7,102 research outputs found
Trajectories of the S-matrix poles in Salamon-Vertse potential
The trajectories of S-matrix poles are calculated in the finite-range
phenomenological potential introduced recently by P. Salamon and T. Vertse
(SV). The trajectories of the resonance poles in this SV potential are compared
to the corresponding trajectories in a cut-off Woods-Saxon (WS) potential for
l>0. The dependence on the cut-off radius is demonstrated. The starting points
of the trajectories turn out to be related to the average ranges of the two
terms in the SV potential
Searching for effects caused by thunderstorms in midlatitude sporadic E layers
Possible thunderstorm - sporadic E (Es) layer coupling effects are
investigated during two measurement periods, one in 2013 and one in 2014. The
analysis was based on ionospheric observations obtained from a Digisonde at
Pruhonice, the Czech Republic, an ionosonde at Nagycenk, Hungary, and a 3.59
MHz five-point continuous HF Doppler system located in the western part of the
Czech Republic. The latter is capable of detecting ionospheric wave-like
variations caused by neutral atmospheric waves generated by thunderstorms. The
present study searches for possible impacts on Es layers caused by the presence
of two active thunderstorms: one passing across the Czech Republic on June 20,
2013 (19:00 - 01:00 LT), and one through Hungary on July 30, 2014 (11:00 -
01:00 LT). During these two time periods, presence and parameters of Es layer
were inferred from ionograms, recorded every minute at Pruhonice and every two
minutes at Nagycenk, whereas concurrent lightning activity was monitored by the
LINET detection network. In addition, transient luminous events (TLEs) were
also observed during both nights from Sopron, Hungary and from Nydek, the Czech
Republic. A noticeable fact was the reduction and disappearance of the ongoing
Es layer activity during part of the time in both of the traversing
thunderstorms. The analysis indicated that the critical frequency foEs dropped
below ionosonde detection levels in both cases, possibly because of
thunderstorm activity effects. This option, however, needs more case studies in
order to be further substantiated
Antibound poles in cutoff Woods-Saxon and in Salamon-Vertse potentials
The motion of l=0 antibound poles of the S-matrix with varying potential
strength is calculated in a cutoff Woods-Saxon (WS) potential and in the
Salamon-Vertse (SV) potential, which goes to zero smoothly at a finite
distance. The pole position of the antibound states as well as of the
resonances depend on the cutoff radius, especially for higher node numbers. The
starting points (at potential zero) of the pole trajectories correlate well
with the range of the potential. The normalized antibound radial wave functions
on the imaginary k-axis below and above the coalescence point have been found
to be real and imaginary, respectively
Systematical Approach to the Exact Solution of the Dirac Equation for A Special Form of the Woods-Saxon Potential
Exact solution of the Dirac equation for a special form of the Woods-Saxon
potential is obtained for the s-states. The energy eigenvalues and
two-component spinor wave functions are derived by using a systematical method
which is called as Nikiforov-Uvarov. It is seen that the energy eigenvalues
strongly depend on the potential parameters. In addition, it is also shown that
the non-relativistic limit can be reached easily and directly.Comment: 10 pages, no figures, submitted for Publicatio
A study of cross sections for excitation of pseudostates
Using the electron-hydrogen scattering Temkin-Poet model we investigate the
behavior of the cross sections for excitation of all of the states used in the
convergent close-coupling (CCC) formalism. In the triplet channel, it is found
that the cross section for exciting the positive-energy states is approximately
zero near-threshold and remains so until a further energy, equal to the energy
of the state, is added to the system. This is consistent with the step-function
hypothesis [Bray, Phys. Rev. Lett. {\bf 78} 4721 (1997)] and inconsistent with
the expectations of Bencze and Chandler [Phys. Rev. A {\bf 59} 3129 (1999)].
Furthermore, we compare the results of the CCC-calculated triplet and singlet
single differential cross sections with the recent benchmark results of
Baertschy et al. [Phys. Rev. A (to be published)], and find consistent
agreement.Comment: Four pages, 5 figure
Electron-impact ionization of atomic hydrogen at 2 eV above threshold
The convergent close-coupling method is applied to the calculation of fully
differential cross sections for ionization of atomic hydrogen by 15.6 eV
electrons. We find that even at this low energy the method is able to yield
predictive results with small uncertainty. As a consequence we suspect that the
experimental normalization at this energy is approximately a factor of two too
high.Comment: 10 page
Long-term trends in the ionosphere and upper atmosphere parameters
The first part of the paper is directed to the investigation of the practical importance of possible longterm trends in the F2-layer for ionospheric prediction models. Using observations of about 50 different ionosonde stations with more than 30 years data series of foF2 and hmF2, trends have been derived with the solar sunspot number R12 as index of the solar activity. The final result of this trend analysis is that the differences between the trends derived from the data of the individual stations are relatively large,
the calculated global mean values of the foF2 and hmF2 trends, however, are relatively small. Therefore, these small global trends can be neglected for practical purposes and must not be considered in ionospheric prediction models. This conclusion is in agreement with the results of other investigations
analyzing data of globally distributed stations. As shown with the data of the ionosonde station Tromsø, however, at individual stations the ionospheric trends may be markedly stronger and lead to essential effects in ionospheric radio propagation. The second part of the paper deals with the reasons for possible
trends in the Earth’s atmo- and ionosphere as investigated by different methods using characteristic parameters of the ionospheric D-, E-, and F-regions. Mainly in the F2-region different analyses have
been carried out. The derived trends are mainly discussed in connection with an increasing greenhouse effect or by long-term changes in geomagnetic activity. In the F1-layer the derived mean global trend
in foF1 is in good agreement with model predictions of an increasing greenhouse effect. In the E-region the derived trends in foE and h´E are compared with model results of an atmospheric greenhouse effect,
or explained by geomagnetic effects or other anthropogenic disturbances. The trend results in the D-region derived from ionospheric reflection height and absorption measurements in the LF, MF and HF
ranges can at least partly be explained by an increasing atmospheric greenhouse effect
First observation of Cherenkov rings with a large area CsI-TGEM-based RICH prototype
We have built a RICH detector prototype consisting of a liquid C6F14 radiator
and six triple Thick Gaseous Electron Multipliers (TGEMs), each of them having
an active area of 10x10 cm2. One triple TGEM has been placed behind the liquid
radiator in order to detect the beam particles, whereas the other five have
been positioned around the central one at a distance to collect the Cherenkov
photons. The upstream electrode of each of the TGEM stacks has been coated with
a 0.4 micron thick CsI layer.
In this paper, we will present the results from a series of laboratory tests
with this prototype carried out using UV light, 6 keV photons from 55Fe and
electrons from 90Sr as well as recent results of tests with a beam of charged
pions where for the first time Cherenkov Ring images have been successfully
recorded with TGEM photodetectors. The achieved results prove the feasibility
of building a large area Cherenkov detector consisting of a matrix of TGEMs.Comment: Presented at the International Conference NDIP-11, Lyon,July201
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