8,128 research outputs found
The non-coplanar baselines effect in radio interferometry: The W-Projection algorithm
We consider a troublesome form of non-isoplanatism in synthesis radio
telescopes: non-coplanar baselines. We present a novel interpretation of the
non-coplanar baselines effect as being due to differential Fresnel diffraction
in the neighborhood of the array antennas.
We have developed a new algorithm to deal with this effect. Our new
algorithm, which we call "W-projection", has markedly superior performance
compared to existing algorithms. At roughly equivalent levels of accuracy,
W-projection can be up to an order of magnitude faster than the corresponding
facet-based algorithms. Furthermore, the precision of result is not tightly
coupled to computing time.
W-projection has important consequences for the design and operation of the
new generation of radio telescopes operating at centimeter and longer
wavelengths.Comment: Accepted for publication in "IEEE Journal of Selected Topics in
Signal Processing
A bi-directional charged particle telescope to observe flux, energy spectrum and angular distribution of relativistic and non-relativistic particles
A Charged Particle Telescope (CPT) was designed, fabricated and calibrated to make the following observations: (1) discrimination between various singly charged particles, e.g., electrons, muons and protons, in about 5 to 100 MeV energy range; (2) measurement of the flux and the energy of the charged particles incident to the telescope from two opposite directions and stopping in the telescope, thus obtaining flux and energy spectrum of downward and upward moving charged particles; and (3) measurement of the broad angular distribution of selected particles as a function of azimuthal angle. This telescope can be used to study low energy electron, muon and proton energy spectra. The experiment was flown in a high altitude balloon from Hyderabad, India, in December 1984. This same equipment is also useful in ground level electron, muon spectrum study
Quantitative Discourse Cohesion Analysis of Scientific Scholarly Texts using Multilayer Networks
Discourse cohesion facilitates text comprehension and helps the reader form a
coherent narrative. In this study, we aim to computationally analyze the
discourse cohesion in scientific scholarly texts using multilayer network
representation and quantify the writing quality of the document. Exploiting the
hierarchical structure of scientific scholarly texts, we design section-level
and document-level metrics to assess the extent of lexical cohesion in text. We
use a publicly available dataset along with a curated set of contrasting
examples to validate the proposed metrics by comparing them against select
indices computed using existing cohesion analysis tools. We observe that the
proposed metrics correlate as expected with the existing cohesion indices.
We also present an analytical framework, CHIAA (CHeck It Again, Author), to
provide pointers to the author for potential improvements in the manuscript
with the help of the section-level and document-level metrics. The proposed
CHIAA framework furnishes a clear and precise prescription to the author for
improving writing by localizing regions in text with cohesion gaps. We
demonstrate the efficacy of CHIAA framework using succinct examples from
cohesion-deficient text excerpts in the experimental dataset.Comment: 26 pages, 8 figures, 4 table
Study on fungicidal effect of plant extracts on plant pathogenic fungi and the economy of extract preparation and efficacy in comparison to synthetic/chemical fungicides
Providing food security to devastatingly increasing population with limited natural resources along with destruction caused by pre- and post-harvest pathogens are the foremost concerns for the developing countries. Numerous pesticides, herbicides and chemical fertilizers are being applied by the farmers to deal with the existing situation but leave very disastrous and undesirable after effects on ecosystem as non-degradable molecules.. Botanicals can be utilized as an ecofriendly and effective alternative against chemical as they are of natural origin. In this context, two chemical/synthetic fungicides namely Manzate and Nystanin in three different concentrations namely 500ppm, 1000 ppm and 1500 ppm were evaluated against Sclerotium rolfsii, Alternaria alternata, Fusarium monilifrome, Rhizoctonia solani and Aspergillus niger in vitro to compare them with ethanolic botanical extracts of spices (clove, cinnamon, thyme) and weeds (parthenium and calotropis) at 5%, 10%, 15%, 20% and 25%. Results revealed the high efficacy of botanicals i.e. clove extracts showed maximum inhibition (100%), followed by reduced inhibition in cinnamon, thyme, Parthenium and Calotropis treated plates against all five pathogens even at 5% concentration in comparison to chemical of 500 ppm concentration i.e. 100% in case of S.rolfsii only. Hence the herbal products can be further analyzed and applied as a potent, ecofriendly and economical substitute to chemicals
âIf You Are Old Enough to Die for Your Country, You Should Be Able to Get a Pinch of Snuffâ: Views of Tobacco 21 Among Appalachian Youth
Background: Multiple strategies have been utilized in attempts to decrease the prevalence of youth tobacco use. One strategy, raising the minimum legal sale age (MLSA) of tobacco products to 21, known as Tobacco 21, has recently gained popularity. Tobacco 21 legislation targets youth tobacco use by obstructing two main sources of youth tobacco products: stores and older friends. Although these sources are the most common for youth across the nation, regional differences have not been explored. Further, youth perspectives about raising the tobacco MLSA have not been considered. Youth may help identify potential challenges to implementing tobacco control measures, as well as suggest alternatives for intervention, thus helping to shape successful tobacco control policies.
