虚拟网络映射问题研究及其进展

随着互联网的快速发展,现有的互联网架构已经难以满足互联网新型应用的发展,在一定程度上呈现出僵化现象.网络虚拟化被认为是解决网络僵化问题的重要途径,其中的虚拟网络映射问题研究如何将具有虚拟节点和虚拟链路约束的虚拟网络映射到基础设施网络中.首先给出了虚拟网络映射问题的形式化定义,分析了虚拟网络映射问题面临的挑战性和求解目标;其次,对各种虚拟网络映射问题的求解方法加以分类,在分类的基础上,介绍了各种典型的求解方法并进行了对比;最后总结了各种虚拟网络映射问题求解方法,并指出了未来的研究趋势.     

Long bone human anlage longitudinal and circumferential growth in the fetal period and comparison with the growth plate cartilage of the postnatal age

The patterns of longitudinal and peripheral growth were analyzed in human autopod cartilage anlagen (fetal developmental stage 20th–22nd week) through morphometric assessment of chondrocyte parameter size, shape, alignment and orientation between peripheral and central sectors of the anlage transition zone defined by primary ossification center and the epiphyseal basis. The aim was to correlate the chondrocyte dynamics with the longitudinal and peripheral growth. A further comparison was carried out between the corresponding sectors of the postnatal (3–5 months old) growth plate cartilage documenting: (1) the different chondrocyte framework and the new peripheral mechanism; (2) the opposite direction of fetal periosteal ossification versus the Lacroix bone bark. Measurement of multiple parameters (% lac area, % total matrix area, total lac density and mean single lac area), which characterize the cartilage Anlage growth, suggested the following correlations with chondrocyte duplication rate: (a) slow duplication rate ≈ coupled, intralacunar chondrocytes (in central epiphysis); (b) repeated/frequent cell duplications ≈ clusters (in the basal epiphyseal layer); (c) clusters of chondrocytes before becoming hypertrophic were stacked up on the top of each other (both in the Anlage transition zone or in the columns of metaphyseal growth plate); (d) enhanced osteoclastic resorption of the Lacroix bone bark lower end, extended to the more external metaphyseal trabeculae counterbalancing the discrepancy between the epiphyseal and the diaphyseal circumferential growth.     

Role of iRhoms 1 and 2 in Endochondral Ossification

Growth of the axial and appendicular skeleton depends on endochondral ossification, which is controlled by tightly regulated cell–cell interactions in the developing growth plates. Previous studies have uncovered an important role of a disintegrin and metalloprotease 17 (ADAM17) in the normal development of the mineralized zone of hypertrophic chondrocytes during endochondral ossification. ADAM17 regulates EGF-receptor signaling by cleaving EGFR-ligands such as TGFα from their membrane-anchored precursor. The activity of ADAM17 is controlled by two regulatory binding partners, the inactive Rhomboids 1 and 2 (iRhom1, 2), raising questions about their role in endochondral ossification. To address this question, we generated mice lacking iRhom2 (iR2−/−) with floxed alleles of iRhom1 that were specifically deleted in chondrocytes by Col2a1-Cre (iR1∆Ch). The resulting iR2−/−iR1∆Ch mice had retarded bone growth compared to iR2−/− mice, caused by a significantly expanded zone of hypertrophic mineralizing chondrocytes in the growth plate. Primary iR2−/−iR1∆Ch chondrocytes had strongly reduced shedding of TGFα and other ADAM17-dependent EGFR-ligands. The enlarged zone of mineralized hypertrophic chondrocytes in iR2−/−iR1∆Ch mice closely resembled the abnormal growth plate in A17∆Ch mice and was similar to growth plates in Tgfα−/− mice or mice with EGFR mutations. These data support a model in which iRhom1 and 2 regulate bone growth by controlling the ADAM17/TGFα/EGFR signaling axis during endochondral ossification.     

β-Tricalcium phosphate silica aerogel as an alternative bioactive ceramic for the potential use in dentistry

ABSTRACT

In this study, a mesoporous silica aerogel with β-tricalcium phosphate (β-TCP-AE) was manufactured. The effect of β-TCP-AE on gene expressions (BMP2, BMP7, Runx2 and OSX) of SAOS-2 cells was tested. For the in vivo evaluation, the ‘calvaria critical-size defect’ model was used: following 1 and 3 months of the artificial surgical bone defects filled with β-TCP-AE, histopathological analyses were performed. Gene expression studies demonstrated a mild osteoblastic differentiation of the SAOS-2 cells triggered after seven days of β-TCP-AE treatment. Digital histology of rat’s calvarial bone defects reconstructed with β-TCP-AE showed that after 1 month, calcifications and early ossifications developed with the presence of capillary-rich fibrous inflammation and remnants of exogenous compounds which nearly disappeared by the third month, and replaced with multiple newly formed bone islets mediated by osteoblasts. Based on our results, this bioceramic compound appears to have favourable properties for the use as a scaffold in the reconstructive medical practice.     

