The Hubble Constant

I review the current state of determinations of the Hubble constant, which gives the length scale of the Universe by relating the expansion velocity of objects to their distance. There are two broad categories of measurements. The first uses individual astrophysical objects which have some property that allows their intrinsic luminosity or size to be determined, or allows the determination of their distance by geometric means. The second category comprises the use of all-sky cosmic microwave background, or correlations between large samples of galaxies, to determine information about the geometry of the Universe and hence the Hubble constant, typically in a combination with other cosmological parameters. Many, but not all, object-based measurements give $H_0$ values of around 72-74km/s/Mpc , with typical errors of 2-3km/s/Mpc. This is in mild discrepancy with CMB-based measurements, in particular those from the Planck satellite, which give values of 67-68km/s/Mpc and typical errors of 1-2km/s/Mpc. The size of the remaining systematics indicate that accuracy rather than precision is the remaining problem in a good determination of the Hubble constant. Whether a discrepancy exists, and whether new physics is needed to resolve it, depends on details of the systematics of the object-based methods, and also on the assumptions about other cosmological parameters and which datasets are combined in the case of the all-sky methods.Comment: Extensively revised and updated since the 2007 version: accepted by Living Reviews in Relativity as a major (2014) update of LRR 10, 4, 200

Myoferlin Depletion in Breast Cancer Cells Promotes Mesenchymal to Epithelial Shape Change and Stalls Invasion

Myoferlin (MYOF) is a mammalian ferlin protein with homology to ancestral Fer-1, a nematode protein that regulates spermatic membrane fusion, which underlies the amoeboid-like movements of its sperm. Studies in muscle and endothelial cells have reported on the role of myoferlin in membrane repair, endocytosis, myoblast fusion, and the proper expression of various plasma membrane receptors. In this study, using an in vitro human breast cancer cell model, we demonstrate that myoferlin is abundantly expressed in invasive breast tumor cells. Depletion of MYOF using lentiviral-driven shRNA expression revealed that MDA-MB-231 cells reverted to an epithelial morphology, suggesting at least some features of mesenchymal to epithelial transition (MET). These observations were confirmed by the down-regulation of some mesenchymal cell markers (e.g., fibronectin and vimentin) and coordinate up-regulation of the E-cadherin epithelial marker. Cell invasion assays using Boyden chambers showed that loss of MYOF led to a significant diminution in invasion through Matrigel or type I collagen, while cell migration was unaffected. PCR array and screening of serum-free culture supernatants from shRNAMYOF transduced MDA-MB-231 cells indicated a significant reduction in the steady-state levels of several matrix metalloproteinases. These data when considered in toto suggest a novel role of MYOF in breast tumor cell invasion and a potential reversion to an epithelial phenotype upon loss of MYOF

Toughenability of Nylon-6 with CaCO3 filler particles: new findings and general principles

The mechanical behavior of Nylon-6 blends modified by two types of CaCO3 particles of 0.7 and 3.5 µm diameter with particle volume fractions ranging from 0.05 to 0.28 was studied between -30 and 60°C in slow tension, and at 20°C in bending impact. Additional experiments were also carried out at 20°C to determine the plane stress fracture toughness of the blends in Single-Edge-Cracked-Plate configurations; all fracture behavior was followed extensively by SEM fractography. Experiments demonstrated that the particles are attached to the matrix only through a differential thermal–contraction–pressure and particle separation preceded plastic response in all instances. As a consequence of the above ease in debonding, the yield strengths of the blends drop systematically with increasing particle concentration. In slow tension all blends showed a well defined plastic stretching response following necking, but the stable post-necking stretch was severely limited by an overabundance of large particle clusters which acted as super-critical flaws to initiate premature termination of stretching. The present findings show that in these blends with their high plastic resistances, critical flaw sizes that trigger brittle response are in the range of 8–12 µm, well under the sizes of many of the particle clusters encountered in the blends. In contrast with the attractively tough response of the rubber modified Nylon-6 blends of Murato lu et al. [Polymer 36 (1995) 921; Polymer 36 (1995) 4771] all present blends showed only disappointing brittle behavior under Izod impact conditions. This was traced to the development of substantial levels of triaxial tensile stresses arising from only partial separation of rigid particles from the matrix in the early phases of impact response. Based on the new findings a number of general principles on toughenability with both compliant and rigid particle modification are presented and supported by simple micro mechanical models. Author Keywords: Nylon-6/CaCO3 blends; Toughenability of brittle polymers; Toughenability with stiff-particle