Experimental Investigation of Transmission Properties and All-Optical Label Swapping of Orthogonal IM/FSK Labeled Signals

Optically labeled IM/FSK signal saretran smitte dover 50km of SMF under different compensation schemes.All-opticallabel swapping based on MZ-SOA and EAM is presented. Transmission followed by label swapping shows a 2dB overall power penalty.     

All-fiber incoherent frequency-to-time mapping method for microwave signal generation with baseband transmission and multicasting support

We present a proof-of-principle experiment for achieving simultaneous distribution of baseband radio-frequency data and up-conversion with broadcasting support over a passive optical network. The technique is based on an incoherent frequency-to-time mapping method for pulse shaping. Specifically, we synthesize the spectral density function of sliced ASE noise from an EDFA with a periodic Mach–Zehnder fiber interferometer optical filter. By using external intensity modulation combined with propagation in an optical fiber, after photodetection, the resultant averaged temporal pulse profile resembles the shape of the incoherent source. The photodetected signal contains both the baseband data and an up-frequency converted copy with central wavelength for the microwave carrier into the ultra-wideband range and tuning capability by selection of the fiber length.     

A-B site-bond correlated percolation for antiferromagnetic Ising model: The Bethe cluster approximation

We study the site-bond percolation problem for clusters of holes and particles with antiferromagnetic order by means of the Bethe cluster approximation. We find that the droplets (i.e.P _B =1?e ^?|K|/2) diverge at the antiferromagnetic critical pointH=0,T=T _c; however forH≠0 they diverge along a percolation line which is different from the Antiferromagnetic Phase Boundary except atT=0.     

Interfacial rheology of polyelectrolytes and polymer monolayers at the air–water interface

In this review, we describe interfacial rheology studies of polymer monolayers at the air–water interface. Since polyelectrolytes are usually soluble in water, the formation of surface monolayers requires the presence of a surfactant of opposite charge. The first part of the review is dedicated to these mixed monolayers. The second part is related to neutral monolayers that can be either adsorbed or deposited at the interface. Interfacial rheology studies of these systems are still scarce, despite a considerable interest: insoluble polymer monolayers in two dimensions are suitable model systems for the tests of polymer theories in two dimensions, such as and glass transition. The rheology of soluble polymer monolayers has important connections with the dynamic properties of dispersions stabilized with these polymers.     

Equilibrium and dynamics of Langmuir monolayers when the interface is a selective solvent: Polystyrene-b-poly(t-butyl acrylate) block copolymers

The surface pressure of monolayers of insoluble diblock copolymers has been measured. One of the blocks is made of poly(t-butyl acrylate) (PtBA), and the other one by polystyrene (PS). The interface is a good solvent for PtBA, while it is a poor solvent for PS. For the sake of comparison, monolayers of a PtBA homopolymer (good solvent conditions) and of poly(4-hydroxy styrene) (P4HS) (poor solvent conditions) have been also measured. It has been found that the relative length of the blocks plays an important role on the shape of the surface pressure Pi versus surface concentration Gamma curves and also on the shape of the equilibrium compressibility versus Gamma curves. However, it does not affect the maximum value of Pi reached at high Gamma's. Surprisingly, the ellipsometric thickness of the copolymer monolayers is almost independent of the relative length of the blocks. The dynamics of the monolayers has been studied by step compression and by surface-light scattering techniques. When M(w,PtBA) > M(w,PS) single exponential relaxations are observed. However, stretched exponentials are obtained for M(w,PS) > or = M(w,PtBA). The relaxation times decrease with increasing Gamma for all the copolymers studied. This is the behavior usually found for poor solvent conditions (P4HS) and opposite to that found for homopolymers under good solvent conditions [PtBA, poly(vinylacetate)]. This means that the solvent quality of the interface does not determine the pressure dependence of tau. The elasticity modulus of the monolayers in the kilohertz range takes values that are similar to those of the high-frequency limit of the relaxation experiments. This means that the relaxation processes have characteristic frequencies below 1 Hz.     

Quantitative assessment of lateral resolution improvement in digital holography

Controllable experimental features such as wavelength, camera’s specifications and reconstruction distance, determine the theoretical limit for lateral resolution in digital holography; however, due to the speckle noise associated to any coherent imaging system it is not possible to reach this theoretical limit. In this paper, a quantitative study the lateral resolution for digital holography under the effect the speckle noise is carried out. It is shown that by reducing the contrast of the speckle noise the resolution capabilities of digital holography are improved; the signal-to-noise ratio of the reconstructed holograms is the metric use to quantitatively assess the reached resolution in the holographic experiments.     

