Filament problems with

Another problem with the filament pyrolysers is the possibility that the filament may be non-uniformly heated over its length. This may determine different Teq s in different points of the filament. If the sample is not always placed in the same point of the filament in repeated experiments, this may introduce a rather drastic reproducibility problem. In spite of these disadvantages, the resistively heated filament pyrolysers are among the most common ones, and very good reproducibility has been reported frequently [12]. 

Another problem with the furnace pyrolysers can be the difference in the temperature between the furnace and the sample. Again, due to the poor contact between the sample and the hot source, the sample may reach a lower actual temperature than the temperature of the furnace wall. It is interesting that in microfurnace systems there were reported variations in the pyrolysis products as compared to the results obtained in inductively or filament heated pyrolysers [7,18]. As an example, a study done on Kraton 1107 [7] decomposition found linearity between the oven temperature and the ratio of two decomposition monomers (styrene and dipentene) only in a narrow temperature range, namely from 450° C to 625° C. Kraton 1107 was found to decompose in filament or Curie point pyrolysers such that linearity can be noticed between temperature and styrene/dipentene ratio from 500° C to 850° C. The reproducibility of pyrolysis in a furnace was also found lower than for other pyrolysers [7]. 

Perhaps the main problem with fungi concerns the question of what to use as the inoculum. Unicellular yeasts can be treated as for bacteria, but whether to use spores (which may be more resistant than the vegetative mycelium) or pieces of hyphae with the filamentous moulds, has yet to be fully resolved. Spore suspensions (in saline containing the wetting agent Tween 80) obtained from 7-day-old cultures... 

Calculations indicate that a cylinder with a W/D ratio of 0.44 and made of carbon-filament-RPs with an effective RP modulus of 0.1 MPa (15 X 10 psi) would not require a stiffening system. With this W/D ratio an unstiffened cylinder of semi-infinite length would have an elastic buckling depth exceeding 21,300 m (70,000 ft). At a depth of 12,200 m (40,000 ft) a RP stress of 690 MPa (100,000 psi) would be developed. Present problems with high-modulus, carbon-fiber RPs have been the inability of laminates to take high-compressive stresses. 

Chemstrand s Acrilan process was based on a wet-spinning technology, which produces a fibrillar microstructure. As a result, early acrylic fiber products suffered from problems with abrasion originating with a lack of coherence in the fibrillar surface of the fibers. This was overcome by adding a steam-annealing step, which, combined with the presence of vinyl acetate as comonomer, makes the fibrils that compose each filament fuse together. 

No significant inhalation problem with filament diameters down to 5 pm... 

At this stage of development, it is doubtful whether a flywheel incorporated in an electrical highway vehicle can replace lead acid batteries due to problems with vibration and safety, but the performance of a lead acid battery deteriorates in hot wet conditions, requires frequent maintenance and has a life expectancy of only about 4 years. The aim of US Flywheel Systems, however, is to drive a car with a flywheel system. It is reckoned that some 16 units would be required to fulfil this objective and adequate protection would have to be supplied, since, in the event of a wheel disintegrating, it would dissipate its energy into hot fluff and high speed dust. A very sophisticated computer control system is used to filament wind each wheel with a high fiber content of 86% w/w [89]. 

Whiskers. Whiskers are faceted filament-tike structures that grow spontaneously on the surface of a plated metal and can cause shorts between closely spaced conductors (see Fig. 57.11). Whiskering can be differentiated from other causes of shorts such as dendritic growth, because neither an electrical field nor moisture is required for whiskers to form. Whiskering is a particular problem with pure tin. The whiskers grow in response to internal stresses in the plating or external loads. Sn whiskers are commonly 50 fan long and 1 to 2 fan in diameter. 

Difficulties in measuring the filament temperature prevented more precise control of this parameter, and obviously affected tiie reproducibility as well as the optimum yield. In experiments 4 -14, over 20 grams of KrF2 were produced in multiple 2 to 4 hour runs. Even though there were significant reliability problems with the filaments, this indicates a substantial capability to produce multigram amounts of material. Because the yield falls off rapidly after approximately an hour, most of the experiments reported here are of short duration, witii repeated additions of krypton to the reactor. Due to the promise shown in these early experiments as weU as the versatility of this reactor, we plan to continue research with this reactor. To improve... 

As for all mass spectrometric techniques, Umitations arise in part from the possibility of generating gas-phase ions. Usually, molecules are vaporized and allowed to react with metal ions. In early studies, alkali metal cations were produced by thermionic emission from a filament coated with an appropriate melt of alkali metal oxide (or carbonate) with silica and alumina. Most recently, electrospray ionization (ESI), one of the atmospheric pressure ion sources mentioned previously, has been used to form gas-phase adducts directly, avoiding some problems associated with volatility, thermal stability, and so on [105],... 

We have seen that rheometers capable of accurate measiuements of extensional flow properties are limited to use at low Hencky strain rates, usually well below 10 s . In order to reach higher strain rates, the drawdown of an extruded filament ( melt spinning ) and the converging flow into an orifice die or capillary have been used to determine an apparent extensional viscosity . Since the stress and strain are not imiform in these flows, it is necessary to model the flow in order to interpret data in terms of material functions or constants. And such a simulation must incorporate a rheological model for the melt under study, but if a reliable rheological model were available, the experiment would not be necessary. This is the basic problem with techniques in which the kinematics is neither controlled nor known with precision. It is necessary to make a rather drastically simplified flow analysis to interpret the data in terms of some approximate material function. 

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