Direct numerical simulation of hypersonic boundary layer transition over a blunt cone with a small angle of attack

The direct numerical simulation of boundary layer transition over a 5° half-cone-angle blunt cone is performed. The free-stream Mach number is 6 and the angle of attack is 1°. Random wall blow-and-suction perturbations are used to trigger the transition. Different from the authors’ previous work [Li et al., AIAA J. 46, 2899(2008)], the whole boundary layer flow over the cone is simulated (while in the author’s previous work, only two 45° regions around the leeward and the windward sections are simulated). The transition location on the cone surface is determined through the rapid increase in skin fraction coefficient (Cf). The transition line on the cone surface shows a nonmonotonic curve and the transition is delayed in the range of 0° ≤ θ ≤ 30° (θ = 0° is the leeward section). The mechanism of the delayed transition is studied by using joint frequency spectrum analysis and linear stability theory (LST). It is shown that the growth rates of unstable waves of the second mode are suppressed in the range of 20° ≤ θ ≤ 30°, which leads to the delayed transition location. Very low frequency waves VLFWs� are found in the time series recorded just before the transition location, and the periodic times of VLFWs are about one order larger than those of ordinary Mack second mode waves. Band-pass filter is used to analyze the low frequency waves, and they are deemed as the effect of large scale nonlinear perturbations triggered by LST waves when they are strong enough.The direct numerical simulation of boundary layer transition over a 5° half-cone-angle blunt cone is performed. The free-stream Mach number is 6 and the angle of attack is 1°. Random wall blow-and-suction perturbations are used to trigger the transition. Different from the authors’ previous work [ Li et al., AIAA J. 46, 2899 (2008) ], the whole boundary layer flow over the cone is simulated (while in the author’s previous work, only two 45° regions around the leeward and the windward sections are simulated). The transition location on the cone surface is determined through the rapid increase in skin fraction coefficient (Cf). The transition line on the cone surface shows a nonmonotonic curve and the transition is delayed in the range of 20° ≤ θ ≤ 30° (θ = 0° is the leeward section). The mechanism of the delayed transition is studied by using joint frequency spectrum analysis and linear stability theory (LST). It is shown that the growth rates of unstable waves of the second mode are suppressed in the range of 20° ≤ θ ≤ 30°, which leads to the delayed transition location. Very low frequency waves (VLFWs) are found in the time series recorded just before the transition location, and the periodic times of VLFWs are about one order larger than those of ordinary Mack second mode waves. Band-pass filter is used to analyze the low frequency waves, and they are deemed as the effect of large scale nonlinear perturbations triggered by LST waves when they are strong enough.

