Rate Of Volumetric Expansion Research Articles

The influence of B4C content on the pore structure of reaction-synthesized porous Ti3AlC2-TiB2 composite ceramics

Using a mixture of TiH2, Al, B4C, and graphite powders with a molar ratio of 3+2 m/1.2/m/2-m (where m ranges from 0 to 0.25, with increments of 0.05), porous Ti3AlC2-TiB2 composite ceramics were successfully synthesized through activated reaction sintering. The effect of B4C content on the phase composition, volumetric expansion, microstructure, and pore structure parameters (including pore size, porosity, and permeability) was systematically studied. When the molar ratio of B4C was less than 0.1, the volumetric expansion rate, average pore size, and permeability increased with the addition of B4C, reaching maximum values of −5.46 %, 2.23 μm, and 92.4 m3 m−2·10 kPa−1 h−1, respectively. Conversely, when the B4C molar ratio exceeded 0.1, the parameters related to the pore structure of the porous Ti3AlC2-TiB2 composite ceramics decreased, with minimum values of −10.40 %, 1.46 μm, and 68 m3 m−2·10 kPa−1 h−1, respectively. In addition, the pore formation mechanism of the porous Ti3AlC2-TiB2 composite ceramics was systematically explored. The revolution tendency of pores is related to the decomposition of TiH2, Kirkendall partial diffusion, diffusion between B and C, and the transition process of the final phase Ti3AlC2-TiB2. This research work could provide a reference for the preparation of the MAX phase composite porous materials.

Hemodynamic predictors of negative false lumen remodeling after frozen elephant trunk for acute aortic dissection.

We evaluated the blood flow within the downstream aortic false lumen after frozen elephant trunk repair for acute aortic dissection and identified hemodynamic predictors of false lumen expansion and negative false lumen remodeling using four-dimensional flow magnetic resonance imaging. Thirty-one patients (Stanford type A, n = 28; Stanford type B, n = 3) with patent false lumen who underwent frozen elephant trunk procedures for acute aortic dissection were included in this observational study. Each patient underwent computed tomography during the follow-up period and four-dimensional flow magnetic resonance imaging within 3 postoperative months. The false lumen volumetric expansion rate was calculated using computed tomography data. The direction and the rate of flow in the lower descending aortic false lumen were analyzed. Negative false lumen remodeling was defined as a volumetric increase of > 10% from the baseline volume. Negative false lumen remodeling had developed in 6 of the 31 patients during the observation period. Most of the false lumen flows were biphasic during systole. The range between peak and nadir flow rates was associated with the false lumen volumetric expansion rate (β coefficient = 6.77; p < 0.01, R2 = 0.43). The range between peak and nadir flow rates may serve as a hemodynamic predictor of negative false lumen remodeling, enabling further treatment for patients at risk of expansion in the downstream aorta.

Feasibility and safety of a non-operative clinical strategy for radiologically diagnosed low grade anterior mesial temporal tumours in the absence of a histological diagnosis

Background Although resection of mesial temporal lobe lesions can be achieved with relatively low morbidity, resective surgery is not without risk. Whilst many lesions found in the anterior mesiotemporal lobe are low-grade entities, transforming and high-grade lesions have also been demonstrated. We investigate the feasibility of utilising serial quantitative volumetric imaging, to determine if a strategy of imaging surveillance can be safely employed for the management of radiologically diagnosed anterior mesial temporal low-grade tumours without a confirmed histological diagnosis. Methods A retrospective case-note and radiology review design were utilised. The primary presenting symptomatology was recorded together with the efficacy of symptomatic control. Volumetric analysis of MRI images was performed using Brainlab software. Pre- and post-operative neuropsychological data were analysed. Results 35 patients were identified with a radiological diagnosis of a low-grade anterior mesial temporal lobe tumour. Of these, 29% (n = 10) underwent surgical resection. For the whole cohort, the mean tumour volume at diagnosis was 6.5cm3, with a mean volumetric expansion of 1.4% per month. A significant difference was found between the volumetric expansion rate of those that underwent surgical treatment and those that did not (4.9% per month vs 0.06% per month, p < .01). Of those cases that did not undergo surgical resection, no significant difference was seen between the initial diagnostic volume and the volume at the time of their most recent interval surveillance scan (p = .97). New onset epilepsy was significantly associated with a requirement for eventual surgical tumour resection; relative risk = 6.25, 95% CI = 1.5–25.9, p = .0114. Conclusion Where medical seizure control is adequate, we suggest that conservative management is feasible even in the absence of a confirmed histological diagnosis. However, in patients aged over 50 years with new onset epilepsy, a lower threshold for intervention should be considered.

