339 research outputs found
Tumour-associated macrophages and oncolytic virotherapies:a mathematical investigation into a complex dynamics
Anti-cancer therapies based on oncolytic viruses are emerging as important approaches in cancer treatment. However, the effectiveness of these therapies depends significantly on the interactions between the oncolytic viruses and the host immune response. Macrophages are one of the most important cell types in the anti-viral immune responses, by acting as a first line of defence against infections. Here, we consider a mathematical approach to investigate the possible outcomes of the interactions between two extreme phenotypes of macrophages (M1 and M2 cells) and an oncolytic virus (VSV), in the context of B16F10 melanoma. We show that polarization towards either an M1 or M2 phenotype can enhance oncolytic virus therapy through either (i) anti-tumour immune activation, or (ii) enhanced oncolysis. Moreover, we show that tumour reduction and elimination does not depend only on the ratio of M1:M2 cells, but also on the number of tumour-infiltrating macrophages
MERLIN/VLA imaging of the gravitational lens system B0218+357
Gravitational lenses offer the possibility of accurately determining the
Hubble parameter (H_0) over cosmological distances, and B0218+357 is one of the
most promising systems for an application of this technique. In particular this
system has an accurately measured time delay (10.5+/-0.4 d; Biggs et al. 1999)
and preliminary mass modelling has given a value for H_0 of 69 +13/-19
km/s/Mpc. The error on this estimate is now dominated by the uncertainty in the
mass modelling. As this system contains an Einstein ring it should be possible
to constrain the model better by imaging the ring at high resolution. To
achieve this we have combined data from MERLIN and the VLA at a frequency of 5
GHz. In particular MERLIN has been used in multi-frequency mode in order to
improve substantially the aperture coverage of the combined data set. The
resulting map is the best that has been made of the ring and contains many new
and interesting features. Efforts are currently underway to exploit the new
data for lensing constraints using the LensClean algorithm (Kochanek & Narayan
1992).Comment: Accepted for publication in MNRAS. 6 pages, 4 included PostScript
figure
Coaxial Jets and Sheaths in Wide-Angle-Tail Radio Galaxies
We add 20, 6 and 3.6 cm wavelength VLA observations of two WATs, 1231+674 and
1433+553, to existing VLA data at 6 and 20 cm, in order to study the variations
of spectral index as a function of position. We apply the spectral tomography
process that we introduced in our analysis of 3C67, 3C190 and 3C449. Both
spectral tomography and polarization maps indicate that there are two distinct
extended components in each source. As in the case of 3C449, we find that each
source has a flat spectrum jet surrounded by a steeper spectrum sheath. The
steep components tend to be more highly polarized than the flat components. We
discuss a number of possibilities for the dynamics of the jet/sheath systems,
and the evolution of their relativistic electron populations. While the exact
nature of these two coaxial components is still uncertain, their existence
requires new models of jets in FR I sources and may also have implications for
the dichotomy between FR Is and FR IIs.Comment: 29 text pages plus 13 figures. Scheduled for publication in May 10,
1999 Ap
Towards Precision LSST Weak-Lensing Measurement - I: Impacts of Atmospheric Turbulence and Optical Aberration
The weak-lensing science of the LSST project drives the need to carefully
model and separate the instrumental artifacts from the intrinsic lensing
signal. The dominant source of the systematics for all ground based telescopes
is the spatial correlation of the PSF modulated by both atmospheric turbulence
and optical aberrations. In this paper, we present a full FOV simulation of the
LSST images by modeling both the atmosphere and the telescope optics with the
most current data for the telescope specifications and the environment. To
simulate the effects of atmospheric turbulence, we generated six-layer phase
screens with the parameters estimated from the on-site measurements. For the
optics, we combined the ray-tracing tool ZEMAX and our simulated focal plane
data to introduce realistic aberrations and focal plane height fluctuations.
