The characteristics of the Geological Survey TRIGA Reactor (GSTR) as a source of fast neutrons for the 40Ar/3 Ar technique of K-Ar dating have been determined using data from more then 45 irradiations in the central thimble (core) facility. The GSTR has a flux over the entire energy spectrum of 1.1 x 1017 n/cm2-MWH and a fast/thermal ratio on the centerline of the central thimble of 117 for fast neutron energies greater than 0.6 MeV. Production of 39Ar is about? x 10~13 mole/gram-percent KgO MWH, and the cross section for the reaction 39K(n, p) 39Ar is 65 ± 4 millibarns for epithermal (> 0.6 MeV) neutrons. Most 4 Ar/ Ar dating applications require about 10-40 hours of irradiation in the GSTR at the maximum continuous power level of 1 MW. The peak neutron flux in the central thimble is 4 cm above the physical centerline, and the verticle flux gradient in the centermost 20 centimeters varies from a small fraction of a percent to a maximum of about 3.5 percent per centimeter. The effect of this gradient can be effectively cancelled by suitable sample encapsulation and the use of a sample holder designed for the purpose. The horizontal flux gradient is less than 0.5 percent over the width of the central thimble. Self-shielding in a solid core of diabase 2.40 cm in diameter and 2.54 cm high is approximately 3 percent from the outside to the center, but self-shielding is probably negligible for the smaller samples usually irradiated for K-Ar dating. Corrections for interfering Ar isotopes produced by neutron reactions with Ca are relatively reproducible with values of 2.64 ± 0.017 x 10~4 for (36Ar/ 37Ar) Ca and 6.73 ± 0.037 x 1Q~4 for (39Ar/37Ar) Ca. The measured values for (40Ar/ 39Ar)ic, however, vary by an order of magnitude. This variability, whose cause is unknown, has been reported from other reactors. The corrections for interfering Ar isotopes can be minimized by using optimization curves for the GSTR to choose the best sample size and irradiation time for a given material. Of more than 100 possible neutron reactions in common rocks and minerals, only 26 need be considered for purposes of radiological safety. The activity produced by these reactions upon irradiation of samples can be conveniently and accurately predicted either by a computer program or from graphs specifically devised for the GSTR.

Context The effects of COVID-19 on the thyroid axis remain uncertain. Recent evidence has been conflicting, with both thyrotoxicosis and suppression of thyroid function reported. Objective We aimed to detail the acute effects of COVID-19 on thyroid function and determine if these effects persisted on recovery from COVID-19. Design A cohort observational study was conducted. Participants and Setting Adult patients admitted to Imperial College Healthcare National Health Service Trust, London, UK, with suspected COVID-19 between March 9 to April 22, 2020, were included, excluding those with preexisting thyroid disease and those missing either free thyroxine (FT4) or thyrotropin (TSH) measurements. Of 456 patients, 334 had COVID-19 and 122 did not. Main Outcome Measures TSH and FT4 measurements were recorded at admission, and where available, in 2019 and at COVID-19 follow-up. Results Most patients (86.6%) presenting with COVID-19 were euthyroid, with none presenting with overt thyrotoxicosis. Patients with COVID-19 had a lower admission TSH and FT4 compared to those without COVID-19. In the COVID-19 patients with matching baseline thyroid function tests from 2019 (n = 185 for TSH and 104 for FT4), TSH and FT4 both were reduced at admission compared to baseline. In a complete case analysis of COVID-19 patients with TSH measurements at follow-up, admission, and baseline (n = 55), TSH was seen to recover to baseline at follow-up. Conclusions Most patients with COVID-19 present with euthyroidism. We observed mild reductions in TSH and FT4 in keeping with a nonthyroidal illness syndrome. Furthermore, in survivors of COVID-19, thyroid function tests at follow-up returned to baseline.

Jumping spiders (Salticidae) rely on accurate depth perception for predation and navigation. They accomplish depth perception, despite their tiny brains, by using specialized optics. Each principal eye includes a multitiered retina that simultaneously receives multiple images with different amounts of defocus, and from these images, distance is decoded with relatively little computation. We introduce a compact depth sensor that is inspired by the jumping spider. It combines metalens optics, which modifies the phase of incident light at a subwavelength scale, with efficient computations to measure depth from image defocus. Instead of using a multitiered retina to transduce multiple simultaneous images, the sensor uses a metalens to split the light that passes through an aperture and concurrently form 2 differently defocused images at distinct regions of a single planar photosensor. We demonstrate a system that deploys a 3-mm-diameter metalens to measure depth over a 10-cm distance range, using fewer than 700 floating point operations per output pixel. Compared with previous passive depth sensors, our metalens depth sensor is compact, single-shot, and requires a small amount of computation. This integration of nanophotonics and efficient computation brings artificial depth sensing closer to being feasible on millimeter-scale, microwatts platforms such as microrobots and microsensor networks.

No abstract

As evidence questioning the rationale behind neoadjuvant chemotherapy in breast cancer grows, Jayant Vaidya and colleagues say we must reconsider the current treatment options

Background: Sub-optimal nutrition among children remains a problem across South Asia (SA). Appropriate complementary feeding practices (CFP) can greatly reduce this risk. The primary objective of this systematic review (SR) of CF studies was to assess timing, dietary diversity, meal frequency and influencing factors in children under two in Bangladesh.

No abstract

ObjectiveSuboptimal nutrition among children remains a problem among South Asian (SA) families. Appropriate complementary feeding (CF) practices can greatly reduce this risk. Thus, we undertook a systematic review of studies assessing CF (timing, dietary diversity, meal frequency and influencing factors) in children aged <2 years in Pakistan.DesignSearches between January 2000 and June 2016 in MEDLINE, EMBASE, Global Health, Web of Science, OVID Maternity & Infant Care, CINAHL, Cochrane Library, BanglaJOL, POPLINE and WHO Global Health Library. Eligibility criteria: primary research on CF practices in SA children aged 0–2 years and/or their families. Search terms: ‘children’, ‘feeding’ and ‘Asians’ with their derivatives. Two researchers undertook study selection, data extraction and quality appraisal (EPPI-Centre Weight of Evidence).ResultsFrom 45 712 results, seventeen studies were included. Despite adopting the WHO Infant and Young Child Feeding guidelines, suboptimal CF was found in all studies. Nine of fifteen studies assessing timing recorded CF introduced between 6 and 9 months. Five of nine observed dietary diversity across four of seven food groups; and two of four, minimum meal frequency in over 50 % of participants. Influencing factors included lack of CF knowledge, low maternal education, socio-economic status and cultural beliefs.ConclusionsThis is the first systematic review to evaluate CF practices in Pakistan. Campaigns to change health and nutrition behaviour are needed to meet the substantial unmet needs of these children.