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The electrical conductivity of solution-grown ethyl cellulose (EC) films, 5–30 μm thick, has been studied in the sandwich configuration (metal–EC–metal) as a function of iodine concentration from 0.5 to 5.0 wt% ratio. The studies were conducted in the temperature range 333–383 K, while the field was varied over the range (3.0–5.5) × 104V/cm. Aluminium was used as the lower electrode, while the upper electrode was of Al, Ag, Cu, Au or Sn. Certain transient effects such as a large burst of current immediately after the application of field were observed. An attempt was made to identify the nature of the current by comparing the observed dependence on electric field, electrode material and temperature with the respective characteristic features of the existing theories of electrical conduction. The results show that the electrical conduction follows Ohm's law at lower fields, while at higher fields, space-charge limited current (SCLC) was observed. It was also found that Richardson–Schottky emission was responsible, to some extent, for the transport of charge carriers in the polymer. The conductivity of the films increased on doping with iodine. The dopant molecules are considered to act as additional trapping centes and provide links between the polymer molecules in the amorphous region, thus resulting in the formation of charge transfer complexes.  相似文献   
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In Japanese culture, your meishi conveys your place in the company, even in society, as well as your name, phone number, and e-mail address. That is to say, in Japan, business cards matter. They convey complex metadata about the people who carry them. Like people, Web pages come in an abundance of shapes and sizes (and sounds). What makes them machine interpretable-and therefore a new medium for communicating information globally-is Hypertext Markup Language. HTML allows the structural markup of Web documents, distinguishing the elements of a page with tags and declaring the physical relationships among the various document elements. This organizes the display of information and allows humans to read and use it. To give machines this capability, however, requires semantic markup, identifying what each particular element means on its own (for example, “this is a home street address” or “this is an e-mail address”). Semantic markup would change what is now simply displayed content to machine readable, structured content. The Extensible Markup Language (XML) specification, first released as two working drafts in 1997 by the World Wide Web Consortium, makes it dramatically easier to develop and deploy domain- and mission-specific Web pages. We describe the evolution of the Web's data representation from display formats to structural markup to semantic markup  相似文献   
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A new manganite type CMR material, La0.7Hg0.3MnO3 has been successfully synthesized and has been found to exhibit magnetoresistance (≈9%) at low fields (≈1.5 kG). The synthesis has been carried out through a solid state reaction route consisting of the formation of La0.7MnO3 followed by diffusion of Hg leading to La0.7Hg0.3MnO3. The as grown samples are polycrystalline and correspond to an orthorhombic unit cell with the lattice parameters; a=5.5183 Å, b=5.6383 Å and c=7.5368 Å. The typical grain size as revealed by scanning electron microscopy is in the range of 0.5–2 μm. The ρT behaviour shows a peak at TIM=227 K. The ρT behaviour above this temperature corresponds to that of an insulator and below this to that of a metal. The ρT behaviour remains unaltered when a magnetic field (Hdc=1.5 kG) is applied. However, with this magnetic field a drop in the resistivity is observed up to 77 K. At room temperature the magnetoresistance ratio (MRR) is too small but it steadily increases as the temperature is decreased. Thus, MRRs at 227.13 and 77 K are 3.41 and 9.05%, respectively, in an applied field of Hdc=1.5 kG. At a given temperature the variation in MRR with field Hdc is rapid at lower field values (Hdc<1.2 kG) and scales linearly for higher field values (Hdc>1.2 kG). It may be mentioned that the present work on the synthesis and magnetoresistance behaviour of La0.7Hg0.3MnO3, is the first of its type.  相似文献   
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Two phase flow in a horizontal pipe, with orifice plates placed at regular intervals as obstructions, was studied for the effect of phase velocities on flow patterns, fractional phase hold-ups, pressure drop and liquid phase axial dispersion. Radioactive technetium-99m (as an aqueous solution of sodium pertechnatate) was used as tracer. A pulse injection technique with two point measurements was employed. Three different orifice diameters were used (8 mm, 16 mm, and 20 mm) in a pipe diameter of 32 mm. The orifice spacing was 500 mm in all cases. Superficial gas (air) velocity was varied over a range from 0.02 m/s to 1.0 m/s and superficial liquid (water) velocity from 0.03 m/s to 0.85 m/s. Different flow patterns under different flow conditions were identified and a generalised flow map is presented. Variations in hold-ups and pressure drop with flow patterns have been explained. Rational correlations have been developed for fractional phase hold-ups and pressure drop. A preliminary comparison of two phase gas-liquid flow in a horizontal pipe with orifice obstructions (to be called orifice pipe reactor), as a gas-liquid contacting device, is made with a conventional bubble column reactor. Recommendations have been made for future work.  相似文献   
