Almost 15 years have passed since the initial demonstrations of terahertz (THz) wireless communications were made using both pulsed and continuous waves. THz technologies are attracting great ...interest and are expected to meet the ever-increasing demand for high-capacity wireless communications. Here, we review the latest trends in THz communications research, focusing on how photonics technologies have played a key role in the development of first-age THz communication systems. We also provide a comparison with other competitive technologies, such as THz transceivers enabled by electronic devices as well as free-space lightwave communications.
Contexte : La viticulture est très exigeante en intrants. La viticulture biologique est souvent considérée comme un système durable, mais elle a des impacts environnementaux. L'analyse du cycle de ...vie (ACV) permet de discriminer les itinéraires viticoles. Objectif : Notre article présente et discute l'intérêt de l'ACV pour évaluer, comparer et améliorer les itinéraires viticoles biologiques par une comparaison (i) des inventaires des pratiques, (ii) des inventaires du cycle de vie (ICV) et (iii) des ACV. Matériel et méthodes : Huit cas ont été étudiés dans trois régions viticoles françaises et deux années. L'ICV et l'ACV ont été calculés, cinq impacts ont été sélectionnés par corrélations (changement climatique, eutrophisation de l'eau douce, écotoxicité terrestre, acidification terrestre, eutrophisation marine). Résultats et discussion : des différences importantes entre les cas pour les pratiques et les quantités d'intrants ont été observées et l'étude des impacts sur le changement climatique a révélé la hiérarchie d'importance des opérations notamment mécaniques et un classement différent pour des impacts au kg de raisin et à l'ha de vigne. Les défis de l'ACV sont de mieux prendre en compte le soufre et le cuivre ; enrichir les bases de données sur les engrais organiques ; et construire des indicateurs de biodiversité. Conclusion : L'ACV est meilleure que les inventaires des pratiques pour évaluer la viticulture biologique. Mots-clés : évaluation environnementale, viticulture durable, conduite de la vigne, cuivre, carburant, fertilisation.
Background: Viticulture is very demanding in inputs. Organic viticulture is often seen as a sustainable system but has also environmental impacts. Life cycle assessment (LCA) is able to discriminate vineyard managements. Aims: Our study explores the interest of LCA to assess, compare and improve organic vineyard management routes through a comparison of information given by practices inventories, Life Cycle Inventories (LCIs) and LCA. LCA methodological challenges are also discussed. Material and methods: Eight cases were studied in three French wine regions and two years. LCI and Life Cycle Impact Assessments (LCIAs) were calculated, five impacts were selected by correlation (climate change, fresh water eutrophication, terrestrial ecotoxicity, terrestrial acidification, marine eutrophication). Results and discussion: Practices and quantity of inputs were contrasted among the cases. The study of impacts on climate change revealed the hierarchy of importance of operations and a different ranking of cases for the functional units Ha and Kg. The LCIAs showed major differences between cases for some impacts and their drivers. LCIA and LCI permitted to account for the life cycle dimension of the impacts and for the toxicity and persistence of pesticides. The challenges of organic vineyard LCA are to (i) better consider sulphur and copper, (ii) enrich databases on organic fertilizer, and (iii) build an LCA indicator of biodiversity impact. Conclusion: LCA is better than practices inventories and LCI to assess organic viticulture.
Keywords:
environmental assessment, sustainable viticulture, vineyard management, copper, fuel, fertilisation.
Abstract In vertebral compression fractures, the potential of kyphoplasty for restoring vertebral height is limited by the loss of restored height that occurs when the balloon is deflated and ...removed. SpineJack® is also inserted percutaneously but is then left within the vertebral body after its expansion to reduce the fracture, thus avoiding loss of correction before the injection of cement. SpineJack® was used in 77 patients to treat 83 recent VCFs (55.4% at L1–L2) due to trauma (59.7%) or osteoporosis (40.3%). Three (3.9%) complications were recorded, but none was related to SpineJack® : there was one case each of symptomatic cement leakage along a secondary pedicular fracture line; infection; and incipient device migration at the beginning of the learning curve. The rate of adjacent fractures was only 2.6%. The 5-year outcomes demonstrate that SpineJack® provides both immediate and long-term benefits in terms of pain relief, functional recovery, and maintenance of vertebral height restoration. Level of evidence IV, retrospective study.