Recent progress in the development of type II interband cascade lasers

Type-II interband cascade lasers combine the advantage of an interband optical transition with interband tunneling to enable the cascading of type-II quantum well active regions as is done in type-I quantum cascade laser. The relatively high radiative efficiency resulting from interband optical transitions translates into very low-threshold current densities, and when combined with the high quantum efficiency of cascade lasers, this diode laser design has the potential to operate under cw conditions at room temperature with high output power. Experimental results have already demonstrated some of this potential including high differential external quantum efficiency (>600%), high peak output power (6 W/facet at 80 K), high cw power conversion efficiency (>17% at 80 K), and operation at 300 K under pulsed conditions. Recent work aimed at reducing device thermal resistance and increasing cw operating temperature is reviewed including the demonstration of significant reductions in thermal resistance (averaging 25 K/W or 40% for 1-mm-long devices), 80 K cw operation at 3.4 μm with high-power conversion efficiency (23%) and high differential external quantum efficiency (532%), and cw operation up to 214 K.     

On the Initial Stages of Electrooxidation of Aqueous Maleic Acid on Bi‐Doped PbO2

Oxidation of maleic acid in aqueous solution on bismuth‐doped lead oxide has been studied. The effects of hydrodynamic conditions on the oxidation rate have been identified. The number of electrons transferred during the initial stages of oxidation as well as the apparent heterogeneous rate constant was obtained from the combined analysis of rotating ring‐disk currents and the decrease of concentration at constant potential, determined from UV‐vis measurements. The number of electrons involved during electrochemical oxidation was found to be 12, indicating full mineralization to CO₂, and the heterogeneous rate constant for oxidation at 1.6 V was 9.8×10⁵ cm s^?1.     

Aging of polyamide 12 in oil at different temperatures and pressures

Polyamide 12 (PA 12) is an alternative to steel in the manufacture of pipes for transporting oil and gas. However, polyamide pipes suffer degradation, triggered by factors such as temperature and exposure to chemicals. In this research, the authors studied the variation of mechanical and thermal properties and of structural characteristics of a PA 12 grade after aging in oil. The aging process lasted 3360 h. It was made at ambient temperature and at 70 °C, under pressures of 1 and 17 atm. At ambient temperature and atmospheric pressure, PA 12 increased in volume, weight and rigidity, and decreased in damping. At 70 °C and atmospheric pressure, there was a smaller increase in volume and weight. PA 12 samples also darkened, showed an increase in crystallinity and damping, and a decrease in rigidity. At 70 °C and 17 atm, a decrease in volume and weight was observed; the samples also darkened, increased in crystallinity and rigidity, and decreased in damping. In all aging conditions, the results of the thermal analysis and the analysis of functional groups showed that the chemical structure of the material was not significantly changed. According to the results, PA 12 has a good resistance to aging under these conditions. Copyright © 2017 John Wiley & Sons, Ltd.     

Polymer monolayers with a small viscoelastic linear regime: equilibrium and rheology of poly(octadecyl acrylate) and poly(vinyl stearate)

The equilibrium properties of monolayers of two polymers: poly(octadecyl acrylate) and poly(vinyl stearate) on water have been measured. The surface pressure (Pi) versus surface concentration (Gamma) curves indicate that the water-air interface is a poor solvent for both polymers. The thermal expansivity shows a sharp change near room temperature. This behavior is typical of a glass transition; this is the first time that such a plot is observed for Langmuir films. The Pi vs Gamma curves measured by the continuous compression method show strong anisotropy effects. They also show that the monolayer is brought into nonequilibrium states depending on the compression rate. Within the linear regime, the relaxation experiments were bimodal. The longest relaxation time strongly increases as T is decreased, which might be compatible with the high increase of viscosity in the glass transition. The oscillatory barrier experiments showed that the maximum strain of the linear regime is smaller than 3% for both monolayers. The Fourier-transform analysis of the oscillatory experiments beyond the linear regime points out the contribution of different harmonics in the response function. Oscillations in the nonlinear regime show hysteresis cycles. The results obtained indicate that some of the previously published data for these polymer monolayers correspond to nonequilibrium states.