Tilted superstructure fiber grating used as a Fourier-transform spectrometer.

We propose and demonstrate a new method for fabricating a compact all-fiber spectrometer by using a tilted superstructure fiber grating to couple light out of a fiber core and produce an interference pattern in the near field. The Fourier transform of the interference pattern serves as a direct measurement of the optical input spectrum, and the superstructure grating design offers several degrees of freedom that permit control over the resolution and bandwidth of the spectrometer. For single-wavelength operation, the proposed scheme offers the possibility of making wavelength measurements with picometer-level precision over a broad 80-nm wavelength range while simultaneously providing coarser precision over a 160-nm range.

Normally incident resonant grating reflection filters for efficient narrow-band spectral filtering of finite beams.

Resonant grating reflection filters operating at normal incidence are investigated. At normal incidence these structures are shown to have characteristics different from those of structures operated at oblique incidence. We show how higher-order diffraction within the structure laterally confines the incident energy about the point of incidence and results in a broadened angular selectivity. Multimode structures are shown to exhibit broader angular selectivities and narrower spectral linewidths than those of single-mode structures, achieving angular selectivities hundreds of times broader than what could be obtained at oblique incidence. When compared with that for oblique incidence, the increase in angular selectivity is shown to greatly improve the performance of these filters for spectrally filtering finite incident beams.

Interference approach applied to dual-grating dielectric resonant grating reflection filters.

The resonant mechanisms associated with dual-grating dielectric resonant grating reflection filters are described by use of an interference approach. These structures consist of two modulated regions of equal period separated by a higher-index film region. We show that the spectral linewidth is dependent on the separation between the modulated regions and can range from theoretically zero to approximately four times what would be obtained by use of a single-grating geometry.

Idiopathic spinal cord herniation: case report and review of the literature.

OBJECTIVE AND IMPORTANCE: Idiopathic spinal cord herniation (ISCH) is a rare condition, reported in only 25 patients thus far, in which the thoracic cord is prolapsed through an anterior dural defect. It typically presents in middle age as either Brown-Sequard syndrome or spastic paraparesis. CLINICAL PRESENTATION: A 55-year-old woman initially presented at the age of 41 years with Brown-Sequard syndrome at the T8 disc space level on the left side. Investigations, including primitive magnetic resonance imaging, were deemed negative at that time. After a stepwise deterioration over 14 years, she presented again with spastic paraparesis and double incontinence, in addition to her previous spinothalamic dysfunction. Magnetic resonance imaging at this stage suggested either ISCH or a dorsal arachnoid cyst. INTERVENTION: Through a T7-T8 laminectomy, a left-of-midline ISCH was identified and easily reduced by gentle cord traction. No dorsal arachnoid cyst was identified. The anterior dural defect was repaired with a XenoDerm patch (LifeCell Corp., Woodlands, TX). After surgery, there was improved motor and sphincter function. However, there was continued sensory disturbance. CONCLUSION: ISCH is rare cause of thoracic cord dysfunction. Despite prolonged diagnostic delay, significant clinical improvement may be obtained with ISCH reduction and anterior dural repair.

Production and reversibility of right ventricular hypertrophy and right heart failure in dogs.

Combined heart-lung transplantation has been used for end-stage primary pulmonary hypertension. Experience with single-lung transplantation for other conditions suggested that associated severe right ventricular dysfunction resulting from increased afterload would recover after placement of a satisfactory lung allograft. Early experience with the application of single-lung transplantation for pulmonary hypertension supports this contention. We devised a reversible canine model of chronic progressive pressure-overloaded right heart failure by pulmonary artery banding to study the echocardiographic, hemodynamic, and pathological reversibility of the failing right heart. Clinical right heart failure was defined as the development of ascites and pleural effusions. Right heart failure developed in 23 dogs 67 to 348 days after banding, and they were divided into two groups to determine its early and long-term effects. Group 1 dogs (n = 11) were either sacrificed immediately after the onset of right heart failure (n = 5) or unbanded (n = 6); group 2 dogs (n = 12) were maintained in right heart failure for 3 months and then either sacrificed (n = 6) or unbanded. Unbanded dogs in both groups were observed for 4 additional months before sacrifice. A control group of 6 normal dogs was sacrificed for pathological comparisons. After unbanding, the right ventricular systolic pressure fell from 97 +/- 17 mm Hg (group 1) and 88 +/- 31 mm Hg (group 2) to 44 +/- 11 mm Hg and 47 +/- 13 mm Hg, respectively. Despite this persistent gradient across the pulmonary artery, echocardiographic and hemodynamic measures of right ventricular function returned to normal, albeit more slowly in the group 2 dogs.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of interactive video on cognitive achievement and attitude toward learning.

The purpose of this experimentally designed study was to determine the effects of an interactive videodisc program, entitled "Diabetic Health Assessment," versus traditional lecture on cognitive learning and affective behaviors of baccalaureate nursing students. It was hypothesized that: 1) there would be no significant difference in the cognitive achievement scores between those students taught by an interactive videodisc program (experimental group) compared to those students taught by a traditional lecture method (control group), and 2) there would be a statistically significant difference in student attitude toward learning between those students taught by an interactive videodisc program compared to students taught by a traditional lecture method. Eighty-three third-year baccalaureate nursing students at a major urban university served as subjects and were randomly assigned to either a control (n = 41) or an experimental group (n = 42). The multivariate analysis of covariance with two criteria and the pretest as the covariate was significant (p = .000, df = 4, 140) indicating that the adjusted posttest scores on the two measures were significantly different for the experimental group compared to the control group. The univariate F for the cognitive measure was nonsignificant (p = .283, df = 2, 72) indicating that students' achievement under interactive video is not significantly different than under traditional lecture. The univariate F for the affective measure was significant (p = .000, df = 2, 72) indicating that the students learning by interactive video possessed a more positive attitude toward learning than those learning by traditional lecture method of instruction.

Measurement of activity of urea resistant neutrophil alkaline phosphatase as an antenatal screening test for Down's syndrome.

OBJECTIVE: To investigate the value of measuring maternal urea resistant neutrophil alkaline phosphatase activity as an antenatal screening test for Down's syndrome. DESIGN: Case-control study of blood samples collected at nine to 27 weeks of pregnancy. SETTING: Antenatal clinics in London and Oxford. PATIENTS: 72 Women whose fetuses had been diagnosed by amniocentesis or chorionic villus sampling as having Down's syndrome and 156 women whose fetuses did not have the syndrome. Only singleton pregnancies were studied. MAIN OUTCOME MEASURE: Activity of urea resistant neutrophil alkaline phosphatase measured cytochemically. RESULTS: The median enzyme activity in the index patients was 1.65 times the expected median for the controls at the same duration of pregnancy (p less than 0.0001; 95% confidence interval 1.56 to 1.74). A cut off value that identified the 5% of control patients with the highest activities yielded a rate of detection of Down's syndrome of 79% (95% confidence interval 70 to 89%). CONCLUSION: Activity of urea resistant neutrophil alkaline phosphatase is an effective maternal blood marker for Down's syndrome. Its use in antenatal screening could lead to a substantial improvement in the detection of this disorder. Before introducing the test into routine medical practice it will have to be automated so that it can be used on a large scale and is less subjective.