Study of Flow and Heat Transfer Characteristics of Lead-Based Liquid Metals in a Turbulent Tube Flow and the Impacts of Roughness

Lead-based liquid metals (LLMs) such as lead–bismuth eutectic (LBE) and lead, are currently the most interesting candidate coolants for fast reactors because of their excellent physical properties, which can improve safety and reduce costs. However, in comparison to other liquid metals, previous research on the flow and heat-transfer characteristics of LLMs has been limited. Therefore, this work carried out flow and heat-transfer experiments in LBE flowing through a circular tube in the Natural Circulation Capability Loop (NCCL) facility. The results show a significantly higher friction factor than that of water flowing in a smooth pipe. Furthermore, the Nusselt numbers were found to be lower than those found in data in the literature for experiments carried out in a smooth tube at low Péclet numbers, while they were higher at high Péclet numbers. Therefore, theoretical analyses were performed for LLMs flowing in both smooth and rough pipes, and the impacts of roughness on the heat transfer of an LLM were examined. The theoretical relations for a smooth pipe and a rough pipe were validated using experimental data from the literature and the results of the NCCL experiments, respectively. The results of the theoretical relation for a smooth pipe fitted the literature data well. The derived theoretical relation for a rough pipe with a relative roughness of 0.004 fitted the NCCL data best. Moreover, it was established from the theoretical analysis that roughness has two competitive impacts on the heat transfer of an LLM: it reduces conductive heat transfer while enhancing convective heat transfer. Because conductive heat transfer is important for liquid metals, even with turbulent flow, a small roughness will lead to heat-transfer deterioration at low Péclet numbers, and it may even deteriorate across the whole typical Péclet-number range. This discovery has important implications for the thermal–hydraulic design of LLM reactors, because corrosion and erosion by an LLM will lead to a rough surface after long operating times.

Nanoscale Correlations of Ice Adhesion Strength and Water Contact Angle

Surfaces with low ice adhesion represent a promising strategy to achieve passive anti-icing performance. However, as a successful and robust low ice adhesion surface must be tested under realistic conditions at low temperatures and for several types of ice, the initial screening of potential low ice adhesion surfaces requires large resources. A theoretical relation between ice adhesion and water wettability in the form of water contact angle exists, but there is disagreement on whether this relation holds for experiments. In this study, we utilised molecular dynamics simulations to examine the fundamental relations between ice adhesion and water contact angle on an ideal graphene surface. The results show a significant correlation according to the theoretic predictions, indicating that the theoretical relation holds for the ice and water when discarding surface material deformations and other experimental factors. The reproduction of the thermodynamic theory at the nanoscale is important due to the gap between experimental observations and theoretical models. The results in this study represent a step forward towards understanding the fundamental mechanisms of water–solid and ice–solid interactions, and the relationship between them.

Theoretical relation between axon initial segment geometry and excitability

In most vertebrate neurons, action potentials are triggered at the distal end of the axon initial segment (AIS). Both position and length of the AIS vary across and within neuron types, with activity, development and pathology. What is the impact of AIS geometry on excitability? Direct empirical assessment has proven difficult because of the many potential confounding factors. Here, we carried a principled theoretical analysis to answer this question. We provide a simple formula relating AIS geometry and sodium conductance density to the somatic voltage threshold. A distal shift of the AIS normally produces a (modest) increase in excitability, but we explain how this pattern can reverse if a hyperpolarizing current is present at the AIS, due to resistive coupling with the soma. This work provides a theoretical tool to assess the significance of structural AIS plasticity for electrical function.

Theoretical relation between axon initial segment geometry and excitability

In most vertebrate neurons, action potentials are triggered at the distal end of the axon initial segment (AIS). Both position and length of the AIS vary across and within neuron types, with activity, development and pathology. What is the impact of AIS geometry on excitability? Direct empirical assessment has proven difficult because of the many potential confounding factors. Here we carried a principled theoretical analysis to answer this question. We provide a simple formula relating AIS geometry and sodium conductance density to the somatic voltage threshold. A distal shift of the AIS normally produces a (modest) increase in excitability, but we explain how this pattern can reverse if a hyperpolarizing current is present at the AIS, due to resistive coupling with the soma. This work provides a theoretical tool to assess the significance of structural AIS plasticity for electrical function.

Collapsing stellar filament and exotic matter in Palatini f(R) gravity

We explore the dynamics of collapsing stellar filament in the presence of exotic material like dark matter. We use Palatini f(R) theory to include exotic substance in the collapsing process. We derive a collapse equation by applying Darmois junction conditions on collapsing surface boundary $$\Sigma $$Σ. It is found that the radial pressure related to baryonic matter remains non-zero at $$\Sigma $$Σ. We then discuss the stability criteria of the collapsing process in the framework of three parameteric model, $$f(R)=R+\lambda R_{c}[ 1-(1+\frac{R^{2}}{R^{2}_{c}})^{-n}]$$f(R)=R+λRc[1-(1+R2Rc2)-n]. It is concluded that the stability of collapsing filament depends upon a directly proportional relation of gravitational effects of exotic terms with the radial pressure of seen matter. Stability criteria of family of polytropic filamentary structures are also discussed. For all stable polytropic filaments, it is found that the density of seen material is exponentially related to the exotic forces. Finally, we explore theoretical relation between gravitational waves and dark terms. It is theoretically predicted that the presence of exotic material can affect the propagation of gravitational waves.

About negative globalisation – Zygmunt Bauman

The value theoretical relation to globalisation is diametrically opposite- positive or negative. Neoliberal globalisation apologists seek tohighlight its positive characteristics, while its critics point to a wholeseries of negative characteristics. This other theoretical orientationbelongs to Zygmunt Bauman. His attitude towards globalisation ishighly negative: in itself, globalisation carries a number of negativerisks, of which the most difficult is the one that leads to the possibleself-destruction of humanity. Therefore, he decisively stated that if wedo not develop the perception of planetary responsibility and the abilityto foresee the future, cataclysm is quite certain and real.