Bimodal distribution of short gamma-ray bursts: evidence for two distinct types of short gamma-ray bursts

Recently, GRB 170817A was confirmed to be associated with GW 170817, which was produced by a neutron star - neutron star merger. It indicates that at least some short gamma-ray bursts come from binary neutron star mergers. Theoretically, it is widely accepted that short gamma-ray bursts can be produced by two distinctly different mechanisms, binary neutron star mergers and neutron star - black hole mergers. These two kinds of bursts should be different observationally due to their different trigger mechanisms. Motivated by this idea, we collect a universal data set constituted of 51 short gamma-ray bursts observed by $Swift$/BAT, among which 14 events have extended emission component. We study the observational features of these 51 events statistically. It is found that our samples are consisted of two distinct groups. They clearly show a bimodal distribution when their peak photon fluxes at 15-150 keV band are plotted against the corresponding fluences. Most interestingly, all the 14 short bursts with extended emission lie in a particular region. When the fluences are plotted against the burst durations, short bursts with extended emission again tend to concentrate in the long duration segment. These features strongly indicate that short gamma-ray bursts really may come from two distinct types of progenitors. We argue that those short gamma-ray bursts with extended emission come from the coalescence of neutron stars, while the short gamma-ray bursts without extended emission come from neutron star - black hole mergers.Comment: 12 pages, 2 figures, 1 table, accepted by New Astronom

"Overconfidence" versus "helplessness": A qualitative study on abstinence self-efficacy of drug users in a male compulsory drug detention center in China.

Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.Background: Compulsory drug detention is the most frequent way to control drug use in China; however, it has often been criticized. This qualitative study aimed to investigate abstinence self-efficacy and its sources of drug users in a compulsory male drug detention center in Shanghai, China, and the attitudes of the drug users to this form of rehabilitation. Methods: Thirty-six participants were interviewed (semi-structured, in depth) about their history of drug use and rehabilitation, self-evaluation of addiction, motivations to abstain, plans for the future and attitudes toward rehabilitation. A thematic analysis was undertaken of the transcripts with responses to interview questions being coded for content. Results: Two main types of self-efficacy were found – “overconfidence” (n = 16) and “helplessness” (n = 17). Overconfident participants underestimated their levels of addiction, overestimated their self-control and held external motivations and attributions. In contrast, helpless participants overestimated their levels of addiction, underestimated their self-control and had internal motivations and attributions. Compared to overconfident participants, helpless participants had more relapse history, and were more inclined to interpret relapse as a failure and attribute relapse to themselves. More helpless participants were abandoned by their family members, and received blame from the family members instead of encouragement, but their family members motivated them to abstain. Helpless participants experienced more negative emotions and had worse physical status. They said compulsory detention was a strong support for them and was the most effective way to abstain; while overconfident participants said compulsory detention was not necessary and not useful. Conclusion: It is important to increase the motivation of overconfident drug users and the perceived control of helpless drug users. Compulsory drug detention has strengths in supporting drug users who feel helpless to resist drug use. Adjustments and improvements of compulsory drug detention are suggested. Keywords: Drug use, Abstinence self-efficacy, Compulsory drug detention, Drug policy, Learned helplessness, Attribution theory, Qualitative metho

Insight into mechanics of AFM tip-based nanomachining: bending of cantilevers and machined grooves

Atomic force microscope (AFM) tip-based nanomachining is currently the object of intense research investigations. Values of the load applied to the tip at the free end of the AFM cantilever probe used for nanomachining are always large enough to induce plastic deformation on the specimen surface contrary to the small load values used for the conventional contact mode AFM imaging. This study describes an important phenomenon specific for AFM nanomachining in the forward direction: under certain processing conditions, the deformed shape of the cantilever probe may change from a convex to a concave orientation. The phenomenon can principally change the depth and width of grooves machined, e.g. the grooves machined on a single crystal copper specimen may increase by 50% on average following such a change in the deformed shape of the cantilever. It is argued that this phenomenon can take place even when the AFM-based tool is operated in the so-called force-controlled mode. The study involves the refined theoretical analysis of cantilever probe bending, the analysis of experimental signals monitored during the backward and forward AFM tip-based machining and the inspection of the topography of produced grooves

Ab initio investigation on oxygen defect clusters in UO2+x

By first-principles LSDA+U calculations, we revealed that the current physical picture of defective uranium dioxide suggested solely by neutron diffraction analysis is unsatisfactory. An understanding based on quantum theory has been established as a thermodynamical competition among point defects and cuboctahedral cluster, which naturally interprets the puzzled origin of the asymmetric O' and O'' interstitials. It also gives a clear and consistent agreement with most available experimental data. Unfortunately, the observed high occupation of O'' site cannot be accounted for in this picture and is still a challenge for theoretical simulations.Comment: 4 pages, 3 figures, title change

Finite dimensional integrable Hamiltonian systems associated with DSI equation by Bargmann constraints

The Davey-Stewartson I equation is a typical integrable equation in 2+1 dimensions. Its Lax system being essentially in 1+1 dimensional form has been found through nonlinearization from 2+1 dimensions to 1+1 dimensions. In the present paper, this essentially 1+1 dimensional Lax system is further nonlinearized into 1+0 dimensional Hamiltonian systems by taking the Bargmann constraints. It is shown that the resulting 1+0 dimensional Hamiltonian systems are completely integrable in Liouville sense by finding a full set of integrals of motion and proving their functional independence.Comment: 10 pages, in LaTeX, to be published in J. Phys. Soc. Jpn. 70 (2001