13,158 research outputs found
Lanthanide Ionization Energies and the Sub-Shell Break. Part 2. The Third and Fourth Ionization Energies
By interpolating a 4fq6s → 4fq7s transition within the sequence f1 → f14 rather than between f0 and f14, revised third and fourth ionization energies of the lanthanides have been obtained. The revised values, together with the second ionization energies calculated in a previous paper, are used to calculate values of the standard enthalpies of formation of the gaseous tripositive ions, ΔfHƟ(M3+,g), and of the lattice and hydration enthalpies of some lanthanide compounds and ions in the trivalent and tetravalent states. The displacements of f0 values from nearly smooth f1 → f14 variations exceed 30 kJ mol-1 and indicate substantial subshell breaks
Valencies of the lanthanides
The valencies of the lanthanides vary more than was once thought. In addition to valencies associated with a half-full shell, there are valencies associated with a quarter- and three-quarter-full shell. This can be explained on the basis of Slater’s theory of many-electron atoms. The same theory explains the variation in complexing constants in the trivalent state (the “tetrad effect”). Valency in metallic and organometallic compounds is also discussed
Big Data, Digitization, and Social Change (Ubiquity Symposium)
The term “big data” is something of a misnomer. Every generation of computers since the 1950s has been confronted with problems where data was way too large for the memory and processing power available. This seemed like an inconvenience of the technology that would someday be resolved when the next generation of computers came along. So what is different about big data today? The revolution is happening at the convergence of two trends: the expansion of the internet into billions of computing devices, and the digitization of almost everything. The internet gives us access to vast amounts of data. Digitization creates digital representations for many things once thought to be beyond the reach of computing technology. The result is an explosion of innovation of network-based big data applications and the automation of cognitive tasks. This revolution is introducing what Brynjolfsson and McAfee call the “Second Machine Age.” This symposium will examine this revolution from a number of angles
Dark Matter Searches with Astroparticle Data
The existence of dark matter (DM) was first noticed by Zwicky in the 1930s,
but its nature remains one of the great unsolved problems of physics. A variety
of observations indicate that it is non-baryonic and non-relativistic. One of
the preferred candidates for non-baryonic DM is a weakly interacting massive
particle (WIMP) that in most models is stable. WIMP self-annihilation can
produce cosmic rays, gamma rays, and other particles with signatures that may
be detectable. Hints of anomalous cosmic-ray spectra found by recent
experiments, such as PAMELA, have motivated interesting interpretations in
terms of DM annihilation and/or decay. However, these signatures also have
standard astrophysical interpretations, so additional evidence is needed in
order to make a case for detection of DM annihilation or decay. Searches by the
Fermi Large Area Telescope for gamma-ray signals from clumps, nearby dwarf
spheroidal galaxies, and galaxy clusters have also been performed, along with
measurements of the diffuse Galactic and extragalactic gamma-ray emission. In
addition, imaging atmospheric Cherenkov telescopes like HESS, MAGIC, and
VERITAS have reported on searches for gamma-ray emission from dwarf galaxies.
In this review, we examine the status of searches for particle DM by these
instruments and discuss the interpretations and resulting DM limits.Comment: Solicited review article to appear in Annual Reviews of Astronomy and
Astrophysics. 52 pages, 10 figures (higher resolution figures will appear in
the journal article
Eurasian watermilfoil biomass associated with insect herbivores in New York
A study of aquatic plant biomass within Cayuga Lake, New
York spans twelve years from 1987-1998. The exotic Eurasian
watermilfoil
(
Myriophyllum spicatum
L.) decreased in the
northwest end of the lake from 55% of the total biomass in
1987 to 0.4% in 1998 and within the southwest end from
50% in 1987 to 11% in 1998. Concurrent with the watermilfoil
decline was the resurgence of native species of submersed
macrophytes. During this time we recorded for the
first time in Cayuga Lake two herbivorous insect species: the
aquatic moth
Acentria ephemerella
, first observed in 1991, and
the aquatic weevil
Euhrychiopsis lecontei
, first found in 1996
.
