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The direct random phase approximation (RPA) and RPA with second-order screened exchange (SOSEX) have been implemented with complex orbitals as a basis for treating open-shell atoms. Both RPA and RPA+SOSEX are natural implicit current density functionals because the paramagnetic current density implicitly is included through the use of complex orbitals. We confirm that inclusion of the SOSEX correction improves the total energy accuracy substantially compared to RPA, especially for smaller-Z atoms. Computational complexity makes post self-consistent-field (post-SCF) evaluation of RPA-type expressions commonplace, so orbital basis origins and properties become important. Sizable differences are found in correlation energies, total atomic energies, and ionization energies for RPA-type functionals evaluated in the post-SCF fashion with orbital sets obtained from different schemes. Reference orbitals from Kohn-Sham calculations with semi-local functionals are more suitable for RPA+SOSEX to generate accurate total energies, but reference orbitals from exact exchange (non-local) yield essentially energetically degenerate open-shell atom ground states. RPA+SOSEX correlation combined with exact exchange calculated from a hybrid reference orbital set (half the exchange calculated from exact-exchange orbitals, the other half of the exchange from orbitals optimized for the Perdew-Burke-Ernzerhof (PBE) exchange functional) gives the best overall performance. Numerical results showthat the RPA-like functional with SOSEX correction can be used as a practical implicit current density functional when current effects should be included. [ABSTRACT FROM AUTHOR]

An effective way to accelerate rare events in molecular dynamics simulations is to apply a bias potential which destabilizes minima without biasing the transitions between stable states. This approach, called hyperdynamics, is limited by our ability to construct general bias potentials without having to understand the reaction mechanisms available to the system, a priori. Current bias potentials are typically constructed in terms of a metric which quantifies the distance that a trajectory deviates from the reactant state minimum. Such metrics include detection of negative curvatures of the potential, an energy increase, or deviations in bond lengths from the minimum. When one of these properties exceeds a critical value, the bias potentials are constructed to approach zero. A problem common to each of these schemes is that their effectiveness decreases rapidly with system size. We attribute this problem to a diminishing volume defined by the metrics around a reactant minimum as compared to the total volume of the reactant state basin. In this work, we mitigate the dimensionality scaling problem by constructing bias potentials that are based upon the distance to the boundary of the reactant basin. This distance is quantified in two ways: (i) by following the minimum mode direction to the reactant boundary and (ii) by training a machine learning algorithm to give an analytic expression for the boundary to which the distance can be calculated. Both of these ridge-based bias potentials are demonstrated to scale qualitatively better with dimensionality than the existing methods. We attribute this improvement to a greater filling fraction of the reactant state using the ridge-based bias potentials as compared to the standard potentials. [ABSTRACT FROM AUTHOR]

A distributed replica dynamics (DRD) method is proposed to calculate rare-event molecular dynamics using distributed computational resources. Similar to Voter's parallel replica dynamics (PRD) method, the dynamics of independent replicas of the system are calculated on different computational clients. In DRD, each replica runs molecular dynamics from an initial state for a fixed simulation time and then reports information about the trajectory back to the server. A simulation clock on the server accumulates the simulation time of each replica until one reports a transition to a new state. Subsequent calculations are initiated from within this new state and the process is repeated to follow the state-to-state evolution of the system. DRD is designed to work with asynchronous and distributed computing resources in which the clients may not be able to communicate with each other. Additionally, clients can be added or removed from the simulation at any point in the calculation. Even with heterogeneous computing clients, we prove that the DRD method reproduces the correct probability distribution of escape times. We also show this correspondence numerically; molecular dynamics simulations of Al(100) adatom diffusion using PRD and DRD give consistent exponential distributions of escape times. Finally, we discuss guidelines for choosing the optimal number of replicas and replica trajectory length for the DRD method. [ABSTRACT FROM AUTHOR]

Poly(vinylidene fluoride) (PVDF) and (Ba0.5Sr0.4Ca0.1)TiO3 (BSCT) are used as matrix and fillers, respectively, to prepare polymer functional composites by solution casting with N,N-dimethyl formamide as a solvent. It is found that the addition of BSCT has significant influence on the crystallization, melting, and glass transition behaviors of the PVDF matrix. The dielectric properties of the BSCT/PVDF composites are studied over a wide frequency range from 100 Hz to 1 GHz and a wide temperature range from -50°C to 100°C to explore the dependences of frequency and temperature. High dielectric constant (E) up to 132 at 100 Hz and low dielectric loss (tan d) down to 0.0045 at 1 GHz are achieved for the BSCT/PVDF composites. The obtained data of e are also theoretically fit by different models, and the modified Lichtenecker equation and Jayasundere-Smith equation show the best match. © 2014 AIP Publishing LLC. [ABSTRACT FROM AUTHOR]

