Repeatability Of Test Results Research Articles

Repeat Placental Growth Factor-Based Testing in Women With Suspected Preterm Preeclampsia: A Stratified Analysis of the PARROT-2 Trial.

PlGF (placental growth factor)-based testing reduces severe maternal adverse outcomes. Repeat PlGF-based testing is not associated with improved perinatal or maternal outcomes. This planned secondary analysis aimed to determine whether there is a subgroup of women who benefit from repeat testing. Pregnant individuals with suspected preterm preeclampsia were randomized to repeat revealed PlGF-based testing, compared with usual care where testing was concealed. Perinatal and maternal outcomes were stratified by trial group, by initial PlGF-based test result, and by PlGF-based test type (PlGF or sFlt-1 [soluble fms-like tyrosine kinase-1]/PlGF ratio). A total of 1252 pregnant individuals were included. Abnormal initial PlGF-based test identified a more severe phenotype of preeclampsia, at increased risk of adverse maternal and perinatal outcomes. Repeat testing was not significantly associated with clinical benefit in women with abnormal initial results. Of women with a normal initial result, 20% developed preeclampsia, with the majority at least 3 to 4 weeks after initial presentation. Repeat test results were more likely to change from normal to abnormal in symptomatic women (112/415; 27%) compared with asymptomatic women (163/890; 18%). A higher proportion of symptomatic women who changed from normal to abnormal were diagnosed with preeclampsia, compared with asymptomatic women. Our results do not demonstrate evidence of the clinical benefit of repeating PlGF-based testing if the initial result is abnormal. Judicious use of repeat PlGF-based testing to stratify risk may be considered at least 2 weeks after a normal initial test result, particularly in women who have symptoms or signs of preeclampsia. URL: https://www.isrctn.com/ISRCTN85912420; Unique identifier: ISRCTN85912420.

An Evaluation of a SARS-CoV-2 Pseudovirus Neutralization Test and A Comparison to a SARS-CoV-2 Surrogate Virus Neutralization Test in a COVID-19 Long-Term Follow-Up Cohort

Background: The detection of neutralizing anti-SARS-CoV-2 antibodies is important since they represent the subset of antibodies able to prevent the virus to invade human cells. The aim of this study is to evaluate the clinical performances of an in-house pseudovirus neutralization test (pVNT) versus a commercial surrogate neutralization test (sVNT). Material and Methods: A total of 114 RT-PCR positives samples from 75 COVID-19 patients were analyzed using a pVNT and an sVNT technique. Fifty-six pre-pandemic samples were also analyzed to assess the specificity of the two techniques. An analysis of the repeatability and the reproducibility of the pVNT was also performed. Results: A coefficient of variation (CV) of 10.27% for the repeatability of the pVNT was computed. For the reproducibility test, CVs ranged from 16.12% for low NAbs titer to 6.40% for high NAbs titer. Regarding the clinical sensitivity, 90 RT-PCR positive samples out of 114 were positive with the pVNT (78.94%), and 97 were positive with the sVNT (84.21%). About the clinical specificity, all 56 pre-pandemic samples were negative in both techniques. When comparing the sVNT to the pVNT, the specificity and sensibility were 66.67% (95%CI: 47.81–85.53%) and 98.88% (95%CI: 96.72–99.99%), respectively. Conclusions: The results obtained with the automated sVNT technique are consistent with those obtained with the pVNT technique developed in-house. The results of the various repeatability and reproducibility tests demonstrate the good robustness of the fully manual pVNT technique.

Analytical Method Validation of Thorium in Ore Sample Using UV-Vis Spectrophotometer

