109 research outputs found
Graphene-based photovoltaic cells for near-field thermal energy conversion
Thermophotovoltaic devices are energy-conversion systems generating an
electric current from the thermal photons radiated by a hot body. In far field,
the efficiency of these systems is limited by the thermodynamic
Schockley-Queisser limit corresponding to the case where the source is a black
body. On the other hand, in near field, the heat flux which can be transferred
to a photovoltaic cell can be several orders of magnitude larger because of the
contribution of evanescent photons. This is particularly true when the source
supports surface polaritons. Unfortunately, in the infrared where these systems
operate, the mismatch between the surface-mode frequency and the semiconductor
gap reduces drastically the potential of this technology. Here we show that
graphene-based hybrid photovoltaic cells can significantly enhance the
generated power paving the way to a promising technology for an intensive
production of electricity from waste heat.Comment: 5 pages, 4 figure
ARPES: A probe of electronic correlations
Angle-resolved photoemission spectroscopy (ARPES) is one of the most direct
methods of studying the electronic structure of solids. By measuring the
kinetic energy and angular distribution of the electrons photoemitted from a
sample illuminated with sufficiently high-energy radiation, one can gain
information on both the energy and momentum of the electrons propagating inside
a material. This is of vital importance in elucidating the connection between
electronic, magnetic, and chemical structure of solids, in particular for those
complex systems which cannot be appropriately described within the
independent-particle picture. Among the various classes of complex systems, of
great interest are the transition metal oxides, which have been at the center
stage in condensed matter physics for the last four decades. Following a
general introduction to the topic, we will lay the theoretical basis needed to
understand the pivotal role of ARPES in the study of such systems. After a
brief overview on the state-of-the-art capabilities of the technique, we will
review some of the most interesting and relevant case studies of the novel
physics revealed by ARPES in 3d-, 4d- and 5d-based oxides.Comment: Chapter to appear in "Strongly Correlated Systems: Experimental
Techniques", edited by A. Avella and F. Mancini, Springer Series in
Solid-State Sciences (2013). A high-resolution version can be found at:
http://www.phas.ubc.ca/~quantmat/ARPES/PUBLICATIONS/Reviews/ARPES_Springer.pdf.
arXiv admin note: text overlap with arXiv:cond-mat/0307085,
arXiv:cond-mat/020850
Angle resolved photoemission spectroscopy of Sr_2CuO_2Cl_2 - a revisit
We have investigated the lowest binding-energy electronic structure of the
model cuprate Sr_2CuO_2Cl_2 using angle resolved photoemission spectroscopy
(ARPES). Our data from about 80 cleavages of Sr_2CuO_2Cl_2 single crystals give
a comprehensive, self-consistent picture of the nature of the first
electron-removal state in this model undoped CuO_2-plane cuprate. Firstly, we
show a strong dependence on the polarization of the excitation light which is
understandable in the context of the matrix element governing the photoemission
process, which gives a state with the symmetry of a Zhang-Rice singlet.
Secondly, the strong, oscillatory dependence of the intensity of the Zhang-Rice
singlet on the exciting photon-energy is shown to be consistent with
interference effects connected with the periodicity of the crystal structure in
the crystallographic c-direction. Thirdly, we measured the dispersion of the
first electron-removal states along G->(pi,pi) and G->(pi,0), the latter being
controversial in the literature, and have shown that the data are best fitted
using an extended t-J-model, and extract the relevant model parameters. An
analysis of the spectral weight of the first ionization states for different
excitation energies within the approach used by Leung et al. (Phys. Rev. B56,
6320 (1997)) results in a strongly photon-energy dependent ratio between the
coherent and incoherent spectral weight. The possible reasons for this
observation and its physical implications are discussed.Comment: 10 pages, 8 figure
An update of the Worldwide Integrated Assessment (WIA) on systemic insecticides. Part 2: impacts on organisms and ecosystems
New information on the lethal and sublethal effects of neonicotinoids and fipronil on organisms is presented in this review, complementing the previous WIA in 2015. The high toxicity of these systemic insecticides to invertebrates has been confirmed and expanded to include more species and compounds. Most of the recent research has focused on bees and the sublethal and ecological impacts these insecticides have on pollinators. Toxic effects on other invertebrate taxa also covered predatory and parasitoid natural enemies and aquatic arthropods. Little, while not much new information has been gathered on soil organisms. The impact on marine coastal ecosystems is still largely uncharted. The chronic lethality of neonicotinoids to insects and crustaceans, and the strengthened evidence that these chemicals also impair the immune system and reproduction, highlights the dangers of this particular insecticidal classneonicotinoids and fipronil. , withContinued large scale – mostly prophylactic – use of these persistent organochlorine pesticides has the potential to greatly decreasecompletely eliminate populations of arthropods in both terrestrial and aquatic environments. Sublethal effects on fish, reptiles, frogs, birds and mammals are also reported, showing a better understanding of the mechanisms of toxicity of these insecticides in vertebrates, and their deleterious impacts on growth, reproduction and neurobehaviour of most of the species tested. This review concludes with a summary of impacts on the ecosystem services and functioning, particularly on pollination, soil biota and aquatic invertebrate communities, thus reinforcing the previous WIA conclusions (van der Sluijs et al. 2015)
