Chaos-controlling technique for suppressing self-modulation in backward-wave tubes

A method for suppressing self-modulation in backward-wave tubes is proposed. Additional delay is introduced into the feedback circuit, owing to which the output signal amplitude affects the electron beam current that enters into the interaction space. Numerical simulations demonstrate that the operating current in the single-frequency oscillation mode may be increased roughly twofold.     

Recognition of the Finite Simple Groups F 4(2m) by Spectrum

The spectrum of a finite group is the set of its element orders. A finite group G is said to be recognizable by spectrum, if every finite group with the same spectrum as G is isomorphic to G. The purpose of the paper is to prove that for every natural m the finite simple Chevalley group F ₄(2 ^m ) is recognizable by spectrum.     

Parametric Quintic-Spline Approach to the Solution of a System of Fourth-Order Boundary-Value Problems

In this paper, we use parametric quintic splines to derive some consistency relations which are then used to develop a numerical method for computing the solution of a system of fourth-order boundary-value problems associated with obstacle, unilateral, and contact problems. It is known that a class of variational inequalities related to contact problems in elastostatics can be characterized by a sequence of variational inequations, which are solved using some numerical method. Numerical evidence is presented to show the applicability and superiority of the new method over other collocation, finite difference, and spline methods.     

Precise measurement of magnetic moment of short-lived β-emitting nuclei12B ( I π=1+, T 1/2=20.18 ms)

The spin polarized β-emitting nuclei¹²B (I ^π=1⁺,T _1/2=20.18 ms) were produced by the nuclear reaction¹¹B(d, p)¹²B and by the selection technique of the incident deuteron energy and the¹²B recoil angle following the nuclear reaction. The nuclear magnetic moment of the short-lived nuclei¹²B was measured by β-NMR with the β-NMR and β-NQR setup established for the first time in China. The nuclear magnetic moment of¹²B was determined to be μ=0.99993±0.00048 nm org=0.99993±0.00048 after the precise correction of the Knight shift.     

Synthesis and electrical characteristics of polyaniline nanoparticles and their polymeric composite

Monodisperse polyaniline nanoparticles (PAPSSA) were synthesized from an oxidative dispersion polymerization using poly(sodium 4-styrenesulfonate) (PSSA) as both a polymeric stabilizer and a dopant agent due to its acidity. The nanoparticles were being stabilized with two different molecular weight of PSSA. Size effect of PAPSSA particles were examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and dynamic light scattering (DLS). The d.c. electrical conductivity of composite films on the glass substrate was measured by a four-probe method. It was found that the electrical properties of the composite films are affected by the content of nano-sized polyaniline and different molecular weights of stabilizer in the poly(vinyl alcohol) (PVA) matrix.     

An effect of application of chiral aluminium alkoxides and amides as adducts to zirconium catalyzed carbo- and cycloalumination of olefins

This paper is dedicated to a study of properties of the following novel optically active organoaluminium compounds (OACs): (1S,2S)-l,7,7-trimethyl-2-[(dialkylalumina)oxy]-bicyclo[2.2.1]heptanes and (1S)-N-(dialkylalumina)-6,7-dimethoxy-1-methyl-1,2,3,4- tetrahydroisoquinolines. The synthesis of the chiral OACs was carried out in the reaction of either natural camphor or salsolidine with both AlEt₃ and i-Bu₂AlH. The main goal of the research was to investigate the stereodifferentiating activity of the chiral OACs in the olefin carbo- and cycloalumination reactions, catalyzed by Cp₂ZrCl₂.     

CuPc molecules adsorbed on Au(1 1 0)-(1 × 2): growth morphology and evolution of valence band states

We present the growth morphology, the long-range ordering, and the evolution of the valence band electronic states of ultrathin films of copper phthalocyanine (CuPc) deposited on the Au(1 1 0)-(1 × 2) reconstructed surface, as a function of the organic molecule coverage. The low energy electron diffraction patterns present a (5 × 3) reconstruction from the early adsorption stages. High-resolution UV photoelectron spectroscopy data show the disappearance of the Au surface states related to the (1 × 2) reconstruction, and the presence of new electronic features related to the molecule-substrate interaction and to the CuPc molecular states. The CuPc highest occupied molecular orbital gradually emerges in the valence band, while the interface electronic states are quenched, upon increasing the coverage.     

Gamow Vectors in Exactly Solvable Models

Through two examples: the Friedrichs model and a particular case of central potential scattering, we illustrate the way of constructing Gamow vectors.     

1,1,3-Trimethyl-3-phenylindan as a Luminescent Additive to a Plastic Scintillator Based on Poly(methyl Methacrylate)

The luminescence and scintillation properties of poly(methyl methacrylate) containing 1,1,3-trimethyl-3-phenylindan were studied.     

NMR excitation by an electric field as a dynamic manifestation of magnetoelectric and antiferroelectric interactions

The possibility of excitation of NMR signals by an ac electric field in magnetically ordered crystals is discussed. Such signals can be recorded using the time-dependent component of the electric polarization vector. It is assumed that the electric and magnetic characteristics are coupled to each other through magnetoelectric and antiferroelectric interactions. Several types of magnetic structures are analyzed in which these interactions are not forbidden by symmetry. Such structures include two-sublattice single-position ferro-and antiferromagnetic phases in centrosymmetrical crystals, two-sublattice magnetic crystals without a center of symmetry (such as KNiPO₄), and four-sublattice antiferromagnetic crystals with three types of antiferromagnetism vectors (such as Cr₂O₃ and α-Fe₂O₃).