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In this study, a three-dimensional model of the planetary gear train with straight cylindrical gears is established, and a virtual prototype model is constructed by using dynamics simulation software. Through the dynamics analysis, the accuracy and feasibility of the virtual prototype simulation model are verified. The study shows that the supporting stiffness of each component in the transmission system has a significant effect on the uniform load characteristics, and the change of the supporting stiffness of the planetary gear has the most sensitive effect on the uniform load characteristics. The uniform load characteristics of the transmission system is not sensitive to the change of the flexible supporting stiffness of the sun gear, but it is more sensitive to the change of the flexible supporting stiffness of the planetary gear, and the uniform load coefficient has obvious changes. The effect of gear tooth meshing stiffness changes on the uniform load characteristics of the transmission system is independent, simultaneously reducing the internal and external meshing stiffness has a more obvious uniform load effect than reducing the meshing stiffness alone.

The distribution of the load on the tooth surface greatly affects the performance of the power split of the planetary transmission system. This study mainly studies the load sharing characteristics of the planetary gear transmission system and summarizes the current research status of this problem. The basic problems related to load sharing are expounded. Then, the analysis methods and calculation models of load sharing characteristics in planetary transmission are compared and analyzed. The methods and mechanisms of load-sharing which are commonly used at present are reviewed. It can be found that error is the root cause of uneven load distribution, and the most effective way to improve the uniform load is to reduce the sensitivity of the system to error. At present, dynamic analysis and the influence of nonlinear factors are the focus of research on uniform load problems. Floating parts and flexible parts are still commonly used uniform load methods.

In order to analyze the lubrication characteristics of the planetary gear transmission of shield main drive reducers, a simulation model of splash lubrication of the single-stage planetary gear train is established using the moving particle semi-implicit (MPS) method. By comparing the distribution of lubricating oil particles, velocity field, pressure field, the number of lubricating oil particles in the meshing area of gear teeth and the churning resistance moment produced by each rotating part during the planetary gear train movement under different working conditions, the influence of input speed, initial oil level height and oil temperature on the system lubrication effect and churning loss power are studied. The results show that the oil particle velocity and pressure increase with the increase of the input speed and oil level, and the low speed and oil level height will lead to the uneven distribution of oil particles in the reducer. The number of particles in the meshing zone between planetary gears, sun gears and inner gear rings decreases with the increase of input speed and oil temperature, and decreases with the decrease of oil level height. The meshing area of sun gears is the risk area of poor lubrication. The power loss of the system is most significantly affected by the input speed, and increases exponentially with the increase of the speed, while the influence of oil level height and oil temperature is relatively small. In each working condition, the churning loss power generated by the three planetary gears takes the largest proportion in the total churning loss power.

The tooth surface friction has an important impact on the tooth surface contact stress and the tooth surface contact fatigue life. In the estimation of the contact fatigue life of the tooth surface, the influence of the friction force of the tooth surface is often ignored, which is not conducive to the accurate prediction of the contact fatigue life of the tooth surface. In order to accurately predict the contact fatigue life of the tooth surface, the R-S-N curves are fitted based on the three-parameter Weibull distribution and the nominal stress method according to the tooth surface contact fatigue test data of 18CrNiMo7-6 gear material. By calculating the contact stress on the tooth surface, the time-varying friction factor is introduced, and the influence of the time-varying friction factor on the contact fatigue life of the tooth surface is analyzed. Finally, the tooth surface contact fatigue test is used to verify the validity. The results show that the contact fatigue limit of tooth surface estimated by the traditional nominal stress method is large due to the influence of the time-varying friction factor, and the influence of the friction factor on contact fatigue life of tooth surfaces decreases with the increase of stress.

