This work focuses on an unmanned aerial vehicle(UAV)-enabled mobile edge computing(MEC) system based on device-to-device(D2D) communication. In this system, the UAV exhibits caching,computing and relaying capabilities...This work focuses on an unmanned aerial vehicle(UAV)-enabled mobile edge computing(MEC) system based on device-to-device(D2D) communication. In this system, the UAV exhibits caching,computing and relaying capabilities to periodically provide specific service to cellular users and D2D receiver nodes in the appointed time slot. Besides, the D2D transmitter can provide additional caching services to D2D receiver to reduce the pressure of the UAV. Note that communication between multi-type nodes is mutually restricted and different links share spectrum resources. To achieve an improved balance between different types of node, we aim to maximize the overall energy efficiency while satisfying the quality-of-service requirements of the cellular nodes.To address this problem, we propose an alternating iteration algorithm to jointly optimize the scheduling strategies of the user, transmitting power of the UAV and D2D-TX nodes, and UAV trajectory. The successive convex approximation, penalty function, and Dinkelbach method are employed to transform the original problem into a group of solvable subproblems and the convergence of the method is proved. Simulation results show that the proposed scheme performs better than other benchmark algorithms, particularly in terms of balancing the tradeoff between minimizing UAV energy consumption and maximizing throughput.展开更多
A simple modification converts an electrospray ion source to an ambient-pressure helium plasma ionization source without the need of additional expensive hardware. Peaks for active ingredients were observed in the spe...A simple modification converts an electrospray ion source to an ambient-pressure helium plasma ionization source without the need of additional expensive hardware. Peaks for active ingredients were observed in the spectra recorded from intact pharmaceutical tablets placed in this source. A flow of heated nitrogen was used to thermally desorb analytes to gas phase. The desorption temperatures were sometimes as low as 50 ℃. For example, negative-ion spectra recorded from an aspirin tablet showed peaks at m/z 137 （salicylate anion） and 179 （acetylsalicylate anion） which were absent in the background spectra. The overall ion intensity increased as the desorption gas temperature was elevated. Within the same acquisition experiment, both positive- and negative-ion signals for acetaminophen were recorded from volatiles emanating from Tylenol tablets by switching the polarity of the capillary back and forth. Moreover, different preparations of acetaminophen tablets could be distinguished by their ion-intensity thermograms.展开更多
In the present study, olfactory ensheathing cells were transplanted into the cortices of infarcted （infarct transplantation group）, normal （normal transplantation group）, and bilateral hemispheres （bilateral tran...In the present study, olfactory ensheathing cells were transplanted into the cortices of infarcted （infarct transplantation group）, normal （normal transplantation group）, and bilateral hemispheres （bilateral transplantation group）. Olfactory ensheathing cells migrated to the infarct focus. The number of growth associated protein 43-positive cells and nerve fibers was slightly increased in the infarct area. These changes were more evident in the bilateral cortical transplantation group. Results demonstrated that transplanted olfactory ensheathing cells can migrate in rats with cerebra infarction. The olfactory ensheathing cells on the normal side can also promote neurological function. Bilateral cortical transplantation exhibited superior effects over unilateral transplantation.展开更多
In the emerging sixth generation(6G)communication network,energy harvesting(EH)is a promising technology to achieve the unlimited energy supply and hence makes the wireless communication systems self-sustainable in te...In the emerging sixth generation(6G)communication network,energy harvesting(EH)is a promising technology to achieve the unlimited energy supply and hence makes the wireless communication systems self-sustainable in terms of energy.However,in practice,the efficiency of energy harvesting is often low due to the limited device capability.In this paper,we formulate three types of different EH architectures,i.e.,the harvest-use architecture,the harvest-store-use architecture,and the harvest-use-store architecture from the perspective of energy storage efficiency.We propose resource allocation schemes to jointly design the sensor power and duty-cycle via an alternating optimization algorithm under the above EH architectures,in both simultaneous and non-simultaneous harvesting and utilization models,aiming at achieving a higher throughput and energy efficiency.Non-ideal circuit power is also considered.Numerical results show that our proposed schemes under EH architectures outperform the existing classic continuous transmission schemes.展开更多
