6,076 research outputs found
The fourth sustainability, creativity: statistical associations and credible mechanisms
In this paper, it is argued that over and above the three city sustainabilities of energy, society and economics, there is a fourth: creativity. It poses the question: can credible mechanisms be identified through which cities are more creative than other forms of settlement, as statistical evidence suggests ? It proposes that just as mechanisms can be identified linking the generic form of cities to âspatial sustainabilityâ for the first three, mechanisms can also be identified for creativity through the ways cities generates social networks. But whereas the first three sustainabilities are consequences of the form of the city, the fourth sustainability, creativity, is argued to be the reason for the form
The effectiveness of word classification techniques on improving word recognition and comprehension, spelling, flow of ideas, and inferential thinking
Thesis (Ed.M.)--Boston Universit
Radial dependence of line profile variability in seven O9--B0.5 stars
Massive stars show a variety of spectral variability: presence of discrete
absorption components in UV P-Cygni profiles, optical line profile variability,
X-ray variability, radial velocity modulations. Our goal is to study the
spectral variability of single OB stars to better understand the relation
between photospheric and wind variability. For that, we rely on high spectral
resolution, high signal-to-noise ratio optical spectra collected with the
spectrograph NARVAL on the Telescope Bernard Lyot at Pic du Midi. We
investigate the variability of twelve spectral lines by means of the Temporal
Variance Spectrum (TVS). The selected lines probe the radial structure of the
atmosphere, from the photosphere to the outer wind. We also perform a
spectroscopic analysis with atmosphere models to derive the stellar and wind
properties, and to constrain the formation region of the selected lines. We
show that variability is observed in the wind lines of all bright giants and
supergiants, on a daily timescale. Lines formed in the photosphere are
sometimes variable, sometimes not. The dwarf stars do not show any sign of
variability. If variability is observed on a daily timescale, it can also (but
not always) be observed on hourly timescales, albeit with lower amplitude.
There is a very clear correlation between amplitude of the variability and
fraction of the line formed in the wind. Strong anti-correlations between the
different part of the temporal variance spectrum are observed. Our results
indicate that variability is stronger in lines formed in the wind. A link
between photospheric and wind variability is not obvious from our study, since
wind variability is observed whatever the level of photospheric variability.
Different photospheric lines also show different degrees of variability.Comment: 13 pages, 9 figures + appendix. A&A accepted. Figures degraded for
arxiv submissio
Sequence and comparative analysis of the chicken genome provide unique perspectives on vertebrate evolution
We present here a draft genome sequence of the red jungle fowl, Gallus gallus. Because the chicken is a modern descendant of the dinosaurs and the first non-mammalian amniote to have its genome sequenced, the draft sequence of its genomeâcomposed of approximately one billion base pairs of sequence and an estimated 20,000â23,000 genesâprovides a new perspective on vertebrate genome evolution, while also improving the annotation of mammalian genomes. For example, the evolutionary distance between chicken and human provides high specificity in detecting functional elements, both non-coding and coding. Notably, many conserved non-coding sequences are far from genes and cannot be assigned to defined functional classes. In coding regions the evolutionary dynamics of protein domains and orthologous groups illustrate processes that distinguish the lineages leading to birds and mammals. The distinctive properties of avian microchromosomes, together with the inferred patterns of conserved synteny, provide additional insights into vertebrate chromosome architecture
The UV Scattering Halo of the Central Source Associated with Eta Carinae
We have made an extensive study of the UV spectrum of Eta Carinae, and find
that we do not directly observe the star and its wind in the UV. Because of
dust along our line of sight, the UV light that we observe arises from
bound-bound scattering at large impact parameters. We obtain a reasonable fit
to the UV spectrum by using only the flux that originates outside 0.033". This
explains why we can still observe the primary star in the UV despite the large
optical extinction -- it is due to the presence of an intrinsic coronagraph in
the Eta Carinae system, and to the extension of the UV emitting region. It is
not due to peculiar dust properties alone. We have computed the spectrum of the
purported companion star, and show that it could only be directly detected in
the UV spectrum preferentially in the Far Ultraviolet Spectroscopic Explorer
(FUSE) spectral region (912-1175 Ang.). However, we find no direct evidence for
a companion star, with the properties indicated by X-ray studies and studies of
the Weigelt blobs, in UV spectra. This might be due to reprocessing of the
companion's light by the dense stellar wind of the primary. Broad FeII and
[FeII] emission lines, which form in the stellar wind, are detected in spectra
taken in the SE lobe, 0.2" from the central star. The wind spectrum shows some
similarities to the spectra of the B & D Weigelt blobs, but also shows some
marked differences in that high excitation lines, and lines pumped by Ly-alpha,
are not seen. The detection of the broad lines lends support to our
interpretation of the UV spectrum, and to our model for Eta Carinae.Comment: To appear in ApJ. 57 pages with 18 figure
What is the initiation step of the Grubbs-Hoveyda olefin metathesis catalyst?
