X-ray Observations of the Warm-Hot Intergalactic Medium

We present Chandra observations that provide the most direct evidence to date for the pervasive, moderate density, shock-heated intergalactic medium predicted by leading cosmological scenarios. We also comment briefly on future observations with Constellation-X.Comment: To be published in the proceedings of the conference "IGM/Galaxy Connection- The Distribution of Baryons at z=0". 6 page

Lukiolaisten ja ammatillista perustutkintoa suorittavien elämäntilanne ja toimeentulo

Tutkimuksessa tarkastellaan toisen asteen opiskelijoiden elämäntilannetta ja toimeentuloa. Ikä ja asumismuoto ovat keskeisimmät heidän toimeentuloonsa vaikuttavat tekijät. Lukiolaisista noin 93 prosenttia ja samanikäisistä ammatillista perustutkintoa suorittavista nuorista noin 70 prosenttia asuu vanhempiensa taloudessa. Yli 20-vuotiaista ammatillista perustutkintoa suorittavista joka viides asuu vanhempiensa kanssa. Lukiolaisista suurin osa (80 prosenttia) kokee pienistä tuloistaan huolimatta taloudellisen asemansa vähintään kohtalaiseksi, mikä heijastelee lähinnä heidän taloudellisesti hyvin epäitsenäistä asemaansa. Huonoksi tai hyvin huonoksi oman taloudellisen asemansa kokee joka viides lukiolainen. Ammatillista tutkintoa suorittavien kokemus omasta taloudellisesta asemasta on huomattavasti negatiivisempi: 45 prosenttia ilmoittaa taloudellisen tilanteensa olevan huono tai hyvin huono. Eroa kokemuksissa eri oppilaitoksissa opiskelevien välillä selittävät ikä, itsenäisempi asuminen ja vanhempien pienemmät tulot. Toisen asteen opiskelijoiden mielestä opintotuki on riittämätön ja järjestelmä epäoikeudenmukainen. Kriittisimpiä ovat opintotukea saaneet. Toisen asteen opintotukeen liittyy olennaisesti kysymys vanhempien, yksilön itsensä ja yhteiskunnan vastuusta opintojen aikaisen toimeentulon rahoittamisessa. Alle 20-vuotiailla, asuivatpa he vanhempiensa taloudessa tai itsenäisesti, opintotukeen vaikuttaa vanhempien tuloja koskeva tiukka tarveharkinta. Lukiolaisista vain 18 prosenttia ja ammatillista perustutkintoa suorittavista noin puolet sai opintorahaa keväällä 2006. Ammatillista tutkintoa suorittavista suurempi osa kuin lukiolaisista on yli 20-vuotiaita ja saa näin ollen opintorahaa. Opintorahan saantiin vaikuttaa heillä myös vanhempien pienemmät tulot sekä yksinhuoltajavanhempien suurempi osuus. 18–19-vuotiaiden opiskelijoiden toimeentulotukiasiakkuudet ovat lisääntyneet merkittävästi 1990-luvun alun jälkeen, minkä taustalla voi olla opintorahan reaaliarvon lasku sekä toisen asteen opintotukeen oikeutettujen osuuden lasku. Heikoimmassa taloudellisessa asemassa ovat itsenäisesti asuvat, etenkin toisella paikkakunnalla opiskelevat nuoret. Itsenäisesti asuvat 16–25-vuotiaat ammatillista perustutkintoa suorittavat ilmoittavat nettokuukausituloikseen 384 euroa kuukaudessa. Itsenäisesti asuvista yli 90 prosenttia ilmoittaa vanhempiensa avustavan säännöllisesti tai satunnaisesti suoraan rahallisesti tai maksamalla asumiskuluja ja laskuja. Kokonaan ilman vanhempien taloudellista tukea on itsenäisesti asuvista alle 20-vuotiaista kahdeksan prosenttia ja noin joka viidennellä tuki on satunnaista. Vuonna 2006 korotettiin vanhempien tulorajoja 15 prosenttia ja vuonna 2007 korotetaan 30 prosenttia. Nykyistä useampi pääsee taas opintorahan piiriin ja osalla tukeen oikeutetuista tuen määrä nousee merkittävästi. Kahden elättäjän lapsiperheissä tulorajojen muutos tuo etuuden saajien joukkoon nuoria verraten läheltä mediaanituloisten ryhmää ja yksinhuoltajien lapsista vain ylimpään tulokymmenykseen kuuluvat lapset tulevat jäämään järjestelmän ulkopuolelle. Tulorajojen indeksijärjestelmä tai säännölliset tulorajojen tarkistukset estäisivät tällaiset vaivihkaa tapahtuvat tuen saatavuuden ja tuen tason laskun.9,00 euro

Uncertainties and implications of applying aggregated data for spatial modelling of atmospheric ammonia emissions

