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41.
The rust fungus Puccinia spegazzinii (Basidiomycotina: Uredinales) has been identified as a potential classical biological control agent for the invasive weed Mikania micrantha (Asteraceae). Long-term, live storage of this pathogen is required for reference. As biotrophs, almost all rusts species cannot be preserved by traditional cryopreservation protocols, which rely on in vitro culture techniques. In addition, the embedded teliospores and delicate basidiospores of this microcyclic rust are not amenable to direct plunge freezing. Continuous culture of the rust on living plants is both laborious and expensive, so a variety of approaches for cryopreservation and storage were tested. These methods included traditional approaches to fungal cryopreservation such as variation of cooling rate regime and alginate encapsulation techniques. However, an in situ cryopreservation technique was the only method identified as having any potential for the long-term cryopreservation of the 10 isolates tested. Material from either petiole or stem tissue remained viable after cryopreservation, determined by the ability of the material to produce basidiospores. However, despite great progress being made in developing an optimal cryopreservation method, infection of the host plant by basidiospores produced from previously cryopreserved teliospores, embedded in leaf petioles, was not achieved. 相似文献
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Molality as a unit of measure for expressing 1H MRS brain metabolite concentrations in vivo 总被引:1,自引:0,他引:1
Knight-Scott J Haley AP Rossmiller SR Farace E Mai VM Christopher JM Manning CA Simnad VI Siragy HM 《Magnetic resonance imaging》2003,21(7):787-797
Absolute concentrations of cerebral metabolite in in vivo 1H magnetic resonance spectroscopy studies (1H-MRS) are widely reported in molar units as moles per liter of tissue, or in molal units as moles per kilogram of tissue. Such measurements require external referencing or assumptions as to local water content. To reduce the scan time, avoid assumptions that may be invalid under specific pathologies, and provide a universally accessible referencing procedure, we suggest that metabolite concentrations from 1H-MRS measurements in vivo be reported in molal units as moles per kilogram of tissue water. Using internal water referencing, a two-compartment water model, a simulated brain spectrum for peak identification, and a spectroscopic bi-exponential spin-spin relaxation segmentation technique, we measured the absolute concentrations for the four common 1H brain metabolites: choline (Cho), myo-inositol (mIno), phosphocreatine + creatine (Cr), and N-acetyl-aspartate (NAA), in the hippocampal region (n = 26) and along the Sylvian fissure (n = 61) of 35 healthy adults. A stimulated echo localization method (20 ms echo time, 10 ms mixing time, 4 s repetition time) yielded metabolite concentrations, uncorrected for metabolite relaxation or contributions from macromolecule resonances, that were expectantly higher than with molar literature values. Along the Sylvian fissure the average concentrations (coefficient of variation (CV)) in mmoles/kg of tissue water were 17.6 (12%) for NAA, 14.2 (9%) for Cr, 3.6 (13%) for Cho, and 13.2 (15%) for mIno. Respective values for the hippocampal region were 15.7 (20%), 14.7 (16%), 4.6 (19%), and 17.7 (26%). The concentrations of the two regions were significantly different (p = 0.001) for NAA, mIno, and Cho, a trend in agreement with previous studies. All gray matter Sylvian fissure CV values, except for NAA, were also in agreement with previous 1H-MRS gray matter studies. The reduced precision of the NAA concentration was attributed to overlapping signal contributions from glutamate and glutamine (Glx), suggesting that a detailed Glx model is critical for accurate quantitation of the NAA 2.02 ppm resonance. The reduced precision of the measurements in the hippocampal region was attributed to poor spectral resolution. 相似文献
43.
