In the Earth's magnetotail, magnetic reconnection releases stored magnetic energy and drives magnetospheric convection. The rate at which magnetic flux is transferred from the reconnection inflow to ...outflow regions is determined by the reconnection electric field Er, which is often referred to as the unnormalized reconnection rate. To better quantify the efficiency of reconnection, this electric field Er is often normalized by the characteristic Alfvén speed and the reconnecting magnetic field. This parameter is generally called the normalized or dimensionless reconnection rate R. In this paper, we employ a two‐dimensional fully kinetic simulation to model a magnetotail reconnection event with weak geomagnetic activity (<200 nT of the AE index) observed by the Magnetospheric Multiscale (MMS) mission on 11 July 2017. We obtain R and Er from direct measurements in the diffusion region and indirect measurements of the rate at the separatrix using a recently proposed remote sensing technique. The measured normalized rate for this MMS event is R ∼0.15–0.2, consistent with theoretical and simulation models of fast collisionless reconnection. This corresponds to an unnormalized rate of Er ∼2–3 mV/m. Based on quantitative consistencies between the simulation and the MMS observations, we conclude that our estimates of the reconnection rates are reasonably accurate. Given that past studies have found Er of the order ∼10 mV/m during strong geomagnetic substorms, these results indicate that the local Er in magnetotail reconnection may be an important parameter controlling the amplitude of geomagnetic disturbances.
Key Points
Reliable reconnection rates are obtained based on virtual observations in a fully kinetic simulation of an MMS tail reconnection event
The normalized rates obtained from the simulation and MMS data are 0.15–0.2, indicating the occurrence of fast reconnection
The observed unnormalized rate is 2–3 mV/m, while higher rates were observed in other events with stronger geomagnetic activities
Abstract
Coalescence of multiple magnetic islands is recognized as an effective process to energize particles during magnetic reconnection, while its energy conversion process still remains unclear. ...Here, a two-dimensional fully kinetic simulation of multiple island coalescence with a small reconnection guide field is studied. In the analysis of energy conversion within a magnetic island, the dot product of
V
e
·
j
×
B
=
w
1
is a useful quantity to compare with
j
·
E
=
w
2
, since the average work done by the Lorentz force on the circulating particles is negligible in the island and
w
2
−
w
1
=
j
·
E
+
V
e
×
B
=
j
·
E
′
=
w
3
. A bipolar pattern of
w
1
is found at a secondary island when the electrons are in circular motion inside the island. Significant energy dynamo (
w
3
< 0) resulting from
j
∥
E
∥
is found at the secondary island, which has not been reported before, where the parallel electric field
E
∥
is highly correlated with
w
3
. Moreover, significant energy dissipation (
w
3
> 0) due to
j
⊥
·
E
⊥
′
is seen in the merging region between two coalescing islands. Both types of energy conversions are accompanied by enhancements in
j
∥
and the parallel electron temperature
T
e
∥
. Three ion-scale magnetic islands (FR1, FR2, and FR3) observed by the Magnetospheric Multiscale spacecraft are compared favorably with the simulated signatures of energy dynamo and dissipation of an evolving secondary island. In particular, FR1 displayed a similar energy dynamo signature as that simulated in an early stage of the secondary island. FR2 and FR3 showed a dominant
j
⊥
·
E
⊥
′
energy conversion similar to that obtained in a later stage of the secondary island.
We examine traversals on 20 November 2001 of the equatorial magnetopause boundary layer simultaneously at ∼1500 magnetic local time (MLT) by the Geotail spacecraft and at ∼1900 MLT by the Cluster ...spacecraft, which detected rolled‐up MHD‐scale vortices generated by the Kelvin‐Helmholtz instability (KHI) under prolonged northward interplanetary magnetic field conditions. Our purpose is to address the excitation process of the KHI, MHD‐scale and ion‐scale structures of the vortices, and the formation mechanism of the low‐latitude boundary layer (LLBL). The observed KH wavelength (>4 × 104 km) is considerably longer than predicted by the linear theory from the thickness (∼1000 km) of the dayside velocity shear layer. Our analyses suggest that the KHI excitation is facilitated by combined effects of the formation of the LLBL presumably through high‐latitude magnetopause reconnection and compressional magnetosheath fluctuations on the dayside, and that breakup and/or coalescence of the vortices are beginning around 1900 MLT. Current layers of thickness a few times ion inertia length ∼100 km and of magnetic shear ∼60° existed at the trailing edges of the vortices. Identified in one such current sheet were signatures of local reconnection: Alfvénic outflow jet within a bifurcated current sheet, nonzero magnetic field component normal to the sheet, and field‐aligned beam of accelerated electrons. Because of its incipient nature, however, this reconnection process is unlikely to lead to the observed dusk‐flank LLBL. It is thus inferred that the flank LLBL resulted from other mechanisms, namely, diffusion and/or remote reconnection unidentified by Cluster.