Context. Over the past 40 years, helioseismology has been enormously successful in the study of the solar interior. A shortcoming has been the lack of a convincing detection of the solar g modes, ...which are oscillations driven by gravity and are hidden in the deepest part of the solar body – its hydrogen-burning core. The detection of g modes is expected to dramatically improve our ability to model this core, the rotational characteristics of which have, until now, remained unknown. Aims. We present the identification of very low frequency g modes in the asymptotic regime and two important parameters that have long been waited for: the core rotation rate, and the asymptotic equidistant period spacing of these g modes. Methods. The GOLF instrument on board the SOHO space observatory has provided two decades of full-disk helioseismic data. The search for g modes in GOLF measurements has been extremely difficult because of solar and instrumental noise. In the present study, the p modes of the GOLF signal are analyzed differently: we search for possible collective frequency modulations that are produced by periodic changes in the deep solar structure. Such modulations provide access to only very low frequency g modes, thus allowing statistical methods to take advantage of their asymptotic properties. Results. For oscillatory periods in the range between 9 and nearly 48 h, almost 100 g modes of spherical harmonic degree 1 and more than 100 g modes of degree 2 are predicted. They are not observed individually, but when combined, they unambiguously provide their asymptotic period equidistance and rotational splittings, in excellent agreement with the requirements of the asymptotic approximations. When the period equidistance has been measured, all of the individual frequencies of each mode can be determined. Previously, p-mode helioseismology allowed the g-mode period equidistance parameter P0 to be bracketed inside a narrow range, between approximately 34 and 35 min. Here, P0 is measured to be 34 min 01 s, with a 1 s uncertainty. The previously unknown g-mode splittings have now been measured from a non-synodic reference with very high accuracy, and they imply a mean weighted rotation of 1277 ± 10 nHz (9-day period) of their kernels, resulting in a rapid rotation frequency of 1644 ± 23 nHz (period of one week) of the solar core itself, which is a factor 3.8 ± 0.1 faster than the rotation of the radiative envelope. Conclusions. The g modes are known to be the keys to a better understanding of the structure and dynamics of the solar core. Their detection with these precise parameters will certainly stimulate a new era of research in this field.
Sudden unexpected death in epilepsy (SUDEP) is the leading epilepsy-related cause of premature mortality in people with intractable epilepsy, who are 27 times more likely to die than the general ...population. Impairment of the central control of breathing following a seizure has been identified as a putative cause of death, but the mechanisms underlying this seizure-induced breathing failure are largely unknown. Our laboratory has advanced a vascular theory of postictal behavioural dysfunction, including SUDEP. We have recently reported that seizure-induced death occurs after seizures invade brainstem breathing centres which then leads to local hypoxia causing breathing failure and death. Here we investigated the effects of caffeine and two adenosine receptors in two models of seizure-induced death. We recorded local oxygen levels in brainstem breathing centres as well as time to cessation of breathing and cardiac activity relative to seizure activity. The administration of the non-selective A1/A2A antagonist caffeine or the selective A1 agonist N6-cyclopentyladenosine reveals a detrimental effect on postictal hypoxia, providing support for caffeine modulating cerebral vasculature leading to brainstem hypoxia and cessation of breathing. Conversely, A2A activation with CGS-21680 was found to increase the lifespan of mice in both our models of seizure-induced death.
