Tailoring the sampling time of single-sample GFR measurement according to expected renal function: a multisite audit.

Background: The 2018 BNMS Glomerular Filtration Rate (GFR) guidelines recommend a single-sample technique with the sampling time dictated by the expected renal function, but this is not known with any accuracy before the test. We aimed to assess whether the sampling regime suggested in the guidelines is optimal and determine the error in GFR result if the sample time is chosen incorrectly. We can then infer the degree of flexibility in the sampling regime.

Observation of residual disorder in the centre of amorphous solid water films after pore collapse at 125 K.

The rapid structural re-organisation of porous amorphous solid water, grown to thicknesses in the range 2.5-70 μm by vapour deposition on a copper substrate at 75 K, after heating to 125 K has been found to leave a μm-wide band of residual disorder-for example, nm-sized closed pores-in the centre of the film. This layer was revealed by thinning the film by sublimation and continuously measuring the fraction of 1.

Structural changes in amorphous solid water films on heating to 120-140 K and 150-160 K seen by positronium annihilation spectroscopy.

Changes in the structure of amorphous solid water films, grown by vapour deposition on a copper substrate at 75 K and then held at 120 K for 10 min to effect pore collapse, have been observed in the ranges 122-139 K and 150-162 K using positronium annihilation spectroscopy. It is proposed that the former is associated with the glass transition, with an effective activation energy of 0.266(3) eV.

Structure and sublimation of water ice films grown in vacuo at 120-190 K studied by positron and positronium annihilation.

The crystalline structure of ∼ 5-20 μm water ice films grown at 165 and 172 K has been probed by measuring the fraction of positrons forming ortho-positronium (ortho-Ps) and decaying into three gamma photons. It has been established that films grown at slower rates (water vapour pressure ≥ 1 mPa) have lower concentrations of lattice defects and closed pores, which act as Ps traps, than those grown at higher rates (vapour pressure ∼ 100 mPa), evidenced by ortho-Ps diffusion lengths being approximately four times greater in the former. By varying the growth temperature between 162 and 182 K it was found that films become less disordered at temperatures above ∼ 172 K, with the ortho-Ps diffusion length rising by ∼ 60%, in this range.

Measuring the three-photon self-annihilation fraction of positronium in and above thin films: a tool for determining film morphology.

A technique is described for evaluating the fraction of positrons F incident on thin film samples which form ortho-positronium and subsequently decay into three gamma photons. The method involves the measurement of two linked phenomena: the decrease in the number of annihilation events involving the emission of two gamma photons with approximately 511 keV in the germanium detector photopeak, and the increase in the number of decays into three gamma photons with energies in the range 395-505 keV. After the application of a number of systematic corrections to the raw data, these measurements allow the determination of the absolute value of F without the need for calibration on a sample with known F values, thereby avoiding problems with changing samples of different geometries measured under different conditions.