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Jes S Lindholt - One of the best experts on this subject based on the ideXlab platform.

  • unfit for repair after screening for abdominal aortic aneurysm do we fail to fulfil the basic who criterion of an available treatment
    European Journal of Vascular and Endovascular Surgery, 2015
    Co-Authors: Jes S Lindholt
    Abstract:

    In this edition of EJVES, the Gloucester group report that 18% of screen diagnosed cases of abdominal aortic aneurysms (AAAs) in need of preventive repair haven’t received repair after 3 months; 22% of these received repair later on with no 30 day post-operative deaths, so the final turn down rate was 13%. 1 The reasons are not given, but could be a sign of a kind of “intelligent waiting” where you take the chance of repair if progression is worrying, weak symptoms develop, or health conditions improve. However, “intelligent waiting” is a dangerous strategy because about 20% of patients in the current report experienced rupture. Clearly, earlier intervention seems more attractive. In addition, three major questions arise from this report if generalisation is possible. When we created a model to evaluate cost-effectiveness of screening for AAA in a Modern Context, we needed to know the proportion not repaired, and studied the four AAA screening randomised controlled trials; 15% didn’t receive repair. 2,3 However, these figures are mainly from the 1990s when the operative risk was 5% before endovascular aneurysm repair and the knowledge that treatment of screen detected cases carries a one third risk compared with incidentally detected cases. 4 However, initial results from the British National AAA screening programme (BNASP) reported that 26% of 417 referred patients weren’t yet repaired, and although probably biased by other factors, the proportion seems very high. 5 The first major question to be raised is whether screening is still beneficial and cost-effective. As mentioned, such rejection fractions for repair were also seen in the MASS and Viborg trials, both of which have reported efficient and cost-effective screening programmes. In order to evaluate the consequences in a Modern Context, 2 we ran sensitivity analyses of our Modern model in which the originally used unfi tp roportion was exchanged with the proportions reported from Gloucester and the BNASP, respectively. It showed decreased efficacy from 32% to 30% and 23% reduced AAA specific mortality, respectively. Whether it remains cost-effective needs further time consuming calculations to clarify. A second major question to be raised is whether one of five or higher deemed unfit initially is acceptable according to the fundamental criteria for screening formulated by the WHO. Although some of them receive repair later, the initial refusal leaves the patients with the knowledge of having a life threatening condition with the obvious risk of losing life and quality of life. However, it seems to be correctable as the potentially maintained high rejection rate is combined with a tremendous decline in the operative risk from about 5% to about 1%. 4 We must not forget when the size criterion of 55 mm is met the condition is life threatening. If we assume the median size of referred AAAs is 6 cm and such an AAA carries an annual rupture risk of 10% with 75% overall mortality, 2,6 then survival curves of early surgery populations will cross those deemed unfit after just 1 year if the operative risk is as high as 7.5%. Modern public surveillance of results and risk of audits may have triggered this development, especially in Great Britain where individual surgeon outcomes are published. 7 Consequently, the third major question is whether we as vascular surgeons have failed by continuing to select people to repair using outdated criteria that are no longer balanced by the decreased risk of repair?

  • cost effectiveness of abdominal aortic aneurysm screening and rescreening in men in a Modern Context evaluation of a hypothetical cohort using a decision analytical model
    BMJ, 2012
    Co-Authors: Rikke Sogaard, Jesper Laustsen, Jes S Lindholt
    Abstract:

    Objective To assess the cost effectiveness of different screening strategies for abdominal aortic aneurysm in men, from the perspective of a national health service.

Vittorio Verda - One of the best experts on this subject based on the ideXlab platform.

