Academic literature on the topic 'Constant inter-layer distance'

BACKGROUND: The subject of research is the process of transverse discarding of soil by the outer disk mounted on the front section of a disk harrow in the conditions of inter-row spacing of a berry plantation. AIMS: Reduction of the range of discarding of a soil layer by the outer disk mounted on the front section of a disk harrow in the conditions of inter-row spacing of a berry plantation. METHODS: All studies were carried out on a raspberry plantation. Soil moisture was 28%. The disc harrow was aggregated with the T-25A tractor moved at a constant speed of 7.29 km/h, had an attack angle of 21 and a processing depth of 0.1 m. While carrying out field experiments, the location of all soil fragments outside the furrow formed by the outer disk of the rear section was considered. Both the distance to the fragment edge furthest from the furrow wall and the fragments slope relative to ч were recorded. RESULTS: According to the results of field experiments, it was found that the value of the transverse discharge of waterlogged and over-compacted soil in inter-row spacing of berry bushes significantly exceeds the amount of overlap between the front and rear sections of the disc harrow. To exclude the soil discarding into the bush area, the disc harrow was equipped with an additional bump shield oriented at an angle of 5354 in horizontal plane and at an angle of 50-58 to the direction of movement of the harrow. CONCLUSIONS: The practical implementation of this technical solution makes it possible to maintain the surface of inter-row spacing at a leveled state throughout their entire service life. At the same time, the disk harrow operates steadily, both with a high degree of impurity of inter-row spacing and excessive soil moisture, as well as provides with grinding and sealing of the annually cut-out raspberry stems.

One of the main and important technological characteristics of filter units is dirt holding capacity, the value of which determines the required frequency of the filter’s inter-flushing period. The object of this study is a vertical pressure filter with an upward flow of purified water and a clamped filter layer. The research methods used include analysis of literary sources on the topic under study, experimental studies to measure the quality of source water entering the filter, particle size distribution, filtration speed, pressure loss in the filter load and the nature of the distribution in the filter layer of the load. The study of the dirt holding capacity of the load by its height, the ultimate goal was to determine the nature of the distribution of contaminants along the height of the load, depending on the given particle size distribution under conditions of ultra-high-speed filtration with a constant speed and the movement of water from bottom to top in the direction of decreasing size grain loading. According to the results of studies based on data collected over a one-year period, it is shown that the retained contaminants along the height of the filter load are distributed unevenly; the largest amount of contaminants is retained in the lower layers of the load and as the distance from the lower boundary of the filter load increases, the content of extracted suspended substances in it gradually decreases, and conclusions are also given that, other things being equal (the same particle size distribution and height of the load, the content of suspended substances in source water), the dirt holding capacity of the filter during ultra-high-speed filtration with an upward flow is two and a half times higher than the dirt holding capacity during filtration with a downward flow, and one and a half times higher than the dirt holding capacity during filtration with an upward flow and a constant filtration speed.

Although measurements of water drawdown by single radish root systems have been previously published by the authors, further research is needed to evaluate water drawdown patterns in multiple-root systems. The objective of this study was to compare water transpiration patterns estimated using X-ray computed tomography (CT) with the traditional gravimetric method and to evaluate the effects of variably spaced multiple root systems on soil water content and corresponding water content gradients. Water drawdown showed a dual pattern in which it increased rapidly when soil water content was high at the beginning of transpiration, then slowed down to an almost constant level with time as water content decreased. These results contrast with the single-root system wherein transpiration rates initially increased rapidly and then slowly increased with time. Water uptake estimated using the CT method was observed to be 27–38% lower than the gravimetrically estimated water uptake; this difference was attributed to lower water uptake for the upper 30 mm layer (CT measured) than lower layers due to differences in root density. However, good correlation (r = 0.97) was found between both measurement methods. The drawdown patterns for multiple root systems showed a convex shape from the root surface to the bulk soil, compared with a nearly linear shape for single roots. The water content drawdown areas and the drawdown distances for multiple root systems were found to be much larger than those corresponding to single radish roots. Differential water content gradients were observed for roots spaced at 15-mm distances compared with 3–4-mm distances. These differential gradients from the bulk soil towards the root-zone occurred probably creating localised water potential gradients within the root-zone, which moved water from between roots to root surfaces. The lowest water content values were located in the inter-root areas. The CT-scanned layer probably acted as one drawdown area with particularly higher water drawdown from the inter-root areas.

