662 research outputs found
Square-Root parametrization of dark energy in cosmology
This paper is a parametrization of the equation of state (EoS) parameter of
dark energy (DE), which is parameterized using Square-Root (SR) form i.e.
\omega _{SR}=\text{\omega _{0}}+\text{\omega
_{1}}\frac{z}{\sqrt{z^{2}+1}}, where and are free
constants. This parametrization will be examined in the context of the recently
suggested gravity theory as an alternative to General Relativity (GR),
in which gravitational effects are attributed to the non-metricity scalar
with the functional form , where and are
arbitrary constants. We derived observational constraints on model parameters
using the Hubble dataset with 31 data points and the Supernovae (SNe) dataset
from the Pantheon samples compilation dataset with 1048 data points. For the
current model, the evolution of the deceleration parameter, density parameter,
EoS for DE, and diagnostic have all been investigated. It has been
shown that the deceleration parameter favors the current accelerated expansion
phase. It has also been shown that the EoS parameter for DE has a quintessence
nature at this time.Comment: Communications in Theoretical Physics accepted versio
Identification of Simple Compounds with Microtubule-Binding Activity That Inhibit Cancer Cell Growth with High Potency
Preparation of porous bio-char and activated carbon from rice husk by leaching ash and chemical activation
Variation of the magnetic ordering in GdTZn (T= Fe, Ru, Os, Co, Rh and Ir) and its correlation with the electronic structure of isostructural YTZn
Magnetization, resistivity and specific heat measurements were performed on
the solution-grown, single crystals of six GdTZn (T = Fe, Ru, Os,
Co, Rh and Ir) compounds, as well as their Y analogues. For the Gd compounds,
the Fe column members manifest a ferromagnetic (FM) ground state (with an
enhanced Curie temperature, , for T = Fe and Ru), whereas the
Co column members manifest an antiferromagnetic (AFM) ground state.
Thermodynamic measurements on the YTZn revealed that the enhanced
for GdFeZn and GdRuZn can be understood
within the framework of Heisenberg moments embedded in a nearly ferromagnetic
Fermi liquid. Furthermore, electronic structure calculations indicate that this
significant enhancement is due to large, close to the Stoner FM criterion,
transition metal partial density of states at Fermi level, whereas the change
of FM to AFM ordering is associated with filling of electronic states with two
additional electrons per formula unit. The degree of this sensitivity is
addressed by the studies of the pseudo-ternary compounds
Gd(FeCo)Zn and Y(FeCo)Zn which
clearly reveal the effect of 3d band filling on their magnetic properties.Comment: 32 pages, 28 figure
Beaconing Approaches in Vehicular Ad Hoc Networks: A Survey
A Vehicular Ad hoc Network (VANET) is a type of wireless ad hoc network that facilitates
ubiquitous connectivity between vehicles in the absence of fixed infrastructure. Beaconing approaches
is an important research challenge in high mobility vehicular networks with enabling safety applications.
In this article, we perform a survey and a comparative study of state-of-the-art adaptive beaconing
approaches in VANET, that explores the main advantages and drawbacks behind their design. The
survey part of the paper presents a review of existing adaptive beaconing approaches such as adaptive
beacon transmission power, beacon rate adaptation, contention window size adjustment and Hybrid
adaptation beaconing techniques. The comparative study of the paper compares the representatives of
adaptive beaconing approaches in terms of their objective of study, summary of their study, the utilized
simulator and the type of vehicular scenario. Finally, we discussed the open issues and research
directions related to VANET adaptive beaconing approaches.Ghafoor, KZ.; Lloret, J.; Abu Bakar, K.; Sadiq, AS.; Ben Mussa, SA. (2013). Beaconing Approaches in Vehicular Ad Hoc Networks: A Survey. Wireless Personal Communications. 73(3):885-912. doi:10.1007/s11277-013-1222-9S885912733ITS-Standards (1996) Intelligent transportation systems, U.S. Department of Transportation, http://www.standards.its.dot.gov/about.aspCheng, L., Henty, B., Stancil, D., Bai, F., & Mudalige, P. (2005). Mobile vehicle-to-vehicle narrow-band channel measurement and characterization of the 5.9 Ghz dedicated short range communication (DSRC) frequency band. IEEE Transactions on Selected Areas in Communications, 25(8), 1501â1516.van Eenennaam, E., Wolterink, K., Karagiannis, G., & Heijenk, G. (2009). Exploring the solution space of beaconing in vanets. In Proceedings of the 2009 IEEE international vehicular networking conference, Tokyo (pp. 1â8).Torrent-Moreno, M. (2007). Inter-vehicle communications: Assessing information dissemination under safety constraints. In Proceedings of the 2007 IEEE conference wireless on demand network systems and services, Austria (pp. 59â64).Lloret, J., Canovas, A., CatalĂĄ, A., & Garcia, M. (2012). Group-based protocol and mobility model for vanets to offer internet access. Journal of Network and Computer Applications 2224â2245 doi: 10.1016j.jnca.2012.02.009 .Nzouonta, J., Rajgure, N., Wang, G., & Borcea, C. (2009). Vanet routing on city roads using real-time vehicular traffic information. IEEE Transactions on Vehicular Technology, 58(7), 3609â3626.Fukui, R., Koike, H., & Okada, H. (2002). Dynamic integrated transmission control(ditrac) over inter-vehicle communications. In Proceedings of the 2002 IEEE vehicular technology conference, Birmingham (pp. 483â487).Schmidt, R., Leinmuller, T., Schoch, E., Kargl, F., & Schafer, G. (2010). Exploration of adaptive beaconing for efficient intervehicle safety communication. 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Book Reviews
