1,777 research outputs found

    Análisis exergético de un sistema de calentamiento de agua cuyo colector posee inercia térmica

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    Se presenta aquí un análisis exergético de un sistema termosifónico con un colector que posee inercia térmica. Este estudio se plantea para el conjunto colector-tanque de almacenamiento utilizando balances de exergía en estado transitorio. Las ecuaciones correspondientes fueron incluidas en un modelo computacional validado experimentalmente, para determinar flujos exergéticos instantáneos, como así también eficiencias exergéticas instantáneas y acumuladas. El modelo fue corrido para días completos con datos climáticos reales y de extracción prefijados para cuatro personas, resolviéndose sistemas de ecuaciones diferenciales mediante diferencias finitas. Considerando la variabilidad de la temperatura ambiente, se propone la utilización de la temperatura promedio diaria como referencia para el estado muerto. Se presentan los resultados mediante gráficos de exergía acumulados en el tanque y en el colector, como así también en diagramas exergéticos que permiten visualizar los efectos transitorios a que se ve sometido el sistema a lo largo del día.An exergetic analysis for a thermosyphonic system with a collector of high thermal mass is presented here. This study is proposed for the whole system collector-storage tank by using exergy balance equations in transient state. The corresponding equations were included in a computational model experimentally validated, in order to determine instantaneous exergy fluxes, exergy efficiencies, and accumulated exergy efficiencies as well. The model was run for complete days using real climatic data and extraction profiles for four people. Then, the solution of differential equation systems were performed by finite difference methods. Considering the variability of the ambient temperature, the use of the daily average temperature is proposed as reference temperature for the dead state. The results are presented by means of plots that show the accumulated exergy in tank and collector and by exergetic diagrams that allow the visualization of the transient effects working on the system.Asociación Argentina de Energías Renovables y Medio Ambiente (ASADES

    Evaluación de un sistema de calentamiento de aire apto para secado solar indirecto de perejil

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    En este trabajo se analiza la viabilidad de un secador solar indirecto, formado por tres componentes básicos: un colector de agua, un intercambiador de calor agua-aire y la cámara de secado. Se considera que el elemento condicionante en esta propuesta lo constituye el intercambiador de calor, ya que debe proporcionar la potencia mínima requerida para el secado y posibilitar el flujo termosifónico. El objetivo de este trabajo fue construir un intercambiador de calor agua-aire de bajo costo, a partir de materiales en desusos y evaluar experimentalmente el flujo termosifónico y la disponibilidad de la potencia térmica mínima requerida para el secado de perejil. El flujo aire a través del intercambiador es forzado, impulsado por un ventilador de 12 V. Los resultados de los ensayos, se presentan en gráficos y se concluye que el sistema propuesto constituye un diseño viable e idóneo en relación al secado indirecto aplicado a productos agrícolas.Tema 2: Energía solar, aplicaciones agrícolas e industriales.Facultad de Arquitectura y Urbanism

    Evaluación de un sistema de calentamiento de aire apto para secado solar indirecto de perejil

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    En este trabajo se analiza la viabilidad de un secador solar indirecto, formado por tres componentes básicos: un colector de agua, un intercambiador de calor agua-aire y la cámara de secado. Se considera que el elemento condicionante en esta propuesta lo constituye el intercambiador de calor, ya que debe proporcionar la potencia mínima requerida para el secado y posibilitar el flujo termosifónico. El objetivo de este trabajo fue construir un intercambiador de calor agua-aire de bajo costo, a partir de materiales en desusos y evaluar experimentalmente el flujo termosifónico y la disponibilidad de la potencia térmica mínima requerida para el secado de perejil. El flujo aire a través del intercambiador es forzado, impulsado por un ventilador de 12 V. Los resultados de los ensayos, se presentan en gráficos y se concluye que el sistema propuesto constituye un diseño viable e idóneo en relación al secado indirecto aplicado a productos agrícolas.Tema 2: Energía solar, aplicaciones agrícolas e industriales.Facultad de Arquitectura y Urbanism

    The impact of surgical delay on resectability of colorectal cancer: An international prospective cohort study

