Microrelief dependent on the temperature and external field on the free surface of a smectic-<Emphasis Type="Italic">A</Emphasis> liquid crystal

A homeotropically oriented smectic-A film on the surface of a solid substrate with a periodic microrelief is considered. Relationships are derived for describing the dependences of the microrelief-induced deformation of the free surface of the film on the film thickness, the temperature, and the external magnetic (electric) field strength. It is shown that, for a specific choice of the microrelief shape on the substrate surface, a variation in the sample temperature and the external magnetic (electric) field strength makes it possible to control not only the microrelief depth but also the shape of the microrelief formed on the free surface of the smectic-A film.     

Temperature-and field-induced transitions in free-standing films of an antiferroelectric liquid crystal

Thin free-standing films of a compound with the smectic-C _A ^* and smectic-C _α ^* phases were investigated by means of depolarized microscopy and optical reflectivity. In thin films, the smectic phase sequence C _A ^* ?C_α/*?A is replaced by a series of temperature-and field-induced transitions into states with the coplanar orientation of molecular tilt planes. Transitions are accompanied by a change in the direction of the electric polarization with respect to the tilt plane of molecules. The coplanar structure of these states is consistent with the Ising model.     

Dissipation of ripplon flow at the surface of superfluid <Superscript>4</Superscript>He

Within the framework of quantum hydrodynamics of a superfluid helium surface, the momentum relaxation rate caused by the annihilation of two ripplons with phonon creation, inelastic phonon scattering with ripplon annihilation, and in the case of helium films one-particle ripplon scattering from the surface-level inhomogeneities introduced by the substrate roughness (new relaxation mechanism) was obtained for a ripplon gas at T?0.25 K. The contribution from the inelastic phonon scattering is negligible at these temperatures. For a film at T≤0.15 K, one-particle scattering dominates, leading to a temperature dependence of the form K∝T^5/3 for the convective thermal conductance.At higher temperatures, phonon creation with annihilation of two ripplons is the dominant mechanism, giving K∝T^?3. These results are in quantitative agreement with the available experimental data.     

Raman scattering spectroscopy of inclusions of carbon in Al<Subscript>2</Subscript>O<Subscript>3</Subscript> films and its solid solutions with HfO<Subscript>2</Subscript>

We apply Raman scattering spectroscopy to study the nature of carbon inclusions in Al₂O₃ and (HfO₂) _x (Al₂O₃)_{1 ? x} films deposited using volatile complex compounds. Raman spectra of the films under investigation contain D and G vibrational modes, which indicate that carbon clusters of the sp ² configuration tend to form in the films. We estimate the size of clusters from the integrated intensity ratio I _D /I _G and find it to be in the range of 14–20 Å. The content of hydrogen in carbon clusters is calculated from the height of the photoluminescence pedestal and is found to vary from 14 to 30 at % depending on the regime of the film’s synthesis.     

Spin fluctuations in the stacked-triangular antiferromagnet YMnO<Subscript>3</Subscript>

The spectrum of spin fluctuations in the stacked-triangular antiferromagnet YMnO₃ was studied above the Néel temperature using both unpolarized and polarized inelastic neutron scattering. We find an in-plane and an out-of-plane excitation. The in-plane mode has two components just above T _N : a resolution-limited central peak and a Debye-like contribution. The quasi-elastic fluctuations have a line width that increases with q as Dq ^z and the dynamical exponent z = 2.3. The out-of-plane fluctuations have a gap at the magnetic zone center and do not show any appreciable q dependence at small wave vectors.     

Elastic Deuteron Scattering on the <Superscript>12</Superscript>C Nucleus within a Three-Body Model

The formalism developed earlier for elastic pd scattering on the basis of Glauber theory with allowance for a total spin dependence is modified by replacing pN amplitudes by amplitudes for N¹²C scattering and is applied to elastic deuteron scattering on the ¹²C nucleus. The amplitudes for elastic N¹²C scattering are obtained within the optical model. Respective numerical calculations performed at the kinetic deuteron-beam energy of 270 MeV lead to results that agree well with data on the differential cross section for d¹²C scattering into the forward hemisphere, but the calculated spin observable A _y ^d agrees with experimental data only qualitatively.     

