Induced side-branching in smooth and faceted dendrites: theory and phase-field simulations

The present work is devoted to the phenomenon of induced side branching stemming from the disruption of free dendrite growth. We postulate that the secondary branching instability can be triggered by the departure of the morphology of the dendrite from its steady state shape. Thence, the instability results from the thermodynamic trade-off between non monotonic variations of interface temperature, surface energy, kinetic anisotropy and interface velocity within the Gibbs–Thomson equation. For the purposes of illustration, the toy model of capillary anisotropy modulation is prospected both analytically and numerically by means of phase-field simulations. It is evidenced that side branching can befall both smooth and faceted dendrites, at a normal angle from the front tip which is specific to the nature of the capillary anisotropy shift applied. This article is part of the theme issue ‘Transport phenomena in complex systems (part 2)’.

Electron Microbursts Induced by Nonducted Chorus Waves

Microbursts, short-lived but intense electron precipitation observed by low-Earth-orbiting satellites, may contribute significantly to the losses of energetic electrons in the outer radiation belt. Their origin is likely due to whistler mode chorus waves, as evidenced by a strong overlap in spatial correlation of the two. Despite previous efforts on modeling bursty electron precipitation induced by chorus waves, most, if not all, rely on the assumption that chorus waves are ducted along the field line with zero wave normal angle. Such ducting is limited to cases when fine-scale plasma density irregularities are present. In contrast, chorus waves propagate in a nonducted way in plasmas with smoothly varying density, allowing wave normals to gradually refract away from the magnetic field line. In this study, the interaction of ducted and nonducted chorus waves with energetic electrons is investigated using test particle simulation. Substantial differences in electron transport are found between the two different scenarios, and resultant electron precipitation patterns are compared. Such a comparison is valuable for interpreting low Earth-orbiting satellite observations of electron flux variation in response to the interaction with magnetospheric chorus waves.

The accuracy of Infrared sensor detection in a smart toilet

Background: Infrared (IR) sensors are useful tools for detecting distance and proximity. However, these sensors are not good at detecting edges of an area, therefore when used in a smart toilet it has difficulty in detecting the orientation and position of the user’s body. The aim of this study was to design an IR sensor for a smart toilet with a more accurate and consistent detection. Methods: A total of 12(six men and six women) participants with different body types were involved in this study. IR sensor detection was tested in the sitting and squatting toilets. For the best accuracy, the IR sensor's angle was measured. Red, blue, and red-blue plastic covers were used, as these colors improve precision. The microcontroller was set up to calculate the participant’s distance and presence in the cubicle. Results: Toilet positioning varied greatly depending on whether one is sitting or squatting. For sitting toilet, the red cover was close to the accurate distance at a 172˚ angle. IR detected a man but not a woman's body. The blue cover provided the same best angle of 172˚ with a higher sensor distance. When the red and blue cover combination was applied, the reading of 141cm detected both men and women, at 172˚ angle. The actual distance for squatting toilets was 158cm. The optimal angle for both red and blue covers was 176˚, however the sensor distance was greater for the blue cover. Finally, the red and blue cover combination gave a more accurate distance of up to 163cm from the actual reading, when detecting both genders at a normal angle of 76˚. Conclusion: The combination of red and blue cover gave the most accurate detection for the squatting and sitting toilets. The best angle for sitting was 172˚, and for squatting was 176˚.

Propagation and Dispersion of Lightning-Generated Whistlers Measured From the Van Allen Probes

We study the propagation and attenuation of lightning-generated whistler (LGW) waves in near-Earth space (L ≤ 3) through the statistical study of three specific quantities extracted from data recorded by NASA’s Van Allen Probes mission, from 2012 to 2019: the LGW electric and magnetic power attenuation with respect to distance from a given lightning stroke, the LGW wave normal angle in space, and the frequency-integrated LGW refractive index. We find that LGW electric field wave power decays with distance mostly quadratically in space, with a power varying between -1 and -2, while the magnetic field wave power decays mostly linearly in space, with a power varying between 0 and -1. At night only, the electric wave power decays as a quadratic law and the magnetic power as a linear law, which is consistent with electric and magnetic ground measurements. Complexity of the dependence of the various quantities is maximal at the lowest L-shells (L < 1.5) and around noon, for which LGW are the rarest in Van Allen Probes measurements. In-space near-equatorial LGW wave normal angle statistics are shown for the first time with respect to magnetic local time (MLT), L-shell (L), geographic longitude, and season. A distribution of predominantly electrostatic waves is peaked at large wave normal angle. Conversely, the distribution of electromagnetic waves with large magnetic component and small electric component is peaked at small wave normal angle. Outside these limits, we show that, as the LGW electric power increases, the LGW wave normal angle increases. But, as the LGW magnetic power increases, the LGW wave normal angle distribution becomes peaked at small wave normal angle with a secondary peak at large wave normal angle. The LGW mean wave-normal angle computed over the whole data set is 41.6° with a ∼24° standard deviation. There is a strong MLT-dependence, with the wave normal angle smaller for daytime (34.4° on average at day and 46.7° at night). There is an absence of strong seasonal and continental dependences of the wave-normal angle. The statistics of the LGW refractive index show a mean LGW refractive index is 32 with a standard deviation of ∼26. There is a strong MLT-dependence, with larger refractive index for daytime 36) than for nighttime (28). Smaller refractive index is found during Northern hemisphere summer for L-shells above 1.8, which is inconsistent with Chapman ionization theory and consistent with the so-called winter/seasonal anomaly. Local minima of the mean refractive index are observed over the three continents. Cross-correlation of these wave parameters in fixed (MLT, L) bins shows that the wave normal angle and refractive index are anti-correlated; large (small) wave normal angles correspond with small (large) refractive indexes. High power attenuation during LGW propagation from the lightning source to the spacecraft is correlated with large refractive index and anti-correlated with small wave normal angle. Correlation and anti-correlation show a smooth and continuous path from one regime (i.e. large wave normal angle, small refractive index, low attenuation) to its opposite (i.e. small wave normal angle, large refractive index, large attenuation), supporting consistency of the results.

