The aim of the present real time in vivo micro-computed tomography (pCT) and histologic experiment was to assess the efficacy of guided bone regeneration (GBR) around standardized calvarial critical size defects ...The aim of the present real time in vivo micro-computed tomography (pCT) and histologic experiment was to assess the efficacy of guided bone regeneration (GBR) around standardized calvarial critical size defects (CSD) using bone marrow-derived mesenchymal stem cells (BMSCs), and collagen membrane (CM) with and without tricalcium phosphate (TCP) graft material. In the calvaria of nine female Sprague-Dawley rats, full-thickness CSD (diameter 4.6 mm) were created under general anesthesia. Treatment-wise, rats were divided into three groups. In group 1, CSD was covered with a resorbable CM; in group 2, BMSCs were filled in CSD and covered with CM; and in group 3, TCP soaked in BMSCs was placed in CSD and covered with CM. All defects were closed using resorbable sutures. Bone volume and bone mineral density of newly formed bone (NFB) and remaining TCP particles and rate of new bone formation was determined at baseline, 2, 4, 6, and 10 weeks using in vivo pCT. At the lOth week, the rats were killed and calvarial segments were assessed histologically. The results showed that the hardness of NFB was similar to that of the native bone in groups I and 2 as compared to the NFB in group 3. Likewise, values for the modulus of elasticity were also significantly higher in group 3 compared to groups 1 and 2. This suggests that TCP when used in combination with BMSCs and without CM was unable to form bone of significant strength that could possibly provide mechanical "lock" between the natural bone and NFB. The use of BMSCs as adjuncts to conventional GBR initiated new bone formation as early as 2 weeks of treatment compared to when GBR is attempted without adiunct BMSC therapy.展开更多
Recently, porous titanium granules (PTGs) have been indicated for the preservation of the dimensions of post-extraction sockets, as a filler in sinus lift procedures and for the treatment of peri-implant and periodo...Recently, porous titanium granules (PTGs) have been indicated for the preservation of the dimensions of post-extraction sockets, as a filler in sinus lift procedures and for the treatment of peri-implant and periodontal defects, based on the osteoconductivity and dimensional stability of the titanium granules. However, there is a lack of information regarding the use of this material in larger defects and in conjunction with membranes. The objective of this study is to test the behavior of PTGs used to fill critical size defects in rabbit tibiae, with and without membranes. Critical defects were created in both tibiae of rabbits, divided randomly into three groups: Group A (defect filled with PTG), Group B (defect filled with PTG+collagen membrane) and a control group (empty defect). After six weeks, histomorphometric analysis was performed. The results showed more defect closures at the cortical area (87.37%±2.2%) and more bone formation at the marrow area (57.6%± 1.3%) in Group B, in comparison with the other groups (P〈0.05); the use of membranes improved the material stability expressed as more percentages of the original material when membranes were used (P〈0.05). Finally, inflammatory reactions were observed when the granules were not protected by membranes. In spite of the limitations of this animal study, it may be concluded that PTG particles are osteoconductive and allow bone growth. The PTG particles must be covered by a membrane, especially when grafting larger defects, in order to control particle migration, promote clot stabilization and separate the PTG graft from undesired soft tissue cells.展开更多
We study the iron atomic aggregates deposited on silicone oil surfaces by using atomic force microscopy. The aggregates are composed of disk-shaped nanoparticles with the mean diameter Φc≈31.7 nm and height Hc≈4.5 ...We study the iron atomic aggregates deposited on silicone oil surfaces by using atomic force microscopy. The aggregates are composed of disk-shaped nanoparticles with the mean diameter Φc≈31.7 nm and height Hc≈4.5 nm, which are nearly independent of the nominal film thickness. The experiment shows that a material condensation process must occur in the nanoparticles during the growth period. The anomalous phenomenon is explained.展开更多
Critical size bone defects represent a significant challenge worldwide,often leading to persistent pain and physical disability that profoundly impact patients’quality of life and mental well-being.To address the int...Critical size bone defects represent a significant challenge worldwide,often leading to persistent pain and physical disability that profoundly impact patients’quality of life and mental well-being.To address the intricate and complex repair processes involved in these defects,we performed single-cell RNA sequencing and revealed notable shifts in cellular populations within regenerative tissue.Specifically,we observed a decrease in progenitor lineage cells and endothelial cells,coupled with an increase in fibrotic lineage cells and pro-inflammatory cells within regenerative tissue.Furthermore,our analysis of differentially expressed genes and associated signaling pathway at the single-cell level highlighted impaired angiogenesis as a central pathway in critical size bone defects,notably influenced by reduction of Spp1 and Cxcl12 expression.This deficiency was particularly pronounced in progenitor lineage cells and myeloid lineage cells,underscoring its significance in the regeneration process.In response to these findings,we developed an innovative approach to enhance bone regeneration in critical size bone defects.Our fabrication process involves the integration of electrospun PCL fibers with electrosprayed PLGA microspheres carrying Spp1 and Cxcl12.This design allows for the gradual release of Spp1 and Cxcl12 in vitro and in vivo.To evaluate the efficacy of our approach,we locally applied PCL scaffolds loaded with Spp1 and Cxcl12 in a murine model of critical size bone defects.Our results demonstrated restored angiogenesis,accelerated bone regeneration,alleviated pain responses and improved mobility in treated mice.展开更多
