Heterogeneities in carbon fibers

Acrylic fibers, stabilized acrylic fibers, and graphite fibers have been selectively etched by ion bombardment. After ion etching, the fibers are characterized by structures oriented transverse to the fiber axis with an average spacing ranging from 500 to 3000 Å. These transverse structures are considered to be representative of structural inhomogeneities in the fibers, which are transmitted from the precursor fiber through the stabilization treatment to the final carbon fibers. The relation between these heterogeneities and the standard microstructura! models of carbon fibers remains to be elucidated satisfactorily.     

In situ FTIR and surface analysis of the reaction of trimethylgallium and ammonia

Using a combination of in situ FTIR spectroscopy and detailed surface analysis, we find that TMGa decomposes at the same rate in either hydrogen or nitrogen forT < 300° C. Although ammonia does not decompose under these conditions, mixing TMGa with ammonia increases the rate of methane formation. Reacting perdeutroammonia with TMGa shows that hydrogen from the ammonia is incorporated into the product methane (whereas deuterium in the gas phase is not incorporated into the gaseous product). TMGa and ND₃ do react; however, nitrogen incorporation in the growing film is temperature dependent. Further, although the decomposition of TMGa occurs in the gas phase, the last steps of the decomposition/reaction occur on the substrate surface.     

Optical loss study of MPEOU-based polyceram planar waveguides

Sol-gel-derived polyceram materials based on organically modified silicon and titanium alkoxides have been synthesized in planar waveguide forms. They exhibit optical losses as low as <0.25 dB/cm and refractive indices as high as 1.685, coupled with exceptional ease of processing. The optical properties of the films (index of refraction, loss, and dispersion) are studied as functions of processing and composition, and the influence of chemistry on volume homogeneities and surface roughness of the films is investigated.     

Particle migration in isobaric and flash evaporation of nanofluids

When nanoparticles are dispersed in a base fluid, the thermophysical properties of the resulting nanofluids can vary considerably from those of the pure basefluid. Thus, numerous applications for nanofluids have been suggested in the past, e.?g. the use in solar thermal absorbers. With increasing heat fluxes and temperatures, a phase change of the absorber fluid can be desirable for instance in solar steam generators. This paper deals with the fundamental question of the nanoparticle migration behavior while the nanofluid is evaporating, as it is commonly presumed that solid particles do not migrate into the gas phase. This assumption however is, to the authors knowledge, insufficiently described in the literature as due to the extremely small size of the nanoparticles, abnormal behavior seems possible. By conducting experiments with isobaric and flash evaporation it is shown, that the classical theory of solid-liquid equilibrium actually applies at this scale and the nanoparticles are entirely separated from the gas phase by evaporation. The particles found in the gas phase can entirely be attributed to entrainment effects.     

Oxidative stabilization of acrylic fibres

The mechanism of oxidative stabilization of acrylic fibres is characterized by two limiting cases which are determined by the fibre chemistry, the reaction conditions, and the diameter of the filament. These limiting cases correspond to diffusion-limited and reaction-limited kinetic processes. Although the chemistry of stabilization is too complex to specify, the various reactions are separated into two categories: those which occur prior to or concurrently with polymerization of the nitrile groups, called prefatory reactions; and those which occur subsequent to nitrile polymerization, called sequent reactions. Under conditions which allow the prefatory reactions to occur significantly before the sequent reactions, the diffusion of oxygen to reactive sites is limited by previously oxidized material; and the fibre shows a typical two-zone morphology. Under conditions where the prefatory and sequent reactions occur sequentially, the overall stabilization process is limited by the rate of the prefatory reactions; but a skin is established at the fibre surface which acts as an oxygen barrier. Data from a variety of sources, including oxygen analysis, microscopic examination, fibre residue after etching, tension developed in fibres held at constant length, and small-angle X-ray patterns, are cited as evidence for the two limiting cases.Based in part on a thesis submitted by SBW in partial fulfilment of the requirements for the Sc.D. degree in materials engineering, MIT, 1976;     

Unscented filtering and nonlinear estimation

The extended Kalman filter (EKF) is probably the most widely used estimation algorithm for nonlinear systems. However, more than 35 years of experience in the estimation community has shown that is difficult to implement, difficult to tune, and only reliable for systems that are almost linear on the time scale of the updates. Many of these difficulties arise from its use of linearization. To overcome this limitation, the unscented transformation (UT) was developed as a method to propagate mean and covariance information through nonlinear transformations. It is more accurate, easier to implement, and uses the same order of calculations as linearization. This paper reviews the motivation, development, use, and implications of the UT.     

The limits of realism: perceptions of virtual landscapes

Communicating planning results within expert groups or to local citizens is crucial to an efficient planning process. In the planning and design disciplines such as landscape and urban planning, recent digital 3D-visualizations have gained increased recognition. However, the validation of simulations of virtual landscapes, in terms of their degree of realism (R’Degree) has so far been neglected in research. This study concentrates on the question whether, how, and to which degree the real visually perceived landscape, represented through photographs, can be validly represented by means of virtual landscapes. The study area comprises the communities of Schwyz and Ingenbohl–Brunnen situated on Lake Lucerne in Central Switzerland.From a modelling point of view, landscapes are highly complex structures. Instead of manually modelling the virtual environment, which is the traditional CAD-approach, a GIS-based approach is pursued. This is the prerequisite for the efficient visualization of large data sets.The validity of the created virtual landscape is tested in an empirical study in which test persons are asked to order a set of real images and variations of the corresponding computer-generated images. In the experiment, approximately 75% of the test persons assigned the highest possible value (very high degree of realism) to one or more scenes of simulated landscapes. In order to achieve an even higher degree of realism, more and very detailed 3D-object-data and accompanying texture information would be necessary.     

Standardized observation of team-work in design

In the research project Team-work in Engineering Design Practice, engineers and psychologists investigate design processes in industry by detailed observation. The aim is to comprehend how the external conditions in conjunction with the individual designer's and the group's prerequisites influence the design process and the solution. Therefore, the design process has to be documented in a standardized form. The paper presents a method for standardized observation of design team-work in industrial practice. In an example of an observed and recorded group setting, some abilities of the protocol analysis methods are demonstrated. After discussing the non-participating observation of design processes with on-line recordings, the planned future work is introduced. Apart from further investigation methods, experiences from first investigations in industry are mentioned.