1,455 research outputs found
Skeleton as a probe of the cosmic web: the 2D case
We discuss the skeleton as a probe of the filamentary structures of a 2D
random field. It can be defined for a smooth field as the ensemble of pairs of
field lines departing from saddle points, initially aligned with the major axis
of local curvature and connecting them to local maxima. This definition is thus
non local and makes analytical predictions difficult, so we propose a local
approximation: the local skeleton is given by the set of points where the
gradient is aligned with the local curvature major axis and where the second
component of the local curvature is negative.
We perform a statistical analysis of the length of the total local skeleton,
chosen for simplicity as the set of all points of space where the gradient is
either parallel or orthogonal to the main curvature axis. In all our numerical
experiments, which include Gaussian and various non Gaussian realizations such
as \chi^2 fields and Zel'dovich maps, the differential length is found within a
normalization factor to be very close to the probability distribution function
of the smoothed field. This is in fact explicitly demonstrated in the Gaussian
case.
This result might be discouraging for using the skeleton as a probe of non
Gausiannity, but our analyses assume that the total length of the skeleton is a
free, adjustable parameter. This total length could in fact be used to
constrain cosmological models, in CMB maps but also in 3D galaxy catalogs,
where it estimates the total length of filaments in the Universe. Making the
link with other works, we also show how the skeleton can be used to study the
dynamics of large scale structure.Comment: 15 pages, 11 figures, submitted to MNRA
Far infrared properties of the rare-earth scandate DyScO3
We present reflectance measurements in the infrared region on a single
crystal the rare earth scandate DyScO3. Measurements performed between room
temperature and 10 K allow to determine the frequency of the infrared-active
phonons, never investigated experimentally, and to get information on their
temperature dependence. A comparison with the phonon peak frequency resulting
from ab-initio computations is also provided. We finally report detailed data
on the frequency dependence of the complex refractive index of DyScO3 in the
terahertz region, which is important in the analysis of terahertz measurements
on thin films deposited on DyScO3
Mono Acyl Glycerol Compound Synthesis Through Partial Transesterification Of Castor Oil (Ricinus communis L.) using KOH as Catalyst
It has been done a study of mono acyl glycerol compound synthesis through partial transesterification of castor oil (Ricinus communis L.) using KOH as catalyst. The product of mono acyl glycerol obtained is 45.4 % with the ratio between castor oil triglyceride and methanol 1:2 at 35 0C temperature with the amount of catalyst 0.5 % (b/b) from the reactant total weight and the reaction time 30 minutes. In this research, it was done a compound characterization using, TLC, FTIR and LC MS to prove the success of targeting compound has been synthesized
First detection of NHD and ND in the interstellar medium
Deuterium fractionation processes in the interstellar medium (ISM) have been
shown to be highly efficient in the family of nitrogen hydrides. To date,
observations were limited to ammonia (NHD, NHD, ND) and imidogen
radical (ND) isotopologues. We want to explore the high frequency windows
offered by the \emph{Herschel Space Observatory} to search for deuterated forms
of amidogen radical NH and to compare the observations against the
predictions of our comprehensive gas-grain chemical model. Making use of the
new molecular spectroscopy data recently obtained at high frequencies for NHD
and ND, both isotopologues have been searched for in the spectral survey
towards the class 0 IRAS 16293-2422, a source in which NH, NH and their
deuterated variants have been previously detected. We used the observations
carried out with HIFI (Heterodyne Instrument for the Far Infrared) in the
framework of the key program "Chemical Herschel surveys of star forming
regions" (CHESS). We report the first detection of interstellar NHD and ND.
Both species are observed in absorption against the continuum of the protostar.
