258 research outputs found
Full stress tensor measurement using colour centres in diamond
Stress and strain are important factors in determining the mechanical,
electronic, and optical properties of materials, relating to each other by the
material's elasticity or stiffness. Both are represented by second rank field
tensors with, in general, six independent components. Measurements of these
quantities are usually achieved by measuring a property that depends on the
translational symmetry and periodicity of the crystal lattice, such as optical
phonon energies using Raman spectroscopy, the electronic band gap using
cathodoluminescence, photoelasticity via the optical birefringence, or Electron
Back Scattering Diffraction (EBSD). A reciprocal relationship therefore exists
between the maximum sensitivity of the measurements and the spatial resolution.
Furthermore, of these techniques, only EBSD and off-axis Raman spectroscopy
allow measurement of all six components of the stress tensor, but neither is
able to provide full 3D maps. Here we demonstrate a method for measuring the
full stress tensor in diamond, using the spectral and optical polarization
properties of the photoluminescence from individual nitrogen vacancy (NV)
colour centres. We demonstrate a sensitivity of order 10 MPa, limited by local
fluctuations in the stress in the sample, and corresponding to a strain of
about 10^-5, comparable with the best sensitivity provided by other techniques.
By using the colour centres as built-in local sensors, the technique overcomes
the reciprocal relationship between spatial resolution and sensitivity and
offers the potential for measuring strains as small as 10^-9 at spatial
resolution of order 10 nm. Furthermore it provides a straightforward route to
volumetric stress mapping. Aside from its value in understanding strain
distributions in diamond, this new approach to stress and strain measurement
could be adapted for use in micro or nanoscale sensors.Comment: 12 pages, 5 figures - supplementary informations included in appendi
Optical properties of a single-colour centre in diamond with a green zero-phonon line
We report the photoluminescence characteristics of a colour centre in diamond grown by plasma-assisted chemical vapour deposition. The colour centre emits with a sharp zero-phonon line at 2.330 eV (λ=532 nm) and a lifetime of 3.3 ns, thus offering potential for a high-speed single-photon source with green emission. It displays a vibronic emission spectrum with a Huang–Rhys parameter of 2.48 at 77 K. Hanbury–Brown and Twiss measurements reveal that the electronic level structure of the defect includes a metastable state that can be populated from the optically excited state
Molecular brakes regulating mTORC1 activation in skeletal muscle following synergist ablation
The goal of the current work was to profile positive (mTORC1 activation, autocrine/paracrine growth factors) and negative [AMPK, unfolded protein response (UPR)] pathways that might regulate overload-induced mTORC1 (mTOR complex 1) activation with the hypothesis that a number of negative regulators of mTORC1 will be engaged during a supraphysiological model of hypertrophy. To achieve this, mTORC1- IRS-1/2 signaling, BiP/CHOP/IRE1, and AMPK activation were determined in rat plantaris muscle following synergist ablation (SA). SA resulted in significant increases in muscle mass of 4% per day throughout the 21 days of the experiment. The expression of the insulin-like growth factors (IGF) were high throughout the 21st day of overload. However, IGF signaling was limited, since IRS-1 and -2 were undetectable in the overloaded muscle from day 3 to day 9. The decreases in IRS-1/2 protein were paralleled by increases in GRB10 Ser501/503 and S6K1 Thr389 phosphorylation, two mTORC1 targets that can destabilize IRS proteins. PKB Ser473 phosphorylation was higher from 3– 6 days, and this was associated with increased TSC2 Thr939 phosphorylation. The phosphorylation of TSC2 Thr1345 (an AMPK site) was also elevated, whereas phosphorylation at the other PKB site, Thr1462, was unchanged at 6 days. In agreement with the phosphorylation of Thr1345, SA led to activation of AMPK1 during the initial growth phase, lasting the first 9 days before returning to baseline by day 12. The UPR markers CHOP and BiP were elevated over the first 12 days following ablation, whereas IRE1 levels decreased. These data suggest that during supraphysiological muscle loading at least three potential molecular brakes engage to downregulate mTORC1. m
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Separation of Nanoparticles in Aqueous Multiphase Systems through Centrifugation
This paper demonstrates the use of aqueous multiphase systems (MuPSs) as media for rate-zonal centrifugation to separate nanoparticles of different shapes and sizes. The properties of MuPSs do not change with time or during centrifugation; this stability facilitates sample collection after separation. A three-phase system demonstrates the separation of the reaction products (nanorods, nanospheres, and large particles) of a synthesis of gold nanorods, and enriches the nanorods from 48 to 99% in less than ten minutes using a benchtop centrifuge.Chemistry and Chemical BiologyEngineering and Applied Science
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Aqueous Multiphase Systems of Polymers and Surfactants Provide Self-Assembling Step-Gradients in Density
This Communication demonstrates the generation of over 300 phase-separated systems—ranging from two to six phases—from mixtures of aqueous solutions of polymers and surfactants. These aqueous multiphase systems (MuPSs) form self-assembling, thermodynamically stable step-gradients in density using a common solvent, water. The steps in density between phases of a MuPS can be very small (Δρ ≈ 0.001 g/cm3), do not change over time, and can be tuned by the addition of co-solutes. We use two sets of similar objects, glass beads and pellets of different formulations of Nylon, to demonstrate the ability of MuPSs to separate mixtures of objects by differences in density. The stable interfaces between phases facilitate the convenient collection of species after separation. These results suggest that the stable, sharp step-gradients in density provided by MuPSs can enable new classes of fractionations and separations based on density.Chemistry and Chemical BiologyEngineering and Applied Science
Hubble Space Telescope Imaging of the CFRS and LDSS Redshift Surveys---III. Field elliptical galaxies at 0.2 < z < 1.0
Surface photometry has been performed on a sample of 46 field elliptical
galaxies. These galaxies are described well by a deVaucouleurs R^{1/4} profile.