Study Aim: This study aimed to 1) examine youth perspectives on raising the tobacco minimum legal sale age to 21 and 2) identify common sources of tobacco products among middle and high school students living in rural, low-income Appalachian communities.
Methods: A cross-sectional survey about perceptions and use of tobacco products was conducted with students in the Appalachian regions of Kentucky and North Carolina (N=426). Questions were asked concerning perspectives on the effect of Tobacco 21 implementation. Descriptive statistics characterized participants by Tobacco 21 perspectives. Participants were given the opportunity to further expand upon their opinions in an open-ended format.
Results: The majority (58.7%) of participants responded that the same number of youth would use tobacco if the legal purchase age were raised, followed by responses that fewer would use (28.9%) and more would use (12.4%). Significant differences emerged based on tobacco use status (p\u3c.05), friendsâ tobacco use (p\u3c.001), and whether participants identified family members as sources of youth tobacco products (p=.047). When given the opportunity to expand upon their views concerning the implementation of Tobacco 21 laws in their communities, many respondents cited poor enforcement of tobacco MLSAs at stores, continued access to tobacco products from family members and friends, and the overall abundance of tobacco in their communities as potential barriers to the successful implementation.
Conclusion: Fewer than one-third of participants believed that Tobacco 21 legislation would succeed in reducing the prevalence of youth tobacco use. Perspectives on the effect of Tobacco 21 legislation were related to personal tobacco use, exposure to tobacco users, and beliefs that family members provide tobacco products to youth. Open-ended responses identify potential obstacles in implementing Tobacco 21 legislation in Appalachia. Future research should attempt to include youth perspectives when designing and implementing tobacco control policies and examine family members as sources of tobacco products for youth
First principles structures and circular dichroism spectra for the close-packed and the 7/2 motif of collagen
The recently proposed close-packed motif for collagen is investigated using
first principles semi-empirical wave function theory and Kohn-Sham density
functional theory. Under these refinements the close-packed motif is shown to
be stable. For the case of the 7/2 motif a similar stability exists. The
electronic circular dichroism of the close-packed model has a significant
negative bias and a large signal. An interesting feature of the close-packed
structure is the existence of a central channel. Simulations show that, if
hydrogen atoms are placed in the cavity, a chain of molecular hydrogens is
formed suggesting a possible biological function for molecular hydrogen.Comment: 12 pages, 3 figures; 3(PPG)_6 xyz file attached; v2: minor
modification
Characteristics of gravity waves generated in a convective and a non-convective environment revealed from hourly radiosonde observation under CPEA-II campaign
Analyses of hourly radiosonde data of temperature, wind, and relative
humidity during four days (two with convection and two with no convection)
as a part of an intensive observation period in CPEA-2 campaign over Koto
Tabang (100.32° E, 0.20° S), Indonesia, are presented.
Characteristics of gravity waves in terms of dominant wave frequencies at
different heights and their vertical wavelengths are shown in the lower
stratosphere during a convective and non-convective period. Gravity waves with
periods ~10 h and ~4â5 h were found dominant near
tropopause (a region of high stability) on all days of
observation. Vertical propagation of gravity waves were seen modified near
heights of the three identified strong wind shears (at ~16, 20, and
25 km heights) due to wave-mean flow interaction. Between 17 and 21 km
heights, meridional wind fluctuations dominated over zonal wind, whereas from
22 to 30 km heights, wave fluctuations with periods ~3â5 h and
~8â10 h in zonal wind and temperature were highly associated,
suggesting zonal orientation of wave propagation. Gravity waves from
tropopause region to 30 km heights were analyzed. In general, vertical
wavelength of 2â5 km dominated in all the mean-removed (~ weekly mean)
wind and temperature hourly profiles. Computed vertical wavelength spectra
are similar, in most of the cases, to the source spectra (1â16 km height)
except that of zonal wind spectra, which is broad during active convection.
Interestingly, during and after convection, gravity waves with short
vertical wavelength (~2 km) and short period (~2â3 h)
emerged, which were confined in the close vicinity of tropopause, and were
not identified on non-convective days, suggesting convection to be the source
for them. Some wave features near strong wind shear (at 25 km height) were
also observed with short vertical wavelengths in both convective and
non-convective days, suggesting wind shear to be the sole cause of generation
and seemingly not associated with deep convection below. A drop in the
temperature up to ~4â5 K (after removal of diurnal component) was
observed at ~16 km height near a strong wind shear (~45â55 m s<sup>â1</sup> km<sup>â1</sup>) during active period of convection
Reduction of spurious velocity in finite difference lattice Boltzmann models for liquid - vapor systems
The origin of the spurious interface velocity in finite difference lattice
Boltzmann models for liquid - vapor systems is related to the first order
upwind scheme used to compute the space derivatives in the evolution equations.
A correction force term is introduced to eliminate the spurious velocity. The
correction term helps to recover sharp interfaces and sets the phase diagram
close to the one derived using the Maxwell construction.Comment: 22 pages, 10 figures (submitted to International Journal of Modern
Physics C- Physics and Computers
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