2,289 research outputs found
Beyond the simple Proximity Force Approximation: geometrical effects on the non-retarded Casimir interaction
We study the geometrical corrections to the simple Proximity Force
Approximation for the non-retarded Casimir force. We present analytical results
for the force between objects of various shapes and substrates, and between
pairs of objects. We compare the results to those from more exact numerical
calculations. We treat spheres, spheroids, cylinders, cubes, cones, and wings;
the analytical PFA results together with the geometrical correction factors are
summarized in a table.Comment: 18 pages, 19 figures, 1 tabl
The 'reach' of Digital Language Archives: towards criteria for evaluation
Over the last decade, and with the help of digital media and technologies, archives (with the focus here on archives for endangered and minority languages) have extended their focus from preservation to also becoming facilities for dissemination. Their innovations have largely been on ‘discovery’: firstly by encouraging digitisation and inclusion of analogue and obscure materials, and by partnership with funding institutions to support the creation of new, ‘born digital’ language resources; and secondly through online provision of language resources via web catalogues driven by standardised metadata and in some cases providing enhanced discovery through web portals aggregating the holdings of multiple archives. These advances have increased the visibility, relevance and authority of archives for language-related disciplines and for language-speaker communities. This paper considers a broader set of parameters describing the ‘reach’ of archives, where ‘reach’ includes (a) archives’ understanding of their key audiences in order to provide appropriate services for them, e.g. identifying a range of relevant audiences, their languages of access, their varied technological and information literacies, interface design and usability; (b) discovery, drawing on the understandings of audiences in order to help them browse, navigate, search, identify and select their items of interest; (c) delivery, i.e. making available selected resources according to users’ preferences whether by download, view-in-browser, through apps or other means; (d) access management such that resource delivery follows depositors’ and communities’ preferences, and where users have ways of applying for and negotiating for access; (e) information accessibility, where the actual desired content is accessible to users, whether in terms of contextualisation or appropriate complexity, language, or modality; and finally (f) feedback channels, where users can utilise the archive to provide feedback to depositors or to enhance deposits with user-generated content. Through considering how a number of archives are providing such services, we can see their transition from repositories of memory to facilities for fostering participation and understanding
The non-perturbative corrections to the photon spectrum in a parton-like model
We derive a new parton-like formula, which establishes a simple connection
between the electroweak decay rate ) and the rate
of a free b-quark decay. The main features of our approach are the treatment of
the b-quark as an on-mass-shell particle and the inclusion of the effects
arising from the b-quark transverse motion in the -meson. Using various
b-quark light-front (LF) distribution functions, both phenomenological one and
the ones derived from current constituent quark models, and neglecting
perturbative corrections we compute the photon energy spectra and the moments
of the shape function. It is shown that the parton-like approach is fully
consistent with the Heavy Quark Effective Theory (HQET) provided the b-quark
constituent mass is redefined in the way similar to that used in HQET to define
the pole mass of the b quark. In this way the correction to first order in
can be eliminated from the total width in agreement with the general
statement of HQET. We have also found that the photon energy spectra calculated
in the LF approach agree well with the ones obtained in the ACM model, provided
the same distribution function is used as input in both cases. In spite of the
simplicity of the model our results show a fair good agreement both with the
HQET predictions and available experimental data.Comment: 14 pages, LaTeX, 3 ps figure
Detection of NMR signals with a radio-frequency atomic magnetometer
We demonstrate detection of proton NMR signals with a radio frequency atomic
magnetometer tuned to the NMR frequency of 62 kHz. High-frequency operation of
the atomic magnetometer makes it relatively insensitive to ambient magnetic
field noise. We obtain magnetic field sensitivity of 7 fT/Hz using only
a thin aluminum shield. We also derive an expression for the fundamental
sensitivity limit of a surface inductive pick-up coil as a function of
frequency and find that an atomic rf magnetometer is intrinsically more
sensitive than a coil of comparable size for frequencies below about 50 MHz.Comment: 7 page
Human papillomavirus 16 L2 inhibits the transcriptional activation function, but not the DNA replication function, of HPV-16 E2
In this study we analysed the outcome of the interaction between HPV-16 L2 and E2 on the transactivation and DNA replication functions of E2. When E2 was expressed on its own, it transactivated a number of E2-responsive promoters but co-expression of L2 led to the down-regulation of the transcription transactivation activity of the E2 protein. This repression is not mediated by an increased degradation of the E2 protein. In contrast, the expression of L2 had no effect on the ability of E2 to activate DNA replication in association with the viral replication factor E1. Deletion mutagenesis identified L2 domains responsible for binding to E2 (first 50 N-terminus amino acid residues) and down-regulating its transactivation function (residues 301–400). The results demonstrate that L2 selectively inhibits the transcriptional activation property of E2 and that there is a direct interaction between the two proteins, although this is not sufficient to mediate the transcriptional repression. The consequences of the L2–E2 interaction for the viral life cycle are discussed
Candidatus Phytoplasma brasiliense associado ao superbrotamento do hibisco (Hibiscus rosa-sinensis L.) no Estado de São Paulo
Black Hole Entropy is Noether Charge
We consider a general, classical theory of gravity in dimensions, arising
from a diffeomorphism invariant Lagrangian. In any such theory, to each vector
field, , on spacetime one can associate a local symmetry and, hence, a
Noether current -form, , and (for solutions to the field
equations) a Noether charge -form, . Assuming only that the
theory admits stationary black hole solutions with a bifurcate Killing horizon,
and that the canonical mass and angular momentum of solutions are well defined
at infinity, we show that the first law of black hole mechanics always holds
for perturbations to nearby stationary black hole solutions. The quantity
playing the role of black hole entropy in this formula is simply times
the integral over of the Noether charge -form associated with
the horizon Killing field, normalized so as to have unit surface gravity.
Furthermore, we show that this black hole entropy always is given by a local
geometrical expression on the horizon of the black hole. We thereby obtain a
natural candidate for the entropy of a dynamical black hole in a general theory
of gravity. Our results show that the validity of the ``second law" of black
hole mechanics in dynamical evolution from an initially stationary black hole
to a final stationary state is equivalent to the positivity of a total Noether
flux, and thus may be intimately related to the positive energy properties of
the theory. The relationship between the derivation of our formula for black
hole entropy and the derivation via ``Euclidean methods" also is explained.Comment: 16 pages, EFI 93-4
Thermodynamic and Tunneling Density of States of the Integer Quantum Hall Critical State
We examine the long wave length limit of the self-consistent Hartree-Fock
approximation irreducible static density-density response function by
evaluating the charge induced by an external charge. Our results are consistent
with the compressibility sum rule and inconsistent with earlier work that did
not account for consistency between the exchange-local-field and the disorder
potential. We conclude that the thermodynamic density of states is finite, in
spite of the vanishing tunneling density of states at the critical energy of
the integer quantum Hall transition.Comment: 5 pages, 4 figures, minor revisions, published versio
Self-folding nano- and micropatterned hydrogel tissue engineering scaffolds by single step photolithographic process
Current progress in tissue engineering is focused on the creation of environments in which cultures of relevant cells can adhere, grow and form functional tissue. We propose a method for controlled chemical and topographical cues through surface patterning of self-folding hydrogel films. This provides a conversion of 2D patterning techniques into a viable method of manufacturing a 3D scaffold. While similar bilayers have previously been demonstrated, here we present a faster and high throughput process for fabricating self-folding hydrogel devices incorporating controllable surface nanotopographies by serial hot embossing of sacrificial layers and photolithography
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