69,299 research outputs found
Size-dependent piezoelectricity
In this paper, a consistent theory is developed for size-dependent
piezoelectricity in dielectric solids. This theory shows that electric
polarization can be generated as the result of coupling to the mean curvature
tensor, unlike previous flexoelectric theories that postulate such couplings
with other forms of curvature and more general strain gradient terms ignoring
the possible couple- stresses. The present formulation represents an extension
of recent work that establishes a consistent size-dependent theory for solid
mechanics. Here by including scale-dependent measures in the energy equation,
the general expressions for force- and couple-stresses, as well as electric
displacement, are obtained. Next, the constitutive relations, displacement
formulations, the uniqueness theorem and the reciprocal theorem for the
corresponding linear small deformation size-dependent piezoelectricity are
developed. As with existing flexoelectric formulations, one finds that the
piezoelectric effect can also exist in isotropic materials, although in the
present theory the coupling is strictly through the skew-symmetric mean
curvature tensor. In the last portion of the paper, this isotropic case is
considered in detail by developing the corresponding boundary value problem for
two dimensional analyses and obtaining a closed form solution for an isotropic
dielectric cylinder.Comment: 37 pages, 4 figure
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ESRI vs BREWER: An Evaluation of Map Use with Alternative Colour Schemes amongst the General Public
This small study evaluates the effectiveness of selected sets of colour schemes used in ESRI‟s ArcMap and ColorBrewer in communicating information on choropleth maps. Subjects conducted map reading tasks using online questionnaires and their performance was captured. The results did not show significant differences in performance associated with colour scheme - subjects were highly successful in direct acquisition tasks irrespective of the set(s) of scheme used. However, performances were consistently poor for „distribution‟ tasks. The results suggest limited spatial capabilities in the sample and highlight the need to test for general spatial ability in such experiments
Asymptotics of Nonlinear LSE Precoders with Applications to Transmit Antenna Selection
This paper studies the large-system performance of Least Square Error (LSE)
precoders which~minimize~the~input-output distortion over an arbitrary support
subject to a general penalty function. The asymptotics are determined via the
replica method in a general form which encloses the Replica Symmetric (RS) and
Replica Symmetry Breaking (RSB) ans\"atze. As a result, the "marginal
decoupling property" of LSE precoders for -steps of RSB is derived. The
generality of the studied setup enables us to address special cases in which
the number of active transmit antennas are constrained. Our numerical
investigations depict that the computationally efficient forms of LSE precoders
based on "-norm" minimization perform close to the cases with
"zero-norm" penalty function which have a considerable improvements compared to
the random antenna selection. For the case with BPSK signals and restricted
number of active antennas, the results show that RS fails to predict the
performance while the RSB ansatz is consistent with theoretical bounds.Comment: 5 pages; 2 figures; to be presented at ISIT 201
Second-order weak lensing from modified gravity
We explore the sensitivity of weak gravitational lensing to second-order
corrections to the spacetime metric within a cosmological adaptation of the
parameterized post-Newtonian framework. Whereas one might expect nonlinearities
of the gravitational field to introduce non-Gaussianity into the statistics of
the lensing convergence field, we show that such corrections are actually
always small within a broad class of scalar-tensor theories of gravity. We show
this by first computing the weak lensing convergence within our parameterized
framework to second order in the gravitational potential, and then computing
the relevant post-Newtonian parameters for scalar-tensor gravity theories. In
doing so we show that this potential systematic factor is generically
negligible, thus clearing the way for weak lensing to provide a direct tracer
of mass on cosmological scales for a wide class of gravity theories despite
uncertainties in the precise nature of the departures from general relativity.Comment: 13 pages, 1 figure; v2: minor edits to match the PRD accepted versio
Hemoglobin Subunit-Subunit Affinity-Determinant of Hemoglobin Formation
Hemoglobin A₂ is often elevated in β-thalassemia and decreased in α-thalassemia. This might be due to hemoglobin subunit-subunit affinity variation. It has been inferred from the study of abnormal hemoglobins that the a subunits have higher affinity for β subunits than for δ subunits. However, only in one study has the affinity of α, β, and δ subunits for each other been measured. In this work we have attempted to measure the hemoglobin subunit-subunit affinity with somewhat different approach, i.e., hybridization of hemoglobin A and A₂. It is shown that hybridization and recombination of equal amounts of hemoglobins A and A₂ lead always to the formation of more hemoglobin A than A₂. Incubation of pure α, β, and δ subunits forms more hemoglobin A than A₂ as the availability of a subunits declines. It is concluded that hemoglobin a subunits have approximately four-fold higher affinity for β subunits than for the δ subunits under these experimental conditions. This subunit-subunit affinity difference, which has been attributed to the variation in molecular electrostatic charges, explains the variation of hemoglobin A₂ levels in thalassemia syndromes
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