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For the problem of horizontal convection the Nusselt number based on entropy production is bounded from above by
as the horizontal convective Rayleigh number
for some constant
(Siggers et al., J. Fluid Mech., vol. 517, 2004, pp. 55–70). We re-examine the variational arguments leading to this ‘ultimate regime’ by using the Wentzel–Kramers–Brillouin method to solve the variational problem in the
limit and exhibiting solutions that achieve the ultimate
scaling. As expected, the optimizing flows have a boundary layer of thickness
pressed against the non-uniformly heated surface; but the variational solutions also have rapid oscillatory variation with wavelength
along the wall. As a result of the exact solution of the variational problem, the constant
is smaller than the previous estimate by a factor of
for no-slip and
for no-stress boundary conditions. This modest reduction in
indicates that the inequalities used by Siggers et al. (J. Fluid Mech., vol. 517, 2004, pp. 55–70) are surprisingly accurate.
We have detected 27 new supernova remnants (SNRs) using a new data release of the GLEAM survey from the Murchison Widefield Array telescope, including the lowest surface brightness SNR ever detected, G 0.1 – 9.7. Our method uses spectral fitting to the radio continuum to derive spectral indices for 26/27 candidates, and our low-frequency observations probe a steeper spectrum population than previously discovered. None of the candidates have coincident WISE mid-IR emission, further showing that the emission is non-thermal. Using pulsar associations we derive physical properties for six candidate SNRs, finding G 0.1 – 9.7 may be younger than 10 kyr. Sixty per cent of the candidates subtend areas larger than 0.2 deg2 on the sky, compared to < 25% of previously detected SNRs. We also make the first detection of two SNRs in the Galactic longitude range 220°–240°.
This work makes available a further
of the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey, covering half of the accessible galactic plane, across 20 frequency bands sampling 72–231 MHz, with resolution
. Unlike previous GLEAM data releases, we used multi-scale CLEAN to better deconvolve large-scale galactic structure. For the galactic longitude ranges
$345^\circ < l < 67^\circ$
$180^\circ < l < 240^\circ$
, we provide a compact source catalogue of 22 037 components selected from a 60-MHz bandwidth image centred at 200 MHz, with RMS noise
and position accuracy better than 2 arcsec. The catalogue has a completeness of 50% at
, and a reliability of 99.86%. It covers galactic latitudes
towards the galactic centre and
for other regions, and is available from Vizier; images covering
for all longitudes are made available on the GLEAM Virtual Observatory (VO).server and SkyView.
We examined the latest data release from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey covering 345° < l < 60° and 180° < l < 240°, using these data and that of the Widefield Infrared Survey Explorer to follow up proposed candidate Supernova Remnant (SNR) from other sources. Of the 101 candidates proposed in the region, we are able to definitively confirm ten as SNRs, tentatively confirm two as SNRs, and reclassify five as H ii regions. A further two are detectable in our images but difficult to classify; the remaining 82 are undetectable in these data. We also investigated the 18 unclassified Multi-Array Galactic Plane Imaging Survey (MAGPIS) candidate SNRs, newly confirming three as SNRs, reclassifying two as H ii regions, and exploring the unusual spectra and morphology of two others.
An outbreak of 18 cases of hepatitis A virus infection across five Canadian provinces was investigated. Case onsets occurred between October 2017 and May 2018. A retrospective matched case-control study was conducted to identify the likely source of the outbreak. Three matched controls were recruited for each case using a previously established control bank, supplemented by landline and cell phone call lists. Univariate and multivariate matched analyses were conducted to identify a potential outbreak source. Seventy-two per cent of controls were recruited through the control bank, and required on average 25.5 calls per recruited control; 20% of controls were recruited through a landline sample and 8% of controls were recruited through a cell phone sample, requiring an average of 847.3 and 331.7 calls per recruited control, respectively. Results of the analysis pointed to shrimp/prawns (odds ratio (OR) 15.75, p = 0.01) and blackberries (OR 7.21, p = 0.02) as foods of interest, however, an outbreak source could not be confirmed. The control bank proved to be a more efficient method for control recruitment than random call lists. Expanding the control bank size and using alternative methods, such as online surveys, may prove beneficial for increasing the timeliness of a case-control study during an outbreak investigation.
Smoking prevalence is higher amongst individuals with schizophrenia and depression compared with the general population. Mendelian randomisation (MR) can examine whether this association is causal using genetic variants identified in genome-wide association studies (GWAS).
We conducted two-sample MR to explore the bi-directional effects of smoking on schizophrenia and depression. For smoking behaviour, we used (1) smoking initiation GWAS from the GSCAN consortium and (2) we conducted our own GWAS of lifetime smoking behaviour (which captures smoking duration, heaviness and cessation) in a sample of 462690 individuals from the UK Biobank. We validated this instrument using positive control outcomes (e.g. lung cancer). For schizophrenia and depression we used GWAS from the PGC consortium.
