953 resultados para cal microprocessada
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本文利用黑潮流域主流轴上的两个柱状沉积物岩芯MD05-2908以及PC-1为研究材料,在AMS14C测年的基础上,利用高分辨率的有机地球化学分析记录结合浮游有孔虫氧、碳同位素,恢复并重建了过去25,000 cal a BP以来黑潮流域古海洋环境演化的历史。以及表层海水生产力以及物质输送状况的演化历史。通过利用Uk’37古海水温度以及盐度指标恢复重建了过去25,000 cal a BP以来海洋表层海水温度、盐度;通过机碳、氮含量以及同位素变化、长链正构烷烃以及正构烷醇等指标重建了过去7000a B.P.以来的陆源物质输入历史;通过长链不饱和烯酮含量以及有机碳同位素指标恢复了过去7000a B.P.以来海水表层生产力的历史。此外,通过基于以上各种指标的环境信息与区域以及全球其它气候记录进行对比研究以及不同环境指标的时间系列分析,探讨了该区表层环流系统以及生产力的演化对于全球气候变化的响应,揭示了不同尺度的短周期高频率全球变化事件在黑潮流域的具体作用过程和响应机制。通过这些研究取得了以下的主要认识: 基于有机地球化学指标的古气候环境记录与黑潮流域已有的研究成果有很好的对应关系,从我们高分辨率的有机地球化学记录中可以识别出全新世黑潮强弱变化的几次明显的事件;25000a B.P.以来黑潮流域的环境变化与全球环境变化有着很好的对应性,黑潮强弱演化总体趋势与全球气候背景演化相一致,黑潮对高频气候变化事件的记录与全球记录具有同步性,这种同步性尤其体现在末次冰消期以来的气候快速高频振荡以及全新世以来的气候突变事件上。 全球性的高频气候事件对黑潮主体本身及黑潮流域的相邻区域的大气和海洋环流都具有重要的控制作用,这种控制作用主要通过副高、ITCZ以及季风三种气候要素之间相互关联、彼此影响造成的。具体表现为:太阳辐射量的减少导致热力差异减小,这种相对减小弱化了热带西太平洋的对流活动,造成了西太平洋副热带高压长期偏南、偏东,ITCZ平均北界位置偏南,降雨带长时间集中在南部地区,增强的降雨量提高了风化剥蚀以及沉积物向海洋搬运的能力,陆源物质供应量增加;同时,辐射量以及热力差的减小又与加强的东亚冬季风相联系,增强的冬季风导致了近底层“雾状层”物质的向海传输,物质传输效率增高。这种物源供应以及搬运量的双重增加导致了冲绳海槽流域物质通量的增加。 基于有机地球化学指标的海洋表层生产力的变化与陆源物质供应量以及黑潮流的强弱变化存在着对应关系,通常情况增加的海洋表层生产力对应着高的陆源物质输入以及相对较弱的黑潮。这种变化与东亚夏季风的以及冬季风的强弱都有很好的一致性。陆源物质的输入增加了表层营养物质的含量,导致生产力的勃发;陆源物质的输入增加又对应着减少的太阳辐射量,偏南的ITCZ北界位置以及副热带高压,这些对应于减弱的东亚夏季风(增强的东亚冬季风)。 黑潮流域的高沉积速率事件对应于减弱的黑潮强度和增加的ENSO频度,这些事件与上述的副热带高压、ITCZ位移和强弱的变化相一致。黑潮流域过去25000a B.P.以来南北温度的差异有冰期加大而全新世减小的趋势,但这种冰期与全新世的差异很小,我们认为末次盛冰期的时候黑潮主流轴没有移出冲绳黑潮,只是由于强度的减弱受陆架水体的影响有所加大。 黑潮流域很好的记录到了包括数千年尺度的D/O旋回周期到大气——海洋系统内部振荡所致的PDO、NAO等数十年尺度的高频振荡,说明黑潮流域对过去全球及区域环境变化事件有很好的响应。黑潮流域各古海洋指标所记录周期上的一致性说明这些环境因子控制机理上具有的一致性,即大背景上受太阳活动所引起的辐射量变化控制,局部的高频快速气候波动又受到局域性的气候因素如海气相互作用的放大影响。
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文章针对机器人系统维护特点,提出将故障预测与健康管理(PHM)技术应用到机器人系统的维护上。论述了PHM关键技术——故障预测技术的特点和研究内容。对故障预测技术进行分类和分析,总结出各种预测方法的特点。最后提出了基于统计过程控制(SPC)进行故障预测的方法,并阐述了进一步研究可能遇到的问题。
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研究了不确定性环境下移动机器人躲避运动轨迹未知的移动障碍物的一种新方法.通过实时最小均方误差估计算法预测每个障碍物的位置及运动轨迹,并利用模式识别中最小均方误差分类器的修正模型计算出机器人的局部避障路径,再运用船舶导航中使用的操纵盘技术来确定每个导航周期中移动机器人的速.度仿真结果表明了该方法的可行性
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In this study, 172 mollusk assemblages from the Weinan loess section in the southeast of Loess Plateau, China, were identified quantitatively at relative high resolution. The results show: 1) the history and processes of paleoclimatic and paleoenvironmental changes in Weinan since the last 70 ka; 2) the characteristics of climatic changes during the period of the last glacial maximum (LGM); 3) the spatial pattern of paleoclimate variations at the south and middle parts of the Loess Plateau during the LGM period; 4) the timing of the last deglaciation and the return event of rapid climate change during the last deglaciation. The main conclusions are as follows: 1) 172 mollusk samples taken from the uppermost 9 m deposits cover the past 70 ka, which were sampled at the internals of 5 cm for