70,300 research outputs found
A new design tool for feature extraction in noisy images based on grayscale hit-or-miss transforms
The Hit-or-Miss transform (HMT) is a well known morphological transform capable of identifying features in digital images. When image features contain noise, texture or some other distortion, the HMT may fail. Various researchers have extended the HMT in different ways to make it more robust to noise. The most successful, and most recent extensions of the HMT for noise robustness, use rank order operators in place of standard morphological erosions and dilations. A major issue with the proposed methods is that no technique is provided for calculating the parameters that are introduced to generalize the HMT, and, in most cases, these parameters are determined empirically. We present here, a new conceptual interpretation of the HMT which uses a percentage occupancy (PO) function to implement the erosion and dilation operators in a single pass of the image. Further, we present a novel design tool, derived from this PO function that can be used to determine the only parameter for our routine and for other generalizations of the HMT proposed in the literature. We demonstrate the power of our technique using a set of very noisy images and draw a comparison between our method and the most recent extensions of the HMT
Solving physics-driven inverse problems via structured least squares
Numerous physical phenomena are well modeled by partial differential equations (PDEs); they describe a wide range of phenomena across many application domains, from model- ing EEG signals in electroencephalography to, modeling the release and propagation of toxic substances in environmental monitoring. In these applications it is often of interest to find the sources of the resulting phenomena, given some sparse sensor measurements of it. This will be the main task of this work. Specifically, we will show that finding the sources of such PDE-driven fields can be turned into solving a class of well-known multi-dimensional structured least squares prob- lems. This link is achieved by leveraging from recent results in modern sampling theory â in particular, the approximate Strang-Fix theory. Subsequently, numerical simulation re- sults are provided in order to demonstrate the validity and robustness of the proposed framework
The Biodegradation of Organic Substrates Under Arctic and Subarctic Conditions
The objective of this research was to obtain data on the metabolic reaction rates of the
microorganisms indigenous to the cold environments of the arctic and sub-arctic in order to
evaluate the natural abilities of the freshwater streams and lakes of Alaska to assimilate the wastes
discharged into them. Microorganisms capable of growth even at subzero temperatures have long
been known; however, most have consistently fared better at higher temperatures, usually above
20° C. Much of the work done with the biological oxidation of wastes at low temperatures has
been with organisms of this type : mesophilic organisms which are able to survive at low
temperatures but which are metabolically much more active in the temperature range from 20 to
45° C. Such organisms might be labeled "cold-tolerant," but they are probably biochemically
quite different from the truly "cold-loving," or psychrophilic, microorganisms which are able not
only to survive but also to thrive at temperatures below 20° C and which, in fact, find temperatures much higher than 25° C intolerable.This work upon which this report (Proj. A-014-ALAS) is based was supported by funds provided by the United States Department of the Interior, Office of Water Resources Research, as
authorized under the Water Resources Act of 1964, as amended
On a dynamic reaction-diffusion mechanism: The spatial patterning of teeth primordia in the alligator
It is now well established both theoretically and, more recently, experimentally, that steady-state spatial chemical concentration patterns can be formed by a number of specific reactionâdiffusion systems. Reactionâdiffusion models have been widely applied to biological pattern formation problems. Here we propose a model mechanism for the initiation and spatial positioning of teeth primordia in the alligator, Alligator mississippiensis, which, from a reactionâdiffusion theory, introduces, among other things, a new element, namely the effect of domain growth on dynamic spatial pattern formation. Detailed embryological studies by Westergaard and Ferguson (B. Westergaard and M. W. J. Ferguson, J. Zool. Lond., 1986, 210, 575; 1987, 212, 191; Am. J. Anatomy, 1990, 187, 393) show that jaw growth plays a crucial role in the developmental patterning of the tooth initiation process. Based on biological data we develop a reactionâdiffusion mechanism, which crucially includes domain growth. The model can reproduce the spatial pattern development of the first seven teeth primordia in the lower half jaw of A. mississippiensis. The results for the precise spatio temporal sequence compare well with detailed developmental experiments
Tilted accretion discs in cataclysmic variables: tidal instabilities and superhumps
We investigate the growth of tidal instabilities in accretion discs in a
binary star potential, using three dimensional numerical simulations. As
expected from analytic work, the disc is prone to an eccentric instability
provided that it is large enough to extend to the 3:1 resonance. The eccentric
disc leads to positive superhumps in the light curve. It has been proposed that
negative superhumps might arise from a tilted disc, but we find no evidence
that the companion gravitational tilt instability can grow fast enough in a
fluid disc to create a measurable inclination. The origin of negative
superhumps in the light curves of cataclysmic variables remains a puzzle.Comment: 7 pages, 7 figures, accepted for publication in MNRA
Modelling delta-notch perturbations during zebrafish somitogenesis
The discovery over the last 15 years of molecular clocks and gradients in the pre-somitic mesoderm of numerous vertebrate species has added significant weight to Cooke and Zeeman's âclock and wavefrontâ model of somitogenesis, in which a travelling wavefront determines the spatial position of somite formation and the somitogenesis clock controls periodicity (Cooke and Zeeman, 1976). However, recent high-throughput measurements of spatiotemporal patterns of gene expression in different zebrafish mutant backgrounds allow further quantitative evaluation of the clock and wavefront hypothesis. In this study we describe how our recently proposed model, in which oscillator coupling drives the propagation of an emergent wavefront, can be used to provide mechanistic and testable explanations for the following observed phenomena in zebrafish embryos: (a) the variation in somite measurements across a number of zebrafish mutants; (b) the delayed formation of somites and the formation of âsalt and pepperâ patterns of gene expression upon disruption of oscillator coupling; and (c) spatial correlations in the âsalt and pepperâ patterns in Delta-Notch mutants. In light of our results, we propose a number of plausible experiments that could be used to further test the model
Model-based target sonification on mobile devices
We investigate the use of audio and haptic feedback to augment the display of a mobile device controlled by tilt input. We provide an example of this based on Doppler effects, which highlight the user's approach to a target, or a target's movement from the current state, in the same way we hear the pitch of a siren change as it passes us. Twelve participants practiced navigation/browsing a state-space that was displayed via audio and vibrotactile modalities. We implemented the experiment on a Pocket PC, with an accelerometer attached to the serial port and a headset attached to audio port. Users navigated through the environment by tilting the device. Feedback was provided via audio displayed via a headset, and by vibrotactile information displayed by a vibrotactile unit in the Pocket PC. Users selected targets placed randomly in the state-space, supported by combinations of audio, visual and vibrotactile cues. The speed of target acquisition and error rate were measured, and summary statistics on the acquisition trajectories were calculated. These data were used to compare different display combinations and configurations. The results in the paper quantified the changes brought by predictive or 'quickened' sonified displays in mobile, gestural interaction
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