Cavity Contraction Research Articles

Cavitation terminology

Among the important contributions Flynn made to the subject of acoustic cavitation was his introduction of concepts and language which have greatly helped our thinking and our communications. In 1964, he defined two acceleration functions and used them for classifying the behavior of gas-filled cavities in a sound field. The more violent kind of behavior, involving ‘‘collapse,’’ occurs when one of the functions, the inertial function, dominates at a critical time during cavity contraction. This type of cavitation was initially called ‘‘transient,’’ partly because the collapse events are of short duration, and partly because the cavities themselves are often short-lived, disappearing through fragmentation and dissolution after collapse events. The other class of cavitation is called ‘‘stable,’’ and represented oscillatory motion which might be complicated but which persists indefinitely. This classification has become very helpful in discussing cavitation phenomena and is widely used in the literature. In recent years, however, the term ‘‘inertial’’ has come into use, replacing ‘‘transient,’’ for cavitation in which Flynn’s inertial function dominates. Examples will be discussed in which Flynn’s classification is applied to experimental situations.

Cylindrical cavity expansion and contraction in pressure sensitive geomaterials

A broad class of plane-strain axially-symmetric deformation patterns in geomaterials is studied within the framework of large strain pressure-sensitive plasticity. Invariant, non-associated deformationtype theories are formulated for the Mohr-Coulomb (M-C) and Drucker-Prager (D-P) solids with arbitrary hardening and accounting for an initial hydrostatic state of stress. With the M-C model we arrive at a single first order differential equation, while for the D-P solid an algebraic constraint supplements the governing differential equation. The analysis centers on the effective stress as the independent variable. A simplified treatment is given for the cavitation limit and some useful relations are derived for thin walled cylinders. The theory is applied to the triaxial calibration test for Castlegate sandstone and then used to simulate the hole closure problem. Numerical examples are provided for the case of a cavity embedded in an infinite medium subjected to external or internal pressure. Results for the D-P inner cone model were found to be in close agreement with those obtained from the M-C model.

A large strain analytical solution for cavity contraction in dilatant soils : H. S. Yu & G. T. Houlsby, International Journal for Numerical & Analytical Methods in Geomechanics, 19(11), 1995, pp 793–811

A large strain analytical solution for cavity contraction in dilatant soils : H. S. Yu & G. T. Houlsby, International Journal for Numerical & Analytical Methods in Geomechanics, 19(11), 1995, pp 793–811

Tunable Q-band resonator for low temperature electron paramagnetic resonance/electron nuclear double resonance measurements

We present a tunable Q-band cavity for performing electron paramagnetic resonance and electron nuclear double resonance experiments at cryogenic temperatures. The resonator is a TE011 brass cavity with radio frequency and magnetic field modulation (100 kHz) posts inside the microwave resonator. These posts are located close to the central sample position and thereby enhance the effective modulation and radio frequency fields. The crucial novel design aspect is the provision for continuously tuning the cavity resonant frequency, even under pumped liquid helium conditions over a broad frequency range (≳2.0 GHz). Such a range will compensate for cooling-induced cavity contraction, presence of cryogenic in the cavity, and insertion of high dielectric frozen aqueous samples. The tuning range is indispensable for use with present commercial Q-band bridges whose low noise Gunn diode oscillators provide a small ∼50 MHz tuning range.

A large strain analytical solution for cavity contraction in dilatant soils

AbstractAn infinite dilatant elastic–plastic soil mass contains a single cylindrical or spherical cavity within which a slowly increasing pressure is applied. The removal of the cavity pressure takes place after a partly plastic state of the soil has been reached. Closed form solutions for the stress and displacement fields in the soil during any stage of the unloading process are derived. The non‐associated Mohr–Coulomb yield criterion is used to account for dilation of the soil during shearing. Large strains are taken into account by adopting an appropriate strain definition within the plastically deforming region.

Lower hybrid dissipative cavitons and ion heating in the auroral ionosphere

In this paper numerical solutions of Zakharov-type equations for lower-hybrid (LH) waves, including pumping at the long wavelengths and dissipation at short wavelengths in the form of dissipative cavitons are described. The caviton is a quasistationary structure undergoing many sequences of collapse due to dissipation, created by ion–wave interactions, which is compensated for by constant pump action. The possibility of trapping of short-wavelength LH oscillations by much broader density cavitons is investigated both analytically and numerically. Analytic self-similar solutions corresponding to collapse of such cavitons are constructed and demonstrate cascading to shorter wavelengths, which develops faster than the three-dimensional (3-D) quasiclassical cavity contraction. Numerical solutions show the development of deep caviton modulation due to the instability of quasiclassical collapse. Results of the numerical and analytical investigation are used to explain the recent observations of cavity formation in the auroral ionosphere, and show that the measured structures could indeed arise from quasiclassical LH collapse.

