Magnetic Flux Braiding: Force-Free Equilibria and Current Sheets

We use a numerical nonlinear multigrid magnetic relaxation technique to investigate the generation of current sheets in three-dimensional magnetic flux braiding experiments. We are able to catalogue the relaxed nonlinear force-free equilibria resulting from the application of deformations to an initially undisturbed region of plasma containing a uniform, vertical magnetic field. The deformations are manifested by imposing motions on the bounding planes to which the magnetic field is anchored. Once imposed the new distribution of magnetic footpoints are then taken to be fixed, so that the rest of the plasma must then relax to a new equilibrium configuration. For the class of footpoint motions we have examined, we find that singular and nonsingular equilibria can be generated. By singular we mean that within the limits imposed by numerical resolution we find that there is no convergence to a well-defined equilibrium as the number of grid points in the numerical domain is increased. These singular equilibria contain current "sheets" of ever-increasing current intensity and decreasing width; they occur when the footpoint motions exceed a certain threshold, and must include both twist and shear to be effective. On the basis of these results we contend that flux braiding will indeed result in significant current generation. We discuss the implications of our results for coronal heating.Comment: 13 pages, 12 figure

The LWA1 Radio Telescope

LWA1 is a new radio telescope operating in the frequency range 10-88 MHz, located in central New Mexico. The telescope consists of 258 pairs of dipole-type antennas whose outputs are individually digitized and formed into beams. Simultaneously, signals from all dipoles can be recorded using one of the instrument's "all dipoles" modes, facilitating all-sky imaging. Notable features of the instrument include high intrinsic sensitivity (about 6 kJy zenith system equivalent flux density), large instantaneous bandwidth (up to 78 MHz), and 4 independently-steerable beams utilizing digital "true time delay" beamforming. This paper summarizes the design of LWA1 and its performance as determined in commissioning experiments. We describe the method currently in use for array calibration, and report on measurements of sensitivity and beamwidth.Comment: 9 pages, 14 figures, accepted by IEEE Trans. Antennas & Propagation. Various minor changes from previous versio

Seasonal dependence of peroxy radical concentrations at a Northern hemisphere marine boundary layer site during summer and winter: evidence for radical activity in winter

Peroxy radicals (HO2+Σ RO2) were measured at the Weybourne Atmospheric Observatory (52° N, 1° E), Norfolk using a PEroxy Radical Chemical Amplifier (PERCA) during the winter and summer of 2002. The peroxy radical diurnal cycles showed a marked difference between the winter and summer campaigns with maximum concentrations of 12 pptv at midday in the summer and maximum concentrations as high as 30 pptv (10 min averages) in winter at night. The corresponding nighttime peroxy radical concentrations were not as high in summer (3 pptv). The peroxy radical concentration shows a distinct anti-correlation with increasing NOx during the daylight hours. At night, peroxy radicals increase with increasing NOx indicative of the role of NO3 chemistry. The average diurnal cycles for net ozone production, N(O3) show a large variability in ozone production, P(O3), and a large ozone loss, L(O3) in summer relative to winter. For a daylight average, net ozone production in summer was higher than winter (1.51±0.5 ppbv h−1 and 1.11±0.47 ppbv h−1, respectively). The variability in NO concentration has a much larger effect on N(O3) than the peroxy radical concentrations. Photostationary state (PSS) calculations show an NO2 lifetime of 5 min in summer and 21 minutes in the winter, implying that steady-state NO-NO2 ratios are not always attained during the winter months. The results show an active peroxy radical chemistry at night and that significant oxidant levels are sustained in winter. The net effect of this with respect to production of ozone in winter is unclear owing to the breakdown in the photostationary state

Azumaya Objects in Triangulated Bicategories

We introduce the notion of Azumaya object in general homotopy-theoretic settings. We give a self-contained account of Azumaya objects and Brauer groups in bicategorical contexts, generalizing the Brauer group of a commutative ring. We go on to describe triangulated bicategories and prove a characterization theorem for Azumaya objects therein. This theory applies to give a homotopical Brauer group for derived categories of rings and ring spectra. We show that the homotopical Brauer group of an Eilenberg-Mac Lane spectrum is isomorphic to the homotopical Brauer group of its underlying commutative ring. We also discuss tilting theory as an application of invertibility in triangulated bicategories.Comment: 23 pages; final version; to appear in Journal of Homotopy and Related Structure

