Model of light collimation by photonic crystal surface modes

We propose a quantitative model explaining the mechanism of light collimation by leaky surface modes that propagate on a corrugated surface around the output of a photonic crystal waveguide. The dispersion relation of these modes is determined for a number of surface terminations. Analytical results obtained on the basis of the model are compared to those of rigorous numerical simulations. Maximum collimation is shown to occur at frequency values corresponding to excitation of surface modes whose wave number retains a nonzero real part.Comment: 6 pages, 7 figures. Version 2: corrected sign of k_x' (sections 4-6, fig. 2), minor clarifications in section 2. Version 3: significant changes, including reformulation of the model using the theory of aperture antennas, as well as extended discussion of the accuracy of the mode

Tweefasenvoedering tijdens de dracht

Op het Praktijkcentrum Sterksel wordt onderzocht wat het effect is van tweefasenvoedering tijdens de dracht op reproductie, gezondheid en berekende mineralenuitscheiding van zeugen. Het onderzoek start met nuldeworps-zeugen die vervolgens vier worpen gevolgd worden

Bacterial Biofilms in Drinking Water Systems: Protecting Patient Health at the Alberta Children’s Hospital

When we hear of bacterial contaminated drinking water, we generally think of microscopic organisms swimming freely throughout the system. Although bacteria are found in this free living form, or planktonically, the majority of microorganisms in natural environments are in fact found growing on a surface. These surface adhered bacteria are called biofilms and can be found anywhere, ranging from implanted medical devices to drinking water pipes. Drinking water system operators use the multiple barrier approach to ensure the microbiological safety of the water. The approach includes primary treatment of the source water with chlorine or UV light; secondary chlorine treatment throughout distribution systems; and routine testing for indicator organisms, such as Escherichia coli. Thus, the presence of indicator organisms signifies that there has been a failure in the treatment process or a contamination in the water system. Regardless of chemical or irradiation treatment, normal flora biofilms continue to grow in these systems. It is theorized that these resident flora biofilms may incorporate and shield pathogenic organisms from chlorine disinfection. The Alberta Children’s Hospital (ACH) water system has a unique design, engineered to reduce bacterial contamination and biofilm growth. This project, done in collaboration with Alberta Health Services and the ACH, aims to evaluate bacterial survival after exposure to low levels of chlorine. It is hypothesized that the chlorine levels maintained in our water systems for secondary treatment may be insufficient to disinfect biofilm growth. Eight isolates were obtained directly from chlorinated water systems, including the ACH. These isolates were tested both planktonically and as biofilms, grown using the Calgary Biofilm Device, under a range of chlorine concentrations. Minimum inhibitory concentration (MIC) and minimum biofilm eradication concentration (MBEC) assays have shown that biofilms can be 2-20 times more resistant to chlorine disinfection when compared to their more vulnerable planktonic counterparts

Low-Mass Pre-Main Sequence Stars in the Large Magellanic Cloud - III: Accretion Rates from HST-WFPC2 Observations

We have measured the present accretion rate of roughly 800 low-mass (~1-1.4 Mo) pre-Main Sequence stars in the field of Supernova 1987A in the Large Magellanic Cloud (LMC, Z~0.3 Zo). It is the first time that this fundamental parameter for star formation is determined for low-mass stars outside our Galaxy. The Balmer continuum emission used to derive the accretion rate positively correlates with the Halpha excess. Both these phenomena are believed to originate from accretion from a circumstellar disk so that their simultaneous detection provides an important confirmation of the pre-Main Sequence nature of the Halpha and UV excess objects, which are likely to be the LMC equivalent of Galactic Classical TTauri stars. The stars with statistically significant excesses are measured to have accretion rates larger than 1.5x10^{-8}Mo/yr at an age of 12-16 Myrs. For comparison, the time scale for disk dissipation observed in the Galaxy is of the order of 6 Myrs. Moreover, the oldest Classical TTauri star known in the Milky Way (TW Hydrae, with 10 Myrs of age) has a measured accretion rate of only 5x10^{-10} Mo/yr, ie 30 times less than what we measure for stars at a comparable age in the LMC. Our findings indicate that metallicity plays a major role in regulating the formation of low-mass stars.Comment: Accepted for publication in the Astrophysical Journal (10 June 2004), 28 pages, 9 figures. Typo corrected in the abstract on 21 February 200

Verteerbaarheid en voederwaarde van eiwitrijke grondstoffen bij biologische biggen

Op Varkensproefbedrijf Raalte is onderzocht wat de nutriëntensamenstelling, verteerbaarheid en EW is van raapzaadeiwit concentraat, erwteneiwit concentraat, tarweglutenmeel en veldboneneiwitconcentraat bij biologisch gehouden gespeende biggen. De resultaten van het onderzoek zijn in dit rapport beschreven

