828 research outputs found
Beitrag zur thermodynamischen Analyse und Bewertung von WasserwÀrmespeichern in Energieumwandlungsketten
WĂ€rmespeicher tragen bei optimierter Integration in WĂ€rme- und KĂ€lteversorgungsanlagen zur Einsparung von installierter Erzeugerleistung, Brennstoffeinsatz und Betriebskosten bei. Leider treten in WĂ€rmespeichern oft noch beachtliche Verluste auf und das Potenzial zur Kosten- und Energieeinsparung wird nicht vollstĂ€ndig ausgeschöpft. Dabei spielen nicht nur WĂ€rmeverluste an die Umgebung, sondern vor allem auch innere Verluste im Speicher eine Rolle. Schwerpunkte der vorliegenden Arbeit sind die Beschreibung der einzelnen Verluste an WasserwĂ€rmespeichern, die Ermittlung ihrer AusmaĂe abhĂ€ngig von der konstruktiven Gestaltung und der Betriebsweise des Speichers sowie die Auswirkungen der Verluste auf einen vorgelagerten WĂ€rmeerzeuger und den Einsatz von PrimĂ€renergie. Die Ergebnisse basieren auf umfangreichen Speichermodellierungen mit dem CFD-Code Fluent sowie experimentellen Untersuchungen an drei Testspeichern. Der quantitative Vergleich der Verluste fĂŒr ausgewĂ€hlte Beispiele zeigt bestehende Defizite sowie die Potenziale fĂŒr die Verbesserung der Konstruktion neuer WasserwĂ€rmespeicher auf.If hot water storage tanks are optimally integrated in heat or cold supply systems, they contribute to a reduction of required capacity, fuel and operation costs. Unfortunately, even today remarkable heat losses and internal losses occur in hot water storage tanks. The potential for cost and energy reductions is not completely utilized yet. Here, not only heat losses to the ambience, but also internal losses play a decisive role. Main focus of the presented work is the description of the single losses at hot water storage tanks and the determination of the correlation between the losses, the tank design and the mode of operation. Furthermore the effects of the losses in the tank on the efficiency of different types of heat generators and the input of primary energy into the system have been examined. The results are based on extended numerical modeling with the CFD-code Fluent as well as experimental test with three storage tanks. The quantitative comparison of the losses for selected examples shows the current shortcomings but even the potential for an optimized hot water storage tank design
Optimierte WasserwĂ€rmespeicher fĂŒr die Nutzung regenerativer und fossiler Energiequellen
Die Nutzung regenerativer Energiequellen stellt in vielen Systemen und Versorgungsnetzen wesentlich höhere Anforderungen an die Konstruktion, Auslegung und BetriebsfĂŒhrung von WĂ€rmespeichern als konventionelle EnergietrĂ€ger. Aber auch das Potenzial eines Brennwertkessels kann mit einem optimierten WasserwĂ€rmespeicher besser ausgeschöpft werden. Entscheidend fĂŒr die Effizienzsteigerung von WĂ€rmespeichern mit ausgeprĂ€gter thermischer Schichtung ist die Ausbildung und Aufrechterhaltung einer schmalen Mischzone zwischen dem wĂ€rmeren und kĂ€lteren Bereich des Speichers. Eine schmale Mischzone und eine niedrige Temperatur im unteren âentladenenâ Speicherbereich wirken sich positiv auf den Wirkungsgrad von Sonnenkollektoren und Brennwertkesseln aus. Beim Einsatz von WĂ€rmepumpen verbessert sich deren Leistungszahl. Der Beitrag zeigt die Auswirkungen der Betriebsweise und der konstruktiven Details des WĂ€rmespeichers, insbesondere der Be- und Entladevorrichtungen, auf, welche durch experimentelle und numerische Untersuchungen ermittelt wurden.The spreading integration of renewable sources of energy into conventional heat supply systems places high demands on the designing, dimensioning and operation of hot water storage tanks. A pronounced thermal stratification is of positive influence for the efficiency of solar collectors, condensing boilers and the COP of heat pumps connected to the storage tank. The extent of the thermal mixing layer determines the volumetric efficiency of the tank and thus the economics of investment and operation. In this paper, a method is presented by which the losses of hot water storage tanks are correlated to the tank design and operating conditions
Spermidine, but not spermine, is essential for pigment pattern formation in zebrafish
Polyamines are small poly-cations essential for all cellular life. The main polyamines present in metazoans are putrescine, spermidine and spermine. Their exact functions are still largely unclear; however, they are involved in a wide variety of processes affecting cell growth, proliferation, apoptosis and aging. Here we identify idefix, a mutation in the zebrafish gene encoding the enzyme spermidine synthase, leading to a severe reduction in spermidine levels as shown by capillary electrophoresis-mass spectrometry. We show that spermidine, but not spermine, is essential for early development, organogenesis and colour pattern formation. Whereas in other vertebrates spermidine deficiency leads to very early embryonic lethality, maternally provided spermidine synthase in zebrafish is sufficient to rescue the early developmental defects. This allows us to uncouple them from events occurring later during colour patterning. Factors involved in the cellular interactions essential for colour patterning, likely targets for spermidine, are the gap junction components Cx41.8, Cx39.4, and Kir7.1, an inwardly rectifying potassium channel, all known to be regulated by polyamines. Thus, zebrafish provide a vertebrate model to study the in vivo effects of polyamines
