Temperature-induced molecular reorganization on Au(111) driven by oligomeric defects.

The formation of ordered molecular structures on surfaces is determined by the balance between molecule-molecule and molecule-substrate interactions. Whether the aggregation process is guided by non-covalent forces or on-surface reactions, a deeper understanding of these interactions is pivotal to formulating a priori predictions of the final structural features and the development of bottom-up fabrication protocols. Theoretical models of molecular systems corroborate the information gathered through experimental observations and help explain the thermodynamic factors that underpin on-surface phase transitions.

Compact high-sensitivity potentiometer for detection of low ion concentrations in liquids.

The compact potentiometer, based on an electronic circuit protected from electrostatic and electromagnetic interference, was developed for the measurement of low ion concentrations in liquids. The electronic circuit of the potentiometer, consisting of analogous and digital parts, enables the measurement of fA currents. This makes it possible to perform reliable measurements of ion concentrations in liquids that are as small as 10-10M.

Exploring the Antipolar Nature of Methylammonium Lead Halides: A Monte Carlo and Pyrocurrent Study.

The high power conversion efficiency of the hybrid CHNHPbX (where X = I, Br, Cl) solar cells is believed to be tightly related to the dynamics and arrangement of the methylammonium cations. In this Letter, we propose a statistical phase transition model which accurately describes the ordering of the CHNH cations and the whole phase transition sequence of the CHNHPbI perovskite. The model is based on the available structural information and involves the short-range strain-mediated and long-range dipolar interactions between the cations.

Effect of some redox mediators on FAD fluorescence of glucose oxidase from Penicillium adametzii LF F-2044.1.

Glucose oxidase (GOx) of Penicillium adametzii LF F-2044.1 recovered by ultrafiltration, was characterized by spectrophotometric and spectrofluorometric methods. It was shown that spectra of GOx from P.

Functionalization of α-synuclein fibrils.

The propensity of peptides and proteins to form self-assembled structures has very promising applications in the development of novel nanomaterials. Under certain conditions, amyloid protein α-synuclein forms well-ordered structures - fibrils, which have proven to be valuable building blocks for bionanotechnological approaches. Herein we demonstrate the functionalization of fibrils formed by a mutant α-synuclein that contains an additional cysteine residue.

Phase transition properties of the Bell-Lavis model.

Using Monte Carlo calculations we analyze the order and the universality class of phase transitions into a low-density (honeycomb) phase of a triangular antiferromagnetic three-state Bell-Lavis model. The results are obtained in a whole interval of chemical potential μ corresponding to the honeycomb phase. Our results demonstrate that the phase transitions might be attributed to the three-state Potts universality class for all μ values except for the edges of the honeycomb phase existence.

Antiferromagnetic triangular Blume-Capel model with hard-core exclusions.

Using Monte Carlo simulation, we analyze phase transitions of two antiferromagnetic (AFM) triangular Blume-Capel (BC) models with AFM interactions between third-nearest neighbors. One model has hard-core exclusions between the nearest-neighbor (1NN) particles (3NN1 model) and the other has them between the nearest-neighbor and next-nearest-neighbor particles (3NN12 model). Finite-size scaling analysis reveals that in these models, the transition from the paramagnetic to long-range order (LRO) AFM phase is either of the first order or goes through an intermediate phase which might be attributed to the Berezinskii-Kosterlitz-Thouless (BKT) type.

A model of melamine molecules ordering on metal surfaces.

The model of melamine molecules ordering into planar honeycomb and closed packed phases is proposed. To account for the "side-to-side" melamine-melamine molecular interactions, we use the version of the antiferromagnetic Blume-Capel model with some exclusions. The model is solved by Monte Carlo calculations on a triangular lattice, a slightly rescaled version of Au(111) and Ag(111) lattices on which the main experimental data are obtained.

Pulsed magnetic field measurement system based on colossal magnetoresistance-B-scalar sensors for railgun investigation.

A high pulsed magnetic field measurement system based on the use of CMR-B-scalar sensors was developed for the investigations of the electrodynamic processes in electromagnetic launchers. The system consists of four independent modules (channels) which are controlled by a personal computer. Each channel is equipped with a CMR-B-scalar sensor connected to the measurement device-B-scalar meter.

