37,174 research outputs found
Controlling secretion to limit chemoresistance
The tumor microenvironment influences cancer progression and therapy outcome by mechanisms not yet fully understood. In this issue, Bent et al. (2016) show how chemotherapy causes endothelial senescence. Interestingly, senescent endothelial cells do not mount a typical senescence-associated secretory phenotype but instead acutely secrete IL-6, promoting chemoresistance. This study unveils a physiological switch involving PI3K/AKT/mTOR signaling that restrains the senescence secretory responses to limit the detrimental consequences of persistent inflammation
Frequency dependence of pulsar radiation patterns
We report on new results from simultaneous, dual frequency, single pulse
observation of PSR B0329+54 using the Giant Metrewave Radio Telescope. We find
that the longitude separation of subpulses at two different frequencies (238
and 612 MHz) is less than that for the corresponding components in the average
profile. A similar behaviour has been noticed before in a number of pulsars. We
argue that subpulses are emitted within narrow flux tubes of the dipolar field
lines and that the mean pulsar beam has a conal structure. In such a model the
longitudes of profile components are determined by the intersection of the line
of sight trajectory with subpulse-associated emission beams. Thus, we show that
the difference in the frequency dependence of subpulse and profile component
longitudes is a natural property of the conal model of pulsar emission beam. We
support our conclusions by numerical modelling of pulsar emission, using the
known parameters for this pulsar, which produce results that agree very well
with our dual frequency observations.Comment: 24 pages, 8 figures. Accepted for publication in Ap
A conic manifold perspective of elliptic operators on graphs
We give a simple, explicit, sufficient condition for the existence of a
sector of minimal growth for second order regular singular differential
operators on graphs. We specifically consider operators with a singular
potential of Coulomb type and base our analysis on the theory of elliptic cone
operators.Comment: 18 page
Adjoints of elliptic cone operators
We study the adjointness problem for the closed extensions of a general
b-elliptic operator A in x^{-\nu}Diff^m_b(M;E), \nu>0, initially defined as an
unbounded operator A:C_c^\infty(M;E)\subset x^\mu L^2_b(M;E)\to x^\mu
L^2_b(M;E), \mu \in \R. The case where A is a symmetric semibounded operator is
of particular interest, and we give a complete description of the domain of the
Friedrichs extension of such an operator.Comment: 40 pages, LaTeX, preliminary versio
Spark Model for Pulsar Radiation Modulation Patterns
A non-stationary polar gap model first proposed by Ruderman & Sutherland
(1975) is modified and applied to spark-associated pulsar emission at radio
wave-lengths. It is argued that under physical and geometrical conditions
prevailing above pulsar polar cap, highly non-stationary spark discharges do
not occur at random positions. Instead, sparks should tend to operate in well
determined preferred regions. At any instant the polar cap is populated as
densely as possible with a number of two-dimensional sparks with a
characteristic dimension as well as a typical distance between adjacent sparks
being about the polar gap height. Our model differs, however, markedly from its
original 'hollow cone' version. The key feature is the quasi-central spark
driven by pair production process and anchored to the local pole of a
sunspot-like surface magnetic field. This fixed spark prevents the motion of
other sparks towards the pole, restricting it to slow circumferential drift
across the planes of field lines converging at the local pole. We argue that
the polar spark constitutes the core pulsar emission, and that the annular
rings of drifting sparks contribute to conal components of the pulsar beam. We
found that the number of nested cones in the beam of typical pulsar should not
excced three; a number also found by Mitra & Deshpande (1999) using a
completely different analysis.Comment: 31 pages, 8 figures, accepted by Ap
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