High-speed real-time heterodyne interferometry using software-defined radio.

This paper describes the design and performance of a phase demodulation scheme based on software-defined radio (SDR), applied in heterodyne interferometry. The phase retrieval is performed in real time by means of a low-cost SDR with a wideband optoelectronic front-end. Compared to other demodulation schemes, the system is quite simpler, versatile, and of lower cost. The performance of the demodulator is demonstrated by measuring the displacement per volt of a thin-film polymeric piezoelectric transducer based on polyvinylidene fluoride for ultrasonic applications. We measured displacements between 3.5 pm and 122 pm with 7% relative uncertainty, in the frequency range from 20 kHz to 1 MHz.

Wideband quad optical sensor for high-speed sub-nanometer interferometry.

This paper describes the design and performance of a low-noise and high-speed optical sensor that provides two output signals in quadrature from the simultaneous detection of four phase-shifted interferograms. The sensor employs four high-speed photodiodes and high-speed, low-noise transimpedance amplifiers. The optical and electronic design was optimized for high-speed displacement measurement interferometry, over a broad range of operating frequencies. Compared to other experimental schemes, the sensor is simpler and of lower cost. The performance of the sensor is demonstrated by characterizing a piezoelectric transducer for ultrasonic applications. We measured displacements between 38 pm and 32 nm with 6% relative uncertainty, in the frequency range from 1 to 2 MHz.

A birefringent polarization modulator: Application to phase measurement in conoscopic interference patterns.

Conoscopic interferometry for crystal characterization is a very well-known technique with increasing applications in different fields of technology. The advantage of the scheme proposed here is the introduction of a polarization modulator that allows the recovery of the phase information contained in conoscopic interferograms. This represents a real advantage since the most relevant physical information of the sample under study is usually contained in the phase of the fringe pattern. Moreover, this technique works successfully even when there are no visible fringes. The setup employed is a simple conoscopic interferometer where the elements under study correspond to two birefringent crystal slabs and a commercial mica wave plate. It allows the crystals to be characterized and the wave plate retardance to be measured as a function of the angle of incidence. The modulator itself consists of a single tiltable crystal plate which, by means of phase shifting techniques, permits the recovery of a phase map for each sample. It is inexpensive and it can be easily calibrated, so it works with a wide range of phase shifting interferometry algorithms. We show that our scheme is easily adaptable to algorithms that require either a low or high amount of interferograms.

Birefringent phase demodulator: application to wave plate characterization.

The scope of this work is to present a phase demodulator that enables the recovery of temporal phase information contained in the phase difference between two signals with different polarizations. This demodulator is a polarization interferometer that may consist only of a uniaxial crystal slab and a polarizer sheet. The phase shift between two orthogonal components of the electric field is translated into space by means of birefringent crystals, which act as demodulators or phase analyzers with great robustness. The experimental scheme utilized is based on a simple conoscopic interference setup. Each portion of the space in which the interference pattern is projected contains not only the unknown temporal phase we want to recover, but also a phase shift due to the uniaxial crystal itself. The underlying idea is developing simultaneous phase shifting with uniaxial crystals. Thus, different phase recovery techniques can be applied in order to maximize their ability to track high-speed signals. Depending on the characteristics of the fringe pattern, it will permit phase recovery via different classical procedures. In order to prove the demodulator under different experimental and signal processing schemes, we employed it for wave plate characterization. The results obtained not only allow some wave plate features such as axes determination and retardance to be characterized, but also prove the working principle and capabilities of the demodulator.

Novel achromatic single reflection quarter-wave retarder: design and measurement.

In this work, we present an achromatic quarter-wave retarder whose design is based upon the reflection properties of an isotropic-anisotropic interface. In theory, it is possible to obtain a π/2 phase shift by means of a total internal reflection at an isotropic-isotropic interface. However, in order to achieve such a phase shift, it is necessary to use a medium with a particularly high refractive index. We have previously shown that these phase shifts can be achieved by means of a total internal reflection in an isotropic-uniaxial interface, which allows the use of smaller refractive index media. By means of this property, we designed, built, and characterized a novel quarter-wave retarder that makes it possible to obtain circularly polarized light from a linear polarization state. We developed some guidelines that allowed us to obtain a device of competitive performance, low cost, and manageable manufacture.

Toxocara infection seroprevalence and its relationship with atopic features in a general adult population.

