Electrophysical properties of nanocomposites based on poly(p-xylylene) and copper nanoparticles

Poly(p-xylylene)-based nanocomposites containing various amounts of copper have been prepared by vacuum codeposition on a cooled substrate. On the basis of the relationship between the electrical conductivity of composites and the volume content of copper, the percolation threshold has been estimated as 10%. This value coincides with the corresponding parameter derived from the concentration dependence of the electrical resistance temperature coefficient. It has been shown that the conductivity of the nanocomposites increases with the moisture content and their moisture sensitivity decreases with an increase in the content of copper from a concentration of 4%. An analysis of the kinetics of the sensor response measured for various moisture contents has shown that the capacity structure of the samples rearranges during adsorption of water. According to the advanced model, the value of the sensor response is determined by a reduction in the height of the potential barrier between nanoparticles and a change in the fractal characteristics of nanocomposites that results from the adsorption of water molecules.     

Effect of Gd-Mn exchange on phase transitions in GdMn<Subscript>2</Subscript>O<Subscript>5</Subscript> induced by a strong magnetic field

Complex studies of the magnetic, magnetoelectric, and magnetoelastic properties of GdMn₂O₅ single crystals in strong pulsed magnetic fields are carried out in order to obtain additional indirect information on the character of the rare-earth and manganese spin ordering. It is shown that magnetic ordering of Gd³⁺ spins affects the manganese sublattice spin orientation and initiates new magnetic phase transitions. The observed magnetoelectric properties of the GdMn₂O₅ system are interpreted in terms of the theory of phase transitions.     

Lower bounds of the Laplacian graph eigenvalues

In this paper we prove that all positive eigenvalues of the Laplacian of an arbitrary simple graph have some positive lower bounds. For a fixed integer k 1 we call a graph without isolated vertices k-minimal if its kth greatest Laplacian eigenvalue reaches this lower bound. We describe all 1-minimal and 2-minimal graphs and we prove that for every k 3 the path P_k+1 on k + 1 vertices is the unique k-minimal graph.     

Nonlinear parametric effects and dynamic chaos in a nonautonomous oscillating system with a nonlinear capacitance

A mathematical model is constructed of a nonautonomous dynamic system containing a nonlinear capacitance and possessing a four-dimensional phase space. A numerical investigation is performed of branching processes and phenomena accompanying variations in the frequency and amplitude of an external force. The existence of complex dynamic processes that are a combination of a nonlinear force resonance and a parametric resonance is demonstrated. It is found that both a strange chaotic and a strange nonchaotic attractor exist in the phase space. It is shown that, in the case of a single-frequency external force, the latter attractor exhibits the property of roughness. The results of numerical calculations are confirmed by the results of laboratory experiments.     

Two-dimensional gas motion in nuclear-pumped laser cells at low energy deposits into the gas

The distribution of the two-dimensional gas velocity inside ion-irradiated laser cells is considered for low ion energy deposits into the gas. It is shown that, if the energy deposit is smoothly nonuniform, the twodimensional motion has two quasi-one-dimensional components: the longitudinal gas velocity is practically uniform across the cell and depends on the transversely averaged energy deposit, while the transverse velocity component depends on the difference between the local energy deposit and energy deposit averaged over the transverse direction.     

Self-broadening of space-time spectra of few-cycle pulses in dielectric media

The nonparaxial dynamics of spectra of pulses comprising a few cycles of a light field is analyzed in transparent nonlinear media with dispersion. It is shown that the inhomogeneous self-broadening of the time spectrum of a pulse proceeds more effectively into the blue region at all spatial frequencies. A decrease in the energy in the central part of the time spectrum is realized mainly at high spatial frequencies.     

Annihilation of positrons in hydrogen-saturated titanium

The effect of atomic hydrogen on the electronic structure of α-titanium samples is studied using the electron-positron annihilation methods. It is shown that different states of hydrogen atoms are manifested in different ways in the positron lifetime distribution spectrum. The results of theoretical calculations of the first component of the positron lifetime are in accord with the obtained experimental data.     

The contribution of the (t(τ)+N) component to the α-particle wave function from data on the reactions p(α,pp)t and p(α,pn)τ at incident α-particle momentum 5 GeV/c

The 2-meter liquid-hydrogen bubble chamber is exposed to a separated beam of α particles from the ITEP synchrotron. The momentum of the incident ⁴He nuclei, averaged over the fiducial volume of the chamber, is 5 GeV/c (the kinetic energy of initial protons in the nucleus rest frame is T _p =620 MeV). The spectral functions of decays α→tp and α→τn) are extracted in the 4π geometry (the latter is extracted for the first time) from the exclusive reactions αp→tpp and αp→τpn in the spectator momentum region 0<q<0.3 GeV/c. The pole dominance criteria are carefully checked. Extrapolation of the nuclear vertex function to the pole gives a lower bound on the nuclear vertex constant. Our experimental data are compared with the results of other studies and with theoretical calculations. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 2, 69–74 (25 July 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.