AlGaN/GaN HEMTS: material, processing, and characterization

The growth of AlGaN/GaN high electron mobility transistor (HEMT) structures on sapphire by metal organic vapor phase epitaxy (MOVPE) is described, with special emphasis on procedures to reduce dislocation density. All the processing steps involved in the fabrication of nitride-based HEMTs have been optimized, including dry etching by ion beam milling, evaporation of Pt/Ti/Au gate contacts, and SiN _x surface passivation. Devices with several gate lengths and different geometries have been fabricated by standard photo- and e-beam lithography. d.c. drain current and transconductance increase when gate length is reduced, up to 950 mA mm^–1 and 230 mS mm^–1, respectively, at V _GS=0 V, in HEMTs with a gate length L _G=0.2 m. A maximum output power higher than 5 W mm^–1 is estimated. Finally, small-signal measurements yield f _T=12 GHz and f _max=25 GHz for HEMTs with L _G=0.5 m, which increase up to 20 and 35 GHz for L _G=0.2 m, respectively. Limitation of high-frequency performance by parasitics is discussed.     

Forensic identification of neat ricin and of ricin from crude castor bean extracts by mass spectrometry

The protein toxin ricin, which originates from the seeds of Ricinus communis plants, has been the subject of increased interest, due to its potential terrorist use. Exceptionally, this toxin is also subject to the Chemical Weapons Convention. In this paper, it is shown that mass spectrometry can be used to unambiguously verify the presence of ricin in crude toxin preparations. It is demonstrated that MALDI MS can be used for screening, either by direct analysis or by trypsin digestion and peptide mapping. Purified ricin from several varieties of R. communis was characterized by LC-ES MS(/MS). A crude ricin preparation from a single bean was similarly characterized. An LC method was set up with product ion MS/MS detection of selected marker peptides specific for ricin: T5, T7, T11, T12, and T13 from the A-chain and T3, T5, T14, T19, and T20 from the B-chain. This method was then used to unambiguously identify ricin in a crude preparation of ricin. The MALDI MS molecular weight analysis and the marker peptides LC-ES MS/MS analysis give a forensic level of identification of ricin when combined with activity testing.     

Job shop management of products under internal lifespan and external due date

Deteriorating items are found in a wide variety of productive environments and have been extensively reported in the literature. However, the evolution of markets demand the development of new products and new forms of work are made necessary to adapt production systems to those changes. The present work focuses on the production control of perishable products in a job shop environment. Specifically, in those products that have an expiration date within the production interval (internal caducity) that must be delivered before a certain date. As far as we know, there are no previous works that focus on the internal caducity of products at the production-control level. Two systems of different nature have been compared: Workload Control (WLC) and Kanban. WLC is usually a benchmark in job shop and made to order environments. Recent studies show that Kanban, traditionally used in JIT (Just in Time) environments, performs similarly or even better than WLC. The study was performed by discrete events simulation using Python© language, SimPy© and DEAP© modules, and considering several responses of the systems. The results show that both systems have a good performance in a variety of scenarios, with overall performance of Kanban in terms of internal caducity and tardy deliveries.     

Proficiency test for the determination of heavy metals in mineral feed. The importance of correctly selecting the certified reference materials during method validation

In 2008, the International Measurement Evaluation Programme, IMEP?, organised two proficiency tests (PTs) for the determination of heavy metals in mineral feed, named IMEP-105 and IMEP-27, respectively. IMEP-105 was organised in support of the activities of the European Union Reference Laboratory for Heavy Metals in Feed and Food, and participation was restricted to the officially nominated National Reference Laboratories (NRLs). IMEP-27 was open to all interested control laboratories in the field. The test material used in the two PTs was the same and the timeframe of the two exercises overlapped. The measurands in both exercises were total Cd, Pb and As and extractable Cd and Pb, as defined in Directive 2002/32/EC of the European Parliament and the Council on undesirable substances in animal feed. Forty-nine laboratories from 25 countries reported results to the two exercises, 29 to IMEP-105 and 20 to IMEP-27. In both PTs, external reference values were used instead of consensus values derived from the participants' results. It was shown that the concentration of total and extractable Cd according to Directive 2002/32/EC were identical, while the concentration of extractable Pb was ~80% of total Pb. The main outcome of these comparisons was that an underestimation of the concentrations of the addressed measurands, in particular total Pb, took place due to an erroneous estimation of the bias of the analytical methods used by most of the participants. It appeared that the nature of the certified reference materials chosen for method validation and recovery estimation was the cause of the problem (insufficient matching of the matrix characteristics between these materials and the test sample). No significant difference between the results reported to IMEP-105 and to IMEP-27 was observed.     

Colorectal cancer: another complication of diabetes mellitus?

Delayed stool transit and other gastrointestinal abnormalities are commonly observed in persons with diabetes mellitus and are also known to be associated with colorectal cancer. Previous studies of the contribution of diabetes to colorectal cancer incidence and mortality have been limited by small sample sizes and failure to adjust for covariates. With more than 1 million respondents, the 1959-1972 Cancer Prevention Study provided a unique opportunity to explore whether persons with diabetes (n=15,487) were more likely to develop colorectal cancer during a 13-year follow-up period than were persons without diabetes (n=850,946). After adjustment for colorectal cancer risk factors, such as race, educational level, body mass index, smoking, alcohol use, dietary intake, aspirin use, physical activity, and family history of colorectal cancer, the incidence density ratio comparing colorectal cancer in those with diabetes and those without diabetes was 1.30 (95% confidence interval 1.03-1.65) for men and 1.16 (95% confidence interval 0.87-1.53) for women. However, diabetes was not associated with greater case fatality. Future studies should explore the possibility of a cancer-promoting gastrointestinal milieu, including delayed stool transit and elevated fecal bile acid concentrations, associated with hyperglycemia and diabetic neuropathy.     

