A cluster computing implementation of a Monte Carlo simulation of a particle growth mechanism

Clusters of computers can be used together to provide a powerful computing resource. Large Monte Carlo simulations, such as those used to model particle growth, are computationally intensive and take considerable time to execute on conventional workstations. By spreading the work of the simulation across a cluster of computers, the elapsed execution time can be greatly reduced. Thus a user has apparently the performance of a supercomputer by using the spare cycles on other workstations.

Analysis of aluminium content and iron homeostasis in nipple aspirate fluids from healthy women and breast cancer-affected patients

Aluminium is not a physiological component of the breast but has been measured recently in human breast tissues and breast cyst fluids at levels above those found in blood serum or milk. Since the presence of aluminium can lead to iron dyshomeostasis, levels of aluminium and iron-binding proteins (ferritin, transferrin) were measured in nipple aspirate fluid (NAF), a fluid present in the breast duct tree and mirroring the breast microenvironment. NAFs were collected noninvasively from healthy women (NoCancer; n = 16) and breast cancer-affected women (Cancer; n = 19), and compared with levels in serum (n = 15) and milk (n = 45) from healthy subjects. The mean level of aluminium, measured by ICP-mass spectrometry, was significantly higher in Cancer NAF (268.4 ± 28.1 μg l−1; n = 19) than in NoCancer NAF (131.3 ± 9.6 μg l−1; n = 16; P < 0.0001). The mean level of ferritin, measured through immunoassay, was also found to be higher in Cancer NAF (280.0 ± 32.3 μg l−1) than in NoCancer NAF (55.5 ± 7.2 μg l−1), and furthermore, a positive correlation was found between levels of aluminium and ferritin in the Cancer NAF (correlation coefficient R = 0.94, P < 0.001). These results may suggest a role for raised levels of aluminium and modulation of proteins that regulate iron homeostasis as biomarkers for identification of women at higher risk of developing breast cancer. The reasons for the high levels of aluminium in NAF remain unknown but possibilities include either exposure to aluminium-based antiperspirant salts in the adjacent underarm area and/or preferential accumulation of aluminium by breast tissues.

Iron and zinc status in multiple sclerosis patients with pressure sores

Measurements of weighted dietary intakes and plasma determinations of albumin, iron, zinc, ascorbic acid and TIBC were carried out on twenty female multiple sclerosis patients in a long-stay hospital for disabled people. The group included ten patients with a recent history of pressure sores, closely matched with ten patients without pressure sores. Mean daily intake of carbohydrate was found to be higher in the non-pressure sore group whilst intake of zinc was lower in this group. Intakes of all other nutrients were comparable between the two groups. For both groups, intakes of energy, folate, vitamin D, iron and zinc were less than recommended values. Mean plasma levels of albumin and iron were towards the lower limit of the normal range, whilst that for zinc was considerably less than the normal range. Plasma TIBC was slightly above the normal range. Levels of plasma iron and zinc were significantly lower in the pressure sore group. The data indicate that severely disabled hospitalized patients with multiple sclerosis may be at risk of poor nutritional status. The results suggest that in the presence of pressure sores, there are increased requirements for specific nutrients, notably zinc and iron. Consideration is given to the possible value of supplementation of these individuals.

Zinc metabolism in pregnant and lactating rats and the effect of varying iron: Zn in the diet

