Table of contents

This special issue of Physica Scripta contains papers presented at the 1st International Meeting on Applied Physics (APHYS-2003), held in Badajoz (Spain), from 13th to 18th October 2003, and more specifically, selected papers presented during the conference sessions mainly on Applied Optics, Laser Physics, Ultrafast Phenomena, Optical Materials, Semiconductor Materials and Devices, Optoelectronics, Quantum Electronics and Applied Solid State Physics-Chemistry. APHYS-2003 was born as an attempt to create a new international forum on Applied Physics in Europe. Since Applied Physics is not really a branch of Physics, but the application of all the branches of Physics to the broad realms of practical problems in Science, Engineering and Industry, this conference was a truly multi and inter-disciplinary event. The organizers called for papers relating Physics with other sciences such as Biology, Chemistry, Information Science, Medicine, etc, or relating different Physics areas, and aimed at solving practical problems. In other words, the Conference was specifically interested in reports applying the techniques, the training, and the culture of Physics to research areas usually associated with other scientific and engineering disciplines. It was extremely rewarding that over 800 researchers, from over 65 countries, attended the conference, where more than 1000 research papers were presented. We feel really proud of this excellent response obtained (in number and quality), for this first edition of the conference. We are very grateful to all the members of the Organizing Committee, for the hard work done for the preparation of the Conference (which began one year before the conference start), and to the members of the International Advisory Committee, for the valuable contribution to the evaluation of submitted works. Also thank to the referees for the excellent work done in the revision of submitted papers. Finally, we would like to thank the Department of Physics of the University of Extremadura, for their support, and the Regional Government (Junta de Extremadura/Consejería de Educación, Ciencia y Tecnología), as well as INNOVA Instrumentación, for sponsoring the Conference.

X-ray fluorescence is a matter of study in fundamental research, in material analysis and in applied research, like for analytical purposes and even the fluorescence in the galactic space produced by cosmic rays. One of the most important parameters in x-ray fluorescence is the ionization cross section which presents a definite target atom to an incident projectile ion, in the case of excitation with particles. Here is presented an analytic curve to describe the ionization cross sections for a variety of target atoms (Z = 13–40) bombarded with protons (energies from a few keV to some tens of MeV). This is a sort of universal curve, for any target at any proton energy. More even, this curve serves to evaluate the ionization cross sections with other heavier ions as incident particles. That is, deuterons and alpha particles and also the so called heavy ions (typically with Z over 6). By means of a scaling law, derived from the Plane Wave Born Approximation (PWBA), the cross sections for a heavier ion can be displayed in the same curve as that for protons. For heavy ions, however, there are other physical phenomena not considered in the PWBA model. That deviates the result for heavy ions from the original curve for protons. Introducing new parameters, according to the heavy ions physics, we can get some success to fit the experimental data in a sole curve. Cross sections data from current literature are included in the construction of this fitted curve.

Data on concentrations and activity ratios of natural and anthropogenic radio-nuclides as well as concentrations of major and trace elements in red-coloured particles (Saharan dusts) collected in Monaco rain in 2001 and 2002 (5 samples from 4 events) are presented. Different distributions of particle size as well as different activities of natural radionuclides and concentrations of trace metals have been observed for two sets of samples. The ²³⁵U/²³⁸U activity ratio is around 0.04 showing virgin natural terrestrial origin of the particles. The anthropogenic radionuclides ¹³⁷Cs, ²³⁸Pu, ^239+240Pu and ²⁴¹Am are of global fallout origin and their annual atmospheric input to the ocean in the particulate form is estimated to be 28–37% for ¹³⁷Cs, 34–45% for ^239+240Pu and 36–51% for ²⁴¹Am of the total annual depositional fluxes of these radionuclides to the northwest Mediterranean.

Radiation Induced Conductivity (RIC) of proton conducting oxide ceramics (SrCe_0.95Yb_0.05O_3-δ) was studied using 1.8 MeV electrons at an ionization dose rate of 10 Gy/s. The observed RIC was enhanced by an increase of the base conductivity without radiation as the irradiation temperature was increased from 298 to 673 K, due to Radiation Induced Electrical Degradation (RIED). It was found that the degradation rate of the base conductivity was strongly dependent on irradiation temperature and fluence.

It was also found that the base conductivity at temperatures above about 433 K did not change due to electron irradiation at the total ionization dose of 2.85 MGy. The result indicates that the radiation effect by the electrons has no influence on protonic or ionic conduction.

This paper analyzes the relationship between ultraviolet erythemal radiation (UVER) measured in Badajoz (Spain) and ozone, cloudiness and aerosols. Initially, the values of transmissivity of UVER are related with three parameters (ozone amount, reflectivity and aerosol index) estimated by the satellite instrument TOMS. The relative importance and dependence of each variable is analyzed by means of a multiple regression analysis with an expression derived from the Lambert-Bouger-Beer law. The results indicate that the aerosol index is not a statistically significant factor for the initial expression. Then, a partial model with only ozone and reflectivity as regressors is proposed and coefficients are obtained using UVER measurements of year 2001. Finally the model is validated comparing its prediction for 2002 with UVER measurements at ground. The agreement between both data sets is reasonably good, suggesting that UVER estimations can be successfully derived from observations of other atmospheric variables, thus providing the basis to obtain spatial distributed maps of UV variations.

This paper aims at analysing the relationship of solar global irradiation and sunshine duration at three stations in Extremadura (Spain) at a daily and monthly basis. Studying this dependence is of great interest since it allows to estimate solar irradiation in many stations where sunshine duration is measured and then, extend the number of locations with data, in order to plot reliable solar radiation spatial distributed maps. The mentioned relationship is investigated at both daily and monthly basis, by fitting the Ångström-Prescott model by regression techniques. The correlation coefficients show notably high values for the three locations, suggesting the suitability of the model for the measured data. Moreover, the regression coefficients are in agreement with those obtained in other works for different locations in the Iberian Peninsula. In the daily analysis, it is also found that residuals show a smooth annual behaviour and, therefore, Ångström-Prescott model was fitted for each calendar month separately. The annual evolution of the regression coefficients and the atmospheric transparency index is analysed and compared for the three stations of measurements.

In order to assess the level of mass concentrations of ambient suspended particles PM10 and PM2.5, a pilot study was performed in the urban area of Belgrade, in winter and summer period from June 2002 to June 2003. The PM10 mass concentrations in Belgrade urban area were high (average value being 72 µg m^-3) in comparison to other European cities and more than 68% of daily samples exceeded the limit value of 50 µg m^-3. Average PM2.5 mass concentration was 61 µg m^-3. Analysis of the PM10 mass concentrations indicated seasonal variation. Frequency distribution of PM10 and PM2.5 mass concentrations and wind speed was best represented by log-normal distribution. Physical and chemical characterization of suspended particulate matter was accomplished by electron microscopy methods.

