78,782 research outputs found
Microscopic chaos and diffusion
We investigate the connections between microscopic chaos, defined on a
dynamical level and arising from collisions between molecules, and diffusion,
characterized by a mean square displacement proportional to the time. We use a
number of models involving a single particle moving in two dimensions and
colliding with fixed scatterers. We find that a number of microscopically
nonchaotic models exhibit diffusion, and that the standard methods of chaotic
time series analysis are ill suited to the problem of distinguishing between
chaotic and nonchaotic microscopic dynamics. However, we show that periodic
orbits play an important role in our models, in that their different properties
in chaotic and nonchaotic systems can be used to distinguish such systems at
the level of time series analysis, and in systems with absorbing boundaries.
Our findings are relevant to experiments aimed at verifying the existence of
chaoticity and related dynamical properties on a microscopic level in diffusive
systems.Comment: 28 pages revtex, 14 figures incorporated with epsfig; see also
chao-dyn/9904041; revised to clarify the definition of chaos and include
discussion of a mixed model with both square and circular scatterer
Microscopic chaos from Brownian motion?
A recent experiment on Brownian motion has been interpreted to exhibit direct
evidence for microscopic chaos. In this note we demonstrate that virtually
identical results can be obtained numerically using a manifestly
microscopically nonchaotic system.Comment: 3 pages, 1 figure, Comment on P. Gaspard et al, Nature vol 394, 865
(1998); rewritten in a more popular styl
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Documentation Related to a 1991 Observation of Sturgeon in the Rio Grande – RÃo Bravo, USA (Texas) and Mexico (Coahuila)
This digital archive provides a compilation of previously unpublished information regarding a 1991 observation of a live sturgeon (Family Acipenseridae) in the Rio Grande-RÃo Bravo of the USA and Mexico. Though a few specimens collected in the 19th century support occurrence of sturgeon in this river basin, lack of credible, recent records has often led to this species not being recognized as part of the basin’s native fish fauna, and certainly not part of its modern fish community.
The second and third authors of this document manage the Fishes of Texas Project (Hendrickson, Dean A., & Cohen, Adam E. (2015). Fishes of Texas Project Database (version 2.0). Texas Advanced Computing Center, University of Texas at Austin. http://doi.org/10.17603/C3WC70) and knew of the unpublished 1991 observation of sturgeon reported here. They requested the content provided here from first author (Platania) who provided what follows below (verbatim as received in April 2018) and permission to archive it for public access.Integrative Biolog
Development of a phase-change thermal storage system using modified anhydrous sodium hydroxide for solar electric power generation
A thermal storage system for use in solar power electricity generation was investigated analytically and experimentally. The thermal storage medium is principally anhydrous NaOH with 8% NaNO3 and 0.2% MnO2. Heat is charged into storage at 584 K and discharged from storage at 582 K by Therminol-66. Physical and thermophysical properties of the storage medium were measured. A mathematical simulation and computer program describing the operation of the system were developed. A 1/10 scale model of a system capable of storing and delivering 3.1 x 10 to the 6th power kJ of heat was designed, built, and tested. Tests included steady state charging, discharging, idling, and charge-discharge conditions simulating a solar daily cycle. Experimental data and computer-predicted results are correlated. A reference design including cost estimates of the full-size system was developed
Stream Sampling for Frequency Cap Statistics
Unaggregated data, in streamed or distributed form, is prevalent and come
from diverse application domains which include interactions of users with web
services and IP traffic. Data elements have {\em keys} (cookies, users,
queries) and elements with different keys interleave. Analytics on such data
typically utilizes statistics stated in terms of the frequencies of keys. The
two most common statistics are {\em distinct}, which is the number of active
keys in a specified segment, and {\em sum}, which is the sum of the frequencies
of keys in the segment. Both are special cases of {\em cap} statistics, defined