Monazite contains several rare earth elements (REE) along with radioactive elements, i.e., thorium (Th) and uranium (U). Thorium content in monazite is several times higher than uranium. Monazite contains around 12% thorium oxide, but the thorium content in this mineral varies depending on location. To determine the thorium content in monazite, an appropriate and validated analytical method is needed so that the reliability of the test results can be trusted. Apart from that, method validation is one of the clauses in SNI ISO/IEC 17025:2017 that must be fulfilled by the laboratory to be certified and produce reliable data. This research aims to validate analytical methods for non-standard and modified methods that are likely to be used outside the scope. In this research, the method used to digest and analyze thorium in mineral samples refers to the ASTM E2941-14 method with several modifications. Therefore, the analysis method needs to be validated. Validation of the analytical method is carried out by testing several parameters such as linearity and working range tests, accuracy, precision (repeatability), Limit of Detection (LOD), and Limit of Quantitation (LOQ). The results of linearity, accuracy, and repeatability tests that meet the acceptance requirements can be used as a method of validation evaluation. The results of the method validation parameter test met the acceptance requirements, with the linearity test showing a coefficient of determination (R2) of 0.997, the accuracy test showing % a recovery value of 106.22%, and the precision (repeatability) test showing %RSD of 3.76% with LOD value is 0.650 mg/L, and LOQ is 0.724 mg/L. Based on the results of these parameter tests, the method for analyzing thorium in mineral samples was validated.

Molybdenum disulfide-based aptamer sensor for high-precision detection of prostate specific antigen in serum

As a representative transition metal dichalcogenide, molybdenum disulfide (MoS2) has unique electronic, optical, and mechanical properties that exhibit advantages in the construction of biosensing interfaces. In this study, we explored the construction of a MoS2-based aptamer sensor and investigated its application for high-precision detection of prostate specific antigen (PSA) in serum. Carboxyl group-modified MoS2 was stably bonded to the surface of an aminated electrode as a substrate structure, and the electrode was further modified with biocompatible membrane polydopamine and PSA aptamers to form an aminated screen-printed electrode/carboxylated MoS2/polydopamine (SPE-NH2/MoS2-COOH/PDA)-based aptamer sensor, which achieved ultrasensitive detection of PSA at 0.001 pg/mL ∼ 1 ng/mL with a limit of detection (LOD) of 0.16 fg/mL. The detection results of related interfering substances, such as L-cysteine, alpha fetoprotein (AFP), carcinoembryonic antigen (CEA) and bovine serum albumin (BSA), proved that the sensor had good selectivity. Then, repeated test results of multiple sensors verified that the aptamer sensors had good reproducibility between sensors. Finally, the practical application of the aptamer sensor was evaluated by a blank spiking method, which demonstrated its great clinical application potential. In summary, our study has provided ideas for the application of MoS2 composite-based aptamer sensing interfaces for potential precision medicine needs.

Development and Validation of a Novel In Vitro Joint Testing System for Reproduction of In Vivo Dynamic Muscle Force.

In vitro biomechanical experiments utilizing cadaveric specimens are one of the most effective methods for rehearsing surgical procedures, testing implants, and guiding postoperative rehabilitation. Applying dynamic physiological muscle force to the specimens is a challenge to reconstructing the environment of bionic mechanics in vivo, which is often ignored in the in vitro experiment. The current work aims to establish a hardware platform and numerical computation methods to reproduce dynamic muscle forces that can be applied to mechanical testing on in vitro specimens. Dynamic muscle loading is simulated through numerical computation, and the inputs of the platform will be derived. Then, the accuracy and robustness of the platform will be evaluated through actual muscle loading tests in vitro. The tests were run on three muscles (gastrocnemius lateralis, the rectus femoris, and the semitendinosus) around the knee joint and the results showed that the platform can accurately reproduce the magnitude of muscle strength (errors range from -6.2% to 1.81%) and changing pattern (goodness-of-fit range coefficient ranges from 0.00 to 0.06) of target muscle forces. The robustness of the platform is mainly manifested in that the platform can still accurately reproduce muscle force after changing the hardware combination. Additionally, the standard deviation of repeated test results is very small (standard ranges of hardware combination 1: 0.34 N~2.79 N vs. hardware combination 2: 0.68 N~2.93 N). Thus, the platform can stably and accurately reproduce muscle forces in vitro, and it has great potential to be applied in the future musculoskeletal loading system.

Music Box-Inspired Semi-Automatic Hematocrit Validation Device.

