bluuebunny/crossref_metadata_2025 huggingface dataset:
Field forms of the layered electromagnetic Green's functions by TE and TM potentials
Authors: Cao Yuejian , Guzina Bojan B.
Published: September 2011

A complete set of 3D layered electromagnetic Green's functions in the spatial domain is derived by way of transverse electric and transverse magnetic potentials, featuring a “direct” formulation for the field forms of the spectral Green's functions. The improper integrals underpinning the computation of the corresponding point‐load solutions in the spatial domain are evaluated via the method of asymptotic decomposition, wherein the singular behaviors are entirely extracted and integrated analytically—so that the remaining residual components can be computed effectively and accurately via adaptive numerical quadrature over a suitable contour path. It is also found that, in the spectral domain, the decay of the (numerically‐integrated) residual field forms is commensurate with that of their potential‐form counterparts, which eliminates the perceived gap between the computation of the field forms and respective potential forms of the Green's functions in the spatial domain. The effectiveness and accuracy of the proposed methodology is evaluated via comparison with relevant examples in the literature.
Optimal multiyear management of a water supply system under uncertainty: Robust counterpart approach
Authors: Housh Mashor , Ostfeld Avi , Shamir Uri
Published: September 2011

In this paper, the robust counterpart (RC) approach (Ben‐Tal et al., 2009) is applied to optimize management of a water supply system (WSS) fed from aquifers and desalination plants. The water is conveyed through a network to meet desired consumptions, where the aquifers recharges are uncertain. The objective is to minimize the net present value cost of multiyear operation, satisfying operational and physical constraints. The RC is a min‐max guided approach, which converts the original problem into a deterministic equivalent problem, requiring only that the uncertain parameters resides within a user‐defined uncertainty set. The robust policy obtained by the RC approach is compared with polices obtained by other decision‐making approaches including stochastic approaches.
A genome‐wide RNA interference screen uncovers two p24 proteins as regulators of Wingless secretion
Authors: Port Fillip , Hausmann George , Basler Konrad
Published: September 2011

Wnt proteins are secreted, lipid‐modified glycoproteins that control animal development and adult tissue homeostasis. Secretion of Wnt proteins is at least partly regulated by a dedicated machinery. Here, we report a genome‐wide RNA interference screen for genes involved in the secretion of Wingless (Wg), a Drosophila Wnt. We identify three new genes required for Wg secretion. Of these, Emp24 and Eclair are required for proper export of Wg from the endoplasmic reticulum (ER). We propose that Emp24 and Eca act as specific cargo receptors for Wg to concentrate it in forming vesicles at sites of ER export.
The interplay between morphogens and tissue growth
Authors: Dekanty Andrés , Milán Marco
Published: September 2011

Morphogens are conserved, secreted signalling molecules that regulate the size, shape and patterning of animal tissues and organs. Recent experimental evidence has emphasized the fundamental role of tissue growth in expanding the expression domains of morphogens and their target genes, in generating morphogen gradients and in modulating the response of cells to morphogens. Moreover, the classic view of how morphogens, particularly through their concentration gradient, regulate tissue size during development has been revisited recently. In this review, we discuss how morphogens and tissue growth affect each other, and we attempt to integrate genetic and molecular evidence from vertebrate and invertebrate model systems to put forward the idea that the interaction between growth and morphogens is a general feature of highly proliferative tissues.
Critical roles of RNA helicase DDX3 and its interactions with eIF4E/PABP1 in stress granule assembly and stress response
Authors: Shih Jing-Wen , Wang Wei-Ting , Tsai Tsung-Yuan , Kuo Chu-Yun , Li Hao-Kang , Wu Lee Yan-Hwa
Published: September 2011

Upon environmental insults, SGs (stress granules) aid cell survival by serving as sites of translational silencing. RNA helicase DDX3 was reported to associate with SGs. However, its role in SG physiology remains undefined. We have demonstrated previously that DDX3 acts as an eIF4E (eukaryotic initiation factor 4E)-inhibitory protein to suppress translation. In the present study, we indentified the SG marker PABP1 [poly(A)-binding protein 1] as another direct interaction partner of DDX3. We established various stimuli as novel stressors that direct DDX3 with eIF4E and PABP1 into SGs, but not to processing bodies. Interestingly, down-regulation of DDX3 interfered with SG assembly, led to nuclear accumulation of PABP1 and reduced cell viability following stress. Conversely, supplementation with a shRNA (short hairpin RNA)-resistant DDX3 restored SG formation, the translocation of PABP1 into SGs and cell survival. Notably, the SG-inducing capacity of DDX3 is independent of its ATPase and helicase activities, but mapped to the eIF4E-binding region. Moreover, the eIF4E-binding-defective mutant DDX3 was impaired in its SG-inducing ability and protective effect on cell survival under adverse conditions. All together, the present study has characterized DDX3 as a pivotal SG-nucleating factor and illustrates co-ordinative roles for DDX3, eIF4E and PABP1 in integrating environmental stress with translational regulation.
Dissecting structure–function–stability relationships of a thermostable GH5-CBM3 cellulase from Bacillus subtilis 168
Authors: Santos Camila R. , Paiva Joice H. , Sforça Maurício L. , Neves Jorge L. , Navarro Rodrigo Z. , Cota Júnio , Akao Patrícia K. , Hoffmam Zaira B. , Meza Andréia N. , Smetana Juliana H. , Nogueira Maria L. , Polikarpov Igor , Xavier-Neto José , Squina Fábio M. , Ward Richard J. , Ruller Roberto , Zeri Ana C. , Murakami Mário T.
Published: September 2011