Ammonia emissions vary greatly at a local scale, and effects (eutrophication, acidification) occur primarily close to sources. Therefore it is important that spatially distributed emission estimates are located as accurately as possible. The main source of ammonia emissions is agriculture, and therefore agricultural survey statistics are the most important input data to an ammonia emission inventory alongside per activity estimates of emission potential. In the UK, agricultural statistics are collected at farm level, but are aggregated to parish level, NUTS-3 level or regular grid resolution for distribution to users. In this study, the Modifiable Areal Unit Problem (MAUP), associated with such amalgamation, is investigated in the context of assessing the spatial distribution of ammonia sources for emission inventories. England was used as a test area to study the effects of the MAUP. Agricultural survey data at farm level (point data) were obtained under license and amalgamated to different areal units or zones: regular 1-km, 5-km, 10-km grids and parish level, before they were imported into the emission model. The results of using the survey data at different levels of amalgamation were assessed to estimate the effects of the MAUP on the spatial inventory. The analysis showed that the size and shape of aggregation zones applied to the farm-level agricultural statistics strongly affect the location of the emissions estimated by the model. If the zones are too small, this may result in false emission “hot spots”, i.e., artificially high emission values that are in reality not confined to the zone to which they are allocated. Conversely, if the zones are too large, detail may be lost and emissions smoothed out, which may give a false impression of the spatial patterns and magnitude of emissions in those zones. The results of the study indicate that the MAUP has a significant effect on the location and local magnitude of emissions in spatial inventories where amalgamated, zonal data are used

Exponential Stellar Disks in Low Surface Brightness Galaxies: A Critical Test of Viscous Evolution

Viscous redistribution of mass in Milky Way-type galactic disks is an appealing way of generating an exponential stellar profile over many scale lengths, almost independent of initial conditions, requiring only that the viscous timescale and star formation timescale are approximately equal. However, galaxies with solid-body rotation curves cannot undergo viscous evolution. Low surface brightness (LSB) galaxies have exponential surface brightness profiles, yet have slowly rising, nearly solid-body, rotation curves. Because of this, viscous evolution may be inefficient in LSB galaxies: the exponential profiles, instead would give important insight into initial conditions for galaxy disk formation. Using star formation laws from the literature, and tuning the efficiency of viscous processes to reproduce an exponential stellar profile in Milky Way-type galaxies, I test the role of viscous evolution in LSB galaxies. Under the conservative and not unreasonable condition that LSB galaxies are gravitationally unstable for at least a part of their lives, I find that it is impossible to rule out a significant role for viscous evolution. This type of model still offers an attractive way of producing exponential disks, even in LSB galaxies with slowly-rising rotation curves

Controlling passively-quenched single photon detectors by bright light

Single photon detectors based on passively-quenched avalanche photodiodes can be temporarily blinded by relatively bright light, of intensity less than a nanowatt. I describe a bright-light regime suitable for attacking a quantum key distribution system containing such detectors. In this regime, all single photon detectors in the receiver Bob are uniformly blinded by continuous illumination coming from the eavesdropper Eve. When Eve needs a certain detector in Bob to produce a click, she modifies polarization (or other parameter used to encode quantum states) of the light she sends to Bob such that the target detector stops receiving light while the other detector(s) continue to be illuminated. The target detector regains single photon sensitivity and, when Eve modifies the polarization again, produces a single click. Thus, Eve has full control of Bob and can do a successful intercept-resend attack. To check the feasibility of the attack, 3 different models of passively-quenched detectors have been tested. In the experiment, I have simulated the intensity diagrams the detectors would receive in a real quantum key distribution system under attack. Control parameters and side effects are considered. It appears that the attack could be practically possible.Comment: Experimental results from a third detector model added. Minor corrections and edits made. 11 pages, 10 figure

Hydrogen-like nitrogen radio line from hot interstellar and warm-hot intergalactic gas

Hyperfine structure lines of highly-charged ions may open a new window in observations of hot rarefied astrophysical plasmas. In this paper we discuss spectral lines of isotopes and ions abundant at temperatures 10^5-10^7 K, characteristic for warm-hot intergalactic medium, hot interstellar medium, starburst galaxies, their superwinds and young supernova remnants. Observations of these lines will allow to study bulk and turbulent motions of the observed target and will broaden the information about the gas ionization state, chemical and isotopic composition. The most prospective is the line of the major nitrogen isotope having wavelength 5.65 mm (Sunyaev and Churazov 1084). Wavelength of this line is well-suited for observation of objects at z=0.15-0.6 when it is redshifted to 6.5-9 mm spectral band widely-used in ground-based radio observations, and, for example, for z>=1.3, when the line can be observed in 1.3 cm band and at lower frequencies. Modern and future radio telescopes and interferometers are able to observe the absorption by 14-N VII in the warm-hot intergalactic medium at redshifts above z=0.15 in spectra of brightest mm-band sources. Sub-millimeter emission lines of several most abundant isotopes having hyperfine splitting might also be detected in spectra of young supernova remnants.Comment: 12 pages, 5 figures, accepted by Astronomy Letters; v3: details added; error fixe

