25 research outputs found
A survey of vernal pools and the effects of climate change on artificially constructed vernal pool replicates.
Rivers, Lakes, & Wetlands and General EcologyVernal pools are important temporary wetlands that support a wide variety of macroinvertebrates and provide safe breeding grounds for amphibians. These pools are precipitation-filled and thus, their hydrology is dependent on precipitation and evaporation; this makes them particularly sensitive to climate. We surveyed three relatively unstudied vernal pools in order to analyze their importance in maintaining high woodland biodiversity and lay baseline data to aid future research. We sampled the chemical and biotic features of the pools. In addition, we studied effects of climate change on vernal pools; this issue is of particular importance given the sensitivity of vernal pools to climate. In order to do this, climate change was simulated on a series of artificially created pools in a mesocosm experiment that assessed algae biomass. We found that climate change did not significantly affect algae biomass. In addition, we analyzed the validity of our mesocosm by comparing the nutrient levels and algae production in our artificial pools to the natural pools we surveyed. Phosphorous levels were found to be significantly higher in the artificial pools and algae biomass was found to be significantly different between the artificial and natural pools. However, the artificial system accurately replicated the biotic community of the natural pools. Our study revealed that algae is resilient and can withstand the predicted effects of climate change. This is of considerable importance to vernal pool communities.http://deepblue.lib.umich.edu/bitstream/2027.42/78507/1/Sasamoto_Ben_2010.pd
From interacting particle systems to random matrices
In this contribution we consider stochastic growth models in the
Kardar-Parisi-Zhang universality class in 1+1 dimension. We discuss the large
time distribution and processes and their dependence on the class on initial
condition. This means that the scaling exponents do not uniquely determine the
large time surface statistics, but one has to further divide into subclasses.
Some of the fluctuation laws were first discovered in random matrix models.
Moreover, the limit process for curved limit shape turned out to show up in a
dynamical version of hermitian random matrices, but this analogy does not
extend to the case of symmetric matrices. Therefore the connections between
growth models and random matrices is only partial.Comment: 18 pages, 8 figures; Contribution to StatPhys24 special issue; minor
corrections in scaling of section 2.
Kalamazoo River Watershed Land Conservation Plan
The Kalamazoo River Watershed Land Conservation Plan was developed to select for
conservation targets among ownership parcels in the Kalamazoo River Watershed (MI). The watershed,
while historically degraded, features large areas of preserved Midwestern habitats. To facilitate for the
permanent protection of these lands, this plan was developed using an ArcGIS-based analysis that
scored ownership parcels based on the following conservation criteria: land cover, presence of wetlands,
proximity to hydrology, proximity to existing conserved lands, presence of cold lands, and presence of
threatened and endangered species habitat. These criteria were developed using a literature review of
existing conservation plans and Kalamazoo River Watershed stakeholder input. The results from this
analysis were used to identify conservation priorities, including: the top 100 scoring parcels in the basin,
a database of the top 20% scoring parcels and their contact information, and priority subwatersheds for
conservation.Master of ScienceNatural Resources and EnvironmentUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/106543/1/KRWLCP_Final_2014.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/106543/2/KRWLCP_Owner_Database.xls
Stochastic Ballistic Annihilation and Coalescence
We study a class of stochastic ballistic annihilation and coalescence models
with a binary velocity distribution in one dimension. We obtain an exact
solution for the density which reveals a universal phase diagram for the
asymptotic density decay. By universal we mean that all models in the class are
described by a single phase diagram spanned by two reduced parameters. The
phase diagram reveals four regimes, two of which contain the previously studied
cases of ballistic annihilation. The two new phases are a direct consequence of
the stochasticity. The solution is obtained through a matrix product approach
and builds on properties of a q-deformed harmonic oscillator algebra.Comment: 4 pages RevTeX, 3 figures; revised version with some corrections,
additional discussion and in RevTeX forma
Vicious walk with a wall, noncolliding meanders, and chiral and Bogoliubov-deGennes random matrices
Spatially and temporally inhomogeneous evolution of one-dimensional vicious
walkers with wall restriction is studied. We show that its continuum version is
equivalent with a noncolliding system of stochastic processes called Brownian
meanders. Here the Brownian meander is a temporally inhomogeneous process
introduced by Yor as a transform of the Bessel process that is a motion of
radial coordinate of the three-dimensional Brownian motion represented in the
spherical coordinates. It is proved that the spatial distribution of vicious
walkers with a wall at the origin can be described by the eigenvalue-statistics
of Gaussian ensembles of Bogoliubov-deGennes Hamiltonians of the mean-field
theory of superconductivity, which have the particle-hole symmetry. We report
that the time evolution of the present stochastic process is fully
characterized by the change of symmetry classes from the type to the type
I in the nonstandard classes of random matrix theory of Altland and
Zirnbauer. The relation between the non-colliding systems of the generalized
meanders of Yor, which are associated with the even-dimensional Bessel
processes, and the chiral random matrix theory is also clarified.Comment: REVTeX4, 16 pages, 4 figures. v2: some additions and correction
A pedestrian's view on interacting particle systems, KPZ universality, and random matrices
These notes are based on lectures delivered by the authors at a Langeoog
seminar of SFB/TR12 "Symmetries and universality in mesoscopic systems" to a
mixed audience of mathematicians and theoretical physicists. After a brief
outline of the basic physical concepts of equilibrium and nonequilibrium
