bluuebunny/crossref_metadata_2025 huggingface dataset:
Speciation Gamma-Spectrometry: the Fate of Environmental Radio-Nuclides in Hard-Water Lakes
Authors: F El-Daoushy  , E Liger  , F Hernández  , P Casper
Published: September 2005

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.
Absolute Distance Measurements with Tunable Semiconductor Laser
Authors: B Mikel  , O Číp  , J Lazar
Published: September 2005

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.
Grating Decay in Reduced Barium Titanate Crystals
Authors: Chi-Yi Huang  , J Y Chang
Published: September 2005

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.
Analysis of Second and Third Diffracted Orders in Volume Diffraction Gratings Recorded on Photopolymers
Authors: S Gallego  , M Ortuño  , I Pascual  , C Neipp  , A Márquez  , A Beléndez
Published: September 2005

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.
Tm3+-Doped Zn-Diffused LiNbO3 Channel Waveguides
Authors: E Cantelar  , G A Torchia  , J A Sanz-García  , P L Pernas  , G Lifante  , F Cussó
Published: September 2005

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.
Second Harmonic Generation Induced by Poling in Zinc Borophosphate Glasses
Authors: Marc Dussauze  , Sébastien Touzeau  , Evelyne Fargin  , Vincent Rodriguez  , Thierry Buffeteau
Published: September 2005

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.
The Concept of White Light Cavities Using Atomic Phase Coherence
Authors: R-H Rinkleff  , A Wicht
Published: September 2005

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.
Optical Spectra of Melanin Films Extracted from Rana esculenta L.
Authors: G Perna  , A Gallone  , V Capozzi  , P F Biagi  , A Fratello  , G Guida  , P Zanna  , E Argenzio  , R Cicero
Published: September 2005

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.
Ternary Optical Computer Architecture
Authors: Jin Yi  , He Huacan  , Lü Yangtian
Published: September 2005

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.
Nonlinear Operation of Planar Waveguide LASER with Photonic Crystal
Authors: K Leśniewska-Matys  , A Mossakowska-Wyszyńska  , P Szczepański
Published: September 2005

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.
Dynamic Operation of Planar Waveguide LASER with 2D Photonic Crystal
Authors: A Mossakowska-Wyszyńska  , P Czuma  , K Leśniewska-Matys  , P Szczepański
Published: September 2005

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 of Optical Waveforms Using a Single Time Lens System
Authors: José Azaña  , Naum K Berger  , Boris Levit  , Baruch Fischer
Published: September 2005

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.
All-Optical Integrated Device for Self-Routing Applications
Authors: E F Mateo  , J Liñares
Published: September 2005

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.
Hump-Doubling-Induced Bifurcations and Chaos in a Damped Driven Pendulum
Authors: R Chacón  , V M Preciado
Published: September 2005

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.
Intensity Noise in Mode-Locked External Cavity Lasers
Authors: Nuran Dogru  , M Sadettin Ozyazici
Published: September 2005

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.
Photodynamic Effect of Modulated and Continuous LASER Radiation on Cancerous Cells Cultivated In Vitro
Authors: Y Zamora-Juárez  , A J Pérez-Zapata  , L Solano Rodriguez  , E Ramón-Gallegos  , A Cruz-Orea
Published: September 2005

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.
A Genetic Algorithm Approach for Localization of Deep Sources in MEG
Authors: C Sequeira  , F Sanchez-Quesada  , M Sancho  , I Hidalgo  , T Ortiz
Published: September 2005

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.
Towards a Model of Local and Collective Mechanisms in Multicellular Tumor Spheroids Growth
Authors: P P Delsanto  , L Morra  , S Delsanto  , M Griffa  , C Guiot
Published: September 2005

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.
Theoretical Aspects of the Metal-Electronegative Plasma Interface in Collisional Plasmas for Finite Positive Ion Temperature
Authors: J I Fernández Palop  , J Ballesteros  , M A Hernández  , R Morales Crespo  , S Borrego del Pino
Published: September 2005

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.
Simulation of the Electron Dynamics in Shockwaves and Implications for the Sensitivity of Energetic Materials
Authors: Didier Mathieu  , Philippe Martin  , Jean-Pierre La Hargue
Published: September 2005

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.
Physical Modelling and Simulations of Tumour Growth and Angiogenesis: Predictions and New Hypotheses
Authors: M Scalerandi  , M Griffa
Published: September 2005

