13,937 research outputs found
VLA neutral hydrogen imaging of compact groups
Images of the neutral hydrogen (H I) in the direction of the compact groups of galaxies, HCG 31, HCG 44, and HCG 79 are presented. The authors find in HCG 31 and HCG 79, emission contained within a cloud much larger than the galaxies as well as the entire group. The H I emission associated with HCG 44 is located within the individual galaxies but shows definite signs of tidal interactions. The authors imaged the distribution and kinematics of neutral hydrogen at the two extremes of group sizes represented in Hickson's sample. HCG 44 is at the upper limit while HCG 18, HCG 31, and HCG 79 are at the lower end. Although the number of groups that have been imaged is still very small, there may be a pattern emerging which describes the H I morphology of compact groups. The true nature of compact groups has been the subject of considerable debate and controversy. The most recent observational and theoretical evidence strongly suggests that compact groups are physically dense, dynamical systems that are in the process of merging into a single object (Williams and Rood 1987, Hickson and Rood 1988, Barnes 1989). The neutral hydrogen deficiency observed by Williams and Rood (1987) is consistent with a model in which frequent galactic collisions and interactions have heated some of the gas during the short lifetime of the group. The H I disks which are normally more extended than the luminous ones are expected to be more sensitive to collisions and to trace the galaxy's response to recent interactions. Very Large Array observations can provide in most cases the spatial resolution needed to confirm the dynamical interactions in these systems
DAzLE: The Dark Ages z (redshift) Lyman-alpha Explorer
DAzLE is an near infrared narrowband differential imager being built by the
Institute of Astronomy, Cambridge, in collaboration with the Anglo-Australian
observatory. It is a special purpose instrument designed with a sole aim; the
detection of redshifted Lyman-alpha emission from star forming galaxies at z>7.
DAzLE will use pairs of high resolution (R=1000) narrowband filters to exploit
low background `windows' in the near infrared sky emission spectrum. This will
enable it to reach sensitivities of ~2E-21 W/m^2, thereby allowing the
detection of z>7 galaxies with star formation rates as low as a few solar
masses per year. The design of the instrument, and in particular the crucial
narrowband filters, are presented. The predicted performance of DAzLE,
including the sensitivity, volume coverage and expected number counts, is
discussed. The current status of the DAzLE project, and its projected timeline,
are also presented.Comment: 11 pages, 7 figures, to appear in Proceedings of SPIE Vol. 5492,
Ground-based Instrumentation for Astronom
Between Philosophy and Art
Similarity and difference, patterns of variation, consistency and coherence: these are the reference points of the philosopher. Understanding experience, exploring ideas through particular instantiations, novel and innovative thinking: these are the reference points of the artist. However, at certain points in the proceedings of our Symposium titled, Next to Nothing: Art as Performance, this characterisation of philosopher and artist respectively might have been construed the other way around. The commentator/philosophers referenced their philosophical interests through the particular examples/instantiations created by the artist and in virtue of which they were then able to engage with novel and innovative thinking. From the artists’ presentations, on the other hand, emerged a series of contrasts within which philosophical and artistic ideas resonated. This interface of philosopher-artist bore witness to the fact that just as art approaches philosophy in providing its own analysis, philosophy approaches art in being a co-creator of art’s meaning. In what follows, we discuss the conception of philosophy-art that emerged from the Symposium, and the methodological minimalism which we employed in order to achieve it. We conclude by drawing out an implication of the Symposium’s achievement which is that a counterpoint to Institutional theories of art may well be the point from which future directions will take hold, if philosophy-art gains traction
Impact case studies submitted to REF2014: the hidden impact of nursing research
The UK’s Research Excellence Framework (REF) 2014 rated the research from 154 universities and the impact of research was evaluated in 6975 impact case studies. Nursing was returned within unit of Assessment (UoA) 3 which also included Dentistry, Pharmacy, Allied Health Professions, although nursing research was also submitted within other UoAs. The study aim was to collate and categorise available REF impact case studies involving nursing researchers or on topics of relevance to nursing. Using nurs* as a search term 469 case study entries were retrieved from the REF database and placed into three categories determined by the level of involvement of nurses. Some 80 impact case studies were submitted by nurses across 11 UoAs: the majority being in UoA3 (n=55). A further 50 revealed some relevant impact, though nurses did not have an obvious research role. A total of 248 case studies described actual or potential impact on health or social care but were not associated specifically with nursing. Nursing research has demonstrable impact, however there is a significant body of research with relevance for nursing that has not been associated with the profession in the REF. More attention should be paid to the ‘hidden impact’ of nursing research to ensure the full impact of nursing is recognised
