γ-辐照尼龙－610的热学性能

尼龙－610除具备一般聚酰胺的优良特点外，与尼龙－6、尼－66等大批量生产的工程塑料相比，还有其独特的优良特性，即尼龙－610吸水性较小，尺寸比较稳定。因而它广泛应用于制造日用、机械、电器及航空等工业制品。尽管尼龙－610 性能优良，但对一些使用温度和尺寸精度要求高的产品而言，还不够理想。如果将尼龙－610经γ－射线辐照，分子间形成空间网络，可能使产品的尺寸更稳定，使用温度更高，使用领域更为扩展。作为高分子材料，尼龙－610的结构和性能方面的研究很少进行，经γ－射线辐照交联后产物的结构与性能的研究则更为少见。这在一定程度上限制了尼龙－610的加工和使用。本文用DSC示差扫描量热仪，广角X－射线衍射仪等手段研究尼龙－610本身的热性能和结构特性，以及辐照后尼龙－610的热性能。采用对尼龙－610样品进行部分湿度扫描、变更升、降温速度及变更等温结晶温度的方法研究了尼龙－610的熔融、结晶行为。发现在等速升温过程中，均有多重熔融峰出现，它们对升温速率、降温速率及等温结晶的湿度分另有没程度的依赖性。高温熔融峰几科不受升温速度、降温速度及等温结晶温度影响，它主要是在扫描过程中试样原有结晶不完善部分在低温下熔化和再结晶或重排而形成的介稳态α－型晶体的熔化，或在玻璃化变温度Tg以上冷结晶形成的介稳态结晶的重组和重排而形成晶体的熔化。低温熔融峰受升温速率、降温速度及等温结晶的温度影响很大，是由热历史造成的结晶的熔融。多重熔融峰不是来自于不同晶型，实验发现尼龙－610在等速降温和等温结晶过程中产生的结晶均为α－型三斜晶系。采用Tm与Tc作图外推的方法，估得尼龙－610样品的平衡熔融温度为。Tm°= 518.1 K。此值与Van krevelen的报导值516K相近。利用聚合物熔化热和与其对应比容Vsp外推的方法，求得尼龙－610的平衡熔融热为：△Hm°= 51.8 cal/gram。用DSC－RC示差扫描量热 仪研究了室温、真空气氛下，经60 ℃ γ射线辐照的尼龙－610的热行为及辐效应。发现随辐照剂量增加，熔融峰湿度向低温方向移动，从熔体等速降温时，只有单一结晶峰出现，随辐照剂量增加，结晶峰变宽，结晶温度下降，且熔融热与结晶热也随剂量增加而减小。尼龙－610样品在400－700Mrad之间的剂量辐照时，第二次等速升温的熔融谱图上，有冷结晶峰出现，此冷结晶峰随热历史及辐照剂量变化。它主要是尚未形成完整间网络和技化的尼龙－610大分子的贡献。辐照尼龙－610也符合charlesby-Pinner无规交联议程。用Charlesby-pinner方程算得尼龙－610样品的辐照交联G（CL）＝ 0.57。选择适当的等温结晶温度，用DSC－RC示差扫描是热仪研究了辐照尼龙－610榈的等温结晶动力学。动力学计算由3600TADS计算机所带部分面积程序给出。实验出现，随辐照剂量增加，尼龙－610的Avrami指数n减小。结晶表面自由能σ＿e随辐照剂量加而增大，在同一结晶条件下，辐照剂量愈大，球晶数目愈多，结晶愈不完整，说明尼龙－610经γ－射线辐照交联后可能由均相三维无热成核变为异相单维无热成核。且化学交联点，可能充当结晶的成核中心。

黄土高原区农田覆盖效应与前景分析

依据黄土高原区的水热条件,结合已有研究结果,简述了黄土高原地区农田不同覆盖类型,诸如秸秆覆盖、聚氯乙烯薄膜覆盖、生物覆盖等。分析了农田覆盖技术的生态环境效应和经济效应,农田覆盖可提高土壤含水率,增加土壤耕层温度,改善土壤肥力状况,减少水土流失,促进作物生长,并指出生物覆盖、秸秆还田和聚氯乙烯薄膜覆盖技术在该区的应用前景。

