Millimeter Wave Localization: Slow Light and Enhanced Absorption

We exploit millimeter wave technology to measure the reflection and transmission response of random dielectric media. Our samples are easily constructed from random stacks of identical, sub-wavelength quartz and Teflon wafers. The measurement allows us to observe the characteristic transmission resonances associated with localization. We show that these resonances give rise to enhanced attenuation even though the attenuation of homogeneous quartz and Teflon is quite low. We provide experimental evidence of disorder-induced slow light and superluminal group velocities, which, in contrast to photonic crystals, are not associated with any periodicity in the system. Furthermore, we observe localization even though the sample is only about four times the localization length, interpreting our data in terms of an effective cavity model. An algorithm for the retrieval of the internal parameters of random samples (localization length and average absorption rate) from the external measurements of the reflection and transmission coefficients is presented and applied to a particular random sample. The retrieved value of the absorption is in agreement with the directly measured value within the accuracy of the experiment.Comment: revised and expande

Vancomycin-induced deletion of the methicillin resistance gene mecA in Staphylococcus aureus

Objective: To elucidate factors that contribute to the development of vancomycin resistance in methicillin-resistant Staphylococcus aureus (MRSA). Methods: Forty-nine MRSA isolates were subjected to passage selection with vancomycin to isolate mutants with reduced susceptibility to vancomycin. One mutant was chosen for detailed molecular and biochemical characterization. Results: Five vancomycin-resistant mutants (vancomycin MICs, 6-12 mg/L) were obtained in vitro from five MRSA parent isolates. Upon acquisition of vancomycin resistance, all mutants showed a concomitant decrease in oxacillin resistance. In one particular MRSA strain, selection for vancomycin resistance repeatedly produced deletions and rearrangements, including loss of the mecA gene. Pleiotropic phenotypical changes, such as yellow pigment formation, loss of haemolysis, thickened cell wall, increased resistance to lysostaphin and reduced cell wall turnover were observed in this mutant. Conclusion: Acquisition of vancomycin resistance in one MRSA strain triggered mecA deletion suggesting that this deletion, coupled to other rearrangements and/or mutations, may be responsible for the increased vancomycin resistance phenotyp

Rapid tyrosine phosphorylation of neuronal proteins including tau and focal adhesion kinase in response to amyloid-beta peptide exposure: Involvement of src family protein kinases

The increased production of amyloid beta -peptide (A beta) in Alzheimer's disease is acknowledged to be a key pathogenic event. In this study, we examined the response of primary human and rat brain cortical cultures to A beta administration and found a marked increase in the tyrosine phosphorylation content of numerous neuronal proteins, including tau and putative microtubule-associated protein 2c (MAP2c). We also found that paired helical filaments of aggregated and hyperphosphorylated tau are tyrosine phosphorylated, indicating that changes in the phosphotyrosine content of cytoplasmic proteins in response to A beta are potentially an important process. Increased tyrosine phosphorylation of cytoskeletal and other neuronal proteins was specific to fibrillar A beta (25-35) and A beta (1-42). The tyrosine phosphorylation was blocked by addition of the Src family tyrosine kinase inhibitor 4-amino-5-( 4-chlorophenyl)- 7(t-butyl) pyrazol(3,4-D) pyramide (PP2) and the phosphatidylinositol 3-kinase inhibitor LY 294002. Tyrosine phosphorylation of tau and MAP2c was concomitant with an increase in the tyrosine phosphorylation and subsequent putative activation of the non-receptor kinase, focal adhesion kinase (FAK). Immunoprecipitation of Fyn, a member of the Src family, from A beta (25-35)-treated neurons showed an increased association of Fyn with FAK. A beta treatment of cells also stimulated the sustained activation of extracellular regulated kinase-2, which was blocked by addition of PP2 and LY 294002, suggesting that FAK/Fyn/PI3-kinase association is upstream of mitogen-activated protein (MAP) kinase signaling in A beta -treated neurons. This cascade of signaling events contains the earliest biochemical changes in neurons to be described in response to A beta exposure and may be critical for subsequent neurodegenerative changes

Improving the thermal stability of Rubisco activase

The major objective is to produce wheat germplasm with improved tolerance to heat stress through the modification of the key photosynthetic enzyme Rubisco activase. Current funds have allowed transformation of “best bet” candidate gene constructs into wheat as part of SP1.5. Joanna Scales, a BBSRC PhD student jointly supervised by Martin Parry, Christine Raines, and Mike Salvucci, generated the transformation constructs and will undertake the molecular and biochemical analysis of transgenic lines