The Fractal Properties of Internet
In this paper we show that the Internet web, from a user's perspective,
manifests robust scaling properties of the type where n
is the size of the basin connected to a given point, represents the density
of probability of finding n points downhill and s a
characteristic universal exponent. This scale-free structure is a result of the
spontaneous growth of the web, but is not necessarily the optimal one for
efficient transport. We introduce an appropriate figure of merit and suggest
that a planning of few big links, acting as information highways, may
noticeably increase the efficiency of the net without affecting its robustness.Comment: 6 pages,2 figures, epl style, to be published on Europhysics Letter
Updated world map of the Köppen-Geiger climate classification
International audienceAlthough now over 100 years old, the classification of climate originally formulated by Wladimir Köppen and modified by his collaborators and successors, is still in widespread use. It is widely used in teaching school and undergraduate courses on climate. It is also still in regular use by researchers across a range of disciplines as a basis for climatic regionalisation of variables and for assessing the output of global climate models. Here we have produced a new global map of climate using the Köppen-Geiger system based on a large global data set of long-term monthly precipitation and temperature station time series. Climatic variables used in the Köppen-Geiger system were calculated at each station and interpolated between stations using a two-dimensional (latitude and longitude) thin-plate spline with tension onto a 0.1°×0.1° grid for each continent. We discuss some problems in dealing with sites that are not uniquely classified into one climate type by the Köppen-Geiger system and assess the outcomes on a continent by continent basis. Globally the most common climate type by land area is BWh (14.2%, Hot desert) followed by Aw (11.5%, Tropical savannah). The updated world Köppen-Geiger climate map is freely available electronically in the Supplementary Material Section
Resolving the Submillimeter Background: the 850-micron Galaxy Counts
Recent deep blank field submillimeter surveys have revealed a population of
luminous high redshift galaxies that emit most of their energy in the
submillimeter. The results suggest that much of the star formation at high
redshift may be hidden to optical observations. In this paper we present
wide-area 850-micron SCUBA data on the Hawaii Survey Fields SSA13, SSA17, and
SSA22. Combining these new data with our previous deep field data, we establish
the 850-micron galaxy counts from 2 mJy to 10 mJy with a >3-sigma detection
limit. The area coverage is 104 square arcmin to 8 mJy and 7.7 square arcmin to
2.3 mJy. The differential 850-micron counts are well described by the function
n(S)=N_0/(a+S^3.2), where S is the flux in mJy, N_0=3.0 x 10^4 per square
degree per mJy, and a=0.4-1.0 is chosen to match the 850-micron extragalactic
background light. Between 20 to 30 per cent of the 850-micron background
resides in sources brighter than 2 mJy. Using an empirical fit to our >2 mJy
data constrained by the EBL at lower fluxes, we argue that the bulk of the
850-micron extragalactic background light resides in sources with fluxes near 1
mJy. The submillimeter sources are plausible progenitors of the present-day
spheroidal population.Comment: 5 pages, accepted by The Astrophysical Journal Letter
Power laws of complex systems from Extreme physical information
Many complex systems obey allometric, or power, laws y=Yx^{a}. Here y is the
measured value of some system attribute a, Y is a constant, and x is a
stochastic variable. Remarkably, for many living systems the exponent a is
limited to values +or- n/4, n=0,1,2... Here x is the mass of a randomly
selected creature in the population. These quarter-power laws hold for many
attributes, such as pulse rate (n=-1). Allometry has, in the past, been
theoretically justified on a case-by-case basis. An ultimate goal is to find a
common cause for allometry of all types and for both living and nonliving
systems. The principle I - J = extrem. of Extreme physical information (EPI) is
found to provide such a cause. It describes the flow of Fisher information J =>
I from an attribute value a on the cell level to its exterior observation y.
Data y are formed via a system channel function y = f(x,a), with f(x,a) to be
found. Extremizing the difference I - J through variation of f(x,a) results in
a general allometric law f(x,a)= y = Yx^{a}. Darwinian evolution is presumed to
cause a second extremization of I - J, now with respect to the choice of a. The
solution is a=+or-n/4, n=0,1,2..., defining the particular powers of biological
allometry. Under special circumstances, the model predicts that such biological
systems are controlled by but two distinct intracellular information sources.
These sources are conjectured to be cellular DNA and cellular transmembrane ion
gradient
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