Key plasma parameters for resonant backward Raman amplification in plasma

Backward Raman amplification and compression in plasma enables pulse compression to intensities not available using material gratings. In order to achieve the highest intensities and efficiencies in the compression effect, in a manner robust both to noise and other competing plasma effects, both resonance effects and detuning effects are exploited. Here we offer a simplified guide to how some of the key plasma parameters and laser parameters should be picked in order to achieve robust and efficient amplification.     

Quasi-optical theory of coaxial and cylindrical relativistic surface-wave oscillators

In terms of a quasi-optical approach, a nonlinear nonstationary theory of surface-wave oscillators, coaxial and cylindrical multiwave Cherenkov oscillators (MCOs) fed by large-diameter tubular electron beams, is constructed. The small curvature of the waveguide walls allows one to appreciably simplify the MCO dynamics analysis by considering a quasi-plane model. In this model, local surface fields near the corrugated cylindrical wall are close to fields of a plane corrugated with the same depth and period and the cylindrical geometry is taken into account by introducing azimuthal periodicity conditions. The results obtained in terms of the averaged approach are compared with those of direct numerical particle-in-cell (PIC) simulation and experimental data. Remarkably, PIC simulation demonstrates the existence of a single-frequency oscillation regime at long perimeters in which the self-synchronization of different azimuthal modes takes place. As a result, an azimuthally asymmetric stationary field distribution sets in, which can be assigned to dissipative structures well known in the theory of self-sustained oscillation systems.     

High-elasticity of polyisobutylene and polystyrene solutions

Summary A study is made of the high-elastic properties of solutions of polyisobutylene and polystyrene in a range of solvents of different quality with respect to these polymers. Measurements were carried out at room temperature in the concentration range 20–100% for polyisobutylene and 20–67% for polystyrene.It is shown that in contrast to the known effect of the nature of solvent on the viscous properties of polystyrene, the modulus of high elasticity of polystyrene solutions, as well as those of the flexible-chain polymer (polyisobutylene), measured in the linear range of mechanical behaviour of the system, depends only on the content of polymer in the solution and is practically independent of the nature of solvent.In the region of fairly high molecular weights the modulus of high elasticity is independent of the molecular weight of monodisperse polymers, but decreases with broadening MWD. The predominating role is not that of the high-molecular-weight fractions, but of the width of MWD.At high shear rates in the case of solutions of polymers in good solvents the variations of the modulus with shear rate is of an external nature, so that with shear rate is of an external nature, so that with a very high viscosity anomaly the modulus can decrease.

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Zusammenfassung Es werden die hochelastischen Eigenschaften von Polyisobutylen-bzw. Polystyrol-Lösungen untersucht, wobei verschiedene Lösungsmittel eingesetzt werden. Die Messungen wurden bei Raumtemperatur im Konzentrationsbereich von 20–100% bei Polyisobutylen und von 20–67% bei Polystyrol durchgeführt.Es zeigt sich, daß sowohl der Hochelastizitätsmodul von Styrol-Lösungen als auch der Modul von Polyisobutylen im linearen mechanischen Bereich nur vom polymeren Gehalt der Lösung und nicht vom Lösungsmittel abhängt. Dieses Verhalten weicht von den Viskositätseigenschaften ab, die bekanntlich durch das Lösungsmittel mitbestimmt werden.Im Bereich recht hoher Molekulargewichte wird der Modul der Hochelastizität unabhängig vom Molekulargewicht monodisperser Systeme, hingegen sinkt er mit breiter werdender Molekulargewichtsverteilung ab. Die beherrschende Rolle spielt nicht der Antcil des hohen Molekulargewichts, sondern die Molekulargewichtsverteilung.Bei hohen Schergeschwindigkeiten ist in guten Lösungsmitteln die Modulabhängigkeit von dieser Geschwindigkeit durch äußere Umstände bedingt, so daß bei sehr großer Viskositätsanomalie der Modul sinken kann.

     

Non-linearity in rheology —an essay of classification

Different non-linear phenomena (such as non-Newtonian flow, large elastic deformations, instabilities of different types and many others) are the heart of rheology. Therefore many attempts were carried out to find quantitative, or at least qualitative, models of non-linear behavior. The general or perhaps most attractive way of developing rheological constitutive equations consists in the search for the most general method to describe everything in the framework of a single approach. Naturally, this leads to very complicated and ambiguous equations. Meanwhile, it is reasonable to try another way based on separating observed phenomena into different types depending on observed phenomena into different types depending on their physical origin. An attempt to propose such their physical origin. An attempt to propose such classification of nonlinear rheological effects is made.According to the assumed scheme three levels of non-linearity are distinguished. There is a group of phenomena which originate as a consequence of finite elastic deformations. This is weak non-linearity related to equilibrium properties of a matter. The second level can be characterized as strong non-linearity. It is related to reversible structure changes, developing in time and connected with changes in relaxation properties of a matter. This group of effects can be treated as kinetic phenomena. Lastly, the third level of non-linearity is connected with breaking or phase transitions induced by deformations. This leads to the most severe consequences and can be treated as effects of thermodynamic nature. It is shown that some well known rheological effects can be explained if we consider them as a superposition of non-linearity of different types.Presented as keynote lecture at the European Rheology Meeting, September 4–9, 1994, Sevilla, Spain     

