Showing papers in "Modern Physics Letters B in 2012"

Recent progress of multiferroic perovskite manganites

Abstract: So far tens of multiferroic materials, with various chemical compositions and crystal structures, have been discovered in the past years. Among these multiferroics, some perovskite manganites with ferroelectricity driven by magnetic orders are of particular interest. In these multiferroic perovskite manganites, the multiferroic phenomena are not only quite prominent, but the involved physical mechanisms are also very plenty and representative. In this brief review, we will introduce some recent theoretical and experimental progress on multiferroic manganites, including the fascinating microscopic physics and very recently addressed experimental findings with attractive multiferroicity.

Seismic Waveguide of Metamaterials

Abstract: We developed a new method of an earthquake-resistant design to support conventional aseismic system using acoustic metamaterials. The device is an attenuator of a seismic wave that reduces the amplitude of the wave exponentially. Constructing a cylindrical shell-type waveguide composed of many Helmholtz resonators that creates a stop-band for the seismic frequency range, we convert the seismic wave into an attenuated one without touching the building that we want to protect. It is a mechanical way to convert the seismic energy into sound and heat.

STRUCTURAL, MAGNETIC AND DIELECTRIC PROPERTIES OF Fe-DOPED BaTiO3 SOLIDS

Abstract: The structural, ferroelectric and magnetic properties of bulk perovskite Fe-doped BaTiO3 (BFTO) prepared by standard solid-state reaction have been investigated. X-ray diffraction (XRD) identifies the tetragonal structure of BFTO samples. Rietveld refinements of XRD data indicates that the doping ions led to ab-plane expansion and out-of-ab-plane shrinkage of the BFTO phases. X-ray photoelectron spectroscopy (XPS) measurements for the prepared samples reveals that Fe3+ and Fe4+ ions replaces Ti4+ ions in the crystal lattice to form single-phase BFTO solids. The results of the temperature-dependent dielectric properties and magnetic hysteresis loops for the BFTO solids show simultaneously the ferroelectric order and ferromagnetic order at room temperature. The doping of magnetic element Fe brings about ferromagnetic order for the samples, and the measured magnetic moment for each Fe atom increases from 0.70 μB to 1.55 μB in BFTO samples. The origin of ferromagnetism of the BFTO samples should be attributed to the double exchange interactions of Fe3+–O2–Fe4+ ions.

DEFORMED GAS OF p, q-BOSONS: VIRIAL EXPANSION AND VIRIAL COEFFICIENTS

Abstract: In the study of many-particle systems both the interaction of particles can be essential and such feature as their internal (composite) structure. To describe these aspects, the theory of deformed oscillators is very efficient. Viewing the particles as p, q-deformed bosons, in the corresponding p, q-Bose gas model we obtain in explicit form virial expansion along with the 2nd to 5th virial coefficients. The obtained virial coefficients depend on the deformation parameters p, q in the form symmetric under p ↔ q, and at p → 1, q → 1 turn into those known for usual bosons. Besides real parameters, we analyze the case of complex mutually conjugate p and q and find interesting implications. Also, the critical temperature is derived (for the p, q-Bose gas) and compared with the Tc of standard case of bosons condensation. Similar results are presented for the deformed Bose gas model of the Tamm–Dancoff (TD) type.

X-ray studies of biological matter in microfluidic environments

Abstract: Biological systems such as cells and cellular components are governed by processes, which take place on nanometer to micrometer length scales. X-ray scattering, diffraction and imaging techniques are extremely well suited to study these processes as the spatial resolution extends well into the relevant length scales. At the same time, the investigation of physical and chemical properties and behavior of such systems requires well-defined and controllable sample environments. One successful way to establish such environments, including specified flow fields, concentration gradients and confinement regimes is by employing microfluidic technology tailored to the particular scientific question. This brief review focuses on microfluidic techniques that have been used to investigate biological matter by X-rays. In particular, we show how the characteristics of flow on the micron scale enable new scientific approaches as compared to macroscale experiments.