A Reanalysis of theUltraviolet Extinction from Interstellar Dust in the Large Magellanic Cloud

We have reanalyzed the Large Magellanic Cloud's (LMC) ultraviolet (UV) extinction using data from the IUE final archive. Our new analysis takes advantage of the improved signal--to--noise of the IUE NEWSIPS reduction, the exclusion of stars with very low reddening, the careful selection of well matched comparison stars, and an analysis of the effects of Galactic foreground dust. Differences between the average extinction curves of the 30 Dor region and the rest of the LMC are reduced compared to previous studies. We find that there is a group of stars with very weak 2175 Ang. bumps that lie in or near the region occupied by the supergiant shell, LMC 2, on the southeast side of 30 Dor. The average extinction curves inside and outside LMC 2 show a very significant difference in 2175 Ang. bump strength, but their far--UV extinctions are similar. While it is unclear whether or not the extinction outside the LMC 2 region can be fit with the relation of Cardelli, Clayton and Mathis (CCM), sightlines near LMC 2 cannot be fit with CCM due to their weak 2175 Ang. bumps. While the extinction properties seen in the LMC lie within the range of properties seen in the Galaxy, the correlations of UV extinction properties with environment seen in the Galaxy do not appear to hold in the LMC.Comment: 29 pages, 10 figures, to be published in Ap

SILAGE IN DIETS FOR ORGANIC SOWS IN GESTATION

This study was conducted to determine whether the supply of grass silage or grass silage mixed with barley or CCM to organically raised gestating sows would allow a reduction of compound feed allowance without loss in animal performance. On average, sows fed grass silage or mixed silage were able to compensate for a pre-set reduction of 1 kg or 1.5 kg compound feed, respectively. However, the variation in silage intake between individual sows was large, with a number of mainly young sows consuming less silage than the required amount. Consequently, these sows showed a net back fat loss during the experimental period from d 7 of gestation to weaning. Our results indicate that more feeder space than 1 for 8 sows is required to allow adequate silage intake in group housed sows. From this study we cannot derive whether that would be also allow young sows to realise an adequate silage intake. In conclusion, it seems possible to replace 1 kg compound feed by free access to grass silage and 1.5 kg compound by mixed barley or CCM silage, provided that variation between sows is reduced and young sows would also be able to ingest an adequate amount of silage

The Distance of the First Overtone RR Lyrae Variables in the MACHO LMC Database: A New Method to Correct for the Effects of Crowding

Previous studies have indicated that many of the RR Lyrae variables in the LMC have properties similar to the ones in the Galactic globular cluster M3. Assuming that the M3 RR Lyrae variables follow the same relationships among period, temperature, amplitude and Fourier phase parameter phi31 as their LMC counterparts, we have used the M3 phi31-logP relation to identify the M3-like unevolved first overtone RR Lyrae variables in 16 fields near the LMC bar. The temperatures of these variables were calculated from the M3 logP-logTe relation so that the extinction could be derived for each star separately. Since blended stars have lower amplitudes for a given period, the period amplitude relation should be a useful tool for identifying which stars are affected by crowding. We find that the low amplitude stars are brighter. We remove them from the sample and derive an LMC distance modulus 18.49+/-0.11.Comment: 30 pages, 7 figures, accepted for publication in the Astronomical Journa

On the optical--infra-red continuum emission from equatorial discs of supergiant B[e] stars

Two models of the circumstellar disc around supergiant B[e] stars are discussed: an equatorial wind model produced by wind bi-stability, and a Keplerian viscous disc model. Both models are successful in providing a site for dust formation once they have cooled sufficiently. However, the optical--infra-red continuum is calculated and it is found that both models have significant trouble in accounting for observations. In particular the optical--near-IR emission is accounted for, but the dust emission is underestimated by at least an order of magnitude. Variations in the structure of the models (the temperature variation with radius, the density structure and the dust opacity) are investigated to assess how (in)appropriate the standard models are for supergiant B[e] star discs. Changing the temperature structure, and making simple dust opacity changes within the disc has little effect on the resultant continuum emission. By altering the density structure of the discs, the continuum may be accounted for by both models: the equatorial wind model requires a very flat density profile which is impossible to explain with any accelerating wind, and the viscous disc model's density structure is required to fall off less steeply with radius than would have been expected, although this may be explained from consideration of viscous processes in the disc. It is recognised that both theoretical interpretations have difficulties and unsolved problems.Comment: 9 pages, 6 figures, accepted by Astronomy and Astrophysic