Pattern recognition algorithms are commonly utilized to discover certain patterns,particularly in image-based data.Our study focuses on quasiperiodic oscillations(QPO)in celestial objects referred to as cataclysmic va...Pattern recognition algorithms are commonly utilized to discover certain patterns,particularly in image-based data.Our study focuses on quasiperiodic oscillations(QPO)in celestial objects referred to as cataclysmic variables(CV).We are dealing with interestingly indistinct QPO signals,which we analyze using a power density spectrum(PDS).The confidence in detecting the latter using certain statistical approaches may come out with less significance than the truth.We work with real and simulated QPO data of a CV called MV Lyrae.Our primary statistical tool for determining confidence levels is sigma intervals.The aforementioned CV has scientifically proven QPO existence,but as indicated by our analysis,the QPO ended up falling below 1-σ,and such QPOs are not noteworthy based on the former approach.We intend to propose and ultimately train a convolutional neural network(CNN)using two types of QPO data with varying amounts of training dataset lengths.We aim to demonstrate the accuracy and viability of the classification using a CNN in comparison to sigma intervals.The resulting detection rate of our algorithm is very plausible,thus proving the effectiveness of CNNs in this scientific area.展开更多
To obtain new unconventional structures with specific mechanical and physical properties is possible not only by the development of new types of materials but also by treatment of conventional materials using unconven...To obtain new unconventional structures with specific mechanical and physical properties is possible not only by the development of new types of materials but also by treatment of conventional materials using unconventional innovative technological procedures.One of these technologies is the forming in semi-solid state involving rapid solidification of miniature components from steels.Production of such components is complicated by a number of technical problems.To explain phenomena of the process and structure development,the production of miniature components from the tool steel X210Cr12 difficult to form was experimentally tested.The structure of this originally ledeburite steel consisted of 95 % of metastable austenite after the treatment.Metastable austenite was located particularly in globular and polygonal grains while the remaining interspaces were filled by lamellar network.The detected high stability of extremely high fraction of metastable austenite was tested under different conditions of thermal exposition and mechanical loading.展开更多
Assembly is currently a very important element in the production process. We can also define it as the last stage in the production process. It greatly affects the quality of the product and especially the time needed...Assembly is currently a very important element in the production process. We can also define it as the last stage in the production process. It greatly affects the quality of the product and especially the time needed to make the final product. The presented article is a contribution to the improvement of methods in the field of technological design of the product in terms of assembly, resp. in the field of methodologies known as DFA, which in its entirety means Design of Assembly. The general objective of improving the assembly process is in most cases reducing the cost of the product. With the gradual development of the technologies coming into practice, companies are focusing mainly on improving the elements of assembled products of the assembly system. This state can be achieved, for example, by reducing the number of components, so the complexity and laboriousness of the assembly will be radically reduced. This in turn leads to a decrease in unit assembly costs. Proper assembly settings can help a company succeed in the competition and thus contribute to a stable position of the company in the market. The aim of the article is to find the other objective indicators of assembly quality evaluation.展开更多
