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Search Results: 1 - 10 of 545620 matches for " C. M. Brown "
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Mineral chemistry, petrology and geochemistry of the Sebago granite-pegmatite system, southern Maine, USA
Wise M,Brown C D
Journal of Geosciences , 2010, DOI: 10.3190/jgeosci.061
Abstract: The Permian (293 ± 2 Ma) Sebago Pluton is a homogeneous, two-mica granite situated in the Oxford pegmatite field, southwestern Maine. Surrounding the pluton is an area designated as the Sebago Migmatite Domain (SMD) dominated by metapelitic migmatites and diatexites with subordinate intrusions of heterogeneous, two-mica and biotite granites, pegmatitic leucogranites and granitic pegmatites. The Sebago Pluton plus the SMD formerly defined the extent of the Sebago Batholith. Most of the granitic pegmatites and bodies of pegmatitic leucogranites occur either within, or barely outside, the margins of the SMD. The pegmatitic leucogranite facies displays units typical of fertile granites (granites that produce granitic pegmatites) and include; megacrystic graphic K-feldspar, sodic aplite and potassic pegmatite pods hosting rare tourmaline, beryl and columbite-tantalite. Over 100 granitic pegmatite bodies (Sebago Pegmatite Group - SPG) intrude the outer portions of the SMD and neighboring granitoids and metasedimentary rocks. The pegmatite population includes mineralogically simple to complexly zoned pegmatites that are characterized by a LCT-type (Li, Cs and Ta) geochemical signature, extensive replacement of primary zones and gem-bearing miarolitic cavities.
Sebago granites are strongly peraluminous and show rare-element enrichment typical of evolved fertile granites (K/Rb = 87-257), Rb/Tl = 10.6-71.3, Ba/Rb = 0.18-5.04, Al/Ga = 1419-1749, Zr/Sn = 1.53-43.9). The SPG shows high levels of Be, Nb > Ta, P, Li and B with subordinate enrichment in Rb and Cs. Moderate to high levels of rare-element fractionation is encountered in pegmatitic K-feldspar (K/Rb ≈ 17, K/Cs ≈ 90, Rb/Tl ≈ 75); muscovite (K/Rb ≈ 6.6, K/Cs ≈ 14.8, Rb/Tl ≈ 127); beryl (Na/Li ≈ 1.77, Cs2O ≈ 3.15 wt. %), garnet [Mn/(Mn + Fe) ≈ 0.60] and manganotantalite and ixiolite/wodginite [Mn/Mn + Fe) ≈ 0.98, Ta/(Ta + Nb) ≈ 0.80-0.93].
Evidence that supports the pegmatitic leucogranites as the likely parent to the SPG includes the close spatial distribution of the pegmatites to the leucogranite bodies, texturally and mineralogically similar units observed within the leucogranite and the neighboring pegmatites plus gradual, yet overlapping, rare-element fractionation from the leucogranites to the associated pegmatites. A few pegmatites (e.g., the Lord Hill pegmatite and amethyst-bearing pegmatites) show NYF tendencies unlike any other pegmatites of the SPG. Differences in fractionation degree, evolution and/or relation to another fertile granite-pegmatite system may be responsible for th
Abundance Distributions in Artificial Life and Stochastic Models: "Age and Area" revisited
C. Adami,C. T. Brown,M. Haggerty
Physics , 1995,
Abstract: Using an artificial system of self-replicating strings, we show a correlation between the age of a genotype and its abundance that reflects a punctuated rather than gradual picture of evolution, as suggested long ago by Willis. In support of this correlation, we measure genotype abundance distributions and find universal coefficients. Finally, we propose a simple stochastic model which describes the dynamics of equilibrium periods and which correctly predicts most of the observed distributions.
