Harnack inequality and regularity for degenerate quasilinear elliptic equations

We prove Harnack inequality and local regularity results for weak solutions of a quasilinear degenerate equation in divergence form under natural growth conditions. The degeneracy is given by a suitable power of a strong $A_\infty$ weight. Regularity results are achieved under minimal assumptions on the coefficients and, as an application, we prove $C^{1,\alpha}$ local estimates for solutions of a degenerate equation in non divergence form

Radiomics : the facts and the challenges of image analysis

Radiomics is an emerging translational field of research aiming to extract mineable high-dimensional data from clinical images. The radiomic process can be divided into distinct steps with definable inputs and outputs, such as image acquisition and reconstruction, image segmentation, features extraction and qualification, analysis, and model building. Each step needs careful evaluation for the construction of robust and reliable models to be transferred into clinical practice for the purposes of prognosis, non-invasive disease tracking, and evaluation of disease response to treatment. After the definition of texture parameters (shape features; first-, second-, and higher-order features), we briefly discuss the origin of the term radiomics and the methods for selecting the parameters useful for a radiomic approach, including cluster analysis, principal component analysis, random forest, neural network, linear/logistic regression, and other. Reproducibility and clinical value of parameters should be firstly tested with internal cross-validation and then validated on independent external cohorts. This article summarises the major issues regarding this multi-step process, focussing in particular on challenges of the extraction of radiomic features from data sets provided by computed tomography, positron emission tomography, and magnetic resonance imaging

miRNA-126 Orchestrates an Oncogenic Program in B Cell Precursor Acute Lymphoblastic Leukemia

MicroRNA (miRNA)-126 is a known regulator of hematopoietic stem cell quiescence. We engineered murine hematopoiesis to express miRNA-126 across all differentiation stages. Thirty percent of mice developed monoclonal B cell leukemia, which was prevented or regressed when a tetracycline-repressible miRNA-126 cassette was switched off. Regression was accompanied by upregulation of cell-cycle regulators and B cell differentiation genes, and downregulation of oncogenic signaling pathways. Expression of dominant-negative p53 delayed blast clearance upon miRNA-126 switch-off, highlighting the relevance of p53 inhibition in miRNA-126 addiction. Forced miRNA-126 expression in mouse and human progenitors reduced p53 transcriptional activity through regulation of multiple p53-related targets. miRNA-126 is highly expressed in a subset of human B-ALL, and antagonizing miRNA-126 in ALL xenograft models triggered apoptosis and reduced disease burden

Gathering dust : A galaxy-wide study of dust emission from cloud complexes in NGC 300

© 2018 ESO. Reproduced with permission from Astronomy & Astrophysics. Content in the UH Research Archive is made available for personal research, educational, and non-commercial purposes only. Unless otherwise stated, all content is protected by copyright, and in the absence of an open license, permissions for further re-use should be sought from the publisher, the author, or other copyright holder.Aims. We use multi-band observations by the Herschel Space Observatory to study the dust emission properties of the nearby spiral galaxy NGC 300. We compile a first catalogue of the population of giant dust clouds (GDCs) in NGC 300, including temperature and mass estimates, and give an estimate of the total dust mass of the galaxy. Methods. We carried out source detection with the multiwavelength source extraction algorithm getsources. We calculated physical properties, including mass and temperature, of the GDCs from five-band Herschel PACS and SPIRE observations from 100 to 500 μm; the final size and mass estimates are based on the observations at 250 μm that have an effective spatial resolution of ~170 pc. We correlated our final catalogue of GDCs to pre-existing catalogues of HII regions to infer the number of GDCs associated with high-mass star formation and determined the Hα emission of the GDCs. Results. Our final catalogue of GDCs includes 146 sources, 90 of which are associated with known HII regions. We find that the dust masses of the GDCs are completely dominated by the cold dust component and range from ~1.1 × 10 3 to 1.4 × 10 4 M. The GDCs have effective temperatures of ~13-23 K and show a distinct cold dust effective temperature gradient from the centre towards the outer parts of the stellar disk. We find that the population of GDCs in our catalogue constitutes ~16% of the total dust mass of NGC 300, which we estimate to be about 5.4 × 10 6 M. At least about 87% of our GDCs have a high enough average dust mass surface density to provide sufficient shielding to harbour molecular clouds. We compare our results to previous pointed molecular gas observations in NGC 300 and results from other nearby galaxies and also conclude that it is very likely that most of our GDCs are associated with complexes of giant molecular clouds.Peer reviewe

