169 research outputs found
Analytical computation of the off-axis Effective Area of grazing incidence X-ray mirrors
Focusing mirrors for X-ray telescopes in grazing incidence, introduced in the
70s, are characterized in terms of their performance by their imaging quality
and effective area, which in turn determines their sensitivity. Even though the
on-axis effective area is assumed in general to characterize the collecting
power of an X-ray optic, the telescope capability of imaging extended X-ray
sources is also determined by the variation in its effective area with the
off-axis angle. [...] The complex task of designing optics for future X-ray
telescopes entails detailed computations of both imaging quality and effective
area on- and off-axis. Because of their apparent complexity, both aspects have
been, so far, treated by using ray-tracing routines aimed at simulating the
interaction of X-ray photons with the reflecting surfaces of a given focusing
system. Although this approach has been widely exploited and proven to be
effective, it would also be attractive to regard the same problem from an
analytical viewpoint, to assess an optical design of an X-ray optical module
with a simpler calculation than a ray-tracing routine. [...] We have developed
useful analytical formulae for the off-axis effective area of a
double-reflection mirror in the double cone approximation, requiring only an
integration and the standard routines to calculate the X-ray coating
reflectivity for a given incidence angle. [...] Algebraic expressions are
provided for the mirror geometric area, as a function of the off-axis angle.
Finally, the results of the analytical computations presented here are
validated by comparison with the corresponding predictions of a ray-tracing
code.Comment: 12 pages, 11 figures, accepted for publication in "Astronomy &
Astrophysics", section "Instruments, observational techniques, and data
processing". Updated version after grammatical revision and typos correctio
Characterization of multilayer stack parameters from X-ray reflectivity data using the PPM program: measurements and comparison with TEM results
Future hard (10 -100 keV) X-ray telescopes (SIMBOL-X, Con-X, HEXIT-SAT, XEUS)
will implement focusing optics with multilayer coatings: in view of the
production of these optics we are exploring several deposition techniques for
the reflective coatings. In order to evaluate the achievable optical
performance X-Ray Reflectivity (XRR) measurements are performed, which are
powerful tools for the in-depth characterization of multilayer properties
(roughness, thickness and density distribution). An exact extraction of the
stack parameters is however difficult because the XRR scans depend on them in a
complex way. The PPM code, developed at ERSF in the past years, is able to
derive the layer-by-layer properties of multilayer structures from
semi-automatic XRR scan fittings by means of a global minimization procedure in
the parameters space. In this work we will present the PPM modeling of some
multilayer stacks (Pt/C and Ni/C) deposited by simple e-beam evaporation.
Moreover, in order to verify the predictions of PPM, the obtained results are
compared with TEM profiles taken on the same set of samples. As we will show,
PPM results are in good agreement with the TEM findings. In addition, we show
that the accurate fitting returns a physically correct evaluation of the
variation of layers thickness through the stack, whereas the thickness trend
derived from TEM profiles can be altered by the superposition of roughness
profiles in the sample image
Viscosity of choline chloride-based deep eutectic solvents: Experiments and modeling
Deep eutectic solvents (DESs) have emerged as promising âgreenâ solvents, but their successful industrial application requires relatively low viscosity. DESs prepared from choline chloride and glycols offer such a possibility. Viscosity and density are reported for a number of DESs obtained by mixing choline chloride and a glycol (ethylene glycol, 1,2-propanediol, 1,3-propanediol, and 1,4-butanediol). The measurements were performed at 101.3 kPa, at temperatures between 293.15 and 333.15 K, and for different mole ratios of glycol and choline chloride. The viscosity was measured with a capillary viscometer, while the density was measured by means of a vibrating U-tube densimeter. The density and viscosity data have expanded relative uncertainties of 0.2 and 2.0%, respectively, with a coverage factor of 2. The viscosity of pure glycols was modeled using the extended hard-sphere (EHS) model that has its basis in kinetic theory and the molecular description of the fluid. Each DES was treated as a binary mixture, and the EHS model was used, with a mole average mixing rule, to calculate its viscosity. The measured DES viscosity data were represented with an average absolute deviation of 1.4% and a maximum deviation of 7%
Effect of intensive treatment on diabetic nephropathy in patients with type I diabetes
