3,297 research outputs found

    Spin measurements for 147Sm+n resonances: Further evidence for non-statistical effects

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    We have determined the spins J of resonances in the 147Sm(n,gamma) reaction by measuring multiplicities of gamma-ray cascades following neutron capture. Using this technique, we were able to determine J values for all but 14 of the 140 known resonances below En = 1 keV, including 41 firm J assignments for resonances whose spins previously were either unknown or tentative. These new spin assignments, together with previously determined resonance parameters, allowed us to extract separate level spacings and neutron strength functions for J = 3 and 4 resonances. Furthermore, several statistical test of the data indicate that very few resonances of either spin have been missed below En = 700eV. Because a non-statistical effect recently was reported near En = 350 eV from an analysis of 147Sm(n,alpha) data, we divided the data into two regions; 0 < En < 350 eV and 350 < En < 700 eV. Using neutron widths from a previous measurement and published techniques for correcting for missed resonances and for testing whether data are consistent with a Porter-Thomas distribution, we found that the reduced-neutron-width distribution for resonances below 350 eV is consistent with the expected Porter-Thomas distribution. On the other hand, we found that reduced-neutron-width data in the 350 < En < 700 eV region are inconsistent with a Porter-Thomas distribution, but in good agreement with a chi-squared distribution having two or more degrees of freedom. We discuss possible explanations for these observed non-statistical effects and their possible relation to similar effects previously observed in other nuclides.Comment: 40 pages, 13 figures, accepted by Phys. Rev.

    Making Communities More Flood Resilient: The Role of Cost Benefit Analysis and Other Decision-support Tools in Disaster Risk Reduction

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    Given the series of large-scale flood disasters that have occurred in recent years, there is a growing recognition among community leaders, businesses, insurers, governments and international donors of the need to invest in risk reduction measures before such events happen. Due to the costs of risk reduction measures, these actions need to be justified and as a result there is an increasing need to utilize decision-support tools, which can help to make the case for action to reduce disaster risks and build flood resilience when faced with limited resources. Across stakeholders, the specific objectives from the use of decision-support tools include (i) demonstrating the efficiency of the action ex-ante (before the flood); (ii) aiding in the selection of a particular intervention in enhancing community flood resilience from a suite of possible options; (iii) helping communities make the right choice when faced with limited investments; (iv) demonstrating the benefits of donor funding of community flood resilience projects; and (v) monitoring the successes and weaknesses of past interventions to generate lessons learned for future work. Typically, discussion on decision-support for disaster risk reduction (DRR) in floods (as well as for other hazards) has focused on cost-benefit analysis (CBA), however there are a number of other tools available to support decision-making. These include cost-effectiveness analysis (CEA), multi-criteria analysis (MCA) and robust-decision-making approaches (RDMA), which have been applied to similar problems, and can also be used to aid decision-making regarding flooding. This white paper provides an overview of the opportunities and challenges of applying these different tools, and guides the reader to select among them. Selection depends on the desired objective, circumstances, data available, timeframe to perform analyses, level of detail, and other considerations. We first focus on the CBA decision-tool, as this has been the mainstay of research and implementation. We then go beyond CBA to consider the other techniques for prioritising DRR investments. While our analysis is specific to flood DRR actions, the conclusion are also applicable to other hazards. The key findings arising from this white paper with relevance to research, policy and implementation of flood DRR decision-support tools, are: (1) Following a comprehensive review of the quantitative CBA flood DRR evidence, we find that flood DRR investments largely pay off, with an average of five dollars saved for every dollar spent through avoided and reduced losses; (2) Using CBA for flood risk reduction assessment should properly account for low-frequency, high-impact flood events, and also tackle key challenges such as intangible impacts; (3) Decision-making can be improved by using various decision support tools tailored to the desired outcomes and contexts. This white paper is the foundation upon which the Zurich flood resilience alliance work on integration of a decision toolbox will proceed "on the ground," with established community-based risk assessment tools, in particular Vulnerability Capacity Assessments (VCA) or Participatory Capacity and Vulnerability Assessments (PCVA). Based on these findings we propose a way forward over the next several years on informing risk-based decision making as part of the alliance program

    Exchange Field Induced Magnetoresistance in Colossal Magnetoresistance Manganites

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    The effect of an exchange field on electrical transport in thin films of metallic ferromagnetic manganites has been investigated. The exchange field was induced both by direct exchange coupling in a ferromagnet/antiferromagnet multilayer and by indirect exchange interaction in a ferromagnet/paramagnet superlattice. The electrical resistance of the manganite layers was found to be determined by the absolute value of the vector sum of the effective exchange field and the external magnetic field.Comment: 5 pages, 4 figure

    Two-photon exclusive decays Bsη(η)γγB_s \to \eta (\eta') \gamma\gamma and BKγγB \to K \gamma\gamma

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    The exclusive decay modes BKγγB \to K \gamma\gamma and Bsη(η)γγB_s \to \eta (\eta') \gamma\gamma are shown to have significant branching ratios of approximately 0.5×1070.5\times 10^{-7}. This first calculation of these modes employs a model based on a cascade transition BVγPγγB\to V\gamma\to P\gamma\gamma for estimating the long-distance contribution and the process bsγγb\to s\gamma\gamma for the short distance one.Comment: 11 Page

