Search

Estimation of ground displacement in landslide susceptible regions is very critical to understanding how landslides develop. The knowledge of ground displacement rates and magnitudes helps plan for the safety of the people and infrastructure. The early detection of landslides in Bududa is still a challenge due to the limited technology, hard to access, and a need for an affordable technique that can monitor a wide area continuously. In recent studies, the use of Persistent Scatterer Interferometry Synthetic Aperture Radar (PS-InSAR) has provided vital information on landslide monitoring through the measurement of ground displacement. In this study, Synthetic Aperture Radar (SAR) band C series of Sentinel 1-A and 1-B Satellite images were acquired between 2019 and 2020 along ascending and descending orbit paths. The Line of Sight Sight (LOS) displacement was determined for both satellite tracks, and then the LOS displacement was projected to the vertical direction. The PS-InSAR derived vertical displacement was then compared with GPS vertical displacement magnitudes over three GPS stations in the area. It was observed that vertical displacement velocity reached 20 cm/yr in Mountain Elgon. This displacement rate showed that there are points in the region that are highly unstable. The displacement velocity and magnitude in Bududa reached 6 cm/yr and 13 cm in two years. This rate and magnitude showed that Bududa is highly unstable compared with displacement velocities and magnitudes in landslide susceptible areas globally. The displacement was generally subsidence over the observation period. The vertical displacement estimated by PS-InSAR was comparable with GPS based on the estimated RMSE. The vertical displacement was highest at slopes between 32° and 60° and lowest between 0° and 9°. The vertical ground displacement was highly correlated with the rainfall that was received. The soil texture in Bududa has high clay content, with clay layering hence low drainage rates, field capacity, saturation and bulk density. It was observed that ground displacement was highly influenced by slope, rainfall and soil texture. Displacement could be estimated in three dimensions using PS-InSAR in the future if sufficient SAR images in ascending and descending tracks are made available with significantly different geometries. This would add to the knowledge of displacement patterns in the east and north directions at a large spatial scale.

Grating couplers (GCs) are devices for transmitting and receiving the light propagated in a waveguide in silicon photonic integrated circuits (PICs). In this study, we propose a polarization splitting GC (PSGC) for the optical antenna of light detection and ranging (LiDAR). The PSGC was designed on the basis of two GCs coupling in a perfectly vertical direction. Our experiment demonstrated that the designed PSGC transmitted a polarization-multiplexed beam. The transmitting and receiving efficiencies of the optical antenna consists of lenses and PSGCs were calculated, and then the optical parameter for maximizing them was clarified.

International audience; When tracking targets moving in various directions with one's eyes, horizontal components of pursuit are more precise than vertical ones. Is this because horizontal target motion is predicted better or because horizontal movements of the eyes are controlled more precisely? When tracking a visual target with the hand, the eyes also track the target. We investigated whether the directional asymmetries that have been found during isolated eye movements are also present during such manual tracking, and if so, whether individual participants' asymmetry in eye movements is accompanied by a similar asymmetry in hand movements. We examined the data of 62 participants who used a joystick to track a visual target with a cursor. The target followed a smooth but unpredictable trajectory in two dimensions. Both the mean gaze-target distance and the mean cursor-target distance were about 20% larger in the vertical direction than in the horizontal direction. Gaze and cursor both followed the target with a slightly longer delay in the vertical than in the horizontal direction, irrespective of the target's trajectory. The delays of gaze and cursor were correlated, as were their errors in tracking the target. Gaze clearly followed the target rather than the cursor, so the asymmetry in both eye and hand movements presumably results from better predictions of the target's horizontal than of its vertical motion. Altogether this study speaks for the presence of anisotropic predictive processes that are shared across effectors.

As the technology is rapidly increasing, the astronauts would often have to undergo the semi-supine posture because of the modern architecture and infrastructure designs that have been employed in the new space vehicle designs. There is a high hazard involved when they are vulnerable to higher vibration levels in that semi-supine posture. Finding out the natural frequencies and the resonant frequency of an Indian male in semi-supine posture using the finite element method (FEM) under undamped free vibration conditions are the objectives of the present study. To achieve the objectives the modal and harmonic analysis were performed on a semi-supine posture model. 50th percentile anthropometric data for a 54- kg Indian male is used in this research to generate the 3-D computer-aided design (CAD) model of the human body in semi-supine position, which is available in the existing literature. The natural frequencies and mode shapes obtained from modal analysis were used to design seats, equipment, and other machine parts. From the harmonic analysis the resonant frequency of the human body in the tri-axial directions are determined. The harmonic analysis was performed on the human body model in tri-axial directions by applying different accelerations, i.e., 0.5, 1.0, and 1.5 m/s2, with frequencies ranging from 0 to 20 Hz. The modal analysis states that the deformations will occur at both the arms and the feet of the human body. The maximum deformation occurs at the joints of the arms and the toes and heels of the foot. The harmonic analysis states that when an acceleration is applied in the fore-and-aft direction or in lateral direction, the body's resonant frequency is 10 Hz. When the acceleration is applied in the vertical direction, the body's resonant frequency is 8 Hz. The harmonic analysis observed two resonant frequencies, i.e., 10 Hz and 14 Hz when the acceleration is applied in the lateral direction. From harmonic analysis, it is clear that maximum deformation values and stress values are occurring in the lateral direction at a particular acceleration.

The growth of fiber/matrix interface cracks (debonds) located on consecutive fibers along the through-the-thickness (vertical) direction is studied in glass fiber-epoxy UD composites. Debonds could appear, along the vertical direction, on the same or on opposite sides of their respective fibers. Determining which configuration is the most energetically favorable to debond growth is the objective of this paper. To this end, two different families of Representative Volume Elements (RVEs) are developed: the first implements the classic condition of coupling of the vertical displacements to model a unit cell repeating symmetrically along the vertical direction; the second uses a novel set of boundary conditions, proposed here by the authors, to represent a unit cell repeating anti-symmetrically along the vertical direction. The model is analyzed in the context of Linear Elastic Fracture Mechanics (LEFM) and the Mode I and Mode II Energy Release Rate are evaluated to investigate crack growth. The calculation is performed using the Virtual Crack Closure Technique (VCCT) in the framework of the Finite Element Method (FEM). It is found that Mode I dominated propagation is favored when debonds are located on the same sides of their respective fibers; while for larger (Mode II-dominated) debonds, Mode II ERR is higher when they lie on the opposite sides. No interaction effect is present when at least two fully bonded fibers are located between the partially debonded ones.

