Observations Upon the Oral Mucosa of the African

A CAJM article on dentistry as practiced in Botswana (formerly Bechuanaland Protectorate) in the 1950's Africa.The oral cavity, quite apart from those structures properly included in the realm of dentistry, is of great clinical importance, for it lends itself readily to inspection and examination and, like the eye, can reflect the presence of disease in other regions. This note describes methods of examination and the findings thereof which, although simple, have yet been found of use in diagnosis, and to some degree in following the course of certain systemic diseases, particularly of malnutrition. It is to be emphasised that as the meaning and significance of these observations are still obscure, and much further inquiry is necessary for their clarification, theoretical considerations and implications will not be discussed. The mucosae of the oral cavity to be considered are (a) the lingual mucosa; (b) the buccal mucosa

Electronic, dynamical, and thermal properties of ultra-incompressible superhard rhenium diboride: A combined first-principles and neutron scattering study

Rhenium diboride is a recently recognized ultra-incompressible superhard material. Here we report the electronic (e), phonon (p), e-p coupling and thermal properties of ReB$_2$ from first-principles density-functional theory (DFT) calculations and neutron scattering measurements. Our calculated elastic constants ($c_{11}$ = 641 GPa, $c_{12}$ = 159 GPa, $c_{13}$ = 128 GPa, $c_{33}$ = 1037 GPa, and $c_{44}$ = 271 GPa), bulk modulus ($B$ $\approx$ 350 GPa) and hardness ($H$ $\approx$ 46 GPa) are in good agreement with the reported experimental data. The calculated phonon density of states (DOS) agrees very well with our neutron vibrational spectroscopy result. Electronic and phonon analysis indicates that the strong covalent B-B and Re-B bonding is the main reason for the super incompressibility and hardness of ReB$_2$. The thermal expansion coefficients, calculated within the quasi-harmonic approximation and measured by neutron powder diffraction, are found to be nearly isotropic in $a$ and $c$ directions and only slightly larger than that of diamond in terms of magnitude. The excellent agreement found between calculations and experimental measurements indicate that first-principles calculations capture the main interactions in this class of superhard materials, and thus can be used to search, predict, and design new materials with desired properties.Comment: submitted to pr

Improvement of Renormalization-Scale Uncertainties Within Empirical Determinations of the b-Quark Mass

Accurate determinations of the MS-bar b-quark mass $m_b(m_b)$ from $\sigma(e^+e^-\to{\rm hadrons})$ experimental data currently contain three comparable sources of uncertainty; the experimental uncertainty from moments of this cross-section, the uncertainty associated with $\alpha_s(M_z)$, and the theoretical uncertainty associated with the renormalization scale. Through resummation of all logarithmic terms explicitly determined in the perturbative series by the renormalization-group (RG) equation, it is shown that the renormalization-scale dependence is virtually eliminated as a source of theoretical uncertainty in $m_b(m_b)$. This resummation also reduces the estimated effect of higher-loop perturbative contributions, further reducing the theoretical uncertainties in $m_b(m_b)$. Furthermore, such resummation techniques improve the agreement between the values of the MS-bar b-quark mass extracted from the various moments of $R(s)=\sigma(e^+e^-\to{\rm hadrons})/\sigma_{pt}$ [$\sigma_{pt}=4\pi\alpha^2/(3s)$], obviating the need to choose an optimummoment for determining $m_b(m_b)$. Resummation techniques are also shown to reduce renormalization-scale dependence in the relation between b-quark MS-bar and pole mass and in the relation between the pole and $1S$ mass.Comment: 19 pages, latex2e, 6 eps figures contained in latex file. Errors corrected in equations (20)--(22

Magnetic spectrum of the two-dimensional antiferromagnet La2CoO4 studied by inelastic neutron scattering

We report measurements of the magnetic excitation spectrum of the layered antiferromagnet La2CoO4 by time-of-flight neutron inelastic scattering. In the energy range probed in our experiments (0-250 meV) the magnetic spectrum consists of spin-wave modes with strong in-plane dispersion extending up to 60 meV, and a nearly dispersionless peak at 190 meV. The spin-wave modes exhibit a small (~1 meV) dispersion along the magnetic zone boundary. We show that the magnetic spectrum can be described very well by a model of a Heisenberg antiferromagnet that includes the full spin and orbital degrees of freedom of Co2+ in an axially-distorted crystal field. The collective magnetic dynamics are found to be controlled by dominant nearest-neighbour exchange interactions, strong XY-like single-ion anisotropy and a substantial unquenched orbital angular momentum.Comment: 8 pages, 7 figure

Kinetics and mechanism of the interconversion of inverse bicontinuous cubic mesophases