Density function theory calculations reveal that the Grubbs-Hoveyda olefin metathesis pre-catalyst is activated by the formation of a complex in which the incoming alkene substrate and outgoing alkoxy ligand are both clearly associated with the ruthenium centre. The computed energies for reaction are in good agreement with the experimental values, reported here
Quiescent Prominence Dynamics Observed with the Hinode Solar Optical Telescope. II. Prominence Bubble Boundary Layer Characteristics and the Onset of a Coupled KelvinâHelmholtz RayleighâTaylor Instability
This is the author accepted manuscript. The final version is available from American Astronomical Society via the DOI in this record.We analyze solar quiescent prominence bubble characteristics and instability dynamics using Hinode/Solar
Optical Telescope (SOT) data. We measure bubble expansion rate, prominence downflows,
and the profile of the boundary layer brightness and thickness as a function of time. The largest
bubble analyzed rises into the prominence with a speed of about 1.3 km sâ1 until it is destabilized
by a localized shear flow on the boundary. Boundary layer thickness grows gradually as prominence
downflows deposit plasma onto the bubble with characteristic speeds of 20 â 35 km sâ1
. Lateral
downflows initiate from the thickened boundary layer with characteristic speeds of 25 â 50 km sâ1
,
âdrainingâ the layer of plasma. Strong shear flow across one bubble boundary leads to an apparent
coupled Kelvin-Helmholtz Rayleigh-Taylor (KH-RT) instability. We measure shear flow speeds above
the bubble of 10 km sâ1 and infer interior bubble flow speeds on the order of 100 km sâ1
. Comparing
the measured growth rate of the instability to analytic expressions, we infer a magnetic flux density
across the bubble boundary of ⌠10â3 T (10 gauss) at an angle of ⌠70âŠ
to the prominence plane.
The results are consistent with the hypothesis that prominence bubbles are caused by magnetic flux
that emerges below a prominence, setting up the conditions for RT, or combined KH-RT, instability
flows that transport flux, helicity, and hot plasma upward into the overlying coronal magnetic flux
ropeTEB was supported by NASA contracts NNM07AA01C (Solar-B FPP), NNG04EA00C (SDO/AIA) while at the Lockheed Martin Solar and Astrophysics Laboratory (LMSAL), and by The National Weather Service (NWS) Office of Science and Technology Integration (OSTI) while at the National Oceanic and Atmospheric Administration (NOAA). A.H. was supported by his STFC Ernest Rutherford Fellowship grant number ST/L00397X/2. W.L. was supported by NASA HGI grant NNX15AR15G and NASA contract NNG09FA40C (IRIS) at LMSAL
Spatial Configuration and Vehicular Movement: a nationwide correlational study
We provide the most comprehensive study to date on the correlation between network
centrality measures and vehicular movement flows, using a model of the UKâs entire road
network (2,031,971 nodes) and a very large dataset of vehicular movement counts (20,752
instances, evenly distributed over the UKâs territory). We describe the statistical
associations between observed vehicular flows and the values of betweenness centrality of
the road-network nodes where such flows were measured, the latter calculated using
Euclidean and angular distance functions, across a number of increasing radii, from the
local to the supra-regional scales. Relations to road capacity are also discussed in principal
road networks where this is known.
The geographical comprehensiveness of our model and the size of our movement sample
allows us to state, with unprecedented statistical validity, the clear outperformance of
angular distance over Euclidean distance, on what concerns the effect sizes of the studied
correlations. We also demonstrate the existence of two clearly different regimes of
association between movement and centrality, occurring on the background and
foreground networks of cities, which may be interpreted as new evidence of the dual
structure of urban form, proposed by space syntax
Wolf-Rayet nebulae as tracers of stellar ionizing fluxes: I. M1-67
We use WR124 (WN8h) and its associated nebula M1-67, to test theoretical
non-LTE models for Wolf-Rayet (WR) stars. Lyman continuum ionizing flux
distributions derived from a stellar analysis of WR124, are compared with
nebular properties via photo-ionization modelling. Our study demonstrates the
significant role that line blanketing plays in affecting the Lyman ionizing
energy distribution of WR stars, of particular relevance to the study of HII
regions containing young stellar populations.
We confirm previous results that non-line blanketed WR energy distributions
fail to explain the observed nebular properties of M1-67, such that the
predicted ionizing spectrum is too hard. A line blanketed analysis of WR124 is
carried out using the method of Hillier & Miller (1998), with stellar
properties in accord with previous results, except that the inclusion of
clumping in the stellar wind reduces its wind performance factor to only
approx2. The ionizing spectrum of the line blanketed model is much softer than
for a comparable temperature unblanketed case, such that negligible flux is
emitted with energy above the HeI 504 edge. Photo-ionization modelling,
incorporating the observed radial density distribution for M1-67 reveals
excellent agreement with the observed nebular electron temperature, ionization
balance and line strengths. An alternative stellar model of WR124 is
calculated, following the technique of de Koter et al. (1997), augmented to
include line blanketing following Schmutz et al. (1991). Good consistency is
reached regarding the stellar properties of WR124, but agreement with the
nebular properties of M1-67 is somewhat poorer than for the Hillier & Miller
code.Comment: 12 pages, 5 figures, latex2e style file, Astronomy & Astrophysics
(accepted
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