Free field representation of Toda field theories

We study the following problem: can a classical $sl_n$ Toda field theory be represented by means of free bosonic oscillators through a Drinfeld--Sokolov construction? We answer affirmatively in the case of a cylindrical space--time and for real hyperbolic solutions of the Toda field equations. We establish in fact a one--to--one correspondence between such solutions and the space of free left and right bosonic oscillators with coincident zero modes. We discuss the same problem for real singular solutions with non hyperbolic monodromy.Comment: 29 pages, Latex, SISSA-ISAS 210/92/E

Dressing Transformations and the Algebraic--Geometrical Solutions in the Conformal Affine sl(2)sl(2) Toda Model

It is shown that the algebraic--geometrical (or quasiperiodic) solutions of the Conformal Affine $sl(2)$ Toda model are generated from the vacuum via dressing transformations. This result generalizes the result of Babelon and Bernard which states that the $N$--soliton solutions are generated from the vacuum by dressing transformations.Comment: 12 pages, latex, no figure

Vertex Operator Representation of the Soliton Tau Functions in the An(1)A_n^{(1)} Toda Models by Dressing Transformations

We study the relation between the group-algebraic approach and the dressing symmetry one to the soliton solutions of the $A_n^{(1)}$ Toda field theory in 1+1 dimensions. Originally solitons in the affine Toda models has been found by Olive, Turok and Underwood. Single solitons are created by exponentials of elements which ad-diagonalize the principal Heisenberg subalgebra. Alternatively Babelon and Bernard exploited the dressing symmetry to reproduce the known expressions for the fundamental tau functions in the sine-Gordon model. In this paper we show the equivalence between these two methods to construct solitons in the $A_n^{(n)}$ Toda models.Comment: 35 pages, LaTe

An ultra melt-resistant hydrogel from food grade carbohydrates

© 2017 The Royal Society of Chemistry. We report a binary hydrogel system made from two food grade biopolymers, agar and methylcellulose (agar-MC), which does not require addition of salt for gelation to occur and has very unusual rheological and thermal properties. It is found that the storage modulus of the agar-MC hydrogel far exceeds those of hydrogels from the individual components. In addition, the agar-MC hydrogel has enhanced mechanical properties over the temperature range 25-85 °C and a maximum storage modulus at 55 °C when the concentration of methylcellulose was 0.75% w/v or higher. This is explained by a sol-gel phase transition of the methylcellulose upon heating as supported by differential scanning calorimetry (DSC) measurements. Above the melting point of agar, the storage modulus of agar-MC hydrogel decreases but is still an elastic hydrogel with mechanical properties dominated by the MC gelation. By varying the mixing ratio of the two polymers, agar and MC, it was possible to engineer a food grade hydrogel of controlled mechanical properties and thermal response. SEM imaging of flash-frozen and freeze-dried samples revealed that the agar-MC hydrogel contains two different types of heterogeneous regions of distinct microstructures. The latter was also tested for its stability towards heat treatment which showed that upon heating to temperatures above 120 °C its structure was retained without melting. The produced highly thermally stable hydrogel shows melt resistance which may find application in high temperature food processing and materials templating

EPIDEMIOLOGICAL ASPECTS OF THE ZOONOTIC INFECTIONS IN VARNA REGION IN 1990-1997

Some epidemiological features of the zoonotic infections in Varna region in 1990-1997 were investigated. The analysis was based on the data of the officially registered incidence rate. A remarkable increase of the number of cases with Lyme borreliosis, boutonneous fever and other diseases in comparison with that in some previous years was estblished. This elevation was due to certain favourable epidemiological factors. Case distributions according to epidemiological indices were shown. This initial investigation serves as a basis for more profound research in the field of zoonotic-infection epidemiology in Varna region

On the Algebraic--Geometrical Solutions of the sine--Gordon Equation

We examine the relation between two known classes of solutions of the sine--Gordon equation, which are expressed by theta functions on hyperelliptic Riemann surfaces. The first one is a consequence of the Fay's trisecant identity. The second class exists only for odd genus hyperelliptic Riemann surfaces which admit a fixed--point--free automorphism of order two. We show that these two classes of solutions coincide. The hyperelliptic surfaces corresponding to the second class appear to be double unramified coverings of the Riemann surfaces corresponding to the first class of solutions. We also discuss the soliton limits of these solutions.Comment: 10 pages, LaTex, SISSA--ISAS 10/94/EP (Revised version: the reference [12] added; small changes in the Introduction

Hierarchically porous composites fabricated by hydrogel templating and viscous trapping techniques

© 2017 Elsevier Ltd Two methods for the preparation of hierarchically porous composites have been developed and explored. The first involved templating mixed slurries of hydrogel beads with two different average bead size distributions with gypsum slurry which allows for precise control over the porosity, pore size distributions and hierarchical microstructure of the hardened composite after the evaporation of the water from the hydrogel beads. The other technique utilised the viscosity of methylcellulose solution to suspend gypsum particles as they form an interlocked network. By varying the volume percentage of methylcellulose solution used, it is possible to control the porosity of the dried sample. The mechanical and thermal insulation properties of the composites as a function of both their porosity and pore size were investigated. Both methods demonstrate an inexpensive approach for introducing porosity in gypsum composites which reduces their thermal conductivity, improves their insulation properties and allows economic use of the matrix material whilst controlling their mechanical properties. Such composites allow for tuneable porosity without significantly compromising their strength which could find applications in the building industry as well as structuring of other composites for a variety of consumer products