6,837 research outputs found
Lower Bound for Convex Hull Area and Universal Cover Problems
In this paper, we provide a lower bound for an area of the convex hull of
points and a rectangle in a plane. We then apply this estimate to establish a
lower bound for a universal cover problem. We showed that a convex universal
cover for a unit length curve has area at least 0.232239. In addition, we show
that a convex universal cover for a unit closed curve has area at least
0.0879873.Comment: 12 pages, 9 figure
Influence of Apple stem grooving virus on Malus sieboldii-derived apple proliferation resistant rootstocks
Apple stem grooving virus (ASGV, Capillovirus) is widely spread in apple growing regions. As it causes no symptoms on most cultivated apple varieties and rootstocks it is considered latent in Malus x domestica. In Asia, however, ASGV has been found associated with topworking disease of apple rootstocks originating from Malus sieboldii. Recently, M. sieboldii and its hybrids have gained new interest in Europe as they confer resistance to apple proliferation (AP) disease. A new breeding program aiming to develop AP-resistant rootstocks of agronomic value for modern apple culture, reported unexpected tree decline which was to be associated with ASGV. As little information is available on the variability of ASGV isolates in Germany, the complete genome of a German isolate of ASGV associated with tree decline was cloned and sequenced. Sequence comparisons with available ASGV isolates revealed two regions of high variability in the genome. The genetic variability of additional isolates from Germany and other countries were collected and the variable areas characterised. In addition ASGV was successfully maintained in micropropagated apple trees and could be transmitted by in vitro grafting to various genotypes, making it possible to study in vitro the effect of the virus and virus/phytoplama combination on M. sieboldii-derived genotypes. Keywords: Latent apple viruses, Candidatus Phytoplasma mali, micropropagation, in vitro grafting, genetic variabilit
Evaluation of the synoptic and mesoscale predictive capabilities of a mesoscale atmospheric simulation system
The overall performance characteristics of a limited area, hydrostatic, fine (52 km) mesh, primitive equation, numerical weather prediction model are determined in anticipation of satellite data assimilations with the model. The synoptic and mesoscale predictive capabilities of version 2.0 of this model, the Mesoscale Atmospheric Simulation System (MASS 2.0), were evaluated. The two part study is based on a sample of approximately thirty 12h and 24h forecasts of atmospheric flow patterns during spring and early summer. The synoptic scale evaluation results benchmark the performance of MASS 2.0 against that of an operational, synoptic scale weather prediction model, the Limited area Fine Mesh (LFM). The large sample allows for the calculation of statistically significant measures of forecast accuracy and the determination of systematic model errors. The synoptic scale benchmark is required before unsmoothed mesoscale forecast fields can be seriously considered
Heterocyst placement strategies to maximize growth of cyanobacterial filaments
Under conditions of limited fixed-nitrogen, some filamentous cyanobacteria
develop a regular pattern of heterocyst cells that fix nitrogen for the
remaining vegetative cells. We examine three different heterocyst placement
strategies by quantitatively modelling filament growth while varying both
external fixed-nitrogen and leakage from the filament. We find that there is an
optimum heterocyst frequency which maximizes the growth rate of the filament;
the optimum frequency decreases as the external fixed-nitrogen concentration
increases but increases as the leakage increases. In the presence of leakage,
filaments implementing a local heterocyst placement strategy grow significantly
faster than filaments implementing random heterocyst placement strategies. With
no extracellular fixed-nitrogen, consistent with recent experimental studies of
Anabaena sp. PCC 7120, the modelled heterocyst spacing distribution using our
local heterocyst placement strategy is qualitatively similar to experimentally
observed patterns. As external fixed-nitrogen is increased, the spacing
distribution for our local placement strategy retains the same shape while the
average spacing between heterocysts continuously increases.Comment: This is an author-created, un-copyedited version of an article
accepted for publication in Physical Biology. IOP Publishing Ltd is not
responsible for any errors or omissions in this version of the manuscript or
any version derived from it. The definitive publisher-authenticated version
will be available onlin
Strong Coupling Constant with Flavour Thresholds at Four Loops in the MS-bar Scheme
We present in analytic form the matching conditions for the strong coupling
constant alpha_s^(n_f)(mu) at the flavour thresholds to three loops in the
modified minimal-subtraction scheme. Taking into account the recently
calculated coefficient beta_3 of the Callan-Symanzik beta function of quantum
chromodynamics, we thus derive a four-loop formula for alpha_s^(n_f)(mu)
together with appropriate relationships between the asymptotic scale parameters
Lambda^(n_f) for different numbers of flavours n_f.Comment: 10 pages (Latex), 3 figures (Postscript
Characterization of a historically nutrient enriched marsh ecosystem : Yorktown Creek, Yorktown, Virginia
In this report, we summarize our initial findings of a nutrient enriched aquatic ecosystem prior to relaxation of sewage input. The studies reported were directed toward characterizing the system prior to relaxation and to begin xperimental studies to accomplish our general objectives
The problem of analytical calculation of barrier crossing characteristics for Levy flights
By using the backward fractional Fokker-Planck equation we investigate the
barrier crossing event in the presence of Levy noise. After shortly review
recent results obtained with different approaches on the time characteristics
of the barrier crossing, we derive a general differential equation useful to
calculate the nonlinear relaxation time. We obtain analytically the nonlinear
relaxation time for free Levy flights and a closed expression in quadrature of
the same characteristics for cubic potential.Comment: 12 pages, 2 figures, presented at 5th International Conference on
Unsolved Problems on Noise, Lyon, France, 2008, to appear in J. Stat. Mech.:
Theory and Experimen
A Non-Perturbative Approach to the Random-Bond Ising Model
We study the N -> 0 limit of the O(N) Gross-Neveu model in the framework of
the massless form-factor approach. This model is related to the continuum limit
of the Ising model with random bonds via the replica method. We discuss how
this method may be useful in calculating correlation functions of physical
operators. The identification of non-perturbative fixed points of the O(N)
Gross-Neveu model is pursued by its mapping to a WZW model.Comment: 17 pages LaTeX, 1 PostScript figure included using psfig.st
Differential Eye Movements in Mild Traumatic Brain Injury vs. Normal Controls
Objective measures to diagnose and to monitor improvement of symptoms following mild traumatic brain injury (mTBI) are lacking. Computerized eye tracking has been advocated as a rapid, user friendly and field ready technique to meet this need. Eye tracking data collected via a head mounted, video-based binocular eye tracker was used to examine saccades, fixations and smooth pursuit movement in 60 military Service Members with post concussive syndrome (PCS) and 26 asymptomatic control subjects in an effort to determine if eye movement differences could be found and quantified. The diagnosis of mTBI was confirmed by the study physiatrist’s history, physical examination, and a review of any medical records. Results demonstrated that subjects with symptomatic mTBI had statistically larger position errors, smaller saccadic amplitudes, smaller predicted peak velocities, smaller peak accelerations, and longer durations. Subjects with symptomatic mTBI were also less likely to follow a target movement (less primary saccades). In general, symptomatic mTBI tracked the stepwise moving targets less accurately, revealing possible brain dysfunction. A reliable, standardized protocol that appears to differentiate mTBI from normals was developed for use in future research. This investigation represents a step toward objective identification of those with PCS. Future studies focused on increasing the specificity of eye movement differences in those with PCS are needed
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