Cavity Boundary Research Articles

Fracture initiation in cavity expansion of rock

Initiation of fracture from a cylindrical opening in blocks of Berea sandstone under plane strain was monitored with a cavity expansion apparatus. Using the particle tracking technique called digital image correlation, a discontinuity in the displacement field near the cavity boundary was identified at 80% of the peak internal pressure, which meant that a process zone developed prior to peak. To investigate the effect of scaling on fracture, a two dimensional bonded particle model was validated, and several specimens sizes with different borehole and tension softening characteristics were tested numerically. It is demonstrated that with increase in specimen size or with increase in borehole size, the peak pressure decreases, and these size effects are governed by both material and structural length scales.

Revisiting the Single-Fluid Modeling of the Solar Wind–Comet Interaction: Closer Look at the Cometosheath

Earlier developed single fluid gas-dynamic model of solar wind–comet ionosphere interaction is applied to reveal some specifics in the morphology of the shocked “contaminated” solar wind region (cometosheath). The model is based on the Euler equations with added mass-loading, mass-loss and frictional force terms. Numerous reactions are taken into account in these terms including photoionization, charge transfer, dissociative recombination and ion-neutral frictional force. The electromagnetic terms are omitted, thus reducing the MHD single-fluid system of equations to gas-dynamic one. The used shock-fitting numerical scheme allows the separation of distinct areas formed by the considered interaction and exploration of their properties in detail. Attention is focused on the region between the shock wave and the contact surface as well as on the positions of these boundaries. Accurate examination of the distribution of density, temperature and velocity reveals spatial variations that resemble the variations registered by a number of spacecraft in the vicinity of comets. No specific comparisons with data are made at this stage. Two very first events of the Rosetta spacecraft’s crossing of the magnetic cavity boundary around Comet 67P/Churyumov–Gerasimenko are discussed using a “faux-transient” application of our steady-state model.

First detection of a diamagnetic cavity at comet 67P/Churyumov-Gerasimenko

Context: The Rosetta magnetometer RPC-MAG has been exploring the plasma environment of comet 67P/Churyumov-Gerasimenko since August 2014. The first months were dominated by low-frequency waves which evolved into more complex features. However, at the end of July 2015, close to perihelion, the magnetometer detected a region that did not contain any magnetic field at all. Aims: These signatures match the appearance of a diamagnetic cavity as was observed at comet 1P/Halley in 1986. The cavity here is more extended than previously predicted by models and features unusual magnetic field configurations, which need to be explained Methods: The onboard magnetometer data were analyzed in detail and used to estimate the outgassing rate. A minimum variance analysis was used to determine boundary normals. Results. Our analysis of the data acquired by the Rosetta Plasma Consortium instrumentation confirms the existence of a diamagnetic cavity. The size is larger than predicted by simulations, however. One possible explanation are instabilities that are propagating along the cavity boundary and possibly a low magnetic pressure in the solar wind. This conclusion is supported by a change in sign of the Sun-pointing component of the magnetic field. Evidence also indicates that the cavity boundary is moving with variable velocities ranging from 230−500 m/s.

Mathematical Model of Cooling by Supercharged Gas

A method is proposed to improve the robot-assisted radical prostatectomy procedure by using a cooling gas of a controlled temperature. To determine the optimal gas flow rate and temperature values, it is necessary to carry out sample calculations taking into account the particular features of the processes taking place. To solve this problem, a mathematical model for the conjugate problem of convective heat transfer in the operational area and adjacent tissues was developed. The model reflects the unsteady cavity boundaries relating to the placement of the surgical incision. The mathematical model can be implemented in a computer program, which permits optimization of the gas parameters to provide the most favorable surgery conditions for the patient.

