bluuebunny/crossref_metadata_2025 huggingface dataset:
Theory of attosecond delays in molecular photoionization
Authors: Baykusheva Denitsa , Wörner Hans Jakob
Published: March 2017

We present a theoretical formalism for the calculation of attosecond delays in molecular photoionization. It is shown how delays relevant to one-photon-ionization, also known as Eisenbud-Wigner-Smith delays, can be obtained from the complex dipole matrix elements provided by molecular quantum scattering theory. These results are used to derive formulae for the delays measured by two-photon attosecond interferometry based on an attosecond pulse train and a dressing femtosecond infrared pulse. These effective delays are first expressed in the molecular frame where maximal information about the molecular photoionization dynamics is available. The effects of averaging over the emission direction of the electron and the molecular orientation are introduced analytically. We illustrate this general formalism for the case of two polyatomic molecules. N2O serves as an example of a polar linear molecule characterized by complex photoionization dynamics resulting from the presence of molecular shape resonances. H2O illustrates the case of a non-linear molecule with comparably simple photoionization dynamics resulting from a flat continuum. Our theory establishes the foundation for interpreting measurements of the photoionization dynamics of all molecules by attosecond metrology.
Modelling the matrix shift on the vibrational frequency of ThO by DFT-D3 calculations
Authors: Kovács Attila , Rode Joanna E.
Published: March 2017

Benchmark calculations with a goal to find dispersion-corrected DFT-D3 methods suitable for a reliable estimation of matrix shifts on the vibrational frequency were carried out on the ThO molecule in three rare gas (Rg = Ne, Ar, and Kr) matrices. The matrices were modelled by the explicit approach, in which a single and a double shell of Rg atoms around ThO was considered. The selection of exchange-correlation functionals was based on test calculations on triatomic ThO⋯Rg models. The B3LYP, PBE0, CAM-B3LYP, and LC-ωPBE functionals were found to be the best suited for the estimation of matrix shifts. The single shell of Rg’s around ThO accounted for a major part of the shifts; the addition of a second Rg shell resulted only in a minor improvement. Continuum solvation models considerably overestimated the effect of Rg matrices both when the whole matrix was treated by the model and when the first shell was treated explicitly and the rest with a continuum solvation model.
Epitaxy of oligothiophenes on alkali metal hydrogen phthalates: Simulations and experiments
Authors: Trabattoni S. , Raimondo L. , Sassella A. , Moret M.
Published: March 2017

Three alkali metal hydrogen phthalate salts (denoted as XAP, X = K+, Rb+, and Cs+) are chosen as substrates for the growth of quaterthiophene (4T) and hexathiophene (6T) thin films by organic molecular beam epitaxy to study the influence of gradual changes of surface unit cell parameters on the epitaxial growth. The increment of substrate lattice parameters increases the distance between the planes that define the furrows where oligothiophene molecules lie, while keeping unmodified the interactions between the overlayer and the substrate. Atom-atom potential simulations predict the preferential azimuthal orientations of the overlayer, which are compared with those experimentally observed. The agreement between simulations and experiments about contact planes and orientation of the crystalline domains in the films is satisfactory for both 4T/XAP and 6T/XAP. The increasing width of the surface furrows existing on moving from KAP to RbAP and CsAP does not cause any significant variation of the orientation and density of the overlayer domains, demonstrating that the interaction between overlayer and substrate is the key factor guiding organic epitaxial growth.
Photodissociation dynamics of the pyridinyl radical: Time-dependent quantum wave-packet calculations
Authors: Ehrmaier Johannes , Picconi David , Karsili Tolga N. V. , Domcke Wolfgang
Published: March 2017

The H-atom photodissociation reaction from the pyridinyl radical (C5H5NH) via the low-lying πσ* excited electronic state is investigated by nonadiabatic time-dependent quantum wave-packet dynamics calculations. A model comprising three electronic states and three nuclear coordinates has been constructed using ab initio multi-configurational self-consistent-field and multi-reference perturbation theory methods. Two conical intersections among the three lowest electronic states have been characterized in the framework of the linear vibronic-coupling model. Time-dependent wave-packet simulations have been performed using the multi-configuration time-dependent Hartree method. The population dynamics of the diabatic and adiabatic electronic states and the time-dependent dissociation behavior are analyzed for various vibrational initial conditions. The results provide detailed mechanistic insight into the photoinduced H-atom dissociation process from a hypervalent aromatic radical and show that an efficient dissociation reaction through two conical intersections is possible.
Inferring directed climatic interactions with renormalized partial directed coherence and directed partial correlation
Authors: Tirabassi Giulio , Sommerlade Linda , Masoller Cristina
Published: March 2017

Inferring interactions between processes promises deeper insight into mechanisms underlying network phenomena. Renormalised partial directed coherence is a frequency-domain representation of the concept of Granger causality, while directed partial correlation is an alternative approach for quantifying Granger causality in the time domain. Both methodologies have been successfully applied to neurophysiological signals for detecting directed relationships. This paper introduces their application to climatological time series. We first discuss the application to El Niño–Southern Oscillation—Monsoon interaction and then apply the methodologies to the more challenging air-sea interaction in the South Atlantic Convergence Zone (SACZ). In the first case, the results obtained are fully consistent with the present knowledge in climate modeling, while in the second case, the results are, as expected, less clear, and to fully elucidate the SACZ air-sea interaction, further investigations on the specificity and sensitivity of these methodologies are needed.
A perturbation-theoretic approach to Lagrangian flow networks
Authors: Fujiwara Naoya , Kirchen Kathrin , Donges Jonathan F. , Donner Reik V.
Published: March 2017

