Reducing the Uncertainty of Industrial Trace Humidity Generators through NIST Permeation-Tube Calibration

Permeation-tube moisture generators (PTGs) are commonly used by the semiconductor industry as transfer standards for the calibration of hygrometer systems measuring trace amounts of water vapor in gases (water vapor mole fractions typically below 1 × 10⁻⁶). They are relatively simple devices that generate a steady stream of humidified gas by diluting water vapor delivered at a constant rate from a permeable capsule with precisely metered purified gas, usually nitrogen. Here a new calibration service enabling the measurement of PTG permeation rates directly in terms of NIST primary standards of trace humidity generation is described. Rather than using commonly employed gravimetric methods for permeation-tube calibration, the method applied here links the permeation rate of the permeation tube to the thermodynamic properties of ice. Using a hygrometer based on cavity ringdown spectroscopy, we compare the water vapor concentrations produced by the NIST low frost-point generator (LFPG) and a specially constructed PTG containing the permeation tube undergoing calibration. A least squares fit of the data determines the permeation rate of the tube under test. We describe the calibration system, experimental procedure and present sample calibration data. The expanded relative uncertainty of NIST permeation-tube calibrations is 1.8% with a coverage factor k = 2, dominated by the Type A uncertainties.     

Dynamic Measurements of the Temperature Coefficient of Resistance in the Transient Plane Source Sensor

The extended dynamic plane source (EDPS) method is one of the transient methods for measurements of the thermal conductivity and thermal diffusivity in solids. This technique uses a transient plane source (TPS) sensor, which serves as the heat source and thermometer. Its calibration consists of measuring the temperature dependence of the TPS sensor resistance and computing the temperature coefficient of resistance (TCR) using least-squares (LS) estimation. The goal of this study is to calibrate the TPS sensor directly in the apparatus for the EDPS method. The article presents an uncertainty assessment of the TCR measurement. The main sources of uncertainty stem from resistance measurements of the constant resistor and platinum thermometer calibration. The LS estimate of the TCR in a nickel TPS sensor is 4.83 × 10⁻³ K⁻¹ at 20 °C and 4.57 × 10⁻³ K⁻¹ at 45 °C with a combined standard uncertainty better than 0.04 × 10⁻³ K⁻¹, which is 0.7 %.     

Workability and strength behaviour of concrete with cold-bonded fly ash aggregate

This paper discusses the development of empirical models for workability and compressive strength of cold-bonded fly ash aggregate concrete in terms of mixture proportioning variables such as cement content, water content and volume fraction of cold-bonded aggregate through statistically designed experiments based on Response Surface Methodology. Factor level of cement is taken from 250 to 450 kg/m³ to introduce weak as well as strong matrix phase in the concrete. Apart from water content, workability of concrete is highly influenced by main and interaction effect of volume fraction of cold-bonded aggregate in the composition. Response surface indicate that increase in cement content causes to change the predominant failure mode from mortar failure to aggregate fracture and concrete strength decreases with increase in volume fraction of aggregate at higher cement contents. The models developed have been found useful in arriving typical relationship to establish a mixture proportioning methodology for cold-bonded fly ash aggregate concrete.     

Study on solid-phase extraction and flame atomic absorption spectrometry for the selective determination of cadmium in water and plant samples with modified clinoptilolite

A sensitive, simple separation and solid-phase procedure, which is sorption and desorption of cadmium on modified clinoptilolite zeolite (with surfactant and neothorine), for preconcentration of cadmium prior to analysis by FAAS is described. The sorbent has exhibited good sorption potential for cadmium at pH 5. Cadmium was eluted from the column by nitric acid which resulted in preconcentration factor of 160. Thermodynamic behaviors for the process are investigated and adsorption process is interpreted in term of Freundlich equation. A detection limit of 0.015 ng mL⁻¹ was obtained and it is shown that calibration curve is linear from 0.01 to 4.0 μg mL⁻¹ in the final solution. Furthermore, the effects of various parameters such as pH, flow rate of the sample and eluent solution were studied. This method was successfully applied for determination of cadmium in various plant and real water samples.     