Compact formulae for number of conduction channels in various types of graphene nanoribbons at various temperatures

Abstract: We present two compact analytic formulae for calculating the channel number in graphene nanoribbons (GNRs), in terms of GNRs' width and Fermi energy. Numerical data obtained from these analytic formulae fit those obtained numerically from the exact formula, with accuracies within 1%. Using appropriate fit parameters, the compact formulae are valid for zigzag, armchair-metallic, and armchair-semiconducting GNRs, at room, liquid nitrogen, and liquid helium temperatures (i.e. 300, 77 and 4.2 K)

Influences of magnetic field on macroscopic properties of water

Abstract: The influences of magnetic field on thermodynamic, mechanical and electromagnetic properties of water including the specific heat, surface tension force, soaking effect or angle of contact, refraction index and electric conductivity are studied From these investigations we know that the magnetic fields reduce the specific heat of water, increase the soaking degree and hydrophobicity of water to materials, depress its surface tension force and increase refractive index and electric conductivity of water relative to those of pure water We can predict that these changes are caused by the changes of microscopic structures and distribution of water molecules under the action of a magnetic field Therefore, our studies have important significations in science and has practical value of application of magnetized water

Pinning-force scaling and its limitation in intermediate and high temperature superconductors

Abstract: We present the scaling law of the pinning force FP in intermediate and high temperature superconductors, the factors which influence its field and temperature dependence, the limitations imposed by the enlarged anisotropy and high operating temperatures, giant creep included. The theoretical developments which incorporate the new features of these classes of superconductors, most of them based on the Anderson–Kim theory, prove to be a useful source of information relative to the nature of the pinning and the characteristic fields. The use of models based on thermal activation integrates into scaling the tail of pinning force and also substantiates the use of the irreversibility field Hirr as scale field. Finally, the data on scaling law in the two class of superconductors are presented and discussed.

Temperature dependence of electrical resistance of individual carbon nanotubes and carbon nanotubes network

Abstract: We present a model to understand the effect of temperature on the electrical resistance of individual semiconducting single wall carbon nanotubes (s-SWCNTs) of various diameters under various electric fields. The temperature dependence of the resistance of s-SWCNTs and metallic SWCNTs (m-SWCNTs) are compared. These results help us to understand the temperature dependence of the resistance of SWCNTs network. We experimentally examine the temperature dependence of the resistance of random networks of SWCNTs, prepared by dispersing CNTs in ethanol and drop-casting the solution on prefabricated metallic electrodes. Examining various samples with different electrode materials and spacings, we find that the dominant resistance in determination of the temperature dependence of resistance of the network is the resistance of individual tubes, rather than the tube–tube resistance or tube–metal contact resistance. It is also found that the tube–tube resistance depends on the electrode spacing and it is more important for larger electrode spacings. By applying high electric field to burn the all-metallic paths of the SWCNTs network, the temperature dependence of the resistance of s-SWCNTs is also examined. We also investigate the effect of acid treatment of CNTs on the temperature dependence of the resistance of SWCNTs and also multi-wall CNTs (MWCNTs) networks.

The role of particles annealing temperature on magnetorheological effect

Abstract: The spinel nanocrystalline cobalt ferrite (CoFe2O4) particles were prepared via a sol–gel method followed by the annealing process. Their structural, magnetic and magnetorheological (MR) properties depending upon the annealing temperature were investigated. The X-ray diffraction analysis revealed that the higher annealing temperature, the larger grain size of CoFe2O4 particles resulting in larger magnetic domains in particles. The saturation magnetization, determined via a vibrating sample magnetometry, increased with annealing temperature and, in contrast, the coercivity decreased. The rheological behavior of CoFe2O4 particles based MR suspensions determined under the small-strain oscillatory shear flow in magnetic field showed that higher annealing temperature reflects in larger changes of rheological properties.

