Specification of Four New Large 4.5 K Helium Refrigerators for the LHC

The cooling capacity for the superconducting magnets in the Large Hadron Collider (LHC) at the European Laboratory for Particle Physics, CERN will be provided by eight helium refrigerators serving the eight 3.3 km long machine sectors. Of these eight refrigerators, four are already existing and are currently used for the Large Electron Positron Collider (LEP) project. These existing refrigerators have to be modified to serve the requirements for the LHC. Four new refrigerators providing cooling capacity down to 4.5 K will be added. All eight 4.5 K refrigerators will be completed by 1.8 K cooling stages. This presentation recalls the cryogenic architecture of the LHC, the constraints in process design resulting from it and from the desired capacity for steady state and transient operation. It then describes how these requirements were expressed in the technical specification for the four new 4.5 K refrigerators to be delivered between the years 2000 and 2002

Economics of Large Helium Cryogenic Systems: experience from Recent Projects at CERN

Large projects based on applied superconductivity, such as particle accelerators, tokamaks or SMES, require powerful and complex helium cryogenic systems, the cost of which represents a significant, if not dominant fraction of the total capital and operational expenditure. It is therefore important to establish guidelines and scaling laws for costing such systems, based on synthetic estimators of their size and performance. Although such data has already been published for many years, the experience recently gathered at CERN with the LEP and LHC projects, which have de facto turned the laboratory into a major world cryogenic center, can be exploited to update this information and broaden the range of application of the scaling laws. We report on the economics of 4.5 K and 1.8 K refrigeration, cryogen distribution and storage systems, and indicate paths towards their cost-to-performance optimisation

A new airborne Polar Nephelometer for the measurement of optical and microphysical cloud properties. Part II: Preliminary tests

International audienceA new optical sensor, the airborne Polar Nephelometer, has been tested in an open wind tunnel. The wind tunnel was operated in cloudy conditions including either cloud water droplets or ice crystals, or a mixture of these particles. The sensor is designed to measure the optical and microphysical parameters of cloud particles sized from a few micrometers to about 500 µm diameter. Basically, the probe measures the scattering phase function of an ensemble of cloud particles which intersect a collimated laser beam near the focal point of a paraboloidal mirror. From the measured scattering phase function the retrieval of the droplet-size spectra and subsequent derived quantities such as liquid water content and size parameters can be calculated using an inversion method. The particle phase discrimination (water droplets/ice particles) can be derived from the shape of the scattering phase function and the sensitivity of the probe allows the detection of small ice crystals (typically of 5 µm diameter). The paper describes the preliminary results obtained by the prototype version of the Polar Nephelometer in various cloudy conditions. These results are compared with direct microphysical measurements obtained by usual PMS probes also mounted in the wind tunnel. Complementary results obtained in a cold chamber are presented in order to illustrate the reliability of the Polar Nephelometer in the presence of small ice crystals

Prospectively reinstated memory drives conscious access of matching visual input

Item does not contain fulltextMaintaining information in visual working memory (VWM) biases attentional selection of concurrent visual input, by favoring VWM-matching over VWM-mismatching visual input. Recently, it was shown that this bias disappears when the same item is memorized on consecutive occasions (as memoranda presumably transit from VWM to long-term memory), but reemerges when observers anticipate to memorize a novel item on a subsequent trial. Here, we aimed to conceptually replicate and extend this intriguing finding, by investigating whether prospectively reinstated memory drives conscious access of memory-matching visual input. We measured the time it took for participants to detect interocularly suppressed target stimuli, which were either from the same color category as a concurrently memorized color or not. Our results showed that the advantage of memory-matching targets in overcoming suppression progresses non-monotonically across consecutive memorizations of the same color ('repetitions'): the advantage for memory-matching visual input initially declined to asymptote, before being fully revived on the last repetition. This revival was not observed in a control experiment in which targets were not interocularly suppressed. The results suggest that, as observers anticipate to memorize a novel item imminently, VWM usage is prospectively reinstated, causing memory-matching visual input to gain accelerated access to consciousness again.12 p

