Pricing dynamics and volatility are accelerating the adoption of global cryptocurrency.Despite challenges,cryptocurrencies such as Bitcoin are gaining widespread acceptance,particularly in countries with unbanked popu...Pricing dynamics and volatility are accelerating the adoption of global cryptocurrency.Despite challenges,cryptocurrencies such as Bitcoin are gaining widespread acceptance,particularly in countries with unbanked populations,the lack of bank controls,and inflation.This study investigates the global patterns of cryptocurrency adoption using Generalized Linear Models and Spatial Autoregressive Models.This research introduces a novel perspective on global cryptocurrency adoption using spatial models.Our findings reveal that cryptocurrency adoption is significantly influenced by economic instability,infrastructure availability,and spatial dynamics,with higher adoption rates in countries with limited access to traditional financial systems.展开更多
With the increased use of renewable energy sources,the need to store large amounts of energy will become increasingly important in the near future.A cost efficient possibility is to use the reaction of recycled Mg was...With the increased use of renewable energy sources,the need to store large amounts of energy will become increasingly important in the near future.A cost efficient possibility is to use the reaction of recycled Mg waste with hydrogen as thermo-chemical energy storage.Owing to the high reaction enthalpy,the moderate pressure and appropriate temperature conditions,the broad abundance and the recyclability,the Mg/Al alloy is perfectly suitable for this purpose.As further development of a previous work,in which the performance of recycled Mg/Al waste was presented,a kinetic model for hydro-and dehydrogenation is derived in this study.Temperature and pressure dependencies are determined,as well as the rate limiting step of the reaction.First experiments are carried out in an autoclave with a scaled-up powder mass,which is also used to validate the model by simulating the geometry with the scaled-up experiments at different conditions.展开更多
Because the U.S.is a major player in the international oil market,it is interesting to study whether aggregate and state-level economic conditions can predict the subse-quent realized volatility of oil price returns.T...Because the U.S.is a major player in the international oil market,it is interesting to study whether aggregate and state-level economic conditions can predict the subse-quent realized volatility of oil price returns.To address this research question,we frame our analysis in terms of variants of the popular heterogeneous autoregressive realized volatility(HAR-RV)model.To estimate the models,we use quantile-regression and quantile machine learning(Lasso)estimators.Our estimation results highlights the dif-ferential effects of economic conditions on the quantiles of the conditional distribution of realized volatility.Using weekly data for the period April 1987 to December 2021,we document evidence of predictability at a biweekly and monthly horizon.展开更多
Constrained Friction Processing(CFP)is a novel solid-state processing technique suitable for lightweight materials,such Mg-and Al-alloys.The technique enables grain size refinement to fine or even ultrafine scale.In t...Constrained Friction Processing(CFP)is a novel solid-state processing technique suitable for lightweight materials,such Mg-and Al-alloys.The technique enables grain size refinement to fine or even ultrafine scale.In this study,the effect of CFP on the microstructural refinement of AM50 rods is investigated in terms of particle size and morphology of the eutectic and secondary phases originally present in the base material,in particular the eutecticβ-Mg_(17)Al_(12)and Al-Mn phases.For that purpose,as-cast and solution heat-treated base material and processed samples were analyzed.The Al_(8)Mn_(5) intermetallic phase was identified as the main secondary phase present in all samples before and after the processing.A notorious refinement of these particles was observed,starting from particles with an average equivalent length of a few micrometers to around 560 nm after the processing.The refinement of the secondary phase refinement is attributed to a mechanism analogous to the attrition comminution,where the combination of temperature increase and shearing of the material enables the continuous breaking of the brittle intermetallic particles into smaller pieces.As for the eutectic phase,the results indicate the presence of the partially divorcedβ-Mg_(17)Al_(12)particles exclusively in the as-cast base material,indicating that no further phase transformations regarding the eutectic phase,such as dynamic precipitation,occurred after the CFP.In the case of the processed as-cast material analyzed after the CFP,the thermal energy generated during the processing led to temperature values above the solvus limit of the eutectic phase,which associated with the mechanical breakage of the particles,enabled the complete dissolution of this phase.Therefore,CFP was successfully demonstrated to promote an extensive microstructure refinement in multiple aspects,in terms of grain sizes of theα-Mg phase and presence and morphology of the Al-Mn and eutecticβ-Mg_(17)Al_(12).展开更多
