Experimental analysis,hybridization and exergetic investigation of an absorption refrigeration unit

In this work, an experimental and theoretical investigation of a frozen and hot water production unit with direct gas absorption is developed. Water/ammonia couple is used.A particular interest is given to the system performances evaluation such as exergetic efficiency and total exergy loss. Parameters analyzed are coefficients of performance, irreversibility and exergetic efficiency.Results show that the machine can reach a COP up to 65% and exergetic efficiency up to 18% for a working temperature and a condensation temperature of 120 °C and 18 °C, respectively. These performances decrease for a condensation temperature of 37 °C and 47 °C. Indeed, the engine is less efficient and presents more irreversibility, which is major in the pre-absorber and the absorber.An improvement of the machine cycle is proposed, in order to adapt it to low grade heat sources, using a compressor upstream of the pre-absorber. Performances of the new hybrid cycle are better than those of the real cycle.     

TLM simulation of microwave sintering of ceramics using SiC stimulus.

Microwave heating technology is becoming a successful technique used for sintering ceramic materials. However, various aspects of sintering experiments, such as the use of process stimulus and the preparation of sample arrangements, depend mainly on human expertise. The Transmission Line Matrix (TLM) method is first used to solve the combined electromagnetic and thermal equations modeling microwave heating of dielectric materials. It is then used to simulate microwave sintering of a low-loss ceramic material in a multimode microwave cavity. To enhance the microwave sintering process, Silicon Carbid (SiC) was first used as a susceptor and in a picket fence arrangement. As multiple samples may be processed in a microwave oven, the TLM was used to model such a process, and the introduction of SiC as a stimulus was also examined. Results show the importance of the stimulus thickness and configuration on the uniformity and density of the electromagnetic field distribution and, therefore, on the power dissipation within the ceramic load.     

Transmission-line-matrix (TLM) modeling of self-heating in AlGaN/GaN transistor structures

Self-heating in AlGaN/GaN (GaN—gallium nitride) heterostructures is an important issue for a large use of these devices in high-density power telecommunication applications. The equation of heat associated with this type of problem does not admit an analytical solution. Hence, we propose a numerical solution based on the use of a transmission line matrix (TLM). The method is easy to program and gives insights on temperature distribution throughout the device. It allows a better understanding of heat behavior and management at each layer that forms the structure. Some TLM simulation results have been compared with those obtained experimentally using integrated micro-Raman/infrared (IR) thermography methods, and have been found to agree within the bounds set by the resolution of the meshes used. The TLM has also the advantage upon other numerical methods of being unconditionally stable, one step and can adapt to complex geometries such as devices with several fingers.     

An efficient microcalcifications detection based on dual spatial/spectral processing

Microcalcifications are tiny deposits of calcium located in breast tissue. They appeared as very small highlighted regions in comparison with their surrounding tissue. Spatial non linear enhancement can be applied for microcalcification detection. However, efficiency of a such approach depends on breast density: in case of extreme breast density, the contrast between microcalcification’s details and their surrounding tissue is attenuated leading to a limitation of spatially based approaches. In that case, frequency analysis such as wavelet based analysis can be more relevant for dissociating microcalcifications. The main goal of Computer Aided Detection systems (CAD) is to detect breast cancer at an early stage for all breast density classes by using entropies to enhance and then detect microcalcification details. Accordingly, we combine our approach a spatial Automatic Non Linear Stretching (ANLS) and Shannon Entropy based Wavelet Coefficient Thresholding (SE_WCT). Validation of the proposed approach is done on the Mammographic Image Analysis Society (MIAS) database. The evaluation of the contrast is based on the Second-Derivative-Like measure of enhancement(SDME). Accordingly, it yields to a mean SDME of 78.8dB on the whole database. The performance metric for evaluating our proposed CAD is the Receiver Operating Characteristic(ROC) curve and the free-response ROC (FROC). An area under the ROC curve A _z = 0.92 is obtained as well as 97.14 % of True Positives (TP) with 0,48 False positives per image (FP).     

