Precision enhancement in 8 mm interferometry

A Q band interferometer for determining the complex permittivity of materials having dielectric loss factor within 10^–3 to 1, has been developed. The technique involves the use of a computer-assisted digital voltmeter for data acquisition and treatment. The method of computing the dielectric parameters from the deduced VSWR and minima displacement is outlined and precision increase with this type of measurement is discussed. Results for polar solutes in non polar and in polar solvants are presented. Measurements on solids within the temperature range 20–400°C are also discussed in conclusion.     

Freak waves in crossing seas

We consider the modulational instability in crossing seas as a potential mechanism for the formation of freak waves. The problem is discussed in terms of a system of two coupled Nonlinear Schr?edinger equations. The asymptotic validity of such system is discussed. For some specific angles between the two wave trains, the equations reduce to an integrable system. A stability analysis of these equations is discussed. Furthermore, we present an analytical study of the maximum amplification factor for an unstable plane wave solution. Results indicate that angles between 10^∘ and 30^∘ are the most probable for establishing a freak wave sea. We show that the theoretical expectations are consistent with numerical simulations of the Euler equations.     

Short baseline projects

In a search for ν_μ → ν_e oscillations, the LSND experiment has observed an excess of events which are consistent with an oscillation signal. The KARMEN experiment, which is the only ongoing experiment which can test the LSND hypothesis, does not observe an excess, but also does not cover the full LSND allowed region. In this report, the results of these two experiments are discussed, together with the expectations of the MiniBooNE experiment which has been approved to run at FNAL in 2001. MiniBooNE's goal is to definitely verify or disprove the LSND oscillation hypothesis. Finally, the implications of the experimental techniques developed for current short baseline experiments for a future short baseline program, assuming the verification of the LSND signal, is also discussed.     

The thermal model and the transition from baryonic to mesonic freeze-out

The present status of the thermal model is reviewed and the recently discovered sharp peak in the K ⁺/π⁺ ratio is discussed in this framework. It is shown that the rapid change is related to a transition from a baryon-dominated hadronic gas to a meson-dominated one. Further experimental tests to clarify the nature of the transition are discussed. In the thermal model the corresponding maxima in the Ξ/π and Ω/π ratios occur at slightly different beam energies.     

Optimization of the characteristics of an acoustooptic cell based on a tellurium crystal

The problem of designing acoustooptic devices based on tellurium crystals intended for operation in the wavelength range λ > 5 μm is discussed. The optimum geometry of the isotropic acoustooptic interaction in this material is found. The problem of searching for the optimum geometry of a filter that uses anisotropic-acoustooptic interaction is analyzed.     

On the d<Subscript>T</Subscript>=0 toy model in reggeon field theory

Reggeon field theory with zero transverse dimensions is critically reanalyzed in the Hamiltonian formulation for both a sub- and a supercritical pomeron. Different mathematical aspects of the model, starting from the scalar products in the space of quantum states, are discussed. The probabilistic picture is addressed in the absence of pomeron merging. The issue of the large loop approximation is discussed in terms of the Hamiltonian evolution and its relation to the probabilistic picture recalled. A perturbative treatment, based on the PT symmetry of the model, is proposed that may be useful for more realistic models. Finally, we present numerical calculations for the various parameters of the models, α(0)-1=μ and the triple-pomeron coupling constant λ, which help one to understand some mathematical aspects and the different approximation regimes. They show that the triple-pomeron interaction always makes amplitudes fall with rapidity, irrespective of the value of the intercept. The smaller the values of the ratio λ/μ, the higher are the rapidities y at which this fall starts, so that at small values of λ it begins at asymptotically high rapidities (for λ/μ<1/4 the fall is noticeable only at μy>100). No visible singularity is seen for the critical pomeron.     

