Experimental investigation on finite-amplitude standingwaves:Ⅰ. The properties of second harmonic

I.IntroductionInrecentyears,theresearchworkonnonlinearacousticshasbeendcvelopedrapid1ybe-causethehigh-intensitysoundismoreandmoreimportantincontcmporarytechnology.Aerodynamicnoiseemittedbyrockctorjetengines,noisetestofairframcs,u1trasonicpro-cessing,andothcrs,a1linvo1vefinitc-amplitudesoundwavesand,mostlystandingwaves.Athcoryofonc-dimensiona1finitc-amp1itudestandingwavesinlosslessmediahasbeenproposedbyMAAonthebasisofthcfundamenta1principlesofhydrodynamics['l,inwhichformulasofstcadywavcformsa…     

Elastic “hard” fibers. I.

Elastic “hard” fibers may be prepared from a number of semicrystalline polymers, notably polypropylene, poly-3-methylbutene-1, and polyoxymethylene. These materials show typically a high degree of length recovery from large extensions, a marked, more-or-less recoverable reduction of apparent density on stretching, and the generation of very large amounts of accessible volume and surface area on stretching. Wide- and low-angle X-ray and electron-microscopic observations indicate that the morphological basis for these properties lies in an array of closely packed lamellae of which the normals lie predominantly parallel to the fiber extrusion direction. It is the tilting and splaying apart of the lamellar network which creates the internal volume and surface area on stretching. The long-range elasticity is believed to be distinctly nonrubberlike, as reflected in an insensitivity of mechanical properties to low temperatures, and to arise from bending of the lamellae. This unusual class of materials provides a significant link between macroscopic properties and a particular morphological structure.     

Orthogonality between scales and wavelets in a representation for correlation functions. The lattice dipole gas and (∇φ)4 models

Exact formulas for the correlation functions of lattice scalar field models in Z^d,d3, such as the dipole gas and anharmonic crystal are derived in terms of the effective action generated aftern applications of the block renormalization group transformation. Utilizing the orthogonality between different momentum scales (relations due to the wavelets implicit in the structure of the block renormalization group transformation), the formulas are quite simple, isolate the dominant term, and, in the thermodynamic andn limits, reduce the analysis to local estimates of the effective action. Based on a large-small field analysis, the two-point function is determined and it is shown how to extend the results to general correlations. The results proved here show the usefulness of the orthogonality-of-scales property for the study of correlation functions.     

Stationary state currents in proton scattering: Alternative representation of “emissive” potentials

The “ψ-potentials” related to the projectile current, introduced in the accompanying paper, are exploited in order to give an alternative and arguably more physical representation of the effect in nucleon scattering which has been shown elsewhere to demand an emissive feature when represented by an l-independent potential. We also show how other l-dependent (Majorana) potentials can be represented as ψ-potentials, but in this case the potential may be essentially emissive by virtue of actual emissive regions within the nucleus.     

Control of sound radiation from vibrating structure using active constrained layer: I. Theoretical analysis

lIntroductionRecentadvancesinhighspeedmicroprocessorsandsignalprocessingchipshaveenabledthesuccessfulimplementationofeffectivedigitalactivecontrollersforattenuatingthesoundradiationfromvibratingstructures.Manyapproacheshavebeenproposed,whichrangefromtheuseofsecondaryacousticsourcestothealterationofstructuraldynamicsthroughappliedpointforcesandbendingmoments.However,traditionalactivecontrolschemesdohavetheirlimitations.Forexample,activedampingmaybecomeunstablebecauseoflargecontrolgainsornoncoll…     

Determination of the time correlation functions of vibrational and rotational relaxation from the anti-stokes Raman scattering lines using the method of direct Fourier transformation of the observed profiles I VV * (ω) and I VH * (ω)

It is shown that the difficulties in obtaining the correlation functions of rotational _2R(t) and vibrational _v(t) relaxation associated with the construction of the profile of isotropic scattering from the observed profiles I _VV ^* () and I _VH ^* () with subsequent Fourier transformation of the constructed profile can be eliminated by a Fourier transformation of the profiles I _VV ^* () and I _VH ^* () directly with subsequent normalization of the obtained correlation functions G _VV ^* (t) and G _VH ^* (t) at the time t=0. The correlation functions _2R(t) and _v(t) are obtained from the profiles of the Stokes and anti-Stokes Raman scattering lines. It is established that for lines with comparatively high polarization (p < 0.20) the correlation function _2R(t) and _v(t) obtained by processing the observed profiles of the Stokes and anti-Stokes lines are almost identical.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 8–13, September, 1980.     

What Is “System”: The Information-Theoretic Arguments

The problem of “what is ‘system’?” is in the very foundations of modern quantum mechanics. Here, we point out the interest in this topic in the information-theoretic context. E.g., we point out the possibility to manipulate a pair of mutually non-interacting, non-entangled systems to employ entanglement of the newly defined “(sub)systems” consisting the one and the same composite system. Given the different divisions of a composite system into “subsystems”, the Hamiltonian of the system may generate in general non-equivalent quantum computations. Redefinition of “subsystems” of a composite system may be regarded as a method for avoiding decoherence in the quantum hardware. In principle, all the notions refer to a composite system as simple as the hydrogen atom.     

