Volume-averaged modeling of multiphase solidification with equiaxed crystal sedimentation in a steel ingot

Macrosegregation is a critical factor that limits the mechanical properties of materials.The impact of equiaxed crystal sedimentation on macrosegregation has been extensively studied,as it plays a significant role in determining the distribution of alloying elements and impurities within a material.To improve macrosegregation in steel connecting shafts,a multiphase solidification model that couples melt flow,heat transfer,microstructure evolution,and solute transport was established based on the volume-averaged Eulerian-Eulerian approach.In this model,the effects of liquid phase,equiaxed crystals,columnar dendrites,and columnar-to-equiaxed transition(CET)during solidification and evolution of microstructure can be considered simultaneously.The sedimentation of equiaxed crystals contributes to negative macrosegregation,where regions between columnar dendrites and equiaxed crystals undergo significant A-type positive macrosegregation due to the CET.Additionally,noticeable positive macrosegregation occurs in the area of final solidification in the ingot.The improvement in macrosegregation is beneficial for enhancing the mechanical properties of connecting shafts.To mitigate the thermal convection of molten steel resulting from excessive superheating,reducing the superheating during casting without employing external fields or altering the design of the ingot mold is indeed an effective approach to control macrosegregation.

Dissecting characteristics and dynamics of differentially expressed proteins during multistage carcinogenesis of human colorectal cancer

AIM: To discover novel biomarkers for early diagnosis, prognosis or treatment of human colorectal cancer. METHODS: i TRAQ 2D LC-MS/MS analysis was used to identify differentially expressed proteins(DEPs) in the human colonic epithelial carcinogenic process using laser capture microdissection-purified colonic epithelial cells from normal colon, adenoma, carcinoma in situ and invasive carcinoma tissues. RESULTS: A total of 326 DEPs were identified, and four DEPs(DMBT1, S100A9, Galectin-10, and S100A8) with progressive alteration in the carcinogenic process were further validated by immunohistochemistry. The DEPs were involved in multiple biological processes including cell cycle, cell adhesion, translation, m RNA processing, and protein synthesis. Some of the DEPs involved in cellular process such as "translation" and "m RNA splicing" were progressively up-regulated, while some DEPs involved in other processes such as "metabolism" and "cell response to stress" was progressively downregulated. Other proteins with up- or down-regulation at certain stages of carcinogenesis may play various roles at different stages of the colorectal carcinogenic process. CONCLUSION: These findings give insights into our understanding of the mechanisms of colorectal carcinogenesis and provide clues for further investigation of carcinogenesis and identification of biomarkers.

Theoretical and experimental study of phase optimization of tapping mode atomic force microscope

Phase image in tapping-mode atomic force microscope(TM-AFM)results from various dissipations in a microcantilever system.The phases mainly reflect the tip-sample contact dissipations which allow the nanoscale characteristics to be distinguished from each other.In this work,two factors affecting the phase and phase contrast are analyzed.It is concluded from the theoretical and experimental results that the phases and phase contrasts in the TM-AFM are related to the excitation frequency and energy dissipation of the system.For a two-component blend,it is theoretically and experimentally proven that there exists an optimal excitation frequency for maximizing the phase contrast.Therefore,selecting the optimal excitation frequency can potentially improve the phase contrast results.In addition,only the key dissipation between the tip and sample is found to accurately reflect the sample properties.Meanwhile,the background dissipation can potentially reduce the contrasts of the phase images and even mask or distort the effective information in the phase images.In order to address the aforementioned issues,a self-excited method is adopted in this study in order to eliminate the effects of the background dissipation on the phases.Subsequently,the real phase information of the samples is successfully obtained.It is shown in this study that the eliminating of the background dissipation can effectively improve the phase contrast results and the real phase information of the samples is accurately reflected.These results are of great significance in optimizing the phases of two-component samples and multi-component samples in atomic force microscope.

Vibration analysis and topology optimization of the header of full-feeding rice combine harvester

The header frame of full-feeding rice combine harvester was characterized by severe vibration due to the excitation force generated by the movement of each working part.In order to solve the problem,the parametric model of the header frame was established,and the accuracy of the finite element model was verified by comparison of the results of the free modal analysis and free vibration modal test based on Eigensystem Realization Algorithm(ERA).Then the constrained modal frequencies were calculated and compared with the external excitation source frequencies,the results showed that the first and eighth order modal natural frequencies were coupled with the excitation frequencies of the threshing cylinder and the engine respectively,which were apt to resonate.To avoid resonance and achieve lightweight design,topology optimization,and finite element analysis were carried out.The optimization results showed that the strength and rigidity meet the requirements and the weight was 14.17%lower than before.The first and eighth order modal natural frequencies were far away from the excitation frequencies range of the threshing cylinder and engine,and the frequencies were far away from the range of each excitation frequency,which effectively avoided the occurrence of resonance.Field experiments showed that the peak value of the vibration acceleration in the three directions of the 8 measuring points of the optimized header frame was significantly reduced,which effectively reduced the vibration of the header frame during harvest.This study provides a method for obtaining the vibration characteristics of key components of agricultural machinery and provides a reference for the weight and vibration reduction of header frames of rice,wheat,rape,and other crop combine harvesters.

Multi-geomagnetic-component assisted localization algorithm for hypersonic vehicles

Owing to the lack of information about geomagnetic anomaly fields,conventional geomagnetic matching algorithms in near space are prone to divergence.Therefore,geomagnetic matching navigation algorithms for hypersonic vehicles are also prone to divergence or mismatch.To address this problem,we propose a multi-geomagnetic-component assisted localization(MCAL)algorithm to improve positioning accuracy using only the information of the main geomagnetic field.First,the main components of the geomagnetic field and a mathematical representation of the Earth’s geomagnetic field(World Magnetic Model 2015)are introduced.The mathematical relationships between the geomagnetic components are given,and the source of geomagnetic matching error is explained.We then propose the MCAL algorithm.The algorithm uses the intersections of the isopleths of the geomagnetic components and a decision method to estimate the real position of a carrier with high positioning accuracy.Finally,inertial/geomagnetic integrated navigation is simulated for hypersonic boost-glide vehicles.The simulation results demonstrate that the proposed algorithm can provide higher positioning accuracy than conventional geomagnetic matching algorithms.When the random error range is±30 nT,the average absolute latitude error and longitude error of the MCAL algorithm are 151 m and 511 m lower,respectively,than those of the Sandia inertial magnetic aided navigation(SIMAN)algorithm.

Analysis of a mutualism model with time-related coefficients in a stochastic environment

In this paper,a mutualism model with stochastic perturbations is considered and some of its coefficients are related to time.Under some assumptions,we make efforts to prove the existence and uniqueness of a positive solution,and the asymptotic behavior to the problem is discussed.Furthermore,we also prove the properties of stochtistic boundedness,uniform continuity and stochastic permanence of this system.At last,some numerical simulations are introduced to illustrate our main results.