23 research outputs found
Economic Fluctuations and Diffusion
Stock price changes occur through transactions, just as diffusion in physical
systems occurs through molecular collisions. We systematically explore this
analogy and quantify the relation between trading activity - measured by the
number of transactions - and the price change ,
for a given stock, over a time interval . To this end, we
analyze a database documenting every transaction for 1000 US stocks over the
two-year period 1994-1995. We find that price movements are equivalent to a
complex variant of diffusion, where the diffusion coefficient fluctuates
drastically in time. We relate the analog of the diffusion coefficient to two
microscopic quantities: (i) the number of transactions in
, which is the analog of the number of collisions and (ii) the local
variance of the price changes for all transactions in , which is the analog of the local mean square displacement between
collisions. We study the distributions of both and , and find that they display power-law tails. Further, we find that
displays long-range power-law correlations in time, whereas
does not. Our results are consistent with the interpretation
that the pronounced tails of the distribution of w_{\Delta t}|
G_{\Delta t} |N_{\Delta t}$.Comment: RevTex 2 column format. 6 pages, 36 references, 15 eps figure
Correlation search for coherent pion emission in heavy ion collisions
The methods allowing to extract the coherent component of pion emission
conditioned by the formation of a quasi-classical pion source in heavy ion
collisions are suggested. They exploit a nontrivial modification of the quantum
statistical and final state interaction effects on the correlation functions of
like and unlike pions in the presence of the coherent radiation. The extraction
of the coherent pion spectrum from pi+pi-, pi+pi+ and pi-pi- correlation
functions and single--pion spectra is discussed in detail for large expanding
systems produced in ultra-relativistic heavy ion collisions.Comment: 21 pages, 3 eps figures, ReVTeX, corrected submission abstract.
Version published in PRC 65 (2002) 064904. Added is a detailed explanation of
the differences between pure coherent states and charge constrained coherent
states in the case of a simple example model. The expressions for
two-particle spectra taking into account both the final state interaction and
the coherent component of pion emission are derived in a more general and
transparent wa
Manufacture of biodegradable scaffold and cell adhesion studies on different surface morphology
Multiphoton imaging of cardiovascular structures
Near infrared (NIR) femtosecond laser imaging systems represent a novel and very promising diagnostic technology for non-invasive cross-sectional analysis of living biological tissues. In this study 3D multiphoton imaging with submicron resolution has been performed for non-invasive analysis of living native and tissue-engineered (TE) heart valves and blood vessels. High-resolution autofluorescence and second harmonic generation (SHG) images of collagenous structures and elastic fibers were demonstrated using multiphoton excitation at two different wavelengths. Non-invasive optical sections have been obtained without the need of staining or embedding. The quality of the resulting three-dimensional images allowed exact differentiation between collagenous structures and elastic fibers. These experimental results are very encouraging for NIR femtosecond laser scanning microscopy as a useful tool for future non-destructive monitoring and characterization of vital and intact TE cardiovascular structures
Facilitated non-invasive visualization of collagen and elastin in blood vessels
Multiphoton imaging is a powerful tool for three-dimensional visualization of extracellular matrix components such as collagen and elastin in fresh, nonfixed, and nonembedded tissues. We have previously published data on the induction of the second harmonic generation signal of collagen and autofluorescence of elastin using a tunable multiphoton laser system. Without staining, a second harmonic generation signal was detected for collagen when excited at wavelength lambda(ind ex) = 840 nm. Switching the excitation wavelength to 760 nm enabled visualization of elastic fiber structures. A limitation of this technology is the laser-tuning process that requires calibration of the system in between the studies. Now we have developed a facilitated method for studying tissues and tissue equivalents that enables simultaneous visualization of collagen and elastin structures using only a single excitation wavelength of 840 nm in combination with two different band-pass filters. This facilitated method will expand the range of application by reducing required time and expenses for the laser system without reducing its capability
Tissue-Engineered Heart Valve Leaflets: An Effective Method for Seeding Autologous Cells on Scaffolds
Numerical simulation techniques to study the structural response of the human chest following median sternotomy
Numerical simulation techniques to study the structural response of the human chest following median sternotom
Age-related changes in the elastic tissue of the human aorta
Background: Age-related arterial alterations affecting cells, matrix and biomolecules are the main culprit for initiation and progression of cardiovascular disease. The objective of this study is to gain further insights into the complex mechanism of elastic tissue ageing in human aortic blood vessels. Methods: One hundred and nineteen human aortic tissue samples were collected from adult patients (101 males, 18 females; age 40-86 years) undergoing coronary artery bypass grafting. Overall extracellular matrix architecture was examined by multiphoton laser scanning microscopy and histology. Matrix metalloproteinases 2 and 9, corresponding tissue inhibitors 1 and 2 as well as desmosine were determined. mRNA levels of tropoelastin were assessed by quantitative RT-PCR. Results: Age-related destruction of the vascular elastic laminas as well as a loss of interlamina cross-links were observed by laser scanning microscopy. These results were confirmed by histology indicating increasing interlamma gaps. There were no significant differences in matrix turnover or desmosine content. A steady decrease in tropoelastin mRNA by about 50% per 10 years of age increase was observed. Conclusions: Our findings indicate that ageing is accompanied by a destruction of the elastic vascular structure. However, tropoelastin expression analysis suggests that elastogenesis occurs throughout life with constantly decreasing levels