Cellulases participate in a number of biological events, such as plant cell wall remodelling, nematode parasitism and microbial carbon uptake. Their ability to depolymerize crystalline cellulose is of great biotechnological interest for environmentally compatible production of fuels from lignocellulosic biomass. However, industrial use of cellulases is somewhat limited by both their low catalytic efficiency and stability. In the present study, we conducted a detailed functional and structural characterization of the thermostable BsCel5A (Bacillus subtilis cellulase 5A), which consists of a GH5 (glycoside hydrolase 5) catalytic domain fused to a CBM3 (family 3 carbohydrate-binding module). NMR structural analysis revealed that the Bacillus CBM3 represents a new subfamily, which lacks the classical calcium-binding motif, and variations in NMR frequencies in the presence of cellopentaose showed the importance of polar residues in the carbohydrate interaction. Together with the catalytic domain, the CBM3 forms a large planar surface for cellulose recognition, which conducts the substrate in a proper conformation to the active site and increases enzymatic efficiency. Notably, the manganese ion was demonstrated to have a hyper-stabilizing effect on BsCel5A, and by using deletion constructs and X-ray crystallography we determined that this effect maps to a negatively charged motif located at the opposite face of the catalytic site.
PTEN interacts with metal-responsive transcription factor 1 and stimulates its transcriptional activity
Authors: Lin Meng-Chieh , Liu Ya-Chuan , Tam Ming F. , Lu Yu-Ju , Hsieh Ya-Ting , Lin Lih-Yuan
Published: September 2011

MTF-1 (metal-responsive transcription factor 1) is an essential mammalian protein for embryonic development and modulates the expression of genes involving in zinc homoeostasis and responding to oxidative stress. We report in the present paper that PTEN (phosphatase and tensin homologue deleted on chromosome 10) associates with MTF-1 in the cells. These two proteins interact via the acidic domain of MTF-1 and the phosphatase/C2 domain of PTEN. Depletion of PTEN reduced MT (metallothionein) gene expression and increased cellular sensitivity to cadmium toxicity. PTEN did not alter the nuclear translocation, protein stability or DNA-binding activity of MTF-1. Zinc increased MTF-1–PTEN interaction in a dose-dependent manner. The interaction elevated within 2 h of zinc addition and declined afterwards in the cells. The enhanced binding activity occurred mainly in the cytoplasm and reduced after translocating the MTF-1 into the nucleus. Blocking signalling through the PI3K (phosphoinositide 3-kinase) pathway did not alter the zinc-induced MT expression. Analysis of enzymatically inactive PTEN mutants demonstrated that protein but not lipid phosphatase activity of PTEN was involved in the regulation of MTF-1 activity. The same regulatory role of PTEN was also noted in the regulation of ZnT1 (zinc transporter 1), another target gene of MTF-1.
Stretching liquid bridges with moving contact lines: The role of inertia
Authors: Dodds Shawn , Carvalho Marcio , Kumar Satish
Published: September 2011

Liquid bridges with moving contact lines are found in a variety of settings such as capillary feeders and high-speed printing. Although it is often assumed that the length scale for these flows is small enough that inertial effects can be neglected, this is not the case in certain applications. To address this issue, we solve the Navier-Stokes equations with the finite element method for the stretching of a liquid drop between two surfaces for non-zero Reynolds numbers. We consider an axisymmetric liquid bridge between a moving flat plate and either a stationary flat plate or a cavity. The contact lines are allowed to slip, and we evaluate the effect of the Reynolds number and contact angles on the transfer of liquid to the moving plate. In the case of two flat plates, we find that inertia forces the interface to map onto a similarity solution in a manner that shifts the breakup point toward the more wettable surface. Inertia and wettability are thus competing effects, with inertia driving fluid toward the surface with the higher contact angle and wettability driving fluid toward the surface with the lower contact angle. When a cavity is present, contact line pinning on the cavity wall biases breakup toward the cavity as the Reynolds number is increased, leading to improved cavity emptying. As the flat plate is made more wettable, a second pinch-off point can form near that plate, leading to a satellite drop and a reduction in liquid transfer to the plate. Therefore, higher liquid transfer is not always obtained with a more wettable substrate when inertia is present, in contrast to Stokes flow. We also compare our results to those obtained using a model based on the long-wave approximation and find good qualitative agreement, with the long-wave model overpredicting the amount of liquid transferred after breakup.
MoO3 as combined hole injection layer and tapered spacer in combinatorial multicolor microcavity organic light emitting diodes
Authors: Liu Rui , Xu Chun , Biswas Rana , Shinar Joseph , Shinar Ruth
Published: September 2011

Multicolor microcavity (μC) organic light-emitting diode (OLED) arrays were fabricated simply by controlling the hole injection and spacer MoO3 layer thickness. The normal emission was tunable from ∼490 to 640 nm and can be further expanded. A compact, integrated spectrometer with two-dimensional combinatorial arrays of μC OLEDs was realized. The MoO3 yields more efficient and stable devices, revealing a new breakdown mechanism. The pixel current density reaches ∼4 A/cm2 and a maximal normal brightness ∼140 000 Cd/m2, which improves photoluminescence-based sensing and absorption measurements.
Orientational imaging in polar polymers by piezoresponse force microscopy
Authors: Sharma Pankaj , Wu Dong , Poddar Shashi , Reece Timothy J. , Ducharme Stephen , Gruverman Alexei
Published: September 2011

