Reactions of pyrimidinophanes and their acyclic analogs with electron-deficient substrates

Acyclic and macrocyclic compounds having different numbers of pyrimidine fragments and nitrogen atoms in the polymethylene bridges or in substituents at the pyrimidine rings reacted with 2,3,5,6-tetrachloro-1,4-benzoquinone and 1,4-benzoquinone according to the charge transfer scheme to give products with an ionic structure. The reaction was accompanied by protonation of nitrogen atoms in the polymethylene bridges or in substiuents at the pyrimidine rings and reduction of 2,3,5,6-tetrachloro-1,4-benzoquinone or 1,4-benzoquinone to 2,3,5,6-tetrachlorobenzene-1,4-diol or benzene-1,4-diol, respectively. The isolated products are dielectrics.     

Oscillation modes,transient chaos and its control in a modulation-doped semiconductor double-heterostructure

The nonlinear dynamics of real space transfer for a 2D electron gas in a system of two adjacent Al _x Ga_1–x As/GaAs-heterolayers under parallel current conduction has been investigated numerically. The mechanisms which have been taken into account are transfer of electrons by thermionic emission and nonresonant tunneling and the delayed dielectric relaxation of the interface potential barrier. We predict bistability of an asymmetric and a symmetric self-generated oscillation mode, a quasiperiodic route to chaos and transient chaos with mean transient times obeying a universal critical scaling law. Unstable periodic orbits of the chaotic repeller can be stabilized by a simple delayed feedback control, thus providing a widely tunable semiconductor oscillator.     

Entanglement from the Vacuum

We explore the entanglement of the vacuum of a relativistic field by letting a pair of causally disconnected probes interact with the field. We find that, even when the probes are initially non-entangled, they can wind up to a final entangled state. This shows that entanglement persists between disconnected regions in the vacuum. However the probe entanglement, unlike correlations, vanishes once the regions become sufficiently separated. The relation between entropy, correlations and entanglement is discussed.     

Near-field microwave tomography of biological objects

A method of finding the subsurface temperature distribution in biological media from near-field microwave probing data is suggested. The electrodynamic problem of probe response to a temperature profile disturbance ΔT(z) in a medium is solved. An integral equation that relates the shift of the resonant frequency of the probe to the function ΔT(z) is derived. The effective near-field probing depth is shown to depend on the probe aperture, its elevation above the surface, and the wavelength. In this method, several probes operate simultaneously, receiving signals from different depths, and the temperature profile is reconstructed by inverting the related integral equation. The components and parameters of a measuring facility that provides the temperature profi le reconstruction accurate to 0.5°C to a depth of up to 5 cm are established. The procedure of near-field diagnostics is simulated in a computer experiment to check the accuracy predicted. Calculation is performed based on a model of permittivity of biological media.     

WHEN DOES A MEASUREMENT OR EVENT OCCUR?

Within quantum mechanics, a complete set of commutting observables can be found which describe the attributes of a system at a given time. However, the correct way to describe attributes of a system in time is still an open question. We discuss the difficulties in extending the standard approach of quantum mechanics to describe attributes of a system in time. We find that measuring when an event occurred and measuring that it occurred, are complimentary in Bohr's sense. To exemplify the differences between measurements at a given time and in time, we will compare Rovelli's recent proposal (quant-ph/9802020), to determine “at what time does a measurement occurred” with another model of a continuous measurement in time. Rovelli's scheme answers the question “has the measurement already occurred at a certain time?”, but does not answer to the more difficult question: “when did the measurement occur?” We also discuss the use of the probability current to measure the time at which a particle arrives to a certain location.     

Intramolecular interactions in acyclic and macrocyclic compounds containing nucleotide bases

Acyclic and cyclic counterparts containing thymine and two 3,6-dimethyluracil fragments bridged by methylene chains have been prepared and studied by UV and NMR spectroscopy; in water the uracil units of the acyclic counterpart form an intramolecular stack but arrange in a linear array in chloroform while the fragments of the uracilophane form an intramolecular stack both in chloroform and water; uracil units of bis(3,6-dimethyluracil-1-yl)butane and the macrocyclic counterpart form a stack in chloroform.     

Reactions of 2-mercaptopyrimidines with α, ω-bromochloro- and α, ω-bromofluoroalkanes

The reactions of 2-mercaptopyridines with , -bromohaloalkanes have given the corresponding haloalkylthiopyrimidines and , -bis(2-pyrimidylthio)alkanes. The IR spectra of the compounds obtained have been recorded and some of their constants have been determined.     

Synthesis and some properties of pyrimidinylalkylphosphonic acids

Conclusions A study was made of the reaction of 6-methyluracil, uracil, and 2-amino-4-hydroxy-6-methylpyrimidine with chloromethylphosphonic acid. The structures of some of the products that were formed here were established.Translated from Izvestiya Akademii NaukSSSR, Seriya Khimicheskaya, No. 10, pp. 2254–2263, October, 1970.