bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature-dependent solubilities and mean ionic activity coefficients of alkali halides in water from molecular dynamics simulations
Authors: Mester Zoltan , Panagiotopoulos Athanassios Z.
Published: July 2015

The mean ionic activity coefficients of aqueous KCl, NaF, NaI, and NaCl solutions of varying concentrations have been obtained from molecular dynamics simulations following a recently developed methodology based on gradual insertions of salt molecules [Z. Mester and A. Z. Panagiotopoulos, J. Chem. Phys. 142, 044507 (2015)]. The non-polarizable ion models of Weerasinghe and Smith [J. Chem. Phys. 119, 11342 (2003)], Gee et al. [J. Chem. Theory Comput. 7, 1369 (2011)], Reiser et al. [J. Chem. Phys. 140, 044504 (2014)], and Joung and Cheatham [J. Phys. Chem. B 112, 9020 (2008)] were used along with the extended simple point charge (SPC/E) water model [Berendsen et al., J. Phys. Chem. 91, 6269 (1987)] in the simulations. In addition to the chemical potentials in solution used to obtain the activity coefficients, we also calculated the chemical potentials of salt crystals and used them to obtain the solubility of these alkali halide models in SPC/E water. The models of Weerasinghe and Smith [J. Chem. Phys. 119, 11342 (2003)] and Gee et al. [J. Chem. Theory Comput. 7, 1369 (2011)] provide excellent predictions of the mean ionic activity coefficients at 298.15 K and 1 bar, but significantly underpredict or overpredict the solubilities. The other two models generally predicted the mean ionic activity coefficients only qualitatively. With the exception of NaF for which the solubility is significantly overpredicted, the model of Joung and Cheatham predicts salt solubilities that are approximately 40%-60% of the experimental values. The models of Reiser et al. [J. Chem. Phys. 140, 044504 (2014)] make good predictions for the NaCl and NaI solubilities, but significantly underpredict the solubilities for KCl and NaF. We also tested the transferability of the models to temperatures much higher than were used to parametrize them by performing simulations for NaCl at 373.15 K and 1 bar, and at 473.15 K and 15.5 bar. All models overpredict the drop in the values of mean ionic activity coefficients with increased temperature seen in experiments. The present results, together with earlier calculations for a number of models for NaCl aqueous solutions at 298.15 K, point to the strong need for development of improved intermolecular potential models for classical simulations of electrolyte solutions.
Kinetic Monte Carlo simulations of surface reactions on supported nanoparticles: A novel approach and computer code
Authors: Kunz Lothar , Kuhn Frank M. , Deutschmann Olaf
Published: July 2015

So far most kinetic Monte Carlo (kMC) simulations of heterogeneously catalyzed gas phase reactions were limited to flat crystal surfaces. The newly developed program MoCKA (Monte Carlo Karlsruhe) combines graph-theoretical and lattice-based principles to be able to efficiently handle multiple lattices with a large number of sites, which account for different facets of the catalytic nanoparticle and the support material, and pursues a general approach, which is not restricted to a specific surface or reaction. The implementation uses the efficient variable step size method and applies a fast update algorithm for its process list. It is shown that the analysis of communication between facets and of (reverse) spillover effects is possible by rewinding the kMC simulation. Hence, this approach offers a wide range of new applications for kMC simulations in heterogeneous catalysis.
On the Grothendieck rings of equivariant fusion categories
Authors: Burciu Sebastian
Published: July 2015

In this paper, we describe a Mackey type decomposition for group actions on abelian categories. This allows us to define new Mackey functors which associates to any subgroup the K-theory of the corresponding equivariantized abelian category. In the case of an action by tensor autoequivalences, the Mackey functor at the level of Grothendieck rings has a Green functor structure. As an application we give a description of the Grothendieck rings of equivariantized fusion categories under group actions by tensor autoequivalences on graded fusion categories. In this settings, a new formula for the tensor product of any two simple objects of an equivariantized fusion category is given, simplifying the fusion formula from Burciu and Natale [J. Math. Phys. 54, 013511 (2013)].
Ion trapping by means of ferroelectric nanoparticles, and the quantification of this process in liquid crystals
Authors: Garbovskiy Yuriy , Glushchenko Iryna
Published: July 2015

Nanoparticles embedded in liquid crystals can trap mobile ions and decrease their concentration. In this paper, we generalize the nanoparticles-based approach and, through the quantitative analysis, identify the ferroelectric micro- and nanomaterials as the most promising “ion traps” that ensure close to 100% liquid crystal purification. We demonstrate that the treatment of liquid crystals with ferroelectric materials leads to a two-order of magnitude decrease in their electrical conductivity. This value exceeds previous data reported for similar systems by a factor of 10. Ferroelectric nanoparticles, when dispersed and stabilized in liquid crystals, act as highly efficient permanent ion traps, solve the problem of uncontrolled ionic contaminations, and eliminate the negative effects caused by ions.
Resonances in rotationally inelastic scattering of NH3 and ND3 with H2
Authors: Ma Qianli , van der Avoird Ad , Loreau Jérôme , Alexander Millard H. , van de Meerakker Sebastiaan Y. T. , Dagdigian Paul J.
Published: July 2015