An experimental and theoretical study of the abrasion performance of digital light processing parts

Generally, interactions at surface asperities are the cause of wear. Two-Thirds of wear in industry occurs because of the abrasive or adhesive mechanisms. This research presents an analytical model for abrasion of additive manufactured Digital Light Processing products using pin-on-disk method. Particularly, the relationship between abrasion volume, normal load, and surface asperities’ angle is investigated. To verify the proposed mathematical model, the results of this model are verified with the practical experiments. Results show that the most influential parameters on abrasion rate are normal load and surface’s normal angle. Abrasion value increases linearly with increasing normal load. The maximum abrasion value occurs when the surface’s normal angle during fabrication is 45°. After the asperities are worn the abrasion volume is the same for all specimens with different surface’s normal angle. Though layer thickness does not directly affect the wear rate, but surface roughness tests show that layer thickness has a great impact on the quality of the abraded surface. When the thickness of the layers is high, the abraded surface has deeper valleys, and thus has a more negative skewness. This paper presents an original approach in abrasion behavior improvement of DLP parts which no research has been done on it so far; thus, bringing the AM one step closer to maturity.

Anatomy of the Aqueous Outflow Drainage Pathways

Lowering intraocular pressure (IOP) has been central to glaucoma care for over a century. Minimally invasive glaucoma surgical (MIGS) devices are able to exploit different aspects of aqueous outflow to reduce IOP. Increasing aqueous humour outflow may be achieved either through facilitating the existing pathways of Schlemm’s canal and the suprachoroidal space or to bypass the normal angle anatomy to create a full thickness fistula into the subconjunctival space. A complete understanding of angle anatomy and outflow pathways is important to develop new treatment strategies, improve current ones and better target the right operation for particular glaucoma subtypes.

Simultaneous Measurement of BRDF and Surface Curvature by using Pattern Illumination

In this study, we propose the simultaneous measurement method of the bidirectional reflection distribution function (BRDF) and the radius of curvature by using pattern illumination. For nonplanar objects, the angle of reflection light changes according to the surface normal angle of curved object. Therefore, it is necessary to consider the effects of curved surfaces when measuring the BRDF on non-planar surfaces. We suppose a convex surface that can be represented by a constant radius of curvature. The pattern of illumination was generated by placing the illumination mask with pattern apertures in the incident light path of the BRDF measurement apparatus in which the incident light is collimated light. We developed the measurement apparatus. We measured four types of sample with different BRDFs on three different radiuses of curvature. The results showed that the BRDF and the radius of curvature can be measured simultaneously by using the pattern illumination.

3D Evaluation of the Relationship between Different Vertical Growth Patterns and Cranial Base Angulations

Objectives This study aimed to compare cranial base angulations in subjects with high-angle, low-angle, and normal-angle vertical growth patterns using cone beam computed tomography (CBCT). Design This study is a retrospective clinical research. Settings This study was carried out at the Dentistry Faculty of Eskisehir Osmangazi University. Participants According to skeletal vertical face growth patterns, 78 subjects (48 females and 30 males, average age: 13.19 ± 1.73 years) were divided equally into three groups: high angle, low angle, and normal angle groups. Main Outcome Measures Cephalometric images were derived from CBCT, and patients were classified according to the SN-GoGn angle (sella-nasion, gonion gnathion angle). Sagittal, axial, and coronal cranial base angulations were measured in three-dimensional (3D) CBCT images. Data were analyzed using the Kolmogorov–Smirnov normality, Kruskal–Wallis, and Mann-Whitney U statistical tests. Results There were statistically significant differences between the low-angle and high-angle groups according to sagittal cranial base angulation parameters (p = 0.01). Conversely, there were no statistically significant differences between vertical facial growth patterns according to coronal and axial cranial angle variables (p > 0.05). Conclusion According to the study results, there were no effects of cranial base angulations in two planes (coronal and axial) on different vertical skeletal growth patterns. In the sagittal cranial base angulation parameter, the high-angle group showed greater angulation values than the low-angle group. CBCT may be helpful for evaluating, diagnosing, and predicting 3D cranial base differences.

The Influence of Single and Double Steel Plate Hardness on Fracture Behavior after Ballistic Impact

This study aims to determine the ballistic characteristics of the two steel plates with different hardness levels and mix in the form of layered in non-permanent constructions. Ballistic testing by caliber 5.56 × 45 mm deformed full metal jacket on a sample plate with each a thickness of 6 mm at a distance of 15 m with a normal angle of attack. The results of ballistic testing on both single plates are they can be pierced by a projectile. While for the layered plate, projectile can only penetrate the front side of the plate. The characteristic of each hole that is formed shows the difference caused by the level of hardness of the plate. On the rear part of the plate, a bulge appears because of an impact from the front side of the plate. In the Soft Plate appear high petals around the hole on the front side with the microstructure deformed on the crater walls. While the hard plate forms small petals on the back side and slightly deformed crater walls. The Soft plate is perforated due to deformation with petaling and fragmentation mechanism, while the hard plate is perforated due to plugging mechanism and adiabatic shear band and cracked.