Rod-like crystal growth of dioctyl substituted polyfluorene from nematic and isotropic states

The growth behavior of the rod-like α-form crystals from both the liquid crystal and the isotropic melt state was studied in situ and in real time using a hot-stage atomic force microscopy. The growth rate and direction of the poly(9,9-dioctylfluorene) (PFO) α-form crystals are greatly affected by the orientation of the polymer chains in the liquid crystal matrix. The pre-existence of chain alignment in the liquid crystal matrix serves as a precursor for crystallization, which greatly reduces the growth energy barrier and promotes the overall growth rate of PFO α-form crystals. Our results provide some valuable information for understanding the relationship between morphology and photoexcited emission behaviors.     

溶胶-凝胶和碳热还原法制备塔状SiC纳米棒

以正硅酸乙酯（TEOS）、聚乙烯基吡咯酮（PVP）为反应前驱体，Fe（NO3）3为催化剂，采用溶胶-凝胶和碳热还原法制得了碳化硅纳米棒。运用XRD、^29Si MAS NMR、TEM和SAED等手段对样品的组成和形貌进行了表征。结果表明：产物的形貌为塔状纳米棒，且晶体沿平行于[111]的方向生长；塔形SiC棒的塔底宽约80nm。100nm，塔层厚度10nm左右，长约0．4μm-1．0μm。在催化剂Fe的作用下，过饱和CO气氛中的动力学控制过程导致了塔状SiC纳米棒的形成。     

一种自适应的Tri-Training半监督算法

Tri-Training算法是半监督算法的一种,在学习过程中容易错误标注无标记样本,从而降低分类性能,为此提出一种ADP-Tri-Training（Adaptive Tri-Training）算法,改进协同工作方式,根据几何中心设置分类器组成,然后应用模糊数学理论将多个独立的分类器组合,使得算法可以在多因素下综合评价样本,并在此基础上引入遗传算法动态设置组合权重以适应于具体的样本集,从而尽可能降低样本标注的错误率,多个实验结果表明ADP-Tri-Training算法具有更好的分类性能.     

Edge-oriented uniform intra prediction

We propose an intra prediction solution to block-based image compression. In order to adapt to local image features during intra prediction, we consider the distinct image singularities within the model of piece-wise smooth functions. With such singularities, i.e., edges in this paper, intra prediction can be performed by solving Laplace equations. Moreover, since edges exhibit spatial correlations, we design a rate-distortion optimized method for edge extraction and edge coding. Our edge-oriented intra prediction thus consists of the prediction of smooth regions as well as the prediction of edges. We compare our intra prediction with that in H.264 and achieve superior performance. Our intra prediction can also be integrated into a block-based image coding scheme, which is comparable to JPEG2000 in terms of objective quality. An important advantage of our intra prediction is the improvement in visual quality at low bit-rate due to the preservation of edges.     

Video loss recovery with FEC and stream replication

Packet loss is inevitable in video multicast. In this paper, we propose and study an effective feedback-free loss recovery scheme for layered video which combines forward error correction (FEC) and stream replication. In our scheme, the server multicasts the video in parallel with FEC packets and a number of replicated delayed (ReD) version of the stream. Receivers autonomously and dynamically join the FEC and ReD streams to repair their losses. On the server side, we analyze and optimize the number of replicated streams and FEC packets to meet a certain residual loss requirement (i.e., error after correction). On the receiver side, we analyze the optimal combination of FEC and ReD packets to minimize its loss. We also present a fast yet accurate approximation algorithm for receiver to make such decision. We show that FEC combined with merely one or two replicated streams can effectively reduce the residual error rate (by as much as 50%) as compared with pure FEC or replication alone. Both subjective and objective video measures confirm that our recovery scheme achieves much better visual quality.     

Characteristics of diethylenetriamine-crosslinked cotton stalk/wheat stalk and their biosorption capacities for phosphate

Two polymeric biosorbents were prepared from cotton stalk (CS) and wheat straw (WS) by the epichlorohydrin-diethylenetriamine-trimethylamine method. Amine-crosslinked cotton stalk (AC-CS) and wheat stalk (AC-WS) were used for the adsorption of phosphate, and their physicochemical properties as well as biosorption properties for phosphate were discussed intensively. Results indicated that the contents of holocellulose in CS and WS corresponded to the distinct phosphate adsorption capacities between AC-CS and AC-WS. Zeta potential and Raman spectra analysis illustrated the electrostatic attraction between phosphate ions and biosorbents. The adsorption of phosphate was not strongly pH dependent when the pH was about 4.0-9.0. The Langmuir isotherm provided the better fit and the maximum adsorption capacity (Q_max) was 51.54 mg/g for AC-CS and 60.61 mg/g for AC-WS. The saturated adsorption capacities of AC-CS and AC-WS in column were 49.05 and 41.9 mg/g, which accounted for about 80.3% and 81.4% of these biosorbents’ Q_max. NaCl and HCl solutions demonstrated the excellent regeneration capacities for the biosorbents, and after three times of adsorption-desorption cycles, the column adsorption capacities of these biosorbents were still higher than 92%.     

