Sub-barrier Coulomb effects on the interference pattern in tunneling ionization photoelectron spectra

We use a quantum trajectory-based semi-classical method to account for Coulomb interaction between the photoelectron and the parent ion in the classically forbidden, sub-barrier region during strong-field tunneling ionization processes. We show that---besides the well-known modification of the tunneling ionization probability---there is also an influence on the interference pattern in the photoelectron spectra. In the long-wavelength limit, the shift of the intra-cycle interference fringes caused by sub-barrier Coulomb effects in the laser polarization direction can be derived analytically. We compare our results with \emph{ab initio} solutions of the time-dependent Schr\"odinger equation and find good agreement in the long-wavelength regime, whereas the standard strong field approximation fails. We show that the nodal structure along low-order above-threshold ionization rings is also affected by sub-barrier Coulomb effects.Comment: 10 pages, 4 figures, RevTe

Performance impact of web services on Internet servers

While traditional Internet servers mainly served static and later also dynamic content, the popularity of Web services is increasing rapidly. Web services incorporate additional overhead compared to traditional web interaction. This overhead increases the demand on Internet servers which is of particular importance when the request rate to the server is high. We conduct experiments that show that the imposed overhead of Web services is non-negligible during server overload. In our experiments the response time for Web services is more than 30% higher and the server throughput more than 25% lower compared to traditional web interaction using dynamically created HTML pages

QoS integration in web services

With the growing popularity of Web services, a general QoS support for Web services will play an important role for the success of this emerging technology. Unfortunately, current Web service environments do not offer comprehensive QoS support. In this paper, we present an approach that does not only enable the QoS integration in Web services, but also the selection of appropriate services based on QoS requirements regarding server and network performance as well as the mapping of QoS requirements onto the underlying QoS aware network at runtime

Feedback local optimality principle applied to rocket vertical landing VTVL

Vertical landing is becoming popular in the last fifteen years, a technology known under the acronym VTVL, Vertical Takeoff and Vertical Landing [1,2]. The interest in such landing technology is dictated by possible cost reductions [3,4], that impose spaceship’s recycling. The rockets are not generally de- signed to perform landing operations, rather their design is aimed at takeoff operations, guaranteeing a very high forward acceleration to gain the velocity needed to escape the gravitational force. In this paper a new control method based on Feedback Local Optimality Principle, named FLOP is applied to the rocket landing problem. The FLOP belongs to a special class of optimal controllers, developed by the mechatronic and vehicle dynamics lab of Sapienza, named Variational Feedback Controllers - VFC, that are part of an ongoing research and are recently applied in different field: nonlinear system [5], marine and terrestrial autonomous vehicles [6,7,8], multi agents interactions and vibration control [9, 10]. The paper is devoted to show the robustness of the nonlinear controlled system, comparing the performances with the LQR, one of the most acknowledged methods in optimal control