1,293 research outputs found
Optical and Radio Polarimetry of the M87 Jet at 0.2" Resolution
We discuss optical (HST/WFPC2 F555W) and radio (15 GHz VLA) polarimetry
observations of the M87 jet taken during 1994-1995. Many knot regions are very
highly polarized (, approaching the theoretical maximum for
optically thin synchrotron radiation), suggesting highly ordered magnetic
fields. High degrees of polarization are also observed in interknot regions.
While the optical and radio polarization maps share many similarities, we
observe significant differences between the radio and optical polarized
structures, particularly for bright knots in the inner jet, giving us important
insight into the jet's radial structure. Unlike in the radio, the optical
magnetic field position angle becomes perpendicular to the jet at the upstream
ends of knots HST-1, D, E and F. Moreover, the optical polarization decreases
markedly at the position of the flux maxima in these knots. In contrast, the
magnetic field position angle observed in the radio remains parallel to the jet
in most of these regions, and the decreases in radio polarization are smaller.
More minor differences are seen in other jet regions. Many of the differences
between optical and radio polarimetry results can be explained in terms of a
model whereby shocks occur in the jet interior, where higher-energy electrons
are concentrated and dominate both polarized and unpolarized emissions in the
optical, while the radio maps show strong contributions from lower-energy
electrons in regions with {\bf B} parallel, near the jet surface.Comment: 28 pages, 7 figures; accepted for publication in AJ (May 1999
A statistical mechanics approach to autopoietic immune networks
The aim of this work is to try to bridge over theoretical immunology and
disordered statistical mechanics. Our long term hope is to contribute to the
development of a quantitative theoretical immunology from which practical
applications may stem. In order to make theoretical immunology appealing to the
statistical physicist audience we are going to work out a research article
which, from one side, may hopefully act as a benchmark for future improvements
and developments, from the other side, it is written in a very pedagogical way
both from a theoretical physics viewpoint as well as from the theoretical
immunology one.
Furthermore, we have chosen to test our model describing a wide range of
features of the adaptive immune response in only a paper: this has been
necessary in order to emphasize the benefit available when using disordered
statistical mechanics as a tool for the investigation. However, as a
consequence, each section is not at all exhaustive and would deserve deep
investigation: for the sake of completeness, we restricted details in the
analysis of each feature with the aim of introducing a self-consistent model.Comment: 22 pages, 14 figur
Random variation in rectal position during radiotherapy for prostate cancer is two to three times greater than that predicted from prostate motion.
OBJECTIVE: Radiotherapy for prostate cancer does not explicitly take into account daily variation in the position of the rectum. It is important to accurately assess accumulated dose (DA) to the rectum in order to understand the relationship between dose and toxicity. The primary objective of this work was to quantify systematic (Σ) and random (σ) variation in the position of the rectum during a course of prostate radiotherapy. METHODS: The rectum was manually outlined on the kilo-voltage planning scan and 37 daily mega-voltage image guidance scans for 10 participants recruited to the VoxTox study. The femoral heads were used to produce a fixed point to which all rectal contours were referenced. RESULTS: Σ [standard deviation (SD) of means] between planning and treatment was 4.2 mm in the anteroposterior (AP) direction and 1.3 mm left-right (LR). σ (root mean square of SDs) was 5.2 mm AP and 2.7 mm LR. Superior-inferior variation was less than one slice above and below the planning position. CONCLUSION: Our results for Σ are in line with published data for prostate motion. σ, however, was approximately twice as great as that seen for prostate motion. This suggests that DA may differ from planned dose in some patients treated with radiotherapy for prostate cancer. ADVANCES IN KNOWLEDGE: This work is the first to use daily imaging to quantify Σ and σ of the rectum in prostate cancer. σ was found to be greater than published data, providing strong rationale for further investigation of individual DA.JS is supported by Cancer Research UK through the Cambridge Cancer Centre. NGB is supported by the NIHR Cambridge Biomedical Research Centre. VoxTox is funded by Cancer Research UK.This is the final published version. It was first available from the British Institute of Radiology at http://dx.doi.org/10.1259/bjr.2014034
Multifrequency Radiation of Extragalactic Large-Scale Jets
Large-scale extragalactic jets, observed to extend from a few to a few
hundred kiloparsecs from active galactic nuclei, are now studied over many
decades in frequency of electromagnetic spectrum, from radio until (possibly)
TeV gamma rays. For hundreds of known radio jets, only about 25 are observed at
optical frequencies. Most of them are relatively short and faint, with only a
few exceptions, like 3C 273 or M 87, allowing for detailed spectroscopic and
morphological studies. Somewhat surprisingly, the large-scale jets can be very
prominent in X-rays. Up to now, about 25 jets were detected within the 1 - 10
keV energy range, although the nature of this emission is still under debate.
