1,359 research outputs found
Elasticity of an interfacial particle raft
We study the collective behaviour of a close packed monolayer of non-Brownian
particles at a fluid-liquid interface. Such a particle raft forms a
two-dimensional elastic solid and can support anisotropic stresses and strains,
e.g. it buckles in uniaxial compression and cracks in tension. We characterise
this solid in terms of a Young's modulus and Poisson ratio derived from simple
theoretical considerations and show the validity of these estimates by using an
experimental buckling assay to deduce the Young's modulus.Comment: 7 pages, 5 figure
Platybunus triangularis and Paroligolophus agrestis: two phalangids introduced to North America (Arachnida, Opiliones)
Volume: 2Start Page: 127End Page: 12
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Achieving environmentally sustainable growing media for soilless plant cultivation systems â a review
Soilless cultivation is recognized globally for its ability to support efficient and intensive plant production. While production systems vary, most utilize a porous substrate or growing medium for plant provision of water and nutrients. Until relatively recently, the main drivers for the selection of the component materials in growing media were largely based on performance and economic considerations. However, increasing concern over the environmental impacts of some commonly used materials, has led researchers to identify and assess more environmentally sound alternatives. There has been an understandable focus on renewable materials from agricultural, industrial and municipal waste streams; while many of these show promise at an experimental level, few have been taken up on a significant scale. To ensure continued growth and sustainable development of soilless cultivation, it is vital that effective and environmentally sustainable materials for growing media are identified. Here we describe the factors influencing material selection, and review the most commonly used organic materials in relation to these. We summarise some of the renewable, primary and waste stream materials that have been investigated to date, highlighting the benefits and challenges associated with their uptake. In response to the need for researchers to better identify promising new materials, we present an evidence-based argument for a more consistent approach to characterising growing media and for a clearer understanding of the practical and economic realities of modern soilless cultivation systems
Collaboration and contestation in further and higher education partnerships in England: a Bourdieusian field analysis
Internationally, âCollege for Allâ policies are creating new forms of vocational higher education (HE), and shifting relationships between HE and further education (FE) institutions. In this paper, we consider the way in which this is being implemented in England, drawing on a detailed qualitative case study of a regional HEâFE partnership to widen participation. We focus on the complex mix of collaboration and contestation that arose within it, and how these affected socially differentiated groups of students following high- and low-status routes through its provision. We outline Bourdieuâs concept of âfieldâ as a framework for our analysis and interpretation, including its theoretical ambiguities regarding the definition and scale of fields. Through hermeneutic dialogue between data and theory, we tentatively suggest that such partnerships represent bridges between HE and FE. These bridges are strong between higher-status institutions, but highly contested between lower-status institutions competing closely for distinction. We conclude that the trajectories and outcomes for socially disadvantaged students require attention and collective action to address the inequalities they face, and that our theoretical approach may have wider international relevance beyond the English case
Logarithmic scaling of higher-order temperature moments in the atmospheric surface layer
A generalized logarithmic law for high-order moments of passive scalars is
proposed for turbulent boundary layers. This law is analogous to the
generalized log law that has been proposed for high-order moments of the
turbulent longitudinal velocity and is derived by combining the random sweeping
decorrelation hypothesis with a spectral model informed by the attached eddy
hypothesis. The proposed theory predicts that the high-order moments of passive
scalar fluctuations within the inertial sublayer will vary logarithmically with
wall-normal distance (). The proposed theory is evaluated using high
frequency time-series measurements of temperature and streamwise velocity
fluctuations obtained in the first meter of the atmospheric surface layer (ASL)
under near-neutral thermal stratification. The logarithmic dependence with
within the inertial sublayer is observed in both the air temperature and
velocity moments, with good agreement to the predictions from the proposed
theory. Surprisingly, the proposed theory appears to be as, if not more, valid
for transported passive scalars than for the longitudinal velocity
Coulomb correlation effects in zinc monochalcogenides
Electronic structure and band characteristics for zinc monochalcogenides with
zinc-blende- and wurtzite-type structures are studied by first-principles
density-functional-theory calculations with different approximations. It is
shown that the local-density approximation underestimates the band gap and
energy splitting between the states at the top of the valence band, misplaces
the energy levels of the Zn-3d states, and overestimates the
crystal-field-splitting energy. Regardless of the structure type considered,
the spin-orbit-coupling energy is found to be overestimated for ZnO and
underestimated for ZnS with wurtzite-type structure, and more or less correct
for ZnSe and ZnTe with zinc-blende-type structure. The order of the states at
the top of the valence band is found to be anomalous for ZnO in both
zinc-blende- and wurtzite-type structure, but is normal for the other zinc
monochalcogenides considered. It is shown that the Zn-3d electrons and their
interference with the O-2p electrons are responsible for the anomalous order.
The typical errors in the calculated band gaps and related parameters for ZnO
originate from strong Coulomb correlations, which are found to be highly
significant for this compound. The LDA+U approach is by and large found to
correct the strong correlation of the Zn-3d electrons, and thus to improve the
agreement with the experimentally established location of the Zn-3d levels
compared with that derived from pure LDA calculations
The sphere-in-contact model of carbon materials
A sphere-in-contact model is presented that is used to build physical models of carbon materials such as graphite, graphene, carbon nanotubes and fullerene. Unlike other molecular models, these models have correct scale and proportions because the carbon atoms are represented by their atomic radius, in contrast to the more commonly used space-fill models, where carbon atoms are represented by their van der Waals radii. Based on a survey taken among 65 undergraduate chemistry students and 28 PhD/postdoctoral students with a background in molecular modeling, we found misconceptions arising from incorrect visualization of the size and location of the electron density located in carbon materials. Based on analysis of the survey and on a conceptual basis we show that the sphere-in-contact model provides an improved molecular representation of the electron density of carbon materials compared to other molecular models commonly used in science textbooks (i.e., wire-frame, ball-and-stick, space-fill). We therefore suggest that its use in chemistry textbooks along with the ball-and-stick model would significantly enhance the visualization of molecular structures according to their electron density
Quantum Nondemolition State Measurement via Atomic Scattering in Bragg Regime
We suggest a quantum nondemolition scheme to measure a quantized cavity field
state using scattering of atoms in general Bragg regime. Our work extends the
QND measurement of a cavity field from Fock state, based on first order Bragg
deflection [9], to any quantum state based on Bragg deflection of arbitrary
order. In addition a set of experimental parameters is provided to perform the
experiment within the frame work of the presently available technology.Comment: 11 pages text, 4 eps figures, to appear in letter section of journal
of physical society of Japa
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