Shield tunneling is easily obstructed by clogging in clayey strata with small soil particles.However,soil clogging rarely occurs in strata with coarse-grained soils.Theoretically,a critical particle size of soils shou...Shield tunneling is easily obstructed by clogging in clayey strata with small soil particles.However,soil clogging rarely occurs in strata with coarse-grained soils.Theoretically,a critical particle size of soils should exist,below which there is a high risk of soil clogging in shield tunneling.To determine the critical particle size,a series of laboratory tests was carried out with a large-scale rotary shear apparatus to measure the tangential adhesion strength of soils with different particle sizes and water contents.It was found that the tangential adhesion strength at the soilesteel interface gradually increased linearly with applied normal pressure.When the particle size of the soil specimen was less than 0.15 mm,the interfacial adhesion force first increased and then decreased as the water content gradually increased;otherwise,the soil specimens did not manifest any interfacial adhesion force.The amount of soil mass adhering to the steel disc was positively correlated with the interfacial adhesion force,thus the interfacial adhesion force was adopted to characterize the soil clogging risk in shield tunneling.The critical particle size of soils causing clogging was determined to be 0.15 mm.Finally,the generation mechanism of interfacial adhesion force was explored for soils with different particle sizes to explain the critical particle size of soil with clogging risk in shield tunneling.展开更多
In order to establish and standardize the rabbit rib segmental bone defect model,it is of vital importance to determine rabbit rib critical size defect(CSD).According to the general time needed for spontaneous long-bo...In order to establish and standardize the rabbit rib segmental bone defect model,it is of vital importance to determine rabbit rib critical size defect(CSD).According to the general time needed for spontaneous long-bone regeneration,three-month observation period was set to determine the CSD.The rabbit rib segmental bone defects with different sizes from 1 to 5cm with or without periosteum were performed in the eighth rib of 4-month-old male New Zealand rabbits and underwent Xray examinations at the 4th,8th and 12th weeks postoperatively.The gross and histological examinations at postoperative week 12 were evaluated,which showed that the critical sizes in the rabbit rib models with and without periosteum were 5 and 2 cm,respectively.This study provides prerequisite data for establishing rabbit rib CSD model and evaluating bonematerials using this model.展开更多
Recent innovations in bone tissue engineering have introduced biomaterials that generate oxygen to substitute vasculature.This strategy provides the immediate oxygen required for tissue viability and graft maturation....Recent innovations in bone tissue engineering have introduced biomaterials that generate oxygen to substitute vasculature.This strategy provides the immediate oxygen required for tissue viability and graft maturation.Here we demonstrate a novel oxygen-generating tissue scaffold with predictable oxygen release kinetics and modular material properties.These hydrogel scaffolds were reinforced with microparticles comprised of emulsified calcium peroxide(CaO_(2))within polycaprolactone(PCL).The alterations of the assembled materials produced constructs within 5±0.81 kPa to 34±0.9 kPa in mechanical strength.The mass swelling ratios varied between 11%and 25%.Our in vitro and in vivo results revealed consistent tissue viability,metabolic activity,and osteogenic differentiation over two weeks.The optimized in vitro cell culture system remained stable at pH 8-9.The in vivo rodent models demonstrated that these scaffolds support a 70 mm^(3) bone volume that was comparable to the native bone and yielded over 90%regeneration in critical size cranial defects.Furthermore,the in vivo bone remodeling and vascularization results were validated by tartrate-resistant acid phosphatase(TRAP)and vascular endothelial growth factor(VEGF)staining.The promising results of this work are translatable to a repertoire of regenerative medicine applications including advancement and expansion of bone substitutes and disease models.展开更多
Nanocrystalline metals with high Gibbs free energy have a strong tendency towards thermally driven grain growth,thus understanding the critical size or temperature of grain growth is vital for their applications.The i...Nanocrystalline metals with high Gibbs free energy have a strong tendency towards thermally driven grain growth,thus understanding the critical size or temperature of grain growth is vital for their applications.The investigations of thermal stability were usually conducted on the materials with a homogeneous structure;however,these methods are time-consuming and expensive.In the present work,we reveal a high-throughput experimental strategy to characterize the size-dependent thermal stability via annealing the gradient structured Ni.Employing this method,the critical size of grain growth(d_(c))at a given annealing temperature was rapidly determined.The critical size of grain growth was~95 nm when annealed at 503 K for 3 h,which is consistent with the value reported in the homogeneous structured Ni.Furthermore,this critical size was found to be identical in three types of gradient structured Ni,i.e.,independent on the gradient structure.Our present work demonstrates a high-throughput strategy for exploring the critical size of grain growth and size-dependent thermal stability of metals.展开更多
Surface tension of sodium aluminate solution and the contact angle between Al(OH)3 particles and aluminate solution were measured, then the dependence of Al(OH)3 solubility on its particle size was calculated and ...Surface tension of sodium aluminate solution and the contact angle between Al(OH)3 particles and aluminate solution were measured, then the dependence of Al(OH)3 solubility on its particle size was calculated and thus the variation of the critical nucleus sizes was determined based on the Ostwald ripening formula. The results show that the Al(OH)3 solubility in sodium aluminate solution decreases with the increment of particle size, and the critical nucleus sizes increase with the rise of alkali concentration, caustic ratio and precipitation temperature. The results also imply that the presence of small particles in seeded precipitation system is an important factor to limit the depth of precipitation.展开更多
We consider a one-dimensional reaction-diffusion equation describing single-and two-species population dynamics in an advective environment,based on the modeling frameworks proposed by Lutscher et al.in 2006.We analyz...We consider a one-dimensional reaction-diffusion equation describing single-and two-species population dynamics in an advective environment,based on the modeling frameworks proposed by Lutscher et al.in 2006.We analyze the effect of rate of loss of individuals at both the upstream and downstream boundaries.In the single-species case,we prove the existence of the critical domain size and provide explicit formulas in terms of model parameters.We further derive qualitative properties of the critical domain size and show that,in some cases,the critical domain size is either strictly decreasing over all diffusion rates,or monotonically increasing after first decreasing to a minimum.We also consider competition between species differing only in their diffusion rates.For two species having large diffusion rates,we give a sufficient condition to determine whether the faster or slower diffuser wins the competition.We also briefly discuss applications of these results to competition in species whose spatial niche is affected by shifting isotherms caused by climate change.展开更多