Background:Moxibustion is a traditional Chinese medicine therapy to cure diseases by fumigating meridians or affected parts via burning of moxa floss.Moxa smoke(MS)is one of the key factors in moxibustion.In this stud...Background:Moxibustion is a traditional Chinese medicine therapy to cure diseases by fumigating meridians or affected parts via burning of moxa floss.Moxa smoke(MS)is one of the key factors in moxibustion.In this study,we adopted digital gene expression profiling,a next-generation gene sequencing technology,to investigate the effect of MS,inhalable particulate matter(PM10),on human lung adenocarcinoma A549 cells.Methods:The effects of MS PM10 on A549 cells,over different treatment durations were investigated in different groups:the 4-h group(4-h MS group and 4-h control group)and the 20-h group(20-h MS group and 20-h control group).Samples collected from the four groups were stored at80C for subsequent digital gene expression analysis.The differentially expressed genes(DEGs),identified after PM10 treatment,were screened,and their expression patterns analyzed by cluster analysis,Gene Ontology term enrichment,and Kyoto Encyclopedia of Genes and Genomes pathway analysis.Results:Compared with two control groups,1109 DEGs were identified after 4 h of MS intervention and 3565 DEGs were found after 20 h of MS intervention,respectively.Compared with that after 4-h intervention,2149 DEGs were identified after 20-h intervention.Cluster analysis demonstrated that PM10 can significantly inhibit cell cycle process with the prolongation of intervention time.Significant pathway enrichment analysis showed that MS PM10 can inhibit A549 cell cycle process at all phases.When MS PM10 exposure time prolongs,the inhibitory effect on cell cycle process becomes more obvious.Conclusion:MS PM10 has many biological activities,and may cause differential expression of genes involved in various biological processes.Nevertheless,further research on MS is warranted for better understanding of the mechanistic details.展开更多
Geopolymers are an important class of materials with potential applications because of their heat resistance,flame resistance,environmental friendliness,and possibilities of being transformed into ceramic matrix compo...Geopolymers are an important class of materials with potential applications because of their heat resistance,flame resistance,environmental friendliness,and possibilities of being transformed into ceramic matrix composites at low cost.However,the low mechanical properties as well as the intrinsic brittleness limit their technological implementations,and it is necessary to enhance the mechanical properties of geopolymers by adopting various kinds of reinforcements.In this work,therefore,two⁃dimensional continuous carbon fiber(Cf)reinforced phosphate⁃based geopolymer composites(Cf/geopolymer)were prepared through ultrasonic⁃assisted impregnation method.Effects of acetone treatment and high⁃temperature treatment on the properties of Cf/geopolymer composites were studied by X⁃ray photoelectron spectroscopy(XPS),X⁃ray diffraction(XRD),and scanning electron microscopy(SEM).Results of the study proved that acetone treatment plays a key role in ameliorating the interfacial interaction between Cf and phosphate matrix,which can thus enhance the mechanical properties of Cf/geopolymer composites.The Cf/geopolymer composites prepared by acetone⁃treated Cf had a flexural strength of 156.1 MPa and an elastic modulus of 39.7 GPa in Y direction.Moreover,an additional Sol⁃SiO2 re⁃impregnation treatment could further enhance the mechanical properties of the acetone⁃treated Cf/geopolymer composites by repairing the cracks and filling the pores.The results in this paper not only provide insights into the surface modification of Cf,but also report a facile and low⁃cost preparation route for Cf/geopolymer composites with potential applications in aerospace and defense technology.展开更多
A novel composite ceramics with excellen mechanical and dielectric properties was fabricated by means of low temperature hot-pressing using mechanically alloyed SiBON powders as raw materials.The influences of SiO_2 c...A novel composite ceramics with excellen mechanical and dielectric properties was fabricated by means of low temperature hot-pressing using mechanically alloyed SiBON powders as raw materials.The influences of SiO_2 content on phase microstructure,mechanical and dielectric properties of the SiBON ceramics were investigated.展开更多
Here,we demonstrated a novel synthesis of a polyborosilazane(PBSN)precursor using hydroboration and aminolysis reaction synergies to modify polysilazane(PSN).Specifically,borane tetrahydrofuran and boron trichloride h...Here,we demonstrated a novel synthesis of a polyborosilazane(PBSN)precursor using hydroboration and aminolysis reaction synergies to modify polysilazane(PSN).Specifically,borane tetrahydrofuran and boron trichloride hexane were used as dual boron sources,which not only reacted展开更多
The fully dense amorphous Si-B-C-N monoliths were fabricated at 1000°-1600°C under5 GPa for 30 min where the mechanically alloyed amorphous Si-B-C-N powders were used as raw material.Crystallization and micr...The fully dense amorphous Si-B-C-N monoliths were fabricated at 1000°-1600°C under5 GPa for 30 min where the mechanically alloyed amorphous Si-B-C-N powders were used as raw material.Crystallization and microstructure evolution of the prepared ceramics were展开更多
Because of the excellent mechanical and dielectric properties,Si BN ceramic was regarded as one of the best comprehensive performance thermal-insulation and wave-transparent material.We prepared amorphous Si BN powder...Because of the excellent mechanical and dielectric properties,Si BN ceramic was regarded as one of the best comprehensive performance thermal-insulation and wave-transparent material.We prepared amorphous Si BN powders by mechanical alloying using amorphous nano-Si3N4and h-BN展开更多
