A current disruption mechanism in the neutral sheet for triggering substorm expansions

Two main areas were addressed in support of an effort to understand mechanism responsible for the broadband electrostatic noise (BEN) observed in the magnetotail. The first area concerns the generation of BEN in the boundary layer region of the magnetotail whereas the second area concerns the occassional presence of BEN in the neutral sheet region. For the generation of BEN in the boundary layer region, a hybrid simulation code was developed to perform reliable longtime, quiet, highly resolved simulations of field aligned electron and ion beam flow. The result of the simulation shows that broadband emissions cannot be generated by beam-plasma instability if realistic values of the ion beam parameters are used. The waves generated from beam-plasma instability are highly discrete and are of high frequencies. For the plasma sheet boundary layer condition, the wave frequencies are in the kHz range, which is incompatible with the observation that the peak power in BEN occur in the 10's of Hz range. It was found that the BEN characteristics are more consistent with lower hybrid drift instability. For the occasional presence of BEN in the neutral sheet region, a linear analysis of the kinetic cross-field streaming instability appropriate to the neutral sheet condition just prior to onset of substorm expansion was performed. By solving numerically the dispersion relation, it was found that the instability has a growth time comparable to the onset time scale of substorm onset. The excited waves have a mixed polarization in the lower hybrid frequency range. The imposed drift driving the instability corresponds to unmagnetized ions undergoing current sheet acceleration in the presence of a cross-tail electric field. The required electric field strength is in the 10 mV/m range which is well within the observed electric field values detected in the neutral sheet during substorms. This finding can potentially account for the disruption of cross-tail current and its diversion to the ionosphere to form the substorm current wedge. Furthermore, a number of features associated with substorm expansion onset can be understood based on this substorm onset scenario

Photon recycling in Fabry-Perot micro-cavities based on Si3_3N4_4 waveguides

We present a numerical analysis and preliminary experimental results on one-dimensional Fabry-Perot micro-cavities in Si$_3$N$_4$ waveguides. The Fabry-Perot micro-cavities are formed by two distributed Bragg reflectors separated by a straight portion of waveguide. The Bragg reflectors are composed by a few air slits produced within the Si$_3$N$_4$ waveguides. In order to increase the quality factor of the micro-cavities, we have minimized, with a multiparametric optimization tool, the insertion loss of the reflectors by varying the length of their first periods (those facing the cavity). To explain the simulation results the coupling of the fundamental waveguide mode with radiative modes in the Fabry-Perot micro-cavities is needed. This effect is described as a recycling of radiative modes in the waveguide. To support the modelling, preliminary experimental results of micro-cavities in Si$_3$N$_4$ waveguides realized with Focused Ion Beam technique are reported.Comment: 5 pages, 5 figure

Assessment of Radiometer Calibration With GPS Radio Occultation for the MiRaTA CubeSat Mission

The microwave radiometer technology acceleration (MiRaTA) is a 3U CubeSat mission sponsored by the NASA Earth Science Technology Office. The science payload on MiRaTA consists of a triband microwave radiometer and global positioning system (GPS) radio occultation (GPSRO) sensor. The microwave radiometer takes measurements of all-weather temperature (V-band, 50-57 GHz), water vapor (G-band, 175-191 GHz), and cloud ice (G-band, 205 GHz) to provide observations used to improve weather forecasting. The Aerospace Corporation's GPSRO experiment, called the compact total electron content and atmospheric GPS sensor (CTAGS), measures profiles of temperature and pressure in the upper troposphere/lower stratosphere (~20 km) and electron density in the ionosphere (over 100 km). The MiRaTA mission will validate new technologies in both passive microwave radiometry and GPSRO: 1) new ultracompact and low-power technology for multichannel and multiband passive microwave radiometers, 2) the application of a commercial off-the-shelf GPS receiver and custom patch antenna array technology to obtain neutral atmospheric GPSRO retrieval from a nanosatellite, and 3) a new approach to space-borne microwave radiometer calibration using adjacent GPSRO measurements. In this paper, we focus on objective 3, developing operational models to meet a mission goal of 100 concurrent radiometer and GPSRO measurements, and estimating the temperature measurement precision for the CTAGS instrument based on thermal noise Based on an analysis of thermal noise of the CTAGS instrument, the expected temperature retrieval precision is between 0.17 and 1.4 K, which supports the improvement of radiometric calibration to 0.25 K

The rhizoferrin biosynthetic gene in the fungal pathogen Rhizopus delemar is a novel member of the NIS gene family

This work was supported by the Natural Sciences and Engineering Research Council of Canada award to MM (grant number 611181). C. Carroll thanks Simon Fraser University for a travel and research award.Iron is essential for growth and in low iron environments such as serum many bacteria and fungi secrete ferric iron-chelating molecules called siderophores. All fungi produce hydroxamate siderophores with the exception of Mucorales fungi, which secrete rhizoferrin, a polycarboxylate siderophore. Here we investigated the biosynthesis of rhizoferrin by the opportunistic human pathogen, Rhizopus delemar. We searched the genome of R. delemar 99–880 for a homologue of the bacterial NRPS-independent siderophore (NIS) protein, SfnaD that is involved in biosynthesis of staphyloferrin A in Staphylococcus aureus. A protein was identified in R. delemar with 22% identity and 37% similarity with SfnaD, containing an N-terminal IucA/IucC family domain, and a C-terminal conserved ferric iron reductase FhuF-like transporter domain. Expression of the putative fungal rhizoferrin synthetase (rfs) gene was repressed by iron. The rfs gene was cloned and expressed in E.coli and siderophore biosynthesis from citrate and diaminobutane was confirmed using high resolution LC–MS. Substrate specificity was investigated showing that Rfs produced AMP when oxaloacetic acid, tricarballylic acid, ornithine, hydroxylamine, diaminopentane and diaminopropane were employed as substrates. Based on the production of AMP and the presence of a mono-substituted rhizoferrin, we suggest that Rfs is a member of the superfamily of adenylating enzymes. We used site-directed mutagenesis to mutate selected conserved residues predicted to be in the Rfs active site. These studies revealed that H484 is essential for Rfs activity and L544 may play a role in amine recognition by the enzyme. This study on Rfs is the first characterization of a fungal NIS enzyme. Future work will determine if rhizoferrin biosynthesis is required for virulence in Mucorales fungi.PostprintPeer reviewe

Uncovering functions of long-chain polyphosphate in higher eukaryotes: storage and synthesis of polyphosphate in matrix vesicles during mineralization

Poster: abstract no. 0052Conference Theme: The Extracellular Matrix NicheInorganic polyphosphate (polyP) is a fundamental molecule that occurs throughout life. PolyP has been found in mammalian tissues with particularly high levels of polyP in bone and cartilage, however its metabolism and functions remain poorly understood. Here, we initially demonstrate the highest concentrations of polyP yet observed in a higher eukaryote in matrix vesicles (MVs) secreted from mineralized osteoblasts. We also observed that MVs isolated from both osteoblasts and chondrocytes have a remarkable ability to synthesize very long-chain polyP under physiological condition. PolyP could be hydrolysed to Pi by one of the critical enzymes of mineralization, tissue non-specific alkaline phosphatase (TNAP). PolyP was consumed during mineralization induced by MVs. Extravesicular PolyP acted as an efficient inhibitor to suppress MV-induced HA formation. Biochemical properties of polyP synthesis were consistent with membrane-bound enzyme activity within the MV. Taken together, our work introduces a new fundamental macromolecule that could be a critical modulator of mineralization in the extracellular matrix.postprin