Effect of intensive treatment on diabetic nephropathy in patients with type I diabetes. We evaluated the long-term effect of an intensive treatment of diabetic nephropathy (anti-hypertensive drugs, low protein diet, multiple insulin injections to achieve a good metabolic control) on glomerular filtration rate (GFR) and albumin excretion rate (AER). Fourteen type I diabetic patients (mean age 45 ± 9.5 years, mean duration of diabetes 23.5 ± 7.3 years, 8 males/6 females) with glomerular filtration rate <70 ml/min-1/1.73 m2 and albumin excretion rate >30 ”g/min were treated intensively for 36 months. This intensive treatment consisted of multiple insulin injections, antihypertensive therapy with ACE inhibitors and a low-protein diet (0.8 g/kg body wt/day.) Renal function was evaluated as GFR and AER. HbA1C mean value decreased significantly from 8.7 ± 0.8% to 6.5 ± 0.5% (P < 0.0002). GFR rose from 58 ± 12 ml/min-1/l.73 m2 to 84 ” 11 ml/min-1/l.73 m2 (P < 0.0008). AER decreased from 208 ”g/min (range: 73 to 500) to 63.8 ”g/min (range 15 to 180; P < 0.05). Systolic and diastolic blood pressure decreased respectively from 144 ± 26 mm Hg to 120 ± 15 mm Hg and from 89 ± 9 mm Hg to 75 ± 8 mm Hg (P < 0.01). We obtained a rise of GFR and a reduction of proteinuria after three years of this treatment. We suggest that this intensive treatment in all patients with early stage diabetic nephropathy may be effective in slowing the progression to renal failure
EVIL: Exploiting Software via Natural Language
Writing exploits for security assessment is a challenging task. The writer needs to master programming and obfuscation techniques to develop a successful exploit. To make the task easier, we propose an approach (EVIL) to automatically generate exploits in assembly/Python language from descriptions in natural language. The approach leverages Neural Machine Translation (NMT) techniques and a dataset that we developed for this work. We present an extensive experimental study to evaluate the feasibility of EVIL, using both automatic and manual analysis, and both at generating individual statements and entire exploits. The generated code achieved high accuracy in terms of syntactic and semantic correctness
Simbol-X Hard X-ray Focusing Mirrors: Results Obtained During the Phase A Study
Simbol-X will push grazing incidence imaging up to 80 keV, providing a strong
improvement both in sensitivity and angular resolution compared to all
instruments that have operated so far above 10 keV. The superb hard X-ray
imaging capability will be guaranteed by a mirror module of 100 electroformed
Nickel shells with a multilayer reflecting coating. Here we will describe the
technogical development and solutions adopted for the fabrication of the mirror
module, that must guarantee an Half Energy Width (HEW) better than 20 arcsec
from 0.5 up to 30 keV and a goal of 40 arcsec at 60 keV. During the phase A,
terminated at the end of 2008, we have developed three engineering models with
two, two and three shells, respectively. The most critical aspects in the
development of the Simbol-X mirrors are i) the production of the 100 mandrels
with very good surface quality within the timeline of the mission; ii) the
replication of shells that must be very thin (a factor of 2 thinner than those
of XMM-Newton) and still have very good image quality up to 80 keV; iii) the
development of an integration process that allows us to integrate these very
thin mirrors maintaining their intrinsic good image quality. The Phase A study
has shown that we can fabricate the mandrels with the needed quality and that
we have developed a valid integration process. The shells that we have produced
so far have a quite good image quality, e.g. HEW <~30 arcsec at 30 keV, and
effective area. However, we still need to make some improvements to reach the
requirements. We will briefly present these results and discuss the possible
improvements that we will investigate during phase B.Comment: 6 pages, 3 figures, invited talk at the conference "2nd International
Simbol-X Symposium", Paris, 2-5 december, 200
The future of Cybersecurity in Italy: Strategic focus area
This volume has been created as a continuation of the previous one, with the aim of outlining a set of focus areas and actions that the Italian Nation research community considers essential. The book touches many aspects of cyber security, ranging from the definition of the infrastructure and controls needed to organize cyberdefence to the actions and technologies to be developed to be better protected, from the identification of the main technologies to be defended to the proposal of a set of horizontal actions for training, awareness raising, and risk management
Technology Requirements for a Square Meter, Arcsecond Resolution Telescope for X-Rays: The SMART-X Mission
Addressing the astrophysical problems of the 2020's requires sub-arcsecond x-ray imaging with square meter effective area. Such requirements can be derived, for example, by considering deep x-ray surveys to find the young black holes in the early universe (large redshifts) which will grow into the first super-massive black holes. We have envisioned a mission, the Square Meter Arcsecond Resolution Telescope for X-rays (SMART-X), based on adjustable x-ray optics technology, incorporating mirrors with the required small ratio of mass to collecting area. We are pursuing technology which achieves sub-arcsecond resolution by on-orbit adjustment via thin film piezoelectric "cells" deposited directly on the non-reflecting sides of thin, slumped glass. While SMART-X will also incorporate state-of-the-art x-ray cameras, the remaining spacecraft systems have no requirements more stringent than those which are well understood and proven on the current Chandra X-ray Observatory
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