457 research outputs found
Executive functioning in preschool children: Performance on A-Not-B and other delayed response format tasks
The A-not-B (AB) task has been hypothesized to measure executive/frontal lobe function; however, the developmental and measurement characteristics of this task have not been investigated. The present study examined performance on AB and comparison tasks adapted from developmental and neuroscience literature in 117 1.9-5.5 yr old preschool children. Age significantly predicted performance on AB, Delayed Alternation, Spatial Reversal, Color Reversal, and Self-Control tasks. A 4-factor analytic model best fit task performance data. AB task indices loaded on 2 factors with measures from the Self-Control and Delayed Alternation tasks, respectively. AB indices did not load with those from the reversal tasks despite similarities in task administration and presumed cognitive demand (working memory). These results indicate that AB is sensitive to individual differences in age-related performance in preschool children and suggest that AB performance is related to both working memory and inhibition processes in this age range
Clustering and the hyperbolic geometry of complex networks
Clustering is a fundamental property of complex networks and it is the
mathematical expression of a ubiquitous phenomenon that arises in various types
of self-organized networks such as biological networks, computer networks or
social networks. In this paper, we consider what is called the global
clustering coefficient of random graphs on the hyperbolic plane. This model of
random graphs was proposed recently by Krioukov et al. as a mathematical model
of complex networks, under the fundamental assumption that hyperbolic geometry
underlies the structure of these networks. We give a rigorous analysis of
clustering and characterize the global clustering coefficient in terms of the
parameters of the model. We show how the global clustering coefficient can be
tuned by these parameters and we give an explicit formula for this function.Comment: 51 pages, 1 figur
Excited states of linear polyenes
We present density matrix renormalisation group calculations of the Pariser-
Parr-Pople-Peierls model of linear polyenes within the adiabatic approximation.
We calculate the vertical and relaxed transition energies, and relaxed
geometries for various excitations on long chains. The triplet (3Bu+) and even-
parity singlet (2Ag+) states have a 2-soliton and 4-soliton form, respectively,
both with large relaxation energies. The dipole-allowed (1Bu-) state forms an
exciton-polaron and has a very small relaxation energy. The relaxed energy of
the 2Ag+ state lies below that of the 1Bu- state. We observe an attraction
between the soliton-antisoliton pairs in the 2Ag+ state. The calculated
excitation energies agree well with the observed values for polyene oligomers;
the agreement with polyacetylene thin films is less good, and we comment on the
possible sources of the discrepencies. The photoinduced absorption is
interpreted. The spin-spin correlation function shows that the unpaired spins
coincide with the geometrical soliton positions. We study the roles of
electron-electron interactions and electron-lattice coupling in determining the
excitation energies and soliton structures. The electronic interactions play
the key role in determining the ground state dimerisation and the excited state
transition energies.Comment: LaTeX, 15 pages, 9 figure
A novel and practical screening tool for the detection of silent myocardial infarction in patients with type 2 diabetes
Silent myocardial infarction (MI) is a prevalent finding in patients with type 2 diabetes and is associated with significant mortality and morbidity. Late gadolinium enhancement (LGE) by cardiovascular magnetic resonance (CMR) is the most validated technique for detection of silent MI but is time consuming, costly and requires administration of intravenous contrast. We therefore planned to develop a simple and low cost population screening tool to identify those at highest risk of silent MI validated against the CMR reference standard.100 asymptomatic patients with type 2 diabetes underwent electrocardiogram (ECG), echocardiography, biomarker assessment and CMR at 3.0T including assessment of left ventricular ejection fraction and LGE. Global longitudinal strain (GLS) from 2 and 4 chamber cines was measured using feature tracking.17/100 patients with no history of cardiovascular disease had silent MI defined by LGE in an infarct pattern on CMR. Only 4 silent MI patients had Q waves on ECG. Patients with silent MI were older (65 vs 60, p=0.05), had lower E/A ratio (0.75 vs 0.89, p=0.004), lower GLS (-15.2% vs -17.7%, p=0.004) and higher NT-proBNP (106ng/L vs 52ng/L, p=0.003). A combined risk score derived from these 4 factors had an area under the receiver operating characteristic (ROC) curve of 0.823 (0.734-0.892), P<0.0001. A score of ?3/5 had 82% sensitivity and 72% specificity for silent MI.Using measures that can be derived in an outpatient clinic setting, we have developed a novel screening tool for the detection of silent MI in type 2 diabetes. The screening tool had significantly superior diagnostic accuracy than current ECG criteria for the detection of silent MI in asymptomatic patients
Online Multi-Coloring with Advice
We consider the problem of online graph multi-coloring with advice.
Multi-coloring is often used to model frequency allocation in cellular
networks. We give several nearly tight upper and lower bounds for the most
standard topologies of cellular networks, paths and hexagonal graphs. For the
path, negative results trivially carry over to bipartite graphs, and our
positive results are also valid for bipartite graphs. The advice given
represents information that is likely to be available, studying for instance
the data from earlier similar periods of time.Comment: IMADA-preprint-c
Pediatric Health-Related Quality of Life: Feasibility, Reliability and Validity of the PedsQL™ Transplant Module
The measurement properties of the newly developed Pediatric Quality of Life Inventory™ (PedsQL™) 3.0 Transplant Module in pediatric solid organ transplant recipients were evaluated. Participants included pediatric recipients of liver, kidney, heart and small bowel transplantation who were cared for at seven medical centers across the United States and their parents. Three hundred and thirty-eight parents of children ages 2–18 and 274 children ages 5–18 completed both the PedsQL™ 4.0 Generic Core Scales and the Transplant Module. Findings suggest that child self-report and parent proxy-report scales on the Transplant Module demonstrated excellent reliability (total scale score for child self-report α= 0.93; total scale score for parent proxy-report α= 0.94). Transplant-specific symptoms or problems were significantly correlated with lower generic HRQOL, supporting construct validity. Children with solid organ transplants and their parents reported statistically significant lower generic HRQOL than healthy children. Parent and child reports showed moderate to good agreement across the scales. In conclusion, the PedsQL™ Transplant Module demonstrated excellent initial feasibility, reliability and construct validity in pediatric patients with solid organ transplants.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/79306/1/j.1600-6143.2010.03149.x.pd
Robustness and Generalization
We derive generalization bounds for learning algorithms based on their
robustness: the property that if a testing sample is "similar" to a training
sample, then the testing error is close to the training error. This provides a
novel approach, different from the complexity or stability arguments, to study
generalization of learning algorithms. We further show that a weak notion of
robustness is both sufficient and necessary for generalizability, which implies
that robustness is a fundamental property for learning algorithms to work
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