EIS study of passivation of austenitic and duplex stainless steels reinforcements in simulated pore solutions

Stainless steel reinforcements have proved to be one of the most effective methods to guarantee the passivity of reinforced concrete structures exposed to highly chloride-contaminated atmospheres. In the present work, the corrosion behaviour of two traditional austenitic stainless steels (AISI 304 and 316L types), and one duplex type (2205) are compared with that of a low-nickel, much more economic, austenitic type (204Cu). Ribbed and ground bars of these four materials are studied in non-carbonated and carbonated, saturated Ca(OH)₂ solutions with different chloride contents, using electrochemical techniques. The low-frequency time constant represents the charge transfer resistance (R_t) in parallel with the double layer capacitance. The R_t value of the passive reinforcements seems to be related with the quality of the passive layer. R_t values increase with the immersion time in the testing solutions and decrease with the chloride content. Moreover, R_t tends to increase when the ribs of the bars are removed.     

Effect of cyclic overload on the crack growth behavior during hold period at elevated temperature

Effect of tensile overload on elevated temperature crack growth behavior during the subsequent load hold period has been studied by numerical and experimental methods. Finite element analysis of compact specimens shows that when the tensile overload precedes the load hold period,C _t during the hold period is significantly smaller (i.e. retarded) compared to the case without the overload. This is due to crack tip stress relaxation associated with large crack tip plasticity generated by the overload. A modifiedC _t estimation scheme is proposed by introducing a new equation fort _pl. Using this scheme, the retardation behavior ofC _t due to the overload is successfully modeled. Creep-fatigue crack growth data for an ex-service 1.25Cr-0.5Mo steel at 538°C (1000°F) were generated in air. The hold times are 10 seconds, 98 seconds and 10 minutes. Time-dependent crack growth rate during the load hold period, (da/dt)_avg, is correlated with (C _t )_avg estimated by the new estimation scheme. (da/dt)_avg data from all the tests with overload are higher than those from the tests without overload. The peak stress associated with the overload seems to have enhanced void nucleation and to incrase the time-dependent crack growth rate due to creep. This argument is supported by microscopic observations.     

An integrated local energy density approach to notch low cycle fatigue life prediction

An approach to notch low cycle fatigue (LCF) life prediction based on hysteresis loop energy is described. The method employs an elastic-plastic finite element model of a notched component and a supplemental post-processor to calculate, order and summate elemental energies. These energies, combined with smooth bar LCF data, are used to predict notch LCF life. Predictions using the method are compared to test results on circumferentially notched René 80 specimens tested at 760 and 982°C with stress concentration factors (K_t) of 3.49 and 2.22. Excellent correlation was obtained for K_t = 3.49 at 982°C when a critical notch root volume equal to the notch root plastic zone was assumed. Correlation at 760°C, K_t = 3.49 and 982°C, K_t = 2.22 was not as good. Limitations due to analytic assumptions and micro-mechanistic features as determined by optical, scanning and transmission electron microscopy are discussed and recommendations for further research indicated.     

Modelling the effect of creep–fatigue interaction on crack growth

Time-dependent creep–fatigue crack growth (CFCG) is a major consideration in estimating the remaining life of elevated temperature components. Fracture mechanics approaches have proven useful in providing a framework for characterizing crack growth under service conditions, and in defining safe operating conditions and selecting inspection criteria and intervals. Experimental and analytical approaches have been developed to characterize crack growth under combined creep and fatigue loading conditions using (C_t )_avg as the crack tip parameter. The analytical approaches that have been proposed to characterize CFCG are limited in their application because they do not completely account for the effect of creep–fatigue interactions in modelling crack tip deformation, and thus, accurately estimating the (C_t )_avg value. A new creep-reversal parameter, C_R , is defined in this study to quantify the extent of creep–fatigue interaction at the crack tip, and is used in an analytical scheme, suitable for components, for calculating (C_t )_avg . This approach does not rely on any simplifying assumptions regarding the extent of reinstatement of C_t , which is dependent on the amount of creep reversal due to cyclic plasticity, during the unloading part of a trapezoidal loading waveform cycle. The (C_t )_avg values calculated by this approach compare well with the experimentally obtained values for compact type (CT) specimens, thus providing an experimental verification of the approach.     

