2,417 research outputs found
Working with OpenCL to Speed Up a Genetic Programming Financial Forecasting Algorithm: Initial Results
The genetic programming tool EDDIE has been shown to be a successful financial forecasting tool, however it has suffered from an increase in execution time as new features have been added. Speed is an important aspect in financial problems, especially in the field of algorithmic trading, where a delay in taking a decision could cost millions. To offset this performance loss, EDDIE has been modified to take advantage of multi-core CPUs and dedicated GPUs. This has been achieved by modifying the candidate solution evaluation to use an OpenCL kernel, allowing the parallel evaluation of solutions. Our computational results have shown improvements in the running time of EDDIE when the evaluation was delegated to the OpenCL kernel running on a multi-core CPU, with speed ups up to 21 times faster than the original EDDIE algorithm. While most previous works in the literature reported significantly improvements in performance when running an OpenCL kernel on a GPU device, we did not observe this in our results. Further investigation revealed that memory copying overheads and branching code in the kernel are potentially causes of the (under-)performance of the OpenCL kernel when running on the GPU device
Common parasites of farm animals : their prevention and treatment
Caption title.Digitized 2006 AES MoU
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Identification and characterization of a novel extracellular matrix protein nephronectin that is associated with integrin alpha8beta1 in the embryonic kidney.
The epithelial-mesenchymal interactions required for kidney organogenesis are disrupted in mice lacking the integrin alpha8beta1. None of this integrin's known ligands, however, appears to account for this phenotype. To identify a more relevant ligand, a soluble integrin alpha8beta1 heterodimer fused to alkaline phosphatase (AP) has been used to probe blots and cDNA libraries. In newborn mouse kidney extracts, alpha8beta1-AP detects a novel ligand of 70-90 kD. This protein, named nephronectin, is an extracellular matrix protein with five EGF-like repeats, a mucin region containing a RGD sequence, and a COOH-terminal MAM domain. Integrin alpha8beta1 and several additional RGD-binding integrins bind nephronectin. Nephronectin mRNA is expressed in the ureteric bud epithelium, whereas alpha8beta1 is expressed in the metanephric mesenchyme. Nephronectin is localized in the extracellular matrix in the same distribution as the ligand detected by alpha8beta1-AP and forms a complex with alpha8beta1 in vivo. Thus, these results strongly suggest that nephronectin is a relevant ligand mediating alpha8beta1 function in the kidney. Nephronectin is expressed at numerous sites outside the kidney, so it may also have wider roles in development. The approaches used here should be generally useful for characterizing the interactions of novel extracellular matrix proteins identified through genomic sequencing projects
Is vertical disparity used to determine azimuth?
AbstractThe azimuth of a stimulus relative to the head can be determined from an extra-retinal, eye-position signal plus an estimate of the retinal eccentricity of the image. Alternatively, azimuth could be determined from retinal-image information alone. Specifically, stimulus azimuth could be estimated from two derivatives of vertical disparity: vertical size ratio (which varies with azimuth), and the horizontal gradient of vertical size ratio (a measure of distance). Here we examine the determinants of perceived azimuth in viewing conditions that, theoretically, should favor the use of vertical disparity. We find no evidence that vertical disparity is used. Perceived azimuth was determined completely by felt eye position and the retinal eccentricity of the image
Self-consistent simulations of a von K\'arm\'an type dynamo in a spherical domain with metallic walls
We have performed numerical simulations of boundary-driven dynamos using a
three-dimensional non-linear magnetohydrodynamical model in a spherical shell
geometry. A conducting fluid of magnetic Prandtl number Pm=0.01 is driven into
motion by the counter-rotation of the two hemispheric walls. The resulting flow
is of von K\'arm\'an type, consisting of a layer of zonal velocity close to the
outer wall and a secondary meridional circulation. Above a certain forcing
threshold, the mean flow is unstable to non-axisymmetric motions within an
equatorial belt. For fixed forcing above this threshold, we have studied the
dynamo properties of this flow. The presence of a conducting outer wall is
essential to the existence of a dynamo at these parameters. We have therefore
studied the effect of changing the material parameters of the wall (magnetic
permeability, electrical conductivity, and thickness) on the dynamo. In common
with previous studies, we find that dynamos are obtained only when either the
conductivity or the permeability is sufficiently large. However, we find that
the effect of these two parameters on the dynamo process are different and can
even compete to the detriment of the dynamo. Our self-consistent approach allow
us to analyze in detail the dynamo feedback loop. The dynamos we obtain are
typically dominated by an axisymmetric toroidal magnetic field and an axial
dipole component. We show that the ability of the outer shear layer to produce
a strong toroidal field depends critically on the presence of a conducting
outer wall, which shields the fluid from the vacuum outside. The generation of
the axisymmetric poloidal field, on the other hand, occurs in the equatorial
belt and does not depend on the wall properties.Comment: accepted for publication in Physical Review
Validated helioseismic inversions for 3-D vector flows
According to time-distance helioseismology, information about internal fluid
motions is encoded in the travel times of solar waves. The inverse problem
consists of inferring 3-D vector flows from a set of travel-time measurements.
