 6 H-SiC, GaN-on-sapphire, and free-standing GaN, resulting in heterostructures with threading dislocation densities of ∼2 × 1010, ∼5 × 108, and ∼5 × 107 cm−2, respectively. All growths were performed under Ga-rich conditions by plasma-assisted molecular beam epitaxy. Dominant scattering mechanisms with variations in threading dislocation density and sheet concentration were indicated through temperature-dependent Hall measurements. The inclusion of an AlN interlayer was also considered. Dislocation scattering contributed to reduced mobility in these heterostructures, especially when sheet concentration was low or when an AlN interlayer was present.
Measurement of the valence band-offset in a PbSe/ZnO heterojunction by x-ray photoelectron spectroscopy
Authors: Li Lin , Qiu Jijun , Weng Binbin , Yuan Zijian , Li Xiaomin , Gan Xiaoyan , Sellers Ian R. , Shi Zhisheng
Published: December 2012

A heterojunction of PbSe/ZnO has been grown by molecular beam epitaxy. X-ray photoelectron spectroscopy was used to directly measure the valence-band offset (VBO) of the heterojunction. The VBO, ΔEV, was determined as 2.51 ± 0.05 eV using the Pb 4p3/2 and Zn 2p3/2 core levels as a reference. The conduction-band offset, ΔEC, was, therefore, determined to be 0.59 ± 0.05 eV based on the above ΔEV value. This analysis indicates that the PbSe/ZnO heterojunction forms a type I (Straddling Gap) heterostructure.
A derivation of the Hardy-Ramanujan formula from an arithmetic formula
Authors: Dewar Michael , Murty M.
Published: December 2012

We re-prove the Hardy-Ramanujan asymptotic formula for the partition function without using the circle method. We derive our result from recent work of Bruinier and Ono on harmonic weak Maass forms.
Brownian motion on ℝ-trees
Authors: Athreya Siva , Eckhoff Michael , Winter Anita
Published: December 2012

The real trees form a class of metric spaces that extends the class of trees with edge lengths by allowing behavior such as locally infinite total edge length and vertices with infinite branching degree. We use Dirichlet form methods to construct Brownian motion on any given locally compact

R

\mathbb {R}

-tree

(
T
,
r
)

(T,r)

equipped with a Radon measure

ν
\nu

on

(
T
,

B

(
T
)
)

(T,{\mathcal B}(T))

. We specify a criterion under which the Brownian motion is recurrent or transient. For compact recurrent

R

\mathbb {R}

-trees we provide bounds on the mixing time.
Genetic Analysis of Adult Plant Resistance to Yellow Rust and Leaf Rust in Common Spring Wheat Quaiu 3
Authors: Basnet B. R. , Singh R. P. , Herrera-Foessel S. A. , Ibrahim A. M. H. , Huerta-Espino J. , Calvo-Salazar V. , Rudd J. C.
Published: December 2012

Identifying and utilizing rust resistance genes in wheat has been hampered by the continuous and rapid emergence of new pathogen races. A major focus of many wheat breeding programs is achieving durable adult plant resistance (APR) to yellow (stripe) rust (YR) and leaf (brown) rust (LR), caused by Puccinia striiformis and P. triticina, respectively. This study aimed to determine the genetic basis of resistance to YR and LR in the common spring wheat ‘Quaiu 3’. To that end, we evaluated 198 F5 recombinant inbred lines (RILs), derived from a cross of susceptible ‘Avocet-YrA’ with Quaiu 3, for APR to LR and YR in artificially inoculated field trials conducted in Mexico during the 2009 and 2010 growing seasons. High narrow-sense heritability (h2) estimates, ranging between 0.91 and 0.95, were obtained for both LR and YR disease severities for both years. The quantitative and qualitative approaches used to estimate gene numbers showed that, in addition to known resistance genes, there are at least two to three APR genes associated with LR and YR resistance in the RIL population. The moderately effective race-specific resistance gene Lr42 and the pleiotropic slow-rusting APR gene Lr46/Yr29 were found to interact with additional unidentified APR genes. The unidentified APR genes should be of particular interest for further characterization through molecular mapping, and for utilization by wheat breeding programs.
Efficacy of Area-Wide Inoculum Reduction and Vector Control on Temporal Progress of Huanglongbing in Young Sweet Orange Plantings
Authors: Bassanezi Renato B. , Montesino Luiz H. , Gimenes-Fernandes Nelson , Yamamoto Pedro T. , Gottwald Tim R. , Amorim Lilian , Filho Armando Bergamin
Published: December 2012

