2,515 research outputs found
The Microbiota and Health Promoting Characteristics of the Fermented Beverage Kefir
peer-reviewedKefir is a complex fermented dairy product created through the symbiotic fermentation of milk by lactic acid bacteria and yeasts contained within an exopolysaccharide and protein complex called a kefir grain. As with other fermented dairy products, kefir has been associated with a range of health benefits such as cholesterol metabolism and angiotensin-converting enzyme (ACE) inhibition, antimicrobial activity, tumor suppression, increased speed of wound healing, and modulation of the immune system including the alleviation of allergy and asthma. These reports have led to increased interest in kefir as a focus of research and as a potential probiotic-containing product. Here, we review those studies with a particular emphasis on the microbial composition and the health benefits of the product, as well as discussing the further development of kefir as an important probiotic product.The authors are funded through the Teagasc Walsh Fellowship Scheme(2014025)and internal Teagasc funding(RMIS6486). BW is supported by the Canada Research Chairs Program and research in the Cotter laboratory is funded by SFI through the PI award “Obesibiotics”(11/PI/1137)and in the form of a center grant (APC Microbiome Institute Grant Number SFI/12/RC/2273)
The first GCT camera for the Cherenkov Telescope Array
The Gamma Cherenkov Telescope (GCT) is proposed to be part of the Small Size
Telescope (SST) array of the Cherenkov Telescope Array (CTA). The GCT
dual-mirror optical design allows the use of a compact camera of diameter
roughly 0.4 m. The curved focal plane is equipped with 2048 pixels of
~0.2{\deg} angular size, resulting in a field of view of ~9{\deg}. The GCT
camera is designed to record the flashes of Cherenkov light from
electromagnetic cascades, which last only a few tens of nanoseconds. Modules
based on custom ASICs provide the required fast electronics, facilitating
sampling and digitisation as well as first level of triggering. The first GCT
camera prototype is currently being commissioned in the UK. On-telescope tests
are planned later this year. Here we give a detailed description of the camera
prototype and present recent progress with testing and commissioning.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherlands. All CTA contributions at
arXiv:1508.0589
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Development of an autonomous design program
Presented is a general approach to the development of an ''intelligent'' computer program that designs technical devices and systematically improves its capability without human intervention. The methodology is based on the recognition that effective use of computers requires employment of clearly defined concepts and precise language, therefore, significant effort is devoted to the formulation of the design problem in mathematical terms. This formulation is based on the introduction of metrizable performance and configuration spaces and on the representation of the design process as a mapping from the performance into the configuration space; the inverse of this mapping represents the design evaluation. An essential part of the design mapping, as we define it, is design optimization. For that purpose we developed a generalized simulated annealing method capable of locating global extrema of multidimensional functions that have numerous local extreme and may not be differentiable. The optimization method is interesting in its own right, for its applicability transcends the original intent. The exploitation of the concept of the design mapping and the optimization algorithm are illustrated with an application to the design of optical lenses. This application was chosen because it offers the possibility to evaluate each design solely by computation and thus validate the program's capability without the need for a physical realization
Besov priors for Bayesian inverse problems
We consider the inverse problem of estimating a function from noisy,
possibly nonlinear, observations. We adopt a Bayesian approach to the problem.