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Graft copolymerization of 4‐vinylpyridine (4‐VP) onto guar gum (GOH) using potassium monopersulfate (PMS)/thioacetamide (TAA) as a redox pair was studied in an aqueous medium under inert atmosphere. The concentration of potassium monopersulfate and thioacetamide should be 1.0 × 10?2 and 5.0 × 10?3 mol dm?3, respectively, for highest grafting ratio and efficiency. Efficient grafting was observed at 19.25 × 10?2 and 4.87 × 10?2 mol dm?3 concentration of 4‐vinylpyridine and sulfuric acid, respectively. The optimum temperature for grafting is 30°C. As the time period of reaction is increased, the grafting ratio increases, whereas efficiency decreases. The plausible mechanism of grafting has been suggested. A sample of guar gum and guar‐ g‐4‐vinylpyridine were subjected to thermogravimetric analysis with the objective of studying the effect of grafting 4‐vinylpyridine on the thermal stability of guar gum. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2380–2385, 2002  相似文献   
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Limb repositioning is necessary for individuals with severe physical disabilities to sustain muscle strength and prevent pressure sores. As robotic technologies become ubiquitous, these tools offer promise to support the repositioning process. However, research has yet to focus on ways in which individuals with severe physical disabilities can control robots for these tasks. This paper presents a study that examines the needs and attitudes of potential users with physical disabilities to control a robotic aid for limb repositioning. Subjects expressed interest in using brain–computer interface (BCI) and speech recognition technologies for purposes of executing robotic tasks. The performance of four subjects controlling arm movements on an avatar through the keyboard, mouse, BCI, and Dragon NaturallySpeaking speech recognition was evaluated. Although BCI and speech technologies may limit physical fatigue, more challenges were faced using BCI and speech conditions compared to the keyboard and mouse. This research promotes accessibility into mainstream robotic technologies and represents the first step in the development of a robotic prototype using a BCI and speech recognition technologies for limb repositioning.  相似文献   
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Rendering animations of scenes with deformable objects, camera motion, and complex illumination, including indirect lighting and arbitrary shading, is a long‐standing challenge. Prior work has shown that complex lighting can be accurately approximated by a large collection of point lights. In this formulation, rendering of animation sequences becomes the problem of efficiently shading many surface samples from many lights across several frames. This paper presents a tensor formulation of the animated many‐light problem, where each element of the tensor expresses the contribution of one light to one pixel in one frame. We sparsely sample rows and columns of the tensor, and introduce a clustering algorithm to select a small number of representative lights to efficiently approximate the animation. Our algorithm achieves efficiency by reusing representatives across frames, while minimizing temporal flicker. We demonstrate our algorithm in a variety of scenes that include deformable objects, complex illumination and arbitrary shading and show that a surprisingly small number of representative lights is sufficient for high quality rendering. We believe out algorithm will find practical use in applications that require fast previews of complex animation.  相似文献   
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A look under the hood of the IETF's file transfer protocol, including a summary of the commands in the FTP standard. Today, FTP is used primarily for maintaining archives of public files, and is losing ground to HTTP even there. FTP simply doesn't maintain as much metadata: not creation date, not original location, not application data type. Its addressing structure is an opaque pathname at a host. Consider that in the context of mirroring or relocating information: FTP mirrors are an ad hoc, user driven abstraction; HTTP can send automatable redirection messages. Per-site metadata is also provided manually as OOindex files, compared to automatable Web spiders  相似文献   
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