1,583 research outputs found
Exploring the magnetic, turbulent Milky Way through radio waves
Cosmic magnetism is a phenomenon observed across a huge range of spatial scales. Magnetic fields exists on planets, stars and nebulae up to galaxies and clusters of galaxies. As a rule of thumb, the larger the typical size of the object, the lower the magnitude of its magnetic field. Regardless of their magnitude, magnetic fields play a relevant role in all of these environments and contribute to a wide spectrum of phenomena. This thesis deals with the interplay between interstellar magnetic fields and turbulent warm phase of the Galactic interstellar medium (ISM). Observational investigations in the radio domain of MHD turbulence in the ISM are challenging and require high performance facilities. New generation aperture array radio telescopes such as LOFAR allow observational studies of the interstellar turbulence with unprecedented accuracy. In the framework of the scientific activity of this Ph.D. project, I also worked as a commissioner of LOFAR, performing data reduction and software testing. In this thesis, I present four observational studies on the MHD turbulence in the warm ionized ISM regarding two complementary science cases: mapping of the magneto-ionic structures in the ISM (Chapter 2) and characterizing the magnetic turbulence of the diffuse warm ionized ISM (Chapters 3, 4 and 5). Note that the study described in Chapter 3 is based on the results of my commissioning activity.UBL - phd migration 201
Splitting neutrino masses and showering into Sky
Neutrino masses might be as light as a few time the atmospheric neutrino mass
splitting. High Energy ZeV cosmic neutrinos (in Z-Showering model) might hit
relic ones at each mass in different resonance energies in our nearby Universe.
This non-degenerated density and energy must split UHE Z-boson secondaries (in
Z-Burst model) leading to multi injection of UHECR nucleons within future
extreme AUGER energy. Secondaries of Z-Burst as neutral gamma, below a few tens
EeV are better surviving local GZK cut-off and they might explain recent Hires
BL-Lac UHECR correlations at small angles. A different high energy resonance
must lead to Glashow's anti-neutrino showers while hitting electrons in matter.
In air, Glashow's anti-neutrino showers lead to collimated and directional
air-showers offering a new Neutrino Astronomy. At greater energy around PeV,
Tau escaping mountains and Earth and decaying in flight are effectively
showering in air sky. These Horizontal showering is splitting by geomagnetic
field in forked shapes. Such air-showers secondaries release amplified and
beamed gamma bursts (like observed TGF), made also by muon and electron pair
bundles, with their accompanying rich Cherenkov flashes. Also planet' s largest
(Saturn, Jupiter) atmosphere limbs offer an ideal screen for UHE GZK and
Z-burst tau neutrino, because their largest sizes. Titan thick atmosphere and
small radius are optimal for discovering up-going resonant Glashow resonant
showers. Earth detection of Neutrino showering by twin Magic Telescopes on top
mountains, or by balloons and satellites arrays facing the limbs are the
simplest and cheapest way toward UHE Neutrino Astronomy .Comment: 4 pages, 7 figures; an author's name correction and Journal Referenc
Cross-Cultural Experiences of Canadian Science Educators Visiting the Sister Schools in Chongqing, China: A Cross-Cultural Experience
The benefit of cross-cultural learning is two-fold: first is recognizing the practices and foundations that build education in another country. The second is reflecting on the educational practices within one’s home country. Cross-cultural learning also allows one to put the practice of education into perspective by having another side to which they can compare their experiences. This research is a narrative inquiry case study of the Canadian perspective and experience of two in-service science teachers who visited sister schools in China. This case study explores Canadian teachers’ perceptions of teaching science, what inquiry-based teaching looks like, what equipment aids in the process, and what experiences and teaching methodologies can be shared between Canadian schools and the Sister Schools in Chongqing, China. This research was funded by the Social Sciences and Humanities Research Council (SSHRC) Partnership Grant
Prognostic value of a novel circulating serum 90K antigen in breast cancer.
