The half metallic character in double perovskites makes them highly sought-after materials for the use in spintronics applications.Spintronic devices can operate at far higher speeds with less power consumption which ...The half metallic character in double perovskites makes them highly sought-after materials for the use in spintronics applications.Spintronic devices can operate at far higher speeds with less power consumption which has the potential to eventually replace traditional electronics.In this manuscript,we theoretically investigated the physical properties of europium based double perovskites Eu_(2)XWO_(6)(X=Mg,Zn).The volume optimization was done for both compounds,which demonstrate complete structural stability,while their thermodynamic stability is confirmed through the calculated formation energies.The mechanical properties reveal that both studied compounds fulfill the Born's stability criteria.The electronic properties of Eu_(2)MgWO_(6)and Eu_(2)ZnWO_(6)reveal that in spin up channel both materials exhibit metallic character,while in spin down channel,indirect band gaps of 4.11 and 3.97 eV are noticed for Eu_(2)MgWO_(6)and Eu_(2)ZnWO_(6),respectively,showing half-metallic behavior.The examination of the magnetic properties shows a significant magnetic moment of 14μ_(B)for Eu_(2)XWO_(6)(X=Mg,Zn).High optical conductivity and absorption are noticed in the UV region as shown by the optical traits of Eu_(2)XWO_(6)(X=Mg,Zn).Both materials show high magnetic moments,which leads to high spin polarization and are considered highly effective for the functioning of spintronic devices.展开更多
An enhanced neutron production and an enhanced nuclear destruction due to secondary fragments have been observed in very thick targets irradiated with high energy ions. This enhancement is beyond theoretical calculati...An enhanced neutron production and an enhanced nuclear destruction due to secondary fragments have been observed in very thick targets irradiated with high energy ions. This enhancement is beyond theoretical calculations and it is an unresolved problem. It is observed only when primary ion interactions exceed an energy threshold (ECM/u ≈ 150 MeV). Investigations using nuclear emulsions for very high-energy nuclear reactions suggest that two distinctly different classes of relativistic projectile-like fragments are emitted in primary interactions: a “cool” channel with a temperature of (T(p)cool ≈ 10 MeV), and a “hot” channel with (T(p)hot ≈ 40 MeV. This second reaction class may induce the above mentioned enhanced reactions of secondary fragments, thus being responsible for unresolved problems. This assumption should be studied in further experiments. Nuclear interactions of secondary particles in thick targets are of interest, in particular in view of radiation protection needs for high energy and high intensity heavy ion accelerators. Many basic ideas of this paper go back to the late Professor E. Schopper (Frankfurt).展开更多
Short-time dynamics and universality are investigated for the random-bond Potts model with a trinary distribu tion of quenched randomness on a two-dimensional triangular lattice. The universal power-law scaling behavi...Short-time dynamics and universality are investigated for the random-bond Potts model with a trinary distribu tion of quenched randomness on a two-dimensional triangular lattice. The universal power-law scaling behaviour is applied to estimate the exponents z and β/v. Emphasis is placed on dynamic Monte Carlo evolutions for different multi-disorder amplitudes. Our results indicate that the quenched impurities cause a change of the critical universality.展开更多
Based on the statistical model proposed by the Berliner group,including the assumption of cluster production and considering energy conservation for each fixed total multiplicity n,good fits to the data of the rapidit...Based on the statistical model proposed by the Berliner group,including the assumption of cluster production and considering energy conservation for each fixed total multiplicity n,good fits to the data of the rapidity distributions for different mutiplicity intervals are obtained.展开更多
We simulate ultra-cold interacting bosons in quasi-one-dimensional, incommensurate optical lattices. In the tight-binding limit, these lattices have pseudo-random on-site energies and thus can potentially lead to Ande...We simulate ultra-cold interacting bosons in quasi-one-dimensional, incommensurate optical lattices. In the tight-binding limit, these lattices have pseudo-random on-site energies and thus can potentially lead to Anderson localization. We use the Hartree-Fock-Bogoliubov formalism in the Bose-Hubbard model to explore the parameter regimes that lead to exponential localization of the ground state in a 3-colour optical lattice and investigate the role of repulsive interactions, harmonic confinement and finite temperature.展开更多
Following the idea of our previous paper we distinguish also in the case of Newtonian gravity as in the electrodynamics between extensive and intensive field quantities. Between both, a “material’’ quantity produce...Following the idea of our previous paper we distinguish also in the case of Newtonian gravity as in the electrodynamics between extensive and intensive field quantities. Between both, a “material’’ quantity produced e.g. by vacuum polarisations induced by the gravitational field strength itself is mediated. It acts in such a way that it amplifies the field strength in weak gravitational fields and reduces the field strength in strong gravitational fields following Lenz’s rule. Newton’s gravity is valid only in a very large intermediate range of middle field strength F?, F0? and F1?critical field strengths). In this way dark matter and black holes may be avoidable.展开更多
