We present an emf-temperature reference function for platinum versus palladium (Pt/Pd) thermocouples in air for the range 0 EC to 1500 EC. The reference function is based on the International Temperature Scale of 1990 (ITS-90) and has an expanded uncertainty (coverage factor of two) of less than the equivalent of 11 mK for temperatures up to 1050 EC and rising smoothly to approximately 0.3 K at 1500 EC. The reference function is based on a set of Pt/Pd thermocouples of exceptional stability and homogeneity constructed from Pt and Pd wire of very high purity (99.999% mass fraction and 99.997% mass fraction, respectively). Experimental results are presented on the thermoelectric stability of Pt/Pd thermocouples at high temperatures and on the calibration of Pt/Pd thermocouples based on this reference function.

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We report the characterization of gold nanoparticles modified with thiol-terminated single stranded DNA (ssDNA) using analytical ultracentrifugation. Dynamic light scattering was used to measure the diameter of bare and ssDNA modified gold nanoparticles to corroborate the predictions of our models. Sedimentation coefficients of nominally 10 and 20 nm diameter gold nanoparticles modified with thiol-terminated thymidine homo-oligonucleotides, 5-30 bases in length, were determined with analytical ultracentrifugation. The sedimentation coefficients of gold nanoparticles modified with ssDNA were found to decrease with increasing coverage of ssDNA and increasing length of ssDNA. The sedimentation coefficients of ssDNA modified gold particles were most closely predicted when the strands were modeled as fully extended chains (FEC). Apparent particle densities of bare gold nanoparticles calculated from measured sedimentation coefficients decreased significantly below that of bulk gold with decreasing size of nanoparticles. This finding suggests that hydration layer effects are an important factor in the sedimentation behavior for both bare and short ssDNA chain modified gold particles.

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The NIST acoustic thermometer determines the thermodynamic temperature from measurements of ratios of the speed of sound of argon in a nearly spherical cavity. We report recent results for T − T 90 on 12 isotherms spanning the range 271-552 K. (T is the thermodynamic temperature and T 90 is the temperature on the International Temperature Scale of 1990.) The results are in excellent agreement with recent acoustic thermometry results reported by Benedetto et al. in the range from 273 to 380 K and with our previously reported results at 303, 430, and 505 K. The combined data sets are sufficiently redundant and sufficiently distributed over the temperature range to support a re-determination of the reference function for standard platinum resistance thermometers for a future temperature scale. The isotherms were analyzed using several methods; the T − T 90 results and related uncertainties are insensitive to the method chosen. The thermal expansion of the stainless-steel resonator was deduced from the frequencies of the microwave resonances of the cavity. To clearly identify two nearly degenerate eigenmodes in our nearly axially symmetric resonator, two phased coupling probes were used to control the azimuthal angle of the microwave excitation.