6,719 research outputs found
Improvement of Fourier Polarimetry for applications in tomographic photoelasticity
The use of the Fourier Polarimetry method has been demonstrated to extract the three characteristic parameters in integrated photoelasticity. In contrast to the phase-stepping method, it has been shown that the Fourier method is more accurate. However, the Fourier method isn't very efficient as it requires that a minimum of nine intensity images be collected during a whole revolution of a polarizer while the phase-stepping method only needs six intensity images. In this paper the Fourier transformation is used to derive the expression for determination of the characteristic parameters. Four Fourier coefficients are clearly identified to calculate the three characteristic parameters. It is found that the angular rotation ratio could be set arbitrarily. The angular rotation ratio is optimized to satisfy the requirements of efficiency and proper data accuracy, which results in data collection about three times faster than the methods suggested by previous researchers. When comparing their performance in terms of efficiency and accuracy, the simulated and experimental results show that these angular rotation ratios have the same accuracy but the optimized angular rotation ratio is significantly faster. The sensitivity to noise is also investigated and further improvement of accuracy is suggested
Design and performance of a 39cm balloon-borne telescope
A system for stabilizing a balloon-borne telescope using a star sensor device is described. Guide stars from minus four to plus four magnitude can be used and the sensor may be offset with respect to the telescope by as much as plus or minus five degrees in elevation and cross elevation to enable parts of the sky containing no suitable guide stars to be viewed. Acquisition of the guide star and setting of the offset coordinates is carried out by ground command and both may be changed in flight. The main design parameters of the equipment are summarized. Block diagrams and circuit diagrams of the star tracker are provided
Local spectroscopy and atomic imaging of tunneling current, forces and dissipation on graphite
Theory predicts that the currents in scanning tunneling microscopy (STM) and
the attractive forces measured in atomic force microscopy (AFM) are directly
related. Atomic images obtained in an attractive AFM mode should therefore be
redundant because they should be \emph{similar} to STM. Here, we show that
while the distance dependence of current and force is similar for graphite,
constant-height AFM- and STM images differ substantially depending on distance
and bias voltage. We perform spectroscopy of the tunneling current, the
frequency shift and the damping signal at high-symmetry lattice sites of the
graphite (0001) surface. The dissipation signal is about twice as sensitive to
distance as the frequency shift, explained by the Prandtl-Tomlinson model of
atomic friction.Comment: 4 pages, 4 figures, accepted at Physical Review Letter
Dynamics of Phononic Dissipation at the Atomic Scale: Dependence on Internal Degrees of Freedom
Dynamics of dissipation of a local phonon distribution to the substrate is a
key issue in friction between sliding surfaces as well as in boundary
lubrication. We consider a model system consisting of an excited nano-particle
which is weakly coupled with a substrate. Using three different methods we
solve the dynamics of energy dissipation for different types of coupling
between the nano-particle and the substrate, where different types of
dimensionality and phonon densities of states were also considered for the
substrate. In this paper, we present our analysis of transient properties of
energy dissipation via phonon discharge in the microscopic level towards the
substrate. Our theoretical analysis can be extended to treat realistic
lubricant molecules or asperities, and also substrates with more complex
densities of states. We found that the decay rate of the nano-particle phonons
increases as the square of the interaction constant in the harmonic
approximation.Comment: 10 pages, 6 figures, submitted to Phys. Rev.
Tawney and the third way
From the 1920s to the 1950s R. H. Tawney was the most influential socialist thinker in Britain. He articulated an ethical socialism at odds with powerful statist and mechanistic traditions in British socialist thinking. Tawney's work is thus an important antecedent to third way thinking. Tawney's religiously-based critique of the morality of capitalism was combined with a concern for detailed institutional reform, challenging simple dichotomies between public and private ownership. He began a debate about democratizing the enterprise and corporate governance though his efforts fell on stony ground. Conversely, Tawney's moralism informed a whole-hearted condemnation of market forces in tension with both his concern with institutional reform and modern third way thought. Unfortunately, he refused to engage seriously with emergent welfare economics which for many social democrats promised a more nuanced understanding of the limits of market forces. Tawney's legacy is a complex one, whose various elements form a vital part of the intellectual background to current third way thinking
Transitions between phyllotactic lattice states in curved geometries
Phyllotaxis, the regular arrangement of leaves or other lateral organs in
plants including pineapples, sunflowers and some cacti, has attracted
scientific interest for centuries. More recently there has been interest in
phyllotaxis within physical systems, especially for cylindrical geometry. In
this letter, we expand from a cylindrical geometry and investigate transitions
between phyllotactic states of soft vortex matter confined to a conical
frustum. We show that the ground states of this system are consistent with
previous results for cylindrical confinement and discuss the resulting defect
structures at the transitions. We then eliminate these defects from the system
by introducing a density gradient to create a configuration in a single state.
The nature of the density gradient limits this approach to a small parameter
range on the conical system. We therefore seek a new surface, the horn, for
which a defect-free state can be maintained for a larger range of parameters.Comment: 16 pages, 6 figure
The Stokes-Einstein Relation in Supercooled Aqueous Solutions of Glycerol
The diffusion of glycerol molecules decreases with decreasing temperature as
its viscosity increases in a manner simply described by the Stokes-Einstein(SE)
relation. Approaching the glass transition, this relation breaks down as it
does with a number of other pure liquid glass formers. We have measured the
diffusion coefficient for binary mixtures of glycerol and water and find that
the Stokes-Einstein relation is restored with increasing water concentration.
Our comparison with theory suggests that addition of water postpones the
formation of frustration domainsComment: 4 Pages and 3 Figure
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The Psy-Security-Curriculum ensemble: British Values curriculum policy in English schools
Framed as being in response to terrorist attacks and concerns about religious bias in some English schools, ‘British Values’ (BV) curriculum policy forms part of the British Government’s Counter-Terrorism and Security Act, 2015. This includes a Duty on teachers in England to actively promote British Values to deter students from radicalisation. This paper, first, traces the history of Britishness in the curriculum to reveal a prevalence of nationalistic, colonial values. Next, an ensemble of recent policies and speeches focusing on British Values is analysed, using a psycho-political approach informed by anti-colonial scholarship. Finally, we interrogate two key critiques of the British Values curriculum discourse: the universality of British Values globally, and concerns over the securitisation of education. Findings indicate that the constitution of white British supremacist subjectivities operate through curriculum as a defence mechanism against perceived threats to white privilege, by normalising a racialised state-controlled social order. The focus is on ‘British’ values, but the analytic framework and findings have wider global significance
An investigation into CLIL-related sections of EFL coursebooks : issues of CLIL inclusion in the publishing market
The current ELT global coursebook market has embraced CLIL as a weak form of bilingual education and an innovative component to include in General English coursebooks for EFL contexts. In this paper I investigate how CLIL is included in ELT coursebooks aimed at
teenaged learners, available to teachers in Argentina. My study is based on the content analysis of four series which include a section advertised as CLIL-oriented. Results suggest that such sections are characterised by (1) little correlation between featured subject specific content and school curricula in L1, (2) oversimplification of contents, and (3) dominance of reading skills development and lower-order thinking tasks. Through this study, I argue that
CLIL components become superficial supplements rather than a meaningful attempt to promote weak forms of bilingual education
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