bluuebunny/crossref_metadata_2025 huggingface dataset:
Folate–PEG functionalized silica CdTe quantum dots as fluorescent probes for cancer cell imaging
Authors: Lu Miao , Zhang Wendian , Gai Yongkang , Yang Tan , Ye Peng , Yang Guang , Ma Xiang , Xiang Guangya
Published: June 2014

CdTe@SiO2–NH–CO–PEG−folate nanoparticles were successfully prepared and demonstrated tumor cell specific targeting through folate receptors via folate mediated endocytosis.
Bi-functionalized PEG1000 ionic liquid [Imim-PEG1000-TEMPO][CuCl2−]: an efficient and reusable catalytic system for solvent-free aerobic oxidation of alcohols
Authors: Wang Zhao-gang , Jin Yong , Cao Xiao-hua , Lu Ming
Published: June 2014

A reusable catalytic system for efficient aerobic oxidation of alcohols with bi-functionalized PEG1000 ionic liquid [Imim-PEG1000-TEMPO][CuCl2−] was described.
Supramolecular silver(i) coordination isomers of different dimensionalities assembled using a conformationally flexible multidentate oligo-α-sulfanylpyrazinyl ligand
Authors: Wang Han , Yang Jin , Mak Thomas C. W.
Published: June 2014

Three silver(i) supramolecular coordination isomers that display different dimensionalities and one homologue are derived from the conformationally flexible multidentate ligand 2,6-bis(pyrazin-2-ylthio)pyrazine (L).
Morphological control and evolution of octahedral and truncated trisoctahedral Pt–Au alloy nanocrystals under microwave irradiation
Authors: Dai Lei , Zhao Yanxi , Chi Quan , Liu Hanfan , Li Jinlin , Huang Tao
Published: June 2014

Truncated trisoctahedral and octahedral Pt–Au alloy nanocrystals were synthesized by reducing the H2PtCl6–HAuCl4 mixture in TEG under microwave irradiation for 140 s. Iodide ions were critical to their synthesis.
Surface Al leached Ti3AlC2as a substitute for carbon for use as a catalyst support in a harsh corrosive electrochemical system
Authors: Xie Xiaohong , Xue Yun , Li Li , Chen Siguo , Nie Yao , Ding Wei , Wei Zidong
Published: June 2014

The surface modified Ti3AlC2supported Pt (Pt/e-TAC) catalyst shows improved activity and enhanced stability toward the oxygen reduction reaction when compared with the commercial Pt/C catalyst.
Water oxidation electrocatalysis by a zeolitic imidazolate framework
Authors: Wang Sibo , Hou Yidong , Lin Sen , Wang Xinchen
Published: June 2014

Co-ZIF-9 was introduced as a heterogeneous catalyst for electrocatalyzing the oxygen-evolution reaction in a wide pH range.
Palladium catalyzed synthesis and physical properties of indolo[2,3-b]quinoxalines
Authors: Hung Tran Quang , Hoang Do Huy , Thang Ngo Ngoc , Dang Tuan Thanh , Ayub Khurshid , Villinger Alexander , Friedrich Aleksej , Lochbrunner Stefan , Flechsig Gerd-Uwe , Langer Peter
Published: June 2014

A series of indolo[2,3-b]quinoxaline derivatives were efficiently synthesized from 2,3-dibromoquinoxaline by two pathways.
Synthetic and mechanistic aspects of the regioselective base-mediated reaction of perfluoroalkyl- and perfluoroarylsilanes with heterocyclic N-oxides
Authors: Stephens David E. , Chavez Gabriel , Valdes Martin , Dovalina Monica , Arman Hadi D. , Larionov Oleg V.
Published: June 2014

Novel and efficient method of direct perfluoroalkylation of azine N-oxides has been developed and interesting mechanistic details have been provided.
Synthesis of poly(vinylidene fluoride-co-bromotrifluoroethylene) and effects of molecular defects on microstructure and dielectric properties
Authors: Gadinski Matthew R. , Chanthad Chalatorn , Han Kuo , Dong Lijie , Wang Qing
Published: June 2014

Copolymers of vinylidene fluoride and bromotrifluoroethylene were synthesized with varying concentrations with the effect of molecular defects on microstructure evaluated.
The dissolution behaviour of chitosan in acetate-based ionic liquids and their interactions: from experimental evidence to density functional theory analysis
Authors: Sun Xiaofu , Tian Qingqing , Xue Zhimin , Zhang Yuwei , Mu Tiancheng
Published: June 2014

Herein, both experimental evidence and density functional theory analysis are used to explore the interactions between IL and chitosan.
Optimal characteristic nanosizes of mineral bridges in mollusk nacre
Authors: Shao Yue , Zhao Hong-Ping , Feng Xi-Qiao
Published: June 2014

The nanosizes of mineral bridges linking neighboring platelets in various types of mollusk nacre dictate the optimal interfacial strength.
One-pot green synthesis of β-artemether/arteether
Authors: Kumar Atul , Bishnoi Ajay Kumar
Published: June 2014

We have developed an efficient one pot green synthesis of β-artemether/arteether from artemisinin, which involves combination of a sodium borohydride – cellulose sulfuric acid (CellSA) catalyst system. This green methodology is high yielding and the catalyst has good recyclability. The developed methodology is simple, cost-effective and the catalyst used is eco-friendly, reusable, and biodegradable.
Non-equilibrium transition state rate theory
Authors: Feng Haidong , Zhang Kun , Wang Jin
Published: June 2014