Clinically-indicated replacement versus routine replacement of peripheral venous catheters

Background US Centers for Disease Control guidelines recommend replacement of peripheral intravenous catheters (PIVC) no more frequently than every 72 to 96 hours. Routine replacement is thought to reduce the risk of phlebitis and bloodstream infection. Catheter insertion is an unpleasant experience for patients and replacement may be unnecessary if the catheter remains functional and there are no signs of inflammation or infection. Costs associated with routine replacement may be considerable. This is the third update of a review first published in 2010. Objectives To assess the effects of removing peripheral intravenous catheters when clinically indicated compared with removing and re-siting the catheter routinely. Search methods The Cochrane Vascular Information Specialist searched the Cochrane Vascular Specialised Register, CENTRAL, MEDLINE, Embase and CINAHL and World Health Organization International Clinical Trials Registry Platform and ClinicalTrials.gov trials registers to 18 April 2018. We also undertook reference checking, and contacted researchers and manufacturers to identify additional studies. Selection criteria We included randomised controlled trials that compared routine removal of PIVC with removal only when clinically indicated, in hospitalised or community-dwelling patients receiving continuous or intermittent infusions. Data collection and analysis Three review authors independently reviewed trials for inclusion, extracted data, and assessed risk of bias using Cochrane methods.We used GRADE to assess the overall evidence certainty. Main results This update contains two new trials, taking the total to nine included studies with 7412 participants. Eight trials were conducted in acute hospitals and one in a community setting. We rated the overall certainty of evidence as moderate for most outcomes, due to serious risk of bias for unblinded outcome assessment or imprecision, or both. Because outcome assessment was unblinded in all of the trials, none met our criteria for high methodological quality. Primary outcomes Seven trials (7323 participants), assessed catheter related bloodstream infection (CRBSI). There is no clear difference in the incidence of CRBSI between the clinically indicated (1/3590) and routine change (2/3733) groups (risk ratio (RR) 0.61, 95% confidence interval (CI) 0.08 to 4.68), low-certainty evidence (downgraded twice for serious imprecision). All trials reported incidence of thrombophlebitis and we combined the results fromseven of these in the analysis (7323 participants).We excluded two studies in the meta-analysis because they contributed to high heterogeneity. There is no clear difference in the incidence of thrombophlebitis whether catheters were changed according to clinical indication or routinely (RR 1.07, 95% CI 0.93 to 1.25; clinically indicated 317/3590; 3-day change 307/3733, moderate certainty evidence, downgraded once for serious risk of bias). The result was unaffected by whether the infusion was continuous or intermittent. Six trials provided thrombophlebitis rates by number of device days (32,709 device days). There is no clear difference between groups (RR 0.90, 95% CI 0.76 to 1.08; clinically indicated 248/17,251; 3-day change 236/15,458; moderate-certainty evidence, downgraded once for serious risk of bias). One trial (3283 participants), assessed all-cause blood stream infection (BSI). We found no clear difference in the all-cause BSI rate between the two groups (RR 0.47, 95% CI 0.15 to 1.53; clinically indicated: 4/1593 (0.02%); routine change 9/1690 (0.05%); moderate certainty evidence, downgraded one level for serious imprecision). Three trials (4244 participants), investigated costs; clinically indicated removal probably reduces device-related costs by approximately AUD 7.00 compared with routine removal (MD −6.96, 95% CI −9.05 to −4.86; moderate-certainty evidence, downgraded once for serious risk of bias). Secondary outcomes Six trials assessed infiltration (7123 participants). Routine replacement probably reduces infiltration of fluid into surrounding tissues compared with a clinically indicated change (RR 1.16 (95% CI 1.06 to 1.26; routine replacement 747/3638 (20.5%); clinically indicated 834/3485 (23.9%); moderate-certainty evidence, downgraded once for serious risk of bias). Meta-analysis of seven trials (7323 participants), found that rates of catheter failure due to blockage were probably lower in the routine replacement group compared to the clinically indicated group (RR 1.14, 95%CI 1.01 to 1.29; routine-replacement 519/3733 (13.9%); clinically indicated 560/3590 (15.6%); moderate-certainty evidence, downgraded once for serious risk of bias). Four studies (4606 participants), reported local infection rates. It is uncertain if there are differences between groups (RR 4.96, 95% CI 0.24 to 102.98; clinically indicated 2/2260 (0.09%); routine replacement 0/2346 (0.0%); very low-certainty evidence, downgraded one level for serious risk of bias and two levels for very serious imprecision). One trial (3283 participants), found no clear difference in the incidence of mortality when clinically indicated removal was compared with routine removal (RR 1.06, 95% CI 0.27 to 4.23; low-certainty evidence, downgraded two levels for very serious imprecision). One small trial (198 participants) reported no clear difference in device-related pain between clinically indicated and routine removal groups (MD −0.60, 95% CI −1.44 to 0.24; low certainty evidence, downgraded one level for serious risk of bias and one level for serious imprecision). The pre-planned outcomes ’number of catheter re-sites per patient’, and ’satisfaction’ were not reported by any studies included in this review. Authors’ conclusions There is moderate-certainty evidence of no clear difference in rates of CRBSI, thrombophlebitis, all-cause BSI, mortality and pain between clinically indicated or routine replacement of PIVC. We are uncertain if local infection is reduced or increased when catheters are changed when clinically indicated. There is moderate-certainty evidence that infiltration and catheter blockage is probably lower when PIVC are changed routinely; and moderate-certainty evidence that clinically indicated removal probably reduces device-related costs. The addition of two new trials for this update found no further evidence to support changing catheters every 72 to 96 hours. Healthcare organisations may consider changing to a policy whereby catheters are changed only if there is a clinical indication to do so, for example, if there were signs of infection, blockage or infiltration. This would provide significant cost savings, spare patients the unnecessary pain of routine re-sites in the absence of clinical indications and would reduce time spent by busy clinicians on this intervention. To minimise PIVC-related complications, staff should inspect the insertion site at each shift change and remove the catheter if signs of inflammation, infiltration, occlusion, infection or blockage are present, or if the catheter is no longer needed for therapy

