Spherical Head Research Articles

Use of a Novel Reverse Hip Replacement System to Address Dislocation and Instability.

While total hip arthroplasty (THA) is an enormously successful treatment for patients with end-stage degenerative arthritis of the hip, and surgeons have optimized existing hip implants and techniques, dislocation and instability persist as a leading cause of failure. Given the tremendous success of reverse total shoulder arthroplasty in enhancing the stability of shoulder reconstruction by reversing the anatomic seating of the ball and socket components, one manufacturer (Hip Innovation Technology, LLC, Woodstock, Georgia) has developed a novel Reverse Hip Replacement System (Reverse HRS) to address the need for greater stability in reconstruction of the arthritic hip joint. Rather than the traditional anatomic components that replace the head of the femur with a spherical ball and the acetabulum with a socket with polyethylene liner mounted into the pelvis, the Reverse HRS features a cup with polyethylene liner attached to the femoral stem and a spherical metal head attached to a central trunnion inside of the porous-coated acetabular shell fixed into the pelvis. This design provides dramatically enhanced stability and improved range of motion. This article reviews relevant published literature, including results from a Canadian clinical trial and case reports from a multicenter American clinical trial monitored by the U.S. Food and Drug Administration. It also describes the components and surgical technique of reverse THA.

Nonspherical humeral arthroplasty increases internal rotation: a biomechanical comparison of the native humeral head to nonspherical and spherical humeral implants

BackgroundNonspherical humeral head implants more closely resemble native humeral anatomy than spherical components and may better replicate native shoulder range of motion (ROM) and kinematics. The purpose of this study was to compare shoulder ROM and kinematics of a commercially available nonspherical humeral head implant with the native humeral head and a height matched, custom manufactured spherical implant. MethodsSix fresh frozen cadaveric shoulder specimens were used with a custom shoulder testing system. The native shoulder was tested in multiple positions under anatomic muscle loading. Each specimen was tested for ROM and glenohumeral joint kinematics by measuring the humeral head apex and humeral head center (HHC) translation per degree of rotation using a MicroScribe digitizer. Measurements were then repeated after implantation of a spherical and, subsequently, a nonspherical humeral head prothesis. ResultsThe nonspherical implant had significantly more internal rotation (IR) compared to the spherical implant at 0° abduction (10.6 ± 6.2° more IR, P = .004, 95% confidence interval [CI]: −13.3, 34.5), 30° abduction (5.7 ± 2.8°, P = .009, 95% CI: −12.6, 24.0) and 60° abduction (6.8 ± 2.7°, P = .002, 95% CI: −8.3, 22.1) in the scapular plane, and 60° abduction (6.9 ± 2.0°, P = .031, 95% CI: −12, 25.6) in the coronal plane. The nonspherical implant had more IR than the native head at 60° of abduction in the scapular plane (7.0 ± 2.2° P = .002, 95% CI: −10.3, 24.3). The spherical head had less IR than the native head at 0° abduction (7.2 ± 4.8°, P = .031, 95% CI: 32.5, 18.1). There were no differences in humeral head apex translation per degree of rotation noted between the spherical implant or nonspherical implant and the native shoulder. The nonspherical head had less HHC translation than the native shoulder at 30° abduction in the forward flexion plane (P = .007); otherwise, there were no statistically significant differences in HHC translation between the native shoulder, the spherical head, and the nonspherical head. There was no significant difference observed between the average difference in anterior-posterior and superior-inferior radius of curvature of the nonspherical implants (2.0 ± 0.7 mm) and the native humeral heads (1.9 ± 1.3 mm) [P = .926]. ConclusionThe results of this biomechanical study suggest that the commercially available nonspherical humeral head has improved IR when compared to a custom, height controlled spherical implant and offers ROM and kinematics similar to the native humeral head in a cadaveric model.

