bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of attractive colloids on the phase separation behaviors of binary polymer blends
Authors: Zhang Xinghua , Chen Yunlin , Qu Lijian , Yan Dadong
Published: August 2013

The attractive colloids are added as fillers to control the phase behaviors of binary polymer blends. Because the colloids attract both components in the blends, aggregates are formed by the colloids coated with both kinds of polymer brushes. The aggregation results in two contradictory effects on the phase separation. First, the formation of aggregate decreases the translational entropy, which promotes the phase separation. On the other hand, the phase separation causes the extra free energy penalty due to the stretch of the chains attaching on the colloids, which prevents the phase separation. Furthermore, as the concentration or adsorbability of the colloids increases the local fluctuations within the aggregates become important. This results in a transition from the macro-phase separation to the micro-phase separation and the existence of the Lifshitz point. All of these effects lead to diverse phase behaviors in the polymer nanocomposites system. In present work, these behaviors are studied theoretically by the random phase approximation in a model system.
Bifurcation theory of a one-dimensional transport model for the L-H transition
Authors: Weymiens W. , de Blank H. J. , Hogeweij G. M. D.
Published: August 2013

Transitions between low and high-confinement (L-H transitions) in magnetically confined plasmas can appear as three qualitatively different types: sharp, smooth, and oscillatory. Bifurcation analysis unravels these possible transition types and how they are situated in parameter space. In this paper the bifurcation analysis is applied to a 1-dimensional model for the radial transport of energy and density near the edge of magnetically confined plasmas. This phenomenological L-H transition model describes the reduction of the turbulent transport by E×B-flow shear self-consistently with the evolution of the radial electric field. Therewith, the exact parameter space, including the threshold values of the control parameters, of the possible L-H transitions in the model is determined. Furthermore, a generalised equal area rule is derived to describe the evolution of the transport barrier in space and time self-consistently. Applying this newly developed rule to the model analysed in this paper reveals a naturally occurring transition to an extra wide transport barrier that may correspond to the improved confinement known as the very-high-confinement mode.
Hot carrier-selective chemical reactions on Ag(110)
Authors: Hahn Jae Ryang , Jang Sang Hoon , Kim Ki Wan , Son Seung Bae
Published: August 2013

Here, we show that the pathways, products, and efficiencies of reactions occurring on a metal surface can be spatially modulated by varying the type and energy of hot carriers produced by injecting tunneling electrons or holes from a scanning tunneling microscope tip into the metal surface. Control over the metal surface reactions was demonstrated for the large-scale dissociation reaction of O2 molecules on a Ag(110) surface. Hot electrons (or holes) transported through the metal surface to chemisorbed O2 selectively dissociated the molecule into two oxygen atoms separated along the $[1\bar 10]$[11¯0] (or [001]) lattice direction. The reaction selectivity was enhanced compared to the selectivity of a direct reaction involving tunneling carriers.
An ab initio study of the ground and low-lying excited states of KBe with the effect of inner-shell electrons
Authors: Xiao Ke-La , Yang Chuan-Lu , Wang Mei-Shan , Ma Xiao-Guang , Liu Wen-Wang
Published: August 2013

The potential energy curves (PECs) of 12Σ+, 22Σ+, 12Π, and 22Π states of KBe are calculated using multireference configuration interaction method and large all-electron basis sets. Four sets of frozen core orbitals (FCOs) are considered to examine the effect of inner-shell correlation electrons on the molecular properties. The ro-vibrational energy levels are obtained by solving the Schrödinger equation of nuclear motion based on the ab initio PECs. The spectroscopic parameters are determined from the ro-vibrational levels with Dunham expansion. The PECs are fitted into analytical potential energy functions using the Morse long-range potential function. The dipole moment functions of the states for KBe calculated with different FCOs are presented. The transition dipole moments for KBe between 12Σ+ and 22Σ+ states, 12Π and 12Σ+ states, and 22Π and 12Σ+ states are also obtained.
Ro-vibrational quenching of CO (v = 1) by He impact in a broad range of temperatures: A benchmark study using mixed quantum/classical inelastic scattering theory
Authors: Semenov Alexander , Ivanov Mikhail , Babikov Dmitri
Published: August 2013

The mixed quantum/classical approach is applied to the problem of ro-vibrational energy transfer in the inelastic collisions of CO(v = 1) with He atom, in order to predict the quenching rate coefficient in a broad range of temperatures 5 < T < 2500 K. Scattering calculations are done in two different ways: direct calculations of quenching cross sections and, alternatively, calculations of the excitation cross sections plus microscopic reversibility. In addition, a symmetrized average-velocity method of Billing is tried. Combination of these methods allows reproducing experiment in a broad range of temperatures. Excellent agreement with experiment is obtained at 400 < T < 2500 K (within 10%), good agreement in the range 100 < T < 400 K (within 25%), and semi-quantitative agreement at 40 < T < 100 K(within a factor of 2). This study provides a stringent test of the mixed quantum/classical theory, because the vibrational quantum in CO molecule is rather large and the quencher is very light (He atom). For heavier quenchers and closer to dissociation limit of the molecule, the mixed quantum/classical theory is expected to work even better.
Electronic states of porphycene-O2 complex and photoinduced singlet O2 production
Authors: Asturiol David , Barbatti Mario
Published: August 2013

