32,546 research outputs found
Presence of the âThreatenedâ \u3ci\u3eTrimerotropis Huroniana\u3c/i\u3e (Orthoptera: Acrididae) in Relation to the Occurrence of Native Dune Plant Species and the Exotic \u3ci\u3eCentaurea Biebersteinii\u3c/i\u3e
Trimerotropis huroniana Wlk. is a âThreatenedâ species in Michigan and Wisconsin with a distribution limited to open dune systems in the northern Great Lakes region of North America. Pitfall traps were utilized in the Grand Sable Dunes of Pictured Rocks National Lakeshore, MI, along with an herbaceous plant survey, to identify the relationship of T. huroniana with native dune plant species, Ammophila breviligulata Fern. (American beachgrass, Poaceae), Artemisia campestris L. (field sagewort, Asteraceae), and the exotic invasive plant Centaurea biebersteinii DC. [=Centaurea maculosa, spotted knapweed, Lamarck] (Asteraceae). The absence of C. biebersteinii resulted in an increased likelihood of capturing T. huroniana. This was most likely due to the increased likelihood of encountering A. campestris in areas without C. biebersteinii. The occurrence of A. breviligulata was independent of C. biebersteinii presence. A significant positive linear relationship occurred between the percent cover of A. campestris and the traps that captured T. huroniana. There was no significant relationship between A. breviligulata percent cover and the traps that captured T. huroniana. The occurrence and distribution of T. huroniana is closely related to the presence and abundance of A. campestris. Habitat conservation and improvement for T. huroniana should include increases in A. campestris populations through the removal of C. biebersteinii
A random hierarchical lattice: the series-parallel graph and its properties
We consider a sequence of random graphs constructed by a hierarchical procedure. The construction replaces existing edges by pairs of edges in series or parallel with probability and respectively. We investigate the effective resistance across the graphs, first-passage percolation on the graphs and the Cheeger constants of the graphs as the number of edges tends to infinity. In each case we find a phase transition at
Preferential duplication graphs
We consider a preferential duplication model for growing random graphs, extending previous models of duplication graphs by selecting the vertex to be duplicated with probability proportional to its degree. We show that a special case of this model can be analysed using the same stochastic approximation as for vertex-reinforced random walks, and show that 'trapping' behaviour can occur, such that the descendants of a particular group of initial vertices come to dominate the graph
Analysis domain model for shared virtual environments
The field of shared virtual environments, which also
encompasses online games and social 3D environments, has a
system landscape consisting of multiple solutions that share great functional overlap. However, there is little system interoperability between the different solutions. A shared virtual environment has an associated problem domain that is highly complex raising difficult challenges to the development process, starting with the architectural design of the underlying system. This paper has two main contributions. The first contribution is a broad domain analysis of shared virtual environments, which enables developers to have a better understanding of the whole rather than the part(s). The second contribution is a reference domain model for discussing and describing solutions - the Analysis Domain Model
Predicting Emerald Ash Borer, \u3ci\u3eAgrilus Planipennis\u3c/i\u3e (Coleoptera: Buprestidae), Landing Behavior on Unwounded Ash
Detection of emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), an invasive forest pest, is difficult in low density populations war- ranting continual development of various trapping techniques and protocols. Understanding and predicting landing behavior of A. planipennis may assist in the further development of trapping techniques and improvement of trapping protocols for widespread survey programs in North America. Three multiple regression models were developed using ash tree vigor and crown light exposure to predict the landing behavior of A. planipennis. These models were then used to predict the landing density of A. planipennis at separate sites and in separate years. Successful prediction of A. planipennis capture density at the test sites was limited. Even though the multiple regression models were not effective at predicting landing behavior of A. planipennis, tree characteristics were used to predict the likelihood of A. planipennis landing. Trees predicted as having high likelihood of landing had 3.5 times as many A. planipennis adults/m2 on stem traps than trees predicted as having low likelihood of landing. While the landing density of A. planipennis may not be efficiently predicted, the utility of these predictions may be in the form of identifying trees with a high likelihood of A. planipennis landing. Those high likelihood trees may assist in improving existing detection programs and techniques in North American forests