Seasonal dependence of peroxy radical concentrations at a northern hemisphere marine boundary layer site during summer and winter: evidence for photochemical activity in winter

International audiencePeroxy radicals (HO2+?RO2) were measured at the Weybourne Atmospheric Observatory (52° N, 1° E), Norfolk using a PEroxy Radical Chemical Amplifier (PERCA) during the winter and summer of 2002. The peroxy radical diurnal cycles showed a marked difference between the winter and summer campaigns with maximum concentrations of 12 pptv at midday in the summer and maximum concentrations as high as 30 pptv (10 min averages) in winter at night. The corresponding nighttime peroxy radical concentrations were not as high in summer (3 pptv). The peroxy radical concentration shows a distinct anti-correlation with increasing NOx during the daylight hours. At night, peroxy radicals increase with increasing NOx indicative of the role of NO3 chemistry. The average diurnal cycles for net ozone production, N(O3) show a large variability in ozone production, P(O3), and a large ozone loss, L(O3) in summer relative to winter. For a daylight average, net ozone production in summer than winter (1.51±0.5 ppbv h?1 and 1.11±0.47 ppbv h?1 respectively) but summer shows more variability of (meteorological) conditions than winter. The variability in NO concentration has a much larger effect on N(O3) than the peroxy radical concentrations. Photostationary state (PSS) calculations show an NO2 lifetime of 5 min in summer and 21 min in the winter, implying that steady-state NO-NO2 ratios are not always attained during the winter months. The results show an active peroxy radical chemistry at night and the ability of winter to make oxidant. The net effect of this with respect to production of ozone in winter is unclear owing to the breakdown in the photostationary state

Interferometric 12CO(J=2-1) image of the Nuclear Region of Seyfert 1 Galaxy NGC 1097

We have mapped the central region of the Seyfert 1 galaxy NGC 1097 in 12CO(J=2-1) with the Submillieter Array (SMA). The 12CO(J=2-1) map shows a central concentration and a surrounding ring, which coincide respectively with the Seyfert nucleus and a starburst ring. The line intensity peaks at the nucleus, whereas in a previously published 12CO(J=1-0) map the intensity peaks at the starburst ring. The molecular ring has an azimuthally averaged 12CO(J=2-1)/(J=1-0) intensity ratio (R21) of about unity, which is similar to those in nearby active star forming galaxies, suggesting that most of the molecular mass in the ring is involved in fueling the starburst. The molecular gas can last for only about 1.2\times10^8 years without further replenishment assuming a constant star formation rate and a perfect conversion of gas to stars. The velocity map shows that the central molecular gas is rotating with the molecular ring in the same direction, while its velocity gradient is much steeper than that of the ring. This velocity gradient of the central gas is similar to what is usually observed in some Seyfert 2 galaxies. To view the active nucleus directly in the optical, the central molecular gas structure can either be a low-inclined disk or torus but not too low to be less massive than the mass of the host galaxy itself, be a highly-inclined thin disk or clumpy and thick torus, or be an inner part of the galactic disk. The R21 value of ~1.9 of the central molecular gas component, which is significantly higher than the value found at the molecular gas ring, indicates that the activity of the Seyfert nucleus may have a significant influence on the conditions of the molecular gas in the central component.Comment: 22 pages, 4 figures, accepted by Ap

