bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanism of mutarotation in supercooled liquid phase: Studies on L-sorbose
Authors: Wlodarczyk P. , Paluch M. , Grzybowski A. , Kaminski K. , Cecotka A. , Ziolo J. , Markowski J.
Published: October 2012

We have studied mutarotation in anhydrous supercooled L-sorbose by means of dielectric spectroscopy. The phenomenon observed in L-sorbose is much faster than in the structurally similar D-fructose. The kinetics of this process has been determined by applying 1st order kinetics model. Activation energy equal to 68 kJ/mol was obtained from temperature dependence of rate constants. To understand differences in mutarotation rate between D-fructose and L-sorbose, quantum mechanical calculations were performed to study mechanism of this phenomenon. The possible impact of water absorbed from air on the mutarotation in supercooled liquid state has been checked. It turned out that the process is probably intermolecular and the water molecules or other carbohydrate molecules assist in the proton transfer process. Finally we have shown that the rate constant can be alternatively determined from frequency of the maximum of peak, obtained by performing Fourier transform of kinetic curve.
Studies on CdS nanoparticles prepared in DNA and bovine serum albumin based biotemplates
Authors: Nithyaja B. , Vishnu K. , Mathew S. , Radhakrishnan P. , Nampoori V. P. N.
Published: October 2012

This paper discusses band gap tunability of CdS nanoparticles in biotemplates deoxyribonucleic acid (DNA) and bovine serum albumin (BSA). DNA is more efficient in controlling the size of the nanoparticles compared to BSA. Since nanoparticles are capped with biomaterials, they are very useful for biolabeling. The photo luminescence spectrum of CdS nanoparticles in DNA template shows sharp emission peak at 490 nm with shoulders at 430 nm and 530 nm while that of CdS in BSA template has emission peak at 530 nm with shoulders at 477 nm and 410 nm. The excitation wavelength dependent shift of photoluminescence peak is found to be between 40 and 50 nm for a change in excitation wavelength from 260 to 420 nm. We also studied excitation wavelength dependence on fluorescence emission of CdS nanoparticles stabilized with DNA and BSA.
On the formulation and solution of the isochronal synchronization stability problem in delay-coupled complex networks
Authors: Grzybowski J. M. V. , Macau E. E. N. , Yoneyama T.
Published: October 2012

We present a new framework to the formulation of the problem of isochronal synchronization for networks of delay-coupled oscillators. Using a linear transformation to change coordinates of the network state vector, this method allows straightforward definition of the error system, which is a critical step in the formulation of the synchronization problem. The synchronization problem is then solved on the basis of Lyapunov-Krasovskii theorem. Following this approach, we show how the error system can be defined such that its dimension can be the same as (or smaller than) that of the network state vector.
Incipient motion of a single particle on regular substrates in laminar shear flow
Authors: Agudo J. R. , Wierschem A.
Published: October 2012

We study experimentally the critical conditions for incipient motion of a single spherical particle deposited on a regular substrate under laminar flow conditions. The substrates are triangular and quadratic arrangements of identical glass spheres. For the latter configuration, the distance between the substrate spheres is varied, resulting in different partial shielding of the deposited particle to the shear flow. For the studied particle Reynolds numbers range between 3 × 10−4 and 3, the critical Shields number is independent from the particle density and from the particle Reynolds number but it depends significantly on the geometry of the substrate. Depending on the spacing between the substrate beads and thus on the exposure of the particle to the flow, we have observed an increase of about 50 percent in the critical Shields number. Studying the onset of particle motion as a function of the orientation of the substrate to the flow direction we find that the critical Shields number changes by up to a factor of 2, which is mainly due to the fact that the particle travels through the troughs of the substrate and hence the shear force in travel direction diminishes if not in line with the flow direction. Besides the critical Shields number we study the initial stage of particle motion by detecting the minimum time that is necessary for maintaining a certain Shields number to change the position of a single particle on the regular substrates. In the range studied, the initial stage of motion on the scale of the substrate's periodicity is mainly governed by the equilibrium particle motion.
Properties of the B+-H2 and B+-D2 complexes: A theoretical and spectroscopic study
Authors: Poad B. L. J. , Dryza V. , Buchachenko A. A. , Kłos J. , Bieske E. J.
Published: October 2012

The rotationally resolved infrared spectrum of the B+-D2 ion-neutral complex is recorded in the D-D stretch vibration region (2805–2875  cm−1) by detecting B+ photofragments. Analysis of the spectrum confirms a T-shaped equilibrium geometry for the B+-D2 complex with a vibrationally averaged intermolecular bond length of 2.247 Å, around 0.02 Å shorter than for the previously characterised B+-H2 complex [V. Dryza, B. L. J. Poad, and E. J. Bieske, J. Am. Chem. Soc. 130, 12986 (2008)10.1021/ja8018302]. The D-D stretch band centre occurs at 2839.76 ± 0.10 cm−1, representing a −153.8  cm−1 shift from the Q1(0) transition of the free D2 molecule. A new three dimensional ab initio potential energy surface for the B++H2 interaction is calculated using the coupled cluster RCCSD(T) method and is used in variational calculations for the rovibrational energies of B+-H2 and B+-D2. The calculations predict dissociation energies of 1254  cm−1 for B+-H2 with respect to the B++H2 (j = 0) limit, and 1313  cm−1 for B+-D2 with respect to the B++D2 (j = 0) limit. The theoretical approach reproduces the rotational and centrifugal constants of the B+-H2 and B+-D2 complexes to within 3%, and the magnitude of the contraction of the intermolecular bond accompanying excitation of the H2 or D2 sub-unit, but underestimates the H-H and D-D vibrational band shifts by 7%–8%. Combining the theoretical and experimental results allows a new, more accurate estimation for the B+-H2 band origin (3939.64 ± 0.10  cm−1).
Optically induced two-dimensional photonic quasicrystal lattices in iron-doped lithium niobate crystal with an amplitude mask
Authors: Jin Wentao , Gao Yuanmei
Published: October 2012

