16,269 research outputs found
\u3ci\u3eBaetis\u3c/i\u3e (Ephemeroptera: Baetidae) of Wisconsin
Data on life histories and environmental requirements for species in many mayfly genera remains sketchy at best This is certainly true of Baetis, which is one of the most common components of Wisconsin\u27s lotic fauna. Most Wisconsin streams that are not grossly pobted contain one or more species of the minnow-like nymphs, which are usually found clinging to surfaces of rocks or aquatic plants. Biological studies of Baetis in North America have been neglected primarily because of their enigmatic taxonomy. Even keys of Needham et al. (1935) and Burks (1953), which are considered standard referenas, are either incomplete or difficult to use when identifying Baetis
Description of the Nymph of \u3ci\u3eCentroptilum Walshi\u3c/i\u3e (Ephemeroptera: Baetidae), with Biological Notes
The nymph of Centroptilum walshi McDunnough is described. C. walshi appears to be bivoltine in Wisconsin, with emergences throughout June into early July and from late August to early November. Mature nymphs were smallest when stream temperatures were the warmest. The nymphs were closely associated with Ranunculus sp., and numbers increased when the Ranunculus beds became more dense
Transform fault earthquakes in the North Atlantic: Source mechanisms and depth of faulting
The centroid depths and source mechanisms of 12 large earthquakes on transform faults of the northern Mid-Atlantic Ridge were determined from an inversion of long-period body waveforms. The earthquakes occurred on the Gibbs, Oceanographer, Hayes, Kane, 15 deg 20 min, and Vema transforms. The depth extent of faulting during each earthquake was estimated from the centroid depth and the fault width. The source mechanisms for all events in this study display the strike slip motion expected for transform fault earthquakes; slip vector azimuths agree to 2 to 3 deg of the local strike of the zone of active faulting. The only anomalies in mechanism were for two earthquakes near the western end of the Vema transform which occurred on significantly nonvertical fault planes. Secondary faulting, occurring either precursory to or near the end of the main episode of strike-slip rupture, was observed for 5 of the 12 earthquakes. For three events the secondary faulting was characterized by reverse motion on fault planes striking oblique to the trend of the transform. In all three cases, the site of secondary reverse faulting is near a compression jog in the current trace of the active transform fault zone. No evidence was found to support the conclusions of Engeln, Wiens, and Stein that oceanic transform faults in general are either hotter than expected from current thermal models or weaker than normal oceanic lithosphere
Squeezed pulsed light from a fiber ring interferometer
Observation of squeezed noise, 5 +/- 0.3 dB below the shot noise level, generated with pulses in a fiber ring interferometer is reported. The interferometric geometry is used to separate the pump pulse from the squeezed vacuum radiation. A portion of the pump is reused as the local oscillator in a homodyne detection. The pump fluctuations are successfully subtracted and shot noise limited performance is achieved at low frequencies (35-85 KHz). A possible utilization of the generated squeezed vacuum in improving a fiber gyro's signal to noise ratio is discussed
Strategic Investments in the Pulp and Paper Industry: A Count Data Regression Analysis
This paper analyses the effects of price and market size variables on the investment propensities in the pulp and paper industry. A panel of 15 European countries in the time period 1984 - 1997 is used in the regression analysis. We find the wages, the US/ECU exchange rate, the price of paper and the installed production capacity to be the main determinants of strategic investments in this industry. Our measure of market size have no - or only very small - effects.Lumpy investments; Prices; Market size; Agglomeration; Distance; Investment determinants
Effective Hamiltonians for some highly frustrated magnets
In prior work, the authors developed a method of degenerate perturbation
theory about the Ising limit to derive an effective Hamiltonian describing
quantum fluctuations in a half-polarized magnetization plateau on the
pyrochlore lattice. Here, we extend this formulation to an arbitrary lattice of
corner sharing simplexes of sites, at a fraction of the
saturation magnetization, with . We present explicit effective
Hamiltonians for the examples of the checkerboard, kagome, and pyrochlore
lattices. The consequent ground states in these cases for are also
discussed.Comment: 10 pages, 2 figures,. Conference proceedings for Highly Frustrated
Magnetism 200
Transient and chaotic low-energy transfers in a system with bistable nonlinearity
The low-energy dynamics of a two-dof system composed of a grounded linear oscillator coupled to
a lightweight mass by means of a spring with both cubic nonlinear and negative linear components
is investigated. The mechanisms leading to intense energy exchanges between the linear oscillator,
excited by a low-energy impulse, and the nonlinear attachment are addressed. For lightly damped
systems, it is shown that two main mechanisms arise: Aperiodic alternating in-well and cross-well
oscillations of the nonlinear attachment, and secondary nonlinear beats occurring once the dynamics
evolves solely in-well. The description of the former dissipative phenomenon is provided in a
two-dimensional projection of the phase space, where transitions between in-well and cross-well
oscillations are associated with sequences of crossings across a pseudo-separatrix. Whereas the second
mechanism is described in terms of secondary limiting phase trajectories of the nonlinear
attachment under certain resonance conditions. The analytical treatment of the two aformentioned
low-energy transfer mechanisms relies on the reduction of the nonlinear dynamics and consequent
analysis of the reduced dynamics by asymptotic techniques. Direct numerical simulations fully
validate our analytical predictions
Moduli Spaces for D-branes at the Tip of a Cone
For physicists: We show that the quiver gauge theory derived from a
Calabi-Yau cone via an exceptional collection of line bundles on the base has
the original cone as a component of its classical moduli space. For
mathematicians: We use data from the derived category of sheaves on a Fano
surface to construct a quiver, and show that its moduli space of
representations has a component which is isomorphic to the anticanonical cone
over the surface.Comment: 8 page
Winding effects on brane/anti-brane pairs
We study a brane/anti-brane configuration which is separated along a compact
direction by constructing a tachyon effective action which takes into account
transverse scalars. Such an action is relevant in the study of HQCD model of
Sakai and Sugimoto of chiral symmetry breaking, where the size of the compact
circle sets the confinement scale. Our approach is motivated by string theory
orbifold constructions and gives a route to model inhomogeneous tachyon decay.
We illustrate the techniques involved with a relatively simple example of a
harmonic oscillator on a circle. We will then repeat the analysis for the
Sakai-Sugimoto model and show that by integrating out the winding modes will
provide us with a renormalized action with a lower energy than that of
truncating to zero winding sector.Comment: 21 pages, 3 figures. v3: discussion and references added, published
versio
Semiclassical dynamics and long time asymptotics of the central-spin problem in a quantum dot
The spin of an electron trapped in a quantum dot is a promising candidate
implementation of a qubit for quantum information processing. We study the
central spin problem of the effect of the hyperfine interaction between such an
electron and a large number of nuclear moments. Using a spin coherent path
integral, we show that in this limit the electron spin evolution is well
described by classical dynamics of both the nuclear and electron spins. We then
introduce approximate yet systematic methods to analyze aspects of the
classical dynamics, and discuss the importance of the exact integrability of
the central spin Hamiltonian. This is compared with numerical simulation.
Finally, we obtain the asymptotic long time decay of the electron spin
polarization. We show that this is insensitive to integrability, and determined
instead by the transfer of angular momentum to very weakly coupled spins far
from the center of the quantum dot. The specific form of the decay is shown to
depend sensitively on the form of the electronic wavefunction.Comment: 13 pages, 4 figures, accepted by PR
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