Planar flexible fiber-optic acoustic sensors

The acoustic sensitivity of optical fibers is considered analytically. High sensitivity is obtained with low bulk modulus, very thick polymeric coatings. The fiber coatings play an important role in determining the fiber acoustic sensitivity. The very thick coating limit is realized by embedding optical fibers in an appropriate elastomer (polyurethane). A planar flexible fiber-optic interferometric acoustic sensor is developed by wrapping optimized single-mode fibers in a planar spiral form, and then embedding the fiber in a thin polyurethane layer. The acoustic sensitivity of the sensor is found to be high, and frequency (0.2-2.5 kHz) and static pressure independent. The sensor is found to be compatible with water, and is compared favorably to that of a planar polyvinylidene fluoride sensor of similar geometry     

Inverse analysis of surface degradation using optical fibers

The authors present a general method based on inverse analysis of light signals from a fiber-optic sensor for in situ detection of metal, film, or coating degradation. This method, which does not, in principle, depend on the geometry of the fiber-optic sensor, is based on analysis of reflected light intensity loss as opposed to reflected or transmitted intensity modulation. Following an inverse-analysis approach, the level and rate of intensity loss are correlated with levels and rates of surface degradation. This approach allows optimization of fiber-optic sensors for specific applications and different environments. Case study analyses using experimental data are used to demonstrate the fundamentals of various aspects of this method.     

Optimizing fiber coatings for interferometric acoustic sensors

The pressure sensitivity of the phase of light propagating in an optical fiber is studied both analytically and experimentally. The analysis, which takes into account the exact composition and geometry of multilayer fibers, is utilized to identify coating properties which optimize the fiber acoustic sensitivity. In order to predict the fiber acoustic sensitivity, the elastic parameters of commonly used coating materials, thermoplastics, and UV curable elastomers have been studied in bulk samples as a function of frequency (10^{2}-10^{4}Hz) and temperature (0-35degC). The analytically predicted frequency dependence of the acoustic sensitivity is found to be in agreement with that obtained experimentally from fibers with coatings of various materials.     

HIV treatment strategies utilizing virologic and immunologic markers as criteria for changing treatments

Currently available antiviral drugs used in the treatment of AIDS patients are effective for a limited time. Therapy consisting of different drugs given in sequence thus has the potential to yield the greatest possible benefit to patients, yet it is not known in what order the drugs should be administered, or for how long. Can patient-specific information, such as viral load or determination of mutation status, be used to make these decisions on a patient by patient basis? We propose a general model for the relationship between treatment, virologic or immunologic markers, and clinical disease progression that can provide answers to these questions. We develop guidelines for optimizing progression under several settings. Optimal survival is derived for full, partial, or no interim information.     

Ultrasonic sensitivity of coated fibers

The acoustic sensitivity of the phase of light propagating in a coated optical fiber is studied for ultrasonic frequencies where the fiber is axially constrained and isotropic. The analysis, which takes into account the exact composition and geometry of multilayer fibers, is utilized to identify coatings compositions which optimize the fiber acoustic sensitivity.     

Evaluating the role of human papillomavirus vaccine in cervical cancer prevention

Persistent genital infection with human papillomavirus (HPV) is a natural candidate as a surrogate marker for cervical cancer because of the strong epidemiologic and molecular evidence that HPV infection is the causative agent for almost all cervical cancers. However, while infection with high-risk types of HPV appears to be necessary for the development of cervical cancer, most infections are controlled by host immune response and do not lead to cancer in the vast majority of infected women. Because diagnostic tests cannot distinguish a persistent infection in the pathogenesis of cervical cancer from a transient infection, it is difficult to describe the disease mechanism as a progressive process based on observations. Therefore, the disease pathogenesis pathway does not fit into the usual surrogate marker framework, raising practical concerns about using HPV infection as a surrogate for a clinical endpoint in vaccine trials. In this paper, we describe the challenges in defining HPV infection as a surrogate endpoint in a HPV vaccine trial that is aimed at reducing cervical cancer rates and examine potential effects of the vaccine. We then outline some issues in the design and analysis of HPV vaccine trials, including the use of operationally defined HPV infection events meant to capture persistent infections. We conclude with a recommendation for a multistate model that uses HPV infection to help explain the mechanisms of vaccine action rather than validate it as an endpoint substitute.     

Dynamic thermal response of single-mode optical fiber for interferometric sensors

The dynamic temperature phase sensitivity of a three-layer optical fiber is calculated for unjacketed as well as Al- and Hytrel-coated fibers. The calculations include both the variation of the refractive index with temperature and the thermally induced axial and radial strains. The calculated phase sensitivity indicates that it is currently possible to measure a 1-microdegree C temperature change at frequencies exceeding 50 kHz with 1 cm of a metal coated optical fiber.     

Assessment of Mechanical Strength Degradation Using an Embedded Fiber-Optic Sensor

A general method is presented for in situ assessment of mechanical strength degradation of materials or components using an embedded interferometric fiber-optic strain sensor. This method is based on the analysis of acoustic signature responses resulting from mechanical excitation of the subject under investigation. Acoustic signature responses are observed by monitoring light intensity changes resulting from the combination of light signals traveling through the embedded optical fiber (experiencing dimensional changes through vibrational excitation) and an external optical fiber. This paper discusses the fundamental aspects of the methodology and its potential investigational pathways and applications. A case study, addressing unobservable corrosion related degradation of aircraft fuselage lap joints is presented as an example for retrieving information and to demonstrate the correlations between material properties and fiber-optic interferometric measurements. The application of inverse method analysis for the interpretation of response signals is also discussed. P.P. Trzaskoma-Paulette is presently working as an Independent Consultant     

Linearly configured embedded fiber-optic acoustic sensor

A linearly configured fiber-optic acoustic sensor has been developed by embedding a single-mode fiber in a polyurethane cylindrical layer. The acoustic sensitivity was studied in the range of 0.75-10 KHz and was found to be frequency independent and significantly higher than that of a free suspended fiber or a solid mandrel fiber sensor. A comparison is mace between this sensor and air-backed fiber-optic mandrel sensors     

Size and power of two-sample tests of repeated measures data

One method of using repeated measures data to compare treatment groups in a clinical trial is to summarize each subject's outcomes with a single summary statistic, and then perform a distribution-free comparison based on the resulting statistics. We examine extensions of this approach and conditions under which they retain proper size in the presence of missing data. The asymptotic relative efficiencies of several summary statistic tests are calculated to show which perform best in a variety of situations. The techniques are illustrated using data from an AIDS clinical trial.