We fabricate two-dimensional photonic quasicrystal lattices in iron-doped lithium niobate photorefractive crystal by a single amplitude mask. The experimental setup of this method is very simple and flexible without complicated optical adjustment system. It can be applied in almost any optical laboratories. We analyze the photonic quasicrystal lattices by plane wave guiding, Brillouin-zone spectroscopy and far field diffraction pattern imaging. The induced photonic quasicrystal lattices can exist stably for a long time in the photorefractive crystal. This method can be easily extended to generate more complex quasi-periodicity microstructures by designing the amplitude mask properly.
Life cycle assessment of energy performance of biodiesel produced from Jatropha curcas
Authors: Chatterjee Rajeshwari , Sharma Vinay , Kumar Surender
Published: October 2012

Jatropha curcas has been widely considered as a potential feedstock for production of biodiesel in several tropical countries. Globally biodiesel is gaining importance because of its environmental advantages. This paper deals with the energy consumption for the biodiesel production from J. curcas. Two plantation models of Jatropha, perennial and annual harvesting and their energy benefits are considered. In perennial plantation, the biodiesel yield is more than the annual harvesting. On the other hand, overall energy output from the annual harvesting system is almost twice than that of perennial system. The energy benefits of Jatropha cultivation on two different types of soil (poor and normal soils) were evaluated with and without irrigation. The energy balance is also calculated on the basis of rainfall and different water level depth. The study estimated the net energy balance and net energy ratio for both the models and found that the energy values were high for both the systems.
Characterization of large-scale interface deformation arising from electrostatic modification of the contact angle of pinned contact lines
Authors: Ibarra-Bracamontes Laura , Mossman Michele , Whitehead Lorne
Published: October 2012

We present an experimental study of the deformation of oil-water interfaces under the influence of applied electric fields. In a new experimental approach, a pattern of regions with hydrophilic or hydrophobic surface properties is formed on a substrate and oil drops in an ambient environment of water are confined to specific regions of the substrate by this pattern. As with electrowetting, the shape of the oil-water interface can be changed by applying an electric field that changes the surface energy relationship at the interface. However, in this new method the contact line does not move. Surprisingly, although this behavior is a result of microscopic-scale electrostatic forces, only small surface shape changes result. Nevertheless, the changing interfacial shape can cause macroscopic fluid flow. In this paper, we use video microscopy and image analysis to investigate the dynamic evolution of the interface under various conditions, in order to explain this counterintuitive result.
Surface and pseudo-surface acoustic waves piezoelectrically excited in diamond-based structures
Authors: Glushkov Evgeny , Glushkova Natalia , Zhang Chuanzeng
Published: October 2012

Surface and pseudo-surface acoustic plane waves generated in two- and three-layer AlN/Diamond and AlN/Diamond/γ-TiAl structures by a point electric source are analyzed in the mathematical framework based on the Green's matrix integral representation and guided wave asymptotics derived using the residue technique. The attention is focused on the effect of pseudo-surface-to-surface wave degeneration at certain discrete values of h/λ (h is the thickness of the piezoelectric layer and λ is the wave-length). Earlier such optimal ratios were discovered and experimentally verified for the first pseudo-surface (Sezawa) wave mode in the AlN/Diamond structure. The present research reveals this effect for higher modes as well as examines its manifestation for three-layer structures with different diamond-to-AlN thickness ratios H/h.
A band-pass filter approach within molecular dynamics for the prediction of intrinsic quality factors of nanoresonators
Authors: Vallabhaneni Ajit K. , Ruan Xiulin , Rhoads Jeffrey F. , Murthy Jayathi
Published: October 2012

The temperature and frequency dependence of the flexural mode quality factors (Q) of doubly clamped single wall carbon nanotube resonators are calculated using classical molecular dynamics simulations. The validity of the various methods available in the literature for calculating Q based on the temporal response of the system during ring-down is discussed and the discrepancies associated with the methods are explained. A new approach based on band-pass filtering is proposed for calculating Q, which reveals classical temperature dependence (Q ∼ T−1) in contrast to the previously reported results (Q ∼ T−β, 0 < β < 1). It is shown that the Q estimated from the temporal response is in good agreement with the Q estimated from frequency response. This work also demonstrates that the proposed method is particularly advantageous when multiple modes are simultaneously excited within the linear regime.
Comment on “Soret motion in non-ionic binary molecular mixtures” [J. Chem. Phys. 135, 054102 (2011)]
Authors: Semenov Semen N. , Schimpf Martin E.
Published: October 2012