Pregnant rats were given control (46 mg iron/kg, 61 mg zinc/kg), low-Zn (6.9 mg Zn/kg) or low-Zn plus Fe (168 mg Fe/kg) diets from day 1 of pregnancy. The animals were allowed to give birth and parturition times recorded. Exactly 24 h after the end of parturition the pups were killed and analysed for water, fat, protein, Fe and Zn contents and the mothers' haemoglobin (Hb) and packed cell volume (PCV) were measured. There were no differences in weight gain or food intakes throughout pregnancy. Parturition times were similar (mean time 123 (SE 15) min) and there were no differences in the number of pups born. Protein, water and fat contents of the pups were similar but the low-Zn Fe-supplemented group had higher pup Fe than the low-Zn unsupplemented group, and the control group had higher pup Zn than both the low-Zn groups. The low-Zn groups had a greater incidence of haemorrhaged or deformed pups, or both, than the controls. Pregnant rats were given diets of adequate Zn level (40 mg/kg) but with varying Fe:Zn (0.8, 1.7, 2.9, 3.7). Zn retention from the diet was measured using 65Zn as an extrinsic label on days 3, 10 and 17 of pregnancy with a whole-body gamma-counter. A group of non-pregnant rats was also included as controls. The 65Zn content of mothers and pups was measured 24-48 h after birth and at 14, 21 and 24 d of age. In all groups Zn retention was highest from the first meal, fell in the second meal and then rose in the third meal of the pregnant but not the non-pregnant rats. There were no differences between the groups given diets of varying Fe:Zn level. Approximately 25% of the 65Zn was transferred from the mothers to the pups by the time they were 48 h old, and a further 17% during the first 14 d of lactation. The pup 65Zn content did not significantly increase after the first 20 d of lactation but the maternal 65Zn level continued to fall gradually.

The effect of iron supplements on pregnancy in rats given a low-zinc diet

1. Female Wistar rats were given an adequate-zinc (60 μg/g) or low-Zn (7 μg/g) diet for a minimum of 2 weeks and then mated. They were then either continued on the same diets (+Zn –Fe or –Zn –Fe) or given similar diets supplemented with four times the normal level of iron (+Zn + Fe or –Zn + Fe). The day before parturition they were killed and the fetuses removed and analysed. 2. There were no differences in numbers of fetuses or the number of resorption sites. In the absence of Fe supplementation, the mean fetal wet weight was significantly less (P < 0.05) in the low-Zn group but there was no effect of Zn in the two Fe-supplemented groups. The addition of Fe significantly decreased (P < 0.05) the mean fetal wet weight in the adequate-Zn groups but had no effect in the low-Zn groups. There were no differences in fetal dry weight, fat, protein or DNA content. Both Fe-supplemented groups produced fetuses of higher Fe concentration (P < 0.01), and mothers with higher bone Fe-concentration (P < 0.01) compared with the non-supplemented groups. The low-Zn groups produced fetuses of lower Zn concentration (P < 0,001) than the adequate-Zn groups but there was no effect on maternal bone Zn concentration. 3. It was concluded that Fe-supplements did not adversely affect fetal growth from mothers given a low-Zn diet, but the addition of Zn to the unsupplemented diet increased fetal wet weight. These findings were not accompanied by any other differences in fetal composition or dry weight, and do not therefore lend support to the suggestion of an Fe-Zn interaction.

Simultaneous observations of reconnection pulses at Cluster and their effects on the cusp aurora observed at the Chinese Yellow River station

While the Cluster spacecraft were located near the high-latitude magnetopause, between 1010 and 1040 UT on 16 January 2004, three typical flux transfer event (FTE) signatures were observed. During this interval, simultaneous and conjugated all‐sky camera measurements, recorded at Yellow River Station, Svalbard, are available at 630.0 and 557.7 nm that show poleward‐moving auroral forms (PMAFs), consistent with magnetic reconnection at the dayside magnetopause. Simultaneous FTEs seen at the magnetopause mainly move northward, but having duskward (eastward) and tailward velocity components, roughly consistent with the observed direction of motion of the PMAFs in all‐sky images. Between the PMAFs meridional keograms, extracted from the all‐sky images, show intervals of lower intensity aurora which migrate equatorward just before the PMAFs intensify. This is strong evidence for an equatorward eroding and poleward moving open‐closed boundary associated with a variable magnetopause reconnection rate under variable IMF conditions. From the durations of the PMAFs, we infer that the evolution time of FTEs is 5–11 minutes from its origin on the magnetopause to its addition to the polar cap.

On merging gradient estimation with mean-tracking techniques for cluster identification

This paper discusses how numerical gradient estimation methods may be used in order to reduce the computational demands on a class of multidimensional clustering algorithms. The study is motivated by the recognition that several current point-density based cluster identification algorithms could benefit from a reduction of computational demand if approximate a-priori estimates of the cluster centres present in a given data set could be supplied as starting conditions for these algorithms. In this particular presentation, the algorithm shown to benefit from the technique is the Mean-Tracking (M-T) cluster algorithm, but the results obtained from the gradient estimation approach may also be applied to other clustering algorithms and their related disciplines.