A high hematocrit (HCT) level is strongly associated with the risk of cardiovascular disease. For early diagnosis of cardiovascular disease, it is vital to regularly measure the HCT, which is typically achieved by centrifuging a blood sample to measure the percentage of red blood cells. However, the centrifugal modalities are usually bulky, expensive, and require a stable electric input, which restrict the availability. This research develops a semi-automatic and portable centrifugal device for HCT measurement. This torque-actuated semi-automatic centrifuge, which we call the tFuge, is inspired by a music box, allowing different operators to generate the same rhythm. It is electricity-free and can be controlled based on a constant torque mechanism. Repeatable test results can be received from among different users regardless of their age, sex, and activity. With the assistance of the Boycott effect on the tFuge, we proved that the HCT level is in high linearity to the length of the sedimentation of the blood cells in a tube (R2 = 0.99, sample HCT range 10-60%). The tFuge takes less than 4 min and requires no more than 10 μL of blood that can be obtained by a less-invasive finger prick to complete the testing procedure. Calibrated gradient numbers are printed onto the rotation disc for instant HCT results that can be read by the naked eye. We expect this proposed point-of-care testing device possesses the potential to replace the microhematocrit centrifuge in the regions with limited resources.

Remote Contrast Sensitivity Testing Seems to Correlate With the Degree of Glaucomatous Macular Damage.

Remote contrast sensitivity (CS) testing through a free downloadable home test correlates with glaucomatous macular damage measured by 10-2 visual field (VF) testing. To assess the feasibility and validity of home CS monitoring as a measure of glaucomatous damage using a free downloadable smartphone application. Twenty-six participants were asked to remotely use the Berkeley Contrast Squares (BCS) application, a free downloadable tool that records the user's CS for varying degrees of visual acuity. An instructional video detailing how to download and use the application was sent to the participants. Subjects were asked to send logarithmic CS results with a minimum 8-week test-retest window, and test-retest reliability was measured. Results were validated against office-based CS testing that was collected within the previous 6 months. Validity analysis was also carried out to determine whether CS as measured by BCS is a good predictor of 10-2 and 24-2 VF mean deviation (MD). There was a high BCS test-retest reliability with an intraclass correlation coefficient score of 0.91 and a significant correlation between repeat test results and baseline test scores (Pearson, 0.86, P < 0.0001). There was significant agreement between unilateral CS scores as measured by BCS and office-based CS testing ( b = 0.94, P < 0.0001, 95% CI: 0.61 to 1.27). Unilateral CS as measured by BCS was significantly associated with 10-2 VF MD ( r2 = 0.27, P = 0.006, 95% CI: 3.7 to 20.6), but not with 24-2 VF MD ( P = 0.151). This study suggests that a free, rapid home CS test correlates with glaucomatous macular damage as measured by 10-2 VF.

Smanjenje potrebe za ponavljanjem testiranja na nedozvoljene supstance u urinu u okviru sive zone uz pomoć merne nesigurnosti

Background: On an initial urine screening test for illegal substances, if the concentration of a substance is at or above the determined legislative threshold, it is reported as positive. Repeating testing with the same sample to verify it before reporting is a common practice in clinical laboratories. This study aimed to determine whether measurement uncertainty (MU) results can be used to detect a grey zone to reduce repeat testing. Methods: A retrospective study was conducted using data from the laboratory information system between January 1, 2020, and July 1, 2022. Samples studied twice within one hour before reporting for the same urine sample were analyzed. The MU values for urinary amphetamine, cannabinoid, cocaine, and opioid parameters were calculated using ADVIA Chemistry reagents on a Siemens ADVIA 1800 chemical analyzer. The grey zone was defined as the cut-off value ± MU. Results: Urine samples, 319 amphetamine, 198 cannabinoid, 112 cocaine, and 125 opiate tests were repeated from 31.839 patients (16-65 years). Ten amphetamine, 12 can - nabinoid and 2 cocaine test results changed from positive to negative or negative to positive on retesting, all within the grey zone level defined by the MU value. Mean biases bet - ween the repeated test results were -7.64 (95% CI: -13.71 to -1.57) ng/mL for the amphetamine and 1.16 (95% CI: 0.31 to 2.01) ng/mL for the cannabinoid results. Conclusion: Repeating only values within the grey area for each illicit substance may be useful to reduce unnecessary duplicate measurements.