We present theoretical studies on the scattering resonances in rotationally inelastic collisions of NH3 and ND3 molecules with H2 molecules. We use the quantum close-coupling method to compute state-to-state integral and differential cross sections for the NH3/ND3–H2 system for collision energies between 5 and 70 cm−1, using a previously reported potential energy surface [Maret et al., Mon. Not. R. Astron. Soc. 399, 425 (2009)]. We identify the resonances as shape or Feshbach resonances. To analyze these, we use an adiabatic bender model, as well as examination at the scattering wave functions and lifetimes. The strength and width of the resonance peaks suggest that they could be observed in a crossed molecular beam experiment involving a Stark-decelerated NH3 beam.
Temperature dependence of the electronic structure of semiconductors and insulators
Authors: Poncé S. , Gillet Y. , Laflamme Janssen J. , Marini A. , Verstraete M. , Gonze X.
Published: July 2015

The renormalization of electronic eigenenergies due to electron-phonon coupling (temperature dependence and zero-point motion effect) is sizable in many materials with light atoms. This effect, often neglected in ab initio calculations, can be computed using the perturbation-based Allen-Heine-Cardona theory in the adiabatic or non-adiabatic harmonic approximation. After a short description of the recent progresses in this field and a brief overview of the theory, we focus on the issue of phonon wavevector sampling convergence, until now poorly understood. Indeed, the renormalization is obtained numerically through a slowly converging q-point integration. For non-zero Born effective charges, we show that a divergence appears in the electron-phonon matrix elements at q → Γ, leading to a divergence of the adiabatic renormalization at band extrema. This problem is exacerbated by the slow convergence of Born effective charges with electronic wavevector sampling, which leaves residual Born effective charges in ab initio calculations on materials that are physically devoid of such charges. Here, we propose a solution that improves this convergence. However, for materials where Born effective charges are physically non-zero, the divergence of the renormalization indicates a breakdown of the adiabatic harmonic approximation, which we assess here by switching to the non-adiabatic harmonic approximation. Also, we study the convergence behavior of the renormalization and develop reliable extrapolation schemes to obtain the converged results. Finally, the adiabatic and non-adiabatic theories, with corrections for the slow Born effective charge convergence problem (and the associated divergence) are applied to the study of five semiconductors and insulators: α-AlN, β-AlN, BN, diamond, and silicon. For these five materials, we present the zero-point renormalization, temperature dependence, phonon-induced lifetime broadening, and the renormalized electronic band structure.
Effect of water on the local electric potential of simulated ionic micelles
Authors: Brodskaya Elena N. , Vanin Alexander A.
Published: July 2015

Ionic micelles in an aqueous solution containing single-charged counter-ions have been simulated by molecular dynamics. For both cationic and anionic micelles, it has been demonstrated that explicit description of solvent has strong effect on the micelle’s electric field. The sign of the local charge alters in the immediate vicinity of the micellar crown and the electric potential varies nonmonotonically. Two micelle models have been examined: the hybrid model with a rigid hydrocarbon core and the atomistic model. For three molecular models of water (Simple Point Charge model (SPC), Transferable Intermolecular Potential 5- Points (TIP5P) and two-centered S2), the results have been compared with those for the continuum solvent model. The orientational ordering of solvent molecules has strong effect on the local electric field surprisingly far from the micelle surface.
Distinct dissociation kinetics between ion pairs: Solvent-coordinate free-energy landscape analysis
Authors: Yonetani Yoshiteru
Published: July 2015

Different ion pairs exhibit different dissociation kinetics; however, while the nature of this process is vital for understanding various molecular systems, the underlying mechanism remains unclear. In this study, to examine the origin of different kinetic rate constants for this process, molecular dynamics simulations were conducted for LiCl, NaCl, KCl, and CsCl in water. The results showed substantial differences in dissociation rate constant, following the trend kLiCl < kNaCl < kKCl < kCsCl. Analysis of the free-energy landscape with a solvent reaction coordinate and subsequent rate component analysis showed that the differences in these rate constants arose predominantly from the variation in solvent-state distribution between the ion pairs. The formation of a water-bridging configuration, in which the water molecule binds to an anion and a cation simultaneously, was identified as a key step in this process: water-bridge formation lowers the related dissociation free-energy barrier, thereby increasing the probability of ion-pair dissociation. Consequently, a higher probability of water-bridge formation leads to a higher ion-pair dissociation rate.
Torsion-vibration coupling in S1 toluene: Implications for IVR, the torsional barrier height, and rotational constants
Authors: Gascooke Jason R. , Virgo Edwina A. , Lawrance Warren D.
Published: July 2015

We have examined the S1←S0 transition of toluene in the region from the 000 band to ∼210 cm−1 above it. The spectrum reveals methyl rotor levels of 00 toluene up to m = 6 and of the lowest frequency vibration, 201, up to m = 4. The rotor levels of both 201 and 00 are perturbed by torsion-vibration coupling. The inclusion of torsion-vibration coupling leads to the S1 torsional barrier, V6, being revised from −26.376 cm−1 to −5.59 cm−1. The torsion-vibration coupling constant is determined to be 21.1 cm−1. This situation is the S1 analogue of that recently reported for S0 toluene [Gascooke et al., J. Chem. Phys. 142, 024315 (2015)]. Torsion-vibration coupling alters both the rotor band positions and the rotational contours, which particularly affects the rotational constants associated with motion around the a-axis, about which the methyl group rotates. Every vibrational state (indicated generically by X) will be involved in the corresponding X − X201 torsion-vibration coupling; so, this interaction permeates the vib-rotor manifold, providing a mechanism to enhance intramolecular vibrational energy redistribution.
XeCl excimer laser with new prism resonator configurations and its performance characteristics
Authors: Benerji N. S. , Singh A. , Varshnay N. , Singh Bijendra
Published: July 2015

