Teaching Learning Based Optimization (TLBO) algorithm has been proved beneficial in many engineering applications. This algorithm is free from any algorithm specific parameters and can be adapted to ...all types of design problems. However, there are some drawbacks like convergence to local optimal solution, large computational time and slow convergence rate for complex functions. Some modifications were introduced to overcome these drawbacks in modified Teaching Learning Based Optimization (mTLBO) algorithm. In this paper mTLBO has been applied to optimize plate fin heat exchanger and pressure vessel design. The performance of mTLBO algorithm was compared with original algorithm and other population based techniques such as Particle Swarm Optimization, Generic Algorithm and Artificial Bee Colony. It was found that mTLBO gives the least value of entropy generation units that is 7.22% less than the value obtained using TLBO. Also cost of pressure vessel design using mTLBO is 3.2% lower than that of TLBO design.
The objective of this paper is to determine the level of obscured star formation activity and dust attenuation in a sample of gamma-ray burst (GRB) hosts, and to test the hypothesis that GRB hosts ...have properties consistent with those of the general star-forming galaxy populations. We present a radio continuum survey of all z < 1 GRB hosts in The Optically Unbiased GRB Host (TOUGH) sample supplemented with radio data for all (mostly pre-Swift) GRB-SN hosts discovered before 2006 October. We present new radio data for 22 objects and have obtained a detection for three of them (GRB 980425, 021211, 031203; none in the TOUGH sample), increasing the number of radio-detected GRB hosts from two to five. The star formation rate (SFR) for the GRB 021211 host of ~825 M sub(middot in circle) yr super(-1), the highest ever reported for a GRB host, places it in the category of ultraluminous infrared galaxies. We found that at least ~63% of GRB hosts have SFR < 100 M sub(middot in circle) yr super(-1) and at most ~8% can have SFR > 500 M sub(middot in circle) yr super(-1). For the undetected hosts the mean radio flux (<35 mu Jy 3sigma) corresponds to an average SFR < 15 M sub(middot in circle) yr super(-1). Moreover, > ~88% of the z <, ~ 1 GRB hosts have ultraviolet dust attenuation A sub(UV) < 6.7 mag (visual attenuation A sub(V) < 3 mag). Hence, we did not find evidence for large dust obscuration in a majority of GRB hosts. Finally, we found that the distributions of SFRs and A sub(UV) of GRB hosts are consistent with those of Lyman break galaxies, H alpha emitters at similar redshifts, and of galaxies from cosmological simulations. The similarity of the GRB population with other star-forming galaxies is consistent with the hypothesis that GRBs, a least at z <, ~ 1, trace a large fraction of all star formation, and are therefore less biased indicators than once thought.
ABSTRACT
A search of the first Data Release of the VISTA Variables in the Via Lactea (VVV) Survey discovered the exceptionally red transient VVV-WIT-01 (H − Ks = 5.2). It peaked before March 2010, ...then faded by ∼9.5 mag over the following 2 yr. The 1.6–22 μm spectral energy distribution in March 2010 was well fit by a highly obscured blackbody with T ∼ 1000 K and $A_{K_s} \sim 6.6$ mag. The source is projected against the Infrared Dark Cloud (IRDC) SDC G331.062−0.294. The chance projection probability is small for any single event (p ≈ 0.01–0.02), which suggests a physical association, e.g. a collision between low mass protostars. However, blackbody emission at T ∼ 1000 K is common in classical novae (especially CO novae) at the infrared peak in the light curve due to condensation of dust ∼30–60 d after the explosion. Radio follow-up with the Australia Telescope Compact Array detected a fading continuum source with properties consistent with a classical nova but probably inconsistent with colliding protostars. Considering all VVV transients that could have been projected against a catalogued IRDC raises the probability of a chance association to p = 0.13–0.24. After weighing several options, it appears likely that VVV-WIT-01 was a classical nova event located behind an IRDC.
Carbon doping from a Ti precursor in TiO
synthesized by a hydrothermal method was studied. The structural, optical and morphological study of the deposited material was carried out using X-ray ...diffraction, UV-vis spectroscopy and scanning electron microscopy characterization techniques. The elemental composition of the TiO
deposited with different precursor concentrations was studied using X-ray photoelectron spectroscopy and electron dispersive X-ray spectroscopy. The amount of elemental carbon in the TiO
matrix is found to be increased as the Ti precursor concentration is increased, which strengthens the proposed idea of carbon doping
a Ti precursor.
