7 research outputs found
Early Universe Dynamics in Semi-Classical Loop Quantum Cosmology
Within the framework of loop quantum cosmology, there exists a semi-classical
regime where spacetime may be approximated in terms of a continuous manifold,
but where the standard Friedmann equations of classical Einstein gravity
receive non-perturbative quantum corrections. An approximate, analytical
approach to studying cosmic dynamics in this regime is developed for both
spatially flat and positively-curved isotropic universes sourced by a
self-interacting scalar field. In the former case, a direct correspondence
between the classical and semi-classical field equations can be established
together with a scale factor duality that directly relates different expanding
and contracting universes. Some examples of non-singular, bouncing cosmologies
are presented together with a scaling, power-law solution.Comment: 14 pages, In Press, JCA
Cosmological evolution of general scalar fields in a brane-world cosmology
We study the cosmology of a general scalar field and barotropic fluid during
the early stage of a brane-world where the Friedmann constraint is dominated by
the square of the energy density. Assuming both the scalar field and fluid are
confined to the brane, we find a range of behaviour depending on the form of
the potential. Generalising an approach developed for a standard Friedmann
cosmology, in \cite{delaMacorra:1999ff}, we show that the potential dependence
can be described through a parameter , where is the 5-dimensional Planck mass, is
the Hubble parameter and . For the case where
asymptotes to zero, we show that the solution exhibits stable
inflationary behaviour. On the other hand if it approaches a finite constant,
then . For
asymptotically, we find examples where it does so both with and without
oscillating. In the latter case, the barotropic fluid dominates the scalar
filed asymptotically. Finally we point out an interesting duality which leads
to identical evolution equations in the high energy dominated regime
and the low energy dominated regime.Comment: 10 pages, 3 figure
Tumor imaging and targeting potential of an Hsp70-derived 14-mer peptide
We have previously used a unique mouse monoclonal antibody cmHsp70.1 to demonstrate the selective presence of a membrane-bound form of Hsp70 (memHsp70) on a variety of leukemia cells and on single cell suspensions derived from solid tumors of different entities, but not on non-transformed cells or cells from corresponding 'healthy' tissue. This antibody can be used to image tumors in vivo and target them for antibody-dependent cellular cytotoxicity. Tumor-specific expression of memHsp70 therefore has the potential to be exploited for theranostic purposes. Given the advantages of peptides as imaging and targeting agents, this study assessed whether a 14-mer tumor penetrating peptide (TPP; TKDNNLLGRFELSG), the sequence of which is derived from the oligomerization domain of Hsp70 which is expressed on the cell surface of tumor cells, can also be used for targeting membrane Hsp70 positive (memHsp70+) tumor cells, in vitro.The specificity of carboxy-fluorescein (CF-) labeled TPP (TPP) to Hsp70 was proven in an Hsp70 knockout mammary tumor cell system. TPP specifically binds to different memHsp70+ mouse and human tumor cell lines and is rapidly taken up via endosomes. Two to four-fold higher levels of CF-labeled TPP were detected in MCF7 (82% memHsp70+) and MDA-MB-231 (75% memHsp70+) cells compared to T47D cells (29% memHsp70+) that exhibit a lower Hsp70 membrane positivity. After 90 min incubation, TPP co-localized with mitochondrial membranes in memHsp70+ tumors. Although there was no evidence that any given vesicle population was specifically localized, fluorophore-labeled cmHsp70.1 antibody and TPP preferentially accumulated in the proximity of the adherent surface of cultured cells. These findings suggest a potential association between membrane Hsp70 expression and cytoskeletal elements that are involved in adherence, the establishment of intercellular synapses and/or membrane reorganization.This study demonstrates the specific binding and rapid internalization of TPP by tumor cells with a memHsp70+ phenotype. TPP might therefore have potential for targeting and imaging the large proportion of tumors (âŒ50%) that express memHsp70
Modulation of immune responses by targeting CD169/Siglec-1 with the glycan ligand
A fundamental role in the plant-bacterium interaction for
Gram-negative phytopathogenic bacteria is played by membrane
constituents, such as proteins, lipopoly- or lipooligosaccharides
(LPS, LOS) and Capsule Polysaccharides (CPS).
In the frame of the understanding the molecular basis of plant bacterium interaction, the Gram-negative bacterium Agrobacterium vitis was selected in this study. It is a phytopathogenic member of the Rhizobiaceae family and it induces the crown gall disease selectively on grapevines (Vitis vinifera).
A. vitis wild type strain F2/5, and its mutant in the quorum
sensing gene ÎaviR, were studied. The wild type produces biosurfactants; it is considered a model to study surface motility, and it causes necrosis on grapevine roots and HR (Hypersensitive
Response) on tobacco. Conversely, the mutant does not show any
surface motility and does not produce any surfactant material;
additionally, it induces neither necrosis on grape, nor HR on
tobacco. Therefore, the two strains were analyzed to shed some
light on the QS regulation of LOS structure and the consequent
variation, if any, on HR response. LOS from both strains were isolated and characterized: the two LOS structures maintained several common features and differed for few others.
With regards to the common patterns, firstly: the Lipid A region
was not phosphorylated at C4 of the non reducing glucosamine
but glycosylated by an uronic acid (GalA) unit, secondly: a third
Kdo and the rare Dha (3-deoxy-lyxo-2-heptulosaric acid) moiety
was present.
Importantly, the third Kdo and the Dha residues were substituted
by rhamnose in a not stoichiometric fashion, giving four different
oligosaccharide species.
The proportions among these four species, is the key difference
between the LOSs from both the two bacteria.
LOS from both strains and Lipid A from wild type A. vitis are
now examined for their HR potential in tobacco leaves and grapevine roots