1,930 research outputs found
On the fundamental solution of linear delay differential equations with multiple delays
For a class of linear autonomous delay differential equations with parameter we give upper bounds for the integral \int_{0}^{\infty}\left|X\left(t,\alpha\right)\right|\mbox{d}t of the fundamental solution . The asymptotic estimations are sharp at a critical value where loses stability. We use these results to study the stability properties of perturbed equations
Local stability implies global stability for the 2-dimensional Ricker map
Consider the difference equation where
is a positive parameter and d is a non-negative integer. The case d =
0 was introduced by W.E. Ricker in 1954. For the delayed version d >= 1 of the
equation S. Levin and R. May conjectured in 1976 that local stability of the
nontrivial equilibrium implies its global stability. Based on rigorous,
computer aided calculations and analytical tools, we prove the conjecture for d
= 1.Comment: for associated C++ program, mathematica worksheet and output, see
http://www.math.u-szeged.hu/~krisztin/ricke
Experimental energy levels and partition function of the C molecule
The carbon dimer, the C molecule, is ubiquitous in astronomical
environments. Experimental-quality rovibronic energy levels are reported for
C, based on rovibronic transitions measured for and among its
singlet, triplet, and quintet electronic states, reported in 42 publications.
The determination utilizes the Measured Active Rotational-Vibrational Energy
Levels (MARVEL) technique. The 23,343 transitions measured experimentally and
validated within this study determine 5,699 rovibronic energy levels, 1,325,
4,309, and 65 levels for the singlet, triplet, and quintet states investigated,
respectively. The MARVEL analysis provides rovibronic energies for six singlet,
six triplet, and two quintet electronic states. For example, the lowest
measurable energy level of the \astate\ state, corresponding to the total
angular momentum quantum number and the spin-multiplet component, is
603.817(5) \cm. This well-determined energy difference should facilitate
observations of singlet--triplet intercombination lines which are thought to
occur in the interstellar medium and comets. The large number of highly
accurate and clearly labeled transitions that can be derived by combining
MARVEL energy levels with computed temperature-dependent intensities should
help a number of astrophysical observations as well as corresponding laboratory
measurements. The experimental rovibronic energy levels, augmented, where
needed, with {\it ab initio} variational ones based on empirically adjusted and
spin-orbit coupled potential energy curves obtained using the \Duo\ code, are
used to obtain a highly accurate partition function, and related thermodynamic
data, for C up to 4,000 K.Comment: ApJ Supplements (in press), 48 page
Detection of ionospheric signatures from GPS-derived total electron content maps
The processing of measurement data from satellite
constellations such as Global Navigation Satellite Systems
(GNSS), including the well-known Global Positioning
System (GPS), have been successfully applied to virtually
all areas of geophysical sciences. In this work, a
method is described where Geographical Information Systems
(GIS) are employed to build hourly ionospheric Total
Electron Content (TEC) maps for 2011 over the southern
Iberian Peninsula. The maps used GPS-derived geometryfree
linear combinations attained from station data from
the Algarve, Alentejo (Portugal), Andalusia, Murcia and
Valencia (Spain) regions. Following the construction of
the ionospheric maps, it was possible to relate these results
to natural phenomena. The observed phenomena included
diurnal and seasonal variations: daytime TEC maxima,
nighttime TEC peaks, summer TEC value decreases,
and spring and fall TEC maxima. After validation of these
periodic phenomena, detection of non-periodic changes,
such as solar flares and tectonic interactions with the ionosphere
were attempted. The results showed a TEC increase
following a selected solar flare event and a potential TEC
build-up prior to the 2011 Lorca earthquake. Further studies
could open up the possibility of building early warning
systems. The presented methods, based on available software
packages, are also of value in monitoring the effect of
the ionosphere on radio signals, satellite and mobile communication,
power grids, and for accurate GNSS navigation
Molecular Spiders with Memory
Synthetic bio-molecular spiders with "legs" made of single-stranded segments
of DNA can move on a surface which is also covered by single-stranded segments
of DNA complementary to the leg DNA. In experimental realizations, when a leg
detaches from a segment of the surface for the first time it alters that
segment, and legs subsequently bound to these altered segments more weakly.
Inspired by these experiments we investigate spiders moving along a
one-dimensional substrate, whose legs leave newly visited sites at a slower
rate than revisited sites. For a random walk (one-leg spider) the slowdown does
not effect the long time behavior. For a bipedal spider, however, the slowdown
generates an effective bias towards unvisited sites, and the spider behaves
similarly to the excited walk. Surprisingly, the slowing down of the spider at
new sites increases the diffusion coefficient and accelerates the growth of the
number of visited sites.Comment: 10 pages, 3 figure
A betonok fagy- és olvasztósóállóság-vizsgálati hámlásának lassulási folyamata
A betonok fagy-, illetve fagy- és olvasztósóállóság-vizsgálati hámlása időben lejátszódó folyamat, amely lassuló vagy gyorsuló jellegének korábban nem túl sok figyelmet szenteltünk. A hámlasztásos fagyasztási lassulás is viszonylag új fogalomnak tekinthető, amely fogalom ilyen elnevezésének a nemzetközi irodalomban sem találtuk a nyomát.
E cikkben – amelyet az NVKP 16-1-2016-0019 pályázati támogatásból dolgoztuk ki – a hámlasztásos fagyasztási lassulási feltételt tartalmazó szabványoknak a lassulási feltétellel kapcsolatos intézkedéseit, valamint a lassulási feltétel e szabványokon túlmenő továbbfejlesztésének lehetőségét mutatjuk be
Distribution of Electric Currents in Solar Active Regions
There has been a long-lasting debate on the question of whether or not
electric currents in solar active regions are neutralized. That is, whether or
not the main (or direct) coronal currents connecting the active region
polarities are surrounded by shielding (or return) currents of equal total
value and opposite direction. Both theory and observations are not yet fully
conclusive regarding this question, and numerical simulations have,
surprisingly, barely been used to address it. Here we quantify the evolution of
electric currents during the formation of a bipolar active region by
considering a three-dimensional magnetohydrodynamic simulation of the emergence
of a sub-photospheric, current-neutralized magnetic flux rope into the solar
atmosphere. We find that a strong deviation from current neutralization
develops simultaneously with the onset of significant flux emergence into the
corona, accompanied by the development of substantial magnetic shear along the
active region's polarity inversion line. After the region has formed and flux
emergence has ceased, the strong magnetic fields in the region's center are
connected solely by direct currents, and the total direct current is several
times larger than the total return current. These results suggest that active
regions, the main sources of coronal mass ejections and flares, are born with
substantial net currents, in agreement with recent observations. Furthermore,
they support eruption models that employ pre-eruption magnetic fields
containing such currents.Comment: 6 pages, 5 figures, to appear in Astrophysical Journal Letter
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