5,886 research outputs found
Edge-Cloud Synergy: Unleashing the Potential of Parallel Processing for Big Data Analytics
If an edge-node orchestrator can partition Big Data tasks of variable computational complexity between the edge and cloud resources, major reductions in total task completion times can be achieved even at low Wide Area Network (WAN) speeds. The percentage time savings are greater with increasing task computational complexity and higher WAN speeds are required for low-complexity tasks. We demonstrate from numerical simulations that low-complexity tasks can benefit either by task partitioning between an edge node and multiple cloud servers. The orchestrator can also achieve greater time benefits by rerouting Big Data tasks directly to a single cloud resource if the balance of parameters (WAN speed and the ratio between edge and cloud processing speeds) is favourable
Discovery of the spectroscopic binary nature of six southern Cepheids
We present the analysis of photometric and spectroscopic data of six bright
Galactic Cepheids: GH Carinae, V419 Centauri, V898 Centauri, AD Puppis, AY
Sagittarii, and ST Velorum. Based on new radial velocity data (in some cases
supplemented with earlier data available in the literature), these Cepheids
have been found to be members in spectroscopic binary systems. V898 Cen turned
out to have one of the largest orbital radial velocity amplitude (> 40 km/s)
among the known binary Cepheids. The data are insufficient to determine the
orbital periods nor other orbital elements for these new spectroscopic
binaries.
These discoveries corroborate the statement on the high frequency of
occurrence of binaries among the classical Cepheids, a fact to be taken into
account when calibrating the period-luminosity relationship for Cepheids.
We have also compiled all available photometric data that revealed that the
pulsation period of AD Pup, the longest period Cepheid in this sample, is
continuously increasing with Delta P = 0.004567 d/century, likely to be caused
by stellar evolution. The wave-like pattern superimposed on the parabolic O-C
graph of AD Pup may well be caused by the light-time effect in the binary
system. ST Vel also pulsates with a continuously increasing period. The other
four Cepheids are characterised with stable pulsation periods in the last half
century.Comment: accepted by the MNRAS, 11 pages, 16 figures, 18 tables, a part of the
data can be downloaded from the online version of this articl
Photometric biases due to stellar blending: implications for measuring distances, constraining binarity and detecting exoplanetary transits
We investigate blending, binarity and photometric biases in crowded-field CCD
imaging. For this, we consider random blend losses, which correspond to the
total number of stars left undetected in unresolved blends. We present a simple
formula to estimate blend losses, which can be converted to apparent magnitude
biases using the luminosity function of the analyzed sample. Because of the
used assumptions, our results give lower limits of the total bias and we show
that in some cases even these limits point toward significant limitations in
measuring apparent brightnesses of ``standard candle'' stars, thus distances to
nearby galaxies. A special application is presented for the OGLE-II BVI maps of
the Large Magellanic Cloud. We find a previously neglected systematic bias up
to 0.2-0.3 mag for faint stars (V~18.0-19.0) in the OGLE-II sample, which
affects LMC distance measurements using RR Lyrae and red clump stars. We also
consider the effects of intrinsic stellar correlations, i.e. binarity, via
calculating two-point correlation functions for stellar fields around seven
recently exploded classical novae. In two cases, for V1494 Aql and V705 Cas,
the reported close optical companions seem to be physically correlated with the
cataclysmic systems. Finally, we find significant blend frequencies up to
50-60% in the samples of wide-field exoplanetary surveys, which suggests that
blending calculations are highly advisable to be included into the regular
reduction procedure.Comment: 10 pages, 7 figures, accepted for publication in MNRA
Discovery of the spectroscopic binary nature of three bright southern Cepheids
We present an analysis of spectroscopic radial velocity and photometric data
of three bright Galactic Cepheids: LR Trianguli Australis (LR TrA), RZ Velorum
(RZ Vel), and BG Velorum (BG Vel). Based on new radial velocity data, these
Cepheids have been found to be members of spectroscopic binary systems.
The ratio of the peak-to-peak radial velocity amplitude to photometric
amplitude indicates the presence of a companion for LR TrA and BG Vel. IUE
spectra indicate that the companions of RZ Vel and BG Vel cannot be hot stars.
The analysis of all available photometric data revealed that the pulsation
period of RZ Vel and BG Vel varies monotonically, due to stellar evolution.
Moreover, the longest period Cepheid in this sample, RZ Vel, shows period
fluctuations superimposed on the monotonic period increase. The light-time
effect interpretation of the observed pattern needs long-term photometric
monitoring of this Cepheid. The pulsation period of LR TrA has remained
constant since the discovery of its brightness variation.