Specification of Eight 2400 W @ 1.8 K Refrigeration Units for the LHC

The cooling capacity below 2 K for the superconducting magnets in the Large Hadron Collider (LHC), at CERN, will be provided by eight refrigeration units at 1.8 K, each of them coupled to a 4.5 K refrigerator. Taking into account the cryogenic architecture of the LHC and corresponding process design constraints, a reference solution based on a combination of cold centrifugal and warm volumetric compressors was established in 1997. The process and technical requirements expressed in the specification issued in 1998 and the procurement scenario based on pre-series acceptance prior to final series delivery between 2002 and 2004 are presented in this paper

Aspects Thérapeutiques du Décollement de la Rétine chez les Évacués Sanitaires de Horns, Bénin, de 2015 à 2020

L’objectif de cette étude est de décrire les aspects thérapeutiques du décollement de la rétine chez les évacués sanitaires hors Bénin de 2015 à 2020. Nous avons réalisé une étude observationnelle transversale descriptive à visée analytique avec collecte rétrospective des données. Elle s’est déroulée à la Direction Générale de la Médecine Hospitalière et des Explorations Diagnostiques et dans des centres d’Ophtalmologie publics et privés. La durée moyenne entre le diagnostic et la chirurgie était de 81,67 ±23,05 jours avec des extrêmes de 2 et 400 jours.  Une chirurgie de DR par voie endoculaire était réalisée sur 28 yeux (60,87%). Notons que des 28 yeux ayant subi une chirurgie endoculaire, 19 ont eu un tamponnement par huile de silicone et les 9 restants, un tamponnement par gaz. Sur les 46 yeux, 25 (54,35%) présentaient des complications postopératoires dont 15 cataractes et 9 récidives du DR. En préopératoire, 28 yeux sur 46 (60,87%) avaient une AV<1/20 et 5 yeux (10,87%) avaient une AV>3/10. En postopératoire, 34 yeux (73,91%) avaient une AV≥1/20 dont 32 (69,57%) une AV >1/20 et 17 (36,96%) une AV>3/10. L’AV était réduite pour 7 yeux (15,22%), stationnaire pour 10 yeux (21,74%) et 29 yeux (63,04%) ont eu un gain d’AV. En préopératoire, 6 yeux (13,04%) avaient une AV<1/20 et 2 yeux (4,35%) avaient une AV>3/10. En postopératoire, 4 yeux (8,70%) avaient une AV<1/20 et 4 yeux (8,70%) avaient une AV>3/10. Chez les 2 sujets opérés dans un délai ≤ 7 jrs (4,35%), l'AV était améliorée et le gain supérieur à 6 lignes. Le décollement de la rétine est une pathologie oculaire grave pouvant causer la cécité. Toutefois, de bonnes pratiques thérapeutiques donnent généralement un bon gain visuel.   The objective of this study is to describe the therapeutic aspects of retinal detachment in medical evacuees outside Benin from 2015 to 2020. We conducted an observational cross-sectional descriptive study with an analytical purpose and retrospective data collection. The study took place at the General Directorate of Hospital Medicine and Diagnostic Explorations and in public and private Ophthalmology centers. The average duration between diagnosis and surgery was 81.67 ± 23.05 days, ranging from 2 to 400 days. Endocular surgery for retinal detachment was performed on 28 eyes (60.87%). Of these 28 eyes undergoing endocular surgery, 19 had tamponade with silicone oil, and the remaining 9 had tamponade with gas. Among the 46 eyes, 25 (54.35%) had postoperative complications, including 15 cataracts and 9 retinal detachment recurrences. Preoperatively, 28 eyes out of 46 (60.87%) had visual acuity (VA) <1/20, and 5 eyes (10.87%) had VA >3/10. Postoperatively, 34 eyes (73.91%) had VA ≥1/20, with 32 (69.57%) having VA >1/20 and 17 (36.96%) having VA >3/10. VA was reduced for 7 eyes (15.22%), remained stationary for 10 eyes (21.74%), and 29 eyes (63.04%) showed a gain in VA. Preoperatively, 6 eyes (13.04%) had VA <1/20, and 2 eyes (4.35%) had VA >3/10. Postoperatively, 4 eyes (8.70%) had VA <1/20, and 4 eyes (8.70%) had VA >3/10. Among the 2 subjects operated within ≤ 7 days (4.35%), VA improved, and the gain was greater than 6 lines. Retinal detachment is a serious ocular condition that can lead to blindness. However, proper therapeutic practices generally result in significant visual improvement