Constant Diameter Research Articles

Simulation of Hydrate Migration and Deposition in Pipe with Diameter Reduction and Direction Variation

Summary Pipes with diameter reduction and direction variation are very common in deepwater extraction. While the high-pressure and low-temperature conditions may trigger severe hydrate problems, current studies on hydrate particle migration and deposition are mainly carried out in pipes with a constant diameter, whereas the law of diameter reduction has been less explored; in particular, the effect of diameter reduction + direction variation in pipe has not been reported. In this study, a model of hydrate particle migration and deposition in special pipelines is established based on the computational fluid dynamics (CFD)-discrete element solver (DEM)-application programming interface (API) method, which can be used to carry out real-time visualization calculations of hydrate particles. Simultaneously, this paper reveals the mechanism of hydrate particle migration and deposition at the diameter reduction and direction variation, which provides a new idea for the design of the pipe. Furthermore, for the pipe with diameter reduction + direction variation, the entire process of deposition blockage is simulated, and dangerous locations of pipe clogging are identified. The simulation results found that there is a maximum hydrate deposition particle diameter (MHDPD) for hydrate deposition in the pipe. The results of this work may provide valuable references for accurate prediction of particle deposition in deepwater development.

Resistance model of an active capsule endoscope in a peristaltic intestine.

In the past studies, the resistance of magnetically controlled capsules running through the small intestine has been modeled assuming that the small intestine was a circular tube with a constant diameter. Peristalsis is an important character of the human gastrointestinal system, and it would result in some changes in the diameter of the intestine, meaning that the existing resistance models would no longer be applicable. In this paper, based on the assumption that intestinal peristalsis is actually a sinusoidal wave, a resistance model of the capsule running in the peristaltic intestine is established, and then it is validated experimentally. The model provides a realistic foundation for the optimization and control of the magnetically controlled endoscopy.

Investigation of the microscopic mechanism of H2O adsorption by low-rank coal slit pores through GCMC and MD simulations

This study investigates the influence of pore structure on H2O adsorption in low-rank coal (LRC) models at a molecular level, employing variously sized LRC slit-pore models·H2O adsorption behavior is analyzed across different pore sizes ranging from 0.001 to 100 kPa fugacity, by employing the Grand canonical Monte Carlo (GCMC) method and molecular dynamics (MD) simulations to explore saturated adsorption kinetics. The findings indicate a positive correlation between H2O adsorption levels and both fugacity and pore diameter. Furthermore, at constant pore diameter, the adsorption heat increases exponentially with increasing adsorption levels. Notably, H2O adsorption in LRC slit pores exhibits multilayer adsorption characteristics. First, adsorption occurs as monomolecular layers on the LRC surface, transitioning to secondary adsorption sites formed by previously adsorbed H2O molecules with increasing fugacity, ultimately saturating the pores. This adsorption process exhibits a correlation with a shift in potential energy distribution from high to low potential energy directions. Moreover, the ordering of H2O molecule arrangements between hydrogen atoms, oxygen atoms, and H2O molecules decreases with increasing pore diameters. Larger pore diameters correspond to increased H2O molecule diffusion, the stronger interaction between the LRC slit pores and H2O molecules but reduced interaction with individual H2O molecules. Overall, this study establishes a theoretical foundation for further studies on coal pore wetting and offer valuable insights for studies aimed at reducing dust and preventing gas outbursts.

Synergistic effect of BNNS and MgAl layered double hydroxide nanosheets on dielectric properties and thermal conductivity of polyetherimide nanocomposite films