Measurements of street-crossing decision-making in pedestrians with low vision

Purpose

Crossing the street is an important but risky activity of daily living. If a pedestrian makes a poor street-crossing decision, the consequence could be serious injury or death. In order to advance our understanding of how visual and auditory information is sampled and processed to make street-crossing decisions, an accurate, reliable, and sensitive psychophysical and/or psychometric method of measurement of the street-crossing decision variable must first be developed and validated. The aim of this paper is to develop and validate a new metric for this variable.

Methods

Using a 5 point rating scale, safety ratings for eight different vehicular gap times of different durations were recorded along an unsignalized, two-lane street of one-way traffic. Safety ratings were collected from 12 normally sighted and 10 visually impaired subjects. Receiver Operating Characteristic (ROC) curves were estimated for all possible gap pairs and the discriminability (d′) of the street-crossing decision variable for all gap pairs was estimated from the area under the ROC curve.

Results

We found that our data conform with the assumptions that the underlying distributions of the decision variable are continuous, monotonic and unbounded. Using the dissimilarity matrix of d’ values for each person (which were computed for all pairings of gap times) in a one-dimensional scaling model, we estimated the means of each distribution of the decision variable relative to a center of gravity (COG) for the person. When plotting the means of the distributions against vehicular gap time, the data are best described as a non-linear function symmetric about the COG. We showed that the x-intercept (t_COG) and slope from the non-linear function can be used to assess a person's street-crossing decision-making performance for different amounts of sensory information. Using our newly developed metrics, we found no significant difference in t_COG (p = 0.30) and in the slopes of the model (p = 0.85) between normally sighted and visually impaired subjects. In addition, both subject groups centered their t_COG close to their actual crossing time.

Conclusions

A newly developed model for measuring a street-crossing decision variable functions as a valid metric that can be used to quantify street-crossing decision-making performance in pedestrians. Using this new metric, we observed that visually impaired subjects who travel independently are able to make street-crossing judgments that are comparable to those of normally sighted subjects.     

Real-time monitoring of the silicidation process of tungsten filaments at high temperature used as catalysers for silane decomposition

The scope of this work is the systematic study of the silicidation process affecting tungsten filaments at high temperature (1900 °C) used for silane decomposition in the hot-wire chemical vapour deposition technique (HWCVD). The correlation between the electrical resistance evolution of the filaments, R_fil(t), and the different stages of the their silicidation process is exposed. Said stages correspond to: the rapid formation of two WSi₂ fronts at the cold ends of the filaments and their further propagation towards the middle of the filaments; and, regarding the hot central portion of the filaments: an initial stage of silicon dissolution into the tungsten bulk, with a random duration for as-manufactured filaments, followed by the inhomogeneous nucleation of W₅Si₃ (which is later replaced by WSi₂) and its further growth towards the filaments core. An electrical model is used to obtain real-time information about the current status of the filaments silicidation process by simply monitoring their R_fil(t) evolution during the HWCVD process. It is shown that implementing an annealing pre-treatment to the filaments leads to a clearly repetitive trend in the monitored R_fil(t) signatures. The influence of hydrogen dilution of silane on the filaments silicidation process is also discussed.     

Elastic J-integral solution for an elbow with axial through-wall crack at crown under in-plane bending

Piping elbows under bending moment are vulnerable to cracking at crown. The structural integrity assessment requires knowledge of the J-integral. The J-integral values for axially through-wall cracked thick elbows are not available in the open literature over a certain range. This paper presents a closed form expression for elastic J-integral for 90°, long radius elbows subjected to bending moment. The expression is derived, based on the results of a large number of finite element analyses covering a wide range of standard geometries. The analyses were performed using WARP3D software. The present study enables the estimation of the elastic J-integral over a range of R_m/t from 5 to 25 (R_m/t = 5, 6, 7.5, 9, 12, 15, 20 and 25) and thus extends the range of earlier solution towards the thicker elbows used in nuclear industry. The crack angles considered were 9°, 18°, 27° and 36°.     