High-order harmonic generation in diatomic molecules: quantum interference, nodal structures and multiple orbitals

Abstract: We present a summarizing account of a series of investigations of high-order harmonic generation (HHG) in diatomic molecules beyond the single-active electron and single-active orbital approximation. In these investigations, we include not only the highest occupied molecular orbital (HOMO), but also the lower lying orbitals and the lowest unoccupied molecular orbital (LUMO) in modified versions of the strong-field approximation. We employ perturbation theory around the HOMO, multielectron wavefunctions and initial coherent superpositions of the HOMO and LUMO. The imprints of multiple orbitals, nodal structures and two-center interference on the HHG spectra are investigated in detail, for homonuclear and heteronuclear molecules. We find that, in many situations, different molecular orbitals can be traced back to different energy regions in the spectra. Furthermore, imprints of nodal structures in heteronuclear molecules can be understood by analyzing nodal planes in isoelectronic homonuclear molecules. This opens up a wide range of possibilities for molecular imaging applications.

Mechanical flexibility of zinc oxide thin-film transistors prepared by transfer printing method

Abstract: In the present study, we demonstrate the performance of Zinc oxide thin film transistors (ZnO TFTs) array subjected to the strain under high bending test and the reliability of TFTs was confirmed for the bending fatigue test of 2000 cycles. Initially, ZnO TFTs were fabricated on Si substrate and subsequently transferred on flexible PET substrate using transfer printing process. It was observed that when the bending radius reached ≥ 11 mm then cracks start to initiate first at SiO2 bridges, acting as interconnecting layers among individual TFT. Whatever the strain is applied to the devices, it is almost equivalently adopted by the SiO2 bridges, as they are relatively weak compared to rest of the part. The initial cracking of destructed SiO2 bridge leads to the secondary cracks to the ITO electrodes upon further increment of bending radius. Numerical simulation suggested that the strain of SiO2 layer reached to fracture level of 0.55% which was concentrated at the edge of SiO2 bridge layer. It also suggests that the round shape of SiO2 bridge can be more fruitful to compensate the stress concentration and to prevent failure of device.

Single on-ramp in asymmetric simple exclusion processes

Abstract: This paper studies the single on-ramp in a totally asymmetric simple exclusion processes (TASEPs). In our model, particles can only attach irreversibly with rate q to a bulk site k + 1, which is far away from boundaries. The model is investigated under random sequential update and open boundary conditions by using Monte Carlo simulations and mean-field calculations. In the case of hopping rate p = 1, when attachment rate q is fixed and q 0.5, the system includes only four phases and the LD/LD phase vanishes.

Bright-like soliton solution in quasi-one-dimensional bec in third order by interaction radius

Abstract: Nonlinear Schrodinger equations and corresponding quantum hydrodynamic (QHD) equations are widely used in studying of ultracold boson–fermion mixtures and superconductors. In this article, we show that more exact account of interaction in Bose–Einstein condensate (BEC), in comparison with the Gross–Pitaevskii (GP) approximation, leads to the existence of a new type of solitons. We use a set of QHD equations in the third order by the interaction radius (TOIR), which corresponds to the GP equation in the first order by the interaction radius. We analytically obtain a soliton solution which is an area of increased atom concentration. The conditions for existence of the soliton are studied. It is shown what solution exists if the interaction between the particles is repulsive. Particle concentration has been achieved experimentally for the BEC is of order of 1012–1014 cm-3. In this case the solution exists if the scattering length is of the order of 1 μm, which can be reached using the Feshbach resonance. It is one of the limit case of existence of the solution. The corresponding scattering length decrease with the increasing of concentration of particles. We have shown that account of interaction up to TOIR approximation leads to new effects. The investigation of effects in the TOIR approximation gives a more detail information on interaction potentials between the atoms and can be used for a more detail investigation of the interatomic potential structure.

A photonic crystal fiber based on surface plasmon resonance temperature sensor with liquid core

Abstract: A Photonic Crystal Fiber based on Surface Plasmon Resonance (PCF-SPR) temperature sensor with liquid core is proposed in this paper. Glycerin liquid with a high refractive index is filled in the central air hole of the hollow core photonic bandgap (PBG) PCF, the transmission type of PCF will change to total internal reflection (TIR), which will significantly broaden its transmission bands. The refractive index of glycerin changes with temperature within a certain temperature range and can be detected by measuring the transmission spectra, thus the accurate ambient temperature can be obtained. Numerical results indicate that the plasmon on the surface of the gold-coated channels containing glycerin liquid can be intensively excited by the core-guided mode and the excitation of the plasmon mode is sensitive to the change of the temperature. Resolution of the PCF-SPR temperature sensor with liquid core is demonstrated to be as low as 4 × 10-6 RIU, where RIU means refractive index unit.