NOx emissions cause many negative impacts on the living environment.The photocatalysis of semiconductors is superior for nitric oxide(NO)degradation due to their low redox potential.In this report,we combine SnO_(2-x)...NOx emissions cause many negative impacts on the living environment.The photocatalysis of semiconductors is superior for nitric oxide(NO)degradation due to their low redox potential.In this report,we combine SnO_(2-x)/g-C_(3)N_(4)heterojunction photocatalyst toward the high selectivity into green products under visible light illumination.Results show that SnO_(2-x)/g-C_(3)N_(4)heterojunction degraded 40.8%of NO,which is 1.6 times higher than that of g-C_(3)N_(4).In addition,the selectivity coefficient of SnO_(2-x)/g-C_(3)N_(4)is higher 3 times than both pure SnO_(2-x)and g-C_(3)N_(4).Furthermore,SnO_(2-x)/g-C_(3)N_(4)expresses a superior stability for NO photocatalytic-degradation after five cycles.The scavenger trapping test results,and electron spin resonance(ESR)analysis also provide more understanding of the charge transfer mechanism of materials.SnO_(2-x)/g-C_(3)N_(4)heterojunction shows a high removal efficiency of NO gas,making it an up-and-coming environmental treatment candidate.展开更多
Relations between the structure, ionic conductivity and dielectric properties of fluoride systems of different structures containing rare earth elements were presented. Superionic conductivities, by fluoride ions, of ...Relations between the structure, ionic conductivity and dielectric properties of fluoride systems of different structures containing rare earth elements were presented. Superionic conductivities, by fluoride ions, of fluorite-structured (MF2-REF3, M=Ba, Pb, RE=La-Lu, Sc, Y), orthorhombic (REF3, RE=Tb-Er, Y), tysonite-structured (REF3-MF2, RE=La-Nd, M=Sr), monoclinic (BaRE2Fs, RE=Ho-Yb, Y) fluoride single crystals and eutectic composites (LiF-REF3, RE=La-Gd, Y) were compared. Anisotropy of electrical properties of crystals with a lower symmetry was explained by modeling optimum ionic paths. For explanation of concentration dependences of fast ionic conductivity, models of aggregation of defects into clusters were proposed. In fluorite-structured crystals, the highest ionic conductivity was found for PbF2:7 mol% ScF3 (at 500 K, σ500=0.13 S/cm). In tysonite-structured crystals, the highest ionic conductivity was found for LaF3:3 mol% SrF2 (σ500=2.4×10^-2 S/cm). Different types of coordination polyhedrons and their different linking in orthorhombic and tysonite structure explained large differences between conductivities in both structures. Eutectic systems, prepared as directionally solidified composites, enabled to study some orthorhombic fluoride phases (GdF3, SmF3), which cannot be prepared as single crystals. An influence of the orthorhombic-tysonite phase transition on the ionic conductivity was shown.展开更多
Platinum diselenide(PtSe_(2))is a promising two-dimensional(2D)material for the terahertz(THz)range as,unlike other transition metal dichalcogenides(TMDs),its bandgap can be uniquely tuned from a semiconductor in the ...Platinum diselenide(PtSe_(2))is a promising two-dimensional(2D)material for the terahertz(THz)range as,unlike other transition metal dichalcogenides(TMDs),its bandgap can be uniquely tuned from a semiconductor in the nearinfrared to a semimetal with the number of atomic layers.This gives the material unique THz photonic properties that can be layer-engineered.Here,we demonstrate that a controlled THz nonlinearity—tuned from monolayer to bulk PtSe_(2)—can be realized in wafer size polycrystalline PtSe_(2)through the generation of ultrafast photocurrents and the engineering of the bandstructure valleys.This is combined with the PtSe_(2)layer interaction with the substrate for a broken material centrosymmetry,permitting a second order nonlinearity.Further,we show layer dependent circular dichroism,where the sign of the ultrafast currents and hence the phase of the emitted THz pulse can be controlled through the excitation of different bandstructure valleys.In particular,we show that a semimetal has a strong dichroism that is absent in the monolayer and few layer semiconducting limit.The microscopic origins of this TMD bandstructure engineering are highlighted through detailed DFT simulations,and shows the circular dichroism can be controlled when PtSe_(2)becomes a semimetal and when the K-valleys can be excited.As well as showing that PtSe_(2)is a promising material for THz generation through layer controlled optical nonlinearities,this work opens up a new class of circular dichroism materials beyond the monolayer limit that has been the case of traditional TMDs,and impacting a range of domains from THz valleytronics,THz spintronics to harmonic generation.展开更多
