Natural convection plays a key role in fluid dynamics owing to its ubiquitous presence in nature and industry. Buoyancy-driven flows are prototypical systems in the study of thermal instabilities and pattern formation...
Natural convection plays a key role in fluid dynamics owing to its ubiquitous presence in nature and industry. Buoyancy-driven flows are prototypical systems in the study of thermal instabilities and pattern formation. The differentially-heated cavity problem has been widely studied for the investigation of buoyancy-induced oscillatory flow. However, far less attention has been devoted to the three-dimensional Lagrangian transport properties in such flows. This study seeks to address this by investigating Lagrangian transport in the steady flow inside differentially-heated cavities. The theoretical and numerical analysis expands on previously reported similarities between the current flow and lid-driven flows. First results reveal that the convective terms in the momentum and energy balances cause non-trivial (and potentially chaotic) Lagrangian transport.
We describe the results of first-principles calculations of the properties of oxygen vacancies in LaNiO3. We consider isolated oxygen vacancies, pairs of vacancies, and vacancies at finite concentrations that form oxy...
详细信息
We describe the results of first-principles calculations of the properties of oxygen vacancies in LaNiO3. We consider isolated oxygen vacancies, pairs of vacancies, and vacancies at finite concentrations that form oxygen-deficient phases of LaNiO3. The key electronic structure question we address is whether and to what extent an oxygen vacancy acts as an electron donor to the Fermi level (mobile and conducting electronic states). More generally, we describe how one can quantify, based on electronic structure calculations, the extent to which a localized point defect in a metallic system donates electrons to the Fermi level compared to trapping electrons in localized defect states. For LaNiO3, we find that an oxygen vacancy does not create mobile carriers but instead makes the two Ni sites adjacent to it turn into Ni2+ cations. Energetically, we compute the formation energy and diffusion barrier for oxygen vacancies. Structurally, we show that pairs of vacancies prefer to form on opposite sides of a Ni cation, aligning along a pseudocubic axis. For finite concentrations of vacancies, we compute the dependence of the LaNiO3 lattice parameters on the vacancy concentration to provide reliable data for experimental determination of the oxygen content in LaNiO3 and LaNiO3 thin films.
In a pressure-temperature (P−T) diagram for synthesizing IrTe2 compounds, the well-studied trigonal (H) phase with the CdI2-type structure is stable at low pressures. The superconducting cubic (C) phase can be synthes...
详细信息
In a pressure-temperature (P−T) diagram for synthesizing IrTe2 compounds, the well-studied trigonal (H) phase with the CdI2-type structure is stable at low pressures. The superconducting cubic (C) phase can be synthesized under higher temperatures and pressures. A rhombohedral phase with the crystal structure similar to the C phase can be made at ambient pressure; but the phase contains a high concentration of Ir deficiency. In this paper we report that a rarely studied monoclinic (M) phase can be stabilized in narrow ranges of pressure and temperature in this P−T diagram. The peculiar crystal structure of the M−IrTe2 eliminates the tendency to form Ir-Ir dimers found in the H phase. The M phase has been fully characterized by structural determination and measurements of electrical resistivity, thermoelectric power, DC magnetization, and specific heat. These physical properties have been compared with those in the H and C phases of Ir1−xTe2. Moreover, magnetic and transport properties and specific heat of the M−IrTe2 can be fully justified by calculations with the density-functional theory presented in this paper.
This paper shows a limitation of signal-to-noise ratio (SNR) for amplitude-bounded noise in control of linear discrete-time systems over channels with feedback. The SNR allowed in stabilizing the closed-loop system is...
详细信息
ISBN:
(纸本)9781479977970
This paper shows a limitation of signal-to-noise ratio (SNR) for amplitude-bounded noise in control of linear discrete-time systems over channels with feedback. The SNR allowed in stabilizing the closed-loop system is shown to depend on the product of unstable poles of the plant. The control law for minimizing the SNR is constructed from state-feedback controller and two observers employed in the data transmission and reception processes. The gain applied to the data to be transmitted is determined from the solution of a Riccati equation in minimum energy control depending on the observer gain. Moreover, we can observe in the case of SISO plants that lack of feedback for communication does not degrade the SNR limitation when the feedback for control is available in communication.
The crystal structure, phase transition, and magnetocaloric effect in Ni42.8Mn40.3Co5.7Sn11.2 alloy are investigated by structure analysis and magnetic measurements. A large magnetic entropy change of 45.6 J/kg.K is o...
详细信息
The crystal structure, phase transition, and magnetocaloric effect in Ni42.8Mn40.3Co5.7Sn11.2 alloy are investigated by structure analysis and magnetic measurements. A large magnetic entropy change of 45.6 J/kg.K is obtained at 215 K under a magnetic field of 30 kOe （1 Oe = 79.5775 A.m-1）. The effective refrigerant capacity of Ni42.8Mn40.3Co5.7Sn11.2 alloy reaches 72.1 J/kg under an applied field changing from 0 to 30 kOe. The external magnetic field shifts the martensitic transition temperature about 3-4 K/10 kOe towards low temperature, indicating that magnetic field can retard the phase transition to a certain extent. The origin of large magnetic entropy change is discussed in the paper.
Here we demonstrate an experimental observation of GHz-scale spin dynamics resolved to sublattice octahedral (Oh) tetrahedral (Td) sites in a spinel ferrimagnet, in this case a Mn-ferrite thin film. X-ray absorption s...
详细信息
Here we demonstrate an experimental observation of GHz-scale spin dynamics resolved to sublattice octahedral (Oh) tetrahedral (Td) sites in a spinel ferrimagnet, in this case a Mn-ferrite thin film. X-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) are used, in combination with multiplet calculations, to uniquely identify the spectral signature from Mn2+ and Fe2+,3+ on Oh and Td lattice sites. With the sample under rf excitation, the spin alignment of the sublattices is tracked with time-resolved XMCD (TR-XMCD). The spin alignment of the sublattices is mostly antiferromagnetic. The phase difference between the Oh Fe2+ [Oh Fe3+] and Td Mn2+ sites is 181.2±3.8∘ [183.3∘±3.7∘] at 150 K and 186.6±2.2∘ [182.0∘±2.2∘] at 300 K. Such direct measurement of the dynamic coupling, exchange stiffness, and damping enabled by TR-XMCD across sublattices will be essential for optimizing the development of future-generation microwave devices.
This work presents an improved approach for multi-objective and multi-physics optimization based on the hierarchical optimization approach of the typical MOCO ("Multi-objective Collaborative Optimization") w...
详细信息
暂无评论