4,088 research outputs found
Spectroscopic studies of fractal aggregates of silver nanospheres undergoing local restructuring
We present an experimental spectroscopic study of large random colloidal
aggregates of silver nanoparticles undergoing local restructuring. We argue
that such well-known phenomena as strong fluctuation of local electromagnetic
fields, appearance of "hot spots" and enhancement of nonlinear optical
responses depend on the local structure on the scales of several nanosphere
diameters, rather that the large-scale fractal geometry of the sample.Comment: 3.5 pages, submitted to J. Chem. Phy
The first light of Mini-MegaTORTORA wide-field monitoring system
Here we describe the first light of the novel 9-channel wide-field optical
monitoring system with sub-second temporal resolution, Mini-MegaTORTORA, which
is being tested now at Special Astrophysical Observatory on Russian Caucasus.
The system is able to observe the sky simultaneously in either wide (~900
square degrees) or narrow (~100 square degrees) fields of view, either in clear
light or with any combination of color (Johnson B, V or R) polarimetric filters
installed, with exposure times ranging from 100 ms to 100 s. The primary goal
of the system is the detection of rapid -- with sub-second characteristic
time-scales -- optical transients, but it may be also used for studying the
variability of the sky objects on longer time scales.Comment: 9 pages, 9 figures, based on the talk presented on "Modern stellar
astronomy-2014" (Rostov-on-Don
Local anisotropy and giant enhancement of local electromagnetic fields in fractal aggregates of metal nanoparticles
We have shown within the quasistatic approximation that the giant
fluctuations of local electromagnetic field in random fractal aggregates of
silver nanospheres are strongly correlated with a local anisotropy factor S
which is defined in this paper. The latter is a purely geometrical parameter
which characterizes the deviation of local environment of a given nanosphere in
an aggregate from spherical symmetry. Therefore, it is possible to predict the
sites with anomalously large local fields in an aggregate without explicitly
solving the electromagnetic problem. We have also demonstrated that the average
(over nanospheres) value of S does not depend noticeably on the fractal
dimension D, except when D approaches the trivial limit D=3. In this case, as
one can expect, the average local environment becomes spherically symmetrical
and S approaches zero. This corresponds to the well-known fact that in trivial
aggregates fluctuations of local electromagnetic fields are much weaker than in
fractal aggregates. Thus, we find that, within the quasistatics, the
large-scale geometry does not have a significant impact on local
electromagnetic responses in nanoaggregates in a wide range of fractal
dimensions. However, this prediction is expected to be not correct in
aggregates which are sufficiently large for the intermediate- and
radiation-zone interaction of individual nanospheres to become important.Comment: 9 pages 9 figures. No revisions from previous version; only figure
layout is change
Thermodynamics of second phase conductive filaments
We present a theory of second phase conductive filaments in phase
transformable systems; applications include threshold switches, phase change
memory, and shunting in thin film structures. We show that the average filament
parameters can be described thermodynamically. In agreement with the published
data, the predicted filament current voltage characteristics exhibit negative
differential resistance vanishing at high currents where the current density
becomes a bulk material property. Our description is extendible to filament
transients and allows for efficient numerical simulation
Photon losses depending on polarization mixedness
We introduce a quantum channel describing photon losses depending on the
degree of polarization mixedness. This can be regarded as a model of quantum
channel with correlated errors between discrete and continuous degrees of
freedom. We consider classical information over a continuous alphabet encoded
on weak coherent states as well as classical information over a discrete
alphabet encoded on single photons using dual rail representation. In both
cases we study the one-shot capacity of the channel and its behaviour in terms
of correlation between losses and polarization mixedness
Purity and Gaussianity bounded uncertainty relation
Bounded uncertainty relations provide the minimum value of the uncertainty
assuming some additional information on the state. We derive analytically an
uncertainty relation bounded by a pair of constraints, those of purity and
Gaussianity. In a limiting case this uncertainty relation reproduces the
purity-bounded derived by V I Man'ko and V V Dodonov and the
Gaussianity-bounded one [Phys. Rev. A 86, 030102R (2012)].Comment: Major changes in the presentation of the results but also in the
proofs which have become more compact. Submitted to Journal of Physics
- …