Conductivity s and thermal conductivity k are directly related to carrier concentration while Seebeck coefficient S is inversely proportional to carrier concentration.Therefore,improving thermoelectric(TE)performance ...Conductivity s and thermal conductivity k are directly related to carrier concentration while Seebeck coefficient S is inversely proportional to carrier concentration.Therefore,improving thermoelectric(TE)performance is challenging.Here,the first-time analysis of secondary phase-controlled TE performance in terms of density-of-state effective mass m*d,weighted mobility mw and quality factor B is discussed in ZnO system.The results show that the secondary spinel phase Ga2O_(3)(ZnO)9 not only impacts on k but also on s and S at high temperature,while the effect of carrier concentration seem to be dominant at low temperature.For the high-spinel-segregation sample,a compensation of dopant atoms from the spinel to substitutional sites in the ZnO matrix at high temperature leads to a low decreased rate of temperaturedependent m*d.The compensation process also induces a band sharpening,a small mw reduction,and a large B enhancement.As a result,In and Ga co-doped ZnO bulk with the highest spinel segregation achieves the greatest PF improvement by 112.8%,owing to enhanced Seebeck coefficient by 110%as compared to the good Zn-substitution sample.展开更多
The development of structural materials resistant to harsh radiation environments requires an in-depth understanding of the early stage of the aging processes.In radiation environments with high transmutation helium p...The development of structural materials resistant to harsh radiation environments requires an in-depth understanding of the early stage of the aging processes.In radiation environments with high transmutation helium production rates such as in fusion and spallation applications,even materials with otherwise acceptable radiation stability may suffer from radiation embrittlement related to helium bubble formation.While theoretical modeling of helium-assisted cavity nucleation in pure metals and simple alloys provides some useful guidelines at the atomic scale level,these,however,do not overlap with the size resolution of available experimental techniques.In this study,we employed slow positron beam spectroscopy to characterize the nucleation and growth of nano-scale helium bubbles in martensitic steels strengthened by thermodynamically stable nano-oxide dispersoids.In combination with transmission electron microscopy,we experimentally characterized the evolution of helium bubbles from small clusters of radiation-induced vacancies to large cavities well resolvable by TEM.Superior radiation resistance of oxide-dispersion strengthened steels dominates only in the early stages of bubble evolution,where positron lifetime measurements provide a missing piece of the microstructural puzzle conventionally constructed by TEM.展开更多
文摘Pattern recognition algorithms are commonly utilized to discover certain patterns,particularly in image-based data.Our study focuses on quasiperiodic oscillations(QPO)in celestial objects referred to as cataclysmic variables(CV).We are dealing with interestingly indistinct QPO signals,which we analyze using a power density spectrum(PDS).The confidence in detecting the latter using certain statistical approaches may come out with less significance than the truth.We work with real and simulated QPO data of a CV called MV Lyrae.Our primary statistical tool for determining confidence levels is sigma intervals.The aforementioned CV has scientifically proven QPO existence,but as indicated by our analysis,the QPO ended up falling below 1-σ,and such QPOs are not noteworthy based on the former approach.We intend to propose and ultimately train a convolutional neural network(CNN)using two types of QPO data with varying amounts of training dataset lengths.We aim to demonstrate the accuracy and viability of the classification using a CNN in comparison to sigma intervals.The resulting detection rate of our algorithm is very plausible,thus proving the effectiveness of CNNs in this scientific area.
基金the project 1M06032 Research Centre of Forming TechnologySlovak and Czech Project SK-CZ-0180-09
文摘To obtain new unconventional structures with specific mechanical and physical properties is possible not only by the development of new types of materials but also by treatment of conventional materials using unconventional innovative technological procedures.One of these technologies is the forming in semi-solid state involving rapid solidification of miniature components from steels.Production of such components is complicated by a number of technical problems.To explain phenomena of the process and structure development,the production of miniature components from the tool steel X210Cr12 difficult to form was experimentally tested.The structure of this originally ledeburite steel consisted of 95 % of metastable austenite after the treatment.Metastable austenite was located particularly in globular and polygonal grains while the remaining interspaces were filled by lamellar network.The detected high stability of extremely high fraction of metastable austenite was tested under different conditions of thermal exposition and mechanical loading.