Objectives
Stroke‐associated pneumonia (SAP) is common and associated with adverse outcomes. Data on its impact beyond 1 year are scarce.
Materials and methods
This observational study was conducted ...in a cohort of stroke patients admitted consecutively to a tertiary referral center in the east of England, UK (January 2003‐April 2015). Logistic regression models examined inpatient mortality and length of stay (LOS). Cox regression models examined longer‐term mortality at predefined time periods (0‐90 days, 90 days‐1 year, 1‐3 years, and 3‐10 years) for SAP. Effect of SAP on functional outcome at discharge was assessed using logistic regression.
Results
A total of 9238 patients (mean age ±SD 77.61 ± 11.88 years) were included. SAP was diagnosed in 1083 (11.7%) patients. The majority of these cases (n = 658; 60.8%) were aspiration pneumonia. After controlling for age, sex, stroke type, Oxfordshire Community Stroke Project (OCSP) classification, prestroke modified Rankin scale, comorbidities, and acute illness markers, mortality estimates remained significant at 3 time periods: inpatient (OR 5.87, 95%CI 4.97‐6.93), 0‐90 days (2.17 1.97‐2.40), and 91‐365 days (HR 1.31 1.03‐1.67). SAP was also associated with higher odds of long LOS (OR 1.93 1.67‐2.22) and worse functional outcome (OR 7.17 5.44‐9.45). In this cohort, SAP did not increase mortality risk beyond 1 year post‐stroke, but it was associated with reduced mortality beyond 3 years.
Conclusions
Stroke‐associated pneumonia is not associated with increased long‐term mortality, but it is linked with increased mortality up to 1 year, prolonged LOS, and poor functional outcome on discharge. Targeted intervention strategies are required to improve outcomes of SAP patients who survive to hospital discharge.
pks+ Escherichia coli
(
E. coli)
triggers genomic instability in normal colon cells which leads to colorectal cancer (CRC) tumorigenesis. Previously, we reported a significant presentation of
pks+ E. ...coli
strains in CRC patients’ biopsies as compared to healthy cohorts. In this work, using an in vitro infection model, we further explored the ability of these strains in modulating cell cycle arrest and activation of apoptotic mediators in both primary colon epithelial cells (PCE) and CRC cells (HCT-116). Sixteen strains, of which eight tumours and the matching non-malignant tissues, respectively, from eight
pks+ E. coli
CRC patients were subjected to BrDU staining and cell cycle analysis via flow cytometry, while a subset of these strains underwent analysis of apoptotic mediators including caspase proteins, cellular reactive oxygen species (cROS) and mitochondrial membrane potential (MMP) via spectrophotometry as well as proinflammatory cytokines via flow cytometry. Data revealed that all strains exerted S-phase cell cycle blockade in both cells and G2/M phase in PCE cells only. Moreover, more significant upregulation of Caspase 9, cROS, proinflammatory cytokines and prominent downregulation of MMP were detected in HCT-116 cells indicating the potential role of
pks
related bacterial toxin as anticancer agent as compared to PCE cells which undergo cellular senescence leading to cell death without apparent upregulation of apoptotic mediators. These findings suggest the existence of discrepancies underlying the mechanism of action of
pks+ E. coli
on both cancer and normal cell lines. This work propounds the rationale to further understand the mechanism underlying
pks+ E. coli
-mediated CRC tumorigenesis and cancer killing.