Monoclonal antibody SP-2 to the tumour-associated antigen 90K was generated by immunisation with conditioned medium of human breast cancer cells. We investigated whether circulating levels of 90K can influence the prognosis of patients with breast cancer. Serum samples were obtained from 425 patients with histologically proven breast cancer with no clinical evidence of disease after surgery (NED) and in 310 patients with metastatic disease. Serum 90K was determined by a new immunoradiometric assay (IRMA). Antigen levels in NED patients were elevated in 18.5% of cases, mean levels being higher than in healthy controls (P = 0.001). Among 375 evaluable patients, the 75-month overall survival for 90K-negative (< or = 11 U ml-1) and 90K-positive (> 11 U ml-1) patients was 78% and 53% respectively (P = 0.004). The prognostic value of 90K appeared to be limited to patients with node-positive disease. Number of metastatic axillary lymph nodes and level of 90K antigen were the only independent variables for predicting overall survival. Patients with metastatic breast cancer had elevated 90K in 51.3% of cases. High 90K levels were significantly associated with the presence of metastases to liver, shorter disease-free interval and younger age. We conclude that an elevated 90K antigen level in serum is a predictor of poor prognosis in breast cancer
Isolated Fetal Ascites Secondary to Persistent Urogenital Sinus
Objective. To present a case of isolated ascites secondary due to urogenital abnormalities (urogenital sinus) without any other prenatal ultrasound marker. Method. A 36-year-old woman with prenatal isolated ascites delivered a female baby, weighing 2.285 g; ascites was drained at birth and the baby underwent several episodes of urinary retention prior to undergoing X-ray investigations. Results. A voiding cystourethrogram revealed a short urogenital sinus: a vesicostomy was performed. A vaginoscopy revealed double vagina with a large posterior vagina. A posterior sagittal anorectal pull-through with genitoplasty was performed at 2 years old with 1-year follow-up. Conclusions. Though rare, a urogenital abnormality is to be suspected in fetal ascites cases with negative viral tests and no cardiac anomalies. The most common ultrasound marker of such abnormalities (fluid filled cavity) may be missing because of complete drainage of urine through the tubes into peritoneum
Metastates in mean-field models with random external fields generated by Markov chains
We extend the construction by Kuelske and Iacobelli of metastates in
finite-state mean-field models in independent disorder to situations where the
local disorder terms are are a sample of an external ergodic Markov chain in
equilibrium. We show that for non-degenerate Markov chains, the structure of
the theorems is analogous to the case of i.i.d. variables when the limiting
weights in the metastate are expressed with the aid of a CLT for the occupation
time measure of the chain. As a new phenomenon we also show in a Potts example
that, for a degenerate non-reversible chain this CLT approximation is not
enough and the metastate can have less symmetry than the symmetry of the
interaction and a Gaussian approximation of disorder fluctuations would
suggest.Comment: 20 pages, 2 figure
A low-frequency view of mixed-morphology supernova remnant VRO 42.05.01, and its neighbourhood
Context. Mixed-morphology supernova remnants (MM SNRs) are a mysterious class of objects that display thermal X-ray emission within their radio shell. They are an older class of SNRs, and as such are profoundly affected by the environment into which they evolve. VRO 42.05.01 is a MM SNR of puzzling morphology in the direction of the Galactic anticentre.
Aims. Low-frequency radio observations of supernova remnants are sensitive to synchrotron electrons accelerated in the shock front. We aim to compare the low-frequency emission to higher frequency observations to understand the environmental and shock acceleration conditions that have given rise to the observed properties of this source.
Methods. We present a LOFAR High Band Antenna map centred at 143 MHz of the region of the Galactic plane centred at l = 166°, b = 3.5° at 143 MHz, with a resolution of 148" and an rms noise of 4.4 mJy bm−1. Our map is sensitive to scales as large as 6°. We compared the LOw Frequency ARay (LOFAR) observations to archival higher frequency radio, infrared, and optical data to study the emission properties of the source in different spectral regimes. We did this both for the SNR and for OA 184, an H II region within our field of view.
Results. We find that the radio spectral index of VRO 42.05.01 increases at low radio frequencies; i.e. the LOFAR flux is higher than expected from the measured spectral index value at higher radio frequencies. This observed curvature in the low-frequency end of the radio spectrum occurs primarily in the brightest regions of the source, while the fainter regions present a roughly constant power-law behaviour between 143 MHz and 2695 MHz. We favour an explanation for this steepening whereby radiative shocks have high compression ratios and electrons of different energies probe different length scales across the shocks, therefore sampling regions of different compression ratios
The nature of the low-frequency emission of M51: First observations of a nearby galaxy with LOFAR
The grand-design spiral galaxy M51 was observed with the LOFAR High Frequency
Antennas (HBA) and imaged in total intensity and polarisation. This observation
covered the frequencies between 115 MHz and 175 MHz. We produced an image of
total emission of M51 at the mean frequency of 151 MHz with 20 arcsec
resolution and 0.3 mJy rms noise, which is the most sensitive image of a galaxy
at frequencies below 300 MHz so far. The integrated spectrum of total radio
emission is described well by a power law, while flat spectral indices in the
central region indicate thermal absorption. We observe that the disk extends
out to 16 kpc and see a break in the radial profile near the optical radius of
the disk. Our main results, the scale lengths of the inner and outer disks at
151 MHz and 1.4 GHz, arm--interarm contrast, and the break scales of the
radio--far-infrared correlations, can be explained consistently by CRE
diffusion, leading to a longer propagation length of CRE of lower energy. The
distribution of CRE sources drops sharply at about 10 kpc radius, where the
star formation rate also decreases sharply. We find evidence that thermal
absorption is primarily caused by HII regions. The non-detection of
polarisation from M51 at 151 MHz is consistent with the estimates of Faraday
depolarisation. Future searches for polarised emission in this frequency range
should concentrate on regions with low star formation rates.Comment: 20 pages, 18 figures, accepted for publication in A&
Injury-specific factors in the cerebrospinal fluid regulate astrocyte plasticity in the human brain
The glial environment influences neurological disease progression, yet much of our knowledge still relies on preclinical animal studies, especially regarding astrocyte heterogeneity. In murine models of traumatic brain injury, beneficial functions of proliferating reactive astrocytes on disease outcome have been unraveled, but little is known regarding if and when they are present in human brain pathology. Here we examined a broad spectrum of pathologies with and without intracerebral hemorrhage and found a striking correlation between lesions involving blood-brain barrier rupture and astrocyte proliferation that was further corroborated in an assay probing for neural stem cell potential. Most importantly, proteomic analysis unraveled a crucial signaling pathway regulating this astrocyte plasticity with GALECTIN3 as a novel marker for proliferating astrocytes and the GALECTIN3-binding protein LGALS3BP as a functional hub mediating astrocyte proliferation and neurosphere formation. Taken together, this work identifies a therapeutically relevant astrocyte response and their molecular regulators in different pathologies affecting the human cerebral cortex. Intracerebral hemorrhage triggers astrocyte proliferation and mediates neural stem cell potential via Galectin3 signaling
- …