Offset-polygon annulus placement problems

An offset-polygon annulus region is defined in terms of a polygon P and a distance δ > 0 (offset of P). In this paper we solve several containment problems for polygon annulus regions with respect to an input point set. Optimization criteria include both maximizing the number of points contained in a fixed size annulus and minimizing the size of the annulus needed to contain all points. We address the following variants of the problem: placement of an annulus of a convex polygon as well as of a simple polygon; placement by translation only, or by translation and rotation; off-line and on-line versions of the corresponding decision problems; and decision as well as optimization versions of the problems. We present efficient algorithms in each case.     

Dynamics of single InGaN quantum dots

Decay dynamics for single InGaN quantum dots are presented using time-resolved photoluminescence. The recombination is shown to be characterized by a single exponential decay, in contrast to the non-exponential recombination dynamics seen in the 2D wetting layer. The lifetimes of single dots in the temperature range 4–60 K decrease with increasing temperature. Different dots show similar lifetimes of 2 ns.     

Equilibrium model of bimodal distributions of epitaxial island growth

We present a nanostructure diagram for use in designing heteroepitaxial systems of quantum dots. The nanostructure diagram is computed using a new equilibrium statistical physics model and predicts the island size and shape distributions for a range of combinations of growth temperature and amount of deposited material. The model is applied to Ge on Si(001), the archetype for bimodal island growth, and the results compare well with data from atomic force microscopy of Ge/Si islands grown by chemical vapor deposition.     

Synthesis of biologically active amines via rhodium-bisphosphite-catalyzed hydroaminomethylation

[reaction: see text] We report the use of a highly regioselective rhodium-bisphosphite catalyst for olefin hydroaminomethylation. This catalyst system was successfully applied in the synthesis of two biologically active tertiary amines, ibutilide and aripiprazole.     

pi-stacking interactions in cis-Bisfullerene

Experimental, molecular modeling, and model compound studies suggest that favorable fullerene[60] pi-stacking interactions in the ground state and in syn-transition states account for the high cis stereoselectivities observed in the reactions between C(60) and 6, 13-disubstituted pentacenes.     

Optical anisotropy of the SiC((001))- (3x2) surface: evidence for the two-adlayer asymmetric-dimer model

The structure of the ( 3x2) reconstruction of beta-SiC(001) surface has been identified by comparing reflectance anisotropy spectra calculated from first principles with recent measurements. Only the calculations for the two-adlayer asymmetric-dimer model agree with experiment. The two prominent peaks at 3.6 and 5.0 eV found experimentally are assigned to electronic transitions between surface and bulklike electronic states. A further pronounced anisotropy at 2.0 eV, due to transitions between surface states, is predicted.     

Selection rules and isotope effects in the full fragmentation of the hydrogen molecule

Selection rules predicting zeros in cross sections for full fragmentation of the hydrogen molecule into specific momentum configurations are presented. Isotope effects are predicted to arise from these selection rules and from the correlated motion of nuclei and electrons in the final state.     

An XPS and ups study of chloride chemisorption on Ag(110)

Chlorine chemisorbs rapidly on Ag(110) at 300 K to a saturation coverage of about one monolayer and with a sticking probability of order unity. The corresponding work function shift is + 1.7 eV. XP and UP spectra are consistent with the presence of a single king of chemisorbed species. It appears that Ag behaves as a single s-band solid and that the adsorbate 3p level is shifted so as to lie in the metal s-band; these observations are in agreement with the recent theoretical predictions of Anderson.     

The extractives of Vitex lucens—I

Vitexin, isolated from Vitex lucens, has been formulated as C₂₁H₂₀O₁₀ and, in agreement with recent workers, structure (I) has been assigned to the compound. β-sitosterol has been isolated from the heartwood.