Interior noise field of a viscoelastic cylindrical shell excited by TBL pressure fluctuations:Ⅰ.Production mechanisms of the noise

I.IntroductionThetowedlinearraywithdeeplay6rofseabedandlongrangedetectioncapabilitybecauseofitslonglength,lowfrequencyandbeingfarawayfromthemothershipapplieswidelyonmarineseismicexploringandlong-rangetargetdetection.Thenoisebackgroundofthetowedlinearrayismoredifferentfromothersonar.Itsarrayismoulltedinaflexiblelongviscoelasticcylindricalshe1lwitharadiusofafewcentimeters.Analysisshowsthatflownoiseisthemajorsourceofthetowedlinearraywhentowedspeedishigh[1].Flownoiseisdefinedasallnoiseinducedbyfl…     

Measurements and analyses of infrasound noise field in the atmosphere

Methods for measuring and analyzing the infrasound noise field inthe atmosphere have been expounded.A set of space correlation radii of noisecorresponding to wind speed 4m/s has been obtained,which can be takenas the tentative basis for an acoustical array design.At the same time,thewind speed-sound pressure relation curves have been measured and calcu-lated,and the anti-jamming ability of the array receiving infrasonic signals isobtained.     

Quantum noise in the mirror–field system: A field theoretic approach

We revisit the quantum noise problem in the mirror–field system by a field-theoretic approach. Here a perfectly reflecting mirror is illuminated by a single-mode coherent state of the massless scalar field. The associated radiation pressure is described by a surface integral of the stress-tensor of the field. The read-out field is measured by a monopole detector, from which the effective distance between the detector and mirror can be obtained. In the slow-motion limit of the mirror, this field-theoretic approach allows to identify various sources of quantum noise that all in all leads to uncertainty of the read-out measurement. In addition to well-known sources from shot noise and radiation pressure fluctuations, a new source of noise is found from field fluctuations modified by the mirror’s displacement. Correlation between different sources of noise can be established in the read-out measurement as the consequence of interference between the incident field and the field reflected off the mirror. In the case of negative correlation, we found that the uncertainty can be lowered than the value predicted by the standard quantum limit. Since the particle-number approach is often used in quantum optics, we compared results obtained by both approaches and examine its validity. We also derive a Langevin equation that describes the stochastic dynamics of the mirror. The underlying fluctuation–dissipation relation is briefly mentioned. Finally we discuss the backreaction induced by the radiation pressure. It will alter the mean displacement of the mirror, but we argue this backreaction can be ignored for a slowly moving mirror.     

Spatial coherences of the sound pressure and the particle velocity in underwater ambient noise

The spatial coherences were investigated between the sound pressure and the three orthogonal components of the particle velocity in underwater ambient noise. Based on the ray theory, integral expression was derived for the spatial coherence matrix of the sound pressure and the particle velocity in a stratified ocean with dipole noise sources homogenously distributed on the surface. The integrand includes a multiplying factor of the vertical directivity of the noise intensity, and the layered ocean environment affects the spatial coherences via this directivity factor. For a shallow water environment and a semi-infinite homogenous medium, the coherence calculation results were given. It was showed that the sound speed profile and the sea bottom could not be neglected in determining the spatial coherences of the ambient noise vector field.     

Interior noise field of a viscoelastic cylindrical shell excited by TBL pressure fluctuations:Ⅱ. finite hydrophone and array

lIntroductionFlownoiseisacriticalfactoraffectingthepropertiesofthetowedlinearraysonar.ThatistheinteriornoiseproducedbytheTBLpressurefluctuationsexertedonouterwallofthetowedlinearray.Thisisaproblemaboutinteractionofflow,structureandsound.ThesolutionofinteriornoisefieldbyapplyingW-F(wavenumberfrequency)spectrumanalysishavebeenobtainedinRef.Ill.TheW-Fspectrumtransferfunctionofthewholesystemincludingstructureandfluidloadingisderivedatfirst.Theintegralexpressionofthecrossspectrumofinteriornois…     

On the concept of “nonlocalization” associated with the gravitational field

The concept of nonlocalization associated with the gravitational field, which is carried by the internal variable () annexed to each point, is considered in connection with the geometrical theory of gauge fields. Two concrete examples of nonlocalization are proposed by taking as a vector and a spinor, respectively.     

