Difluoroalkylamines from high temperature vapor phase reactions of nitrogen trifluoride with alkanes, ethers and benzene

At temperatures around 400 °C, nitrogen trifluoride (NF₃) readily reacts with alkanes and benzene as well as ethers. In all cases, products were N,N-difluoroamines. This is in contrast to difluoroamination of benzylic substrates where the initial N,N-difluoroamines underwent eliminations or rearrangements and were not isolated. Cyclic and acyclic alkanes generated N,N-difluoroaminoalkanes. Benzene substituted on the ring to form N,N-difluoroaniline. Ethers reacted to generate α-N,N-difluoroamino ethers. Little direct fluorination was observed.     

Metric Theorems for Distribution Measures of Pseudorandom Sequences

 We improve a recent result of Mauduit and Sárk?zy (2000) on the well-distribution measure of pseudorandom sequences and complement another of their results on the correlation measure.     

Data quality assurance for thermophysical property databases--applications to the TRC SOURCE data system

To a significant degree processes of database development are based upon human activities, which are susceptible to various errors. Propagation of errors in the processing leads to a decrease in the value of original data as well as that of any database products. Data quality is a critical issue that every database producer must handle as an inseparable part of the database management. Within the Thermodynamics Research Center (TRC), a systematic approach to implement database integrity rules was established through the use of modern database technology, statistical methods, and thermodynamic principles. The four major functions of the system--error prevention, database integrity enforcement, scientific data integrity protection, and database traceability--are detailed in this paper.     

The hierarchical basis multigrid method

Summary We derive and analyze the hierarchical basis-multigrid method for solving discretizations of self-adjoint, elliptic boundary value problems using piecewise linear triangular finite elements. The method is analyzed as a block symmetric Gauß-Seidel iteration with inner iterations, but it is strongly related to 2-level methods, to the standard multigridV-cycle, and to earlier Jacobi-like hierarchical basis methods. The method is very robust, and has a nearly optimal convergence rate and work estimate. It is especially well suited to difficult problems with rough solutions, discretized using highly nonuniform, adaptively refined meshes.     

Non-ohmic behaviour of iodine-doped polyacetylene

We report on the temperature and electric field strength dependence of the conductivity of iodine-doped polyacetylene in the metallic regime. The experimental results are discussed in terms of Sheng model of fluctuation induced tunneling and characteristic dimensions of the tunneling zones between fibres are deduced from a fit between this theory and our experiments.     

An automatic scaling procedure for a D'Yakanov-Gunn iteration scheme

An automatic computational procedure for scaling a D'Yakanov-Gunn iteration for nonseparable elliptic equations is described. This method is used in conjunction with a preconditioned conjugate gradient iteration employing a nearby separable approximation of the scaled nonseparable matrix. This results in an operation count of $\text{O(n}{}^2\text{log}\text{(}\text{n}\text{k}\text{)}\text{log}\text{(}\text{1}\text{ε}\text{))}$ to reduce the initial error by a factor of ε.     

O,N,N'-trialkylisoureas as mild activating reagents for N-acylsulfonamide anchors

[chemical reaction: see text]. Prior to detachment of compounds synthesized on sulfonamide based safety-catch linkers, the molecular anchor has to be activated. This is achieved by alkylation of the nitrogen atom of the N-acylsulfonamide using different established protocols. As an addition to the existing repertoire of activating reagents, we suggest the use of O,N,N'-trialkylisoureas. Besides the demonstration of the feasibility of these mild alkylating agents for this purpose, custom-tailored novel O,N,N'-trialkylisoureas prepared from electron-deficient alcohols are reported.     

Hydrogen control of ferromagnetism in a dilute magnetic semiconductor

We show that upon exposure to a remote dc hydrogen plasma, the magnetic and electronic properties of the dilute magnetic semiconductor Ga1-xMnxAs change qualitatively. While the as-grown Ga1-xMnxAs thin films are ferromagnetic at temperatures T less, similar 70 K, the samples are found to be paramagnetic after the hydrogenation, with a Brillouin-type magnetization curve even at T=2 K. Comparing magnetization and electronic transport measurements, we conclude that the density of free holes p is significantly reduced by the plasma process, while the density of Mn magnetic moments does not change.