247 research outputs found
An efficient hardware architecture for a neural network activation function generator
This paper proposes an efficient hardware architecture for a function generator suitable for an artificial neural network (ANN). A spline-based approximation function is designed that provides a good trade-off between accuracy and silicon area, whilst also being inherently scalable and adaptable for numerous activation functions. This has been achieved by using a minimax polynomial and through optimal placement of the approximating polynomials based on the results of a genetic algorithm. The approximation error of the proposed method compares favourably to all related research in this field. Efficient hardware multiplication circuitry is used in the implementation, which reduces the area overhead and increases the throughput
On the Reported Death of the MACHO Era
We present radial velocity measurements of four wide halo binary candidates
from the sample in Chaname & Gould (2004; CG04) which, to date, is the only
sample containing a large number of such candidates. The four candidates that
we have observed have projected separations >0.1 pc, and include the two widest
binaries from the sample, with separations of 0.45 and 1.1 pc. We confirm that
three of the four CG04 candidates are genuine, including the one with the
largest separation. The fourth candidate, however, is spurious at the 5-sigma
level. In the light of these measurements we re-examine the implications for
MACHO models of the Galactic halo. Our analysis casts doubt on what MACHO
constraints can be drawn from the existing sample of wide halo binaries.Comment: 6 Pages, 4 Figures, Accepted for MNRAS Letter
Pseudo-Stable Bubbles
The evolution of spherically symmetric unstable scalar field configurations
(``bubbles'') is examined for both symmetric (SDWP) and asymmetric (ADWP)
double-well potentials. Bubbles with initial static energies E_0\la E_{{\rm
crit}}, where is some critical value, shrink in a time scale
determined by their linear dimension, or ``radius''. Bubbles with E_0\ga
E_{{\rm crit}} evolve into time-dependent, localized configurations which are
{\it very} long-lived compared to characteristic time-scales in the models
examined. The stability of these configurations is investigated and possible
applications are briefly discussed.tic time-scales in the models examined. The
stability of these configurations is investigated and possible applications are
briefly discussed.Comment: 10 pages, LaTeX (uses revtex 3.0), 4 figures (postscript files of
figs.1 and 2 appended starting on line 497), report DART-HEP-93/0
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An Overview of the Use of Neural Networks for Data Mining Tasks
In the recent years the area of data mining has experienced a considerable demand for technologies that extract knowledge from large and complex data sources. There is a substantial commercial interest as well as research investigations in the area that aim to develop new and improved approaches for extracting information, relationships, and patterns from datasets. Artificial Neural Networks (NN) are popular biologically inspired intelligent methodologies, whose classification, prediction and pattern recognition capabilities have been utilised successfully in many areas, including science, engineering, medicine, business, banking, telecommunication, and many other fields. This paper highlights from a data mining perspective the implementation of NN, using supervised and unsupervised learning, for pattern recognition, classification, prediction and cluster analysis, and focuses the discussion on their usage in bioinformatics and financial data analysis tasks
EGMF Constraints from Simultaneous GeV-TeV Observations of Blazars
Attenuation of the TeV gamma-ray flux from distant blazars through pair
production with extragalactic background light leads to the development of
electromagnetic cascades and subsequent, lower energy, GeV secondary gamma-ray
emission. Due to the deflection of VHE cascade electrons by extragalactic
magnetic fields (EGMF), the spectral shape of this arriving cascade gamma-ray
emission is dependent on the strength of the EGMF. Thus, the spectral shape of
the GeV-TeV emission from blazars has the potential to probe the EGMF strength
along the line of sight to the object. We investigate constraints on the EGMF
derived from observations of blazars for which TeV observations simultaneous
with those by the Fermi telescope were reported. We study the dependence of the
EGMF bound on the hidden assumptions it rests upon. We select blazar objects
for which simultaneous Fermi/LAT GeV and Veritas, MAGIC or HESS TeV emission
have been published. We model the development of electromagnetic cascades along
the gamma-ray beams from these sources using Monte Carlo simulations, including
the calculation of the temporal delay incurred by cascade photons, relative to
the light propagation time of direct gamma-rays from the source. Constraints on
EGMF could be derived from the simultaneous GeV-TeV data on the blazars RGB
J0710+591, 1ES 0229+200, and 1ES 1218+304. The measured source flux level in
the GeV band is lower than the expected cascade component calculated under the