Modeling of arrayed waveguide grating for wavelength interrogation application

We have proposed and discussed a design of arrayed waveguide grating (AWG) for the application of wavelength interrogation. The spectral responses of a silica-based 16 channel AWG with channel spacing 1.6 nm have been simulated when different receiver waveguide spacing are used. It was found that the 3-dB bandwidth is reduced about 50% as the receiver waveguide spacing increasing from 20 μm to 30 μm. The effect of bandwidth of the spectral response on wavelength resolution of AWG based interrogator has been estimated and discussed.     

Quantum switch based on coupled waveguides

The problem of construction of quantum multiplexer is discussed. A possible construction based on resonance transport properties of quantum waveguides coupled through small windows is considered. Small apertures play double role of “connecting channels" and “resonant elements". Transmission coefficients for the system are determined. The workability of the device as a quantum switch to one of three (or to two of three) channels is discussed. Control parameters for the switch are electron energy and bias voltage. Received 13 August 2000 and Received in final form 19 February 2001     

Relativistic charged particles in the field of an electromagnetic plane wave in a medium

Solutions of the Klein-Gordon and Dirac equation for a charged particle in the field of an electromagnetic plane wave in a medium with a constant refractive index n are discussed. Generally, for n² < 1, spontaneous pair creation from the vacuum, and for n² > 1, energy bands are observed. The interplay of Compton and Cherenkov scattering is discussed. Some doubts are formulated as to the physical relevance of calculating pair creation in a homogeneous electric field as it is usually done.     

Spectrophotometric calibration of a quarterwave plate

A new photometric method for calibrating a quarterwave phase plate is presented and the underlying physical phenomenon is explained. A mica sheet of thickness about 30 μm was found to introduce quarterwave phase retardance at 515 nm. The accuracy of the method and the sources of error are discussed.     

The local adsorption structure of methylthiolate and butylthiolate on Au(1 1 1): A photoemission core-level shift investigation

Measurements of the core-level shifts in Au 4f photoemission spectra from Au(1 1 1) at different coverages of methylthiolate and butylthiolate are reported. Adsorption leads to two components in addition to that from the bulk, one at lower photoelectron binding energy attributed to surface atoms not bonded to thiolate species, while the second component has a higher binding energy and is attributed to Au atoms bonded to the surface thiolate. The relative intensities of these surface components for the saturation coverage (mainly (√3 × √3)R30°) phases are discussed in terms of different local adsorption sites in a well-ordered surface, and favour adsorption of the thiolate species atop Au adatoms. Alternative interpretations that might be consistent with an Au-adatom-dithiolate model are discussed, particularly in the context of the possible influence of reduced coverage associated with a disordered surface. Marked differences from previously-reported results for longer-chain alkylthiolate layers are highlighted.     

The effect of the averaged structural and energetic features on the cohesive energy of nanocrystals

The size dependency of the cohesive energy of nanocrystals is obtained in terms of their averaged structural and energetic properties, which are in direct proportion with their cohesive energies. The significance of the effect of the geometrical shape of nanoparticles on their thermal stability has been discussed. The model has been found to have good prediction for the case of Cu and Al nanoparticles, with sizes in the ranges of 1–22 nm and 2–22 nm, respectively. Defining a new parameter, named as the surface-to-volume energy-contribution ratio, the relative thermal stabilities of different nanoclusters and their different surface-crystalline faces are discussed and compared to the molecular dynamic (MD) simulation results of copper nanoclusters. Finally, based on the size dependency of the cohesive energy, a formula for the size-dependent diffusion coefficient has been presented which includes the structural and energetic effects. Using this formula, the faster-than-expected interdiffusion/alloying of Au_(core)–Ag_(shell) nanoparticles with the core–shell structure, the Au-core diameter of 20 nm and the Ag-shell thickness of 2.91 nm, has been discussed and the calculated diffusion coefficient has been found to be consistent with its corresponding experimental value.     

Spin resonance of irradiated luminescent LiH crystals

ESR line width and strength are reported for crystals exposed at room temperature to the unfiltered light of a SVD-120 mercury arc and to the electrons from a betatron operated at 8–10 MeV. There is a knee in the fall in the intensity and in the increase in the line width at 90 °–120 ° C (g = 2.001 ± ± 0.001) for crystals showing blue fluorescence. The relation of the ESR spectrum to the optical absorption and to the luminescence centers is discussed.We are indebted to M. D. Lemberberg for assistance in recording the optical absorption spectra of LiH.     

