796 research outputs found
Evidence for an Additional Heat Source in the Warm Ionized Medium of Galaxies
Spatial variations of the [S II]/H-Alpha and [N II]/H-Alpha line intensity
ratios observed in the gaseous halo of the Milky Way and other galaxies are
inconsistent with pure photoionization models. They appear to require a
supplemental heating mechanism that increases the electron temperature at low
densities n_e. This would imply that in addition to photoionization, which has
a heating rate per unit volume proportional to n_e^2, there is another source
of heat with a rate per unit volume proportional to a lower power of n_e. One
possible mechanism is the dissipation of interstellar plasma turbulence, which
according to Minter & Spangler (1997) heats the ionized interstellar medium in
the Milky Way at a rate ~ 1x10^-25 n_e ergs cm^-3 s^-1. If such a source were
present, it would dominate over photoionization heating in regions where n_e <
0.1 cm^-3, producing the observed increases in the [S II]/H-Alpha and [N
II]/H-Alpha intensity ratios at large distances from the galactic midplane, as
well as accounting for the constancy of [S II]/[N II], which is not explained
by pure photoionization. Other supplemental heating sources, such as magnetic
reconnection, cosmic rays, or photoelectric emission from small grains, could
also account for these observations, provided they supply to the warm ionized
medium ~ 10^-5 ergs s^-1 per cm^2 of Galactic disk.Comment: 10 pages, 1 figur
WHAM Observations of H-Alpha, [S II], and [N II] toward the Orion and Perseus Arms: Probing the Physical Conditions of the Warm Ionized Medium
A large portion of the Galaxy (l = 123 deg to 164 deg, b = -6 deg to -35
deg), which samples regions of the Local (Orion) spiral arm and the more
distant Perseus arm, has been mapped with the Wisconsin H-Alpha Mapper (WHAM)
in the H-Alpha, [S II] 6716, and [N II] 6583 lines. Several trends noticed in
emission-line investigations of diffuse gas in other galaxies are confirmed in
the Milky Way and extended to much fainter emission. We find that the [S
II]/H-Alpha and [N II]/H-Alpha ratios increase as absolute H-Alpha intensities
decrease. For the more distant Perseus arm emission, the increase in these
ratios is a strong function of Galactic latitude and thus, of height above the
Galactic plane. The [S II]/[N II] ratio is relatively independent of H-Alpha
intensity. Scatter in this ratio appears to be physically significant, and maps
of it suggest regions with similar ratios are spatially correlated. The Perseus
arm [S II]/[N II] ratio is systematically lower than Local emission by 10%-20%.
With [S II]/[N II] fairly constant over a large range of H-Alpha intensities,
the increase of [S II]/H-Alpha and [N II]/H-Alpha with |z| seems to reflect an
increase in temperature. Such an interpretation allows us to estimate the
temperature and ionization conditions in our large sample of observations. We
find that WIM temperatures range from 6,000 K to 9,000 K with temperature
increasing from bright to faint H-Alpha emission (low to high [S II]/H-Alpha
and [N II]/H-Alpha) respectively. Changes in [S II]/[N II] appear to reflect
changes in the local ionization conditions (e.g. the S+/S++ ratio). We also
measure the electron scale height in the Perseus arm to be 1.0+/-0.1 kpc,
confirming earlier, less accurate determinations.Comment: 28 pages, 10 figures. Figures 2 and 3 are full color--GIFs provided
here, original PS figures at link below. Accepted for publication in ApJ.
More information about the WHAM project can be found at
http://www.astro.wisc.edu/wham/ . REVISION: Figure 6, bottom panel now
contains the proper points. No other changes have been mad
A Map of the Ionized Component of the Intermediate Velocity Cloud Complex K
The Wisconsin H-Alpha Mapper (WHAM) Northern Sky Survey is revealing that
many intermediate-velocity (|v_LSR| <= 100 km/s) neutral clouds and complexes
have an associated ionized component. We present the first map of the H-Alpha
emission from an intermediate- or high-velocity structure: Complex K. This
large, high-latitude feature stretches from l = 10 to 70 degrees, b = +30 to
+70 degrees and peaks in velocity over v_LSR ~ -60 to -80 km/s. The neutral and
ionized gas generally trace each other quite well in the complex, but the
detailed structure is not identical. In particular, the H-Alpha emission peaks
in brightness at slightly higher Galactic longitudes than corresponding 21 cm
features. The ionized gas has a peak H-Alpha intensity of 0.5 Rayleighs,
corresponding to an emission measure of 1.1 cm^-6 pc. Structures in the complex
are traced by WHAM down to about 0.1 Rayleighs (0.2 cm^-6 pc). Typical line
widths of the H-Alpha emission are ~ 30 km/s, limiting temperatures in the
ionized gas to < 20,000 K. If radiation is the primary ionizing mechanism, the
Lyman continuum flux required to sustain the most strongly emitting ionized
regions is 1.2 x 10^6 photons cm^-2 s^-1. There appears to be no local, stellar
source capable of maintaining the ionization of the gas; however, the required
ionizing flux is consistent with current models of the escape of Lyman
continuum radiation from OB stars in the disk and of ionizing radiation
produced by cooling supernova remnants.Comment: 12 pages, 3 figures, Figure 1 is full color and a higher quality
version will be available on our web site. Published in Astrophysical Journal
(Letters). Visit http://www.astro.wisc.edu/wham/ for more informatio
Support for graphicacy: a review of textbooks available to accounting students
This Teaching Note reports on the support available in textbooks for graphicacy that will help students understand the complexities of graphical displays. Graphical displays play a significant role in financial reporting, and studies have found evidence of measurement distortion and selection bias. To understand the complexities of graphical displays, students need a sound understanding of graphicacy and support from the textbooks available to them to develop that understanding. The Teaching Note reports on a survey that examined the textbooks available to students attending two Scottish universities. The support of critical graphicacy skills was examined in conjunction with textbook characteristics. The survey, which was not restricted to textbooks designated as required reading, examined the textbooks for content on data measurement and graphical displays. The findings highlight a lack of support for graphicacy in the textbooks selected. The study concludes that accounting educators need to scrutinize more closely the selection of textbooks and calls for more extensive research into textbooks as a pedagogic tool
