2,012 research outputs found
Direct reconstruction of dynamical dark energy from observational Hubble parameter data
Reconstructing the evolution history of the dark energy equation of state
parameter directly from observational data is highly valuable in
cosmology, since it contains substantial clues in understanding the nature of
the accelerated expansion of the Universe. Many works have focused on
reconstructing using Type Ia supernova data, however, only a few studies
pay attention to Hubble parameter data. In the present work, we explore the
merit of Hubble parameter data and make an attempt to reconstruct from
them through the principle component analysis approach. We find that current
Hubble parameter data perform well in reconstructing ; though, when
compared to supernova data, the data are scant and their quality is worse. Both
CDM and evolving models can be constrained within at
redshifts
and even at redshifts 0.1 z 1 by
using simulated data of observational quality.Comment: 25 pages, 11 figure
Two-layer Thermally Driven Turbulence: Mechanisms for Interface Breakup
It is commonly accepted that the breakup criteria of drops or bubbles in
turbulence is governed by surface tension and inertia. However, also
{\it{buoyancy}} can play an important role at breakup. In order to better
understand this role, here we numerically study Rayleigh-B\'enard convection
for two immiscible fluid layers, in order to identify the effects of buoyancy
on interface breakup. We explore the parameter space spanned by the Weber
number (the ratio of inertia to surface tension) and the
density ratio between the two fluids , at fixed
Rayleigh number and Prandtl number . At low , the interface
undulates due to plumes. When is larger than a critical value, the
interface eventually breaks up. Depending on , two breakup types are
observed: The first type occurs at small (e.g. air-water
systems) when local filament thicknesses exceed the Hinze length scale. The
second, strikingly different, type occurs at large with roughly (e.g. oil-water systems): The layers undergo a periodic
overturning caused by buoyancy overwhelming surface tension. For both types the
breakup criteria can be derived from force balance arguments and show good
agreement with the numerical results.Comment: 13 pages, 7 figure
Effects of aromatizable and nonaromatizable androgens on the sex inversion of red-spotted grouper (Epinephelus akaara)
The effects of aromatizable 17Ī±-methyltestosterone (MT) and non-aromatizable 17Ī±-methyldihydrotestosterone (MDHT) on sex inversion in red-spotted grouper, Epinephelus akaara, were investigated. Fish were implanted with MT, MDHT and MT+AI (aromatase inhibitor, AI) respectively for one month. The results showed that the three treated groups turned into transitional stage with intersex gonads, which contained atretic oocytes and spermatogenic germ cells at all stages of spermatogenesis. The controls did not change sex. The gonads of more than half MT-implanted fish were in early transitional stages of sex inversion, whereas those of more than half MDHT and MT+AI-implanted fish were in late transitional stages of sex inversion. No difference in serum estradiol-17Ī² (E2) levels between the controls and the treated groups were observed, whereas 11-ketotestosterone (11-KT) and testosterone (T) levels increased in all treated groups. Significantly lower gonadosomatic index (GSI) and gonadal aromatase activity were observed in the treated groups, which were in accordance with the lower mRNA expression of P450aromA. However, P450aromB mRNA expression increased in the MT group, while it did not change in the MDHT group. These results suggest that the sex inversion of red-spotted grouper by MT and MDHT implantation might be due to the suppression of P450aromA gene expression, and resulting in both the decrease of the ovarian estrogen āsecretion, as well as the increase in the 11-KT levels. Furthermore, the main reason for MT being less effective than MDHT might be due to partial aromatization of MT to estrogen
Relationship between Successive Flares in the Same Active Region and Space-Weather HMI Active Region Patch (SHARP) Parameters
A solar active region (AR) may produce multiple notable flares during its
passage across the solar disk. We investigate successive flares from
flare-eruptive active regions, and explore their relationship with solar
magnetic parameters. We examine six ARs in this study, each with at least one
major flare above X1.0. The Space-Weather HMI Active Region Patch (SHARP) is
employed in this study to parameterize the ARs. We aim to identify the most
flare-related SHARP parameters and lay foundation for future practical flare
forecasts. We first evaluate the correlation coefficients between the SHARP
parameters and the successive flare production. Then we adopt a Natural
Gradient Boost (NGBoost) method to analyze the relationship between the SHARP
parameters and the successive flare bursts. Based on the correlation analysis
and the importance distribution returned from NGBoost, we select 8 most
flare-related SHARP parameters. Finally, we discuss the physical meanings of
the 8 selected parameters and their relationship with flare production.Comment: 18 pages; 9 figures; Accepted for publication in Ap
Effects Of Simultaneous CO2 Addition To The Fuel And Oxidizer Streams On Soot Formation In Co-flow Diffusion Ethylene Flame
Soot formation in a co-flow diffusion ethylene flame with the addition of CO2 to the fuel (the CO2-F), oxidizer (the CO2-O), and fuel/oxidizer (the CO2-F/O) streams was numerically and experimentally investigated in this study. The effects of different CO2 addition ways on soot inception, soot condensation, H-abstraction-C2H2-addition (HACA) and oxidation by O2/OH processes, were quantitatively analyzed by introducing the integrated reaction rates over the whole computational domain. The simulated and experimental results showed that the CO2-F/O was the most effective in inhibiting soot formation and flame temperature, followed by the CO2-O, and the CO2-F. Compared with the CO2-F, the suppression effect of the CO2-O on soot inception was weaker due to the higher concentration of benzo(ghi) fluoranthene (BGHIF). Since the rate of C4H2 formation via C2H4 ā C2H3 ā C2H2 ā C4H2 was inhibited by the CO2-O, lowering the consumption rate of acenaphthalene (A2R5) via C4H2 + A2R5=\u3eA4, more A2R5 converted to BGHIF via A2R5 ā A2- ā A2 ā BGHIF. The suppression effects of different ways of CO2 addition on HACA surface growth and soot condensation were identical: CO2-F \u3c CO2-O \u3c CO2-F/O. The decrease of benzo(a)pyrene (BAPYR) mole fraction accounted for the decline of soot condensation rate, and the decreases of H and OH mole fractions were responsible for the drop of HACA surface growth rate. Compared with the CO2-F, the CO2-O and the CO2-F/O had stronger suppression effects on the soot oxidation by O2 process due to the lower concentration of O2 in the oxidizer stream. Whichever CO2 addition ways were adopted, the soot oxidation by O2 process was more sensitive than the soot oxidation by OH process with the CO2 addition
Comparaison de la morphologie du pied entre les enfants chinois et mongoliens
Knowledge of foot morphology is fundamental to optimize childrenās footwear design. The aim of this study is to compare the foot morphology of Chinese and Mongolian children from 7 to 14 years old. Relative data of 339 Mongolian children and another matched 379 Chinese children were collected using 3D foot scanner. The findings of this study are as follows: i) the absolute foot length of Chinese children is significantly greater than that of Mongolian children of the same age; ii) Mongolian children show significantly greater heel width, toe thickness, lateral malleolus height, instep height and ball girth compared to Chinese children of the same age. The foot width of Chinese children is significantly greater than that of Mongolian children of the same age; iii) Chinese children have a higher risk of hallux valgus than Mongolian children of both sexes. Small variations in foot morphology discussed in this paper could be useful when considering the shoes design for Mongolian and Chinese children. Ā© 2020 by the author(s)
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