Complex network approaches have been successfully applied for studying transport processes in complex systems ranging from road, railway, or airline infrastructures over industrial manufacturing to fluid dynamics. Here, we utilize a generic framework for describing the dynamics of geophysical flows such as ocean currents or atmospheric wind fields in terms of Lagrangian flow networks. In this approach, information on the passive advection of particles is transformed into a Markov chain based on transition probabilities of particles between the volume elements of a given partition of space for a fixed time step. We employ perturbation-theoretic methods to investigate the effects of modifications of transport processes in the underlying flow for three different problem classes: efficient absorption (corresponding to particle trapping or leaking), constant input of particles (with additional source terms modeling, e.g., localized contamination), and shifts of the steady state under probability mass conservation (as arising if the background flow is perturbed itself). Our results demonstrate that in all three cases, changes to the steady state solution can be analytically expressed in terms of the eigensystem of the unperturbed flow and the perturbation itself. These results are potentially relevant for developing more efficient strategies for coping with contaminations of fluid or gaseous media such as ocean and atmosphere by oil spills, radioactive substances, non-reactive chemicals, or volcanic aerosols.
Eutectic pattern transition under different temperature gradients: A phase field study coupled with the parallel adaptive-mesh-refinement algorithm
Authors: Zhang A. , Guo Z. , Xiong S.-M.
Published: March 2017

Eutectic pattern transition under an externally imposed temperature gradient was studied using the phase field method coupled with a novel parallel adaptive-mesh-refinement (Para-AMR) algorithm. Numerical tests revealed that the Para-AMR algorithm could improve the computational efficiency by two orders of magnitude and thus made it possible to perform large-scale simulations without any compromising accuracy. Results showed that the direction of the temperature gradient played a crucial role in determining the eutectic patterns during solidification, which agreed well with experimental observations. In particular, the presence of the transverse temperature gradient could tilt the eutectic patterns, and in 3D simulations, the eutectic microstructure would alter from lamellar to rod-like and/or from rod-like to dumbbell-shaped. Furthermore, under a radial temperature gradient, the eutectic would evolve from a dumbbell-shaped or clover-shaped pattern to an isolated rod-like pattern.
Fragmentation dynamics of meso-tetraphenyl iron (III) porphyrin chloride dication under energy control
Authors: Li B. , Allouche A. R. , Bernard J. , Brédy R. , Qian D. B. , Ma X. , Martin S. , Chen L.
Published: March 2017

Meso-tetraphenyl iron (III) porphyrin chloride dications (FeTPPCl2+)* were prepared in collisions with F+ and H+ at 3 keV. The dominant fragmentation channels were observed to involve the loss of the Cl atom and the successive loss of neutral phenyl groups for both collisional systems. The mass spectra in correlation with the deposited excitation energy distributions of the parent ions for the main fragmentation channels were measured by using the collision induced dissociation under energy control method. The global excitation energy distribution was found to be shifted to lower energies in collisions with H+ compared to collisions with F+ showing a noteworthy change of the excitation energy window using different projectile ions. Partial excitation energy distributions of the parent ions FeTPPCl2+ were obtained for each fragmentation group. In a theoretical work, we have calculated the dissociation energies for the loss of one and two phenyl groups, including phenyl and (phenyl ± H). The energy barrier for the hydrogen atom transfer during the loss of (phenyl-H) has been also calculated. The measured energy difference for the successive loss of two phenyl groups was compared with the theoretical values.
Revealing the properties of defects formed by CH3NH2 molecules in organic-inorganic hybrid perovskite MAPbBr3
Authors: Wang Ji , Zhang Ao , Yan Jun , Li Dan , Chen Yunlin
Published: March 2017

The properties of defects in organic-inorganic hybrid perovskite are widely studied from the first-principles calculation. However, the defects of methylamine (methylamine = CH3NH2), which would be easily formed during the preparation of the organic-inorganic hybrid perovskite, are rarely investigated. Thermodynamic properties as well as defect states of methylamine embedded MAPbX3 (MA = methyl-ammonium = CH3NH3, X = Br, I) are studied based on first-principles calculations of density functional theory. It was found that there is a shallow defect level near the highest occupied molecular orbital, which induced by the interstitial methylamine defect in MAPbBr3, will lead to an increase of photoluminescence. The calculation results showed that interstitial defect states of methylamine may move deeper due to the interaction between methylamine molecules and methyl-ammonium cations. It was also showed that the interstitial methylamine defect is stable at room temperature, and the defect can be removed easily by annealing.
Quantum and quasiclassical dynamics of the multi-channel H + H2S reaction
Authors: Qi Ji , Lu Dandan , Song Hongwei , Li Jun , Yang Minghui
Published: March 2017

