Electrical conductivities of pure organic liquids

This contribution presents a method of evaluating electrical conductivities of pure organic liquids. Emphasis is placed on the methodology of selection, correlation and analysis of experimental data. The proposed method brings order out of conflicting, confusing and chaotic experimental observations. It is also shown that the consistent and evaluated data are generated at a fraction of the cost and time required for producing the original raw experimental data.     

Radiation transfer through specular passages—a simple approximation

A new technique is developed for approximating exchange factors for specular radiation passages. It is shown that for a large class of configurations, even with curved reflector surfaces, the average number of reflections <n> can be calculated by a simple analytic formula and without any ray tracing. The fraction of radiation transmitted through the passage, τ (one of the exchange factors), can then be approximated by $\text{τ ≈ p}{}^{\mathrm{<mtext>n</mtext><mtext>?</mtext><mtext>></mtext>}}$ if the specular reflectivity ρ of the passage wall is high. A rigorous lower bound is derived which agrees with the exact result within a few percent for any ε = 1 ?ρ, provided ε<n> is not too large. Several examples are discussed, including cylindrical passages, V-troughs and compound parabolic concentrators. The method is particularly useful for calculating transmission and absorption of radiation in solar concentrators.     

Prisms with total internal reflection as solar reflectors

For the sake of good optical efficiency, the reflectivity of mirror surfaces in solar collectors should be as high as possible. Until now, most solar reflectors have used aluminum with values of in the 80–90 per cent range. Even the best material, silver, allows reflectivities only up to 95 per cent. With total internal reflection (TIR), on the other hand, the effective reflectivity is limited only by absorption in the transparent medium, and absorption losses can as easily be kept below 5 per cent. In certain solar collectors, conventional mirrors can be replaced by an array of small rectangular glass prisms, an optical trick well known from binoculars. The only problem is that TIR occurs for a restricted range of incidence angles, limited by the low value of the refractive index n 1.5 of commonly available glass or acrylic. However, an additional degree of freedom is gained in the design of solar collectors because only concentration, not imaging, is relevant. The suitability of TIR prismatic reflectors for solar energy collection is investigated systematically, and the following applications are found to be promising: (i) heliostats for central receiver; (ii) parabolic reflectors with point focus; (iii) line focus systems (both parabolic and Fresnel reflectors) tracking around north-south axis, provided the tilt of the system is adjusted seasonally; (iv) under some conditions, V- and Compound Parabolic Concentrators, in trough or cone geometry. (This is important for second stage concentrators which are to maintain high reflectivity when exposed to air at high temperatures.) Of course, reflection at the front surface of a prism will split any incident ray into separate rays which may leave the prism in two different directions. However, in all the designs considered here, all these rays will reach the absorber, and thus the effective reflectivity is indeed 100 per cent apart from absorption losses. Even if TIR fails at certain times of the day, prismatic reflectors may be advantageous in some applications; one can place a metallic reflector behind the prism to avoid leakage of radiation, and thus one can obtain an effective reflectivity which surpasses that of a conventional reflector.     

An Efficient Adaptive Algorithm for Constructing the Convex Differences Tree of a Simple Polygon

The convex differences tree (CDT) representation of a simple polygon is useful in computer graphics, computer vision, computer aided design and robotics. The root of the tree contains the convex hull of the polygon and there is a child node recursively representing every connectivity component of the set difference between the convex hull and the polygon. We give an O(n log K + K log² n) time algorithm for constructing the CDT, where n is the number of polygon vertices and K is the number of nodes in the CDT. The algorithm is adaptive to a complexity measure defined on its output while still being worst case efficient. For simply shaped polygons, where K is a constant, the algorithm is linear. In the worst case K = O(n) and the complexity is O(n log² n). We also give an O(n log n) algorithm which is an application of the recently introduced compact interval tree data structure.     

On the summation of certain legendre series

Summary The purpose of this paper is to find some recurrence relations for sums of infinite series of the form P _l ⁿ (cos)t ^l+m/(l+m). This is achieved by transforming the sums into integrals and then using the recurrence relations for these integrals.On leave from the Department of Mathematics, Kurukshetra University, Kurukshetra, India.     

