Electrodynamic behaviour of the LHC superconducting magnet string during a discharge

A string of three dipole magnets and one quadrupole magnet, representing a half cell of the future LHC collider, has been assembled and tested at CERN. In order to avoid high temperatures in the magnets and high voltages between coils and ground in case of a quench, a reliable magnet protection system is necessary. The magnets are by-passed by protection diodes which are located in the cold mass. In case of a quench most of the stored magnetic energy is dissipated in the resistive parts of the magnets. Many natural and heater provoked quenches have been performed during the two experimental runs of the string at 1.9 K. This paper describes the electrodynamic behaviour during a fast discharge (i.e. after a quench) of the magnet string configuration. A simulation program was developed to evaluate parameters which cannot be directly measured, such as the current sharing between magnets and diodes, as well as the dissipated energy. The simulation program gives also the possibility for worst-case calculations, for example non-uniform magnet quench characteristics and protection heater delays

Quench propagation tests on the LHC superconducting magnet string

The installation and testing of a series connection of superconducting magnets (three 10 m long dipoles and one 3 m long quadrupole) has been a necessary step in the verification of the viability of the Large Hadron Collider at CERN. In the LHC machine, if one of the lattice dipoles or quadrupoles quenches, the current will be by-passed through cold diodes and the whole magnet chain will be de-excited by opening dump switches. In such a scenario it is very important to know whether the quench propagates from the initially quenching magnet to adjacent ones. A series of experiments have been performed with the LHC Test String powered at different current levels and at different de-excitation rates in order to understand possible mechanisms for such a propagation, and the time delays involved. Results of the tests and implications regarding the LHC machine operation are described in this paper

Rapid Increases in the Steady-state Concentration of Reactive Oxygen Species in the Lungs and Heart After Particulate Air Pollution Inhalation.

In vitro studies suggest that reactive oxygen species contribute to the cardiopulmonary toxicity of particulate air pollution. To evaluate the ability of particulate air pollution to promote oxidative stress and tissue damage in vivo, we studied a rat model of short-term exposure to concentrated ambient particles (CAPs). We exposed adult Sprague-Dawley rats to either CAPs aerosols (group 1; average CAPs mass concentration, 300 +/- 60 micro g/m3) or filtered air (sham controls) for periods of 1-5 hr. Rats breathing CAPs aerosols for 5 hr showed significant oxidative stress, determined as in situ chemiluminescence in the lung [group 1, 41 +/- 4; sham, 24 +/- 1 counts per second (cps)/cm2] and heart (group 1, 45 +/- 4; sham, 24 +/- 2 cps/cm2) but not liver (group 1, 10 +/- 3; sham, 13 +/- 3 cps/cm2). Increases in oxidant levels were also triggered by highly toxic residual oil fly ash particles (lung chemiluminescence, 90 +/- 10 cps/cm2; heart chemiluminescence, 50 +/- 3 cps/cm2) but not by particle-free air or by inert carbon black aerosols (control particles). Increases in chemiluminescence showed strong associations with the CAPs content of iron, manganese, copper, and zinc in the lung and with Fe, aluminum, silicon, and titanium in the heart. The oxidant stress imposed by 5-hr exposure to CAPs was associated with slight but significant increases in the lung and heart water content (approximately 5% in both tissues, p < 0.05) and with increased serum levels of lactate dehydrogenase (approximately 80%), indicating mild damage to both tissues. Strikingly, CAPs inhalation also led to tissue-specific increases in the activities of the antioxidant enzymes superoxide dismutase and catalase, suggesting that episodes of increased particulate air pollution not only have potential for oxidant injurious effects but may also trigger adaptive responses

Bayesian Variable Selection Methods for Matched Case-Control Studies

Abstract Matched case-control designs are currently used in many biomedical applications. To ensure high efficiency and statistical power in identifying features that best discriminate cases from controls, it is important to account for the use of matched designs. However, in the setting of high dimensional data, few variable selection methods account for matching. Bayesian approaches to variable selection have several advantages, including the fact that such approaches visit a wider range of model subsets. In this paper, we propose a variable selection method to account for case-control matching in a Bayesian context and apply it using simulation studies, a matched brain imaging study conducted at Massachusetts General Hospital, and a matched cardiovascular biomarker study conducted by the High Risk Plaque Initiative

