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 type catalogue of Campylopodioideae and Paraleucobryoideae (Musci, Dicranaceae) : part 2, Campylopus

All species of Campylopus Brid. are listed, including citations of basionyms and homotypic synonyms, completed by citation of the type specimen and its location, as well as the current use or other uses of the name

A contribution to the Campylopus flora of Chile

A key to the species of Campylopus known from Chile is given, completed by records of Campylopodioideae of the author in southern Chile. Campylopus acuminatus Mitt. var. kirkii (Mitt.) J.-P. Frahm is reported for the first time for Chile

Campylopus, a modern and successful genus!?

Campylopus with nearly 200 revised species is one of the largest genera of mosses in the world and has extremely broad geographical, altitudinal and ecological ranges. Factors to be considered for the rich speciation are 1) the enormous anatomical plasticity of the structure of the costa, 2) the ability for vegetative propagation utilizing different methods, and 3) the special twist mechanism of the cygneous setae. Phytogeographical interpretations of present ranges of species of Campylopus lead to the conclusion that this genus is of Gondwanalandic origin. Most of the species seem to be cool temperate in origin. They have adapted to dry habitats in the Mesozoic and invaded the tropical mountains during the Tertiary, accompanied by rich speciation. This is supported by the physiology of these species. According to preliminary gas exchange measurements, tropical montane species do not differ from temperate species, and are not able to stand climatic conditions of the tropical lowland rainforests; a relatively young habitat for bryophytes. A cladistic analysis of the infrageneric categories of Campylopus using phytogeographical evaluations of apomorphic character states shows that the section Homalocarpus seems to be the most primitive and the subgenera Campylopidulum and Thysanomitrion the most derived

Localization and absence of Breit-Wigner form for Cauchy random band matrices

We analytically calculate the local density of states for Cauchy random band matrices with strongly fluctuating diagonal elements. The Breit-Wigner form for ordinary band matrices is replaced by a Levy distribution of index $\mu=1/2$ and the characteristic energy scale $\alpha$ is strongly enhanced as compared to the Breit-Wigner width. The unperturbed eigenstates decay according to the non-exponential law $\propto e^{-\sqrt{\alpha t}}$. We analytically determine the localization length by a new method to derive the supersymmetric non-linear $\sigma$ model for this type of band matrices.Comment: 4 pages, 1 figur

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