Fluctuations in diffusion reaction systems. I: Adiabatic elimination of transport modes from a mesoscopicN-body system and the Ω-expansion

We develop a concise method to compute the corrections to the master equation for chemically reacting systems in particle number space that arise if the system is not a well-stirred tank reactor, but the transport occurs by diffusion. Starting from the master equation in theR ^N space of all reactant particle positions, we expand in inverse powers of the diffusion constant and eliminate all transport modes adiabatically. It is found that the overall effect of spatially nonuniform fluctuations cannot be treated as a mere renormalization of the reaction rate constants. From second order on there appear correction terms with a new structure that corresponds formally to additional virtual reaction paths. An intuitive interpretation along this line is impeded, however, by the formal occurrence of negative reaction rate constants in these terms, i.e., the reaction rate may depend on the concentrations of the final products of the virtual reaction rather than on the ingoing products. We also identify Avogadro's constant as the suitable parameter and extend van Kampen's-expansion systematically, to spatially continuous systems. This secondary expansion then serves to interpret the corrections to the rate equation, and the average and autocorrelation of the density in the stationary state. It is seen that the limitsD and do not commute. The relevant length and time scales are discussed.     

Enhanced near-neighbour aggregation of dichloro- and trichloromethane in liquid methane solution from molecular dynamics simulation of radial site–site distribution functions: a simple predictor of solute–solvent compatibility

Molecular dynamics simulations have been performed for a range of equi-site and site–site radial distribution functions for the five-atom halomethane species dichloro-, trichloro-, and tetrachloromethane dissolved in the low-molecular weight hydrocarbons liquefied methane and cyclopropane, with the general aim of using this approach to predict good or bad solvent characteristics. It was found that methane solutions of dichloro- and trichloromethane showed an enhancement of near-neighbour occupancy, the methane solvent seemingly exhibiting a phobic, structure-promoting solvation behaviour towards the two solutes by increasing the number of nearest neighbours above the values that would result from a pure dilution effect caused by the solvent. It was verified that there were no significant regions of solid-like conformations nor remnants of imperfect average homogeneity within the system at the necessarily low temperature (183?K). On the other hand, simulated site–site radial functions with solvents tetrachloromethane and cyclopropane indicate normal solution characteristics towards solutes dichloro- and trichloromethane. The cause of the phobic solvation behaviour of solvent liquid methane towards di- and trichloromethane is not obvious, except that it seemingly involves the presence of hydrogen atoms on the solute species because the site–site centre-of-mass radial distribution functions of tetrachloromethane in liquid methane implied normal solution behaviour.     

Absorption of gamma-ray photons in a vacuum neutron star magnetosphere: II. The formation of “lightnings”

The absorption of a high-energy photon from the external cosmic gamma-ray background in the inner neutron star magnetosphere triggers the generation of a secondary electron-positron plasma and gives rise to a lightning—a lengthening and simultaneously expanding plasma tube. It propagates along magnetic fields lines with a velocity close to the speed of light. The high electron-positron plasma generation rate leads to dynamical screening of the longitudinal electric field that is provided not by charge separation but by electric current growth in the lightning. The lightning radius is comparable to the polar cap radius of a radio pulsar. The number of electron-positron pairs produced in the lightning in its lifetime reaches 10²⁸. The density of the forming plasma is comparable to or even higher than that in the polar cap regions of ordinary pulsars. This suggests that the radio emission from individual lightnings can be observed. Since the formation time of the radio emission is limited by the lightning lifetime, the possible single short radio bursts may be associated with rotating radio transients (RRATs).     

Comment on “Role of the velocity frame of reference in thermodiffusion in liquid mixtures” by M. Eslamian,C.G. Jiang and M.Z. Saghir

We analyze the material transport equations (MTE) derived by Eslamian and co-authors and address the criticism expressed regarding the approach formulated in our previous work. In doing so, we show that the MTE formulated by Eslamian and co-authors are valid only in closed stationary non-isothermal systems in combination with the restrictions on the Onsager coefficients formulated in our work which is criticized, and that for non-stationary systems the approach we took can be used.     

Quasichanneling of ions in crystals. I. Elastic scattering of ions on atomic “chains” and planes

The scattering of quasichanneled particles on atomic chains and planes is studied by computer simulation for the crystals of chemical compounds. It is shown that quasichanneling is the specific regime of ion motion in the lattice. Its main features are: (1) a sharp increase of the backscattering probability; (2) transition of the ions from the quasichanneled component into a random one; (3) high sensitivity to the structure and the composition of the atomic “chain”; (4) dependence on the value and the direction of the atomic displacements.