Non-commutative desingularization of determinantal varieties, I

We show that determinantal varieties defined by maximal minors of a generic matrix have a non-commutative desingularization, in that we construct a maximal Cohen-Macaulay module over such a variety whose endomorphism ring is Cohen-Macaulay and has finite global dimension. In the case of the determinant of a square matrix, this gives a non-commutative crepant resolution.Comment: 52 pages, 3 figures, all comments welcom

Fabrication and characterization of dual function nanoscale pH-scanning ion conductance microscopy (SICM) probes for high resolution pH mapping

The easy fabrication and use of nanoscale dual function pH-scanning ion conductance microscopy (SICM) probes is reported. These probes incorporate an iridium oxide coated carbon electrode for pH measurement and an SICM barrel for distance control, enabling simultaneous pH and topography mapping. These pH-SICM probes were fabricated rapidly from laser pulled theta quartz pipets, with the pH electrode prepared by in situ carbon filling of one of the barrels by the pyrolytic decomposition of butane, followed by electrodeposition of a thin layer of hydrous iridium oxide. The other barrel was filled with an electrolyte solution and Ag/AgCl electrode as part of a conductance cell for SICM. The fabricated probes, with pH and SICM sensing elements typically on the 100 nm scale, were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and various electrochemical measurements. They showed a linear super-Nernstian pH response over a range of pH (pH 2–10). The capability of the pH-SICM probe was demonstrated by detecting both pH and topographical changes during the dissolution of a calcite microcrystal in aqueous solution. This system illustrates the quantitative nature of pH-SICM imaging, because the dissolution process changes the crystal height and interfacial pH (compared to bulk), and each is sensitive to the rate. Both measurements reveal similar dissolution rates, which are in agreement with previously reported literature values measured by classical bulk methods

Age structure, dispersion and diet of a population of stoats (Mustela erminea) in southern Fiordland during the decline phase of the beechmast cycle

The dispersion, age structure and diet of stoats (Mustela erminea) in beech forest in the Borland and Grebe Valleys, Fiordland National Park, were examined during December and January 2000/01, 20 months after a heavy seed-fall in 1999. Thirty trap stations were set along a 38-km transect through almost continuous beech forest, at least 1 km apart. Mice were very scarce (nights, C/100TN) along two standard index lines placed at either end of the transect, compared with November 1999 (>60/100TN), but mice were detected (from footprints in stoat tunnels) along an 8 km central section of the transect (stations 14-22). Live trapping with one trap per station (total 317.5 trap nights) in December 2000 caught 2 female and 23 male stoats, of which 10 (including both females) were radio collared. The minimum range lengths of the two females along the transect represented by the trap line were 2.2 and 6.0 km; those of eight radio-tracked males averaged 2.9 ± 1.7 km. Stations 14-22 tended to be visited more often, by more marked individual stoats, than the other 21 stations. Fenn trapping at the same 30 sites, but with multiple traps per station (1333.5 trap nights), in late January 2001 collected carcasses of 35 males and 28 females (including 12 of the marked live-trapped ones). Another two marked males were recovered dead. The stoat population showed no sign of chronic nutritional stress (average fat reserve index = 2.8 on a scale of 1-4 where 4 = highest fat content); and only one of 63 guts analysed was empty. Nevertheless, all 76 stoats handled were adults with 1-3 cementum annuli in their teeth, showing that reproduction had failed that season. Prey categories recorded in descending frequency of occurrence were birds, carabid beetle (ground beetle), weta, possum, rat, and mouse. The frequencies of occurrence of mice and birds in the diet of these stoats (10% and 48%, respectively) were quite different from those in stoats collected in Pig Creek, a tributary of the Borland River (87%, 5%), 12 months previously when mice were still abundant. Five of the six stoat guts containing mice were collected within 1 km of stations 14-22