3,628 research outputs found
TG, FT-IR and NMR characterization of n-C16H34 contaminated alumina and silica after mechanochemical treatment
This paper deals with the application of mechanochemistry to model systems composed of alumina or silica artificially contaminated with n-C16H34. The mechanochemical treatment was carried out by means of a ring mill for times ranging from 10 to 40 h. Thermogravimetry and infrared and nuclear magnetic resonance spectroscopies were used for the characterization of the mechanochemical products. The results have indicated that, in the case of alumina, almost all the contaminant n-C16H34 undergoes a complex oxidative reaction path whose end products are strongly held on the surface. These end products are most likely made of crosslinked, partially oxidized hydrocarbon chains bond to the solid surface via COOâ groups. In the case of silica, the hydrocarbon undergoes a different, equally complex reaction path, but to a lower extent. In this case the end products are most probably carbonylic compounds and graphitic carbon. Then, for both solid matrices, the mechanochemical treatment promotes significant modification of the chemical nature of the polluting hydrocarbon with end products much more difficult to remove from the surface. As the systems studied are models of sites contaminated by aliphatic hydrocarbon, the results are worthy of consideration in relation to the mobility of the contaminants in the environment
A robust approach for the determination of Gurson model parameters
Among the most promising models introduced in recent years, with which it is possible to obtain very useful results for a better understanding of the physical phenomena involved in the macroscopic mechanism of crack propagation, the one proposed by Gurson and Tvergaard links the propagation of a crack to the nucleation, growth and coalescence of micro-voids, which is likely to connect the micromechanical characteristics of the component under examination to crack initiation and propagation up to a macroscopic scale. It must be pointed out that, even if the statistical character of some of the many physical parameters involved in the said model has been put in evidence, no serious attempt has been made insofar to link the corresponding statistic to the experimental and macroscopic results, as for example crack initiation time, material toughness, residual strength of the cracked component (R-Curve), and so on. In this work, such an analysis was carried out in a twofold way: the former concerned the study of the influence exerted by each of the physical parameters on the material toughness, and the latter concerned the use of the Stochastic Design Improvement (SDI) technique to perform a "robust" numerical calibration of the model evaluating the nominal values of the physical and correction parameters, which fit a particular experimental result even in the presence of their "natural" variability
OGSA/Globus Evaluation for Data Intensive Applications
We present an architecture of Globus Toolkit 3 based testbed intended for
evaluation of applicability of the Open Grid Service Architecture (OGSA) for
Data Intensive Applications.Comment: To be published in the proceedings of the XIX International Symposium
on Nuclear Electronics and Computing (NEC'2003), Bulgaria, Varna, 15-20
September, 200
Numerical investigation on the influence of tightening in bolted joints
In a bolted joint, the preload level resulting from the tightening torque represents a very important parameter governing the stresses distributions involving the joint under the real loading conditions. This paper deals with the development of a Finite Element (FE) model for the investigation of the effects of some selected preload levels on the stress-strain states affecting both bolt and plate in a single lap joint. The aim of this FE model is to support the design phase of strain gauges instrumented bolt to evaluate experimentally the rate of tensile load applied to the joint that the bolt absorbs with different preloads. The test article consists of two steel plates, a steel bolt and an aluminum nut. The results herein presented showed firstly that, without bolt preload, the tensile load applied to the joint is completely transferred to the bolt and that the load transferred to the bolt almost linearly decreases as the preload increases. Moreover, at a selected preload level, the transversal and longitudinal stresses (with respect to the load direction) increase as the tensile load increases, while the stress along the plate thickness direction decreases, reaching negative values. On the other hand, at a selected tensile load level, the transversal and longitudinal stresses as well as the stress along the thickness direction decrease as the preload level increases. Predicting the mechanical behaviour of the only bolted joint, if the same bolt model will be used to simulate the mechanical behaviour in a hybrid single-lap joint, possible imperfections of the model will have to certainly be linked to the modelling of the adhesive
Parametric simulation of LVI test onto CFRP plates
The paper deals with the study of the structural behaviour of laminated composite plates under low
velocity impacts. Three test cases, respectively with 6J, 10J and 13J impact energies have been
experimentally carried out under ASTM D7136 (American Standard Test Method for Measuring the
Damage Resistance of a Fiber âReinforced Polymer Matrix Composite to a Drop-Weight Impact)
requirements. Within this work, virtual simulations of such impact tests have been developed by using
the finite element code AbaqusÂź. The numerical model, based on explicit finite element theory, allows
predicting the onset and evolution of both inter-laminar and intra-laminar damages. The former have
been considered by using special-purpose elements (cohesive elements); the latter thanks to Hashin
criteria. For validation purpose, numerical results have been compared with the experimental ones.
After the validation phase, a parametric analysis has been numerically performed; the size of the panel
support fixture has been considered as main parameter
A method to localize gamma-ray bursts using POLAR
The hard X-ray polarimeter POLAR aims to measure the linear polarization of
the 50-500 keV photons arriving from the prompt emission of gamma-ray bursts
(GRBs). The position in the sky of the detected GRBs is needed to determine
their level of polarization. We present here a method by which, despite of the
polarimeter incapability of taking images, GRBs can be roughly localized using
POLAR alone. For this purpose scalers are attached to the output of the 25
multi-anode photomultipliers (MAPMs) that collect the light from the POLAR
scintillator target. Each scaler measures how many GRB photons produce at least
one energy deposition above 50 keV in the corresponding MAPM. Simulations show
that the relative outputs of the 25 scalers depend on the GRB position. A
database of very strong GRBs simulated at 10201 positions has been produced.
When a GRB is detected, its location is calculated searching the minimum of the
chi2 obtained in the comparison between the measured scaler pattern and the
database. This GRB localization technique brings enough accuracy so that the
error transmitted to the 100% modulation factor is kept below 10% for GRBs with
fluence Ftot \geq 10^(-5) erg cm^(-2) . The POLAR localization capability will
be useful for those cases where no other instruments are simultaneously
observing the same field of view.Comment: 13 pages, 10 figure
GPU-based Real-time Triggering in the NA62 Experiment
Over the last few years the GPGPU (General-Purpose computing on Graphics
Processing Units) paradigm represented a remarkable development in the world of
computing. Computing for High-Energy Physics is no exception: several works
have demonstrated the effectiveness of the integration of GPU-based systems in
high level trigger of different experiments. On the other hand the use of GPUs
in the low level trigger systems, characterized by stringent real-time
constraints, such as tight time budget and high throughput, poses several
challenges. In this paper we focus on the low level trigger in the CERN NA62
experiment, investigating the use of real-time computing on GPUs in this
synchronous system. Our approach aimed at harvesting the GPU computing power to
build in real-time refined physics-related trigger primitives for the RICH
detector, as the the knowledge of Cerenkov rings parameters allows to build
stringent conditions for data selection at trigger level. Latencies of all
components of the trigger chain have been analyzed, pointing out that
networking is the most critical one. To keep the latency of data transfer task
under control, we devised NaNet, an FPGA-based PCIe Network Interface Card
(NIC) with GPUDirect capabilities. For the processing task, we developed
specific multiple ring trigger algorithms to leverage the parallel architecture
of GPUs and increase the processing throughput to keep up with the high event
rate. Results obtained during the first months of 2016 NA62 run are presented
and discussed
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