Behavior Of Acoustic Modes Research Articles

A comparative study of thermal stability of TNT, RDX, CL20 and ANTA explosives using UV 266 nm-time resolved photoacoustic pyrolysis technique.

The paper reports the potential use of UV based pulsed photoacoustic spectroscopy to study the thermal stability of some well-known premier explosives such as TNT, RDX, CL20, and ANTA between 30 and 350 °C range. The thermal PA spectra of samples were recorded using fourth harmonic wavelength i.e. 266 nm of pulse duration 7 ns and repetition rate 10 Hz obtained from Q-switched Nd: YAG laser system. Under the influence of UV radiation, the explosive molecules in vapor phase follow the photodissociation process and converted into their byproducts such as NO, NO2 and N2O etc. due to π* ← n transitions, which are responsible for the generation resultant PA signal at 266 nm wavelength. The results obtained from PA spectra as a function of temperature are cross verified with Thermo gravimetric-differential thermal analysis (TG-DTA) to ascertain the thermal stability of these samples. The comparative PA spectra of samples were analyzed and shown the behavior of acoustic modes with respect to incident laser energy, and data acquisition time. Finally, the thermal quality factor "Q" is measured to test the stability of reported explosives.

Comparative Study of Ultraviolet Laser-Based Time-Resolved Photoacoustic Fingerprint Spectra and Thermal Decomposition Mechanisms of Energetic 1,2,3-1H-Triazole Derivatives Under Controlled Pyrolysis.

We report the comparative study of photoacoustic (PA) fingerprint spectra, thermal decomposition, and stability mechanism of some phenyl and bis series energetic compounds named 1-(2-methoxy,-3,5-dinitrophenyl)-1H-1,2,3-triazole ( S5), 1-(3-methoxy, 2, 6 dinitrophenyl) 1H-1, 2, 3 triazole ( S10), 1-(4-nitrophenyl)-1H-1,2,3-triazole ( S8), and 2,6-bis ((4-(nitromethyl)-1H-1,2,3-triazol-1-yl)methyl) pyridine ( S9). Fourth harmonic wavelength, i.e., 266 nm of pulse duration 7 ns and 10 Hz repetition rate obtained from Q-switched Nd: YAG laser, was used to record the thermal PA spectra of these compounds under controlled pyrolysis condition in the range of 30-350 ℃. The PA fingerprint spectra are produced due to entire molecule vapor along with principal functional byproduct NO2 molecule. NO2 molecule is a major gas released during thermal decomposition due to weakest nature of C-NO2 bond. Further, NO2 molecules are involved in photodissociation process due to π*← n transition and converted into NO molecules inside the PA cell due to excitation by 266 nm wavelength. The combined results of PA and gas chromatography-mass spectrometry (GC-MS) spectra along with thermo gravimetric-differential thermal analysis (TG-DTA) data confirm the thermal decomposition mechanism process that can be completed in multiple steps. In addition, GC-MS spectra also confirm the release of NO and NO2 molecules. The effect of incident laser energy and data acquisition time has been carried out for understanding the behavior of acoustic modes. Finally, the thermal quality factor "Q" is measured to test the stability of compounds.

Modernized active spectroscopic diagnostics (CXRS) of the T-10 tokamak

This work presents the results of modernization of the CXRS (charge exchange recombination spectroscopy) diagnostics [1] at the T-10 tokamak. The relevance of this work is due to the importance of measurements of the ion temperature and nuclei density of the working gas and impurities for analysis of transport processes in the plasma ion component. Measurements of radial profiles of the ion temperature are extremely important for investigating the geodesic acoustic mode behavior which is conducted at the T-10 [2]. The modernized scheme of CXRS measurements, as well as the design and operational features of the spectrometer created for the new diagnostics, is described. Principles of data recording and further processing are considered in detail; attention is given to the problem of calibration of the whole complex of equipment. The performed changes in diagnostics allow the measurements to be taken simultaneously in three spectral intervals: in the region of the beam line Hα, the CXRS line of carbon ion C5+, and the CXRS line of one of the hydrogen-like ions: He1+, Li2+, N6+, O7+ or Ne9+. This makes it possible to measure the density profiles of two plasma impurities simultaneously, as well as the ion temperature from CXRS lines of different elements. The modernized diagnostics significantly broadens the possibilities of studying the physics of transport processes and quasi-coherent modes of plasma oscillations at the T-10.

