12,189 research outputs found
Intestinal macromolecular transport supporting adaptive immunity
The gastrointestinal tract performs opposing functions of nutrient absorption, barrier maintenance, and the delivery of luminal substances for the appropriate induction of tolerogenic or protective adaptive immunity. The single-layer epithelium lining the gastrointestinal tract is central to each of these functions by facilitating the uptake and processing of nutrients, providing a physical and chemical barrier to potential pathogens, and delivering macromolecular substances to the immune system to initiate adaptive immune responses. Specific transport mechanisms allow nutrient uptake and the delivery of macromolecules to the immune system while maintaining the epithelial barrier. This review examines historical observations supporting macromolecular transport by the intestinal epithelium, recent insights into the transport of luminal macromolecules to promote adaptive immunity, and how this process is regulated to promote appropriate immune responses. Understanding how luminal macromolecules are delivered to the immune system and how this is regulated may provide insight into the pathophysiology of inflammatory diseases of the gastrointestinal tract and potential preventative or therapeutic strategies. Keywords: Antigen Transport, Mucosal Tolerance, Goblet Cell
Fractional vortices in the XY model with bonds
We define a new set of excitations in the XY model which we call ``fractional
vortices''. In the frustrated XY model containing bonds, we make the
ansatz that the ground state configurations can be characterized by pairs of
oppositely charged fractional vortices. For a chain of bonds, the ground
state energy and the phase configurations calculated on the basis of this
ansatz agree well with the results from direct numerical simulations. Finally,
we discuss the possible connection of these results to some recent experiments
by Kirtley {\it et al} [Phys. Rev. B {\bf 51}, R12057 (1995)] on high-T
superconductors where fractional flux trapping was observed along certain grain
boundaries.Comment: 13 pages, 14 figures included (.eps). No essential differences to
previous version, however more compact forma
J0041+3224: a new double-double radio galaxy
We report the discovery of a double-double radio galaxy (DDRG), J0041+3224,
with the Giant Metrewave Radio Telescope (GMRT) and subsequent high-frequency
observations with the Very Large Array (VLA). The inner and outer doubles are
aligned within about 4 deg and are reasonably collinear with the parent optical
galaxy. The outer double has a steeper radio spectrum compared with the inner
one. Using an estimated redshift of 0.45, the projected linear sizes of the
outer and inner doubles are 969 and 171 kpc respectively. The time scale of
interruption of jet activity has been estimated to be about 20 Myr, similar to
other known DDRGs. We have compiled a sample of known DDRGs, and have
re-examined the inverse correlation between the ratio of the luminosities of
the outer to the inner double and the size of the inner double, l_{in}. Unlike
the other DDRGs with l_{in} larger than about 50 kpc, the inner double of
J0041+3224 is marginally more luminous than the outer one. The two DDRGs with
l_{in} less than about a few kpc have a more luminous inner double than the
outer one, possibly due to a higher efficiency of conversion of beam energy as
the jets propagate through the dense interstellar medium. We have examined the
symmetry parameters and find that the inner doubles appear to be more
asymmetric in both its armlength and flux density ratios compared with the
outer doubles, although they appear marginally more collinear with the core
than the outer double. We discuss briefly possible implications of these
trends.Comment: Accepted for publication in MNRAS, 9 pages, 10 figure
SN1998bw: The Case for a Relativistic Shock
SN1998bw shot to fame by claims of association with GRB980425. Independent of
its presumed association with a GRB, this SN is unusual in its radio
properties. A simple interpretation of the unusually bright radio emission
leads us to the conclusion that there are two shocks in this SN: a slow moving
shock containing most of the ejecta and a relativistic shock (Gamma=2) which is
responsible for the radio emission. This is the first evidence for the
existence of relativistic shocks in supernovae. It is quite plausible that this
shock may produce high energy emission (at early times and by inverse Compton
scattering). As with other supernovae, we expect radio emission at much later
times powered primarily by the slow moving ejecta. This expectation has
motivated us to continue monitoring this unusual SN.Comment: A&A (in press), Rome GRB Symposium, Nov. 199
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