7,779 research outputs found
On Keller Theorem for Anisotropic Media
The Keller theorem in the problem of effective conductivity in anisotropic
two-dimensional (2D) many-component composites makes it possible to establish a
simple inequality for the isotropic part of
the 2-nd rank symmetric tensor of effective
conductivity.Comment: 1 page, 1 figur
An application of the requirement vs capability analysis to estimating design reliability of solid rocket motors
Design reliability parameters for solid propellant rocket engine
Noise diffraction patterns eliminated in coherent optical systems
Lens rotation technique of noise diffraction pattern elimination spreads diffracted energy, normally concentrated over small area of image, over much larger annular area. Technique advantages include simplified lens selecting process, reduced clean room requirements, and low cost equipment requirements
Geometrical classification of Killing tensors on bidimensional flat manifolds
Valence two Killing tensors in the Euclidean and Minkowski planes are
classified under the action of the group which preserves the type of the
corresponding Killing web. The classification is based on an analysis of the
system of determining partial differential equations for the group invariants
and is entirely algebraic. The approach allows to classify both characteristic
and non characteristic Killing tensors.Comment: 27 pages, 20 figures, pictures format changed to .eps, typos
correcte
Elimination of coherent noise in a coherent light imaging system
Optical imaging systems using coherent light introduce objectionable noise into the output image plane. Dust and bubbles on and in lenses cause most of the noise in the output image. This noise usually appears as bull's-eye diffraction patterns in the image. By rotating the lens about the optical axis these diffraction patterns can be essentially eliminated. The technique does not destroy the spatial coherence of the light and permits spatial filtering of the input plane
Possible mechanism for achieving glass-like thermal conductivities in crystals with off-center atoms
In the filled Ga/Ge clathrate, Eu and Sr are off-center in site 2 but Ba is
on-center. All three filler atoms (Ba,Eu,Sr) have low temperature Einstein
modes; yet only for the Eu and Sr systems is there a large dip in the thermal
conductivity, attributed to the Einstein modes. No dip is observed for Ba. Here
we argue that it is the off-center displacement that is crucial for
understanding this unexplained difference in behavior. It enhances the coupling
between the "rattler" motion and the lattice phonons for the Eu and Sr systems,
and turns on/off another scattering mechanism (for 1K < T < 20K) produced by
the presence/absence of off-center sites. The random occupation of different
off-center sites produces a high density of symmetry-breaking defects which
scatters phonons. It may also be important for improving our understanding of
other glassy systems.Comment: 4 pages, 1 figure (2 parts) -- v2: intro broadened; strengthened
arguments regarding need for additional phonon scattering mechanis
Heavy metals in agricultural soils of the European Union with implications for food safety
Soil plays a central role in food safety as it determines the possible composition of food and feed at the root of the
food chain. However, the quality of soil resources as defined by their potential impact on human health by propagation
of harmful elements through the food chain has been poorly studied in Europe due to the lack of data of
adequate detail and reliability. The European Union's first harmonized topsoil sampling and coherent analytical
procedure produced trace element measurements fromapproximately 22,000 locations. This unique collection of
information enables a reliable overview of the concentration of heavy metals, also referred to as metal(loid)s including
As, Cd, Cr, Cu, Hg, Pb, Zn, Sb. Co, and Ni. In this article we propose that in some cases (e.g. Hg and Cd) the
high concentrations of soil heavy metal attributed to human activity can be detected at a regional level.While the
immense majority of European agricultural land can be considered adequately safe for food production, an estimated
6.24% or 137,000 km2 needs local assessment and eventual remediation action
- …