中能Abrasion-Ablation模型的核内核子密度分布修正

将具体的核内核子 (包括中子、质子 )密度分布引入到中能Abrasion -Ab lation模型中 ,用修正后的模型计算了 30MeV/u　 4 0 Ar +natAg反应中的弹核碎裂过程 .结果表明 ,在非常周边的碰撞中 ,修正后的模型计算的碎片截面与修正前的计算相比有明显的差别 ,反映了核密度边缘弥散的影响 .与实验结果的比较验证了中能弹核碎裂碎片能量相对于束流能量的降低是由摩擦作用引起的 .

一种利用相位掩模版对光栅波长进行微调的光栅刻写方法

提出并实验证实了一种刻写光栅时既能保护相位版又能对光栅的反射波长进行微调的方法．通过调整光纤和相位版之间的距离，利用1550nm单模光纤和掺铒分别实现了0．48nm和2．2nm的光栅反射波长的调节．在相位版和光纤之间的距离保持在3mm的条件下，既可以保护相位版又可以获得高质量的光栅．

中能重离子引起的碎裂及转移反应研究

重离子核反应机制的研究一直是人们关注的课题。入射能量较低时，集体效应占主要地位，反应为熔合反应及深部非弹性碰撞，实验可用平均场理论进行解释。当入射能量较高时，平均场效应消失，核子-核子碰撞起主要作用，实验可用参加者-旁观者模型来描述。中能区（10-100 MeV/u）的重离子反应既具有低能下一体耗散的特点，又具有高能下核子-核子碰撞的特征，由于作用时间短，非平衡现象变得很重要。在这一能区，多种反应机制共存并相互竞争。对这一能区的重离子核反应制的研究将有助于我们更清楚地了解原子核的结构。为此，我们在兰州重离子加速器HIRFL上进行了46.7 MeV/u ~(12)C引起的重离子反应中前方向出射产物的测量，着重讨论了周边反应中的弹核碎裂和转移反应以及它们的相互竞争。实验中用46.7 MeV/u ~(12)C束流轰击四种靶核：~(58)Ni、~(64)Ni、~(115)In和~(197)Au。通过对前方向出射的类弹碎片的测量，发现它们的平行动量分布宽度满足Goldhaber关系式，提取的约化平行动量分布宽度σ_0 = 80 ± 10 MeV/c，与相对论情形下的值接近，并且σ_0对于各种反应系统均相同。反应中弹核碎裂产物的最可几能量可用Abrasion图象来解释。对于质量接近弹核的类弹碎片，将碎裂部分和转移部分分开后，提取的转移部分的约化平行动量分布宽度为44 ± 10 MeV/c，这比弹核碎裂部分的宽度要窄，说明转移反应比弹核裂受到相空间中更严格的限制。弹核碎裂和转移反应的几率都随靶核质量增加而增加，并且与被转移结团的结构有关。转移反应主要对弹核附近的类弹碎片有贡献，当类弹碎片质量与弹核质量相差较大时，主要是弹核碎裂的贡献。对反应中的同位素产额分布也进行了分析，结果表明，类弹碎片的同位素分布对靶核有依赖关系，当靶核的N/Z增加时，产物的N/Z也增加，并且低能部分的N/Z比高能部分的N/Z要大。当角度变大时，~7Li/~6Li、~9Be/~7Be、~(11)B/~(10)B等同位素产额比随之变化，低能部分变化缓慢，高能部分则变化明显。产物的同位素产额分布或同位素产额比反映了系统由非平衡向平衡演化的过程。实验中对于BaF_2晶体与半导体组成的望远镜探测器的性能进行了测量。圆柱形BaF_2晶体后配以XP2020Q型光电倍增管，输出信号送入不同的QDC，以获得BaF_2中光输出的快慢成分。ΔE-E方法可以得到较好的元素鉴别，即使对低能的p、d、t也能分开，用快慢成分关联方法可对较高能量的轻带电粒子很好地鉴别。入射离子越重，相同能量的离子在BaF_2晶体中引起的光输出越小。BaF_2对入射离子的响应在较大的能区内是线性的，在低能时存在轻微的非线性。对80 cm大面积位置灵敏电离室与一维位置灵敏塑料闪烁体组成的探测系统首次在中能重离子反应中进行了测试。电离室可以测量较重的低能离子，有较好的粒子鉴别能力，能给出能量信息及两维位置信息。闪烁体则使得该系统可用于较高能量轻带电粒子的测量，它能给出能量吸一维位置信息，与电离室配合可以进行元素鉴别。它将在以后的中能重离子实验中得到广泛的应用

