Advances in Condensed Matter Physics
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Open Access journal
ISSN (Print) 1687-8108 - ISSN (Online) 1687-8124
Published by Hindawi Publishing Corporation [439 journals]
- Molecular Dynamics Simulation of Aggregates in the Dodecane/span80 System
and Their Behaviour in an Electric Field
Abstract: Molecular dynamics simulation of self-assembly of surfactant span80 molecules to form reverse micelles in nonpolar liquid dodecane is carried out. Simulations are performed using a united atom model for dodecane and a hybrid model for span80 molecules. Various physical characteristics of reverse micelle are measured, and the same are compared with available experimental results. Presence of charge carriers in the form of solvated ions in the core of reverse micelles is confirmed by the simulation. Movement of reverse micelles under the effect of uniform external electric field is also discussed.
PubDate: Mon, 23 Nov 2015 09:42:29 +000
- Analysis for the Sorption Kinetics of Ag Nanoparticles on Natural
Abstract: The kinetic adsorption behavior of silver nanoparticles deposited on a natural zeolite from Oaxaca is presented. Theoretical models as Lagergren first-order, pseudo-second-order, Elovich, and intraparticle diffusion were employed and compared with experimental data obtained by atomic absorption spectrophotometry technique. Correlation factors of the order of 0.99 were observed. Analysis by transmission electron microscopy revealed that the silver nanoparticles were homogeneously distributed on the zeolite. Additionally, chemical characterization of the material was carried out through a dilution process with lithium metaborate. An average value of 9.3 in the Si/Al ratio was observed and related to the kinetic adsorption behavior of the zeolite.
PubDate: Sun, 22 Nov 2015 09:53:46 +000
- Ultrasonic Studies of Emulsion Stability in the Presence of Magnetic
Abstract: Pickering emulsions are made of solid particle-stabilized droplets suspended in an immiscible continuous liquid phase. A magnetic emulsion can be obtained using magnetic particles. Solid magnetic nanoparticles are adsorbed strongly at the oil-water interface and are able to stabilize emulsions of oil and water. In this work emulsions stabilized by magnetite nanoparticles were obtained using high-energy ultrasound waves and a cavitation mechanism and, next, their stability in time was tested by means of acoustic waves with a low energy, without affecting the structure. An acoustic study showed high stability in time of magnetic emulsions stabilized by magnetite particles. The study also showed a strong influence of an external magnetic field, which can lead to changes of the emulsion properties. It is possible to control Pickering emulsion stability with the help of an external stimulus—a magnetic field.
PubDate: Thu, 12 Nov 2015 11:09:04 +000
- Noise and Electrical Oscillations Generation during the Investigation of
the Resistive Switching in the Yttria Stabilized Zirconia Films by
Conductive Atomic Force Microscopy
Abstract: The effect of resistive switching in the yttria stabilized zirconia (YSZ) thin films on Si substrates has been studied by Conductive Atomic Force Microscopy (CAFM). The resistive switching of the YSZ films from the low conductive state to the highly conductive one has been found to be associated with the increasing of the noise with broad frequency spectrum related to the redistribution of the oxygen vacancies in YSZ. The electrical oscillations in oscillation loop connected in series to the CAFM probe, the sample, and the bias source related to the excitation of the oscillation loop by the noise in the probe-to-sample contact film have been observed. The effect discovered is promising for application in the memristor devices of new generation.
PubDate: Thu, 29 Oct 2015 12:41:16 +000
- A Process for Modelling Diffuse Scattering from Disordered Molecular
Crystals, Illustrated by Application to Monoclinic
Abstract: Diffuse scattering from a crystal contains valuable information about the two-body correlations (related to the nanoscale order) in the material. Despite years of development, the detailed analysis of single crystal diffuse scattering (SCDS) has yet to become part of the everyday toolbox of the structural scientist. Recent decades have seen the pair distribution function approach to diffuse scattering (in fact, total scattering) from powders become a relatively routine tool. However, analysing the detailed, complex, and often highly anisotropic three-dimensional distribution of SCDS remains valuable yet rare because there is no routine method for undertaking the analysis. At present, analysis requires significant investment of time to develop specialist expertise, which means that the analysis of diffuse scattering, which has much to offer, is not incorporated thorough studies of many compounds even though it has the potential to be a very useful adjunct to existing techniques. This article endeavours to outline in some detail how the diffuse scattering from a molecular crystal can be modelled relatively quickly and largely using existing software tools. It is hoped this will provide a template for other studies. To enable this, the entire simulation is included as deposited material.