Abstract Lead borate glasses of the system 25PbO-(75-x) B2O3-xCuO (x = 0, 0.025, 0.05, and 0.1) in mol.% were synthesized via the traditional melt quenching method abbreviated as (BPbCu0, BPbCu1, BPbCu2, and BPbCu3) respectively. XRD diffraction confirmed the amorphous nature of the samples. According to FTIR spectroscopy, the function groups (BO3 and BO4) and the fraction of boron tetrahedral units (N4) were determined. The density, molar volume, packing density, and some other physical parameters were calculated and discussed. The density was increased by incorporating CuO as a substitution for B2O3, while the molar volume was decreased. The ion concentrations of Cu, inter-nuclear distance, field strength, and polaron radius were also computed. The optical absorption study suggested that the copper ions exist in the Cu2+ and act as a modifier by increasing the disorder in the glass network. Hence, the present glass behaves as a bandpass filter in the UV-Vis. region. The radiation shielding properties of the as-prepared samples were theoretically calculated using the Phy-X program at energies ranging from 0.015 to 1.5 MeV. The linear and mass attenuation coefficients, as well as the half-value layer (HVL) and exposure buildup factor (EBF), have been evaluated. The results revealed that shielding parameters are affected by CuO concentrations and photon energy. Based on the results presented in the manuscript, the glass sample with 0.1 mol% CuO doping (BPbCu3) showed the best properties overall for optical and radiation shielding applications. Specifically, BPbCu3 had the highest density, refractive index, optical dielectric constant, and radiation shielding parameters such as linear attenuation coefficient and half value layer among the glass samples. The addition of 0.1 mol% CuO introduced Cu2+ ions which acted as network modifiers, increasing the disorder in the glass structure. This in turn enhanced the optical bandgap as well as the shielding capabilities against gamma radiation.

Particle effects on the amplitude modulation are investigated in this study based on observational data with various mass loading acquired from long-term measurements of aeolian sandstorms in high-Reynolds-number ( $Re_{\tau }\sim O(10^6)$ ) near-neutral atmospheric surface layers. In both particle-laden and unladen flows, in addition to the positive top–down modulation behaviour in the logarithmic region, a significant modulation effect that exists for some specific motions is also found for the single-point amplitude modulation. The most energetic turbulent motions exhibit the strongest modulation effect, and the modulating signals do not change with the small-scale motions being modulated. In particle-laden flows, the length of the most energetic structure is almost constant, thus the scales of the modulating signal and carrier signal are hardly affected by particles. However, the addition of particles changes the distribution of energy between multi-scale turbulent motions. The kinetic energy of the large-scale component is less enhanced than the total kinetic energy by particles. This leads to a reduced energy proportion of the large-scale component and an augmented one of the small-scale component. Moreover, the particles produce a large damping in the degree of the amplitude modulation and move down the positions of the modulating signals and carrier signals corresponding to the strongest inter-layer modulation, but the damping is weakened with the wall-normal distance due to the decreased mass loading. This study may provide a more general insight into the modulation mechanism between multi-scale turbulent motions and the effect of particles on turbulence.