The electrification of powertrains leads to an increasing diversification of powertrain configurations. Each single configuration has its specific advantages which appear depending on the usage profile. To find the us...The electrification of powertrains leads to an increasing diversification of powertrain configurations. Each single configuration has its specific advantages which appear depending on the usage profile. To find the usage based optimal powertrain in consideration of a variety of evaluation criteria, the powertrains have to be optimized for the usage profile and characteristics have to be extracted from the usage profile. The carbon dioxide emissions of the optimized powertrains and usage based criteria are used in a multi-criteria decision analysis to determine the optimal powertrain for a specific usage profile. The description of characteristic maps forms the objective function of a minimization problem. The determined carbon dioxide emissions are one criterion in a multi-criteria decision process. All considered criteria are at least partly objective so that subjective ratings are eliminated as far as possible. The result is an optimized powertrain for a desired usage under the consideration of objective criteria that are extracted from the usage profile.展开更多
Solid-state hydrides can reversibly absorb and desorb H_(2) under comparatively mild temperature and pressure conditions,making them promising candidates for H_(2) storage in renewable energy applications.The underlyi...Solid-state hydrides can reversibly absorb and desorb H_(2) under comparatively mild temperature and pressure conditions,making them promising candidates for H_(2) storage in renewable energy applications.The underlying gas-solid interactions are complex and involve multiple intermediary steps.Because they occur in series,by fitting experimental data employing several proposed models,it is possible to identify the rate-limiting step of the reaction,driving the development of new catalysts and the design of H_(2)-storage systems.The corresponding state-of-the-art method for model identification is the reduced-time method(RTM),which is time-consuming and often yields inconclusive results.To overcome these limitations and to facilitate automatization,this work proposes a framework with 12 unsupervised neural networks(NNs)which are trained using simulated curves from selected kinetic models.These networks are applied to a dataset of 144 experimental kinetic curves of an AB_(2) hydride-forming alloy as a blueprint material.Each NN attempts to reconstruct the input data,and the model with the lowest reconstruction loss is selected.The machine learning algorithm achieved a match of 97%and 91%for the absorption/desorption curves compared to the benchmark.Both reactions follow predominantly the Avrami-Erofeyev model with exponents(n)between 0.8 and 0.9.The kinetic constants(k)derived from the assigned model are used to simulate kinetic curves,showing excellent agreement with experimental data and RTM results.The proposed method provides an advantageous approach that can be applied to most gas-solid or even solid-solid reactions.展开更多
Turbulent reacting flows in a generic swirl gas turbine combustor model are investigated both numerically and experimentally.In the investigation,an emphasis is placed upon the external flue gas recirculation,which is...Turbulent reacting flows in a generic swirl gas turbine combustor model are investigated both numerically and experimentally.In the investigation,an emphasis is placed upon the external flue gas recirculation,which is a promising technology for increasing the efficiency of the carbon capture and storage process,which,however,can change the combustion behaviour significantly.A further emphasis is placed upon the investigation of alternative fuels such as biogas and syngas in comparison to the conventional natural gas.Flames are also investigated numerically using the open source CFD software OpenFOAM.In the numerical simulations,a laminar flamelet model based on mixture fraction and reaction progress variable is adopted.As turbulence model,the SST model is used within a URANS concept.Computational results are compared with the experimental data,where a fair agreement is observed.展开更多
The study is focussing towards Metal Injection Moulding (MIM) of Mg-alloys for biomedical implantapplications. Especially the influence of the sintering processing necessary for the consolidation of thefinished part i...The study is focussing towards Metal Injection Moulding (MIM) of Mg-alloys for biomedical implantapplications. Especially the influence of the sintering processing necessary for the consolidation of thefinished part is in focus of this study. In doing so, the chosen high strength EZK400 Mg-alloy powdermaterial was sintered using different sintering support bottom plate materials to evaluate the possibilityof iron impurity pick up during sintering. It can be shown that iron pick up took place from the steelbottom plate into the specimen. Despite the fact that a separating boron nitrite (BN) barrier layer wasused and the Mg-Fe phase diagram is not predicting any significant solubility to each other. As a result ofthis study a new bottom plate material not harming the sintering and the biodegradation performance ofthe as sintered material, namely a carbon plate material, was found.展开更多