Raman spectra of tetrapyrrole photosensitizer chlorin <Emphasis Type="Italic">e</Emphasis><Subscript>6</Subscript> and their interpretation

The resonance and surface enhanced Raman scattering (SERS) spectra of chlorin e 6 trisodium salt in aqueous solutions, solid films, and adsorbed on the silver-coated surface of porous silicon are presented. Using the quantum-mechanical density functional method, the geometric structure and vibrational frequencies of the chlorin e ₆ molecule are calculated and the Raman spectrum of this molecule is interpreted for the first time. The geometry of sorption of chlorin e ₆ on the surface of a nanostructured silver film is considered based on a comparative analysis of the resonance Raman and SERS Raman spectra in the approximation of a short-range mechanism of Raman scattering enhancement.     

Diffuse X-ray scattering from a calomel crystal near the temperature of the structural phase transition

X-ray scattering from a calomel crystal near the temperature of a structural phase transition is analyzed theoretically. It is shown that the diffuse lines of the x-ray diffraction, which correspond to both the X points and Z point of the Brillouin zone, are formed in the high-temperature phase. The latter lines result from the scattering by the beats of fluctuations of two components of the order parameter. Such lines were previously observed experimentally, but the nature of the lines corresponding to the Z point remained unclear. It is shown that the Z line at the point (5, 0, 0) should be an order of magnitude stronger than the observed Z line at the point (4, 3, 0).     

Geometrical effects in nanodimensional epitaxial films of barium strontium titanate

The effect of the thickness of 6- to 950-nm-thick Ba_0.8Sr_0.2TiO₃ films epitaxially grown on (001)MgO on their ferroelectric properties is investigated. Raman scattering and X-ray diffraction data indicate a structural phase transition taking place at a film thickness of ≈70 nm, which changes drastically the lattice parameters of the film. Raman spectra taken of the films confirm that they are in the ferroelectric state and that their symmetry changes in going over a critical thickness, as revealed by a sharp displacement of the peaks corresponding to the A ₁(TO) and E(TO) components of the soft mode. At film thicknesses of <100 nm, the permittivity versus thickness dependence exhibits two peaks at thicknesses of ～18 and ～36 nm. Near the first peak, the dielectric nonlinearity is considerably higher than near the second one.     

Notes on number density fluctuations and the scattering cross section for electromagnetic waves scattered from a thermal nonequilibrium plasma

The scattering cross section and the Doppler spectrum for electromagnetic waves scattered by the electron density fluctuations of a plasma, where the mean kinetic temperature of the electronsT _e may differ from that of the ionsT _i , has been obtained among others byFejer, Buneman, Renau, Camnitz andFlood, andSalpeter. These authors use different methods of approach to calculate the autocovariance of the electron number-density fluctuations (from the mean) and then obtain the scattering cross section. Because of the differing results, the methods, concepts, and derivations of the scattering cross section are carefully examined in this paper. It is shown that the short-time dynamical considerations incorporated in the formulation of the statistical theory of the electron number-density fluctuations of the plasma as used by several authors (for instanceFejer, Buneman, Salpeter,) leads to results of limited validity. In addition, a fundamental error in calculating the electron density fluctuations leads these latter authors to an incorrect scattering cross section. The theory of scattering of electromagnetic waves from a plasma, where the electrons arenot in thermal equilibrium with the ions but statistical equilibrium exists, is developed in a general way. The covariance of the number-density fluctuations from the mean of the charged species of the plasma and the scattering cross sectionσ(q) are obtained. In particular it is shown that for a wavelength λ much greater than the effective Debye lengthd, the backscattering cross section increases and approaches complete incoherent scattering asT _e /T _i increases. This result is explained by noting that in the case of thermal equilibrium, the predicted value of the back-scattering cross section is smaller than that of the backscattering cross section from completely uncorrelated electron density fluctuations because the electrostatic interaction between the charged particles of the plasma, which is a function ofT _e andT _i , introduces a certain amount of organization in otherwise completely uncorrelated electron density fluctuations. When the mean temperature of the electrons increases relative to that of the ions, the organization introduced in the fluctuations diminishes because of the increasing thermal agitation of the electrons relative to that of the ions, and the backscattering process approaches that of incoherent backscattering (Thomson-type scattering). The spectrum function of incoherent scattering of electromagnetic waves from a nonequilibrium plasma is obtained and some cases of current interest are plotted.     

