ABSTRACTmA fiber optic sensor capable of measuring two independent components of transverse strain is described. The sensor consists of a single Bragg grating written into highbirefringent, polarization-maintaining optical fiber. When light from a broadband source is used to illuminate the sensor, the spectra of light reflected from the Bragg grating contain two peaks corresponding to the two orthogonal polarization modes of the fiber. Two independent components of transverse strain in the core of the fiber can be computed from the changes in wavelength of the two peaks if axial strain and temperature changes in the fiber are zero or known. Experiments were performed to determine the response of the sensor by loading an uncoated sensor in diametral compression over a range of fiber orientations relative to the loading. The results of these experiments were used with a finite element model to determine a calibration matrix relating the transverse strain in the sensor to the wavelength shifts of the Bragg peaks. The performance of the sensor was then verified by measuring the transverse strains produced by loading the fiber in a V-groove fixture.KEY WORDSmBragg grating, fiber optic sensor, transverse strain, polarization-maintaining filter Fiber optic sensors can be embedded in polymer-matrix composites and other materials to measure internal strain, temperature and other parameters. These small, highly responsive sensors have been demonstrated in many applications, including manufacturing process monitoring, impact and damage detection and structural health monitoring.1 Fiber optic strain sensors have been the focus of increasing attention as a potentially low-cost, nondestructive means of determining the internal strains and stresses in a material.A schematic of an embedded fiber optic strain sensor is shown in Fig. 1. The axes xl-x2-x3 form the basis for the fiber coordinate system, where Xl is parallel to the axial direction of the fiber and the transverse directions (x2 and x3) are located in the plane of the cross section of the fiber. An embedded sensor may be subjected to an arbitrary strain field, ~, consisting of six components, 8i (i = 1 ..... 6), where the components of strain are presented in contracted notation Original manuscript submitted. " January 14, 1998. Final manuscript received: January 19, 1999 within the fiber; however, in this paper, the terms ei will refer to the average strains in the core of the fiber.Most fiber optic strain sensors are capable of measuring only the axial component of strain in the fiber (e 1). In embedded applications, it is often desirable to measure components of strain transverse to the optical fiber for several reasons. First, for stress measurements, the state of stress within a material will be a function of the complete state of strain, and cannot be computed from a single axial strain measurement. Several individual fiber optic sensors, oriented in different directions, would be required to determine the complete state of strain in these applications.2 A larg...

The product of the Schizosaccharomyces pombe cwg2+ gene is involved in the biosynthesis of beta‐D‐glucan. When grown at the non‐permissive temperature, cwg2‐1 mutant cells lyse in the absence of an osmotic stabilizer and display a reduced (1‐3) beta‐D‐glucan content and (1‐3) beta‐D‐glucan synthase activity. The cwg2+ gene was cloned by the rescue of the cwg2‐1 mutant phenotype using an S. pombe genomic library and subsequently verified by integration of the appropriate insert into the S. pombe genome. Determination of the nucleotide sequence of this gene revealed a putative open reading frame of 1065 bp encoding a polypeptide of 355 amino acids with a calculated M(r) of 40,019. The cwg2+ DNA hybridizes to a main transcript, the 5′ end of which maps to a position 469 bp upstream of the predicted start of translation. The sequence between the transcription and the translation start sites is unusually long and has several short open reading frames which suggest a translational control of the gene expression. Comparative analysis of the predicted amino acid sequence shows that it possesses significant similarity to three Saccharomyces cerevisiae proteins, encoded by the DPR1/RAM1, CDC43/CAL1 and ORF2/BET2 genes respectively, which are beta subunits of different prenyltransferases. When grown at 37 degrees C, cwg2‐1 mutant extracts were specifically deficient in geranylgeranyltransferase type I activity, as measured in vitro. Multiple copies of the CDC43 gene can partially suppress the growth and (1‐3) beta‐D‐glucan synthase defect of the cwg2‐1 mutant at the restrictive temperature. In a similar manner, the cwg2+ gene can partially suppress the cdc43‐2 growth defect. These results indicate that cwg2+ is the structural gene for the beta subunit of geranylgeranyltransferase type I in S. pombe and that this enzyme is required for (1‐3) beta‐D‐glucan synthase activity. The functional homology of Cwg2 with Cdc43, which has been implicated in the control of cell polarity, suggests a link between two morphogenetic events such as establishment of cell polarity and cell wall biosynthesis.

Bacteroides fragilis is an important opportunistic pathogen of humans and is resistant to many drugs commonly used to treat anaerobic infections, including P-lactams. A strain set comprised of B. fragilis isolates producing either low or high levels of the endogenous cephalosporinase activity, CepA, has been described previously (M. B. Rogers, A. C. Parker, and C. J. Smith, Antimicrob. Agents Chemother. 37:2391-2400.Clones containing cepA genes from each of seven representative strains were isolated, and the DNA sequences were determined. Nucleotide sequence comparisons revealed that there were few differences between the cepA coding sequences of the low-and high-activity strains. The cepA coding sequences were cloned into an expression vector, pFD340, and analyzed in a B.fragilis 638 cepA mutant. The results of j-lactamase assays and ampicillin MICs showed that there was no significant difference in the enzymatic activity of structural genes from the high-or low-activity strains. Comparison of sequences upstream of the cepA coding region revealed that 50 bp prior to the translation start codon, the sequence for high-activity strains change dramatically. This region of the high-activity strains shared extensive homology with IS21, suggesting that an insertion was responsible for the increased expression of cepA in these isolates. Northern (RNA) blot analysis of total RNA by using cepA-specific DNA probes supported the idea that differential cepA expression in low-and high-activity strains was controlled at the level of transcription. However, the insertion did not alter the cepA transcription start site, which occurred 27 bp upstream of the ATG translation start codon in both expression classes. Possible mechanisms of cepA activation are discussed.The anaerobe Bacteroides fragilis contains an endogenous, chromosomally encoded P-lactamase which preferentially hydrolyzes cephalosporins and is responsible for the intrinsic resistance to most penicillins and cephalosporins (6, 15). These organisms are generally susceptible to some of the newer ,B-lactams such as cephamycins (cefoxitin) and carbapenems (imipenem), although newly acquired 3-lactamases capable of degrading these antibiotics have been described (18,21,38).The indigenous 3-lactamase is present in between 90 and 99% of B. fragilis strains and at the biochemical level, this P-lactamase has been shown to be species specific (8,16). Recently, the gene for this enzyme, cepA, was cloned and the nucleotide sequence was determined (27). Southern hybridization analyses with a cepA probe showed that there was homology only with other B. fragilis strains, and construction of a cepA mutant provided evidence that this gene did in fact encode for the endogenous ,-lactamase. Comparison of the predicted CepA amino acid sequence with other 3-lactamase sequences indicated that it was not in the Ambler molecular class C like the chromosomal ,-lactamases of most other gram-negative bacteria, but rather CepA belonged to the class A 3-lactamases. The CepA enzyme together with...

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