Field assisted and flash sintering of alumina and its relationship to conductivity and MgO-doping

We show that flash-sintering in MgO-doped alumina is accompanied by a sharp increase in electrical conductivity. Experiments that measure conductivity in fully dense specimens, prepared by conventional sintering, prove that this is not a cause-and-effect relationship, but instead that the concomitant increase in the sintering rate and the conductivity share a common mechanism. The underlying mechanism, however, is mystifying since electrical conductivity is controlled by the transport of the fastest moving charged species, while sintering, which requires molecular transport or chemical diffusion, is limited by the slow moving charged species. Joule heating of the specimen during flash sintering cannot account for the anomalously high sintering rates. The sintering behavior of MgO-doped alumina is compared to that of nominally pure-alumina: the differences provide insight into the underlying mechanism for flash-sintering. We show that the pre-exponential in the Arrhenius equation for conductivity is enhanced in the non-linear regime, while the activation energy remains unchanged. The nucleation of Frenkel pairs is proposed as a mechanism to explain the coupling between flash-sintering and the non-linear increase in the conductivity.     

Contamination of surface and potable water in South Asia by Salmonellae: Culture-independent quantification with molecular beacon real-time PCR

Low numbers (15-100 CFU) of Salmonella in food or water may pose a public health risk. The management of infections caused by Salmonella spp. during outbreaks or forecasting of contamination of aquatic resources largely depends on rapid, sensitive and accurate diagnostic in few hours. In this study, a real-time PCR assay in Molecular-Beacon format was developed and culture-independent quantitative enumeration of Salmonella spp. in surface and potable water is being reported for the first time from northern part of India. Molecular Beacon was designed in highly conserved region of invA gene (present in wide range of Salmonella serotypes including all subspecies) encoding an essential component of the invasion associated specialized type Ø protein secretion apparatus for detection of Salmonella spp. in water. The assay could detect directly 10 and 1 genomic equivalent of Salmonella typhimurium ATCC 14028 per PCR with detection probability of 100 and 20%, respectively. Further, the assay could detect 10 CFU/PCR or more of reference strain (S. typhimurium ATCC 14028) without any enrichment in the presence of 10⁸ CFU ml^− 1 of non-pathogenic E. coli (E. coli DH5α) with 100% detection probability. The assay could enumerate Salmonella spp. in surface (n = 40) and potable waters (n = 10) directly (without enrichment). Results indicate that northern India is at high risk of developing Salmonella borne infections. Further, real-time PCR assay in Molecular Beacon format can be used for identification of critical contamination points in natural water resources and potable water distribution systems, necessary to implement vaccination plan timely for prevention of waterborne outbreaks caused by Salmonella spp.     

达芬奇效应:简便的数字视频

数字视频将引发人们与电子产品交互方式的变革。实现数字视频不但复杂,而且费时费钱。而这一切难题在达芬奇技术面前全部烟消云散。     

Strengthening in MULTIPHASE(MP35N) alloy: Part II. elevated temperature tensile and creep deformation

The strengthening mechanisms in the cobalt alloy MP35N have been investigated by tensile and creep deformation at elevated temperatures and by transmission electron microscopy (TEM) of the deformed alloy. A high ultimate tensile strength (UTS) of 800 to 900 MPa was maintained at all test temperatures from 300 to 873 K due to the maintenance of high strain hardening. On straining, there was the usual initial fall of the strain-hardening rate with stress, but above a critical stress of about 500 MPa, the strain-hardening rate stopped falling and was held almost constant at about 2000 MPa. At 973 and 1073 K, this high strain-hardening rate suddenly ceased during the test, while at 1123 K, negligible strain hardening was seen. At temperatures between 673 and 1073 K, tensile load drops were seen whose magnitude increased with strain, and thus stress, at a fixed temperature. The load drops also increased with increased temperature. How-ever, in conditions when the strain-hardening rate fell to a low value, the load drops ceased. In a tensile test in which small increments of strain were applied as the temperature was increased in 10 K intervals, a steadily rising flow stress with temperature was seen up to a critical temperature of 1073 K, beyond which the flow stress fell and the load drops also ceased. In conditions where the high rate of strain hardening was found, fine platelike structures were seen by transmission electron microscopy (TEM) to form on {111} planes in the face-centered cubic (fcc) matrix. Diffraction evidence showed that these were faulted hexagonal close-packed (hep) plates. Creep tests carried out above and below the critical temperature of 1073 K showed very different behavior. At 1098 K, the sample showed conventional creep behavior, while at a temperature of 973 K, the material showed sigmoidal creep strain rate. At low strains, up to a strain of about 0.02, there was an initial steady-state creep rate. The creep strain rate then increased and fell back to a second steady-state creep rate. During the accelerated creep stage, hexagonal plates were again seen to form. Strain-induced martensite forming at temperatures up to and including 1073 K, but not at higher temperatures, appears to account satisfactorily for all of the behavior seen in this study. It is proposed that the hexagonal plates form martensitically at high speed, but as proposed in Part I,^[1] solute partitioning occurs between the closely spaced fcc and hcp phases. At 1025 and 1073 K, the end of both the load drops and the high strain hardening during a tensile test may be explained by the stabilization of the remaining fcc matrix by loss of hexagonal phase stabilizing solute. The critical temperature of approximately 1073 K seen in this study is close to the critical softening temperature of 1083 K, above which recrystallization of cold-worked MP35N occurs readily (Part I^[1])- The critical temperature is proposed to be close to the transus temperature, above which single-phase fcc is the stable structure of MP35N.     

A Huge Effect of Weak dc Electrical Fields on Grain Growth in Zirconia

We show that the application of a modest dc electrical field, about 4 V/cm, can significantly reduce grain growth in yttria-stabilized polycrystalline zirconia. These measurements were made by annealing samples, for 10 h at 1300°C, with and without an electrical field. The finding adds a new dimension to the role of applied electrical fields in sintering and superplasticity, phenomena that are critical to the net-shape processing of ceramics. Grain-growth retardation will considerably enhance the rates of sintering and superplasticity, leading to significant energy efficiencies in the processing of ceramics.     

Fed batch enzymatic saccharification of newspaper cellulosics improves the sugar content in the hydrolysates and eventually the ethanol fermentation by Saccharomyces cerevisiae

The newspaper is comprised of (w w^?1) holocellulose (70.0%) with substantial amount of lignin (16.0%). Bioconversion of the carbohydrate component of newspaper to sugars by enzymatic saccharification, and its fermentation to ethanol was investigated. Of various enzymatic treatments using cellulase, xylanase and laccase, cellulase enzyme system was found to deink the newspaper most efficiently. The saccharification of deinked paper pulp using enzyme cocktail containing exoglucanase (20 U g^?1), β-glucosidase (60 U g^?1) and xylanase (80 U g^?1) resulted in 59.8% saccharification. Among additives, 1% (v v^?1) Tween 80 and 10 mol m^?3 CoCl₂ improved the enzymatic hydrolysis of newspaper maximally, releasing 14.64 g L^?1 sugars. The fed batch enzymatic saccharification of the newspaper increased the sugar concentration in hydrolysate from 14.64 g L^?1 to 38.21 g L^?1. Moreover, the batch and fed batch enzymatic hydrolysates when fermented with Saccharomyces cerevisiae produced 5.64 g L^?1 and 14.77 g L^?1 ethanol, respectively.