27 research outputs found
Dust Devil Tracks
Dust devils that leave dark- or light-toned tracks are common on Mars and they can also be found on the Earth’s surface. Dust devil tracks (hereinafter DDTs) are ephemeral surface features with mostly sub-annual lifetimes. Regarding their size, DDT widths can range between ∼1 m and ∼1 km, depending on the diameter of dust devil that created the track, and DDT lengths range from a few tens of meters to several kilometers, limited by the duration and horizontal ground speed of dust devils. DDTs can be classified into three main types based on their morphology and albedo in contrast to their surroundings; all are found on both planets: (a) dark continuous DDTs, (b) dark cycloidal DDTs, and (c) bright DDTs. Dark continuous DDTs are the most common type on Mars. They are characterized by their relatively homogenous and continuous low albedo surface tracks. Based on terrestrial and martian in situ studies, these DDTs most likely form when surficial dust layers are removed to expose larger-grained substrate material (coarse sands of ≥500 μm in diameter). The exposure of larger-grained materials changes the photometric properties of the surface; hence leading to lower albedo tracks because grain size is photometrically inversely proportional to the surface reflectance. However, although not observed so far, compositional differences (i.e., color differences) might also lead to albedo contrasts when dust is removed to expose substrate materials with mineralogical differences. For dark continuous DDTs, albedo drop measurements are around 2.5 % in the wavelength range of 550–850 nm on Mars and around 0.5 % in the wavelength range from 300–1100 nm on Earth. The removal of an equivalent layer thickness around 1 μm is sufficient for the formation of visible dark continuous DDTs on Mars and Earth. The next type of DDTs, dark cycloidal DDTs, are characterized by their low albedo pattern of overlapping scallops. Terrestrial in situ studies imply that they are formed when sand-sized material that is eroded from the outer vortex area of a dust devil is redeposited in annular patterns in the central vortex region. This type of DDT can also be found in on Mars in orbital image data, and although in situ studies are lacking, terrestrial analog studies, laboratory work, and numerical modeling suggest they have the same formation mechanism as those on Earth. Finally, bright DDTs are characterized by their continuous track pattern and high albedo compared to their undisturbed surroundings. They are found on both planets, but to date they have only been analyzed in situ on Earth. Here, the destruction of aggregates of dust, silt and sand by dust devils leads to smooth surfaces in contrast to the undisturbed rough surfaces surrounding the track. The resulting change in photometric properties occurs because the smoother surfaces have a higher reflectance compared to the surrounding rough surface, leading to bright DDTs. On Mars, the destruction of surficial dust-aggregates may also lead to bright DDTs. However, higher reflective surfaces may be produced by other formation mechanisms, such as dust compaction by passing dust devils, as this may also cause changes in photometric properties. On Mars, DDTs in general are found at all elevations and on a global scale, except on the permanent polar caps. DDT maximum areal densities occur during spring and summer in both hemispheres produced by an increase in dust devil activity caused by maximum insolation. Regionally, dust devil densities vary spatially likely controlled by changes in dust cover thicknesses and substrate materials. This variability makes it difficult to infer dust devil activity from DDT frequencies. Furthermore, only a fraction of dust devils leave tracks. However, DDTs can be used as proxies for dust devil lifetimes and wind directions and speeds, and they can also be used to predict lander or rover solar panel clearing events. Overall, the high DDT frequency in many areas on Mars leads to drastic albedo changes that affect large-scale weather patterns
The LHCb upgrade I
The LHCb upgrade represents a major change of the experiment. The detectors have been almost completely renewed to allow running at an instantaneous luminosity five times larger than that of the previous running periods. Readout of all detectors into an all-software trigger is central to the new design, facilitating the reconstruction of events at the maximum LHC interaction rate, and their selection in real time. The experiment's tracking system has been completely upgraded with a new pixel vertex detector, a silicon tracker upstream of the dipole magnet and three scintillating fibre tracking stations downstream of the magnet. The whole photon detection system of the RICH detectors has been renewed and the readout electronics of the calorimeter and muon systems have been fully overhauled. The first stage of the all-software trigger is implemented on a GPU farm. The output of the trigger provides a combination of totally reconstructed physics objects, such as tracks and vertices, ready for final analysis, and of entire events which need further offline reprocessing. This scheme required a complete revision of the computing model and rewriting of the experiment's software
The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance
INTRODUCTION
Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic.