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.
Environmental Physical Modulation of Intrinsic Tendency to Growth of Multicellular Tumour Spheroids: In Silico Experiments
Authors: M Griffa  , M Scalerandi
Published: September 2005

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.
Charge Transport Mechanism in Native Deoxyribonucleic Acid
Authors: Z Kutnjak  , C Filipič  , R Podgornik  , L Nordenskiöld  , N Korolev
Published: September 2005

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.
Comparative Use of Tree Leaves, Needles, Tree Barks and Lichens for Air Pollution Biomonitoring
Authors: T El Khoukhi  , R Cherkaoui El Moursli  , A Chouak  , Z Moutia  , M Lferde  , A Senhou  , A Gaudry  , S Ayrault  , M Chakir
Published: September 2005

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 k
0 method (INAA-k
0) 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.
Why Does the Human Body Maintain a Constant 37-Degree Temperature?: Thermodynamic Switch Controls Chemical Equilibrium in Biological Systems
Authors: Paul W Chun
Published: September 2005

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.
Stability of γ-Irradiated Carmine
Authors: Hélio M Cosentino  , Rinaldo S Fontenele  , Nélida L Del Mastro
Published: September 2005

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.
Engineering Semiconductor Heterostructures for TeraHertz Radiation
Authors: R M Gutiérrez  , M A Camargo  , A S Camacho
Published: September 2005

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 for PIXE and PIGE Analysis used for the Study of Colour-Zoned Tourmaline
Authors: R Mateus  , L C Alves  , A P Jesus  , A F Faria  , J P Ribeiro
Published: September 2005

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.
Emission Spectrum of an Electron in a Double Quantum Well Driven by Ultrashort Half-Cycle Pulses
Authors: A Matos-Abiague  , J Berakdar
Published: September 2005

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.
Transport Barriers and Diffusion Phenomena for the Magnetic Field Lines in Tokamak
Authors: D Constantinescu  , R Constantinescu
Published: September 2005

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.
Manganese Sites and Valence States in RCu3-xMn4+xO12(R = Ca or La) Magnetoresistive Perovskites
Authors: J Sánchez-Benítez  , A Pérez-Junquera  , M Vila  , A de Andrés  , C Prieto  , J L Martínez  , J A Alonso  , M J Martínez-Lope  , M T Casais  , S Ramos
Published: September 2005

The manganese environment has been investigated by X-ray Absorption Spectroscopy (XAS) in RCu3-x
Mn4+x
O12(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 eg electrons at B site (mixed valence Mn) and not to the localized electrons from Mn at A site of the perovskite.
Plasmon Excitations for Cylindrical Nanotubes in a Transverse Magnetic Field
Authors: Godfrey Gumbs
Published: September 2005

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.
Role of the Surface Anisotropy in Magnetization Reversal of a Spherical Nanoparticle
Authors: O Nedelko  , A Ślawska-Waniewska
Published: September 2005

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.
Measurement and Comparison of Mechanical Properties of Nitinol Stents
Authors: Josef Hanus  , Jiri Zahora
Published: September 2005

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 Phase Models under Driving Fields
Authors: Takaaki Kawaguchi
Published: September 2005

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.
Electronic Properties of Layered Ba0.5Sr0.5TiO3 Heterostructure: Ab initio Hybrid Density Functional Calculations
Authors: S Dorfman  , S Piskunov  , E A Kotomin  , D Fuks
Published: September 2005

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 Ba0.5Sr0.5TiO3 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.
The Role of Selection in the Evolution of Human Mitochondrial Genomes
Authors: Kivisild Toomas , Shen Peidong , Wall Dennis P , Do Bao , Sung Raphael , Davis Karen , Passarino Giuseppe , Underhill Peter A , Scharfe Curt , Torroni Antonio , Scozzari Rosaria , Modiano David , Coppa Alfredo , de Knijff Peter , Feldman Marcus , Cavalli-Sforza Luca L , Oefner Peter J
Published: September 2005

