Zur Theorie des aus zweiC 6 12 -Kernen bestehenden Kernmoleküls

With the aid of a variational method it is shown that on the basis of the energy expression of Skyrme the “nuclear molecule” consisting of twoC ₆ ¹² nuclei has a stable state of equilibrium, which is in agreement with recent experimental results. The energy levels of the nuclear molecule have been calculated and above 13 MeV no energy level has been found, which is in qualitativ agreement with the the resonance structure of the empirical cross-sections.     

Polarization in charge exchange reaction π−+p→π0+n at 40 GeV/c for the 4-momentum transfer range 0<|t|<2 (GeV/c)2

The results on measuring polarization in charge exchange reaction π^?+p→π⁰+n at 40 GeV/c are presented for the 4-momentum transfer range from 0 up to 2 (GeV/c)². At |t|≦0.4 (GeV/c)² the polarization has a positive sign. In the “crossover” region of π^± elastic scattering a possible minimum in the polarization behaviour has been seen for the first time. the polarization is zero within the statistical accuracy near this point. In the “deep” region of the charge-exchange differential cross-section the polarization has a negative sign. The presented data are not in agreement with the modern theoretical models.     

On the Energy of a “One-Dimensional” Two-Electron Atom

Based on the perturbation theory and variational method long known for a “three-dimensional” atom, the ground and first excited state energies are calculated for a “one-dimensional” two-electron atom in the “one-dimensional ortho-helium” configuration, which can be obtained experimentally in principle, as has been already done for a Na Bose condensate, or produced in a super strong magnetic field B ? (2α)²B₀ (B₀ = m²c³/e? ≈ 4.41 × 10¹³ G). The “screening constant” σ for this atom in the ground and excited states was about 0.20 and 0.17, 0.18, respectively, depending on the relative parity PP' of the electronic states, which is somewhat smaller than in “two-dimensional” and “three-dimensional” variants (in these cases, this constant in the ground state is almost the same and about 0.3). The frequencies of the main spectral lines of a “onedimensional” He atom representing a doublet split over the relative parity PP' are found. The presence of the close lines of this doublet in the emission spectrum of magnetars at frequencies ω_{1, 2} ≈ {1.15; 1.17}α²(c/λC) (α = e²/?c, λ_C =?/mc) corresponding to the “one-dimensional ortho-helium” would suggest the existence of a superstrong magnetic field in such astrophysical objects.     

Mott-Hubbard transition and antiferromagnetism on the honeycomb lattice

The Hubbard model is investigated for a halffilled honeycomb lattice, using a variational method. Two trial wave functions are introduced, the Gutzwiller wave function, well suited for describing the “metallic” phase at small U and a complementary wave function for the insulating regime at large values of U. The comparison of the two variational ground states at the mean-field level yields a Mott transition at U _c /t ≈ 5:3. In addition, a variational Monte Carlo calculation is performed in order to locate the instability of the “metallic” wave function with respect to antiferromagnetism. The critical value U _m/t ≈ 3:7 obtained in this way is considered to be a lower bound for the true critical point for antiferromagnetism, whereas there are good arguments that the mean-field value U _c/t ≈ 5:3 represents an upper bound for the Mott transition. Therefore the “metal”- insulator transition for the honeycomb lattice may indeed be simultaneously driven by the antiferromagnetic instability and the Mott phenomenon.     

A study of reaction rates of (n, f ) , (n, \gamma) and (n, 2n) reactions in natU and 232Th by the neutron fluence produced in the graphite set-up (GAMMA-3) irradiated by 2.33 GeV deuteron beam

Spallation neutrons produced in the collision of a 2.33GeV deuteron beam with a large lead target are moderated by a thick graphite block surrounding the target and used to activate the radioactive samples of ^natU and Th put at three different positions, identified as holes “a”, “b” and “c” in the graphite block. Rates of the (n, f), (n, $ \gamma$ and (n, 2n) reactions in the two samples are determined using the gamma spectrometry. The ratios of the experimental reaction rates, R (n, 2n)/R (n, f), for ²³²Th and ^natU are estimated in order to understand the role of the (n, x n) kind of reactions in Accelerator-Driven Sub-critical Systems. For the Th-sample, the ratio is ～ 54 (10)% in the case of hole “a” and ～ 95 (57)% in the case of hole “b” compared to 1.73(20)% for hole “a” and 0.710(9)% for hole “b” in the case of the ^natU sample. Also the ratio of fission rates in uranium to thorium, ^natU (n, f)/ ²³²Th (n, f), is ～ 11.2 (17) in the case of hole “a” and 26.8(85) in hole “b”. Similarly, the ratio ²³⁸U (n, 2n)/ ²³²Th (n, 2n) is 0.36(4) for hole “a” and 0.20(10) for hole “b” showing that ²³²Th is more prone to the (n, x n) reaction than ²³⁸U . All the experimental reaction rates are compared with the simulated ones by generating neutron fluxes at the three holes from MCNPX 2.6c and making use of the LA150 library of cross-sections. The experimental and calculated reaction rates of all the three reactions are in reasonably good agreement. The transmutation power, P _norm as well as P _norm/P _beam of the set-up is estimated using the reaction rates of the (n, $ \gamma$ and (n, 2n) reactions for both the samples in the three holes and compared with some of the results of the “Energy plus Transmutation” set-up and TARC experiment.     