RATIONALE
We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs).
RESULTS
Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants.
CONCLUSION
Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century
Hydrothermal Formation Of Clay-carbonate Alteration Assemblages In The Nili Fossae Region Of Mars
The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) has returned observations of the Nili Fossae region indicating the presence of Mg-carbonate in small (<10km sq2), relatively bright rock units that are commonly fractured (Ehlmann et al., 2008b). We have analyzed spectra from CRISM images and used co-located HiRISE images in order to further characterize these carbonate-bearing units. We applied absorption band mapping techniques to investigate a range of possible phyllosilicate and carbonate minerals that could be present in the Nili Fossae region. We also describe a clay-carbonate hydrothermal alteration mineral assemblage in the Archean Warrawoona Group of Western Australia that is a potential Earth analog to the Nili Fossae carbonate-bearing rock units. We discuss the geological and biological implications for hydrothermal processes on Noachian Mars. © 2010 Elsevier B.V.2971-2174182Baird, A.K., Clark, B.C., On the Original Igneous Source of Martian Fines (1981) Icarus, 45, pp. 113-123Bandfield, J.L., Spectroscopic identification of carbonate minerals in the martian dust (2003) Science, 301, pp. 1084-1087Bell, J.F., Spectroscopy of Mars from 2.04 to 2.44 Mu-M During the 1993 Opposition - Absolute Calibration and Atmospheric Vs Mineralogic Origin of Narrow Absorption Features (1994) Icarus, 111, pp. 106-123Bibring, J.-P., Global Mineralogical and Aqueous Mars History Derived from OMEGA/Mars Express Data (2006) Science, 312, pp. 400-404Bishop, J.L., Recognition of minor constituents in reflectance spectra of Allan Hills 84001 chips and the importance for remote sensing on Mars (1998) Meteorit. Planet. Sci., 33, pp. 693-698Bishop, J.L., Spectroscopic analysis of Martian meteorite Allan Hills 84001 powder and applications for spectral identification of minerals and other soil components on Mars (1998) Meteorit. Planet. Sci., 33, pp. 699-707Blaney, D.L., McCord, T.B., An observational search for carbonates on Mars (1989) J. Geophys. Res., 94, pp. 10159-10166Booth, M.C., Kieffer, H.H., Carbonate formation in Marslike environments (1978) J. Geophys. Res., 83, pp. 1809-1915Boynton, W.V., Evidence for Calcium Carbonate at the Mars Phoenix Landing Site (2009) Science, 325, pp. 61-64Brauhart, C.W., Geochemical Mass-Transfer Patterns as Indicators of the Architecture of a Complete Volcanic-Hosted Massive Sulfide Hydrothermal Alteration System, Panorama District, Pilbara, Western Australia (2001) Econ. Geol., 96, pp. 1263-1278Bridges, J.C., Alteration Assemblages in Martian Meteorites: Implications for Near-Surface Processes (2001) Space Sci. Rev., 96, pp. 365-392Brown, A.J., Spectral Curve Fitting for Automatic Hyperspectral Data Analysis (2006) IEEE Trans. Geosci. Remote Sens., 44, pp. 1601-1608Brown, A.J., Hyperspectral Mapping of Ancient Hydrothermal Systems. Earth and Planetary Sciences, Vol. PhD. Macquarie University, Sydney, N.S.W., 2006bBrown, A.J., Short Wave Infrared Reflectance Investigation of Sites of Palaeobiological interest: Applications for Mars Exploration (2004) Astrobiology, 4, pp. 359-376Brown, A.J., Hyperspectral and field mapping of an Archaean Komatiite Unit in the Pilbara Craton (2004) Western Australia: Applications for