Reaction Mechanism of the Multi-channel Decomposition Reactions of C_(10)H_(14)^+·

n-Butylbenzene cations C10H14^＋ serve as a model compound to investigate the reaction mechanisms of alkylbenzene cations. The reactions of C10H14^＋. decomposition reaction system have been studied extensively at the B3LYP/6-311＋＋G^＊＊ level with Gaussion98 package. The chain reaction of C10H14^＋ dissociation was initiated by C-H bond rupture. All reaction channels initiated by C-H rupture were fully investigated with the vibrational mode analvsis to confirm the transition states and to reveal the reaction mechanism. A theoretical investigation on the reactions of this positive ion free radical can help us fully understand the decomposition processes.

Direct analysis method of^(14)C radioactivity concentration in urine samples

Objective:To establish a rapid analysis method for the activity concentration of carbon-14(14C)in urine,in order to estimate the internal dose of 14C exposure,and to protect the health of occupational population.Methods:Liquid scintillation counting(LSC)combined with the function of transformed spectral index of the external standard spectrum(tSIE)was used to measure the quenching level and counting rate,and the spiked urine samples with different shades of color were measured by LSC.After establishing the efficiency-quenching curve,the quenching correction and activity concentration analysis of the actual samples were carried out.Results:By LSC and the data fitting,the relationship between efficiency and quenching index could be represented using the equation y=0.0013x-0.0177(R^(2)=0.978).Three actual spiked samples were tested to verify this method,with recoveries of 97%,102%,and 89%,respectively.14C activity concentration of 4 actual urine samples were 0.12,0.11,0.10 and 0.08 Bq/mL,respectively,while the corresponding extended relative uncertainties were 0.0652,0.0929,0.0893 and 0.1043,respectively.Conclusion:The direct analysis method of 14C activity concentration in urine samples was established using LSC.The recovery of 14C activity concentration in urine samples showed that the proposed method had relatively high accuracy.By studying on the source of uncertainty,the uncertainty of the analysis results mainly came from the statistical error of LSC,and the uncertainty component of counting efficiency.

Early Holocene environment at a key location of the northwest boundary of the Asian summer monsoon: a synthesis on chronologies of Zhuye Lake, Northwest China

The intensified monsoon increases summer rainfall and creates wet conditions in the Asian summer monsoon region during the early Holocene. Along with millennial-scale changes of the monsoon intensity, it is still unclear whether the boundary of the monsoon region changes according to monsoon variability. Investigations into the early Holocene environment in monsoon marginal zones are crucial for understanding the monsoon boundary changes. Zhuye Lake is located at the northwest edge of the Asian summer monsoon, the northern Qilian Mountains, which are less affected by modern summer monsoon water vapor. Previous studies have reached different conclusions regarding the early Holocene climatic and environmental changes based on different dating methods（^14C and OSL（optically stimulated luminescence）） and materials（shells, carbonate, pollen concentrates and bulk organic carbon）. In this study, we synthesized 102 ^14C dates and 35 OSL dates from ten Holocene sedimentary sections and ten paleo-shorelines in the lake basin. A comparison between ages from different dating methods and materials generally shows that carbon reservoir effects are relatively slight in Zhuye Lake while the disordered chronologies are mainly related to the erosion processes and reworking effects. In addition, proxy data, including lithology, pollen, total organic carbon and carbonate, were collected from different sites of Zhuye Lake. According to the new synthesis, the early Holocene environment was relatively humid, associated with high runoff and lake water levels. The result indicates that the monsoon boundary moves to the north during the period of the intensified monsoon. A typical arid-area lake was formed during the mid-Holocene when carbonate accumulation and high organic matter contents were the main features of this period. The lake retreated strongly during the late Holocene, showing a drought trend. Overall, the lake evolution is generally consistent with the Holocene Asian summer monsoon change, showing the monsoon influence to monsoon marginal zones.

Radiocarbon ages of different fractions of peat on coastal lowland of Bohai Bay: marine influence?