Experimental Study of the Mechanical and Acoustic Emission Characteristics of Sandstone by Using High-Temperature Water-Cooling Cycles

In order to study the physical and mechanical properties of sandstone under high-temperature water-cooling cycling conditions, an RMT-150B electrohydraulic servo rock testing system and a DS-5 acoustic emission detection and analysis system were used to conduct uniaxial compression acoustic emission tests on sandstone after high-temperature water-cooling cycles. The deformation, strength, and acoustic emission characteristics of sandstone were analyzed under different temperatures and cycle times. The results show that the high-temperature water-cooling effect caused changes in the physical properties of sandstone. The volumetric expansion rate of the rock samples first decreased, then increased in temperature, and the strength first increased, then decreased, whereas the number of cycles had less of an impact on the physical properties. At 200 °C, with increased cycle number, the elastic modulus increased by 20.1%, and the compressive strength increased from 63.9 MPa to 71.46 MPa. At 300–600 °C, the elastic modulus and compressive strength of sandstone gradually decreased with increases in the temperature and cycle number, with reductions of 6.04%, 7.24%, 28.7%, 35.57%, 17.6%, 18.2%, 20.4%, and 60.5%, respectively. With increased temperature and cycle times, the acoustic emission ringing counts increased, ringing counts and cumulative energy appeared earlier, the rock samples entered elastic deformation earlier, the yield stage length increased, and the samples showed a tendency to transition from brittle to ductile damage.

Insight into the evolution of laser-induced plasma during successive deposition of laser energy

The interaction of high-temperature plasma with the matter has several potential applications. This study generated laser-induced plasma through single and successive laser energy deposition. The lifetime of the plasma is of paramount importance in most practical applications. However, this cannot be achieved with a single high-energy pulse due to certain practical challenges. Therefore, we carried out experimental and numerical investigations on the successive laser energy deposition and demonstrated its importance compared to the single pulse energy deposition. It has been observed that during successive energy deposition, the absorption of energy from the second pulse is nonlinear, and the reason for such behavior is explained in this study. Due to the nonlinear absorption from the second pulse, this study aims to present the pulse-interval configuration between the successive pulses with which it can be effective for practical use. In this study, some interesting physical phenomena (generation of fourth-lobe and multiple shock waves) are observed during successive energy deposition when the pulse interval is 50 and 100 μs. This study also adopted a new approach based on Maxwell’s theory of momentum exchange between light and matter to provide a plausible explanation for the generation of the fourth-lobe. Finally, to understand the evolution of the laser-induced plasma, the volume and volumetric expansion rate are calculated, which can be useful in determining its lifetime and mixing rate with the surrounding medium.

Briquettes of acai seeds: characterization of the biomass and influence of the parameters of production temperature and pressure in the physical-mechanical and energy quality.

