Linaria subbaetica (Plantaginaceae), a new species from the south of the Iberian Peninsula

Linaria subbaetica, a new species from the south of the Iberian Peninsula, is here described, illustrated, and compared with its morphologically closest relatives from L. sect. Supinae: L. badalii, L. caesia, and L. supina. The species is characterised by being annual, and having usually revolute leaves, a short and corymbiform inflorescence at anthesis with a pilose-glandulose axis, a white to pale-yellow corolla (yellow to orangish palate), bearing a spur equalling to slightly longer that the rest of the corolla, and black seeds with a tuberculate and papillose disc surface and a thickened wing. L. subbaetica is an endemic species, growing on calcareous mountains, in the Sierras Subbéticas Natural Park, Córdoba province (Andalusia, Spain).

Optimal design of the disc vents for high-speed railway vehicles using thermal-structural coupled analysis with genetic algorithm

Braking devices are devices that convert kinetic energy into thermal energy using frictional force. A disc-type brake uses the frictional force to brake and can be used in a wide range of applications, such as automobiles, railway vehicles, and aircraft. However, heat dissipation of the disc has been considered a major problem. High temperatures during the braking process cause thermal stress and deformation problems of the disc because the physical properties of metal composing the disc change drastically with temperature. In this study, vents were applied on the disc surface to increase their heat dissipation performance. In general, vents are structurally susceptible to stress and deformation. However, heat dissipation is essential because the disc surface rises to high temperatures. Therefore, a thermal-structural coupled analysis was performed using the computational fluid dynamics and finite element method methods. Five different rotational speeds and surface temperatures of the disc were considered. Design of experiments was used to determine an optimized design utilizing the data from the coupled analysis, and Latin hypercube sampling was used to generate samples from a set of N regions. And the genetic algorithm was used to conduct a sensitivity analysis of the design parameters. The optimized design was determined for harsh conditions. The diameters of vents were selected 6.87 mm, 6.12 mm, and 5.99 mm in a radial direction through the optimization. Thermal stress and deformation acting on the disc were reduced in the optimally designed disc. The optimized disc model experiences a 7.01% decrease in maximum equivalent stress when compared to the original disc. The model also decreased by 7.63% in maximum equivalent elastic strain. So, through enhanced convection-induced heat dissipation, the vents can be considered as a new way to prevent problems with the thermal stress and deformation that were apparent at high temperatures.

Super-Resolution Imaging with Patchy Microspheres

The diffraction limit is a fundamental barrier in optical microscopy, which restricts the smallest resolvable feature size of a microscopic system. Microsphere-based microscopy has proven to be a promising tool for challenging the diffraction limit. Nevertheless, the microspheres have a low imaging contrast in air, which hinders the application of this technique. In this work, we demonstrate that this challenge can be effectively overcome by using partially Ag-plated microspheres. The deposited Ag film acts as an aperture stop that blocks a portion of the incident beam, forming a photonic hook and an oblique near-field illumination. Such a photonic hook significantly enhanced the imaging contrast of the system, as experimentally verified by imaging the Blu-ray disc surface and colloidal particle arrays.

Effect of triangular oil pockets on friction reduction

The effect of the apex angle of triangular oil pockets created on a disc surface on friction was studied. Experiments were carried out using an Optimol SRV5 tribotester equipped with a pin-on-disc module under unidirectional lubricated sliding. Both the sample and counter sample was made of steel of 45 Hardness Rockwell C (HRC) hardness. Only 1 ml of oil was put to the inlet side of the contact area at the beginning of each test. All textured surfaces had the same pit-area ratio and an average depth of dimples. Oil pockets were positioned in the spiral array. It was found that the effect of the apex angle of triangular dimples on friction reduction was important. When the normal load was lower, the smallest coefficient of friction was achieved for the sliding pair with a disc apex angle of 60°. Under a larger normal load, a higher apex angle corresponded to a higher coefficient of friction.

Modeling the Average and Instantaneous Friction Coefficient of a Disc Brake on the Basis of Bench Tests

This article presents the results of tests conducted on the average and instantaneous friction coefficients of railway vehicle disc brakes. The tests were carried out independently of various states of wear on the friction linings and the brake disc. The requirements of the International Union of Railways (UIC) regarding the approval of brake linings for use were taken into account. Based on many years of research using a brake bench to test railway disc brakes, the authors developed multiple regression models for the average friction coefficient and fluctuations (tolerances) in the instantaneous friction coefficient and achieved 870 results. The models proposed three types of variables: the input braking parameters (speed, pressure, and mass to be braked), operational parameters (the wear on the friction linings and the brake disc), and design parameters (perforations in the form of holes on the disc surface). The above two models were validated on the basis of 384 brakes, and in subsequent stages a further evaluation was performed. The coefficients were determined to be, respectively, 0.99 for the model of the average friction coefficient and 0.71 for the model of tolerance (fluctuations) of the instantaneous friction coefficient.

