On the dynamics and instability of bubbles formed during underwater explosions

Dynamics of explosion bubbles formed during underwater detonations are studied experimentally by exploding fuel (hydrogen and/or carbon monoxide)–oxygen mixture in a laboratory water tank. Sub-scale explosions are instrumented to provide detailed histories of bubble shape and pressure. Using geometric and dynamic scaling analyses it has been shown that these sub-scale bubbles are reasonable approximations of bubbles formed during deep sea underwater explosions. The explosion bubble undergoes pulsation and loses energy in each oscillation cycle. The observed energy loss, which cannot be fully explained by acoustic losses, is shown here to be partly due to the excitation of instability at the interface between the gaseous bubble and the surrounding water. Various possible mechanisms for the dissipation of bubble energy are addressed. The analysis of the experimental data gives quantitative evidence (confirmed by recent numerical studies) that the Rayleigh–Taylor instability is excited near the bubble minimum. The dynamics of the bubble oscillation observed in these experiments are in good agreement with experimental data obtained from deep sea explosions     

Ammonium and potassium fluoromonooxalatomanganates(II), A[MnF(C2O4)] (A = NH4 or K) and sodium fluoromonooxalatomanganate(II) dihydrate,Na[MnF(C2O4)] · 2H2O

Summary Light pink-white microcrystalline ammonium and potassium fluoromonooxalatomanganates(II), A[MnF(C₂O₄)] (A = NH₄ or K), and sodium fluoromonooxalatomanganate(II) dihydrate, Na[MnF(C₂O₄)] · 2H₂O, have been synthesized by two different methods. Either KMnO₄ is reduced in the presence of 40% HF and alkali metal oxalate, A₂C₂O₄ (A = NH₄, Na or K), or MnO(OH) in 40% HF reacts with A₂C₂O₄. Characterisation was made by elemental analyses, determination of oxidation states, magnetic susceptibility measurements and infrared spectral studies.     

On the equilibrium of circular flows under gravity

This paper investigates the stability of an incompressible inviscid rotatory couette flow confined between two corotating and coaxial vertical cylinders under the force field of gravity. The stationary distributions of density and pressure are functions of the radial and axial coordinates with the azimuthal component of velocity being an arbitrary function of radial coordinate. The perturbations concerned are axisymmetric and infinitesimaly small in nature. Sufficient criteria of instability are derived for both vertically stable and unstable density stratifications¹ and this clearly shows that the necessary and sufficient character of Rayleigh's criterion does not hold good in the present circumstances.     

Negation and Paraconsistent Logics

Does there exist any equivalence between the notions of inconsistency and consequence in paraconsistent logics as is present in the classical two valued logic? This is the key issue of this paper. Starting with a language where negation (?{neg}) is the only connective, two sets of axioms for consequence and inconsistency of paraconsistent logics are presented. During this study two points have come out. The first one is that the notion of inconsistency of paraconsistent logics turns out to be a formula-dependent notion and the second one is that the characterization (i.e. equivalence) appears to be pertinent to a class of paraconsistent logics which have double negation property.     

Effect of configuration symmetry on synchronization in a Van der Pol ring with nonlocal interactions

Nonlinear Dynamics - This paper discusses the influence of configuration symmetry on synchronization of coupled Van der Pol oscillators in a ring, where the inherent symmetry in an even number ring...     

Absorption and circular dichroism spectra of a single crystal of K3Pr2(NO3)9

Low-temperature absorption and circular dichroism spectroscopy have been used to study single crystals of cubic potassium praseodymium double nitrate (anhydrous), K₃Pr₂(NO₃)₉. A model calculation of the optical activity has been performed to correlate the observed rotational strengths for crystal-field component-to-component transitions.     

Microwave conductivity of K-TCNQ

Measurements of microwave conductivity of K-TCNQ in the temperature range 300–450 K are reported. K-TCNQ behaves as an extrinsic semiconductor with an activation energy of 0.26 eV below the spin-Peierls transition temperature of 396 K and 0.13 eV above the transition. A hystersis of about 1.5 K was observed. Carrier mobility appears to be reduced by a factor of 30 in the high temperature phase. A second type of crystal has been identified with room temperature conductivity two orders of magnitude higher than previously reported.     

Electron beam damage of chemisorbed surface species: A tunneling spectroscopy study

Electron beam damage is a problem for low-energy electron diffraction, Auger electron spectroscopy, and electron microscopy. We have used tunneling spectroscopy to study the damage caused by 30 keV incident electrons on chemisorbed monolayer films of hexanoic acid, 2,4-hexadienoic acid, and benzoic acid. Our results on monolayer films are compared to existing work on bulk samples. Damage cross sections are similar to bulk values; molecules with more delocalized electrons are more resistant to damage. In contrast to bulk results, however, we find little if any conjugation or cross linking after irradiation.     

Analysis of diffraction efficiency of a holographic coupler with respect to angular divergence

We present a method to optimize the Coupling efficiency between two fibers using a Holographic Coupler taking diffraction effect into account. For this we obtain expressions for field distributions at the end facet of a fiber. The results obtained by using the expression is found to be in good agreement with the finite element method in literature, the small deviation is attributed to the negligence of field in the cladding. We then use the Kogelnik theory to obtain useful formulae suitable for diffracted optical elements. The diffraction efficiency expressions are then used to predict the different parameters of Holograting so as to get maximum diffraction efficiency in a direction where the field distribution from the end facet is minimum thereby increasing the coupling efficiency.      

A Degenerate Birdcage with Integrated Tx/Rx Switches and Butler Matrix for the Human Limbs at 7 T

The theoretically known degeneracy condition of the band-pass birdcage coil has rarely been exploited in transmit coil designs. We have created an eight-channel degenerate birdcage for the human limbs at 7 T, with dedicated Tx/Rx switches and a Butler matrix. The coil can be split into two half cylinders, as required for its application to patients with limited mobility. The design of the coil, the Butler matrix, and Tx/Rx switches relied on a combination of analytical, circuital, and numerical simulations. The birdcage theory was extended to the degenerate case. The theoretical and practical aspects of the design and construction of the coil are presented. The performance of the coil was demonstrated by simulations, workbench, and scanner measurements. The fully assembled prototype presents good performance in terms of efficiency, B₁ homogeneity, and signal-to-noise ratio, despite the asymmetry introduced by the splittable design. The first in vivo images of the knee are also shown. A novel RF coil design consisting of an eight-channel splittable degenerate birdcage has been developed, and it is now available for 7 T MRI applications of the human lower limbs, including high-resolution imaging of the knee cartilages and of the patellar trabecular structure.