16,061 research outputs found
A novel scheme to aid coherent detection of GMSK signals in fast Rayleigh fading channels
A novel scheme to insert carrier pilot to Gaussian Minimum Shift Keying (GMSK) signal using Binary Block Code (BBC) and a highpass filter in baseband is proposed. This allows the signal to be coherently demodulated even in a fast Rayleigh fading environment. As an illustrative example, the scheme is applied to a 16 kb/s GMSK signal, and its performance over a fast Rayleigh fading channel is investigated using computer simulation. This modem's 'irreducible error rate' is found to be Pe = 5.5 x 10(exp -5) which is more than that of differential detection. The modem's performance in Rician fading channel is currently under investigation
Ordering dynamics of the driven lattice gas model
The evolution of a two-dimensional driven lattice-gas model is studied on an
L_x X L_y lattice. Scaling arguments and extensive numerical simulations are
used to show that starting from random initial configuration the model evolves
via two stages: (a) an early stage in which alternating stripes of particles
and vacancies are formed along the direction y of the driving field, and (b) a
stripe coarsening stage, in which the number of stripes is reduced and their
average width increases. The number of stripes formed at the end of the first
stage is shown to be a function of L_x/L_y^\phi, with \phi ~ 0.2. Thus,
depending on this parameter, the resulting state could be either single or
multi striped. In the second, stripe coarsening stage, the coarsening time is
found to be proportional to L_y, becoming infinitely long in the thermodynamic
limit. This implies that the multi striped state is thermodynamically stable.
The results put previous studies of the model in a more general framework
Viability of competing field theories for the driven lattice gas
It has recently been suggested that the driven lattice gas should be
described by a novel field theory in the limit of infinite drive. We review the
original and the new field theory, invoking several well-documented key
features of the microscopics. Since the new field theory fails to reproduce
these characteristics, we argue that it cannot serve as a viable description of
the driven lattice gas. Recent results, for the critical exponents associated
with this theory, are re-analyzed and shown to be incorrect.Comment: 4 pages, revtex, no figure
Perturbative Analysis of Universality and Individuality in Gravitational Waves from Neutron Stars
The universality observed in gravitational wave spectra of non-rotating
neutron stars is analyzed here. We show that the universality in the axial
oscillation mode can be reproduced with a simple stellar model, namely the
centrifugal barrier approximation (CBA), which captures the essence of the
Tolman VII model of compact stars. Through the establishment of scaled
co-ordinate logarithmic perturbation theory (SCLPT), we are able to explain and
quantitatively predict such universal behavior. In addition, quasi-normal modes
of individual neutron stars characterized by different equations of state can
be obtained from those of CBA with SCLPT.Comment: 29 pages, 10 figures, submitted to Astrophysical Journa
Determination of the internal structure of neutron stars from gravitational wave spectra
In this paper the internal structure of a neutron star is shown to be
inferrable from its gravitational-wave spectrum. Iteratively applying the
inverse scheme of the scaled coordinate logarithmic perturbation method for
neutron stars proposed by Tsui and Leung [Astrophys. J. {\bf 631}, 495 (2005)],
we are able to determine the mass, the radius and the mass distribution of a
star from its quasi-normal mode frequencies of stellar pulsation. In addition,
accurate equation of state of nuclear matter can be obtained from such
inversion scheme. Explicit formulas for the case of axial -mode oscillation
are derived here and numerical results for neutron stars characterized by
different equations of state are shown.Comment: 26 pages, 14 figures, submitted to Physical Review
Wave Propagation in Gravitational Systems: Completeness of Quasinormal Modes
The dynamics of relativistic stars and black holes are often studied in terms
of the quasinormal modes (QNM's) of the Klein-Gordon (KG) equation with
different effective potentials . In this paper we present a systematic
study of the relation between the structure of the QNM's of the KG equation and
the form of . In particular, we determine the requirements on in
order for the QNM's to form complete sets, and discuss in what sense they form
complete sets. Among other implications, this study opens up the possibility of
using QNM expansions to analyse the behavior of waves in relativistic systems,
even for systems whose QNM's do {\it not} form a complete set. For such
systems, we show that a complete set of QNM's can often be obtained by
introducing an infinitesimal change in the effective potential
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