34,053 research outputs found
Peak-Dip-Hump from Holographic Superconductivity
We study the fermionic spectral function in a holographic superconductor
model. At zero temperature, the black hole has zero horizon and hence the
entropy of the system is zero after the back reaction of the condensate is
taken into account. We find the system exhibits the famous peak-dip-hump
lineshape with a sharp low-energy peak followed by a dip then a hump at higher
energies. This feature is widely observed in the spectrum of several high-T_c
superconductors. We also find a linear relation between the gap in the
fermionic spectrum and the condensate, indicating the condensate is formed by
fermion pairing.Comment: 4 pages, revtex
Giant Magnons and Spiky Strings on S^3 with B-field
We study solutions for a rotating string on S^3 with a background NS-NS
B-field and show the existence of spiky string and giant magnon as two limiting
solutions. We make a connection to the sine-Gordon model via the Polyakov
worldsheet action and study the effect of B-field. In particular, we find the
magnon solution can be mapped to the excitation of a fractional spin chain. We
conjecture a B-deformed SYM to be the gauge theory dual to this background.Comment: 22 pages, 3 figures, more references adde
Tailoring Accelerating Beams in Phase Space
An appropriate design of wavefront will enable light fields propagating along
arbitrary trajectories thus forming accelerating beams in free space. Previous
ways of designing such accelerating beams mainly rely on caustic methods, which
start from diffraction integrals and only deal with two-dimensional fields.
Here we introduce a new perspective to construct accelerating beams in phase
space by designing the corresponding Wigner distribution function (WDF). We
find such a WDF-based method is capable of providing both the initial field
distribution and the angular spectrum in need by projecting the WDF into the
real space and the Fourier space respectively. Moreover, this approach applies
to the construction of both two- and three-dimensional fields, greatly
generalizing previous caustic methods. It may therefore open up a new route to
construct highly-tailored accelerating beams and facilitate applications
ranging from particle manipulation and trapping to optical routing as well as
material processing.Comment: 8 pages, 6 figure
The Electrochemical Oxidation of Substituted Catechols
The oxidation of substituted catechols was studied by cyclic voltammetry, chronoamperometry, rotating ringâdisk electrode, and coulometry. The results showed that the quinones that were formed from the oxidation of substituted catechols reacted with the basic forms of the starting material to yield the dimeric product. These products were generally unstable and rapidly polymerized or underwent some other irreversible reaction to form an electroinactive product. For 3,4âdihydroxyacetophenone and propriophenone, the intermediate was stable long enough to be observed in cyclic voltammetry. The rate of the coupling reaction was found to correlate well with the Hammett ÏâÏ parameters and indicated that there was substantial negative charge in the transition state. Finally, an analysis of the coulometric nâvalues along with the iat1/2/C values indicated that the initial coupling product was a diphenyl ether. Analysis of the coulometry products showed extensive polymerization
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