351 research outputs found
Elastic properties of small-world spring networks
We construct small-world spring networks based on a one dimensional chain and
study its static and quasistatic behavior with respect to external forces.
Regular bonds and shortcuts are assigned linear springs of constant and
, respectively. In our models, shortcuts can only stand extensions less
than beyond which they are removed from the network. First we
consider the simple cases of a hierarchical small-world network and a complete
network. In the main part of this paper we study random small-world networks
(RSWN) in which each pair of nodes is connected by a shortcut with probability
. We obtain a scaling relation for the effective stiffness of RSWN when
. In this case the extension distribution of shortcuts is scale free with
the exponent -2. There is a strong positive correlation between the extension
of shortcuts and their betweenness. We find that the chemical end-to-end
distance (CEED) could change either abruptly or continuously with respect to
the external force. In the former case, the critical force is determined by the
average number of shortcuts emanating from a node. In the latter case, the
distribution of changes in CEED obeys power laws of the exponent with
.Comment: 16 pages, 14 figures, 1 table, published versio
Design and Applications of In-Situ Differential Scanning Electron Microscopy
Contrast enhancement in the scanning electron microscope (SEM) is usually achieved by either of the two techniques of black level suppression, and differential imaging. This paper is mainly concerned with the latter method. Differential imaging of SEM images is commonly accomplished by either using a selective electronic filtering circuit (time sensitive) on the video signals, or the post processing of a collected digitized image (application of special kernel operatives). A technique is described that is capable of generating true in-situ SEM differential video signals of local sample features. Characteristics of this method are enhanced sample feature-boundary sensitivity, suppression of large background signals, and the ability to perform critical pattern alignments prior to feature measurements. Results are presented on the application of the technique to the general field of electron microscopy, as well as to integrated circuit micro-metrology
An investigation on cardioprotective potential of Marrubium vulgare aqueous fraction against ischaemia-reperfusion injury in isolated rat heart
Background: The aim of this study was to evaluate the cardioprotective effects of aqueous fraction of Marrubium vulgare hydroalcoholic extract on cardiac parameters in ischaemic-reperfused isolated rat hearts.
Materials and methods: The aerial parts of the plant were extracted with methanol 70% by maceration. The water-soluble portion of the total hydroalcoholic extract was prepared with liquid-liquid extraction (LLE). Afterwards, the antioxidant activity, total phenolic and flavonoids content of the aqueous fraction were determined. In order to evaluate the effects of the aqueous fraction on cardiac parameters and ischaemia-reperfusion (I/R) injury, the Langendroff method was used on male Wistar rats. Harvested hearts were cannulated immediately to the Langendroff apparatus and subjected into 30 min regional ischaemia and 2 h reperfusion, either by a modified Krebs-Henseleit buffer (KHB) solution or enriched KHB solution with plant extract (10, 20, 40 μg/mL).
Results: The aqueous fraction was found to be a scavenger of DPPH radical with RC50 value of 47 μg/mL. The total phenolic and flavonoids content of the fraction was 6.05 g gallic acid equivalent and 36.13 mg quercetin equivalent per 100 g of dry plant material. In addition, 40 μg/mL of Marrubium vulgare aqueous fraction significantly decreased infarct size in comparison to control group. All doses considerably reduced the total ventricular ectopic beats during 30 min of ischaemia. The extract at dose of 40 μg/mL noticeably decreased the arrhythmias during the first 30 min of reperfusion.
Conclusions: The results of the study indicated aqueous fraction of Marrubium vulgare possesses a protective effect against I/R injuries in isolated rat heart
Stochastic Analysis and Regeneration of Rough Surfaces
We investigate Markov property of rough surfaces. Using stochastic analysis
we characterize the complexity of the surface roughness by means of a
Fokker-Planck or Langevin equation. The obtained Langevin equation enables us
to regenerate surfaces with similar statistical properties compared with the
observed morphology by atomic force microscopy.Comment: 4 pages, 7 figure
Localization of elastic waves in heterogeneous media with off-diagonal disorder and long-range correlations
Using the Martin-Siggia-Rose method, we study propagation of acoustic waves
in strongly heterogeneous media which are characterized by a broad distribution
of the elastic constants. Gaussian-white distributed elastic constants, as well
as those with long-range correlations with non-decaying power-law correlation
functions, are considered. The study is motivated in part by a recent discovery
that the elastic moduli of rock at large length scales may be characterized by
long-range power-law correlation functions. Depending on the disorder, the
renormalization group (RG) flows exhibit a transition to localized regime in
{\it any} dimension. We have numerically checked the RG results using the
transfer-matrix method and direct numerical simulations for one- and
two-dimensional systems, respectively.Comment: 5 pages, 4 figures, to appear in Phys. Rev. Let
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