High mutation rate in mammalian mitochondrial DNA generates a highly divergent pool of alleles even within species that have dispersed and expanded in size recently. Phylogenetic analysis of 277 human mitochondrial genomes revealed a significant (P < 0.01) excess of rRNA and nonsynonymous base substitutions among hotspots of recurrent mutation. Most hotspots involved transitions from guanine to adenine that, with thymine-to-cytosine transitions, illustrate the asymmetric bias in codon usage at synonymous sites on the heavy-strand DNA. The mitochondrion-encoded tRNAThr varied significantly more than any other tRNA gene. Threonine and valine codons were involved in 259 of the 414 amino acid replacements observed. The ratio of nonsynonymous changes from and to threonine and valine differed significantly (P = 0.003) between populations with neutral (22/58) and populations with significantly negative Tajima's D values (70/76), independent of their geographic location. In contrast to a recent suggestion that the excess of nonsilent mutations is characteristic of Arctic populations, implying their role in cold adaptation, we demonstrate that the surplus of nonsynonymous mutations is a general feature of the young branches of the phylogenetic tree, affecting also those that are found only in Africa. We introduce a new calibration method of the mutation rate of synonymous transitions to estimate the coalescent times of mtDNA haplogroups.
Modeling Population Genetic Data in Autotetraploid Species
Authors: Luo Z W , Zhang Ze , Zhang R M , Pandey Madhav , Gailing Oliver , Hattemer Hans H , Finkeldey Reiner
Published: September 2005

Allozyme and PCR-based molecular markers have been widely used to investigate genetic diversity and population genetic structure in autotetraploid species. However, an empirical but inaccurate approach was often used to infer marker genotype from the pattern and intensity of gel bands. Obviously, this introduces serious errors in prediction of the marker genotypes and severely biases the data analysis. This article developed a theoretical model to characterize genetic segregation of alleles at genetic marker loci in autotetraploid populations and a novel likelihood-based method to estimate the model parameters. The model properly accounts for segregation complexities due to multiple alleles and double reduction at autotetrasomic loci in natural populations, and the method takes appropriate account of incomplete marker phenotype information with respect to genotype due to multiple-dosage allele segregation at marker loci in tetraploids. The theoretical analyses were validated by making use of a computer simulation study and their utility is demonstrated by analyzing microsatellite marker data collected from two populations of sycamore maple (Acer pseudoplatanus L.), an economically important autotetraploid tree species. Numerical analyses based on simulation data indicate that the model parameters can be adequately estimated and double reduction is detected with good power using reasonable sample size.
Subgingival Microbiota in Peri‐Implant Mucosa Lesions and Adjacent Teeth in Partially Edentulous Patients
Authors: Botero Javier E. , González Ana M. , Mercado Ramiro A. , Olave Gilberto , Contreras Adolfo
Published: September 2005

Background: Osseointegrated dental implants have been shown to be a predictable approach to provide the adequate support for the replacement of missing teeth. It has been observed that implants showing signs of peri‐implantitis contain subgingival microbiota similar to that around natural teeth with periodontal disease. This study identified the subgingival microbiota around implants with peri‐implant lesions and natural teeth in partially edentulous patients.

Methods: Clinical and radiographic parameters were recorded and microbial samples taken from 16 implants with signs of pocketing, 12 neighboring and 11 non‐neighboring teeth to the affected implants in 11 patients and 15 stable implants in eight patients (controls). Samples were cultured using techniques for Enterobacteriaceae spp and facultative/anaerobic periodontal pathogens. Statistical analysis included Friedman test to establish differences between the subgingival microbiota cultured from implants and teeth and two‐tailed Mann Whitney test and chi square to find differences in two separate samples (P ≤0.05).

Results: There were statistical differences between the subgingival microbiota in peri‐implant lesions and stable implants for Gram‐negative enteric rods (P <0.05). P. gingivalis (1.42%) was detected in peri‐implant lesions but not in stable implants. A significant correlation between the subgingival microbiota from implants and neighboring teeth for Gram‐negative enteric rods (P = 0.023) and implants and non‐neighboring teeth for P. gingivalis (P = 0.042) was found. The frequency detection of Gram‐negative enteric rods (75%) and P. intermedia/nigrescens (25%) was higher in peri‐implant lesions (P <0.05).

Conclusions: The subgingival microbiota in peri‐implant lesions showed high levels of periodontopathic bacteria and superinfecting bacteria compared to healthy stable implants. The role of superinfecting bacteria in the pathogenesis of periimplant lesions needs further investigation. J Periodontol 2005; 76:1490‐1495.
Effects of Chitosan on Human Periodontal Ligament Fibroblasts In Vitro and on Bone Formation in Rat Calvarial Defects
Authors: Pang Eun‐Kyoung , Paik Jeong‐Won , Kim Soo‐Kyoung , Jung Ui‐Won , Kim Chang‐Sung , Cho Kyoo‐Sung , Kim Chong‐Kwan , Choi Seong‐Ho
Published: September 2005

Background: The purpose of this study was to evaluate the effect of chitosan on human periodontal ligament fibroblasts (hPDLF) in vitro and on bone formation in rat calvarial defects in vivo.