The prototypical multi-channel reaction H + H2S → H2 + SH/H + H2S has been investigated using the full-dimensional quantum scattering and quasi-classical trajectory methods to unveil the underlying competition mechanism between different product channels and the mode specificity. This reaction favors the abstraction channel over the exchange channel. For both channels, excitations in the two stretching modes promote the reaction with nearly equal efficiency and are more efficient than the bending mode excitation. However, they are all less efficient than the translational energy. In addition, the experimentally observed non-Arrhenius temperature dependence of the thermal rate constants is reasonably reproduced by the quantum dynamics calculations, confirming that the non-Arrhenius behavior is caused by the pronounced quantum tunneling.
Curvature effect on the surface topography evolution during oxidation at small scale
Authors: Fang Xufei , Li Yan , Feng Xue
Published: March 2017

We use high temperature scanning probe microscopy (SPM) to in situ and real time characterize the evolution of surface topography of metals during oxidation. A nanoindentation method was used to create nanoindents as markers to pinpoint the locations where the evolution of the surface topography was studied. The SPM images reveal that during oxidation, the originally sharp tip of the indented pits exhibits a chamfering and flattening effect, suggesting that the tip curvature affects the surface topography evolution at the nanoscale/sub-microscale during the oxidation process. A model is proposed to explain the experimental result by considering the surface diffusion as well as the curvature effect.
Elastic strain field due to an inclusion of a polyhedral shape with a non-uniform lattice misfit
Authors: Nenashev A. V. , Dvurechenskii A. V.
Published: March 2017

An analytical solution in a closed form is obtained for the three-dimensional elastic strain distribution in an unlimited medium containing an inclusion with a coordinate-dependent lattice mismatch (an eigenstrain). Quantum dots consisting of a solid solution with a spatially varying composition are examples of such inclusions. It is assumed that both the inclusion and the surrounding medium (the matrix) are elastically isotropic and have the same Young's modulus and Poisson ratio. The inclusion shape is supposed to be an arbitrary polyhedron, and the coordinate dependence of the lattice misfit, with respect to the matrix, is assumed to be a polynomial of any degree. It is shown that, both inside and outside the inclusion, the strain tensor is expressed as a sum of contributions of all faces, edges, and vertices of the inclusion. Each of these contributions, as a function of the observation point's coordinates, is a product of some polynomial and a simple analytical function, which is the solid angle subtended by the face from the observation point (for a contribution of a face), or the potential of the uniformly charged edge (for a contribution of an edge), or the distance from the vertex to the observation point (for a contribution of a vertex). The method of constructing the relevant polynomial functions is suggested. We also found out that similar expressions describe an electrostatic or gravitational potential, as well as its first and second derivatives, of a polyhedral body with a charge/mass density that depends on coordinates polynomially.
Potential application of X-ray communication through a plasma sheath encountered during spacecraft reentry into earth's atmosphere
Authors: Li Huan , Tang Xiaobin , Hang Shuang , Liu Yunpeng , Chen Da
Published: March 2017

Rapid progress in exploiting X-ray science has fueled its potential application in communication networks as a carrier wave for transmitting information through a plasma sheath during spacecraft reentry into earth's atmosphere. In this study, we addressed the physical transmission process of X-rays in the reentry plasma sheath and near-earth space theoretically. The interactions between the X-rays and reentry plasma sheath were investigated through the theoretical Wentzel–Kramers–Brillouin method, and the Monte Carlo simulation was employed to explore the transmission properties of X-rays in the near-earth space. The simulation results indicated that X-ray transmission was not influenced by the reentry plasma sheath compared with regular RF signals, and adopting various X-ray energies according to different spacecraft reentry altitudes is imperative when using X-ray uplink communication especially in the near-earth space. Additionally, the performance of the X-ray communication system was evaluated by applying the additive white Gaussian noise, Rayleigh fading channel, and plasma sheath channel. The Doppler shift, as a result of spacecraft velocity changes, was also calculated through the Matlab Simulink simulation, and various plasma sheath environments have no significant influence on X-ray communication owing to its exceedingly high carrier frequency.
Mechanism of total electron emission yield reduction using a micro-porous surface
Authors: Ye Ming , Wang Dan , He Yongning
Published: March 2017

Suppression of the total secondary electron yield (TEY) of metal surfaces is important in many areas such as accelerator, satellite, and Hall thruster. Among TEY suppression techniques, micro-porous surfaces have been demonstrated as an effective method. In this work, we developed an analytical model that is able to obtain the contributions of TEY from both the 1st and 2nd generation secondary electrons (SEs). Calculation results show that the TEY contributed by the bottom of the hole dominates the TEY of the micro-porous surface with the aspect ratio we have chosen. Thus, we developed the following design guidance for the improvement of the TEY suppression efficiency of the micro-porous surface: either lower the TEY of the bottom or guide its SEs to the lateral side of the hole. To verify this idea, we performed the following numerical simulations: a micro-hole with its inner surfaces coated with a low TEY material and a micro-hole with nano-triangular grooves or nano-truncated cone pillars embedded at its bottom. Compared with a usual micro-hole, the proposed hybrid micro/nano structures show improved TEY suppression efficiency as expected from the analytical model. The percentage ratios of the 1st and 2nd generation SEs obtained from the simulation agree well with the predictions of the analytical model. What is more, we also present the results of the emitting angle distribution of SEs which represent remarkable deviation from the usual cosine distribution.
Multiple plasmon resonance in a concentric silver-atomic medium nanoshell
Authors: Liu Wenxiao , Wang Xin , Chai Yaqin , Gao Shaoyan , Li Fuli
Published: March 2017

