Inhomogeneity effects on HPGe gamma spectrometry detection efficiency using Monte Carlo technique

This work deals with the inhomogeneity effects on the full energy peak efficiency determination with HPGe gamma spectrometry. The inhomogeneity of the sample was defined in this work as being the fraction of its volume, which does not contain gamma emitters. We applied the Monte Carlo technique based on the GEANT4 code of CERN to study these effects for soil samples for the case of high density (1.54 g/cm³) where the attenuation effects are expected to increase the errors on the activity measurement due to the inhomogeneity. The correction of the efficiency against these effects using Monte Carlo method has been applied in two cases. The first is between samples with different homogeneity values and a calibration standard, which is perfectly homogeneous, and the second is between a sample and a calibration standard with different imperfect homogeneities.     

A surface crack in a graded coating bonded to a homogeneous substrate under dynamic loading conditions

The elastodynamic problem of a surface crack in a graded coating bonded to a homogeneous substrate under dynamic loading is considered. The coating is graded along the thickness direction and modeled as a nonhomogeneous medium with an isotropic stress-strain law. The problem is solved under the assumption of plane strain or generalized plane stress conditions. The crack surfaces are subjected to arbitrary dynamic loadings which give rise to mixed fracture modes which turn out to be uncoupled due to the fact that the crack axis is parallel to the material gradient. Using integral transforms, the resulting mixed-boundary value problem is reduced to a set of two uncoupled singular integral equations which are solved numerically to obtain the crack-tip stress intensity factors. The main objective of the paper is to study the effect of the coating thickness and nonhomogeneity parameter on the crack tip dynamic stress intensity factors for the purpose of gaining better understanding on the behavior of graded coatings.     

Joint production and supply control in three levels flexible manufacturing systems

This paper considers a stochastic optimal control problem of a three stages Flexible Manufacturing System. The supplier (i.e., upstream FMS) and the transformation stage (i.e., FMS) are both subject to random events. Our objective is to find a feedback control policy for the supply and production activities that minimizes the incurred cost. It is shown that the considered joint production and supply control problem is difficult to tackle using a dissociated analytical approach. A simulation based approach is thus proposed to achieve a close approximation of the optimal policy. The advantages of the approach include possible extensions after numerical characterization of the optimal control policy.     

Study of solution properties of poly(deamino‐tyr‐tyr carbonate hexyl ester) by light scattering and viscometry in dilute and semidilute regime

The structure and properties of poly(deamino‐tyr‐tyr carbonate hexyl ester), in dilute and semidilute solutions, were studied using static, dynamic light scattering, and viscometry. The overlap concentration, c^* is determined by viscosity. The angular dependence of Zimm plots shows no downturn at low angles. In addition, bimodal distribution curves were computed from the quasielastic measurements. The radius of gyration and the second virial coefficient A₂ are found to be respectively 45.8 nm and 9.4 mol cm³ g^?2. The correlation and persistence lengths are discussed. The poly (deamino‐tyr‐tyr carbonate hexyl ester) or poly(DTH‐carbonate) chain in THF, at T = 20°C, behaves as a wormlike chain with persistence length. The persistence length obtained using light scattering is compared with that obtained using viscosity with good agreement. These values obtained from these measurements reflect a high degree of local chain persistence. The reduced viscosity in dilute regime provides a value of apparent viscosity hydrodynamic radius three times lower than obtained by static light scattering. POLYM. ENG. SCI., 50:1605–1612, 2010. © 2010 Society of Plastics Engineers     

Intercalation de solvants organiques polaires dans la structure lamellaire des gels de V2O5

The swelling of vanadium pentoxide gels has been measured in three polar organic solvents: sulfolane, dimethylsulfoxide and propylene carbonate. These solvents take the place of the interfoliar water in the V₂O₅ xerogel. Propylene carbonate forms double-layer intercalates corresponding to a basal spacing of 21.5 Å. DMSO leads to a single-layer compound ($\text{d}\text{= 16.5}\text{A}\text{?}$); the same conclusion could probably apply for the sulfolane compound ($\text{d}\text{= 17.6}\text{A}\text{?}$).     

