Institute for Atomic Energy Research

Relativistic quantum mechanics of a finite one-dimensional continuum is studied in the framework of Dirac's generalized Hamiltonian dynamics. It is shown that the wave equation and subsidiary conditions found by Virasoro in the dual resonance model are equivalent to relativistic quantum mechanics in our system. Interaction with external fields is also studied briefly.

A simple method for deriving the Bäcklund transformation from the Riccatti form of inverse method is presented for the nonlinear evolution equations.

The apparent discrepancy between the reported preferential occurrence of bronchial carcinomas in central bronchial airways and current dose estimates for inhaled particles suggests that experimentally observed local accumulations of particles within bronchial airway bifurcations may play a crucial role in lung cancer induction. Here, we computed three-dimensional particle deposition patterns in lobar-segmental airway bifurcations and quantified the resulting inhomogeneous deposition patterns in terms of deposition enhancement factors, which are defined as the ratio of local to average deposition densities. Our results revealed that a small fraction of epithelial cells located at carinal ridges can receive massive doses that may be even a few hundred times higher than the average dose for the whole airway. This lends further credence to the hypothesis that the apparent site selectivity of neoplastic lesions may indeed be caused by the enhanced deposition of toxic particulate matter at bronchial airway bifurcations.

Automodulation of ion oscillation mode is investigated by applying the reductive perturbation theory to the fluid equation of a plasma composed of cold ions and isothermal electrons. It is shown that an oscillatory solution of the Korteweg-de Vries equation in the small wave number region satisfies a small wave number limit of the nonlinear Schrödinger type equation obtained in the finite wave number region.

Reitz, G., Berger, T., Bilski, P., Facius, R., Hajek, M., Petrov, V., Puchalska, M., Zhou, D., Bossler, J., Akatov, Y., Shurshakov, V., Olko, P., Ptaszkiewicz, M., Bergmann, R., Fugger, M., Vana, N., Beaujean, R., Burmeister, S., Bartlett, D., Hager, L., Pálfalvi, J., Szabó, J., O'Sullivan, D., Kitamura, H., Uchihori, Y., Yasuda, N., Nagamatsu, A., Tawara, H., Benton, E., Gaza, R., McKeever, S., Sawakuchi, G., Yukihara, E., Cucinotta, F., Semones, E., Zapp, N., Miller, J. and Dettmann, J. Astronaut's Organ Doses Inferred from Measurements in a Human Phantom Outside the International Space Station. Radiat. Res. 171, 225–235 (2009).Space radiation hazards are recognized as a key concern for human space flight. For long-term interplanetary missions, they constitute a potentially limiting factor since current protection limits for low-Earth orbit missions may be approached or even exceeded. In such a situation, an accurate risk assessment requires knowledge of equivalent doses in critical radiosensitive organs rather than only skin doses or ambient doses from area monitoring. To achieve this, the MATROSHKA experiment uses a human phantom torso equipped with dedicated detector systems. We measured for the first time the doses from the diverse components of ionizing space radiation at the surface and at different locations inside the phantom positioned outside the International Space Station, thereby simulating an extravehicular activity of an astronaut. The relationships between the skin and organ absorbed doses obtained in such an exposure show a steep gradient between the doses in the uppermost layer of the skin and the deep organs with a ratio close to 20. This decrease due to the body self-shielding and a concomitant increase of the radiation quality factor by 1.7 highlight the complexities of an adequate dosimetry of space radiation. The depth-dose distributions established by MATROSHKA serve as benchmarks for space radiation models and radiation transport calculations that are needed for mission planning.

A versatile Monte Carlo program for quantitative particle analysis in electron probe X-ray microanalysis is presented. The program includes routines for simulating electron-solid interactions in microparticles lying on a flat surface and calculating the generated X-ray signal. Simulation of the whole X-ray spectrum as well as phi(z) curves is possible. The most important facility of the program is the reverse Monte Carlo quantification of the chemical composition of microparticles, including low-Z elements, such as C, N, O, and F. This quantification method is based on the combination of a single scattering Monte Carlo simulation and a robust successive approximation. An iteration procedure is employed; in each iteration step, the Monte Carlo simulation program calculates characteristic X-ray intensities, and a new set of concentration values for chemical elements in the particle is determined. When the simulated X-ray intensities converge to the measured ones, the input values of elemental concentrations used for the simulation are determined as chemical compositions of the particle. This quantification procedure was evaluated by investigating various types of standard particles, and good accuracy of the methodology was demonstrated. A methodology for heterogeneity assessment of single particles is also described.