AbstractThe development of polymer‐based dielectric nanocomposites with superior dielectric properties, heat dissipation, and excellent thermal stability remains a significant challenge for advanced electronic and electrical systems. In this work, boron nitride nanosheets (BNNS) and MgAl layered double hydroxide nanosheets (MgAl LDHNS) were utilized as binary fillers and incorporated into polyetherimide (PEI) to fabricate BNNS‐MgAl LDHNS/PEI nanocomposite films by ball milling dispersion and solution casting method. Owing to the exceptional synergistic effect of BNNS with high thermal conductivity and large diameter, combined with MgAl LDHNS with high dielectric constant and small diameter, the dielectric constant and thermal conductivity of the nanocomposite film were enhanced while maintaining low dielectric loss and high breakdown strength. For the BNNS‐MgAl LDHNS/PEI nanocomposite films with filler loading of 12 wt%, the dielectric constant (6.47 at 100 Hz) increased by 73%, the in‐plane thermal conductivity (6.932 W/m·K) and through‐plane thermal conductivity (0.407 W/m·K) increased by 561% and 111%, respectively. And the breakdown strength of the nanocomposite film remains at 82.1 kV/mm. Simultaneously, the thermal stability and mechanical flexibility of the nanocomposite film were maintained. This work presents a promising PEI‐based composite material and offers new insights into the role of two‐dimensional binary fillers with varying sheet diameters in enhancing the properties of polymer‐based composites.Highlights BNNS‐MgAl LDHNS/PEI nanocomposite film was prepared. The nanocomposite film has high dielectric and thermal properties. The interfacial polarization synergistic enhanced by the 2D binary fillers. A high thermal conductivity path was formed between 2D binary fillers.

Variable diameter pile foundations – advantages and disadvantages

Variable diameter pile foundations can be an efficient foundation solution used for special structures, mainly for the ones with increased heights. For economic efficiency in land use, especially in urban areas, there is a tendency to build very high constructions with very small footprint related to their height, which transmit large loads to the foundation soil. Based on these aspects, it is necessary to consider pile foundations in order to ensure the desired safety and stability requirements. The technologies for piles constructions evolved a lot and a main objective was to better use the interaction between the soil and the pile. From this point a view the paper presents a comparison between the bearing capacities of a constant diameter pile and a variable diameter pile, considering different soil conditions. All the calculations were performed using finite element analyses.

Adiabatic gas transport in the long flow channels

The paper present the determination of the state parameters of natural gas at the pipeline inlet based on knowledge of the pressure and temperature at the receiving point. Natural gas transport will be carried out through an offshore section of a transmission pipeline. The equations of the Fanno flow model will be used to describe the thermodynamic parameters of the gas in the flow lines. The mathematical equations of the flow mentioned above models have been derived from an analysis of the mass, energy and momentum balance equations. They also take into account the viscous friction forces in the transported gas. Based on the carried out calculations, changes in the Mach number, pressure and velocity of methane transported along the analysed pipeline were determined. In addition, the total entropy gain in the analysed methane flow was determined. The novelty of the calculations presented is the use of the Fanno flow model, which considers a realistic adiabatic gas flow. This is in contrast to the isothermal flow model, which assumes an unchanging temperature of the transported gas. In the case under consideration, the adopting model was possible because of the similar temperature values of the gas flowing in the pipeline and the corresponding temperature values of the surrounding seawater. The fundamental advantage of the Fanno flow model is that it satisfies the mass balance of the flowing gas in each cross-section. Thus, the product of the velocity and density of the gas in a pipeline of constant diameter assumes a constant value.

Three-atom-wide gold quantum rods with periodic elongation and strongly polarized excitons

Atomically precise control over anisotropic nanoclusters constitutes a grand challenge in nanoscience. In this work, we report our success in achieving a periodic series of atomically precise gold quantum rods (abbrev. Au QRs) with unusual excitonic properties. These QRs possess hexagonal close-packed kernels with a constant three-atom diameter but increasing aspect ratios (ARs) from 6.3 to 18.7, all being protected by the same thiolate (SR) ligand. The kernels of the QRs are in a Au1-(Au3)n-Au1 configuration (where n is the number of Au3 layers) and follow a periodic elongation with a uniform Au18(SR)12 increment consisting of four Au3 layers. These Au QRs possess distinct HOMO-LUMO gaps (Eg = 0.6 to 1.3 eV) and exhibit strongly polarized excitonic transition along the longitudinal direction, resulting in very intense absorption in the near-infrared (800 to 1,700 nm). While excitons in gapped systems and plasmons in gapless systems are distinctly different types of excitations, the strongly polarized excitons in Au QRs surprisingly exhibit plasmon-like behaviors manifested in the shape-induced polarization, very intense absorption (~106 M-1 cm-1), and linear scaling relations with the AR, all of which resemble the behaviors of conventional metallic-state Au nanorods (i.e., gapless systems), but the QRs possess distinct gaps and very long excited-state lifetimes (10 to 2,122 ns), which hold promise in applications such as near-infrared solar energy utilization, hot carrier generation and transfer. The observation of plasmon-like behaviors from single-electron transitions in Au QRs elegantly bridges the distinct realms of single-electron and collective-electron excitations and may stimulate more research on excitonics and plasmonics.