PubDate: Tue, 27 Oct 2015 09:08:41 +000
- Rare Gas Adsorption to Silver-Exchanged Zeolites
Abstract: The adsorption of rare gas atoms to silver aluminosilicate has been investigated using density functional theory (DFT) with the local density approximation, generalized gradient approximation, and dispersion correction. The adsorption energies of rare gas atoms to the honeycomb lattice of silver aluminosilicate were calculated, and the results are discussed. The relationship between the electric charge density distribution and the adsorption energy is discussed. It indicates that the xenon atom has the most electrons to affect the van der Waals dispersion, so it has the highest minimum charge density, strongest polarization, most spacious spherical scope, and most favorable adsorption on silver zeolites.
PubDate: Thu, 22 Oct 2015 12:31:44 +000
- Influence of Electric Field in the Adsorption of Atomic Hydrogen on
Abstract: The influence of external electric field (EF) in the adsorption of atomic hydrogen on graphene (H/G) was studied by means of electronic structure calculations based on spin-polarized density functional theory with generalized gradient approximation (GGA). The changes in atomic hydrogen physisorption-chemisorption on graphene owed to EF (which ranged between −1.25 V/Å and 0.75 V/Å) were determined. Analysis of the electronic charge density for an H/G system explained the EF influences on the adsorption properties (analyzing changes in electronic charge density for H/G system). A decrease of more than 100% in the chemisorption barrier for an EF of −1.25 V/Å was found. The changes in the electronic charge density confirm the possibility of manipulating the physical-chemical adsorption of hydrogen on graphene by applying electric fields.
PubDate: Thu, 22 Oct 2015 08:28:20 +000
- Precipitation Behavior and Magnetic Properties of Cu-Fe-Co Alloys
Containing Nanogranular Ferromagnetic-Element Particles
Abstract: This work investigates the evolution of microstructures and magnetic properties during isothermal annealing of Cu-Fe-Co alloys, using electron microscopy and superconducting quantum interference device (SQUID) magnetometry. Small coherent granular precipitates composed of iron and cobalt formed in the copper matrix in the early stage of precipitation. As annealing proceeded, the precipitates lost coherency to the matrix after reaching a size of 15–20 nm and twin-like structures were consecutively introduced in the particles. The SQUID measurements revealed that the magnetic properties of the specimens correlated with the microstructural evolution. The coercive force initially increased with annealing time but decreased after reaching a peak. Lorentz Microscopy suggested that the initial large increase of magnetization was invoked by a structural transition from fcc to B2 in the precipitates.
PubDate: Tue, 20 Oct 2015 12:00:18 +000
- Superconductivity, Antiferromagnetism, and Kinetic Correlation in Strongly
Correlated Electron Systems
Abstract: We investigate the ground state of two-dimensional Hubbard model on the basis of the variational Monte Carlo method. We use wave functions that include kinetic correlation and doublon-holon correlation beyond the Gutzwiller ansatz. It is still not clear whether the Hubbard model accounts for high-temperature superconductivity. The antiferromagnetic correlation plays a key role in the study of pairing mechanism because the superconductive phase exists usually close to the antiferromagnetic phase. We investigate the stability of the antiferromagnetic state when holes are doped as a function of the Coulomb repulsion . We show that the antiferromagnetic correlation is suppressed as is increased exceeding the bandwidth. High-temperature superconductivity is possible in this region with enhanced antiferromagnetic spin fluctuation and pairing interaction.