The effect of temperature on the mechanical behaviour of clay-based geomaterials is relevant in several geotechnical applications (e.g., low enthalpy geothermal systems, energy geostructures and nuclear waste disposal). The mechanical response of (saturated) normally consolidated (NC) clay to temperature variation is not intuitive as the material irreversibly contracts upon heating. Since the thermal contraction observed at the engineering scale does not correspond to the thermal expansion of the clay constituents, both in sign and amplitude, the thermo-mechanical response is usually attributed to temperature-induced changes in the arrangement of clay particles/aggregates (changes in the inter-particle/aggregate porosity) [4] or to the nano-scale thermo-mechanical behaviour of the adsorbed water between clay unit layers (changes in the intra-particle porosity) [3]. Especially for clay minerals with a large amount of adsorbed water, such as swelling clays (tens of % of the total water is absorbed in saturated swelling clay samples), the latter hypothesis has been investigated numerically by molecular dynamics modelling of a layer-water-layer system in non-isothermal conditions [3,8] and experimentally through X-ray diffraction and scattering experiments (XRD, SAXS) [5,6,7]. According to the numerical simulations in [3,8], the free energy barrier between stable system states (the number of adsorbed water layers surrounding a clay particle) decreases with temperature, inducing a possible transition between mobile and immobile water. This nanometric phenomenon may result in a macroscopic volumetric thermal contraction. A similar picture comes from the in-situ diffraction and scattering experiments [5,6,7], where a slight decrease in clay basal spacing (distance between two consecutive clay’s aluminosilicate layers) is measured for increasing temperature. However, the experiments reported are performed in unsaturated conditions at controlled humidity and cannot be confronted with the fully saturated samples usually employed in geomechanical testing. Measurements for monitoring nano-scale changes of fine-grained soils in their natural wet states are needed to prove the nano-scale origin of the thermo-mechanical behaviour of clays. Small-angle X-ray scattering (SAXS) has often been used to study particle orientation in compacted saturated clay [1]. Smaller features of the mineralogy and sub-particle behaviour of clays can be instead accessed by X-ray diffraction (XRD) and wide-angle X-ray scattering (WAXS) [2]. In principle, SAXS/WAXS measurements capture the inter-particle and intra-particle distances by measuring the scattered intensity of an X-ray beam hitting a sample. This research uses combined SAXS/WAXS measurements to monitor nano-scale changes induced in the clay basal distances of several fine-grained natural soils in their saturated state by temperature variations. The experiments were performed with a SAXSLAB Mat:Nordic Instrument at the Chalmers Material Analysis Laboratory on reconstituted samples of natural sensitive clay (refer to [1]) and remoulded samples of swelling (bentonite) and non-swelling (kaolin) clays. Figure 1 shows the absolute scattering intensities I [a.U.] as functions of the scattering vector q [Å-1] recorded at different temperatures for remoulded kaolin clay (Figure 1a) and bentonite (Figure 1b) samples (both remoulded at 0 kPa). The kaolinite (q=0.898 Å-1) and montmorillonite (q=0.312 Å-1) peaks are clearly visible in Figure 1a and Figure 1b, respectively. In the q-intensity plot, a change of the peak width, or a shift of the peak, indicates nano-scale strain in the material. However, no significant differences in the two peaks are recorded after a temperature increase of ΔT=+45ºC and ΔT=+95ºC, respectively; therefore, temperature variations, within the range considered for most thermal applications, do not affect both kaolinite and montmorillonite basal spacings. The results in Figure 1a (kaolin clay) are consistent with the idea that the amount of adsorbed water in the intra-particle porosity is significantly low in non-swelling clay minerals. As a result, the kaolinite macroscopic thermomechanical response cannot be associated with nanometric changes in the intra-particle absorbed water. On the other hand, a significantly similar scattering response is recorded for bentonite in Figure 1b. Therefore, the activity (swelling capability) of the clay mineral and, thus, the amount of the sample absorbed water seems not to affect the response of the basal spacing to temperature, which stays constant upon heating. Differently from what has been observed by [5,6,7] in unsaturated conditions, the current SAXS/WAXS measurements show that, for modest temperature changes, intra-particle changes upon heating in saturated samples do not play a major role in the macroscopic thermo-mechanical response of clay within the temperature range considered for most thermal applications, and this is independent by clay mineralogy. Therefore, thermo-mechanical strains must be investigated at a scale beyond what is accessible for a laboratory WAXS/SAXS instrument (> 200 nm), focusing on temperature-induced particle/aggregate rearrangement.

