MINIATURE PULSE TUBE FOR THE COOLING OF ELECTRONIC DEVICES: FUNCTIONING PRINCIPLES AND PRACTICAL MODELING

The miniaturization of refrigerating systems represents a very current scientific and technical challenge to improve the performances of numerous electronic components. This work presents a global approach to the problem and suggests studying the cooling by means of small channels filled with an oscillating gas: the double inlet pulse tube refrigerator (DIPTR). A great level of miniaturization based on the technology of carving silicon is exposed. This study proposes to apply an electric analogy for modeling both hydrodynamic and thermal phenomena. Considering the complexity of the theoretical problem including mechanical, thermal, thermodynamical, and acoustic considerations, the authors take care to summarize the main governing equations in a particular form so any scientific engineer could understand the DIPTR principle.     

On the distribution of sequential jobs in random brokering for heterogeneous computational grids

Scheduling stochastic workloads is a difficult task. In order to design efficient scheduling algorithms for such workloads, it is required to have a good in-depth knowledge of basic random scheduling strategies. This paper analyzes the distribution of sequential jobs and the system behavior in heterogeneous computational grid environments where the brokering is done in such a way that each computing element has a probability to be chosen proportional to its number of CPUs and (new from the previous paper) its relative speed. We provide the asymptotic behavior for several metrics (queue-sizes, slowdowns, etc.) or, in some cases, an approximation of this behavior. We study these metrics for a variety of workload configurations (load, distribution, etc.). We compare our probabilistic analysis to simulations in order to validate our results. These results provide a good understanding of the system behavior for each metric proposed. This enables us to design advanced and efficient algorithms for more complex cases.     

Mechanism of triazolo-benzodiazepine and benzodiazepine action in anxiety and depression: behavioral studies with concomitant in vivo CA1 hippocampal norepinephrine and serotonin release detection in the behaving animal

1. Real time, in vivo microvoltammetric studies were performed, using miniature carbon-based sensors, to concurrently detect norepinephrine (NE) release and serotonin (5-HT) release, in 2 separate electrochemical signals, within CA1 region of hippocampus in the freely moving and behaving, male, Sprague Dawley laboratory rat. 2. Concurrently, four parameters of open-field behavior, i.e. Ambulations, Rearing, Fine Movements and Central Ambulatory behavior (a measure of anxiety reduction behavior), were assayed by infrared photobeam detection. 3. Time course studies showed that the mechanism of action of the triazolobenzodiazepine (TBZD), adinazolam, (Deracyn) is dramatically different from that of the classical benzodiazepine (BZD), diazepam (Valium, i.e., adinazolam increased, whereas diazepam decreased, 5-HT release within CA1 region of hippocampus in the freely moving and behaving rat. 4. Adinazolam initially increased NE release and then decreased NE release in CA1 region of hippocampus in the freely moving and behaving rat whereas diazepam only decreased the electrochemical signal for NE; the decrease in NE produced by adinazolam was greater than the decrease in NE release produced by diazepam. 5. The Behavioral Activity Patterns, derived from same animal controls, simultaneously with detection of in vivo microvoltammetric signals for NE release and 5-HT release, showed that the BZD, diazepam, exhibited more potent sedative properties than did the TBZD adinazolam. 6. Hippocampal 5-HT and NE release effects of the TBZD, adinazolam, concomitant with behavioral effects lends explanation to the dual anxiolytic/antidepressant properties of the TBZDs.     

Make arc erosion and welding in the automotive area

A make arc has been investigated using a new testing apparatus. This apparatus which includes a piezo-translator, enables controlled bouncing to be studied at make under mechanical conditions similar to those encountered in automotive relays. Material transfer and welding tendency of silver, silver alloys and silver metal oxide contact materials have been studied under inductive, resistive and lamp loads at 14 V dc and 10-70 A. With all loads, anode to cathode material transfer has been observed. AgCdO, Ag and AgNi under lamp and resistive loads show the highest material transfer, as opposed to non doped and doped AgSnO₂ under inductive loads. This well known transfer is due to the anodic arc, which occurs during bounces when the gap between the contacts is shorter than ~5 μm, at the beginning and the end of the bounce. We have demonstrated that welding occurs at the beginning of the bounce, i.e. when the contacts begin to separate under arc, and not when the contacts close under arc at the end of the bounce. It was found that welding occurs mainly with Ag, AgCdO, AgZnO, AgFeRe, and AgFeO_x contact materials, and under high inrush current produced by lamp loads     

Reduction by CO-CO2 and cracking of iron ore sinters,part 2: cracking

The cracking of iron ore sinters during their low-temperature reduction to magnetite, in the upper part of the blast furnace, is a considerable handicap for the operation of the furnace. However, in spite of numerous previous investigations, it is not fully understood. Dealing with two different sinters, a synthetic and an industrial one, their hematite was reduced to magnetite by CO-CO₂, with varied temperatures and gas compositions. Cracking is strongly favoured by low temperature and low CO partial pressure. Under such conditions, the cracks are initiated by localized nucleation and there is no need for extended stress along the hematite-magnetite interface. The crack propagation is independent of the hematite crystals orientation, and the glassy gangue grain boundaries easily transmit the stress.     