PubDate: Tue, 13 Oct 2015 16:42:52 +000
- The Electronic Structure of Short Carbon Nanotubes: The Effects of
Abstract: This paper presents a tight binding and ab initio study of finite zig-zag nanotubes of various diameters and lengths. The vertical energy spectra of such nanotubes are presented, as well as their spin multiplicities. The calculations performed using the tight binding approach show the existence of quasi-degenerate orbitals located around the Fermi level, thus suggesting the importance of high-quality ab initio methods, capable of a correct description of the nondynamical correlation. Such approaches (Complete Active Space SCF and Multireference Perturbation Theory calculations) were used in order to get accurate ground and nearest excited-state energies, along with the corresponding spin multiplicities.
PubDate: Mon, 12 Oct 2015 07:35:37 +000
- Recent Approaches for Broadening the Spectral Bandwidth in Resonant Cavity
Abstract: Resonant cavity optoelectronic devices, such as vertical cavity surface emitting lasers (VCSELs), resonant cavity enhanced photodetectors (RCEPDs), and electroabsorption modulators (EAMs), show improved performance over their predecessors by placing the active device structure inside a resonant cavity. The effect of the optical cavity, which allows wavelength selectivity and enhancement of the optical field due to resonance, allows the devices to be made thinner and therefore faster, while simultaneously increasing the quantum efficiency at the resonant wavelengths. However, the narrow spectral bandwidth significantly reduces operating tolerances, which leads to severe problems in applications such as optical communication, imaging, and biosensing. Recently, in order to overcome such drawbacks and/or to accomplish multiple functionalities, several approaches for broadening the spectral bandwidth in resonant cavity optoelectronic devices have been extensively studied. This paper reviews the recent progress in techniques for wide spectral bandwidth that include a coupled microcavity, asymmetric tandem quantum wells, and high index contrast distributed Bragg-reflectors. This review will describe design guidelines for specific devices together with experimental considerations in practical applications.
PubDate: Wed, 07 Oct 2015 13:40:32 +000
- Electrical Switching in Thin Film Structures Based on Transition Metal
Abstract: Electrical switching, manifesting itself in the nonlinear current-voltage characteristics with S- and N-type NDR (negative differential resistance), is inherent in a variety of materials, in particular, transition metal oxides. Although this phenomenon has been known for a long time, recent suggestions to use oxide-based switching elements as neuristor synapses and relaxation-oscillation circuit components have resumed the interest in this area. In the present review, we describe the experimental facts and theoretical models, mainly on the basis of the Mott transition in vanadium dioxide as a model object, of the switching effect with special emphasis on the emerging applied potentialities for oxide electronics.
PubDate: Mon, 05 Oct 2015 09:23:13 +000
- Theoretical Approach to the Gauge Invariant Linear Response Theories for
Ultracold Fermi Gases with Pseudogap
Abstract: Recent experimental progress allows for exploring some important physical quantities of ultracold Fermi gases, such as the compressibility, spin susceptibility, viscosity, optical conductivity, and spin diffusivity. Theoretically, these quantities can be evaluated from suitable linear response theories. For BCS superfluid, it has been found that the gauge invariant linear response theories can be fully consistent with some stringent consistency constraints. When the theory is generalized to stronger than BCS regime, one may meet serious difficulties to satisfy the gauge invariance conditions. In this paper, we try to construct density and spin linear response theories which are formally gauge invariant for a Fermi gas undergoing BCS-Bose-Einstein Condensation (BEC) crossover, especially below the superfluid transition temperature . We adapt a particular -matrix approach which is close to the formalism to incorporate noncondensed pairing in the normal state. We explicitly show that the fundamental constraints imposed by the Ward identities and -limit Ward identity are indeed satisfied.
