Watt Linkage–Based Legged Deployable Landing Mechanism for Reusable Launch Vehicle: Principle, Prototype Design, and Experimental Validation

The reusable launch vehicle (RLV) presents a new avenue for reducing cost of space transportation. The landing mechanism, which provides landing support and impact absorption, is a vital component of the RLV at final stage of recovery. This study proposes a novel legged deployable landing mechanism (LDLM) for RLV. The Watt-II six-bar mechanism is adopted to obtain the preferred configuration via the application of the linkage variation approach. To endow the proposed LDLM with advantages of large landing support region, lightweight, and reasonable linkage internal forces, a multi-objective optimization paradigm is developed. Furthermore, the optimal scale parameters for guiding the LDLM prototype design is obtained numerically using the non-dominated sorting genetic algorithm-II (NSGA-II) evolutionary algorithm. A fully-functional scaled RLV prototype is developed by integrating the gravity-governed deploying scheme to facilitate unfolding action to avoid full-range actuation, a dual-backup locking mechanism to enhance reliability of structure stiffening as fully deployed, and a shock absorber (SA) with multistage honeycomb to offer reliable shock absorbing performance. The experimental results demonstrate that the proposed LDLM is capable of providing rapid and smooth deployment (duration less than 1.5 s) with mild posture disturbance to the cabin (yaw and pitch fluctuations less than 6°). In addition, it provides satisfactory impact attenuation (acceleration peak less than 10g (g is the gravitational acceleration)) in the 0.2 m freefall test, which makes the proposed LDLM a potential alternative for developing future RLV archetype.

疫情背景下大规模开放在线课程(慕课)的创新教学——以“名侦探柯南与化学探秘”课程为例

“名侦探柯南与化学探秘”是中南大学开设的大规模开放在线课程(慕课,MOOC)。新冠疫情期间,课程团队基于现有的慕课视频教学资源,结合课程特色,推出了一系列以学生为中心的创新教学办法,同时,发挥慕课、QQ群、问卷星等各个网络信息平台的优势,打造互联网+的精彩课堂,提升学生的学习“获得感”,加强教师的教学引导作用,促进学生的主动学习。

Physicochemical Characteristics of Calamondin(Citrus microcarpa)from Hainan

Some physicochemical characteristics of calamondin(Citrus microcarpa)from Hainan were determined in this study.The mean length,width,and thickness of calamondin were(2.763±0.262),(2.721±0.189),and(2.684±0.201)cm,respectively.The average values for geometric mean diameter,sphericity,fruit shape index,mass,surface area,volume,true density,bulk density and porosity were(2.721±0.196)cm,(98.79±5.149)%,(101.64±7.609)%,(11.18±2.149)g,(23.36±3.362)cm2,(11.16±2.115)cm3,(1.00±0.060)g/cm3,0.44 g/cm3,and(56.40±0.027)%,respectively.The mean edible part,juice rate,and soluble solids were(85.77±3.53),(48.36±4.20),and(7.86±0.09)%,respectively.The total flavonoids,pectin,limonin,reducing sugar and volatile oil contents of the peel were 1.00,7.14,0.51,5.98,and 4.25%,respectively.The total flavonoids,pectin,limonin and reducing sugar contents of the pulp were 0.02,5.04,0.03 and 4.56%,respectively.The total flavonoids,total acid,reducing sugar and vitamin E contents of the juice were 0.11,6.74,0.37%,and 1.68 mg/kg,respectively,while the content of vitamins A,B1,B2,B3,B6,and D in the juice was very low.The seeds had limonin,reducing sugar and oil contents of 0.46,1.39,and 30.46%,respectively.The vitamin B2,B3,B6 and E contents of the fruit residue were 44.83,19.31,17.55,and 15.72 mg/kg,respectively.The amino acid profile of the residue included aspartic acid,glutamate,cystine,serine,glycine,histidine,arginine,threonine,alanine,proline,tyrosine,valine,methionine,isoleucine,leucine,phenylalanine and lysine,with respective contents of 4.42,1.81,2.10,0.78,0.59,0.20,0.72,0.160.67,3.650.50,0.67,0.59,1.00,0.76,0.57 and 0.91 g/kg.