Fluctuations of charged-particle multiplicities over narrow rapidity intervals in <Emphasis Type="Italic">π</Emphasis><Superscript>−</Superscript><Emphasis Type="Italic">A</Emphasis> collisions at 40 GeV/<Emphasis Type="Italic">c</Emphasis>

Maximum fluctuations of charged-particle multiplicities over narrow rapidity intervals are investigated for high-P_⊥ processes in π^?A collisions (where A=H, D, C, Cu, Pb) at 40 GeV/c. The observed fluctuations are studied by the method of factorial moments. The results show that the factorial moments 〈F _i 〉 vary in proportion to a power of the rapidity gap δy. This suggests that there are dynamical fluctuations in the processes under study. The experimental data are compared with theoretical results obtained on the basis of the model of quark-gluon strings by using the FRITIOF-7.02 package.     

Cluster-Type Structure of Amorphous Smooth Hydrocarbon CD<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Films (<Emphasis Type="Italic">x</Emphasis> ~ 0.5) from T-10 Tokamak

Structure of smooth hydrocarbon CD _x films with a high deuterium ratio x ~ 0.5 redeposited from T-10 tokamak D-plasma discharges (NRC Kurchatov Institute, Moscow) has been studied. For the first time, small and wide angle X-ray scattering technique using synchrotron radiation and neutron diffraction have been employed. A fractal structure of CD _x films is found to consist of mass-fractals with rough border, surface fractals (with rough surface), plane scatterers and linear chains forming a branched and highly cross-linked 3D carbon network. The found fractals, including sp² clusters, are of typical size ~1.60 nm. They include a C₁₃ fragment consisting of three interconnected aromatic rings forming a minimal fractal sp² aggregate 9 × C₁₃. These graphene-like sp² clusters are interconnected and form a 3D lattice which can be alternatively interpreted as a highly defective graphene layer with a large concentration of vacancies. The unsaturated chemical bonds are filled with D, H atoms, linear sp² C=C, C=O, and sp³ structural elements like C-C, C-H(D), C-D_2,3, C-O, O-H, COOH, C _x D(H) _y found earlier from the infrared spectra of CD _x films, which are binding linear elements of a carbon network. The amorphous structure of CD _x films has been confirmed by the results of earlier fractal structure modeling, as well as by researches with X-ray photoelectron spectroscopy which allow finding a definite similarity with the electron structure of their model analogues — polymeric a-C:H and a-C:D films with a disordered carbon network consisting of atoms in sp³ + sp² states.     

Correlation between the properties of the deuteron and the low-energy triplet parameters of neutron-proton scattering

The correlation between the asymptotic normalization constant for the deuteron, A_S, and the neutron-proton scattering length for the triplet case, a_t, is investigated. It is found that 99.7% of the asymptotic constant A_S is determined by the scattering length a_t. It is shown that the linear correlation between the quantities A _S ^?2 and 1/a_t provides a good test of correctness of various models of nucleon-nucleon interaction. It is revealed that, for the normalization constant A_S and for the root-mean-square deuteron radius r_d, the results obtained with the experimental value recommended at present for the triplet scattering length a_t are exaggerated with respect to their experimental counterparts. By using the latest experimental data obtained for phase shifts by the group headed by Arndt, it proved to be possible to derive, for the low-energy parameters of scattering (a_t, r_t, P_t) and for the properties of the deuteron (A_S, r_d) results that comply well with experimental data.     

The Effect of Specular Reflectances on the Interaction of an Electromagnetic <Emphasis Type="Italic">E</Emphasis> Wave with a Thin Metal Film Placed between Two Dielectric Media

The interaction of an electromagnetic E wave with a thin metal film placed between two dielectric media is calculated in the case of different specular reflectances q₁ and q₂ for the reflection of electrons from the surface of the thin metal layer, in the case of variations in the values of dielectric permittivities ε₁ and ε₂ of the media, and in the case of different values of angle of incidence θ of the electromagnetic wave. The behavior of reflection coefficient R, transmission coefficient T, and absorption coefficient A in relation to the frequency of the external field is analyzed.     

Lower critical field of a long Josephson <Emphasis Type="Italic">S-I-S</Emphasis> tunnel junction with quantum jumpers in <Emphasis Type="Italic">I</Emphasis> layer

The formulas in which the lower critical field and its mesoscopic structural fluctuations in the energy range of tunnel resonances of a long S-I-S (superconductor-insulator-superconductor) tunnel junction with weak (low impurity concentrations) structural disorder in the I layer at T = 0 are represented as sums over quantum resonant percolation trajectories (quantum jumpers), randomly formed in the disordered I layer [1], are derived.     