Recapitulation of In Situ Endochondral Ossification Using an Injectable Hypoxia-Mimetic Hydrogel

Due to the limited ability for perfusion, traditional intramembranous ossification (IMO) often fails to recapitulate the natural regeneration process of most long bones and craniofacial bones. Alternatively, endochondral ossification (ECO) strategy has emerged and has been evidenced to circumvent the drawbacks in the routine application of IMO. Here, an injectable, poly(glycerol sebacate)-co-poly (ethylene glycol)/polyacrylic acid (PEGS/PAA) hydrogels are successfully developed to induce a hypoxia-mimicking environment and subsequently recapitulate ECO via in situ iron chelation. With the incorporation of PAA, these hydrogels present remarkable viscoelasticity and high efficacy of iron ion-chelating after injection, giving rise to the activation of HIF-1α signaling pathway and suppression of inflammatory responses, and thereby improving chondrogenic differentiation in the early stage and facilitating vascularization in the later stage, which consequently trigger typical ECO. More importantly, through sustained and stable expression of HIF-1α regulated by PEGS/PAA hydrogels throughout the regeneration, a harmonious chondrogenic/osteogenic balance can be struck and thereby accelerating the progress of ECO compared to the PEGS. The findings provide an efficient strategy to achieve in situ ECO via biomaterial-based iron ion-chelating and ensuing hypoxia-mimicking, representing a novel and promising concept for future application in bone regeneration.     

Bone age estimation from carpal radiography images using deep learning

Bone age estimation has been used in medicine to verify whether the bone structure development degree of a person corresponds to their chronological age. Such estimate is useful for prognosis about the development of children and adolescents, as well as for the diagnosis of endocrinological diseases. This work proposes a fully automated methodology for bone age estimation from carpal radiography images. The methodology comprises two steps, the preprocessing of the image and the classification using a convolutional neural network. The system accuracy for different types of preprocessing is evaluated. We compare the accuracy achieved using the full radiography image as input for the neural network and using only parts of the image corresponding to the Phalangeal region, the Epiphyseal region, and the concatenation of these parts with a crop around the wrist. Digital image processing techniques are employed to segment these regions. Experiments are performed using radiography images from the California University Database. The impact of using different pre-trained neural networks for transfer learning is evaluated.     

直排尾矿固化回填梅山铁矿地表塌陷坑试验研究

为了解决尾矿库库存不足和地下崩落法采矿引起的地表塌陷坑所带来的土地浪费和安全隐患问题,梅山铁矿拟将尾矿分级浓缩后添加固化剂直接向地表塌陷坑内堆存。由于地下采矿活动在继续,塌陷坑处于活跃状态,尾矿固化堆存后,会引起崩落法开采的覆盖层构成发生变化。为此,通过对覆盖层的安全结构特性和安全堆存技术进行相应的相似模拟试验研究,摸索出了尾矿固化充填塌陷坑后一些规律,对矿山工程实施具有重要意义。     

A Novel Ex Vivo Bone Culture Model for Regulation of Collagen/Apatite Preferential Orientation by Mechanical Loading

The anisotropic microstructure of bone, composed of collagen fibers and biological apatite crystallites, is an important determinant of its mechanical properties. Recent studies have revealed that the preferential orientation of collagen/apatite composites is closely related to the direction and magnitude of in vivo principal stress. However, the mechanism of alteration in the collagen/apatite microstructure to adapt to the mechanical environment remains unclear. In this study, we established a novel ex vivo bone culture system using embryonic mouse femurs, which enabled artificial control of the mechanical environment. The mineralized femur length significantly increased following cultivation; uniaxial mechanical loading promoted chondrocyte hypertrophy in the growth plates of embryonic mouse femurs. Compressive mechanical loading using the ex vivo bone culture system induced a higher anisotropic microstructure than that observed in the unloaded femur. Osteocytes in the anisotropic bone microstructure were elongated and aligned along the long axis of the femur, which corresponded to the principal loading direction. The ex vivo uniaxial mechanical loading successfully induced the formation of an oriented collagen/apatite microstructure via osteocyte mechano-sensation in a manner quite similar to the in vivo environment.