We report orientational imaging of the polarization distribution in nanostructured ferroelectric copolymer of polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) and collagen fibrils using vertical and lateral modes of piezoresponse force microscopy (PFM). In PVDF-TrFE, detection of azimuthal variations in the lateral PFM signal is attributed to the alignment of the molecular chains along different directions. Local switching in PVDF-TrFE is shown to proceed via 120° or 180° rotation of dipoles around the molecular chain, depending upon the strength of the applied electric field. Analysis of the vertical and lateral PFM signals in collagen reveals polar anisotropy of the electromechanical properties along the axes of the fibrils. The surface plots of the piezoelectric response are constructed for both materials based on their piezoelectric tensors and are shown to be consistent with the observed vertical and lateral PFM maps.
Nanoscale electromechanical properties of CaCu3Ti4O12 ceramics
Authors: Tararam R. , Bdikin I. K. , Panwar N. , Varela J. A. , Bueno P. R. , Kholkin A. L.
Published: September 2011

Piezoresponse Force Microscopy (PFM) is used to characterize the nanoscale electromechanical properties of centrosymmetric CaCu3Ti4O12 ceramics with giant dielectric constant. Clear PFM contrast both in vertical (out-of-plane) and lateral (in-plane) modes is observed on the ceramic surface with varying magnitude and polarization direction depending on the grain crystalline orientation. Lateral signal changes its sign upon 180° rotation of the sample thus ruling out spurious electrostatic contribution and confirming piezoelectric nature of the effect. Piezoresponse could be locally reversed by suitable electrical bias (local poling) and induced polarization was quite stable showing long-time relaxation (∼3 hrs). The electromechanical contrast in unpoled ceramics is attributed to the surface flexoelectric effect (strain gradient induced polarization) while piezoresponse hysteresis and ferroelectric-like behavior are discussed in terms of structural instabilities due to Ti off-center displacements and structural defects in this material.
Ferroelectric domain structure of PbZr0.35Ti0.65O3 single crystals by piezoresponse force microscopy
Authors: Bdikin I. K. , Pérez J. A. , Coondoo I. , Senos A. M. R. , Mantas P. Q. , Kholkin A. L.
Published: September 2011

Ti-rich PbZr1−xTixO3 (x = 0.65, PZT65) single crystals with the dimensions of 1 × 1 × 0.2 mm3 were grown by the self-flux method. Micron-sized ferroelectric domains were observed and characterized via piezoresponse force microscopy (PFM) and switching spectroscopy PFM. Both out-of-plane and in-plane components of polarization were obtained by detecting vertical and lateral vibrations of the PFM cantilever. The piezoresponse image examination revealed a clear lamellar domain structure due to apparent twinning and the formation of 90° domains. A negative self-polarization was observed in the studied crystals leading to the asymmetry of piezoresponse hysteresis loops and the polarization imprint. The polarization switching mechanism under the external electric field applied via a PFM tip was investigated. The 90° domain wall width was determined from the local PFM measurements and tentatively attributed to the oblique domain walls and chemical disorder. The time-dependent PFM imaging revealed a slow polarization relaxation process with a characteristic time of about 200 min.
Thermal variation of piezoresponse in microscopically poled poly(vinylidene fluoride-trifluoroethylene) ferroelectric copolymers approaching Curie temperature
Authors: Liu Yuanming , Xie Shuhong , Liu Xiaoyan , Kitamura Kenji , Li Jiangyu
Published: September 2011

The piezoelectric and ferroelectric properties of microscopically poled poly(vinylidene fluoride trifluoroethylene) [P(VDF-TrFE)] copolymer films have been examined at different temperatures approaching Curie point using piezoresponse force microscopy in combination with dual frequency resonance tracking technique, with the amplitude, phase, quality factor, and resonance frequency of the piezoresponse simultaneously quantitatively determined. It is observed that the piezoresponse remains relatively stable up to 110 °C, and then drops rapidly to zero. The variations of the quality factor and resonance frequency with respect to the temperature change are also observed, which is consistent with thermal induced softening in films. The switching characteristics of films have also been examined, showing a characteristic hysteresis loop up to 110 °C with small asymmetries. The work helps illustrate the thermal stability of ferroelectric polymers poled at nanoscale.
Anomalous domain inversion in LiNbO3 single crystals investigated by scanning probe microscopy
Authors: Lilienblum M. , Soergel E.
Published: September 2011

Ferroelectric domains were written in lithium niobate (LiNbO3) single crystals by applying voltage pulses to the tip of a scanning force microscope. The generated domains are subsequently imaged by piezoresponse force microscopy. As it has been previously observed not only full domains but also doughnut-shaped ones arise from tip-based domain formation. In this contribution, we present our experiments which were carried out with 10-20 μm thin LiNbO3 single crystals. We show that by choosing appropriate writing parameters, domains of predetermined shape (full or doughnut) can be reliably generated. In addition to the duration and the amplitude of the voltage pulse the moment of the retraction of the tip from the sample surface was found to be a crucial parameter for reproducible domain formation.
Manipulation of ferroelectric vortex domains in hexagonal manganites
Authors: Lilienblum M. , Soergel E. , Fiebig M.
Published: September 2011