Phonon dispersion and specific heat in ω-helical poly-N ∊(p-bromobenzoyl-l-ornithine)

Poly-N ^?(p-bromobenzoyl-l-ornithine) (PBrBO) is one of the few biopolymers existing in the rare ω-helical (fourfold) conformation. It can be obtained from the α form through an irreversible heat treatment. A study of its normal modes and dispersive behavior shows several interesting features such as “crossing over,” “repulsion with character exchange,” and Von Hove type “singularities” which lead to a fuller interpretation of its IR spectra. The existence of alternately different side-chain conformations, which makes the phonon problem too large to solve directly, has been taken into account by considering the vibrations of the PBrBO chains with two independent conformations. Detailed study of skeletal, amide, and side-chain modes is reported, and the results have been used for the calculation of specific heat via density of states.     

Thermodynamics of 3He solid monolayers in the Heisenberg model

The two-dimensional Heisenberg model is applied to the interpretation of the experimental data on the thermodynamic and magnetic properties of ³He monoatomic films in the millikelvin temperature range, i.e., under conditions when these properties are completely governed by the dynamics of the nuclear spin subsystem. The theoretical results obtained make it possible to describe the internal energy E, the heat capacity C _s, and the magnetic susceptibility χ of the two-dimensional spin-1/2 Heisenberg ferromagnets and antiferromagnets on a triangular lattice within the unified approach over the entire range of temperatures. The data available in the literature on the heat capacity and magnetic susceptibility of ³He films are interpreted in the framework of the advanced theory. Most attention is concentrated on the layers characterized by the ferromagnetic exchange. Comparative analysis of theoretical and experimental data is carried out with the use of two fitting parameters: the exchange interaction constant J and the number of “active” spins n ₂ in the layer that is determined from the entropy of the system in the limit T → ∞. It is demonstrated that, for the ferromagnetic layers, the theoretical results obtained within the Heisenberg model are in very good agreement with the experimental data reported by different authors.     

Thermally assisted hopping transport in disordered systems

The response to an external field of localized electrons coupled to phonons is investigated. The low frequency (ω<T) linear response function is shown to obey a kinetic equation. The transition probabilities (including multiphonon contributions) can be expressed in terms of the dynamical correlation functions(k, ?) of the phonons. The low temperature d.c. conductivity in three dimensions obeys a law σ(0)=σ₀ · exp(? (T ₀/T)^1/4). By a combined variational and “nearest neighbor” approximation upper limits for the exponential as well as the pre-exponential factor are obtained. In two dimensions the 1/4 in the exponent has to be replaced by 1/3. The one-dimensional case requires separate considerations which do not simply lead to an exponent 1/2. An expression for the thermopower in the hopping regime is derived and evaluated.     

A k-distribution-based radiation code and its computational optimization for an atmospheric general circulation model

The gas absorption process scheme in the broadband radiative transfer code “mstrn8”, which is used to calculate atmospheric radiative transfer efficiently in a general circulation model, is improved. Three major improvements are made. The first is an update of the database of line absorption parameters and the continuum absorption model. The second is a change to the definition of the selection rule for gas absorption used to choose which absorption bands to include. The last is an upgrade of the optimization method used to decrease the number of quadrature points used for numerical integration in the correlated k-distribution approach, thereby realizing higher computational efficiency without losing accuracy. The new radiation package termed “mstrnX” computes radiation fluxes and heating rates with errors less than 0.6 W/m² and 0.3 K/day, respectively, through the troposphere and the lower stratosphere for any standard AFGL atmospheres. A serious cold bias problem of an atmospheric general circulation model using the ancestor code “mstrn8” is almost solved by the upgrade to “mstrnX”.     