Porphycene (PC), a structural isomer of porphine, is a promising photosensitizer for photodynamic therapy. Its excited states can be quenched by molecular oxygen, generating singlet O2. The electronic structures of PC and of the PC⋯O2 complex were investigated using complete active space perturbation theory. It is shown that singlet oxygen generation involves 12 electronic states of the complex, with singlet, triplet, and quintet multiplicities. Two scenarios for singlet-O2 yield are analyzed: (I) quenching of triplet states of PC and (II) quenching of singlet states of PC. In the first scenario, which is favored under low O2 concentration, singlet-O2 yield is limited by the relatively low triplet quantum yield of PC. We discuss how the singlet-O2 yield would be busted if conditions for occurrence of the second scenario could be achieved.
Nanostructural and electronic properties of polytypes in InN nanocolumns
Authors: Kioseoglou J. , Koukoula T. , Komninou Ph. , Georgakilas A. , Androulidaki M. , Kehagias Th.
Published: August 2013

Transmission electron microscopy techniques and density functional theory calculations were employed to investigate the nanostructural and electronic properties of InN polytypes observed in InN nanocolumns, grown on Si(111) by molecular beam epitaxy. Moiré fringes and alternating hexagonal and cubic lattice stacking sequences along the c-axis, observed among the wurtzite layers, implied the presence of different structures embedded in the basic 2H structure of the nanocolumns. Quantitative electron diffraction analysis and high-resolution image simulations verified the coexistence of the wurtzite structure with the 4H, 6H, and the 3C zinc-blende structural polytypes. Total energies calculations established the 2H wurtzite structure as the most stable polytype. The band gap of all polytypes was found direct with the energies and the band gaps of the 4H (Eg = 0.64 eV) and 6H (Eg = 0.60 eV) structures calculated between the corresponding values of the 2H (Eg = 0.75 eV) and 3C (Eg = 0.49 eV) basic structures. Theoretical and experimental analysis showed that at the initial stages of growth InN nanocolumns were under tensile strain along both the basal plane and growth direction. Structural polytypes were then introduced in the form of embedded inclusions to accommodate the excess tensile strain along the growth direction, allowing the entire process of polymorphism to be the dominant strain relaxation mechanism of InN nanocolumns. Moreover, the lattice and energetic properties and band gap values of InN polytypes showed a linear dependence on hexagonality, while the presence of polytypes led to a characteristic broadening of the photoluminescence emission peak toward lower emission energies.
Hybrid flexure hinges
Authors: Lin Rongzhou , Zhang Xianmin , Long Xuejun , Fatikow Sergej
Published: August 2013

This paper designs and analyzes the hybrid flexure hinge composed of half a hyperbolic flexure hinge and half a corner-filleted flexure hinge. As it is transversely asymmetric, it has different performance when the fixed and free ends switch. Considering the diversion of rotation center from midpoint, closed-form equations are formulated to characterize both the active rotation and all other in-plane parasitic motion by the Castigliano's second theorem. The maximum stress is evaluated as well. These equations are verified by the finite element analysis and experimentation. The compliance precision ratios are proposed to indicate flexure hinges’ ability of preserving the rotation center when they have the same displacement at the free end. The hybrid flexure hinges are compared with five kinds of common notch flexure hinges (circular, corner-filleted, elliptical, hyperbolic, and parabolic flexure hinges) quantitatively based on compliance, precision, compliance precision ratios, and the maximum stress. Conclusions are drawn regarding the performance of these six kinds of flexure hinges.
Optical preparation of H2 rovibrational levels with almost complete population transfer
Authors: Dong Wenrui , Mukherjee Nandini , Zare Richard N.
Published: August 2013

Using stimulated Raman adiabatic passage (SARP), it is possible, in principle, to transfer all the population in a rovibrational level of an isolated diatomic molecule to an excited rovibrational level. We use an overlapping sequence of pump (532 nm) and dump (683 nm) single-mode laser pulses of unequal fluence to prepare isolated H2 molecules in a molecular beam. In a first series of experiments we were able to transfer more than half the population to an excited rovibrational level [N. Mukherjee, W. R. Dong, J. A. Harrison, and R. N. Zare, J. Chem. Phys. 138(5), 051101–1051101–4 (2013)]10.1063/1.4790402. Since then, we have achieved almost complete transfer (97% ± 7%) of population from the H2 (v = 0, J = 0) ground rovibrational level to the H2 (v = 1, J = 0) excited rovibrational level. An explanation is presented of the SARP process and how these results are obtained.
K+-hydration in a low-energy two-dimensional wetting layer on the basal surface of muscovite
Authors: Feibelman Peter J.
Published: August 2013

Density Functional Theory points to a key role of K+ solvation in the low-energy two-dimensional arrangement of water molecules on the basal surface of muscovite. At a coverage of 9 water molecules per 2 surface potassium ions, there is room to accommodate the ions into wetting layers wherein half of them are hydrated by 3 and the other half by 4 water molecules, with no broken H-bonds, or wherein all are hydrated by 4. Relative to the “fully connected network of H-bonded water molecules” that Odelius et al. found to form “a cage around the potassium ions,” the hydrating arrangements are several tens of meV/H2O better bound. Thus, low-temperature wetting on muscovite is not driven towards “ice-like” hexagonal coordination. Instead, solvation forces dominate.
First glimpse of the soft x-ray induced excited spin-state trapping effect dynamics on spin cross-over molecules
Authors: Davesne V. , Gruber M. , Miyamachi T. , Da Costa V. , Boukari S. , Scheurer F. , Joly L. , Ohresser P. , Otero E. , Choueikani F. , Gaspar A. B. , Real J. A. , Wulfhekel W. , Bowen M. , Beaurepaire E.
Published: August 2013