耐酸产甲烷菌的分离及其复合菌剂的研究

本文从成都龙泉垃圾填埋场和宜宾造纸厂分离到耐酸性能优良的高温产甲烷菌RY3和中温产甲烷菌SH4，并将其与实验室现有的利用不同底物的产甲烷菌配伍组合成了复合菌剂。采用活性污泥作为固体附着物，研制出了固体产甲烷菌复合菌剂。 菌株RY3的pH耐受范围为5.5～10.5，最适生长pH 6.0～8.0。菌株RY3为革兰氏阳性，长杆状，多数单生，不运动；菌落浅黄色，形状近圆形；利用H2+CO2或甲酸盐作为唯一碳源生长，不利用乙酸盐，对氯霉素非常敏感。该菌最适生长温度为55℃～65℃，最适NaCl浓度为0～2%。根据形态和生理生化特性及16S rDNA序列分析将其初步定为热自养甲烷热杆菌（Methanothermobacter thermautotrophicus）。添加RY3菌液与仅添加厌氧污泥作为接种物相比一周内可使达到最大产甲烷速率所需时间缩短三分之二，甲烷总产量提高约1.8倍。菌株SH4的生长pH范围5.5～9.5，其对酸碱具有良好的适应性，培养3天后，在初始pH值为6.0～8.0的培养基中甲烷产量相差不大，且基本达到最大产量。SH4革兰氏染色阳性，短杆状，多数单生，不运动；菌落近圆形，微黄；利用H2+CO2或甲酸盐作为唯一碳源生长，不利用乙酸盐，对氯霉素非常敏感。SH4最适生长pH 为7.0，最适生长温度为35℃，最适NaCl浓度为0～1.5%。实验表明，添加SH4菌液与仅添加厌氧污泥作为接种物相比可使产甲烷启动时间缩短三分之一，甲烷总产量亦有大幅提高。从形态和生理生化特征以及16S rDNA序列分析表明SH4为嗜树木甲烷短杆菌（Methanobrevibacter arboriphilus）。 以活性污泥为附着物，与培养基和菌种经搅拌后厌氧发酵可得产甲烷菌固体复合菌剂。固体复合菌剂的pH耐受范围为5.5～9.5，温度耐受范围为15℃～65℃，表明其对环境的适应性较强。以猪粪为底物进行厌氧发酵，接种复合菌剂进行试验，以接种实验室长期富集的产甲烷厌氧污泥作为对照，在20℃时，发酵甲烷浓度与对照基本一致，但每日产气量优于对照，第15天时接种复合菌剂的发酵瓶每日产气量是对照的1.59倍；50℃时达到最大甲烷含量所需时间比对照缩短三分之二，三周内总产气量约为对照的2.7倍，甲烷总产量约为2.8倍。以不加接种物为对照，接种复合菌剂20℃时发酵甲烷含量达到50%约需2周，对照2周内甲烷含量最高仅为4.3%；50℃时接种复合菌剂发酵仅需约1周甲烷含量便可达50%，对照则至少需要2周。 In this paper, high-temperature Methanogen RY3 and middle-temperature SH4 were isolated from Chengdu Longquan refuse landfill and Yibin paper mill. They could be used to make compound inoculum that producing methane with the existing Methanogens utilized different substrate. With using anaerobic activated sludge be solid fixture, the process had been designed to produce solid compound inoculum. Strain RY3 possessed excellent capacity of acid and alkali-tolerant. The pH-tolerant scale of RY3 was 5.5～10.5 and its optimum pH value for growth was 6.0～8.0. RY3 was G+, long-rod shape, monothetic and nonmotile, the colony was pale yellow with suborbicular-shape. Formate or H2+CO2 but not acetate was utilized by RY3 as sole C-source, and it was very sensitive to chloramphenicol. Besides, strain RY3 grew fastest at 55℃～65 and 0℃～2% NaCl. Characteristics of modality and physiology with sequence analysis of the 16s rDNA gene of strain RY3 preliminarily showed that it was Methanothermobacter thermautotrophicus. The experiments indicated that the time which began to produce methane with the highest velocity could be shortened two third by adding RY3 in one week, and the total methane production also was 1.8 times than before. Strain SH4 possessed wide scale of growing pH（5.5～9.5）and excellent ability of acclimatizing itself to acid-alkali. The methane production had no apparent difference among those cultivated in different initial pH（6.0～8.0）after three days and equaled to the maximum production basically. Cells of SH4 were G+, short-rod sharp, monothetic and nonmotile. The colony was pale yellow with suborbicular-shape. Formate or H2+CO2 but not acetate was utilized by SH4 as sole C-source, and it was very sensitive to chloramphenicol. Besides, it grew fastest at pH 7.0，55 ℃～65 and 0℃～2% NaCl concentration. The experiment indicated the time that began to produce methane could be shortening one third by adding SH4. And the total methane production also rose apparently. Characteristic of modality and physiology with sequence analysis of the 16S rDNA gene of strain SH4 demonstrated it was Methanobrevibacter arboriphilus. The activated sludge was utilized as fixture, mixed with culture medium and inocolum, that the solid compound inoculum could be produced by anaerobic fermentation. The compound inoculum could grow between pH 5.5～9.5, 15℃～65. It demonstrated the compound inoculum ha℃ve great ability of adapting to circumstance. In the experiment that making pig manure be substrate and taking the anaerobic sludge producing methane that cultured in long term in laboratory to be comparison, the concentration of methane in fermentation added compound inoculum almost equal to the comparison at 20℃, but the volume of gas production could be a little higher. The gas production everyday inoculated compound inoculum was 1.59 times to comparison. The time that the concentration of methane to maximum could be shortening by two third by adding compound inoculum, and the total gas production was 2.7 times to comprison while the total methane production was 2.8 times. If take the no inoculum be the comprasion, anaerobic fermentation added compound inoculum made the concentration of methane to 50% in 2 weeks but the comparison only to 4.3% at 20℃. The time that the concentration of methane to 50% by adding compound inoculum only need 1 week, but the comparison need 2 weeks at 50℃.

