Nitrite Accumulation by denitrifiers isolated from fluidized Bed Reactors operated in an Aquaculture Unit

In fluidized bed rnactors, applled for nitrate removal in an aquaculture unit, denitrificatlon of nitrate was found to result in an accumulation of nitrite. Isolation of denltrifylng bacteria from these reactors revealed that most of these isolates produced nitrite from nitrate under controlled laboratory. conditions. Two of the isolates, one with accumulated nitrite while respiring on nitrate, and the other not, were subject to further studies. It was found that nitrite accumulation in one of these isolates could be adequately explained by differences in the relative rates of nitrate and nitrite reduction. Inhibiting concentrations of nitrite were lower for the isolate which did not accumulate nitrite. Incubation of the nitrite-accumulating isolate with different carbon sources resulted ln differences in the relative nitrite accumulation (as compared with the runount of nitrate reduced

Polarization bistability and resultant spin rings in semiconductor microcavities

The transmission of a pump laser resonant with the lower polariton branch of a semiconductor microcavity is shown to be highly dependent on the degree of circular polarization of the pump. Spin dependent anisotropy of polariton-polariton interactions allows the internal polarization to be controlled by varying the pump power. The formation of spatial patterns, spin rings with high degree of circular polarization, arising as a result of polarization bistability, is observed. A phenomenological model based on spin dependent Gross-Pitaevskii equations provides a good description of the experimental results. Inclusion of interactions with the incoherent exciton reservoir, which provides spin-independent blueshifts of the polariton modes, is found to be essential.Comment: 5 pages, 3 figure

Effect of the GaAsP shell on optical properties of self-catalyzed GaAs nanowires grown on silicon

We realize growth of self-catalyzed core-shell GaAs/GaAsP nanowires (NWs) on Si substrates using molecular-beam epitaxy. Transmission electron microscopy (TEM) of single GaAs/GaAsP NWs confirms their high crystal quality and shows domination of the zinc-blende phase. This is further confirmed in optics of single NWs, studied using cw and time-resolved photoluminescence (PL). A detailed comparison with uncapped GaAs NWs emphasizes the effect of the GaAsP capping in suppressing the non-radiative surface states: significant PL enhancement in the core-shell structures exceeding 2000 times at 10K is observed; in uncapped NWs PL is quenched at 60K whereas single core-shell GaAs/GaAsP NWs exhibit bright emission even at room temperature. From analysis of the PL temperature dependence in both types of NW we are able to determine the main carrier escape mechanisms leading to the PL quench

Symmetry-breaking Effects for Polariton Condensates in Double-Well Potentials

We study the existence, stability, and dynamics of symmetric and anti-symmetric states of quasi-one-dimensional polariton condensates in double-well potentials, in the presence of nonresonant pumping and nonlinear damping. Some prototypical features of the system, such as the bifurcation of asymmetric solutions, are similar to the Hamiltonian analog of the double-well system considered in the realm of atomic condensates. Nevertheless, there are also some nontrivial differences including, e.g., the unstable nature of both the parent and the daughter branch emerging in the relevant pitchfork bifurcation for slightly larger values of atom numbers. Another interesting feature that does not appear in the atomic condensate case is that the bifurcation for attractive interactions is slightly sub-critical instead of supercritical. These conclusions of the bifurcation analysis are corroborated by direct numerical simulations examining the dynamics of the system in the unstable regime.MICINN (Spain) project FIS2008- 0484

Spin domains in one-dimensional conservative polariton solitons

We report stable orthogonally polarized domains in high-density polariton solitons propagating in a semiconductor microcavity wire. This effect arises from spin-dependent polariton–polariton interactions and pump-induced imbalance of polariton spin populations. The interactions result in an effective magnetic field acting on polariton spin across the soliton profile, leading to the formation of polarization domains. Our experimental findings are in excellent agreement with theoretical modeling taking into account these effects

Ultra-low-power hybrid light-matter solitons.

New functionalities in nonlinear optics will require systems with giant optical nonlinearity as well as compatibility with photonic circuit fabrication techniques. Here we introduce a platform based on strong light-matter coupling between waveguide photons and quantum-well excitons. On a sub-millimetre length scale we generate picosecond bright temporal solitons at a pulse energy of only 0.5 pJ. From this we deduce a nonlinear refractive index three orders of magnitude larger than in any other ultrafast system. We study both temporal and spatio-temporal nonlinear effects and observe dark-bright spatio-temporal polariton solitons. Theoretical modelling of soliton formation in the strongly coupled system confirms the experimental observations. These results show the promise of our system as a high speed, low power, integrated platform for physics and devices based on strong interactions between photons

Ultrafast-nonlinear ultraviolet pulse modulation in an AlInGaN polariton waveguide operating up to room temperature

Ultrafast nonlinear photonics enables a host of applications in advanced on-chip spectroscopy and information processing. These rely on a strong intensity dependent (nonlinear) refractive index capable of modulating optical pulses on sub-picosecond timescales and on length scales suitable for integrated photonics. Currently there is no platform that can provide this for the UV spectral range where broadband spectra generated by nonlinear modulation can pave the way to new on-chip ultrafast (bio-) chemical spectroscopy devices. We introduce an AlInGaN waveguide supporting highly nonlinear UV hybrid light-matter states (exciton-polaritons) up to room temperature. We experimentally demonstrate ultrafast nonlinear spectral broadening of UV pulses in a compact 100 micrometer long device and measure a nonlinearity 1000 times that in common UV nonlinear materials and comparable to non-UV polariton devices. Our demonstration, utilising the mature AlInGaN platform, promises to underpin a new generation of integrated UV nonlinear light sources for advanced spectroscopy and measurement

Die benthische Ciliatenfauna bei Gabelsflach (Kieler Bucht) und deren Beeinflussung durch Bakterien Eine Studie ueber Menge, Biomasse, Produktion, Bakterieningestion und Ultrastruktur von Mikroorganismen

TIB Hannover: RN 3292(191) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Sediment bacteria attached to sand grains - indications to a protection from feeding by ciliates

Microbiological investigations of a marine, brackish sandy sediment area in a water depth of 10 to 12 m showed relatively high numbers of bacteria (4 x 108 - 2,4 x 109 bacteria g-1 dry weight of sediment). Benthic ciliates were estimated too. Their numbers varied between 1 and 87, with a mean of 21 individuals per gram dry weight of sediment. In general, the overwhelming part (80%), were small forms of about 30 µm length. 54% of the ciliates were predominantly bacterivorous. In feeding experiments using a fluorescent dye (DT AF), stained bacteria could be seen directly within the food vacuoles of the small ciliates, but this was the case only when free suspended bacteria were present. No uptake was visible if sand grains were added, which were colonized with stained bacteria. From these results, indications can be seen that small benthic ciliates cannot remove attached sediment bacteria. Taking into account that ciliates choose distinct size classes and certain strains of bacteria, less than a fraction of the total mass of bacteria is probably available as a potential food. This fact, together with a permanent reduction of ciliates by metazoa, ciliates themselves and hydrodynamic perturbations can explain the relatively low, but more or less constant number of the ciliate fauna at such locations