Modelling diffractive effects in silicon pore optics for the ATHENA X-ray telescope

Silicon Pore Optics (SPO) are the technology selected for the assembly of the mirror module of the ATHENA X-ray telescope. An SPO mirror module consists of a quadruple stack of etched and wedged silicon wafers, in order to create a stiff and lightweight structure, able to reproduce in each pore the Wolter-I geometry required to image X-rays on the telescope focal plane. Due to the small pore size (a few mm2), aperture diffraction effects in X-rays are small, but not totally negligible to the angular resolutions at play. In contrast, diffraction effects are the dominant term in the UV light illumination that will be used to co-align the 600 mirror modules of ATHENA to a common focus. For this reason, diffractive effects need to be properly modeled, and this constitutes a specific task of the ESA-led SImPOSIUM (SIlicon Pore Optic SImUlation and Modelling) project, involving INAF-Brera and DTU. In this context, a specific software tool (SWORDS: SoftWare fOR Diffraction of Silicon pore optics) has been developed to the end of simulating diffraction effects in SPO mirror modules. This approach also allows the user to effectively predict the effects of various imperfections (figure errors, misalignments) in a self-consistent way, in different experimental configurations (X-ray source off-axis or at finite distance), as a fast and reliable alternative to ray-tracing, also at X-ray wavelengths

A fully-analytical treatment of stray light in silicon pore optics for the ATHENA X-ray telescope

Just like in any other X-ray telescope, stray light is expected to be a potential issue for the ATHENA X-ray telescope, with a significant impact on the scientific goals. The most prominent cause of stray light in Wolter-I type optics is represented by rays that did not undergo double reflection and were reflected only singly, on either the parabolic or the hyperbolic segment. A minor contribution may, additionally, arise from the diffuse reflections on the backside of the pore membrane and ribs. Aiming at determining whether the resulting background is tolerable or not, the effective area for stray light has to be calculated. While ray-tracing is a standard and well-assessed tool to perform this task, it usually takes a considerable amount of computation time to trace a number of rays sufficient to reach an appropriate statistical significance, because only a minority of stray rays emerge unobstructed from the mirror assembly. In contrast, approaching the stray light from the analytical viewpoint takes several upsides: it is faster than ray-tracing, does not suffer from any statistical uncertainties, and allows one to better understand the role of the parameters at play. The only approximation involved is the double cone geometry, which however is largely applicable to ATHENA as far as the sole effective area is concerned. In this paper, we show how the analytical approach can be successfully adopted to model the stray light effective area in the ATHENA mirror assembly, as a function of the X-ray energy and of the source off-axis angle

Provider payments and patient charges as policy tools for cost-containment: How successful are they in high-income countries?

In this paper, we focus on those policy instruments with monetary incentives that are used to contain public health expenditure in high-income countries. First, a schematic view of the main cost-containment methods and the variables in the health system they intend to influence is presented. Two types of instruments to control the level and growth of public health expenditure are considered: (i) provider payment methods that influence the price and quantity of health care, and (ii) cost-containment measures that influence the behaviour of patients. Belonging to the first type of instruments, we have: fee-for-service, per diem payment, case payment, capitation, salaries and budgets. The second type of instruments consists of patient charges and reference price systems for pharmaceuticals. Secondly, we provide an overview of experience in high-income countries that use or have used these particular instruments. Finally, the paper assesses the overall potential of these instruments in cost-containment policies

Cost calculation and prediction in adult intensive care: A ground-up utilization study

Publisher's copy made available with the permission of the publisherThe ability of various proxy cost measures, including therapeutic activity scores (TISS and Omega) and cumulative daily severity of illness scores, to predict individual ICU patient costs was assessed in a prospective “ground-up” utilization costing study over a six month period in 1991. Daily activity (TISS and Omega scores) and utilization in consecutive admissions to three adult university associated ICUs was recorded by dedicated data collectors. Cost prediction used linear regression with determination (80%) and validation (20%) data sets. The cohort, 1333 patients, had a mean (SD) age 57.5 (19.4) years, (41% female) and admission APACHE III score of 58 (27). ICU length of stay and mortality were 3.9 (6.1) days and 17.6% respectively. Mean total TISS and Omega scores were 117 (157) and 72 (113) respectively. Mean patient costs per ICU episode (1991 $AUS) were$6801 ($10311), with median costs of$2534, range $106 to$95,602. Dominant cost fractions were nursing 43.3% and overheads 16.9%. Inflation adjusted year 2002 (mean) costs were $9343 ($ AUS). Total costs in survivors were predicted by Omega score, summed APACHE III score and ICU length of stay; determination R2, 0.91; validation 0.88. Omega was the preferred activity score. Without the Omega score, predictors were age, summed APACHE III score and ICU length of stay; determination R2, 0.73; validation 0.73. In non-survivors, predictors were age and ICU length of stay (plus interaction), and Omega score (determination R2, 0.97; validation 0.91). Patient costs may be predicted by a combination of ICU activity indices and severity scores.J. L. Moran, A. R. Peisach, P. J. Solomon, J. Martinhttp://www.aaic.net.au/Article.asp?D=200403