53,786 research outputs found
How does the chain extension of poly (acrylic acid) scale in aqueous solution? A combined study with light scattering and computer simulation
This work adresses the question of the scaling behaviour of polyelectrolytes
in solution for a realistic prototype: We show results of a combined
experimental (light scattering) and theoretical (computer simulations)
investigation of structural properties of poly (acrylic acid) (PAA).
Experimentally, we determined the molecular weight (M_W) and the hydrodynamic
radius (R_H) by static light scattering for six different PAA samples in
aqueous NaCl-containing solution (0.1-1 mol/L) of polydispersity D_P between
1.5 and 1.8. On the computational side, three different variants of a newly
developed mesoscopic force field for PAA were employed to determine R_H for
monodisperse systems of the same M_W as in the experiments. The force field
effectively incorporates atomistic information and one coarse-grained bead
corresponds to one PAA monomer. We find that R_H matches with the experimental
data for all investigated samples. The effective scaling exponent for R_H is
found to be around 0.55, which is well below its asymptotic value for good
solvents. Additionally, data for the radius of gyration (R_G) are presented.Comment: 17 pages, 3 figures, submitted to Macromolecule
Hadron annihilation into two photons and backward dVCS in the scaling regime of QCD
We study the scaling regime of hadron-(anti)-hadron annihilation into a
deeply virtual photon and a real photon, H anti-H -> gamma^* gamma, and deep
backward virtual Compton scattering, gamma^* H -> H gamma. We advocate that
there is a kinematical region where the scattering amplitude factorizes into a
short-distance matrix element and a long-distance dominated object: a
transition distribution amplitude which describes the hadron to photon
transition.Comment: 4 pages, 1 .eps figure, to be published in Phys. Rev. D Rapid Com
--Oscillations for Correlated Electron Pairs in Disordered Mesoscopic Rings
The full spectrum of two interacting electrons in a disordered mesoscopic
one--dimensional ring threaded by a magnetic flux is calculated numerically.
For ring sizes far exceeding the one--particle localization length we
find several --periodic states whose eigenfunctions exhibit a pairing
effect. This represents the first direct observation of interaction--assisted
coherent pair propagation, the pair being delocalized on the scale of the whole
ring.Comment: 4 pages, uuencoded PostScript, containing 5 figures
Unlocking the Potential of Flexible Energy Resources to Help Balance the Power Grid
Flexible energy resources can help balance the power grid by providing
different types of ancillary services. However, the balancing potential of most
types of resources is restricted by physical constraints such as the size of
their energy buffer, limits on power-ramp rates, or control delays. Using the
example of Secondary Frequency Regulation, this paper shows how the flexibility
of various resources can be exploited more efficiently by considering multiple
resources with complementary physical properties and controlling them in a
coordinated way. To this end, optimal adjustable control policies are computed
based on robust optimization. Our problem formulation takes into account power
ramp-rate constraints explicitly, and accurately models the different
timescales and lead times of the energy and reserve markets. Simulations
demonstrate that aggregations of select resources can offer significantly more
regulation capacity than the resources could provide individually.Comment: arXiv admin note: text overlap with arXiv:1804.0389
Collective cyclotron motion of the relativistic plasma in graphene
We present a theory of the finite temperature thermo-electric response
functions of graphene, in the hydrodynamic regime induced by electron-electron
collisions. In moderate magnetic fields, the Dirac particles undergo a
collective cyclotron motion with a temperature-dependent relativistic cyclotron
frequency proportional to the net charge density of the Dirac plasma. In
contrast to the undamped cyclotron pole in Galilean-invariant systems (Kohn's
theorem), here there is a finite damping induced by collisions between the
counter-propagating particles and holes. This cyclotron motion shows up as a
damped pole in the frequency dependent conductivities, and should be readily
detectable in microwave measurements at room temperature. We also discuss the
large Nernst effect to be expected in graphene.Comment: 16 pages, 2 figures; calculation of giant Nernst effect in graphene
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