7,169 research outputs found

    Spin accumulation created electrically in an n-type germanium channel using Schottky tunnel contacts

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    Using high-quality Fe3_{3}Si/n+n^{+}-Ge Schottky-tunnel-barrier contacts, we study spin accumulation in an nn-type germanium (nn-Ge) channel. In the three- or two-terminal voltage measurements with low bias current conditions at 50 K, Hanle-effect signals are clearly detected only at a forward-biased contact. These are reliable evidence for electrical detection of the spin accumulation created in the nn-Ge channel. The estimated spin lifetime in nn-Ge at 50 K is one order of magnitude shorter than those in nn-Si reported recently. The magnitude of the spin signals cannot be explained by the commonly used spin diffusion model. We discuss a possible origin of the difference between experimental data and theoretical values.Comment: 4 pages, 3 figures, To appear in J. Appl. Phy

    Compact Claude cycle refrigerator for laboratory use

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    A Claude cycle refrigerator with a three stage reciprocating expansion engine is described. Instead of a cam mechanism, valves are driven directly by magnetic solenoids operated by means of a micro processor control system. A swash plate mechanism is used to convert reciprocating motion of the expander pistons to rotary motion. A refrigeration capacity of 8 watts was achieved at 4.5 K with the operating pressure of 1.1 MPa and flow rate of 2.4 g/sec.. An effect of overintake operation was studied. Experimental results show that the efficiency of the expander has a peak point in the region of overintake operation with constant cycle speed, which agrees with theoretical results. The electrically controlled valve system is useful to vary the valve timing to achieve an optimum condition of operation

    Neutrino texture saturating the CP asymmetry

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    We study a neutrino mass texture which can explain the neutrino oscillation data and also saturate the upper bound of the CP asymmetry ϵ1\epsilon_1 in the leptogenesis. We consider the thermal and non-thermal leptogenesis based on the right-handed neutrino decay in this model. A lower bound of the reheating temperature required for the explanation of the baryon number asymmetry is estimated as O(108)O(10^8)GeV for the thermal leptogenesis and O(106)O(10^{6})GeV for the non-thermal one.It can be lower than the upper bound of the reheating temperature imposed by the cosmological gravitino problem. An example of the construction of the discussed texture is also presented.Comment: 23 pages, 6 figure

    V1647 Orionis (IRAS 05436-0007) : A New Look at McNeil's Nebula

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    We present a study of the newly discovered McNeil's nebula in Orion using the JHKs-band simultaneous observations with the near-infrared (NIR) camera SIRIUS on the IRSF 1.4m telescope. The cometary infrared nebula is clearly seen extending toward north and south from the NIR source (V1647 Orionis) that illuminates McNeil's nebula. The compact nebula has an apparent diameter of about 70 arcsec. The nebula is blue (bright in J) and has a cavity structure with two rims extending toward north-east and north-west. The north-east rim is brighter and sharp, while the north-west rim is diffuse. The north-east rim can be traced out to ~ 40 arcsec from the location of the NIR source. In contrast, no cavity structure is seen toward the south, although diffuse nebula is extended out to ~ 20 arcsec. New NIR photometric data show a significant variation in the magnitudes (> 0.15 mag) of the source of McNeil's nebula within a period of one week, that is possibly under the phase of eruptive variables like FUors or EXors.Comment: 13 pages, 5 figures in JPEG format. Accepted for the publication in PASJ Letter

    Light-cone Gauge NSR Strings in Noncritical Dimensions II -- Ramond Sector

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    Light-cone gauge superstring theory in noncritical dimensions corresponds to a worldsheet theory with nonstandard longitudinal part in the conformal gauge. The longitudinal part of the worldsheet theory is a superconformal field theory called X^{\pm} CFT. We show that the X^{\pm} CFT combined with the super-reparametrization ghost system can be described by free variables. It is possible to express the correlation functions in terms of these free variables. Bosonizing the free variables, we construct the spin fields and BRST invariant vertex operators for the Ramond sector in the conformal gauge formulation. By using these vertex operators, we can rewrite the tree amplitudes of the noncritical light-cone gauge string field theory, with external lines in the (R,R) sector as well as those in the (NS,NS) sector, in a BRST invariant way.Comment: 33 pages; v2: minor modification

    Economic Analysis of Crop Production under Jibiya Irrigation Project, Katsina State, Nigeria

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    The study examined costs and returns of crop production under Jibiya Irrigation Project as well as problems that were militating against the achievement of the Project objectives. 120 farmers were randomly sampled and interviewed. The data were analysed using descriptive statistics and farm budgeting model. The average age and land holding of the farmers were 42 years and 0.8ha, respectively. Majority of the farmers were married and can read and write. Most of them had between 0 - 5 and 0 - 3 children and dependants, respectively. Their average costs of crop production were N 94,513.61, N 90,969.20 and N 3,544.41 per hectare of total, variable and fixed cost, respectively. Whereas the total revenue, gross margin and net farm income they obtained were N 190,329.36, N 99,360.16 and N 95,815.75 per hectare, respectively. They enjoyed a net return on investment of N 1.01. There were many problems facing the farmers, which if not addressed adequately, will not only significantly reduce the productivity of crop production but will also discourage farmers from farming under the Project. The performance of the farmers, though good, could be improved if there is adequate funding of the Project; inputs are made readily available to farmers at subsidized rate and in good time and the farmers offer hands in ensuring the safety and security of the Project’s facilities.Keywords: Economic analysis, Crop production, Jibiya irrigation project

    The dynamics of spiral arms in pure stellar disks

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    It has been believed that spirals in pure stellar disks, especially the ones spontaneously formed, decay in several galactic rotations due to the increase of stellar velocity dispersions. Therefore, some cooling mechanism, for example dissipational effects of the interstellar medium, was assumed to be necessary to keep the spiral arms. Here we show that stellar disks can maintain spiral features for several tens of rotations without the help of cooling, using a series of high-resolution three-dimensional NN-body simulations of pure stellar disks. We found that if the number of particles is sufficiently large, e.g., 3Ă—1063\times 10^6, multi-arm spirals developed in an isolated disk can survive for more than 10 Gyrs. We confirmed that there is a self-regulating mechanism that maintains the amplitude of the spiral arms. Spiral arms increase Toomre's QQ of the disk, and the heating rate correlates with the squared amplitude of the spirals. Since the amplitude itself is limited by the value of QQ, this makes the dynamical heating less effective in the later phase of evolution. A simple analytical argument suggests that the heating is caused by gravitational scattering of stars by spiral arms, and that the self-regulating mechanism in pure-stellar disks can effectively maintain spiral arms on a cosmological timescale. In the case of a smaller number of particles, e.g., 3Ă—1053\times 10^5, spiral arms grow faster in the beginning of the simulation (while QQ is small) and they cause a rapid increase of QQ. As a result, the spiral arms become faint in several Gyrs.Comment: 18 pages, 19 figures, accepted for Ap
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