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The calibration of Pt/Rh thermocouples up to 1560 $$^{\circ }\hbox {C}$$ at NMIA currently uses the conventional 'melt-wire technique' to realize Gold (Au) and Palladium (Pd) melting points, resulting in the loss of 20 mm of wire from the junction end for each calibration. To avoid this loss, NMIA intends to replace the melt-wire technique with the use of miniature fixed-point cells. NMIA has established Copper (Cu) and Cobalt-Carbon (Co-C) eutectic cells for calibration of thermocouples to 1324 $$^{\circ }\hbox {C}$$ . To extend the calibration up to 1500 $$^{\circ }\hbox {C}$$ , miniature Palladium-Carbon (Pd-C) eutectic cells (1492 $$^{\circ }\hbox {C}$$ ) have been constructed and tested in collaboration with NMIJ, AIST. Although these cells are made of high-purity reference materials, careful consideration must be given to contamination introduced during the manufacture and filling of the crucibles and by their long-term use. These issues can only be assessed by measurement of cell-to-cell temperature differences within the ensemble of cells traceable to ITS-90. In the work presented here, 3 NMIA-design mini Pd-C cells were constructed: 1 at NMIA and 2 at NMIJ. These cells were compared, together with a 'large' NMIJ Pd-C cell, using type-R, type-B and Pt/Pd thermocouples and radiation thermometry. Although the cells are found to be stable and repeatable, significant problems arising from migration of Pd to the thermocouples were identified. [ABSTRACT FROM AUTHOR]

Comparisons between NMIA and NMIJ on the melting temperatures of the Co-C eutectic point and the Pd-C eutectic point were performed using an NMIJ high-temperature furnace. The eutectic-point cells were constructed by NMIA and NMIJ following two different specifications. NMIA designed two miniature crucibles, one for Co-C and one for Pd-C eutectic-point cells. NMIJ designed larger eutectic-point cells, one for Co-C and one for Pd-C eutectic-point cells. Prior to performing the comparisons, the effect of conductive heat flow through the thermocouple stem was evaluated during the melting. The comparisons of the Co-C eutectic-point cells and of the Pd-C eutectic-point cells were performed using types R, B and Pt/Pd thermocouples. Despite the different cell designs and different material sources, the melting temperatures of the Co-C and Pd-C eutectic-point cells under investigation agreed within 0.1 $$\,{^{\circ }}\hbox {C}$$ . [ABSTRACT FROM AUTHOR]

The growing complexity and functionality of modern microwave systems put increasing demands on the performance and reliability of RF control devices. Low channel sheet resistance in the on-state and small leakage currents in the off-state, extremely high breakdown voltages, chemical inertness and planar structure make III-nitride heterostructure-based devices uniquely suitable for the next-generation switching devices. The AlInN-based devices and devices using low-conducting layers for controlling surface field and surface charges are expected to further boost the performance. This paper presents a review of III-nitride control devices based on heterostructure field-effect transistors (HFETs), insulated gate HFETs (MISHFETs) and novel capacitively coupled contact and frequency configurable electronics technologies. [ABSTRACT FROM AUTHOR]

NMIA, radiation thermometers are calibrated by comparison with a number of reference radiation thermometers which are themselves calibrated using fixed-point cells on the ITS-90 temperature scale (In, Sn, Zn, Al, Ag, and Au). The suitability of NMIA fixed-point cells used for standard platinum resistance thermometers (SPRTs) is evaluated by the comparison of ensembles of cells at each fixed point, and by participation in the international BIPM Key-Comparisons K3 and K4. However, the NMIA fixed-point cells used for radiation thermometry are typically much smaller (only 110 mm in length) and the thermowell length immersed in the metal much shorter (85 mm) than those used for SPRTs. Further, the insulation at the front of the crucible needs to accommodate the F/10 viewing cone of the radiation thermometers, so significant temperature gradients exist near the top of the crucible. As a consequence, the conduction errors obtained using SPRTs are too large to be of practical use. A convenient methodology based on the use of a Au/Pt thermocouple, together with a protective tube assembly to reduce conduction errors, has been developed. This allows the convenient measurement of the phase transition temperature traceable, at the 30 mK level, to the fixed-point cells used at NMIA to realize and maintain the ITS-90 scale. As the measurements are made in situ, the temperature environment, and hence the geometry and formation of the liquid-solid interface during melting and freezing, are similar to that occurring when used with radiation thermometers. Results are presented for ITS-90 fixed points up to Ag, establishing formal traceability of radiation thermometry fixed-point cells to NMIA's primary ITS-90 cells. [ABSTRACT FROM AUTHOR]

Type R (Pt-13 %Rh versus Pt) and type S (Pt-10 %Rh versus Pt) thermocouples are widely used as reference and working standards for temperature measurements both in calibration laboratories and in industry for temperatures up to 1600 °C. Many laboratories claim that the best achievable uncertainty is 0.1 °C up to 1000 °C and 0.3 °C up to 1550 °C, and international comparisons confirm that this is achievable practically. However, due to (i) preferential Rh oxidation of the Pt-Rh alloy thermoelement and (ii) defect quenching effects, these thermocouples suffer from reversible hysteresis in their calibration. As a result, calibration laboratories usually perform some heat treatment of the wire prior to calibration to attain a specific 'annealing state', at which the calibration is performed. Internationally, there are two commonly used annealing states for these thermocouples: the '450 °C annealed state' and the '1100 °C quenched state'. High-level comparisons between laboratories in the calibration of type R or type S thermocouples will rigorously specify the annealing state in the protocol, so any systematic differences due to the choice of annealing state will be masked. This article compares the calibration of several thermocouples using the two common annealing states, finding that the difference can be as large as 0.2 °C at 961 °C, larger than the best calibration uncertainties reported. The article examines the advantages and disadvantages to the user of calibrations performed in each state, and the implications for the uncertainty analysis for calibration and use of type R and type S thermocouples. [ABSTRACT FROM AUTHOR]

