2,870 research outputs found
Parametric investigation of nonlinear fluctuations in a dc glow discharge plasma
Glow discharge plasmas exhibit various types of self excited oscillations for
different initial conditions like discharge voltages and filling pressures. The
behavior of such oscillations associated with the anode glow have been
investigated using nonlinear techniques like correlation dimension, largest
Lyapunov exponent etc. It is seen that these oscillations go to an ordered
state from a chaotic state with increase in input energy i.e. with discharge
voltages implying occurrence of inverse bifurcations. These results are
different from the other observations wherein the fluctuations have been
observed to go from ordered to chaotic state.Comment: Submitted to Chao
Oscillation modes of dc microdischarges with parallel-plate geometry
Two different oscillation modes in microdischarge with parallel-plate
geometry has been observed: relaxation oscillations with frequency range
between 1.23 and 2.1 kHz and free-running oscillations with 7 kHz frequency.
The oscillation modes are induced by increasing power supply voltage or
discharge current. For a given power supply voltage, there is a spontaneous
transition from one to other oscillation mode and vice versa. Before the
transition from relaxation to free-running oscillations, the spontaneous
increase of oscillation frequency of relaxation oscillations form 1.3 kHz to
2.1 kHz is measured. Fourier Transform Spectra of relaxation oscillations
reveal chaotic behaviour of microdischarge. Volt-Ampere characteristics
associated with relaxation oscillations describes periodical transition between
low current, diffuse discharge and normal glow. However, free-running
oscillations appear in subnormal glow only.Comment: Submitted to: New Journal of Physic
On the jets, kinks, and spheromaks formed by a planar magnetized coaxial gun
Measurements of the various plasma configurations produced by a planar
magnetized coaxial gun provide insight into the magnetic topology evolution
resulting from magnetic helicity injection. Important features of the
experiments are a very simple coaxial gun design so that all observed
geometrical complexity is due to the intrinsic physical dynamics rather than
the source shape and use of a fast multiple-frame digital camera which provides
direct imaging of topologically complex shapes and dynamics. Three key
experimental findings were obtained: (1) formation of an axial collimated jet
[Hsu and Bellan, Mon. Not. R. Astron. Soc. 334, 257 (2002)] that is consistent
with a magnetohydrodynamic description of astrophysical jets, (2)
identification of the kink instability when this jet satisfies the
Kruskal-Shafranov limit, and (3) the nonlinear properties of the kink
instability providing a conversion of toroidal to poloidal flux as required for
spheromak formation by a coaxial magnetized source [Hsu and Bellan, Phys. Rev.
Lett. 90, 215002 (2003)]. A new interpretation is proposed for how the n=1
central column instability provides flux amplification during spheromak
formation and sustainment, and it is shown that jet collimation can occur
within one rotation of the background poloidal field.Comment: Physics of Plasmas (accepted
The impact of mixing across the polar vortex edge on Match ozone loss estimates
The Match method for quantification of polar chemical ozone loss is investigated mainly with respect to the impact of mixing across the vortex edge onto this estimate. We show for the winter 2002/03 that significant mixing across the vortex edge occurred and was accurately modeled by the Chemical Lagrangian Model of the Stratosphere. Observations of inert tracers and ozone in-situ from HAGAR on the Geophysica aircraft and sondes and also remote from MIPAS on ENVISAT were reproduced well. The model even reproduced a small vortex remnant that was isolated until June 2003 and was observed in-situ by a balloon-borne whole air sampler. We use this CLaMS simulation to quantify the impact of cross vortex edge mixing on the results of the Match method. It is shown that a time integration of the determined vortex average ozone loss rates as performed in Match results in larger ozone loss than the polar vortex average ozone loss in CLaMS. Also, the determination of the Match ozone loss rates can be influenced by mixing. This is especially important below 430 K, where ozone outside the vortex is lower than inside and the vortex boundary is not a strong transport barrier. This effect and further sampling effects cause an offset between vortex average ozone loss rates derived from Match and deduced from CLaMS with an even sampling for the entire vortex. Both, the time-integration of ozone loss and the determination of ozone loss rates for Match are evaluated using the winter 2002/03 CLaMS simulation. These impacts can explain the differences between CLaMS and Match column ozone loss. While the investigated effects somewhat reduce the apparent discrepancy in January ozone loss rates, a discrepancy between simulations and Match remains. However, its contribution to the accumulated ozone loss over the winter is not large
A conic manifold perspective of elliptic operators on graphs
We give a simple, explicit, sufficient condition for the existence of a
sector of minimal growth for second order regular singular differential
operators on graphs. We specifically consider operators with a singular
potential of Coulomb type and base our analysis on the theory of elliptic cone
operators.Comment: 18 page
Periodic Structures with Rashba Interaction in Magnetic Field
We analyze the behaviour of a system of particles living on a periodic
crystal in the presence of a magnetic field B. This can be done by involving a
periodic potential U(x) and the Rashba interaction of coupling constant k_{so}.
