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Nishimura O.,Nagano National College of Technology
Astrophysical Journal | Year: 2011

I model cyclotron lines by calculating a superposition of a large number of cyclotron line spectra emerging from different heights of a line-forming region of a non-uniform density and temperature of an electron-proton plasma threaded by a dipole magnetic field. In this paper, I mainly discuss the properties of the cyclotron lines in accreting X-ray pulsars with long spin periods (100-800s). My simplified model succeeds in reproducing asymmetric line profiles, anharmonic ratios of line energy, relationship between the width and the depth of the line, and correlation between cyclotron line energy and X-ray intensity in the main pulse. In addition, I demonstrate that a shallower and broader fundamental (= first harmonic) line and a deeper second harmonic line as observed in accreting X-ray pulsars such as Vela X-1 and A0535+26 can be produced via a superposition of a large number of cyclotron lines formed at numerous different heights in a line-forming region with a dipole magnetic field. In this case, the ratio of the peak energy of the second harmonic absorption line to the fundamental can be larger than harmonic ratio 2. Furthermore, the width of the fundamental line is comparable to or larger than that of the second harmonic. These characteristics of the cyclotron lines are consistent with those observed in Vela X-1 and A0535+26. © 2011. The American Astronomical Society. All rights reserved. Source

Hachisuga A.,Shinshu University | Yoshioka M.,Shinshu University | Ohta K.,Shinshu University | Itaya T.,Nagano National College of Technology
Journal of Materials Chemistry C | Year: 2013

In our previous work, we synthesized a series of phthalocyanine-based flying-seed-like compounds, (nPh-PhO)4PcCu (n = 3, 2, 1 and 0 in nPh-PhO: a-d), and revealed that each of them shows a columnar liquid crystalline phase (Colho or Colrho) from rt to an extremely high temperature near 500 °C. Thus, we could obtain columnar liquid crystalline phases for discotic compounds by using bulky substituents (a-d) instead of long alkyl chains. In order to further study the utility of these bulky substituents (a-d) on the induction of mesomorphism for other shaped molecules, we have synthesized novel flying-seed-like calamitic phenoxybenzoic acid derivatives, nPh-PhOBA (3a-d), and their Mitsubishi-Mark-shaped terbium complexes, (nPh-PhOBA)3Tb·mMeOH (4a-d), in this work. Very interestingly, the mesomorphism of the phenoxybenzoic aids derivatives nPh-PhOBA (n = 0-3) was induced to show a mesophase (Mx) only by the bulky substituent d (n = 0), whereas the mesomorphism of their corresponding terbium complexes (nPh-PhOBA)3Tb(III) (n = 0-3) was induced to show rectangular columnar (Colr) mesophases by the bulky substituents c and d (n = 1, 0). On the other hand, the mesomorphism of the PcCu complexes (nPh-PhOBA)4PcCu (n = 0-3) in our previous work was induced by all the bulky substituents a, b, c and d (n = 0-3). Thus, it becomes apparent that both calamitic and columnar mesomorphism can be induced by the substitution of bulky groups instead of long alkyl chains, and that the balance of the core size and the bulkiness of the substituents is very important to obtain mesomorphism in flying-seed-like compounds. We believe that this is a new guideline for the induction of mesomorphism by using bulky groups instead of long alkyl chains. © 2013 The Royal Society of Chemistry. Source

Kim B.-H.,Chonnam National University | Yang K.S.,Chonnam National University | Kim Y.A.,Shinshu University | Kim Y.J.,Korea Advanced Institute of Science and Technology | And 2 more authors.
Journal of Power Sources | Year: 2011

A simple and scalable method is reported for fabricating a porosity-controlled carbon nanofibers with a skin-core texture by electrospinning a selected blend of polymer solutions. Simple thermal treatment of the electrospun nanofibers from solution blends of various compositions creates suitable ultramicropores on the surface of carbon nanofibers that can accommodate many ions, removing the need for an activation step. The intrinsic properties of the electrode (e.g., nanometre-size diameter, high specific surface area, narrow pore size distribution, tuneable porosity, shallow pore depth, and good ionic accessibility) enable construction of supercapacitors with large specific capacitance (130.7 F g-1), high power (100 kW kg -1), and energy density (15.0 Wh kg-1). © 2011 Elsevier B.V. All rights reserved. Source

Nishimura O.,Nagano National College of Technology
Astrophysical Journal | Year: 2015

I examine the characteristics of profiles of cyclotron lines formed by the superposition of a number of lines formed at a number of altitudes in line-forming regions illuminated by anisotropic injections in an accretion column, which formed around the polar cap of Roche-lobe-type accretion-powered X-ray pulsars. In the present paper, I consider the line-forming region near the walls of a cylindrical geometry illuminated from the inside of the cylinder. I also examine how the direction of the peak of a beam pattern affects the profiles of cyclotron lines. I found that the width and depth of the line in a phase-averaged spectrum provide information concerning the direction of a beam. I demonstrate that the cyclotron line has a pure absorption in the phase-averaged spectrum regardless of the height of the cylinder, which is expected to change with luminosity. On the other hand, in phase-resolved spectra, an emission-like feature can be formed in the phase with lower intensity in a short cylinder, which is expected at L ∼ 1036 erg s?1, while a pure absorption feature tends to appear in all phases due to the superposition of a large number of lines in a tall cylinder, which is expected at L ≳ 1037 erg s?1. © 2015. The American Astronomical Society. All rights reserved. Source

Nishimura O.,Nagano National College of Technology
Astrophysical Journal | Year: 2014

I develop a new model for changes of cyclotron line energy with luminosity based on changes in polar cap dimensions and the direction of photon propagation as well as a shock height. In X0115+63 and V0332+53, the fundamental cyclotron line energy has been observed to decrease with increasing luminosity. This phenomenon has been interpreted as a change of a shock height with luminosity. However, the rates of the observed changes are quite different, in which the line energy in V0332+53 varies slowly with luminosity compared with that in X0115+63. I demonstrate that a new model successfully reproduces the changes of the fundamental cyclotron line energies with luminosity in both X0115+63 and V0332+53. On the other hand, the cyclotron line energies in Her X-1, GX301-2, and GX304-1 were reported to increase with increasing luminosity. I discuss the positive correlation between the cyclotron line energy and luminosity based on changes in a beam pattern for Her X-1, GX301-2, and GX304-1. In addition, I discuss how a switch of the predominant, observed emission region from pole1 to pole2 influences cyclotron line energy for GX304-1 and A0535+26. © 2014. The American Astronomical Society. All rights reserved. Source

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