808 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.
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Revolution of digital communication and Asian competitive creativity chasm
This study aims to identify changes that have taken place in the Asian technological creativity after the post-communication revolution of digital technologies. After examining the utility patent applications forwarded to the US Patent Office by 24 Asian countries between 1965 to 2007, the study partially supports the claim that the “digital communication revolution have influenced the
competitive creativity development in Asia.” However, the development growth model is shaped like a snail shell, and digital technologies have not been the silver bullet that promoted the leapfrogging of creativity in stagnating countries. Information and communication technologies (ICT) should be considered as a means of technological learning rather than the end of creativity development. The challenge of strengthening stagnating Asian countries to become competitive and innovative nations will continue until the next decade. Unless necessary steps are taken to improve technological learning and local innovations in stagnating countries, their technological dependency will increase and thus deepen the marginalization in the coming eras
Galactic Center Extinction: Evidence for Metallic Needles in the General Interstellar Medium
The extinction curve derived from ISO mid-infrared (IR) observations of the
Galactic center (GC) exhibits a surprisingly flat behavior in the ~ 3 to 8
micron region, contrary to the deep minimum expected from standard interstellar
dust models consisting of bare silicate and graphite dust particles. We show
that this extinction is likely caused by the presence of metallic needles in
the interstellar medium (ISM) towards the Galactic center. If the needles
contribute only to the 3 - 8 micron extinction, they must have a long
wavelength cutoff at ~ 8 microns, and therefore a typical length over radius
ratio of about 600, smaller than the 3000 aspect ratio determined for the
needles in Cas A. Homogeneously distributed throughout the ISM, they comprise
only a minor mass fraction of the ISM, with a needle-to-H mass ratio of
\~5x10^{-6}, which is equivalent to 0.14% of the silicate dust mass. Their
total ISM abundance can then be readily explained by the combined production in
SNe and O-rich stellar outflows. It is currently unclear how universal the GC
extinction law is. Local 2 - 5 micron extinction measurements seem to be
consistent with the standard extinction law, suggesting a non uniform
distribution of needles in the ISM. The GC observations show that metallic
needles, in spite of their low abundance or non uniform distribution, can be
the dominant source of opacity in the 3 - 8 micron wavelength region. However,
expelled into the intergalactic medium, their abundance is too low to cause any
dimming of cosmological sources, and their length is too short to make them a
significant source of submillimeter emission.Comment: 9 pages, 1 figure, to appear in the ApJ Letter
Detection of microorganisms at high altitudes
This article does not have an abstract
Structure-based stabilization of insulin as a therapeutic protein assembly via enhanced aromatic-aromatic interactions
Key contributions to protein structure and stability are provided by weakly polar interactions, which arise from asymmetric electronic distributions within amino acids and peptide bonds. Of particular interest are aromatic side chains whose directional π-systems commonly stabilize protein interiors and interfaces. Here, we consider aromatic-aromatic interactions within a model protein assembly: the dimer interface of insulin. Semi-classical simulations of aromatic-aromatic interactions at this interface suggested that substitution of residue TyrB26 by Trp would preserve native structure while enhancing dimerization (and hence hexamer stability). The crystal structure of a [TrpB26]insulin analog (determined as a T3Rf3 zinc hexamer at a resolution of 2.25 Å) was observed to be essentially identical to that of WT insulin. Remarkably and yet in general accordance with theoretical expectations, spectroscopic studies demonstrated a 150-fold increase in the in vitro lifetime of the variant hexamer, a critical pharmacokinetic parameter influencing design of long-acting formulations. Functional studies in diabetic rats indeed revealed prolonged action following subcutaneous injection. The potency of the TrpB26-modified analog was equal to or greater than an unmodified control. Thus, exploiting a general quantum-chemical feature of protein structure and stability, our results exemplify a mechanism-based approach to the optimization of a therapeutic protein assembly
CCmH: The cloud computing paradigm for mobile health (mHealth)
Cloud computing is a complex infrastructure revolved around (mobile and non-mobile) computing, database and storage capacity, and service delivery. This evolving concept aims to serve as the next generation heterogeneous service-based model, with centralized and decentralized clients, servers, services, and data storage entities across multiple platforms. Mobile cloud computing (mcc), which is a subset of the cloud computing space, is where a number of the cloud entities are mobile-based. This paper is focused around the idea of mcc deployment in the healthcare areas, defining the cloud computing mobile health (mhealth), (ccmh), which includes the relevant issues and challenges. The main contribution of this paper is a set of recommendations for the future expansions of both cloud computing and emerging mhealth technologies when they are merged together
On the formation of graphite grains in cool stars
Graphite grain formation in cool stars examined on basis of molecular equilibrium data for stellar atmosphere
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