2,030 research outputs found
Searching Signals in Chinese Ancient Records for the C Increases in AD 774-775 and in AD 992-993
According to the analysis of the C content of two Japanese trees over
a period of approximately 3000 years at high time resolution, Miyake (2012)
found a rapid increase at AD 774-775 and later on at AD 992-993 (Miyake 2013).
This corresponds to a high-energy event happened within one year that input
-ray energy about 710erg to the Earth, leaving the
origin a mystery. Such strong event should have an unusual optical counterpart,
and have been recorded in historical literature. We searched Chinese historical
materials around AD 744-775 and AD 992-993, but no remarkable event was found
except a violent thunderstorm in AD 775. However, the possibility of a
thunderstorm containing so much energy is still unlikely. We conclude the event
caused the C increase is still unclear. This event most probably has no
optical counterpart, and short gamma-ray burst, giant flare of a soft gamma-ray
repeater and terrestrial -ray flash may all be the candidates.Comment: 8 pages, 3 figure
Constraining the Mass of the Photon with Gamma-Ray Bursts
One of the cornerstones of modern physics is Einstein's special relativity,
with its constant speed of light and zero photon mass assumptions. Constraint
on the rest mass m_{\gamma} of photons is a fundamental way to test Einstein's
theory, as well as other essential electromagnetic and particle theories. Since
non-zero photon mass can give rise to frequency-(or energy-) dependent
dispersions, measuring the time delay of photons with different frequencies
emitted from explosive astrophysical events is an important and
model-independent method to put such a constraint. The cosmological gamma-ray
bursts (GRBs), with short time scales, high redshifts as well as broadband
prompt and afterglow emissions, provide an ideal testbed for m_{\gamma}
constraints. In this paper we calculate the upper limits of the photon mass
with GRB early time radio afterglow observations as well as multi-band radio
peaks, thus improve the results of Schaefer (1999) by nearly half an order of
magnitude.Comment: 25 pages, 2 tables, Accepted by Journal of High Energy Astrophysic
New Generalizations of Cosmography Inspired by the Pade Approximant
The current accelerated expansion of the universe has been one of the most
important fields in physics and astronomy since 1998. Many cosmological models
have been proposed in the literature to explain this mysterious phenomenon.
Since the nature and cause of the cosmic acceleration are still unknown,
model-independent approaches to study the evolution of the universe are
welcome. One of the powerful model-independent approaches is the so-called
cosmography. It only relies on the cosmological principle, without postulating
any underlying theoretical model. However, there are several shortcomings in
the usual cosmography. For instance, it is plagued with the problem of
divergence (or an unacceptably large error), and it fails to predict the future
evolution of the universe. In the present work, we try to overcome or at least
alleviate these problems, and we propose two new generalizations of cosmography
inspired by the Pad\'e approximant. One is to directly parameterize the
luminosity distance based on the Pad\'e approximant, while the other is to
generalize cosmography with respect to a so-called -shift
, which is also inspired by the Pad\'e approximant.
Then, we confront them with the observational data with the help of the Markov
chain Monte Carlo (MCMC) code emcee, and find that they work fairly well.Comment: 16 pages, 3 tables, 5 figures, revtex4; v2: discussions added, Eur.
Phys. J. C in press; v3: published versio
Orbital density wave induced by electron-lattice coupling in orthorhombic iron pnictides
In this paper we explore the magnetic and orbital properties closely related
to a tetragonal-orthorhombic structural phase transition in iron pnictides
based on both two- and five-orbital Hubbard models. The electron-lattice
coupling, which interplays with electronic interaction, is self-consistently
treated. Our results reveal that the orbital polarization stabilizes the spin
density wave (SDW) order in both tetragonal and orthorhombic phases. However,
the ferro-orbital density wave (F-ODW) only occurs in the orthorhombic phase
rather than in the tetragonal one. Magnetic moments of Fe are small in the
intermediate Coulomb interaction region for the striped antiferromangnetic
phase in the realistic five orbital model. The anisotropic Fermi surface in the
SDW/ODW orthorhombic phase is well in agreement with the recent angle-resolved
photoemission spectroscopy experiments. These results suggest a scenario that
the magnetic phase transition is driven by the ODW order mainly arising from
the electron-lattice coupling.Comment: 21 pages, 10 figure
Relationship between Human Body Anthropometric Measurements and Basal Metabolic Rate
Through the use of 3D body measurement technology and cardiopulmonary function test equipment, obtaining the body size data and basal metabolic rate of 116 young healthy subjects, this study aims to find the relationship between the size of human body and basal metabolic rate. Factor analysis, univariate analysis, and linear regression analysis were performed on 13 observed items (selected from 152 human data) by SPSS data analysis software. The 13 observed items include the largest abdominal circumference, waist circumference, chest circumference (horizontal), thigh circumference, hip circumference, weight, total shoulder width, neck circumference, height, waist height, high cervical point, hip height, and chest height. The results indicate that girth and height factors are correlated with the predicted basal metabolic rate as well as the measured basal metabolic rate. The predicted basal metabolic rate is significantly correlated with weight, height, hip circumference, and neck circumference. The measured basal metabolic rate is significantly correlated with the neck circumference as well as height
On the measurement of the Hubble constant in a local low-density universe
Astrophysical observations indicate that the ``Local Universe" has a
relatively lower matter density () than the predictions of the
standard inflation cosmology and the large-scale motions of galaxies which
provide a mean mass density to be very close to unity. In such a local
underdense region the Hubble expansion may not be representative of the global
behaviour. Utilizing an underdense sphere embedded in a flat universe as the
model of our ``Local Universe", we show that the local Hubble constant would be
1.2 -- 1.4 times larger than the global value on scale of Mpc,
depending on the variation of . This may account for the recent
measurements of the unpleasantly large Hubble constant of 80 km/s/Mpc
using the Cepheid variables in the Virgo cluster and the relative distance
between Virgo and Coma cluster and removes the resulted apparent paradox of the
age of our universe.Comment: 9 pages, Latex file, 3 figures available by reques
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