From real materials to model Hamiltonians with density matrix downfolding

Due to advances in computer hardware and new algorithms, it is now possible to perform highly accurate many-body simulations of realistic materials with all their intrinsic complications. The success of these simulations leaves us with a conundrum: how do we extract useful physical models and insight from these simulations? In this article, we present a formal theory of downfolding--extracting an effective Hamiltonian from first-principles calculations. The theory maps the downfolding problem into fitting information derived from wave functions sampled from a low-energy subspace of the full Hilbert space. Since this fitting process most commonly uses reduced density matrices, we term it density matrix downfolding (DMD).Comment: 24 pages, 12 figures; Huihuo Zheng and Hitesh J. Changlani contributed equally to this wor

Dynamic Parameters of Balance Which Correlate to Elderly Persons with a History of Falls

Poor balance in older persons contributes to a rise in fall risk and serious injury, yet no consensus has developed on which measures of postural sway can identify those at greatest risk of falling. Postural sway was measured in 161 elderly individuals (81.8y±7.4), 24 of which had at least one self-reported fall in the prior six months, and compared to sway measured in 37 young adults (34.9y±7.1). Center of pressure (COP) was measured during 4 minutes of quiet stance with eyes opened. In the elderly with fall history, all measures but one were worse than those taken from young adults (e.g., maximal COP velocity was 2.7× greater in fallers than young adults; p<0.05), while three measures of balance were significantly worse in fallers as compared to older persons with no recent fall history (COP Displacement, Short Term Diffusion Coefficient, and Critical Displacement). Variance of elderly subjects' COP measures from the young adult cohort were weighted to establish a balance score (“B-score”) algorithm designed to distinguish subjects with a fall history from those more sure on their feet. Relative to a young adult B-score of zero, elderly “non-fallers” had a B-score of 0.334, compared to 0.645 for those with a fall history (p<0.001). A weighted amalgam of postural sway elements may identify individuals at greatest risk of falling, allowing interventions to target those with greatest need of attention

Self-reported Adherence with the Use of a Device in a Clinical Trial as Validated by Electronic Monitors: the VIBES Study

Background: Adherences to treatments that require a behavioral action often rely on self-reported recall, yet it is vital to determine whether real time self reporting of adherence using a simple logbook accurately captures adherence. The purpose of this study was to determine whether real time self-reported adherence is an accurate measurement of device usage during a clinical trial by comparing it to electronic recording. Methods: Using data collected from older adult men and women (N=135, mean age 82.3 yrs; range 66 to 98 yrs) participating in a clinical trial evaluating a vibrating platform for the treatment of osteoporosis, daily adherence to platform treatment was monitored using both self-reported written logs and electronically recorded radio-frequency identification card usage, enabling a direct comparison of the two methods over one year. Agreement between methods was also evaluated after stratification by age, gender, time in study, and cognition status. Results: The two methods were in high agreement (overall intraclass correlation coefficient = 0.96). The agreement between the two methods did not differ between age groups, sex, time in study and cognitive function. Conclusions: Using a log book to report adherence to a daily intervention requiring a behavioral action in older adults is an accurate and simple approach to use in clinical trials, as evidenced by the high degree of concordance with an electronic monitor

Discrete Model of Ideological Struggle Accounting for Migration

A discrete in time model of ideological competition is formulated taking into account population migration. The model is based on interactions between global populations of non-believers and followers of different ideologies. The complex dynamics of the attracting manifolds is investigated. Conversion from one ideology to another by means of (i) mass media influence and (ii) interpersonal relations is considered. Moreover a different birth rate is assumed for different ideologies, the rate being assumed to be positive for the reference population, made of initially non-believers. Ideological competition can happen in one or several regions in space. In the latter case, migration of non-believers and adepts is allowed; this leads to an enrichment of the ideological dynamics. Finally, the current ideological situation in the Arab countries and China is commented upon from the point of view of the presently developed mathematical model. The massive forced conversion by Ottoman Turks in the Balkans is briefly discussed.Comment: 24 pages, with 5 figures and 52 refs.; prepared for a Special issue of Advances in Complex System