26,520 research outputs found
Review of finite fields: Applications to discrete Fourier, transforms and Reed-Solomon coding
An attempt is made to provide a step-by-step approach to the subject of finite fields. Rigorous proofs and highly theoretical materials are avoided. The simple concepts of groups, rings, and fields are discussed and developed more or less heuristically. Examples are used liberally to illustrate the meaning of definitions and theories. Applications include discrete Fourier transforms and Reed-Solomon coding
Radio Galaxy Zoo: Cosmological Alignment of Radio Sources
We study the mutual alignment of radio sources within two surveys, FIRST and
TGSS. This is done by producing two position angle catalogues containing the
preferential directions of respectively and extended
sources distributed over more than and square degrees. The
identification of the sources in the FIRST sample was performed in advance by
volunteers of the Radio Galaxy Zoo project, while for the TGSS sample it is the
result of an automated process presented here. After taking into account
systematic effects, marginal evidence of a local alignment on scales smaller
than is found in the FIRST sample. The probability of this happening
by chance is found to be less than per cent. Further study suggests that on
scales up to the alignment is maximal. For one third of the sources,
the Radio Galaxy Zoo volunteers identified an optical counterpart. Assuming a
flat CDM cosmology with , we
convert the maximum angular scale on which alignment is seen into a physical
scale in the range Mpc . This result supports recent
evidence reported by Taylor and Jagannathan of radio jet alignment in the
deg ELAIS N1 field observed with the Giant Metrewave Radio Telescope. The
TGSS sample is found to be too sparsely populated to manifest a similar signal
A Spectroscopic Survey of the Fields of 28 Strong Gravitational Lenses: Implications for
Strong gravitational lensing provides an independent measurement of the
Hubble parameter (). One remaining systematic is a bias from the
additional mass due to a galaxy group at the lens redshift or along the
sightline. We quantify this bias for more than 20 strong lenses that have
well-sampled sightline mass distributions, focusing on the convergence
and shear . In 23% of these fields, a lens group contributes a 1%
convergence bias; in 57%, there is a similarly significant line-of-sight group.
For the nine time delay lens systems, is overestimated by 11%
on average when groups are ignored. In 67% of fields with total
0.01, line-of-sight groups contribute more convergence than
do lens groups, indicating that the lens group is not the only important mass.
Lens environment affects the ratio of four (quad) to two (double) image
systems; all seven quads have lens groups while only three of 10 doubles do,
and the highest convergences due to lens groups are in quads. We calibrate the
- relation: with a rms scatter of 0.34 dex.
Shear, which, unlike convergence, can be measured directly from lensed images,
can be a poor predictor of ; for 19% of our fields, is
. Thus, accurate cosmology using strong gravitational lenses
requires precise measurement and correction for all significant structures in
each lens field.Comment: 34 pages, 11 figures, accepted for publication in Ap
Radio Galaxy Zoo: Knowledge Transfer Using Rotationally Invariant Self-Organising Maps
With the advent of large scale surveys the manual analysis and classification
of individual radio source morphologies is rendered impossible as existing
approaches do not scale. The analysis of complex morphological features in the
spatial domain is a particularly important task. Here we discuss the challenges
of transferring crowdsourced labels obtained from the Radio Galaxy Zoo project
and introduce a proper transfer mechanism via quantile random forest
regression. By using parallelized rotation and flipping invariant Kohonen-maps,
image cubes of Radio Galaxy Zoo selected galaxies formed from the FIRST radio
continuum and WISE infrared all sky surveys are first projected down to a
two-dimensional embedding in an unsupervised way. This embedding can be seen as
a discretised space of shapes with the coordinates reflecting morphological
features as expressed by the automatically derived prototypes. We find that
these prototypes have reconstructed physically meaningful processes across two
channel images at radio and infrared wavelengths in an unsupervised manner. In
the second step, images are compared with those prototypes to create a
heat-map, which is the morphological fingerprint of each object and the basis
for transferring the user generated labels. These heat-maps have reduced the
feature space by a factor of 248 and are able to be used as the basis for
subsequent ML methods. Using an ensemble of decision trees we achieve upwards
of 85.7% and 80.7% accuracy when predicting the number of components and peaks
in an image, respectively, using these heat-maps. We also question the
currently used discrete classification schema and introduce a continuous scale
that better reflects the uncertainty in transition between two classes, caused
by sensitivity and resolution limits
Performance evaluation of video streaming on LTE with coexistence of Wi-Fi signal
