Increase In Fractional Area Research Articles

Evolving black holes in inflation

We present an analytic, perturbative solution to the Einstein equations with a scalar field that describes dynamical black holes in a slow-roll inflationary cosmology. We show that the metric evolves quasi-statically through a sequence of Schwarzschild–de Sitter like metrics with time dependent cosmological constant and mass parameters, such that the cosmological constant is instantaneously equal to the value of the scalar potential. The areas of the black hole and cosmological horizons each increase in time as the effective cosmological constant decreases, and the fractional area increase is proportional to the fractional change of the cosmological constant, times a geometrical factor. For black holes ranging in size from much smaller than to comparable to the cosmological horizon, the pre-factor varies from very small to order one. The ‘mass first law’ and the ‘Schwarzchild–de Sitter patch first law’ of thermodynamics are satisfied throughout the evolution.

Nanoindentation creep of quartz, with implications for rate- and state-variable friction laws relevant to earthquake mechanics

The frictional behavior of rocks in the laboratory is reasonably well described by rate- and state-variable friction laws, which reproduce a rich variety of natural phenomena when used in models of earthquakes. Despite the widespread adoption of the rate and state formalism in earthquake mechanics, the physical mechanisms that occur at microscopic contacting asperities on the sliding surface, which give rise to the observed rate and state effects, are still poorly understood. In an attempt to identify these underlying mechanisms, a series of nanoindentation experiments on quartz, an abundant mineral in the earth’s crust, was conducted. These experiments demonstrate the utility of using continuous stiffness measurements as a means of obtaining reliable indentation creep data on hard materials like quartz at room temperature. The projected area of indentation in quartz increases linearly with the logarithm of the time of indentation, in agreement with the increase in real area of contact with log time inferred from slide-hold-slide friction experiments on quartz rocks. However, the increase in fractional area with time in the indentation tests was larger than that inferred from friction experiments by a factor of 1.7. Differences between the rates of fractional area increase in the two tests may indicate that the increase in contact area during the hold portion of slide-hold-slide tests was modulated by slip that occurs during reloading after the hold, as was observed for other materials. The nanoindentation results suggest that the increase in frictional strength (i.e., the increase of state in the rate- and state-variable friction laws) during slide-hold-slide friction experiments was caused by creep of the highly stressed asperity contacts.

Defibrillation Causes Immediate Cardiac Dilation in Humans

Defibrillation Causes Dilation. Prior studies in isolated heart tissue have shown both excitation and deexcitation to be the primary mechanism of defibrillation. This article presents the first evidence in man of deexcitation immediately following defibrillation by tracking the heart's mechanical response. The geometric changes of the ventricular chambers were measured before and after defibrillation in seven human subjects receiving an implantable cardioverter defibrillator (ICD). The ICD was used to produce approximately three episodes of ventricular fibrillation and defibrillation in each subject. Twenty-two two-dimensional echocardiographic images of the right ventricle (RV) and 11 images of the left ventricle (LV) were recorded and analyzed at 30 frames per second. Just over 2 seconds of each episode were digitized, beginning half a second before the defibrillation shock. Individual frames were analyzed to yield cross-sectional, ventricular chamber area as a function of time. Immediately following defibrillation, ventricular chambers dilated with significant fractional area increase (RV: 1.58 +/- 0.25, LV: 1.10 +/- 0.06), with peak dilation at 194 +/- 114 msec. Defibrillation causes a rapid increase in ventricular chamber area due to relaxation of the myocardium, suggesting that defibrillation synchronizes the cardiac cells to the deexcited state in man.

Defibrillation and the geometry of the heart: a novel measurement with implications fordefibrillation mechanisms

We present a novel measurement for studying defibrillation mechanisms:the time course of changes in the size of the left ventricular (LV) cavitywithin 500 ms following defibrillation. Mechanical changes can be linked toelectrical mechanisms via an understanding of excitation-contraction coupling.Eight mongrel dogs were internally defibrillated 5-50 seconds (includingbackup shocks) after the onset of 20 ventricular fibrillation (VF) episodesper animal. Two dimensional, short axis, LV cavity, ultrasound images wererecorded at 30 frames per second just prior to inducing VF, duringdefibrillation and following the shock. Each frame was individually analysedto yield the LV cavity area as a function of time. Defibrillation shocks werefollowed by a highly reproducible phenomenon: (1) a dramatic and rapidincrease in LV area, (2) a more or less prominent LV area plateau and (3) adecrease in the LV area. The peak fractional area increase ranged from 1.65 to4.64 times larger than the baseline (LV area just prior to defibrillation),averaging 2.18±0.686. Successful shocks took significantly longer (p < 0.01)to return to 1.3 times the baseline (407±209 ms) than unsuccessful shocks(296±130 ms). Extrapolating to electrical mechanisms, our novelmeasurement demonstrates that defibrillation causes immediate relaxation andtherefore suggests a significant role for de-excitation in defibrillation.

Coenzyme Q10 exogenous administration attenuates cold stress cardiac injury.

