Biomineralization was a key development in a wide variety of organisms,yet its history prior to the Ediacaran remains poorly understood.In this paper,we describe~1420-1330 million year old microscopic tubes preserved ...Biomineralization was a key development in a wide variety of organisms,yet its history prior to the Ediacaran remains poorly understood.In this paper,we describe~1420-1330 million year old microscopic tubes preserved as siderite(FeCO_(3)).In size and shape these tubes closely resemble cyanobacterial sheaths forming mineralized mats.We consider two competing explanations for their formation.First,the tubes and associated sediment were originally composed of Ca-carbonate that was subsequently replaced by siderite.In this case,siderite mineralization was early,but post-mortem,as in early silicification,and preferentially preserved the more resilient sheath.However,no relict calcite is observed.Second,the Fe-carbonate mineralogy of the tubes and sediment is synsedimentary.In this case,photosynthetic oxygen may have precipitated Fe-oxyhydroxide that was promptly converted to siderite by dissimilatory iron reduction(DIR).Primary siderite mineralization of cyanobacteria has not been described before.Both explanations link photosynthetic processes to preferential sheath mineralization during the life of the cyanobacteria,as observed in present-day calcified cyanobacteria.This process might include CO_(2)-concentrating mechanisms(CCMs)linked to relatively low levels of atmospheric CO_(2),consistent with empirical estimates of mid-Proterozoic CO_(2)levels based on paleosols and weathering rinds.In either case,these cyanobacterium-like fossils preserved in siderite provide an early example of biomineralization and suggest the interactive in-fluences of both metabolic processes and ambient seawater chemistry.展开更多
The advantages of the demand control ventilation system(DCV)have been widely discussed in previous research studies.However,the literature has not addressed the benefits of DCV on controlling indoor CO_(2)concentratio...The advantages of the demand control ventilation system(DCV)have been widely discussed in previous research studies.However,the literature has not addressed the benefits of DCV on controlling indoor CO_(2)concentration and minimizing cooling energy consumption for school buildings located in extremely hot climates.Therefore,this paper contributes to the development of DCV and mechanical ventilation systems through a comprehensive evaluation of these systems to maintain acceptable indoor air quality(IAQ)while minimizing cooling energy demands for school buildings located in the harsh hot climate of Saudi Arabia.The evaluation is based on a calibrated whole-building energy model and validated IAQ predictions using field data obtained from a school case study in Jeddah.The results of this research study confirm that hourly and sub-hourly monitoring of indoor CO_(2)concentration is required to ensure optimal design and operation of the ventilation systems in schools.In addition,the analyses indicate that a 13%increase in cooling energy end-use can result for any additional 0.1 students/m^(2)density increase in the classrooms.However,the energy penalties related to ventilation needs can be reduced by up to 25%using DCV instead of conventional mechanical ventilation systems for school buildings located in Saudi Arabia’s hot climate.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.41930320,41972028)the National Key Research and Development Project of China(Grant No.2020YFA0714803)the Chinese"111"Project(Grant No.B20011)。
文摘Biomineralization was a key development in a wide variety of organisms,yet its history prior to the Ediacaran remains poorly understood.In this paper,we describe~1420-1330 million year old microscopic tubes preserved as siderite(FeCO_(3)).In size and shape these tubes closely resemble cyanobacterial sheaths forming mineralized mats.We consider two competing explanations for their formation.First,the tubes and associated sediment were originally composed of Ca-carbonate that was subsequently replaced by siderite.In this case,siderite mineralization was early,but post-mortem,as in early silicification,and preferentially preserved the more resilient sheath.However,no relict calcite is observed.Second,the Fe-carbonate mineralogy of the tubes and sediment is synsedimentary.In this case,photosynthetic oxygen may have precipitated Fe-oxyhydroxide that was promptly converted to siderite by dissimilatory iron reduction(DIR).Primary siderite mineralization of cyanobacteria has not been described before.Both explanations link photosynthetic processes to preferential sheath mineralization during the life of the cyanobacteria,as observed in present-day calcified cyanobacteria.This process might include CO_(2)-concentrating mechanisms(CCMs)linked to relatively low levels of atmospheric CO_(2),consistent with empirical estimates of mid-Proterozoic CO_(2)levels based on paleosols and weathering rinds.In either case,these cyanobacterium-like fossils preserved in siderite provide an early example of biomineralization and suggest the interactive in-fluences of both metabolic processes and ambient seawater chemistry.
基金was funded by the Deanship of Scientific Research(DSR)at King Abdulaziz University,Jeddah(No.KEP-1-135-41).
文摘The advantages of the demand control ventilation system(DCV)have been widely discussed in previous research studies.However,the literature has not addressed the benefits of DCV on controlling indoor CO_(2)concentration and minimizing cooling energy consumption for school buildings located in extremely hot climates.Therefore,this paper contributes to the development of DCV and mechanical ventilation systems through a comprehensive evaluation of these systems to maintain acceptable indoor air quality(IAQ)while minimizing cooling energy demands for school buildings located in the harsh hot climate of Saudi Arabia.The evaluation is based on a calibrated whole-building energy model and validated IAQ predictions using field data obtained from a school case study in Jeddah.The results of this research study confirm that hourly and sub-hourly monitoring of indoor CO_(2)concentration is required to ensure optimal design and operation of the ventilation systems in schools.In addition,the analyses indicate that a 13%increase in cooling energy end-use can result for any additional 0.1 students/m^(2)density increase in the classrooms.However,the energy penalties related to ventilation needs can be reduced by up to 25%using DCV instead of conventional mechanical ventilation systems for school buildings located in Saudi Arabia’s hot climate.
