Asymmetric Collapse Research Articles

Modeling core collapse supernovae in 2 and 3 dimensions with spectral neutrino transport

The overwhelming evidence that the core collapse supernova mechanism is inherently multidimensional, the complexity of the physical processes involved, and the increasing evidence from simulations that the explosion is marginal presents great computational challenges for the realistic modeling of this event, particularly in 3 spatial dimensions. We have developed a code scalable to computations in 3 dimensions that couples PPM Lagrangian-withremap hydrodynamics, multigroup flux-limited diffusion neutrino transport (with many improvements), and a nuclear network. The neutrino transport is performed in a ‘‘ray-by-ray-plus’’ approximation, wherein all the lateral effects of neutrinos are included (e.g., pressure, velocity corrections, advection) except lateral transport. A moving radial grid option permits the evolution to be carried out from initial core collapse with only modest demands on the number of radial zones. The inner part of the core is evolved after collapse, along with the rest of the core and mantle, by subcycling the lateral evolution near the center as demanded by the small Courant times. We present results of 2-D simulations of a symmetric and an asymmetric collapse of both a 15 and an 11 M⊙ progenitor. In each of these simulations we have discovered that once the oxygen-rich material reaches the shock there is a synergistic interplay between the reduced ram pressure, the energy released by the burning of the shock-heated oxygen-rich material, and the neutrino energy deposition that leads to a revival of the shock and an explosion.

They Came from the Deep in the Supernova: The Origin of TiC and Metal Subgrains in Presolar Graphite Grains

A new formation scenario for TiC and Fe-Ni metal inclusions in presolar graphite grains of supernova origin is described. The mineralogy and chemistry require condensation of Fe-Ni titanides from Fe-, Ni-, and Ti-rich gaseous ejecta, subsequent carburization to make TiC and metal, and encapsulation into graphite. Titanides only condense if Si is depleted relative to heavier elements, which requires α-rich freeze-out and a deep mass cut for the supernova ejecta. This Si-poor core material must remain unmixed with other supernova zones until the titanides condense. This can be accomplished by transport of core ejecta in bipolar jets through the major expanding supernova zone ejecta. If the jets stall in regions dominated by C-rich ejecta such as the C-He zone, where graphite condenses, thermochemically favored in situ carburization of the titanides—either before or during encapsulation into condensing graphite—leads to a TiC-and-metal composite. This scenario agrees with theoretical models and observations of asymmetric core collapse in supernovae that are associated with bipolar jets loaded with iron-peak elements.

Wavelet analysis of active cavitation detector output

Active cavitation detectors (ACDs) have provided useful information concerning the dynamics of microbubbles exposed to intense pulsed ultrasound. In an examination of the effects of nearby solid surfaces on the asymmetrical collapse of bubbles, ACD signals consisting of 60‐cycle 30‐MHz tone bursts of <0.1 MPa peak negative pressure returned complex echoes for individual bubbles and groups of bubbles. The Gauss‐Harmite wavelet transform was used to analyze these signals to differentiate between symmetrical and asymmetrical collapse signatures, with the goal of identifying the percentage of asymmetrical bubble collapses in a cavitation field. [Work supported by NIH R‐15 EB004630‐01.]

Current-induced asymmetric transport in La0.8Ca0.2MnO3 epitaxial thin films

We investigated the influence of a dc current on the transport properties in La0.8Ca0.2MnO3 epitaxial thin films grown on SrTiO3 substrates. A prominent finding is the appearance of asymmetric transport properties, like the behavior of p-n junctions, in a wide temperature range from 10Kto300K after the films were applied by a dc current over a threshold value. The asymmetric behavior resulted from a relative weak excitation is unstable and even spontaneously disappears. By optimizing excitation condition, the rectifyinglike behavior turns to be more significant and stable. Applying a small ac current could make the asymmetric transport collapse, subsequently, conventional symmetric transport behaviors appear. Phase separation and the coexistent ferromagnetic phases with different orbital order are taken into account in the interpretation of the observed phenomena.

Backflow-Induced Asymmetric Collapse of Disclination Lines in Liquid Crystals

We present experiments where opposed pairs of planar parallel disclination lines of topological strength s=+/-1 move due to their mutual attraction. Our measurements show that their motion is clearly asymmetric, with +1 defects moving up to twice as fast as -1 ones. This is a clear indication of backflow, given the intrinsic isotropic elasticity of our system. A phenomenological model is able to account for the experimental observations by renormalizing the orientational diffusivity estimated from the velocity of each defect.