Effects of chitosan on experimental abscess with Staphylococcus aureus in dogs.

An abscess was developed experimentally by a subcutaneous inoculation of Stapylococcus (S.) aureus T-6 with a 4-cm silk suture in dogs. After draining the pus, the abscess was treated with a suspension of finely granulated chitosan (chitosan group), ampicillin (ampicillin group), or saline (control group) (Day 0). The chitosan group was further divided into 3 subgroups (0.01, 0.1, and 1.0 mg/subgroups). Similar treatment was repeated after 4 days (Day 4), followed by euthanasia on Day 8. The wound cavity contraction rate was calculated by measuring the wound cavity diameter by a sound on Days 0, 4 and 8. The wound cavity contraction rate was significantly higher in the ampicillin, 0.1 mg chitosan, and 1.0 mg chitosan groups than in the 0.01 mg chitosan and control groups on Days 4 and 8 (p < 0.05). In the 0.1 and 1.0 mg chitosan groups, the abscess healed completely in 6 out of 11 (55%), and 9 out of 10 cases (90%), respectively, by Day 8. In the ampicillin group, 4 out of 10 cases (40%) healed completely by Day 8. No healing occurred in the 0.01 mg chitosan and control groups. Histologically, the granulation tissue formed had abundant vascularization in the 0.1 and 1.0 mg chitosan groups on Day 8.

Behaviour of offshore soils containing gas bubbles

An extensive programme of research into the influence of undissolved gas bubbles on the behaviour of fine-grained onshore soils is reviewed. The programme has been based on the development of a laboratory technique for the preparation of reconstituted soil samples containing a uniform distribution of gas bubbles. The structure of these samples is similar to that observed in sediment recovered from the sea bed, and consists of large gas-filled cavities surrounded by a matrix of saturated soil. It is found that surface tension effects limit the difference between gas pressure and pore water pressure, and that the overall void size is effectively a function of the strength of the matrix, so that changes in void volume may be modelled by cavity expansion and contraction in an ideal plastic medium, leading to limits on the difference between gas pressure and mean total stress. A new parameter, operative stress, is shown to influence both the consolidation and the strength of these gassy soils. Thus, during consolidation, the gas volume is controlled by the total stress and the water volume by the operative stress; the undrained shear strength may be increased or decreased by the presence of the gas, depending on the specific values of total stress and operative stress. The operative stress for a gassy soil may therefore be seen as being analogous in its definition (total stress minus pore water pressure) to the effective stress for a saturated soil, but different from the effective stress in that it does not, on its own, control the strains and strength. Gas bubbles are shown to have a major influence on the acoustic behaviour of fine-grained offshore soils. L'article passe en revue un programme de grande envergure pour étudier l'influence exercée par des bulles de gaz non-dissoutes sur le comportement des sols à grains fins en mer. Le programme a été basé sur le développement d'une technique de laboratoire pour la préparation d'échantillons de sols reconstitués comprenant une distribution uniforme de bulles de gaz. La structure de ces échantillons ressemble à celle observée dans des sédiments obtenus au fond de la mer, comprenant de grandes cavités remplies de gaz entourées d'une matrice de sol saturé. Il a été trouvé que des effets de tension superficielle limitent la différence entre la pression du gaz et la pression de l'eau interstitielle et aussi que la valeur totale des vides dépend effectivement de la résistance de la matrice, de sorte que des changements dans le volume des vides peuvent être modelesés par l'expansion et la contraction des cavités dans un milieu idéal plastique, conduisant à des limites sur la différence entre la pression du gaz et la contrainte totale moyenne. On démontre la façon dont cette différence représente un nouveau paramètre (contrainte effective) qui influence à la fois la consolidation et la résistance de ces sols gazeux. Par exemple, pendant la consolidation le volume de gaz est contrôlé par la contrainte totale, tandis que le volume d'eau est contrôlé par cette contrainte effective. Selon les valeurs spécifiques de la contrainte totale et de la contrainte effective la résistance au cisaillement non-drainé peut être augmentée ou diminuée par la présence du gaz. On peut alors considérer que cette définition de la contrainte effective dans le cas d'un sol gazeux (contrainte totale moins pression d'eau interstitielle) est analogue à la contrainte effective pour un sol saturé mais diffère de celle-ci en ce qu'elle seul ne contrôle pas les déformations ni la résistance. On démontre que les bulles de gaz exercent une influence très importante sur le comportement acoustique des sols à grains fins en mer.

