551 research outputs found
Influence of process parameters on physical dimensions of AA6063 aluminium alloy coating on mild steel in friction surfacing
AbstractAn attempt is made in the present study to obtain the relationships among process parameters and physical dimensions of AA6063 aluminium alloy coating on IS2062 mild steel obtained through friction surfacing and their impact on strength and ductility of the coating. Factorial experimental design technique was used to investigate and select the parameter combination to achieve a coating with adequate strength and ductility. Spindle speed, axial force and table traverse speed were observed to be the most significant factors on physical dimensions. It was observed that the thickness of the coating decreased as the coating width increased. In addition, the width and thickness of the coatings are higher at low and high torques. At intermediate torque values, when the force is high, the width of the coating is high, and its thickness is thin; and when the force is low, the width and thickness are low. The interaction effect between axial force (F) – table traverse speed (Vx) and spindle speed (N) – table traverse speed (Vx) produced an increasing effect on coating width and thickness, but other interactions exhibited decreasing influence. It has also been observed that sound coatings could be obtained in a narrow set of parameter range as the substrate-coating materials are metallurgically incompatible and have a propensity to form brittle intermetallics
Detection of Planetary Emission from the Exoplanet TrES-2 using Spitzer /IRAC
We present here the results of our observations of TrES-2 using the Infrared
Array Camera on Spitzer. We monitored this transiting system during two
secondary eclipses, when the planetary emission is blocked by the star. The
resulting decrease in flux is 0.127%+-0.021%, 0.230%+-0.024%, 0.199%+-0.054%,
and 0.359%+-0.060%, at 3.6 microns, 4.5 microns, 5.8 microns, and 8.0 microns,
respectively. We show that three of these flux contrasts are well fit by a
black body spectrum with T_{eff}=1500 K, as well as by a more detailed model
spectrum of a planetary atmosphere. The observed planet-to-star flux ratios in
all four IRAC channels can be explained by models with and without a thermal
inversion in the atmosphere of TrES-2, although with different atmospheric
chemistry. Based on the assumption of thermochemical equilibrium, the chemical
composition of the inversion model seems more plausible, making it a more
favorable scenario. TrES-2 also falls in the category of highly irradiated
planets which have been theoretically predicted to exhibit thermal inversions.
However, more observations at infrared and visible wavelengths would be needed
to confirm a thermal inversion in this system. Furthermore, we find that the
times of the secondary eclipses are consistent with previously published times
of transit and the expectation from a circular orbit. This implies that TrES-2
most likely has a circular orbit, and thus does not obtain additional thermal
energy from tidal dissipation of a non-zero orbital eccentricity, a proposed
explanation for the large radius of this planet.Comment: 8 pages, 4 figures, 2 tables. Accepted for publication in the
Astrophysical Journal. V2: New figure added ; other minor changes throughou
Elastic energy storage in the shoulder and the evolution of high-speed throwing in Homo
Although some primates, including chimpanzees, throw objects occasionally1,2, only humans regularly throw projectiles with high speed and great accuracy. Darwin noted that humans’ unique throwing abilities, made possible when bipedalism emancipated the arms, enabled foragers to effectively hunt using projectiles3. However, there has been little consideration of the evolution of throwing in the years since Darwin made his observations, in part because of a lack of evidence on when, how, and why hominins evolved the ability to generate high-speed throws4-8. Here, we show using experimental studies of throwers that human throwing capabilities largely result from several derived anatomical features that enable elastic energy storage and release at the shoulder. These features first appear together approximately two million years ago in the species Homo erectus. Given archaeological evidence that suggests hunting activity intensified around this time9, we conclude that selection for throwing in order to hunt likely played an important role in the evolution of the human genus
Assessing telluric correction methods for Na detections with high-resolution exoplanet transmission spectroscopy.
Using high-resolution ground-based transmission spectroscopy to probe
exoplanetary atmospheres is difficult due to the inherent telluric
contamination from absorption in Earth's atmosphere. A variety of methods have
previously been used to remove telluric features in the optical regime and
calculate the planetary transmission spectrum. In this paper we present and
compare two such methods, specifically focusing on Na detections using
high-resolution optical transmission spectra: (a) calculating the telluric
absorption empirically based on the airmass, and (b) using a model of the
Earth's transmission spectrum. We test these methods on the transmission
spectrum of the hot Jupiter HD 189733 b using archival data obtained with the
HARPS spectrograph during three transits. Using models for Centre-to-Limb
Variation and the Rossiter-McLaughlin effect, spurious signals which are
imprinted within the transmission spectrum are reduced. We find that correcting
tellurics with an atmospheric model of the Earth is more robust and produces
consistent results when applied to data from different nights with changing
atmospheric conditions. We confirm the detection of sodium in the atmosphere of
HD 189733 b, with doublet line contrasts of -0.64 0.07 % (D2) and -0.53
0.07 % (D1). The average line contrast corresponds to an effective
photosphere in the Na line located around 1.13 . We also confirm an
overall blueshift of the line centroids corresponding to net atmospheric
eastward winds with a speed of 1.8 1.2 km/s. Our study highlights the
importance of accurate telluric removal for consistent and reliable
characterisation of exoplanetary atmospheres using high-resolution transmission
spectroscopy
Performance prediction of riser termination devices using barracuda
In fluidized bed reactors, one of the locations where attrition is significant is cyclones. One way to reduce the attrition in cyclones is to reduce the amount of catalyst going into the cyclones. This is achieved by separating the catalyst particles from the combined gas solid flow before the stream enters the cyclones. Using a riser flow along with a riser terminator, some of the catalyst particles can be separated from gas stream. In this work, we will discuss how Barracuda has been used at The Dow Chemical Company to investigate two riser termination devices for separating catalyst particles from gas phase. The two types of riser terminators simulated are (1) flat disk and (2) slots-elbow, as shown below in Figure 1. The results indicate that the slots-elbow type terminator has an overall separation efficiency of more than 95% whereas the disk terminator has approximately 80% efficiency.
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Characterizing exoplanetary atmospheres through infrared polarimetry
Planets can emit polarized thermal radiation, just like brown dwarfs. We
present calculated thermal polarization signals from hot exoplanets, using an
advanced radiative transfer code that fully includes all orders of scattering
by gaseous molecules and cloud particles. The code spatially resolves the disk
of the planet, allowing simulations for horizontally inhomogeneous planets. Our
results show that the degree of linear polarization, P, of an exoplanet's
thermal radiation is expected to be highest near the planet's limb and that
this P depends on the temperature and its gradient, the scattering properties
and the distribution of the cloud particles. Integrated over the disk of a
spherically symmetric planet, P of the thermal radiation equals zero. However,
for planets that appear spherically asymmetric, e.g. due to flattening, cloud
bands or spots in their atmosphere, differences in their day and night sides,
and/or obscuring rings, P is often larger than 0.1 %, in favorable cases even
reaching several percent at near-infrared wavelengths. Detection of thermal
polarization signals can give access to planetary parameters that are otherwise
hard to obtain: it immediately confirms the presence of clouds, and P can then
constrain atmospheric inhomogeneities and the flattening due to the planet's
rotation rate. For zonally symmetric planets, the angle of polarization will
yield the components of the planet's spin axis normal to the line-of-sight.
Finally, our simulations show that P is generally more sensitive to variability
in a cloudy planet's atmosphere than the thermal flux is, and could hence
better reveal certain dynamical processes.Comment: 9 pages, 5 figures, accepted for publication in Ap
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
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