Gamble BM Gallagher PA Shoemaker JA Parks AN Freeman DM Schwegel CA Creed JT 《The Analyst》2003,128(12):1458-1461
This paper evaluates the chemical stability of four arsenosugars using tetramethylammonium hydroxide (TMAOH) as an extraction solvent. This solvent was chosen because of the near quantitative removal of these arsenicals from difficult to extract seafood (oysters and shellfish). Four arsenosugars (3-[5'-deoxy-5'-(dimethylarsinoyl)-beta-ribofuranosyloxy]-2-hydroxypropylene glycol--As(328), 3-5'-deoxy-5'-(dimethylarsinoyl)-beta-ribofuranosyloxy]-2-hydroxypropanesulfonic acid--As(392), 3-[5'-deoxy-5'-(dimethylarsinoyl)-beta-ribofuranosyloxy]-2-hydroxypropyl hydrogen sulfate--As(408), and 3-[5'-deoxy-5'-(dimethylarsinoyl)-beta-ribofuranosyloxy]-2-hydroxypropyl-2,3-hydroxypropyl phosphate--As(482)) were evaluated. The stability of these four arsenosugars were studied independently in a solution of 2.5% TMAOH at 60 degrees C over a period of up to 8 h. Two arsenosugars, As(328) and As(392), were found to be relatively stable in this solution for up to 8 h. However, As(408) and As(482) formed detectable quantities of dimethylarsinic acid (DMAA) and As(328) within 0.5 and 2 h, respectively. It was found that 97% of As(408) degrades after 8 h of treatment producing 3.4 times as much DMAA as As(328). This is contrary to As(482), which produces 13 times as much As(328) as DMAA and only 37% of the As(482) was converted by the 8 h treatment at 60 degrees C. These degradation products led to the investigation of weaker TMAOH extraction solvents. Three different concentrations (2.5%, 0.83% and 0.25%) were used to determine the effect of TMAOH concentration on the degradation rate of As(408). By reducing the TMAOH concentration to 0.83%, the conversion of the arsenosugar to As(328) and DMAA is nearly eliminated (less than 5% loss). Arsenosugars, As(408) and As(482), were also studied in 253 mM NaOH to verify the degradation products. The NaOH experiments were conducted to investigate a possible hydroxide based reaction mechanism. Similar degradation plots were found for each arsenosugar when compared to the 2.5% TMAOH data. A mechanism has been proposed for the formation of As(328) from As(408) and As(482) in base via an SN2 reaction (hydroxide attack) at the side chain carbon adjacent to the inorganic ester. The formation of DMAA is observed in all arsenosugars after prolonged exposure. This probably occurs via an SN2 attack at the arsenic atom. 相似文献
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Symonds Ria; Lawson Duncan; Robinson Carol 《Teaching Mathematics and its Applications》2008,27(3):140-149
This article reports the findings of qualitative research undertakento seek to identify the key reasons why some students are notengaging with mathematics support provided by Loughborough University.The research involved a number of focus groups and onthe spot interviews with non-users fromacross the campus. Barriers identified include a lack of awarenessof the location of support and a fear of embarrassment. Furtherinterviews were conducted with regular users of the supportin an attempt to understand how some of these barriers to usagemight be overcome. The article will discuss actions that maybe taken to improve student engagement with mathematics supportand the issue of how student motivation may affect such action. 相似文献
47.
Lowe Terry C. Bishop Alan Burns Carol Hartford Allen Parkin Don Trewhella Jill 《Journal of nanoparticle research》2000,2(3):249-266
Research in the emerging field of nanoscale science and technology has grown steadily at Los Alamos National Laboratory since 1990. This article summarizes some of this work, examining research highlights within the seven key categories of nanoscience in which Los Alamos has ongoing projects, capabilities, and facilities: (1) Materials and chemistry, (2) Theory and modeling, (3) Bioscience, (4) Investigative tools and facilities, (5) Sensors and devices, (6) Synthesis and fabrication, and (7) Education and outreach. Future research horizons are indicated throughout while institutional strategies for advancing nanoscale science are summarized at the end. 相似文献
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Gloria Dion Anne Harvey Carol Jackson Patricia Klag Jinghua Liu Craig Wright 《School science and mathematics》2001,101(8):427-438
This survey investigated the current status of calculator use in classrooms and schools. The results indicated that the prevailing policy in the sample of high schools is to allow the use of calculators during classroom learning activities and tests. Scientific calculators are more frequently used than graphing calculators in algebra I and geometry; whereas, graphing calculators are more frequently used in algebra II and precalculus/trigonometry. At the time of this survey, school policies regarding the use of graphing calculators with symbolic algebra capabilities were still not determined. 相似文献
50.
Nα-tert-Butoxycarbonyl-L-trans-4-hydroxyproline allyl ester (Boc-Hyp-OAll) was glycosylated with 2,3,5-tri-O-benzyl-L-arabinose p-cresylthioglycoside in 60% yield with 4:1 β:α stereoselectivity. Deprotection of N- and C-terminii independently gave a prolyl amine and prolyl carboxylate respectively that were coupled under standard conditions with 1-[bis-(dimethylamino)methylene]-1H-1,2,3-triazolo-[4,5,b]-pyridininium hexafluorophosphate 3-oxide (N-HATU) to give the dimer 1 in 46% yield. These results represent the first steps toward the production of homogeneous oligomers to determine the minimal epitope of the Art v 1 allergen. 相似文献