Force Sensitivity Research Articles

A Ring Core Fiber Sensor Based on Mach–Zehnder Interferometer for Transversal Force Sensing With Solvable Temperature Cross Sensitivity

In this work, we proposed a ring core fiber (RCF)-based all-fiber sensor used for transverse force sensing. The sensor is composed of 1-mm coreless fiber (CLF) and 2.5-cm RCF. Then, the coreless (CL)-ring core (RC) fiber structure is connected to two segments of single-mode fibers to form a Mach–Zehnder interferometer (MZI). The transmission spectrum of the MZI structure has a large extinction ratio (ER) of up to 20 dB with a free spectral range (FSR) of 9.3 nm. After the fabrication, the MZI sensor is packaged for force sensing at different temperatures. The different values of forces are applied on the fiber sensor, which are tuned from around 0.26 to 1.5 N/mm. With the increase of transverse force, the spectra of output signals show a linear redshift. The force sensitivity of the proposed MZI sensor reaches up to 4.109 nm/(N/mm) with a good linearity of 0.9824. By using a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times2$ </tex-math></inline-formula> matrix, the temperature cross sensitivity can be extracted. The proposed force sensor based on the MZI fiber structure shows great potential applications in the field of structural health monitoring and supercapacitor safety detection.

The effect of physiological and pharmacological inotropic interventionson the regulatory state of the thick filament in intact cardiac trabeculae.

In the cardiac muscle in diastole myosin motors are packed on the surface of the thick filament in three-stranded helical tracks, folded toward the centre of the sarcomere and unable to bind actin and hydrolyse ATP (OFF state; Woodhead et al. 2005, Nature 436:1195). In the X-ray diffraction pattern of intact trabeculae from rat heart this OFF state is marked by the intensity of the corresponding myosin-based layer lines and axial reflections (Reconditi et al. 2017, PNAS 114:3240). In trabeculae electrically paced at 0.5 Hz (temperature 27 °C), during diastole none of the X-ray signals related to the OFF state of the myosin motors are affected by inotropic interventions which increase by twofold the systolic peak force, like increase in sarcomere length (1.95-2.25 μm) or addition of 10−7 M isoprenaline, indicating that these inotropic interventions acts downstream with respect to Ca2+-activation (Caremani et al. 2019, J. Gen. Physiol. 151:53). Instead, the addition of the cardiac activator omecamtiv mecarbil (OM, 1 μM), a small molecule that binds to the catalytic domain of cardiac myosin and has been found to increase the systolic ejection fraction in animal models (Malik et al. 2011, Science 331:1439) and the Ca2+ sensitivity of force in demembranated cardiac myocytes (Nagy et al. 2015, Brit. J. Pharmacol. 172:4506), induces a partial switching ON of motors in diastole, mainly at the expense of the filament regions outside the central 1/3 containing the Myosin Binding Protein C. The specific effect that different inotropic interventions exert on the regulatory state of the thick filament in diastole reflects on the different mechanisms by which these interventions potentiate the systolic performance. Supported by ECR, University of Florence and MUR (Italy) and ESRF (France).

Sarcomere dynamics simulations to uncover mechanisms in hypertrophic cardiomyopathy.

Mutations in the beta myosin heavy chain (MYH7) can cause hypercontractility and cardiac remodeling in hypertrophic cardiomyopathy (HCM), but the mechanisms of specific mutations can be difficult to predict. Many mutations change intrinsic rates of myosin activity and their force sensitivity, which can dynamically alter chemo-mechanical cycle events and resultant force generation during cardiac contraction. Our team's multiscale approach enables measurement of the kinetics and force generation in purified myosin proteins, isolated myofibrils, and single and multicellular human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) platforms. Computational modeling can integrate results across these scales and provide additional insights into the individual and combinatorial effects of different changes in myosin kinetics. We have previously used a continuum model to highlight the significance of dysregulation of the super relaxed state of myosin driving hypercontractility in hiPSC-CMs with the P710R mutation. Sensitivity analysis also supported variable myofibril density and sarcomeric organization as a source of population heterogeneity in the force generating capacity of individual hiPSC-CMs. In our ongoing studies, we are leveraging computational modeling to compare the predicted and measured effects of HCM mutations in our different experiments. We have incorporated the measured changes in unloaded myosin to predict force generation after isometric maximal calcium activation (myofibril measurements) and twitch stimulation in single hiPSC-CMs on gels of physiologic stiffness. Additional simulations with spatially explicit models enable more direct prediction of the impact of heterogeneous mixtures of myosins with different molecular profiles and on cooperativity effects associated with the transmission of tension along the length of a sarcomere. Finally, we have visualized the strain profiles of individual sarcomeres in contracting myofibrils in live cells and are correlating these measurements to our simulations. These studies will give new insights into the key biophysical drivers of HCM.

