31 research outputs found
All-optical switching at the two-photon limit with interference-localized states
We propose a single-photon-by-single-photon all-optical switch concept based
on interference-localized states on lattices and their delocalization by
interaction. In its 'open' operation, the switch stops single photons while
allows photon pairs to pass the switch. Alternatively, in the 'closed'
operation, the switch geometrically separates single-photon and two-photon
states. We demonstrate the concept using a three-site Stub unit cell and the
diamond chain. The systems are modeled by Bose-Hubbard Hamiltonians, and the
dynamics is solved by exact diagonalization with Lindblad master equation. We
discuss realization of the switch using photonic lattices with nonlinearities,
superconductive qubit arrays, and ultracold atoms. We show that the switch
allows arbitrary 'ON'/'OFF' contrast while achieving picosecond switching time
at the single-photon switching energy with contemporary photonic materials
Flat band transport and Josephson effect through a finite-size sawtooth lattice
We study theoretically the transport through a finite-size sawtooth lattice
coupled to two fermionic reservoirs kept in the superfluid state. We focus on
the DC Josephson effect and find that the flat band states of the sawtooth
lattice can support larger critical current and at higher temperature than the
dispersive band states. However, for this to occur the boundary states of the
finite-size lattice need to be tuned at resonance with the bulk flat band
states by means of additional boundary potentials. We show that transport in a
two-terminal configuration can reveal the salient features of the geometric
contribution of flat band superconductivity, namely the linear dependence of
key quantities, such as the critical current and critical temperature, on the
interaction. Our results are based on parameters of a realistic experimental
lattice potential, and we discuss the conditions one needs to reach to observe
the predicted effects experimentally.Comment: 11 pages, 5 figure
Computational NMR of the iron pyrazolylborate complexes [Tp₂Fe]⁺ and Tp₂Fe including solvation and spin-crossover effects
Abstract
Transition metal complexes have important roles in many biological processes as well as applications in fields such as pharmacy, chemistry and materials science. Paramagnetic nuclear magnetic resonance (pNMR) is a valuable tool in understanding such molecules, and theoretical computations are often advantageous or even necessary in the assignment of experimental pNMR signals. We have employed density functional theory (DFT) and the domain-based local pair natural orbital coupled-cluster method with single and double excitations (DLPNO-CCSD), as well as a number of model improvements, to determine the critical hyperfine part of the chemical shifts of the iron pyrazolylborate complexes [Tp₂Fe]⁺ and Tp₂Fe using a modern version of the Kurland–McGarvey theory, which is based on parameterising the hyperfine, electronic Zeeman and zero-field splitting interactions via the parameters of the electron paramagnetic resonance Hamiltonian. In the doublet [Tp₂Fe]⁺ system, the calculations suggest a re-assignment of the ¹³C signal shifts. Consideration of solvent via the conductor-like polarisable continuum model (C-PCM) versus explicit solvent molecules reveals C-PCM alone to be insufficient in capturing the most important solvation effects. Tp₂Fe exhibits a spin-crossover effect between a high-spin quintet (S = 2) and a low-spin singlet (S = 0) state, and its recorded temperature dependence can only be reproduced theoretically by accounting for the thermal Boltzmann distribution of the open-shell excited state and the closed-shell ground-state occupations. In these two cases, DLPNO-CCSD is found, in calculating the hyperfine couplings, to be a viable alternative to DFT, the demonstrated shortcomings of which have been a significant issue in the development of computational pNMR
The Effect of Contact with Conspecifics and Humans on Calves' Behaviour and stress responses
v2003okMTT maatalousteknologian tutkimus (Vakola
Semi-automatic optimization of steel heat treatments for achieving desired microstructure
Abstract
The thermo-mechanical processing history together with the steel composition defines the final microstructure, which in turn produces the macroscopic mechanical properties of the final product. In many industrial processes it is therefore of paramount importance to find the optimal thermal path that produces the desired microstructure. In the current study an optimization method has been developed to calculate the optimal thermal path for producing desired amounts of microstructural constituents (ferrite, bainite, martensite) of a medium carbon, low-alloy steel, and a low carbon microalloyed steel. The optimization is performed for two separate industrial processes: induction hardening of a pipeline steel and a water cooling of hot rolled steel strip. The optimization workflow consists of first setting the desired amounts of microstructural constituents, and subsequent optimization of the thermal path, which produces these desired amounts. For the water cooling of a steel strip we additionally employed previously developed tool to calculate the cooling water fluxes that are needed to realize the optimized cooling path in water cooling line after hot rolling. To demonstrate the applicability of the method, we present results that were obtained for different case studies related to the industrial processes
Flat-band transport and Josephson effect through a finite-size sawtooth lattice
ISSN:1098-0121ISSN:0163-1829ISSN:1550-235XISSN:0556-2805ISSN:2469-9969ISSN:1095-379
Paramagnetic pyrazolylborate complexes Tp₂M and Tp*₂M: ¹H, ¹³C, ¹¹B, and ¹⁴N NMR spectra and first-principles studies of chemical shifts
Abstract
The paramagnetic pyrazolylborates Tp₂M and Tp*₂M (M = Cu, Ni, Co, Fe, Mn, Cr, V) as well as [Tp₂M]+ and [Tp*₂M]+ (M = Fe, Cr, V) have been synthesized and their NMR spectra recorded. The ¹H signal shift ranges vary from ∼30 ppm (Cu(II) and V(III)) to ∼220 ppm (Co(II)), and the ¹³C signal shift ranges from ∼180 ppm (Fe(III)) to ∼1150 ppm (Cr(II)). The ¹¹B and ¹⁴N shifts are ∼360 and ∼730 ppm, respectively. Both negative and positive shifts have been observed for all nuclei. The narrow NMR signals of the Co(II), Fe(II), Fe(III), and V(III) derivatives provide resolved ¹³C,¹H couplings. All chemical shifts have been calculated from first-principles on a modern version of Kurland–McGarvey theory which includes optimized structures, zero-field splitting, and g tensors, as well as signal shift contributions. Temperature dependence in the Fe(II) spin-crossover complex results from the equilibrium of the ground singlet and the excited quintet. We illustrate both the assignment and analysis capabilities, as well as the shortcomings of the current computational methodology