Transition state or Kramers' rate theory has been used to quantify the kinetic speed of many chemical, physical and biological equilibrium processes successfully.
Polymorphism-dependent and piezochromic luminescence based on molecular packing of a conjugated molecule
Authors: Li Ruohan , Xiao Shuzhang , Li Yi , Lin Qifei , Zhang Ronghua , Zhao Jun , Yang Changying , Zou Kun , Li Dongsheng , Yi Tao
Published: June 2014

We report a unique example of polymorphism-dependent and piezochromic fluorescence, based on 2-(anthracen-9-yl)-4,5-diphenyl-1H-imidazole.
A bio-inspired microstructure induced by slow injection moulding of cylindrical block copolymers
Authors: Stasiak Joanna , Brubert Jacob , Serrani Marta , Nair Sukumaran , de Gaetano Francesco , Costantino Maria Laura , Moggridge Geoff D.
Published: June 2014

A bi-directional, layered microstructure in cylinder forming block copolymers results from the local balance of shear and extensional flow during slow injection moulding.
The potential of the F127–water soft system towards selective solubilisation of iridium(iii) octahedral complexes
Authors: Talarico Anna Maria , Szerb Elisabeta Ildyko , Ghedini Mauro , Rossi Cesare Oliviero
Published: June 2014

The position of an Iridium(III) water soluble chromophore inside the micellar, cubic and hexagonal phases of the F127 polymeric neutral surfactant in water was effectively determined by combined spectral and time-resolved photophysical techniques.
Incorporating fluorescent dyes into monodisperse melamine–formaldehyde resin microspheres via an organic sol–gel process: a pre-polymer doping strategy
Authors: Wu Youshen , Li Yan , Xu Jianhua , Wu Daocheng
Published: June 2014

An organic sol–gel process is developed to incorporate various organic fluorescent dyes into monodisperse melamine–formaldehyde (MF) resin microspheres. The dye incorporating mechanism is investigated and fluorescence-encoded microsphere arrays are prepared.
Photochemically assisted formation of silver nanoparticles by dithizone, and its application in amperometric sensing of cefotaxime
Authors: Gupta Sandeep , Prakash Rajiv
Published: June 2014

Hybrid nanomaterial (Ag–DTZH) derived from nanoscale silver protected with dithizone and its oxidation product for the electrosensing of cefotaxime (CFX), which is a third-generation cephalosporin antibiotic drug.
Generalised array low‐density parity‐check codes
Authors: Sobhani Reza
Published: June 2014

In this study, using Group Permutation Low‐Density Parity‐Check (GP‐LDPC) codes, the authors generalise the concept of array Low‐Density Parity‐Check (LDPC) codes from fields of prime order to those of prime power order. In fact, they consider the additive group of the finite field GF(q), q a prime power, as the underlying group for the GP‐LDPC code construction and since when q is a prime, the author's code construction method coincides with that of quasi‐cyclic array LDPC codes, they call their codes, generalised array LDPC (GA‐LDPC) codes. First, they prove that, like array LDPC codes, GA‐LDPC codes are quasi‐cyclic codes. Then, they analyse the girth of GA‐LDPC codes in a way similar to that for array LDPC codes and introduce some shortened GA‐LDPC codes with girths 8, 10 and 12. For many values of g, J and L, the lengths of (J, L)‐regular shortened GA‐LDPC codes of girth g and rate at least 1 − J/L, constructed in this study, are smaller than the lengths of (J, L)‐regular LDPC codes of girth g and rate at least 1 − J/L, constructed in the literature. Also, simulation results show that GA‐LDPC codes perform well with the iterative message‐passing decoding.
Behandlung rezidivierender Epistaxis durch Gefäßligatur: zeitgerecht oder überholt?
Authors: Weller P. , Christov F. , Bergmann C. , Lang S. , Lehnerdt G.
Published: June 2014

Einleitung:Trotz der Weiterentwicklung chirurgischer Techniken vor allem auf dem Gebiet der endoskopischen minimal-invasiven Therapie kann hartnäckiges, rezidivierendes Nasenbluten eine Herausforderung für den HNO-Arzt sein. Ziel der vorliegenden Untersuchung war es, eigene Ergebnisse verschiedener Interventionsmöglichkeiten zur Behandlung rezidivierender Epistaxis zu vergleichen.

Material und Methoden: Von 2007 bis 2013 wurde bei 148 Patienten eine operative Blutstillung in Vollnarkose durchgeführt. Während die Ursache in der Mehrheit idiopathisch war (n=98), trat Epistaxis außerdem postoperativ (n=30), posttraumatisch (n=7) oder im Rahmen eines M. Osler (n=12) auf.

Therapie: In 141/148 Fällen erfolgte die Blutstillung mittels mono- oder bipolarer Koagula­tion im Bereich der Blutungsquelle – dies implizierte in 17 Fällen eine Ethmoidektomie. In 19 Fällen wurde der Eingriff mit einer Septumplastik kombiniert. Bei 4 Patienten erfolgte nach frustraner Elektrokoagulation und schwerster Epistaxis mit unklarer Blutungslokalisation als Ultima Ratio das transorbitale Clipping der Ethmoidalarterien und/oder der A. maxillaris in der Fossa pterygopalatina; im Verlauf traten hiernach weder weitere Blutungsepisoden noch Komplikationen auf. Bei 3 weiteren Patienten wurde neuroradiologisch nach erfolgloser operativer Koagulation eine Embolisation durchgeführt.

