Two-step digit-set-restricted modified signed-digit addition-subtraction algorithm and its optoelectronic implementation

A novel, to our knowledge, two-step digit-set-restricted modified signed-digit (MSD) addition-subtraction algorithm is proposed. With the introduction of the reference digits, the operand words are mapped into an intermediate carry word with all digits restricted to the set {(1) over bar, 0} and an intermediate sum word with all digits restricted to the set {0, 1}, which can be summed to form the final result without carry generation. The operation can be performed in parallel by use of binary logic. An optical system that utilizes an electron-trapping device is suggested for accomplishing the required binary logic operations. By programming of the illumination of data arrays, any complex logic operations of multiple variables can be realized without additional temporal latency of the intermediate results. This technique has a high space-bandwidth product and signal-to-noise ratio. The main structure can be stacked to construct a compact optoelectronic MSD adder-subtracter. (C) 1999 Optical Society of America.

Reversible Resistance Switching Effect in Amorphous Ge1Sb4Te7 Thin Films without Phase Transformation

We demonstrate a reversible resistance switching effect that does not rely on amorphous-crystalline phase transformation in a nanoscale capacitor-like cell using Ge1Sb4Te7 films as the working material. The polarity and amplitude of the applied electric voltage switches the cell resistance between low- and high-resistance states, as revealed in the current-voltage characteristics of the film by conductive atomic force microscopy (CAFM). This reversible SET/RESET switching effect is induced by voltage pulses and their polarity. The change of electrical resistance due to the switching effect is approximately two orders of magnitude.

a real-time path planning approach without the computation of cspace obstacles

An important concept proposed in the early stage of robot path planning field is the shrinking of the robot to a point and meanwhile expanding of the obstacles in the workspace as a set of new obstacles. The resulting grown obstacles are called the Configuration Space (Cspace) obstacles. The find-path problem is then transformed into that of finding a collision free path for a point robot among the Cspace obstacles. However, the research experiences obtained so far have shown that the calculation of the Cspace obstacles is very hard work when the following situations occur: 1. both the robot and obstacles are not polygons and 2. the robot is allowed to rotate. This situation is even worse when the robot and obstacles are three dimensional (3D) objects with various shapes. Obviously a direct path planning approach without the calculation of the Cspace obstacles is strongly needed. This paper presents such a new real-time robot path planning approach which, to the best of our knowledge, is the first one in the robotic community. The fundamental ideas are the utilization of inequality and optimization technique. Simulation results have been presented to show its merits.

A Relay Level Set Method for Automatic Image Segmentation

This paper presents a new image segmentation method that applies an edge-based level set method in a relay fashion. The proposed method segments an image in a series of nested subregions that are automatically created by shrinking the stabilized curves in their previous subregions. The final result is obtained by combining all boundaries detected in these subregions. The proposed method has the following three advantages: 1) It can be automatically executed without human-computer interactions; 2) it applies the edge-based level set method with relay fashion to detect all boundaries; and 3) it automatically obtains a full segmentation without specifying the number of relays in advance. The comparison experiments illustrate that the proposed method performs better than the representative level set methods, and it can obtain similar or better results compared with other popular segmentation algorithms.

Bioorganic/inorganic hybrid composition of sponge spicules: Matrix of the giant spicules and of the comitalia of the deep sea hexactinellid Monorhaphis