Intense phase-locked terahertz(THz)pulses are the bedrock of THz lightwave electronics,where the carrier field creates a transient bias to control electrons on sub-cycle time scales.Key applications such as THz scanni...Intense phase-locked terahertz(THz)pulses are the bedrock of THz lightwave electronics,where the carrier field creates a transient bias to control electrons on sub-cycle time scales.Key applications such as THz scanning tunnelling microscopy or electronic devices operating at optical clock rates call for ultimately short,almost unipolar waveforms,at megahertz(MHz)repetition rates.Here,we present a flexible and scalable scheme for the generation of strong phase-locked THz pulses based on shift currents in type-ll-aligned epitaxial semiconductor heterostructures.The measured THz waveforms exhibit only 0.45 optical cycles at their centre frequency within the full width at half maximum of the intensity envelope,peak fields above 1.1 kVcm^(-1) and spectral components up to the mid-infrared,at a repetition rate of 4 MHz.The only positive half-cycle of this waveform exceeds all negative half-cycles by almost four times,which is unexpected from shift currents alone.Our detailed analysis reveals that local charging dynamics induces the pronounced positive THz-emission peak as electrons and holes approach charge neutrality after separation by the optical pump pulse,also enabling ultrabroadband operation.Our unipolar emitters mark a milestone for flexibly scalable,next-generation high-repetition-rate sources of intense and strongly asymmetric electric field transients.展开更多
The quantification of interphase properties between metals and their corresponding hydrides is crucial for modeling the thermodynamics and kinetics of the hydrogenation processes in solid-state hydrogen storage materi...The quantification of interphase properties between metals and their corresponding hydrides is crucial for modeling the thermodynamics and kinetics of the hydrogenation processes in solid-state hydrogen storage materials.In particular,interphase boundary energies assume a pivotal role in determining the kinetics of nucleation,growth,and coarsening of hydrides,alongside accompanying morphological evolution during hydrogenation.The total interphase energy arises from both chemical bonding and mechanical strains in these solid-state systems.Since these contributions are usually coupled,it is challenging to distinguish via conventional computational approaches.Here,a comprehensive atomistic modeling methodology is developed to decouple chemical and mechanical energy contributions using first-principles calculations,of which feasibility is demonstrated by quantifying chemical and elastic strain energies of key interfaces within the FeTi metal-hydride system.Derived materials parameters are then employed for mesoscopic micromechanical analysis,predicting crystallographic orientations in line with experimental observations.The multiscale approach outlined verifies the importance of the chemo-mechanical interplay in the morphological evolution of growing hydride phases,and can be generalized to investigate other systems.In addition,it can streamline the design of atomistic models for the quantitative evaluation of interphase properties between dissimilar phases and allow for efficient predictions of their preferred phase boundary orientations.展开更多
Measurements of the bunch arrival times at the European X-ray free-electron laser show noise contributions in the spectral range between 0.05 and 0.5 Hz with peak-to-peak jitter of up to 25 fs.Correlation with distrib...Measurements of the bunch arrival times at the European X-ray free-electron laser show noise contributions in the spectral range between 0.05 and 0.5 Hz with peak-to-peak jitter of up to 25 fs.Correlation with distributed acoustic sensing measurements confirms the seismic origin.The seismic noise in this frequency band is known to be oceangenerated microseism.Both primary and secondary ocean-generated microseisms were identified using seismometers and a numerical ocean wave model.Whereas secondary microseism has a strong impact on the bunch arrival time,primary microseism has no notable effect.Rayleigh waves cause the effect,while Love waves have minimal impact.In the presented cases,the noise originates from the North Atlantic and/or the North Sea.The amplitude of the noise depends on the local weather conditions and is much stronger in winter.Ocean-generated microseism is a significant bottleneck that must be addressed to achieve femtosecond bunch arrival time stability in the sub-Hz regime.展开更多
文摘Pricing dynamics and volatility are accelerating the adoption of global cryptocurrency.Despite challenges,cryptocurrencies such as Bitcoin are gaining widespread acceptance,particularly in countries with unbanked populations,the lack of bank controls,and inflation.This study investigates the global patterns of cryptocurrency adoption using Generalized Linear Models and Spatial Autoregressive Models.This research introduces a novel perspective on global cryptocurrency adoption using spatial models.Our findings reveal that cryptocurrency adoption is significantly influenced by economic instability,infrastructure availability,and spatial dynamics,with higher adoption rates in countries with limited access to traditional financial systems.