Optical properties of a concentric silver-atomic medium nanoshell are investigated based on the quasi-static and Maxwell-Garnett approximations. We consider the atomic medium as Λ-type three-level atoms driven simultaneously by a coupling field and a probe field. It is shown that the strong coupling between atoms and sphere plasmon of silver core emerges of multiple-mode and ultra narrow-band absorption spectra by controlling the permittivity of the atomic medium. In particular, coherent driving of the coupling field allows us to manipulate surface plasmon resonances, including frequency shift and bandwidth modification. Furthermore, we demonstrate that selective absorption enhancement of different modes can be achieved by tuning the radius of the core and the shell. These absorption properties yield potential applications of the nanoshells as ultracompact tunable nonlinear optical devices.
Numerical study of Hall effects on counter-helicity spheromak merging by two-dimensional Hall-MHD simulations
Authors: Kaminou Yasuhiro , Guo Xuehan , Inomoto Michiaki , Ono Yasushi , Horiuchi Ritoku
Published: March 2017

Hall effects on counter-helicity spheromak merging were investigated by two-dimensional MHD and Hall-MHD simulations of merging two axisymmetric toroidal flux tubes. In Hall-MHD cases, the structure of the reconnection current sheet and reconnection outflow are modified from the MHD case due to the Hall effect. We compared two cases (called “case-O” and “case-I”) of counter-helicity merging, which are distinguished by the polarity of toroidal magnetic fluxes. Radial motion of the reconnection X-point is controlled by poloidal electron flow accompanying the toroidal flux of the merging two spheromaks, and this creates a large difference in the current sheet and flow structure between the two cases of the Hall-MHD regime. The radial shift of the reconnection X-point depending on the polarity of toroidal magnetic flux of the spheromaks breaks the symmetry between the two cases. It was also found that there widely exists separation of ion and electron flow which are affected by the modification of the current sheet structure due to the radial shift of the X-point in the downstream side of the merging, and its spatial scale of the distribution of the Hall electric field is larger than the ion skin depth.
An in situ trap capacitance measurement and ion-trapping detection scheme for a Penning ion trap facility
Authors: Reza Ashif , Banerjee Kumardeb , Das Parnika , Ray Kalyankumar , Bandyopadhyay Subhankar , Dam Bivas
Published: March 2017

This paper presents the design and implementation of an in situ measurement setup for the capacitance of a five electrode Penning ion trap (PIT) facility at room temperature. For implementing a high Q resonant circuit for the detection of trapped electrons/ions in a PIT, the value of the capacitance of the trap assembly is of prime importance. A tunable Colpitts oscillator followed by a unity gain buffer and a low pass filter is designed and successfully implemented for a two-fold purpose: in situ measurement of the trap capacitance when the electric and magnetic fields are turned off and also providing RF power at the desired frequency to the PIT for exciting the trapped ions and subsequent detection. The setup is tested for the in situ measurement of trap capacitance at room temperature and the results are found to comply with those obtained from measurements using a high Q parallel resonant circuit setup driven by a standard RF signal generator. The Colpitts oscillator is also tested successfully for supplying RF power to the high Q resonant circuit, which is required for the detection of trapped electrons/ions.
Persistent photoconductivity in ZnO nanowires: Influence of oxygen and argon ambient
Authors: Madel M. , Huber F. , Mueller R. , Amann B. , Dickel M. , Xie Y. , Thonke K.
Published: March 2017

ZnO nanowires typically show persistent photoconductivity (PPC), which depends in their temporal behaviour on the ambient. We investigate ZnO nanowires in oxygen and argon ambient and analyze the PPC both on the short and on the long time scale to sort out the underlying mechanisms. Wavelength dependent excitation shows the energy barrier for the PPC to be around 150 meV below the band gap of ZnO, independent of the ambient atmosphere. In photocurrent measurements at constant wavelength, a log-logistic dependence of the conductivity on the partial oxygen pressure is observed. The experimental results are compared to a model of Bonasewicz et al. [J. Electrochem. Soc. 133, 2270 (1986)] and can be explained by oxygen adsorption processes occurring on the surface of the ZnO nanowires. From temperature dependent measurements of the decay times in oxygen and argon ambient, the related activation energies for the fast and slow decay processes are determined. Comparing our results to theoretical calculations of energy levels of intrinsic defects [Janotti and Van de Walle, Phys. Status Solidi B 248, 799 (2011)], we find oxygen vacancies to be related to the fast decay processes, whereas adsorption and desorption processes of oxygen on the ZnO nanowire surface account for the slow part.
Enhanced positron trapping by Ag nanoclusters at low temperatures: A challenge of positron sensitivity to quantum dots
Authors: Zou B. , Qi N. , Liu Z. W. , Chen Z. Q. , Liu H. Q. , Yi D. Q. , Tang Z.
Published: March 2017