Facile Synthesis of Cr2O3 Embedded g-C3N4 Composites with Excellent Visible-Light Photocatalytic

Metal-free graphite carbon nitride (g-C3N4) has shown great potential in the environmental and energy fields. Herein, we illustrate the facile synthesis of Cr2O3-embedded g-C3N4 interlayer composites using an oil bath and thermal polymerization. The as-prepared 0.3-Cr2O3/g-C3N4 composite photocatalyst exhibited many excellent properties, including significantly promoting charge transfer and separation by establishing interlayer paths, having a large specific surface area, and significantly improving the light absorption intensity. Therefore, the composites of Cr2O3 embedded in g-C3N4 exhibit visible-light photocatalysis. After 50[Formula: see text]min of visible light illumination, the degradation rate reached 99%, which was approximately 9.5 times that of pure g-C3N4. Repeatability test results show that the prepared 0.3-Cr2O3/g-C3N4 catalyst has prominent stability and repeatability. Then, we explain the mechanism of RhB degradation using the synthesized photocatalyst. This work provides a reference for the comprehensive development of g-C3N4 and offers broad prospects for photocatalytic applications of other layered materials.

Prediction of the Physical Properties of a Structural Member by the Impact Hammer Test.

The frequency response function (FRF) in the frequency domain is a black box used to collect physical information and to indicate the modal characteristics of a dynamic system. Analyzing the collected FRF data through the impact hammer test, dynamic parameters, such as stiffness, mass, and the damping matrix, can be estimated. By extracting and analyzing the FRFs within certain ranges of the lowest few resonance frequencies, this study presents a nondestructive method to estimate the dynamic parameters and the material properties. Updating of the dynamic parameters and material properties is a crucial process for the subsequent design and maintenance. This study presents a method to estimate the physical properties of structural members using measured FRF data and generalized inverse. By extracting and analyzing the FRFs within certain ranges of the lowest few resonance frequencies, the dynamic parameters were predicted. It was observed in numerical experiments that the proposed method could properly estimate the elastic modulus and dynamic parameters of steel beams, although the results were affected by the extracted FRF ranges. The physical properties were close to more accurate values in taking the FRFs at more resonance frequencies, as the member was flexible. The proposed method was also extended to a nondestructive test for an estimation of the compressive strength of concrete. However, it faced difficulty due to the external noise contained in the measured data. It was found sin the nondestructive test that the proposed technique was affected by external noise, unlike a simple steel beam. The concrete strength could be predicted by taking the FRFs in a wide frequency range containing the lowest two resonance frequencies and by averaging the repeated test results.

Focus on Bioburden Culture Media and Medical Devices.

Medical devices are a vital part of the global health care system that can have a far-reaching impact on patient treatment. Therefore, they must be sterile to ensure patient safety. The prevalent microorganism's type on a medical device, also known as "bioburden", is a useful indicator of a potential contamination source. Indeed, bioburden is a potential risk to the patient not only because the sterilization process might not be completely effective, but also post-processing because of the possible presence of residual materials. Although bioburden may be confidently killed by destructive sterilization processes, its proliferation before sterilization should be avoided. For the bioburden determination, the culture media and incubation conditions must be carefully selected. The culture medium is of fundamental importance for most microbiological tests: to obtain pure cultures, to grow and count microbial cells, and to cultivate and select microorganisms. A culture medium is essentially composed of basic elements (water, nutrients) to which must be added different growth factors that will be specific to each bacterium and necessary for their growth. Without high-quality media, the possibility of achieving accurate, reproducible, and repeatable microbiological test results is reduced. In ISO 11737-1:2018 "Sterilization of Health Care Products-Microbiological Methods-Part 1: Determination of a Population of Microorganisms on Products", methods for the determination and microbial characterization of bioburden are proposed. However, few guidelines are given as to culture media other than examples and incubation times. Several studies show that other culture media can also be effective, such as Plate Count Agar (PCA). The purpose of this review was to focus on parameters that can have an impact on the bioburden evaluation, specifically the culture medium type for the microorganisms' detection on medical devices. Experimentations conducted in our laboratories showed that PCA appeared to be a medium of primary importance for the detection of bioburden on medical devices; this medium also respects the 3Rs rule.

