A study of some deactivation methods for fused silica capillary columns by CP-MAS NMR and capillary gas chromatography

The effect of deactivating a fused silica surface by silylation with 1,1,3,3-tetraphenyl-1,3-dimethylilazane (TPDMDS), triphenylsilylamine (TPSA), and octamethylcyclotetrasiloxane (D4) and by polydimethylsiloxane degradation (PSD) is studied. Rehydrated, dried, and deactivated Cab-O-Sil M5 samples are used as model materials for ²⁹Si CP-MAS NMR analysis. At about 350 °C, TPDMDS yelds mainly diphenylmethylsiloxysilane, dimethyldisiloxysilane, and triphenylsiloxysilane groups. TPSA yields phenyltrisiloxysilane, diphenyldisiloxysilane, and triphenylsiloxysilane groups. At 400°C, the products formed initially are eventually replaced by methyltrisiloxysilane or phenyltrisiloxysilane groups, while a substantial number of silanol groups still remains. The possible consequences for wettability are discussed. D4 reacts with Cab-O-Sil even at 200°C, but a large number of silanol groups remains. This number decreases gradually at higher temperatures and becomes negligible above 400°C. The formation of methyltrisiloxysilane groups, which starts at 425°C, is predominant at 490°C.     

Integrals and derivatives of regularly varying functions in Rd and domains of attraction of stable distributions II.

A theorem on regularly varying functions in $\text{R}$² is proved and applied to domains of attraction of stable laws with index 1 ? α ? 2. We also present a theory of Π-variation in $\text{R}$². Unlike the situation in $\text{R}$¹ the latter is not connected with domain of attraction theory. The situation in $\text{R}$^d (d > 1) is more complicated but not essentially different; for simplicity we limit ourselves to $\text{R}$². This article complements de Haan and Resnick (1979) where the situation for 0 < α < 1 was considered.     

The large-N deconfinement phase transition in a partially reduced Eguchi-Kawal model

We construct generalized twisted Eguchi-Kawai models which for large-N reduce space-time to a lattice of arbitrary size. Large-N lattice gauge theory at finite temperature is investigated in a model on a lattice with L₀ time slices and two lattice points in very time slice. We observe the large-N deconfinement phase transition in the weak coupling region. Assuming asymptotic scaling we find a transition temperature T_c = (101±4)Λ_L.     

Numerical analysis of the twisted Eguchi-Kawai model in four dimensions

We perform a high statistics Monte Carlo calculation of the string tension in the twisted SU(N) Eguchi-Kawai model for N=36 and N=64. The string tension, calculated from Wilson loops not larger than 3 × 3, clearly shows the renormalization group scaling behaviour.     

Eine Methode zur ldentifizierung von Gitter-Leerstellen in Zeolithen

A Method for the Identification of T-Atom Vacancies in the Lattices of Zeolites Silanol groups in the lattices of zeolites can be silylated with trimethylchlorosilane and the products can be characterized by means of ²⁹Si (CP) MAS NMR. T-atom vacancies are indicated by the formation of silylation products with three or four siloxy-linkages under mild reaction conditions as this requires the presence of three or silanol groups in favourable geometrical arrangements.     

Linear Korrelation der 13C-Kernresonanzfrequenzen mit den LCAO-MO-π-Elektronendichten in substituierten Benzonitrilen

The ¹³C NMR. spectra of seventeen m- and p- subsituted benzonitriles were examined and partially anlayzed. The C-1 carbon shieldings can be expressed in terms of a linear correlation with the LCAO-MO-π-electron density at C-1. No such correlation was found for the cyanocarbon, whose electron density shows only slight varriations for the different substitutents. This fact is consistent with the relatively small range of the chemical shifts at this center.     

Update on design simulations for NIF ignition targets, and the rollup of all specifications into an error budget

Targets intended to produce ignition on NIF are being simulated and the simulations are used to set specifications for target fabrication and other program elements. Recent design work has focused on designs that assume only 1.0 MJ of laser energy instead of the previous 1.6 MJ. To perform with less laser energy, the hohlraum has been redesigned to be more efficient than previously, and the capsules are slightly smaller. Three hohlraum designs are being examined: gas fill, SiO₂ foam fill, and SiO₂ lined. All have a cocktail wall, and shields mounted between the capsule and the laser entrance holes. Two capsule designs are being considered. One has a graded doped Be(Cu) ablator, and the other graded doped CH(Ge). Both can perform acceptably with recently demonstrated ice layer quality, and with recently demonstrated outer surface roughness. Complete tables of specifications are being prepared for both targets, to be completed this fiscal year. All the specifications are being rolled together into an error budget indicating adequate margin for ignition with the new designs. The dominant source of error is hohlraum asymmetry at intermediate modes 4–8, indicating the importance of experimental techniques to measure and control this asymmetry.     

Ageing processes of alkyl bonded phases in HPLC; a chromatographic and spectroscopic approach

Summary Laboratory use of HPLC columns packed with C₈ and C₁₈ bonded phases leads to changes in selectivities and retention volumes. FTIR,¹H NMR of hydrolysed bonded phases and solid state¹³C- and²⁹Si NMR were applied to characterize the materials. The results of the various techniques are in fair agreement except solid state NMR. Loss of silane and hydrolysis of surface siloxane groups have been observed for the C₈ bondes phase, while for the C₁₈ material the latter process seems to dominate. The solid state NMR results have been tentatively explained in terms of changing chain arrangements and mobilities.Dedicated to Professor J. F. K. Huber on the occasion of his 60th birthday.