A review of nonlinear constitutive models for metals

Over the past two decades a number of thermomechanical constitutive theories have been proposed for viscoplastic metals. These models are in most cases similar in that they utilize a set of internal state variables which provide locally averaged representations of microphysical phenomena such as dislocation rearrangement and grain boundary sliding. The state of development of several of these models is now at the point where accurate theoretical solutions can be obtained for a wide variety of structural problems at elevated temperatures. The fundamentals of viscoplasticity are briefly reviewed and a general framework is outlined. Several of the more prominent models are reviewed, and predictions from models are compared to experimental results

Congenital Long QT Syndrome:: A cardiac ion channelopathy with important anesthetic considerations

Context: Congenital long QT syndrome (cLQTS) is the most common genetic cardiac ion channelopathy in the US. Patients with cLQTS are at risk for ventricular tachycardia (VT) in the “torsades de pointes” (TdP) pattern from physical and emotional stress, including during the perioperative period. Purpose: This narrative review outlines the history and pathophysiology of the most common types of cLQTS, describes treatments for cLQTS, discusses the experience of anesthesia providers with cLQTS, and reports recommendations for safe administration of anesthesia to these patients. Methods: Searches of MEDLINE (PubMed) and Google Scholar were conducted using the terms “congenital long QT syndrome”, “LQTS”, and “cardiac ion channelopathy” combined with “surgery” and “anesthesia”. Findings: The most common types of cLQTS (LQT1-3) are caused by loss of function mutations to potassium channels responsible for ventricular repolarization or gain of function mutations to a sodium channel responsible for depolarization. cLQTS is diagnosed using the Schwartz Criteria which considers ECG findings, clinical history, and family history. It is treated with beta blocking medication, implantable cardioverter defibrillator (ICD) insertion, or left cardiac sympathetic denervation (LCSD).  Patients with cLQTS may require anesthesia for disease-related procedures (e.g. ICD insertion or LCSD), or for treatment of issues related to cLQTS (e.g. cochlear implants for congenital sensorineural deafness). To provide a safe anesthetic, providers need to avoid medications that prolong the QTc, minimize sympathetic stimulation, assure proper function of but prevent electrical interference with ICDs, correct electrolyte imbalances, and be prepared to treat TdP.  Importance: Pre-anesthetic precautions include considering a cardiologist consultation, checking the function of the ICD, determining a baseline QTc, correcting electrolyte imbalances, premedicating to prevent anxiety, and continuing beta blocking medications on the day of surgery. Intraoperative, the anesthesia provider should apply external defibrillator pads and all monitors prior to induction, turn off ICD or adjust its settings to avoid electromagnetic interference, monitor the QT interval, have magnesium salts ready if TdP develops, consider TIVA and use sevoflurane if an inhalation agent is needed, use propofol and/or fentanyl (or an analogue) to blunt the sympathetic response of airway manipulation, and avoid ketamine, suxamethonium, and pancuronium. During emergence, the provider should consider alternatives to anticholinesterase/ anticholinergic drug combinations, avoid droperidol or ondansetron, but consider dexamethasone as prophylaxis against PONV. Limitations: Because there are no definitive guidelines for the anesthetic management of patients with cLQTS, the anesthesia provider must rely on case studies and review articles to choose a safe anesthetic for this challenging patient population

Progressive failure methodologies for predicting residual strength and life of laminated composites

Two progressive failure methodologies currently under development by the Mechanics of Materials Branch at NASA Langley Research Center are discussed. The damage tolerance/fail safety methodology developed by O'Brien is an engineering approach to ensuring adequate durability and damage tolerance by treating only delamination onset and the subsequent delamination accumulation through the laminate thickness. The continuum damage model developed by Allen and Harris employs continuum damage laws to predict laminate strength and life. The philosophy, mechanics framework, and current implementation status of each methodology are presented

Symmetric photon-photon coupling by atoms with Zeeman-split sublevels

We propose a simple scheme for highly efficient nonlinear interaction between two weak optical fields. The scheme is based on the attainment of electromagnetically induced transparency simultaneously for both fields via transitions between magnetically split F=1 atomic sublevels, in the presence of two driving fields. Thereby, equal slow group velocities and symmetric cross-coupling of the weak fields over long distances are achieved. By simply tuning the fields, this scheme can either yield giant cross-phase modulation or ultrasensitive two-photon switching.Comment: Modified scheme, 4 pages, 1 figur

Outdoor Smoke-Free Policies in Maine

Incontrovertible evidence of the deadly impacts from both direct tobacco use and environmental exposure to tobacco smoke has led to the institution of smoking bans, first in indoor venues and, more recently, in some outdoor area. This article reviews the science behind smoking bans as well as the history and policy implications of smoking bans with an emphasis on the experience in Maine. As examples we focus on recent outdoor smoking bans in South Portland (parks and beaches) and smoke-free campus rules at a Maine hospital (Franklin Memorial Hospital) and a part of the University of Maine system (University of Southern Maine). Our conclusions highlight the interconnections among federal, state, municipal, and public institutional efforts to limit smoking and suggest pathways by which smoke-free areas can be expanded in Maine and elsewhere

Electronic Cigarettes in Maine: Health Effects, Marketing, Use, and Regulation

Electronic cigarettes (e-cigarettes) are electronic nicotine-delivery systems (ENDS) that deliver a vapor of nicotine and other potentially dangerous chemicals to the user; nonusers are also exposed. Driven by a well-funded advertising campaign, use of e-cigarettes has increased in Maine until it now exceeds the use of combustible cigarettes among youth. In 2015, 14.5 percent of female high school students and 18.8 percent of male high school students in Maine reported current use of e-cigarettes. Maine laws and city ordinances restrict e-cigarette use in some places where combustible cigarettes are banned, but legislative gaps remain. Most Maine schools, colleges, and hospitals also ban e-cigarettes, but again gaps remain. This article explores the marketing and use of e-cigarettes nationwide and in Maine and proposes policies to restrict access and use, particularly by youth