753 research outputs found
Constants of motion in stationary axisymmetric gravitational fields
This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of record Markakis, C. (2014). "Constants of motion in stationary axisymmetric gravitational fields." Monthly Notices of the Royal Astronomical Society 441(4): 2974-2985. is available online at: https://doi.org/10.1093/mnras/stu71513 pages, matches published versionThis work was supported in part by the Greek State Scholarships Foundation, by National Science Foundation Grant PHY1001515 and by German Research Foundation grant SFB/Transregio 7 ‘Gravitational Wave Astronomy
Air quality in the mid-21st century for the city of Paris under two climate scenarios; from the regional to local scale
Ozone and PM<sub>2.5</sub> concentrations over the city of Paris are modeled with
the CHIMERE air-quality model at 4 km × 4 km horizontal resolution for two
future emission scenarios. A high-resolution (1 km × 1 km) emission projection
until 2020 for the greater Paris region is developed by local experts
(AIRPARIF) and is further extended to year 2050 based on regional-scale
emission projections developed by the Global Energy Assessment. Model
evaluation is performed based on a 10-year control simulation. Ozone is in
very good agreement with measurements while PM<sub>2.5</sub> is underestimated by
20% over the urban area mainly due to a large wet bias in wintertime
precipitation. A significant increase of maximum ozone relative to present-day levels over Paris is modeled under the "business-as-usual" scenario
(+7 ppb) while a more optimistic "mitigation" scenario leads to a moderate
ozone decrease (−3.5 ppb) in year 2050. These results are substantially
different to previous regional-scale projections where 2050 ozone is found
to decrease under both future scenarios. A sensitivity analysis showed that
this difference is due to the fact that ozone formation over Paris at the
current urban-scale study is driven by volatile organic compound (VOC)-limited chemistry, whereas at
the regional-scale ozone formation occurs under NO<sub>x</sub>-sensitive
conditions. This explains why the sharp NO<sub>x</sub> reductions implemented in
the future scenarios have a different effect on ozone projections at
different scales. In rural areas, projections at both scales yield similar
results showing that the longer timescale processes of emission transport
and ozone formation are less sensitive to model resolution. PM<sub>2.5</sub> concentrations decrease by 78% and 89% under business-as-usual
and mitigation scenarios, respectively, compared to the present-day period.
The reduction is much more prominent over the urban part of the domain due
to the effective reductions of road transport and residential emissions
resulting in the smoothing of the large urban increment modeled in the
control simulation
Effects on surface atmospheric photo-oxidants over Greece during the total solar eclipse event of 29 March 2006
International audienceThis study investigates the effects of the total solar eclipse of 29 March 2006 on surface air-quality levels over Greece based on observations at a number of sites in conjunction with chemical box modelling and 3-D air-quality modelling. Emphasis is given on surface ozone and other photooxidants at four Greek sites Kastelorizo, Finokalia (Crete), Pallini (Athens) and Thessaloniki, which are located at gradually increasing distances from the path of the eclipse totality and are characterized by different air pollution levels. The eclipse offered the opportunity to test our understanding of air pollution build-up and the response of the gas-phase chemistry of photo-oxidants during a photolytical perturbation using both a photochemical box model and a regional air-quality offline model based on the modeling system WRF/CAMx. At the relatively unpolluted sites of Kastelorizo and Finokalia no clear impact of the solar eclipse on surface O3, NO2 and NO concentrations can be deduced from the observations and model simulations as the calculated changes in net ozone production rates between eclipse and non eclipse conditions are rather small compared to the ozone variability and hence the solar eclipse effects on ozone can be easily masked by transport. At the polluted sites of Thessaloniki and Pallini, the solar eclipse effects on O3, NO2 and NO concentrations are clearly revealed from both the measurements and 3-D air-quality modeling with the net effect being a decrease in O3 and NO and an increase in NO2 as NO2 formed from the reaction of O3 with NO while at the same time NO2 is not efficiently photolysed. It is evident from the 3-D air quality modeling over Greece that the maximum effects of the eclipse on O3, NO2 and NO are reflected at the large urban agglomerations of Athens, and Thessaloniki where the maximum of the emissions occur
Small-bowel necrosis complicating a cytomegalovirus-induced superior mesenteric vein thrombosis in an immunocompetent patient: a case report
<p>Abstract</p> <p>Introduction</p> <p>Superior mesenteric venous thrombosis as a result of acute cytomegalovirus infection is rare, with only a few cases reported in the literature.</p> <p>Case presentation</p> <p>We present the case of a 40-year-old Caucasian man who was admitted to our hospital with a 5-day history of fever. His serological test and pp65 antigen detection of cytomegalovirus were positive, suggesting acute infection. On the sixth day after his admission, the patient complained of acute, progressive abdominal pain. Abdominal computed tomography revealed acute superior mesenteric venous thrombosis. An emergency laparotomy showed diffuse edema and ischemic lesions of the small bowel and its associated mesentery with a 50-cm-long segmental infarction of the proximal jejunum. An extensive enterectomy of about 100 cm of jejunum that included the necrotic segment was performed, followed by an end-to-end anastomosis. Anti-coagulation therapy was administered pre-operatively in the form of small-fractionated heparin and continued postoperatively. The patient had an uneventful recovery and was discharged on the 11th postoperative day.</p> <p>Conclusion</p> <p>Acute cytomegalovirus infection can contribute to the occurrence of mesenteric venous thrombosis in immunocompetent patients. It is important for physicians and internists to be aware of the possible thrombotic complications of cytomegalovirus infection. A high level of clinical suspicion is essential to successfully treat a potentially lethal condition such as superior mesenteric venous thrombosis.</p
Conservation laws and evolution schemes in geodesic, hydrodynamic, and magnetohydrodynamic flows
Carter and Lichnerowicz have established that barotropic fluid flows are
conformally geodesic and obey Hamilton's principle. This variational approach
can accommodate neutral, or charged and poorly conducting, fluids. We show
that, unlike what has been previously thought, this approach can also
accommodate perfectly conducting magnetofluids, via the Bekenstein-Oron
description of ideal magnetohydrodynamics. When Noether symmetries associated
with Killing vectors or tensors are present in geodesic flows, they lead to
constants of motion polynomial in the momenta. We generalize these concepts to
hydrodynamic flows. Moreover, the Hamiltonian descriptions of ideal
magnetohydrodynamics allow one to cast the evolution equations into a
hyperbolic form useful for evolving rotating or binary compact objects with
magnetic fields in numerical general relativity. Conserved circulation laws,
such as those of Kelvin, Alfv\'en and Bekenstein-Oron, emerge simply as special
cases of the Poincar\'e-Cartan integral invariant of Hamiltonian systems. We
use this approach to obtain an extension of Kelvin's theorem to baroclinic
(non-isentropic) fluids, based on a temperature-dependent time parameter. We
further extend this result to perfectly or poorly conducting baroclinic
magnetoflows. Finally, in the barotropic case, such magnetoflows are shown to
also be geodesic, albeit in a Finsler (rather than Riemann) space.Comment: 23 page
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