3,359 research outputs found
Examining Elementary School Students\u27 Attitudes toward Writing
The purpose of this study was to examine elementary students\u27 attitudes towards writing and experiences that have shaped their identities as writers. Through grade level focus group interviews, we learned more about how children’s writing attitudes develop over time and how these factors can be used to improve instructional practices
Spatial patterns and scale freedom in a Prisoner's Dilemma cellular automata with Pavlovian strategies
A cellular automaton in which cells represent agents playing the Prisoner's
Dilemma (PD) game following the simple "win-stay, loose-shift" strategy is
studied. Individuals with binary behavior, such as they can either cooperate
(C) or defect (D), play repeatedly with their neighbors (Von Neumann's and
Moore's neighborhoods). Their utilities in each round of the game are given by
a rescaled payoff matrix described by a single parameter Tau, which measures
the ratio of 'temptation to defect' to 'reward for cooperation'. Depending on
the region of the parameter space Tau, the system self-organizes - after a
transient - into dynamical equilibrium states characterized by different
definite fractions of C agents (2 states for the Von Neumann neighborhood and 4
for Moore neighborhood). For some ranges of Tau the cluster size distributions,
the power spectrums P(f) and the perimeter-area curves follow power-law
scalings. Percolation below threshold is also found for D agent clusters. We
also analyze the asynchronous dynamics version of this model and compare
results.Comment: Accepted for publication in JSTA
Quantum Games and Quantum Strategies
We investigate the quantization of non-zero sum games. For the particular
case of the Prisoners' Dilemma we show that this game ceases to pose a dilemma
if quantum strategies are allowed for. We also construct a particular quantum
strategy which always gives reward if played against any classical strategy.Comment: 4 pages, 4 figures, typographic sign error in the definition of the
operator J correcte
Hawks and Doves on Small-World Networks
We explore the Hawk-Dove game on networks with topologies ranging from
regular lattices to random graphs with small-world networks in between. This is
done by means of computer simulations using several update rules for the
population evolutionary dynamics. We find the overall result that cooperation
is sometimes inhibited and sometimes enhanced in those network structures, with
respect to the mixing population case. The differences are due to different
update rules and depend on the gain-to-cost ratio. We analyse and qualitatively
explain this behavior by using local topological arguments.Comment: 12 pages, 8 figure
Berezin Quantization of Gauged WZW and Coset Models
Gauged WZW and coset models are known to be useful to prove holomorphic
factorization of the partition function of WZW and coset models. In this note
we show that these gauged models can be also important to quantize the theory
in the context of the Berezin formalism. For gauged coset models Berezin
quantization procedure also admits a further holomorphic factorization in the
complex structure of the moduli space.Comment: 15+1 pages, no figures, revte
Higher Volume at Time of Breast Conserving Surgery Reduces Re-Excision in DCIS
Purpose. The purpose of this study was to compare the surgical and pathological variables which impact rate of re-excision following breast conserving therapy (BCS) with or without concurrent additional margin excision (AM). Methods. The pathology database was queried for all patients with DCIS from January 2004 to September 2008. Pathologic assessment included volume of excision, subtype, size, distance from margin, grade, necrosis, multifocality, calcifications, and ER/PR status. Results. 405 cases were identified and 201 underwent BCS, 151-BCS-AM, and 53-mastectomy. Among the 201 BCS patients, 190 underwent re-excision for close or involved margins. 129 of these were treated with BCS and 61 with BCS-AM (P < .0001). The incidence of residual DCIS in the re-excision specimens was 32% (n = 65) for BCS and 22% (n = 33) for BCS-AM (P < .05). For both the BCS and the BCS-AM cohorts, volume of tissue excised is inversely correlated to the rate of re-excision (P = .0284). Multifocality (P = .0002) and ER status (P = .0382) were also significant predictors for rate of re-excision and variation in surgical technique was insignificant. Conclusions. The rate of positive margins, re-excision, and residual disease was significantly higher in patients with lower volume of excision. The performance of concurrent additional margin excision increases the efficacy of BCS for DCIS
Systematic Evaluation of Pancreas Allograft Quality, Outcomes and Geographic Variation in Utilization
Pancreas allograft acceptance is markedly more selective than other solid organs. The number of pancreata recovered is insufficient to meet the demand for pancreas transplants (PTx), particularly for patients awaiting simultaneous kidney-pancreas (SPK) transplant. Development of a pancreas donor risk index (PDRI) to identify factors associated with an increased risk of allograft failure in the context of SPK, pancreas after kidney (PAK) or pancreas transplant alone (PTA), and to assess variation in allograft utilization by geography and center volume was undertaken. Retrospective analysis of all PTx performed from 2000 to 2006 (n = 9401) was performed using Cox regression controlling for donor and recipient characteristics. Ten donor variables and one transplant factor (ischemia time) were subsequently combined into the PDRI. Increased PDRI was associated with a significant, graded reduction in 1-year pancreas graft survival. Recipients of PTAs or PAKs whose organs came from donors with an elevated PDRI (1.57–2.11) experienced a lower rate of 1-year graft survival (77%) compared with SPK transplant recipients (88%). Pancreas allograft acceptance varied significantly by region particularly for PAK/PTA transplants (p < 0.0001). This analysis demonstrates the potential value of the PDRI to inform organ acceptance and potentially improve the utilization of higher risk organs in appropriate clinical settings.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/78607/1/j.1600-6143.2009.02996.x.pd
Evolutionary Dynamics of Populations with Conflicting Interactions: Classification and Analytical Treatment Considering Asymmetry and Power
Evolutionary game theory has been successfully used to investigate the
dynamics of systems, in which many entities have competitive interactions. From
a physics point of view, it is interesting to study conditions under which a
coordination or cooperation of interacting entities will occur, be it spins,
particles, bacteria, animals, or humans. Here, we analyze the case, where the
entities are heterogeneous, particularly the case of two populations with
conflicting interactions and two possible states. For such systems, explicit
mathematical formulas will be determined for the stationary solutions and the
associated eigenvalues, which determine their stability. In this way, four
different types of system dynamics can be classified, and the various kinds of
phase transitions between them will be discussed. While these results are
interesting from a physics point of view, they are also relevant for social,
economic, and biological systems, as they allow one to understand conditions
for (1) the breakdown of cooperation, (2) the coexistence of different
behaviors ("subcultures"), (2) the evolution of commonly shared behaviors
("norms"), and (4) the occurrence of polarization or conflict. We point out
that norms have a similar function in social systems that forces have in
physics
Promote cooperation by localised small-world communication
The emergence and maintenance of cooperation within sizable groups of
unrelated humans offer many challenges for our understanding. We propose that
the humans' capacity of communication, such as how many and how far away the
fellows can build up mutual communications, may affect the evolution of
cooperation. We study this issue by means of the public goods game (PGG) with a
two-layered network of contacts. Players obtain payoffs from five-person public
goods interactions on a square lattice (the interaction layer). Also, they
update strategies after communicating with neighbours in learning layer, where
two players build up mutual communication with a power law probability
depending on their spatial distance. Our simulation results indicate that the
evolution of cooperation is indeed sensitive to how players choose others to
communicate with, including the amount as well as the locations. The tendency
of localised communication is proved to be a new mechanism to promote
cooperation.Comment: 6 pages, 4 figure
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