Higher absorption enhancement of black carbon in summer shown by 2-year measurements at the high-altitude mountain site of Pic du Midi Observatory in the French Pyrenees

Abstract. Black-carbon-containing particles strongly absorb light, causing substantial radiative heating of the atmosphere. The climate-relevant properties of black carbon (BC) are poorly constrained in high-altitude mountain regions, where many complex interactions between BC, radiation, clouds and snow have important climate implications. This study presents 2-year measurements of BC microphysical and optical properties at the Pic du Midi (PDM) research station, a high-altitude observatory located at 2877 m above sea level in the French Pyrenees. Among the long-term monitoring sites in the world, PDM is subject to limited influence from the planetary boundary layer (PBL), making it a suitable site for characterizing the BC in the free troposphere (FT). The classification of the dominant aerosol type using aerosol spectral optical properties indicates that BC is the predominant aerosol absorption component at PDM and controls the variation in single-scattering albedo (SSA) throughout the 2 years. Single-particle soot photometer (SP2) measurements of refractory BC (rBC) show a mean mass concentration (MrBC) of 35 ng m−3 and a relatively constant rBC core mass-equivalent diameter of about 180 nm, which are typical values for remote mountain sites. Combining the MrBC with in situ absorption measurements, a rBC mass absorption cross-section (MACrBC) of 9.2 ± 3.7 m2 g−1 at λ=880 nm has been obtained, which corresponds to an absorption enhancement (Eabs) of ∼2.2 compared to that of bare rBC particles with equal rBC core size distribution. A significant reduction in the ΔMrBC/ΔCO ratio when precipitation occurred along the air mass transport suggests wet removal of rBC. However we found that the wet removal process did not affect the rBC size, resulting in unchanged Eabs. We observed a large seasonal contrast in rBC properties with higher MrBC and Eabs in summer than in winter. In winter a high diurnal variability in MrBC (Eabs) with higher (lower) values in the middle of the day was linked to the injection of rBC originating from the PBL. On the contrary, in summer, MrBC showed no diurnal variation despite more frequent PBL conditions, implying that MrBC fluctuations are rather dominated by regional and long-range transport in the FT. Combining the ΔMrBC/ΔCO ratio with air mass transport analysis, we observed additional sources from biomass burning in summer leading to an increase in MrBC and Eabs. The diurnal pattern of Eabs in summer was opposite to that observed in winter with maximum values of ∼2.9 observed at midday. We suggest that this daily variation may result from a photochemical process driving the rBC mixing state rather than a change in BC emission sources. Such direct 2-year observations of BC properties provide quantitative constraints for both regional and global climate models and have the potential to close the gap between model-predicted and observed effects of BC on the regional radiation budget and climate. The results demonstrate the complex influence of BC emission sources, transport pathways, atmospheric dynamics and chemical reactivity in driving the light absorption of BC.

A New Calculation Model for Equivalent Circulating Density Considering Interface Effect between Various Fluids during Cementing Process

Summary Equivalent circulating density (ECD) is an essential parameter in the construction of oil and gas wells, which can be used to control the downhole pressure and prevent serious incidents such as well leakage or blowouts. Different engineering tasks will lead to changes in the ECD calculation model; the classical pipe flow theory can be used to calculate the ECD of circulating drilling fluid, but it is not suitable for the cementing displacement because it does not consider the interface effect between various fluids. In this paper, a new ECD calculation model has been developed that accounts for the changes in fluid interface morphology between displacing fluid and displaced fluid during the cementing process. Moreover, a simulation of the effects of borehole radius, casing eccentricity, displaced fluid density, and flow rate on the ECD were analyzed and quantified by a numerical approach to solve the fluid dynamics equilibrium equations that describe the flow in the eccentric annuli based on the semi-implicit method for pressure-linked equations (SIMPLE) algorithm. The results show that the calculated ECD predicted by the proposed model is larger than the traditional model with the reduction in the borehole radius, and the maximum deviation at the inlet position can reach 0.03 g·cm−3. Variation in the length of the interface transition zone is the main reason for the deviation in ECD prediction accuracy. In the case of constant casing outer diameter, fluid rheology, and displaced fluid density, the ECD decreases with increasing borehole radius. Meanwhile, it increases with higher displaced fluid density, eccentricity, and annular velocity. It is also shown that the length of the mixing zone can reach up to 40% of the pipe length under the conditions of eccentricity and displacement described in the paper. The proposed model predicts the ECD in the annulus by considering the influence of different engineering parameters on the movement of displacement interface, which can effectively ensure the safety of the cementing operation.

