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

Crossover of magnetoconductance autocorrelation for a ballistic chaotic quantum dot

The autocorrelation function C_{\varphi,\eps}(\Delta\varphi,\,\Delta \eps)= \langle \delta g(\varphi,\,\eps)\, \delta g(\varphi+\Delta\varphi,\,\eps+\Delta \eps)\rangle ($\varphi$ and \eps are rescaled magnetic flux and energy) for the magnetoconductance of a ballistic chaotic quantum dot is calculated in the framework of the supersymmetric non-linear $\sigma$-model. The Hamiltonian of the quantum dot is modelled by a Gaussian random matrix. The particular form of the symmetry breaking matrix is found to be relevant for the autocorrelation function but not for the average conductance. Our results are valid for the complete crossover from orthogonal to unitary symmetry and their relation with semiclassical theory and an $S$-matrix Brownian motion ensemble is discussed.Comment: 7 pages, no figures, accepted for publication in Europhysics Letter

New bryophyte taxon records for tropical countries 2

Norris & T. Kop. Sabah, Mt. Kinabalu, Mary Strong Clemens. 10741, 15.11.1915 (L) as „Campylopus metzlerioides Broth. nom. nud.“ The species was known before (mostly as Atractylocarpus comosus Dix.) from Sumatra, Celebes, New Guinea, Bhutan and Nepal [JPF]

Doping-dependent magnetization plateaux in p-merized Hubbard chains

We study zero-temperature Hubbard chains with periodically modulated hopping at arbitrary filling n and magnetization m. We show that the magnetization curves have plateaux at certain values of m which depend on the periodicity p and the filling. At commensurate filling n a charge gap opens and then magnetization plateaux correspond to fully gapped situations. However, plateaux also arise in the magnetization curves at fixed n between the commensurate values and then the plateau-value of of m depends continuously on n and can thus also become irrational. In particular for the case of dimerized hopping (p=2) and fixed doping we find that a plateau appears at m=1-n. In this case, there is still a gapless mode on the plateau leading to thermodynamic behavior which is different from a completely gapped situation.Comment: 9 pages REVTeX, 3 PostScript figures included using psfig.sty; this is the final version to appear in Phys. Lett. A; substantial changes: Lanczos part removed to gain space for further explanations (refer to original version for details on the numerics

Vasculature of the paraventricular nucleus of the hypothalamus: influence of development, gamma-aminobutyric acid (GABA) receptors, and prenatal glucocorticoids, The

2014 Spring.The paraventricular nucleus of the hypothalamus (PVN) is a critical brain region that regulates many homeostatic and stress responses. In addition to its dense cytoarchitecture, it also contains a vast network of blood vessels. These blood vessels within the mouse PVN have a higher density than other brain regions, which develops postnatally. Loss of gamma aminobutyric acid (GABA) signaling or prenatal dexamethasone (dex) treatment decreased the blood vessel density. Dex also decreased blood brain barrier (BBB) competency while increasing desmin-immunoreactive pericytes at postnatal day (P)20. Long-term consequences included a decrease in GFAP contact with blood vessels selectively in dex-treated females, and an increase in depression-like behaviors in dex-treated males. Chapter 2 examines the blood vessel density within the PVN. Initially the blood vessel density is similar than surrounding brain regions, then after P8 there was an increase that resulted in a highly vascularized network around P20. The highest densities were restricted to the rostral and mid regions of the PVN, where the neuroendocrine neurons are housed. In addition, mice lacking a functional GABAB receptor had a significant decrease in blood vessel density in the mid region at P20. The protein endocan has been proposed to be a "tip cell" marker, indicating angiogenesis. To further characterize the postnatal angiogenic period within the PVN, recently developed antibodies against endocan were used. Chapter 3 provides evidence that endocan is normally expressed in the mouse brain but not restricted to tip cells. In addition, prior perfusion with fluorescein isothiocyanate (FITC) prevents endocan-immunoreactivity (ir) and provides a novel method for identifying non-functional blood vessels. Chapters 4 and 5 show that excess fetal glucocorticoids alters the BBB within the PVN at two time points. At P20, there was a loss of BBB integrity accompanied by an increase in desmin-ir pericytes on a reduced blood vessel network due to dex-treatment for both prepubertal males and females. In contrast at P50, the blood vessel density and BBB were no longer disrupted following fetal dex-treatment. However, there was a decrease in glial fibrillary acidic protein (GFAP)-ir astrocytes in dex-treated females and an increase in desmin-ir pericytes in dextreated males. In conclusion, the work set forth in this dissertation indicates that the dense vascular network within the PVN develops postnatally and is susceptible to regulation by both exogenous and endogenous factors

