1,376 research outputs found
Nondestructive Evaluation of Composite Materials with Backscattering Measurements
Initial experiments have been performed to characterize the scattering of acoustic waves from glass/ epoxy and graphite/epoxy composite panels. Experiments were conducted in the region 0.1 †ka †1.0 on both types of fiber reinforced composites. The data clearly show that a maximum in the backscattering ultrasonic energy occurs for orientations which place the fiber axis perpendicular to the propagation vector
Spectral Analysis and the Dynamic Response of Complex Networks
The eigenvalues and eigenvectors of the connectivity matrix of complex
networks contain information about its topology and its collective behavior. In
particular, the spectral density of this matrix reveals
important network characteristics: random networks follow Wigner's semicircular
law whereas scale-free networks exhibit a triangular distribution. In this
paper we show that the spectral density of hierarchical networks follow a very
different pattern, which can be used as a fingerprint of modularity. Of
particular importance is the value , related to the homeostatic
response of the network: it is maximum for random and scale free networks but
very small for hierarchical modular networks. It is also large for an actual
biological protein-protein interaction network, demonstrating that the current
leading model for such networks is not adequate.Comment: 4 pages 14 figure
Determination of the Elastic Constants of Composites Through the Inversion of Leaky Lamb Wave Data
Analysis and prediction of the response of composite laminates to external loads are essential for the design of composite structures. This in turn requires a precise knowledge of their mechanical properties including their constitutive behavior. It is reasonable to assume that, in the bulk, the overall behavior of unidirectional graphite/epoxy composites is the same as that of a homogeneous, transversely isotropic material with its symmetry axis along the fiber direction. Then the linear elastic response of the material can be described by means of five elastic constants. If the values of these constants can be determined, then the stress analysis of a laminate with a given number and stacking order of the laminae can, in principle, be carried out. However, the measurement of the elastic constants by conventional, destructive techniques is difficult and often, inaccurate. Thus, the availability of alternative, preferably nondestructive methods, for the determination of the elastic costants of the material would be extremely helpfu
Phase transition in the bounded one-dimensional multitrap system
We have previously discussed the diffusion limited problem of the bounded
one-dimensional multitrap system where no external fiel is included and pay
special attention to the transmission of the diffusing particles through the
system of imperfect traps. We discuss here the case in which an external field
is included to each trap and find not only the transmission but also the energy
associated with the diffusing particles in the presence and absence of such
fields. From the energy we find the specific heat and show that for
certain values of the parameters associated with the multitrap system it
behaves in a manner which is suggestive of phase transition. Moreover, this
phase transition is demonstrated not only through the conventional single peak
at which the specific heat function is undifferentiable but also through the
less frequent phenomenon of double peaks.Comment: 25 pages, 6 PS Figures, there have been introduced many changes
including the remove of two figure
Neuroprotective Effect of Hyperbaric Oxygen Therapy on Anterior Ischemic Optic Neuropathy
The study investigated the therapeutic effect of hyperbaric oxygen (HBO) on anterior ischemic optic neuropathy in a rodent model (rAION). rAION was laser-induced in one eye of 63 mice. The fellow (uninjured) eye served as an internal control. Thirty-three mice underwent two 90-min sessions of 100% oxygen (2âatm) treatment immediately following injury and one session daily thereafter for up to 14âdays. The remaining mice were untreated. Retinas were harvested at different time points, and mRNA levels of various genes were analyzed by real-time polymerase chain reaction and histologic study. Untreated mice: day 1 post-rAION â SOD-1 (oxidative-stress-related) decreased to 82% of control (uninjured eye) levels (Pâ<â0.05), Caspase-3 (proapoptotic) decreased to 89%, Bcl-xL mildly increased (117%; all NS); day 3 â HO-1 and endothelial nitric oxide synthase (eNOS; ischaemia-related) decreased to 74%, and Bcl-2-associated X protein, Caspase-3, and B-cell lymphoma 2 (Bcl-2; apoptotic) increased by 170, 120, and 111%, respectively (all NS); day 21 â HO-1 increased to 222% (NS) and eNOS decreased to 48% (Pâ<â0.05). Treated mice: day 1 â SOD-1 and Caspase-3 remained unchanged, Bcl-2 and Bcl-xL mildly increased (112 and 126% respectively); day 3 â HO-1 and eNOS increased, apoptosis-related gene decreased; day 21 â SOD-1 decreased whereas eNOS increased (Pâ<â0.05), and HO-1 increased to a lesser degree than without treatment. None of the oxygen-treated animals had retinal ganglion cell loss or a decrease in Thy-1 expression. In conclusion, HBO treatment after rAION induction influences the expression of apoptosis-related genes as well as oxidative-stress-induced and ischaemia-related genes and may exert a neuroprotective effect
CP Nonconservation in at the Tevatron
The reaction is found to be rather rich in exhibiting
several different types of CP asymmetries. The spin of the top quark plays an
important role. Asymmetries are related to form factors arising from radiative
corrections of the production vertex due to non-standard physics. As
illustrations, effects are studied in two Higgs Doublet Models and in
Supersymmetric Models; asymmetries up to a few percent may be possible.Comment: 14 pages, 3 figures. Note: replaced due to minor problems that
appeared on some postscript previewers. No change in conten
A k-shell decomposition method for weighted networks
We present a generalized method for calculating the k-shell structure of
weighted networks. The method takes into account both the weight and the degree
of a network, in such a way that in the absence of weights we resume the shell
structure obtained by the classic k-shell decomposition. In the presence of
weights, we show that the method is able to partition the network in a more
refined way, without the need of any arbitrary threshold on the weight values.
Furthermore, by simulating spreading processes using the
susceptible-infectious-recovered model in four different weighted real-world
networks, we show that the weighted k-shell decomposition method ranks the
nodes more accurately, by placing nodes with higher spreading potential into
shells closer to the core. In addition, we demonstrate our new method on a real
economic network and show that the core calculated using the weighted k-shell
method is more meaningful from an economic perspective when compared with the
unweighted one.Comment: 17 pages, 6 figure
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Structural Characterization of Charcoal Exposed to High and Low pH: Implications for 14C Sample Preparation and Charcoal Preservation
Chemical and structural similarities between poorly preserved charcoal and its contaminants, as well as low radiocarbon concentrations in old samples, complicate 14C age determinations. Here, we characterize 4 fossil charcoal samples from the late Middle Paleolithic and early Upper Paleolithic strata of Kebara Cave, Israel, with respect to the structural and chemical changes that occur when they are subjected to the acid-base-acid (ABA) treatment. Differential thermal analysis and TEM show that acid treatment disrupts the structure, whereas alkali treatment results in the reformation of molecular aggregates. The major changes are ascribed to the formation of salt bridges at high pH and the disruption of the graphite-like crystallites at low pH. Weight losses during the treatments are consistently greater for older samples, implying that they are less well preserved. Based on the changes observed in vitro due to pH fluctuations, various methods for removing contamination, as well as a mechanism for preferential preservation of charcoal in nature, are proposed.Anthropolog
Greedy D-Approximation Algorithm for Covering with Arbitrary Constraints and Submodular Cost
This paper describes a simple greedy D-approximation algorithm for any
covering problem whose objective function is submodular and non-decreasing, and
whose feasible region can be expressed as the intersection of arbitrary (closed
upwards) covering constraints, each of which constrains at most D variables of
the problem. (A simple example is Vertex Cover, with D = 2.) The algorithm
generalizes previous approximation algorithms for fundamental covering problems
and online paging and caching problems
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