A systematic survey to establish the true incidence rate of Blazhko modulation among short-period, fundamental-mode, Galactic field RR Lyrae stars has been carried out. The Konkoly Blazhko Survey (KBS) was initiated in 2004. Since then, more than 750 nights of observation have been devoted to this project. A sample of 30 RRab stars was extensively observed, and light-curve modulation was detected in 14 cases. The 47 per cent occurrence rate of the modulation is much larger than any previous estimate. The significant increase of the detected incidence rate is mostly a result of the discovery of small-amplitude modulation. Half of the Blazhko variables in our sample show the modulation with such a small amplitude that they would definitely have been missed in previous surveys. We have found that the modulation can be very unstable in some cases; for example, RY Com showed regular modulation during only one part of the observations, and had a stable light curve with abrupt, small changes in the pulsation amplitude during two observing seasons. This type of light-curve variability is hard to detect in the data from other surveys. The higher frequency of the light-curve modulation of RRab stars makes it even more important to find an explanation for the Blazhko phenomenon. The validity of the [Fe/H](P, ϕ31) relationship using the mean light curves of Blazhko variables is checked in our sample. We found that the formula gives accurate result for small-modulation-amplitude Blazhko stars, and this is also the case for large-modulation-amplitude stars if the light curve has complete phase coverage. However, if the data for large-modulation-amplitude Blazhko stars are not extended enough (e.g. fewer than 500 data points from fewer than 15 nights), the formula may give false result owing to the distorted shape of the mean light curve used.

The wave propagation in an infinite one-dimensional anharmonic lattice is studied under the influence of an anharmonic potential and a weak dislocation potential. It is found that the equation for the nonlinear wave propagation has N -kink solution. The properties of one and two kink solutions are discussed in detail. It is also found that there exists the critical eigenvalue due to the competition between the above two kinds of potentials . A few conservation laws are obtained.

A generalized inverse scheme of the integrable, dispersionless system is proposed from the group theoretical point of view.

Recently we have given evidence for the existence of the σ particle. In these previous works, the ππ S-wave phase shift is reanalyzed, by introducing a repulsive background suggested by the chiral symmetry, and by applying the new method of Interfering Breit-Wigner amplitudes. In this work we also show, reanalyzing the Kπ S-wave phase shift from a similar standpoint, evidence for the possible existence of κ(900), to be assigned as a member of the σ nonet.

Density functional theory (DFT) and second-order Møller−Plesset perturbation theory (MP2) are applied to determine the hydrogen bonding interaction energies in pyridine−water and in a set of methyl-substituted pyridine−water complexes. The results show that methyl substitution stabilizes the hydrogen bond and the degree of stabilization varies with the number and the position of methyl groups. It is demonstrated that the MP2 method yields more reliable relative stabilities for these complexes than does the applied DFT method, which does not take proper account of the dispersion interactions between water and the methyl groups in ortho positions. The comparison of the order of the computed association energies of methyl-substituted pyridine−water complexes with the experimentally observed sequence of the ease of miscibility of these molecules with water shows that there is no simple relationship between the miscibility behavior and the strength of hydrogen bond formed between water and methyl derivatives of pyridine.

The reductive perturbation method is applied to the Vlasov equation which governs the one dimensional motion of collisionless plasmas. The present formulation makes it possible to investigate the nonlinear modulation of the plasma waves with an arbitrary dispersion. Structures of the resulting nonlinear Schrödinger equation have been studied explicitly for the electron plasma wave and for the ion plasma wave.

An extension of the pseudopotential lattice Boltzmann method is introduced to simulate heat transfer problems involving phase transition. Using this model, evaporation through a plane interface and two-phase Poiseuille flow were simulated and the macroscopic jump conditions were utilized to evaluate the accuracy of the method. We have found that the simulation results are in very good agreement with the analytical solutions as far as we take into account the extent of the interface during the evaluation. Using the same model heterogeneous boiling was simulated taking into account the geometry of a cavity and the important features of the boiling process could be observed in the simulation results.

Three wave mode coupling effects on ion acoustic waves are examined by applying the Fourier transformation method of separation of the nonlinear slow processes for a two component plasma described by the Vlasov equation. Contribution of the three mode coupling terms gives rise to a modified Korteweg de Vries equation with a nonlinear term of the form of { B φ+( C /2)φ 2 }φ x , where B and C are constants determined by the unperturbed state of plasmas. It is found that velocity of a stationary solitary wave depends sensitively on the electronion temperature ratio, and that the equation obtained here enables us to account for the amplitude dependence of the solitary wave velocity observed by Ikezi, Baker and Taylor.

A general method for generating higher conservation laws is derived for a broad class of nonlinear-evolution equations, which has been systematically discussed by Ablowitz, Kaup, Newell and Segur.