Diskussion: Falls konservative Maßnahmen bei Epistaxis versagen, stellt die operative Elektrokoagulation eine effiziente nächste Therapiestufe in über 95% der Fälle dar. Sollte diese bei schwersten Blutungen ohne exakte Blutungslokalisation weitere Blutungsepisoden nicht vermeiden, so ist das Clippen der ipsilateralen vorderen und hinteren Ethmoidal- und/oder Maxillararterie eine Ultima Ratio, welche in ihrer Effizienz einer neuroradiologischen Intervention gleichkommt.
Dynamics, stability, and statistics on lattices and networks
Authors: Livi Roberto
Published: June 2014

These lectures aim at surveying some dynamical models that have been widely explored in the recent scientific literature as case studies of complex dynamical evolution, emerging from the spatio-temporal organization of several coupled dynamical variables. The first message is that a suitable mathematical description of such models needs tools and concepts borrowed from the general theory of dynamical systems and from out-of-equilibrium statistical mechanics. The second message is that the overall scenario is definitely reacher than the standard problems in these fields. For instance, systems exhibiting complex unpredictable evolution do not necessarily exhibit deterministic chaotic behavior (i.e., Lyapunov chaos) as it happens for dynamical models made of a few degrees of freedom. In fact, a very large number of spatially organized dynamical variables may yield unpredictable evolution even in the absence of Lyapunov instability. Such a mechanism may emerge from the combination of spatial extension and nonlinearity. Moreover, spatial extension allows one to introduce naturally disorder, or heterogeneity of the interactions as important ingredients for complex evolution. It is worth to point out that the models discussed in these lectures share such features, despite they have been inspired by quite different physical and biological problems. Along these lectures we describe also some of the technical tools employed for the study of such models, e.g., Lyapunov stability analysis, unpredictability indicators for “stable chaos,” hydrodynamic description of transport in low spatial dimension, spectral decomposition of stochastic dynamics on directed networks, etc.
Minimal time trajectories for two-level quantum systems with two bounded controls
Authors: Boscain Ugo , Grönberg Fredrik , Long Ruixing , Rabitz Herschel
Published: June 2014

In this paper we consider the minimum time population transfer problem for a two level quantum system driven by two external fields with bounded amplitude. The controls are modeled as real functions and we do not use the Rotating Wave Approximation. After projection on the Bloch sphere, we treat the time-optimal control problem with techniques of optimal synthesis on 2D manifolds. Based on the Pontryagin Maximum Principle, we characterize a restricted set of candidate optimal trajectories. Properties on this set, crucial for complete optimal synthesis, are illustrated by numerical simulations. Furthermore, when the two controls have the same bound and this bound is small with respect to the difference of the two energy levels, we get a complete optimal synthesis up to a small neighborhood of the antipodal point of the initial condition.
A subgrid-scale eddy-viscosity model based on the volumetric strain-stretching
Authors: Ryu Sungmin , Iaccarino Gianluca
Published: June 2014

We propose a novel subgrid-scale (SGS) eddy-viscosity model for large eddy simulation (LES) to accurately reproduce the effect of subgrid stresses on the resolved scales. The developed SGS model is based on the second-order volumetric strain-stretching (VSS) tensor, which is constructed by the multiplication of diagonal components of the strain-rate tensor with its off-diagonal components. The proposed VSS-model is validated in typical flow cases: freely decaying isotropic turbulence, incompressible turbulent channel flow at Reτ = 395, compressible turbulent channel flows at Ma = 1.5 and Reτ = 221, and Ma = 3.0 and Reτ = 556. LESs with the dynamic Smagorinsky model and the Vreman model are also performed to compare the performance of the VSS-model. The proposed model correctly recovers cubic wall behavior in the vicinity of solid boundaries in incompressible flow regime, and it has no limitation in its application to geometrically complex flows.
Sample-charged mode scanning polarization force microscopy for characterizing reduced graphene oxide sheets
Authors: Shen Yue , Wang Ying , Zhang Jinjin , Hai Chunxi , Zhou Yuan , Hu Jun , Zhang Yi
Published: June 2014

A unique operation mode of scanning polarization force microscopy (SPFM) was developed for characterizing reduced graphene oxide (rGO) sheets that were individually charged, mainly by monitoring the change of the sample's apparent height along with its surface potential. The principles and features of this sample-charged mode SPFM (SC-SPFM) were introduced. By comparing with other scanning-probe based techniques that characterize the surface electrical properties, including the traditional tip-biased mode SPFM, electrostatic force microscopy, and Kelvin probe force microscopy, it was found that the SC-SPFM has higher sensitivity and lateral resolution. Furthermore, by monitoring charge transfer between two rGO sheets with SC-SPFM, the “good” or “bad” contacts related to junction geometry at the nanometer scale can be visualized clearly.
Photofragmentation, state interaction, and energetics of Rydberg and ion-pair states: Resonance enhanced multiphoton ionization of HI
Authors: Hróðmarsson Helgi Rafn , Wang Huasheng , Kvaran Ágúst
Published: June 2014

Mass resolved resonance enhanced multiphoton ionization data for hydrogen iodide (HI), for two-photon resonance excitation to Rydberg and ion-pair states in the 69 600–72 400 cm−1 region were recorded and analyzed. Spectral perturbations due to homogeneous and heterogeneous interactions between Rydberg and ion-pair states, showing as deformations in line-positions, line-intensities, and line-widths, were focused on. Parameters relevant to photodissociation processes, state interaction strengths and spectroscopic parameters for deperturbed states were derived. Overall interaction and dynamical schemes to describe the observations are proposed.
Resonant vibrational energy transfer in ice Ih
Authors: Shi L. , Li F. , Skinner J. L.
Published: June 2014