In the simulation of rupture processes of seismic sources by using either numerical method or rock mechanics experiments, improper setting of the specimen size will influence the stress field near the faults. In this ...In the simulation of rupture processes of seismic sources by using either numerical method or rock mechanics experiments, improper setting of the specimen size will influence the stress field near the faults. In this study, 2D finite element method (FEM) was used to calculate the stress field of rock specimens in different sizes with fixed-size elliptic holes. The calculated stress field was compared with analytic solution for elliptic-hole problem in an infinite medium. Numerical results showed that boundary effect of a rock specimen with an elliptic hole on stress field under uniaxial compression cannot be neglected. Critical aspect ratio of the specimen is about 3:2, and critical ratio of distance between the tip of the hole and the border of specimen (d) to the major axis of the elliptic hole (l) is about 7.3. Numerical analysis on rock specimen size can provide theoretical reference for rock specimen experiments, and it is also helpful for setting of model sizes in numerical simulations of fault movement.展开更多
The problem of habitat fragmentation is recently an important issue in ecological research as well as in the practical approach of nature conservation. According to the most popular approaches, habitats are considered...The problem of habitat fragmentation is recently an important issue in ecological research as well as in the practical approach of nature conservation. According to the most popular approaches, habitats are considered as the homogenous parts of the landscape. Also the metapopulation concept problem of the inert habitat heterogenity is considered quite seldom. These approaches have some weak points resulting from the assumption that the border between habitat patches and the metapopulation matrix is fairly sharp. This paper presents a resource-based concept of habitats, based on mathematical theory of point processes, which can be easily applied to analysing the problem of uneven distribution of resources. The basic assumption is that the random distribution of resources may be mathematically described as the realisation of a certain point process. According to our method, it is possible to calculate the expected quantities of available resources as well as the minimum area of habitat that includes the expected abundance of the resource. This approach may be very useful to understand some crucial phenomena in landscape ecology, such as the patch size effect and its connection to habitat loss and fragmentation.展开更多
By employing the two-dimensional analysis, i.e.,plane strain and plane stress, a semi-analytical method is developed to investigate the interfacial delamination in electrodes. The key parameters are obtained from the ...By employing the two-dimensional analysis, i.e.,plane strain and plane stress, a semi-analytical method is developed to investigate the interfacial delamination in electrodes. The key parameters are obtained from the governing equations, and their effects on the evolution of the delamination are evaluated. The impact of constraint perpendicular to the plane is also investigated by comparing the plane strain and plane stress. It is found that the delamination in the plane strain condition occurs easier, indicating that the constraint is harmful to maintain the structure stability. According to the obtained governing equations, a formula of the dimensionless critical size for delamination is provided, which is a function of the maximum volumetric strain and the Poisson’s ratio of the active layer.展开更多
Large coarse aggregates used in fully-graded hydraulic concrete necessitate large specimens for numerical modeling.This leads to a high computational cost for mesoscale modeling and thus slows the development of multi...Large coarse aggregates used in fully-graded hydraulic concrete necessitate large specimens for numerical modeling.This leads to a high computational cost for mesoscale modeling and thus slows the development of multiscale modeling of hydraulic mass concrete structures.To overcome this obstacle,an efficient approach for mesoscale fracture modeling of fully-graded hydraulic concrete was developed based on the concept of the governing mesostructure.The mesostructure was characterized by a critical aggregate size.Coarse aggregates smaller than the critical size were homogenized into mortar matrices.Key issues in mesostructure generation of fully-graded hydraulic concrete are discussed,as is the development of mesoscale finite element modeling methodology.The basic concept and implementation procedures of the proposed approach are also described in detail.The numerical results indicated that the proposed approach not only significantly improves the compu-tational efficiency of mesoscale modeling but also captures the dominant fracturing mechanism at the mesoscale and reproduces reasonable fracture properties at the macroscale.Therefore,the proposed approach can serve as a basis for multiscale fracture modeling of hydraulic mass concrete structures.展开更多
The enumerating algorithm has been introduced into the fitting procedure of the ASR model. Based on the detailed study of 21 large earthquakes with M≥6. 8 in the Chinese Mainland,the statistical features of seismic s...The enumerating algorithm has been introduced into the fitting procedure of the ASR model. Based on the detailed study of 21 large earthquakes with M≥6. 8 in the Chinese Mainland,the statistical features of seismic strain release before large earthquakes have been summarized. In the mass,the strain release models can be divided into five types. The first is the DA model,in which the strain release accelerates in broader areas and decelerates in small areas around the epicenter. Approximately 38% of earthquake samples are of this type. The second is the AD model,in which the strain release decelerates in broader areas and accelerates in smaller areas around the epicenter with an occupying ratioof approximately 19%. The third is ASR,in which only accelerating strain release can be observed. Cases of this model amount to about 14%. The fourth is DSR,in which only decelerating strain release can be checked,amounting to about 24%. There is only one earthquake sample of the fifth type (LSR),which shows a linear strain release. There is a 3~6 years difference in the duration of pre-shock sequences between the accelerating and decelerating models. This means that seismic quiescence against a background of increased seismicity of small earthquakes before large earthquakes are a typical feature in general. For the DA model,the average size of critical regions for steady accelerating and decelerating strain release is about 260km to 400km and 100km to 200km,respectively,3 to 5 times and 1 to 2 times the rupture size of an earthquake of magnitude 7. 