Site-directed cross-linking of mRNA analogues to 16S ribosomal RNA; a complete scan of cross-links from all positions between '+1' and '+16' on the mRNA, downstream from the decoding site

mRNA analogues containing 4-thiouridine residues at selected sites were used to extend our analysis of photo-induced cross-links between mRNA and 16S RNA to cover the entire downstream range between positions +1 and +16 on the mRNA (position +1 is the 5'-base of the P-site codon). No tRNA-dependent cross-links were observed from positions +1, +2, +3 or +5. Position +4 on the mRNA was cross-linked in a tRNA-dependent manner to 16S RNA at a site between nucleotides ca 1402-1415 (most probably to the modified residue 1402), and this was absolutely specific for the +4 position. Similarly, the previously observed cross-link to nucleotide 1052 was absolutely specific for the +6 position. The previously observed cross-links from +7 to nucleotide 1395 and from +11 to 532 were however seen to a lesser extent with certain types of mRNA sequence from neighbouring positions (+6 to +10, and +10 to +13, respectively); no tRNA-dependent cross-links to other sites on 16S RNA were found from these positions, and no cross-linking was seen from positions +14 to +16. In each case the effect of a second cognate tRNA (at the ribosomal A-site) on the level of cross-linking was studied, and the specificity of each cross-link was confirmed by translocation experiments with elongation factor G, using appropriate mRNA analogues.     

The Periventricular Nucleus as a Brain Center Containing Dopaminergic Neurons and Neurons Expressing Individual Enzymes of Dopamine Synthesis

Since the 1980s, the concept of dopamine-rich brain centers as clusters of only dopaminergic neurons has been fundamentally revised. It has been shown that, in addition to dopaminergic neurons, most of these centers contain neurons expressing one of the enzymes of dopamine synthesis: tyrosine hydroxylase (TH) or aromatic L-amino acid decarboxylase (AADC). We have obtained convincing evidence that in rats, the hypothalamic periventricular nucleus (PeVN) is one of the largest dopamine-rich centers, containing dopaminergic and monoenzymatic neurons. Indeed, using double immunostaining for TH and AADC, the PeVN was shown to contain almost three thousand dopaminergic and monoenzymatic neurons. According to high-performance liquid chromatography, PeVN contains L-DOPA and dopamine, which, apparently, are synthesized in monoenzymatic TH neurons and bienzymatic neurons, respectively. According to confocal microscopy, neurons (cell bodies, fibers), which were immunopositive only to TH, only to AADC, or both, are in close topographic relationships with each other and with the 3rd ventricle. These data suggest the mutual regulation of the neurons, as well as the delivery of dopamine and L-DOPA to the third ventricle, which is confirmed by their detection in the cerebrospinal fluid. Thus, evidence has been obtained that PeVN is one of the largest dopamine-rich centers of the brain, containing dopaminergic and monoenzymatic neurons.     

Room-Temperature Exceptional-Point-Driven Polariton Lasing from Perovskite Metasurface

Excitons in lead bromide perovskites exhibit high binding energy and high oscillator strength, allowing for a strong light-matter coupling regime in the perovskite-based cavities localizing photons at the nanoscale. This opens up the way for the realization of exciton-polariton Bose–Einstein condensation and polariton lasing at room temperature – the inversion-free low-threshold stimulated emission. However, polariton lasing in perovskite planar photon cavities without Bragg mirrors has not yet been observed and proved experimentally. In this study, perovskite metasurface is employed, fabricated with nanoimprint lithography, supporting so-called exceptional points to demonstrate the room-temperature polariton lasing. The exceptional points in exciton-polariton dispersion of the metasurface appear upon optically pumping in the nonlinear regime in the spectral vicinity of a symmetry-protected bound state in the continuum providing high mode confinement with the enhanced local density of states beneficial for polariton condensation. The observed lasing emission possesses high directivity with a divergence angle of 1° over one axis. The employed nanoimprinting approach for solution-processable large-scale polariton lasers is compatible with various planar photonic platforms suitable for on-chip integration.     

Statechart testing method for aircraft control systems

A number of current control systems for aircraft have been specified with statecharts. The risk of failures requires the use of a formal testing approach to ensure that all possible faults are considered. However, testing the compliance of an implementation of a system to its specification is dependent on the specification method and little work has been reported relating to the use of statechart-specific methods. This paper describes a modification of a formal testing method for extended finite-state machines to handle the above problem. The method allows one to demonstrate correct behaviour of an implementation of some system, with respect to its specification, provided certain specific requirements for both of them are satisfied. The case study illustrates these and shows the applicability of the method. By considering the process used to develop the system it is possible to reduce the size of the test set dramatically; the method to be described is easy to automate. Copyright © 2001 John Wiley & Sons, Ltd.