CRISM Mission. LPSC XXXV, , LPI, Houston, Vol. abstract 1420Brown, A.J., Hyperspectral Imaging Spectroscopy of a Mars Analog Environment at the North Pole Dome, Pilbara Craton, Western Australia (2005) Aust. J. Earth Sci., 52, pp. 353-364Brown, A.J., Hydrothermal alteration at the Panorama Formation, North Pole Dome, Pilbara Craton, Western Australia (2006) Precambrian Res., 151, pp. 211-223Brown, A.J., Talc carbonate Weathering as a Possible Terrestrial Analog for Alteration Assemblages in the Nili Fossae Region of Mars (2008) Astrobiology, 8, p. 432Brown, A.J., The MARTE Imaging Spectrometer Experiment: Design and Analysis (2008) Astrobiology, 8, pp. 1001-1011Calvin, W.M., Hydrous Carbonates on Mars - Evidence from Mariner 6/7 Infrared Spectrometer and Ground-Based Telescopic Spectra (1994) J. Geophys. Res.-Planets, 99, pp. 14659-14675Campbell, I.H., Melting in an Archaean mantle plume: heads it's basalts, tails it's komatiites (1989) Nature, 339, pp. 697-699Carr, M.H., Retention of an atmosphere on early Mars (1999) J. Geophys. Res.-Planets, 104, pp. 21897-21909Catling, D.C., A chemical model for evaporites on early Mars: Possible sedimentary tracers of the climate and implications for exploration (1999) J. Geophys. Res., 104, pp. 16453-16469Clark, R.N., High spectral resolution reflectance spectroscopy of minerals (1990) J. Geophys. Res., 95 (B), pp. 12653-12680Clark, R.N., (2007), http://speclab.cr.usgs.gov/spectral.lib06, USGS digital spectral library splib06a Digital Data Series 231. U.S. Geological SurveyCloutis, E.A., (2000) Hydrated Carbonate Minerals: Spectral Reflectance Properties and Possibility of Detection in Martian Spectra. LPSC XXXI, , LPI, Houston, TX, pp. Abstract 1152Dalton, J.B., Identification of spectrally similar materials using the USGS Tetracorder algorithm: the calcite-epidote-chlorite problem (2004) Remote Sens. Environ., 89, pp. 455-466Donaldson, M.J., Redistribution of ore elements during serpentinization and talc-carbonate alteration of some Archean dunites, Western Australia (1981) Econ. Geol., 76, pp. 1698-1713Ehlmann, B.L., New secondary minerals detected by MRO CRISM and their geologic settings: Kaolinite, chlorite, Illite/Muscovite and the possibility of serpentine or carbonate in Nili Fossae (2007) Seventh International Conference on Mars, , LPI, Pasadena, CAEhlmann, B.L., Clay minerals in delta deposit and organic preservation potential on Mars (2008) Nat. Geosci.Ehlmann, B.L., Orbital Identification of Carbonate-Bearing Rocks on Mars (2008) Science, 322, pp. 1828-1832Ehlmann, B.L., Identification of hydrated silicate minerals on Mars using MRO-CRISM: Geologic context near Nili Fossae and implications for aqueous alteration (2009) J. Geophys. Res., 114Ehlmann, B.L., Geologic setting of serpentine deposits on Mars (2010) Geophys. Res. Lett., 37, pp. L06201Fairen, A.G., Inhibition of carbonate synthesis in acidic oceans on early Mars (2004) Nature, 431, pp. 423-426Farmer, J.D., Des Marais, D.J., Exploring for a record of ancient Martian life (1999) J. Geophys. Res.