314 research outputs found
Above threshold ionization by few-cycle spatially inhomogeneous fields
We present theoretical studies of above threshold ionization (ATI) produced
by spatially inhomogeneous fields. This kind of field appears as a result of
the illumination of plasmonic nanostructures and metal nanoparticles with a
short laser pulse. We use the time-dependent Schr\"odinger equation (TDSE) in
reduced dimensions to understand and characterize the ATI features in these
fields. It is demonstrated that the inhomogeneity of the laser electric field
plays an important role in the ATI process and it produces appreciable
modifications to the energy-resolved photoelectron spectra. In fact, our
numerical simulations reveal that high energy electrons can be generated.
Specifically, using a linear approximation for the spatial dependence of the
enhanced plasmonic field and with a near infrared laser with intensities in the
mid- 10^{14} W/cm^{2} range, we show it is possible to drive electrons with
energies in the near-keV regime. Furthermore, we study how the carrier envelope
phase influences the emission of ATI photoelectrons for few-cycle pulses. Our
quantum mechanical calculations are supported by their classical counterparts
A Pliant-based Virtual Machine Scheduling Solution to Improve the Energy Efficiency of IaaS Clouds
Finite-size scaling of the photon-blockade breakdown dissipative quantum phase transition
We prove that the observable telegraph signal accompanying the bistability in the photon-blockade-breakdown regime of the driven and lossy Jaynes–Cummings model is the finite-size precursor of what in the thermodynamic limit is a genuine first-order phase transition. We construct a finite-size scaling of the system parameters to a well-defined thermodynamic limit, in which the system remains the same microscopic system, but the telegraph signal becomes macroscopic both in its timescale and intensity. The existence of such a finite-size scaling completes and justifies the classification of the photon-blockade-breakdown effect as a first-order dissipative quantum phase transition
Learning Ordinal Preferences on Multiattribute Domains: the Case of CP-nets
International audienceA recurrent issue in decision making is to extract a preference structure by observing the user's behavior in different situations. In this paper, we investigate the problem of learning ordinal preference orderings over discrete multi-attribute, or combinatorial, domains. Specifically, we focus on the learnability issue of conditional preference networks, or CP- nets, that have recently emerged as a popular graphical language for representing ordinal preferences in a concise and intuitive manner. This paper provides results in both passive and active learning. In the passive setting, the learner aims at finding a CP-net compatible with a supplied set of examples, while in the active setting the learner searches for the cheapest interaction policy with the user for acquiring the target CP-net
Pre-Excitation Studies for Rubidium-Plasma Generation
The key element in the Proton-Driven-Plasma-Wake-Field-Accelerator (AWAKE)
project is the generation of highly uniform plasma from Rubidium vapor. The
standard way to achieve full ionization is to use high power laser which can
assure the over-barrier-ionization (OBI) along the 10 meters long active
region. The Wigner-team in Budapest is investigating an alternative way of
uniform plasma generation. The proposed Resonance Enhanced Multi Photon
Ionization (REMPI) scheme probably can be realized by much less laser power. In
the following the resonant pre-excitations of the Rb atoms are investigated,
theoretically and the status report about the preparatory work on the
experiment are presented.Comment: 8 pages, 6 figures, submitted to Nucl. Inst. and Meth. in Phys. Res.
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