Universal Scaling of Cavity Volume Pathways in Globular Proteins

Molecular packing is studied over a dataset of crystal structures representing 500 diverse globular proteins in their native state ranging in size from 34 to 839 residues. Different size cavities are ubiquitously present due to the presence of void between atoms not accessible to solvent. Using a new algorithm we recently developed, void within a protein is classified as a cavity when large enough to hold a spherical shaped probe of radius, R, otherwise a microvoid. Although microvoid cannot fit an object (e.g. molecule or ion) that is the size of the probe or larger, total microvoid volume is a major contribution to protein volume. As microvoid volume increases the free volume of solution decreases. Importantly, the cavity and microvoid classification depends on probe radius. As probe size decreases, less microvoid forms in favor of more cavities, and vice versa. Microvoid is partitioned into distinct clusters, where a cluster is defined by a contiguous region of space that allows a minimum size object of width, w, to transverse. Cavity and microvoid pathways are visualized and their cluster statistics collected. The linear length scale of a protein, L, is also defined. Universal scaling is demonstrated through data collapse in microvoid cluster statistics as a function of probe size, R, spatial resolution, w, and protein size, L. Characteristics for microvoid, cavity, and solvent accessible boundary volumes are quantified. As probe size is varied from large to small, many disconnected cavities merge to form a percolating path. For fixed probe size, microvoid, cavity and solvent accessible boundary volume properties reflect conformational fluctuations. These results suggest interconversion between microvoid and cavity pathways regulate the dynamics of solvent and substrate penetration that are important to protein function, as well as crowding and pressure effects.

ИЗМЕРЕНИЕ ТЕМПЕРАТУРНЫХ ПОЛЕЙ ПОВЕРХНОСТИ ЖИДКОСТИ ПРИ ПОМОЩИ ТОНКОЙ ПЛАСТИНКИ И ТЕПЛОВИЗОРА

In the study of thermal convection in the opaque magnetic fluids convective rolls can be visualized using the thin textolite plate and infrared camera. The plate is one of the boundaries of the convective cavity - vertical layer. The possibility of quantitative measurements of temperature fields of the liquid surface is evaluated by this method. Temperature fields in thin textolite plate, bounding the fluid layer, non-uniform temperature, have been calculated. Laboratory modeling of periodic convective structures to study the temperature distribution along the plate, obtained with an infrared thermal imager, has been performed. According to the results of calculations and experiments systematic measurement errors of spatial harmonics of the thermal field, generated by a convective flow, have been evaluated.Received 11.11.2015; accepted 18.01.2016

弾性球介在物を含む無限体の引張り（はめあい状態を考慮した混合境界値問題）

This report deals with the influence of the interference between an elastic sphere and a spherical cavity on the stress distribution and displacement around cavity, which has simply a smooth elastic sphere, in an elastic solid under tension at infinity. The contact stress between the sphere and the cavity is expressed with series of Legendre functions, and the stress and displacement are numerically analyzed by point matching method. Using the numerical results for the elastic solid, the effects of interference and loads are shown on the stresses around the spherical cavity boundary. The main results are as follows: (1) The contact region and stress distribution of the elastic solid are independent of the magnitude of load, when diameter of sphere and spherical cavity are initially the same. (2) When diameters of them are not same, the contact region and stress distribution of the elastic solid vary with a change in magnitude of load.

Statistical characteristics of the motion of a pair of heavy ions in non-convex cavities of complicated geometry with fixed crosspieces and charges

Using the method of classical trajectories, the motion of a pair of ions Cs+ and Cl– in three non-convex closed cavities of complicated geometry containing neutral cylindrical “crosspieces” and charged spherical “nuclei” is simulated. The collisions of the ions with the cavity boundary, crosspieces, and nuclei are supposed to be inelastic. The signs of the charges of the nuclei are varied. In each cavity, in one of the calculation series, the nuclei are assumed to be shielded (to carry charges smaller than 1 a.u. in absolute value), whereas in another calculation series, the possibility of the mutual neutralization of an ion and an oppositely charged nucleus at their encounter is taken into account. The statistics of various events, such as the “stickings” of ions to nuclei, neutralizations of ions and nuclei, collisions of ions with obstacles, recombinations of ions, and dissociations of the CsCl ionic-bond molecule are analyzed.

