1,053 research outputs found
Operation and maintenance in the cooling and ventilation group
A core team of CERN staff is running the daily operations of the cooling and ventilation equipment at CERN, thus assuring multiple interfaces such as constant contact with the users of existing installations, the project leaders for new installations and intern-divisional communication. As support of this team, re-tendered contracts with external companies for the maintenance and operational tasks have been put into place multiple years ago. Higherlevel maintenance continues to be entrusted to the equipmentsâ constructor. The new taskand result-oriented contract E071/ST for maintenance and operation started on January 1st 2003 is briefly described. Tools for running the contract and responsibility limits on both sides of the contract are displayed. Training needs of personnel and knowledge transfer to maintain the mastering of the functioning of the machine park are briefly analyzed
Effects of Nacelle configuration/position on performance of subsonic transport
An experimental study was conducted to explore possible reductions in installed propulsion system drag due to underwing aft nacelle locations. Both circular (C) and D inlet cross section nacelles were tested. The primary objectives were: to determine the relative installed drag of the C and D nacelle installations; and, to compare the drag of each aft nacelle installation with that of a conventional underwing forward, drag of each aft nacelle installation with that of a conventional underwing forward, pylon mounted (UTW) nacelle installation. The tests were performed in the NASA-Langley Research Center 16-Foot Transonic Wind Tunnel at Mach numbers from 0.70 to 0.85, airplane angles of attack from -2.5 to 4.1 degrees, and Reynolds numbers per foot from 3.4 to 4.0 million. The nacelles were installed on the NASA USB full span transonic transport model with horizontal tail on. The D nacelle installation had the smallest drag of those tested. The UTW nacelle installation had the largest drag, at 6.8 percent larger than the D at Mach number 0.80 and lift coefficient (C sub L) 0.45. Each tested configuration still had some interference drag, however. The effect of the aft nacelles on airplane lift was to increase C sub L at a fixed angle of attack relative to the wing body. There was higher lift on the inboard wing sections because of higher pressures on the wing lower surface. The effects of the UTW installation on lift were opposite to those of the aft nacelles
Operation of the Four 12 kW at 4.5 K Refrigerators for LEP
In 1998 the first energy upgrade of the LEP Electron/Positron collider, LEP2, was completed at CERN. Sixty-eight superconducting modules supplied by four 12 kW @ 4.5 K equivalent power refrigerators have been operated allowing a colliding beam energy of 94.5 GeV. Meanwhile, the operation and maintenance responsibilities were transferred to an industrial firm on the basis of a result-oriented contract. After a short description of the operational organization, we report on the operation of the LEP2 cryogenic system over the past three years. Particular attention is given to power availability, failure statistics and recovery time after interruptions. The most relevant problems and their solutions are exposed. Finally, we review the interactions between the cryogenic system and the particle beams, which are limiting the ultimate performance of the LEP collider
Insecurity for compact surfaces of positive genus
A pair of points in a riemannian manifold is secure if the geodesics
between the points can be blocked by a finite number of point obstacles;
otherwise the pair of points is insecure. A manifold is secure if all pairs of
points in are secure. A manifold is insecure if there exists an insecure
point pair, and totally insecure if all point pairs are insecure.
Compact, flat manifolds are secure. A standing conjecture says that these are
the only secure, compact riemannian manifolds. We prove this for surfaces of
genus greater than zero. We also prove that a closed surface of genus greater
than one with any riemannian metric and a closed surface of genus one with
generic metric are totally insecure.Comment: 37 pages, 11 figure
Small-Angle X-ray and neutron scattering from diamond single crystals
Results of Small-Angle Scattering study of diamonds with various types of
point and extended defects and different degrees of annealing are presented. It
is shown that thermal annealing and/or mechanical deformation cause formation
of nanosized planar and threedimensional defects giving rise to Small-Angle
Scattering. The defects are often facetted by crystallographic planes 111, 100,
110, 311, 211 common for diamond. The scattering defects likely consist of
clusters of intrinsic and impurity-related defects; boundaries of mechanical
twins also contribute to the SAS signal. There is no clear correlation between
concentration of nitrogen impurity and intensity of the scattering.Comment: 6 pages, 5 figures; presented at SANS-YuMO User Meeting 2011, Dubna,
Russi
On the number of Mather measures of Lagrangian systems
In 1996, Ricardo Ricardo Ma\~n\'e discovered that Mather measures are in fact
the minimizers of a "universal" infinite dimensional linear programming
problem. This fundamental result has many applications, one of the most
important is to the estimates of the generic number of Mather measures.
