Containment of explosions in water-filled right-circular cylinders

The formulation of basic explosion-containment equations for idealized water-filled right-circular cylinders is summarized. The equations express explosive-charge weight as a function of vessel geometry and conventional material properties. Extensive experiments with models verified the relations for a wide range of vessels, materials and sizes. The basic containment relations were modified to provide safe and reasonable solutions for less-adverse accident conditions and for real vessels, i.e., vessels with welds, nozzles and end constraints.     

Orbifold homeomorphism finiteness based on geometric constraints

We show that any collection of n-dimensional orbifolds with sectional curvature and volume uniformly bounded below, diameter bounded above, and with only isolated singular points contains orbifolds of only finitely many orbifold homeomorphism types. This is a generalization to the orbifold category of a similar result for manifolds proven by Grove, Petersen, and Wu. It follows that any Laplace isospectral collection of orbifolds with sectional curvature uniformly bounded below and having only isolated singular points also contains only finitely many orbifold homeomorphism types. The main steps of the argument are to show that any sequence from the collection has subsequence that converges to an orbifold, and then to show that the homeomorphism between the underlying spaces of the limit orbifold and an orbifold from the subsequence that is guaranteed by Perelman’s stability theorem must preserve orbifold structure.     

High pressure Raman spectroscopy of single-walled carbon nanotubes: Effect of chemical environment on individual nanotubes and the nanotube bundle

The pressure-induced tangential mode Raman peak shifts for single-walled carbon nanotubes (SWNTs) have been studied using a variety of different solvents as hydrostatic pressure-transmitting media. The variation in the nanotube response to hydrostatic pressure with different pressure transmitting media is evidence that the common solvents used are able to penetrate the interstitial spaces in the nanotube bundle. With hexane, we find the surprising result that the individual nanotubes appear unaffected by hydrostatic pressures (i.e. a flat Raman response) up to 0.7 GPa. Qualitatively similar results have been obtained with butanol. Following the approach of Amer et al. [J. Chem. Phys. 121 (2004) 2752], we speculate that this is due to the inability of SWNTs to adsorb some solvents onto their surface at lower pressures. We also find that the role of cohesive energy density in the solvent-nanotube interaction is more complex than previously thought.     

Chloromethyl chlorosulfate: a new, catalytic method of preparation and reactions with some nucleophiles

The reaction of liquid (gamma-) SO3 with CH2Cl2 at room temperature leads to SO3 insertion into the C-Cl bonds, giving the useful chloromethylating agent chloromethyl chlorosulfate (CMCS). The process is very slow but becomes rapid on addition of catalytic quantities of trimethyl borate. The product mixture consists almost entirely of CMCS and the product of further sulfation, methylene bis(chlorosulfate)(MBCS), in a ratio of ca. 2 : 1, but typical yields of CMCS, isolated by distillation, are only 30-35%. The catalysed reaction in the homogeneous liquid phase at -45 degrees C has been followed as a function of time and of reactant concentration by 1H nmr spectroscopy. It is observed that, besides CMCS and MBCS, three additional, transient products (designated A, B and C) are formed. Products A, B and C decompose slowly at -45 degrees C but much more rapidly if the reaction mixture is raised to room temperature, giving additional CMCS and MBCS. From an analysis of the SO3 balance, it is inferred that products A, B and C arise from the reaction of one molecule of CH2Cl2 with respectively two, three and four molecules of SO3; they are suggested to be chloromethyl chloropolysulfates. By measuring initial rates of CMCS formation or total CH2Cl2 consumption, it is shown that the reaction is first order in the catalyst and roughly third order in SO3. A mechanistic scheme is proposed in which SO3 forms equilibrating zwitterionic molecular complexes with CH2Cl2. of 1 : 1, 2 : 1 and higher stoichiometries. The boron-containing catalyst can activate these complexes towards nucleophilic attack at carbon by the negatively charged oxygen of another zwitterion. An analogous mechanism can be written for the conversion of CMCS into MBCS by SO3 in the presence of trimethyl borate. CMCS reacts rapidly with anionic nucleophiles, such as halide or acetate ions (X-), in homogeneous solution of their tetrabutylammonium salts in CD3CN, or in a two-phase system (CDCl3/H2O) using alkali-metal salts in conjunction with a phase-transfer catalyst. In both situations the products (ClCH2X) arise by rapid nucleophilic displacement of the chlorosulfate moiety; this then more slowly liberates chloride ion, which converts further CMCS into CH2Cl2. The reactivity of CMCS has been compared with that of MBCS and methyl chlorosulfate (MCS) in competitive experiments; the reactivity order is MCS > MBCS > CMCS > CH2Cl2. Evidence is also presented suggesting that, in contrast to the halide nucleophiles, reaction of CMCS with sodium phenoxide in tetrahydrofuran solution leads to nucleophilic displacement of the sulfur-bound chloride.     

Intramolecular 2h group-transfer in heterocyclic bridged-ring systems (dyotropic rearrangements)

Diarylnitrilimines, derived by thermolysis of appropriate diaryltetrazoles, form(4+2)π cyclo-adducts with dipolarophiles of the isodrin type, e.g. $\text{(1)}$; the resulting 2-pyrazolines thermally rearrange into pyrazoles by hydrogen group transfer. Kinetic data for examples of this and related reactions are reported.     

Evidence for a strongly deformed prolate shape at N = 87 from 154Eu and 152Eu(p,t) reactions

The (p, t) reaction on radioactive targets of ^152,154Eu has been used to study rotational states associated with the configuration in the transitional odd-odd ¹⁵²Eu and ¹⁵⁰Eu nuclei. Our studies yieldcompelling evidence that this configuration in ¹⁵⁰Eu has a prolate structure which is strongly deformed and occurs at excitation energy of 1224 keV.     

Yeast deoxyribodipyrimidine photolyase (photoreactivating enzyme): optimum conditions for activity and competitive inhibition

Abstract— Using flash photolytic techniques and direct chemical measurements of the conversion of the substrate (conversion of thymine dimers in DNA to monomeric thymine), we have determined photolyase concentrations in partially purified preparations of soluble proteins from yeast and have determined under continuous intense light the forward rate constant k₁ for binding of the enzyme and its substrate under a variety of conditions. The ionic requirements and the sharp peak of ionic strength dependence are independent of the species of uni-univalent salts used in the assay. At infinite dilution, the k₁ for denatured DNA, and its ionic strength dependence, both appear identical to the values for native DNA. Both unirradiated denatured and unirradiated native DNA inhibit binding, denatured DNA being 10- to 20-fold more effective. These combined factors have been taken into account to devise a sensitive assay for photoreactivable lesions in unlabeled DNA by competition in a flash photoreactivation reaction. The assay is used to measure dark repair in Micrococcus luteus in complete medium. After a dose of 100 J/m² the wild type of this organism removes photoreactivable lesions (pyrimidine dimers) from its DNA with a half-time of 7 min at 35°C.