The modification of ferroelectric vortex domain patterns in hexagonal manganites (here exemplified by YMnO3 and HoMnO3) owing to chemical treatment, thermal annealing, and local electric-field poling is investigated by piezoresponse force microscopy. Chemical treatment transfers the domain pattern into a topographical pattern by domain selective etching. Thermal annealing alters the domain pattern without any sign of temperature memory effects. Local electric fields affect the domain structure with possible signs of electric memory effects. These observations are important for future investigations of the microscopic mechanisms and macroscopic parameters defining the formation of ferroelectric domains in this unusual multiferroic.
Investigation of the nanodomain structure formation by piezoelectric force microscopy and Raman confocal microscopy in LiNbO3 and LiTaO3 crystals
Authors: Shur V. Ya. , Zelenovskiy P. S. , Nebogatikov M. S. , Alikin D. O. , Sarmanova M. F. , Ievlev A. V. , Mingaliev E. A. , Kuznetsov D. K.
Published: September 2011

Piezoelectric force microscopy (PFM) and Raman confocal microscopy have been used for studying the nanodomain structures in congruent LiNbO3 and LiTaO3 crystals. The high-resolution nanodomain images at the surface were observed via PFM. Raman confocal microscopy has been used for the visualization of the nanodomain structures in the bulk via layer-by-layer scanning at various depths. It has been shown experimentally that the nanodomain images obtained at different depths correspond to domain images at the polar surface obtained at different moments: the deeper the nanodomain, the earlier the moment. Such a correlation was applied for the reconstruction of the evolution of the domain structures with charged domain walls. The studied domain structures were obtained in highly non-equilibrium switching conditions realized in LiNbO3 and LiTaO3 via pulse laser irradiation and the electric field poling of LiNbO3, with the surface layer modified by ion implantation. The revealed main stages of the domain structure evolution allow the authors to demonstrate that all geometrically different nanodomain structures observed in LiNbO3 and LiTaO3 appeared as a result of discrete switching.
A constrained approach to multiscale stochastic simulation of chemically reacting systems
Authors: Cotter Simon L. , Zygalakis Konstantinos C. , Kevrekidis Ioannis G. , Erban Radek
Published: September 2011

Stochastic simulation of coupled chemical reactions is often computationally intensive, especially if a chemical system contains reactions occurring on different time scales. In this paper, we introduce a multiscale methodology suitable to address this problem, assuming that the evolution of the slow species in the system is well approximated by a Langevin process. It is based on the conditional stochastic simulation algorithm (CSSA) which samples from the conditional distribution of the suitably defined fast variables, given values for the slow variables. In the constrained multiscale algorithm (CMA) a single realization of the CSSA is then used for each value of the slow variable to approximate the effective drift and diffusion terms, in a similar manner to the constrained mean-force computations in other applications such as molecular dynamics. We then show how using the ensuing Fokker-Planck equation approximation, we can in turn approximate average switching times in stochastic chemical systems.
Low-temperature tunneling and rotational dynamics of the ammonium cations in (NH4)2B12H12
Authors: Verdal Nina , Udovic Terrence J. , Rush John J. , Stavila Vitalie , Wu Hui , Zhou Wei , Jenkins Timothy
Published: September 2011

Low-temperature neutron scattering spectra of diammonium dodecahydro-closo-dodecaborate [(NH4)2B12H12] reveal two NH4+ rotational tunneling peaks (e.g., 18.5 μeV and 37 μeV at 4 K), consistent with the tetrahedral symmetry and environment of the cations. The tunneling peaks persist between 4 K and 40 K. An estimate was made for the tunnel splitting of the first NH4+ librational state from a fit of the observed ground-state tunnel splitting as a function of temperature. At temperatures of 50 K–70 K, classical neutron quasi-elastic scattering appears to dominate the spectra and is attributed to NH4+ cation jump reorientation about the four C3 axes defined by the N–H bonds. A reorientational activation energy of 8.1 ± 0.6 meV (0.79 ± 0.06 kJ/mol) is determined from the behavior of the quasi-elastic linewidths in this temperature regime. This activation energy is in accord with a change in NH4+ dynamical behavior above 70 K. A low-temperature inelastic neutron scattering feature at 7.8 meV is assigned to a NH4+ librational mode. At increased temperatures, this feature drops in intensity, having shifted entirely to higher energies by 200 K, suggesting the onset of quasi-free NH4+ rotation. This is consistent with neutron-diffraction-based model refinements, which derive very large thermal ellipsoids for the ammonium-ion hydrogen atoms at room temperature in the direction of reorientation.
On the area of excursion sets of spherical Gaussian eigenfunctions
Authors: Marinucci Domenico , Wigman Igor
Published: September 2011

The high frequency behaviour for random eigenfunctions of the spherical Laplacian has been recently the object of considerable interest, also because of strong motivation arising from physics and cosmology. In this paper, we are concerned with the high frequency behaviour of excursion sets; in particular, we establish a uniform central limit theorem for the empirical measure, i.e., the proportion of spherical surface, where spherical Gaussian eigenfunctions lie below a level z. Our proofs borrow some techniques from the literature on stationary long memory processes; in particular, we expand the empirical measure into Hermite polynomials, and establish a uniform weak reduction principle, entailing that the asymptotic behaviour is asymptotically dominated by a single term in the expansion. As a result, we establish a functional central limit theorem; the limiting process is fully degenerate.
Magneto-hydrodynamically stable axisymmetric mirrors
Authors: Ryutov D. D. , Berk H. L. , Cohen B. I. , Molvik A. W. , Simonen T. C.
Published: September 2011

