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Rachkov V.A.,Joint Institute for Nuclear Research | Karpov A.V.,Joint Institute for Nuclear Research | Denikin A.S.,International University | Zagrebaev V.I.,Joint Institute for Nuclear Research
Physical Review C - Nuclear Physics | Year: 2014

Background: Significant enhancement of sub-barrier fusion cross sections owing to neutron rearrangement with positive Q values were found for many combinations of colliding nuclei. However, several experimental results on fusion reactions were reported recently in which such enhancement has not been observed in spite of a possibility for neutron rearrangement with positive Q values. Purpose: We aim to clarify much better the mechanism of neutron rearrangement in sub-barrier fusion reactions to find the other requirements (beside positive Q values) which favor (or prevent) sub-barrier fusion enhancement. Methods: A channel coupling approach along with the semiclassical model for neutron transfer has been used for analysis of available experimental data on sub-barrier fusion of heavy ions. Results: The role and interplay of different factors determining the enhancement of sub-barrier fusion (such as Q values for neutron rearrangement, properties of collective excitations, and neutron binding energies) have been studied and clarified. Conclusions: (1) Only 1n and 2n transfers with positive Q values have a noticeable impact on sub-barrier fusion. A positive Q value for neutron rearrangement is a necessary but not sufficient requirement for additional sub-barrier fusion enhancement to take place. (2) The œrigidity of colliding nuclei with respect to collective excitations is important for sub-barrier fusion enhancement due to neutron rearrangement with positive Q values to be clearly visible. (3) The neutron binding energy of the œdonor nucleus has a strong impact only in the case of fusion of light weakly bound nuclei. © 2014 American Physical Society.

Le C.V.,International University | Askes H.,University of Sheffield | Gilbert M.,University of Sheffield
Computers and Structures | Year: 2012

An element free Galerkin (EFG) based formulation for limit analysis of rigid-perfectly plastic plane strain problems is presented. In the paper it is demonstrated that volumetric locking and instability problems can be avoided by using a stabilized conforming nodal integration scheme. Furthermore, the stabilized EFG method described allows stable and accurate solutions to be obtained with minimal computational effort. The discrete kinematic formulation is cast in the form of a second-order cone problem, allowing efficient interior-point solvers to be used to obtain solutions. Finally, the performance of the stabilized EFG method is illustrated by considering several numerical examples. © 2012 Elsevier Ltd. All rights reserved.

Pham V.-H.,International University | Dacier M.,Symantec
Future Generation Computer Systems | Year: 2011

In this paper, we propose a method to identify and group together traces left on low interaction honeypots by machines belonging to the same botnet(s) without having any a priori information at our disposal regarding these botnets. In other words, we offer a solution to detect new botnets thanks to very cheap and easily deployable solutions. The approach is validated thanks to several months of data collected with the worldwide distributed Leurr.com system. To distinguish the relevant traces from the other ones, we group them according to either the platforms, i.e. targets hit or the countries of origin of the attackers. We show that the choice of one of these two observation viewpoints dramatically influences the results obtained. Each one reveals unique botnets. We explain why. Last but not the least, we show that these botnets remain active during very long periods of times, up to 700 days, even if the traces they left are only visible from time to time.1 © 2010 Elsevier B.V. All rights reserved.

Torabi A.R.,University of Tehran | Jafarinezhad M.R.,International University
Materials Science and Engineering A | Year: 2012

Stress distribution was analyzed around the tip of U-notches in a disc-type test sample, called U-notched Brazilian disc (UNBD), under combined tensile-shear loading. The notch stress intensity factors (NSIFs) which are vital parameters in brittle fracture investigation of U-notched engineering components were computed for UNBD specimen utilizing the finite element (FE) method for different notch geometries and wide range of mode mixities from pure mode I to pure mode II. To simplify the results to be used in engineering design, the NSIFs were converted to the dimensionless parameters called the notch shape factors (NSFs). These parameters are useful to compute more rapidly and conveniently the NSIFs in UNBD specimen for different notch tip radii. As a main result, it is shown that the NSFs presented in this work combined with the appropriate fracture criteria can be used to predict the load-cell capacity of the test machine required for fracture test of UNBD specimens made of various brittle materials. © 2012 Elsevier B.V.

Ngoc P.H.A.,International University
IEEE Transactions on Automatic Control | Year: 2015

General nonlinear differential systems with time-varying delay are considered. Several explicit criteria for global exponential stability are presented. Two examples are given to illustrate the obtained results. © 1963-2012 IEEE.

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