Magnetic properties of doped Heisenberg chains

The magnetic susceptibility of systems from a class of integrable models for doped spin-$S$ Heisenberg chains is calculated in the limit of vanishing magnetic field. For small concentrations $x_h$ of the mobile spin-$(S-1/2)$ charge carriers we find an explicit expression for the contribution of the gapless mode associated to the magnetic degrees of freedom of these holes to the susceptibility which exhibits a singularity for $x_h\to0$ for sufficiently large $S$. We prove a sum rule for the contributions of the two gapless magnetic modes in the system to the susceptibility which holds for arbitrary hole concentration. This sum rule complements the one for the low temperature specific heat which has been obtained previously.Comment: Latex2e, 22 pp, 3 figures include

A brief history of the bryological exploration of the Azores

An account of the bryological activities on the Azores is given. Three phases can be distinguished: one at the end of the 19. century, when first collections of non-bryologists were made, which resulted in the discovery of less than one third of the presently known species and the description of many so called endemics. A second phase in the thirties of the 20. century is characterized by an intensive collecting activity of some bryologists, which enormously raised the species numbers. In a third phase at the end of the 20. century, tourism as well as activities of local bryologists raised again the species numbers. Revisions of genera reduced the number of endemic species and revisions of herbarium specimens of doubtful records even reduced the species numbers of hepatics

Tunneling singularities in the open Hubbard chain

We study singularities in the I-V characteristics for sequential tunneling from resonant localized levels (e.g. a quantum dot) into a one dimensional electron system described by a Hubbard model. Boundary conformal field theory together with the exact solution of the Hubbard model subject to boundary fields allows to compute the exponents describing the singularity arising when the energy of the local level is tuned through the Fermi energy of the wire as a function of electron density and magnetic field. For boundary potentials with bound states a sequence of such singularities can be observed.Comment: LaTeX2e, 16 pp. incl. 9 figure

More records of mosses from Dominican amber

Hypnum spec., Orthostichella cf. pentasticha, Syrrhopodon flexifolius and Porotrichum aff. substriatum are recorded from Dominican amber (c. 25 mio yrs. b.p.). The first two species were known before from Dominican amber, the last two are newly reported

Interaction induced delocalization of two particles: large system size calculations and dependence on interaction strength

The localization length $L_2$ of two interacting particles in a one-dimensional disordered system is studied for very large system sizes by two efficient and accurate variants of the Green function method. The numerical results (at the band center) can be well described by the functional form $L_2=L_1[0.5+c(U) L_1]$ where $L_1$ is the one-particle localization length and the coefficient $c(U)\approx 0.074 |U|/(1+|U|)$ depends on the strength $U$ of the on-site Hubbard interaction. The Breit-Wigner width or equivalently the (inverse) life time of non-interacting pair states is analytically calculated for small disorder and taking into account the energy dependence of the one-particle localization length. This provides a consistent theoretical explanation of the numerically found $U$-dependence of $c(U)$.Comment: 8 pages, 5 figures, LaTeX, EPJ macro package, submitted to the European Physical Journal

An evaluation of the bryophyte flora of the Azores

The diversity of bryophytes on the different islands of the Azores varies much between 104 and 324 species. Attempts have been made to explain the heterogenity of the bryoflora. There is a correlation between species numbers and age of the islands in the way that the youngest islands (Pico) has the lowest species numbers in spite of the fact that it is the highest island. The species numbers of the other islands are correlated with the maximum elevation and with the size of the islands. The liverwort-moss ratio varies between 1.21 and 1.67 and shows a distinct humidity gradient between the islands. The floristic affinities between the islands are calculated by a cluster analysis. They show no correlation with the location of the islands (nearest neighbour), size, age, elevation or species numbers, which indicates that the species composition is mainly determined by chance. Ten species (2,3%) are endemic to the Azores and 14 species (including one genus) are endemic to the Macaronesian Islands. Some of the endemics are questionable, others may occur elsewhere in the tropics under a different name, but there is fossil prove that the others are relicts from the Tertiary which survived extinction during Quaternary in Europe

