687 research outputs found
Secondary electron emission yield in the limit of low electron energy
Secondary electron emission (SEE) from solids plays an important role in many
areas of science and technology.1 In recent years, there has been renewed
interest in the experimental and theoretical studies of SEE. A recent study
proposed that the reflectivity of very low energy electrons from solid surface
approaches unity in the limit of zero electron energy2,3,4, If this was indeed
the case, this effect would have profound implications on the formation of
electron clouds in particle accelerators,2-4 plasma measurements with
electrostatic Langmuir probes, and operation of Hall plasma thrusters for
spacecraft propulsion5,6. It appears that, the proposed high electron
reflectivity at low electron energies contradicts to numerous previous
experimental studies of the secondary electron emission7. The goal of this note
is to discuss possible causes of these contradictions.Comment: 3 pages, contribution to the Joint INFN-CERN-EuCARD-AccNet Workshop
on Electron-Cloud Effects: ECLOUD'12; 5-9 Jun 2012, La Biodola, Isola d'Elba,
Ital
Heartbeat of the Southern Oscillation explains ENSO climatic resonances
The El Ni~no-Southern Oscillation (ENSO) nonlinear oscillator phenomenon has a far reaching
influence on the climate and human activities. The up to 10 year quasi-period cycle of the El Ni~no and
subsequent La Ni~na is known to be dominated in the tropics by nonlinear physical interaction of wind with
the equatorial waveguide in the Pacific. Long-term cyclic phenomena do not feature in the current theory
of the ENSO process. We update the theory by assessing low (>10 years) and high (<10 years) frequency
coupling using evidence across tropical, extratropical, and Pacific basin scales. We analyze observations and
model simulations with a highly accurate method called Dominant Frequency State Analysis (DFSA) to
provide evidence of stable ENSO features. The observational data sets of the Southern Oscillation Index
(SOI), North Pacific Index Anomaly, and ENSO Sea Surface Temperature Anomaly, as well as a theoretical
model all confirm the existence of long-term and short-term climatic cycles of the ENSO process with
resonance frequencies of {2.5, 3.8, 5, 12–14, 61–75, 180} years. This fundamental result shows long-term and
short-term signal coupling with mode locking across the dominant ENSO dynamics. These dominant
oscillation frequency dynamics, defined as ENSO frequency states, contain a stable attractor with three
frequencies in resonance allowing us to coin the term Heartbeat of the Southern Oscillation due to its
characteristic shape. We predict future ENSO states based on a stable hysteresis scenario of short-term and
long-term ENSO oscillations over the next century
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The present paper features the publication of an unedited manuscript by the Soviet linguist E.D. Polivanov, submitted in November 1927 by its author not for publication but just as a contribu- tion to the discussion around the so-called Abkhaz Analytical Alphabet. is graphic system was devised by the academician Nikolay Yakovlevich Marr on the basis of the Latin alphabet for the representation of all Japhetic (Caucasian) languages. In the rst section of the introduction, the main characteristics of Marr\u2019s Analytical Alphabet are presented; the second section addresses the linguistic discussion that followed its introduction in Abkhazia as the o cial alphabet in 1926 and its replacement two years later by a Latin-based alphabet. e third section gives comment on some questions of Abkhaz phonetics and transcription; the fourth is devoted to textual and editorial is- sues. e edition of the Russian text is accompanied by an English translation, prepared by Grazia Giannetta (Macerata)
Factorization and Lie point symmetries of general Lienard-type equation in the complex plane
We present a variational approach to a general Lienard-type equation in order
to linearize it and, as an example, the Van der Pol oscillator is discussed.
The new equation which is almost linear is factorized. The point symmetries of
the deformed equation are also discussed and the two-dimensional Lie algebraic
generators are obtained
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