181 research outputs found
Cognitive radio DAB MAC protocol performance using a CR specific simulator and software defined radio
Abstract: With the constant advances in wireless technology, radio spectrum has become a very scarce resource. Cognitive Radio (CR) has emerged as a viable way to deal with our inefficient use of the radio spectrum by utilizing unused spectrum holes or white spaces, as they are referred to. Using Software Defined Radio (SDR) we are able to realize CRs and their unique properties. Most of the research that has been done on CR protocols has been based on analytical assessments and simulations using non-CR specific network simulators. In this paper we code and compare two existing CR specific Medium Access Control (MAC) protocols using a CR specific simulator. We then prototype the chosen protocols using the Universal Software Radio Peripheral (USRP). This allows us to see how close the simulated performance results come to those actually achieved in a real prototype
The quantitative determination and some values of dimethyl sulphide in white table wines
A gaschromatographic headspace method has been developed for the quantitative determination of dimethyl sulphide (DMS) in wines. The standard deviation of the method was in the order of 6%.Application of the method to the analysis of several white wines showed DMS values which varied from O to over 400 µg/1. From analytical data it appeared that DMS developed in the bottle and could as such possibly contribute to bottle bouquet. It was found that maturecl Riesling wines had particularly high concentrations of DMS.Die quantitative Bestimmung von Dimethylsulfid in weißen Tafelweinen sowieeinige Angaben über seine KonzentrationFür die quantitative Bestimmung von Dimethylsulfid (DMS) in Wein wurde unter Verwendung der „headspace"-Technik und von Dichlormethan als Standard eine gaschromatographische Methode entwickelt. Die Genauigkeit der Methode liegt bei einer Standardabweichung von 6%. Bei der Anwendung der Methode auf eine Reihe von Weißweinen wurden DMS-Werte zwischen O und über 400 µg/l ermittelt. DMS scheint sich während der Ausreifung des Weines in der Flasche zu entwickeln und könnte zum sogenannten Lagerungsbukett beitragen. Besonders hohe DMS-Konzentrationen wurden in älteren Riesling-Weinen festgestellt
Polarization-selective excitation of N-V centers in diamond
The nitrogen-vacancy (N-V) center in diamond is promising as an electron spin
qubit due to its long-lived coherence and optical addressability. The ground
state is a spin triplet with two levels () degenerate at zero
magnetic field. Polarization-selective microwave excitation is an attractive
method to address the spin transitions independently, since this allows
operation down to zero magnetic field. Using a resonator designed to produce
circularly polarized microwaves, we have investigated the polarization
selection rules of the N-V center. We first apply this technique to N-V
ensembles in [100] and [111]-oriented samples. Next, we demonstrate an imaging
technique, based on optical polarization dependence, that allows rapid
identification of the orientations of many single N-V centers. Finally, we test
the microwave polarization selection rules of individual N-V centers of known
orientation
The MeerKAT Fornax Survey
We present the science case and observations plan of the MeerKAT Fornax
Survey, an HI and radio continuum survey of the Fornax galaxy cluster to be
carried out with the SKA precursor MeerKAT. Fornax is the second most massive
cluster within 20 Mpc and the largest nearby cluster in the southern
hemisphere. Its low X-ray luminosity makes it representative of the environment
where most galaxies live and where substantial galaxy evolution takes place.
Fornax's ongoing growth makes it an excellent laboratory for studying the
assembly of clusters, the physics of gas accretion and stripping in galaxies
falling in the cluster, and the connection between these processes and the
neutral medium in the cosmic web.