h/2eh/2e--Oscillations for Correlated Electron Pairs in Disordered Mesoscopic Rings

The full spectrum of two interacting electrons in a disordered mesoscopic one--dimensional ring threaded by a magnetic flux is calculated numerically. For ring sizes far exceeding the one--particle localization length $L_1$ we find several $h/2e$--periodic states whose eigenfunctions exhibit a pairing effect. This represents the first direct observation of interaction--assisted coherent pair propagation, the pair being delocalized on the scale of the whole ring.Comment: 4 pages, uuencoded PostScript, containing 5 figures

Spin-spin correlations between two Kondo impurities coupled to an open Hubbard chain

In order to study the interplay between Kondo and Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, we calculate the spin-spin correlation functions between two Kondo impurities coupled to different sites of a half-filled open Hubbard chain. Using the density-matrix renormalization group (DMRG), we re-examine the exponents for the power-law decay of the correlation function between the two impurity spins as a function of the antiferromagnetic coupling J, the Hubbard interaction U, and the distance R between the impurities. The exponents for finite systems obtained in this work deviate from previously published DMRG calculations. We furthermore show that the long-distance behavior of the exponents is the same for impurities coupled to the bulk or to both ends of the chain. We note that a universal exponent for the asymptotic behavior cannot be extracted from these finite-size systems with open boundary conditions.Comment: 8 pages, 10 figures; v2: final version, references and Fig. 8 adde

Thermodynamic performance testing of the orbiter flash evaporator system

System level testing of the space shuttle orbiter's development flash evaporator system (FES) was performed in a thermal vacuum chamber capable of simulating ambient ascent, orbital, and entry temperature and pressure profiles. The test article included the evaporator assembly, high load and topping exhaust duct and nozzle assemblies, and feedwater supply assembly. Steady state and transient heat load, water pressure/temperature and ambient pressure/temperature profiles were imposed by especially designed supporting test hardware. Testing in 1978 verified evaporator and duct heater thermal design, determined FES performance boundaries, and assessed topping evaporator plume characteristics. Testing in 1979 combined the FES with the other systems in the orbiter active thermal control subsystem (ATCS). The FES met or exceeded all nominal and contingency performance requirements during operation with the integrated ATCS. During both tests stability problems were encountered during steady state operations which resulted in subsequent design changes to the water spray nozzle and valve plate assemblies

Correlation functions of one-dimensional Bose-Fermi mixtures

We calculate the asymptotic behaviour of correlation functions as a function of the microscopic parameters for a Bose-Fermi mixture with repulsive interaction in one dimension. For two cases, namely polarized and unpolarized fermions the singularities of the momentum distribution functions are characterized as a function of the coupling constant and the relative density of bosons.Comment: RevTeX 4, 10 pages, 2 figure

Anderson-like impurity in the one-dimensional t-J model: formation of local states and magnetic behaviour

We consider an integrable model describing an Anderson-like impurity coupled to an open $t$--$J$ chain. Both the hybridization (i.e. its coupling to bulk chain) and the local spectrum can be controlled without breaking the integrability of the model. As the hybridization is varied, holon and spinon bound states appear in the many body ground state. Based on the exact solution we study the state of the impurity and its contribution to thermodynamic quantities as a function of an applied magnetic field. Kondo behaviour in the magnetic response of the impurity can be observed provided that its parameters have been adjusted properly to the energy scales of the holon and spinon excitations of the one-dimensional bulk.Comment: 32 pages, 11 figure