30MeV/u~(40)Ar引起反应中的碎片发射机制

本论文中重点研究了30MeV/u 40Ar+58Ni，64Ni和115In反应中中等质量碎片（IMF）的发射机制。实验中，测量了实验室系5°～140°角度范围内出射碎片的能谱和角分布。对前角区出射的IMF（3≤Z≤13）实现了同位素鉴别，对中后角区出射的碎片在低探测阈（<2MeV/u ）的前提下实现了直到Z～30的元素鉴别。 用运动源模型对不同角度下出射的碎片能谱进行了分析和讨论，并结合角分布特征定性地研究了碎片的三个发射源。通过对各源的贡献随角度以及出射碎片电荷数Z的演化，观察到：类弹源主要发射的是那些前角区出射的、接近束流速度的高能碎片；中等速度源的发射是中角度区出射碎片和前角区低能碎片的主要来源；后角区出射的碎片则主要来自于类熔合源的发射。并观察到相对于类熔合源非平衡源更容易发射较轻的碎片。 通过对前角区出射IMF（3≤Z≤13）的能谱和同位素分布的分析，确定了那些基本保持束流速度的碎片主要来自于弹核碎裂过程。用各种模型对实验同位素分布进行了拟合，发现Sümmerer等人给出的经验公式和abrasion-ablation模型均能比较满意地拟合实验同位素分布的宽度和峰位。同时也观察到abrasion-ablation模型计算对奇Z元素的同位素分布能给出较好的拟合，但对偶Z元素的同位素分布，计算结果与实验值相比出现向丰中子方向的系统性偏移（～lamu）。另外，还着重研究了这些产物的靶核相关性问题。通过系统性分析以及同位旋相关的量子分子动力学（IQMD）模型计算，得出了弹核碎裂产物的靶核相关性是源于靶核表面中子与质子分布的不同和平均场及核子核子相互作用的同位旋效应相关。并且，通过计算还指出了靶核中子皮的厚度对于用弹核碎裂方法产生丰中子同位素的重要性。 通过用统计模型拟合后角区出射碎片的电荷分布，指出了这些碎片主要来自于非完全熔合过程中形成的复合系统的统计发射。 实验中观察到30MeV/u 40Ar轰击Ni和In靶在中角区出射的碎片的电荷分布有不同的特征。相对来说，前者更服从power-law，后者则倾向于服从指数规律。结合核态方程和QMD模型计算分析得出，在30MeV/u 的40Ar引起的反应中，对于弾靶质量接近对称的碰撞对所形成的系统，在一定的碰撞条件下可能已进入spinodal区，而非对称碰撞对的碰撞中压缩能还难以使得系统在膨胀时进入力学不稳定区。从而对观察到的实验现象进行了说明，并认为30MeV/u 40Ar轰击与其质量接近的靶核的反应中出射的碎片中已有相当数量的动力学发射成分的贡献。 利用实验中在前角区出射的接近束流速度的碎片的同位素产额提取了类弹源的温度参数。观察到直接由实验同位素产额比得到的表观核温度与所选择的同位素组合有较强烈的依赖关系，而与靶核和实验室探测角基本无关。利用M.B.Tsang等人给出的修正方法，提取了经边馈效应修正后的发射源温度。得到该温度值与反应靶、探测角以及用于提出温度的同位素组合没有明显的依赖关系，均为～4MeV。并用abrasion-ablation模型计算进行了讨论，得到在假定能级密度参数的倒数k=10MeV时，该温度值与abrasion-ablation模型计算是一致的。

Pervasive autocorrelation of the chemical index of alteration in sedimentary profiles and its palaeoenvironmental implications

The chemical index of alteration has been used widely for reconstruction of the palaeoclimate. However, the mechanisms and environmental factors controlling the chemical index of alteration of sediments are not yet fully understood. In this study, autocorrelations of the chemical index of alteration in nine sedimentary profiles, from both the land and the sea, spanning different geological times, are discussed. The sediments of these profiles have different origins (dust, fluvial or ocean sediments) and are from various climate situations and sedimentary environments. Autocorrelations of chemical index of alteration series are ubiquitously evident in all profiles. It is suggested here that autocorrelations may be caused by post-depositional changes such as persistent weathering and diagenesis. As a result, the chemical index of alteration may not reflect climatic conditions during the time of sediment deposition. This study strongly recommends the confirmation of the reliability and veracity of the chemical index of alteration before it is adopted to evaluate the weathering degree of parent rocks and to reconstruct the past climate. Significant autocorrelations in loess profiles were specifically observed, suggesting that the existing understanding of loess deposition in terms of climate conditions requires re-examination, and that previous reconstructions of rapid climate changes (for example, in centennial-millennial scales) should be treated with caution.

