512 research outputs found
Supersymmetry-generated complex optical potentials with real spectra
We show that the formalism of supersymmetry (SUSY), when applied to
parity-time (PT) symmetric optical potentials, can give rise to novel
refractive index landscapes with altogether non-trivial properties. In
particular, we find that the presence of gain and loss allows for arbitrarily
removing bound states from the spectrum of a structure. This is in stark
contrast to the Hermitian case, where the SUSY formalism can only address the
fundamental mode of a potential. Subsequently we investigate isospectral
families of complex potentials that exhibit entirely real spectra, despite the
fact that their shapes violate PT-symmetry. Finally, the role of SUSY
transformations in the regime of spontaneously broken PT symmetry is
investigated.Comment: 6 pages, 4 figure
Deep Vein Thrombosis among Intensive Care Unit Patients; an Epidemiologic Study
Introduction: Deep vein thrombosis (DVT) is a major cause of morbidity and mortality in intensive care unit (ICU) patients despite use of prophylactic anticoagulant therapy. The aim of the present study was to determine the incidence of DVT among medical and surgical ICU patients.Methods: In this cross sectional study, patients older than 18 years who were hospitalized in the ICU of Imam Hossein educational Hospital, Tehran, Iran, for ≥ 2 days, during August 2008 to July 2011 were evaluated regarding DVT incidence. Demographic data, comorbidities, acute physiology and chronic health evaluation (APACHE) II scores, ICU length of stay, type of DVT prophylaxis, and patient outcomes were analyzed using SPSS 19.Results: Out of the 1387 reviewed patient files, 500 (36.04%) patients had been classified as potential DVT cases. DVT occurred in 3.5% of them with the mean age of 60 ± 18 years (62.5% male) and mortality rate of 27.1%. Significant independent risk factors of DVT incidence were age (p = 0.02) and length of ICU stay (p = 0.01).Conclusion: The results of this study showed the 3.5% incidence of DVT in ICU admitted patients. Longer ICU stay and older age were independent risk factors of DVT development
Universal Unitary Photonic Circuits by Interlacing Discrete Fractional Fourier Transform and Phase Modulation
We introduce a novel parameterization of complex unitary matrices, which
allows for the efficient photonic implementation of arbitrary linear discrete
unitary operators. The proposed architecture is built on factorizing an unitary matrix into interlaced discrete fractional Fourier transforms
and -parameter diagonal phase shifts. We show that such a configuration can
represent arbitrary unitary operators with phase layers. We discuss a
gradient-based algorithm for finding the optimal phase parameters for
implementing a given unitary matrix. By increasing the number of phase layers
beyond the critical value of , the optimization consistently converges
faster as the system becomes over-determined. We propose an integrated photonic
circuit realization of this architecture with coupled waveguide arrays and
reconfigurable phase modulators. The proposed architecture can pave the way for
developing novel families of programmable photonic circuits for optical
classical and quantum information processing.Comment: Under review since January 15, 202
Integrated Photonic Fractional Convolution Accelerator
An integrated photonic circuit architecture to perform a modified-convolution
operation based on the Discrete Fractional Fourier Transform (DFrFT) is
introduced. This is accomplished by utilizing two nonuniformly-coupled
waveguide lattices with equally-spaced eigenmode spectra and with different
lengths that perform DFrDT operations of complementary orders sandwiching a
modulator array. Numerical simulations show that smoothing and edge detection
tasks are indeed performed even for noisy input signals
Nonlinear reversal of PT symmetric phase transition in a system of coupled semiconductor micro-ring resonators
A system of two coupled semiconductor-based resonators is studied when lasing
around an exceptional point. We show that the presence of nonlinear saturation
effects can have important ramifications on the transition behavior of this
system. In sharp contrast with linear PT-symmetric configurations, nonlinear
processes are capable of reversing the order in which the symmetry breaking
occurs. Yet, even in the nonlinear regime, the resulting non-Hermitian states
still retain the structural form of the corresponding linear eigenvectors
expected above and below the phase transition point. The conclusions of our
analysis are in agreement with experimental data.Comment: 9 pages, 8 figure
Integrable nonlinear parity-time symmetric optical oscillator
The nonlinear dynamics of a balanced parity-time symmetric optical microring
arrangement are analytically investigated. By considering gain and loss
saturation effects, the pertinent conservation laws are explicitly obtained in
the Stokes domain-thus establishing integrability. Our analysis indicates the
existence of two regimes of oscillatory dynamics and frequency locking, both of
which are analogous to those expected in linear parity-time symmetric systems.
Unlike other saturable parity time symmetric systems considered before, the
model studied in this work first operates in the symmetric regime and then
enters the broken parity-time phase.Comment: 6 pages, 5 figures, accepted for publicatio
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