Strain Release Behaviour during Crack Growth of a Polymeric Beam under Elastic Loads for Self-Healing.

The response of polymeric beams made of Acrylonitrile butadiene styrene (ABS) and thermoplastic polyurethane (TPU) in the form of 3D printed beams is investigated to test their elastic and plastic responses under different bending loads. Two types of 3D printed beams were designed to test their elastic and plastic responses under different bending loads. These responses were used to develop an origami capsule-based novel self-healing mechanism that can be triggered by crack propagation due to strain release in a structure. Origami capsules of TPU in the form of a cross with four small beams, either folded or elastically deformed, were embedded in a simple ABS beam. Crack propagation in the ABS beam released the strain, and the TPU capsule unfolded with the arms of the cross in the direction of the crack path, and this increased the crack resistance of the ABS beam. This increase in the crack resistance was validated in a delamination test of a double cantilever specimen under quasi-static load conditions. Repeated test results demonstrated the effect of self-healing on structural crack growth. The results show the potential of the proposed self-healing mechanism as a novel contribution to existing practices which are primarily based on external healing agents.

Electrochemical Immunoassay for Tumor Marker CA19-9 Detection Based on Self-Assembled Monolayer.

A CA19-9 electrochemical immunosensor was constructed using a hybrid self-assembled membrane modified with a gold electrode and applied to detect real samples. Hybrid self-assembled membranes were selected for electrode modification and used to detect antigens. First, the pretreated working electrodes were placed in a 3-mercaptopropionic acid (MPA)/β-mercaptoethanol (ME) mixture for 24 h for self-assembly. The electrodes were then placed in an EDC/NHS mixture for 1 h. Layer modification was performed by stepwise dropwise addition of CA19-9 antibody, BSA, and antigen. Differential pulse voltammetry was used to characterize this immunosensor preparation process. The assembled electrochemical immunosensor enables linear detection in the concentration range of 0.05–500 U/mL of CA19-9, and the detection limit was calculated as 0.01 U/mL. The results of the specificity measurement test showed that the signal change of the interfering substance was much lower than the response value of the detected antigen, indicating that the sensor has good specificity and strong anti-interference ability. The repeatability test results showed that the relative standard deviations were less than 5%, showing good accuracy and precision. The CA19-9 electrochemical immunosensor was used for the actual sample detection, and the experimental results of the standard serum addition method showed that the RSD values of the test concentrations were all less than 10%. The recoveries were 102.4–115.0%, indicating that the assay has high precision, good accuracy, and high potential application value.

Virological outcomes and risk factors for non-suppression for routine and repeat viral load testing after enhanced adherence counselling during viral load testing scale-up in Zimbabwe: analytic cross-sectional study using laboratory data from 2014 to 2018

BackgroundSince the scale-up of routine viral load (VL) testing started in 2016, there is limited evidence on VL suppression rates under programmatic settings and groups at risk of non-suppression. We conducted a study to estimate VL non-suppression (> 1000 copies/ml) and its risk factors using "routine" and "repeat after enhanced adherence counselling (EAC)" VL results.MethodsWe conducted an analytic cross-sectional study using secondary VL testing data collected between 2014 and 2018 from a centrally located laboratory. We analysed data from routine tests and repeat tests after an individual received EAC. Our outcome was viral load non-suppression. Bivariable and multivariable logistic regression was performed to identify factors associated with having VL non-suppression for routine and repeat VL.ResultsWe analysed 103,609 VL test results (101,725 routine and 1884 repeat test results) collected from the country’s ten provinces. Of the 101,725 routine and 1884 repeat VL tests, 13.8% and 52.9% were non-suppressed, respectively. Only one in seven (1:7) of the non-suppressed routine VL tests had a repeat test after EAC. For routine VL tests; males (vs females, adjusted odds ratio (aOR) = 1.19, [95% CI 1.14–1.24]) and adolescents (10–19 years) (vs adults (25–49 years), aOR = 3.11, [95% CI 2.9–3.31]) were more at risk of VL non-suppression. The patients who received care at the secondary level (vs primary, aOR = 1.21, [95% CI 1.17–1.26]) and tertiary level (vs primary, aOR = 1.63, [95% CI 1.44–1.85]) had a higher risk of VL non-suppression compared to the primary level. Those that started ART in 2014–2015 (vs < 2010, aOR = 0.83, [95% CI 0.79–0.88]) and from 2016 onwards (vs < 2010, aOR = 0.84, [95% CI 0.79–0.89]) had a lower risk of VL non-suppression. For repeat VL tests; young adults (20–24 years) (vs adults (25–49 years), (aOR) = 3.48, [95% CI 2.16 -5.83]), adolescents (10–19 years) (vs adults (25–49 years), aOR = 2.76, [95% CI 2.11–3.72]) and children (0–9 years) (vs adults (25–49 years), aOR = 1.51, [95% CI 1.03–2.22]) were at risk of VL non-suppression.ConclusionClose to 90% suppression in routine VL shows that Zimbabwe is on track to reach the third UNAIDS target. Strategies to improve the identification of clients with high routine VL results for repeating testing after EAC and ART adherence in subpopulations (men, adolescents and young adolescents) at risk of viral non-suppression should be prioritised.