Atomic scale investigation of temperature-dependent two-dimensional (2 D) crystallization processes of fullerene-C60 on pentacene-covered Ag(111) surface has been carried out by in situ low-temperature scanning tunneling microscopy (LT-STM) experiments. To evaluate the effect of molecule-substrate interfacial interactions on the 2 D crystallization of C60: pentacene binary system, we also carried out the same self-assembly experiments of C60 on monolayer pentacene covered graphite substrate. It is revealed that temperature-dependent structural transition of various ordered C60 nanoassemblies is strongly influenced by the molecule-Ag(111) interfacial interactions, and further mediated by the weak C60-pentacene intermolecular interactions. In situ ultraviolet photoelectron spectroscopy (UPS) has been used to evaluate the nature of the intermolecular interactions between C60 and pentacene films. [ABSTRACT FROM AUTHOR]

Based on the topological models of cluster-lines and crystal clusters destabilization, we propose a modified cluster model for designing metallic glasses based on the proposition that distortion of idealized glass-favoring clusters by addition of solute atoms within their solubility limit can enhance glass forming ability. Using the model, two CoSiB metallic glasses of low Co contents (Co63.1B27Si9.9 and Co65B24.4Si10.6) with good mechanical properties are designed. Despite the similar compositions, these two metallic glasses consist of different clusters, and therefore exhibit different magnetic behaviors. Co63.1B27Si9.9 metallic glass, based on the Co7B3 cluster, shows good soft magnetic properties with low coercivity smaller than 0.9 A/m, while Co65B24.4Si10.6 metallic glass, based on the Co8B3 cluster, exhibits paramagnetic behavior. The origin of these magnetic behaviors was discussed in view of the electronic structures of the metallic glasses. The results indicate that the model was valid not only for glass forming ability but also for tuning properties dominated by short-range orders. [ABSTRACT FROM AUTHOR]

The Nakajima-Zwanzig generalized quantum master equation provides a general, and formally exact, prescription for simulating the reduced dynamics of a quantum system coupled to a quantum bath. In this equation, the memory kernel accounts for the influence of the bath on the system’s dynamics, and the inhomogeneous term accounts for initial system-bath correlations. In this paper, we propose a new approach for calculating the memory kernel and inhomogeneous term for arbitrary initial state and system-bath coupling. The memory kernel and inhomogeneous term are obtained by numerically solving a single inhomogeneous Volterra equation of the second kind for each. The new approach can accommodate a very wide range of projection operators, and requires projection-free two-time correlation functions as input. An application to the case of a two-state system with diagonal coupling to an arbitrary bath is described in detail. Finally, the utility and self-consistency of the formalism are demonstrated by an explicit calculation on a spin-boson model. [ABSTRACT FROM AUTHOR]

In a previous paper [J. Chem. Phys. 119, 11864 (2003)], we derived a set of two coupled equations which describe electron transfer in the presence of dissipation at high temperature. Employing the low temperature extension of the Fokker-Planck operator, suggested by Haake and Reibold [Phys. Rev. A 32, 2462 (1985)] and Ankerhold [Europhys. Lett. 61, 301 (2003)], we show that one may extend the generalized Zusman equations in a similar manner to low temperature. Numerical simulation shows that addition of the temperature-dependent term which couples the coordinate and momentum causes an increase in the electron transfer rate as compared to the rate obtained from the previous high temperature equations. The increase in the rate comes from the increase in the equilibrium variances of the coordinate and momentum. The low temperature quantum theory allows for higher energy portions of phase space to contribute to the electron transfer rate where the rate is higher thus enhancing the overall rate. [ABSTRACT FROM AUTHOR]

