Electrical conductivity in iodine-doped ethyl cellulose

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.     

XML: a door to automated Web applications

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     

On the synthesis and characterization of a new manganite type CMR material: La0.7Hg0.3MnO3

A new manganite type CMR material, La_0.7Hg_0.3MnO₃ 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 La_0.7MnO₃ followed by diffusion of Hg leading to La_0.7Hg_0.3MnO₃. 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 ρ–T behaviour shows a peak at T_IM=227 K. The ρ–T behaviour above this temperature corresponds to that of an insulator and below this to that of a metal. The ρ–T behaviour remains unaltered when a magnetic field (H_dc=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 H_dc=1.5 kG. At a given temperature the variation in MRR with field H_dc is rapid at lower field values (H_dc<1.2 kG) and scales linearly for higher field values (H_dc>1.2 kG). It may be mentioned that the present work on the synthesis and magnetoresistance behaviour of La_0.7Hg_0.3MnO₃, is the first of its type.     

Hydrodynamics and liquid phase axial mixing in orifice pipe reactor

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.     

I want my FTP: bits on demand

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     

FPGA Implementation of Cross Virtual Concatenation Transmitter/ Receiver for Data Transmission over Next Generation SDH Systems

Cross Virtual Concatenation is the new technique proposed for bandwidth efficient transmission of data over SDH networks. SDH networks came into existence for reliable voice transmission. As the demand of data traffic grew in wide area networks, new technologies were developed and standardized for data transmission over SDH networks. The technologies used namely, GFP (generic framing procedure), VCAT (virtual concatenation) and LCAS (link capacity adjustment scheme) enable network operator to provide integrated voice and data services over their legacy SDH infrastructure. Data packets are encapsulated using framing protocols GFP. VCAT is a process of distributing the GFP framed data payload in number of virtual channels of same capacity forming a Virtually Concatenated Group (VCG). LCAS is used for dynamic bandwidth allocation. LCAS enhances the VCAT scheme with hitless in service addition and removal of VC’s to/from the VCG.VCAT combines homogeneous virtual channels together which in some cases limits the performance of VCAT. This paper describes the implementation of new concatenation technology named cross virtual concatenation (CVC), which combines heterogeneous VC’s together to utilize the SDH bandwidth more efficiently. CVC implementation requires only end node equipments to be upgraded as VCG members travel through the link similar to the conventional VCAT. This paper proposes FPGA implementation of transmitter and receiver circuits for 100 Mbps Ethernet data transmission over next Generation SDH systems using CVC, where two types of VC’s namely VC-3 and VC-12 are used for data transmission. Total Transmission delay is calculated as 125 μs. There is no complexity added at the receiver side due to this delay. The receiver is designed for 32 ms differential delay compensation which can be increased up to maximum 256 ms by increasing the buffer size at the receiver.     

A review of particle swarm optimization and its applications in Solar Photovoltaic system

Particle swarm optimization is a stochastic optimization, evolutionary and simulating algorithm derived from human behaviour and animal behaviour as well. Special property of particle swarm optimization is that it can be operated in continuous real number space directly, does not use gradient of an objective function similar to other algorithms. Particle swarm optimization has few parameters to adjust, is easy to implement and has special characteristic of memory. Paper presents extensive review of literature available on concept, development and modification of Particle swarm optimization. This paper is structured as first concept and development of PSO is discussed then modification with inertia weight and constriction factor is discussed. Issues related to parameter tuning, dynamic environments, stagnation, and hybridization are also discussed, including a brief review of selected works on particle swarm optimization, followed by application of PSO in Solar Photovoltaics.     

Comparison of Flux Pinning Mechanism in Laser Ablated YBCO and YBCO:BaZrO3 Nanocomposite Thin Films

Thin films of YBCO and YBCO:BaZrO₃ (BZO) nanocomposite have been deposited using the pulsed laser deposition technique. Substantial increase in critical current density (J _C ) and pinning force density (F _p ) of the nanocomposite thin films was observed. The possible pinning mechanism in YBCO:BZO nanocomposite thin films has been explored and compared with the pinning mechanism in pure YBCO thin film by studying the variation of J _C with magnetic field (B) and temperature. In the intermediate field regime (0.1–1 T), J _C follows B ^−α with nearly similar values of α for YBCO and YBCO:BZO nanocomposite thin films indicating similar pinning mechanism in both thin films. The variation of J _C with reduced temperature (t=T/T _C ) has been studied for both the films and it was observed that the mechanism of pinning in both YBCO and YBCO:BZO thin films is similar (δT _C pinning). The observed enhanced values of J _C and F _p of the nanocomposite thin film is attributed to the presence of BZO nanoparticles, which induces more defects due to lattice mismatch between YBCO and BZO leading to improved flux pinning properties of the nanocomposite thin film.