The results obtained utilising radiochromic films (Gafchromic MD-55 and HD-810, ISP Technologies Inc.), radiographic films (Kodak EDR2) and laboratory-made Fricke-xylenol-orange-infused gel dosimeters in form of layers have been intercompared. Dose calibration curves have been attained for all kinds of dosimeters and in-phantom measurements have been performed. From the detected in-phantom dose images, depth-dose profiles have been extracted and compared with reference values obtained with an ionisation chamber. The performance of the different dosimeters, their precision and reliability, are presented.

A sequential fractionation method for simultaneous and absolute measurement of environmental radio-nuclides, ²⁴¹Am, ²¹⁰Pb, ²²⁶Ra, ¹³⁷Cs, ⁴⁰K and ²³⁴Th/²³⁸U, by gamma-spectrometry was tested and applied to hard-water lake-sediments. The carbonate, fulvic, humic and mineral insoluble fractions were extracted from the sediments. Correction of self-absorption and geometrical effects, arising from the conditioning of bulk and fractionated sediments, were done using Monte Carlo simulations. This "non-destructive" fractionation procedure allows further analysis of other chemical species in the same fractions thus creating possibilities to study the dynamics of self-cleaning mechanism in lakes. The results demonstrate that the procedure is quantitative and suitable for the determination of environmental key radio-tracers in different fractions. Unlike other fresh-water sediments the major part of the environmental radio-nuclides is associated with "mineral" fractions. This speciation gamma-spectrometry procedure was supplemented by isotope-dilution alpha-spectrometry ²¹⁰Po (²¹⁰Pb), for determining the acid-soluble organic fractions in fresh-water lakes. The overall speciation procedure demonstrated that carbonate fractions, extracted from hard-water lake sediments, could be separated either free from, or associated with, fulvic-compounds. This speciation procedure can be applied to other aquatic deposits, however supplementary steps can be added if other data are required.

Particles of uranium oxides were produced by combustion of depleted uranium (isotopic contents: 99.8% ²³⁸U, 0.2% ²³⁵U). Solubility of uranium oxides as well as solubility of metallic uranium in water of various pH values was investigated by x-ray spectroscopy. Also, eventual absorption of dissolved uranium oxides by plants from uranium contaminated ground was investigated. A thin uranium-oxide layer was spread on the soil planted with various vegetables. After a two-month vegetation period the uranium originated radioactivity in the vegetable samples were measured by x-ray spectroscopy and compared with the measurements of samples treated likewise, but in soil without addition of uranium. Due to low radioactivity of the vegetable samples, the spectra were analyzed using Bayesian inference, too.

The work is oriented to development of an absolute distance interferometer with a narrow-linewidth tunable VCSEL laser (Vertical-Cavity Surface-Emitting Laser) at 760 nm and a wavelength-scanning interferometry technique improved by an amplitude division of interference fringe [Xiaoli D et al, Meas. Sci. Technol.9 1031 (1998); Creath K Appl. Opt.26 2810 (1987)]. This laser performs the mod-hop free tuning range up to 1.4 nm and the value of the injection current controls the wavelength. With respect to the high sensitivity of the emitted wavelength to injection current fluctuations, we provided stabilization of laser frequency by means of an electronic frequency lock to modes of the Fabry-Perot glass etalon. Instantaneous values of the interference phase before and after the scanning process are recorded for a longer interval due to data averaging. For the first laboratory experiments, we have measured preliminary results with relative uncertainty of absolute distance measurement at 8 × 10^-5 level.

Length measurements in the region of nanometers by help of laser interferometers are influenced by the nonlinearity of their scale, which is usually ten or more nanometers. We developed and experimentally verified a new method, which has the resolution and linearity of the scale in the order of hundredth part of a nanometer. This method uses an optical Fabry-Perot resonator as a measuring element and by its help it is possible to measure small lengths and to test the nonlinearity of any interferometer with an uncertainty smaller than 0.1 nm The method takes advantage of a direct conversion of the relative changes of the optical path in measuring the arm of the Michelson interferometer to relative changes of the resonant optical frequency of the Fabry-Perot resonator. Frequency changes of the resonator resonance frequency have been monitored by a beat-frequency comparison between tunable He-Ne or semiconductor ECL (Extended Cavity Laser) laser and He-Ne-I₂ optical frequency standard at 633 nm.

Laser interferometers are precise distance measurement devices with resolution in nanometer or sub-nanometer region. If interferometric measurements are carried out under atmospheric conditions (usual situation in industry), they measure the optical path length of an unknown distance instead of its true geometrical value. It is caused by an index of refraction of air that introduces a multiplicative constant to measured results. If we would like to obtain correct values of the unknown distance the knowledge of the index of refraction is necessary. In this work, we present design and the first experimental results of two methods of the direct measurement of the index of refraction, where a Fabry-Perot (FP) interferometer is used as a detection system. The first method employs an evacuable cell inserted into the mirrors of the FP interferometer and the other method consists of a differential setup of two FP interferometers, one of which is permanently evacuated.

Under inhomogeneous illumination, a refractive index grating will form in a barium titanate crystal through the photorefractive effect. Due to its large electro-optic coefficients and self-pumped phase conjugation, a photorefractive barium titanate crystal is of a special interest for many applications such as optical signal processing, optical phase conjugation and optical information storage. In general, the grating stored in a barium titanate crystal will fade in the dark soon. That is a barrier for the applications of optical information storage. Here we made a series of reduced BaTiO₃ crystals and investigated the optical absorption, the dark decay and the light-induced decay. We found that the decay time of the grating can be lengthened by the reduction treatment. The grating can be kept in the crystal reduced around compensation point for more than a month. At high intensity, the speed of writing/erasing a grating can be determined by the optical absorption.

In this work we study the properties offered by holographically recorded volume gratings when applied to image processing in imaging systems. Angular selectivity due to Bragg diffraction modifies the transfer function of the imaging system and spatial filtering operations are performed with no need of a Fourier plane. We use Kogelnik's coupled wave theory to calculate these transfer functions. We demonstrate both edge enhancement and image smoothing in amplitude objects and in phase-only objects. To obtain satisfactory processed images we analyze the influence of the different parameters of the volume grating. Both experimental and simulated results are shown with an excellent agreement. In certain applications image processing by Bragg diffraction offers an interesting alternative with respect to Fourier plane based strategies.

