一种不含介晶基团的两亲性高分子的热致液晶行为

一种不含介晶基团的两亲性高分子的热致液晶行为张希，张瑞丰，沈家骢，赵晓光，周恩乐（吉林大学化学系，长春，１３００２３）（中国科学院长春应用化学研究所，中国科学院长春高分子物理开放实验室）关键词两亲性高分子，疏水作用，热致液晶热致液晶分子结构中含有几何...

MELTING BEHAVIOR OF DRAWN POLYPROPYLENE

The melting behavior of drawn, compression-molded isotactic polypropylene has been examined in terms of the influence of drawing conditions on the observed properties. Two endothermic peaks were observed on differential scanning calorimetry (DSC) for samples when high draw ratios and high heating rates were used during DSC tests. The peak at lower temperature is influenced by draw ratio, temperature, and rate, and exhibits a strong superheating effect. The species associated with this peak can partially recrystallize into another species associated with the peak at higher temperature during DSC measurements. The position of the peak at higher temperature depends only on draw ratio. It is proposed that the double-melting peaks at lower and higher temperature result from extremely thin quasi-amorphous or crystalline layers between microfibrils and the lamellar crystals within microfibrils, respectively. (C) 1993 John Wiley & Sons, Inc.

用NMR方法研究稀土离子对DPPC脂质体构象的影响

随着稀土元素在工农业中的广泛应用,稀土进入机体内的作用机理是人们日益关心的问题.而稀土对生物体的作用,首先是通过生物膜.因此研究稀土与生物膜的作用是阐明其生理过程的重要环节.生物膜的结构比较复杂,而磷脂脂质体却能表现出生物膜膜脂结构的许

浅海贝藻养殖水域沉积物再悬浮的发生机制及生态效应

沉积物再悬浮作为一个比较普遍的物理现象，对浅海生态系统污染物的生物地球化学循环具有强烈的干扰作用。本研究以我国北方重要养殖海湾——桑沟湾为研究对象，从物理、化学、生物三个角度出发，研究了沉积物再悬浮的发生过程以及再悬浮介质-沉积物的源汇转换角色及其与养殖藻类的关系，构建了波流耦合模型和再悬浮颗粒物浓度预测数学模型。主要研究结果如下： 1）桑沟湾的海湾动力比约为1.54，沉积物具有发生再悬浮的潜在动力条件；推导出波流耦合切应力的计算公式。 2）悬浮颗粒物浓度（SSC）与浊度（NTU）之间符合线性方程SSC=15.908×ln（NTU）+7.0888（n＝33，R2＝0.7209）；碎屑有机碳库是桑沟湾养殖生态系统中最大的有机碳库，占总POC库储量的81.87%。 3）沉积物再悬浮的临界切应力在0.059 N/m2左右，耦合切应力与悬浮颗粒物浓度符合方程= 238.06 SSC + 25.215（n=25，R2 = 0.7298）；最大剪切深度可达8.81 cm；桑沟湾沉积物再悬浮通量的数量级在10-5~10-6 kg·m-2·s-1之间，再悬浮临界风速约为5.51 m/s，全年约有171天沉积物处于再悬浮状态；构建了沉积物再悬浮颗粒物浓度预测数学模型。 4）桑沟湾表层沉积物总氮的含量范围313.09~1094.44µg/g，有机氮是总氮的主要形态，平均占总氮的60.86%；交换态氮是无机氮的主要形式，平均占无机氮的71.40%，交换态氮中NO3--N的含量最大；桑沟湾表层沉积物的TOC/TN比值为9.38，表明沉积物中有机质具有混合来源的特征；无机磷是桑沟湾表层沉积物中磷的主要形态，平均占总磷的73.33%，钙结合磷是无机磷的主要赋存形态；表层沉积物中潜在生物有效性磷的含量占总磷的86.54%，具有很强的释磷潜力。桑沟湾重金属的潜在生态危害指数RI约为36.17，表明重金属的潜在生态危害轻微。 5）再悬浮过程中沉积物春季表现为氮磷源，释放溶解无机氮和磷酸盐；夏、秋季表现为氮汇磷源，释放磷酸盐而吸附溶解无机氮；冬季表现为氮磷汇，吸附磷酸盐和溶解无机氮。

大陆坡折对黑潮路径的影响

一个数值计算模式用以模拟黑潮受南东海大陆坡折阻挡时的路径变化，参照台湾东北部实际地形，本文设计了一个理想化的计算区域。来自菲律宾东部的黑潮进入计算区域，来流与左侧固体边界（模拟台湾岛）平行而与大陆坡折正交。数值求解二维正压原始方程采用ADI差分方法。计算结果表明：一部分黑潮水受阻于坡折而直接右拐，另一部分爬坡侵入陆架，而后回到坡折，与前一部分汇合一起几乎沿着坡折前进。这些结果至少与实测黑潮层水运动状态一致。通过数值分析，我们得到，在台湾东部及东北部附近，非线性效应不可忽略，而在其他海区，地转平衡是一种很好的近似。惯性效应是黑潮源地涡漩的主要形成机制。东海南部的反气旋涡及琉球群岛以南的暖涡是位涡守恒的体现，台湾东南海区的气旋涡则是陆架波沿台湾东海岸向南传播与黑潮来流相互作用的结果。黑潮在陆架坡折附近的流型是以定态地形Rossby波表现出来的。通过量级分析，我们导出了一个地形Rossby定常波的波长表达式。波长与基本流的流速、涡度及涡度的侧向剪切有关。另外波长分布不但与地形坡度，而且也与水深有关。在坡折附近，随着水深变浅，其波长逐渐变短。我们的数值模拟结果也显示出这种性质，黑潮左侧（浅水区）等水位线呈现波状弯曲，而右侧（深水区）等水位线比较平滑。这与实测资料中的陆架坡折附近水温等值线的弯曲形态是一致的。

