Simulations of Spinodal Nucleation in Systems with Elastic Interactions

Systems with long-range interactions quenched into a metastable state near the pseudospinodal exhibit nucleation that is qualitatively different than the classical nucleation observed near the coexistence curve. We have observed nucleation droplets in our Langevin simulations of a two-dimensional model of martensitic transformations and have determined that the structure of the nucleating droplet differs from the stable martensite structure. Our results, together with experimental measurements of the phonon dispersion curve, allow us to predict the nature of the droplet. These results have implications for nucleation in many solid-solid transitions and the structure of the final state

Geometric scaling in the spectrum of an electron captured by a stationary finite dipole

We examine the energy spectrum of a charged particle in the presence of a {\it non-rotating} finite electric dipole. For {\emph{any}} value of the dipole moment $p$ above a certain critical value p_{\mathrm{c}}$ an infinite series of bound states arises of which the energy eigenvalues obey an Efimov-like geometric scaling law with an accumulation point at zero energy. These properties are largely destroyed in a realistic situation when rotations are included. Nevertheless, our analysis of the idealised case is of interest because it may possibly be realised using quantum dots as artificial atoms.Comment: 5 figures; references added, outlook section reduce

Nucleation in Systems with Elastic Forces

Systems with long-range interactions when quenced into a metastable state near the pseudo-spinodal exhibit nucleation processes that are quite different from the classical nucleation seen near the coexistence curve. In systems with long-range elastic forces the description of the nucleation process can be quite subtle due to the presence of bulk/interface elastic compatibility constraints. We analyze the nucleation process in a simple 2d model with elastic forces and show that the nucleation process generates critical droplets with a different structure than the stable phase. This has implications for nucleation in many crystal-crystal transitions and the structure of the final state

Emerging antiretroviral drug resistance in sub-Saharan Africa: novel affordable technologies are needed to provide resistance testing for individual and public health benefits

In industrialized countries, viral load monitoring and genotypic antiretroviral drug resistance testing (GART) play an important role in the selection of initial and subsequent combination antiretroviral therapy (cART) regimens. In contrast, resource constraints in Africa limit access to assays that could detect virologic failure, transmitted drug resistance (TDR) and acquired drug resistance to cART. This has adverse consequences for both individual and public health. Although the further roll-out of antiretrovirals for prevention, including preexposure prophylaxis (PrEP) and universal test and treat (UTT) strategies, could reduce HIV-1 incidence, these strategies may increase TDR [1,2]. Here, we present arguments that the scale up of antiretrovirals use should be accompanied by cost-effective assays for early detection of virologic failure, surveillance of TDR and GART for individual patient management

EVALUATION OF THE COMPRESSIVE MECHANICAL PROPERTIES OF CELLULAR DMLS STRUCTURES FOR BIOMEDICAL APPLICATIONS

Published Conference ProceedingsThe type of material used in biomedical applications depends on specific implant applications; different types of implant need different mechanical properties. Since the architectures of bone tissues in the human body are not completely dense and solid, it is desirable to produce biomimic structures as a replacement for damaged bone tissues. Learning from nature, it can be understood that cellular structures would be more preferable for biomedical implants than dense solid structures. Verification of mechanical properties of DMLS PA 2200 cellular structures should be conducted since scaffolds from this material have been proven for biomedical applications. Ti6Al4V alloy is well known to have a superior track record as leading material for bone replacement since it is a light-weight and biocompatible material, but the density of human cortical bone is less than half that of solid Ti6Al4V implants. The mismatch of the elastic modulus between such implants and bone tissue is one of the major causes of stress shielding, bone resorption and implant loosening. Finite element analysis showed big differences in strains of jaw bone and an implanted solid Ti6Al4V part. The elastic modulus of lattice structures was used to simulate a complex mandible to obtain foreknowledge of manufacturing advanced light-weight implants with suitable biomechanical properties. Compressive properties of proposed cellular structures were determined to demonstrate the viability of attaining different effective elastic moduli for Ti6Al4V implants