0. The AD model is the opposite of the DA model. The model parameter,m value,has good stability. The ratio of ASR is about the same for accelerating seismic strain release phenomena,no matter what the strain release models are,or how large the strain release quantity is. With regard to decelerating seismic strain release phenomena, the DA model has the most distinctive decelerating strain release characteristic and is the typical feature of seismic strain release,i. e. "decelerating in-accelerating out seismic strain model".展开更多
The stability of vapor nanobubbles in bulk liquid was investigated theoretically and the critical bubble size was derived from macroscale thermodynamic equations,below which the system destabilizes with sharp drop in ...The stability of vapor nanobubbles in bulk liquid was investigated theoretically and the critical bubble size was derived from macroscale thermodynamic equations,below which the system destabilizes with sharp drop in pressure.This critical size was quantitatively verified in molecular dynamic simulation using the Lennard-Jones model of argon,where stronger attraction between the molecules at lower density is found to contribute most to the drop of system pressure and,as the Laplace pressure on the curved bubble interface fails to balance the pressure difference across the interface,the bubbles become unstable.The theoretical model could be extended to other systems where reliable equations of state and interfacial tension are available.展开更多
This paper shows that for DEM simulations of triaxial tests using samples with a grading that is repre- sentative of a real soil, the sample size significantly influences the observed material response. Four DEM sampl...This paper shows that for DEM simulations of triaxial tests using samples with a grading that is repre- sentative of a real soil, the sample size significantly influences the observed material response. Four DEM samples with identical initial states were produced: three cylindrical samples bounded by rigid wails and one bounded by a cubical periodic cell, When subjected to triaxial loading, the samples with rigid boundaries were more dilative, stiffer and reached a higher peak stress ratio than the sample enclosed by periodic boundaries. For the rigid-wall samples, dilatancy increased and stiffness decreased with increasing sample size, The periodic sample was effectively homogeneous, The void ratio increased and the contact density decreased close to the rigid walls, This heterogeneity reduced with increasing sample size. The positions of the critical state lines (CSLs) of the overall response in e-log p' space were sensitive to the sample size, although no difference was observed between their slopes. The critical states of the interior regions of the rigid-wall-bounded samples approached that of the homogeneous periodic sample with increasing sample size. The ultimate strength of the material at the critical state is independent of sample size.展开更多
How cells accomplish cell size homeostasis is a fascinating topic, and several cell size regulation mechanisms were proposed: timer, sizer, and adder. Recently the adder model has received a great deal of attention. A...How cells accomplish cell size homeostasis is a fascinating topic, and several cell size regulation mechanisms were proposed: timer, sizer, and adder. Recently the adder model has received a great deal of attention. Adder property was also found in the DNA replication cycle. This paper aims to explain the adder phenomenon both in the division-centric picture and replication-centric picture at the molecular level. We established a self-replication model, and the system reached a steady state quickly based on evolution rules. We collected tens of thousands of cells in the same trajectory and calculated the Pearson correlation coefficient between biological variables to decide which regulatory mechanism was adopted by cells. Our simulation results confirmed the double-adder mechanism. Chromosome replication initiation and cell division control are independent and regulated by respective proteins.Cell size homeostasis originates from division control and has nothing to do with replication initiation control. At a slow growth rate, the deviation from adder toward sizer comes from a significant division protein degradation rate when division protein is auto-inhibited. Our results indicated the two necessary conditions in the double-adder mechanism: one is balanced biosynthesis, and the other is that there is a protein trigger threshold to inspire DNA replication initiation and cell division. Our results give insight to the regulatory mechanism of cell size and instructive to synthetic biology.展开更多
Fatigue properties of high-strength steels become more and more sensitive to inclusions with enhancing the ultimate tensile strength (UTS) because the inclusions often cause a relatively low fatigue strength and a lar...Fatigue properties of high-strength steels become more and more sensitive to inclusions with enhancing the ultimate tensile strength (UTS) because the inclusions often cause a relatively low fatigue strength and a large scatter of fatigue lives. In this work, four S–N curves and more than 200 fatigue fracture morphologies were comprehensively investigated with a special focus on the size and type of inclusions at the fatigue cracking origin in GCr15 steel with a wide strength range by different heat treatments after high-cycle fatigue (HCF). It is found that the percentage of fatigue failure induced by the inclusion including Al2 O3 and TiN gradually increases with increasing the UTS, while the percentage of failure at sample surfaces decreases conversely and the fatigue strength first increases and then decreases. Besides, it is interestingly noted that the inclusion sizes at the cracking origin for TiN are smaller than that for Al2 O3 because the stress concentration factor for TiN is larger than that for Al2 O3 based on the finite element simulation. For the first time, a new fatigue cracking criterion including the isometric inclusion size line in the strength-toughness coordinate system with specific physical meaning was established to reveal the relationship among the UTS, fracture toughness, and the critical inclusion size considering different types of inclusions based on the fracture mechanics. And the critical inclusion size of Al2 O3 is about 1.33 times of TiN. The fatigue cracking criterion could be used to judge whether fatigue fracture occurred at inclusions or not and provides a theoretical basis for controlling the scale of different inclusion types for high-strength steels. Our work may offer a new perspective on the critical inclusion size in terms of the inclusion types, which is of scientific interest and has great merit to industrial metallurgical control for anti-fatigue design.展开更多