PubDate: Thu, 01 Oct 2015 13:36:24 +000
- The Correlation between the Energy Gap and the Pseudogap Temperature in
Cuprates: The YCBCZO and LSHCO Case
Abstract: The paper analyzes the influence of the hole density, the out-of-plane or in-plane disorder, and the isotopic oxygen mass on the zero temperature energy gap (2Δ(0)) (YCBCZO) and (LSHCO) superconductors. It has been found that the energy gap is visibly correlated with the value of the pseudogap temperature (). On the other hand, no correlation between 2Δ(0) and the critical temperature () has been found. The above results mean that the value of the dimensionless ratio can vary very strongly together with the chemical composition, while the parameter does not change significantly. In the paper, the analytical formula which binds the zero temperature energy gap and the pseudogap temperature has been also presented.
PubDate: Thu, 01 Oct 2015 09:42:09 +000
- On New Families of Integrals in Analytical Studies of Superconductors
within the Conformal Transformation Method
Abstract: We show that, by applying the conformal transformation method, strongly correlated superconducting systems can be discussed in terms of the Fermi liquid with a variable density of states function. Within this approach, it is possible to formulate and carry out purely analytical study based on a set of fundamental equations. After presenting the mathematical structure of the -wave superconducting gap and other quantitative characteristics of superconductors, we evaluate and discuss integrals inherent in fundamental equations describing superconducting systems. The results presented here extend the approach formulated by Abrikosov and Maki, which was restricted to the first-order expansion. A few infinite families of integrals are derived and allow us to express the fundamental equations by means of analytical formulas. They can be then exploited in order to find quantitative characteristics of superconducting systems by the method of successive approximations. We show that the results can be applied in studies of high- superconductors and other superconducting materials of the new generation.
PubDate: Thu, 01 Oct 2015 09:39:20 +000
- Momentum Distribution Functions in a One-Dimensional Extended Periodic
Abstract: We study the momentum distribution of the electrons in an extended periodic Anderson model, where the interaction, , between itinerant and localized electrons is taken into account. In the symmetric half-filled model, due to the increase of the interorbital interaction, the electrons become more and more delocalized, while the itinerancy of conduction electrons decreases. Above a certain value of the electrons become again localized together with the conduction electrons. In the less than half-filled case, we observe that causes strong correlations between the electrons in the mixed valence regime.
PubDate: Sun, 20 Sep 2015 11:10:49 +000
- Progress in the Characterization of the Surface Species in Activated
Carbons by means of INS Spectroscopy Coupled with Detailed DFT
Abstract: Activated carbons are materials with relevance in different industrial applications. Due to the inherent complexity and heterogeneity of their structures, an easy assignment of the species present on their surface has a challenging result. Only recently, with the possibility to collect well-resolved inelastic neutron spectra and to simulate by DFT methods more or less extended graphitic clusters, this task is starting to become feasible. Here we report our investigation on a steam activated carbon and we show that different vibrations in the region of out-of-plane C-H bending modes are specifically connected to hydrogen terminations belonging to extended and regular borders or to short and defective ones. Furthermore, simulations including heteroatoms such as oxygen allowed us to point out spectral regions with a contribution from carboxyl species.
PubDate: Thu, 17 Sep 2015 07:12:08 +000
- Propagation Effects in the Spin-Wave Spectrum of the Ferromagnetic Thin
Abstract: Exchange spin waves propagating in magnetic thin films exhibit some dynamic effects, that is, the effects caused solely by the wave propagation. In this paper we put our attention in four phenomena of such kind: the surface (and subsurface) localization, the collapse of the bulk band into a single energy level, the reversal of the mode order in the spin-wave spectrum, and the dynamic separation of the thin film into two subsystems. We link these effects to properties of Hamiltonian matrix elements inherited from the spatial distribution of neighboring spins with respect to the film surface. We also provide necessary conditions for the occurrence of these effects.
