4,043 research outputs found
Retransmission of water resources data using the ERTS-1 data collection system
There are no author-identified significant results in this report
Exact 1/N and Optimized Perturbative Evaluation of mu_c for Homogeneous Interacting Bose Gases
In the framework of the O(N) three-dimensional effective scalar field model
for homogeneous dilute weakly interacting Bose gases we use the 1/N expansion
to evaluate, within the large N limit, the parameter r_c which is directly
related to the critical chemical potential mu_c. This quantity enters the
order-a^2 n^{2/3} coefficient contributing to the critical temperature shift
Delta T_c where a represents the s-wave scattering length and n represents the
density. Compared to the recent precise numerical lattice simulation results,
our calculation suggests that the large N approximation performs rather well
even for the physical case N=2. We then calculate the same quantity but using
different forms of the optimized perturbative (variational) method, showing
that these produce excellent results both for the finite N and large-N cases.Comment: 12 pages, 2 figures. We have performed a refined and extended
numerical analysis to take into account the very recent results of Ref. [15
Convergence of the Optimized Delta Expansion for the Connected Vacuum Amplitude: Zero Dimensions
Recent proofs of the convergence of the linear delta expansion in zero and in
one dimensions have been limited to the analogue of the vacuum generating
functional in field theory. In zero dimensions it was shown that with an
appropriate, -dependent, choice of an optimizing parameter \l, which is an
important feature of the method, the sequence of approximants tends to
with an error proportional to . In the present paper we
establish the convergence of the linear delta expansion for the connected
vacuum function . We show that with the same choice of \l the
corresponding sequence tends to with an error proportional to . The rate of convergence of the latter sequence is governed by
the positions of the zeros of .Comment: 20 pages, LaTeX, Imperial/TP/92-93/5
Depth dependent dynamics in the hydration shell of a protein
We study the dynamics of hydration water/protein association in folded
proteins, using lysozyme and myoglobin as examples. Extensive molecular
dynamics simulations are performed to identify underlying mechanisms of the
dynamical transition that corresponds to the onset of amplified atomic
fluctuations in proteins. The number of water molecules within a cutoff
distance of each residue scales linearly with protein depth index and is not
affected by the local dynamics of the backbone. Keeping track of the water
molecules within the cutoff sphere, we observe an effective residence time,
scaling inversely with depth index at physiological temperatures while the
diffusive escape is highly reduced below the transition. A depth independent
orientational memory loss is obtained for the average dipole vector of the
water molecules within the sphere when the protein is functional. While below
the transition temperature, the solvent is in a glassy state, acting as a solid
crust around the protein, inhibiting any large scale conformational
fluctuations. At the transition, most of the hydration shell unfreezes and
water molecules collectively make the protein more flexible.Comment: Journal of Chemical Physics in pres
First impressions and perceived roles: Palestinian perceptions on foreign aid
This paper summarizes some results of a wider research on foreign aid that was conducted in the West Bank and Gaza Strip in 2010. It seeks to describe the impressions and feelings of Palestinian aid beneficiaries as well as the roles and functions they attached to foreign aid. To capture and measure local perceptions on Western assistance a series of individual in depth interviews and few focus group interviews were conducted in the Palestinian territories. The interview transcripts were processed by content analysis. As research results show â from the perspective of aid beneficiaries â foreign aid is more related to human dignity than to any economic development. All this implies that frustration with the ongoing Israeli-Palestinian conflict inevitably embraces the donor policies and practices too
'The heart of what we do': policies on teaching, learning and assessment in the learning and skills sector
One of the stated aims of government policy in England is to put teaching, training,and learning at the heart of the learning and skills system. This paper provides a critical review of policies on teaching, learning and assessment in the learning and skills sector over the past five years. It draws upon data collected and analysed in the early stages of an ESRC-funded Teaching and Learning Research Programme project. Using evidence from policy sources, we argue that despite policy rhetoric about devolution of responsibility to the 'front line', the dominant 'images' that government has of putting teaching, learning and assessment at the heart of the Learning and Skills Sector involves a narrow concept of learning and skills; an idealisation of learner agency lacking an appreciation of the pivotal role of the learner/tutor relationship and a top-down view of change in which central government agencies are relied on to secure education standards
Images in Christmas Balls
We describe light-reflection properties of spherically curved mirrors, like
balls in the Christmas tree. In particular, we study the position of the image
which is formed somewhere beyond the surface of a spherical mirror, when an eye
observes the image of a pointlike light source. The considered problem,
originally posed by Abu Ali Hasan Ibn al-Haitham -- alias Alhazen -- more than
a millennium ago, turned out to have the now well known analytic solution of a
biquadratic equation, being still of great relevance, e.g. for the
aberration-free construction of telescopes. We do not attempt to perform an
exhaustive survey of the rich historical and engineering literature on the
subject, but develop a simple pedagogical approach to the issue, which we
believe to be of continuing interest in view of its maltreating in many
high-school textbooks.Comment: 13 pages, 7 figures plain LaTeX; Also see
http://cft.fis.uc.pt/eef/mirrors.htm, revised version has simplified
formulas, more transparent for a wider audience, one reference adde
Azospirillum brasilense Az39, a model rhizobacterium with AHL quorum quenching capacity
AimsThe aim of this research was to analyze the Quorum sensing (QS) and Quorum quenching (QQ) mechanisms based on NâacylâLâhomoserine lactones (AHLs) in A. brasilense Az39, a strain with remarkable capacity to benefit a wide range of crops under agronomic conditions. Methods and ResultsWe performed an in silico and in vitro analysis of the quorum mechanisms in A. brasilense Az39. The results obtained in vitro using the reporter strains C. violaceum and A. tumefaciens and Liquid Chromatography coupled to MassâMass Spectrometry (LCâMS/MS) analysis showed that although Az39 does not produce AHL molecules, it is capable of degrading them by at least two hypothetical enzymes identified by bioinformatics approach, associated to the bacterial cell. In Az39 cultures supplemented with 500 nmol lâ1 of the C3 unsubstituted AHLs (C4, C6, C8, C10, C12, C14), AHL levels were lower than in nonâinoculated LB media controls. Similar results were observed upon addition of AHLs with hydroxy (OHâ) and keto (oxoâ) substitutions in carbon 3. These results not only demonstrate the ability of Az39 to degrade AHLs. They also show the wide spectrum of molecules that can be degraded by this bacterium. ConclusionsAlthough A.brasilense Az39 is a silent bacterium unable to produce AHL signals, it is able to interrupt the communications between other bacteria and/or plants by a quorum quenching activity
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