Untersuchungen an der Dieselmaschine

Zusammenfassung Der Arbeitsproze? der verlustlosen Luftspeicher-Dieselmaschine wird thermodynamisch untersucht. Durch den unterteilten Verdichtungsraum werden beim Arbeitshub Str?mungen im Zylinder erzeugt, die die Verbrennung beeinflussen. Es wird der zeitliche Verlauf des Zylinderund Speicherdruckes ermittelt. Aus der Untersuchung der Wechselbeziehung zwischen Zylinderund Speicher folgen alle Eigenschaften der Speichermaschine, insbesondere der Einflu? der Maschinenabmessungen, der Drehzahl, der Verbrennung im Zylinder und der Hilfsverbrennung im Speicher. W?hrend des Arbeitshubes sind zwei Wirbel wirksam: der Speicherwirbel und der Saugwirbel des Kolbens. Ihre Lage und St?rke wird abh?ngig von den Bauelementen der Maschine angegeben. Die Ergebnisse werden auf ein Zahlenbeispiel angewendet, wobei auch das Indikatordiagramm der verlustlosen Maschine erhalten wird. Der Einflu? von ?nderungen der verschiedenen Ver?nderlichen auf den Arbeitsproze? wird festgestellt. Aus dem Institut für Verbrennungskraftmaschinen und Technische W?rmelehre der Technischen Hochschule Hannover     

A monotonic projective algorithm for fractional linear programming

We demonstrate that Karmarkar's projective algorithm is fundamentally an algorithm for fractional linear programming on the simplex. Convergence for the latter problem is established assuming only an initial lower bound on the optimal objective value. We also show that the algorithm can be easily modified so as to assure monotonicity of the true objective values, while retaining all global convergence properties. Finally, we show how the monotonic algorithm can be used to obtain an initial lower bound when none is otherwise available.     

Stabilization of polyacetals

A brief introduction describes the main differences between homo, and copolymer polyacetals and their main degradation mechanisms. A short overview describes the importance of stabilization and the necessity of using antioxidants and costabilizers during manufacturing, processing and end use of polyoxymethylene(polyacetals). Various stabilizer systems are presented and studies on the interaction of antioxidants with costabilizers added. The criteria for testing the performance of these additives are discussed and demonstrated by many examples. In a second part the increasing importance of light stabilized polyacetal is mentioned and investigations on the performance of light stabilizer systems are highlighted.     

Isotropic Constitutive Model for Sintering Particle Packings

This paper presents an isotropic model for the effective viscosities of sintering particle packings. The relationship between the macroscopic stress and deformation rate is based on the behavior of individual interparticle contacts, represented by contact viscosities, and the statistics of the packing. The contact viscosities depend on the contact area, which is the primary variable used to describe the state of the packing. A direct consequence of this choice of state variable is that the effective viscosities are identically zero for an undeformed and unsintered packing. Specific results are presented for the case of Newtonian viscous materials. The model is compared with existing models for porous Newtonian viscous materials. Experiments conducted with spherical glass powder packings show good agreement with the model. Finite-element simulations using the model have been used to study forging of a pellet.     

Silica and Magnesia Dopant Distributions in Alumina by High-Resolution Scanning Secondary Ion Mass Spectrometry

Trace SiO₂ and MgO additive distributions in sintered alumina have been studied using high-resolution scanning secondary ion mass spectrometry (SIMS). When doped with each additive individually, evidence is seen for both strong silicon segregation to grain boundaries ( C _gb/ C _grain similar/congruent 300) in SiO₂-doped alumina and strong magnesium segregation to grain boundaries ( C _gb/ C _grain similar/congruent 400) in MgO-doped alumina. When codoped with both SiO₂ and MgO, segregation of both ions to grain boundaries is reduced by a factor of 5 or more over single doping. The additive concentrations increase proportionally in the grains, and both dopants become more uniformly distributed throughout the bulk. It is concluded that codoping with these additives increases their mutual bulk solid solubility and decreases their interfacial segregation over single doping. The beneficial effect of MgO additions in controlling microstructure development in alumina and improving corrosion resistance to aqueous HF stems from its ability to redistribute silicon ions from grain boundaries into the bulk.     

Community similarity and the analysis of multispecies environmental data: A unified statistical approach

The number of species or variables in some designed environmental studies is too large for analysis using standard inferential statistics. To analyze the type of data, a two-stage procedure and follow-up methods are described. First, data are reduced using a measure of similarity or distance. Then, a permutation procedure is used to make inferences. Assuming the hypothesis is rejected, several follow-up analyses are presented as tools in understanding the causes of rejection. For example, to further understand treatment effects, a randomization based, multiple comparison procedure may be used; to better understand what differences the similarity or distance measure describes, a method based on removal of a species is given. The methods are illustrated on a study of the effects of zinc on the periphyton community in the New River, Va, U.S.A.