Ion radial diffusion in an electrostatic impulse model for stormtime ring current formation

Guiding-center simulations of stormtime transport of ring-current and radiation-belt ions having first adiabatic invariants mu is approximately greater than 15 MeV/G (E is approximately greater than 165 keV at L is approximately 3) are surprisingly well described (typically within a factor of approximately less than 4) by the quasilinear theory of radial diffusion. This holds even for the case of an individual model storm characterized by substorm-associated impulses in the convection electric field, provided that the actual spectrum of the electric field is incorporated in the quasilinear theory. Correction of the quasilinear diffusion coefficient D(sub LL)(sup ql) for drift-resonance broadening (so as to define D(sub LL)(sup ql)) reduced the typical discrepancy with the diffusion coefficients D(sub LL)(sup sim) deduced from guiding-center simulations of representative-particle trajectories to a factor of approximately 3. The typical discrepancy was reduced to a factor of approximately 1.4 by averaging D(sub LL)(sup sim), D(sub LL)(sup ql), and D(sub LL)(sup rb) over an ensemble of model storms characterized by different (but statistically equivalent) sets of substorm-onset times

Incisional hernia repair after caesarean section: a population based study

BACKGROUND Incisional hernias occur at surgical abdominal incision sites but the association with caesarean section (CS) has not been examined. AIM: To determine whether CS is a risk factor for incisional hernia repair. MATERIAL and METHODS: Population-based cohort study in Australia using linked birth and hospital data for women who gave birth from 2000 to 2011. (n=642,578) Survival analysis was used to explore the association between CS and subsequent incisional hernia repair. Analyses were adjusted for confounding factors including other abdominal surgery. The main outcome measure was surgical repair of an incisional hernia. RESULTS: 217,555 women (33.9%) had at least one CS and 1,554 (0.2%) had an incisional hernia repair. The frequency of incisional hernia repair in women who had ever had a caesarean section was 0.47%, compared to 0.12% in women who never had a caesarean section. After controlling for different follow up lengths and known explanatory variables, the adjusted hazard ratio (aHR) was 2.73 (95%CI 2.45-3.06, P <0.001). Incisional hernia repair risk increased with number of caesarean sections: women with two CS had a threefold increased risk of incisional hernia repair, which increased to 6 fold after five CS (aHR=6.29, 95%CI 3.99-9.93, P<0.001) compared to women with no CS. Prior abdominal surgery including other hernia repair also increased the risk of incisional hernia repair (all p<0.001). CONCLUSIONS: There was a strong association between maternal CS and subsequent incisional hernia repair, which increased as the number of CSs increased, but the absolute risk of incisional hernia repair was low.We thank the New South Wales (NSW) Ministry of Health for access to the population health data and the NSW Centre for Health Record Linkage for linking the data sets. This work was supported by an Australian National Health and Medical Research Council (NHMRC) Centre for Research Excellence Grant (1001066). CLR is supported by a NHMRC Senior Research Fellowship (#APP1021025)

Stormtime transport of ring current and radiation belt ions

This is an investigation of stormtime particle transport that leads to formation of the ring current. Our method is to trace the guiding-center motion of representative ions (having selected first adiabatic invariants mu) in response to model substorm-associated impulses in the convection electric field. We compare our simulation results qualitatively with existing analytically tractable idealizations of particle transport (direct convective access and radial diffusion) in order to assess the limits of validity of these approximations. For mu approximately less than 10 MeV/G (E approximately less than 10 keV at L equivalent to 3) the ion drift period on the final (ring-current) drift shell of interest (L equivalent to 3) exceeds the duration of the main phase of our model storm, and we find that the transport of ions to this drift shell is appropriately idealized as direct convective access, typically from open drift paths. Ion transport to a final closed drift path from an open (plasma-sheet) drift trajectory is possible for those portions of that drift path that lie outside the mean stormtime separatrix between closed and open drift trajectories, For mu approximately 10-25 MeV/G (110 keV approximately less than E approximately less than 280 keV at L equivalent to 3) the drift period at L equivalent to 3 is comparable to the postulated 3-hr duration of the storm, and the mode of transport is transitional between direct convective access and transport that resembles radial diffusion. (This particle population is transitional between the ring current and radiation belt). For mu approximately greater than 25 MeV/G (radiation-belt ions having E approximately greater than 280 keV at L equivalent to 3) the ion drift period is considerably shorter than the main phase of a typical storm, and ions gain access to the ring-current region essentially via radial diffusion. By computing the mean and mean-square cumulative changes in 1/L among (in this case) 12 representative ions equally spaced in drift time around the steady-state drift shell of interest (L equivalent to 3), we have estimated (from both our forward and our time-reversed simulations) the time-integrated radial-diffusion coefficients D(sup sim)(sub LL) for particles having selected values of mu approximately greater than 15 MeV/G. The results agree surprisingly well with the predictions (D(sup ql)(sub LL)) of quasilinear radial diffusion theory, despite the rather brief duration (approximately 3 hrs) of our model storm and despite the extreme variability (with frequency) of the spectral-density function that characterizes the applied electric field during our model storm. As expected, the values of D(sup sim)(sub LL) deduced (respectively) from our forward and time-reversed simulations agree even better with each other and with D(sup sim)(sub LL) when the impulse amplitudes which characterize the individual substorms of our model storm are systematically reduced