In this paper the importance of the second and the third diffraction orders in volume holographic gratings recorded on photopolymers is analyzed. The existence of higher harmonics in the refractive index is also evaluated using the Rigorous Coupled Wave Theory (RCW) to fit the curves and to obtain quantitative information of these higher harmonics. Two different types of gratings are analyzed, on the first hand gratings with 35 µm of thickness and 1125 lines/mm are studied and on the second gratings with 70 µm of thickness and 545 lines/mm. Finally, the results obtained for the efficiency of the first diffraction order using Kogelnik's Theory are compared with those obtained using the RCW.

We analyzed the large deflections of a uniform cantilever beam under the action of a combined load consisting of an external vertical concentrated load at the free end and a uniformly distributed load. The problem involves geometrical non-linearity and a differential equation governing the behavior of the beam is presented. The numerical solution was obtained using an algorithm based on the Runge-Kutta-Felhberg method. This algorithm was used to numerically evaluate the system, and the slopes and deflections were determined for various loads. Finally, we compared the numerical results with the experimental ones obtained in the laboratory and calculated Young's modulus for the beam material.

In this study we analyze the holographic behaviour of an acrylamide/bisacrylamide photopolymer in layers that range in thickness from 40 to 1000 µm. The photopolymer is composed of acrylamide as polymerizable monomer, N,N' methylene-bis-acrylamide as crosslinker, triethanolamine as radical generator, yellowish eosin as sensitizer and polyvinyl alcohol as binder. The composition and method of depositing the solution varies depending on the desired thickness of the final layer. For each thickness we analyze the holographic behaviour of the material during recording of unslanted diffraction gratings using a continuous argon laser (514 nm) at an intensity of 5 mW/cm². The response of the material is monitored in real time with an He-Ne laser. The results obtained for the different parameters evaluated vary considerably depends on the layer thickness. Therefore, the different potential applications of the material (fabrication of holographic optical elements, use as recording material in holographic interferometry, or manufacture of holographic memories) depends on its thickness.

Tm³⁺-doped LiNbO₃ channel waveguides have been fabricated by Zn-diffusion from the vapour phase following a two step procedure. The waveguides have a depth of around 6.5 µm in both polarizations (TM and TE), being multimode at 632.8 nm and single mode at around 2 µm. The spectroscopic properties of the active ions in the waveguides have been explored and compared with that in bulk. The results indicate that Zn-diffusion does not introduce important changes in the optical features of Tm³⁺ ions, being an adequate technique to produce optical waveguides based on this material.

An approximate method is here proposed for modelling two-dimensional sub-wavelength periodic structures. The method is based on the effective index method, where the two-dimensional problem structure is split on two one-dimensional problems, which can be solved by conventional tools. It provides in a natural way the biaxial character of a two-dimensional periodic structure with different period along different directions. The method has been tested by comparing the effective refractive index provided by more exact algorithms with the one provided by the effective index method, showing quite good agreement. Also, the EIM has been used to simulate the reflectance and transmittance behaviour of pyramidal profiles, showing also good agreement with the results supplied by exact calculations using RCWA technique. The main advantages of the method are that it is easy to implement, and the short computational time required to model a given structure.

In the development of high bit-rate capacity in telecom systems, fiber technology and/or integrated glass waveguides provide a means to implement low cost active optical devices with low insertion losses and fiber compatibility. Presently glass-based devices are limited in efficiency and it is of the utmost importance to increase the non linear optical response. In this context the present investigation compares the induced second-order optical nonlinearity generated after electro-thermal poling process in a series of borophosphate glasses of molar compositions 0.3[(0.9 - x) Ca(PO₃)₂–x Zn(PO₃)₂–0.1 CaB₄O₇]–0.3 Nb₂O₅ (x = 0–0.4). The mechanisms involved are tentatively explored.

We present theoretical and experimental investigations on a new optical feedback concept for single mode diode lasers. It is based on the optical feedback from a resonant external cavity coupled to the diode laser through the 1st order diffraction of a grating. With a single mode diode laser operating at 852 nm we demonstrate a short term line width of less than 60 kHz, an overall tuneability in excess of 36.4 nm and a continuous tuning range in excess of 45 GHz, both at constant diode temperature.

We describe a concept to realize a broadband high finesse optical cavity (white light cavity) using low-loss negative dispersive media. Two atomic systems are discussed, which allow transparency and λ-compensation, i.e. the dispersion of the medium compensates the frequency dependence of the vacuum wavelength. These atomic systems are (i) the driven two-level system and (ii) two closely spaced gain lines. We explain why the second scheme should provide better performance in terms of the realization of a white light cavity.

The melanin pigment extracted from the liver of Rana esculenta L. has been deposited as thin film on quartz substrate. The Raman spectra, as well as optical absorption and photoluminescence measurements have been investigated. The results show that the melanin can be described as a network of clusters having different size. The larger size clusters determine the absorption edge of the film and the smaller size ones are mainly involved in the radiative emission process.

With the increasing sophistication required in integrated-optical devices it has become necessary to develop accurate methods that allow for an optimization of component design. In this paper we present an overview of the theory and the experimental conditions needed to obtain optical cross sections applicable to rare-earth doped materials. The values generated by the method provide the accuracy needed in the modelling of rare earth-doped integrated devices. As a test case, we have applied the method to the ⁴I_13/2 → ⁴I_15/2 transition of Er³⁺-doped LiNbO₃ crystals and Zn diffused Er:LiNbO₃ channel waveguides developed in our laboratory. Adverse effects of concentration determination and ion-clustering are investigated.

A fire-new way to construct an optical computer is put forward in this paper. Distinguished from others, the optical computer in this study expresses information by two polarized states with orthogonal vibration directions and no-intensity of light, therefore it was named ternary optical computer. Constituting its general architecture by the good combination of electric control and optical calculation, the ternary optical computer employs optical fiber ring as register, semiconductor memory as ternary cell, and liquid crystal as modulator and adder. Meanwhile, an electronic computer group produces signals to control every part of the ternary optical computer. The superiority of this novel ternary optical computer was also introduced in this paper.

In-line holography is a simple technique for high-resolution imaging, however, due to the fact that the reference and illuminating lights are overlapped during the hologram is recorded, the real image and its twin image are in the same position, which will bring difficulties to distinguish the real one. The Yang-Gu (YG) and Gerchberg-Saxton (GS) algorithms are used to reconstruct pure real object from a single in-line hologram. The differences between the YG and GS algorithms are shown. The modified GS algorithm is also used for phase-contrast imaging and optical metrology. This method can present quantitative phase-contrast image based on only one in-line hologram. The image reconstructed from experimentally obtained data shows the good agreement with the sample.

