511 research outputs found
Synchronization Based Approach for Estimating All Model Parameters of Chaotic Systems
The problem of dynamic estimation of all parameters of a model representing
chaotic and hyperchaotic systems using information from a scalar measured
output is solved. The variational calculus based method is robust in the
presence of noise, enables online estimation of the parameters and is also able
to rapidly track changes in operating parameters of the experimental system.
The method is demonstrated using the Lorenz, Rossler chaos and hyperchaos
models. Its possible application in decoding communications using chaos is
discussed.Comment: 13 pages, 4 figure
Sub-natural linewidth in room-temperature Rb vapor using a control laser
We demonstrate two ways of obtaining sub-natural linewidth for probe
absorption through room-temperature Rb vapor. Both techniques use a control
laser that drives the transition from a different ground state. The coherent
drive splits the excited state into two dressed states (Autler-Townes doublet),
which have asymmetric linewidths when the control laser is detuned from
resonance. In the first technique, the laser has a large detuning of 1.18 GHz
to reduce the linewidth to 5.1 MHz from the Doppler width of 560 MHz. In the
second technique, we use a counter-propagating pump beam to eliminate the
first-order Doppler effect. The unperturbed probe linewidth is about 13 MHz,
which is reduced below 3 MHz (0.5 \Gamma) at a detuning of 11.5 MHz.Comment: 4 pages, 7 figure
Self-trapped bidirectional waveguides in a saturable photorefractive medium
We introduce a time-dependent model for the generation of joint solitary
waveguides by counter-propagating light beams in a photorefractive crystal.
Depending on initial conditions, beams form stable steady-state structures or
display periodic and irregular temporal dynamics. The steady-state solutions
are non-uniform in the direction of propagation and represent a general class
of self-trapped waveguides, including counterpropagating spatial vector
solitons as a particular case.Comment: 4 pages, 5 figure
Cavity implementation of quantum interference in a -type atom
A scheme for engineering quantum interference in a -type atom
coupled to a frequency-tunable, single-mode cavity field with a pre-selected
polarization at finite temperature is proposed. Interference-assisted
population trapping, population inversions and probe gain at one sideband of
the Autler-Townes spectrum are predicted for certain cavity resonant
frequencies.Comment: 2 postscript figures are adde
Quantum Coherence in a Single Ion due to strong Excitation of a metastable Transition
We consider pump-probe spectroscopy of a single ion with a highly metastable
(probe) clock transition which is monitored by using the quantum jump
technique. For a weak clock laser we obtain the well known Autler-Townes
splitting. For stronger powers of the clock laser we demonstrate the transition
to a new regime. The two regimes are distinguished by the transition of two
complex eigenvalues to purely imaginary ones which can be very different in
magnitude. The transition is controlled by the power of the clock laser. For
pump on resonance we present simple analytical expressions for various
linewidths and line positions.Comment: 6 figures. accepted for publication in PR
Quantum jumps induced by the center-of-mass motion of a trapped atom
We theoretically study the occurrence of quantum jumps in the resonance
fluorescence of a trapped atom. Here, the atom is laser cooled in a
configuration of level such that the occurrence of a quantum jump is associated
to a change of the vibrational center-of-mass motion by one phonon. The
statistics of the occurrence of the dark fluorescence period is studied as a
function of the physical parameters and the corresponding features in the
spectrum of resonance fluorescence are identified. We discuss the information
which can be extracted on the atomic motion from the observation of a quantum
jump in the considered setup
General Stability Analysis of Synchronized Dynamics in Coupled Systems
We consider the stability of synchronized states (including equilibrium
point, periodic orbit or chaotic attractor) in arbitrarily coupled dynamical
systems (maps or ordinary differential equations). We develop a general
approach, based on the master stability function and Gershgorin disc theory, to
yield constraints on the coupling strengths to ensure the stability of
synchronized dynamics. Systems with specific coupling schemes are used as
examples to illustrate our general method.Comment: 8 pages, 1 figur
Post-natal parental care in a Cretaceous diapsid from northeastern China
Post-natal parental care seems to have evolved numerous times in vertebrates. Among extant amniotes, it is present in crocodilians, birds, and mammals. However, evidence of this behavior is extremely rare in the fossil record and is only reported for two types of dinosaurs, and a varanopid ‘pelycosaur’. Here we report new evidence for post-natal parental care in Philydrosaurus, a choristodere, from the Yixian Formation of western Liaoning Province, China. We review the fossil record of reproduction in choristoderes, and this represents the oldest record of post-natal parental care in diapsids to our knowledge
Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at sqrt(s) = 7 TeV
Results are presented from a search for a W' boson using a dataset
corresponding to 5.0 inverse femtobarns of integrated luminosity collected
during 2011 by the CMS experiment at the LHC in pp collisions at sqrt(s)=7 TeV.
The W' boson is modeled as a heavy W boson, but different scenarios for the
couplings to fermions are considered, involving both left-handed and
right-handed chiral projections of the fermions, as well as an arbitrary
mixture of the two. The search is performed in the decay channel W' to t b,
leading to a final state signature with a single lepton (e, mu), missing
transverse energy, and jets, at least one of which is tagged as a b-jet. A W'
boson that couples to fermions with the same coupling constant as the W, but to
the right-handed rather than left-handed chiral projections, is excluded for
masses below 1.85 TeV at the 95% confidence level. For the first time using LHC
data, constraints on the W' gauge coupling for a set of left- and right-handed
coupling combinations have been placed. These results represent a significant
improvement over previously published limits.Comment: Submitted to Physics Letters B. Replaced with version publishe
Search for the standard model Higgs boson decaying into two photons in pp collisions at sqrt(s)=7 TeV
A search for a Higgs boson decaying into two photons is described. The
analysis is performed using a dataset recorded by the CMS experiment at the LHC
from pp collisions at a centre-of-mass energy of 7 TeV, which corresponds to an
integrated luminosity of 4.8 inverse femtobarns. Limits are set on the cross
section of the standard model Higgs boson decaying to two photons. The expected
exclusion limit at 95% confidence level is between 1.4 and 2.4 times the
standard model cross section in the mass range between 110 and 150 GeV. The
analysis of the data excludes, at 95% confidence level, the standard model
Higgs boson decaying into two photons in the mass range 128 to 132 GeV. The
largest excess of events above the expected standard model background is
observed for a Higgs boson mass hypothesis of 124 GeV with a local significance
of 3.1 sigma. The global significance of observing an excess with a local
significance greater than 3.1 sigma anywhere in the search range 110-150 GeV is
estimated to be 1.8 sigma. More data are required to ascertain the origin of
this excess.Comment: Submitted to Physics Letters
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