Evolution of a localized thermal explosion in a reactive gas

Experimental observations of ignition in premixed gaseous reactants indicate that perfectly homogeneous initiation is practically unrealizable. Instead, combustion first sets in, as a rule, at small, discrete sites where inherent inhomogeneities cause chemical activity to proceed preferentially and lead to localized explosions. Combustion waves propagating away from these hot spots or reaction centers eventually envelop the remaining bulk. This study examines the spatial structure and temporal evolution of a hot spot for a model involving Arrhenius kinetics. The hot spot, characterized by peaks in pressure and temperature with little diminution in local density, is shown to have one of two possible self-similar structures. The analysis employs a combination of asymptotics and numerics, and terminates when pressure and temperature in the explosion have peaked

Ignition of thermally sensitive explosives between a contact surface and a shock

The dynamics of ignition between a contact surface and a shock wave is investigated using a one-step reaction model with Arrhenius kinetics. Both large activation energy asymptotics and high-resolution finite activation energy numerical simulations are employed. Emphasis is on comparing and contrasting the solutions with those of the ignition process between a piston and a shock, considered previously. The large activation energy asymptotic solutions are found to be qualitatively different from the piston driven shock case, in that thermal runaway first occurs ahead of the contact surface, and both forward and backward moving reaction waves emerge. These waves take the form of quasi-steady weak detonations that may later transition into strong detonation waves. For the finite activation energies considered in the numerical simulations, the results are qualitatively different to the asymptotic predictions in that no backward weak detonation wave forms, and there is only a weak dependence of the evolutionary events on the acoustic impedance of the contact surface. The above conclusions are relevant to gas phase equation of state models. However, when a large polytropic index more representative of condensed phase explosives is used, the large activation energy asymptotic and finite activation energy numerical results are found to be in quantitative agreement

Puffy Foot Syndrome: An Important Often Overlooked Clinical Entity

The puffy foot syndrome, a novel clinical entity, describes the complication of secondary lymphedema with chronic progression in the feet, a finding that has often been overlooked in the non-tropical setting. While previously well described in the upper extremities, this complication has not been fully explored in the lower extremities. However, given increasing rates of diabetes mellitus, obesity, and a myriad of other possible etiologies in the United States, it is important to understand this entity and its non-viral, non-parasitic causes in non-tropical regions. This review delineates common illustrative properties of this syndrome observed in clinical practice as well as long-term complications, including Ruocco’s immunocompromised cutaneous district, that are often overlooked. Furthermore, a novel method of staging is suggested for this condition, reflective of increasing risk of complication, infection, and malignancy. We also highlight the increased need for improved detection and recognition of this condition to avoid possibly deleterious outcomes

Puffy Foot Syndrome: An Important Often Overlooked Clinical Entity

The puffy foot syndrome, a novel clinical entity, describes the complication of secondary lymphedema with chronic progression in the feet, a finding that has often been overlooked in the non-tropical setting. While previously well described in the upper extremities, this complication has not been fully explored in the lower extremities. However, given increasing rates of diabetes mellitus, obesity, and a myriad of other possible etiologies in the United States, it is important to understand this entity and its non-viral, non-parasitic causes in non-tropical regions. This review delineates common illustrative properties of this syndrome observed in clinical practice as well as long-term complications, including Ruocco’s immunocompromised cutaneous district, that are often overlooked. Furthermore, a novel method of staging is suggested for this condition, reflective of increasing risk of complication, infection, and malignancy. We also highlight the increased need for improved detection and recognition of this condition to avoid possibly deleterious outcomes

Reactive-diffuse System with Arrhenius Kinetics: Peculiarities of the Spherical Goemetry

The steady reactive-diffusive problem for a non isothermal permeable pellet with first-order Arrhenius kinetics is studied. In the large activation-energy limit, asymptotic solutions are derived for the spherical geometry. The solutions exhibit multiplicity and it is shown that a suitable choice of parameters can lead to an arbitrarily large number of solutions, thereby confirming a conjecture based upon past computational experiments. Explicit analytical expressions are given for the multiplicity bounds (ignition and extinction limits). The asymptotic results compare very well with those obtained numerically, even for moderate values of the activation energy

Application of a Two-Fluid Model to Simulate the Heating of Two-Phase Flows

International audienceThis paper is dedicated to the simulation of two-phase flows on the basis of a two-fluid model that allows to account for the disequilibrium of velocities, pressures , temperatures and chemical potentials (mass transfer). The numerical simulations are performed using a fractional step method treating separately the convective part of the model and the source terms. The scheme dealing with the convective part of the model follows a Finite Volume approach and is based on a relaxation scheme. In the sequel, a special focus is put on the discretization of the terms that rule the mass transfer. The scheme proposed is a first order implicit scheme and can be verified using an analytical solution. Eventually, a test case of the heating of a mixture of steam and water is presented, which is representative of a steam generator device

Average Rate Analysis of Cooperative NOMA aided Underwater Optical Wireless Systems

In this paper, we consider a cooperative non-orthogonal multiple access (NOMA) aided underwater optical wireless system in which the source transmits to two users where the near user serves as a relay node to the far user. Our proposed system consists of multiple narrow-angle light-emitting diode (LED)/photodiode (PD) elements at the source, near user, and far user. In order to achieve communication, our system selects a single LED/PD at each node. We propose several low complexity LED/PD selection schemes that aim to maximize the link throughput and in addition consider optimal and random LED/PD selection for benchmarking. In order to characterize the performance of each scheme, bounds and closed-form tight approximations on the average achievable sum rates are presented. The use of multi element nodes and NOMA increase the average sum rate significantly over conventional orthogonal access. Moreover, near-optimal throughput can be achieved using channel gain based and line-of-sight based LED/PD selection schemes in the medium-to-high transmit power regimes. The derived expressions are also useful to investigate the impact of key system and channel parameters such as the source transmit power, power allocation factor, node placement, and the number of elements at each node

Personalized and precision orthodontic therapy

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111225/1/ocr12089.pd