8,452 research outputs found
Cosmic axion background propagation in galaxies
Many extensions of the Standard Model include axions or axion-like particles
(ALPs). Here we study ALP to photon conversion in the magnetic field of the
Milky Way and starburst galaxies. By modelling the effects of the coherent and
random magnetic fields, the warm ionized medium and the warm neutral medium on
the conversion process, we simulate maps of the conversion probability across
the sky for a range of ALP energies. In particular, we consider a diffuse
cosmic ALP background (CAB) analogous to the CMB, whose existence is suggested
by string models of inflation. ALP-photon conversion of a CAB in the magnetic
fields of galaxy clusters has been proposed as an explanation of the cluster
soft X-ray excess. We therefore study the phenomenology and expected photon
signal of CAB propagation in the Milky Way. We find that, for the CAB
parameters required to explain the cluster soft X-ray excess, the photon flux
from ALP-photon conversion in the Milky Way would be unobservably small. The
ALP-photon conversion probability in galaxy clusters is 3 orders of magnitude
higher than that in the Milky Way. Furthermore, the morphology of the
unresolved cosmic X-ray background is incompatible with a significant component
from ALP-photon conversion. We also consider ALP-photon conversion in starburst
galaxies, which host much higher magnetic fields. By considering the clumpy
structure of the galactic plasma, we find that conversion probabilities
comparable to those in clusters may be possible in starburst galaxies.Comment: Version accepted by Physics Letters
VEWS: A Wikipedia Vandal Early Warning System
We study the problem of detecting vandals on Wikipedia before any human or
known vandalism detection system reports flagging potential vandals so that
such users can be presented early to Wikipedia administrators. We leverage
multiple classical ML approaches, but develop 3 novel sets of features. Our
Wikipedia Vandal Behavior (WVB) approach uses a novel set of user editing
patterns as features to classify some users as vandals. Our Wikipedia
Transition Probability Matrix (WTPM) approach uses a set of features derived
from a transition probability matrix and then reduces it via a neural net
auto-encoder to classify some users as vandals. The VEWS approach merges the
previous two approaches. Without using any information (e.g. reverts) provided
by other users, these algorithms each have over 85% classification accuracy.
Moreover, when temporal recency is considered, accuracy goes to almost 90%. We
carry out detailed experiments on a new data set we have created consisting of
about 33K Wikipedia users (including both a black list and a white list of
editors) and containing 770K edits. We describe specific behaviors that
distinguish between vandals and non-vandals. We show that VEWS beats ClueBot NG
and STiki, the best known algorithms today for vandalism detection. Moreover,
VEWS detects far more vandals than ClueBot NG and on average, detects them 2.39
edits before ClueBot NG when both detect the vandal. However, we show that the
combination of VEWS and ClueBot NG can give a fully automated vandal early
warning system with even higher accuracy.Comment: To appear in Proceedings of the 21st ACM SIGKDD Conference of
Knowledge Discovery and Data Mining (KDD 2015
PET/PDT theranostics: Synthesis and biological evaluation of a peptide-targeted gallium porphyrin
The development of novel theranostic agents is an important step in the pathway towards personalised medicine, with the combination of diagnostic and therapeutic modalities into a single treatment agent naturally lending itself to the optimisation and personalisation of treatment. In pursuit of the goal of a molecular theranostic suitable for use as a PET radiotracer and a photosensitiser for PDT, a novel radiolabelled peptide–porphyrin conjugate targeting the α6β1-integrin has been developed. 69/71Ga and 68Ga labelling of an azide-functionalised porphyrin has been carried out in excellent yields, with subsequent bioconjugation to an alkyne-functionalised peptide demonstrated. α6β1-integrin expression of two cell lines has been evaluated by flow cytometry, and therapeutic potential of the conjugate demonstrated. Evaluation of the phototoxicity of the porphyrin–peptide theranostic conjugate in comparison to an untargeted control porphyrin in vitro, demonstrated significantly enhanced activity for a cell line with higher α6β1-integrin expression when compared with a cell line exhibiting lower α6β1-integrin expression
YOUNG WOMEN’S NARRATIVES OF DECISION-MAKING ABOUT HUMAN PAPILLOMAVIRUS VACCINATION
This thesis examines young women’s decision-making regarding Human Papillomavirus (HPV) vaccination. Using a narrative approach, five young women were asked to share their stories of how they came to be or not be vaccinated. Two in-depth interviews were used to elicit participants’ stories, and an overall narrative for each young woman was constructed. The five individual narratives reveal a number of themes that capture the diversity of young women’s decision-making experiences and point to the complex ways in which young women are negotiating decisions regarding vaccination. Within this thesis, I take a critical stance on the topic of HPV vaccine decision-making in order to illuminate how young women’s decisions are embedded within broader social and discursive contexts. This critical approach to understanding participant narratives was informed by a strong sensitivity to conceptual frames of medicalization, healthism, and neo-medicalization and dominant discourses related to health risk and individual responsibility
