1,149 research outputs found
Cosmic Needles versus Cosmic Microwave Background Radiation
It has been suggested by a number of authors that the 2.7K cosmic microwave
background (CMB) radiation might have arisen from the radiation from Population
III objects thermalized by conducting cosmic graphite/iron needle-shaped dust.
Due to lack of an accurate solution to the absorption properties of exceedingly
elongated grains, in existing literature which studies the CMB thermalizing
process they are generally modelled as (1) needle-like spheroids in terms of
the Rayleigh approximation; (2) infinite cylinders; and (3) the antenna theory.
We show here that the Rayleigh approximation is not valid since the Rayleigh
criterion is not satisfied for highly conducting needles. We also show that the
available intergalactic iron dust, if modelled as infinite cylinders, is not
sufficient to supply the required opacity at long wavelengths to obtain the
observed isotropy and Planckian nature of the CMB. If appealing to the antenna
theory, conducting iron needles with exceedingly large elongations (10^4)
appear able to provide sufficient opacity to thermalize the CMB within the iron
density limit. But the applicability of the antenna theory to exceedingly thin
needles of nanometer/micrometer in thickness needs to be justified.Comment: 13 pages, 4 figures; submitted to ApJ
The Detection of Cold Dust in Cas A: Evidence for the Formation of Metallic Needles in the Ejecta
Recently, Dunne et al. (2003) obtained 450 and 850 micron SCUBA images of
CasA, and reported the detection of 2-4 M_sun of cold, 18K, dust in the
remnant. Here we show that their interpretation of the observations faces
serious difficulties. Their inferred dust mass is larger than the mass of
refractory material in the ejecta of a 10 to 30 M_sun star. The cold dust model
faces even more difficulties if the 170 micron observations of the remnant are
included in the analysis, decreasing the cold dust temperature to ~ 8K, and
increasing its mass to > 20 M_sun. We offer here a more plausible
interpretation of their observation, in which the cold dust emission is
generated by conducting needles with properties that are completely determined
by the combined submillimeter and X-ray observations of the remnant. The
needles consist of metallic whiskers with <1% of embedded impurities that may
have condensed out of blobs of material that were expelled at high velocities
from the inner metal-rich layers of the star in an asymmetric explosion. The
needles are collisionally heated by the shocked gas to a temperature of 8K.
Taking the destruction of needles into account, a dust mass of only 1E-4 to
1E-3M_sun is needed to account for the observed SCUBA emission. Aligned in the
magnetic field, needles may give rise to observable polarized emission. The
detection of submillimeter polarization will therefore offer definitive proof
for a needle origin for the cold dust emission. Supernovae may still be proven
to be important sources of interstellar dust, but the evidence is still
inconclusive.Comment: 18 pages including 4 figures. Accepted for publication in the ApJ.
Missing reference adde
Is the present expansion of the universe really accelerating?
The current observations are usually explained by an accelerating expansion
of the present universe. However, with the present quality of the supernovae Ia
data, the allowed parameter space is wide enough to accommodate the
decelerating models as well. This is shown by considering a particular example
of the dark energy equation-of-state ,
which is equivalent to modifying the \emph{geometrical curvature} index of
the standard cosmology by shifting it to where is a
constant. The resulting decelerating model is consistent with the recent CMB
observations made by WMAP, as well as, with the high redshift supernovae Ia
data including SN 1997ff at . It is also consistent with the newly
discovered supernovae SN 2002dc at and SN 2002dd at which
have a general tendency to improve the fit.Comment: Replaced with the accepted version to appear in MNRA
Identification of Important Physical Properties and Amylose Content in Commercially Available Improved and Traditional Rice Varieties in Sri Lanka
Commercially available, fourteen different rice varieties (improved and traditional) in Sri Lanka were subjected to determine amylose content and important physical properties. Under physical properties, milling parameters (such as brown rice content, husk content and total milling recovery), hardness and dimensions (length, width & thickness) including water absorption capacity (by dipping at 70°C for four hours) were measured. Amylose content of each rice variety was determined by measuring the optical density of amylose-iodine complex using spectrophotometer, while amylopectin content was obtained using the relationship equation. Results revealed, brown rice content, husk content, total milling recovery, hardness and water absorption capacities of these rice varieties were within the range of 76-78%, 20-23%, 69-72% & 28-30% respectively. Statistical analysis also indicated, those physical properties of fourteen rice varieties were significantly different to each other (p0.05)
Green intraprenurial flexibility towards sustaining competitive advantage: A case of South Asian context
This study explores how green based intrapreneurial flexibility affects sustainable business performance of the Sri Lankan hotel industry. A survey was administered to a random sample of senior managers of hotels in Sri Lanka. Linear regression analysis revealed a significant path coefficient which explained green based intrapreneurial flexibility positively influenced sustainable competitive advantage. The findings suggest that hotel industry policy makers develop green specific intrapreneurial capabilities so that they can quickly adapt their green based product and service offerings in responding to changes of the green market requirements by focusing on green based new venture creation, green innovation, green related self-renewal exercises, and eco-friendly proactive decision making in order to sustain their competitive advantage from green initiatives
An Empirical Study on Ambient Conditions and Learning Effectiveness of State Universities in Sri Lanka: A Case Study in Selected Faculties of the University of Sri Jayewardenepura
This study examined the relationship between the ambient conditions and the learning effectiveness of undergraduates at state universities in Sri Lanka based on a case study conducted at University of Sri Jayewardenepura. A The general objective of this research is to identify the relationship between ambient conditions in the physical environment to enhance the learning effectiveness of state university undergraduates. Ambient conditions: temperature, Lighting, Seat Arrangements, Ambient Intelligence, and Color were the independent variables of the research whereas Learning effectiveness was the dependent variable. A hundred undergraduates from two faculties of the university were selected through a random sampling method and collected data through a structured questionnaire. Both quantitative and qualitative approaches were utilized in the analysis. The correlation analysis has been employed to identify the relationship between ambient conditions and learning effectiveness. Ten hypotheses were tested using the Pearson correlation test and all the hypotheses were rejected. Further, the study employed another four tests named Mean analysis, Demographic profile, Existing facilities, and Ambient preferences. As per the findings of the study all the tested ambient conditions create a positive relationship with the learning effectiveness of the undergraduates in both faculties. However, due to the multiple regression results, only the Temperature and Lighting create an impact on learning effectiveness. Most of the architects and educational administers were faced with difficulties in creating comfortable environments to develop learning effectiveness. Therefore, these findings can suggest the best solutions for a better learning environment. Moreover, developers can add some features to the learning environment based on student’s feedback.
