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21.
A new approach to the synthesis of indolizidine and pyrrolizidine skeletons is reported. (-)-Lentiginosine and (1R,2R,7aR)-dihydroxypyrrolizidine have both been synthesized in 13 steps from di-O-isopropylidene-d-mannitol. The common key intermediate is (-)-dihydroxyproline benzyl ester 10. 相似文献
22.
A general synthesis approach to pyrroloquinolizidines (3,4,5,5a,6,7,8-heptahydropyrrolo[2,1,5-de]quinolizines) via a münchnone 1,3-dipolar cycloaddition is reported. The approach was applied to the synthesis of an unnatural pyrroloquinolizidine homologue of myrmicarin 215B. 相似文献
23.
A De A Mitra A Ray SR Banerjee M Sengupta A Chatterjee S Kailas HS Patel MG Betigiri SK Dutta 《Pramana》1999,53(3):549-552
In this paper, we report our measurements of back-angle oxygen and carbon particle yields from 16O+89Y, 12C+93Nb reactions forming the same compound nucleus 105Ag at the same excitation energy and spin distribution. We find anomalously large oxygen yield and entrance channel dependence
at high excitation energies from 16O+89Y reaction implying formation of a dinuclear orbiting complex. Possible connection between nuclear orbiting and fast fission
is also discussed. 相似文献
24.
John Angle 《The Journal of mathematical sociology》2013,37(4):217-270
Population biologists and comparative animal behaviorists assume that competition between members of the same species allocates resource utility, but they cannot validate that assumption without a unidimensional measure of resource utility such as money, which they do not have since they leave humans to the social sciences. One of the social sciences, economics takes the point of view that pervasive zero-sum competition between people does not determine wage andsalary incomes. The present article validates the assumption of populationbiology and comparative animal behavior that competition within a species allocates resource utility by finding the statistical signature of pervasive zero-sum competition in longitudinal data on individual wage and salary incomes. 相似文献
25.
Soni Mehul N. Kumar Sivakumar Prasanth Johar SR Kaid Pandya Himanshu A. 《Structural chemistry》2019,30(4):1323-1334
Structural Chemistry - Rheumatoid arthritis (RA) is an autoimmune disorder that causes chronic inflammation with periodic bursts of activity in multiple synovial joints which lead to irreversible... 相似文献
26.
Indolizidine type alkaloids have been attractive synthetic targets due to their biological activity. The total synthesis of (-)-indolizidine 195B via a general route, which could potentially be used to prepare other indolizidine alkaloids such as (-)-gephyrotoxin 223AB and (-)-myrmicarin 237A, is described. 相似文献
27.
Angle J Aprile E Arneodo F Baudis L Bernstein A Bolozdynya AI Coelho LC Dahl CE DeViveiros L Ferella AD Fernandes LM Fiorucci S Gaitskell RJ Giboni KL Gomez R Hasty R Kastens L Kwong J Lopes JA Madden N Manalaysay A Manzur A McKinsey DN Monzani ME Ni K Oberlack U Orboeck J Plante G Santorelli R dos Santos JM Schulte S Shagin P Shutt T Sorensen P Winant C Yamashita M;XENON Collaboration 《Physical review letters》2011,107(5):051301
We report results of a search for light (?10 GeV) particle dark matter with the XENON10 detector. The event trigger was sensitive to a single electron, with the analysis threshold of 5 electrons corresponding to 1.4 keV nuclear recoil energy. Considering spin-independent dark matter-nucleon scattering, we exclude cross sections σ(n)>7×10(-42) cm(2), for a dark matter particle mass m(χ)=7 GeV. We find that our data strongly constrain recent elastic dark matter interpretations of excess low-energy events observed by CoGeNT and CRESST-II, as well as the DAMA annual modulation signal. 相似文献
28.
Low-intensity pulsed ultrasound (LIPUS) is an established therapy for fracture repair and has been used widely in the clinics, but its underlying mechanism of action remains unclear. The aim of the current research was to determine the effect of LIPUS on gap junctional cell-to-cell intercellular communication in rat bone marrow stromal cells (BMSC) in vitro and to determine whether the ability of BMSCs to communicate by gap junctions would affect their response to LIPUS. Single or daily-multiple LIPUS treatment at 1.5 MHz, 30 mW/cm2, for 20 min was applied to BMSC. We demonstrated that BMSC form functional gap junctions and single LIPUS treatment significantly increased the intracellular dye transfer between BMSC. In addition, activated phosphorylation of ERK1/2 and p38 by LIPUS stimulation was diminished when cells were treated with a gap junction inhibitor 18β-glycyrrhetinic acid (18β). We further demonstrated that 18β diminished the significant increase in alkaline phosphatase activity following LIPUS stimulation. These results suggest a potential role of gap junctional cell-to-cell intercellular communication on the effects of LIPUS in BMSC. 相似文献
29.
Kinks in the STEM Pipeline: Tracking STEM Graduation Rates Using Science and Mathematics Performance
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In an effort to maintain the global competitiveness of the United States, ensuring a strong Science, Technology, Engineering and Mathematics (STEM) workforce is essential. The purpose of this study was to identify high school courses that serve as predictors of success in college level gatekeeper courses, which in turn led to the successful completion of STEM degrees. Using a purposive sample of 893 students who had declared a STEM major between the fall of 2006 and the spring of 2008, data were collected on students' high school grades, college grades, national test scores, grade point average, gender, and ethnicity. Using analysis of variance, correlations, multiple discriminant function analysis, and multiple regression models we found that high school calculus, physics, and chemistry (respectively) were predictors of success in STEM gatekeeper college courses. Then using those courses, we constructed a predictive model of STEM degree completion. The implications of this study highlight and reinforce the importance of providing rigorous mathematics and science courses at the high school level, as well as provide some evidence of a potential mediated model of the relationship between high school performance, college performance, and graduating with a STEM degree. 相似文献