Hardness of Demineralized Enamel with the Application of Toothpaste Containing Green Tea Extract

The aim of this study was to analyze the influence of toothpastes with or without green tea extract on the enamel hardness. Human teeth were used as specimens and surface enamel demineralization by soaking in 1% citric acid. Teeth that have been demineralized were applied with a toothpaste containing green tea extract with concentrations of up to 15% on the surface of the enamel teeth and then proceed with surface hardness measurement using Knoop system. The results showed that soaking the teeth (enamel) in a demineralized solution has significantly decreased the hardness of tooth enamel. Applications of toothpaste without (0%) and with green tea extract 5% or 10% or 15% on the demineralized enamel surface have increased the enamel hardness significantly. However, no significant differences were seen between the demineralized enamel and enamel applied with toothpaste containing green tea 5% or 10% or 15%. It was concluded that the application of toothpaste containing 5% green tea extract was able to increase the hardness of demineralized enamel.   &nbsp

Preparation of Hydroxyapatite Nanocrystaline for Scaffold Bone Tissue Engineering

The synthesis and characterization of hydroxyapatite nanoparticles by using precipitation method have been carried out. Hydroxyapatite samples were prepared by mixing Ca(OH)2 powder and H3PO4 liquid with a mole ratio of 10 : 6. The samples were calcined at temperatures varying from 100 - 900 °C, each for 3 hours. The refinement results of X-Ray Diffraction patterns showed that all samples are single phase of Ca10(PO4)6(OH)2. The Ca10(PO4)6(OH)2 has a hexagonal structure (P63/m). Based on the refinement results, increasing the calcination tempertatures of HA from 100 to 900 °C, HA exists in higher volume, atomic density and crystalinity, as well as smaller of crystalites diameter. It is concluded that at the lowest calcination temperature of HA, the lowest volume, atomic density and crystallinity and the diameter of crystallites as well

Sedimentary exhalative venting of bioavailable nitrogen into the early ocean

EES acknowledges financial support from the School of Earth & Environmental Sciences, St Andrews. DDG acknowledges the support of NSERC for his Discovery grant (grant number 04834).Ore deposits found in Proterozoic marine sedimentary basins supply much of the world's zinc. Many of the deposits formed contemporaneously with their host sediments when saline brines circulating from deeper in the basin reached the sea floor. Textural, geochemical and isotopic features of these SEDEX (‘sedimentary-exhalative’) deposits and their host sediments indicate that biologically active seeps, vents and brine pools were a feature of many ore-forming systems. In mineralised pockets of mid-Proterozoic basins, these ‘microbial oases’ were productive areas in an otherwise low productivity, anoxic, deep marine realm. Here we hypothesize that these metal-rich brines which circulated through organic matter-rich substrate also carried high levels of fixed nitrogen and stimulated distinct ecosystems at sites of mineralisation, or enhanced productivity more broadly in the basin. We tested this hypothesis with organic carbon and nitrogen analyses of samples of carbonaceous siltstone and shale from the 1.64 Ga Barney Creek Formation of northern Australia. The Barney Creek Formation hosts several SEDEX Zn systems, including one of the world's largest deposits at McArthur River Mine (the HYC deposit). Samples come from the mineralised edge of HYC and from correlated strata in drill cores at varying distances (1-60 km) from the deposit. The data reveal lower ratios of total organic carbon (TOC) to total nitrogen (TN) closer to the ore body. Strong correlations (r2>0.7) between TOC and TN and the absence of excess N in the samples suggest that most N was buried as bound to organic matter. Bioavailable N was thus probably more abundant closer to HYC, consistent with fixed nitrogen input by hydrothermal fluids. If correct, our data may suggest that such a hydrothermal nitrogen point source enabled microbes to develop lower C:N ratios in their biomass. A hydrothermal nitrogen source is also supported by a gradient in δ15N values from = +4‰ proximal to the vent to +7.5‰ in distal sites, which may point towards recycling of ammonium from the underlying Wollogorang Formation (1.73 Ga). This unit has previously been identified as a source of over-mature hydrocarbons to the ore-forming fluid. We speculate that, during the mid-Proterozoic, fixed nitrogen carried by SEDEX hydrothermal brines may have locally offset the lack of aerobic nutrient remineralization that characterized most of the anoxic Precambrian deep ocean and thus stimulated biological productivity in areas where the brines reached the sea floor, and, possibly, more broadly as spent brines mixed into the water column.PostprintPeer reviewe

Collinear N\'eel-type ordering in partially frustrated lattices

We consider two partially frustrated S = 1/2 antiferromagnetic spin systems on the triangular and pentagonal lattices. In an elementary plaquette of the two lattices, one bond has exchange interaction strength $\alpha$ ($\alpha \leq 1$) whereas all other bonds have exchange interaction strength unity. We show that for $\alpha$ less than a critical value $\alpha_{c}$, collinear N\'eel-type ordering is possible in the ground state. The ground state energy and the excitation spectrum have been determined using linear spin wave theory based on the Holstein-Primakoff transformation.Comment: Four pages, LaTeX, Four postscripts figures, Phys. Rev. B58, 73 (1998

Stochastic model of transcription factor-regulated gene expression

We consider a stochastic model of transcription factor (TF)-regulated gene expression. The model describes two genes: Gene A and Gene B which synthesize the TFs and the target gene proteins respectively. We show through analytic calculations that the TF fluctuations have a significant effect on the distribution of the target gene protein levels when the mean TF level falls in the highest sensitive region of the dose-response curve. We further study the effect of reducing the copy number of Gene A from two to one. The enhanced TF fluctuations yield results different from those in the deterministic case. The probability that the target gene protein level exceeds a threshold value is calculated with a knowledge of the probability density functions associated with the TF and target gene protein levels. Numerical simulation results for a more detailed stochastic model are shown to be in agreement with those obtained through analytic calculations. The relevance of these results in the context of the genetic disorder haploinsufficiency is pointed out. Some experimental observations on the haploinsufficiency of the tumour suppressor gene, Nkx3.1, are explained with the help of the stochastic model of TF-regulated gene expression.Comment: 17 pages, 11 figures. Accepted for publication in Physical Biolog

A Molecular Hydrodynamic Theory of Supercooled Liquids and Colloidal Suspensions under Shear

We extend the conventional mode-coupling theory of supercooled liquids to systems under stationary shear flow. Starting from generalized fluctuating hydrodynamics, a nonlinear equation for the intermediate scattering function is constructed. We evaluate the solution numerically for a model of a two dimensional colloidal suspension and find that the structural relaxation time decreases as $\dot{\gamma}^{-\nu}$ with an exponent $\nu \leq 1$, where $\dot{\gamma}$ is the shear rate. The results are in qualitative agreement with recent molecular dynamics simulations. We discuss the physical implications of the results.Comment: 5 pages, 1 figur

Mixed-spin systems: coexistence of Haldane gap and antiferromagnetic long range order

Recent experiments on the quasi-1D antiferromagnets $R_{2}BaNiO_{5}$ (R = rare earth) have shown the existence of purely 1D Haldane gap excitations propagating on the Ni chains. Below an ordering temperature, the gap excitations survive and coexist with the conventional spin waves in the ordered phase. We construct a model mixed-spin system in 2D for which the ground state can be exactly specified. Using the Matrix Product Method, we show the existence of Haldane gap excitations in the ordered phase. We consider different cases of ordering to study the effect of ordering on the degeneracy of the Haldane gap excitations.Comment: 13 pages, LaTeX, 2 Postscript figures, communicated to Phys. Rev.