Ultra-broadband contactless imaging power meter

Knowledge of the spatial and temporal distribution of heat flux is of great interest for the quantification of heat sources. In this work, we describe the development of a new ultra-broadband contactless imaging power meter based on electromagnetic to infrared technology. This new sensor and the mathematical processing of images enable the reconstruction of both spatial and amplitude distributions through a wide spectral range of sources. The full modeling of the thermoconverter based on 3D formalism of thermal quadrupoles is presented first before deriving a reduced model more suitable for quick and robust inverse processing. The inverse method makes it possible to simultaneously identify the heat losses and the spatial and temporal source distribution for the first time, to the best of our knowledge. Finally, measurements of multispectral sources are presented and discussed, with an emphasis on the spatial and temporal resolution, accuracy and capabilities of the power meter.

Pressure ulcers prevention efficacy of an alternating pressure air mattress in elderly patients: E²MAO a randomised study

OBJECTIVE

Our aim was to compare Axtair One, an alternating pressure air mattress (APAM), with a viscoelastic foam mattress (VFM) in elderly patients at moderate to high risk of developing pressure ulcers (PUs).

METHOD

A randomised, controlled, superiority, parallel-group, open-label, multicentre study, was conducted, between February 2012 and March 2015, in nine French, medium- and long-term stay facilities. Eligible patients were aged 70 and over, had no PUs on enrolment, were bedridden for at least 15 hours per day, had reduced mobility, an absent or minimal positioning capability, a Braden score <14, a nutritional status score >12 and a Karnofsky score <40%. The primary endpoint was the appearance of PUs over a 30-day monitoring period. The primary objective was to demonstrate a 50% reduction in instantaneous risk of PUs in the APAM versus the VFM group. Secondary objectives were to determine if preventive care was less frequent in the APAM group, the instantaneous relative risk of PUs (hazard ratio) was constant over time and the comfort experienced was higher in the APAM group and to verify the uniformity of the preventive benefit of an APAM, regardless of the level of exposure to major risk factors for PUs.

RESULTS

We randomised 76 patients (39 in the APAM group and 37 in the VFM group). The groups were comparable on enrolment and throughout the study. The cumulative risk of PUs was estimated at 6.46% [95% confidence interval (CI): 1.64; 23.66] in the APAM group and at 38.91% [95% CI: 24.66; 57.59] in the VFM group, p=0.001 (log-rank test). The adjusted hazard ratio according to the Cox model with four prognostic factors for the appearance of PUs was 7.57 [95% CI: 1.67; 34.38, p=0.009]. Preventive care proved to be equivalent in both groups. The only risk factor significantly associated with an increased risk of PUs was the type of mattress (VFM). The comfort and tolerance perceived by the patients were both high and similar in the two groups. The constancy over time of the preventive benefit of an APAM could not be verified because of the lack of a sufficient number of events (appearance of PUs) in the APAM group.

CONCLUSION

The APAM was superior to a VFM for preventing PUs in elderly patients, bedridden for more than 15 hours per day, severely dependent, at moderate-to high-risk of PUs, with an instantaneous risk for the appearance of PUs 7.57 times greater in the VFM group than in the APAM group. This study provides descriptive information and evidence for practice.

Thermoreflectance temperature measurement with millimeter wave

GigaHertz (GHz) thermoreflectance technique is developed to measure the transient temperature of metal and semiconductor materials located behind an opaque surface. The principle is based on the synchronous detection, using a commercial THz pyrometer, of a modulated millimeter wave (at 110 GHz) reflected by the sample hidden behind a shield layer. Measurements were performed on aluminum, copper, and silicon bulks hidden by a 5 cm thick Teflon plate. We report the first measurement of the thermoreflectance coefficient which exhibits a value 100 times higher at 2.8 mm radiation than those measured at visible wavelengths for both metallic and semiconductor materials. This giant thermoreflectance coefficient κ, close to 10(-3) K(-1) versus 10(-5) K(-1) for the visible domain, is very promising for future thermoreflectance applications.

High speed heterodyne infrared thermography applied to thermal diffusivity identification

We have combined InfraRed thermography and thermal wave techniques to perform microscale, ultrafast (microsecond) temperature field measurements. The method is based on an IR camera coupled to a microscope and synchronized to the heat source by means of phase locked function generators. The principle is based on electronic stroboscopic sampling where the low IR camera acquisition frequency f(acq) (25 Hz) undersamples a high frequency thermal wave. This technique permits the measurement of the emissive thermal response at a (microsecond) short time scale (microsecond) with the full frame mode of the IR camera with a spatial thermal resolution of 7 μm. Then it becomes possible to study 3D transient heat transfer in heterogeneous and high thermal conductive thin layers. Thus it is possible for the first time in our knowledge to achieve temperature field measurements in heterogeneous media within a wide range of time domains. The IR camera is now a suitable instrument for multiscale thermal analysis.

From intermittent to nonintermittent behavior in two dimensional thermal convection in a soap bubble

Turbulent thermal convection in half a soap bubble heated from below displays a new and surprising transition from intermittent to nonintermittent behavior for the temperature field. This transition is observed here by studying the high order moments of temperature increments. For high temperature gradients, these structure functions display Bolgiano-like scaling predicted some 60 years ago with no observable deviations. The probability distribution functions of these increments are Gaussian throughout the scaling range. These measurements are corroborated with additional velocity structure function measurements.