ABSTRACT
This paper demonstrates an optical technique to measure magnetostrictive strain in a cryogenic environment using a Fabry-Pérot resonator spaced by crystal samples. Optical measurement techniques are calibration-free and highly sensitive. This technique was used to measure the magnetostrictive strain of neodymium gallate at a temperature of 49 mK to be λ = 1.3 × 10-5 at 3 T, with a sensitivity of 3.0 × 10-8. We highlight the interesting properties of the crystal's magnetic ordering. The sensitivity of this technique was limited by the wavemeter used to measure the laser frequency, and significant improvements in the sensitivity should be possible.
ABSTRACT
The intra-cavity electro-magnetic field distribution in a microdisk resonator can be visualised by inducing a phase shift via a scanning probe beam.
ABSTRACT
Small perturbations in the dielectric environment around resonant dielectric structures usually lead to a frequency shift of the resonator modes directly proportional to the polarizability of the perturbation. Here, we report experimental observations of strong frequency shifts that can oppose and even exceed the contribution of the perturbations' polarizability. We show in particular how the mode frequencies of a lithium niobate whispering-gallery-mode resonator are shifted by planar substrates-of refractive indices ranging from 1.50 to 4.22-contacting the resonator rim. Both blue- and redshifts are observed, as well as an increase in mode linewidth, when substrates are moved into the evanescent field of the whispering gallery mode. We compare the experimental results to a theoretical model by Foreman et al. [J. Opt. Soc. Am. B33, 2177 (2016)JOBPDE0740-322410.1364/JOSAB.33.002177] and provide an additional intuitive explanation based on the Goos-Hänchen shift for the optical domain, with applications to dielectric structures ranging from meta-surfaces to photonic crystal cavities.
ABSTRACT
PURPOSE: To explore the factors involved in the demise of tunnelled central vascular access devices (CVADs) in children and describe patterns of failure. METHODS: A retrospective study including children under 16 years of age undergoing CVAD insertion in a tertiary centre between October 2014 and December 2019. The Kaplan-Meier estimator was used to study CVAD survival and piecewise exponential curves to approximate hazard rates. Related factors were analysed using multivariable regression. RESULTS: Totally, 684 CVADs were inserted in 499 children. Devices were in situ for 213,821 days (median 244.5). Of those, 261 CVADs (38.2%) failed prematurely; 176 (67%) required replacement. Tunnelled external lines (TELs) failed more frequently than totally implantable devices (p < 0.005).TEL displacement occurred in two high-risk phases, falling to baseline after 90 days. Low age at device insertion and open placement were strongly associated with an increased failure rate. Previous CVAD failure did not increase subsequent failure rate. Premature failure increased procedural cost by £153,949 per year. CONCLUSIONS: TIDs should be placed in preference to TELs where appropriate. TELs are at highest risk of displacement for 90 days and must be well secured for this duration. Meticulous line care offers significant potential cost savings by reducing line replacements. LEVEL OF EVIDENCE: Level III.
Subject(s)
Catheterization, Central Venous/instrumentation , Catheters, Indwelling/adverse effects , Central Venous Catheters/adverse effects , Equipment Failure/statistics & numerical data , Child , Child, Preschool , Female , Humans , Male , Retrospective Studies , Survival Analysis , United KingdomABSTRACT
A metallic double dot is measured with radio frequency reflectometry. Changes in the total electron number of the double dot are determined via single electron tunnelling contributions to the complex electrical impedance. Electron counting experiments are performed by monitoring the impedance, demonstrating operation of a single electron ammeter without the need for external charge detection.