A novel laboratory technique for open-hole gravel-pack design

Gravel-pack completion is implemented in the wellbores to prevent sand production and minimize formation damage due to fines migration. As higher flow velocities exist near the wellbore region, sanding and fines migration are expected to occur in the wellbore vicinity. Therefore, wellbore productivity depends on the gravel-pack performance in allowing the passage of fine particles into the wellbore while preventing the entry of sand particles into the gravel-pack. The gravel design criterion proposed in the literature has been used as a guideline for gravel design, and it has typically provided adequate sand control for field operations. This study introduces a Sand Retention Test (SRT) setup to evaluate the sand production and fines plugging in wellbores completed with open-hole gravel-pack (OHGP). The SRT testing is used to replicate the widely used experimental procedure performed for gravel-pack applications and prove the reasonable repeatability of the results with respect to differential pressure measurements and the effluent fines concentration.SRT experiments with single-phase flow were conducted on a specific formation particle size distribution (PSD), incorporating the gravel-pack and wellbore screen coupon. The application of the SRT facility for OHGP is validated against pioneering experiments in the literature. The results reasonably agree on solid production and gravel-pack impairment trends between the replication and literature test results. Besides, the repeatability test results indicate reasonable agreement between the differential pressures across the sand-pack and gravel-pack and fines production in different tests.This research validates a novel laboratory testing against a gravel sizing criterion that has been commonly used in the industry. The proposed technique can customize testing for gravel-pack design and be employed for further research on the OHGP scenarios.

Hydrogen Production by Water Electrolysis with Low Power and High Efficiency Based on Pre-Magnetic Polarization

In this paper, a method of efficient hydrogen production using low-power electrolysis based on pre-magnetic polarization was proposed in order to improve the rate of hydrogen production by water electrolysis, with reduced energy consumption, molecular polarity, and stress–strain characteristics of distilled water under the condition of a pre-magnetic field. By constructing a microphysical model of hydrogen proton energy-level transition and a macroscopic mathematical model corresponding to magnetization vector-polarization hydrogen proton concentration in the pre-magnetic field, the ionic conductivity, electrolyte current density, interelectrode voltage, and hydrogen production efficiency under a varying magnetic field were qualitatively and quantitatively analyzed. In addition, an adjustable pre-magnetic polarization hydrolyzing hydrogen production test platform was set up to verify the effectiveness of the proposed method. The repeated test results, within a magnetic field strength range of 0–10,000 GS, showed that the conductivity of distilled water after pre-magnetic polarization treatment increased by 2–3 times, the electrolytic current density of the PEM (Proton Exchange Membrane) increased with increasing magnetic field strength, the voltage between the poles continuously decreased, and the hydrogen production rate was significantly improved. When the magnetic field strength reached 10,000 GS, the rate of hydrogen production by the electrolysis of distilled water increased by 15–20% within a certain period of time.

