33 research outputs found
Comment on "a Generalized Langevin Equation for 1/Æ Noise"
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
Superdiffusive Conduction: AC Conductivity with Correlated Noise
We present evidence of the existence of a superdiffusive regime in systems
with correlated disorder for which localization is suppressed. An expression
for anomalous electrical conductivity at low frequencies is found by using a
generalized Langevin equation whose memory function accounts for the
interactions between the carriers. New mechanisms inducing a superdiffusive
conductivity are discussed and experimental possibilities for observing that
phenomenon in nanotubes and superlattices are presented.Comment: 7 pages, no figure
Interaction model for magnetic holes in a ferrofluid layer
Nonmagnetic spheres confined in a ferrofluid layer (magnetic holes) present
dipolar interactions when an external magnetic field is exerted. The
interaction potential of a microsphere pair is derived analytically, with a
precise care for the boundary conditions along the glass plates confining the
system. Considering external fields consisting of a constant normal component
and a high frequency rotating in-plane component, this interaction potential is
averaged over time to exhibit the average interparticular forces acting when
the imposed frequency exceeds the inverse of the viscous relaxation time of the
system. The existence of an equilibrium configuration without contact between
the particles is demonstrated for a whole range of exciting fields, and the
equilibrium separation distance depending on the structure of the external
field is established. The stability of the system under out-of-plane buckling
is also studied. The dynamics of such a particle pair is simulated and
validated by experiments.Comment: 15 pages, 11 figures (18 with subfigures). to appear in Phys. Rev.
A Quantum-mechanical Approach for Constrained Macromolecular Chains
Many approaches to three-dimensional constrained macromolecular chains at
thermal equilibrium, at about room temperatures, are based upon constrained
Classical Hamiltonian Dynamics (cCHDa). Quantum-mechanical approaches (QMa)
have also been treated by different researchers for decades. QMa address a
fundamental issue (constraints versus the uncertainty principle) and are
versatile: they also yield classical descriptions (which may not coincide with
those from cCHDa, although they may agree for certain relevant quantities).
Open issues include whether QMa have enough practical consequences which differ
from and/or improve those from cCHDa. We shall treat cCHDa briefly and deal
with QMa, by outlining old approaches and focusing on recent ones.Comment: Expands review published in The European Physical Journal (Special
Topics) Vol. 200, pp. 225-258 (2011
Planck early results III : First assessment of the Low Frequency Instrument in-flight performance
Peer reviewe
Planck 2018 results. XII. Galactic astrophysics using polarized dust emission
We present 353 GHz full-sky maps of the polarization fraction p, angle \u3c8, and dispersion of angles S of Galactic dust thermal emission produced from the 2018 release of Planck data. We confirm that the mean and maximum of p decrease with increasing NH. The uncertainty on the maximum polarization fraction, pmax=22.0% at 80 arcmin resolution, is dominated by the uncertainty on the zero level in total intensity. The observed inverse behaviour between p and S is interpreted with models of the polarized sky that include effects from only the topology of the turbulent Galactic magnetic field. Thus, the statistical properties of p, \u3c8, and S mostly reflect the structure of the magnetic field. Nevertheless, we search for potential signatures of varying grain alignment and dust properties. First, we analyse the product map S
7p, looking for residual trends. While p decreases by a factor of 3--4 between NH=1020 cm 122 and NH=2
71022 cm 122, S
7p decreases by only about 25%, a systematic trend observed in both the diffuse ISM and molecular clouds. Second, we find no systematic trend of S
7p with the dust temperature, even though in the diffuse ISM lines of sight with high p and low S tend to have colder dust. We also compare Planck data with starlight polarization in the visible at high latitudes. The agreement in polarization angles is remarkable. Two polarization emission-to-extinction ratios that characterize dust optical properties depend only weakly on NH and converge towards the values previously determined for translucent lines of sight. We determine an upper limit for the polarization fraction in extinction of 13%, compatible with the pmax observed in emission. These results provide strong constraints for models of Galactic dust in diffuse gas
Engineering tube shapes to control confined transport
Transport of particles in confined structures can be modeled by means of diffusion in a potential of entropic nature. The entropic transport model proposes a drift-diffusion kinetic equation for the evolution of the probability density in which the diffusion coefficient depends on position and the drift term contains an entropic force. The model has been applied to analyze transport in single cavities and through periodic structures of different shape, and to investigate the nature of non-equilibrium fluctuations as well. The transport characteristics depends strongly on the contour of the region through which particles move, which defines the entropic potential. We show that the form of the entropic potential can be properly designed to optimize and govern how molecules diffuse and get drifted in tortuous channels. The shape of a tube or channel can be smartly engineered to control transport for the desired application
Author Correction: Casimir forces exerted by epsilon-near-zero hyperbolic materials (Scientific Reports, (2020), 10, 1, (16831), 10.1038/s41598-020-73995-0)
In the original version of this Article, Igor S. Nefedov was incorrectly affiliated with âSaratov State University, Astrakhanskaya 83, Saratov, Russian Federation, 410012â. The correct affiliation is listed below: Peoplesâ Friendship University of Russia (RUDN University), 6 Miklukho-Maklaya St., Moscow 117198, Russia. This error has now been corrected in the HTML and PDF versions of the Article. © 2020, The Author(s)