24 research outputs found
Mesangial cell-derived transforming growth factor-β1 reduces macrophage adhesiveness with consequent deactivation
Mesangial cell-derived transforming growth factor-β1 reduces macrophage adhesiveness with consequent deactivation. Adhesion of macrophages is a crucial event that determines the number and function of macrophages at inflammatory sites. The aim of this study was to elucidate the role of mesangial cells in the regulation of macrophage adhesiveness. J774.2 macrophages were suspended in serial dilutions of mesangial cell conditioned medium (MC medium) and seeded on plastic tissue culture plates. MC medium did not affect the initial adhesion of macrophages but induced subsequent detachment in a concentration-dependent manner. A similar effect was observed when macrophages were plated on plastic coated with laminin, collagen type IV or Matrigel. The reduced adhesiveness was reversible, and cell viability was unaffected by MC medium, indicating that the effect is not due to cytotoxicity. Conditioned media from fibroblastic, epithelial and endothelial cell lines did not induce macrophage detachment. To identify the active component in MC medium, we examined the involvement of transforming growth factor-β1 (TGF-β1) in the process. Mesangial cells constitutively expressed TGF-β1 mRNA, and MC medium contained the active form of TGF-β1. Exogenously added TGF-β1 induced macrophage detachment in a dose-dependent manner, and an anti-TGF-β1 neutralizing antibody partially abolished the activity of MC medium, indicating the involvement of TGF-β1 as an active component. Compared to adherent cells, detached macrophages showed reduced mitogenic activity and blunted induction of IL-1β and IL-6 in response to lipopolysaccharide. These data demonstrate that TGF-β1 is a mesangial cell-derived factor that impairs adhesiveness of macrophages and confers blunted responses to a specific stimulus. These findings suggest one potential mechanism for macrophage clearance from inflamed glomeruli
From the Hofstadter to the Fibonacci butterfly
We show that the electronic spectrum of a tight-binding Hamiltonian defined
in a quasiperiodic chain with an on-site potential given by a Fibonacci
sequence, can be obtained as a superposition of Harper potentials. The
electronic spectrum of the Harper equation is a fractal set, known as
Hofstadter butterfly. Here we show that is possible to construct a similar
butterfly for the Fibonacci potential just by adding harmonics to the Harper
potential. As a result, the equations in reciprocal space for the Fibonacci
case have the form of a chain with a long range interaction between Fourier
components. Then we explore the transformation between both spectra, and
specifically the origin of energy gaps due to the analytical calculation of the
components in reciprocal space of the potentials. We also calculate some
localization properties by finding the correlator of each potential.Comment: 7 pages, 4 figure
Striped periodic minimizers of a two-dimensional model for martensitic phase transitions
In this paper we consider a simplified two-dimensional scalar model for the
formation of mesoscopic domain patterns in martensitic shape-memory alloys at
the interface between a region occupied by the parent (austenite) phase and a
region occupied by the product (martensite) phase, which can occur in two
variants (twins). The model, first proposed by Kohn and Mueller, is defined by
the following functional: where
is periodic in and almost everywhere.
Conti proved that if then the minimal specific
energy scales like ,
as . In the regime , we improve Conti's results, by computing exactly the
minimal energy and by proving that minimizers are periodic one-dimensional
sawtooth functions.Comment: 29 pages, 3 figure
Froth-like minimizers of a non local free energy functional with competing interactions
We investigate the ground and low energy states of a one dimensional non
local free energy functional describing at a mean field level a spin system
with both ferromagnetic and antiferromagnetic interactions. In particular, the
antiferromagnetic interaction is assumed to have a range much larger than the
ferromagnetic one. The competition between these two effects is expected to
lead to the spontaneous emergence of a regular alternation of long intervals on
which the spin profile is magnetized either up or down, with an oscillation
scale intermediate between the range of the ferromagnetic and that of the
antiferromagnetic interaction. In this sense, the optimal or quasi-optimal
profiles are "froth-like": if seen on the scale of the antiferromagnetic
potential they look neutral, but if seen at the microscope they actually
consist of big bubbles of two different phases alternating among each other. In
this paper we prove the validity of this picture, we compute the oscillation
scale of the quasi-optimal profiles and we quantify their distance in norm from
a reference periodic profile. The proof consists of two main steps: we first
coarse grain the system on a scale intermediate between the range of the
ferromagnetic potential and the expected optimal oscillation scale; in this way
we reduce the original functional to an effective "sharp interface" one. Next,
we study the latter by reflection positivity methods, which require as a key
ingredient the exact locality of the short range term. Our proof has the
conceptual interest of combining coarse graining with reflection positivity
methods, an idea that is presumably useful in much more general contexts than
the one studied here.Comment: 38 pages, 2 figure
Flatness is a Criterion for Selection of Maximizing Measures
For a full shift with Np+1 symbols and for a non-positive potential, locally
proportional to the distance to one of N disjoint full shifts with p symbols,
we prove that the equilibrium state converges as the temperature goes to 0. The
main result is that the limit is a convex combination of the two ergodic
measures with maximal entropy among maximizing measures and whose supports are
the two shifts where the potential is the flattest. In particular, this is a
hint to solve the open problem of selection, and this indicates that flatness
is probably a/the criterion for selection as it was conjectured by A.O. Lopes.
As a by product we get convergence of the eigenfunction at the log-scale to a
unique calibrated subaction
Some New Results on Complex-Temperature Singularities in Potts Models on the Square Lattice
We report some new results on the complex-temperature (CT) singularities of
-state Potts models on the square lattice. We concentrate on the problematic
region (where ) in which CT zeros of the partition function
are sensitive to finite lattice artifacts. From analyses of low-temperature
series expansions for , we establish the existence, in this
region, of complex-conjugate CT singularities at which the magnetization and
susceptibility diverge. From calculations of zeros of the partition function,
we obtain evidence consistent with the inference that these singularities occur
at endpoints of arcs protruding into the (complex-temperature
extension of the) FM phase. Exponents for these singularities are determined;
e.g., for , we find , consistent with .
By duality, these results also imply associated arcs extending to the (CT
extension of the) symmetric PM phase. Analytic expressions are suggested for
the positions of some of these singularities; e.g., for , our finding is
consistent with the exact value . Further discussions of
complex-temperature phase diagrams are given.Comment: 26 pages, latex, with eight epsf figure