Effect of pH on cellulose digestion under in vitro conditions

The extent of cellulose digestion by rumen micro-organisms in vitro is dependent on the pH of the medium. Digestion is greatly reduced at pH values similar to those found within the rumen of sheep fed with diets rich in readily digestible carbohydrates. It is suggested that this may be one of the reasons for reduced digestion of the fibre component of forages when carbohydrate supplements are fed.     

Luminescent passive-oxidized silicon quantum dots as biological staining labels and their cytotoxicity effects at high concentration

Semiconductor quantum dots (QDs) hold some advantages over conventional organic fluorescent dyes. Due to these advantages, they are becoming increasingly popular in the field of bioimaging. However, recent work suggests that cadmium based QDs affect cellular activity. As a substitute for cadmium based QDs, we have developed photoluminescent stable silicon quantum dots (Si-QDs) with a passive-oxidation technique. Si-QDs (size: 6.5 ± 1.5?nm) emit green light, and they have been used as biological labels for living cell imaging. In order to determine the minimum concentration for cytotoxicity, we investigated the response of HeLa cells. We have shown that the toxicity of Si-QDs was not observed at 112?μg?ml(-1) and that Si-QDs were less toxic than CdSe-QDs at high concentration in mitochondrial assays and with lactate dehydrogenase (LDH) assays. Especially under UV exposure, Si-QDs were more than ten times safer than CdSe-QDs. We suggest that one mechanism for the cytotoxicity is that Si-QDs can generate oxygen radicals and these radicals are associated with membrane damages. This work has demonstrated the suitability of Si-QDs for bioimaging in lower concentration, and their cytotoxicity and one toxicity mechanism at high concentration.     

Synthetic development and chemical reactivity of transition-metal silylene complexes

A variety of transition-metal complexes with terminal silylene ligands have become available in recent years, because of the discovery of several preparative methods. In particular, three general synthetic routes to these complexes have emerged, on the basis of anionic group abstraction, coordination of a free silylene, and alpha-hydrogen migration. The direct transformation of organosilanes to silylene ligands at a metal center (silylene extrusion) has also been observed, and this has further spurred the exploration of silylenes as ligands. This Account describes the synthetic development of silylene ligands in our laboratory and resulting investigations of stoichiometric and catalytic chemistry for these species.     

Fate of the pathogen indicators phage ΦX174 and Ascaris suum eggs during the production of struvite fertilizer from source-separated urine

Human urine has the potential to be a sustainable, locally and continuously available source of nutrients for agriculture. Phosphate can be efficiently recovered from human urine in the form of the mineral struvite (MgNH₄PO₄·6H₂O). However, struvite formation may be coupled with the precipitation of other constituents present in urine including pathogens, pharmaceuticals, and heavy metals. To determine if struvite fertilizer presents a microbiological health risk to producers and end users, we characterized the fate of a human virus surrogate (phage ΦX174) and the eggs of the helminth Ascaris suum during a low-cost struvite recovery process. While the concentration of phages was similar in both the struvite and the urine, Ascaris eggs accumulated within the solid during the precipitation and filtration process. Subsequent air-drying of the struvite filter cake partially inactivated both microorganisms; however, viable Ascaris eggs and infective phages were still detected after several days of drying. The infectivity of both viruses and eggs was affected by the specific struvite drying conditions: higher inactivation generally occurred with increased air temperature and decreased relative humidity. On a log-log scale, phage inactivation increased linearly with decreasing moisture content of the struvite, while Ascaris inactivation occurred only after achieving a minimum moisture threshold. Sunlight exposure did not directly affect the infectivity of phages or Ascaris eggs in struvite cakes, though the resultant rise in temperature accelerated the drying of the struvite cake, which contributed to inactivation.     

On Taylor dispersion effects for transient solutions in geothermal heating systems

Residential geothermal heating systems have been developed over the past few decades as an alternative to fossil-fuel based heating. Through mathematical modeling the relationship between the operating parameters of the heat pump and the piping length of the geothermal system, which is directly correlated to the cost of the system is investigated. The effect of Taylor dispersion of heat in the fluid which is not yet addressed in the literature with respect to geothermal systems is included. A model of a simple configuration of a single pipe surrounded concentrically by grout and then by soil is considered, where the soil region has a constant ambient temperature. The conduction between the two regions is modeled with a classical thermal resistance. Taylor dispersion effects are significant at higher Peclet numbers associated with this system, and Taylor dispersion in the fluid and thermostat frequency dictate the minimum tubing length needed for successful operation in an insulated subsystem. We consider both steady state and transient (cyclic operation) analyses and find that the axial dispersion increases linearly in the cycle rate for large flow rates. We find that the estimated tubing length for complete energy transport is increased when Taylor dispersion is included, but that this effect can be mitigated with an appropriate choice of the borehole radius.     

The formation of zirconium tungsten bronzes of the perovskite type

The oxygen rich corner of the ZrO₂-WO₃-WO₂ system has been studied by means of x-ray powder diffraction and electron microscopy at room temperature of specimens quenched from the preparation temperatures of 1000°C and 1100°C. Zirconium tungsten bronzes of formula Zr_xWO₃ are formed for 0<x<0.075. The symmetry of the unit cell increases with rising zirconium content x from monoclinic through orthorhombic to tetragonal (pseudocubic) at approximate x-values of 0.027 and 0.047, respectively. The zirconium atoms enter the empty cages in the tungsten trioxide structure in the same manner as for tungsten bronzes of the perovskite type. No evidence was observed for the formation of any crystallographic shear planes in these bronzes.     

Influence of radiation intensity upon photo-oxidation of unstabilised PVC

Films of unstabilised PVC have been exposed to xenon-arc irradiation at various levels of intensity within a limited temperature range, and the rates of photo-oxidation have been determined by infra-red spectroscopy. It has been found that the rate of reaction is directly proportional to radiation intensity measured in absolute units, and that transposition of time and radiation intensity is valid. The consequences of this finding have been discussed in terms of reaction mechanism and acceleration of the time scale for oxidation of PVC under artificial exposures to the xenon-arc, compared with outdoors exposure to solar radiation at Melbourne and London.     

Crystallographic shear phases in the system TixWO3

Samples of tungsten trioxide doped with titanium, and having the overall formula Ti_xWO₃ (0 < x < 0.04) and Ti_0·01W_0·99O_2·90 have been studied by x-ray diffraction and electron microscopy. All samples were inhomogeneous and contained a variety of structural types. The major components present were tungsten trioxide and crystallographic shear (CS) phases based upon {102}, {103} and {001} CS planes. In general the CS plane type altered from {102} through {103} to {001} as the degree of reduction increased. Intergrowths of {103} and {001} CS planes were seen, but no CS planes with indices between {102} and {103} or {103} and {001} were found.