Abnormal kinetics of contraction caused by an α-actinin 2 missense variant in the EF-3-4 hand domain in human myocardium.

ACTN2 gene encodes α-actinin 2 protein, which binds actin. In cardiac muscle, α-actinin 2 is located in the Z-disc of the sarcomere, where it anchors myofibrillar actin filaments. A 48-years old female presented with out-of-hospital ventricular fibrillation arrest. Echocardiogram showed stage II diastolic dysfunction, elevated RVSP, and abnormal global longitudinal strain consistent with early LV systolic dysfunction. Cardiopulmonary testing indicated AHA functional class IV HF. Genetic testing identified a missense heterozygous variant of unknown significance in ACTN2 (gene previously associated with HCM and DCM), and SCNB2 (β-2 subunit of type II voltage-gated sodium channel). Histopathology demonstrated mild interstitial fibrosis of the LV free wall. We investigated the effects of the heterozygous A868T variant in α-actinin 2 on cardiac muscle mechanics. LV free wall samples were obtained from the patient's explanted heart at the time of cardiac transplantation. Permeabilized cardiac muscle preparations (CMPs) containing A868T and WT proteins displayed increased myofilament Ca2+-sensitivity of isometric force and lower maximal isometric specific force when compared to human donor samples. Sinusoidal stiffness was decreased at all levels of Ca2+-activation in A8686T CMPs. The rate of tension redevelopment (kTR) was faster at all levels of Ca2+-activation in A8686T CMPs. Computational modeling suggests that faster kTR in A868T CMPs is mainly due to faster cross-bridge detachment (g). The kinetic changes are consistent with decreased force generation by A868T CMPs being due to abnormalities in the cross-bridge interaction. Molecular dynamics simulation did not find significant differences in the interaction of A868T variant with titin and α-actinin. This project establishes the importance of α-actinin 2 variant in the Z-disc mechanosensitive interaction of thin- and thick-filament distal from its structural role in the sarcomere.

Mechanics of divalent ion sensitivity of the manganese-sensing riboswitch measured by combined high-resolution optical tweezers and single-molecule fluorescence.

Riboswitches are structured non-coding RNA typically found in the 5′ untranslated regions of bacterial mRNAs. They modulate gene expression through the binding of specific ligands that induce changes in the riboswitch structure, most often at the level of transcription and translation. The Mn2+-sensing yybP-ykoY RNA motif is one of the most widespread riboswitches across bacteria, including human and plant pathogens. It contains two divalent metal ion binding sites: one is specific for Mn2+ whereas the other is nonspecific for a divalent metal ion, including Mg2+. Previous crystal structures have shown that Mn2+ binds in between the two distal helical legs of a four-way junction and induces a large “docking” conformational change. It is unclear how competition between Mn2+ and Mg2+ for the two binding sites and the associated RNA conformational changes give rise to Mn2+ detection function and sensitivity. Therefore, we explored the global structural dynamics of the L. lactis Mn2+-sensing riboswitch in the presence of competing divalent cations using high-resolution optical tweezers simultaneous with confocal Förster resonance energy transfer (FRET) spectroscopy. Initial non-equilibrium force ramp measurements revealed force-dependent docking distribution, suggesting a highly selective docked state at suboptimal Mn2+ ion concentration. Follow-up high-resolution equilibrium fixed-force measurements directly measured docking and undocking rate constants versus force to determine docking and undocking mechanics, including transition states and pathways, at varying Mn2+ vs Mg2+ concentrations. Simultaneous FRET measurements confirmed specific conformational transitions. Docking and undocking were symmetric processes with nearly equal force sensitivity and a transition state located nearly midway between the docked and undocked states. Mn2+ sensitivity appears to optimize at a concentration where further increasing Mn2+ competes with Mg2+ ions for the non-specific divalent metal ion binding site.

