Null vectors of the WBC2WBC_2 algebra

Using the fusion principle of Bauer et al. we give explicit expressions for some null vectors in the highest weight representations of the \bc algebra in two different forms. These null vectors are the generalization of the Virasoro ones described by Benoit and Saint-Aubin and analogues of the $W_3$ ones constructed by Bowcock and Watts. We find connection between quantum Toda models and the fusion method.Comment: 8 pages, LaTeX, ITP Budapest 50

Quantum corrections of Abelian Duality Transformations

A modification of the Abelian Duality transformations is proposed guaranteeing that a (not necessarily conformally invariant) $\sigma$-model be quantum equivalent (at least up to two loops in perturbation theory) to its dual. This requires a somewhat non standard perturbative treatment of the {\sl dual} $\sigma$-model. Explicit formulae of the modified duality transformation are presented for a special class of block diagonal purely metric $\sigma$-models.Comment: Latex 11 pages; remarks on a free model and references adde

The Nappi-Witten string in the light-cone gauge

Some of the motivations for as well as the main points of the quantization of the Nappi Witten string in the light cone gauge are reviewed.Comment: 21 pages, Plain Tex, to appear in the E.P. Wigner memorial volume of Acta Physica Hungaric

A fast method to identify mean motion resonances

The identification of mean motion resonances in exoplanetary systems or in the Solar System might be cumbersome when several planets and large number of smaller bodies are to be considered. Based on the geometrical meaning of the resonance variable, an efficient method is introduced and described here, by which mean motion resonances can be easily find without any a priori knowledge on them. The efficiency of this method is clearly demonstrated by using known exoplanets engaged in mean motion resonances, and also some members of different families of asteroids and Kuiper-belt objects being in mean motion resonances with Jupiter and Neptune respectively.Comment: 7 pages, 13 figures, accepted by Monthly Notices of the Royal Astronomical Societ

Lattice Classification of 8-Dimensional Chiral Heterotic Strings

The eight-dimensional chiral rank 18 heterotic strings are classified using the covariant lattice approach

Multiple and changing cycles of active stars I. Methods of analysis and application to the solar cycles

Long-term observational data have information on the magnetic cycles of active stars and that of the Sun. The changes in the activity of our central star have basic effects on Earth, like variations in the global climate. Therefore understanding the nature of these variations is extremely important. The observed variations related to magnetic activity cannot be treated as stationary periodic variations, therefore methods like Fourier transform or different versions of periodogramms give only partial information on the nature of the light variability. We demonstrate that time-frequency distributions provide useful tools for analyzing the observations of active stars. With test data we demonstrate that the observational noise has practically no effect on the determination in the the long-term changes of time-series observations of active stars. The rotational signal may modify the determined cycles, therefore it is advisable to remove it from the data. Wavelets are less powerful in recovering complex long-term changes than other distributions which are discussed. Applying our technique to the sunspot data we find a complicated, multi-scale evolution in the solar activity.Comment: Accepted to Astronomy and Astrophysic

A new family of SU(2)SU(2) symmetric integrable sigma models

(Minor corrections and reference added)Comment: (ITP Budapest Report No. 502) (11 page

Perturbative Quantum (In)equivalence of Dual σ\sigma Models in 22 dimensions

Various examples of target space duality transformations are investigated up to two loop order in perturbation theory. Our results show that when using the tree level (`naive') transformation rules the dual theories are in general {\it inequivalent} at two loops to the original ones, (both for the Abelian and the non Abelian duality).Comment: 11 pages, Latex, uses espcrc2.st

Effect of Nickel Administration in vivo on the Testicular Structure in Male Mice

The aim of this study was to describe the effects of nickel (NiCl2) on murine testicular structure. Experimental animals were injected intraperitoneally with a single dose of 20 mg NiCl2 per kg of body mass (group A, n = 5) and 40 mg NiCl2 per kg b. m. (group B, n = 5). The group without injection (n = 5) was the control (C). Animals were killed 48 hours after administration of nickel. The body mass of animals, the mass of testes and the testes : body mass ratio were not significantly affected. In both experimental groups a significant (p p p < 0.05 - 0.001) after nickel administration. Evaluation of the lumen diameter in the seminiferous tubule showed a significant increase in both experimental groups. The data of the perimeter of seminiferous tubules corresponded with those of the seminiferous tubule diameter. TUNEL assay detected a higher frequency of localized apoptosis in the interstitium of nickel-administered animals compared to control group. Our findings clearly suggest a negative effect of nickel on the structure as well as on the function of the seminferous epithelium at the site of spermatozoa production