Refractive index change in ytterbium-doped fibers induced by photodarkening and thermal bleaching

High-accuracy measurements and analysis of refractive index change induced by photodarkening and thermal bleaching in ytterbium-doped fibers are presented, based on a modal interference method. Photodarkening-induced refractive index change is positive at the ytterbium lasing wavelengths near 1080 nm, and it approaches a saturated level, which is in the order of 10(-6)～10(-5) for the tested fiber samples. It is found that the value of this refractive index change is linearly proportional to the photodarkening-induced excess loss at an arbitrary probe wavelength in the visible band. Thermal bleaching can only partially erase the photodarkening-induced refractive index change, leaving a residual index change of (0.2～0.3)×10(-5). The influence of the photodarkening-induced refractive index change on fiber lasers is discussed.     

Polarization properties of two-dimensional slot waveguides

We propose and study slot waveguide geometries where both quasi-TE and quasi-TM modes may propagate highly confined within the same low-index slot region. Conventional horizontal and vertical slot waveguides can only provide high slot confinement for either the quasi-TM or quasi-TE modes, respectively. Different two-dimensional slot waveguide structures are analyzed in terms of their mode characteristics, such as the effective index, the confinement factor, and the overlap of quasi-TE and -TM modes within the slot. Attention is also paid to practical manufacturability. Various waveguide structures can be tailored to have zero birefringence or equal confinement at both polarizations. Values for the confinement factors and the overlap of the two polarizations, in the slot region, can reach 0.4 to 0.5.     

Substrate-facilitated nanoparticle sintering and component interconnection procedure

Room temperature substrate-facilitated sintering of nanoparticles is demonstrated using commercially available silver nanoparticle ink and inkjet printing substrates. The sintering mechanism is based on the chemical removal of the nanoparticle stabilizing ligand and is shown to provide conductivity above one-fourth that of bulk silver. A novel approach to attach discrete components to printed conductors is presented, where the sintered silver provides the metallic interconnects with good electrical and mechanical properties. A process for printing and chip-on-demand assembly is suggested.     

Bromine as an ash forming element in a fluidised bed boiler combusting solid recovered fuel

Plastic materials are the main sources of chlorine in solid recovered fuels (SRF). Chlorine is attributed to be the main initiator of slagging, fouling and corrosion in biomass and waste combustion as it lowers the melting point of ash forming matter and reacts chemically with the heat transfer surface steels. SRF may also contain sources of bromine in the form of brominated flame retardants (BFRs) applied in many plastics and textiles. Results presented in this paper from an experimental campaign at an 80 MW_th bubbling fluidised bed (BFB) boiler show that bromine is behaving in a similar manner as chlorine: bromine was found at the corrosion front in boiler membrane wall tubes, and as water soluble salts in aerosol samples collected from the furnace and electrostatic precipitator (ESP) ash. It is evident from these results and the data in the literature that most of the salts of bromine are, by both their fate and physical and chemical properties, similar to those of chlorine. It can be concluded that it if there is a source of bromine in the fuel corrosive high vapour pressure bromides can be formed analogously to chlorides.     

Effects of small octahedral mono,di, and trivalent hexafluoroanions on electronic and molecular structures of polypyrrole monitored by in situ UV–vis–NIR and resonance Raman spectroelectrochemical measurements

In situ UV–vis–NIR and Raman spectra were recorded for three polypyrroles of different compositions established by the specific redox responses of the polymers. Polypyrrole has been electrodeposited in the reversibly oxidized state and concomitantly doped with a small octahedral counterion from aqueous solution of sodium hexafluorophosphate, sodium hexafluorosilicate or sodium hexafluoroaluminate. The dopant anions differ from each other by the charge valency, having at the same time very similar ionic radii. The spectra of the resulting three polypyrroles were found to differ noticeably. An origin of the differences was discussed. The doping level and/or structure of a polymer phase can be invoked to explain the observed spectral changes of the polymer due to the anion dopants. As expected, the most counterion sensitive are the N–H bond and the polaron and bipolaron electronic levels. Polypyrrole doped with hexafluoroaluminate has generated the spectra that differ markedly from that recorded for polypyrrole hexafluorosilicate and polypyrrole hexafluorophosphate. The spectroscopic results are in agreement with earlier findings concerning electrochemical properties of polypyrrole hexafluoroaluminate and polypyrrole hexafluorosilicate. Raman bands that are usually assigned to the ring deformation vibrations were shown to decrease significantly in energy on oxidation of polypyrrole (900–1000 cm^?1). Raman bands intensities are complex function of laser energy and electrode potentials so their analysis on the anion effects should be performed rather at a constant length of laser excitation.