Experimental and numerical cross-validation of flow in real porous media. Part 1: Experimental framework

International audienceIn this study, we present the design of a purpose-built test cell, capable of closely mimicking boundary conditions which can be routinely imposed in fluid flow simulators. The test cell permits conducting systematic studies on the influence of unresolved pore-scale wall-roughness and pore space morphology on the hydraulic conductivity: it is therefore an ideal instrument for the generation of validation datasets for the next generation numerical flow models

Thermal Design and Performance of the Electrical Distribution Feed Box of the LHC prototype cell

The Electrical Distribution Feed Box (DFBS) is a 4.5 K saturated liquid helium cryostat constructed for the Large Hadron Collider (LHC) Prototype Cell (String 2). The thermal design of the DFBS is presented, with emphasis on the modelling of the cooling of the current lead chimneys via the helium bath boil-off gas and on the design of the lambda plate. The expected performance is compared to measurements done during the first operation phase of the LHC prototype cell

Molecular typing of Clostridioides difficile from frozen stool samples to investigate cross-transmissions: A proof of concept.

Toxigenic Clostridioides difficile is responsible for up to one third of post antibiotic diarrhea and for more than 95% of pseudomembranous colitis. Nowadays, diagnosis relies on the documentation of the presence of the toxin in stools by specific antigenic or PCR tests. Stool cultures have been mostly abandoned, leading to the absence of isolates for further epidemiological analyses. Aliquots of stool samples, frozen for up to two years, were thawed and inoculated onto commercial C. difficile media. Eighteen stools were recovered from patients hospitalized in the pediatric ward where at that time a chain of transmission was suspected. Eleven stools were recovered from patients hospitalized in a medical ward over a three months period with no suspected transmission event. Up to 16 characteristic colonies were isolates per culture. PCR of toxins genes and molecular typing by Double Locus Sequence Typing (DLST) were performed on these colonies. Whole genome multi locus sequence typing (wgMLST) was performed on selected isolates. Among the 29 stool specimens, no growth was observed for four stools and only one colony grew for one stool. Except the latter, all 16 colonies of the 24 stools showed identical toxin genes profiles than the original stool. However, variant DLST genotypes was observed within 20% of investigated stools. The majority of variants were single locus variant due to an IN/DEL of the repeat in one of the two DLST locus. Despite this variation, results of molecular typing overrule the putative transmission chain in the pediatric ward and revealed undetected chains of transmission in the medical ward. These results were confirmed with wgMLST. The developed protocol allows prospective and retrospective molecular and genomic epidemiological investigation of C. difficile infections for infection control purpose

Core genome multilocus sequence typing of Clostridioides difficile to investigate transmission in the hospital setting.

Traditional epidemiological investigations of healthcare-associated Clostridioides difficile infection (HA-CDI) are often insufficient. This study aimed to evaluate a procedure that includes secondary isolation and genomic typing of single toxigenic colonies using core genome multilocus sequence typing (cgMLST) for the investigation of C. difficile transmission. We analyzed retrospectively all toxigenic C. difficile-positive stool samples stored at the Lausanne University Hospital over 6 consecutive months. All isolates were initially typed and classified using a modified double-locus sequence typing (DLST) method. Genome comparison of isolates with the same DLST and clustering were subsequently performed using cgMLST. The electronic administrative records of patients with CDI were investigated for spatiotemporal epidemiological links supporting hospital transmission. A comparative descriptive analysis between genomic and epidemiological data was then performed. From January to June 2021, 86 C. difficile isolates were recovered from thawed samples of 71 patients. Thirteen different DLST types were shared by > 1 patient, and 13 were observed in single patients. A genomic cluster was defined as a set of isolates from different patients with ≤ 3 locus differences, determined by cgMLST. Seven genomic clusters were identified, among which plausible epidemiological links were identified in only 4/7 clusters. Among clusters determined by cgMLST analysis, roughly 40% included unexplained HA-CDI acquisitions, which may be explained by unidentified epidemiological links, asymptomatic colonization, and/or shared common community reservoirs. The use of DLST, followed by whole genome sequencing analysis, is a promising and cost-effective stepwise approach for the investigation of CDI transmission in the hospital setting

Cryogenic and vacuum sectorisation of the LHC arcs

Following the recommendation of the LHC TC of June 20th, 1995 to introduce a separate cryogenic distribution line (QRL), which opened the possibility to have a finer cryogenic and vacuum sectorisation of the LHC machine than the original 8 arcs scheme, a working group was set up to study the implications: technical feasibility, advantages and drawbacks as well as cost of such a sectorisation (DG/DI/LE/dl, 26 July 1995). This report presents the conclusions of the Working Group. In the LHC Conceptual Design Report, ref. CERN/AC/95-05 (LHC), 20 October 1995, the so-called "Yellow Book", a complete cryostat arc (~ 2.9 km) would have to be warmed up in order to replace a defective cryomagnet. Even by coupling the two large refrigerators feeding adjacent arcs at even points to speed up the warm-up and cool down of one arc, the minimum down-time of the machine needed to replace a cryomagnet would be more than a full month (and even 52 days with only one cryoplant). Cryogenic and vacuum sectorisation of an arc into smaller sectors is technically feasible and would allow to reduce the down-times considerably (by one to three weeks with four sectors of 750 m in length, with respectively two or one cryoplants). In addition, sectorisation of the arcs may permit a more flexible quality control and commissioning of the main machine systems, including cold testing of small magnet strings. Sectorisation, described in detail in the following paragraphs, consists essentially of installing several additional cryogenic and vacuum valves as well as some insulation vacuum barriers. Additional cryogenic valves are needed in the return lines of the circuits feeding each half-cell in order to complete the isolation of the cryoline QRL from the machine, allowing intervention (i.e. venting to atmospheric pressure) on machine sectors without affecting the rest of an arc. Secondly, and for the same purpose, special vacuum and cryogenic valves must be installed, at the boundaries of machine sectors, for the circuits not passing through the cryoline QRL. Finally, some additional vacuum barriers must be installed around the magnet cold masses to divide the insulation vacuum of the magnet cryostats into independent sub-sectors, permitting to keep under insulating vacuum the cryogenically floating cold masses, while a sector (or part of it) is warmed up and opened to atmosphere. A reasonable scenario of sectorisation, namely with four 650-750 m long sectors per arc, and each consisting of 3 or 4 insulation vacuum sub-sectors with two to four half-cells, would represent an additional total cost of about 6.6 MCHF for the machine. It is estimated that this capital investment would be paid off by time savings in less than three long unscheduled interventions such as the change of a cryomagnet

Update of the LHC Arc Cryostat Systems Layouts and Integration

Since the LHC Conceptual Design report's publication in October 1995 [1], and subsequent evolutions [2], the LHC Arc Cryostat System has undergone recently a number of significant changes, dictated by the natural evolution of the project. Most noteworthy are the recent decisions to route the large number of auxiliary circuits feeding the arc corrector magnets in a separate tube placed inside the cryostat with connections to the magnets every half-cell. Further decisions concern simplification of the baseline vacuum and cryogenic sectorization, the finalization of the design of the arc cryogenic modules and the layout of the arc electrical distribution feedboxes. The most recent features of the highly intricate cryogenics, magnetic, vacuum and electrical distribution systems of the LHC are presente