Magnetic targeting and pH-microwave dual responsive Janus mesoporous silica nanoparticles for drug encapsulation and delivery

In this paper, a new Janus-structured nano drug delivery carrier Fe3O4@TiO2&mSiO2 was designed and synthesized, which consisted of a spherical head and a closely connected rod. The head was a nanocomposite of core/shell structure with magnetic spinel ferric tetraoxide core and anatase titanium dioxide shell (Fe3O4@TiO2), and the rod was ordered mesoporous silica (mSiO2). The nanocarriers showed excellent magnetic targeting capability (saturation magnetization, 25.18 emu g−1). The core/shell heads endowed the carriers with fine microwave responsiveness. The pore volume of mesoporous nanocarriers was 0.101 cm3 g−1, and the specific surface area was 489.0 m2 g−1. Anticancer drug doxorubicin could be loaded in the mesoporous of the carriers to form Fe3O4@TiO2&mSiO2-DOX. The drug loading capacity was 10.4%. Fe3O4@TiO2&mSiO2-DOX exhibited acid-sensitive and microwave-sensitive release properties along with good bio-compatibility. Fe3O4@TiO2&mSiO2 Janus nanoparticles are expected to be ideal drug carriers.

A hybrid boundary element-finite element approach for solving the EEG forward problem in brain modeling.

This article introduces a hybrid BE-FE method for solving the EEG forward problem, leveraging the strengths of both the Boundary Element Method (BEM) and Finite Element Method (FEM). FEM accurately models complex and anisotropic tissue properties for realistic head geometries, while BEM excels in handling isotropic tissue regions and dipolar sources efficiently. The proposed hybrid method divides regions into homogeneous boundary element (BE) regions that include sources and heterogeneous anisotropic finite element (FE) regions. So, BEM models the brain, including dipole sources, and FEM models other head layers. Validation includes inhomogeneous isotropic/anisotropic three- and four-layer spherical head models, and a four-layer MRI-based realistic head model. Results for six dipole eccentricities and two orientations are computed using BEM, FEM, and hybrid BE-FE method. Statistical analysis, comparing error criteria of RDM and MAG, reveals notable improvements using the hybrid FE-BE method. In the spherical head model, the hybrid BE-FE method compared with FEM demonstrates enhancements of at least 1.05 and 38.31% in RDM and MAG criteria, respectively. Notably, in the anisotropic four-layer head model, improvements reach a maximum of 88.3% for RDM and 93.27% for MAG over FEM. Moreover, in the anisotropic four-layer realistic head model, the proposed hybrid method exhibits 55.4% improvement in RDM and 89.3% improvement in MAG compared to FEM. These findings underscore the proposed method is a promising approach for solving the realistic EEG forward problems, advancing neuroimaging techniques and enhancing understanding of brain function.

Hindlimb Skeletal Structure of the Green-winged Macaw: An Anatomical Study

In birds, the forelimb bones undergo modification to facilitate muscle attachment for flight, enabling the movement of wings up and down. Conversely, hindlimb bones primarily support walking and perching functions, necessitating evolutionary adaptations in their structure. Therefore, this study aims to document the gross anatomical features of hind limb bones in Green-winged Macaws, including the femur, tibio-tarsus, tarsometatarsus, and digits. The bones were sourced from six Green-winged Macaw carcasses undergoing post-mortem examination at the Department of Veterinary Pathology, Madras Veterinary College, Chennai. Preparation was conducted using the wet maceration technique. In the femur, the proximal end displayed a large, well-defined spherical head medially, accompanied by a small depression called the fovea capitis, and a distinct neck. The tibio-tarsus exhibited a small roughened area on its lateral border for fibula attachment, with a larger medial and smaller lateral condyle at the proximal extremity, along with a linear cinemal crest along the medial border. The fibula's distal extremity tapered into a free point, articulating at the caudolateral aspect of the tarsometatarsus. The tarsometatarsus displayed fused distal tarsals with metatarsals II, III, and IV, while Metatarsus I remained a separate bone, forming the base of the first toe. The proximal extremity of the tarsometatarsus featured two large concave articular facets for condyles from the distal extremity of the tibio-tarsus, and a facet for the distal end of the fibula caudolaterally. The Macaw's hind limb consisted of four digits, forming a zygodactyl foot arrangement.

Updating the Knowledge on the Secretory Machinery of Hops (Humulus lupulus L., Cannabaceae).