基金King Saud University,through Vice Deanship of Research Chairs
文摘The aim of the present real time in vivo micro-computed tomography (pCT) and histologic experiment was to assess the efficacy of guided bone regeneration (GBR) around standardized calvarial critical size defects (CSD) using bone marrow-derived mesenchymal stem cells (BMSCs), and collagen membrane (CM) with and without tricalcium phosphate (TCP) graft material. In the calvaria of nine female Sprague-Dawley rats, full-thickness CSD (diameter 4.6 mm) were created under general anesthesia. Treatment-wise, rats were divided into three groups. In group 1, CSD was covered with a resorbable CM; in group 2, BMSCs were filled in CSD and covered with CM; and in group 3, TCP soaked in BMSCs was placed in CSD and covered with CM. All defects were closed using resorbable sutures. Bone volume and bone mineral density of newly formed bone (NFB) and remaining TCP particles and rate of new bone formation was determined at baseline, 2, 4, 6, and 10 weeks using in vivo pCT. At the lOth week, the rats were killed and calvarial segments were assessed histologically. The results showed that the hardness of NFB was similar to that of the native bone in groups I and 2 as compared to the NFB in group 3. Likewise, values for the modulus of elasticity were also significantly higher in group 3 compared to groups 1 and 2. This suggests that TCP when used in combination with BMSCs and without CM was unable to form bone of significant strength that could possibly provide mechanical "lock" between the natural bone and NFB. The use of BMSCs as adjuncts to conventional GBR initiated new bone formation as early as 2 weeks of treatment compared to when GBR is attempted without adiunct BMSC therapy.
文摘Recently, porous titanium granules (PTGs) have been indicated for the preservation of the dimensions of post-extraction sockets, as a filler in sinus lift procedures and for the treatment of peri-implant and periodontal defects, based on the osteoconductivity and dimensional stability of the titanium granules. However, there is a lack of information regarding the use of this material in larger defects and in conjunction with membranes. The objective of this study is to test the behavior of PTGs used to fill critical size defects in rabbit tibiae, with and without membranes. Critical defects were created in both tibiae of rabbits, divided randomly into three groups: Group A (defect filled with PTG), Group B (defect filled with PTG+collagen membrane) and a control group (empty defect). After six weeks, histomorphometric analysis was performed. The results showed more defect closures at the cortical area (87.37%±2.2%) and more bone formation at the marrow area (57.6%± 1.3%) in Group B, in comparison with the other groups (P〈0.05); the use of membranes improved the material stability expressed as more percentages of the original material when membranes were used (P〈0.05). Finally, inflammatory reactions were observed when the granules were not protected by membranes. In spite of the limitations of this animal study, it may be concluded that PTG particles are osteoconductive and allow bone growth. The PTG particles must be covered by a membrane, especially when grafting larger defects, in order to control particle migration, promote clot stabilization and separate the PTG graft from undesired soft tissue cells.
基金Project supported by the National Natural Science Foundation of China(Grant No.11074215)the Fundamental Research Funds for Central Universities of Ministry of Education of China(Grant No.2012QNA3010)
文摘We study the iron atomic aggregates deposited on silicone oil surfaces by using atomic force microscopy. The aggregates are composed of disk-shaped nanoparticles with the mean diameter Φc≈31.7 nm and height Hc≈4.5 nm, which are nearly independent of the nominal film thickness. The experiment shows that a material condensation process must occur in the nanoparticles during the growth period. The anomalous phenomenon is explained.
基金supported by the following NIH grants:R01 grants(AR075860,AR077616,and AR083900 to JSHL138175,HL164062,and DK133949 to JG)and a R21 grant(AR077226 to JS)a P30 Core Center grant(AR074992 to the Musculoskeletal Research Center at Washington University in St.Louis).
文摘Critical size bone defects represent a significant challenge worldwide,often leading to persistent pain and physical disability that profoundly impact patients’quality of life and mental well-being.To address the intricate and complex repair processes involved in these defects,we performed single-cell RNA sequencing and revealed notable shifts in cellular populations within regenerative tissue.Specifically,we observed a decrease in progenitor lineage cells and endothelial cells,coupled with an increase in fibrotic lineage cells and pro-inflammatory cells within regenerative tissue.Furthermore,our analysis of differentially expressed genes and associated signaling pathway at the single-cell level highlighted impaired angiogenesis as a central pathway in critical size bone defects,notably influenced by reduction of Spp1 and Cxcl12 expression.This deficiency was particularly pronounced in progenitor lineage cells and myeloid lineage cells,underscoring its significance in the regeneration process.In response to these findings,we developed an innovative approach to enhance bone regeneration in critical size bone defects.Our fabrication process involves the integration of electrospun PCL fibers with electrosprayed PLGA microspheres carrying Spp1 and Cxcl12.This design allows for the gradual release of Spp1 and Cxcl12 in vitro and in vivo.To evaluate the efficacy of our approach,we locally applied PCL scaffolds loaded with Spp1 and Cxcl12 in a murine model of critical size bone defects.Our results demonstrated restored angiogenesis,accelerated bone regeneration,alleviated pain responses and improved mobility in treated mice.
基金The financial support from the National Natural Science Foun-dation of China(Grant Nos.52022112 and 51778637)the Sci-ence and Technology Innovation Program of Hunan Province(Grant No.2021RC3015)are acknowledged and appreciated.
