443 research outputs found
Moisture processes accompanying convective activity
A moisture budget analysis was performed on data collected during the AVE 7 (May 2 to 3, 1978) and AVE-SESAME1 (April 10 to 11, 1979) experiments. Local rates-of-change of moisture were compared with average moisture divergence in the same time period. Results were presented as contoured plots in the horizontal and as vertical cross sections. These results were used to develop models of the distribution of moisture processes in the vicinity of convective areas in two layers representing lower and middle tropospheric conditions. Good correspondence was found between the residual term of the moisture budget and actual precipitation
Dynamic structural and topological phase transitions on the Warsaw Stock Exchange: A phenomenological approach
We study the crash dynamics of the Warsaw Stock Exchange (WSE) by using the
Minimal Spanning Tree (MST) networks. We find the transition of the complex
network during its evolution from a (hierarchical) power law MST network,
representing the stable state of WSE before the recent worldwide financial
crash, to a superstar-like (or superhub) MST network of the market decorated by
a hierarchy of trees (being, perhaps, an unstable, intermediate market state).
Subsequently, we observed a transition from this complex tree to the topology
of the (hierarchical) power law MST network decorated by several star-like
trees or hubs. This structure and topology represent, perhaps, the WSE after
the worldwide financial crash, and could be considered to be an aftershock. Our
results can serve as an empirical foundation for a future theory of dynamic
structural and topological phase transitions on financial markets
Helioseismology and the solar age
The problem of measuring the solar age by means of helioseismology hasbeen
recently revisited by Guenther & Demarque (1997) and by Weiss & Schlattl
(1998). Different best values for and different assessment of
the uncertainty resulted from these two works. We show that depending on the
way seismic data are used, one may obtain the value
Gy, close to the age of the oldest meteorites, Gy, like in
the first paper, or above 5 Gy like in the second paper. The discrepancy in the
seismic estimates of the solar age may be eliminated by assuming higher than
the standard metal abundance and/or an upward revision of the opacities in the
solar radiative interior.We argue that the most accurate and robust seismic
measure of the solar age are the small frequency separations,
, for spherical harmonic degrees
and radial orders .The seismic age inferred by
minimization of the sum of squared differences between the model and the solar
small separations is , a number consistent with
meteoritic data.Our analysis supports earlier suggestions of using small
frequency separations as stellar age indicators.Comment: 8 pages + 4 ps figures included, LaTeX file with l-aa.sty, submitted
to Astronomy and Astrophysic
Structural and topological phase transitions on the German Stock Exchange
We find numerical and empirical evidence for dynamical, structural and
topological phase transitions on the (German) Frankfurt Stock Exchange (FSE) in
the temporal vicinity of the worldwide financial crash. Using the Minimal
Spanning Tree (MST) technique, a particularly useful canonical tool of the
graph theory, two transitions of the topology of a complex network representing
FSE were found. First transition is from a hierarchical scale-free MST
representing the stock market before the recent worldwide financial crash, to a
superstar-like MST decorated by a scale-free hierarchy of trees representing
the market's state for the period containing the crash. Subsequently, a
transition is observed from this transient, (meta)stable state of the crash, to
a hierarchical scale-free MST decorated by several star-like trees after the
worldwide financial crash. The phase transitions observed are analogous to the
ones we obtained earlier for the Warsaw Stock Exchange and more pronounced than
those found by Onnela-Chakraborti-Kaski-Kert\'esz for S&P 500 index in the
vicinity of Black Monday (October 19, 1987) and also in the vicinity of January
1, 1998. Our results provide an empirical foundation for the future theory of
dynamical, structural and topological phase transitions on financial markets
Statistical analysis of 22 public transport networks in Poland
Public transport systems in 22 Polish cities have been analyzed. Sizes of
these networks range from N=152 to N=2881. Depending on the assumed definition
of network topology the degree distribution can follow a power law or can be
described by an exponential function. Distributions of paths in all considered
networks are given by asymmetric, unimodal functions. Clustering, assortativity
and betweenness are studied. All considered networks exhibit small world
behavior and are hierarchically organized. A transition between dissortative
small networks N=500 is observed.Comment: 11 pages, 17 figures, 2 tables, REVTEX4 forma
Universal scaling of distances in complex networks
Universal scaling of distances between vertices of Erdos-Renyi random graphs,
scale-free Barabasi-Albert models, science collaboration networks, biological
networks, Internet Autonomous Systems and public transport networks are
observed. A mean distance between two nodes of degrees k_i and k_j equals to
=A-B log(k_i k_j). The scaling is valid over several decades. A simple
theory for the appearance of this scaling is presented. Parameters A and B
depend on the mean value of a node degree _nn calculated for the nearest
neighbors and on network clustering coefficients.Comment: 4 pages, 3 figures, 1 tabl
Thermally Stable Nuclear Burning on Accreting White Dwarfs
One of the challenges to increasing the mass of a white dwarf through
accretion is the tendency for the accumulating hydrogen to ignite unstably and
potentially trigger mass loss. It has been known for many years that there is a
narrow range of accretion rates for which the hydrogen can burn stably,
allowing for the white dwarf mass to increase as a pure helium layer
accumulates. We first review the physics of stable burning, providing a clear
explanation for why radiation pressure stabilization leads to a narrow range of
accretion rates for stable burning near the Eddington limit, confirming the
recent work of Nomoto and collaborators. We also explore the possibility of
stabilization due to a high luminosity from beneath the burning layer. We then
examine the impact of the beta-decay-limited ''hot'' CNO cycle on the stability
of burning. Though this plays a significant role for accreting neutron stars,
we find that for accreting white dwarfs, it can only increase the range of
stably-burning accretion rates for metallicities below 0.01 solar metallicity.Comment: Accepted for publication in The Astrophysical Journal, 7 pages, 4
figures; v2: Minor changes to correct typos and clarify conten
Grain size influences the corrosion and cavitation of Ni3Al intermetallic alloys
Influence of grain size on corrosion and cavitation of the Ni3Al - based intermetallic alloy was studied in recent paper. The research was conducted on Ni3Al - based intermetallic alloy doped with boron and zirconium. The initial grain size of 6, 20 and 45 μm the investigated samples was obtained through cold rolling followed by recrystallization annealing. It was found that initial grain size does not influence the breakthrough potential neither repassivation potential. On the other hand, various types of pits were found for alloys with different grain size during corrosion tests in sodium chloride solutions. It was found that increase of grain size results with reducing the depth of cavitational pits. However, surface area of the pits increases with increasing grain size
Silicon dendritic web material
The development of a low cost and reliable contact system for solar cells and the fabrication of several solar cell modules using ultrasonic bonding for the interconnection of cells and ethylene vinyl acetate as the potting material for module encapsulation are examined. The cells in the modules were made from dendritic web silicon. To reduce cost, the electroplated layer of silver was replaced with an electroplated layer of copper. The modules that were fabricated used the evaporated Ti, Pd, Ag and electroplated Cu (TiPdAg/Cu) system. Adherence of Ni to Si is improved if a nickel silicide can be formed by heat treatment. The effectiveness of Ni as a diffusion barrier to Cu and the ease with which nickel silicide is formed is discussed. The fabrication of three modules using dendritic web silicon and employing ultrasonic bonding for interconnecting calls and ethylene vinyl acetate as the potting material is examined
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