Gas pressure in unsaturated offshore soils

Direct measurement of gas pressure within unsaturated offshore soils is very difficult because the gas occurs in the form of large, discrete bubbles. However, consideration of the soil structure and analysis of a continuum model for the soil suggest two independent sets of limits for the gas bubble pressure. Surface tension effects limit the difference between gas pressure and pore-water pressure, while cavity expansion and contraction considerations limit the difference between gas pressure and mean total stress. If the gas pressure lies within these limits, it should remain almost unaffected by changes to the total stress or pore-water pressure. These suggestions are supported by results from an oedometer test on a reconstituted soil sample containing large bubbles of methane gas. Key words: bubbles, cavity expansion, gas, oedometer tests, offshore geotechnics, pore pressure, surface tension, unsaturated.

Sectional and segmental variability of left ventricular function: Experimental and clinical studies using ultrafast computed tomography

In this study, ultrafast computed tomography, a new high spatial and temporal resolution imaging system, was employed to define the range of sectional (tomographic) and segmental left ventricular function in 11 normal anesthetized dogs and 11 normal human volunteers. After intravenous infusion of contrast agent, multilevel tomographic images of the left ventricle (apex to base) were acquired at a rate of 17 frames/s. Analysis of these studies demonstrated substantial but predictable heterogeneity in left ventricular contraction from apex to base. In dogs and humans, for example, the average tomographic ejection fraction of the most basal level of the left ventricle was 40% less than that of the most apical level (p < 0.05).In humans, circumferential segmental cavity contraction at the mid-papillary muscle level was relatively homogeneous (range 50 to 92% for 12 wedge-shaped segments around the tomographic circumference) if the reference system employed an endocardial centroid, but was less uniform if it used an epicardial centroid (range 22 to 98%).It is concluded that contraction of the normal left ventricle in dogs and humans is heterogeneous both between levels (apex to base) and within a single level (circumferential cavity contraction). However, the patterns of cavity contraction from apex to base and circumferential segmentai cavity contraction within a given level as defined by ultrafast computed tomography are sufficiently narrow and predictable in normal individuals that these variables may be useful to define regional contraction abnormalities in pathologic conditions.

Preparation and Crystal Structure of the Potassium-Priderite Type Solid Solutions

This study is concerned with the formation, structure and color development of the potassium-priderite type solid solutions in the system Kx(Ti, M)8O16 (M=Mg, Al, Sc, Cr, Mn, Fe, Co, Ni, Cu and Zn). The results are summarized as follows;(1) Priderite-type solid solutions with the composition of K2xMxTi8-xO16 (M=Mg, Co, Ni, Cu and Zn) are formed in the following ranges: 0.75≤x≤0.9 in Mg-system, 0.85≤x≤1.0 in Co-system, 0.8≤x≤1.0 in Ni-system, x=1 in Cu-system and 0.75≤x≤0.9 in Zn-system.(2) Priderite-type solid solutions with the composition of K2xM2xTi8-2xO16(M=Al, Cr, Mn and Fe) are formed at x=1 except for Mn-system.(3) The unit cell volume of each solid sulution increases depending on the ionic radius of the octahedral site cation. In each system, the lattice parameter c expands by the replacement with larger divalent cations for the titanium sites. The lattice parameter a shrinks by the tunnel cavity contraction by the increasing amount of potassium ion.(4) The reflectance spectra show typical six coordinated states of Co2+ and Ni2+ in the priderite-type solid solutions. The color of the priderite-type solid solutions is light yellowish brown in Co-system and changes from bright greenish yellow to strong greenish yellow in Ni-system.(5) According to the results of the structure refinement by the pattern fitting method of X-ray powder diffraction patterns, the special position, 2 (a), is not occupied by K+-ions, but a half of the more stable site, 4 (e), is occupied by K+-ions in K2CoTi7O16, K2NiTi7O16, K2Al2Ti6O16 and K2Sc2Ti6O16(C. S.: tetragonal, S. G.: I4/m, Z=1).