4,027 research outputs found
Room-temperature exciton-polaritons with two-dimensional WS2
Two-dimensional transition metal dichalcogenides exhibit strong optical
transitions with significant potential for optoelectronic devices. In
particular they are suited for cavity quantum electrodynamics in which strong
coupling leads to polariton formation as a root to realisation of inversionless
lasing, polariton condensationand superfluidity. Demonstrations of such
strongly correlated phenomena to date have often relied on cryogenic
temperatures, high excitation densities and were frequently impaired by strong
material disorder. At room-temperature, experiments approaching the strong
coupling regime with transition metal dichalcogenides have been reported, but
well resolved exciton-polaritons have yet to be achieved. Here we report a
study of monolayer WS coupled to an open Fabry-Perot cavity at
room-temperature, in which polariton eigenstates are unambiguously displayed.
In-situ tunability of the cavity length results in a maximal Rabi splitting of
meV, exceeding the exciton linewidth. Our data
are well described by a transfer matrix model appropriate for the large
linewidth regime. This work provides a platform towards observing strongly
correlated polariton phenomena in compact photonic devices for ambient
temperature applications.Comment: 12 pages, 6 figure
The component masses of the cataclysmic variable V347 Puppis
We present time-resolved spectroscopy and photometry of the double-lined eclipsing cataclysmic variable V347 Pup (=LB 1800). There is evidence of irradiation on the inner hemisphere of the secondary star, which we correct for using a model to give a secondary-star radial velocity of KR= 198 ± 5 km sâ1. The rotational velocity of the secondary star in V347 Pup is found to be v sin i= 131 ± 5 km sâ1 and the system inclination is i= 840 ± 23. From these parameters we obtain masses of M1= 0.63 ± 0.04 Mâ for the white dwarf primary and M2= 0.52 ± 0.06 Mâ for the M0.5V secondary star, giving a mass ratio of q= 0.83 ± 0.05. On the basis of the component masses, and the spectral type and radius of the secondary star in V347 Pup, we find tentative evidence for an evolved companion. V347 Pup shows many of the characteristics of the SW Sex stars, exhibiting single-peaked emission lines, high-velocity S-wave components and phase-offsets in the radial velocity curve. We find spiral arms in the accretion disc of V347 Pup and measure the disc radius to be close to the maximum allowed in a pressureless disc
V348 Puppis: a new SW Sex star in the period gap
We present time-resolved optical spectroscopy and photometry of the nova-like
cataclysmic variable V348 Puppis. The system displays the same spectroscopic
behaviour as SW Sex stars, so we classify V348 Pup as a new member of the
class. V348 Pup is the second SW Sex system (the first is V795 Herculis) which
lies in the period gap. The spectra exhibit enhanced HeII 4686 emission,
reminiscent of magnetic cataclysmic variables. The study of this emission line
gives a primary velocity semi-amplitude of K1 ~= 100 km/s. We have also derived
the system parameters, obtaining: M1 ~= 0.65 Msun, M2 ~= 0.20 Msun (q ~= 0.31),
i ~= 80 deg and K2 ~= 323 km/s. The spectroscopic behaviour of V348 Pup is very
similar to that of V795 Her, with the exception that V348 Pup shows deep
eclipses. We have computed the ``0.5-absorption'' spectrum of both systems,
obtaining spectra which resemble the absorption spectrum of a B0 V star. We
propose that absorption in SW Sex systems can be produced by a vertically
extended atmosphere which forms where the gas stream re-impacts the system,
either at the accretion disc or at the white dwarf's magnetosphere (assuming a
magnetic scenario).Comment: 6 pages, 10 figures, accepted for publication in MNRA
The bacterial community associated with adult vine weevil (Otiorhynchus sulcatus) in UK populations growing on strawberry is dominated by Candidatus Nardonella
Otiorhynchus sulcatus (Fabricius) (Coleoptera: Curculionidae), commonly known as black vine weevil or simply vine weevil, is an important pest of soft fruit and ornamental crops. This species is endemic to temperate areas of Europe but has spread to many other areas over the last century, including North America and Australasia. The ability of vine weevils to adapt to such different environments is difficult to reconcile with the parthenogenetic reproduction strategy, which is likely to underpin a low genetic diversity. It is therefore tempting to hypothesize that weevil adaptation to different environments is mediated, at least partly, by the microbial communities inhabiting these insects. As a first step towards testing this hypothesis we characterized the composition of the bacterial microbiota in weevils from populations feeding on strawberry plants across four geographically separate locations in the UK. We performed 16S rRNA gene Illumina amplicon sequencing, generating 2 882 853 highâquality reads. Ecological indices, namely Chao1 and Shannon, revealed that the populations used for this study harboured a low diversity and an uneven bacterial microbiota. Furthermore, ÎČâdiversity analysis failed to identify a clear association between microbiota composition and location. Notably, a single operational taxonomic unit phylogenetically related to Candidatus Nardonella accounted for 81% of the total sequencing reads for all tested insects. Our results indicate that vine weevil bacterial microbiota resembles that of other insects as it has low diversity and it is dominated by few taxa. A prediction of this observation is that location per se may not be a determinant of the microbiota inhabiting weevil populations. Rather, other or additional selective pressures, such as the plant species used as a food source, ultimately shape the weevil bacterial microbiota. Our results will serve as a reference framework to investigate other or additional hypotheses aimed at elucidating vine weevil adaptation to its environment
