113 research outputs found
Application of a hygroscopicity tandem differential mobility analyzer for characterizing PMÂ emissions in exhaust plumes from an aircraft engine burning conventional and alternative fuels
In the last several decades, significant efforts have been directed toward
better understanding the gaseous and particulate matter (PM) emissions from
aircraft gas turbine engines. However, limited information is available on
the hygroscopic properties of aircraft engine PM emissions which play an
important role in the water absorption, airborne lifetime, obscuring effect,
and detrimental health effects of these particles. This paper reports the
description and detailed lab-based performance evaluation of a robust
hygroscopicity tandem differential
mobility analyzer (HTDMA) in terms of hygroscopic properties such as growth
factor (GF) and the hygroscopicity parameter (Îș). The HTDMA system was
subsequently deployed during the Alternative Aviation Fuel
EXperiment (AAFEX) II field campaign to measure the hygroscopic properties of
aircraft engine PMÂ emissions in the exhaust plumes from a CFM56-2C1 engine
burning several types of fuels. The fuels used were conventional JP-8,
tallow-based hydroprocessed esters and fatty acids (HEFA), FischerâTropsch,
a blend of HEFA and JP-8, and FischerâTropsch doped with tetrahydrothiophene
(an organosulfur compound). It was observed that GF and ÎșÂ increased
with fuel sulfur content and engine thrust condition, and decreased with
increasing dry particle diameter. The highest GF and ÎșÂ values were
found in the smallest particles, typically those with diameters of 10 nm.</p
Postoperative IOP prophylaxis practice following uncomplicated cataract surgery: a UK-wide consultant survey
BACKGROUND: In order to minimise postoperative intraocular pressure (IOP) rise, after routine uncomplicated cataract surgery, prophylaxis may be adopted. Currently, there are no specific guidelines in this regard resulting in wide variation in practice across the UK. We sought to document these variations through a questionnaire survey. METHODS: A questionnaire was sent to all consultant ophthalmic surgeons in the UK. RESULTS: 62.6% of surgeons did not use any IOP lowering agents. 37.4% surgeons routinely prescribed some form of medication. The majority (86.8%) used oral diamox. 20.6% of surgeons said they based their practice on evidence, 43.3% on personal experience, and 17.6% on unit policy. Surprisingly, among the two groups of surgeons (those who gave routine prophylaxis, and those who did not) the percentages of surgeons quoting personal experience, unit policy, or presence of evidence was strikingly similar. The timing of the first postoperative IOP check varied from the same day to beyond 2 weeks. Only 20.2% of surgeons had ever seen an adverse event related to IOP rise; this complication is thus very rare. CONCLUSION: This survey highlights a wide variation in the practice and postoperative management of phacoemulsification cataract surgery. What is very striking is that there is a similar proportion of surgeons in the diametrically opposite groups (those who give or do not give routine IOP lowering prophylaxis) who believe that there practice is evidence based. The merits of this study suggests that consideration must be given to drafting a uniform guideline in this area of practice
The Jahn-Teller Polaron in Comparison with the Holstein Polaron
Based on an exact expression for the self-energy of the Jahn-Teller polaron,
we find that symmetry of pseudospin rotation makes the vertex correction much
less effective than that for the Holstein polaron. This ineffectiveness brings
about a smaller effective mass m^* and a quantitatively differenent
large-to-small polaron crossover, as examined by exact diagonalization in a
two-site system. In the strong-coupling and antiadiabatic region, a rigorous
analytic expression is found for m^*
Theory of Spin-Resolved Auger-Electron Spectroscopy from Ferromagnetic 3d-Transition Metals
CVV Auger electron spectra are calculated for a multi-band Hubbard model
including correlations among the valence electrons as well as correlations
between core and valence electrons. The interest is focused on the
ferromagnetic 3d-transition metals. The Auger line shape is calculated from a
three-particle Green function. A realistic one-particle input is taken from
tight-binding band-structure calculations. Within a diagrammatic approach we
can distinguish between the \textit{direct} correlations among those electrons
participating in the Auger process and the \textit{indirect} correlations in
the rest system. The indirect correlations are treated within second-order
perturbation theory for the self-energy. The direct correlations are treated
using the valence-valence ladder approximation and the first-order perturbation
theory with respect to valence-valence and core-valence interactions. The
theory is evaluated numerically for ferromagnetic Ni. We discuss the
spin-resolved quasi-particle band structure and the Auger spectra and
investigate the influence of the core hole.Comment: LaTeX, 12 pages, 8 eps figures included, Phys. Rev. B (in press
Climate change curricula for adult audiences in agriculture and forestry: A review
Agricultural and forestry advisers and other technical service providers play an important role in supporting farmers and foresters to adapt to climate change. However, not all agricultural and forestry advisers are comfortable talking about climate change with land managers. While there is a demonstrated interest related to climate related professional development, few examples of curricula developed with the express purpose of serving this audience and a systematic review of these curricula has not been conducted. To address this gap, we reviewed 12 curricula which were developed and implemented between 2001 and 2017. The goal of this review is to apply the lessons learned from a range of climate change-focused curricula to new, regionally or sector-specific educational programs targeting both agricultural advisers and innovative farmers. Our findings suggest that developers of future educational programs consider the following: (a) the specific needs of their audience, including topical interests and learning needs; (b) the use of interdisciplinary teams for curricula development; (c) trade-offs associated with inclusivity and depth of course content; and (d) the advantages of project-based education approaches suited for adult learning audiences. By applying these concepts to future curricula, these curricula are likely to have the greatest level of impact
