170 research outputs found
Size effect of Ruderman-Kittel-Kasuya-Yosida interaction mediated by electrons in nanoribbons
We calculated the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between
the magnetic impurities mediated by electrons in nanoribbons. It was shown that
the RKKY interaction is strongly dependent on the width of the nanoribbon and
the transverse positions of the impurities. The transverse confinement of
electrons is responsible for the above size effect of the RKKY interaction. It
provides a potential way to control the RKKY interaction by changing
nanostructure geometry
Ferromagnetism in diluted magnetic semiconductor quantum dot arrays embedded in semiconductors
We present an Anderson-type model Hamiltonian with exchange coupling between
the localized spins and the confined holes in the quantum dots to study the
ferromagnetism in diluted magnetic semiconductor (DMS) quantum dot arrays
embedded in semiconductors. The hybridization between the quantum-confined
holes in the DMS quantum dots and the itinerant holes in the semiconductor
valence band makes hole transfer between quantum dots, which can induce the
long range ferromagnetic order of the localized spins. In addition, it makes
the carrier spins both in the DMS quantum dots and in the semiconductors
polarized. The spontaneous magnetization of the localized spins and the spin
polarization of the holes are calculated using both the Weiss mean field
approximation and the self-consistent spin wave approximation, which are
developed for the present model.Comment: 6 pages, 6 figure
Gene regulatory networks controlling temporal patterning, neurogenesis, and cell-fate specification in mammalian retina
Gene regulatory networks (GRNs), consisting of transcription factors and their target sites, control neurogenesis and cell-fate specification in the developing central nervous system. In this study, we use integrated single-cell RNA and single-cell ATAC sequencing (scATAC-seq) analysis in developing mouse and human retina to identify multiple interconnected, evolutionarily conserved GRNs composed of cell-type-specific transcription factors that both activate genes within their own network and inhibit genes in other networks. These GRNs control temporal patterning in primary progenitors, regulate transition from primary to neurogenic progenitors, and drive specification of each major retinal cell type. We confirm that NFI transcription factors selectively activate expression of genes promoting late-stage temporal identity in primary retinal progenitors and identify other transcription factors that regulate rod photoreceptor specification in postnatal retina. This study inventories cis- and trans-acting factors that control retinal development and can guide cell-based therapies aimed at replacing retinal neurons lost to disease
Tunneling magnetoresistance in diluted magnetic semiconductor tunnel junctions
Using the spin-polarized tunneling model and taking into account the basic
physics of ferromagnetic semiconductors, we study the temperature dependence of
the tunneling magnetoresistance (TMR) in the diluted magnetic semiconductor
(DMS) trilayer heterostructure system (Ga,Mn)As/AlAs/(Ga,Mn)As. The
experimentally observed TMR ratio is in reasonable agreement with our result
based on the typical material parameters. It is also shown that the TMR ratio
has a strong dependence on both the itinerant-carrier density and the magnetic
ion density in the DMS electrodes. This can provide a potential way to achieve
larger TMR ratio by optimally adjusting the material parameters.Comment: 5 pages (RevTex), 3 figures (eps), submitted to PR
A fast implicit difference scheme for solving the generalized time-space fractional diffusion equations with variable coefficients
In this paper, we first propose an unconditionally stable implicit difference
scheme for solving generalized time-space fractional diffusion equations
(GTSFDEs) with variable coefficients. The numerical scheme utilizes the
-type formula for the generalized Caputo fractional derivative in time
discretization and the second-order weighted and shifted Gr\"{u}nwald
difference (WSGD) formula in spatial discretization, respectively. Theoretical
results and numerical tests are conducted to verify the -order
and 2-order of temporal and spatial convergence with the order
of Caputo fractional derivative, respectively. The fast sum-of-exponential
approximation of the generalized Caputo fractional derivative and Toeplitz-like
coefficient matrices are also developed to accelerate the proposed implicit
difference scheme. Numerical experiments show the effectiveness of the proposed
numerical scheme and its good potential for large-scale simulation of GTSFDEs.Comment: 23 pages, 10 tables, 1 figure. Make several corrections again and
have been submitted to a journal at Sept. 20, 2019. Version 2: Make some
necessary corrections and symbols, 13 Jan. 2020. Revised manuscript has been
resubmitted to journa
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