The exchange fluctuation theorem in quantum mechanics

We study the heat transfer between two finite quantum systems initially at different temperatures. We find that a recently proposed fluctuation theorem for heat exchange, namely the exchange fluctuation theorem [C. Jarzynski and D. K. Wojcik, Phys. Rev. Lett. 92, 230602 (2004)], does not generally hold in the presence of a finite heat transfer as in the original form proved for weak coupling. As the coupling is weakened, the deviation from the theorem and the heat transfer vanish in the same order of the coupling. We then discover a condition for the exchange fluctuation theorem to hold in the presence of a finite heat transfer, namely the commutable-coupling condition. We explicitly calculate the deviation from the exchange fluctuation theorem as well as the heat transfer for simple models. We confirm for the models that the deviation indeed has a finite value as far as the coupling between the two systems is finite except for the special point of the commutable-coupling condition. We also confirm analytically that the commutable-coupling condition indeed lets the exchange fluctuation theorem hold exactly under a finite heat transfer.Comment: 16 pages, 3 figures, to appear in Progress of Theoretical Physics, Vol. 121, No. 6 (2009

From pilot data to clinical trial: observing the effects of vitamin D dosage on bone quality

INTRODUCTION The relationship between vitamin D and bone quality has been widely researched. Vitamin D is an essential component of normal bone health as well as calcium/phosphate metabolism. Despite significant research efforts, the optimum level of vitamin D intake remains a topic of controversy amongst industry experts. For example, the Institute of Medicine recommends between 600 and 800 international units (IU) per day [1,2]. In contrast, both the osteoporosis Canada and the Endocrine Society guidelines recommend a higher daily dosage of 400 to 2000 IU [3,4]. To date, there have been no studies assessing dose-related vitamin D intake and bone health. The absence of research in this area was the major motivation for both the pilot study and clinical trial presented in this abstract. METHODS: PILOT DATA Participants included in this study were patients from the Pure North S’Energy Foundation (PNSF). All participants received a series of blood draws from PNSF, which determined the vitamin D levels in their blood. These levels were then used to divide participants into four different groups: low vitamin D (<90 mmol/L), normal vitamin D (>90 mmol/L, <175 mmol/L), one time high vitamin D (>175 mmol/L for <6 months), and high vitamin D (>175 mmol/L for >6 months). Participants were then scanned using high resolution peripheral quantitative computed tomography (HR-pQCT, Scanco Medical), to analyze their bone micro-architecture in both the non-dominant tibia and radius. SPSS (version 21) was used to analyze the differences between groups with a One-Way ANOVA and a Tukey Post-Hoc test. Significance was set at p<0.05. RESULTS: PILOT DATA Overall, 113 participants were scanned using HR-pQCT while only 105 were included in the final analysis. Participants were on average 56 years old and 62% female. Both vitamin D (p<0.01) and calcium (p<0.05) were statistically significant between groups using a One-Way ANOVA. At the radius, cortical thickness (p<0.05) and cortical area (p<0.05) were statistically significant across groups. Results from the Tukey Post-Hoc test showed that cortical thickness was significantly lower for low vitamin D compared to the high vitamin D group, as well as lower for the one-time high compared to the high vitamin D group. For cortical area, the one-time high group was significantly lower than the high vitamin D group. For the tibia, trabecular thickness was the only significant variable across groups (p<0.05), with low vitamin D being lower than the one time high vitamin D.   CONCLUSIONS: PILOT DATA There were some bone parameters that were statistically different between vitamin D groups. Of these statistically significant parameters, results differed between the radius and the tibia, as well as between cortical and trabecular bone. Most variables differed between the one-time high group and either the low or high groups. The only difference between the low and high groups was cortical thickness. This pilot data shows some interesting results, and the need for further, more controlled studies. FUTURE WORK: CLINICAL TRIAL This project will move forward in the form of a clinical trial entitled “A randomized double-blind study investigating dose-dependent longitudinal effects of vitamin D supplementation on bone health”. The study will include approximately 300 healthy men and women between the ages of 55-70 years. Similar to the pilot study, participants will be assigned to one of three vitamin D dosages and HR-pQCT will be used to assess bone quality. Other methods such as Dual X-ray Absorptiometry and health questionnaires will also be used to assess overall skeletal, physical and mental health

