10,634 research outputs found
Broad distribution effects in sums of lognormal random variables
The lognormal distribution describing, e.g., exponentials of Gaussian random
variables is one of the most common statistical distributions in physics. It
can exhibit features of broad distributions that imply qualitative departure
from the usual statistical scaling associated to narrow distributions.
Approximate formulae are derived for the typical sums of lognormal random
variables. The validity of these formulae is numerically checked and the
physical consequences, e.g., for the current flowing through small tunnel
junctions, are pointed out.Comment: 14 pages, 9 figures. Minor changes + Gini coefficient and 4 refs.
adde
Spontaneous CPT Violation in Confined QED
Symmetry breaking induced by untwisted fermions in QED in a nonsimply
connected spacetime with topology is investigated. It is
found that the discrete CPT symmetry of the theory is spontaneously broken by
the appearance of a constant vacuum expectation value of the electromagnetic
potential along the direction of space periodicity. The constant potential is
shown to be gauge nonequivalent to zero in the nonsimply connected spacetime
under consideration. Due to the symmetry breaking, one of the electromagnetic
modes of propagation is massive with a mass that depends on the inverse of the
compactification length. As a result, the system exhibits a sort of topological
directional superconductivity.Comment: 6 pages, revte
3D simulations of the early stages of AGN jets: geometry, thermodynamics and backflow
We investigate the interplay between jets from Active Galactic Nuclei (AGNs)
and the surrounding InterStellar Medium (ISM) through full 3D, high resolution,
Adaptive Mesh Refinement simulations performed with the FLASH code. We follow
the jet- ISM system for several Myr in its transition from an early, compact
source to an extended one including a large cocoon. During the jet evolution,
we identify three major evolutionary stages and we find that, contrary to the
prediction of popular theoretical models, none of the simulations shows a
self-similar behavior. We also follow the evolution of the energy budget, and
find that the fraction of input power deposited into the ISM (the AGN coupling
constant) is of order of a few percent during the first few Myr. This is in
broad agreement with galaxy formation models employing AGN feedback. However,
we find that in these early stages, this energy is deposited only in a small
fraction (< 1%) of the total ISM volume. Finally we demonstrate the relevance
of backflows arising within the extended cocoon generated by a relativistic AGN
jet within the ISM of its host galaxy, previously proposed as a mechanism for
self-regulating the gas accretion onto the central object. These backflows tend
later to be destabilized by the 3D dynamics, rather than by hydrodynamic
(Kelvin- Helmholtz) instabilities. Yet, in the first few hundred thousand
years, backflows may create a central accretion region of significant extent,
and convey there as much as a few millions of solar masses.Comment: Accepted in MNRAS - 16 pages, 12 figures - Multimedia available on
the author's webpage: http://www.mpia.de/~ciel
Noise-assisted Thouless pump in elastically deformable molecular junctions
We study a Thouless pump realized with an elastically \textit{deformable
quantum dot} whose center of mass follows a non-linear stochastic dynamics. The
interplay of noise, non-linear effects, dissipation and interaction with an
external time-dependent driving on the pumped charge is fully analyzed. The
results show that the quantum pumping mechanism not only is not destroyed by
the force fluctuations, but it becomes stronger when the forcing signal
frequency is tuned close to the resonance of the vibrational mode. The
robustness of the quantum pump with temperature is also investigated and an
exponential decay of the pumped charge is found when the coupling to the
vibrational mode is present. Implications of our results for
nano-electromechanical systems are also discussed.Comment: 2 Appendices and figures adde
Understanding rapid internationalization of new low-technology ventures from emerging economies
An Autoethnographic Inquiry into the Emergence of New Forms and Ways of Organizing
This paper employs analytic autoethnography within a previous life in an organization and within social science to explore the emergence of new forms and ways of organizing in a new venture that was launched as a branch in an emerging market by an international non-for-profit organization. It responds to extant scarcity of knowledge about internal organization of entrepreneurial ventures as most of research about internal organization of firms comes from the research on large established organizations. In the early stage of new venture emergence, entrepreneurs shall be aware of the interplay between: understanding the new venture socio-politically and cognitively through unsophisticated uncertainty; timing of acquiring socio-political and cognitive legitimacy through legitimation temporaling; shared and non-shared understanding of the value (problem) of the new venture through disguised and true value theorizing; dependent and independent organization through diversifying funding sources; and headquarters and branch visions and missions through dominant logic crisis
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