Metal-insulator transition in vanadium dioxide nanobeams: probing sub-domain properties of strongly correlated materials

Many strongly correlated electronic materials, including high-temperature superconductors, colossal magnetoresistance and metal-insulator-transition (MIT) materials, are inhomogeneous on a microscopic scale as a result of domain structure or compositional variations. An important potential advantage of nanoscale samples is that they exhibit the homogeneous properties, which can differ greatly from those of the bulk. We demonstrate this principle using vanadium dioxide, which has domain structure associated with its dramatic MIT at 68 degrees C. Our studies of single-domain vanadium dioxide nanobeams reveal new aspects of this famous MIT, including supercooling of the metallic phase by 50 degrees C; an activation energy in the insulating phase consistent with the optical gap; and a connection between the transition and the equilibrium carrier density in the insulating phase. Our devices also provide a nanomechanical method of determining the transition temperature, enable measurements on individual metal-insulator interphase walls, and allow general investigations of a phase transition in quasi-one-dimensional geometry.Comment: 9 pages, 3 figures, original submitted in June 200

Interface modification of clay and graphene platelets reinforced epoxy nanocomposites: a comparative study

The interface between the matrix phase and dispersed phase of a composite plays a critical role in influencing its properties. However, the intricate mecha-nisms of interface are not fully understood, and polymer nanocomposites are no exception. This study compares the fabrication, morphology, and mechanical and thermal properties of epoxy nanocomposites tuned by clay layers (denoted as m-clay) and graphene platelets (denoted as m-GP). It was found that a chemical modification, layer expansion and dispersion of filler within the epoxy matrix resulted in an improved interface between the filler mate-rial and epoxy matrix. This was confirmed by Fourier transform infrared spectroscopy and transmission electron microscope. The enhanced interface led to improved mechanical properties (i.e. stiffness modulus, fracture toughness) and higher glass transition temperatures (Tg) compared with neat epoxy. At 4 wt% m-GP, the critical strain energy release rate G1c of neat epoxy improved by 240 % from 179.1 to 608.6 J/m2 and Tg increased from 93.7 to 106.4 �C. In contrast to m-clay, which at 4 wt%, only improved the G1c by 45 % and Tg by 7.1 %. The higher level of improvement offered by m-GP is attributed to the strong interaction of graphene sheets with epoxy because the covalent bonds between the carbon atoms of graphene sheets are much stronger than silicon-based clay

Multilevel Deconstruction of the In Vivo Behavior of Looped DNA-Protein Complexes

Protein-DNA complexes with loops play a fundamental role in a wide variety of cellular processes, ranging from the regulation of DNA transcription to telomere maintenance. As ubiquitous as they are, their precise in vivo properties and their integration into the cellular function still remain largely unexplored. Here, we present a multilevel approach that efficiently connects in both directions molecular properties with cell physiology and use it to characterize the molecular properties of the looped DNA-lac repressor complex while functioning in vivo. The properties we uncover include the presence of two representative conformations of the complex, the stabilization of one conformation by DNA architectural proteins, and precise values of the underlying twisting elastic constants and bending free energies. Incorporation of all this molecular information into gene-regulation models reveals an unprecedented versatility of looped DNA-protein complexes at shaping the properties of gene expression.Comment: Open Access article available at http://www.plosone.org/article/fetchArticle.action?articleURI=info%3Adoi%2F10.1371%2Fjournal.pone.000035

Interface of culture, insecurity and HIV and AIDS: Lessons from displaced communities in Pader District, Northern Uganda

<p>Abstract</p> <p>Background</p> <p>Northern Uganda unlike other rural regions has registered high HIV prevalence rates comparable to those of urbanized Kampala and the central region. This could be due to the linkages of culture, insecurity and HIV. We explored community perceptions of HIV and AIDS as a problem and its inter-linkage with culture and insecurity in Pader District.</p> <p>Methods</p> <p>A cross sectional qualitative study was conducted in four sub-counties of Pader District, Uganda between May and June 2008. Data for the study were collected through 12 focus group discussions (FGDs) held separately; 2 FGDs with men, 6 FGDs with women, and 4 FGDs with the youth (2 for each sex). In addition we conducted 15 key informant interviews with; 3 health workers, 4 community leaders at village and parish levels, 3 persons living with HIV and 5 district officials. Data were analysed using the content thematic approach. This process involved identification of the study themes and sub-themes following multiple reading of interview and discussion transcripts. Relevant quotations per thematic area were identified and have been used in the presentation of study findings.</p> <p>Results</p> <p>The struggles to meet the basic and survival needs by individuals and households overshadowed HIV as a major community problem. Conflict and risky sexual related cultural practices were perceived by communities as major drivers of HIV and AIDS in the district. Insecurity had led to congestion in the camps leading to moral decadence, rape and defilement, prostitution and poverty which increased vulnerability to HIV infection. The cultural drivers of HIV and AIDS were; widow inheritance, polygamy, early marriages, family expectations, silence about sex and alcoholism.</p> <p>Conclusions</p> <p>Development partners including civil society organisations, central government, district administration, religious and cultural leaders as well as other stakeholders should mainstream HIV in all community development and livelihood interventions in the post conflict Pader district to curtail the likely escalation of the HIV epidemic. A comprehensive behaviour change communication strategy is urgently needed to address the negative cultural practices. Real progress in the region lies in advocacy and negotiation to realise lasting peace.</p

An in vitro assay to study the recruitment and substrate specificity of chromatin modifying enzymes

Post-translational modifications of core histones play an important role in regulating fundamental biological processes such as DNA repair, transcription and replication. In this paper, we describe a novel assay that allows sequential targeting of distinct histone modifying enzymes to immobilized nucleosomal templates using recombinant chimeric targeting molecules. The assay can be used to study the histone substrate specificity of chromatin modifying enzymes as well as whether and how certain enzymes affect each other's histone modifying activities. As such the assay can help to understand how a certain histone code is established and interpreted