Online influence mximization in non-stationary social networks

Social networks have been popular platforms for information propagation. An important use case is viral marketing: given a promotion budget, an advertiser can choose some influential users as the seed set and provide them free or discounted sample products; in this way, the advertiser hopes to increase the popularity of the product in the users' friend circles by the world-of-mouth effect, and thus maximizes the number of users that information of the production can reach. There has been a body of literature studying the influence maximization problem. Nevertheless, the existing studies mostly investigate the problem on a one-off basis, assuming fixed known influence probabilities among users, or the knowledge of the exact social network topology. In practice, the social network topology and the influence probabilities are typically unknown to the advertiser, which can be varying over time, i.e., in cases of newly established, strengthened or weakened social ties. In this paper, we focus on a dynamic non-stationary social network and design a randomized algorithm, RSB, based on multi-armed bandit optimization, to maximize influence propagation over time. The algorithm produces a sequence of online decisions and calibrates its explore-exploit strategy utilizing outcomes of previous decisions. It is rigorously proven to achieve an upper-bounded regret in reward and applicable to large-scale social networks. Practical effectiveness of the algorithm is evaluated using both synthetic and real-world datasets, which demonstrates that our algorithm outperforms previous stationary methods under non-stationary conditions.postprin

The Temporal and Spectral Characteristics of "Fast Rise and Exponential Decay" Gamma-Ray Burst Pulses

In this paper we have analyzed the temporal and spectral behavior of 52 Fast Rise and Exponential Decay (FRED) pulses in 48 long-duration gamma-ray bursts (GRBs) observed by the CGRO/BATSE, using a pulse model with two shape parameters and the Band model with three shape parameters, respectively. It is found that these FRED pulses are distinguished both temporally and spectrally from those in long-lag pulses. Different from these long-lag pulses only one parameter pair indicates an evident correlation among the five parameters, which suggests that at least $\sim$4 parameters are needed to model burst temporal and spectral behavior. In addition, our studies reveal that these FRED pulses have correlated properties: (i) long-duration pulses have harder spectra and are less luminous than short-duration pulses; (ii) the more asymmetric the pulses are the steeper the evolutionary curves of the peak energy ($E_{p}$) in the $\nu f_{\nu}$ spectrum within pulse decay phase are. Our statistical results give some constrains on the current GRB models.Comment: 18 pages, 7 figures, accepted for publication in the Astrophysical Journa

Combined regenerated fibre Bragg gratings and Fabry-Perot etalons for dual strain and temperature sensing

© 2015 SPIE. A highly integrated fibre-optic sensor with regenerated fibre Bragg grating (RFBG) and a micro Fabry-Pérot (MFP) is proposed and demonstrated for simultaneous measurement of temperature and strain under high temperature (> 600°C). The MFP is fabricated by using a 157 nm fluorine gas (F2) laser to micromachine the core of a standard optical fibre. The RFBG is fabricated by regenerating a seed grating written over the Fabry-Pérot. Since the MFP and RFBG have different sensitivity coefficients, their combination can be used to realise simultaneous measurement of temperature and strain. It is believed that such a high-temperature strain sensor could find important applications in many areas where simultaneous measurement of temperature and strain under high temperature is required

The shock-induced chemical reaction behaviour of Al/Ni composites by cold rolling and powder compaction

© 2019, Springer Science+Business Media, LLC, part of Springer Nature. Al/Ni composites are typical structural energetic materials, which have dual functions of structural and energetic characteristics. In order to investigate the influence of manufacturing methods on shock-induced chemical reaction (SICR) behaviour of Al/Ni composites, Al/Ni multi-layered composites with 3–5 cold-rolling passes and Al/Ni powder composites were obtained. Microstructural observation using scanning electron microscopy (SEM) and two-step impact initiation experiments were performed on the four Al/Ni composites. Furthermore, mesoscale simulations, through importing SEM images into the finite element analysis to reflect the real microstructures of the composites, were performed to analyse the particle deformation and temperature rise under shock compression conditions. The experimental results showed the distinct differences on the SICR characteristics among the four Al/Ni composites (i.e. by 3, 4 and 5 cold-rolling passes and powder compaction). The manufacturing methods provided the control of the particle sizes, particle distribution and the content of the interfacial intermetallics at scale of different microstructures, which ultimately affected the temperature distribution, as well as the contact between Al and Ni in Al/Ni composites under shock loading. As a result, the Al/Ni powder composites showed the highest energy release capacity among the four composites, while the energy release capability of Al/Ni multi-layered composites decreased with the growth of rolling passes