The material transport equations derived in the article by Leroyer and Würger [J. Chem. Phys. 135, 054102 (2011)10.1063/1.3615954] do not adequately provide a description of material transport in liquid binary systems. An alternate approach based on non-equilibrium thermodynamics is presented.
Extension of local response dispersion method to excited-state calculation based on time-dependent density functional theory
Authors: Ikabata Yasuhiro , Nakai Hiromi
Published: October 2012

We report the extension of the local response dispersion (LRD) method to the excited-state calculation based on time-dependent density functional theory. The difference density matrix, which is usually used for excited-state response properties, enables a state-specific dispersion correction. The numerical assessment proves that interaction energies of exciton-localized molecular complexes and their shifts from the ground state are accurately reproduced by the LRD method. Furthermore, we find that the dispersion correction is important in reproducing binding energies of aromatic excimers, despite the existence of other attractive forces such as exciton delocalization and charge-transfer interaction.
On the stability of ion water clusters at atmospheric conditions: Open system Monte Carlo simulation
Authors: Zidi Zouhaier S.
Published: October 2012

The formation of water clusters on Li+, Na+, K+, Cl−, and I− ions from water vapor at atmospheric conditions have been studied using Monte Carlo simulations. The extended simple point charge model has been employed for water molecules. The polarization of ions in the field of molecules and the polarization of molecules in the field of ions have been considered explicitly in the total Hamiltonian of the molecular system. The cluster formation work and the Gibbs free energy and enthalpy of attachment reactions of one water molecule to the cluster have been calculated via the bicanonical ensemble method. Our results reveal the formation of stable clusters in equilibrium with the moist atmosphere in a wide range of vapor pressure values, with largest clusters are formed around cations. Decreasing the temperature, from 293 K to 253 K, leads to the formation of larger equilibrium clusters, and enhances the stability of systems as whole. According to clusters’ molecular structures, negative ions are expected to be more active in atmospheric processes, including chemical reactions and cloud formation, than positive ones.
Structural, dielectric, magnetic, and nuclear magnetic resonance studies of multiferroic Y-type hexaferrites
Authors: Khanduri H. , Chandra Dimri M. , Kooskora H. , Heinmaa I. , Viola G. , Ning H. , Reece M. J. , Krustok J. , Stern R.
Published: October 2012

The effect of strontium substitution on structural, magnetic, and dielectric properties of a multiferroic Y-type hexaferrite (chemical formula Ba2−xSrxMg2Fe12O22 with 0 ≤ x ≤ 2) was investigated. Y-type hexaferrite phase formation was not affected by strontium substitution for barium, in the range 0 ≤ x ≤ 1.5, confirmed by x-ray diffraction and Raman spectroscopy measured at room temperature. Two intermediate magnetic spin phase transitions (at tempertures TI and TII) and a ferrimagnetic-paramagnetic transition (at Curie temperature TC) were identified from the temperature dependence of the magnetic susceptibility. Magnetic transition temperatures (TI, TII, and TC) increased with increasing strontium content. Magnetic hysteresis measurements indicated that by increasing strontium concentration, the coercivity increases, while the saturation magnetization decreases. The 57Fe NMR spectrum of the Y-type hexaferrite measured at 5 K and in zero magnetic field showed remarkable differences compared to that of other hexaferrites due to their different number of tetrahedral and octahedral iron sites. The temperature and frequency dependence of the dielectric permittivity evidenced broad peaks with frequency dispersion in correspondence of the Curie temperature.
Influence of the polymer concentration on the electroluminescence of ZnO nanorod/polymer hybrid light emitting diodes
Authors: Zaman Saima , Zainelabdin Ahmed , Amin Gul , Nur Omer , Willander Magnus
Published: October 2012

The effects of the polymer concentration on the performance of hybrid light emitting diodes (LEDs) based on zinc oxide nanorods (ZnO NRs) and poly(9,9-dioctylfluorene) (PFO) were investigated. Various characterization techniques were applied to study the performance of the PFO/ZnO NR hybrid LEDs fabricated with various PFO concentrations. The fabricated hybrid LEDs demonstrated stable rectifying diode behavior, and it was observed that the turn-on voltage of the LEDs is concentration dependent. The measured room temperature electroluminescence (EL) showed that the PFO concentration plays a critical role in the emission spectra of the hybrid LEDs. At lower PFO concentrations of 2-6 mg/ml, the EL spectra are dominated by blue emission. However, by increasing the concentration to more than 8 mg/ml, the blue emission was completely suppressed while the green emission was dominant. This EL behavior was explained by a double trap system of excitons that were trapped in the β-phase and/or in the fluorenone defects in the PFO side. The effects of current injection on the hybrid LEDs and on the EL emission were also investigated. Under a high injection current, a new blue peak was observed in the EL spectrum, which was correlated to the creation of a new chemical species on the PFO chain. The green emission peak was also enhanced with increasing injection current because of the fluorenone defects. These results indicate that the emission spectra of the hybrid LEDs can be tuned by using different polymer concentrations and by varying the current injected into the device.
Temperature induced delocalization of charge carriers and metallic phase in Co0.6Sn0.4Fe2O4 nanoparticles
Authors: ur Rahman Atta , Rafiq M. A. , Maaz K. , Karim S. , Oh Cho Sung , Hasan M. M.
Published: October 2012

