Frequency stabilization and noise-induced spectral narrowing in resonators with zero dispersion

Nonlinearity-Induced Asymmetric Synchronization Region in Micromechanical Oscillators

Synchronization in microstructures is a widely explored domain due to its diverse dynamic traits and promising practical applications. Within synchronization analysis, the synchronization bandwidth serves as a pivotal metric. While current research predominantly focuses on symmetric evaluations of synchronization bandwidth, the investigation into potential asymmetries within nonlinear oscillators remains unexplored, carrying implications for sensor application performance. This paper conducts a comprehensive exploration employing straight and arch beams capable of demonstrating linear, hardening, and softening characteristics to thoroughly scrutinize potential asymmetry within the synchronization region. Through the introduction of weak harmonic forces to induce synchronization within the oscillator, we observe distinct asymmetry within its synchronization range. Additionally, we present a robust theoretical model capable of fully capturing the linear, hardening, and softening traits of resonators synchronized to external perturbation. Further investigation into the effects of feedback strength and phase delay on synchronization region asymmetry, conducted through analytical and experimental approaches, reveals a consistent alignment between theoretical predictions and experimental outcomes. These findings hold promise in providing crucial technical insights to enhance resonator performance and broaden the application landscape of MEMS (Micro-Electro-Mechanical Systems) technology.

Sliding nanomechanical resonators

The motion of a vibrating object is determined by the way it is held. This simple observation has long inspired string instrument makers to create new sounds by devising elegant string clamping mechanisms, whereby the distance between the clamping points is modulated as the string vibrates. At the nanoscale, the simplest way to emulate this principle would be to controllably make nanoresonators slide across their clamping points, which would effectively modulate their vibrating length. Here, we report measurements of flexural vibrations in nanomechanical resonators that reveal such a sliding motion. Surprisingly, the resonant frequency of vibrations draws a loop as a tuning gate voltage is cycled. This behavior indicates that sliding is accompanied by a delayed frequency response of the resonators, making their dynamics richer than that of resonators with fixed clamping points. Our work elucidates the dynamics of nanomechanical resonators with unconventional boundary conditions, and offers opportunities for studying friction at the nanoscale from resonant frequency measurements.

The motion of a vibrating object is set by the way it is held. Here, the authors show a nanomechanical resonator reversibly slides on its supporting substrate as it vibrates and exploit this unconventional dynamics to quantify friction at the nanoscale.

Bifurcation Analysis on the Periodic Response of a Comb Drive MEMS Resonator

In this paper, we investigate the bifurcation characteristics of a comb drive MEMS resonator. The method of averaging and the residue theorem are used to get a more accurate analytical solution for the periodic response. Then, the singularity theory is employed to give the transition sets on the DC-AC voltage plane and the lateral separation-quality factor plane, which divide the planes into 9 persist regions. The corresponding bifurcation diagrams are present to discuss the jump phenomena of the periodic response, and the influences of the parameters on the amplitude-frequency response are studied. We also attempt to analyze the feasibility for the resonators working in the nonlinear regions and give the available frequency range and the available maximum amplitude of the nonlinear response. With the increase of the DC voltage, the amplitude-frequency curves change from hardening to softening, and the lateral separation has the opposite effect. The amplitude-frequency curves increase along the backbone curves with the AC voltage and quality factor. The response curves of softening or hardening characteristics have enough available frequency range and large available amplitudes, which may be more appropriate for the operation of the resonator than those of the mixture characteristics.

Intelligent photothermal dendritic cells restart the cancer immunity cycle through enhanced immunogenic cell death

Dendritic cells (DCs) play a pivotal role in initiating antigen-specific tumor immunity. However, the abnormal function of DCs owing to the immunosuppressive tumor microenvironment (TME) and the insufficient number of tumor infiltrating DCs could promote immune tolerance and tumor immune escape. Thus, there is great potential to employ DCs to induce efficient antitumor immunity. In this paper, we developed intelligent DCs (iDCs), which consist of nanoparticles loaded with photothermal agents (IR-797) and coated with a mature DC membrane. The DC cell membrane on the surface of iDCs preserves the ability to present antigens and prime T cells. The iDCs can also enter the lymph node and stimulate T cells. The activated T cells reduced the expression of heat shock proteins (HSPs) in tumor cells, rendering them more sensitive to heat stress. Subsequently, we used mild photothermal therapy (42-45 °C) to induce immunogenic cell death and contribute to a synergistic antitumor effect. iDCs as a refined and precise system in combination with DC-based immunotherapy and thermal therapy can be stored long-term and on a large scale, so they can be applied in many patients.

Using the transient trajectories of an optically levitated nanoparticle to characterize a stochastic Duffing oscillator

We propose a novel methodology to estimate parameters characterizing a weakly nonlinear Duffing oscillator represented by an optically levitating nanoparticle. The method is based on averaging recorded trajectories with defined initial positions in the phase space of nanoparticle position and momentum and allows us to study the transient dynamics of the nonlinear system. This technique provides us with the parameters of a levitated nanoparticle such as eigenfrequency, damping, coefficient of nonlinearity and effective temperature directly from the recorded transient particle motion without any need for external driving or modification of an experimental system. Comparison of this innovative approach with a commonly used method based on fitting the power spectrum density profile shows that the proposed complementary method is applicable even at lower pressures where the nonlinearity starts to play a significant role and thus the power spectrum density method predicts steady state parameters. The technique is applicable also at low temperatures and extendable to recent quantum experiments. The proposed method is applied on experimental data and its validity for one-dimensional and three-dimensional motion of a levitated nanoparticle is verified by extensive numerical simulations.