Influence of the “intrinsic” effect of the field on the thermally stimulated conductivity of ferroelectrics-semiconductors

Based on investigations of thermally stimulated conduction (TSC) in Sn₂P₂S₆ single crystals and the effect of the surrounding gas on the character of the thermally stimulated current, it is concluded that the degree of unipolarity of ferroelectrics-semiconductors and the screening conditions play a significant and sometimes determining role in the filling of local levels, manifested in the TSC curves. By combining the standard method of TSC with the method of TSC in the photoelectret regime based on the intrinsic effect of the field, it is possible to distinguish the surface and volume attachment levels. The greatest filling of surface levels at the ends of domains is obtained from TSC curves measured in a vacuum on single-domain samples with the pulling field oriented in the same direction as the internal field and the greatest filling of volume levels is obtained with minimum unipolarity of the crystal and the creation of depleted layers on its free surface by adsorption.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 86–90, March, 1990.     

Symmetry breaking and restoring under high pressure: the amazing behaviour of the “simple” alkali metals

We argue that an ionic lattice surrounded by a Fermi liquid changes phase several times under pressure, oscillating between the symmetric phase and a low-symmetry dimerized structure, as a consequence of Friedel oscillations in the pair potential. Phase oscillations explain the tendency towards dimerization which has been recently reported for the light alkali metals under high pressure. Moreover, a restoring of the symmetric phase is predicted for such elements at an even higher density. Received 17 January 2003 Published online 11 April 2003 RID="a" ID="a"e-mail: giuseppe.angilella@ct.infn.it     

Destruction of the long-range antiferromagnetic order by defects of the “random local field” type

The behavior of diluted antiferromagnets in an external magnetic field has been considered. It has been shown that, because the “force” of induced defects of the “random local field” type depends on the magnetic induction, the destruction of the long-range antiferromagnetic order by these defects in space of dimension d ≥ 2 is impossible.     

Prediction of line-spectrum noise induced by high speed vehicle counter-rotation propellers in water

llntroductionPropu1sionnoise,flownoise,andmachinerynoisearethreemainpartsofunderwatervehiclesnoise.TheconiributionofthethreepartstoshipnoiseleveldependonnoisefrequencyIthasbeenpointedoutbymallyexperimelltsl1-3]thatpropulsionnoiseandshellvibrationnoiseinducedbypropulsionsetarethemainsourceofthehighspeedvehicleradiatednoise,andthevehicleselfnoiseisdecidedbytheflownoiseinducedbypulsatingsource[4'5lonthesurfaceofthevehicle.Uptonow,counter-rotationpropellerisamainkindofpropulsionaspectforhighspeedv…     

The determination of the parameters of “spherical” motion in a kerr field

The problem of the existence of class M geodesic motions on the surface r=const, all of whose mechanical parameters in the specified Kerr field are determined only from stability conditions, is posed and investigated. A system of equations which determines this class is derived and solved. It is shown that in the general case this motion does not cover the entire surface r=const and is restricted by the condition ₀ }- ₀. Simple algebraic expressions are found for all the parameters of these configurations-energy, momentum, radius, and the angle ₀-as functions of the specific angular momentuma of the Kerr field. It is shown that these motions can exist only in Kerr fields with a value of the parametera larger or equal to r_g/2. In a Kerr field with a fixed value ofa there exist only two configurations with the indicated properties. In conclusion, the properties of the M-solutions associated with the appearance of configurations with negative energies and negativeness of g₀₀ within the limits of some configurations and values ofa larger than r_g/2 are discussed. It is noted that the negative values of the energy occur only in those configurations within whose limits g₀₀ < 0. It is also pointed out that the Kerr field is free of pathological properties associated with the breakdown of causality whena > r_g/2 if one does not made the assumption, unnecessary within the framework of the problem under discussion, that the sources of the Kerr field are in the region r=0.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 17–25, May, 1979.The authors express their gratitude to A. A. Grib for useful discussions.     