Preparation et caracterisation des ferrites de calcium CaFe2+nO4+n a valeurs fractionnaires de n (32, 52) et leur incidence sur le diagramme Fe-Ca-O A 1120°C

The synthesis of two new calcium ferrites belonging to the CaFe_2+nO_4+n family, with the fractional values $\text{n =}\text{3}\text{2}$ and $\text{5}\text{2}$, has been done.Their crystalline structures have been determined. A stacking process of blocks with the CaFe₂O₄ composition and blocks with the FeO composition, like for the other terms of the series with n integer (1, 2, 3) allows to describe them.The schematic representation of this new example of intergrowth has been carried out according to A.F. Wells' method.The existence of these ferrites has lead us to specify the Fe-Ca-O diagram at 1120°C in the FeO-Ca₂Fe₂O₅-CaFe₂O₄ - Fe₃O₄ region.     

Low energy impact damage monitoring of composites using dynamic strain signals from FBG sensors - Part II: Damage identification

In part I of this two-paper series, a method for the localization of an impact using dynamic strain signals from fiber Bragg grating (FBG) sensors is presented. In this paper, an inverse numerical-experimental method allowing to identify the damage based on experimentally measured eigenfrequency changes is developed and validated. The damage identification is limited to a region in the vicinity of the impact position predicted by the localization method. The eigenfrequency changes are determined experimentally from dynamic strain signals obtained with embedded FBG sensors and the parameters of a homogenized damage model are adjusted to fit the numerical results to the experimental data.     

Modified Fluoroquinolones as Antimicrobial Compounds Targeting Chlamydia trachomatis

Chlamydia trachomatis causes the most common sexually transmitted bacterial infection and trachoma, an eye infection. Untreated infections can lead to sequelae, such as infertility and ectopic pregnancy in women and blindness. We previously enhanced the antichlamydial activity of the fluoroquinolone ciprofloxacin by grafting a metal chelating moiety onto it. In the present study, we pursued this pharmacomodulation and obtained nanomolar active molecules (EC₅₀) against this pathogen. This gain in activity prompted us to evaluate the antibacterial activity of this family of molecules against other pathogenic bacteria, such as Neisseria gonorrhoeae and bacteria from the ESKAPE group. The results show that the novel molecules have selectively improved activity against C. trachomatis and demonstrate how the antichlamydial effect of fluoroquinolones can be enhanced.     

Current Instability, Permittivity Variation With Frequency, and Their Relationship in Ta2O5 Capacitor

In this paper, Ta₂O₅ current instability in MIM and MIS capacitors is studied over several sample thicknesses with a current-versus-time measurement and low-frequency dielectric spectroscopy. Three types of phenomena are identified. The first one is attributed to polarization current correlated to flat loss behavior. The second mechanism corresponds to the conduction current identified as a steady state: a unique mechanism, probably a Poole-Frenkel one, is observed on the whole investigated voltage range. Finally, a resistance degradation phenomenon occurs that has been attributed to ionic diffusion in dielectric and follows the space-charge-limited theory. According to physical characterization, a model based on oxygen vacancies migration in the dielectric is suggested. Moreover, according to low-frequency dielectric spectroscopy measurements, it has been identified that the low-frequency loss peak is created by the same defects and is well modeled by the Maxwell-Wagner approach.     

Headspace solvent microextraction.

A hanging microliter drop of 1-octanol is shown to be an excellent preconcentration medium for headspace analysis of volatile compounds in an aqueous matrix by gas chromatography (GC) or gas chromatography/mass spectrometry (GC/MS). Model compounds benzene, toluene, ethylbenzene, and o-xylene (BTEX) are conveniently and rapidly preconcentrated in the microdrop. An internal standard, decane, is present in the organic extracting solvent, and linear calibration curves of relative peak area versus aqueous concentration are obtained for the four model compounds. Detailed kinetic studies reveal that the overall rate of mass transfer is limited by both the aqueous-phase stirring rate and the degree of convection within the organic phase. The very low vapor pressure of 1-octanol results in minimal evaporation of the microdrop during the extraction time. This system represents an inexpensive, convenient, and precise sample cleanup and preconcentration method for the determination of volatile organic compounds at trace levels.