As a fundamental parameter of the optical crystals,birefringence plays a vital role in many optical applications,such as phase modulation,light splitting,and polarization,especially the phase matching process of the n...As a fundamental parameter of the optical crystals,birefringence plays a vital role in many optical applications,such as phase modulation,light splitting,and polarization,especially the phase matching process of the nonlinear optical crystals.The big birefringence not only benefits to the miniaturization of related devices,but also broadens the phase-matching wavelength range of nonlinear optical crystals.The design and synthesis of crystals with large birefringence becomes a hot research topic due to its more and more important applications in the optical modulation and laser technology fields.Herein,crystals with birefringence greater than 0.05 in the borate system are reviewed and classified according to different birefringent active groups,and the relationship between structure and properties is thoroughly explored.It is hoped that this review will provide a clear understanding of what kinds of building units and arrangements would have more opportunity to get adequate birefringence in borate systems and provide the statistical references to encourage the emergence of better crystal materials with large birefringence.展开更多
To improve the oxidation resistance of short carbon fiber(C_(sf))-reinforced mechanically alloyed SiBCN(MA-SiBCN)(C_(sf)/MA-SiBCN)composites,dense amorphous C_(sf)/SiBCN composites containing both MA-SiBCN and polymer...To improve the oxidation resistance of short carbon fiber(C_(sf))-reinforced mechanically alloyed SiBCN(MA-SiBCN)(C_(sf)/MA-SiBCN)composites,dense amorphous C_(sf)/SiBCN composites containing both MA-SiBCN and polymer-derived ceramics SiBCN(PDCs-SiBCN)were prepared by repeated polymer infiltration and pyrolysis(PIP)of layered C_(sf)/MA-SiBCN composites at 1100℃,and the oxidation behavior and damage mechanism of the as-prepared C_(sf)/SiBCN at 1300–1600℃ were compared and discussed with those of C_(sf)/MA-SiBCN.The C_(sf)/MA-SiBCN composites resist oxidation attack up to 1400℃ but fail at 1500℃ due to the collapse of the porous framework,while the PIP-densified C_(sf)/SiBCN composites are resistant to static air up to 1600℃.During oxidation,oxygen diffuses through preexisting pores and the pores left by oxidation of carbon fibers and pyrolytic carbon(PyC)to the interior of the matrix.Owing to the oxidative coupling effect of the MA-SiBCN and PDCs-SiBCN matrices,a relatively continuous and dense oxide layer is formed on the sample surface,and the interfacial region between the oxide layer and the matrix of the as-prepared composite contains an amorphous glassy structure mainly consisting of Si and O and an incompletely oxidized but partially crystallized matrix,which is primarily responsible for improving the oxidation resistance.展开更多
In this study,a crack-free pyrolysis process of partially cured precursor powder compacts was developed to prepare dense silicon boron carbonitride(SiBCN)monoliths at much lower temperatures(1300℃),thereby circumvent...In this study,a crack-free pyrolysis process of partially cured precursor powder compacts was developed to prepare dense silicon boron carbonitride(SiBCN)monoliths at much lower temperatures(1300℃),thereby circumventing the challenges of sintering densification(>1800℃).Unlike the elastic fracture in over-cured precursors or the viscoelastic deformation in under-cured precursors,the partially cured precursor,exhibiting elastic-plastic deformation behavior,facilitates limited nanoscale pore formation in a dense structure,achieving a balance between crack-free pyrolysis and densification.Compared to SiBCN derived from the over-cured precursor(σ=~159 MPa,K_(IC)=1.9 MPa:m^(1/2),Vickers hardness(HV)=7.8 GPa,and E=122 GPa),the resulting SiBCN monolith exhibited significantly improved mechanical properties(σ=~304 MPa,K_(IC)=3.7 MPa-m12,HV=10.6 GPa,and E=161 GPa)and oxidation resistance.In addition,this study investigated the high-temperature performance of SiBCN monoliths,including crystallization and oxidation,and determined the oxidation kinetics induced by pore structure healing and the different oxidation mechanisms of Si-C-N and B-C-N clusters in the amorphous structure.Due to its unique composition and structure,the SiBCN ceramic oxide layer exhibits exceptional self-healing effects on repairing the nanoporous system in the initial stage and shows outstanding high-temperature stability during prolonged oxidation,mitigating adverse effects from bubble formation and crystallization.Due to the nanoporous structure,the oxidation rate is initially controlled by gas diffusion following a linear law before transitioning to oxide layer diffusion characterized by a parabolic law.Finally,due to different valence bond configurations,Si-C-N transforms into an amorphous SiCNO structure after phase separation,unlike the nucleation and growth of residual B-N-C.展开更多
