Accelerating AGN jets to parsec scales using general relativistic MHD simulations

Accreting black holes produce collimated outflows, or jets, that traverse many orders of magnitude in distance, accelerate to relativistic velocities, and collimate into tight opening angles. Of these, perhaps the least understood is jet collimation due to the interaction with the ambient medium. In order to investigate this interaction, we carried out axisymmetric general relativistic magnetohydrodynamic simulations of jets produced by a large accretion disc, spanning over 5 orders of magnitude in time and distance, at an unprecedented resolution. Supported by such a disc, the jet attains a parabolic shape, similar to the M87 galaxy jet, and the product of the Lorentz factor and the jet half-opening angle, $\gamma\theta\ll 1$, similar to values found from very long baseline interferometry (VLBI) observations of active galactic nuclei (AGN) jets; this suggests extended discs in AGN. We find that the interaction between the jet and the ambient medium leads to the development of pinch instabilities, which produce significant radial and lateral variability across the jet by converting magnetic and kinetic energy into heat. Thus pinched regions in the jet can be detectable as radiating hotspots and may provide an ideal site for particle acceleration. Pinching also causes gas from the ambient medium to become squeezed between magnetic field lines in the jet, leading to enhanced mass-loading of the jet and potentially contributing to the spine-sheath structure observed in AGN outflows.Comment: 18 pages, 24 figures, submitted to MNRAS, revised version. See our Youtube channel for accompanying animations: https://www.youtube.com/playlist?list=PLjldVlE2vDFzHMGn75tgc2Lod0kcTWZd

A Phase Lag between Disk and Corona in GRMHD Simulations of Precessing Tilted Accretion Disks

In the course of its evolution, a black hole (BH) accretes gas from a wide range of directions. Given a random accretion event, the typical angular momentum of an accretion disc would be tilted by $\sim$60$^\circ$ relative to the BH spin. Misalignment causes the disc to precess at a rate that increases with BH spin and tilt angle. We present the first general-relativistic magnetohydrodynamic (GRMHD) simulations spanning a full precession period of highly tilted (60$^\circ$), moderately thin ($h/r=0.1$) accretion discs around a rapidly spinning ($a\simeq0.9$) BH. While the disc and jets precess in phase, we find that the corona, sandwiched between the two, lags behind by $\gtrsim 10^{\circ}$. For spectral models of BH accretion, the implication is that hard non-thermal (corona) emission lags behind the softer (disc) emission, thus potentially explaining some properties of the hard energy lags seen in Type-C low frequency quasi-periodic oscillations in X-Ray binaries. While strong jets are unaffected by this disc-corona lag, weak jets stall when encountering the lagging corona at distances $r \sim 100$ black hole radii. This interaction may quench large-scale jet formation.Comment: 5 pages, 4 figures, submitted to MNRAS, see YouTube playlist for 3D renderings: https://www.youtube.com/playlist?list=PLDO1oeU33GwmwOV_Hp9s7572JdU8JPSS

A review of the importance of the Caribbean region in Oligo-Miocene low latitude planktonic foraminiferal biostratigraphy and the implications for modern biogeochronological schemes