Directed electrochemical nanowire assembly: precise nanostructure assembly via dendritic solidification

Abstract: The electrode-nanowire-target architecture, where the target is a second electrode or, say, a biological cell, is critical to fundamental experiments and high performance devices in low dimensional charge transport and nanomaterials based bio-instrumentation. The relatively new technique of directed electrochemical nanowire assembly, which is based on the diffusion limited process of dendritic solidification, permits the single step fabrication of electrode-nanowire-target assemblies. Hence, this technique is reviewed here in order to assess its current state and to elucidate aspects where further study of the underlying solidification process would be likely to expand its capabilities and applications.

ANOMALOUS ELASTIC BEHAVIOR AND ITS CORRELATION WITH SUPERCONDUCTIVITY IN IRON-BASED SUPERCONDUCTOR Ba(Fe1-xCox)2As2

Abstract: Elastic properties of iron-based superconductor Ba(Fe1-xCox)2As2 with various Co concentrations x were reviewed. Among all elastic constants, C66 shows remarkable softening associated with the structural transition from tetragonal to orthorhombic. The amount of anomaly in C66 is 90% for the underdoped samples of x < 0.07 For the overdoped samples, the anomalies in C66 gradually disappear with the increasing of Co concentration. The elastic compliance S66 (= 1/C66) shows a quantum critical behavior, which behaves just like the magnetic susceptibility of unconventional superconductors. There exists a clear correlation between the superconducting transition temperature and the amount of anomaly in S66. It was suggested that the structural fluctuation, which is measured by S66, plays an important role in the emergence of superconductivity. The elastic anomaly of Ba(Fe1-xCox)2As2 is characterized by a strong electron–lattice coupling, which would be originated from the 3d orbitals of iron. This might be a universal phenomenon not only in iron-based superconductors but also d-electron based superconductors. The results on Ba(Fe1-xCox)2As2 would reveal relevant roles of the structural fluctuations due to the orbitals, which should be taken into account for the understanding of a whole picture of the superconductivity in iron-based superconductors and related materials.

Biophysical applications of scanning ion conductance microscopy (sicm)

Abstract: Scanning probe microscopy (SPM) techniques represent one of the most promising approaches to probe the physical and chemical properties of nanoscale materials. The growing convergence of physics and biology has demanded nanotechnology tools to understand the fundamental physics of biological systems. Despite the advantages of SPM techniques, there have been challenges with its application to characterization of biological specimens. In recent times, the development of one class of SPM technique, scanning ion conductance microscopy (SICM), has overcome these limitations and enabled noninvasive, nanoscale investigation of live cells. In this review article, we present the theory behind the SICM operating principles and data modeling. Based on this framework, we discuss recent research advances where the SICM technique has proven technically superior. SICM applications discussed herein include imaging of cell topography, monitoring of live cell dynamics, mechanical stimulation of live cells, and surface patterning. Additional findings on the combination of SICM with other SPM techniques as well as patch clamp electrophysiology are presented in the context of building integrated knowledge on the structure and function of live cells. In summary, SICM bridges physics and biology to enable a range of important biomedical applications.

Domains of solvated ions in aqueous solutions, their characteristics and impact on electric conductivity: theory and experimental evidence

Abstract: In this paper, we identify a yet unreported, quantum-electro-dynamic (QED) interactions induced, self-organization in aqueous solutions. We show that its characteristics conform to hitherto unexplained experimental findings, reported in the literature. Specifically, our analysis shows: (a) Solvated ions may organize into micrometer (μm) sized domains, wherein the plasma oscillations of identical ions are in-phase. (b) These liquid domains have a crystalline-like lattice structure. (c) For salt solutions, for concentrations C below a solute specific transition concentration Ctrans, the ions organize into the "in-phase" domains. For C larger than Ctrans, domains form wherein the plasma oscillations of the solvated ions are just coherent. Previous studies provided theoretical and experimental evidence for the "coherent" domains. However, they did not show that the "coherent" domains only exist for C > Ctrans. Typically, at room temperature and pressure, C trans is about 10-4 M or below. (d) At Ctrans, the molar electric conductivity sharply changes, i.e. for C Ctrans.

