Fade Characteristics Research Articles

Light stability of pyrazolotriazole azamethine dyes at oil/aqueous interfaces

Film and dispersion coatings of two pyrazolotriazole azamethine (PT) dyes are used to study the effect of increasing the surface-area-to-volume (SA : V) ratio of the oil/aqueous (solvent/gelatin) interface on nonoxidative and oxidative fade characteristics. High concentration solutions of the dyes in a poly(vinyl acetate)dicyclohexylphthalate mixture as solvent are coated on glass substrates with a gelatin overcoat to produce thin film coatings and are also dispersed in gelatin to create "oil-in-gelatin" dispersion coatings. It is calculated that the dispersion coatings possess a SA : V ratio of approximately 20x greater than the film coatings. In nonoxidative fade conditions both the film and dispersion samples possess similar quantum yields of fade, implying that the presence of a solvent/gelatin interface does not significantly affect any electron transfer fade mechanisms. However, in oxidative fade conditions increasing the SA : V ratio of the interface by 20x leads to an increase in the quantum yield of fade of only a factor of 1.5-2. This disproportionate increase in the fade kinetics in dispersion coatings is explained by a kinetic scheme modelling oxygen diffusion through the coatings. It shows that the rate determining step for dye fade starts to become the diffusion of oxygen through the air/gelatin interface, and explains why changes in the SA : V ratio are not fully transferred to the quantum yield of fade.

Ku‐band diurnal fade characteristics and fade event duration data from three, two‐year, Earth–space radiometric experiments in Equatorial Africa

The move to provide direct to home (DTH) multi-media services from satellites requires a number of new insights to be gleaned from the propagation effects that occur along satellite-to-ground paths. Annual statistics will not be sufficient to describe the likely performance of the link, nor will they provide information on the likely customer acceptance of the DTH service. What are required are the likely number of outages due to rain attenuation in a given period, their duration, the time between the outages, and the diurnal characteristics of rain attenuation along the link. This paper presents results obtained in three, two-year, Ku-band experiments in tropical Africa on diurnal attenuation effects, as well as on rain and attenuation event duration and inter-event duration. The implications of the results are discussed. Copyright © 2000 John Wiley & Sons, Ltd.

Ku-band diurnal fade characteristics and fade event duration data from three, two-year, Earth-space radiometric experiments in Equatorial Africa

Ku-band diurnal fade characteristics and fade event duration data from three, two-year, Earth-space radiometric experiments in Equatorial Africa

Fade characteristics for K-band land-mobile satellitechannelsin Tokyo measured using COMETS

The K-band fade statistics in Tokyo were measured using an antenna (beamwidth of 19.5° in elevation and 6.5° in azimuth) at elevations ranging from 37 to 80°. The results show that line-of-sight communication is possible only ~33% of the distance at elevations < 50°, but it is 98% at 80°.

Electrochemical Performance of Amorphous and Crystalline Sn2 P 2 O 7 Anodes in Secondary Lithium Batteries

Amorphous and crystalline can be considered as intrinsic P‐doped glasses, similar to the products from the binary solid state reaction between SnO and . Amorphous was prepared by melt‐quenching the crystalline form. IR spectroscopy and inductively coupled plasma measurements indicated that both forms are phase pure homogeneous materials. In the potential range 0-1.2 V (vs. ), amorphous and crystalline can deliver reversible specific capacities of 520 and 400 mAh/g, respectively. However both display nearly the same capacity and fade characteristics when the upper cutoff limit is increased to 1.4 V. Cyclic voltammetry and differential capacity plots indicated the presence of two energetically different sites in crystalline . A higher potential is required for the complete release of in crystalline and this explains the lower capacity of this polymorph. X‐ray diffraction detected the presence of tin and tin alloy phases in charged and discharged samples, and an alloying mechanism is proposed to explain the reversibility in charge and discharge reactions. Dissociation of into and after repeated cycling was evidenced by IR spectroscopy. The large initial capacity loss could be explained by the requisite initial irreversible reaction to form metallic tin. © 1999 The Electrochemical Society. All rights reserved.

Bit error rate performances of M‐QAM orthogonal multicarrier modulation in presence of time‐selective multipath fading

AbstractOrthogonal Frequency Division Multiplexing (OFDM) is considered as an effective technique in high speed digital transmission under multipath fading. In this paper we theoretically analyze the behaviour of a coherent pilot‐symbol aided M‐QAM‐OFDM system in presence of time selective multipath channel. In the analyzed scheme, pilot symbols are periodically inserted to monitor the channel characteristics. The fading process experienced by the pilot symbols is used to estimate the fade characteristics at symbol‐rate through interpolation. The estimated channel is used to compensate for the random phase variation caused by the Doppler spread, so that the signal can be coherently demodulated. The bit error rate (BER) performance of this coherent OFDM modulation scheme is derived. The obtained results show that, with a reasonable amount of redundancy (frequency of the pilot symbols) introduced, the system performance approaches that of the ideal coherent demodulation, as long as a suitable channel estimate procedure is adopted.

