15,743 research outputs found
Usability evaluation of digital libraries: a tutorial
This one-day tutorial is an introduction to usability evaluation for Digital
Libraries. In particular, we will introduce Claims Analysis. This approach
focuses on the designersâ motivations and reasons for making particular
design decisions and examines the effect on the userâs interaction with
the system. The general approach, as presented by Carroll and
Rosson(1992), has been tailored specifically to the design of digital
libraries.
Digital libraries are notoriously difficult to design well in terms of their
eventual usability. In this tutorial, we will present an overview of
usability issues and techniques for digital libraries, and a more detailed
account of claims analysis, including two supporting techniques â
simple cognitive analysis based on Normanâs âaction cycleâ and
Scenarios and personas. Through a graduated series of worked
examples, participants will get hands-on experience of applying this
approach to developing more usable digital libraries. This tutorial
assumes no prior knowledge of usability evaluation, and is aimed at all
those involved in the development and deployment of digital libraries
Environmental Dependence of Masses and Coupling Constants
We construct a class of scalar field models coupled to matter that lead to
the dependence of masses and coupling constants on the ambient matter density.
Such models predict a deviation of couplings measured on the Earth from values
determined in low-density astrophysical environments, but do not necessarily
require the evolution of coupling constants with the redshift in the recent
cosmological past. Additional laboratory and astrophysical tests of \Delta
\alpha and \Delta(m_p/m_e) as functions of the ambient matter density are
warranted.Comment: 20 pages, no figures, references added, minor editorial change
Estimating the Knowledge-Capital Model of the Multinational Enterprise: Comment
A recent American Economic Review article by David L. Carr, James R. Markusen, and Keith E. Maskus (CMM) estimates a regression specification based upon the 'knowledge-capital' model of the Multinational Enterprise (MNE). The knowledge-capital model combines 'horizontal' motivations for FDI -- the desire to place production close to customers and thereby avoid trade costs -- with 'vertical' motivations -- the desire to carry out unskilled-labor intensive production activities in locations with relatively abundant unskilled labor. The CMM estimates pool inward and outward U.S. affiliate sales data from 1986 through 1994 and appear to support the knowledge-capital model of the MNE. We show that CMM's empirical framework mis-specifies the terms measuring differences in skilled-labor abundance, key variables that identify vertical MNE motivations. After correcting this specification error estimates no longer reject the horizontal model in favor of the knowledge-capital model. Instead, the data strongly support the predictions of the horizontal model of MNEs: affiliate activity between countries decreases as absolute differences in skill-labor abundance widen. Qualitatively identical results are also found using data that include a wider variety of parent and host countries, including data for the OECD.
Origin and Detection of Microstructural Clustering in Fluids with Spatial-Range Competitive Interactions
Fluids with competing short-range attractions and long-range repulsions mimic
dispersions of charge-stabilized colloids that can display equilibrium
structures with intermediate range order (IRO), including particle clusters.
Using simulations and analytical theory, we demonstrate how to detect cluster
formation in such systems from the static structure factor and elucidate links
to macrophase separation in purely attractive reference fluids. We find that
clusters emerge when the thermal correlation length encoded in the IRO peak of
the structure factor exceeds the characteristic lengthscale of interparticle
repulsions. We also identify qualitative differences between the dynamics of
systems that form amorphous versus micro-crystalline clusters.Comment: 6 pages, 5 figure
Moral Grandstanding in Public Discourse: Status-Seeking Motives as a Potential Explanatory Mechanism in Predicting Conflict
Public discourse is often caustic and conflict-filled. This trend seems to be particularly evident when the content of such discourse is around moral issues (broadly defined) and when the discourse occurs on social media. Several explanatory mechanisms for such conflict have been explored in recent psychological and social-science literatures. The present work sought to examine a potentially novel explanatory mechanism defined in philosophical literature: Moral Grandstanding. According to philosophical accounts, Moral Grandstanding is the use of moral talk to seek social status. For the present work, we conducted six studies, using two undergraduate samples (Study 1, N = 361; Study 2, N = 356); a sample matched to U.S. norms for age, gender, race, income, Census region (Study 3, N = 1,063); a YouGov sample matched to U.S. demographic norms (Study 4, N = 2,000); and a brief, one-month longitudinal study of Mechanical Turk workers in the U.S. (Study 5, Baseline N = 499, follow-up n = 296), and a large, one-week YouGov sample matched to U.S. demographic norms (Baseline N = 2,519, follow-up n = 1,776). Across studies, we found initial support for the validity of Moral Grandstanding as a construct. Specifically, moral grandstanding motivation was associated with status-seeking personality traits, as well as greater political and moral conflict in daily life