The transition to turbulence in flows where the laminar profile is linearly stable requires perturbations of finite amplitude. ＂Optimal＂ perturbations are distinguished as extrema of certain functionals, and differe...The transition to turbulence in flows where the laminar profile is linearly stable requires perturbations of finite amplitude. ＂Optimal＂ perturbations are distinguished as extrema of certain functionals, and different functionals give different optima. We here discuss the phase space structure of a 2D simplified model of the transition to turbulence and discuss optimal perturbations with respect to three criteria： energy of the initial condition, energy dissipation of the initial condition, and amplitude of noise in a stochastic transition. We find that the states triggering the transition are different in the three cases, but show the same scaling with Reynolds number.展开更多
A new approach to solving the observation of enhanced neutron production in high-energy heavy ion induced reactions in thick targets is presented. Two different reaction mechanisms in these interactions are considered...A new approach to solving the observation of enhanced neutron production in high-energy heavy ion induced reactions in thick targets is presented. Two different reaction mechanisms in these interactions are considered: 1) Limited fragmentation of the projectile, called SPALLATION;2) Complete nuclear fragmentation of the projectile fragment into individual relativistic hadrons only, referred to as “BURST”. The abundance of this second path increases with the charge and energy of the projectile and may be responsible for enhanced neutron production observed with radiochemical methods in 44 GeV 12C and 72 GeV 40Ar irradiations. Interactions of 72 GeV 22Ne in nuclear emulsions show that SPALLATION and BURST have strongly different interaction signatures, and also that the rate of BURSTS increases from (26 ± 3)% of all interactions in the 1st generation to (78 ± 6)% in the 2nd generation. Further experimental signatures of BURSTS will be described;however, no model based on physics concepts can be presented. This effect may have practical consequences for neutron safety considerations in the construction of advanced heavy ion accelerators.展开更多
We argue that in Universes where future and past differ only by the entropy content a psychological arrow of time pointing in the direction of entropy increase can arise from natural selection in biological evolution....We argue that in Universes where future and past differ only by the entropy content a psychological arrow of time pointing in the direction of entropy increase can arise from natural selection in biological evolution. We show that this effect can be demonstrated in very simple toy computer simulations of evolution in an entropy increasing or decreasing environment.展开更多
We use a diagrammatic hopping expansion to calculate finite-temperature Green functions of the Bose-Hubbard model which describes bosons in an optical lattice. This technique allows for a summation of subsets of diagr...We use a diagrammatic hopping expansion to calculate finite-temperature Green functions of the Bose-Hubbard model which describes bosons in an optical lattice. This technique allows for a summation of subsets of diagrams, so the divergence of the Green function leads to non-perturbative results for the boundary between the superfluid and the Mott phase for finite temperatures. Whereas the first-order calculation reproduces the seminal mean-field result, the second order goes beyond and shifts the phase boundary in the immediate vicinity of the critical parameters determined by high-precision Monte-Carlo simulations of the Bose-Hubbard model. In addition, our Green’s function approach allows for calculating the excitation spectrum both for zero and finite temperature and for determining the effective masses of particles and holes.展开更多
Starting with the nineties of the last century disc-shaped dielectric cavities have received a lot of attention because of their interest in the design of micro-lasers and integrated optics applications[1-5].The light...Starting with the nineties of the last century disc-shaped dielectric cavities have received a lot of attention because of their interest in the design of micro-lasers and integrated optics applications[1-5].The light can be trapped inside the dielectric cavity by total internal reflection,or can partly escape by refraction,depending on the angle of incidence with respect to the boundary.The emission patterns of circular cavities obviously are isotropic.Therefore,there had been efforts from the very beginning to design the shape of the cavity with the aim of obtaining preferentially unidirectional light emission patterns.展开更多
