141,450 research outputs found
Some q-analogues of supercongruences of Rodriguez-Villegas
We study different q-analogues and generalizations of the ex-conjectures of
Rodriguez-Villegas. For example, for any odd prime p, we show that the known
congruence \sum_{k=0}^{p-1}\frac{{2k\choose k}^2}{16^k} \equiv
(-1)^{\frac{p-1}{2}}\pmod{p^2} has the following two nice q-analogues with
[p]=1+q+...+q^{p-1}:
\sum_{k=0}^{p-1}\frac{(q;q^2)_k^2}{(q^2;q^2)_k^2}q^{(1+\varepsilon)k} &\equiv
(-1)^{\frac{p-1}{2}}q^{\frac{(p^2-1)\varepsilon}{4}}\pmod{[p]^2}, where
(a;q)_0=1, (a;q)_n=(1-a)(1-aq)...(1-aq^{n-1}) for n=1,2,..., and
\varepsilon=\pm1. Several related conjectures are also proposed.Comment: 14 pages, to appear in J. Number Theor
SS 433: Radio/X-ray anti-correlation and fast-time variability
We briefly review the Galactic microquasar SS 433/W50 and present a new RXTE
spectral and timing study. We show that the X-ray flux decreases during radio
flares, a behavior seen in other microquasars. We also find short time-scale
variability unveiling emission regions from within the binary system.Comment: 4 pages, 3 figures, mq.sty included. A higher resolution version can
be found at http://aurora.physics.umanitoba.ca/~samar/4MQ/ss433/. Proceedings
of the 4th Microquasar Workshop, eds. Ph. Durouchoux, Y. Fuchs and J.
Rodriguez, published by the Center for Space Physics: Kolkata (in press
Solar Energy Harvesting on S- and N-doped nanoporous Carbons
Nowadays heteroatom-containing carbonaceous materials such as graphene or CNT have gained more and more attention of the scientists searching for inexpensive substitutes of the catalysts for energy related applications such an oxygen reduction reactions.
Discovery of graphene and an extensive characterization of its electronic properties caused that the surface of traditional activated carbon has been viewed from other, unexplored before, angles. The main advantage of activated or nanoporous carbons, within the family of carbonaceous materials, is their porosity where the confined pore space effect can be utilized.
Recently we have shown that specific nanoporous carbons obtained from commodity polymers can catalyze oxygen evolution reactions1, oxygen reduction reaction2 and exhibit photoluminescence properties3. This behavior was attributed to the specificity of surface microstructure, texture, and chemistry. It was found that the carbons obtained at relatively low temperature (800 oC) contain 10 nm graphic units enhancing their DC conductivity. They have also rich surface chemistry based on sulfur, nitrogen and oxygen containing groups. Even though small sp2 clusters should be important to affect the width of the band gap, the sulfur and nitrogen containing groups are hypothesized to act as chromophores/antenna accepting visible light energy. Electron deficiency on them promotes water splitting in small pores. These groups also change the electronic structure of the carbons surface and bring some level hydrophobicity to it. These features were found as important for oxygen reduction reactions4. These reactions enhance the performance of carbons as supercapcitors when the process takes place in the visible light5.
References
1. Ania, C.O.; Seredych, M.; Rodriguez-Castellon, E.; Bandosz, T.J. Visible light driven photoelectrochemical water splitting on metal free nanoporous carbon promoted by chromophoric functional groups. Carbon 79 (2014) 432–441.
2. Seredych, M.; Idrobo, J-C.; Bandosz, T.J. Effect of confined space reduction of graphite oxide followed by sulfur doping on oxygen reduction reaction in neutral electrolyte. J. Mater. Chem. A. 1 (2013) 7059-7067.
3. Bandosz, T.J.; Rodriguez-Castellon, E.; Montenegro J.M.; Seredych, M. Photoluminescence of nanoporous carbons: Opening a new application route for old materials.. Carbon 77 (2014) 651–659.
4. Confined space reduced graphite oxide doped with sulfur as metal-free oxygen reduction catalyst. Seredych, M.; Rodriguez-Castellon, E.; Bandosz, T.J. Carbon 66 (2014) 227-233.
5. Seredych, M.; Rodriguez-Castellon, E.; Biggs, MJ. Skinner, W.l Bandosz, T.J. Effect of visible light and electrode wetting on the capacitive performance of S- and N-doped nanoporous carbons: Importance of surface chemistry. Carbon 78 (2014) 540–558.Universidad de Málaga. Campus de Excelencia Internacional AndalucĂa Tech
GX 339-4: back to life
We report preliminary results of a RossiXTE campaign on the 2002 outburst of
the black-hole candidate GX 339-4. We show power density spectra of five
observations during the early phase of the outburst. The first four power
spectra show a smooth transition between a Low State and a Very High State. The
fifth power spectrum resembles a High State, but a strong 6 Hz QPO appears
suddenly within 16 seconds.Comment: 3 pages, 3 figures; to appear in Proceedings of the 4th Microquasar
Workshop, eds. Ph Durouchoux, Y. Fuchs and J. Rodriguez, published by the
Center for Space Physics: Kolkat
Environmental Issues and Legislation, 2003-2004
John Laird, Chair
Members:Greg Aghazarian, Vice ChairJudy ChuLoni HancockLloyd E. LevineSally J. LieberAlan LowenthalTim LeslieKen Maddox
Committee Staff:Michael B. Endicott, Chief ConsultantJoanne M. L. Wong, Senior ConsultantLinda R. Rodriguez, Committee Secretar
Environmental Issues and Legislation, 2003-2004
John Laird, Chair
Members:Greg Aghazarian, Vice ChairJudy ChuLoni HancockLloyd E. LevineSally J. LieberAlan LowenthalTim LeslieKen Maddox
Committee Staff:Michael B. Endicott, Chief ConsultantJoanne M. L. Wong, Senior ConsultantLinda R. Rodriguez, Committee Secretar
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