Critical magnetic field of the vortex-free state in NbC thin films and prospects for its observation in MgB<Subscript>2</Subscript>

The critical magnetic fields H _c‖ and H _c2 are measured for thin films of the isotropic superconductor NbC. It is revealed that the critical fields exhibit strong anisotropy due to the vortex-free state of the film in a magnetic field aligned parallel to its surface. The H _c‖/H _c2 ratio at 2 K exceeds 6 and increases with increasing temperature. The dependence H _c‖(T) agrees quantitatively with the concepts of microscopic theory on the vortex-free state of a thin film of a clean superconductor in the temperature range below T _c . As the electron mean free path decreases under irradiation of the film with a low dose of He⁺ ions, the critical field H _c‖ remains unchanged near T _c but increases significantly at lower temperatures. The well-known theoretical models are used to estimate the electronic parameters and thicknesses of MgB₂ films for which the specific features associated with the vortex-free state of the two-gap superconductor can manifest themselves in the temperature dependence of the critical magnetic field H _c‖(T).     

Spin observables in <Emphasis Type="Italic">np</Emphasis> elastic scattering in the energy range 200–600 MeV. Complete experiment

A survey of available experimental data on the measurement of spin observables in neutron-proton (np) elastic scattering in the neutron energy range 200–600 MeV is presented. Sixteen spin observables (the polarization of recoil particles P _0n00, the analyzing power A _00n0, the spin correlation parameters A _00nn , A _00ss , A _00sk , and A _00kk , the spin transfer parameters K _0nn0, K _0ss0, and K _0sk0, the depolarization parameters D _0n0n , D _0s0s , and D _0s0k , and the three-spin parameters N _0nkk , N _0skn , N _0ssn , and N _0sns for energies of 200–590 MeV and scattering angles in the center of mass system of 60°–164°) were studied in experiments using polarized neutron beams and polarized proton targets at the Paul Scherrer Institute. The results of these investigations present a complete set of precision data on np elastic scattering which, along with the complete set of data for proton-proton (pp) elastic scattering obtained earlier, provides a basis for unambiguous determination of the amplitudes of the scattering matrix for nucleon-nucleon (NN) elastic scattering for the channel with the isotopic spin I = 0 and makes it possible to describe NN interaction in a model-independent way.     

Messungen des van der Waals-Potentials zwischen Alkaliatomen

Total collision cross sections for the interaction between alkali atoms have been measured using a modulated atomic beam technique. Since the determination of the density in the scattering chamber is the main source of error in absolute scattering measurements, particular attention is given to this problem: The cross section for partnersA andB is measured first withA as beam particles anB as target particles, and then withB as beam particles andA as target particles. The data are used to deduce the long rangevan der Waals (inverse sixth power) potential constants, which can be compared with theoretically calculated values of different authors. The interaction constants resulting from the present measurements are in good agreement with those calculated byFontana, while other calculations give much larger values.     

Study of the heavy-fermion compound CeRu<Subscript>2</Subscript>Si<Subscript>2</Subscript> by the small-angle neutron scattering method

In order to directly observe neutron scattering by heavy fermion quasiparticles at low temperatures, a CeRu₂Si₂ single crystal has been studied by the small-angle neutron scattering method. In the experiment, neutron scattering is observed at T = 0.85 K for momentum transfers q ≤ 0.04 Å^?1, which is treated as the orbital component of magnetic scattering by heavy fermion quasiparticles. It has been found that the application of a magnetic field H = 1 T leads to both an increase in the observed scattering and its anisotropy with respect to the field direction. Moreover, measurements in the magnetic field reveal additional scattering for q > 0.04 Å^?1, which is well described by a Lorentzian and is interpreted as neutron magnetic scattering by spin-density fluctuations with a correlation radius R_c ≈ 30 Å.     

Measurement of total cross sections for <Emphasis Type="Italic">pp</Emphasis> interactions at colliders by new methods

It is proposed to extract the total cross section for proton-proton (pp) interaction from the results obtained by measuring the analyzing power for elastic pp scattering in the region of Coulomb-nuclear interference. Contributions to the cross section are estimated that affect the accuracy in determining σ _T (pp) and which originate from various sources, including single-spin-flip interactions. The applicability of the factor of merit to extracting σ _T (pp) from experimental data is briefly discussed. It is concluded that, under some conditions, measurement of the analyzing power A _N (t) may be a good approach to determining σ _T (pp).