Showing papers by "Chris Peterson published in 1997"

Processing, characterization, and performance of eight fuels from lipids.

Abstract: Test quantities of ethyl and methyl esters of four renewable fuels were processed, characterized and performance tested. Canola, rapeseed, soybean oils, and beef tallow were the feedstocks for the methyl and ethyl esters. A complete set of fuel properties and a comparison of each fuel in engine performance tests are reported. The study examines short term engine tests with both methyl and ethyl ester fuels compared to number 2 diesel fuel (D2). Three engine performance tests were conducted including an engine mapping procedure, an injector coking screening test, and an engine power study. The gross heat contents of the biodiesel fuels, on a mass basis, were 9 to 13% lower than D2. The viscosities of biodiesel were twice that of diesel. The cloud and pour points of D2 were significantly lower than the biodiesel fuels. The biodiesel fuels produced slightly lower power and torque and higher fuel consumption than D2. In general, the physical and chemical properties and the performance of ethyl esters were comparable to those of the methyl esters. Ethyl and methyl esters have almost the same energy. The viscosity of the ethyl esters is slightly higher and the cloud and pour points are slightly lower than those of methyl esters. Engine tests demonstrated that methyl esters produced slightly higher power and torque than ethyl esters. Fuel consumption when using the methyl and ethyl esters is nearly identical. Some desirable attributes of the ethyl esters over methyl esters were: significantly lower smoke opacity, lower exhaust temperatures, and lower pour point. The ethyl esters tended to have more injector coking than the methyl esters, and the ethyl esters had a higher glycerol content than the methyl esters

A construction of codimension three arithmetically Gorenstein subschemes of projective space

Abstract: This paper presents a construction method for a class of codimension three arithmetically Gorenstein subschemes of projective space. These schemes are obtained from degeneracy loci of sections of certain specially constructed rank three reflexive sheaves. In contrast to the structure theorem of Buchsbaum and Eisenbud, we cannot obtain every arithmetically Gorenstein codimension three subscheme by our method. However, certain geometric applications are facilitated by the geometric aspect of this construction, and we discuss several examples of this in the final section.

Gender differences in distress and depression following cardiac surgery

Abstract: This study examined the effects of physical health and other psychosocial variables on psychological distress and depression following coronary artery bypass graft surgery (CABG), with a focus on gender differences. Information regarding psychological distress one year following surgery was obtained from a sample of 151 patients (112 males, 39 females), who also provided retrospective information about noncardiac chronic conditions, preoperative socioeconomic variables, postoperative social support, and immediately post-CABG depression. Medical and surgical data and postoperative cardiac conditions were retrieved from computerized medical records. Structural equation modeling with LISREL showed that distress one year following surgery was predicted by the number of noncardiac chronic illnesses, controlling for immediately post-CABG depression. Gender had only an indirect effect on distress; women reported more chronic medical conditions than did men. Analysis also revealed an interaction between gender and income: higher income men and lower income women were most likely to report depression immediately following surgery.

Determinantal schemes and Buchsbaum-Rim sheaves

Abstract: Let $\phi$ be a generically surjective morphism between direct sums of line bundles on $\proj{n}$ and assume that the degeneracy locus, $X$, of $\phi$ has the expected codimension. We call $B_{\phi} = \ker \phi$ a (first) Buchsbaum-Rim sheaf and we call $X$ a standard determinantal scheme. Viewing $\phi$ as a matrix (after choosing bases), we say that $X$ is good if one can delete a generalized row from $\phi$ and have the maximal minors of the resulting submatrix define a scheme of the expected codimension. In this paper we give several characterizations of good determinantal schemes. In particular, it is shown that being a good determinantal scheme of codimension $r+1$ is equivalent to being the zero-locus of a regular section of the dual of a first Buchsbaum-Rim sheaf of rank $r+1$. It is also equivalent to being standard determinantal and locally a complete intersection outside a subscheme $Y \subset X$ of codimension $r+2$. Furthermore, for any good determinantal subscheme $X$ of codimension $r+1$ there is a good determinantal subscheme $S$ codimension $r$ such that $X$ sits in $S$ in a nice way. This leads to several generalizations of a theorem of Kreuzer. For example, we show that for a zeroscheme $X$ in $\proj{3}$, being good determinantal is equivalent to the existence of an arithmetically Cohen-Macaulay curve $S$, which is a local complete intersection, such that $X$ is a subcanonical Cartier divisor on $S$.

Buchsbaum-Rim sheaves and their multiple sections

Abstract: This paper begins by introducing and characterizing Buchsbaum-Rim sheaves on $Z = \Proj R$ where $R$ is a graded Gorenstein K-algebra. They are reflexive sheaves arising as the sheafification of kernels of sufficiently general maps between free R-modules. Then we study multiple sections of a Buchsbaum-Rim sheaf $\cBf$, i.e, we consider morphisms $\psi: \cP \to \cBf$ of sheaves on $Z$ dropping rank in the expected codimension, where $H^0_*(Z,\cP)$ is a free R-module. The main purpose of this paper is to study properties of schemes associated to the degeneracy locus $S$ of $\psi$. It turns out that $S$ is often not equidimensional. Let $X$ denote the top-dimensional part of $S$. In this paper we measure the ``difference'' between $X$ and $S$, compute their cohomology modules and describe ring-theoretic properties of their coordinate rings. Moreover, we produce graded free resolutions of $X$ (and $S$) which are in general minimal. Among the applications we show how one can embed a subscheme into an arithmetically Gorenstein subscheme of the same dimension and prove that zero-loci of sections of the dual of a null correlation bundle are arithmetically Buchsbaum.