The continuous growth in mobile data traffic and limited license wireless spectrum have led to dramatically increase the demand of the radio spectrum. It is widespread the concern about the coexistence of long term evolution (LTE) and Wi-Fi in the unlicensed band. There are several techniques have been proposed to enable the coexistence of LTE and Wi-Fi in the unlicensed band, but these works are targeted on the impact of the LTE to the Wi-Fi network performance. An experiment is carried out in this work to evaluate the impact of Wi-Fi signal on the video streaming in the LTE network. The experimental test comprised of the national instrument (NI) universal software radio peripheral (USRP) 2953R that is controlled by the LabVIEW Communication LTE application framework. Extensiveexperiments are carried out under two scenarios, i.e. (1) Coexistence of LTE and Wi-Fi signal, (2) LTE signal only. Performance evaluations are carried out with different Modulation and coding schemes (MCS) values and different mode of operations, i.e. frequency division duplex (FDD) and time division duplex (TDD) mode. The results illustrated that the interference from Wi-Fi signal caused the performance degradation of the LTE network in throughput and the power received by user equipment (UE)
Enhanced exponential rule scheduling algorithm for real-time traffic in LTE network
Nowadays, mobile communication is growing rapidly and become an everyday commodity. The vast deployment of real-time services in Long Term Evolution (LTE) network demands for the scheduling techniques that support the Quality of Service (QoS) requirements. LTE is designed and implemented to fulfill the users’ QoS. However, 3GPP does not define the specific scheduling technique for resource distribution which leads to vast research and development of the scheduling techniques. In this context, a review of the recent scheduling algorithm is reported in the literature. These schedulers in the literature cause high Packet Loss Rate (PLR), low fairness, and high delay. To cope with these disadvantages, we propose an enhanced EXPRULE (eEXPRULE) scheduler to improve the radio resource utilization in the LTE network. Extensive simulation works are carried out and the proposed scheduler provides a significant performance improvement for video application without sacrificing the VoIP performance. The eEXPRULE scheduler increases video throughput, spectrum efficiency, and fairness by 50%, 13%, and 11%, respectively, and reduces the video PLR by 11%
Post-Covid-19-vaccination adverse events and healthcare utilization among individuals with or without previous SARS-CoV-2 infection
Background:
Post-marketing pharmacovigilance data are scant on the safety of Covid-19 vaccines among people with previous SARS-CoV-2 infection compared with ordinary vaccine recipients. We compared the post-vaccination adverse events of special interests (AESI), accident and emergency room (A&E) visit, and hospitalization between these two groups.
Methods:
We conducted a retrospective cohort study using a territory-wide public healthcare database with population-based vaccination records in Hong Kong.
Results:
In total, 3922 vaccine recipients with previous SARS‑CoV‑2 infection and 1,137,583 vaccine recipients without previous SARS‑CoV‑2 infection were included. No significant association was observed between previous SARS‑CoV‑2 infection and AESI or hospitalization. Previous SARS‑CoV‑2 infection was significantly associated with a lower risk of A&E visit (CoronaVac: hazard ratios [HR] = 0.56, 95% confidence intervals [CI]: 0.32–0.99; Comirnaty: HR = 0.62, 95% CI: 0.47–0.82).
Conclusion:
No safety signal of Covid-19 vaccination was detected from the comparison between vaccine recipients with previous SARS-CoV-2 infection and those without infection
Phase preparation by atom counting of Bose-Einstein condensates in mixed states
We study the build up of quantum coherence between two Bose-Einstein
condensates which are initially in mixed states. We consider in detail the two
cases where each condensate is initially in a thermal or a Poisson distribution
of atom number. Although initially there is no relative phase between the
condensates, a sequence of spatial atom detections produces an interference
pattern with arbitrary but fixed relative phase. The visibility of this
interference pattern is close to one for the Poisson distribution of two
condensates with equal counting rates but it becomes a stochastic variable in
the thermal case, where the visibility will vary from run to run around an
average visibility of In both cases, the variance of the phase
distribution is inversely proportional to the number of atom detections in the
regime where this number is large compared to one but small compared with the
total number of atoms in the condensates.Comment: 9 pages, 6 PostScript figure, submitted to PR
Collective Deceleration of Ultrarelativistic Nuclei and Creation of Quark-Gluon Plasma
We propose a unified space-time picture of baryon stopping and quark-gluon
plasma creation in ultrarelativistic heavy-ion collisions. It is assumed that
the highly Lorentz contracted nuclei are decelerated by the coherent color
field which is formed between them after they pass through each other. This
process continues until the field is neutralized by the Schwinger mechanism.
Conservation of energy and momentum allow us to calculate the energy losses of
the nuclear slabs and the initial energy density of the quark-gluon plasma.Comment: 11 pages in revtex, 2 eps figure
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