34 research outputs found
The variation of G in a negatively curved space-time
Scalar-tensor (ST) gravity theories provide an appropriate theoretical
framework for the variation of Newton's fundamental constant, conveyed by the
dynamics of a scalar-field non-minimally coupled to the space-time geometry.
The experimental scrutiny of scalar-tensor gravity theories has led to a
detailed analysis of their post-newtonian features, and is encapsulated into
the so-called parametrised post-newtonian formalism (PPN). Of course this
approach can only be applied whenever there is a newtonian limit, and the
latter is related to the GR solution that is generalized by a given ST solution
under consideration. This procedure thus assumes two hypothesis: On the one
hand, that there should be a weak field limit of the GR solution; On the other
hand that the latter corresponds to the limit case of given ST solution. In the
present work we consider a ST solution with negative spatial curvature. It
generalizes a general relativistic solution known as being of a degenerate
class (A) for its unusual properties. In particular, the GR solution does not
exhibit the usual weak field limit in the region where the gravitational field
is static. The absence of a weak field limit for the hyperbolic GR solution
means that such limit is also absent for comparison with the ST solution, and
thus one cannot barely apply the PPN formalism. We therefore analyse the
properties of the hyperbolic ST solution, and discuss the question o defining a
generalised newtonian limit both for the GR solution and for the purpose of
contrasting it with the ST solution. This contributes a basic framework to
build up a parametrised pseudo-newtonian formalism adequate to test ST
negatively curved space-times.Comment: 7 pages, 5 figures. Contribution to the Joint European and National
Astronomy Meeting (JENAM) 2010; based on a talk given by JPM in the "From
Varying Couplings to Fundamental Physics" Symposiu
Toll-like receptor 4 signaling in liver injury and hepatic fibrogenesis
Toll-like receptors (TLRs) are a family of transmembrane pattern recognition receptors (PRR) that play a key role in innate and adaptive immunity by recognizing structural components unique to bacteria, fungi and viruses. TLR4 is the most studied of the TLRs, and its primary exogenous ligand is lipopolysaccharide, a component of Gram-negative bacterial walls. In the absence of exogenous microbes, endogenous ligands including damage-associated molecular pattern molecules from damaged matrix and injured cells can also activate TLR4 signaling. In humans, single nucleotide polymorphisms of the TLR4 gene have an effect on its signal transduction and on associated risks of specific diseases, including cirrhosis. In liver, TLR4 is expressed by all parenchymal and non-parenchymal cell types, and contributes to tissue damage caused by a variety of etiologies. Intact TLR4 signaling was identified in hepatic stellate cells (HSCs), the major fibrogenic cell type in injured liver, and mediates key responses including an inflammatory phenotype, fibrogenesis and anti-apoptotic properties. Further clarification of the function and endogenous ligands of TLR4 signaling in HSCs and other liver cells could uncover novel mechanisms of fibrogenesis and facilitate the development of therapeutic strategies
Occurrence and Functions of PACAP in the Placenta
Pituitary adenylate cyclase activating polypeptide (PACAP) is an endogenous neuropeptide with a widespread distribution both in the nervous system and peripheral organs. The peptide is also present in the female gonadal
system, indicating its role in reproductive functions. While a lot of data are known on PACAP-induced effects in oogenesis and in the regulation of gonadotropin secretion at pituitary level, its placental effects are somewhat
neglected in spite of the documented implantation deficit in mice lacking endogenous PACAP. The aim of the present review is to give a brief summary on the occurrence and actions of PACAP and its receptors in the placenta.
Radioimmunoassay (RIA) measurements revealed increased serum PACAP levels during the third trimester and several changes in placental PACAP content in obstetrical pathological conditions, further supporting the function
of PACAP during pregnancy. Both the peptide and its receptors have been shown in different parts of the
placenta and the umbilical cord. PACAP influences blood vessel and smooth muscle contractility of the uteroplacental unit and is involved in regulation of local hormone secretion. The effects of PACAP on trophoblast cells have been mainly studied in vitro. Effects of PACAP on cell survival, angiogenesis
and invasion/proliferation have been described in different trophoblast cell lines. PACAP increases proliferation and decreases invasion in proliferative
extravillous trophoblast cells, but not in primary trophoblast cells, where PACAP decreased the secretion of various angiogenic markers. PACAP pretreatment enhances survival of non-tumorous primary trophoblast cells exposed to oxidative stress, but it does not influence the cell death-inducing effects of methotrexate in proliferative extravillous cytotrophoblast cells. Interestingly, PACAP has pro-apoptotic effect in choriocarcinoma cells suggesting that the effect of PACAP depends on the type of trophoblast cells. These data strongly support that PACAP plays a role in normal and pathological pregnancies and our review provides an overview of currently available experimental data worth to be further investigated to elucidate the exact role of this peptide in the placenta
Risk assessment and management of individuals convicted of a sexual offence in the UK
The UK has seen changes in sexual abuse policy and practice over the last 10 – 15 years that have been driven by austerity, risk management, public protection and the socio-political climate; these changes have been problematic and challenging as well as positive and proactive. In recent years there has been an increasing move amongst professionals, practitioners and policy makers stating to think of sexual abuse as more than just a criminal justice issue, but reframing it as a public health and criminal justice issue; although this has not filtered down to the public and the media yet. This article will look at the current status of sexual abuse policy and practice in the UK, what has changed, its impact and where it is moving in the future