2,409 research outputs found
Cross phase modulation in a five--level atomic medium: Semiclassical theory
The interaction of a five-level atomic system involving electromagnetically
induced transparency with four light fields is investigated. Two different
light-atom configurations are considered, and their efficiency in generating
large nonlinear cross-phase shifts compared. The dispersive properties of those
schemes are analyzed in detail, and the conditions leading to group velocity
matching for two of the light fields identified. An analytical treatment based
on amplitude equations is used in order to obtain approximate solutions for the
susceptibilities, ehich are shown to fit well with the numerical simulations of
the full Bloch equations in a large parameter region.Comment: New version: section on pulse propagation added, reference list
expanded; 17 pages, 15 figure
What is the best drug to treat COVID-19? The need for randomized controlled trials
The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is currently the biggest public health challenge to the biomedical community of the last century. Despite multiple public health measures,1, 2, 3 there remains an urgent need for pharmacologic therapies to treat infected patients, minimize mortality, and decrease pressures on intensive care units and health systems and optimally, they should also decrease subsequent transmission
Quantum theory of a polarization phase-gate in an atomic tripod configuration
We present the quantum theory of a polarization phase-gate that can be
realized in a sample of ultracold rubidium atoms driven into a tripod
configuration. The main advantages of this scheme are in its relative
simplicity and inherent symmetry. It is shown that the conditional phase shifts
of order can be attained.Comment: X International Conference on Quantum Optics, Minsk, Belaru
Deep Saturated Free Electron Laser Oscillators and Frozen Spikes
We analyze the behavior of Free Electron Laser (FEL) oscillators operating in
the deep saturated regime and point out the formation of sub-peaks of the
optical pulse. They are very stable configurations, having a width
corresponding to a coherence length. We speculate on the physical mechanisms
underlying their growth and attempt an identification with FEL mode locked
structures associated with Super Modes. Their impact on the intra-cavity
nonlinear harmonic generation is also discussed along with the possibility of
exploiting them as cavity out-coupler.Comment: 28 page
Vocalization-related stapedius muscle activity in different age chickens (Gallus gallus), and its role in vocal development
The stapedius muscle activity associated with vocalization was analyzed in young and adult roosters. Our results show that remarkable differences in the behavior of vocalization-related stapedius muscle activity exist between these two ages. Unlike young roosters, electrical stimulation in the midbrain of adult cocks yields vocalizations associated with stapedius muscle EMG responses that always show a higher threshold and a longer latency than those of the vocalization induced. Moreover, the maximal amplitude of the stapedius muscleEMG response is consistently lower than that detected in young roosters, despite the fact that the maximal vocalization amplitude of the adult birds is much higher. Onthewholeourresultsdemonstrate thatvocalization-relatedstapediusmuscleactivityisstronglyreducedinadulthood.Thepossibility that stapedius muscle may play a role during the vocal development was verified by comparing the crow of normal roosters with that of cocks from which the stapedius muscle had been removed shortly after hatching. Strong differences exist in the amplitude/frequency distribution of the crowing of normal and stapedectomized roosters, suggesting that the stapedius muscle exerts an important role in auditory feedback modulation, and that this feedback is used for normal vocal development
Functional differentiation of central Apennine grasslands under mowing and grazing disturbance regimes
This research dealt to two grasslands potentially developing the same vegetation type because sited in the same environmental contest (bioclimate, substratum, soil, slope, altitude) but under diverse management regimes (grazing and mowing) for many decades. The evidenced differentiation between the two pastoral vegetations can be attributed to disturbance type and the statistical functional analysis performed through seven plant traits (prostrate form, early
flowering, storage organs, clonal ability, basal meristems, chemical defences and hairs), revealed the distinguishing patterns. Discriminant analysis pointed out typical biological
attributes for each disturbance conditions, while from correlation analysis emerged different possible traits combinations which do not follow the previous traits separation. Such outcomes are explainable because both grazing and mowing provoke aboveground phytomass removal, although grazing is a selective pressure, while mowing gives to all the species the same development
chances. It is reasonable to conclude that convergent strategies within the two systems are possible and frequent
- …