ABOUT ESTIMATION OF THE INFLUENCE OF NON-UNIFORMITY OF INITIAL STATES ON LIFETIME OF FRICTION PAIRS AND TRIBO-FATIGUE SYSTEMS

The article analyzes relationships of the non-uniformity of the initial states and the lifetime of friction pairs and tribo-fatigue systems based on the results of the inspection of the technical condition after operating time and laboratory tests. The non-uniformity of the initial states is determined by the variation within the tolerances of the geometry of the elements due to the manufacturing technology, and its influence on the wear rate, dynamic characteristics and lifetime of mechanical systems is estimated on the example of automobile sliding friction bearing pairs and rolling bearings. A laboratory experiment to assess the performance of a model of a tribo-fatigue system “shaft (steel 45) — roller (25ХГТ (25KhGT) steel)” due to local violation of the shaft geometry during rolling is analyzed. The correlation equations are given that link the integral characteristics of the local process of wear-fatigue damage, based on measurements of the circular contour of the test specimen (coefficients of asymmetry and non-uniformity), with the relative number of cycles until the limiting wear of the tribo-fatigue system “shaft (steel 45) — liner (silumin)” under sliding friction is reached.

Eccentricity Effect of Deformation Detection for Radial Frequency Patterns With Their Centers at Fixation Point

We measured the eccentricity effect of deformation thresholds of circular contours for two types of the radial frequency (RF) patterns with their centers at the fixation point: constant circular contour frequency (CCF) RF patterns and constant RF magnified (retino-cortical scaling) RF patterns. We varied the eccentricity by changing the mean radius of the RF patterns while keeping the centers of the RF patterns at the fixation point. Our peripheral stimulus presentation was distinguished from previous studies which have simply translated RF patterns at different locations in the visual field. Sensitivity for such shape discrimination fell off as the moderate and high CCF patterns were presented on more eccentric sites but did not as the low CCF patterns. However, sensitivity held constant as the magnified RF patterns were presented on more eccentric sites, indicating that the eccentricity effects observed for the high and moderate CCF patterns were neutralized by retinocortical mapping. Notably, sensitivity for the magnified RF patterns with large radii (4°–16°) presented in the peripheral field revealed a similar RF dependence observed for RF patterns with small radii (0.25°–1.0°) presented at the fovea in previous studies.

Inconsistencies of the New No-Boundary Proposal

In previous works, we have demonstrated that the path integral for real, Lorentzian four-geometries in Einstein gravity yields sensible results in well-understood physical situations, but leads to uncontrolled fluctuations when the “no boundary” condition proposed by Hartle and Hawking is imposed. In order to circumvent our result, new definitions for the gravitational path integral have been sought, involving specific choices for a class of complex four-geometries to be included. In their latest proposal, Diaz Dorronsoro et al. advocate for integrating the lapse over a complex circular contour enclosing the origin. In this note, we show that, like their earlier proposal, this leads to mathematical and physical inconsistencies and thus cannot be regarded as a basis for quantum cosmology. We also comment on Vilenkin and Yamada’s recent modification of the “tunneling" proposal, made in order to avoid the same problems. We show that it leads to the breakdown of perturbation theory in a strong coupling regime.

Wideband Circularly Polarized Ellipse Antenna Array with Gain Enhancement

In this paper, a wideband circularly polarized (CP) antenna element and array with gain enhancement are presented. The original antenna element adopts two orthogonal ellipse dipoles with end-loading pillars. In order to achieve a wide impedance bandwidth (IBW), a harpoon-shaped feed patch (HSFP) as electromagnetic coupling-feed is utilized. By introducing a coupled frame and a loop cavity, the gain of the element is crucially improved. Then, four sequentially rotated elements placed in a circular contour act as 2 × 2 array, and a similar loop metal cavity is employed to the array to reach gain enhancement. For the wideband CP performance of the proposed antenna, a wideband phase shifting feed network (WPSFN) is used to construct the antenna. Finally, to verify the feasibility of the proposed antenna, a prototype array is manufactured and measured. Experimental results are found in acceptable agreement with the simulated ones in terms of gain, radiation efficiency, radiation pattern, reflection coefficient, and axial ratio (AR). The result indicates that the proposed antenna has an IBW for reflection coefficient S11 ≤ − 10 dB of 85.7% (0.80–2.00 GHz). Moreover, benefit from the sequentially rotated technique (SRT), the AR at broadside direction keeps blow 3 dB during the overlapped bandwidth of S11≤ − 10 dB, and the ARBW for AR ≤ 1 dB of 74.4% (0.85–1.78 GHz) can be achieved. By employing the loop cavity, the right hand circularly polarization (RHCP) gain is significantly improved, which keeps above 10.00 dBic from 1.05 GHz to 1.85 GHz, and the peak gain reaches to 13.91 dBic.

A Study on Surface Roughness and Cutting Width for Circular Contour Machining of Stir Cast AA6063/SiC Composites in WEDM

Wire electrical discharge machining is used in machining electric conductive materials with intricate shapes and profiles. This paper presents an experimental investigation on the influence of cutting conditions of WEDM on surface roughness and cutting width of machining of AA6063/SiC composites. Here a semi cylindrical piece is removed from a rectangular plate of AA6063/SiC composites plate fabricated with reinforcing SiC in 0%, 5%, 10% and 15% weight fractions through stir casting. The effect of WEDM parameters such as pulse on time, pulse off time and peak current on surface roughness and cutting width on different composition of AA6063/SiC were analyzed for circular contour machining. The experimental results show that increase in percentage of SiC has high influence in mechanical behavior of AA6063/SiC composites and the effect of pulse on time is very significant in reducing the surface roughness and pulse off time plays an important role in producing minimum cutting width.