18,607 research outputs found
Averaged residence times of stochastic motions in bounded domains
Two years ago, Blanco and Fournier (Blanco S. and Fournier R., Europhys.
Lett. 2003) calculated the mean first exit time of a domain of a particle
undergoing a randomly reoriented ballistic motion which starts from the
boundary. They showed that it is simply related to the ratio of the volume's
domain over its surface. This work was extended by Mazzolo (Mazzolo A.,
Europhys. Lett. 2004) who studied the case of trajectories which start inside
the volume. In this letter, we propose an alternative formulation of the
problem which allows us to calculate not only the mean exit time, but also the
mean residence time inside a sub-domain. The cases of any combinations of
reflecting and absorbing boundary conditions are considered. Lastly, we
generalize our results for a wide class of stochastic motions.Comment: 7 pages, 3 figure
First exit times and residence times for discrete random walks on finite lattices
In this paper, we derive explicit formulas for the surface averaged first
exit time of a discrete random walk on a finite lattice. We consider a wide
class of random walks and lattices, including random walks in a non-trivial
potential landscape. We also compute quantities of interest for modelling
surface reactions and other dynamic processes, such as the residence time in a
subvolume, the joint residence time of several particles and the number of hits
on a reflecting surface.Comment: 19 pages, 2 figure
In pursuit of causality in leadership training research: A review and pragmatic recommendations
Although research shows a reliable association between leadership training and positive organizational outcomes, a range of research design issues mean we do not know to what degree the former causes the later. Accordingly, the paper has two main aims. First, to describe the conditions necessary to determine causality in leadership training research and the ability of different research designs to achieve this. Six important, but often ignored, issues associated with determining causality are described (control conditions, sample representation, condition randomization, condition independence, temporal design, and author involvement). Second, to review the extent to which the leadership training literature is able to demonstrate causality. The review shows that the majority of studies do not meet many of the criteria, even the most basic criteria, required to establish causality. Finally, we provide guidelines for designing future research to improve causal identification and is capable of generating meaningful theory and policy recommendations
Wake Flows in Coastal Oceans: An Experimental Study of Topographic Effects
We consider the effects of coastal topography on the wake of an idealised headland model in a laboratory flume. Under a range of Reynolds numbers relevant to coastal oceans, we find that coherent eddies interact strongly with the headland shear layer and wake, affecting the width of the shear layer and the length of the wake. A preliminary investigation of turbulence statistics indicates that topography upstream of a headland can lead to a wider shear layer, a headland wake that extends further downstream, and enhanced horizontal diffusion out of the wake relative to the case with unperturbed oncoming flow
Love kills: Simulations in Penna Ageing Model
The standard Penna ageing model with sexual reproduction is enlarged by
adding additional bit-strings for love: Marriage happens only if the male love
strings are sufficiently different from the female ones. We simulate at what
level of required difference the population dies out.Comment: 14 pages, including numerous figure
Extreme times in financial markets
We apply the theory of continuous time random walks to study some aspects of
the extreme value problem applied to financial time series. We focus our
attention on extreme times, specifically the mean exit time and the mean
first-passage time. We set the general equations for these extremes and
evaluate the mean exit time for actual data.Comment: 6 pages, 3 figure
Chandra X-Ray Study of Galactic Supernova Remnant G299.2-2.9
We report on observations of the Galactic supernova remnant (SNR)
G299.22.9 with the {\it Chandra X-Ray Observatory}. The high resolution
images with {\it Chandra} resolve the X-ray-bright knots, shell, and diffuse
emission extending beyond the bright shell. Interior to the X-ray shell is
faint diffuse emission occupying the central regions of the SNR.
Spatially-resolved spectroscopy indicates a large foreground absorption
( 3.5 10 cm), which supports a
relatively distant location ( 5 kpc) for the SNR. The blast wave is
encountering a highly inhomogeneous ambient medium with the densities ranging
over more than an order of magnitude ( 0.1 4 cm).
Assuming the distance of 5 kpc, we derive a Sedov age of
4500 yr and an explosion energy of 1.6 10
ergs. The ambient density structure and the overall morphology suggest that
G299.22.9 may be a limb-brightened partial shell extending to 7 pc
radius surrounded by fainter emission extending beyond that to a radius of
9 pc. This suggests the SNR exploded in a region of space where there is
a density gradient whose direction lies roughly along the line of sight. The
faint central region shows strong line emission from heavy elements of Si and
Fe, which is caused by the presence of the overabundant stellar ejecta there.
We find no evidence for stellar ejecta enriched in light elements of O and Ne.
The observed abundance structure of the metal-rich ejecta supports a Type Ia
origin for G299.22.9.Comment: 16 pages (AASTex emulator style), 3 Tables, 10 Figures (including 1
color: Figure 1), Accepted by Ap
3D geological models and their hydrogeological applications : supporting urban development : a case study in Glasgow-Clyde, UK
Urban planners and developers in some parts of the United Kingdom can now access geodata in an easy-to-retrieve and understandable format. 3D attributed geological framework models and associated GIS outputs, developed by the British Geological Survey (BGS), provide a predictive tool for planning site investigations for some of the UK's largest regeneration projects in the Thames and Clyde River catchments.
Using the 3D models, planners can get a 3D preview of properties of the subsurface using virtual cross-section and borehole tools in visualisation software, allowing critical decisions to be made before any expensive site investigation takes place, and potentially saving time and money. 3D models can integrate artificial and superficial deposits and bedrock geology, and can be used for recognition of major resources (such as water, thermal and sand and gravel), for example in buried valleys, groundwater modelling and assessing impacts of underground mining. A preliminary groundwater recharge and flow model for a pilot area in Glasgow has been developed using the 3D geological models as a framework.
This paper focuses on the River Clyde and the Glasgow conurbation, and the BGS's Clyde Urban Super-Project (CUSP) in particular, which supports major regeneration projects in and around the City of Glasgow in the West of Scotland
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