3,555 research outputs found
Unimodular Loop Quantum Cosmology
Unimodular gravity is based on a modification of the usual Einstein-Hilbert
action that allows one to recover general relativity with a dynamical
cosmological constant. It also has the interesting property of providing, as
the momentum conjugate to the cosmological constant, an emergent clock
variable. In this paper we investigate the cosmological reduction of unimodular
gravity, and its quantization within the framework of flat homogeneous and
isotropic loop quantum cosmology. It is shown that the unimodular clock can be
used to construct the physical state space, and that the fundamental features
of the previous models featuring scalar field clocks are reproduced. In
particular, the classical singularity is replaced by a quantum bounce, which
takes place in the same condition as obtained previously. We also find that
requirement of semi-classicality demands the expectation value of the
cosmological constant to be small (in Planck units). The relation to spin foam
models is also studied, and we show that the use of the unimodular time
variable leads to a unique vertex expansion.Comment: 26 pages. Revised version taking into account referee's comment
Numerical simulation of time delay interferometry for eLISA/NGO
eLISA/NGO is a new gravitational wave detection proposal with arm length of
10^6 km and one interferometer down-scaled from LISA. Just like LISA and
ASTROD-GW, in order to attain the requisite sensitivity for eLISA/NGO, laser
frequency noise must be suppressed to below the secondary noises such as the
optical path noise, acceleration noise etc. In previous papers, we have
performed the numerical simulation of the time delay interferometry (TDI) for
LISA and ASTROD-GW with one arm dysfunctional by using the CGC 2.7 ephemeris.
The results are well below their respective limits which the laser frequency
noise is required to be suppressed. In this paper, we follow the same procedure
to simulate the time delay interferometry numerically. To do this, we work out
a set of 1000-day optimized mission orbits of the eLISA/NGO spacecraft starting
at January 1st, 2021 using the CGC 2.7 ephemeris framework. We then use the
numerical method to calculate the residual optical path differences in the
second-generation TDI solutions as in our previous papers. The maximum path
length difference, for all configurations calculated, is below 13 mm (43 ps).
It is well below the limit which the laser frequency noise is required to be
suppressed for eLISA/NGO. We compare and discuss the resulting differences due
to the different arm lengths for various mission proposals -- eLISA/NGO, an
NGO-LISA-type mission with a nominal arm length of 2 x 10^6 km, LISA and
ASTROD-GW.Comment: 17 pages, 13 figures, 3 tables, minor changes in description to match
the accepted version of Classical and Quantum Gravity. arXiv admin note: text
overlap with arXiv:1102.496
Apical membrane rupture and backward bile flooding in acetaminophen-induced hepatocyte necrosis
Morphological changes of hepatocyte death have so far only been described on cells in culture or in tissue sections. Using a high-resolution and high-magnification multiphoton microscopic system, we recorded in living mice serial changes of acetaminophen (APAP)-induced hepatocyte necrosis in relevance to metabolism of a fluorogenic bile solute. Initial changes of hepatocyte injury included basal membrane disruption and loss of mitochondrial membrane potential. An overwhelming event of rupture at adjacent apical membrane resulting in flooding of bile into these hepatocytes might ensue. Belbs formed on basal membrane and then dislodged into the sinusoid circulation. Transmission electron microscopy disclosed a necrotic hepatocyte depicting well the changes after apical membrane rupture and bile flooding. Administration of the antidote N-acetylcysteine dramatically reduced the occurrence of apical membrane rupture. The present results demonstrated a hidden but critical step of apical membrane rupture leading to irreversible APAP-induced hepatocyte injury
Backpropagation neural network as earthquake early warning tool using a new modified elementary Levenberg–Marquardt Algorithm to minimise backpropagation errors
A new modified elementary Levenberg–Marquardt Algorithm (M-LMA) was used to minimise
backpropagation errors in training a backpropagation neural network (BPNN) to
predict the records related to the Chi-Chi earthquake from four seismic
stations: Station-TAP003, Station-TAP005, Station-TCU084, and Station-TCU078
belonging to the Free Field Strong Earthquake Observation Network, with the
learning rates of 0.3, 0.05, 0.2, and 0.28, respectively. For these four
recording stations, the M-LMA has been shown to produce smaller predicted
errors compared to the Levenberg–Marquardt Algorithm (LMA). A sudden predicted
error could be an indicator for Early Earthquake Warning (EEW), which
indicated the initiation of strong motion due to large earthquakes. A
trade-Off decision-making process with BPNN (TDPB), using two alarms,
adjusted the threshold of the magnitude of predicted error without a mistaken
alarm. With this approach, it is unnecessary to consider the problems of
characterising the wave phases and pre-processing, and does not require
complex hardware; an existing seismic monitoring network-covered research
area was already sufficient for these purposes.</p
Nitrogen-Functionalized Graphene Nanoflakes (GNFs:N): Tunable Photoluminescence and Electronic Structures
This study investigates the strong photoluminescence (PL) and X-ray excited
optical luminescence observed in nitrogen-functionalized 2D graphene nanoflakes
(GNFs:N), which arise from the significantly enhanced density of states in the
region of {\pi} states and the gap between {\pi} and {\pi}* states. The
increase in the number of the sp2 clusters in the form of pyridine-like N-C,
graphite-N-like, and the C=O bonding and the resonant energy transfer from the
N and O atoms to the sp2 clusters were found to be responsible for the blue
shift and the enhancement of the main PL emission feature. The enhanced PL is
strongly related to the induced changes of the electronic structures and
bonding properties, which were revealed by the X-ray absorption near-edge
structure, X-ray emission spectroscopy, and resonance inelastic X-ray
scattering. The study demonstrates that PL emission can be tailored through
appropriate tuning of the nitrogen and oxygen contents in GNFs and pave the way
for new optoelectronic devices.Comment: 8 pages, 6 figures (including toc figure
Orbit optimization for ASTROD-GW and its time delay interferometry with two arms using CGC ephemeris
ASTROD-GW (ASTROD [Astrodynamical Space Test of Relativity using Optical
Devices] optimized for Gravitation Wave detection) is an optimization of ASTROD
to focus on the goal of detection of gravitation waves. The detection
sensitivity is shifted 52 times toward larger wavelength compared to that of
LISA. The mission orbits of the 3 spacecraft forming a nearly equilateral
triangular array are chosen to be near the Sun-Earth Lagrange points L3, L4 and
L5. The 3 spacecraft range interferometrically with one another with arm length
about 260 million kilometers. In order to attain the requisite sensitivity for
ASTROD-GW, laser frequency noise must be suppressed below the secondary noises
such as the optical path noise, acceleration noise etc. For suppressing laser
frequency noise, we need to use time delay interferometry (TDI) to match the
two different optical paths (times of travel). Since planets and other
solar-system bodies perturb the orbits of ASTROD-GW spacecraft and affect the
(TDI), we simulate the time delay numerically using CGC 2.7 ephemeris
framework. To conform to the ASTROD-GW planning, we work out a set of 20-year
optimized mission orbits of ASTROD-GW spacecraft starting at June 21, 2028, and
calculate the residual optical path differences in the first and second
generation TDI for one-detector case. In our optimized mission orbits for 20
years, changes of arm length are less than 0.0003 AU; the relative Doppler
velocities are less than 3m/s. All the second generation TDI for one-detector
case satisfies the ASTROD-GW requirement.Comment: 17 pages, 7 figures, 1 tabl
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