Unexpected Occurrence of Mesospheric Frontal Gravity Wave Events Over the South Pole (90 degrees S)

Since 2010, Utah State University has operated an infrared Advanced Mesospheric Temperature Mapper at the Amundsen–Scott South Pole station to investigate the upper atmosphere dynamics and temperature deep within the vortex. A surprising number of “frontal” gravity wave events (86) were recorded in the mesospheric OH(3,1) band intensity and rotational temperature images (typical altitude of ~87 km) during four austral winters (2012–2015). These events are gravity waves (GWs) characterized by a sharp leading wave front followed by a quasi-monochromatic wave train that grows with time. A particular subset of frontal gravity wave events has been identified in the past (Dewan & Picard, 1998) as “bores.” These are usually associated with wave ducting within stable mesospheric inversion layers, which allow them to propagate over very large distances. They have been observed on numerous occasions from low-latitude and midlatitude sites, but to date, very few have been reported at high latitudes. This study provides new analyses of the characteristics of frontal events at high latitudes and shows that most of them are likely ducted. The occurrence of these frontal GW events over this isolated region strongly supports the existence of horizontally extensive mesospheric thermal inversion layers over Antarctica, leading to regions of enhanced stability necessary for GW trapping and ducting

An Army of Me: Sockpuppets in Online Discussion Communities

In online discussion communities, users can interact and share information and opinions on a wide variety of topics. However, some users may create multiple identities, or sockpuppets, and engage in undesired behavior by deceiving others or manipulating discussions. In this work, we study sockpuppetry across nine discussion communities, and show that sockpuppets differ from ordinary users in terms of their posting behavior, linguistic traits, as well as social network structure. Sockpuppets tend to start fewer discussions, write shorter posts, use more personal pronouns such as "I", and have more clustered ego-networks. Further, pairs of sockpuppets controlled by the same individual are more likely to interact on the same discussion at the same time than pairs of ordinary users. Our analysis suggests a taxonomy of deceptive behavior in discussion communities. Pairs of sockpuppets can vary in their deceptiveness, i.e., whether they pretend to be different users, or their supportiveness, i.e., if they support arguments of other sockpuppets controlled by the same user. We apply these findings to a series of prediction tasks, notably, to identify whether a pair of accounts belongs to the same underlying user or not. Altogether, this work presents a data-driven view of deception in online discussion communities and paves the way towards the automatic detection of sockpuppets.Comment: 26th International World Wide Web conference 2017 (WWW 2017

Profile alterations of a symmetrical light pulse coming through a quantum well

The theory of a response of a two-energy-level system, irradiated by symmetrical light pulses, has been developed.(Suchlike electronic system approximates under the definite conditions a single ideal quantum well (QW) in a strong magnetic field {\bf H}, directed perpendicularly to the QW's plane, or in magnetic field absence.) The general formulae for the time-dependence of non-dimensional reflection {\cal R}(t), absorption {\cal A}(t) and transmission {\cal T}(t) of a symmetrical light pulse have been obtained. It has been shown that the singularities of three types exist on the dependencies {\cal R}(t), {\cal A}(t), {\cal T}(t). The oscillating time dependence of {\cal R}(t), {\cal A}(t), {\cal T}(t) on the detuning frequency \Delta\omega=\omega_l-\omega_0 takes place. The oscillations are more easily observable when \Delta\omega\simeq\gamma_l. The positions of the total absorption, reflection and transparency singularities are examined when the frequency \omega_l is detuned.Comment: 9 pages, 13 figures with caption

Backbone‐Degradable Polymers Prepared by Chemical Vapor Deposition

Polymers prepared by chemical vapor deposition (CVD) polymerization have found broad acceptance in research and industrial applications. However, their intrinsic lack of degradability has limited wider applicability in many areas, such as biomedical devices or regenerative medicine. Herein, we demonstrate, for the first time, a backbone‐degradable polymer directly synthesized via CVD. The CVD co‐polymerization of [2.2]para‐cyclophanes with cyclic ketene acetals, specifically 5,6‐benzo‐2‐methylene‐1,3‐dioxepane (BMDO), results in well‐defined, hydrolytically degradable polymers, as confirmed by FTIR spectroscopy and ellipsometry. The degradation kinetics are dependent on the ratio of ketene acetals to [2.2]para‐cyclophanes as well as the hydrophobicity of the films. These coatings address an unmet need in the biomedical polymer field, as they provide access to a wide range of reactive polymer coatings that combine interfacial multifunctionality with degradability.Verletzliches Rückgrat: Beschichtungen aus Polymeren mit abbaubarem Rückgrat wurden durch Copolymerisation mittels chemischer Dampfabscheidung erhalten. Die Beschichtungen vereinen die Möglichkeit zur mehrfachen Funktionalisierung von Grenzflächen mit einer Abbaufähigkeit, was insbesondere für biomedizinische Anwendungen von Interesse ist.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135566/1/ange201609307-sup-0001-misc_information.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/135566/2/ange201609307_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/135566/3/ange201609307.pd

