Predation of livestock ticks by chickens as a tick-control method in a resource-poor urban environment

The increasing prevalence of streptococci as causes of potentially fatal nosocomial bacteremia requires that antimicrobial agents used for empiric therapy in hospitalized patients include both pneumococci and viridans group streptococci as well as beta-hemolytic streptococci in their activity profile. In this study, the in vitro activity of cefepime, a new fourth-generation cephalosporin, was compared with other cephalosporins versus 197 nosocomial blood stream isolates of streptococci (20 Streptococcus pneumoniae, 104 viridans group, and 73 beta-hemolytic) isolated from patients at more than 30 medial centers from 1995 to 1997. Additional agents tested included penicillin, erythromycin, and vancomycin. Overall, cefepime inhibited 83% of the isolates at concentrations < or = 0.5 microgram/mL and 100% at < or = 8 micrograms/mL. By comparison, ceftazidime inhibited 35 and 88% of isolates at the same concentrations. Cefepime was approximately eightfold more potent than ceftazidime against S. pneumoniae, viridans group streptococci, and beta-hemolytic streptococci. Among the 42 isolates with penicillin MICs > 0.12 microgram/mL, 100% were inhibited by cefepime and only 48% by ceftazidime at < or = 8 micrograms/mL. The rank order of activity for all six agents against the 197 isolates was vancomycin > ceftriaxone > cefepime > penicillin > erythromycin > ceftazidime. Based on the results of the present study, cefepime and ceftriaxone were the superior cephalosporins in potency and spectrum for empiric coverage of patients at risk for streptococcal blood stream infections.     

Generation, Characterization, and Impact of Mesopores in Zeolite Catalysts

Amongst the current developments in the field of hierarchical pore structures, the creation of mesopores in zeolite crystals is the most frequently employed way to combine micropores with mesopores in one material. In this review an overview is presented of the different approaches to generate and characterize mesopores in zeolite crystals and establish their impact on the catalytic action. Mesopores can be created via several routes from which steaming and acid leaching are the most frequently applied. Novel approaches using secondary carbon templates that are removed after synthesis have recently been launched. For the characterization of mesopores, nitrogen physisorption and electron microscopy are commonly used. More recently, it was shown that electron tomography, a form of three-dimensional transmission electron microscopy, is able to reveal the three-dimensional shape, size, and connectivity of the mesopores. The effect of the presence of mesopores for catalysis is demonstrated for several industrially applied processes that make use of zeolite catalysts: the cracking of heavy oil fractions over zeolite Y, the production of cumene and hydroisomerization of alkanes over mordenite, and synthesis of fine chemicals over Y, ZSM-5, and Beta. For these processes, the mesopores ensure an optimal accessibility and transport of reactants and products, while the zeolite micropores induce the preferred shape-selective properties.     

Numerical Modeling of Cemented Mine Backfill Deposition

In current underground mining practice, it is common to use tailings, without added cement, to fill mined-out voids (“stopes”). If fine-grained tailings are used, the high placement rates and low permeability can often result in undrained loading conditions and, hence, lower effective stress, when assessed in the conventional manner. Where cement is added, the cement modifies the consolidation characteristics in a number of ways, including increasing the strength and stiffness, reducing the permeability, and inducing volumetric changes associated with the hydration reactions leading to “self-desiccation.” As a result, conventional consolidation-analysis techniques are unsuitable for assessing the behavior. The one-dimensional mine-tailings-consolidation program (MinTaCo) has been modified, and renamed CeMinTaCo, to couple cement hydration with conventional consolidation analysis. The fundamental theory behind the modifications is presented. The model is used to undertake a sensitivity study, which highlights some of the important features of the behavior of cemented backfill, and shows how complex interactions between the various properties produce some outcomes that are counterintuitive.     

A Compact Model for Valence-Band Electron Tunneling Current in Partially Depleted SOI MOSFETs

The valence-band electron (EVB) tunneling current in partially depleted silicon-on-insulator (SOI) MOSFETs increases as the gate oxide gets thinner and affects the dynamic behavior of devices and circuits. We present an engineering model of EVB tunneling current based on the surface-potential formulation. The new model is implemented in a SOI MOSFET compact model and is used to study the impact of EVB tunneling on circuit performance. Simulations of stacked logic gates show that the EVB tunneling current not only boosts circuit switching speed but also mitigates the history dependence of propagation delays     

Application of a rapid transesterification method for identification of individual fatty acids by gas chromatography on three different nut oils

The lack of uniformity of analytical techniques employed for quantification of fatty acids led to the successful implementation of a rapid transesterification method using tetramethylammonium hydroxide to determine and compare the total fatty acid content of almond, pecan and macadamia oils. Palmitic, oleic and linoleic acids comprised the largest part of the total fatty acid content in almond and pecan oils. Although oleic acid was also the main constituent of macadamia oil, its concentration was substantially lower than in the other oils.     

Improved estimates of power consumption during dewatering of mine tailings using electrokinetic geosynthetics (EKGs)

Electrokinetic geosynthetics (EKGs) were developed about a decade ago, producing a material that did not experience the same corrosion problems as metal electrodes when used in electro-osmotic (EO) dewatering applications. The conductive polymeric material from which EKGs are made has the additional advantage of being able to be formed into a variety of shapes, including drainage tubes such as those used in this study. One of the primary concerns regarding EO dewatering applications is the rate of energy consumption. This paper reports experiments at three different scales, on different mine tailings materials, that illustrates the potentially misleading results obtained from small scale laboratory tests. Using large, outdoor tests, power consumption rates for treating a kaolinitic mineral sands tailings and a smectitic diamond tailings were found to be up to 30 times lower than the power consumption rates obtained from laboratory tests using small samples in a purpose built EO cell. The primary reason for the improved performance is thought to be the lower voltage gradient used in the field tests, plus the geometric advantages offered by a field layout where a greater volume of material is exposed to the EO effect than only the material directly between the electrodes, which is the case in the EO cell tests. Finally, in the field tests the EO treatment caused the early development of vertical cracks in the tailings, resulting in increased exposure of the tailings to the effects of solar drying. This effect cannot obviously be reproduced in the EO cell laboratory tests, and can be a major advantage for the in situ treatment of mine tailings lagoons, where in some materials the onset of cracking is significantly delayed by the development of an impermeable surface crust.     

Images obtained in STEM of gold particles condensed on the top of thick single crystals of copper

It is proposed that when a thin sample is mounted on the top surface of a thick single crystal foil, this foil may function as a collector aperture with regard to the radiation transmitted through the thin sample. The detailed aspects of how the crystal foil may perform as an aperture are discussed in terms of the electron equivalent of the Borrmann effect in crystals. Experiments are presented which demonstrate that the image of the thin sample is sensitive to the thickness of the single crystal foil and to its orientation with regard to the beam axis. It is concluded from the experimental results that the crystal foil does perform a collector aperture-like function.