The giant basal spicules of the siliceous sponges Monorhaphis chuni and Monorhaphis intermedia (Hexactinellida) represent the largest biosilica structures on earth (up to 3 m long). Here we describe the construction (lamellar organization) of these spicules and of the comitalia and highlight their organic matrix in order to understand their mechanical properties. The spicules display three distinct regions built of biosilica: (i) the outer lamellar zone (radius: >300 mu m), (ii) the bulky axial cylinder (radius: <75 mu m), and (iii) the central axial canal (diameter: <2 mu m) with its organic axial filament. The spicules are loosely covered with a collagen net which is regularly perforated by 7-10 mu m large holes; the net can be silicified. The silica layers forming the lamellar zone are approximate to 5 mu m thick; the central axial cylinder appears to be composed of almost solid silica which becomes porous after etching with hydrofluoric acid (HF). Dissolution of a complete spicule discloses its complex structure with distinct lamellae in the outer zone (lamellar coating) and a more resistant central part (axial barrel). Rapidly after the release of the organic coating from the lamellar zone the protein layers disintegrate to form irregular clumps/aggregates. In contrast, the proteinaceous axial barrel, hidden in the siliceous axial cylinder, is set up by rope-like filaments. Biochemical analysis revealed that the (dominant) molecule of the lamellar coating is a 27-kDa protein which displays catalytic, proteolytic activity. High resolution electron microscopic analysis showed that this protein is arranged within the lamellae and stabilizes these surfaces by palisade-like pillars. The mechanical behavior of the spicules was analyzed by a 3-point bending assay, coupled with scanning electron microscopy. The load-extension curve of the spicule shows a biphasic breakage/cracking pattern. The outer lamellar zone cracks in several distinct steps showing high resistance in concert with comparably low elasticity, while the axial cylinder breaks with high elasticity and lower stiffness. The complex bioorganic/inorganic hybrid composition and structure of the Monorhaphis spicules might provide the blueprint for the synthesis of bio-inspired material, with unusual mechanical properties (strength, stiffness) without losing the exceptional properties of optical transmission. (C) 2007 Elsevier Inc. All rights reserved.

趋磁细菌AMB-1培养条件优化及磁小体变化过程研究

趋磁细菌(Magnetotactic bacteria)的研究是国际微生物学研究热点之一。趋磁细菌体内含有纳米单磁畴的氧化铁/硫化铁(Fe3O4或Fe3S4)晶体，称为磁小体。由于趋磁细菌营养条件要求苛刻，在环境中需要微好氧条件，且营养类型属于化能自养，使得培养趋磁细菌时常遇到问题。 本研究首先通过正交试验优化趋磁细菌AMB-1菌株培养条件，在培养条件铁源为奎尼酸铁0.02 mmol/L，装瓶量75% ，pH值6.7，温度25 ℃时，AMB-1 OD600达到0.440(1.166×109 cells/ml)。同时运用磁收集传代法，使带有磁小体的AMB-1细胞比例占95％以上(Cmag值稳定在1.9-2.0)。 在AMB-1具有较好的生物量，同时又具有较好的含磁小体细胞比例后，研究磁小体的变化过程。通过透射电镜观察磁小体变化过程，发现培养24 h细菌体内已有较小晶体形成(平均27 nm，n=188)且沿长轴分布；48 h晶体长大(平均43 nm，n=203)且形成分段链沿长轴排列；72 h晶体进一步成熟(平均50 nm，n=191)仍以分段链沿长轴排列；随后细菌逐渐衰亡磁小体变小，168 h可见部分自溶细菌中仍有磁小体链(平均37 nm，n=186)；192 h细菌自溶磁小体链(平均33 nm，n=184)分散到环境中。 通过透射电镜在细胞水平上研究趋磁细菌细胞分裂时发现，磁小体在细菌分裂时采用两种分离方式：一种为磁小体分配到两个子细胞；另一种为磁小体只分配到一个子细胞。无磁小体的子细胞，在随后的生长过程又分为两种情况：一种为细胞逐渐产生磁小体，另一种为不再产生磁小体。这种现象的发现，解释了随着传代次数的增多，细菌磁性有所下降的原因(Cmag值降低)。 在对趋磁细菌磁小体合成机制的研究中，常使用基因敲除的办法获得缺陷型，并与野生型对比进行研究。但是，利用基因敲除获得缺陷型不仅操作繁琐并且所得缺陷型不稳定。本研究利用特殊的磁富集传代法，先将带有磁小体的菌体收集并连续传代，筛选获得了高磁菌株；利用这种方法，收集不含磁小体的菌体并连续传代，筛选获得了无磁菌株。 趋磁细菌磁小体在医疗、环保等领域具有广阔应用价值，但是目前由于趋磁细菌难以大规模培养，并且磁小体纯化存在成本高等原因，将磁小体真正实际应用尚有一段距离。通过研究磁小体在趋磁细菌中的变化过程发现，AMB-1菌株在培养192 h后自溶，并且磁小体随着细胞的破碎释放到环境中去。