Making axisymmetric mirrors magnetohydrodynamically (MHD) stable opens up exciting opportunities for using mirror devices as neutron sources, fusion-fission hybrids, and pure-fusion reactors. This is also of interest from a general physics standpoint (as it seemingly contradicts well-established criteria of curvature-driven instabilities). The axial symmetry allows for much simpler and more reliable designs of mirror-based fusion facilities than the well-known quadrupole mirror configurations. In this tutorial, after a summary of classical results, several techniques for achieving MHD stabilization of the axisymmetric mirrors are considered, in particular: (1) employing the favorable field-line curvature in the end tanks; (2) using the line-tying effect; (3) controlling the radial potential distribution; (4) imposing a divertor configuration on the solenoidal magnetic field; and (5) affecting the plasma dynamics by the ponderomotive force. Some illuminative theoretical approaches for understanding axisymmetric mirror stability are described. The applicability of the various stabilization techniques to axisymmetric mirrors as neutron sources, hybrids, and pure-fusion reactors are discussed; and the constraints on the plasma parameters are formulated.
Influence of adsorbed surface layer on domain growth in the field produced by conductive tip of scanning probe microscope in lithium niobate
Authors: Shur V. Ya. , Ievlev A. V. , Nikolaeva E. V. , Shishkin E. I. , Neradovskiy M. M.
Published: September 2011

The results of investigation of the single domain growth in electric field applied by conductive tip of the scanning probe microscope in thin plates of lithium niobate (LiNbO3) crystals doped with MgO after various surface preparations and at various ambient conditions are presented. It has been shown that the sizes of the produced domain can exceed by several orders of magnitude the value of the tip curvature radius. The observed effect has been explained taking into account the existence of the conductive adsorbed surface layer in all experimental conditions. We have demonstrated that the domain growth decelerates with decreasing of the layer conductivity. The existence of the conductive adsorbed surface layers drastically changes the spatial distribution of electric field. In addition to strongly localized electric field, just in the vicinity of the tip there exists the field component remaining homogeneous over the distance exceeding the radius of any experimentally produced domain. The crucial role of the conductive properties of the adsorbed surface layers on the screening of the depolarization field has been revealed. Within proposed approach the domain growth is controlled by the current in the external circuit including the surface layer with low conductivity. The proposed model allows us to explain time and field dependences of the domain size for various types of surface treatment.
Second harmonic generation in microdomain gratings fabricated in strontium-barium niobate crystals with an atomic force microscope
Authors: Simagina L. V. , Mishina E. D. , Semin S. V. , Ilyin N. A. , Volk T. R. , Gainutdinov R. V. , Ivleva L. I.
Published: September 2011

Regular surface domain gratings were created in strontium barium niobate crystals by local poling with an AFM-tip. Piezoresponse force microscopy was utilized to subsequently image the domain patterns and to investigate their temporal and thermal stability. The gratings were examined by means of nonlinear diffraction in reflection geometry using a Ti-sapphire laser (800 nm) as pump source. The well-resolved second harmonic diffraction patterns were recorded for various angles of incidence of the fundamental wave. The origin of the observed nonlinear diffraction is discussed.
Ferroelectric and dielectric properties of Bi3.15Nd0.85Ti3O12 nanotubes
Authors: Cai Wei , Lu Xiaomei , Bo Huifeng , Kan Yi , Weng Yuyan , Zhang Liang , Wu Xiaobo , Huang Fengzhen , Eng Lukas M. , Zhu Jinsong , Yan Feng
Published: September 2011

In order to match the high-density requirement of ferroelectric memories, ferroelectric Bi3.15Nd0.85Ti3O12 nanotubes with outer diameter of about 100 nm and wall thickness of about 30 nm were synthesized using a sol-gel method. Transmission electron microscope images and Raman spectra revealed the Bi-layered perovskite structure of these nanotubes. Their dielectric constant and remnant polarization were comparable with those of thin film form. Piezoelectric hysteresis loops of individual nanotube measured by piezoresponse force microscope indicate their asymmetry, and the switched nanotubes show long term retention.
Local domain engineering in relaxor 0.77PbMg1/3Nb2/3O3-0.23PbSc1/2Nb1/2O3 single crystals
Authors: Bdikin I. K. , Grácio J. , Kiselev D. A. , Raevskaya S. I. , Raevski I. P. , Prosandeev S. A. , Kholkin A. L.
Published: September 2011

We used piezoresponse force microscopy (PFM) to study the dc bias field-induced domain structure of the (001) oriented single crystals of 0.77PbMg1/3Nb2/3O3-0.23PbSc1/2Nb1/2O3 relaxor. In the as-grown state, no polarization contrast was observed due to the average cubic symmetry of the crystal. Upon application of a dc bias applied via a PFM tip, a stable complex domain pattern, corresponding to a hedgehog-type topological defect, appeared on the surface of the crystal. The shape of these domains depended on the magnitude of the field. If the field was below a threshold, the domains possessed a cylindrical form. Above the threshold, the border between domains became close to a straight line. At high biases and large separation between the pulses, the development of the domains obeyed an avalanche-type dynamics.
Variational quantum mechanical and active database approaches to the rotational-vibrational spectroscopy of ketene, H2CCO
Authors: Fábri Csaba , Mátyus Edit , Furtenbacher Tibor , Nemes László , Mihály Béla , Zoltáni Tímea , Császár Attila G.
Published: September 2011

