1,506 research outputs found
Design, development and demonstration of a Shallow solar tunnel dryer for non-electrified areas
This paper presents the design, construction and performance evaluation of a shallow solar tunnel dryer for agro and industrial products. In the shallow solar tunnel dryer, there are three separate units viz.: an air heating unit, drying unit and air diversion unit. Total area of the solar tunnel dryer was 21 m². The heated air from a separate solar air heating zone is passed through a product bed, and at the same time, the drying tunnel bed absorbs solar energy directly through the transparent UV stabilized plastic sheet used as covering material. This dryer was not required any external sources of the power to operate the electrical fan. The system was designed to operate at a temperature of 50 to 60oC. The system was installed at the institute and initial testing was conducted. After that the system was also demonstrated at the actual potential user’s site. The results obtained during the test period revealed that the temperatures inside the tunnel drying zone and solar air heating zone were much higher than the ambient air temperature during most hours of the day-light. The temperature rise inside the drying tunnel was up to 67.4°C at peak hour’s period (noon). The drying rat e and thermal efficiency of the collector were 1.73 kg/h and 26.0% respectively. The high outlet temperature indicated the scope of loading the dryer further
No evidence for mass segregation in massive young clusters
Aims. We investigate the validity of the mass segregation indicators commonly
used in analysing young stellar clusters. Methods. We simulate observations by
constructing synthetic seeing-limited images of a 1000 massive clusters (10^4
Msun) with a standard IMF and a King-density distribution function. Results. We
find that commonly used indicators are highly sensitive to sample
incompleteness in observational data and that radial completeness
determinations do not provide satisfactory corrections, rendering the studies
of radial properties highly uncertain. On the other hand, we find that, under
certain conditions, the global completeness can be estimated accurately,
allowing for the correction of the global luminosity and mass functions of the
cluster. Conclusions. We argue that there is currently no observational
evidence of mass segregation in young compact clusters since there is no robust
way to differentiate between true mass segregation and sample incompleteness
effects. Caution should then be exercised when interpreting results from
observations as evidence of mass segregation.Comment: 10 pages, 12 figures, typos corrected. Download a high-resolution
version at http://www.astro.up.pt/~jascenso/mseg_v2.pdf (1 MB
Optical observations of the bright long duration peculiar GRB 021004 afterglow
The CCD magnitudes in Johnson and Cousins and photometric
passbands are determined for the bright long duration GRB 021004 afterglow from
2002 October 4 to 16 starting 3 hours after the ray burst.
Light curves of the afterglow emission in ,, and passbands are
obtained by combining these measurements with other published data. The
earliest optical emission appears to originate in a revese shock. Flux decay of
the afterglow shows a very uncommon variation relative to other well-observed
GRBs. Rapid light variations, especially during early times (
days) is superposed on an underlying broken power law decay typical of a jetted
afterglow. The flux decay constants at early and late times derived from least
square fits to the light curve are and respectively,
with a jet break at around 7 day. Comparison with a standard fireball model
indicates a total extinction of mag in the direction of the
burst. Our low-resolution spectra corrected for this extinction provide a
spectral slope . This value and the flux decay constants
agree well with the electron energy index used in the model. The
derived jet opening angle of about implies a total emitted
gamma-ray energy erg at a cosmological distance
of about 20 Gpc. Multiwavelength observations indicate association of this GRB
with a star forming region, supporting the case for collapsar origin of long
duration GRBs.Comment: 19 pages, 3 figures, BASI, 31, 1
Multi-frequency VLBA study of the blazar S5 0716+714 during the active state in 2004: I. Inner jet kinematics
We observed the blazar \object{0716+714} with the
VLBA during its active state in 2003-2004. In this paper we discuss
multi-frequency analysis of the inner jet (first 1 mas) kinematics. The
unprecedentedly dense time sampling allows us to trace jet components without
misidentification and to calculate the component speeds with good accuracy. In
the smooth superluminal jet we were able to identify and track three components
over time moving outwards with relatively high apparent superluminal speeds
(8.5-19.4 ), which contradicts the hypothesis of a stationary oscillating
jet in this source. Component ejections occur at a relatively high rate (once
in two months), and they are accompanied by mm-continuum outbursts.
Superluminal jet components move along wiggling trajectories, which is an
indication of actual helical motion. Fast proper motion and rapid decay of the
components suggest that this source should be observed with the VLBI at a rate
of at least once in one or two months in order to trace superluminal jet
components without confusion.Comment: 4 pages, 3 figures, Astronomy & Astrophysics Letter, language
corrections adde
Red Giant stars in the Large Magellanic Cloud clusters
We present deep J,H,Ks photometry and accurate Color Magnitude Diagrams down
to K ~18.5, for a sample of 13 globular clusters in the Large Magellanic Cloud.
This data set combined with the previous sample of 6 clusters published by our
group gives the opportunity to study the properties of giant stars in clusters
with different ages (ranging from ~80 Myr up to ~3.5 Gyr). Quantitative
estimates of star population ratios (by number and luminosity) in the
Asymptotic Giant Branch, the Red Giant Branch and the He-clump, have been
obtained and compared with theoretical models in the framework of probing the
so-called phase transitions. The AGB contribution to the total luminosity
starts to be significant at ~200 Myr and reaches its maximum at ~5-600 Myr,
when the RGB Phase Transition is starting. At ~900 Myr the full developing of
an extended and well populated RGB has been completed. Both the occurrence of
the AGB and RGB Phase Transitions are sharp events, lasting a few hundreds Myr
only. These empirical results agree very well with the theoretical predictions
of simple stellar population models based on canonical tracks and the
fuel-consumption approach.Comment: 32 pages, 11 figures, accepted to Ap
On the Iron content of NGC 1978 in the LMC: a metal rich, chemically homogeneous cluster
We present a detailed abundance analysis of giant stars in NGC 1978, a
massive, intermediate-age stellar cluster in the Large Magellanic Cloud,
characterized by a high ellipticity and suspected to have a metallicity spread.