Discourses on Violence in Costa Rica, El Salvador, and Nicaragua: Youth, Crime, and the Responses of the State
A Human-Health Risk Assessment for West Nile Virus and Insecticides Used in Mosquito Management
West Nile virus (WNV) has been a major public health concern in North America since 1999, when the first outbreak in the Western Hemisphere occurred in New York City. As a result of this ongoing disease outbreak, management of mosquitoes that vector WNV throughout the United States and Canada has necessitated using insecticides in areas where they traditionally have not been used or have been used less frequently. This has resulted in concerns by the public about the risks from insecticide use. The objective of this study was to use reasonable worst-case risk assessment methodologies to evaluate human-health risks for WNV and the insecticides most commonly used to control adult mosquitoes. We evaluated documented health effects from WNV infection and determined potential population risks based on reported frequencies. We determined potential acute (1-day) and subchronic (90-day) multiroute residential exposures from each insecticide for several human subgroups during a WNV disease outbreak scenario. We then compared potential insecticide exposures to toxicologic and regulatory effect levels. Risk quotients (RQs, the ratio of exposure to toxicologic effect) were < 1.0 for all subgroups. Acute RQs ranged from 0.0004 to 0.4726, and subchronic RQs ranged from 0.00014 to 0.2074. Results from our risk assessment and the current weight of scientific evidence indicate that human-health risks from residential exposure to mosquito insecticides are low and are not likely to exceed levels of concern. Further, our results indicate that, based on human-health criteria, the risks from WNV exceed the risks from exposure to mosquito insecticides
Spectrum of Infection and Risk Factors for Human Monkeypox, United States, 2003
Infection is associated with proximity to virus-infected animals and their excretions and secretions
Driving pressure during general anesthesia for open abdominal surgery (DESIGNATION) : study protocol of a randomized clinical trial
Background
Intraoperative driving pressure (Delta P) is associated with development of postoperative pulmonary complications (PPC). When tidal volume (V-T) is kept constant, Delta P may change according to positive end-expiratory pressure (PEEP)-induced changes in lung aeration. Delta P may decrease if PEEP leads to a recruitment of collapsed lung tissue but will increase if PEEP mainly causes pulmonary overdistension. This study tests the hypothesis that individualized high PEEP, when compared to fixed low PEEP, protects against PPC in patients undergoing open abdominal surgery.
Methods
The "Driving prESsure durIng GeNeral AnesThesIa for Open abdomiNal surgery trial" (DESIGNATION) is an international, multicenter, two-group, double-blind randomized clinical superiority trial. A total of 1468 patients will be randomly assigned to one of the two intraoperative ventilation strategies. Investigators screen patients aged >= 18 years and with a body mass index <= 40 kg/m(2), scheduled for open abdominal surgery and at risk for PPC. Patients either receive an intraoperative ventilation strategy with individualized high PEEP with recruitment maneuvers (RM) ("individualized high PEEP") or one in which PEEP of 5 cm H2O without RM is used ("low PEEP"). In the "individualized high PEEP" group, PEEP is set at the level at which Delta P is lowest. In both groups of the trial, V-T is kept at 8 mL/kg predicted body weight. The primary endpoint is the occurrence of PPC, recorded as a collapsed composite of adverse pulmonary events. Discussion DESIGNATION will be the first randomized clinical trial that is adequately powered to compare the effects of individualized high PEEP with RM versus fixed low PEEP without RM on the occurrence of PPC after open abdominal surgery. The results of DESIGNATION will support anesthesiologists in their decisions regarding PEEP settings during open abdominal surgery
Validation of Online Versions of Tinnitus Questionnaires Translated into Swedish