Metasurface-based perfect vortex beam for optical eraser

Perfect vortex beams (PVBs) take advantage of conventional vortex beams regarding their property of constant diameter of the annular intensity distribution on different topological charges (TCs), facilitating spatially coupling multiple beams with different TCs simultaneously. However, there are demands for PVBs with larger TCs that can be integrated with CMOS-fabrication processes in applications since conditional PVBs are composed of bulky optical components. In this work, we demonstrate metasurface-based PVBs (MPVBs) with TCs as high as −32 and 16 in the visible, manifesting annular intensity distributions capable of broadband operation. The optical eraser concept by integrating MPVBs has been conducted, and the flower-like interference performs a helicity switch to facilitate the uniformization of ring-shaped intensity profiles for the MPVBs with different TCs. The optical eraser experiments demonstrate the potential of MPVBs in advancing both quantum optics and optical device engineering and pave the way for probing quantum behaviors in optics.

High-impedance arc fault modeling for distribution networks based on dynamic geometry dimension

Accurate modeling of high-impedance arc fault (HIAF) is of great significance for studying the characteristics of arc fault and suppressing its harm. In traditional arc models, the arc column is usually considered a cylindrical channel with constant length and diameter. However, the arc-burning process is susceptible to the environment. The changes in arc length and diameter present complex characteristics. Therefore, this study proposes a new HIAF model for distribution networks based on the arc's dynamic geometry dimension (DGD). First, the arc length, diameter, and field strength expressions are improved based on the classical cybernetic model. Next, an automatic parameter optimization method for the DGD model is proposed, and then this model is compared with existing advanced models. After that, the effects of the variable parameters of this model on arc characteristics are analyzed. Finally, the practical application effect of this model is tested. The experimental results show that the DGD model can accurately describe the dynamic arc development process, approximate the given arc waveform closely, and generate high-quality samples, which has certain advantages.

Analyzing Single Peristaltic Wave Behavior in Ureter with Variable Diameters: A Ureterdynamic Study

Ureters are muscular tubes that transport urine from the kidney to the bladder. The peristalsis wave is responsible for carrying urine to the bladder. With the regular appearance of peristalsis, areas with anatomic narrowing junctions are crucial for ureteral diseases. A three-dimensional flow analysis is performed for different time steps to understand the effect of the urine bolus formation and the reflux phenomenon on variable diameter ureters. For the constant and variable diameter ureter, the pressure is obtained behind and in front of the propagating bolus respectively. The peristalsis wave creates the high-velocity of a jet in the neck region of the ureter. The contraction produces the trapping of the bolus leading to adverse flow in the contraction region. By virtue tapering, the high-pressure gradient builds up, leading to high wall shear in the ureter. The main goal is to determine the pressure, velocity, gradient pressure, and shear force on the ureter wall during peristaltic motion. These parameters are very important for clinicians to understand its effect in the unobstructed variable diameter ureter. This article may help to build a medical device for engineers. The physical significance of this information lies in its profound insights into the biomechanics and functionality of the ureters, which are essential components of the human urinary system.

Comparative evaluation conducted on the selection of the type of roller shredder for the cultivation of plowed land

The results of experimental investigations into the features of the roller shredder that breaks down plowed land one by one are presented in this article. This allowed for the determination of the optimum roller parameter values and the examination of the shredder type selection. According to experimental research, selecting the right type of roller is primarily responsible for guaranteeing that the field surface is completely treated. Typically, these rollers are working parts with slats, gear-slats, or rods for installation on a reel that provide moisture feeding at the level necessary for germination in compliance with agrotechnical requirements. Slatted, toothed-slatted, and rod roller shredders with comparable diameters were designed and used in experimental investigations to confirm the results that we had acquired. In experimental studies, after using different constant diameter roller shredder, the influence of soil on the degree of abrasion, its density and drag resistance was studied. To reduce the influence of various variable factors on the results obtained, the experiments were carried out on a specially prepared agricultural background, which was first plowed and then leveled. In order to test the theoretically based parameters of the roller shredder selected for experimental research in the field, a fixed-diameter roller shredder base with a coverage width of 1.5 m and strips with gear strips and rod strips that can be installed on them were developed and prepared. Based on the results of experimental studies, the following can be noted: in order for the quality and density of soil abrasion to meet agrotechnical requirements, and the tensile resistance of the coil to be minimal, the roller shredder must be with a slatt.