S_0, 3 cm for L_(1-1) and L_(1-2), and 10 cm for L_(1-3), L_(1-4) and L_(1-5). Author analyzed quantitatively all individuals including broken pieces of snail shells, percentages of 15 species identified from 172 samples. Three main groups were determined according to the ecological requirement of each taxon. Based on the variations of three ecological groups and typical ecological species, The author intended to reconstruct the history of and processes of climate and environment since the last 70 ka in the Weinan region. The climate and environment in this region experienced the following changes: relative warm and humid stage from 67.5-20.3 cal. ka B.P., a period of forest-steppe or steppe developed; cold and arid stage from 20.3-15.5 cal. ka B.P., a dry steppe period, later wetter and colder; cold and humid period once time from 15.5 to 12.3 cal. ka B.P., a typical steppe or forest-steppe stage; cold and humid again from 12.3 cal. ka B.P. to 8.2 cal. ka B.P., a tropical steppe stage; warm and humid climate, a forest-steppe developed. 2) The climate during the period of the last glacial maximum (LGM) in Weinan was characterized by a general cold-humid condition, represented by occurrence of a number of the cool-humidiphilous mollusk species such as Gastocopta amigerella and Vallonia cf. pulchella in the section. 3) Comparison of the variations in abundance of Puncture orphana at Weinan with those at Luochuan and Changwu sections suggests that the summer monsoon intensity influenced differently at the three regions during the LGM period. The Weinan was weaker summer monsoon impact during all the period, the Luochuan was influenced occasionally, and Changwu was only a very short time affected, which indicated it might be located at the western margin of the summer monsoon influence during that period. 4) The ratio of thermo-humidiphilous mollusk group to cold-aridiphilous one shows an increase tendency at about 15 cal. ka B.P., reflecting the climate warming after the deglaciation in Weinan, which is approximately corresponding to the timing of warming period of the last deglaciation, found in the East Atlantic Ocean, the South China Sea and the Loess Plateau (indicated by the phytolith study). 5) A remarkable decrease in the number of thermo-humidiphilous and cool-humidiphilous mollusk species from 12.7 - 11.6 cal. ka B.P. indicates a cooling in climate and might be the reflection of the Younger Dryas event in Weinan. 6) Variations in the ratios of thermo-humidiphilous mollusk species to cold-aridiphilous ones reflect the climate instability in Holocene. There were four warm-humid periods (10-8.1 cal. ka B.P., 6.9-6.1 cal. ka B.P., 5.2-2.6cal. ka B.P., 1.6cal. ka B.P. to the present ) and three relative cold-arid periods (8.1-6.9 cal. ka B.P., 6.1-5.2 cal. ka B.P., 2.6-1.6 cal. ka B.P.), showing about a 1,000 year climatic oscillation.