Measurement of Workability of Fresh Concrete Using a Mixing Truck

The main objective of this study is to evaluate the workability of fresh portland cement concrete while it is still in the mixing truck by determining fundamental rheological parameters (plastic viscosity and yield stress). Nine concrete mixtures with different values of yield stress and plastic viscosity were tested in a concrete truck. The measurements made with the truck were based on the typical method of determining the flow behavior in a traditional fluid rheometer; that is, the shear rate in the mixing truck was swept from high to low by varying the rotation speed of the drum. The results of these experiments are discussed and compared with data provided by the ICAR rheometer, a portable rheometer designed for measuring concrete rheology. The test results indicate that the mixing truck equipment is sufficiently sensitive to detect differences in yield stress, slump, and plastic viscosity. However, the plastic viscosity determined by the truck measurement did not correlate with plastic viscosity as measured by the ICAR rheometer, while the yield stress determined by the truck measurement did correlate well with the measured slump and the ICAR rheometer resultsSuggestions are given on how to improve the mixing truck for better use as a rheometer.     

The drilling resistance test for the assessment of fire damaged concrete

In this paper, the evaluation of the drilling resistance is regarded as a method to ascertain the thermal damage undergone by concrete members after fire. Some preliminary tests on a good quality concrete were functional in defining the test procedure, the optimal bit diameter and the effect of the drilling thrust. A further study on uniformly damaged concrete cubes (ordinary and lightweight concretes – R_cm = 50 N/mm²) allowed to ascertain the sensitivity of the method. The reliability of this technique for the assessment of the damage depth within structural members exposed to fire has then been checked by testing some concrete panels exposed to marked temperature gradients. Finally, the viability of the method for in situ applications has been confirmed by testing the members of a precast RC structure which survived a real fire.     

Quantitative analysis of hemoglobin content in polymeric nanoparticles as blood substitutes using Fourier transform infrared spectroscopy

Based on the penetrability of IR within the polymeric nanoparticles, a novel Fourier transform infrared spectroscopy (FTIR) method, with polyacrylonitrile (PAN) as the internal reference standard, was developed to quantify the hemoglobin (Hb) content in Hb-based polymeric nanoparticles (HbPN). The HbPN was fabricated by double emulsion method from poly(ethylene glycol)–poly(lactic acid)–poly(ethylene glycol) triblock copolymers. Depending on the characteristic un-overlapped IR absorbances at 1540 cm⁻¹ of Hb (amide II) and at 2241 cm⁻¹ of PAN (–C≡N), calibration equations, presenting the peak height ratio of Hb and PAN as a function of the weight ratio of Hb and PAN, were established. This new quantification method is validated and used to the determination Hb content in HbPN. Due to the good results of this calibration strategy, the proposed simple FTIR approach with minimal sample-needed and solvent-free makes it useful for routine analysis of protein content and could be also applied to any other drug/protein encapsulated particles.     

Studies of Excess Heat and Convection in a Water Calorimeter

To explain a difference of 0.5 % between the absorbed-dose standards of the National Institute of Standards and Technology (NIST) and the National Research Council of Canada (NRCC), Seuntjens et al. suggest the fault lies with the NIST water calorimeter being operated at 22 °C and the method with which the measurements were made. Their calculations show that this difference is due to overprediction of temperature rises of six consecutive ⁶⁰Co radiation runs at NIST. However, the consecutive runs they refer to were merely preliminary measurements to determine the procedure for the NIST beam calibration. The beam calibration was determined from only two consecutive runs followed by water circulation to re-establish temperature equilibrium. This procedure was used for measurements on 77 days, with 32 runs per day. Convection external to the glass cylindrical detector assembly performed a beneficial role. It aided (along with conduction) in increasing the rate of excess heat transported away from the thin cylindrical wall. This decreased the rate of heat conducted toward the axially located thermistors. The other sources of excess heat are the: (1) non-water materials in the temperature probe, and (2) exothermic effect of the once-distilled water external to the cylinder. Finite-element calculations were made to determine the separate and combined effects of the excess heat sources for the afterdrift. From this analysis, extrapolation of the measured afterdrifts of two consecutive runs to mid radiation leads to an estimated over-prediction of no more than about 0.1 %. Experimental measurements contradict the calculated results of Seuntjens et al. that convective motion (a plume) originates from the thermistors operated with an electrical power dissipation as low as 0.6 μW, well below the measured threshold of 50 μW. The method used for detecting a plume was sensitive enough to measure a convective plume (if it had started) down to about the 10 μW power level. Measurements also contradict the NRCC calculations in predicting the behavior of the NIST afterdrifts.     