Hydrogenation of cinnamaldehyde over Pt/RHCs in supercritical carbon dioxide - Influence of support pretreatment and phase behavior

The selective hydrogenation of cinnamaldehyde (CAL) was investigated using rice husk-based porous carbon (RHCs) supported platinum catalysts in supercritical carbon dioxide (SCCO2). The effects of surface chemistry treatment of the support and the reaction phase behavior have been examined. The Pt/H-RHCs (HNO3-pretreated) was more active for CAL hydrogenation compared with Pt/NH3 - RHCs (NH3 center dot H2O-pretreated). The Pt/RHCs catalyst exhibited a higher selectivity to cinnamyl alcohol (COL) compared with commercial catalyst of Pt/C, which is relative to the micro - mesoporosity structure of the RHCs.

Energetic basis of molecular recognition in a DNA aptamer

The thermal stability and ligand binding properties of the L-argininamide-binding DNA aptamer (5'-GATCGAAACGTAGCGCCTTCGATC3') were studied by spectroscopic and calorimetric methods. Differential calorimetric studies showed that the uncomplexed aptamer melted in a two-state reaction with a melting temperature T-m = 50.2 +/- 0.2 degrees C and a folding enthalpy Delta H degrees(fold) = -49.0 +/- 2.1 kcal mol(-1). These values agree with values of T-m = 49.6 degrees C and Delta H degrees(fold) = -51.2 kcal mol(-1) predicted for a simple hairpin structure. Melting of the uncomplexed aptamer was dependent upon salt concentration, but independent of strand concentration. The T of aptamer melting was found to increase as L-argininamide concentrations increased. Analysis of circular dichroism titration data using a single-site binding model resulted in the determination of a binding free energy Delta G degrees(bind) = -5.1 kcal mol(-1). Isothermal titration calorimetry studies revealed an exothermic binding reaction with Delta H degrees(bind) = -8.7 kcal mol(-1). Combination of enthalpy and free energy produce ail unfavorable entropy of -T Delta S degrees = +3.6 kcal mol(-1). A molar heat capacity change of -116 cal mol(-1) K-1 was determined from calorimetric measurements at four temperatures over the range of 15-40 degrees C. Molecular dynamics simulations were used to explore the structures of the unligated and ligated aptamer structures.

Syntheses and crystal structures of [Mn(H2O)(4)(bpy)]L center dot 4H(2)O, [Mn(H2O)(4)(bpy)]L ' center dot 4H(2)O (H2L = SUCCINIC ACID, H2L ' = FUMARIC ACID)

Reactions of freshly prepared M(OH)(2-2x)(CO3)(x) (.) yH(2)O (M = Mn, Zn) and 4,4'-bipyridine (bpy) with succinic acid (H2L) or famaric acid (H2L') in CH3OH-H2O afforded [Mn(H2O)(4)(bpy)]L (.) 4H(2)O, 1, [Mn(H2O)(4)(bpy)]L' (.) 4H(2)O, 2 and [Zn(H2O)(4)(bpy)]L (.) 4H(2)O, 3. The three coordination polymers are isostructural and consist of (1)(infinity)[M(H2O)(4)(bpy)(2/2)](2+) cationic chains, crystal H2O molecules and dicarboxylate anions (succinate or fumarate anions). Within the chains, the metal atoms are each octahedrally coordinated by four aqua oxygen atoms and two pyridyl nitrogen atoms from two 4,4'-bipyridine ligands. The crystal H2O molecules are hydrogen bonded to dicarboxylate anions to form ribbon-like anionic chains. The cationic and anionic chains are interconnected via hyqrogen bonds to generate a 3D network. Crystal data: 1 triclinic, P (1) over bar, a = 7.235(1), b = 7.749(2), c = 10.020(2) Angstrom, alpha = 79.95(3), beta = 88.79(3), gamma = 71.39(3)degrees, V = 523.9(2) Angstrom(3) and D-cal = 1.494 g cm(-3) for Z = 1; 2 triclinic, P (1) over bar, a = 7.127(1), b = 7.800(2), c = 9.945(2) Angstrom, alpha = 80.26(3), beta = 87.86(3), gamma = 72.69(3)degrees, V = 520.2(2) Angstrom(3) and D-cal = 1.498 g cm(-3) for Z = 1; 3 triclinic, P (1) over bar, a = 7.189(1), b = 7.764(2), c = 9.843(2) Angstrom, alpha = 79.16(3), beta = 87.80(3), gamma = 71.29(3)degrees, V = 510.9(2) Angstrom(3) and D-cal = 1.559 g cm(-3) for Z = 1.