Response of an ultrasonically excited bubble near a fixed rigid object

Various independent studies suggest that echo-contrast agents can increase the likelihood of ultrasonic bioeffects. To better understand bioeffects involving cavitation, a two-dimensional boundary element model was used to simulate ultrasonically excited bubble behavior near a rigid object, either a plane, sphere, or disk, the approximate size of a red blood cell. As the distance between the object and bubble increases, the bubble collapse becomes more spherically symmetric, producing higher maximum bubble pressures. Pressure and velocity fields around a bubble collapsing near a rigid disk are compared for two distances, demonstrating differences between more spherically symmetric and asymmetric bubble collapses.

Ultrasonic excitation of a bubble near a rigid or deformable sphere: Implications for ultrasonically induced hemolysis

A number of independent studies have reported increased ultrasound bioeffects, such as hemolysis and hemorrhage, when ultrasound contrast agents are present. To better understand the role of cavitation in these bioeffects, one- and two-dimensional models have been developed to investigate the interactions between ultrasonically excited bubbles and model "cells." First, a simple one-dimensional model based on the Rayleigh-Plesset equation was developed to estimate upper bounds for strain, strain rate, and areal expansion of a simulated red blood cell. Then, two-dimensional boundary element models were developed (with DynaFlow Inc.) to obtain simulations of asymmetric bubble dynamics in the presence of rigid and deformable spheres. The deformable spherical "cell" was modeled using Tait's equation of state for water, with a membrane approximated by surface tension that increases linearly with areal expansion. The presence of a rigid or deformable sphere had little effect on the bubble expansion, but caused an asymmetric collapse and jetting for the conditions considered. Predicted membrane areal expansions were found to be below critical values for hemolysis reported in the literature for the cases considered near the inertial cavitation threshold.

Evaluation of Local Gas Exchange in a Pulsating Respiratory Support Catheter

An intravenous respiratory support catheter, the next generation of artificial lungs, is being developed in our laboratory to potentially support acute respiratory failure or patients with chronic obstructive pulmonary disease with acute exacerbations. A rapidly pulsating 25 ml balloon inside a bundle of hollow fiber membranes facilitates supplemental oxygenation and CO2 removal. In this study, we hypothesized that non-uniform gas exchange in different regions of this fiber bundle was present because of asymmetric balloon collapse and the interaction of longitudinal flow. Four quarter regions and two rings around the central balloon were selectively perfused to evaluate local gas exchange in a 3.18 cm test section using helium as the sweep gas. Quarter region CO2 exchange rates at 400 beats per minute were 156.8 +/- 0.8, 162.5 +/- 1.8, 157.2 +/- 0.2, and 196.6 +/- 0.8 ml/min/m2 (top, front, bottom, and back, respectively). The back section, adjacent to convex balloon collapse, had 17-20% higher exchange than the other sections caused by higher relative velocities past its stationary fibers. Inner and outer ring maximum pulsation gas exchange rates were 174.4 +/- 1.8 and 174.6 +/- 0.9 ml/min/m2, respectively, showing that fluid flow was equally distributed throughout the fiber bundle.

Langerhans cell histiocytosis of the spine in children. Long-term follow-up.

Langerhans cell histiocytosis causes destructive lesions in a child's spine. Few large, long-term studies have evaluated the clinical and radiographic presentation, natural history, outcomes of modern treatment approaches, and maintenance of normal spinal growth and stability after the diagnosis of this disease in children. Twenty-six children with biopsy-proven Langerhans cell histiocytosis involving the spine were treated at our institution between 1970 and 2003. They had a total of forty-four involved vertebrae (twenty cervical, fourteen thoracic, and ten lumbar). Vertebral body collapse was measured on radiographs and classified as grade I (0% to 50% collapse) or grade II (51% to 100% collapse) and subclassified as A (symmetric collapse) or B (asymmetric collapse). Lesions of the posterior elements of the spine were classified as grade III. Twenty-three children were followed for two years or more (mean, 9.4 years), and the analyses of treatment and long-term outcomes were performed in that group of patients. There was a predominance of lesions in the cervical spine (p </= 0.02). Sixteen (62%) of the twenty-six children were found to have multifocal skeletal disease. Cervical and lumbar lesions were more commonly associated with multilevel spinal disease. The extent of the initial collapse seen radiographically was grade IA for twenty vertebrae, IB for three, IIA for ten, IIB for nine, and III for two. Grade-I lesions were more likely to be associated with symmetric collapse than were grade-II lesions. Spinal deformity developed in four children, and two later required spinal fusion. No relationship was observed between the grade of the initial collapse and the subsequent development of spinal deformity. Despite heterogeneous treatment, all patients were alive and well with resolution of all presenting signs and symptoms and no evidence of active disease at the time of the most recent follow-up. We found a particularly high prevalence of lesions in the cervical spine and a high prevalence of multiple skeletal lesions. In contrast to the classic finding of vertebra plana, we found that more severe lesions often led to asymmetric collapse; yet, asymmetric collapse was not found to be associated with the development of subsequent spinal deformity. The natural history of these lesions in the spine in the absence of systemic disease or spinal deformity is such that aggressive surgical management is usually not indicated; only follow-up is necessary to monitor recovery and spinal balance.