Sympathetic cooling and squeezing of two colevitated nanoparticles

Levitated particles are an ideal tool for measuring weak forces and investigating quantum mechanics in macroscopic objects. Arrays of two or more of these particles have been suggested for improving force sensitivity and entangling macroscopic objects. In this article, two charged, silica nanoparticles, that are coupled through their mutual Coulomb repulsion, are trapped in a Paul trap, and the individual masses and charges of both particles are characterized. We demonstrate sympathetic cooling of one nanoparticle coupled via the Coulomb interaction to the second nanoparticle to which feedback cooling is directly applied. We also implement sympathetic squeezing through a similar process showing nonthermal motional states can be transferred by the Coulomb interaction. This work establishes protocols to cool and manipulate arrays of nanoparticles for sensing and minimizing the effect of optical heating in future experiments.

RLC phosphorylation amplifies Ca2+ sensitivity of force in myocardium from cMyBP-C knockout mice.

Hypertrophic cardiomyopathy (HCM) is the leading genetic cause of heart disease. The heart comprises several proteins that work together to properly facilitate force production and pump blood throughout the body. Cardiac myosin binding protein-C (cMyBP-C) is a thick-filament protein, and mutations in cMyBP-C are frequently linked with clinical cases of HCM. Within the sarcomere, the N-terminus of cMyBP-C likely interacts with the myosin regulatory light chain (RLC); RLC is a subunit of myosin located within the myosin neck region that modulates contractile dynamics via its phosphorylation state. Phosphorylation of RLC is thought to influence myosin head position along the thick-filament backbone, making it more favorable to bind the thin filament of actin and facilitate force production. However, little is known about how these two proteins interact. We tested the effects of RLC phosphorylation on Ca2+-regulated contractility using biomechanical assays on skinned papillary muscle strips isolated from cMyBP-C KO mice and WT mice. RLC phosphorylation increased Ca2+ sensitivity of contraction (i.e., pCa50) from 5.80 ± 0.02 to 5.95 ± 0.03 in WT strips, whereas RLC phosphorylation increased Ca2+ sensitivity of contraction from 5.86 ± 0.02 to 6.15 ± 0.03 in cMyBP-C KO strips. These data suggest that the effects of RLC phosphorylation on Ca2+ sensitivity of contraction are amplified when cMyBP-C is absent from the sarcomere. This implies that cMyBP-C and RLC act in concert to regulate contractility in healthy hearts, and mutations to these proteins that lead to HCM (or a loss of phosphorylation with disease progression) may disrupt important interactions between these thick-filament regulatory proteins.

Parameter Sensitivity Analysis of the Seismic Response of a Piled Wharf Structure

To investigate the seismic response characteristics of piled wharf structures, a numerical model of the soil-structure interaction system is established. Extensive fiducial error and grey correlation analyses are also conducted to obtain the grey correlation degree sequence of the internal force of piled wharf structure and deformation, as well as the acceleration of surrounding soils. The results show that the peak acceleration at the typical point of the soil is more sensitive to the variations in friction angle and ground motion intensity, while the lateral extreme displacement is the most sensitive to the variations in the elastic modulus of the soil. The grey correlation sequences of the peak acceleration and lateral extreme displacement at the feature points of the soil around the pile greatly vary, indicating that the key factors of the different sequences control the target parameters corresponding to them. The sensitivity of the internal force of the pile foundation of the pier structure to the ground motion intensity and friction angle is more sensitive than the elastic modulus and cohesion. This presented parameter sensitivity analysis procedure for the seismic response of piled wharf structures can provide a reference for the seismic design of piled wharf structures, as well as for disaster prevention prediction.

Vessel Wake Impact Forces on Marsh Scarps

Priestas, A.M.; Styles, R., and Bain, R., 2023. Vessel wake impact forces on marsh scarps. Journal of Coastal Research, 39(2), 207–220. Charlotte (North Carolina), ISSN 0749-0208. A common morphological feature of high-energy coastal plain salt marshes is an erosive scarp separating the marsh platform from the abutting tidal flat. A noted deficiency in the understanding of scarp erosion is a lack of direct wave impact measurements to better constrain the physical processes driving material loss. To measure wave impact forces, load cells were embedded into a scarp face along the Intracoastal Waterway in northern Florida, which is frequented by shallow-draft vessels. The largest impact forces occurred when the mean water surface elevation was just below the midpoint of the scarp and decayed as the mean depth either increased or decreased. Early wave breaking around low tide reduced the direct impact on the scarp, whereas wave reflection around high tide reduced wave breaking and the associated maximum impact force. The sensitivity of impact force to tidal stage suggests that wave energetics (breaking vs. reflection) and scarp morphology (ramp vs. near-vertical surface) combine to produce a force pattern that favors maximum impact around midtide. Regression analysis indicated that the impact pressures were positively correlated with wave power and dynamic pressure, which are primary metrics used to model shoreline erosion. This study argues that the critical threshold for erosion may be refined by evaluating the relationship between impact pressures and marsh resistance, since wave exposure alone does not necessarily initiate erosion.

