Local stability analysis of a low-dissipation cyclic refrigerator

We study the local stability near the maximum figure of merit for the low-dissipation cyclic refrigerator, where the irreversible dissipation occurs not only in the thermal contacts but also the adiabatic strokes. We find that the bounds of the coefficient of performance at maximum figure of merit or maximum cooling rate in presence of internal dissipation are identical to corresponding those in absence of internal dissipation. Using two different scenarios, we prove the existence of a single stable steady state for the refrigerator, and clarify the role of internal dissipation on the stability of thermodynamic steady state, showing that the speed of system evolution to the steady state decreases due to internal dissipation.

Spectral index-flux relation for investigating the origins of steep decay in γ-ray bursts

Abstractγ-ray bursts (GRBs) are short-lived transients releasing a large amount of energy (1051 − 1053 erg) in the keV-MeV energy range. GRBs are thought to originate from internal dissipation of the energy carried by ultra-relativistic jets launched by the remnant of a massive star’s death or a compact binary coalescence. While thousands of GRBs have been observed over the last thirty years, we still have an incomplete understanding of where and how the radiation is generated in the jet. Here we show a relation between the spectral index and the flux found by investigating the X-ray tails of bright GRB pulses via time-resolved spectral analysis. This relation is incompatible with the long standing scenario which invokes the delayed arrival of photons from high-latitude parts of the jet. While the alternative scenarios cannot be firmly excluded, the adiabatic cooling of the emitting particles is the most plausible explanation for the discovered relation, suggesting a proton-synchrotron origin of the GRB emission.

Flagellar energetics from high-resolution imaging of beating patterns in tethered mouse sperm

We demonstrate a technique for investigating the energetics of flagella or cilia. We record the planar beating of tethered mouse sperm at high-resolution. Beating waveforms are reconstructed using Proper Orthogonal Decomposition of the centerline tangent-angle profiles. Energy conservation is employed to obtain the mechanical power exerted by the dynein motors from the observed kinematics. A large proportion of the mechanical power exerted by the dynein motors is dissipated internally by the motors themselves. There could also be significant dissipation within the passive structures of the flagellum. The total internal dissipation is considerably greater than the hydrodynamic dissipation in the aqueous medium outside. The net power input from the dynein motors in sperm from Crisp2-knockout mice is significantly smaller than in wildtype samples, indicating that ion-channel regulation by cysteine-rich secretory proteins (CRISPs) controls energy flows powering the axoneme.

Unveiling the origin of steep decay in γ-ray bursts

γ-ray bursts (GRBs) are short-lived transients releasing a large amount of energy (10^51-10^53 erg) in the keV-MeV energy range. GRBs are thought to originate from internal dissipation of the energy carried by ultra-relativistic jets launched by the remnant of a massive star’s death or a compact binary coalescence. While thousands of GRBs have been observed over the last thirty years, we still have an incomplete understanding of where and how the radiation is generated in the jet. A novel investigation of the GRB emission mechanism, via time-resolved spectral analysis of the X-ray tails of bright GRB pulses, enables us to discover a unique relation between the spectral index and the flux. This relation is incompatible with the long standing scenario invoked to interpret X-ray tails, that is, the delayed arrival of pho-tons from high-latitude parts of the jet. We show that our results provide for the first time evidence of adiabatic cooling and efficient energy exchange between the emitting particles in the relativistic outflows of GRBs.

Flagellar energetics from high-resolution imaging of beating patterns in tethered mouse sperm

While much is known about the microstructure of sperm flagella, the mechanisms behind the generation of flagellar beating patterns by the axoneme are still not fully understood. We demonstrate a technique for investigating the energetics of flagella or cilia. We record the planar beating of tethered wildtype and Crisp2-knockout mouse sperm at high-speed and high-resolution and extract centerlines using digital image processing techniques. We accurately reconstruct beating waveforms using a Chebyshev-polynomial based Proper Orthogonal Decomposition of the centerline tangent-angle profiles. External hydrodynamic forces and the internal resistance from the passive flagellar material are calculated from the observed kinematics of the beating patterns using a Soft, Internally-Driven Kirchhoff-Rod (SIDKR) model. Energy conservation is employed to further compute the flagellar energetics. We thus obtain the distribution of mechanical power exerted by the dynein motors without any further assumptions about mechanisms regulating axonemal function. We find that, in both the mouse genotypes studied, a large proportion of the mechanical power exerted by the dynein motors is dissipated internally, within the passive structures of the flagellum and by the motors themselves. This internal dissipation is considerably greater than the hydrodynamic dissipation in the aqueous medium outside. The net power input from the dynein motors in sperm from Crisp2-knockout mice is significantly smaller than in corresponding wildtype samples. The reduced power is correlated with slower beating and smaller amplitudes. These measurements of flagellar energetics indicate that the ion-channel regulating cysteine-rich secretory proteins (CRISPs) may also be involved in regulating mammalian sperm motility.

Temperature development of cardboard in contact with high-frequency vibrating metal surfaces

The heating of cardboard was studied when it is in contact with ultrasonic sonotrodes, whose vibrations were orientated parallel and perpendicular to the material surface. The parameters that were varied included the contact pressure on the sonotrode, vibration amplitude, and moisture content of the material. It was shown that there was a major decrease in the contact pressure shortly after the beginning of the experiment when the gap between the sonotrode and anvil was kept constant and thus a decrease in the temperature gradient of the material occurred. With parallel vibration, the material heated up from the sonotrode side, whereas heating started from the center of the material in the case of vertical vibration. This suggested that in cases of vertical vibration, heat is mostly generated by internal dissipation, and in cases of parallel vibration, heat is generated by friction losses on the surface. Furthermore, the results revealed the influence of the parameters on the initial temperature gradient, the maximum temperature, and the moisture content of the material.

Dynamics of Enzyme Action

This chapter discusses the deformability of enzymes. This property allows enzymes to couple a chemical process to a cycle of deformations of the molecule, which can perform a task in the cell. This is the celebrated “molecular machine” aspect of enzymes. The dynamics of enzyme deformability presents universal features when ensemble-averaged trajectories are examined. The mechanical response is viscoelastic. The remainder of the chapter covers the nonlinearity of the enzyme's mechanics, timescales, enzymatic cycle and viscoelasticity, internal dissipation, origin of the restoring force g, models based on chemical kinetics, different levels of microscopic description, connection to information flow, normal mode analysis, many states of the folded protein, and interesting topics in nonequilibrium thermodynamics relating to enzyme dynamics.