Production of heavy fragments in interactions of high-energy protons with silver

A silver target was exposed to 14, 18 and 23 GeV protons. The values of the cross-sections for production of events with two and three fragments have been determined by the use of a polycarbonate detector. The results obtained show that these events are due to fission as well as to fragmentation and spallation.     

NMR phase noise in bitter magnets

We have studied the temporal instability of a high field resistive Bitter magnet through nuclear magnetic resonance (NMR). This instability leads to transverse spin decoherence in repeated and accumulated NMR experiments as is normally performed during signal averaging. We demonstrate this effect via Hahn echo and Carr--Purcell--Meiboom--Gill (CPMG) transverse relaxation experiments in a 23-T resistive magnet. Quantitative analysis was found to be consistent with separate measurements of the magnetic field frequency fluctuation spectrum, as well as with independent NMR experiments performed in a magnetic field with a controlled instability. Finally, the CPMG sequence with short pulse delays is shown to be successful in recovering the intrinsic spin--spin relaxation even in the presence of magnetic field temporal instability.     

Effect of atmospheric pressure pulsed discharge spatial inhomogeneity on Ar I and H I lines: Electron number density study

The spatial inhomogeneity of pulsed atmospheric pressure discharge in argon is investigated using the electron number density N_e diagnostics procedure applied to asymmetrically broadened Ar I lines. A dedicated fitting procedure is used for describing Ar I 703.0 nm line shape recorded from argon gas discharge and H I (at 486.13 and 656.28 nm) lines recorded from Ar-H₂ gas mixture discharge. The results revealed the change in N_e in both axial and radial directions. The additional Ar I lines at 614.5, 710.7, 731.2, and 731.6 nm, recorded from integral spatial radiation, are analysed as well to confirm the results from the plasma column region. The possibility of using AlO (B²∑⁺–X²∑⁺) and CN (B²∑⁺–X²∑⁺) molecular bands for gas temperature T_g measurements in this type of gas discharge source is demonstrated and T_g used as an input parameter for the N_e diagnostics procedure. For the proper identification of molecular band spectral lines, the Fortrat parabolas are constructed. The results obtained from Ar I 703.0 nm line indicate three different N_e values, with N_e1 ≈ 0.6 × 10¹⁶ cm⁻³, N_e2 ≈ 3.6 × 10¹⁶ cm⁻³, and N_e3 ≈ 19 × 10¹⁶ cm⁻³ measured from the plasma column. These N_e values increase in the cathode and anode region.     

Nonordered quantum logic and its YES-NO representation

It is shown that an orthomodular lattice is an ortholattice in which aunique operation of bi-implication corresponds to the equality relation and that the ordering relation in the binary formulation of quantum logic as well as the operation of implication (conditional) in quantum logic are completely irrelevant for their axiomatization. The soundness and completeness theorems for the corresponding algebraic unified quantum logic are proved. A proper semantics, i.e., a representation of quantum logic, is given by means of a new YES-NO relation which might enable a proof of the finite model property and the decidability of quantum logic. A statistical YES-NO physical interpretation of the quantum logical propositions is provided.     

Adsorption on stepped substrates

An analysis is given of the behavior of an interface above a stepped substrate in the presence of an external pinning potential for the lattice solid-on-solid (SOS) interface model in 2D. Step-free energy including step-step interaction free energy is calculated, for large step separation. It is found it vanishes at temperatures lower thanT _w (wetting transition temperature), which is different from the case having only one step on a substrate where, as it is well known, step-free energy vanishes at the wetting transition.     

Interplay between phase defects and spin polarization in the specific heat of the spin-density-wave compound (TMTTF)2Br in a magnetic field

Equilibrium heat relaxation experiments provide evidence that the ground state of the commensurate spin-density-wave compound (TMTTF)2Br after the application of a sufficient magnetic field is different from the conventional ground state. The experiments are interpreted on the basis of the local model of strong pinning as the deconfinement of soliton-antisoliton pairs triggered by the Zeeman coupling to spin degrees of freedom, resulting in a magnetic-field-induced density-wave glass for the spin carrying the phase configuration.     

Post-processing synchronization and characterization of generated signals by a repetitive Marx generator

In the present paper, a new approach was developed for solving the problem of time synchronization of a set of signals obtained by different measurement techniques without a common trigger. The recorded signals were the result of sparks and bursts generated by a repetitive Marx generator. A thermal imaging camera, a high speed camera and an audio recorder were used to obtain the necessary data for synchronization and characterization. Moreover, a piezoelectric sensor was applied for shock waves characterization during the early stages of bursts. In the first place, different data with evident time shifts were acquired. Then, A set of simple operations such as maximum selection and localization, threshold comparison, Euclidean distance calculation and minimization were employed for signal analysis and pattern matching to ensure a good data synchronization, which allowed a detailed analysis of the phenomenon in the end.     

Discrete and selective absorption in crystalline molecular nanofilms

Recent research in nano-optical engineering and in nanomedicine as well, seeks for methods of construction of various types of nano-markers, nano-carriers, and ways to deliver drugs to the exactly determined regions of body. In this process it is important to find methods of recognition of certain types of molecules. It is obvious that optical recognition would be the easiest and the most effective way to do it. Our research presents a model of a molecular ultrathin crystalline film and generated exciton system inside it and corresponding methodology of analysis of their optical characteristics. Properties of these spatially very restricted structures are very sensitive to their surrounding surfaces. Using the two-time Green’s functions adapted for crystalline structures with symmetry breaking, and graphical-numerical software, we have calculated the energy spectra and possible exciton states. We have shown that the appearance and the presence of localized states on the surfaces and in the boundary layers of the film depend on the thickness of the film and the film surroundings, presented through the perturbation of parameters on surfaces. Optical properties in these structures demonstrate discrete and very selective resonant absorption spectra, depending on the perturbation on their surfaces.     

Optimization of cubic GaN/AlGaN quantum cascade structures for negative refraction in the THz spectral range

In this work we theoretically investigate a possibility to use cubic nitride based multi-layer periodic nanostructure as a semiconductor metamaterial. The structure design is based on an active region of a quantum cascade laser optimized to achieve optical gain in the Terahertz (THz) spectral range. In particular, we test the GaN/AlGaN quantum well configurations, which should exhibit important advantages compared to GaAs-based structures, namely room temperature operation without the assistance of magnetic field and lower doping densities. Our numerical rate-equations model is solved self-consistently and it takes into account electron-longitudinal optical phonon scattering between all the relevant states among the adjacent periods of the structure. A global optimization routine, specifically genetic algorithm is then used to generate new gain-optimized structures. This work confirms the advantages of cubic GaN designs over GaAs ones, namely feasibility of negative refraction at room temperature without the assistance of magnetic field while keeping the doping densities of the same order of magnitude.