assumption of zero EGMF. Assuming that the reason for the suppression of the
cascade component is the extended nature of the cascade emission, we find that
B>10^{-15} G (assuming EGMF correlation length of ~1 Mpc) is consistent with
the data. Alternatively, the assumption that the suppression of the cascade
emission is caused by the time delay of the cascade photons the data are
consistent with B>10^{-17} G for the same correlation length.Comment: 9 pages, 9 figure
Public access defibrillation: Suppression of 16.7 Hz interference generated by the power supply of the railway systems
BACKGROUND: A specific problem using the public access defibrillators (PADs) arises at the railway stations. Some countries as Germany, Austria, Switzerland, Norway and Sweden are using AC railroad net power-supply system with rated 16.7 Hz frequency modulated from 15.69 Hz to 17.36 Hz. The power supply frequency contaminates the electrocardiogram (ECG). It is difficult to be suppressed or eliminated due to the fact that it considerably overlaps the frequency spectra of the ECG. The interference impedes the automated decision of the PADs whether a patient should be (or should not be) shocked. The aim of this study is the suppression of the 16.7 Hz interference generated by the power supply of the railway systems. METHODS: Software solution using adaptive filtering method was proposed for 16.7 Hz interference suppression. The optimal performance of the filter is achieved, embedding a reference channel in the PADs to record the interference. The method was tested with ECGs from AHA database. RESULTS: The method was tested with patients of normal sinus rhythms, symptoms of tachycardia and ventricular fibrillation. Simulated interference with frequency modulation from 15.69 Hz to 17.36 Hz changing at a rate of 2% per second was added to the ECGs, and then processed by the suggested adaptive filtering. The method totally suppresses the noise with no visible distortions of the original signals. CONCLUSION: The proposed adaptive filter for noise suppression generated by the power supply of the railway systems has a simple structure requiring a low level of computational resources, but a good reference signal as well
The dynamics of curved gravitating walls
We examine the dynamics of a self-gravitating domain wall using the model as a specific example. We find that the Nambu motion of the wall
is quite generic and dominates the wall motion even in the presence of gravity.
We calculate the corrections to this leading order motion, and estimate the
effect of the inclusion of gravity on the dynamics of the wall. We then treat
the case of a spherical gravitating thick wall as a particular example, solving
the field equations and calculating the corrections to the Nambu motion
analytically for this specific case. We find that the presence of gravity
retards collapse in this case.Comment: 19 pages revtex, 3 figures, references added, equations correcte
The Schrdinger-Poisson equations as the large-N limit of the Newtonian N-body system: applications to the large scale dark matter dynamics
In this paper it is argued how the dynamics of the classical Newtonian N-body
system can be described in terms of the Schrdinger-Poisson equations
in the large limit. This result is based on the stochastic quantization
introduced by Nelson, and on the Calogero conjecture. According to the Calogero
conjecture, the emerging effective Planck constant is computed in terms of the
parameters of the N-body system as , where is the gravitational constant, and are the
number and the mass of the bodies, and is their average density. The
relevance of this result in the context of large scale structure formation is
discussed. In particular, this finding gives a further argument in support of
the validity of the Schrdinger method as numerical double of the
N-body simulations of dark matter dynamics at large cosmological scales.Comment: Accepted for publication in the Euro. Phys. J.
The properties of the local spiral arms from RAVE data: two-dimensional density wave approach
Using the RAVE survey, we recently brought to light a gradient in the mean
galactocentric radial velocity of stars in the extended solar neighbourhood.
This gradient likely originates from non-axisymmetric perturbations of the
potential, among which a perturbation by spiral arms is a possible explanation.
Here, we apply the traditional density wave theory and analytically model the
radial component of the two-dimensional velocity field. Provided that the
radial velocity gradient is caused by relatively long-lived spiral arms that
can affect stars substantially above the plane, this analytic model provides
new independent estimates for the parameters of the Milky Way spiral structure.
Our analysis favours a two-armed perturbation with the Sun close to the inner
ultra-harmonic 4:1 resonance, with a pattern speed \Omega_p=18.6^{+0.3}_{-0.2}
km/s/kpc and a small amplitude A=0.55 \pm 0.02% of the background potential
(14% of the background density). This model can serve as a basis for numerical
simulations in three dimensions, additionally including a possible influence of
the galactic bar and/or other non-axisymmetric modes.Comment: 9 pages, 4 figures, accepted for publication in MNRA
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