© 2022 The Authors. Published by Department of Estate Management and Valuation, University of Sri Jayewardenepura.
Keywords: Learning Effectiveness, Undergraduates, Education, Ambient Condition
The Cyclotron Fundamental Exposed in the High-Field Magnetic Variable V884 Her
High-quality phase-resolved optical spectropolarimetry is presented for the
magnetic cataclysmic variable V884 Her. The overall circular polarization
during active accretion states is low and only slightly variable in the range
5000-8000A. However, the polarization is highly structured with wavelength,
showing very broad polarization humps, narrow features that are associated with
weak absorption lines in the total spectral flux, and sharp reversals across
each major emission line. The polarization reversals arise from Zeeman
splitting in the funnel gas in a longitudinal magnetic field B~30kG. The set of
narrow, polarized absorption features matches the Zeeman pattern of hydrogen
for a nearly uniform magnetic field of B=150MG, indicating that the features
are "halo" absorption lines formed in a relatively cool reversing layer above
the shock. With this identification, the broad polarization humps centered near
7150A and below 4000A are assigned to cyclotron emission from the fundamental
and first harmonic (n=2), respectively. V884 Her is only the second AM Her
system known with a field exceeding 100MG, and the first case in which the
cyclotron fundamental has been directly observed from a magnetic white dwarf.Comment: 14 pages, 6 figures, LaTeX, to appear in The Astrophysical Journal,
Part
Heterogeneous processor pipeline for a product cipher application
Processing data received as a stream is a task commonly performed by modern
embedded devices, in a wide range of applications such as multimedia
(encoding/decoding/ playing media), networking (switching and routing), digital
security, scientific data processing, etc. Such processing normally tends to be
calculation intensive and therefore requiring significant processing power.
Therefore, hardware acceleration methods to increase the performance of such
applications constitute an important area of study. In this paper, we present
an evaluation of one such method to process streaming data, namely
multi-processor pipeline architecture. The hardware is based on a
Multiple-Processor System on Chip (MPSoC), using a data encryption algorithm as
a case study. The algorithm is partitioned on a coarse grained level and mapped
on to an MPSoC with five processor cores in a pipeline, using specifically
configured Xtensa LX3 cores. The system is then selectively optimized by
strengthening and pruning the resources of each processor core. The optimized
system is evaluated and compared against an optimal single-processor System on
Chip (SoC) for the same application. The multiple-processor pipeline system for
data encryption algorithms used was observed to provide significant speed ups,
up to 4.45 times that of the single-processor system, which is close to the
ideal speed up from a five-stage pipeline
The Mystery Deepens: Spitzer Observations of Cool White Dwarfs
We present 4.5m and 8m photometric observations of 18 cool white
dwarfs obtained with the Spitzer Space Telescope. Our observations demonstrate
that four white dwarfs with T_eff< 6000 K show slightly depressed mid-infrared
fluxes relative to white dwarf models. In addition, another white dwarf with a
peculiar optical and near-infrared spectral energy distribution (LHS 1126) is
found to display significant flux deficits in Spitzer observations. These
mid-infrared flux deficits are not predicted by the current white dwarf models
including collision induced absorption due to molecular hydrogen. We postulate
that either the collision induced absorption calculations are incomplete or
there are other unrecognized physical processes occuring in cool white dwarf
atmospheres. The spectral energy distribution of LHS 1126 surprisingly fits a
Rayleigh-Jeans spectrum in the infrared, mimicking a hot white dwarf with
effective temperature well in excess of 10 K. This implies that the source
of this flux deficit is probably not molecular absorption but some other
process.Comment: 17 pages, 4 figures, ApJ in press, 10 May 200
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