Neural network basis function center selection using cluster analysis

This paper deals with the selection of centres for radial basis function (RBF) networks. A novel mean-tracking clustering algorithm is described as a way in which centers can be chosen based on a batch of collected data. A direct comparison is made between the mean-tracking algorithm and k-means clustering and it is shown how mean-tracking clustering is significantly better in terms of achieving an RBF network which performs accurate function modelling.

Cluster analysis for multivariable process control

This paper describes the novel use of cluster analysis in the field of industrial process control. The severe multivariable process problems encountered in manufacturing have often led to machine shutdowns, where the need for corrective actions arises in order to resume operation. Production faults which are caused by processes running in less efficient regions may be prevented or diagnosed using a reasoning based on cluster analysis. Indeed the intemal complexity of a production machinery may be depicted in clusters of multidimensional data points which characterise the manufacturing process. The application of a Mean-Tracking cluster algorithm (developed in Reading) to field data acquired from a high-speed machinery will be discussed. The objective of such an application is to illustrate how machine behaviour can be studied, in particular how regions of erroneous and stable running behaviour can be identified.

Iron homeostasis and management of oxidative stress response in bacteria

Iron is both an essential nutrient for the growth of microorganisms, as well as a dangerous metal due to its capacity to generate reactive oxygen species (ROS) via the Fenton reaction. For these reasons, bacteria must tightly control the uptake and storage of iron in a manner that restricts the build-up of ROS. Therefore, it is not surprising to find that the control of iron homeostasis and responses to oxidative stress are coordinated. The mechanisms concerned with these processes, and the interactions involved, are the subject of this review.

Making DNA without iron: induction of a manganese-dependent ribonucleotide reductase in response to iron starvation

Ribonucleotide reductases supply cells with their deoxyribonucleotides. Three enzyme types are known, classes I, II and III. Class II enzymes are anaerobic whereas class I enzymes are aerobic, and so class I and II enzymes are often produced by the same organism under opposing oxygen regimes. Escherichia coli contains two types of class I enzyme (Ia and Ib) with the Fe-dependent Ia enzyme (NrdAB) performing the major role aerobically, leaving the purpose of the Ib enzyme (NrdEF) unclear. Several papers have recently focused on the class Ib enzymes showing that they are Mn (rather than Fe) dependent and suggesting that the E. coli NrdEF may function under redox-stress conditions. A paper published in this issue of Molecular Microbiology from James Imlay's group confirms that this unexplained NrdEF Ib enzyme is Mn-dependent, but shows that it does not substitute for NrdAB during redox stress. Instead, a role during iron restriction is demonstrated. Thus, the purpose of NrdEF (and possibly other class Ib enzymes) is to enhance growth under aerobic, low-iron conditions, and to functionally replace the Fe-dependent NrdAB when iron is unavailable. This finding reveals a new mechanism by which bacteria adjust to life under iron deprivation.

A new role for heme, facilitating release of iron from the bacterioferritin iron biomineral

Bacterioferritin (BFR) from Escherichia coli is a member of the ferritin family of iron storage proteins and has the capacity to store very large amounts of iron as an Fe(3+) mineral inside its central cavity. The ability of organisms to tap into their cellular stores in times of iron deprivation requires that iron must be released from ferritin mineral stores. Currently, relatively little is known about the mechanisms by which this occurs, particularly in prokaryotic ferritins. Here we show that the bis-Met-coordinated heme groups of E. coli BFR, which are not found in other members of the ferritin family, play an important role in iron release from the BFR iron biomineral: kinetic iron release experiments revealed that the transfer of electrons into the internal cavity is the rate-limiting step of the release reaction and that the rate and extent of iron release were significantly increased in the presence of heme. Despite previous reports that a high affinity Fe(2+) chelator is required for iron release, we show that a large proportion of BFR core iron is released in the absence of such a chelator and further that chelators are not passive participants in iron release reactions. Finally, we show that the catalytic ferroxidase center, which is central to the mechanism of mineralization, is not involved in iron release; thus, core mineralization and release processes utilize distinct pathways.