Impact of Iron Availability on Bacillus amyloliquefaciens Growth  [PDF]
D. Clark, C. Youngblood, M. Taplin, E. Brown, B. S. Williams, C. Phillips, B. Garner
Advances in Microbiology (AiM) , 2014, DOI: 10.4236/aim.2014.413107
Abstract:

Bacillus amyloliquefaciens is a biocontrol agent whose genome has been sequenced. Within the genome of B. amyloliquefaciens are genes associated with iron chelation, but these genes are not found within all sequenced strains. The impact of iron availability on the B. amyloliquefaciens physiology was examined in this study. B. amyloliquefaciens ATCC 23843 was cultured under ironreplete and iron-deplete conditions for 48 hours, at 37°C. Final growth yields were dependent on iron concentration. Cultures grown in the absence of detectable iron were restricted in growth, but reached their highest yields at 48 hours. Iron restriction was confirmed by the presence of iron chelators in the filtrates. In contrast, B. amyloliquefaciens ATCC 23843 cultures grown with ferric ammonium citrate as the iron source research reached the highest yields at 24 hours. Iron chelator production was not detected in the ferric ammonium samples. A significant decrease in turbidity was observed for these cultures, which coincided with elevated spore production in B. amyloliquefaciens ATCC 23843. A decrease in turbidity was also observed on blood agar, where hemolysis was readily evident. We propose that iron impacts numerous physiological responses and further studies will elucidate the complex regulatory mechanisms governed by iron availability.

Both Canonical and Non-Canonical Wnt Signaling Independently Promote Stem Cell Growth in Mammospheres
Alexander M. Many, Anthony M. C. Brown
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0101800
Abstract: The characterization of mammary stem cells, and signals that regulate their behavior, is of central importance in understanding developmental changes in the mammary gland and possibly for targeting stem-like cells in breast cancer. The canonical Wnt/β-catenin pathway is a signaling mechanism associated with maintenance of self-renewing stem cells in many tissues, including mammary epithelium, and can be oncogenic when deregulated. Wnt1 and Wnt3a are examples of ligands that activate the canonical pathway. Other Wnt ligands, such as Wnt5a, typically signal via non-canonical, β-catenin-independent, pathways that in some cases can antagonize canonical signaling. Since the role of non-canonical Wnt signaling in stem cell regulation is not well characterized, we set out to investigate this using mammosphere formation assays that reflect and quantify stem cell properties. Ex vivo mammosphere cultures were established from both wild-type and Wnt1 transgenic mice and were analyzed in response to manipulation of both canonical and non-canonical Wnt signaling. An increased level of mammosphere formation was observed in cultures derived from MMTV-Wnt1 versus wild-type animals, and this was blocked by treatment with Dkk1, a selective inhibitor of canonical Wnt signaling. Consistent with this, we found that a single dose of recombinant Wnt3a was sufficient to increase mammosphere formation in wild-type cultures. Surprisingly, we found that Wnt5a also increased mammosphere formation in these assays. We confirmed that this was not caused by an increase in canonical Wnt/β-catenin signaling but was instead mediated by non-canonical Wnt signals requiring the receptor tyrosine kinase Ror2 and activity of the Jun N-terminal kinase, JNK. We conclude that both canonical and non-canonical Wnt signals have positive effects promoting stem cell activity in mammosphere assays and that they do so via independent signaling mechanisms.
Doubling of crop yield through permutation of metabolic pathways  [PDF]
Godson O. Osuji, Tassin K. Brown, Sanique M. South, Justin C. Duncan, Dwiesha Johnson
Advances in Bioscience and Biotechnology (ABB) , 2011, DOI: 10.4236/abb.2011.25054
Abstract: Hunger and food insecurity can be minimized by doubling crop yield without increasing cultivated land area and fertilizer applied. Since plant breeding has not genetically doubled photosynthesis per unit leaf area, an approach for doubling crop yield would be through a biotechnology that reprograms metabolic pathways in favor of photosynthesis. The anchor of this biotechnology is glutamate dehydrogenase (GDH) including the RNAs it synthesizes. Peanut was treated with stoichiometric combinations of mineral salt solutions to synchronize the GDH subunit polypeptides. Matured seeds were analyzed for fats by HPLC; the RNA biosynthetic activity of GDH, and mRNAs encoding yield-specific enzymes by Northern hybridization. In the PK-treated peanut, the GDH-synthesized RNAs silenced the mRNAs encoding granule-bound starch synthase, phosphoglucomutase (glycolysis), glucosyltransferase (cellulose biosynthesis), and nitrate reductase leaving unaffected the mRNAs encoding acetylcoenzyme A carboxylase (fatty acid biosynthesis), phosphate translocator, and NADH-glutamate synthase resulting to double seed (4342 kg/ha), cellulose (1829 kg/ha), and fat (1381 kg/ha) yields compared with the controls. Down-regulation of phosphate translocator and acetylcoenzyme A carboxylase caused decreased pod yields. GDH-synthesized RNAs that were homologous to yield-specific mRNAs shared extensive plus/plus and plus/minus sequence similarities, and they reprogrammed metabolism by permuting the partially down-regulated, not down-regulated, and down-regulated yield-specific pathways. Control peanut produced 70, NPKS-treated produced 420, NS-treated produced 1680, and PK-treated produced 280 probable rearrangements of the pathways. Therefore, down-regulation of metabolic reactions followed by permutation of yield-related pathways, and redistribution of metabolite load to molecularly connected pathways controls crop yield. Operating as efficient bioreactor, peanut can be maximized to 10000 kg pod/ha, more than enough vegetable oil for nine billion people.
