596 research outputs found
Distributional energy momentum tensor of the extended Kerr geometry
We generalize previous work on the energy-momentum tensor-distribution of the
Kerr geometry by extending the manifold structure into the negative mass
region. Since the extension of the flat part of the Kerr-Schild decomposition
from one sheet to the double cover develops a singularity at the branch surface
we have to take its non-smoothness into account. It is however possible to find
a geometry within the generalized Kerr-Schild class that is in the
Colombeau-sense associated to the maximally analytic Kerr-metric.Comment: 12 pages, latex2e, amslatex and epsf macro
Total flow intensity, active flow intensity and volume related flow intensity as new quantitative metrics in optical coherence tomography angiography
Optical coherence tomography (OCT) angiography (OCTA) is a non-invasive tool for the in-vivo study of the intraretinal vascular network. It is based on the analysis of motion particles within the retina to reconstruct the paths followed by the erythrocytes, i.e. retinal capillaries. To date, qualitative and quantitative information are based on the morphological features disclosed by retinal capillaries. In the present study, we proposed new quantitative functional metrics, named Total Flow Intensity (TFI), Active Flow Intensity (AFI), and Volume-related Flow Intensity (VFI), based on the processing of the blood flow signal detected by OCTA. We studied these metrics in a cohort of healthy subjects, and we assessed their clinical utility by including a cohort of age-matched patients affected by Stargardt disease. Moreover, we compared TFI, AFI, and VFI to the widely used vessel density (VD) parameter. TFI, AFI, and VFI were able to describe in detail the different properties of the retinal vascular compartment. In particular, TFI was intended as the overall amount of volumetric retinal blood flow. AFI represented a selective measure of voxels disclosing blood flow signal. VFI was developed to put in relationship the volumetric blood flow information with the not vascularized retinal volume. In conclusion, TFI, AFI, and VFI were proposed as feasible functional OCTA biomarkers based on the analysis of retinal blood flow signal
Hypoxia inducible factor-1 alpha expression is increased in infected positive HPV16 DNA oral squamous cell carcinoma and positively associated with HPV16 E7 oncoprotein
<p>Abstract</p> <p>Background</p> <p>There is increasing evidence for the role of High Risk (HR) Human PapillomaVirus (HPV) in the pathogenesis of Oral Squamous Cell Carcinoma (OSCC). The E6 and E7 oncogenes from HR HPVs are responsible for the deregulation of p53 and pRB proteins involved in cell cycle and apoptotic pathways. In cell lines experiments, the HPV E7 protein seems to be able to enhance Hypoxia Inducible Factor-1 alpha (HIF-1α) activity, normally involved in the response to hypoxia and able to enhance angiogenesis.</p> <p>Results</p> <p>We studied tumor specimens from 62 OSCC; a higher prevalence of tumors in TNM stage II and also in pT2 class between OSCC infected positive HPV16 DNA than non-infected ones was observed. HIF-1α positivity was detected throughout the analysed fields, not associated with areas of necrosis and also observed in cells immediately adjacent to blood vessels. A significant increase in mean values of the HIF-1α labeling indexes was observed for pT1-T2, as well for stage I-II, in the infected positive HPV16 DNA tumors than non-infected ones. HIF-1α and HPV16 E7 labeling indexes showed a significantly positive correlation which suggested a positive association between HPV16 E7 and HIF-1α expression.</p> <p>Conclusions</p> <p>In our specimens HIF-1α immunoreactivity hints for an O<sub>2</sub>-independent regulatory mechanism in infected positive HPV16 DNA tumors, especially for pT1-T2 and stage I-II tumors, suggesting a very early involvement in the development of HPV-induced OSCC. HIF-1α and HPV16 E7 labeling indexes suggest also a positive association between the two proteins in infected positive HPV16 DNA OSCC.</p
Semi-invariants of symmetric quivers of finite type
Let be a symmetric quiver, where is a finite
quiver without oriented cycles and is a contravariant involution on
. The involution allows us to define a nondegenerate bilinear
form on a representation $V$ of $Q$. We shall call the representation
orthogonal if is symmetric and symplectic if is skew-symmetric.
Moreover we can define an action of products of classical groups on the space
of orthogonal representations and on the space of symplectic representations.
For symmetric quivers of finite type, we prove that the rings of
semi-invariants for this action are spanned by the semi-invariants of
determinantal type and, in the case when matrix defining is
skew-symmetric, by the Pfaffians
Semi-invariants of symmetric quivers of tame type
A symmetric quiver is a finite quiver without oriented cycles
equipped with a contravariant involution on . The involution allows us to define a nondegenerate bilinear form on
a representation $V$ of $Q$. We shall say that $V$ is orthogonal if is
symmetric and symplectic if is skew-symmetric. Moreover, we define an
action of products of classical groups on the space of orthogonal
representations and on the space of symplectic representations. So we prove
that if is a symmetric quiver of tame type then the rings of
semi-invariants for this action are spanned by the semi-invariants of
determinantal type and, when matrix defining is skew-symmetric, by
the Pfaffians . To prove it, moreover, we describe the symplectic and
orthogonal generic decomposition of a symmetric dimension vector
Search for radio pulsations in LS I +61 303
Context. LS I +61 303 is a member of the select group of gamma-ray binaries:
galactic binary systems that contain a massive star and a compact object, show
a changing milliarcsecond morphology and a similar broad spectral energy
distribution (SED) that peaks at MeV-TeV energies and is modulated by the
orbital motion. The nature of the compact object is unclear in LS I +61 303, LS
5039 and HESS J0632+057, whereas PSR B1259-63 harbours a 47.74 ms radio pulsar.
Aims. A scenario in which a young pulsar wind interacts with the stellar wind
has been proposed to explain the very high energy (VHE, E > 100 GeV) gamma-ray
emission detected from LS I +61 303, although no pulses have been reported from
this system at any wavelength. We aim to find evidence of the pulsar nature of
the compact object. Methods. We performed phased array observations with the
Giant Metrewave Radio Telescope (GMRT) at 1280 MHz centred at phase 0.54.
Simultaneous data from the multi-bit phased array (PA) back-end with a sampling
time of tsamp = 128 microsec and from the polarimeter (PMT) back-end with tsamp
= 256 microsec where taken. Results. No pulses have been found in the data set,
with a minimum detectable mean flux density of \sim 0.38 mJy at 8-sigma level
for the pulsed emission from a putative pulsar with period P >2 ms and duty
cycle D = 10% in the direction of LS I +61 303. Conclusions. The detection of
posible radio pulsations will require deep and sensitive observations at
frequencies \sim0.5-5 GHz and orbital phases 0.6-0.7. However, it may be
unfeasible to detect pulses if the putative pulsar is not beamed at the Earth
or if there is a strong absorption within the binary system.Comment: 8 pages. 5 figures. Accepted for publication in Astronomy and
Astrophysic
- …