8,624 research outputs found
The ground state of a class of noncritical 1D quantum spin systems can be approximated efficiently
We study families H_n of 1D quantum spin systems, where n is the number of
spins, which have a spectral gap \Delta E between the ground-state and
first-excited state energy that scales, asymptotically, as a constant in n. We
show that if the ground state |\Omega_m> of the hamiltonian H_m on m spins,
where m is an O(1) constant, is locally the same as the ground state
|\Omega_n>, for arbitrarily large n, then an arbitrarily good approximation to
the ground state of H_n can be stored efficiently for all n. We formulate a
conjecture that, if true, would imply our result applies to all noncritical 1D
spin systems. We also include an appendix on quasi-adiabatic evolutions.Comment: 9 pages, 1 eps figure, minor change
Random Responding from Participants is a Threat to the Validity of Social Science Research Results
Research in the social sciences often relies upon the motivation and goodwill of research participants (e.g., teachers, students) to do their best on low stakes assessments of the effects of interventions. Research participants who are unmotivated to perform well can engage in random responding on outcome measures, which can cause substantial mis-estimation of results, biasing results toward the null hypothesis. Data from a recent educational intervention study served as an example of this problem: participants identified as random responders showed substantially lower scores than other participants on tests during the study, and failed to show growth in scores from pre- to post-test, while those not engaging in random responding showed much higher scores and significant growth over time. Furthermore, the hypothesized differences across instructional method were masked when random responders were retained in the sample but were significant when removed. We remind researchers in the social sciences to screen their data for random responding in their outcome measures in order to improve the odds of detecting effects of their interventions
A study of the immunity of FM discriminators to 2 pi frequency impulses
Frequency impulse response of selected FM discriminator
TechMiner: Extracting Technologies from Academic Publications
In recent years we have seen the emergence of a variety of scholarly datasets. Typically these capture ‘standard’ scholarly entities and their connections, such as authors, affiliations, venues, publications, citations, and others. However, as the repositories grow and the technology improves, researchers are adding new entities to these repositories to develop a richer model of the scholarly domain. In this paper, we introduce TechMiner, a new approach, which combines NLP, machine learning and semantic technologies, for mining technologies from research publications and generating an OWL ontology describing their relationships with other research entities. The resulting knowledge base can support a number of tasks, such as: richer semantic search, which can exploit the technology dimension to support better retrieval of publications; richer expert search; monitoring the emergence and impact of new technologies, both within and across scientific fields; studying the scholarly dynamics associated with the emergence of new technologies; and others. TechMiner was evaluated on a manually annotated gold standard and the results indicate that it significantly outperforms alternative NLP approaches and that its semantic features improve performance significantly with respect to both recall and precision
Opinion formation models based on game theory
A way to simulate the basic interactions between two individuals with
different opinions, in the context of strategic game theory, is proposed.
Various games are considered, which produce different kinds of opinion
formation dynamics. First, by assuming that all individuals (players) are
equals, we obtain the bounded confidence model of continuous opinion dynamics
proposed by Deffuant et al. In such a model a tolerance threshold is defined,
such that individuals with difference in opinion larger than the threshold can
not interact. Then, we consider that the individuals have different
inclinations to change opinion and different abilities in convincing the
others. In this way, we obtain the so-called ``Stubborn individuals and
Orators'' (SO) model, a generalization of the Deffuant et al. model, in which
the threshold tolerance is different for every couple of individuals. We
explore, by numerical simulations, the dynamics of the SO model, and we propose
further generalizations that can be implemented.Comment: 18 pages, 4 figure
Triple-q octupolar ordering in NpO_2
We report the results of resonant X-ray scattering experiments performed at
the Np M_4,5 edges in NpO_2. Below T_0 = 25 K, the development of long-range
order of Np electric quadrupoles is revealed by the growth of superlattice
Bragg peaks. The electronic transition is not accompanied by any measurable
crystallographic distortion, either internal or external, so the symmetry of
the system remains cubic. The polarization and azimuthal dependence of the
intensity of the resonant peaks is well reproduced assuming Templeton
scattering from a triple-q longitudinal antiferroquadrupolar structure.
Electric quadrupole order in NpO_2 could be driven by the ordering at T_0 of
magnetic octupoles of Gamma_5 symmetry, splitting the Np ground state quartet
and leading to a singlet ground state with zero dipole magnetic moment.Comment: 4 Pages, 3 Figures, submitted to Phys. Rev. Lett. v2: resubmitted
after referee report
Multiplayer Cost Games with Simple Nash Equilibria
Multiplayer games with selfish agents naturally occur in the design of
distributed and embedded systems. As the goals of selfish agents are usually
neither equivalent nor antagonistic to each other, such games are non zero-sum
games. We study such games and show that a large class of these games,
including games where the individual objectives are mean- or discounted-payoff,
or quantitative reachability, and show that they do not only have a solution,
but a simple solution. We establish the existence of Nash equilibria that are
composed of k memoryless strategies for each agent in a setting with k agents,
one main and k-1 minor strategies. The main strategy describes what happens
when all agents comply, whereas the minor strategies ensure that all other
agents immediately start to co-operate against the agent who first deviates
from the plan. This simplicity is important, as rational agents are an
idealisation. Realistically, agents have to decide on their moves with very
limited resources, and complicated strategies that require exponential--or even
non-elementary--implementations cannot realistically be implemented. The
existence of simple strategies that we prove in this paper therefore holds a
promise of implementability.Comment: 23 page
The Early Spectrophotometric Evolution of V1186 Scorpii (Nova Scorpii 2004 #1)
We report optical photometry and optical through mid-infrared spectroscopy of
the classical nova V1186 Sco. This slowly developing nova had an complex light
curve with multiple secondary peaks similar to those seen in PW Vul. The time
to decline 2 magnitudes, t, was 20 days but the erratic nature of the light
curve makes determination of intrinsic properties based on the decline time
(e.g., luminosity) problematic, and the often cited MMRD relationship of Della
Valle and Livio (1995) fails to yield a plausible distance. Spectra covering
0.35 to 35 m were obtained in two separate epochs during the first year of
outburst. The first set of spectra, taken about 2 months after visible maximum,
are typical of a CO-type nova with narrow line emission from \ion{H}{1},
\ion{Fe}{2}, \ion{O}{1} and \ion{He}{1}. Later data, obtained between 260 and
380 days after maximum, reveal an emerging nebular spectrum. \textit{Spitzer}
spectra show weakening hydrogen recombination emission with the emergence of
[\ion{Ne}{2}] (12.81 m) as the strongest line. Strong emission from
[\ion{Ne}{3}] (15.56 m) is also detected. Photoionization models with low
effective temperature sources and only marginal neon enhancement (Ne 1.3
Ne) are consistent with these IR fine-structure neon lines indicating
that V1186 Sco did not occur on a ONeMg white dwarf. In contrast, the slow and
erratic light curve evolution, spectral development, and photoionization
analysis of the ejecta imply the outburst occurred on a low mass CO white
dwarf. We note that this is the first time strong [\ion{Ne}{2}] lines have been
detected so early in the outburst of a CO nova and suggests that the presence
of mid-infrared neon lines is not directly indicative of a ONeMg nova event.Comment: 7 figures, 37 pages. Astronimocal Journal accepte
- …