BACKGROUND: The relationship of helminth infection with atopy is controversial. Toxocariasis is the most common helminth infection in industrialized countries. The study aimed to investigate the association between Toxocara exposure and atopic features. METHODS: The study is based on a cross-sectional survey of 463 subjects, randomly selected (stratified by decades of age) from a general adult population. Toxocara exposure was defined by the presence of serum Toxocara antibodies. Main outcome measures included total serum IgE levels, skin prick tests (SPT) to a panel of 13 relevant aeroallergens, specific IgE to aeroallergens (Phadiatop test), and respiratory symptoms evaluated by means of a questionnaire. RESULTS: A total of 134 subjects (weighted proportion 28.6%, 95% CI 26.5-30.7%) showed Toxocara exposure. Pet ownership, rural habitat, farming, and low educational level were associated with Toxocara exposure. Toxocara exposure was associated with both positive SPT (particularly to mites) and positive specific IgE (Phadiatop test) after adjusting for potential confounders. The effect of Toxocara exposure on total serum IgE levels and blood eosinophil count was different in SPT-positive subjects and SPT-negative individuals. In SPT-negative individuals, Toxocara exposure was associated with an increase in both serum IgE levels and eosinophil counts, whereas an opposite trend was observed in SPT-positive individuals. Toxocara exposure was not associated with respiratory symptoms. CONCLUSIONS: In this adult population, Toxocara exposure is associated with allergic sensitization, particularly to mites. There is evidence of an intriguing interaction between Toxocara exposure and allergic sensitization for both total serum IgE levels and blood eosinophil counts.

[Assessment of 4 commercial immunoenzymatic assays for the serologic diagnosis of Helicobacter pylori infection]. / Evaluación de cuatro enzimoinmunoanálisis comerciales para el diagnóstico serológico de la infección por Helicobacter pylori.

BACKGROUND: The aim of this study was to evaluate four commercial tests for the serologic diagnosis of infection by Helicobacter pylori based on the detection of IgG class antibodies versus this microorganism. METHODS: Four commercial kits were analyzed based on the ELISA method in serum samples of 48 patients admitted for digestive endoscopy. The data of the serologic tests were compared with those provided by the culture, the histologic observation and the urease test of gastric biopsy specimens. The calculation of seroprevalence of anti-H. pylori antibodies in serum of 60 asymptomatic subjects was carried out. RESULTS: The seroprevalence of infection by H. pylori in an asymptomatic population of between 18 to 78 years of age was 58.33%. A sensitivity of 94.3% and a specificity of 88.9% were observed with the Pyloriset EIA-G test. The positive predictive value (PPV) was 92.2% and the negative predictive value (NPV) 91.5%. With the Chemifarma commercial kit the sensitivity was 78.8% and the specificity 100% with a PPV of 100% and NPV of 76.7%. Plate showed a sensitivity of 85.3% and a specificity of 87.5% with a PPV of 90% and a NPV of 80.76%. Milenia had a sensitivity of 80% and a specificity of 66.7% and a PPV of 77% and a NPV of 70.7%. CONCLUSIONS: The usefulness of the serologic tests for the diagnosis of Helicobacter pylori infection is herein confirmed with the test evaluated showing a high sensitivity and specificity as well as high predictive values.

Comparison of a new commercial enzyme immunoassay for rapid detection of respiratory syncytial virus.

Two rapid methods for detection of respiratory syncytial virus in respiratory specimens were compared: direct immunofluorescence assay (DFA) with monoclonal antibody and an enzyme immunoassay (EIA) (Test-Pack RSV). Ninety-five nasopharyngeal washings and aspirates from 51 children were examined; the patients were hospitalized during a winter outbreak of RSV infection in the first trimester of 1990. A total of 41.0% and 56.8% of these samples were positive by EIA and DFA respectively. Considering only the 51 specimens collected at the onset of illness, EIA detected 72.5% positive samples and DFA detected 78.4%. In comparison with DFA, EIA was 92.5% sensitive and 100% specific for the acute phase of illness. When all the samples were taken into account, specificity was maintained but sensitivity fell to 72.2%. The results show that both methods are useful during the acute phase of the illness, when the viral load is important. However, later on in the course of the infection DFA appears to be more sensitive than EIA.

[Resistance of Streptococcus pneumoniae in Galicia]. / Resistencias de Streptococcus pneumoniae en Galicia.

We studied the antibiotic sensitivity of 130 Streptococcus pneumonia strains isolated from respiratory samples (96 cases), blood (13 cases), CSF (6 cases), ocular secretions (5 cases) and other origins (10 cases). High-level penicillin-resistance was found in 13.08% of strains, and intermediate-level penicillin resistance was also found in 22.3% of strains. A multiple-antibiotic resistance pattern was shown by 80.44% of all penicillin-resistant strains. Resistance rates found against antibiotics were as follows: tetracycline, 41.53%; chloramphenicol 17.69%; cotrimoxazole, 16.92% and erythromycin 6.92%. All isolated strains were sensitive to rifampin and vancomycin.

Phase shift in dielectric reflection.

The phase shifts in external dielectric reflection were analyzed as a function of the incident angle. The contrast of the interference fringes formed between the incident and the reflected beams was considered. For the parallel mode the phase shift disappears between 45 degrees and the Brewster angle. Experimental results are shown which demonstrate the contrast inversion in this region.