Indentation parameters for Brinell hardness measurement of low carbon steels

Brinell hardness of steel 20 was measured with a ball of constant diameter according to the standard technique D=10 mm at different test load values from the range F=62.5…3000 kgf. The diameter d of the reconstructed indentation was measured. According to the developed method the deformation resistance of the sample material in the plastic zone bounded by a hemisphere was determined. The highest values of deformation resistance were recorded at indentation up to the ratio of d/D=0.245. Based on the results obtained, it is recommended to measure the Brinell hardness of steel 20 at the degree of loading F/D2=5. During the ball indentation process, the sample material undergoes significant deformation, which must be taken into account when measuring hardness.

Investigating the mechanical properties of sintered 440 C stainless steel produced by an extrusion-based 3D printer

Extrusion-based 3D printing of parts is one of the simplest, cheapest, and most widely used additive manufacturing (AM) methods. The raw materials in this process are generally filaments with a constant diameter. By equipping extrusion-based 3D printers with the barrel and screw system and removing the filament manufacturing step, a wide range of materials can be 3D printed. In this research, the parts were 3D printed using a feedstock of metal powder injection molding process and with a direct granule extruder system equipped with a barrel and screw. Then, on the printed parts, debinding, sintering, and grinding processes were performed, and finally, their tensile and impact mechanical properties were evaluated. The average tensile strength and modulus are equal to 295 MPa and 85 GPa, respectively, the average of impact resistance is equal to 12.5 J and the hardness number is equal to 118 HB. In addition, by calculating the amount of porosity in the samples, the low value of the mechanical properties of the samples was justified.

Low-threshold single-mode nanowire array flat-band photonic-crystal surface-emitting lasers with high-reflectivity bottom mirrors.

A Si-based nanowire array photonic-crystal surface-emitting laser based on a flat band is designed and simulated. By introducing an air gap between the nanowire and substrate, the bottom reflectivity is significantly enhanced, resulting in much lower threshold and smaller cutoff diameter. Through adjusting the lattice constant (the distance between neighboring nanowires) and nanowire diameter, a photonic crystal structure with a flat band is achieved, in which strong interaction between light and matter occurs in the flat band mode. For the device with a small size, single-mode lasing is obtained with a side-mode suppression ratio of 21 dB, high quality factor of 3940, low threshold gain of 624 cm-1, and small beam divergency angle of ∼7.5°. This work may pave the way for the development of high-performance Si-based surface-emitting nanolasers and high-density photonic integrated circuits.

Linear Recurrent Equations in the Space of Convex Compact Sets and the Diameters of Their Solutions

In the space of convex compact sets with the Minkowski addition operation and the operation of multiplication of a matrix by a set, we consider linear recurrent equations of the first order. We give a complete description of such equations whose all solutions have a constant diameter. For equations of a special form, the Lyapunov exponents of the sequences of diameters of their solutions are calculated.

VOF study of mesoscale bubble flow dynamics in the side-blown gas–liquid two-phase reactor

Understanding the flow and mixing characteristics of mesoscale bubbles within side-blown gas–liquid two-phase systems is paramount for the design and optimization of associated industrial processes. This study elucidates the gas–liquid side-blown two-phase reactor, employing the volume of fluid method coupled with the realizable k-ε turbulence model. Following the model validation through experimental measurements, the mesoscale bubble dynamics, flow characteristics, and multiscale coupling mechanisms inherent to side-blown gas–liquid reactor are explored. The key insights can be obtained: (1) the upward trajectory of bubbles originating from side-injection gas can be categorically divided into four phases with different bubble behaviors. (2) A reduction in the ratio of inertial forces to buoyancy forces during bubble ascent induces a decrease in the bubble shape factor. This transition manifests as a shift from vertical to flattened bubble shapes within the transition and plume regions. (3) Bubbles undergo transitions between states characterized by high buoyancy and low surface tension, accompanied by varying levels of viscous forces during their ascent. These dynamic states render bubbles susceptible to breakup. Under conditions of a constant nozzle diameter, the maximum bubble size within the reactor is inherently restricted. (4) Drawing upon the correlation between bubble Weber and Reynolds numbers, a predictive formula for determining the characteristic velocity of bubbles within side-blown reactors is proposed:uc=σ1-0.456(ρlLC)0.456512μl11.36Overall, this work offers meaningful insights into the fundamental mechanisms governing bubble cluster dynamics within side-blown gas–liquid reactors.