Active cavitation detection of asymmetrical inertial cavitation

The active cavitation detector (ACD) developed in Bob Apfel’s laboratory has often been employed to quantify pressure thresholds for inception of symmetrical inertial cavitation of microbubbles. In the current application, however, a 30-MHz ACD interrogates individual echo-contrast agent bubbles adhering to a Mylar(TM) sheet that are driven into asymmetrical (jet-producing) collapse by a 1-MHz toneburst (&amp;gt;1 MPa pp). The resulting ACD output suggests that asymmetrical bubble collapse is slower than symmetrical collapse, producing less total radiated acoustic power. ACD output mixed with reference sinusoids at 30 MHz and low pass filtered yields Doppler signals that may be useful in quantifying asymmetrical collapses under biomedically relevant conditions, such as on endothelial walls.

Neutron Star Kicks from Asymmetric Collapse

Many neutron stars are observed to be moving with spatial velocities, in excess of 500km/s. A number of mechanisms have been proposed to give neutron stars these high velocities. One of the leading classes of models proposed invokes asymmetries in the core of a massive star just prior to collapse. These asymmetries grow during the collapse, causing the resultant supernova to also be asymmetric. As the ejecta is launched, it pushes off (or ``kicks'') the newly formed neutron star. This paper presents the first 3-dimensional supernova simulations of this process. The ejecta is not the only matter that kicks the newly-formed neutron star. Neutrinos also carry away momentum and the asymmetric collapse leads also to asymmetries in the neutrinos. However, the neutrino asymmetries tend to damp out the neutron star motions and even the most extreme asymmetric collapses presented here do not produce final neutron star velocities above 200km/s.

An analytical solution for unsteady, inviscid jet formation due to asymmetric 2-d ring collapse

Here we derive a closed form analytical solution for an unsteady inviscid jet caused by the asymmetric collapse of a 2-d ring using linearized, small disturbance, velocity potential theory and classical analytical methods. Use is made of both the Laplace transformation and elementary eigenfunction expansions to solve the associated governing equations. The streamwise diffusion term, e.g. φ rr is shown to be second order and is neglected. Jet shape that was computed using the analytical model is compared with CTH (hydrocode) simulations and limited experimental data and shown to provide reasonable agreement. Jet spreading is shown to be consistent with classical turbulent jet scaling in accordance with known shaped charge jet hydrodynamic assumptions. With confidence that the analytical solution is a viable tool we consider the numerical issues associated with rotational symmetry, the effect of boundary loading disturbance to the jet and the effect of finite arrival time detonation wave conditions. Thus we conclude that this model provides a simple, but useful supplement to conventional hydrocode simulation jetting phenomenon due to asymmetric loading of 2-d circular rings.

Asymmetric collapse and micro-jetting in shock wave propagation in porous materials

Streak records of the observation, with a nanosecond and micrometer scale resolution, of the light emitted during the Shock Wave [SW] propagation in epoxy Syntactic Foams [SF], are presented as a function of the HGMS sizes (d 50 = 42, 92 and 135 μm), the initial density (0.64, 0.81 and 0.92 g/cm 3 ) and the loading intensity (20.0 and 9.6 GPa). The obtained streak records allowed the determination of the SW velocity, the spatial profile of the intensity of the transmitted SW and the period of light oscillations. The SW velocity was found to change with the density and with the size of the HGMS. The intensity of the transmitted wave, for the samples prepared with medium and large HGMS sizes, shows to be above the values for the samples prepared with small size HGMS. For the samples with the smallest density the values of the period of light oscillation are very close to the time for the propagation between two consecutive layers of HGMS. The experimental facts point to a pulsed propagation process where the mechanism of asymmetric collapse and jet formation is dominant.