The dynamics of the soft x-ray induced excited spin state trapping (SOXIESST) effect of Fe(phen)2(NCS)2 (Fe-phen) powder have been investigated by x-ray absorption spectroscopy (XAS) using the total electron yield method, in a wide temperature range. The low-spin (LS) state is excited into the metastable high-spin (HS) state at a rate that depends on the intensity of the x-ray illumination it receives, and both the temperature and the intensity of the x-ray illumination will affect the maximum HS proportion that is reached. We find that the SOXIESST HS spin state transforms back to the LS state at a rate that is similar to that found for the light induced excited spin state trapping (LIESST) effect. We show that it is possible to use the SOXIESST effect in combination with the LIESST effect to investigate the influence of cooperative behavior on the dynamics of both effects. To investigate the impact of molecular cooperativity, we compare our results on Fe-phen with those obtained for Fe{[Me2Pyrz]3BH}2 (Fe-pyrz) powder, which exhibits a similar thermal transition temperature but with a hysteresis. We find that, while the time constant of the dynamic is identical for both molecules, the SOXIESST effect is less efficient at exciting the HS state in Fe-pyrz than in Fe-phen.
Engineering single-valley forward transport in strained graphene by magnetic-electric modulation
Authors: Wang Yu
Published: August 2013

Based on the distinct response of valley transport in graphene under the uniform strain, magnetic barrier, and electrostatic barrier manipulation, completely single-valley forward transport has been theoretically demonstrated by aligning deliberately the field profile of magnetic barrier and strain field. Further imposing electrostatic engineering, the receiving single-valley transport can be flexibly tuned to adapt much realistic field modulation, improve its ability to resist the temperature-induced thermal smooth, and even turn on or off this single-valley transport mode, displaying the appealing features for valleytronic device application.
Thermoelectric properties of gamma-graphyne nanoribbons and nanojunctions
Authors: Ouyang Tao , Xiao Huaping , Xie Yuee , Wei Xiaolin , Chen Yuanping , Zhong Jianxin
Published: August 2013

Using the Nonequilibrium Green's function approach, we investigate the thermoelectric properties of gamma-graphyne nanostructures. Compared with the graphene nanoribbons (GNRs), gamma-graphyne nanoribbons (GYNRs) are found to possess superior thermoelectric performance. Its thermoelectric figure of merit ZT is about 3∼13 times larger than that in the GNRs. Meanwhile, the results show that the thermoelectric efficiency of GYNRs decreases as the ribbon width increases, while it increases monotonically with temperature. For the gamma-graphyne nanojunctions (GYNJs), the value of ZT increases dramatically as the width discrepancy between the left and right leads becomes more obvious. This improvement is mainly originated from the fact that the enhanced thermopower and degraded thermal conductance (including the electron and phonon contributions) outweigh the reduction of electronic conductance. Moreover, it is found that the thermoelectric behavior of GYNJs also depends on the geometric shape, which is explained by analyzing the unique width distribution of phonon contributed thermal conductance of GYNRs. These findings qualify gamma-graphyne as a promising candidate for thermoelectric applications and provide useful guideline for enhancing the thermoelectric performance in experiment.
Thin-film flow in helically wound rectangular channels with small torsion
Authors: Stokes Y. M. , Duffy B. R. , Wilson S. K. , Tronnolone H.
Published: August 2013

Laminar gravity-driven thin-film flow down a helically wound channel of rectangular cross-section with small torsion in which the fluid depth is small is considered. Neglecting the entrance and exit regions we obtain the steady-state solution that is independent of position along the axis of the channel, so that the flow, which comprises a primary flow in the direction of the axis of the channel and a secondary flow in the cross-sectional plane, depends only on position in the two-dimensional cross-section of the channel. A thin-film approximation yields explicit expressions for the fluid velocity and pressure in terms of the free-surface shape, the latter satisfying a nonlinear ordinary differential equation that has a simple exact solution in the special case of a channel of rectangular cross-section. The predictions of the thin-film model are shown to be in good agreement with much more computationally intensive solutions of the small-helix-torsion Navier–Stokes equations. The present work has particular relevance to spiral particle separators used in the mineral-processing industry. The validity of an assumption commonly used in modelling flow in spiral separators, namely, that the flow in the outer region of the separator cross-section is described by a free vortex, is shown to depend on the problem parameters.
Non-linear piezoelectricity in zinc blende GaAs and InAs semiconductors
Authors: Tse G. , Pal J. , Monteverde U. , Garg R. , Haxha V. , Migliorato M. A. , Tomić S.
Published: August 2013

