The Role of Damage and Recrystallization in the Elastic Properties of Columnar Ice

Effects of damage on elastic properties were studied in columnar-grained specimens of freshwater and saline ice, subjected, at −10°C, to varying levels of inelastic strain. The ice was compressed uniaxially at constant strain rates up to 0.20 strain, which caused localized recrystallization and imparted damage in the form of non-propagating cracks. Damage was quantified in terms of dimensionless crack density, which, along with recrystallized area fraction, was determined from thin sections. The change in porosity due to stress-induced cracks served as another indicator of damage. Elastic properties were derived using P-wave and S-wave ultrasonic transmission velocities measured in across-column directions through the damaged ice, either parallel (x 1) or perpendicular (x 2) to the initial loading direction. In general, as damage increased with greater strain, the ice became more compliant and (particularly freshwater ice) more anisotropic. Furthermore, with increasing strain rate, the magnitude of these effects and crack density tended to increase, in contrast to the recrystallized area fraction, which tended to decrease. We observed compliance to correspond closely with porosity and with dimensionless crack density, for strains up to 0.10. At greater levels of strain these correspondences became less clear due, in part, to the different character of the damage

Effects of prestrain on the ductile-to-brittle transition of ice

AbstractThe ductile-to-brittle transition was investigated in prestrained columnar ice at −10 °C. Laboratory-grown specimens of freshwater and saline ice were prestrained under uniaxial across-column compression (to levels from εp = 0.003 to εp = 0.20, at constant strain rates in the ductile regime) and likewise reloaded (at rates from 1 × 10−6s−1 to 3 × 10−2s−1). Prestrain caused solid-state recrystallization as well as damage in the form of non-propagating microcracks. The ductile-to-brittle transition strain rate ε˙D/B increased by a factor of 3–10 after prestrain of εp = 0.035 in both freshwater and saline ice, compared to that of initially undamaged ice of the same type. Additional prestrain had little further effect on ε˙D/B. The results are interpreted within the framework of a model (proposed by Schulson, 1990, and Renshaw and Schulson, 2001) that predicts the transition strain rate based on the micromechanical boundary between creep and fracture processes. Model parameters primarily affected by prestrain were the power-law creep coefficient B (more so than the creep exponent n), Young's modulus E and, by extension, the fracture toughness KIc

Understanding Traumatic Brain Injury in the Primary Care Setting

poster abstractBackground: TBI is being re-conceptualized as a chronic disease causative agent rather than as a single, acute event. This study examined how familiar family medicine physicians (PCPs) are with TBI and their level of confidence in treating TBI sequelae likely to be seen in primary care. We also examined PCP attitudes regarding care for post-acute mild TBI and moderate/severe TBI in primary care and how recently the respondent had cared for a mild TBI and/or moderate/severe TBI patient. Methods: The study featured a mixed methods study design. A survey was administered on paper and electronically. A semi-structured qualitative interview guide was developed based upon survey responses. Descriptive statistics were calculated. Results: Most respondents associated neurological symptoms/conditions as TBI sequelae: irritability, 100.0%, fatigue, 98.0%; insomnia, 88.2%, depression, 98.0%, headaches, 98.0%, anxiety, 80.4%. Two-thirds (66.7%) identified epilepsy as a condition associated with TBI. Just over one-half associated tinnitus (51.0%) or loss of libido (52.9%) with TBI while only one-third (33.3%) associated incontinence with TBI. Most physicians felt confident treating depression (84.0%), anxiety (82.4%), headache (80.4%) and insomnia (76.0%). Physicians felt less confident in treating fatigue (68.0%), irritability (68.0%), incontinence (51.2%) and loss of libido (50.0%). The least amount of confidence was claimed in treating epilepsy (37.5%) and tinnitus (36.4%). All respondents (100.0%) believed that a PCP can manage post-acute mild TBI (concussion) care while 52.0% agreed that a PCP can manage post-acute care for moderate/severe TBI. Only one respondent (2.0%) had never cared for a mild TBI patient. Most (70.6%) had cared for a moderate/severe TBI patient within the past two years while 5.9% had cared for one of these patients more than a year ago. Nearly twenty percent (19.7%) had never cared for a moderate/severe TBI patient and 3.9% were unsure if they had

