Study on the Strength Similarity Theory-Based Blasting Compaction Parameters Optimization

The current blasting compaction faces technical difficulties brought by mud depth increment. The strength similarity theory provides theoretic support for deep mud blasting compaction, offering a large room for blasting parameters optimization. The author applied the strength similarity theory to engineering practice and introduced the deep mud soft foundation blasting compaction, blasting parameters selection, blasting safety and processing effect. According to detection results, the riprap settlement elevation and width can meet design requirements. The riprap bottom interface and bearing layer are well connected. Obvious mud layer is not found in the embankment core. It shows that the application of strength similarity theory achieves the satisfactory effect in the engineering practice.

Extent of Soil Acidity in No-Tillage Systems in the Western Cape Province of South Africa

Roughly 90% of farmers in the Western Cape Province of South Africa have converted to no-tillage systems to improve the efficiency of crop production. Implementation of no-tillage restricts the mixing of soil amendments, such as limestone, into soil. Stratification of nutrients and pH is expected. A soil survey was conducted to determine the extent and geographical spread of acid soils and pH stratification throughout the Western Cape. Soil samples (n = 653) were taken at three depths (0–5, 5–15, 15–30 cm) from no-tillage fields. Differential responses (p ≤ 0.05) between the two regions (Swartland and southern Cape), as well as soil depth, and annual rainfall influenced (p ≤ 0.05) exchangeable acidity, Ca and Mg, pH(KCl), and acid saturation. A large portion (19.3%) of soils (specifically in the Swartland region) had at least one depth increment with pH(KCl) ≤ 5.0, which is suboptimal for wheat (Triticum aestivum), barley (Hordeum vulgare), and canola (Brassica napus). Acid saturation in the 5–15 cm depth increment in the Swartland was above the 8% threshold for production of most crops. Acid soils are a significant threat to crop production in the region and needs tactical agronomic intervention (e.g. strategic tillage) to ensure sustainability.

Deficient stereopsis in the normal population revisited: why current clinical stereo tests may not be adequate

Significance statementApplied applications for occupational screening, clinical tests should assess sensitivity to the sign as well as the magnitude of disparity.PurposeTo determine why the high incidence of stereo anomaly found using laboratory tests with polarity-based increment judgements (i.e., depth sign) is not reflected in clinical measurements that involve single-polarity incremental judgements (i.e., depth magnitude).MethodsAn iPod-based measurement that involved the detection of an oriented shape defined by a single polarity-depth increment within a random dot display was used. A staircase procedure was used to gather sufficient trials to derive a meaningful measure of variance for the measurement of stereopsis over a large disparity range. Forty-five adults with normal binocular vision (20 - 65 years old) and normal or corrected-to-normal (0 logMAR or better) monocular vision participated in this study.ResultsObservers’ stereo acuities ranged between 10 and 100 arc seconds, and were normally distributed on a log scale (p = 0.90, 2-tailed Shapiro-Wilk test). The present results using a single polarity depth increment task (i.e., depth magnitude) show a similar distribution to those using a similar task using the Randot preschool stereo test on individuals between the ages of 19-35 using either the 4-book test (n = 33) or the 3-book test (n = 40), but very different results when the iPod test involved a polarity-based increment judgement (i.e., depth sign).ConclusionsThe present clinical stereo tests are based on magnitude judgements and are unable to detect the high percentage of stereo anomalous individuals in the normal population revealed using depth sign judgements.

Surface Roughness in Incremental Sheet Metal Forming of AA5052

This paper presents the effect of forming parameters on the arithmetic mean surface roughness (Ra) of aluminum alloy built by a single-point incremental sheet metal forming process. Three investigated parameters are feed rate (12.5, 25 and 50 in/min), depth increment (0.015 and 0.030 in), and wall angle (45° and 60°). The results show that wall angle, depth increment and its interaction play an important role on the surface roughness, while feed rate has little effect. The optimal forming conditions for minimum surface roughness are feed rate of 25 in/min, depth increment of 0.015 in and wall angle of 45°.

Influences of Process Parameters on Forming Performance of Sheet Metal Incremental Forming Based on Numerical Simulation

In order to investigate the process of ISF through numerical and experimental approaches, finite element method (FEM) models for two truncated pyramids were developed to simulate the process and the simulated thickness distributions were compared with experimental results. The influences of process parameters on equivalent plastic strain, the maximum equivalent plastic stress and forming force were also discussed. The results show that ISF process is basically to be a plane strain deformation. Wall angle is a more significant influence factor of forming performance than tool diameter and depth increment. With increasing tool diameter, decreasing wall angle and step increment, uniform thickness distribution will be achieved. However, more wall angel, less tool diameter and depth increment contributes to decrease forming force. Additionally, process parameters have no connection with work hardening for a certain material during ISF.

Spatial Scale Interactions in Stereo Sensitivity and the Neural Representation of Binocular Disparity

How are binocular disparities encoded and represented in the human visual system? An ‘encoding cube’ diagram is introduced to visualise differences between competing models. To distinguish the models experimentally, the depth-increment-detection function (discriminating disparity d from d ± Δ d) was measured as a function of standing disparity ( d) with spatially filtered random-dot stereograms of different centre spatial frequencies. Stereothresholds degraded more quickly as standing disparity was increased with stimuli defined by high rather than low centre spatial frequency. This is consistent with a close correlation between the spatial scale of detection mechanisms and the disparities they process. It is shown that a simple model, where discrimination is limited by the noisy ratio of outputs of three disparity-selective mechanisms at each spatial scale, can account for the data. It is not necessary to invoke a population code for disparity to model the depth-increment-detection function. This type of encoding scheme implies insensitivity to large interocular phase differences. Might the system have developed a strategy to disambiguate or shift the matches made at fine scales with those made at the coarse scales at large standing disparities? In agreement with Rohaly and Wilson, no evidence was found that this is so. Such a scheme would predict that stereothresholds determined with targets composed of compounds of high and low frequency should be superior to those of either component alone. Although a small stereoacuity benefit was found at small disparities, the more striking result was that stereothresholds for compound-frequency targets were actually degraded at large standing disparities. The results argue against neural shifting of the matching range of fine scales by coarse-scale matches posited by certain stereo models.

VERTICAL AND LATERAL VARIABILITY OF VANE SHEAR TEST DATA FOR A CLAYEY SOIL

Vane shear (VS) strength in the upper 2 m of a relatively uniform clay soil varied both vertically and laterally. Obtaining VS values which are reliable at the 80% confidence level for the transect tested required measurements at three sites for a depth increment within the upper meter, but a single site would be adequate for depth increments between 1 and 2 m. A preferred procedure to that of characterizing a modal pedon is outlined for estimating VS strength in soil survey. Key words: Vane shear, variability