Amplified Spontaneous Emission in Slab Amplifiers

Amplified spontaneous emission (ASE) occurs in media with large gain, and affects both the magnitude and the spatial distribution of the inversion. In this work we theoretically study the effect of ASE in three-dimensional, rectangular slab amplifiers, using Monte Carlo type computer simulations. We found that in one-dimensional amplifiers ASE is always larger at the edges so that the inversion has a maxima at the center of the amplifier. However, in two- and three-dimensional amplifiers, the inversion has a minimum at the center of the amplifier for low gain, and a maximum at the center of the amplifier for high gain. Thus, the inversion profile can be changed by increasing the gain from a minimum at the center, through a plateau, to a maximum at the center. A simple analytical theory was developed and agrees with these results     

Process and formulation variables of pregabalin microspheres prepared by w/o/o double emulsion solvent diffusion method and their clinical application by animal modeling studies

Pregabalin is an anticonvulsant drug used for neuropathic pain and as an adjunct therapy for partial seizures with or without secondary generalization in adults. In conventional therapy recommended dose for pregabalin is 75?mg twice daily or 50?mg three times a day, with maximum dosage of 600?mg/d. To achieve maximum therapeutic effect with a low risk of adverse effects and to reduce often drug dosing, modified release preparations; such as microspheres might be helpful. However, most of the microencapsulation techniques have been used for lipophilic drugs, since hydrophilic drugs like pregabalin, showed low-loading efficiency and rapid dissolution of compounds into the aqueous continous phase. The purpose of this study was to improve loading efficiency of a water-soluble drug and modulate release profiles, and to test the efficiency of the prepared microspheres with the help of animal modeling studies. Pregabalin is a water soluble drug, and it was encapsulated within anionic acrylic resin (Eudragit S 100) microspheres by water in oil in oil (w/o/o) double emulsion solvent diffusion method. Dichloromethane and corn oil were chosen primary and secondary oil phases, respectively. The presence of internal water phase was necessary to form stable emulsion droplets and it accelerated the hardening of microspheres. Tween 80 and Span 80 were used as surfactants to stabilize the water and corn oil phases, respectively. The optimum concentration of Tween 80 was 0.25% (v/v) and Span 80 was 0.02% (v/v). The volume of the continous phase was affected the size of the microspheres. As the volume of the continous phase increased, the size of microspheres decreased. All microsphere formulations were evaluated with the help of in vitro characterization parameters. Microsphere formulations (P1–P5) exhibited entrapment efficiency ranged between 57.00?±?0.72 and 69.70?±?0.49%; yield ranged between 80.95?±?1.21 and 93.05?±?1.42%; and mean particle size were between 136.09?±?2.57 and 279.09?±?1.97?µm. Pregabalin microspheres having better results among all formulations (Table 3) were chosen for further studies such as differential scanning calorimetry, Fourier transform infrared analysis and dissolution studies. In the last step, the best pregabalin microsphere formulation (P3) was chosen for in vivo animal studies. The pregabalin-loaded microspheres (P3) and conventional pregabalin capsules were applied orally in rats for three days, resulted in clinical improvement of cold allodynia, an indicator of peripheral neuropathy. This result when evaluated together with the serum pregabalin levels and in vitro release studies suggests that the pregabalin microspheres prepared with w/o/o double emulsion solvent diffusion method can be an alternative form for neuropathic pain therapy. Conclusively, a drug delivery system successfully developed that showed modified release up to 10?h and could be potentially useful to overcome the frequent dosing problems associated with pregabalin conventional dosage form.     

Comparison of surface roughness of Locust acacia (Robinia pseudoacacia L.) and European oak (Quercus petraea (Mattu.) Lieble.) in terms of the preparative process by planing

Effects of number of the cutters (planing knives), feed rate (operational speed) and cutting depth (biting thickness) on the surface roughness of Locust acacia (Robinia pseudoacacia L.) and European oak (Quercus petraea (Mattu.) Lieble.) were investigated on the base of the preparative differences by planing. The specimens were prepared by planing with two and four knives at 5 and 9 m/min feed rates in 1, 2 and 4 mm cutting depths. Surface roughness was measured from the radial face of each sample according to TS 930 (1989) by using Mitutoyo SJ-301 stylus scanner device. These measurements were performed perpendicular to the fibers by the sampling length of 12.5 mm at a sensitivity level of ±0.01 μm. Considering between all types of the experimental preparations, Locust acacia had the smoothest surfaces than that of European oak. Comparing the results of the surface roughness of both species, it has been obtained that the surface roughness decreases when the feed rate and the cutting depth decreases, whereas it increases when the knives on the cutter heads decreases. Therefore, it may be suggested that the perfect faces could be particularly prepared for this considered species by the greater number of the knives (four) at the slow feed rate (5 m/min) in the condition of the light cutting depth (1 mm).     

