8,715 research outputs found
SEPARATION OF STAGES IN THE DEVELOPMENT OF THE "T" CELLS INVOLVED IN CELL-MEDIATED IMMUNITY
Density distribution analysis in continuous gradients of albumin has been used to study the development of cytotoxic lymphocytes (CL), to separate and characterize the progenitors of CL, and to determine their relationship to subpopulations of T cells. CL progenitors in the thymus were a homogeneous, medium-density population, distinct from the typical, dense, thymus small-lymphocyte. Activity seemed to be associated with one minor subpopulation of cells with surface antigenic properties characteristic of peripheral T cells (high levels of H-2 antigen, low levels of θ-antigen). CL progenitors in the spleen differed from those in the thymus and normally had the high buoyant density of typical small T lymphocytes. In states of antigenic stimulation, some lighter-density CL progenitors were found in the spleen. The buoyant density of the CL population developing in the spleens of immunized animals showed progressive changes with time. Early, "immature" CL had the light-density characteristics of large, activated lymphocytes. As the response developed, the density of the CL population increased, and finally approached that of CL progenitors and of typical small lymphocytes. The data suggest that density subpopulations of T cells represent stages in the development of immunocompetent cells. Possible differentiation pathways of T lymphocytes in the thymus and in the spleen are discussed
Defect flows in minimal models
In this paper we study a simple example of a two-parameter space of
renormalisation group flows of defects in Virasoro minimal models. We use a
combination of exact results, perturbation theory and the truncated conformal
space approach to search for fixed points and investigate their nature. For the
Ising model, we confirm the recent results of Fendley et al. In the case of
central charge close to one, we find six fixed points, five of which we can
identify in terms of known defects and one of which we conjecture is a new
non-trivial conformal defect. We also include several new results on exact
properties of perturbed defects and on the renormalisation group in the
truncated conformal space approach.Comment: 35 pages, 21 figures. 1 reference adde
D-brane Categories for Orientifolds -- The Landau-Ginzburg Case
We construct and classify categories of D-branes in orientifolds based on
Landau-Ginzburg models and their orbifolds. Consistency of the worldsheet
parity action on the matrix factorizations plays the key role. This provides
all the requisite data for an orientifold construction after embedding in
string theory. One of our main results is a computation of topological field
theory correlators on unoriented worldsheets, generalizing the formulas of Vafa
and Kapustin-Li for oriented worldsheets, as well as the extension of these
results to orbifolds. We also find a doubling of Knoerrer periodicity in the
orientifold context.Comment: 45 pages, 6 figure
Lithographic engineering of anisotropies in (Ga,Mn)As
The focus of studies on ferromagnetic semiconductors is moving from material
issues to device functionalities based on novel phenomena often associated with
the anisotropy properties of these materials. This is driving a need for a
method to locally control the anisotropy in order to allow the elaboration of
devices. Here we present a method which provides patterning induced anisotropy
which not only can be applied locally, but also dominates over the intrinsic
material anisotropy at all temperatures
B-type defects in Landau-Ginzburg models
We consider Landau-Ginzburg models with possibly different superpotentials
glued together along one-dimensional defect lines. Defects preserving B-type
supersymmetry can be represented by matrix factorisations of the difference of
the superpotentials. The composition of these defects and their action on
B-type boundary conditions is described in this framework. The cases of
Landau-Ginzburg models with superpotential W=X^d and W=X^d+Z^2 are analysed in
detail, and the results are compared to the CFT treatment of defects in N=2
superconformal minimal models to which these Landau-Ginzburg models flow in the
IR.Comment: 50 pages, 2 figure
Measuring the equation of state of a hard-disc fluid
We use video microscopy to study a two-dimensional (2D) model fluid of
charged colloidal particles suspended in water and compute the pressure from
the measured particle configurations. Direct experimental control over the
particle density by means of optical tweezers allows the precise measurement of
pressure as a function of density. We compare our data with theoretical
predictions for the equation of state, the pair-correlation function and the
compressibility of a hard-disc fluid and find good agreement, both for the
fluid and the solid phase. In particular the location of the transition point
agrees well with results from Monte Carlo simulations.Comment: 7 pages, to appear in EPL, slightly corrected versio
CELLULAR AND HUMORAL RESPONSE TO TRANSPLANTATION ANTIGENS : I. DEVELOPMENT OF ALLOANTIBODY-FORMING CELLS AND CYTOTOXIC LYMPHOCYTES IN THE GRAFT-VERSUS-HOST REACTION
After transfer into heavily-irradiated allogeneic mice, spleen cells were found to produce two types of effector cells directed against the recipient alloantigens, namely alloantibody plaque-forming cells (PFC) and cytotoxic lymphocytes (CL). Both types of effector cells were detectable in vitro by virtue of their lytic effect on target cells carrying the recipient alloantigens. Alloantibody PFC activity was dependent on the presence of an exogenous source of complement and could be inhibited by the addition of heterologous antisera to mouse µ-chain or Fab fragment in the assay system. CL activity was independent of added complement, was not affected by anti-immunoglobulin antisera, but was inhibited by the addition of antibody against target cell alloantigens. Treatment of the transferred spleen cells with anti-θ-serum and complement before in vitro assays for PFC and CL completely abolished the CL activity but had no effect on alloantibody-plaque formation. These results indicate that the two types of effector cells can be differentiated in vitro by virtue of their susceptibility to anti-θ-serum and the mechanisms by which they cause cell lysis
Quantum-dot-based optical polarization conversion
We report circular-to-linear and linear-to-circular conversion of optical
polarization by semiconductor quantum dots. The polarization conversion occurs
under continuous wave excitation in absence of any magnetic field. The effect
originates from quantum interference of linearly and circularly polarized
photon states, induced by the natural anisotropic shape of the self assembled
dots. The behavior can be qualitatively explained in terms of a pseudospin
formalism.Comment: 5 pages, 3 figures; a reference adde
Single electron charging of impurity sites visualized by scanning gate experiments on a quantum point contact
A quantum point contact (QPC) patterned on a two-dimensional electron gas is
investigated with a scanning gate setup operated at a temperature of 300 mK.
The conductance of the point contact is recorded while the local potential is
modified by scanning the tip. Single electron charging of impurities induced by
the local potential is observed as a stepwise conductance change of the
constriction. By selectively changing the state of some of these impurities, it
is possible to observe changes in transmission resonances of the QPC. The
location of such impurities is determined, and their density is estimated to be
below 50 per \mu m^2, corresponding to less than 1 % of the doping
concentration
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