We present a semi-analytical, approximate model of nonlinear operation of planar waveguide laser manufactured on the base of 2D photonic crystal. We consider laser structure with F-P and DFB cavities, and take into account the gain saturation effect, spatial hole burning effect, transverse as well as longitudinal field distribution. Our model, based on energy theory, allows to investigate in a relatively easy way the influence of the real structure parameters such as photonic crystal geometry, waveguide geometry, losses as well as strength of feedback (i.e. cavity parameters) on output power level. The laser characteristics obtained reveal an optimal feedback strength for given laser structure, which provide maximal power efficiency for a given pumping level.

We present an analysis of dynamic operation of planar waveguide laser in which modal confinement in lateral direction is provided by 2D photon crystal of square lattice. In our theoretical model, we take into account the gain saturation effect, transverse and longitudinal field distribution. We consider laser structures with F-P and DFB cavities. That model allows to define in an easy way the influence of real structure parameters such as photonic crystal geometry, waveguide geometry, losses as well as strength of feedback on the damping rate and the frequency of relaxation oscillations and 3 dB modulation bandwidth. With the help of this model it is possible to define optimal geometry of the laser structures having F-P and DFB cavities, which provides maximal modulation bandwidth for a given pumping level (characterized by small signal gain).

Time-to-frequency conversion (spectro-temporal imaging) constitutes a simple and direct (single-shot) technique for the high-resolution measurement of fast optical temporal waveforms. Here, we experimentally demonstrate that spectro-temporal imaging of an optical pulse can be achieved with a single time lens (quadratic phase modulator) operating under the appropriate conditions (i.e. spectral Fraunhofer conditions). As compared with the conventional solution, our proposal avoids the use of an input dispersive device preceding the time lens, thus representing a much simpler and more practical alternative for implementing spectro-temporal imaging.

Bulk-phonon mechanisms of decoherence of an exciton confined in a quantum dot (QD) are considered in order to establish time limitations for the coherent control of the exciton with relevance to its application in quantum information processing. These are the formation and decay of the excitonic polaron. The estimations of characteristic dephasing times for the InAs/GaAs QD are discussed.

We present the theory and design of a fiber compatible all-optical integrated device which, by means of the swing effect experimented by a Gaussian beam propagating in a nonlinear planar waveguide with variable core width, presents a new kind of all-optical self-routing operation. The corresponding local modal amplitude distribution in this guide provides an integrated device with an effective graded index integrated lens immersed in a nonlinear planar medium with an effective transverse dependence of the Kerr coefficient; therefore, by a suitable design of the integrated device, the power-depending swing effect of the center of a Gaussian beam envelope can be used in all-optical processing and routing where header-data separation is required.

The onset of homoclinic chaos in a damped driven pendulum by hump-doubling of an ac force which is initially formed by a periodic string of single-humped symmetric pulses is theoretically demonstrated by means of Melnikov's method. The analysis reveals that the chaotic threshold amplitude when altering solely the pulse shape presents a minimum as a single-humped pulse transforms into a double-humped pulse, the remaining parameters being held constant. Computer simulations show that the corresponding order-chaos route appears to be especially rich, including different types of crises.

Effect of spontaneous and carrier density noise on a mode-locked hybrid soliton pulse source (HSPS) utilizing linearly chirped fiber Bragg grating is investigated by using coupled mode-equations. It is found that transform-limited pulses are generated from mode-locked HSPS over a wide tuning range around the fundamental mode-locking frequency without noise and with low level of both spontaneous and carrier densiy noise sources. However, mode-locking is difficult to achieve for large value of spontaneous coupling factor, linewidth enhancement factor, gain saturation parameter and some value of rf and dc currents because of increasing noise. High noise introduces a noise peak in the relative intensity noise (RIN) spectrum making transform-limited pulses unobtainable. Hence, the proper mode-locking range where transform-limited pulses are generated reduces.

In this work we present a new idea to develop a method to separate stochastic and deterministic information contained in an electrocardiogram, ECG, which may provide new sources of information with diagnostic purposes. We assume that the ECG has information corresponding to many different processes related with the cardiac activity as well as contamination from different sources related with the measurement procedure and the nature of the observed system itself. The method starts with the application of an improved archetypal analysis to separate the mentioned stochastic and deterministic information. From the stochastic point of view we analyze Renyi entropies, and with respect to the deterministic perspective we calculate the autocorrelation function and the corresponding correlation time. We show that healthy and pathologic information may be stochastic and/or deterministic, can be identified by different measures and located in different parts of the ECG.

Photodynamic therapy (PDT) is a cancer therapy that uses nonionizing photons and a photosensitizer to treat solid tumors and surface malignancies. Experiments with cells in vitro have been useful in order to investigate cellular effects due to PDT. In this work, we study the photodynamic effect of modulated and continuous laser radiation on cancerous cells cultivated in vitro. Three experiments were performed for this study. For the first one, HeLa cells were exposed to δ-Aminolevulinic acid (ALA) at concentrations of 0, 10, 20, 40, 80 and 160 µg of ALA/ml of Dulbecco's modified Eagle's medium (DMEM) and were irradiated at total light dose of 80 J/cm² by using continuous and modulated argon laser light. In the case of modulated radiation, at 1000 Hz, we observed more cellular death (20%) than those produced by continuous light (0%) when these cells were exposed at 20 µg of ALA/ml of DMEM. For other ALA doses cellular deaths were similar in both irradiation types. The death percentage in cancerous cell, after application of PDT with continuous and modulated irradiation, was determined by means of the neutral-red spectrophotometric assay. In the second experiment HeLa cells were exposed only at 20 µg of ALA/ml of DMEM and irradiated with argon laser at total light dose of 80 J/cm² but using different light modulation frequencies: 100, 160, 600, 1250, 1500, 1850 Hz. Finally in the third experiment, where the HeLa cells were exposed in the same conditions of second experiment, the modulation frequencies used to irradiate the cell were: 10, 20, 40, 80 Hz. It was observed that light modulation frequency at 40 Hz produces maximum cellular death (36%). These results showed that modulated light used in PDT, for low ALA doses in HeLa cells, is more efficient than continuous light irradiation. Modulated irradiation in PDT could reduce the quantity of required ALA, and in consequence to reduce possible collateral damage, for application of this therapy.

The development of efficient methods for the reconstruction of sources underlying MEG measurements coming from deep brain activity is an important goal in neuroimaging research. In this communication we describe an optimization method based on a genetic algorithm (GA) of the multi-object type, to address the inverse problem, lending some weight to the proximity of the source to a given deep brain structure. The fundamental mechanism, as usual, operates on a population of individuals, each representing a current dipole or a set of dipoles (position and orientation), which is supposed to be a solution of the inverse problem and represented by binary coded strings of 51 bits for each source. The results show the efficiency of the algorithm to deal with neuromagnetic activity ascribed to deep brain regions.

