Chiral pumping effect induced by rotating electric fields

We propose an experimental setup using 3D Dirac semimetals to access a novel phenomenon induced by the chiral anomaly. We show that the combination of a magnetic field and a circularly polarized laser induces a finite charge density with an accompanying axial current. This is because the circularly polarized laser breaks time-reversal symmetry and the Dirac point splits into two Weyl points, which results in an axial-vector field. We elucidate the appearance of the axial-vector field with the help of the Floquet theory by deriving an effective Hamiltonian for high-frequency electric fields. This anomalous charge density, i.e. the chiral pumping effect, is a phenomenon reminiscent of the chiral magnetic effect with a chiral chemical potential. We explicitly compute the pumped density and the axial-current expectation value. We also take account of coupling to the chiral magnetic effect to calculate a balanced distribution of charge and chirality in a material that behaves as a chiral battery.Comment: 6 pages, 3 figures; a new section added to discuss coupling of the CPE and the CME, a wrong sign corrected, typos fixed, elaborated for better readabilit

How do auroral substorms depend on Earth's dipole magnetic moment?

Earth's dipole magnetic moment M is known to decrease by ∼9% over the past 150 years. It has been argued that the decrease in M makes the near-Earth space environment different. We investigated how the change in M affects the development of an auroral substorm by increasing and decreasing M by a factor of 1.5 in global magnetohydrodynamics simulation. The ionospheric conductivity decreases with increasing M, in accordance with the aid of empirical relations. When we imposed the southward interplanetary magnetic field, an auroral substorm took place regardless of M, but its development depends largely on M. When M is lower, (1) the expansion onset takes place later, (2) the auroral electrojet develops slowly, and (3) the maximum auroral electrojet increases. The first two consequences are probably associated with the slow magnetospheric convection as manifested by the polar cap potential drop. The third consequence is associated with the nonlinear dependence of substorm-associated field-aligned currents (FACs) on the ionospheric conductivity. The maximum values of the westward auroral electrojet and the net FACs increase with decreasing M, whereas the incident magnetic energy into the magnetosphere decreases with decreasing M. This implies that the efficiency of the generation of the substorm-associated FACs increases with decreasing M. It is also found that, for the lower M-value, the auroral oval shifts equatorward during the growth phase and expands more equatorward and poleward during the expansion phase. Evolution of substorms depends largely on the value of Earth's dipole moment and the ionospheric conductivity

Generation of Field-Aligned Currents During Substorm Expansion: An Update

We investigated generation processes of field-aligned currents (FACs) that are abruptly intensified at the beginning of the substorm expansion phase by tracing a packet of the Alfvén wave backward in time from the onset position in the ionosphere in the global magnetohydrodynamics (MHD) simulation. The generation region is found in the near-Earth plasma sheet, in which (a) azimuthally moving plasma pulls the magnetic field line, and performs negative work against the magnetic tension force to excite the Alfvén waves, (b) FACs are generated from the requirement of Ampère and Faraday laws, and (c) field-perpendicular current is converted to FACs. We call this near-Earth FAC dynamo. The plasma involved originates in the tail lobe region. When near-Earth reconnection occurs in the plasma sheet, the plasma is accelerated earthward by the Lorentz force, and decelerated by the plasma pressure gradient force, followed by the Lorentz force. The flow is deflected to the west and east directions by the plasma pressure gradient force and the Lorentz force, resulting in the excitation of Alfvén waves and FACs. The Alfvén waves propagate along the magnetic field in the rest frame of the moving plasma. When it arrives at the ionosphere, the auroral electrojet starts developing and the substorm expansion phase begins. The near-Earth FAC dynamo can be distinguished from the near-Earth dynamo (J · E < 0, where J is the current density and E is the electric field). We suggest that the evolution of the substorm can be understood in terms of the development of FACs

Evolution of auroral substorm as viewed from MHD simulations: dynamics, energy transfer and energy conversion

An auroral substorm is a visual manifestation of large-scale, transient disturbances taking place in space surrounding the Earth, and is one of the central issues in the space plasma physics. While a number of studies have been conducted, a unified picture of the overall evolution of the auroral substorm has not been drawn. This paper is aimed to overview the recently obtained results of global magnetohydrodynamics (MHD) simulations in a context of a priori presence of anomalous resistivity leading to magnetic reconnection, and to illuminate what the global MHD simulation can sufficiently reproduce the auroral transients during the auroral substorm. Some auroral transients are found to be seamlessly reproduced by the MHD simulation, including complicated auroral structures moving equatorward during the growth phase, auroral brightening starting to appear near the equatorward border of the preexisting auroral arc, and an auroral surge traveling westward. Possible energy transfer and conversion from the solar wind to the Earth are also overviewed on the basis of the MHD simulation. At least, 4 dynamo regions appear sequentially in the course of the development of the auroral substorm. Although the MHD simulation reproduces some transients, further studies are needed to investigate the role of kinetic processes