There was strong evidence to suggest smoking is a risk factor for both schizophrenia (odds ratio (OR) 2.27, 95% confidence interval (CI) 1.67–3.08, p < 0.001) and depression (OR 1.99, 95% CI 1.71–2.32, p < 0.001). Results were consistent across both lifetime smoking and smoking initiation. We found some evidence that genetic liability to depression increases smoking (β = 0.091, 95% CI 0.027–0.155, p = 0.005) but evidence was mixed for schizophrenia (β = 0.022, 95% CI 0.005–0.038, p = 0.009) with very weak evidence for an effect on smoking initiation.
These findings suggest that the association between smoking, schizophrenia and depression is due, at least in part, to a causal effect of smoking, providing further evidence for the detrimental consequences of smoking on mental health.
This chapter provides an overview of the rapid decline of commercial inland rice cultivation in the South Carolina Lowcountry after the Civil War. Faced with new questions of labor and economies, land owners looked toward new commodities to produce on the former rice plantations. Timber companies began purchasing these tracts in large numbers and agressively harvesting trees and, once again, dramatically altering the landscape. By the turn of the twentieth century, these tracts became part of the United States Forestry Service or incorporated into the growing development surrounding Charleston.
Chapter 6 documents inland cultivation strategies during the final two decades of the antebellum period. Using as a model the Biggin Basin, located at the headwaters of the Cooper River, this chapter discusses how a community of former inland rice planters revitalized the practice to supplement cotton production as a way to counter the fluctuating market. Revival of inland rice was a consequence of agricultural reform that took hold in select planter circles in the mid-nineteenth century. Lowcountry planters were part of this larger population having received the message through agricultural journals and societies, and scientific books. Promoters of agricultural reform called for a modern and scientific practice of agriculture to maintain soil fertility and crop output, halt westward migration, and curb the loss of status and political power by the South Atlantic states.
Chapter 3 discusses the dramatic transformation of inland rice cultivation between 1730 and the end of the American Revolution as it coincided with the appearance of tidal irrigation. Spurred by the land boom, planters moved rice cultivation from small-stream floodplains down to broad inland basins. To build elaborate infrastructures on these low-lying wetlands, planters had to invest in additional enslaved labor. This chapter argues that the dramatic change in inland rice cultivation was modeled on planters’ development of tidal irrigation along the Lowcountry rivers throughout the mid-eighteenth century. Both the evolving inland system and emerging tidal system required more extensive labor forces than before to create precisely leveled fields, massive embankments, and extensive canals. Creating a more extensive irrigation and drainage network called for a sophisticated understanding of hydrology and soils. With the intense development of rice fields in the Lowcountry basins, inland planters also encountered new problems. Malaria, declining soil fertility, pests, freshets, and droughts all documented how the natural and the built environments could work at cross-purposes.
Chapter 4 highlights the collective effort of four rice plantations on the Wando River headwaters in Charleston County that enabled the owners to cultivate the crop up to the Civil War. This chapter explains how inland cultivation maintained an important presence in the Lowcountry landscape. To illustrate the complex role that inland rice plantations played in contrast to the predominant tidal system, this chapter provides a microanalysis of these four inland plantations – Charleywood, Fairlawn, Clayfield, and Wythewood – from 1783 to 1860. The owners of these tracts aggressively annexed surrounding plantations, intensified water management through canalization, and maintained a substantial enslaved labor population to carry out these tasks. Highlighting these four plantations, this chapter traces the evolution of inland rice culture and describes how it resembled and then swayed from tidal cultivation practices.
Chapter 5 explains how aspiring planters used inland rice plantations as a way of entering the planter aristocracy before the Civil War. Land values, as they relate to shifts in technology and agricultural output, reveal the accessibility for an emerging upper middle-class to enter into the planter elite. During the antebellum period, most productive rice lands were beyond the means of professionals and merchants striving to enter into the upper echelons of society. When put up for sale, tidal rice plantations received a premium price, and most desired lands stayed in families through inheritance or marriage. Land, and rice production, was a means to reflect one’s status and define one’s title in the rigid Lowcountry social hierarchy. Inland rice plantations, on the other hand, were more affordable and did become available to people aspiring to obtain rice planter status, although attempting this mode of social elevation came with monetary and emotional costs. Planters still had to populate their fields with a labor force, often in limited numbers, while the inland environment made difficult any attempts to plant the grain.
Chapter 2 discusses early rice-cultivation strategies in South Carolina from the grain’s approximate introduction in 1685 to the end of the proprietary period in 1729. During this time, colonists transformed the grain from one of several experimental commercial ventures into the central cash crop of early-colonial South Carolina. This chapter also discusses the dynamic relationship of rice farming with topography and culture. European colonists began experimenting with rice cultivation alongside wheat and barley, as well as cotton and tobacco. At the same time, Africans' knowledgeable of growing rice made it thrive in wetland areas for the necessary subsistence gardens. By the turn of the eighteenth century, these two cultural interpretations of rice farming merged to produce grain on small-stream floodplains. At the heart of this chapter is an analysis of how both free and enslaved people used various topographies to cultivate a particular grain and the lasting results that evolved from the early plantation landscape.