Frequency shift algorithm: Application to a frequency-domain multiplexing readout of x-ray transition-edge sensor microcalorimeters.

In the frequency-domain multiplexing (FDM) scheme, transition-edge sensors (TESs) are individually coupled to superconducting LC filters and AC biased at MHz frequencies through a common readout line. To make efficient use of the available readout bandwidth and to minimize the effect of non-linearities, the LC resonators are usually designed to be on a regular grid. The lithographic processes, however, pose a limit on the accuracy of the effective filter resonance frequencies. Off-resonance bias carriers could be used to suppress the impact of intermodulation distortions, which, nonetheless, would significantly affect the effective bias circuit and the detector spectral performance. In this paper, we present a frequency shift algorithm (FSA) to allow off-resonance readout of TESs, while preserving the on-resonance bias circuit and spectral performance, demonstrating its application to the FDM readout of an x-ray TES microcalorimeter array. We discuss the benefits in terms of mitigation of the impact of intermodulation distortions at the cost of increased bias voltage and the scalability of the algorithm to multi-pixel FDM readout. We show that with FSA, in the multi-pixel and frequencies shifted on-grid, the line noises due to intermodulation distortion are placed away from the sensitive region in the TES response and the x-ray performance is consistent with the single-pixel, on-resonance level.

Study of the Dependency on Magnetic Field and Bias Voltage of an AC-Biased TES Microcalorimeter.

At SRON we are studying the performance of a Goddard Space Flight Center single pixel TES microcalorimeter operated in an AC bias configuration. For x-ray photons at 6 keV the pixel shows an x-ray energy resolution ΔEFWHM =3.7 eV, which is about a factor 2 worse than the energy resolution observed in an identical DC-biased pixel. In order to better understand the reasons for this discrepancy we characterised the detector as a function of temperature, bias working point and applied perpendicular magnetic field. A strong periodic dependency of the detector noise on the TES AC bias voltage is measured. We discuss the results in the framework of the recently observed weak-link behaviour of a TES microcalorimeter.

A transiting giant planet with a temperature between 250 K and 430 K.

Of the over 400 known exoplanets, there are about 70 planets that transit their central star, a situation that permits the derivation of their basic parameters and facilitates investigations of their atmospheres. Some short-period planets, including the first terrestrial exoplanet (CoRoT-7b), have been discovered using a space mission designed to find smaller and more distant planets than can be seen from the ground. Here we report transit observations of CoRoT-9b, which orbits with a period of 95.274 days on a low eccentricity of 0.11 +/- 0.04 around a solar-like star. Its periastron distance of 0.36 astronomical units is by far the largest of all transiting planets, yielding a 'temperate' photospheric temperature estimated to be between 250 and 430 K. Unlike previously known transiting planets, the present size of CoRoT-9b should not have been affected by tidal heat dissipation processes. Indeed, the planet is found to be well described by standard evolution models with an inferred interior composition consistent with that of Jupiter and Saturn.

A comparison of hand-held isometric strength measurement with isokinetic muscle strength measurement in the elderly.

OBJECTIVE: To compare hand-held isometric muscle strength measurement to an isokinetic muscle strength measurement in a healthy elderly population. DESIGN: Cross-sectional survey. SETTING: Retirement community in Southeastern Arizona. PARTICIPANTS: Thirty-two volunteers (16 men and 16 women) age 60 and over (mean age 70.3 years) who were free of musculoskeletal problems and did not have significant health problems. INTERVENTIONS: None. MEASUREMENTS: Isometric muscle strength was determined using a hand-held isometric strength device (Penny and Giles) for elbow flexion and extension and knee flexion and extension. Isokinetic muscle strength (average peak torque and average work per repetition) was measured on the same individuals using a Lido isokinetic dynamometer. RESULTS: Correlations between the strength measurement techniques were generally favorable with the lowest correlation being .72, (95 percent confidence interval .50-.86) and the highest being .85, (95 percent confidence interval .72-.93). However, there was substantial variability of hand-held strength reading at some levels of isokinetic strength. CONCLUSIONS: Hand-held dynamometry for strength measurement correlates strongly with measurement of strength using isokinetic dynamometry. Despite these high correlations, there is remaining variability of hand-held muscle strength readings when compared with isokinetic strength measurement at some levels of isokinetic muscle strength. Modification of the testing methodology or instrumentation used in this study is needed to improve the consistency of these measurements.