Planktonic foraminifera are widely used in marine biostratigraphy thanks to their small size, limited stratigraphic range and abundance in oceanic sediments. The utility of planktonic foraminifera in biostratigraphy was first fully recognised within the Caribbean region during the middle of the 20th century. The area was critical for the subsequent development of the low latitude biostratigraphic schemes and remains fundamental for modern day biogeochronologies. This study presents a historical review of the Oligo-Miocene component of these biostratigraphic schemes, including the first proposed scheme of Cushman and Stainforth (1945) and the subsequent development. The work of Hans Bolli and Walter Blow is particularly highlighted due to their heavy influence on modern day biostratigraphy, including these authors initially recognising the biostratigraphic utility of a number of bioevents still applied today. These Caribbean-centric schemes are correlated to the modern-day low latitude biogeochronology of Wade et al. (2011), with this synthesis highlighting that a number of bioevents (e.g. Top Paragloborotalia kugleri and Top Catapsydrax dissimilis) have been applied consistently since their initial recognition. This in turn allows the recognisability of these bioevents to be deduced based on how consistently applied each datum has been. In addition, the range charts of six studies focusing heavily on the Caribbean have been reassessed to determine whether there is potential to apply a given bioevent, and the original author merely did not recognise the biostratigraphic utility of the species or favoured another bioevent. In considering this historical review, a number of amendments to Wade et al. (2011) and future priorities to planktonic foraminifera biogeochronologies are suggested. Most notably, the re-introduction of Base Globigerinatella insueta as a primary bioevent due to the historical biostratigraphic importance of this species. This event now defines early Miocene Subzone M3b (Gt. insueta/Ct. dissimilis PRZ) dividing Zone M3 into an upper Subzone M3b (Base Gt. insueta) and lower Subzone M3a (Base Globigerinatella sp.). Finally, the Miocene to Recent timescale of Wade et al. (2011) has been recalibrated following more recent updates to the magnetostratigraphy (Kochhann et al., 2016; Ogg et al., 2016; Drury et al., 2017; Beddow et al., 2018) and cyclostratigraphy (Wilkens et al., 2017). The overall effect on the planktonic foraminifera biogeochronology is minor but our results become the suggested biostratigraphic framework for the low latitudes

Potential Vorticity Evolution of a Protoplanetary Disk with An Embedded Protoplanet

We present two-dimensional inviscid hydrodynamic simulations of a protoplanetary disk with an embedded planet, emphasizing the evolution of potential vorticity (the ratio of vorticity to density) and its dependence on numerical resolutions. By analyzing the structure of spiral shocks made by the planet, we show that progressive changes of the potential vorticity caused by spiral shocks ultimately lead to the excitation of a secondary instability. We also demonstrate that very high numerical resolution is required to both follow the potential vorticity changes and identify the location where the secondary instability is first excited. Low-resolution results are shown to give the wrong location. We establish the robustness of a secondary instability and its impact on the torque onto the planet. After the saturation of the instability, the disk shows large-scale non-axisymmetry, causing the torque on the planet to oscillate with large amplitude. The impact of the oscillating torque on the protoplanet's migration remains to be investigated.Comment: 17 pages total with 9 figures (Fig.4,5,9 are in .jpg), accepted to Ap

TFLink: an integrated gateway to access transcription factor-target gene interactions for multiple species

Analysis of transcriptional regulatory interactions and their comparisons across multiple species are crucial for progress in various fields in biology, from functional genomics to the evolution of signal transduction pathways. However, despite the rapidly growing body of data on regulatory interactions in several eukaryotes, no databases exist to provide curated high-quality information on transcription factor-target gene interactions for multiple species. Here, we address this gap by introducing the TFLink gateway, which uniquely provides experimentally explored and highly accurate information on transcription factor-target gene interactions (∼12 million), nucleotide sequences and genomic locations of transcription factor binding sites (∼9 million) for human and six model organisms: mouse, rat, zebrafish, fruit fly, worm and yeast by integrating 10 resources. TFLink provides user-friendly access to data on transcription factor-target gene interactions, interactive network visualizations and transcription factor binding sites, with cross-links to several other databases. Besides containing accurate information on transcription factors, with a clear labelling of the type/volume of the experiments (small-scale or high-throughput), the source database and the original publications, TFLink also provides a wealth of standardized regulatory data available for download in multiple formats. The database offers easy access to high-quality data for wet-lab researchers, supplies data for gene set enrichment analyses and facilitates systems biology and comparative gene regulation studies. Database URL https://tflink.net/

