2,820 research outputs found

    Mode mixing in asymmetric double trench photonic crystal waveguides

    Full text link
    e investigate both experimentally and theoretically the waveguiding properties of a novel double trench waveguide where a conventional single-mode strip waveguide is embedded in a two dimensional photonic crystal (PhC) slab formed in silicon on insulator (SOI) wafers. We demonstrate that the bandwidth for relatively low-loss (50dB/cm) waveguiding is significantly expanded to 250nm covering almost all the photonic band gap owing to nearly linear dispersion of the TE-like waveguiding mode. The flat transmission spectrum however is interrupted by numerous narrow stop bands. We found that these stop bands can be attributed to anti-crossing between TE-like (positive parity) and TM-like (negative parity) modes. This effect is a direct result of the strong asymmetry of the waveguides that have an upper cladding of air and lower cladding of oxide. To our knowledge this is the first demonstration of the effects of cladding asymmetry on the transmission characteristics of the PhC slab waveguides.Comment: 7 pages, 6 figure

    Did You Not Understand The Question Or Not? An Investigation Of Negatively Worded Questions In Survey Research

    Get PDF
    This study compared participant responses to negatively versus positively worded questionnaire statements.  The literature suggested that one could expect the wording of questionnaire items (i.e., negatively worded vs. positively worded) to influence participant responses to those scale items.  The study consisted of one control group and two experimental groups.   The Fashion Consciousness scale (Wilkes 1992;  Lumpkin and Darden 1982), a uni-dimensional, all-positive seven-item instrument was adapted for use in the study.  Three hypotheses regarding the factor structure and internal reliability of the scale were empirically investigated.  Results showed statistically significant differences in the psychometrics of the scale when negative or double negative wording was added to scale items.  Managerial implications are discussed

    Intracellular nitrate of marine diatoms as a driver of anaerobic nitrogen cycling in sinking aggregates

    Get PDF
    Diatom-bacteria aggregates are key for the vertical transport of organic carbon in the ocean. Sinking aggregates also represent pelagic microniches with intensified microbial activity, oxygen depletion in the center, and anaerobic nitrogen cycling. Since some of the aggregate-forming diatom species store nitrate intracellularly, we explored the fate of intracellular nitrate and its availability for microbial metabolism within anoxic diatom-bacteria aggregates. The ubiquitous nitrate-storing diatom Skeletonema marinoi was studied as both axenic cultures and laboratory-produced diatom-bacteria aggregates. Stable 15N isotope incubations under dark and anoxic conditions revealed that axenic S. marinoi is able to reduce intracellular nitrate to ammonium that is immediately excreted by the cells. When exposed to a light:dark cycle and oxic conditions, S. marinoi stored nitrate intracellularly in concentrations > 60 mmol L-1 both as free-living cells and associated to aggregates. Intracellular nitrate concentrations exceeded extracellular concentrations by three orders of magnitude. Intracellular nitrate was used up within 2-3 days after shifting diatom-bacteria aggregates to dark and anoxic conditions. Thirty-one percent of the diatom-derived nitrate was converted to nitrogen gas, indicating that a substantial fraction of the intracellular nitrate pool of S. marinoi becomes available to the aggregate-associated bacterial community. Only 5% of the intracellular nitrate was reduced to ammonium, while 59% was recovered as nitrite. Hence, aggregate-associated diatoms accumulate nitrate from the surrounding water and sustain complex nitrogen transformations, including loss of fixed nitrogen, in anoxic, pelagic microniches. Additionally, it may be expected that intracellular nitrate not converted before the aggregates have settled onto the seafloor could fuel benthic nitrogen transformations

    The other side of surveillance: Monitoring, application, and integration of tuberculosis data to guide and evaluate programme activities in South Africa

    Get PDF
    Background. The importance of using surveillance data to monitor and evaluate programme activities has been emphasised in international policies for tuberculosis (TB) control.Objectives. A survey was conducted to assess the use of TB surveillance data to monitor and guide TB programme activities in South Africa (SA).Methods. As part of an evaluation of the SA national TB surveillance system, semi-structured interviews were conducted among TB staff at health facilities and offices in three provinces. At each site, all persons involved with TB care, management and surveillance were invited to participate.Results. At least one person (range 1 - 4) was interviewed at 47/54 health facilities (87.0%), 11/13 subdistrict and district TB offices (84.6%), 2/3 provincial TB offices (66.7%), and at the national level (1/1, 100.0%). Of 119 TB staff, 64.7% recognised the purpose of TB surveillance as guiding programme planning, implementation and evaluation. However, only 16.0% reported using data to measure disease burden, 8.4% to monitor trends, and 9.2% to inform resource allocation. The majority reported using TB management tools provided by the national programme, but 44.5% also described using additional tools. Personnel mentioned the need for dedicated surveillance staff, training on recording and reporting, improved computer access, and methods to apply information from surveillance data to the programme.Conclusions. The majority of TB staff understood the purpose of surveillance but did not routinely use data to guide programme planning, implementation and evaluation. Training and supporting TB staff to utilise surveillance data will help improve the TB surveillance system
    corecore