Correlation of p16(INK4A) expression and HPV copy number with cellular FTIR spectroscopic signatures of cervical cancer cells

Cervical cancer, a potentially preventable disease, has its main aetiology in infection by high risk human papillomavirus (HR-HPV). Approaches to improving cervical cancer screening and diagnostic methodologies include molecular biological analysis, targeting of biomarker proteins, but also exploration and implementation of new techniques such as vibrational spectroscopy. This study correlates the biomarker protein p16(INK4A) expression levels dependent on HPV copy number with the infrared absorption spectral signatures of the cervical cancer cell lines, HPV negative C33A, HPV-16 positive SiHa and CaSki and HPV-18 positive HeLa. Confocal fluorescence microscopy demonstrated that p16(INK4A) is expressed in all investigated cell lines in both nuclear and cytoplasmic regions, although predominantly in the cytoplasm. Flow cytometry was used to quantify the p16(INK4A) expression levels and demonstrated a correlation, albeit nonlinear, between the reported number of integrated HPV copies and p16(INK4A) expression levels. CaSki cells were found to have the highest level of expression, HeLa intermediate levels, and SiHa and C33A the lowest levels. FTIR spectra revealed differences in nucleic acid, lipid and protein signatures between the cell lines with varying HPV copy number. Peak intensities exhibited increasing tendency in nucleic acid levels and decreasing tendency in lipid levels with increasing HPV copy number, and although they were found to be nonlinearly correlated with the HPV copy number, their dependence on p16(INK4A) levels was found to be close to linear. Principal Component Analysis (PCA) of the infrared absorption spectra revealed differences between nuclear and cytoplasmic spectroscopic signatures for all cell lines, and furthermore clearly differentiated the groups of spectra representing each cell line. Finally, Partial Least Squares (PLS) analysis was employed to construct a model which can predict the p16(INK4A) expression level based on a spectral fingerprint of a cell line, demonstrating the diagnostic potential of spectroscopic techniques.     

The dual photochemical reactivity of 1,2-dihydroquinolines

Conclusions The lack of electrocyclic ring opening in 1,2-dihydroquinolines not containing a substituent at the nitrogen atom is related to the possibility of efficient homolytic dissociation in the excited state.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 768–772, April, 1985.     

Multifrequency EPR spectroscopy of Ho3+ ions in synthetic forsterite

Electron paramagnetic resonance (EPR) of Ho³⁺ single ions and Ho³⁺?Mg²⁺-vacancy-Ho³⁺ associates in holmium-doped forsterite single crystals are studied at 9.4, 37.3 and 65–250 GHz. Crystals were grown from melt by the Czochralski technique in slightly oxidizing atmosphere. For both centers, directions of the principal magnetic axes and parameters of the effective spin Hamiltonians describing dependences of electron-nuclear levels on applied magnetic field are obtained. For Ho³⁺ substituting Mg²⁺ in the M2 site as the single ion and for Ho³⁺ ions in dimer centers, values of crystal field parameters related to a real crystal lattice structure are estimated in the framework of the exchange charge model. The calculated crystal field energies, values of theg-factors of the ground Ho³⁺ quasi-doublet and the directions of the corresponding magnetic moments agree satisfactorily with the data obtained from measurements of EPR and optical absorption and site-selective luminescence spectra.     

Symplectic structures associated to Lie-Poisson groups

The Lie-Poisson analogues of the cotangent bundle and coadjoint orbits of a Lie group are considered. For the natural Poisson brackets the symplectic leaves in these manifolds are classified, and the corresponding symplectic forms are described. Thus the construction of the Kirillov symplectic form is generalized for Lie-Poisson groups.Supported in part by a Soros Foundation Grant awarded by the American Physical SocietyUnité Associée au C.N.R.S., URA 280     

Photodissociation of aromatic thiols and disulfides

For the first time, the quantum yields of cleavage of SS and SH bonds in a disulfide and a thiol and also the extinction coefficient of the photoinduced aminophenylthiyl radical were determined, on the basis of which the relation of the photodissociation quantum yield to the energy of an absorbed quantum was observed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 540–543, March, 1990.