Evaluation of Portland limestone cements for use in concrete construction

The paper describes a study carried out to examine the performance of concrete produced using combinations of Portland cement (PC) and limestone (LS), covering compositions for Portland limestone cement (PLC) conforming to BS EN 197-1: 2000, and up to 45% LS. In particular, key engineering (mechanical) and durability properties of concrete were studied. The results indicate only minor differences in performance between PC and 15% PLC concretes of the same cement content and water/cement (w/c) ratio (cement = Portland cement + addition). However, there was an adverse effect with increasing LS content beyond 15% of the cement content for many properties. It is shown that for 35 N/mm² cube strength concrete the adjustment to w/c ratio to match the compressive strength of PC concrete was in the region of 0.08 for each 10% LS added (water curing at 20°C) above this level. Studies of permeation and concrete durability performance, including, initial surface absorption, carbonation resistance, chloride diffusion, freeze/thaw scaling and abrasion resistance, indicate that in general the test concretes followed single relationships with strength for most properties. Consideration is given to the practical implications of the main outcomes of the study.     

Scaling resistance of high performance concretes containing a small portion of pre-wetted lightweight fine aggregate

The subject of the investigation was the influence of pre-wetted lightweight aggregate on damage of the concrete surface due to cyclic freezing and thawing in the presence of de-icing salts tested according to the Swedish Standard SS 13 72 44 (the Borås method). Six series of concrete specimens were made with the same water/binder (w/b) ratio 0.32, cement volume 400 kg/m³ and content of superplasticiser 8.8 kg/m³. One series, S3/2, contained an air-entraining agent. Series S4/7 and S4/8 were made with water/cement ratio equal to 0.45 and a lower cement content 340 kg/m³. In a few series the sand fraction 0–2 mm and basalt fraction 2–4 mm were partly or totally replaced by wetted lightweight aggregate. Concretes S3/1, S3/3, S4/7 and S4/8, failed the test. The best results were obtained for concrete S3/6 (with the 2–4 mm fraction replaced by half) and S3/2 (air-entrained). The application of an air-entraining agent is more expensive than LWA, and at a construction site it is not always easy to control. It seems that the replacement of a part of aggregate by LWA could be a more effective way to improve the scaling resistance.     

Deformation behavior of cement treated demolition waste with recycled masonry and concrete subjected to drying and temperature change

Cement treated materials are widely used as road bases in pavements. Shrinkage of these materials due to moisture and temperature changes is a critical issue for determining shrinkage cracking in pavements. This paper presents the influence of four mixture variables (masonry content, cement content, water content and degree of compaction) on drying shrinkage and coefficient of thermal expansion (CTE) of cement treated demolition waste with recycled masonry and concrete (CTM_iG_r). The experimental results showed that the masonry content was the dominating factor affecting dry shrinkage and CTE of CTM_iG_r. Increasing the masonry content can not only lead to an obvious decrease of dry shrinkage of CTM_iG_r, but also a low CTE level. Dry shrinkage of CTM_iG_r increased as the increase of cement content as well as degree of compaction and water content. The CTE of CTM_iG_r was between 7.58 × 10⁻⁶/°C and 10.22 × 10⁻⁶/°C, which was mainly determined by the masonry and cement content.     