New Results of Studying the Lower Ionosphere by the Method of Resonance Scattering of Radio Waves from Artificial Periodic Inhomogeneities

We present the results of studying the lower ionosphere in 2000–2004 at the “Sura” heating facility by the method of resonance scattering of radio waves from artificial periodic inhomogeneities of the ionospheric plasma. Experimental data on a study of the sunset–sunrise phenomena in the ionospheric D region and the possibility of determining the concentrations of atomic oxygen and excited molecular oxygen are discussed. The results of studying the sporadic layers of ionization are presented and the method for a study of ion composition of the E_s layer is discussed. Data of the August 2004 experiments on a study of the influence of heating the ionosphere on the E_s layer and characteristics of artificial periodic inhomogeneities are presented. Prospects for further research are discussed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 9, pp. 757–771, September 2005.     

Double beta decay experiments

The present status of double beta decay experiments is reviewed. The results of the most sensitive experiments are discussed. Proposals for future double beta decay experiments with a sensitivity to the 〈m _ν〉 at the level of (0.01–0.1) eV are considered.     

Ribs effects in acoustic radiation of a gearbox — their modelling in a boundary element method

Boundary element methods are nowadays currently used for acoustic radiation prediction of complex mechanic structures. Many of those structures contain an important account of ribs. The present paper deals with the acoustic influence of ribs and their modelling in a boundary element method. The influence of ribs is theoreticaly discussed and three different physical effects are distinguished : the “vibrating”, the “obstacle” and the ”source” effects. Further the modelling of ribs in boundary element meshes is discussed. An application to an automotive gearbox housing is then proposed. The vibrating behaviour of the structure is calculated with a finite element model, which has been updated thanks to an experimental modal analysis. The boundary element modelling necessity and the acoustic effects of the different ribs of the gearbox housing are studied.     

Search for the neutron EDM by crystal-diffraction method. Test experiment and future progress

Possible future progress of the crystal-diffraction neutron electric dipole moment search experiment is discussed. A storage modification of the experiment is proposed. It is demonstrated that sensitivity of the method can be a few 10⁻²⁷ e cm for the BSO crystal with the size 10×10×10 cm³ and expected luminosity of European Spallation Source (ESS).     

QCW diode-side-pumped Nd:YAG ceramic laser with 247 W output power at 1123 nm

We demonstrate for the first time a diode-side-pumped quasi-continuous-wave (QCW) operation of a 1123 nm Nd:YAG ceramic laser. The single 1123 nm wavelength is acquired through precise coating. With a pump power of 1000 W, an output power of 247 W is obtained, corresponding to an optical–optical conversion efficiency of 24.7%. At the maximal output power, the pulse repetition rate and pulse width are measured to be 1.1 kHz and 180 μs, respectively. The numerical simulations for wavelength selectivity from 1112, 1116 and 1123 nm are discussed in detail.     

Terahertz radiation generation by beating of two spatial-Gaussian lasers

Terahertz radiation generation is proposed based on beating of two spatial-Gaussian lasers in a periodic density plasma, where a transverse component of current is realized that resonantly excites the radiation with efficiency ∼10⁻³. Importance of laser-beam-width, amplitude and periodicity of density structure is discussed for the efficient THz generation.     

Two-vertex loop diagrams in the two-dimensional subspace induced by a superstrong magnetic field: polarization operator and photon and axion decay to neutrinos

The absence of divergences and singularities in effectively two-dimensional field theory induced by a superstrong magnetic field is demonstrated for the example where loop diagrams involving two vector and two pseudovector vertices are calculated. The form of effective low-energy Lagrangians for (γνν) and (aνν) interactions in a superstrong magnetic field is presented. The role of photon and axion decays to neutrinos in the early universe is discussed.