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The carbon isotope compositions of plants in Xilinguole, Haibei and Jilong and the tooth enamel of animals in Jilong have been analyzed. The study of carbon isotope discrimination of plants along altitude gradient among the three areas has found decreased discrimination.The eolian deposits of Heyeping can be used to reconstruct Holocene climate variability in the region. Some proxies indicates that the 8. 2 ka event can be found in north China, and it is warm and arid in the 4900~6800(or 6900) cal. a BP.
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Sediment cores DH99a and DH99b recovered in the central part of Daihai Lake in north-central China were analysed at 2- to 4-crn intervals for grain-size distribution. Grain-size distributions of the lake sediments are inferred to be a proxy for past changes in East Asian monsoon precipitation, such that greater silt-size percentage and higher median grain size reflect increased monsoonal precipitation rates. The grain-size record of Daihai Lake sediments spanning the last ca 11,000 yr indicates that the monsoonal precipitation in the lake region can be divided into three stages: the Early, Middle and Late Holocene. During the Early Holocene before ca 7900 cal yr BP, the median grain size (Md) and the silt-fraction content were relatively low and constant, suggesting relatively low precipitation over the lake region. The Middle Holocene between ca 7900 and 3100 cal yr BP was marked by intensified and highly variable monsoonal precipitation, as indicated by high and variable Md values and silt contents of the lake sediments. During this period, average precipitation rate gradually increased from ca 7900 to 6900 cal yr BP, displayed intense oscillations between ca 6900 and 4400 cal yr BP, and exhibited a decreasing trend while fluctuating from ca 4400 to 3100 cal yr BP Although generally high during the Middle Holocene, both the Md and the silt content assumed distinctly low values at the short intervals of ca 6500-6400, 6000-5900, 5700-5600, 4400-4200 cal yr BP, implying that monsoonal precipitation might have been significantly reduced during these intervals. During the Late Holocene since ca 3100 cal yr BP, grain-size values suggest that precipitation decreased. However, during the Late Holocene, relatively higher Md values and silt contents occurring between ca 1700 to 1000 cal yr BP may denote an intensification of hydrological cycles in the lake area. Changes in the East Asian monsoonal precipitation were not only directly linked with the changing seasonality of solar insolation resulting from progressive changes in the Earth's orbital parameters, but also may have been closely related to variations in the temperature and size of the Western Pacific Warm Pool, in the intensity of the El Nino-Southern Oscillation, and in the path and strength of the North Equatorial Current in the western Pacific.