Quantum Metrology Without Quantum Entanglement

Abstract: We scrutinize the role of quantum entanglement in quantum metrology and discuss recent advances in nonlinear quantum metrology that allow improved scalings of the measurement precision with respect to the available resources. Such schemes can surpass the conventional Heisenberg limited scaling of 1/N of quantum enhanced metrology. Without investing in the preparation of entangled states, we review how systems with intrinsic nonlinearities such as Bose–Einstein condensates and light-matter interfaces can provide improved scaling in single parameter estimation.

Molecular dynamics study of the disruption of h-bonds by water molecules and its diffusion behavior in amorphous cellulose

Abstract: Hydrolysis is an important component of the aging of cellulose, and it severely affects the insulating performance of cellulosic materials. The diffusion behavior of water molecules in amorphous cellulose and their destructive effect on the hydrogen bonding structure of cellulose were investigated by molecular dynamics. The change in the hydrogen bonding structure indicates that water molecules have a considerable effect on the hydrogen bonding structure within cellulose: both intermolecular and intramolecular hydrogen bonds decreased with an increase in ingressive water molecules. Moreover, the stabilities of the cellulose molecules were disrupted when the number of intermolecular hydrogen bonds declined to a certain degree. Both the free volumes of amorphous cells and water molecule-cellulose interaction affect the diffusion of water molecules. The latter, especially the hydrogen bonding interaction between water molecules and cellulose, plays a predominant role in the diffusion behavior of water molecules in the models of which the free volume rarely varies. The diffusion coefficient of water molecules has an excellent correlation with water molecule-cellulose interaction and the average hydrogen bonds between each water molecule and cellulose; however, this relationship was not apparent between the diffusion coefficient and free volume.

SPECIFIC HEAT AND THERMODYNAMIC CRITICAL FIELD FOR CALCIUM UNDER THE PRESSURE AT 120 GPa

Abstract: In the paper, the thermodynamic parameters of the superconducting state for Calcium under the pressure at 120 GPa have been determined. The numerical analysis has been made in the framework of the Eliashberg approach. In particular, the free energy difference between the superconducting and normal state has been calculated. On the basis of the obtained results, the specific heat for the superconducting (CS) and normal (CN) state, as well as the thermodynamic critical field (HC) have been determined. It has been shown that the characteristic values of the considered thermodynamic functions do not obey the BCS universal laws: ΔC(TC)/CN(TC) = 2.48 and .

Electrical power prediction of proton exchange membrane fuel cell by using support vector regression

Abstract: Studies have shown that numerous operating parameters affecting the proton exchange membrane fuel cell (PEMFC) performance, such as fuel cell operating temperature, operating pressure, anode/cathode humidification temperatures, anode/cathode stoichiometric flow ratios. In order to improve performance of fuel cell systems, it is advantageous to have an accurate model with which one can predict fuel cell behavior at different operating conditions. In this paper, a model using support vector regression (SVR) approach combining with particle swarm optimization (PSO) algorithm for its parameter optimization was developed to modeling and predicting the electrical power of proton exchange membrane fuel cell. The accuracy and reliability of the constructed support vector regression model are validated by leave-one-out cross-validation. Prediction results show that the maximum absolute percentage error does not exceed 5%, the mean absolute percentage error (MAPE) reached 0.68% and the correlation coefficient (R2) as high as 0.998. This implies that one can estimate an available combination of controller parameters by using support vector regression model to get suitable electrical power of proton exchange membrane fuel cell system.

Frequency dependent phonon transport in two-dimensional silicon and diamond thin films

Abstract: Phonon transport in two-dimensional silicon and aluminum films is investigated. The frequency dependent solution of Boltzmann transport equation is obtained numerically to account for the acoustic and optical phonon branches. The influence of film size on equivalent equilibrium temperature distribution in silicon and aluminum films is presented. It is found that increasing film width influences phonon transport in the film; in which case, the difference between the equivalent equilibrium temperature due to silicon and diamond films becomes smaller for wider films than that of the thinner films.

