A laboratory study on reducing the quantity of rock fines at failure: application to rock blasting and crushing

This paper presents laboratory work to determine whether decreasing the strength of rock through water-saturating the specimens can reduce the amount of generated fines at failure. Three types of rocks were tested using the indirect tensile (Brazilian) test. The samples were randomly divided into two groups of gneiss, diorite and diabase (dolerite), one group of each rock type being tested in dry and the other in saturated conditions. The results indicated that the dry samples produced both higher tensile strength values and more fines than the saturated specimens. Electronic Publication     

Use of antibiotics in livestock and human health concerns

Animal feed additives have for many years constituted the largest and most controversial category of antimicrobial use. The primary concerns addressed have been the generation of antibiotic resistance in animal bacterial and the influence of such resistance on human health. Studies designed to shed light on the controversy generally have yielded information leading to ambiguous conclusions. A 1989 report from the National Academy of Sciences was the latest of a long collection of assessments that have been meant to provide expert guidance to regulatory authorities on this matter. The FDA has been trying for some time to determine whether a regulatory decision on existing products is warranted. After several decades of research directed at this question, most qualified study groups have reported a paucity of appropriate information necessary to judge the reality of a public health risk.     

Strong field theory of low loss optical switching and three-wavemixing in a semiconductor quantum well

A density matrix analysis based on radiative renormalization predicts significant changes in band-edge absorption, index of refraction, and three-wave-mixing susceptibility in a quantum well when two conduction subbands are strongly coupled by an electromagnetic field     

Silica sol for rock grouting: Laboratory testing of strength,fracture behaviour and hydraulic conductivity

A recently introduced non-cementitious grout silica sol is a refined product of colloidal silica, where the particle sizes have been reduced to between 5 and 100 nm. Laboratory tests were performed to determine the behaviour of silica sol as a permeation grout in hard rock. The tests have involved methods such as fall-cone, unconfined compression, triaxial, and oedometer tests. Samples were tested at different time intervals and in different storage environments. Results showed that the initial strength of silica sol, a few kPa, increases over time. Silica sol has a ductile behaviour during the first few days and then becomes elastic–plastic. Its hydraulic conductivity ranges from 10^?10 to 10^?11 m/s. When immersed in water, silica sol hardens and a thin layer of weaker strength is formed at the surface. However, this layer only extends a couple of millimetres into the sample; beyond that the silica sol is not affected, rendering breakdown by erosion a negligible risk. The conclusions are: (1) the strength obtained in silica sol after hardening is sufficient to withstand most grouting conditions; (2) when sufficiently confined, silica sol is able to withstand loading and unloading cycles; (3) a pH environment of around 11 does not appreciably change the strength of the silica sol; (4) silica sol is a material with low risk of failure under blasting vibrations; and (5) due to its low hydraulic conductivity, silica sol can be compared to low permeable clays.     

Source of stray voltage and effect on cow health and performance

In dairy cows, two distinct and important aspects of the interrelationship between stray voltage problems on the farm and dairy cow productivity can be identified. One is behavioral modification that increases in intensity when currents associated with neutral-to-earth voltages above .7 V find a pathway through the cow. The other is immediate endocrine response. Results of research are less clear on the current necessary for the latter to occur; it may require 8 mA or more. This implies, depending on the pathway and the cow's pathway resistance, that voltage difference between two cow contact points must exceed 3 V. Resistance of different cow pathways range from 350 to 1700 omega. Milk production is more likely to be affected adversely when cows are subjected to shock patterns both intermittent and irregular. Less than 10% of the dairy cow population are thought to perceive any electrical currents upon contact with conductive grounding equipment provided voltages on the farm electrical neutral system remain below .35 V. This paper also identifies various sources of stray voltage problems and discusses appropriate procedures for correction.     

Relating nutrient and herbicide fate with landscape features and characteristics of 15 subwatersheds in the Choptank River watershed

Excess nutrients and agrochemicals from non-point sources contribute to water quality impairment in the Chesapeake Bay watershed and their loading rates are related to land use, agricultural practices, hydrology, and pollutant fate and transport processes. In this study, monthly baseflow stream samples from 15 agricultural subwatersheds of the Choptank River in Maryland USA (2005 to 2007) were characterized for nutrients, herbicides, and herbicide transformation products. High-resolution digital maps of land use and forested wetlands were derived from remote sensing imagery. Examination of landscape metrics and water quality data, partitioned according to hydrogeomorphic class, provided insight into the fate, delivery, and transport mechanisms associated with agricultural pollutants. Mean Nitrate-N concentrations (4.9 mg/L) were correlated positively with percent agriculture (R² = 0.56) and negatively with percent forest (R² = 0.60). Concentrations were greater (p = 0.0001) in the well-drained upland (WDU) hydrogeomorphic region than in poorly drained upland (PDU), reflecting increased denitrification and reduced agricultural land use intensity in the PDU landscape due to the prevalence of hydric soils. Atrazine and metolachlor concentrations (mean 0.29 μg/L and 0.19 μg/L) were also greater (p = 0.0001) in WDU subwatersheds than in PDU subwatersheds. Springtime herbicide concentrations exhibited a strong, positive correlation (R² = 0.90) with percent forest in the WDU subwatersheds but not in the PDU subwatersheds. In addition, forested riparian stream buffers in the WDU were more prevalent than in the PDU where forested patches are typically not located near streams, suggesting an alternative delivery mechanism whereby volatilized herbicides are captured by the riparian forest canopy and subsequently washed off during rainfall. Orthophosphate, CIAT (6-chloro-N-(1-methylethyl)-1,3,5-triazine-2,4-diamine), CEAT (6-chloro-N-ethyl-1,3,5-triazine-2,4-diamine), and MESA (2-[(2-ethyl-6-methylphenyl) (2-methoxy-1-methylethyl)amino]-2-oxoethanesulfonic acid) were also analyzed. These findings will assist efforts in targeting implementation of conservation practices to the most environmentally-critical areas within watersheds to achieve water quality improvements in a cost-effective manner.