Agro-industries, leveraged by the high demand of acai products, promote environmental impact through the generation of wastes in several locals in Amazon. The use with bioenergetic purposes has capacity to mitigate these scenario. Thus, the aim of the study was to characterize the biomass of acai seeds and establish the technical parameters of temperature and pressure of work to the production of briquettes of physical, mechanical and thermal quality. Temperatures of 120, 140 and 160°C; and pressures of 15, 20 and 25MPa were studied. We analyzed the briquettes mechanical compressive strength, rate of water absorption, rate of volumetric expansion and energy and apparent density. To the characterization of in natura seeds, the proximate analysis, chemical composition (extractives, holocellulose and lignin contents), higher, lower and useful heating value were determined. The proximate analysis indicated biomass thermal resistance, potential to direct burning and conversion by thermochemical processes. The lignin content may increase briquettes compressive strength produced in high temperatures. It was observed that the temperature had more influence in the evaluated briquettes characteristics than the pressure. The compressive strength was greater in 160°C and 15MPa briquettes, indicating that the lignin works as binder in this temperature, however, with pressure improvement the resistance is not favored due to the limit of resistance to compaction. The rate of water absorption decreased with the pressure increase and the temperature statistically affected in 140°C briquettes. We observed volumetric expansion values in consonance to other found in dense biofuels of the literature. Further, the apparent density and energy density were favored by pressure improvement and the temperature helped in the increase of the apparent density. Moreover, the produced briquettes presented gain in the apparent density regarding the in natura biomass and had energy density comparable to coal and adequate to co-firing in boilers.

Estimation of bulk viscosity of dilute gases using a nonequilibrium molecular dynamics approach.

A method is proposed for the calculation of bulk viscosity, μ_{b}, of dilute gases using nonequilibrium molecular dynamics (NEMD) simulations. The method uses measurement of mechanical (P_{mech}) and thermodynamic pressure (P_{thermo}) in a NEMD simulation of an expanding fluid and then relates the bulk viscosity to them by the relation μ_{b}=(P_{mech}-P_{thermo})/∇·u[over ⃗], where ∇·u[over ⃗] is the controlled rate of expansion of the fluid per unit volume. A special emphasis is given to the fundamental physical understanding of bulk viscosity in this work. The proposed method is demonstrated for the estimation of bulk viscosity of dilute nitrogen gas in the temperature range of 200-800K. Variation of bulk viscosity with temperature is reported in the above-mentioned temperature range and is found to be in a reasonably good agreement with the data available in the literature. Furthermore, variation of bulk viscosity with pressure and volumetric expansion rate is obtained. A weak linear dependency of bulk viscosity with pressure is observed, which increases with temperature. However, no significant effect of the rate of volumetric expansion is observed until 10^{8}s^{-1}. Moreover, the effect of the direction of volumetric change (expansion vs. compression) is also demonstrated in this work.

Numerical simulation of pressure-controlled cavity expansion process in clay at constant volumetric expansion rate

The cavity expansion theory is being applied to describe many geotechnical engineering processes. Many of these processes are controlled by the cavity volumetric expansion rate in practice. As soil is not an elastic material, the injection pressure is a non-linear function of the cavity volume, rendering it very difficult to produce the appropriate time history of injection pressure so that the controlled cavity volumetric expansion rate can be simulated. In this technical note, an algorithm to develop the time history of injection pressure using appropriate soil properties to generate the required cavity volumetric expansion rate in clay is presented. The simulation and experimental results of a series of laboratory-scale compaction grouting experiments are presented as an example to demonstrate the validity of the approach.

An extraordinary episode of Yellowstone caldera uplift, 2004–2010, from GPS and InSAR observations

Geodetic measurements of Yellowstone ground deformation from 2006 to June 2010 reveal deceleration of the recent uplift of the Yellowstone caldera following an unprecedented period of uplift that began in 2004. In 2006–2008 uplift rates decreased from 7 to 5 cm/yr and 4 to 2 cm/yr in the northern and southwest caldera, respectively, and in 2009 rates further reduced to 2 cm/yr and 0.5 cm/yr in the same areas. Elastic‐dislocation modeling of the deformation data robustly indicates an expanding sill at ∼7–10 km depth near the top of a seismically imaged, crystallizing magma reservoir, with a 60% decrease in the volumetric expansion rate between 2006 and 2009. Reduction of hydrothermal‐volcanic recharge from beneath the northeast caldera and seismic moment release of the 2008 and 2010 large earthquake swarms are plausible mechanisms for decelerating the caldera uplift and may have influenced the change in recent caldera motion from uplift to subsidence.

