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At least 1,495 records · Page 83Linked to original sources
PubMed2002

Cooling of a lattice granular fluid as an ordering process.

We present a microscopic model of granular medium to study the role of dynamical correlations and the onset of spatial order induced by the inelasticity of the interactions on the velocity field. In spite of its simplicity and intrinsic limitations, it features several aspects of the rich phenomenology observed in granular materials and allows to make contact with other topics of statistical mechanics such as diffusion processes, domain growth, aging phenomena. Interestingly, while local observables, being controlled by the largest wavelength fluctuations, seem to suggest a purely diffusive behavior, the formation of spatially extended structures and topological defects, such as vortices and shocks, reveals a more complex scenario. Finally, only for quasielastic systems, we observe a neat scale separation, which represents a fundamental hypothesis to develop a granular hydrodynamics.

Journal Article↗
PubMed2005

Longitudinal analysis of the relationship between regular eye examinations and changes in visual and functional status.

OBJECTIVES: To determine whether regular eye examinations are associated with a greater or lesser rate of loss of ability to read newsprint, onset of blindness or low vision, or onset of limitations in instrumental activities of daily living (IADLs) and activities of daily living (ADLs). DESIGN: A sample of 14,215 Medicare beneficiaries observed between 1994 and 1999 linked to the 1994 and 1999 National Long-Term Care Surveys (NLTCS). Effects of annual examinations were assessed using instrumental variables. SETTING: The Medicare-linked NLTCS is representative of U.S. elderly persons from 1994 to 1999. PARTICIPANTS: Longitudinal observational study of persons aged 65 and older. MEASUREMENTS: Change in self-reported and provider-reported vision and change in functional limitations associated with vision related to the number of years with eye examinations and other factors. RESULTS: Persons with more-regular eye examinations between 1994 and 1998 were less likely to have experienced a decline in vision or in functional status between 1994 and 1999. On average, an additional year with an eye examination was associated with a decrease in the probability of becoming unable to read newsprint of 0.12 (P=.03), a lower probability of onset of low vision or blindness of 0.009 (P=.06), and a decrease in the probability that the number of functional limitations increased of 0.13 (P=.002) for IADLs and 0.05 (P=.003) for ADLs. CONCLUSION: Elderly persons who have regular eye examinations experience less decline in vision and functional status.

Activities of Daily Living↗
PubMed2005

Nonparametric estimation of asymptomatic duration from a randomized prospective cancer screening trial.

We propose a nonparametric estimation of preclinical duration distribution in cancer based on data from a randomized early detection trial. In cancer screening studies, the preclinical duration of a disease is of great interest for better understanding the natural history of the disease, and for developing optimal screening strategies. To estimate the sojourn time distribution nonparametrically, we first estimate the distribution of the age at onset of preclinical disease nonparametrically using data from the screening arm in a randomized screening trial, and the distribution for the age at onset of clinical disease from the control arm of the randomized screening trial. Finally, by using deconvolution the two estimated distributions lead to a nonparametric estimate of the distribution for the gap time between the onset of preclinical disease and the onset of clinical disease. We illustrate the methodology using data from a randomized breast cancer screening trial.

Adult↗