Graviton dominance in quantum Kaluza-Klein theory

We compute, at the one-loop level, the effective potential for pure gravity in a Kaluza-Klein background geometry which is the direct product of four-dimensional Minkowski spacetime M⁴ with the N-sphere S^N, N odd. The computation is performed in the physical Lorentz-signature spacetime, avoiding the difficulties of “euclideanization”. We find that the contribution of each gravitational degree of freedom to the O(?) part of the effective potential is significantly greater than that of a scalar or spinor in the same background geometry. No stable minima of the effective potential exist for 3 ≤ N ≤ 13. Geometries which may be interpreted as “unstable solutions” are found for all N from 3 through 13. These results, obtained in Lorentz-signature spacetimes, differ from those obtained by “euclideanization”; our “euclideanized” results agree with those obtained by Chodos and Myers using a different regularization scheme.     

Nuclear magnetic resonance study of 31P and 195Pt in the metallic glass system (NixPt1−x)75P25

Measurements of the ³¹P and ¹⁹⁵Pt nuclear magnetic resonance are reported for metallic glasses of the composition (Ni_xPt_1?x)₇₅P₂₅, where x = 0.20, 0.30, 0.40, 0.50, 0.60, 0.64 and 0.68. Spectra were obtained at room temperature, for frequencies from 4 to 16 MHz. The results provide support for certain aspects of the “dense random packing” structure and a transfer of charge from the metalloid to the transition metal atoms.     

Die Anregung von Rb+ in einem Kryptongitter durch die plötzliche Zentralfeldänderung beim β-Zerfall von Kr85

After theβ-decay of Kr⁸⁵ in solid Krypton the Rb⁺-ion, resulting from this decay, is excited in 4p⁵ 5p(J=0)-states with a certain probability. The photon-spectrum, due to dipole-transitions from these excited states, selected with narrow-band-filters and measured in coincidence with the emittedβ-particles, shows narrow bands (“lines”) and broad bands. The “lines” are not shifted with respect to the atomic Rb⁺-lines, whereas each broad band can be interpreted as a component of each “line”, being shifted about 800 cm^?1 to the blue end of the spectrum. The measured lifetime of the excited states is (7.5±0.5) ns in the “lines” and (5±0.5) ns in the bands, the measured excitation-probability is (8±1) · 10^?2 perβ-decay. A calculation of the magnitude of the spectral shift and the excitation-probability with the LCAO-approximation is made under the following assumptions: the “lines” are due to Rb⁺-ions on regular crystal-sites; the shifted bands are caused by Rb⁺-ions, trapped at octaedral interstitial-sites, after being displaced from their original regular crystal-sites by theβ-recoil. A comparison between the experimental and calculated values confirms these assumptions.     

Theoretical investigations of the processes of selective laser interaction with melanin granules in pigmented tissues for laser applications in medicine

Theoretical investigations and the results of computer modeling of optical, thermophysical, thermochemical, and hydrodynamical processes during selective laser interaction with melanoprotein granules (melanosomes) in heterogeneous pigmented tissues (retinal pigment epithelium) are reviewed in this paper. Physico-mathematical models and system of equations are formulated which describe interaction processes for “short” laser pulses of duration t _p < 10^?6 s and for “long” pulses of duration t _p > 10^?6 s. The results of numerical simulation of the processes give the space-time distributions of temperature and degrees of thermodenaturation of the protein molecules inside and around melanosomes and in the volume of irradiated tissue. Energy absorption, heat transfer, and thermochemical processes occurring during the interaction of laser pulses with pigmented spherical and spheroidal granules in heterogeneous tissues are theoretically investigated. The possibility for selective interaction of short laser pulses with pigmented granules, which results in the formation of denaturation microregions inside and near the pigmented granules (granular thermodenaturation) without origination of a continuous macroscopic thermodenaturation lesion in tissue, is discussed. An analytical model of heating of a single spherical and spheroidal granule by a laser pulse is presented. Simple equations for the time dependences of particle temperature are obtained. Vapor generation under the action of a laser pulse on pigmented spherical granules in a water-containing tissue and the formation and dynamics of a vapor blanket are theoretically investigated. The values of pulse energy which give rise to granular and ophthalmoscopically visible thermodenaturation lesions on the retina and to vapor generation are discussed, as well as laser-induced breakdown on granules in pigmented tissues, on the basis of experimental results and numerical and analytical calculations. The comparison and agreement of the numerical results with the experimental data validate the models and techniques developed. The presented results are of essential interest for laser applications in ophthalmology and can be used to investigate laser interaction with heterogeneous tissues in dermatology and various fields of laser medicine.     

