High Pressure Calorimetry. Comparison of two systems (differential vs. single cell). Application to the phase change of water under pressure

In high pressure calorimetry the pressure change is used to obtain the desired phenomenon (i.e. phase change) at constant temperature. Two high pressure calorimeters have been developed to measure the latent heat of fusion of pure water (hexagonal ice-type I) at subzero temperature. Both calorimeters used a constant pressurisation rate produced with a high pressure pump driven by a step motor. The first calorimeter was a single cell calorimeter where mercury acted as the pressurisation fluid, while the second one was differential (two cells) and was pressurised with pentane. Both calorimeters gave high accuracy data of latent heat of fusion of pure water, which were determined taking into account that either the fluid used to pressurise or the pressurisation rate affected the calorimetric signal. This revised version was published online in July 2006 with corrections to the Cover Date.     

东海区海岸带景观格局变化对生态系统服务价值的影响

对大尺度、长时序的海岸带景观格局和生态系统服务价值(ecosystem services value,ESV)的研究,有利于更好地促进区域生态系统保护工作的开展。以1990,1995,2000,2005,2010,2015年6期遥感影像解译结果为基础,对东海区海岸带景观格局变化特征和ESV时空演变进行了分析,并探讨了ESV与景观格局变化二者间的关系。结果表明,1990—2015年的25 a间,受人类活动的影响,东海区海岸带农田和海域面积大量减少,建设用地面积大幅增加;在所研究的5类地貌类型中,除中起伏山地外,其余地貌类型景观面积转移都较为剧烈。25 a间东海区海岸带斑块数量、斑块密度、边界密度、shannon多样性指数等不断增加,景观破碎化、复杂化、多样化增强。农田景观的最大斑块指数、形态指数、边界密度等变化均较大。东海区海岸带ESV呈先增加后减小的趋势,其中森林景观对ESV总量贡献最大;水文调节、生物多样性维持、气候调节、土壤保持、废物处理和气体调节是东海区海岸带主要的生态系统服务功能;在空间上表现出以单位面积中、低ESV为主导的空间分布,高、极高和极低ESV分布较少。研究区ESV总量与农田和海域以及水域和建设用地面积显著相关;与斑块密度、边界密度和形态指数呈显著负相关。同时,食物生产、气体调节、气候调节、土壤保持和生物多样性维持的服务价值与景观指数间均显著相关。     

基于多角度偏振特性的云相态识别及验证

云相态识别是云参数研究的重要组成部分,为了有效识别水云和冰云,根据水云和冰云微物理性质的差别,研究了水云和冰云的单次散射特性,采用基丁倍加累加法的,人量辐射传输方程模拟了水云和冰云的多角度偏振特件.模拟结果表明,光谱的多角度偏振特件能够体现山水云粒子和冰云粒子微物理性质的差异,云在特定方向反射的偏振辐射强度对云相态非常敏感,可以用米进行云相念的识别,在模拟的基础上进行了云相态识别算法的研究,并利用多角度偏振卫星数据--POLDER 0.865μm通道数据进行了实例分析.识别结果与MODIS云相态产品及其1.38μm卷云榆测结果进行了比较.分析结果表明,基于多角度偏振特性云相态识别算法可以有效地进行云相态识别.     

基于Mie散射的卷云光学特性

基于中纬度卷云冰晶双峰、热带卷云冰晶三峰分布模型,利用Mie散射理论计算了1～13脚范围内中纬度及热带卷云的消光系数、散射系数、吸收系数。计算结果表明,由不同形状冰晶构成的热带卷云的相应光学参数比中纬度卷云的光学参数大些,但11支子弹玫瑰形状的相应参数要小一些;两种卷云在2．8～3．1μm,9．8～13μm范围内都存在两个基本相同的透射通带;在计算中纬度卷云的光学参数时,可以只考虑中空六棱柱与实心六棱柱中的一种,但计算热带卷云的光学参数时,实心六棱柱与空心六棱柱需要同时考虑。     

Grain boundary premelting of monolayer ices in 2D nano-channels

ABSTRACT

We employ molecular-dynamics (MD) simulations to study grain boundary (GB) premelting in ices confined in two-dimensional hydrophobic nano-channels. Premelting transitions are observed in symmetric tilt GBs in monolayer ices and involve the formation of a premelting band of liquid phase water with a width that grows logarithmically as the melting temperature is approached from below, consistent with the existing theory of GB premelting. The premelted GB is found rough for a broad range of temperature below the melting temperature, the two ice-premelt interfaces bounding the melted GB are engaged with long wave-length parallel coupled fluctuations. Based on current MD simulation study, one may expect GB premelting transitions exist over a wide range of low dimensional phases of confined ice and shows important consequences for crystal growth of low dimensional ices.     