文摘With the increased use of renewable energy sources,the need to store large amounts of energy will become increasingly important in the near future.A cost efficient possibility is to use the reaction of recycled Mg waste with hydrogen as thermo-chemical energy storage.Owing to the high reaction enthalpy,the moderate pressure and appropriate temperature conditions,the broad abundance and the recyclability,the Mg/Al alloy is perfectly suitable for this purpose.As further development of a previous work,in which the performance of recycled Mg/Al waste was presented,a kinetic model for hydro-and dehydrogenation is derived in this study.Temperature and pressure dependencies are determined,as well as the rate limiting step of the reaction.First experiments are carried out in an autoclave with a scaled-up powder mass,which is also used to validate the model by simulating the geometry with the scaled-up experiments at different conditions.
文摘Because the U.S.is a major player in the international oil market,it is interesting to study whether aggregate and state-level economic conditions can predict the subse-quent realized volatility of oil price returns.To address this research question,we frame our analysis in terms of variants of the popular heterogeneous autoregressive realized volatility(HAR-RV)model.To estimate the models,we use quantile-regression and quantile machine learning(Lasso)estimators.Our estimation results highlights the dif-ferential effects of economic conditions on the quantiles of the conditional distribution of realized volatility.Using weekly data for the period April 1987 to December 2021,we document evidence of predictability at a biweekly and monthly horizon.
文摘Constrained Friction Processing(CFP)is a novel solid-state processing technique suitable for lightweight materials,such Mg-and Al-alloys.The technique enables grain size refinement to fine or even ultrafine scale.In this study,the effect of CFP on the microstructural refinement of AM50 rods is investigated in terms of particle size and morphology of the eutectic and secondary phases originally present in the base material,in particular the eutecticβ-Mg_(17)Al_(12)and Al-Mn phases.For that purpose,as-cast and solution heat-treated base material and processed samples were analyzed.The Al_(8)Mn_(5) intermetallic phase was identified as the main secondary phase present in all samples before and after the processing.A notorious refinement of these particles was observed,starting from particles with an average equivalent length of a few micrometers to around 560 nm after the processing.The refinement of the secondary phase refinement is attributed to a mechanism analogous to the attrition comminution,where the combination of temperature increase and shearing of the material enables the continuous breaking of the brittle intermetallic particles into smaller pieces.As for the eutectic phase,the results indicate the presence of the partially divorcedβ-Mg_(17)Al_(12)particles exclusively in the as-cast base material,indicating that no further phase transformations regarding the eutectic phase,such as dynamic precipitation,occurred after the CFP.In the case of the processed as-cast material analyzed after the CFP,the thermal energy generated during the processing led to temperature values above the solvus limit of the eutectic phase,which associated with the mechanical breakage of the particles,enabled the complete dissolution of this phase.Therefore,CFP was successfully demonstrated to promote an extensive microstructure refinement in multiple aspects,in terms of grain sizes of theα-Mg phase and presence and morphology of the Al-Mn and eutecticβ-Mg_(17)Al_(12).