Inhibitory action of purified hydroxytyrosol from stored olive mill waste on intestinal disaccharidases and lipase activities and pancreatic toxicity in diabetic rats

This study was established that after 3 months storage, olive mill waste (OMW) was enriched with hydroxytyrosol (HT) (2,652 mg/L) and contained only phenolic monomers. It also showed that HT supplementation to surviving diabetic rats decreases considerably intestinal maltase, lactase, sucrose, and lipase activities by 49, 31, 42, and 40%, respectively. In addition, HT enhanced the superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX) activities by 330, 170, and 301%, respectively and reduced gluthation (GSH) level by 79% in pancreas compared to diabetic rats. Moreover, a significant decrease in the thiobarbituric acid reactive substances (TBARs) level and lactate dehydrogenase (LDH) activity in diabetic rats pancreas by 34 and 49% respectively after administration of HT. In addition, HT improved plasma triglyceride and cholesterol levels in diabetic rats by lowering low density lipoprotein (LDL)-cholesterol and triglycerides (TG) by 27 and 53%, respectively and increasing high density lipoprotein (HDL)-cholesterol content by 72%. These properties of HT are interesting regarding its use as therapeutic agent in biotechnological applications, especially in developing anti-diabetic and hypocholesterolemic drugs.     

Local spectral information in the near field with wavelet analysis and entropy

In near-field optical microscopy the resolution is strongly related to the experimental illumination conditions and to the separation between tip and sample. Therefore the spectral information in near-field data (related to the resolution in images) can be described only locally as a function of the tip-sample position. To make a local study of the spectral information in near-field data, we use wavelet decomposition that is associated with the calculation of entropy. We deduce the resolution from the characteristics of the wavelet, which leads to an automatic and numerical evaluation of the resolution in near-field data.     

An algorithmic approach for analysis of finite-source retrial systems with unreliable servers

This paper aims at presenting an approach for analyzing finite-source retrial systems with servers subject to breakdowns and repairs, using Generalized Stochastic Petri Nets (GSPNs). This high-level formalism allows a simple representation of such systems with different breakdown disciplines. From the GSPN model, a Continuous Time Markov Chain (CTMC) can be automatically derived. However, for multiserver retrial systems with unreliable servers, the models may have a huge state space. Using the GSPN model as a support, we propose an algorithm for directly computing the infinitesimal generator of the CTMC without generating the reachability graph. In addition, we develop the formulas of the main stationary performance and reliability indices, as a function of the number of servers, the size of the customer source and the stationary probabilities. Through numerical examples, we discuss the effect of the system parameters and the breakdown disciplines on performance.     

A 2D design and modeling of micro strip structures on inhomogeneous substrate

The wave concept iterative process method (WCIP) is presented for full wave investigation of a microwave structure on inhomogeneous substrate. These structures can be exploited to achieve a high performance due to their versatility, which can reduce manufacturing cost, size, and weight. Using the spectral operator in the WCIP method permits to resolve this inhomogeneous problem. The use of the spectral operator keeps the advantages of the 2D mesh of the circuit plan. Two different examples are studied; the dispersion characteristics of a microstrip transmission line on inhomogeneous substrate and a microstrip T‐resonator on a low temperature Co‐fired ceramic (LTCC) with embedded vertical air cavities. Compared with measurement and the finite different method, the present technique is found to be efficient with 2D analysis and a required low memory. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.     

Analysis of a microstrip antenna with fractal multilayer substrate using iterative method

A microstrip antenna with fractal multilayer substrates is studied by using an iterative method based on the concept of waves. A two‐dimensional fast Fourier transformation algorithm is introduced to simplify calculations and accelerate the convergence with reduced central processing unit time. Good agreements are obtained with already published results on fractal antenna. © 2001 John Wiley & Sons, Inc. Int J RF and Microwave CAE 11: 212–218, 2001.