104 research outputs found
Two Populations of Young Massive Star Clusters in Arp 220
We present new optical observations of young massive star clusters in Arp
220, the nearest ultraluminous infrared galaxy, taken in UBVI with the Hubble
Space Telescope ACS/HRC camera. We find a total of 206 probable clusters whose
spatial distribution is centrally concentrated toward the nucleus of Arp 220.
We use model star cluster tracks to determine ages, luminosities, and masses
for 14 clusters with complete UBVI indices or previously published
near-infrared data. We estimate rough masses for 24 additional clusters with I
< 24 mag from BVI indices alone. The clusters with useful ages fall into two
distinct groups: a ``young'' population (< 10 Myr) and an intermediate-age
population (~300 Myr). There are many clusters with masses clearly above 10^6
Msun and possibly even above 10^7 Msun in the most extreme instances. These
masses are high enough that the clusters being formed in the Arp 220 starburst
can be considered as genuine young globular clusters. In addition, this study
allows us to extend the observed correlation between global star formation rate
and maximum cluster luminosity by more than an order of magnitude in star
formation rate.Comment: 30 pages, 8 figures; figs 1-3 in color; accepted to Ap
Magnetic local time variation and scaling of poleward auroral boundary dynamics
The balance of dayside and nightside reconnection processes within the Earth's magnetosphere, and its effect on the amount of open magnetic flux threading the ionosphere is well understood in terms of the expanding-contracting polar cap model. However, the nature and character of the consequential fluctuations in the polar cap boundary are poorly understood. By using the poleward auroral luminosity boundary (PALB), as measured by the FUV instrument of the IMAGE spacecraft, as a proxy for the polar cap boundary we have studied the motion of this boundary for more than two years across the complete range of magnetic local time. Our results show that the dayside PALB dynamics are broadly self-similar on timescales of 12âminutes to 6âhours and appear to be monofractal. Similarity with the characteristics of solar wind and interplanetary magnetic field (IMF) variability suggest that this dayside monofractal behaviour is predominantly inherited from the solar wind via the reconnection process. The nightside PALB dynamics exhibit scale-free behaviour at intermediate timescales (12-90 minutes) and appear to be multifractal. We propose that this character is a result of the intermittent multifractal structure of magnetotail reconnection
The driving mechanisms of particle precipitation during the moderate geomagnetic storm of 7 January 2005
International audienceThe arrival of an interplanetary coronal mass ejection (ICME) triggered a sudden storm commencement (SSC) at ~09:22 UT on the 7 January 2005. The ICME followed a quiet period in the solar wind and interplanetary magnetic field (IMF). We present global scale observations of energetic electron precipitation during the moderate geomagnetic storm driven by the ICME. Energetic electron precipitation is inferred from increases in cosmic noise absorption (CNA) recorded by stations in the Global Riometer Array (GLORIA). No evidence of CNA was observed during the first four hours of passage of the ICME or following the sudden commencement (SC) of the storm. This is consistent with the findings of Osepian and Kirkwood (2004) that SCs will only trigger precipitation during periods of geomagnetic activity or when the magnetic perturbation in the magnetosphere is substantial. CNA was only observed following enhanced coupling between the IMF and the magnetosphere, resulting from southward oriented IMF. Precipitation was observed due to substorm activity, as a result of the initial injection and particles drifting from the injection region. During the recovery phase of the storm, when substorm activity diminished, precipitation due to density driven increases in the solar wind dynamic pressure (Pdyn) were identified. A number of increases in Pdyn were shown to drive sudden impulses (SIs) in the geomagnetic field. While many of these SIs appear coincident with CNA, SIs without CNA were also observed. During this period, the threshold of geomagnetic activity required for SC driven precipitation was exceeded. This implies that solar wind density driven SIs occurring during storm recovery can drive a different response in particle precipitation to typical SCs
The impact of near-term climate policy choices on technology and emission transition pathways
This paper explores the implications of delays (to 2030) in implementing optimal policies for long-term transition pathways to limit climate forcing to 450 ppm CO2e on the basis of the AMPERE Work Package 2 model comparison study.
The paper highlights the critical importance of the period 2030-2050 for ambitious mitigation strategies. In this period, the most rapid shift to low greenhouse gas emitting technology occurs. In the delayed response emission mitigation scenarios, an even faster transition rate in this period is required to compensate for the additional emissions before 2030. Our physical deployment measures indicate that the availability of CCS technology could play a critical role in facilitating the attainment of ambitious mitigation goals. Without CCS, deployment of other mitigation technologies would become extremely high in the 2030-2050 period. Yet the presence of CCS greatly alleviates the challenges to the transition particularly after the delayed climate policies, lowering the risk that the long-term goal becomes unattainable.
The results also highlight the important role of bioenergy with CO2 capture and storage (BECCS), which facilitates energy production with negative carbon emissions. If BECCS is available, transition pathways exceed the emission budget in the mid-term, removing the excess with BECCS in the long term. Excluding either BE or CCS from the technology portfolio implies that emission reductions need to take place much earlier
Recovery phase of magnetic storms induced by different interplanetary drivers
Statistical analysis of Dst behaviour during recovery phase of magnetic
storms induced by different types of interplanetary drivers is made on the
basis of OMNI data in period 1976-2000. We study storms induced by ICMEs
(including magnetic clouds (MC) and Ejecta) and both types of compressed
regions: corotating interaction regions (CIR) and Sheaths. The shortest,
moderate and longest durations of recovery phase are observed in ICME-, CIR-,
and Sheath-induced storms, respectively. Recovery phases of strong ( nT) magnetic storms are well approximated by hyperbolic functions
with constant times for all types of drivers
while for moderate ( nT) storms profile can not
be approximated by hyperbolic function with constant because
hyperbolic time increases with increasing time of recovery phase.
