A Laboratory Investigation of Supersonic Clumpy Flows: Experimental Design and Theoretical Analysis

We present a design for high energy density laboratory experiments studying the interaction of hypersonic shocks with a large number of inhomogeneities. These ``clumpy'' flows are relevant to a wide variety of astrophysical environments including the evolution of molecular clouds, outflows from young stars, Planetary Nebulae and Active Galactic Nuclei. The experiment consists of a strong shock (driven by a pulsed power machine or a high intensity laser) impinging on a region of randomly placed plastic rods. We discuss the goals of the specific design and how they are met by specific choices of target components. An adaptive mesh refinement hydrodynamic code is used to analyze the design and establish a predictive baseline for the experiments. The simulations confirm the effectiveness of the design in terms of articulating the differences between shocks propagating through smooth and clumpy environments. In particular, we find significant differences between the shock propagation speeds in a clumpy medium compared to a smooth one with the same average density. The simulation results are of general interest for foams in both inertial confinement fusion and laboratory astrophysics studies. Our results highlight the danger of using average properties of inhomogeneous astrophysical environments when comparing timescales for critical processes such as shock crossing and gravitational collapse times.Comment: 7 pages, 6 figures. Submitted to the Astrophysical Journal. For additional information, including simulation animations and the pdf and ps files of the paper with embedded high-quality images, see http://pas.rochester.edu/~wm

Atomistic simulations of dislocation mobility in Al, Ni and Al/Mg alloys

Dislocation velocities and mobilities are studied by Molecular Dynamics simulations for edge and screw dislocations in pure aluminum and nickel, and edge dislocations in Al-2.5%Mg and Al-5.0%Mg random substitutional alloys using EAM potentials. In the pure materials, the velocities of all dislocations are close to linear with the ratio of (applied stress)/(temperature) at low velocities, consistent with phonon drag models and quantitative agreement with experiment is obtained for the mobility in Al. At higher velocities, different behavior is observed. The edge dislocation velocity remains dependent solely on (applied stress)/(temperature) up to approximately 1.0 MPa/K, and approaches a plateau velocity that is lower than the smallest "forbidden" speed predicted by continuum models. In contrast, above a velocity around half of the smallest continuum wave speed, the screw dislocation damping has a contribution dependent solely on stress with a functional form close to that predicted by a radiation damping model of Eshelby. At the highest applied stresses, there are several regimes of nearly constant (transonic or supersonic) velocity separated by velocity gaps in the vicinity of forbidden velocities; various modes of dislocation disintegration and destabilization were also encountered in this regime. In the alloy systems, there is a temperature- and concentration-dependent pinning regime where the velocity drops sharply below the pure metal velocity. Above the pinning regime but at moderate stresses, the velocity is again linear in (applied stress)/(temperature) but with a lower mobility than in the pure metal.Comment: PDF, 30 pages including figures, submitted to Modelling Simul. Mater. Sci. En

Initiation of secondary explosives measured using embedded electromagnetic gauges

There is considerable evidence that secondary explosive materials having a relatively large (10-12%) proportion of HTPB binder do not exhibit DDT under cook-off. However, the understanding of the mechanisms controlling the growth of reaction in such experiments is incomplete. Most importantly, it is not known whether a mechanistic reason exists to preclude DDT; it is possible that existing techniques to explore cook-off simply do not offer the correct conditions to allow DDT to occur. We present experiments in which impacts were made against a RDX/HTPB PBX using a single-stage light gas gun. Electromagnetic particle velocity gauges were embedded within the targets at different distances from the impact face to record the onset of reaction, and in some cases detonation. These experiments were also performed against RDX/TNT targets. The time-resolved particle velocity histories have allowed comparison of some of the factors governing growth of reaction, and have provided run-to-detonation distance data for different impact stresses

Expression Templates in Ada

High-order matrix or vector expressions tend to be penalized by the use of huge temporary variables. Expression templates is a C++ technique which can be used to avoid these temporaries, in a way that is transparent to the user. We present an Ada adaptation of this technique which --- while not transparent --- addresses the same e#ciency issue as the original. We make intensive use of the signature idiom to combine packages together, and discuss its importance in generic programming

State of the art opioid-sparing strategies for post-operative pain in adult surgical patients.

INTRODUCTION:There are various important implications associated with poorly controlled postoperative pain in the adult surgical patient - this includes cardiopulmonary complications, opioid-related side effects, unplanned hospital admissions, prolonged hospital stay, and the subsequent development of chronic pain or opioid addiction. With the ongoing national opioid crisis, it is imperative that perioperative providers implement pathways for surgical patients that reduce opioid requirements and pain-related complications. AREAS COVERED:In this review, the authors discuss the components of a multimodal opioid-sparing analgesia pathway as it pertains to the perioperative environment. Medications reviewed include gabapentinoids, acetaminophen, non-steroidal anti-inflammatory drugs, ketamine, intravenous lidocaine, dexmedetomidine, and glucocorticoids. The use of peripheral nerve blocks and neuraxial analgesia are also discussed. EXPERT OPINION:In appropriate cases, regional anesthetic interventions are extremely useful for postoperative analgesia, including peripheral nerve blocks and neuraxial analgesia and while newer postoperative analgesics have been postulated, the literature on such is presently controversial. Coordinated approaches to pain management are recommended to reduce the need for opioids and to improve patient satisfaction post-surgery