Ma\~n\'e obtained the first estimation of that sort by using finite dimensional
approximations. Recently, we were able with Gonzalo Contreras to use this
method of finite dimensional approximation in order to solve a conjecture of
John Mather concerning the generic number of Mather measures for families of
Lagrangian systems. In the present paper we obtain finer results in that
direction by applying directly some classical tools of convex analysis to the
infinite dimensional problem. We use a notion of countably rectifiable sets of
finite codimension in Banach (and Frechet) spaces which may deserve independent
interest
The first year of the ST Operation Committee: is there a future ?
The main objective of the ST Operation Committee (STOC) was to develop a proactive and homogeneous service of operation that satisfies the needs of the service users. Furthermore, the role of the Technical Control Room (TCR) should have been developed to a unique and competent entry point for ST operation by bringing the operation teams closer together on a daily basis. Have these objectives been achieved and to what extend? Is there a future for this committee and what could it look like? What are the implications of the first year of work on ST operation as a whole? This paper answers these questions and gives recommendations how to make best use of the STOC for the ST partners and ST, respectively
The type numbers of closed geodesics
A short survey on the type numbers of closed geodesics, on applications of
the Morse theory to proving the existence of closed geodesics and on the recent
progress in applying variational methods to the periodic problem for Finsler
and magnetic geodesicsComment: 29 pages, an appendix to the Russian translation of "The calculus of
variations in the large" by M. Mors
Patient journey during and after a pre-eclampsia-complicated pregnancy:a cross-sectional patient registry study
OBJECTIVES: To gain insight into the patient journey through a pre-eclampsia-complicated pregnancy. DESIGN: Cross-sectional patient registry study. SETTING: Online patient registry initiated by the Preeclampsia Foundation. PARTICIPANTS: Women with a history of pre-eclampsia enrolled in The Preeclampsia Registry (TPR). PRIMARY AND SECONDARY OUTCOME MEASURES: Retrospective patient-reported experience measures concerning awareness of pre-eclampsia, timing and type of information on pre-eclampsia received, involvement in decision making regarding medical care, mental/emotional impact of the pre-eclampsia-complicated pregnancy and impact on future pregnancy planning. RESULTS: Of 3618 TPR-participants invited to complete the Patient Journey questionnaire, data from 833 (23%) responders were available for analysis. Most responders were white (n=795, 95.4%) and lived in the USA (n=728, 87.4%). Before their pre-eclampsia diagnosis, 599 (73.9%) responders were aware of the term âpre-eclampsiaâ, but only 348 (43.7%) were aware of its associated symptoms. Women with a lower level of education were less likely to have heard of pre-eclampsia (OR 0.36, 95%âCI 0.21 to 0.62). Around the time of diagnosis, 29.2% of responders did not feel involved in the decision making, which was associated with reporting a serious mental/emotional impact of the pre-eclampsia experience (OR 2.46, 95%âCI 1.58 to 3.84). Over time, there was an increase in the proportion of women who were aware of the symptoms of pre-eclampsia (32.2% before 2011 to 52.5% after 2016; p<0.001) and in the proportion of responders stating they received counselling about the later-life health risks associated with pre-eclampsia (14.2% before 2011 to 25.6% after 2016; p=0.005). CONCLUSIONS: This study demonstrates that improved patient education regarding pre-eclampsia is needed, that shared decision making is of great importance to patients to enhance their healthcare experience, and that healthcare providers should make efforts to routinely incorporate counselling about the later-life health risks associated with pre-eclampsia. TRIAL REGISTRATION NUMBER: NCT02020174
On recurrence and ergodicity for geodesic flows on noncompact periodic polygonal surfaces
We study the recurrence and ergodicity for the billiard on noncompact
polygonal surfaces with a free, cocompact action of or . In the
-periodic case, we establish criteria for recurrence. In the more difficult
-periodic case, we establish some general results. For a particular
family of -periodic polygonal surfaces, known in the physics literature
as the wind-tree model, assuming certain restrictions of geometric nature, we
obtain the ergodic decomposition of directional billiard dynamics for a dense,
countable set of directions. This is a consequence of our results on the
ergodicity of \ZZ-valued cocycles over irrational rotations.Comment: 48 pages, 12 figure
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