New evidence for the antiquity of man in North America deduced from aspartic acid racemization

Ages of several Californzia Paleo-Indlian skeletons have been deduced from the extent of aspartic acid racemization. These dates suggest that man was present in North America at least 50,000 years before the present.     

Diketopiperazine formation during investigations of amino Acid racemization in dipeptides

The formation of diketopiperazines from the dipeptides isoleucylglycine and glycylisoleucine was investigated at 132 degrees C over the pH range approximately 2 to 10. At pH 6.2, approximately 50 percent of the original dipeptides were converted to the diketopiperazines during the heating experiments. Hydrolysis of the diketopiperazines can yield either the original dipetide or an inverted dipeptide product. The isoleucine in the diketopiperazines was the most highly epimerized component in the system. Previous racemization and epimerization studies with dipeptides have not taken into account the formation of diketopiperazines and, as a result, the cortclusions about the mechanism and geochemical implications of amino acid racemization in dipeptides will require revision.     

干旱胁迫下玉米叶-气温差与叶温差日变化特征及其品种差异

为进一步明确玉米叶-气温差和叶温差日变化特征及其对干旱的响应与品种差异,通过人工旱棚控水,设置充分供水、轻度胁迫、中度胁迫和重度胁迫4个土壤水分处理,研究5个玉米杂交种功能叶片表面温度及环境光温湿度日周期变化特征,比较分析了不同生育时期叶-气温差和叶温差的变化特性及其与环境因子的关系。结果表明:1)叶-气温差是衡量玉米水分丰缺状况的1项有效指标。在充足供水条件下玉米叶-气温差较为稳定,维持在-4.0~-1.0℃范围内,干旱胁迫下均表现出升高趋势,重度胁迫与充足供水处理之间的差值可达5℃以上,且多出现于12:00—16:00;2)叶温差日变化表现为先升高后降低趋势,并随着干旱胁迫程度的加大而增大;3)干旱处理叶-气温差与光合有效辐射和大气温度的相关性高于空气湿度和饱和水汽压差,均达到显著或极显著水平;4)杂交种间叶-气温差差异不显著,叶温差则差异显著,但不同时间和不同生育时期表现不一致。总之,梯度土壤干旱胁迫导致了叶-气温差和叶温差的逐级升高,叶-气温差可有效反映玉米植株水分丰缺状况,而叶温差在玉米抗旱品种筛选方面的意义尚需进一步研究。     

Oxygen-isotope ratios in phosphate from fossil marine organisms

Well-preserved fossil marine organisms generally yield very positive delta(18)(PO(4)(3-)) values which are considered to result from relatively good preservation of the original oxygen-isotope composition of phosphatic material deposited under isotopic equilibrium conditions in oceanic water whose O(18):O(16) ratio was more positive than that of modern oceans.     

Identification of widespread pollution in the southern hemisphere deduced from satellite analyses

Vertical profiles of ozone obtained from ozonesondes in Brazzaville, Congo (4 degrees S, 15 degrees E), and Ascension Island (8 degrees S, 15 degrees W) show that large quantities of tropospheric ozone are present over southern Africa and the adjacent eastern tropical South Atlantic Ocean. The origin of this pollution is widespread biomass burning in Africa. These measurements support satellite-derived tropospheric ozone data that demonstrate that ozone originating from this region is transported throughout most of the Southern Hemisphere. Seasonally high levels of carbon monoxide and methane observed at middle- and high-latitude stations in Africa, Australia, and Antarctica likely reflect the effects of this distant biomass burning. These data suggest that even the most remote regions on this planet may be significantly more polluted than previously believed.     

Separate evolutionary origins of teeth from evidence in fossil jawed vertebrates

Placoderms are extinct jawed fishes of the class Placodermi and are basal among jawed vertebrates. It is generally thought that teeth are absent in placoderms and that the phylogenetic origin of teeth occurred after the evolution of jaws. However, we now report the presence of tooth rows in more derived placoderms, the arthrodires. New teeth are composed of gnathostome-type dentine and develop at specific locations. Hence, it appears that these placoderm teeth develop and are regulated as in other jawed vertebrates. Because tooth development occurs only in derived forms of placoderms, we suggest that teeth evolved at least twice, through a mechanism of convergent evolution.     

