Phonon, Two-Magnon and Electronic Raman Scattering of Fe1+yTe1-xSex

We have measured Raman scattering spectra of single-crystalline FeTe0.6Se0.4 (T_c ~ 14.5 K) and its parent compound Fe1.074Te at various temperatures. In the parent compound Fe1.074Te, A1g and B1g modes have been observed at 157.5 and 202.3 cm-1, respectively, at 5 K. These frequencies qualitatively agree with the calculated results. Two-magnon excitation has been observed around 2300 cm-1 for both compounds. Temperature dependence between the electronic Raman spectra below and above T_c has been observed and 2\Delta and 2\Delta/k_BT_C have been estimated as 5.0 meV and 4.0, respectively.Comment: 8 pages, 8 figures, to be published in Phys. Rev.

Quasi Periodic Oscillations (QPOs) and frequencies in an accretion disk and comparison with the numerical results from non-rotating black hole computed by the GRH code

The shocked wave created on the accretion disk after different physical phenomena (accretion flows with pressure gradients, star-disk interaction etc.) may be responsible observed Quasi Periodic Oscillations (QPOs) in $X-$ray binaries. We present the set of characteristics frequencies associated with accretion disk around the rotating and non-rotating black holes for one particle case. These persistent frequencies are results of the rotating pattern in an accretion disk. We compare the frequency's from two different numerical results for fluid flow around the non-rotating black hole with one particle case. The numerical results are taken from our papers Refs.\refcite{Donmez2} and \refcite{Donmez3} using fully general relativistic hydrodynamical code with non-selfgravitating disk. While the first numerical result has a relativistic tori around the black hole, the second one includes one-armed spiral shock wave produced from star-disk interaction. Some physical modes presented in the QPOs can be excited in numerical simulation of relativistic tori and spiral waves on the accretion disk. The results of these different dynamical structures on the accretion disk responsible for QPOs are discussed in detail.Comment: 13 figures, added reference, accepted for publication in Modern Physics Letters

Can Any "Invariants" Be Revealed in Quasi-periodic Phenomena Observed From Sco X-1?

Using large number of Rossi X-ray Time Explorer observations of Sco X-1 we present a detailed investigation of the transition layer (TL) and the relativistic precession (RP) models. These models predict the existence of the invariant quantities: an inclination angle delta of the magnetospheric axis with the normal to the disk for the TLM and a neutron star (NS) mass M_{NS} for the RPM. Theoretical predictions of both models are tested and their self-consistency is checked. We establish that: (1) The inferred delta angle is 5.56+/-0.09 degrees. Correlation of the delta-values with the horizontal branch oscillation (HBO) frequency is rather weak. (2) There is a strong correlation between an inferred M_{NS} and the HBO frequency in the RPM frameworks. (3) We infer M_{NS} for different assumptions regarding the relations between the HBO frequency and the nodal frequency. We find that the inferred M_{NS}=2.7+/-0.1 M_sun cannot be consistent with any EOS of NS matter. We conclude that RPM fails to describe the data while TLM seems to be compatible.Comment: Accepted for publication in Astrophysical Journal Letters (2002 June/571 issue), 5 pages, 4 figures, uses emulateapj5.st

Orbital Decay and Tidal Disruption of a Star Cluster: Analytical Calculation

The orbital decay and tidal disruption of a star cluster in a galaxy is studied in an analytical manner. Owing to dynamical friction, the star cluster spirals in toward the center of the galaxy. Simultaneously, the galactic tidal field strips stars from the outskirts of the star cluster. Under an assumption that the star cluster undergoes a self-similar evolution, we obtain the condition and timescale for the star cluster to reach the galaxy center before its disruption. The result is used to discuss the fate of so-called intermediate-mass black holes with >10^3 M(sun) found recently in young star clusters of starburst galaxies and also the mass function of globular clusters in galaxies.Comment: 12 pages, 1 PS file for 2 figures, to appear in The Astrophysical Journa

Aging of poled ferroelectric ceramics due to relaxation of random depolarization fields by space-charge accumulation near grain boundaries

Migration of charged point defects triggered by the local random depolarization field is shown to plausibly explain aging of poled ferroelectric ceramics providing reasonable time and acceptor concentration dependences of the emerging internal bias field. The theory is based on the evaluation of the energy of the local depolarization field caused by mismatch of the polarizations of neighbor grains. The kinetics of charge migration assumes presence of mobile oxygen vacancies in the material due to the intentional or unintentional acceptor doping. Satisfactory agreement of the theory with experiment on the Fe-doped lead zirconate titanate is demonstrated.Comment: theory and experiment, 22 pages, 3 figure

Correlations in the QPO Frequencies of Low Mass X-Ray Binaries and the Relativistic Precession Model

A remarkable correlation between the centroid frequencies of quasi periodic oscillations, QPOs, (or peaked noise components) from low mass X-ray binaries, has been recently discovered by Psaltis, Belloni and van der Klis (1999). This correlation extends over nearly 3 decades in frequency and encompasses both neutron star and black hole candidate systems. We discuss this result in the light of the relativistic precession model, which has been proposed to interpret the kHz QPOs as well as some of the lower frequency QPOs of neutron star low mass X-ray binaries of the Atoll and Z classes. Unlike other models the relativistic precession model does not require the compact object to be a neutron star and can be applied to black hole candidates as well. We show that the predictions of the relativistic precession model match both the value and dependence of the correlation to a very good accuracy without resorting to additional assumptions.Comment: To appear in ApJ Letters. AASTEX Latex v. 5.0, 1 figure not include

Semiconductor-enriched single wall carbon nanotube networks applied to field effect transistors

Substantial progress on field effect transistors "FETs" consisting of semiconducting single wall carbon nanotubes "s-SWNTs" without detectable traces of metallic nanotubes and impurities is reported. Nearly perfect removal of metallic nanotubes is confirmed by optical absorption, Raman measurements, and electrical measurements. This outstanding result was made possible in particular by ultracentrifugation (150 000 g) of solutions prepared from SWNT powders using polyfluorene as an extracting agent in toluene. Such s-SWNTs processable solutions were applied to realize FET, embodying randomly or preferentially oriented nanotube networks prepared by spin coating or dielectrophoresis. Devices exhibit stable p-type semiconductor behavior in air with very promising characteristics. The on-off current ratio is 10^5, the on-current level is around 10 $\mu$A, and the estimated hole mobility is larger than 2 cm2 / V s