文摘Assembly is currently a very important element in the production process. We can also define it as the last stage in the production process. It greatly affects the quality of the product and especially the time needed to make the final product. The presented article is a contribution to the improvement of methods in the field of technological design of the product in terms of assembly, resp. in the field of methodologies known as DFA, which in its entirety means Design of Assembly. The general objective of improving the assembly process is in most cases reducing the cost of the product. With the gradual development of the technologies coming into practice, companies are focusing mainly on improving the elements of assembled products of the assembly system. This state can be achieved, for example, by reducing the number of components, so the complexity and laboriousness of the assembly will be radically reduced. This in turn leads to a decrease in unit assembly costs. Proper assembly settings can help a company succeed in the competition and thus contribute to a stable position of the company in the market. The aim of the article is to find the other objective indicators of assembly quality evaluation.
基金funded by Vietnam National Foundation for Science and Technology Development(NAFOSTED)under grant number 103.02-2019.343.
文摘NOx emissions cause many negative impacts on the living environment.The photocatalysis of semiconductors is superior for nitric oxide(NO)degradation due to their low redox potential.In this report,we combine SnO_(2-x)/g-C_(3)N_(4)heterojunction photocatalyst toward the high selectivity into green products under visible light illumination.Results show that SnO_(2-x)/g-C_(3)N_(4)heterojunction degraded 40.8%of NO,which is 1.6 times higher than that of g-C_(3)N_(4).In addition,the selectivity coefficient of SnO_(2-x)/g-C_(3)N_(4)is higher 3 times than both pure SnO_(2-x)and g-C_(3)N_(4).Furthermore,SnO_(2-x)/g-C_(3)N_(4)expresses a superior stability for NO photocatalytic-degradation after five cycles.The scavenger trapping test results,and electron spin resonance(ESR)analysis also provide more understanding of the charge transfer mechanism of materials.SnO_(2-x)/g-C_(3)N_(4)heterojunction shows a high removal efficiency of NO gas,making it an up-and-coming environmental treatment candidate.
基金the Scientific Grant Agency VEGA, Slovak Republic (1/2100/05 and 1/0173/08)
文摘Relations between the structure, ionic conductivity and dielectric properties of fluoride systems of different structures containing rare earth elements were presented. Superionic conductivities, by fluoride ions, of fluorite-structured (MF2-REF3, M=Ba, Pb, RE=La-Lu, Sc, Y), orthorhombic (REF3, RE=Tb-Er, Y), tysonite-structured (REF3-MF2, RE=La-Nd, M=Sr), monoclinic (BaRE2Fs, RE=Ho-Yb, Y) fluoride single crystals and eutectic composites (LiF-REF3, RE=La-Gd, Y) were compared. Anisotropy of electrical properties of crystals with a lower symmetry was explained by modeling optimum ionic paths. For explanation of concentration dependences of fast ionic conductivity, models of aggregation of defects into clusters were proposed. In fluorite-structured crystals, the highest ionic conductivity was found for PbF2:7 mol% ScF3 (at 500 K, σ500=0.13 S/cm). In tysonite-structured crystals, the highest ionic conductivity was found for LaF3:3 mol% SrF2 (σ500=2.4×10^-2 S/cm). Different types of coordination polyhedrons and their different linking in orthorhombic and tysonite structure explained large differences between conductivities in both structures. Eutectic systems, prepared as directionally solidified composites, enabled to study some orthorhombic fluoride phases (GdF3, SmF3), which cannot be prepared as single crystals. An influence of the orthorhombic-tysonite phase transition on the ionic conductivity was shown.
