50,423 research outputs found
Collective Dynamics of Random Polyampholytes
We consider the Langevin dynamics of a semi-dilute system of chains which are
random polyampholytes of average monomer charge and with a fluctuations in
this charge of the size and with freely floating counter-ions in the
surrounding. We cast the dynamics into the functional integral formalism and
average over the quenched charge distribution in order to compute the dynamic
structure factor and the effective collective potential matrix. The results are
given for small charge fluctuations. In the limit of finite we then find
that the scattering approaches the limit of polyelectrolyte solutions.Comment: 13 pages including 6 figures, submitted J. Chem. Phy
Fast analytical methods for the correction of signal random time-shifts and application to segmented HPGe detectors
Detection systems rely more and more on on-line or off-line comparison of
detected signals with basis signals in order to determine the characteristics
of the impinging particles. Unfortunately, these comparisons are very sensitive
to the random time shifts that may alter the signal delivered by the detectors.
We present two fast algebraic methods to determine the value of the time shift
and to enhance the reliability of the comparison to the basis signals.Comment: 13 pages, 8 figure
Kolmogorov-Smirnov method for the determination of signal time-shifts
A new method for the determination of electric signal time-shifts is
introduced. As the Kolmogorov-Smirnov test, it is based on the comparison of
the cumulative distribution functions of the reference signal with the test
signal. This method is very fast and thus well suited for on-line applications.
It is robust to noise and its performances in terms of precision are excellent
for time-shifts ranging from a fraction to several sample durations.
PACS. 29.40.Gx (Tracking and position-sensitive detectors), 29.30.Kv (X- and
-ray spectroscopy), 07.50.Qx (Signal processing electronics)Comment: 8 pages, 7 figure
Interference Effects Due to Commensurate Electron Trajectories and Topological Crossovers in (TMTSF)2ClO4
We report angle-dependent magnetoresistance measurements on (TMTSF)2ClO4 that
provide strong support for a new macroscopic quantum phenomenon, the
interference commensurate (IC) effect, in quasi-one dimensional metals. In
addition to observing rich magnetoresistance oscillations, and fitting them
with one-electron calculations, we observe a clear demarcation of
field-dependent behavior at local resistance minima and maxima (versus field
angle). Anticipated by a theoretical treatment of the IC effect in terms of
Bragg reflections in the extended Brillouin zone, this behavior results from
1D-2D topological crossovers of electron wave functions as a function of field
orientation.Comment: 14 page
Antonio Gramsci’s impact on critical pedagogy
This paper provides an account of Antonio Gramsci’s impact on the area of critical pedagogy. It indicates the Gramscian influence on the thinking of major exponents of the field. It foregrounds Gramsci's ideas and then indicates how they have been taken up by a selection of critical pedagogy exponents who were chosen on the strength of their identification and engagement with Gramsci's ideas, some of them even having written entire essays on Gramsci. The essay concludes with a discussion concerning an aspect of Gramsci's concerns, the question of powerful knowledge, which, in the present author's view, provides a formidable challenge to critical pedagogues.peer-reviewe
Exactly Solvable Pairing Model Using an Extension of Richardson-Gaudin Approach
We introduce a new class of exactly solvable boson pairing models using the
technique of Richardson and Gaudin. Analytical expressions for all energy
eigenvalues and first few energy eigenstates are given. In addition, another
solution to Gaudin's equation is also mentioned. A relation with the
Calogero-Sutherland model is suggested.Comment: 9 pages of Latex. In the proceedings of Blueprints for the Nucleus:
From First Principles to Collective Motion: A Festschrift in Honor of
Professor Bruce Barrett, Istanbul, Turkey, 17-23 May 200
1/t pressure and fermion behaviour of water in two dimensions
A variety of metal vacuum systems display the celebrated 1/t pressure, namely
power-law dependence on time t, with the exponent close to unity, the origin of
which has been a long-standing controversy. Here we propose a chemisorption
model for water adsorbates, based on the argument for fermion behaviour of
water vapour adsorbed on a stainless-steel surface, and obtain analytically the
power-law behaviour of pressure, with an exponent of unity. Further, the model
predicts that the pressure should depend on the temperature T according to
T^(3/2), which is indeed confirmed by our experiment. Our results should help
elucidate the unique characteristics of the adsorbed water.Comment: 11 pages, 4 figure
Size dependent line broadening in the emission spectra of single GaAs quantum dots: Impact of surface charges on spectral diffusion
Making use of droplet epitaxy, we systematically controlled the height of
self-assembled GaAs quantum dots by more than one order of magnitude. The
photoluminescence spectra of single quantum dots revealed the strong dependence
of the spectral linewidth on the dot height. Tall dots with a height of ~30 nm
showed broad spectral peaks with an average width as large as ~5 meV, but
shallow dots with a height of ~2 nm showed resolution-limited spectral lines
(<120 micro eV). The measured height dependence of the linewidths is in good
agreement with Stark coefficients calculated for the experimental shape
variation. We attribute the microscopic source of fluctuating electric fields
to the random motion of surface charges at the vacuum-semiconductor interface.
Our results offer guidelines for creating frequency-locked photon sources,
which will serve as key devices for long-distance quantum key distribution.Comment: 6 pages, 6 figures; updated figs and their description
Singular Cucker-Smale Dynamics
The existing state of the art for singular models of flocking is overviewed,
starting from microscopic model of Cucker and Smale with singular communication
weight, through its mesoscopic mean-filed limit, up to the corresponding
macroscopic regime. For the microscopic Cucker-Smale (CS) model, the
collision-avoidance phenomenon is discussed, also in the presence of bonding
forces and the decentralized control. For the kinetic mean-field model, the
existence of global-in-time measure-valued solutions, with a special emphasis
on a weak atomic uniqueness of solutions is sketched. Ultimately, for the
macroscopic singular model, the summary of the existence results for the
Euler-type alignment system is provided, including existence of strong
solutions on one-dimensional torus, and the extension of this result to higher
dimensions upon restriction on the smallness of initial data. Additionally, the
pressureless Navier-Stokes-type system corresponding to particular choice of
alignment kernel is presented, and compared - analytically and numerically - to
the porous medium equation
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