文摘Shield tunneling is easily obstructed by clogging in clayey strata with small soil particles.However,soil clogging rarely occurs in strata with coarse-grained soils.Theoretically,a critical particle size of soils should exist,below which there is a high risk of soil clogging in shield tunneling.To determine the critical particle size,a series of laboratory tests was carried out with a large-scale rotary shear apparatus to measure the tangential adhesion strength of soils with different particle sizes and water contents.It was found that the tangential adhesion strength at the soilesteel interface gradually increased linearly with applied normal pressure.When the particle size of the soil specimen was less than 0.15 mm,the interfacial adhesion force first increased and then decreased as the water content gradually increased;otherwise,the soil specimens did not manifest any interfacial adhesion force.The amount of soil mass adhering to the steel disc was positively correlated with the interfacial adhesion force,thus the interfacial adhesion force was adopted to characterize the soil clogging risk in shield tunneling.The critical particle size of soils causing clogging was determined to be 0.15 mm.Finally,the generation mechanism of interfacial adhesion force was explored for soils with different particle sizes to explain the critical particle size of soil with clogging risk in shield tunneling.
基金This study is in part supported by Science Foundation of Shandong Province of China(ZR2015EL002)National Natural Science Foundation of China(51572144).
文摘In order to establish and standardize the rabbit rib segmental bone defect model,it is of vital importance to determine rabbit rib critical size defect(CSD).According to the general time needed for spontaneous long-bone regeneration,three-month observation period was set to determine the CSD.The rabbit rib segmental bone defects with different sizes from 1 to 5cm with or without periosteum were performed in the eighth rib of 4-month-old male New Zealand rabbits and underwent Xray examinations at the 4th,8th and 12th weeks postoperatively.The gross and histological examinations at postoperative week 12 were evaluated,which showed that the critical sizes in the rabbit rib models with and without periosteum were 5 and 2 cm,respectively.This study provides prerequisite data for establishing rabbit rib CSD model and evaluating bonematerials using this model.
基金This research was partially supported by the American Heart Association(AHA)(19TPA34910111)the University of Massachusetts Lowell faculty start-up funds,and the National Institutes of Health(NIH)(R01DE030129)。
文摘Recent innovations in bone tissue engineering have introduced biomaterials that generate oxygen to substitute vasculature.This strategy provides the immediate oxygen required for tissue viability and graft maturation.Here we demonstrate a novel oxygen-generating tissue scaffold with predictable oxygen release kinetics and modular material properties.These hydrogel scaffolds were reinforced with microparticles comprised of emulsified calcium peroxide(CaO_(2))within polycaprolactone(PCL).The alterations of the assembled materials produced constructs within 5±0.81 kPa to 34±0.9 kPa in mechanical strength.The mass swelling ratios varied between 11%and 25%.Our in vitro and in vivo results revealed consistent tissue viability,metabolic activity,and osteogenic differentiation over two weeks.The optimized in vitro cell culture system remained stable at pH 8-9.The in vivo rodent models demonstrated that these scaffolds support a 70 mm^(3) bone volume that was comparable to the native bone and yielded over 90%regeneration in critical size cranial defects.Furthermore,the in vivo bone remodeling and vascularization results were validated by tartrate-resistant acid phosphatase(TRAP)and vascular endothelial growth factor(VEGF)staining.The promising results of this work are translatable to a repertoire of regenerative medicine applications including advancement and expansion of bone substitutes and disease models.
基金financially supported by the National Key Research and Development Program of China(No.2017YFB0702003)the National Natural Science Foundation of China(No.51871217)support from the Youth Innovation Promotion Association,Chinese Academy of Sciences(No.2020194)。
文摘Nanocrystalline metals with high Gibbs free energy have a strong tendency towards thermally driven grain growth,thus understanding the critical size or temperature of grain growth is vital for their applications.The investigations of thermal stability were usually conducted on the materials with a homogeneous structure;however,these methods are time-consuming and expensive.In the present work,we reveal a high-throughput experimental strategy to characterize the size-dependent thermal stability via annealing the gradient structured Ni.Employing this method,the critical size of grain growth(d_(c))at a given annealing temperature was rapidly determined.The critical size of grain growth was~95 nm when annealed at 503 K for 3 h,which is consistent with the value reported in the homogeneous structured Ni.Furthermore,this critical size was found to be identical in three types of gradient structured Ni,i.e.,independent on the gradient structure.Our present work demonstrates a high-throughput strategy for exploring the critical size of grain growth and size-dependent thermal stability of metals.
基金Project(51274242)supported by the National Natural Science Foundation of China
文摘Surface tension of sodium aluminate solution and the contact angle between Al(OH)3 particles and aluminate solution were measured, then the dependence of Al(OH)3 solubility on its particle size was calculated and thus the variation of the critical nucleus sizes was determined based on the Ostwald ripening formula. The results show that the Al(OH)3 solubility in sodium aluminate solution decreases with the increment of particle size, and the critical nucleus sizes increase with the rise of alkali concentration, caustic ratio and precipitation temperature. The results also imply that the presence of small particles in seeded precipitation system is an important factor to limit the depth of precipitation.
基金supported by the National Science Foundation grant DMS-1853561supported by the National Science Foundation of China grants No.12250710674,12261160366,12226328.
