493 research outputs found
Lagrangian Volume Deformations around Simulated Galaxies
We present a detailed analysis of the local evolution of 206 Lagrangian
Volumes (LVs) selected at high redshift around galaxy seeds, identified in a
large-volume cold dark matter (CDM) hydrodynamical
simulation. The LVs have a mass range of . We
follow the dynamical evolution of the density field inside these initially
spherical LVs from up to , witnessing highly
non-linear, anisotropic mass rearrangements within them, leading to the
emergence of the local cosmic web (CW). These mass arrangements have been
analysed in terms of the reduced inertia tensor , focusing on the
evolution of the principal axes of inertia and their corresponding
eigendirections, and paying particular attention to the times when the
evolution of these two structural elements declines. In addition, mass and
component effects along this process have also been investigated. We have found
that deformations are led by dark matter dynamics and they transform most of
the initially spherical LVs into prolate shapes, i.e. filamentary structures.
An analysis of the individual freezing-out time distributions for shapes and
eigendirections shows that first most of the LVs fix their three axes of
symmetry (like a skeleton) early on, while accretion flows towards them still
continue. Very remarkably, we have found that more massive LVs fix their
skeleton earlier on than less massive ones. We briefly discuss the
astrophysical implications our findings could have, including the galaxy
mass-morphology relation and the effects on the galaxy-galaxy merger parameter
space, among others.Comment: 23 pages, 20 figures. Minor editorial improvement
Password secured sites: stepping forward with keystroke dynamics
Computer Authentication is a critical component of
most computer systems – especially those used in e-
Commerce activities over the internet. Global access
to information makes security, namely the
authentication process, a critical design issue in these
systems. In what concerns to authentication, what is
required is a reliable, hardware independent and
efficient security system. In this paper, we propose an
extension to a keystroke dynamics based security
system. We provide evidence that completely software
based systems can be as effective as expensive and
cumbersome hardware based systems. Our system is a
behavioral based system that captures the normal
typing patterns of a user and uses that information, in
addition to standard login/password security to
provide a system that is user-friendly and very effective
at detecting imposters. The results provide a means of
dealing with enhanced security that is growing in
demand in web-based applications based on ECommerce
Analysis of Systems with Backlash and Impacts through the Describing Function
This paper analyses the dynamical properties of systems with backlash
and impact phenomena based on the describing function method. The dynamics is illustrated
using the Nyquist and Bode plots and the results are compared with those
of standard models
Development of fractional order capacitors based on electrolyte processes
In recent years, significant research in the field of electrochemistry was developed. The performance of electrical devices, depending on the processes of the electrolytes, was described and the physical origin of each parameter was established. However, the influence of the irregularity of the electrodes was not a subject of study and only recently this problem became relevant in the viewpoint of fractional calculus. This paper describes an electrolytic process in the perspective of fractional order capacitors. In this line of thought, are developed several experiments for measuring the electrical impedance of the devices. The results are analyzed through the frequency response, revealing capacitances of fractional order that can constitute an alternative to the classical integer order elements. Fractional order electric circuits are used to model and study the performance of the electrolyte processes
Fractional control of heat diffusion systems
The concept of differentiation and integration to non-integer order has its origins in the seventeen century. However, only in the second-half of the twenty century appeared the first applications related to the area of control theory. In this paper we consider the study of a heat diffusion system based on the application of the fractional calculus concepts. In this perspective, several control methodologies are investigated and compared. Simulations are presented assessing the performance of the proposed fractional-order algorithms
Fractional Hamiltonian analysis of higher order derivatives systems
The fractional Hamiltonian analysis of 1+1 dimensional field theory is
investigated and the fractional Ostrogradski's formulation is obtained. The
fractional path integral of both simple harmonic oscillator with an
acceleration-squares part and a damped oscillator are analyzed. The classical
results are obtained when fractional derivatives are replaced with the integer
order derivatives.Comment: 13 page
Effect of fractional orders in the velocity control of a servo system
AbstractThe application of fractional-order PID controllers is now an active field of research. This article investigates the effect of fractional (derivative and integral) orders upon system’s performance in the velocity control of a servo system. The servo system consists of a digital servomechanism and an open-architecture software environment for real-time control experiments using MATLAB/Simulink tools. Experimental responses are presented and analyzed, showing the effectiveness of fractional controllers. Comparison with classical PID controllers is also investigated
Fractional order dynamics in some distributed parameter systems
Fractional Calculus (FC) goes back to the beginning of the theory of differential calculus. Nevertheless, the application of FC just emerged in the last two decades, due to the progress in the area of chaos that revealed subtle relationships with the FC concepts. In the field of dynamical systems theory some work has been carried out but the proposed models and algorithms are still in a preliminary stage of establishment. Having these ideas in mind, the paper discusses a FC perspective in the study of the dynamics and control of some distributed parameter systems.N/
Hamiltonian formulation of systems with linear velocities within Riemann-Liouville fractional derivatives
The link between the treatments of constrained systems with fractional
derivatives by using both Hamiltonian and Lagrangian formulations is studied.
It is shown that both treatments for systems with linear velocities are
equivalent.Comment: 10 page
Fractional modelling of the electrical conduction in nacl electrolyte
The fractional calculus (FC) constitutes a mathematical tool that presently is being applied in many emerging scientific areas, such as electricity, magnetism, mechanics, fluid dynamics and medicine. This paper describes the use of an electrolytic process for developing fractional order capacitors. The study includes several experiments for measuring the electrical impedance of the devices. The results are analyzed through the frequency response revealing capacitances of fractional order.N/
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