Fascinating anisotropy decay experiments have recently been performed on H2O ice Ih by Timmer and Bakker [R. L. A. Timmer, and H. J. Bakker, J. Phys. Chem. A 114, 4148 (2010)]. The very fast decay (on the order of 100 fs) is indicative of resonant energy transfer between OH stretches on different molecules. Isotope dilution experiments with deuterium show a dramatic dependence on the hydrogen mole fraction, which confirms the energy transfer picture. Timmer and Bakker have interpreted the experiments with a Förster incoherent hopping model, finding that energy transfer within the first solvation shell dominates the relaxation process. We have developed a microscopic theory of vibrational spectroscopy of water and ice, and herein we use this theory to calculate the anisotropy decay in ice as a function of hydrogen mole fraction. We obtain very good agreement with experiment. Interpretation of our results shows that four nearest-neighbor acceptors dominate the energy transfer, and that while the incoherent hopping picture is qualitatively correct, vibrational energy transport is partially coherent on the relevant timescale.
NMR relaxation of the orientation of single segments in semiflexible dendrimers
Authors: Markelov Denis A. , Dolgushev Maxim , Gotlib Yuli Ya. , Blumen Alexander
Published: June 2014

We study the orientational properties of labeled segments in semiflexible dendrimers making use of the viscoelastic approach of Dolgushev and Blumen [J. Chem. Phys. 131, 044905 (2009)]. We focus on the segmental orientational autocorrelation functions (ACFs), which are fundamental for the frequency-dependent spin-lattice relaxation times T1(ω). We show that semiflexibility leads to an increase of the contribution of large-scale motions to the ACF. This fact influences the position of the maxima of the [1/T1]-functions. Thus, going from outer to inner segments, the maxima shift to lower frequencies. Remarkably, this feature is not obtained in the classical bead-spring model of flexible dendrimers, although many experiments on dendrimers manifest such a behavior.
Development of a cell culture surface conversion technique using alginate thin film for evaluating effect upon cellular differentiation
Authors: Nakashima Y. , Tsusu K. , Minami K. , Nakanishi Y.
Published: June 2014

Here, we sought to develop a cell culture surface conversion technique that would not damage living cells. An alginate thin film, formed on a glass plate by spin coating of sodium alginate solution and dipping into calcium chloride solution, was used to inhibit adhesion of cells. The film could be removed by ethylenediaminetetraacetate (EDTA) at any time during cell culture, permitting observation of cellular responses to conversion of the culture surface in real time. Additionally, we demonstrated the validity of the alginate thin film coating method and the performance of the film. The thickness of the alginate thin film was controlled by varying the rotation speed during spin coating. Moreover, the alginate thin film completely inhibited the adhesion of cultured cells to the culture surface, irrespective of the thickness of the film. When the alginate thin film was removed from the culture surface by EDTA, the cultured cells adhered to the culture surface, and their morphology changed. Finally, we achieved effective differentiation of C2C12 myoblasts into myotube cells by cell culture on the convertible culture surface, demonstrating the utility of our novel technique.
Lift enhancement by dynamically changing wingspan in forward flapping flight
Authors: Wang Shizhao , Zhang Xing , He Guowei , Liu Tianshu
Published: June 2014

Dynamically stretching and retracting wingspan has been widely observed in the flight of birds and bats, and its effects on the aerodynamic performance particularly lift generation are intriguing. The rectangular flat-plate flapping wing with a sinusoidally stretching and retracting wingspan is proposed as a simple model for biologically inspired dynamic morphing wings. Numerical simulations of the low-Reynolds-number flows around the flapping morphing wing are conducted in a parametric space by using the immersed boundary method. It is found that the instantaneous and time-averaged lift coefficients of the wing can be significantly enhanced by dynamically changing wingspan in a flapping cycle. The lift enhancement is caused by both changing the lifting surface area and manipulating the flow structures responsible to the vortex lift generation. The physical mechanisms behind the lift enhancement are explored by examining the three-dimensional flow structures around the flapping wing.
Efficient and accurate treatment of weak pairs in local CCSD(T) calculations. II. Beyond the ring approximation
Authors: Schütz Martin , Masur Oliver , Usvyat Denis
Published: June 2014

In order to arrive at linear scaling of the computational cost with molecular size, local coupled cluster methods discriminate pairs of local molecular orbitals according to the spatial separation R of the latter. Only strong pairs are treated at the full coupled cluster level, whereas for weak pairs a lower level of theory (usually Møller-Plesset perturbation theory of second order, MP2) is used. Yet an MP2 treatment of weak pairs is inadequate in certain situations (for example, for describing π-stacking), which calls for an improved but still inexpensive method for dealing with the weak pairs. In a previous contribution, we proposed as a substituent for MP2 the LrCCD3 method, which is based on ring coupled cluster doubles (ring-CCD) and includes all third-order diagrams with energy contributions decaying not quicker than R−6. In the present work, we explore a still more accurate method, which is based on the same principles. It turned out to be essential to abandon the restriction to ring-CCD, i.e., to include further CCD diagrams beyond the ring approximation. The occurring intermediates turn out to be formally very similar to LMP2 density matrices, such that an efficient evaluation of these non-ring CCD diagrams is possible. Furthermore, a computationally cheap a posteriori estimate for the fourth-order singles contribution to the weak pair energy, which also exhibits a decay behavior of R−6, is introduced. The resulting method, denoted as LCCD[S]-R−6, indeed provides a substantial improvement in accuracy over the previous LrCCD3 method at a relatively modest additional computational cost.
Investigation of A-site La substituted BaTi0.96Mn0.04O3 ceramics: Searching for ferromagnetic origin
Authors: Gong Gaoshang , Fang Yujiao , Zerihun Gebru , Yin Chongyang , Huang Shuai , Yuan Songliu
Published: June 2014

