Recoverable reserves and support effects when optimizing open pit mine designs

Orebody modelling, support effects and the estimation of recoverable reserves are key parts of open pit optimization studies. A case study is presented on the estimation of recoverable reserves using an implementation of indicator kriging where metal quantity is used to select cutoffs, and support corrections founded on a conditional simulation approach. Mining selectivity is explored in the subsequent optimization study to compare results from indicator kriging of grade estimates on a regular size blocks and indicator kriging estimates on small size blocks. The use of indicator kriging models adjusted for a given selectivity and the use of grade proportions in each block for the optimization study, provide a presentation of the expected ore recovery for a predefined level of selectivity. The case study shows that indicator kriging estimation with full accounting of block grade distributions generates substantially better results in the pit optimization study. In addition, the adverse effects of small blocks and over-smoothing on optimization results are illustrated.

Circular proteins - no end in sight

Circular proteins are a recently discovered phenomenon. They presumably evolved to confer advantages over ancestral linear proteins while maintaining the intrinsic biological functions of those proteins. In general, these advantages include a reduced sensitivity to proteolytic cleavage and enhanced stability. In one remarkable family of circular proteins, the cyclotides, the cyclic backbone is additionally braced by a knotted arrangement of disulfide bonds that confers additional stability and topological complexity upon the family. This article describes the discovery, structure, function and biosynthesis of the currently known circular proteins. The discovery of naturally occurring circular proteins in the past few years has been complemented by new chemical and biochemical methods to make synthetic circular proteins; these are also briefly described.

Present and future pharmacotherapy for benign prostatic hyperplasia

Around 50% of men 51-60 years of age have pathological benign prostatic hyperplasia (BPH). Pharmacotherapy for BPH includes the 5alpha-reductase inhibitor finasteride, and alpha(1)-adrenoceptor antagonists. Finasteride reduces prostate volume and symptom scores, while increasing peak urinary flow rates. The main problem with finasteride treatment is that it increases the incidence of ejaculation disorders. All of the alpha(1)-adrenoceptor antagonists have been shown to reduce symptom scores and increase peak urinary flow rates in BPH. The nonselective alpha(1)-adrenoceptor antagonists (prazosin, terazosin and doxazosin) were developed as antihypertensives, and hypotensive-related side effects are the main problem with these agents in BPH. These side effects can be diminished by reducing peak concentrations of the drugs, as with once-daily alfuzosin, or by using the uroselective antagonist tamsulosin. Phytopharmaceuticals are commonly used in the treatment of BPH, such as saw palmetto berry which has been shown to improve the symptoms and peak urinary flow rate. Androgen receptor antagonists are not used in BPH because of their adverse effects. Newer drugs under development for the treatment of BPH include alpha(1)-adrenoceptor antagonists that show more selectivity for alpha(1A)-adrenoceptors than tamsulosin, combined 5alpha-reductase/alpha(1)-adrenoceptor inhibitors and combined type 1/type 2 5alpha-reductase inhibitors. New targets for the drug treatment of BPH include indothelin, growth factors, estrogens and the phosphodiesterase isoenzymes.

The rheology of flotation froths

A literature review has highlighted the need to measure flotation froth rheology in order to fully characterise the role of the froth in the flotation process. The initial investigation using a coaxial cylinder viscometer for froth rheology measurement led to the development of a new device employing a vane measuring head. The modified rheometer was used in industrial scale flotation tests at Mt. Isa Copper Concentrator. The measured froth rheograms show a non-Newtonian nature for the flotation froths (pseudoplastic flow). The evidence of the non-Newtonian flow has questioned the validity of application of the Laplace equation in froth motion modelling as used by a number of researchers, since the assumption of irrotational flow is violated. Correlations between the froth rheology and the froth retention time, water hold-up in the froth and concentrate grades have been found. These correlations are independent of air flow rate (test data at various air flow rates fall on one similar trend line). This implies that froth rheology may be used as a lumped parameter for other operating variables in flotation modelling and scale up. (C) 2003 Elsevier Science B.V. All rights reserved.

Acoustic analysis of speech through a hearing aid: perceptual effects of changes with two-channel compression

Compression amplification significantly alters the acoustic speech signal in comparison to linear amplification. The central hypothesis of the present study was that the compression settings of a two-channel aid that best preserved the acoustic properties of speech compared to linear amplification would yield the best perceptual results, and that the compression settings that most altered the acoustic properties of speech compared to linear would yield significantly poorer speech perception. On the basis of initial acoustic analysis of the test stimuli recorded through a hearing aid, two different compression amplification settings were chosen for the perceptual study. Participants were 74 adults with mild to moderate sensorineural hearing impairment. Overall, the speech perception results supported the hypothesis. A further aim of the study was to determine if variation in participants' speech perception with compression amplification (compared to linear amplification) could be explained by the individual characteristics of age, degree of loss, dynamic range, temporal resolution, and frequency selectivity; however, no significant relationships were found.

