429 research outputs found
Thermal emission from WASP-24b at 3.6 and 4.5 {\mu}m
Aims. We observe occultations of WASP-24b to measure brightness temperatures
and to determine whether or not its atmosphere exhibits a thermal inversion
(stratosphere). Methods. We observed occultations of WASP-24b at 3.6 and 4.5
{\mu}m using the Spitzer Space Telescope. It has been suggested that there is a
correlation between stellar activity and the presence of inversions, so we
analysed existing HARPS spectra in order to calculate log R'HK for WASP-24 and
thus determine whether or not the star is chromospherically active. We also
observed a transit of WASP-24b in the Str\"{o}mgren u and y bands, with the
CAHA 2.2-m telescope. Results. We measure occultation depths of 0.159 \pm 0.013
per cent at 3.6 {\mu}m and 0.202 \pm 0.018 per cent at 4.5 {\mu}m. The
corresponding planetary brightness temperatures are 1974 \pm 71 K and 1944 \pm
85 K respectively. Atmosphere models with and without a thermal inversion fit
the data equally well; we are unable to constrain the presence of an inversion
without additional occultation measurements in the near-IR. We find log R'HK =
-4.98 \pm 0.12, indicating that WASP-24 is not a chromospherically active star.
Our global analysis of new and previously-published data has refined the system
parameters, and we find no evidence that the orbit of WASP-24b is non-circular.
Conclusions. These results emphasise the importance of complementing Spitzer
measurements with observations at shorter wavelengths to gain a full
understanding of hot Jupiter atmospheres.Comment: 7 pages, 4 figures, 3 tables. Accepted for publication in A&
Hybrid Approach for Resource Allocation in Cloud Infrastructure Using Random Forest and Genetic Algorithm
In cloud computing, the virtualization technique is a significant technology to optimize the power consumption of the cloud data center. In this generation, most of the services are moving to the cloud resulting in increased load on data centers. As a result, the size of the data center grows and hence there is more energy consumption. To resolve this issue, an efficient optimization algorithm is required for resource allocation. In this work, a hybrid approach for virtual machine allocation based on genetic algorithm (GA) and the random forest (RF) is proposed which belongs to a class of supervised machine learning techniques. The aim of the work is to minimize power consumption while maintaining better load balance among available resources and maximizing resource utilization. The proposed model used a genetic algorithm to generate a training dataset for the random forest model and further get a trained model. The real-time workload traces from PlanetLab are used to evaluate the approach. The results showed that the proposed GA-RF model improves energy consumption, execution time, and resource utilization of the data center and hosts as compared to the existing models. The work used power consumption, execution time, resource utilization, average start time, and average finish time as performance metrics
Intelligent Fault-Tolerant Mechanism for Data Centers of Cloud Infrastructure
Fault tolerance in cloud computing is considered as one of the most vital issues to deliver reliable services. Checkpoint/restart is one of the methods used to enhance the reliability of the cloud services. However, many existing methods do not focus on virtual machine (VM) failure that occurs due to the higher response time of a node, byzantine fault, and performance fault, and existing methods also ignore the optimization during the recovery phase. This paper proposes a checkpoint/restart mechanism to enhance reliability of cloud services. Our work is threefold: (1) we design an algorithm to identify virtual machine failure due to several faults; (2) an algorithm to optimize the checkpoint interval time is designed; (3) lastly, the asynchronous checkpoint/restart with log-based recovery mechanism is used to restart the failed tasks. The valuation results obtained using a real-time dataset shows that the proposed model reduces power consumption and improves the performance with a better fault tolerance solution compared to the nonoptimization method
Effect of inducers against tobamovirus infection in tomato and bell Pepper
Tomato and bell pepper seeds were treated with salicylic acid (50 mM), neem oil (5%) and Pseudomonas fluorescens (slurry). The seedlings were sprayed with salicylic acid (50 mM) and neem oil (5%). The concentration of Tomato mosaic tobamovirus (ToMV) and Tobacco mosaic tobamovirus (TMV) was assessed based on the number of local lesions on Nicotiana glutinosa. The results showed that the seed/seedling treatment with inducers reduced the number of local lesions when compared to untreated ones. Salicylic acid was an effective inducer
Hyperfast pulsars as the remnants of massive stars ejected from young star clusters
Recent proper motion and parallax measurements for the pulsar PSR B1508+55
indicate a transverse velocity of ~1100 km/s, which exceeds earlier
measurements for any neutron star. The spin-down characteristics of PSR
B1508+55 are typical for a non-recycled pulsar, which implies that the velocity
of the pulsar cannot have originated from the second supernova disruption of a
massive binary system. The high velocity of PSR B1508+55 can be accounted for
by assuming that it received a kick at birth or that the neutron star was
accelerated after its formation in the supernova explosion. We propose an
explanation for the origin of hyperfast neutron stars based on the hypothesis
that they could be the remnants of a symmetric supernova explosion of a
high-velocity massive star which attained its peculiar velocity (similar to
that of the pulsar) in the course of a strong dynamical three- or four-body
encounter in the core of dense young star cluster. To check this hypothesis we
investigated three dynamical processes involving close encounters between: (i)
two hard massive binaries, (ii) a hard binary and an intermediate-mass black
hole, and (iii) a single star and a hard binary intermediate-mass black hole.