Sedimentation rates and provenance analysis in the Southwestern Okinawa Trough since the mid-Holocene

As a high-sedimentation rate depocenter along the path of the Kuroshio Current, the southwesternmost part of the Okinawa Trough is a key area to understand the Kuroshio history and sediments transportation. A 34.17-m-long sediment core was obtained by the advanced piston corer of Marco Polo/IMAGES XII MARION DUFRESNE during the May 2005 from the Southern Okinawa Trough at site MD05-2908. The recovered sediments were analyzed by AMS C-14 dating, coarse size fraction (> 63 mu m) extraction and moisture content determination in order to study its sedimentation flux and provenance. The depth-age relationship of core MD05-2908 was well constrained by 17 C-14 dating points. The sediments span across the mid-Holocene (6.8 ka B.P.) and have remarkablely high sedimentation rates between 1.8 and 21-2 m/ka, which is well consistent with the modern observations from sediment traps. We identified five 70-200 a periods of abnormally rapid sedimentation events at 6790-6600 a B.P., 5690-5600 a B.P., 4820-4720 a B.P., 1090-880 a B.P., and 260-190 a B.P., during which the highest sedimentation rate is up to 21-2 m/ka. In general, the lithology of the sediments were dominated by silt and clay, associated with less than 5% coarse size fraction (a parts per thousand << 63 mu m). As the most significant sediment source, the Lanyang River in northeastern Taiwan annually deliver about 10Mt materials to the coastal and offshore region of northeast Taiwan, a portion of which could be carried northward by currents toward the study area. Therefore, we concluded that the 5 abnormally rapid sedimentation events may be related to intensified rainfall in Taiwan and thus increased materials to our study area at that time. However, a few extreme-rapid sedimentation events cannot be explained by normal river runoff alone. The large earthquakes or typhoons induced hyperpycnal discharge of fluvial sediment to the ocean may also act as a potential source supply to the Okinawa Trough.

REE and epsilon(Nd) of clay fractions in sediments from the eastern Pacific Ocean: Evidence for clay sources

Clay fractions in the non-calcareous surface sediments from the eastern Pacific were analyzed for clay minerals, REE and Nd-143/Nd-144. Montmorillonite/illite ratio (M/I ratio), total REE contents (Sigma REE), LREE/HREE ratio and cerium anomaly (delta Ce) may effectively indicate the genesis of clay minerals. Clay fractions with M/I ratio > 1, delta Ce < 0.85, Sigma REE > 400 mu g/g, LREE/HREE ratio approximate to 4, and REE patterns similar to those of pelagic sediments are terrigenous and autogenetic mixed clay fractions and contain more autogenetic montmorillonite. Clay fractions with M/I ratio < 1, delta Ce=0.86 to 1.5, Sigma REE=200 to 350 mu g/g, LREE/HREE ratio approximate to 6 and REE distribution patterns similar to that of China loess are identified as terrigenous clay fraction. The Nd-143/Nd-144 ratios or epsilon(Nd) values of clay fractions inherit the features of terrigenous sources of clay minerals. Clay fractions are divided into 4 types according to epsilon(Nd) values. Terrigenous clay minerals of type I with the eNd values of -8 to -6 originate mainly from North American fluvial deposits. Those of type 11 with the epsilon(Nd) Values of -9 to -7 are mainly from the East Asia and North American fluvial deposits. Those of type III with epsilon(Nd) values of -6 to -3 could come from the central and eastern Pacific volcanic islands. Those of type IV with epsilon(Nd) values of -13 to -12 may be from East Asia eolian. The terrigenous and autogenetic mixed clay fractions show patchy distributions, indicating that there are volcanic or hot-spot activities in the eastern Pacific plate, while the terrigenous clay fractions cover a large part of the study area, proving that the terrigenous clay minerals are dominant in the eastern Pacific.

Development of the East Asian monsoon: Mineralogical and sedimentologic records in the northern South China Sea since 20 Ma

