39,381 research outputs found
On the Bergman representative coordinates
We study the set where the so-called Bergman representative coordinates (or
Bergman functions) form an immersion. We provide an estimate of the size of a
maximal geodesic ball with respect to the Bergman metric, contained in this
set. By concrete examples we show that these estimates are the best possible.Comment: 20 page
From the Complete Yang Model to Snyder's Model, de Sitter Special Relativity and Their Duality
By means of Dirac procedure, we re-examine Yang's quantized space-time model,
its relation to Snyder's model, the de Sitter special relativity and their
UV-IR duality. Starting from a dimensionless dS_5-space in a 5+1-d Mink-space a
complete Yang model at both classical and quantum level can be presented and
there really exist Snyder's model, the dS special relativity and the duality.Comment: 7 papge
Ultrasonic-assisted extraction and evaluation of biological activities of flavonoids from Flemingia philippinensis Merr et Rolfe
Purpose: To develop a simple and rapid method for extracting total flavonoids from the roots of Flemingia philippinensis and to investigate the antioxidant and anti-tumor activities of the extracts of the materials from various locations in China.Methods: The total flavonoids in F. philippinensis were obtained by ultrasonic-assisted conventional solvent extraction method, and the extraction conditions were optimized by single factor and orthogonal test. 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging and anti-tumor activities, using 3-(4,5- dimethylthiazol-2-yl)- 2,5-diphenyltetrazolium bromide (MTT) assay, of the extract were evaluated. The contents of flemiphilippinin A, auriculasin, 5,7,3',4'-tetrahydroxy-6,8 –diprenylisoflavone and dorsmanins I were also determined.Results: Optimal extraction conditions were as follows: extraction time, 40 min; methanol concentration, 85 %; and solvent to solid ratio, 40 mL/g; and number of extraction, once. Total flavonoid content varied greatly (3.7 - 14.35 %) among the 19 samples collected from different origins in China. Flemiphilippin A, 5,7,3',4'- tetrahydroxy-6,8 -diprenylisoflavone, auriculasin and dorsmanins I showed varying DPPH radical scavenging activities with effective half maximal concentration (EC50) of 18.36, 23.59, 57.25 and 63.54 μg/mL, respectively. Flemiphilippinin A (5 μg/mL) also exhibited some level of antitumor activity against human hepatocellular carcinoma cell (BEL-7402), human lung epithelial (A-549) and human ileocecal adenocarcinoma cell (HCT-8) with inhibition of 91.13 ± 1.6, 91.22 ± 3.23, and 79.77 ± 3.57 %, respectively.Conclusion: Total flavonoids can be extracted efficiently from F. philippinensis by ultrasonic-assisted extraction method. Flemiphilippinin A has a potential for use in medicine as an antioxidant and antitumor drug
Magnetic Reconnection resulting from Flux Emergence: Implications for Jet Formation in the lower solar atmosphere?
We aim at investigating the formation of jet-like features in the lower solar
atmosphere, e.g. chromosphere and transition region, as a result of magnetic
reconnection. Magnetic reconnection as occurring at chromospheric and
transition regions densities and triggered by magnetic flux emergence is
studied using a 2.5D MHD code. The initial atmosphere is static and isothermal,
with a temperature of 20,000 K. The initial magnetic field is uniform and
vertical. Two physical environments with different magnetic field strength (25
G and 50 G) are presented. In each case, two sub-cases are discussed, where the
environments have different initial mass density. In the case where we have a
weaker magnetic field (25 G) and higher plasma density (
cm), valid for the typical quiet Sun chromosphere, a plasma jet would be
observed with a temperature of 2--3 K and a velocity as high as
40 km/s. The opposite case of a medium with a lower electron density
( cm), i.e. more typical for the transition region,
and a stronger magnetic field of 50 G, up-flows with line-of-sight velocities
as high as 90 km/s and temperatures of 6 10 K, i.e. upper
transition region -- low coronal temperatures, are produced. Only in the latter
case, the low corona Fe IX 171 \AA\ shows a response in the jet which is
comparable to the O V increase. The results show that magnetic reconnection can
be an efficient mechanism to drive plasma outflows in the chromosphere and
transition region. The model can reproduce characteristics, such as temperature
and velocity for a range of jet features like a fibril, a spicule, an hot X-ray
jet or a transition region jet by changing either the magnetic field strength
or the electron density, i.e. where in the atmosphere the reconnection occurs.Comment: 11 pages, 13 figures, 2 table
- …