Stokes flow over a cavity on a superhydrophobic surface containing a gas bubble

Within the approximation of Stokes hydrodynamics, several problems of a steady-state flow over a two-dimensional cavity containing a gas bubble are solved using the method of boundary integral equations. In contrast to previous publications, the method developed makes it possible to study the situation in which the cavity is only partially filled with gas, and the edges of a curved phase interface do not coincide with the cavity corners. Using periodic boundary conditions for the velocity, the flows with pure-shear and parabolic velocity profiles, and also the flow over a group of cavities were considered. The aim of the study was to calculate the effective (average) slip velocity over a microcavity, as applied to flows near textured superhydrophobic surfaces. A parametric numerical study of the effective velocity slip as a function of the radius of curvature of the interface and the position of the interface relative to the cavity boundaries was performed. The accuracy of the method is validated by the calculations of a number of limiting flows over a cavity, for which a quantitative agreement with the results known in the literature is demonstrated.

Quantitative test of general theories of the intrinsic laser linewidth

We perform a first-principles calculation of the quantum-limited laser linewidth, testing the predictions of recently developed theories of the laser linewidth based on fluctuations about the known steady-state laser solutions against traditional forms of the Schawlow-Townes linewidth. The numerical study is based on finite-difference time-domain simulations of the semiclassical Maxwell-Bloch lasing equations, augmented with Langevin force terms, and includes the effects of dispersion, losses due to the open boundary of the laser cavity, and non-linear coupling between the amplitude and phase fluctuations (α factor). We find quantitative agreement between the numerical results and the predictions of the noisy steady-state ab initio laser theory (N-SALT), both in the variation of the linewidth with output power, as well as the emergence of side-peaks due to relaxation oscillations.

Regimes of photon generation in Dynamical Casimir Effect under various resonance conditions

We investigate spectral and statistical properties of the field generated in dynamical Casimir effect under various resonance conditions appeared from periodical motion of cavity boundary. In particular we are interested in single and two-mode squeezing effects which take place for each resonant frequency under the cases of bounded and unbounded cavity spectrum.

Wave-Field Shaping in Cavities: Waves Trapped in a Box with Controllable Boundaries.

Electromagnetic cavities are used in numerous domains of applied and fundamental physics, from microwave ovens and electromagnetic compatibility to masers, quantum electrodynamics (QED), and quantum chaos. The wave fields established in cavities are statically fixed by their geometry, which are usually modified by using mechanical parts like mode stirrers in reverberation chambers or screws in masers and QED. Nevertheless, thanks to integral theorems, tailoring the cavity boundaries theoretically permits us to design at will the wave fields they support. Here, we show in the microwave domain that it is achievable dynamically simply by using electronically tunable metasurfaces that locally modify the boundaries, switching them in real time from Dirichlet to Neumann conditions. We prove that at a high modal density, counterintuitively, it permits us to create wave patterns presenting hot spots of intense energy. We explain and model the physical mechanism underlying the concept, which allows us to find a criterion ensuring that modifying parts of a cavity's boundaries turn it into a completely different one. We finally prove that this approach even permits us, in the limiting case where the cavity supports only well-separated resonances, to choose the frequencies at which the latter occur.

The influence of a pressure wavepacket's characteristics on its acoustic radiation.

