The Stiles–Crawford effect: a theoretical revisit

Abstract

In 1973, Snyder and Pask published an explanation of the Stiles–Crawford effect based on optical-waveguide theory, but used only one set of experimental data for comparison. Since then there have been many new experiments and comments on the theory. In this paper we examine the assumptions made in the original theory, introduce some refinements, address some of the comments and examine how well the theory explains the experimental results obtained since 1973. We conclude that the waveguide theory, with some minor improvements, provides the theoretical basis for understanding the Stiles–Crawford effect.     

Uniaxial flicker analysis of the psychophysical Stiles–Crawford effects

Purpose: We report on a semi-automated system for frequency analysis of the Stiles–Crawford effect of the first kind (SCE-I) using flicker methodology designed to gain insight into the temporal dynamics of the perceived visibility for alternating pupil entrance points. We describe the system and its calibration in detail and discuss psychophysical measurement data obtained for the two authors. Methods: A uniaxial system is used for SCE-I characterization of two emmetropic subjects as a function of flicker frequency for narrow wavelength bands chosen in the range of 450–700 nm using a fibre-guided tungsten–halogen lamp as light source. The flicker is realized using two orthogonally mounted galvanometric scanning mirrors that allow linear trajectories at any angle across the pupil. A fast tuneable liquid-crystal neutral density filter is used for brightness adjustment and another liquid-crystal filter is used for wavelength adjustment at each pupil point allowing simultaneous hue-shift determination for the Stiles–Crawford effect of the second kind (SCE-II). Results: Validation of the system is realized with a CCD camera, a spectrometer and a powermeter, and the data obtained are used in the software to calibrate all subsequent human subject measurements. The psychophysical data obtained show a strong frequency dependence of the Gaussian SCE-I with a characteristic directionality parameter, ρ, that is found to increase from 0.03 to 0.06/mm² with flicker in the range of 1–10 Hz. The simultaneously determined hue shift could not be determined beyond 1 Hz due to the longer time required for a subjective determination. Conclusion: We have reported on a fast uniaxial system for temporal characterization of the SCE-I. The psychophysical results obtained show that accurate specification of frequency in flicker analysis is mandatory when comparing SCE-I visibility and directionality curves obtained with those obtained using quasi-static bipartite fields. A uniaxial design offers unique advantages over that of common two-channel systems by completely eliminating spectral errors or brightness differences in the two branches that otherwise will impose on those of the visual system and degrade the psychophysical data. Future work with more subjects will be used to narrow the uncertainty and the causes of the effects observed.     

Incorporating small fatigue crack growth in probabilistic life prediction: Effect of stress ratio in Ti–6Al–2Sn–4Zr–6Mo

The effect of stress ratio on the statistical aspects of small fatigue crack growth behavior was studied in a duplex microstructure of Ti–6Al–2Sn–4Zr–6Mo (Ti-6-2-4-6) at 260 °C with particular emphasis on incorporating small-crack data into probabilistic life prediction and the influence of stress ratio on probabilistic lifetime limits. A Focused Ion Beam (FIB) was used to machine micro-notches in test specimens, which served as crack-initiation sites and enabled the acquisition of multiple small-crack growth data sets from single experiment. Stress ratios of −0.5, 0.05, and 0.5 were employed, and small-crack growth was monitored by the acetate replication method. Qualitatively, change in the stress ratio produced almost negligible influence on the small-crack growth behavior when plotted as crack growth rate (da/dN) vs. applied stress intensity factor range (ΔK). A probabilistic method was employed to represent the variability in the small-crack growth behavior and the statistical differences with respect to stress ratio where a method of optimization of the small-crack growth model parameters, based on a minimization of the error between the predicted and the measured crack length vs. cycles (a vs. N) data, was used. In spite of qualitative similarity, differences in the statistical parameters of small-crack growth as a function of stress ratio were found to be significant in life prediction. The methods for representation and probabilistic treatment of small-crack data were also shown to be important factors in incorporation of the small-crack regime in probabilistic life prediction.     

Effect of mixing ratio on bactericidal action of MgO–CaO powders

MgO–CaO powders were prepared with different molar ratios (MgO/CaO) at 1400 °C for 2 h in air. By using the powder samples obtained, the change in bactericidal effect as a function of MgO–CaO composition was studied by colony count method. From the XRD measurements, it was found that CaO solid solution was formed by the replacement of Mg²⁺ ion with larger Ca²⁺ ion. However, no formation of MgO solid solution was observed. The average particle size and the specific surface area of the samples used in this study were about 0.2 m and 10.5m²g^–1, respectively. The pH values of physiological saline containing powder samples increased with the increase of CaO content, and the value reached 12.1 in sample with the molar ratio (MgO/CaO) of 0.25. From the results of bactericidal tests for Staphylococcus aureus, it was found that the bactericidal effect increased with the increase of CaO content in the samples.     

