Proton-rich material in a state of nuclear statistical equilibrium (NSE) is one of the least studied regimes of nucleosynthesis. One reason for this is that after hydrogen burning, stellar evolution proceeds at conditions of an equal number of neutrons and protons or at a slight degree of neutron-richness. Proton-rich nucleosynthesis in stars tends to occur only when hydrogen-rich material that accretes onto a white dwarf or a neutron star explodes, or when neutrino interactions in the winds from a nascent proto-neutron star or collapsar disk drive the matter proton-rich prior to or during the nucleosynthesis. In this Letter we solve the NSE equations for a range of proton-rich thermodynamic conditions. We show that cold proton-rich NSE is qualitatively different from neutron-rich NSE. Instead of being dominated by the Fe-peak nuclei with the largest binding energy per nucleon that have a proton-to-nucleon ratio close to the prescribed electron fraction, NSE for proton-rich material near freezeout temperature is mainly composed of and free protons. Previous results of nuclear reaction 56 Ni network calculations rely on this nonintuitive high-proton abundance, which this Letter explains. We show how the differences and especially the large fraction of free protons arises from the minimization of the free energy as a result of a delicate competition between the entropy and nuclear binding energy.

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Applied electrochemistry plays a key role in many technologies, such as Li-ion batteries, fuel cells, supercapacitors, solar cells, etc. It is therefore at the core of many research programs all over the world. However, fundamental electrochemical investigations remain scarce. In particular, electrochemistry is among the fields for which the gap between theory and experiment is the largest. From the computational point of view, there is no classical molecular dynamics (MD) software devoted to the simulation of electrochemical systems while other fields such as biochemistry or material science have dedicated tools. "MetalWalls" (MW), a MD code dedicated to electrochemistry, fills this gap. Its main originality is the inclusion of a series of methods which allow a constant electrical potential to be applied to the electrode materials. It also allows the simulation of bulk liquids or solids using the polarizable ion model and the aspherical ion model. MW is designed to be used on high-performance computers and it has already been employed in a number of scientific publications. It was for example used to study the charging mechanism of supercapacitors, nanoelectrowetting and water desalination devices.

A B S T R A C TUsing a combination of cyclic voltammetry experiments and molecular dynamics simulations, we study the effect of microporous carbon structure on the performance of aqueous supercapacitors using carbide derived carbon (CDC) electrodes. The structures investigated by molecular simulations are compatible with the experimental results for CDC synthesized at 800 C, but not with the other two materials (CDC-1100 and YP-50F), which are more graphitic. In fact, the specific capacitance obtained for the latter two are in good agreement with molecular simulations of graphite electrodes, assuming that all the charge is localized in the first plane in contact with the electrode (a very good approximation). Our molecular simulations further allow to examine the solvation of ions inside the electrodes. Unlike what was observed for large organic ions dissolved in acetonitrile, we find that most Na þ cations remain fully solvated. Overall, microporous carbons such as CDCs are good candidates for applications involving aqueous supercapacitors, in particular the harvesting of blue energy or desalination, but their performance remains to be optimized by tailoring their microstructure. * Corresponding author. Sorbonne Universit e, CNRS, Physico-chimie des electrolytes et nano-syst emes interfaciaux, PHENIX, F-75005,

Electrochemistry is central to many applications, ranging from biology to energy science. Studies now involve a wide range of techniques, both experimental and theoretical. Modelling and simulations methods, such as density functional theory or molecular dynamics, provide key information on the structural and dynamic properties of the systems. Of particular importance are polarization effects the electrode/electrolyte interface, which are difficult to simulate accurately. Here we show how these electrostatic interactions are taken into account in the framework of the Ewald summation method. We discuss, in particular, the formal set up for calculations that enforce periodic boundary conditions in two directions, a geometry that more closely reflects the characteristics of typical electrolyte/electrode systems and presents some differences with respect to the more common case of periodic boundary conditions in three dimensions. These formal developments are implemented and tested in MetalWalls, a molecular dynamics software which captures the polarization of the electrolyte and allows the simulation of electrodes maintained at a constant potential. We also discuss the technical aspects involved in the calculation of two sets of coupled degrees of freedom, namely the induced dipoles and the electrode charges. We validate the implementation, first on simple systems, then on the well-known interface between graphite electrodes and a room-temperature ionic liquid. We finally illustrate the capabilities of MetalWalls by studying the adsorption of a complex functionalized electrolyte on a graphite electrode.

