Optical transitions between Landau levels: AA-stacked bilayer graphene

The low-frequency optical excitations of AA-stacked bilayer graphene are investigated by the tight-binding model. Two groups of asymmetric LLs lead to two kinds of absorption peaks resulting from only intragroup excitations. Each absorption peak obeys a single selection rule similar to that of monolayer graphene. The excitation channel of each peak is changed as the field strength approaches a critical strength. This alteration of the excitation channel is strongly related to the setting of the Fermi level. The peculiar optical properties can be attributed to the characteristics of the LL wave functions of the two LL groups. A detailed comparison of optical properties between AA-stacked and AB-stacked bilayer graphenes is also offered. The compared results demonstrate that the optical properties are strongly dominated by the stacking symmetry. Furthermore, the presented results may be used to discriminate AABG from MG, which can be hardly done by STM

Shining a Gluon Beam Through Quark-Gluon Plasma

We compute the energy density radiated by a quark undergoing circular motion in strongly coupled $\mathcal N = 4$ supersymmetric Yang-Mills plasma. If it were in vacuum, this quark would radiate a beam of strongly coupled radiation whose angular distribution has been characterized and is very similar to that of synchrotron radiation produced by an electron in circular motion in electrodynamics. Here, we watch this beam of gluons getting quenched by the strongly coupled plasma. We find that a beam of gluons of momenta $\sim q \gg \pi T$ is attenuated rapidly, over a distance $\sim q^{1/3} (\pi T)^{-4/3}$ in a plasma with temperature $T$. As the beam propagates through the plasma at the speed of light, it sheds trailing sound waves with momenta $\lesssim \pi T$. Presumably these sound waves would thermalize in the plasma if they were not hit soon after their production by the next pulse of gluons from the lighthouse-like rotating quark. At larger and larger $q$, the trailing sound wave becomes less and less prominent. The outward going beam of gluon radiation itself shows no tendency to spread in angle or to shift toward larger wavelengths, even as it is completely attenuated. In this regard, the behavior of the beam of gluons that we analyze is reminiscent of the behavior of jets produced in heavy ion collisions at the LHC that lose a significant fraction of their energy without appreciable change in their angular distribution or their momentum distribution as they plow through the strongly coupled quark-gluon plasma produced in these collisions.Comment: 16 pages, 4 figure

Occult thoraco-abdominal injuries from an airbag and seatbelt

AbstractA combination of a seatbelt and airbags decreases the risk of injury for most body regions in motor vehicle crashes. Although the severity of injuries decreases, injuries still occur. We report a case of occult thoraco-abdominal trauma in a patient who was wearing a three-point seatbelt and had airbag protection. A 59-year-old man presented to the emergency department in shock after a motor vehicle accident. He was protected by a three-point seatbelt and airbag. Chest radiographs and focused assessment with sonography for trauma showed no abnormalities. However, computed tomography revealed multiple injuries in the chest and abdomen. This case report highlights occult thoraco-abdominal trauma in a victim protected by a seatbelt and airbag, which may be a pitfall for emergency physicians. Emergency physicians should understand the limitations of chest radiographs in trauma evaluation and carry out a complete evaluation of patients

The influence of the internet on catering and accommodation industry efficiency

Accommodation and catering industry efficiencies have been widely evaluated from destination, market concentration, and catering supply chain management perspectives; however, few studies have dynamically evaluated the overall accommodation and catering industry efficiencies under the influence of the internet. Therefore, to go some way to filling this research gap, this study used catering and accommodation industry data and related internet data from 31 Chinese provinces from 2012 to 2016 and employed a Dynamic DDF DEA model to evaluate the catering and accommodation industry efficiencies and the influence of the rising internet connections. It found that: 1. the overall catering and accommodation revenue efficiencies were higher when the internet connection inputs were considered; and 2. there were significant catering and accommodation income distribution differences between the eastern, central and western regions, with higher efficiencies being found in the more developed east

Antioxidant Activities and Phytochemical Study of Leaf Extracts from 18 Indigenous Tree Species in Taiwan

The objective of this study is to assess antioxidant activities of methanolic extracts from the leaves of 18 indigenous tree species in Taiwan. Results revealed that, among 18 species, Acer oliverianum exhibited the best free radical scavenging activities. The IC50 values were 5.8 and 11.8 μg/mL on DPPH radical and superoxide radical scavenging activities, respectively. In addition, A. oliverianum also exhibited the strongest ferrous ion chelating activity. Based on a bioactivity-guided isolation principle, the resulting methanolic crude extracts of A. oliverianum leaves were fractionated to yield soluble fractions of hexane, EtOAc, BuOH, and water. Of these, the EtOAc fraction had the best antioxidant activity. Furthermore, 8 specific phytochemicals were isolated and identified from the EtOAc fraction. Among them, 1,2,3,4,6-O-penta-galloyl-β-D-glucopyranose had the best free radical scavenging activity. These results demonstrate that methanolic extracts and their derived phytochemicals of A. oliverianum leaves have excellent antioxidant activities and thus they have great potential as sources for natural health products

Development of a high-density CHO-C system enables rapid protein production in 10 days

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