We analyzed 11 giants, all cluster members, by using high resolution spectra
acquired with the UVES/FLAMES spectrograph at the ESO-Very Large Telescope. We
find an iron content of [Fe/H]=-0.38 dex with very low (0.07 dex) dispersion,
and a mean heliocentric radial velocity Vr=293.1 (with an error of 0.9 km/s)
and a velocity dispersion (3.1 km/s), thus excluding the presence of a
significant metallicity, as well as velocity, spread within the cluster.Comment: 14 pages, 4 figures, accepted for publication by Apj
Atomistic structural ensemble refinement reveals non-native structure stabilizes a sub-millisecond folding intermediate of CheY
The dynamics of globular proteins can be described in terms of transitions between a folded native state and less-populated intermediates, or excited states, which can play critical roles in both protein folding and function. Excited states are by definition transient species, and therefore are difficult to characterize using current experimental techniques. Here, we report an atomistic model of the excited state ensemble of a stabilized mutant of an extensively studied flavodoxin fold protein CheY. We employed a hybrid simulation and experimental approach in which an aggregate 42 milliseconds of all-atom molecular dynamics were used as an informative prior for the structure of the excited state ensemble. This prior was then refined against small-angle X-ray scattering (SAXS) data employing an established method (EROS). The most striking feature of the resulting excited state ensemble was an unstructured N-terminus stabilized by non-native contacts in a conformation that is topologically simpler than the native state. Using these results, we then predict incisive single molecule FRET experiments as a means of model validation. This study demonstrates the paradigm of uniting simulation and experiment in a statistical model to study the structure of protein excited states and rationally design validating experiments
Evolution of the Type IIb SN 2011fu
The UBVRI photometric follow-up of SN 2011fu has been initiated a few days after the explosion, shows a rise followed by steep decay in all bands and shares properties very similar to that seen in case of SN 1993J, with a possible detection of the adiabatic cooling phase at very early epochs. The spectral modeling performed with SYNOW suggests that the early-phase line velocities for H and Fe ii features were ~ 16000 km s−1 and ~ 14000 km s−1, respectively. Studies of rare class of type IIb SNe are important to understand the evolution of the possible progenitors of core-collapse SNe in more details
Discovery of unusual pulsations in the cool, evolved Am stars HD 98851 and HD 102480
The chemically peculiar (CP) stars HD 98851 and HD 102480 have been
discovered to be unusual pulsators during the ``Naini Tal Cape Survey''
programme to search for pulsational variability in CP stars. Time series
photometric and spectroscopic observations of these newly discovered stars are
reported here. Fourier analyses of the time series photometry reveal that HD
98851 is pulsating mainly with frequencies 0.208 mHz and 0.103 mHz, and HD
102480 is pulsating with frequencies 0.107 mHz, 0.156 mHz and 0.198 mHz. The
frequency identifications are all subject to 1 d cycle count
ambiguities. We have matched the observed low resolution spectra of HD 98851
and HD 102480 in the range 3500-7400 \AA with theoretical synthetic spectra
using Kurucz models with solar metallicity and a micro-turbulent velocity 2 km
s. These yield K, log for HD 98851
and K, log for HD 102480. We
determined the equivalent H-line spectral class of these stars to be F1 IV and
F3 III/IV, respectively. A comparison of the location of HD 98851 and HD 102480
in the HR diagram with theoretical stellar evolutionary tracks indicates that
both stars are about 1-Gyr-old, 2- stars that lie towards the red
edge of the Sct instability strip. We conclude that HD 98851 and HD
102480 are cool, evolved Am pulsators. The light curves of these pulsating
stars have alternating high and low amplitudes, nearly harmonic (or
sub-harmonic) period ratios, high pulsational overtones and Am spectral types.
This is unusual for both Am and Sct pulsators, making these stars
interesting objects.Comment: 9 pages, 6 Figures, Accepted for publication in MNRA
Optical variability properties of high luminosity AGN classes
We present the results of a comparative study of the intra-night optical
variability (INOV) characteristics of radio-loud and radio-quiet quasars, which
involves a systematic intra-night optical monitoring of seven sets of high
luminosity AGNs covering the redshift range {\it z} to {\it z}
. The sample, matched in the optical luminosity -- redshift (M
-- z) plane, consists of seven radio-quiet quasars (RQQs), eight radio
lobe-dominated quasars (LDQs), six radio core-dominated quasars (CDQs) and five
BL Lac objects (BLs). Systematic CCD observations, aided by a careful data
analysis procedure, have allowed us to detect INOV with amplitudes as low as
1%. Present observations cover a total of 113 nights (720 hours) with only a
single quasar monitored as continuously as possible on a night. Considering
cases of only unambiguous detections of INOV we have estimated duty cycles
(DCs) of 17%, 12%, 20% and 72% respectively for RQQs, LDQs, CDQs, and BLs. The
low amplitude and low DC of INOV shown by RQQs compared to BLs can be
understood in terms of their having optical synchrotron jets which are modestly
misdirected from us. From our fairly extensive dataset, no unambiguous general
trend of a correlation between the INOV amplitude and the apparent optical
brightness of the quasar is noticed.Comment: 36 pages, 14 Figures, due to large size Fig. 5,6,11 and 12 are not
included. Intersted people contact to [email protected]. Submitted to
Journal of Astrophysics and Astronom
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