413 research outputs found
Development of a mass spectrometer design Final report, Jun. 1, 1964 - Dec. 31, 1964
Cold cathode ion source mated to quadrupole mass spectrometer for use as residual gas analyze
A cold cathode ion source mass spectrometer employing ion counting techniques
Design and construction of mass spectrometer using cold cathode source of ions, quadrupole mass analyzer, and ion counting detector
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Assessing rotation-invariant feature classification for automated wildebeest population counts
Accurate and on-demand animal population counts are the holy grail for wildlife conservation organizations throughout the world because they enable fast and responsive adaptive management policies. While the collection of image data from camera traps, satellites, and manned or unmanned aircraft has advanced significantly, the detection and identification of animals within images remains a major bottleneck since counting is primarily conducted by dedicated enumerators or citizen scientists. Recent developments in the field of computer vision suggest a potential resolution to this issue through the use of rotation-invariant object descriptors combined with machine learning algorithms. Here we implement an algorithm to detect and count wildebeest from aerial images collected in the Serengeti National Park in 2009 as part of the biennial wildebeest count. We find that the per image error rates are greater than, but comparable to, two separate human counts. For the total count, the algorithm is more accurate than both manual counts, suggesting that human counters have a tendency to systematically over or under count images. While the accuracy of the algorithm is not yet at an acceptable level for fully automatic counts, our results show this method is a promising avenue for further research and we highlight specific areas where future research should focus in order to develop fast and accurate enumeration of aerial count data. If combined with a bespoke image collection protocol, this approach may yield a fully automated wildebeest count in the near future
Two-Scale Annihilation
The kinetics of single-species annihilation, , is investigated in
which each particle has a fixed velocity which may be either with equal
probability, and a finite diffusivity. In one dimension, the interplay between
convection and diffusion leads to a decay of the density which is proportional
to . At long times, the reactants organize into domains of right- and
left-moving particles, with the typical distance between particles in a single
domain growing as , and the distance between domains growing as .
The probability that an arbitrary particle reacts with its
neighbor is found to decay as for same-velocity pairs and as
for pairs. These kinetic and spatial exponents and their
interrelations are obtained by scaling arguments. Our predictions are in
excellent agreement with numerical simulations.Comment: revtex, 5 pages, 5 figures, also available from
http://arnold.uchicago.edu/~eb
Fast-diffusion mean-field theory for k-body reactions in one dimension
We derive an improved mean-field approximation for k-body annihilation
reactions kA --> inert, for hard-core diffusing particles on a line,
annihilating in groups of k neighbors with probability 0 < q <= 1. The hopping
and annihilation processes are correlated to mimic chemical reactions. Our new
mean-field theory accounts for hard-core particle properties and has a larger
region of applicability than the standard chemical rate equation especially for
large k values. Criteria for validity of the mean-field theory and its use in
phenomenological data fits are derived. Numerical tests are reported for
k=3,4,5,6.Comment: 16 pages, TeX (plain
Model of Cluster Growth and Phase Separation: Exact Results in One Dimension
We present exact results for a lattice model of cluster growth in 1D. The
growth mechanism involves interface hopping and pairwise annihilation
supplemented by spontaneous creation of the stable-phase, +1, regions by
overturning the unstable-phase, -1, spins with probability p. For cluster
coarsening at phase coexistence, p=0, the conventional structure-factor scaling
applies. In this limit our model falls in the class of diffusion-limited
reactions A+A->inert. The +1 cluster size grows diffusively, ~t**(1/2), and the
two-point correlation function obeys scaling. However, for p>0, i.e., for the
dynamics of formation of stable phase from unstable phase, we find that
structure-factor scaling breaks down; the length scale associated with the size
of the growing +1 clusters reflects only the short-distance properties of the
two-point correlations.Comment: 12 page
Spatial distribution of persistent sites
We study the distribution of persistent sites (sites unvisited by particles
) in one dimensional reaction-diffusion model. We define
the {\it empty intervals} as the separations between adjacent persistent sites,
and study their size distribution as a function of interval length
and time . The decay of persistence is the process of irreversible
coalescence of these empty intervals, which we study analytically under the
Independent Interval Approximation (IIA). Physical considerations suggest that
the asymptotic solution is given by the dynamic scaling form
with the average interval size . We show
under the IIA that the scaling function as and
decays exponentially at large . The exponent is related to the
persistence exponent through the scaling relation .
We compare these predictions with the results of numerical simulations. We
determine the two-point correlation function under the IIA. We find
that for , where , in agreement
with our earlier numerical results.Comment: 15 pages in RevTeX, 5 postscript figure
The duality relation between Glauber dynamics and the diffusion-annihilation model as a similarity transformation
In this paper we address the relationship between zero temperature Glauber
dynamics and the diffusion-annihilation problem in the free fermion case. We
show that the well-known duality transformation between the two problems can be
formulated as a similarity transformation if one uses appropriate (toroidal)
boundary conditions. This allow us to establish and clarify the precise nature
of the relationship between the two models. In this way we obtain a one-to-one
correspondence between observables and initial states in the two problems. A
random initial state in Glauber dynamics is related to a short range correlated
state in the annihilation problem. In particular the long-time behaviour of the
density in this state is seen to depend on the initial conditions. Hence, we
show that the presence of correlations in the initial state determine the
dependence of the long time behaviour of the density on the initial conditions,
even if such correlations are short-ranged. We also apply a field-theoretical
method to the calculation of multi-time correlation functions in this initial
state.Comment: 15 pages, Latex file, no figures. To be published in J. Phys. A.
Minor changes were made to the previous version to conform with the referee's
Repor
Particle Dynamics in a Mass-Conserving Coalescence Process
We consider a fully asymmetric one-dimensional model with mass-conserving
coalescence. Particles of unit mass enter at one edge of the chain and
coalescence while performing a biased random walk towards the other edge where
they exit. The conserved particle mass acts as a passive scalar in the reaction
process , and allows an exact mapping to a restricted ballistic
surface deposition model for which exact results exist. In particular, the
mass- mass correlation function is exactly known. These results complement
earlier exact results for the process without mass. We introduce a
comprehensive scaling theory for this process. The exact anaytical and
numerical results confirm its validity.Comment: 5 pages, 6 figure
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