Flow through very porous inclined screens

The steady, inviscid flow through and around a screen inclined at a uniform angle to the incoming flow was investigated. For a screen placed in an infinite flow field, an asymptotic analysis for small resistance coefficients was performed, and the effects of inclination were determined. The velocity at first order in the asymptotic expansion was nonuniform along the screen. This nonuniformity caused the wake behind the screen to contain distributed vorticity at second order. These effects therefore occurred at one order lower than for normal screens

Flow through very porous screens

Flow through and around screens with small resistance coefficient were analyzed. Both steady and oscillatory flows are considered, however, the case of a screen normal to the flow is treated. At second order in the asymptotic expansion the steady flow normal to the screen is nonuniform along the screen, due to components induced by the wake and by tangential drag. The third order pressure drop is nonuniform and the wake contains distributed vorticity, in addition to the vortex sheet along its boundary. The unsteady drag coefficient is found as a function of frequency

The Risk of Injury to Children in Compact Pickup Trucks

Nearly one million compact pickup trucks were sold last year in the US. Manufacturers now produce extended-cab models of pickups such as the Ford Ranger, Chevrolet S-10, Dodge Dakota, and Toyota Tacoma that can accommodate at least two rear-seated passengers, making them attractive to families with children. However, the safety of these rear seats for children has not been determined. This Issue Brief summarizes a new study that examines and quantifies the risk of injury to children riding in compact pickup trucks. Based on these findings, parents should be advised against using these vehicles as family transportation

Asymptotic Level Density of the Elastic Net Self-Organizing Feature Map

Whileas the Kohonen Self Organizing Map shows an asymptotic level density following a power law with a magnification exponent 2/3, it would be desired to have an exponent 1 in order to provide optimal mapping in the sense of information theory. In this paper, we study analytically and numerically the magnification behaviour of the Elastic Net algorithm as a model for self-organizing feature maps. In contrast to the Kohonen map the Elastic Net shows no power law, but for onedimensional maps nevertheless the density follows an universal magnification law, i.e. depends on the local stimulus density only and is independent on position and decouples from the stimulus density at other positions.Comment: 8 pages, 10 figures. Link to publisher under http://link.springer.de/link/service/series/0558/bibs/2415/24150939.ht

Modelling the dynamics of turbulent floods

Consider the dynamics of turbulent flow in rivers, estuaries and floods. Based on the widely used k-epsilon model for turbulence, we use the techniques of centre manifold theory to derive dynamical models for the evolution of the water depth and of vertically averaged flow velocity and turbulent parameters. This new model for the shallow water dynamics of turbulent flow: resolves the vertical structure of the flow and the turbulence; includes interaction between turbulence and long waves; and gives a rational alternative to classical models for turbulent environmental flows

Spatial and temporal variation in otolith chemistry for tautog (Tautoga onitis) in Narragansett Bay and Rhode Island coastal ponds

The elemental composition of otoliths may provide valuable information for establishing connectivity between fish nursery grounds and adult fish populations. Concentrations of Rb, Mg, Ca, Mn, Sr, Na, K, Sr, Pb, and Ba were determined by using solution-based inductively coupled plasma mass spectrometry in otoliths of young-of-the year tautog (Tautoga onitis) captured in nursery areas along the Rhode Island coast during two consecutive years. Stable oxygen (δ18O) and carbon (δ13C) isotopic ratios in young-of-the year otoliths were also analyzed with isotope ratio mass spectrometry. Chemical signatures differed significantly among the distinct nurseries within Narragansett Bay and the coastal ponds across years. Significant differences were also observed within nurseries from year to year. Classification accuracy to each of the five tautog nursery areas ranged from 85% to 92% across years. Because accurate classification of juvenile tautog nursery sites was achieved, otolith chemistry can potentially be used as a natural habitat tag

Effects of zooplankton size and concentration and light intensity on the feeding behavior of Atlantic mackerel \u3cem\u3eScomber scombrus\u3c/em\u3e

Atlantic mackerel Scomber scombrus had low clearance rates when fed older stage copepodites of the copepod Calanus finmarchicus at high concentrations and high clearance rates at low concentrations. These rates were consistent with filter feeding at high concentrations and particulate feeding at low concentrations. Intermediate and small copepods presented together at high concentrations were cleared at lower rates than the large C. finmarchicus, suggesting lower filtration efficiencies. Intermediate and small copepods were presented over a range of light intensities (8.2 x 10-8 to 1.6 x 100 µE m-2 s-1). Feeding rate did not change significantly between 1.6 x 100 and 2.0 x 10-6 µE m-2 s-1, but decreased to nearly zero at 8.2 x 10-8 µE m-2 s-1, indicating a light intensity threshold for feeding of about 10-7 µE m-2 s-1. This threshold enables mackerel to feed throughout the night near the ocean surface. Swimming speed decreased to a lesser degree than feeding rate at the lowest light intensity, indicating that the change in filter-feeding rate is only partially due to the change in speed. The school dispersed in both low and high light levels, but spacing between fish did not appear to be related to feeding rate

Goodness-of-Fit Tests for Symmetric Stable Distributions -- Empirical Characteristic Function Approach

We consider goodness-of-fit tests of symmetric stable distributions based on weighted integrals of the squared distance between the empirical characteristic function of the standardized data and the characteristic function of the standard symmetric stable distribution with the characteristic exponent $\alpha$ estimated from the data. We treat $\alpha$ as an unknown parameter, but for theoretical simplicity we also consider the case that $\alpha$ is fixed. For estimation of parameters and the standardization of data we use maximum likelihood estimator (MLE) and an equivariant integrated squared error estimator (EISE) which minimizes the weighted integral. We derive the asymptotic covariance function of the characteristic function process with parameters estimated by MLE and EISE. For the case of MLE, the eigenvalues of the covariance function are numerically evaluated and asymptotic distribution of the test statistic is obtained using complex integration. Simulation studies show that the asymptotic distribution of the test statistics is very accurate. We also present a formula of the asymptotic covariance function of the characteristic function process with parameters estimated by an efficient estimator for general distributions

Neutron Diffraction Study of Field Cooling Effects on Relaxor Ferroelectrics Pb[(Zn_{1/3} Nb_{2/3})_{0.92} Ti_{0.08}] O_{3}

High-temperature (T) and high-electric-field (E) effects on Pb[(Zn_{1/3} Nb_{2/3})_{0.92} Ti_{0.08}]O_3 (PZN-8%PT) were studied comprehensively by neutron diffraction in the ranges 300 <= T <= 550 K and 0 <= E <= 15 kV/cm. We have focused on how phase transitions depend on preceding thermal and electrical sequences. In the field cooling process (FC, E parallel [001] >= 0.5 kV/cm), a successive cubic (C) --> tetragonal (T) --> monoclinic (M_C) transition was observed. In the zero field cooling process (ZFC), however, we have found that the system does not transform to the rhombohedral (R) phase as widely believed, but to a new, unidentified phase, which we call X. X gives a Bragg peak profile similar to that expected for R, but the c-axis is always slightly shorter than the a-axis. As for field effects on the X phase, we found an irreversible X --> M_C transition via another monoclinic phase (M_A) as expected from a previous report [Noheda et al. Phys. Rev. Lett. 86, 3891 (2001)]. At a higher electric field, we confirmed a c-axis jump associated with the field-induced M_C --> T transition, which was observed by strain and x-ray diffraction measurements.Comment: 8 pages, 9 figures, revise