Properties of diode lasers with intensity noise control

The effect of the reduction of intensity noise by electronic feedback on the frequency stability of a GaAlAs laser is investigated. Only a small increase (approximately 30%) in stability was observed because the intensity and frequency noise were found to be not completely correlated. The technique described can also be used to estimate the coherence function gamma2 between the various noise properties of the laser's emission without using a correlator.     

H.F. ionospheric radar ground-scatter map showing land-sea boundaries by a spectral-separation technique

Ionospherically propagated h.f. radio waves that have been backscattered from the sea can often be distinguished from those backscattered from land because of their different Doppler spectra. This characteristic has been exploited to generate an ionospheric radar map of the south-east United States from Boulder, Colo., by gating out the sea-scatter Doppler components. The agreement between the observed and actual land-sea boundaries is good.     

Which contacts of patients with meningococcal disease carry the pathogenic strain of Neisseria meningitidis? A population based study

OBJECTIVES: To determine the prevalence of the pathogenic strain of Neisseria meningitidis in contacts of patients with meningococcal disease, and to determine which contact groups are likely to be carriers and warrant chemoprophylaxis. DESIGN: Population based study. SETTING: Norwegian county of Telemark. SUBJECTS: 1535 primary contacts of 48 patients with meningococcal disease, and 78 secondary contacts. INTERVENTIONS: Carriers of the pathogenic strain were treated with rifampicin. All household members and kissing contacts under 15 years of age were treated with oral penicillin. Contacts were taught to recognise the symptoms of meningococcal disease. RESULTS: In 27 of 48 cases investigated, contacts carrying the pathogenic strain of N meningitidis were found. A total of 42 such contacts were identified. Contacts were stratified into three classes according to the assumed closeness of contact with patients. In class 1 (household members and kissing contacts) the prevalence of the pathogenic strain was 12.4% (95% confidence interval 5.5% to 19.3%). In classes 2 and 3 the prevalence was 1.9% (0.9% to 3.4%) and 1.6% (0.14% to 3.1%). CONCLUSIONS: There is a high rate of carriage of the pathogenic strain of N meningitidis in patients' household members and kissing contacts, and this supports the practice of giving chemoprophylaxis to these contacts. The prevalence of carriage among other contacts is 2-3 times that found in the general population (0.7%); the benefits of chemoprophylaxis to these contacts may be marginal.     

Multiplexing of interferometric sensors using phase carrier techniques

This paper demonstrates the multiplexing of fiber-optic interferometric sensors using a CW phase generated carrier technique. The technique employs modulated diode laser sources at different carrier frequencies, nearly balanced interferometers (∼4-cm path difference), and phase generated carrier demultiplexing demodulation. This approach leads to a simple all-passive sensor array which has intrinsically low crosstalk. The system is analyzed in terms of shot noise performance and crosstalk. An experimental all optical implementation of a four sensor array was demonstrated; both the single sensor and multisensor arrays were limited by the laser phase noise to a sensitivity ofsim 18 murad/sqrt{Hz}. Crosstalk between individual channels was better than -60 dB and crosstalk between three sensors and the test sensor was better than -55 dB. In the absence of laser phase noise the demodulator/demultiplexer demonstratedsim 2-murad performance with both single sensor and four element array operation.     

Thermal phase compensation in fiber-optic interferometers

A method to hold an interferometer in quadrature by thermal phase tracking is described. The phase tracker has an extremely large tracking range (>10^{4}rad) such that the interferometer may be locked to zero path-length difference. The advantages and operation of this scheme to fiber-optic interferometry are described.     

Self-Repairing Metal Oxides

The oxidation of Cu, Zr, and alloys forming chromia, alumina, and zirconia was studied in a closed reaction chamber in O₂ gas near 20 mbar. Information on the position of oxide growth has been gained from the ¹⁸O/SIMS technique. Rates of O₂ dissociation on metal oxides, Au, and Pt have been evaluated from measurements in labeled O₂. The experimental results indicate that hydrogen in the metal substrates induces increased metal-ion transport in internal oxide surfaces during oxidation, which leads to increased oxide growth at the oxide–gas interface. Experiments also show that oxides of rare-earth metals (REM) and Pt catalyze the dissociation of O₂. An increased rate of O₂ dissociation can lead to increased transport of oxygen ions in the oxides and increased oxide growth at the substrate–oxide interface. A balanced transport of metal and oxygen ions in metal oxides that leads to oxide growth at both the metal–oxide and at the oxide–gas interface is found to be favorable for the formation of protective oxides with good adherence to the metal substrate. Depending on the original proporation of metal–to–oxygen ion transport in the oxide, an addition of hydrogen will increase or decrease the oxidation kinetics. In analogy, an addition of REM will increase or decrease the oxidation kinetics, depending on the original proportion of metal-to-oxygen ion transport.     

Optimization and stabilization of visibility in interferometricfiber-optic sensors using input-polarization control

The effects of input polarization on the output fringe visibility of two-beam interferometric fiber-optic sensors are investigated, and an analysis which predicts the existence of input states of polarization of eigenmodes of the interferometer for which optimum output visibility is obtained is presented. Experimental results obtained using both a bulk-optic and a fiber Mach-Zehnder interferometer are reported that verify this analysis. Active feedback stabilization of the output fringe visibility of an interferometric sensor using automatic input-polarization control is demonstrated     

20-Hydroxyecdysone stimulates proliferation of glial cells in the developing brain of the moth Manduca sexta

The steroid hormone 20-hydroxyecdysone (20-HE) controls diverse aspects of neuronal differentiation during metamorphosis in the hawkmoth Manduca sexta. In the present study we have examined the effect of 20-HE on glial cells of the brain during the metamorphic period. The antennal (olfactory) lobe of Manduca provides an ideal system in which to study effects of hormones on glial cells, since three known classes of glial cells participate in its development, and at least one type is critically important for establishment of normal neuronal morphology. These glial cells, associated with the neuropil, form boundaries for developing olfactory glomeruli as a result of proliferation and migration. We determined whether glial cells proliferate in response to 20-HE by injecting a pulse of 20-HE into the hemolymph at different stages of development and monitoring proliferation of all three types of glial cells. Hormone injections at the beginning and end of metamorphic development, when hormone titers are normally low, did not stimulate proliferation of neuropil-associated glial cells. Injections during the period when hormone titers are normally rising produced significant increases in their proliferation. Injections when hormone titers are normally high were ineffective at enhancing their proliferation. One other class of glial cells, the perineurial cells, also proliferate in response to 20-HE. Thus, glial proliferation in the brain is under the control of steroid hormones during metamorphic development.     

Chemical characterization and mutagenicity testing of chlorinated trihydroxybenzenes identified in spent bleach liquors from a sulphite plant

The spent bleach liquors from a sulphite plant have been investigated for their content of phenols. Seventeen phenols were identified by gas chromatography—mass spectrometry analysis and chlorinated trihydroxybenzenes were found to be the main components.The effluent showed mutagenic activity in the Ames' Salmonella test and some of the identified phenols were synthesized to investigate if these compounds could be responsible for the observed effect.