Integration of graphene in silicon-based micro-/nanoelectromechanical systems(MEMS/NEMS)marries the robustness of silicon-based materials with the exceptional physical properties of graphene,drastically enhancing the ...Integration of graphene in silicon-based micro-/nanoelectromechanical systems(MEMS/NEMS)marries the robustness of silicon-based materials with the exceptional physical properties of graphene,drastically enhancing the system’s regulation performance which now is key for many advanced applications in nanotechnology.Here,we experimentally demonstrate and theoretically analyze a powerful on-chip integration principle consisting of a hybrid graphene/silicon nitride membrane with metallic leads on top that enables an extremely large static and dynamic parameter regulation.When a static voltage is applied to the leads of the integrated structure,a spatially confined localized electrothermomechanical(ETM)effect results in ultra-wide frequency tuning,deformation(buckling transition)and regulation of the mechanical properties.Moreover,by injecting an alternating voltage to the leads,we can excite the resonator vibrating even far beyond its linear regime without a complex and space consuming actuation system.Our results prove that the scheme provides a compact integrated system possessing mechanical robustness,high controllability,and fast response.It not only expands the limit of the application range of MEMS/NEMS devices,but also enables the further miniaturization of the device.展开更多
基金financially supported by Ongoing Research Funding Program,(ORF-2025-445),King Saud University,Riyadh,Saudi Arabia。
文摘The half metallic character in double perovskites makes them highly sought-after materials for the use in spintronics applications.Spintronic devices can operate at far higher speeds with less power consumption which has the potential to eventually replace traditional electronics.In this manuscript,we theoretically investigated the physical properties of europium based double perovskites Eu_(2)XWO_(6)(X=Mg,Zn).The volume optimization was done for both compounds,which demonstrate complete structural stability,while their thermodynamic stability is confirmed through the calculated formation energies.The mechanical properties reveal that both studied compounds fulfill the Born's stability criteria.The electronic properties of Eu_(2)MgWO_(6)and Eu_(2)ZnWO_(6)reveal that in spin up channel both materials exhibit metallic character,while in spin down channel,indirect band gaps of 4.11 and 3.97 eV are noticed for Eu_(2)MgWO_(6)and Eu_(2)ZnWO_(6),respectively,showing half-metallic behavior.The examination of the magnetic properties shows a significant magnetic moment of 14μ_(B)for Eu_(2)XWO_(6)(X=Mg,Zn).High optical conductivity and absorption are noticed in the UV region as shown by the optical traits of Eu_(2)XWO_(6)(X=Mg,Zn).Both materials show high magnetic moments,which leads to high spin polarization and are considered highly effective for the functioning of spintronic devices.
文摘An enhanced neutron production and an enhanced nuclear destruction due to secondary fragments have been observed in very thick targets irradiated with high energy ions. This enhancement is beyond theoretical calculations and it is an unresolved problem. It is observed only when primary ion interactions exceed an energy threshold (ECM/u ≈ 150 MeV). Investigations using nuclear emulsions for very high-energy nuclear reactions suggest that two distinctly different classes of relativistic projectile-like fragments are emitted in primary interactions: a “cool” channel with a temperature of (T(p)cool ≈ 10 MeV), and a “hot” channel with (T(p)hot ≈ 40 MeV. This second reaction class may induce the above mentioned enhanced reactions of secondary fragments, thus being responsible for unresolved problems. This assumption should be studied in further experiments. Nuclear interactions of secondary particles in thick targets are of interest, in particular in view of radiation protection needs for high energy and high intensity heavy ion accelerators. Many basic ideas of this paper go back to the late Professor E. Schopper (Frankfurt).
基金Supported by the National Natural Science Foundation of China under Grant Nos.19975041 and 19631050。
文摘Short-time dynamics and universality are investigated for the random-bond Potts model with a trinary distribu tion of quenched randomness on a two-dimensional triangular lattice. The universal power-law scaling behaviour is applied to estimate the exponents z and β/v. Emphasis is placed on dynamic Monte Carlo evolutions for different multi-disorder amplitudes. Our results indicate that the quenched impurities cause a change of the critical universality.
基金This work was supported in part by Deutsche Forschungsgemeinschaft(Me470/5-1)Max-Planck Gesellschaft and the National Science Fundation of China。
文摘Based on the statistical model proposed by the Berliner group,including the assumption of cluster production and considering energy conservation for each fixed total multiplicity n,good fits to the data of the rapidity distributions for different mutiplicity intervals are obtained.
基金supported by contract SFB/TR 12 of the German Research Foundation and through the IB BMBF(Project NZL 07/006)by the New Zealand Foundation for Research,Science and Technology through contract NERF-UOOX0703:Quantum Technologies and the New Zealand International Science and Technology Linkages FundJT and DAWH also acknowledge support from the National Research Foundation and Ministry of Education of Singapor.
文摘We simulate ultra-cold interacting bosons in quasi-one-dimensional, incommensurate optical lattices. In the tight-binding limit, these lattices have pseudo-random on-site energies and thus can potentially lead to Anderson localization. We use the Hartree-Fock-Bogoliubov formalism in the Bose-Hubbard model to explore the parameter regimes that lead to exponential localization of the ground state in a 3-colour optical lattice and investigate the role of repulsive interactions, harmonic confinement and finite temperature.
