1,306 research outputs found
Understanding and Improving Optimization in Predictive Coding Networks
Backpropagation (BP), the standard learning algorithm for artificial neural
networks, is often considered biologically implausible. In contrast, the
standard learning algorithm for predictive coding (PC) models in neuroscience,
known as the inference learning algorithm (IL), is a promising, bio-plausible
alternative. However, several challenges and questions hinder IL's application
to real-world problems. For example, IL is computationally demanding, and
without memory-intensive optimizers like Adam, IL may converge to poor local
minima. Moreover, although IL can reduce loss more quickly than BP, the reasons
for these speedups or their robustness remains unclear. In this paper, we
tackle these challenges by 1) altering the standard implementation of PC
circuits to substantially reduce computation, 2) developing a novel optimizer
that improves the convergence of IL without increasing memory usage, and 3)
establishing theoretical results that help elucidate the conditions under which
IL is sensitive to second and higher-order information
Massive Star Formation in Luminous Infrared Galaxies: Giant HII Regions and their relation to Super Star Clusters
We have used HST/NICMOS H-band narrow-band Pa-alpha (at rest 1.87micron)
images to identify star clusters and HII regions respectively in a sample of 8
luminous infrared galaxies (LIRGs). These observations have revealed the
presence of a large population of super star clusters (SSC) and bright HII
regions. A significant fraction of the HII regions shows H-alpha luminosities
above that of 30 Doradus, the prototypical giant HII region. The excess of
extremely luminous HII regions in LIRGs has been confirmed by comparison with
normal galaxies observed at similar spatial resolutions. Despite the large
numbers of identified star clusters and HII regions in LIRGs, we only find a
small fraction of coincidences, between 4% and 30%. Using synthesis models we
have reproduced the relative fractions of young HII regions, intermediate and
old star clusters observed in Arp299 and the central region NGC3256 using a
Salpeter IMF and instantaneous star formation. HII regions with no detected
near-infrared cluster counterpart (25-39%) represent the youngest sites of star
formation, with ages of up to approximately 5Myr and mostly intermediate mass
(~10^5Msun) ionizing clusters. For these two galaxies, and within the present
detection threshold we can only detect coincidences (4-10%) between an HII
region and a near-infrared star cluster for the most massive star clusters
(~10^6Msun) during the first 7Myr of their evolution. The identified
near-infrared SSCs with no detectable Pa-alpha emission represent the ``old''
population (53-66% of the detected sources), with ages of between 7 and
20-40Myr. Older clusters possibly created in this or previous episodes of star
formation are likely to exist in these systems but cannot be identified with
the present detection threshold. (Abridged)Comment: Accepted for publication in AJ (July issue). Figure 2 not included.
Go to: http://nicmos2.as.arizona.edu/~aalonso/work/papers/lirghii_v2.ps for a
complete version of pape
Study on the effectiveness of commercial anti‐islanding algorithms in the prospect of mass penetration of PVs in low‐voltage distribution networks
In the coming years, distribution grids will be progressively flooded by renewable energy sources (RES) that will be interconnected with the main grid through power electronic converters. Photovoltaics (PVs) are one of the most promising renewable technologies even for densely built-up areas where space problems are inevitable. The high penetration prospect of PV facilities on low-voltage distribution networks raises questions regarding the necessity of advanced functions that will enable electronically coupled RES to support the operation of distribution grids and to enhance their reliability. In this context, the objective of this study is to investigate the effectiveness of various islanding prevention measures installed in commercial PV inverters, when multiple inverters are operating in parallel with a low-voltage distribution network (LVDN). Extensive experiments were performed under various PV penetration levels, linear/non-linear load and over/under voltage and over/under frequency conditions, as well as for various values of total harmonic distortion of the mains voltage. Further to the primary statistical analysis, the results were analysed in depth by advanced mathematical methods such as box plot and cluster analysis. The findings of this study indicate that commercial anti-islanding techniques present a high probability of failure in the case of multiple PV units at the same point of common coupling, calling for new and more advanced algorithms.European Commission, H2020, 65411
Ultra-Short Pulse Laser Cleaning of Contaminated Pleistocene Bone: A Comprehensive Study on the Influence of Pulse Duration and Wavelength
