The self-focusing of a laser pulse through a tunnel ionizing gas (helium) has been studied in both non-relativistic and relativistic
regimes, relaxing the near-axis approximation. In the non-relativistic regime, the laser pulse produces multiple ionization
of the gas and faces strong defocusing due to the steep radial density gradient caused by the same. The uneven defocusing
of paraxial and marginal rays leads to a beam acquiring a ring shaped intensity distribution. In the relativistic regime,
the laser pulse produces fully ionized plasma within a few wave periods, subsequently the relativistic mass effect and the
ponderomotive force induced electron cavitation cause periodic self-focusing.
PACS 52.38.Hb; 42.65.Jx 相似文献
Sunto Si danno dei teoremi di esistenza dell'estremo assoluto per gli integrali doppi della forma
.
Lavoro eseguito nel Seminario Matematico della R. Scuola Normale Superiore di Pisa. 相似文献
A numerical semigroup is a submonoid of \({{\mathbb {Z}}}_{\ge 0}\) whose complement in \({{\mathbb {Z}}}_{\ge 0}\) is finite. For any set of positive integers a, b, c, the numerical semigroup S(a, b, c) formed by the set of solutions of the inequality \(ax \bmod {b} \le cx\) is said to be proportionally modular. For any interval \([\alpha ,\beta ]\), \(S\big ([\alpha ,\beta ]\big )\) is the submonoid of \({{\mathbb {Z}}}_{\ge 0}\) obtained by intersecting the submonoid of \({{\mathbb {Q}}}_{\ge 0}\) generated by \([\alpha ,\beta ]\) with \({{\mathbb {Z}}}_{\ge 0}\). For the numerical semigroup S generated by a given arithmetic progression, we characterize a, b, c and \(\alpha ,\beta \) such that both S(a, b, c) and \(S\big ([\alpha ,\beta ]\big )\) equal S.
This is the report of the neutrino physics working group at WHEPP-X. We summarize the problems selected and discussed at the
workshop and the papers which have resulted subsequently.
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An organocatalytic enantioselective synthesis of the title compounds has been achieved. The stereogenic centers were generated by the iterative use of proline catalyzed α-aminoxylations and HWE olefination of aldehydes while the lactone ring was constructed by ring closing metathesis. 相似文献
Three diogenite meteorites ALHA77256-121, Tatahounie and Bilanga are studied using Mössbauer spectroscopy to look at the iron occupancy in the two inequivalent pyroxene sites. Though the three meteorites belong to three different conditions, one is an Antarctica find, one is 75 years old fall and one is a recent fall, the iron occupancy in pyroxene sites is very similar. Fe2?+? occupies only the less distorted site and hence a single sharp doublet is observed in the Mössbauer spectra of all these samples. In contrast eucrites show a distribution of iron ions in the two sites of pyroxenes. 相似文献
2-Ethylhexyl-2-ethylhexyl phosphonic acid (PC-88A) and Tributylphosphate (TBP) extractants have been attached to polypropylene
(PP) in granular, film and non-woven fabric forms, by a simultaneous γ-ray irradiation method. The extraction of plutonium
from the acidic radioactive liquid waste by modified polymers was studied by varying the γ-ray dose. The uptake of plutonium
was also studied by polyethylene (PE) in film form. This modified polymer also showed extraction capability for plutonium
from nitric acid medium. The uptake of plutonium depends upon the γ-ray dose as well as the nature and source of the polymer.
Liquid–solid extraction studies showed that the equivalent amount of uptake of plutonium on TBP–polyethylene film requires
twice the γ-ray dose as compare to TBP–polypropylene film. It was observed that at given γ-ray dose polypropylene fabric is
not sturdy, compare to the granules and films, and material leach out in aqueous phase. The presence of other solvents like
di-methyl formamide (DMF) and cyclohexane during γ-ray irradiation were able to enhance the extraction capabilities. The optimum
conditions established during this study was successfully applied for the separation of plutonium, uranium and thorium from
the fission products in acidic waste solution. 相似文献
Optical diagnostics of laser-produced plasma requires a coherent, polarized probe beam synchronized with the pump beam. The
probe beam should have energy above the background emission of plasma. Though the second harmonic probe beam satisfies most
of the requirements, the plasma emission is larger at the harmonic frequencies of the pump. Hence, at high intensities we
need a probe beam at non-harmonic frequencies. We have set up a Raman frequency shifted probe beam using a pressurized hydrogen
cell that is pumped by the second harmonic of the Nd glass laser that operates at only one Stokes line of 673.75 nm. 相似文献
A headspace solid-phase microextraction method has been developed for the determination of 8 pesticides in vegetables and fruits by using gas chromatography with an electron capture detector. Two types of fibers (polyacrylate, 85 microm and polydimethylsiloxane, 100 microm) have been assayed and compared. The main factors: extraction and desorption parameters, ionic strength, and the effects of dilution and organic solvents, were studied and optimized. The optimized procedures resulted in more than 80% recovery for all the investigated vegetable and fruit samples with RSD values below 10%. 相似文献