Fish schooling as a basis for vertical axis wind turbine farm design

Most wind farms consist of horizontal axis wind turbines (HAWTs) due to the high power coefficient (mechanical power output divided by the power of the free-stream air through the turbine cross-sectional area) of an isolated turbine. However when in close proximity to neighbouring turbines, HAWTs suffer from a reduced power coefficient. In contrast, previous research on vertical axis wind turbines (VAWTs) suggests that closely-spaced VAWTs may experience only small decreases (or even increases) in an individual turbine's power coefficient when placed in close proximity to neighbours, thus yielding much higher power outputs for a given area of land. A potential flow model of inter-VAWT interactions is developed to investigate the effect of changes in VAWT spatial arrangement on the array performance coefficient, which compares the expected average power coefficient of turbines in an array to a spatially-isolated turbine. A geometric arrangement based on the configuration of shed vortices in the wake of schooling fish is shown to significantly increase the array performance coefficient based upon an array of 16x16 wind turbines. Results suggest increases in power output of over one order of magnitude for a given area of land as compared to HAWTs.Comment: Submitted for publication in BioInspiration and Biomimetics. Note: The technology described in this paper is protected under both US and international pending patents filed by the California Institute of Technolog

Artificial diets for rearing the Colorado potato beetle, Leptinotarsa decemlineata

Colorado potato beetles have been reared successfully through 12 generations on artificial diets containing either 2.5% potato leaf powder or 2.5% lettuce leaf powder/0.75% potato leaf powder. For all but one of the treatment groups, the mean duration of each of the four larval stages was between 0.8 and 1.5 days longer than the durations exhibited by control beetles that had been fed on potato leaves. Maximum weights of prepupae, newly emerged adults and day 5 – 9 adults were approximately 78, 80 and 82%, respectively, of the weights for comparable stages of control beetles. Mean percent mortality for 1(st) instars was two to six times higher for artificial diet-fed CPBs than for leaf-fed beetles. However, since pupal mortality was four times higher for control beetles than for beetles reared on artificial diet, mean percent total mortality (newly hatched through the 9 day old adult) was equivalent for leaf-fed beetles and for later generations of potato and Lettuce+Potato diet-fed CPBs. Hemolymph ecdysteroid levels and fluctuations in mature 4(th) instar larvae and prepupae were similar in controls and experimental groups. Number of hatchlings produced per adult pair per day (fertility) was approximately eight times greater in control beetles than in later generations of artificial diet-fed beetles, primarily because fewer egg masses were laid per day, percent hatch was lower and cannibalism of eggs was higher in these latter groups. Interestingly, the mean percent hatch, although only 68% of the control value, was 1.5 times greater for beetles reared on diet containing lettuce-leaf powder, and a small percentage of potato leaf powder, than on diet containing only potato leaf powder. Percent hatch was equal for beetles fed on diet containing only lettuce-leaf powder and those fed on potato leaves. Finally, it is noteworthy that the quality of eggs, as judged by the ability of the wasp parasitoid, Edovum puttleri, to parasitize and develop in the eggs, was similar for eggs produced by control beetles and for those produced by beetles fed on potato and Lettuce+Potato diets. The diets and rearing system described here will be useful for providing beetles on a year-round basis for experiments designed to evaluate the effects of potential insect control agents, to investigate the mechanism(s) by which insects become resistant to control agents and for other applied and fundamental studies related to the control of this serious pest. The use of lettuce leaf powder in place of most of the potato leaf powder is especially advantageous because of the much reduced cost and greater availability of lettuce as compared to potato leaves

Discovery of Five New Pulsars in Archival Data

Reprocessing of the Parkes Multibeam Pulsar Survey has resulted in the discovery of five previously unknown pulsars and several as-yet-unconfirmed candidates. PSR J0922-52 has a period of 9.68 ms and a DM of 122.4 pc cm^-3. PSR J1147-66 has a period of 3.72 ms and a DM of 133.8 pc cm^-3. PSR J1227-6208 has a period of 34.53 ms, a DM of 362.6 pc cm^-3, is in a 6.7 day binary orbit, and was independently detected in an ongoing high-resolution Parkes survey by Thornton et al. and also in independent processing by Einstein@Home volunteers. PSR J1546-59 has a period of 7.80 ms and a DM of 168.3 pc cm^-3. PSR J1725-3853 is an isolated 4.79-ms pulsar with a DM of 158.2 pc cm^-3. These pulsars were likely missed in earlier processing efforts due to their high DMs and short periods and the large number of candidates that needed to be looked through. These discoveries suggest that further pulsars are awaiting discovery in the multibeam survey data.Comment: 12 pages, 2 figures, 2 tables, accepted to Ap