In this paper technology and device for automated detection of the location and size of defects in the stator core of a powerful turbine generator (TG) during assembly at the manufacturing plant is proposed. The core is assembled and pressed in a vertical position in separate parts and at each stage of assembly it is necessary to find places with a weakened solidity. Existing control methods, including automatic ones, will not allow quality control. Using the proposed technology, places in the core with weakened solidity can be detected. In this case, measurements of the specific pressing pressure are carried out at certain points of the end surface of the core, where special control samples from an easily deformable material are installed. The device is implemented as a ring installed on the end surface of the core, in which N cells with control samples are installed. During pressing, the thickness of the samples decreases and the greatest decrease in the thickness of the sample, caused by the corresponding highest specific pressure, corresponds to the smallest defect, and vice versa. Flat metal membrane with a rigid center as a primary pressure transducer has been proposed to use, on which an optical fiber with Bragg gratings is fixed, one of which measures the tangential relative deformation in the membrane, and the second serves for thermal compensation. In paper it has been shown that tangential deformation in a flat membrane depends on the specific pressing pressure. The characteristics of the converter are calculated. The measurement results are processed using an interrogator and a personal computer. The use of the device makes it possible to increase labor productivity when monitoring the core, as well as more reliably diagnose its defects with their subsequent elimination, which ultimately will increase the reliability of the TG and its durability.

Over the past decade, Chengdu has become one of the fastest growing urban centers in China. However, the massive expansion of the infrastructure and the transportation network has resulted in surface subsidence which typically presents as a hard to detect geological hazard. As an all-day, all-weather, high-precision, and wide-range surface deformation monitoring tool, interferometric synthetic aperture radar (InSAR) technology has unique advantages with respect to monitoring long-period surface subsidence. In this article, the Sentinel satellite data from March 2018 to March 2021 for the ascending and descending orbits are used to obtain the deformation fields of Chengdu's surface in two different satellite line of sight directions using the time-series InSAR technique. The results are then used to invert the surface deformation field in the vertical direction and analyze it via the Peck and Logistic models. In addition, wavelet transform technology was used to investigate the relationship between deformation and climate. The results show that the surface deformation in Chengdu is stable, and the rate of deformation in the center of the urban area is within 5 mm/year. The main reason for the emergence of ground settlement funnels is the construction of subways and real estate development. It was also observed that the deformation of the buildings shows a clear periodic pattern, which is closely related to the seasonal rainfall and temperature in Chengdu.

Reducing the weight of modern bodies and simplifying the design often lead to a significant reduction in structural rigidity and damping, which leads to easier excitation of elastic vibrations, which have a negative impact on passenger comfort and durability of the structure. In many cases, the first symmetrical shape of the body’s bending vibrations has the greatest effect on the comfort index, so suppressing or reducing the body’s bending vibrations in the vertical direction is important. The aim of this work is to draw attention to the new technical ideas and solutions in this area that have emerged in recent years, which may be of interest to professionals. A brief overview of works, of a practical nature mainly, aimed at increasing the structural rigidity of bodies, their vibration isolation and damping, with the aim of suppressing bending vibrations. The conducted analysis testifies to a variety of methods of struggle against bending fluctuations of bodies and allows defining tendencies of development in this area.

Energy consumption is an important comprehensive index of the hydraulic hexapod robot (HHR). In this paper, the kinematics model and the hydraulic system energy consumption model of HHR are established. In order to reduce the energy consumption, a centroid fluctuation gait that adds the movement of the centroid in the vertical direction is proposed. Then the gait parameters such as step length, gait cycle, average centroid height, centroid fluctuation height, and phase that influence the energy consumption are studied which could provide a theoretical basis for parameter optimization. In the same gait parameters, compared with using constant height gait, the energy consumption of HHR using centroid fluctuation gait is generally reduced, and the maximum energy saving can be more than 10%. Finally, a virtual prototype is used to verify the effectiveness of the proposed methods.

The amount of the work in the vineyard, its yield greatly depends on what type of grape trellis is used in the vineyard.The most common is the Vertical Shoot Position. The advantages of the Vertical Shoot Position is the simplicity of the device and the use of inexpensive building materials. It is less time consuming and easily accessible for vineyard care.The disadvantages are that the maximum area of the green mass and the maximum yield cannot be obtained. The horizontal grape trellis system - pergola - allows to get the maximum area of green mass, the maximum assimilation of solar energy takes place, that increase yields by 2-3 times and provide the best quality of grapes.The disadvantages is that the care of vines grown on horizontal trellis is very time-consuming. Because the vintner is forced to work with his head constantly pulled back and his arms raised high.The authors have developed a new type of grape trellis - a mobile pergola - which during the vegetation - during the development of green mass and fruit ripening are placed horizontally, and during the green operations - pruning, spraying, harvesting - in a vertical position. As a result, we get a high yield typical for the pergola, which is 2-3 times higher than the yield obtained on the vertical grape trellis, and its maintenance is just as convenient and simplified as that of the vertical grape trellis.

Double dielectric DBR based GaN-based micro cavity light emitting devices with two different structures were fabricated, and their thermal characteristics were investigated. To improve thermal dissipation, an AlN current confinement layer with a much higher thermal conductivity than SiO2 and an electroplated copper heat sink were utilized. The thermal resistance of the device decreased from 923 K/W to 457 K/W, half of that obtained with the typically used SiO2 current confinement layer and bonded substrate. This is the lowest reported value in GaN-based micro cavity light-emitting devices with double dielectric DBRs. Temperature distribution and heat flux inside of the device was simulated based on a steady state quasi three-dimensional cylindrical model. The results show that heat transport in vertical direction is efficiently bypassing the bottom DBR to the copper plate. This work provides an effective method to improve thermal characteristics of GaN-based micro cavity light-emitting devices with double dielectric DBR structure.

The grain boundary strengthening effect (GBSE) was investigated for nickel-based superalloy bicrystals with various misorientations under different temperatures and loading directions. The results show that the GBSE is enhanced with the increase of misorientation and insensitive to the temperature. Besides, the loading direction relative to GB also has strong effect on GBSE. On the other hand, the GBSE is often accompanied by GB cracking. The trend of GB cracking is heightened with the increase of misorientation and temperature. However, the trend of GB cracking is reduced strongly when the loading direction transforms from parallel direction to vertical direction.

