Dusty globules in the Crab Nebula

From existing broad-band images obtained with the Hubble Space Telescope, we located 92 globules, for which we derived positions, dimensions, orientations, extinctions, masses, proper motions, and their distributions. The globules have mean radii ranging from 400 to 2000 AU and are not resolved in current infrared images of the nebula. The extinction law for dust grains in these globules matches a normal interstellar extinction law. Derived masses of dust range from 1 to 60 x 10^(-6) solar masses, and the total mass contained in globules constitute a fraction of approximately 2% or less of the total dust content of the nebula. The globules are spread over the outer part of the nebula, and a fraction of them coincide in position with emission filaments, where we find elongated globules that are aligned with these filaments. Only 10% of the globules are coincident in position with the numerous H2-emitting knots found in previous studies. All globules move outwards from the centre with transversal velocities of 60 to 1600 km/s, along with the general expansion of the remnant. We discuss various hypotheses for the formation of globules in the Crab Nebula.Comment: 11 page

Heavy and Excited Leptons in the OPAL Detector?

This M.Sc. thesis describes a search for exotic leptons. The search has been performed using data from the OPAL detector at the Large Electron Positron collider at CERN. The total integrated luminosity was 663 pb$^{-1}$ with center of mass energies in the range of 183-209 GeV. The work has been concentrated on the study of production of heavy leptons via the charged current channel and disintegration of the $W$ into two quarks. In particular, single production of heavy leptons in the mass region 100-170 GeV has been extensively studied. No evidence for any new particles has been found. The results translate into upper limits on the mixing between the heavy and the ordinary lepton for different heavy lepton masses. The limits on the mixing angles are generally improved in comparison with the nominal value $\zeta^2\sim 0.005$.Comment: 85 pages, 38 figures, MSc thesis at Universite de Montrea

Does medial knee pain decrease when the hip muscle strength increases? A literature review

Background: The knee joint is a common source of pain and the most common localization of this pain is the medial part of the humero-tibial joint. Pain can induce a change in the recruitment of muscles, there may be a change in the power and the distribution of muscle activity within the muscles in order to protect the painful structure. In addition to reduced strength in the quadriceps muscle in persons with knee joint pain, it has also been seen a decreased strength in the hip joint muscles, compared to healthy people. Purpose: The purpose of this study was to determine whether resistance training of the hip joint muscles may reduce medial knee joint pain. Method: A literature review was conducted searching the following databases, PubMed, SveMed, Pedro, Amed, Embase, SportDiscuss and Cinahl. Personal contacts with authors of articles were also taken. Four articles were included in the study. The articles were reviewed for methodological quality by a modified review template. Result: Two of the studies included resistance training of both knee joint- and hip joint muscles. All the included studies showed a significant decrease of the knee pain all though there was no significant increase of the hip muscle strength in one of the studies and no significant difference in the increase of the hip muscle strength between control- and intervention group in another study. The studies were found to be of moderate quality (2 pre-post intervention design) and of high quality (2 RCT-design). Conclusion: The result of the literature review implies that persons with medial knee pain could benefit from including resistance training of the hip muscles in the rehabilitation when the purpose is reducing pain. However, more studies are required to confirm this.Bakgrund: Knäsmärta är vanligt förekommande och den vanligaste lokalisationen för knäsmärta är medialt i femurotibialleden. Smärta kan leda till att muskelrekrytering sker på annat sätt än i smärtfritt tillstånd vad gäller till exempel kraft och distribution av aktivitet inom muskeln. Syftet med detta är att skydda den smärtande strukturen. Förutom minskad styrka i quadricepsmuskeln vid knäsmärta har även nedsatt styrka i höftmuskulaturen setts, vid jämförelse med friska individer. Syfte: Syftet var att undersöka om styrketräning av höftmuskulatur kan minska smärta medialt i knäleden. Metod: En litteraturstudie genomfördes med sökningar i PubMed, SveMed, Pedro, Amed, Embase, SportDiscuss och Cinahl, även kontakter med artikelförfattare togs. Studierna granskades enligt en modifierad kvalitetsgranskningsmall. Resultat: Två av studierna inkluderade styrketräning av både höft- och knämuskler. Alla studierna visade en signifikant minskning av medial knäsmärta, en studie visade ingen styrkeökning och en annan studie visade ingen signifikant skillnad mellan försöks- och kontrollgrupp vad gäller styrkeökning. Studiernas metodologiska kvalitet var måttlig (2 pre-post interventionsdesign) respektive hög (2 RCT-studier). Konklusion: Resultatet tyder på att det finns viss grund för personer med medial knäsmärta att inkludera styrketräning av höftmuskulaturen i sin rehabilitering när syftet är att minska smärtan, men fler studier behövs för att ytterligare bekräfta detta