文摘Following the idea of our previous paper we distinguish also in the case of Newtonian gravity as in the electrodynamics between extensive and intensive field quantities. Between both, a “material’’ quantity produced e.g. by vacuum polarisations induced by the gravitational field strength itself is mediated. It acts in such a way that it amplifies the field strength in weak gravitational fields and reduces the field strength in strong gravitational fields following Lenz’s rule. Newton’s gravity is valid only in a very large intermediate range of middle field strength F?, F0? and F1?critical field strengths). In this way dark matter and black holes may be avoidable.
基金supported in part by the German Research Foundation within FOR 1182
文摘The transition to turbulence in flows where the laminar profile is linearly stable requires perturbations of finite amplitude. ＂Optimal＂ perturbations are distinguished as extrema of certain functionals, and different functionals give different optima. We here discuss the phase space structure of a 2D simplified model of the transition to turbulence and discuss optimal perturbations with respect to three criteria： energy of the initial condition, energy dissipation of the initial condition, and amplitude of noise in a stochastic transition. We find that the states triggering the transition are different in the three cases, but show the same scaling with Reynolds number.
文摘A new approach to solving the observation of enhanced neutron production in high-energy heavy ion induced reactions in thick targets is presented. Two different reaction mechanisms in these interactions are considered: 1) Limited fragmentation of the projectile, called SPALLATION;2) Complete nuclear fragmentation of the projectile fragment into individual relativistic hadrons only, referred to as “BURST”. The abundance of this second path increases with the charge and energy of the projectile and may be responsible for enhanced neutron production observed with radiochemical methods in 44 GeV 12C and 72 GeV 40Ar irradiations. Interactions of 72 GeV 22Ne in nuclear emulsions show that SPALLATION and BURST have strongly different interaction signatures, and also that the rate of BURSTS increases from (26 ± 3)% of all interactions in the 1st generation to (78 ± 6)% in the 2nd generation. Further experimental signatures of BURSTS will be described;however, no model based on physics concepts can be presented. This effect may have practical consequences for neutron safety considerations in the construction of advanced heavy ion accelerators.
文摘We argue that in Universes where future and past differ only by the entropy content a psychological arrow of time pointing in the direction of entropy increase can arise from natural selection in biological evolution. We show that this effect can be demonstrated in very simple toy computer simulations of evolution in an entropy increasing or decreasing environment.
文摘We use a diagrammatic hopping expansion to calculate finite-temperature Green functions of the Bose-Hubbard model which describes bosons in an optical lattice. This technique allows for a summation of subsets of diagrams, so the divergence of the Green function leads to non-perturbative results for the boundary between the superfluid and the Mott phase for finite temperatures. Whereas the first-order calculation reproduces the seminal mean-field result, the second order goes beyond and shifts the phase boundary in the immediate vicinity of the critical parameters determined by high-precision Monte-Carlo simulations of the Bose-Hubbard model. In addition, our Green’s function approach allows for calculating the excitation spectrum both for zero and finite temperature and for determining the effective masses of particles and holes.
文摘Starting with the nineties of the last century disc-shaped dielectric cavities have received a lot of attention because of their interest in the design of micro-lasers and integrated optics applications[1-5].The light can be trapped inside the dielectric cavity by total internal reflection,or can partly escape by refraction,depending on the angle of incidence with respect to the boundary.The emission patterns of circular cavities obviously are isotropic.Therefore,there had been efforts from the very beginning to design the shape of the cavity with the aim of obtaining preferentially unidirectional light emission patterns.
基金financial support from the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)through Project-ID 425217212(SFB 1432)and project 510766045the major program in digital intelligence,Shapingba,Chongqing(Grant No.20240204)the Wisconsin Alumni Research Foundation(WARF)via the Accelerator Program.
文摘Integration of graphene in silicon-based micro-/nanoelectromechanical systems(MEMS/NEMS)marries the robustness of silicon-based materials with the exceptional physical properties of graphene,drastically enhancing the system’s regulation performance which now is key for many advanced applications in nanotechnology.Here,we experimentally demonstrate and theoretically analyze a powerful on-chip integration principle consisting of a hybrid graphene/silicon nitride membrane with metallic leads on top that enables an extremely large static and dynamic parameter regulation.When a static voltage is applied to the leads of the integrated structure,a spatially confined localized electrothermomechanical(ETM)effect results in ultra-wide frequency tuning,deformation(buckling transition)and regulation of the mechanical properties.Moreover,by injecting an alternating voltage to the leads,we can excite the resonator vibrating even far beyond its linear regime without a complex and space consuming actuation system.Our results prove that the scheme provides a compact integrated system possessing mechanical robustness,high controllability,and fast response.It not only expands the limit of the application range of MEMS/NEMS devices,but also enables the further miniaturization of the device.