Here we investigate the potential of time-distance helioseismology to infer 3-D
convective velocities in the near-surface layers of the Sun. We developed a new
Subtractive Optimally Localised Averaging (SOLA) code suitable for pipeline
pseudo-automatic processing. Compared to its predecessor, the code was improved
by accounting for additional constraints in order to get the right answer
within a given noise level. The main aim of this study is to validate results
obtained by our inversion code. We simulate travel-time maps using a snapshot
from a numerical simulation of solar convective flows, realistic Born
travel-time sensitivity kernels, and a realistic model of travel-time noise.
These synthetic travel times are inverted for flows and the results compared
with the known input flow field. Additional constraints are implemented in the
inversion: cross-talk minimization between flow components and spatial
localization of inversion coefficients. Using modes f, p1 through p4, we show
that horizontal convective flow velocities can be inferred without bias, at a
signal-to-noise ratio greater than one in the top 3.5 Mm, provided that
observations span at least four days. The vertical component of velocity (v_z),
if it were to be weak, is more difficult to infer and is seriously affected by
cross-talk from horizontal velocity components. We emphasise that this
cross-talk must be explicitly minimised in order to retrieve v_z in the top 1
Mm. We also show that statistical averaging over many different areas of the
Sun allows for reliably measuring of average properties of all three flow
components in the top 5.5 Mm of the convection zone.Comment: 14 pages main paper, 9 pages electronic supplement, 28 figures.
Accepted for publication in Astronomy & Astrophysic
Perceived Visual Direction near an Occluder
When an opaque object occludes a more distant object, the two eyes often see different parts of the
distant object. Hering s laws of visual direction make an interesting prediction for this situation: the
part seen by both eyes should be seen in a different direction than the part seen by one eye. We
examined whether this prediction holds by asking observers to align a vertical monocular line
segment with a nearby vertical binocular segment. We found it necessary to correct the alignment
data for vergence errors, which were measured in a control experiment, and for monocular spatial
distortions, which were also measured in a control experiment. Settings were reasonably consistent
with Hering's laws when the monocular and binocular targets were separated by 30 arcmin or more.
Observers aligned the targets as if they were viewing them from one eye only when they were
separated by 2 arcmin; this behavior is consistent with an observation reported by Erkelens and
colleagues. The same behavior was observed when the segments were horizontal and when no
visible occluder was present. Perceived visual direction when the two eyes see different parts of a
distant target is assigned in a fashion that minimizes, but does not eliminate, distortions of the shape
of the occluded object
An analysis of binocular slant contrast
When a small frontoparallel surface (a test strip) is surrounded by a larger slanted surface (an
inducer), the test strip is perceived as slanted in the direction opposite to the inducer. This has been
called the depth-contrast effect, but we call it the slant-contrast effect. In nearly all demonstrations of
this effect, the inducers slant is specified by stereoscopic signals, and other signals, such as the texture
gradient, specify that it is frontoparallel. We present a theory of slant estimation that determines surface
slant via linear combination of various slant estimators; the weight of each estimator is proportional to
its reliability. The theory explains slant contrast because the absolute slant of the inducer and the
relative slant between test strip and inducer are both estimated with greater reliability than the absolute
slant of the test strip. The theory predicts that slant contrast will be eliminated if the signals specifying
the inducers slant are consistent with one another. It also predicts reversed slant contrast if the
inducers slant is specified by nonstereoscopic signals rather than by stereo signals. These predictions
were tested and confirmed in three experiments. The first showed that slant contrast is greatly reduced
when the stereo- and nonstereo-specified slants of the inducer are made consistent with one another.
The second showed that slant contrast is eliminated altogether when the stimulus consists of real planes
rather than images on a display screen. The third showed that slant contrast is reversed when the
nonstereo-specified slant of the inducer varies and the stereo-specified slant is zero. We conclude that
slant contrast is a byproduct of the visual systems reconciliation of conflicting information while it
attempts to determine surface slant
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