Cannabaceae species garner attention in plant research due to their diverse secretory structures and pharmacological potential associated with the production of secondary metabolites. This study aims to update our understanding of the secretory system in Hops (Humulus lupulus L.), an economically important species especially known for its usage in beer production. For that, stems, leaves, roots, and inflorescences were collected and processed for external morphology, anatomical, histochemical, ultrastructural and cytochemical analyses of the secretory sites. Our findings reveal three types of secretory structures comprising the secretory machinery of Hops: laticifer, phenolic idioblasts and glandular trichomes. The laticifer system is articulated, anastomosing and unbranched, traversing all plant organs, except the roots. Phenolic idioblasts are widely dispersed throughout the leaves, roots and floral parts of the species. Glandular trichomes appear as two distinct morphological types: capitate (spherical head) and peltate (radial head) and are found mainly in foliar and floral parts. The often-mixed chemical composition in the secretory sites serves to shield the plant from excessive UVB radiation, elevated temperatures, and damage inflicted by herbivorous animals or pathogenic microorganisms. Besides the exudate from peltate glandular trichomes (lupulin glands), latex and idioblast content are also likely contributors to the pharmacological properties of different Hop varieties, given their extensive presence in the plant body.

Anatomic total shoulder arthroplasty with stemless humeral component, nonspherical head, and inlay glenoid: clinical outcomes at mean 4.4-year follow-up

BackgroundLimitations of traditional stemmed anatomic total shoulder arthroplasty (aTSA) with a spherical head and onlay glenoid include 1) inaccurate replication of native nonspherical humeral head kinematics, 2) substantial bone resection, and 3) susceptibility to glenoid loosening. Our purpose was to examine the outcomes of stemless aTSA with a nonspherical head and inlay glenoid. MethodsSixty patients (63 shoulders) with end-stage glenohumeral osteoarthritis were treated by a single surgeon. The study population was limited to 22 patients/25 shoulders (13 male, 12 female; mean age 65.6 years) with 2-year minimum follow-up (mean 51.8 months) subdivided into 2 groups by age. The young group included 5 patients/5 shoulders (3 male, 2 female; mean age 52.2 years; mean follow-up 62.4 months), while the elderly group included 17 patients/20 shoulders (10 male, 10 female; mean age 68.9 years; mean follow-up 49.2 months). At the final follow-up, patient satisfaction and complications were evaluated and the Constant-Murley, American Shoulder and Elbow Surgeons, and SF-36 scores were compared to preoperative values. First postoperative radiographs were compared to the final follow-up for signs of gross loosening, implant tilt, subsidence, and periprosthetic radiolucency. ResultsNo humeral shaft fractures, infections, glenoid/humeral component loosening, radiolucencies, shoulder dislocations, or neurovascular complications were encountered. No reoperations or revisions were performed. The entire study population (25 shoulders) showed significant increases in the Constant score (47.4-82.8, P < .001), American Shoulder and Elbow Surgeons score (36.9-88.1, P < .001), and all components of the SF-36 score (P < .014) except general health perceptions (P = .490), role imitations (emotional) (P = .232), and mental health (P = .746), with a 95% patient satisfaction rate. There were no significant differences between the young and elderly groups in any outcomes (P > .107). ConclusionOur results suggest that stemless aTSA performed with a nonspherical humeral head and inlay glenoid is a safe and effective treatment for glenohumeral osteoarthritis in both young and elderly patients. However, longer term studies with larger patient populations will be required for corroboration.

Feasibility of In Vivo Semen Collection and Description of the Morphology and Ultrastructure of the Spermatozoa of Arapaima gigas (Schinz, 1822)

The pirarucu, Arapaima gigas, is an emblematic endangered Amazon osteoglossid with high potential for aquaculture development. In this study, we report the in vivo collection of semen from pirarucu for the first-time and a complete description of the spermatozoa ultrastructure using scanning and transmission electron microscopy (SEM and TEM). The spermatozoon of pirarucu is biflagellate with no acrosomal cell, comprising a spherical head (8.26 ± 2.19 µm2), a short intermediate piece region and two long flagella (68.34 ± 5.69 µm). The nucleus is spherical and electron-dense, and at its base, there are two nuclear fossae where the centrioles are found. The anterior part of the flagellum is positioned at the lateral base of the nucleus, forming an intermediate piece. Lateral to the intermediate piece, an abundant number of mitochondria are present and occupy most of the cytoplasmic volume. The two flagella were found with a 9 + 2 axonemal structure (nine peripheral doublets and two central microtubules). The central microtubules are aligned with two side fins formed laterally by the axoneme plasma membrane. Side fins were observed from the anterior region to the posterior end. The results show that the spermatozoa of A. gigas are biflagellate, mitochondria-rich and robust, corroborating the external fertilization characteristic of the species. The novel description of sperm morphology presented herein will contribute to advancing the knowledge of and aiding future research on the reproductive biology of this species.