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泥炭作为一种地质档案,其发育形成过程中包含了丰富的古气候和古环境的变化信息。由于泥炭沉积中植物残体的碳、氧等稳定同位素组成与气候变化之间存在着密切关系,其稳定同位素时间序列已作为气候变化的代用指标逐渐用于古气候的恢复和重建,尤其是在以高时间分辨率重建全新世以来的气候环境变化方面已取得一些重要进展。 本论文通过对湖北省神农架地区大九湖泥炭中植物残体的氧、碳同位素的研究,同时以温度和湿度这两种重要的气候参数代用指标,恢复和重建全新世以来中国中部地区的气候状况。通过本论文的工作并与其它相关成果综合对比研究,对从末次冰消期晚期和全新世以来中国中部地区气候状况有如下的认识: 1. 末次冰消期晚期至全新世阶段,大九湖泥炭纤维素δ18O敏感地记录了发生在约14.67~12.89 cal. kaBP的BA暖期以及在此期间所发生的两次冷事件:Oder Dryas冷事件和Intra-Allerød冷事件;并指示随后的Allerød暖期明显较Bølling暖期偏冷;在新仙女木时期(YD),神农架地区温度较低,事件中后期温度开始回升;在11.0~9.0 cal. kaBP的早全新世时期,大九湖泥炭δ18O在波动中升高,指示了整体上的温暖气候,期间存在一系列的气候变冷事件。这些冷事件基本都是叠加在一种长期的、相对较暖的变化趋势上,有别于末次冰消期的突然变冷事件;在9.0~5.0 cal. kaBP的中全新世阶段,神农架地区总体上处于相对温暖的适宜阶段,但波动较为频繁,期间记录到了著名的“8.2ka”冷事件;约5.0 cal. kaBP开始,大九湖泥炭δ18O值持续升高,指示以一次快速的升温过程开始了晚全新世阶段并保持在一个相对较高的温度水平;在整体温暖的气候背景下也明显记录有“4.2ka”、“小冰期”等全球性冷事件;大九湖泥炭纤维素δ18O所记录的温度变化趋势与中国大陆地区其他一些气候代用指标所记录的温度变化趋势有很好的相似性,说明中国大陆地区温度变化的趋势基本一致。 2. 大九湖泥炭δ18O温度变化序列所记录到的历次突然气候变冷事件,与格陵兰冰芯和北大西洋冷事件的发生具有很好的一致性,这说明对应于北半球高纬度区域的气候变化,在中低纬度的中国地区同样存在响应和变化,并且这种响应贯穿于整个全新世阶段。 3. 大九湖泥炭纤维素δ13C敏感地记录了末次冰消期以来东亚季风的演变历史。东亚季风在整个末次冰消期至晚全新世阶段始终处于一种强弱交替的波动态势。在末次冰消期至全新世早期,其整体上表现为一种由弱转强的态势;在全新世早期和中期阶段,东亚季风活动强度整体较高,表现为整个时间序列中的高活动时段,而其中也出现了数次明显的减弱迹象;全新世晚期阶段,东亚季风的活动强度较中期和早期为弱,整体上表现出低幅的波动但没有恢复到前两个时期的活动强度。在中世纪温暖期阶段的中后期,东亚季风的活动强度开始在波动中逐渐升高。 4. 该泥炭纤维素代用指标所记录的一些东亚季风突变(增强)事件与同一时期所发生的印度季风的突变(减弱)事件具有很好的对应关系;进一步证实这两个季风系统之间所存在的反相变化关系;同时,这些突变事件与北大西洋IRD冷事件在发生时间段也具有较好的对应关系,即每当北大西洋地区气候变冷时,东亚季风都表现出增强的迹象。 5. 综合分析中国泥炭同位素古气候记录和其它研究结果,对气候驱动机制有如下认识:当太阳活动发生百年至千年时间尺度的减弱时,由大气臭氧层变化所触发的影响向大气层下部延伸,导致北半球气候变冷;同时,减弱的太阳活动可能在赤道太平洋触发类厄尔尼诺状态出现,并引发印度洋夏季风减弱和东亚夏季风增强;早全新世北半球冰盖周围大冰湖冰岸坍塌,湖中巨量体积淡水突然流入北大西洋,导致海洋温盐环流传送带运转放慢甚致停顿,通过跨赤道的温盐环流向北输送的热量大大减少,引起北半球气候变冷;由于海洋温盐环流的变化改变了全球热量的分配,暖水在地球南部积累,导致西太平洋暖池区域海表面水与深层水温度之间反差的增加,从而有利于类厄尔尼诺状态出现,同样将可能引起印度洋夏季风减弱和东亚夏季风增强。
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泥炭的形成和积累主要受控于气候,其次是地质、地貌和水文等因素。作为一种重要和理想的气候信息载体,泥炭己经与冰芯、海洋及湖泊沉积、黄土堆积、洞穴碳酸盐沉积、树轮和珊瑚礁等其它类型的自然地质档案一样,逐渐为国内外致力于古气候变化研究的学者所接受,并将其重点应用于全新世以来气候变化信息的提取。本研究在已有的泥炭混合植物残体纤维素碳稳定同位素记录青藏高原东部地区气候信息的基础上,首次提取泥炭中单一种属植物残体一木里苔草(Calexmulieensis)纤维素,测定其碳稳定同位素,并以其时间序列作为一种新的西南季风代用指标,揭示该区域全新世以来气候变化。研究表明:1.木里苔草的碳稳定同位素时间序列是西南季风强度变化的敏感代用指标。约11800~11加0 cal aBP期间,木里苔草纤维素的613C记录处于最大值,表明该时段西南季风活动鼻弱,气候干冷,对应于普遍发生并存在的新仙女木事件;它清晰地指示了该区全新世的下限年龄为约11200 cal aBP(14c年龄约9900aB玲从约11200 oal aBP起该区迅速进入湿暖的全新世阶段,季风活动迅速增强;在约10800~5500 cal aBP期间,季风总体保持在强盛状态,但其间有4次突然减弱,气候变干冷;约从5500 cala即起季风活动在波动中逐渐减弱,其中有4次减弱最为明显。2.