Systematic characterization of mutations in yeast acetohydroxyacid synthase: Interpretation of herbicide-resistance data

Acetohydroxyacid synthase (AHAS, EC 4.1.3.18) catalyses the first step in branched-chain amino acid biosynthesis and is the target for sulfonylurea and imidazolinone herbicides, which act as potent and specific inhibitors. Mutants of the enzyme have been identified that are resistant to particular herbicides. However, the selectivity of these mutants towards various sulfonylureas and imidazolinones has not been determined systematically. Now that the structure of the yeast enzyme is known, both in the absence and presence of a bound herbicide, a detailed understanding of the molecular interactions between the enzyme and its inhibitors becomes possible. Here we construct 10 active mutants of yeast AHAS, purify the enzymes and determine their sensitivity to six sulfonylureas and three imidazolinones. An additional three active mutants were constructed with a view to increasing imidazolinone sensitivity. These three variants were purified and tested for their sensitivity to the imidazolinones only. Substantial differences are observed in the sensitivity of the 13 mutants to the various inhibitors and these differences are interpreted in terms of the structure of the herbicide-binding site on the enzyme.

alpha-conotoxins PnIA and [A10L] PnIA stabilize different states of the alpha 7-L247T nicotinic acetylcholine receptor

The effects of the native alpha-conotoxin PnIA, its synthetic derivative [ A10L] PnIA and alanine scan derivatives of [ A10L] PnIA were investigated on chick wild type alpha7 and alpha7-L247T mutant nicotinic acetylcholine receptors (nAChRs) expressed in Xenopus oocytes. PnIA and [A10L] PnIA inhibited acetylcholine (ACh)-activated currents at wtalpha7 receptors with IC50 values of 349 and 168 nM, respectively. Rates of onset of inhibition were similar for PnIA and [ A10L] PnIA; however, the rate of recovery was slower for [ A10L] PnIA, indicating that the increased potency of [ A10L] PnIA at alpha7 receptors is conveyed by its slower rate of dissociation from the receptors. All the alanine mutants of [ A10L] PnIA inhibited ACh-activated currents at wtalpha7 receptors. Insertion of an alanine residue between position 5 and 13 and at position 15 significantly reduced the ability of [ A10L] PnIA to inhibit ACh-evoked currents. PnIA inhibited the non-desensitizing ACh-activated currents at alpha7-L247T receptors with an IC50 194 nM. In contrast, [ A10L] PnIA and the alanine mutants potentiated the ACh-activated current alpha7-L247T receptors and in addition [ A10L] PnIA acted as an agonist. PnIA stabilized the receptor in a state that is non-conducting in both the wild type and mutant receptors, whereas [ A10L] PnIA stabilized a state that is non-conducting in the wild type receptor and conducting in the alpha7-L247T mutant. These data indicate that the change of a single amino acid side-chain, at position 10, is sufficient to change the toxin specificity for receptor states in the alpha7-L247T mutant.

Chemical characterisation of deep profile Ferrosols under sugarcane in wet tropical northern Queensland

The chemical properties of deep profile samples ( up to 12 m) of Ferrosols from northern Queensland were investigated to provide an understanding of the accumulation of nitrate ( NO3) within these soil profiles. The influence of other cations and anions present in the soil solution or on the exchange and the charge chemistry of the profiles were examined with respect to the NO3 accumulations. The major ions in the soil solution were Na, NO3, and chloride ( Cl). Distinct regions of anion accumulation were observed; SO4 accumulated in the upper profile of all cores, whereas NO3 and Cl accumulations were restricted to the lower profile of cores with appreciable AEC (> 1 cmol(c)/kg). Gaines-Thomas selectivity coefficients were used to indicate exchange preference for cations and anions, and are as follows: Al > Ca similar to Mg > K > Na and sulfate (SO4) > Cl similar to NO3. The selectivity of SO4 increased and the extractable SO4 decreased in the lower profile of all cores. This has important implications for the adsorption of NO3 and Cl. The NO3 and Cl accumulations were shown to correspond to a region of low SO4 occupancy of the exchange sites in the lower profile. Along with the high SO4 selectivity, this suggests that SO4 may control the positioning of the NO3 accumulations. It was concluded that the NO3 accumulations were relatively stable under current management practices, although the reduction in NO3 inputs would likely see the gradual replacement of NO3 with Cl as a result of their comparable selectivity for exchange sites.

Dendritic branching of pyramidal cells in the visual cortex of the nocturnal owl monkey: A fractal analysis

The branching structure of neurones is thought to influence patterns of connectivity and how inputs are integrated within the arbor. Recent studies have revealed a remarkable degree of variation in the branching structure of pyramidal cells in the cerebral cortex of diurnal primates, suggesting regional specialization in neuronal function. Such specialization in pyramidal cell structure may be important for various aspects of visual function, such as object recognition and color processing. To better understand the functional role of regional variation in the pyramidal cell phenotype in visual processing, we determined the complexity of the dendritic branching pattern of pyramidal cells in visual cortex of the nocturnal New World owl monkey. We used the fractal dilation method to quantify the branching structure of pyramidal cells in the primary visual area (V1), the second visual area (V2) and the caudal and rostral subdivisions of inferotemporal cortex (ITc and ITr, respectively), which are often associated with color processing. We found that, as in diurnal monkeys, there was a trend for cells of increasing fractal dimension with progression through these cortical areas. The increasing complexity paralleled a trend for increasing symmetry. That we found a similar trend in both diurnal and nocturnal monkeys suggests that it was a feature of a common anthropoid ancestor.

Effect of pore-network connectivity on multicomponent adsorption of large molecules

The effect of pore-network connectivity on binary liquid-phase adsorption equilibria using the ideal adsorbed solution theory (LAST) was studied. The liquid-phase binary adsorption experiments used ethyl propionate, ethyl butyrate, and ethyl isovalerate as the adsorbates and commercial activated carbons Filtrasorb-400 and Norit ROW 0.8 as adsorbents. As the single-component isotherm, a modified Dubinin-Radushkevich equation was used. A comparison with experimental data shows that incorporating the connectivity of the pore network and considering percolation processes associated with different molecular sizes of the adsorptives in the mixture, as well as their different corresponding accessibility, can improve the prediction of binary adsorption equilibria using the LAST Selectivity of adsorption for the larger molecule in binary systems increases with an increase in the pore-network coordination number, as well with an increase in the mean pore width and in the spread of the pore-size distribution.