This work explores the strain dependence of the piezoelectric effect in GaAs and InAs zinc blende crystals. We write the polarization in terms of the internal anion-cation displacement and the ionic and dipole charges. We then use ab initio density functional theory to evaluate the dependence of all quantities on the strain tensor. We investigate which aspects of the elastic and dielectric response of zinc blende crystals are sources of non-linearities in the piezoelectric effect. We observe that the main source of non-linearities is the response to elastic deformation and, in particular, the internal sublattice displacement of the interpenetrating cation and anion sublattices. We show that the internal sublattice displacement dependence on the diagonal stress components is neither symmetric nor antisymmetric in the strain. Therefore, non-linear coefficients of order higher than quadratic are needed to correctly describe non-linear effects. Using a fitting procedure of the ab initio data, we also determine all non-linear piezoelectric coefficients up to the third power in the diagonal components of the strain tensor. We can report that non-linear effects up to third order can be significant in precisely determining the magnitude of the piezoelectric polarization if compressive or tensile strains larger than 10% are present. We notice however that, in nanostructures such as quantum dots, the optical properties are less sensitive to the third order non-linear piezoelectric effect and that third order coefficients can therefore be neglected.
Measurement of the true transverse nuclear magnetic resonance relaxation in the presence of field gradients
Authors: Mitchell J. , Chandrasekera T. C. , Gladden L. F.
Published: August 2013

A measure of the nuclear spin transverse relaxation time T2, as determined using the nuclear magnetic resonance Carr-Purcell Meiboom-Gill (CPMG) experiment, provides unique information characterizing the microstructure of porous media which are themselves ubiquitous across fields of petrophysics, biophysics, and chemical engineering. However, the CPMG measurement is sensitive to diffusion in large magnetic field gradients. Under such conditions an effective relaxation time \documentclass[12pt]{minimal}\begin{document}$T_{2,\rm eff}$\end{document}T2, eff is observed instead, described by a combination of relaxation and diffusion exponents. The relaxation exponent always varies as nte (where n is the number, and te is the temporal separation, of spin echoes). The diffusion exponent varies as \documentclass[12pt]{minimal}\begin{document}$nt_{\rm e}^k$\end{document}ntek, where 1 < k ⩽ 3, although the exact analytic form is often unknown. Here we present a general approach to separating the influence of relaxation and diffusion by utilizing a composite diffusion exponent. Any \documentclass[12pt]{minimal}\begin{document}$T_{2,\rm eff}$\end{document}T2, eff component with a power of k > 1 is removed to provide a measure of the true T2 relaxation time distribution from CPMG data acquired in the presence of a strong background gradient. We apply the technique to discriminate between the effects of relaxation and diffusion in porous media using catalysts and rocks as examples. The method is generally applicable to any CPMG measurements conducted in the presence of a static magnetic field gradient.
Randomized scalable checkerboard geometries: The electrostatic problem
Authors: Olariu C. S. , Lasquellec S. , Brosseau C.
Published: August 2013

Motivated by the spate of recent experimental and theoretical interest in effective dielectric properties of composite materials, we consider randomised scalable checkerboard geometries. Earlier calculations of their effective permittivity are subject to various numerical difficulties which give rise to significant errors, especially for high permittivity contrast ratio between the phases. We describe a numerical protocol for estimating the permittivity with attention to its application in the analysis of randomization of phases and scaling. We apply this protocol to different N × N checkerboard geometries and provide explicit calculations of the effective permittivity and field average. We also discuss, in detail, the influence that topological defects, i.e., phase contacts at corners, have on the effective dielectric properties. The associated statistics of the permittivity for the half-filling case is Gaussian for small permittivity ratios. Our results support the suggestion that the deviation function for the half filling case obeys a power-law scaling with N due to finite-size effects as we let the length scale of the stochastic inhomogeneities approach zero. We show how these results are generic for two-color random checkerboards. We argue that the effect of spatial fluctuations of permittivity is weak as N is increased. We also discuss the potential, the challenges, and the limitations of these calculations.
A semi-analytical, two-dimensional model for AlGaN/GaN high-electron-mobility-transistor Schottky currents at high reverse voltages
Authors: Jos Rik
Published: August 2013

A semi-analytical model is derived for the reverse Schottky gate current in AlGaN-GaN high-electron-mobility-transistors (HEMTs) in off-state at high drain voltage. At elevated drain voltages, the depletion of the two-dimensional electron gas (2-DEG) not only exists directly underneath the gate contact but also extends from the gate towards the drain. This increases the electric fields at the gate edge on the drain side, which causes an increase in the gate leakage current. In this paper, a new method is proposed to calculate the electric fields at the gate edge using conformal mapping of the charge configuration in the device. This method also allows calculation of the influence of charges trapped at the interface between the semiconductor and the passivation layer next to the gate. It is shown that direct tunneling is the dominant current mechanism at high drain voltages, such that the current becomes insensitive to temperature variation. Interface charges next to the gate exert a large influence on the high voltage leakage current. It is argued that temperature variations of the high voltage leakage current are caused by temperature dependent changes in trapped charge.
Blueshifts of the emission energy in type-II quantum dot and quantum ring nanostructures
Authors: Hodgson P. D. , Young R. J. , Ahmad Kamarudin M. , Carrington P. J. , Krier A. , Zhuang Q. D. , Smakman E. P. , Koenraad P. M. , Hayne M.
Published: August 2013

