Multi-wavelength observations of the energetic GRB 080810: detailed mapping of the broadband spectral evolution

GRB 080810 was one of the first bursts to trigger both Swift and the Fermi Gamma-ray Space Telescope. It was subsequently monitored over the X-ray and UV/optical bands by Swift, in the optical by ROTSE and a host of other telescopes and was detected in the radio by the VLA. The redshift of z= 3.355 +/- 0.005 was determined by Keck/HIRES and confirmed by RTT150 and NOT. The prompt gamma/X-ray emission, detected over 0.3-10^3 keV, systematically softens over time, with E_peak moving from ~600 keV at the start to ~40 keV around 100 s after the trigger; alternatively, this spectral evolution could be identified with the blackbody temperature of a quasithermal model shifting from ~60 keV to ~3 keV over the same time interval. The first optical detection was made at 38 s, but the smooth, featureless profile of the full optical coverage implies that this originated from the afterglow component, not the pulsed/flaring prompt emission. Broadband optical and X-ray coverage of the afterglow at the start of the final X-ray decay (~8 ks) reveals a spectral break between the optical and X-ray bands in the range 10^15 - 2x10^16 Hz. The decay profiles of the X-ray and optical bands show that this break initially migrates blueward to this frequency and then subsequently drifts redward to below the optical band by ~3x10^5 s. GRB 080810 was very energetic, with an isotropic energy output for the prompt component of 3x10^53 erg and 1.6x10^52 erg for the afterglow; there is no evidence for a jet break in the afterglow up to six days following the burst.Comment: 15 pages, 9 figures, 4 in colour. Accepted for publication in MNRA

Data query mechanism based on hash computing power of blockchain in internet of things

Funding: This work is supported by the NSFC (61772280, 61772454, 61811530332, 61811540410), the PAPD fund from NUIST. This work was funded by the Researchers Supporting Project No. (RSP-2019/102) King Saud University, Riyadh, Saudi Arabia. Jin Wang and Osama Alfarraj are the corresponding authors. Acknowledgments: We thank Researchers Supporting Project No. (RSP-2019/102) King Saud University, Riyadh, Saudi Arabia for funding this paper. Author Contributions: Y.R., F.Z. and O.A. conceived the mechanism design and wrote the paper, P.K.S. built the models. T.W. and A.T. developed the mechanism, J.W. and O.A. revised the manuscript. All authors have read and agreed to the published version of the manuscript.Peer reviewedPublisher PD

A Survey of DeFi Security: Challenges and Opportunities

DeFi, or Decentralized Finance, is based on a distributed ledger called blockchain technology. Using blockchain, DeFi may customize the execution of predetermined operations between parties. The DeFi system use blockchain technology to execute user transactions, such as lending and exchanging. The total value locked in DeFi decreased from \$200 billion in April 2022 to \$80 billion in July 2022, indicating that security in this area remained problematic. In this paper, we address the deficiency in DeFi security studies. To our best knowledge, our paper is the first to make a systematic analysis of DeFi security. First, we summarize the DeFi-related vulnerabilities in each blockchain layer. Additionally, application-level vulnerabilities are also analyzed. Then we classify and analyze real-world DeFi attacks based on the principles that correlate to the vulnerabilities. In addition, we collect optimization strategies from the data, network, consensus, smart contract, and application layers. And then, we describe the weaknesses and technical approaches they address. On the basis of this comprehensive analysis, we summarize several challenges and possible future directions in DeFi to offer ideas for further research

Particles in the Pacific: how productivity and zooplankton relate to particles in the deep sea

Thesis (M.S.) University of Alaska Fairbanks, 2019The magnitude and spatio-temporal patterns of particulate material flux from the surface ocean through mesopelagic and bathypelagic depths determines sequestration of atmospheric carbon and the food supplied to deep-dwelling ocean life. The factors that influence how and where this organic material is exported from euphotic depths are poorly understood. Zooplankton are thought to play a key role in modulating the transport of surface-produced particles to depths through consumption, fragmentation, active diel vertical migration, and fecal pellet production, thus it is important to study both particulate matter and zooplankton in tandem. In this study, I use an in-situ optical instrument, the Underwater Video Profiler 5 (UVP5), to describe broad scale patterns of large (> 100 μm) particles and zooplankton across a longitudinal transect of the Pacific Ocean during April to June 2015. Satellite-derived surface chlorophyll-a was employed to describe the timescales over which particles arrive in meso- and bathypelagic depths after a productivity peak. High abundances and volumes of particles are noticeable beyond the euphotic zone across the Equator, transition zone, and the sub-arctic Pacific, indicating increased export in these high-nutrient low-chlorophyll (HNLC) areas. In two of these areas, the Equator and transition zone, large abundances and volumes of particles extend into bathypelagic depths. High abundances of zooplankton were seen in all areas where high abundances of particles are seen in bathypelagic waters. Rhizaria were revealed to be pervasive across all biogeographic regions, and appear to play a role in particle attenuation in the sub-arctic Pacific. The insight into patterns between particles, zooplankton, and productivity identify HNLC regions as deserving more detailed examination in future studies of biological pump efficiency.National Science Foundation (OCE #: 1421118, 145983,1654663