Molecular Adaptation of Peanut Metabolic Pathways to Wide Variations of Mineral Ion Composition and Concentration  [PDF]
Godson O. Osuji, Tassine K. Brown, Sanique M. South, Justin C. Duncan, Dwiesha Johnson, Shanique Hyllam
American Journal of Plant Sciences (AJPS) , 2012, DOI: 10.4236/ajps.2012.31003
Abstract: Plant evolution, nutritional genomics, and mineral nutrition have been well documented but no studies have focused on the molecular adaptation of crop metabolism to wide variations of mineral ion composition and concentration. Diversification of peanut species from primary centers of domestication in South America depended on metabolic adaptation to the mineral ion conditions of the newer habitats. Understanding the diversification molecular biology of peanut metabolic pathways will permit the synthesis of the best mineral ion combinations for doubling CO2 assimilation. Valencia and Virginia cultivars belong to different subspecies of the tetraploid Arachis hypogaea. They were planted in the absence and presence of up to 99 mM (equivalent to 166 moles per hectare) of different mineral ions. Molecular properties of the primary metabolic pathways were studied by Northern analyses using Valencia GDH-synthesized RNAs as probes for Virginia mRNA and GDH-synthesized RNAs. Messenger RNAs are silenced by homologous RNAs synthesized by GDH. Peanut cellulose was analyzed by gravimetry; and fatty acids by HPLC. Complementary DNA probes made from Valencia GDH-synthesized RNAs hybridized perfectly to Virginia mRNAs and GDH-synthesized RNAs. Wide variations in mineral ion compositions and concentrations induced the GDHs of Valencia and Virginia to synthesize RNAs that differentially down-regulated the mRNAs encoding phosphate translocator, granule-bound starch synthase, phosphoglucomutase, glucosyltransferase, acetyl CoA carboxylase, nitrate reductase, and NADH-glutamate synthase so that the percent weights of oil (41.53 ± 8.75) and cellulose (30.29 ± 3.12) were similar in the control and mineral-treated peanuts. Therefore, RNA sequences that defined the molecular adaptation of mRNAs encoding the enzymes of primary metabolism were the same in the varietal types of A. hypogaea, in agreement with genetic data suggesting that tetraploid Arachis evolved relatively recently from the wild diploid ancestral species. Another molecular adaptation was to phosphate with or without K+ ion, and it prevented the silencing by GDH-synthesized RNAs of the mRNA encoding phosphate translocator resulting to doubling of cellulosic biomass yield (41323 kg/ha) compared with the N + P + K + S-treated positive control peanut (19428 kg/ha). Molecular adaptation of primary metabolic pathways at the mRNA level to SO42- ion with or without SO42- ion did not increase cellulosic biomass yields (27057 kg/ha) compared with negative control
Mark-recapture and behavioral ecology: a case study of Cliff Swallows
Brown, C. R.,Bronw, M. B.