木里苔草纤维素碳同位素所记录的犯000年以来的所有9次西南季风活动的突然减弱与同时期北大西洋发生的冰力}漂移碎屑沉积物事件(IRD事件)一一对应。这种密切的相关关系表明,西南季风强度的波动可能是对全球气候变化特别是对海洋热盐环流引起的地球南北方气撇动变化的响应。3.木里苔草纤维素碳稳定同位素所指示的西南季风有952,乓57,475,312,211和77年等一系列周期。其中557年和77年两个周期分别与北大西洋深层海水环流的550年的周期和76年的气候周期非常吻合。这表明西南季风与北大西洋气候间有很好的相关关系。由于557年和77年的季风周期又都分别类似于53。年和80年的太阳活动周期,这表明太阳活动可能对西南季风和北大西洋气候间的联系有着影响。4.红原泥炭木里苔草纤维素和泥炭混合纤维素别3c时间序列在千年至万年时间尺度上的变化趋势很相近。两种代用记录都一致反映了冰后期的气候变化,即均指示西南季风强度变化可分为三个明显的大阶段。这说明它们对过去12000年的西南季风变化具有相同的响应。对于目前经过较详细研究的那些全球大范围发生的突然气候变化事件,木里苔草纤维素δ~(13)C代用记录与泥炭混合纤维素δ~(13)C代用记录一样,都有相同的响应,但是,相对于泥炭中单一的木里苔草敏感地记录到历次北大西洋I劝事件而言,泥炭混合纤维素δ~(13)C记录对其中的几次突然气候变化事件似乎没有表现出明显的响应。这个结果表明对数百年尺度的突然气候变化,木里苔草纤维素比混合纤维素的酬3c指标似乎要更敏感一点。因此,在能获得足够数量的单种植物·残体的情况下,单种植物残体纤维素的δ~(13)C指标有很好的使用价值。
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碳硅钙石—Ca_7[Si_6O_(18)] [CO_3]·2H_2O是钙的碳酸盐硅酸盐矿物的第三个成员(Pluth and Smith, 1973)。前人曾做过某些碳硅钙石的一般矿物学研究(McConnell, 1955; Murdoch, 1955和曹正民等,1987)。Pluth和Smith (1973)利用X射线四园衍射仪进行结构测定,但未能确定其空间群,给出的结果是I2/m或Im。与此相关,他们未能确定该矿物结构中CO_3的有序或无序;对Ca的配位亦不明了。另外,前人对Ca的碳酸盐硅酸盐矿物未作系统比较。1972年在安徽省濉溪县邹楼铁矿床的钻钆岩芯中也发现了碳硅钙石。作者对该地碳硅钙石样品进行了矿物学、晶体结构和晶体化学研究。作者对采自安徽的碳硅钙品进行了一系列矿物学研究后发现,本文碳硅钙石的一般矿物学特征和前人研究结果基本相同。这说明:(1)本文样品确为碳硅钙石;(2)不同产地和产状的碳硅钙石的矿物学特征相同,由此进一步反映该矿物具有极苛刻的生成条件。作者发现前人对碳硅钙石X射线粉晶衍射线条的指标化有不少错误或不足,并予以纠正。通过晶体结构测定与修正,作用确认碳硅钙石的空间群应为Cm。结构中CO_3有序。它属于等腰三角形几何构型;并呈“受压”迹象。该结构中SiO_4四面体连成稳定的Si_6O_(18)六元环。碳硅钙石结构中水以结晶小的形式存在。该结构中存在氢键。该结构中共有四种Ca的配位多面体;Cal的配位数为8,Ca2, Ca3和Ca4配位数为6。Ca-0多面体相互以复杂的共棱方式连接成层。层间夹有CO_3, Si_6O_(18)和H_2O。Ca-0多面体畸变程度不同。碳硅钙石的晶体化学式应表示为Ca~([8])Ca~([6])_6[Si~([4])_6O_(18)] [C~([3])O_3]·2H_2O。作者发现,可以用配位中心原子(或离子)的键价和讨论配位多面体的结构畸变;并证明对于中心原子(或离子)、配位原子(或离子)、配位数及R(平均键长)均相同的几个配位多面体,畸变程度越强,中心原子(或离子)的键价和越大。此外,作者认识到,离子键和共价键的判别在键价和上也有所体现。根据晶体结构信息,作者对碳硅钙石的某些矿物学特征进行了满意的解释,从而使两者得到相互印证。通过认真全面的比较,作者发现碳硅钙石及其类似古物——Ca的碳酸盐硅酸盐矿物是复杂多样的。除去具有相同或相近的元素组成和地质产状外,它们几乎不再有共同点。碳硅钙石均产自火成岩和沉积岩的接触带。它的结晶温压范围是非常狭窄的。这也正是碳硅钙石等矿物在自然界比较罕见的重要原因。本文碳硅钙石结晶于较晚期的低温热液阶段;并且直接结晶于溶液环境。
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Hunt, C. Elrishi, H. Gilbertson, D. Grattan, J. McLaren, S. Pyatt, B. Rushworth, G. Barker, G. Early-Holocene environments in the Wadi Faynan, Jordan. The Holocene. 2004. 14,6 pp 921-930
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Grattan, J.P., Gilbertson, D.D., Hunt, C.O. (2007). The local and global dimensions of metaliferrous air pollution derived from a reconstruction of an 8 thousand year record of copper smelting and mining at a desert-mountain frontier in southern Jordan. Journal of Archaeological Science 34, 83-110