Peat in boreholes is the most important ^(14)C dating material used for constructing age framework. 20 bulk peat samples were collected from five boreholes, the ^(14)C ages of two fractions(organic sediment fraction and peat fraction) of the bulk peat samples were investigated by AMS-dating and which fraction is better to help construct an age framework for the boreholes were compared and discussed. The results indicated that the peat fraction give a good dating results sequence in the boreholes, compared with the corresponding organic sediment fraction. And the dating results of organic sediment fraction show 161-6 702 years older than corresponding peat fraction, which was caused by marine influence. Then, we suggest an experience formula as y =0.99 x-466.5 by the correlation analysis for correcting the marine influenced organic sediment ages within the conventional ages between 4 000 to 9 000 yrs BP, and more study should be carried out for the AMS ^(14)C dating of the bulk organic sediments.

Sedimentary facies and paleoenvironmental interpretation of a Holocene marsh in the Gironde Estuary in France

The Monards Marsh is located on the northeastern bank of the Gironde Estuary in France. Lithological, sedimentolngical and mi- cropalacontological investigations were made on four cores to determine the evolution of Holocene sedimentary environments and processes in this area over the last 6 000 a. Three main lithological facies are distinguished from bottom to top： （ 1 ） grey laminated silty-sandy clay ; （2） homogeneous dark grey silty clay ; and （ 3 ） compact silty clay. About 26 benthic foraminifera species are identified and divided into six groups according to their ecological characteristics. In association with lithology, sedimentary structures and grainuiometry, the distribution of foraminifera group is used to define external slikke, internal slikke, external schorre, internal schorre, and continental marsh facies. Combined with 14C（AMS） dating, these data indicate four successive paleoenvironments in the Monards Marsh： （ 1 ） Holocene transgression resuited in the development of a basal schorre facies overlying fluvial deposits that transformed to slikke facies sedimentation; the transgression maximum occurred around 5 600 to 5 4430 a BP and was inferred to be associated with the last phase of the rapid Holocene sea-level rise; （2） post-trangressive maximum sedimentation resuited in a regressive sequence of deposits prograding towards the estuary, corresponding to the stahilisation of sea level after 5 4430 a BP; （3） a slight positive tendency in the sea level around 2 800 a BP recorded in the central part of the marsh; and （4） the wetland to a continental marsh environment. The sequential pattern for the evolution of wetlands in this estuarine area during the Holocene is fluvial facies - blackish schorre facies - slikke facies - blackish schorre facies - continental marsh facies. Characteristics of sedimentary facies distribution and evolution reveal that the development of Holocene salt marsh in this area was controlled by the sea-level change and tidal range. The sedimentary facies show an obvious surficial and vertical banding distribution in which the texture and structure, authigenie mineral, foraminifera distribution and bioturbation indicate many distinct difference characteristics.

兴县碧村遗址小玉梁台地F5建筑遗存研究

碧村遗址地处蔚汾河与黄河交汇处,是一处具有内外双重城垣的石城聚落。本文对碧村遗址小玉梁台地F5 (1)出土的6块木炭进行了树种鉴定、树轮年代学和碳十四年代加速器质谱测定。树种鉴定表明F5的建筑木材为松属双维管束亚属硬木松(Subgen. Diploxylon);利用木炭横切面年轮曲率和photoshop软件判断建筑木材年龄不小于119年,直径不小于27.06厘米;利用树轮年代学方法建立了跨度为68年的硬木松浮动树木年轮年表;对木炭系列样品进行碳十四年代质谱测定,最后一个年轮的年代约为公元前2027年(95.4%),F5建筑营建或修葺年代约为公元前2027年。该研究为小玉梁台地F5建筑构建或修葺提供了基础性资料。

乌兰布和沙漠形成时代的初步判定及意义

根据乌兰布和沙漠和沙漠北部出露的剖面记录，初步确认了全新统风成砂沉积层的划分，并据此作14C测年分析，认为全新世风成砂至少形成于2个时期：早全新世，14C年龄为距今7255a之前;晚全新世，14C年龄为距今2255或2630a以近，两期风成砂之间则是一个湖沼广泛发育的时期，乌兰布和沙漠形成时代的初步判定，至少可以认为在人类大规模开垦的汉代之前沙漠就已形成，且已经历了风成砂一湖沼的变化过程，说明沙漠的形成仍是以自然因素为主的过程，人类活动影响只是一个叠加于其上的因素．

ON THE INFORMATION OF MIRE DEPOSITIONAL ENVIRONMENT

Mire is the product of the Quaternary. It mostly formed, developed and declined after the postglacial age. Therefore the chemical element analysis, spore-pollen analysis, 14C dating, mire plant determination for mire sediment, and the study on hierarchy relation of mire sediment, can provide a lot of information for restoring paleogeography, paleoclimate and environmental change. So some people called mire sediment-peat as 'database of environment'.