Thermally induced semiconductor to metal transition has been investigated for tin doped cobalt ferrite nanoparticles using impedance spectroscopy in a wide frequency range (100 Hz-2 MHz) from 300 K to 400 K. In addition dc measurements are carried out in temperature range from 285 K to 410 K. Temperature dependence of impedance spectroscopy and dc resistivity reveal semiconductor to metal transition around 360 K. Metallic nature of the system above 360 K has been attributed to dominancy of delocalized charge carriers Fe3+–Fe2+/Co3+–Co2+ interactions over localized charge carriers Fe3–O2−–Fe3+/Co2+–O2−–Co2+ interactions. Interesting temperature dependent electrical behavior of the grain boundaries is reported and has been discussed in term of depletion space-charge layer in the vicinity of grain boundaries.
Investigation of nonuniformity phenomenon in nanoscale SiO2 and high-k gate dielectrics
Authors: Lin Chien-Chih , Hwu Jenn-Gwo
Published: October 2012

We proposed the concept of effective uniform area ratio (Keff) to evaluate the nonuniformity phenomena of SiO2 and HfO2 gate dielectrics below 3 nm. Keff can be considered as an indication of gate oxide uniformity. It is found that Keff increases with the thickness of SiO2, whereas decreases with increasing effective oxide thickness for HfO2. The reason for the observed phenomena is given in this work. The electrical and reliability characteristics were examined to check the feasibility of our concept. The tendency of Keff values was reconfirmed by the uniformity of leakage current and constant field stress test. It is believed that this methodology is useful for the future oxide quality test.
Effect of fast neutron irradiation induced defects on the metamagnetic transition In Ce(Fe0.96Ru0.04)2
Authors: Prajapat C. L. , Dube V. , Rajarajan A. K. , Thakare S. V. , Jagadeesan K. C. , Mishra P. K. , Singh M. R. , Gupta S. K. , Ravikumar G.
Published: October 2012

Effect of fast neutron irradiation induced defects on the anti-ferromagnetic (AFM) to ferromagnetic (FM) transition in Ce(Fe0.96Ru0.04)2 is studied by magnetic measurements. We observe that at a given temperature, AFM–FM transition occurs at a lower field in irradiated specimens compared to that in pristine samples. While irradiation does not seem to affect the hysteresis of the transition, zero field susceptibility is enhanced by more than an order of magnitude. Analysis of reversible magnetization vs field data at low fields indicates superparamagnetic behavior of nano-sized FM domains, which are conjectured to nucleate on the crystal defects produced by the fast neutron irradiation. The number density and size of the nano-sized domains in the irradiated and pristine samples are estimated from the magnetization data.
Progressive transformations of silica glass upon densification
Authors: Sonneville C. , Mermet A. , Champagnon B. , Martinet C. , Margueritat J. , de Ligny D. , Deschamps T. , Balima F.
Published: October 2012

The elastic and plastic behaviors of silica glasses densified at various maximum pressure reached (12 GPa, 15 GPa, 19 GPa, and 22 GPa), were analyzed using in situ Raman and Brillouin spectroscopies. The elastic anomaly was observed to progressively vanish up to a maximum pressure reached of 12 GPa, beyond which it is completely suppressed. Above the elastic anomaly the mechanical behavior of silica glass, as derived from Brillouin measurements, is interpreted in terms of pressure induced transformation of low density amorphous silica into high density amorphous silica.
Tapered and aperiodic silicon nanostructures with very low reflectance for solar hydrogen evolution
Authors: Tan Siah Hong , Soh Chew Beng , Wang Wei , Chua Soo Jin , Chi Dongzhi
Published: October 2012

We introduce a facile method to generate silicon nanostructures with superior anti-reflectance (AR) properties. These nanostructures possess the ideal tapered structure and aperiodic distribution required for low reflectance over a broad range of wavelengths. Consideration of effective medium theories might explain the behavior between structure and reflectance, and suggest the advantage of aperiodicity in affording the material broadband AR properties. We then implemented these nanostructures as photocathodes to drive the hydrogen evolution reaction in AM 1.5 illumination. These nanostructures showed a significant improvement in photoelectrochemical performance over their planar counterpart, with the best performances corresponding to nanostructures which possessed AR properties matching the solar spectrum output.
A platform to parallelize planar surfaces and control their spatial separation with nanometer resolution
Authors: Ganjeh Y. , Song B. , Pagadala K. , Kim K. , Sadat S. , Jeong W. , Kurabayashi K. , Meyhofer E. , Reddy P.
Published: October 2012