JINGLE – IV. Dust, H I gas and metal scaling laws in the local Universe

Scaling laws of dust, Hi gas and metal mass with stellar mass, specific star formation rate and metallicity are crucial to our understanding of the buildup of galaxies through their enrichment with metals and dust. In this work, we analyse how the dust and metal content varies with specific gas mass (MHI/M?) across a diverse sample of 423 nearby galaxies. The observed trends are interpreted with a set of Dust and Element evolUtion modelS (DEUS) – including stellar dust production, grain growth, and dust destruction – within a Bayesian framework to enable a rigorous search of the multi-dimensional parameter space. We find that these scaling laws for galaxies with −1.0 . logMHI/M? . 0 can be reproduced using closed-box models with high fractions (37-89%) of supernova dust surviving a reverse shock, relatively low grain growth efficiencies (=30-40), and long dust lifetimes (1-2Gyr). The models have present-day dust masses with similar contributions from stellar sources (50-80%) and grain growth (20-50%). Over the entire lifetime of these galaxies, the contribution from stardust (>90%) outweighs the fraction of dust grown in the interstellar medium (<10%). Our results provide an alternative for the chemical evolution models that require extremely low supernova dust production efficiencies and short grain growth timescales to reproduce local scaling laws, and could help solving the conundrum on whether or not grains can grow efficiently in the interstellar medium

JCMT POL-2 and BISTRO Survey Observations of Magnetic Fields in the L1689 Molecular Cloud

We present 850 μm polarization observations of the L1689 molecular cloud, part of the nearby Ophiuchus molecular cloud complex, taken with the POL-2 polarimeter on the James Clerk Maxwell Telescope (JCMT). We observe three regions of L1689: the clump L1689N which houses the IRAS 16293-2433 protostellar system, the starless clump SMM-16, and the starless core L1689B. We use the Davis–Chandrasekhar–Fermi method to estimate plane-of-sky field strengths of 366 ± 55 μG in L1689N, 284 ± 34 μG in SMM-16, and 72 ± 33 μG in L1689B, for our fiducial value of dust opacity. These values indicate that all three regions are likely to be magnetically transcritical with sub-Alfvénic turbulence. In all three regions, the inferred mean magnetic field direction is approximately perpendicular to the local filament direction identified in Herschel Space Telescope observations. The core-scale field morphologies for L1689N and L1689B are consistent with the cloud-scale field morphology measured by the Planck Space Observatory, suggesting that material can flow freely from large to small scales for these sources. Based on these magnetic field measurements, we posit that accretion from the cloud onto L1689N and L1689B may be magnetically regulated. However, in SMM-16, the clump-scale field is nearly perpendicular to the field seen on cloud scales by Planck, suggesting that it may be unable to efficiently accrete further material from its surroundings

The JCMT BISTRO-2 Survey: The Magnetic Field in the Center of the Rosette Molecular Cloud

We present the first 850 μm polarization observations in the most active star-forming site of the Rosette Molecular Cloud (d ~ 1.6 kpc) in the wall of the Rosette Nebula, imaged with the SCUBA-2/POL-2 instruments of the James Clerk Maxwell telescope, as part of the B-Fields In Star-forming Region Observations 2 (BISTRO-2) survey. From the POL-2 data we find that the polarization fraction decreases with the 850 μm continuum intensity with α = 0.49 ± 0.08 in the p ∝ I−α relation, which suggests that some fraction of the dust grains remain aligned at high densities. The north of our 850 μm image reveals a "gemstone ring" morphology, which is a ~1 pc diameter ring-like structure with extended emission in the "head" to the southwest. We hypothesize that it might have been blown by feedback in its interior, while the B-field is parallel to its circumference in most places. In the south of our SCUBA-2 field the clumps are apparently connected with filaments that follow infrared dark clouds. Here, the POL-2 magnetic field orientations appear bimodal with respect to the large-scale Planck field. The mass of our effective mapped area is ~174 M⊙, which we calculate from 850 μm flux densities. We compare our results with masses from large-scale emission-subtracted Herschel 250 μm data and find agreement within 30%. We estimate the plane-of-sky B-field strength in one typical subregion using the Davis–Chandrasekhar–Fermi technique and find 80 ± 30 μG toward a clump and its outskirts. The estimated mass-to-flux ratio of λ = 2.3 ± 1.0 suggests that the B-field is not sufficiently strong to prevent gravitational collapse in this subregion

The JCMT BISTRO Survey: Evidence for Pinched Magnetic Fields in Quiescent Filaments of NGC 1333

We investigate the internal 3D magnetic structure of dense interstellar filaments within NGC 1333 using polarization data at 850 μm from the B-fields In STar-forming Region Observations survey at the James Clerk Maxwell Telescope. Theoretical models predict that the magnetic field lines in a filament will tend to be dragged radially inward (i.e., pinched) toward the central axis due to the filament's self-gravity. We study the cross-sectional profiles of the total intensity (I) and polarized intensity (PI) of dust emission in four segments of filaments unaffected by local star formation that are expected to retain a pristine magnetic field structure. We find that the filaments' FWHMs in PI are not the same as those in I, with two segments being appreciably narrower in PI (FWHM ratio ≃0.7–0.8) and one segment being wider (FWHM ratio ≃1.3). The filament profiles of the polarization fraction (P) do not show a minimum at the spine of the filament, which is not in line with an anticorrelation between P and I normally seen in molecular clouds and protostellar cores. Dust grain alignment variation with density cannot reproduce the observed P distribution. We demonstrate numerically that the I and PI cross-sectional profiles of filaments in magnetohydrostatic equilibrium will have differing relative widths depending on the viewing angle. The observed variations of FWHM ratios in NGC 1333 are therefore consistent with models of pinched magnetic field structures inside filaments, especially if they are magnetically near-critical or supercritical