Although this expected flatness deviation for LSST is small compared with that
of other existing cameras, the fast f-ratio of the LSST optics makes this focal
plane flatness variation and the resulting PSF discontinuities across the CCD
boundaries significant challenges in our removal of the systematics. We resolve
this complication by performing PCA CCD-by-CCD, and interpolating the basis
functions using conventional polynomials. We demonstrate that this PSF
correction scheme reduces the residual PSF ellipticity correlation below 10^-7
over the cosmologically interesting scale. From a null test using HST/UDF
galaxy images without input shear, we verify that the amplitude of the galaxy
ellipticity correlation function, after the PSF correction, is consistent with
the shot noise set by the finite number of objects. Therefore, we conclude that
the current optical design and specification for the accuracy in the focal
plane assembly are sufficient to enable the control of the PSF systematics
required for weak-lensing science with the LSST.Comment: Accepted to PASP. High-resolution version is available at
http://dls.physics.ucdavis.edu/~mkjee/LSST_weak_lensing_simulation.pd
Inverse Compton Scattering as the Source of Diffuse EUV Emission in the Coma Cluster of Galaxies
We have examined the hypothesis that the majority of the diffuse EUV flux in
the Coma cluster is due to inverse Compton scattering of low energy cosmic ray
electrons (0.16 < epsilon < 0.31 GeV) against the 3K black-body background. We
present data on the two-dimensional spatial distribution of the EUV flux and
show that these data provide strong support for a non-thermal origin for the
EUV flux. However, we show that this emission cannot be produced by an
extrapolation to lower energies of the observed synchrotron radio emitting
electrons and an additional component of low energy cosmic ray electrons is
required.Comment: 11 pages, 5 figure
The Bologna Complete Sample of Nearby Radio Sources
We present a new, complete, sample of 95 radio sources selected from the B2
and 3CR catalogues, with z < 0.1. Since no selection effect on the core radio
power, jet velocity, or source orientation is present, this sample is well
suited for statistical studies. In this first paper we present the
observational status of all sources on the parsec (mas) and kiloparsec (arcsec)
scale; we give new parsec-scale data for 28 sources and discuss their
parsec-scale properties. Combining these data with those in the literature,
information on the parsec-scale morphology is available for a total of 53 radio
sources with different radio power and kpc-scale morphology. We investigate
their properties. We find a dramatically higher fraction of two-sided sources
in comparison to previous flux limited VLBI surveys.Comment: 29 pages, 21 figures - ApJ in press (10 Jan 2005 issue
Probing dark energy with cluster counts and cosmic shear power spectra: including the full covariance
(Abridged) Combining cosmic shear power spectra and cluster counts is
powerful to improve cosmological parameter constraints and/or test inherent
systematics. However they probe the same cosmic mass density field, if the two
are drawn from the same survey region, and therefore the combination may be
less powerful than first thought. We investigate the cross-covariance between
the cosmic shear power spectra and the cluster counts based on the halo model
approach, where the cross-covariance arises from the three-point correlations
of the underlying mass density field. Fully taking into account the
cross-covariance as well as non-Gaussian errors on the lensing power spectrum
covariance, we find a significant cross-correlation between the lensing power
spectrum signals at multipoles l~10^3 and the cluster counts containing halos
with masses M>10^{14}Msun. Including the cross-covariance for the combined
measurement degrades and in some cases improves the total signal-to-noise
ratios up to plus or minus 20% relative to when the two are independent. For
cosmological parameter determination, the cross-covariance has a smaller effect
as a result of working in a multi-dimensional parameter space, implying that
the two observables can be considered independent to a good approximation. We
also discuss that cluster count experiments using lensing-selected mass peaks
could be more complementary to cosmic shear tomography than mass-selected
cluster counts of the corresponding mass threshold. Using lensing selected
clusters with a realistic usable detection threshold (S/N~6 for a ground-based
survey), the uncertainty on each dark energy parameter may be roughly halved by
the combined experiments, relative to using the power spectra alone.Comment: 32 pages, 15 figures. Revised version, invited original contribution
to gravitational lensing focus issue, New Journal of Physic
Simulating cosmic rays in clusters of galaxies - II. A unified scheme for radio halos and relics with predictions of the gamma-ray emission
The thermal plasma of galaxy clusters lost most of its information on how
structure formation proceeded as a result of dissipative processes. In
contrast, non-equilibrium distributions of cosmic rays (CR) preserve the
information about their injection and transport processes and provide thus a
unique window of current and past structure formation processes. This
information can be unveiled by observations of non-thermal radiative processes,
including radio synchrotron, hard X-ray, and gamma-ray emission. To explore
this, we use high-resolution simulations of a sample of galaxy clusters
spanning a mass range of about two orders of magnitudes, and follow
self-consistent CR physics on top of the radiative hydrodynamics. We model CR
electrons that are accelerated at cosmological structure formation shocks and
those that are produced in hadronic interactions of CRs with ambient gas
protons. We find that CR protons trace the time integrated non-equilibrium
activities of clusters while shock-accelerated CR electrons probe current
accretion and merging shock waves. The resulting inhomogeneous synchrotron
emission matches the properties of observed radio relics. We propose a unified
model for the generation of radio halos. Giant radio halos are dominated in the
centre by secondary synchrotron emission with a transition to the synchrotron
radiation emitted from shock-accelerated electrons in the cluster periphery.