Equilibration processes in the Warm-Hot Intergalactic Medium

The Warm-Hot Intergalactic Medium (WHIM) is thought to contribute about 40-50 % to the baryonic budget at the present evolution stage of the universe. The observed large scale structure is likely to be due to gravitational growth of density fluctuations in the post-inflation era. The evolving cosmic web is governed by non-linear gravitational growth of the initially weak density fluctuations in the dark energy dominated cosmology. Non-linear structure formation, accretion and merging processes, star forming and AGN activity produce gas shocks in the WHIM. Shock waves are converting a fraction of the gravitation power to thermal and non-thermal emission of baryonic/leptonic matter. They provide the most likely way to power the luminous matter in the WHIM. The plasma shocks in the WHIM are expected to be collisionless. Collisionless shocks produce a highly non-equilibrium state with anisotropic temperatures and a large differences in ion and electron temperatures. We discuss the ion and electron heating by the collisionless shocks and then review the plasma processes responsible for the Coulomb equilibration and collisional ionisation equilibrium of oxygen ions in the WHIM. MHD-turbulence produced by the strong collisionless shocks could provide a sizeable non-thermal contribution to the observed Doppler parameter of the UV line spectra of the WHIM.Comment: 13 pages, 4 figures, accepted for publication in Space Science Reviews, special issue "Clusters of galaxies: beyond the thermal view", Editor J.S. Kaastra, Chapter 8; work done by an international team at the International Space Science Institute (ISSI), Bern, organised by J.S. Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke

Suv4-20h Histone Methyltransferases Promote Neuroectodermal Differentiation by Silencing the Pluripotency-Associated Oct-25 Gene

Post-translational modifications (PTMs) of histones exert fundamental roles in regulating gene expression. During development, groups of PTMs are constrained by unknown mechanisms into combinatorial patterns, which facilitate transitions from uncommitted embryonic cells into differentiated somatic cell lineages. Repressive histone modifications such as H3K9me3 or H3K27me3 have been investigated in detail, but the role of H4K20me3 in development is currently unknown. Here we show that Xenopus laevis Suv4-20h1 and h2 histone methyltransferases (HMTases) are essential for induction and differentiation of the neuroectoderm. Morpholino-mediated knockdown of the two HMTases leads to a selective and specific downregulation of genes controlling neural induction, thereby effectively blocking differentiation of the neuroectoderm. Global transcriptome analysis supports the notion that these effects arise from the transcriptional deregulation of specific genes rather than widespread, pleiotropic effects. Interestingly, morphant embryos fail to repress the Oct4-related Xenopus gene Oct-25. We validate Oct-25 as a direct target of xSu4-20h enzyme mediated gene repression, showing by chromatin immunoprecipitaton that it is decorated with the H4K20me3 mark downstream of the promoter in normal, but not in double-morphant, embryos. Since knockdown of Oct-25 protein significantly rescues the neural differentiation defect in xSuv4-20h double-morphant embryos, we conclude that the epistatic relationship between Suv4-20h enzymes and Oct-25 controls the transit from pluripotent to differentiation-competent neural cells. Consistent with these results in Xenopus, murine Suv4-20h1/h2 double-knockout embryonic stem (DKO ES) cells exhibit increased Oct4 protein levels before and during EB formation, and reveal a compromised and biased capacity for in vitro differentiation, when compared to normal ES cells. Together, these results suggest a regulatory mechanism, conserved between amphibians and mammals, in which H4K20me3-dependent restriction of specific POU-V genes directs cell fate decisions, when embryonic cells exit the pluripotent state

Thyrotropin-releasing hormone (TRH) promotes wound re-epithelialisation in frog and human skin

There remains a critical need for new therapeutics that promote wound healing in patients suffering from chronic skin wounds. This is, in part, due to a shortage of simple, physiologically and clinically relevant test systems for investigating candidate agents. The skin of amphibians possesses a remarkable regenerative capacity, which remains insufficiently explored for clinical purposes. Combining comparative biology with a translational medicine approach, we report the development and application of a simple ex vivo frog (Xenopus tropicalis) skin organ culture system that permits exploration of the effects of amphibian skin-derived agents on re-epithelialisation in both frog and human skin. Using this amphibian model, we identify thyrotropin-releasing hormone (TRH) as a novel stimulant of epidermal regeneration. Moving to a complementary human ex vivo wounded skin assay, we demonstrate that the effects of TRH are conserved across the amphibian-mammalian divide: TRH stimulates wound closure and formation of neo-epidermis in organ-cultured human skin, accompanied by increased keratinocyte proliferation and wound healing-associated differentiation (cytokeratin 6 expression). Thus, TRH represents a novel, clinically relevant neuroendocrine wound repair promoter that deserves further exploration. These complementary frog and human skin ex vivo assays encourage a comparative biology approach in future wound healing research so as to facilitate the rapid identification and preclinical testing of novel, evolutionarily conserved, and clinically relevant wound healing promoters