Aim: to identify the influence of body length on the indicators of vegetative-vascular regulation of student-athletes. Material and methods. The study involved 42 second-year students who play sports at the amateur level (qualification level - 2-3 sports degree). The following research methods were used in the work: method of analysis of literary sources; method of determining body length; orthostatic test method; method of determining stroke volume and minute blood volume. Results. It was found that the increase in systolic blood pressure during the transition from horizontal to vertical position in students whose body length is above 190, significantly higher than in students whose body length does not exceed 175 cm (p

Layered materials that do not form a covalent bond in a vertical direction can be prepared in a few atoms to one atom thickness without dangling bonds. This distinctive characteristic of limiting thickness around the sub-nanometer level allowed scientists to explore various physical phenomena in the quantum realm. In addition to the contribution to fundamental science, various applications were proposed. Representatively, they were suggested as a promising material for future electronics. This is because (i) the dangling-bond-free nature inhibits surface scattering, thus carrier mobility can be maintained at sub-nanometer range; (ii) the ultrathin nature allows the short-channel effect to be overcome. In order to establish fundamental discoveries and utilize them in practical applications, appropriate preparation methods are required. On the other hand, adjusting properties to fit the desired application properly is another critical issue. Hence, in this review, we first describe the preparation method of layered materials. Proper growth techniques for target applications and the growth of emerging materials at the beginning stage will be extensively discussed. In addition, we suggest interlayer engineering

Aiming at the rapid planning of the optimal flight path of the intelligent aircraft, considering the error constraints and correction probability constraints, a model for intelligent aircraft path planning under multiple constraints is constructed, and a global search algorithm based on Dijkstra algorithm is proposed to solve the model. By calculating the residual error and restricts flight distance, the basic Dijkstra algorithm is improved to make it more adaptable to solve the path planning under multiple constraints. At the same time, simulation experiment is conducted with the optimal goal of the shortest track length and satisfying the error constraints. The experimental results show that the aircraft passed a total of 18 correction points when it reached the destination. The total track length was 144 287.932 m, the vertical position error was 17.254 units, and the horizontal position error was 6.420 units. The results meet the error requirements. The results show that the intelligent aircraft path planning model and Dijkstra-based global search algorithm with multiple constraints are reasonable in solving such problems.

Aeroengine is one of the main vibration sources that affect the passenger comfort. The contribution of engine vibration to the vibration response of seat will provide basic data for the design of airliner vibration comfort and engine vibration isolation installation. Firstly, the dynamical model of middle fuselage compartment with double-beam wing was established. Then, based on the typical vibration load spectrum of the engine, the acceleration responses of the key nodes of the wing beam and the seat connection points were analyzed, and the main path of engine vibration transmission to seats was identified. Finally, using operational transfer path analysis (OTPA) method, the contribution of engine front and rear mount point vibration to the vertical acceleration response of the seats was compared, and the three-dimensional information of wing structure vibration transmission was explored. The results show that the fundamental frequency component of low-pressure rotor of engine vibration has the greatest impact on the seat vertical response under takeoff and cruise conditions, the contribution rate of the front mount point vibration is about 71% and 67% respectively. However, the fundamental and its 3/2 times frequency components of high-pressure rotor have relatively large impact on the seats vertical response under flight idle state, and the contribution rate of engine front mount point vibration is about 45% and 60% respectively. In addition, the engine vibration is mainly transmitted from the wing front beam to the seat vertical response. The vertical direction of the wing beam and the rotation direction around the fuselage are also the main direction of vibration transmission.

The goal of this work is to construct an efficient parallel numerical solution for a nonstationary diffusion–convection problem on a multiprocessor computer system with distributed memory. Economical explicit-implicit difference schemes and the method of splitting into physical processes are taken as a basis. When using these schemes, it becomes possible to pass to a chain of one-dimensional and two-dimensional difference problems that approximate the original problem in an overall sense. The explicit-implicit difference schemes suggest an explicit approximation in horizontal directions and an implicit approximation with weights in a vertical direction, taking less time to solve the diffusion–convection problem compared to the explicit schemes while retaining an admissible accuracy of the solution. We propose an algorithm for finding an optimal weight that provides a minimum approximation error in the solution of the diffusion–convection problem in a vertical direction for given time grid steps. Computational experiments have been carried out using the three-dimensional model problem of suspension transport in a water environment as an example. The model takes into account the following processes: the advective transport due to the motion of the water environment, the microturbulent diffusion and gravitational settling of suspension particles, and the change in the geometry of the bottom caused by the settling of suspension particles or the rise of bottom sediment particles. The presented parallel approach to the numerical simulation of suspension transport processes will allow one to improve the real-time forecast accuracy manifold and the validity of the engineering decisions being made when creating the objects of coastal infrastructure.

For extensive use of low global warming potential refrigerants with low flammability, there is a need to develop a simple method to distinguish the lower flammability refrigerants from the higher flammability ones. The purpose of this paper is to investigate the applicability of the test method for flat-plate quenching distance (dq) for predicting the maximum burning velocity (Su0, max) of near 10 cm s−1. The dq measurement was carried out by the ASTM E582–07 method and the modified method for six binary blends that all have Su0, max of approximately 10 cm s−1. It was found that the standard 25-mm diameter glass plates placed in the vertical position give at most 11% smaller dq values than 50-mm diameter plates placed in the horizontal position, which was due to the upward motion by the buoyancy. Based on the thermal loss theory, a simple equation using the experimental dq was obtained to predict the Su0, max of the lower flammability blends.

The differences between temperatures in the animal occupied zone (AOZ) and temperatures measured by control system sensors are rarely explored. This experimental study quantifies the dry-bulb air temperature [hereinafter temperature] distribution inside a finisher pig building that combines natural ventilation through automatically controlled openings with a mechanical ventilation system. Year-long temperature data from 28 sensors located at 3 different heights in the building was analysed to help understand the temperature distributions and indicate the temperatures below or above an assumed optimal temperature range, defined as between 14 °C and 24 °C. Relatively large variations in the spatial temperature distribution were found, and they were higher in the vertical direction than in the longitudinal direction. The temperatures measured in the AOZ at 0.25 m height, were on average, 7 °C warmer than that at 1.5 m height. The AOZ temperature correlated better with temperatures measured at 0.7 m or 1.5 m height in the same pen than with temperatures measured in the AOZ at other pens. The analyses show that a proportional–integral based control system effectively counteracts the effects of outdoor wind conditions, and the control system is capable of maintaining the defined optimal temperature at the measurement height. However, the optimum temperatures at the measurement heights above AOZ do not correspond to the measured temperatures in the AOZ.