Ba1-xLaxTi0.96Mn0.04O3 ceramics (x = 0, 3%, 7%) were prepared by a modified Pechini method and the structure, morphology, magnetic and electric properties have been investigated. X-ray diffraction analysis reveals La3+ ions could suppress the formation of hexagonal phase effectively. The cell parameter c decreases firstly and then increases with the increase of La content, which indicates that La ions have been incorporated into the lattice of BaTi0.96Mn0.04O3, and that Mn ions transform from high valence to low valence. The magnetization, polarization and leakage currents are also influenced by La doping greatly. Detailed analysis of magnetic variation with structural change attributes the room temperature ferromagnetism to double exchange interactions between Mn3+ and Mn4+ ions.
Structural and metal-insulator transitions in ionic liquid-gated Ca3Ru2O7 surface
Authors: Puls Conor P. , Cai Xinxin , Zhang Yuhe , Peng Jin , Mao Zhiqiang , Liu Ying
Published: June 2014

We report the fabrication and measurements of ionic liquid gated Hall bar devices prepared on the ab face of a thin Ca3Ru2O7 flake exfoliated from bulk single crystals that were grown by a floating zone method. The devices were categorized into two types: those with their electrical transport properties dominated by c-axis transport in type A or that of the in-plane in type B devices. Bulk physical phenomena, including a magnetic transition near 56 K, a structural and metal-insulator transition at a slightly lower temperature, as well as the emergence of a highly unusual metallic state as the temperature is further lowered, were found in both types of devices. However, the Shubnikov-de Haas oscillations were found in type A but not type B devices, most likely due to enhanced disorder on the flake surface. Finally, the ionic liquid gating of a type B device revealed a shift in critical temperature of the structural and metal-insulator transition, suggesting that this transition is tunable by the electric field effect.
Cloaking via heating: Approach to acoustic cloaking of an actuated boundary in a rarefied gas
Authors: Manela A. , Pogorelyuk L.
Published: June 2014

Existing studies on sound wave propagation in rarefied gases examine sound generation by actuated boundaries subject to isothermal boundary conditions. While these conditions are simple to analyze theoretically, they are more challenging to apply in practice compared to heat-flux conditions. To study the effect of modifying the thermal boundary conditions, the present work investigates the impact of replacing the isothermal with heat-flux conditions on propagation of acoustic waves in a microchannel. The linearized problem is formulated for an ideal hard-sphere gas, and the effect of heat-flux prescription is demonstrated through comparison with counterpart results for isothermal boundaries. Analytical solutions are obtained for a gas at collisionless (highly rarefied) and continuum-limit conditions, and validated through comparison with direct simulation Mote Carlo predictions. Remarkably, it is found that prescription of heat flux at the walls, altering the energy balance within the medium, has a significant effect on acoustic wave propagation in the gas. In particular, when optimized with respect to the boundary acoustic signal applied, the heat flux condition may be used to achieve “acoustic cloaking” of the moving wall, a much desired property in classical acoustics.
Improved master equation approach to quantum transport: From Born to self-consistent Born approximation
Authors: Jin Jinshuang , Li Jun , Liu Yu , Li Xin-Qi , Yan YiJing
Published: June 2014

Beyond the second-order Born approximation, we propose an improved master equation approach to quantum transport under self-consistent Born approximation. The basic idea is to replace the free Green's function in the tunneling self-energy diagram by an effectivereduced propagator under the Born approximation. This simple modification has remarkable consequences. It not only recovers the exact results for quantum transport through noninteracting systems under arbitrary voltages, but also predicts the challenging nonequilibrium Kondo effect. Compared to the nonequilibrium Green's function technique that formulates the calculation of specific correlation functions, the master equation approach contains richer dynamical information to allow more efficient studies for such as the shot noise and full counting statistics.
Equilibrium limit of thermal conduction and boundary scattering in nanostructures
Authors: Haskins Justin B. , Kınacı Alper , Sevik Cem , Çağın Tahir
Published: June 2014