Mean thickness at which vapour-deposited thin films reach continuity

An expression is derived for the mean thickness N₉₉ of vapour-deposited thin films at the moment t₉₉ of 99% substrate coverage. This quantity, characterizing the mean thickness at which thin films reach continuity, decreases with decreasing substrate temperature T and/or increasing deposition rate R. A formula is also obtained for t₉₉ as a function of R and T. Based on the N₉₉(R, T) dependence a growth diagram is constructed in coordinates 1n R versus 1/T and regions of high and variable and of low and constant N₉₉ are determined. The island and normal modes of film growth are discussed and the critical values of R and T are found for the transition from high to low island growth of thin films deposited from vapour. The theoretical results are illustrated with existing experimental data on the deposition of gold on NaCl.     

Anomalous variation of resistance in bismuth thin films and the effect of substrate temperature

Bismuth thin films of thickness 720 Å have been vacuum deposited at various substrate temperatures on glass substrates and their resistances are recorded as a function of temperature after annealing the films at 200°C. The resistance (R) versus temperature (t) curves show anomalous behaviour, in that the resistance first decreases as the temperature increases and then increases as the temperature increases, thus showing a minimum in resistance, R_min at a temperature t_min. The position of R_min (i.e. t_min) and the magnitude of R_min vary with substrate temperature. However, no such anomalous behaviour is observed for the film deposited at room temperature and its resistance monotonically decreases with increase in temperature. These observations have been explained by considering that the bismuth films behave as narrow band gap semiconductors because of the quantum size effect and by the facts that in polycrystalline films the electronic mean free path will be limited by the grain size and also that the average grain size of the film increases as the substrate temperature during deposition increases.     

An equilibrated method of fundamental solutions to choose the best source points for the Laplace equation

For the method of fundamental solutions (MFS), a trial solution is expressed as a linear combination of fundamental solutions. However, the accuracy of MFS is heavily dependent on the distribution of source points. Two distributions of source points are frequently adopted: one on a circle with a radius R, and another along an offset D to the boundary, where R and D are problem dependent constants. In the present paper, we propose a new method to choose the best source points, by using the MFS with multiple lengths R_k for the distribution of source points, which are solved from an uncoupled system of nonlinear algebraic equations. Based on the concept of equilibrated matrix, the multiple-length R_k is fully determined by the collocated points and a parameter R or D, such that the condition number of the multiple-length MFS (MLMFS) can be reduced smaller than that of the original MFS. This new technique significantly improves the accuracy of the numerical solution in several orders than the MFS with the distribution of source points using R or D. Some numerical tests for the Laplace equation confirm that the MLMFS has a good efficiency and accuracy, and the computational cost is rather cheap.     

The surface topography of retrieved femoral heads

Excessive wear of UHMWPE sockets is considered detrimental to the long-term performance of total hip replacement procedures. Although many factors contribute to the wear process, laboratory experiments have indicated that one of the most important factors affecting the wear rate is surface topography and in particular, the arithmetic mean surface roughness, R _a, of the hard counterface. Surface roughness values were therefore obtained from the heads of 37 explanted and five new Charnley prostheses. The surface topography was measured using a Rodenstock RM 600 non-contacting profilometer. Five parameters were used to give a quantitative characterization of the surface texture; arithmetic mean surface roughness, R _a, root mean square (RMS) surface roughness, R _q, peak to valley height, R _t, average single peak to valley height from five adjoining sample lengths, R _z, and the skewness of the height distribution, Sk. Further, qualitative investigations were undertaken using a Joel-JSM-IC848 scanning electron microscope (SEM). The median values of R _a, R _q, R _t and R _z for explanted heads showed statistically significant increases when compared with values from new prostheses. No significant difference was found between any of these parameters measured in the anterior-posterior and the medial-lateral directions. This result may have important implications for the design of joint simulators. No correlation was found between any of the parameters and implant period.     