Chemical Characterization and Source Apportionment of Household Fine Particulate Matter in Rural, Peri-urban, and Urban West Africa

Household air pollution in sub-Saharan Africa and other developing regions is an important cause of disease burden. Little is known about the chemical composition and sources of household air pollution in sub-Saharan Africa, and how they differ between rural and urban homes. We analyzed the chemical composition and sources of fine particles (PM2.5) in household cooking areas of multiple neighborhoods in Accra, Ghana, and in peri-urban (Banjul) and rural (Basse) areas in The Gambia. In Accra, biomass burning accounted for 39–62% of total PM2.5 mass in the cooking area in different neighborhoods; the absolute contributions were 10–45 μg/m3. Road dust and vehicle emissions comprised 12–33% of PM2.5 mass. Solid waste burning was also a significant contributor to household PM2.5 in a low-income neighborhood but not for those living in better-off areas. In Banjul and Basse, biomass burning was the single dominant source of cooking-area PM2.5, accounting for 74–87% of its total mass; the relative and absolute contributions of biomass smoke to PM2.5 mass were larger in households that used firewood than in those using charcoal, reaching as high as 463 μg/m3 in Basse homes that used firewood for cooking. Our findings demonstrate the need for policies that enhance access to cleaner fuels in both rural and urban areas, and for controlling traffic emissions in cities in sub-Saharan Africa

Ovarian hyperstimulation syndrome and prophylactic human embryo cryopreservation: analysis of reproductive outcome following thawed embryo transfer

<p>Abstract</p> <p>Objective</p> <p>To review utilisation of elective embryo cryopreservation in the expectant management of patients at risk for developing ovarian hyperstimulation syndrome (OHSS), and report on reproductive outcome following transfer of thawed embryos.</p> <p>Materials and methods</p> <p>Medical records were reviewed for patients undergoing IVF from 2000–2008 to identify cases at risk for OHSS where cryopreservation was electively performed on all embryos at the 2 <it>pn </it>stage. Patient age, total number of oocytes retrieved, number of 2 pn embryos cryopreserved, interval between retrieval and thaw/transfer, number (and developmental stage) of embryos transferred (ET), and delivery rate after IVF were recorded for all patients.</p> <p>Results</p> <p>From a total of 2892 IVF cycles undertaken during the study period, 51 IVF cases (1.8%) were noted where follicle number exceeded 20 and pelvic fluid collection was present. Elective embryo freeze was performed as OHSS prophylaxis in each instance. Mean (± SD) age of these patients was 32 ± 3.8 yrs. Average number of oocytes retrieved in this group was 23 ± 8.7, which after fertilisation yielded an average of 14 ± 5.7 embryos cryopreserved per patient. Thaw and ET was performed an average of 115 ± 65 d (range 30–377 d) after oocyte retrieval with a mean of 2 ± 0.6 embryos transferred. Grow-out to blastocyst stage was achieved in 88.2% of cases. Delivery/livebirth rate was 33.3% per initiated cycle and 43.6% per transfer. Non-transferred blastocysts remained in cryostorage for 24 of 51 patients (46.1%) after ET, with an average of 3 ± 3 blastocysts refrozen per patient.</p> <p>Conclusion</p> <p>OHSS prophylaxis was used in 1.8% of IVF cycles at this institution; no serious OHSS complications were encountered during the study period. Management based on elective 2 <it>pn </it>embryo cryopreservation with subsequent thaw and grow-out to blastocyst stage for transfer did not appear to compromise embryo viability or overall reproductive outcome. For these patients, immediate elective embryo cryopreservation and delay of ET by as little as 30 d allowed for satisfactory conclusion of the IVF sequence, yielding a livebirth-delivery rate (per ET) >40%.</p