Dust Distribution during Reionization

The dust produced by the first generation of stars will be a foreground to cosmic microwave background. In order to evaluate the effect of this early dust, we calculate the power spectrum of the dust emission anisotropies and compare it with the sensitivity limit of the Planck satellite. The spatial distribution of the dust is estimated through the distribution of dark matter. At small angular scales ($\ell \gtrsim 1000$) the dust signal is found to be noticeable with the Planck detector for certain values of dust lifetime and production rates. The dust signal is also compared to sensitivities of other instruments. The early dust emission anisotropies are finally compared to those of local dust and they are found to be similar in magnitude at mm wavelengths.Comment: 6 pages, 6 figures; Typos fixed. Clarifications in the abstract, sections 2 and 4.1 and fig

Dynamic changes in the functional anatomy of the human brain during recall of abstract designs related to practice

In the present PET study we explore some functional aspects of the interaction between attentional/control processes and learning/memory processes. The network of brain regions supporting recall of abstract designs were studied in a less practiced and in a well practiced state. The results indicate that automaticity, i.e., a decreased dependence on attentional and working memory resources, develops as a consequence of practice. This corresponds to the practice related decreases of activity in the prefrontal, anterior cingulate, and posterior parietal regions. In addition, the activity of the medial temporal regions decreased as a function of practice. This indicates an inverse relation between the strength of encoding and the activation of the MTL during retrieval. Furthermore, the pattern of practice related increases in the auditory, posterior insular-opercular extending into perisylvian supra marginal region, and the right mid occipito-temporal region, may reflect a lower degree of inhibitory attentional modulation of task irrelevant processing and more fully developed representations of the abstract designs, respectively. We also suggest that free recall is dependent on bilateral prefrontal processing, in particular non-automatic free recall. The present results cofirm previous functional neuroimaging studies of memory retrieval indicating that recall is subserved by a network of interacting brain regions. Furthermore, the results indicate that some components of the neural network subserving free recall may have a dynamic role and that there is a functional restructuring of the information processing networks during the learning process

Detection of a Hypercharge Axion in ATLAS

This Master of Science thesis treats the hypercharge axion, which is a hypothetical pseudo-scalar particle with electroweak interactions. First, the theoretical context and the motivations for this study are discussed. In short, the hypercharge axion is introduced to explain the dominance of matter over antimatter in the universe and the existence of large-scale magnetic fields. Second, the phenomenological properties are analyzed and the distinguishing marks are underlined. These are basically the products of photons and $Z^0$s with high transverse momenta and invariant mass equal to that of the axion. Third, the simulation is carried out with two photons producing the axion which decays into $Z^0$s and/or photons. The event simulation is run through the simulator ATLFAST of ATLAS (A Toroidal Large Hadron Collider ApparatuS) at CERN. Finally, the characteristics of the axion decay are analyzed and the criteria for detection are presented. A study of the background is also included. The result is that for certain values of the axion mass and the mass scale (both in the order of a TeV), the hypercharge axion could be detected in ATLAS

Freeze-thaw damage evaluation and model creation for concrete exposed to freeze–thaw cycles at early-age

Concrete subjected to freeze–thaw cycles action at early-age will suffer serious physical damage, resulting in degradation of the concrete’s performance. The subsequent curing conditions after early-age freeze–thaw cycles (E-FTCs) are critical to the development of the properties of frost-damaged concrete. Four test environments were set up for this study, based on different numbers of E-FTCs and subsequent curing conditions. The later-age resistance to freeze–thaw of concrete exposed to E-FTCs was evaluated by analysing the influence of precuring times and curing conditions. Results show that the earlier the FTCs occur, the worse the later-age freeze–thaw resistance is. In particular, for the frost-damaged concrete with a pre-curing time of 18 h, its freeze–thaw resistance is significantlypublishedVersio