An analytic study of the density matrix and Wigner representation equations for dissipative electron transfer is presented. An explicit expression is derived for the off-diagonal Green’s function, which shows a very fast relaxation in time if the barrier to reaction is greater than the thermal energy. This fast relaxation invalidates previous attempts to derive coupled equations for the density in the large friction limit. The fast off-diagonal relaxation disallows an adiabatic elimination of the momentum even in the large friction limit. We then show, with the aid of the boundary layer method, how one can use the same analysis to derive a set of two coupled equations for the diagonal densities. These equations are a generalization to phase space of the large friction Zusman equations [Chem. Phys. 49, 295 (1980)]. Adiabatic elimination of the momentum from these generalized Zusman equations is correct in the large friction limit and naturally leads back to the Zusman equations. Numerical solution of the generalized Zusman equations is presented for symmetric electron transfer for weak and strong electronic coupling, moderate and high barriers, and a large range of damping. The numerical results provide new insight into the friction dependence of the rate in the weak damping regime and show that previous analytic expressions for the rate are only qualitative in nature. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

An energy extraction technology based on motion-constrained tandem oscillating hydrofoils is presented in this paper. The turbine for extracting energy from the flow field is designed and built based on the measured frequency and energy extraction performance analysis of motion-constrained tandem oscillating hydrofoils. The instantaneous rotating speed and torque for the output shaft of the turbine are measured using a torque meter to determine the instantaneous power extracted by the turbine. Experimental results for this energy extraction turbine show that the optimal reduced frequency for both a single oscillating hydrofoil and tandem oscillating hydrofoils is about 0.1 and that the cycle-averaged energy extraction efficiency of the turbine with motion-constrained tandem oscillating hydrofoils reaches 29.2%. [ABSTRACT FROM AUTHOR]

Understanding the effect of edge relaxation in nanotubes (NTs) with two kinds of surfaces has been of central importance in the exploration thermal transportation properties for their applications in thermoelectric energy harvesting and heat management in nanoelectronics. In order to pursue a quantitative description of thermal transportation of SiNTs, we propose a theoretical model to deal with the lattice thermal conductivity by taking into account the sandwiched configurations based on the atomic-bondrelaxation correlation mechanism. It is found that the lattice thermal conductivity can be effectively tuned by different types of surface effect in Si nanostructures. As comparable to the Si nanowires and nanofilms, the SiNTs have the lowest thermal conductivity under identical conditions. [ABSTRACT FROM AUTHOR]

Lead-trihalide perovskite solar cells are an important photovoltaic technology. We investigate the effect of light induced degradation on perovskite solar cells. During exposure, the open-circuit voltage (Voc) of the device increases, whereas the short-circuit current (Isc) shows a decrease. The degradation can be completely recovered using thermal annealing in dark. We develop a model based on light induced generation of ions and migration of these ions inside the material to explain the changes in Isc, Voc, capacitance and dark current upon light exposure and post-exposure recovery. There was no change in defect density in the material upon exposure. [ABSTRACT FROM AUTHOR]

Raman spectroscopy was applied to investigate the speciation in both single and mixed solutions of molybdate and vanadate at pH values from 10.0 to 1.0. Evidence was obtained for the difference of existing forms between these two elements. Vanadium mainly exists as (VO3)nn- while Mo is MoO42- in the pH range of 9.0-7.5. This difference is the theoretical basis for many available separation process. The species in the binary system was identified by comparing the Raman spectra with that in the single systems. Molybvanadates are formed below pH=6.5, which may partly be ascribed to the replacement of V atoms by Mo atoms in some V-O-V groups. Vanadium mainly exists as the decavanadate species in the pH range of 6.0-2.0. The predominant species of Mo are heteropolyanions having structural features of heptamolybdate rather than Mo8O264- and Mo36O1128- which are the predominant Mo species in single solution at pH=2.0-1.0. [ABSTRACT FROM AUTHOR]

Photovoltaic devices with perovskite materials as light absorbing material were fabricated through sequential vapor deposition of lead iodide and methylammonium iodide with undoped poly3hexylthiophene (P3HT) as a hole transporting layer. The sequential vapor deposition process produced films and devices with the large grains and low defect densities, very small values of dark current, and high open circuit voltages. The thickness of the P3HT layer was a critical parameter for achieving high solar conversion efficiencies of 13.7%. The vapor deposition process also produced devices with a tight distribution of performance characteristics and very high open circuit voltages (0.99 V). [ABSTRACT FROM AUTHOR]