New resonator cavity configurations, namely, the prism resonator and unstable prism resonator, are demonstrated for the first time in an excimer (XeCl) laser with interesting and novel results. High misalignment tolerance ∼50 mrad is achieved with considerably reduced beam divergence of less than ∼1 mrad without reduction in output power capabilities of the laser. The misalignment tolerance of ∼50 mrad is a dramatic improvement of ∼25 times compared to ∼2 mrad normally observed in standard excimer laser with plane-plane cavity. Increase in depth of focus from 3 mm to 5.5 mm was also achieved in case of prism resonator configuration with an improvement of about 60%. Unstable prism resonator configuration is demonstrated here in this paper with further reduction in beam divergence to about 0.5 mrad using plano-convex lens as output coupler. The misalignment tolerance in case of unstable prism resonator was retained at about 30 mrad which is a high value compared to standard unstable resonators. The output beam spot was completely filled with flat-top profile with prism resonator configurations, which is desired for various material processing applications. Focusing properties and beam divergence in case of prism resonator have been investigated using SEM (scanning electron microscope) images. SEM images of the focused spot size (∼20 μm holes) on metal sheet indicate beam divergence of about 0.05 mrad which is about 1.5 times diffraction limit. Energy contained in this angle is thus sufficient for micro-machining applications. Clean and sharp edges of the micro-holes show high pointing stability with multiple shot exposures. Such characteristics of the excimer laser system will be extremely useful in micro-machining and other field applications.
Atomic vapor spectroscopy in integrated photonic structures
Authors: Ritter Ralf , Gruhler Nico , Pernice Wolfram , Kübler Harald , Pfau Tilman , Löw Robert
Published: July 2015

We investigate an integrated optical chip immersed in atomic vapor providing several waveguide geometries for spectroscopy applications. The narrow-band transmission through a silicon nitride waveguide and interferometer is altered when the guided light is coupled to a vapor of rubidium atoms via the evanescent tail of the waveguide mode. We use grating couplers to couple between the waveguide mode and the radiating wave, which allow for addressing arbitrary coupling positions on the chip surface. The evanescent atom-light interaction can be numerically simulated and shows excellent agreement with our experimental data. This work demonstrates a next step towards miniaturization and integration of alkali atom spectroscopy and provides a platform for further fundamental studies of complex waveguide structures.
A new potentiometric SO2 sensor based on Li3PO4 electrolyte film and its response characteristics
Authors: Wang H. , Liu Z. , Chen D. , Jiang Z.
Published: July 2015

A potentiometric SO2 gas sensor based on Li3PO4 solid electrolyte has been developed using Au as the reference electrode and Li2SO4/V2O5 as the sensing electrode. The Li3PO4 film was deposited on Al2O3 substrate by resistance heating evaporation. Two Au films with designed patterns were formed on the Li3PO4 film by micro-fabrication technologies. The sensing electrode covers one electrode partly using thick-film technology. The electromotive force values between the sensing electrode and the reference electrode were measured and various characteristics were studied including sensitivity, response characteristics, and stability and selectivity. According to the results, we conclude that an optimal working temperature of the SO2 sensor is 500 °C, the measurement range is 0-100 ppm, the sensitivity is about 32.47 mV/dec, the response and the recovery time is about 5 min and 10 min, respectively. And the stability and the selectivity of the sensor are good, making it have potential in SO2 measurement of living environment.
Electron channeling contrast imaging of anti-phase boundaries in coherently strained La0.7Sr0.3MnO3 thin films on (110)-oriented SrTiO3
Authors: Yan Miaolei , De Graef Marc , Picard Yoosuf N. , Salvador Paul A.
Published: July 2015

Electron channeling contrast imaging (ECCI) was used to characterize coherently strained La0.7Sr0.3MnO3 (LSM) films grown on (110)cubic-SrTiO3 (STO) and (100)orthorhombic-NdGaO3 (NGO). We focus on the characterization of a relatively low density (1–3 μm/μm2) of meandering loops (MLs) found in the LSM film on STO and absent in the film on NGO. The MLs exhibit a uniform contrast variation from the background and a strong contrast dependence on the diffraction vector g. The MLs are quantitatively consistent with LSM anti-phase boundaries (APBs) having a displacement vector R=12[001]LSM. These APBs are consistent with a “double positioning” degeneracy of tilted octahedra along [001]LSM on untilted octahedra along [001]STO. The results highlight the non-destructive capacity of ECCI to characterize extended defects in oxide films.
Isomeric signatures in the fragmentation of pyridazine and pyrimidine induced by fast ion impact
Authors: Wolff Wania , Luna Hugo , Montenegro Eduardo C.
Published: July 2015