-Planets., 104, pp. 26977-26995Gaffey, S.J., Spectral reflectance of carbonate minerals in the visible and near infrared (0.35-2.55 microns): anhydrous carbonate minerals (1987) J. Geophys. Res., 92, pp. 1429-1440Gooding, J.L., Chemical weathering on Mars: Thermodynamic stabilities of primary minerals (and their alteration products) from mafic igneous rocks (1978) Icarus, 33, pp. 483-513Gooding, J.L., Aqueous alteration of the Nakhla meteorite (1991) Meteoritics., 26, pp. 135-143Griffith, L.L., Shock, E.L., A Geochemical Model for the Formation of Hydrothermal Carbonates on Mars (1995) Nature, 377, pp. 406-408Haberle, R.M., A Model for the Evolution of Co2 on Mars (1994) Icarus, 109, pp. 102-120Hamilton, V.E., Christensen, P.R., Evidence for extensive, olivine-rich bedrock on Mars (2005) Geology, 33, pp. 433-436Hoefen, T.M., Discovery of Olivine in the Nili Fossae Region of Mars (2003) Science, 302, pp. 627-630Hunt, G.R., Salisbury, J.W., Visible and Near-Infrared Spectra of Minerals and Rocks: II Carbonates. (1971) Mod. Geol., 2, pp. 23-30Jakosky, B.M., Mars Atmospheric Loss and Isotopic Fractionation by Solar-Wind- Induced Sputtering and Photochemical Escape (1994) Icarus, 111, pp. 271-288Jouglet, D., Search for Carbonates on Mars with the OMEGA/Mars Express Data (2007) Seventh International Conference on Mars, , LPI, Pasadena, CA, pp. Abstract #3153Kahn, R., The evolution of CO2 on Mars (1985) Icarus, 62, pp. 175-190Kirkland, L.E., Thermal Infrared Spectral Band Detection Limits for Unidentified Surface Materials (2001) Appl. Opt., 40, pp. 4852-4862Lellouch, E., The 2.4-45 mu m spectrum of Mars observed with the Infrared Space Observatory (2000) Planet. Space Sci., 48, pp. 1393-1405Loizeau, D., Phyllosilicates in the Mawrth Vallis region of Mars (2007) J. Geophys. Res., 112. , E08S08Loizeau, D., Stratigraphy in the Mawrth Vallis region through OMEGA, HRSC color imagery and DTM (2010) Icarus, 205, pp. 396-418Longhi, J., Takahashi, T., (2006) Oceans on Mars: Whither Carbonate? , LPSC XXXVII, , LPI, Houston, TX, pp. Abstract 2455Lowell, R.P., Rona, P.A., Hydrothermal models for the generation of massive sulfide ore deposits (1985) J. Geophys. Res., 90, pp. 8769-8783Mangold, N., Mineralogy of the Nili Fossae region with OMEGA/Mars Express data: 2. Aqueous alteration of the crust. (2007) J. Geophys. Res., 112McGuire, P.C., An improvement to the volcano-scan algorithm for atmospheric correction of CRISM and OMEGA spectral data (2009) Planet. Space Sci., 57, pp. 809-815McKay, C.P., Nedell, S.S., Are there carbonate deposits in the Valles Marineris, Mars? (1988) Icarus, 73, pp. 142-148McKay, D.S., Search for past life on Mars: Possible relic biogenic activity in Martian meteorite ALH84001 (1996) Science, 273, pp. 924-930Moody, J.B., Serpentinization: a review (1976) Lithos, 9, pp. 125-138Moore, J.M., Blueberry fields for ever (2004) Nature, 428, pp. 711-712Morris, R.V., (2010), Identification of Carbonate-Rich Outcrops on Mars by the Spirit Rover. Science. science.1189667Morse, J.W., Marion, G.M., The role of carbonates in the evolution of early Martian oceans (1999) Am. J. Sci., 299, pp. 738-761Mumma, M.J., Strong Release of Methane on Mars in Northern Summer 2003 (2009) Science, 323, pp. 1041-1045Murchie, S., Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on Mars Reconnaissance Orbiter (MRO) (2007) J. Geophys. Res., 112, pp. E05S03Mustard, J.F., Mineralogy of the Nili Fossae region with OMEGA/Mars Express data: 1. Ancient impact melt in the Isidis Basin and implications for the transition from the Noachian to Hesperian (2007) J. Geophys. Res., 112Mustard, J.F., The Surface of Syrtis Major - Composition of the Volcanic Substrate and Mixing with Altered Dust and Soil (1993) J. Geophys. Res.