Equatorial pacific SSTA-related decadal variations of potential predictability of ENSO and interannual climate

Based on analysis of NCEP reanalysis data and SST indices of the recent 50 years, decadal changes of the potential predictability of ENSO and interannual climate anomalies were investigated. Autocorrelation of Nino3 SST anomalies (SSTA) and correlation between atmospheric anomalies fields and Nino3 SSTA exhibit obvious variation in different decades, which indicates that Nino3 SSTA-related potential predictability of ENSO and interannual climate anomalies has significant decadal changes. Time around 1977 is not only a shift point of climate on the interdecadal time scale but also a catastrophe point of potential predictability of ENSO and interannual climate. As a whole, ENSO and the PNA pattern in boreal winter are more predictable in 1980s than in 1960s and 1970s, while the Nino3 SSTA-related potential predictability of the Indian monsoon and the East Asian Monsoon is lower in 1980s than in 1960s and 1970s.

北天山新生代构造演化与古环境演变

The Tianshan Mountains is located about 1000-2000 km north of the India-Asia suture and is the most outstanding topography in central Asia, with transmeridional length of nearly 2500 km, north-southern wideness of ~ 300-500 km, peaks exceeding 7000 m above sea level (asl.), and average altitude of over 4000 m asl. Much of the modern relief of the Tianshan Range is a result of contraction driven by the collision of the India subcontinent with the southern margin of Asia, which began in early Tertiary and continues today. Understanding where, when and how the deformation of the Tianshan Mountains occurred is essential to decipher the mechanism of intracontinental tectonics, the process of foreland basin evolution and mountain building, and the history of climate change in central Asia. In order to better constrain the Cenozoic building history of the Tianshan Mountains and the climate change in the southern margin of the Junggar Basin, we carried out multiple studies of magnetostratigraphy, sedimentology, and stable isotopes of paleosol carbonate at the Jingou River section, which is located at the Huoerguosi anticline, the westernest one of the second folds and thrust faults zone in the northern piedmont of the Tianshan Mountains. The Jingou River section with a thickness of about 4160 m is continuous in deposits according to the observed gradual change in sedimentary environments and can be divided into five formations: Anjihaihe, Shawan, Taxihe, Dushanzi and Xiyu in upward sequence. Characteristic remamences were isolated by progressive thermal demagnetization, generally between 300 and 680℃. A total of 1133 out of 1607 samples yielded well-defined ChRMs and were used to establish the magnetostratigraphic column of a 3270-m-thick section from the exposed base of the Anjihaihe Formation to the middle of the Xiyu Formation. Two vertebrate fossil sites and a good correlation with the CK95 geomagnetic polarity time scale suggest that the section was deposited from ~30.5 to ~4.6 Ma and the age of the top of the Xiyu formation is ~2.6 Ma based on an extrapolation of the sedimentation rates. A plot of magnetostratigraphic age vs. height at the Jingou River section shows that significant increases in sedimentation rates as well as notable changes in depositional environments occurred at ~26-22.5 Ma, ~13-11 Ma and ~7 Ma, which represent the initial uplift of the Tianshan Mountains and two subsequent rapid uplift events. In addition, changes in sedimentation rates display characteristic alternations between increases and decreases, which probably indicate that the uplift of the Tianshan Mountains was episodic. We discussed the history of C4 biomass and climatic conditions in the southern margin of the Junggur Basin using the stable carbon and oxygen isotope composition of paleosol carbonates from the Jingou River section during ~17.5-6.5 Ma. The δ13C values indicate that the proportion of C4 biomass was uniform and moderate (15-20 %) during the interval of ~17.5-6.5 Ma. We proposed three hypotheses for this pattern of C4 biomass: (1) counteraction of two opposed factors (global cooling since ~15 Ma and thereafter increased dry and seasonality in central Asia) controlling the growth of C4 grasses, (2) variability in abundance of C3 grasses relative to C3 trees and shrubs if vegetation had ever changed in ecosystems, and (3) the higher latitude of the studied region. The δ18O values show a stepwise negative trend since ~13 Ma which may be attributed to three factors: (1) the temperature decreasing gradually after the middle Miocene (~15 Ma), (2) the increasing contribution of the moistures carried by the polar air masses from the Arctic Ocean to precipitation, and (3) the gradual retreat westward and disappearance of the Paratethys Ocean. Among them, which one played a more important role will need further study of the paleoclimate in central Asia.