What has changed in canine pyoderma? A narrative review
Canine pyoderma is a common presentation in small animal practice and frequently leads to prescription of systemic antimicrobial agents. A good foundation of knowledge on pyoderma was established during the 1970s and 1980s, when treatment of infection provided relatively few challenges. However, the ability to treat canine pyoderma effectively is now limited substantially by the emergence of multidrug-resistant, methicillin-resistant staphylococci (MRS) and, in some countries, by restrictions on antimicrobial prescribing for pets. The threat from rising antimicrobial resistance and the zoonotic potential of MRS add a new dimension of public health implications to the management of canine pyoderma and necessitate a revisit and the search for new best management strategies. This narrative review focusses on the impact of MRS on how canine pyoderma is managed and how traditional treatment recommendations need to be updated in the interest of good antimicrobial stewardship. Background information on clinical characteristics, pathogens, and appropriate clinical and microbiological diagnostic techniques, are reviewed in so far as they can support early identification of multidrug-resistant pathogens. The potential of new approaches for the control and treatment of bacterial skin infections is examined and the role of owner education and hygiene is highlighted. Dogs with pyoderma offer opportunities for good antimicrobial stewardship by making use of the unique accessibility of the skin through cytology, bacterial culture and topical therapy. In order to achieve long term success and to limit the spread of multidrug resistance, there is a need to focus on identification and correction of underlying diseases that trigger pyoderma in order to avoid repeated treatment
Angle-resolved photoemission spectroscopy of the cuprate superconductors
This paper reviews the most recent ARPES results on the cuprate
superconductors and their insulating parent and sister compounds, with the
purpose of providing an updated summary of the extensive literature in this
field. The low energy excitations are discussed with emphasis on some of the
most relevant issues, such as the Fermi surface and remnant Fermi surface, the
superconducting gap, the pseudogap and d-wave-like dispersion, evidence of
electronic inhomogeneity and nano-scale phase separation, the emergence of
coherent quasiparticles through the superconducting transition, and many-body
effects in the one-particle spectral function due to the interaction of the
charge with magnetic and/or lattice degrees of freedom. The first part of the
paper introduces photoemission spectroscopy in the context of strongly
interacting systems, along with an update on the state-of-the-art
instrumentation. The second part provides a brief overview of the scientific
issues relevant to the investigation of the low energy electronic structure by
ARPES. The rest of the paper is devoted to the review of experimental results
from the cuprates and the discussion is organized along conceptual lines:
normal-state electronic structure, interlayer interaction, superconducting gap,
coherent superconducting peak, pseudogap, electron self energy and collective
modes. Within each topic, ARPES data from the various copper oxides are
presented.Comment: Reviews of Modern Physics, in press. A HIGH-QUALITY pdf file is
available at http://www.physics.ubc.ca/~damascel/RMP_ARPES.pd
Befunde von Uterus und Ovarien geschlachteter Eringerkühe mit Fruchtbarkeitsproblemen
Eringer cows are often slaughtered due to fertility problems which result from inflammatory and degenerative changes of the uterus or hormonal imbalances. Twenty-one genital tracts from Eringer cows suffering from fertility problems were collected in the abattoir. The purpose of the study was the macroscopic evaluation of the ovaries and the uterus followed by a histological and microbiological analysis of the uterus. Data from inseminations and calvings were provided by the Eringer breeding association and through the internet portal www.agate.ch. Median age of the cows was 6.9 years, number of calves per cow was 2.5 and median period between last calving and slaughter was 1.5 years. In 13 from 21 of the urogenital tracts examined, macroscopic abnormalities of the ovaries and/or histologic or microbiologic findings in the uterus could explain fertility-associated slaughter.Fruchtbarkeitsprobleme gelten als einer der Hauptabgangsgründe für Eringerkühe. Als Ursache kommen entzündliche und degenerative Veränderungen des Uterus oder hormonelle Störungen in Frage. Für die vorliegende Studie wurde der Genitaltrakt von insgesamt 21 Eringerkühen mit Fruchtbarkeitsproblemen im Schlachthof gesammelt. Ziel der Studie war die makroskopische Beurteilung von Ovarien und Uterus gefolgt von einer histologischen und bakteriologischen Untersuchung des Uterus. Die Besamungs- und Kalbedaten wurden uns vom Eringerzuchtverband zur Verfügung gestellt bzw. aus dem Internetportal www.agate.ch erhoben. Das durchschnittliche Alter der geschlachteten Eringerkühe betrug 6.9 Jahre, die Anzahl Kälber pro Kuh lag bei 2.5 und das durchschnittliche Zeitintervall zwischen der letzten Abkalbung und der Schlachtung betrug 1.5 Jahre. Bei 13 von 21 der untersuchten Genitalorgane konnten makroskopische Veränderungen an den Ovarien und/oder histologische Veränderungen am Uterus gefunden werden oder es wurden Bakterien aus dem Uterus isoliert, die einen fruchtbarkeitsbedingten Abgang erklären können
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