Noise generation by flows is modeled using a pressure wavepacket to excite the acoustic medium via a boundary condition of the homogeneous wave equation. The pressure wavepacket is a generic representation of the flow unsteadiness, and is characterized by a space envelope of pseudo-Gaussian shape and by a subsonic phase velocity. The space modulation yields energy in the supersonic range of the wavenumber spectrum, which is directly responsible for sound radiation and directivity. The influence of the envelope's shape on the noise emission is studied analytically and numerically, using an acoustic efficiency defined as the ratio of the acoustic power generated by the wavepacket to that involved in the modeled flow. The methodology is also extended to the case of acoustic propagation in a uniformly moving medium, broadening possibilities toward practical flows where organized structures play a major role, such as co-flow around cruising jet, cavity, and turbulent boundary layer flows. The results of the acoustic efficiency show significant sound pressure levels, especially for asymmetric wavepackets radiating in a moving medium.

Efficient integral cylindrical transmission‐line matrix modelling of a coaxially loaded probe‐coupled cavity

The transmission-line matrix method enhanced with the compact wire model in a cylindrical grid is used for modelling of a coaxially loaded cylindrical cavity resonator with probes inserted into the cavity. Benefits of using a cylindrical grid instead of rectangular, related to precise modelling of cavity boundaries, a coaxially shaped dielectric sample and radially placed wire elements, are explored. The accuracy of the simulated results is verified by measurements of an experimental model of the cavity-wire structure.

耦合腔光力学系统的绝热理论及其计算方法

Following a direct physical picture, this paper presents a simple but general study on the coupled cavity optomechanical system as well as some other similar systems based on the adiabatic approximation theory. The basic theoretical model and the relevant mathematical method are provided in this paper. The cavity optomechanics is a very quickly developing field and its basic theoretical model is an essential starting point to study the physical properties of the system. The traditional theoretical method to derive the model is based on the Maxwell equations with a moving cavity boundary condition. This method involves a complicated calculation procedure which lacks clear physical picture and misses general connections to other similar systems. This paper adopts the adiabatic theory and the transfer matrix method instead to investigate the coupled Fabry-Perot cavities with the membrane-in-the-middle scheme, and gives a universal calculation on the cavity- mode frequency and the transmission rate modulating by the collective motion of the membranes. The method not only leads to the same model as that derived from Maxwell equations, but also presents a more general physical background to the study of cavity-coupled mechanical systems.

A comparison of cardiac motion analysis software packages: application to left ventricular deformation analysis in hypertensive patients

Background Although myocardial function is clinically assessed with global measurements (ventricular volumes, ejection fraction), recent research has shown that regional measurements, such as wall-thickening, strain, and torsion, could provide earlier sub-clinical markers to examine left ventricular (LV) dysfunction and myocardial diseases. Cardiovascular Magnetic Resonance myocardial feature tracking (CMR-FT) technique is used to post-process cine CMR images to provide a quantitative assessment of LV motion deformation parameters. It derives myocardial motion deformation from image features such as myocardium-blood cavity boundary and pixel intensities, and relies only on standard cine images to extract motion deformation. The main objective of this study is to compare two current feature tracking software packages in hypertensive patients. Methods 29 hypertensive subjects were prospectively recruited from a tertiary hypertension clinic and enrolled to undergo CMR examinations. All images were acquired using a 1.5T scanner (Siemens Medical Imaging, Germany), and a cardiac surface coil. LV function was assessed with cine acquisitions in the following planes: 2-chamber, 4-chamber and short-axis slices (basal, mid and apical levels). LV deformation was analysed using: 2D Cardiac Performance Analysis, MR (TomTec Imaging Systems, Munich, Germany) and CVI42 (Circle Cardiovascular Imaging Inc. Calgary, Canada). Endocardial and epicardial LV contours were drawn manually at the end diastolic phase in order to achieve best tracking results; the software packages then allow semi-automated analysis to provide quantitative measurement of global and regional deformation parameters. Results Results of circumferential, radial, and longitudinal strains are given in table 1. Statistical analysis was performed using the student’s paired t-test for dependent sample in order to assess the difference between the two software packages.All radial strain mean values obtained with CVI42 were higher than with Tomtec and the difference was statistically significant for all short-axis circumferential strains. This was also the case for shortaxis apical and 4-chamber radial strains. In total five parameters (short-axis apical and 4-chamber radial strains, all 3 short-axis slices circumferential strains) were statistically different and 5 were not. Conclusions From our results, there is a trend in circumferential strain in short-axis (apical, mid, and basal) where there is a significant difference in the values obtained by the two software packages, whereas radial and longitudinal strain values showed no clear trend. Therefore, there is a clear need for a gold standard validation to assess the accuracy of cardiac motion analysis software packages.

