P-type carbon doping of GaSb

The growth of carbon-doped GaSb by MOVPE has never been reported to our knowledge, despite increasing interest in carbon-doped GaAsSb alloys for heterojunction bipolar transistor applications. In this work, we report the use of carbon tetrachloride (CCl₄) in conjunction with triethylgallium (TEGa) and trimethylantimony (TMSb) to achieve p-type doping levels in GaSb from 5 10¹⁶ cm⁻³ to greater than 10¹⁹ cm⁻³. High resolution x-ray diffraction measurements confirm that the effect of carbon on the lattice parameter is significant for hole concentrations above 1 10¹⁹ cm⁻³ as in the case of GaAs. By introducing controlled low doping levels of carbon into thick homoepitaxial samples, we have succeeded in identifying a carbon-related low temperature photoluminescence band at 795 meV, which we ascribe to band-to-acceptor transitions of carbon acceptors. Temperature-dependent Hall measurements on lightly carbon-doped samples yield somewhat lower binding energies than the spectroscopic data due to impurity banding in the acceptor excited states.     

Flow characterization of flickering methane/air diffusion flames using particle image velocimetry

Phase-resolved measurements of the velocity field in acoustically forced, flickering laminar co-flowing methane/air diffusion flames were made. Identical flames have been studied extensively in the past in order to characterize the effects of the vortical structures responsible for the flicker on the flame structure, but the initial velocity perturbation and the velocity fields have not been reported previously. Phase-locked measurements of the instantaneous two-dimensional velocity field at ten phases within a full excitation cycle were made using particle image velocimetry. The velocity measurements were complemented by phase-resolved shadowgraphs recorded in the vicinity of the flame base. Measurements are reported for the two forcing conditions that have most often been studied for this burner. When integrated with the results of previous studies, these measurements provide a clearer picture of the interactions between the buoyancy-induced vortical structures and the flame sheets, as well as providing the initial conditions required for realistic modeling of these flames.     

Massive Nordström scalar (density) gravities from universal coupling

Both particle physics and the 1890s Seeliger–Neumann modification of Newtonian gravity suggest considering a “mass term” for gravity, yielding a finite range due to an exponentially decaying Yukawa potential. Unlike Nordström’s “massless” theory, massive scalar gravities are strictly Special Relativistic, being invariant under the Poincaré group but not the conformal group. Geometry is a poor guide to understanding massive scalar gravities: matter sees a conformally flat metric, but gravity also sees the rest of the flat metric, barely, in the mass term. Infinitely many theories exhibit this bimetric ‘geometry,’ all with the total stress–energy’s trace as source. All are new except the Freund–Nambu theory. The smooth massless limit indicates underdetermination of theories by data between massless and massive scalar gravities. The ease of accommodating electrons, protons and other fermions using density-weighted Ogievetsky–Polubarinov spinors in scalar gravity is noted.     

Fuzzy sets do not form a topos

The relationship between fuzzy sets and H-valued sets is briefly examined and a claim of Eytan's that the former comprise the objects of a topos is corrected.     

Approximations for the moments of ruin time in the compound Poisson model

In the classical risk model with Poisson arrivals, we study a functional approach which can be used to obtain new approximation formulae for the moments of the time to ruin. We explain how establishing differentiability of a functional, in appropriate function spaces, may lead to approximations for these moments. We consider various choices for the function spaces, which are suitable both for heavy-tailed and light-tailed claim-size distributions. The results are illustrated by some particular examples.     

Formation of alkyl nitrates from the reaction of branched and cyclic alkyl peroxy radicals with NO