We present fast proton impact induced fragmentations of pyrimidine and pyridazine as an experimental resource to investigate isomeric signatures. Major isomeric imprints are identified for few fragment ions and differences of more than an order of magnitude for the cross sections of fragments of the same mass were measured. The observation of the molecular structure of these isomers gives no apparent indication for the reasons for such substantial differences. It is verified that the simple displacement of the position of one nitrogen atom strongly inhibits or favors the production of some ionic fragment species. The dependency of the fragmentation cross sections on the proton impact energy, investigated by means of time of flight mass spectroscopy and of a model calculation based in first order perturbation theory, allows us to disentangle the complex collision dynamics of the ionic fragments. The proton-induced fragmentation discriminates rather directly the association between a molecular orbital ionization and the fragment-ions creation and abundance, as well as how the redistribution of the energy imparted to the molecules takes place, triggering not only single but also double vacancy and leads to specific fragmentation pathways.
Spectral parameter power series for Sturm-Liouville equations with a potential polynomially dependent on the spectral parameter and Zakharov-Shabat systems
Authors: Kravchenko Vladislav V. , Torba Sergii M. , Velasco-García Ulises
Published: July 2015

A spectral parameter power series (SPPS) representation for solutions of Sturm-Liouville equations of the form pu′′+qu=u∑k=1Nλkrk is obtained. Such equations are known as Sturm-Liouville equations with potentials polynomially dependent on the spectral parameter or Sturm-Liouville pencils (SLP). It allows one to write a general solution of the equation as a power series in terms of the spectral parameter λ. The coefficients of the series are given in terms of recursive integrals involving a particular solution of the equation pu0′′+qu0=0. The convenient form of the solution of SLP provides an efficient numerical method for solving corresponding initial value, boundary value, and spectral problems. A special case of the SLP arises in relation with the Zakharov-Shabat system. We derive a SPPS representation for its general solution and consider other applications as the one-dimensional Dirac system and the equation describing a damped string. Several numerical examples illustrate the efficiency and the accuracy of the numerical method based on the SPPS representations which besides its natural advantages like the simplicity in implementation and accuracy is applicable to the problems admitting complex coefficients, spectral parameter dependent boundary conditions, and complex spectrum.
Multiple solutions for a class of quasilinear Schrödinger equations in ℝN
Authors: Chen Caisheng
Published: July 2015

In this work, we study the existence of multiple solutions to a class of quasilinear Schrödinger equation −Δpu+V(x)up−2u−Δp(u2α)u2α−2u=g(u),x∈RN, where Δpu=div(∇up−2∇u) is the p − Laplacian operator and p ∈ [2α, N], α>12 is a parameter. The potential V ∈ C(ℝN) is positive and bounded in ℝN. g(u) is odd and continuous. Using symmetric mountain pass lemma, we obtain infinitely many solutions to Schrödinger equation.
Analytic representations with theta functions for systems on ℤ(d) and on 𝕊
Authors: Evangelides P. , Lei C. , Vourdas A.
Published: July 2015

An analytic representation with theta functions on a torus, for systems with variables in ℤ(d), is considered. Another analytic representation with theta functions on a strip, for systems with positions in a circle 𝕊 and momenta in ℤ, is also considered. The reproducing kernel formalism for these two systems is studied. Wigner and Weyl functions in this language are also studied.
Invited Article: First flight in space of a wide-field-of-view soft x-ray imager using lobster-eye optics: Instrument description and initial flight results
Authors: Collier Michael R. , Porter F. Scott , Sibeck David G. , Carter Jenny A. , Chiao Meng P. , Chornay Dennis J. , Cravens Thomas E. , Galeazzi Massimiliano , Keller John W. , Koutroumpa Dimitra , Kujawski Joseph , Kuntz Kip , Read Andy M. , Robertson Ina P. , Sembay Steve , Snowden Steven L. , Thomas Nicholas , Uprety Youaraj , Walsh Brian M.
Published: July 2015

We describe the development, launch into space, and initial results from a prototype wide field-of-view soft X-ray imager that employs lobster-eye optics and targets heliophysics, planetary, and astrophysics science. The sheath transport observer for the redistribution of mass is the first instrument using this type of optics launched into space and provides proof-of-concept for future flight instruments capable of imaging structures such as the terrestrial cusp, the entire dayside magnetosheath from outside the magnetosphere, comets, the Moon, and the solar wind interaction with planetary bodies like Venus and Mars [Kuntz et al., Astrophys. J. (in press)].
Quantum mechanics without potential function
Authors: Alhaidari A. D. , Ismail M. E. H.
Published: July 2015

In the standard formulation of quantum mechanics, one starts by proposing a potential function that models the physical system. The potential is then inserted into the Schrödinger equation, which is solved for the wavefunction, bound states energy spectrum, and/or scattering phase shift. In this work, however, we propose an alternative formulation in which the potential function does not appear. The aim is to obtain a set of analytically realizable systems, which is larger than in the standard formulation and may or may not be associated with any given or previously known potential functions. We start with the wavefunction, which is written as a bounded infinite sum of elements of a complete basis with polynomial coefficients that are orthogonal on an appropriate domain in the energy space. Using the asymptotic properties of these polynomials, we obtain the scattering phase shift, bound states, and resonances. This formulation enables one to handle not only the well-known quantum systems but also previously untreated ones. Illustrative examples are given for two- and three-parameter systems.
Point-contacting by localised dielectric breakdown: Characterisation of a metallisation technique for the rear surface of a solar cell
Authors: Western Ned J. , Perez-Wurfl Ivan , Wenham Stuart R. , Bremner Stephen P.
Published: July 2015