Lubricant-infused anodic aluminum oxide surface (AAO-LIS) for durable slipperiness under harsh conditions

The wettability of surfaces plays a crucial role in determining their applications, and slippery surfaces have been utilized in various fields. Especially, lubricant-infused surface (LIS) has been undergone extensive research over the past decade. However, LIS tends to lose its infused lubricant and consequently lose its slippery properties when exposed to harsh conditions. Therefore, there is a strong need to enhance the durability of the infused lubricant. Herein, two strategies are adopted to improve the durability of slippery properties against centrifugal forces and high-speed shear flows. One strategy is using re-entrant shaped nanocavities, and the other is grafting PDMS brush onto the surface. Anodic aluminum oxide (AAO) is employed to fabricate the re-entrant shaped nanocavities, and the durability of the infused lubricant is improved when the cavities have a smaller diameter. Furthermore, the re-entrant shape of nanocavity significantly improves the durability compared to nanocavity with a constant diameter. The grafting of PDMS brush is essential for enhancing the durability, and an increase in the length of the PDMS brush also improves the durability. The fabricated AAO-based LIS (AAO-LIS) maintains the slippery properties for 50 min under a high-speed water flow of 12 m/s. In addition, it maintains its superior slipperiness for more than a few days when exposed to actual seawater. Furthermore, the frictional drag reduction performance of the fabricated AAO-LIS is assessed. The proposed AAO-LIS maintains a certain drag reduction performance durably even after losing its superior slipperiness, demonstrating its strong potential for practical applications across various industrial fields.

Study on articular surface morphology of atlantoaxial lateral mass based on differential manifold

ObjectivesTo propose a surface reconstruction algorithm based on a differential manifold (a space with local Euclidean space properties), which can be used for processing of clinical images and for modeling of the atlantoaxial joint. To describe the ideal anatomy of the lateral atlantoaxial articular surface by measuring the anatomical data.MethodsComputed tomography data of 80 healthy subjects who underwent cervical spine examinations at our institution were collected between October 2019 and June 2022, including 46 males and 34 females, aged 37.8 ± 5.1 years (28–59 years). A differential manifold surface reconstruction algorithm was used to generate the model based on DICOM data derived by Vision PACS system. The lateral mass articular surface was measured and compared in terms of its sagittal diameter, transverse diameter, articular surface area, articular curvature and joint space height.ResultsThere was no statistically significant difference between left and right sides of the measured data in normal adults (P > 0.05). The atlantoaxial articular surface sagittal diameter length was (15.83 ± 1.85) and (16.22 ± 1.57) mm on average, respectively. The transverse diameter length of the articular surface was (16.29 ± 2.16) and (16.49 ± 1.84) mm. The lateral articular surface area was (166.53 ± 7.69) and (174.48 ± 6.73) mm2 and the curvature was (164.03 ± 5.27) and (153.23 ± 9.03)°, respectively. The joint space height was 3.05 ± 0.11mm, respectively. There is an irregular articular space in the lateral mass of atlantoaxial, and both upper and lower surfaces of the articular space are concave. A sagittal plane view shows that the inferior articular surface of the atlas is mainly concave above; however, the superior articular surface of the axis is mainly convex above. In the coronal plane, the inferior articular surface of the atlas is mostly concave above, with most concave vertices located in the medial region, and the superior articular surface of the axis is mainly concave below, with most convex vertices located centrally and laterally.ConclusionA differential manifold algorithm can effectively process atlantoaxial imaging data, fit and control mesh topology, and reconstruct curved surfaces to meet clinical measurement applications with high accuracy and efficiency; the articular surface of the lateral mass of atlantoaxial mass in normal adults has relatively constant sagittal diameter, transverse diameter and area. The distance difference between joint spaces is small, but the shape difference of articular surfaces differs greatly.