Measurements of turbulence in the venus atmosphere deduced from pioneer venus multiprobe radio scintillations

The 2.3-gigahertz log-amplitude fluctuations observed in the radio links of the Pioneer Venus entry probes during Venus encounter have been used to study turbulence in the Venus atmosphere. The deduced estimates of the upper bound of structure constant c(n) of the refractive index fluctuations (c(n) less, similar 4 x 10(-8) cm(-(1/3))) are inconsistent with similar entry probe measurements by Veneras 4 to 8 but are consistent with the radio occultation measurements by flyby (Mariners 5 and 10) and orbiting (Venerat 9) spacecraft. The Pioneer Venus measurements therefore provide a resolution of the long-standing order of magnitude discrepancy between these earlier measurements of c(n).     

Irradiation history of Itokawa regolith material deduced from noble gases in the Hayabusa samples

Noble gas isotopes were measured in three rocky grains from asteroid Itokawa to elucidate a history of irradiation from cosmic rays and solar wind on its surface. Large amounts of solar helium (He), neon (Ne), and argon (Ar) trapped in various depths in the grains were observed, which can be explained by multiple implantations of solar wind particles into the grains, combined with preferential He loss caused by frictional wear of space-weathered rims on the grains. Short residence time of less than 8 million years was implied for the grains by an estimate on cosmic-ray-produced (21)Ne. Our results suggest that Itokawa is continuously losing its surface materials into space at a rate of tens of centimeters per million years. The lifetime of Itokawa should be much shorter than the age of our solar system.     

Magnetic properties of hexagonal closed-packed iron deduced from direct observations in a diamond anvil cell

The attraction of hexagonal closed packed (hcp) iron to a magnet at 16.9 gigapascals and 261 degrees centigrade suggests that hcp iron is either paramagnetic or ferromagnetic with susceptibilities from 0. 15 to 0.001 and magnetizations from 1800 to 15 amperes per meter. If dominant in Earth's inner core, paramagnetic hcp iron could stabilize the geodynamo.     

平流二沉池中计及温差影响的异重流数值模拟

【目的】在同时考虑进水与池内水的污泥质量浓度差异和温度差异的条件下,对平流式二沉池内的异重流现象进行数值模拟,重点研究异重流对池内流场及污泥沉降规律的影响,为优化沉淀池结构设计及提高沉淀池工作效率提供理论支持。【方法】选取Mixture模型和RNGκ-ε2方程紊流模型,设初始时刻二沉池内水为清水,进水为含一定质量浓度污泥的污水,并通过设置池内水与进水的不同温差模拟夏季与冬季环境,利用模拟数据分析不同时刻各工况下异重流的演变规律。【结果】池内水与进水的单纯污泥质量浓度差异会产生下异重流,小温差低温水与夏季大温差低温水进入均会导致下异重流产生,温差增大,下异重流作用更为明显;高温水进入会同时产生上异重流与下异重流,冬季温差高温水进入时上异重流起主导作用,异重流产生的旋流作用明显,对沉淀池工作效率的影响很大。【结论】温差异重流与污泥质量浓度差异重流本质均为密度差异,低温水进入增强下异重流,高温水进入削弱下异重流,温度影响会消失,污泥质量浓度差异重流作用时间更长。     

Carbon-14 in methane sources and in atmospheric methane: the contribution from fossil carbon

Measurements of carbon-14 in small samples of methane from major biogenic sources, from biomass burning, and in "clean air" samples from both the Northern and Southern hemispheres reveal that methane from ruminants contains contemporary carbon, whereas that from wetlands, pat bogs, rice fields, and tundra is somewhat, depleted in carbon-14. Atmospheric (14)GH(4) seems to have increased from 1986 to 1987, and levels at the end of 1987 were 123.3 +/- 0.8 percent modern carbon (pMC) in the Northern Hemisphere and 120.0 +/- 0.7 pMC in the Southern Hemisphere. Model calculations of source partitioning based on the carbon-14 data, CH(4) concentrations, and delta(13)C in CH(4) indicate that 21 +/- 3% of atmospheric CH(4) was derived from fossil carbon at the end of 1987. The data also indicate that pressurized water reactors are an increasingly important source of (14)CH(4).     

