113 research outputs found
The Dynamics of Group Codes: Dual Abelian Group Codes and Systems
Fundamental results concerning the dynamics of abelian group codes
(behaviors) and their duals are developed. Duals of sequence spaces over
locally compact abelian groups may be defined via Pontryagin duality; dual
group codes are orthogonal subgroups of dual sequence spaces. The dual of a
complete code or system is finite, and the dual of a Laurent code or system is
(anti-)Laurent. If C and C^\perp are dual codes, then the state spaces of C act
as the character groups of the state spaces of C^\perp. The controllability
properties of C are the observability properties of C^\perp. In particular, C
is (strongly) controllable if and only if C^\perp is (strongly) observable, and
the controller memory of C is the observer memory of C^\perp. The controller
granules of C act as the character groups of the observer granules of C^\perp.
Examples of minimal observer-form encoder and syndrome-former constructions are
given. Finally, every observer granule of C is an "end-around" controller
granule of C.Comment: 30 pages, 11 figures. To appear in IEEE Trans. Inform. Theory, 200
Rateless Coding for Gaussian Channels
A rateless code-i.e., a rate-compatible family of codes-has the property that
codewords of the higher rate codes are prefixes of those of the lower rate
ones. A perfect family of such codes is one in which each of the codes in the
family is capacity-achieving. We show by construction that perfect rateless
codes with low-complexity decoding algorithms exist for additive white Gaussian
noise channels. Our construction involves the use of layered encoding and
successive decoding, together with repetition using time-varying layer weights.
As an illustration of our framework, we design a practical three-rate code
family. We further construct rich sets of near-perfect rateless codes within
our architecture that require either significantly fewer layers or lower
complexity than their perfect counterparts. Variations of the basic
construction are also developed, including one for time-varying channels in
which there is no a priori stochastic model.Comment: 18 page
Relative performance of antimicrobial susceptibility assays on clinical Escherichia coli isolates from animals
The assessment of antimicrobial resistance in bacteria derived from animals is often performed using the disc diffusion assay. However broth-microdilution is the preferred assay for national antimicrobial resistance surveillance programs. This study aimed to evaluate the accuracy of disc diffusion relative to broth-microdilution across a panel of 12 antimicrobials using data from a collection of 994 clinical Escherichia coli isolates from animals. Disc diffusion performance was evaluated by diagnostic sensitivity, specificity, likelihood ratio pairs and receive-operating characteristic (ROC) analysis. Data was dichotomised using CLSI susceptible and resistant clinical breakpoints. In addition, disc diffusion breakpoints produced using diffusion Breakpoint Estimation Testing Software (dBETS) were evaluated. Analysis revealed considerable variability in performance estimates for disc diffusion susceptible and resistant breakpoints (AUC ranges: 0.78–0.99 and 0.92–1.0, respectively) across the panel of antimicrobials. Ciprofloxacin, tetracycline, and ampicillin estimates were robust across both breakpoints, whereas estimates for several antimicrobials including amoxicillin-clavulanic acid, cefoxitin and gentamicin were less favourable using susceptible breakpoints. Overall performance estimates were moderately improved when dBETS susceptible breakpoints were applied. For most antimicrobials, disc diffusion was accurate at predicting resistance of clinical E. coli from animals that could otherwise be determined by broth-microdilution. While disc diffusion is suboptimal for assessing the proportion of fully susceptible isolates for some drugs, sensitivity and specificity estimates provided here allow for the use of standard formula to correct this. For this reason, disc diffusion has applicability in national surveillance provided the performance of the assay is taken into account
Modelling and peeling extended sources with shapelets: a Fornax A case study
To make a power spectrum (PS) detection of the 21 cm signal from the Epoch of
Reionisation (EoR), one must avoid/subtract bright foreground sources. Sources
such as Fornax A present a modelling challenge due to spatial structures
spanning from arc seconds up to a degree. We compare modelling with multi-scale
(MS) CLEAN components to 'shapelets', an alternative set of basis functions. We
introduce a new image-based shapelet modelling package, SHAMFI. We also
introduce a new CUDA simulation code (WODEN) to generate point source,
Gaussian, and shapelet components into visibilities. We test performance by
modelling a simulation of Fornax A, peeling the model from simulated
visibilities, and producing a residual PS. We find the shapelet method
consistently subtracts large-angular-scale emission well, even when the
angular-resolution of the data is changed. We find that when increasing the
angular-resolution of the data, the MS CLEAN model worsens at large
angular-scales. When testing on real MWA data, the expected improvement is not
seen in real data because of the other dominating systematics still present.