We find that main-sequence O-type stars cannot be ejected from young massive
star clusters with peculiar velocities high enough to explain the origin of
hyperfast neutron stars, but lower mass main-sequence stars or the stripped
helium cores of massive stars could be accelerated to hypervelocities. Our
explanation for the origin of hyperfast pulsars requires a very dense stellar
environment of the order of 10^6 -10^7 stars pc^{-3}. Although such high
densities may exist during the core collapse of young massive star clusters, we
caution that they have never been observed.Comment: 11 pages, 6 figures, 1 table, accepted to MNRA
Thermal emission at 3.6-8 micron from WASP-19b: a hot Jupiter without a stratosphere orbiting an active star
We report detection of thermal emission from the exoplanet WASP-19b at 3.6,
4.5, 5.8 and 8.0 micron. We used the InfraRed Array Camera on the Spitzer Space
Telescope to observe two occultations of WASP-19b by its host star. We combine
our new detections with previous measurements of WASP-19b's emission at 1.6 and
2.09 micron to construct a spectral energy distribution of the planet's dayside
atmosphere. By comparing this with model-atmosphere spectra, we find that the
dayside atmosphere of WASP-19b lacks a strong temperature inversion. As WASP-19
is an active star (log RHK = -4.50 +/- 0.03), this finding supports the
hypothesis of Knutson, Howard & Isaacson (2010) that inversions are suppressed
in hot Jupiters orbiting active stars. The available data are unable to
differentiate between a carbon-rich and an oxygen-rich atmosphere.Comment: As accepted for publication in MNRAS. 12 pages, 5 figures, 3 table
The GTC exoplanet transit spectroscopy survey IX. Detection of haze, Na, K, and Li in the super-Neptune WASP-127b
Exoplanets with relatively clear atmospheres are prime targets for detailed
studies of chemical compositions and abundances in their atmospheres. Alkali
metals have long been suggested to exhibit broad wings due to pressure
broadening, but most of the alkali detections only show very narrow absorption
cores, probably because of the presence of clouds. We report the strong
detection of the pressure-broadened spectral profiles of Na, K, and Li
absorption in the atmosphere of the super-Neptune WASP-127b, at 4.1,
5.0, and 3.4, respectively. We performed a spectral retrieval
modeling on the high-quality optical transmission spectrum newly acquired with
the 10.4 m Gran Telescopio Canarias (GTC), in combination with the re-analyzed
optical transmission spectrum obtained with the 2.5 m Nordic Optical Telescope
(NOT). By assuming a patchy cloudy model, we retrieved the abundances of Na, K,
and Li, which are super-solar at 3.7 for K and 5.1 for Li (and
only 1.8 for Na). We constrained the presence of haze coverage to be
around 52%. We also found a hint of water absorption, but cannot constrain it
with the global retrieval owing to larger uncertainties in the probed
wavelengths. WASP-127b will be extremely valuable for atmospheric
characterization in the era of James Webb Space Telescope
Characterizing Exoplanets in the Visible and Infrared: A Spectrometer Concept for the EChO Space Mission
Transit-spectroscopy of exoplanets is one of the key observational techniques
to characterize the extrasolar planet and its atmosphere. The observational
challenges of these measurements require dedicated instrumentation and only the
space environment allows an undisturbed access to earth-like atmospheric
features such as water or carbon-dioxide. Therefore, several exoplanet-specific
space missions are currently being studied. One of them is EChO, the Exoplanet
Characterization Observatory, which is part of ESA's Cosmic Vision 2015-2025
program, and which is one of four candidates for the M3 launch slot in 2024. In
this paper we present the results of our assessment study of the EChO
spectrometer, the only science instrument onboard this spacecraft. The
instrument is a multi-channel all-reflective dispersive spectrometer, covering
the wavelength range from 400 nm to 16 microns simultaneously with a moderately
low spectral resolution. We illustrate how the key technical challenge of the
EChO mission - the high photometric stability - influences the choice of
spectrometer concept and drives fundamentally the instrument design. First
performance evaluations underline the fitness of the elaborated design solution
for the needs of the EChO mission.Comment: 20 pages, 8 figures, accepted for publication in the Journal of
Astronomical Instrumentatio
Exoplanet Atmosphere Measurements from Transmission Spectroscopy and other Planet-Star Combined Light Observations
It is possible to learn a great deal about exoplanet atmospheres even when we
cannot spatially resolve the planets from their host stars. In this chapter, we
overview the basic techniques used to characterize transiting exoplanets -
transmission spectroscopy, emission and reflection spectroscopy, and full-orbit
phase curve observations. We discuss practical considerations, including
current and future observing facilities and best practices for measuring
precise spectra. We also highlight major observational results on the
chemistry, climate, and cloud properties of exoplanets.Comment: Accepted review chapter; Handbook of Exoplanets, eds. Hans J. Deeg
and Juan Antonio Belmonte (Springer-Verlag). 22 pages, 6 figure
A review on a deep learning perspective in brain cancer classification
AWorld Health Organization (WHO) Feb 2018 report has recently shown that mortality rate due to brain or central nervous system (CNS) cancer is the highest in the Asian continent. It is of critical importance that cancer be detected earlier so that many of these lives can be saved. Cancer grading is an important aspect for targeted therapy. As cancer diagnosis is highly invasive, time consuming and expensive, there is an immediate requirement to develop a non-invasive, cost-effective and efficient tools for brain cancer characterization and grade estimation. Brain scans using magnetic resonance imaging (MRI), computed tomography (CT), as well as other imaging modalities, are fast and safer methods for tumor detection. In this paper, we tried to summarize the pathophysiology of brain cancer, imaging modalities of brain cancer and automatic computer assisted methods for brain cancer characterization in a machine and deep learning paradigm. Another objective of this paper is to find the current issues in existing engineering methods and also project a future paradigm. Further, we have highlighted the relationship between brain cancer and other brain disorders like stroke, Alzheimer’s, Parkinson’s, andWilson’s disease, leukoriaosis, and other neurological disorders in the context of machine learning and the deep learning paradigm
- …