Improved direct measurement of the parity-violation parameter Ab using a mass tag and momentum-weighted track charge

We present an improved direct measurement of the parity-violation parameter A(b) in the Z boson-b-quark coupling using a self-calibrating track-charge technique applied to a sample enriched in Z-->bb events via the topological reconstruction of the B hadron mass. Manipulation of the Stanford Linear Collider electron-beam polarization permits the measurement of A(b) to be made independently of other Z-pole coupling parameters. From the 1996-1998 sample of 400,000 hadronic Z decays, produced with an average beam polarization of 73.4%, we find A(b)=0.906+/-0.022(stat)+/-0.023(syst).     

A Lower Bound for the Determinantal Complexity of a Hypersurface

We prove that the determinantal complexity of a hypersurface of degree \(d > 2\) is bounded below by one more than the codimension of the singular locus, provided that this codimension is at least 5. As a result, we obtain that the determinantal complexity of the \(3 \times 3\) permanent is 7. We also prove that for \(n> 3\), there is no nonsingular hypersurface in \({\mathbb {P}}^n\) of degree d that has an expression as a determinant of a \(d \times d\) matrix of linear forms, while on the other hand for \(n \le 3\), a general determinantal expression is nonsingular. Finally, we answer a question of Ressayre by showing that the determinantal complexity of the unique (singular) cubic surface containing a single line is 5.     

Oxidation of a guanine derivative coordinated to a Pt(IV) complex initiated by intermolecular nucleophilic attacks

In this study we report that fac-[Pt(IV)(dach)(9-EtG)Cl(3)](+) (dach = d,l-1,2-diaminocyclohexane, 9-EtG = 9-ethylguanine) in high pH (pH 12) or phosphate solution (pH 7.4) produces 8-oxo-9-EtG and Pt(II) species. The reaction in H(2)(18)O revealed that the oxygen atom in hydroxide or phosphate ends up at the C8 position of 8-oxo-G. The kinetics of the redox reaction was first order with respect to both Pt(IV)-G and free nucleophiles (OH(-) and phosphate). The oxidation of G initiated by hydroxide was approximately 30～50 times faster than by phosphate in 100 mM NaCl solutions. The large entropy of activation of OH(-1) (ΔS(?) = 26.6 ± 4.3 J mol(-1) K(-1)) due to the smaller size of OH(-) is interpreted to be responsible for the faster kinetics compared to phosphate (ΔS(?) = -195.5 ± 11.1 J mol(-1) K(-1)). The enthalpy of activation for phosphate reaction is more favorable relative to the OH(-) reaction (ΔH(?) = 35.4 ± 3.5 kJ mol(-1) for phosphate vs. 96.6 ± 11.4 kJ mol(-1) for OH(-1)). The kinetic isotope effect of H8 was determined to be 7.2 ± 0.2. The rate law, kinetic isotope effect, and isotopic labeling are consistent with a mechanism involving proton ionization at the C8 position as the rate determining step followed by two-electron transfer from G to Pt(IV).     

Structure-property relationships in polycaprolactone-polyurethanes

The structure-property relationships of polycaprolactone-based segmented polyurethanes were studied using differential scanning calorimetry (DSC), small-angle x-ray scattering (SAXS), wide-angle x-ray diffraction (WAXD), dynamic mechanical, and stress-strain testing. The materials studied varied in hard-segment type [4,4′-diphenylmethane diisocyanate/butanediol (MDI/BD) or 4,4′-dicyclohexyl methane diisocyanate/butanediol (H₁₂MDI/BD)], soft-segment molecular weight (830 or 2000 MW polycaprolactone), hard-segment content (23–77% by weight), and thermal history. The materials with aromatic (MDI/BD) hard segments had semicrystalline hard-segment domains, while the materials with aliphatic (H₁₂MDI/BD) hard segment had mostly amorphous domains. Materials with the shorter polycaprolactone soft segment (830 MW) exhibited thermal and mechanical behavior which indicated a considerable degree of hard- and soft-segment compatibility. The materials which contained a 2000-MW polycaprolactone soft segment exhibited better-defined microphase separation. SAXS was used to characterize the microphase structure of each system. The effects of hard-segment content and soft-segment molecular weight were similar for the aromatic (MDI) and aliphatic (H₁₂MDI) hard-segment-based block copolymers. Changing the hard segment from aromatic to aliphatic gave materials with larger interfacial area and slightly higher tensile strength. A range of morphologies between isolated hard domains in a rubbery matrix and isolated rubbery domains in a hard matrix was observed.     

Proper and Unit Trapezoid Orders and Graphs

We show that the class of trapezoid orders in which no trapezoid strictly contains any other trapezoid strictly contains the class of trapezoid orders in which every trapezoid can be drawn with unit area. This is different from the case of interval orders, where the class of proper interval orders is exactly the same as the class of unit interval orders.     

Maximal dimensional partially ordered sets III: a characterization of Hiraguchi's inequality for interval dimension

Dushnik and Miller defined the dimensions of a partially ordered set X,denoted dim X, as the smallest positive integer t for which there exist t linear extensions of X whose intersection is the partial ordering on X. Hiraguchi proved that if n ≥2 and |X| ≤2n+1, then dim X ≤ n. Bogart, Trotter and Kimble have given a forbidden subposet characterization of Hiraguchi's inequality by determining for each n ≥ 2, the minimum collection of posets ?_n such that if |X| ?2n+1, the dim X < n unless X contains one of the posets from ?_n. Although |?₃|=24, for each n ≥ 4, ?_n contains only the crown S⁰_n — the poset consisting of all 1 element and n ? 1 element subsets of an n element set ordered by inclusion. In this paper, we consider a variant of dimension, called interval dimension, and prove a forbidden subposet characterization of Hiraguchi's inequality for interval dimension: If n ≥2 and |X 2n+1, the interval dimension of X is less than n unless X contains S⁰_n.