Isochoric, isobaric and ultrafast conductivities of aluminum, lithium and carbon in the warm dense matter (WDM) regime

We study the conductivities $\sigma$ of (i) the equilibrium isochoric state ($\sigma_{\rm is}$), (ii) the equilibrium isobaric state ($\sigma_{\rm ib}$), and also the (iii) non-equilibrium ultrafast matter (UFM) state ($\sigma_{\rm uf}$) with the ion temperature $T_i$ less than the the electron temperature $T_e$. Aluminum, lithium and carbon are considered, being increasingly complex warm dense matter (WDM) systems, with carbon having transient covalent bonds. First-principles calculations, i.e., neutral-pseudoatom (NPA) calculations and density-functional theory (DFT) with molecular-dynamics (MD) simulations, are compared where possible with experimental data to characterize $\sigma_{\rm ic}, \sigma_{\rm ib}$ and $\sigma_{\rm uf}$. The NPA $\sigma_{\rm ib}$ are closest to the available experimental data when compared to results from DFT+MD, where simulations of about 64-125 atoms are typically used. The published conductivities for Li are reviewed and the value at a temperature of 4.5 eV is examined using supporting X-ray Thomson scattering calculations. A physical picture of the variations of $\sigma$ with temperature and density applicable to these materials is given. The insensitivity of $\sigma$ to $T_e$ below 10 eV for carbon, compared to Al and Li, is clarified.Comment: 10 figure

Two-temperature pair potentials and phonon spectra for simple metals in the warm dense matter regime

We develop ion-ion pair potentials for Al, Na and K for densities and temperatures relevant to the warm-dense-matter (WDM) regime. Furthermore, we emphasize non-equilibrium states where the ion temperature $T_i$ differs from the electron temperature $T_e$. This work focuses mainly on ultra-fast laser-metal interactions where the energy of the laser is almost exclusively transferred to the electron sub-system over femtosecond time scales. This results in a two-temperature system with $T_e>T_i$ and with the ions still at the initial room temperature $T_i=T_r$. First-principles calculations, such as density functional theory (DFT) or quantum Monte Carlo, are as yet not fully feasible for WDM conditions due to lack of finite-$T$ features, e.g. pseudopotentials, and extensive CPU time requirements. Simpler methods are needed to study these highly complex systems. We propose to use two-temperature pair potentials $U_{ii}(r, T_i,T_e)$ constructed from linear-response theory using the non-linear electron density $n(\mathbf{r})$ obtained from finite-$T$ DFT with a single ion immersed in the appropriate electron fluid. We compute equilibrium phonon spectra at $T_r$ which are found to be in very good agreement with experiments. This gives credibility to our non-equilibrium phonon dispersion relations which are important in determining thermophysical properties, stability, energy-relaxation mechanisms and transport coefficients.Comment: International Conf. on Strongly-Coupled Coulombo Systems (SCCS) 201

Ion-ion dynamic structure factor, acoustic modes and equation of state of two-temperature warm dense aluminum

The ion-ion dynamical structure factor and the equation of state of warm dense aluminum in a two-temperature quasi-equilibrium state, with the electron temperature higher than the ion temperature, are investigated using molecular-dynamics simulations based on ion-ion pair potentials constructed from a neutral pseudoatom model. Such pair potentials based on density functional theory are parameter-free and depend directly on the electron temperature and indirectly on the ion temperature, enabling efficient computation of two-temperature properties. Comparison with ab initio simulations and with other average-atom calculations for equilibrium aluminum shows good agreement, justifying a study of quasi-equilibrium situations. Analyzing the van Hove function, we find that ion-ion correlations vanish in a time significantly smaller than the electron-ion relaxation time so that dynamical properties have a physical meaning for the quasi-equilibrium state. A significant increase in the speed of sound is predicted from the modification of the dispersion relation of the ion acoustic mode as the electron temperature is increased. The two-temperature equation of state including the free energy, internal energy and pressure is also presented

Effect of food composition on egg production and hatching success rate of two copepod species (<i>Calanoides carinatus</i> and <i>Rhincalanus nasutus</i>) in the Benguela upwelling system

We have analysed the daily egg production (EPR) and hatching success rates of the calanoid copepods Calanoides carinatus and Rhincalanus nasutus as a function of nano- and microplankton concentration and composition in the northern Benguela upwelling system off Namibia. Food concentration explained 55% (R. nasutus) to 62% (C. carinatus) of the EPR variability. We found no relation between the residuals of the food concentration–EPR regression and the percentage of the different taxonomic components of the nano- and microplankton. Nor was there a relation with the proportion of the diatom Skeletonema costatum that dominated the major blooms or with the number of nano- and microplankton species. We conclude that food quality differences could not be attributed to the relative composition of microplanktonic particles of the different groups (i.e. taxonomic composition)

Temporary Memory Neuron for the Leaky Integrate and Fire Neuron Model

Low-level terrain-following systems require the ability to rapidly and accurately respond to the environment to prevent inadvertent actions. Catastrophic and fatal results could occur if missed cues or latency issues in data processing are encountered. Spiking neural networks (SNNs) have the computational ability to continuously process spike trains from rapid sensory input. However, most models of SNNs do not retain information from the spike train of a previous time step because the membrane potential is rapidly reset to a resting potential after activation. A novel approach is presented, allowing the spike train of a previous time step to be \u27remembered.\u27 Results are presented showing rapid onset of a membrane potential that exceeds the threshold and spikes in the presence of the same continuous spike train without the latency of increasing the membrane potential from its resting state

Perceptual and Adaptation Implications with Display 3-D Spatial Location: Retrofit of HUD on a Tactical Airlift Platform

The retrofitting of a cockpit with a Head-Up-Display (HUD) raises potential accommodation and perceptual issues for pilots that must be addressed. For maximum optical efficiency, the goal is to be able to place every pilot’s eye into the HUD Eye Motion Box (EMB) given a seat adjustment range. Initially, the Eye Reference Point (ERP) of the EMB should theoretically be located on the aircraft’s original cockpit Design Eye Point (DEP) while horizontal and vertical seat adjustment would allow pilots to position their eyes inside the EMB. However, human postures vary, and HUD systems may not be optimally placed. In reality there is a distribution of pilot eyes around the DEP (which is dominant eye dependent) therefore this must be accounted for in order to obtain appropriate visibility of all of the symbology based on photonic characteristics of the HUD. Pilot size and postural variation need to be taken into consideration when positioning the HUD system to ensure proper vision of all HUD symbology in addition to meeting the basic physical accommodation requirements of the cockpit. The innovative process and data collection methods for maximizing accommodation and pilot perception on a new “tactical airlift” platform are discussed as well as the related neurocognitive factors and the effects of information display design on cognitive phenomena