Determining the lattice thermal conductivity (κ) of nanostructures is especially challenging in that, aside from the phonon-phonon scattering present in large systems, the scattering of phonons from the system boundary greatly influences heat transport, particularly when system length (L) is less than the average phonon mean free path (MFP). One possible route to modeling κ in these systems is through molecular dynamics (MD) simulations, inherently including both phonon-phonon and phonon-boundary scattering effects in the classical limit. Here, we compare current MD methods for computing κ in nanostructures with both L ⩽ MFP and L ≫ MFP, referred to as mean free path constrained (cMFP) and unconstrained (uMFP), respectively. Using a (10,0) CNT (carbon nanotube) as a benchmark case, we find that while the uMFP limit of κ is well-defined through the use of equilibrium MD and the time-correlation formalism, the standard equilibrium procedure for κ is not appropriate for the treatment of the cMFP limit because of the large influence of boundary scattering. To address this issue, we define an appropriate equilibrium procedure for cMFP systems that, through comparison to high-fidelity non-equilibrium methods, is shown to be the low thermal gradient limit to non-equilibrium results. Further, as a means of predicting κ in systems having L ≫ MFP from cMFP results, we employ an extrapolation procedure based on the phenomenological, boundary scattering inclusive expression of Callaway [Phys. Rev. 113, 1046 (1959)]. Using κ from systems with L ⩽ 3 μm in the extrapolation, we find that the equilibrium uMFP κ of a (10,0) CNT can be predicted within 5%. The equilibrium procedure is then applied to a variety of carbon-based nanostructures, such as graphene flakes (GF), graphene nanoribbons (GNRs), CNTs, and icosahedral fullerenes, to determine the influence of size and environment (suspended versus supported) on κ. Concerning the GF and GNR systems, we find that the supported samples yield consistently lower values of κ and that the phonon-boundary scattering remains dominant at large lengths, with L = 0.4 μm structures exhibiting a third of the periodic result. We finally characterize the effect of shape in CNTs and fullerenes on κ, showing the angular components of conductivity in CNTs and icosahedral fullerenes are similar for a given circumference.
Local flow topologies and scalar structures in a turbulent premixed flame
Authors: Cifuentes Luis , Dopazo Cesar , Martin Jesus , Jimenez Carmen
Published: June 2014

A three-dimensional direct numerical simulation of a propagating turbulent premixed flame is performed using one-step Arrhenius model chemistry. The interaction of the flame thermochemical processes with the local geometries of the scalar field and flow topologies is studied. Four regions (“fresh reactants,” “preheating,” “burning,” and “hot products”), characterized by their reaction rate and mass fraction values, are examined. Thermochemical processes in the “preheating” and “burning” regions smooth out highly contorted iso-scalar surfaces, present in the “fresh reactants,” and annihilate large curvatures. Positive volumetric dilatation rates, −P = ∇ · u, display maxima for elliptic concave and minima for convex scalar micro-structures. Constant average tangential strain rates, aT, with large fluctuations, occur throughout the flow domain, whereas normal strain rates, aN, follow the trends of volumetric dilatation rates. Focal topologies, present in the “fresh reactants,” tend to disappear in favor of nodal structures as moving towards the “hot products.” The vorticity vector is predominantly tangential to the iso-scalar surfaces. The Unstable Node/Saddle/Saddle and Stable Focus/Stretching topologies, present in the “fresh reactants,” correlate with large values of aN and aT providing hints on the flow topologies fostering scalar mixing.
Third and fourth virial coefficients for hard disks in narrow channels
Authors: Mon K. K.
Published: June 2014

The third (B3) and fourth (B4) virial coefficients of hard disks in narrow channels have been evaluated accurately by Gaussian quadrature for a range of channel widths (2Rp), \documentclass[12pt]{minimal}\begin{document}$R_{p} < ({\sqrt{3}} + 2)/4\break = 0.9330...$\end{document}Rp<(3+2)/4=0.9330... (in units of the hard disk diameter). These widths correspond to the important regime of fluids in single file formations with only nearest-neighbor interactions. Accurate results are obtained by using N-point Gaussian quadrature and extrapolating to the infinite N limits. Since not much is known about these B3 and B4, our new results should provide guidance for exact calculations of the virial coefficients and benchmarks for other numerical methods.
Ion acoustic solitons/double layers in two-ion plasma revisited
Authors: Lakhina G. S. , Singh S. V. , Kakad A. P.
Published: June 2014

Ion acoustic solitons and double layers are studied in a collisionless plasma consisting of cold heavier ion species, a warm lighter ion species, and hot electrons having Boltzmann distributions by Sagdeev pseudo-potential technique. In contrast to the previous results, no double layers and super-solitons are found when both the heavy and lighter ion species are treated as cold. Only the positive potential solitons are found in this case. When the thermal effects of the lighter ion species are included, in addition to the usual ion-acoustic solitons occurring at M > 1 (where the Mach number, M, is defined as the ratio of the speed of the solitary wave and the ion-acoustic speed considering temperature of hot electrons and mass of the heavier ion species), slow ion-acoustic solitons/double layers are found to occur at low Mach number (M < 1). The slow ion-acoustic mode is actually a new ion-ion hybrid acoustic mode which disappears when the normalized number density of lighter ion species tends to 1 (i.e., no heavier species). An interesting property of the new slow ion-acoustic mode is that at low number density of the lighter ion species, only negative potential solitons/double layers are found whereas for increasing densities there is a transition first to positive solitons/double layers, and then only positive solitons. The model can be easily applicable to the dusty plasmas having positively charged dust grains by replacing the heavier ion species by the dust mass and doing a simple normalization to take account of the dust charge.
A pulse chemisorption/reaction system for in situ and time-resolved DRIFTS studies of catalytic reactions on solid surfaces
Authors: Luo Liangfeng , Hua Qing , Jiang Zhiquan , Huang Weixin
Published: June 2014