Microstructure evolution of three Al-Ag alloys with different Ag contents (1 wt. % Ag, 5 wt. % Ag, and 15 wt. % Ag) was studied by positron annihilation spectroscopy during the aging process. In situ measurements of the positron lifetime and Doppler broadening of annihilation radiation indicate the fast formation of Ag-rich clusters during natural aging of the alloys. The formation of Ag-rich clusters was further confirmed by coincidence Doppler broadening measurements. The Ag signal reflected by the Coincidence Doppler broadening spectrum increases with increasing Ag content and is further enhanced after subsequent artificial aging at 140 °C. This might be due to the increase in the size of Ag clusters. The temperature dependence of the Doppler broadening spectra between 10 K and 290 K was measured for the Al-Ag alloys after natural and artificial aging. Detrapping of positrons from Ag clusters with increasing temperature was observed for all the three Al-Ag alloys after natural aging and for the Al-1 wt. % Ag after artificial aging. This indicates that Ag clusters act as shallow positron trapping centers. The thermal detrapping of positrons becomes ambiguous with increasing Ag content in the alloy and is nearly invisible in the artificially aged Al-5 wt. % Ag and Al-15 wt. % Ag. The positron binding energy of the Ag cluster is roughly estimated to be about 18.8 meV and 50 meV in the Al-1 wt. % Ag sample after natural aging and artificial aging at 140 °C, respectively, which suggests that the confinement of positrons in the quantum-dot like state depends on the size or chemical composition of clusters. Theoretical calculations confirm positron trapping by Ag nanoclusters, and the confinement of positrons is enhanced with increasing Ag cluster size.
Giant magnetoimpedance effect in a thin-film multilayer meander-like sensor
Authors: Vilela G. L. S. , Monsalve J. G. , Rodrigues A. R. , Azevedo A. , Machado F. L. A.
Published: March 2017

A meander-like magnetic sensing element based on the giant magnetoimpedance (GMI) effect was prepared by using optical lithography and sputtering deposition techniques. The structure of the sensing element consists of layers of Permalloy (Py = Ni81Fe19), titanium (Ti), and copper (Cu) with composition [Py(100 nm)/Ti(6 nm)]4/Cu(400 nm)/[Py(100 nm)/Ti(6 nm)]4. The GMI was investigated at room temperature under applied magnetic fields (H) varying in the range of ±4.0 kOe in both longitudinal and transversal geometries. The amplitude Iac and frequency f of the ac electrical current were varied in the range of 0.35–6.50 mA and 0.1–20 MHz, respectively. The overall dc electrical resistance of the sensing element was found to be 45.6 Ω. The sensing element yielded a GMI of 53.5% for H≃ 5.0 Oe and f= 7.0 MHz, and the corresponding maximum average sensitivity of about 5 Ω/Oe. The sensing element was used for measuring the local Earth magnetic field (Hlocal=0.26±0.03 Oe) yielding a value close to the one measured by using a Hall sensor probe (=0.23±0.01 Oe). GMI sensors are being used in applications such as accelerometers, magnetometers, biomagnetism, magnetic compasses, traffic control, non-destructive analysis, and virus and cancer cell detection.
Bio-assembled, piezoelectric prawn shell made self-powered wearable sensor for non-invasive physiological signal monitoring
Authors: Ghosh Sujoy Kumar , Mandal Dipankar
Published: March 2017

A human interactive self-powered wearable sensor is designed using waste by-product prawn shells. The structural origin of intrinsic piezoelectric characteristics of bio-assembled chitin nanofibers has been investigated. It allows the prawn shell to make a tactile sensor that performs also as a highly durable mechanical energy harvester/nanogenerator. The feasibility and fundamental physics of self-powered consumer electronics even from human perception is highlighted by prawn shells made nanogenerator (PSNG). High fidelity and non-invasive monitoring of vital signs, such as radial artery pulse wave and coughing actions, may lead to the potential use of PSNG for early intervention. It is presumed that PSNG has enormous future aspects in real-time as well as remote health care assessment.
Acoustic levitation of soap bubbles in air: Beyond the half-wavelength limit of sound
Authors: Zang Duyang , Lin Kejun , Li Lin , Chen Zhen , Li Xiaoguang , Geng Xingguo
Published: March 2017

We report on the behavior of levitated soap bubbles in a single-axis acoustic field. For a single bubble, its surface in the polar regions is under compression, but in the equatorial region, it is under suction. Levitation becomes unstable when the height of the bubble approaches half the wavelength of the sound wave because horizontal fluctuations lead to a negative recovery force and a negative levitation force. Vertically stacked double bubbles notably can be stable under levitation if their total vertical length is ∼5λ/6, significantly beyond λ/2 in consequence of the formation of a toroidal high-pressure region around the waist of the two bubbles. Our results provide a deeper insight into the stability of acoustic levitation and the coupling between bubbles and sound field.
High-performance GaAs metal-oxide-semiconductor capacitor by using NbAlON as high-k gate dielectric
Authors: Liu L. N. , Choi H. W. , Xu J. P. , Lai P. T.
Published: March 2017

A GaAs metal-oxide-semiconductor (MOS) capacitor using NbAlON as a gate dielectric with different Nb contents is fabricated. Experimental results show that the k value and crystallization temperature of the AlON dielectric can be improved by Nb incorporation, together with reduction in negative oxide charges. However, the interface quality and gate leakage become poorer as the Nb content increases, as confirmed by TEM and X-ray photoelectron spectroscopy results. Therefore, through comprehensively considering the advantages and disadvantages, the sample with a Nb/(Al+Nb) atomic ratio of 62.5% exhibits the best characteristics: high k value (23.3), low interface-state density (2.7 × 1012 cm−2/eV), small hysteresis (55 mV), small frequency dispersion, and low gate leakage current (2.66 × 10−5A/cm2 at Vfb + 1 V). By comparing with reported GaAs MOS devices with different high-k gate dielectrics, it can be suggested that NbAlON is a promising gate dielectric material to achieve excellent electrical performance for GaAs MOS devices.
Realization of acoustic wave directivity at low frequencies with a subwavelength Mie resonant structure
Authors: Lu Gengxi , Ding Erliang , Wang Yangyang , Peng Xiuyuan , Cui Jun , Liu Xiaozhou , Liu Xiaojun
Published: March 2017