Plastic Faulting in Saltwater Ice

Compression experiments on laboratory-grown columnar S2 saltwater ice loaded triaxially through proportional loading at T = –20°C at applied strain rates of ε = 10–5–10–1 s–1 demonstrate that plastic (P) faulting is a mode of failure in saltwater ice when rapidly loaded under a high degree of confinement. In terms of microstructure, mechanical behavior and strength, saltwater ice that fails via P-faulting is almost indistinguishable from columnar S2 freshwater ice that fails via P-faulting loaded under the same conditions. The results also demonstrate that saltwater ice loaded rapidly may exhibit yet another mode of failure, in addition to P-faulting, through what appears to be a mechanism of pore collapse

Opioid Overdose Prevention in Family Medicine Clerkships: A CERA Study

BACKGROUND AND OBJECTIVES: The national opioid crisis requires medical education to develop a proactive response centering on prevention and treatment. Primary care providers (PCPs)—many of whom are family medicine physicians—commonly treat patients on opiates, and write nearly 50% of opioid prescriptions. Despite linkages between PCP opioid prescribing patterns and the associated potential for overdose, little is known about how family medicine clerkship students are trained to prevent opioid overdose, including training on the use of naloxone. This study describes the presence of opioid overdose education at the national level and barriers to inclusion. It also discusses implementation strategies along with instructional methodology and learner evaluation. METHODS: Data were collected as part of a cross-sectional survey administered electronically by the Council of Academic Family Medicine Educational Research Alliance to 139 family medicine clerkship directors. RESULTS: A total of 99 clerkship directors (71.2% response rate) responded to the survey. A large majority (86.4%) agreed that it is important to offer opioid overdose prevention education in the clerkship, yet only 25.8% include this topic. Of these, only 50.0% address naloxone use. The most common barriers to including opioid overdose prevention education were prioritization of educational topics (82.1%) followed by lack of available faculty with sufficient experience/expertise (67.7%). CONCLUSIONS: Findings point to a disparity between perceived importance of opioid overdose prevention education and inclusion of this topic in family medicine clerkship-level medical education. Innovative use of online education and partnering with community resources may address barriers related to curricular prioritization while supporting interprofessional education principles

Brain Phosphorus Magnetic Resonance Spectroscopy Imaging of Sleep Homeostasis and Restoration in Drug Dependence

Numerous reports have documented a high occurrence of sleep difficulties in drug-dependent populations, prompting researchers to characterize sleep profiles and physiology in drug abusing populations. This mini-review examines studies indicating that drug-dependent populations exhibit alterations in sleep homeostatic and restoration processes in response to sleep deprivation. Sleep deprivation is a principal sleep research tool that results in marked physiological challenge, which provides a means to examine sleep homeostatic processes in response to extended wakefulness. A report from our laboratory demonstrated that following recovery sleep from sleep deprivation, brain high-energy phosphates particularly beta–nucleoside triphosphate (beta-NTP) are markedly increased as measured with phosphorus magnetic resonance spectroscopy (MRS). A more recent study examined the effects of sleep deprivation in opiate-dependent methadone-maintained (MM) subjects. The study demonstrated increases in brain beta-NTP following recovery sleep. Interestingly, these increases were of a markedly greater magnitude in MM subjects compared to control subjects. A similar study examined sleep deprivation in cocaine-dependent subjects demonstrating that cocaine-dependent subjects exhibit greater increases in brain beta-NTP following recovery sleep when compared to control subjects. The studies suggest that sleep deprivation in both MM subjects and cocaine-dependent subjects is characterized by greater changes in brain ATP levels than control subjects. Greater enhancements in brain ATP following recovery sleep may reflect a greater disruption to or impact of sleep deprivation in drug dependent subjects, whereby sleep restoration processes may be unable to properly regulate brain ATP and maintain brain high-energy equilibrium. These studies support the notion of a greater susceptibility to sleep loss in drug dependent populations. Additional sleep studies in drug abusing populations are needed, particularly those that examine potential differential effects of sleep deprivation

Effects of Sleep Deprivation on Brain Bioenergetics, Sleep, and Cognitive Performance in Cocaine-Dependent Individuals

In cocaine-dependent individuals, sleep is disturbed during cocaine use and abstinence, highlighting the importance of examining the behavioral and homeostatic response to acute sleep loss in these individuals. The current study was designed to identify a differential effect of sleep deprivation on brain bioenergetics, cognitive performance, and sleep between cocaine-dependent and healthy control participants. 14 healthy control and 8 cocaine-dependent participants experienced consecutive nights of baseline, total sleep deprivation, and recovery sleep in the research laboratory. Participants underwent [31]P magnetic resonance spectroscopy (MRS) brain imaging, polysomnography, Continuous Performance Task, and Digit Symbol Substitution Task. Following recovery sleep, [31]P MRS scans revealed that cocaine-dependent participants exhibited elevated global brain β-NTP (direct measure of adenosine triphosphate), α-NTP, and total NTP levels compared to those of healthy controls. Cocaine-dependent participants performed worse on the Continuous Performance Task and Digit Symbol Substitution Task at baseline compared to healthy control participants, but sleep deprivation did not worsen cognitive performance in either group. Enhancements of brain ATP levels in cocaine dependent participants following recovery sleep may reflect a greater impact of sleep deprivation on sleep homeostasis, which may highlight the importance of monitoring sleep during abstinence and the potential influence of sleep loss in drug relapse

