2,458 research outputs found
Convective instability and mass transport of diffusion layers in a Hele-Shaw geometry
We consider experimentally the instability and mass transport of a
porous-medium flow in a Hele-Shaw geometry. In an initially stable
configuration, a lighter fluid (water) is located over a heavier fluid
(propylene glycol). The fluids mix via diffusion with some regions of the
resulting mixture being heavier than either pure fluid. Density-driven
convection occurs with downward penetrating dense fingers that transport mass
much more effectively than diffusion alone. We investigate the initial
instability and the quasi steady state. The convective time and velocity
scales, finger width, wave number selection, and normalized mass transport are
determined for 6,000<Ra<90,000. The results have important implications for
determining the time scales and rates of dissolution trapping of carbon dioxide
in brine aquifers proposed as possible geologic repositories for sequestering
carbon dioxide.Comment: 4 page, 3 figure
Movement patterns of cheetahs ( Acinonyx jubatus ) in farmlands in Botswana
Botswana has the second highest population of cheetah (Acinonyx jubatus) with most living outside protected areas. As a result, many cheetahs are found in farming areas which occasionally results in human-wildlife conflict. This study aimed to look at movement patterns of cheetahs in farming environments to determine whether cheetahs have adapted their movements in these human-dominated landscapes. We fitted high-time resolution GPS collars to cheetahs in the Ghanzi farmlands of Botswana. GPS locations were used to calculate home range sizes as well as number and duration of visits to landscape features using a time-based local convex hull method. Cheetahs had medium-sized home ranges compared to previously studied cheetah in similar farming environments. Results showed that cheetahs actively visited scent marking trees and avoided visiting homesteads. A slight preference for visiting game farms over cattle farms was found, but there was no difference in duration of visits between farm types. We conclude that cheetahs selected for areas that are important for their dietary and social needs and prefer to avoid human-occupied areas. Improved knowledge of how cheetahs use farmlands can allow farmers to make informed decisions when developing management practices and can be an important tool for reducing human-wildlife conflict
Learned-Norm Pooling for Deep Feedforward and Recurrent Neural Networks
In this paper we propose and investigate a novel nonlinear unit, called
unit, for deep neural networks. The proposed unit receives signals from
several projections of a subset of units in the layer below and computes a
normalized norm. We notice two interesting interpretations of the
unit. First, the proposed unit can be understood as a generalization of a
number of conventional pooling operators such as average, root-mean-square and
max pooling widely used in, for instance, convolutional neural networks (CNN),
HMAX models and neocognitrons. Furthermore, the unit is, to a certain
degree, similar to the recently proposed maxout unit (Goodfellow et al., 2013)
which achieved the state-of-the-art object recognition results on a number of
benchmark datasets. Secondly, we provide a geometrical interpretation of the
activation function based on which we argue that the unit is more
efficient at representing complex, nonlinear separating boundaries. Each
unit defines a superelliptic boundary, with its exact shape defined by the
order . We claim that this makes it possible to model arbitrarily shaped,
curved boundaries more efficiently by combining a few units of different
orders. This insight justifies the need for learning different orders for each
unit in the model. We empirically evaluate the proposed units on a number
of datasets and show that multilayer perceptrons (MLP) consisting of the
units achieve the state-of-the-art results on a number of benchmark datasets.
Furthermore, we evaluate the proposed unit on the recently proposed deep
recurrent neural networks (RNN).Comment: ECML/PKDD 201
Wake structure and kinematics in two insectivorous bats
We compare kinematics and wake structure over a range of flight speeds (4.0–8.2 m s(−1)) for two bats that pursue insect prey aerially, Tadarida brasiliensis and Myotis velifer. Body mass and wingspan are similar in these species, but M. velifer has broader wings and lower wing loading. By using high-speed videography and particle image velocimetry of steady flight in a wind tunnel, we show that three-dimensional kinematics and wake structure are similar in the two species at the higher speeds studied, but differ at lower speeds. At lower speeds, the two species show significant differences in mean angle of attack, body–wingtip distance and sweep angle. The distinct body vortex seen at low speed in T. brasiliensis and other bats studied to date is considerably weaker or absent in M. velifer. We suggest that this could be influenced by morphology: (i) the narrower thorax in this species probably reduces the body-induced discontinuity in circulation between the two wings and (ii) the wing loading is lower, hence the lift coefficient required for weight support is lower. As a result, in M. velifer, there may be a decreased disruption in the lift generation between the body and the wing, and the strength of the characteristic root vortex is greatly diminished, both suggesting increased flight efficiency. This article is part of the themed issue ‘Moving in a moving medium: new perspectives on flight’
A Practical Approach to Assess Combined Levee Erosion, Seepage, and Slope Stability Failure Modes
Solvable model of a phase oscillator network on a circle with infinite-range Mexican-hat-type interaction
We describe a solvable model of a phase oscillator network on a circle with
infinite-range Mexican-hat-type interaction. We derive self-consistent
equations of the order parameters and obtain three non-trivial solutions
characterized by the rotation number. We also derive relevant characteristics
such as the location-dependent distributions of the resultant frequencies of
desynchronized oscillators. Simulation results closely agree with the
theoretical ones
Biomechanics of predator–prey arms race in lion, zebra, cheetah and impala
The fastest and most manoeuvrable terrestrial animals are found in savannah habitats, where predators chase and capture running prey. Hunt outcome and success rate are critical to survival, so both predator and prey should evolve to be faster and/or more manoeuvrable. Here we compare locomotor characteristics in two pursuit predator–prey pairs, lion–zebra and cheetah–impala, in their natural savannah habitat in Botswana. We show that although cheetahs and impalas were universally more athletic than lions and zebras in terms of speed, acceleration and turning, within each predator–prey pair, the predators had 20% higher muscle fibre power than prey, 37% greater acceleration and 72% greater deceleration capacity than their prey. We simulated hunt dynamics with these data and showed that hunts at lower speeds enable prey to use their maximum manoeuvring capacity and favour prey survival, and that the predator needs to be more athletic than its prey to sustain a viable success rate
Comprehensive analysis of preeclampsia-associated DNA methylation in the placenta
Background:A small number of recent reports have suggested that altered placental DNA methylation may be associated with early onset preeclampsia. It is important that further studies be undertaken to confirm and develop these findings. We therefore undertook a systematic analysis of DNA methylation patterns in placental tissue from 24 women with preeclampsia and 24 with uncomplicated pregnancy outcome
Co-existing structures in 105Ru
New positive-parity states, having a band-like structure, were observed in
105Ru. The nucleus was produced in induced fission reaction and the prompt
gamma-rays, emitted from the fragments, were detected by the EUROBALL III
multi-detector array. The partial scheme of excited 105Ru levels is analyzed
within the Triaxial-Rotor-plus-Particle approach
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