Ueber die Formung von Gelatine durch Salzniederschläge und Kristalle

Ohne Zusammenfassung     

The analysis of cylindrical shell roofs with post tensioned edge beams

A new characteristic equation for cylindrical shell roofs is developed, together with a method for obtaining the solution and its derivatives. Post tension is introduced into the edge beam by shearing forces varying linearly from a maximum at the transverse to zero at the quarter points. The Fourier series for this converges rapidly. An end correction is then made to restore the post tension to the end of the edge beam and obtain compatibility of strain with the shell edge. The method is compared with experimental results on a model shell and with the results of a finite element program.     

Wachsende Kieselsäuregele

Ohne Zusammenfassung(Neurologisches Institut, Frankfurt am Main, Dir. L. Edinger.)     

Free-surface flow of concentrated suspensions

Free-surface flows of concentrated suspensions exhibit many interesting phenomena such as particle segregation and surface corrugation. In this work the flow structures associated with free-surface has been studied experimentally. The free-surface velocity for neutrally buoyant suspension of uniform spheres in a gravity driven inclined channel flow was determined by particle imaging velocimetry (PIV) technique. Experiments were carried out for concentrated suspensions with particle fractions ? ranging from 0.40 to 0.50. The measured velocities show blunted profile in the channel. The blunting of the velocity profile increases with the particle concentration. The rms velocity fluctuations measured at the free-surface progressively increase with particle fraction ? and are linear in shear rate γ. The surface roughness were characterized by analyzing the power spectral density of the refracted light from the free-surface. The characteristics observed are in support of earlier findings.     

Uniform diagonalisation of matrices over regular rings

The fundamental Separativity Problem for von Neumann regular rings is shown to be equivalent to a linear algebra problem: for a field F, is there a ``uniform formula' for diagonalising a matrix A over , independently of n? Here P and Q are required to be invertible matrices whose entries are fixed regular algebra expressions in the entries of A. Received July 10, 2000; accepted in final form September 26, 2000.     

Stable,Reactive, and Orthogonal Tetrazines: Dispersion Forces Promote the Cycloaddition with Isonitriles

The isocyano group is a structurally compact bioorthogonal functional group that reacts with tetrazines under physiological conditions. Now it is shown that bulky tetrazine substituents accelerate this cycloaddition. Computational studies suggest that dispersion forces between the isocyano group and the tetrazine substituents in the transition state contribute to the atypical structure–activity relationship. Stable asymmetric tetrazines that react with isonitriles at rate constants as high as 57 L mol^?1 s^?1 were accessible by combining bulky and electron‐withdrawing substituents. Sterically encumbered tetrazines react selectively with isonitriles in the presence of strained alkenes/alkynes, which allows for the orthogonal labeling of three proteins. The established principles will open new opportunities for developing tetrazine reactants with improved characteristics for diverse labeling and release applications with isonitriles.     

Catalyst‐Free Reductive Coupling of Aromatic and Aliphatic Nitro Compounds with Organohalides

A rare reductive coupling of nitro compounds with organohalides has been realized. The reaction is initiated by a partial reduction of the nitro group to a nitrenoid intermediate. Therefore, not only aromatic but also aliphatic nitro compounds are efficiently transformed into monoalkylated amines, with organohalides as the alkylating agent. Given the innate reactivity of the nitrenoid, a catalyst is not required, resulting in a high tolerance for aryl halide substituents in both starting materials.