Spatial distribution of manganese in enamel and coronal dentine of human primary teeth

Emerging evidence indicates that excessive exposure to manganese (Mn) during the prenatal period and early childhood may result in neurodevelopmental deficits. However, accurate exposure biomarkers are not well established, limiting our understanding of exposure-response relationships over these susceptible periods of development. Naturally shed deciduous teeth are potentially a useful biomarker of environmental exposure to Mn. However, the uptake and distribution of Mn in human teeth has not been studied in detail.Mn distribution was measured at high resolution (~ 20 μm) in eight human primary teeth using laser ablation-inductively coupled plasma-mass spectrometry. A bio-imaging methodology was applied to construct detailed elemental maps of three incisors, and bone meal (NIST SRM 1486) was used to validate the analyses.The distribution of Mn in enamel and coronal dentine showed a distinct and reproducible pattern. In enamel, the ⁵⁵Mn:⁴³Ca ratio was highest at the outer edge of enamel (range = 0.57 to 4.74) for approximately 20-40 μm but was substantially lower in deeper layers (range = 0.005 to 0.013). The highest levels of Mn were observed in dentine immediately adjacent the pulpal margin (⁵⁵Mn:⁴³Ca range = 2.27 to 6.95). Importantly, a clearly demarcated high Mn zone was observed in dentine at the incisal end of the teeth. Using confocal laser scanning microscopy to visualize the neonatal line, this region was identified as being in the prenatally formed dentine.The high-resolution map of the spatial distribution of Mn in human primary teeth highlighted specific reproducible patterns of Mn distribution in enamel and coronal dentine.     

Biodegradation of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) by Phanerochaete chrysosporium: new insight into the degradation pathway

Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) is a recalcitrant energetic chemical that tends to accumulate in soil, close to the surface. The present study describes the aerobic biodegradability of HMX using Phanerochaete chrysosporium. When added to 7 day old static P. chrysosporium liquid cultures, HMX (600 nmol) degraded within 25 days of incubation. The removal of HMX was concomitant with the formation of transient amounts of its mono-nitroso derivative (1-NO-HMX). The latter apparently degraded via two potential routes: the first involved N-denitration followed by hydrolytic ring cleavage, and the second involved alpha-hydroxylation prior to ring cleavage. The degradation of 1-NO-HMX gave the ring-cleavage product 4-nitro-2,4-diazabutanal (NDAB), nitrite (NO2 -), nitrous oxide (N2O), and formaldehyde (HCHO). Using [14C]-HMX, we obtained 14CO2 (70% in 50 days), representing three C atoms of HMX. Incubation of real soils, contaminated with either HMX (403 micromol kg(-1)) (military base soil) or HMX (3057 micromol kg(-1)), and RDX (342 micromol kg(-1)) (ammunition soil) with the fungus led to 75 and 19.8% mineralization of HMX (liberated 14CO2), respectively, also via the intermediary formation of 1-NO-HMX. Mineralization in the latter soil increased to 35% after the addition of glucose, indicating that a fungus-based remediation process for heavily contaminated soils is promising. The present findings improve our understanding about the degradation pathway of HMX and demonstrate the utility of using the robust and versatile fungus P. chrysosporium to develop effective remediation processes for the removal of HMX.     

In-situ observations of phase transformations in titanium

An in-situ laser-scanning confocal microscopy study has been undertaken on the phase transformations in highpurity titanium. Observations of the β-Ti to α-Ti were observed to proceed with a pronounced Widmanstätten plate morphology due to the large β-Ti grain size. An anomalous transformation was also observed, with the α-Ti growing with a defined ledge-like surface relief. The observed transformation morphologies are discussed with reference to the crystallography of the regions, analyzed using electron-backscatter diffraction.     

The mental health arena.

