Realising traceable electrostatic forces despite non-linear balance motion

Direct realisation of force, traceable to fundamental constants via electromagnetic balances, is a key goal of the proposed redefinition of the international system of units (SI). This will allow small force metrology to be performed using an electrostatic force balance (EFB) rather than subdivision of larger forces. Such a balance uses the electrostatic force across a capacitor to balance an external force. In this paper we model the capacitance of a concentric cylinder EFB design as a function of the displacement of its free electrode, accounting for the arcuate motion produced by parallelogram linkages commonly used in EFB mechanisms. From this model we suggest new fitting procedures to reduce uncertainties arising from non-linear motion as well as methods to identify misalignment of the mechanism. Experimental studies on both a test capacitor and the NIST EFB validate the model

Linear sections of GL(4, 2)

For V = V (n; q); a linear section of GL(V ) = GL(n; q) is a vector subspace S of the n 2 -dimensional vector space End(V ) which is contained in GL(V ) [ f0g: We pose the problem, for given (n; q); of classifying the di erent kinds of maximal linear sections of GL(n; q): If S is any linear section of GL(n; q) then dim S n: The case of GL(4; 2) is examined fully. Up to a suitable notion of equiv- alence there are just two classes of 3-dimensional maximal normalized linear sections M3;M0 3 , and three classes M4;M0 4 ;M00 4 of 4-dimensional sections. The subgroups of GL(4; 2) generated by representatives of these ve classes are respectively G3 = A7; G 0 3 = GL(4; 2); G4 = Z15; G 0 4 = Z3 A5; G 00 4 = GL(4; 2): On various occasions use is made of an isomorphism T : A8 ! GL(4; 2): In particular a representative of the class M3 is the image under T of a subset f1; ::: ; 7g of A7 with the property that 1 i j is of order 6 for all i =6 j: The classes M3;M0 3 give rise to two classes of maximal partial spreads of order 9 in PG(7; 2); and the classes M0 4 ;M00 4 yield the two isomorphism classes of proper semi eld planes of order 16

Realising traceable electrostatic forces despite non-linear balance motion

Direct realisation of force, traceable to fundamental constants via electromagnetic balances, is a key goal of the proposed redefinition of the international system of units (SI). This will allow small force metrology to be performed using an electrostatic force balance (EFB) rather than subdivision of larger forces. Such a balance uses the electrostatic force across a capacitor to balance an external force. In this paper we model the capacitance of a concentric cylinder EFB design as a function of the displacement of its free electrode, accounting for the arcuate motion produced by parallelogram linkages commonly used in EFB mechanisms. From this model we suggest new fitting procedures to reduce uncertainties arising from non-linear motion as well as methods to identify misalignment of the mechanism. Experimental studies on both a test capacitor and the NIST EFB validate the model

Measurement of Submilligram Masses Using Electrostatic Force

The redefinition of the kilogram within the International system of units provides a direct link between mass and Planck's constant. With this in place, it becomes possible to realize the kilogram using electrical metrology. We describe a method that scales this mass measurement approach to the submilligram level using an electrostatic force balance (EFB). Through traceable determination of capacitance, voltage, and position within the balance, the mass values of submilligram artifacts are determined. An uncertainty analysis is carried out on these measurements. Results show a substantial reduction in uncertainty relative to those currently available through conventional approaches based on kilogram subdivision for true mass. Since the EFB measurements are carried out in a vacuum, conversion to conventional mass requires an air buoyancy correction at the location of use. Despite additional uncertainty added by buoyancy correction, the use of the EFB method decreases uncertainty in submilligram mass measurement by an order of magnitude

Prevalence of liver fluke (Fasciola hepatica) in wild Red Deer (Cervus elaphus): coproantigen ELISA is a practicable alternative to faecal egg counting for surveillance in remote populations

Red deer (Cervus elaphus) are hosts of liver fluke (Fasciola hepatica); yet, prevalence is rarely quantified in wild populations. Testing fresh samples from remote regions by faecal examination (FE) can be logistically challenging; hence, we appraise frozen storage and the use of a coproantigen ELISA (cELISA) for F. hepatica surveillance. We also present cELISA surveillance data for red deer from the Highlands of Scotland. Diagnoses in faecal samples (207 frozen, 146 fresh) were compared using a cELISA and by FE. For each storage method (frozen or fresh), agreement between the two diagnostics was estimated at individual and population levels, where population prevalence was stratified into cohorts (e.g., by sampling location). To approximate sensitivity and specificity, 65 post-slaughter whole liver examinations were used as a reference. At the individual level, FE and cELISA diagnoses agreed moderately (κfrozen = 0.46; κfresh = 0.51), a likely reflection of their underlying principles. At the population level, FE and cELISA cohort prevalence correlated strongly (Pearson’s R = 0.89, p < 0.0001), reflecting good agreement on relative differences between cohort prevalence. In frozen samples, prevalence by cELISA exceeded FE overall (42.8% vs. 25.8%) and in 9/12 cohorts, alluding to differences in sensitivity; though, in fresh samples, no significant difference was found. In 959 deer tested by cELISA across the Scottish Highlands, infection prevalence ranged from 9.6% to 53% by sampling location. We highlight two key advantages of cELISA over FE: i) the ability to store samples long term (frozen) without apparent loss in diagnostic power; and ii) reduced labour and the ability to process large batches. Further evaluation of cELISA sensitivity in red deer, where a range of fluke burdens can be obtained, is desirable. In the interim, the cELISA is a practicable diagnostic for F. hepatica surveillance in red deer, and its application here has revealed considerable geographic, temporal, sex and age related differences in F. hepatica prevalence in wild Scottish Highland red deer

