Thermodynamic effects in a gas modulated Invar-based dual Fabry-Pérot cavity refractometer

By measuring the refractivity and the temperature of a gas, its pressure can be assessed from fundamental principles. The highest performing instruments are based on Fabry-Perot cavities (FPC). Gas modulation refractometry (GAMOR) is a methodology that has the ability to reduce the influence of disturbances to such an extent that high-precision (sub-parts-per-million) assessments of pressure can be made by the use of FPCs of Invar. To allow for high accuracy assessments, it is of importance to assess the uncertainty contribution from the thermodynamic effects that are associated with the gas filling and emptying of the cavity (pV-work). This paper presents a detailed scrutiny of the influence of the gas exchange process on the assessment of gas temperature on an Invar-based dual-FPC (DFPC) instrumentation. It is shown that by virtue of a combination of a number of carefully selected design entities (a small cavity volume with a bore radius of 3 mm, a spacer material with high heat capacitance, large thermal conductivity, and no regions that are connected with low thermal conductance, i.e. no heat islands, and a continuous assessment of temperature of the cavity spacer) the system is not significantly affected by pV-work. Simulations show that 10 s after the filling all temperature gradients in the system are well into the sub-mK range. Experiments support that refractivity assessments initiated after 40 s are not significantly affected by the pV-work. The analysis given in this work indicates that an upper limit for the influence of pV-work on the Invar-based DFPC system using 100 s long gas modulation cycles is 0.5 mK/100 kPa (or 1.8 ppm/100 kPa). Consequently, thermodynamic effects will not be a limiting factor when the Invar-based DFPC GAMOR system is used for assessments of pressure or as a primary pressure standard up to atmospheric pressures

P-fimbriae in the presence of anti-PapA antibodies : new insight of antibodies action against pathogens

Uropathogenic strains of Escherichia coli establish urinary tract infections by attaching to host epithelial cells using adhesive organelles called fimbriae. Fimbriae are helix-like structures with a remarkable adaptability, offering safeguarding for bacteria exposed to changing fluid forces in the urinary tract. We challenged this property of P-fimbriae by cross-linking their subunits with shaft-specific antibodies and measuring the corresponding force response at a single organelle level. Our data show compromised extension and rewinding of P-fimbriae in the presence of antibodies and reduced fimbrial elasticity, which are important properties of fimbriae contributing to the ability of bacteria to cause urinary tract infections. The reduced elasticity found by cross-linking fimbrial subunits could thus be another assignment for antibodies; in addition to marking bacteria as foreign, antibodies physically compromise fimbrial function. We suggest that our assay and results will be a starting point for further investigations aimed at inhibiting sustained bacterial adhesion by antibodies