The atomic structural features and the mechanical properties of amorphous silicoboron carbonitride ceramics with 13 different compositions in the Si–BN–C phase diagram are investigated employing ab-initio calculatio...The atomic structural features and the mechanical properties of amorphous silicoboron carbonitride ceramics with 13 different compositions in the Si–BN–C phase diagram are investigated employing ab-initio calculations.Both chemical bonds and local structures within the amorphous network relate to the elemental composition.The distribution of nine types of chemical bonds is composition-dependent,where the B–C,Si–N,Si–C,and B–N bonds hold a large proportion for all compositions.Si prefers to be tetrahedrally coordinated,while B and N prefer sp^(2)-like trigonal coordination.In the case of C,the tetrahedral coordination is predominant at relatively low C contents,while the trigonal coordination is found to be the main feature with the increasing C content.Such local structural characteristics greatly influence the mechanical properties of SiBCN ceramics.Among the studied amorphous ceramics,SiB_(2)C_(3)N_(2) and SiB_(3)C_(2)N_(3) with low Si contents and moderate C and/or BN contents have high elastic moduli,high tensile/shear strengths,and good debonding capability.The increment of Si,C,and BN contents on this basis results in the decrease of mechanical properties.The increasing Si content leads to the increment of Si-contained bonds that reduce the bond strength of SiBCN ceramics,while the latter two cases are attributed to the raise of sp^(2)-like trigonal configuration of C and BN.These discoveries are expected to guide the composition-tailored optimization of SiBCN ceramics.展开更多
The atomic structural features and the mechanical properties of the Si_(2)BC_(3)N are investigated employ-ing ab-initio calculations.The chemical bonding types and their proportion are clarified.The tetrahedral and tr...The atomic structural features and the mechanical properties of the Si_(2)BC_(3)N are investigated employ-ing ab-initio calculations.The chemical bonding types and their proportion are clarified.The tetrahedral and trigonal configurations,together with their nesting,are identified,which contribute to the flexibil-ity of structural characteristics.The Si-related coordination aggravates the inhomogeneous distribution of chemical bonding and weakens the tetrahedral units.The accompanying polyhedral distortion is quanti-tatively reflected by the bond length and its deviation of polyhedron units.The elastic moduli and the ideal strengths of Si_(2)BC_(3)N are found to be lower than SiC and Si_(3)N_(4),as a result of the weakening effect of coordination Si on tetrahedral units and the existence of easily distorted trigona.The balance between tetrahedral and trigonal features through composition tailor is believed an effective way for the design of Si-B-C-N ceramics for structural applications.展开更多
Infrared(IR)birefringent materials with large optical anisotropy and wide transparency range are important for efficient light manipulation in various IR optical devices.Herein,two new IR birefringent materials AMgGeS...Infrared(IR)birefringent materials with large optical anisotropy and wide transparency range are important for efficient light manipulation in various IR optical devices.Herein,two new IR birefringent materials AMgGeSe_(3)(A=Li,Na)with large optical anisotropy were rationally designed by a rigid octahedron and flexible dimer combined strategy and fabricated in experiment.The introduction of rigid[LiSe_(6)]/[NaSe_(6)]and[MgSe_(6)]octahedra effectively regulates the geometry and arrangement of the flexible[Ge2Se6]dimers,resulting in the birefringence as large as 0.334@1,064 nm in LiMgGeSe_(3) and 0.445@1,064 nm(the largest one in the reported[Ge_(2)Se_(6)]dimer-contained selenides)in NaMgGeSe_(3).Density functional theory(DFT)calculations and statistical analyses highlight the influence of polarizability anisotropy,density,arrangement of units,as well as layer distance on birefringence.The results indicate that AMgGeSe_(3)(A=Li,Na)crystals are the promising IR birefringent materials and it gives an insight into the exploration of new IR birefringent materials with large birefringence based on the clamping effect from rigid groups.展开更多
基金the supports from the National Natural Science Foundation of China (61571156)Basic Research Project of Shenzhen (JCYJ20170413110004682 and JCYJ20150403161923521)。
文摘This work focuses on an unmanned aerial vehicle(UAV)-enabled mobile edge computing(MEC) system based on device-to-device(D2D) communication. In this system, the UAV exhibits caching,computing and relaying capabilities to periodically provide specific service to cellular users and D2D receiver nodes in the appointed time slot. Besides, the D2D transmitter can provide additional caching services to D2D receiver to reduce the pressure of the UAV. Note that communication between multi-type nodes is mutually restricted and different links share spectrum resources. To achieve an improved balance between different types of node, we aim to maximize the overall energy efficiency while satisfying the quality-of-service requirements of the cellular nodes.To address this problem, we propose an alternating iteration algorithm to jointly optimize the scheduling strategies of the user, transmitting power of the UAV and D2D-TX nodes, and UAV trajectory. The successive convex approximation, penalty function, and Dinkelbach method are employed to transform the original problem into a group of solvable subproblems and the convergence of the method is proved. Simulation results show that the proposed scheme performs better than other benchmark algorithms, particularly in terms of balancing the tradeoff between minimizing UAV energy consumption and maximizing throughput.