Methods: Fibroblast populations were obtained from individuals with a healthy periodontium and cultured in α minimum essential medium (MEM) for the control group. For the experimental groups, cells were cultured in α‐MEM containing chitosan at concentrations of 0.01, 0.1, 1, or 2 mg/ml. The 3‐(4,5‐dimethyl‐thiazole‐2‐yl)‐2,5‐diphenyl tetrazolium bromide (MTT) assay, reverse transcription‐polymerase chain reaction (RT‐PCR) and the assay of alkaline phosphatase (ALPase) activity were performed. Eight mm calvarial critical‐sized defects were created in 30 male Sprague‐Dawley rats. The animals were divided into three groups of 10 animals each. The defects were treated with either chitosan/absorbable collagen sponge (ACS) or ACS alone in the experimental groups or were left untreated (surgical controls). The animals were sacrificed at 2 or 8 weeks post‐surgery and the treatment outcomes were evaluated using histological and histomorphometric parameters.

Results: The chitosan‐induced proliferative responses of the hPDLF reached a plateau at a concentration of 0.1 mg/ml (P <0.05). When the hPDLF were stimulated with 0.1 mg/ml chitosan, both the mRNA expression of type I collagen and the ALP activity were significantly up‐regulated (P <0.05). The surgical implantation of chitosan/ACS enhanced the new bone formation at 8 weeks post‐surgery and the amount of new bone formation of the chitosan/ACS group was significantly greater than that of both the ACS alone group and the surgical control group (P <0.01).

The new bone area and defect closure in the chitosan/ACS group were significantly greater than those in the ACS control and sham surgery control groups at 8 weeks (P <0.01). However, the chitosan/ ACS group exhibited significantly less bone density than both the ACS control and the sham surgery control group at 8 weeks (P <0.01).

Conclusions: Chitosan (0.1 mg/ml) enhanced the type I collagen synthesis and facilitated the differentiation into osteogenic cells. Chitosan reconstituted with ACS has a significant potential to accelerate the regeneration of bone in rat calvarial critical size defects. J Periodontol 2005;76:1526‐1533.
Tetraploid/Diploid Mosaicism With Generalized Aggressive Periodontitis
Authors: Tözüm Tolga F. , Berker Ezel , Akincibay Hakan , Özer Özlem , Aktaş Dilek , Tezcan Ilhan , Şekerci Sükran Ç. , El Hakan , Eratalay Kenan , Tunçbilek Ergül
Published: September 2005

Background: Changes of chromosome number diploid to triploid or tetraploid states are rare in human pregnancies, where the main clinical features of tetraploidy are delayed growth and/or craniofacial abnormalities. The present report describes the oral features of tetraploid/diploid mosaicism. Although the medical literature described the physical manifestations of this genetic abnormality, the oral features of this disorder were not previously described.

Methods: A 13‐year‐old patient presented because of his severe periodontal conditions. Clinical, radiological, microbiologic, immunologic, and genetic examinations were conducted.

Results: Long eyelashes and mandibular micrognathia were noticeable in his extraoral examination. Intraoral examination revealed significant generalized edema of the gingiva and severe sulcular bleeding on probing. Generalized maxillary and mandibular alveolar destruction was determined with radiographic examination. Actinobacillus actinomycetemcomitans was also detected in his subgingival samples. He was diagnosed as generalized aggressive periodontitis. His medical cytogenetic examination revealed 92,XXYY (25%)/46,XY (75%) karyotype indicating tetraploid/diploid mosaicism. He was given initial and advanced periodontal therapy and he is currently under a routine follow‐up period.

Conclusions: This report provides information on the oral characteristics of tetraploid/diploid mosaicism and describes periodontal treatment. Severe periodontal conditions such as aggressive periodontitis may accompany tetraploid/diploid mosaicism subjects and these patients should be frequently seen by their dental practitioners. It is suggested that initial and/or advanced periodontal procedures may be a way of treating tetraploid/diploid mosaicism subjects with aggressive periodontitis. The importance of physical examination and medical consultation is also discussed. J Periodontol 2005;76:1567‐1571.