The yields of C₅ and C₆ alkyl nitrates from neopentane, 2-methylbutane, 2-methylpentane, 3-methylpentane, and cyclohexane have been measured in irradiated CH₃ONONO-alkane-air mixtures at 298 ± 2 K and 735-torr total pressure. Additionally, OH radical rate constants for neopentyl nitrate, 3-nitro-2-methylbutane, 2-nitro-2-methylpentane, 2-nitro-3-methylpentane, and cyclohexyl nitrate, relative to that for n-butane, have been determined at 298 ± 2 K. Using a rate constant for the reaction of OH radicals with n-butane of 2.58 × 10^?12 cm³ molecule^?1 s^?1, these OH radical rate constants are (in units of 10^?12 cm³ molecule^?1 s^?1): neopentyl nitrate, 0.87 ± 0.21; cyclohexyl nitrate, 3.35 ± 0.36; 3-nitro-2-methylbutane, 1.75 ± 0.06; 2-nitro-2-methylpentane, 1.75 ± 0.22; and 2-nitro-3-methylpentane, 3.07 ± 0.08. After accounting for consumption of the alkyl nitrates by OH radical reaction and for the yields of the individual alkyl peroxy radicals formed in the reaction of OH radicals with the alkanes studied, the alkyl nitrate yields (which reflect the fraction of the individual RO₂ radicals reacting with NO to form RONO₂) determined were: neopentyl nitrate, 0.0513 ± 0.0053; cyclohexyl nitrate, 0.160 ± 0.015; 3-nitro-2-methylbutane, 0.109 ± 0.003; 2-nitro-2methylbutane, 0.0533 ± 0.0022; 2-nitro-2-methylpentane, 0.0350 ± 0.0096; 3- + 4-nitro-2-methylpentane, 0.165 ± 0.016; and 2-nitro-3-methylpentane, 0.140 ± 0.014. These results are discussed and compared with previous literature values for the alkyl nitrates formed from primary and secondary alkyl peroxy radicals generated from a series of n-alkanes.     

Nonparametric estimation of compound distributions with applications in insurance

A nonparametric estimator of the distribution functionG of a random sum of independent identically distributed random variables, with distribution functionF, is proposed in the case where the distribution of the number of summands is known and a random sample fromF is available. This estimator is found by evaluating the functional that mapsF ontoG at the empirical distribution function based on the random sample. Strong consistency and asymptotic normality of the resulting estimator in a suitable function space are established using appropriate continuity and differentiability results for the functional. Bootstrap confidence bands are also obtained. Applications to the aggregate claims distribution function and to the probability of ruin in the Poisson risk model are presented.     

A study of the reaction NO3 + NO2 + M → N2O5 + M(M = N2, O2)

The gas-phase reaction of the NO₃ radical with NO₂ was investigated, using a flash photolysis-visible absorption technique, over the total pressure range 25–400 Torr of nitrogen or oxygen diluent at 298 ± 2 K. The absolute rate constants determined (in units of 10^?13 cm³ molecule^?1 s^?1) at 25, 100, and 400 Torr total pressure were, respectively, (4.0 ± 0.5), (7.0 ± 0.7), and (10 ± 2) for M = N₂ and (4.5 ± 0.5), (8.0 ± 0.4), and (8.8 ± 2.0) for M = O₂. These data show that the third-body efficiencies of N₂ and O₂ are identical, within the error limits, and that previous evaluations for M = N₂ are applicable to the atmosphere. In addition, upper limits were determined for the rate constants of the reactions of the NO₃ radical with methanol, ethanol, and propan-2-ol of ?6 × 10^?16, ?9 × 10^?16, and ?2.3 × 10^?15 cm³ molecule^?1 s^?1, respectively, at 298 ± 2 K.     

The Supramolecular Structural Chemistry of Pentafluorosulfanyl and Tetrafluorosulfanylene Compounds

The analysis of crystal structures of SF₅- or SF₄-containing molecules revealed that these groups are often surrounded by hydrogen or other fluorine atoms. Even though fluorine prefers F⋅⋅⋅H over F⋅⋅⋅F contacts, the latter appeared to be important in many compounds. In a significant number of datasets, the closest F⋅⋅⋅F contacts are below 95 % of the van der Waals distance of two F atoms. Moreover, a number of repeating structural motifs formed by contacts between SF₅ groups was identified, including different supramolecular dimers and infinite chains. Among SF₄-containing molecules, the study focused on SF₄Cl compounds, including the first solid-state structure analyses of these reactive species. Additionally, electrostatic potential surfaces of a series of Ph-SF₅ derivatives were calculated, pointing out the substituent influence on the ability of F⋅⋅⋅X contact formation (X=F or other electronegative atom). Interaction energies were calculated for different dimeric arrangements of Ph-SF₅, which were extracted from experimental crystal structure determinations.