Aiming at the problem that the rack and pinion for the Three Gorges ship lift may face fatigue failure during its whole life cycle, the load spectrum including the stressed tooth surface and the number of load cycles is constructed in this study based on the rack and pinion load calculated by the torques of the driving motors and the synchronous shafts. Combined with the S-N curve of racks and Miner's linear cumulative damage criterion, the damage degree and residual fatigue life of racks within 35 years of design life are calculated. In addition, the cumulative iteration method is used to calculate the contact and bending safety factors of the rack, which realizes the comparison between the actual load and the design load of the rack and the operation safety performance verification. The results show that, the upper tooth surface of the rack has more meshing times, and its probability is 73.03%. During the design life, the total contact fatigue damage degree of the upper tooth surface of the rack is 1.65×10-12, and the total number of cycles according to the load spectrum is 1.87×1017. The total damage degree of the bending fatigue of the upper tooth surface of the rack is 8.15×10-14; the total number of cycles according to the load spectrum is 3.78×1018; the rack has a long residual fatigue life after 35 years of design life. The contact safety factor of the racks SH=2.958, bending safety factor SF=8.106, are both greater than the selected minimum safety factor under high reliability and the calculated safety factor under design load, and the safety margin of ship lift racks is sufficient. The research content of this study has enriched the relevant research in the field of fatigue life of super-large modulus racks and pinions, and provides theoretical basis and data support for the operation and maintenance of the Three Gorges ship lift.

The rack and pinion of the three gorges ship lift is a low speed and heavy load open gear transmission with hard tooth surface. Once the lubrication is poor, it is easy to cause damage such as tooth surface scuffing, which will affect the operation safety and reliability of the ship lift. This study is based on the actual operation data of the three gorges ship lift, and the lubrication of racks and pinions under various typical service conditions is systematically analyzed using the oil film thickness criterion. The relationship between the false water depth and the film thickness ratio in the ship compartment is deduced and the film thickness ratio of the lubrication state of the most dangerous meshing point under typical false water depth is calculated when the ship compartment is under constant speed. The worst lubrication condition of the rack and pinion is determined when the ship compartment is ascending and descending with variable speeds, and the relationship between the water depth in the ship compartment and the lubrication condition under variable speed typical operating conditions is analyzed. The position where the scuffing damage is more likely to occur is further determined. The results show that, when the ship lift is running at a constant speed, the lubrication state of the rack and pinion is the best under the optimum water depth in the ship compartment, and the film thickness ratio of the deviation from the optimal water level decreases with the power function λ∝±Δh-0.13 of the false water depth. When the rack and pinion is at the most dangerous meshing point, the root of the pinion and the top of the rack are in contact, and the lubrication condition between tooth surfaces is worse under large false water depth. When the ship lift moves at variable speeds, the working condition with poor lubrication condition is the upward acceleration and downward deceleration when the water depth of the ship chamber is 3.6 m. Due to the high contact frequency of the upper tooth surface on the rack and poor lubrication state, the risk of scuffing damage is higher.

The mesh stiffness calculation and load distribution among teeth of helical gear are the basis of its dynamics analysis and strength calculation. Aiming at the accuracy of approximate replacement method of mesh stiffness of helical gear, the quasi-static elastic model of helical gear was established based on the change rule of contact length, quasi-parabolic model of single tooth mesh stiffness per unit of contact length and ISO6336-1 standard, and a comparative study was conducted with the approximate replacement method based on quasi-static rigid model and ISO6336-1 standard. The results showed that the results calculated by quasi-static elastic model were in good agreement with the ISO standard results when the ratio of the minimum stiffness to the maximum stiffness of single tooth αk is 0.55, and the errors of the quasi-static rigid model and ISO standard were large. Based on the quasi-static elastic model, the effects of geometric parameters and broken teeth failure on meshing stiffness and load distribution coefficient of helical gear were analyzed and discussed, which provided a basis for the study of fault dynamics.

In recent years, as a new type of anti-corrosion material, polyurea coatings have been widely applied to the protection of internal and external walls for pipes. In order to overcome the shortage of traditional ultrasonic testing with low efficiency, the imagine of detecting some cracks in polyurea anti-corrosive pipes was proposed, which based on ultrasonic guided wave detection technology, and it would be studied by numerical simulation. By analyzing the analytical model in the polyurea anti-corrosion pipes, established the three-dimensional cylindrical model of the viscoelastic-elastic composite material by finite element software Abaqus, and simulated the propagation state in which the L（0,2） modal guided wave with the different excited frequencies. Combined with the study of its dispersion and attenuation for selecting optimize frequency, and the analysis of defect detection for the model were accomplished the simulated. The results of research show that the results of numerical simulation are basically consistent with experimental verification, which show that it is effective to use the ultrasonic guided waves for detecting defects of polyurea anti-corrosion pipes and realizing the location of defects.