基金H2020 Future and Emerging Technologies,Grant/Award Number:964735H2020 Excellent Science,Grant/Award Number:881603+3 种基金Agence Nationale de la Recherche,Grant/Award Numbers:ANR-16-CE24-0023,ANR-2018-CE08-018-05National Research Foundation Singapore,Grant/Award Number:NRF-CRP26-2021-0004Region Ile de FranceEquipMeso,Grant/Award Number:ANR-10-EQPX-29-01。
文摘Platinum diselenide(PtSe_(2))is a promising two-dimensional(2D)material for the terahertz(THz)range as,unlike other transition metal dichalcogenides(TMDs),its bandgap can be uniquely tuned from a semiconductor in the nearinfrared to a semimetal with the number of atomic layers.This gives the material unique THz photonic properties that can be layer-engineered.Here,we demonstrate that a controlled THz nonlinearity—tuned from monolayer to bulk PtSe_(2)—can be realized in wafer size polycrystalline PtSe_(2)through the generation of ultrafast photocurrents and the engineering of the bandstructure valleys.This is combined with the PtSe_(2)layer interaction with the substrate for a broken material centrosymmetry,permitting a second order nonlinearity.Further,we show layer dependent circular dichroism,where the sign of the ultrafast currents and hence the phase of the emitted THz pulse can be controlled through the excitation of different bandstructure valleys.In particular,we show that a semimetal has a strong dichroism that is absent in the monolayer and few layer semiconducting limit.The microscopic origins of this TMD bandstructure engineering are highlighted through detailed DFT simulations,and shows the circular dichroism can be controlled when PtSe_(2)becomes a semimetal and when the K-valleys can be excited.As well as showing that PtSe_(2)is a promising material for THz generation through layer controlled optical nonlinearities,this work opens up a new class of circular dichroism materials beyond the monolayer limit that has been the case of traditional TMDs,and impacting a range of domains from THz valleytronics,THz spintronics to harmonic generation.
基金supported by the Vietnam Ministry of Science and Technology under grant numberÐTÐL.CN-23/18.
文摘Conductivity s and thermal conductivity k are directly related to carrier concentration while Seebeck coefficient S is inversely proportional to carrier concentration.Therefore,improving thermoelectric(TE)performance is challenging.Here,the first-time analysis of secondary phase-controlled TE performance in terms of density-of-state effective mass m*d,weighted mobility mw and quality factor B is discussed in ZnO system.The results show that the secondary spinel phase Ga2O_(3)(ZnO)9 not only impacts on k but also on s and S at high temperature,while the effect of carrier concentration seem to be dominant at low temperature.For the high-spinel-segregation sample,a compensation of dopant atoms from the spinel to substitutional sites in the ZnO matrix at high temperature leads to a low decreased rate of temperaturedependent m*d.The compensation process also induces a band sharpening,a small mw reduction,and a large B enhancement.As a result,In and Ga co-doped ZnO bulk with the highest spinel segregation achieves the greatest PF improvement by 112.8%,owing to enhanced Seebeck coefficient by 110%as compared to the good Zn-substitution sample.
基金the contribution of the Slovak Research and Development Agency under the project APVV-20-0010financial contributions from the Scientifc Grant Agency of the Ministry of Education,Science,Research and Sport of the Slovak Republic and the Slovak Academy of Sciences,grant numbers VEGA 1/0382/20 and VEGA 1/0395/20the European Regional Development Fund project No.ITMS2014+:313011W085。
文摘The development of structural materials resistant to harsh radiation environments requires an in-depth understanding of the early stage of the aging processes.In radiation environments with high transmutation helium production rates such as in fusion and spallation applications,even materials with otherwise acceptable radiation stability may suffer from radiation embrittlement related to helium bubble formation.While theoretical modeling of helium-assisted cavity nucleation in pure metals and simple alloys provides some useful guidelines at the atomic scale level,these,however,do not overlap with the size resolution of available experimental techniques.In this study,we employed slow positron beam spectroscopy to characterize the nucleation and growth of nano-scale helium bubbles in martensitic steels strengthened by thermodynamically stable nano-oxide dispersoids.In combination with transmission electron microscopy,we experimentally characterized the evolution of helium bubbles from small clusters of radiation-induced vacancies to large cavities well resolvable by TEM.Superior radiation resistance of oxide-dispersion strengthened steels dominates only in the early stages of bubble evolution,where positron lifetime measurements provide a missing piece of the microstructural puzzle conventionally constructed by TEM.