PubDate: Tue, 15 Sep 2015 09:54:12 +000
- Finite Conductivity Effects in Electrostatic Force Microscopy on Thin
Dielectric Films: A Theoretical Model
Abstract: A study of the electrostatic force between an Electrostatic Force Microscope tip and a dielectric thin film with finite conductivity is presented. By using the Thomas-Fermi approximation and the method of image charges, we calculate the electrostatic potential and force as a function of the thin film screening length, which is a magnitude related to the amount of free charge in the thin film and is defined as the maximum length that the electric field is able to penetrate in the sample. We show the microscope’s signal on dielectric films can change significantly in the presence of a finite conductivity even in the limit of large screening lengths. This is particularly relevant in determining the effective dielectric constant of thin films from Electrostatic Force Microscopy measurements. According to our model, for example, a small conductivity can induce an error of more than two orders of magnitude in the determination of the dielectric constant of a material. Finally, we suggest a method to discriminate between permittivity and conductivity effects by analyzing the dependence of the signal with the tip-sample distance.
PubDate: Sun, 13 Sep 2015 12:55:10 +000
- Formation, Energetics, and Electronic Properties of Graphene Monolayer and
Bilayer Doped with Heteroatoms
Abstract: Doping with heteroatoms is one of the most effective methods to tailor the electronic properties of carbon nanomaterials such as graphene and carbon nanotubes, and such nanomaterials doped with heteroatom dopants might therefore provide not only new physical and chemical properties but also novel nanoelectronics/optoelectronics device applications. The boron and nitrogen are neighboring elements to carbon in the periodic table, and they are considered to be good dopants for carbon nanomaterials. We here review the recent work of boron and nitrogen doping effects into graphene monolayer as well as bilayer on the basis of the first-principles electronic structure calculations in the framework of the density-functional theory. We show the energetics and the electronic properties of boron and nitrogen defects in graphene monolayer and bilayer. As for the nitrogen doping, we further discuss the stabilities, the growth processes, and the electronic properties associated with the plausible nitrogen defect formation in graphene which is suggested by experimental observations.
PubDate: Thu, 10 Sep 2015 13:57:16 +000
- Importance of Molecular Interactions in Colloidal Dispersions
Abstract: We review briefly the concept of colloidal dispersions, their general properties, and some of their most important applications, as well as the basic molecular interactions that give rise to their properties in equilibrium. Similarly, we revisit Brownian motion and hydrodynamic interactions associated with the concept of viscosity of colloidal dispersion. It is argued that the use of modern research tools, such as computer simulations, allows one to predict accurately some macroscopically measurable properties by solving relatively simple models of molecular interactions for a large number of particles. Lastly, as a case study, we report the prediction of rheological properties of polymer brushes using state-of-the-art, coarse-grained computer simulations, which are in excellent agreement with experiments.
PubDate: Wed, 09 Sep 2015 13:22:21 +000
- Electrochemical Characterization of Nanoporous Nickel Oxide Thin Films
Spray-Deposited onto Indium-Doped Tin Oxide for Solar Conversion Scopes
Abstract: Nonstoichiometric nickel oxide () has been deposited as thin film utilizing indium-doped tin oxide as transparent and electrically conductive substrate. Spray deposition of a suspension of nanoparticles in alcoholic medium allowed the preparation of uniform coatings. Sintering of the coatings was conducted at temperatures below 500°C for few minutes. This scalable procedure allowed the attainment of films with mesoporous morphology and reticulated structure. The electrochemical characterization showed that electrodes possess large surface area (about 1000 times larger than their geometrical area). Due to the openness of the morphology, the underlying conductive substrate can be contacted by the electrolyte and undergo redox processes within the potential range in which is electroactive. This requires careful control of the conditions of polarization in order to prevent the simultaneous occurrence of reduction/oxidation processes in both components of the multilayered electrode. The combination of the open structure with optical transparency and elevated electroactivity in organic electrolytes motivated us to analyze the potential of the spray-deposited films as semiconducting cathodes of dye-sensitized solar cells of p-type when erythrosine B was the sensitizer.