The Surgical Learning Curve: Does Robotic Technical Skill Explain Differences in Operative Performance?

Background: Prior studies on technical skills use small collections of videos for assessment. However, there is likely heterogeneity of performance among surgeons and likely improvement after training. If technical skill explains these differences, then it should vary among practicing surgeons and improve over time. Materials and Methods: Sleeve gastrectomy cases (n = 162) between July 2018 and January 2021 at one health system were included. Global evaluative assessment of robotic skills (GEARS) scores were assigned by crowdsourced evaluators. Videos were manually annotated. Analysis of variance was used to compare continuous variables between surgeons. Tamhane's post hoc test was used to define differences between surgeons with the eta-squared value for effect size. Linear regression was used for temporal changes. A P value <.05 was considered significant. Results: Variations in operative time discriminated between individuals (e.g., between 2 surgeons, means were 91 and 112 minutes, Tamhane's = 0.001). Overall, GEARS scores did not vary significantly (e.g., between those 2 surgeons, means were 20.32 and 20.6, Tamhane's = 0.151). Operative time and total GEARS score did not change over time (R2 = 0.0001-0.096). Subcomponent scores showed idiosyncratic temporal changes, although force sensitivity increased among all (R2 = 0.172-0.243). For a novice surgeon, phase-adjusted operative time (R2 = 0.24), but not overall GEARS scores (R2 = 0.04), improved over time. Conclusions: GEARS scores showed less variability and did not improve with time for a novice surgeon. Improved technical skill does not explain the learning curve of a novice surgeon or variation among surgeons. More work could define valid surrogate metrics for performance analysis.

Enhanced Piezoelectric Performance of Electrospun PVDF‐TrFE by Polydopamine‐Assisted Attachment of ZnO Nanowires for Impact Force Sensing

AbstractIn this work, piezoelectric PVDF‐TrFE electrospun fibers (EFs) were fabricated using a high‐throughput nozzle‐free electrospinning process. Zinc oxide (ZnO) nanoparticles were robustly anchored to the PVDF‐TrFE EFs, assisted by a self‐polymerized polydopamine (PDA) layer, and subsequently grown into ZnO nanowires (NWs) using a low‐temperature hydrothermal growth method. The EF mats were investigated for active impact force transduction and the piezoelectric voltage outputs of different combinations of PVDF‐TrFE and ZnO nanomaterials were compared using two different impact force testing setups. The horizontal impact force test saw an increase in force sensitivity by a factor of 2.5 for the nanowires compared to the unmodified PVDF‐TrFE EFs. Similarly, vertical drop impact testing demonstrated a 5.8‐fold increase in sensitivity with a linear response (R2 = 0.986) for a large range of impact forces up to 970 N. The EFs were also tested as a wearable impact force sensor to quantify soccer ball heading force, which was measured as 291.3 ± 51.0 N for a vertical ball speed of 7.8 ± 1.5 ms−11 with an 8.2% average error compared to theoretical force values. It is believed the enhanced piezoelectric performance of these materials could provide a useful platform for wearable sensing and energy harvesting.

Force Sensor Based on FBG Embedded in Silicone Rubber

Force sensing is a key enabler for getting haptic feedback, useful in a variety of applications, especially in the fields of robotics, automation, and health. Indeed, equipping machines, vehicles, robots, and even humans with force sensors provides controlled processes and production, safe and enhanced external interaction, and capability to perform efficient manipulation and precise movements. Aiming to develop an alternative solution to electrical force sensors, in this work a fiber Bragg grating (FBG) is embedded inside a patch made of silicone rubber. Such embedding strategy allows to make the FBG sensitive to the force variations, obtain a flexible patch having a moldable shape, and protect the most fragile areas of the optical fiber. Moreover, due to its high flexibility and stretchability, the sensing patch can be easily employed as portable and wearable device. Besides reporting fabrication process and results of the performed force tests, this work provides a systematic study of the FBG embedding in a silicone matrix. Indeed, for this purpose, three sensing patches having different thicknesses are developed and tested in temperature, strain, and force, finding that the patch thickness influences the sensing performances of the device. The resulting force sensitivity varies in the range from 9.2 to 19.0 pm/N, based on the sensor thickness. Temperature sensitivity, instead, is comparable with respect to bare FBGs, while strain sensitivity is enormously reduced, obtaining a patch able to insulate the FBG from the strain variations.