Defect detection of spherical heads by time-of-flight diffraction

Inspecting spherical heads with ultrasonic time-of-flight diffraction (TOFD) is restricted in quantitative accuracy, since the travel path of lateral wave is not along with the structured surface. Meanwhile, a layered dead zone related to lateral wave generates at the near-surface zone and is greater than that in flat plate. In this paper, the vertical inner-wall defects outside and inside the dead zone in the girth weld of spherical head are detected and located by establishing the quantitative relationship between concerned signals (diffracted longitudinal wave or mode-converted wave) and defect depths. Focusing on the aluminum alloy spherical head with 60.0 mm curvature radius and 20.0 mm thickness, the positioning errors of defects with depths of 15.0 mm and 5.0 mm in simulation and experiments are no more than 9.6 % at 5 MHz inspection frequency. Finally, we verify the theoretical relationship by combining simulated and experimental images, analyze the variation of the dead zone in spherical head with the scanning position under different curvature radii and discuss the influence of curvature radius on location accuracy.

Parameter study for critical heat flux under external reactor vessel cooling condition based on a mechanism model

External reactor vessel cooling has been adopted an important method to implement In Vessel Retention severe accident mitigation strategy for many advanced passive pressurized water reactors. Critical heat flux is one of the important criteria to evaluate the success or failure of this strategy. The uncertainty of engineering factors in practical design and operation conditions may make influence on critical heat flux more or less. In this paper, a parameter study for critical heat flux was carried out based on a new critical heat flux mechanism model. This mechanism model is developed based on the mechanism of liquid film dryout, and the predicted results of this model are in good agreement with the experimental results. Five important parameters, namely, coolant subcooling degree, geometry of lower head, system pressure, flow rate and heating power shape are analyzed based on this mechanism model. The results of parameter study show that the decrease of inlet coolant temperature and lower head radius are beneficial to the increase of critical heat flux. And the critical heat flux increases with the increase of system pressure. While the change of flow rate and heating power shape have little effect on critical heat flux. Under the condition of same circumference, the critical heat flux of spherical lower head is higher than that of elliptical lower head in the middle and low inclination angle region, while the trend is opposite in high inclination angle region, but not significant.

Asymmetric bistability of chiral particle orientation in viscous shear flows.

The migration of helical particles in viscous shear flows plays a crucial role in chiral particle sorting. Attaching a nonchiral head to a helical particle leads to a rheotactic torque inducing particle reorientation. This phenomenon is responsible for bacterial rheotaxis observed for flagellated bacteria as Escherichia coli in shear flows. Here, we use a high-resolution microprinting technique to fabricate microparticles with controlled and tunable chiral shape consisting of a spherical head and helical tails of various pitch and handedness. By observing the fully time-resolved dynamics of these microparticles in microfluidic channel flow, we gain valuable insights into chirality-induced orientation dynamics. Our experimental model system allows us to examine the effects of particle elongation, chirality, and head heaviness for different flow rates on the orientation dynamics, while minimizing the influence of Brownian noise. Through our model experiments, we demonstrate the existence of asymmetric bistability of the particle orientation perpendicular to the flow direction. We quantitatively explain the particle equilibrium orientations as a function of particle properties, initial conditions and flow rates, as well as the time-dependence of the reorientation dynamics through a theoretical model. The model parameters are determined using boundary element simulations, and excellent agreement with experiments is obtained without any adjustable parameters. Our findings lead to a better understanding of chiral particle transport and bacterial rheotaxis and might allow the development of targeted delivery applications.

Material Removal Mechanism and Force Modeling in Ultrasonic Vibration-Assisted Micro-Grinding Biological Bone