TaCHP encoding C1-domain protein stably enhances wheat yield in saline-alkaline fields

Salt and saline-alkaline stress seriously threaten crop production and food security worldwide(Yang and Guo,2018).Identifying genes that confer tolerance to these conditions without yield penalty would help mitigate this problem through molecular breeding(Liang et al.,2023;Sahu and Liu,2023).Although numerous stress-tolerance genes have been identified,their application potential in molecular breeding has rarely been confirmed through multi-year and multi-site field trials.

Li-Mg-Si bioceramics provide a dynamic immuno-modulatory and repair-supportive microenvironment for peripheral nerve regeneration

Biomaterials can modulate the local immune and repair-supportive microenvironments to promote peripheral nerve regeneration. Inorganic bioceramics have been widely used for regulating tissue regeneration and local immune response. However, little is known on whether inorganic bioceramics can have potential for enhancing peripheral nerve regeneration and what are the mechanisms underlying their actions. Here, the inorganic lithium-magnesium-silicon (Li-Mg-Si, LMS) bioceramics containing scaffolds are fabricated and characterized. The LMS-containing scaffolds had no cytotoxicity against rat Schwann cells (SCs), but promoted their migration and differentiation towards a remyelination state by up-regulating the expression of neurotrophic factors in a β-catenin-dependent manner. Furthermore, using single cell-sequencing, we showed that LMS-containing scaffolds promoted macrophage polarization towards the pro-regenerative M2-like cells, which subsequently facilitated the migration and differentiation of SCs. Moreover, implantation with the LMS-containing nerve guidance conduits (NGCs) increased the frequency of M2-like macrophage infiltration and enhanced nerve regeneration and motor functional recovery in a rat model of sciatic nerve injury. Collectively, these findings indicated that the inorganic LMS bioceramics offered a potential strategy for enhancing peripheral nerve regeneration by modulating the immune microenvironment and promoting SCs remyelination.

CT引导下经皮穿刺置管硬化治疗卵巢巧克力囊肿的临床疗效分析

目的探讨CT引导下经皮穿刺置管硬化治疗卵巢巧克力囊肿的临床疗效与安全性。方法回顾性分析51例卵巢巧克力囊肿患者资料,其中8例经前腹壁穿刺置管,43例经臀部穿刺置管,随后经引流管注入聚桂醇泡沫硬化剂硬化治疗巧克力囊肿,分析治疗前后巧克力囊肿最大径、糖类抗原125(CA125)、抗缪勒管激素(AMH)变化情况及术后并发症情况。结果51例患者的整体有效率为98.0%。患者术后3、6个月的囊肿最大径均较术前显著性缩小(P值均<0.001);CA125水平均较术前显著性降低(P值均<0.001)。患者术后6个月与术前、术后3个月的AMH水平差异均无统计学意义(P=0.421,0.182)。无相关严重手术并发症出现。结论CT引导下经皮穿刺置管硬化治疗卵巢巧克力囊肿安全、有效,可作为较大(直径≥4 cm)卵巢巧克力囊肿的替代治疗方案。

A comparative study of two porous sponge scaffolds prepared by collagen derived from porcine skin and fish scales as burn wound dressings in a rabbit model

Collagen is widely used in biomedical applications due to its outstanding properties.In this study,highly porous sponge scaffolds were developed by using porcine skin-derived collagen(PSC)and fish scale-derived collagen(FSC),respectively.The morphology and composition of these PSC and FSC scaffolds were compared.The water uptake ratio of FSC scaffolds reached 47.8,which is 1.7 times of PSC scaffolds.The water vapour transmission rates(WVTR)of PSC and FSC scaffolds were 952.6655.5 and 1090.9677.1 g/m2/day,which could produce a moist healing environment for wounds.Both scaffolds show non-toxicity to L929 fibroblast cells.The burn wound healing efficiency of these two scaffolds was examined in vivo using rabbits.No scars around the wounds were observed after applying PSC and SFC scaffolds.Histopathological studies reveal that the wound treated with PSC and FSC scaffolds showed much better wound recovery than gauze and vaseline gauze groups.It was suggested that FSC scaffolds have great potential as same as PSC to be used as burn wound dressing materials.

