Constant Test Conditions Research Articles

Improved FPGA controlled artificial vascular system for plethysmographic measurements

Abstract The fetal oxygen saturation is an important parameter to determine the health status of a fetus, which is until now mostly acquired invasively. The transabdominal, fetal pulse oximetry is a promising approach to measure this non-invasively and continuously. The fetal pulse curve has to be extracted from the mixed signal of mother and fetus to determine its oxygen saturation. For this purpose efficient algorithms are necessary, which have to be evaluated under constant and reproducable test conditions. This paper presents the improved version of a phantom which can generate artificial pulse waves in a synthetic tissue phantom. The tissue phantom consists of several layers that mimic the different optical properties of the fetal and maternal tissue layers. Additionally an artificial vascular system and a dome, which mimics the bending of the belly of a pregnant woman, are incorporated. To obtain data on the pulse waves, several measurement methods are included, to help understand the behavior of the signals gained from the pulse waves. Besides pressure sensors and a transmissive method we integrated a capacitive approach, that makes use of the so called “Pin Oscillator” method. Apart from the enhancements in the tissue phantom and the measurements, we also improved the used blood substitute, which reproduces the different absorption characteristics of fetal and maternal blood. The results show that the phantom can generate pulse waves similar to the natural ones. Furthermore, the phantom represents a reference that can be used to evaluate the algorithms for transabdominal, fetal pulse oximetry.

Effect of microporous membrane properties and operating conditions on particle retention: Measurements and model studies

ABSTRACTDepth filtration with microporous membranes has been modelled by extending upon previous approaches of Polyakov[1–4] to incorporate pore size distribution, tortuosity, and cake buildup. The model-forecasts were benchmarked against filtration measurements performed with colloidal particles using three very different commercial membrane morphologies with the same nominal average pore size. The critical flux for each membrane was determined by a standard flux-stepping method. Particle retention and permeance were studied under constant flux or transmembrane pressure test conditions. Comparison of the forecast results with data shows reasonable qualitative agreement, but the results are very sensitive to the measurement uncertainties of the various properties.

열펌프 열량계 구조 및 성능 특성 연구

The efficiency, reliability and performance of any heat pump unit can only be ascertained after it has been tested and rated. For this reason, specific facilities, equiped with testing plants are built. Heat pump calorimeter is the facilities used by most of these testing facilities in their rating and certification process. The ultimate function of calorimeters is to, control and maintain the constant standard test conditions (indoor/outdoor entering temperatures and flow rate etc) during testing period. In this study, the test standards of heat pump unit and the structure of the calorimeter are surveyed. In addition, this study analyzes the total energy consumption of a water to water heat pump calorimeter. Heat pump calorimeter consumed much energy to excute the heat pump tests. The energy consumption of the calorimeter was higher than the heat pump unit, and it was increased as the heat pump unit capacity decreased.

Experimental investigation of pneumatic tire performance on ice: Part 2 – Outdoor study

The concept of ‘Lab to the Road’ is very challenging, especially for tire operation on ice. The changing ambient and ice conditions necessitate the need for robust engineering for the safety of vehicles on icy roads. Test method has a direct effect in measuring tire behavior on ice, with differences in the test setup and ability to maintain constant test conditions. The purpose of design for each test method also varies; certain test methods are designed to understand absolute tire performance, as compared to studying relative tire performance. This paper examines the performance of tires on ice through field tests conducted at the Keweenaw Research Center. Part-1 (Bhoopalam et al., 2015) presented a detailed indoor test program conducted on the Terramechanics Rig at the Advanced Vehicle Dynamics Laboratory, Virginia Tech, including the ice preparation procedure, test method, and test results. The two tests procedures were performed to understand how each test method influences the test results. A comparison of the laboratory (Bhoopalam et al., 2015) and field test method is also presented in this paper, with reasons for the differences in the measured values presented.