Stormtime ring current and radiation belt ion transport: Simulations and interpretations

We use a dynamical guiding-center model to investigate the stormtime transport of ring current and radiation-belt ions. We trace the motion of representative ions' guiding centers in response to model substorm-associated impulses in the convection electric field for a range of ion energies. Our simple magnetospheric model allows us to compare our numerical results quantitatively with analytical descriptions of particle transport, (e.g., with the quasilinear theory of radial diffusion). We find that 10-145-keV ions gain access to L approximately 3, where they can form the stormtime ring current, mainly from outside the (trapping) region in which particles execute closed drift paths. Conversely, the transport of higher-energy ions (approximately greater than 145 keV at L approximately 3) turns out to resemble radial diffusion. The quasilinear diffusion coefficient calculated for our model storm does not vary smoothly with particle energy, since our impulses occur at specific (although randomly determined) times. Despite the spectral irregularity, quasilinear theory provides a surprisingly accurate description of the transport process for approximately greater than 145-keV ions, even for the case of an individual storm. For 4 different realizations of our model storm, the geometric mean discrepancies between diffusion coefficients D(sup sim, sub LL) obtained from the simulations and the quasilinear diffusion coefficient D(sup ql, sub LL) amount to factors of 2.3, 2.3, 1.5, and 3.0, respectively. We have found that these discrepancies between D(sup sim, sub LL) and D(sup ql, sub LL) can be reduced slightly by invoking drift-resonance broadening to smooth out the sharp minima and maxima in D(sup ql, sub LL). The mean of the remaining discrepancies between D(sup sim, sub LL) and D(sup ql, sub LL) for the 4 different storms then amount to factors of 1.9, 2.1, 1.5, and 2.7, respectively. We find even better agreement when we reduce the impulse amplitudes systematically in a given model storm (e.g., reduction of all the impulse amplitudes by half reduces the discrepancy factor by at least its square root) and also when we average our results over an ensemble of 20 model storms (agreement is within a factor of 1.2 without impulse-amplitude reduction). We use our simulation results also to map phase-space densities f in accordance with Liouville's theorem. We find that the stormtime transport of approximately greater than 145-keV ions produces little change in f-bar the drift-averaged phase-space density on any drift shell of interest. However, the stormtime transport produces a major enhancement from the pre-storm phase-space density at energies approximately 30-145 keV, which are representative of the stormtime ring current

A CRISPR-based screen for Hedgehog signaling provides insights into ciliary function and ciliopathies.

Primary cilia organize Hedgehog signaling and shape embryonic development, and their dysregulation is the unifying cause of ciliopathies. We conducted a functional genomic screen for Hedgehog signaling by engineering antibiotic-based selection of Hedgehog-responsive cells and applying genome-wide CRISPR-mediated gene disruption. The screen can robustly identify factors required for ciliary signaling with few false positives or false negatives. Characterization of hit genes uncovered novel components of several ciliary structures, including a protein complex that contains δ-tubulin and ε-tubulin and is required for centriole maintenance. The screen also provides an unbiased tool for classifying ciliopathies and showed that many congenital heart disorders are caused by loss of ciliary signaling. Collectively, our study enables a systematic analysis of ciliary function and of ciliopathies, and also defines a versatile platform for dissecting signaling pathways through CRISPR-based screening

WormBase: a comprehensive resource for nematode research

WormBase (http://www.wormbase.org) is a central data repository for nematode biology. Initially created as a service to the Caenorhabditis elegans research field, WormBase has evolved into a powerful research tool in its own right. In the past 2 years, we expanded WormBase to include the complete genomic sequence, gene predictions and orthology assignments from a range of related nematodes. This comparative data enrich the C. elegans data with improved gene predictions and a better understanding of gene function. In turn, they bring the wealth of experimental knowledge of C. elegans to other systems of medical and agricultural importance. Here, we describe new species and data types now available at WormBase. In addition, we detail enhancements to our curatorial pipeline and website infrastructure to accommodate new genomes and an extensive user base

Influence of microscopic and macroscopic effects on attosecond pulse generation using two-color laser fields

Attosecond pulses and pulse trains generated by high-order harmonic generation are finding broad applications in advanced spectroscopies and imaging, enabling sub-femtosecond electron dynamics to be probed in atomic, molecular and material systems. To date, isolated attosecond pulses have been generated either by using very short few-cycle driving pulses, or by using temporal and polarization gating, or by taking advantage of phase-matching gating. Here we show that by driving high harmonics with a two-color linearly polarized laser field, the temporal window for time-gated phase matching is shorter than for the equivalent singe-color driving laser. As a result, we can generate quasi-isolated attosecond pulses with a peak width of ∼ 450 as using relatively long 26 femtosecond laser pulses. Our experimental data are in good agreement with theoretical simulations, and show that the phase matching window decreases by a factor of 4 - from four optical cycles in the case of a single-color fundamental driving laser, to one optical cycle in the case of two-color (ω-2ω) laser drivers. Finally, we also demonstrate that by changing the relative delay between the two-color laser fields, we can control the duration of the attosecond bursts from 450 as to 1.2 fs.National Science Foundation (NSF) (1125844); Air Force Office of Scientific Research (FA9550-16-1-0121); REA (328334); Junta de Castilla y León (SA046U16); MINECO (FIS2013-44174-P, FIS2016-75652-P)