We investigate a lattice of coupled logistic maps where, in addition to the usual diffusive coupling, an advection term parameterized by an asymmetry in the coupling is introduced. The advection term induces periodic behavior on a significant number of non-periodic solutions of the purely diffusive case. Our results are based on the characteristic exponents for such systems, namely the mean Lyapunov exponent and the co-moving Lyapunov exponent. In addition, we study how to deal with more complex phenomena in which the advective velocity may vary from site to site. In particular, we observe wave-like pulses to appear and disappear intermittently whenever the advection is spatially inhomogeneous.

The different kinds of behavior exhibited by the system in a laser dynamics simulation using a cellular automata model are analyzed. Three distinct types of behavior have been found: laser constant operation, laser spiking and a complex behavior showing irregular oscillations. In the last case, the power spectrum follows a power law of the type 1/f^−β with exponent close to β = 2. In the laser spiking regime, the dependence of the decay rate of the oscillations is found to be in good agreement with the predictions of the theoretical laser rate equations and the experimental phenomenology. In our model the system components evolve under local rules which reproduce the physics of the laser system at the microscopic level, and the laser properties appear as cooperative emergent phenomena associated to these rules.

We present a performance study of alpha-particle spectra fitting using parallel Genetic Algorithm (GA). The method uses a two-step approach. In the first step we run parallel GA to find an initial solution for the second step, in which we use Levenberg-Marquardt (LM) method for a precise final fit. GA is a high resources-demanding method, so we use a Beowulf cluster for parallel simulation. The relationship between simulation time (and parallel efficiency) and processors number is studied using several alpha spectra, with the aim of obtaining a method to estimate the optimal processors number that must be used in a simulation.

A basic mesoscopic model of MTS growth is proposed. Taking advantage of the spherical symmetry, the model allows to fully explore the parameter space and investigate alternative interaction mechanisms, in view also of comparisons with macroscopic "universal laws". Preliminary results are in good agreement with available experimental data.

The interface between a metallic plane surface and an electronegative plasma is analyzed by using a theoretical model. The model includes ionization, positive ion collisions and positive ion thermal motion. Some physical quantities of great interest in plasma surface treatment and plasma diagnostic are analyzed, such as the positive ion current collected by the metal and the floating potential. The effect produced by each process (collisions, ionizations and positive ion thermal motion) is analyzed.

We investigate the influence of lattice geometry in network dynamics, using a cellular automaton with nearest-neighbor interactions and two admissible local states. We show that there are significant geometric effects in the distribution of local states and in the distribution of clusters, even when the connection topology is kept constant. Moreover, we show that some geometric structures are more cohesive than others, tending to keep a given initial configuration. To characterize the dynamics, we determine the distributions of local states and introduce a cluster coefficient. The lattice geometry is defined from the number of nearest neighbors and their disposition in 'space', and here we consider four different geometries: a chain, a hexagonal lattice, a square lattice and a cubic lattice.

Wistar rats were exposed to 2.45 GHz continuous, radiofrequency microwave (RF/MW) field 2 hours daily, 7 days weekly, at power density 5–10 mW/cm². Four subgroups were created in order to be irradiated 4, 16, 30 and 60 hours. Sham-exposed controls were included in the study. Animals were euthanized on the final irradiation day of each treated subgroup. Bone marrow smears were examined to determine the extent of genotoxicity after the particular treatment time. Mann-Whitney test was used for statistical evaluation of data. In comparison to the sham-exposed subgroups, the findings of polychromatic erythrocytes revealed significant differences for the 8th and 15th experimental day. Bone marrow erythrocyte maturation and/or proliferation initiated by subthermogenic RF/MW irradiation showed temporary disturbance. Thereafter, the frequency of micronucleated bone marrow red cells was significantly increased after 15 irradiation treatments. Comparison of micronucleus frequency data obtained after 2, 8 and 30 irradiation treatments did not reveal statistically significant differences between sham and treated subgroups. Under the applied experimental conditions, RF/MW irradiation initiates transitory cytogenetic effect manifested with micronucleus formation in erythropoietic cells.

The relevance of non-adiabatic electronic effects to shock initiation of energetic materials is discussed on the basis of simulation results. The latter are obtained using a classical path approach to the electron dynamics in shockwaves. The time-dependent electron wavefunction is propagated coherently, and attempts are made to introduce environment effects. The results are analysed in term of a parameter η defined as the fraction of electrons promoted into virtual orbitals as a result of non-adiabatic transitions.

The reaction of CO and O over a catalytic surface is studied with a cellular automata (CA) model. We extend the CA model proposed by Mai and von Niessen [Phys. Rev. A 44 R6165 (1991).] taking into account the variation of the temperature of the catalyst with the aim of analyzing the existence of oscillations in this reaction. The rate constants for the different processes which govern the reaction are chosen in the Arrhenius form. Aperiodic and quasiperiodic regimes are observed within certain limits of the surface temperature relaxation parameter. The results from the CA model presented are in agreement with several oscillatory behaviours which the catalyzed oxidation of CO exhibits.

The initial stages of tumour growth (avascular phase) are characterised by a low nutrient availability, which soon become a limiting factor for the progression of the neoplasm. Normally a transition to a vascular phase occurs, during which cancer cells stimulate the proliferation of endothelial cells belonging to vessels, hence the formation of new capillaries. The newly formed vascular system rapidly approaches the tumour surface and even infiltrates it, providing additional nutrients which allow further growth (angiogenesis). Blocking the process, might induce tumour to latency, with the consequent implications from therapeutical point of view. In the present contribution we will consider angiogenesis as a case study to show how mathematical models help in the interpretation and quantification of the experimental results.

Lowering in nutrient local availability and rising in host mechanical rigidity are two distinct boundary conditions that affect the growth of solid a-vascular cancers in similar ways (inhibition of growth). In silico experiments based on a physical-mathematical model can shed light on some of the mechanisms at the basis of these effects and suggest that the self-organizing properties of neoplastic populations are greatly modulated by environmental restrictions.

Analytical expressions to determine sheath thickness surrounding cylindrical or spherical Langmuir probes are obtained using a radial model for cold electropositive plasmas. As has been shown by the authors, a radial model can be used to obtain numerical results to locate the sheath edge considering three different criteria, when it is parameterized according to the radius and the potential of the probe. Expressions to fit these results are provided.