Parallelizing planar surfaces and manipulating them into close proximity with spatial separation of nanoscale dimensions is critical for probing phenomena such as near-field radiative heat transport and Casimir forces. Here, we report on a novel platform, with an integrated reflected light microscope, that is capable of parallelizing two planar surfaces such that the angular deviation is <6 μrad, while simultaneously allowing control of the gap from 15 μm down to contact with ∼0.15 nm resolution. The capabilities of this platform were verified by using two custom-fabricated micro-devices with planar surfaces, 60 × 60 μm2 each, whose flatness and surface roughness were experimentally quantified. We first parallelized the two micro-devices by using the developed platform in conjunction with a simple optical approach that relies on the shallow depth of field (∼2 μm) of a long working distance microscope objective. Subsequently, we experimentally tested the parallelism achieved via the optical alignment procedure by taking advantage of electrodes integrated into the micro-devices. Our measurements unambiguously show that the simple depth-of-field based optical approach enables parallelization such that the angular deviation between the two surfaces is within ∼500 μrad. This ensures that the separation between any two corresponding points on the parallel surfaces deviate by ∼30 nm or less from the expected value. Further, we show that improved parallelization can be achieved using the integrated micro-electrodes which enable surface roughness limited parallelization with deviations of ∼5 nm from parallelism.
Transition energies and polarizabilities of hydrogen like ions in plasma
Authors: Das Madhusmita
Published: October 2012

Effect of plasma screening on various properties like transition energy, polarizability (dipole and quadrupole), etc. of hydrogen like ions is studied. The bound and free state wave functions and transition matrix elements are obtained by numerically integrating the radial Schrodinger equation for appropriate plasma potential. We have used adaptive step size controlled Runge-Kutta method to perform the numerical integration. Debye-Huckel potential is used to investigate the variation in transition lines and polarizabilities (dipole and quadrupole) with increasing plasma screening. For a strongly coupled plasma, ion sphere potential is used to show the variation in excitation energy with decreasing ion sphere radius. It is observed that plasma screening sets in phenomena like continuum lowering and pressure ionization, which are unique to ions in plasma. Of particular interest is the blue (red) shift in transitions conserving (non-conserving) principal quantum number. The plasma environment also affects the dipole and quadrupole polarizability of ions in a significant manner. The bound state contribution to polarizabilities decreases with increase in plasma density whereas the continuum contribution is significantly enhanced. This is a result of variation in the behavior of bound and continuum state wave functions in the presence of plasma. We have compared the results with existing theoretical and experimental data wherever present.
Mechanical properties and local mobility of atactic-polystyrene films under constant-shear deformation
Authors: Hudzinskyy D. , Michels M. A. J. , Lyulin A. V.
Published: October 2012

We have performed molecular-dynamics simulations of atactic polystyrene thin films to study the effect of shear rate, pressure, and temperature on the stress-strain behaviour, the relevant energetic contributions and non-affine displacements of polymer chains during constant-shear deformation. Under this deformation sliding motion is observed at high shear rates between the top substrate and top polymer layer, which disappears when the shear rate decreases. At low shear rates stick-slip motion of the whole film with respect to the bottom substrate takes place. We found that at low shear rates the yield stress logarithmically depends on the shear rate; this behaviour can be explained in terms of the Eyring model. It was also observed that an increase in the normal pressure leads to an increase in the yield stress in agreement with experiments. The contributions to the total shear stress and energy are mainly given by the excluded-volume interactions. It corresponds to a local translational dynamics under constant shear in which particles are forced to leave their original cages much earlier as compared to the case of the isotropic, non-sheared film. Moreover, it was observed that under constant-shear deformation the polymer glass is deformed non-affinely. As a result, the middle part of the film is much more deformed than the layers close to the supporting substrates, meaning that the well-known effect of shear-banding occurs.
Determination of electron and hole lifetimes of rutile and anatase TiO2 single crystals
Authors: Yamada Yasuhiro , Kanemitsu Yoshihiko
Published: October 2012

The dynamical behavior of photoexcited states of TiO2 governs the activities of TiO2-based solar cells and photocatalysts. We determined the lifetimes of photoexcited electrons and holes in rutile and anatase TiO2 single crystals by combining advantages of time-resolved photoluminescence, photoconductance, and transient absorption spectroscopy. Electrons and holes in rutile show exponential decays with the lifetime of a few tens of nanoseconds, while non-exponential decays are observed in anatase, indicating the presence of multiple carrier trapping processes. We revealed the generic features of the carrier recombination processes in rutile and anatase TiO2.
Free minimization of the fundamental measure theory functional: Freezing of parallel hard squares and cubes
Authors: Belli S. , Dijkstra M. , van Roij R.
Published: October 2012

Due to remarkable advances in colloid synthesis techniques, systems of squares and cubes, once an academic abstraction for theorists and simulators, are nowadays an experimental reality. By means of a free minimization of the free-energy functional, we apply fundamental measure theory to analyze the phase behavior of parallel hard squares and hard cubes. We compare our results with those obtained by the traditional approach based on the Gaussian parameterization, finding small deviations and good overall agreement between the two methods. For hard squares, our predictions feature at intermediate packing fraction a smectic phase, which is however expected to be unstable due to thermal fluctuations. Due to this inconsistency, we cannot determine unambiguously the prediction of the theory for the expected fluid-to-crystal transition of parallel hard squares, but we deduce two alternative scenarios: (i) a second-order transition with a coexisting vacancy-rich crystal or (ii) a higher-density first-order transition with a coexisting crystal characterized by a lower vacancy concentration. In accordance with previous studies, a second-order transition with a high vacancy concentration is predicted for hard cubes.
Self-powered microwave devices based on graphene ink decorated with gold nanoislands
Authors: Radoi Anotonio , Dragoman M. , Cismaru Alina , Konstantinidis George , Dragoman Daniela
Published: October 2012