This paper describes time-resolved x-ray diffraction data monitoring the transformation of one inverse bicontinuous cubic mesophase into another, in a hydrated lipid system. The first section of the paper describes a mechanism for the transformation that conserves the topology of the bilayer, based on the work of Charvolin and Sadoc, Fogden and Hyde, and Benedicto and O'Brien in this area. We show a pictorial representation of this mechanism, in terms of both the water channels and the lipid bilayer. The second section describes the experimental results obtained. The system under investigation was 2:1 lauric acid: dilauroylphosphatidylcholine at a hydration of 50% water by weight. A pressure-jump was used to induce a phase transition from the gyroid (Q(II)(G)) to the diamond (Q(II)(D)) bicontinuous cubic mesophase, which was monitored by time-resolved x-ray diffraction. The lattice parameter of both mesophases was found to decrease slightly throughout the transformation, but at the stage where the Q(II)(D) phase first appeared, the ratio of lattice parameters of the two phases was found to be approximately constant for all pressure-jump experiments. The value is consistent with a topology-preserving mechanism. However, the polydomain nature of our sample prevents us from confirming that the specific pathway is that described in the first section of the paper. Our data also reveal signals from two different intermediate structures, one of which we have identified as the inverse hexagonal (H-II) mesophase. We suggest that it plays a role in the transfer of water during the transformation. The rate of the phase transition was found to increase with both temperature and pressure-jump amplitude, and its time scale varied from the order of seconds to minutes, depending on the conditions employed

Naturally occurring bacteriophages lyse a large proportion of canine and feline uropathogenic Escherichia coli isolates in vitro

We investigated the feasibility of bacteriophage therapy to combat canine and feline Escherichia coli urinary tract infections (UTIs) by testing the in vitro lytic ability of 40 naturally occurring bacteriophages on 53 uropathogenic E. coli (UPEC). The mean number of UPEC strains lysed by an individual bacteriophage was 21/53 (40%, range 17–72%). In total, 50/53 (94%) of the UPEC strains were killed by one or more of the bacteriophages. Ten bacteriophages lysed P51% of UPEC strains individually and 92% of UPEC strains as a group. Electron microscopy and DNA sequencing of 5 ‘promising’ bacteriophages revealed that 4 bacteriophages belonged to the lytic T4-like genus, while one displayed morphologic similarity to temperate P2-like bacteriophages. Overall, these results indicate that the majority of UPEC are susceptible to lysis by naturally occurring bacteriophages. Thus, bacteriophages show promise as therapeutic agents for treatment of canine and feline E. coli UTIs

E-cadherin and cell adhesion: a role in architecture and function in the pancreatic islet

Background/Aims: The efficient secretion of insulin from beta-cells requires extensive intra-islet communication. The cell surface adhesion protein epithelial (E)-cadherin (ECAD) establishes and maintains epithelial tissues such as the islets of Langerhans. In this study, the role of ECAD in regulating insulin secretion from pseudoislets was investigated. Methods: The effect of an immuno-neutralising ECAD on gross morphology, cytosolic calcium signalling, direct cell-to-cell communication and insulin secretion was assessed by fura-2 microfluorimetry, Lucifer Yellow dye injection and insulin ELISA in an insulin-secreting model system. Results: Antibody blockade of ECAD reduces glucose-evoked changes in [Ca2+](i) and insulin secretion. Neutralisation of ECAD causes a breakdown in the glucose-stimulated synchronicity of calcium oscillations between discrete regions within the pseudoislet, and the transfer of dye from an individual cell within a cell cluster is attenuated in the absence of ECAD ligation, demonstrating that gap junction communication is disrupted. The functional consequence of neutralising ECAD is a significant reduction in insulin secretion. Conclusion: Cell adhesion via ECAD has distinct roles in the regulation of intercellular communication between beta-cells within islets, with potential repercussions for insulin secretion. Copyright (C) 2007 S. Karger AG, Basel

Magnon Dispersion and Anisotropies in SrCu2_2(BO3_3)2_2

We study the dispersion of the magnons (triplet states) in SrCu$_2$(BO$_3$)$_2$ including all symmetry-allowed Dzyaloshinskii-Moriya interactions. We can reduce the complexity of the general Hamiltonian to a new simpler form by appropriate rotations of the spin operators. The resulting Hamiltonian is studied by both perturbation theory and exact numerical diagonalization on a 32-site cluster. We argue that the dispersion is dominated by Dzyaloshinskii-Moriya interactions. We point out which combinations of these anisotropies affect the dispersion to linear-order, and extract their magnitudes.Comment: 11 pages, 7 figures, 1 table, v2 conclusion shortened, figs clarifie

Longitudinal SDW order in a quasi-1D Ising-like quantum antiferromagnet

From neutron diffraction measurements on a quasi-1D Ising-like Co$^{\rm 2+}$ spin compound BaCo$_{\rm 2}$V$_{\rm 2}$O$_{\rm 8}$, we observed an appearance of a novel type of incommensurate ordering in magnetic fields. This ordering is essentially different from the N{\' e}el-type ordering, which is expected for the classical system, and is caused by quantum fluctuation inherent in the quantum spin chain. A Tomonaga-Luttinger liquid (TLL) nature characteristic of the gapless quantum 1D system is responsible for the realization of the incommensurate ordering.Comment: 4pages, 4figur