Dendrimers are nanometric-size macromolecules with a regular tree-dimensional like array of branch units. Within this macromolecular structure it is possible to encapsulate a variety of guest molecules. In this paper we show that the photophysical properties of Rhodamine-B encapsulated into the dendritic box can be easily modulated by the innovative quantum confinement effect. The emission frequencies of this organic dye incorporated within the dendritic structure can effectively be red shifted with respect to their emission in solution and contrary to other confined spaces of considerable hardness, the magnitude of this shifting can be regulated under appropriate experimental conditions. This effect could have unprecedented applications in the development of supramolecular devices relating to the frequency tuning of organic laser dyes.

In bio-micro devices, numerous functions of liquid flow such as elongation, expansion and transportation are required. Electro-wetting is one of the methods to control the liquid flow. In the present study, a water droplet was elongated in a channel based upon electro-wetting, and the effect of electrode diameter and shape of electrode immersed in a water droplet on the elongation was examined. The elongation increased as a diameter of electrode, and significantly increased when the electrode with a T-shape was employed. The electric field at the edge of water droplet is kept relatively large when the rod electrode with a large diameter or the T-shape electrode is employed. The present result can be explained by this effect, the change of local electric energy at the edge of the droplet.

In recent papers we combined molecular dynamics (MD) simulations with the quasi Gaussian entropy (QGE) theory, in order to model the statistical mechanics and thermodynamics of simple solute molecules in water. In this paper we apply this approach to a more complex solute in water: a 9 residues peptide, Contryphan Vn. Results show that this approach can provide an accurate theoretical description of this complex solute-solvent system over a wide range of temperature.

This study was aimed to characterize by Raman spectroscopy (excitation line 633 nm) different redox states of the mitochondrial cytochrome c oxidase. The results obtained from a systematic analysis carried out on the mitochondrial enzyme prepared under redox conditions, differently affecting the valence state of the metal prosthetic groups, and a comparison with homologous bacterial heme-copper oxidases, cytochrome c and pyridine hemo-chrome extract revealed a novel redox state marker specifically linked to the redox transition of heme a, peaking at 1645 cm^-1, and tentatively assigned to the C=C and/or C=N streching mode of the imidazole ring of a proxymal histidine ligand. The possible involvment of this redox-linked conformational change in the catalytic activity of cytochrome oxidase is discussed.

The aim of this interdisciplinary study was to investigate the effects of a range of static magnetic fields (up to 5 T) on intracellular signalling cascades in primary rat cultured cortical neurons. Magnetic field exposures were conducted using a superconducting magnet with primary rat cultured cortical neurons maintained at 37°C. A series of test were carried out to investigate the effect of magnetic field strength on the activation of the proteins kinases, extracellular-signal regulated kinase (ERK) and c-Jun N terminal kinase (JNK). Cells were exposed to the magnetic fields for one hour, fixed in 4% paraformaldehyde and examined for ERK and JNK activation using antibodies which recognise the phosphorylated (i.e., active) form of ERK or JNK.

This immunocytochemical data demonstrate a differential activation of ERK and JNK when cells are exposed to increasing magnetic field. Thus, ERK activation was increased when cells were exposed to 0.75 T whereas JNK activation was increased at a higher magnetic field strength of 5 T.

Since ERK and JNK have been implicated in cellular differentiation and stress response, respectively, the results presented here suggest that static magnetic field strength may influence those cellular parameters.

The frequency dependent electrical conductivity below 1 MHz was studied on wet-spun, macroscopically oriented, calf thymus DNA bulk samples. Temperature dependence of the quasistatic electrical conductivity measured perpendicular to the long DNA axis is discussed within the framework of activated variable range hopping mechanism. It is shown that the frequency dependence of the electrical conductivity in the frequency range of approximately 10^-3 Hz–10¹⁵ Hz agrees well with predictions of the hole hopping mechanism. Temperature dependence of the electrical conductivity at various frequencies exhibits a crossover at lower temperatures to almost temperature independent mechanism.

The aim of this work is to determine the most suitable bioaccumulators for air pollution survey in Morocco. For this, we compare in this paper heavy metals uptake efficiencies for different types of biomonitors: leaves of oak and eucalyptus trees, needles of coniferous trees, tree-barks and lichens collected at the same site. Instrumental neutron activation analysis using the k₀ method (INAA-k₀) was used for its adequate characteristics to analyze accurately a wide number of elements. Reference materials were analyzed to check the reliability and the accuracy of this technique. The results obtained for all these bioaccumulators lead to the following conclusions. For the major elements, leaves and needles are more accumulating than tree barks and lichens. While for the intermediate and trace elements, there is an obvious accumulation in lichens in comparison with tree barks, leaves and needles. This work shows the possibility to use these four bioaccumulators according to their availability in an area. It will be useful however to set up an inter calibration between these bioaccumulators.

In 1999, Ramon et al examined the effects of δ-aminolevulinic acid (δ-ALA) on two cervical cancer cell lines (HeLa and CaLo) and normal cervical cells. The results reported additionally support the proposal that Photodynamic Therapy (PDT) could be an effective tool for treatment of cervical cancer (CeCa) by protoporphyrin IX (PpIX) accumulation. This cancer is in México considered a problem of public health.

In this project PDT was applied in a CeCa mouse model by implantation of HeLa cells in nu/nu mice, exposing it to δ-ALA to a dose that induces the greater concentration of PpIX by intratumoral and oral route, as well as the power and the number of optimal irradiations at 630 nm with a diode laser; verifying which of the used doses does not produce significant damage to the organs by means of histopatologic techniques: liver, spleen, brain and kidney, the determination of reactive substances to tiobarbituric acid (TBAR'S) and measured the amount of residual δ-ALA, the size of the tumor at the beginning and at the end of the application of the PDT.

Results. The cervical cancer mouse model is developed by implantation of 1,5 million HeLa cells, appearing at 15 days. The dose of δ-ALA that induces the greater concentration of PpIX in the tumor by intratumoral route was 40 mg of δ-ALA/kg body weight and for oral route it was 20 mg of δ-ALA/kg body weight, both routes did not present significant damage in the organs and according to the Analysis of Bifactorial Variance for the doses of δ-ALA and the organs no difference exists (p > 0.05).

The power of the used laser was 150 J/cm² and 250 J/cm², both applied by intratumoral and oral route after the δ-ALA administration. The greater diminution in the size of the tumor (53%) was by the δ-ALA oral route administration to a power of 150 J/cm² with 5 irradiations in intervals of 48 h.

