289 research outputs found
Macroscopic effects in attosecond pulse generation
We examine how the generation and propagation of high-order harmonics in a
partly ionized gas medium affect their strength and synchronization. The
temporal properties of the resulting attosecond pulses generated in long gas
targets can be significantly influenced by macroscopic effects, in particular
by the intensity in the medium and the degree of ionization. Under some
conditions, the use of gas targets longer than the absorption length can lead
to the generation of self-compressed attosecond pulses. We show this effect
experimentally, using long argon-filled gas cells as generating medium.Comment: 5 pages 4 figure
Milk whey protein concentration and mRNA associated with β-lactoglobulin phenotype
Two common genetic variants of β-lactoglobulin (β-lg), A and B, exist as co- dominant alleles in dairy cattle (Aschaffenburg, 1968). Numerous studies have shown that cows homozygous for β-lg A have more β-lg and less α-lactalbumin (α-la) and casein in their milk than cows expressing only the B variant of β-lg (Ng-Kwai-Hang et al. 1987; Graml et al. 1989; Hill, 1993; Hill et al. 1995, 1997). These differences have a significant impact on the processing characteristics of the milk. For instance, the moisture-adjusted yield of Cheddar cheese is up to 10% higher using milk from cows of the β-lg BB phenotype compared with milk from cows expressing only the A variant (Hill et al. 1997). All these studies, however, describe compositional differences associated with β-lg phenotype in established lactation only. No information is available on the first few weeks of lactation, when there are marked changes in the concentrations of β-lg and α-la (Pérez et al. 1990)
Variabilité de la fertilité des vertisols non magnésiens : résultats du second cycle cultural des expérimentations des vallées de la Tamoa et de la Nindia : rapport
Variabilité de la fertilité des vertisols non magnésiens : résultats du troisième cycle cultural des expérimentations de la Tamoa et de la Nindia
Phase Measurement of Resonant Two-Photon Ionization in Helium
We study resonant two-color two-photon ionization of Helium via the 1s3p 1P1
state. The first color is the 15th harmonic of a tunable titanium sapphire
laser, while the second color is the fundamental laser radiation. Our method
uses phase-locked high-order harmonics to determine the {\it phase} of the
two-photon process by interferometry. The measurement of the two-photon
ionization phase variation as a function of detuning from the resonance and
intensity of the dressing field allows us to determine the intensity dependence
of the transition energy.Comment: 4 pages, 5 figures, under consideratio
High-order Harmonic Generation and Dynamic Localization in a driven two-level system, a non-perturbative solution using the Floquet-Green formalism
We apply the Floquet-Green operator formalism to the case of a
harmonically-driven two-level system. We derive exact expressions for the
quasi-energies and the components of the Floquet eigenstates with the use of
continued fractions. We study the avoided crossings structure of the
quasi-energies as a function of the strength of the driving field and give an
interpretation in terms of resonant multi-photon processes. From the Floquet
eigenstates we obtain the time-evolution operator. Using this operator we study
Dynamic Localization and High-order Harmonic Generation in the non-perturbative
regime
Etude des effets des amendements calciques sur un vertisol hyper-magnésien : résultats du cinquième cycle cultural de l'expérimentation au champ
Application des harmoniques générées dans un jet de gaz : mesure de sections efficaces d´ionisation des états excités de l´hélium
Les sections efficaces d'ionisation des états excités de l'hélium 1s2p 1P et 1s3p 1P ont été mesurées au voisinage du seuil d'ionisation en observant la saturation de l'ionisation. Les états excités de l'hélium sont préparés par l'absorption résonnante d'une harmonique d'ordre élevée produite par un laser picoseconde accordable. Ces états sont ensuite ionisés par un faisceau sonde en absorbant un photon. La modification de la fréquence du faisceau sonde, du proche infrarouge à l'ultraviolet, nous a permis de déterminer la dépendance de la section efficace d'ionisation en fonction de l'énergie de l'électron arraché. Les résultats expérimentaux confirment quantitativement les travaux théoriques effectués auparavant
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