基金supported by the Project SEED Summer Research Program of the American Chemical Society
文摘A simple modification converts an electrospray ion source to an ambient-pressure helium plasma ionization source without the need of additional expensive hardware. Peaks for active ingredients were observed in the spectra recorded from intact pharmaceutical tablets placed in this source. A flow of heated nitrogen was used to thermally desorb analytes to gas phase. The desorption temperatures were sometimes as low as 50 ℃. For example, negative-ion spectra recorded from an aspirin tablet showed peaks at m/z 137 （salicylate anion） and 179 （acetylsalicylate anion） which were absent in the background spectra. The overall ion intensity increased as the desorption gas temperature was elevated. Within the same acquisition experiment, both positive- and negative-ion signals for acetaminophen were recorded from volatiles emanating from Tylenol tablets by switching the polarity of the capillary back and forth. Moreover, different preparations of acetaminophen tablets could be distinguished by their ion-intensity thermograms.
基金the National Natural Science Foundation of China,No.39700048, 30271378a grant from Education Bureau of Guangzhou,No.61092a grant from Science and Technology Department of Guangdong Province,No. 2009B030801354
文摘In the present study, olfactory ensheathing cells were transplanted into the cortices of infarcted （infarct transplantation group）, normal （normal transplantation group）, and bilateral hemispheres （bilateral transplantation group）. Olfactory ensheathing cells migrated to the infarct focus. The number of growth associated protein 43-positive cells and nerve fibers was slightly increased in the infarct area. These changes were more evident in the bilateral cortical transplantation group. Results demonstrated that transplanted olfactory ensheathing cells can migrate in rats with cerebra infarction. The olfactory ensheathing cells on the normal side can also promote neurological function. Bilateral cortical transplantation exhibited superior effects over unilateral transplantation.
基金This work was supported in part by the National Natural Science Foundation of China under Grants 61801145,61972113,61901138,and 61871426in part by the Shenzhen Science and Technology Program under Grants JCYJ20180306171800589,JCYJ20190806112215116,and KQTD 20190929172545139+2 种基金in part by the Natural Science Foundation of Guangdong Province under Grant 2018A030313298in part by the Guangdong Science and Technology Planning Project under Grant 2018B030322004in part by the Natural Scientific Research Innovation Foundation in Harbin Institute of Technology under Grant HIT.NSRIF.2020076.
文摘In the emerging sixth generation(6G)communication network,energy harvesting(EH)is a promising technology to achieve the unlimited energy supply and hence makes the wireless communication systems self-sustainable in terms of energy.However,in practice,the efficiency of energy harvesting is often low due to the limited device capability.In this paper,we formulate three types of different EH architectures,i.e.,the harvest-use architecture,the harvest-store-use architecture,and the harvest-use-store architecture from the perspective of energy storage efficiency.We propose resource allocation schemes to jointly design the sensor power and duty-cycle via an alternating optimization algorithm under the above EH architectures,in both simultaneous and non-simultaneous harvesting and utilization models,aiming at achieving a higher throughput and energy efficiency.Non-ideal circuit power is also considered.Numerical results show that our proposed schemes under EH architectures outperform the existing classic continuous transmission schemes.
基金This work was supported by the National Natural Science Foundation of China(81574068).
文摘Background:Moxibustion is a traditional Chinese medicine therapy to cure diseases by fumigating meridians or affected parts via burning of moxa floss.Moxa smoke(MS)is one of the key factors in moxibustion.In this study,we adopted digital gene expression profiling,a next-generation gene sequencing technology,to investigate the effect of MS,inhalable particulate matter(PM10),on human lung adenocarcinoma A549 cells.Methods:The effects of MS PM10 on A549 cells,over different treatment durations were investigated in different groups:the 4-h group(4-h MS group and 4-h control group)and the 20-h group(20-h MS group and 20-h control group).Samples collected from the four groups were stored at80C for subsequent digital gene expression analysis.The differentially expressed genes(DEGs),identified after PM10 treatment,were screened,and their expression patterns analyzed by cluster analysis,Gene Ontology term enrichment,and Kyoto Encyclopedia of Genes and Genomes pathway analysis.Results:Compared with two control groups,1109 DEGs were identified after 4 h of MS intervention and 3565 DEGs were found after 20 h of MS intervention,respectively.Compared with that after 4-h intervention,2149 DEGs were identified after 20-h intervention.Cluster analysis demonstrated that PM10 can significantly inhibit cell cycle process with the prolongation of intervention time.Significant pathway enrichment analysis showed that MS PM10 can inhibit A549 cell cycle process at all phases.When MS PM10 exposure time prolongs,the inhibitory effect on cell cycle process becomes more obvious.Conclusion:MS PM10 has many biological activities,and may cause differential expression of genes involved in various biological processes.Nevertheless,further research on MS is warranted for better understanding of the mechanistic details.
