Light filaments in air for ultraviolet and infrared wavelengths

The propagation of femtosecond UV laser pulses in air is numerically shown to form intense light filaments over several tenths of Rayleigh lengths. We compare UV filamentation with IR filamentation and show that the balance of the physical processes supporting the filaments is identical in both cases. For IR and UV wavelengths, it is shown that the intensity in the filament and the density of the electron plasma created by ionization of air molecules reach similar values as high as 10(14) W/cm(2) and 10(17) cm(-3). Spectral data exhibit a large broadening in the IR filament and a limited one for UV, which justifies the white-light generation associated with IR filamentation only.     

Monte Carlo simulations with Symanzik's improved actions in the lattice O(3) non-linear σ-model

The scaling properties of the lattice O(3) non-linear σ-model are studied. The mass-gap, energy momentum dispersion, correlation functions are measured by numerical Monte Carlo methods. Symanzik's tree-level and one loop improved actions are compared to the standard (nearest neighbour) action.     

The boson gas on a Cayley tree

We analyze the free boson gas on a Cayley tree using two alternative methods. The spectrum of the lattice Laplacian on a finite tree is obtained using a direct iterative method for solving the associated characteristic equation and also using a random walk representation for the corresponding fermion lattice gas. The existence of the thermodynamic limit for the pressure of the boson lattice gas is proven and it is shown that the model exhibits boson condensation into the ground state. The random walk representation is also used to derive an expression for the Bethe approximation to the infinite-volume spectrum. This spectrum turns out to be continuous instead of a dense point spectrum, but there is still boson condensation in this approximation.     

A comparative study of the electric giant dipole resonance of 24−26Mg

The electric giant dipole resonance of ^24?26Mg has been explored up to 30 MeV excitation energy with bremsstrahlung. ΔE, E spectra of charged photo-particles and spectra of prompt deexcitation γ-rays from excited residual nuclear states were obtained at various bremsstrahlung endpoint energies. The ²⁵Mg(γ, p₀), (γ, d), ^24,25Mg(γ, α) differential cross sections as well as ^24?26Mg(γ, xγ′) integrated cross sections are presented. The results are discussed in terms of one-particle, one-hole excitations and isospin composition of giant resonance states. A comparison with calculations for ²⁴Mg gives poor agreement. Excitations from deeper shells were found in the giant dipole resonance of ²⁴Mg, but do not seem to be concentrated at higher energies. In ²⁵Mg, only weak excitations of this kind were found, and they are completely absent in ²⁶Mg.     

Hydrodynamic resistance of concentration polarization boundary layers in ultrafiltration

The influence of concentration polarization on the permeate flux in the ultrafiltration of aqueous Dextran T70 solutions can be described by (i) the osmotic pressure model and (ii) the boundary layer resistance model. In the latter model the hydrodynamic resistance of the non-gelled boundary layer is computed using permeability data of the Dextran molecules obtained by sedimentation experiments. It is shown both in theory and experiment that the two models are equivalent.     

Die Aktivierungsfläche bei der Versetzungsbewegung

The activation area for the motion of dislocations is deduced by means of thermodynamic theory of the transition state. Assuming an exponential dependence of the slip velocity as a function of the applied stress and using additional simple statements the activation area is obtained in terms of parameters, which can be determined experimentally. Further on it is shown that one has to distinguish between different definitions of the activation area.     

BIOLOGISCHE WIRKUNGEN PHOTOCHEMISCHER WASSERSTOFFPEROXYDBILDUNG:

Abstract— As previously demonstrated, there is a considerable increase in the photodynamic activity of anthraquinone-sulphonic acid on the addition of ethylene glycol, glycerol and sugars in concentrations of the order of 0.4 M . This system exhibits cytostatic activity. With H₂O₂ at higher concentrations there is also formation of aldehydes in approximately equivalent yields as follows:
R.CH₂OH+Q → QH₂+R.CHO
QH₂+O₂→ Q+H₂O₂
In accordance with the recent results of Warburg this accounts for the fundamental importance of glyceraldehyde in cancer research.
Our results on the irradiation of Proteus vulgaris SG2 in buffered medium with the addition of glycerin to anthraquinone-sulphonic acid show the existence of a similar cytostatic effect. One hour's irradiation with visible light reduces the cell count by about 50 per cent.