Susceptibility of the one-dimensional, dimerized Hubbard model

We show that the zero temperature susceptibility of the one-dimensional, dimerized Hubbard model at quarter-filling can be accurately determined on the basis of exact diagonalization of small clusters. The best procedure is to perform a finite-size scaling of the spin velocity $u_\sigma$, and to calculate the susceptibility from the Luttinger liquid relation $\chi=2/\pi u_\sigma$. We show that these results are reliable by comparing them with the analytical results that can be obtained in the weak and strong coupling limits. We have also used quantum Monte Carlo simulations to calculate the temperature dependence of the susceptibility for parameters that should be relevant to the Bechgaard salts. This shows that, used together, these numerical techniques are able to give precise estimates of the low temperature susceptibility of realistic one-dimensional models of correlated electrons.Comment: 10 pages, latex, figures available from the authors. To appear in Phys. Rev. B, Rapid Comm

Nearly universal crossing point of the specific heat curves of Hubbard models

A nearly universal feature of the specific heat curves C(T,U) vs. T for different U of a general class of Hubbard models is observed. That is, the value C_+ of the specific heat curves at their high-temperature crossing point T_+ is almost independent of lattice structure and spatial dimension d, with C_+/k_B \approx 0.34. This surprising feature is explained within second order perturbation theory in U by identifying two small parameters controlling the value of C_+: the integral over the deviation of the density of states N(\epsilon) from a constant value, characterized by \delta N=\int d\epsilon |N(\epsilon)-1/2|, and the inverse dimension, 1/d.Comment: Revtex, 9 pages, 6 figure

Elastic Convection in Vibrated Viscoplastic Fluids

We observe a new type of behavior in a shear thinning yield stress fluid: freestanding convection rolls driven by vertical oscillation. The convection occurs without the constraint of container boundaries yet the diameter of the rolls is spontaneously selected for a wide range of parameters. The transition to the convecting state occurs without hysteresis when the amplitude of the plate acceleration exceeds a critical value. We find that a non-dimensional stress, the stress due to the inertia of the fluid normalized by the yield stress, governs the onset of the convective motion.Comment: 4 pages, 6 figure

The calpastatin-derived calpain inhibitor CP1B reduces mRNA expression of matrix metalloproteinase-2 and-9 and invasion by leukemic THP-1 cells

The ubiquitous proteases μ- and m-calpain are Ca2+-dependent cysteine endopeptidases. Besides involvement in a variety of physio(patho)logical processes, recent studies suggest a pivotal role of calpains in differentiation of hematopoietic cells and tumor cell invasion. However, the precise actions of calpains and their endogenous inhibitor, calpastatin, in these processes are only partially understood. Here we have studied the role of the calpain/calpastatin system in the invasion of leukemic cells under basal and differentiationstimulating conditions. To further differentiate the human leukaemic cell line THP-1 (monocytic), the cells were treated for 24 hours with the differentiationstimulating reagents phorbol 12-myristate 13-acetate (PMA) and dimethyl sulfoxide (DMSO). Macrophage and granulocytelike differentiation was confirmed by induction of vimentin expression as well as by microscopic and fluorescence assisted cytometric analysis. Extracellular matrix (ECM) invasion of both the basal and differentiation stimulated cells in a Matrigel assay was inhibited by preincubation of the cells with the specific calpain inhibitor CP1B for 24 hours. Inhibition of invasiveness correlated with decreased mRNA expression and secretion of the matrix metalloproteinases MMP-2 and MMP-9. In contrast, addition of CP1B only during the invasion process did neither influence transmigration nor MMP release. This is the first report showing that the calpain/calpastatin system mediates MMPmRNA expression of the leukemic THP-1 cells and as a consequence their invasiveness

Variational Monte Carlo Study of the Kondo Necklace Model with Geometrical Frustration

We investigate the ground state of the Kondo necklace model on geometrically-frustrated lattices by the variational Monte Carlo simulation. To explore the possibility of a partially-ordered phase, we employ an extension of the Yosida-type wave function as a variational state, which can describe a coexistence of spin-singlet formation due to the Kondo coupling and magnetic ordering by the Ruderman-Kittel-Kasuya-Yosida interaction. We show the benchmark of the numerical simulation to demonstrate the high precision brought by the optimization of a large number of variational parameters. We discuss the ground-state phase diagram for the model on the kagome lattice in comparison with that for the triangular-lattice case.Comment: 3 pages, proceedings for ICHE201