Isothermal crystallization of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

Isothermal crystallization behavior of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was investigated by means of differential scanning calorimetry and polarized optical microscopy (POM). The Avrami analysis can be used successfully to describe the isothermal crystallization kinetics of PHBV, which indicates that the Avrami exponent n = 3 is good for all the temperatures investigated. The spherulitic growth rate, G, was determined by POM. The result shows that the G has a maximum value at about 353 K. Using the equilibrium melting temperature (448 K) determined by the Flory equation for melting point depression together with U-* = 1500 cal mol(-1), T-infinity = 30 K and T-g = 278 K, the nucleation parameter K-g was determined, which was found to be 3.14+/-0.07 x 10(5) (K-2), lower than that for pure PHB. The surface-free energy sigma = 2.55 x 10(-2) J m(-2) and sigma(e) = 2.70+/-0.06 x 10-2 J m(-2) were estimated and the work of chain-folding (q = 12.5+/-0.2 kJ mol(-1)) was derived from sigma(e), and found to be lower than that for PHB. This implies that the chains of PHBV are more flexible than that of PHB.

Crystal structure of mixed sodium-potassium paradodecatungstate 6-hydrate

The crystal structure of K7Na3[H2W12O42]3 . 6H(2)O was determined by X-ray crystallography,and refined to R=0.0864 based on 7024 observed reflections (I>2 sigma(I)). The crystallographic parameters are a=11.755(2), b=13.0493(3), c=16.289(3) Angstrom; alpha=77.13(3)degrees, beta=82.92(3)degrees, gamma=89.65(3)degrees, triclinic, space group, P (1) over bar, V=2416.7(8) Angstrom(3), Z=2, M-r=3330.98, D-cal=4.578Mg/m(3), F(000)=2904; mu (MoK alpha)=29.170mm(-1), T=293K. Two independent polyanions are centered respectively at 1,1,1/2 and 1/2, 1/2, 0, approximately perpendicular to each other with dihedral angle between the equatorial planes of the molecules at 96 degrees. K+ and Na+ respectively occupy the clefts of the two discrete polyanions.

Palaeoenvironmental changes from pollen record in deep sea core PC-1 from northern Okinawa Trough, East China Sea during the past 24 ka

A pollen record of core PC-1 from the northern Okinawa Trough, East China Sea (ECS), provides information on vegetation and climate changes since 24 cal. kaBP. A total of 103 samples were palynologically analyzed at 8 cm intervals with a time resolution of 230 a. Four pollen zones are recognized: zone I (812-715 cm, 24.2-21.1 cal. kaBP), zone II (715-451 cm, 21.1-15.2 cal. kaBP), zone III (451-251 cm, 15.2-10.8 cal. kaBP), zone IV (251-0 cm, 10.8-0.3 cal. kaBP), corresponding to Late MIS 3, Last Glacial Maximum (LGM), deglaciation and Holocene, respectively. The LGM is characterized by the dominance of herbs, mainly Artemisia, and high pollen influx, implying an open vegetation on the exposed continental shelf and a cool and dry climate. The deglaciation is a climate warming stage with Pinus percentage increased and Artemisia percentage decreased and a rapid sea-level rise. The Holocene is characterized by predominance of tree pollen with rapid increase in Castanea-Castanopsis indicating the development of mixed evergreen and deciduous broad-leaved forest and a warm, humid climate. Low pollen influx during the Holocene probably implies submergence of the continental shelf and retreat of the pollen source area. The vegetation indicated by pollen assemblage found in this upper zone is consistent with the present vegetation found in Kyushu, Japan. Originating from the humid mountain area of North Luzon of the Philippines, Tasmania and New Zealand, Phyllocladus with sporadic occurrence throughout PC-1 core probably suggests the influence of Palaeo-Kuroshio Current or intense summer monsoon. The observed changes in Pinus and Herbs percentage indicate fluctuations of the sea level, and high Pinus percentage corresponds to high sea level. Spectrum analysis of the pollen percentage record reveals many millennial-scale periodicities, such as periodicities of 6.8, 3.85 2.2, 1.6 ka.