Nanocomposite films with cerium oxide (CeO2) nanoparticles as functional fillers and polystyrene (PS) as polymer matrix were prepared using solution casting method. Physical properties including both weak frequency dependence of dielectric permittivity and low dielectric loss were experimentally discovered in the CeO2/PS nanocomposite films. To improve the dielectric properties of films further, the surface of CeO2 nanoparticles was treated by H2O2 to increase the homogeneity of the nanocomposite film, which was confirmed by scanning electron microscopy (SEM) results. Furthermore, it was found that both the filler size and the filler volume fraction played a role on the dielectric properties of the nanocomposite films. [ABSTRACT FROM AUTHOR]

Nanodielectric elastomer films consisting of a silicone rubber as the matrix and conductive polyaniline nanorods (PANI-NR) as the filler were fabricated and their electro-mechanical actuation performance was investigated. The nanodielectric elastomers displayed a typical insulator-toconductor transition as the content of PANI-NR increased. The percolation threshold was observed to show a relatively low value of 5.2 vol. %, which should be mainly ascribed to the onedimensional structure of the nanorods. As the concentration of PANI-NR approached to the percolation threshold, the electro-mechanical actuation strain of the elastomer films was significantly enhanced. The actuation coefficient of nanodielectric elastomer films with only 4.0 vol.% PANI-NR loading was about 5 times higher than that of pure silicone rubber matrix. [ABSTRACT FROM AUTHOR]

A three-step graded undoped-InGaN layers embedded between the GaN last quantum barrier layer and the p-AlGaN electron blocking layer was proposed and its effect on the performance of InGaN/GaN light-emitting diodes was investigated both experimentally and theoretically. In the proposed structure, the electron leakage is found to be effectively reduced, while the hole injection efficiency is simultaneously increased significantly, hence enabling a greatly enhanced radiative recombination rate within the active region. As a result, improvements of 12.25% in the optical output power and 11.98% in the external quantum efficiency are obtained from the proposed device with the respect to the reference device. [ABSTRACT FROM AUTHOR]

We investigate magnetotransport in the vicinity of the charge neutral point (CNP) in bilayer graphene at low temperatures. The CNP is found to vary with applied magnetic fields. Through measuring the transfer curves under different magnetic fields and at different temperatures, the temperature dependence of the peak resistivity at the CNP and under a fixed magnetic field is extracted. At low temperatures, it is found that the peak resistivity at the CNP increases exponentially with decreasing temperature under 14 T, which indicates the gap opening in zero-energy Landau level. The origins of such magnetic field induced insulating behavior are discussed. [ABSTRACT FROM AUTHOR]

Dynamic optimization is likely to play an important role in the reliability, quality, and efficiency of future power system, specifically for microgrid with renewable generation. This paper presents an improved hybrid optimization algorithm, called information exchange particle swarm optimization (IEPSO), to deal with the problem of dynamic optimal control in a microgrid with multiple distributed generations (DGs), such as wind power, small hydro, and energy storage. Based on the actual application of DG in Southwest China, we propose an optimization model for grid-connected microgrid that introduces a contribution rate of energy storage into the model and incorporates practical engineering constraints. The performance of different optimization control strategies for active and reactive power is investigated, and the results indicate that the IEPSO algorithm is efficient for dynamic optimization, and the dynamic contribution rate control strategy for energy storage is more effective than static strategy. [ABSTRACT FROM AUTHOR]

We present the design and realization of ultra-thin chiral metasurfaces with giant broadband optical activity in the infrared wavelength. The chiral metasurfaces consisting of periodic hole arrays of complementary asymmetric split ring resonators are fabricated by femtosecond laser two-photon polymerization. Enhanced transmission with strong polarization conversion up to 97% is observed owing to the chiral surface plasmons resulting from mirror symmetry broken. The dependence of optical activity on the degree of structural asymmetry is investigated. This simple planar metasurface is expected to be useful for designing ultra-thin active devices and tailoring the polarization behavior of complex metallic nanostructures. [ABSTRACT FROM AUTHOR]

The effect of n-AlGaN versus p-AlGaN electron-blocking layers (EBLs) on the performance of InGaN/GaN light-emitting diodes is studied in this work. Experimental results suggest that the n-type EBL leads to higher optical output power and external quantum efficiency, compared to the devices with p-AlGaN EBL, which is commonly used today. Numerical simulations on the carrier distribution and energy band diagram reveal that the n-AlGaN EBL is more efficient in preventing electron overflow, while not blocking the hole injection into the active region, hence leading to higher radiative recombination rate within the multiple quantum wells active region. [ABSTRACT FROM AUTHOR]