Abstract Driving quantum phase transitions in the 3D topological insulators offers pathways to tuning the topological states and their properties. We use DFT-based calculations to systematically investigate topological phase transitions in Bi2Se3, Sb2Se3, Bi2Te3 and Sb2Te3 by varying the c/a ratio of lattice constants. This ensures no net hydrostatic pressure under anisotropic stress and strain and allows a clear identification of the physics leading to the transition. As a function of c/a, all of these materials exhibit structural and electronic stability of the quintuple layers (QLs), and quasi-linear behavior of both the inter-quintuple layer distance and the energy gap near the topological transition. Our results show that the transition is predominantly controlled by the inter-QL physics, namely by competing Coulomb and van der Waals interactions between the outer atomic sheets in neighboring quintuple layers. We discuss the implications of our results for topological tuning by alloying.

The structural, stability, and electronic properties and optimized inter-wall distances of double-walled boron nitride nanotubes (DWBNNTs) are investigated based on density functional theory (DFT) with the SIESTA code. The computations are done on the zigzag ([Formula: see text],0)@([Formula: see text],0) DWBNNTs with chirality of ([Formula: see text], 7 and [Formula: see text]–18) and the armchair ([Formula: see text] with chirality of ([Formula: see text], 6 and [Formula: see text]–15). The calculated binding and formation energies revealed that the armchair and the zigzag DWBNNTs with chirality differences of ([Formula: see text] and 9) ([Formula: see text]), ([Formula: see text]) and inter-layer spacing of about 4.22Å and 3.62Å are the best favorable nanotubes, respectively. Analyzing the electronic structures revealed that all considered armchair and zigzag BNNTs are semiconductors. Furthermore, it is concluded that with increasing diameters of the tubes and the spaces between walls, the value of the band gap rises, and the change process is almost constant at larger distances between the walls. Also, compared to single-walled nanotubes, DWBNNTs have a narrower bandgap. Future empirical investigations can definitely benefit from the implications of this research.

La fabrication additive par dépôt sous énergie concentrée (DED) permet la fabrication rapide de petites séries de pièces. Cependant, les trajectoires usuellement utilisées pour les pièces présentant du porte-à-faux nécessitent l’utilisation de supports, matériau non utile à la pièce finale dont le dépôt et l’enlèvement sont chronophages. Si les trajectoires multi-axes permettent de s’en passer, elles présentent généralement des distances locales inter-couches hétérogènes, nécessitant d’ajuster la hauteur de couche par la paramétrie de dépôt, pouvant alors impacter les caractéristiques mécaniques de la pièce finie. Cette thèse propose, dans un premier temps, une méthode de génération de trajectoire multi axes à distance locale inter-couches constante pour des tubulures définies par des courbes guides paramétrées et pouvant présenter des variations de rayon de profil. Les trajectoires proposées ont ensuite été validées par la fabrication additive robotisée de démonstrateurs en matériau polymère. La rotation autour de l’axe d’un outil de dépôt coaxial n’ayant pas d’incidence sur le dépôt, l’utilisation de robots 6-axes admet une redondance. En utilisant cette redondance, une méthode d’optimisation couche par couche de la trajectoire dans l’espace articulaire est finalement proposée. Pour une configuration de robot contrainte, l’optimisation permet la fabrication de pièces impossibles à produire de manière classique et apporte une amélioration de leur qualité géométrique ainsi qu’une meilleure répétabilité
Additive manufacturing through Directed Energy Deposition (DED) enables small batches of parts to be rapidly manufactured. However, manufacturing trajectories usually used for the manufacture of overhanging parts require the use of supports, material which is not useful for the finished part and time consuming. If multi-axis trajectories can be used to avoid them, they present generally a heterogeneous local inter-layer distance, thus requiring a variation of the deposition parameters to adapt the layer height ; variation that can be harmful to the mechanical characteristics of the final part. This thesis first proposes a constant local inter-layer trajectory generation method for DED additive manufacturing of tubular parts defined by parametric curves and which can have profile radius variations. The proposed trajectories have been validated by robotized manufacturing trials of polymer parts. Since the rotation about a coaxial deposition tool axis has no impact on the deposit, the use of 6-axis robots offers a redundancy. Using this redundancy, a layer by layer optimization of the trajectory in the robot space is then proposed. In a constrained robot configuration, the trajectory optimization allows the manufacturing of parts that cannot be manufactured in the usual way, and improves the geometrical quality of the parts with a better repeatability