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

Constructive or Disruptive? How Active Learning Environments Shape Instructional Decision-Making

This study examined instructional shifts associated with teaching in environments optimized for active learning, including how faculty made decisions about teaching and their perceptions of how students responded to those changes. The interviews and subsequent analysis reveal a broad range of course changes, from small modifications of existing activities to large shifts towards collaborative learning, many of which emerged during the term rather than being planned in advance. The faculty discuss several factors that influenced their decisions, including prior experience, professional identity, student engagement, and perceived and realized affordances of the environments

Gender differences in skin and core body temperature during exercise in a hot, humid environment.

Background. It is universally accepted that men and women regulate heat differently during exercise in hot, humid environments. Despite this common knowledge, little empirical data is available to explain how gender differences effect core/skin temperature changes. Further, the data that is available includes only limited measurement sites and/or time points. Methods. The purpose of this study was to measure the heat regulatory patterns for both men and women during 60-min of exercise in a hot, humid environment. Twenty aerobically fit subjects (10 men; 10 women) completed an acclimation session followed by a 60-min exercise protocol in an environmental chamber set at 39.9 ± 1.1 °C and 46.4 ± 4% relative humidity. Each exercise protocol consisted of four intervals of an 8-min walk (mean ± SD; men: 4.0 ± 0.3, women: 3.0 ± 0.2 mph) and 7-min light jog (men: 5.4 ± 0.5, women: 5.0 ± 0.3 mph). Subjects were confirmed to be euhydrated (urine specific gravity) prior to exercise and were encouraged to drink water to maintain hydration during exercise. Pre- and Post-exercise body weights did not differ, thus it appears hydration was maintained during exercise. Skin temperatures (iButton wireless loggers) were recorded every minute at seventeen sites (right and left: upper chest, mid-chest, abdomen, upper back, mid-back, lower back, upper arm, and lower arm, and back of the neck). In addition, core body temperature (rectal), rating of perceived exertion (RPE), and heart rate (wireless telemetry) were also recorded at the end of each interval of the protocol. Statistical analysis was carried out using a 2 (gender) x 60 (time) repeated measures ANOVA. Other variables were analyzed using a 2 (gender) x 8 (time) ANOVA with repeated measures on the 2nd factor. Any non-normally distributed data was log transformed. Significance was set at p\u3c0.05 and location of effects will be determined using individual t-tests with a Bonferroni correction for multiple comparisons. Results. Analysis revealed significantly higher skin temperatures in four locations on men compared to women: right upper back (p=0.048), right mid-back (p=0.001), right lower back (p=0.001), and left upper back (p\u3c0.001). Additionally, these changes were seen despite no significant differences between genders in core body temperature, RPE, and heart rate. This latter finding supports the conclusion that a similar degree of exercise, heat stress was applied to both men and women. Conclusions. We found gender differences at four different skin temperature locations. These changes might suggest that men retain more metabolic heat in various locations on the back when exercising in a hot, humid environment compared to women. Further research is needed to understand how these changes may affect post-exercise recovery return to baseline skin and core temperature values

Comparing Three Methods of Measuring Skin Temperature during Exercise in a Hot, Humid Environment

Exercise in a hot, humid environment substantially increases the physiological stress of exercise. Most of the techniques that are currently used to monitor changes in skin temperature have been in use for more than 20 years with little innovation. The purpose of the present study was two-fold: 1) to compare three techniques for measuring skin temperature (wired skin electrode, wireless temperature data logger, and thermal imaging) and 2) to compare and contrast these measures in men and women completing 45-min of cycling in a hot (39±2°C), humid (45±5% RH) environment. The CPHS committee approved all procedures described in this report and subjects gave written consent to participate. Men (N=14) and women (N=18) completed all study requirements out of 45 subjects that were enrolled. Following a baseline screening session that included a measurement of body composition (whole body DXA scan) and an aerobic fitness test (VO2peak), subjects were scheduled for an experimental exercise trial between 0500 and 0800. Subjects arrived to the laboratory and were tested for hydration using urine specific gravity and if dehydrated, they were provided water to drink before starting the exercise trial. Exercise consisted of 50-min of cycling. After 50-min, subjects were asked to continue cycling until their rectal core body temperature exceeded 39.3°C. The time they were able to exercise beyond 50-min was recorded and compared between individuals. Wired skin temperature was monitored using YSI400 banjo probes, wireless skin temperature was monitored using a data logging system (iButton), and thermal skin temperature was measured from images taken with a thermal camera (RAZR Max-IR). These skin measurements were made on the bicep and abdomen. All body temperatures were recorded at rest, every 10-min during exercise, and immediately following the end of exercise. Data was statistically analyzed using a 2 (gender: men & women) x sensor method (wired, wireless, and thermal) x time (0, 10, 20, 30, 40, 50, end) ANOVA with repeated measures on the 2nd and 3rd factors. Significance was set a

Inter-individual variation in nucleotide excision repair in young adults: effects of age, adiposity, micronutrient supplementation and genotype

Nucleotide excision repair (NER) is responsible for repairing bulky helix-distorting DNA lesions and is essential for the maintenance of genomic integrity. Severe hereditary impairment of NER leads to cancers such as those in xeroderma pigmentosum, and more moderate reductions in NER capacity have been associated with an increased cancer risk. Diet is a proven modifier of cancer risk but few studies have investigated the potential relationships between diet and NER. In the present study, the plasmid-based host cell reactivation assay was used to measure the NER capacity in peripheral blood mononuclear cells from fifty-seven volunteers aged 18–30 years before and after 6 weeks of supplementation with micronutrients (selenium and vitamins A, C and E). As a control, nine individuals remained unsupplemented over the same period. Volunteers were genotyped for the following polymorphisms in NER genes: ERCC5 Asp1104His (rs17655); XPC Lys939Gln (rs2228001); ERCC2 Lys751Gnl (rs13181); XPC PAT (an 83 bp poly A/T insertion–deletion polymorphism in the XPC gene). NER capacity varied 11-fold between individuals and was inversely associated with age and endogenous DNA strand breaks. For the first time, we observed an inverse association between adiposity and NER. No single polymorphism was associated with the NER capacity, although significant gene–gene interactions were observed between XPC Lys939Gln and ERCC5 Asp1104His and XPC Lys939Gln and ERCC2 Lys751Gnl. While there was no detectable effect of micronutrient supplementation on NER capacity, there was evidence that the effect of fruit intake on the NER capacity may be modulated by the ERCC2 Lys751Gnl single nucleotide polymorphism