1,960 research outputs found
Revisiting the distance, environment and supernova properties of SNR G57.2+0.8 that hosts SGR 1935+2154
We have performed a multi-wavelength study of supernova remnant (SNR)
G57.2+0.8 and its environment. The SNR hosts the magnetar SGR 1935+2154, which
emitted an extremely bright ms-duration radio burst on 2020 Apr 28 (The
Chime/Frb Collaboration et al. 2020; Bochenek et al. 2020). We used the 12CO
and 13CO J=1-0 data from the Milky Way Image Scroll Painting (MWISP) CO line
survey to search for molecular gas associated with G57.2+0.8, in order to
constrain the physical parameters (e.g., the distance) of the SNR and its
magnetar. We report that SNR G57.2+0.8 is likely impacting the molecular clouds
(MCs) at the local standard of rest (LSR) velocity V_{LSR} ~ 30 km/s and
excites a weak 1720 MHz OH maser with a peak flux density of 47 mJy/beam. The
chance coincidence of a random OH spot falling in the SNR is <12%, and the
OH-CO correspondence chance is 7% at the maser spot. This combines to give < 1%
false probability of the OH maser, suggesting a real maser detection. The LSR
velocity of the MCs places the SNR and magnetar at a kinematic distance of
d=6.6 +/- 0.7 kpc. The nondetection of thermal X-ray emission from the SNR and
the relatively dense environment suggests G57.2+0.8 be an evolved SNR with an
age (d/6.6 kpc) yr. The explosion energy of G57.2+0.8 is
lower than erg,
which is not very energetic even assuming a high ambient density = 10
cm. This reinforces the opinion that magnetars do not necessarily result
from very energetic supernova explosions.Comment: 9 pages, 5 figures, accepted for publication in the Astrophysical
Journa
Analysis on fatigue life of a certain gear transmission system
As the certain gear transmission system becomes more complex and precise, the flexibility of shaft will influence the dynamic response of system. Build the rigid model of gear system and the finite element model of the gear shaft. Establish the rigid-flex coupling model with the virtual prototype technology, simulation and make a contrast between rigid model and rigid-flex model. Find the influence of shaft flexibility on the dynamic response of gear system, which can enhance the accuracy rating of the model. With the increase of the bearing interval, the impact of coupling will become severely. Furthermore, we analysis the influencing factor of the fatigue life of the shaft. Analysis the law of the fatigue life in the different d/D, the result can provide a reference for the optimum structural design of the gear transmission system
Efficient Fully Convolution Neural Network for Generating Pixel Wise Robotic Grasps With High Resolution Images
This paper presents an efficient neural network model to generate robotic
grasps with high resolution images. The proposed model uses fully convolution
neural network to generate robotic grasps for each pixel using 400 400
high resolution RGB-D images. It first down-sample the images to get features
and then up-sample those features to the original size of the input as well as
combines local and global features from different feature maps. Compared to
other regression or classification methods for detecting robotic grasps, our
method looks more like the segmentation methods which solves the problem
through pixel-wise ways. We use Cornell Grasp Dataset to train and evaluate the
model and get high accuracy about 94.42% for image-wise and 91.02% for
object-wise and fast prediction time about 8ms. We also demonstrate that
without training on the multiple objects dataset, our model can directly output
robotic grasps candidates for different objects because of the pixel wise
implementation.Comment: Submitted to ROBIO 201
Application of EMD-WVD and particle filter for gearbox fault feature extraction and remaining useful life prediction
Fault feature extraction and remaining useful life (RUL) prediction are important to condition based maintenance (CBM). In order to realize the fault feature extraction of gearbox vibration signal presenting nonlinear and non-Gaussian, the integration of empirical mode decomposition (EMD) and Wigner-Ville distribution (WVD) are proposed in this paper. Taking the kurtosis as standard, the WVD is applied to some IMFs with larger kurtosis to calculate the time-frequency distribution, with an effective suppress on mode mixing and the cross-term interference. Afterwards, particle filter (PF) with the state space model based on Wiener process is proposed to predict the RUL of gearbox considering degradation feature, gearbox teeth wear and nonlinear and non-Gaussian system. The gearbox life cycle test shows that the EMD-WVD method can extract the valued characteristics of vibration signal accurately, and the particle filter can provide an effective way to predict the RUL of gearbox
Engine remaining useful life prediction based on trajectory similarity
The traditional remaining useful life prediction methods need to study the mechanism failure of equipment and the vibration signals can easily be submerged by the noise in the actual operation, in order to solve these problems, the methods of Trajectory similarity based prediction (TSBP) and condition monitoring based on lubricant information are proposed in this paper. The gradient model of lubricant data information which is processed by principal component analysis (PCA) is used to monitor equipment status. Additionally, degradation trajectory abstraction procedure and similarity evaluation procedure are studied in detail. Finally, the both studies are combined for the research of engine remaining useful life prediction and case study proves the simplicity and effectiveness of this method
Why torus-unstable solar filaments experience failed eruption?
To investigate the factors that control the success and/or failure of solar
eruptions, we study the magnetic field and 3-Dimensional (3D) configuration of
16 filament eruptions during 2010 July - 2013 February. All these events, i.e.,
erupted but failed to be ejected to become a coronal mass ejection (CME), are
failed eruptions with the filament maximum height exceeding . The
magnetic field of filament source regions is approximated by a potential field
extrapolation method. The filament 3D configuration is reconstructed from three
vantage points by the observations of STEREO Ahead/Behind and SDO spacecraft.
We calculate the decay index at the apex of these failed filaments and find
that in 7 cases, their apex decay indexes exceed the theoretical threshold
() of the torus instability. We further determine the
orientation change or rotation angle of each filament top during the eruption.
Finally, the distribution of these events in the parameter space of rotation
angle versus decay index is established. Four distinct regimes in the parameter
space are empirically identified. We find that, all the torus-unstable cases
(decay index ), have a large rotation angles ranging from . The possible mechanisms leading to the rotation and failed eruption
are discussed. These results imply that, besides the torus instability, the
rotation motion during the eruption may also play a significant role in solar
eruptions
Collective unitary evolution with linear optics by Cartan decomposition
Unitary operation is an essential step for quantum information processing. We
first propose an iterative procedure for decomposing a general unitary
operation without resorting to controlled-NOT gate and single-qubit rotation
library. Based on the results of decomposition, we design two compact
architectures to deterministically implement arbitrary two-qubit
polarization-spatial and spatial-polarization collective unitary operations,
respectively. The involved linear optical elements are reduced from 25 to 20
and 21 to 20, respectively. Moreover, the parameterized quantum computation can
be flexibly manipulated by wave plates and phase shifters. As an application,
we construct the specific quantum circuits to realize two-dimensional quantum
walk and quantum Fourier transformation. Our schemes are simple and feasible
with the current technology.Comment: 9 figure
Excited oscillons: cascading levels and higher multipoles
Two types of excited oscillons are investigated. We first focus on spherical
symmetry and find that there are a tower of spherical oscillons with higher
energies. Despite having multiple approximate "nodes" in their energy density
profiles, these oscillons are long-lived. We find that during the lifetime of a
highly excited oscillon it will cascade down all the lower energy levels before
its disintegration. We also point out the existence of excited oscillons with
higher approximate multipoles, which generally have shorter lifespans than the
spherical ones. Apart from performing nonlinear simulations with absorbing
boundary conditions, we also apply a perturbative method to analyze some
features of these excited oscillons.Comment: 27 pages, 17 figure
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