促肾上腺皮质激素释放激素及去甲肾上腺素对高原鼠兔体液免疫的抑制作用

采用第三脑室注入CRF 及N E 的方法观察对高原鼠兔(Ochotona curzoniae) 体液免疫的影响。结果表明: 第三脑室注入CRF 1 μg 可抑制抗体生成, 比对照下降29.2% (P < 0.01) , 而在第三脑室注入CRF 受体阻断剂α-helical CRF- (9241) 50μg 后再注入CRF 1μg 则可取消CRF 对抗体生成的抑制作用; 第三脑室注入5 nM N E, 与对照相比, 抗体水平下降38.85%(P < 0.01) , 而使用6-OHDA 损毁脑内交感神经系统则使抗体水平升高24.31% (P < 0.01)。这些结果表明, 高原鼠兔中枢CRF 升高对体液免疫有抑制作用, 中枢交感神经系统对体液免疫也具有紧张性抑制作用。

陆地生态系统植物的氮源及氮素吸收

氮是植物生长发育所必需的营养元素,也是其主要的限制因子之一。陆地生态系统植物所需氮的来源及植物对氮素的吸收利用均受控于其种类和生长环境。环境条件的改变,一方面可能改变植物生长区原有氮的形态、浓度、赋存方式等,从而改变氮对植物的供给状况;另一方面可能引起植物生长区土壤质量、水分利用状况、光照等的改变,从而产生耦合现象,直接影响植物的生理生态特性,使植物对氮素的吸收利用发生改变,导致植物生长区的种群类型及物种多样性发生改变,并直接影响到生态系统的功能及演替。本文主要对陆地生态系统中高等植物生长发育所需氮素的来源及植物对氮素吸收利用过程中的影响因素进行了综述和讨论,并结合国内外在该领域的研究现状对其研究前景进行了展望。

Intelligence in Scientific Computing

Combining numerical techniques with ideas from symbolic computation and with methods incorporating knowledge of science and mathematics leads to a new category of intelligent computational tools for scientists and engineers. These tools autonomously prepare simulation experiments from high-level specifications of physical models. For computationally intensive experiments, they automatically design special-purpose numerical engines optimized to perform the necessary computations. They actively monitor numerical and physical experiments. They interpret experimental data and formulate numerical results in qualitative terms. They enable their human users to control computational experiments in terms of high-level behavioral descriptions.

Elaboración de porcelana.

[96] hojas : ilustraciones.

Bound on quantum computation time: Quantum error correction in a critical environment

We obtain an upper bound on the time available for quantum computation for a given quantum computer and decohering environment with quantum error correction implemented. First, we derive an explicit quantum evolution operator for the logical qubits and show that it has the same form as that for the physical qubits but with a reduced coupling strength to the environment. Using this evolution operator, we find the trace distance between the real and ideal states of the logical qubits in two cases. For a super-Ohmic bath, the trace distance saturates, while for Ohmic or sub-Ohmic baths, there is a finite time before the trace distance exceeds a value set by the user. © 2010 The American Physical Society.

Surface-electrode point Paul trap

We present a model as well as experimental results for a surface electrode radiofrequency Paul trap that has a circular electrode geometry well suited for trapping single ions and two-dimensional planar ion crystals. The trap design is compatible with microfabrication and offers a simple method by which the height of the trapped ions above the surface may be changed in situ. We demonstrate trapping of single Sr88+ ions over an ion height range of 200-1000 μm for several hours under Doppler laser cooling and use these to characterize the trap, finding good agreement with our model. © 2010 The American Physical Society.

Performance metrics of an optical spectral imaging system for intra-operative assessment of breast tumor margins.

As many as 20-70% of patients undergoing breast conserving surgery require repeat surgeries due to a close or positive surgical margin diagnosed post-operatively [1]. Currently there are no widely accepted tools for intra-operative margin assessment which is a significant unmet clinical need. Our group has developed a first-generation optical visible spectral imaging platform to image the molecular composition of breast tumor margins and has tested it clinically in 48 patients in a previously published study [2]. The goal of this paper is to report on the performance metrics of the system and compare it to clinical criteria for intra-operative tumor margin assessment. The system was found to have an average signal to noise ratio (SNR) >100 and <15% error in the extraction of optical properties indicating that there is sufficient SNR to leverage the differences in optical properties between negative and close/positive margins. The probe had a sensing depth of 0.5-2.2 mm over the wavelength range of 450-600 nm which is consistent with the pathologic criterion for clear margins of 0-2 mm. There was <1% cross-talk between adjacent channels of the multi-channel probe which shows that multiple sites can be measured simultaneously with negligible cross-talk between adjacent sites. Lastly, the system and measurement procedure were found to be reproducible when evaluated with repeated measures, with a low coefficient of variation (<0.11). The only aspect of the system not optimized for intra-operative use was the imaging time. The manuscript includes a discussion of how the speed of the system can be improved to work within the time constraints of an intra-operative setting.

Automatic segmentation of seven retinal layers in SDOCT images congruent with expert manual segmentation.

Segmentation of anatomical and pathological structures in ophthalmic images is crucial for the diagnosis and study of ocular diseases. However, manual segmentation is often a time-consuming and subjective process. This paper presents an automatic approach for segmenting retinal layers in Spectral Domain Optical Coherence Tomography images using graph theory and dynamic programming. Results show that this method accurately segments eight retinal layer boundaries in normal adult eyes more closely to an expert grader as compared to a second expert grader.