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    AIM: The SARS-CoV-2 pandemic has provided a unique opportunity to explore the impact of surgical delays on cancer resectability. This study aimed to compare resectability for colorectal cancer patients undergoing delayed versus non-delayed surgery. METHODS: This was an international prospective cohort study of consecutive colorectal cancer patients with a decision for curative surgery (January-April 2020). Surgical delay was defined as an operation taking place more than 4 weeks after treatment decision, in a patient who did not receive neoadjuvant therapy. A subgroup analysis explored the effects of delay in elective patients only. The impact of longer delays was explored in a sensitivity analysis. The primary outcome was complete resection, defined as curative resection with an R0 margin. RESULTS: Overall, 5453 patients from 304 hospitals in 47 countries were included, of whom 6.6% (358/5453) did not receive their planned operation. Of the 4304 operated patients without neoadjuvant therapy, 40.5% (1744/4304) were delayed beyond 4 weeks. Delayed patients were more likely to be older, men, more comorbid, have higher body mass index and have rectal cancer and early stage disease. Delayed patients had higher unadjusted rates of complete resection (93.7% vs. 91.9%, P = 0.032) and lower rates of emergency surgery (4.5% vs. 22.5%, P < 0.001). After adjustment, delay was not associated with a lower rate of complete resection (OR 1.18, 95% CI 0.90-1.55, P = 0.224), which was consistent in elective patients only (OR 0.94, 95% CI 0.69-1.27, P = 0.672). Longer delays were not associated with poorer outcomes. CONCLUSION: One in 15 colorectal cancer patients did not receive their planned operation during the first wave of COVID-19. Surgical delay did not appear to compromise resectability, raising the hypothesis that any reduction in long-term survival attributable to delays is likely to be due to micro-metastatic disease

    Optimasi Portofolio Resiko Menggunakan Model Markowitz MVO Dikaitkan dengan Keterbatasan Manusia dalam Memprediksi Masa Depan dalam Perspektif Al-Qur`an

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    Risk portfolio on modern finance has become increasingly technical, requiring the use of sophisticated mathematical tools in both research and practice. Since companies cannot insure themselves completely against risk, as human incompetence in predicting the future precisely that written in Al-Quran surah Luqman verse 34, they have to manage it to yield an optimal portfolio. The objective here is to minimize the variance among all portfolios, or alternatively, to maximize expected return among all portfolios that has at least a certain expected return. Furthermore, this study focuses on optimizing risk portfolio so called Markowitz MVO (Mean-Variance Optimization). Some theoretical frameworks for analysis are arithmetic mean, geometric mean, variance, covariance, linear programming, and quadratic programming. Moreover, finding a minimum variance portfolio produces a convex quadratic programming, that is minimizing the objective function ðð¥with constraintsð ð 𥠥 ðandð´ð¥ = ð. The outcome of this research is the solution of optimal risk portofolio in some investments that could be finished smoothly using MATLAB R2007b software together with its graphic analysis

    Penilaian Kinerja Keuangan Koperasi di Kabupaten Pelalawan

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    This paper describe development and financial performance of cooperative in District Pelalawan among 2007 - 2008. Studies on primary and secondary cooperative in 12 sub-districts. Method in this stady use performance measuring of productivity, efficiency, growth, liquidity, and solvability of cooperative. Productivity of cooperative in Pelalawan was highly but efficiency still low. Profit and income were highly, even liquidity of cooperative very high, and solvability was good

    Differential cross section measurements for the production of a W boson in association with jets in proton–proton collisions at √s = 7 TeV

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    Measurements are reported of differential cross sections for the production of a W boson, which decays into a muon and a neutrino, in association with jets, as a function of several variables, including the transverse momenta (pT) and pseudorapidities of the four leading jets, the scalar sum of jet transverse momenta (HT), and the difference in azimuthal angle between the directions of each jet and the muon. The data sample of pp collisions at a centre-of-mass energy of 7 TeV was collected with the CMS detector at the LHC and corresponds to an integrated luminosity of 5.0 fb[superscript −1]. The measured cross sections are compared to predictions from Monte Carlo generators, MadGraph + pythia and sherpa, and to next-to-leading-order calculations from BlackHat + sherpa. The differential cross sections are found to be in agreement with the predictions, apart from the pT distributions of the leading jets at high pT values, the distributions of the HT at high-HT and low jet multiplicity, and the distribution of the difference in azimuthal angle between the leading jet and the muon at low values.United States. Dept. of EnergyNational Science Foundation (U.S.)Alfred P. Sloan Foundatio