Effect of Variation of Pin-fin Height on Jet Impingement Heat Transfer on a Rotating Surface

Heat transfer over rotating surfaces is of particular interest in rotating machinery such as gas turbine engines. The rotation of the gas turbine disc creates a radially outward flow on the disc surface, which may lead to ingress of hot gases into the narrow cavity between the disc and the stator. Impingement of cooling jet is an effective way of cooling the disc and countering the ingress of the hot gases. Present study focusses on investigating the effect of introducing pin-fins over the rotating disc on the heat transfer. The jet Reynolds number has been varied from 5000 to 18000, and the rotating Reynolds number has been varied from 5487 to 12803 for an aluminum disc of thickness 6.35mm and diameter 10.16 cm, over which square pins have been arranged in an inline fashion. Steady state temperature measurements have been taken using thermocouples embedded in the disc close to the target surface, and area average Nusselt number has been calculated. The effects of varying the height of the pin-fins, distance between nozzle and the disc surface and the inclination of the impinging jet with the axis of rotation have also been studied. The results have been compared with those for a smooth aluminum disc of equal dimensions and without any pin-fins. The average Nusselt number is significantly enhanced by the presence of pin fins. In the impingement dominant regime, where the effect of disc rotation is minimal for a smooth disc, the heat transfer increases with rotational speed in case of pin fins. The effect of inclination angle of the impinging jet is insignificant in the range explored in this paper (0° to 20°).

Lubrication performance of magnetorheological fluid in shear mode magnetorheological clutch with and without groove

In this work, the lubrication performance of magnetorheological fluid-filled parallel discs of shear mode magnetorheological clutch is investigated. A magnetorheological fluid contains magnetic particles responsible for the yield strength and hence torque transmission capability in the magnetorheological clutch. The wear damages of magnetic particles of a magnetorheological fluid and magnetorheological clutch discs are examined by scanning electron microscopy and optical microscopy. Energy-dispersive X-ray spectroscopy is used to investigate the variation in chemical composition before and after the experimental test. A test rig is developed to test the torque transmission for a fabricated magnetorheological clutch with a grooved and non-grooved disc. The grooves' impact on both magnetorheological clutch discs' wear and magnetorheological fluid is investigated. It has been observed that the minimum wear damage occurs in the magnetic particles and the disc surface for the circular grooved magnetorheological clutch disc surface than the non-grooved disc surface. An effect of surface texture on the temperature distribution of the magnetorheological clutch is studied through simulation. Simulation results show that the groove's presence on the disc surface can improve the magnetorheological clutch's heat transfer. Hence, the grooved texture improves the lubrication performance and durability of both magnetorheological fluid and magnetorheological clutch.

Constraining planetesimal stirring: how sharp are debris disc edges?

ABSTRACT The dust production in debris discs by grinding collisions of planetesimals requires their orbits to be stirred. However, stirring levels remain largely unconstrained, and consequently the stirring mechanisms as well. This work shows how the sharpness of the outer edge of discs can be used to constrain the stirring levels. Namely, the sharper the edge the lower the eccentricity dispersion must be. For a Rayleigh distribution of eccentricities (e), I find that the disc surface density near the outer edge can be parametrized as tanh [(rmax − r)/lout], where rmax approximates the maximum semimajor axis and lout defines the edge smoothness. If the semimajor axis distribution has sharp edges erms is roughly 1.2lout/rmax or erms = 0.77lout/rmax if semimajor axes have diffused due to self-stirring. This model is fitted to Atacama Large Millimeter/submillimeter Array data of five wide discs: HD 107146, HD 92945, HD 206893, AU Mic, and HR 8799. The results show that HD 107146, HD 92945, and AU Mic have the sharpest outer edges, corresponding to erms values of 0.121 ± 0.05, $0.15^{+0.07}_{-0.05}$, and 0.10 ± 0.02 if their discs are self-stirred, suggesting the presence of Pluto-sized objects embedded in the disc. Although these stirring values are larger than typically assumed, the radial stirring of HD 92945 is in good agreement with its vertical stirring constrained by the disc height. HD 206893 and HR 8799, on the other hand, have smooth outer edges that are indicative of scattered discs since both systems have massive inner companions.

Influence of stress state of brake disk on parameters of microgeometry of its surface that is out of contact area

The paper shows results of the study dedicated to influence of contact area stress state on a trend of changes for roughness and waviness parameters of brake disc surface located on the periphery of contact with a brake pad in the coverage area of preferred compression and tensile stresses. It also displays that the main trend of surface deformation under the influence of growing mechanical compression stresses consists in increase of altitude and decrease of step parameters of roughness and waviness. The authors have established that in the coverage area of tensile stresses the roughness and the waviness of the brake disk surface returns to initial values determined in condition of absence of external power influence. On the basis of the results, the authors have explained the process of waviness appearance on the brake disc surface. Results of the study are recommended for the application at solving tasks on friction and wear.

Shear-Thinning Effect of the Spinning Disc Mixer on Starch Nanoparticle Precipitation

Spinning disc technology is capable of achieving intensified micromixing within thin liquid films created through large shear rates, typically of the order of 103 s−1, generated by means of fast disc surface rotation. In this study the effect of the high shear on solvent–antisolvent mixing and starch nanoparticle precipitation is reported. Rheological studies of starch solutions at 2% w/v and 4% w/v have demonstrated their shear-thinning behaviour at the large shear rates experienced on the spinning disc surface. The effect of such high shear rate on starch nanoparticle precipitation is investigated alongside solute concentration and several other operating parameters such as flow rate, disc rotational speed, and solvent/antisolvent ratio. A reduction in nanoparticle size has been observed with an increase in starch concentration, although agglomeration was found to be more prevalent amongst these smaller particles particularly at larger flow rates and disc rotational speeds. Micromixing time, estimated on the basis of an engulfment mechanism, has been correlated against shear rate. With fast micromixing of the order of 1 ms observed at higher shear rates, and which are practically unaffected by the starch concentrations used, micromixing is not thought to be influential in determining the particle characteristics highlighted in this work.