Measuring thermodynamic length

Thermodynamic length is a metric distance between equilibrium thermodynamic states. Among other interesting properties, this metric asymptotically bounds the dissipation induced by a finite time transformation of a thermodynamic system. It is also connected to the Jensen-Shannon divergence, Fisher information and Rao's entropy differential metric. Therefore, thermodynamic length is of central interest in understanding matter out-of-equilibrium. In this paper, we will consider how to define thermodynamic length for a small system described by equilibrium statistical mechanics and how to measure thermodynamic length within a computer simulation. Surprisingly, Bennett's classic acceptance ratio method for measuring free energy differences also measures thermodynamic length.Comment: 4 pages; Typos correcte

Near-equilibrium measurements of nonequilibrium free energy

A central endeavor of thermodynamics is the measurement of free energy changes. Regrettably, although we can measure the free energy of a system in thermodynamic equilibrium, typically all we can say about the free energy of a non-equilibrium ensemble is that it is larger than that of the same system at equilibrium. Herein, we derive a formally exact expression for the probability distribution of a driven system, which involves path ensemble averages of the work over trajectories of the time-reversed system. From this we find a simple near-equilibrium approximation for the free energy in terms of an excess mean time-reversed work, which can be experimentally measured on real systems. With analysis and computer simulation, we demonstrate the accuracy of our approximations for several simple models.Comment: 5 pages, 3 figure

The relative contributions of cereal production, imports, and aid to somali food security

Somalia is among the poorest countries on the planet. Since the fall of Siad Barre’s regime in 1991, the country has been in a near-constant state of food insecurity and suffered two officially declared famines. In order to address the issue of food insecurity in Somalia, a greater understanding of each of the components that contribute to the Somali food supply is merited. Cereal crops make up a third to half of the Somali diet by calories and are among the most important food crops produced by the country. This study investigated the historic trends in domestic cereal production, cereal imports, and food aid (reported in cereal equivalents) in Somalia by exploring secondary data publicly available from the Food and Agriculture Organization (FAO) of the United Nations, and the World Food Programme. These data were related to World Bank population data in Microsoft Excel and average per capita production, import, and aid figures were calculated. Median changes over time and their associated interquartile ranges were reported. The data demonstrated that Somali cereal production levels have not improved since the 1960’s, and since that time, they have been characterized by an extreme amount of year-to-year volatility. Moreover, maize and sorghum are the only meaningful fractions of Somalia’s domestic cereal production, and recent total production of each crop is well below the levels observed in the 1980’s. When combined, per capita production of maize and sorghum has decreased precipitously over time (falling from a high of 91 kg per capita in 1972 to just 30 kg per capita in 2012). This is likely due to a combination of stagnant production and rapidly increasing Somali population (up over 350% since 1961). This has increased the importance of cereal imports and aid to Somalia and has made the country vulnerable to disruptions in international cereal markets and foreign government policies. Improving domestic cereal production in Somalia should be part of any future food security strategy for the country. Recent agricultural research in Somalia suggests that the implementation of simple agricultural best management practices can increase cereal production in the country.Keywords: Somalia, Population Growth, Cereal Production, Cereal Imports, Food AidAfr. J. Food Agric. Nutr. Dev. 2019; 19(3): 14587-1460

The Renormalized Stress Tensor in Kerr Space-Time: Numerical Results for the Hartle-Hawking Vacuum

We show that the pathology which afflicts the Hartle-Hawking vacuum on the Kerr black hole space-time can be regarded as due to rigid rotation of the state with the horizon in the sense that when the region outside the speed-of-light surface is removed by introducing a mirror, there is a state with the defining features of the Hartle-Hawking vacuum. In addition, we show that when the field is in this state, the expectation value of the energy-momentum stress tensor measured by an observer close to the horizon and rigidly rotating with it corresponds to that of a thermal distribution at the Hawking temperature rigidly rotating with the horizon.Comment: 17 pages, 7 figure

Sialic Acid Mutarotation Is Catalyzed by the Escherichia coli β-Propeller Protein YjhT

The acquisition of host-derived sialic acid is an important virulence factor for some bacterial pathogens, but in vivo this sugar acid is sequestered in sialoconjugates as the {alpha}-anomer. In solution, however, sialic acid is present mainly as the β-anomer, formed by a slow spontaneous mutarotation. We studied the Escherichia coli protein YjhT as a member of a family of uncharacterized proteins present in many sialic acid-utilizing pathogens. This protein is able to accelerate the equilibration of the {alpha}- and β-anomers of the sialic acid N-acetylneuraminic acid, thus describing a novel sialic acid mutarotase activity. The structure of this periplasmic protein, solved to 1.5Å resolution, reveals a dimeric 6-bladed unclosed β-propeller, the first of a bacterial Kelch domain protein. Mutagenesis of conserved residues in YjhT demonstrated an important role for Glu-209 and Arg-215 in mutarotase activity. We also present data suggesting that the ability to utilize {alpha}-N-acetylneuraminic acid released from complex sialoconjugates in vivo provides a physiological advantage to bacteria containing YjhT

The thermodynamics of prediction

A system responding to a stochastic driving signal can be interpreted as computing, by means of its dynamics, an implicit model of the environmental variables. The system's state retains information about past environmental fluctuations, and a fraction of this information is predictive of future ones. The remaining nonpredictive information reflects model complexity that does not improve predictive power, and thus represents the ineffectiveness of the model. We expose the fundamental equivalence between this model inefficiency and thermodynamic inefficiency, measured by dissipation. Our results hold arbitrarily far from thermodynamic equilibrium and are applicable to a wide range of systems, including biomolecular machines. They highlight a profound connection between the effective use of information and efficient thermodynamic operation: any system constructed to keep memory about its environment and to operate with maximal energetic efficiency has to be predictive.Comment: 5 pages, 1 figur

