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The study investigated the role of excitation in energy harvesting applications. While the energy ultimately comes from the excitation, it was shown that the excitation may not always behave as a source. When the device characteristics do not perfectly match the excitation, the excitation alternately behaves as a source and a sink. The extent to which the excitation behaves as a sink determines the energy harvesting efficiency. Such contradictory roles were shown to be dictated by a generalized phase defined as the instantaneous phase angle between the velocity of the device and the excitation. An inductive prototype device with a diamagnetically levitated seismic mass was proposed to take advantage of the well established phase changing mechanism of vibro-impact to achieve a broader device bandwidth. Results suggest that the vibro-impact can generate an instantaneous, significant phase shift in response velocity that switches the role of the excitation. If introduced properly outside the resonance zone it could dramatically increase the energy harvesting efficiency.

Phospholipids self-assembled into reverse micelles in benzene are introduced as a new model system to study elementary processes relevant for energy transport in hydrated biological membranes. Femtosecond vibrational spectroscopy gives insight into the dynamics of the antisymmetric phosphate stretching vibration ν(AS)(PO(2))(-), a sensitive probe of local phosphate-water interactions and energy transport. The decay of the ν(AS)(PO(2))(-) mode with a 300-fs lifetime transfers excess energy to a subgroup of phospholipid low-frequency modes, followed by redistribution among phospholipid vibrations within a few picoseconds. The latter relaxation is accelerated by adding a confined water pool, an efficient heat sink in which the excess energy induces weakening or breaking of water-water and water-phospholipid hydrogen bonds. In parallel to vibrational relaxation, resonant energy transfer between ν(AS)(PO(2))(-) oscillators delocalizes the initial excitation.

The theory of two seemingly different quantum/classical approaches to collisional energy transfer and ro-vibrational energy flow is reviewed: a heuristic fluid-rotor method, introduced earlier to treat recombination reactions [M. Ivanov and D. Babikov, J. Chem. Phys. 134, 144107 (2011)10.1063/1.3576103], and a more rigorous method based on the Ehrenfest theorem. It is shown analytically that for the case of a diatomic molecule + quencher these two methods are entirely equivalent. Notably, they both make use of the average moment of inertia computed as inverse of average of inverse of the distributed moment of inertia. Despite this equivalence, each of the two formulations has its own advantages, and is interesting on its own. Numerical results presented here illustrate energy and momentum conservation in the mixed quantum/classical approach and open opportunities for computationally affordable treatment of collisional energy transfer.

The automotive and aerospace industries increasingly use lightweight materials to improve performance while reducing fuel consumption. Lightweight materials are frequently used in electric vehicles (EVs). However, using these materials can increase airborne and structure-borne noise. Furthermore, EV noise occurs at high frequencies, and conventional materials have small damping. Thus, there is an increasing need for procedures that help design new materials and coatings to reduce the transferred and radiated noise at desired frequencies. This study pioneered new techniques for microstructure modeling of coated and uncoated materials with improved noise, vibration, and harshness (NVH) performance. This work uses the microstructure of materials to study their vibration-damping capacity. Images from an environmental scanning electron microscope (ESEM) show the microstructure of a sample polymer and its coating. Tensile tests and experimental modal analysis were used to obtain the material properties of the polymer for microstructure modeling. The current work investigates how different microstructure parameters, such as fiberglass volume fraction and orientation, can change the vibration performance of materials. The damping ratio in the study was found to be affected by changes in both the direction and volume ratio of fiberglass. Furthermore, the effects of the coating are investigated in this work. Through modal analysis, it was observed that increasing the thickness of aluminum and aluminum bronze coatings caused a rightward shift in resonance frequency. Coatings with a thickness of 2 mm were found to perform better than those with lower thicknesses. Furthermore, the aluminum coating resulted in a greater shift in frequency than the aluminum bronze coating. Additionally, the coating with a higher damping ratio (i.e., aluminum bronze) significantly reduced the amplitude of surface velocity due to excitation, particularly at higher frequencies. This study provides engineers with an understanding of the effects of layer coating on the NVH performance of components and a modeling approach that can be used to design vehicles with enhanced noise and vibration performance.

