2,333 research outputs found
Multiwavelength properties of a new Geminga-like pulsar: PSR J2021+4026
In this paper, we report a detailed investigation of the multiwavelength
properties of a newly detected gamma-ray pulsar, PSR J2021+4026, in both
observational and theoretical aspects. We firstly identify an X-ray source in
the XMM-Newton serendipitous source catalogue, 2XMM J202131.0+402645, located
within the 95% confidence circle of PSR J2021+4026. With an archival Chandra
observation, this identification provides an X-ray position with arcsecond
accuracy which is helpful in facilitating further investigations. Searching for
the pulsed radio emission at the position of 2XMM J202131.0+402645 with a 25-m
telescope at Urumqi Astronomical Observatory resulted in null detection and
places an upper-limit of 0.1~mJy for any pulsed signal at 18~cm. Together with
the emission properties in X-ray and gamma-ray, the radio quietness suggests
PSR J2021+4026 to be another member of Geminga-like pulsars. In the radio sky
survey data, extended emission features have been identified in the gamma-ray
error circle of PSR J2021+4026. We have also re-analyzed the gamma-ray data
collected by FERMI's Large Area Telescope. We found that the X-ray position of
2XMM J202131.0+402645 is consistent with that of the optimal gamma-ray timing
solution. We have further modeled the results in the context of outer gap model
which provides us with constraints for the pulsar emission geometry such as
magnetic inclination angle and the viewing angle. We have also discussed the
possibility of whether PSR J2021+4026 has any physical association with the
supernova remnant G78.2+2.1 (gamma-Cygni).Comment: 11 pages, 14 figure
Strong valence fluctuation in the quantum critical heavy fermion superconductor beta-YbAlB4: A hard x-ray photoemission study
Electronic structures of the quantum critical superconductor beta-YbAlB4 and
its polymorph alpha-YbAlB4 are investigated by using bulk-sensitive hard x-ray
photoemission spectroscopy. From the Yb 3d core level spectra, the values of
the Yb valence are estimated to be ~2.73 and ~2.75 for alpha- and beta-YbAlB4,
respectively, thus providing clear evidence for valence fluctuations. The
valence band spectra of these compounds also show Yb2+ peaks at the Fermi
level. These observations establish an unambiguous case of a strong mixed
valence at quantum criticality for the first time among heavy fermion systems,
calling for a novel scheme for a quantum critical model beyond the conventional
Doniach picture in beta-YbAlB4.Comment: 4 pages, 3 figures, revised version accepted for publication in PR
Study on the behavior of small droplet impinging onto a hot surface
This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.The effects of droplet diameter, surface roughness, and impinging velocity on the behavior of droplet impinging onto a hot surface have been studied. The surface samples used in the experiment were cylinder blocks of stainless steel having four different degrees of roughness, i.e., Ra 0.04, 0.2, 3, and 10. The diameter and impinging velocity were controlled independently by using a micro-jet dispenser. Their values were in the ranges of 300–700 μm and 1.0–4.0 m/s, respectively. The contact time was found to increase with an increase in the surface roughness and was of the order of the self-oscillation of the water droplet. The maximum spread of droplet decreased with increasing impinging velocity. The cooling curve was obtained
for the range of surface temperatures from 500 oC to 100 oC, and it was found that the cooling time decreased with an increase in the surface roughness of stainless steel. Moreover, the cooling effectiveness of each
droplet increased with an increase in the surface roughness.This study was supported by the Grant-in-Aid for Scientific Research (A) 21246036 from MEXT
Layer dependent band dispersion and correlations using tunable Soft X-ray ARPES
Soft X-ray Angle-Resolved Photoemission Spectroscopy is applied to study
in-plane band dispersions of Nickel as a function of probing depth. Photon
energies between 190 and 780 eV were used to effectively probe up to 3-7
layers. The results show layer dependent band dispersion of the Delta_2
minority-spin band which crosses the Fermi level in 3 or more layers, in
contrast to known top 1-2 layers dispersion obtained using ultra-violet rays.
The layer dependence corresponds to an increased value of exchange splitting
and suggests reduced correlation effects in the bulk compared to the surface.Comment: 7 pages, 3 figures Revised text and figur
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