Planck intermediate results. XX. Comparison of polarized thermal emission from Galactic dust with simulations of MHD turbulence

Polarized emission observed by Planck HFI at 353GHz towards a sample of nearby fields is presented, focusing on the statistics of polarization fractions p and angles psi. The polarization fractions and column densities in these nearby fields are representative of the range of values obtained over the whole sky. We find that: (i) the largest polarization fractions are reached in the most diffuse fields; (ii) the maximum polarization fraction p(max) decreases with column density N-H in the more opaque fields with N-H > 10(21) cm(-2); and (iii) the polarization fraction along a given line of sight is correlated with the local spatial coherence of the polarization angle. These observations are compared to polarized emission maps computed in simulations of anisotropic magnetohydrodynamical turbulence in which we assume a uniform intrinsic polarization fraction of the dust grains. We find that an estimate of this parameter may be recovered from the maximum polarization fraction p(max) in diffuse regions where the magnetic field is ordered on large scales and perpendicular to the line of sight. This emphasizes the impact of anisotropies of the magnetic field on the emerging polarization signal. The decrease of the maximum polarization fraction with column density in nearby molecular clouds is well reproduced in the simulations, indicating that it is essentially due to the turbulent structure of the magnetic field: an accumulation of variously polarized structures along the line of sight leads to such an anti-correlation. In the simulations, polarization fractions are also found to anti-correlate with the angle dispersion function S. However, the dispersion of the polarization angle for a given polarization fraction is found to be larger in the simulations than in the observations, suggesting a shortcoming in the physical content of these numerical models. In summary, we find that the turbulent structure of the magnetic field is able to reproduce the main statistical properties of the dust polarization as observed in a variety of nearby clouds, dense cores excluded, and that the large-scale field orientation with respect to the line of sight plays a major role in the quantitative analysis of these statistical properties.Peer reviewe

Planck intermediate results. XXI. Comparison of polarized thermal emission from Galactic dust at 353 GHz with interstellar polarization in the visible

The Planck survey provides unprecedented full-sky coverage of the submillimetre polarized emission from Galactic dust. In addition to the information on the direction of the Galactic magnetic field, this also brings new constraints on the properties of dust. The dust grains that emit the radiation seen by Planck in the submillimetre also extinguish and polarize starlight in the visible. Comparison of the polarization of the emission and of the interstellar polarization on selected lines of sight probed by stars provides unique new diagnostics of the emission and light scattering properties of dust, and therefore of the important dust model parameters, composition, size, and shape. Using ancillary catalogues of interstellar polarization and extinction of starlight, we obtain the degree of polarization, p(V), and the optical depth in the V band to the star, tau(V). Toward these stars we measure the submillimetre polarized intensity, P-S, and total intensity, I-S,I- in the Planck 353 GHz channel. We compare the column density measure in the visible, E(B - V), with that inferred from the Planck product map of the submillimetre dust optical depth and compare the polarization direction (position angle) in the visible with that in the submillimetre. For those lines of sight through the di ff use interstellar medium with comparable values of the estimated column density and polarization directions close to orthogonal, we correlate properties in the submillimetre and visible to find two ratios, R-S/V = (P-S/I-S) = (p(V)/tau(V)) and R-P/p = P-S/p(V), the latter focusing directly on the polarization properties of the aligned grain population alone. We find R-S/V = 4.2, with statistical and systematic uncertainties 0.2 and 0.3, respectively, and R-P/p = 5.4 MJy sr(-1), with uncertainties 0.2 and 0.3 MJy sr(-1), respectively. Our estimate of R-S/V is compatible with predictions based on a range of polarizing dust models that have been developed for the di ff use interstellar medium. This estimate provides new empirical validation of many of the common underlying assumptions of the models, but is not yet very discriminating among them. However, our estimate of R-P/p is not compatible with predictions, which are too low by a factor of about 2.5. This more discriminating diagnostic, R-P/p, indicates that changes to the optical properties in the models of the aligned grain population are required. These new diagnostics, together with the spectral dependence in the submillimetre from Planck, will be important for constraining and understanding the full complexity of the grain models, and for interpreting the Planck thermal dust polarization and refinement of the separation of this contamination of the cosmic microwave background.Peer reviewe