We will observe a region of 12 deg reaching a projected distance of 1.5
Mpc from the cluster centre. This will cover a wide range of environment
density out to the outskirts of the cluster, where gas-rich in-falling groups
are found. We will: study the HI morphology of resolved galaxies down to a
column density of a few times 1e+19 cm at a resolution of 1 kpc; measure
the slope of the HI mass function down to M(HI) 5e+5 M(sun); and attempt to
detect HI in the cosmic web reaching a column density of 1e+18 cm at a
resolution of 10 kpc.Comment: Proceedings of Science, "MeerKAT Science: On the Pathway to the SKA",
Stellenbosch, 25-27 May 201
Controlling the quantum dynamics of a mesoscopic spin bath in diamond
Understanding and mitigating decoherence is a key challenge for quantum
science and technology. The main source of decoherence for solid-state spin
systems is the uncontrolled spin bath environment. Here, we demonstrate quantum
control of a mesoscopic spin bath in diamond at room temperature that is
composed of electron spins of substitutional nitrogen impurities. The resulting
spin bath dynamics are probed using a single nitrogen-vacancy (NV) centre
electron spin as a magnetic field sensor. We exploit the spin bath control to
dynamically suppress dephasing of the NV spin by the spin bath. Furthermore, by
combining spin bath control with dynamical decoupling, we directly measure the
coherence and temporal correlations of different groups of bath spins. These
results uncover a new arena for fundamental studies on decoherence and enable
novel avenues for spin-based magnetometry and quantum information processing
The negatively charged nitrogen-vacancy centre in diamond: the electronic solution
The negatively charged nitrogen-vacancy centre is a unique defect in diamond
that possesses properties highly suited to many applications, including quantum
information processing, quantum metrology, and biolabelling. Although the
unique properties of the centre have been extensively documented and utilised,
a detailed understanding of the physics of the centre has not yet been
achieved. Indeed there persists a number of points of contention regarding the
electronic structure of the centre, such as the ordering of the dark
intermediate singlet states. Without a sound model of the centre's electronic
structure, the understanding of the system's unique dynamical properties can
not effectively progress. In this work, the molecular model of the defect
centre is fully developed to provide a self consistent model of the complete
electronic structure of the centre. The application of the model to describe
the effects of electric, magnetic and strain interactions, as well as the
variation of the centre's fine structure with temperature, provides an
invaluable tool to those studying the centre and a means to design future
empirical and ab initio studies of this important defect.Comment: 24 pages, 6 figures, 10 table
Spatial kinematics of Brightest Cluster Galaxies and their close companions from Integral Field Unit spectroscopy
We present Integral Field Unit (IFU) spectroscopy of four brightest cluster
galaxies (BCGs) at z~0.1. Three of the BCGs have close companions within a
projected radius of 20 kpc and one has no companion within that radius. We
calculate the dynamical masses of the BCGs and their companions to be
1.4x10^11<M_dyn (M_solar)<1.5x10^12. We estimate the probability that the
companions of the BCGs are bound using the observed masses and velocity
offsets. We show that the lowest mass companion (1:4) is not bound while the
two nearly equal mass (1:1.45 and 1:1.25) companions are likely to merge with
their host BCGs in 0.35 Gyr in major, dry mergers. We conclude that some BCGs
continue to grow from major merging even at z~0. We analyse the stellar
kinematics of these systems using the \lambda_R parameter developed by the
SAURON team. This offers a new and unique means to measure the stellar angular
momentum of BCGs and make a direct comparison to other early-type galaxies. The
BCGs and their companions have similar ellipticities to those of other
early-type galaxies but are more massive. We find that not all these massive
galaxies have low \lambda_R_e as one might expect. One of the four BCGs and the
two massive companions are found to be fast-rotating galaxies with high angular
momentum, thereby providing a new test for models of galaxy evolution and the
formation of Intra-Cluster Light.Comment: 5 pages. Accepted for publication in MNRAS Letter
The MeerKAT Fornax Survey -- II. The rapid removal of HI from dwarf galaxies in the Fornax cluster
We present MeerKAT Fornax Survey atomic hydrogen (HI) observations of the
dwarf galaxies located in the central ~2.5 x 4 deg of the Fornax galaxy
cluster. The HI images presented in this work have a column density
sensitivity between 2.7 and 50 x 10 cm over 25 km s for
spatial resolution between 4 and 1 kpc. We are able to detect an impressive MHI
= 5 x 10 Msun 3 point source with a line width of 50 km s
at a distance of 20 Mpc. We detect HI in 17 out of the 304 dwarfs in our field
-- 14 out of the 36 late type dwarfs (LTDs), and 3 of the 268 early type dwarfs
