Immune cells use active tugging forces to distinguish affinity and accelerate evolution

Cells are known to exert forces to sense their physical surroundings for guidance of motion and fate decisions. Here, we propose that cells might do mechanical work to drive their own evolution, taking inspiration from the adaptive immune system. Growing evidence indicates that immune B cells - capable of rapid Darwinian evolution - use cytoskeletal forces to actively extract antigen from other cells' surface. To elucidate the evolutionary significance of force usage, we develop a theory of tug-of-war antigen extraction that maps receptor binding characteristics to clonal reproductive fitness, revealing physical determinants of selection strength. This framework unifies mechanosensing and affinity-discrimination capabilities of evolving cells: pulling against stiff antigen tethers enhances discrimination stringency at the expense of absolute extraction. As a consequence, active force usage can accelerate adaptation but may also cause extinction of cell populations, resulting in an optimal range of pulling strength that matches molecular rupture forces observed in cells. Our work suggests that nonequilibrium, physical extraction of environmental signals can make biological systems more evolvable at a moderate energy cost.Comment: 14 pages, 6 figure

Parametric optimization and heat transfer analysis of a dual loop ORC (organic Rankine cycle) system for CNG engine waste heat recovery

In this study, a dual loop ORC (organic Rankine cycle) system is adopted to recover exhaust energy, waste heat from the coolant system, and intercooler heat rejection of a six-cylinder CNG (compressed natural gas) engine. The thermodynamic, heat transfer, and optimization models for the dual loop ORC system are established. On the basis of the waste heat characteristics of the CNG engine over the whole operating range, a GA (genetic algorithm) is used to solve the Pareto solution for the thermodynamic and heat transfer performances to maximize net power output and minimize heat transfer area. Combined with optimization results, the optimal parameter regions of the dual loop ORC system are determined under various operating conditions. Then, the variation in the heat transfer area with the operating conditions of the CNG engine is analyzed. The results show that the optimal evaporation pressure and superheat degree of the HT (high temperature) cycle are mainly influenced by the operating conditions of the CNG engine. The optimal evaporation pressure and superheat degree of the HT cycle over the whole operating range are within 2.5–2.9 MPa and 0.43–12.35 K, respectively. The optimal condensation temperature of the HT cycle, evaporation and condensation temperatures of the LT (low temperature) cycle, and exhaust temperature at the outlet of evaporator 1 are kept nearly constant under various operating conditions of the CNG engine. The thermal efficiency of the dual loop ORC system is within the range of 8.79%–10.17%. The dual loop ORC system achieves the maximum net power output of 23.62 kW under the engine rated condition. In addition, the operating conditions of the CNG engine and the operating parameters of the dual loop ORC system significantly influence the heat transfer areas for each heat exchanger

Ambient Noise Tomography and Earth Structure Inversions with Amphibious Seismic Arrays

We have seen great progress of ambient seismic noise tomography in the last two decades, and a large number of ambient noise tomography studies have been conducted on different continents worldwide. The availability of ocean bottom seismometers (OBSs) and developments in data processing techniques have made OBS ambient noise study more and more promising. In this thesis, we combine land seismic stations and OBSs to derive amphibious surface wave tomography measurements. We apply Bayesian Monte-Carlo inver- sions to infer shear wave structures during different stages of the life cycle of oceanic plates. We produce shear wave inversion results and infer how Earth structure changes during the creation, evolution and destruction of oceanic plates. In the first part of this thesis, I use an amphibious seismic array near the Hikurangi margin at North Island, New Zealand to calculate ambient noise cross correlations. By analyzing Rayleigh wave signal drift in cross correlation functions, clock error in one of the OBSs is identified and corrected. Rayleigh wave group and phase speed tomographic measurements are made at 4 to 14 s periods using a fast marching tomographic method which accounts for the off great circle propagation of surface wave signals across the coast. 1D shear wave velocities inversions for continental, coastal and oceanic locations are applied to study the sediment and crust structures at these locations. In the second part of this thesis, I apply ambient noise Rayleigh wave tomography to an amphibious array at northwest U.S. Rayleigh wave phase speed measurements made with traditional two-station ambient noise analysis is compared to and combined with three-station ambient noise interferometry and earthquake tomography to construct a Rayleigh wave phase dispersion measurement dataset at periods of 10 to 80 s. In the third part of this thesis, I apply Bayesian Monte-Carlo inversions to the composite Rayleigh wave phase speed dispersion dataset over the Juan de Fuca (JdF) and Gorda plates. A 3D shear wave velocity model for the JdF and Gorda plates is constructed and we observe the thickening of oceanic lithosphere and deepening of low velocity zones in oceanic mantle as we move away from the mid ocean ridge.</p