By resorting the corresponding spectrum, we explicitly determine the band
structures and the Bloch spinors. These allow us to discuss the system
symmetries in terms of the polarizations where they are shown to be broken. The
dynamical spin will be studied by calculating different quantities. In the
limits: k_{so} and U(x)=0, we analyze again the system by deriving different
results. Considering the strong case, we obtain an interesting result that
is the conservation of the polarizations. Analyzing the critical point
\lambda_{k,\sigma}=\pm\sq{1\over 2}, we show that the Hilbert space associated
to the spectrum in z-direction has a zero mode energy similar to that of
massless Dirac fermions in graphene. Finally, we give the resulting energy
spectrum when B=0 and U(x) is arbitrary.Comment: 24 pages, references added, misprints corrected. Version to appear in
JP
Analysis of OPM potentials for multiplet states of 3d transition metal atoms
We apply the optimized effective potential method (OPM) to the multiplet
energies of the 3d transition metal atoms, where the orbital dependence of
the energy functional with respect to orbital wave function is the
single-configuration HF form. We find that the calculated OPM exchange
potential can be represented by the following two forms. Firstly, the
difference between OPM exchange potentials of the multiplet states can be
approximated by the linear combination of the potentials derived from the
Slater integrals and for the average
energy of the configuration. Secondly, the OPM exchange potential can be
expressed as the linear combination of the OPM exchange potentials of the
single determinants.Comment: 15 pages, 6 figures, to be published in J. Phys.
Reaction Time of a Group of Physics Students
The reaction time of a group of students majoring in Physics is reported
here. Strong co-relation between fatigue, reaction time and performance have
been seen and may be useful for academicians and administrators responsible of
working out time-tables, course structures, students counsellings etc.Comment: 10 pages, 4 figure
Atmospheric observation-based global SF6 emissions - comparison of top-down and bottom-up estimates
Emissions of sulphur hexafluoride (SF6), one of the strongest greenhouse gases on a per molecule basis, are targeted to be collectively reduced under the Kyoto Protocol. Because of its long atmospheric lifetime (≈3000 years), the accumulation of SF6 in the atmosphere is a direct measure of its global emissions. Examination of our extended data set of globally distributed high-precision SF6 observations shows an increase in SF6 abundance from near zero in the 1970s to a global mean of 6.7 ppt by the end of 2008. In-depth evaluation of our long-term data records shows that the global source of SF6 decreased after 1995, most likely due to SF6 emission reductions in industrialised countries, but increased again after 1998. By subtracting those emissions reported by Annex I countries to the United Nations Framework Convention of Climatic Change (UNFCCC) from our observation-inferred SF6 source leaves a surprisingly large gap of more than 70–80% of non-reported SF6 emissions in the last decade
Frequency Scaling of Microwave Conductivity in the Integer Quantum Hall Effect Minima
We measure the longitudinal conductivity at frequencies GHz over a range of temperatures K with particular emphasis on the Quantum Hall plateaus. We find that
scales linearly with frequency for a range of magnetic field
around the center of the plateaus, i.e. where . The width of this scaling region decreases with higher
temperature and vanishes by 1.2 K altogether. Comparison between localization
length determined from and DC measurements on the same
wafer show good agreement.Comment: latex 4 pages, 4 figure
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