1,281 research outputs found
Probing and controlling spin chirality in Mott insulators by circularly polarized laser
Scalar spin chirality, a three-body spin correlation that breaks
time-reversal symmetry, is revealed to couple directly to circularly polarized
laser. This is shown by the Floquet formalism for the periodically driven
repulsive Hubbard model with a strong-coupling expansion. A systematic
derivation of the effective low-energy Hamiltonian for a spin degree of freedom
reveals that the coupling constant for scalar spin chirality can become
significant for a situation in which the driving frequency and the on-site
interaction are comparable. This implies that the scalar chirality can be
induced by circularly polarized lights, or that it can be used conversely for
probing the chirality in Mott insulators as a circular dichroism.Comment: 10 pages, 8 figure
Emergent Weyl nodes and Fermi arcs in a Floquet Weyl semimetal
When a Dirac semimetal is subject to a circularly polarized laser, it is
predicted that the Dirac cone splits into two Weyl nodes and a nonequilibrium
transient state called the Floquet Weyl semimetal is realized. We focus on the
previously unexplored low-frequency regime, where the upper and lower Dirac
bands resonantly couple with each other through multi-photon processes, which
is a realistic situation in solid state ultrafast pump-probe experiments. We
find a series of new Weyl nodes emerging in pairs when the Floquet replica
bands hybridize with each other. The nature of the Floquet Weyl semimetal with
regard to the number, locations, and monopole charges of these Weyl nodes is
highly tunable with the amplitude and frequency of the light. We derive an
effective low energy theory using Brillouin-Wigner expansion and further
regularize the theory on a cubic lattice. The monopole charges obtained from
the low-energy Hamiltonian can be reconciled with the number of Fermi arcs on
the lattice which we find numerically.Comment: 4 pages, 5 figures + references + supplementary materia
Shock melting origin of a troilite-rich clast in the Moorabiechondrite (L3)
A troilite-rich clast enclosing chondrules was found in the Moorabie chondrite (L3). This chondrite is characterized by elongate morphology of chondrules produced by shock deformation. Average composition of the metal and troilite grains in the clast is close to the eutectic composition of the Fe-S system, indicating the melting origin of the clast. The eutectic composition provides the heating temperature to be around 1000℃. Size and distribution of troilite and metal grains in the clast suggest the slow cooling after the melting. Pentlandite as an exsolved phase of troilite in the clast, found first in ordinary chondrites, also supports the melting and slow cooling. Thermal history of the clast indicates that the melting of the opaque minerals and the elongate morphology of chondrules were caused inside the parent body by the shock event which occurred at an early hot stage (around 400℃) of the cooling after the accretion of the chondrite
Active Suppression of Chatter by Programed Variation of Spindle Speed
By a programed variation of the spindle speed of machine tools, it is possible to control the onset of regenerative-type self-excited chatter, which restricts the maximum depth of cut allowable in rough cutting operations. This paper presents a theoretical basis of this phenomenon, together with experimental proofs demonstrated in turning operations
Entorhinal–hippocampal neuronal circuits bridge temporally discontiguous events
The entorhinal cortex (EC)–hippocampal (HPC) network plays an essential role for episodic memory, which preserves spatial and temporal information about the occurrence of past events. Although there has been significant progress toward understanding the neural circuits underlying the spatial dimension of episodic memory, the relevant circuits subserving the temporal dimension are just beginning to be understood. In this review, we examine the evidence concerning the role of the EC in associating events separated by time—or temporal associative learning—with emphasis on the function of persistent activity in the medial entorhinal cortex layer III (MECIII) and their direct inputs into the CA1 region of HPC. We also discuss the unique role of Island cells in the medial entorhinal cortex layer II (MECII), which is a newly discovered direct feedforward inhibitory circuit to CA1. Finally, we relate the function of these entorhinal cortical circuits to recent findings concerning hippocampal time cells, which may collectively activate in sequence to bridge temporal gaps between discontiguous events in an episode.RIKEN Brain Science InstituteHoward Hughes Medical InstituteJPB Foundatio
A Rapporteur\u27s Summary : Research on Dengue Vaccine
Dengue virus is a member of flavivirus group. Diseases caused by flaviviruses have been a scourge of mankind for long history of human kind; with yellow fever at the top, followed by dengue fever, Japanese encephalitis (JE) and Russian spring-summer encephalitis (RSSE). Due to the dvevelopment of a safe and efficacious live-attenuated vaccine against yellow fever as a first laboratory-designed virus vaccine, this disease is no longer a threat in countries where adequate vaccination is practiced. Similarly, safe and efficacious inactivated vaccines against JE and tick-borne encephalitis (TBE) have also been developed, resulting in dramatical reduction in the disease incidences. In spite of these successes, the development of vaccines against other pathogenic flaviviruses, such as dengue fever and RSSE have not been successful. Control of dengue virus became rather urgent because of the emergence of new syndrome, dengue hemorrhagic fever (DHF), which causes high mortality among infants. The present review attempts to summarize the characteristics of dengue fever and DHF, common features of flavivirus infections as the basis vaccine development and recent advances and problems encountered in dengue vaccine research
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