Visual geographies : an editorial

The use of image-processing procedures and techniques and their products – photographs, aerial photographs, satellite images, maps – and the application of GIS and GPS, so-called "geomatics" (Thornes, 2004:787), are taken for granted in academic geographical practice today..

Doped Heisenberg chains: spin-S generalizations of the supersymmetric t-J model

A family of exactly solvable models describing a spin-S Heisenberg chain doped with mobile spin-(S-1/2) carriers is constructed from gl(2|1)-invariant solutions of the Yang-Baxter equation. The models are generalizations of the supersymmetric t-J model which is obtained for S=1/2. We solve the model by means of the algebraic Bethe Ansatz and present results for the zero temperature and thermodynamic properties. At low temperatures the models show spin charge separation, i.e. contain contributions of a free bosonic theory in the charge sector and an SU(2)-invariant theory describing the magnetic excitations. For small carrier concentration the latter can be decomposed further into an SU(2) level-2S Wess-Zumino-Novikov-Witten model and the minimal unitary model M_p with p=2S+1.Comment: LaTeX, 24 pp. incl. 4 figure

Analytical results for the Coqblin-Schrieffer model with generalized magnetic fields

Using the approach alternative to the traditional Thermodynamic Bethe Ansatz, we derive analytical expressions for the free energy of Coqblin-Schrieffer model with arbitrary magnetic and crystal fields. In Appendix we discuss two concrete examples including the field generated crossover from the SU(4) to the SU(2) symmetry in the SU(4)-symmetric model.Comment: 5 page

Exactly Solvable Model of Superconducting Magnetic Alloys

A model describing the Anderson impurity in the Bardeen-Cooper-Schriffer superconductor is proven to exhibit hidden integrability and is diagonalized exactly by the Bethe ansatz.Comment: 10 pages, RevTEX, Phys. Lett. A. (in press

Algebraic properties of an integrable t-J model with impurities

We investigate the algebraic structure of a recently proposed integrable $t-J$ model with impurities. Three forms of the Bethe ansatz equations are presented corresponding to the three choices for the grading. We prove that the Bethe ansatz states are highest weight vectors of the underlying $gl(2|1)$ supersymmetry algebra. By acting with the $gl(2|1)$ generators we construct a complete set of states for the model.Comment: 20 pages, LaTe

Time Dependent Effects and Transport Evidence for Phase Separation in La_{0.5}Ca_{0.5}MnO_{3}

The ground state of La_{1-x}Ca_{x}MnO_{3} changes from a ferromagnetic metallic to an antiferromagnetic charge-ordered state as a function of Ca concentration at x ~ 0.50. We present evidence from transport measurements on a sample with x = 0.50 that the two phases can coexist, in agreement with other observations of phase separation in these materials. We also observe that, by applying and then removing a magnetic field to the mainly charge-ordered state at some temperatures, we can "magnetically anneal" the charge order, resulting in a higher zero-field resistivity. We also observe logarithmic time dependence in both resistivity and magnetization after a field sweep at low temperatures.Comment: 9 pages, LATEX, 3 postscript figure

Effect of Chitosan as a Stabilizer in Hot Sauce

By the use of mild demineralization in the purification of chitin from shrimp shells and optimizing the deacetylation of this chitin, chitosan capable of producing viscosities of 9600 cps were produced. This is substantially higher than the viscosity of the commercial product, whose viscosity is only 1000 cps. The effectiveness of this high quality chitosan as a stabilizer in hot sauces was then investigated. From prelim­inary studies using the commercially produced chitosan, it was concluded that the method of incorporating the gum into the hot sauces was very important. Therefore, three methods of adding the chitosan to the hot sauces were examined. These methods mainly differed in the sequence in which chitosan and acetic acid were combined in order to form a viscous solution. Results indicated that if the chitosan was mixed with the solid components of the hot sauce before the acid, no viscous solutions were formed. Apparently the high salt content (over 5%) of the hot sauces nullifies the viscosity producing potential of chitosan. If the viscous solution was produced before it was mixed with the solids, the two components repelled each other and the solids sedimented to the bottom of the bottle

Superconductivity and Antiferromagnetism: Hybridization Impurities in a Two-Band Spin-Gapped Electron System

We present the exact solution of a one-dimensional model of a spin-gapped correlated electron system with hybridization impurities exhibiting both magnetic and mixed-valence properties. The host supports superconducting fluctuations, with a spin gap. The localized electrons create a band of antiferromagnetic spin excitations inside the gap for concentrations x of the impurities below some critical value x_c. When x = x_c the spin gap closes and a ferrimagnetic phase appears. This is the first example of an exactly solvable model with coexisting superconducting and antiferromagnetic fluctuations which in addition supports a quantum phase transition to a (compensated) ferrimagnetic phase. We discuss the possible relevance of our results for experimental systems, in particular the U-based heavy-fermion materials.Comment: 4 page