Time-of-Flight Measurements of Vortices Emitted from Quantum Turbulence in Superfluid 4He

An oscillating obstacle generates quantum turbulence in superfluids, when vortices remained attached to obstacle surfaces or vortex rings collided with it during oscillation. Turbulence provides a source of vortices; however, the characteristics of these vortices are not clear. In the present work, we report the flight of vortices emitted from quantum turbulence in superfluid ⁴He at low temperatures, using vibrating wires as a generator and a detector of vortices. A vortex-free vibrating wire can detect only the first colliding vortex ring, though it will be refreshed after low vibration and be able to detect a vortex ring again. By measuring a period from the start of turbulence generation to the vortex detection repeatedly, we find an exponential distribution of time-of-flights with a non-detection period t ₀ and a mean detection period t ₁, suggesting a Poisson process. Both periods t ₀ and t ₁ increase with increasing distance between a generator and a detector. A vortex flight velocity estimated from period t ₀ suggests that the sizes of the emitted vortex rings distribute to a range smaller than a generator thickness or a generator vibration amplitude. Vortices are emitted radially from a turbulence region, at least in the direction of oscillator vibration.     

Implementation of Clinical Diagnostic Criteria and Universal Symptom Survey Contributed to Lower Magnitude and Faster Resolution of the COVID-19 Epidemic in Wuhan

The majority of cases infected with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in China centered in the city of Wuhan. Despite a rapid increase in the number of cases and deaths due to the coronavirus disease 2019 (COVID-19), the epidemic was stemmed via a combination of epidemic mitigation and control measures. This study evaluates how the implementation of clinical diagnostics and universal symptom surveys contributed to epidemic control in Wuhan. We extended the susceptibles-exposed-infectious-removed (SEIR) transmission dynamics model by considering three quarantined compartments (SEIR^+Q). The SEIR^+Q dynamics model was fitted using the daily reported number of confirmed infections and unconfirmed cases by clinical diagnostic criteria up to February 14, 2020, in Wuhan. Applying the model to carry forward the pre-February 14 trend in Wuhan, the number of daily new diagnosed cases would be expected to drop below 100 by March 25, below 10 by April 29, and reach 0 by May 31, 2020. The observed case counts after February 14 demonstrated that the daily new cases fell below 100 by March 6, below 10 by March 11, and reached 0 by March 18, respectively, 19, 49, and 74 d earlier than model predictions. By March 30, the observed number of cumulative confirmed cases was 50 006, which was 19 951 cases fewer than the predicted count. Effective reproductive number R(t) analysis using observed frequencies showed a remarkable decline after the implementation of clinical diagnostic criteria and universal symptom surveys, which was significantly below the R(t) curve estimated by the model assuming that the pre-February 14 trend was carried forward. In conclusion, the proposed SEIR^+Q dynamics model was a good fit for the epidemic data in Wuhan and explained the large increase in the number of infections during February 12–14, 2020. The implementation of clinical diagnostic criteria and universal symptom surveys contributed to a contraction in both the magnitude and the duration of the epidemic in Wuhan.     

The ductile-brittle transition in a polyethylene copolymer

The ductile-brittle transition of an ethylene-hexene copolymer was measured from 80 to 24° C. The basic curves of stress against time to failure could all be unified in terms of a single equation based on normalizing the stress relative to the transition stress between the ductile and brittle regions and using a single thermal activation parameter. This unity is based on the observations which show that the ductile and brittle failure processes are both associated with a shear process. The unifying equation is $$\left( {\frac{\sigma }{{\sigma _{\text{c}} }}} \right)^n = \left( {\frac{{t_{\text{R}} }}{{t_{\text{f}} }}} \right){\text{ exp }}\left[ {{\text{85 500/}}R\left( {\frac{1}{T} - \frac{1}{{T_{\text{R}} }}} \right)} \right]$$ where σ _c is the minimum stress for ductile failure at an arbitrary temperature, T _R; t _R is the time to failure at an arbitrary reference temperature T _R; n equals 34 and 3.3 for the ductile and brittle regions, respectively and R is in J mol^?1 K^?1.     

T-Stress solutions for a semi-elliptical axial surface crack in a cylinder subjected to mode-I non-uniform stress distributions

This paper presents the T-stress solutions (T₁₁ and T₃₃) for semi-elliptical axial surface cracks in a cylinder subjected to mode-I non-uniform stress on the crack surface. Two cylindrical geometries with inner radius (R_i) to wall thickness (t) ratios R_i/t = 5 and 10 were considered. The T-stresses were applied along the crack front for normalized crack depth values a/t of 0.2, 0.4 and 0.5 and aspect ratios a/c of 0.2, 0.4, 0.6 and 1.0. Three stress distribution; uniform, linear and parabolic were applied to the crack face. In addition to these solutions, concrete formulation of the superposition principle is given for the T₃₃-stress, which is known as an elastic parameter that describes the out-of-plane crack tip constraint effect. Then, the validity of the formulation was shown through application of our T-stress solutions to the problem of an axial semi-elliptical surface crack in a cylinder subjected to internal pressure, and checking that the principle of superposition holds for the problem.     

