13 research outputs found
Investigation on unfrozen water content models of freezing soils
Unfrozen water content is a significant hydro-thermal property in numerical modeling in cold regions. Although numerous models have been developed to mimic the variation of unfrozen water content with subzero temperature, comprehensive evaluation of unfrozen water content models is scarce. This study collected a total of 29 models and divided them into four categories, namely, theoretical models, soil water characteristic curve (SWCC)-based models, empirical models, and estimation models. These models were evaluated with 1278 experimental points from 16 studies covering multiple soil types, including 24 clays, 18 silty clays, 7 silts, 19 sands, and 10 sandstones. Root mean square error and average deviations were applied to judge the performance of these models. Most unfrozen water content models can well simulate the relationship between unfrozen water content and subzero temperature. Among the aforementioned four categories of unfrozen water content models, Lizhm et al. model, Fredlund and Xing (C=1)-Wen model, Kozlowski empirical model, and Kozlowski estimation model performed best in their respective categories. Compared to the rest three categories, estimation models can be applied to predict the variation of unfrozen water content with subzero temperature by some easy-to-obtain soil physical parameters and provide guidance for the development of unfrozen water content models
Probing the Galactic halo with RR Lyrae stars -- IV. On the Oosterhoff dichotomy of RR Lyrae stars
We use 3653 (2661 RRab, 992 RRc) RR Lyrae stars (RRLs) with 7D (3D position,
3D velocity, and metallicity) information selected from SDSS, LAMOST, and Gaia
EDR3, and divide the sample into two Oosterhoff groups (Oo I and Oo II)
according to their amplitude-period behaviour in the Bailey Diagram. We present
a comparative study of these two groups based on chemistry, kinematics, and
dynamics. We find that Oo I RRLs are relatively more metal rich, with
predominately radially dominated orbits and large eccentricities, while Oo II
RRLs are relatively more metal poor, and have mildly radially dominated orbits.
The Oosterhoff dichotomy of the Milky Way's halo is more apparent for the
inner-halo region than for the outer-halo region. Additionally, we also search
for this phenomenon in the halos of the two largest satellite galaxies, the
Large and Small Magellanic clouds (LMC, SMC), and compare over different bins
in metallicity. We find that the Oosterhoff dichotomy is not immutable, and
varies based on position in the Galaxy and from galaxy-to-galaxy. We conclude
that the Oosterhoff dichotomy is the result of a combination of stellar and
galactic evolution, and that it is much more complex than the dichotomy
originally identified in Galactic globular clusters