A variational quantum mechanical protocol is presented for the computation of rovibrational energy levels of semirigid molecules using discrete variable representation of the Eckart−Watson Hamiltonian, a complete, “exact” inclusion of the potential energy surface, and selection of a vibrational subspace. Molecular symmetry is exploited via a symmetry-adapted Lanczos algorithm. Besides symmetry labels, zeroth-order rigid-rotor and harmonic-oscillator quantum numbers are employed to characterize the computed rovibrational states. Using the computational molecular spectroscopy algorithm presented, a large number of rovibrational states, up to J = 50, of the ground electronic state of the parent isotopologue of ketene, H212C=12C=16O, were computed and characterized. Based on 12 references, altogether 3982 measured and assigned rovibrational transitions of H212C=12C=16O have been collected, from which 3194 were validated. These transitions form two spectroscopic networks (SN). The ortho and the para SNs contain 2489 and 705 validated transitions and 1251 and 471 validated energy levels, respectively. The computed energy levels are compared with energy levels obtained, up to J = 41, via an inversion protocol based on this collection of validated measured rovibrational transitions. The accurate inverted energy levels allow new assignments to be proposed. Some regularities and irregularities in the rovibrational spectrum of ketene are elucidated.
Experimental study of fundamental mechanisms in inductive heating of ferromagnetic nanoparticles suspension (Fe3O4 Iron Oxide Ferrofluid)
Authors: Li Calvin H. , Hodgins Paul , Peterson G. P.
Published: September 2011

An experimental investigation of the initial heating rate of 50 nm ferromagnetic nanoparticles (Fe3O4) suspended in water and incorporated in an agar gel was conducted to study the thermal heating effects resulting from Brownian motion and hysteresis losses. Particles were placed in an alternating current magnetic field with intensities of 28.6, 35.8, 38.9, and 43.0 kA m−1, at frequencies ranging from 161 to 284 kHz. The specific absorption rate based on the heating rate was calculated and the contributions from the Brownian motion and hysteresis losses are compared and analyzed.
Investigation on the structural and magnetic properties of sputtered TbFe2/Fe3Ga heterostructures
Authors: Ranchal R. , González-Martín V.
Published: September 2011

We have analyzed the structural and magnetic properties of as-grown and annealed [TbFe2/Fe3Ga]n heterostructures grown by sputtering. Evidence of the bcc structure in the Fe3Ga layers has been found. The diffraction peak related to this structure shifts to high angles with the annealing temperature. Also, we have observed a change in the microstructure of the Tb-Fe layers when the thickness layer is reduced in the as-grown heterostructures. Moreover, the Tb content is lower than 33% of the TbFe2 Laves phase and it depends on the layer thickness. The thermal treatments promote the increase of the Tb content, but only in the heterostructures with thick layers. The strong lattice mismatch between the Tb-Fe and Fe-Ga layers seems to prevent a complete Tb diffusion upon the annealing process. Thus, the crystallization of the TbFe2 Laves phase is inhibited in the heterostructures with thin layers, although our experimental results indicate the presence of potential magnetostrictive TbFeGa alloys.
Investigation of the deep level involved in InGaN laser degradation by deep level transient spectroscopy
Authors: Meneghini M. , de Santi C. , Trivellin N. , Orita K. , Takigawa S. , Tanaka T. , Ueda D. , Meneghesso G. , Zanoni E.
Published: September 2011

This paper reports an extensive analysis of the properties of the deep level responsible for the degradation of InGaN-based laser diodes. The analysis is based on combined optical measurements and Deep-Level Transient Spectroscopy (DLTS) investigation. Results indicate that stress induces a significant increase in threshold current of the devices, which is strongly correlated to the increase in the concentration of a deep level (DL) detected by DLTS. The DL involved in the degradation process is located 0.35–0.45 eV below the conduction band. 2D simulation indicates that degradation occurs within the quantum-well region.
Adhesion selectivity by electrostatic complementarity. I. One-dimensional stripes of charge
Authors: Bai Ying , Jin Congrui , Jagota Anand , Hui C.-Y.
Published: September 2011

Highly enhanced and selective adhesion can be achieved between surfaces patterned with charges even when each one has no net charge. In this and a companion paper [C. Jin, Y. Bai, A. Jagota, and C.-Y. Hui, J. Appl. Phys. 110, 054903 (2011)] we analyze the possibility of adhesion selectivity between two flat surfaces patterned with stripes of surface charge chosen such that each surface initially carries no net charge. A few combinations, with appropriately matching strip widths, are predicted to adhere to each other. We also find that the deformability of the materials plays a critical role in defining the range of patterns that recognize each other, i.e., their selectivity. With increasing compliance, a significant enhancement of adhesion can be achieved by deformation that allows better matching between charge patterns.
Description of the geometric and electronic structures responsible for the photoelectron spectrum of FeO4−
Authors: Tran Van Tan , Hendrickx Marc F. A.
Published: September 2011