基金National Natural Science Foundation of China(Grant Nos.51872063,51832002 and 51621091)the Natural Science Foundation of Heilongjiang Province(Grant No.YQ2019E002)the National Key Research and Development Program of China(Grant No.2017YFB0703200)。
文摘Geopolymers are an important class of materials with potential applications because of their heat resistance,flame resistance,environmental friendliness,and possibilities of being transformed into ceramic matrix composites at low cost.However,the low mechanical properties as well as the intrinsic brittleness limit their technological implementations,and it is necessary to enhance the mechanical properties of geopolymers by adopting various kinds of reinforcements.In this work,therefore,two⁃dimensional continuous carbon fiber(Cf)reinforced phosphate⁃based geopolymer composites(Cf/geopolymer)were prepared through ultrasonic⁃assisted impregnation method.Effects of acetone treatment and high⁃temperature treatment on the properties of Cf/geopolymer composites were studied by X⁃ray photoelectron spectroscopy(XPS),X⁃ray diffraction(XRD),and scanning electron microscopy(SEM).Results of the study proved that acetone treatment plays a key role in ameliorating the interfacial interaction between Cf and phosphate matrix,which can thus enhance the mechanical properties of Cf/geopolymer composites.The Cf/geopolymer composites prepared by acetone⁃treated Cf had a flexural strength of 156.1 MPa and an elastic modulus of 39.7 GPa in Y direction.Moreover,an additional Sol⁃SiO2 re⁃impregnation treatment could further enhance the mechanical properties of the acetone⁃treated Cf/geopolymer composites by repairing the cracks and filling the pores.The results in this paper not only provide insights into the surface modification of Cf,but also report a facile and low⁃cost preparation route for Cf/geopolymer composites with potential applications in aerospace and defense technology.
文摘A novel composite ceramics with excellen mechanical and dielectric properties was fabricated by means of low temperature hot-pressing using mechanically alloyed SiBON powders as raw materials.The influences of SiO_2 content on phase microstructure,mechanical and dielectric properties of the SiBON ceramics were investigated.
文摘Here,we demonstrated a novel synthesis of a polyborosilazane(PBSN)precursor using hydroboration and aminolysis reaction synergies to modify polysilazane(PSN).Specifically,borane tetrahydrofuran and boron trichloride hexane were used as dual boron sources,which not only reacted
文摘The fully dense amorphous Si-B-C-N monoliths were fabricated at 1000°-1600°C under5 GPa for 30 min where the mechanically alloyed amorphous Si-B-C-N powders were used as raw material.Crystallization and microstructure evolution of the prepared ceramics were
文摘Because of the excellent mechanical and dielectric properties,Si BN ceramic was regarded as one of the best comprehensive performance thermal-insulation and wave-transparent material.We prepared amorphous Si BN powders by mechanical alloying using amorphous nano-Si3N4and h-BN
基金supported by Shanghai Cooperation Organization Science and Technology Partnership Program(2020E01039)the Scientific Instrument Developing Project,CAS(YJKYYQ20210033)+3 种基金CAS Youth Interdisciplinary Team(JCTD-2021–18)the West Light Foundation of CAS(2021-XBQNXZ-004)the Outstanding Youth Science Fund Project of Natural Science Foundation of Xinjiang(2022D01E90)Key Training Object of Talent Project of Urumqi。
文摘As a fundamental parameter of the optical crystals,birefringence plays a vital role in many optical applications,such as phase modulation,light splitting,and polarization,especially the phase matching process of the nonlinear optical crystals.The big birefringence not only benefits to the miniaturization of related devices,but also broadens the phase-matching wavelength range of nonlinear optical crystals.The design and synthesis of crystals with large birefringence becomes a hot research topic due to its more and more important applications in the optical modulation and laser technology fields.Herein,crystals with birefringence greater than 0.05 in the borate system are reviewed and classified according to different birefringent active groups,and the relationship between structure and properties is thoroughly explored.It is hoped that this review will provide a clear understanding of what kinds of building units and arrangements would have more opportunity to get adequate birefringence in borate systems and provide the statistical references to encourage the emergence of better crystal materials with large birefringence.
基金the National Natural Science Foundation of China(Nos.52372059,52172068,52232004,and 52002092)the Heilongjiang Natural Science Fund for Young Scholars(No.YQ2021E017)+3 种基金the Fundamental Research Funds for the Central Universities(No.2022FRFK060012)the Heilongjiang Touyan Team Program,and the Advanced Talents Scientific Research Foundation of Shenzhen:Yu Zhou.the Beijing Engineering Research Center of Efficient and Green Aerospace Propulsion Technology and Advanced Space Propulsion Laboratory of BICE(No.LabASP-2023-11)the Huiyan Action(No.1A423653)the Key Technologies R&D Program of CNBM(No.2023SJYL05).Ralf Riedel also gratefully acknowledges the financial support provided by the Research Training Group 2561“MatCom-ComMat:Materials Compounds from Composite Materials for Applications in Extreme Conditions”funded by the Deutsche Forschungsgemeinschaft(DFG),Bonn,Germany.