Through further simulation we find the expected differences to be lower than
obtainable through current processing pipelines. We conclude shapelets are
worthwhile for subtracting extended galaxies, and may prove essential for an
EoR detection in the future, once other systematics have been addressed.Comment: 17 pages, 11 Figures, accepted for publication in Publications of the
Astronomical Society of Australia (18/05/2020). "For the SHAMFI code, see:
https://github.com/JLBLine/SHAMFI" . "For the SHAMFI documentation, see:
https://shamfi.readthedocs.io/" . "For the WODEN code and documentation see:
https://github.com/JLBLine/WODEN
A high resolution foreground model for the MWA EoR1 field : model and implications for EoR power spectrum analysis
This article has been published in a revised form in Publications of the Astronomical Society of Australia https://doi.org/10.1017/pasa.2017.26 This version is free to view and download for private research and study only. Not for re-distribution, re-sale or use in derivative works. Under embargo. Embargo end date: 10 February 2018. © Astronomical Society of Australia 2017.The current generation of experiments aiming to detect the neutral hydrogen signal from the Epoch of Reionisation (EoR) is likely to be limited by systematic effects associated with removing foreground sources from target fields. In this paper we develop a model for the compact foreground sources in one of the target fields of the MWA's EoR key science experiment: the `EoR1' field. The model is based on both the MWA's GLEAM survey and GMRT 150 MHz data from the TGSS survey, the latter providing higher angular resolution and better astrometric accuracy for compact sources than is available from the MWA alone. The model contains 5049 sources, some of which have complicated morphology in MWA data, Fornax A being the most complex. The higher resolution data show that 13% of sources that appear point-like to the MWA have complicated morphology such as double and quad structure, with a typical separation of 33~arcsec. We derive an analytic expression for the error introduced into the EoR two-dimensional power spectrum due to peeling close double sources as single point sources and show that for the measured source properties, the error in the power spectrum is confined to high modes that do not affect the overall result for the large-scale cosmological signal of interest. The brightest ten mis-modelled sources in the field contribute 90% of the power bias in the data, suggesting that it is most critical to improve the models of the brightest sources. With this hybrid model we reprocess data from the EoR1 field and show a maximum of 8% improved calibration accuracy and a factor of two reduction in residual power in -space from peeling these sources. Implications for future EoR experiments including the SKA are discussed in relation to the improvements obtained.Peer reviewedFinal Accepted Versio
Gridded and direct Epoch of Reionisation bispectrum estimates using the Murchison Widefield Array
We apply two methods to estimate the 21~cm bispectrum from data taken within
the Epoch of Reionisation (EoR) project of the Murchison Widefield Array (MWA).
Using data acquired with the Phase II compact array allows a direct bispectrum
estimate to be undertaken on the multiple redundantly-spaced triangles of
antenna tiles, as well as an estimate based on data gridded to the -plane.
The direct and gridded bispectrum estimators are applied to 21 hours of
high-band (167--197~MHz; =6.2--7.5) data from the 2016 and 2017 observing
seasons. Analytic predictions for the bispectrum bias and variance for point
source foregrounds are derived. We compare the output of these approaches, the
foreground contribution to the signal, and future prospects for measuring the
bispectra with redundant and non-redundant arrays. We find that some triangle
configurations yield bispectrum estimates that are consistent with the expected
noise level after 10 hours, while equilateral configurations are strongly
foreground-dominated. Careful choice of triangle configurations may be made to
reduce foreground bias that hinders power spectrum estimators, and the 21~cm
bispectrum may be accessible in less time than the 21~cm power spectrum for
some wave modes, with detections in hundreds of hours.Comment: 19 pages, 10 figures, accepted for publication in PAS
The EoR Sensitivity of the Murchison Widefield Array
Using the final 128 antenna locations of the Murchison Widefield Array (MWA),
we calculate its sensitivity to the Epoch of Reionization (EoR) power spectrum
of red- shifted 21 cm emission for a fiducial model and provide the tools to
calculate the sensitivity for any model. Our calculation takes into account
synthesis rotation, chro- matic and asymmetrical baseline effects, and excludes
modes that will be contaminated by foreground subtraction. For the fiducial
model, the MWA will be capable of a 14{\sigma} detection of the EoR signal with
one full season of observation on two fields (900 and 700 hours).Comment: 5 pages, 4 figures, 1 table, Accepted for publication in MNRAS
Letters. Supplementary material will be available in the published version,
or by contacting the author
Molecular epidemiology of methicillin-resistant Staphylococcus aureus isolated from Australian veterinarians
This work investigated the molecular epidemiology and antimicrobial resistance of methicillinresistant Staphylococcus aureus (MRSA) isolated from veterinarians in Australia in 2009. The collection (n = 44) was subjected to extensive molecular typing (MLST, spa, SCCmec, dru, PFGE, virulence and antimicrobial resistance genotyping) and antimicrobial resistance phenotyping by disk diffusion. MRSA was isolated from Australian veterinarians representing various occupational emphases. The isolate collection was dominated by MRSA strains belonging to clonal complex (CC) 8 and multilocus sequence type (ST) 22. CC8 MRSA (ST8-IV [2B], spa t064; and ST612-IV [2B] , spa variable,) were strongly associated with equine practice veterinarians (OR = 17.5, 95% CI = 3.3-92.5, P < 0.001) and were often resistant to gentamicin and rifampicin. ST22-IV [2B], spa variable, were strongly associated with companion animal practice veterinarians (OR = 52.5, 95% CI = 5.2-532.7, P < 0.001) and were resistant to ciprofloxacin. A single pig practice veterinarian carried ST398-V [5C2], spa t1451. Equine practice and companion animal practice veterinarians frequently carried multiresistant-CC8 and ST22 MRSA, respectively, whereas only a single swine specialist carried MRSA ST398. The presence of these strains in veterinarians may be associated with specific antimicrobial administration practices in each animal species
How control systems influence product innovation processes: examining the role of entrepreneurial orientation
This paper yields insights into the channels through which Management Accounting and Control Systems (MACS) exert an influence on product innovation by examining the extent to which different forms of control (i.e. value systems, diagnostic control systems, interactive control systems) are directly associated with the distinct phases of innovation processes. Using survey data collected from 118 medium and large Spanish companies, we find that: (1) value systems and interactive control systems have significant main effects on the creativity, coordination and knowledge integration, and filtering (sub-)phases of innovation processes; and (2) the significance and direction of these influences vary depending on the Entrepreneurial Orientation (EO) of firms. By highlighting the relevance of EO in shaping the influence of MACS on product innovation processes, this study calls for caution in generalising the expected effects of MACS on innovation
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