Load, speed and temperature sensitivities of a carbon-fiber-reinforced phenolic friction material

A model friction material was formulated with a cashew-modified phenolic resin, short carbon fiber, phenolic particles, barytes and steel fiber. The friction, wear and fade characteristics of this material were determined using a Chase friction material testing machine. The coefficient of friction was found to vary between 0.2 and 0.5 with lower values associated with higher loads, speeds and drum temperatures and vice versa. Conditioning the specimens with several fade-recovery test cycles resulted in steady friction during subsequent fade tests followed by excellent recovery characteristics. The specific wear rate per unit load and sliding distance decreased with increasing loads, but increased with increasing drum speeds and temperatures due to thermal degradation of the resin. The carbon-fiber-reinforced friction material showed lower specific wear rates than that of a milled-glass-fiber-based friction material at low speeds and temperatures over a wide load range.

Fade and wear characteristics of a glass-fiber-reinforced phenolic friction material

The fade and wear characteristics of a glass-fiber-reinforced friction material were studied using a Chase friction material testing machine. At low counterface temperatures, the friction material showed relatively high friction in the range 0.4–0.5. During fade tests, the coefficient of friction dropped to about 0.18 at 343 °C. Re-conditioning the wear surface at the end of a fade test altered the frictional behavior during a subsequent fade test. The wear tests showed that the specific weight loss per unit load and sliding distance decreases with increasing applied load and speed, but increases with increasing bulk drum temperature. At high temperatures, thermochemical degradation and fiber pull-out appear to contribute to higher specific wear rate. The worn surfaces of the specimens were observed by scanning electron microscopy and analyzed by energy-dispersive X-ray analysis. The results were consistent with low friction coefficients due to film formation on the worn surfaces of glass fiber at high temperatures. This film could be removed at lower temperatures by either sliding (application) or by sanding.

Pilot-symbol aided coherent M-ary PSK in frequency-selective fast Rayleigh fading channels

Pilot-symbol aided coherent M-ary PSK modems in digital cellular mobile radio systems are analyzed theoretically. The error-floors caused by the Doppler spread in a fast fading channel are removed in both flat and selective fading channels. However, the error-floors caused by the delay spread are lower-bounded by those that exist in the ideal coherent detection. The systems are modeled as frequency-selective fast Rayleigh fading channels, corrupted by co-channel interference (CCI) and additive white Gaussian noise (AWGN). In the proposed scheme, pilot symbols are inserted periodically to monitor the channel characteristics. The fading processes experienced by the pilot symbols are used to estimate those suffered by the data symbols using interpolation or filtering. The estimated fade characteristics are used to compensate the random phase variation caused by the Doppler spread, so that the signals can be demodulated coherently. The theoretical performances of the fade compensated coherent modems are evaluated. The results show that the fade compensated coherent demodulation with the least redundancy achieves the same performance as the ideal differential detection in a fading channel. The performance approaches that of the ideal coherent demodulation as more redundancy is allowed. The pilot-symbol-insertion (PSI) scheme is also applicable to M-ary QAM modems and Rician channels. The residual frequency offset can also be compensated by the PSI technique.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The Application of Radiophotoluminescent Glass to Gamma Dosimetry in Mixed n-Gamma Fields

Abstract High Z radiophotoluminescent glass of British manufacture has been studied with a view to using it as a ? ray dosemeter in mixed n-? fields at ambient and elevated temperatures. Environments such as these are widespread amongst nuclear enginering, accident dosimetry and military application areas. The radiation response of the glass has been fully characterised and the results are presented. The photon response over the energy range 16 keV-7 MeV has been determined and interpreted within the framework of a simplified model. The neutron response from thermal energies to 15 MeV has been measured using reactor and accelerator based sources. The fast neutron response was found to be small, although the thermal neutron sensitivity is too high for most in-core applications without a thermal neutron shield. The results are also compared with new measurements of the neutron response of Toshiba FD7 glass over the energy range thermal - 2.2 MeV. The signal build-up and fade characteristics of the dosemeter at ambient temperatures and 100 oC are presented for irradiations carried out both at ambient and 100 oC. Acceptable stability is found at these elevated temperatures. The potential use of this high Z glass in tandem with low Z beryllium oxide dosemeters as a measure of gamma ray spectra is also discussed.

An Analysis of Heat Transfer and Fade in Disk Brakes

The heat transfer and fade characteristics of automotive disk brakes are studied. A distributed model for the disk is employed, with convection from the sides and edge of the disk and conduction to the hub included. Available expimental data for friction coefficient as a function of temperature for two different lining materials is included in the analysis. The heat transfer equations and dynamic equations of the vehicle are solved numerically. Results presented include the effects on brake pad pressure required and on stopping distance of a sequence of repeated stops with cooling perds between each stop. Also included are deceleration versus time curves, sample temperature distributions in the disk, and a study of the manner in which the heat generated in braking is distributed to storage in the disk, conduction to the hub, and convection to the air.