We here reconstruct the past change of the East Asian monsoon since 20 Ma using samples from Ocean Drilling Program (ODP) Site 1146 in the northern South China Sea based On a multi-proxy approach including a monomineralic quartz isolation procedure, identification of clay minerals by X-ray Diffraction (XRD) and grain-size analysis of isolated terrigenous materials. Terrigenous supply to ODP Site 1146 was dominated by changes in the strength of multiple sources and transport processes. Grain-size data modeled by an end-member modeling algorithm indicate that eolian dust from the and Asian inland and fluvial input have contributed on average 20% and 80% of total terrigenous material to ODP Site 1146, respectively. Specifically, about 40-53% of the total (quartz+feldspar) and only 6-11% of the total clay is related to eolian supply at the study site. Detailed analysis of the sedimentary environment, and clay minerals combined with previous studies shows that smectite originates mainly from Luzon, kaolinite from the Pearl River and illite and chlorite from the Pearl River, Taiwan and/or the Yangtze River. The proportion and mass accumulation rate (MAR) of the coarsest end-member EM1 (interpreted as eolian dust), ratios of (illite+chlorite)/smectite, (quartz+feldspar)% and mean grain-size of terrigenous materials at ODP Site 1146 were adopted as proxies for East Asian monsoon evolution. The consistent variation of these independent proxies since 20 Ma shows three profound shifts in the intensity of East Asian winter monsoon relative to summer monsoon, as well as aridity of the Asian continent, occurred at similar to 15 Ma, similar to 8 Ma and the youngest at about 3 Ma. In comparison, the summer monsoon intensified contemporaneously with the winter monsoon at 3 Ma. The phased uplift of the Himalaya-Tibetan plateau may have played a significant role in strengthening the Asian monsoon at similar to 15 Ma, 8 Ma and 3 Ma. (C) 2007 Elsevier B.V. All rights reserved.

Seismic profiles across the middle Tan-Lu fault zone in Laizhou Bay, Bohai Sea, eastern China

The stratigraphic architecture, structure and Cenozoic tectonic evolution of the Tan-Lu fault zone in Laizhou Bay, eastern China, are analyzed based on interpretations of 31 new 2D seismic lines across Laizhou Bay. Cenozoic strata in the study area are divided into two layers separated by a prominent and widespread unconformity. The upper sedimentary layer is made up of Neogene and Quaternary fluvial and marine sediments, while the lower layer consists of Paleogene lacustrine and fluvial facies. In terms of tectonics, the sediments beneath the unconformity can be divided into four main structural units: the west depression, central uplift, east depression and Ludong uplift. The two branches of the middle Tan-Lu fault zone differ in their geometry and offset: the east branch fault is a steeply dipping S-shaped strike-slip fault that cuts acoustic basement at depths greater than 8 km, whereas the west branch fault is a relatively shallow normal fault. The Tan-Lu fault zone is the key fault in the study area, having controlled its Cenozoic evolution. Based on balanced cross-sections constructed along transverse seismic line 99.8 and longitudinal seismic line 699.0, the Cenozoic evolution of the middle Tan-Lu fault zone is divided into three stages: Paleocene-Eocene transtension, Oligocene-Early Miocene transpression and Middle Miocene to present-day stable subsidence. The reasons for the contrasting tectonic features of the two branch faults and the timing of the change from transtension to transpression are discussed. Crown Copyright (C) 2008 Published by Elsevier Ltd. All rights reserved.

River mouth bar formation, riverbed aggradation and channel migration in the modern Huanghe (Yellow) River delta, China

This paper addresses the recent (1970s-1990s) processes of river mouth bar formation, riverbed aggradation and distributary migration in the Huanghe River mouth area, in the light of station-based monitoring, field measurements and remote sensing interpretation. The results show that the morphological changes of the river mouth bar have been closely associated with the largely reduced fluvial discharge and sediment load. Landforrn development such as bar progradation occurred in two phases, i.e. before and after 1989, which correspond to faster and lower bar growth rates, respectively. Fast riverbed aggradation in the mouth channel was strongly related to river mouth bar progradation. During 1976-1996, about 2.8% of the total sediment loads were deposited in the river channel on the upper to middle delta. Therefore, the river water level rose by a few meters from 1984 to 1996. The frequent distributary channel migration, which switched the radial channel pattern into the SE-directed pattern in the mid-1980s, was linked with mouth bar formation. Marine conditions also constrain seaward bar progradation. Furthermore, the history of river mouth bar formation reflects human impacts, such as dredging and dyking in order to stabilize the coastal area. (c) 2005 Elsevier B.V. All rights reserved.

Effects of different seed pretreatments on germination of ten Calligonum species

In order to determine the optimum seed pre??sowing treatments and patterns of germination,a greenhouse experiment was conducted to study the effects of abrasion,sulphuric acid,boiling water,cold stratification and seed exudate treatments on the germination of ten Calligonum species.The results showed that the response of seed germination to the different pretreatments was similar for all ten Calligonum species.The abrasion,sulphuric acid and cold stratification treatments significantly promoted overall germinability.Compared with the control,the exudate treatment significantly decreased the percent germination,hampered the rate of germination and bolstered dormancy for almost all species.The cold stratification treatment can break the dormancy of viable Calligonum seeds and increased the germination,but it has a little lethal effect on viable seeds probably as well as the boiling water treatments.The germinaton patterns performed significant difference between the pre-sowing treatments for all ten Calligonum species,and the speed and percent germination of the Calligonum species can be greatly increased by mechanical scarification or sulphuric acid treatments.The results showed that seeds of C.junceum have strong ability of germinating.