Effect of Fragmentation and Habitat Type on Coastal Nekton in Mississippi

Coastal wetlands are extremely productive ecosystems that support an abundance of organisms at higher tropic levels. Coastal wetlands also act as important buffers from storms and help protect major cornerstones of coastal economies, such as tourism and fisheries. Despite the clear need for the protection of these habitats, anthropogenic use of coastal wetlands has increased in frequency and intensity, resulting in the fragmentation of once continuous habitats. A central challenge to assessing the impact of marsh fragmentation is the lack of quantitative distribution and abundance data from specific habitat types. This is especially true for species that are not commercially or recreationally harvested and are, therefore, not regularly monitored by state and federal resource management agencies. This study makes use of quantitative density, habitat use, and distribution data for non-harvested marsh nekton collected in oligohaline marshes (salinity 0.5-5ppt) of coastal Mississippi. To assess how nekton assemblages varied by habitat, fragmentation level and position in patch (core vs. edge), four sites along coastal Mississippi were sampled in the summers of 2014 and 2015. Nekton were sampled in adjacent patches of submerged aquatic vegetation and emergent vegetation using a 1 m2 throw trap. Marsh patch fragmentation was quantified using aerial pictures taken with a GoPro camera secured to the end of a 20ft pole. Points around the patch were digitized in TPS software and analyzed using R. The results of this study indicate that diversity and density of nekton in Mississippi marshes vary significantly based on habitat type

Fluctuation Theorems

Fluctuation theorems, which have been developed over the past 15 years, have resulted in fundamental breakthroughs in our understanding of how irreversibility emerges from reversible dynamics, and have provided new statistical mechanical relationships for free energy changes. They describe the statistical fluctuations in time-averaged properties of many-particle systems such as fluids driven to nonequilibrium states, and provide some of the very few analytical expressions that describe nonequilibrium states. Quantitative predictions on fluctuations in small systems that are monitored over short periods can also be made, and therefore the fluctuation theorems allow thermodynamic concepts to be extended to apply to finite systems. For this reason, fluctuation theorems are anticipated to play an important role in the design of nanotechnological devices and in understanding biological processes. These theorems, their physical significance and results for experimental and model systems are discussed.Comment: A review, submitted to Annual Reviews in Physical Chemistry, July 2007 Acknowledgements corrected in revisio

Experimental study of the fluctuation theorem in a nonequilibrium steady state

The fluctuation theorem (FT) quantifies the probability of second law violations in small systems over short time scales. While this theorem has been experimentally demonstrated for systems that are perturbed from an initial equilibrium state, there are a number of studies suggesting that the theorem applies asymptotically in the long time limit to systems in a nonequilibrium steady state. The asymptotic application of the FT to such nonequilibrium steady states has been referred to in the literature as the steady-state fluctuation theorem (or SSFT). In this paper, we demonstrate experimentally the application of the FT to nonequilibrium steady states, using a colloidal particle localized in a translating optical trap. Furthermore, we show, for this colloidal system, that the FT holds under nonequilibrium steady states for all time, and not just in the long time limit, as in the SSFT

Equilibrium binding energies from fluctuation theorems and force spectroscopy simulations