We have studied the ensemble photoluminescence (PL) of 11 GaSb/GaAs quantum dot/ring (QD/QR) samples over ≥5 orders of magnitude of laser power. All samples exhibit a blueshift of PL energy, ΔE, with increasing excitation power, as expected for type-II structures. It is often assumed that this blueshift is due to band-bending at the type-II interface. However, for a sample where charge-state sub-peaks are observed within the PL emission, it is unequivocally shown that the blueshift due to capacitive charging is an order of magnitude larger than the band bending contribution. Moreover, the size of the blueshift and its linear dependence on occupancy predicted by a simple capacitive model are faithfully replicated in the data. In contrast, when QD/QR emission intensity, I, is used to infer QD/QR occupancy, n, via the bimolecular recombination approximation (I∝n2), exponents, x, in ΔE∝Ix are consistently lower than expected, and strongly sample dependent. We conclude that the exponent x cannot be used to differentiate between capacitive charging and band bending as the origin of the blueshift in type-II QD/QRs, because the bimolecular recombination is not applicable to type-II QD/QRs.
A universal way to determine Hirota's bilinear equation of KdV type
Authors: Ye Yi-Chao , Zhou Zi-Xiang
Published: August 2013

A universal way, which is independent of computer programming, is presented to determine whether a given nonlinear partial differential equation can be transformed to a bilinear equation of KdV type via a logarithmic transformation. When it can be transformed, all the parameters are determined so that the bilinear equation is written explicitly.
Ion-acoustic supersolitons in plasmas with two-temperature electrons: Boltzmann and kappa distributions
Authors: Verheest Frank , Hellberg Manfred A. , Kourakis Ioannis
Published: August 2013

Acoustic supersolitons arise when a plasma model is able to support three consecutive local extrema of the Sagdeev pseudopotential between the undisturbed conditions and an accessible root. This leads to a characteristic electric field signature, where a simple bipolar shape is enriched by subsidiary maxima. Large-amplitude nonlinear acoustic modes are investigated, using a pseudopotential approach, for plasmas containing two-temperature electrons having Boltzmann or kappa distributions, in the presence of cold fluid ions. The existence domains for positive supersolitons are derived in a methodological way, both for structure velocities and amplitudes, in terms of plasma compositional parameters. In addition, typical pseudopotentials, soliton, and electric field profiles have been given to illustrate that positive supersolitons can be found in the whole range of electron distributions from Maxwellian to a very hard nonthermal spectrum in kappa. However, it is found that the parameter ranges that support supersolitons vary significantly over the wide range of kappa considered.
Bohm velocity in the presence of a hot cathode
Authors: Palacio Mizrahi J. H. , Krasik Ya. E.
Published: August 2013

The spatial distribution of the plasma and beam electrons in a region whose extension from a hot cathode is larger than the Debye length, but smaller than the electron mean free path, is analyzed. In addition, the influence of electrons thermionically emitted from a hot cathode and the ratio of electron-to-ion mass on the Bohm velocity and on the ion and electron densities at the plasma-sheath boundary in a gas discharge are studied. It is shown that thermionic emission has the effect of increasing the Bohm velocity, and this effect is more pronounced for lighter ions. In addition, it is shown that the Bohm velocity cannot be increased to more than 24% above its value when there is no electron emission.
Radiation-assisted Frenkel-Poole transport in single-crystal diamond
Authors: Girolami M. , Bellucci A. , Calvani P. , Flammini R. , Trucchi D. M.
Published: August 2013

The measurement of the density of occupied states as a function of the applied electric field, performed on single-crystal chemical vapour deposition diamond by x-ray modulated photocurrent technique, is reported. Two regimes of non-linear charge transport were observed: a classical Frenkel-Poole (FP) process at high electric fields (>6800 V/cm), and a radiation-assisted transport mechanism at intermediate electric fields (2000 to 6800 V/cm), consisting of a double-step process in which the direct re-emission into the extended band occurs following multiple photo-induced FP-like hopping transitions.
Vortex-aided inertial microfluidic device for continuous particle separation with high size-selectivity, efficiency, and purity
Authors: Wang Xiao , Zhou Jian , Papautsky Ian
Published: August 2013

In this paper, we report an inertial microfluidic device with simple geometry for continuous extraction of large particles with high size-selectivity (<2 μm), high efficiency (∼90%), and high purity (>90%). The design takes advantage of a high-aspect-ratio microchannel to inertially equilibrate cells and symmetric chambers for microvortex-aided cell extraction. A side outlet in each chamber continuously siphons larger particles, while the smaller particles or cells exit through the main outlet. The design has several advantages, including simple design, small footprint, ease of paralleling and cascading, one-step operation, and continuous separation with ultra-selectivity, high efficiency and purity. The described approach is applied to manipulating cells and particles for ultra-selective separation, quickly and effectively extracting larger sizes from the main flow, with broad applications in cell separations.
Sorting of circulating tumor cells (MV3-melanoma) and red blood cells using non-inertial lift
Authors: Geislinger Thomas M. , Franke Thomas
Published: August 2013

We demonstrate the method of non-inertial lift induced cell sorting (NILICS), a continuous, passive, and label-free cell sorting approach in a simple single layer microfluidic device at low Reynolds number flow conditions. In the experiments, we exploit the non-inertial lift effect to sort circulating MV3-melanoma cells from red blood cell suspensions at different hematocrits as high as 9%. We analyze the separation process and the influence of hematocrit and volume flow rates. We achieve sorting efficiencies for MV3-cells up to EMV3 = 100% at Hct = 9% and demonstrate cell viability by recultivation of the sorted cells.
Non-destructive Faraday imaging of dynamically controlled ultracold atoms
Authors: Gajdacz Miroslav , Pedersen Poul L. , Mørch Troels , Hilliard Andrew J. , Arlt Jan , Sherson Jacob F.
Published: August 2013