A pulse chemisorption/reaction system in combination with Fourier transform infrared spectrometer equipped with a diffuse reflectance infrared Fourier transformed spectroscopy (DRIFTS) reaction cell and online mass spectrometer is described in detail. Such a system provides an approach to effectively suppress the interference of the gas-phase reactants to the vibrational signals of surface adsorbates during the operando DRIFTS measurements and, thus, allows for in situ and real-time monitor of surface species on catalyst surfaces during chemisorption/reaction processes. Employing this system, we successfully acquired DRIFTS spectra that clearly demonstrate surface species formed by propylene chemisorption and reaction on octahedral Cu2O nanocrystals; we also observed simultaneous chemisorption of CO on top, twofold, and threefold bridged sites of Pd nanoparticles supported on SiO2 upon the collision of CO prior to the saturation of strongly bound sites and the transformation of weakly bound CO(a) into strongly bound CO(a) during the dynamic chemisorption-desorption processes.
Note: Numerical simulation and experimental validation of accelerating voltage formation for a pulsed electron accelerator
Authors: Egorov I.
Published: June 2014

This paper describes the development of a computation model of a pulsed voltage generator for a repetitive electron accelerator. The model is based on a principle circuit of the generator, supplemented with the parasitics elements of the construction. Verification of the principle model was achieved by comparison of simulation with experimental results, where reasonable agreement was demonstrated for a wide range of generator load resistance.
Tantalum and vanadium response to shock-wave loading at normal and elevated temperatures. Non-monotonous decay of the elastic wave in vanadium
Authors: Zaretsky E. B. , Kanel G. I.
Published: June 2014

The evolution of the elastic precursor waves in pure tantalum and vanadium is presented at normal and elevated temperatures over propagation distances that ranged from 0.125 to 3 mm. Measurements were performed in order to obtain experimental data about the temperature-rate dependence of the yield stress of the two metals. With increasing propagation distance, the rate of the decay of elastic precursor decreases, as the shear stress in the elastic precursor wave approaches the Peierls stresses. It has been found that the decay, with propagation distance, of the post-spike minimum of the spike-like elastic precursor wave in vanadium is essentially non-monotonous. The experiments also revealed that annealing of tantalum and vanadium increases their Hugoniot elastic limit. The anomalous increase of the high strain rate yield stress with temperature, as observed earlier for some FCC and HCP metals, has not been detected in these measurements.
Comprehensive studies of response characteristics of organic photodetectors based on rubrene and C60
Authors: Yang Dezhi , Xu Kai , Zhou Xiaokang , Wang Yanping , Ma Dongge
Published: June 2014

We studied the transient response characteristics of organic photodetectors composing of high mobility materials of rubrene and C60, respectively, as donor and acceptor. It was found that the response speed was limited by the delay time of both exciton diffusion and transit, and an anomalous phenomenon that the bandwidth decreases as the reverse bias increases was found for the first time. The investigation of frequency dependence at different device structures and light excitations demonstrated that the light absorption of rubrene prevents the photodetector from obtaining a fast response. With the help of magnetic field effect study, it was clearly elucidated that the slow diffusion time of the long lifetime triplet excitons generated from singlet fission in rubrene limited the bandwidth of the device. Moreover, the simulation of the response of photodetector under transient and steady state by exciton transport-diffusion equation showed that the exciton dissociation efficiency in rubrene increases more quickly than that in C60, which should account for the negative dependence of bandwidth on the reverse bias in rubrene-based device.
Integrable perturbed magnetic fields in toroidal geometry: An exact analytical flux surface label for large aspect ratio
Authors: Kallinikos N. , Isliker H. , Vlahos L. , Meletlidou E.
Published: June 2014

An analytical description of magnetic islands is presented for the typical case of a single perturbation mode introduced to tokamak plasma equilibrium in the large aspect ratio approximation. Following the Hamiltonian structure directly in terms of toroidal coordinates, the well known integrability of this system is exploited, laying out a precise and practical way for determining the island topology features, as required in various applications, through an analytical and exact flux surface label.
Demand side management of smart grid: Load shifting and incentives
Authors: Logenthiran Thillainathan , Srinivasan Dipti , Vanessa K. W. M.
Published: June 2014

This paper presents a load shifting algorithm for optimizing consumption patterns by taking preferences of customers and electricity costs into account. A load shifting cost component is introduced for recording inconvenience experienced by customers while load shifting. Load shifting cost reflects the reluctance of customers for their inconvenience where the customers are unique in terms of their preferences and costs. The proposed algorithm would allow demand side management to be conducted in a decentralized manner, where no problem of load synchronization exists. Multi-agent system based simulation studies were carried out on three types of customers namely, residential, commercial, and industrial customers to verify this algorithm. The simulation results show that substantial load levelling is achieved by the proposed algorithm. This study is further extended to examine the effects of incentives that encourage customers to participate in load shifting. However, this does not lead to a better load levelling perhaps due to the small sample sized simulation systems. Instead, incentives could be used as a short-term measure for customers to know that how the mechanism would work for them.
Large eddy simulation of wind turbine wake dynamics in the stable boundary layer using the Weather Research and Forecasting Model
Authors: Aitken Matthew L. , Kosović Branko , Mirocha Jeffrey D. , Lundquist Julie K.
Published: June 2014