文摘To improve the oxidation resistance of short carbon fiber(C_(sf))-reinforced mechanically alloyed SiBCN(MA-SiBCN)(C_(sf)/MA-SiBCN)composites,dense amorphous C_(sf)/SiBCN composites containing both MA-SiBCN and polymer-derived ceramics SiBCN(PDCs-SiBCN)were prepared by repeated polymer infiltration and pyrolysis(PIP)of layered C_(sf)/MA-SiBCN composites at 1100℃,and the oxidation behavior and damage mechanism of the as-prepared C_(sf)/SiBCN at 1300–1600℃ were compared and discussed with those of C_(sf)/MA-SiBCN.The C_(sf)/MA-SiBCN composites resist oxidation attack up to 1400℃ but fail at 1500℃ due to the collapse of the porous framework,while the PIP-densified C_(sf)/SiBCN composites are resistant to static air up to 1600℃.During oxidation,oxygen diffuses through preexisting pores and the pores left by oxidation of carbon fibers and pyrolytic carbon(PyC)to the interior of the matrix.Owing to the oxidative coupling effect of the MA-SiBCN and PDCs-SiBCN matrices,a relatively continuous and dense oxide layer is formed on the sample surface,and the interfacial region between the oxide layer and the matrix of the as-prepared composite contains an amorphous glassy structure mainly consisting of Si and O and an incompletely oxidized but partially crystallized matrix,which is primarily responsible for improving the oxidation resistance.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.52372059,52172068,52232004,and 52002092)the Heilong Jiang Natural Science Fund for Young Scholars(No.YQ2021E017)+2 种基金the Fundamental Research Funds for the Central Universities(No.2022FRFK060012)the Heilongjiang Touyan Team Program,and the Advanced Talents Scientific Research Foundation of Shenzhen:Yu ZhouThis work was also funded by the Beijing Engineering Research Center of Efficient and Green Aerospace PropulsionTechnology and Advanced Space Propulsion Laboratory of Beijing Institute of Control Engineering(BICE)(No.LabASP-2023-11).
文摘In this study,a crack-free pyrolysis process of partially cured precursor powder compacts was developed to prepare dense silicon boron carbonitride(SiBCN)monoliths at much lower temperatures(1300℃),thereby circumventing the challenges of sintering densification(>1800℃).Unlike the elastic fracture in over-cured precursors or the viscoelastic deformation in under-cured precursors,the partially cured precursor,exhibiting elastic-plastic deformation behavior,facilitates limited nanoscale pore formation in a dense structure,achieving a balance between crack-free pyrolysis and densification.Compared to SiBCN derived from the over-cured precursor(σ=~159 MPa,K_(IC)=1.9 MPa:m^(1/2),Vickers hardness(HV)=7.8 GPa,and E=122 GPa),the resulting SiBCN monolith exhibited significantly improved mechanical properties(σ=~304 MPa,K_(IC)=3.7 MPa-m12,HV=10.6 GPa,and E=161 GPa)and oxidation resistance.In addition,this study investigated the high-temperature performance of SiBCN monoliths,including crystallization and oxidation,and determined the oxidation kinetics induced by pore structure healing and the different oxidation mechanisms of Si-C-N and B-C-N clusters in the amorphous structure.Due to its unique composition and structure,the SiBCN ceramic oxide layer exhibits exceptional self-healing effects on repairing the nanoporous system in the initial stage and shows outstanding high-temperature stability during prolonged oxidation,mitigating adverse effects from bubble formation and crystallization.Due to the nanoporous structure,the oxidation rate is initially controlled by gas diffusion following a linear law before transitioning to oxide layer diffusion characterized by a parabolic law.Finally,due to different valence bond configurations,Si-C-N transforms into an amorphous SiCNO structure after phase separation,unlike the nucleation and growth of residual B-N-C.
基金supported by the Natural Science Foundation of Xinjiang (2023D01E17)the National Natural Science Foundation of China (22335007)+2 种基金Tianshan Talents-Young Science and Technology Top Talents Project (2022TSYCCX0078 and 2022TSYCTD0005)Xinjiang Major Science and Technology Project (2021A01001 and2022A01005-5)the Key Research Program of Frontier Sciences,CAS(ZDBS-LY-SLH035)。
基金supported by the National Natural Science Foundation of China(Nos.52002092,51832002,and 52172071)the Program for Professor of Special Appointment(Eastern Scholar)at Shanghai Institutions of Higher Learning(No.GZ2020012)+1 种基金Heilongjiang Natural Science Fund for Young Scholars(No.YQ2021E017)the Heilongjiang Touyan Innovation Team Program.Ralf Riedel thanks the German Science Foundation(DFG,Bonn,Germany)for financial support within the graduate school GRK 2561.