Densities of
Acentria
in southwest Cayuga Lake averaged 1.04
individuals per apical meristem of Eurasian watermilfoil for
the three-year period 1996-1998. These same meristems had
Euhrychiopsis
densities on average of only 0.02 individuals per
apical meristem over the same three-year period. A comparison
of herbivore densities and lake sizes from five lakes in
1997 shows that
Acentria
densities correlate positively with
lake surface area and mean depth, while
Euhrychiopsis
densities
correlate negatively with lake surface area and mean
depth. In these five lakes,
Acentria
densities correlate negatively
with percent composition and dry mass of watermilfoil.
However,
Euhrychiopsis
densities correlate positively with percent
composition and dry mass of watermilfoil. Finally,
Acentria
densities correlate negatively with
Euhrychiopsis
densities
suggesting interspecific competition
Characterizing New Channels of Communication: A Case Study of Municipal 311 Requests in Edmonton, Canada
City governments around the world are developing and expanding how they connect to citizens. Technologies play an important role in making this connection, and one frequent way that cities connect with citizens is through 311-style request systems. 311 is a non-emergency municipal notification system that uses telephone, email, web forms, and increasingly, mobile applications to allow citizens to notify government of infrastructure issues and make requests for municipal services. In many ways, this process of citizen contribution mirrors the provision of volunteered geographic information, that is spatially-referenced user generated content. This research presents a case study of the city of Edmonton, Canada, an early adopter of multi-channel 311 service request systems, including telephone, email, web form, and mobile app 311 request channels. Three methods of analysis are used to characterize and compare these different channels over three years of request data; a comparison of relative request share for each channel, a spatial hot spot analysis, and regression models to compare channel usage with sociodemographic variables. The results of this study indicate a shift in channel usage from traditional to Internet-enabled, that this shift is mirrored in the hotspots of request activity, and that specific digital inequalities exist that reinforce this distinction between traditional and Internet-enabled reporting channels
High Reynolds number tests of a Douglas DLBA 032 airfoil in the Langley 0.3-meter transonic cryogenic tunnel
A wind-tunnel investigation of a Douglas advanced-technology airfoil was conducted in the Langley 0.3-Meter Transonic Cryogenic Tunnel (0.3-m TCT). The temperature was varied from 227 K (409 R) to 100 K (180 R) at pressures ranging from about 159 kPa (1.57 atm) to about 514 kPa (5.07 atm). Mach number was varied from 0.50 to 0.78. These variables provided a Reynolds number range (based on airfoil chord) from 6.0 to 30.0 x 10 to the 6th power. This investigation was specifically designed to: (1) test a Douglas airfoil from moderately low to flight-equivalent Reynolds numbers, and (2) evaluate sidewall-boundary-layer effects on transonic airfoil performance characteristics by a systematic variation of Mach number, Reynolds number, and sidewall-boundary-layer removal. Data are included which demonstrate the effects of fixing transition, Mach number, Reynolds number, and sidewall-boundary-layer removal on the aerodynamic characteristics of the airfoil. Also included are remarks on model design and model structural integrity
The Geoweb for community-based organizations: Tool development, implementation, and sustainability in an era of Google Maps
Recent advances in web-based geospatial tools (the Geoweb) show promise as low-cost and easy-to-use methods to support citizen participation. This research presents two case studies of Geoweb implementation set in community-based organizations in rural Quebec, Canada. When comparing the development and sustainability of each Geoweb tool, the implementation time frame plays a key role. Two implementation time frames are defined; a discrete, or ‘one-off’ time frame associated with lower resource requirements, and a continuous, or ongoing time frame, that has a higher total resource cost, but can fulfill a different set of goals than a discrete implementation
Civic Hackathons: New Terrain for Local Government-Citizen Interaction?
As more and more governments share open data, tech developers respond by creating apps using these data to generate content or provide services that citizens may find useful. More recently, there is an increase in popularity of the civic hackathon. These time-limited events gather tech enthusiasts, government workers and interested citizens, in a collaborative environment to apply government open data in developing software applications that address issues of shared civic importance. Building on the Johnson and Robinson (2014) framework for understanding the civic hackathon phenomenon, Canadian municipal staff with civic hackathon experience were interviewed about their motivations for and benefits derived from participation in these events. Two broad themes emerged from these interviews. First, through the development of prototypical apps using municipal open data and other data sets, civic hackathons help put open data into public use. Second, civic hackathons provide government staff with valuable feedback about municipal open data sets informing and evolving future open data releases. This paper concludes with reflections for urban planners about how civic hackathons might be used in their practice and with recommendations for municipal staff considering using civic hackathons to add value to municipal open data
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