(Never) Mind your p's and q's: Von Neumann versus Jordan on the Foundations of Quantum Theory
In two papers entitled "On a new foundation [Neue Begr\"undung] of quantum
mechanics," Pascual Jordan (1927b,g) presented his version of what came to be
known as the Dirac-Jordan statistical transformation theory. As an alternative
that avoids the mathematical difficulties facing the approach of Jordan and
Paul A. M. Dirac (1927), John von Neumann (1927a) developed the modern Hilbert
space formalism of quantum mechanics. In this paper, we focus on Jordan and von
Neumann. Central to the formalisms of both are expressions for conditional
probabilities of finding some value for one quantity given the value of
another. Beyond that Jordan and von Neumann had very different views about the
appropriate formulation of problems in quantum mechanics. For Jordan, unable to
let go of the analogy to classical mechanics, the solution of such problems
required the identication of sets of canonically conjugate variables, i.e., p's
and q's. For von Neumann, not constrained by the analogy to classical
mechanics, it required only the identication of a maximal set of commuting
operators with simultaneous eigenstates. He had no need for p's and q's. Jordan
and von Neumann also stated the characteristic new rules for probabilities in
quantum mechanics somewhat differently. Jordan (1927b) was the first to state
those rules in full generality. Von Neumann (1927a) rephrased them and, in a
subsequent paper (von Neumann, 1927b), sought to derive them from more basic
considerations. In this paper we reconstruct the central arguments of these
1927 papers by Jordan and von Neumann and of a paper on Jordan's approach by
Hilbert, von Neumann, and Nordheim (1928). We highlight those elements in these
papers that bring out the gradual loosening of the ties between the new quantum
formalism and classical mechanics.Comment: New version. The main difference with the old version is that the
introduction has been rewritten. Sec. 1 (pp. 2-12) in the old version has
been replaced by Secs. 1.1-1.4 (pp. 2-31) in the new version. The paper has
been accepted for publication in European Physical Journal
Photoassociative Frequency Shift in a Quantum Degenerate Gas
We observe a light-induced frequency shift in single-photon photoassociative
spectra of magnetically trapped, quantum degenerate 7Li. The shift is a
manifestation of the coupling between the threshold continuum scattering states
and discrete bound levels in the excited-state molecular potential induced by
the photoassociation laser. The frequency shift is observed to be linear in the
laser intensity with a measured proportionality constant that is in good
agreement with theoretical predictions. The frequency shift has important
implications for a scheme to alter the interactions between atoms in a
Bose-Einstein condensate using photoassociation resonances.Comment: 3 figure
Constraining the Sub-AU-Scale Distribution of Hydrogen and Carbon Monoxide Gas around Young Stars with the Keck Interferometer
We present Keck Interferometer observations of T Tauri and Herbig Ae/Be stars
with a spatial resolution of a few milliarcseconds and a spectral resolution of
~2000. Our observations span the K-band, and include the Br gamma transition of
Hydrogen and the v=2-0 and v=3-1 transitions of carbon monoxide. For several
targets we also present data from Keck/NIRSPEC that provide higher spectral
resolution, but a seeing-limited spatial resolution, of the same spectral
features. We analyze the Br gamma emission in the context of both disk and
infall/outflow models, and conclude that the Br gamma emission traces gas at
very small stellocentric radii, consistent with the magnetospheric scale.
However some Br gamma-emitting gas also seems to be located at radii of >0.1
AU, perhaps tracing the inner regions of magnetically launched outflows. CO
emission is detected from several objects, and we generate disk models that
reproduce both the KI and NIRSPEC data well. We infer the CO spatial
distribution to be coincident with the distribution of continuum emission in
most cases. Furthermore the Br gamma emission in these objects is roughly
coincident with both the CO and continuum emission. We present potential
explanations for the spatial coincidence of continuum, Br gamma, and CO
overtone emission, and explore the implications for the low occurrence rate of
CO overtone emission in young stars. Finally, we provide additional discussion
of V1685 Cyg, which is unusual among our sample in showing large differences in
emitting region size and spatial position as a function of wavelength.Comment: Accepted for publication in MNRA
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