  • Valeria Pavese Mechanical Efficiency of Hydraulic Air Compressors
    2020
    Co-Authors: Dean Millar, Vittorio Verda
    Abstract:

    After air and water mixing, the process of gas compression in the downcomer shaft or pipe of a hydraulic air compressor is considered nearly isothermal due to (i) the mass flow rate of water being typically of three orders higher than that of the gas it compresses, (ii) water having a heat capacity approximately four times that of air, and (iii) the intimate contact and large heat transfer area between the gas phase and the liquid phase of the bubbly flow. A formulation for estimation of the efficiency of a closed-or open-loop hydraulic air compressor, expressed in terms of the principal hydraulic air compressor design variables, is presented. The influence of a hitherto underappreciated factor affecting the performance of these installations, such as the solubility of the gas being compressed in the water, is explored. A procedure for estimating the yield of compressed gas, accounting for these solubility losses, is explained and used to determine the mechanical efficiency of historical hydraulic air compressor installations from reported performance data. The result is a significant downward revision of hydraulic air compressor efficiency by approximately 20% points in comparison to most reported efficiencies. However, through manipulation of cosolute concentrations in the water, and the temperature of the water (through regulation of the ejection of compression heat), the mechanical efficiency can be increased to the formerly reported levels. The thermoeconomic implication of these efficiency determinations is that in a Modern Context, hydraulic air compressors may be able to outperform conventional mechanical gas compression equipment

  • Mechanical Efficiency of Hydraulic Air Compressors
    Journal of Energy Resources Technology, 2016
    Co-Authors: Valeria Pavese, Dean L. Millar, Vittorio Verda
    Abstract:

    After air and water mixing, the process of gas compression in the downcomer shaft or pipe of a hydraulic air compressor is considered nearly isothermal due to (i) the mass flow rate of water being typically of three orders higher than that of the gas it compresses, (ii) water having a heat capacity approximately four times that of air, and (iii) the intimate contact and large heat transfer area between the gas phase and the liquid phase of the bubbly flow. A formulation for estimation of the efficiency of a closed- or open-loop hydraulic air compressor, expressed in terms of the principal hydraulic air compressor design variables, is presented. The influence of a hitherto underappreciated factor affecting the performance of these installations, such as the solubility of the gas being compressed in the water, is explored. A procedure for estimating the yield of compressed gas, accounting for these solubility losses, is explained and used to determine the mechanical efficiency of historical hydraulic air compressor installations from reported performance data. The result is a significant downward revision of hydraulic air compressor efficiency by approximately 20% points in comparison to most reported efficiencies. However, through manipulation of cosolute concentrations in the water, and the temperature of the water (through regulation of the ejection of compression heat), the mechanical efficiency can be increased to the formerly reported levels. The thermo-economic implication of these efficiency determinations is that in a Modern Context, hydraulic air compressors may be able to outperform conventional mechanical gas compression equipment.

Cedric Foellmi - One of the best experts on this subject based on the ideXlab platform.

  • intensity interferometry and the second order correlation function g 2 in astrophysics
    Astronomy and Astrophysics, 2009
    Co-Authors: Cedric Foellmi
    Abstract:

    Most observational techniques in astronomy can be understood as exploiting the various forms of the first-order correlation function g (1) . As demonstrated by the Narrabri stellar intensity interferometer back in the 1960s by Hanbury Brown & Twiss, the first experiment to measure the second-order correlation function g (2) , light can carry more information than simply its intensity, spectrum, and polarization. Since this experiment, theoretical and laboratory studies of non-classical properties of light have become a very active field of research, called quantum optics. Despite the variety of results in this field, astrophysics remained focused essentially on first-order coherence. In this paper, we study the possibility that quantum properties of light could be observed in cosmic sources. We provide the basic mathematical ingredients about the first and the second order correlation functions, applied to the Modern Context of astronomical observations. We aim at replacing the Hanbury Brown & Twiss experiment in this Context, and present two fundamental limitations of an intensity interferometer: the requirement of a chaotic light source and the rapid decrease of the amount of correlated fluctuations with the surface temperature. The first of these limitations paradoxically emphasizes that the exploitation of g (2) is richer than what a Modern intensity interferometer could bring and is particularly interesting for sources of nonthermal light. We also discuss new photon-counting avalanche photodiodes currently being developed in Grenoble, and their impact on limiting magnitudes of an intensity interferometer. We conclude by briefly presenting why microquasars in our galaxy and their extragalactic parents can represent an excellent first target in the optical/near-infrared where to observe nonthermal light and to test the use of g (2) in astrophysical

  • on the intensity interferometry and the second order correlation function g 2 in astrophysics
    arXiv: Instrumentation and Methods for Astrophysics, 2009
    Co-Authors: Cedric Foellmi
    Abstract:

