369 research outputs found
Singularities and the Finale of Black Hole Evaporation
In this essay we argue that once quantum gravitational effects change the
classical geometry of a black hole and remove the curvature singularity, the
black hole would not evaporate entirely but approach a remnant. In a modified
Schwarzschild spacetime characterized by a finite Kretschmann scalar, a minimal
mass of the black hole is naturally bounded by the existence of the horizon
rather than introduced by hand. A thermodynamical analysis discloses that the
temperature, heat capacity and the luminosity are vanishing naturally when the
black hole mass approaches the minimal value. This phenomenon may be attributed
to the existence of the minimal length in quantum gravity. It can also be
understood heuristically by connecting the generalized uncertainty principle
with the running of Newton's gravitational constant.Comment: 10 page
Artificial-Noise-Aided Physical Layer Phase Challenge-Response Authentication for Practical OFDM Transmission
Recently, we have developed a PHYsical layer Phase Challenge-Response
Authentication Scheme (PHY-PCRAS) for independent multicarrier transmission. In
this paper, we make a further step by proposing a novel artificial-noise-aided
PHY-PCRAS (ANA-PHY-PCRAS) for practical orthogonal frequency division
multiplexing (OFDM) transmission, where the Tikhonov-distributed artificial
noise is introduced to interfere with the phase-modulated key for resisting
potential key-recovery attacks whenever a static channel between two legitimate
users is unfortunately encountered. Then, we address various practical issues
for ANA-PHY-PCRAS with OFDM transmission, including correlation among
subchannels, imperfect carrier and timing recoveries. Among them, we show that
the effect of sampling offset is very significant and a search procedure in the
frequency domain should be incorporated for verification. With practical OFDM
transmission, the number of uncorrelated subchannels is often not sufficient.
Hence, we employ a time-separated approach for allocating enough subchannels
and a modified ANA-PHY-PCRAS is proposed to alleviate the discontinuity of
channel phase at far-separated time slots. Finally, the key equivocation is
derived for the worst case scenario. We conclude that the enhanced security of
ANA-PHY-PCRAS comes from the uncertainty of both the wireless channel and
introduced artificial noise, compared to the traditional challenge-response
authentication scheme implemented at the upper layer.Comment: 33 pages, 13 figures, submitted for possible publicatio
Learn to Play: From Knowledge to Repeated Gameplay
Online games are popular computer applications around the globe. Games are frequently designed to require extensive in-game knowledge to attain in-game goals, so it may be central to continued gameplay. Little is known about how players seek knowledge, internalize knowledge, and subsequently use it to attain in-game goals. We used theories of flow and learning to build a theoretical framework and examined it by using responses from more than four thousand players. We found that encouraging players to seek and internalize in-game knowledge is an effective strategy to increase gameplay. Interestingly, learning satisfaction was more important than knowledge internalization in predicting goal progress, showing a novel insight for game providers to nudge their players in their knowledge searching. We concluded that asking players to search and internalize in-game knowledge may be a more effective strategy than creating their focused immersion to encourage repeated gameplay
In Vitro Activity of Plant Extracts and Alkaloids against Clinical Isolates of Extended-Spectrum b-Lactamase (ESBL)-Producing Strains
The antibacterial activity of 80% ethanol extracts of 10 medicinal plants collected in Yunnan (Southwest China), was tested against clinical isolates of extended-spectrum b-lactamase (ESBL)-producing strains. Their MIC values ranged between 1.56–12.50 mg/mL. The most active plant extract was Chelidonium majus L. (MIC = 1.56 mg/mL). Two potent isoquinoline alkaloids, 8-hydroxydihydrosanguinarine and 8-hydroxydihydrochelerythrine, were identified as the major active principles through bioassay-guided fractionation and identification of the active ethyl acetate fraction from C. majus, with minimum MIC/MBC values of 15.63/62.50 mg/mL
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