Using statistical data, it is also shown that a large number of spectroscopic
binaries still remain to be discovered among bright classical Cepheids.Comment: 9 pages, 14 figure
Beyond clustering: mean-field dynamics on networks with arbitrary subgraph composition
Clustering is the propensity of nodes that share a common neighbour to be connected. It is ubiquitous in many networks but poses many modelling challenges. Clustering typically manifests itself by a higher than expected frequency of triangles, and this has led to the principle of constructing networks from such building blocks. This approach has been generalised to networks being constructed from a set of more exotic subgraphs. As long as these are fully connected, it is then possible to derive mean-field models that approximate epidemic dynamics well. However, there are virtually no results for non-fully connected subgraphs. In this paper, we provide a general and automated approach to deriving a set of ordinary differential equations, or mean-field model, that describes, to a high degree of accuracy, the expected values of system-level quantities, such as the prevalence of infection. Our approach offers a previously unattainable degree of control over the arrangement of subgraphs and network characteristics such as classical node degree, variance and clustering. The combination of these features makes it possible to generate families of networks with different subgraph compositions while keeping classical network metrics constant. Using our approach, we show that higher-order structure realised either through the introduction of loops of different sizes or by generating networks based on different subgraphs but with identical degree distribution and clustering, leads to non-negligible differences in epidemic dynamics
Happiness, environmental protection and market economy
The manufacturing sector is leaving the West for Asiaâs low wages and good working culture. Europe would be better off keeping these manufacturing activities, slowing down wage inflation and what is more, letting a young, cheaper workforce from the East settle down within their borders. This would aid in preserving the diverse economic structure which has been characteristic for Europe.Beside the economic growth there are two more concepts which have turned into the âholy cowsâ of economics during the last fifty years. One is the need to constantly improve labor productivity and the other is increasing competitiveness of nations. The high labor productivity of some countries, induces severe unemployment in the globalized world. In the other hand it is high time we understood that it is not competition, but cooperation that brings more happiness to humanity.Should we still opt for âhappinessâ and âsanityâ, it is quite obvious that we all should, in economistsâ terms, define our individual welfare functions corresponding to our own set of values, staying free from the influence of media, advertisements and fashion. The cornerstone to all this is the intelligent citizen who prefers local goods and services
Evidence for Low-Dimensional Chaos in Semiregular Variable Stars
An analysis of the photometric observations of the light curves of the five
large amplitude, irregularly pulsating stars R UMi, RS Cyg, V CVn, UX Dra and
SX Her is presented. First, multi-periodicity is eliminated for these
pulsations, i.e. they are not caused by the excitation of a small number of
pulsation modes with constant amplitudes. Next, on the basis of energetics we
also eliminate stochasticity as a cause, leaving low dimensional chaos as the
only alternative. We then use a global flow reconstruction technique in an
attempt to extract quantitative information from the light curves, and to
uncover common physical features in this class of irregular variable stars that
straddle the RV Tau to the Mira variables. Evidence is presented that the
pulsational behavior of R UMi, RS Cyg, V CVn and UX Dra takes place in a
4-dimensional dynamical phase space, suggesting that two vibrational modes are
involved in the pulsation. A linear stability analysis of the fixed points of
the maps further indicates the existence of a two-mode resonance, similar to
the one we had uncovered earlier in R Sct: The irregular pulsations are the
result of a continual energy exchange between two strongly nonadiabatic modes,
a lower frequency pulsation mode and an overtone that are in a close 2:1
resonance. The evidence is particularly convincing for R UMi, RS Cyg and V CVn,
but much weaker for UX Dra. In contrast, the pulsations of SX Her appear to be
more complex and may require a 6D space.Comment: 20 pages, 14 figures, accepted in ApJ - paper with clearer figures is
available at http://www.phys.ufl.edu/~buchler/publications/u12.ps.gz (1Mb
Red variables in the OGLE-II data base -- III. Constraints on the three-dimensional structures of the LMC and SMC
We present an analysis of the 3-D structure of the Magellanic Clouds, using
period-luminosity (P-L) relations of pulsating red giants in the OGLE-II
sample. By interpreting deviations from the mean P-L relations as distance
modulus variations, we examine the three-dimensional distributions of the
sample. The results for the Large Magellanic Cloud, based solely on stars below
the tip of the Red Giant Branch, confirm previous results on the inclined and
possibly warped bar of the LMC. The depth variation across the OGLE-II field is
about 2.4 kpc, interpreted as the distance range of a thin but inclined
structure. The inclination angle is about 29 deg. A comparison with OGLE-II red
clump distances revealed intriguing differences that seem to be connected to
the red clump reddening correction. A spatially variable red clump population
in the LMC can explain the deviations, which may have a broader impact on our
understanding of the LMC formation history. For the Small Magellanic Cloud, we
find a complex structure showing patchy distribution scattered within 3.2 kpc
of the mean. However, the larger range of the overall depth on every
line-of-sight is likely to smooth out significantly the real variations.Comment: 5 pages, 4 figures, accepted for publication in MNRAS (online
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