Convection in a colloidal suspension in a closed horizontal cell

The experimentally detected [1] oscillatory regimes of convection in a colloidal suspension of nanoparticles with a large anomalous thermal diffusivity in a closed horizontal cell heated from below have been simulated numerically. The concentration inhomogeneity near the vertical cavity boundaries arising from the interaction of thermal-diffusion separation and convective mixing has been proven to serve as a source of oscillatory regimes (traveling waves). The dependence of the Rayleigh number at the boundary of existence of the traveling-wave regime on the aspect ratio of the closed cavity has been established. The spatial characteristics of the emerging traveling waves have been determined.

A new technique of pulmonary hernia surgical repair using intramedullary titanium implants.

IntroductionIn this paper we present a new method of pulmonary hernia surgical treatment. Pulmonary hernia is a rare pathology. The first description of pulmonary hernia was made by Roland in 1499. The world literature describes only a little more than 300 cases of pulmonary hernia. Pulmonary hernia is defined as the projection of the lung tissue covered by the parietal pleura beyond the normal boundaries of the pleural cavity, through the pathological holes in the chest wall. During our work as thoracic surgeons, we have used different ways of thoracic chest wall reconstructive operations and anastomoses of the broken ribs.Aim of the studyTo search for optimal methods of pulmonary hernia surgery and to evaluate a new technique of pulmonary hernia surgical repair using intramedullary titanium implants.Material and methodsIn 2013 in our clinic, we diagnosed and cured two patients with idiopathic pulmonary hernia. We performed a reconstructive operation of the chest wall with anastomosis of the broken ribs using titanium intramedullary stabilization implants – splints.ResultsTo date, the annual observation has revealed no recurrence of pulmonary hernia or postoperative complications. At present, the patients demonstrate full life activity.ConclusionsSo far, in the world literature, we have not encountered any information about using such methods to repair pulmonary hernia. We regard our method as safe, easy to use and giving good therapeutic results.

Collapse of spherical cavities and energy cumulation in an ideal compressible liquid

Analytical solutions of the problem of collapsing of a spherical shell or cavity in an ideal compressible liquid having a constant density during its motion are constructed. The influence of the gas located in the cavity on the motion of the cavity boundary is studied. A quantitative characteristic of energy cumulation is proposed. An expression for energy cumulation in the case of shell or cavity collapsing is derived. The energy cumulation obtained in this study is compared with Zababakhin’s results.

Probing complex reflection coefficients in one-dimensional surface plasmon polariton waveguides and cavities using STEM EELS.

The resonant properties of a plasmonic cavity are determined by the size of the cavity, the surface plasmon polariton (SPP) dispersion relationship, and the complex reflection coefficients of the cavity boundaries. In small wavelength-scale cavities, the phase propagation due to reflections from the cavity walls is of a similar magnitude to propagation due to traversing the cavity. Until now, this reflection phase has been inferred from measurements of the resonant frequencies of a cavity of known dispersion and length. In this work, we present a method for measuring the complex reflection coefficients of a truncation in a 1D surface plasmon waveguide using electron energy loss spectroscopy in the scanning transmission electron microscope (STEM EELS) and show that this insight can be used to engineer custom cavities with engineered reflecting boundaries, whose resonant wavelengths and internal mode density profiles can be analytically predicted given knowledge of the cavity dimensions and complex reflection coefficients of the boundaries.