Critical Slow Dynamics of Detonation in a Gas with Non-Uniform Initial Temperature and Composition: A Large-Activation-Energy Analysis

We study the dynamic conditions of existence of the self-sustained detonation regime in gases with non-uniform initial temperature and dilution in the case where the gradients of initial state are parallel to the propagation direction. We analyze the slow dynamics of the detonation supposing that the initial variations have the same order of smallness as the unsteadiness and curvature of the leading shock of the detonation front. We obtain a hyperbolic evolution law for the detonation shock front as a solution to an eigenvalue problem solved in the asymptotic limit of large activation energies for which the induction time of the chemical decomposition process is considered much larger than the heat-release time. We study the effect of the shock dynamics of this self-sustained detonation front on the induction time and we integrate the evolution law for some examples of distinct or combined, dispersive or localized, initial variations in the temperature and diluent mass fraction. We show the existence of a bifurcation set of initial conditions that separates the self-sustained detonations that will continuously achieve the CJ regime from those whose dynamics eventually fail to initiate the chemical decomposition because the dynamic induction length becomes too long. We find that the characteristic critical lengths associated with the initial or boundary conditions are larger than the reference CJ characteristic chemical length by several orders of magnitude, a well-established experimental feature of gaseous detonations. We identify subcritical and supercritical limits which, respectively, give necessary and sufficient conditions for detonation. Below the subcritical limit, the combustion front cannot be coupled to the shock front because the volumetric expansion rate behind the shock is too large. Above the supercritical limit, the relaxation from an overdriven detonation regime to the self-sustained regime is a continuous process, without decoupling and recoupling of the combustion and shock fronts. We interpret the critical domain between these limits as the parametric zone in which experiments show successive decouplings and transverse recouplings of the combustion and shock fronts before the final self-sustained CJ regime.

Numerical and experimental study of the phase change process for underwater glider propelled by ocean thermal energy

Ocean thermal energy is a type of renewable energy. The phase change process of the thermal glider propelled by ocean thermal energy was numerically and experimentally investigated in this paper. The gliding process was analyzed and optimized while the glider was operating in the ocean thermocline near the equator. The results showed that the time of a cycle decreases by 30% and the gliding depth decreases by 40% after optimization. The gliding process was also analyzed when the PCMs were partly melted with the volumetric expansion rate at 50%, 60%, 70%, 80% and 90% of the total value. With the decreasing of the volumetric expansion rate, the depth and the duration of a cycle decrease significantly, but the output work does not decrease obviously. It is helpful to reduce the manufacturing cost and prolong the duration of the glider. In addition, it can improve the energy harvest efficiency from the ocean thermocline. The vehicle's gliding process can be further investigated in different ocean thermoclines based on the numerical model presented in this paper, which can provide helpful information for optimal design of the thermal glider.

Theoretical and experimental study of volumetric change rate during phase change process

The solid-to-liquid phase change material can be used to convert the thermal energy of low quality into mechanical energy. Its volumetric change rate has a great effect on the converting efficiency. The mathematical model of the volumetric change rate for the phase change processes of hexadecane within a cylindrical container was presented. A special experimental device was designed and constructed to verify the numerical model. The results at different Stefan numbers of the experiments matched well with those from the numerical simulations. The influences of Stefan number, Biot number and radius of cylinder on the volumetric change rate were studied and analyzed. The results showed that the volumetric change rate depends on the mass fraction of liquid phase and the difference between liquid and solid density of the materials. All the factors affecting the phase change rate will influence the volumetric change rate. The volumetric expansion rate is less than theoretical value under an external pressure. While a high-pressure situation is taken into consideration, the numerical model should also be modified by adding a function calculating density varying with pressure to ensure that the model operates properly. The power output can be enhanced by reducing the total time of melting. It can also be improved when the phase change material is partly melted at a volumetric expansion rate less than 100% of the total value. Copyright © 2008 John Wiley & Sons, Ltd.