文摘We consider a one-dimensional reaction-diffusion equation describing single-and two-species population dynamics in an advective environment,based on the modeling frameworks proposed by Lutscher et al.in 2006.We analyze the effect of rate of loss of individuals at both the upstream and downstream boundaries.In the single-species case,we prove the existence of the critical domain size and provide explicit formulas in terms of model parameters.We further derive qualitative properties of the critical domain size and show that,in some cases,the critical domain size is either strictly decreasing over all diffusion rates,or monotonically increasing after first decreasing to a minimum.We also consider competition between species differing only in their diffusion rates.For two species having large diffusion rates,we give a sufficient condition to determine whether the faster or slower diffuser wins the competition.We also briefly discuss applications of these results to competition in species whose spatial niche is affected by shifting isotherms caused by climate change.
基金National Natural Science Foundation of China (40234042).
文摘In the simulation of rupture processes of seismic sources by using either numerical method or rock mechanics experiments, improper setting of the specimen size will influence the stress field near the faults. In this study, 2D finite element method (FEM) was used to calculate the stress field of rock specimens in different sizes with fixed-size elliptic holes. The calculated stress field was compared with analytic solution for elliptic-hole problem in an infinite medium. Numerical results showed that boundary effect of a rock specimen with an elliptic hole on stress field under uniaxial compression cannot be neglected. Critical aspect ratio of the specimen is about 3:2, and critical ratio of distance between the tip of the hole and the border of specimen (d) to the major axis of the elliptic hole (l) is about 7.3. Numerical analysis on rock specimen size can provide theoretical reference for rock specimen experiments, and it is also helpful for setting of model sizes in numerical simulations of fault movement.
基金funded by Institute of Nature Conservation PASpartly by a Polish State Committee for Scientific Research/National Science Centre grant No.N N304 325836.
文摘The problem of habitat fragmentation is recently an important issue in ecological research as well as in the practical approach of nature conservation. According to the most popular approaches, habitats are considered as the homogenous parts of the landscape. Also the metapopulation concept problem of the inert habitat heterogenity is considered quite seldom. These approaches have some weak points resulting from the assumption that the border between habitat patches and the metapopulation matrix is fairly sharp. This paper presents a resource-based concept of habitats, based on mathematical theory of point processes, which can be easily applied to analysing the problem of uneven distribution of resources. The basic assumption is that the random distribution of resources may be mathematically described as the realisation of a certain point process. According to our method, it is possible to calculate the expected quantities of available resources as well as the minimum area of habitat that includes the expected abundance of the resource. This approach may be very useful to understand some crucial phenomena in landscape ecology, such as the patch size effect and its connection to habitat loss and fragmentation.
文摘By employing the two-dimensional analysis, i.e.,plane strain and plane stress, a semi-analytical method is developed to investigate the interfacial delamination in electrodes. The key parameters are obtained from the governing equations, and their effects on the evolution of the delamination are evaluated. The impact of constraint perpendicular to the plane is also investigated by comparing the plane strain and plane stress. It is found that the delamination in the plane strain condition occurs easier, indicating that the constraint is harmful to maintain the structure stability. According to the obtained governing equations, a formula of the dimensionless critical size for delamination is provided, which is a function of the maximum volumetric strain and the Poisson’s ratio of the active layer.
基金the National Natural Science Foundation of China(Grants No.51979092,51739006,and U1765204).
文摘Large coarse aggregates used in fully-graded hydraulic concrete necessitate large specimens for numerical modeling.This leads to a high computational cost for mesoscale modeling and thus slows the development of multiscale modeling of hydraulic mass concrete structures.To overcome this obstacle,an efficient approach for mesoscale fracture modeling of fully-graded hydraulic concrete was developed based on the concept of the governing mesostructure.The mesostructure was characterized by a critical aggregate size.Coarse aggregates smaller than the critical size were homogenized into mortar matrices.Key issues in mesostructure generation of fully-graded hydraulic concrete are discussed,as is the development of mesoscale finite element modeling methodology.The basic concept and implementation procedures of the proposed approach are also described in detail.The numerical results indicated that the proposed approach not only significantly improves the compu-tational efficiency of mesoscale modeling but also captures the dominant fracturing mechanism at the mesoscale and reproduces reasonable fracture properties at the macroscale.Therefore,the proposed approach can serve as a basis for multiscale fracture modeling of hydraulic mass concrete structures.
基金supported by a grant from the National Key Technology R&D Program in the Eleventh"Five-year Plan"Period ( 20070403-2006BAC01B03-02-02)fund for earthquake research (200708020),China
文摘The enumerating algorithm has been introduced into the fitting procedure of the ASR model. Based on the detailed study of 21 large earthquakes with M≥6. 8 in the Chinese Mainland,the statistical features of seismic strain release before large earthquakes have been summarized. In the mass,the strain release models can be divided into five types. The first is the DA model,in which the strain release accelerates in broader areas and decelerates in small areas around the epicenter. Approximately 38% of earthquake samples are of this type. The second is the AD model,in which the strain release decelerates in broader areas and accelerates in smaller areas around the epicenter with an occupying ratioof approximately 19%. The third is ASR,in which only accelerating strain release can be observed. Cases of this model amount to about 14%. The fourth is DSR,in which only decelerating strain release can be checked,amounting to about 24%. There is only one earthquake sample of the fifth type (LSR),which shows a linear strain release. There is a 3~6 years difference in the duration of pre-shock sequences between the accelerating and decelerating models. This means that seismic quiescence against a background of increased seismicity of small earthquakes before large earthquakes are a typical feature in general. For the DA model,the average size of critical regions for steady accelerating and decelerating strain release is about 260km to 400km and 100km to 200km,respectively,3 to 5 times and 1 to 2 times the rupture size of an earthquake of magnitude 7. 0. The AD model is the opposite of the DA model. The model parameter,m value,has good stability. The ratio of ASR is about the same for accelerating seismic strain release phenomena,no matter what the strain release models are,or how large the strain release quantity is. With regard to decelerating seismic strain release phenomena, the DA model has the most distinctive decelerating strain release characteristic and is the typical feature of seismic strain release,i. e. "decelerating in-accelerating out seismic strain model".
