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

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

Dust during the Reionization

The possibility that population III stars have reionized the Universe at redshifts greater than 6 has recently gained momentum with WMAP polarization results. Here we analyse the role of early dust produced by these stars and ejected into the intergalactic medium. We show that this dust, heated by the radiation from the same population III stars, produces a submillimetre excess. The electromagnetic spectrum of this excess could account for a significant fraction of the FIRAS (Far Infrared Absolute Spectrophotometer) cosmic far infrared background above 700 micron. This spectrum, a primary anisotropy ($\Delta T$) spectrum times the $\nu^2$ dust emissivity law, peaking in the submillimetre domain around 750 micron, is generic and does not depend on other detailed dust properties. Arcminute--scale anisotropies, coming from inhomogeneities in this early dust, could be detected by future submillimetre experiments such as Planck HFI.Comment: 6 pages, 8 figures, accepted by A&A; clarifications made, typos fixed, results more exactly calculate

The Infrared Luminosity of Galaxy Clusters

The aim of this study is to quantify the infrared luminosity of clusters as a function of redshift and compare this with the X-ray luminosity. This can potentially constrain the origin of the infrared emission to be intracluster dust and/or dust heated by star formation in the cluster galaxies. We perform a statistical analysis of a large sample of galaxy clusters selected from existing databases and catalogues.We coadd the infrared IRAS and X-ray RASS images in the direction of the selected clusters within successive redshift intervals up to z = 1. We find that the total infrared luminosity is very high and on average 20 times higher than the X-ray luminosity. If all the infrared luminosity is to be attributed to emission from diffuse intracluster dust, then the IR to X-ray ratio implies a dust-to-gas mass abundance of 5e-4. However, the infrared luminosity shows a strong enhancement for 0.1 < z < 1, which cannot be attributed to cluster selection effects. We show that this enhancement is compatible with a star formation rate in the member galaxies that is typical of the central Mpc of the Coma cluster at z = 0 and evolves with the redshift as (1+z)^5. It is likely that most of the infrared luminosity that we measure is generated by the ongoing star formation in the member galaxies. From theoretical predictions calibrated on extinction measurements (dust mass abundance equal to 1e-5), we expect only a minor contribution, of a few percent, from intracluster dust.Comment: 9 pages, 7 figures, accepted july 31st 2008 for publication in Astronomy and Astrophysics, language improved for this versio

Structural correlates of semantic and phonemic fluency ability in first and second languages

Category and letter fluency tasks are commonly used clinically to investigate the semantic and phonological processes central to speech production, but the neural correlates of these processes are difficult to establish with functional neuroimaging because of the relatively unconstrained nature of the tasks. This study investigated whether differential performance on semantic (category) and phonemic (letter) fluency in neurologically normal participants was reflected in regional gray matter density. The participants were 59 highly proficient speakers of 2 languages. Our findings corroborate the importance of the left inferior temporal cortex in semantic relative to phonemic fluency and show this effect to be the same in a first language (L1) and second language (L2). Additionally, we show that the pre-supplementary motor area (pre-SMA) and head of caudate bilaterally are associated with phonemic more than semantic fluency, and this effect is stronger for L2 than L1 in the caudate nuclei. To further validate these structural results, we reanalyzed previously reported functional data and found that pre-SMA and left caudate activation was higher for phonemic than semantic fluency. On the basis of our findings, we also predict that lesions to the pre-SMA and caudate nuclei may have a greater impact on phonemic than semantic fluency, particularly in L2 speakers

Mass limits for heavy neutrinos

Neutrinos heavier than $M_Z/2\sim 45$ GeV are not excluded by particle physics data. Stable neutrinos heavier than this might contribute to the cosmic gamma ray background through annihilation in distant galaxies as well as to the dark matter content of the universe. We calculate the evolution of the heavy neutrino density in the universe as a function of its mass, $M_N$, and then the subsequent gamma ray spectrum from annihilation of distant $N\bar{N}$ (from $0<z<5$). The evolution of the heavy neutrino density in the universe is calculated numerically. In order to obtain the enhancement due to structure formation in the universe, we approximate the distribution of $N$ to be proportional to that of dark matter in the GalICS model. The calculated gamma ray spectrum is compared to the measured EGRET data. A conservative exclusion region for the heavy neutrino mass is 100 to 200 GeV, both from EGRET data and our re-evalutation of the Kamiokande data. The heavy neutrino contribution to dark matter is found to be at most 15%.Comment: 8 pages, 10 figures (Major revision

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