The relative stabilities of all low-lying conformations of FeO40/− stoichiometry were investigated at the quantum mechanical BPW91, CASPT2, and RCCSD(T) levels of theory. For both the anionic and neutral clusters, the determination of the most stable structure appears to be a demanding task. The density functional theory and wave function second-order perturbation theory computational techniques place the doublet state of the tetrahedron-like O4Fe− conformation substantially lower, up to 0.81 eV, than the doublet state of η2-(O2)FeO2−. The coupled-cluster method reduces the energy difference to less than 0.01 eV. This equal stability of the ground states of O4Fe− and η2-(O2)FeO2− leads to the assignment of the experimental photoelectron spectrum of FeO4−. The lowest binding energy band (X band) is ascribed to the 2A1 → 1A1 ionization of η2-(O2)FeO2−, while the higher energy band (A band) mainly corresponds to the 2E → 1A1 transition between the O4Fe0/− conformations. For a specific conformation, CASPT2 calculates the best electron detachment energies. The highest energy peak in this band with the weakest intensity could be ascribed to the 2A2 → 3A2 transition between the η2-(O2)FeO2 conformations. The two progressions are the result of ionizations from the anti-bonding orbitals of predominant iron 3d. For a specific conformation, CASPT2 calculates the best electron detachment energies. A BPW91 Franck-Condon simulation of the observed vibrational progressions further confirms the proposed assignments
Accurate predictions of the energetics of silicon compounds using the multireference correlation consistent composite approach
Authors: Oyedepo Gbenga A. , Peterson Charles , Wilson Angela K.
Published: September 2011

Theoretical studies, using the multireference correlation consistent composite approach (MR-ccCA), have been carried out on the ground and lowest lying spin-forbidden excited states of a series of silicon-containing systems. The MR-ccCA method is the multireference equivalent of the successful single reference ccCA method that has been shown to produce chemically accurate (within ±1.0 kcal mol−1 of reliable, well-established experiment) results. The percentage contributions of the SCF configurations to complete active space self-consistent field wave functions together with the Frobenius norm of the t1 vectors and related D1 diagnostics of the coupled-cluster single double wave function with the cc-pVTZ basis set have been utilized to illustrate the multi-configurational characteristics of the compounds considered. MR-ccCA incorporates additive terms to account for relativistic effects, atomic spin-orbit coupling, scalar relativistic effects, and core-valence correlation. MR-ccCA has been utilized to predict the atomization energies, enthalpies of formation, and the lowest energy spin-forbidden transitions for SinXm (2 ≤ n + m ≥ 3 where n ≠ 0 and X = B, C, N, Al, P), silicon hydrides, and analogous compounds of carbon. The energetics of small silicon aluminides and phosphorides are predicted for the first time.
“Adiabatic-hindered-rotor” treatment of the parahydrogen-water complex
Authors: Zeng Tao , Li Hui , Le Roy Robert J. , Roy Pierre-Nicholas
Published: September 2011

Inspired by a recent successful adiabatic-hindered-rotor treatment for parahydrogen pH2 in CO2–H2 complexes [H. Li, P.-N. Roy, and R. J. Le Roy, J. Chem. Phys. 133, 104305 (2010); H. Li, R. J. Le Roy, P.-N. Roy, and A. R. W. McKellar, Phys. Rev. Lett. 105, 133401 (2010)], we apply the same approximation to the more challenging H2O–H2 system. This approximation reduces the dimension of the H2O–H2 potential from 5D to 3D and greatly enhances the computational efficiency. The global minimum of the original 5D potential is missing from the adiabatic 3D potential for reasons based on solution of the hindered-rotor Schrödinger equation of the pH2. Energies and wave functions of the discrete rovibrational levels of H2O–pH2 complexes obtained from the adiabatic 3D potential are in good agreement with the results from calculations with the full 5D potential. This comparison validates our approximation, although it is a relatively cruder treatment for pH2–H2O than it is for pH2–CO2. This adiabatic approximation makes large-scale simulations of H2O–pH2 systems possible via a pairwise additive interaction model in which pH2 is treated as a point-like particle. The poor performance of the diabatically spherical treatment of pH2 rotation excludes the possibility of approximating pH2 as a simple sphere in its interaction with H2O.
ZnO homojunction white light-emitting diodes
Authors: Baltakesmez Ali , Tekmen Süleyman , Tüzemen Sebahattin
Published: September 2011

p-Type-doped ZnO films were grown on nominally undoped n-ZnO, which is deposited on p-Si:B by electrochemical deposition. The electrical properties of individually doped ZnO:Na/Mg/Sb/Ti films were determined by means of the Hall system at the room temperature. Our results showed that doped ZnO films had high mobility ranging from 11 to 638 cm2/V s, carrier concentration ranging from 6.00 × 1016 to 3.37 ×1019 cm−3, and low resistivity ranging from 1.62 × 10−2 to 21.9 × 10−2 Ω cm. Electroluminescence measurements of obtained homojunctions exhibited three main broad luminescence bands peaking at 2.8, 2.5, and 1.98 eV, respectively. In addition to these broadbands, Fabry–Pérot oscillations were also observed.
Photovoltaic effect in a wide-area semiconductor-ferroelectric device
Authors: Katiyar R. K. , Kumar A. , Morell G. , Scott J. F. , Katiyar R. S.
Published: September 2011

Millimeter-diameter planar devices of glass/ZnO:Al/BiFeO3/La0.67Sr0.33CoO3 (LSCO) heterostructures were fabricated by pulsed laser deposition (PLD) techniques. Diode-like behavior with high short-circuit current (SSC ∼ 4 mA/cm2) and open-circuit voltage (OCV ∼ 0.22 V) was obtained under the illumination of about 1% of maximum solar energy. Impedance spectroscopy revealed that electrode/dielectric interface and grain-boundary conduction are mainly responsible for the photo-current. Electrode/dielectric interface, grain boundary impedance, and low-frequency ac conductivity change by almost three orders of magnitude under weak light. Relaxation time of the photo-carriers changes from 80 ms to 96 μs suggesting that with optimal collecting instruments, one should expect currents several orders higher.
Forces at individual pseudopod-filament adhesive contacts
Authors: Paneru Govind , Thapa Prem S. , McBride Sean P. , Moore-Nichols David , Law Bruce M. , Flanders Bret N.
Published: September 2011

