Modal filtering for midinfrared nulling interferometry using single mode silver halide fibers.

We demonstrate the modal filtering properties of newly developed single mode silver halide fibers for use at midinfrared wavelengths, centered at 10.5 microm. The goal was to achieve a suppression of nonfundamental modes greater than a factor of 300 to enable the detection and characterization of Earthlike exoplanets with a space-based nulling interferometer. Fiber segments of 4.5 cm, 10.5 cm, 15 cm, and 20 cm lengths were tested. We find that the performance of the fiber was limited not by the modal filtering properties of the core but by the unsuppressed cladding modes present at the output of the fiber. In 10.5 cm and longer sections, this effect can be alleviated by properly aperturing the output. Exclusive of coupling losses, the fiber segments of 10.5-20 cm length can provide power suppression of undesirable components of the input field by a factor of 15,000 at least. The demonstrated performance thus far surpasses our requirements, such that even very short sections of fiber provide adequate modal filtering for exoplanet characterization.

A novel PCR-based technique using expressed sequence tags and gene homology for murine genetic mapping: localization of the complement genes.

The complement system is a cascade of serum proteins and receptors which forms a vital arm of innate immunity and enhances the adaptive immune response. This work establishes the chromosomal localization of four key genes of the murine complement system. Mapping was performed using a novel and rapid PCR restriction length polymorphism method which was developed to exploit the murine expressed sequence tag (EST) database. This technique circumvents the laborious cDNA or genomic cloning steps of other mapping methods by relying on EST data and the prediction of exon-intron boundaries. This method can be easily applied to the genes of other systems, ranging from the interests of the individual researcher to large-scale gene localization projects. Here the complement system, probably one of the most well-characterized areas of immunology, was used as a model system. It was shown that the C3a receptor C1r and C1s genes form an unexpected complement gene cluster towards the telomeric end of chromosome 6. The second mannose binding lectin-associated serine protease gene was mapped to the telomeric end of chromosome 4, which is distinct from other complement-activating serine proteases. These results provide new insights into the evolution of this group of proteins.

The roles of surfactant proteins A and D in innate immunity.

Research over the last decade on the surfactant proteins SP-A and SP-D suggests roles beyond surfactant lipid homeostasis, involving their participation in innate immune defence. SP-A and SP-D bind and agglutinate an impressive array of non-self structures, ranging from bacteria and fungi to allergens and environmental inorganic substrates. Complementing binding. SP-A and SP-D initiate and enhance immune cell ingestion and killing of targets. Recently, some exciting developments have extended and clarified their contributions to innate immunity. Knockout mice for SP-A and SP-D have been developed. The SP-A knockout confirms that SP-A plays a key role in defence against lung pathogens and reveals the underlying defense mechanisms that require SP-A. These surfactant proteins have also been shown to have important roles in modulating the immune response, instructing, yet quenching, the immune reactions in the lung. The crystal structure of SP-D plus functional studies with recombinantly altered forms of SP-A and SP-D has begun to characterise the structural motifs responsible for mediating their immune functions. Linkage and polymorphism analysis is explaining the role these genes may play in lung diseases and infection.

Porcine lung surfactant protein D: complementary DNA cloning, chromosomal localization, and tissue distribution.

Porcine organs and lung surfactant have medically important applications in both xenotransplantation and therapy. We have started to characterize porcine lung surfactant by cloning the cDNA of porcine surfactant protein D (SP-D). SP-D and SP-A are important mediators in innate immune defense for the lung and possibly other mucosal surfaces. Porcine SP-D will also be an important reagent for use in existing porcine animal models for human lung infections. The complete cDNA sequence of porcine SP-D, including the 5' and 3' untranslated regions, was determined from two overlapping bacteriophage clones and by PCR cloning. Three unique features were revealed from the porcine sequence in comparison to SP-D from other previously characterized species, making porcine SP-D an intriguing species addition to the SP-D/collectin family. The collagen region contains an extra cysteine residue, which may have important structural consequences. The other two differences, a potential glycosylation site and an insertion of three amino acids, lie in the loop regions of the carbohydrate recognition domain, close to the carbohydrate binding region and thus may have functional implications. These variations were ruled out as polymorphisms or mutations by confirming the sequence at the genomic level in four different pig breeds. Porcine SP-D was shown to localize primarily to the lung and with less abundance to the duodenum, jejunum, and ileum. The genes for SP-D and SP-A were also shown to colocalize to a region of porcine chromosome 14 that is syntenic with the human and murine collectin loci.

