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Disuse osteoporosis is a metabolic bone disease resulting from skeletal unloading (e.g., during extended bed rest, limb immobilization, and spaceflight), and the slow and insufficient bone recovery during reambulation remains an unresolved medical challenge. Here, we demonstrated that loading-induced increase in bone architecture/strength was suppressed in skeletons previously exposed to unloading. This reduction in bone mechanosensitivity was directly associated with attenuated osteocytic [Ca.sup.2+] oscillatory dynamics. The unloading-induced compromised osteocytic [Ca.sup.2+] response to reloading resulted from the HIF-1[alpha]/PDK1 axis-mediated increase in glycolysis, and a subsequent reduction in ATP synthesis. HIF-1[alpha] also transcriptionally induced substantial glutaminase 2 expression and thereby glutamine addiction in osteocytes. Inhibition of glycolysis by blockade of PDK1 or glutamine supplementation restored the mechanosensitivity in those skeletons with previous unloading by fueling the tricarboxylic acid cycle and rescuing subsequent [Ca.sup.2+] oscillations in osteocytes. Thus, we provide mechanistic insight into disuse-induced deterioration of bone mechanosensitivity and a promising therapeutic approach to accelerate bone recovery after long-duration disuse., Introduction Bone is a highly mechanosensitive and adaptive system, the internal structure of which can be remodeled to accommodate the prevailing mechanical environment. Load-bearing physical activity is essential for promoting [...]

In order to meet the requirements of autonomous, accuracy and reliability of vehicle navigation system for weapon launch vehicles, a fault-tolerant integrated navigation scheme of RSINS/odometer is designed. Based on the analysis of the characteristics of different odometer measurement information, the RSINS/odometer integrated navigation system model based on mileage increment matching mode is established. According to the results of the observability analysis of the RSINS/odometer integrated navigation system model, an observable RSINS/odometer integrated navigation system model is established. A fault-tolerant integrated navigation information fusion scheme of RSINS/odometer based on sequential Kalman filter is designed to solve the problem that odometer measurement information may not be available during vehicle driving. Finally, the simulation results show that the RSINS/odometer fault-tolerant integrated navigation scheme can ensure the navigation accuracy and reliability of the integrated system.

In order to shorten the calibration time and simplify the calibration process, the missile and launch box are jointly involved in the calibration, so as to complete the calibration of the inertial group on the missile without opening box. However, due to the large volume and mass of the missile, the rotation of the turntable is limited. Based on this, an integrated calibration method of the inertial group on missile without opening box is proposed. According to the limitation of turntable rotation and considering the characteristics of accelerometer and fiber optic gyroscope (FOG) calibration method, a rotation path including six static positions is designed.Through the continuous rotation of the turntable, the accelerometer and FOG can be calibrated together. Due to the short rotation time of turntable, the accumulated error of FOG constant drift is small, so it is difficult to estimate. Therefore, the double position drift method is used to calibrate the constant drift. The simulation results show that the proposed calibration method can achieve the same calibration effect as the traditional calibration method, and has high calibration accuracy. After compensating the constant drift with the calibration results, the calibration accuracy is improved.

Global navigation satellite system (GNSS) has the characteristics of strong autonomy, high real-time, high positioning accuracy and low cost, and it has been widely used by ground, low earth orbit (LEO) and medium earth orbit (MEO) users. However, in the high orbit environment, the availability of GNSS signal is greatly limited due to the earth’s blocking and the increase of signal’s transmission distance, which restricts the application and development of GNSS in the autonomous navigation of high orbit satellites. Aiming at the unknown problem of GNSS signal’s availability in high orbit, the availability of GNSS signal in high orbit is systematically analyzed from the aspects of GNSS satellite’s visibility, Doppler frequency shift and its rate of change, geometric dilution of precision, etc. Based on the characteristics of GNSS link propagation, the spatial coverage characteristics and strength distribution characteristics of GNSS signal in high orbit are analyzed, and then the visibility of GNSS satellites in high orbit is evaluated. The effects of Doppler frequency shift and its rate of change on the performance of signal acquisition and tracking are explored by using the acquisition model and the phase-locked loop model, and geometric dilution of precision of different GNSS combinations and their changes are quantitatively calculated.

To efficiently establish a finite element model that is highly compatible with the intricate microstructure of foam materials, this study carries out simulation and experimental investigations into open cell foams and explores their compression behavior assuming isotropy. Using an in-house algorithm, we optimize the traditional power diagram model, which is widely used in foam finite element simulation. Specifically, a parameterized geometric foam model is developed based on the centroidal and capacity constrained power diagram (CCCPD), which accurately reflects the internal meso-structure of foam materials. The optimized foam model can restore the typical deformation process of foams under compressive load, thus addressing the limitations of existing foam models. The accuracy of the optimized model is validated by conducting uniaxial Quasi-static compression experiments on foamed thermoplastic polyurethane (TPU) material and comparing the experimental results of the 3D printing model with the simulation results of the optimized model. The improved foam model serves as a basis for future research on open cell foam materials. [ABSTRACT FROM AUTHOR]

Silicon carbide fiber reinforced silicon carbide matrix (SiCf/SiC) composite is the key cladding material of nuclear fuel, which determines the safety and reliability of nuclear fuel storage and transportation. The replacement of its storage and transportation scenario needs to be completed by the manipulator, but the application of SiCf/SiC wear, fracture, and nuclear leakage in the snatching process of brittle-flexible-rigid contact in the irradiation environment has been seriously restricted due to unclear understanding of the damage mechanism. Therefore, the effects of irradiation dose and clamping load on the friction characteristics of the contact interface between SiCf/SiC clad tube are studied in this paper, and the effects of irradiation parameters and clamping force on the static friction coefficient of the contact interface between the clad tube and flexible nitrile are obtained. Based on the Greenwood-Williamson tribological model, a numerical model of the shape and structure of the contact micro-convex at the micro-scale of the clamping interface is constructed by introducing the multi-surface integral, and finally verified by experiments. The research results show that there is a unique "Irradiation suppression zone" under the clamping condition of SiCf/SiC cladding tube under the nuclear irradiation environment, and the growth of static friction coefficient slows down until stagnates after irradiation reaches a certain extent (600 kGy), and there will be a decline when the irradiation dose continues to increase, among which the clamping force of 15.2 N within the irradiation interval of 1,000 kGy can meet the safety of nuclear environment operation. The results of this paper can provide an important theoretical basis and application guidance for the safe operation of SiCf/SiC cladding tubes in the storage and transportation clamping process. [ABSTRACT FROM AUTHOR]