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Distribution by Scientific Domains

Medical Sciences	50%

Selected Abstracts

RAPID EVOLUTIONARY ESCAPE BY LARGE POPULATIONS FROM LOCAL FITNESS PEAKS IS LIKELY IN NATURE

EVOLUTION, Issue 6 2005
Daniel M. Weinreich
Abstract Fitness interactions between loci in the genome, or epistasis, can result in mutations that are individually deleterious but jointly beneficial. Such epistasis gives rise to multiple peaks on the genotypic fitness landscape. The problem of evolutionary escape from such local peaks has been a central problem of evolutionary genetics for at least 75 years. Much attention has focused on models of small populations, in which the sequential fixation of valley genotypes carrying individually deleterious mutations operates most quickly owing to genetic drift. However, valley genotypes can also be subject to mutation while transiently segregating, giving rise to copies of the high fitness escape genotype carrying the jointly beneficial mutations. In the absence of genetic recombination, these mutations may then fix simultaneously. The time for this process declines sharply with increasing population size, and it eventually comes to dominate evolutionary behavior. Here we develop an analytic expression for Ncrit, the critical population size that defines the boundary between these regimes, which shows that both are likely to operate in nature. Frequent recombination may disrupt high-fitness escape genotypes produced in populations larger than Ncrit before they reach fixation, defining a third regime whose rate again slows with increasing population size. We develop a novel expression for this critical recombination rate, which shows that in large populations the simultaneous fixation of mutations that are beneficial only jointly is unlikely to be disrupted by genetic recombination if their map distance is on the order of the size of single genes. Thus, counterintuitively, mass selection alone offers a biologically realistic resolution to the problem of evolutionary escape from local fitness peaks in natural populations. [source]

Modeling an industrial energy system: Perspectives on regional heat cooperation

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 9 2008
S. Klugman
Abstract Through energy efficiency measures, it is possible to reduce heat surplus in the pulp and paper industry. Yet pulp and paper mills situated in countries with a heat demand for residential and commercial buildings for the major part of the year are potential heat suppliers. However, striving to utilize the heat within the mills for efficient energy use could conflict with the delivery of excess heat to a district heating system. As part of a project to optimize a regional energy system, a sulfate pulp mill situated in central Sweden is analyzed, focusing on providing heat and electricity to the mill and its surrounding energy systems. An energy system optimization method based on mixed integer linear programming is used for studying energy system measures on an aggregated level. An extended system, where the mill is integrated in a regional heat market (HM), is evaluated in parallel with the present system. The use of either hot sewage or a heat pump for heat deliveries is analyzed along with process integration measures. The benefits of adding a condensing unit to the back-pressure steam turbine are also investigated. The results show that the use of hot sewage or a heat pump for heat deliveries is beneficial only in combination with extended heat deliveries to an HM. Process integration measures are beneficial and even increase the benefit of selling more heat for district heating. Adding a condensing turbine unit is most beneficial in combination with extended heat deliveries and process integration. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Scandinavian Clinical practice guidelines for therapeutic hypothermia and post-resuscitation care after cardiac arrest

ACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 3 2009
M. CASTRÉN
Background and aim: Sudden cardiac arrest survivors suffer from ischaemic brain injury that may lead to poor neurological outcome and death. The reperfusion injury that occurs is associated with damaging biochemical reactions, which are suppressed by mild therapeutic hypothermia (MTH). In several studies MTH has been proven to be safe, with few complications and improved survival, and is recommended by the International Liaison of Committee on Resuscitation. The aim of this paper is to recommend clinical practice guidelines for MTH treatment after cardiac arrest from the Scandinavian Society of Anaesthesiology and Intensive Care Medicine (SSAI). Methods: Relevant studies were identified after two consensus meetings of the SSAI Task Force on Therapeutic Hypothermia (SSAITFTH) and via literature search of the Cochrane Central Register of Controlled Trials and Medline. Evidence was assessed and consensus opinion was used when high-grade evidence (Grade of Recommendation, GOR) was unavailable. A management strategy was developed as a consensus from the evidence and the protocols in the participating countries. Results and conclusion: Although proven beneficial only for patients with initial ventricular fibrillation (GOR A), the SSAITFTH also recommend MTH after restored spontaneous circulation, if active treatment is chosen, in patients with initial pulseless electrical activity and asystole (GOR D). Normal ethical considerations, premorbid status, total anoxia time and general condition should decide whether active treatment is required or not. MTH should be part of a standardized treatment protocol, and initiated as early as possible after indication and treatment have been decided (GOR E). There is insufficient evidence to make definitive recommendations among techniques to induce MTH, and we do not know the optimal target temperature, duration of cooling and rewarming time. New studies are needed to address the question as to how MTH affects, for example, prognostic factors. [source]

Target-organ protection with combination renin-angiotensin-system blockade

CLINICAL CARDIOLOGY, Issue 1 2009
L. Michael PrisantMD FACC
Abstract Pharmacologic blockade of the renin-angiotensin-aldosterone system (RAS) has antihypertensive, anti-atherogenic, antioxidant, and anti-inflammatory effects. Treatment with angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) has been demonstrated to prevent atrial fibrillation and new-onset diabetes, and provide cardiac, cerebral, and renal protection. Combination therapy with ACEIs and ARBs, compared with monotherapy, provides enhanced reno- and cardioprotection, although available data indicate that combination RAS blockade may be beneficial only in select patient groups, such as those with diabetes mellitus, chronic kidney disease, or heart failure (HF). In certain high-risk patients, the use of ARBs provides comparable efficacy to that observed with ACEIs. The efficacy of these agents may stem from pleiotropic effects beyond blood pressure (BP) reduction. Several studies demonstrate achievement of clinical endpoints without significant effects on BP. Copyright © 2009 Wiley Periodicals, Inc. [source]