Characterisation results are presented for ohmic contacts to passivated crystalline silicon, formed using the point-contacting by localised dielectric breakdown technique. Self aligned contact is made between the metal and heavily doped surface regions through an intrinsic a-Si:H passivation layer. Local doping is provided by a laser using a standard technique identical to that for selective emitter formation. Our results for gate metals of Au, Al, and Ti show that the technique does not rely on reactivity between the dielectric and the metal, excluding metal induced crystallisation from the contacting process. Diffusion of the gate metal into the dielectric is observed in transmission electron microscope images suggesting high temperatures are present locally during the breakdown process. The technique is equally applicable to contacting of n and p-type silicon, making it a potential alternative for ohmic contacting to silicon to passivated rear surfaces.
Boundary transfer matrices and boundary quantum KZ equations
Authors: Vlaar Bart
Published: July 2015

A simple relation between inhomogeneous transfer matrices and boundary quantum Knizhnik-Zamolodchikov (KZ) equations is exhibited for quantum integrable systems with reflecting boundary conditions, analogous to an observation by Gaudin for periodic systems. Thus, the boundary quantum KZ equations receive a new motivation. We also derive the commutativity of Sklyanin’s boundary transfer matrices by merely imposing appropriate reflection equations, in particular without using the conditions of crossing symmetry and unitarity of the R-matrix.
High-speed quantum-random number generation by continuous measurement of arrival time of photons
Authors: Yan Qiurong , Zhao Baosheng , Hua Zhang , Liao Qinghong , Yang Hao
Published: July 2015

We demonstrate a novel high speed and multi-bit optical quantum random number generator by continuously measuring arrival time of photons with a common starting point. To obtain the unbiased and post-processing free random bits, the measured photon arrival time is converted into the sum of integral multiple of a fixed period and a phase time. Theoretical and experimental results show that the phase time is an independent and uniform random variable. A random bit extraction method by encoding the phase time is proposed. An experimental setup has been built and the unbiased random bit generation rate could reach 128 Mb/s, with random bit generation efficiency of 8 bits per detected photon. The random numbers passed all tests in the statistical test suite.
Adsorption of biomedical coating molecules, amino acids, and short peptides on magnetite (110)
Authors: Aschauer Ulrich , Selloni Annabella
Published: July 2015

Superparamagnetic iron oxide nanoparticles for biomedical applications are usually coated with organic molecules to form a steric barrier against agglomeration. The stability of these coatings is well established in the synthesis medium but is more difficult to assess in physiological environment. To obtain a first theoretical estimate of their stability in such an environment, we perform density functional theory calculations of the adsorption of water, polyvinyl alcohol (PVA) and polyethylene glycol (PEG) coating molecules, as well as the monomer and dimer of glycine as a prototype short peptide, on the (110) surface of magnetite (Fe3O4) in vacuo. Our results show that PVA binds significantly stronger to the surface than both PEG and glycine, while the difference between the latter two is quite small. Depending on the coverage, the water adsorption strength is intermediate between PVA and glycine. Due to its strongly interacting OH side groups, PVA is likely to remain bound to the surface in the presence of short peptides. This stability will have to be further assessed by molecular dynamics in the solvated state for which the present work forms the basis.
Liquid jet breakup and subsequent droplet dynamics under normal gravity and in microgravity conditions
Authors: Suñol Francesc , González-Cinca Ricard
Published: July 2015

We present an experimental study on the characteristics of liquid jets in different configurations. We consider jets injected perpendicular to gravity, jets injected parallel to gravity, and jets injected in a microgravity environment. We study the role played by gravity in the jet breakup length and in the dynamics of the droplets generated after breakup. We analyze droplets obtained in the dripping and jetting regimes, focusing the study on their size, trajectory, oscillation, and rotation. The particularities of the considered injection configurations are analyzed. In normal gravity conditions, in the dripping and jetting regimes, the breakup length increases with the Weber number. The transition between these regimes occurs at Wecr ≈ 3.2. Droplets are notably larger in the dripping regime than in the jetting one. In the latter case, droplet mean size decreases as the liquid flow rate is increased. In microgravity conditions, droplet trajectories form a conical shape due to droplet bouncing after collision. When a collision takes place, coalescence tends to occur at low modified Weber numbers (Wem < 2) while bouncing is observed at higher values (Wem > 2). The surface of a droplet oscillates after bouncing or coalescence events, following a damped oscillator behavior. The observed oscillation frequency agrees with theoretical predictions.
Isotopic fractionation in proteins as a measure of hydrogen bond length
Authors: McKenzie Ross H. , Athokpam Bijyalaxmi , Ramesh Sai G.
Published: July 2015