Pin-wheel hexagons: a model for anthraquinone ordering on Cu(111).

The 4-state model of anthraquinone molecules ordering in a pin-wheel large-pore honeycomb phase on Cu(111) is proposed and solved by Monte Carlo simulation. The model is defined on a rescaled triangular lattice with the lattice constant a being equal to intermolecular distance in the honeycomb phase. The pin-wheel triangle formations are obtained taking into account the elongated shape of the molecules and anisotropic interactions for main two attractive short range (double and single dimeric) H-bond interactions.

Statistical model for self-assembly of trimesic acid molecules into homologous series of flower phases.

The statistical three-state model is proposed to describe the ordering of triangular TMA molecules into flower phases. The model is solved on a rescaled triangular lattice, assuming following intermolecular interactions: exclusion of any molecules on nearest neighbor sites, triangular trio H-bonding interactions for molecules of the same orientation on next-nearest neighbor sites, and dimeric H-bonding interactions for molecules of different ("tip-to-tip") orientations on third-nearest neighbor sites. The model allows us to obtain the analytical solution for the ground state phase diagram with all homologous series of flower phases included, starting with the honeycomb phase (n=1) and ending with the superflower structure (n=∞).

Polarized photoreflectance and photoluminescence spectroscopy of InGaAs/GaAs quantum rods grown with As2 and As4 sources.

: We report photoreflectance (PR) and photoluminescence (PL) investigations of the electronic and polarization properties of different aspect ratio (height/diameter) InGaAs quantum rods (QRs) embedded in InGaAs quantum wells (QWs). These nanostructures were grown by molecular beam epitaxy using As2or As4sources. The impact of the As source on the spectral and polarization features of the QR- and QW-related interband transitions was investigated and explained in terms of the carrier confinement effects caused by variation of composition contrast between the QR material and the surrounding well.

Ordered assemblies of triangular-shaped molecules with strongly interacting vertices: phase diagrams for honeycomb and zigzag structures on triangular lattice.

The model for ordering of triangular-shaped molecules with strongly interacting vertices is proposed and solved by the Monte Carlo method. The model accounts for three main intermolecular interactions and three states (two main orientations and a vacancy state) of a molecule on triangular lattice, the situation which is encountered in self-assembly of TMA molecules characterized by strongly directional H-bonding. Distinguishing the main "tip-to-tip" interaction, we calculate the phase diagrams for the honeycomb and frustrated honeycomb structures and demonstrate how these structures shrink and vanish with gradual increase of two other ("side-to-side" and "tip-to-side") interactions.

Stabilization of saddle steady states of conservative and weakly damped dissipative dynamical systems.

An adaptive feedback method for tracking and stabilizing unknown and/or slowly varying saddle-type steady states of conservative and weakly damped dissipative dynamical systems is proposed. We demonstrate that a conservative saddle point can be stabilized with neither unstable nor stable filter technique. The proposed controller involves both filters working in parallel.

Using ergodicity of chaotic systems for improving the global properties of the delayed feedback control method.

A modified delayed feedback control algorithm with the improved global properties is proposed. The modification is based on the ergodic features of chaotic systems. We do not perturb the system until its state approaches a desired unstable periodic orbit and then we activate the delayed feedback control force.

Digital time stamping system based on open source technologies.

A digital time stamping system based on open source technologies (LINUX-UBUNTU, OpenTSA, OpenSSL, MySQL) is described in detail, including all important testing results. The system, called BALTICTIME, was developed under a project sponsored by the European Commission under the Program FP 6. It was designed to meet the requirements posed to the systems of legal and accountable time stamping and to be applicable to the hardware commonly used by the national time metrology laboratories.

Extending anticipation horizon of chaos synchronization schemes with time-delay coupling.

We analyse anticipating synchronization in chaotic systems with time-delay coupling. Two algorithms for extending the prediction horizon are considered. One of them is based on the design of a suitable coupling matrix compensating the phase lag in the time-delay feedback term of the slave system.

GaN-based two-dimensional channels: hot-electron fluctuations and dissipation.