PubDate: Sun, 06 Sep 2015 06:26:19 +000
- Strain and Dimension Effects on the Threshold Voltage of Nanoscale Fully
Depleted Strained-SOI TFETs
Abstract: A novel nanoscale fully depleted strained-SOI TFET (FD-SSOI TFET) is proposed and exhaustively simulated through Atlas Device Simulator. It is found that FD-SSOI TFET has the potential of improved on-current and steep subthreshold swing. Furthermore, the effect of strain and dimension on the threshold voltage of FD-SSOI TFET is thoroughly studied by developing a model based on its physical definition. The validity of the model is tested for FD-SSOI TFET by comparison to 2D device simulations. It is shown that the proposed model can predict the trends of threshold voltage very well. This proposed model provides valuable reference to the FD-SSOI TFETs design, simulation, and fabrication.
PubDate: Thu, 03 Sep 2015 13:07:00 +000
- Rare Earth-Doped BiFeO3 Thin Films: Relationship between Structural and
Abstract: Rare Earth- (RE-) doped BiFeO3 (BFO) thin films were grown on LaAlO3 substrates by using pulsed laser deposition technique. All of BFO films doped with 10% of RE show a single phase of rhombohedral structure. The saturated magnetization in the Ho- and Sm-doped films is much larger than those reported in literature and was observed at a quite low field as of 0.2 T. As for Pr- and Nd-doped BFO films, Fe2+ amount is not dominant; thus, ferromagnetism is not favored. As the RE concentration goes up to 20%, all compounds have drastically gone through a structural transition. The RE-doped BFO films have changed from rhombohedral to either pure orthorhombic phase (for Ho, Sm), or a mixed phase of orthorhombic and tetragonal (for Pr, Nd), or pure tetragonal (for Eu). We observed magnetic properties of RE-doped BFO films have significantly changed. While 20% Ho/Sm-doped BFO films have ferromagnetism degraded in comparison with the 10% doping case, the 20% Pr/Nd-doped BFO thin films, whose structure is a mixed phase, have magnetic ordering improved due to the fact that the Fe2+ amount has become greater. It seems that one can control the magnetic properties of BFO films by using appropriate RE dopants and concentrations.
PubDate: Mon, 31 Aug 2015 11:57:14 +000
- An Infrared Spectroscopy Study of the Conformational Evolution of the
Bis(trifluoromethanesulfonyl)imide Ion in the Liquid and in the Glass
Abstract: We measure the far-infrared spectrum of N,N-Dimethyl-N-ethyl-N-benzylammonium (DEBA) bis(trifluoromethanesulfonyl)imide (TFSI) ionic liquid (IL) in the temperature range between 160 and 307 K. Differential scanning calorimetry measurements indicate that such IL undergoes a glass transition around 210 K. DFT calculations allow us to assign all the experimental absorptions to specific vibrations of the DEBA cation or of the two conformers of the TFSI anion. We find that the vibration frequencies calculated by means of the PBE0 functional are in better agreement with the experimental ones than those calculated at the B3LYP level, largely used for the attribution of vibration lines of ionic liquids. Experimentally we show that, in the liquid state, the relative concentrations of the two conformers of TFSI depend on temperature through the Boltzmann factor and the energy separation, H, is found to be 2 kJ/mol, in agreement with previous calculations and literature. However, in the glassy state, the concentrations of the cis-TFSI and trans-TFSI remain fixed, witnessing the frozen state of this phase.
PubDate: Sun, 30 Aug 2015 12:20:27 +000
- Photoproducts Formation from Salicylic Acid and Poly(allylamine
hydrochloride) in Aqueous Solution Induced by UV-B Radiation
Abstract: We report on the investigation of the influence of UV-B radiation (306 nm) on the salicylic acid mixed with poly(allylamine hydrochloride), PAH, in aqueous solution. UV-Vis spectra versus irradiation time reveal kinetics of photoproducts formation. At pH 9 and 10 are found a growth regime and another of decay of photoproducts formation. In addition, the growth does not depend on temperature, whereas the decay showed a significant dependence on this parameter suggesting a thermally activated process. These processes were well fitted with first-order exponential functions.