SUMMARYUNIC is the neutronics component of the massively parallel, multi-physics SHARP (Simulation for High-efficiency Advanced Reactor Prototyping) framework under development at Argonne National Laboratory. During this fiscal year, the SN2ND solver, MOCFE solver, and NODAL solver received significant development to meet the needs of the SHARP project. Additional follow-on analysis of the ZPR-6/6A from the previous year was performed in addition to new analysis of the ZPR-6/7 experiments where UNIC predictions of ZPR foil activation were made against experimentally measured values.The SN2ND solver was applied to a plate-by-plate model of ZPR-6/6A using 294,912 cores of BlueGene/P and 222,912 cores of XT5, the two largest open-science high performance computing machines. The calculations proved that the SN2ND solver could be applied to heterogeneous reactor modeling problems, but more solver development (e.g., multigrid preconditioner) and computing power are required before such calculations are routine. As a consequence, the SN2ND solver was revised to incorporate a new multigrid preconditioner concept in addition to removing the remaining inappropriate spherical harmonics related quantities left over from its beginning (i.e. PN2ND). At the time of this report, the new version of SN2ND has not been completed, and the follow on work for SN2ND will continue to focus on updating the preconditioner as outlined in this report.The MOCFE solver was rebuilt into UNIC in the previous year such that it obeyed the basic concepts of parallelism (scalable memory and communication). The MOCFE parallel algorithm was fully debugged this year and initial scalability tests on over 2048 processors were carried out such that the parallel algorithm could be assessed. That work indicated that a significant load imbalance in the coefficient matrix-vector application exists. A possible solution was formulated, but it has not been fully tested at the time of this report. Various setbacks caused by numerous ray tracing problems and a mistake in the implementation were unanticipated thus delaying progress on the MOCFE solver and the targeted development tasks for MOCFE were not completed this year.In addition to the high fidelity solvers SN2ND and MOCFE, some time was spent implementing the NODAL solver. NODAL is similar to an existing legacy tool, but employs parallelism for enhanced performance and a capability to map a heterogeneous geometry into the homogenized geometry. This solver would provide a path to improve upon the existing homogenization approaches used for fuel cycle analysis, transient analysis, and perturbation theory calculations. An appropriate preconditioner was identified for NODAL this year and the solver algorithm was partially completed in UNIC. To facilitate the validation tests of UNIC using the ZPR-6 critical experiments, the BuildZPRmodel tool was also updated and a mesh merging algorithm was created. In addition to the newly implemented "solution along a line" analysis capability, these tools proved crucial t...

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Proton-rich material in a state of nuclear statistical equilibrium (NSE) is one of the least studied regimes of nucleosynthesis. One reason for this is that after hydrogen burning, stellar evolution proceeds at conditions of equal number of neutrons and protons or at a slight degree of neutron richness. Proton-rich nucleosynthesis in stars tends to occur only when hydrogen-rich material that accretes onto a white dwarf of neutron star explodes, or when neutrino interactions in the winds from a nascent proto-neutron star or collapsar-disk drive the matter proton rich prior to or during the nucleosynthesis. In this paper we solve the NSE equations for a range of proton-rich thermodynamic conditions. We show that cold proton-rich NSE is qualitatively different from neutron-rich NSE. Instead of being dominated by the iron-peak nuclei with the largest binding energy per nucleon that have a proton to nucleon ratio close to the prescribed electron fraction, NSE for proton-rich material near freeze-out temperature is mainly composed of 56 Ni and free protons. Previous results of nuclear reaction network calculations rely on this non-intuitive fact, which this paper will explain. We show how the differences and especially the large fraction of free protons arises as a direct result from the minimization of the Helmholtz free energy.10th Symposium on Nuclei in the Cosmos