The Effect of Plastification of Cu–14Al–4Ni Alloy with the Shape Memory Effect in High-Temperature Isothermal Precipitation

Technical Physics Letters - It was found that deformation by the uniaxial compression scheme (while measuring mechanical properties under isothermal conditions) at 600–800°C leads to a...     

The Casimir Effect in a Dilute Bose Gas in Canonical Ensemble within Improved Hartree–Fock Approximation

Journal of Low Temperature Physics - The Casimir effect in a dilute Bose gas confined between two parallel plates is investigated at zero temperature by means of...     

The “Paramagnetic” Meissner Effect in Superconductors

There are a number of publications concerning the observation of a paramagnetic signal in HTSC ceramic samples during field-cooling procedures. Some authors assume that this signal is connected with spontaneous currents and discuss the possibility of the existence of -junctions in Josephson media. In this work, it is shown that the paramagnetic signal could appear in the case of capture and compression of the magnetic flux in a sample during field-cooling procedures. The results of numerical calculation of the magnetic moment for different configurations of the sample and flux compression are presented. The unusual behavior of longtime relaxation of the magnetic moment in experiments on capture of magnetic flux is discussed.     

Effect of cold drawing ratio on γ′ precipitation in Inconel X-750

Inconel X-750 is a Ni-based precipitation-hardened superalloy having large tensile and fracture strengths. In the study, X-750 wires were cold drawn to different extents. Small angle neutron scattering was employed to quantitatively measure the size and volume fraction of the γ′ phase as a function of the cold drawing ratio (DR) and aging temperature. The presence and size of γ′ precipitates were confirmed by transmission electron microscopy. The drawing ratio had an important effect on the volume fraction of the γ′ precipitates. However, the size of the precipitates was independent on the drawing ratio. The specimen with the minimum drawing ratio (DR0) produced the largest volume fraction of γ′ as compared with large drawing ratio (DR) specimens such as DR17 and DR42. The small volume fraction of the γ′ phase for a sizeable drawing ratio was associated with the large amount of nucleation sites for secondary carbides, M₂₃C₆, and the fast diffusion path, i.e., dislocation, needed to form M₂₃C₆. A Cr depletion zone around the secondary carbides raised the solubility of γ′. Therefore, the significant drawing ratio contributing to the large volume fraction of the secondary carbides decreased the volume fraction of the γ′ precipitates in Inconel X-750.     

Development of constant output–input force ratio in slider–crank mechanisms

In the slider–crank mechanism whereby output piston force is produced against an input force at crank pin centre, the output force varies rapidly when the crank changes its position. For the applications that require a constant piston pushing force as in feeder mechanisms, a method is needed for identifying the parameters to keep output force at a constant value for any crank angle position. Hence in this study, two methods are shown for a slider–crank mechanism operating in horizontal plane. In the first one, a manual control process to generate a constant piston force and the resulting errors are demonstrated. In the second one, identifying the parameters of a mechanical controller for a readily available slider–crank mechanism in an open force control process and the associated error state are shown. Then, an approach to optimize the results of open force control is explained. Finally, the developed methods are generalized for any orientation of the whole slider–crank mechanism. A user friendly interface is developed to transform all the processes into a computer programme. The effectiveness of the methods are numerically illustrated on examples. The results of these examples show that ±4% deviation from the required output force can be obtained pending on the user’s ability while the optimized open force control process provides a maximum error of ±0.4% without any user intervention during operation.     

The Superconducting Magnetoresistance Effect in Ni80Fe20–Nb–Ni80Fe20 and Co–Nb–Co Trilayers: Requisites for Tailoring its Magnitude

The superconducting magnetoresistance effect (SMRE) observed in trilayers (TLs) consisting of a superconducting (SC) Nb interlayer and two outer ferromagnetic (FM) Ni₈₀Fe₂₀ and Co layers is studied. We observed that the SMRE exhibits a pronounced magnitude (R _max?R _min)/R _nor of order 45 % and 86 % for the NiFe-based and Co-based TLs, respectively. For the NiFe-based TLs, the dynamic transport behavior of the observed SMRE is presented through detailed I–V characteristics that exhibit a nonlinear character even extremely close to the critical temperature, $T_{c}^{\mathrm{SC}}$ . Also, the detailed evolution of the longitudinal and transverse components of the TL magnetization from close to well below $T_{c}^{\mathrm{SC}}$ is presented. For the Co-based TLs, the obtained magnetization and transport data justify that a strict requisite for the observation of a pronounced SMRE across $T_{c}^{\mathrm{SC}}$ is that the coercivities of the FM layers should be similar. The combined data on the NiFe-based and Co-based TLs show that across the superconducting transition the SMRE is influenced by out-of-plane stray-fields, attaining pronounced values when the respective coercive fields coincide, thus enabling the transverse magnetic coupling of the outer FM layers through the SC interlayer.     

The Pinski–Narin influence weight and the Ramanujacharyulu power-weakness ratio indicators revisited

Scientometrics - A graph theoretic approach from social network analysis allows size-dependent and size-independent bibliometric indicators to be identified from what is called the citation matrix....     

