59 research outputs found

    Correlation functions near Modulated and Rough Surfaces

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    In a system with long-ranged correlations, the behavior of correlation functions is sensitive to the presence of a boundary. We show that surface deformations strongly modify this behavior as compared to a flat surface. The modified near surface correlations can be measured by scattering probes. To determine these correlations, we develop a perturbative calculation in the deformations in height from a flat surface. Detailed results are given for a regularly patterned surface, as well as for a self-affinely rough surface with roughness exponent ζ\zeta. By combining this perturbative calculation in height deformations with the field-theoretic renormalization group approach, we also estimate the values of critical exponents governing the behavior of the decay of correlation functions near a self-affinely rough surface. We find that for the interacting theory, a large enough ζ\zeta can lead to novel surface critical behavior. We also provide scaling relations between roughness induced critical exponents for thermodynamic surface quantities.Comment: 31 pages, 2 figure

    Impact of COVID-19 on cardiovascular testing in the United States versus the rest of the world

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    Objectives: This study sought to quantify and compare the decline in volumes of cardiovascular procedures between the United States and non-US institutions during the early phase of the coronavirus disease-2019 (COVID-19) pandemic. Background: The COVID-19 pandemic has disrupted the care of many non-COVID-19 illnesses. Reductions in diagnostic cardiovascular testing around the world have led to concerns over the implications of reduced testing for cardiovascular disease (CVD) morbidity and mortality. Methods: Data were submitted to the INCAPS-COVID (International Atomic Energy Agency Non-Invasive Cardiology Protocols Study of COVID-19), a multinational registry comprising 909 institutions in 108 countries (including 155 facilities in 40 U.S. states), assessing the impact of the COVID-19 pandemic on volumes of diagnostic cardiovascular procedures. Data were obtained for April 2020 and compared with volumes of baseline procedures from March 2019. We compared laboratory characteristics, practices, and procedure volumes between U.S. and non-U.S. facilities and between U.S. geographic regions and identified factors associated with volume reduction in the United States. Results: Reductions in the volumes of procedures in the United States were similar to those in non-U.S. facilities (68% vs. 63%, respectively; p = 0.237), although U.S. facilities reported greater reductions in invasive coronary angiography (69% vs. 53%, respectively; p < 0.001). Significantly more U.S. facilities reported increased use of telehealth and patient screening measures than non-U.S. facilities, such as temperature checks, symptom screenings, and COVID-19 testing. Reductions in volumes of procedures differed between U.S. regions, with larger declines observed in the Northeast (76%) and Midwest (74%) than in the South (62%) and West (44%). Prevalence of COVID-19, staff redeployments, outpatient centers, and urban centers were associated with greater reductions in volume in U.S. facilities in a multivariable analysis. Conclusions: We observed marked reductions in U.S. cardiovascular testing in the early phase of the pandemic and significant variability between U.S. regions. The association between reductions of volumes and COVID-19 prevalence in the United States highlighted the need for proactive efforts to maintain access to cardiovascular testing in areas most affected by outbreaks of COVID-19 infection

    Kaelteanlagen mit nichtazeotropen ZKM zur Abloesung der FCKW

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    Die Anwendung nichtazeotroper Kaeltemittel in Kaelte und Waermepumpanlagen weist energetisch guenstigere Eigenschaften aus. Dies wurde durch Prozessberechnungen von Ein- und Zweistoffkaeltemitteln bestaetigt. Die Arbeit traegt zur Loesung anlagetechnischer Probleme und der kontinuierlichen Konzentrationsbestimmung von nichtazeotropen Kaeltemitteln sowie der Regelung von Kaelteanlagen mit Kaeltemitteln bei. (VTThe use of non-azeotropic refrigerant mixtures in cooling and heat pump systems is energetically favourable. This was proved in process calculations with refrigerants and two-component refrigerant mixtures. The work helps to solve plant problems and shows ways for continuous concentration determination of non-azeotropic refrigerants as well as for the control of refrigeration system in which refrigerant mixtuers are used. (VT)SIGLEAvailable from TIB Hannover: H93B1704 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

    Near-surface x-ray critical scattering from a NH4Br(1ˉ10)NH_4Br (\bar 110) surface

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    We present the first observations of near-surface critical phenomena of a phase transition in a molecular solid showing both an order-disorder and a strong displacive component. The surface x-ray scattering experiments were performed on an NH4BrNH_4Br single crystal (TcT_c=235 K). For the order parameter they show a crossover from a power law with the bulk critical exponent ÎČ=0.3±0.05 to a surface behavior with exponent ÎČ1=0.8±0.1. From the diffuse intensity we have determined the critical exponents η∄=1.3±0.15, Îœ=0.5±0.15, and the correlation length Ο0+Ο^+_0=4±0.5A˚4±0.5 Å

    High-Order Supersatellite Reflections in Labradorite. A Synchrotron X-ray Diffraction Study

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    The supersatellite reflections in the feldspar mineral labradorite are related to the Bþggild intergrowth, a lamellar structure with a periodicity of about 1500 Å. With high-resolution X-ray diffraction using synchrotron radiation, supersatellites up to fourth order are observed. The system is an example for a natural superstructure with high-order diffraction harmonics. The satellite intensities reflect a transverse displacement modulation with a large amplitude. The complete unit cell of labradorite is affected by the displacement. In this context, various possible displacement functions are discussed. A Fourier expansion of the displacement function that yields the best agreement between measurement and theory has nearly triangular shape. The line width of the satellites characterizes imperfections of the lamellar superstructure: It increases linearly with satellite order, which is ascribed to uncorrelated variations (FWHM = 480 Å) of the lamellar thickness

    Die SitzflĂ€chenneigung bei BĂŒrostĂŒhlen

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