Reported is a low-loss RF power limiter built using a voltage-controlled capacitor formed by two planar Schottky contacts deposited over an AlGaN/GaN heterostructure. The symmetrical structure of the varactor enables dual-polarity voltage clamping. Small electrode size and electrode spacing of 2 µm ensures a low impedance and low loss. Varying the varactor width in the range 0.25 - 1 mm allows tuning of the limiting powers in the range 17 - 40 dBm, also dependent on the operating frequency. The small-signal loss at 10 GHz is 0.2 - 0.67 dB. The varactor structure fabrication does not require gate alignment or annealing; the device is robust and fully compatible with MMICs; it also provides the DC block with around 95 V breakdown. The PL operation in the temperature range 25 - 200oC without significant parameter degradation was demonstrated. Power limiter CW stress during 100 h at 24 dBm revealed no performance degradation. [ABSTRACT FROM AUTHOR]

Background: Learning of basic clinical skills is introduced in Years 1 and 2 of the MBBS Program at the Aga Khan University, Pakistan, through a structured Clinical Skills Teaching program. Acquisition of competence in performing these skills is assessed through use of the Objective Structured Clinical Examination (OSCE). Self-assessment is defined broadly as the involvement of learners in judging whether or not learner-identified standards have been met. Objective: We compared Year 2 students' self-assessment of clinical skills with examiners' assessment of performance in an OSCE using a standard rating scale. Methods: A self-assessment questionnaire was completed by all Year 2 students immediately after the OSCE. Students assessed their performance at three stations, using a performance rating scale. Examiners observed and evaluated the students during history-taking and physical examination using the same rating scale. Results: There were significant positive correlations between examiners' assessments of performance and students' self-assessed ratings in taking consent, obtaining demographic information, history of presenting problems and summarization. Significant differences were observed in pre-procedural skills, comment on prostate, liver palpation percussion and spleen percussion. Conclusions: Findings highlight the strengths and weaknesses in clinical competence at the end of Year 2 and provide a direction to improve the gaps in the Clinical Skills Teaching program [ABSTRACT FROM AUTHOR]

A new laser-based technique to examine heat transfer and energetics of phase transitions in metal-carbon fixed points and potentially to improve the quality of phase transitions in furnaces with poor uniformity is reported. Being reproducible below 0.1 K, metal-carbon fixed points are increasingly used as reference standards for the calibration of thermocouples and radiation thermometers. At NMIA, the Co-C eutectic point is used for the calibration of thermocouples, with the fixed point traceable to the International Temperature Scale (ITS-90) using radiation thermometry. For thermocouple use, these cells are deep inside a high-uniformity furnace, easily obtaining excellent melting plateaus. However, when used with radiation thermometers, the essential large viewing cone to the crucible restricts the furnace depth and introduces large heat losses from the front furnace zone, affecting the quality of the phase transition. Short $$\hbox {CO}_{2}$$ laser bursts have been used to illuminate the cavity of a conventional Co-C fixed-point cell during various points in its melting phase transition. The laser is employed to partially melt the metal at the rear of the crucible providing a liquid-solid interface close to the region being observed by the reference pyrometer. As the laser power is known, a quantitative estimate of $$(166 \pm 30) \hbox { J}{\cdot }\hbox {g}^{-1}$$ can be made for the Co-C latent heat of fusion. Using a single laser pulse during a furnace-induced melt, a plateau up to 8 min is observed before the crucible resumes a characteristic conventional melt curve. Although this plateau is satisfyingly flat, well within 100 mK, it is observed that the plateau is laser energy dependent and elevates from the conventional melt 'inflection-point' value. [ABSTRACT FROM AUTHOR]

Objectives: To evaluate the effect of vitamin A supplementation 24 h after delivery on breastmilk retinol concentration.Methods: Fifty low income women were randomly assigned to a single oral dose of 209 micromol of Vitamin A or none at delivery. Maternal serum and breastmilk retinol levels and infant morbidity and anthropometry were serially assessed.Results: Mean (95% CI) serum retinol levels increased in the supplemented mothers at 2.77 (2.3, 3.2) compared to 1.15 (0.9, 1.4) micromol/l in controls (P < 0.05) and remained at a significantly higher level of 1.59 (1.4, 1.8) micromol/l compared to 1.33 (1.8, 1.5) micromol/l in the control group (P < 0.001) up to a period of three months. Breastmilk retinol concentration was also greater at 24 h after supplementation, mean (CI) 11.34 (9.0, 13.7) micromol/l, compared to 2.95 (2.3, 3.6) micromol/l in the control group (P < 0.0001), and remained higher for the next six months at 1.06 (0.9, , 1.3) micromol/l compared to 0.73 (0.6, 0.8) micromol/l in the control group (P < 0.02). Infants of the supplemented mothers had reduced mean duration of respiratory tract infection of 3.1 (2.7, 3.5) days compared to 3.7 (3.3, 4.2) days (P < 0.03) and mean incidence of febrile illness 0.1 (0.1, 0.1) compared to control infants 0.3 (0.3, 0.3) days, (P < 0.002).Conclusion: Vitamin A supplementation of malnourished mothers maintains higher breastmilk retinol concentration for at least six months and reduces the duration of respiratory tract infection and febrile illness in their breastfed infants. [ABSTRACT FROM AUTHOR]