We demonstrate that a photovoltaic device, able to harvest light energy from UV to IR, can be implemented using a coplanar electrode configuration consisting of three electrodes deposited on high-resistivity n-Si, in which the central electrode is interdigitated with different metal electrodes, Au and Pt, respectively, and further covered with graphene ink functionalized with gold nanoislands. Also, this device can act as a wideband photodetector with good responsivity if biased. We have also identified light-induced negative differential resistance behavior with a high peak-to-valley ratio due to charging/discharging effects in the gold nanoislands.
Resistance coefficients for Stokes flow around a disk with a Navier slip condition
Authors: Sherwood J. D.
Published: October 2012

The Stokes drag and couple acting on a disk of zero thickness as it moves through Newtonian fluid are investigated for the case when slip can occur at the surface of the disk. It is shown that when the disk translates parallel to its axis, the well-known velocity field for a no-slip boundary condition exerts zero shear stress on the surface of the disk. The flow is therefore unchanged if the boundary condition on the disk is modified to a stress-free or to a Navier slip boundary condition. This invariance also holds for a disk that rotates about a diameter. However, flow around a disk that rotates about its axis, or that translates in its own plane (edgewise), is modified when the no-slip boundary condition is changed to a Navier slip condition. The fluid velocity can be expressed in terms of Hankel transforms, and the resulting dual integral equations are solved numerically. Results for the torque and drag on the disk are presented as functions of the slip length in the Navier boundary condition.
Conformational transitions in semiflexible dendrimers induced by bond orientations
Authors: Kumar Amit , Biswas Parbati
Published: October 2012

We theoretically investigate the conformational properties of semiflexible dendrimers where the semiflexibility is implemented by topologically restricting the bond directions and orientations of the respective bond vectors. Molecular size (radius of gyration, Rg and Wiener index, W), shape factor ρ, configurational free energy F, and the static structure factor, S(q) of semiflexible dendrimers are analyzed as a function of the bond orientation angle, ϕ. The size of the lower generation dendrimers decreases with increasing ϕ throughout the entire range of ϕ, ϕ ∈ (0, π). The higher generation dendrimers show a non-uniform behavior, for compressed conformations the size decreases with increasing ϕ, while for the expanded ones it increases with the increase in ϕ. A conformational transition occurs for the higher generation dendrimers from the limiting value of the hard sphere to an ideal chain with the change in ϕ. This conformational transition at ϕ = π/2 is also reflected in the configurational free energy. The configurational free energy exhibits a discontinuous behavior with the variation of ϕ, and this discontinuity occurs at ϕ = π/2. However, no such conformational transition is observed with the variation of the bond direction angle, θ, generation, G and functionality, f of the semiflexible dendrimers. The flexible dendrimer, i.e., at ϕ = π/2 is flanked between the compressed and expanded conformations of the semiflexible dendrimers resembling a hard sphere. The Kratky plot of the structure factor of all conformations quantitatively match with the results obtained from experiments and simulations in the low q-region in respect to the position of the major Kratky peak. For higher wave numbers, the Kratky plots for all conformations of semiflexible dendrimers agree with earlier theoretical results of model dendrimers [R. La Ferla, J. Chem. Phys. 106, 688 (1997)10.1063/1.473405; F. Ganazzoli, R. La Ferla, and G. Raffaini, Macromolecules 34, 4222 (2001)10.1021/ma001613z] but are in sharp contrast to the experimental [S. Rathgeber et al., J. Chem. Phys. 117, 4047 (2002)10.1063/1.1493771; S. Rathgeber, T. Pakula, and V. Urban, J. Chem. Phys. 121, 3840 (2004)10.1063/1.1768516] and simulated [M. L. Mansfield and L. I. Klushin, Macromolecules 26, 4262 (1993)10.1021/ma00068a029] scattering curves for the higher generation dendrimers. All compressed conformations (0 < ϕ < π/2) behave as compact hard spheres, while the expanded conformations (π/2 < ϕ < π) are relatively more open, partially decongesting the steric crowding among the monomers with increasing ϕ.
Note: Micro-cantilevers with AlN actuators and PtSi tips for multi-frequency atomic force microscopy
Authors: Sebastian Abu , Shamsudhin Naveen , Rothuizen Hugo , Drechsler Ute , Koelmans Wabe W. , Bhaskaran Harish , Quenzer Hans Joachim , Wagner Bernhard , Despont Michel
Published: October 2012

We report the design, fabrication, and characterization of cantilevers with integrated AlN actuators and conductive PtSi tips for multi-frequency atomic force microscopy. These cantilevers also possess a stepped-rectangular geometry. The excellent dynamic behavior of these cantilevers is investigated using both finite-element simulations and experimental methods. Several imaging experiments are presented to illustrate the efficacy and versatility of these cantilevers.
Enhanced photoanode properties of epitaxial Ti doped α-Fe2O3 (0001) thin films
Authors: Magnan H. , Stanescu D. , Rioult M. , Fonda E. , Barbier A.
Published: October 2012