The objectives of study was to evaluate the vertical space of flying insects using YST (yellow sticky traps) trapping in a strawberry farm with a high-raised bed system; with assuming the presence of species-specific flying zone. The experimental farm used styrofoam beds (width 30 cm, depth 20 cm) placed on a supporting frame 70 cm high. Small YSTs (12.5 × 7.5 cm, single sticky side) were installed vertically around the high-raised bed system in a 3 × 7 configuration (column × row) vertically at 30-cm intervals, reaching 270 cm high, and spaced 50 cm apart horizontally. The trap positions within the second-ranking (here referred to as ‘zone’) to attract thrips were 60 cm traps above the top of the bed center (TBC), 30 cm traps above the side of the bed (SOB), and 70 cm traps from the ground on the SOB. The attraction zone of whiteflies was the same as that of the thrips except of the 60 cm traps above the SOB. The zones for leafhoppers were formed in all 60 cm traps above the top of the bed (TOB), the 90 cm side traps above the TOB, and 30 cm traps above the TBC. Aphids were frequently attracted at all 90 cm traps above the TBC and 60 cm above the TBC. Sciarid pests were mostly attracted to the traps placed just below the bed center. The zones of natural enemies (total) were formed in 30 cm above the TBC and 70 cm from the ground at the SOB. Thus, the zone 60 cm above the TBC was common position where various pests were frequently attracted with reducing a harmful effect on natural enemies. Consequently, our results could be used as a guideline for the use of YSTs in strawberry farms with high-raised bed systems until new directions are developed.

As the first link element for the transmission of shaft vibration to the pedestal and even to the hull, water-lubricated bearing plays a key role in suppressing vibration. Although the porous structure is considered as one of the main methods for improving the wideband vibration and noise reduction performance of materials in many industrial fields, the studies in the field of water-lubricated bearing remain insufficient. To enhance vibration reduction performance, a fluid-saturated perforated slab is designed in this study, and via the establishment of a fluid-solid coupled vibration model, the influence law and impact levels were analyzed and verified by simulation and experiments. The results obtained verified that the total vibration amplitude of damping-enhanced stern bearing in the vertical direction was smaller than that of the normal stern bearing, and the reduction amplitude of the characteristic frequency agreed with the optimal value at approximately 0.1 of the volume fraction of the liquid phase when the solid-fluid phase was rubber–water. Additionally, the increase in fluid fraction did not enhance the damping effect, instead, it unexpectedly reduced the natural frequency of the raw material significantly. This research indicates that the design of the fluid-saturated perforated slab is effective in reducing the transmission of the vibration amplitude from the shaft, and presents the best volume fraction of the liquid phase.

Suction caissons can readily penetrate into the seabed under the combination of the self-weight and suction resulted from the encased water being increasingly pumped out. During suction-assisted penetration, the equivalent overburden at the skirt-tip level outside the caisson is generally higher than that inside because the vertical stress within the soil plug is reduced by the exerted suction. This may result in a uniform shear stress developing over the base of the skirt-tip as the soil below the skirt-tip tends to move into the caisson, which leads to an asymmetric failure wedge existing below the base of the skirt-tip. Besides, different adhesion factors along the inside (α1) and outside (αo) of the skirt wall will cause asymmetric plastic zones inside and outside the caisson. Accordingly, an asymmetric failure mechanism is therefore proposed to calculate the penetration resistance of the skirt-tip. The proposed failure mechanism is the first to consider the effect of different adhesion factors (αi) and (αo) on the failure mechanism at the skirt-tip, and involves the contribution from the weighted average of equivalent overburdens inside and outside caisson at the skirt-tip level. The required suction pressure can be obtained in terms of force equilibrium of the caisson in a vertical direction. Finally, the asymmetric failure mechanism at the skirt-tip is validated with the FE calculations. By comparing with the measured data, the predictions of the required suction pressure are found to be in good agreement with the experimental results.

Columnar dangerous rock mass is widely developed in many high and steep mountain areas around the world. It often collapses, disintegrates and produces debris flow, which is disastrous. The collapse process of the columnar dangerous rock mass is very similar to the collapse of granular column. In this paper, we report the results of an experimental investigation of the flow induced by the collapse of a column of granular material over a horizontal surface. Two different setups are used, namely, a channelized granular column collapse (i.e., two-dimensional) and an unchannelized granular column collapse (i.e., three-dimensional), allowing us to compare channelized and unchannelized collapses flows. The experimental data suggest that our experimental findings were markedly different from those reported by previous authors (i.e., include the channelized and unchannelized collapse flows showed differences in energy conversion and dissipation). In channelized collapse flows, the maximum vertical speed appears in the free fall regime, while, the maximum speed in the vertical direction of unchannelized collapse flows appears in the spreading regime. During the whole collapse process, i.e., in channelized and unchannelized collapse flows, the conversion of potential energy and kinetic energy does not occur uniformly, and the maximum kinetic energy of the channelized collapse flows is higher than that of the unchannelized collapse flows, and compared with the unchannelized collapse flows, the dissipation energy in the channelized collapse flows is lower. A series of experiments was performed to predict the behaviour of different granular columns (characterized by different initial aspect ratio (a), varying from 1 to 4). The data obtained from 2D experimental model and 3D experimental model have certain amount of difference, such as the particle runout distance (d1), the maximum central height (h2), and the deposition angle (i.e., β1, β2). These differences show that the 2D experimental model does not fully represent the 3D conditions (i.e., the role of side-walls on the channelized collapse flows characteristic is non-negligible). Accordingly, care must be taken when validating 3D models with 2D experimental data. The movement of the tower dangerous rock masses with collapse failure mode could be evaluated using this channelized and unchannelized granular column experimental results.