气相色谱-质谱法测定黑木耳中草甘膦和氨甲基膦酸残留量

目的 采用气相色谱-质谱法建立一种黑木耳中草甘膦和氨甲基膦酸残留的分析方法。方法 干制黑木耳样品经二氯甲烷脱色、水提取、盐酸沉淀蛋白、乙醇沉淀多糖后, 与三氟乙酸酐和七氟丁醇进行衍生化反应, 经气相色谱柱分离后, 在选择离子监测（selected ions monitoring, SIM）模式下进行草甘膦和氨甲基膦酸含量的测定, 外标法定量。结果 干制黑木耳中草甘膦在0.001~0.050 μg/mL浓度范围内呈现良好线性(相关系数R2=0.9993), 表现为弱基质抑制效应, 检出限为0.02 mg/kg, 定量限为0.04 mg/kg, 在0.04、0.08、0.20 mg/kg 3个添加水平下, 平均回收率为82.4%~93.4%, 相对标准偏差为7.8%~9.5%(n=6); 氨甲基膦酸在0.0005~0.050 μg/mL浓度范围内呈现良好线性(相关系数R2=0.9996), 表现为弱基质增强效应, 检出限为0.01 mg/kg, 定量限为0.02 mg/kg, 在0.02、0.08、0.20 mg/kg 3个添加水平下, 平均回收率为85.6%~96.8%, 相对标准偏差为5.7%~9.3%(n=6)。结论 该方法针对干制黑木耳基质, 样品前处理过程简单, 净化除杂效果好且回收率高, 满足农药残留分析实验室对黑木耳中草甘膦和氨甲基膦酸残留的检测要求。     

肉品中β-受体激动剂类药物残留检测技术研究进展

肉品中β-受体激动剂类药物残留问题严重影响着人体健康。近几年来暴露出来的肉品中β-受体激动剂类药物残留事件层出不穷,为了加强监控,越来越多的检测方法被建立起来,极大地提高了肉品中β-受体激动剂类药物残留检测的效率。本文综述了检测肉品中β-受体激动剂类药物残留的色谱法、酶联免疫法、胶体金法和其他一些新方法的研究进展,以及我国现行的β-受体激动剂类药物残留标准检测方法。对现有的检测方法的优缺点和发展阶段作了归纳总结,并对β-受体激动剂类药物残留检测方法发展的方向提出了一些展望。未来的发展主要是一些特异性和灵敏度更高的快检方法和样品前处理更加简化的液质色谱联用法。     

Online rate control for video streams

A mechanism for varying the frame rate of pre-encoded video clips online is described. The mechanism relies on two different encoders. An offline encoder creates a high-quality bit stream encoded at 30 fps, as well as separate files containing motion vectors for the same clip at lower frame rates. An online encoder decodes the bit stream (if necessary) and re-encodes it at lower frame rates in real time using the precomputed, stored motion information. Online frame rate control, used in conjunction with dynamic bit rate control, allows clients to solve the rate mismatch between the bandwidth available to them and the bit rate of the pre-encoded bit stream. Clients can therefore choose the amount of trade-off between temporal and spatial quality while resolving the rate mismatch problem. Moreover, online frame rate control provides a natural means for implementing a VCR-like fast forward control for video streaming applications, without increasing bandwidth consumption.An earlier version of this paper appeared in Proceedings of ACM Multimedia, 1999, pp. 141–144.     

Optical flow-based motion compensation algorithm for very low-bit-rate video coding

In this article, we propose an efficient compression algorithm for very low-bit-rate video applications. The algorithm is based on (a) an optical-flow motion estimation to achieve more accurate motion prediction fields; (b) discrete cosine transformation (DCT) coding of the motion vectors from the optical-flow estimation to reduce the motion overheads; and (c) an adaptive threshold technique to match optical flow motion prediction and minimize the residual errors. Unlike the classic block-matching based DCT video coding schemes in MPEG-1/2 and H.261/3, the proposed algorithm uses optical flow for motion compensation and the DCT is applied to the optical flow field instead of predictive errors. Thresholding techniques are used to treat different regions to complement optical flow technique and to efficiently code residual data. While maintaining a comparable peak signal-to-noise ratio (PSNR) and computational complexity with that of ITU-T H.263/TMN5, the reconstructed video frames of the proposed coder are free of annoying blocking artifacts, and hence visually much more pleasant. The computer simulation are conducted to show the feasibility and effectiveness of the algorithm. Results at 11 kbps are presented which can be used for videophone applications in the existing public switched telephone network (PSTN). © 1998 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 9, 230–237, 1998