Synthesis under high-oxygen pressure, magnetic and structural characterization from neutron powder diffraction data of YGa1−xMn1+xO5 (x = 0.23): A comparison with YMn2O5

A new material of nominal stoichiometry YGaMnO₅ has been prepared in polycrystalline form from citrate precursors followed by thermal treatments under high-oxygen pressure. This compound has been characterized from neutron powder diffraction (NPD) data and magnetic measurements. For comparison, the parent compound YMn₂O₅ has also been synthesized and its crystal structure refined by NPD data. The new oxide has an actual stoichiometry YGa_1−xMn_1+xO₅ (x = 0.23), determined by NPD, showing an important cationic disorder between both metal sites; it is orthorhombic, Pbam (SG), and its crystal structure contains chains of Mn⁴⁺O₆ edge-sharing octahedra, linked together by Ga³⁺O₅ pyramids and YO₈ units. With respect to YMn₂O₅, containing axially elongated MnO₅ pyramids due to the Jahn-Teller effect of Mn³⁺ cations, the GaO₅ pyramidal units in YGa_0.77Mn_1.23O₅ are substantially flattened. This compound has a paramagnetic behaviour with two weak anomalies at about 50 K and 350 K. The magnetic structures, studied at 1.4 K and 100 K show a ferromagnetic coupling along the chains of MnO₆ octahedra.     

Exploration of trabecular bone nonlinear elasticity using time-of-flight modulation

Bone tissue contains microcracks that may affect its mechanical properties as well as the whole trabecular structure. The relationship between crack density and bone strength is nevertheless poorly understood. Linear ultrasound techniques being almost insensitive to the level of damage, we propose a method to measure acoustic non- linearity in trabecular bone using time-of-flight modulation (TOFM) measurements. Ultrasonic short bursts times-of- flight (TOF) are modulated as a result of nonlinear interaction with a low-frequency (LF) wave in the medium. TOF variations are directly related to elastic modulus variations. Classical and nonclassical nonlinear parameters beta, delta, and alpha can be derived from these measurements. The method was validated in materials with classical, quadratic, nonlinear elasticity. In dense trabecular bone region, TOFM related to classical, quadratic, nonlinear elasticity as a function of the LF pressure exhibits tension-compression asymmetry. The TOFM amplitude measured in dense areas of trabecular bone is almost one order of magnitude higher than in a low-density area, but the linear parameters show much smaller variations: 5% for ultrasound propagation velocity and 100% for broadband ultrasonic attenuation (BUA). In high-density trabecular bone regions, beta depends on the LF pressure amplitude and can reach 400 at 50 kPa.     

注塑模热流道技术的发展与应用

介绍了注塑模热流道成型技术的概念和应用的优缺点,概述了注塑模热流道技术的发展现状,说明了热流道技术的特殊应用场合及主要生产厂商对中国市场的影响,并对热流道成型技术今后的市场前景和发展趋势进行了预测和总结,提出推广热流道技术应注意的问题.     

Experimental study of lateral pass width in conventional and vibrations-assisted ball burnishing

Burnishing is a mechanical finishing operation performed on workpieces to enhance their surface quality through plastic deformation. One of the main issues to understand the overall process is the behavior of the elastoplastic deformations caused by the burnishing ball on the workpiece. The first burnishing passes performed on the workpiece surface lead to its plastic strain and self-hardening, thus influencing the results of consecutive passes. Some references have studied the phenomenon of indentation, finding that there is a certain self-hardening coefficient threshold which allows to predict the presence of pile-ups at the edges of the indentation path. Nevertheless, burnishing is not a single-pass operation. On the contrary, burnishing a whole surface requires successive adjacent and/or overlapping passes, i.e., parallel passes separated consecutively a certain lateral pass width. No reference has been found in the literature defining the adequate values of the lateral pass width with regards to the pile-up effect to enhance the final topology of the burnished surface. This paper explores that influence by studying the presence of the pile-up effect after burnishing a single or several overlapping passes on two materials (aluminum and steel), by characterizing the topology of the generated path. Afterwards, two adjacent passes are performed, varying the lateral pass width, to compare the final surface roughness derived from each operation. An optimum value for the lateral pass width was found, to improve the final roughness after burnishing in different conditions and to increase the productivity of the process.     

Supercritical CO(2) extraction of PAHs on spiked soil Co-solvent effect and solvent regeneration by ozonization

The supercritical CO(2) extraction of four PAHs (acenaphthene, phenanthrene, anthracene and fluoranthene) from an artificially contaminated soil has been investigated. The effect of temperature (40-60 degrees C), pressure (300-500 bar) and extraction time (90-150 min) has been assessed by conducting a Box-Behnken experimental design. The results suggest the existence of perturbation variables other than the aforementioned controlled variables leading to a significant dispersion of extraction recoveries. With the exception of anthracene, an optimum in temperature (50 degrees C) is envisaged when extracting the PAHs. Analogously, with the exception of anthracene (positive effect), pressure does not have a significant influence. The recovery yield increases as extraction time is increased to a value of 120 min. No further improvement is experienced thereafter. If a co-solvent is used (H(2)O(2) aqueous solution) a beneficial effect can be noticed. Hydrogen peroxide concentration did exert no significant influence in the process. Methanol used to collect the extracted PAHs could be regenerated by gaseous ozone and reused in several consecutive runs.