3,461 research outputs found
Gamma-Ray Burst Jet Breaks Revisited
Gamma-ray Burst (GRB) collimation has been inferred with the observations of achromatic steepening in GRB light curves, known as jet breaks. Identifying a jet break from a GRB afterglow light curve allows a measurement of the jet opening angle and true energetics of GRBs. In this paper, we re-investigate this problem using a large sample of GRBs that have an optical jet break that is consistent with being achromatic in the X-ray band. Our sample includes 99 GRBs from 1997 February to 2015 March that have optical and, for Swift GRBs, X-ray light curves that are consistent with the jet break interpretation. Out of the 99 GRBs we have studied, 55 GRBs are found to have temporal and spectral behaviors both before and after the break, consistent with the theoretical predictions of the jet break models, respectively. These include 53 long/soft (Type II) and 2 short/hard (Type I) GRBs. Only 1 GRB is classified as the candidate of a jet break with energy injection. Another 41 and 3 GRBs are classified as the candidates with the lower and upper limits of the jet break time, respectively. Most jet breaks occur at 90 ks, with a typical opening angle θj = (2.5 ± 1.0)°. This gives a typical beaming correction factor for Type II GRBs, suggesting an even higher total GRB event rate density in the universe. Both isotropic and jet-corrected energies have a wide span in their distributions: log(Eγ,iso/erg) = 53.11 with σ = 0.84; log(EK,iso/erg) = 54.82 with σ = 0.56; log(Eγ/erg) = 49.54 with σ = 1.29; and log(EK/erg) = 51.33 with σ = 0.58. We also investigate several empirical correlations (Amati, Frail, Ghirlanda, and Liang–Zhang) previously discussed in the literature. We find that in general most of these relations are less tight than before. The existence of early jet breaks and hence small opening angle jets, which were detected in the Swfit era, is most likely the source of scatter. If one limits the sample to jet breaks later than 104 s, the Liang–Zhang relation remains tight and the Ghirlanda relation still exists. These relations are derived from Type II GRBs, and Type I GRBs usually deviate from them
The coevolution of overconfidence and bluffing in the resource competition game
Resources are often limited, therefore it is essential how convincingly competitors present their claims
for them. Beside a player’s natural capacity, here overconfidence and bluffing may also play a decisive
role and influence how to share a restricted reward. While bluff provides clear, but risky advantage,
overconfidence, as a form of self-deception, could be harmful to its user. Still, it is a long-standing
puzzle why these potentially damaging biases are maintained and evolving to a high level in the
human society. Within the framework of evolutionary game theory, we present a simple version of
resource competition game in which the coevolution of overconfidence and bluffing is fundamental,
which is capable to explain their prevalence in structured populations. Interestingly, bluffing seems
apt to evolve to higher level than corresponding overconfidence and in general the former is less
resistant to punishment than the latter. Moreover, topological feature of the social network plays an
intricate role in the spreading of overconfidence and bluffing. While the heterogeneity of interactions
facilitates bluffing, it also increases efficiency of adequate punishment against overconfident behavior.
Furthermore, increasing the degree of homogeneous networks can trigger similar effect. We also
observed that having high real capability may accommodate both bluffing ability and overconfidence
simultaneously
Robust and accurate depth estimation by fusing LiDAR and Stereo
Depth estimation is one of the key technologies in some fields such as
autonomous driving and robot navigation. However, the traditional method of
using a single sensor is inevitably limited by the performance of the sensor.
Therefore, a precision and robust method for fusing the LiDAR and stereo
cameras is proposed. This method fully combines the advantages of the LiDAR and
stereo camera, which can retain the advantages of the high precision of the
LiDAR and the high resolution of images respectively. Compared with the
traditional stereo matching method, the texture of the object and lighting
conditions have less influence on the algorithm. Firstly, the depth of the
LiDAR data is converted to the disparity of the stereo camera. Because the
density of the LiDAR data is relatively sparse on the y-axis, the converted
disparity map is up-sampled using the interpolation method. Secondly, in order
to make full use of the precise disparity map, the disparity map and stereo
matching are fused to propagate the accurate disparity. Finally, the disparity
map is converted to the depth map. Moreover, the converted disparity map can
also increase the speed of the algorithm. We evaluate the proposed pipeline on
the KITTI benchmark. The experiment demonstrates that our algorithm has higher
accuracy than several classic methods
Spectrum Comparative Study of Commutation Failure and Short-Circuit Fault in UHVDC Transmission System
When commutation failure occurs in UHVDC transmission system, the transient process of DC voltage and current are similar to grounding short-circuit fault. In order to differentiate them effectively, the paper introduces mathematical morphology methods to analysis the spectrum of transient current. Base on Yunnan-Guangzhou kV UHVDC transmission system, the paper simulates the commutation failure and DC line short-circuit fault under different fault conditions in PSCAD/EMTDC. By modified morphology filter, the transient signal of DC () is decomposed into six scales, and morphological characteristics of aerial mode component of  is analyzed under different scales. The simulation results show that when DC line short-circuit faults occurs, wherever in the rectifier side, in the DC transmission line midpoint or in the inverter side, the aerial mode component of  have more high frequency weight in ~ and decays gradually; When commutation failures, which are caused by the inverter side AC system single-phase grounding fault, phase to phase fault, three phase grounding fault or the inverter side transformer ratio increased, the aerial mode component of  have less frequency weight in
Linear Stability Analysis of the Herringbone Groove Journal Bearings in Microsystems: Consideration of Gas Rarefaction Effects
The dynamic performance of the herringbone groove journal bearings (HGJBs
Exploiting Entity BIO Tag Embeddings and Multi-task Learning for Relation Extraction with Imbalanced Data
In practical scenario, relation extraction needs to first identify entity
pairs that have relation and then assign a correct relation class. However, the
number of non-relation entity pairs in context (negative instances) usually far
exceeds the others (positive instances), which negatively affects a model's
performance. To mitigate this problem, we propose a multi-task architecture
which jointly trains a model to perform relation identification with
cross-entropy loss and relation classification with ranking loss. Meanwhile, we
observe that a sentence may have multiple entities and relation mentions, and
the patterns in which the entities appear in a sentence may contain useful
semantic information that can be utilized to distinguish between positive and
negative instances. Thus we further incorporate the embeddings of
character-wise/word-wise BIO tag from the named entity recognition task into
character/word embeddings to enrich the input representation. Experiment
results show that our proposed approach can significantly improve the
performance of a baseline model with more than 10% absolute increase in
F1-score, and outperform the state-of-the-art models on ACE 2005 Chinese and
English corpus. Moreover, BIO tag embeddings are particularly effective and can
be used to improve other models as well
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