Performance of an inductive fault current limiter employing BSCCOsuperconducting cylinders

Inductive fault current limiters operating at high levels of short-circuit currents are plagued by appearance of overheated thermal domains in active superconducting elements. Excessive growth of thermal domains may lead to a fatal mechanical destruction of the superconducting element during a fault event. It has been determined that employment of superconductors with gradual dissipation onset controlled by flux relaxation processes can efficiently prevent local overheating. Operation of such elements, fabricated by melt cast technique, has been investigated experimentally in a small-scale open-core model of an inductive fault current limiter. The results of the experiments demonstrate the feasibility of application of superconducting cylinders having properties dominated by flux relaxation processes in inductive current limiters. The most important parameter of a superconducting element designated to operate in such devices is the rate of flux relaxation and its dependence on ac current amplitude. It has been found that ac losses associated with flux relaxation in the investigated cylinders allow for a reliable limiter operation at the nominal current level. Projection of the parameters of the investigated small-scale model to the full-scale device has been performed using the concept of physical modeling. The obtained results indicate that it is possible to build a full-scale device based on flux creep dissipation mechanisms for distribution networks     

The interface of metalorganic chemical vapor deposition-CdTe/HgCdTe

The metalorganic chemical vapor deposition (MOCVD) growth of CdTe on bulk n-type HgCdTe is reported and the resulting interfaces are investigated. Metalinsulator-semiconductor test structures are processed and their electrical properties are measured by capacitance-voltage and current-voltage characteristics. The MOCVD CdTe which was developed in this study, exhibits excellent dielectric, insulating, and mechano-chemical properties as well as interface properties, as exhibited by MIS devices where the MOCVD CdTe is the single insulator. Interfaces characterized by slight accumulation and a small or negligible hysteresis, are demonstrated. The passivation properties of CdTe/ HgCdTe heterostructures are predicted by modeling the band diagram of abrupt and graded P-CdTe/n-HgCdTe heterostructures. The analysis includes the effect of valence band offset and interface charges on the surface potentials at abrupt hetero-interface, for typical doping levels of the n-type layers and the MOCVD grown CdTe. In the case of graded heterojunctions, the effect of grading on the band diagram for various doping levels is studied, while taking into consideration a generally accepted valence band offset. The MOCVD CdTe with additional pre and post treatments and anneal form the basis of a photodiode with a new design. The new device architecture is based on a combination of a p-on-n homojunction in a single layer of n-type HgCdTe and the CdTe/HgCdTe heterostructure for passivation.     

Similar bioavailability of single-dose oral and intravenous mesna in the blood and urine of healthy human subjects

Although mesna has been used for more than a decade to reduce the incidence of hemorrhagic cystitis induced by ifosfamide and cyclophosphamide, the disposition of i.v. and oral mesna has not been adequately described. To obtain accurate bioavailability data for the design of mesna regimens, we developed procedures to preserve and measure mesna and dimesna in the blood and urine and studied 25 volunteer subjects who received single doses of i.v. mesna and four different formulations of oral mesna in a five-way randomized crossover study. The dose-adjusted area under the blood concentration-time curve showed no difference in bioavailability for i.v. and oral mesna; however, the maximum mesna concentration after oral doses was 16% of that estimated for i.v. doses. The short initial half-life of i.v. mesna indicated that mesna was rapidly cleared; however, the blood concentrations of mesna uniformly exceeded those of dimesna after oral as well as i.v. doses, which suggested that reduced mesna and oxidized mesna disulfide are in equilibrium. The ratio of mesna:dimesna was higher in protein-free plasma than it was in the urine, which suggested that most urinary mesna is produced by glomerular filtration of mesna rather than by renal tubular reduction of dimesna. The sum of mesna and dimesna excretion after the i.v. doses (73% of the dose) and the four oral formulations (68-73%) showed no difference in urinary bioavailability, consistent with the blood data. However, the urinary bioavailability of the therapeutically active free-thiol mesna was greater after i.v. doses (40% of the dose) than it was after oral doses (31-33%). The ratio of oral:i.v. mesna excretion ranged from 0.52-1.23 (mean, 0.82) among the 24 subjects. Urinary mesna concentrations exceeded 50 microM in all subjects for up to 12 h after oral doses as compared to 4 h after i.v. doses. About 90% of this mesna was excreted by hour 2 after i.v. doses and by hour 9 after oral doses. The mean maximum concentration of mesna in blood and excretion into urine were both 2.6 h after dosing. The oral formulations thus showed sustained urinary excretion, and their urinary bioavailability approached that of i.v. mesna.     

Simulating colliding flows in smoothed particle hydrodynamics with fractional derivatives

We propose a new method based on the use of fractional differentiation for improving the efficiency and realism of simulations based on smoothed particle hydrodynamics (SPH). SPH represents a popular particle‐based approach for fluid simulation and a high number of particles is typically needed for achieving high quality results. However, as the number of simulated particles increase, the speed of computation degrades accordingly. The proposed method employs fractional differentiation to improve the results obtained with SPH in a given resolution. The approach is based on the observation that effects requiring a high number of particles are most often produced from colliding flows, and therefore, when the modeling of this behavior is improved, higher quality results can be achieved without changing the number of particles being simulated. Our method can be employed to reduce the resolution without significant loss of quality, or to improve the quality of the simulation in the current chosen resolution. The advantages of our method are demonstrated with several quantitative evaluations. Copyright © 2013 John Wiley & Sons, Ltd.     

Recent Developments in Friction Stir Welding of Al-alloys

The diversity and never-ending desire for a better life standard result in a continuous development of the existing manufacturing technologies. In line with these developments in the existing production technologies the demand for more complex products increases, which also stimulates new approaches in production routes of such products, e.g., novel welding procedures. For instance, the friction stir welding (FSW) technology, developed for joining difficult-to-weld Al-alloys, has been implemented by industry in manufacturing of several products. There are also numerous attempts to apply this method to other materials beyond Al-alloys. However, the process has not yet been implemented by industry for joining these materials with the exception of some limited applications. The microstructures and mechanical properties of friction stir welded Al-alloys existing in the open literature will be discussed in detail in this review. The correlations between weld parameters used during FSW and the microstructures evolved in the weld region and thus mechanical properties of the joints produced will be highlighted. However, the modeling studies, material flow, texture formation and developments in tool design are out of the scope of this work as well as the other variants of this technology, such as friction stir spot welding (FSSW).