763 research outputs found
CELLULAR RECOGNITION IN VITRO BY MOUSE LYMPHOCYTES : EFFECTS OF NEONATAL THYMECTOMY AND THYMUS GRAFT RESTORATION ON ALLOANTIGEN AND PHA STIMULATION OF WHOLE AND GRADIENT-SEPARATED SUBPOPULATIONS OF SPLEEN CELLS
The effects of thymectomy and thymus graft restoration upon the in vitro primary responses to alloantigens and PHA have been studied. It has been found that neonatal thymectomy substantially eliminates both PHA reactivity and responsiveness to alloantigens assayed in vitro in host spleen cell populations. Analysis of albumin density gradient-separated subpopulations of the spleen and thymus in such animals was also performed. It was found that the total and proportional representation of the individual density subpopulations was identical in neonatally thymectomized, in normal, and in thymectomized and thymus graft-restored animals. Therefore, thymectomized mice appear to retain a nonfunctioning, small, dense, lymphocyte population. Reconstitution of thymic-dependent in vitro reactivity was nearly complete when syngeneic, but not allogeneic or semisyngeneic thymus was employed. Occasional partial restoration did occur when F1 thymus was employed, but never when allogeneic thymus was grafted. The grafted thymus contained PHA and alloantigen-reactive cells in a large, less dense B layer subpopulation, whereas the restored animals, as in the case of normals, showed these reactivities to be a property of a small, more dense cell population
Nematic and Polar order in Active Filament Solutions
Using a microscopic model of interacting polar biofilaments and motor
proteins, we characterize the phase diagram of both homogeneous and
inhomogeneous states in terms of experimental parameters. The polarity of motor
clusters is key in determining the organization of the filaments in homogeneous
isotropic, polarized and nematic states, while motor-induced bundling yields
spatially inhomogeneous structures.Comment: 4 pages. 3 figure
Rheology of Active Filament Solutions
We study the viscoelasticity of an active solution of polar biofilaments and
motor proteins. Using a molecular model, we derive the constitutive equations
for the stress tensor in the isotropic phase and in phases with liquid
crystalline order. The stress relaxation in the various phases is discussed.
Contractile activity is responsible for a spectacular difference in the
viscoelastic properties on opposite sides of the order-disorder transition.Comment: 4 pages, 1 figur
Recasting women's stories : in the poetry of Felicia Hemans, Letitia Landon, and Christina Rossetti
The dissertation reads the poetry
written by three British women, Felicia Hemans, Letitia Landon, and
Christina Rossetti, exploring the ways they present, and recast,
conventional stories of women. The two Romantic poets make use of
narrative strategies to overturn the story’s meanings from within. The
Victorian poet, Rossetti, takes over their theme of love, reworking it
from the perspective of Christianity. Like her predecessors, Rossetti
presents her heroines as experiencing displacement and loss in society,
thereby upending traditional Christian views of women. Focusing on the
conventional figures featured in their poetry, such as Sappho, Corinne,
Eve and other female sufferers, the dissertation repeatedly pays
attention to a poetic genre the three women often adopt: the dramatic
monologue. The soliloquists in their poems occasionally address their
interlocutors as “friends”, asking them for commitment to their songs.
The three poets explore the relation between the poet and her audience,
her society, and their questioning persists, ever asking the reader to
give them back a response to their gift of poetry.LEI Universiteit LeidenModern and Contemporary Studie
CELLULAR RECOGNITION BY MOUSE LYMPHOCYTES IN VITRO : I. DEFINITION OF A NEW TECHNIQUE AND RESULTS OF STIMULATION BY PHYTOHEMAGGLUTININ AND SPECIFIC ANTIGENS
The media and culture conditions required for in vitro stimulation of mouse lymphoid cells are described. The medium was arginine-rich and contained heat-inactivated human serum. A component of the human sera necessary for stimulation of the cells was a natural mouse cell agglutinin, which affected both background stimulation and the degree of induced stimulation with phytohemagglutinin (PHA). Absorption of the agglutinin from the human serum rendered the medium incapable of sustaining DNA synthesis in the presence of PHA. The response to PHA of mouse spleen and thymus cells was age-dependent and, although this response was not present at birth, it rapidly rose to adult levels. Spleen cells from mice immunized with bacillus Calmette-Guérin (BCG) or sheep erythrocytes (SRBC) showed increased in vitro reactivity to added purified protein derivative (PPD) or SRBC stroma, dependent on the time of immunization. The dose response curve for the SRBC stroma stimulated, immune spleen cells is compatible with a theory of cell to cell interaction being necessary for an in vitro reaction to antigen. The possible role of the mouse cell agglutinin (AMLG) is discussed
Bridging the microscopic and the hydrodynamic in active filament solutions
Hydrodynamic equations for an isotropic solution of active polar filaments
are derived from a microscopic mean-field model of the forces exchanged between
motors and filaments. We find that a spatial dependence of the motor stepping
rate along the filament is essential to drive bundle formation. A number of
differences arise as compared to hydrodynamics derived (earlier) from a
mesoscopic model where relative filament velocities were obtained on the basis
of symmetry considerations. Due to the anisotropy of filament diffusion, motors
are capable of generating net filament motion relative to the solvent. The
effect of this new term on the stability of the homogeneous state is
investigated.Comment: 7 pages, 2 figures, submitted to Europhys. Let
Megabits secure key rate quantum key distribution
Quantum cryptography (QC) can provide unconditional secure communication
between two authorized parties based on the basic principles of quantum
mechanics. However, imperfect practical conditions limit its transmission
distance and communication speed. Here we implemented the differential phase
shift (DPS) quantum key distribution (QKD) with up-conversion assisted hybrid
photon detector (HPD) and achieved 1.3 M bits per second secure key rate over a
10-km fiber, which is tolerant against the photon number splitting (PNS)
attack, general collective attacks on individual photons, and any other known
sequential unambiguous state discrimination (USD) attacks.Comment: 14 pages, 4 figure
Generic phase diagram of active polar films
We study theoretically the phase diagram of compressible active polar gels
such as the actin network of eukaryotic cells. Using generalized hydrodynamics
equations, we perform a linear stability analysis of the uniform states in the
case of an infinite bidimensional active gel to obtain the dynamic phase
diagram of active polar films. We predict in particular modulated flowing
phases, and a macroscopic phase separation at high activity. This qualitatively
accounts for experimental observations of various active systems, such as
acto-myosin gels, microtubules and kinesins in vitro solutions, or swimming
bacterial colonies.Comment: 4 pages, 1 figur
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