Measurement of covered curvature based on a tape of integrated accelerometers

Quantitative measurements of spinal curvature can indicate the health of the human musculoskeletal system. However, existing measurement techniques are not feasible for unexposed back. This study used accelerometers to develop a portable, noninvasive, nonradiative, and cost-efficient device to quantitatively measure spinal curvature in real time. The measurement accuracy is approximately 99% when measuring a ø200-mm circle. Compared with the results of the three-dimensional motion analysis system, the device exhibited curvature results that were highly consistent in the Bland-Altman test (cervical lordosis angle (CLA): r = 0.973, thoracic kyphosis angle (TKA): r = 0.993, lumbar lordosis angle (LLA): r = 0.961, and spinal alignment trendline (SAT): r = 0.978). Repeatability test results: CLA = 37.63 ± 2.24°, TKA = 32.48 ± 0.98°, and LLA = 15.64 ± 1.12°. Thus, the proposed device can provide accurate and reliable quantitative measurements and can be used for spinal curvature measurements in the supine position.

Impact resistance test system for the helmet based on a polyvinylidene fluoride piezoelectric sensor array

As the most commonly used personal protection equipment (PPE) in various production activities, the impact resistance of the helmet is of great importance. Referred to the conventional experimental method, this study constructs a helmet impact resistance test system with a polyvinylidene fluoride (PVDF) sensor array. Compared with the traditional test method, this study installed PVDF sensors on the contact surface between the headform and the helmet. The stress and its distribution on the headform are measured directly, which is helpful to evaluate the impact resistance of the helmet more accurately and comprehensively. Finally, the intra-group correlation coefficient (ICC) and the coefficient of variation (CV) of peak pressure of the repeated test results are calculated to evaluate the reliability of the test system, which shows high reliability. The test system is helpful for optimization of the helmet production design and further related research.

Strain Sweep Fatigue Testing of Sand Asphalt Mortar to Investigate the Effects of Sample Geometry, Binder Film Thickness, and Testing Temperature

This study evaluated the viscoelastic fatigue behavior of binder using strain sweep fatigue testing of cylindrical sand asphalt mortar (SAM) samples. The SAM samples can represent the realistic film thickness (such as 10–70 μm thick) of the binder in mixtures, while testing repeatability-efficiency can still be met as a result of the use of a standard sand as a load carrier between binder films. A proper testing protocol is still under development, and one of the unknowns in the field is a set of testing conditions that can provide repeatable and case-sensitive test results. Toward that end, SAM samples with different dosages of binder in three geometries were tested at varying temperatures in this study. A PG 64-34 binder was used, and a strain sweep test using a dynamic shear rheometer was conducted to compare the test results from the different cases. Four parameters resulting from the SAM testing were examined: two accounting for material linear viscoelastic behavior and two accounting for fatigue damage characteristics. The parameters were incorporated with statistical analyses to quantitatively evaluate data variability and sensitivity influenced by the binder film thickness, SAM specimen geometry, and testing temperature. The coefficient of variation was less than 20% for all the cases, which indicated the validity of the SAM method attempted in this study. Results also indicated that fatigue behavior was independent of the SAM geometries used in this study, while binder film thickness and testing temperature significantly affected test results.

A novel vertical stress-controlled apparatus for studying suffusion along horizontal seepage through soils

In this study, a novel apparatus was developed for the study of horizontal suffusion behavior of compacted soils under vertical stress. The apparatus consists of a permeameter chamber to accommodate specimen preparation and testing, a pressurized water supply system to generate horizontal seepage flow, a vertical loading system to apply and maintain the vertical stress onto the specimen, a pore water pressure measuring system and a soil–water collection system both to capture the characteristics of the suffusion. The apparatus is featured with a tailor-made flexible pressure bladder for vertical stress control and a modified vacuumizing method for specimen saturation. It has been verified to well perform during the horizontal suffusion, in terms of the specimen uniformity and repeatability of test results. Preliminary tests with this apparatus have been carried out to investigate the suffusion behavior of a gap-graded cohesionless soil. It can be found that suffusion can heterogenize the soil specimen along the seepage direction and that the level of vertical stress significantly affects the horizontal suffusion, such as the initiation and failure hydraulic gradient for suffusion as well as accumulated eroded weight.