40 research outputs found
Quenching depends on morphologies: implications from the ultraviolet-optical radial color distributions in Green Valley Galaxies
In this Letter, we analyse the radial UV-optical color distributions in a
sample of low redshift green valley (GV) galaxies, with the Galaxy Evolution
Explorer (GALEX)+Sloan Digital Sky Survey (SDSS) images, to investigate how the
residual recent star formation distribute in these galaxies. We find that the
dust-corrected colors of early-type galaxies (ETGs) are flat out to
, while the colors turn blue monotonously when for
late-type galaxies (LTGs). More than a half of the ETGs are blue-cored and have
remarkable positive NUV color gradients, suggesting that their star
formation are centrally concentrated; the rest have flat color distributions
out to . The centrally concentrated star formation activity in a large
portion of ETGs is confirmed by the SDSS spectroscopy, showing that 50 %
ETGs have EW(H) \AA. For the LTGs, 95% of them show uniform
radial color profiles, which can be interpreted as a red bulge plus an extended
blue disk. The links between the two kinds of ETGs, e.g., those objects having
remarkable "blue-cored" and those having flat color gradients, are less known
and require future investigations. It is suggested that the LTGs follow a
general picture that quenching first occur in the core regions, and then
finally extend to the rest of the galaxy. Our results can be re-examined and
have important implications for the IFU surveys, such as MaNGA and SAMI.Comment: ApJ Letter, accepted. Five figure
An Econometric Model of Credit Spreads with Rebalancing, ARCH and Jump Effects
In this paper, we examine the dynamic behavior of credit spreads on corporate bond portfolios. We propose an econometric model of credit spreads that incorporates portfolio rebalancing, the near unit root property of spreads, the autocorrelation in spread changes, the ARCH conditional heteroscedasticity, jumps, and lagged market factors. In particular, our model is the first that takes into account explicitly the impact of rebalancing and yields estimates of the absorbing bounds on credit spreads induced by such rebalancing. We apply our model to nine Merrill Lynch daily series of option-adjusted spreads with ratings from AAA to C for the period January 1997 through August 2002. We find no evidence of mean reversion in these credit-spread series over our sample period. However, we find ample evidence of both the ARCH effect and jumps in the data especially in the investment-grade credit spread indices. Incorporating jumps into the ARCH type conditional variance results in significant improvements in model diagnostic tests. We also find that while log spread variations depend on both the lagged Russell 2000 index return and lagged changes in the slope of the yield curve, the time-varying jump intensity of log credit spreads is correlated with the lagged stock market volatility. Finally, our results indicate the ARCH-jump specification outperforms the ARCH specification in the out-of-sample, one-step-ahead forecast of credit spreads
An Econometric Model of Credit Spreads with Rebalancing, ARCH and Jump Effects
In this paper, we examine the dynamic behavior of credit spreads on corporate bond portfolios. We propose an econometric model of credit spreads that incorporates portfolio rebalancing, the near unit root property of spreads, the autocorrelation in spread changes, the ARCH conditional heteroscedasticity, jumps, and lagged market factors. In particular, our model is the first that takes into account explicitly the impact of rebalancing and yields estimates of the absorbing bounds on credit spreads induced by such rebalancing. We apply our model to nine Merrill Lynch daily series of option-adjusted spreads with ratings from AAA to C for the period January 1997 through August 2002. We find no evidence of mean reversion in these credit-spread series over our sample period. However, we find ample evidence of both the ARCH effect and jumps in the data especially in the investment-grade credit spread indices. Incorporating jumps into the ARCH type conditional variance results in significant improvements in model diagnostic tests. We also find that while log spread variations depend on both the lagged Russell 2000 index return and lagged changes in the slope of the yield curve, the time-varying jump intensity of log credit spreads is correlated with the lagged stock market volatility. Finally, our results indicate the ARCH-jump specification outperforms the ARCH specification in the out-of-sample, one-step-ahead forecast of credit spreads