This article presents the evolution law of temperature fields in a large-scale laboratory Underground Coal Gasification reactions using Ulanqab lignite under actual conditions. The results show that in the cultivation stage of oxidation zone, the main direction of the temperature field expansion is consistent with the crack direction of the coal seam. In the gasification stabilization stage, the main direction of the temperature field expansion is along the channel. The temperature of the coal seam and the overlying rock mass at its interface with the furnace directly above the gasification channel is equivalent to that of the coal seam temperature, and this temperature is much greater than the temperatures observed near both side walls of the gasification channel at the interface. However, temperatures perpendicular to the axis of the gasification channel are similar at a vertical distance of 40 cm away from the interface. The temperature distributions indicate that the transmission of heat through the overlying rock mass is more rapid in the vertical direction than in the horizontal direction. Moreover, some degree of thermal dispersion is observed in the vertical direction near the outlet. The thermal dispersion coefficient is 0.72 and dispersion angle γ is 78.7°.

The high-frequency (HF) square-wave voltage injection sensorless control method will bring additional HF torque ripple to interior permanent magnet synchronous motor (IPMSM). Focused on this problem, this article analyzes the relationship between the HF response current and the HF torque ripple resulting from HF square-wave voltage injection. It is concluded that when the fluctuation direction of HF response current is vertical to the stator current vector direction at the maximum torque per ampere (MTPA) operating point, the resulting HF torque ripple reaches its minimum. Based on this conclusion, a novel HF square-wave voltage injection sensorless control method is proposed in this article, which can realize the sensorless control and minimize the HF torque ripple at the same time. The injection angle of HF square-wave voltage in the estimated synchronous rotating reference frame is adjusted in real time according to the operating conditions, so that the HF response current always fluctuates along the vertical direction of the stator current vector at the MTPA operating point. Besides, the corresponding demodulation method of the rotor position estimation error is illustrated. Finally, the experiments are performed on a 20-kW IPMSM platform and the results verify the effectiveness of the proposed method.

In this paper, an analysis is given about dynamic characteristics for a quasi-zero-stiffness isolator coupled with mechanical disturbance from a view of engineering application. In addition to traditional Columbo friction and linear damping in the vertical direction, the influence of other disturbing parameters such as geometrically nonlinear damping, friction and inertia of rods is also taken into consideration. The dynamic equation is formulated with parameters above to give an investigation of static characteristics, respectively, based on Newton’s second law and D’Alembert’s principle. Moreover, the frequency–amplitude response and transmissibility characteristics are obtained for this model subjected to the vibrating base by using average method with the introduction of piecewise function and then analyze the effect on the vibration response and isolation caused by disturbance. Furthermore, the passive vibration isolation simulation is conducted to verify the theorem. Therefore, it is recommended that the geometrically nonlinear damping can be introduced to the quasi-zero-stiffness system appropriately which can decrease the peak value of transmissibility in the low-frequency range, and nearly has no effect on the high-frequency region. And the mass of the rod should not be bigger than $$10^{-3}$$ times of the isolator. The conclusions can provide engineering guidance for design and application about quasi-zero-stiffness system.

The photosynthetic rates of leaves depend on the vertical position and cultivation conditions. However, few models have been proposed to express photosynthesis according to leaf position, and there was a lack of quantitative analysis between physiological indicators and model parameters. The objectives of this study were to analyze the leaf photosynthetic characteristics of paprika plants according to leaf vertical position using photosynthesis models, and to analyze the relationship between the total nitrogen content and the photosynthetic model parameters. Leaf photosynthetic rates at different vertical positions were measured under varying light intensities and CO2 concentrations in triplicate. Rectangular hyperbola and FvCB (Farquhar, von Caemmerer, and Berry) models were selected, calibrated, and validated as multivariable photosynthesis models. Total nitrogen contents and SPAD values were measured at each leaf position and the coefficients of the photosynthetic rate models were compared. The R2 values for the rectangular hyperbola and FvCB models were 0.86 and 0.91, and the RMSE values were 4.651 and 2.104, respectively. Total nitrogen content linearly increased with increasing vertical leaf position and it was linearly related to the maximum carboxylation capacity and maximum electron transport rate, estimated in the FvCB model. In this study, the FvCB model was considered more suitable for expressing the relationship between total nitrogen contents and plant’s physiological responses according to the vertical position of leaves. The vertical leaf photosynthetic rate models established in this study will contribute to determining optimal environmental conditions for maximizing crop photosynthesis and establish the criteria for precise CO2 enrichment in greenhouses.

We have systematically studied the spatial and temporal variation characteristics of deformation and ground temperature based on measuring the values of corresponding data in the Harbin-Dalian high-speed railway roadbed. The regularity and non-uniformity of roadbed deformation distribution were analyzed based on the relationships between its values and structure type, development of freezing depth, roadbed filling, and transverse position. We also compared the difference of freezing conditions at different locations and heat absorption of the roadbed; then we analyzed the differences of freezing depth in four selected roadbed sections and the characteristics of average ground temperature along the vertical direction in the coldest and hottest months. Based on the above analyses, the source of the spatial and temporal characteristics of roadbed deformation, influencing factors, and the potential hazards of transverse thermal difference to roadbed stability have been discussed. The results showed that the distribution of roadbed deformation in seasonal frozen regions had certain regularity, non-uniformity, and randomness. Roadbed freezing processes of roadbed at different transverse locations in different regions were similar. The differences of transverse thermal regime were widespread, and the influence of external temperature on the west shoulder was most obvious. The coldest and warmest month temperatures at a certain depth followed a spindle-shaped trend. Both the increase of latitude and height of roadbed may affect the difference of transverse ground temperatures.

An integral model of steam-assisted gravity drainage is described and modified with account for inequality of heat fluxes and the steam chamber growth in the vertical direction. The model is brought into the dimensionless form convenient for analyzing the influence of different phenomena on the process and verified by means of the calculations based on the Chung and Butler experiments. Within the framework of the model the main effects occurring during the process are described.

The diffusion profiles of the front floating emitter (FFE) and front surface field (FSF) in a bifacial interdigitated back contact solar cell are optimized. The optimization results revealed that the FFE and FSF schemes are beneficial for enhancing the cell performance at the front and rear sides, respectively. Lighter doping is particularly better for the FSF scheme, and the FFE scheme requires a large diffusion depth for improving the performance. Increasing the area of the rear emitter boosts the performance of the cell, and an FFE scheme with 90 $\%$ rear emitter area is found to be the best design. Quantum efficiency mapping demonstrated that the FFE scheme suppresses the loss at the back surface field region, thereby enhancing the performance of the total cell. The FSF scheme improves the quantum efficiency for the entire region by enhancing the carrier transport in the vertical direction. Furthermore, loss analysis revealed that the FFE scheme suppresses the recombination loss at the maximum power point, which is an important advantage over the FSF scheme.

