Gaussian excitations model for glass-former dynamics and thermodynamics

We describe a model for the thermodynamics and dynamics of glass-forming liquids in terms of excitations from an ideal glass state to a Gaussian manifold of configurationally excited states. The quantitative fit of this three parameter model to the experimental data on excess entropy and heat capacity shows that ``fragile'' behavior, indicated by a sharply rising excess heat capacity as the glass transition is approached from above, occurs in anticipation of a first-order transition -- usually hidden below the glass transition -- to a ``strong'' liquid state of low excess entropy. The dynamic model relates relaxation to a hierarchical sequence of excitation events each involving the probability of accumulating sufficient kinetic energy on a separate excitable unit. Super-Arrhenius behavior of the relaxation rates, and the known correlation of kinetic with thermodynamic fragility, both follow from the way the rugged landscape induces fluctuations in the partitioning of energy between vibrational and configurational manifolds. A relation is derived in which the configurational heat capacity, rather than the configurational entropy of the Adam Gibbs equation, controls the temperature dependence of the relaxation times, and this gives a comparable account of the experimental observations.Comment: 21 pp., 17 fig

Codimension Two Branes and Distributional Curvature

In general relativity, there is a well-developed formalism for working with the approximation that a gravitational source is concentrated on a shell, or codimension one surface. By contrast, there are obstacles to concentrating sources on surfaces that have a higher codimension, for example, a string in a spacetime with dimension greater than or equal to four. Here it is shown that, by giving up some of the generality of the codimension one case, curvature can be concentrated on submanifolds that have codimension two. A class of metrics is identified such that (1) the scalar curvature and Ricci densities exist as distributions with support on a co-dimension two submanifold, and (2) using the Einstein equation, the distributional curvature corresponds to a concentrated stress-energy with equation of state p equals minus the energy density, where p is the isotropic pressure tangent to the submanifold. This is the appropriate stress-energy to describe a self-gravitating brane that is governed by an area action, or a brane world deSitter cosmology. The possibility of having a different equation of state arise from a wider class of metrics is discussed.Comment: 18 pages; v2 references added; typos corrected, references added; additional references adde

Thermodynamics and Dynamics of a Monoatomic Glass-Former. Constant Pressure and Constant Volume Behavior

We report constant-volume and constant-pressure simulations of the thermodynamic and dynamic properties of the low-temperature liquid and crystalline phases of the modified Stillinger-Weber (mSW) model. We have found an approximately linear increase of the effective Gaussian width of the distribution of inherent structures. This effect comes from non-Gaussianity of the landscape and is consistent with the predictions of the Gaussian excitations model representing the thermodynamics of the configurational manifold as an ensemble of excitations, each carrying an excitation entropy. The mSW model provides us with both the configurational and excess entropies, with the difference mostly attributed to vibrational anharmonicity. We therefore can address the distinction between the excess thermodynamic quantities often used in the Adam-Gibbs (AG) equation. We find a new break in the slope of the constant pressure AG plot when the excess entropy is used in the AG equation. The simulation diffusivity data are equally well fitted by applying a new equation, derived within the Gaussian excitations model, that emphasizes enthalpy over entropy as the thermodynamic control variable for transport in viscous liquids.Comment: 14 pages, 14 figure

The Glass Transition Temperature of Water: A Simulation Study

We report a computer simulation study of the glass transition for water. To mimic the difference between standard and hyperquenched glass, we generate glassy configurations with different cooling rates and calculate the $T$ dependence of the specific heat on heating. The absence of crystallization phenomena allows us, for properly annealed samples, to detect in the specific heat the simultaneous presence of a weak pre-peak (``shadow transition''), and an intense glass transition peak at higher temperature. We discuss the implications for the currently debated value of the glass transition temperature of water. We also compare our simulation results with the Tool-Narayanaswamy-Moynihan phenomenological model.Comment: submitted to Phys. Re

Advice on using nature based interventions to reach net zero greenhouse gas emissions by 2050

This is the final version. Available from the UK Department for Environment, Food & Rural Affairs via the link in this recordThis paper sets out the NCC’s advice to government on taking a natural capital approach to attaining net zero. Nature based interventions for attaining the government’s net zero target should be viewed in the broader context of the 25 YEP goals. This should be delivered through a joined-up government response to climate change.DEFR

Final response to the 25 Year Environment Plan progress report

This is the final version. Available from the Natural Capital Committee via the link in this recordExecutive summary The Natural Capital Committee’s (NCC) final response to the second 25 Year Environment Plan (25 YEP) Progress Report – follows its interim response published in July 2020. In its interim response, the NCC raised concerns that the evidence presented in the Progress Report at best provides only a partial picture, given the narrow range of datasets considered, and mostly shows declines in England’s environment. The Committee also set out a natural capital approach to assessing progress. This report covers three areas, as follows: i) Sets out a natural capital asset based framework for assessing progress against the 25 YEP; ii) Demonstrates how this natural capital framework can be applied to independently scrutinise progress, with the NCC’s assessment of seven natural assets summarised, and further detail provided across the associated technical annexes – thereby laying the foundation for the Office for Environmental Protection (OEP) to undertake this function from 2021; and iii) Highlights the priority areas where the government should focus in order to turnaround the evidenced declines in natural assets and get on track to meet the 25 YEP objective to improve the natural environment within a generation

Chiral two-pion exchange and proton-proton partial-wave analysis

The chiral two-pion exchange component of the long-range pp interaction is studied in an energy-dependent partial-wave analysis. We demonstrate its presence and importance, and determine the chiral parameters c_i (i=1,3,4). The values agree well with those obtained from pion-nucleon amplitudes.Comment: 13 pages, no figure

How a firm can induce legislators to adopt a bad policy

This paper shows why a majority of legislators may vote for a policy that benefits a firm but harms all legislators. The firm may induce legislators to support the policy by suggesting that it is more likely to invest in a district where voters or their representative support the policy. In equilibrium, no one vote may be decisive, so each legislator who seeks the firm’s investment votes for the policy, though all legislators would be better off if they all voted against the policy. And when votes reveal information about the district, the firm’s implicit promise or threat can be credible. Unlike influence mechanisms based on contributions or bribes, the behavior considered is time consistent and in line with the low campaign contributions by special interests