The Age of the Old Transgression Sequence in the Pearl River Delta, China

The Pearl River Delta （PRD） is located in the north coast area of the South China Sea （SCS）. As one of the largest delta in China, only the two latest events among the several tens of eustatic fluctuations occurring in the Quaternary were recorded in almost whole area of the PRD.

The age measures and its layer sequence tratigraphy of Late Quaternary sediment in Lushan Dajiaochang of China

Through the scientific investigation on Lushan for a long time, detailed studies have been carried out on the geologic stratum section of Late Quaternary in Dajiaochang. The series age data of complete stratigraphic section and full time formation since 400 kaBP were based on the results of the analyses using the dating methods with various instruments such as the ancient geomagnetism, electronics spin resonance （ESR）, 36C1 and lumines- cence dating, etc. Corresponding to these data, it identified the paleomagnetic polarity events including Biwa- III event （320 kaBP）, Biwa- 1I event （260 kaBP）, Biwa- I event （180 kaBP, scarcity due to the disturbance of the iron dish）, Blake event （100 kaBP） and Laschamp event （20 kaBP, didn＇t grow due to the activities of the surface）, etc. Combined with the sequence stratigraphy, layer type characteristics and its sediment environment, the strati- graphic can be divided into 4 stages of development respectively ： Stage [ is the climate period of glacial epoch （200-400 kaBP）; stage 11 is the climate period of interglacial epoch （100-200 kaBP）; stage llI is the climate peri- od of periglacial epoch （10-100 kaBP）; stage IV is the climate period ofpostglacial epoch （0-10 kaBP）.

The reliability of age measurements for Young Stellar Objects from Hertzsprung-Russell or color-magnitude diagrams

The possibility to estimate ages and masses of Young Stellar Objects （YSOs） from their location in the Hertzsprnng-Russell diagram （HRD） or a color- magnitude diagram provides a very important tool for the investigation of fundamen- tal questions related to the processes of star formation and early stellar evolution. Age estimates are essential for studies of the temporal evolution of circumstellar material around YSOs and the conditions for planet formation. The characterization of the age distribution of the YSOs in a star forming region allows researchers to reconstruct the star formation history and provides important information on the fundamental ques- tion of whether star formation is a slow or a fast process. However, the reliability of these age measurements and the ability to detect possible age spreads in the stellar population of star forming regions are fundamentally limited by several factors. The variability of YSOs, unresolved binary components, and uncertainties in the calibra- tions of the stellar parameters cause uncertainties in the derived luminosities that are usually much larger than the typical photometry errors. Furthermore, the pre-main se- quence evolution track of a YSO depends to some degree on the initial conditions and the details of its individual accretion history. I discuss how these observational and model uncertainties affect the derived isochronal ages, and demonstrate how neglect- ing or underestimating these uncertainties can easily lead to severe misinterpretations, gross overestimates of the age spread, and ill-based conclusions about the star for- marion history. These effects are illustrated by means of Monte-Carlo simulations of observed star clusters with realistic observational uncertainties. The most important points are as follows. First, the observed scatter in the HRD must not be confused with a genuine age spread, but is always just an upper limit to the true age spread. Second, histograms of isochronal ages naturally show a decreasing number of stars for ages above the median, a pattern that can be misinterpreted as an accelerating star formation rate. Third, it is emphasized that many star forming regions consist of sev- eral sub-groups, which often have different ages. If these distinct stellar populations cannot be disentangled （e.g., due to projection effects） and the HRD of all stars in the region is used for an age analysis, it is very difficult （often impossible） to discern between the scenario of an extended period of star formation （i.e. a large age spread） and the alternative concept of a temporal sequence of several discrete star formation episodes. Considering these factors, most observations of star forming regions suggest that age spreads are usually smaller than the corresponding crossing times, supporting the scenario of fast and dynamic star formation.

Molecular analysis of bacterial community in the tap water with different water ages of a drinking water distribution system

Bacterial community in the drinking water distribution system （DWDS） was regulated by multiple environmental factors, many of which varied as a function of water age. In this study, four water samples with different water ages, including finished water （FW, 0 d） and tap water （TW） [TWI （1 d）, TW2（2 d） and TW3（3 d）], were collected along with the mains of a practical DWDS, and the bacterial community was investigated by high-throughput sequencing technique. Results indicated that the residual chlorine declined with the increase of water age, accompanied by the increase of dissolved organic matter, total bacteria counts and bacterial diversity （Shannon）. For bacterial community composition, although Proteobacteria phylum （84.12%-97.6%） and Alphaproteobacteria class （67.42c/,~93.09%） kept dominate, an evident regular was observed at the order level. In detail, the relative abundance of most of other residual orders increased with different degrees from the start to the end of the DWDS, while a downward trend was uniquely observed in terms of Rhizobiales, who was inferred to be chlorine-resistant and be helpful for inhibiting pipes corrosion. Moreover, some OTUs were found to be closely related with species possessing pathogenicity and chlorine-resistant ability, so it was recommended that the use of agents other than chlorine or agents that can act synergically with chlorine should be developed for drinking water disinfection. This paper revealed bacterial community variations along the mains of the DWDS and the result was helpful for understanding bacterial ecology in the DWDS.