文摘The electrification of powertrains leads to an increasing diversification of powertrain configurations. Each single configuration has its specific advantages which appear depending on the usage profile. To find the usage based optimal powertrain in consideration of a variety of evaluation criteria, the powertrains have to be optimized for the usage profile and characteristics have to be extracted from the usage profile. The carbon dioxide emissions of the optimized powertrains and usage based criteria are used in a multi-criteria decision analysis to determine the optimal powertrain for a specific usage profile. The description of characteristic maps forms the objective function of a minimization problem. The determined carbon dioxide emissions are one criterion in a multi-criteria decision process. All considered criteria are at least partly objective so that subjective ratings are eliminated as far as possible. The result is an optimized powertrain for a desired usage under the consideration of objective criteria that are extracted from the usage profile.
文摘Solid-state hydrides can reversibly absorb and desorb H_(2) under comparatively mild temperature and pressure conditions,making them promising candidates for H_(2) storage in renewable energy applications.The underlying gas-solid interactions are complex and involve multiple intermediary steps.Because they occur in series,by fitting experimental data employing several proposed models,it is possible to identify the rate-limiting step of the reaction,driving the development of new catalysts and the design of H_(2)-storage systems.The corresponding state-of-the-art method for model identification is the reduced-time method(RTM),which is time-consuming and often yields inconclusive results.To overcome these limitations and to facilitate automatization,this work proposes a framework with 12 unsupervised neural networks(NNs)which are trained using simulated curves from selected kinetic models.These networks are applied to a dataset of 144 experimental kinetic curves of an AB_(2) hydride-forming alloy as a blueprint material.Each NN attempts to reconstruct the input data,and the model with the lowest reconstruction loss is selected.The machine learning algorithm achieved a match of 97%and 91%for the absorption/desorption curves compared to the benchmark.Both reactions follow predominantly the Avrami-Erofeyev model with exponents(n)between 0.8 and 0.9.The kinetic constants(k)derived from the assigned model are used to simulate kinetic curves,showing excellent agreement with experimental data and RTM results.The proposed method provides an advantageous approach that can be applied to most gas-solid or even solid-solid reactions.
文摘Turbulent reacting flows in a generic swirl gas turbine combustor model are investigated both numerically and experimentally.In the investigation,an emphasis is placed upon the external flue gas recirculation,which is a promising technology for increasing the efficiency of the carbon capture and storage process,which,however,can change the combustion behaviour significantly.A further emphasis is placed upon the investigation of alternative fuels such as biogas and syngas in comparison to the conventional natural gas.Flames are also investigated numerically using the open source CFD software OpenFOAM.In the numerical simulations,a laminar flamelet model based on mixture fraction and reaction progress variable is adopted.As turbulence model,the SST model is used within a URANS concept.Computational results are compared with the experimental data,where a fair agreement is observed.
文摘The study is focussing towards Metal Injection Moulding (MIM) of Mg-alloys for biomedical implantapplications. Especially the influence of the sintering processing necessary for the consolidation of thefinished part is in focus of this study. In doing so, the chosen high strength EZK400 Mg-alloy powdermaterial was sintered using different sintering support bottom plate materials to evaluate the possibilityof iron impurity pick up during sintering. It can be shown that iron pick up took place from the steelbottom plate into the specimen. Despite the fact that a separating boron nitrite (BN) barrier layer wasused and the Mg-Fe phase diagram is not predicting any significant solubility to each other. As a result ofthis study a new bottom plate material not harming the sintering and the biodegradation performance ofthe as sintered material, namely a carbon plate material, was found.
基金We thank M.Furthmeier,I.Laepple and I.Gronwald for assistance.Financial support from the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)through Project ID 422314695032-SFB 1277(Subprojects A01 and B02)Project ID 223848855-SFB 1083(Subproject B2)as well as Research Grant HU1598/8 and Research Grant CH660/8 is acknowledgedThe work in Ann Arbor was supported by the W.M.Keck Foundation,and through NSF DMREF award#2118809.
