Autocorrelation of the polarization-dependent loss in fiber routes.

We study the spectral properties of polarization-dependent loss (PDL) in fiber routes with multiple spans and amplifiers. In these systems, PDL stems from a small number of lumped WDM components interconnected by PDL-free fibers, a configuration that is poorly described by the popular model of distributed PDL. We derive transparent and practical analytical expressions for the autocorrelation functions of the PDL vector and of the square PDL magnitude and show that they are strongly affected by the order of the individual PDL elements.

Experimental comparison of coherent polarization-switched QPSK to polarization-multiplexed QPSK for 10 × 100 km WDM transmission.

Polarization-switched quadrature phase-shift keying has been demonstrated experimentally at 40.5 Gb/s with a coherent receiver and digital signal processing. Compared to polarization-multiplexed QPSK at the same bit rate, its back-to-back sensitivity at 10(-3) bit-error-ratio shows 0.9dB improvement, and it tolerates about 1.6 dB higher launch power for 10 × 100 km, 50 GHz-spaced WDM transmission allowing 1 dB penalty in required optical-signal-to-noise ratio relative to back-to-back.

Interferometric optical signal-to-noise ratio measurements of telecom signals with degraded extinction ratio.

We measure full interferograms of telecom signals impaired by noise and investigate their applicability to in-band optical signal-to-noise ratio (OSNR) monitoring in practical systems. We experimentally establish that the dependence of overall shape of the interferogram on a signal's extinction ratio (ER) is strong but not unique. As the ER is being degraded the interferogram evolves in two distinct ways depending on the modulation conditions. The resulting ambiguity in the interferogram shape prevents OSNR measurements on completely unknown signals and necessitates a calibration for each modulator condition. With appropriate calibration, we experimentally demonstrate reliable OSNR measurements in the 5 to 25 dB range for 42.8 Gb/s nonreturn-to-zero, return-to-zero, and carrier-suppressed return-to-zero on-off-keyed signals.

The sedative component of anesthesia is mediated by GABA(A) receptors in an endogenous sleep pathway.

We investigated the role of regionally discrete GABA (gamma-aminobutyric acid) receptors in the sedative response to pharmacological agents that act on GABA(A) receptors (muscimol, propofol and pentobarbital; 'GABAergic agents') and to ketamine, a general anesthetic that does not affect GABA(A) receptors. Behavioral studies in rats showed that the sedative response to centrally administered GABAergic agents was attenuated by the GABA(A) receptor antagonist gabazine (systemically administered). The sedative response to ketamine, by contrast, was unaffected by gabazine. Using c-Fos as a marker of neuronal activation, we identified a possible role for the tuberomammillary nucleus (TMN): when gabazine was microinjected directly into the TMN, it attenuated the sedative response to GABAergic agents. Furthermore, the GABA(A) receptor agonist muscimol produced a dose-dependent sedation when it was administered into the TMN. We conclude that the TMN is a discrete neural locus that has a key role in the sedative response to GABAergic anesthetics.

Shared kangaroo care for triplets.

The mother in this case study already had four children at home and was afraid she would be unable to bond to three additional babies. This article describes her experiences with shared kangaroo care (holding all three infants at once), how these experiences relieved her fears, and how kangaroo care was extended by co-bedding the triplets in a single pediatric crib. Clinical nurse specialists and advanced nurse practitioners can use the successful outcome reported here to promote kangaroo care for families with naturally occurring triplets as well as those families whose triplets result from treatment for infertility.

Aminoglycoside-resistance mechanisms for cystic fibrosis Pseudomonas aeruginosa isolates are unchanged by long-term, intermittent, inhaled tobramycin treatment.

Aminoglycoside-resistance mechanisms were characterized in Pseudomonas aeruginosa isolates from cystic fibrosis (CF) patients during a recent clinical trial of inhaled tobramycin. Impermeability, in which bacteria have reduced susceptibility to all aminoglycosides, was the predominant mode of resistance in isolates obtained both before and after 6 months of cyclic treatment with tobramycin or placebo administered by aerosol. Enzymatic resistance mechanisms were found in fewer than 10% of resistant isolates. P. aeruginosa from individual patients could be grouped on the basis of genetic relatedness. When enzymatic resistance was involved, all isolates in a group had elevated tobramycin MICs. When impermeability occurred, MICs of a genotypic group varied from susceptible to resistant. These findings suggest that impermeability resistance occurs in only a fraction of the P. aeruginosa population in lungs of persons with CF and that this form of resistance arises by a process involving multiple small changes in MIC.

