5,541 research outputs found
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
Insulin-like growth factor-1 is a negative modulator of glucagon secretion
Glucagon secretion involves a combination of paracrine, autocrine, hormonal, and autonomic neural mechanisms. Type 2 diabetes often presents impaired glucagon suppression by insulin and glucose. Insulin-like growth factor-I (IGF-1) has elevated homology with insulin, and regulates pancreatic β-cells insulin secretion. Insulin and IGF-1 receptors share considerable structure homology and function. We hypothesized the existence of a mechanism linking the inhibition of α-cells glucagon secretion to IGF-1. Herein, we evaluated the association between plasma IGF-1 and glucagon levels in 116 nondiabetic adults. After adjusting for age gender and BMI, fasting glucagon levels were positively correlated with 2-h post-load glycaemia, HOMA index and fasting insulin, and were negatively correlated with IGF-1 levels. In a multivariable regression, the variables independently associated to fasting glucagon were circulating IGF-1 levels, HOMA index and BMI, explaining 20.7% variation. To unravel the molecular mechanisms beneath IGF-1 and glucagon association, we investigated whether IGF-1 directly modulates glucagon expression and secretion in an in vitro model of α-cells. Our data showed that IGF-1 inhibits the ability of low glucose concentration to stimulate glucagon expression and secretion via activation of the phosphatidylinositol-3-kinase/Akt/FoxO1 pathway. Collectively, our results suggest a new regulatory role of IGF-1 on α-cells biological function
Strong scaling of general-purpose molecular dynamics simulations on GPUs
We describe a highly optimized implementation of MPI domain decomposition in
a GPU-enabled, general-purpose molecular dynamics code, HOOMD-blue (Anderson
and Glotzer, arXiv:1308.5587). Our approach is inspired by a traditional
CPU-based code, LAMMPS (Plimpton, J. Comp. Phys. 117, 1995), but is implemented
within a code that was designed for execution on GPUs from the start (Anderson
et al., J. Comp. Phys. 227, 2008). The software supports short-ranged pair
force and bond force fields and achieves optimal GPU performance using an
autotuning algorithm. We are able to demonstrate equivalent or superior scaling
on up to 3,375 GPUs in Lennard-Jones and dissipative particle dynamics (DPD)
simulations of up to 108 million particles. GPUDirect RDMA capabilities in
recent GPU generations provide better performance in full double precision
calculations. For a representative polymer physics application, HOOMD-blue 1.0
provides an effective GPU vs. CPU node speed-up of 12.5x.Comment: 30 pages, 14 figure
Design and advancement status of the Beam Expander Testing X-ray facility (BEaTriX)
The BEaTriX (Beam Expander Testing X-ray facility) project is an X-ray
apparatus under construction at INAF/OAB to generate a broad (200 x 60 mm2),
uniform and low-divergent X-ray beam within a small lab (6 x 15 m2). BEaTriX
will consist of an X-ray source in the focus a grazing incidence paraboloidal
mirror to obtain a parallel beam, followed by a crystal monochromation system
and by an asymmetrically-cut diffracting crystal to perform the beam expansion
to the desired size. Once completed, BEaTriX will be used to directly perform
the quality control of focusing modules of large X-ray optics such as those for
the ATHENA X-ray observatory, based on either Silicon Pore Optics (baseline) or
Slumped Glass Optics (alternative), and will thereby enable a direct quality
control of angular resolution and effective area on a number of mirror modules
in a short time, in full X-ray illumination and without being affected by the
finite distance of the X-ray source. However, since the individual mirror
modules for ATHENA will have an optical quality of 3-4 arcsec HEW or better,
BEaTriX is required to produce a broad beam with divergence below 1-2 arcsec,
and sufficient flux to quickly characterize the PSF of the module without being
significantly affected by statistical uncertainties. Therefore, the optical
components of BEaTriX have to be selected and/or manufactured with excellent
optical properties in order to guarantee the final performance of the system.