非均匀温差下埋地双层管道过渡段长度的计算

在管道输送介质过程中,由于管内温度和周围环境温度的差别,热量传播不可避免,温差沿管道的分布是变化 的。引入了温度衰减长度概念,在温差沿管道均匀分布时过渡段长度计算方法的基础上。     

晚熟柑橘山地果园小区域环境温湿度差异调查

为完善南充地区晚熟柑橘越冬技术理论体系,探寻山地果园不同小区域环境的温湿度差异,便于科学进行晚熟柑橘越冬管理。本研究于2021-2022年冬季在四川省南充市开展了山地果园不同地势、不同天气下的温湿度差异调查。调查得知,同一山地果园不同地势的温湿度差异明显,尤其是温度的差异。同一果园洼地的平均温度和最低温度最低,≦0 ℃和≦-1 ℃的天数及最长持续时长均为洼地>半山腰>山顶。同时,无论在何种天气条件下,山顶的最低温度都是最高的,洼地的最低温度都是最低。低温霜冻天气下,在凌晨和夜间等温度较低时段内,始终是山顶温度最高,洼地温度最低。在山地果园中洼地整体平均温度、最低温度、低温天数、低温持续时长都是最低或最长的,尤其在霜冻天气时洼地温度低、湿度大,最容易遭受低温冻害,而山顶的晚熟柑橘相对容易越冬。     

链格孢菌毒素细交链孢菌酮酸在土壤中的降解研究

细交链孢菌酮酸是病原真菌链格孢菌（A lternaria sp．）产生的主要毒素之一,在霉变的粮食、感病的植物和腐烂的水果中都能检测到,其具有较强的动物毒性,给食品安全带来一定的隐患。分别在实验室和大田条件下对链格孢菌毒素细交链孢菌酮酸在土壤中的降解动态进行了观察。结果表明,在实验室条件下,微生物对细交链孢菌酮酸在土壤中的降解影响较大,光照的影响较弱,不灭菌条件下,其半衰期小于10d,加药10d时,其降解率就大于50％;灭菌条件下,其半衰期大于30d,加药40d时,其降解率才超过50％。土壤含水量的增加和土壤温度在一定范围内的升高可促进其降解,土壤含水量为12．5％-50％,其半衰期为11．38-5．14d,加药10d时其降解率为38．98％-62．14％,温度为20—40℃时,其半衰期为14．26-5．11d,加药10d时其降解率为36．94％-62．45％。田间研究表明．细交链孢菌酮酸在自然条件下降解的半衰期约为3．22d,20d后就可完全降解。可认为细交链孢菌酮酸属于易降解类物质。     

高山被孢霉△~6-脂肪酸脱氢酶基因在大豆中的表达

 将从高山被孢霉中克隆的△6-脂肪酸脱氢酶基因与植物表达载体pBI121连接,构建了重组质粒pBMICL6,采用农杆菌介导的大豆子叶节转化系统成功地将该基因导入到栽培大豆吉林35、吉林43、吉林47、绥农10、绥农14和黑农37等品种中,获得了一批转基因植株。经PCR检测和Southern杂交分析,证明外源基因已导入并整合到大豆的基因组中。Northern杂交结果表明,该基因在转基因大豆的mRNA水平上获得表达。通过气相色谱(GC-MS)对大豆种子进行脂肪酸成分分析,发现转基因大豆产生了γ-亚麻酸,其含量最高     

庄河产薏苡仁中氨基酸含量的测定

按照国标GB/T 5009.124-2003方法处理样品,对庄河产薏苡仁中氨基酸的含量进行了测定。结果表明,庄河产薏苡仁中含有16种氨基酸,Asp、Thr、Ser、Glu、Gly、Ala、Val、Met、Ile、Leu、Tyr、Phe、Lys、His、Arg、Pro的含量分别为1 350.0、252.0、349.0、1 480.0、214.0、699.0、297.0、84.3、181.0、544.0、169.0、215.0、208.0、170.0、456.0、846.0μg/kg。     

煤质腐植酸在农业生产中的作用

煤质腐植酸粗略分为腐植酸（ＨＡ）和黄腐酸（ＦＡ）两大类，是芳香稠环缩合程度不同、取代度不同的多取代芳香羧酸混合体，不可能用单一的化学结构表示。煤质腐植酸在农业上有广阔的应用前景，在改良盐碱地上有明显效应，能够促进土壤微生物活动，增加土壤酶活性；应用于化肥可作为缓释剂、包衣剂，可增加肥效，减少挥发，提高化肥利用率；有促进植物呼吸和新陈代谢功能，用来生产各种植物生长调节剂和增糖剂、抗旱剂、抗寒剂等；与农药配合使用有缓释和增效作用；在养殖业中可配制各种饲料添加剂。     

石榴皮制取鞣花酸技术研究进展

本文对近年来以石榴皮为原料制取鞣花酸的相关研究及其进展情况进行了综述,归纳了相关的制取工艺及其优缺点,对石榴皮鞣花酸的应用前景进行简要分析,以期为石榴皮的加工利用提供参考。