文摘Intense phase-locked terahertz(THz)pulses are the bedrock of THz lightwave electronics,where the carrier field creates a transient bias to control electrons on sub-cycle time scales.Key applications such as THz scanning tunnelling microscopy or electronic devices operating at optical clock rates call for ultimately short,almost unipolar waveforms,at megahertz(MHz)repetition rates.Here,we present a flexible and scalable scheme for the generation of strong phase-locked THz pulses based on shift currents in type-ll-aligned epitaxial semiconductor heterostructures.The measured THz waveforms exhibit only 0.45 optical cycles at their centre frequency within the full width at half maximum of the intensity envelope,peak fields above 1.1 kVcm^(-1) and spectral components up to the mid-infrared,at a repetition rate of 4 MHz.The only positive half-cycle of this waveform exceeds all negative half-cycles by almost four times,which is unexpected from shift currents alone.Our detailed analysis reveals that local charging dynamics induces the pronounced positive THz-emission peak as electrons and holes approach charge neutrality after separation by the optical pump pulse,also enabling ultrabroadband operation.Our unipolar emitters mark a milestone for flexibly scalable,next-generation high-repetition-rate sources of intense and strongly asymmetric electric field transients.
基金This publication was made possible by the NZMat4H2Sto project,funded by the German Federal Ministry of Education and Research(BMBF)funded by the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)-506703280supported by the Hydrogen Storage Materials Advanced Research Consortium(HyMARC)of the U.S.Department of Energy(DOE),Office of Energy Efficiency and Renewable Energy,Hydrogen and Fuel Cell Technologies Office under Contract DE-AC52-07NA27344.
文摘The quantification of interphase properties between metals and their corresponding hydrides is crucial for modeling the thermodynamics and kinetics of the hydrogenation processes in solid-state hydrogen storage materials.In particular,interphase boundary energies assume a pivotal role in determining the kinetics of nucleation,growth,and coarsening of hydrides,alongside accompanying morphological evolution during hydrogenation.The total interphase energy arises from both chemical bonding and mechanical strains in these solid-state systems.Since these contributions are usually coupled,it is challenging to distinguish via conventional computational approaches.Here,a comprehensive atomistic modeling methodology is developed to decouple chemical and mechanical energy contributions using first-principles calculations,of which feasibility is demonstrated by quantifying chemical and elastic strain energies of key interfaces within the FeTi metal-hydride system.Derived materials parameters are then employed for mesoscopic micromechanical analysis,predicting crystallographic orientations in line with experimental observations.The multiscale approach outlined verifies the importance of the chemo-mechanical interplay in the morphological evolution of growing hydride phases,and can be generalized to investigate other systems.In addition,it can streamline the design of atomistic models for the quantitative evaluation of interphase properties between dissimilar phases and allow for efficient predictions of their preferred phase boundary orientations.
基金funding for the DAS Interrogator.Finally,Oliver Gerberding and Katharina-Sophie Isleif acknowledge support of the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)under Germany’s Excellence Strategy-EXC 2121‘Quantum Universe’-390833306.
文摘Measurements of the bunch arrival times at the European X-ray free-electron laser show noise contributions in the spectral range between 0.05 and 0.5 Hz with peak-to-peak jitter of up to 25 fs.Correlation with distributed acoustic sensing measurements confirms the seismic origin.The seismic noise in this frequency band is known to be oceangenerated microseism.Both primary and secondary ocean-generated microseisms were identified using seismometers and a numerical ocean wave model.Whereas secondary microseism has a strong impact on the bunch arrival time,primary microseism has no notable effect.Rayleigh waves cause the effect,while Love waves have minimal impact.In the presented cases,the noise originates from the North Atlantic and/or the North Sea.The amplitude of the noise depends on the local weather conditions and is much stronger in winter.Ocean-generated microseism is a significant bottleneck that must be addressed to achieve femtosecond bunch arrival time stability in the sub-Hz regime.
