219 research outputs found
Modeling the QSO luminosity and spatial clustering at low redshifts
We investigate the ability of hierarchical models of QSO formation and
evolution to match the observed luminosity, number counts and spatial
clustering of quasars at redshift z<2. These models assume that the QSO
emission is triggered by galaxy mergers, that the mass of the central black
hole correlates with halo properties and that quasars shine at their Eddington
luminosity except, perhaps, during the very early stages of evolution. We find
that models based on simple analytic approximations successfully reproduce the
observed B-band QSO luminosity function at all redshifts, provided that some
mechanisms is advocated to quench mass accretion within haloes larger than
about 1e13 Msun that host bright quasars. These models also match the observed
strength of QSO clustering at z~0.8. At larger redshifts, however, they
underpredict the QSO biasing which, instead, is correctly reproduced by
semi-analytic models in which the halo merger history and associated BHs are
followed by Monte Carlo realizations of the merger hierarchy. We show that the
disagreement between the luminosity function predicted by semi-analytic models
and observations can be ascribed to the use of B-band data, which are a biased
tracer of the quasar population, due to obscuration.Comment: 13 pages, 9 figures. Accepted by MNRA
Cosmic reionization in a dynamic quintessence cosmology
In this paper we investigate the effects that a dynamic dark energy component
dominant in the universe at late epochs has on reionization. We follow the
evolution of HII regions with the analytic approach of Furlanetto and Oh (2005)
in two different universes for which we assume the Peebles and Ratra (2003) and
Brax and Martin (2000) quintessence models and we compare our results to the
LCDM scenario. We show that, for a fixed ionization efficiency, at the same
cosmological epoch the topology of bubbles is dominated by high-mass objects
and the characteristic size of the ionized regions is slightly smaller than in
the LCDM model, especially at the latest stages of reionization, due to the
higher recombination efficiency. As a consequence, the bubbles' `epoch of
overlap' happens earlier than in LCDM. Finally, we show how the different
evolution of the HII regions affects the transmission of the high-z QSO
spectra, reducing the Lyman flux absorption at small optical depths.Comment: 10 pages, minor changes to match the version accepted for publication
by MNRA
Masculinity, affect and the search for certainty in an age of precarity.
This article examines the affective dynamics of masculinity as a psychosocial process within a mediatised realm that includes parts of the informal cyberspace known as the Manosphere. Focusing on the relationship between masculinity and discourses of menâs rights, we explore the implications of the shifting psychosocial and political legacy of that relationship since the late 20th century for the shaping of masculinities today, where the psychosocial dynamics of victimisation and of being âdone toâ are recurring themes. We ground our analysis of contemporary masculinity through a case study of the online media coverage of the controversial Canadian Professor of Psychology, Jordan Peterson, and discuss the nature of his appeal for his followers on Reddit and YouTube. Peterson has become a celebrity public intellectual and his pronouncements on issues such as free speech, education and gender politics resonate for those men who feel confused and persecuted by the forces of feminism and identity politics. We argue that Petersonâs affective appeal is linked more widely to a public mood underpinned by a defensive wish for certainty in an age of precarity
The effects of primordial non-Gaussianity on the cosmological reionization
We investigate the effects of non-Gaussianity in the primordial density field
on the reionization history. We rely on a semi-analytic method to describe the
processes acting on the intergalactic medium (IGM), relating the distribution
of the ionizing sources to that of dark matter haloes. Extending previous work
in the literature, we consider models in which the primordial non-Gaussianity
is measured by the dimensionless non-linearity parameter f_NL, using the
constraints recently obtained from cosmic microwave background data. We predict
the ionized fraction and the optical depth at different cosmological epochs
assuming two different kinds of non-Gaussianity, characterized by a
scale-independent and a scale-dependent f_NL and comparing the results to those
for the standard Gaussian scenario. We find that a positive f_NL enhances the
formation of high-mass haloes at early epochs, when reionization begins, and,
as a consequence, the IGM ionized fraction can grow by a factor up to 5 with
respect to the corresponding Gaussian model. The increase of the filling factor
has a small impact on the reionization optical depth and is of order ~ 10 per
cent if a scale-dependent non-Gaussianity is assumed. Our predictions for
non-Gaussian models are in agreement with the latest WMAP results within the
error bars, but a higher precision is required to constrain the scale
dependence of non-Gaussianity.Comment: 10 pages, 8 figures, minor changes to match the version accepted for
publication by MNRA
HERG potassium channels are constitutively expressed in primary human acute myeloid leukemias and regulate cell proliferation of normal and leukemic hemopoietic progenitors
An important target in the understanding of the pathogenesis of acute myeloid leukemias (AML) relies on deciphering the molecular features of normal and leukemic hemopoietic progenitors. In particular, the analysis of the mechanisms involved in the regulation of cell proliferation is decisive for the establishment of new targeted therapies. To gain further insight into this topic we report herein a novel approach by analyzing the role of HERG K+ channels in the regulation of hemopoietic cell proliferation. These channels, encoded by the human ether-a-go-go-related gene (herg), belong to a family of K, channels, whose role in oncogenesis has been recently demonstrated. We report here that herg is switched off in normal peripheral blood mononuclear cells (PBMNC) as well as in circulating CD34(+) cells, however, it is rapidly turned on in the latter upon induction of the mitotic cycle. Moreover, herg appears to be constitutively activated in leukemic cell lines as well as in the majority of circulating blasts from primary AML. Evidence is also provided that HERG channel activity regulates cell proliferation in stimulated CD34(+) as well as in blast cells from AML patients. These results open new perspectives on the pathogenetic role of HERG K+ channels in leukemias
Herg1 gene and HERG1 protein are overespressed in colorectal cancers and regulate cell invasion of tumor cells
The acquisition of the capacity to invade surrounding tissues confers a more malignant phenotype to tumor cells and is necessary for the establishment of metastases. The understanding of the molecular mechanisms underlying cell invasion in human solid tumors such as colorectal cancers could provide not only more sensitive prognostic analyses but also novel molecular targets for cancer therapy.We report in this article that K+ ion channels belonging to the HERG family are important determinants for the acquisition of an invasive phenotype in colorectal cancers. The herg1 gene and HERG1 protein are expressed in many colon cancer cell lines, and the activity of HERG channels modulates colon cancer cell invasiveness. Moreover, the amount of HERG1 protein expressed on the plasma membrane is directly related to the invasive phenotype of colon cancer cells.Finally, both the herg1 gene and HERG1 protein were expressed in a high percentage of primary human colorectal cancers, with the highest incidence occurring in metastatic cancers, whereas no expression could be detected either in normal colonic mucosa or in adenomas
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