Inelastic scattering and nucleon transfer in the system232Th+206Pb near the Coulomb barrier

Nucleon transfer accompanied by Coulomb excitation was studied in the system²⁰⁶Pb+²³²Th atE _Lab=6.4 MeV/u. Particle-particle-gamma coincidence techniques were used to identify excited states of reaction products populated through inelastic scattering and nucleon transfer reactions. The mean excitation energy was measured by means of aγ-ray energy and multiplicity filter consisting of 6 NaI detectors. Large cross sections for one-neutron and two-neutron pick-up from²³²Th are observed. The impact-parameter dependence of the neutron transfer is analyzed in terms of semiclassical barrier penetration models. Using realistic neutron potentials with a diffuse surface, the experimental data are in accordance with the assumption of a “cold” transfer to states near the yrast line.     

Angular distributions of penning electrons

Angular distributions of electrons ejected in thermal collisions of He(2¹ S, 2³ S)-metastables with Ar, Kr, Xe, Hg, CO, N₂ are measured with respect to the vector of relative velocity of the colliding particles. Except for preliminary results on the He(2₁S, 2³ S)-/Ar-system, these are the first such distributions reported. They are found to be strongly anisotropic and asymmetric in some cases, and approximately isotropic in those cases where the interaction potential between the metastable- and the target particle is strong. For the cases of weak interaction potential, the connection between the “internal” angular distribution in the frame fixed to the internuclear axis and the laboratory angular distribution, has been derived. Calculations of laboratory angular distributions involving an assumed “internal” distribution and the kinematics of a hard core collision show good qualitative agreement with the experimental results.     

Atomic tunneling states with dissipation in glasses: temperature-dependent two-level systems

By taking account of the influence of dissipation on atomic tunneling states in glasses, we introduce a density of states of two-level systems which is non-linearly temperature dependent. Based on this model, we can explain the “excess T³” anomaly in the specific heat and the “plateau” in the thermal conductivity of glasses.     

Nuclear transparency in a relativistic quark model

We examine the nuclear transparency for the quasi-elastic (e,e′p) process at large momentum transfers in a relativistic quantum-mechanical model for the internal structure of the proton, using a relativistic harmonic oscillator model. A proton in a nuclear target is struck by the incident electron and then propagates through the residual nucleus suffering from soft interactions with other nucleons. We call the proton “dynamical” when we take into account of internal excitations, and “inert” when we freeze it to the ground state. When the dynamical proton is struck with a hard (large-momentum transfer) interaction, it shrinks, i.e. small-sized configuration dominates the process. It the travels through nuclear medium as a time-dependent mixture of nitrinsic excited states and thus changing its size. Its absorption due to the soft interactions with nuclear medium depends on its transverse-size. Since the nuclear transparency is a measure of the absorption strength, we calculate it in our model for the dynamical case, and compare the results with those for the inert case. The effect of the internal dynamics is observed, which is in accord with the idea of the “color transparency”. We also compare our results with the experimental data in regard of q²-dependence as well as A-dependence, and find that the A-dependence may reveal the color-transparency effect more clearly. Similar effects of the internal dynamics in the other semi-exclusive hard processes are briefly discussed.     

Observation of a maximum roton velocity in superfluid 4He

Using heat pulses, we detect atoms “evaporated” by ballistic rotons at the free liquid surface. A maximum roton velocity of 160 ± 10ms^?1 is observed.     

Directed energy transfer due to orientational broadening of energy levels in photosynthetic pigment solutions

The directed non-radiative energy transfer through monomeric molecules of chlorophyll “a” and pheophytin “a” at high concentrations (c~10^-2 M) in a rigid matrix of polyvinylbutyral has been found by using the nanosecond laser spectrofluorimeter. The phenomenon is caused by orientational broadening of pigment molecular spectra owing to its interaction with a solvent. The observed temporal shift of the luminescence spectrum to the red region in a nanosecond time scale as well as the red shift of the time integrated spectrum at a high concentration of pigment molecules and the monotonic growth of the luminescence lifetime with a shift to the red region of the spectrum served as indications of the directed energy transfer in the sample. The non-radiative energy transfer from monomeric molecules towards aggregates is also directly demonstrated by the deformation of instantaneous luminescence spectra in the long-wavelength range (λ>700 nm). The role and the possibility of the directed energy transfer between molecules with orientationally broadened spectra in the biological systens are discussed.