The growth, crystal and electronic structures, and photo-electrochemical properties of undoped and Ti doped hematite epitaxial films were studied. We evidence that Ti4+ substitutes Fe3+ in the hematite lattice inducing a slight modification of the oxygen octahedron. Ti doping is shown to induce a shift of the valence band toward higher binding energy due to a movement of the Fermi level toward the conduction band. The resulting modification of electrical conductivity appears as a possible origin of the improvement of photo-electrochemical properties in the doped sample.
The adsorption-controlled growth of LuFe2O4 by molecular-beam epitaxy
Authors: Brooks Charles M. , Misra Rajiv , Mundy Julia A. , Zhang Lei A. , Holinsworth Brian S. , O'Neal Kenneth R. , Heeg Tassilo , Zander Willi , Schubert J. , Musfeldt Janice L. , Liu Zi-Kui , Muller David A. , Schiffer Peter , Schlom Darrell G.
Published: October 2012

We report the growth of single-phase (0001)-oriented epitaxial films of the purported electronically driven multiferroic, LuFe2O4, on (111) MgAl2O4, (111) MgO, and (0001) 6H-SiC substrates. Film stoichiometry was regulated using an adsorption-controlled growth process by depositing LuFe2O4 in an iron-rich environment at pressures and temperatures where excess iron desorbs from the film surface during growth. Scanning transmission electron microscopy reveals reaction-free film-substrate interfaces. The magnetization increases rapidly below 240 K, consistent with the paramagnetic-to-ferrimagnetic phase transition of bulk LuFe2O4. In addition to the ∼0.35 eV indirect band gap, optical spectroscopy reveals a 3.4 eV direct band gap at the gamma point.
Disorder induced semiconductor to metal transition and modifications of grain boundaries in nanocrystalline zinc oxide thin film
Authors: Singh Fouran , Chaudhary Babloo , Kumar Vinod , Singh R. G. , Kumar Sanjeev , Kapoor A.
Published: October 2012

This paper report on the disorder induced semiconductor to metal transition (SMT) and modifications of grain boundaries in nanocrystalline zinc oxide thin film. Disorder is induced using energetic ion irradiation. It eliminates the possibility of impurities induced transition. However, it is revealed that some critical concentration of defects is needed for inducing such kind of SMT at certain critical temperature. Above room temperature, the current-voltage characteristics in reverse bias attributes some interesting phenomenon, such as electric field induced charge transfer, charge trapping, and diffusion of defects. The transition is explained by the defects induced disorder and strain in ZnO crystallites created by high density of electronic excitations.
Reduction in interface state density of Al2O3/InGaAs metal-oxide-semiconductor interfaces by InGaAs surface nitridation
Authors: Hoshii Takuya , Lee Sunghoon , Suzuki Rena , Taoka Noriyuki , Yokoyama Masafumi , Yamada Hishashi , Hata Masahiko , Yasuda Tetsuji , Takenaka Mitsuru , Takagi Shinichi
Published: October 2012

We report the decrease in interface trap density (Dit) in Al2O3/InGaAs metal-oxide-semiconductor (MOS) capacitors by using electron cyclotron resonance plasma nitridation of the InGaAs surfaces. The impact of the nitridation process on the MOS interface properties is quantitatively examined. The plasma nitridation process is observed to form a nitrided layer at the InGaAs surface. The nitridation using microwave power (Pmicrowave) of 250 W and nitridation time (tnitridation) of 420 s can form Al2O3/InGaAs MOS interfaces with a minimum Dit value of 2.0 × 1011 cm−2 eV−1. On the other hand, the nitridation process parameters such as Pmicrowave and tnitridation are found to strongly alter Dit (both decrease and increase are observed) and capacitance equivalent thickness (CET). It is found that the nitridation with higher Pmicrowave and shorter tnitridation can reduce Dit with less CET increase. Also, it is observed that as tnitridation increases, Dit decreases first and increases later. It is revealed from XPS analyses that minimum Dit can be determined by the balance between the saturation of nitridation and the progress of oxidation. As a result, it is found that the superior MOS interface formed by the nitridation is attributable to the existence of oxide-less InGaN/InGaAs interfaces.
The intrinsic electrical breakdown strength of insulators from first principles
Authors: Sun Y. , Boggs S. A. , Ramprasad R.
Published: October 2012

A first principles quantum-mechanical method for estimating intrinsic breakdown strength of insulating materials has been implemented based on an average electron model which assumes that the breakdown occurs when the average electron energy gain from the electric field exceeds the average energy loss to phonons. The approach is based on density functional perturbation theory and on the direct integration of electronic scattering probabilities over all possible final states, with no adjustable parameters. The computed intrinsic breakdown field for several prototypical materials compares favorably with available experimental data. This model also provides physical insight into the material properties that affect breakdown.
Luminescence of free-standing versus matrix-embedded oxide-passivated silicon nanocrystals: The role of matrix-induced strain
Authors: Kůsová Kateřina , Ondič Lukáš , Klimešová Eva , Herynková Kateřina , Pelant Ivan , Daniš Stanislav , Valenta Jan , Gallart Mathieu , Ziegler Marc , Hönerlage Bernd , Gilliot Pierre
Published: October 2012