How the Surface Resistance R s of Patterned High-T c Superconducting Thin Film Is Affected by the Film's Edge

This paper defines an effective microwave surface resistance $R_{\text{s}}^{{\text{eff}}}$ for the nonuniform distribution of microwave surface resistance R _s in the strip of a microstrip. It is proved that $R_{\text{s}}^{{\text{eff}}}$ is equivalent to the expression of R _s used in experiments, and that the $R_{\text{s}}^{{\text{eff}}}$ is dominated by the edge part, i.e., the area of width λ²/2t from the strip edge, where λ is the magnetic penetration depth and t is the film thickness. Under the assumption that $R_s \sim \left( {H_{{\text{rf}}}^y } \right)^n$ where $H_{{\text{rf}}}^y$ is the component of rf magnetic field along the film thickness and n is an integer, the ratio of the contributions of the edge part and the rest of the strip to $R_s^{{\text{eff}}}$ is calculated by using an approximate analytical expression of the surface current density distribution J _s in the strip and $H_{{\text{rf}}}^y$ calculated by the London equation. The effect of film's edge on R _s was studied using a microstrip resonator. It is found that the perfectness of the edge could affect the magnitude of the power dependence of R _s significantly, which agreed with our analysis.     

A synergistic creep fatigue failure model damage (case of the alloy Z5NCTA at 550 °C)

Creep-fatigue tests have been performed on nickel base alloy Z5NCTA 33-21 grade 1. Hold time varied from 0, 10, 30, 90, 300, 1440 and 10,080 min at two values of strain range. It was found that the number of cycles to failure N_R decreases with holding time t_m, according to a power law:

N_R=1.88×10³·(t_m)^-0.39.     

Accelerated life-test experiments on low-power rectifier diodes

Low-power rectifier diodes were stressed by different forward currents I_F, reverse voltages U_R, and ambient temperatures _a for a time interval (0, t*) in order to analyse the resulting distributions. Owing to the limitations in the test time, t*, the gathering of comprehensive information about their performance requires high stress levels without exceeding either physical limits or the limits for initiating thermal runaway. First, the results of lifetime experiments related to the middle stress region were described by a Weibull distribution with constant shape parameter and stress-dependent scale parameter. This model, however, did not fit sufficiently the typical features of the real-life distribution. Therefore a non-parametric measure called the average initial reliability in (O,t*) was defined using the experimental results. Its stress dependence was estimated. The results are guiding figures of stress conditions both for accelerated tests and for circuits with high demands on reliability.     

Optimization of the TES-Bias Circuit for a Multiplexed Microcalorimeter Array

A transition-edge-sensor (TES) microcalorimeter’s shunt resistor (R _sh) and thermal conductance to the cryogenic bath (G) are often considered to be interchangeable knobs with which to control detector speed. Indeed, for otherwise-identical TES-parameter models, there are many combinations of R _sh and G that give the same decay time-constant (τ _crit). However, our previous work showed that with time- or code-division-multiplexed readout, the distribution of signal-to-noise ratio with frequency, which depends strongly on R _sh and G, is just as important as τ _crit. Here, we present a set of calculations to select the optimal values of R _sh and G, given a linear TES model and count-rate and energy-resolution requirements. Lower G and lower R _sh make multiplexing easier. Our calculations also determine the allowed combination of SQUID-readout noise (S _Φ ) and multiplexer row-period (t _row) and row-count (N _rows). Recent improvements to S _Φ and t _row in the NIST time-division-multiplexing architecture have allowed a NIST eight-pixel TES array to be read out with 2.70?eV (full-width at half-maximum) average energy resolution at 6?keV. The improvements make the X-ray Microcalorimeter Spectrometer co-proposed by NASA and NIST for ESA’s Athena X-ray observatory straightforwardly achievable, including engineering margin, with N _rows=16.