The generation and evolution of artificial plasma clouds is a complicated process that is strongly dependent on the background environment and release conditions. In this paper, based on a three-dimensional two-species fluid model, the evolution characteristics of artificial plasma clouds under various release conditions were analyzed numerically. In particular, the effect of ionospheric density gradient and ambient horizontal wind field was taken into account in our simulation. The results show that an asymmetric plasma cloud structure occurs in the vertical direction when a nonuniform ionosphere is assumed. The density, volume, and expansion velocity of the artificial plasma cloud vary with the release altitude, mass, and initial ionization rate. The initial release velocity can change the cloud's movement and overall distribution. With an initial velocity perpendicular to the magnetic field, an O+ density cavity and two bumps exist. When there is an initial velocity parallel to the magnetic field, the generated plasma cloud is bulb-shaped, and only one O+ density cavity and one density bump are created. Compared to the cesium case, barium clouds expand more rapidly. Moreover, Cs+ clouds have a higher density than Ba+ clouds, and the snowplow effect of Cs+ is also stronger.

Sill emplacement mechanisms are very complex, diverse, and regional, and insights from sill reflections are helpful for understanding the emplacement process of magma in the Tarim Basin. This study takes advantage of high-quality 2D seismic data, which are rarely used to study sills in the Tarim Basin, to analyze the sills’ geometric characteristics, plan-view distributions, emplacement timing, and emplacement mechanisms with unconformity surfaces. In the seismic-reflection profiles of the middle-upper Ordovician in the North depression and the southern part of the Tabei uplift in the Tarim Basin, sills with strong positive polarity reflections appear, and they are closely distributed near the Tg52 unconformity surface, which represents the interface between Middle Ordovician limestone and Upper Ordovician mudstone. According to the vertical position of the sills relative to the unconformity, we can divide the sills into saucer-shaped or quasi-saucer-shaped sills above the unconformity surface, sill complexes and saucer-shaped sills on the unconformity surface, and saucer-shaped sills below the unconformity surface. Potential hydrothermal vents and peripheral faults associated with sill intrusion terminate upward in the Middle Permian strata, suggesting that these sills formed in the Middle Permian. Sills with inner flat sheets on the Tg52 unconformity surface formed when the magma ascended and encountered an abrupt change in the fracture toughness and tensile strength between the two adjacent host rock layers. The sills above and on the Tg52 unconformity surface overlap or are vertically linked; therefore, the sills above the Tg52 unconformity surface are the result of the continuous upward expansion of the sills on the unconformity surface, forming sill complexes. Our findings further confirm that unconformities are important interfaces that affect the emplacement of sills.

Based on the similarity theory, a physical testing model with scale of 1:10 was designed and fabricated. The Wenchuan wave (WC-XZ), Darui artificial wave (DR-XZ) and Kobe wave (K-XZ) were adopted as excitation waves which was XZ directions (horizontal and vertical loading at the same time). A series of shaking table tests were carried out to study the effect of the types, directions and peaks acceleration of the seismic waves on the acceleration response laws of the shallow-buried bias tunnels with small distance. The results show that: (1) in the horizontal direction, the types of the seismic waves have a little effect on the acceleration response, but the law is opposite with Kobe wave being the most serious, followed by Darui artificial wave and Wenchuan wave in the vertical direction. (2) The existing slope has a significant effect on the acceleration response of the right hole which is different from that of the left hole. (3) The acceleration response of the tunnel in the vertical direction is more severe than that of the horizontal direction and the acceleration amplification factors in vertical direction are is generally 1.02-3.94 times that of the horizontal direction. (4) in the seismic design of tunnel, different seismic measures should be adopted in different directions. The results have a significant reference for the anti-seismic design of the tunnel.

The draw ratio (DR) is an important parameter in the process of spinning hollow fiber membranes, by which their separation and performance characteristics can be controlled over a wide range of values. For the first time, a method for determining the DR using a roller movable in the vertical direction is described, which makes it possible to establish the ratio of the dope extrusion linear flow rate to the take-up speed. In the course of the work, polysulfone hollow-fiber membranes were obtained at various DR values. The influence of the draw ratio on the morphology and geometric and gas transport properties of the resulting polysulfone hollow fiber membranes has been examined.

The mode-2 internal solitary waves (ISWs) generated by mode-2 internal tide (IT) are identified by mooring observations in the northern South China Sea (SCS) from 2016 to 2017. Two mode-2 ISWs with a re-appearance period of 24.9 h observed on 29 and 30 July 2016 are characterized by type-b ISWs. They occurred when the isotherms compressed obviously in the vertical direction. Modal decomposition of IT horizontal currents shows that the vertical compression of the isotherms is mainly caused by diurnal mode-2 IT. The analysis of the role of the density stratification reveals that a deeper and thinner pycnocline is favorable for generation of mode-2 ISWs rather than pycnocline intensity. By comparing the mode-2 nonlinear, dispersion coefficients and the Ursell numbers calculated based on the stratification associated with different kinds of ITs with the observation results, it is shown that the diurnal mode-2 IT plays a crucial role in the generation of the mode-2 ISWs. When the diurnal mode-2 IT interacts with the semidiurnal IT and causes a deeper and thinner pycnocline, the mode-2 ISWs are easily excited.

UAS navigational error is one of the concerns leading to non-conformance of assigned flight volume. This is especially noticeable in urban environment where global navigation satellite system (GNSS) positioning capability are affected by influencing factors such as signal blockage and multipath errors caused by surrounding objects like buildings, trees, and other obstructions [1]. This paper presents a study on how the vertical navigation performance is affected by the cause of change in the sky openness ratio (i.e., GNSS signal blockage) above the drone when a self-built UAS is operating near several types of urban obstructions in flight tests. Test sites are carefully selected to ensure they are representative to urban environments, which includes 1) open space carpark with a few short trees, 2) running parallel to row of buildings, 3) surrounded by buildings (narrow urban canyon), and 4) constraint area with a building and some tall trees. The data will be analysed to obtain the vertical position error with considerations for (i) Number of visible satellites versus flight altitude, (ii) Sensor-reported vertical co-variance (EPV), (iii) Vertical position errors at various locations by comparing the reported position (GNSS) to a reference value, and (iv) Factors contributing to vertical positional errors at various locations, (v) The influence of sky openness to the vertical position error. The measurement of sky-openness ratio is to determine whether 3D city model of the flight area is sufficient to predict the vertical navigation performance that could be expected. Civil Aviation Authority of Singapore (CAAS) National Research Foundation (NRF) This research is supported by the National Research Foundation, Singapore, and the Civil Aviation Authority of Singapore, under the Aviation Transformation Programme.