    Juxtaposing BTE and ATE – on the role of the European insurance industry in funding civil litigation

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    One of the ways in which legal services are financed, and indeed shaped, is through private insurance arrangement. Two contrasting types of legal expenses insurance contracts (LEI) seem to dominate in Europe: before the event (BTE) and after the event (ATE) legal expenses insurance. Notwithstanding institutional differences between different legal systems, BTE and ATE insurance arrangements may be instrumental if government policy is geared towards strengthening a market-oriented system of financing access to justice for individuals and business. At the same time, emphasizing the role of a private industry as a keeper of the gates to justice raises issues of accountability and transparency, not readily reconcilable with demands of competition. Moreover, multiple actors (clients, lawyers, courts, insurers) are involved, causing behavioural dynamics which are not easily predicted or influenced. Against this background, this paper looks into BTE and ATE arrangements by analysing the particularities of BTE and ATE arrangements currently available in some European jurisdictions and by painting a picture of their respective markets and legal contexts. This allows for some reflection on the performance of BTE and ATE providers as both financiers and keepers. Two issues emerge from the analysis that are worthy of some further reflection. Firstly, there is the problematic long-term sustainability of some ATE products. Secondly, the challenges faced by policymakers that would like to nudge consumers into voluntarily taking out BTE LEI

    Search for stop and higgsino production using diphoton Higgs boson decays

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    Results are presented of a search for a "natural" supersymmetry scenario with gauge mediated symmetry breaking. It is assumed that only the supersymmetric partners of the top-quark (stop) and the Higgs boson (higgsino) are accessible. Events are examined in which there are two photons forming a Higgs boson candidate, and at least two b-quark jets. In 19.7 inverse femtobarns of proton-proton collision data at sqrt(s) = 8 TeV, recorded in the CMS experiment, no evidence of a signal is found and lower limits at the 95% confidence level are set, excluding the stop mass below 360 to 410 GeV, depending on the higgsino mass

    Impacts of the Tropical Pacific/Indian Oceans on the Seasonal Cycle of the West African Monsoon

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    The current consensus is that drought has developed in the Sahel during the second half of the twentieth century as a result of remote effects of oceanic anomalies amplified by local land–atmosphere interactions. This paper focuses on the impacts of oceanic anomalies upon West African climate and specifically aims to identify those from SST anomalies in the Pacific/Indian Oceans during spring and summer seasons, when they were significant. Idealized sensitivity experiments are performed with four atmospheric general circulation models (AGCMs). The prescribed SST patterns used in the AGCMs are based on the leading mode of covariability between SST anomalies over the Pacific/Indian Oceans and summer rainfall over West Africa. The results show that such oceanic anomalies in the Pacific/Indian Ocean lead to a northward shift of an anomalous dry belt from the Gulf of Guinea to the Sahel as the season advances. In the Sahel, the magnitude of rainfall anomalies is comparable to that obtained by other authors using SST anomalies confined to the proximity of the Atlantic Ocean. The mechanism connecting the Pacific/Indian SST anomalies with West African rainfall has a strong seasonal cycle. In spring (May and June), anomalous subsidence develops over both the Maritime Continent and the equatorial Atlantic in response to the enhanced equatorial heating. Precipitation increases over continental West Africa in association with stronger zonal convergence of moisture. In addition, precipitation decreases over the Gulf of Guinea. During the monsoon peak (July and August), the SST anomalies move westward over the equatorial Pacific and the two regions where subsidence occurred earlier in the seasons merge over West Africa. The monsoon weakens and rainfall decreases over the Sahel, especially in August.Peer reviewe
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