Conformal geometry of escort probability and its applications

Abstract: Escort probability is a certain modification of ordinary probability and a conformally transformed structure can be introduced on the space of its distributions. In this contribution applications of escort probabilities and such a structure are focused on. We demonstrate that they naturally appear and play important roles for computationally efficient method to construct α-Voronoi partitions and analysis of related dynamical systems on the simplex.

Concentrating arbitrary four-photon less-entangled cluster state by single photons

Abstract: We present a protocol for concentrating an arbitrary four-photon entangled state into a maximally entangled state assisted with singled photons. The concentration protocol uses the linear optics and the cross-Kerr nonlinearity based on the post selection principle. Four parties called Alice, Bob, Charlie and Dan in different distant locations can obtain the cluster state from an arbitrary entangled four-photon state with a certain probability. Quantum non-demolition (QND) measurements are available in this protocol. Moreover, this scheme can be steady with a higher success possibility.

Electron spin resonance as a probe of collective modes in anisotropic exchange-coupled paramagnets

Abstract: Electron spin resonance (ESR) in exchanged-coupled paramagnets is a probe of field-dependent collective modes in a strongly coupled many-body system. We utilize a previously developed approach for the analysis of collective modes in such systems to express the experimentally determined g-factors of the ESR modes in an anisotropic magnet in terms of the microscopic (isolated spin) g-factors and the ratios of the static susceptibilities along the principal directions. Applications of the theory to the ferromagnetic insulator CrBr3 and the Kondo lattice systems YbRh2Si2, YbCo2Si2, YbIr2Si2 and CeRuPO are discussed.

INVESTIGATION OF TRANSPORT AND OPTICAL PROPERTIES OF MESOPOROUS ANATASE AND RUTILE TiO2 FILMS FOR APPLICATION IN DYE-SENSITIZED SOLAR CELLS

Abstract: The transport of electrons through TiO2 anatase and rutile thin films synthesized via sol–gel route has been investigated using electronic and optical spectroscopic studies. Mesoporosity of the films is confirmed by poroellipsometry. A smaller electron effective mass in anatase can be accounted for larger effective Bohr radius of trap electrons observed in anatase than in rutile. Further, the smaller effective mass in anatase favors high mobility. A mott transition is observed in anatase with change in temperature but not in rutile. Luminescence of self-trapped excitons is observed in anatase thin films, that implies a strong lattice relaxation.

Channel conductance of ABA stacking trilayer graphene nanoribbon field-effect transistor

Abstract: In this paper, our focus is on ABA trilayer graphene nanoribbon (TGN), in which the middle layer is horizontally shifted from the top and bottom layers. The conductance model of TGN as a FET channel is presented based on Landauer formula. Besides the good reported agreement with experimental study lending support to our model, the presented model demonstrates that minimum conductivity increases dramatically by temperature. It also draws parallels between TGN and bilayer graphene nanoribbon, in which similar thermal behavior is observed. Maxwell-Boltzmann approximation is employed to form the conductance of TGN near the neutrality point. Analytical model in degenerate regime in comparison with reported data proves that TGN-based transistor will operate in degenerate regime like what we expect in conventional semiconductors. Moreover, our model confirms that in similar condition, the conductivity of TGN is less than bilayer graphene nanoribbon as reported in some experiments.

LOCALIZATION EFFECT AND PSEUDOGAP IN PRASEODYMIUM DOPED Y1-zPrzBa2Cu3O7-δ SINGLE CRYSTALS

Abstract: In this paper, we investigate the temperature dependence of the transverse conductivity in Y1-zPrzBa2Cu3O7-δ single crystals with different praseodymium concentrations. It is determined that the increase of the praseodymium concentration in Y1-zPrzBa2Cu3O7-δ leads to the enhancement of localization effects. This in turn results to the transition from the pseudo-gap regime to the variable-range-hopping regime.