5,452 research outputs found
Learning Action Models: Qualitative Approach
In dynamic epistemic logic, actions are described using action models. In
this paper we introduce a framework for studying learnability of action models
from observations. We present first results concerning propositional action
models. First we check two basic learnability criteria: finite identifiability
(conclusively inferring the appropriate action model in finite time) and
identifiability in the limit (inconclusive convergence to the right action
model). We show that deterministic actions are finitely identifiable, while
non-deterministic actions require more learning power-they are identifiable in
the limit. We then move on to a particular learning method, which proceeds via
restriction of a space of events within a learning-specific action model. This
way of learning closely resembles the well-known update method from dynamic
epistemic logic. We introduce several different learning methods suited for
finite identifiability of particular types of deterministic actions.Comment: 18 pages, accepted for LORI-V: The Fifth International Conference on
Logic, Rationality and Interaction, October 28-31, 2015, National Taiwan
University, Taipei, Taiwa
Digital Collaboration and Classroom Practice: Educator Use of ARIS Connect
A major focus of the booming education technology sector is on products that aim to help teachers improve classroom practice. For their part, districts must figure out which of these resources will be most useful to schools. In New York City, the Department of Education developed its own Achievement Reporting and Innovation System (ARIS), which was rolled out in 2008. ARIS was an early effort at a system-wide data and teacher collaboration platform, and a major undertaking for the nation's largest school district. In 2011, the Research Alliance received a grant from the Spencer Foundation to investigate how this ambitious initiative played out in schools. Our first report focused on overall use and perceptions of ARIS. In the current phase of our study, we honed our focus onto ARIS Connect -- a component designed specifically to help educators improve their practice by sharing resources, posting questions, and giving one another feedback, both within schools and across the district. Our investigation sought to understand what educators thought of Connect, and whether, as its designers intended, Connect supported their ability to communicate with other educators and improve classroom practice. The study is based on two years of "clickstream" data, which tracks user visits to and navigation through ARIS. We also visited nine middle schools that recorded higher-than-average use of Connect, where we interviewed administrators and held focus groups with teachers. This report presents our findings, including insights on why educators did or did not use Connect; what might have made Connect more useful; and what external tools educators use for similar purposes
Melting and Freezing Lines for a Mixture of Charged Colloidal Spheres with Spindle-Type Phase Diagram
We have measured the phase behavior of a binary mixture of like-charged
colloidal spheres with a size ratio of 0.9 and a charge ratio of 0.96 as a
function of particle number density n and composition p. Under exhaustively
deionized conditions the aqueous suspension forms solid solutions of body
centered cubic structure for all compositions. The freezing and melting lines
as a function of composition show opposite behavior and open a wide, spindle
shaped coexistence region. Lacking more sophisticated treatments, we model the
interaction in our mixtures as an effective one-component pair energy
accounting for number weighted effective charge and screening constant. Using
this description, we find that within experimental error the location of the
experimental melting points meets the range of melting points predicted for
monodisperse, one component Yukawa systems made in several theoretical
approaches. We further discuss that a detailed understanding of the exact phase
diagram shape including the composition dependent width of the coexistence
region will need an extended theoretical treatment.Comment: 25 pages, 4 figure
The origin of RXJ1856.5-3754 and RXJ0720.4-3125 -- updated using new parallax measurements
RXJ1856 and RXJ0720 are the only young isolated radio-quiet neutron stars
(NSs) for which trigonometric parallaxes were measured. Due to detection of
their thermal emission in X-rays they are important to study NS cooling and to
probe theoretical cooling models. Hence, a precise determination of their age
is essential. Recently, new parallax measurements of RXJ1856 and RXJ0720 were
obtained. Considering that NSs may originate from binary systems that got
disrupted due to an asymmetric supernova, we attempt to identify runaway stars
which may have been former companions to the NS progenitors. Such an
identification would strongly support a particular birth scenario with time and
place. We trace back each NS, runaway star and the centres of possible birth
associations to find close encounters. The kinematic age is then given by the
time since the encounter. We use Monte Carlo simulations to account for
observational uncertainties. Using the most recent parallax measurement of
8.16+/-0.80 mas for RXJ1856, we find that it originated in the U Sco
association 0.46+/-0.05 Myr ago. This is slightly larger than the value we
reported earlier (0.3 Myr). Our result is strongly supported by its current
radial velocity that we predict to be 6+19-20 km/s. This implies an inclination
angle of 88+/-6 deg consistent with the bow shock. No suitable runaway star was
found to be a potential former companion of RXJ1856. Making use of a recent
parallax measurement for RXJ0720 of 3.6+/-1.6 mas, we find that this NS was
possibly born in Tr 10 0.85+/-0.15 Myr ago. This is somewhat larger than the
one obtained using the old parallax value (0.5 Myr). We suggest the B0 runaway
supergiant HIP 43158 as a candidate for a former companion. Then, the current
distance of RXJ0720 to the Sun should be 286+27-23 pc, in agreement with recent
measurements. We then expect the radial velocity of RXJ0720 to be -76+34-17
km/s.Comment: accepted for publication in MNRAS additional supporting material can
be found at http://www.astro.uni-jena.de/~nina/supporting_info.pdf the
abstract has been adjusted to fit the length requirement (RXJ1856 =
RXJ1856.5-3754, RXJ0720 = RXJ0720.4-3125, U Sco = Upper Scorpius, Tr 10 =
Trumpler 10
Biomechanical factors may explain why grasping violates Weber's law
Copyright Ā© 2015. Published by Elsevier Ltd. Acknowledgments The experiment was part of N. Aschennellerās MD thesis. The study was funded by the Staedtler Stiftung (Nuremberg, Germany).Peer reviewedPostprin
ESTIMATING GENDER DIFFERENCES IN AGRICULTURAL PRODUCTIVITY: BIASES DUE TO OMISSION OF GENDER-INFLUENCED VARIABLES AND ENDOGENEITY OF REGRESSORS
This study evaluates managerial differences between men and women and assesses the degree of bias introduced by omission of gender-influenced variables and ignoring the endogeneity of farmer characteristics and input levels. The results also give insight to improving research methods for isolating the gender impact on productivity.Labor and Human Capital, Productivity Analysis,
An Experimental Study of Two Methods of Teaching Mathematics in Second Grade
It was the purpose of this study to compare two methods of teaching arithmetic in the second grade, an individualized method and a one group method, to determine if there were any differences in the achievement made by the two groups
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