Huanglongbing (HLB), caused by ‘Candidatus Liberibacter’ spp. and transmitted by the Asian citrus psyllid Diaphorina citri (ACP), is an important threat to citrus industries worldwide, causing significant yield loss. The current recommended strategies to manage HLB are to eliminate HLB-symptomatic trees to reduce sources of bacterial inoculum and to apply insecticides to reduce psyllid vector populations. The objective of this study was to assess the effectiveness and the importance of both strategies applied within young citrus plots (local management), in different frequencies and combinations, on HLB temporal progress. Two factorial field experiments, E1 and E2, were initiated in a new plantation of sweet orange in an HLB epidemic region of Sao Paulo, Brazil, in October 2005 and May 2006, respectively. Local inoculum reduction (tree removal) intervals for E1 were every 4, 8, and 16 weeks and, for E2, every 2, 4, 12, and 26 weeks. Local vector control strategies for E1 were no control, program A (PA), and program B (PB); and, for E2, no control and program C (PC), as follows. Psyllids were controlled with two 56-day-interval soil or drench applications of systemic insecticides concurrently with the rainy season each year and, during the rest of the year, with insecticide sprays every 28 days for PA and every 14 days for PB and PC. Regional HLB management was present for E1 and absent for E2. The beginning of the HLB epidemic was delayed for 10 months in E1 compared with appearance of the first diseased tree in E2 but wasn't affected by different local strategies in either experiment. After 60 (E1) and 53 (E2) months, the HLB incidence and progress rates were not affected by different frequencies of local inoculum reduction in either experiment, and were different only in plots with and without local vector control in E2. In E1, the disease incidence was reduced by 90% and the disease progress rate by 50% in plots both with and without vector control. These reductions were explained by smaller psyllid populations and lower frequency of bacterialiferous psyllids in E1 compared with E2. Annual productivity increased over time in E1, as expected for young plantings, but remained stable or decreased in E2. These results confirm that immigration of bacterialiferous ACP vectors plays a critical role in HLB epidemics and suggest that area-wide inoculum reduction and ACP management strongly affect HLB control.
Aspects of Pathogen Genomics, Diversity, Epidemiology, Vector Dynamics, and Disease Management for a Newly Emerged Disease of Potato: Zebra Chip
Authors: Lin Hong , Gudmestad Neil C.
Published: December 2012

An overview is provided for the aspects of history, biology, genomics, genetics, and epidemiology of zebra chip (ZC), a destructive disease of potato (Solanum tuberosum) that represents a major threat to the potato industries in the United States as well as other potato-production regions in the world. The disease is associated with a gram-negative, phloem-limited, insect-vectored, unculturable prokaryote, ‘Candidatus Liberibacter solanacearum’, that belongs to the Rhizobiaceae family of α-Proteobacteria. The closest cultivated relatives of ‘Ca. L. solanacearum’ are members of the group of bacteria known as the α-2 subgroup. In spite of the fact that Koch's postulates sensu stricto have not been fulfilled, a great deal of progress has been made in understanding the ZC disease complex since discovery of the disease. Nevertheless, more research is needed to better understand vector biology, disease mechanisms, host response, and epidemiology in the context of vector–pathogen–plant interactions. Current ZC management strategies focus primarily on psyllid control. The ultimate control of ZC likely relies on host resistance. Unfortunately, all commercial potato cultivars are susceptible to ZC. Elucidation of the ‘Ca. L. solanacearum’ genome sequence has provided insights into the genetic basis of virulence and physiological and metabolic capability of this organism. Finally, the most effective, sustainable management of ZC is likely to be based on integrated strategies, including removal or reduction of vectors or inocula, improvement of host resistance to the presumptive pathogen and psyllid vectors, and novel gene-based therapeutic treatment.
Relative contribution of free-virus and synaptic transmission to the spread of HIV-1 through target cell populations
Authors: Komarova Natalia L. , Anghelina Daniela , Voznesensky Igor , Trinité Benjamin , Levy David N. , Wodarz Dominik
Published: December 2012

Human immunodeficiency virus can spread through target cells by transmission of cell-free virus or directly from cell-to-cell via formation of virological synapses. Although cell-to-cell transmission has been described as much more efficient than cell-free infection, the relative contribution of the two transmission pathways to virus growth during multiple rounds of replication remains poorly defined. Here, we fit a mathematical model to previously published and newly generatedin vitrodata, and determine that free-virus and synaptic transmission contribute approximately equally to the growth of the virus population.
An automated approach for three-dimensional quantification of fibrillar structures in optically cleared soft biological tissues
Authors: Schriefl Andreas J. , Wolinski Heimo , Regitnig Peter , Kohlwein Sepp D. , Holzapfel Gerhard A.
Published: December 2012

We present a novel approach allowing for a simple, fast and automated morphological analysis of three-dimensional image stacks (
z
-stacks) featuring fibrillar structures from optically cleared soft biological tissues. Five non-atherosclerotic tissue samples from human abdominal aortas were used to outline the multi-purpose methodology, applicable to various tissue types. It yields a three-dimensional orientational distribution of relative amplitudes, representing the original collagen fibre morphology, identifies regions of isotropy where no preferred fibre orientations are observed and determines structural parameters throughout anisotropic regions for the analysis and numerical modelling of biomechanical quantities such as stress and strain. Our method combines optical tissue clearing with second-harmonic generation imaging, Fourier-based image analysis and maximum-likelihood estimation for distribution fitting. With a new sample preparation method for arteries, we present, for the first time to our knowledge, a continuous three-dimensional distribution of collagen fibres throughout the entire thickness of the aortic wall, revealing novel structural and organizational insights into the three arterial layers.
Controlling the hydration of the skin though the application of occluding barrier creams
Authors: Sparr Emma , Millecamps Danielle , Isoir Muriel , Burnier Véronique , Larsson Åsa , Cabane Bernard
Published: December 2012