Context. Long gamma-ray bursts (GRBs) give us the chance to study both their extreme physics and the star-forming galaxies in which they form. Aims. GRB 100418A, at a redshift of z = 0.6239, had a ...bright optical and radio afterglow, and a luminous star-forming host galaxy. This allowed us to study the radiation of the explosion as well as the interstellar medium of the host both in absorption and emission. Methods. We collected photometric data from radio to X-ray wavelengths to study the evolution of the afterglow and the contribution of a possible supernova (SN) and three X-shooter spectra obtained during the first 60 h. Results. The light curve shows a very fast optical rebrightening, with an amplitude of ∼3 magnitudes, starting 2.4 h after the GRB onset. This cannot be explained by a standard external shock model and requires other contributions, such as late central-engine activity. Two weeks after the burst we detect an excess in the light curve consistent with a SN with peak absolute magnitude MV = −18.5 mag, among the faintest GRB-SNe detected to date. The host galaxy shows two components in emission, with velocities differing by 130 km s−1, but otherwise having similar properties. While some absorption and emission components coincide, the absorbing gas spans much higher velocities, indicating the presence of gas beyond the star-forming regions. The host has a star formation rate of SFR = 12.2 M⊙ yr−1, a metallicity of 12 + log(O/H) = 8.55, and a mass of 1.6 × 109 M⊙. Conclusions. GRB 100418A is a member of a class of afterglow light curves which show a steep rebrightening in the optical during the first day, which cannot be explained by traditional models. Its very faint associated SN shows that GRB-SNe can have a larger dispersion in luminosities than previously seen. Furthermore, we have obtained a complete view of the host of GRB 100418A owing to its spectrum, which contains a remarkable number of both emission and absorption lines.
Nanowires and nanowalls of the Cadmium oxide (CdO) films were synthesized by a simple one pot chemical bath deposition (CBD) method at room temperature. The Triton X-100 (TX) was used as a structure ...directing agent/surfactant to tune the morphology of CdO thin films. Its effect on the film thickness, crystallinity, wettability and ethanol gas sensitivity is studied. The thickness of the film is increased from 0.11
μm to 0.51
μm with the addition of TX in the growth solution. X-ray diffraction (XRD) patterns reveal the improvement in crystallinity of CdO for TX assisted films. Scanning electron micrographs (SEMs) show the transformation of morphology from nanowires to the bundle of nano-sheets. Ethanol gas sensitivity is found to be enhanced for TX assisted CdO films. Enhancement in gas sensitivity is due to formation of highly porous nanowalls and increment in the hydrophilicity of the CdO films.
Imaging the expanding shell of SN 2011dh de Witt, A; Bietenholz, M. F; Kamble, A ...
Monthly Notices of the Royal Astronomical Society,
01/2016, Volume:
455, Issue:
1
Journal Article
Peer reviewed
Open access
We report on the third epoch of very long baseline interferometry (VLBI) observations of the radio-bright supernova SN 2011dh, located in the nearby (7.8 Mpc) galaxy M51. The observations took place ...at t = 453 d after the explosion and at a frequency of 8.4 GHz. We obtained a fairly well-resolved image of the shell of SN 2011dh, making it one of only six recent supernovae for which resolved images of the ejecta are available. SN 2011dh has a relatively clear shell morphology, being almost circular in outline, although there may be some asymmetry in brightness around the ridge. By fitting a spherical shell model directly to the visibility measurements we determine the angular radius of SN 2011dh's radio emission to be 636 ± 29 μas. At a distance of 7.8 Mpc, this angular radius corresponds to a linear radius of (7.4 ± 0.3) × 1016 cm and an average expansion velocity since the explosion of
$19\, 000^{+2800}_{-2400}$
km s−1. We combine our VLBI measurements of SN 2011dh's radius with values determined from the radio spectral energy distribution under the assumption of a synchrotron-self-absorbed spectrum, and find all the radii are consistent with a power-law evolution, with R ∼ t
0.97±0.01, implying almost free expansion over the period t = 4 d to 453 d.
▶ The morphological transition from nanowires (NWs) to microcubes (MCs). ▶ The CdO nanowires deposited for 75
h showed the better ethanol gas performance as compared to other films. ▶ The CdO thin ...films are chemically deposited via acetate medium using CBD method.
The cadmium oxide (CdO) thin films have been synthesized by chemical bath deposition (CBD) method from an aqueous cadmium acetate solution for different time periods. The effect of film thickness on structural, morphological and wettability properties have been investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and contact angle measurements. The chemically deposited CdO thin films were polycrystalline with face centered cubic crystal structure. The average crystallite size was found to be in the range of 28–31
nm. An interesting morphological transition from nanowires to microcubes was observed with change in deposition time from 25 to 100
h at room temperature. The deposited CdO films exhibit excellent sensing properties against ethanol at 673
K. The 0.8239
μm thick films comprising nanowires deposited for 75
h showed the better ethanol gas performance as compared to other films.
In situ-generated palladium nanoparticles (Pd NPs) using Triton X-100 non-ionic surfactant-catalyzed one-pot sequential Hiyama and Heck coupling reactions in water under aerobic conditions has been ...demonstrated. The reaction was highly efficient for the synthesis of symmetrical stillbenes utilizing arenediazonium salts and vinyl triethoxy silane. The in situ-generated Pd NPs were characterized by transmission electron microscopy analysis and had a size below 20 nm. The aqueous system containing the surfactant along with the Pd NPs was recycled five times, without significant loss of catalytic activity.
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