Luminosity Functions of Gamma-Ray Burst Afterglows

Aims: Use the standard fireball model to create virtual populations of gamma-ray burst afterglows and study their luminosity functions. Methods: We randomly vary the parameters of the standard fireball model to create virtual populations of afterglows. We use the luminosity of each burst at an observer's time of 1 day to create a luminosity function and compare our results with available observational data to assess the internal consistency of the standard fireball model. Results: We show that the luminosity functions can be described by a function similar to a log normal distribution with an exponential cutoff. The function parameters are frequency dependent but not very dependent on the model parameter distributions used to create the virtual populations. Comparison with observations shows that while there is good general agreement with the data, it is difficult to explain simultaneously the X-ray and optical data. Possible reasons for this are discussed and the most likely one is that the standard fireball model is incomplete and that decoupling of the X-ray and optical emission mechanism may be needed.Comment: 5 pages, 4 figures; accepted for publication in A&

Þankabrot um spánsku veikina 1918-1919

Neðst á síðunni er hægt að nálgast greinina í heild sinni með því að smella á hlekkinn View/OpenÍ tímaritinu Sögu á þessu ári er grein um spánsku veikina á Íslandi sem er að stofni til BA-ritgerð í sagnfræði við Háskóla Íslands (1). Ritgerðin er vel unnin og hefur meðal annars sér til ágætis, að vitnað er í samtöl við fólk sem mundi veikina, - ekki síst í Reykjavík þar sem hún var verst - en er nú gengið til feðra sinna. Höfundur getur þess að spánska veikin hafi lítið verið rannsökuð sagnfræðilega hér á landi. Við lestur þessara orða vaknaði sú spurning, hvort nokkru betur hefði verið staðið að læknisfræðilegum rannsóknum á spánsku veikinni. Eftir að hafa skoðað hvað hefði verið unnið í þessu efni fannst mér, að svarið væri fremur neikvætt en jákvætt. Mér rann á endanum blóðið til skyldunnar og ég ákvað að setja saman þennan pistil sem er vissulega engin heildarúttekt, heldur þankabrot um áhugavert efni. Ég fjalla um störf þeirra tveggja lækna og tengdafeðga, Þórðar J. Thoroddsen og Steingríms Matthíassonar, sem öðrum læknum fremur hafa skrifað um spánsku veikina 1918-1919. Þá þykir mér hlýða að halda á loft framlagi tveggja ólæknislærðra manna, þeirra Lárusar H. Bjarnasonar, prófessors, og Thors Jensens, útgerðarmanns, til annars vegar hjúkrunar og skipulags lækninga og hins vegar matargjafa í spánsku veikinni. Ég hef velt nokkuð fyrir mér gagnsemi eða gagnsleysi lyfja, sem notuð voru gegn spánsku veikinni og er því kafli um þetta efni, þótt aðgengilegar heimildir séu allnokkuð í molum. Að síðustu er stutt umræða og ályktanir

Icelandic avalanche run out models compared with topographical models used in other countries

A statistical topographical model for the computation of runout for snow avalanches in Iceland has been derived from a recently assembled data sel of long Icelandic snow avalanches. The avalanches are from hills above towns in western, northern and eastern Iceland. The model, a = O.85ß, expresses the average slope of the avalanche path, a, as directly proportional to the average slope of the avalanche track, ß. A similar model for a dala sel of avalanches collected through systematic investigations of several regions in western Norway is found to be a = 0.93 ß. The residual standard error in a for the models is similar, O"ó,a = 2. 20 for the Icelandic dala and O"ó,a = 2.10 for the Norwegian data. The models thus indicate that avalanches in the Icelandic data set reach somewhat further than avalanches in the Norwegian dala set for similar ß-angles, but the relationship between aand ß-angles in the two data sets is nevertheless quite similar (cf Fig. 2). Worthwhile improvements in the models were not obtained by adding intercept or curvature terms or terms corresponding to other parameters than ß. Statistical models based on run out ratios were not found to be an improvement over models based on a- and ß-angles

Survival of the Mýrdalsjökull ice cap through the Holocene thermal maximum: evidence from sulphur contents in Katla tephra layers (Iceland) from the last ∼8400 years

International audienceThe climate in Iceland was drier and warmer during the Holocene thermal maximum than it is today and it has been suggested that ice caps disappeared entirely. Katla, a volcano covered by the Mýrdalsjökull ice cap in southern Iceland, has erupted rather steadily throughout the Holocene. Preand post-eruption sulphur concentrations in its products have been determined in previous studies, through melt inclusions trapped in phenocrysts (pre-eruption mean values of 2155 ± 165 ppm) and fully degassed magmatic tephra (post-eruption mean values of 445 ± 130 ppm). The phreatomagmatic tephra has much more variable S contents (550-1775 ppm) and spans the compositional gap between magmatic tephra and melt inclusions. These variable sulphur values are attributed to arresting of degassing as the magma is quenched upon contact with external water in the shallow levels of the volcano conduit. Sulphur in Katla tephra can thus be used to evaluate whether Mýrdalsjökull survived the warm spells of the Holocene. In this study, sulphur concentrations in tephra layers representing the last ∼8400 years of the volcano's eruption history were measured, revealing concentrations in the phreatomagmatic range (600-1600 ppm). Hence, we conclude that over the last ∼8400 years, explosive activity at Katla has been dominated by phreatomagmatic eruptions, implying that the Mýrdalsjökull ice cap has been present throughout the Holocene

Iron and iron/manganese ratio in forage from Icelandic sheep farms: relation to scrapie

