1,031 research outputs found
Stochastic Data Clustering
In 1961 Herbert Simon and Albert Ando published the theory behind the
long-term behavior of a dynamical system that can be described by a nearly
uncoupled matrix. Over the past fifty years this theory has been used in a
variety of contexts, including queueing theory, brain organization, and
ecology. In all these applications, the structure of the system is known and
the point of interest is the various stages the system passes through on its
way to some long-term equilibrium.
This paper looks at this problem from the other direction. That is, we
develop a technique for using the evolution of the system to tell us about its
initial structure, and we use this technique to develop a new algorithm for
data clustering.Comment: 23 page
Performance of a turbojet engine with adjustable first-stage turbine stator and variable-area exhaust nozzle
The performance of a turbojet engine with a two-stage turbine, an adjustable first-stage turbine stator, and a variable-area exhaust nozzle was investigated at selected constant engine speeds and two simulated flight conditions. For the particular component characteristics of the engine investigated, little improvement in thrust levels of interest by use of an adjustable rather than an optimum fixed first-stage turbine stator
A stand-alone tree demography and landscape structure module for Earth system models
We propose and demonstrate a new approach for the simulation of woody ecosystem stand dynamics, demography, and disturbance-mediated heterogeneity suitable for continental to global applications and designed for coupling to the terrestrial ecosystem component of any earth system model. The approach is encoded in a model called Populations-Order-Physiology (POP). We demonstrate the behavior and performance of POP coupled to the Community Atmosphere Biosphere Land Exchange model (CABLE) applied along the Northern Australian Tropical Transect, featuring gradients in rainfall and fire disturbance. The model is able to simultaneously reproduce observation-based estimates of key functional and structural variables along the transect, namely gross primary production, tree foliage projective cover, basal area, and maximum tree height. Prospects for the use of POP to address current vegetation dynamic deficiencies in earth system modeling are discussed
A search for new particles in protonânucleus collisions at 400 GeV/c
We report preliminary results from a search for new particles produced in protonânucleus collisions at 400 GeV/c. A doubleâarm spectrometer is used to detect twoâbody final states where each spectrometer arm has the capability of uniquely identifying Π±, K±, p, ?, Ό±, and Ï. The JÏ is measured in the ÎŒ+ÎŒâ mode.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87398/2/30_1.pd
Graniteâa new telescope for TeV gamma ray astronomy
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87435/2/253_1.pd
Observations of TeV photons at the Whipple Observatory
The Whipple Observatory 10 m gammaâray telescope has been used to search for TeV gammaâray emission from a number of objects. This paper reports observations of six galactic and three extragalactic objects using the Cherenkov image technique. With the introduction of a highâresolution camera (1/4° pixel) in 1988, the Crab Nebula was detected at a significance level of 20 Ï in 30 hours of onâsource observation. Upper limits at a fraction of the Crab flux are set for most of the other objects, based on the absence of any significant dc excess or periodic effect when an a priori Monte Carlo determined imaging selection criterion (the ââazwidth cutââ) is employed. There are weak indications that one source, Hercules Xâ1, may be an episodic emitter. The Whipple detection system will be improved shortly with the addition of a second reflector 11 m in diameter (GRANITE) for stereoscopic viewing of showers. The combination of the twoâreflector system should have a signalâtoânoise advantage of 103 over a simple nonimaging Cherenkov receiver.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87437/2/47_1.pd
Harmonic Vibrational Excitations in Disordered Solids and the "Boson Peak"
We consider a system of coupled classical harmonic oscillators with spatially
fluctuating nearest-neighbor force constants on a simple cubic lattice. The
model is solved both by numerically diagonalizing the Hamiltonian and by
applying the single-bond coherent potential approximation. The results for the
density of states are in excellent agreement with each other. As
the degree of disorder is increased the system becomes unstable due to the
presence of negative force constants. If the system is near the borderline of
stability a low-frequency peak appears in the reduced density of states
as a precursor of the instability. We argue that this peak
is the analogon of the "boson peak", observed in structural glasses. By means
of the level distance statistics we show that the peak is not associated with
localized states
Negative impacts of invasive predators used as biological control agents against the pest snail Lissachatina fulica: the snail Euglandina âroseaâ and the flatworm Platydemus manokwari
Since 1955 snails of the Euglandina rosea
species complex and Platydemus manokwari flatworms were widely introduced in attempted biological
control of giant African snails (Lissachatina fulica)
but have been implicated in the mass extinction of
Pacific island snails. We review the histories of the 60
introductions and their impacts on L. fulica and native
snails. Since 1993 there have been unofficial releases
of Euglandina within island groups. Only three official
P. manokwari releases took place, but new populations
are being recorded at an increasing rate, probably
because of accidental introduction. Claims that these
predators controlled L. fulica cannot be substantiated;
in some cases pest snail declines coincided with
predator arrival but concomitant declines occurred
elsewhere in the absence of the predator and the
declines in some cases were only temporary. In the
Hawaiian Islands, although there had been some earlier declines of native snails, the Euglandina
impacts on native snails are clear with rapid decline
of many endemic Hawaiian Achatinellinae following
predator arrival. In the Society Islands, Partulidae tree
snail populations remained stable until Euglandina
introduction, when declines were extremely rapid with
an exact correspondence between predator arrival and
tree snail decline. Platydemus manokwari invasion
coincides with native snail declines on some islands,
notably the Ogasawara Islands of Japan, and its
invasion of Florida has led to mass mortality of
Liguus spp. tree snails. We conclude that Euglandina
and P. manokwari are not effective biocontrol agents,
but do have major negative effects on native snail
faunas. These predatory snails and flatworms are
generalist predators and as such are not suitable for
biological control
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