76 research outputs found
Dynamics of nonequilibrium magnons in gapped Heisenberg antiferromagnets
Nonequilibrium dynamics in spin systems is a topic currently under intense
investigation as it provides fundamental insights into thermalization,
universality, and exotic transport phenomena. While most of the studies have
been focused on ideal closed quantum many-body systems such as ultracold atomic
quantum gases and one-dimensional spin chains, driven-dissipative Bose gases in
steady states away from equilibrium in classical systems also lead to
intriguing nonequilibrium physics. In this work, we theoretically investigate
out-of-equilibrium dynamics of magnons in a gapped Heisenberg quantum
antiferromagnet based on Boltzmann transport theory. We show that, by treating
scattering terms beyond the relaxation time approximation in the Boltzmann
transport equation, energy and particle number conservation mandate that
nonequilibrium magnons cannot relax to equilibrium, but decay to other
nonequilibrium stationary states, partially containing information about the
initial states. The only decay channel for these stationary states back to
equilibrium is through the non-conserving interactions such as boundary or
magnon-phonon scattering. At low temperatures, these non-conserving
interactions are much slower processes than intrinsic magnon-magnon interaction
in a gapped spin system. Using magnon-phonon interaction as a quintessential
type of non-conserving interaction, we then propose that nonequilibrium steady
states of magnons can be maintained and tailored using periodic driving at
frequencies faster than relaxation due to phonon interactions. These findings
reveal a class of classical material systems that are suitable platforms to
study nonequilibrium statistical physics and macroscopic phenomena such as
classical Bose-Einstein condensation of quasiparticles and magnon supercurrents
that are relevant for spintronic applications
ab initio informed inelastic neutron scattering for time-resolved local dynamics in molten MgCl2
Ion dynamics that drive the transport and thermophysical properties of molten
salts are poorly understood due to challenges in precisely quantifying the
spatial and temporal fluctuations of specific ions in highly disordered
systems. While the Van Hove correlation function (VHF) obtained from inelastic
neutron scattering (INS) probes these dynamics directly, its interpretation is
limited by the inherent species-averaging of experiments, which obscures
analysis of key ion transport and solvation mechanisms. Here, ab initio
molecular dynamics (AIMD) is used to model the VHF, unravel its partial
contributions, and elucidate its underlying ionic transport mechanisms. Slow
decorrelation is revealed for oppositely charged ions (Mg2+ and Cl-) caused by
ion exchange across the solvation shell between adjoining ionocovalent
complexes. Furthermore, transport coefficients are accurately recovered and
connections between macroscopic properties and ion dynamics are revealed. This
study demonstrates the potential of ab initio-informed VHF to resolve
long-standing challenges in uncovering relationships between picosecond-scale
ion dynamics, mechanisms, and emergent physical properties of molten salts
pH-resistant Inhibitor of Mitochondrial ADP/ATP Carrier
Bongkrekic acid (BKA), isolated from Burkholderia cocovenenans, is known to specifically inhibit the mitochondrial ADP/ATP carrier. However, the manner of its interaction with the carrier remains elusive. In the present study, we tested the inhibitory effects of 17 bongkrekic acid analogues, derived from the intermediates obtained during its total synthesis, on the mitochondrial ATP/ATP carrier. Rough screening of these chemicals, done by measuring their inhibitory effects on the mitochondrial ATP synthesis, revealed that 4 of them, KH-1, 7, 16, and 17, had moderate inhibitory effects. Further characterization of the actions of these 4 analogues on mitochondrial function showed that KH-16 had moderate; KH-1 and KH-17, weak; and KH-7, negligible side effects of both permeabilization of the mitochondrial inner membrane and inhibition of the electron transport, indicating that only KH-7 had a specific inhibitory effect on the mitochondrial ADP/ATP carrier. Although the parental bongkrekic acid showed a strong pH dependency of its action, the inhibitory effect of KH-7 was almost insensitive to the pH of the reaction medium, indicating the importance of the 3 carboxyl groups of BKA for its pH- dependent action. A direct inhibitory effect of KH-7 on the mitochondrial ADP/ATP carrier was also clearly demonstrated
Photochemical OFF/ON Cytotoxicity Switching by Using a Photochromic Surfactant with Visible Light Irradiation
Photochemical switching of cytotoxicity by using spiropyran compounds with pyridinium and alkyl groups was investigated. The spiropyran compound, SP6, with a hexyl group as the alkyl group displayed negative photochromism, in which the hydrophilic open merocyanine form (MC form) was stable and isomerized to the hydrophobic closed spiro form (SP form) by visible light irradiation. Both MC and SP forms exhibited amphiphilicity because of the hydrophobic hexyl and hydrophilic pyridinium groups introduced. Cytotoxicity toward HeLa cells was observed for both MC and SP forms of SP6 at concentrations higher than the critical aggregation concentration of the isomers CACMC and CACSP (CACMC > CACSP), respectively. In contrast, cytotoxicity by SP6 was activated by visible light irradiation at concentrations between CACMC and CACSP; thus, photochemical switching of cytotoxicity from the OFF to ON state was achieved. Cytotoxicity was revealed to be caused by disruption of the cell membrane. The results provide an important step in developing novel next-generation photochemotherapy drugs
The liquid-liquid transition and its order parameter
この論文は国立情報学研究所の電子図書館事業により電子化されました。研究会報告我々はTriphenyl Phosphite(TPP)およびnormal butanolという分子性液体において液体・液体相転移を発見した。そのキネティクスを顕微鏡、熱量測定を用いた調べた結果、核形成・成長型(NG-type)相転移とスピノーダル分解型(SD-type)相転移の2種類の相転移過程があることがわかった。スピノーダル分解型相転移を詳細に調べた結果、液体・液体相転移を支配する秩序変数は非保存系であることがわかった。そこで、Photon Factory(PF)において放射光X線回折実験を行い、液体・液体相転移中における液体のミクロスコピックな変化を調べた。その結果、液体・液体相転移の秩序変数は局所安定構造の数密度であることが示唆された
Atomic real-space perspective of light-field-driven currents in graphene
When graphene is exposed to a strong few-cycle optical field, a directional electric current can be induced depending on the carrier-envelope phase of the field. This phenomenon has successfully been explained by the charge dynamics in reciprocal space, namely an asymmetry in the conduction band population left after the laser excitation. However, the corresponding real-space perspective has not been explored so far although it could yield knowledge about the atomic origin of the macroscopic currents. In this work, by adapting the nearest-neighbor tight-binding model including overlap integrals and the semiconductor Bloch equation, we reveal the spatial distributions of the light-field-driven currents on the atomic scale and show how they are related to the light-induced changes of charge densities. The atomic-scale currents flow dominantly through the network of the π bonds and are the strongest at the bonds parallel to the field polarization, where an increase of the charge density is observed. The real-space maps of the currents and changes in charge densities are elucidated using simple symmetries connecting real and reciprocal space. We also discuss the strong-field-driven Rabi oscillations appearing in the atomic-scale charge densities. This work highlights the importance of real-space measurements and stimulates future time-resolved atomic-scale experimental studies with high-energy electrons or x-rays, for examples
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