    Most observational techniques in astronomy can be understood as exploiting the various forms of the first-order correlation function g^(1). As however demonstrated by the Narrabri Stellar Intensity Interferometer back in the 1960's by Hanbury Brown & Twiss, and which is the first experiment to measure the second-order correlation function g^(2), light can carry more information than simply its intensity, spectrum and polarization. Since this experiment, theoretical and laboratory studies of non-classical properties of light have become a very active field of research, namely quantum optics. Despite the variety of results in this field, astrophysics remained focused essentially on first-order coherence. In this paper, we study the possibility that quantum properties of light could be observed in cosmic sources. We provide the basic mathematical ingredients about the first and the second order correlation functions, applied to the Modern Context of astronomical observations. The exploitation of g^(2) is certainly richer than what a Modern intensity interferometer could bring and is particularly interesting for sources of non-thermal light. We conclude by briefly presenting why microquasars in our galaxy and their extragalactic parents can represent an excellent first target in the optical/near-infrared where to observe non-thermal light, and test the use of g^(2) in astrophysical sources.

Dean Millar - One of the best experts on this subject based on the ideXlab platform.

  • Valeria Pavese Mechanical Efficiency of Hydraulic Air Compressors
    2020
    Co-Authors: Dean Millar, Vittorio Verda
    Abstract:

    After air and water mixing, the process of gas compression in the downcomer shaft or pipe of a hydraulic air compressor is considered nearly isothermal due to (i) the mass flow rate of water being typically of three orders higher than that of the gas it compresses, (ii) water having a heat capacity approximately four times that of air, and (iii) the intimate contact and large heat transfer area between the gas phase and the liquid phase of the bubbly flow. A formulation for estimation of the efficiency of a closed-or open-loop hydraulic air compressor, expressed in terms of the principal hydraulic air compressor design variables, is presented. The influence of a hitherto underappreciated factor affecting the performance of these installations, such as the solubility of the gas being compressed in the water, is explored. A procedure for estimating the yield of compressed gas, accounting for these solubility losses, is explained and used to determine the mechanical efficiency of historical hydraulic air compressor installations from reported performance data. The result is a significant downward revision of hydraulic air compressor efficiency by approximately 20% points in comparison to most reported efficiencies. However, through manipulation of cosolute concentrations in the water, and the temperature of the water (through regulation of the ejection of compression heat), the mechanical efficiency can be increased to the formerly reported levels. The thermoeconomic implication of these efficiency determinations is that in a Modern Context, hydraulic air compressors may be able to outperform conventional mechanical gas compression equipment

Valeria Pavese - One of the best experts on this subject based on the ideXlab platform.

  • Mechanical Efficiency of Hydraulic Air Compressors
    Journal of Energy Resources Technology, 2016
    Co-Authors: Valeria Pavese, Dean L. Millar, Vittorio Verda
    Abstract:

    After air and water mixing, the process of gas compression in the downcomer shaft or pipe of a hydraulic air compressor is considered nearly isothermal due to (i) the mass flow rate of water being typically of three orders higher than that of the gas it compresses, (ii) water having a heat capacity approximately four times that of air, and (iii) the intimate contact and large heat transfer area between the gas phase and the liquid phase of the bubbly flow. A formulation for estimation of the efficiency of a closed- or open-loop hydraulic air compressor, expressed in terms of the principal hydraulic air compressor design variables, is presented. The influence of a hitherto underappreciated factor affecting the performance of these installations, such as the solubility of the gas being compressed in the water, is explored. A procedure for estimating the yield of compressed gas, accounting for these solubility losses, is explained and used to determine the mechanical efficiency of historical hydraulic air compressor installations from reported performance data. The result is a significant downward revision of hydraulic air compressor efficiency by approximately 20% points in comparison to most reported efficiencies. However, through manipulation of cosolute concentrations in the water, and the temperature of the water (through regulation of the ejection of compression heat), the mechanical efficiency can be increased to the formerly reported levels. The thermo-economic implication of these efficiency determinations is that in a Modern Context, hydraulic air compressors may be able to outperform conventional mechanical gas compression equipment.