Dichotomous Regulation of Acquired Immunity by Innate Lymphoid Cells

The concept of innate lymphoid cells (ILCs) includes both conventional natural killer (NK) cells and helper ILCs, which resemble CD8+ killer T cells and CD4+ helper T cells in acquired immunity, respectively. Conventional NK cells are migratory cytotoxic cells that find tumor cells or cells infected with microbes. Helper ILCs are localized at peripheral tissue and are responsible for innate helper-cytokine production. Helper ILCs are classified into three subpopulations: TH1-like ILC1s, TH2-like ILC2s, and TH17/TH22-like ILC3s. Because of the functional similarities between ILCs and T cells, ILCs can serve as an innate component that augments each corresponding type of acquired immunity. However, the physiological functions of ILCs are more plastic and complicated than expected and are a ected by environmental cues and types of inflammation. Here, we review recent advances in understanding the interaction between ILCs and acquired immunity, including T- and B-cell responses at various conditions. Immune suppressive activities by ILCs in particular are discussed in comparison to their immune stimulatory e ects to gain precise knowledge of ILC biology and the physiological relevance of ILCs in human diseases

The Use Of Lasers For Direct Pulp Capping

Direct pulp capping helps extend the life of a diseased tooth by maintaining tooth vitality. Nowadays, lasers are more frequently used during direct pulp capping in the clinic, but their use has not been previously reviewed. This review presents the basic properties of currently available lasers, scientific evidence on the effects of laser application on direct pulp capping, and future directions for this technology. An extensive literature search was conducted in various databases for articles published up to January 2015. Original in vitro, in vivo, and clinical studies, reviews, and book chapters published in English were included. Various laser systems have been increasingly and successfully applied in direct pulp capping. Lasers offer excellent characteristics in terms of hemostasis and decontamination for field preparation during direct pulp capping treatment; however, the sealing of exposed pulp with one of the dental materials, such as calcium hydroxide, mineral trioxide aggregates, and bonded composite resins, is still required after laser treatment. Clinicians should consider the characteristics of each wavelength, the emission mode, irradiation exposure time, power, type of laser tip, and the distance between the laser tip and the surface being irradiated

Energy Flow in the Region 2 Field‐Aligned Current Region Under Quasi‐steady Convection

We investigated energy flow in the inner magnetosphere on the basis of the results obtained by a global magnetohydrodynamic simulation. When the magnetosphere is exposed to a southward interplanetary magnetic field, the magnetosphere undergoes quasi-steady convection. Downward (earthward) Poynting flux is found in the polar cap, which is consistent with previous observations. However, Poynting flux appears to be upward (antiearthward) in the equatorward region of the auroral oval. The Region 2 field-aligned current (FAC) is embedded in the upward Poynting flux region. The upward Poynting flux is closely associated with space charge deposited by the ionospheric Hall current under inhomogeneous ionospheric conductivity. The space charge gives rise to shear flow of plasma, which is transmitted upward to the magnetosphere. The shear flow generates additional Region 2 FAC, at least, in the low-altitude magnetosphere. Spatial distribution of the Region 2 FAC appears to depend on altitude, suggesting the significant influence of the ionosphere in the Region 2 FAC region. We traced integral curves of Poynting flux (S curves) backward from a magnetic field line in the Region 2 FAC region and found that the S curves originate either in the solar wind and in the earthward-most boundary of the simulation. These simulation results suggest that the ionosphere participates in the generation of the Region 2 FAC, and the ionosphere is a mediator to feed energy to the inner magnetosphere under the quasi-steady convection

Transcription Factors in the Development and Function of Group 2 Innate Lymphoid Cells

Group 2 innate lymphoid cells (ILC2s) are tissue-resident cells and are a major source of innate TH2 cytokine secretion upon allergen exposure or parasitic-worm infection. Accumulating studies have revealed that transcription factors, including GATA-3, Bcl11b, Gfi1, ROR , and Ets-1, play a role in ILC2 differentiation. Recent reports have further revealed that the characteristics and functions of ILC2 are influenced by the physiological state of the tissues. Specifically, the type of inflammation strongly affects the ILC2 phenotype in tissues. Inhibitory ILC2s, memory-like ILC2s, and ex-ILC2s with ILC1 features acquire their characteristic properties following exposure to their specific inflammatory environment. We have recently reported a new ILC2 population, designated as exhausted-like ILC2s, which emerges after a severe allergic inflammation. Exhausted-like ILC2s are featured with low reactivity and high expression of inhibitory receptors. Therefore, for a more comprehensive understanding of ILC2 function and differentiation, we review the recent knowledge of transcriptional regulation of ILC2 differentiation and discuss the roles of the Runx transcription factor in controlling the emergence of exhausted-like ILC2s. The concept of exhausted-like ILC2s sheds a light on a new aspect of ILC2 biology in allergic diseases

Formation of Electron Zebra Stripes Observed on 8 September 2017

Zebra stripes are the characteristic structures having repeated hills and valleys in the electron flux intensities observed below L = 3. We delineate the fundamental properties and evolution of electron zebra stripes by modeling advection using time-dependent electric fields provided by a global magnetohydrodynamics simulation. At the beginning of the simulation, the electrons were uniformly distributed in longitude. Some electrons moved inward due to enhanced westward electric field transients in the premidnight-postdawn region. The inwardly displaced electrons were confined in a narrow longitudinal range and underwent grad-B and curvature drifts. For any specific fixed position, the electrons periodically passed through the point with an energy dependent period, giving rise to the hills and valleys in the electron differential flux also known as zebra stripes. The valleys of the zebra stripes are composed of the electrons that underwent outward displacement, or no significant radial displacement. On the nightside, the duskside convection cell is skewed toward dawn in the equatorward of the auroral oval, and the westward electric field becomes dominant in the postdawn region, which results in the inward motion of the electrons. The spatial distribution of the westward electric field is consistent with observation. Zebra stripes are a mixture of the electrons that have and have not experienced inward transport due to solar wind-inner magnetosphere coupling by way of the ionosphere