Enhanced activity of demineralised bone matrix augmented with xenogeneic bone morphogenetic protein complex in rats

INTRODUCTION: Demineralised bone matrix (DBM) is an allograft material widely used as a bone filler and bone graft substitute. DBM contains bone morphogenetic proteins (BMPs), which induce and regulate bone formation during embryogenesis and in postnatal life. AIMS AND OBJECTIVES: To investigate the osteoinductivity of DBM augmented with xenogeneic BMP-complex at different doses. MATERIALS AND METHODS: Rat DBM was augmented with BMP-complex purified from porcine diaphyseal bone. RESULTS: Dorsal subcutaneous implantation of 25 mg rat allogeneic DBM augmented with 0, 3, 6 and 12 mg BMPcomplex per gram of DBM resulted in dose dependant upregulation of bone formation on day 21, as scored histologically and biochemically. CONCLUSIONS: Allogeneic DBM can be augmented with xenogeneically sourced BMP-complex to improve DBM performance in vivo. This work demonstrates the potential of BMP-complex augmented DBM to induce new bone formation with improved parameters of bone formation.http://www.sadanet.co.zaam2013ay201

Correlation between dysplasia and ploidy status in oral leukoplakia

Oral leukoplakia and other potentially malignant disorders (PMD) may progress to oral squamous cell carcinoma (OSCC). The gold standard for assessing the potential for malignant transformation remains histologic examination with the aim of grading the dysplastic changes. However, not all lesions with dysplasia will progress to OSCC. DNA ploidy has been suggested as a method to predict the clinical behaviour of PMD. This study reports on the use of high-resolution flow cytometry to determine the ploidy status of formalin-fixed, paraffin-embedded material from PMD compared to their dysplasia grade on histology. Aneuploidy was found in 13 % of mild, 31 % of moderate, and 54 % of severe dysplasia cases. This difference was statistically significant (p = 0.011). The differences in ploidy status were more significant when grouping the dysplasia into low-risk and high-risk categories (p = 0.008). These findings indicate that the ploidy status of PMD as determined by high-resolution flow cytometry may be of value in predicting biological behaviour in PMD such as leukoplakia.The National Research Foundation of South Africahttp://link.springer.com/journal/1210

Hubble Space Telescope Observations of UV Oscillations in WZ Sagittae During the Decline from Outburst

We present a time series analysis of Hubble Space Telescope observations of WZ Sge obtained in 2001 September, October, November and December as WZ Sge declined from its 2001 July superoutburst. Previous analysis of these data showed the temperature of the white dwarf decreased from ~29,000 K to ~18,000 K. In this study we binned the spectra over wavelength to yield ultraviolet light curves at each epoch that were then analyzed for the presence of the well-known 27.87 s and 28.96 s oscillations. We detect the 29 s periodicity at all four epochs, but the 28 s periodicity is absent. The origin of these oscillations has been debated since their discovery in the 1970s and competing hypotheses are based on either white dwarf non-radial g-mode pulsations or magnetically-channelled accretion onto a rotating white dwarf. By analogy with the ZZ Ceti stars, we argue that the non-radial g-mode pulsation model demands a strong dependence of pulse period on the white dwarf's temperature. However, these observations show the 29 s oscillation is independent of the white dwarf's temperature. Thus we reject the white dwarf non-radial g-mode pulsation hypothesis as the sole origin of the oscillations. It remains unclear if magnetically-funnelled accretion onto a rapidly rotating white dwarf (or belt on the white dwarf) is responsible for producing the oscillations. We also report the detection of a QPO with period ~18 s in the September light curve. The amplitudes of the 29 s oscillation and the QPO vary erratically on short timescales and are not correlated with the mean system brightness nor with each other.Comment: 20 pages, 3 figures, 1 table; accepted for publication in Ap