The effect of exercise on nasal uptake of ozone in healthy human adults

The nose may help protect the lower respiratory tract from the effects of ambient ozone by scrubbing ozone from inspired air. Reductions in both nasal resistance and nitric oxide production with exercise may influence the efficiency of ozone uptake in the nose. Nasal ozone uptake was measured in 10 healthy volunteers before and after 15 min of moderate bicycle exercise. Ozone (0.2 parts/million) was pulled through both nostrils and out of the mouth at a constant flow while the subjects closed their epiglottises. Nasal uptake of ozone was determined by comparing the ozone concentration entering the nostrils to that exiting the mouth. Average preexercise uptake of ozone was 56 +/- 7.8 and 37 +/- 4.9% at 10 and 20 l/min, respectively. These averages did not significantly differ from those immediately postexercise (55 and 37%). Nasal ozone uptake increased significantly (P < 0.001) with decreasing flow rate, but intersubject variability in uptake could not be predicted by nasal volume or cross-sectional areas (as measured by acoustic rhinometry) or endogenous nitric oxide production. However, the percent change in ozone uptake after exercise, within an individual, was correlated with both 1) percent change in nasal volume (r = 0.70 at 10 l/min) and 2) percent change in the rate of volumetric expansion between the nasal valve and turbinates (r = 0.82 at 10 l/min). These results may be useful for assessing human risk associated with ozone exposure during exercise.

On the shock-induced explosion resulting from an impact by a planar detonation

We analyse the processes which occur when a planar detonation propagating from the fixed end of a donor explosive charge impacts on an acceptor homogeneous explosive. We propose a model for estimating the minimal length of the donor charge for which an explosion can be generated in the acceptor. We show that the self-similarity of the donor flow imposes a minimal length on the donor charge so its piston effect be capable of keeping the volumetric-expansion rate of the shocked acceptor to small-enough values and, thereby, of triggering explosion in a finite time. The donor detonation is represented as a Chapman-Jouguet discontinuity; the chemical decomposition in the acceptor is described by the Arrhenius global rate law. The model reproduces the experimental trend according to which the smaller minimal lengths are obtained with donor explosives that have larger heats of reaction and initial pressures. The minimal lengths predicted by the model agree well with those obtained by means of one-dimensional numerical simulations. Additional simulations show that the minimal length for generating an explosion is smaller than, but perhaps of the same order as, the minimal length for generating a transition to detonation. Further work is necessary to (i) analyse the case of donor explosives with finite reaction rates, and to (ii) account for the detonation cellular structure in the simulations of shock-to-detonation transitions.

Optimization of the rapid supercritical extraction process for aerogels

A partial differential equation is derived that describes the pressure developed in the pores of a gel during the rapid supercritical extraction process. A comparative analysis of the strains caused by syneresis and expansion of the fluid, respectively, suggests that the latter is the dominant effect for this process. Experimental results indicate that the rate of leakage from the mold is equal to the rate of volumetric expansion of the fluid, so this was used as the boundary condition for the calculation. An analytical solution is obtained for the strain produced in a purely elastic gel. The strain is found to develop most rapidly at high temperatures, where the thermal expansion of the fluid increases sharply. The model predicts a temperature dependent heating rate that can be used to avoid irreversible strains by compensating for the increase in thermal expansion coefficient.

Analysis of critical dynamics for shock-induced adiabatic explosions by means of the Cauchy problem for the shock transformation

