Phylogenetic multi-locus codon models and molecular clocks reveal the monophyly of haematophagous reduviid bugs and their evolution at the formation of South America.

We previously constructed a single molecular clock to date insect evolution that remains a cornerstone within entomological dating. The insect clock predicts that triatomine bugs, the vectors of South American trypanosomiasis, originated with the formation of South America. We addressed this hypothesis using the insectivorous reduviid bugs and their phylogenetic relationship with the haematophagous reduviid bugs, as well as their biogeographic distribution. Putative paraphyly or monophyly of Triatominae, by non-haematophagous reduviids, have both previously been hypothesized and identified. We sampled a broad range of predatory reduviids, viz. Ectrichodiinae, Emesinae, Hammacerinae, Harpactorinae, Reduviinae, Salyavatinae, Steniopodainae and Vesciinae, including both New World and Old World representatives and sequenced the nuclear 28S ribosomal gene locus and the mitochondrial loci 5' cytochrome oxidase 1 (cox1 [COI]), cox1 3', cytochrome oxidase 2 (cox2 [COII]) and cytochrome oxidase b (cob [cytb]). Robust evidence for the monophyly of Triatominae was observed in 5/5 loci using codon/nucleotide (28S) based maximum likelihood phylogenies, 3/5 loci using codon-based Bayesian phylogenies and in cox2 using amino acid Bayesian phylogenies. Several South American members of the Reduviinae, that are morphologically and phylogenetically a sister group to triatomine bugs, have a modal divergence date with the Triatominae of 109-107 million years ago (MYA). This creates a scenario where the closest (non-haematophagous) ancestor to triatomine bugs evolved immediately prior to the breakup of Gondwanaland whilst the triatomine bugs evolved 95MYA, putatively linking the origin of haematophagous behaviour to the origin of South America and in particular infers a delayed onset to the evolution of haematophagy. The placement of the enigmatic tribe Bolboderini as an ingroup to the Triatominae monophyly, confirms the 95MYA node as the most ancient in the subfamily

Ion beam sputtering in electric propulsion facilities

Experiments were undertaken to determine sputter yields of potential ion beam target materials, to assess the impact of charge exchange on beam diagnostics in large facilities, and to examine material erosion and deposition after a 957 hr test of a 5 kW-class ion thruster. The xenon ion sputter yield of flexible graphite was lower than other graphite forms especially at high angles of incidence. Ion beam charge exchange effects were found to hamper beam probe current collection diagnostics even at pressures from 0.7 to 1.7 mPa. Estimates of the xenon ion beam envelope were made and predictions of the thickness of sputter deposited coatings in the facility were compared with measurements

The evolutionary development of high specific impulse electric thruster technology

Electric propulsion flight and technology demonstrations conducted primarily by Europe, Japan, China, the U.S., and the USSR are reviewed. Evolutionary mission applications for high specific impulse electric thruster systems are discussed, and the status of arcjet, ion, and magnetoplasmadynamic thrusters and associated power processor technologies are summarized

Ion Thruster Development at NASA Lewis Research Center

Recent ion propulsion technology efforts at NASA's Lewis Research Center including development of kW-class xenon ion thrusters, high power xenon and krypton ion thrusters, and power processors are reviewed. Thruster physical characteristics, performance data, life projections, and power processor component technology are summarized. The ion propulsion technology program is structured to address a broad set of mission applications from satellite stationkeeping and repositioning to primary propulsion using solar or nuclear power systems

Development of arcjet and ion propulsion for spacecraft stationkeeping

Near term flight applications of arc jet and ion thruster satellite station-keeping systems as well as development activities in Europe, Japan, and the United States are reviewed. At least two arc jet and three ion propulsion flights are scheduled during the 1992-1995 period. Ground demonstration technology programs are focusing on the development of kW-class hydrazine and ammonia arc jets and xenon ion thrusters. Recent work at NASA LeRC on electric thruster and system integration technologies relating to satellite station keeping and repositioning will also be summarized