If a deuterated molecule containing strong intramolecular hydrogen bonds is placed in a hydrogenated solvent, it may preferentially exchange deuterium for hydrogen. This preference is due to the difference between the vibrational zero-point energy for hydrogen and deuterium. It is found that the associated fractionation factor Φ is correlated with the strength of the intramolecular hydrogen bonds. This correlation has been used to determine the length of the H-bonds (donor-acceptor separation) in a diverse range of enzymes and has been argued to support the existence of short low-barrier H-bonds. Starting with a potential energy surface based on a simple diabatic state model for H-bonds, we calculate Φ as a function of the proton donor-acceptor distance R. For numerical results, we use a parameterization of the model for symmetric O–H⋯O bonds [R. H. McKenzie, Chem. Phys. Lett. 535, 196 (2012)]. We consider the relative contributions of the O–H stretch vibration, O–H bend vibrations (both in plane and out of plane), tunneling splitting effects at finite temperature, and the secondary geometric isotope effect. We compare our total Φ as a function of R with NMR experimental results for enzymes, and in particular with an earlier model parametrization Φ(R), used previously to determine bond lengths.
Apparent self-accelerating alternating assembly of semiconductor nanoparticles and polymers
Authors: Horvath R. , Gardner H. C. , Ramsden J. J.
Published: July 2015

Alternating polyelectrolyte deposition is a promising route to the low-cost fabrication of electroluminescent devices based on semiconductor nanoparticles, but optimization and exploitation demand a deeper understanding of the fabrication mechanism, which has not hitherto been scrutinized in detail. Nanoparticle–polymer composites were assembled by repeated alternate exposures of a substrate to polyanionic thioglycolate-coated CdTe nanoparticles and the organic polycation polydiallyldimethylammonium while monitoring the process kinetics in situ using optical waveguide lightmode spectroscopy, which enabled detailed structural information to be obtained with good time resolution. This complements the previously reported device characterization. Two hitherto unnoticed features were observed: (i) apparently spontaneous acceleration of addition of semiconductor nanoparticles after a certain quantity has already been deposited and (ii) during subsequent exposure to the organic polycation, an appreciable proportion of the immediately previously deposited nanoparticles is removed. Analysis of the evolution of the optogeometrical parameters of the assembly revealed that during the initial slow addition the nanoparticles enter nanopores in the immediately previously deposited polymer. The deposition régime then switches abruptly to the formation of an adlayer of the nanoparticles. These are initially deposited in considerable excess, which is removable by simple dilution of the system. Further nanoparticle removal takes place during the following phase of polycation deposition via a process of particle scavenging by the polycation molecules. Changes in film refractive index during these various processes show that the predominantly columnar (rather than laminar) molecular arrangement established for polyelectrolyte-only films is maintained in the hybrid polymer–particle films, although the filling of the polyelectrolyte pores makes the film more isotropic.
Magnetocaloric properties of rare-earth substituted DyCrO3
Authors: McDannald A. , Jain M.
Published: July 2015

Recently, there has been a focus on the need for efficient refrigeration technology without the use of expensive or harmful working fluids, especially at temperatures below 30 K. Solid state refrigeration, based on the magnetocaloric effect, provides a possible solution to this problem. The rare-earth chromites (RCrO3), especially DyCrO3, with its large magnetic moment dysprosium ion, are potential candidates for such an application. The Dy3+ ordering transition at low temperatures (<10 K) likely causes a large magnetocaloric response in this material. This study investigates the possibility of tuning the magnetocaloric properties through the use of rare-earth substitution. Both Y3+ and Ho3+ substitutions were found to decrease the magnetocaloric response by disrupting the R3+ ordering. Whereas Er3+ substitution was found to increase the magnetocaloric response, likely due to an increase in the R3+ ordering temperature. The large magnetocaloric entropy change of Er3+ substituted DyCrO3 (10.92 J/kg K with a relative cooling power of 237 J/kg at 40 kOe and 5 K) indicates that this material system is well suited for low temperature (<30 K) solid state refrigeration applications.
Effect of interlayer exchange coupling on magnetic chiral structures
Authors: Kang S. P. , Kwon H. Y. , Kim H. S. , Shim J. H. , Won C.
Published: July 2015

We numerically investigated the effect of interlayer exchange coupling on magnetic chiral structures, such as a helical/cycloidal spin structure and magnetic skyrmion crystal (SkX), which are produced in a magnetic system involving the Dzyaloshinskii-Moriya interaction (DMI). We report the existence of a phase transition where the length scale of magnetic structure discontinuously changes, and that there can be a novel magnetic structure around the phase boundary that exhibits double-ordering lengths of magnetic structure. Therefore, the system has multiple ground phases determined by the ratio of interlayer exchange coupling strength and DMI strength. Furthermore, we investigated the critical condition of the external perpendicular field required for the SkX. The critical field is significantly reduced under the effect of interlayer exchange coupling, which can stabilize the SkX without the external field.
Transient electrically detected magnetic resonance spectroscopy applied to organic solar cells
Authors: Kraffert Felix , Steyrleuthner Robert , Meier Christoph , Bittl Robert , Behrends Jan
Published: July 2015

The influence of light-induced paramagnetic states on the photocurrent generated by polymer:fullerene solar cells is studied using spin-sensitive techniques in combination with laser-flash excitation. For this purpose, we developed a setup that allows for simultaneous detection of transient electron paramagnetic resonance as well as transient electrically detected magnetic resonance (trEDMR) signals from fully processed and encapsulated solar cells. Combining both techniques provides a direct link between photoinduced triplet excitons, charge transfer states, and free charge carriers as well as their influence on the photocurrent generated by organic photovoltaic devices. Our results obtained from solar cells based on poly(3-hexylthiophene) as electron donor and a fullerene-based electron acceptor show that the resonant signals observed in low-temperature (T = 80 K) trEDMR spectra can be attributed to positive polarons in the polymer as well as negative polarons in the fullerene phase, indicating that both centers are involved in spin-dependent processes that directly influence the photocurrent.
Spin pumping from spinwaves in thin film YIG
Authors: Manuilov S. A. , Du C. H. , Adur R. , Wang H. L. , Bhallamudi V. P. , Yang F. Y. , Hammel P. C.
Published: July 2015