This model is able to explain the observed correlation of mergers with radio
halos, the larger peripheral variation of the spectral index, and the large
scatter in the scaling relation between cluster mass and synchrotron emission.
Future low-frequency radio telescopes (LOFAR, GMRT, MWA, LWA) are expected to
probe the accretion shocks of clusters. [abridged]Comment: 32 pages, 19 figures, small changes to match the version to be
published by MNRAS, full resolution version available at
http://www.cita.utoronto.ca/~pfrommer/Publications/CRs_non-thermal.pd
Multifrequency VLA observations of the FR I radio galaxy 3C 31: morphology, spectrum and magnetic field
We present high-quality VLA images of the FR I radio galaxy 3C 31 in the
frequency range 1365 to 8440 MHz with angular resolutions from 0.25 to 40
arcsec. Our new images reveal complex, well resolved filamentary substructure
in the radio jets and tails. We also use these images to explore the spectral
structure of 3C 31 on large and small scales. We infer the apparent magnetic
field structure by correcting for Faraday rotation. Some of the intensity
substructure in the jets is clearly related to structure in their apparent
magnetic field: there are arcs of emission where the degree of linear
polarization increases, with the apparent magnetic field parallel to the ridges
of the arcs. The spectral indices are significantly steeper (0.62) within 7
arcsec of the nucleus than between 7 and 50 arcsec (0.52 - 0.57). The spectra
of the jet edges are also slightly flatter than the average for their
surroundings. At larger distances, the jets are clearly delimited from
surrounding larger-scale emission both by their flatter radio spectra and by
sharp brightness gradients. The spectral index of 0.62 in the first 7 arcsec of
3C 31's jets is very close to that found in other FR I galaxies where their
jets first brighten in the radio and where X-ray synchrotron emission is most
prominent. Farther from the nucleus, where the spectra flatten, X-ray emission
is fainter relative to the radio. The brightest X-ray emission from FR I jets
is therefore not associated with the flattest radio spectra, but with a
particle-acceleration process whose characteristic energy index is 2.24. The
spectral flattening with distance from the nucleus occurs where our
relativistic jet models require deceleration, and the flatter-spectra at the
jet edges may be associated with transverse velocity shear. (Slightly abridged)Comment: 17 pages, 13 figures, accepted for publication in MNRA
Resonant Kelvin-Helmholtz modes in sheared relativistic flows
Qualitatively new aspects of the (linear and non-linear) stability of sheared
relativistic (slab) jets are analyzed. The linear problem has been solved for a
wide range of jet models well inside the ultrarelativistic domain (flow Lorentz
factors up to 20; specific internal energies ). As a distinct
feature of our work, we have combined the analytical linear approach with
high-resolution relativistic hydrodynamical simulations, which has allowed us
i) to identify, in the linear regime, resonant modes specific to the
relativistic shear layer ii) to confirm the result of the linear analysis with
numerical simulations and, iii) more interestingly, to follow the instability
development through the non-linear regime. We find that very high-order
reflection modes with dominant growth rates can modify the global, long-term
stability of the relativistic flow. We discuss the dependence of these resonant
modes on the jet flow Lorentz factor and specific internal energy, and on the
shear layer thickness. The results could have potential applications in the
field of extragalactic relativistic jets.Comment: Accepted for publication in Physical Review E. For better quality
images, please check
http://www.mpifr-bonn.mpg.de/staff/mperucho/Research.htm
- âŠ