This study was undertaken in order to examine whether any connection existed between the amounts of iron in forage and the sporadic occurrence of scrapie observed in certain parts of Iceland. As iron and manganese are considered antagonistic in plants, calculation of the Fe/Mn ratios was also included by using results from Mn determination earlier performed in the same samples. Forage samples (n = 170) from the summer harvests of 2001–2003, were collected from 47 farms for iron and manganese analysis. The farms were divided into four categories: 1. Scrapie-free farms in scrapie-free areas (n = 9); 2. Scrapie-free farms in scrapie-afflicted areas (n = 17); 3. Scrapie-prone farms (earlier scrapie-afflicted, restocked farms) (n = 12); 4. Scrapie-afflicted farms (n = 9). Farms in categories 1 and 2 are collectively referred to as scrapie-free farms. The mean iron concentration in forage samples from scrapie-afflicted farms was significantly higher than in forage samples from farms in the other scrapie categories (P = 0.001). The mean Fe/Mn ratio in forage from scrapie-afflicted farms was significantly higher than in forage from scrapie-free and scrapie-prone farms (P < 0.001). The results indicated relative dominance of iron over manganese in forage from scrapie-afflicted farms as compared to farms in the other categories. Thus thorough knowledge of iron, along with manganese, in soil and vegetation on sheep farms could be a pivot in studies on sporadic scrapie

Thalidomide: Drug of horror and last resort. A review. Part 2: Actions, mechanisms of actions and therapeutic uses of thalidomide

Neðst á síðunni er hægt að nálgast greinina í heild sinni með því að smella á hlekkinn View/OpenThe story of thalidomide to 1964 or thereabout is the topic of Part 1 of this review. Part 2 deals with recent work on the actions and mechanisms of actions of thalidomide and clinical trials with the drug up to the present day. In 1964 it was found that thalidomide had an unexpected therapeutic effect on erythema nodosum leprosum. About the same time it was suggested that thalidomide might be effective against malignant diseases. Due to molecular similarities between thalidomide and guanosine it is considered likely that thalidomide molecules intercalate in guanosine-rich promoter regions in genes of certain integrins that steer vascularization, and at the same time formation of other tissues, especially in limbs of the fetus. This could interfere with transcription of particular genes and explain fetal damage due to thalidomide and in part, at least, its effect on neoplastic diseases. Thalidomide has a remarkable inhibitory effect on production of TNFa, which is central to its therapeutic effect on inflammatory diseases like erythema nodosum leprosum and Crohn's disease. Thalidomide also induces proliferation in T cells and increases their output of IL-2 and INFg. This could, along with other things, explain its effects on neoplastic diseases. Thalidomide, with dexamethasone, is now the drug of choice in treatment of multiple myeloma. Thalidomide and its derivatives (analogues), considered to have a more specific and intense effect than thalidomide itself, are now being tested in well planned clinical trials for treatment of neoplastic diseases. These are diseases where few or no other therapeutic options are present. The path of thalidomide through time is quite remarkable: From being the drug of sheer horror 40 years ago, it is now occasionally the drug of last resort for heavily suffering and often dying patients.Saga talídómíðs fram til 1964 eða þar um bil er rakin í fyrri hluta þessa yfirlits. Í síðari hluta er fjallað um rannsóknir á verkunum og verkunarháttum talídómíðs og rannsóknum á gildi þess til lækninga fram á þennan dag. Árið 1964 fannst að talídómíð hafði óvænta verkun á húðhnútabólgu í holdsveiki (erythema nodosum leprosum). Skömmu síðar var og bent á hugsanlega gagnsemi talídómíðs við illkynja sjúkdóma. Vegna líkinda milli sameinda talídómíðs og gvanósíns er talið að sameindir talídómíðs skjóti sér inn í gvanósínríkar stýriraðir gena tiltekinna integrína, sem ráða æðamyndun og samhliða því myndun annarra vefja, einkum í útlimum, og hamli umritun þeirra. Þetta gæti skýrt fósturskemmandi verkun talídómíðs og að hluta, að minnsta kosti, verkun þess á illkynja sjúkdóma. Talídómíð hefur enn fremur marktæka hamlandi verkun á TNFa sem er miðsvæðis í verkun þess á bólgusjúkdóma á borð við húðhnútabólgu í holdsveiki og svæðisþarmabólgu (Crohnsjúkdóm). Talídómíð örvar jafnframt T lymfufrumur (T eitilfrumur) til þess að skipta sér og auka myndun á IL-2 og INFg. Kann það ásamt öðru að skýra verkun þess á illkynja sjúkdóma. Talídómíð er nú ásamt dexametasóni kjörlyf við meðferð á mergæxli (multiple myeloma). Talídómíð og afleiður þess, sem eiga að hafa öflugri og sértækari verkun en það, eru nú reynd til hlítar í vel skipulögðum klínískum rannsóknum við meðferð á erfiðum illkynja sjúkdómum. Þetta eru sjúkdómar þar sem fárra eða engra annarra kosta er völ. Ferill talídómíðs er sérstakur: Frá því að vera lyf hörmunga er það nú 40 árum síðar stundum lyf hjálpræðis fyrir sárþjáða og langt leidda sjúklinga. Í fyrri hluta þessa yfirlits er fjallað um tilurð talídómíðs, sameindargerð og fyrsta feril og er í stórum dráttum saga talídómíðs til 1963 eða þar um bil (1). Í þessum hluta verður fjallað um verkanir og verkunarhætti talídómíðs og notkun þess til lækninga og framtíðarhorfur í því efni