We report on the efficiency of spin pumping from parametrically excited propagating high-k spinwaves in a YIG(25 nm)/Pt(5 nm) bilayer. We observe clear signals, detected using the inverse spin Hall effect. The measured spin pumping efficiency and microwave thresholds needed for parametric excitation indicate that spin pumping is insensitive to the spinwave wavevector magnitude and propagation direction in the range 0≤k≲20 μm−1. This finding is consistent with the fact that for thin films, the variation of spin wave amplitude across the film thickness is only weakly dependent on the wavevector. Our results are promising for the development of spin-based devices operated by spinwaves.
An array of virtual Frisch-grid CdZnTe detectors and a front-end application-specific integrated circuit for large-area position-sensitive gamma-ray cameras
Authors: Bolotnikov A. E. , Ackley K. , Camarda G. S. , Cherches C. , Cui Y. , De Geronimo G. , Fried J. , Hodges D. , Hossain A. , Lee W. , Mahler G. , Maritato M. , Petryk M. , Roy U. , Salwen C. , Vernon E. , Yang G. , James R. B.
Published: July 2015

We developed a robust and low-cost array of virtual Frisch-grid CdZnTe detectors coupled to a front-end readout application-specific integrated circuit (ASIC) for spectroscopy and imaging of gamma rays. The array operates as a self-reliant detector module. It is comprised of 36 close-packed 6 × 6 × 15 mm3 detectors grouped into 3 × 3 sub-arrays of 2 × 2 detectors with the common cathodes. The front-end analog ASIC accommodates up to 36 anode and 9 cathode inputs. Several detector modules can be integrated into a single- or multi-layer unit operating as a Compton or a coded-aperture camera. We present the results from testing two fully assembled modules and readout electronics. The further enhancement of the arrays’ performance and reduction of their cost are possible by using position-sensitive virtual Frisch-grid detectors, which allow for accurate corrections of the response of material non-uniformities caused by crystal defects.
Effect of kinetic energy on the doping efficiency of cesium cations into superfluid helium droplets
Authors: Chen Lei , Zhang Jie , Freund William M. , Kong Wei
Published: July 2015

We present an experimental investigation of the effect of kinetic energy on the ion doping efficiency of superfluid helium droplets using cesium cations from a thermionic emission source. The kinetic energy of Cs+ is controlled by the bias voltage of a collection grid collinearly arranged with the droplet beam. Efficient doping from ions with kinetic energies from 20 eV up to 480 V has been observed in different sized helium droplets. The relative ion doping efficiency is determined by both the kinetic energy of the ions and the average size of the droplet beam. At a fixed source temperature, the number of doped droplets increases with increasing grid voltage, while the relative ion doping efficiency decreases. This result implies that not all ions are captured upon encountering with a sufficiently large droplet, a deviation from the near unity doping efficiency for closed shell neutral molecules. We propose that this drop in ion doping efficiency with kinetic energy is related to the limited deceleration rate inside a helium droplet. When the source temperature changes from 14 K to 17 K, the relative ion doping efficiency decreases rapidly, perhaps due to the lack of viable sized droplets. The size distribution of the Cs+-doped droplet beam can be measured by deflection and by energy filtering. The observed doped droplet size is about 5 × 106 helium atoms when the source temperature is between 14 K and 17 K.
Investigation on ultracold RbCs molecules in (2)0+ long-range state below the Rb(5S1/2) + Cs(6P1/2) asymptote by high resolution photoassociation spectroscopy
Authors: Yuan Jinpeng , Ji Zhonghua , Li Zhonghao , Zhao Yanting , Xiao Liantuan , Jia Suotang
Published: July 2015

We present high resolution photoassociation spectroscopy of RbCs molecules in (2)0+ long-range state below the Rb(5S1/2) + Cs(6P1/2) asymptote and derive the corresponding C6 coefficient, which is used to revise the potential energy curves. The excited state molecules are produced in a dual-species dark spontaneous force optical trap and detected by ionizing ground state molecules after spontaneous decay, using a high sensitive time-of-flight mass spectrum. With the help of resonance-enhanced two-photon ionization technique, we obtain considerable high resolution photoassociation spectrum with rovibrational states, some of which have never been observed before. By applying the LeRoy-Bernstein method, we assign the vibrational quantum numbers and deduce C6 coefficient, which agrees with the theoretical value of A1Σ+ state correlated to Rb(5S1/2) + Cs(6P1/2) asymptote. The obtained C6 coefficient is used to revise the long-range potential energy curve for (2)0+ state, which possesses unique A − b mixing characteristic and can be a good candidate for the production of absolutely ground state molecule.
Realization of spin-dependent splitting with arbitrary intensity patterns based on all-dielectric metasurfaces
Authors: Ke Yougang , Liu Yachao , He Yongli , Zhou Junxiao , Luo Hailu , Wen Shuangchun
Published: July 2015

