Spectral Network Principle for Frequency Synchronization in Repulsive Laser Networks

Network synchronization of lasers is critical for reaching high-power levels and for effective optical computing. Yet, the role of network topology for the frequency synchronization of lasers is not well understood. Here, we report our significant progress toward solving this critical problem for networks of heterogeneous laser model oscillators with repulsive coupling. We discover a general approximate principle for predicting the onset of frequency synchronization from the spectral knowledge of a complex matrix representing a combination of the signless Laplacian induced by repulsive coupling and a matrix associated with intrinsic frequency detuning. We show that the gap between the two smallest eigenvalues of the complex matrix generally controls the coupling threshold for frequency synchronization. In stark contrast with Laplacian networks, we demonstrate that local rings and all-to-all networks prevent frequency synchronization, whereas full bipartite networks have optimal synchronization properties. Beyond laser models, we show that, with a few exceptions, the spectral principle can be applied to repulsive Kuramoto networks. Our results may provide guidelines for optimal designs of scalable laser networks capable of achieving reliable synchronization

Optical Potts Machine through Networks of Three-Photon Down-Conversion Oscillators

In recent years there has been a growing interest in optical simulation of lattice spin models for applications in classical computing. Here, we propose optical implementation of a three-state Potts spin model by using networks of coupled parametric oscillators with phase tristability. We first show that the cubic nonlinear process of spontaneous three-photon down-conversion is accompanied by a tristability in the phase of the subharmonic signal between three states with 2��/3 phase contrast. The phase of such a parametric oscillator behaves like a three-state spin system. Next, we show that a network of dissipatively coupled three-photon down-conversion oscillators emulates the three-state planar Potts model. We discuss potential applications of the proposed system for all-optical optimization of combinatorial problems such as graph 3-COL and MAX-3-CUT

Combinatorial Optimization with Photonics-Inspired Clock Models

NP-hard combinatorial optimization problems are in general hard problems that their computational complexity grows faster than polynomial scaling with the size of the problem. Thus, over the years there has been a great interest in developing unconventional methods and algorithms for solving such problems. Here, inspired by the nonlinear optical process of q-photon down-conversion, in which a photon is converted into q degenerate lower energy photons, we introduce a nonlinear dynamical model that builds on coupled single-variable phase oscillators and allows for efficiently approximating the ground state of the classical q-state planar Potts Hamiltonian. This reduces the exhaustive search in the large discrete solution space of a large class of combinatorial problems that are represented by the Potts Hamiltonian to solving a system of coupled dynamical equations. To reduce the problem of trapping into local minima, we introduce two different mechanisms by utilizing controlled chaotic dynamics and by dynamical formation of the cost function through adiabatic parameter tuning. The proposed algorithm is applied to graph-q-partitioning problems on several complex graphs

Arrayed Waveguide Lens for Beam Steering

Integrated planar lenses are critical components for analog optical information processing that enable a wide range of applications including beam steering. Conventional planar lenses require gradient index control which makes their on-chip realization challenging. Here, we introduce a new approach for beam steering by designing an array of coupled waveguides with segmented tails that allow for simultaneously achieving planar lensing and off-chip radiation. The proposed arrayed waveguide lens is built on engineering the evanescent coupling between adjacent channels to realize a photonic lattice with an equi-distant ladder of propagation constants that emulates the continuous parabolic index profile. Through coupled-mode analysis and full-wave numerical simulations, we show that selective excitation of waveguide channels enables beam steering with large field-of-views of ∼60°. The proposed arrayed waveguide lens can serve as a compact component in integrated photonic circuits for applications in imaging, sensing, and metrology

Improvement in Cardiac Function following Transplantation of Human Umbilical Cord Matrix-Derived Mesenchymal Cells

Objectives: Human umbilical cord mesenchymal cells (hUCM) can be easily obtained and processed in a laboratory. These cells may be considered as a suitable source in the repair of heart failure diseases. We, therefore, examined whether these cells may contribute to heart regeneration following an acute experimental myocardial infarction (MI). Methods: MI-induced animals received 5 ! 10 6 hUCM cells, 5 ! 10 6 5-azacytidine-treated cells (dhUCM), or PBS alone, subepicardially. A group of animals with MI and no other former intervention served as controls. dhUCM cells were assessed for F-actin, myogenin and troponin-I expression. Re-sults: dhUCM cells appeared as binucleated cells with extensive cytoplasmic processes. These differentiated cells were F-actin and myogenin positive. Thirty days after LAD ligation, left ventricular ejection fraction and the percentage of fractional shortening improved significantly in cell-receiving animals. In addition, the amount of scar tissue was significantly reduced in hUCM and dhUCM groups compared to MI group (p ! 0.05). These parameters were comparable between hUCM and dhUCM groups. Histopathological evaluations revealed that some engrafted cells adjacent to and remote from the MI area expressed troponin-I, F-actin and connexin43. Conclusion: These findings demonstrated the potential therapeutic use of either differentiated or undifferentiated hUCM cells in treatment of heart failure conditions

Optical Potts machine through networks of three-photon down-conversion oscillators

In recent years, there has been a growing interest in optical simulation of lattice spin models for applications in unconventional computing. Here, we propose optical implementation of a three-state Potts spin model by using networks of coupled parametric oscillators with phase tristability. We first show that the cubic nonlinear process of spontaneous three-photon down-conversion is accompanied by a tristability in the phase of the subharmonic signal between three states with 2π/3 phase contrast. The phase of such a parametric oscillator behaves like a three-state spin system. Next, we show that a network of dissipatively coupled three-photon down-conversion oscillators emulates the three-state planar Potts model. We discuss potential applications of the proposed system for all-optical optimization of combinatorial problems such as graph 3-COL and MAX 3-CUT

FREQUENCY OF EXTENDED-SPECTRUM BETA-LACTAMASE-PRODUCING KLEBSIELLA PNEUMONIAE ISOLATES FROM URINARY TRACT INFECTIONS IN TEACHING HOSPITAL IN SHAHREKORD BY PCR METHOD

Background: The aim of this study was to investigate the frequency of ESBL producing Klebsiella pneumonia at an educational hospital in shahrekord, Iran. Methods: This study was conducted at Shahrekord University of medical science. Totally, 150 isolates of Klebsiella pneumonia bacteria were selected from out-patient of Hajar and kashani university hospitals. Uropathogens were identified through culture, microscopy and biochemical tests. To detect possible ESBL production, combined double disc synergy test was performed by disc of ceftazidime (30 mg) alone and in the presence of clavulanate (30 mg/10 mg) at a distance of 25 mm, on a Mueller–Hinton agar plate. Detection of SHV gene was examined in ESBL positive strains by PCR. Results: Combined double disc synergy test was applied to detect ESBL in 75 Klebsiella pneumoniae isolates that are resistant to ceftazidime using ceftazidime. Among the 48 ESBL-producing K. pneumonia strains, 18 (37.5%) were identified as SHV producing strains. Conclusion: The spread of ESBL-producing bacteria has been strikingly rapid worldwide, indicating that continuous monitoring systems and effective infection control measures are required. Therapeutic options for infections due to ESBL producers become increasingly limited. Molecular detection and identification of beta lactamases would be essential for a reliable epidemiological investigation of antimicrobial resistance. Therefore, ESBL producing organisms should be identified quickly so that appropriate antibiotic usage and infection control measures can be implemented