Recently, an actuator disk parameterization was implemented in the Weather Research and Forecasting (WRF) Model for large eddy simulation (LES) of wind turbine wakes. To thoroughly verify this model, simulations of various types of turbines and atmospheric conditions must be evaluated against corresponding experimental data. In this work, numerical simulations are compared to nacelle-based scanning lidar measurements taken in stable atmospheric conditions during a field campaign conducted at a wind farm in the western United States. Using several wake characteristics—such as the velocity deficit, centerline location, and wake width—as metrics for model verification, the simulations show good agreement with the observations. Notable results include a high average velocity deficit, decreasing from 73% at a downwind distance x of 1.2 rotor diameters (D) to 25% at x = 6.6D, resulting from a low average wind speed and therefore high average turbine thrust coefficient. Moreover, the wake width expands from 1.4D at x = 1.2D to 2.3D at x = 6.6D. Finally, new features—namely rotor tilt and drag from the nacelle and tower—are added to the existing actuator disk model in WRF-LES. Compared to the rotor, the effect of the tower and nacelle on the flow is relatively small but nevertheless important for an accurate representation of the entire turbine. Adding rotor tilt to the model causes the vertical location of the wake center to shift upward. Continued advancement of the actuator disk model in WRF-LES will help lead to optimized turbine siting and controls at wind farms.
Live-monitoring of Te inclusions laser-induced thermo-diffusion and annealing in CdZnTe crystals
Authors: Zappettini A. , Zambelli N. , Benassi G. , Calestani D. , Pavesi M.
Published: June 2014

The presence of Te inclusions is one of the main factors limiting performances of CdZnTe crystals as X-ray detectors. We show that by means of infrared laser radiation it is possible to move and anneal tellurium inclusions exploiting a thermo-diffusion mechanism. The process is studied live during irradiation by means of an optical microscope equipment. Experimental conditions, and, in particular, energy laser fluence, for annealing inclusions of different dimensions are determined.
Metallization selection and the performance of amorphous In-Zn-O thin film transistors
Authors: Lee Sunghwan , Paine David C.
Published: June 2014

We report on the effect of two different source/drain metallizations (Ti, Mo) on the performance and stability of amorphous In-Zn-O (IZO) thin film transistors (TFTs). In the as-deposited state, stable Mo/IZO TFTs show low threshold voltage (VT) and clear drain current saturation behavior compared to Ti/IZO devices, despite both having similar channel conductivity. Low temperature annealing (200 °C) results in VT shifts in Ti/IZO TFTs (ΔVT ∼ −33 V) that are significantly larger than in Mo/IZO TFTs (ΔVT ∼ −14 V). These differences are attributed to the injection of additional carriers into the channel of Ti/IZO devices due to reaction at the unstable Ti/IZO interface.
Economic evaluation of demand response in power systems with high wind power penetration
Authors: Saebi Javad , Hossein Javidi Mohammad
Published: June 2014

The penetration of wind power generation is expected to increase in power systems, dramatically. The unpredictable nature of the wind generation poses an obstacle to high penetration of wind energy in the electric power systems. Demand response (DR) may be considered as an efficient approach to cope with the energy unbalances caused by the wind power intermittency. Fair mechanism for pricing of the DR may increase the demand-side participation which consequently facilitates wind power integration in the power systems. This paper focuses on the economic evaluation of the DR according to its potential for mitigating the wind power forecast error in the power system operation. Demand increase, similar to the demand curtailment, is considered as a DR resource and evaluated in this paper. For this purpose, first an insight is provided into the power system operation under the high wind power penetration with the aim of extracting the DR benefits. Based on the DR benefits, a mathematical model is developed to find the maximum monetary incentive for the DR that the system operator is willing to pay to the DR providers. In the proposed model, DR's potential in reducing the cost of supplying load as well as its capability in reducing the cost of system reserve, start up and shut down of units, load shedding, and wind power spillage are considered. The results of the proposed evaluation method provide valuable information for both the system operator and demand response providers. The proposed method is implemented on an example and a realistic case study and discussions on results are presented.
Ferroelectric field effect of the bulk heterojunction in polymer solar cells
Authors: Li Meng , Ma Heng , Liu Hairui , Jiang Yurong , Niu Heying , Amat Adil
Published: June 2014

A ferroelectric field effect in the bulk heterojunction was found when an external electric field (EEF) was applied on the active layer of polymer solar cells (PSCs) during the annealing process of the active layer spin-coated with poly(3-hexylthiophene):[6,6]-phenyl-C61 butyric acid methyl ester. For one direction field, the short circuit current density of PSCs was improved from 7.2 to 8.0 mA/cm2, the power conversion efficiency increased from 2.4% to 2.8%, and the incident photon-to-current conversion efficiency increased from 42% to 49% corresponding to the different EEF magnitude. For an opposite direction field, the applied EEF brought a minus effect on the performance mentioned above. EEF treatment can orientate molecular ordering of the polymer, and change the morphology of the active layer. The authors suggest a explanation that the ferroelectric field has been built in the active layer, and therefore it plays a key role in PSCs system. A needle-like surface morphology of the active film was also discussed.
Comparison of Au and TiO2 based catalysts for the synthesis of chalcogenide nanowires
Authors: Schönherr P. , Prabhakaran D. , Jones W. , Dimitratos N. , Bowker M. , Hesjedal T.
Published: June 2014

We present a comparative study of TiO2-based and Au catalysts for the physical vapor deposition of (Bi1−xSbx)2Se3 topological insulator nanowires. The standard Au nanoparticle catalyst was compared to five TiO2 nanoparticle based catalysts (anatase, rutile, P-25, high surface area anatase, and TiO2 supported Au particles). The use of Au nanoparticles seriously harms the properties of nanowires, thereby limiting their application. In contrast, TiO2 based catalysts lead to the residue-free growth of nanowires with a higher degree of crystallinity. Homogeneous nanowire ensembles are achieved with the mixed phase P-25 catalyst, and a possible growth mechanism is proposed.