We collect a large number of experimental data from various sources to demonstrate that free-standing (FS) oxide-passivated silicon nanocrystals (SiNCs) exhibit considerably blueshifted emission, by 200 meV on average, compared to those prepared as matrix-embedded (ME) ones of the same size. This is suggested to arise from compressive strain, exerted on the nanocrystals by their matrix, which plays an important role in the light-emission process; this strain has been neglected up to now as opposed to the impact of quantum confinement or surface passivation. Our conclusion is also supported by the comparison of low-temperature behavior of photoluminescence of matrix-embedded and free-standing silicon nanocrystals.
Equilibrium magnetic states in individual hemispherical permalloy caps
Authors: Streubel Robert , Kravchuk Volodymyr P. , Sheka Denis D. , Makarov Denys , Kronast Florian , Schmidt Oliver G. , Gaididei Yuri
Published: October 2012

The magnetization distributions in individual soft magnetic permalloy caps on non-magnetic spherical particles with sizes ranging from 50 to 800 nm are investigated. We experimentally visualize the magnetic structures at the resolution limit of the x-ray magnetic circular dichroism photoelectron emission microscopy (XMCD-PEEM). By analyzing the so-called tail contrast in XMCD-PEEM, the spatial resolution is significantly enhanced, which allowed us to explore magnetic vortices and their displacement on curved surfaces. Furthermore, cap nanostructures are modeled as extruded hemispheres to determine theoretically the phase diagram of equilibrium magnetic states. The calculated phase diagram agrees well with the experimental observations.
Multi-range free-electron laser with a pair of dielectric multilayer mirrors
Authors: Sei Norihiro , Ogawa Hiroshi , Yamada Kawakatsu
Published: October 2012

We report the experimental achievement of a free-electron laser in three wavelength regions, mid-infrared, near-infrared, and visible, using a pair of dielectric multilayer mirrors in the storage ring NIJI-IV. Dielectric multilayer mirrors can have high reflectivity at wavelength regions corresponding to higher-diffraction orders of the target wavelength. A narrowing of the relative bandwidth of the dielectric multilayer mirrors was observed in the higher-diffraction orders of the target wavelength and was found to be caused by high diffraction and carbon contamination. Our experimental results will be applied to development of a multi-rang laser that have a gain in a wade wavelength region.
Development of high-performance fully depleted silicon-on-insulator based extended-gate field-effect transistor using the parasitic bipolar junction transistor effect
Authors: Park Jin-Kwon , Cho Won-Ju
Published: October 2012

Latch based extended-gate field effect transistors (EGFETs) with a high on/off current ratio were realized on the fully depleted silicon-on-insulator (SOI) substrate. A large on/off current ratio characteristic as high as 104 with a very steep subthreshold swing close to 0 mV/dec was achieved by using the latch characteristic of the SOI substrate, which means it is highly sensitive to the small surface potential variation of biomaterials. Therefore, latch based EGFET sensors are a very promising candidate to break through the poor signal to the noise ratio exposed on conventional biosensors.
Tellurium-modified silicon nanowires with a large negative temperature coefficient of resistance
Authors: Yang Li , Lin Haiyang , Wang Tao , Ye Shiyong , Shao Mingwang , Lee Shuit-Tong
Published: October 2012

The paper reported a thermosensitive material based on tellurium nanoparticle-decorated silicon nanowires with large negative temperature coefficient of resistance. In the fabrication progress, silicon nanowires were etched with HF to get hydrogen-terminated ones, which could reduce TeO32− ion to form Te-modified silicon nanowires. Such Te-modified silicon nanowires showed good temperature-dependent performance as a linear relationship between resistivity and temperature in the range from 30 to 100 °C with high negative temperature coefficient of resistance being 8.2 × 10−3 °C−1.
A reaction diffusion model of pattern formation in clustering of adatoms on silicon surfaces
Authors: Bagarti Trilochan , Roy Anupam , Kundu K. , Dev B. N.
Published: October 2012

We study a reaction diffusion model which describes the formation of patterns on surfaces having defects. Through this model, the primary goal is to study the growth process of Ge on Si surface. We consider a two species reaction diffusion process where the reacting species are assumed to diffuse on the two dimensional surface with first order interconversion reaction occuring at various defect sites which we call reaction centers. Two models of defects, namely a ring defect and a point defect are considered separately. As reaction centers are assumed to be strongly localized in space, the proposed reaction-diffusion model is found to be exactly solvable. We use Green's function method to study the dynamics of reaction diffusion processes. Further we explore this model through Monte Carlo (MC) simulations to study the growth processes in the presence of a large number of defects. The first passage time statistics has been studied numerically.
Obama, Romney agree on support for basic research, but little else
Authors: Kramer David
Published: October 2012

The GOP challenger would halt federal funding for technology commercialization. Both candidates have given short shrift to climate change.
Superfluid helium interferometers
Authors: Sato Yuki , Packard Richard
Published: October 2012

Emerging devices for measuring quantum phase offer a possible new window into phenomena far outside condensed-matter physics.
Alexander Friedmann and the origins of modern cosmology
Authors: Belenkiy Ari
Published: October 2012

Friedmann, who died young in 1925, deserves to be called the father of Big Bang cosmology. But his seminal contributions have been widely misrepresented and undervalued.
The birth and death of star clusters in the Milky Way
Authors: Stahler Steven W.
Published: October 2012

Simple though admittedly speculative considerations explain why most of our galaxy’s stellar nurseries are highly fragile but a few survive for a remarkably long time.