Power conditioning units in grid-connected photovoltaic systems: A comparison with different technologies and wide range of power ratings

Nowadays, the electronic converter which connects the photovoltaic array (PV) with the utility grid is subject to multiple requirements in terms of energy efficiency, power quality and grid stability. The paper focuses on a comparison among grid-connected Power Conditioning Units (PCUs) with different sizes, technologies and PV system architectures. In particular, the comparison includes the following items: single-phase and three-phase systems; with low-frequency or high-frequency transformers and transformerless version; with MOSFETs and IGBTs transistors. The comparison, based on experimental tests in which the signals of voltage, current and power are sampled at fast rate and with low uncertainty, is performed thanks to the normalisation of the input/output powers with respect to the power ratings. A set of meaningful parameters permits to characterise the behaviour of the PCUs which are studied both in field operation and in laboratory with known and constant test conditions. Regarding the PV systems in field operation, five plants have been analysed with PCUs from 230kW down to 3kW. The PCUs under study in laboratory include 1-kW inverter, one string-inverter with multi-MPPT, one per string, and two module integrated inverters. The experimental results demonstrate that the different PCUs mostly have similar performance, although the single-phase PCUs exhibit lower DC–AC efficiency at partial load, whereas a three-phase PCU shows lower MPPT efficiency, when defects in the solar cells generate multiple maximum power points in the current–voltage curve of the PV array.

Constitutive description for the design of hot-working operations of a 20MnCr5 steel grade

The development of sound constitutive descriptions able to predict accurately the changes in flow stress during plastic deformation, under changing temperature and strain rate conditions is of utmost importance for the correct prediction of the mechanical response of metals and alloys, which undergo deformation under hot-working conditions. Therefore, the present work has been conducted with the aim of developing a constitutive model of such characteristics, able to describe as accurate as possible the changes in flow stress of a commercial 20MnCr5 steel, when this material is deformed at elevated temperatures and different strain rates. Particular attention has been paid to the analysis of the flow stress, work-hardening and work-softening behavior when this material is subjected to transient testing conditions, that is to say, changes in strain rate and deformation temperature in the course of plastic deformation. The constitutive description is initially developed from the analysis of the stress–strain curves obtained from axisymmetric compression tests conducted under nominal constant testing conditions, which involved the deformation of the material at temperatures in the range of 1123–1473K and strain rates of 0.01–10s−1, up to effective strains spanning from approximately 0.6 to 1. The initial work-hardening and the subsequent work-softening behavior exhibited by the material during plastic deformation have been thoroughly characterized on a rational basis. The temperature and strain rate dependence of the yield stress, critical stress for the initiation of dynamic recrystallization, apparent saturation stress and actual steady-state flow stress have been described by means of the Sellars–Tegart–Garofalo model. The time to 50% dynamic recrystallization has also been described as a function of deformation temperature and strain rate, by means of a simple parametric relationship commonly employed for this purpose. The proposed constitutive description employs a single activation energy, whose value is close to that required for the self-diffusion of Fe in austenite, of approximately 284kJmol−1. Further experiments involving changes in deformation temperature and strain rate have been carried out in order to validate the constitutive model. The results indicate that the proposed approach is able to describe satisfactorily the changes in flow stress, work-hardening and work-softening of the investigated material during transient testing conditions.

Sedimentation dynamics in combined sewer systems

Sediments in combined sewers may negatively affect the performance of sewer systems and significantly promote the formation of hydrogen sulfide. To prevent this, German sewer systems are cleaned regularly but at high costs. In order to optimize the cleaning intervals, this study investigates how deposits build up and change over a defined period under constant conditions. The experiments were performed using real wastewater at a pilot plant consisting of three 10 m long acrylic glass pipes with a diameter of 300 mm, a slope of I = 1‰, a discharge of Q = 2 L/s and a roughness of kS = 0.4 mm. Within the first 30 d, a slow increase of the deposit height (averaged over the pipe length) of 0.75 mm/d was observed. The deposits did not build up continuously, but in between times also decreased due to erosion. The daily changes in deposit amounts occurred partly as a function of the rainfall conditions and could go beyond the average growth many times. Within a day, the deposit height (averaged over pipe length) changed by up to 20 mm, at single measuring points even up to 100 mm. After about 50 d under constant test conditions, the deposit height came to a state of equilibrium between sedimentation and erosion.

Effects of temperature on mechanical and tribological properties of dental restorative composite materials

The purpose of this study is to evaluate the effects of temperature on the mechanical and tribological properties of three commercial posterior direct filling resin based restorative composite materials, Synergy (Coltene/Whaledent, Altstätten, Switzerland), Surefil (Dentsply/Caulk, New York, USA) and Alert (Pentron Clinical, Wallingford, USA). The aim of this paper was to evaluate how temperature influences; the hardness, flexural modulus and strength, elastic modulus, and wear of the listed commercial restorative materials.Three commercial resin composites were tested at several temperatures. A closed control system was used to ensure constant test conditions that simulated the temperatures found in an oral environment. For each of the tests, the following mechanical and tribological properties were determined, microhardness (Vickers micro-indentation), elastic modulus (determined both by dynamical methods and by bending tests), flexural resistance and work of fracture parameter (bending tests), and wear (reciprocating tests).Following the tests, the evaluation of the mechanical and tribological properties of the resins suggests that their performance in an oral environment can be significantly affected by temperature, especially the wear resistance. Surefil is the resin least sensitive to temperature variation, while Synergy exhibited the best resistance to wear with respect to temperature variation.