We realized high-efficiency acoustic directivity at low frequencies based on monopolar Mie resonance. This is caused by micro structures that have a high refractive index relative to the background medium. The structures can strongly control the radiation pattern though the acoustic wavelength is much larger than its dimensions. We herein discuss how to enhance the directivity through modifying the structure's parameters. Furthermore, our structure is proposed for use in obtaining an acoustic collimated beam without sidelobes. The structure characteristics and applications are demonstrated both theoretically and experimentally. Potential applications of our structures include acoustic device miniaturization, noise control, and medical ultrasonics.
Pressure-induced permanent metallization with reversible structural transition in molybdenum disulfide
Authors: Zhuang YuKai , Dai LiDong , Wu Lei , Li HePing , Hu HaiYing , Liu KaiXiang , Yang LinFei , Pu Chang
Published: March 2017

This report presents a pressure-induced permanent metallization for MoS2 under non-hydrostatic conditions. Impedance and Raman spectra were measured to study the pressure-induced structural and electronic transformations of MoS2 at up to ∼25 GPa in diamond anvil cells under both non-hydrostatic and hydrostatic conditions. The results show evidence for isostructural hexagonal distortion from 2Hc to 2Ha and metallization at ∼17 GPa and ∼20 GPa under non-hydrostatic and hydrostatic conditions, respectively. Interestingly, the metallization is irreversible only under non-hydrostatic compression. We attribute this phenomenon to the incorporation of molecules of pressure medium between layers, which mitigate compressed stress and reduce interlayer interaction.
Structure and Magnetic Studies on a Series of Two-Dimensional Iron(II) Framework Materials with Varying Ligand Characteristics
Authors: Roxburgh Matthew A. D. , Zaiter Samantha , Hudson Xina I. B. , Mullaney Benjamin R. , Clements John E. , Moubaraki Boujemaa , Murray Keith S. , Neville Suzanne M. , Kepert Cameron J.
Published: March 2017

Targeting the general (4,4)-grid structural motif, we have prepared seven new coordination polymers in the general family [Fe(NCX)2(L)2]·(guest) (L = bis-pyridyl-type bridging ligands; X = S, Se) as an extension of the well-established spin crossover framework (SCOF) family. In all cases, the (4,4)-grid topology is formed by the bridging of octahedral iron(ii) sites in the equatorial plane by bis-pyridyl ligands of varying length, flexibility, and intermolecular interaction capacity. In particular, the six ligands n-(4-pyridyl)-isonicotinamide (pin), trans-1,2-bis(4′-pyridyl)ethane (tvp), 1,2-dibromo-1,2-bis(4′-pyridyl)ethane (dbbpe), bis(4-pyridyl)-1,2,4,5-tetrazine (bptz), 4,4′-bis(pyridyl)acetylene (bpac), and 1,4-bis(4-pyridylethynyl)benzene (bpeben) have been utilised. The seven new materials [Fe(NCS)2(pin)2]·2(MeCN) (pin-S), [Fe(tvp)2(NCS)2]·1/2(tvp)·(CH3CH2OH) (tvp-S), [Fe(dbbpe)2(NCS)2]·6(CH3CN) (dbbpe-S), [Fe(NCS)2(bptz)2]·2(CHCl3)·6(EtOH) (bptz-S), [Fe(NCSe)2(bptz)2]·4(CHCl3)·(EtOH)·(H2O) (bptz-Se), [Fe(NCS)2(bpac)2]·2(PrOH) (bpac-S), and [Fe(NCS)2(bpeben)2]·2(CHCl3) (bpeben-S) all form (4,4)-grids of varying size that are arranged in a parallel stacked topology. Despite being in the [FeN6] coordination environment known to be conducive to spin crossover, these materials all remain high-spin with thermal variation. These results are discussed in context with the large family of SCOFs that show varied spin crossover behaviours.
Field effects in the saturation region of space charge limited current in molecular crystals
Authors: Bonham JS , Lyons LE
Published: March 2017

Current-voltage curves in the saturation region of hole injection from aqueous
Ce(SO4)2, KI3, and SnCl4 solutions into anthracene are reported. These, and some
curves for similar systems appearing in the literature, contrast with the prediction of a
flat saturation region from the theory developed by Mehl and Hale. They are inter-
preted in terms of field assisted emission from the surface into the bulk of the crystal,
although in some systems, particularly Ce(SO4), 1 anthracene, two mechanisms appear
to operate. In an Appendix the effects of space charge on the shape of the saturation
curve are shown to be small, except near the saturation point in some cases.
Acetylenic Acids. I. The reaction of arylpropiolic acids with carbodiimides
Authors: Cadby PA , Hearn MTW , Ward AD
Published: March 2017