Dynamical excitations in the collision of 2D Bose-Einstein condensates
We carry out simulations of the collision of two components of an
adiabatically divided, quasi-2D BEC. We identify under, over and critically
damped regimes in the dipole oscillations of the components according to the
balance of internal and centre-of-mass (c.m.) energies of the components and
investigate the creation of internal excitations. We distinguish the behaviour
of this system from previous studies of quasi-1D BEC's. In particular we note
that the nature of the internal excitations is only essentially sensitive to an
initial phase difference between the components in the overdamped regime.Comment: 17 pages, 9 figure
Structural Relationship between Negative Thermal Expansion and Quartic Anharmonicity of Cubic ScF_3
Cubic scandium trifluoride (ScF_3) has a large negative thermal expansion over a wide range of temperatures. Inelastic neutron scattering experiments were performed to study the temperature dependence of the lattice dynamics of ScF3 from 7 to 750 K. The measured phonon densities of states show a large anharmonic contribution with a thermal stiffening of modes around 25 meV. Phonon calculations with first-principles methods identified the individual modes in the densities of states, and frozen phonon calculations showed that some of the modes with motions of F atoms transverse to their bond direction behave as quantum quartic oscillators. The quartic potential originates from harmonic interatomic forces in the DO_9 structure of ScF_3, and accounts for phonon stiffening with the temperature and a significant part of the negative thermal expansion
A Bayesian Estimate of the Primordial Helium Abundance
We introduce a new statistical method to estimate the primordial helium
abundance, Y_p from observed abundances in a sample of galaxies which have
experienced stellar helium enrichment. Rather than using linear regression on
metal abundance we construct a likelihood function using a Bayesian prior,
where the key assumption is that the true helium abundance must always exceed
the primordial value. Using a sample of measurements compiled from the
literature we find estimates of Y_p between 0.221 and 0.236, depending on the
specific subsample and prior adopted, consistent with previous estimates either
from a linear extrapolation of the helium abundance with respect to
metallicity, or from the helium abundance of the lowest metallicity HII region,
I Zw 18. We also find an upper limit which is insensitive to the specific
subsample or prior, and estimate a model-independent bound Y_p < 0.243 at 95%
confidence, favoring a low cosmic baryon density and a high primordial
deuterium abundance. The main uncertainty is not the model of stellar
enrichment but possible common systematic biases in the estimate of Y in each
individual HII region.Comment: 14 pages, latex, 3 ps figure
Myelin contributes to the parallel orientation of axonal growth on white matter in vitro
BACKGROUND: Brain and spinal cord white matter can support extensive axonal growth. This growth is generally constrained to an orientation that is parallel to the longitudinal axis of the fiber tract. This constraint is presumably due to permissive and non-permissive substrates that are interleaved with each other and oriented in parallel within the tract. RESULTS: Embryonic chick sympathetic neurons were cultured on cryostat sections of rat brain and the orientation of neurite growth on white matter was assessed. To determine if haptotaxis is sufficient to guide parallel neurite growth, neurons were cultured under conditions designed to interfere with interactions between growing neurites and factors that act as biochemical contact guidance cues but not interactions with haptotactic cues. Under these conditions, neurites extending on white matter were not exclusively oriented in parallel to the fiber tract, suggesting that biochemical cues are involved. To assess the role of myelin in guiding parallel neurite growth, neurons were cultured on myelin-deficient corpus callosum. These neurons also extended neurites that were not constrained to a parallel orientation. Moreover, preincubation with NGF and treatment with cAMP analogs, manipulations that attenuate overall myelin-mediated inhibition of neurite growth, also led to a reduced parallel orientation of neurite growth. CONCLUSIONS: The present studies suggest that some of the relevant factors that constrain axonal growth on white matter are not haptotactic in nature and appear to be partly mediated by factors that are associated with myelin and may involve myelin-associated "inhibitors"
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