We describe an easily implementable method for non-destructive measurements of ultracold atomic clouds based on dark field imaging of spatially resolved Faraday rotation. The signal-to-noise ratio is analyzed theoretically and, in the absence of experimental imperfections, the sensitivity limit is found to be identical to other conventional dispersive imaging techniques. The dependence on laser detuning, atomic density, and temperature is characterized in a detailed comparison with theory. Due to low destructiveness, spatially resolved images of the same cloud can be acquired up to 2000 times. The technique is applied to avoid the effect of shot-to-shot fluctuations in atom number calibration, to demonstrate single-run vector magnetic field imaging and single-run spatial imaging of the system's dynamic behavior. This demonstrates that the method is a useful tool for the characterization of static and dynamically changing properties of ultracold atomic clouds.
Double-walled ice nanotubes grown in carbon nanotubes: Molecular dynamics simulations
Authors: Chang Xu , Li Huichao , Fa Wei
Published: August 2013

Using the classical molecular dynamics method, we have investigated the structure and behavior of the confined water in (20, 0) and (19, 0) single-walled carbon nanotubes (SWCNs). It has been found that several kinds of the double-walled ice nanotubes (Ice-NTs) can indeed be obtained, depending on the diameter of confined SWCNs and the axial pressure. Furthermore, a first-order phase transition—a liquid to double-walled Ice-NT occurs for water in the (20, 0) SWCN at 300 MPa with the melting temperature lower than that of the bulk water. It is noted that water molecules in the tube wall present square lattices at lower pressure, and triangular lattices at higher pressure. More interestingly, high-density nano-ice displays regular chiral double-walled Ice-NT within (19, 0) SWCN at 1.2 GPa, and the outer wall can be considered as (11, 3) Ice-NT resembling the gold nanotube.
Impurity-to-band activation energy in phosphorus doped diamond
Authors: Stenger I. , Pinault-Thaury M.-A. , Kociniewski T. , Lusson A. , Chikoidze E. , Jomard F. , Dumont Y. , Chevallier J. , Barjon J.
Published: August 2013

The value of the impurity-to-band activation energy EA of a dopant is a basic feature of the electrical conductivity of semiconductors. Various techniques were used to determine EA in n-type diamond doped with phosphorus, giving values of EA varying from 0.43 eV to 0.63 eV, the value EA of 0.6 eV being commonly accepted for the ionization energy of phosphorus donors in diamond. Nevertheless, up to now, the dispersion of the experimental values of EA remains unexplained. In this work, we investigate the electrical properties of a set of n-type diamond homoepitaxial films with different phosphorus concentrations by Hall effect measurements in order to deduce EA and to understand the evolution of this energy with the dopant concentration. We show that, below 2 × 1019 cm−3 phosphorus, the decrease of EA is mainly controlled by the concentration of ionized defects resulting from the donor compensation. The role of ionized defects in the decrease of EA is analyzed on the basis of existing models adapted to the case of diamond. The proposed model provides a correct description of the experimental data. It can be used to quantitatively predict the activation energy of phosphorus in n-type diamond for given donor and compensating acceptor concentrations.
Electrostatic model of radial pn junction nanowires
Authors: Chia A. C. E. , LaPierre R. R.
Published: August 2013

Poisson's equation is solved for a radial pn junction nanowire (NW) with surface depletion. This resulted in a model capable of giving radial energy band and electric field profiles for any arbitrary core/shell doping density, core/shell dimensions, and surface state density. Specific cases were analyzed to extract pertinent underlying physics, while the relationship between NW specifications and the depletion of the NW were examined to optimize the built-in potential across the junction. Additionally, the model results were compared with experimental results in literature to good agreement. Finally, an optimum device design is proposed to satisfy material, optical, and electrostatic constraints in high efficiency NW solar cells.
Predicted alternative structure for tantalum metal under high pressure and high temperature
Authors: Liu Zhong-Li , Cai Ling-Cang , Zhang Xiu-Lu , Xi Feng
Published: August 2013

First-principles simulations have been performed to investigate the phase stability of tantalum (Ta) metal under high pressure and high temperature. We searched its low-energy structures globally using our developed multi-algorithm collaborative crystal structure prediction technique. The body-centered cubic (bcc) was found to be stable at pressure up to 300 GPa. The previously reported ω and A15 structures were also reproduced successfully. More interestingly, we observed another phase (space group: Pnma, 62) that is more stable than ω and A15. Its stability is confirmed by its phonon spectra and elastic constants. For ω-Ta, the calculated elastic constants and high-temperature phonon spectra both imply that it is neither mechanically nor dynamically stable. Thus, ω is not the structure to which bcc-Ta transits before melting. On the contrary, the good agreement of Pnma-Ta shear sound velocities with experiment suggests Pnma is the new structure of Ta implied by the discontinuation of shear sound velocities in recent shock experiment [J. Appl. Phys. 111, 033511 (2012)].
Magnetorotational instability, current relaxation, and current-vortex sheet
Authors: Silveira F. E. M. , Galvão R. M. O.
Published: August 2013