The formation of
substituted 1-phenylnaphthalene-2,3-dicarboxylic anhydrides from substituted
phenylpropiolic acids by carbodiimides is shown to be a general reaction and
proceeds in high yields under mild conditions. Heterocyclic acetylenic acids
also form analogous products in high yield. The reaction is confined to
α,β-acetylenic acids conjugated with an aromatic ring, as
alkylpropiolic acids form mixtures of alkylpropiolic anhydrides and N-acylureas
under the same conditions and esters of arylpropiolic acids do not react. The
effects of temperature, bases, and solvents on the reaction are described. Some
features of the nuclear magnetic resonance spectra of the 1- phenylnaphthalene
products are discussed.
Reaction of Cholesta-2,4-dien-6-one with hydrazoic acid
Authors: Ahmad MS , Pillai NK
Published: March 2017

Reaction of
cholesta-2,4-dien-6-one (1) with hydrazoic acid gave cholest-4-ene-3,6-dione
(2), 6-aza-B-homocholest-2,4-dien-7-one (3), and 6-aza-B-homocholest-4-ene-3,7-dione
(4). The structures of these compounds have been established by their spectral
properties and comparison with available authentic samples. It is shown that
neither (2) nor (3) is the precursor of (4).
Triterpene metabolite of Trametes stowardii
Authors: Cheung HT , Seeto JCF , Watson TR
Published: March 2017

The fungus Trametes stowardii produces a
triterpenoid metabolite with an uncommon malonate conjugate group. Chemical and
spectroscopic evidence indicate the structure (1)
(3α-carboxyacetoxy-24ξ-methyl-23- oxolanosta-8,25-dien-27-oic acid)
for the triterpene. Both (1) and the recently reported fungal metabolite carboxyacetyl-quercinic acid (6)1 are converted
into an identical pair of butenolides (8).
The use of atom-atom potentials in the calculation of intermolecular forces between large molecules
Authors: Morris JM
Published: March 2017

The crystal structure of
acenaphthylene has been calculated by assuming the intermolecular forces may be
represented as a sum of pairwise interactions between atoms. The calculated
structure is shown to be remarkably insensitive to the values of the parameters
used in an ?exp- 6? type atom-atom potential; variation of the parameters
associated with the attractive part of the exp-6 potential has less effect than
variation of the repulsive parameters. It is deduced that the actual values of
the parameters in the atom-atom potential have little significance and that the
correct crystal structures could be predicted by any approximately correct
repulsive potential.
Falling apart? Insights and lessons from three recent studies documenting rapid and severe decline in terrestrial mammal assemblages of northern, south-eastern and south-western Australia
Authors: Wayne A. F. , Wilson B. A. , Woinarski J. C. Z.
Published: March 2017

Context
Since European settlement in 1788, much of the Australian terrestrial mammal fauna has declined or become extinct. The pattern of, and reason for, that decline was little documented, and is now difficult to decipher. Many mammal species are still declining, providing (an unfortunate) opportunity to better document the process, identify the causal factors and attempt to redress the problem.

Aim
We compare trends in mammal abundance reported in three recent longitudinal studies in conservation reserves in Australia. The studies were not established with the intention of documenting mammal decline, but marked simultaneous decline of co-existing species was the most striking feature of their results.

Methods
Long-term monitoring in Kakadu National Park, Northern Territory (2001–04 and 2007–09), the Upper Warren region of Western Australia (since 1974) and the Great Otway National Park, Victoria (since 1975) principally relied on trapping, but also some spotlighting and sand plots, to document changes and trends in abundance in their respective mammal assemblages.

Key results
Decline was reported in most mammal species, across taxonomic groups, diets and size classes, but mostly involved species <5500g. The studies differed in their monitoring protocols and varied in the degree to which potential causal factors were monitored, thereby constraining interpretation of the drivers of declines. Inappropriate fire regimes and predation by feral cats are likely contributing factors in at least two study areas, and periods of markedly below-average rainfall are implicated in two areas.

Conclusions
We conclude the following: (1) conservation reserves in Australia may be failing to maintain at least some elements of the biodiversity that they were established to protect, and substantially enhanced management is required to redress this problem; (2) with current threats, mammal assemblages in Australia may be highly unstable; (3) substantial increase in effective long-term biodiversity monitoring programs in an adaptive management framework is needed; and (4) such monitoring programs will be more insightful if they also monitor factors driving population change.

Implications
Native mammal species declines and community disassembly may be occurring elsewhere. Long-term monitoring is critical for assessing trends in biodiversity and if done well, it can guide more effective and efficient management to deliver better conservation outcomes.
Wildlife in the line of fire: evaluating the stress physiology of a critically endangered Australian marsupial after bushfire
Authors: Hing Stephanie , Jones Krista L. , Rafferty Christine , Thompson R. C. Andrew , Narayan Edward J. , Godfrey Stephanie S.
Published: March 2017