Transcriptional Response of Two Core Photosystem Genes in Symbiodinium spp. Exposed to Thermal Stress
Mutualistic symbioses between scleractinian corals and endosymbiotic dinoflagellates (Symbiodinium spp.) are the foundation of coral reef ecosystems. For many coral-algal symbioses, prolonged episodes of thermal stress damage the symbiont\u27s photosynthetic capability, resulting in its expulsion from the host. Despite the link between photosynthetic competency and symbiont expulsion, little is known about the effect of thermal stress on the expression of photosystem genes in Symbiodinium. This study used real-time PCR to monitor the transcript abundance of two important photosynthetic reaction center genes, psbA(encoding the D1 protein of photosystem II) and psaA (encoding the P700 protein of photosystem I), in four cultured isolates (representing ITS2-types A13, A20, B1, and F2) and two in hospite Symbiodinium spp. within the coral Pocillopora spp. (ITS2-types C1b-c and D1). Both cultured and in hospite Symbiodinium samples were exposed to elevated temperatures (32°C) over a 7-day period and examined for changes in photochemistry and transcript abundance. Symbiodinium A13 and C1b-c (both thermally sensitive) demonstrated significant declines in both psbA and psaA during the thermal stress treatment, whereas the transcript levels of the other Symbiodinium types remained stable. The downregulation of both core photosystem genes could be the result of several different physiological mechanisms, but may ultimately limit repair rates of photosynthetic proteins, rendering some Symbiodinium spp. especially susceptible to thermal stress
Agricultural climate change mitigation : Carbon calculators as a guide for decision making
This is an Accepted Manuscript of an article published by Taylor & Francis Group in International Journal of Agricultural Sustainability on 9 November 2017, available online: https://doi.org/10.1080/14735903.2017.1398628. Under embargo. Embargo end date: 9 November 2018.The dairy industry is receiving considerable attention in relation to both its significant greenhouse gas (GHG) emissions, and itâs potential for reducing those emissions, contributing towards meeting national targets and driving the industry towards sustainable intensification. However, the extent to which improvements can be made is dependent on the decision making processes of individual producers, so there has been a proliferation of carbon accounting tools seeking to influence those processes. This paper evaluates the suitability of such tools for driving environmental change by influencing on-farm management decisions. Seven tools suitable for the European dairy industry were identified, their characteristics evaluated, and used to process data relating to six scenario farms, emulating process undertaken in real farm management situations. As a result of the range of approaches taken by the tools, there was limited agreement between them as to GHG emissions magnitude, and no consistent pattern as to which tools resulted in the highest/lowest results. Despite this it is argued, that as there was agreement as to the farm activities responsible for the greatest emissions, the more complex tools were still capable of performing a âdecision supportâ role, and guiding management decisions, whilst others could merely focus attention on key issues.Peer reviewe
PROTHROMBIN DEFICIENCY AND THE BLEEDING TENDENCY IN LIVER INJURY (CHLOROFORM INTOXICATION)
The Active Quiescence of HR Del (Nova Del 1967)
This new UV study of the ex-nova HR Del is based on all of the data obtained
with the IUE satellite, and includes the important series of spectra taken in
1988 and 1992 that have not been analyzed so far. After the correction for the
reddening (EB-V)=0.16), adopting a distance d =850 pc, we have derived a mean
UV luminosity close to Luv ~ 56 Lsun, the highest value among classical novae
in "quiescence". Also the "average" optical absolute magnitude Mv=+2.30 is
indicative of a bright object. The UV continuum luminosity, the HeII 1640 A
emission line luminosity, and the optical absolute magnitude all give a mass
accretion rate Mdot very close to 1.4*10**(-7) Msun/yr, if one assumes that the
luminosity of the old nova is due to a non-irradiated accretion disk. The
continuum distribution is well fitted with either a black body of 33,900 K, or
a power-law F(lambda) ~ lambda**(-2.20). We show that the "quiescent" optical
magnitude at mv ~ 12 comes from the hot component and not from the companion
star. Since most IUE observations correspond to the "quiescent" magnitude at mv
~ 12, the same as in the pre-eruption stage, we infer that the pre-nova, for at
least 70 years prior to eruption, was also very bright at near the same Luv,
Mv, Mdot and T values as derived in the present study for the ex-nova. The wind
components in the P Cyg profiles of the CIV 1550 A and NV 1240 A resonance
lines are strong and variable on short timescales, with vedge up to -5000 km/s,
a remarkably high value. The phenomenology in the short-time variations of the
wind indicates the presence of an inhomogeneous outflow. We discuss the nature
of the strong UV continuum and wind features and the implications of the
presence of a "bright" state a long time before and after outburst on our
present knowledge of the pre-nova and post-nova behavior.Comment: 15 pages, 10 figures, accepted for Astronomy and Astrophysic
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