Analysis of a dry friction problem under small displacements: application to a bolted joint

This study presents an analysis of the problem of macroscopic contact of steel upon steel with dry friction, in the specific case of a bolted joint. The configurations of these types of joints result in very small displacements and interface sliding velocities. To understand how the system formed by the two surfaces in contact works, an experiment was carried out. The analysis of the results obtained made it possible to define the behavior of the system and to model the variations of the main parameters by original and continuous laws. These laws accurately correlate to all the results of the tests effectuated

Nonperturbative Corrections to One Gluon Exchange Quark Potentials

The leading nonperturbative QCD corrections to the one gluon exchange quark-quark, quark-antiquark and $q \bar{q}$ pair-excitation potentials are derived by using a covariant form of nonlocal two-quark and two-gluon vacuum expectation values. Our numerical calculation indicates that the correction of quark and gluon condensates to the quark-antiquark potential improves the heavy quarkonium spectra to some degree.Comment: LaTex, 16 pages, three figures, to appear in Nucl. Phys.

Mineralogical evolution of Portland cement blended with silica nanoparticles and its effect on mechanical strength

Mineralogical analysis on pastes of Spanish Portland cement Type I, blended with nanosilica was carried out by conventional and high-resolution thermogravimetric analysis (TG-HRTG) and X-ray diffraction (XRD) in order to determine the quantity of the different mineralogical phases obtained during the hydration process. Simultaneously, mortars with the same materials and replacement ratio were made in order to assess their compressive strength for up to 28 days of curing time. In this paper, the rate and quantity of each one of the main constituent phases of the cement during its hydration process (CSH, portlandite, stratlingite, etc.) were determined. A correlation between the quantity of CSH and the development of compressive strength was established. Additionally, the pozzolanic activity of nanosilica was evaluated by quantifying the fixation of calcium hydroxide and its impact on the development of the compressive strength. © 2012 Elsevier Ltd. All rights reserved.The authors express their thanks to Cementos Argos S.A. and to COLCIENCIAS (Project 20201007768) of Colombia for their financial support in the execution of this research.Tobón, JI.; Paya Bernabeu, JJ.; Borrachero Rosado, MV.; Restrepo Baena, OJ. (2012). Mineralogical evolution of Portland cement blended with silica nanoparticles and its effect on mechanical strength. Construction and Building Materials. 36:736-742. https://doi.org/10.1016/j.conbuildmat.2012.06.043S7367423

Elucidating the native sources of an invasive tree species, Acacia pycnantha, reveals unexpected native range diversity and structure

† Background and Aims Understanding the introduction history of invasive plant species is important for their management and identifying effective host-specific biological control agents. However, uncertain taxonomy, intra- and interspecific hybridization, and cryptic speciation may obscure introduction histories, making it difficult to identify native regions to explore for host-specific agents. The overall aim of this study was to identify the native source populations of Acacia pycnantha, a tree native to south-eastern Australia and invasive in South Africa, Western Australia and Portugal. Using a phylogeographical approach also allowed an exploration of the historical processes that have shaped the genetic structure of A. pycnantha in its native range. † Methods Nuclear (nDNA) and plastid DNA sequence data were used in network and tree-building analyses to reconstruct phylogeographical relationships between native and invasive A. pycnantha populations. In addition, mismatch distributions, relative rates and Bayesian analyses were used to infer recent demographic processes and timing of events in Australia that led to population structure and diversification. † Key Results The plastid network indicated that Australian populations of A. pycnantha are geographically structured into two informally recognized lineages, the wetland and dryland forms, whereas the nuclear phylogeny showed little geographical structure between these two forms. Moreover, the dryland form of A. pycnantha showed close genetic similarity to the wetland form based on nDNA sequence data. Hybrid zones may explain these findings, supported here by incongruent phylogenetic placement of some of these taxa between nuclear and plastid genealogies. †Conclusions It is hypothesized that habitat fragmentation due to cycles of aridity inter-dispersed with periods of abundant rainfall during the Pleistocene (approx. 100 kya) probably gave rise to native dryland and wetland forms of A. pycnantha. Although the different lineages were confined to different ecological regions, we also found evidence for intraspecific hybridization in Victoria. The invasive populations in Portugal and South Africa represent wetland forms, whereas some South African populations resemble the Victorian dryland form. The success of the biological control programme for A. pycnantha in South Africa may therefore be attributed to the fact that the gall-forming wasp Trichilogaster signiventris was sourced from South Australian populations, which closely match most of the invasive populations in South Africa

Football in the community schemes: Exploring the effectiveness of an intervention in promoting healthful behaviour change

This study aims to examine the effectiveness of a Premier League football club’s Football in the Community (FitC) schemes intervention in promoting positive healthful behaviour change in children. Specifically, exploring the effectiveness of this intervention from the perspectives of the participants involved (i.e. the researcher, teachers, children and coaches). A range of data collection techniques were utilized including the principles of ethnography (i.e. immersion, engagement and observations), alongside conducting focus groups with the children. The results allude to the intervention merely ‘keeping active children active’ via (mostly) fun, football sessions. Results highlight the important contribution the ‘coach’ plays in the effectiveness of the intervention. Results relating to working practice (i.e. coaching practice and coach recruitment) are discussed and highlighted as areas to be addressed. FitC schemes appear to require a process of positive organizational change to increase their effectiveness in strategically attending to the health agenda

Improved lower bounds for the ground-state energy of many-body systems

New lower bounds for the binding energy of a quantum-mechanical system of interacting particles are presented. The new bounds are expressed in terms of two-particle quantities and improve the conventional bounds of the Hall-Post type. They are constructed by considering not only the energy in the two-particle system, but also the structure of the pair wave function. We apply the formal results to various numerical examples, and show that in some cases dramatic improvement over the existing bounds is reached.Comment: 29 pages, 5 figures, to be published in Phys. Rev.

Improving the timeliness of meticillin-resistant Staphylococcus aureus antimicrobial decolonization therapy administration : a descriptive account

SummaryBackgroundIt is important to ensure that the timely administration of appropriate antimicrobial decolonization therapy occurs when patients are identified as meticillin-resistant Staphylococcus aureus (MRSA)-colonized. Computerized Provider Order Entry (CPOE) with embedded Clinical Decision Support (CDS) may help to facilitate this.AimTo investigate changes in the average time from patient admission to administration of MRSA decolonization antimicrobial therapy in the context of various national and local infection control interventions, including the use of CPOE.MethodsData concerning the time of admission and of administration of patients' first MRSA decolonization antimicrobials were extracted from a locally developed CPOE system (Prescribing Investigation and Communications System: PICS) which was introduced at a large university teaching hospital in the UK in 1998. Data were extracted retrospectively from January 2006 to March 2012.FindingsA variety of relevant local and national interventions occurred from 2006 to 2012. Notably, the automatic charting of MRSA decolonization antimicrobial therapy was introduced in December 2007. There was a significant decline of 15.0% per year (95% confidence interval: 11.1–18.7%; P < 0.001) in the time taken from admission to administration of MRSA decolonization antimicrobial therapy during the study period.ConclusionsNumerous factors may have contributed to the observed reductions in the time from admission to administration of MRSA decolonization antimicrobials, including the implementation of specific features within a CPOE system. By rapidly attending to positive MRSA colonizations there is decreased potential for MRSA to spread, which may help to reduce the prevalence of MRSA colonizations within hospitals and improve patient outcomes