A general representation of dynamical systems for reservoir computing
Dynamical systems are capable of performing computation in a reservoir
computing paradigm. This paper presents a general representation of these
systems as an artificial neural network (ANN). Initially, we implement the
simplest dynamical system, a cellular automaton. The mathematical fundamentals
behind an ANN are maintained, but the weights of the connections and the
activation function are adjusted to work as an update rule in the context of
cellular automata. The advantages of such implementation are its usage on
specialized and optimized deep learning libraries, the capabilities to
generalize it to other types of networks and the possibility to evolve cellular
automata and other dynamical systems in terms of connectivity, update and
learning rules. Our implementation of cellular automata constitutes an initial
step towards a general framework for dynamical systems. It aims to evolve such
systems to optimize their usage in reservoir computing and to model physical
computing substrates.Comment: 5 pages, 3 figures, accepted workshop paper at Workshop on Novel
Substrates and Models for the Emergence of Developmental, Learning and
Cognitive Capabilities at IEEE ICDL-EPIROB 201
Measurement of a Magnetic Field in a Leading Arm High Velocity Cloud
Using a recent catalogue of extragalactic Faraday rotation derived from the
NRAO VLA Sky Survey we have found an agreement between Faraday rotation
structure and the HI emission structure of a High Velocity Cloud (HVC)
associated with the Leading Arm of the Magellanic System. We suggest that this
morphological agreement is indicative of Faraday rotation through the HVC.
Under this assumption we have used 48 rotation measures through the HVC,
together with estimates of the electron column density from H-\alpha\
measurements and QSO absorption lines to estimate a strength for the
line-of-sight component of the coherent magnetic field in the HVC of >
6 {\rm \mu G}B_{r}/B_{||} < 0.8$, which suggests that the random field does not dominate
over the coherent field as it does in the Magellanic Clouds from which this HVC
likely originates.Comment: 17 pages, 3 figure
The extragalactic background and its fluctuations in the far-infrared wavelengths
A Cosmic Far-InfraRed Background (CFIRB) has long been predicted that would
traces the intial phases of galaxy formation. It has been first detected by
Puget et al.(1996) using COBE data and has been later confirmed by several
recent studies (Fixsen et al. 1998, Hauser et al. 1998, Lagache et al. 1999).
We will present a new determination of the CFIRB that uses for the first time,
in addition to COBE data, two independent gas tracers: the HI survey of
Leiden/Dwingeloo (hartmann, 1998) and the WHAM H survey (Reynolds et
al 1998). We will see that the CFIRB above 100 micron is now very well
constrained. The next step is to see if we can detect its fluctuations. To
search for the CFIRB fluctuations, we have used the FIRBACK observations.
FIRBACK is a deep cosmological survey conducted at 170 micron with ISOPHOT
(Dole et al., 2000). We show that the emission of unresolved extra-galactic
sources clearly dominates, at arcminute scales, the background fluctuations in
the lowest galactic emission regions. This is the first detection of the CFIRB
fluctuations.Comment: To appear in "ISO Surveys of a Dusty Universe", Workshop at Ringberg
Castle, November 8 - 12, 199
Some considerations for the communication of results of air pollution health effects tracking
Communicating effectively and efficiently on air quality and its health impacts is an important but difficult and complex task. It requires careful consideration of the audience one wants to reach, the messages one is trying to present, the venue through which the message will be delivered. The audience, context, technique, and content factors may affect how well it is heard and how appropriately it is interpreted. In this short paper, I describe many of these concerns and provide some suggestions for how best to address them. However, since every audience differs in goals, characteristics, and nature, what is most important is implementing an effective communications program. This program should include frequent two-way communication, repeated and on-going evaluation of how well the audience understands the messages, and consideration of how to improve the delivery
What About Interaction Geography to Evaluate Physical Learning Spaces?
This paper reviews and explores how interaction geography, a new approach to visualize peopleâs interaction over space and time, extends current approaches to evaluate physical learning spaces. This chapter begins by reviewing representations produced using interaction geography to study visitor engagement and learning in a museum. In particular, this review illustrates Mondrian Transcription, a method to map peopleâs movement and conversation over space and time, and the Interaction Geography Slicer (IGS), a dynamic visualisation tool that supports new forms of interaction and multi-modal analysis. Subsequently, this chapter explores how interaction geography may advance the evaluation of physical learning spaces by providing dynamic information visualisation methods that support more expansive views of learning and the evaluation of the alignment between space and pedagogy. This chapter concludes by outlining significant limitations and next steps to expand interaction geography to evaluate physical learning spaces
15 years of protest and media technologies scholarship: A sociotechnical timeline
This article investigates the relationship between the invention of new media technologies and scholarship concerning protest and political engagement. Building on an innovative approach that moves beyond a systematic literature review, this article contributes to our understanding of scholarship concerning digital communication technologies and how they may have been adopted and shaped protest movements and political engagement. Based on visualizations, we draw a sociotechnical timeline of protest and media technology scholarship within three dimensions: technological development, methods and techniques, and the social phenomena under investigation. The article concludes by identifying major trends in protest and media technologies scholarship over the past 15âyears. The sociotechnical timeline enhances our understanding of academic discourse at the intersection of protest and media technologies by highlighting shortcomings and potential for future research
- âŠ