Comparison of electrostatic and photon pressure force references at the nanonewton level

This work describes a metrological comparison between nanonewton force references derived from an electrostatic force balance (EFB) and photon pressure from laser optical power in the 1 Watt range. An EFB is used to measure photon pressure force in the 10 nanonewton range from the reflection of a laser from a low (approximately 10−5) loss III–V semiconductor distributed Bragg reflector (DBR) mirror while the power of the reflected beam was simultaneously monitored with a traceable thermopile detector. This work demonstrates a method to link mass, force and laser power within the international system of units (SI) with explicit treatment of absorption, diffuse reflection, and a detailed uncertainty analysis. Additionally, it demonstrates a viable method to scale this force continuously using a pulsed laser technique while maintaining the constant thermal load necessary for precision measurement of nanonewton forces with a mechanical balance

The role of socially driven community food projects in a networked approach to tackling food insecurity

Food insecurity, commonly defined as the inability to acquire or consume an adequate quality or sufficient quantity of food in socially acceptable ways, or the uncertainty that one will be able to do so (Dowler et al, 2001), has come to the forefront of UK political, media and public attention. Neoliberal policies are often cited as a determinant of food insecurity, ultimately leading to inequalities. However the current UK reality of a 'leaner welfare state and an ever-increasing reluctance to interfere with any kind of market' (Lambie-Mumford, 2015, pg. 19) requires the pressing problem of food insecurity to be addressed not only by the State or individual stakeholders but rather by taking a 'networked approach' (ibid). Community food projects may have a role to play in this networked approach. These socially driven, locally based, grass roots organisations are often located in low income communities and undertake a range of initiatives which may have outcomes including increasing economic and physical access to food, improving participants confidence, reducing social isolation (McGlone, 1999). They may also undertake advocacy and lobbying (Lambie-Mumford et al 2014). Whilst 'shifting the responsibility' for tackling food insecurity away from the State toward civil society has been criticised (eg. Fabian Society 2015) the recognition of the current need for a networked approach re-energises the identification of other stakeholders. Therefore, utilising an ongoing case study approach, this research reports on initial findings as to the extent which community food projects can contribute to a networked approach to tackling food insecurit

Potential implications of coronary artery calcium testing for guiding aspirin use among asymptomatic individuals with diabetes.

ObjectiveIt is unclear whether coronary artery calcium (CAC) is effective for risk stratifying patients with diabetes in whom treatment decisions are uncertain.Research design and methodsOf 44,052 asymptomatic individuals referred for CAC testing, we studied 2,384 individuals with diabetes. Subjects were followed for a mean of 5.6 ± 2.6 years for the end point of all-cause mortality.ResultsThere were 162 deaths (6.8%) in the population. CAC was a strong predictor of mortality across age-groups (age <50, 50-59, ≥60), sex, and risk factor burden (0 vs. ≥1 additional risk factor). In individuals without a clear indication for aspirin per current guidelines, CAC stratified risk, identifying patients above and below the 10% risk threshold of presumed aspirin benefit.ConclusionsCAC can help risk stratify individuals with diabetes and may aid in selection of patients who may benefit from therapies such as low-dose aspirin for primary prevention

Milligram mass metrology using an electrostatic force balance

Although mass is typically defined within the International System of Units (SI) at the kilogram level, the pending SI redefinition provides an opportunity to realize mass at any scale using electrical metrology. We propose the use of an electromechanical balance to realize mass at the milligram level using SI electrical units. An integrated concentric-cylinder vacuum gap capacitor allows us to leverage the highly precise references available for capacitance, voltage and length to generate an electrostatic reference force. Weighing experiments performed on 1 mg and 20 mg artifacts show the same or lower uncertainty than similar experiments performed by subdividing the kilogram. The measurement is currently limited by the stability of the materials that compose the mass artifacts and the changes in adsorbed layers on the artifact surfaces as they are transferred from vacuum to air