Applying the Planck-Benzinger methodology to biological systems, we have established that the negative Gibbs free energy minimum at a well-defined stable temperature, ⟨T_S⟩, where the bound unavailable energy TΔS° = 0, has its origin in the sequence-specific hydrophobic interactions. Each such system we have examined confirms the existence of a thermodynamic molecular switch wherein a change of sign in [ΔC_p°]_reaction leads to a true negative minimum in the Gibbs free energy change of reaction, and hence a maximum in the related equilibrium constant, K_eq. At this temperature, ⟨T_S⟩, where ΔH°(T_S)(-) = ΔG°(T_S)(-)_min, the maximum work can be accomplished in transpiration, digestion, reproduction or locomotion. In the human body, this temperature is 37°C. The ⟨T_S⟩ values may vary from one living organism to another, but the fact that the value of TΔS°(T) = 0 will not. There is a lower cutoff point, ⟨T_h⟩, where enthalpy is unfavorable but entropy is favorable, i.e. ΔH°(T_h)(+) = TΔS°(T_h)(+), and an upper limit, ⟨T_m⟩, above which enthalpy is favorable but entropy is unfavorable, i.e. ΔH°(T_m)(−) = TΔS°(T_m)(−). Only between these two temperature limits, where ΔG°(T) = 0, is the net chemical driving force favorable for such biological processes as protein folding, protein-protein, protein-nucleic acid or protein-membrane interactions, and protein self-assembly. All interacting biological systems examined using the Planck-Benzinger methodology have shown such a thermodynamic switch at the molecular level, suggesting that its existence may be universal.

Carmine is a dye used mainly for coloring food products and galenicals but also in inks. As food irradiation is becoming a regular treatment for food preservation, it is desirable to have a proper knowledge about the radiation sensitivity of additives that can be included in the food formula. The aim of this work was to establish the radiation stability of carmine against Co-60 gamma radiation. Samples of 50% pure carmine powder as well as 50%, 10% and 5% aqueous solutions were irradiated in a Gammacell 220, dose rate of about 5.2 kGy/h, with doses of 0, 1, 2, 4, 8, 16 and 32 kGy. Spectrophotometric readings at 494 nm show a slight decrease of the absorbance as a function of dose: Samples irradiated with 4 and 32 kGy retained 95% and 90% of absorbance of the unirradiated samples respectively. These results indicate a rather good stability of carmine against γ-irradiation.

Cytochromes c₃ are soluble electron transfer proteins in the periplasm of sulphate-reducing bacteria. They act as electron-proton couplers between hydrogenase and the electron transfer chain of sulphate respiration. In this work, cytochrome c₃ (Cyt-c₃) obtained from both Desulfovibrio vulgaris and Desulfovibrio gigas, is electrostatically adsorbed on Ag electrodes coated with self-assembled monolayers of 11-mercaptoundecanoic acid. The redox equilibria of the adsorbed tetraheme protein are studied by surface enhanced resonance Raman spectroscopy (SERRS).

The quantitative analysis of the SERR spectra, which were measured as a function of the electrode potential, allows determining the redox potentials for the individual hemes of Cyt-c₃. The values obtained of the redox potentials are compared with the data provided by NMR experiments and by molecular dynamics simulation studies of the electrostatically bound protein on a coated electrode. It is found that immobilisation causes substantial shifts of the redox potential, which would have an impact on the intramolecular electron flow.

Three-dimensional low-resolution models of the biochemically and biotechno- logically significant enzyme cellobiose dehydrogenase (CDH) were predicted by advanced modeling approaches based on experimental one-dimensional low-resolution small-angle x-ray scattering (SAXS) data. In particular, the ab initio modeling program DAMMIN by Svergun was used to predict the shape of both the whole protein and the two major constituent units (heme and FAD domains). The validity of the approach applied was tested in a systematic way by a critical assessment of scattering profiles (scattering intensities, pair-distance distribution functions) and structural and hydrodynamic parameters (hydrated particle volume, radius of gyration, maximum particle diameter, sedimentation and diffusion coefficients) and a comparison to available experimental data. Obviously, the applied approach enables the prediction of the solution structure of both CDH and its domains with a high degree of probability, though the problem of shape uniqueness remains crucial, similar to the use of other solution methods. The obtained results demonstrate the possibility to unravel particle shapes by ab initio calculations, without knowledge of high-resolution data, and confirm earlier trial-and-error models.

This work presents an extensive calculation of parameters of semiconductor heterostructures in the ranges where TeraHertz radiation may be generated. In a previous work [Gutiérrez and Camacho, Phys. Stat. Sol. A 195, 600 (2003).] a model was presented to describe the carrier dynamics of semiconductor hetero- structures as sources of THz radiation. In this model the solutions are very sensitive to the geometric parameters of the asymmetric Double Quantum Well representing the semiconductor heterostructure. The model gives a good description of the TeraHertz radiation observed in laboratories and originated in microscopic processes. Therefore, the model allows us to control the TeraHertz radiation through the engineering of the semiconductor heterostructures. The results of this work give precise specifications of the semiconductor heterostructures suitable to generate TeraHertz radiation that can be verified in the laboratory.

A "milliprobe" system was implemented by using the focusing properties of a Van de Graaff accelerator, together with a collimator system including 1 mm diameter apertures, to impose the appropriate dimension to the beam spot. The scanning of the sample surface was achieved by X-Y movements of the sample holder (the Z axis being coincident with the beam direction). These movements were accomplished by a motorised X-Y table, with a travel of 25 mm × 25 mm, connected to the sample holder.

This system was used to study specimens of the mineral tourmaline. Two samples, of the "watermelon" zoned tourmaline variety, originating from the Alto Ligonha pegmatite district in northern Mozambique, were analysed by the simultaneous use of PIXE (Proton-Induced X-Ray Emission) and PIGE (Proton-Induced Gamma-Ray Emission) techniques, in order to quantify their composition and try to establish a correlation between the elements (major and trace elements) and colour zoning.

In order to validate the "milliprobe" analysis and study in more detail the frontier between zones of different colours, a microprobe analysis of the samples was also done.

In this work, the mineralogical classification of the samples was accomplished. A correlation was established between the presence of Fe and green colour. It was also concluded that the presence of Mn by itself is not enough to lead to pink colour, which gives support to previous studies that claim that only Mn³⁺ and not the more common form Mn²⁺ is responsible for the pink colour.

The emission properties of an electron in a double quantum well driven by ultrashort electromagnetic half-cycle pulses are studied. By numerically solving the corresponding time-dependent Schrödinger equation we show that the emission spectrum can be designed by appropriately choosing the parameters of the pulses. Low-frequency generation (LFG) is observed, and conditions for intense LFG and strong induced localization are found. The effects of absence of generalized parity of the Floquet modes on the emission spectrum are discussed. Simple relations for determining the values of the pulse parameters for controlling the localization process and the emission properties are found from an analytical approximation.

