Empiric Models of the Earth's Free Core Nutation

Free core nutation (FCN) is the main factor that limits the accuracy of the modeling of the motion of Earth's rotational axis in the celestial coordinate system. Several FCN models have been proposed. A comparative analysis is made of the known models including the model proposed by the author. The use of the FCN model is shown to substantially increase the accuracy of the modeling of Earth's rotation. Furthermore, the FCN component extracted from the observed motion of Earth's rotational axis is an important source for the study of the shape and rotation of the Earth's core. A comparison of different FCN models has shown that the proposed model is better than other models if used to extract the geophysical signal (the amplitude and phase of FCN) from observational data.Comment: 8 pages, 3 figures; minor update of the journal published versio

Surface Shubnikov-de Hass oscillations and non-zero Berry phases of the topological hole conduction in Tl1−x_{1-x}Bi1+x_{1+x}Se2_2

We report the observation of two-dimensional Shubnikov-de Hass (SdH) oscillations in the topological insulator Tl$_{1-x}$Bi$_{1+x}$Se$_2$. Hall effect measurements exhibited electron-hole inversion in samples with bulk insulating properties. The SdH oscillations accompanying the hole conduction yielded a large surface carrier density of $n_{\rm{s}}=5.1 \times10^{12}$/cm$^2$, with the Landau-level fan diagram exhibiting the $\pi$ Berry phase. These results showed the electron-hole reversibility around the in-gap Dirac point and the hole conduction on the surface Dirac cone without involving the bulk metallic conduction.Comment: 5 pages, 4 figure

Urban Demand for Wild Foods in Northeast Thailand: A survey of edible wild species sold in the Khon Kaen municipal market

Rural people in Northeast Thailand consume a wide range of wild species. Little is known, however, about the extent to which the urban populations of the region’s rapidly growing towns and cities consume these products, and no detailed study has been made of the edible wild species that are sold in urban markets. To help fill this knowledge gap, this paper presents findings of a survey about the wild species sold in the main urban market in Khon Kaen Municipality. The survey included identification of all species of plants, fungi, and animals being sold and recording of the quantities and prices of each species. Data were obtained by interviewing vendors selling these products in the market on 18 randomly selected nights in the dry season and 12 nights in the rainy season. The diversity of wild species sold in the market is high. Eighty-one species were identified, of which 54 were plants, 6 were fungi, and 21 were animals. Species diversity was greater in the rainy season, when 65 species were on sale, than in the dry season, when 49 species were available. Plant species were much more diverse in the rainy season than in the dry season, reflecting the better growth conditions for vegetation when water is not a limiting factor. Many species were available only in a specific season. The wild species were obtained from several different habitats. Upland fields were the habitat for the largest number of species, followed by house areas, forests, and paddy fields. Gardens and aquatic ecosystems were habitats for a smaller number of species. The supply-shed for the urban market in Khon Kaen Municipality is quite a large one. Wild species sold in the market are obtained from 8 provinces in the Northeast, although rural areas of Khon Kaen Province itself are the source of the largest number of species. Collection of wild species to supply the urban market can have both negative and positive effects on rural biodiversity in Northeast Thailand. In their desire to earn cash income, villagers may over-exploit some of these species, causing wild populations to decline in numbers or even become locally extinct. On the other hand, villagers may intensify their efforts to cultivate them so as to allow more stable production, thus contributing to biodiversity conservation. This has already begun to happen in the case of some highly valued species

Precise determination of two-carrier transport properties in the topological insulator TlBiSe2_2

We report the electric transport study of the three-dimensional topological insulator TlBiSe$_2$. We applied a newly developed analysis procedure and precisely determined two-carrier transport properties. Magnetotransport properties revealed a multicarrier conduction of high- and low-mobility electrons in the bulk, which was in qualitative agreement with angle-resolved photoemission results~[K. Kuroda $et~al.$, Phys. Rev. Lett. $\bm{105}$, 146801 (2010)]. The temperature dependence of the Hall mobility was explained well with the conventional Bloch-Gr{\"u}neisen formula and yielded the Debye temperature $\varTheta_{\rm{D}}=113 \pm 14$~K. The results indicate that the scattering of bulk electrons is dominated by acoustic phonons.Comment: 6 pages, 5 figures, to be published in Physical Review

Half-metallic ferromagnets for magnetic tunnel junctions

Using theoretical arguments, we show that, in order to exploit half-metallic ferromagnets in tunneling magnetoresistance (TMR) junctions, it is crucial to eliminate interface states at the Fermi level within the half-metallic gap; contrary to this, no such problem arises in giant magnetoresistance elements. Moreover, based on an a priori understanding of the electronic structure, we propose an antiferromagnetically coupled TMR element, in which interface states are eliminated, as a paradigm of materials design from first principles. Our conclusions are supported by ab-initio calculations

Eigenfunctions decay for magnetic pseudodifferential operators

We prove rapid decay (even exponential decay under some stronger assumptions) of the eigenfunctions associated to discrete eigenvalues, for a class of self-adjoint operators in $L^2(\mathbb{R}^d)$ defined by ``magnetic'' pseudodifferential operators (studied in \cite{IMP1}). This class contains the relativistic Schr\"{o}dinger operator with magnetic field

MnAs dots grown on GaN(0001)-(1x1) surface

MnAs has been grown by means of MBE on the GaN(0001)-(1x1) surface. Two options of initiating the crystal growth were applied: (a) a regular MBE procedure (manganese and arsenic were delivered simultaneously) and (b) subsequent deposition of manganese and arsenic layers. It was shown that spontaneous formation of MnAs dots with the surface density of 1$\cdot 10^{11}$ cm$^{-2}$ and $2.5\cdot 10^{11}$ cm$^{-2}$, respectively (as observed by AFM), occurred for the layer thickness higher than 5 ML. Electronic structure of the MnAs/GaN systems was studied by resonant photoemission spectroscopy. That led to determination of the Mn 3d - related contribution to the total density of states (DOS) distribution of MnAs. It has been proven that the electronic structures of the MnAs dots grown by the two procedures differ markedly. One corresponds to metallic, ferromagnetic NiAs-type MnAs, the other is similar to that reported for half-metallic zinc-blende MnAs. Both system behave superparamagnetically (as revealed by magnetization measurements), but with both the blocking temperatures and the intra-dot Curie temperatures substantially different. The intra-dot Curie temperature is about 260 K for the former system while markedly higher than room temperature for the latter one. Relations between growth process, electronic structure and other properties of the studied systems are discussed. Possible mechanisms of half-metallic MnAs formation on GaN are considered.Comment: 20+ pages, 8 figure