In this paper we report the final design of the facility and a detailed
performance simulation.Comment: Accepted paper, pre-print version. The finally published manuscript
can be downloaded from http://dx.doi.org/10.1117/12.223895
Association between serum Mg2+ concentrations and cardiovascular organ damage in a cohort of adult subjects
Magnesium (Mg2+) levels are associated with insulin resistance, hypertension, atherosclerosis, and type 2 diabetes (T2DM). We evaluated the clinical utility of physiological Mg2+ in assessing subclinical cardiovascular organ damage including increased carotid artery intima-media thickness (c-IMT) and left ventricular mass index (LVMI) in a cohort of well-characterized adult non-diabetic individuals. Age-and gender-adjusted correlations between Mg2+ and metabolic parameters showed that Mg2+ circulating levels were correlated negatively with body mass index (BMI), fasting glucose, and 2h-oral glucose tolerance test (OGTT) glucose. Similarly, Mg2+ levels were significantly and negatively related to c-IMT and LVMI. A multivariate regression analysis revealed that age (β = 0.440; p < 0.0001), BMI (β = 0.225; p < 0.0001), and Mg2+ concentration (β = −0.122; p < 0.01) were independently associated with c-IMT. Age (β = 0.244; p = 0.012), Mg2+ (β = −0.177; p = 0.019), and diastolic blood pressure (β = 0.184; p = 0.038) were significantly associated with LVMI in women, while age (β = 0.211; p = 0.019), Mg2+ (β = −0.171; p = 0.038) and the homeostasis model assessment index of insulin resistance (HOMA-IR) (β = −0.211; p = 0.041) were the sole variables associated with LVMI in men. In conclusion, our data support the hypothesis that the assessment of Mg2+ as part of the initial work-up might help unravel the presence of subclinical organ damage in subjects at increased risk of cardiovascular complications
The 2DECOMP&FFT library: an update with new CPU/GPU capabilities
The 2DECOMP&FFT library is a software framework written in modern Fortran to build large-scale parallel applications. It is designed for applications using three-dimensional structured meshes with a particular focus on spatially implicit numerical algorithms. However, the library can be easily used with other discretisation schemes based on a structured layout and where pencil decomposition can apply. It is based on a general-purpose 2D pencil decomposition for data distribution and data Input Output (I/O). A 1D slab decomposition is also available as a special case of the 2D pencil decomposition. The library includes a highly scalable and efficient interface to perform three-dimensional Fast Fourier Transforms (FFTs). The library has been designed to be user-friendly, with a clean application programming interface hiding most communication details from application developers, and portable with support for modern CPUs and NVIDIA GPUs (support for AMD and Intel GPUs to follow)
Active shape correction of a thin glass/plastic X-ray mirror
Optics for future X-ray telescopes will be characterized by very large
aperture and focal length, and will be made of lightweight materials like glass
or plastic in order to keep the total mass within acceptable limits. Optics
based on thin slumped glass foils are currently in use in the NuSTAR telescope
and are being developed at various institutes like INAF/OAB, aiming at
improving the angular resolution to a few arcsec HEW. Another possibility would
be the use of thin plastic foils, being developed at SAO and the Palermo
University. Even if relevant progresses in the achieved angular resolution were
recently made, a viable possibility to further improve the mirror figure would
be the application of piezoelectric actuators onto the non-optical side of the
mirrors. In fact, thin mirrors are prone to deform, so they require a careful
integration to avoid deformations and even correct forming errors. This however
offers the possibility to actively correct the residual deformation. Even if
other groups are already at work on this idea, we are pursuing the concept of
active integration of thin glass or plastic foils with piezoelectric patches,
fed by voltages driven by the feedback provided by X-rays, in intra-focal setup
at the XACT facility at INAF/OAPA. In this work, we show the preliminary
simulations and the first steps taken in this project
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