Increased Orbitofrontal Brain Activation after Administration of a Selective Adenosine A2A Antagonist in Cocaine Dependent Subjects

Background: Positron Emission Tomography imaging studies provide evidence of reduced dopamine function in cocaine dependent subjects in the striatum, which is correlated with prefrontal cortical glucose metabolism, particularly in the orbitofrontal cortex. However, whether enhancement of dopamine in the striatum in cocaine dependent subjects would be associated with changes in prefrontal cortical brain activation is unknown. One novel class of medications that enhance dopamine function via heteromer formation with dopamine receptors in the striatum is the selective adenosine A2A receptor antagonists. This study sought to determine the effects administration of the selective adenosine A2A receptor antagonist SYN115 on brain function in cocaine dependent subjects. Methodology/Principle Findings: Twelve cocaine dependent subjects underwent two fMRI scans (one after a dose of placebo and one after a dose of 100 mg of SYN115) while performing a working memory task with three levels of difficulty (3, 5, and 7 digits). fMRI results showed that for 7-digit working memory activation there was significantly greater activation from SYN115 compared to placebo in portions of left (L) lateral orbitofrontal cortex, L insula, and L superior and middle temporal pole. Conclusion/Significance: These findings are consistent with enhanced dopamine function in the striatum in cocaine dependent subjects via blockade of adenosine A2A receptors producing increased brain activation in the orbitofrontal cortex and other cortical regions. This suggests that at least some of the changes in brain activation in prefrontal cortical regions in cocaine dependent subjects may be related to altered striatal dopamine function, and that enhancement of dopamine function via adenosine A2A receptor blockade could be explored further for amelioration of neurobehavioral deficits associated with chronic cocaine use

Markovian Dynamics on Complex Reaction Networks

Complex networks, comprised of individual elements that interact with each other through reaction channels, are ubiquitous across many scientific and engineering disciplines. Examples include biochemical, pharmacokinetic, epidemiological, ecological, social, neural, and multi-agent networks. A common approach to modeling such networks is by a master equation that governs the dynamic evolution of the joint probability mass function of the underling population process and naturally leads to Markovian dynamics for such process. Due however to the nonlinear nature of most reactions, the computation and analysis of the resulting stochastic population dynamics is a difficult task. This review article provides a coherent and comprehensive coverage of recently developed approaches and methods to tackle this problem. After reviewing a general framework for modeling Markovian reaction networks and giving specific examples, the authors present numerical and computational techniques capable of evaluating or approximating the solution of the master equation, discuss a recently developed approach for studying the stationary behavior of Markovian reaction networks using a potential energy landscape perspective, and provide an introduction to the emerging theory of thermodynamic analysis of such networks. Three representative problems of opinion formation, transcription regulation, and neural network dynamics are used as illustrative examples.Comment: 52 pages, 11 figures, for freely available MATLAB software, see http://www.cis.jhu.edu/~goutsias/CSS%20lab/software.htm

Climate change, water rights, and water supply: The case of irrigated agriculture in Idaho

We conduct a hedonic analysis to estimate the response of agricultural land use to water supply information under the Prior Appropriation Doctrine by using Idaho as a case study. Our analysis includes long-term climate (weather) trends and water supply conditions as well as seasonal water supply forecasts. A farm-level panel data set, which accounts for the priority effects of water rights and controls for diversified crop mixes and rotation practices, is used. Our results indicate that farmers respond to the long-term surface and ground water conditions as well as to the seasonal water supply variations. Climate change-induced variations in climate and water supply conditions could lead to substantial damages to irrigated agriculture. We project substantial losses (up to 32%) of the average crop revenue for major agricultural areas under future climate scenarios in Idaho. Finally, farmers demonstrate significantly varied responses given their water rights priorities, which imply that the distributional impact of climate change is sensitive to institutions such as the Prior Appropriation Doctrine. ? 2014. American Geophysical Union. All Rights Reserved