Relation between duration and value for storms induced by ICME and
Sheath has 2 parts: and duration correlate at small durations while
they anticorrelate at large durations.Comment: 18 pages, 4 figures, 2 tables, submitted to JGR special issue
"Response of Geospace to High-Speed Streams
Geoeffectiveness and efficiency of CIR, Sheath and ICME in generation of magnetic storms
We investigate relative role of various types of solar wind streams in
generation of magnetic storms. On the basis of the OMNI data of interplanetary
measurements for the period of 1976-2000 we analyze 798 geomagnetic storms with
Dst < -50 nT and their interplanetary sources: corotating interaction regions
(CIR), interplanetary CME (ICME) including magnetic clouds (MC) and Ejecta and
compression regions Sheath before both types of ICME. For various types of
solar wind we study following relative characteristics: occurrence rate; mass,
momentum, energy and magnetic fluxes; probability of generation of magnetic
storm (geoeffectiveness) and efficiency of process of this generation. Obtained
results show that despite magnetic clouds have lower occurrence rate and lower
efficiency than CIR and Sheath they play an essential role in generation of
magnetic storms due to higher geoeffectiveness of storm generation (i.e higher
probability to contain large and long-term southward IMF Bz component).Comment: 23 pages, 4 figures, 3 tables, submitted to JGR special issue
"Response of Geospace to High-Speed Streams
Assessing the Impact and Effectiveness of Hearing Voices Network Self-Help Groups
The Hearing Voices Network (HVN) is an influential service-user led organisation that
promotes self-help as an important aspect of recovery. This study presents the first systematic
assessment of the impact and effectiveness of HVN self-help groups. A customized 45-item
questionnaire, the Hearing Voices Groups Survey, was sent to 62 groups affiliated with the
English HVN. 101 responses were received. Group attendance was credited with a range of
positive emotional, social and clinical outcomes. Aspects that were particularly valued
included: opportunities to meet other voice hearers, provision of support that was unavailable
elsewhere, and the group being a safe and confidential place to discuss difficult issues.
Participants perceived HVN groups to facilitate recovery processes and to be an important
resource for helping them cope with their experiences. Mental health professionals can use
their expertise to support the successful running of these groups
Biogeochemical signatures in the lichen Hypogymnia physodes in the mid Urals
Abstract Multi-element content and uranium (U) isotopes were investigated in the lichen Hypogymnia physodes (native and transplants) sampled across a 60-km transect, centred on Karabash smelter town, from Turgoyak Lake (SW) to Kyshtym (NE) to investigate the origin of U. Kyshtym was the site of a major nuclear accident in 1957. 234 U/ 238 U activity ratios in native thalli sampled during July 2001 were within the natural isotopic ratio in minerals. Uranium/thorium (U/Th) ratios were higher in native thalli towards the NE (average 0.73) than those in the SW (average 0.57). Element signatures in native thalli and transplants suggest U was derived from fossil fuel combustion from Karabash and sources lying further to the east. Systematic and significant U enrichment indicative of a nuclear fuel cycle source was not detected in any sample. Element signatures in epiphytic lichen transplants and native thalli provide a powerful method to evaluate U deposition
A discursive approach to narrative accounts of hearing voices and recovery
Substantive objective: To research the range of discursive constructions ârecoveredâ voice hearers employ to describe hearing voices and the implications for positioning and subjectivity (what can be thought and felt) using each construction.
Methodological objective and method: To explore a âsympatheticâ application of Foucauldian discourse analysis, adapting Willigâs (2008 Willig, C. 2008. Introducing Qualitative Research in Psychology, Maidenhead: Open University Press. ) method, analysing two published accounts.
Results and conclusions: Heterogeneous discursive constructions for talking about hearing voices were identified, including: âmany-âselvesââ, âtaking-the-lead-in-your-own-recoveryâ, âvoices-as-an-âimagined-worldââ and âvoices-as-a-coping-strategy-for-dealing-with-traumaâ. The discourse of the biomedical model was not prominent, suggesting alternate discursive constructions may create subjects with a greater capacity for âliving with voicesâ and create a subjectivity from which vantage point the experience holds meaning and value and can be integrated into life experiences. This research may have useful clinical applications for mental health services aiming to collaboratively explore service usersâ ways of understanding hearing voices
Social Pedagogy: An Approach Without Fixed Recipes
A historical and theoretical reconstruction of the specificity and peculiarity of the discipline of social pedagogy, as it has developed in Denmark. Social pedagogy takes its departure from the idea that the individual person and the community are complementary but at the same time opposed to each other, so the task of social pedagogy is rebalancing the dynamics between the two. Social pedagogy is also characterised as a discipline with three dimensions: a practical dimension, a theoretical dimension and a professional dimension. The
professionalâs task is neither to apply theory in practice nor to uphold the usual practice; it is to mediate between theory and practice. The specificity of the discipline gives rise to particular challenges and
dilemmas that theorists make understandable and transparent and practitioners have to deal with. A big challenge for social pedagogy is the quest for evidence-based methods that overrides the specificity of the
social pedagogical approach. Balancing different forms of knowledge implies that programmes and methods are used as inspiration that can be contained in a social pedagogical approach
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