as the sum of frequencies {\em capped} by a parameter , which are popular in
online advertising platforms. Aggregation by key, however, is costly, requiring
state proportional to the number of distinct keys, and therefore we are
interested in estimating these statistics or more generally, sampling the data,
without aggregation. We present a sampling framework for unaggregated data that
uses a single pass (for streams) or two passes (for distributed data) and state
proportional to the desired sample size. Our design provides the first
effective solution for general frequency cap statistics. Our -capped
samples provide estimates with tight statistical guarantees for cap statistics
with and nonnegative unbiased estimates of {\em any} monotone
non-decreasing frequency statistics. An added benefit of our unified design is
facilitating {\em multi-objective samples}, which provide estimates with
statistical guarantees for a specified set of different statistics, using a
single, smaller sample.Comment: 21 pages, 4 figures, preliminary version will appear in KDD 201
Large Magnetic Fields and Motions of OH Masers in W75 N
We report on a second epoch of VLBA observations of the 1665 and 1667 MHz OH
masers in the massive star-forming region W75 N. We find evidence to confirm
the existence of very strong (~40 mG) magnetic fields near source VLA 2. The
masers near VLA 2 are dynamically distinct and include a very bright spot
apparently moving at 50 km/s relative to those around VLA 1. This fast-moving
spot may be an example of a rare class of OH masers seen in outflows in
star-forming regions. Due to the variability of these masers and the rapidity
of their motions, tracking these motions will require multiple observations
over a significantly shorter time baseline than obtained here. Proper motions
of the masers near VLA 1 are more suggestive of streaming along magnetized
shocks rather than Keplerian rotation in a disk. The motions of the easternmost
cluster of masers in W75 N (B) may be tracing slow expansion around an unseen
exciting source.Comment: 7 pages including 4 figures (2 color) & 3 tables, to appear in Ap
Holocene-Neogene volcanism in northeastern Australia: chronology and eruption history
Quaternary and late Neogene volcanism is widespread in northeastern Australia, producing at least 397 eruptions covering more than 20,000 km2, including at least 20 flows over 50 km long. Despite this abundance of young volcanism, before this study numerous eruptions had tentative ages or were undated, and the area requires a comprehensive evaluation of eruption patterns through time. To help address these issues we applied multi-collector ARGUS-V 40Ar/39Ar geochronology to determine the age of four of the younger extensive flows: Undara (160 km long, 189 ± 4/4 ka; 2σ, with full analytical/external uncertainties), Murronga (40 km long, 153 ± 5/5 ka), Toomba (120 km long, 21 ± 3/3 ka), and Kinrara (55 km long, 7 ± 2/2 ka). Verbal traditions of the Gugu Badhun Aboriginal people contain features that may potentially describe the eruption of Kinrara. If the traditions do record this eruption, they would have been passed down for 230 ± 70 generations – a period of time exceeding the earliest written historical records. To further examine north Queensland volcanism through time we compiled a database of 337 ages, including 179 previously unpublished K-Ar and radiocarbon results. The compiled ages demonstrate that volcanic activity has occurred without major time breaks since at least 9 Ma. The greatest frequency of eruptions occurred in the last 2 Ma, with an average recurrence interval of <10–22 ka between eruptions. Activity was at times likely more frequent than these calculations indicate, as the geochronologic dataset is incomplete, with undated eruptions, and intraplate volcanism is often episodic. The duration, frequency, and youthfulness of activity indicate that north Queensland volcanism should be considered as potentially still active, and there are now two confirmed areas of Holocene volcanism in eastern Australia – one at each end of the continent. More broadly, our data provides another example of 40Ar/39Ar geochronology applied to Holocene and latest Pleistocene mafic eruptions, further demonstrating that this method has the ability to examine eruptions and hazards at the youngest volcanoes on Earth
Stability of attitude control systems acted upon by random perturbations
Mathematical models on stability of attitude control systems acted upon by random perturbation processe
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