The effect of thermo chemical treatments on the mechanical properties of tool steel

The effect of a range of surface treatment processes on the properties of a group of tool steels has been examined. In this first part attention is concentrated on the various nitriding processes.     

Wear prevention in molds used to mold boron filled elastomers

An investigation was conducted to identify surface coatings which would improve the wear characteristics of compression molds used to mold contoured parts from elastomers filled with crystalline boron particles. An analysis was made of the mode of wear present on the surfaces of a production mold, followed by selection and modification of a capillary rheometer as the test device. Test specimens were coated by electroplating, electroless plating, plasma spraying, chemical vapor deposition, sputtering and a fused salt process. Testing was conducted under conditions simulating those encountered in the production molding operation.Techniques used in evaluating the results included optical microscopy, scanning electron microscopy, transmission electron microscopy and surface profilometry. The results are expressed as a ratio of volumetric wear of the tested coating to that of unprotected mold steel.Results indicate that titanium diboride (TiB₂) applied by chemical vapor deposition provides wear resistance superior to plasma sprayed aluminum oxide mixed with titanium dioxide, plasma sprayed chromium oxide, electrodeposited chromium, electroless nickel containing synthetic diamond powder, chemical vapor deposited tungsten carbide (W/W₂C), aluminum oxide and aluminum oxide over chromium carbide. Sputtered titanium diboride was also superior to these coatings and to sputtered titanium carbide and boron carbide.     

An FDTD near- to far-zone transformation for scatterers buried instratified grounds

The finite-difference time-domain (EDTD) technique is being used with increasing frequency for modeling the scattering characteristics of buried objects. The FDTD has, for some time, been able to model the near-zone scattered fields of buried objects due to near-zone sources. This is adequate for modeling the scattered returns of ground-based ground-penetrating radar, but not for airborne radar. This paper describes an FDTD-compatible technique whereby far-zone scattered fields of objects buried in a stratified ground can be calculated. This technique uses the equivalence principle to model a buried object in terms of equivalent electric and magnetic currents. The fields radiated by these currents in the presence of a stratified ground are then calculated using the reciprocity theorem and the well-known field equations for plane waves in a stratified media. Numerical results are presented that show excellent agreement between this technique and both analytical and numerical results     

Modeling baluns with the method of moments

When using the method of moments (MoM) to model large arrays with large numbers of balanced feeds, the feed baluns can always be incorporated into the analysis by combining the multiport admittance matrix for the array with the admittance matrices of the baluns. This technique is straightforward but requires that the MoM equations be solved for a large number of right-hand sides. The paper shows how the effects of perfect baluns can be incorporated directly into the MoM equations, requiring only one right-hand side. This technique yields the exact results with a significant savings in computing resources     

Interspecies differences and variability with time of protein precipitation activity of extractable tannins,crude protein,ash, and dry matter content of leaves from 13 species of Nepalese fodder trees

Dry matter, ash, crude protein, and protein precipitation activity (PPA) of 13 Nepalese tree fodder species were monitored in dried samples prepared monthly between November 1990 and May 1991, and additionally in November 1991, covering the season when they are particularly important as fodder. Monthly levels of dry matter, ash, and crude protein were fairly stable except when there was new leaf growth, although year to year differences in dry matter were found inBrassaiopsis hainla (Bh),Dendrocalamus strictus (Ds),Ficus roxburghii (Fr), andQuercus semecarpifolia (Qs). Tannin PPA fluctuated considerably inArtocarpus lakoocha (Al),Ficus glaberrima (Fg),F. nerrifolia (Fn), Fr,F. semicordata (Fs),Litsea polyantha (Lp), andPrunus cerasoides (Pc), and to a lesser extent in Bh,Castanopsis indica (Ci),C. tribuloides (Ct),Quercus lamellosa (Ql), and Qs. Similar fluctuations in PPA were observed in fresh leaf samples taken weekly. Ds did not have any detectable PPA. Trends in PPA fluctuation were generally similar for trees located at similar altitudes. Fr, Pc, Al, Fn, Ql, and Ci had falling PPAs before shedding leaves. Some of the fluctuations in Fr, Fs, Fg, Pc, and Lp were apparently due to changes in the extractability and quantity of condensed tannins. These fluctuations in PPA may affect the nutritive value of the fodders.     

A note on the iron-organic relationship in natural water

The percentage of iron in the aquatic environment which is associated with organic matter can be measured by fractionating unconcentrated water samples on Sephadex gel filtration columns. The use of concentrated samples should be avoided since they exaggerate the importance of the iron-organic relationship.     

Picosecond pulse generation by lateral mode switching of (GaAl)As-heterostructure stripe lasers

The presence of `kinks? in the light/current characteristics of (GaAl)As injection lasers is investigated by applying large amplitude electrical RF modulation. It is suggested that the 20 ps pulses which have been observed may be produced through mechanisms associated with these kinks.     

Time-domain modeling of mode suppression in 1.3-/spl mu/m Fabry-Perot lasers

Fabry-Perot lasers still comprise the bulk of lasers used in optical fiber systems. The spectral envelope, of the Fabry-Perot modes, can be modulated either deliberately or as a consequence of processing stages. This can be beneficial, in the case of modal sculpturing where specific Fabry-Perot modes are suppressed, or a hindrance in the case of poor devices. A time-domain model is used to model 1.3-/spl mu/m Fabry-Perot lasers. Simulated power conserving reflective sites are introduced between sections in the model to simulate the effect of reflective sites from etch pits on the output characteristics of real lasers. Spectral modulation of the laser output is reported in agreement with previous experimental results and the strength of reflections required is investigated. We also report the use of the model to investigate the effect of fiber dispersion on the modulated laser output with different spectral mode modulation.