Formation and evolution of the modern warm current system in the East China Sea and the Yellow Sea since the last deglaciation

To reconstruct the formation and evolution process of the warm current system within the East China Sea (ECS) and the Yellow Sea (YS) since the last deglaciation, the paleoceangraphic records in core DGKS9603, core CSH1 and core YSDP102, which were retrieved from the mainstream of the Kuroshio Current (KC), the edge of the modern Tsushima Warm Current (TWC) and muddy region under cold waters accreted with the Yellow Sea Warm Current (YSWC) respectively, were synthetically analyzed. The results indicate that the formation and evolution of the modern warm current system in the ECS and the YS has been accompanied by the development of the KC and impulse rising of the sea level since the last deglaciation. The influence of the KC on the Okinawa Trough had enhanced since 16 cal kyr BP, and synchronously the modern TWC began to develop with the rising of sea level and finally formed at about 8.5 cal kyr BP. The KC had experienced two weakening process during the Heinrich event 1 and the Younger Drays event from 16 to 8.5 cal kyr BP. The period of 7-6 cal kyr BP was the strongest stage of the KC and the TWC since the last deglaciation. The YSWC has appeared at about 6.4 cal kyr BP. Thus, the warm current system of the ECS and the YS has ultimately formed. The weakness of the KC, indicated by the occurrence of Pulleniatina minimum event (PME) during the period from 5.3 to 2.8 cal kyr BP, caused the main stream of the TWC to shift eastward to the Pacific Ocean around about 3 cal kyr BP. The process resulted in the intruding of continent shelf cold water mass with rich nutrients. Synchronously, the strength of the YSWC was relatively weak and the related cold water body was active at the early-mid stage of its appearance against the PME background, which resulted in the quick formation of muddy deposit system in the southeastern YS. The strength of the warm current system in the ECS and the YS has enhanced evidently, and approached to the modern condition gradually since 3 cal kyr BP.

Benthic foraminifera and bottom water evolution in the middle-southern Okinawa Trough during the last 18 ka

A piston sediment core E017 from the middle-southern Okinawa Trough was investigated. A preliminary study of the deep-water evolution since 18 cal. ka BP was performed based on the quantitative census data of benthic foraminiferal fauna, together with planktonic foraminiferal oxygen and carbon isotope, AMS(14)C dating, and the previous results achieved in the southern Okinawa Trough. The result shows that the benthic fauna was dominated by Bulimina aculeata (d'Orbigny), Uvigerina peregrina (Cushman), Hispid Uvigerina and Uvigerina dirupta (Todd) during the glaciation-deglaciation before 9.2 cal. ka BP, while Epistominella exigua (Brady), Pullenia bulloides (d'Orbigny), Cibicidoides hyalina (Hofker), Sphaeroidina bulloides (d'Orbigny) and Globocassidulina subglobosa (Brady) predominated the fauna in the post-glacial period after 9.2 cal. ka BP. The benthic foraminifera accumulation rate (BFAR), paleoproductivity estimates and benthic foraminiferal assemblage conformably indicate that surface water paleoproductivity and organic matter flux during the glaciation-deglaciation were higher than those of the post-glacial period in the middle-southern Okinawa Trough, and gradually enhanced from the southern to the central Okinawa Trough during the glaciation-deglaciation, which could be caused by the discrepancy of the terrigenous nutrients supply. High abundances of E exigua, an indicator of pulsed organic matter input, after 9.2 cal. ka. BP may indicate that the intensity of seasonally riverine pulsed flux during the post-glacial period was stronger than that of the glaciation-deglaciation period, and the seasonal influx in the central trough might be stronger than in the south. The temporal distributions of the typical species indicating bottom water oxygen content and ventilation condition show that the ventilation of the bottom water during the post-glacial period is more active than the glaciation-deglaciation, which reflects that the evolution of the intermediate and deep waters of the northwestern Pacific during the last glaciation has no evident influence on the deep-water of the middle-southern Okinawa Trough. Additionally, the variations in agglutinated benthic foraminiferal abundance and other carbonate dissolution proxies indicate that carbonate dissolution gradually increased since the last 18 ka in the Okinawa Trough and rapidly enhanced at 9.2 cal. ka BP. The modern shallow carbonate lysocline could form at 3 cal. ka BP.