The aim of this study is to localize and to describe the transport barriers and the diffusion phenomena that appear in tokamak in two Hamiltonian models for the study of magnetic field line dynamics: a twist map (tokamap) and a non-twist one (rev-tokamap). New results obtained for rev-tokamap will be compared to the already known ones on tokamap and with those concerning the non-twist standard model.

The analysis will be done in terms of a stochasticity parameter describing the perturbation amplitude of the ideal magnetic configuration, and of the q-profiles.

The manganese environment has been investigated by X-ray Absorption Spectroscopy (XAS) in RCu_3-xMn_4+xO₁₂(R = Ca or La) magnetoresistive perovskites. The analysis of the data evidence the presence of two different Mn edges, each one related with the two different sites in which Mn can be located. Mn-O distances at both sublattices were obtained by Extended X-ray Absorption Fine Structure (EXAFS) analysis. The variation of the threshold energy corresponding to the Mn at A sites is driven by the changes in the Mn-O distances. On the contrary, the edge of Mn at Mn-O₆ sites, which is equivalent to the one observed in manganites, is dominated by the change in its valence. The results suggest that electrical conduction in this series of compounds is due to the Mn e_g electrons at B site (mixed valence Mn) and not to the localized electrons from Mn at A site of the perovskite.

The dispersion relation of the collective magnetoplasmon excitations is obtained for an electron gas confined to the surface of a cylindrical nanotube when a magnetic field is perpendicular to its axis. We use the random phase approximation in our calculations. Numerical results for the magnetoplasmons are presented for the plasmon dispersion showing a rich structure due to splitting of the energy bands into Landau levels in a strong magnetic field.

Optically stimulated luminescence (OSL) and thermoluminescence (TL) dating were applied for studying the evolution of a dune at the archaeological site of Kałdus (Lower Vistula Valley, Poland), where excavation revealed a settlement sequence. The dating results are supported by investigations of optical bleaching characteristics of the dune quartz. The luminescence studies presented here are a part of a wider interdisciplinary project studying the dynamics of the local geomorphology and its relationship to human activity at the site from prehistoric times until early medieval ages.

Numerical micromagnetics is used to investigate the influence of the surface anisotropy on the magnetic behaviour of single domain spherical nanoparticles. Two kinds of surface anisotropy are considered: easy axis type (radial) and easy plane type (tangential). It is shown that the coercivity increases whereas the remanence decreases with the increase of the surface anisotropy and this tendency is more pronounced for radial surface anisotropy (K_s < 0) than for tangential one (K_s > 0). It is additionally shown that the enhancement of the coercivity depends on the particle size and is the strongest for the smallest particles.

The self expandable Nitinol stents or stentgrafts are typically used for miniinvasive treatment of stenosis and aneurysms in the cardiovascular system. The minimal traumatisation of the patient, shorter time of hospitalization are typical advantages of these methods. More than ten years of experience has yielded also important information about the performance of stents in interaction with biological system and the possible problems related with it. The leakage or the shift of stent are some typical disadvantages, that can be related among other in the construction of the stent. The problem is that the mechanical properties, dimensions and the dynamical properties of the stent do not exactly correspond to the properties of the vessel or generally of tissue where this stent is introduced. The measurement, the description and the comparison of the relations between the mechanical properties of stents and tissues can be one of the possible ways to minimize these disadvantages. The developed original computer controlled measuring system allows the measurement of mechanical properties of stents, the measurement of strain-stress curves or simulation of interaction of the stent and vessel for exactly defined hemodynamic conditions. We measured and compared the mechanical parameters of different selfexpandable Nitinol stents, which differed in geometry (radius and length), in the type of construction (number of branches and rising of winding) and in the diameter of used wire. The results of measurements confirmed the theoretical assumptions that just the diameter of the Nitinol wire significantly influences the rigidity and the level of compressibility of the stent as well. A compromise must be found between the required rigidity of the stent and the minimal size of the delivery system. The exact description of the relation between the mechanical properties and geometry and construction of the stents enables to design the stent to fit the patient and it is expected that this access improves the efficiency of treatment. The results of measurement are also necessary for the design and identification of the parameters of the models of the stents.

Tribological phenomena in driven phase models related to disordered Josephson junction networks (JJN) in two-dimensions are studied using numerical simulations. Two types of disorder in JJN are considered. In the tribological phenomena caused by the disorder, we focus on pinning and plastic flow of vortices. We investigate the relationship between the strength of the critical current of JJN and the pinning and flow effects of vortices. On the basis of a scaling theory of pinning, it is found that the critical current follows certain scaling relations. In particular, in a weak disorder case, the scaling relation is obtained using an effective dimension of vortex-vortex correlation in the plastic flow state and an anisotropy parameter of junction critical currents. Based on the scaling analysis, we discuss a universal nature of the critical current in JJN.

Maximally entangled states are of utmost importance to quantum communication, dense coding, and quantum teleportation. With a trapped ion placed inside a high finesse optical cavity, interacting with field of an external laser and quantized cavity field, a scheme to generate a maximally entangled three qubit GHZ state, is proposed. The dynamics of tripartite entanglement is investigated, using negativity as an entanglement measure and linear entropy as a measure of mixedness of a state. It is found that (a) the number of modes available to the subsystem determines the maximum entanglement of a subsystem, (b) at entanglement maxima and minima, linear entropy and negativity uniquely determine the nature of state, but the two measures do not induce the same ordering of states, and (c) for a special choice of system parameters maximally entangled tripartite two mode GHZ state is generated. The scheme presented for GHZ state generation is a single step process and is reduction-free.

Ab initio calculations of the BST heterostructure with equiatomic constituent of Sr and Ba species has been carried out within hybrid functional B3PW involving a hybrid of non-local Fock exchange and Becke's gradient corrected exchange functional combined with the non-local gradient corrected correlation potential by Perdew and Wang. The suggested scheme of calculations reproduces experimental lattice parameters of both pure BaTiO₃ and SrTiO₃. The calculated optical band gap for the pure SrTiO₃ (BaTiO₃) is 3.56 (3.46) eV (expt. 3.25 and 3.20 eV, respectively), i.e. agreement is much better than in the standard LDA or HF calculations. In the Ba_0.5Sr_0.5TiO₃ solid solution the gap is reduced by 0.2 eV. The BST upper valence band consists of O 2p atomic orbitals (AO) with a small admixture of Ti 3d, whereas the conduction band bottom consists mostly of Ti 3d orbitals with a small contribution of O orbitals. The Sr (Ba) atomic orbitals make a significant contribution to the higher part of the conduction band. The electron density maps demonstrate the covalency effects in the Ti-O bonding. The electron density near the Sr atoms is stronger localized, as compared with the Ba ions.