Animal Biodiversity and Conservation , 2004,
Abstract: Mark-recapture and the statistical analysis methods associated with it offer great potential for investigating fitness components associated with particular behavioral traits. However, few behavioral ecologists have used these techniques. We illustrate the insights that have come from a long-term mark-recapture study of social behavior in Cliff Swallows (Petrochelidon pyrrhonota). The number of transient swallows passing through a colony per hour increased with colony size and was responsible in part for increased rates of ectoparasite introduction from outside the group into the larger colonies. Annual survival probabilities of males engaging in extra-pair copulation attempts were lower than those of males not seen to commit extra-pair copulations, suggesting that males who engage in this behavior may be inferior individuals and that females do not benefit from copulating with them. Females engaging in intraspecific brood parasitism had higher annual survival probabilities than ones either parasitized by others or not known to be either hosts or parasites. This suggests that parasitic females are high-quality birds and that brood parasitism is an effective reproductive tactic for increasing their fitness. By estimating first-year survival of chicks, we found that a clutch size of 4 eggs is often the most productive, on average, as measured by recruitment of offspring as breeders, although birds laying the more uncommon clutch size of 5 fledge more young on average. This helps to explain the observed clutch-size distribution in which clutch size 4 is the most commonly produced.
Quaoar: A Rock in the Kuiper belt
W. C. Fraser,M. E. Brown
Physics , 2010, DOI: 10.1088/0004-637X/714/2/1547
Abstract: Here we report WFPC2 observations of the Quaoar-Weywot Kuiper belt binary. From these observations we find that Weywot is on an elliptical orbit with eccentricity of 0.14 {\pm} 0.04, period of 12.438 {\pm} 0.005 days, and a semi-major axis of 1.45 {\pm} 0.08 {\times} 104 km. The orbit reveals a surpsingly high Quaoar-Weywot system mass of 1.6{\pm}0.3{\times}10^21 kg. Using the surface properties of the Uranian and Neptunian satellites as a proxy for Quaoar's surface, we reanalyze the size estimate from Brown and Trujillo (2004). We find, from a mean of available published size estimates, a diameter for Quaoar of 890 {\pm} 70 km. We find Quaoar's density to be \rho = 4.2 {\pm} 1.3 g cm^-3, possibly the highest density in the Kuiper belt.
UV Emission from Elliptical Galaxies Near and Far
Henry C. Ferguson,Thomas M. Brown
Physics , 1997, DOI: 10.1063/1.53743
Abstract: The far-ultraviolet is the most rapidly evolving portion of the spectrum in both very young galaxies and very old galaxies. The ``UV upturn'' in the spectra of elliptical galaxies shortward of 2000 Angstroms offers a promising probe of the ages and chemical evolution of very old galaxies. In early-type non-active galaxies with the bluest 1550-V colors, the bulk of the emission arises from Extreme Horizontal Branch (EHB) stars, along their evolution from the zero-age HB to the white-dwarf cooling curve. The strength of the UV-upturn is governed by the fraction of stars that evolve through the EHB phase, which is in turn governed by age, metallicity, helium abundance, and other parameters such as stellar rotation and binarity that might influence the amount of mass loss on the RGB. Spectral constraints on the nature of the hot stellar population from Astro-2 are reviewed, and new imaging results from the HST Faint Object Camera are presented. Attempts to measure evolution through observations of high-redshift elliptical galaxies in the rest-frame UV are reviewed.
NICMOS Photometry of the Unusual Dwarf Planet Haumea and its Satellites
W. C. Fraser,M. E. Brown
Physics , 2009, DOI: 10.1088/0004-637X/695/1/L1
Abstract: We present here HST NICMOS F110W and F160W observations of Haumea, and its two satellites Hi'iaka and Namaka. From the measured (F110W-F160W) colours of -1.209 +/-0.004, -1.48 +/- 0.06, and -1.4 +/- 0.2 mag for each object, respectively, we infer that the 1.6 imcron water-ice absorption feature depths on Hi'iaka and Namaka are at least as deep as that of Haumea. The light-curve of Haumea is detected in both filters, and we find that the infrared colour is bluer by approximately 2-3% at the phase of the red spot. These observations suggest that the satellites of Haumea were formed from the collision that produced the Haumea collisional family.
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