Constraints on Superconducting Cosmic Strings from Early Reionization

Electromagnetic radiation from superconducting cosmic string loops can reionize neutral hydrogen in the universe at very early epochs, and affect the cosmic microwave background (CMB) temperature and polarization correlation functions at large angular scales. We constrain the string tension and current using WMAP7 data, and compare with earlier constraints that employed CMB spectral distortions. Over a wide range of string tensions, the current on the string has to be less than 10^7 GeV.Comment: 7 pages, 6 figures, Submitted to PR

Asymptotic behavior of the mean square displacement of the Brownian parametric oscillator near the singular point

A parametric oscillator with damping driven by white noise is studied. The mean square displacement (MSD) in the long-time limit is derived analytically for the case that the static force vanishes, which was not treated in the past work \cite{tashiro07}. The formula is asymptotic but is applicable to a general periodic function. On the basis of this formula, some periodic functions reducing MSD remarkably are proposed

Cosmological constraints from CMB distortion

We examine bounds on adiabatic and isocurvature density fluctuations from $\mu$-type spectral distortions of the cosmic microwave background (CMB). Studies of such distortion are complementary to CMB measurements of the spectral index and its running, and will help to constrain these parameters on significantly smaller scales. We show that a detection on the order of $\mu \sim 10^{-7}$ would strongly be at odds with the standard cosmological model of a nearly scale-invariant spectrum of adiabatic perturbations. Further, we find that given the current CMB constraints on the isocurvature mode amplitude, a nearly scale-invariant isocurvature mode (common in many curvaton models) cannot produce significant $\mu$-distortion. Finally, we show that future experiments will strongly constrain the amplitude of the isocurvature modes with a highly blue spectrum as predicted by certain axion models.Comment: 6 pages, 4 figures, version 3 contains a new figure showing the contribution to \mu_k as a function of k, and a clarification regarding the acoustic wave energy, accompanied by a related acknowledgement and referenc

Kaehler Manifolds of Quasi-Constant Holomorphic Sectional Curvatures

The Kaehler manifolds of quasi-constant holomorphic sectional curvatures are introduced as Kaehler manifolds with complex distribution of codimension two, whose holomorphic sectional curvature only depends on the corresponding point and the geometric angle, associated with the section. A curvature identity characterizing such manifolds is found. The biconformal group of transformations whose elements transform Kaehler metrics into Kaehler ones is introduced and biconformal tensor invariants are obtained. This makes it possible to classify the manifolds under consideration locally. The class of locally biconformal flat Kaehler metrics is shown to be exactly the class of Kaehler metrics whose potential function is only a function of the distance from the origin in complex Euclidean space. Finally we show that any rotational even dimensional hypersurface carries locally a natural Kaehler structure, which is of quasi-constant holomorphic sectional curvatures.Comment: 36 page

Leading Effects in Hadroproductions of Lambda_c and D From Constituent Quark-Diquark Cascade Picture

We discuss the hadroproductions of Lambda_c, Lambda_c bar, D and D bar in the framework of the constituent quark-diquark cascade model taking into account the valence quark annihilation. The spectra of Lambda_c and Lambda_c bar in pA, Sigma^-A and pi^-A collisions are well explained by the model using the values of parameters used in hadroproductions of D and D bar. It is shown that the role of valence diquark in the incident baryon is important for D bar productions as well as for Lambda_c production.Comment: 11 pages, 5 figures, v2:some explanations added, references added, typos corrected, v3: top margin change

On the Thermal Instability in a Contracting Gas Cloud and Formation of a Bound Cluster

We perform linear analysis of thermal instability in a contracting large cloud filled with warm HI gas and investigate the effect of metallicity and radiation flux. When the cloud reaches critical density n_f, the cloud fragments into cool, dense condensations because of thermal instability. For a lower metallicity gas cloud, the value of n_f is high. Collision between condensations will produce self-gravitating clumps and stars thereafter. From the result of calculation, we suggest that high star formation efficiency and bound cluster formation are realized in low-metallicity and/or strong-radiation environments.Comment: 7 pages, including 7 figures, LaTeX2e(emulateapj5.sty) To appear in ApJ, Jun 10, 200

CMB Distortions from Superconducting Cosmic Strings

We reconsider the effect of electromagnetic radiation from superconducting strings on cosmic microwave background (CMB) mu- and y-distortions and derive present (COBE-FIRAS) and future (PIXIE) constraints on the string tension, mu_s, and electric current, I. We show that absence of distortions of the CMB in PIXIE will impose strong constraints on mu_s and I, leaving the possibility of light strings (G mu_s < 10^{-18}) or relatively weak currents (I < 10 TeV).Comment: 10pages, 5 figures, Submitted to PRD, v2:References added, replaced to match the PRD versio

Residual magnetization measurements of a motor to be used in satellites

Thursday 3 December 2009, Gwangju, Korea, Republic of ICMIT 2009: Mechatronics and Information TechnologyA simple magnetic shielding system for residual magnetization measurements of a motor to be used in satellites is studied. The system consists of same-sized square coils, namely three sets of Simple Cubic-3 coil system. Because the system can generate a uniform magnetic field, we investigate the uniformity of the site. With a first-order gradient coil, the geomagnetic field can be reduced to less than 100 nT in a relatively large area. Inside of the system, the residual magnetization measurements of a step motor are demonstrated. An approach to reduce the magnetic field leakage from the step motor is also presented.ArticleA. Matsuoka, K. Matsumura, A. Kubota, K. Tashiro and H. Wakiwaka, "Residual magnetization measurements of a motor to be used in satellites", Proc. SPIE 7500, 750012 (2009).journal articl