The influence of coenzyme Q10 (CoQ10) in cold stress test (-15 degrees C for 4 hours) cardiac functional impairment was studied in isolated isovolumic heart of control rats (C; n=12) and of placebo (P; n=11) and treated rats (CoQ10; n=10). In addition, electron microscopic evaluation of left ventricular (LV) slices (n=3 in each group) allowed us to analyze the myocardial ultrastructure. Maximal values of developed pressure (DPmax) were similarly decreased in cold stressed animals (C=129+/-3.9 mmHg; P=106+/-6.7 mmHg; CoQ10=91+/-3.9 mmHg); however, volume-induced enhancement of pressure generation (slope of DP volume relations: C=0.248+/-0.0203 mmHg / microl; P=0.2831+/-0.0187 mmHg / microl; CoQ10=0.2387 ( 0.0225 mmHg / microl; p > 0.05), and the duration of systole (C=80+/-1.6 ms; P=78+/-1.3 ms; CoQ10=80+/-2.7 ms) were not altered. Myocardial relaxation, evaluated by the relaxation constant (C=39+/-1.9 ms; P=42+/-3.4 ms; CoQ10=51+/-6.0 ms), as well as resting stress / strain relations were unaffected by cold stress. Myocardial samples showed that pretreatment with CoQ10 attenuates myofibrillar and mitochondrial lesions, and prevents mitochondrial fractional area increase (P: 53.11%>CoQ10: 38.78%=C: 33.87%; p< 0.005) indicating that the exogenous administration of CoQ10 can reduce cold stress myocardial injury.

Echocardiographic assessment of right and left ventricular function after single-lung transplantation

To evaluate the impact of single-lung transplantation on right and left ventricular performance and to identify potential preoperative characteristics that could predict postoperative outcome, a large group of patients were retrospectively evaluated by means of serial Doppler echocardiography. Twenty-six of 57 consecutive single-lung transplant patients had satisfactory Doppler echocardiographic studies before and after surgery. A significant reduction in right ventricular diastolic and systolic areas and an increase in right ventricular fractional area were noted after transplantation. The left ventricular contractility remained unchanged. In addition, significant reduction in right atrial area, right ventricular free wall thickness, and tricuspid regurgitation were also seen. Paradoxical septal motion present in eight patients before the procedure resolved in all of them after single-lung transplantation. Transthoracic echocardiography is a useful technique to document improvement in right ventricular function in 63% of patients following single-lung transplantation. Preoperative paradoxical septal motion identifies single-lung transplant recipients who have the largest postoperative right ventricular area reduction and fractional area increase. Alternative imaging modalities should be sought for single-lung transplant candidates in whom conventional transthoracic echocardiography is suboptimal.

Temperature-dependent ultrasound color flow doppler imaging in the study of a VX2 tumor in rabbits: Preliminary findings

Neovascularity in a VX2 carcinoma in rabbit liver was detectable, using an ultrasonic color Doppler flow imager. Intraportal infusion of heated saline increased the fractional area of color flow Doppler signals by at least 5% and as much as 30%, within and surrounding the tumors of all six rabbits studied. The effect of the fluid load was an increase in fractional area of color flow Doppler signals by 5 to 20% and was determined by the measurements following infusion and return to baseline temperature. The largest increment in color Doppler signal was observed in peritumoral vessels (10-40%). In contrast, the fractional area of color-coded pixels within the tumor was only slightly higher or lower (5-10%) at the peak temperature than at the baseline measurements. The temperature within the tumors was as much as 1 degree lower than parenchymal tissue in all animals measured. This was presumably due to the portal vein blood supply to normal tissue and predominantly hepatic artery supply to the pathological tissue. High velocities and persistent bidirectional flow were observed within the tumors only at the peak temperatures (> 43.5 degrees C). This experiment suggests that thermal stress may enhance tumor detectability by color Doppler imaging. Further development of a quantitative analysis method for color Doppler studies is needed.

The evolution of surfaces in turbulence

There are several phenomena that can be described to advantage in terms of surfaces within a turbulent fluid. Examples are: turbulent mixing (particularly at high Schmidt number); turbulent premixed flames; and, turbulent diffusion flames. These phenomena can (under appropriate conditions) be analyzed in terms of material surfaces, propagating surfaces, and constant-property surfaces, respectively. Deterministic and probabilistic equations are developed for the evolution of the local properties of these surfaces. The local geometry of regular surfaces is described by the surface element properties: position; normal to the surface; principal curvatures and directions; and, fractional area increase. Exact evolution equations for these properties are derived which reveal the effects of various processes—straining, and surface propagation, for example. For material surfaces and simple propagating surfaces these equations are closed with respect to surface properties:, that is, given the velocity field, the equations can be solved from specified initial conditions. The circumstances that can lead to a breakdown of regularity of an initially regular surface are determined. The fundamental one-point Eulerian probabilistic descriptor of a regular surface is the surface density function. From this can be determined the expected surface-to-volume ratio and the joint probability density function of the surface properties. An exact evolution equation for the surface density function is derived and discussed. For material surfaces and simple propagating surfaces the only unknowns in this equation are statistics of the velocity field. These statistics can be modelled (via Langevin equations, for example) and then the surface-density-function equation can be solved by a Monte Carlo method.

Dimensional changes during solvent‐induced crystallization of poly(ethylene terephthalate) films

AbstractThe sample dimensional changes accompanying diffusion with induced crystallization in amorphous poly(ethylene terephthalate) (PET) films are analyzed. Initially, the film's lateral area remains practically constant, but near the end of the process, it increases rapidly, consistent with non‐Fickian models for diffusion. The ultimate relative thickness increase is about double that for the lateral dimension, implying that plastic deformation in the thickness direction accompanies the sorption. Plots of fractional area increase (ΔA/ΔA∞) vs. fractional weight gain (W/W∞) indicate severe softening of the polymer by the penetrant.