[EN] Recent trends in waste management have initiated interest in recycled materials for sound absorption applications. The present paper studies the possibility of paper sludge to be recycled as material for sound absorption applications. Paper sludge (PS) is the water treatment waste, produced during paper production. Two different methods were studied to produce paper sludge and slaked lime composite acoustic panels for sound absorption applications at low and mid-frequencies. The sound absorption coefficient of paper sludge composite panels is measured in an impedance tube using the two-microphone method. The samples produced with different methods showed different behaviours of sound absorption. The primary method to produce showed acoustic asymmetry in the vertical direction of the samples, and it was considerably fragile as well. An improved method to produce PS composite panels was proposed in this paper. Using this method, homogenous and robust acoustic panels were obtained., The authors would like to kindly thank the technician Javier Zaragoza Dolz and Dr. Olga Kizinievi for their fruitful suggestions on this study. This research was financially supported by the Ministry of Science and Innovation and the European Union FEDER through Project PID2019-109175GB-C22

Made available in DSpace on 2022-05-01T10:35:02Z (GMT). No. of bitstreams: 0 Previous issue date: 2022-02-01 Vision is crucial for humans to interact with their surrounding environment, and postural sway is reduced to allow short eye movements. However, the extent of subtle changes in postural control for horizontal and vertical eye movements remains unclear. The goal of this study was to investigate the effects of vertical and horizontal eye movements on head and trunk control in young adults. Fifteen healthy adults (23.4 ± 4.7 years) stood upright in three conditions for 60 s: fixation, horizontal, and vertical guided eye movements. In fixation, participants had to fixate on a stationary target. In both the horizontal and vertical eye movements, the target was presented with a frequency of 0.5 Hz and a visual angle of 11°. Eye displacement was monitored using a SMI eye tracker (ETG2.0) and trunk and head sway were monitored using infrared markers (Optotrak 3020, NDI). The mean sway amplitude was lower in both directions for eye movements and lowest in the vertical direction compared to the fixation condition. The sway area was also lower in vertical eye movement than in the fixation condition. We also found that the sway reduction was greater at head than at trunk level. The median frequency sway in the anterior–posterior direction was higher in both eye movements than in fixation. Based upon these results, we suggest that to perform short eye movements, postural sway is more strongly controlled at the head level than at the trunk and in vertical eye movements than in horizontal movements. Institute of Biosciences São Paulo State University, SP Institute of Physical Activity and Sport Science Cruzeiro do Sul University, SP Univ. Lille CNRS UMR 9193 - SCALab - Sciences Cognitives et Sciences Affectives Departmento de Educação Física Instituto de Biociências Universidade Estadual Paulista, Av. 24-A, 1515, SP Institute of Biosciences São Paulo State University, SP Departmento de Educação Física Instituto de Biociências Universidade Estadual Paulista, Av. 24-A, 1515, SP

Currently, shallow coal resources are being exhausted gradually, mining depth is continuing to extend downward, and hydrogeological conditions are becoming increasingly complex. Therefore, accurate determination of the failure floor position is necessary to perform multiple-seam mining. In this study, the 7255 working face of the Renlou coal mine is regarded as the research object. Through a comprehensive measurement of ground penetrating radar detection and fixed-point grating optical fibers, the law of floor deformation and failure is analyzed dynamically, and the characteristics of the floor rock deformation response are discussed. The results of on-site monitoring indicate that the mining effect of the working face is greater than that of the tectonic stress. With the advance of the working face, the deformation of the shallow area (0–8 m) first increases gradually, then increases rapidly, and finally increases gradually again; the middle area (8–19 m) experiences three stages, from a gentle increase to temporary stability and then a rapid increase; the deep area (19–29 m) undergoes three stages, from being stable to increasing and then being stable again. After mining, the floor of the working face can be classified into four areas in the vertical direction: complete failure area (0–5 m), poor severe influence area (5–11 m), failure development area (11–19 m), and elastic deformation area (19–29 m). Mining-induced stresses cause resistance at the interface of different lithologies and weaken the effect of downward propagation. Coal seams and the interface between different lithologies are more prone to deformation. The results can provide a certain reference basis for the advanced exploration scheme of the underlying seam mining under the multiple-seam mining method, as well as provide a new approach for floor failure depth measurement.

Ergonomics is the key to make the machine “worker friendly”. In this paper, the humble effort is carried out to present the outline of the tractor industry of India as well as Ukraine for the subsequent analysis of the operator's working conditions and negative production factors that affect his health. Experiment was conducted in Ukraine for three different tractor models i.e. HTZ-181, HTZ-200, HTZ-200B. Vibrations were measured at frame between cab brackets (on left side member), cab floor at the operator's feet and cab frame (on rear crossmember at the rear window base) for plowing and harrowing operations. Research of structural elements vibration parameters of some tractor models (for harrowing and plowing operation) showed that the cab frame has the highest vibration activity in the vertical direction with a peak in the octave band with a geometric mean frequency of 16 Hz. In the transverse direction, the tractor frame has the highest vibration acceleration amplitude, while the maximum vibration acceleration amplitude falls on the octave band of 16 Hz, but its value is two times lower than in the vertical direction. It was also observed that the amplitudes of vibration accelerations of the elements of the tested tractors during plowing the field had higher values than during harrowing, but these excesses were not significant. Analysis of the test results shows that the tractors' suspensions have practically the same vibration characteristics, and therefore, it is recommended to conduct further studies of the parameters of general vibration (on the operator's seat) and local vibration (on the steering wheel) in order to assess the tractor operator' working conditions, his safety and develop technical solutions to improve the devices/machines. The study practical value and originality consists in identifying the structural elements of mobile agricultural machinery (for example, tractors) that have the highest vibrations, which affect the operator for their further improvement, but not for replacing the machinery. This approach to improving the working conditions of mobile agricultural machinery operators is driven by the country's weak economy and can be beneficial for developing countries in the face of a lack of funds to purchase new ergonomic machines.