Rashba Effect in IV–VI Semiconductor Quantum Wells

The spin–orbit split quantized states for electrons confined in IV–VI lead-salt asymmetric quantum wells (QWs), grown on both (100) and (111) substrates, are obtained analytically within the envelope function approximation with a k p four-band model for the bulk. Nonparabolicity, anisotropy, and break of valley degeneracy are included. In (111) QWs, it is shown that for the valley along the growth direction the Rashba splitting is like the one in III–V QWs, i.e., isotropic and linear in k (for k 0). For the oblique valleys, contrary to the III–V case, a Rashba effect is obtained that is anisotropic and described by an effective magnetic field with nonzero component along the growth direction. Specific results for PbTe/PbEuTe asymmetric QWs with large Rashba splittings are shown.     

Effect of Heterostructure-Modified Separator in Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries with high energy density and low cost are the most promising competitor in the next generation of new energy reserve devices. However, there are still many problems that hinder its commercialization, mainly including shuttle of soluble polysulfides, slow reaction kinetics, and growth of Li dendrites. In order to solve above issues, various explorations have been carried out for various configurations, such as electrodes, separators, and electrolytes. Among them, the separator in contact with both anode and cathode is in a particularly special position. Reasonable design-modified material of separator can solve above key problems. Heterostructure engineering as a promising modification method can combine characteristics of different materials to generate synergistic effect at heterogeneous interface that is conducive to Li–S electrochemical behavior. This review not only elaborates the role of heterostructure-modified separators in dealing with above problems, but also analyzes the improvement of wettability and thermal stability of separators by modification of heterostructure materials, systematically clarifies its advantages, and summarizes some related progress in recent years. Finally, future development direction of heterostructure-based separator in Li–S batteries is given.     

The Fulde–Ferrell–Larkin–Ovchinnikov State in Pnictides

We present experimental results on crosstalk of non-electrical origin between high frequency quartz tuning forks immersed in the same volume of helium gas, liquid or superfluid. We compare these results with various observations of other groups and propose an explanation of this puzzling phenomenon. To the best of our knowledge, notable crosstalk has only been observed in superfluid helium both in the two-fluid regime and at very low temperatures, but was rarely seen to behave in a systematic way. We demonstrate some of its most significant properties—amplitude dependence within a short time span, long-term temporal instability, effects of the geometry of the setup and of obstacles placed between the tuning forks. Although the results are not fully understood, as the most likely explanation, we ascribe the observations to the coupling of tuning forks to standing acoustic modes inside the experimental volume, emphasizing the importance of second sound for understanding the observations at temperatures within the two-fluid regime (1 K<T<2.17 K). Finally, we suggest simple precautions leading to suppression of excessive acoustic crosstalk between oscillating objects in He II.     

The role of Chinese–American scientists in China–US scientific collaboration: a study in nanotechnology

In this paper, we use bibliometric methods and social network analysis to analyze the pattern of China–US scientific collaboration on individual level in nanotechnology. Results show that Chinese–American scientists have been playing an important role in China–US scientific collaboration. We find that China–US collaboration in nanotechnology mainly occurs between Chinese and Chinese–American scientists. In the co-authorship network, Chinese–American scientists tend to have higher betweenness centrality. Moreover, the series of polices implemented by the Chinese government to recruit oversea experts seems to contribute a lot to China–US scientific collaboration.     

Tunneling Conductance in Strained Graphene-Based Superconductor: Effect of Asymmetric Weyl–Dirac Fermions

Based on the BTK theory, we investigate the tunneling conductance in uniaxially strained graphene-based normal metal (NG)/barrier (I)/superconductor (SG) junctions. In the present model, we assume that by depositing the conventional superconductor on the top of the uniaxially strained graphene, normal graphene may turn to superconducting graphene with the Cooper pairs formed by the asymmetric Weyl–Dirac electrons, the massless fermions with direction-dependent velocity. The highly asymmetrical velocity, v _y /v _x ≫1, may be created by strain in the zigzag direction near the transition point between gapless and gapped graphene. In the case of highly asymmetrical velocity, we find that the Andreev reflection strongly depends on the direction of strain, and the current perpendicular to the direction of strain can flow through the junction as if there were no barrier. Also, the current parallel to the direction of strain anomalously oscillates as a function of the gate voltage with very high frequency. Our predicted result is quite different from the feature of the quasiparticle tunneling in the unstrained graphene-based NG/I/SG conventional junction. This is because of the presence of the direction-dependent-velocity quasiparticles in the highly strained graphene system.     

The Effect of Hysteresis Loss on Magnetic Entropy Change in Highly Textured Mn-Ni–Sn Melt-Spun Ribbons

Journal of Superconductivity and Novel Magnetism - Highly textured Heusler alloy Mn44.7Ni43.5Sn11.8 ribbons were prepared by melt spinning. The magnetocaloric properties were evaluated by the...