Sense of Purpose in Life and Five Health Behaviors in Older Adults

Accumulating evidence shows that a higher sense of purpose in life is associated with lower risk of chronic conditions and premature mortality. Health behaviors might partially explain these findings, however, the prospective association between sense of purpose and health behaviors is understudied. We tested whether a higher sense of purpose at baseline was associated with lower likelihood of developing unhealthy behaviors over time. Prospective data were from the Health and Retirement Study, a national sample of U.S. older adults. Our sample included 13,770 adults assessed up to five times across eight years. Among people who met recommended guidelines for a given health behavior outcome at baseline, those in the top versus lowest quartile of purpose in life had 24% lower likelihood of becoming physically inactive (95% CI: 0.68–0.85), 33% lower likelihood of developing sleep problems (95% CI: 0.58–0.79), and 22% lower likelihood of developing unhealthy body mass index (BMI) (95% CI: 0.69–0.87) in sociodemographic-adjusted models. Further there was a marginal reduction in smoking relapse (HR = 0.65, 95% CI: 0.41–1.03) and no association with heavy alcohol use (HR = 1.02, 95% CI: 0.81–1.29). Findings for physical inactivity, sleep problems, and unhealthy BMI remained evident after further adjusting for baseline health status and depression. Our results, suggest that a sense of purpose in life might emerge (with further research) as a valuable target to consider for interventions aimed at helping older adults maintain some health behaviors

Tail States in Disordered Superconductors with Magnetic Impurities: the Unitarity Limit

When subject to a weak magnetic impurity distribution, the order parameter and quasi-particle energy gap of a weakly disordered bulk s-wave superconductor are suppressed. In the Born scattering limit, recent investigations have shown that `optimal fluctuations' of the random impurity potential can lead to the nucleation of `domains' of localised states within the gap region predicted by the conventional Abrikosov-Gor'kov mean-field theory, rendering the superconducting system gapless at any finite impurity concentration. By implementing a field theoretic scheme tailored to the weakly disordered system, the aim of the present paper is to extend this analysis to the consideration of magnetic impurities in the unitarity scattering limit. This investigation reveals that the qualitative behaviour is maintained while the density of states exhibits a rich structure.Comment: 18 pages AMSLaTeX (with LaTeX2e), 6 eps figure

Field-Induced Two-Step Phase Transitions in the Singlet Ground State Triangular Antiferromagnet CsFeBr3_3

The ground state of the stacked triangular antiferromagnet CsFeBr$_3$ is a spin singlet due to the large single ion anisotropy $D(S^z)^2$. The field-induced magnetic ordering in this compound was investigated by the magnetic susceptibility, the magnetization process and specific heat measurements for an external field parallel to the $c$-axis. Unexpectedly, two phase transitions were observed in the magnetic field $H$ higher than 3 T. The phase diagram for temperature versus magnetic field was obtained. The mechanism leading to the successive phase transitions is discussed.Comment: 8 pages, 9 figures, 10 eps files, jpsj styl

Crossover from Spin-Density-Wave to Neel-like Ground state

The characterization and evolution of a Spin Density Wave into the Quantum Neel ground state is considered in the context of a weak coupling theory of the half-filled Hubbard model. Magnetic properties obtained from this weak coupling approach in one dimension compare favorably with exact results from Bethe ansatz (BA). A study of the evolution of several length scales from weak to strong coupling is also presented.Comment: [email protected] Pages: 18 (REVTEX 3.0). 6 postscript figures available upon reques

Kinky Behavior in Josephson Junctions

We analyze nonperturbatively the behavior of a Josephson junction in which two BCS superconductors are coupled through an Anderson impurity. We recover earlier perturbative results which found that a $\delta=\pi$ phase difference is preferred when the impurity is singly occupied and the on-site Coulomb interaction is large. We find a novel intermediate phase in which one of $\delta=0$ and $\delta=\pi$ is stable while the other is metastable, with the energy $E(\delta)$ having a kink somewhere in between. As a consequence of the kink, the $I-V$ characteristics of the junction are modified at low voltages.Comment: 7 pages, 7 encapsulated PostScript figures; figure 3 correcte