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Ibaraki, Japan

Yamashita O.,Materials Science Co.
Applied Energy | Year: 2011

The resultant thermoelectric (TE) figure of merit Z, the coefficient of performance (COP), the heat pumping capacity per unit area (Qc/S) were derived analytically as functions of l0, ρc, κc and sc for a single thermoelement (STE) by taking into account the interface layers, where l0 is a length of a TE material, ρc the electrical interface resistivity, κc the thermal interface conductivity and sc the ratio of the Seebeck coefficient of an interface layer to that of a TE material. As a result, it was first revealed that the increase in Z0T of a TE material is not necessarily reflected in the increase in ZT of an STE as long as the interface layers are present. The COP and Qc/S are lowered remarkably for sc=0 and κc≤104W/m2K. However, it was clarified that even for low values of κc, the COP and Qc/S return to the original high values (obtained for κc≥105W/m2K) at sc=0.45 and 0.90, respectively. The definite criterion of sc whether or not the boundary Seebeck coefficient has an effect on the enhancement of the cooling performance was indicated quantitatively for an STE with interface layers. © 2011 Elsevier Ltd.

The intrinsic spin and extrinsic orbital angular momenta (S and L) and their torque densities are derived and formulated using the plane waves for light propagating in coiled optically active fiber cores which have homogeneity and inhomogeneity of refractive index n. The effect of the geometrical phase shift χ on S, L, their densities (per unit volume) and their torque densities of the right and left circularly polarized plane waves split in such a fiber is analyzed using the locally inertial coordinate frame for a fiber core with homogeneity of n and the non-inertial coordinate frame for a fiber core with inhomogeneity of n. © 2012 Elsevier B.V. All rights reserved.

We calculate the intrinsic spin and extrinsic orbital angular momentum densities of an electromagnetic plane wave propagating in a helically wound optical fiber. The geometrical phase shift of the extrinsic angular momentum density of light traveling in such a fiber is derived analytically and discussed in comparison with that of the intrinsic angular momentum density. © 2012 Elsevier B.V. All rights reserved.

A circularly polarized plane wave of infinite transverse extent (δ ∞) has no spin angular momentum, while a realistic light does carry it. This paradox originates from the presence (δ =∞) and absence (δ = 0) of the surface integral in the total angular momentum J. The same holds for the torque equation of dJ/dt, so that δ is also connected with the relative Faraday rotation angle Θ F/θ F when a radius (a) of a cylindrical medium with optical activity is only a little larger than that (b) of light beam, where Θ F is the Faraday rotation angle and θ F is the intrinsic Faraday rotation angle of a medium. It is shown here that it is possible to estimate δ for a realistic light from the drastic variation in Θ F/ θ F near b/a = 1. © 2011 Elsevier B.V.

Yamashita O.,Materials Science Co.
Applied Physics A: Materials Science and Processing | Year: 2011

The three thermal rate equations were built newly up at both ends and at the junction of a p-n diode, in order to derive analytically the temperature difference δT (between a junction and both ends) and the internal cooling efficiency ? defined newly for a homojunction diode. The maxima δT and n of a diode were derived analytically as a function of Vj within the short-length approximation and calculated numerically as a function of V j or Vbi, where Vj is a voltage across the junction and Vbi is a built-in voltage at the junction. As a result, δT increases abruptly with an increase of Vj below V j = 0.050 V or of Vbi below Vbi = 0.10 V, while above their values, it increases slowly with an increase of Vj or Vbi to saturate a certain value. For example, δT was estimated as 14.6 K for Hg0.8Cd0.2Te diode with Vbi = 0.36 V. n has a local maximum of 63% at Vj ≈ 0.01 V or at V bi ≈ 0.03 V, while above their respective values, it decreases abruptly with an increase of Vj or Vbi and falls to 4.4% at Vbi = 0.80 V which is equivalent to that of a diode emitting a laser for fiber optical communication. However, the greater enhancements in δT and n of a diode are required to apply the internal cooling system to a laser-emitting diode which needs the exact control of temperature. These results should be useful for the application of the internal cooling system to the double heterojunction diode used in the optical communication. © Springer-Verlag 2011.

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