We present a theoretical and numerical study on the induction of adiabatic explosions by accelerated curved shocks in homogeneous explosives, and pay a special attention to critical conditions for initiation. We characterize the first stage of the decomposition process, or induction, as an initial-value problem. During induction, the reaction progress-variable remains small; the induction time is given by the runaway of the dependent variables and corresponds to a logarithmic singularity in theirs material distributions. We express these distributions as first-order expansions in the progress variable about the shock. Then, the framework of our procedure is the formal Cauchy problem for quasi-linear hyperbolic sets of first-order differential equations, such as the balance laws for adiabatic flows of inviscid fluids considered in this study. When a shock front is used as data surface, the solution to the Cauchy problem yields the flow derivatives at the shock, then the induction time, as functions of the shock normal velocity and acceleration, \(D_{n}\) and \(\delta D_{n}/\delta t\), and the shock total curvature C. We next derive a necessary condition for explosion as a constraint among \(D_{n}\), \(\delta D_{n}/\delta t\) and C that ensures bounded values of the induction time. This criterion is akin to Semenov's, in the sense that the critical condition for explosion is that the heat-production rate must just exceed the heat-loss rate, here given by the volumetric expansion rate at the shock. The violation of the criterion defines a critical shock dynamics as a relationship among \(D_{n}\), \(\delta D_{n}/\delta t\) and C that generates infinite induction times. Depending on the rear-boundary conditions, which determine the shock dynamics, this event can be interpreted as either a non-initiation, or the decoupling of the shock and of the flame front induced by the shock. We illustrate our approach by a simple solution to the problem of the initiation by impact of a noncompressible piston. From the continuity constraint in the material speed and acceleration at the contact surface of the piston and the explosive, we first derive the initial shock dynamics, and then rewrite the induction time and the initiation condition in terms of the piston speed, acceleration and curvature. We compare these theoretical predictions to those of our direct numerical simulations, and to numerical results obtained by other authors, in the case of impacts on a gaseous explosive.

Dynamic growth of microvoids under combined hydrostatic and deviatoric stresses

This paper deals with the analytical study of the dynamic plastic growth of microvoids under the combined action of hydrostatic and deviatoric stresses. The results of this analysis are discussed with the help of a numerical study of the void growth relationship derived, and applied to the case of spall fracture. The conclusion is that void expansion may be affected in different manners by the presence of a field of deviatoric (purely distortional) strain rates. If the deviatoric plastic strain rate is not large compared with the rate of volumetric expansion, then, for void growth controlled fracture, the spall strength of the material tends to decrease with respect to a purely hydrostatic stress. The quantitative loss of strength may be important, depending upon the loading conditions. When void growth initiates in a state of very large deviatoric strain rates then, under the conditions of the analysis, the volumetric expansion of the voids may require excessive large stresses, so as to become very difficult in practice. Then, in such a situation a different mechanism, such as void nucleation for instance, might control the fracture process rather than plastic void growth.

Volumetric Changes in Rice Kernels During Desorption and Adsorption

Experiments were conducted to obtain information on volumetric changes of rough, brown, and milled rice due to changes in moisture content and temperature. Volumetric change of rough, brown, and milled rice was linearly related to changes in moisture content and temperature. For all three forms of rice kernels, the coefficients of cubical and linear hygroscopic expansion were higher during adsorption than during desorption. The coefficient of linear hygroscopic expansion of thickness was higher than that of length and width during desorption and adsorption; and it was higher for brown rice than for rough and milled rice during desorption. However, the coefficient of cubical thermal expansion was higher for milled rice than for brown and rough rice during desorption. Decrease in head yield ratio was correlated with rate of volumetric expansion of rough rice during adsorption.

Specific volume studies of γ‐irradiated polytetrafluoroethylene from 40 to 150°C

AbstractThe effect of γ‐irradiation and post‐irradiation heat treatment on the specific volume versus temperature relationships of polytetrafluoroethylene (PTFE) samples (1/2‐in. diameter rods) have been studied over the 40–150°C. temperature range for radiation doses up to 8.9 X 108 rad. At low doses the specific volume at any temperature decreased with dose, but above about 108 rad it increased with dose. Similarly, the rate of volumetric expansion initially decreased with dose, while, at very high doses (8.9 X 108 rad) the rate of expansion at temperatures above 100°C. exceeded that of the unirradiated PTFE. Heating at 150°C. for 100 hr. produced a substantial decrease in the specific volume and a decrease in the rate of expansion for the irradiated samples. Irradiation effects in PTFE are considered to be a result of such factors as radiation‐induced chain scission, increased crystallinity, and increased void content. Changes resulting from post‐irradiation heat treatment can be attributed to increased crystallinity, decreased void content, and weight loss.