Satoshi Hiura

A pair of transposons coordinately suppresses gene expression, independent of pathways mediated by siRNA in Antirrhinum

Our knowledge is limited regarding mechanisms by which transposable elements control host gene expression. Two Antirrhinum lines, HAM2 and HAM5, show different petal colors, pale-red and white, respectively, although these lines contain the same insertion of transposon Tam3 in the promoter region of the nivea (niv) locus encoding chalcone synthase. Among 1000 progeny from HAM5 grown under the preferred conditions for the Tam3 transposition, a few showed an intermediate petal color between HAM2 and HAM5. Transposon tagging using these progeny identified a causative insertion of Tam3 for the HAM5 type (white) petal color, which was found 1.6 kb downstream of the niv gene. Insertion of Tam3 at the position 1.6 kb downstream of niv alone showed nearly wildtype petal pigmentation, and the niv expression reduced by only 50%. Severe suppression of niv observed in HAM5 required interaction of two Tam3 copies on either side of the niv coding sequence. DNA methylation and small interfering RNAs (siRNAs) were not associated with the suppression of niv expression in HAM5. Insertion of a pair of transposons in close proximity can interfere with the expression of gene located between the two copies, and also provide evidence that this interference is not directly associated with pathways mediated by siRNAs.

Correlation between OH density and Fe electronic states of H/Fe3O4(001) film surfaces studied by scanning tunneling microscopy/spectroscopy

We report two types of adsorption structures in H/Fe3O4(001) film surfaces and the correlation between OH density and Fe electronic states, which have been studied by scanning tunneling microscopy/spectroscopy (STM/STS). Two types of bright protrusions (BPs), whose lengths along the atomic rows are different, are observed in the STM images. The shorter and longer BPs consist of Fe atoms with one and with two OH groups neighbor, respectively. In addition, STS measurements show the higher local density of states (LDOS) just below the Fermi level of Fe atoms with increasing neighboring OH groups. The variation can be attributed to the difference in the gain of electrons from H atoms, which is due to the difference in the number of neighboring OH groups. These results reveal that surface OH density is a factor for determining the LDOS just below the Fermi level of surface Fe atoms.

Atomically Resolved Observations of Antiphase Domain Boundaries in Epitaxial Fe3O4 Films on MgO(001) by Scanning Tunneling Microscopy

We have studied the surface atomic configurations around antiphase domain boundaries (APBs) in epitaxial magnetite (Fe3O4) thin films on MgO(001) by scanning tunneling microscopy (STM). The observed surface of the Fe3O4 films is the B-plane terminating surface with the (√2×√2)R45° reconstruction. Several variations of APBs are observed by STM at atomic resolution. The observed APBs are categorized into a APBs labeled by three different phase shift vectors: in-plane 1/4[110], in-plane 1/2[100], and out-of-plane 1/4[101]. We discussed how these APBs appear on the surface. The proportions of the APBs with 1/4[110], 1/2[100], and 1/4[101] shifts are about 38, 1, and 61%, respectively, in our experiment.

Interdot spin transfer dynamics in laterally coupled excited spin ensemble of high-density InGaAs quantum dots

Interdot spin transfer dynamics is studied in a laterally coupled excited spin ensemble of high-density InGaAs quantum dots (QDs). We observe a rise time of the photoluminescence intensity of ∼100 ps and a simultaneous increase in the spin polarization of the excited spin ensemble, indicating spin injection from higher-energy levels in smaller QDs. Moreover, this coupled ensemble exhibits decay properties of the spin polarization that vary with the excited spin density. This phenomenon can be quantitatively understood by considering interdot spin transfer into lower-energy levels of the surrounding QDs, where the transfer rate depends on the degree of state filling of each QD level.Interdot spin transfer dynamics is studied in a laterally coupled excited spin ensemble of high-density InGaAs quantum dots (QDs). We observe a rise time of the photoluminescence intensity of ∼100 ps and a simultaneous increase in the spin polarization of the excited spin ensemble, indicating spin injection from higher-energy levels in smaller QDs. Moreover, this coupled ensemble exhibits decay properties of the spin polarization that vary with the excited spin density. This phenomenon can be quantitatively understood by considering interdot spin transfer into lower-energy levels of the surrounding QDs, where the transfer rate depends on the degree of state filling of each QD level.

Direct observation of subsurface charge ordering in Fe3O4(001) by scanning tunneling microscopy/spectroscopy

In this study, we characterized Fe3O4(001) films using scanning tunneling microscopy/spectroscopy (STM/STS). On the film surfaces, individual iron atoms and ()R45° reconstructed structures were observed by STM. The STS results showed that the local density of states just below the Fermi level was higher in narrow sections than in wide sections of the surface reconstruction perpendicular to the iron rows. Periodic density of states modulations reproducing this electronic structure were clearly observed in the differential tunneling conductance map. These experimental results revealed the presence of subsurface charge ordering of Fe2+–Fe2+ and Fe3+–Fe3+ dimers, as proposed in previous density functional theory studies.

Noncontact Atomic Force Microscopy Observation of Fe3O4(001) Surface

Fe3O4 is one of the important oxide materials and its surface structure should be well understood to enable application of this material. We report the first noncontact atomic force microscopy (NC-AFM) results for Fe3O4(001) thin films. The observed films were grown homoepitaxially on magnetite thin films substrate. A low-energy electron diffraction pattern shows the well-known (√2×√2)R45° reconstructed structure. The observed minimum step height is 0.21 nm, corresponding to the distance between the same planes. We obtain two types of atomic-scale NC-AFM images. One image shows bright protrusions along the [100] and [010] directions at intervals of 0.84 nm corresponding to a unit cell of the (√2×√2)R45° reconstructed structure. The other image shows a more detailed atomic structure with 0.6 and 0.3 nm corrugations.