Artificial ionospheric layers driven by high-frequency radiowaves : an assessment

High-power ordinary mode radio waves produce artificial ionization in the F-region ionosphere at the European Incoherent Scatter (EISCAT at Tromsø, Norway) and High-frequency Active Auroral Research Program (HAARP at Gakona, Alaska, USA) facilities. We have summarized the features of the excited plasma turbulence and descending layers of freshly-ionized (“artificial”) plasma. The concept of an ionizing wavefront created by accelerated suprathermal electrons appears to be in accordance with the data. The strong Langmuir turbulence (SLT) regime is revealed by the specific spectral features of incoherent radar backscatter and stimulated electromagnetic emissions. Theory predicts that the SLT acceleration is facilitated in the presence of photoelectrons. This agrees with the intensified artificial plasma production and the greater speeds of descent but weaker incoherent radar backscatter in the sunlit ionosphere. Numerical investigation of propagation of O-mode waves and the development of SLT and descending layers have been performed. The greater extent of the SLT region at the magnetic zenith than at vertical appears to make magnetic zenith injections more efficient for electron acceleration and descending layers. At high powers, anomalous absorption is suppressed, leading to the Langmuir and upper hybrid processes during the whole heater-on period. The data suggest that parametric UH interactions mitigate anomalous absorption at heating frequencies far from electron gyroharmonics and also generate SLT in the upper hybrid layer. The persistence of artificial plasma at the terminal altitude depends on how close the heating frequency is to the local gyroharmonic

Comparative Analysis of the Dynamical Spectra of a Polarization of an Active Medium and an Electromagnetic Field in the Superradiant Heterolasers

The complicated pulsed generation regimes of a CW-pumped superradiant semiconductor laser are analyzed via the dynamical spectra of the dipole optical oscillations of active centers. This novel approach appears to be more informative than the standard analysis of the dynamical spectra of laser emission if a dipole relaxation rate is less than a cavity relaxation rate. The advantages of the method are demonstrated for a number of superradiant lasing regimes on the basis of the numerical solution to 1D Maxwell–Bloch equations for a two-level active medium in a low-Q cavity within one-dimensional approximation

A clinical case of restoration of the destroyed crown part of the tooth complicated by changes in the bifurcation area

The destruction of the tooth crown should be regarded as the cause leading over time to the disruption of the morphofunctional unity of the dentition and pathological condition of the entire dentoalveolar system. Untimely treatment of defects of hard tooth tissues leads to functional disorganization of the dentoalveolar system. The most eliminated defects are those of crowns of teeth determining the quality of aesthetics, phonetics, functions of biting and chewing. The destruction of the tooth crowns, which do not cause significant disruption of the above functions, are painless and almost asymptomatic. In such cases, deformation of the dentition and occlusion, dysfunction of masticatory muscles and temporomandibular joints as well as the development of pathological changes in periodontium occur slowly. Of great importance are the early diagnosis of pathological reconstruction of dentoalveolar system and the knowledge of pathogenesis of possible complications after the extraction of the teeth that determine the indications for prophylactic orthopedic dental treatment. The article presents a clinical case of restoration of destructed tooth crown 3.6 complicated by changes in bifurcation area. The patient underwent coronary-radicular separation with the use of cast metal cores, which allowed restoration of the sufficient size of the stump, function and anatomical shape of the tooth and hence the unity of dental arch

New Insights Into the Neuraminidase-Mediated Hemagglutination Activity of Influenza A(H3N2) Viruses

Influenza virus neuraminidase (NA) can act as a receptor-binding protein, a role commonly attributed to hemagglutinin (HA). In influenza A(H3N2) viruses, three NA amino acid residues have previously been associated with NA-mediated hemagglutination: T148, D151, and more recently, H150. These residues are part of the 150-loop of the NA monomer. Substitutions at 148 and 151 arise from virus propagation in laboratory cell cultures, whereas changes at 150 occurred during virus evolution in the human host. In this study, we examined the effect of natural amino acid polymorphism at position 150 on NA-mediated hemagglutination. Using the A/Puerto Rico/8/34 backbone, we generated a comprehensive panel of recombinant A(H3N2) viruses that have different NAs but shared an HA that displays poor binding to red blood cells (RBCs). None of the tested substitutions at 150 (C, H, L, R, and S) promoted NA-binding. However, we identified two new determinants of NA-binding, Q136K and T439R, that emerged during virus culturing. Similar to T148I, both Q136K and T439R reduced NA enzyme activity by 48-86% and inhibition (14- to 173-fold) by the NA inhibitor zanamivir. NA-binding was observed when a virus preparation contained approximately 10% of NA variants with either T148I or T439R, highlighting the benefit of using deep sequencing in virus characterization. Taken together, our findings provide new insights into the molecular mechanisms underlying the ability of NA to function as a binding protein. Information gained may aid in the design of new and improved NA-targeting antivirals

Fingering Instability of Dislocations and Related Defects

We identify a fundamental morphological instability of mobile dislocations in crystals and related line defects. A positive gradient in the local driving force along the direction of defect motion destabilizes long-wavelength vibrational modes, producing a ``fingering'' pattern. The minimum unstable wavelength scales as the inverse square root of the force gradient. We demonstrate the instability's onset in simulations of a screw dislocation in Al (via molecular dynamics) and of a vortex in a 3-d XY ``rotator'' model.Comment: 4 pages, 3 figure