Genomic organization of the mouse gene for lung surfactant protein D.

Lung surfactant protein (SP)-D belongs to the family of soluble collagenous C-type lectins, named collectins. SP-D participates in the local innate immune defense of the lung, eliciting various effector functions by acting as a pattern recognition receptor for the carbohydrate structures on inhaled microorganisms and particulate matter. This work describes the isolation and characterization of the mouse SP-D gene (Sftpd), which spans 8 exons over 14 kb of sequence and shows an overall organization similar to other collectin genes. The complete 5' untranslated region of the messenger RNA, absent from the published complementary DNA for mouse SP-D, was also cloned and is shown to be encoded by a single exon. Analysis of 3.5 kb of 5' flanking nucleotide sequence for Sftpd is described and reveals positional conservation of a number of transcription factor binding sites on comparison of Sftpd with the human SP-D gene and the bovine conglutinin gene. In addition, a single copy SP-D-like gene has been shown to be present in mammals, birds, and amphibians but is absent in fish. An atypical, rodent-specific, long terminal repeat of retroviral origin containing a minisatellite that has become inserted in Sftpd is described. Three new polymorphic microsatellites are also described, one of which is just 160 base pairs upstream of Sftpd. This microsatellite was used to map the gene to the central region of chromosome 14; fine-scale mapping indicates that it lies in a 5. 64-centimorgan area between D14Mit45 and D14Mit60. This will allow the easy identification of the collectin gene cluster and aid in the construction of a physical map over this region.

Dispersion compensation in stellar interferometry.

In long-baseline stellar interferometry, spectrometers are used to disperse starlight for measuring visibility at multiple wavelengths and for fringe tracking with channeled spectra. However, neither prisms nor gratings are well suited to the observation of fringes with wide spectral bandwidths because the mapping from wave number to detector coordinate is nonlinear. The visibility-measurement and fringe-tracking performance are affected by nonlinearity and in many cases it is important to compensate for this. Longitudinal-dispersion correctors may be used to compensate for differential air paths in an interferometer, and we show that these may also be used to correct the nonlinear mapping of a spectrometer.

Dispersed fringe tracking with the multi-r(0) apertures of the Grand Interféromètre à 2 Télescopes.

A new fringe tracker based on photon-counting detectors and real-time image processing has been implemented on the Grand Interféromètre à 2 Télescopes at the Observatoire de la Cote d'Azur. Fringe visibilities have been recorded on P Cygni and other stars across the Hαemission line with optical path differences stabilized to between 4 and 7 µm rms (1% of the coherence length). We present our initial results and describe the principle, implementation, and performance of the fringe tracker.

Bandwidth limitations and dispersion in optical stellar interferometry.

The fringe visibility measured by a stellar interferometer may be degraded if the interferometer uses an air delay line without compensating for longitudinal dispersion. Whereas in such circumstances simultaneous observations across the visible spectrum are shown to be impracticable at baselines as short as 10 m, it is shown possible to detect 95% of the visibility amplitude if the measurements are made sequentially at different wavelengths and the fractional bandwidth Δλ/λ at 950 nm is restricted to less than 10% when the baseline is 10 m, 6% at 30 m, and 3% at 100 m.

Artifacts in PAPA camera images.

The PAPA detector uses optical masks to decode the location of a photon event on the output phosphor of a high-gain image intensifier. Its use of Gray-coded masks creates image artifacts that are unique to this detector. The artifacts can arise from errors in mask alignment, incorrect discriminator settings, vignetting in the optics, and faults relating to the performance of the image intensifier. The symptoms and causes of the different image artifacts are discussed, and methods are presented to identify and correct these errors.