Australian native fauna are thought to be well adapted to fire-prone landscapes, but bushfires may still pose considerable challenges or stressors to wildlife. We investigated the impact of bushfire on the stress physiology of the woylie (brush-tailed bettong, Bettongia penicillata) a critically endangered Australian marsupial, and assessed whether fitness indices (body condition and parasite load) influenced stress physiology before and after the fire. We hypothesised that there would be a significant change in stress physiology indicators (in the form of faecal cortisol metabolites, FCM) following the fire, compared with the months previous. We trapped woylies (n = 19) at Whiteman Park Reserve in Perth, Western Australia, two days after a major bushfire and measured FCM concentration by enzyme immunoassay. Population-level comparisons of FCM were made between these samples and those collected in previous months (n = 58). While mean FCM varied by month of sample collection, it was not higher after the fire. We suggest that woylies may be able to maintain homeostasis through change (allostasis), at least in the period immediately after the fire. This is supported by our finding that FCM did not relate significantly to body condition or parasite load. Our results potentially highlight the physiological and behavioural adaptations of woylies to fire, which could be further explored in future studies.
Dual-utility NLS drives RNF169-dependent DNA damage responses
Authors: An Liwei , Jiang Yiyang , Ng Howin H. W. , Man Ellen P. S. , Chen Jie , Khoo Ui-Soon , Gong Qingguo , Huen Michael S. Y.
Published: March 2017

Significance

The work describes the first nuclear localization signal (NLS) peptide that not only promotes nuclear shuttling of a DNA damage response (DDR) protein but mediates a direct interaction with a deubiquitylase for enhanced stability. Its identification suggests that NLS peptides, aside from their canonical function in nuclear import, may have acquired additional properties. The study also reports on an important role of the ubiquitin-specific protease 7 (USP7)–ring finger protein 169 (RNF169) axis in driving DNA repair and poly (ADP-ribose) polymerase inhibition resistance. Several lines of evidence indicate that USP7 deubiquitylates and enforces RNF169-dependent DDRs. Together, these data highlight a critically important role of the USP7–RNF169 axis in genome stability maintenance.
Ion and inhibitor binding of the double-ring ion selectivity filter of the mitochondrial calcium uniporter
Authors: Cao Chan , Wang Shuqing , Cui Tanxing , Su Xun-Cheng , Chou James J.
Published: March 2017

Significance

Mitochondrial calcium homeostasis is vital to cellular activities such as aerobic ATP production and cell death. Calcium uptake by mitochondria is achieved using an intricately regulated calcium channel, known as mitochondrial calcium uniporter (MCU). MCU demonstrates high calcium selectivity and conductance but little is known about its ion selectivity filter. We used paramagnetic NMR to show that the double carboxylate rings formed by the “DXXE” signature sequence of MCU is the ion selectivity filter and that the two ion binding sites can afford high ion affinity via positive cooperativity. We also showed that the channel inhibitor Ru360 directly blocks at the selectivity filter. Our approach demonstrates the promising application of NMR in investigating ion channels interacting with ions and blockers.
Spatiotemporal Reproduction and Larval Habitat Associations of Nonnative Silver Carp and Bighead Carp
Authors: Hintz William D. , Glover David C. , Szynkowski Brittany C. , Garvey James E.
Published: March 2017

The establishment of nonnative Silver Carp Hypophthalmichthys molitrix and Bighead Carp H. nobilis (collectively referred to as “bigheaded carp”) in the central United States may have negative ecological consequences and economic impacts. Our objectives were to quantify patterns and habitat associations of adult bigheaded carp reproduction, larval production, and habitat use; such information is important for control strategies and identifying recruitment sources. During May–August 2011, we sampled adults and larvae at 10 sites distributed adjacent to and within the main channel of the Mississippi River at Pool 26 (study area = 28 river kilometers). Female reproductive status, adult location, and larval density were compared to environmental conditions, including temperature, site velocity, and turbidity. Large females spawned earlier than their smaller counterparts. No clear spawning aggregations of adults were observed, suggesting plasticity in staging habitat. Larvae were distributed across all sites during flooding. Larval density was positively related to velocity and turbidity, suggesting that nondepositional areas may facilitate recruitment. Bigheaded carp larvae comprised 10% of the ichthyofauna. Although pooled reaches are a source of recruitment for bigheaded carp in the Mississippi River system, the low densities of bigheaded carp larvae relative to native larvae cannot explain the dominance of adults in this system. Our findings provide insights into the plastic nature of bigheaded carp reproduction and habitats associated with larval development. Control efforts that target large adult females should be conducted earlier during the spring spawn. To maintain fishing pressure, such control efforts would likely need to continue through the summer, when smaller individuals spawn, discharge decreases, and CPUE increases. However, we found no specific mass staging area or habitat type where adult females could be targeted.

Received July 19, 2016; accepted December 14, 2016 Published online March 21, 2017
School-based linguistic and cultural revitalization as a local practice: Sakha language education in the city of Yakutsk, Russian Federation
Authors: Chevalier Joan F.
Published: March 2017

In the 1990s, efforts were launched in the Republic of Sakha (Yakutia) in the Russian Federation to support the revival of Sakha (Yakut) language education. This interdisciplinary study examines the evolution of school-based Sakha language education in the city of Yakutsk over a 25-year period beginning with the launching of the first reforms in the 1990s. Language education reform in the capital city has been shaped by a dynamic interplay between federal, regional, and local factors. Grassroots social and cultural activism continues to play a key role in school-based language revitalization in Yakutsk, influencing how policies have been received and implemented at the local level. Local community stakeholders are working together to counteract federal education policies, which direct school resources away from minority language education. This case study shows that the Sakha (Yakut) language revival has taken root in the capital city, and it provides important evidence that civic activism continues to develop in urban areas of the republic.