-Planets., 98, pp. 3387-3400Mustard, J.F., Olivine and Pyroxene Diversity in the Crust of Mars (2005) Science, 307, pp. 1594-1597Mustard, J.F., Hydrated silicate minerals on Mars observed by the Mars Reconnaissance Orbiter CRISM instrument (2008) Nature, 454, pp. 305-309Nelder, J.A., Mead, R., A simplex method for function minimization (1965) Comput. J., 7, pp. 308-313Niles, P.B., Insights into the formation of Fe- and Mg-rich aqueous solutions on early Mars provided by the ALH 84001 carbonates (2009) Earth Planet. Sci. Lett., 286, pp. 122-130O'Connor, J.T., Mineral Stability at the Martian Surface (1968) J. Geophys. Res., 73, pp. 5301-5311Oze, C., Sharma, M., Have olivine, will gas: Serpentinization and the abiogenic production of methane on Mars (2005) Geophys. Res. Lett., 32, p. 10203Palomba, E., Evidence for Mg-rich carbonates on Mars from a 3.9 [mu]m absorption feature (2009) Icarus, 203, pp. 58-65Perry, K.A., (2010) Mineralogy of Libya Montes, Mars and Applications of Phyllosiliate-Carbonate-Olivine Mixtures. LPSC XXXXI, , LPI, Houston, TX, pp. Abstract #2605Pollack, J.B., The case for a wet, warm climate on early Mars (1987) Icarus, 71, pp. 203-224Pollack, J.B., Thermal emission spectra of Mars (5.4-10.5um): Evidence for sulfates, carbonates and hydrates (1990) J. Geophys. Res., 95, pp. 14595-14627Quinn, R., The Photochemical Stability of Carbonates on Mars (2006) Astrobiology, 6, pp. 581-591Reyes, D.P., Christensen, P.R., Evidence for Komatiite-Type Lavas on Mars from Phobos Ism Data and Other Observations (1994) Geophys. Res. Lett., 21, pp. 887-890Romanek, C.S., Martian Carbonates in Alh 84001 - Textural, Elemental, and Stable Isotopic Compositional Evidence on Their Formation (1994) Meteoritics., 29, pp. 523-523Sarrazin, P., Field deployment of a portable X-ray diffraction/X-ray florescence instrument on Mars analog terrain (2005) Powder Diffr., 20, pp. 128-133Savitzky, A., Golay, M.J.E., Smoothing and differentiation of data by simplified least squares procedures (1964) Anal. Chem., 36, pp. 1627-1639Schaefer, M.W., Geochemical Evolution of the Northern Plains of Mars: Early Hydrosphere, Carbonate Development, and Present Morphology (1990) J. Geophys. Res., 95, pp. 14291-14300Schaefer, M.W., Aqueous geochemistry on early Mars (1993) Geochimica et Cosmochemica Acta., 57, pp. 4619-4625Treiman, A.H., Hydrothermal origin for carbonate globules in Martian meteorite ALH84001: a terrestrial analogue from Spitsbergen (Norway) (2002) Earth Planet. Sci. Lett., 204, pp. 323-332Ueno, Y., Carbon isotopes and petrography of kerogens in 3.5-Ga hydrothermal silica dikes in the North Pole area, Western Australia (2004) Geochim. Cosmochim. Acta, 68, pp. 573-589Van Kranendonk, M.J., Geology and tectonic evolution of the archean North Pilbara terrain, Pilbara Craton, Western Australia (2002) Econ. Geol. Bull. Soc. Econ. Geol., 97, pp. 695-732Van Kranendonk, M.J., Geological setting of Earth's oldest fossils in the ca. 3.5†Ga Dresser Formation, Pilbara Craton, Western Australia (2008) Precambrian Res., 167, pp. 93-124Wagner, C., Schade, U., Measurements and calculations for estimating the spectrometric detection limit for carbonates in Martian soil (1996) Icarus, 123, pp. 256-268Walter, M.R., Des Marais, D.J., Preservation of Biological Information in Thermal-Spring Deposits - Developing a Strategy for the Search for Fossil Life on Mars (1993) Icarus, 101, pp. 129-143Walter, M.R., Stromatolites 3400-3500 Myr old from the North Pole area, Western Australia (1980) Nature, 284, pp. 443-445Welhan, J.A., Origins of methane in hydrothermal systems (1988) Chem. Geol., 71, pp. 183-198Wentworth, S.J., Gooding, J.L., Carbonate and Sulfate Minerals in the Chassigny Meteorite (1991) Meteoritics., 26, pp. 408-409Wentworth, S.J., Gooding, J.L., Carbonates and Sulfates in the Chassigny Meteorite - Further Evidence for Aqueous Chemistry on the Snc Parent Planet (1994) Meteoritics., 29, pp. 860-863White, W.B., The carbonate minerals (1974) The Infra-Red Spectra of Minerals, pp. 227-284. , Mineralogical Society, London, UK, V.C. Farmer (Ed.)Zahnle, K., (2010) Is there Methane on Mars? , LPSC 41, , LPI, Houston, TX, pp. Abs. #245