We report the realization of spin-dependent splitting with arbitrary intensity patterns based on all-dielectric metasurfaces. Compared with the plasmonic metasurfaces, the all-dielectric metasurface exhibits more high transmission efficiency and conversion efficiency, which makes it possible to achieve the spin-dependent splitting with arbitrary intensity patterns. Our findings suggest a way for generation and manipulation of spin photons, and thereby offer the possibility of developing spin-based nanophotonic applications.
Ion field-evaporation from ionic liquids infusing carbon xerogel microtips
Authors: Perez-Martinez C. S. , Lozano P. C.
Published: July 2015

Ionic liquid ion sources capable of producing positive and negative molecular ion beams from room-temperature molten salts have applications in diverse fields, from materials science to space propulsion. The electrostatic stressing of these ionic liquids places the liquid surfaces in a delicate balance that could yield unwanted droplet emission when not properly controlled. Micro-tip emitter configurations are required to guarantee that these sources will operate in a pure ionic regime with no additional droplets. Porous carbon based on resorcinol-formaldehyde xerogels is introduced as an emitter substrate. It is demonstrated that this material can be shaped to the required micron-sized geometry and has appropriate transport properties to favor pure ionic emission. Time-of-flight mass spectrometry is used to verify that charged particle beams contain solvated ions exclusively.
Progress, perspective, and commercialization of heavy metal ion detection technology into China
Authors: Han Aixia , Zang Ling , An Dingming , Lindsay Jeff , Watts Ed
Published: July 2015

Heavy metals contamination resulting from fossil fuel combustion among other sources has been become a focus of the community of nations. New detection methods can help to manage this growing concern. In 2008, Dr. Zang and his colleagues succeeded in building a fluorescent sensor based on a perylene modification with two thymine moieties to successfully detect mercury in water. Through the sub-national EcoPartnership program sponsored by the U.S. and China, the development of this technology has been advanced and is now ready for demonstration as a real time, in situ testing procedure. The Utah-Qinghai EcoPartnership is also helping to facilitate commercialization of new technologies through the coordination of government entities, local universities, and commercial partners. Adapting new technology for deployment in China depends on understanding the specific roles of all these partners. Dr. Dingman offers an instructive insight on new technology implementation based on his years of involvement with Chinese government agencies and research institutions. Finally, new advances in intellectual property (IP) protection are enabling the successful deployment of useful technologies into China.
Twin photon pairs in a high-Q silicon microresonator
Authors: Rogers Steven , Lu Xiyuan , Jiang Wei C. , Lin Qiang
Published: July 2015

We report the generation of high-purity twin photon pairs through cavity-enhanced non-degenerate four-wave mixing (FWM) in a high-Q silicon microdisk resonator. Twin photon pairs are created within the same cavity mode and are consequently expected to be identical in all degrees of freedom. The device is able to produce twin photons at telecommunication wavelengths with a pair generation rate as large as (3.96 ± 0.03) × 105 pairs/s, within a narrow bandwidth of 0.72 GHz. A coincidence-to-accidental ratio of 660 ± 62 was measured, the highest value reported to date for twin photon pairs, at a pair generation rate of (2.47 ± 0.04) × 104 pairs/s. Through careful engineering of the dispersion matching window, we have reduced the ratio of photons resulting from degenerate FWM to non-degenerate FWM to less than 0.15.
An insight into the origin of low-symmetry bridging phase and enhanced functionality in systems containing competing phases
Authors: Kong Lingping , Liu Gang , Yang Wenge , Cao Wenwu
Published: July 2015

High piezoelectric activity of ferroelectrics with morphotropic phase boundary (MPB) compositions has been the focus of numerous recent investigations. The concept of a bridging low-symmetry phase between competing phase structures of the MPB composition remains controversial due to the compositional inhomogeneity near the MPB and the lack of appropriate experimental techniques to delineate the complex crystal structures. We have studied a simple ferroelectric BaTiO3 by employing a high resolution synchrotron-based technique, in which the formation of different symmetry regions due to chemical inhomogeneity can be ruled out. We observed two types of thermotropic phase boundaries, revealing the importance of interphase-strain in the formation of a bridging phase between competing phases and the enhancement of functionality.
The effect of mass loading on spurious modes in micro-resonators
Authors: Charmet Jérôme , Daly Ronan , Thiruvenkatanathan Pradyumna , Seshia Ashwin A.
Published: July 2015

Dissipation mechanisms severely compromise the performance of micro-resonator based sensors. In this letter, we specifically examine the shift in resonant frequency of spurious modes towards the mode of interest during mass loading. This can result in modal interaction that degrades the response of the sensor. However, by understanding and controlling this effect we can overcome this key barrier to micro-resonator applications.
Electron beam induced etching of carbon
Authors: Martin Aiden A. , McCredie Geoffrey , Toth Milos
Published: July 2015

Nanopatterning of graphene and diamond by low energy (≤30 keV) electrons has previously been attributed to mechanisms that include atomic displacements caused by knock-on, electron beam heating, sputtering by ionized gas molecules, and chemical etching driven by a number of gases that include N2. Here, we show that a number of these mechanisms are insignificant, and the nanopatterning process can instead be explained by etching caused by electron induced dissociation of residual H2O molecules. Our results have significant practical implications for gas-mediated electron beam nanopatterning techniques and help elucidate the underlying mechanisms.