The 2.3 kW Ion Thruster Wear Test

A 30-cm diameter xenon ion thruster is under development at NASA to provide an ion propulsion option for auxiliary and primary propulsion on missions of national interest. Specific efforts include thruster design optimizations, component life testing and validation, and performance characterizations. Under this program, the ion thruster will be brought to engineering model development status. This paper describes the results of a 2.3-kW 2000-hour wear test performed to identify life limiting phenomena, measure the performance and characterize the operation of the thruster, and obtain wear, erosion, and surface contamination data. These data are being using as a data base for proceeding with additional life validation tests, and to provide input to flight thruster design requirements

The Metal-Poor Halo of the Andromeda Spiral Galaxy (M31)

We present spectroscopic observations of red giant branch (RGB) stars over a large expanse in the halo of the Andromeda spiral galaxy (M31), acquired with the DEIMOS instrument on the Keck II 10-m telescope. Using a combination of five photometric/spectroscopic diagnostics -- (1) radial velocity, (2) intermediate-width DDO51 photometry, (3) Na I equivalent width (surface gravity sensitive), (4) position in the color-magnitude diagram, and (5) comparison between photometric and spectroscopic [Fe/H] estimates -- we isolate over 250 bona fide M31 bulge and halo RGB stars located in twelve fields ranging from R = 12-165kpc from the center of M31 (47 of these stars are halo members with R > 60 kpc). We derive the photometric and spectroscopic metallicity distribution function of M31 RGB stars in each of these fields. The mean of the resulting M31 spheroid (bulge and halo) metallicity distribution is found to be systematically more metal-poor with increasing radius, shifting from = -0.47+/-0.03 (sigma = 0.39) at R = -0.94+/-0.06 (sigma = 0.60) at R ~ 30 kpc to = -1.26+/-0.10 (sigma = 0.72) at R > 60 kpc, assuming [alpha/Fe] = 0.0. These results indicate the presence of a metal-poor RGB population at large radial distances out to at least R = 160 kpc, thereby supporting our recent discovery of a stellar halo in M31: its halo and bulge (defined as the structural components with R^{-2} power law and de Vaucouleurs R^{1/4} law surface brightness profiles, respectively) are shown to have distinct metallicity distributions. If we assume an alpha-enhancement of [alpha/Fe] = +0.3 for M31's halo, we derive = -1.5+/-0.1 (sigma = 0.7). Therefore, the mean metallicity and metallicity spread of this newly found remote M31 RGB population are similar to those of the Milky Way halo.Comment: Accepted for publication in ApJ on May 4th, 2006 (submitted on Jan 30, 2006). 16 pages, 13 figures, 3 table

A compositional account of motifs, mechanisms, and dynamics in biochemical regulatory networks

Regulatory networks depict promoting or inhibiting interactions between molecules in a biochemical system. We introduce a category-theoretic formalism for regulatory networks, using signed graphs to model the networks and signed functors to describe occurrences of one network in another, especially occurrences of network motifs. With this foundation, we establish functorial mappings between regulatory networks and other mathematical models in biochemistry. We construct a functor from reaction networks, modeled as Petri nets with signed links, to regulatory networks, enabling us to precisely define when a reaction network could be a physical mechanism underlying a regulatory network. Turning to quantitative models, we associate a regulatory network with a Lotka-Volterra system of differential equations, defining a functor from the category of signed graphs to a category of parameterized dynamical systems. We extend this result from closed to open systems, demonstrating that Lotka-Volterra dynamics respects not only inclusions and collapsings of regulatory networks, but also the process of building up complex regulatory networks by gluing together simpler pieces. Formally, we use the theory of structured cospans to produce a lax double functor from the double category of open signed graphs to that of open parameterized dynamical systems. Throughout the paper, we ground the categorical formalism in examples inspired by systems biology.Comment: 33 pages. Added several examples, plus minor revision

Using MGA to shorten the beef breeding season (2002)

Modified conventional synchronization systems for beef cows boost fertility and increase the total number of females that can be inseminated.New March 2002 -- Extension website