On-chip cellular force sensors are fabricated from cantilever poly(3,4-ethylene dioxythiophene) filaments that visibly deflect under forces exerted at individual pseudopod-filament adhesive contacts. The shape of the deflected filaments and their ∼3 nN/μm spring constants are predicted by cantilever rod theory. Pulling forces exerted by Dictyostelium discoideum cells at these contacts are observed to reach ∼20 nN without breaking the contact.
Reentrant insulating state in ultrathin manganite films
Authors: Kim Bongju , Kwon Daeyoung , Yajima Takeaki , Bell Christopher , Hikita Yasuyuki , Kim Bog G. , Hwang Harold Y.
Published: September 2011

The transport and magnetic properties of La0.7Sr0.3MnO3 thin-films grown by pulsed laser deposition on (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7 single crystal substrates have been investigated. A systematic series with various thicknesses of La0.7Sr0.3MnO3 was used to establish a phase diagram which showed a clear difference compared to films grown on SrTiO3 substrates, highlighting the importance of film thickness, and substrate strain. At 8 unit cells, the boundary between the metallic and insulating groundstates, a second abrupt metal-insulator transition was observed at low temperatures, which could be tuned by magnetic field, and was interpreted as a signature of electronic phase separation.
On the low frequency loss peak in the dielectric spectrum of glycerol
Authors: Casalini R. , Roland C. M.
Published: September 2011

We measured dielectric spectra of glycerol at pressures exceeding 1 GPa in order to examine the slow Debye-like peak. This peak is not a relaxation process, but its frequency is consistent with an origin in dielectric discontinuities due to impurities. These heterogeneities have a non-negligible bulk modulus and are identified as volatile, relatively non-polar liquid contaminants. Although this slow peak is often found in the dielectric spectra of polyalcohols, it is not an intrinsic feature thereof, unlike the ostensibly similar relaxation peak in monoalcohols.
Second-order perturbation theory with a density matrix renormalization group self-consistent field reference function: Theory and application to the study of chromium dimer
Authors: Kurashige Yuki , Yanai Takeshi
Published: September 2011

We present a second-order perturbation theory based on a density matrix renormalization group self-consistent field (DMRG-SCF) reference function. The method reproduces the solution of the complete active space with second-order perturbation theory (CASPT2) when the DMRG reference function is represented by a sufficiently large number of renormalized many-body basis, thereby being named DMRG-CASPT2 method. The DMRG-SCF is able to describe non-dynamical correlation with large active space that is insurmountable to the conventional CASSCF method, while the second-order perturbation theory provides an efficient description of dynamical correlation effects. The capability of our implementation is demonstrated for an application to the potential energy curve of the chromium dimer, which is one of the most demanding multireference systems that require best electronic structure treatment for non-dynamical and dynamical correlation as well as large basis sets. The DMRG-CASPT2/cc-pwCV5Z calculations were performed with a large (3d double-shell) active space consisting of 28 orbitals. Our approach using large-size DMRG reference addressed the problems of why the dissociation energy is largely overestimated by CASPT2 with the small active space consisting of 12 orbitals (3d4s), and also is oversensitive to the choice of the zeroth-order Hamiltonian.
Dispersion energy evaluated by using locally projected occupied and excited molecular orbitals for molecular interaction
Authors: Iwata Suehiro
Published: September 2011

The dispersion terms are evaluated with the perturbation theory based on the locally projected molecular orbitals. A series of model systems, including some of the S22 set, is examined, and the calculated binding energies are compared with the published results. The basis set dependence is also examined. The dispersion energy correction is evaluated by taking into account the double excitations only of the dispersion type electron configurations and is added to the 3rd order single excitation perturbation energy, which is a good approximation to the counterpoise (CP) corrected Hartree-Fock (HF) binding energy. The procedure is the approximate “CP corrected HF + D” method. It ensures that the evaluated binding energy is approximately free of the basis set superposition error without the CP procedure. If the augmented basis functions are used, the evaluated binding energies for the predominantly dispersion-bound systems, such as rare gas dimers and halogen bonded clusters, agree with those of the reference calculations within 1 kcal mol−1 (4 kJ mol−1). The limitation of the present method is also discussed.
Investigation for coexistence of dual resistive switching characteristics in DyMn2O5 memory devices
Authors: Tsai Yu-Ting , Chang Ting-Chang , Huang Wei-Li , Huang Chih-Wen , Syu Yong-En , Chen Shih-Cheng , Sze Simon M. , Tsai Ming-Jinn , Tseng Tseung-Yuen
Published: September 2011

Dual bipolar resistive switching characteristics were observed in the Pt/DyMn2O5/TiN memory devices. The typical switching effect could be attributed to the formation and rupture of the conducting filament in DyMn2O5 films. The parasitic switching behavior can be observed in the specific operation condition. Dual bipolar resistance switching behaviors of filament-type and interface-type can coexist in the devices by appropriate voltage operation. The operating current can be significantly decreased (100 times) by parasitic switching operation for portable electronic product application. In addition, the relationship between filament-type and interface-type switching behaviors were studied in this paper.