文摘The atomic structural features and the mechanical properties of amorphous silicoboron carbonitride ceramics with 13 different compositions in the Si–BN–C phase diagram are investigated employing ab-initio calculations.Both chemical bonds and local structures within the amorphous network relate to the elemental composition.The distribution of nine types of chemical bonds is composition-dependent,where the B–C,Si–N,Si–C,and B–N bonds hold a large proportion for all compositions.Si prefers to be tetrahedrally coordinated,while B and N prefer sp^(2)-like trigonal coordination.In the case of C,the tetrahedral coordination is predominant at relatively low C contents,while the trigonal coordination is found to be the main feature with the increasing C content.Such local structural characteristics greatly influence the mechanical properties of SiBCN ceramics.Among the studied amorphous ceramics,SiB_(2)C_(3)N_(2) and SiB_(3)C_(2)N_(3) with low Si contents and moderate C and/or BN contents have high elastic moduli,high tensile/shear strengths,and good debonding capability.The increment of Si,C,and BN contents on this basis results in the decrease of mechanical properties.The increasing Si content leads to the increment of Si-contained bonds that reduce the bond strength of SiBCN ceramics,while the latter two cases are attributed to the raise of sp^(2)-like trigonal configuration of C and BN.These discoveries are expected to guide the composition-tailored optimization of SiBCN ceramics.
基金supported by the Key Laboratory Opening Foundation of Xinjiang Uygur Autonomous Region (2022D04013)the High-level Talent Project of Xinjiang Uygur Autonomous Region (2022D000039)+5 种基金the West Light Foundation of the Chinese Academy of Sciences (2019-YDYLTD-002)the National Natural Science Foundation of China (61835014 and 51972336)Xinjiang Major Science and Technology Project (2021A01001)the International Partnership Program of CAS (1A1365KYSB20200008)the Instrument Developing Project of CAS (GJJSTD20200007)the Science and Technology Service Network Initiative of CAS (KFJ-STS-QYZD-130).
基金This work was financially supported by the National Natu-ral Science Foundation of China(Nos.52002092,51832002,and 52172071)the Program for Professor of Special Appointment(East-ern Scholar)at Shanghai Institutions of Higher Learning(No.GZ2020012)+1 种基金Key Research Project of Zhejiang Laboratory(No.2021PE0AC02)Heilong Jiang Natural Science Fund for Young Scholars(No.YQ2021E017)。
文摘The atomic structural features and the mechanical properties of the Si_(2)BC_(3)N are investigated employ-ing ab-initio calculations.The chemical bonding types and their proportion are clarified.The tetrahedral and trigonal configurations,together with their nesting,are identified,which contribute to the flexibil-ity of structural characteristics.The Si-related coordination aggravates the inhomogeneous distribution of chemical bonding and weakens the tetrahedral units.The accompanying polyhedral distortion is quanti-tatively reflected by the bond length and its deviation of polyhedron units.The elastic moduli and the ideal strengths of Si_(2)BC_(3)N are found to be lower than SiC and Si_(3)N_(4),as a result of the weakening effect of coordination Si on tetrahedral units and the existence of easily distorted trigona.The balance between tetrahedral and trigonal features through composition tailor is believed an effective way for the design of Si-B-C-N ceramics for structural applications.
基金supported by the High-level Talent Project of Xinjiang Uygur Autonomous Region(2020000039)the National Natural Science Foundation of China(52002398,61835014,51972336)the Xinjiang Key Laboratory of Electronic Information Materials and Devices(2017D04029)。
文摘Infrared(IR)birefringent materials with large optical anisotropy and wide transparency range are important for efficient light manipulation in various IR optical devices.Herein,two new IR birefringent materials AMgGeSe_(3)(A=Li,Na)with large optical anisotropy were rationally designed by a rigid octahedron and flexible dimer combined strategy and fabricated in experiment.The introduction of rigid[LiSe_(6)]/[NaSe_(6)]and[MgSe_(6)]octahedra effectively regulates the geometry and arrangement of the flexible[Ge2Se6]dimers,resulting in the birefringence as large as 0.334@1,064 nm in LiMgGeSe_(3) and 0.445@1,064 nm(the largest one in the reported[Ge_(2)Se_(6)]dimer-contained selenides)in NaMgGeSe_(3).Density functional theory(DFT)calculations and statistical analyses highlight the influence of polarizability anisotropy,density,arrangement of units,as well as layer distance on birefringence.The results indicate that AMgGeSe_(3)(A=Li,Na)crystals are the promising IR birefringent materials and it gives an insight into the exploration of new IR birefringent materials with large birefringence based on the clamping effect from rigid groups.
基金financially supported by the National Natural Science Foundation of China(52002092,52172068,52232004)Heilongjiang Natural Science Fund for Young Scholars(YQ2021E017)+1 种基金Heilongjiang Touyan Team Program and Advanced Talents Scientific Research Foundation of Shenzhenthe financial support provided by the Research Training Group GRK 2561“Mat ComCom Mat:Materials Compounds from Composite Materials for Applications in Extreme Conditions”funded by the Deutsche Forschungsgemeinschaft(DFG),Bonn,Germany。