Alternative Aviation Fuel Experiment (AAFEX)
The rising cost of oil coupled with the need to reduce pollution and dependence on foreign suppliers has spurred great interest and activity in developing alternative aviation fuels. Although a variety of fuels have been produced that have similar properties to standard Jet A, detailed studies are required to ascertain the exact impacts of the fuels on engine operation and exhaust composition. In response to this need, NASA acquired and burned a variety of alternative aviation fuel mixtures in the Dryden Flight Research Center DC-8 to assess changes in the aircraft s CFM-56 engine performance and emission parameters relative to operation with standard JP-8. This Alternative Aviation Fuel Experiment, or AAFEX, was conducted at NASA Dryden s Aircraft Operations Facility (DAOF) in Palmdale, California, from January 19 to February 3, 2009 and specifically sought to establish fuel matrix effects on: 1) engine and exhaust gas temperatures and compressor speeds; 2) engine and auxiliary power unit (APU) gas phase and particle emissions and characteristics; and 3) volatile aerosol formation in aging exhaust plume
CLOUD: an atmospheric research facility at CERN
This report is the second of two addenda to the CLOUD proposal at CERN (physics/0104048), which aims to test experimentally the existence a link between cosmic rays and cloud formation, and to understand the microphysical mechanism. The document places CLOUD in the framework of a CERN facility for atmospheric research, and provides further details on the particle beam requirements
Addendum to the CLOUD proposal
This report is the first of two addenda to the CLOUD proposal at CERN (physics/0104048), which aims to test experimentally the existence a link between cosmic rays and cloud formation, and to understand the microphysical mechanism. The document provides further details on the detector design, scientific motivation and experimental programme
A study of the link between cosmic rays and clouds with a cloud chamber at the CERN PS
Recent satellite data have revealed a surprising correlation between galactic cosmic ray (GCR) intensity and the fraction of the Earth covered by clouds. If this correlation were to be established by a causal mechanism, it could provide a crucial step in understanding the long-sought mechanism connecting solar and climate variability. The Earth's climate seems to be remarkably sensitive to solar activity, but variations of the Sun's electromagnetic radiation appear to be too small to account for the observed climate variability. However, since the GCR intensity is strongly modulated by the solar wind, a GCR-cloud link may provide a sufficient amplifying mechanism. Moreover if this connection were to be confirmed, it could have profound consequences for our understanding of the solar contributions to the current global warming. The CLOUD (Cosmics Leaving OUtdoor Droplets) project proposes to test experimentally the existence a link between cosmic rays and cloud formation, and to understand the microphysical mechanism. CLOUD plans to perform detailed laboratory measurements in a particle beam at CERN, where all the parameters can be precisely controlled and measured. The beam will pass through an expansion cloud chamber and a reactor chamber where the atmosphere is to be duplicated by moist air charged with selected aerosols and trace condensable vapours. An array of external detectors and mass spectrometers is used to analyse the physical and chemical characteristics of the aerosols and trace gases during beam exposure. Where beam effects are found, the experiment will seek to evaluate their significance in the atmosphere by incorporating them into aerosol and cloud models.Recent satellite data have revealed a surprising correlation between galactic cosmic ray (GCR) intensity and the fraction of the Earth covered by clouds. If this correlation were to be established by a causal mechanism, it could provide a crucial step in understanding the long-sought mechanism connecting solar and climate variability. The Earth's climate seems to be remarkably sensitive to solar activity, but variations of the Sun's electromagnetic radiation appear to be too small to account for the observed climate variability. However, since the GCR intensity is strongly modulated by the solar wind, a GCR-cloud link may provide a sufficient amplifying mechanism. Moreover if this connection were to be confirmed, it could have profound consequences for our understanding of the solar contributions to the current global warming. The CLOUD (Cosmics Leaving OUtdoor Droplets) project proposes to test experimentally the existence a link between cosmic rays and cloud formation, and to understand the microphysical mechanism. CLOUD plans to perform detailed laboratory measurements in a particle beam at CERN, where all the parameters can be precisely controlled and measured. The beam will pass through an expansion cloud chamber and a reactor chamber where the atmosphere is to be duplicated by moist air charged with selected aerosols and trace condensable vapours. An array of external detectors and mass spectrometers is used to analyse the physical and chemical characteristics of the aerosols and trace gases during beam exposure. Where beam effects are found, the experiment will seek to evaluate their significance in the atmosphere by incorporating them into aerosol and cloud models
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