440 research outputs found
Transverse Instabilities of Coasting Beams with Space Charge
Transverse beam stability is strongly affected by the beam space charge.
Usually it is analyzed with the rigid-beam model. However this model is only
valid when a bare (not affected by the space charge) tune spread is small
compared to the space charge tune shift. This condition specifies a relatively
small area of parameters which, however, is the most interesting for practical
applications. The Landau damping rate and the beam Schottky spectra are
computed assuming that validity condition is satisfied. The results are applied
to a round Gaussian beam. The stability thresholds are described by simple fits
for the cases of chromatic and octupole tune spreads.Comment: 6 pages, 2 figures, accepted by Phys. Rev. ST - Accel. Beam
Transverse instability of the antiproton beam in the Recycler Ring
The brightness of the antiproton beam in Fermilab's 8 GeV Recycler ring is
limited by a transverse instability. This instability has occurred during the
extraction process to the Tevatron for large stacks of antiprotons even with
dampers in operation. This paper describes observed features of the
instability, introduces the threshold phase density to characterize the beam
stability, and finds the results to be in agreement with a resistive wall
instability model. Effective exclusion of the longitudinal tails from Landau
damping by decreasing the depth of the RF potential well is observed to lower
the threshold density by up to a factor of two.Comment: 3 pp. Particle Accelerator, 24th Conference (PAC'11) 2011. 28 Mar - 1
Apr 2011. New York, US
Fractive antennas on the flying mashines
Проведен обзор существующих щелевых антенн, которые могут устанавливаться на летательных аппаратах. Необходимость работы в этой области диктуется требованиями аэродинамических характеристик антенн, размещенных на подвижных объектах. Модификация формы линии передачи и щелевой антенны позволяет обеспечить точное его совпадение с обшивкой летательного аппарата и обеспечение необходимой механической прочности. Более того, несмотря на все это, необходимо еще и обеспечить заданную диаграмму направленности антенны. Все эти результаты могут достигаться варьированием количества щелевых отверстий, а также расстоянием между ними. Кроме того, большое влияние на полученное излучение оказывает форма самого щелевого отверстия и местом расположения щели. Зная принцип работы щелевых антенн, можно получать при изготовлении качественные высотомерные устройства, измерители скорости объекта и т.п.This text made review the types of the fricative antennas, which can be built on the flying machines. This work is very necessary because of the requirement, that antennas on the flying machines must have aerodynamic parameters. Modification of the form of the transmission line and fricative antenna can ensure exact coincidence with encasement of the flying machine and supporting necessary mechanical strength. Moreover, despite all this facts, it is necessary to make right directivity pattern of the antenna. All this results can be obtain by variation the number of the fricative holes, and the distance between them. Then, the big influence on the radiation makes the design of the fricative hole, and the place, where thus hole can be built in. If we would know the principles of working of the fricative antennas, we can derive qualitative devices, like devises which can be used for: dimension of the height, dimension of the speed pf the object and many other engineering problems
Neutron electric form factor at large momentum transfer
Based on the recent, high precision data for elastic electron scattering from
protons and deuterons, at relatively large momentum transfer , we
determine the neutron electric form factor up to GeV. The values
obtained from the data (in the framework of the nonrelativistic impulse
approximation) are larger than commonly assumed and are in good agreement with
the Gari-Kr\"umpelmann parametrization of the nucleon electromagnetic form
factors.Comment: 11 pages 2 figure
On isovector meson exchange currents in the Bethe-Salpeter approach
We investigate the nonrelativistic reduction of the Bethe-Salpeter amplitude
for the deuteron electrodisintegration near threshold energies. To this end,
two assumptions have been used in the calculations: 1) the static approximation
and 2) the one iteration approximation. Within these assumptions it is possible
to recover the nonrelativistic result including a systematic extension to
relativistic corrections. We find that the so-called pair current term can be
constructed from the -wave contribution of the deuteron Bethe-Salpeter
amplitude. The form factor that enters into the calculation of the pair current
is constrained by the manifestly gauge independent matrix elements.Comment: 15 pages, incl. 3 figures, to be published Phys. Rev.
Superscaling and Neutral Current Quasielastic Neutrino-Nucleus Scattering beyond the Relativistic Fermi Gas Model
The superscaling analysis is extended to include quasielastic (QE) scattering
via the weak neutral current of neutrinos and antineutrinos from nuclei. The
scaling function obtained within the coherent density fluctuation model (used
previously in calculations of QE inclusive electron and charge-changing (CC)
neutrino scattering) is applied to neutral current neutrino and antineutrino
scattering with energies of 1 GeV from C with a proton and neutron
knockout (u-channel inclusive processes). The results are compared with those
obtained using the scaling function from the relativistic Fermi gas model and
the scaling function as determined from the superscaling analysis (SuSA) of QE
electron scattering.Comment: 10 pages, 6 figures, published in Phys. Rev.
Development the emitter, which can based on the waveguide with the special form
Необходимость работы в этой области диктуется требованиями аэродинамических характеристик антенн, размещенных на подвижных объектах. Модификация формы линии передачи ищелевой антенны позволяет обеспечить точное его совпадение с обшивкой летательного аппарата и обеспечение необходимой механической прочности. Более того, несмотря на все это, необходимо еще и обеспечить заданную диаграмму направленности антенны. Все эти результаты могут достигаться варьированием количества щелевых отверстий, а также расстоянием между ними. Кроме того, большое влияние на полученное излучение оказывает форма самого щелевого отверстия и местом расположения щели. Зная принцип работы щелевых антенн, можно получать при изготовлении качественные высотомерные устройства, измерители скорости объекта и т.п.This work is very necessary because of the requirement, that antennas on the flying machines must have aerodynamic parameters. Modification of the form of the transmission line and fricative antenna can ensure exact coincidence with encasement of the flying machine and supporting necessary mechanical strength. Moreover, despite all this facts, it is necessary to make right directivity pattern of the antenna. All this results can be obtain by variation the number of the fricative holes, and the distance between them. Then, the big influence on the radiation makes the design of the fricative hole, and the place, where thus hole can be built in. If we would know the principles of working of the fricative antennas, we can derive qualitative devices, like devises which can be used for: dimension of the height, dimension of the speed pf the object and many other engineering problems
Antibacterial effect of nisin in vitro
Results of experimental studies of antimicrobial action of gel compositions containing active substance nisin are presented in the article. It is shown that increasing concentration of nisin at constant concentrations of the other components in the mixture inhibits growth of Staphylococcus aureus and Pseudomonas aeruginosa. The optimal concentration of nisin at which the process of pathogens growth inhibition is the most effective was determined in the experiment
Transverse Instabilities in the Fermilab Recycler
Transverse instabilities of the antiproton beam have been observed in the
Recycler ring soon after its commissioning. After installation of transverse
dampers, the threshold for the instability limit increased significantly but
the instability is still found to limit the brightness of the antiprotons
extracted from the Recycler for Tevatron shots. In this paper, we describe
observations of the instabilities during the extraction process as well as
during dedicated studies. The measured instability threshold phase density
agrees with the prediction of the rigid beam model within a factor of 2. Also,
we conclude that the instability threshold can be significantly lowered for a
bunch contained in a narrow and shallow potential well due to effective
exclusion of the longitudinal tails from Landau damping.Comment: 17 pages, 'Technical' Note, Use of 'internal' jargon and reference
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