Transmission of a Symmetric Light Pulse through a Wide QW

The reflection, transmission and absorption of a symmetric electromagnetic pulse, which carrying frequency is close to the frequency of an interband transition in a QW (QW), are obtained. The energy levels of a QW are assumed discrete, one exited level is taken into account. The case of a wide QW is considered when a length of the pulse wave, appropriate to the carrying frequency, is comparable to the QW's width. In figures the time dependencies of the dimensionless reflection, absorption are transmission are represented. It is shown, that the spatial dispersion and a distinction in refraction indexes influence stronger reflection.Comment: 8 pages,8 figures with caption

Towards 50% Efficiency in Solar Cells

International audienc

Fast Fragile Watermark Embedding and Iterative Mechanism With High Self-Restoration Performance

This paper presents a new algorithm to reduce significantly the computational cost of one of the best methods with self-recovery capabilities in the fragile watermarking literature. This is achieved by generating two sequences of reference bits associated to the 5 most significant bit-planes (MSBPs) of the image. The reference bits and some authentication bits are then allocated to the 3 least significant bit-planes (LSBPs) of the image. The receiver uses the authentication bits to localise altered pixel-blocks and then executes an iterative restoration mechanism to calculate the original value of the watermarked pixels. Experimental results demonstrate that the embedding method executes significantly faster compared to the state-of-the-art method while achieving a high restoration performance

Elastic Light Scattering by Semiconductor Quantum Dots

Elastic light scattering by low-dimensional semiconductor objects is investigated theoretically. The differential cross section of resonant light scattering on excitons in quantum dots is calculated. The polarization and angular distribution of scattered light do not depend on the quantum-dot form, sizes and potential configuration if light wave lengths exceed considerably the quantum-dot size. In this case the magnitude of the total light scattering cross section does not depend on quantum-dot sizes. The resonant total light scattering cross section is about a square of light wave length if the exciton radiative broadening exceeds the nonradiative broadening. Radiative broadenings are calculated

Effect of Defoliation Frequency on Forage Yield from Intensive Silvopastoral Systems Compared to a Monoculture Grassland

Livestock production in the tropical regions of the world faces serious constraints as a result of climate change. Monoculture based pastures require the use of large amounts of nitrogen fertilizers to sustain production throughout the year. In general terms, tropical grasses are of low quality and when consumed by ruminant species, contribute to the emission of greenhouse gases (methane, carbon dioxide and nitrous oxide) (Herrero et al. 2009; Place et al. 2009). The establishment of intensive silvopastoral systems (iSPS) with associated shrubs legumes and grasses can increase the yield and quality of forage as well as fixation and transfer of atmospheric nitrogen (N) (Murgueitio et al. 2011). Therefore, the costs of nitrogen fertilizers and the emissions of greenhouse gases under practical conditions can be reduced. The intensive silvopastoral system is a kind of agroforestal practice that it is environmentally friendly and at the same time improves productivity of livestock systems. However, several aspects of its management have not been fully evaluated. This is the case of the response to defoliation, which is an important management factor associated to the overall biomass productivity (Solorio 2005)

Urinary Excretion of Mimosine Derivatives by Cows with and without Experience in Consumption of \u3cem\u3eLeucaena leucocephala\u3c/em\u3e

Leucaena leucocephala is a leguminous tree widely distributed in the tropical regions of the world. In Mexico, it has been incorporated into silvopastoral systems and is highly regarded, owing to its high content of crude protein. Nonetheless, L. leucocephala contains secondary metab-olites, such as mimosine, a non-protein free amino acid, which may induce toxic effects in unadapted ruminants that consume the forage (Hammond 1995). Although Synergistes jonesii, an anaerobic bacterium, has the ability to degrade 3,4-DHP and 2,3-DHP to non-toxic compounds (Allison et al. 1992), in Mexico its presence has not yet been confirmed. Recent work has suggested the occurrence of sub-clinical toxicity to 3,4-DHP and 2,3-DHP in cattle grazing L. leucocephala in Australia and Thailand (Graham 2007; Dalzell et al. 2012; Phaikaew et al. 2012). Several options such as the transfer of rumen liquor and the adaptation of ruminants to the intake of L. leucocephala have been studied in an attempt to reduce the excretion of mimosine and its metabolites (Palmer et al. 2010). The aim of the present work was to evaluate the effect of the experience of consumption of L. leucocephala on excretion of mimosine derivatives (3,4-DHP and 2,3-DHP) in the urine of cattle