Improving the thermal stability of Rubisco activase

The thermal sensitivity of the key photosynthetic enzyme Rubisco activase limits wheat photosynthesis at moderately high temperatures. Introduction of a more thermal tolerant form of Rubisco activase, such as that from cotton, into wheat is predicted to broaden the temperature range of optimal Rubisco activation and photosynthetic CO2 assimilation. Transgenic lines have been produced to express the cotton Rubisco activase in wheat and current efforts are characterizing the most promising lines for further studies of photosynthetic performance at moderately high temperatures. Joanna Scales, a BBSRC PhD student jointly supervised by Martin Parry, Christine Raines, and Mike Salvucci, generated the transformation constructs and will undertake the molecular and biochemical analysis of the transformant lines. It is predicted that the cotton Rubisco activase will confer superior thermal tolerance to wheat photosynthesis

Unpicking the links between research and teaching in Higher Education

ABSTRACT The Bradley Report (2008) highlights a need to investigate the experiences of international students in regard to learning and teaching with a focus on local and contextual issues. This presentation results from Participatory Action Research (Haslett, 2009) to explore learning and teaching issues relevant to international undergraduate nursing students at one campus of a Queensland University. Nursing education research is informed by many approaches, including the traditional science positivist approaches. The positivist approaches assume an ordered 'real' world of teaching, which is in stark contrast to the experience of many neophyte nurse educators. In this project, PAR exposed the differences between espoused teaching theories and best practice as promoted by the University and actual teaching beliefs and practices of staff. There were commonalities in staff perceptions that international nursing student learners have different and specific needs and international students were initially conceptualised as 'the problem'. Through PAR meetings, staff revealed different understandings of 'the problem', tensions between workload and University promotion of an internationalised curriculum. In these discussions, different teaching and learning strategies were shared. The differences between these reflected the experience of the teachers, revealing the different underlying beliefs about teaching and learning and exposing different staff values. Some staff employed a framework of equity to help contextualise the issues and their response to the challenges of teaching international student learners. Through discussions and sharing a real 'sense of the possible' was created for staff. This engagement in the process and the realisation that action was possible was a highlight of the project to date. The next step is enacting agreed upon actions. This project provides a concrete experience of PAR, which we can share and offer for further consideration

Positive Youth Development Interventions Impacting the Sexual Health of Young Minority Adolescents: A Systematic Review

A systematic literature review was conducted to assess the utility of Positive Youth Development (PYD) concepts in promoting positive sexual health behaviors in young minority adolescents (n = 12 studies). Interventions reported significant associations between PYD-focused interventions and ever having sex, sexual partners in the last 30 days, using protection at the last sexual encounter, and decreased pregnancy rates. Outcomes were reviewed by age, gender, PYD constructs, cultural tailoring of interventions, and retention rates. Few interventions focused exclusively on young minority adolescents. PYD can be an effective tool in promoting sexual health in younger minority adolescents, but additional research is needed to determine beneficial strategies for this age group and timing of interventions. Recommendations for future studies include additional guidance on operationalization of PYD concepts, effective cultural tailoring methods, dosage of intervention components, and de-linking minority status from socioeconomic status (SES) and high-risk behaviors.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline

Bifurcations in annular electroconvection with an imposed shear

We report an experimental study of the primary bifurcation in electrically-driven convection in a freely suspended film. A weakly conducting, submicron thick smectic liquid crystal film was supported by concentric circular electrodes. It electroconvected when a sufficiently large voltage $V$ was applied between its inner and outer edges. The film could sustain rapid flows and yet remain strictly two-dimensional. By rotation of the inner electrode, a circular Couette shear could be independently imposed. The control parameters were a dimensionless number ${\cal R}$, analogous to the Rayleigh number, which is $\propto V^2$ and the Reynolds number ${\cal R}e$ of the azimuthal shear flow. The geometrical and material properties of the film were characterized by the radius ratio $\alpha$, and a Prandtl-like number ${\cal P}$. Using measurements of current-voltage characteristics of a large number of films, we examined the onset of electroconvection over a broad range of $\alpha$, ${\cal P}$ and ${\cal R}e$. We compared this data quantitatively to the results of linear stability theory. This could be done with essentially no adjustable parameters. The current-voltage data above onset were then used to infer the amplitude of electroconvection in the weakly nonlinear regime by fitting them to a steady-state amplitude equation of the Landau form. We show how the primary bifurcation can be tuned between supercritical and subcritical by changing $\alpha$ and ${\cal R}e$.Comment: 17 pages, 12 figures. Submitted to Phys. Rev. E. Minor changes after refereeing. See also http://mobydick.physics.utoronto.c