250,239 research outputs found
Surface Percolation and Growth. An alternative scheme for breaking the diffraction limit in optical patterning
A nanopatterning scheme is presented by which the structure height can be
controlled in the tens of nanometers range and the lateral resolution is a
factor at least three times better than the point spread function of the
writing beam. The method relies on the initiation of the polymerization
mediated by a very inefficient energy transfer from a fluorescent dye molecule
after single photon absorption. The mechanism has the following distinctive
steps: the dye adsorbs on the substrate surface with a higher concentration
than in the bulk, upon illumination it triggers the polymerization, then
isolated islands develop and merge into a uniform structure (percolation),
which subsequently grows until the illumination is interrupted. This
percolation mechanism has a threshold that introduces the needed nonlinearity
for the fabrication of structures beyond the diffraction limit.Comment: 10 pages, 8 figure
Interaction of a Nanomagnet with a Weak Superconducting Link
We study electromagnetic interaction of a nanomagnet with a weak
superconducting link. Equations that govern coupled dynamics of the two systems
are derived and investigated numerically. We show that the presence of a small
magnet in the proximity of a weak link may be detected through Shapiro-like
steps caused by the precession of the magnetic moment. Despite very weak
magnetic field generated by the weak link, a time-dependent bias voltage
applied to the link can initiate a non-linear dynamics of the nanomagnet that
leads to the reversal of its magnetic moment. We also consider quantum problem
in which a nanomagnet interacting with a weak link is treated as a two-state
spin system due to quantum tunneling between spin-up and spin-down states.Comment: 7 pages, 4 figure
Analytic continuation by averaging Pad\'e approximants
The ill-posed analytic continuation problem for Green's functions and
self-energies is investigated by revisiting the Pad\'{e} approximants
technique. We propose to remedy the well-known problems of the Pad\'{e}
approximants by performing an average of several continuations, obtained by
varying the number of fitted input points and Pad\'{e} coefficients
independently. The suggested approach is then applied to several test cases,
including Sm and Pr atomic self-energies, the Green's functions of the Hubbard
model for a Bethe lattice and of the Haldane model for a nano-ribbon, as well
as two special test functions. The sensitivity to numerical noise and the
dependence on the precision of the numerical libraries are analysed in detail.
The present approach is compared to a number of other techniques, i.e. the
non-negative least-square method, the non-negative Tikhonov method and the
maximum entropy method, and is shown to perform well for the chosen test cases.
This conclusion holds even when the noise on the input data is increased to
reach values typical for quantum Monte Carlo simulations. The ability of the
algorithm to resolve fine structures is finally illustrated for two relevant
test functions.Comment: 10 figure
Geomagnetic control of the spectrum of traveling ionospheric disturbances based on data from a global GPS network
In this paper an attempt is made to verify the hypothesis on the role of
geomagnetic disturbances as a factor determining the intensity of traveling
ionospheric disturbances (TIDs). To improve the statistical validity of the
data, we have used the based on the new GLOBDET technology method involving a
global spatial averaging of disturbance spectra of the total electron content
(TEC). To characterize the TID intensity quantitatively, we suggest that a new
global index of the degree of disturbance should be used, which is equal to the
mean value of the rms variations in TEC within the selected range of spectral
periods (of 20-60 min in the present case). It was found that power spectra of
daytime TEC variations in the range of 20-60 min periods under quiet conditions
have a power-law form, with the slope index k = -2.5. With an increase of the
level of magnetic disturbance, there is an increase in total intensity of TIDs,
with a concurrent kink of the spectrum caused by an increase in oscillation
intensity in the range of 20-60 min. It was found that an increase in the level
of geomagnetic activity is accompanied by an increase in total intensity of
TEC; however, it correlates not with the absolute level of Dst, but with the
value of the time derivative of Dst (a maximum correlation coefficient reaches
-0.94). The delay of the TID response of the order of 2 hours is consistent
with the view that TIDs are generated in auroral regions, and propagate
equatorward with the velocity of about 300-400 m/s.Comment: LaTeX2.09, 16 pages, 5 figures, 1 table, egs.cls, egs.bst (the style
files
Electron self-energy in A3C60 (A=K, Rb): Effects of t1u plasmon in GW approximation
The electron self-energy of the t1u states in A3C60 (A=K, Rb) is calculated
using the so-called GW approximation. The calculation is performed within a
model which considers the t1u charge carrier plasmon at 0.5 eV and takes into
account scattering of the electrons within the t1u band. A moderate reduction
(35 %) of the t1u band width is obtained.Comment: 4 pages, revtex, 1 figure more information at
http://www.mpi-stuttgart.mpg.de/dokumente/andersen/fullerene
Mandelstam cuts and light-like Wilson loops in N=4 SUSY
We perform an analytic continuation of the two-loop remainder function for
the six-point planar MHV amplitude in N=4 SUSY, found by Goncharov, Spradlin,
Vergu and Volovich from the light-like Wilson loop representation. The
remainder function is continued into a physical region, where all but two
energy invariants are negative. It turns out to be pure imaginary in the
multi-Regge kinematics, which is in an agreement with the predictions based on
the Steinmann relations for the Regge poles and Mandelstam cut contributions.
The leading term reproduces correctly the expression calculated by one of the
authors in the BFKL approach, while the subleading term presents a result, that
was not yet found with the use of the unitarity techniques. This supports the
applicability of the Wilson loop approach to the planar MHV amplitudes in N=4
SUSY.Comment: 11 pages, 4 figure
Vitamin D as One of Predicators of the Stable Viral Response to Antiviral Therapy in Patients with Chronis Hepatitis С
Chronic hepatitis C (CHC) it is not exceptionally medical problem but a significant social and economic threat, taking into account the unfavorable consequences of this disease: cirrhosis and hepatocellular carcinoma. And as a result - the high level of disability. In the article are presented the results of examination of 41 patients with chronic hepatitis C, with 1 genotype, who received the antiviral therapy (AVT). All patients underwent determination of the level of 5-hydroxycholeсalсeferol (25-OH vit D3), vitamin D and also the study of IL-28B polymorphism as the one of predicators of response to AVT. It was demonstrated, that in patients with hepatitis was observed the deficit of 25-OH vit D3 and general vitamin D. It was established, that in patients with the normal 25-OH vit D3 level SVR (stable viral response) was observed in 1,4 times more often than in patients with deficit of 25-OH vit D3. That is the level of 25-OH vit D3 can be considered as a predicator of SVR to AVT
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