Objective To evaluate the performance and application efficacies of a ultra-fast thermocycling fluorescence quantitative PCR system for detection of influenza A virus (IAV) and influenza B virus (IBV). Methods Our constructed plasmids of IAV and IBV was employed as standards, and then the concentration was diluted gradiently. After each concentration was repeatedly detected with the ultra-fast thermocycling fluorescence quantitative PCR system for 20 times, a standard curve was drawn to verify the minimum detection limit and liner range of the system and correlative coefficient. A total of 278 clinical samples (88 IAV-positive, 87 IBV-positive, and 103 negative samples) were collected from the Biosafety Section of Center for Disease Control and Prevention, Southern Theater Command. They were isolated during 2016 and 2018, from the patients of 164 males (59%) and 114 females (41%), and at an average age of 24 years. The repeatability of the system was analyzed through the system repeatedly detect the identified 88 IAV-positive and 87 IBV-positive samples. The results of the system and traditional real-time q-PCR (RT q-PCR) were compared to evaluate the efficacy of the system. Results The results of ultra-fast thermocycling fluorescence quantitative PCR system showed that the minimum detection limit for detection of IAV and IBV plasmids was 1×100 copies/μL, and the liner range ranged from 1×100 to 1×105 copies/μL. In detection of clinical samples, this system obtained a sensitivity of 92.57%, a specificity of 100%, and negative and positive predictive values of 88.79% and 100%, respectively, with a coincidence rate of 95.32% when compared with the results of traditional RT q-PCR. There were no cross-reactions between IAV and IBV or among them with other pathogens. No interference was observed in the detection results of influenza in presence of 30 g/dL hemoglobin, 3.2 g/dL triglyceride and 100 μg/mL ceftriaxone sodium. Conclusion The system shows good detection performance in detection of clinical samples, with advantages of small in size, light in weight, short in time, and no procedure of nucleic acid extraction, and is suitable for point-of-care testing (POCT).

The stomach's ability to store, mix, propel, and empty its content requires highly coordinated motor functions. However, current diagnostic tools cannot simultaneously assess these motor processes. This study aimed to use magnetic resonance imaging (MRI) to map multifaceted gastric motor functions, including accommodation, tonic and peristaltic contractions, and emptying, through a single noninvasive experiment for both humans and rats. Ten humans and 10 Sprague-Dawley rats consumed MRI-visible semisolid meals and underwent MRI scans. We used a surface model to analyze MRI data, capturing the deformation of the stomach wall on ingestion or during digestion. We inferred muscle activity, mapped motor processes, parcellated the stomach into functional regions, and revealed cross-species distinctions. In humans, both the fundus and antrum distended postmeal, followed by sustained tonic contractions to regulate intragastric pressure. Peristaltic contractions initiated from the distal fundus, including three concurrent wavefronts oscillating at 3.3 cycles/min and traveling at 1.7 to 2.9 mm/s. These motor functions facilitated linear gastric emptying with a 61-min half-time. In contrast, rats exhibited peristalsis from the midcorpus, showing two wavefronts oscillating at 5.0 cycles/min and traveling at 0.4 to 0.9 mm/s. For both species, motility features allowed functional parcellation of the stomach along a midcorpus division. This study maps region- and species-specific gastric motor functions. We demonstrate the value of MRI with surface modeling in understanding gastric physiology and its potential to become a new standard for clinical and preclinical investigations of gastric disorders at both individual and group levels. NEW & NOTEWORTHY: A novel MRI technique can visualize how the stomach accommodates, mixes, and propels food for digestion in humans and animals alike. Digital models of gastric MRI reveal the functional maps, organization, and distinction of the stomach across individuals and species. This technique holds the unique potential to advance basic and clinical studies of functional gastric disorders. [ABSTRACT FROM AUTHOR]

Humans actively observe the visual surroundings by focusing on salient objects and ignoring trivial details. However, computer vision models based on convolutional neural networks (CNN) often analyze visual input all at once through a single feedforward pass. In this study, we designed a dual-stream vision model inspired by the human brain. This model features retina-like input layers and includes two streams: one determining the next point of focus (the fixation), while the other interprets the visuals surrounding the fixation. Trained on image recognition, this model examines an image through a sequence of fixations, each time focusing on different parts, thereby progressively building a representation of the image. We evaluated this model against various benchmarks in terms of object recognition, gaze behavior, and adversarial robustness. Our findings suggest that the model can attend and gaze in ways similar to humans without being explicitly trained to mimic human attention and that the model can enhance robustness against adversarial attacks due to its retinal sampling and recurrent processing. In particular, the model can correct its perceptual errors by taking more glances, setting itself apart from all feedforward-only models. In conclusion, the interactions of retinal sampling, eye movement, and recurrent dynamics are important to human-like visual exploration and inference. [ABSTRACT FROM AUTHOR]