Investigation of thermal stability and fingerprint spectra of energetic 1,2,3-triazole using pulsed photoacoustic pyrolysis technique

This paper reports on a comparative study of UV and visible radiation-based pulsed photoacoustic (PA) pyrolysis technique examining thermal stability and acoustic fingerprint spectra of a newly synthesized high-energy molecule named 1-(2,4-dinitrobenzyl)-4-nitro-1H-1,2,3-triazole (S6). The thermal PA spectra of S6 were recorded in temperatures ranging between 30 and 350 °C using second and fourth harmonic wavelengths (i.e., 532 and 266 nm), obtained from Q-switched Nd:YAG laser pulses of duration 7 ns at 10 Hz repetition rate. The PA results are further compared with TG–DTA data to understand the release mechanism of NO2 along with other gaseous by-products. The difference in thermal PA spectra of S6 which follows two different mechanisms, such as vibronic transition V–V and V–T relaxation in NO2 functional group, while electronic π* ← n transition in the entire molecule, is due to selection of visible and UV wavelengths. In addition, the effect of data acquisition time and incident laser energy has been examined in order to understand the behavior of acoustic modes of a PA cavity at the desired vapor temperature. The stability of the compound is also evaluated on the basis of thermal quality factor (Q), of PA cavity.

Inelastic X-ray scattering in metallic glasses

The behavior of acoustic modes in solids can yield information on the glass dynamics at different length and frequency scales. Inelastic X-ray scattering (IXS) using Synchrotron radiation allows us to obtain detailed information on the sound speed behavior at different length scales as well as approaching the macroscopic limit. This gives an insight to the microscopic mechanisms responsible for the mechanical properties in the THz frequency domain. IXS also provides a method to investigate the fragility of glass-forming liquids via the non-ergodicity factor of the corresponding glasses. Moreover, some questions arise about how phenomena such as the polyamorphism, observed, e.g. in Ce55Al44 upon application of pressure, affect the mechanical properties of a metallic glass at a microscopic level. In this article we reveal a change in the high frequency response at the mesoscopic length scale with respect to the ultrasounds limit in metallic glasses. We will also review further applications of IXS on Pd and Ce-based metallic glasses to determine elastic constants, changes in sound speed due to polyamorphism and to investigate their fragility.

Acoustic Mode Behavior in Ferroelectric Phase Transition of Li Doped ZnO Semiconductor and its Photoinduced Effect

Acoustic phonon behavior and photoexcited effect in Li-doped ZnO ceramics were investigated at around the ferroelectric phase transition point Tc = 350 K by Brillouin scattering using a Sandercock-type tandem Fabry-Perot interferometer. The temperature dependence of Brillouin scattering spectra was obtained from 300 K to 500 K through Tc. A bunch of longitudinal-acoustic (LA) phonons did not show any anomaly at around Tc accompanied to the ferroelectric phase transition, although the LA mode is coupled to the spontaneous polarization in the ferroelectric phase with point group of 6 mm. The result indicates that the mechanism of the ferroelectric phase transition is not an order-disorder type related to size mismatch of the doped Li cation. No photoinduced effect was observed in the LA phonon bunch around Tc under ultraviolet (UV) excitation with energies higher than the band gap energy, although the intensity of base line in Brillouin scattering spectrum increased under UV. The component of base line includes an emission spectrum and /or a central peak component, which might be related to an electronic ferroelectricity.

Vortex magnetodynamics: Ferromagnetic resonance in permalloy dot arrays

Permalloy dot arrays (square lattices of 100, 200, 500, and 1000 nm dots, 40 nm thick) have been fabricated using e-beam lithography. Hysteresis loops show vortex states at remanence in all samples. Variable frequency ferromagnetic resonance was used to probe the dynamics of both vortex and single domain states. The uniform resonance mode is present at fields above the vortex annihilation when field sweeping up and vortex nucleation field when field sweeping down. In the vortex state multiple resonances are observed in the 500 and 1000 nm samples, but interestingly, not in the 100 and 200 nm. In the frequency/field dispersion curve, these vortex resonances exhibit optical mode characteristics, whereas the uniform mode exhibits the expected acoustic mode behavior. Resonance modes corresponding to the annihilation and creation field (transition from vortex to single domain or verse versa) are also observed and discussed.

On the convergence behavior of the exterior acoustic modes of structures

The use of a modal-style approach for the analysis of the exterior radiation characteristics of structures has recently received increasing attention. This approach generally seeks to find a set of orthogonal functions, or acoustic modes, that diagonalize a radiation operator. These acoustic modes are found through an eigenfunction or singular value decomposition analysis of the radiation operator. The eigenvalue or singular value associated with a given mode is directly proportional to the radiation efficiency of that mode. One advantage of this acoustic modal approach is that the total radiated power can be found by simply summing the contributions from individual acoustic modes, since they are completely decoupled. It is shown that the accuracy of the acoustic modal representation depends on the number of degrees of freedom permitted in the derivation of the radiation operator. The most efficient acoustic modes are least sensitive to increasing degrees of freedom. The least efficient acoustic modes are most sensitive to changes in degrees of freedom. Further, it is shown that this convergence behavior of the acoustic modes can be related to the familiar convergence behavior of structural modes, through the Rayleigh quotient.

