282 research outputs found
ADI splitting schemes for a fourth-order nonlinear partial differential equation from image processing
We present directional operator splitting schemes for the numerical solution of a fourth-order, nonlinear partial differential evolution equation which arises in image processing. This equation constitutes the H−1-gradient flow of the total variation and represents a prototype of higher-order equations of similar type which are popular in imaging for denoising, deblurring and inpainting problems. The efficient numerical solution of this equation is very challenging due to the stiffness of most numerical schemes. We show that the combination of directional splitting schemes with implicit time-stepping provides a stable and computationally cheap numerical realisation of the equation
Some doubts on the validity of the foreground Galactic contribution subtraction from microwave anisotropies
The Galactic foreground contamination in CMBR anisotropies, especially from
the dust component, is not easily separable from the cosmological or
extragalactic component. In this paper, some doubts will be raised concerning
the validity of the methods used to date to remove Galactic dust emission in
order to show that none of them achieves its goal.
First, I review the recent bibliography on the topic and discuss critically
the methods of foreground subtraction: the cross-correlation with templates,
analysis assuming the spectral shape of the Galactic components, the "maximum
entropy method", "internal linear combination", and "wavelet-based high
resolution fitting of internal templates". Second, I analyse the galactic
latitude dependence from WMAP data. The frequency dependence is discussed with
the data in the available literature. The result is that all methods of
subtracting the Galactic contamination are inaccurate. The galactic latitude
dependence analysis or the frequency dependence of the anisotropies in the
range 50-250 GHz put a constraint on the maximum Galactic contribution in the
power spectrum to be less than a ~10% (68% C. L.) for a ~1 degree scale, and
possibly higher for larger scales.
The origin of most of the signal in the CMBR anisotropies is not Galactic. In
any case, the subtraction of the Galaxy is not accurate enough to allow a
"precision Cosmology"; other sources of contamination (extragalactic, solar
system) are also present.Comment: 24 pages, 1 figure, accepted to be published in J. Astrophys. Ast
LoCuSS: Testing hydrostatic equilibrium in galaxy clusters
We test the assumption of hydrostatic equilibrium in an X-ray luminosity selected sample of 50 galaxy clusters at from the Local Cluster Substructure Survey (LoCuSS). Our weak-lensing measurements of control systematic biases to sub-4 per cent, and our hydrostatic measurements of the same achieve excellent agreement between XMM-Newton and Chandra. The mean ratio of X-ray to lensing mass for these 50 clusters is , and for the 44 clusters also detected by Planck, the mean ratio of Planck mass estimate to LoCuSS lensing mass is . Based on a careful like-for-like analysis, we find that LoCuSS, the Canadian Cluster Comparison Project (CCCP), and Weighing the Giants (WtG) agree on at . This small level of hydrostatic bias disagrees at with the level required to reconcile Planck cosmology results from the cosmic microwave background and galaxy cluster counts
Nonthermal radiation mechanisms
In this paper we review the possible radiation mechanisms for the observed
non-thermal emission in clusters of galaxies, with a primary focus on the radio
and hard X-ray emission. We show that the difficulty with the non-thermal,
non-relativistic Bremsstrahlung model for the hard X-ray emission, first
pointed out by Petrosian (2001) using a cold target approximation, is somewhat
alleviated when one treats the problem more exactly by including the fact that
the background plasma particle energies are on average a factor of 10 below the
energy of the non-thermal particles. This increases the lifetime of the
non-thermal particles, and as a result decreases the extreme energy
requirement, but at most by a factor of three. We then review the synchrotron
and so-called inverse Compton emission by relativistic electrons, which when
compared with observations can constrain the value of the magnetic field and
energy of relativistic electrons. This model requires a low value of the
magnetic field which is far from the equipartition value. We briefly review the
possibilities of gamma-ray emission and prospects for GLAST observations. We
also present a toy model of the non-thermal electron spectra that are produced
by the acceleration mechanisms discussed in an accompanying paper.Comment: 17 pages, 6 figures, accepted for publication in Space Science
Reviews, special issue "Clusters of galaxies: beyond the thermal view",
Editor J.S. Kaastra, Chapter 10; work done by an international team at the
International Space Science Institute (ISSI), Bern, organised by J.S.
Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke
LoCuSS: Testing hydrostatic equilibrium in galaxy clusters
We test the assumption of hydrostatic equilibrium in an X-ray luminosity selected sample of 50 galaxy clusters at from the Local Cluster Substructure Survey (LoCuSS). Our weak-lensing measurements of control systematic biases to sub-4 per cent, and our hydrostatic measurements of the same achieve excellent agreement between XMM-Newton and Chandra. The mean ratio of X-ray to lensing mass for these 50 clusters is , and for the 44 clusters also detected by Planck, the mean ratio of Planck mass estimate to LoCuSS lensing mass is . Based on a careful like-for-like analysis, we find that LoCuSS, the Canadian Cluster Comparison Project (CCCP), and Weighing the Giants (WtG) agree on at . This small level of hydrostatic bias disagrees at with the level required to reconcile Planck cosmology results from the cosmic microwave background and galaxy cluster counts
Numerical simulations of the Warm-Hot Intergalactic Medium
In this paper we review the current predictions of numerical simulations for
the origin and observability of the warm hot intergalactic medium (WHIM), the
diffuse gas that contains up to 50 per cent of the baryons at z~0. During
structure formation, gravitational accretion shocks emerging from collapsing
regions gradually heat the intergalactic medium (IGM) to temperatures in the
range T~10^5-10^7 K. The WHIM is predicted to radiate most of its energy in the
ultraviolet (UV) and X-ray bands and to contribute a significant fraction of
the soft X-ray background emission. While O VI and C IV absorption systems
arising in the cooler fraction of the WHIM with T~10^5-10^5.5 K are seen in
FUSE and HST observations, models agree that current X-ray telescopes such as
Chandra and XMM-Newton do not have enough sensitivity to detect the hotter
WHIM. However, future missions such as Constellation-X and XEUS might be able
to detect both emission lines and absorption systems from highly ionised atoms
such as O VII, O VIII and Fe XVII.Comment: 18 pages, 5 figures, accepted for publication in Space Science
Reviews, special issue "Clusters of galaxies: beyond the thermal view",
Editor J.S. Kaastra, Chapter 14; work done by an international team at the
International Space Science Institute (ISSI), Bern, organised by J.S.
Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke
Dnmt3a regulates myeloproliferation and liver-specific expansion of hematopoietic stem and progenitor cells
DNMT3A mutations are observed in myeloid malignancies, including myeloproliferative neoplasms (MPN), myelodysplastic syndromes (MDS), and acute myeloid leukemia (AML). Transplantation studies have elucidated an important role for Dnmt3a in stem cell self-renewal and in myeloid differentiation. Here we investigated the impact of conditional hematopoietic Dnmt3a loss on disease phenotype in primary mice. Mx1-Cre-mediated Dnmt3a ablation led to the development of a lethal, fully penetrant myeloproliferative neoplasm with myelodysplasia (MDS/MPN) characterized by peripheral cytopenias and by marked, progressive hepatomegaly. We detected expanded stem/progenitor populations in the liver of Dnmt3a-ablated mice. The MDS/MPN induced by Dnmt3a ablation was transplantable, including the marked hepatomegaly. Homing studies showed that Dnmt3a-deleted bone marrow cells preferentially migrated to the liver. Gene expression and DNA methylation analyses of progenitor cell populations identified differential regulation of hematopoietic regulatory pathways, including fetal liver hematopoiesis transcriptional programs. These data demonstrate that Dnmt3a ablation in the hematopoietic system leads to myeloid transformation in vivo, with cell autonomous aberrant tissue tropism and marked extramedullary hematopoiesis (EMH) with liver involvement. Hence, in addition to the established role of Dnmt3a in regulating self-renewal, Dnmt3a regulates tissue tropism and limits myeloid progenitor expansion in vivo
Expression of p89c-Mybex9b, an alternatively spliced form of c-Myb, is required for proliferation and survival of p210BCR/ABL-expressing cells
The c-Myb gene encodes the p75c-Myb isoform and less-abundant proteins generated by alternatively spliced transcripts. Among these, the best known is pc-Mybex9b, which contains 121 additional amino acids between exon 9 and 10, in a domain involved in protein–protein interactions and negative regulation. In hematopoietic cells, expression of pc-Mybex9b accounts for 10–15% of total c-Myb; these levels may be biologically relevant because modest changes in c-Myb expression affects proliferation and survival of leukemic cells and lineage choice and frequency of normal hematopoietic progenitors. In this study, we assessed biochemical activities of pc-Mybex9b and the consequences of perturbing its expression in K562 and primary chronic myeloid leukemia (CML) progenitor cells. Compared with p75c-Myb, pc-Mybex9b is more stable and more effective in transactivating Myb-regulated promoters. Ectopic expression of pc-Mybex9b enhanced proliferation and colony formation and reduced imatinib (IM) sensitivity of K562 cells; conversely, specific downregulation of pc-Mybex9b reduced proliferation and colony formation, enhanced IM sensitivity of K562 cells and markedly suppressed colony formation of CML CD34+ cells, without affecting the levels of p75c-Myb. Together, these studies indicate that expression of the low-abundance pc-Mybex9b isoform has an important role for the overall biological effects of c-Myb in BCR/ABL-transformed cells
Interplay of Non-Relativistic and Relativistic Effects in Neutrino Oscillations
A theoretical structure that involves neutrino mass eigenstates at non
relativistic as well as relativistic energies is presented. Using this
framework, we find that if the particle X, with mass 33.9 MeV, of the KARMEN
collaboration anomaly is identified with the third neutrino mass eigenstate,
then the present limit of 23 MeV upper bound on the tau neutrino mass implies
|U_{\tau 3}| < 0.82.Comment: Revtex 3.0, 12 page
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