Objective: Consuming less water (systemic dehydration) has long been thought to dehydrate the vocal folds. An "in vivo," repeated measures study tested the assumption that systemic dehydration causes vocal fold dehydration. Proton density (PD)-weighted magnetic resonance imaging (MRI) of rat vocal folds was employed to investigate (a) whether varying magnitudes of systemic dehydration would dehydrate the vocal folds and (b) whether systemic rehydration would rehydrate the vocal folds. Method: Male (n = 25) and female (n = 14) Sprague Dawley rats were imaged with 7T MRI, and normalized PD-weighted signal intensities were obtained at predehydration, following dehydration, and following rehydration. Animals were dehydrated to 1 of 3 levels by water withholding to induce body weight loss: mild (< 6% body weight loss), moderate (6%-10% body weight loss), and marked (> 10% body weight loss). Results: There was a significant decrease in vocal fold signal intensities after moderate and marked dehydration (p < 0.0167). Rehydration increased the normalized signal intensity to predehydration levels for only the moderate group (p < 0.0167). Normalized signal intensity did not significantly change after mild dehydration or when the mildly dehydrated animals were rehydrated. Additionally, there were no significant differences in PD-weighted MRI normalized signal intensity between male and female rats (p > 0.05). Conclusion: This study provides evidence supporting clinical voice recommendations for rehydration by increasing water intake after an acute, moderate systemic dehydration event. However, acute systemic dehydration of mild levels did not dehydrate the vocal folds as observed by PD-weighted MRI. Future programmatic research will focus on chronic, recurring systemic dehydration.

In order to study the influence of the three-dimensional appearance of the gear pitting pits on the stress concentration of the tooth surface, the effect of pitting pits with different shapes on stress concentration factor of gear was analyzed by finite element method. By changing the length, width and depth of ellipsoid pitting pits, the influence of different length-width ratio and depth-width ratio on stress concentration factor was analyzed, and the approximate calculation model of stress concentration factor of ellipsoid pitting pits was established. According to the contact fatigue test data of a gear, the calculation model established by this method was analyzed and verified, and the influence of the change of pitting pit size on the stress concentration factor of the gear was further analyzed and discussed. The results show that: the stress concentration of ellipsoid pits on the tooth surface was the most obvious, followed by conical pits, pentagonal pits and triangular pits when the basic size of pitting pits was the same. The stress concentration factor increases with the increase of depth-width ratio and length-width ratio of ellipsoidal pit.

Objective To establish a simple and rapid paper-based extraction method for human papilloma virus (HPV) DNA and to evaluate the method. Methods The plasmid containing HPV type 16 gene fragment was employed as the test subjects, and then 6 different paper materials were compared and selected by ultraviolet spectrophotometry and real-time fluorescence quantitative PCR (qPCR). Then, according to the efficiency of nucleic acid extraction and the optimal binding area, a convenient paper strip was designed. Finally, the designed paper strip was applied to extract HPV DNA from 18 clinical cervical exfoliated cell samples (13 positives and 5 negatives), with its performance being evaluated after comparing with the conventional boiling method. Results The qualitative filter paper with a nucleic acid binding zone of 2 mm×10 mm could successfully extract HPV DNA from clinical cervical exfoliated cells. When this test strip was used for DNA extraction, all the 13 high-risk HPV positives were successfully detected out of the 18 clinical samples, which was consistent with the results of the conventional boiling method. In addition, the extraction time of the test strip was less than 1 min for each sample, with a detection limit of 8×102 copies/mL and relative standard deviation of 1.15%. Conclusion Our paper-based rapid extraction for HPV DNA does not require pipetting, heating and centrifugation, and the eluent can be directly used as the PCR template for amplification, which greatly simplifies the extraction process of HPV DNA from clinical cervical exfoliated cell samples.