Ecology of bryophytes along altitudinal and latitudinal gradients in Chile

The bryophyte vegetation in twenty-eight hectare plots in forests of S-Chile between 38° and 42°S and sea level and the forest line has been studied. Since bryophytes are fully dependend on atmospheric water and nutrient supply, they are good indicators of ecological conditions, especially for humidity. Therefore cover of epiphytic bryophytes, percentage of hepatics, composition of life forms and phytomass of epiphytic bryophytes were used as parameters. Cover and phytomass of epiphytic bryophytes as well as percentage of hepatics show moderate values in the lowlands, peak values in the montane belt (400-800m) and low values in the high montane to subalpine forests. This zonation corresponds with the composition of life forms and is attributed to a higher humidity in the montane belt. Life forms characteristic for the lowlands and submontane belts are pendants, those for the montane belt are wefts and tails, and those for the high montane and and subalpine belts are mats and cushions. The same zonation is found in New Zealand at comparable latitudes. The altitudinal differences are much stronger than the latitudinal ones. Compared with similar transect studies in New Zealand, there is a comparable zonation based on bryphytes. The percentage of hepatics as a good indicator of humidity, is – both in Chile and New Zealand - higher in the transects along the coast with higher precipitation, lower in transects in the inland with less precipitation, and increasing with altitude. Compared with tropical rain forests, the “mossiness” of temperate rain forests expressed by phytomass of epiphytic bryophytes per hectare, cover and percentage of hepatics is comparable to tropical rain forests above 2000 m, which is the corresponding elevation with regard to the mean annual precipitation. In Chile, however, there is a distinct decrease of “mossiness” in the high montane and subalpine forests, which is attributed to special climatological conditions, whereas bryophytes reach maximum cover and phytomass in the tropical high montane and subalpine forests. A comparison with montane forests in Europe in 48°N reveal, that phytomass and percentage of hepatics is distinctly less than in the true rain forests of the southern hemisphere

Eigenfunction structure and scaling of two interacting particles in the one-dimensional Anderson model

The localization properties of eigenfunctions for two interacting particles in the one-dimensional Anderson model are studied for system sizes up to $N=5000$ sites corresponding to a Hilbert space of dimension $\approx 10^7$ using the Green function Arnoldi method. The eigenfunction structure is illustrated in position, momentum and energy representation, the latter corresponding to an expansion in non-interacting product eigenfunctions. Different types of localization lengths are computed for parameter ranges in system size, disorder and interaction strengths inaccessible until now. We confirm that one-parameter scaling theory can be successfully applied provided that the condition of $N$ being significantly larger than the one-particle localization length $L_1$ is verified. The enhancement effect of the two-particle localization length $L_2$ behaving as $L_2\sim L_1^2$ is clearly confirmed for a certain quite large interval of optimal interactions strengths. Further new results for the interaction dependence in a very large interval, an energy value outside the band center, and different interaction ranges are obtained.Comment: 26 pages, 19 png and pdf figures, high quality gif files for panels of figures 1-4 are available at http://www.quantware.ups-tlse.fr/QWLIB/tipdisorder1d, final published version with minor corrections/revisions, addition of Journal reference and DO

New combinations in the genera Atractylocarpus and Metzleria

The type species of Atractylocarpus has revealed to be a species of a genus which was later introduced as Camylopodiella. To avoid taxonomic confusions, it was proposed to keep the current use of Atractylocarpus and Campylopodiella by amending the genus Atractylocarpus. This proposal was rejected by the ICBN committee. Therefore the valid genus for all species so far comprised in Atractylocarpus is Metzleria and all species so far included in Campylopodiella must be transferred to Atractylocarpus. Accoringly, all necessary new combinations are introduced here: Atractylocarpus himalayanus (Broth.) J.-P. Frahm , Atractylocarpus malagensis (Herz.) J.-P. Frahm Metzleria comosa (Dix.) J.-P. Frahm, Metzleria madagascariensis (Thér.) J.-P. Frahm, Metzleria nana (Williams) J.-P. Frahm, Metzleria patagonica (Herz. et Thér.) J.-P. Frahm