The 1952-88 cancer mortality records for inhabitants of the Misasa spa area, Japan, which has a high radon background, and a neighboring control area without any radon spa were analyzed (average outdoor Rn concentration: 26 mBq.liter-1 in Misasa vs. 11 mBq.liter-1 in the control area). Standardized mortality ratios (SMRs) for cancers of all sites were significantly lower among the inhabitants of both Misasa (male 0.538; female 0.463) and the control area (male 0.850; female 0.770), than in the whole Japanese population. Poisson regression analysis showed that the relative risks among the inhabitants of Misasa were significantly lower than in the control area for deaths from cancers of all sites (0.67) and stomach cancer (0.59). The relative risk of lung cancer death was also lower (0.55 times) in Misasa than in the control area, although the difference was not statistically significant. These results suggest that the linear no-threshold hypothesis for radiation risk may not be valid for exposure to low doses of radon.

The giant magnetoresistance (GMR) effect was studied on electrodeposited Co-Cu/Cu multilayers of 300 bilayer repeats which were produced in an electrochemical cell with homogeneous current distribution from a bath with two solutes The preparation employed the conventional potentiostatic/potentiostatic and galvanostatic/galvanostatic, as well as an unprecedented galvanostatic/potentiostatic (G/P) control. We find that the specific deposition parameters rather than the deposition mode itself are decisive for the magnitude of the GMR which could be as high as 10% measured at 1 kOe on substrate-free multilayers in optimized G/P conditions. For this new deposition mode, detailed studies on the dependence of GMR on Co and Cu layer thicknesses as well as the bath pH were performed. No oscillatory behavior of the GMR as a function of the Cu layer thickness could be observed. The results suggest the importance of a Co-dissolution and/or a Co vs. Cu exchange reaction after completing the deposition of each magnetic layer. These reactions lead to the formation of a Cu or Cu-rich interface layer prior to the electrochemical deposition of the actual Cu layer during the subsequent pulse in either deposition mode. It turned out that the properties of this interfacial layer (thickness, degree of chemical intermixing) strongly influence the resulting GMR behavior of the multilayer. © 2003 The Electrochemical Society. All rights reserved.

The Karlsruhe Dynamo experiment is aimed at showing that an array of columnar helical vortices in liquid sodium, confined in a cylindrical container, can generate a magnetic field by self-excitation. In three test series it has been demonstrated that magnetic self-excitation occurs and a permanent magnetic saturation field develops which oscillates about a well-defined mean value for fixed flow rates. Dynamo action is observed as an imperfect bifurcation from a seed magnetic field of the environment. Two quasi-dipolar magnetic fields of opposite direction have been realized. A transition between these two states can be enforced through imposition of a sufficiently strong external magnetic perturbation on the existent dynamo field. These perturbations were induced with the aid of two Helmholtz coils. A time series analysis of the magnetic field fluctuations shows several characteristic dynamic features, which are in agreement with theoretical predictions from turbulence models available in the literature.

We carried out molecular dynamics simulations to describe the properties of water inside a narrow graphite channel. Two stable phases were found: a low-density one made of water clusters adsorbed on the graphite sheets and a liquid one that fills the entire channel, forming several layers around a bulk-like region. We analyzed the interfacial structure, orientational order, water residence times in several regions, and hydrogen bonding of this last water phase, calculating also a quantity of electrochemical interest, the probability of electron tunneling through interfacial water. The results are in good qualitative agreement with the available experimental data.

Rare earth intermetallic compounds in Gd(Ag, Cd, In) and Gd(Cu, Ag, Au) systems have been studied. Most of these compounds have the CsCl type of crystal structure. Magnetization measurements have been made on these compounds to determine the type of the magnetic order and its relationship to the number of conduction electrons. GdAg, GdAg 0.9 In 0.1 , GdAg 0.2 In 0.8 , GdAg 0.1 In 0.9 , and GdIn in the Gd(Ag, In) system and GdCu, GdAg, GdAg 0.7 Au 0.3 , and GdAg 0.5 Au 0.5 in the Gd(Cu, Ag, Au) system are antiferromagnetic at low temperatures. On the contrary, GdCd, GdAg 0.8 In 0.2 , GdAg 0.7 In 0.3 , GdAg 0.5 In 0.5 , and GdAg 0.3 In 0.7 are ferromagnetic at low temperatures. GdCd has a very high Curie temperature of 262°K. In the Gd(Cu, Ag, Au) system, the Néel temperature increases with the increase in the lattice constant. The remarkable difference in magnetic behavior between the Gd(Ag, Cd, In) system and the Gd(Cu, Ag, Au) system is considered to be associated with the fact that the number of conduction electrons plays more important role in determining the magnetic behaviors than the interatomic separation.