Coated long-period fiber gratings as high-sensitivity optochemical sensors

In this paper, the numerical and the experimental analyses of coated long-period fiber gratings (LPFGs) as a high-sensitivity optochemical sensor are presented. The proposed structure relies on LPFGs coated with nanoscale high refractive index chemical-sensitive overlays. The deposition of overlays with refractive index higher than the cladding one leads to a modification of the cladding-mode distribution. If the overlay features are properly chosen, a strong field enhancement within the overlay occurs, leading to an excellent sensitivity of the cladding-mode distribution to the coating properties. The effects of overlay thickness and cladding-mode order on sensor performances have been numerically and experimentally investigated. In order to provide a high-sensitivity and species-specific optochemical sensor, this mechanism has been proved with nanoscale overlays of syndiotactic polystyrene (sPS) in the nanoporous crystalline /spl delta/ form. The sensitive material has been chosen in light of its selectivity and high sorption properties towards chlorinated and aromatic compounds. Sensor probes were prepared by using dip-coating technique and an adequate procedure to obtain the /spl delta/-form sPS. Experimental demonstration of the sensor capability to perform subparts-per-million detection of chloroform in water at room temperature is also reported.     

Real time monitoring of cure and gelification of a thermoset matrix

The consolidation of a commercial thermoset resin has been completely monitored by using a unique fiber optic sensor integrating a refractometer and a fiber Bragg grating. In particular, the advancement and the evolution of the resin polymerization reaction have been followed by measuring the optical properties changes induced by the thermo-chemical transformations. On the other hand, the fiber Bragg grating has been used to detect on-line the resin gelification onset. The experimental results demonstrated the capability and the efficiency of the developed sensor system to provide complete information on the main phenomena occurring during the cure cycle of a thermoset based system.     

Optoelectronic refractive index measurements: application to smart processing

In the last decade, polymeric-based composites, in light of their low weight/mechanical strength ratio, have been widely used in many industrial areas, such as automotive, aeronautic, and aerospace areas. Because of the dependence of their properties on the manufacturing stage, real-time monitoring of the processing stage has been indicated as the key point for improving the quality and reducing manufacturing process costs through an intelligent control of the manufacture itself. To this aim, optimal monitoring systems should be non-intrusive, real-time, and able to measure a physical property changing during the process development. Refractive index is a suitable state parameter being directly correlated to the material density. In this work, the assessment of the performances of a fiber-optic refractometer has been presented. Experimental results demonstrate the capability of the sensor system to monitor the cure kinetics of a polymeric thermoset and to measure its glassy transition temperature.     

Charge transfer effects on the sensing properties of fiber optic chemical nano-sensors based on single-walled carbon nanotubes

The effects of charge transfer induced by analyte molecule adsorption on the sensing properties of single-walled carbon nanotube (SWCNT) fiber optic chemical nano-sensors has been investigated. Experimental evidence indicates that extrinsic fiber optic Fabry-Perot (FP) interferometers incorporating nano-scale sensitive layers of SWCNTs and cadmium arachidate exhibit responses of opposite sign on exposure to electron donating (xylene and ethanol vapors) or accepting (NO₂) analytes, at room temperature. This reveals the strong influence of the electrical nature of the adsorbed species on the optical properties of carbon nanotube overlays. To take account of this influence, the plasma optic effect has been considered, which allows one to relate the modulation of the optical properties of sensitive overlays to the changes of carrier concentration. The results reveal that in analogy with resistive sensors based on SWCNTs, charge transfer phenomena play a significant role in optical detection, providing the possibility of enhancing the sensing performance and discriminating between accepting or donating analytes.     

Response of fiber Bragg gratings to longitudinal ultrasonic waves

In the last years, fiber optic sensors have been widely exploited for several sensing applications, including static and dynamic strain measurements up to acoustic detection. Among these, fiber Bragg grating sensors have been indicated as the ideal candidate for practical structural health monitoring in light of their unique advantages over conventional sensing devices. Although this class of sensors has been successfully tested for static and low-frequency measurements, the identification of sensor performances for high-frequency detection, including acoustic emission and ultrasonic investigations, is required. To this aim, the analysis of feasibilty on the use of fiber Bragg grating sensors as ultrasonic detectors has been carried out. In particular, the response of fiber Bragg gratings subjected to the longitudinal ultrasonic (US) field has been theoretically and numerically investigated. Ultrasonic field interaction has been modeled, taking into account the direct deformation of the grating pitch combined with changes in local refractive index due to the elasto-optic effect. Numerical results, obtained for both uniform and Gaussian-apodized fiber Bragg gratings, show that the grating spectrum is strongly influenced by the US field in terms of shape and central wavelength. In particular, a key parameter affecting the grating response is the ratio between the US wavelength and the grating length. Normal operation characterized by changes in wavelength of undistorted Bragg peak is possible only for US wavelengths longer than the grating length. For US wavelengths approaching the grating length, the wavelength change is accompanied by subpeaks formation and main peak amplitude modulation. This effect can be attributed to the nonuniformity of the US perturbation along the grating length. At very high US frequencies, the grating is not sensitive any longer. The results of this analysis provide useful tools for the design of grating-based ultrasound sensors for meeting specific requirements in terms of field intensity and frequencies.     