The impact of wavelength and pulse duration in laser cleaning of hard blackish contaminants crust from archaeologically significant Pleistocene bone is investigated in this research. The objective is to determine the practical cleaning procedures and identify adequate laser parameters for cleaning archaeological bone from Sima de los Huesos (Spain) based on conservation and restoration perspectives. Bone surface cleaning was performed utilizing two Q-switched Nd:YAG lasers: sub-nanosecond pulsed lasers with emission wavelengths at 355 nm and 1064 nm, respectively, and a Yb:KGW femtosecond pulsed laser with an emission wavelength in the third harmonic at 343 nm. In all experiments, the laser beam scanning mode was applied to measure cleaning efficiency in removing contaminants and degradation products while assessing the underlying substrate surface damage. Several properties, including wavelength-dependent absorption, pulse repetition rate, and thermal properties of the material, are analyzed when evaluating the ability of these lasers to boost the cleaning efficiency of the deteriorated bone surface. Bone surface morphology and composition were studied and compared before and after laser irradiation, using Optical Microscopy, Scanning Electron Microscopy with Energy Dispersive X-ray Spectrometry (SEM-EDS), Fourier Transform Infrared Spectroscopy (FTIR), and X-ray Photoelectron Spectroscopy (XPS) characterization methods. The results indicate that 238-femtosecond UV laser irradiation with 2.37 TWcm−2 is significantly safer and more efficient toward surface contaminant desorption than sub-nanosecond laser irradiation. The results herein presented suggest that these types of fs lasers may be considered for realistic laser conservation of valuable historic and archaeological museum artifacts
Qualitative spatial representation in agent-based models
One of the advantages of agent-based models as simulations of social systems is the ease with which it is possible to spatially embed the agents and their interactions. Spatially explicit representations in agent-based models most typically take the form of raster-based representations in which the space is represented as a grid of squares. More recently, vectorbased representations have been used, usually importing data for the polygons from geographical information systems (GIS). However, for some models, what matters about the space for the purposes of simulation is less the quantitative spatial relationships among entities (e.g. area, distance or direction) than the qualitative relations these quantitative data are used to determine: neighbourhood, and accessibility (which is a general term covering movement and sensing from one region to another). This paper gives consideration to the use of qualitative spatial representations in agent-based modelling, using a model of everyday pro-environmental behaviour in the workplace as an example
The Gaussian-Linear Hidden Markov model: a Python package
We propose the Gaussian-Linear Hidden Markov model (GLHMM), a generalisation
of different types of HMMs commonly used in neuroscience. In short, the GLHMM
is a general framework where linear regression is used to flexibly parameterise
the Gaussian state distribution, thereby accommodating a wide range of uses
-including unsupervised, encoding and decoding models. GLHMM is implemented as
a Python toolbox with an emphasis on statistical testing and out-of-sample
prediction -i.e. aimed at finding and characterising brain-behaviour
associations. The toolbox uses a stochastic variational inference approach,
enabling it to handle large data sets at reasonable computational time.
Overall, the approach can be applied to several data modalities, including
animal recordings or non-brain data, and applied over a broad range of
experimental paradigms. For demonstration, we show examples with fMRI,
electrocorticography, magnetoencephalo-graphy and pupillometry.Comment: 22 pages, 7 figures, 1 tabl
Ultrashort pulsed Femtosecond UV laser for selective cleaning of significant Cretaceous flints
This work reports on studies aimed to evaluate the utilization of ultrashort 238 fs (fs) pulsed UV laser emission at 343 nm for eliminating colored crusts and surface deposits on significant Cretaceous flint surfaces, in an attempt to safeguard its aesthetic appearance and archaeological value. The results indicate that fs UV lasers may be an ideal, non-contact tool for selective surface cleaning of sensitive archaeological artefacts, since they enable contaminant desorption while avoiding photothermal damage
The Grizzly, March 1, 2012
Grasso Hosts Leadership Summit • Board Meets on Diversity Reports • Psychology Major Organizes Autism Discussion • Lt. Gen. Helmick of the US Army to Speak on Campus Tonight at 7 P.M. • Murphy-Stout Interns at South London Hospital • EV Premieres On the Edge • Kelly Herr Competes in Special Olympics in Korea • Opinion: Republicans Need Focus to Win • International Trio Dazzles Students and Faculty • Senior Spotlight: Al Desiderio, Men\u27s Track • Spring Break in Florida for Bears Baseball • Championship Weekend Recaphttps://digitalcommons.ursinus.edu/grizzlynews/1854/thumbnail.jp
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