This approach has a long history for inversion, dating back to 1970, and has,
over the last decade, gained importance as a practical tool. However most of
the existing theory has been developed for Gaussian prior measures. Recently
Lassas, Saksman and Siltanen (Inv. Prob. Imag. 2009) showed how to construct
Besov prior measures, based on wavelet expansions with random coefficients, and
used these prior measures to study linear inverse problems. In this paper we
build on this development of Besov priors to include the case of nonlinear
measurements. In doing so a key technical tool, established here, is a
Fernique-like theorem for Besov measures. This theorem enables us to identify
appropriate conditions on the forward solution operator which, when matched to
properties of the prior Besov measure, imply the well-definedness and
well-posedness of the posterior measure. We then consider the application of
these results to the inverse problem of finding the diffusion coefficient of an
elliptic partial differential equation, given noisy measurements of its
solution.Comment: 18 page
Bayesian modelling of clusters of galaxies from multi-frequency pointed Sunyaev--Zel'dovich observations
We present a Bayesian approach to modelling galaxy clusters using
multi-frequency pointed observations from telescopes that exploit the
Sunyaev--Zel'dovich effect. We use the recently developed MultiNest technique
(Feroz, Hobson & Bridges, 2008) to explore the high-dimensional parameter
spaces and also to calculate the Bayesian evidence. This permits robust
parameter estimation as well as model comparison. Tests on simulated Arcminute
Microkelvin Imager observations of a cluster, in the presence of primary CMB
signal, radio point sources (detected as well as an unresolved background) and
receiver noise, show that our algorithm is able to analyse jointly the data
from six frequency channels, sample the posterior space of the model and
calculate the Bayesian evidence very efficiently on a single processor. We also
illustrate the robustness of our detection process by applying it to a field
with radio sources and primordial CMB but no cluster, and show that indeed no
cluster is identified. The extension of our methodology to the detection and
modelling of multiple clusters in multi-frequency SZ survey data will be
described in a future work.Comment: 12 pages, 7 figures, submitted to MNRA
Characteristics of EGRET Blazars in the VLBA Imaging and Polarimetry Survey (VIPS)
We examine the radio properties of EGRET-detected blazars observed as part of
the VLBA Imaging and Polarimetry Survey (VIPS). VIPS has a flux limit roughly
an order of magnitude below the MOJAVE survey and most other samples that have
been used to study the properties of EGRET blazars. At lower flux levels, radio
flux density does not directly correlate with gamma-ray flux density. We do
find that the EGRET-detected blazars tend to have higher brightness
temperatures, greater core fractions, and possibly larger than average jet
opening angles. A weak correlation is also found with jet length and with
polarization. All of the well-established trends can be explained by
systematically larger Doppler factors in the gamma-ray loud blazars, consistent
with the measurements of higher apparent velocities found in monitoring
programs carried out at radio frequencies above 10 GHz.Comment: 20 pages, 7 figures, accepted to Ap
The Lifetime of FRIIs in Groups and Clusters: Implications for Radio-Mode Feedback
We determine the maximum lifetime t_max of 52 FRII radio sources found in 26
central group galaxies from cross correlation of the Berlind SDSS group catalog
with the VLA FIRST survey. Mock catalogs of FRII sources were produced to match
the selection criteria of FIRST and the redshift distribution of our parent
sample, while an analytical model was used to calculate source sizes and
luminosities. The maximum lifetime of FRII sources was then determined via a
comparison of the observed and model projected length distributions. We
estimate the average FRII lifetime is 1.5x10^7 years and the duty cycle is
~8x10^8 years. Degeneracies between t_max and the model parameters: jet power
distribution, axial ratio, energy injection index, and ambient density
introduce at most a factor of two uncertainty in our lifetime estimate. In
addition, we calculate the radio active galactic nuclei (AGN) fraction in
central group galaxies as a function of several group and host galaxy
properties. The lifetime of radio sources recorded here is consistent with the
quasar lifetime, even though these FRIIs have substantially sub-Eddington
accretion. These results suggest a fiducial time frame for energy injection
from AGN in feedback models. If the morphology of a given extended radio source
is set by large-scale environment, while the lifetime is determined by the
details of the accretion physics, this FRII lifetime is relevant for all
extended radio sources.Comment: 18 pages, 7 figures. Accepted for publication in ApJ. High resolution
paper available at http://www.astronomy.ohio-state.edu/~bird/BMK07.pd
Effects of Noise on Ecological Invasion Processes: Bacteriophage-mediated Competition in Bacteria
Pathogen-mediated competition, through which an invasive species carrying and
transmitting a pathogen can be a superior competitor to a more vulnerable
resident species, is one of the principle driving forces influencing
biodiversity in nature. Using an experimental system of bacteriophage-mediated
competition in bacterial populations and a deterministic model, we have shown
in [Joo et al 2005] that the competitive advantage conferred by the phage
depends only on the relative phage pathology and is independent of the initial
phage concentration and other phage and host parameters such as the
infection-causing contact rate, the spontaneous and infection-induced lysis
rates, and the phage burst size. Here we investigate the effects of stochastic
fluctuations on bacterial invasion facilitated by bacteriophage, and examine
the validity of the deterministic approach. We use both numerical and
analytical methods of stochastic processes to identify the source of noise and
assess its magnitude. We show that the conclusions obtained from the
deterministic model are robust against stochastic fluctuations, yet deviations
become prominently large when the phage are more pathological to the invading
bacterial strain.Comment: 39 pages, 7 figure
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