17,066 research outputs found
Distributed lag models for hydrological data
The distributed lag model (DLM), used most prominently in air pollution studies, finds application
wherever the effect of a covariate is delayed and distributed through time. We explore the use of modified formulations
of DLMs to provide flexible varying-coeficient models with smoothness constraints, applicable in any setting in which
lagged covariates are regressed on a time-dependent response. The models are applied to simulated flow and rainfall
data and to flow data from a Scottish mountain river, with particular emphasis on approximating the relationship
between environmental covariates and flow regimes in order to detect the influence of unobserved processes. It was
found that under certain rainfall conditions some of the variability in the influence of rainfall on flow arises through
a complex interaction between antecedent ground wetness and the time-delay in rainfall. The models are able to
identify subtle changes in rainfall response, particularly in the location of peak influence in the lag structure and offer
a computationally attractive approach for fitting DLMs
2-Player Nash and Nonsymmetric Bargaining Games: Algorithms and Structural Properties
The solution to a Nash or a nonsymmetric bargaining game is obtained by
maximizing a concave function over a convex set, i.e., it is the solution to a
convex program. We show that each 2-player game whose convex program has linear
constraints, admits a rational solution and such a solution can be found in
polynomial time using only an LP solver. If in addition, the game is succinct,
i.e., the coefficients in its convex program are ``small'', then its solution
can be found in strongly polynomial time. We also give a non-succinct linear
game whose solution can be found in strongly polynomial time
Endocrine disrupting effects on the nesting behaviour of male three-spined stickleback Gasterosteus aculeatus L
The analysis of patterns of temporal variability in the nesting behaviour of male threespined stickleback (Gasterosteus aculeatus) exposed to the synthetic oestrogen, 17β-ethinylestradiol, revealed immediate, but transient, treatment-related effects. Gluing frequency and time spent near nest were significantly reduced in exposed fish at the beginning of the experiment. The expression of these behaviours subsequently recovered and there was no effect of treatment on nest building success. The potential causes and implications of these findings are discussed
Analysis of dynamic stall using unsteady boundary-layer theory
The unsteady turbulent boundary layer and potential flow about a pitching airfoil are analyzed using numerical methods to determine the effect of pitch rate on the delay in forward movement of the rear flow reversal point. An explicit finite difference scheme is used to integrate the unsteady boundary layer equations, which are coupled at each instant of time to a fully unsteady and nonlinear potential flow analysis. A substantial delay in forward movement of the reversal point is demonstrated with increasing pitch rate, and it is shown that the delay results partly from the alleviation of the gradients in the potential flow, and partly from the effects of unsteadiness in the boundary layer itself. The predicted delay in flow-reversal onset, and its variation with pitch rate, are shown to be in reasonable agreement with experimental data relating to the delay in dynamic stall. From the comparisons it can be concluded (a) that the effects of time-dependence are sufficient to explain the failure of the boundary layer to separate during the dynamic overshoot, and (b) that there may be some link between forward movement of the reversal point and dynamic stall
Run-and-tumble particles with hydrodynamics: sedimentation, trapping and upstream swimming
We simulate by lattice Boltzmann the nonequilibrium steady states of
run-and-tumble particles (inspired by a minimal model of bacteria), interacting
by far-field hydrodynamics, subject to confinement. Under gravity, hydrodynamic
interactions barely perturb the steady state found without them, but for
particles in a harmonic trap such a state is quite changed if the run length is
larger than the confinement length: a self-assembled pump is formed. Particles
likewise confined in a narrow channel show a generic upstream flux in
Poiseuille flow: chiral swimming is not required
Meltwater Intrusions Reveal Mechanisms for Rapid Submarine Melt at a Tidewater Glacier
Submarine melting has been implicated as a driver of glacier retreat and sea level rise, but to date melting has been difficult to observe and quantify. As a result, melt rates have been estimated from parameterizations that are largely unconstrained by observations, particularly at the near-vertical termini of tidewater glaciers. With standard coefficients, these melt parameterizations predict that ambient
melting (the melt away from subglacial discharge outlets) is negligible compared to discharge-driven melting for typical tidewater glaciers. Here, we present new data from LeConte Glacier, Alaska, that challenges this paradigm. Using autonomous kayaks, we observe ambient meltwater intrusions that are ubiquitous within 400 m of the terminus, and we provide the first characterization of their properties, structure, and distribution. Our results suggest that ambient melt rates are substantially higher (Ă—100) than standard theory predicts and that ambient melting is a significant part of the total submarine melt flux. We explore modifications to the prevalent melt parameterization to provide a path forward for improved modeling of ocean-glacier interactions.This work was funded by NSF OPP Grants 1503910, 1504191, 1504288,
and 1504521 and National Geographic Grant CP4-171R-17. Additionally, this research was supported by the NOAA Climate and Global Change Postdoctoral Fellowship Program, administered by UCAR’s Cooperative Programs for the Advancement of Earth System Science (CPAESS) under award #NA18NWS4620043B. These observations would not be possible without the skilled engineering team who developed the autonomous kayaks—including Jasmine Nahorniak, June Marion, Nick McComb, Anthony Grana, and Corwin Perren—and also the Captain and crew of the M/V Amber Anne. We thank Donald Slater and an anonymous reviewer for valuable feedback that improved this manuscript. Data availability: All of the oceanographic data collected by ship and kayak have been archived with the National Centers for Environmental Information (Accession 0189574, https://accession.nodc.noaa.gov/ 0189574). The glacier data have been archived at the Arctic Data Center (https://doi.org/10.18739/A22G44).Ye
Relaxation of strained silicon on Si0.5Ge0.5 virtual substrates
Strain relaxation has been studied in tensile strained silicon layers grown on Si0.5Ge0.5 virtual substrates, for layers many times the critical thickness, using high resolution x-ray diffraction. Layers up to 30 nm thick were found to relax less than 2% by the glide of preexisting 60° dislocations. Relaxation is limited because many of these dislocations dissociate into extended stacking faults that impede the dislocation glide. For thicker layers, nucleated microtwins were observed, which significantly increased relaxation to 14%. All these tensile strained layers are found to be much more stable than layers with comparable compressive strain
Spectroscopy of drums and quantum billiards: perturbative and non-perturbative results
We develop powerful numerical and analytical techniques for the solution of
the Helmholtz equation on general domains. We prove two theorems: the first
theorem provides an exact formula for the ground state of an arbirtrary
membrane, while the second theorem generalizes this result to any excited state
of the membrane. We also develop a systematic perturbative scheme which can be
used to study the small deformations of a membrane of circular or square
shapes. We discuss several applications, obtaining numerical and analytical
results.Comment: 29 pages, 12 figures, 7 tabl
Lack of fractalkine receptor on macrophages impairs spontaneous recovery of ribbon synapses after moderate noise trauma in C57BL/6 mice
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