In general, both optical and X-ray jet observations present serious problems
for standard radiation models for the considered objects. Recent TeV
observations of M 87 suggest the possibility of generating large photon fluxes
at these high energies by its extended jet.
In this paper we summarize information about multiwavelength emission of the
large-scale jets, and we point out several modifications of the standard jet
radiation models (connected with relativistic bulk velocities, jet radial
stratification and particle energization all the way along the jet), which can
possibly explain some of the mentioned puzzling observations. We also comment
on gamma-ray emission of the discussed objects.Comment: 29 pages. Modified version, accepted for publication in Chinese
Journal of Astronomy and Astrophysic
Common genetic variation associated with increased susceptibility to prostate cancer does not increase risk of radiotherapy toxicity.
BACKGROUND: Numerous germline single-nucleotide polymorphisms increase susceptibility to prostate cancer, some lying near genes involved in cellular radiation response. This study investigated whether prostate cancer patients with a high genetic risk have increased toxicity following radiotherapy. METHODS: The study included 1560 prostate cancer patients from four radiotherapy cohorts: RAPPER (n=533), RADIOGEN (n=597), GenePARE (n=290) and CCI (n=150). Data from genome-wide association studies were imputed with the 1000 Genomes reference panel. Individuals were genetically similar with a European ancestry based on principal component analysis. Genetic risks were quantified using polygenic risk scores. Regression models tested associations between risk scores and 2-year toxicity (overall, urinary frequency, decreased stream, rectal bleeding). Results were combined across studies using standard inverse-variance fixed effects meta-analysis methods. RESULTS: A total of 75 variants were genotyped/imputed successfully. Neither non-weighted nor weighted polygenic risk scores were associated with late radiation toxicity in individual studies (P>0.11) or after meta-analysis (P>0.24). No individual variant was associated with 2-year toxicity. CONCLUSION: Patients with a high polygenic susceptibility for prostate cancer have no increased risk for developing late radiotherapy toxicity. These findings suggest that patients with a genetic predisposition for prostate cancer, inferred by common variants, can be safely treated using current standard radiotherapy regimens
Equilibrium statistical mechanics on correlated random graphs
Biological and social networks have recently attracted enormous attention
between physicists. Among several, two main aspects may be stressed: A non
trivial topology of the graph describing the mutual interactions between agents
exists and/or, typically, such interactions are essentially (weighted)
imitative. Despite such aspects are widely accepted and empirically confirmed,
the schemes currently exploited in order to generate the expected topology are
based on a-priori assumptions and in most cases still implement constant
intensities for links. Here we propose a simple shift in the definition of
patterns in an Hopfield model to convert frustration into dilution: By varying
the bias of the pattern distribution, the network topology -which is generated
by the reciprocal affinities among agents - crosses various well known regimes
(fully connected, linearly diverging connectivity, extreme dilution scenario,
no network), coupled with small world properties, which, in this context, are
emergent and no longer imposed a-priori. The model is investigated at first
focusing on these topological properties of the emergent network, then its
thermodynamics is analytically solved (at a replica symmetric level) by
extending the double stochastic stability technique, and presented together
with its fluctuation theory for a picture of criticality. At least at
equilibrium, dilution simply decreases the strength of the coupling felt by the
spins, but leaves the paramagnetic/ferromagnetic flavors unchanged. The main
difference with respect to previous investigations and a naive picture is that
within our approach replicas do not appear: instead of (multi)-overlaps as
order parameters, we introduce a class of magnetizations on all the possible
sub-graphs belonging to the main one investigated: As a consequence, for these
objects a closure for a self-consistent relation is achieved.Comment: 30 pages, 4 figure
First AMBER/VLTI observations of hot massive stars
AMBER is the first near infrared focal instrument of the VLTI. It combines
three telescopes and produces spectrally resolved interferometric measures.
This paper discusses some preliminary results of the first scientific
observations of AMBER with three Unit Telescopes at medium (1500) and high
(12000) spectral resolution. We derive a first set of constraints on the
structure of the circumstellar material around the Wolf Rayet Gamma2 Velorum
and the LBV Eta Carinae
Liver-Targeting of Interferon-Alpha with Tissue-Specific Domain Antibodies
PMCID: PMC3581439This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
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