Geological records of marine environmental changes in the southern Okinawa Trough

Indexes of sediment grain size, sedimentation rates, geochemical composition, heavy minerals, benthic foraminiferal fauna, indicator species of the Kuroshio Current, paleo-SST and carbonate dissolution of core E017 conformably suggest a great marine environmental change occurring at about 10.1-9.2 cal. kaBP in the southern Okinawa Trough, which may correspond to the strengthening of the Kuroshio Warm Current and re-entering the Okinawa Trough through the sea area off northeast Taiwan. The invasion of Kuroshio current has experienced a process of gradual strengthening and then weakening, and its intensity became more fluctuation during the last 5000 years. Compared to the transition of sediment grain size, geochemical composition and heavy minerals, the foraminiferal faunas show a 900-year lag, which may indicate that the invasion of Kuroshio Current and the consequent sea surface and deep-water environmental changes is a gradual process, and fauna has an obvious lag compared to environment altering. The carbonate dissolution of the Okinawa Trough has had an apparent strengthening since 9.2 cal. kaBP, and reached a maximum in the late 3000 years, which may be caused by the deep-water environmental changes due to the invasion of Kuroshio Current.

A broad deglacial delta C-13 minimum event in planktonic foraminiferal records in the Okinawa Trough

The equatorial Pacific upwelling zone has been suspected of playing an important role in the global atmospheric CO2 changes associated with glacial-interglacial cycles. In order to assess the influencing scope of the surface water deglacial delta(13)C minimum in the tropical low-latitude Pacific, the core DGKS9603, collected from the middle Okinawa Trough, was examined for 4513 C records of planktonic foraminifera N. dutertrei and G. ruber. The planktonic foraminiferal delta(13)C records show a clear decreasing event from 20 to 6 cal. kaBP., which is characterized by long duration of about 14 ka and amplitude shift of 0.4 x 10(-3). Its minimum value occurred at 15.7 cal kaBP. The event shows fairly synchrony with the surface water deglacial delta(13)C minimum identified in the tropical Pacific and its marginal seas. Because there is no evidence in planktonic foraminiferal fauna and 45180 records for upwelling and river runoff enhancement, the broad deglacial delta(13)C minimum event in planktonic foraminiferal records revealed in core DGKS9603 might have been the direct influencing result of the deglacial surface water of the tropical Pacific. The identification for the event in the Okinawa Trough provides new evidence that the water evolution in the tropical low-latitude Pacific plays a key role in large regional, even global carbon cycle.

Heinrich event imprints in the Okinawa Trough: evidence from oxygen isotope and planktonic foraminifera

Planktonic foraminiferal faunas, oxygen isotope and modern analog technique sea surface temperature records were obtained in piston core DGKS9603 (28degrees08.869'N, 127degrees16.238'E, water depth 1100 in) collected from the middle Okinawa Trough. During the last glaciation, four cold events were identified and correlate Heinrich events (HE) H2-5 of the last 45 ka. During the last deglaciation, core DGKS9603 has begun to be influenced by the Kuroshio since about 16 cal ka BP. Three weakenings of this warm current occurred at about 2.8-5.3, 11.4 and 15.5 cal ka BP respectively. Among the three fluctuations, the oldest one is synchronous with HE1 and could be a response to the strong cooling observed in the North Atlantic Ocean. The fluctuation occurring at about 11.4 cal ka ago corresponds to the Younger Dryas within the age error bars. Our observations provide new evidence that the HEs documented from Greenland and the northern North Atlantic had a global climatic impact. Changes in the intensity of the East Asian monsoon could be the main mechanism responsible for the paleoccanographic variations observed in the Okinawa Trough. (C) 2001 Elsevier Science B.V. All rights reserved.