Ultra-lightweight concrete: Conceptual design and performance evaluation

The present study presents a methodology to design ultra-lightweight concrete that could be potentially applied in monolithic concrete structures, performing as both load bearing element and thermal insulator. A particle grading model is employed to secure a densely packed matrix, composed of a binder and lightweight aggregates produced from recycled glass.The developed ultra-lightweight concrete, with a dry density of about 650–700 kg/m³, shows excellent thermal properties, with a thermal conductivity of about 0.12 W/(m K); and moderate mechanical properties, with a 28-day compressive strength of about 10–12 N/mm². Furthermore, the developed concrete exhibits excellent resistance against water penetration.     

Characterization of air entraining admixtures in concrete using surface tension measurements

Air entraining admixtures (AEA) are generally used for increasing the workability and resistance to freezing and thawing in concrete. These admixtures generate air bubbles with diameters ranging from 10 μm to 1 mm, providing spaces for the expansion of ice, and therefore facilitate frost protection. In this study, performances of AEAs were investigated based on surface tension measurements, accounting for the effect of AEAs on surface tension. For this purpose, a new test method was developed which depends on surface tension measurements according to the Du Nouy ring method. All types of AEAs used in the scope of this research presented a substantial influence on the surface tension. It was observed that a significant relationship between the air void system and surface tension exists. The surface tension method was found as a useful tool to determine the AEA type and content to obtain the desired air void system in concrete.     

Replicating cohesive and stress-history-dependent behavior of bulk solids: Feasibility and definiteness in DEM calibration procedure

This paper presents a multi-step DEM calibration procedure for cohesive solid materials, incorporating feasibility in finding a non-empty solution space and definiteness in capturing bulk responses independently of calibration targets. Our procedure follows four steps: (I) feasibility; (II) screening of DEM variables; (III) surrogate modeling-based optimization; and (IV) verification. Both types of input parameter, continuous (e.g. coefficient of static friction) and categorical (e.g. contact module), can be used in our calibration procedure. The cohesive and stress-history-dependent behavior of a moist iron ore sample is replicated using experimental data from four different laboratory tests, such as a ring shear test. This results in a high number of bulk responses (i.e. ≥ 4) as calibration targets in combination with a high number of significant DEM input variables (i.e. > 2) in the calibration procedure. Coefficient of static friction, surface energy, and particle shear modulus are found to be the most significant continuous variables for the simulated processes. The optimal DEM parameter set and its definiteness are verified using 20 different bulk response values. The multi-step optimization framework thus can be used to calibrate material models when both a high number of input variables (i.e. > 2) and a high number of calibration targets (i.e. ≥ 4) are involved.     

Investigation on the scattering-filling coarse aggregate self-consolidating concrete

To secure good flowability and workability of SCC, the volume fraction of coarse aggregate keep at an extremely low level. A new kind of SCC pouring method named scattering-filling coarse aggregate process was invented: it was method to scatter 20% (volume fraction to the finished concrete) of extra coarse aggregate into the fresh SCC mixture to replace the fresh concrete mixture while the concrete was pouring. A high strength (82 MPa) SCC just composing 360 kg/m³ cement and 120 kg/m³ class F fly ash was prepared with this process. With an increase of the extra coarse aggregate replacing ratio from 0 to 30%, the compressive strength of SCC increased steadily and reached a peak value when this ratio is 20%, then the strength dropped sharply. The drying shrinkage ratio and the chloride ion permeability decreased with the increase of that ratio. The scattering-filling coarse aggregate process can cast high strength SCC with lower cementitious materials content and produce concrete with better performance than the ordinary process.     