Thermodynamics and lattice vibrations of minerals: 5. Applications to phase equilibria, isotopic fractionation, and high‐pressure thermodynamic properties

In previous papers in this series, a model that uses available elastic, structural, and spectroscopic data on minerals has been used to predict the thermodynamic functions Cv (heat capacity), S (entropy), E (internal energy), and F (Helmholtz free energy). In this paper, four applications to problems of current geochemical and geophysical interest are presented: (1) interpretation of complex trends of calorimetric data; (2) calculation of phase equilibria; (3) calculation of oxygen‐isotopic fractionation factors; and (4) estimation of the effect of pressure on thermodynamic functions. The model demonstrates that trends in high‐temperature thermodynamic properties of silicates are determined by the position and relative numbers of high‐frequency modes, generally antisymmetric (Si, Al)‐O stretching modes. The position of these modes varies systematically with degree of polymerization of tetrahedra, and therefore high‐temperature calorimetric behavior is relatively systematic as a function of crystal structure and mineral composition. Trends at low frequency are much more complex because the low‐frequency optic modes that most strongly influence the low‐temperature thermodynamic functions depend in a complex way on the size, coordination, and mass of cations and various polyhedra in the minerals. The heat capacity curves of kyanite, andalusite, and sillimanite and of quartz, coesite, and stishovite show crossovers that cannot be explained by Debye theory, which accounts only for acoustic mode behavior, but can be explained by the model spectra proposed because proper account is taken of the changing low‐ and high‐frequency optic modes upon polymorphic transformations. The proposed model is sufficiently accurate that phase equilibrium problems can be addressed: the quartz‐coesite‐stishovite equilibrium curves, the kyanite‐andalusite‐sillimanite triple point, and the breakdown of albite to jadeite‐plus‐quartz are cited as specific examples. For each example, predicted slopes of equilibrium curves agree moderately well to excellently with slopes determined experimentally. The calculated slopes are sensitive to spectroscopic parameters, particularly to the distribution of optic modes in the far infrared; this sensitivity is discussed in detail for the albite breakdown reaction. The model can be used for prediction of isotopic fractionation factors if spectra of the isotopic forms of the mineral are known or postulated. A simple set of ‘rules’ for generating hypothetical spectra of 18O minerals from measured spectra of the 16O forms is given. Reduced partition functions are calculated for 13 minerals. At 298°K the model values of reduced partition function, 1000 ln α, of these minerals decrease in the order quartz > calcite ≳ albite > muscovite > clinoenstatite ≈ anorthite > diopside > pyrope > grossular > zircon > forsterite > andradite > rutile, in good agreement with experimental data. At 1000°K the first six minerals show small crossovers so that the order becomes calcite, muscovite ≈ albite, quartz, anorthite, and clinoenstatite; the differences in 1000 ln α at high temperature for these minerals are so small that the model probably cannot address the deviations from experimental trends. The model clearly defines the region in which the fractionation factors do not follow a 1/T² trend and should be useful for extrapolation of experimental data to low temperatures. Finally, a modified Grüneisen parameter model is proposed for shift of the lattice vibrational frequencies under compression, and thermodynamic properties to 1000 kbar, 1000°K, are given for nine minerals. At 1 Mbar, the predicted decrease in entropy at 298°K ranges from 54% (of the 1‐bar value) for periclase to 25% for stishovite.

Pressure dependences of the elastic constants of semiconducting NbO2at 296 K

The pressure dependences of the elastic-stiffiness moduli of Nb${\mathrm{O}}_{2}$ at 296 K have been obtained by measuring the velocities of ultrasonic waves as a function of hydrostatic pressure to 5 kbar. Most modes stiffen with pressure. However, those involving ${C}_{Q{S}^{\ensuremath{'}}}$ and ${C}_{66}$ soften. Using the pressure dependences of the elastic constants of Nb${\mathrm{O}}_{2}$, we find anomalous contributions to the temperature dependences of ${C}_{44}$ and ${C}_{66}$ due to dilatational effects. The behavior of acoustic modes in semiconducting Nb${\mathrm{O}}_{2}$ is compared with that of corresponding modes in pseudoisomorphic crystals. These results suggest the possibility of a high-pressure monoclinic phase of Nb${\mathrm{O}}_{2}$ and, more generally, that structures with edge-shared anion octahedra may be intrinsically unstable.