Evolution and variation of the Tsushima warm current during the late Quaternary: Evidence from planktonic foraminifera, oxygen and carbon isotopes

The evolution and variation history of the Tsushima warm current during the late Quaternary was reconstructed based on the quantitative census data of planktonic foraminiferal fauna, together with oxygen and carbon isotope records of mixed layer dweller a ruber and thermocline dweller N. dutertrei in piston core CSH1 and core DGKS9603 collected separately from the Tsushima warm current and the Kuroshio dominated area. The result showed that the Tsushima warm current vanished in the lowstand period during 40-24 cal ka BP, while the Kuroshio still flowed across the Okinawa Trough, arousing strong upwelling in the northern Trough. Meanwhile, the influence of freshwater greatly increased in the northern Okinawa Trough, as the broad East China Sea continental shelf emerged. The freshwater reached its maximum during the last glacial maximum (LGM), when the upwelling obviously weakened for the lowest sea-level and the depression of the Kuroshio. The modern Tsushima warm current began its development since 16 cal ka BP, and the impact of the Kuroshio increased in the middle and northern Okinawa Trough synchronously during the deglaciation and gradually evolved as the main water source of the Tsushima current. The modern Tsushima current finally formed at about 8.5 cal ka BP, since then the circulation structure has been relatively stable. The water of the modern Tsushima current primarily came from the Kuroshio axis. A short-term wiggle of the current occurred at about 3 cal ka BP, probably for the influences from the enhancement of the winter monsoon and the depression of the Kuroshio. The cold water masses greatly strengthened during the wiggle.

Paleoenvironmental change in the middle Okinawa Trough since the last deglaciation: Evidence from the sedimentation rate and planktonic foraminiferal record

Well-dated, high-resolution records of planktonic foraminifera and oxygen isotopes from two sediment cores, A7 and E017, in the middle Okinawa Trough reveal strong and rapid millennial-scale climate changes since similar to 18 to 17 thousand years before present (kyr B.P.). Sedimentation rate shows a sudden drop at similar to 11.2 cal. kyr B.P. due to a rapid rise of sea level after the Younger Dryas (YD) and consequently submergence of the large continental shelf on the East China Sea (ECS) and the retreat of the estuary providing sediment to the basin. During the last deglaciation, the relative abundance of warm and cold species of planktonic foraminifera fluctuates strongly, consistent with the timing of sea surface temperature (SST) variations determined from Mg/Ca measurements of planktonic foraminifera from one of the two cores. These fluctuations are coeval with climate variation recorded in the Greenland ice cores and North Atlantic sediments, namely Heinrich event 1 (H1), Bolling-Allerod (B/A) and YD events. At about 9.4 kyr B.P., a sudden change in the relative abundance of shallow to deep planktonic species probably indicates a sudden strengthening of the Kuroshio Current in the Okinawa Trough, which was synchronous with a rapid sea-level rise at 9.5-9.2 kyr B.P. in the ECS, Yellow Sea (YS) and South China Sea (SCS). The abundance of planktonic foraminiferal species, together with Mg/Ca based SST, exhibits millennial-scale oscillations during the Holocene, with 7 cold events (at about 1.7, 2.3-4.6, 6.2, 7.3, 8.2, 9.6, 10.6 cal. kyr BP) superimposed on a Holocene warming trend. This Holocene trend, together with centennial-scale SST variations superimposed on the last deglacial trend, suggests that both high and low latitude influences affected the climatology of the Okinawa Trough. (c) 2006 Elsevier B.V. All rights reserved.