The conjugate effect of current relaxation and of current-vortex sheet formation on the magnetorotational instability is explored in a conducting fluid. It is found that the relative amplification of the magnetic viscosity from marginal stability to the instability determined by the maximum growth rate is around 924% when resistive effects dominate, while the corresponding quantity is around 220% in the ideal limit. This shows that the conjugate influence is much more efficient to amplify the magnetic viscosity than just the effect due to the standard magnetic tension. It is also found that the magnitude of the magnetic viscosity is effectively enhanced by the conjugate influence. The results presented here may contribute to the understanding of the various processes that play a significant role in the mechanism of anomalous viscosity observed in Keplerian disks. It is argued that the new effect shall be relevant in thin accretion disks. It is also mentioned that the proposed formulation may be of interest for some theories of magnetic reconnection. Possible extensions of this work are suggested.
Terahertz quantum well photodetectors with improved designs by exploiting many-body effects
Authors: Ferré Simon , Razavipour Seyed Ghasem , Ban Dayan
Published: August 2013

A systematic study on many-body effects on Terahertz Quantum Well Photodetectors (THZ QWPs) is reported. Peak absorption frequency differs by more than 20% when taking many-body effects into account. The phenomenon is shown to be critical in designs with a small barrier height and a high doping density. In order to exploit them and minimize their adverse impacts, a doping profile symmetrically split in the barrier layers, resembling a double-barrier QWP, is proposed. Simulation results show the design reduces dark current by one order of magnitude compared against conventional designs with a uniform doping profile in the quantum well.
A droplet-based novel approach for viable and low volume consumption surface plasmon resonance bio-sensing inside a polydimethylsiloxane microchip
Authors: Ghosh T. , Xie Y. , Mastrangelo C.
Published: August 2013

Over the course of last two decades, surface plasmon resonance (SPR) has emerged as a viable candidate for label-free detection and characterization for a large pool of biological interactions, ranging from hybridization of oligonucleotides to high throughput drug-screening. Conventional SPR bio-sensing involves a step-response method where the SPR sensorgram in response to a switched sequential flow of analyte and buffer is plotted in real-time and fitted to an exponential curve to extract the associative and dissociative reaction rates. Such measurement schemes involve continuous flow conditions where a substantial reagent volume is consumed and is subject to dispersive mixing at flow switching zones. In this paper, we demonstrate a new plug-train SPR technique in a microfluidic chip that separates and singulates solvent plugs in analyte and buffer by an immiscible air phase. Bio-samples are first discretized within plug droplets with volumes in order of few hundred nanoliters or less followed by pressure-driven transport onto SPR sensing sites of this hydrophobically modified SPR microdevise. The kinetic constants ka and kd for a model protein-small molecule interaction pair are extracted from a plug-train signal and are shown to be in reasonable agreement with our previous reports.
Transient hot-carrier optical gain in a gain-switched semiconductor laser
Authors: Ito Takashi , Chen Shaoqiang , Yoshita Masahiro , Mochizuki Toshimitsu , Kim Changsu , Akiyama Hidefumi , Pfeiffer Loren N. , West Ken W.
Published: August 2013

The transient optical gain was quantitatively determined from the rise time of output pulses of a gain-switched semiconductor laser via impulsive optical pumping. The optical gain for a high carrier density during gain switching was greatly reduced from that during steady-state operation because of hot carriers.
Dynamic interactions between oscillating cantilevers: Nanomechanical modulation using surface forces
Authors: Basarir O. , Ekinci K. L.
Published: August 2013

Dynamic interactions between two oscillating micromechanical cantilevers are studied. In the experiment, the tip of a high-frequency cantilever is positioned near the surface of a second low-frequency cantilever. Due to the highly nonlinear interaction forces between the two surfaces, thermal oscillations of the low-frequency cantilever modulate the driven oscillations of the high-frequency cantilever. The dissipations and the frequencies of the two cantilevers are shown to be coupled, and a simple model for the interactions is presented. The interactions studied here may be useful for the design of future micro and nanoelectromechanical systems for mechanical signal processing; they may also help realize coupled mechanical modes for experiments in non-linear dynamics.
Temperature-independent ferroelectric property and characterization of high-TC 0.2Bi(Mg1/2Ti1/2)O3-0.8PbTiO3 thin films
Authors: Zhang Linxing , Chen Jun , Zhao Hanqing , Fan Longlong , Rong Yangchun , Deng Jinxia , Yu Ranbo , Xing Xianran
Published: August 2013

Ferroelectric property stability against elevated temperature is significant for ferroelectric film applications, such as non-volatile ferroelectric random access memories. The high-TC 0.2Bi(Mg1/2Ti1/2)O3-0.8PbTiO3 thin films show the temperature-independent ferroelectric properties, which were fabricated on Pt(111)/Ti/SiO2/Si substrates via sol-gel method. The present thin films were well crystallized in a phase-pure perovskite structure with a high (100) orientation and uniform texture. A remanent polarization (2Pr) of 77 μC cm−2 and a local effective piezoelectric coefficient d33* of 60 pm/V were observed in the 0.2Bi(Mg1/2Ti1/2)O3-0.8PbTiO3 thin films. It is interesting to observe a behavior of temperature-independent ferroelectric property in the temperature range of room temperature to 125 °C. The remanent polarization, coercive field, and polarization at the maximum field are almost constant in the investigated temperature range. Furthermore, the dielectric loss and fatigue properties of 0.2Bi(Mg1/2Ti1/2)O3-0.8PbTiO3 thin films have been effectively improved by the Mn-doping.
Optical properties of hexagonal boron nanotubes by first-principles calculations
Authors: Kumar Jain Sandeep , Srivastava Pankaj
Published: August 2013