Asymmetric collapse and micro-jetting in shock wave propagation in porous materials

Asymmetric collapse and micro-jetting in shock wave propagation in porous materials

Gravitational Radiation from Gamma‐Ray Burst Progenitors

We study gravitational radiation from various proposed gamma-ray burst (GRB) progenitor models, in particular compact mergers and massive stellar collapses. These models have in common a high angular rotation rate, and the final stage involves a rotating black hole and accretion disk system. We consider the in-spiral, merger and ringing phases, and for massive collapses we consider the possible effects of asymmetric collapse and break-up, as well bar-mode instabilities in the disks. We calculate the strain and frequency of the gravitational waves expected from various progenitors, at distances based on occurrence rate estimates. Based on simplifying assumptions, we give estimates of the probability of detection of gravitational waves by the advanced LIGO system from the different GRB scenarios.

The Asymmetric Collapse of Bubbles in Compressible Liquid**The project supported by National Natural Science Foundation of China (10247008), Natural Science Foundation of Gansu Province (YS021-A22-018), the Scientific Research Foundation (SRF) for the Returned Overseas Chinese Scholars (ROCF), State Education Ministry (SEM), and the Natural Science Foundation of Northwest Normal University (NWNU-KJCXGC-215)

The analytical solution of a bubble collapse close to a solid boundary in a compressible water is investigated by means of a perturbation method to first order in the bubble wall Mach number. It is shown, in this paper, that it is the Rayleigh–Plesset equation for incompressible liquid to zero order solution or similar to the Gilmore equation for compressible water to first order solution when the effect of solid boundary is negligibly small enough, i.e., sufficiently far away from the bubble center.

Acoustic cavitation movies

Acoustic cavitation is a phenomenon that occurs on microsecond time scales and micron length scales, yet, it has many macroscopic manifestations. Accordingly, it is often difficult, at least for the author, to form realistic physical descriptions of the specific mechanisms through which it expresses itself in our macroscopic world. For example, there are still many who believe that cavitation erosion is due to the shock wave that is emitted by bubble implosion, rather than the liquid jet created on asymmetric collapse...and they may be right. Over the years, the author has accumulated a number of movies and high-speed photographs of cavitation activity, which he uses to form his own visual references. In the time allotted, he will show a number of these movies and photographs and discuss their relevance to existing technological problems. A limited number of CDs containing the presented materials will be available to interested individuals. [Work supported in part by the NIH, USAMRMC, and the ONR.]

Bolometric images of the three-dimensional structure of asymmetric radiative collapse in LHD

The infrared (IR) imaging bolometer has the merit of being able to measure wide two-dimensional images of the plasma radiation. Two IR imaging video bolometers (IRVB, one type of IR imaging bolometer system) were installed on the large helical device (LHD). Using these IRVBs, the asymmetric radiation collapse that is similar to the multifaceted asymmetric radiation from the edge was measured in LHD. From the results of the asymmetric collapse study in LHD, the high radiation region is localized on the inboard side and under the midplane on the vacuum vessel, but this region is not the nearest point from the plasma to the first wall. From other reports on LHD, it is written that the wall recycling is not a trigger for the asymmetric radiation onset, which is confirmed by this new result.

30 MHz backscatter and Doppler signals from individual microbubbles undergoing inertial cavitation

Short pulses (1–2 microseconds duration) of 30 MHz ultrasound were used to interrogate individual OptisonTM and PESDA microbubbles convected in a coaxial jet flow or adhering to a thin MylarTM window. Backscattered signals were recorded as the bubbles were forced into symmetrical or asymmetrical collapse by application of 1 MHz ultrasound pulses from a focused source in water. Peak-to-peak amplitudes of the backscattered signal were converted to radius–time curves via comparison with similar signals from a monodisperse population of polystyrene spheres of known diameter. Additionally, backscattered signals were mixed with reference sinusoids at 30 MHz and low-pass filtered to yield Doppler signals. Results are consistent with theoretical models and provide a possible method to quantify asymmetrical bubble collapse via Doppler signature.

Derivation of plastic framing requirements for polar ships

A new International Association of Classification Societies standard for polar ship design, in the form of a unified requirement is being developed by an international committee with representatives from many classification societies and with the active participation of many polar nations. The framing structural requirements have been developed by a combination of analysis of existing rules and ships, finite element (FE) analysis and analytical solutions of plastic collapse mechanisms. This paper describes the derivation of the 3-hinge and asymmetrical shear plastic collapse mechanisms using work–energy principles. Energy methods are robust and well suited for developing design standards. The results are shown to compare well with non-linear FE analyses of frame strength.