Ultrafast electronic and phononic processes are investigated in voltage-biased GaN-based two-dimensional channels of interest for heterostructure field-effect transistors. The accumulation of non-equilibrium longitudinal optical phonons (hot phonons) is treated for AlGaN/GaN, AlGaN/AlN/GaN, AlGaN/GaN/AlN/GaN, and AlInN/AlN/GaN structures in terms of the hot-phonon temperature and hot-phonon lifetime. The hot-phonon effect on hot-electron energy relaxation and hot-phonon number relaxation is extracted from an experimental investigation of hot-electron fluctuations and power dissipation.

Coupling design for a long-term anticipating synchronization of chaos.

We propose an algorithm of coupling design for a long-term anticipating synchronization of chaos and demonstrate its efficacy for typical chaotic systems: namely, the Rössler system, the double-scroll Chua circuit, and the Lorenz system. The maximum prediction time attained with our algorithm is several times larger than with the diagonal coupling usually used in the literature.

Rectified oscillatory motion of the self-ordered front under zero-mean ac force: role of symmetry of the rate function.

The rectified oscillatory motion of the "bistable" fronts (BFs) joining two states of the different stability in a spatially extended system with two stable equilibria is studied by use of the macroscopic kinetic equation of the reaction-diffusion type. The adiabatic approximation is used: We assume that the period of the ac force acting on the front in the system significantly exceeds the characteristic relaxation time of the system. By using the arguments based on the symmetry properties of the rate function in the governing equation of the ac driven front, we show that a close corelation (one-to-one correspondence) between the rate functions of the different symmetry, the symmetrical and asymmetrical ones, and the response functions performing the "input-output" conversion between the oscillatory forcing (input) function and the speed (output) function, which describes the temporal oscillations of the moment velocity of the ac driven BF, exists.

Switching from stable to unknown unstable steady states of dynamical systems.

We demonstrate that a dynamical system can be switched from a stable steady state to a previously unknown unstable (saddle) steady state using proportional feedback coupling to an auxiliary unstable system. The simplest one-dimensional nonlinear model is treated analytically, the more complicated two-dimensional pendulum is considered numerically, while the damped Duffing-Holmes oscillator is investigated analytically, numerically, and experimentally. Experiments have been performed using a simplified version of the electronic Young-Silva circuit imitating the dynamical behavior of the Duffing-Holmes system.

Terahertz generation in nitrides due to transit-time resonance assisted by optical phonon emission.

The conditions for THz radiation generation caused by electron transit-time resonance in momentum and real spaces under optical phonon emission are analyzed for nitride-based materials and their structures. It is shown that such a mechanism provides a unique possibility to realize sub-THz and THz radiation generation at the border between the electro-optical and electronic techniques by using two alternative approaches: (i) amplification of transverse electromagnetic waves in 3D bulk materials and 2D quantum wells, and (ii) longitudinal current-field instabilities in sub-micron and micron n(+)nn(+) diodes. Estimations of frequency regions, output power and efficiency of the generation demonstrate that nitrides are promising materials for THz radiation generation.

Terahertz-frequency InN/GaN heterostructure-barrier varactor diodes.

Frequency multipliers based on the single-barrier and double-barrier InN/GaN heterostructure varactor diodes are suggested. The DC and large-signal AC vertical electron transport in the InN/GaN diodes are investigated by ensemble Monte Carlo simulations. It is found that InN/GaN heterostructure-barrier varactor diodes are able to operate as efficient frequency multipliers in the frequency range up to 1 THz.

The surface hydro-oxidation of LaNiO(3-delta) thin films.

The chemical structure and possible hydro-oxidation of LaNiO(3-delta) films were studied by means of tuneable high-energy X-ray photoelectron spectroscopy using synchrotron radiation. It was shown that the hydroxyl-containing phase, located near the film surface, may be attributed to the lanthanum and nickel hydroxide species. The thickness of a hydroxide-enriched layer was estimated from the oxide/hydroxide ratio measured at normal and grazing conditions.

The metals chemical states in hydrated vanadium oxides.

The X-ray photoelectron spectroscopy (XPS) spectra of hydrated vanadium oxides (VO)Mo(x)V(12-x).nH(2)O (x=0, 1, 2, 3) were studied to provide the vanadium ions reduction ratio (RR)=V(4+)/(V(4+)+V(5+)) dependence on the molybdenum ions concentration and thermal treatment. The vanadium valence does not depend on Mo doping (x View Article and Find Full Text PDF