Resolving ambiguity in broadband waveguide permittivitymeasurements on moist materials

The dielectric properties of moist materials depend strongly on free water content. Moisture content may be conveniently sensed using microwaves, provided that calibration data is available. One common method utilizes network analyzer transmission measurements on waveguide cells filled with samples of known water content. Since this technique yields multiple solutions for the complex permittivity, a simple procedure has been developed to identify the correct solution. This has proved to be highly reliable and lends itself to measurement automation     

Transport properties of high-volume fly ash concrete: Capillary water sorption,water sorption under vacuum and gas permeability

Studying concrete’s resistance to carbonation-induced corrosion usually involves exposing the material to CO₂ for quite some time. To estimate the performance of high-volume fly ash (HVFA) concrete more quickly, two key properties governing this process can be studied, namely water penetrability and gas permeability. With respect to HVFA mixtures optimized for usage in an environment exposed to carbonation with wetting and drying, we adopted the latter approach. This paper presents a full assessment of concrete mixtures with varying fly ash amounts. A 50% fly ash mixture by mass with a binder content of 400 kg/m³ and a water-to-binder ratio of 0.4 had a lower capillary water uptake (?32.6%), water sorption under vacuum (?10.7%) and gas permeability (?78.9%) than a proper reference normally used in this environment. The fly ash applied had an excellent quality regarding loss on ignition (3.5%) and fineness (19% retained on a 45 μm sieve).     

Calibration of pressure sensors in an industrial environment

National Measurements Institutes calibrate vacuum pressure sensors a few gauges at a time in a time-consuming fashion, resulting in an accurate calibration with small uncertainty estimates. A manufacturer produces a comparatively large number of sensors a day which must be economically calibrated. Here, we investigate a procedure for rapid calibration of combination vacuum gauges while following as closely as possible the relevant norms published by the international standards organizations. The investigated procedure increases the uncertainty estimate by up to 10%, but the gauges are still within common accuracies (<15% of reading in the range of 1×10⁻⁶ to 1×10⁻² hPa) for this type of measurement instrument.     

Thermophysical Properties of Swine Myocardium

This paper presents the experimental technique and results for the thermal conductivity, thermal diffusivity, and density of swine myocardial tissue. These properties were measured for freshly excised tissue. Thermal properties were measured using a self-heated thermistor probe, while the density was measured using a water displacement method. Thermistor probes were inserted into the tissue of interest and were used to supply heat within the tissue as well as to monitor the temperature rise in the tissue. An empirical calibration procedure was used to measure the properties of the tissue at different temperatures. The measurement instrument was first calibrated against agar-gelled water and glycerol at each temperature. The measurements were made at temperatures of 25, 37, 50, 62, and 76°C. The uncertainty in the measurement ranges from 2% at lower temperatures to about 5% at higher temperatures (T > 50°C). The properties of the tissue depend significantly on the water content. At temperatures higher than 50°C, there is significant water loss from the tissue during the procedure. The water loss is found to vary exponentially with the increase in temperature relative to ambient. Consequently, there is a decrease in the thermal conductivity values with increasing temperature. This decrease, however, is not as much as one would expect from the water loss data. A hypothesis to explain the relationships among water loss, cell damage, and thermal properties is proposed.     

A highly sensitive and selective electrochemical sensor for determination of Cr(VI) in the presence of Cr(III) using modified multi-walled carbon nanotubes/quercetin screen-printed electrode

A novel screen-printed carbon electrode modified with quercetin/multi-walled carbon nanotubes was fabricated for determination of Cr(VI) in the presence of excess of Cr(III) without any pretreatment. The method is based on accumulation of the quercetin–Cr(III) complex generated in situ from Cr(VI) at the modified electrode surface in an open circuit followed by differential pulse voltammetry detection. The new method allowed selective determination of Cr(VI) in the presence of Cr(III). The influence of various parameters affecting the adsorptive stripping voltammetry performance was investigated. Under the optimum conditions, the calibration plot was found to be linear in the Cr(VI) concentration range from 1.0 to 200 μmol^? 1 with a limit of detection(S/N = 3) of 0.3 μmol L^– 1. The relative standard deviation (RSD%) of seven replicates of the current measurements for a 50 μmol^? 1 of Cr(VI) solution was 3.0%. The developed electrode displayed a very low or no sensitivity to alkali, alkali-earth and transition metal cations and was successfully applied for the determination of Cr(VI) in drinking water samples.