This paper describes the advantages that the introduction of photonic integration technologies can bring to the development of photonic-enabled wireless communications systems operating in the ...millimeter wave frequency range. We present two approaches for the development of dual wavelength sources for heterodyne-based millimeter wave generation realized using active/passive photonic integration technology. One approach integrates monolithically two distributed feedback semiconductor lasers along with semiconductor optical amplifiers, wavelength combiners, electro-optic modulators and broad bandwidth photodiodes. The other uses a generic photonic integration platform, developing narrow linewidth dual wavelength lasers based on arrayed waveguide gratings. Moreover, data transmission over a wireless link at a carrier wave frequency above 100 GHz is presented, in which the two lasers are free-running, and the modulation is directly applied to the single photonic chip without the requirement of any additional component.
EBSD measurements performed on polycrystalline UO2 samples were analyzed to obtain the linear fraction distribution of grain boundaries as a function of their Coincidence Site Lattice (CSL) indexes. ...In parallel, molecular dynamics simulations of 26 CSL grain boundaries were performed to calculate their formation energies using four different empirical potentials. Comparing calculated formation energies and measured linear fractions allowed us to select the best suited empirical potential for the study of grain boundaries and to evidence a decrease in the formation energy of a given grain boundary when its length fraction increases. Cleavage energies were calculated using the selected potential and the toughness of a grain boundary was estimated, since this property corresponds to the energy needed to open it. An interesting relation is observed: the cleavage energy seems to decrease when the misorientation angle of the boundary increases. Finally, a first step towards the study of non-CSL (i.e. general) grain boundaries was taken by simulating three semi-general grain boundaries built by sticking two halves of CSL boundaries.
TeraHertz Photonics for Wireless Communications Seeds, Alwyn J.; Shams, Haymen; Fice, Martyn J. ...
Journal of lightwave technology,
2015-Feb.1,-1, 2015-2-1, Letnik:
33, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Optical fibre transmission has enabled greatly increased transmission rates with 10 Gb/s common in local area networks. End users find wireless access highly convenient for mobile communication. ...However, limited spectrum availability at microwave frequencies results in per-user transmission rates limited to much lower values, e.g., 500 Mb/s for 5-GHz band IEEE 802.11ac. Extending the high data-rate capacity of optical fiber transmission to wireless devices requires greatly increased carrier frequencies. This paper will describe how photonic techniques can enable ultrahigh capacity wireless data distribution and transmission using signals at millimeter-wave and TeraHertz (THz) frequencies.
Abstract
We present a generalized differential image motion monitor (GDIMM). It is a compact instrument dedicated to the measurement of four parameters of optical turbulence: seeing, isoplanatic ...angle, coherence time and wavefront coherence outer scale. The GDIMM is based on a small telescope (28 cm diameter) equipped with a three-hole mask at its entrance pupil. The instrument is fully automatic, and performs continuous monitoring of turbulence parameters at the Calern Observatory (France). This paper gives a description of the instrument, data processing and error budget. We also present statistics of three and a half years of monitoring of turbulence parameters above the Calern Observatory.
ABSTRACT
The forecast for atmospheric and turbulence conditions above astronomical observatories is of interest to the astronomical community because it allows observations to be planned with maximum ...efficiency, a process called flexible scheduling. It can also be used to simulate long-term site testing to provide local information useful for the conception of focal and post-focal instrumentation. We have presented our forecasting tool in previous publications, but in this paper we focus on the importance of using local measurements to improve the predictive turbulence model and to better consider the local specificities of a given site, a process we call site learning. For this study, we use a local data base provided by the Calern Atmospheric Turbulence Station, which has been operational since 2015 at Calern Observatory. In addition, we use a set of several months of predictions to feed the turbulence model, taking into account daytime and nighttime conditions. This upgrade improves the quality of our forecasting by reducing the absolute bias between measurements and predictions from 25 to 50 per cent for each layer of the $C_n^2$, by 25 per cent for the seeing, and by 70 per cent for the isoplanatic angle.
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