Thermodynamic metrics and optimal paths

A fundamental problem in modern thermodynamics is how a molecular-scale machine performs useful work, while operating away from thermal equilibrium without excessive dissipation. To this end, we derive a friction tensor that induces a Riemannian manifold on the space of thermodynamic states. Within the linear-response regime, this metric structure controls the dissipation of finite-time transformations, and bestows optimal protocols with many useful properties. We discuss the connection to the existing thermodynamic length formalism, and demonstrate the utility of this metric by solving for optimal control parameter protocols in a simple nonequilibrium model.Comment: 5 page

On the Quantum Jarzynski Identity

In this note, we will discuss how to compactly express and prove the Jarzynski identity for an open quantum system with dissipative dynamics. We will avoid explicitly measuring the work directly, which is tantamount to continuously monitoring the system, and instead measure the heat flow from the environment. We represent the measurement of heat flow with Hermitian map superoperators that act on the system density matrix. Hermitian maps provide a convenient and compact representation of sequential measurement and correlation functions.Comment: 4 page

Modelling the hydrological impacts of climate change on UK lowland wet grassland

Hydrological impacts of climate change upon the Elmley Marshes, southeast England, are simulated using a coupled hydrological/hydraulic model developed using MIKE SHE/MIKE 11 and calibrated to contemporary conditions. Predicted changes in precipitation, temperature, radiation and wind speed from the UK Climate Impacts Programme associated with four emissions scenarios for the 2050s are used to modify precipitation and potential evapotranspiration data. For each emissions scenario two sets of potential evapotranspiration data are derived, one using changes in temperature (PETtemp), the other incorporating changes in temperature, radiation and wind speed (PETtrws). Results indicate drier conditions through the progressively higher emissions scenarios when compared to contemporary conditions. Changes are particularly pronounced when using PETtrws. Summer water tables are lower (PETtemp 0.01�0.08 m; PETtrws 0.07�0.27 m) and the duration of high winter water tables is reduced. Although water tables still intercept the surface in winter when using PETtemp, this ceases when PETtrws is employed. Summer ditch water levels for the PETtemp scenarios are lower (0.01�0.21 m) and in dry winters they do not reach mean field level. Under the PETtrws scenarios summer and winter ditch water levels are lower by on average 0.21 and 0.30 m, respectively. Levels never reach the elevation of the marsh surface. Lower groundwater and ditch water levels result in declines in the magnitude and duration of surface inundation which is virtually eliminated with the PETtrws scenarios. The changes in hydrological conditions simulated by the model are of sufficiently fine resolution to infer ecological impacts which are likely to include the loss of some grassland species adapted to high water tables. Reductions in the extent of surface water in spring, especially for the PETtrws scenarios, are likely to reduce suitability for wading birds including lapwing (Vanellus vanellus) and redshank (Tringa totanus) for which the marshes are internationally renowned

Rheumatoid arthritis is associated with reduced adiposity but not with unfavorable major cardiovascular risk factor profiles and enhanced carotid atherosclerosis in black Africans from a developing population: a cross-sectional study

INTRODUCTION: Rheumatoid arthritis (RA) is characterized by inflamed joint-derived cytokine-mediated high-grade systemic inflammation that enhances cardiovascular metabolic risk and disease in developed populations. We investigated the potential impact of RA on cardiovascular risk factors including systemic inflammation and atherosclerosis, and their relationships in black Africans from a developing population. METHODS: We evaluated demographic features, adiposity indices, major traditional cardiovascular risk factors, circulating C-reactive protein and interleukin-6 concentrations and ultrasound determined carotid intima-media thickness (cIMT) in 274 black Africans; 115 had established RA. Data were analyzed in confounder-adjusted mixed regression models. RESULTS: The body mass index and waist-height ratio were lower in RA compared to non-RA subjects (29.2 (6.6) versus 33.7 (8.0), P < 0.0001 and 0.58 (0.09) versus 0.62 (0.1), P = 0.0003, respectively). Dyslipidemia was less prevalent in patients with RA (odds ratio (OR) (95% confidence interval (CI) = 0.54 (0.30 to1.00)); this disparity was no longer significant after further adjustment for reduced adiposity and chloroquine use. RA was also not associated with hypertension, current smoking and diabetes. The number of major traditional risk factors did not differ by RA status (1.1 (0.8) versus 1.2 (0.9), P = 0.7). Circulating C-reactive protein concentrations were similar and serum interleukin-6 concentrations reduced in RA (7.2 (3.1) versus 6.7 (3.1) mg/l, P = 0.7 and 3.9 (1.9) versus 6.3 (1.9) pg/ml, P < 0.0001, respectively). The cIMT was 0.700 (0.085) and 0.701 (0.111) mm in RA and non-RA subjects, respectively (P = 0.7). RA disease activity and severity parameters were consistently unrelated to systemic inflammation, despite the presence of clinically active disease in 82.6% of patients. In all participants, adiposity indices, smoking and converting angiotensin inhibitor non-use were associated with increased systemic inflammation, which related to more atherogenic lipid profiles, and circulating low density lipoprotein concentrations were associated with cIMT (partial R = 0.153, P = 0.032); RA did not impact on these relationships (interaction P ≥0.1). CONCLUSIONS: Among black Africans, patients with established RA experience reduced overall and abdominal adiposity but no enhanced major traditional risk factor and atherosclerosis burden. This study further suggests that an absent interleukin-6 release by inflamed RA joints into the circulation may account for this unaltered cardiovascular disease risk