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Vibrational and rotational spectra of liquid para-H2 at temperature T=14–26 K and of solid at T=6–13 K have been obtained using coherent anti-Stokes Raman scattering technique. The vibrational frequency in the liquid increases with temperature by about 2 cm-1 and the shift scales with the square of the sample’s density. An extrapolation of the vibrational frequency in the metastable para-H2 liquid below the freezing point is discussed. The results indicate that the vibron hopping between the molecules is active in the liquid, similar to that previously found in the solid. [ABSTRACT FROM AUTHOR]

In order to reduce line spectrum of radiation noise from submarine, a type of weak radiation double cylindrical ring stiffened shell was proposed. Mechanical impedance theory was used to analyze mechanism of controlling the modal response amplitude of ring-stiffened cylindrical shell. Radial modal mechanical impedance of the ring was derived by introducing the assumption of inner-motion of cylindrical shell's section. Based on the concepts of impedance mismatch and wave conversion, the model of impedance enhancement rib was built and its isolation performance was analyzed. With the consideration of the brace's strong coupling effect, the brace's wave attenuation was designed. Combining the structures of reinforced impedance rib and wave attenuation brace, the structure-borne sound design of double cylindrical shell was done. Further, the characteristics of vibration and sound radiation were numerical analyzed. The results show that the proposed double cylindrical ring stiffened shell could realize radiation noise line spectrum reduction effectively. The vibration mean square velocity, radiation sound power and sound pressure are depressed greatly. The effect of noise depression and vibration reduction is obvious. [ABSTRACT FROM AUTHOR]

Highlights: [•] A new time resolved PA spectroscopy of Br2 molecules using a nanosecond pulses. [•] To understand the coupling mechanism of optical energy into the acoustic energy. [•] Clustering of acoustic frequencies in Br2 molecules for the first time. [•] Decay behavior of Br2 molecules with respect to time. [Copyright &y& Elsevier]

Acoustical spectroscopy at frequencies up to 10 GHz gives the possibility of the investigation of liquid substances, where the relaxation process observed is caused by energy transfer between translational and vibrational degrees of freedom. The compounds presented in this article belong to this group of liquids. The acoustic investigations in the group of benzene derivatives, particularly research of the dependencies of acoustic parameters and the structure of organic liquids, demonstrated some interesting regularities in the group of these compounds in gas and liquid states. In this article, the results of research on five cyclic liquids: bromo-, chloro-, fluoro-, iodo-, and nitrobenzene as well as toluene and aniline are discussed and compared to benzene. The acoustic relaxation observed in all these compounds was found to result from Kneser's processes (vibrational relaxation). Based on investigations reported in this article, as well as by other authors, and taking into account experimental and literature data concerning a great number of compounds, one can draw a conclusion that almost all acoustic relaxation (Kneser-type) processes in liquids can be described using a single relaxation time. It also seems that all vibrational degrees of freedom of the molecule take part in this process. It is known that the appearance of differences in transition probabilities could be caused by additional attraction in interactions of molecules having dipole moments. Halogen derivatives have higher values of dipole moments than benzene. This difference could be responsible for the difference of transition probabilities and changes in the relaxation times. However, benzene derivatives with amino, nitro, and methyl groups and halides show the other type of relaxation. [ABSTRACT FROM AUTHOR]

The method of Rutherford backscattering spectrometry in combination with channeling is used to study the accumulation of structural defects in silicon at room temperature as a result of irradiation with P+ and F+ atomic ions and also with cluster PF ions ( n = 1, ..., 4) with the energy of 2.1 keV/amu and with identical generation rate of primary defects. The conditions for correct comparison of the results of bombardment with atomic and cluster ions composed of atoms of various types are suggested. It is found that the characteristics of accumulation of structural defects in silicon in the case of bombardment with PF cluster ions differ widely from those under irradiation with both atomic ions that are involved in the cluster ion (P+ and F+) and with atomic heavy ions that have atomic mass close to that of the mass of a PF cluster. It is shown that, with irradiation conditions being the same, cluster ions produce much more radiation defects in the surface region than do atomic ions; i.e., a molecular effect is observed. Plausible mechanisms of this phenomenon are considered. [ABSTRACT FROM AUTHOR]

The architecture and operation of a trace hydrogen cyanide (HCN) gas sensor based on quartz-enhanced photoacoustic spectroscopy and using a λ=1.53 μm telecommunication diode laser are described. The influence of humidity content in the analyzed gas on the sensor performance is investigated. A kinetic model describing the vibrational to translational (V–T) energy transfer following the laser excitation of a HCN molecule is developed. Based on this model and the experimental data, the V–T relaxation time of HCN was found to be (1.91±0.07)10-3 s Torr in collisions with N2 molecules and (2.1±0.2)10-6 s Torr in collisions with H2O molecules. The noise-equivalent concentration of HCN in air at normal indoor conditions was determined to be at the 155-ppbv level with a 1-s sensor time constant. [ABSTRACT FROM AUTHOR]

Abstract: The acoustic spectrum of cavities can be identified using integral equation formulations. Because of the transcendental dependence on frequency of the Green function, difficulties arise in calculating acoustic frequencies and modes of vibration when the Kirchhoff–Helmholtz boundary-integral operator is applied. This trouble is circumvented by the present, nonstandard, integral formulation that, by using the fundamental solution of the Laplace operator, allows the identification of acoustic spectra of cavities through solution of a standard eigenvalue problem. This formulation is compared both with that based on the Kirchhoff–Helmholtz operator and with an alternative integral approach introduced in the past that, akin to the one used here, analyzes cavity acoustics in terms of an eigenvalue problem. The numerical investigation deals both with a simple box-shaped cavity and with cavities related to applications of aeronautical interest. [Copyright &y& Elsevier]

Abstract: Ultrasonic studies of the group of halogens of benzene and particularly dependence of acoustic parameters on the structure of organic liquids, demonstrate some interesting regularities in the group of these compounds in gas and liquid states. In this paper results for five cyclic liquids: bromo-, chloro-, fluoro- and jodobenzene are discussed and compared to benzene. Vibrational relaxation was observed in all the compounds. The studies reported here as well as other experimental for great number of compounds support the conclusion that almost all vibrational relaxation processes in liquids can be described using a single relaxation time. It also seems that all vibrational degrees of freedom of the molecule take part in this vibrational process. It seems that differences in transition probabilities between molecules studied could be caused by additional attraction between of molecules having a significant dipole moments. [Copyright &y& Elsevier]