Micro-grinding with a spherical grinding head has been deemed an indispensable method in high-risk surgeries, such as neurosurgery and spine surgery, where bone grinding has long been plagued by the technical bottleneck of mechanical stress-induced crack damage. In response to this challenge, the ultrasound-assisted biological bone micro-grinding novel process with a spherical grinding head has been proposed by researchers. Force modeling is a prerequisite for process parameter determination in orthopedic surgery, and the difficulty in establishing and accurately predicting bone micro-grinding force prediction models is due to the geometric distribution of abrasive grains and the dynamic changes in geometry and kinematics during the cutting process. In addressing these critical needs and technical problems, the shape and protrusion heights of the wear particle of the spherical grinding head were first studied, and the gradual rule of the contact arc length under the action of high-speed rotating ultrasonic vibration was proposed. Second, the mathematical model of the maximum thickness of undeformed chips under ultrasonic vibration of the spherical grinding head was established. Results showed that ultrasonic vibration can reduce the maximum thickness of undeformed chips and increase the range of ductile and bone meal removals, revealing the mechanism of reducing grinding force. Further, the dynamic grinding behavior of different layers of abrasive particles under different instantaneous interaction states was studied. Finally, a prediction model of micro-grinding force was established in accordance with the relationship between grinding force and cutting depth, revealing the mechanism of micro-grinding force transfer under ultrasonic vibration. The theoretical model’s average deviations are 10.37% in x-axis direction, 6.85% in y-axis direction, and 7.81% in z-axis direction compared with the experimental results. This study provides theoretical guidance and technical support for clinical bone micro-grinding.

Numerical resolution of the inverse source problem for EEG using the quasi-reversibility method

The paper concerns the numerical resolution of the inverse source problem for electroencephalography. We propose an approach which is able to take into account some heterogeneity properties (namely a varying electrical conductivity) of the head tissues, in particular of the skull layer. It combines two consecutive steps: (i) a data completion procedure from the scalp to the cortex using the quasi-reversibility method, (ii) a source estimation method from these cortical transmitted data within the brain (modeled as sphere), developed in the software tool FindSources3D. Numerical simulations in the case of the multi-layered spherical head model illustrate both the promising and limiting features of the approach.

Outcome Prediction Model Following Proximal Femoral Osteotomy in Legg-Calvé-Perthes Disease Using Machine Learning Algorithms.

The purpose of the current study was (1) to analyze various factors that may be associated with the outcomes of Legg-Calvé-Perthes disease (LCPD), and (2) to develop and internally validate machine learning algorithms capable of providing patient-specific predictions of which patients with LCPD will achieve relevant improvement in radiologic outcomes after proximal femoral varus osteotomy (PFVO). We examined several variables, previously identified as factors, that may influence the outcome of LCPD and developed a machine learning algorithm based on them. In this retrospective study, we analyzed patients aged older than 6 years at the time of LCPD diagnosis who underwent PFVO at our institution between 1979 and 2015. Univariate and multivariate logistic regression analyses were used to examine the effects of variables on the sphericity of the femoral head at skeletal maturity, including age at onset, sex, stage at operation, extent of epiphyseal involvement and collapse, presence of specific epiphyseal, metaphyseal, and acetabular changes, and postoperative neck shaft angle (NSA). Recursive feature selection was used to identify the combination of variables from an initial pool of 13 features that optimized the model performance. Five machine learning algorithms [extreme gradient boosting (XGBoost), multilayer perception, support vector machine, elastic-net penalized logistic regression, and random forest) were trained using 5-fold cross-validation 3 times and applied to an independent testing set of patients. Ninety patients with LCPD who underwent PFVO were included in this study. The mean age at diagnosis was 7.93 (range, 6.0 to 12.33) years. The average follow-up period was 10.11 (range, 5.25 to 22.92) years. A combination of 8 variables, optimized algorithm performance, and specific cutoffs were found to decrease the likelihood of achieving the 1 or 2 Stulberg classification: age at onset ≤ 8.06, lateral classification ≤ B, 12.40 < preoperative migration percentage (MP) ≤ 22.85, Catterall classification ≤ 2, 117.4 < postoperative NSA ≤ 122.90, -10.8 < postoperative MP ≤ 6.5, 139.65 < preoperative NSA ≤ 144.67, and operation at stage 1. The XGBoost model demonstrated the best performance (F1 score: 0.78; area under the curve: 0.84). The XGBoost machine learning algorithm achieved the best performance in predicting the postoperative radiologic outcomes in patients with LCPD who underwent PFVO. In our population, age at onset ≤ 8.06, lateral classification ≤ B, 12.40 < preoperative MP ≤ 22.85, Catterall classification ≤ 2, 117.4 < postoperative NSA ≤ 122.90, -10.8 < postoperative MP ≤ 6.5, 139.65 < preoperative NSA ≤ 144.67, and operation at an early stage had the likelihood of achieving the spherical femoral head for the patients with LCPD that underwent PFVO. After external validation, the online application of this model may enhance shared decision-making. Level III-retrospective cohort study.