BackgroundDue to the lack of objective measures for assessing tinnitus, its clinical evaluation largely relies on the use of questionnaires and psychoacoustic tests. A global assessment of tinnitus burden would largely benefit from holistic approaches that not only incorporate measures of tinnitus but also take into account associated fears, emotional aspects (stress, anxiety, and depression), and quality of life. In Sweden, only a few instruments are available for assessing tinnitus, and the existing tools lack validation. Therefore, we translated a set of questionnaires into Swedish and evaluated their reliability and validity in a group of tinnitus subjects. MethodsWe translated the English versions of the Tinnitus Functional Index (TFI), the Fear of Tinnitus Questionnaire (FTQ), the Tinnitus Catastrophizing Scale (TCS), the Perceived Stress Questionnaire (PSQ-30), and the Tinnitus Sample Case History Questionnaire (TSCHQ) into Swedish. These translations were delivered via the internet with the already existing Swedish versions of the Tinnitus Handicap Inventory (THI), the Hospital Anxiety and Depression Scale (HADS), the Hyperacusis Questionnaire (HQ), and the World Health Organization Quality of Life questionnaire (WHOQoL-BREF). Psychometric properties were evaluated by means of internal consistency (Cronbachâs alpha α) and test-retest reliability across a 9-week interval (Intraclass Correlation Coefficient ICC, Cohenâs kappa) in order to establish construct as well as clinical validity using a sample of 260 subjects from a population-based cohort.ResultsInternal consistency was acceptable for all questionnaires (α >0.7) with the exception of the âsocial relationshipsâ subscale of the WHOQoL-BREF. Test-retest reliability was generally acceptable (ICC >.70, Cohens Kappa >.60) for the tinnitus-related questionnaires, except for the TFI âsense of controlâ subscale and 15 items of the TSCHQ. Spearmen rank correlations showed that almost all questionnaires on tinnitus are significantly related, indicating that these questionnaires measure different aspects of the same construct. The data supported good clinical validity of the tinnitus-related questionnaires. ConclusionOur results suggest that most Swedish adaptations of the questionnaires are suitable for clinical and research settings and should facilitate the assessment of treatment outcomes using a more holistic approach by including measures of tinnitus fears, emotional burden, and quality of life
Why Reform Fails : The âPolitics of Policiesâ in Costa Rican Telecommunications Liberalization
As the \u27Washington Consensus\u27 reforms are losing momentum in Latin America, the Inter-
American Development Bank (IDB) is calling for shifting the focus from the content of policy
choices to the political process of their implementation. As this paper studies the paradigmatic
case of telecommunications reform in Costa Rica it underscores the importance
of these \u27politics of policies\u27. The analysis finds, however, that the failure of repeated liberalization
initiatives was not only due to policy-makers\u27 errors in steering the project
through \u27the messy world of politics\u27 (IDB); instead, as liberalization remained unpopular,
policy content indeed mattered, and only the interaction of both explains the outcome.
Particular attention is drawn to the political feed-back effects, as the failed reform, precisely
because it had been backed by bi-partisan support, became a catalyst for the disintegration
of the country\u27s long-standing two-party system.In dem MaĂe, in dem die mit dem âWashington Consensusâ verbundenen Reformen in Lateinamerika
ins Stocken geraten sind, plÀdiert die Inter-American Development Bank (IDB)
fĂŒr eine stĂ€rkere BerĂŒcksichtigung nicht nur der Politikinhalte (policies), sondern auch des
politischen Prozesses von deren Umsetzung (politics). Die vorliegende Untersuchung zum
paradigmatischen Fall der Reform des Telekommunikationssektors in Costa Rica unterstreicht
die Bedeutung dieser âpolitics of policiesâ. Sie zeigt allerdings auch, dass Ursache
fĂŒr das Scheiten wiederholter Liberalisierungsinitiativen nicht nur Fehler der Politiker sind,
das Vorhaben durch âdie unordentliche Welt der politicsâ (IDB) zu steuern. Die breite gesellschaftliche
Opposition gegen den Liberalisierungskurs bleibt. Nur die Interaktion von beiden,
politics und policies, erklÀrt Verlauf und Ergebnis der Reform. Besonderes Augenmerk
widmet die Studie den politischen RĂŒckwirkungen der gescheiterten Reform: Sie wurde,
just weil sie von beiden etablierten Parteien unterstĂŒtzt wurde, zum Katalysator fĂŒr den Zerfall
des seit Jahrzehnten etablierten Zweiparteiensystems des Landes
Serologic evidence of human orthopoxvirus infections in Sierra Leone
<p>Abstract</p> <p>Background</p> <p>Orthopoxviruses, including variola virus, vaccinia virus, and monkeypox virus, have previously been documented in humans in West Africa, however, no cases of human orthopoxvirus infection have been reported in the region since 1986. We conducted a serosurvey to determine whether human exposure to orthopoxviruses continues to occur in eastern Sierra Leone.</p> <p>Findings</p> <p>To examine evidence of exposure to orthopoxviruses in the Kenema District of Sierra Leone, we collected and tested sera from 1596 persons by IgG ELISA and a subset of 313 by IgM capture ELISA. Eleven persons born after the cessation of smallpox vaccination had high orthopoxvirus-specific IgG values, and an additional 6 persons had positive IgM responses. No geographic clustering was noted.</p> <p>Conclusions</p> <p>These data suggest that orthopoxviruses continue to circulate in Sierra Leone. Studies aimed at obtaining orthopoxvirus isolates and/or genetic sequences from rodents and symptomatic humans in the area are indicated.</p
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