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Flexible capacitive humidity sensors are promising for low-cost, wearable, and radio frequency identification sensors, but their nonlinear response is an important issue for practical applications. Herein, the linearity of humidity response was controlled by surface water wettability and operating frequency of sensor, and the mechanism was explained in detail by surface water condensation. For a sensor with a Ag interdigitated electrode (IDE) on a poly(ethylene terephthalate) substrate, the capacitance showed a small linear increase with humidity up to 70% RH but a large nonlinear increase in the higher range. The response linearity was increased by a hydrophobic surface treatment of self-assembled monolayer coating while it was decreased by an ultraviolet/ozone irradiation for hydrophilicity. It was also increased by increasing the frequency in the range of 1–100 kHz, more prominently on a more hydrophilic surface. Based on experiment and simulation, the increase in sensor capacitance was greatly dependent on the geometric pattern (e.g., size, number, and contact angle) and electrical permittivity of surface water droplets. A larger and more nonlinear humidity response resulted from a larger increase in the number of droplets with a smaller contact angle on a sensor surface with higher water wettability and also from a higher permittivity of water at a lower frequency.

A mammography system, a conventional radiological equipment and a CT scanner operated at 120 kV were used to investigate the reproducibility, the sensitivity and the response linearity to a variety of X-ray tube current, high-voltage and dose values of a radio-luminescent dosimeter based on a Ce-doped optical fiber. The dosimeter reproducibility was very close to the ionization chamber reproducibility. The detector sensitivity was also calculated in order to evaluate the minimum detectable dose rate and a minimum detectable dose, considering a sampling time of 10 ms. All curves have a very good linear course with a correlation coefficient greater than 0.999. The fiber sensitivity (counts per unit dose) as a function of the X-ray tube voltage obtained with the conventional X-ray equipment decreases by increasing the photon energy, losing about 10% of its value from 60 to 120 kV. Also for CT scanner, the fiber responses are very good and reproducible. The new dosimetric system is complementary to usual dosimetry systems as ionization chambers, since it is mostly suitable for in vivo and on-line dosimetry. Scintillating fibers are very safe because they are not electrically powered and moreover they assure very high spatial resolution due to their reduced dimensions. © 2009 Elsevier B.V. All rights reserved.

The present study was conducted in order to (1) investigate the linearity of subjec-tive sleepiness scales and (2) to contribute to the debate about the nature of the in-teraction between circadian (C) and homeostatic (S) processes in models of alert-ness-sleepiness regulation. In this study, a partial sleep deprivation experiment was conducted and replicated using symbolic stimuli. Our findings provide support for the linearity of subjective sleepiness scales. Consistent with the basic assumptions of the model an additive integration of processes S and C was observed in a major-ity of participants, which suggests the independence of both processes during the biological day.

The present studies were conducted in order to contribute to the debate about the interaction between circadian (C) and homeostatic (S) processes in models of sleep regulation. One of the basic assumptions of Borbély's Two-Process Model of Sleep Regulation (Hum Neurobiol 1982) is that Process S and Process C act independently from each other. However, forced desynchrony studies and experiments where participants were subjected to different light exposure suggest an interaction between Process S and C. Whether this interaction is linear or non-linear, let alone genuine, remains undetermined as long as no evidence is reported of the linearity of the used metrics. Within psychophysics, Functional Measurement (Anderson, LEA 2001) allows for validation of both the response scale and the integration of both processes. Within this framework we propose a partial (n=13) and a total sleep deprivation study (n=23) along with their experimental replications using symbolic stimuli in order to assess the linearity of response scales. Our findings suggest that the integration of Process S and C is strictly additive during the course of the biological day and provide proof of the linearity of subjective sleepiness measures (KSS, VAS). According to the concept of generality (Anderson, LEA 2001), if a response measure is found to be linear in a specific integration task, it is likely to be linear in other similar integration tasks. Therefore, non-linear interactions suggested in models of sleep regulations using subjective measures of sleepiness may be considered as genuine.

This paper describes the measurement methods and the instrumentation used in the realization and transfer of the NBS scale of spectral irradiance. The basic measurement equation for the irradiance realization is derived. The spectral responsivity function, linearity of response, and “size of source” effect of the spectroradiometer are described. The analysis of sources of error and the estimates of uncertainty are described. The assigned uncertainties (3σ level) in spectral irradiance range from 2.2% at 250 nm to 1.0% at 654.6 nm to 6.5% at 2400 nm.

This paper describes the measurement methods and instrumentation used in the realization and transfer of the In­ ternational Practical Temperature Scale (lPTS-68) above the temperature of. freezing gold. The determination of the ratios of spectral radiance of tung­ sten-strip lamps to a gold-point black­ body at a wavelength of 654.6 nm is detailed. The response linearity, spec­ tral responsivity, scattering error, and polarization properties of the instru­ mentation are described. The analysis of sources of error and estimates of uncertainty are presented. The as­ signed uncertainties (three standard deviations) in radiance temperature range from ±2 K at 2573 K to ±O.5 Kat 1073 K.