222 research outputs found
Adiabatic corrections for velocity-gauge simulations of electron dynamics in periodic potentials
We show how to significantly reduce the number of energy bands required to
model the interaction of light with crystalline solids in the velocity gauge.
We achieve this by deriving analytical corrections to the electric current
density. These corrections depend only on band energies, the matrix elements of
the momentum operator, and the macroscopic vector potential. Thus, the
corrections can be evaluated independently from modeling the interaction with
light. In addition to improving the convergence of velocity-gauge calculations,
our analytical approach overcomes the long-standing problem of divergences in
expressions for linear and nonlinear susceptibilities.Comment: Submitted to Computer Physics Communication
Quantum beats in the polarization response of a dielectric to intense few-cycle laser pulses
We have investigated the polarization response of a dielectric to intense
few-cycle laser pulses with a focus on interband tunnelling. Once charge
carriers are created in an initially empty conduction band, they make a
significant contribution to the polarization response. In particular, the
coherent superposition of conduction- and valence-band states results in
quantum beats. This quantum-beat part of the polarization response is affected
by the excitation dynamics and attosecond-scale motion of charge carriers in an
intense laser field. Our analysis shows that, with the onset of Bloch
oscillations or tunnelling, the nonlinear polarization response becomes
sensitive to the carrier-envelope phase of the laser pulse.Comment: 10 pages, 5 figure
Dressed bound states for attosecond dynamics in strong laser fields
We propose a theoretical approach for the interpretation of pump-probe
measurements where an attosecond pulse is absorbed in the presence of an
intense laser pulse. This approach is based on abstractly defined dressed bound
states, which capture the essential aspects of the interaction with the laser
pulse and facilitate a perturbative description of transitions induced by the
attosecond pulse. Necessary properties of dressed bound states are defined and
various choices are discussed and compared to accurate numerical solutions of
the time-dependent Schroedinger equation.Comment: accepted for publication in Chemical Physic
Deriving Petri nets from finite transition systems
This paper presents a novel method to derive a Petri net from any specification model that can be mapped into a state-based representation with arcs labeled with symbols from an alphabet of events (a Transition System, TS). The method is based on the theory of regions for Elementary Transition Systems (ETS). Previous work has shown that, for any ETS, there exists a Petri Net with minimum transition count (one transition for each label) with a reachability graph isomorphic to the original Transition System. Our method extends and implements that theory by using the following three mechanisms that provide a framework for synthesis of safe Petri nets from arbitrary TSs. First, the requirement of isomorphism is relaxed to bisimulation of TSs, thus extending the class of synthesizable TSs to a new class called Excitation-Closed Transition Systems (ECTS). Second, for the first time, we propose a method of PN synthesis for an arbitrary TS based on mapping a TS event into a set of transition labels in a PN. Third, the notion of irredundant region set is exploited, to minimize the number of places in the net without affecting its behavior. The synthesis method can derive different classes of place-irredundant Petri Nets (e.g., pure, free choice, unique choice) from the same TS, depending on the constraints imposed on the synthesis algorithm. This method has been implemented and applied in different frameworks. The results obtained from the experiments have demonstrated the wide applicability of the method.Peer ReviewedPostprint (published version
Application of laser scanners and rangefinders technology in problem of industrial and natural objects control.
An overview of application of modern technology of laser scanners and range finders for measuring natural and industrial objects is done in this paper. The technique of phase measurements based on multi-frequency modulation of the laser radiation was proposed, which simplifies  phase ambiguous resolution when measuring large distances to the object. A model of scanning allows effective spatial scanning of industrial and natural sites. On the basis of this model, scheme remote geophysical measurements was proposed, which encompasses corner reflectors , with the possibility of using active reflectors. Rangefinder with active reflector increases the range of the device several times. It can be effectively used in geophysical studies of Earth's surface and in control of shear deformations. Keywords: laser, rangefinder, scanner, atmosphere, distanc
Automatic synthesis and optimization of partially specified asynchronous systems
A method for automating the synthesis of asynchronous control circuits from high level (CSP-like) and/or partial STG (involving only functionally critical events) specifications is presented. The method solves two key subtasks in this new, more flexible, design flow: handshake expansion, i.e. inserting reset events with maximum concurrency, and event reshuffling under interface and concurrency constraints, by means of concurrency reduction. In doing so, the algorithm optimizes the circuit both for size and performance. Experimental results show a significant increase in the solution space explored when compared to existing CSP-based or STG-based synthesis tools.Peer ReviewedPostprint (author's final draft
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