东北四海龙湾玛珥湖啊1500年来长链烯酮不饱和度温标与古水温重建

The alkenone unsaturation paleothermometer is an important proxy to reconstruct water temperature, and is widely applied to reconstructing sea surface temperature in most oceanographic settings. Recent research indicates that long chain alkenone is preserved in lacustrine sediments, and the alkenone unsaturation has good relationship with mean annual temperature in studied lakes. Thus, the alkenone unsaturation could be used as a temperature proxy to reconstruct temperature in limnic systems. In this study, we analyzed long chain alkenone from the varved sediments in Lake Sihailongwan, northeastern China. Based on the counting varves, we established time scale during the past 1500 years. The distribution pattern in the sediment is similar with the previous study in lacustrine environment. The ratio of C37:4 methyl ketone to the sum of C37 alkenones is high. Based on the published temperature- alkenone unsaturation equation, we reconstructed the mean air temperature and July water temperature during the past 1500 years. Three major cold periods are in AD560-950, AD 1540-1600 and AD1800-1920. Three major warm periods are AD450-550, AD 950-1400 and AD 1600-1800. The Medieval Warm Period was a significant warm periods. However, the traditional “Little Ice Age” was not a persistent cold period, and interrupted by relative longer warm period. The temperature variations in this study show a general similar pattern with the summer temperature reconstruction from Shihua Cave and the winter temperature from historical documents. The temperature variations from long chain alknone record show a good agreement with solar activity (10Be data from ice core and sunspot number from tree rings). It may suggest that solar activity is most important forcing in the studied area.

中国南方热带地区田洋玛珥湖24万年以来的气候变化及湖泊演变

A continuous long (224m) and high-resolution core TY2 was recovered from paleo-maar-lake Tianyang, tropical South China. Based on the diatom records of the upper 130-m core, this paper focuses on exploring climate change and the lake evolution history in tropical South China during the past 240ka. The most typical and unique characteristics of the diatom assemblages is that, Aulacoseira granulata was dominant or absolutely dominant species (80-90%) during most parts of the 130-m core, while Cyclotella stelligera var. tenuis and Fragilaria construens var. venter were subdominant species in only limited parts of the lower and upper core, respectively. Time scale is always the biggest problem for the study of TY2 core, so although diatom is seldom used for establishing time scale, here we attempt this by correlating the diatom-reconstructed temperature sequence with the time scale of ODP core 806B from Equatorial Western Pacific. Verified by the few most reliable ages from TY2 core and the parallel core TYl, a rather reasonable and reliable time scale was established. 01S 7/6 falls at the depth of 100m (ca. 194kaBP), OIS 6/5 at 75m (ca. 132kaBP), OIS 5/4 at 46m (ca. 75kaBP), OIS 4-3 at 35m (ca. 60kaBP). Qualitative and quantitative environmental reconstructions are made on the basis of diatom assemblage ecotype and EDDI dataset. Correlation of diatom-reconstructed temperature and moisture changes of Core TY2 with pollen-reconstructed temperature and rainfall sequence of Core TYl proves that the results are quite consistent in most periods. Thus the reconstruction results from diatom are quite reliable, and probably have a much higher resolution than pollen results. Combined with lithological and magnetic susceptibility variations, the diatom analysis reveals that, the general climate in tropical South China during the past 240ka was warm and wet. On the time scale of glacial-interglacial, warm and wet, cool and dry are not always synchronous. It was relatively warm-wet during the penultimate interglacial, cool-dry during the penultimate glacial, warm-dry during the last interglacial, and cooler-drier during the last glacial. In contrast, on the time scale of subglacial-subinterglacial scales, warm and dry, cool and wet corresponds very obviously, showing very clear 21-23 ka precession cycle. Analysis also shows that, the water of Tianyang paleo-maar-lake was generally warm, turbulent, turbid, meso-trophic, slightly alkaline, low conductivity and fresh during the past 240 kaBP, with small variations in some parts. Tianyang paleolake experienced shallow to semi-deep lake in OIS7d, open shallow lake in OIS7c-OIS5b, shallow coastal lake in OIS5a-OIS4c, swamp in OIS4b, and then completely dried up in OIS3c. The lake evolution was mainly controlled by temperature and precipitation changes in tropical China. While temperature and precipitation changes were probably controlled by the migrations of monsoon rainband and the evaporation rate, which was in turn controlled by the evolution of East Asian monsoon. Therefore, when the summer monsoon was strongest the climate was warm-dry, when stronger the climate was warm-wet; when the winter monsoon was strongest the climate was cool-dry, stronger cool-wet. This mechanism caused the warm-dry sub interglacial and cool-wet subglacial climate in the tropical South China.