The influence of optical properties of shallow shelf seas on temperature structure and acoustic propagation

The penetration of solar radiation below the sea surface is not always taken into account in numerical ocean models, even though its influence on the temperature (and therefore sound speed), structure of the water column can be significant, especially in shallow shelf seas where water turbidity tends to be high. Variations in sound speed structure have a consequent effect on the propagation of sound underwater which, in turn, influences the performance of sonar systems. A double exponential parameterization for the penetration of solar radiation with depth was implemented in an N × 1D turbulence closure model of the UK shelf seas. The model was run along a section through the Celtic Sea Front, with sets of optical extinction coefficients representing different water clarities, for one month to simulate the generation of the front, and the results were compared with a control model run in which all solar radiation was absorbed in the surface layer. Temperature structure and sound propagation were only affected by changes to the optical parameterization on the stratified side of the front, where consequent variations in acoustic propagation loss of up to 10 dB relative to the control were simulated using an acoustic model. Changes in propagation loss were greatest for acoustic sources placed in the stratified water above the thermocline. Similar changes to the optical parameterization made on the well-mixed side of the front had no discernible effect.     

强耦合磁失措自旋冰系统Dy2Ti2O7单晶生长和基本磁性质测量

利用红外光源浮区法生长出大尺寸、高质量的磁失措自旋冰化合物Dy₂Ti₂O₇单晶体.X射线衍射实验证实晶体具有面心立方结构，空间群为Fd3m，晶胞参数a＝1.0112(2) nm，［111］和［400］方向X射线衍射摇摆曲线半高宽分别仅为0.07°和0.05°.直流磁化率与温度关系测量给出晶体的Van Vleck顺磁因子为2.46×10^-5 m³/mol，有效磁矩μ_eff＝10.24(4)μ_B，Cure-Weiss温度Θ_CW＝1.1 K，揭示Dy₂Ti₂O₇具有弱的铁磁性.对磁性起源的综合分析表明，该自旋冰晶体磁性质主要来源于磁偶极相互作用，且相关最近邻长程偶极相互作用能量标度D_nn＝3.00 K. 关键词： 2Ti₂O₇')" href="#">Dy₂Ti₂O₇ 浮区法晶体生长 关联电子系统 自旋冰     

Dynamic SIMS analysis of cryo-prepared biological and geological specimens

The modification of a dynamic magnetic sector secondary ion mass spectrometry (SIMS) instrument to permit the analysis of frozen biological and geological samples is described. The SIMS instrument used for this study combines SIMS analysis with the generation of ion-induced secondary electron images, allowing direct superposition of the SIMS image onto the image of cellular structures. Secondary ion maps have been acquired with sub-micron resolution, permitting the characterisation of sub-cellular elemental distributions in plant cells and human fibroblast cells, as well as the distribution of chemical impurities at grain boundaries in polar ice samples. This cryo-preparation technique clearly extends the applicability of SIMS analysis to a wide range of samples.     

Onsager,ice, biomembranes,dimer models and the F-model

Personal recollections give a sampling of some of Onsager's later interests in ice and biomembranes. The author's involvement in these topics led to modeling a particular biomembrane phase transition using dimer models. Recent work is described for a particularly rich dimer model which is isomorphic to the F-model in three kinds of fields (direct, staggered, and quarter). New results for the full three-dimensional phase diagram show (1) how the anomalous OK multicritical point is destroyed by a direct field, and (2) how a new line of critical points must be added to the phase diagram in direct and staggered fields obtained previously by Baxter, due to diverging susceptibilities in the quarter field.     

A stochastic model for backscattering on the sea

Backscattering of radar waves on the sea takes place even when there is no target. It appears as a noise which it is necessary to study in decision problems. Today, the model of a mixing of Gaussian for spectra seems widely agreed. In this paper, we show that it is equivalent to a mixing of monochromatic waves whose trajectories are time perturbed by Gaussian processes. In addition, this model explains linear variations of Doppler shifts and spectral widths with the emitted frequencies.