(ETDs). The HI-detected LTDs have likely just joined the cluster and are on
their first infall as they are located at large clustocentric radii, with
comparable MHI and mean stellar surface brightness at fixed luminosity as blue,
star-forming LTDs in the field. The HI-detected ETDs have likely been in the
cluster longer than the LTDs and acquired their HI through a recent merger or
accretion from nearby HI. Eight of the HI-detected LTDs host irregular or
asymmetric HI emission and disturbed or lopsided stellar emission. There are
two clear cases of ram-pressure shaping the HI, with the LTDs displaying
compressed HI on the side closest to the cluster centre and a one-sided,
starless tail pointing away from the cluster centre. The HI-detected dwarfs
avoid the most massive potentials, consistent with massive galaxies playing an
active role in the removal of HI. We create a simple toy model to quantify the
timescale of HI stripping in the cluster. We find that a MHI = 10 Msun
dwarf will be stripped in ~ 240 Myr. The model is consistent with our
observations, where low mass LTDs are directly stripped of their HI from a
single encounter and more massive LTDs can harbour a disturbed HI morphology
due to longer times or multiple encounters being required to fully strip their
HI.Comment: Accepted in Astronomy & Astrophysics. 21 pages, 10 figures. Data
available at the MeerKAT Fornax Survey website
https://sites.google.com/inaf.it/meerkatfornaxsurve
Advancing animal tuberculosis surveillance using culture-independent long-read whole-genome sequencing
Animal tuberculosis is a significant infectious disease affecting both livestock and wildlife populations worldwide. Effective disease surveillance and characterization of Mycobacterium bovis (M. bovis) strains are essential for understanding transmission dynamics and implementing control measures. Currently, sequencing of genomic information has relied on culture-based methods, which are time-consuming, resource-demanding, and concerning in terms of biosafety. This study explores the use of culture-independent long-read whole-genome sequencing (WGS) for a better understanding of M. bovis epidemiology in African buffaloes (Syncerus caffer). By comparing two sequencing approaches, we evaluated the efficacy of Illumina WGS performed on culture extracts and culture-independent Oxford Nanopore adaptive sampling (NAS). Our objective was to assess the potential of NAS to detect genomic variants without sample culture. In addition, culture-independent amplicon sequencing, targeting mycobacterial-specific housekeeping and full-length 16S rRNA genes, was applied to investigate the presence of microorganisms, including nontuberculous mycobacteria. The sequencing quality obtained from DNA extracted directly from tissues using NAS is comparable to the sequencing quality of reads generated from culture-derived DNA using both NAS and Illumina technologies. We present a new approach that provides complete and accurate genome sequence reconstruction, culture independently, and using an economically affordable technique
The dark halo of the Hydra I galaxy cluster: core, cusp, cosmological? Dynamics of NGC 3311 and its globular cluster system
NGC 3311 is the central cD galaxy of the Hydra I cluster. We use globular
clusters around NGC 3311, combined with kinematical data of the galaxy itself,
to investigate the dark matter distribution in the central region of Hydra I.
Radial velocities of 118 bright globular clusters, based on VLT/VIMOS mask
spectroscopy, are used to calculate velocity dispersions which are well defined
out to 100 kpc. NGC 3311 is the most distant galaxy for which this kind of
study has been performed. We also determine velocity dispersions of the stellar
component from long slit spectroscopy out to 20 kpc. Moreover, we present a new
photometric model for NGC 3311 in the V-band. We search for a dark halo which
in the context of a spherical Jeans model. We also compare the radial velocity
distributions of globular clusters and planetary nebulae. The projected stellar
velocity dispersion rises from 185 km/s to 350 km/s at a radius of 20 kpc. The
globular cluster dispersion rises as well from 500 km/s at 10 kpc to about 800
km/s at 100 kpc, comparable to the velocity dispersion of the cluster galaxies.
A dark matter halo with a core reproduces well the velocity dispersions of
stars and globular clusters simultaneously under isotropy. The central stellar
velocity dispersions predicted by cosmological NFW halos are less good
representations, while the globular clusters allow a wide range of halo
parameters. A suspected radial anisotropy of the stellar population aggravates
the deviations. However, we find discrepancies with previous kinematical data,
which we cannot resolve and may indicate a more complicated velocity pattern.
Although one cannot conclusively demonstrate that the dark matter halo of NGC
3311 has a core rather than a cusp, a core seems to be preferred by the present
data. A more complete velocity field and an analysis of the anisotropy is
required to reach firm conclusions.Comment: 8 pages, 5 figures, abstract abridged, accepted for publication in
A&
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