PubDate: Wed, 26 Aug 2015 14:21:12 +000
- Self-Organization of Polymeric Fluids in Strong Stress Fields
Abstract: Analysis of literature data and our own experimental observations have led to the conclusion that, at high deformation rates, viscoelastic liquids come to behave as rubbery materials, with strong domination by elastic deformations over flow. This can be regarded as a deformation-induced fluid-to-rubbery transition. This transition is accompanied by elastic instability, which can lead to the formation of regular structures. So, a general explanation for these effects requires the treatment of viscoelastic liquids beyond critical deformation rates as rubbery media. Behaviouristic modeling of their behaviour is based on a new concept, which considers the medium as consisting of discrete elastic elements. Such a type of modeling introduces a set of discrete rotators settled on a lattice with two modes of elastic interaction. The first of these is their transformation from spherical to ellipsoidal shapes and orientation in an external field. The second is elastic collisions between rotators. Computer calculations have demonstrated that this discrete model correctly describes the observed structural effects, eventually resulting in a “chaos-to-order” transformation. These predictions correspond to real-world experimental data obtained under different modes of deformation. We presume that the developed concept can play a central role in understanding strong nonlinear effects in the rheology of viscoelastic liquids.
PubDate: Wed, 26 Aug 2015 09:45:22 +000
- Assessment of Functionals for First-Principle Studies of the Structural
and Electronic Properties of -Bi2O3
Abstract: Fully relativistic full-potential density functional calculations with an all-electron linearized augmented plane waves plus local orbitals method were carried out to perform a comparative study on the structural and electronic properties of the cubic oxide -Bi2O3 phase, which is considered as one of the most promising materials in a variety of applications including fuel cells, sensors, and catalysts. Three different density functionals were used in our calculations, LDA, the GGA scheme in the parametrization of Perdew, Burke, and Ernzerhof (PBE96), and the hybrid scheme of Perdew-Wang B3PW91. The examined properties include lattice parameter, band structure and density of states, and charge density profiles. For this modification the three functionals reveal the characteristics of a metal and the existence of minigaps at high symmetry points of the band structure when spin-orbit coupling is taken into account. Density of states exhibits hybridization of Bi 6s and O 2p orbitals and the calculated charge density profiles exhibit the ionic character in the chemical bonding of this compound. The B3PW91 hybrid functional provided a better agreement with the experimental result for the lattice parameter, revealing the importance of Hartree-Fock exchange in this compound.
PubDate: Tue, 25 Aug 2015 12:43:32 +000
- Particle and Particle-Surfactant Mixtures at Fluid Interfaces: Assembly,
Morphology, and Rheological Description
Abstract: We report here a review of particle-laden interfaces. We discuss the importance of the particle’s wettability, accounted for by the definition of a contact angle, on the attachment of particles to the fluid interface and how the contact angle is strongly affected by several physicochemical parameters. The different mechanisms of interfacial assembly are also addressed, being the adsorption and spreading the most widely used processes leading to the well-known adsorbed and spread layers, respectively. The different steps involved in the adsorption of the particles and the particle-surfactant mixtures from bulk to the interface are also discussed. We also include here the different equations of state provided so far to explain the interfacial behavior of the nanoparticles. Finally, we discuss the mechanical properties of the interfacial particle layers via dilatational and shear rheology. We emphasize along that section the importance of the shear rheology to know the intrinsic morphology of such particulate system and to understand how the flow-field-dependent evolution of the interfacial morphology might eventually affect some properties of materials such as foams and emulsions. We dedicated the last section to explaining the importance of the particulate interfacial systems in the stabilization of foams and emulsions.
PubDate: Thu, 20 Aug 2015 12:44:13 +000
- New Topological Configurations in the Continuous Heisenberg Spin Chain:
Lower Bound for the Energy
Abstract: In order to study the spin configurations of the classical one-dimensional Heisenberg model, we map the normalized unit vector, representing the spin, on a space curve. We show that the total chirality of the configuration is a conserved quantity. If, for example, one end of the space curve is rotated by an angle of 2π relative to the other, the Frenet frame traces out a noncontractible loop in and this defines a new class of topological spin configurations for the Heisenberg model.
PubDate: Wed, 19 Aug 2015 11:30:33 +000