Surface emitting linearly polarized InGaN/GaN light emitting diode (LED) is demonstrated using a subwavelength metallic nanograting. The aluminum based grating with a period of 150 nm is fabricated on top of the p-contact layer in a conventional InGaN LED structure grown on (0001) oriented sapphire substrate. Polarization ratio can reach 7:1, the highest ever reported polarization ratio directly from a light emitting diode. The polarization characteristics are studied in details both experimentally and theoretically, suggesting an effective way to make polarized light emission devices. [ABSTRACT FROM AUTHOR]

We report a unique substrate for surface-enhanced raman spectroscopy (SERS) based on silver nanoparticles-embedded silicon nanowires (SiNWs). The SiNWs were prepared by thermal evaporation of SiO powder via oxide-assisted growth, oxide removed with HF, and then used to reduce silver ions to form a highly decorated Ag-embedded surface. Such modified SiNWs substrates yielded ultrahigh SERS sensitivity, which could detect 25 μl of 1×10-16M Rhodamine 6G, 1×10-16M crystal violet, and 1×10-14M nicotine in methanol solutions. An Ag-modified SiNW strand could also enable SERS detection of 25 μl of 1×10-8 mg/ml calf thymus DNA. The possible mechanisms for the ultrahigh SERS sensitivity were discussed. [ABSTRACT FROM AUTHOR]

An experimental study is presented of a cold atmospheric Ar plasma jet with distinct advantages of low-working voltage and high plasma stability. To effectively improve the performance of the jet, a pair of pin electrodes with one floating in the air is applied. Variation in the applied voltage and/or the Ar gas flow causes the transition of the jet plasma from ignition, through stable plume to an unstable stage. The characteristics of the jet discharge are also studied by means of the electrical and spectroscopic diagnosis. [ABSTRACT FROM AUTHOR]

We have fabricated well-ordered organic donor/acceptor nanojunction arrays comprising p-sexiphenyl (6P) and C60 via self-assembly of C60 on the molecular nanotemplate of 6P nanostripes on Ag(111). Our scanning tunneling microscopy measurements show that the preferential trapping of C60 triplets atop 6P single molecule leads to the formation of the C60/6P vertical nanojunctions with well-defined two-dimensional arrangement. Annealing this binary molecular superstructure at 380 K results in the insertion of C60 linear chains between the neighboring 6P nanostripes and thereby the appearance of the periodic C60/6P lateral nanojunction arrays. [ABSTRACT FROM AUTHOR]

Using the terahertz time-domain spectroscopy, the complex refraction index and dielectric function of the pure 2,4,6-trinitro-1,3,5-trihydroxybenzene (TNPG) are calculated with the obtained parameters of the pure polyethylene (PE) and a mixture of TNPG and PE based on the Bruggeman effective medium theory. The theoretical investigation consistent with the experimental data in the vibration spectra of TNPG is presented in the range of 0.2–2.5 THz. The results reveal that the two absorption features identified as the fingerprint of TNPG in our studied range are mainly dominated by the intramolecular collective vibration modes. [ABSTRACT FROM AUTHOR]

Strands of aligned silicon nanowires (SiNWs) with lengths over 2 mm and diameters of 35 nm were synthesized via a two-step controlled growth. The large dimensionality made it possible to fabricate an individual strand of SiNWs into an electrode for cyclic voltammetric detection of bovine serum albumin (BSA). The strand sensor with the immense surface area and electrical conductivity of SiNWs shows the highest sensitivity and widest linear range ever reported for BSA detection. [ABSTRACT FROM AUTHOR]

Junctionless oxide-based neuron thin-film transistors with in-plane-gate structure are fabricated at room temperature by a laser scribing process. The neuron transistors are composed of a bottom indium-tin-oxide floating gate and multiples of in-plane control gates. The control gates, coupling with the floating gate, control the 'on' and 'off' of the transistor. Effective field-effect modulation of the drain current has been realized. AND logic is demonstrated on a dual in-plane gate neuron transistor. The developed laser scribing technology is highly desirable in terms of the fabrication of high performance neuron transistors with low-cost. [ABSTRACT FROM AUTHOR]

A correction to the article "A Surface-Enhanced Raman Spectroscopy Substrate for Highly Sensitive Label-Free Immunoassay" is presented.