Brownian dynamics simulations are used to study the detachment of a particle from a substrate. Although the model is simple and generic, we attempt to map its energy, length and time scales onto a specific experimental system, namely a bead that is weakly bound to a cell and then removed by an optical tweezer. The external driving force arises from the combined optical tweezer and substrate potentials, and thermal fluctuations are taken into account by a Brownian force. The Jarzynski equality and Crooks' fluctuation theorem are applied to obtain the equilibrium free energy difference between the final and initial states. To this end, we sample non--equilibrium work trajectories for various tweezer pulling rates. We argue that this methodology should also be feasible experimentally for the envisioned system. Furthermore, we outline how the measurement of a whole free energy profile would allow the experimentalist to retrieve the unknown substrate potential by means of a suitable deconvolution. The influence of the pulling rate on the accuracy of the results is investigated, and umbrella sampling is used to obtain the equilibrium probability of particle escape for a variety of trap potentials.Comment: 21 pages, 11 figures, To appear in Soft Matte

Conformational isomers of linear rotaxanes

We examine a simple model of rotaxane structure, with 3 asymmetric rings interacting via repulsive power-law forces. This interlocked molecule exhibits conformational isomerisation which is different from that of molecules whose connectedness is through covalent bonds. The rings are free to translate along and rotate around the axle, and hence weak interaction forces between the rings can lead to distinct rotamer states. We use energy minimisation to determine these states exactly, and show that there can be transitions from asymmetric to symmetric states by varying the bond lengths. We also use classical statistical mechanics to show the effect of thermal noise

Coarse-graining intramolecular hydrodynamic interaction in dilute solutions of flexible polymers

We present a scheme for coarse-graining hydrodynamic interactions in an isolated flexible homopolymer molecule in solution. In contrast to the conventional bead-spring model that employs spherical beads of fixed radii to represent the hydrodynamic characteristics of coarse-grained segments, we show that our procedure leads naturally to a discrete model of a polymer molecule as a chain of orientable and stretchable Gaussian blobs. This model accounts for both intrablob and interblob hydrodynamic interactions, which depend on the instantaneous shapes of the blobs. In Brownian dynamics simulations of initially stretched chains relaxing under quiescent conditions, the transient evolution of the mean-square end-to-end distance and first normal stress difference obtained with the Gaussian-blob model are found to be less sensitive to the degree of coarse graining, in comparison with the conventional bead-spring model with Rotne-Prager-Yamakawa hydrodynamic interactions

Non-equilibrium umbrella sampling applied to force spectroscopy of soft matter

Physical systems often respond on a timescale which is longer than that of the measurement. This is particularly true in soft matter where direct experimental measurement, for example in force spectroscopy, drives the soft system out of equilibrium and provides a non-equilibrium measure. Here we demonstrate experimentally for the first time that equilibrium physical quantities (such as the mean square displacement) can be obtained from non-equilibrium measurements via umbrella sampling. Our model experimental system is a bead fluctuating in a time-varying optical trap. We also show this for simulated force spectroscopy on a complex soft molecule--a piston-rotaxane

Racial differences in diabetes-related psychosocial factors and glycemic control in patients with type 2 diabetes

BACKGROUND: We examined whether diabetes-related psychosocial factors differ between African American and white patients with type 2 diabetes. We also tested whether racial differences in glycemic control are independent of such factors. METHODS: Baseline glycosylated hemoglobin (HbA(1c)) and survey measures from 79 African American and 203 white adult participants in a diabetes self-management clinical trial were analyzed. RESULTS: Several psychosocial characteristics varied by race. Perceived interference of diabetes with daily life, perceived diabetes severity, and diabetes-related emotional distress were higher for African Americans than for whites, as were access to illness-management resources and social support. Mean HbA(1c) levels were higher among African Americans than whites (8.14 vs 7.40, beta = 0.17). This difference persisted after adjusting for demographic, clinical, and diabetes-related psychosocial characteristics that differed by race (beta = 0.18). Less access to illness-management resources (beta = -0.25) and greater perceived severity of diabetes (beta = 0.21) also predicted higher HbA(1c). DISCUSSION: Although racial differences in diabetes-related psychosocial factors were observed, African Americans continued to have poorer glycemic control than whites even after such differences were taken into account. Interventions that target psychosocial factors related to diabetes management, particularly illness-management resources, may be a promising way to improve glycemic control for all patients