states, the one-dimensional simple exclusion process is introduced as a
paradigmatic nonequilibrium interacting particle system. The stationary measure
on the ring is derived and the idea of the hydrodynamic limit is sketched. We
then introduce the phenomenological Kardar-Parisi-Zhang (KPZ) equation and
explain the associated universality conjecture for surface fluctuations in
growth models. This is followed by a detailed exposition of a seminal paper of
Johansson that relates the current fluctuations of the totally asymmetric
simple exclusion process (TASEP) to the Tracy-Widom distribution of random
matrix theory. The implications of this result are discussed within the
framework of the KPZ conjecture.Comment: 52 pages, 4 figures; to appear in J. Phys. A: Math. Theo
Applications of Field-Theoretic Renormalization Group Methods to Reaction-Diffusion Problems
We review the application of field-theoretic renormalization group (RG)
methods to the study of fluctuations in reaction-diffusion problems. We first
investigate the physical origin of universality in these systems, before
comparing RG methods to other available analytic techniques, including exact
solutions and Smoluchowski-type approximations. Starting from the microscopic
reaction-diffusion master equation, we then pedagogically detail the mapping to
a field theory for the single-species reaction k A -> l A (l < k). We employ
this particularly simple but non-trivial system to introduce the
field-theoretic RG tools, including the diagrammatic perturbation expansion,
renormalization, and Callan-Symanzik RG flow equation. We demonstrate how these
techniques permit the calculation of universal quantities such as density decay
exponents and amplitudes via perturbative eps = d_c - d expansions with respect
to the upper critical dimension d_c. With these basics established, we then
provide an overview of more sophisticated applications to multiple species
reactions, disorder effects, L'evy flights, persistence problems, and the
influence of spatial boundaries. We also analyze field-theoretic approaches to
nonequilibrium phase transitions separating active from absorbing states. We
focus particularly on the generic directed percolation universality class, as
well as on the most prominent exception to this class: even-offspring branching
and annihilating random walks. Finally, we summarize the state of the field and
present our perspective on outstanding problems for the future.Comment: 10 figures include
Traffic and Related Self-Driven Many-Particle Systems
Since the subject of traffic dynamics has captured the interest of
physicists, many astonishing effects have been revealed and explained. Some of
the questions now understood are the following: Why are vehicles sometimes
stopped by so-called ``phantom traffic jams'', although they all like to drive
fast? What are the mechanisms behind stop-and-go traffic? Why are there several
different kinds of congestion, and how are they related? Why do most traffic
jams occur considerably before the road capacity is reached? Can a temporary
reduction of the traffic volume cause a lasting traffic jam? Under which
conditions can speed limits speed up traffic? Why do pedestrians moving in
opposite directions normally organize in lanes, while similar systems are
``freezing by heating''? Why do self-organizing systems tend to reach an
optimal state? Why do panicking pedestrians produce dangerous deadlocks? All
these questions have been answered by applying and extending methods from
statistical physics and non-linear dynamics to self-driven many-particle
systems. This review article on traffic introduces (i) empirically data, facts,
and observations, (ii) the main approaches to pedestrian, highway, and city
traffic, (iii) microscopic (particle-based), mesoscopic (gas-kinetic), and
macroscopic (fluid-dynamic) models. Attention is also paid to the formulation
of a micro-macro link, to aspects of universality, and to other unifying
concepts like a general modelling framework for self-driven many-particle
systems, including spin systems. Subjects such as the optimization of traffic
flows and relations to biological or socio-economic systems such as bacterial
colonies, flocks of birds, panics, and stock market dynamics are discussed as
well.Comment: A shortened version of this article will appear in Reviews of Modern
Physics, an extended one as a book. The 63 figures were omitted because of
storage capacity. For related work see http://www.helbing.org
FUNDUS AUTOFLUORESCENCE LIFETIMES AND CENTRAL SEROUS CHORIORETINOPATHY.
PURPOSE
To quantify retinal fluorescence lifetimes in patients with central serous chorioretinopathy (CSC) and to identify disease specific lifetime characteristics over the course of disease.
METHODS
Forty-seven participants were included in this study. Patients with central serous chorioretinopathy were imaged with fundus photography, fundus autofluorescence, optical coherence tomography, and fluorescence lifetime imaging ophthalmoscopy (FLIO) and compared with age-matched controls. Retinal autofluorescence was excited using a 473-nm blue laser light and emitted fluorescence light was detected in 2 distinct wavelengths channels (498-560 nm and 560-720 nm). Clinical features, mean retinal autofluorescence lifetimes, autofluorescence intensity, and corresponding optical coherence tomography (OCT) images were further analyzed.
RESULTS
Thirty-five central serous chorioretinopathy patients with a mean visual acuity of 78 ETDRS letters (range, 50-90; mean Snellen equivalent: 20/32) and 12 age-matched controls were included. In the acute stage of central serous chorioretinopathy, retinal fluorescence lifetimes were shortened by 15% and 17% in the respective wavelength channels. Multiple linear regression analysis showed that fluorescence lifetimes were significantly influenced by the disease duration (P < 0.001) and accumulation of photoreceptor outer segments (P = 0.03) but independent of the presence or absence of subretinal fluid. Prolonged central macular autofluorescence lifetimes, particularly in eyes with retinal pigment epithelial atrophy, were associated with poor visual acuity.
CONCLUSION
This study establishes that autofluorescence lifetime changes occurring in central serous chorioretinopathy exhibit explicit patterns which can be used to estimate perturbations of the outer retinal layers with a high degree of statistical significance.This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially without permission from the journal