Human disturbance exacerbated erosion and deposition in the karst peak-cluster depressions during the Ming and Qing dynasties

Under the background of large-scale ecological restoration, China's southwestern karst region has become a hotspot of global vegetation cover “greening” in the past 20 years. However, because of geological constraints, it is difficult to restore the forest landscapes in some areas. It is urgent to understand the impacts of human disturbances during the historical period on the difficult-to-forestation rocky-desertification areas of the karst region in order to guide future afforestation. In this study, we quantified the changes of specific sediment yield in typical karst depressions over the past 500 years by using ^(137)Cs,^(210)Pb, and ^(14)C dating methods in karst depressions, and identified the main human disturbances related to historical erosion and sedimentation by combining with historical data. The results showed that the erosion and sedimentation of the three depressions in 1921–1963 were significantly higher than that in 1963–2021, and the sedimentation rate(0.64–1.33 cm a^(-1)) and the specific sediment yield(2.51–13.11 t ha^(-1)a^(-1)) during Ming and Qing dynasties(1504–1812) were higher than the sedimentation rate(0.26–0.95 cm a^(-1)) and specific sediment yield(0.95–6.99 t ha^(-1)a^(-1)) in the recent century(1921–2021). Reconstruction data and literature from the Ming and Qing dynasties show an empirical link between changes in population, arable land, food, forest area,and deforestation events during the same period. It was found that the population and arable land in Guangxi increased more than three-fold and the forest area decreased significantly in the 17th century after the migration of the Yao ethnic group and the introduction of maize to the region, which may be the main reason for intensifying the erosion of depressions. This study is of great significance to understanding the evolution history of rocky desertification in this region and to answer the potential of afforestation.

Relationship between the rise and fall of Loulan ancient city and centennial-scale climate events and cycles

The discovery of Loulan ancient city(LA)in the early 20th century has important significance for understanding the history of Western regions and the Silk Road civilization.The current academic community still has disputes on whether LA was the capital of Loulan Kingdom,the time of its rise,peak and decline,and the process,rate and driving mechanism of human activity change.This study uses the radio carbon dates(^(14)C)database of LA to reconstruct the history of the rise and fall of human activity,and finds that LA experienced more than~500 years from its rise to its peak and then to its decline:1)the city rose rapidly,and the population increased rapidly from~A.D.0 to 230;2)the city was prosperous and flourishing,and the intensity of human activity reached its peak from~A.D.160 to 340,especially in~A.D.230,when the population reached its peak;3)the city accelerated its decline,and the intensity of human activity decreased significantly,and the population shrank rapidly from~A.D.230 to 500;4)LA was completely abandoned after~A.D.560.The results of the ^(14)C dating database do not support that LA was the early capital of the Loulan Kingdom.By comparing the human activity record of LA with the existing high-resolution palaeoclimate records in the surrounding mountainous areas of the Tarim Basin and South Asia,it is found that the superposition of centennial-scale westerly circulation strength events and the~500-year cycle of the Indian monsoon jointly controlled the precipitation and meltwater(snow)supply of the mountains in the Tarim Basin,affecting the changes of surface runoff and oasis area in the basin,which is one of the important factors causing the rise and fall of LA.

“高资人”化石与股骨形态变异的生物力学分析

运用生物力学方法对1980年在江苏镇江高资镇采集的2件完全石化的人类股骨进行分析,并在常规形态观测和加速器质谱14C测年的基础上对更新世人类化石及全新世现代人股骨形态的变异进行讨论.测年数据显示,"高资人"股骨可能属于全新世现代智人,但基于CT扫描数据计算出的骨干抗压抗拉强度、抗弯强度及其他形态特征都呈现某些较全新世现代人更显古老的特征.对比分析表明,人类股骨形态及测量值因其功能状况等原因具有相当大的变异,股骨形态特征不能作为判断化石系统发育地位的最关键证据.股骨生物力学参数是其功能状况的直接反映,在人类不同演化阶段因运动行为模式差异,其相对大小在不同人群存在更加明显分异,因而生物力学分析在长骨功能状况研究上具有很大应用价值.化石石化程度不是判断其年代的可靠标准.