Describing fatigue crack growth and load ratio effects in Al 2524 T3 alloy with an enhanced exponential model

The fatigue crack behavior in metals and alloys under constant amplitude test conditions is usually described by relationships between the crack growth rate da/dN and the stress intensity factor range ΔK. In the present work, an enhanced two-parameter exponential equation of fatigue crack growth was introduced in order to describe sub-critical crack propagation behavior of Al 2524-T3 alloy, commonly used in aircraft engineering applications. It was demonstrated that besides adequately correlating the load ratio effects, the exponential model also accounts for the slight deviations from linearity shown by the experimental curves. A comparison with Elber, Kujawski and “Unified Approach” models allowed for verifying the better performance, when confronted to the other tested models, presented by the exponential model.

Crack Closure Behavior under High-Load Ratio for AISI 4340 Steel

In this paper, fatigue crack growth rate (FCGR) analyses were conducted on compact specimens of an AISI 4340 alloy to study the behavior over a range in load ratios (0.1 ≤ R ≤ 0.95) and constant maximum stress intensity factor (Kmax) condition. Previous study had indicated that high R > 0.7 and constant Kmax test conditions near threshold conditions were suspected to be free of crack-closure and that any differences were caused by Kmax effects, from threshold to near fracture conditions. Cracks in high-cycle fatigue (HCF) components spend a large portion of their fatigue life near threshold conditions. In order to characterize the evolution of damage and crack propagation during these conditions, fatigue crack growth rate (FCGR) data at threshold and near-threshold conditions are essential in predicting service life and in determining the proper inspection intervals. Fatigue crack growth model, namely the Forman model were examined, this model implicit the effect of R ratio and ease of curve fitting to measured data. The Forman model may be suggested for use in critical applications in studying fatigue crack growth for different load ratios.

Crack-Closure Behavior of 7050 Aluminum Alloy near Threshold Conditions for Wide Range in Load Ratios and ConstantKmax Tests

AbstractFatigue-crack-growth rate tests were conducted on compact specimens made of a 7050-T7451 aluminum alloy to study the behavior over a range in load ratios (0.1≤R≤0.9) and constant Kmax test conditions. Previous research had suggested that differences in the threshold regime at high load ratios were attributed to Kmax effects. But recent measurements of crack-closure behavior under high R and constant Kmax test conditions near threshold conditions on a variety of materials have indicated that these tests may not be crack-closure free as suspected. Strain gages were placed near and ahead of the crack tip to measure crack-opening loads from local strain records. In addition, a back-face strain (BFS) gage was used to monitor crack sizes and to measure crack-opening loads from remote strain records during the same tests. The 7050 alloy produced very rough crack-surface profiles. For R=0.1, the BFS and local gages indicated very similar high crack-opening loads. For R≥0.7 and Kmax test results in the threshold regime, the BFS gages indicated lower crack-opening loads than the local gages. Based on local measurements, crack-closure-free fatigue-crack-growth data (ΔKeff against rate) were calculated. These results indicated that the ΔKeff against rate relation is nearly a unique function over a wide range of R values even in the threshold regime, if crack-opening loads were measured from local strain gages. At low R, all three major shielding mechanisms (plasticity, roughness, and fretting debris) are suspected to cause crack closure. But for high R and Kmax tests, roughness and fretting debris are suspected to cause crack closure above the minimum load. A strip-yield model was also used to correlate the data over a wide range in load ratios and rates, but required a very low constraint factor (α=1.3), due to the high crack-opening loads.

