54 research outputs found
The effects of dissolved solids in process cooling water and mine water on concrete corrosion.
Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1998.An investigation has been carried out to determine the effects of the dissolved solids in process cooling water (pcw) and mine water (mw) on concrete corrosion. An experimental set up was designed to simulate the process in the cooling towers of Sasol (Pty) Ltd at Secunda. The investigation was carried out using Ordinary Portland Cement (OPC) and Portland Blastfurnace Cement (PBFC). The corrosion process was
monitored as a function of time by determining the concentrations of the ions left in solution. This was done using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) and Ion Chromatography (lC). The observation, identification and characterization of the secondary phases formed during the corrosion process were analyzed using the Scanning Electron Microscopy(SEM). Energy Dispersive X-ray Microanalysis (EDX) made it possible to identify the various microstructures and quantify their elemental composition. This made it possible to monitor the penetration of sulphate ions in the mortar. Powder X-ray Diffraction (XRD) qualitative analysis was also performed on the test mortar specimens. The organic constituents in process cooling water were determined using
Gas Chromatography coupled with a Mass Spectrometer (GC-MS). The corrosion indices which measures the aggressiveness of water solutions towards cement and concrete were calculated for both process cooling water and mine water. The results of the investigation showed that mine water is more corrosive than process cooling water. This observation has been linked to the presence of the organic compounds in process cooling water. The results also indicated that PBFC was mores resistant to chemical attack than ope
Energy and momentum of Bianchi Type VI_h Universes
We obtain the energy and momentum of the Bianchi type VI_h universes using
different prescriptions for the energy-momentum complexes in the framework of
general relativity. The energy and momentum of the Bianchi VI_h universe are
found to be zero for the parameter h = -1 of the metric. The vanishing of these
results support the conjecture of Tryon that Universe must have a zero net
value for all conserved quantities.This also supports the work of Nathan Rosen
with the Robertson-Walker metric. Moreover, it raises an interesting question:
"Why h=-1 case is so special?
Energy Distribution of a Stationary Beam of Light
Aguirregabiria et al showed that Einstein, Landau and Lifshitz, Papapetrou,
and Weinberg energy-momentum complexes coincide for all Kerr-Schild metric.
Bringely used their general expression of the Kerr-Schild class and found
energy and momentum densities for the Bonnor metric. We obtain these results
without using Aguirregabiria et al results and verify that Bringley's results
are correct. This also supports Aguirregabiria et al results as well as
Cooperstock hypothesis. Further, we obtain the energy distribution of the
space-time under consideration.Comment: Latex, no figures [Admin note: substantial overlap with gr-qc/9910015
and hep-th/0308070
Energy-Momentum Distribution: Some Examples
In this paper, we elaborate the problem of energy-momentum in General
Relativity with the help of some well-known solutions. In this connection, we
use the prescriptions of Einstein, Landau-Lifshitz, Papapetrou and M\"{o}ller
to compute the energy-momentum densities for four exact solutions of the
Einstein field equations. We take the gravitational waves, special class of
Ferrari-Ibanez degenerate solution, Senovilla-Vera dust solution and
Wainwright-Marshman solution. It turns out that these prescriptions do provide
consistent results for special class of Ferrari-Ibanez degenerate solution and
Wainwright-Marshman solution but inconsistent results for gravitational waves
and Senovilla-Vera dust solution.Comment: 20 pages, accepted for publication in Int. J. Mod. Phys.
M{\o}ller's energy of the Kerr-NUT Metric
The energy distribution of the Kerr-NUT space-time is calculated using M\o
ller's energy-momentum complex within the framework of the Riemannian geometry.Comment: 6 pages Late
Cysteine dependence of Lactobacillus iners is a potential therapeutic target for vaginal microbiota modulation
Vaginal microbiota composition affects many facets of reproductive health. Lactobacillus iners-dominated microbial communities are associated with poorer outcomes, including higher risk of bacterial vaginosis (BV), compared with vaginal microbiota rich in L. crispatus. Unfortunately, standard-of-care metronidazole therapy for BV typically results in dominance of L. iners, probably contributing to post-treatment relapse. Here we generate an L. iners isolate collection comprising 34 previously unreported isolates from 14 South African women with and without BV and 4 previously unreported isolates from 3 US women. We also report an associated genome catalogue comprising 1,218 vaginal Lactobacillus isolate genomes and metagenome-assembled genomes from >300 women across 4 continents. We show that, unlike L. crispatus, L. iners growth is dependent on L-cysteine in vitro and we trace this phenotype to the absence of canonical cysteine biosynthesis pathways and a restricted repertoire of cysteine-related transport mechanisms. We further show that cysteine concentrations in cervicovaginal lavage samples correlate with Lactobacillus abundance in vivo and that cystine uptake inhibitors selectively inhibit L. iners growth in vitro. Combining an inhibitor with metronidazole promotes L. crispatus dominance of defined BV-like communities in vitro by suppressing L. iners growth. Our findings enable a better understanding of L. iners biology and suggest candidate treatments to modulate the vaginal microbiota to improve reproductive health for women globally
Naked singularities and Seifert's conjecture
It is shown that for a general nonstatic spherically symmetric metric of the
Kerr-Schild class several energy-momentum complexes give the same energy
distribution as in the Penrose prescription, obtained by Tod. This result is
useful for investigating the Seifert conjecture for naked singularities. The
naked singularity forming in the Vaidya null dust collapse supports the Seifert
conjecture. Further, an example and a counterexample to this conjecture are
presented in the Einstein massless scalar theory.Comment: RevTex, no figures, new results included, published in Physical
Review D 60, 104041 (1999
- …