    Weak Decays in the light--front Quark Model

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    We study the form factors of heavy--to--heavy and heavy--to--light weak decays using the light--front relativistic quark model. For the heavy--to--heavy B \ra D^{(\ast)} semileptonic decays we calculate the corresponding Isgur--Wise function for the whole kinematic region. For the heavy--to--light B\ra P and B\ra V semileptonic decays we calculate the form factors at q2=0q^2 = 0; in particular, we have derived the dependence of the form factors on the bb--quark mass in the m_b \ra \infty limit. This dependence can not be produced by extrapolating the scaling behavior of the form factors at qmax2q^2_{max} using the single--pole assumption. This shows that the q2q^2 dependence of the form factors in regions far away from the zero--recoil could be much more complicated than that predicted by the single--pole assumption.Comment: 24 pages, Latex, Postscript figure included at the en

    Does impaired O-2 delivery during exercise accentuate central and peripheral fatigue in patients with coexistent COPD-CHF?

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    Impairment in oxygen (O-2) delivery to the central nervous system (brain) and skeletal locomotor muscle during exercise has been associated with central and peripheral neuromuscular fatigue in healthy humans. From a clinical perspective, impaired tissue O-2 transport is a key pathophysiological mechanism shared by cardiopulmonary diseases, such as chronic obstructive pulmonary disease (COPD) and chronic heart failure (CHF). in addition to arterial hypoxemic conditions in COPD, there is growing evidence that cerebral and muscle blood flow and oxygenation can be reduced during exercise in both isolated COPD and CHF. Compromised cardiac output due to impaired cardiopulmonary function/interactions and blood flow redistribution to the overloaded respiratory muscles (i.e., up arrow work of breathing) may underpin these abnormalities. Unfortunately, COPD and CHF coexist in almost a third of elderly patients making these mechanisms potentially more relevant to exercise intolerance. in this context, it remains unknown whether decreased O-2 delivery accentuates neuromuscular manifestations of central and peripheral fatigue in coexistent COPD-CHF If this holds true, it is conceivable that delivering a low-density gas mixture (heliox) through non-invasive positive pressure ventilation could ameliorate cardiopulmonary function/interactions and reduce the work of breathing during exercise in these patients. the major consequence would be increased O-2 delivery to the brain and active muscles with potential benefits to exercise capacity (i.e.,,central and peripheral neuromuscular fatigue, respectively). We therefore hypothesize that patients with coexistent COPD-CHF stop exercising prematurely due to impaired central motor drive and muscle contractility as the cardiorespiratory system fails to deliver sufficient O-2 to simultaneously attend the metabolic demands of the brain and the active limb muscles.Universidade Federal de São Paulo, Dept Med, Pulm Funct & Clin Exercise Physiol Unit SEFICE, Resp Div,Sch Med,UNIFESP, São Paulo, BrazilQueens Univ, Dept Med, Lab Clin Exercise Physiol, Div Resp & Crit Care Med, Kingston, ON K7L 3N6, CanadaQueens Univ, Dept Med, Resp Invest Unit, Div Resp & Crit Care Med, Kingston, ON K7L 3N6, CanadaGrenoble Alpes Univ, Lab HP2, Grenoble, FranceUniversidade Federal de São Paulo, Dept Med, Pulm Funct & Clin Exercise Physiol Unit SEFICE, Resp Div,Sch Med,UNIFESP, São Paulo, BrazilWeb of Scienc

    Baryon and Lepton Number Assignment in E6E_6 Models

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    In E6E_6 models there are new particles whose baryon number is not uniquely assigned. We point out that the baryon and lepton number assignment to these particles can change the baryogenesis scenario significantly. We consider left-right symmetric extension of the standard model in which (BL)(B-L) quantum number is gauged. The identification of (BL)(B-L) with a generator of E6E_6 is used to define the baryon and lepton numbers for the exotic particles in a way that the electroweak baryon and lepton number anomaly corresponding to the SU(2)LSU(2)_L group vanishes, {\it i.e.}, there is no non-perturbative baryon or lepton number violation during the electroweak phase transition. We study some consequences of the new assignment.Comment: 14 pages, LaTeX file, 1 submitted Figure file(.eps

    A compact ultra-clean system for deploying radioactive sources inside the KamLAND detector

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    We describe a compact, ultra-clean device used to deploy radioactive sources along the vertical axis of the KamLAND liquid-scintillator neutrino detector for purposes of calibration. The device worked by paying out and reeling in precise lengths of a hanging, small-gauge wire rope (cable); an assortment of interchangeable radioactive sources could be attached to a weight at the end of the cable. All components exposed to the radiopure liquid scintillator were made of chemically compatible UHV-cleaned materials, primarily stainless steel, in order to avoid contaminating or degrading the scintillator. To prevent radon intrusion, the apparatus was enclosed in a hermetically sealed housing inside a glove box, and both volumes were regularly flushed with purified nitrogen gas. An infrared camera attached to the side of the housing permitted real-time visual monitoring of the cable's motion, and the system was controlled via a graphical user interface.Comment: Revised author affiliations, corrected typos, made minor improvements to text, and revised reference
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