A user-friendly yield criterion for metals exhibiting tension-compression asymmetry

The aim of this paper is to model the yielding asymmetry of pressure-insensitive metals,including but not limited to Ni3 Al alloys.The main focuses are put on the flexibility and manipulative convenience.The parameters of theory are kept to a minimum and can be determined by as few tests as possible.These requirements are fulfilled by constructing a yield function using the second and third-invariants of a linearly transformed stress tensor.The proposed yield criterion has a simple mathematical form and has only seven parameters when used in three-dimensional stresses.Compared with existing theories,the new yield criterion has much fewer parameters,which makes it very convenient for practical applications.The coefficients of the criterion are identified by an error minimization procedure.Applications to a Ni3 Al based intermetallic alloy as well as a Cu-Al-Be shape memory alloy and comparison to other criteria show that the proposed criterion has nearly the same predictive ability and flexibility with other criteria.The proposed yield criterion can estimate the coefficients by using less data,which is a big advantage compared with other similar theories,especially when there is a limited number of experimental data.

Multiaxial fatigue life prediction of composite materials

In order to analyze the stress and strain fields in the fibers and the matrix in composite materials,a fiber-scale unit cell model is established and the corresponding periodical boundary conditions are introduced.Assuming matrix cracking as the failure mode of composite materials,an energy-based fatigue damage parameter and a multiaxial fatigue life prediction method are established.This method only needs the material properties of the fibers and the matrix to be known.After the relationship between the fatigue damage parameter and the fatigue life under any arbitrary test condition is established,the multiaxial fatigue life under any other load condition can be predicted.The proposed method has been verified using two different kinds of load forms.One is unidirectional laminates subjected to cyclic off-axis loading,and the other is filament wound composites subjected to cyclic tension-torsion loading.The fatigue lives predicted using the proposed model are in good agreements with the experimental results for both kinds of load forms.

Fertilizer sphericity measuring device based on equatorial and meridian circles

Fertilizer sphericity is an important assessment index of appearance quality that affects the fertilization effect.A fertilizer sphericity measuring device based on machine vision was designed aimed at low precision and heavy workload of manual fertilizer measurement,and high cost and complicated operation of high precision measuring instruments.A fertilizer sphericity measuring method based on equatorial and meridian circles was proposed.The device works in an intermittent static acquisition mode to simultaneously obtain both top and side images of a single fertilizer.First,the method performs gamma correction on the top and side images of the single fertilizer,and uses the Canny operator to detect the edge of the image to obtain the equatorial and meridian circular contour images of the fertilizer.Second,based on the fertilizer equatorial and meridian circular contour,the Least Squares Circle method was used to evaluate the roundness of the single fertilizer.Finally,the average roundness value of the equatorial and meridian circles was used as the final sphericity value of the fertilizer.The sphericity measurement test was carried out on the same batch of compound,organic and biological fertilizers by using the sphericity measuring device.The fertilizer sphericity data were obtained by different measurement and evaluation methods.The variation coefficient was used to evaluate the difference in fertilizer sphericity measured by different sphericity measurement and evaluation methods.The results show that among the different measurement and evaluation methods,the coefficient of variation of fertilizer sphericity measured by the equatorial and meridian circle method was the smallest,and the coefficient of variation of sphericity measured by the Least Squares Circle method was the smallest and accurate.This study shows that the sphericity measuring device and method can accurately measure the fertilizer sphericity,and has a significant potential to facilitate fertilizer production and quality inspection.