With high time‐resolution field and plasma measurements by the Magnetospheric Multiscale spacecraft, interior fine structures of two ion‐scale magnetic flux ropes (~5 and ~11 ion inertial length ...radius) separated by ~14 s are resolved. These two ion‐scale flux ropes (FR1 and FR2) show non‐frozen‐in ion behavior and consist of a strong axial magnetic field at the reversal of the negative‐then‐positive bipolar field component. The negative bipolar field component of the FR2 is found to be depressed, where magnetic pressure and total pressure decrease, but ion and electron thermal pressures increase, a feature akin to a crater‐like flux rope. The pressure enhancement is due to the magnetosheath plasma feeding into the flux rope along the field lines. Magnetic field draping and energetic electrons are also observed in the trailing part of the FR2. The ratio of perpendicular and parallel currents indicates that the FR1 appears force‐free but the FR2 seems not. Moreover, the FR2 is time‐dependent as a result of a low correlation coefficient (CC = 0.75) for the derivation of the deHoffmann‐Teller frame using the direct measured electric fields, while the FR1 is in quasi‐steady conditions (CC = 0.94). It is concluded that the crater formation within the FR2 can be interpreted by the analytical flux rope simulation as the evolution of typical flux rope to crater‐like one due to the thermal pressure enhancement, which could be induced by the depression of transverse magnetic fields of the flux rope.
Key Points
Interior fine structures of two ion‐scale flux ropes are resolved for which some of their flux rope properties are contrasted
Crater is formed within one flux rope where magnetic pressure decreases while thermal pressure increases
Crater formation can be interpreted by flux rope simulation as evolution of typical flux rope to crater‐like one due to pressure increase
Abstract
Background
In the general population, an increase in low-density lipoprotein cholesterol (LDL-C) predicts higher cardiovascular disease risk, and lowering LDL-C can prevent cardiovascular ...disease and reduces mortality risk. Interestingly, in cohort studies that include very old populations, no or inverse associations between LDL-C and mortality have been observed. This study aims to investigate whether the association between LDL-C and mortality in the very old is modified by a composite fitness score.
Methods
A 2-stage meta-analysis of individual participant data from the 5 observational cohort studies. The composite fitness score was operationalized by performance on a combination of 4 markers: functional ability, cognitive function, grip strength, and morbidity. We pooled hazard ratios (HR) from Cox proportional-hazards models for 5-year mortality risk for a 1 mmol/L increase in LDL-C. Models were stratified by high/low composite fitness score.
Results
Composite fitness scores were calculated for 2 317 participants (median 85 years, 60% females participants), of which 994 (42.9%) had a high composite fitness score, and 694 (30.0%) had a low-composite fitness score. There was an inverse association between LDL-C and 5-year mortality risk (HR 0.87 95% CI: 0.80–0.94; p < .01), most pronounced in participants with a low-composite fitness score (HR 0.85 95% CI: 0.75–0.96; p = .01), compared to those with a high composite fitness score (HR = 0.98 95% CI: 0.83–1.15; p = .78), the test for subgroups differences was not significant.
Conclusions
In this very old population, there was an inverse association between LDL-C and all-cause mortality, which was most pronounced in participants with a low-composite fitness scores.
There is a lack of information regarding the provision of parental leave for surgical careers. This survey study aims to evaluate the experience of maternity/paternity leave and views on work-life ...balance globally.
A 55-item online survey in 24 languages was distributed via social media as per CHERRIES guideline from February to March 2020. It explored parental leave entitlements, attitude towards leave taking, financial impact, time spent with children and compatibility of parenthood with surgical career.
Of the 1393 (male : female, 514 : 829) respondents from 65 countries, there were 479 medical students, 349 surgical trainees and 513 consultants. Consultants had less than the recommended duration of maternity leave (43.8 versus 29.1 per cent), no paid maternity (8.3 versus 3.2 per cent) or paternity leave (19.3 versus 11.0 per cent) compared with trainees. Females were less likely to have children than males (36.8 versus 45.6 per cent, P = 0.010) and were more often told surgery is incompatible with parenthood (80.2 versus 59.5 per cent, P < 0.001). Males spent less than 20 per cent of their salary on childcare and fewer than 30 hours/week with their children. More than half (59.2 per cent) of medical students did not believe a surgical career allowed work-life balance.
Surgeons across the globe had inadequate parental leave. Significant gender disparity was seen in multiple aspects.
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