The sample was selected from the combined Canada-France and LDSS redshift
surveys and spans the range 0.20 < z < 1.00. The relationship between galaxy
half-light radius and luminosity evolves such that a galaxy of a given size is
more luminous by Delta M_B=-0.97 \pm 0.14 mag at z=0.92 and the mean rest-frame
color shifts blueward by Delta (U-V) =-0.68 \pm 0.11 at z=0.92 relative to the
local cluster relations. Approximately 1/3 of these elliptical galaxies exhibit
[OII] 3727 emission lines with equivalent widths > 15 angstroms indicating
ongoing star formation. Estimated star-formation rates imply that \le 5% of the
stellar mass in the elliptical galaxy population has been formed since z=1. We
see no evidence for a decline in the space density of early-type galaxies with
look-back time. The statistics and a comparison with local
luminosity functions are both consistent with the view that the population of
massive early-type galaxies was largely in place by z~1. This implies that
merging is not required since that time to produce the present-day space
density of elliptical galaxies.Comment: 21 pages plus 8 figures plus 5 tables. Accepted by Astrophysical
Journa
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Evaluation of a Density-Based Rapid Diagnostic Test for Sickle Cell Disease in a Clinical Setting in Zambia
Although simple and low-cost interventions for sickle cell disease (SCD) exist in many developing countries, child mortality associated with SCD remains high, in part, because of the lack of access to diagnostic tests for SCD. A density-based test using aqueous multiphase systems (SCD-AMPS) is a candidate for a low-cost, point-of-care diagnostic for SCD. In this paper, the field evaluation of SCD-AMPS in a large (n = 505) case-control study in Zambia is described. Of the two variations of the SCD-AMPS used, the best system (SCD-AMPS-2) demonstrated a sensitivity of 86% (82–90%) and a specificity of 60% (53–67%). Subsequent analysis identified potential sources of false positives that include clotting, variation between batches of SCD-AMPS, and shipping conditions. Importantly, SCD-AMPS-2 was 84% (62–94%) sensitive in detecting SCD in children between 6 months and 1 year old. In addition to an evaluation of performance, an assessment of end-user operability was done with health workers in rural clinics in Zambia. These health workers rated the SCD-AMPS tests to be as simple to use as lateral flow tests for malaria and HIV
Faculty members engaging in transformative PETE: a feminist perspective
The purpose of this study was to describe sport pedagogy faculty members’ (FMs) efforts at engaging in transformative physical education teacher education (T-PETE). T-PETE stresses the importance of FMs creating social change through their pedagogical approach and begins by asking preservice teachers (PTs) to reflect on their perspectives and practices (Tinning, 2017 Tinning, R. (2017). Transformative pedagogies and physical education. In C. Ennis (Ed.), The Routledge handbook of physical education pedagogies (pp. 295–306). New York: Taylor & Francis. [Google Scholar]. Transformative pedagogies and physical education. In C. Ennis (Ed.), The Routledge handbook of physical education pedagogies (pp. 295–306). New York: Taylor & Francis; Ukpokodu, 2009. The practice of transformative pedagogy. Journal on Excellence in College Teaching, 20(2), 43–67.). Participants were three white, female, able-bodied, lesbian/gay sport pedagogy FMs. The study was conducted in the United States. Feminist theory and feminist pedagogy drove data collection and analysis. Data were collected by employing a series of qualitative methods. An inductive and deductive analysis revealed that FMs had specific T-PETE goals, content, and pedagogies. Furthermore, several factors served to facilitate and limit the FMs’ effectiveness when engaging in T-PETE. The findings suggest that program-wide PETE reform is necessary in the United States for creating social change, and influencing PTs perspectives and practices. In addition, they suggest that American PETE programs might benefit from greater diversity among the FMs who staff them
‘It brings the lads together’: A critical exploration of older men’s experiences of a weight management programme delivered through a Healthy Stadia project
Older men whose weight is considered unhealthy may experience particular barriers that can restrict their adoption of health improvement interventions. Despite promising findings recommending the use of sports settings to facilitate health promotion with men, little evidence has addressed older men’s health needs for, or experiences of, these settings. Using a qualitative methodology, this study explored the experiences of 14 ageing men attending a football-led weight management programme delivered at a community sports setting. The thematic analysis of semi-structured interviews elucidates important insights regarding the provision of sports-led health improvement interventions for this population. Men especially valued the opportunity to play sports and do physical activity in an environment that promotes ‘inclusive’ competition and caring interpersonal relationships. Implicit in the findings is the key role of practitioners in promoting social engagement. We conclude the paper with key practical implications of this research
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