From outside-in to inside-out: galaxy assembly mode depends on stellar mass
In this Letter, we investigate how galaxy mass assembly mode depends on
stellar mass , using a large sample of 10, 000 low redshift
galaxies. Our galaxy sample is selected to have SDSS R_{90}>5\arcsec.0, which
allows the measures of both the integrated and the central NUV color
indices. We find that: in the NUV) green valley, the
M_{\ast}<10^{10}~M_{\sun} galaxies mostly have positive or flat color
gradients, while most of the M_{\ast}>10^{10.5}~M_{\sun} galaxies have
negative color gradients. When their central index values exceed
1.6, the M_{\ast}<10^{10.0}~M_{\sun} galaxies have moved to the UV red
sequence, whereas a large fraction of the M_{\ast}>10^{10.5}~M_{\sun}
galaxies still lie on the UV blue cloud or the green valley region. We conclude
that the main galaxy assembly mode is transiting from "the outside-in" mode to
"the inside-out" mode at M_{\ast}
10^{10.5}~M_{\sun}. We argue that the physical origin of this is the
compromise between the internal and the external process that driving the star
formation quenching in galaxies. These results can be checked with the upcoming
large data produced by the on-going IFS survey projects, such as CALIFA, MaNGA
and SAMI in the near future.Comment: Accepted for publication in ApJL,6 pages, 5 figure
An Economeic Model of Credit Spreads with Rebalancing, ARCH and Jump Effects
In this paper, we examine the dynamic behavior of credit spreads on corporate bond portfolios. We propose an economeic model of credit spreads that incorporates portfolio rebalancing, the near unit root property of spreads, the autocorrelation in spread changes, the ARCH conditional heteroscedasticity, jumps, and lagged market factors. In particular, our model is the first that takes into account explicitly the impact of rebalancing and yields estimates of the absorbing bounds on credit spreads induced by such rebalancing. We apply our model to nine Merrill Lynch daily series of option-adjusted spreads with ratings from AAA to C for the period January, 1997 through August, 2002. We find no evidence of mean reversion in these credit spread series over our sample period. However, we find ample evidence of both the ARCH effect and jumps in the data especially in the investment-grade credit spread indices. Incorporating jumps into the ARCH type conditional variance results in significant improvements in model diagnostic tests. We also find that while log spread variations depend on both the lagged Russell 2000 index return and lagged changes in the slope of the yield curve, the time-varying jump intensity of log credit spreads is correlated with the lagged stock market volatility. Finally, our results indicate the ARCH-jump specification outperforms the ARCH specification in the out-of-sample, one-step-ahead forecast of credit spreads
Explicit Topology Optimization of Conforming Voronoi Foams
Topology optimization is able to maximally leverage the high DOFs and
mechanical potentiality of porous foams but faces three fundamental challenges:
conforming to free-form outer shapes, maintaining geometric connectivity
between adjacent cells, and achieving high simulation accuracy. To resolve the
issues, borrowing the concept from Voronoi tessellation, we propose to use the
site (or seed) positions and radii of the beams as the DOFs for open-cell foam
design. Such DOFs cover extensive design space and have clear geometrical
meaning, which makes it easy to provide explicit controls (e.g. granularity).