On the performance of the base-stock inventory system under a compound Erlang demand distribution

In this paper, we propose a new method for determining the optimal base-stock level in a single echelon inventory system where the demand is a compound Erlang process and the lead-time is constant. The demand inter-arrival follows an Erlang distribution and the demand size follows a Gamma distribution. The stock is controlled according to a continuous review base-stock policy where unfilled demands are backordered. The optimal base-stock level is derived based on a minimization of the total expected inventory cost. A numerical investigation is conducted to analyze the performance of the inventory system with respect to the different system parameters and also to show the outperformance of the approach that is based on the compound Erlang demand assumption as compared to the classical Newsboy approach. This work allows insights to be gained on stock control related issues for both slow and fast moving stock keeping units.     

Preparation of functionalized Kraft lignin beads

Kraft lignin from black liquor wastes have been converted into epichlorohydrin‐crosslinked beads by inverse suspension polymerization. A careful control of the different parameters allowed the preparation of spherical beads with a relatively narrow diameter size distribution. The obtained beads, without permanent porosity, swell well in hydroalcoholic media. Grafting of the sulfonylhydrazine moiety using a two‐step route was further performed to apply them to carbonyl compounds scavenging. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Fluorescence spectroscopy of the longwave chlorophylls in trimeric and monomeric photosystem I core complexes from the cyanobacterium Spirulina platensis

The organization and interaction of chlorophylls (Chl) and the kinetics of the energy transfer in the core antenna of photosystem I (PSI) trimeric and monomeric complexes, isolated from Spirulina platensis with Triton X-100 have been studied by stationary and time-resolved fluorescence. At 295 K both complexes show an unusually intense long-wavelength emission band with prominent peaks at 730 nm (trimers) or 715 nm (monomers), whose intensity is independent of the redox state of P700. A broad band extending from 710 to 740 nm in the absorption and fluorescence excitation spectra of trimers also indicates the existence of the longwave Chls at 295 K. The 77 K fluorescence emission of PSI trimers frozen after addition of dithionite under illumination (P700 and the PSI acceptor side reduced) shows an intense band at 760 (F760) and a smaller one at 725 nm (F725); when P700 is oxidized, the intensity of F760 decreases about 15 times. In the 77 K spectrum of monomers only F725 is present in the longwave region, and its intensity does not depend on the redox state of P700. Bands of Chls with maxima near 680, 710, and 738 nm were found in the 77 K excitation spectrum of trimers, and bands near 680 and 710 nm were seen in the spectrum of monomers. Five spectrally different red Chl forms in PSI trimers and three red Chl in monomers have been resolved by deconvolution of their 77 K absorption spectra. The difference absorption spectrum, trimers-minus-monomers, shows that the appearance of the 735 nm band in trimers is accompanied by a decrease of 708, 698, and 688 nm bands present in monomers. The reversible changes of F760 intensity of Spirulina membranes as a result of their salt treatment confirm the idea that the most longwave Chl form originates from an interaction of Chls bound to different monomeric PSI subunits forming the trimer. The time-resolved fluorescence spectra of PSI trimers and monomers, measured at 287 K in the region 680-770 nm, are substantially different, although a set of similar lifetimes (9, approximately 30, approximately 66, and 1400-2200 ps) was necessary for a good fit. No effect of P700 redox state was observed on the fluorescence kinetics of both complexes at 287 K.     

Numerical modelling for simulation and treatment planning of prostate thermal therapy

A 2D transmission line matrix model is used to study thermal transfer in living tissues exposed to laser energy. Damage size because of thermal coagulation in thermal treatment of benign prostate hyperplasia is determined quantitatively. Results show a quasilinear dependency of blood perfusion on temperature at the beginning of coagulation. Immediately thereafter, blood perfusion decreases considerably until it shuts down when the tissue under investigation has been coagulated. Increase in perfusion rate (ω) leads to high values of t₁₀₀, which is the time required to reach a primary zone temperature of about 100 °C, and reflects the increased cooling created by perfusion. The transmission line matrix numerical model predicts the coagulation damage contours; that way, it has a clinical interest in therapy as an aid for clinicians because damage cannot be easily measured within patients. Results are validated through comparison with other researches. Copyright © 2014 John Wiley & Sons, Ltd.