Experimental analysis of the quasi-static penetration test on fiber metal laminated plate reinforced by nano-silica

FMLs are lightweight hybrid materials that possess specific static properties, impact resistance, fracture resistance, and fatigue resistance. These characteristics make FMLs highly desirable for various applications in the transportation industry (Hu et al., 2015 Dec 1) [2].The present study aims to scrutinize the energy absorption and strength characteristics of a kind of Fiber Metal Laminate (FML) reinforced with Nano silica (0, 0.3, 0.6, and 0.9 wt %) that is fabricated from braided fiberglass and carbon fiber sleeve and aluminum 2024-T3. Sleeve-type braided fiberglass, carbon fiber and highly adhesive resin were introduced as interlayers. The arrangement of FMLs layers was in 2 types, first AL/Glass/Glass/Glass/Glass/AL and second AL/Glass/Carbon/Carbon/Glass/AL. The produced FMLs were tested to evaluate the behavior and strength characteristics under quasi-static indention. Quasi-static indentation test performed with spherical head penetrators at a 5 mm/min rate. The experiment continued until the indenter fully penetrated the specimen. These FMLs crushed progressively and are unlikely to fail under catastrophic failure, although specimens with 0.6% Nano silica in glass fiber and specimens with 0.3% in the glass and carbon fiber have better performance. A comparison of the results of glass FMLs with hybrid FMLs shows that Nano silica-reinforced glass fibers have achieved better results than hybrid fiber. To study the structure of amplified FMLs, electron microscopy (SEM) imaging was used which showed that in FMLs with better results, Nano silica was evenly distributed on the layer of epoxy resin. The results also indicate that the mechanical performance of a new FML has a good potential to be applied as a new and efficient energy absorber.

Contact Mechanics of Elliptical and Spherical Head Implants during Axial Rotation in Anatomic Total Shoulder Arthroplasty: A Biomechanical Comparison.

Elliptical humeral head implants have been proposed to result in more anatomic kinematics following total shoulder arthroplasty (aTSA). The purpose of this study was to compare glenohumeral contact mechanics during axial rotation using spherical and elliptical humeral head implants in the setting of aTSA. Seven fresh-frozen cadaveric shoulders were utilized for biomechanical testing in neutral (NR), internal (IR), and external (ER) rotation at various levels of abduction (0°, 15°, 30°, 45°, 60°) with lines of pull along each of the rotator cuff muscles. Each specimen underwent the following three conditions: (1) native, and TSA using (2) an elliptical and (3) spherical humeral head implant. Glenohumeral contact mechanics, including contact pressure (CP; kPa), peak contact pressure (PCP; kPa), and contact area (CA; mm2), were measured in neutral rotation as well as external and internal rotation using a pressure mapping sensor. Elliptical head implants showed a significantly lower PCP in ER compared to spherical implants at 0° (Δ-712.0 kPa; p = 0.034), 15° (Δ-894.9 kPa; p = 0.004), 30° (Δ-897.7 kPa; p = 0.004), and 45° (Δ-796.9 kPa; p = 0.010) of abduction, while no significant difference was observed in ER at 60° of abduction or at all angles in NR and IR. Both implant designs had similar CA in NR, ER, and IR at all tested angles of abduction (p > 0.05, respectively). In the setting of aTSA, elliptical heads showed significantly lower PCP during ER at 0° to 45° of abduction, when compared to spherical head implants. However, in NR and IR, PCP was similar between implant designs. Both designs showed similar CA during NR, ER, and IR at all abduction angles. basic science; controlled laboratory study.