We present optical properties of hexagonal boron nanotubes (BNTs) for different schemes of incident light in the framework of density functional theory. We have considered three models of small diameter (below 5 Å) BNTs namely armchair (3,3), zigzag (5,0), and chiral (4,2) consisting 12, 20, and 56 atoms, respectively. In this convolution, we have investigated various optical parameters such as static dielectric constant, plasma frequency, absorption coefficient, refractive index, reflectivity, and optical conductivity for unpolarized [100], parallel polarized [001], and perpendicular polarized light [100]. The parallel and perpendicular polarized lights ensure the anisotropic nature of BNTs. The study reveals the highest static dielectric constants for chiral BNTs correspond to parallel polarized and unpolarized light, indicating good dielectric materials. The highest absorption coefficient is reported for armchair (3,3) BNT among all the considered models. Moreover, small absorption is noticed in comparison to CNTs. The small electron energy loss is obtained for parallel polarized light in contrast to perpendicular ones. The static refractive index follows the same trend as that of static dielectric constant, i.e., (4,2)>(3,3)>(5,0) for unpolarized and parallel polarized lights. Whereas, for perpendicular polarized light, they exhibit different order, i.e., (3,3)>(5,0)>(4,2). However, the static and maximum refractive indices are obtained high for chiral (4,2) BNT correspond to parallel polarized light. Further, the reflectivity and conductivity of (3,3) BNT bring out to be the highest for all the incident light. The high conductivity is predicted for armchair and chiral BNTs correspond to parallel polarized light. These predictions proved to be promising candidate for field emission and opto-electronic devices. The present calculated findings are well compared with the available experimental and theoretical results of other nanotubes.
Gallium nitride nanowires by maskless hot phosphoric wet etching
Authors: Bharrat D. , Hosalli A. M. , Van Den Broeck D. M. , Samberg J. P. , Bedair S. M. , El-Masry N. A.
Published: August 2013

We demonstrate gallium nitride (GaN) nanowires formation by controlling the selective and anisotropic etching of N-polar GaN in hot phosphoric acid. Nanowires of ∼109/cm,2 total height of ∼400 nm, and diameters of 170–200 nm were obtained. These nanowires have both non-polar {11¯00}/ {112¯0} and semi-polar {1011¯} facets. X–Ray Diffraction characterization shows that screw dislocations are primarily responsible for preferential etching to create nanowires. Indium gallium nitride multi-quantum wells (MQWs) grown on these GaN nanowires showed a blue shift in peak emission wavelength of photoluminescence spectra, and full width at half maximum decreased relative to MQWs grown on planar N-polar GaN, respectively.
Crossover from stochastic activation to cooperative motions of shear transformation zones in metallic glasses
Authors: Jiao W. , Sun B. A. , Wen P. , Bai H. Y. , Kong Q. P. , Wang W. H.
Published: August 2013

We observe that the stress relaxation of metallic glasses below glass transition temperatures presents a universal double power-law decay behavior, indicating that relaxation dynamics transforms from a fast mode to a slow mode. This is attributed to a crossover from the stochastic activation to the self-organized cooperative motion of localized shear transformation zones. The phenomenon is further confirmed via strain recovery experiments and illustrated by a stochastic model. The results demonstrate that the plastic deformation exhibits the hallmarks of critical phenomenon, and offer a picture on the onset of deformation and evolution of relaxations in metallic glasses.
Study of H2 physical adsorption in single-walled carbon nanotube array
Authors: Zhou Shiqi , Liu Xuejuan , Yang Kaiwei , Zou Hui
Published: August 2013

The potential energies of a single H2 inside and outside an armchair single-walled carbon nanotube (SWCNT) are calculated by the electronic density functional theory (DFT), and influences of the SWCNT tube diameter on the potential energy minimum and equilibrium position are studied. Hydrogen storage capacity of the armchair SWCNTs in the rhombic arrays is estimated by using grand canonical Monte Carlo (GCMC) simulations in a pressure range from 10 to 100 bar and at temperatures of 77 K, 150 K, 220 K, 298 K, and 318 K, respectively; influences of the SWCNT diameter and VDW distance on the hydrogen storage capacity, and the isosteric heats of the H2-armchair SWCNTs arrays at several discrete temperatures and pressures are also investigated. The present main discoveries include (i) variation pattern of the H2 adsorption saturation pressure with the tube diameter and temperature; (ii) existence of extremum of the hydrogen storage capacity as a function of the VDW distance and tube diameter; (iii) diametrically opposite change of H2 storage capacity with the tube diameter in different pressure domains; (iv) layered distribution of the H2 adsorbed inside the tube. A theoretical mode is suggested to explain self-consistently all of these discoveries by combining the potential field information with the arguments of liquid state theories, and further verified by snapshots of representative configuration. The present discoveries, particularly, the theoretical mode explaining them, may serve to provide some guidance in improving the hydrogen storage capacity by doping the CNT and optimization of parameters.