汉字形音义加工时间进程的事件相关电位（ERP）研究

The time-courses of orthographic, phonological and semantic processing of Chinese characters were investigated systematically with multi-channel event-related potentials (ERPs). New evidences concerning whether phonology or semantics is processed first and whether phonology mediates semantic access were obtained, supporting and developing the new concept of repetition, overlapping, and alternating processing in Chinese character recognition. Statistic parameter mapping based on physiological double dissociation has been developed. Seven experiments were conducted: I) deciding which type of structure, left-right or non-left-right, the character displayed on the screen was; 2) deciding whether or not there was a vowel/a/in the pronunciation of the character; 3) deciding which classification, natural object or non-natural object, the character was; 4) deciding which color, red or green, the character was; 5) deciding which color, red or green, the non-character was; 6) fixing on the non-character; 7) fixing on the crosslet. The main results are: 1. N240 and P240:N240 and P240 localized at occipital and prefrontal respectively were found in experiments 1, 2, 3, and 4, but not in experiments 5, 6, or 7. The difference between the former 4 and the latter 3 experiments was only their stimuli: the former's were true Chinese characters while the latter's were non-characters or crosslet. Thus Chinese characters were related to these two components, which reflected unique processing of Chinese characters peaking at about 240 msec. 2. Basic visual feature analysis: In comparison with experiment 7 there was a common cognitive process in experiments 1, 2, 4, and 6 - basic visual feature analysis. The corresponding ERP amplitude increase in most sites started from about 60 msec. 3. Orthography: The ERP differences located at the main processing area of orthography (occipital) between experiments 1, 2, 3, 4 and experiment 5 started from about 130 msec. This was the category difference between Chinese characters and non-characters, which revealed that orthographic processing started from about 130 msec. The ERP differences between the experiments 1, 2, 3 and the experiment 4 occurred in 210-250, 230-240, and 190-250 msec respectively, suggesting orthography was processed again. These were the differences between language and non-language tasks, which revealed a higher level processing than that in the above mentioned 130 msec. All the phenomena imply that the orthographic processing does not finished in one time of processing; the second time of processing is not a simple repetition, but a higher level one. 4. Phonology: The ERPs of experiment 2 (phonological task) were significantly stronger than those of experiment 3 (semantic task) at the main processing areas of phonology (temporal and left prefrontal) starting from about 270 msec, which revealed phonologic processing. The ERP differences at left frontal between experiment 2 and experiment 1 (orthographic task) started from about 250 msec. When comparing phonological task with experiment 4 (character color decision), the ERP differences at left temporal and prefrontal started from about 220 msec. Thus phonological processing may start before 220 msec. 5. Semantic: The ERPs of experiment 3 (semantic task) were significantly stronger than those of experiment 2 (phonological task) at the main processing areas of semantics (parietal and occipital) starting from about 290 msec, which revealed semantic processing. The ERP differences at these areas between experiment 3 and experiment 4 (character color decision) started from about 270 msec. The ERP differences between experiment 3 and experiment 1 (orthographic task) started from about 260 msec. Thus semantic processing may start before 260 msec. 6. Overlapping of phonological and semantic processing: From about 270 to 350 msec, the ERPs of experiment 2 (phonological task) were significantly larger than those of experiment 3 (semantic task) at the main processing areas of phonology (temporal and left prefrontal); while from about 290-360 msec, the ERPs of experiment 3 were significantly larger than those of experiment 2 at the main processing areas of semantics (frontal, parietal, and occipital). Thus phonological processing may start earlier than semantic and their time-courses may alternate, which reveals parallel processing. 7. Semantic processing needs part phonology: When experiment 1 (orthographic task) served as baseline, the ERPs of experiment 2 and 3 (phonological and semantic tasks) significantly increased at the main processing areas of phonology (left temporal and frontal) starting from about 250 msec. The ERPs of experiment 3, besides, increased significantly at the main processing areas of semantics (parietal and frontal) starting from about 260 msec. When experiment 4 (character color decision) served as baseline, the ERPs of experiment 2 and 3 significantly increased at phonological areas (left temporal and frontal) starting from about 220 msec. The ERPs of experiment 3, similarly, increased significantly at semantic areas (parietal and frontal) starting from about270 msec. Hence, before semantic processing, a part of phonological information may be required. The conclusion could be got from above results in the present experimental conditions: 1. The basic visual feature processing starts from about 60 msec; 2. Orthographic processing starts from about 130 msec, and repeats at about 240 msec. The second processing is not simple repetition of the first one, but a higher level processing; 3. Phonological processing begins earlier than semantic, and their time-courses overlap; 4. Before semantic processing, a part of phonological information may be required; 5. The repetition, overlapping, and alternating of the orthographic, phonological and semantic processing of Chinese characters could exist in cognition. Thus the problem of whether phonology mediates semantics access is not a simple, but a complicated issue.