The skin is a barrier membrane that separates environments with profoundly different water contents. The barrier properties are assured by the outer layer of the skin, the stratum corneum (SC), which controls the transepidermal water loss. The SC acts as a responding membrane, since its hydration and permeability vary with the boundary condition, which is the activity of water at the outer surface of the skin. We show how this boundary condition can be changed by the application of a barrier cream that makes a film with a high resistance to the transport of water. We present a quantitative model that predicts hydration and water transport in SC that is covered by such a film. We also develop an experimental method for measuring the specific resistance to water transport of films made of occluding barrier creams. Finally, we combine the theoretical model with the measured properties of the barrier creams to predict how a film of cream changes the activity of water at the outer surface of the SC. Using the known variations of SC permeability and hydration with the water activity in its environment (i.e. the relative humidity), we can thus predict how a film of barrier cream changes SC hydration.
S-band ferromagnetic resonance spectroscopy and the detection of magnetofossils
Authors: Gehring Andreas U. , Kind Jessica , Charilaou Michalis , García-Rubio Inés
Published: December 2012

We report the use of S-band ferromagnetic resonance (FMR) spectroscopy to compare the anisotropic properties of magnetite particles in chains of cultured intact magnetotactic bacteria (MTB) between 300 and 15 K with those of sediment samples of Holocene age in order to infer the presence of magnetofossils and their preservation in a geological time frame. The spectrum of intact MTB at 300 K exhibits distinct uniaxial anisotropy because of the chain alignment of the cellular magnetite particles and their easy axes. This anisotropy becomes less pronounced upon cooling and below the Verwey transition (TV) it is nearly vanished mainly owing to the change of direction of the easy axes. In a natural sample, magnetofossils were detected by uniaxial anisotropy traits similar to those obtained from cultured MTB aboveTV. Our comparative study emphasizes that indispensable information can be obtained from S-band FMR spectra, which offers even a better resolution than X-band FMR for discovering magnetofossils, and this in turn can contribute towards strengthening our relatively sparse database for deciphering the microbial ecology during the Earth's history.
Buckling as an origin of ordered cuticular patterns in flower petals
Authors: Antoniou Kourounioti Rea L. , Band Leah R. , Fozard John A. , Hampstead Anthony , Lovrics Anna , Moyroud Edwige , Vignolini Silvia , King John R. , Jensen Oliver E. , Glover Beverley J.
Published: December 2012

The optical properties of plant surfaces are strongly determined by the shape of epidermal cells and by the patterning of the cuticle on top of the cells. Combinations of particular cell shapes with particular nanoscale structures can generate a wide range of optical effects. Perhaps most notably, the development of ordered ridges of cuticle on top of flat petal cells can produce diffraction-grating-like structures. A diffraction grating is one of a number of mechanisms known to produce ‘structural colours’, which are more intense and pure than chemical colours and can appear iridescent. We explore the concept that mechanical buckling of the cuticle on the petal epidermis might explain the formation of cuticular ridges, using a theoretical model that accounts for the development of compressive stresses in the cuticle arising from competition between anisotropic expansion of epidermal cells and isotropic cuticle production. Model predictions rationalize cuticle patterns, including those with long-range order having the potential to generate iridescence, for a range of different flower species.
The evolutionary dynamics of within-generation immune priming in invertebrate hosts
Authors: Best Alex , Tidbury Hannah , White Andy , Boots Mike
Published: December 2012

While invertebrates lack the machinery necessary for ‘acquired immunity’, there is increasing empirical evidence that exposure to low levels of disease may ‘prime’ an invertebrate's immune response, increasing its defence to subsequent exposure. Despite this increasing empirical data, there has been little theoretical attention paid to immune priming. Here, we investigate the evolution of immune priming, focusing on the role of the unique feedbacks generated by a newly developed susceptible–primed–infected epidemiological model. Contrasting our results with previous models on the evolution of acquired immunity, we highlight that there are important implications to the evolution of immunity through priming owing to these different epidemiological feedbacks. In particular, we find that in contrast to acquired immunity, priming is strongly selected for at high as well as intermediate pathogen virulence. We also find that priming may be greatest at either intermediate or high host lifespans depending on the severity of disease. Furthermore, hosts faced with more severe pathogens are more likely to evolve diversity in priming. Finally, we show when the evolution of priming leads to the exclusion of the pathogens or hosts experiencing population cycles. Overall the model acts as a baseline for understanding the evolution of priming in host–pathogen systems.