Challenging Filipino Colonial Mentality with Philippine Art
For 350 years, the Philippines was colonized by Spain and the United States. The Philippines became a sovereign nation in 1946 yet, fifty years later, colonial teachings continue to oppress Filipinos due to their colonial mentality (CM.) CM is an internalized oppression among Filipinos in which they experience an automatic preference for anything Western—European or U.S. American—and rejection of anything Filipino. Although Filipinos show signs of a CM, there are Filipinos who are challenging CM by engaging in Philippine art. Philippine art is defined as Filipino-made visual art, literature, music, and dance intended to promote Philippine culture. This research project analyzes the Philippine art community and discovers that those involved in the Philippine art community are conscious of how colonialism dictates standards today. They also actively challenge colonial affects by creating and/or supporting artists whom promote Filipino cultures. However, Philippine art’s ability to decrease CM among Filipinos is not evenly accessible among classes
On the correctness and efficiency of independent and-parallelism in logic programs
This paper presents and proves some fundamental results for independent and-parallelism (IAP). First, the paper treats the issues of correctness and efficiency: after defining strict and non-strict goal independence, it is proved that if strictly independent goals are executed in parallel the solutions obtained are the same as those produced by standard sequential execution. It is also shown that, in the absence of failure, the parallel proof procedure doesn't genérate any additional work (with respect to standard SLDresolution) while the actual execution time is reduced. The same results hold even if non-strictly independent goals are executed in parallel, provided a trivial rewriting of such goals is performed. In addition, and most importantly, treats the issue of compile-time generation of IAP by proposing conditions, to be written at compile-time, to efficiently check strict and non-strict goal independence at run-time and proving the sufficiency of such conditions. It is also shown how simpler conditions can be constructed if some information regarding the binding context of the goals to be executed in parallel is available to the compiler trough either local or program-level analysis. These results therefore provide a formal basis for the automatic compile-time generation of IAP. As a corollary of such results, the paper also proves that negative goals are always non-strictly independent, and
that goals which share a first occurrence of an existential variable are never independent
Non-strict independent and-parallelism
This paper presents and develops a generalized concept of Non-Strict Independent And Parallelism (NSIAP). NSIAP extends the applicability of Independent And- Parallelism (IAP) by enlarging the class of goals which are eligible for parallel execution. At the same time it maintains IAP's ability to run non-deterministic goals in parallel and to preserve the computational complexity expected in the execution of the program by the programmer. First, a parallel execution framework is defined and some fundamental correctness results, in the sense of equivalence of solutions with the sequential model, are discussed for this framework. The issue of efficiency is then considered. Two new definitions of NSI are given for the cases of puré and impure goals respectively and efficiency results are provided for programs parallelized under these definitions which include treatment of the case of goal failure: not only is reduction of execution time guaranteed (modulo run-time overheads) in the absence of failure but it is also shown that in the worst case of
failure no speed-down will occur. In addition to applying to NSI, these results carry over and complete previous results shown in the context of IAP which did not deal with the case of goal failure. Finally, some practical examples of the application of the NSIAP concept to the parallelization of a set of programs are presented and performance results, showing the advantage of using NSI, are given
Is mass loss along the red giant branch of globular clusters sharply peaked? The case of M3
There is a growing evidence that several globular clusters must contain
multiple stellar generations, differing in helium content. This hypothesis has
helped to interpret peculiar unexplained features in their horizontal branches.
In this framework we model the peaked distribution of the RR Lyr periods in M3,
that has defied explanation until now. At the same time, we try to reproduce
the colour distribution of M3 horizontal branch stars. We find that only a very
small dispersion in mass loss along the red giant branch reproduces with good
accuracy the observational data. The enhanced and variable helium content among
cluster stars is at the origin of the extension in colour of the horizontal
branch, while the sharply peaked mass loss is necessary to reproduce the
sharply peaked period distribution of RR Lyr variables. The dispersion in mass
loss has to be <~ 0.003 Msun, to be compared with the usually assumed values of
~0.02 Msun. This requirement represents a substantial change in the
interpretation of the physical mechanisms regulating the evolution of globular
cluster stars.Comment: Accepted for publication in The Astrophysical Journa
Implementing optimal control in cointegrated I(1) structural VAR models
JEL Classification: C32, C61, E52optimal control, VAR models
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