Narrow escape in composite domains forming heterogeneous networks

Cellular networks are often composed of thin tubules connecting much larger node compartments. These structures serve for active or diffusion transport of proteins. Examples are glial networks in the brain, the endoplasmic reticulum in cells or dendritic spines. In this latter case, a large ball forming the head is connected to the dendrite by a narrow passage. In all cases, how the transport of molecules, ions or proteins is regulated determines the time scale of chemical reactions or signal transduction. In the present study, based on modeling diffusion in three dimensions, we compute the mean time for a Brownian particle to reach a narrow target inside such a composite network made of tubules connected to spherical nodes. We derive asymptotic formulas by solving a mixed Neumann–Dirichlet boundary value problem with small Dirichlet part. We first consider the general case of a network domain organized in a 2-D lattice structure that consists of spherical ball compartments connected via narrow cylindrical passages. For a single target located on the boundary of one of the spherical domains, we derive a sparse linear system of equations for each Mean First Passage Time (MFPT) averaged over the different compartments. We then consider a composite domain consisting of a spherical head-like domain, with narrow absorbing targets on its boundary, that is connected to a large cylinder via a narrow cylindrical neck. For Brownian particles starting within the neck, we derive an asymptotic formula for the MFPT. When diffusing particles can be absorbed upon hitting additional absorbing boundaries of the large cylindrical compartment, we derive asymptotic formulas for the splitting probability and conditional MFPT to reach a target on the spherical head. We compare these formulas with numerical solutions of the mixed boundary value problem and with Brownian simulations, allowing to explore geometrical parameter ranges. To conclude, the present analysis reveals that the mean arrival time, driven by diffusion in heterogeneous networks, is controlled by the targets and tubules sizes, as well as the size of the nodal compartments.

Design and Experimental Study of Ball-Head Cone-Tail Injection Mixer Based on Computational Fluid Dynamics

The uniform and accurate mixing of pesticides in water is a necessary prerequisite for plant protection, especially for enabling precise variable spraying, and is also an important method to achieve a precise reduction in pesticide spraying. In order to ensure the uniform mixing of pesticides and water and solve the problems of traditional injection mixers, such as the limited range in the mixing ratio and unadjustable proportion, an active injection liquid mixer is designed in this paper. The mixer can be matched with an online mixing and spraying device to achieve accuracy in mixing and spraying. In this paper, a computational fluid dynamics (CFD) method is used to optimize the structure of the mixer. Through comparative analysis, the optimal structure of the mixer was found. It has a spherical head and conical tail, the number of guide plates is seven, and the shape is semicircular. By calculating the volume fraction of pesticide distribution under different cross-sections, the coefficient of variation in the process of mixing is obtained. The analysis shows that the maximum coefficient of variation of the ball-head cone-tail active injection mixer was 2.88% (lower than the allowable 5%) with a mixing ratio ranging from 300:1 to 3000:1. At the same time, image analysis methods of high-definition photography and ultraviolet spectrophotometry were used to analyze the mixing effect of the mixer. The test results show that, when the pressure of the pesticide injection is 1 MPa, the distribution of the pesticide and water in the ball-head cone-tail injection mixer is more uniform under different mixing ratios, and it has a better spatio-temporal distribution uniformity with the concentration changing a little at different times and different spatial locations. The mixer can provide a theoretical reference and technical support for the subsequent realization of an accurate online variable spray.

The electro-mechanics of piezoelectric coating structure under frictional contacts

In papers of the piezoelectric coating/substrate system under smooth spherical contact (DOI: 10.1177/1081 286519 865773), conical contact (DOI: 10.1016/j.ijsolstr.2019.08.031), and cylinder flat head contact (DOI: 10.1007/s11012-019-01085-1), Green’s function method has been applied to solve the problem of piezoelectric friction contact. We deduced the analytical expression of piezoelectric coating structure, which is expressed by elementary functions. The numerical results highlight the best thickness to maintain a higher potential difference and a critical potential difference. This study has guiding significance for the future research and analysis of friction signals in intelligent manufacturing, such as piezoelectric tactile sensors.

Analysis of Arbitrary EM Field Exposure to a Multilayer Spherical Head Model Using Spherical Vector Wave Functions

A semi-analytical method is presented for the assessment of induced electromagnetic field inside a multilayer head model exposed to radiated field of an arbitrary source antenna. First the source antenna is simulated by a full-wave software in the absence of the head model to evaluate its radiating characteristics. Then, by sampling of the source radiated fields, its spherical vector wave function (SVWF) amplitudes are evaluated. The well-known translation addition theorem for spherical vector wave functions (SVWFs) is implemented to translate radiating field SVWFs to the local coordinates system of head model. Neglecting the reaction of model on source fields, using boundary conditions on the interfaces of adjacent layers, the unknown SVWF amplitudes of the fields inside each layer as well as those of the scattered field outside the head model are evaluated. Some numerical examples are presented for the verification of the proposed method. The acceptable consistency between the results obtained by the proposed method and full-wave simulations of the problem verifies the authenticity of the proposed method. In comparison to a full-wave numerical method, the proposed method provides an efficient repeatable simulation approach due to the independency of the source and head model analyses.