With the observation of high-energy astrophysical neutrinos by the IceCube Neutrino Observatory, interest has risen in models of PeV-mass decaying dark matter particles to explain the observed flux. We present two dedicated experimental analyses to test this hypothesis. One analysis uses 6 years of IceCube data focusing on muon neutrino âtrackâ events from the Northern Hemisphere, while the second analysis uses 2 years of âcascadeâ events from the full sky. Known background components and the hypothetical flux from unstable dark matter are fitted to the experimental data. Since no significant excess is observed in either analysis, lower limits on the lifetime of dark matter particles are derived: we obtain the strongest constraint to date, excluding lifetimes shorter than s at 90% CL for dark matter masses above 10 TeV
Differential limit on the extremely-high-energy cosmic neutrino flux in the presence of astrophysical background from nine years of IceCube data
We report a quasi-differential upper limit on the extremely-high-energy (EHE)
neutrino flux above GeV based on an analysis of nine years of
IceCube data. The astrophysical neutrino flux measured by IceCube extends to
PeV energies, and it is a background flux when searching for an independent
signal flux at higher energies, such as the cosmogenic neutrino signal. We have
developed a new method to place robust limits on the EHE neutrino flux in the
presence of an astrophysical background, whose spectrum has yet to be
understood with high precision at PeV energies. A distinct event with a
deposited energy above GeV was found in the new two-year sample, in
addition to the one event previously found in the seven-year EHE neutrino
search. These two events represent a neutrino flux that is incompatible with
predictions for a cosmogenic neutrino flux and are considered to be an
astrophysical background in the current study. The obtained limit is the most
stringent to date in the energy range between and GeV. This result constrains neutrino models predicting a three-flavor
neutrino flux of $E_\nu^2\phi_{\nu_e+\nu_\mu+\nu_\tau}\simeq2\times 10^{-8}\
{\rm GeV}/{\rm cm}^2\ \sec\ {\rm sr}10^9\ {\rm GeV}$. A significant part
of the parameter-space for EHE neutrino production scenarios assuming a
proton-dominated composition of ultra-high-energy cosmic rays is excluded.Comment: The version accepted for publication in Physical Review
Neutrinos below 100 TeV from the southern sky employing refined veto techniques to IceCube data
Many Galactic sources of gamma rays, such as supernova remnants, are expected
to produce neutrinos with a typical energy cutoff well below 100 TeV. For the
IceCube Neutrino Observatory located at the South Pole, the southern sky,
containing the inner part of the Galactic plane and the Galactic Center, is a
particularly challenging region at these energies, because of the large
background of atmospheric muons. In this paper, we present recent advancements
in data selection strategies for track-like muon neutrino events with energies
below 100 TeV from the southern sky. The strategies utilize the outer detector
regions as veto and features of the signal pattern to reduce the background of
atmospheric muons to a level which, for the first time, allows IceCube
searching for point-like sources of neutrinos in the southern sky at energies
between 100 GeV and several TeV in the muon neutrino charged current channel.
No significant clustering of neutrinos above background expectation was
observed in four years of data recorded with the completed IceCube detector.
Upper limits on the neutrino flux for a number of spectral hypotheses are
reported for a list of astrophysical objects in the southern hemisphere.Comment: 19 pages, 17 figures, 2 table
Search for transient optical counterparts to high-energy IceCube neutrinos with Pan-STARRS1
In order to identify the sources of the observed diffuse high-energy neutrino
flux, it is crucial to discover their electromagnetic counterparts. IceCube
began releasing alerts for single high-energy ( TeV) neutrino
detections with sky localisation regions of order 1 deg radius in 2016. We used
Pan-STARRS1 to follow-up five of these alerts during 2016-2017 to search for
any optical transients that may be related to the neutrinos. Typically 10-20
faint ( mag) extragalactic transients are found within the
Pan-STARRS1 footprints and are generally consistent with being unrelated field
supernovae (SNe) and AGN. We looked for unusual properties of the detected
transients, such as temporal coincidence of explosion epoch with the IceCube
timestamp. We found only one transient that had properties worthy of a specific
follow-up. In the Pan-STARRS1 imaging for IceCube-160427A (probability to be of
astrophysical origin of 50 %), we found a SN PS16cgx, located at 10.0'
from the nominal IceCube direction. Spectroscopic observations of PS16cgx
showed that it was an H-poor SN at z = 0.2895. The spectra and light curve
resemble some high-energy Type Ic SNe, raising the possibility of a jet driven
SN with an explosion epoch temporally coincident with the neutrino detection.
However, distinguishing Type Ia and Type Ic SNe at this redshift is notoriously
difficult. Based on all available data we conclude that the transient is more
likely to be a Type Ia with relatively weak SiII absorption and a fairly normal
rest-frame r-band light curve. If, as predicted, there is no high-energy
neutrino emission from Type Ia SNe, then PS16cgx must be a random coincidence,
and unrelated to the IceCube-160427A. We find no other plausible optical
transient for any of the five IceCube events observed down to a 5
limiting magnitude of mag, between 1 day and 25 days after
detection.Comment: 20 pages, 6 figures, accepted to A&
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