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Urquhart, C. (editor for JUSTEIS team), Spink, S., Thomas, R., Yeoman, A., Durbin, J., Turner, J., Armstrong, A., Lonsdale, R. & Fenton, R. (2003). JUSTEIS (JISC Usage Surveys: Trends in Electronic Information Services) Strand A: survey of end users of all electronic information services (HE and FE), with Action research report. Final report 2002/2003 Cycle Four. Aberystwyth: Department of Information Studies, University of Wales Aberystwyth with Information Automation Ltd (CIQM). Sponsorship: JISC
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The current congestion-oriented design of TCP hinders its ability to perform well in hybrid wireless/wired networks. We propose a new improvement on TCP NewReno (NewReno-FF) using a new loss labeling technique to discriminate wireless from congestion losses. The proposed technique is based on the estimation of average and variance of the round trip time using a filter cal led Flip Flop filter that is augmented with history information. We show the comparative performance of TCP NewReno, NewReno-FF, and TCP Westwood through extensive simulations. We study the fundamental gains and limits using TCP NewReno with varying Loss Labeling accuracy (NewReno-LL) as a benchmark. Lastly our investigation opens up important research directions. First, there is a need for a finer grained classification of losses (even within congestion and wireless losses) for TCP in heterogeneous networks. Second, it is essential to develop an appropriate control strategy for recovery after the correct classification of a packet loss.
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UNLABELLED: Newly discovered fossil assemblages of small bodied Homo sapiens from Palau, Micronesia possess characters thought to be taxonomically primitive for the genus Homo. BACKGROUND: Recent surface collection and test excavation in limestone caves in the rock islands of Palau, Micronesia, has produced a sizeable sample of human skeletal remains dating roughly between 940-2890 cal ybp. PRINCIPLE FINDINGS: Preliminary analysis indicates that this material is important for two reasons. First, individuals from the older time horizons are small in body size even relative to "pygmoid" populations from Southeast Asia and Indonesia, and thus may represent a marked case of human insular dwarfism. Second, while possessing a number of derived features that align them with Homo sapiens, the human remains from Palau also exhibit several skeletal traits that are considered to be primitive for the genus Homo. SIGNIFICANCE: These features may be previously unrecognized developmental correlates of small body size and, if so, they may have important implications for interpreting the taxonomic affinities of fossil specimens of Homo.
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Gemstone Team Crime Prevention and Perception