“Switching” of the nanodomain state of the frustrated ferromagnet-antiferromagnet system by an external magnetic field

The phenomenon of ??switching?? of the domain walls generated by frustrations in a two-layer ferromagnet-antiferromagnet nanostructure has been studied using numerical simulation methods. This phenomenon manifests itself in the fact that, as the magnetic field increases, the ferromagnetic layer divided into nanodomains by domain walls perpendicular to the layer plane becomes single-domain, and the antiferromagnetic layer that is uniform in weak fields is divided into 180° domains by the domain walls perpendicular to the layer. The structures of these domain walls have been calculated in various magnetic fields.     

A review of: “Comparative crystal chemistry: temperature,pressure, composition and the variation of crystal structure”

By R. M. Hazen and L. W. Finger. Wiley (1982). Price: £19.50 (U.K.)     

Is the electromagnetic field an invariant superposition of the 42 states of a basic field?

It is shown that an invariant superposition of 42 symmetry-related states of a basic field can account for the experimental value of the fine-structure constant. Such a theory yields the formulac/e ²=N(N–1)/4=137.0324, withN=42 the order of the invariance group.     

On a class of stable “spherical” configurations in the Kerr field

It is well known that among the plane (=const) circular (r=const) stable motions of a test particle in the Schwarzschild field there is one which has a smallest value of the radius. A similar (lower) bound for equatorial circular orbits exists in the kerr field (for =/2, a=r_g/2–, 0 < < r_g) [2, 3]. In the present paper, a study is made of the possibility of obtaining similar results in the case of spherical motion (r = const, const) in the Kerr field with no a priori bound on the value of the parametera.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 3–6, August, 1980.     

Sound field characteristics of underground railway stations – Effect of interior materials and noise source positions

In the case of most underground railway stations, no acoustical solutions are used to reduce train noise. Because the reflecting features of train noise in an underground station are not known, appropriate methods for controlling these features have yet to be established. The aim of this study was to clarify the sound field characteristics of underground stations by putting a sound source and receiver on the railway track and platform, respectively. The impulse responses for two vacant underground stations were measured to clarify the effects of the interior materials of the station (Comparison I), and the sound source was put in each station and tunnel to clarify the effect of the noise source positions (Comparison II). Results showed that the sound fields were similar between the stations whose lateral walls were covered with either metallic or fire-resistant wooden panels (Comparison I), and that the sound field for the sound sources near or in the tunnel presented a higher strength (G) by 5.1 dB and longer reverberation time (EDT) by 0.7 s compared to the sound source in the station (Comparison II). The sound sources in the tunnel presented strong and long reverberations at around 500 Hz due to the convergence effect of the tunnel. Therefore, this study proposes a platform screen with doors to limit noise transmission into the platform.     

Energy-momentum tensor of a spinor field in the “mixed universe” cosmological model

The energy-momentum tensor of a massless spinor field is constructed and studied based on the previously proposed interpretation of quantum effects of such a field in the anisotropic metric of Bianci type IX. The characteristic properties of the energy-momentum tensor in the mixed universe model are discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 45–50, September, 1988.I am grateful to A. A. Grib and A. V. Nesteruk for their interest in this work and for useful discussions.     

Measurement of sensitivity of transducer in the field of NDT by the reciprocity technique

The sensitivity of a transducer should be an important characteristic inthe field of NDT.But so far,no method for this measurement of the sensitivity of atransducer applied to the ultrasonic flaw detection is available.In this paper thetransducer is regarded as a plane source and the reciprocity parameter under thecondition of the far field is derived.We have calibrated the sensitivity of ultrasonictransducers with the reciprocity technique in the solid sample.The experimentsshow and confirm that the transmitting and receiving sensitivities of the transducerapplied to NDT can be exactly measured.The precision of the measurement is with-in ± 1dB under a certain coupling condition.