Topical NSAID allergic contact dermatitis. Italian experience

The clinical, parasitological, hematological, and serological evolution of visceral leishmaniasis in Brazilian patients was assessed during treatment with human recombinant interferon-gamma (rIFN-gamma; 0.1 mg/m2 i.m. days 1-14) followed by pentavalent antimony (Sbv; 10 mg/kg days 22-28). At day 30, 6 patients had improved, 2 had slightly improved, and 1 patient had deteriorated. IFN-gamma was well tolerated in the dose tested and may be very effective as an adjunct to conventional therapy with antimony.     

Stimuli-responsive hybrid microgels for controlled drug delivery: Sorafenib as a model drug

Microgels (MGs) are synthetic colloidal hydrogel particles made of three dimensional polymer networks. Their chemical composition is crucial for their use as intelligent drug release systems operated by temperature control. Herein, several MGs using N-isopropylacrylamide (Nipam)/N-isopropylmethacrylamide (Nipmam), chitosan and acrylic/methacrylic acid have been synthesized by free radical polymerization reactions (NC MGs) and the effects of surfactants and different reaction times on size and swelling properties have been investigated. MGs have been identified and characterized by dynamic light scattering and atomic force microscopy, and finally used to optimize the encapsulation protocol of the hydrophobic drug sorafenib. The drug delivery system here described has encapsulation efficiency of 40% and releases 10% of the entrapped drug over about 16 h after the temperature is raised above the volume phase transition temperature. Data suggest that MGs with optimized composition may act as properly instructed entities able to trap and release biomolecules following external stimuli.     

The effect of variable permeability on the performance characteristics of porous bearing

An analytical solution for the performance characteristics of a short bearing having an axial and radial permeability of $\text{k}{}_{\mathrm{z}}\text{[1 + cos(}\text{πz}\text{L}\text{)]}$ and $\text{k}{}_{\mathrm{z}}\text{[1 + (}\text{2}\text{π}\text{)]}$, respectively, is obtained. Results are presented which relate the eccentricity ratio and coefficient of friction as functions of load number for various design variables. These results are compared to the results obtained for an isotropic bearing having a permeability of $\text{k}{}_{\mathrm{z}}\text{[1 + (}\text{2}\text{π}\text{)]}$.     

Scuffing of Area Contacts Under Starved Lubrication Conditions

The scuffing behavior of 390-T6 and DHT3 aluminum alloys, Si-Pb brass and gray cast iron, sliding against 1018 carburized steel, is experimentally studied under starved lubrication conditions. The major emphasis of the study is on the 390-T6 aluminum alloy. All tests are conducted in a high pressure tribometer (HPT) under RI34a (tetrafluoroethane) environment with polyalkylene glycol (PAG) and polyolester (POE) lubricants to simulate failures of critical tribocontacts in refrigerant compressors. An area contact, pin-on-disc geometry, is used to examine the effects of degree of lubricant starvation, sliding velocity, materials, and lubricant/refrigerant mixtures on scuffing. The scuffing transitions characteristics of 390-T6 aluminum as a function of lubricant supply rate are also examined. The processes leading to scuffing and failure mechanisms are studied by examination of scuffed surfaces and subsurfaces. Based on the experimental observations, it is hypothesized that bulk material failure during scuffing is due to plastic shearing or smearing.     

Thermally-Induced Failures in Railroad Tapered Roller Bearings

An Association of American Railroads (AAR) class F (6 1/2 × 12) tapered-roller bearing assembly is modeled, using finite elements, to examine thermally-induced failures observed in the laboratory when the bearing is operating at relatively high speeds. It is hypothesized that this failure is caused by an unstable thermal expansion/internal bearing load feedback process. Sequentially-coupled, transient thermal and static structural models are used to obtain the thermal-mechanical transient time response as a function of speed, seal type, and lubricant starvation at the rib contact. The model assumes no external loads and zero initial preload (zero end-play). Therefore, the loads developed in the bearing are thermally-induced and self-equilibrated. Two train speeds, viz. 80 and 100 mph, are considered. Simulation results indicate that at axle rotational speeds equivalent to a train speed of 100 mph, a combination of grease starvation and heat flux from the contact seals cause high rib temperature and subsequent unstable load growth which will lead to failure. At rotational speeds equivalent to train speeds of 80 mph or for bearing assemblies that utilize special design seals, the rib temperature is relatively low and no operational instabilities were observed for the model used.