53 research outputs found
Experimental Observation of “Shadowing” in Optical Transition Radiation
We report the observation of shadowing between two optical transition radiation (OTR) sources from a 205Â MeV electron beam. The total optical intensity is measured as a function of the distance between the sources, covering the range , where is the formation length of the particles. Data show that the total optical intensity starts decreasing due to shadowing when approaches until it becomes undetectable for very short distances . A model based solely on interference between the two OTR sources is in good agreement with experimental data. To the knowledge of the authors this is the first systematic experimental observation of shadowing in OTR
Slow Light in Doppler Broadened Two level Systems
We show that the propagation of light in a Doppler broadened medium can be
slowed down considerably eventhough such medium exhibits very flat dispersion.
The slowing down is achieved by the application of a saturating counter
propagating beam that produces a hole in the inhomogeneous line shape. In
atomic vapors, we calculate group indices of the order of 10^3. The
calculations include all coherence effects.Comment: 6 pages, 5 figure
Stopping of Charged Particles in a Magnetized Classical Plasma
The analytical and numerical investigations of the energy loss rate of the
test particle in a magnetized electron plasma are developed on the basis of the
Vlasov-Poisson equations, and the main results are presented. The Larmor
rotation of a test particle in a magnetic field is taken into account. The
analysis is based on the assumption that the energy variation of the test
particle is much less than its kinetic energy. The obtained general expression
for stopping power is analyzed for three cases: (i) the particle moves through
a collisionless plasma in a strong homogeneous magnetic field; (ii) the fast
particle moves through a magnetized collisionless plasma along the magnetic
field; and (iii) the particle moves through a magnetized collisional plasma
across a magnetic field. Calculations are carried out for the arbitrary test
particle velocities in the first case, and for fast particles in the second and
third cases. It is shown that the rate at which a fast test particle loses
energy while moving across a magnetic field may be much higher than the loss in
the case of motion through plasma without magnetic field.Comment: 14 pages, 3 figures, LaTe
From Bengali to English: sequential bilingualism of a second-generation British Bangladeshi
The paper discusses sequential language acquisition of the researcher's daughter Safa who transformed from a monolingual Bengali speaker to an almost monolingual English speaker in a few months after moving to the UK. Safa was born in Bangladesh and was a monolingual Bengali speaker until she was three years and nine months when the family moved to the UK. Unlike most research on sequential bilingualism, Safa's transition from Bengali to English went through a period of an invented language, which she developed and used for a few months. Safa then underwent language shift as Bengali became her passive language. Safa's loss of fluency in Bengali was mainly due to the absence of Bengali linguistic environment, because her family lived outside the community. Safa's mother's indifference to Bangladeshi ethnicity and her parents’ positive attitude towards Britishness meant that her decline in Bengali did not cause them much concern. Despite the lack of proficiency in Bengali, Safa still retains a strong ethnic Bangladeshi identity. Tabors and Snow’s four-stage developmental process of sequential second-language acquisition has been applied to find the similarities and differences in Safa's case, while language maintenance and shift theories have contributed to the analysis of the process of her language shift
Passive Q-switching and mode-locking for the generation of nanosecond to femtosecond pulses
The X-ray transition radiation
The interest of producing high-energy radiation using a small-size electron accelerator is growing since many years. It appeared that such accelerators should drive x-ray sources to produce a high flux of radiation. The range of photon-energy available when using electron linacs, for example, is between a few tens of eV and the maximum electron kinetic energy. The transition radiation, which is produced when a charged particle crosses the interface between two media of different permittivities, is a very promising way due to its high production rate. We present here a study of this physical process involving moderate-energy relativistic electrons (20 MeV). We recall the main characteristics of the radiation when the interface is crossed at normal incidence and derive the analytical production yields when the interaction takes place at grazing incidence. The results for both geometries are compared. Finally, the scale laws allowing the optimization of the spectral source brilliance are presented
Continuous-wave two-photon spectroscopy of the 1S-2S transition in hydrogen.
We have observed the 1S-2S transition in atomic hydrogen gas with a resolution of 5 parts in 109 by Doppler-free two-photon spectroscopy, using multimilliwatt cw radiation near 243 nm generated by sum-frequency mixing. The experiment opens the way to substantial increases in the accuracy of the Rydberg constant, the electron/proton mass ratio, and the Lamb shift of the hydrogen 1S ground state. © 1985 The American Physical Society
Transesterification of juvenile hormone occurs in vivo in locust when injected in alcoholic solvents
International audienc
Processing social indicators at individual, houshold [i.e. household] level and their aggregation at different scales : Technical report
ORIENTATIONAL DYNAMICS IN MICRO-EMULSION DROPLETS WITH PICOSECOND TIME RESOLUTION
no abstrac
- …