From the analysis of their hyperfine structure, accurate excitation temperature
and column density values have been determined. The latter were combined with
the column density of the parent species NH to derive the deuterium
fractionation in amidogen. The amidogen D/H ratio measured in the low-mass
protostar IRAS 16293-2422 is comparable to the one derived for the related
species imidogen and much higher than that observed for ammonia. Additional
observations of these species will give more insights into the mechanism of
ammonia formation and deuteration in the ISM. We finally indicate the current
possibilities to further explore these species at submillimeter wavelengths.Comment: 11 pages, 5 figures, 7 tables. Accepted for publication in A&
Fast, exact CMB power spectrum estimation for a certain class of observational strategies
We describe a class of observational strategies for probing the anisotropies
in the cosmic microwave background (CMB) where the instrument scans on rings
which can be combined into an n-torus, the {\em ring torus}. This class has the
remarkable property that it allows exact maximum likelihood power spectrum
estimation in of order operations (if the size of the data set is )
under circumstances which would previously have made this analysis intractable:
correlated receiver noise, arbitrary asymmetric beam shapes and far side lobes,
non-uniform distribution of integration time on the sky and partial sky
coverage. This ease of computation gives us an important theoretical tool for
understanding the impact of instrumental effects on CMB observables and hence
for the design and analysis of the CMB observations of the future. There are
members of this class which closely approximate the MAP and Planck satellite
missions. We present a numerical example where we apply our ring torus methods
to a simulated data set from a CMB mission covering a 20 degree patch on the
sky to compute the maximum likelihood estimate of the power spectrum
with unprecedented efficiency.Comment: RevTeX, 14 pages, 5 figures. A full resolution version of Figure 1
and additional materials are at http://feynman.princeton.edu/~bwandelt/RT
Specificity and sensitivity evaluation of novel and existing Bacteroidales and Bifidobacteria-specific PCR assays on feces and sewage samples and their application for microbial source tracking in Ireland
Three novel ruminant-specific PCR assays, an existing ruminant-specific PCR assay and five existing human-specific PCR assays, which target 16S rDNA from Bacteroidales or Bifidobacteria, were evaluated. The assays were tested on DNA extracted from ruminant (n = 74), human (n = 59) and non-ruminant animal (n = 44) sewage/fecal samples collected in Ireland. The three novel PCR assays compared favourably to the existing ruminant-specific assay, exhibiting sensitivities of 91 - 100% and specificities of 95 - 100% as compared to a sensitivity of 95% and specificity of 94%, for the existing ruminant-specific assay. Of the five human-specific PCR assays, the assay targeting the Bifidobacterium catenulatum group was the most promising, exhibiting a sensitivity of 100% (with human sewage samples) and a specificity of 87%. When tested on rural water samples that were naturally contaminated by ruminant feces, the three novel PCR assays tested positive with a much greater percentage (52 - 87%) of samples than the existing ruminant-specific assay (17%). These novel ruminant-specific assays show promise for microbial source tracking and merit further field testing and specificity evaluation.ERTD
A hepatitis C avidity test for determining recent and past infections in both plasma and dried blood spots
DBS testing has been used successfully to detect HCV antibody positive individuals. Determining how long someone has been infected is important for surveillance initiatives. Antibody avidity is a method that can be used to calculate recency of infection. A HCV avidity assay was evaluated for both plasma and DBS. Study design: To measure antibody avidity a commercial HCV ELISA was modified using 7 M urea. The plasma samples were split into: group 1 (recently infected N = 19), group 2 (chronic carrier N = 300) and group 3 (resolved infection N = 82). Mock DBS made from group 1 (N = 12), group 2 (N = 50), group 3 (N = 25) and two seroconverter panels were evaluated. 133 DBS taken from patients known to have a resolved infection or be a chronic carrier were also tested. The avidity assay cut-off was set at AI †30 for a recent infection. Using sequential samples the assay could detect a recent infection in the first 4â5 months from the point of infection. Most of the false positive results (AI < 30 among cases known not to have had recent infection) were detected among known resolved infections, in both the plasma and DBS; as a result, a testing algorithm has been designed incorporating both PCR and two dilution factors. The sensitivity and specificity of the assay on plasma was 100% and 99.3%, respectively, while DBS had 100% sensitivity and 98.3% specificity. The HCV avidity assay can be used to distinguish between chronic and recent infection using either plasma or DBS as the sample type
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