234 research outputs found
Post-Newtonian parameters of ghost-free parity-violating gravities
We investigate the slow-motion and weak-field approximation of the general
ghost-free parity-violating (PV) theory of gravity in the parametrized
post-Newtonian (PPN) framework and derive the perturbative field equations,
which are modified by the PV terms of this theory. The complete PPN parameters
are obtained by solving the perturbative field equations. We find that all the
PPN parameters are exactly the same as those in general relativity, except for
an extra parameter , which is caused by the new curl-type term in the
gravitomagnetic sector of the metric in this theory. We calculate the
precession effects of gyroscopes in this theory and constrain the model
parameters by the observations of the Gravity Probe B experiment.Comment: 20 pages, 1 figur
Local Buckling of Concrete Filled Rectangular Steel Tube with Longitudinal Stiffener under Axial Compression
Width-thickness ratio was an important parameter for designing Concrete Filled Rectangular Steel Tube (CFRST). Welding longitudinal stiffener on the internal wall of steel pipe could delay the local buckling, which increased the limit of width-thickness ratio. If there was not enough stiffener and its sectional dimension was too small, the local buckling of steel pipe would occur, inducing its bearing capacity seriously. If the stiffener sectional dimension was too large, concrete filled in steel tube would be broken up, which reduces its bearing capacity. To solve that problem, this paper studied local buckling of CFRST with longitudinal stiffener under axial compression and design of longitudinal stiffener. It established buckling analysis model, simplified local buckling analysis as calculating buckling load of thin plate clamped on loading side and unloading side under axial force. It deduced buckling load and buckling coefficient based on the principle of energy. The results showed that buckling mode depended on stiffening rigidity. Therefore, it put forward minimum stiffening rigidity ratio that controlled the stiffener design. This paper also came up with a formula to calculate minimum stiffening rigidity ratio. It provided guidance on designing number, sectional dimension and material performance
Testing parity symmetry of gravity with gravitational waves
The examination of parity symmetry in gravitational interactions has drawn
increasing attention. Although Einstein's General Relativity is
parity-conserved, numerous theories of parity-violating (PV) gravity in
different frameworks have recently been proposed for different motivations. In
this review, we briefly summarize the recent progress of these theories, and
focus on the observable effects of PV terms in the gravitational waves (GWs),
which are mainly reflected in the difference between the left-hand and
right-hand polarization modes. We are primarily concerned with the implications
of these theories for GWs generated by the compact binary coalescences and the
primordial GWs generated in the early Universe. The deviation of GW waveforms
and/or primordial power spectrum can always be quantified by the energy scale
of parity violation of the theory. Applying the current and future GW
observation from laser interferometers and cosmic microwave background
radiation, the current and potential constraints on the PV energy scales are
presented, which indicates that the parity symmetry of gravity can be tested in
high energy scale in this new era of gravitational waves.Comment: 22 pages, no figure
Constraints on the ghost-free parity-violating gravity from Laser-ranged Satellites
This paper explores the evolutionary behavior of the Earth-satellite binary
system within the framework of the ghost-free parity-violating gravity and the
corresponding discussion on the parity-violating effect from the laser-ranged
satellites. For this purpose, we start our study with the Parameterized
Post-Newtonian (PPN) metric of this gravity theory to study the orbital
evolution of the satellites in which the spatial-time sector of the spacetime
is modified due to the parity violation. With this modified PPN metric, we
calculate the effects of the parity-violating sector of metrics on the time
evolution of the orbital elements for an Earth-satellite binary system. We find
that among the five orbital elements, the parity violation has no effect on the
semi-latus rectum, inclination and ascending node, which are the same as the
results of general relativity and consistent with the observations of the
current experiment. In particular, parity violation produces non-zero
corrections to the eccentricity and pericenter, which will accumulate with the
evolution of time, indicating that the parity violation of gravity produces
observable effects. The observational constraint on the parity-violating effect
is derived by confronting the theoretical prediction with the observation by
the LAGEOS II pericenter advance, giving a constraint on the parity-violating
parameter space from the satellite experiments.Comment: 13 pages, no figur
La\u3csub\u3e0.7\u3c/sub\u3eSr\u3csub\u3e0.3\u3c/sub\u3eFe\u3csub\u3e0.7\u3c/sub\u3eGa\u3csub\u3e0.3\u3c/sub\u3eO\u3csub\u3e3-δ\u3c/sub\u3e as Electrode Material for a Symmetrical Solid Oxide Fuel Cell
In this research, La0.7Sr0.3Fe0.7Ga0.3O3−δ (LSFG) perovskite oxide was successfully prepared using a microwave-assisted combustion method, and employed as both anode and cathode in symmetrical solid oxide fuel cells. A maximum power density of 489 mW cm−2 was achieved at 800 °C with wet H2 as the fuel and ambient air as the oxidant in a single cell with the configuration LSFG|La0.8Sr0.2Ga0.83Mg0.17O3−δ|LSFG. Furthermore, the cells demonstrated good stability in H2 and acceptable sulfur tolerance
ACQ: Improving Generative Data-free Quantization Via Attention Correction
Data-free quantization aims to achieve model quantization without accessing
any authentic sample. It is significant in an application-oriented context
involving data privacy. Converting noise vectors into synthetic samples through
a generator is a popular data-free quantization method, which is called
generative data-free quantization. However, there is a difference in attention
between synthetic samples and authentic samples. This is always ignored and
restricts the quantization performance. First, since synthetic samples of the
same class are prone to have homogenous attention, the quantized network can
only learn limited modes of attention. Second, synthetic samples in eval mode
and training mode exhibit different attention. Hence, the batch-normalization
statistics matching tends to be inaccurate. ACQ is proposed in this paper to
fix the attention of synthetic samples. An attention center position-condition
generator is established regarding the homogenization of intra-class attention.
Restricted by the attention center matching loss, the attention center position
is treated as the generator's condition input to guide synthetic samples in
obtaining diverse attention. Moreover, we design adversarial loss of paired
synthetic samples under the same condition to prevent the generator from paying
overmuch attention to the condition, which may result in mode collapse. To
improve the attention similarity of synthetic samples in different network
modes, we introduce a consistency penalty to guarantee accurate BN statistics
matching. The experimental results demonstrate that ACQ effectively improves
the attention problems of synthetic samples. Under various training settings,
ACQ achieves the best quantization performance. For the 4-bit quantization of
Resnet18 and Resnet50, ACQ reaches 67.55% and 72.23% accuracy, respectively
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