Processing effects on the stability of amorphous indium gallium zinc oxide thin-film transistors

Amorphous oxide semiconductors are attracting much attention due to their high electron mobility even when processed at low temperatures. One such material is indium gallium zinc oxide (IGZO). At a temperature of 175°C, an IGZO thin-film transistor (TFT) is demonstrated to exhibit an incremental channel mobility (μinc) of ∼17cm2V−1s−1 and a turn-on voltage (Von) of ∼1V. Given this performance, IGZO seems well-suited for TFT applications. We report on how decreasing oxygen partial pressure and increasing RF power during the sputtering deposition decreases Von towards 0V and increases mobility. Two types of stability, constant bias testing conditions and idle shelf life, are explored and it is found that stress test stability is closely correlated to the initial value of Von, with an initial Von of 0V resulting in improved stability.

Physical model of the interference immunity of electronic devices and conclusions concerning their testing and operating characteristics

Switching and fault processes in power-supply systems cause pulse-shaped disturbances which may stress electronic devices of protection and control systems. For test purposes such disturbances can be simulated. But despite of the constant test conditions the reaction of the device on the disturbance can vary in a certain range. Assuming similar internal structures of protection and control devices the coupling path and the effects of the disturbance are described. The variation in device reaction due to the disturbance is explained on the basis of different models which imitate the impact of the disturbances especially on the logical part of the circuit. By applying sensors with constant threshold the effectiveness (function) of several EMC measures can be evaluated independently from the reaction of the special device.

Relationship between formability and cast structures in end-chill directionally solidified Al–Cu alloys

End-chill unidirectional solidification experiments have been conducted on pure Al and Al–Cu alloys with 1, 3 and 4.5 wt.% Cu, using melt superheat varying between 50 and 200 K. The specimens produced were 50 mm in diameter and 150–200 mm long. Studying the solidification structure indicated that most of the specimens exhibited a columnar structure growing perpendicular to the chill surface, followed by equiaxed grains. The volume fraction of the columnar structure and the grain size of the equiaxed one are related to the Cu content, superheat and the cooling rate. The volume fraction of the eutectic phase varied, depending on the casting parameters. Compression testing has been performed, in order to study the formability of the columnar and equiaxed grain structures. Constant testing conditions of a specimen slenderness ratio (8: 8) and strain rate of 1 mm/s were used, as well as a lubricant. In the relationship σ= kε n , describing the true stress/true strain relationship for the region between the limits of initial yielding and necking in ductile materials, the strength coefficient ( k) and strain hardening coefficient ( n) are used as indices for formability. Hence, the difference in formability behaviour between the columnar and equiaxed grains is presented.

The new Behr climatic wind tunnel

A new climatic wind tunnel has been developed at the Behr GmbH & Co. Research & Development Centre, with the goal of reproducing as closely as possible actual vehicle dynamics and climatic conditions on the road. The special features of the wind tunnel are extremely good airflow properties, a wide range of adjustable climate conditions and excellent dynamics. In this new climatic wind tunnel, in contrast to conventional models, it is now possible to reproduce both constant test conditions and the rapid alterations that occur in road travel. The facility was constructed by Sverdrup Technology, Inc. in a period of just less than two years.

Toughened poly(butylene terephthalate) by blending with a metallocenic poly(ethylene–octene) copolymer

New toughened poly(butylene terephthalate) (PBT) materials were obtained by melt blending with poly(ethylene–octene) copolymer (PEO) and maleic anhydride grafted PEO (gPEO) in a twin screw extruder followed by injection moulding at two injection speeds. The presence of either PEO or gPEO did not influence either the nature of the PBT phase or the crystallisation of PBT. Low injection speeds (7 cm 3/s) and gPEO provided the best mechanical response. Increasing levels of maleic anhydride in gPEO led to a continuous overall decrease in the particle size, that was the most important when the particle size of the ungrafted PEO and that of the PEO at the minimum grafting level were compared. The decrease stopped at a grafting level between 1.14 and 1.80 due to the viscosity increase with the grafting level. Super-tough PBT based blends with impact strength more than twenty-fold that of PBT were obtained at PEO contents equal to or higher than 15%, and at decreasing PEO contents when the grafting level increased. The inter-particle distance ( τ) is the parameter that controls toughness in these PBT/PEO blends. When the critical τ ( τ c) measured in this work for PBT was compared with those obtained in other toughened blends at constant test conditions and rubber properties, τ c decreased as the modulus of elasticity of the matrix increased. When τ c of this work was compared with those obtained in other PBT/rubber blends, it depended on the modulus of elasticity of the dispersed phase, and it increased rather linearly as the PBT modulus to rubber modulus ratio increased.