If C. A. Kiesler's (1977) comparative analysis of the training of psychologists vs psychiatrists proves to be true after closer inspection, this analysis can document that doctoral-level psychologists have as much (or more) training as psychiatrists yet receive considerably less income. The reasons that psychiatrists dominate mental health settings are reviewed, and it is argued that the mythical nature of the public's collective approaches to physicians should be exposed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Properties of an elementary class of fluids with nondissipative viscous stresses

A class of fluids with both dissipative and nondissipative viscous stresses is analyzed. The class is delineated by the three assumptions, (1) the stress is isotropic, (2) the fluid admits no natural time scale, (3) the Stoke's assumption, tr(t) = − 3p, is satisfied. The constitutive relations are shown to be uniquely determined in terms of the linear bulk viscosity and the linear shear viscosity. The characteristic features of such fluids are obtained and experimental distinguishability between these fluids and the classic Navier-Stokes fluid is examined in detail. In general, it is surprisingly difficult to distinguish between the fluids considered here and the classic Navier-Stokes fluids, even though there are characteristic anomalies associated with the nondissipative stresses.     

On the functional forms of activity coefficients and their properties

A complete system of partial differential equations is obtained for the logarithms of activity coefficients of real chemical mixtures. All solutions of these equations are obtained under mild regularity conditions and the conditions that the limit of ln (f_α), as n_α/n tends to unity, is equal to zero. It is shown that all of the functions ln (f_α) can be determined if any one of them is a known function of temperature, pressure and the independent mole fractions. These results are used to compute the deviations of partial and total volume, entropy and specific heats at constant pressure, and the laws of mass action from what would be given for ideal mixtures. Conditions for static and dynamic stability of equilibrium are obtained, and a forward time integration procedure is given for satisfaction of the laws of mass balance and the full form of the laws of mass action.     

On a closure of the governing equations of defect dynamics and the resulting theory of the plastic state

The equations of defect dynamics are derived from the single system of relations that specifies the time rate of change of the dislocation densities. The resulting source equations are shown to admit a 12-fold gauge group and the resulting kinematic equations are shown to admit a 15-fold gauge group. The generators of the two gauge groups are determined by the requirements that the Burgers and Frank vectors have their classical representations. This determination results in a unique decomposition of all quantities in terms of sums of internal variables and external geometric variables, and represents the first and second closures of the field equations. The presence of a unique external system of geometric variables permits derivation of the forms of the equations of balance of mass, momentum, moment of momentum and energy. The third closure is obtained through use of the practices of nonequilibrium thermodynamics. This results in a system of equations that determines the dislocation currents in terms of the distortion, the dislocation density and the geometric strain measures. A class of models is exhibited wherein most of the properties of plasticity theories are obtained.     

Programs for computer implementation of the exterior calculus with applications to isovector calculations

Program listings are given in the REDUCE 2 Algebraic Programming system that implement the following operations of the exterior calculus: exterior multiplication, exterior differentiation, inner multiplication, Lie differentiation, and Lie multiplication. These programs realize exterior forms and vector fields by resolving them on unevaluated systems of operators with the necessary algebraic properties. Use of these programs in the computation of isovectors of ideals of exterior forms is illustrated for the case where the ideal is generated by the system of exterior forms of degree two that characterize the equations for shallow water waves.     

The net effect of ultraviolet radiation on atmospheric dimethylsulphide over the Southern Indian Ocean

Dimethylsulphide (DMS) in the atmosphere may play an important role in the climate system. This study shows an inverse relationship between ultraviolet extremes and atmospheric DMS, independent of changes in wind speed, sea-surface temperature and photosynthetically active radiation, as measured at Amsterdam Island in the Southern Indian Ocean.     

Thermodynamic analysis of arsenic methylation

The Challenger mechanism for the methylation of arsenic is a repeating sequence of a two-electron reduction of pentavalent arsenic As(V) species to trivalent arsenic As(III) species followed by a methylation-oxidation reaction forming the successive methyl As(V) species. This unusual oxidation-reduction sequence prompted an examination of the thermodynamics of these reactions. Quantum chemical methods are employed to estimate the thermodynamic parameters for the methyl arsenic species. The sequence is thermodynamically favored at neutral pH for redox potentials with pe < 0 and methyl cation activities pCH3+ < -3 to -7 depending on the precise situation analyzed. The observed distribution of methyl arsenic species in human urine, which is remarkably constant across many studied populations, can be reproduced using an equilibrium model if the formation of TMA species is prevented. The estimated thermodynamic parameters are sufficiently accurate to evaluate questions of thermodynamic plausibility but not the precise details of speciation.