Significance Photosynthetic light-harvesting antennae transfer energy toward reaction centers with high efficiency, but in high light or oxidative environments, the antennae divert energy to protect the photosynthetic apparatus. For a decade, quantum effects driven by vibronic coupling, where electronic and vibrational states couple, have been suggested to explain the energy transfer efficiency, but questions remain whether quantum effects are merely consequences of molecular systems. Here, we show evidence that biology tunes interpigment vibronic coupling, indicating that the quantum mechanism is operative in the efficient transfer regime and exploited by evolution for photoprotection. Specifically, the Fenna–Matthews–Olson complex uses redox-active cysteine residues to tune the resonance between its excitons and a pigment vibration to steer excess excitation toward a quenching site.

Recent ultrafast optical experiments show that excitons in large biological light-harvesting complexes are coupled to molecular vibration modes. These high-frequency vibrations will not only affect the optical response, but also drive the exciton transport. Here, using a model dimer system, the frequency of the underdamped vibration is shown to have a strong effect on the exciton dynamics such that quantum coherent oscillations in the system can be present even in the case of strong noise. Two mechanisms are identified to be responsible for the enhanced transport efficiency: critical damping due to the tunable effective strength of the coupling to the bath, and resonance coupling where the vibrational frequency coincides with the energy gap in the system. The interplay of these two mechanisms determines parameters responsible for the most efficient transport, and these optimal control parameters are comparable to those in realistic light-harvesting complexes. Interestingly, oscillations in the excitonic coherence at resonance are suppressed in comparison to the case of an off-resonant vibration.

Here we extend a recently introduced state-to-state kinetic model describing single- and multi-quantum vibrational excitation of molecular beams of NO scattering from a Au(111) metal surface. We derive an analytical expression for the rate of electronically non-adiabatic vibrational energy transfer, which is then employed in the analysis of the temperature dependence of the kinetics of direct overtone and two-step sequential energy transfer mechanisms. We show that the Arrhenius surface temperature dependence for vibrational excitation probability reported in many previous studies emerges as a low temperature limit of a more general solution that describes the approach to thermal equilibrium in the limit of infinite interaction time and that the pre-exponential term of the Arrhenius expression can be used not only to distinguish between the direct overtone and sequential mechanisms, but also to deduce their relative contributions. We also apply the analytical expression for the vibrational energy transfer rates introduced in this work to the full kinetic model and obtain an excellent fit to experimental data, the results of which show how to extract numerical values of the molecule-surface coupling strength and its fundamental properties.

Triboelectric-nano-generator (TENG) is able to produce a very small current and a large voltage compared to piezoelectric or electromagnetic generators. The large voltages from the TENGs are suitable for operating MEMS devices without external AC or DC generators. Producing micro-sized TENG using MEMS fabrication process enables integration of them with MEMS sensors and actuators. This combination is useful because the required voltage for driving MEMS is obtained from the motion of the event that is being measured. In this work, an event-driven vibration sensor is introduced which actuates a switch as the frequency or amplitude of the vibration exceeds a desired threshold. Using CMOS micromachining, a 1.5 mm × 1.5 mm TENG in contact-separation (CS) mode is fabricated to convert ambient vibrations to a voltage generated between a conductive aluminum layer and a dielectric Polyimide layer. The large generated voltage between the electrodes can operate a low-frequency electrostatic MEMS switch. Two events are able to produce the resonant dynamic pull-in needed to close the switch. Event one is when the input amplitude exceeds the dynamic pull-in threshold which is called acceleration sensitive mode. Event two is when the frequency of the vibration exceeds a specified threshold. An electromechanical model for the MEMS switch part of the vibration sensor is also presented. Results show that MEMS-TENG is able to supply the MEMS switch in the frequency sensitive and acceleration sensitive modes with a good signal-to-noise-ratio, sensitivity, and accuracy.