Without the assistance of Global Positioning System (GPS), estimating the 3D position of indoor and outdoor pedestrians using a single wearable device is a daunting if not impossible task, especially if micro-sensors are used. Here, we present a novel 3D position estimation method using one integrated ankle sensing device, which consists of an accelerometer, a gyroscope, a magnetometer, and a barometer. Pedestrians’ vertical position is estimated by fusing the acceleration and angular velocity as well as the height derived from barometer data. To estimate pedestrians’ horizontal position, we proposed an adaptive multimodal stride length model and a multi-sensor-fusion-based heading angle estimation method, using the Pedestrian Dead Reckoning (PDR) mechanism. By introducing a vertical variable into the stride length model, this new model greatly improved the applicability and accuracy of PDR in horizontal position estimation. Based on this new model, PDR can be used not only for estimating the horizontal position of the pedestrian walking on flat areas but also for those walking up and down stairs. The effectiveness and applicability of our method in 3D position estimation have been demonstrated in several different experiments of indoor and outdoor scenes. The first is when a pedestrian walks on an indoor flat ground, following a spiral trajectory. The estimation accuracy of pedestrians’ height position is 1.5cm and the ratio of horizontal walking estimation error is 1.02m with a total walking distance of 53.1m. The second is when a pedestrian walks up staircases from Floor 4 to Floor 8 in a building. The cumulative error of the estimated height is 0.23m with a total height of 14.4m, and the root mean square error of the estimated horizontal 2D position is 15cm compared to a total horizontal walking distance of 38.4m. The third case involves a pedestrian walking on audience stands of an outdoor stadium and returns to the starting position for a total distance of 94.4m. The estimation error from the sensing device is 0.92m in this case, with mean error of the estimated height position of each step at 3.3cm. Having the capability to provide centimeter-level position estimation of pedestrians, this sensing device can be applied for 3D body tracking and indoor/outdoor pedestrian positioning and navigation.

The main purpose of this study is to investigate the spatiotemporal interstitial fluid dynamics in a vibrating vocal fold. A self-oscillating poroelastic model is proposed to study the liquid dynamics in the vibrating vocal folds by treating the vocal fold tissue as a transversally isotropic, fluid-saturated, porous material. Rich spatiotemporal liquid dynamics have been found. Specifically, in the vertical direction, the liquid is transported from the inferior side to the superior side due to the propagation of the mucosal wave. In the longitudinal direction, the liquid accumulates at the anterior-posterior midpoint. However, the contact between the two vocal folds forces the accumulated liquid out laterally in a very short time span. These findings could be helpful for exploring etiology of some laryngeal pathologies, optimizing laryngeal disease treatment, and understanding hemodynamics in the vocal folds.

The flow of small particles in porous media is of interest in many branches of science. In geotechnical engineering, this phenomenon usually occurs in graded granular materials and is termed as internal erosion. In this work, graded granular materials are simplified as binary mixtures under vertical compression, and water flows perpendicular to the vertical direction. We use the coupled Lattice Boltzmann method (LBM) and discrete element method (DEM) to investigate the initiation of internal erosion under different stress levels and hydraulic gradients. Suffusion was observed as the fine particles are transported by the seepage flow. The change of void ratio due to water flow and vertical compression demonstrates three patterns: erosion, stability, and compaction. Particles with low engagement in force transmission are more prone to erosion, while the hydraulic gradient is an external disturbance factor. The ballistic, caging, and diffusive regimes are observed in the initial process of internal erosion.

Cohesionless granular soils display stiffness anisotropy, and accurately characterizing it is essential for numerous geotechnical applications. The inherent anisotropic behaviour of geomaterials is not comprehensively understood; hence, research on the development of novel geophysical testing methods for assessing multidirectional stiffness is important. This contribution presents an innovative arrangement of vertical and horizontal planar piezoelectric transducers to describe the stiffness anisotropy of soils. The transducer assembly can be used to measure nine different elastic wave velocities of a soil specimen in three directions of principal axes having a wide range of median particle sizes. To describe the performance of the developed transducer assembly, four different types of cohesionless granular materials: Toyoura sand, Kashima river sand, glass beads, and Oiso gravel were tested in a large-sized triaxial apparatus having a rectangular specimen of size 235 × 235 × 500 mm. All the tested materials displayed considerably stiffer responses in the horizontal direction as compared to the vertical direction. Except for the coarse gravel, natural sands and glass beads demonstrated isotropic behaviour in the horizontal direction. No significant influence of specimen dimension on the measured vertical wave velocities was detected when the large triaxial test results and medium-sized triaxial test results were compared. The paper also provides a comparison of the vertical stiffness evaluated using planar piezoelectric transducers with those measured statically by applying small-amplitude vertical cyclic loading.

In this work, we describe man-made structures via an appropriate structure assumption, called the Atlanta world assumption , which contains a vertical direction (typically the gravity direction) and a set of horizontal directions orthogonal to the vertical direction. Contrary to the commonly used Manhattan world assumption, the horizontal directions in Atlanta world are not necessarily orthogonal to each other. While Atlanta world can encompass a wider range of scenes, this makes the search space much larger and the problem more challenging. Our input data is a set of surface normals, for example, acquired from RGB-D cameras or 3D laser scanners, as well as lines from calibrated images. Given this input data, we propose the first globally optimal method of inlier set maximization for Atlanta direction estimation. We define a novel search space for Atlanta world, as well as its parametrization, and solve this challenging problem using a branch-and-bound (BnB) framework. To alleviate the computational bottleneck in BnB, i.e., the bound computation, we present two bound computation strategies: rectangular bound and slice bound in an efficient measurement domain, i.e., the extended Gaussian image (EGI). In addition, we propose an efficient two-stage method which automatically estimates the number of horizontal directions of a scene. Experimental results with synthetic and real-world datasets have successfully confirmed the validity of our approach.

In this new study, we investigate the motion of a forced mass-spring-damper in a vertical position. First, the classical Lagrangian as well as the classical Euler–Lagrange equation of motion are constructed. Then the fractional Euler–Lagrange equation is derived by extending the classical Lagrangian in the fractional sense. In this extension, a new form of the fractional derivative is employed including a general function as its kernel. The derived fractional Euler–Lagrange equation is then converted into a system of linear algebraic equation by designing an efficient matrix approximation approach. The numerical findings are reported verifying the theoretical investigations. According to the results, some remarkable thinks are achieved; indeed, the numerical simulations show that different aspects of the system under study can be explored with regard to the flexibility found in selecting the kernel contrary to the traditional fractional models.