Anxiety, defence and the elevated plus-maze

The elevated plus-maze test has been in use as a rodent model of anxiety for a decade, and is representative of those tests that are based upon the study of spontaneous behaviour patterns and which ave high ecological validity. The origins of the test in studies of the relationship between exploration and fear are reviewed, and attention is drawn to the distinct possibility that variation in the pharmaco-sensitivity of the procedure may be attributable to often extreme methodological variation between laboratories. In considering further this issue, attention is also drawn to the need to collect data under constant test conditions and to provide the minimum database necessary to reach conclusions regarding the behavioural specificity of drug action. Recent research, which has extended the conventional plus-maze scoring technique to include specific behavioural acts and postures (in particular, those relating to defensive behaviour), is described. The value of such an ethological approach to the plus-maze is then exemplified with original data that demonstrate behaviourally selective, anti-anxiety effects of the GABA A receptor agonist, muscimol (0.125–1.0 mg/kg). It is concluded that, when used appropriately, the elevated plus-maze test can be a very valuable tool in drug screening and in the study of the neurobiology of anxiety and defence. More attention to behaviour and somewhat less emphasis on test simplicity and convenience would seem to be warranted,

Antagonist cocontraction of knee extensors during constant velocity muscle shortening and lengthening

Electromyography (EMG) was used to study the role of antagonist cocontraction of the quadriceps muscles of 24 normal subjects during constant velocity muscle performance tests on a KIN/COM dynamometer. The hypothesis tested the dependence of antagonist cocontraction on joint angle, limb velocity and type of contraction. Seated subjects performed two dynamic tests of resisted muscle shortening and lengthening of the knee flexors through a 65 ° range of knee motion under two constant velocity conditions in a single session. Each test consisted of four repetitions of maximum voluntary contractions (MVC) of constant velocity muscle shortening and lengthening of the knee flexors; one test was performed at 30 ° s −1, the other at 90 ° s −1. The sequence of velocity testing was randomized. Normalized (%Max) values of peak amplitude EMG of knee extensors were measured every 5 ° in the constant velocity phase of each test and compared in a paired manner for each angle, contraction type and velocity, by split-plot two-way analysis of variance (ANOVA). The level of antagonist quadriceps cocontraction was low, ranging from 5–8% Max between 70 ° and 15 ° of knee flexion for both velocities and contraction types. Antagonist quadriceps activity was found to be velocity dependent during agonist muscle shortening ( P < 0.02). However, no other effects of angle, contraction type, or velocity were found for antagonist quadriceps. It is concluded that antagonist quadriceps and the previously reported hamstrings 46 respond differently under typical constant velocity test conditions, and these differences need to be accounted for when intepreting muscle performance tests.

Fatigue crack propagation mechanisms in an aluminium lithium alloy

Different fatigue micromechanisms have been identified by fractographic observations in an aluminium-lithium alloy tested in vacuum and in air under constant and variable amplitude loading conditions. In vacuum, large crystallographic facets are observed for all the studied test conditions. In air, for constant amplitude test conditions, the different cracking mechanisms observed are (apart from facetted crack growth) quasi intergranular cracking and cracking by formation of Herringbone patterns. Under certain variable amplidude loading conditions crystallographic facets are not observed and evidence of striation formation is found. The morphology of these striations is different from that of classical ductile striations. This change in cracking mechanism is attributed to multiple slip activity and slip homogenization operating only in air for particular loading conditions.

Visusprüfung bei Kindern

Measurement of visual acuity in children is more difficult than in adults. Children tend to riet when the threshold is reached and become inattentive. However the exact determination of visual acuity in children is important in some situations (Screening, Amblyopia). In this paper we examined whether an automated procedure is more exact than measurement by an examiner. Three series of experiments were done. In n = 173 we measured visual acuity first by an examiner using an optotype projector and second by an automated procedure (computer, keyboard, television screen). Both, the examiner and the computer used the same test-procedure and threshold criterion (DIN-Norm). The correlation coefficient was 0.84. In n = 53 children (age 4 to 7) visual acuity was measured by an examiner without a special strategy. Afterwards visual acuity was measured by the automated procedure. The correlation coefficient was 0.1. In n = 63 children (age 5-7) visual acuity was measured by an examiner using a strategy and a threshold criterion. Afterwards the automated procedure was used. The correlation coefficient was 0.69. The results show, that without a strategy and defined threshold criterion it is not possible to compare the measurements of visual acuity in different times. An automated procedure presented in this paper guaranties constant test conditions in an optimal way.