基金support from the Major Program of the National Natural Science Foundation of China (grant No.22293024)the Science Fund for Creative Research Groups of the National Natural Science Foundation of China (grant No.21821005)the Project for Young Scientists in Basic Research of Chinese Academy of Sciences (grant No.YSBR-043).
文摘The stability of vapor nanobubbles in bulk liquid was investigated theoretically and the critical bubble size was derived from macroscale thermodynamic equations,below which the system destabilizes with sharp drop in pressure.This critical size was quantitatively verified in molecular dynamic simulation using the Lennard-Jones model of argon,where stronger attraction between the molecules at lower density is found to contribute most to the drop of system pressure and,as the Laplace pressure on the curved bubble interface fails to balance the pressure difference across the interface,the bubbles become unstable.The theoretical model could be extended to other systems where reliable equations of state and interfacial tension are available.
基金funding from the Royal Commission for the Exhibition of 1851provided as part of grant EP/1006761/1 from the Engineering and Physical Sciences Research Council
文摘This paper shows that for DEM simulations of triaxial tests using samples with a grading that is repre- sentative of a real soil, the sample size significantly influences the observed material response. Four DEM samples with identical initial states were produced: three cylindrical samples bounded by rigid wails and one bounded by a cubical periodic cell, When subjected to triaxial loading, the samples with rigid boundaries were more dilative, stiffer and reached a higher peak stress ratio than the sample enclosed by periodic boundaries. For the rigid-wall samples, dilatancy increased and stiffness decreased with increasing sample size, The periodic sample was effectively homogeneous, The void ratio increased and the contact density decreased close to the rigid walls, This heterogeneity reduced with increasing sample size. The positions of the critical state lines (CSLs) of the overall response in e-log p' space were sensitive to the sample size, although no difference was observed between their slopes. The critical states of the interior regions of the rigid-wall-bounded samples approached that of the homogeneous periodic sample with increasing sample size. The ultimate strength of the material at the critical state is independent of sample size.
文摘How cells accomplish cell size homeostasis is a fascinating topic, and several cell size regulation mechanisms were proposed: timer, sizer, and adder. Recently the adder model has received a great deal of attention. Adder property was also found in the DNA replication cycle. This paper aims to explain the adder phenomenon both in the division-centric picture and replication-centric picture at the molecular level. We established a self-replication model, and the system reached a steady state quickly based on evolution rules. We collected tens of thousands of cells in the same trajectory and calculated the Pearson correlation coefficient between biological variables to decide which regulatory mechanism was adopted by cells. Our simulation results confirmed the double-adder mechanism. Chromosome replication initiation and cell division control are independent and regulated by respective proteins.Cell size homeostasis originates from division control and has nothing to do with replication initiation control. At a slow growth rate, the deviation from adder toward sizer comes from a significant division protein degradation rate when division protein is auto-inhibited. Our results indicated the two necessary conditions in the double-adder mechanism: one is balanced biosynthesis, and the other is that there is a protein trigger threshold to inspire DNA replication initiation and cell division. Our results give insight to the regulatory mechanism of cell size and instructive to synthetic biology.
基金financially sup-ported by the National Natural Science Foundation of China(NSFC)(Grant Nos.52001310,52130002,and 51771208)the Strategic Pri-ority Research Program of the Chinese Academy of Sciences(Grant No.XDC04040502)+3 种基金the National Science and Technology Major Project(No.J2019-VI-0019-0134)Outstanding Postgraduate Inno-vative Research Project of Institute of Metal Research,CAS(No.1193002090)KC Wong Education Foundation(No.GJTD-2020-09)Institute of Metal Research Innovation Fund(No.2023-ZD01).
文摘Fatigue properties of high-strength steels become more and more sensitive to inclusions with enhancing the ultimate tensile strength (UTS) because the inclusions often cause a relatively low fatigue strength and a large scatter of fatigue lives. In this work, four S–N curves and more than 200 fatigue fracture morphologies were comprehensively investigated with a special focus on the size and type of inclusions at the fatigue cracking origin in GCr15 steel with a wide strength range by different heat treatments after high-cycle fatigue (HCF). It is found that the percentage of fatigue failure induced by the inclusion including Al2 O3 and TiN gradually increases with increasing the UTS, while the percentage of failure at sample surfaces decreases conversely and the fatigue strength first increases and then decreases. Besides, it is interestingly noted that the inclusion sizes at the cracking origin for TiN are smaller than that for Al2 O3 because the stress concentration factor for TiN is larger than that for Al2 O3 based on the finite element simulation. For the first time, a new fatigue cracking criterion including the isometric inclusion size line in the strength-toughness coordinate system with specific physical meaning was established to reveal the relationship among the UTS, fracture toughness, and the critical inclusion size considering different types of inclusions based on the fracture mechanics. And the critical inclusion size of Al2 O3 is about 1.33 times of TiN. The fatigue cracking criterion could be used to judge whether fatigue fracture occurred at inclusions or not and provides a theoretical basis for controlling the scale of different inclusion types for high-strength steels. Our work may offer a new perspective on the critical inclusion size in terms of the inclusion types, which is of scientific interest and has great merit to industrial metallurgical control for anti-fatigue design.