Jones matrix for second-order polarization mode dispersion.

A Jones matrix is constructed for a fiber that exhibits first- and second-order polarization mode dispersion (PMD). It permits the modeling of pulse transmission for fibers whose PMD vectors have been measured or whose statistics have been determined by established PMD theory. The central portion of our model is a correction to the Bruyère model.

Optical Coherence Tomographic Imaging of Human Tissue at 1.55 µm and 1.81 µm Using Er- and Tm-Doped Fiber Sources.

We demonstrate two short-coherence-length, rare-earth-doped fiber optical sources for performing optical coherence tomography (OCT) in human tissue. The first source is a stretched-pulse, mode-locked Er-doped fiber laser with a center wavelength of 1.55 µm, a power of 100 mW, and a bandwidth of 80 nm. The second is a Tm-doped silica fiber fluorescent source emitting up to 7 mW of power at 1.81 µm with a bandwidth of 80 nm. The OCT imaging depth of penetration in in vitro human aorta is compared using these sources and conventional 1.3-µm sources. © 1998 Society of Photo-Optical Instrumentation Engineers.

Onlay patch repair of tracheobronchial rupture.

Two cases are reported of tracheobronchial repair in which a posteriorly based intercostal muscle flap was incorporated into the membranous portion of the airway to increase the diameter of the reconstruction or to relieve tension in the suture lines. This technique permits repair of a small left main bronchus without compromise to the lumen and tension-free repair of the membranous trachea.

Efficient frequency doubling of a femtosecond fiber laser.

We report optimization of a stretched-pulse erbium-doped fiber laser for second-harmonic generation and the evaluation of several nonlinear crystals for this application. With compressed fundamental pulse energies of 2.7 nJ at 31.8 MHz, we achieved 10% conversion efficiency and 86-fs, 771-nm pulses with energies of 270 pJ. Frequency-resolved optical gating was used to analyze both the fundamental and the frequencydoubled pulses.

Technique for obtaining high-energy ultrashort pulses from an additive-pulse mode-locked erbium-doped fiber ring laser.

We report a self-starting stretched-pulse polarization additive-pulse mode-locked erbium-doped fiber ring laser with high output power. By using the light normally absorbed by the intracavity polarizer as the output, we obtained pulses with energies greater than 0.5 nJ at a repetition rate of 48 MHz. External chirp compensation was used to shorten the highly chirped output pulses to durations of less than 100 fs. The power levels suggest that erbium-doped fiber lasers may replace bulk solid-state lasers, such as the color-center laser, for some applications.

Effect of third-order dispersion on passive mode locking.

The effect of third-order dispersion on the width of mode-locked pulses is investigated analytically and numerically. The pulse width increases monotonically with increasing third-order dispersion as a consequence of the symmetric chirp introduced by it. The chirp broadens the bandwidth and lowers the gain. Computer simulations show the appearance of a resonant sideband that also taxes the gain. Reducing the filter bandwidth partially suppresses the sideband and narrows the pulse.

The association of congenital ptosis and congenital heart disease.

Congenital ptosis and congenital heart disease are known to occur simultaneously in the presence of several well-recognized clinical syndromes. We report seven cases of documented, structural congenital heart defects found among 156 consecutive congenital ptosis patients operated at the Wills Eye Hospital. The possibility that the concurrence found in the patients was a manifestation of a dysmorphic syndrome was carefully excluded by observers skilled in the recognition of such anomalies. The observed rate of congenital heart disease, in otherwise normal congenital ptosis patients, was five times the expected rate in the pediatric population at large. This should alert ophthalmologists examining pediatric ptosis patients to the possibility of a coexisting structural heart defect.

Adenocarcinoma in the columnar-lined (Barrett) esophagus. Case report and review of the literature.

As of 1975, forty-nine cases of adenocarcinoma arising in the columnar-lined lower esophagus (CLLE) were reported in the literature. We add three more cases, including the youngest male to our knowledge. All survived esophagogastrectomy and radiotherapy, but each had metastatic disease and a guarded prognosis. Review of the literature revealed a male/female ratio of 3:1 for this disorder with a mean age for men of 53 years, less than that for women, (61 women). Columnar-lined lower esophagus is seen in up to 11% of patients with reflux esophagitis and probably does not regress, once present. Adenocarcinoma later develops in 2.4% to 8.5%. The CLLE is not rare and should be followed up as carefully as any other premalignant lesion.