Brazilian Analog For Ancient Marine Environments On Mars
[No abstract available]8936329330Bibring, J., Mars surface diversity as revealed by the OMEGA/Mars Express observations (2005) Science, 307, pp. 1576-1581Christensen, P.R., Detection of crystalline hematite mineralization on Mars by the Thermal Emission Spectrometer. Evidence for near-surface water (2000) J. Geophys. Res, 105, pp. 9623-9642Connerney, J.E.P., Magnetic lineations in the ancient crust of Mars (1999) Science, 284, pp. 794-798Crowley, J.K., Spectral diversity of terrestrial banded iron formations and associated rocks: Implications for Mars remote sensing (2008) Lunar Planet Sci, 39, p. 1263Dalstra, H., Guedes, S., Giant hydrothermal hematite deposits with Mg-Fe metasomatism: A comparison of the Carajas, Hamersley, and other iron ores (2004) Econ. Geol, 99, pp. 1793-1800Fallacaro, A., Calvin, W.M., Spectral properties of Lake Superior banded iron formation: Application to Martian hematite deposits (2006) Astrobiology, 6, pp. 563-580Klein, C., Some Precambrian banded-iron formations (BIFs) from around the world: Their age, geologic setting, mineralogy, metamorphism, geochemistry, and origin (2005) Am. Mineral, 90, pp. 1473-1499Klein, C., Ladeira, E.A., Petrography and geochemistry of the least altered banded iron-formation of the Archean Carajas Formation, northern Brazil (2002) Econ. Geol, 97, pp. 643-651Squyres, S.W., In situ evidence for an ancient aqueous environment at Meridiani Planum, Mars (2004) Science, 306, pp. 1709-1714Trendall, A.F., The significance of iron-formation in the Precambrian stratigraphic record (2002) Spec. Publ. Int. Assoc. Sedimentol, 33, pp. 33-66Trendall, A.F., Basei, M.A.S., de Laeter, J.R., Nelson, D.R., Ion microprobe zircon, U-Pb results from the Carajas area of the Amazon craton (1998) J. S. Am. Earth Sci, 11, pp. 265-27
Discovery and Development of a Potent and Highly Selective Small Molecule Muscarinic Acetylcholine Receptor Subtype I (mAChR 1 or M-1) Antagonist In Vitro and In Vivo Probe
This article describes the discovery and development of the first highly selective, small molecule antagonist of the muscarinic acetylcholine receptor subtype I (mAChR1 or M(1)). An M(1) functional, cell-based calcium-mobilization assay identified three distinct chemical series with initial selectivity for M(1) versus M(4). An iterative parallel synthesis approach was employed to optimize all three series in parallel, which led to the development of novel microwave-assisted chemistry and provided important take home lessons for probe development projects. Ultimately, this effort produced VU0255035, a potent (IC(50) = 130 nM) and selective (>75-fold vs. M(2)-M(5) and > 10 μM vs. a panel of 75 GPCRs, ion channels and transporters) small molecule M(1) antagonist. Further profiling demonstrated that VU0255035 was centrally penetrant (Brain(AUC)/Plasma(AUC) of 0.48) and active in vivo, rendering it acceptable as both an in vitro and in vivo MLSCN/ MLPCN probe molecule for studying and dissecting M(1) function