During the gradient-based optimization, the foam topology can change freely,
and some seeds may even be pushed out of the shape, which greatly alleviates
the challenges of prescribing a fixed underlying grid. The mechanical property
of our foam is computed from its highly heterogeneous density field counterpart
discretized on a background mesh, with a much improved accuracy via a new
material-aware numerical coarsening method. We also explore the
differentiability of the open-cell Voronoi foams w.r.t. its seed locations, and
propose a local finite difference method to estimate the derivatives
efficiently. We do not only show the improved foam performance of our Voronoi
foam in comparison with classical topology optimization approaches, but also
demonstrate its advantages in various settings, especially when the target
volume fraction is extremely low
Spatially resolved Spectro-photometry of M81: Age, Metallicity and Reddening Maps
In this paper, we present a multi-color photometric study of the nearby
spiral galaxy M81, using images obtained with the Beijing Astronomical
Observatory 60/90 cm Schmidt Telescope in 13 intermediate-band filters from
3800 to 10000{\AA}. The observations cover the whole area of M81 with a total
integration of 51 hours from February 1995 to February 1997. This provides a
multi-color map of M81 in pixels of 1\arcsec.7 \times 1\arcsec.7. Using
theoretical stellar population synthesis models, we demonstrate that some BATC
colors and color indices can be used to disentangle the age and metallicity
effect. We compare in detail the observed properties of M81 with the
predictions from population synthesis models and quantify the relative chemical
abundance, age and reddening distributions for different components of M81. We
find that the metallicity of M81 is about with no significant
difference over the whole galaxy. In contrast, an age gradient is found between
stellar populations of the central regions and of the bulge and disk regions of
M81: the stellar population in its central regions is older than 8 Gyr while
the disk stars are considerably younger, Gyr. We also give the
reddening distribution in M81. Some dust lanes are found in the galaxy bulge
region and the reddening in the outer disk is higher than that in the central
regions.Comment: Accepted for publication in AJ (May 2000 issue). 27 pages including 6
figures. Uses AASTeX aasms4 styl
Association between pelvic floor muscle strength and sexual function based on PISQ-12—an analysis of data from a multicenter cross-sectional study on 735 nulliparae during pregnancy
BackgroundPelvic floor muscle strength is well-known to be associated with female sexual function. However, there were a few studies that reported on the relationship between pelvic floor muscle strength and female sexual function in pregnant women, and the presented results were inconsistent. Nulliparae represent a specific cohort with simplicity to exclude confounding factors that are caused by parity. The present study aimed to explore the association of pelvic floor muscle strength and sexual function based on the Pelvic Organ Prolapse/Urinary Incontinence Sexual Questionnaire (PISQ-12) of nulliparae during pregnancy.MethodsThis is the second analysis of the baseline data from a randomized controlled trial (RCT), which aimed to study the protective efficacy of pelvic floor muscle training on stress urinary incontinence at 6th week postpartum (registration number: ChiCTR2000029618). Nulliparae aged 20–40 years with singleton pregnancy before 16 weeks of gestation were enrolled in this study, and data, including participants' demographic information, the Modified Oxford Scale (MOS), and PISQ-12, were collected. Eligible nulliparae were divided into two groups: Group MOS > 3 and Group MOS ≤ 3. Demographic information of the two groups was compared. Sexual function based on the PISQ-12 scores of the two groups was compared. A comparison of the PISQ-12 scores between the two groups was calculated by the Mann–Whitney U-test using SPSS version 23.0.ResultsA total of 735 eligible nulliparae were enrolled in this study. Along with MOS grading up, PISQ-12 scores tended to get lower. Of the 735 nulliparae, there were 378 and 357 participants included in Group MOS > 3 and Group MOS ≤ 3, respectively. The PISQ-12 scores of Group MOS > 3 were significantly lower than those of Group MOS ≤ 3 (11 vs. 12, p < 0.001). The scores of the frequency of feeling sexual desire, orgasm achievement, sexual excitement, sexual activity satisfaction, sexual intercourse pain, fear of urinary incontinence, and negative emotion reactions with the sexual intercourse of Group MOS > 3 were lower than those of Group MOS ≤ 3 (p < 0.05).ConclusionPelvic floor muscle strength was positively associated with sexual function based on the questionnaire of young nulliparae during their first trimester. Up to half of the nulliparae during the first trimester were suffering from weak pelvic floor muscle strength and nearly a quarter of the nulliparae were facing this weakness combined with sexual dysfunction.Trial registrationThis study has been registered at http://www.chictr.org.cn (registration number: ChiCTR2000029618)