16,748 research outputs found
Sub-femtosecond electron bunches created by direct laser acceleration in a laser wakefield accelerator with ionization injection
In this work, we will show through three-dimensional particle-in-cell
simulations that direct laser acceleration in laser a wakefield accelerator can
generate sub-femtosecond electron bunches. Two simulations were done with two
laser pulse durations, such that the shortest laser pulse occupies only a
fraction of the first bubble, whereas the longer pulse fills the entire first
bubble. In the latter case, as the trapped electrons moved forward and
interacted with the high intensity region of the laser pulse, micro-bunching
occurred naturally, producing 0.5 fs electron bunches. This is not observed in
the short pulse simulation.Comment: AAC 201
Direct images of bundles under Frobenius morphisms
Let be a smooth projective variety of dimension over an algebraically
closed field with and be the relative
Frobenius morphism. For any vector bundle on , we prove that instability
of is bounded by instability of
()(Corollary \ref{cor3.8}). When is a smooth
projective curve of genus , it implies being stable whenever
is stable.Comment: the final version to appear in Invent. math. (2008
EFFICACY OF IMIDACLOPRID (CONFIDOR 200 SL) AGAINST APHIDS INFESTING WHEAT CROP
Imidacloprid (Confidor 200 SL) was evaluated either alone or with a fungicide (Tilt 0.01%) against wheat aphids. There were seven different treatments, including an untreated control. All the treatments were replicated three times in a similar field environment. Population of wheat aphids was recorded on randomly selected five plants in each plot at different intervals, both before and after the spraying. Confidor 200 SL @ 400 ml/ha treatment was found most effective against wheat aphids. However, mixing of Confidor 200 SL @ 100 ml/ha with Tilt @ 0.01 %, was found
significantly least effective for wheat aphids control
An improved magnetic field simulator - MAGFLD.
An improved two-dimensional simulator MAGFLD has been developed which is useful for the design and simulation of periodic permanent magnet (PPM) focusing system for linear beam tubes. At present, input is possible only through the input file, which is very simple and user friendly. A complete PPM circuit is generated using the coordinates of first pole piece, first magnet, gun adapter (if the structure is a-periodic) and the region of computation. Small mesh units of either square or rectangular shapes can be used with mesh refinement capability in one or more regions in any or both directions for better accuracy of the solution. Materials with different magnetic permeability can be modeled by defining a characteristic value for each mesh point of the geometry. The effective potential value at each point in the region of interest is calculated based on the vector potential model by using the 5-point finite difference method and the solution is achieved by over relaxation technique for faster convergence. This package has an interface with EGUN to model the electron gun and collector under the influence of magnetic field. Versatile color graphics are capable of plotting both axial magnetic field and flux lines along with the magnetic circuit. MAGFLD has been validated against some published data and experimental results
North-South Distribution of Solar Flares during Cycle 23
In this paper, we investigate the spatial distribution of solar flares in the
northern and southern hemisphere of the Sun that occurred during the period
1996 to 2003. This period of investigation includes the ascending phase, the
maximum and part of descending phase of solar cycle 23. It is revealed that the
flare activity during this cycle is low compared to previous solar cycle,
indicating the violation of Gnevyshev-Ohl rule. The distribution of flares with
respect to heliographic latitudes shows a significant asymmetry between
northern and southern hemisphere which is maximum during the minimum phase of
the solar cycle. The present study indicates that the activity dominates the
northern hemisphere in general during the rising phase of the cycle
(1997-2000). The dominance of northern hemisphere is shifted towards the
southern hemisphere after the solar maximum in 2000 and remained there in the
successive years. Although the annual variations in the asymmetry time series
during cycle 23 are quite different from cycle 22, they are comparable to cycle
21.Comment: 6 pages, 2 figures, 1 table; Accepted for the publication in the
proceedings of international solar workshop held at ARIES, Nainital, India on
"Transient Phenomena on the Sun and Interplanetary Medium" in a special issue
of "Journal of Astrophysics and Astronomy (JAA)
Formation of a rotating jet during the filament eruption on 10-11 April 2013
We analyze multi-wavelength and multi-viewpoint observations of a helically
twisted plasma jet formed during a confined filament eruption on 10-11 April
2013. Given a rather large scale event with its high spatial and temporal
resolution observations, it allows us to clearly understand some new physical
details about the formation and triggering mechanism of twisting jet. We
identify a pre-existing flux rope associated with a sinistral filament, which
was observed several days before the event. The confined eruption of the
filament within a null point topology, also known as an Eiffel tower (or
inverted-Y) magnetic field configuration results in the formation of a twisted
jet after the magnetic reconnection near a null point. The sign of helicity in
the jet is found to be the same as that of the sign of helicity in the
filament. Untwisting motion of the reconnected magnetic field lines gives rise
to the accelerating plasma along the jet axis. The event clearly shows the
twist injection from the pre-eruptive magnetic field to the jet.Comment: 14 pages, 12 figures, to appear in MNRA
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