Phase-Locked Impact of the 11-Year Solar Cycle on Tropical Pacific Decadal Variability

Abstract As an important external forcing, the effect of the 11-yr solar cycle on the tropical Pacific decadal variability is an interesting question. Here, we systematically investigate the phase-locking of the atmosphere and ocean covariations to the solar cycle in the tropical Pacific and propose a new mechanism to explain these decadal covariations. In both observation/reanalysis datasets and a solar cycle forced sensitivity experiment (named the SOL experiment), the ocean heat content anomalies (OHCa; 300 m) resemble a La Niña–like pattern in the solar cycle ascending phase, and the Walker circulation shifts westward. In the declining phase, the opposite is true. The accumulative solar irradiation directly contributes to this coherent decadal variability via changing the warm water volume and the solar-related heat is redistributed by the ocean dynamic processes. During the 11-yr solar cycle, the Pacific Walker circulation anomalies maintain the OHCa in the western equatorial Pacific and work as negative feedback for the eastern Pacific to help the OHCa phase transition. In addition, oceanic meridional heat transport via the subtropical cells and the propagation of off-equatorial Rossby waves also provide a lagged negative feedback to the OHCa phase transition according to the 11-yr solar cycle. The decadal coupled responses of the tropical Pacific climate system are 2 years more lag in the SOL experiment than in the observation/reanalysis. Significance Statement Here, we propose a new mechanism that the heating effect of the accumulative solar irradiation during the 11-yr solar cycle can be “integrated” into the tropical Pacific OHC and then provide a bottom-up effect on the atmosphere at decadal time scales. The strongly coupled processes in this region amplify the decadal phase-locking of the covariations to the 11-yr solar cycle. Our study demonstrates the role of the 11-yr solar cycle in the tropical Pacific decadal variability and provides a new explanation for the “bottom-up” mechanism of the solar cycle forcing. Our results update the understanding of the tropical Pacific decadal variability and may help to improve climate predictions at decadal time scales.

Proposal for the search for exotic spin-spin interactions at the micrometer scale using functionalized cantilever force sensors

Spin-dependent exotic interactions can be generated by exchanging hypothetical bosons, which were introduced to solve some puzzles in physics. Many precision experiments have been performed to search for such interactions, but no confirmed observations have been made. We propose new experiments to search for the exotic spin-spin interactions that can be mediated by axions or ${\mathrm{Z}}^{\ensuremath{'}}$ bosons. A sensitive functionalized cantilever is utilized as a force sensor to measure the interactions between the spin-polarized electrons in a periodic magnetic source structure and a closed-loop magnetic structure integrated on the cantilever. The source is set to oscillate during data acquisition to modulate the exotic force signal to high harmonics of the oscillating frequency. This helps to suppress the spurious signals at the signal frequency. Different magnetic source structures are designed for different interaction detections. A magnetic stripe structure is designed for ${\mathrm{Z}}^{\ensuremath{'}}$-mediated interactions, which are insensitive to the detection of axion-mediated interactions. This allows us to measure the coupling constant of both if we assume that both exist. With the force sensitivity achievable at low temperatures, the proposed experiments are expected to search for parameter spaces with much smaller coupling constants than the current stringent constraints from micrometer to millimeter range. Specifically, the lower bound of the parameter space will be 7 orders of magnitude lower than the stringent constraints for ${\mathrm{Z}}^{\ensuremath{'}}$-mediated interactions, and an order of magnitude lower for axion-mediated interactions, at the interaction range of $10\text{ }\text{ }\mathrm{\ensuremath{\mu}}\mathrm{m}$.

Do Skills Naturally Transfer Between Multiport and Single-Port Robotic Platforms? A Comparative Study in a Simulated Environment.

Introduction and Objective: With introduction of the da Vinci single-port (SP) system, we evaluated which multiport (MP) robotic skills are naturally transferable to the SP platform. Methods: Three groups of urologists: Group 1 (5 inexperienced in MP and SP), Group 2 (5 experienced in MP without SP experience), and Group 3 (2 experienced in both MP and SP) were recruited to complete a validated urethrovesical anastomosis simulation using MP followed by SP robots. Performance was graded using both GEARS and RACE scales. Subjective cognitive load measurements (Surg-TLX and difficulty ratings [/20] of instrument collisions camera and EndoWrist movement) were collected. Results: GEARS and RACE scores for Groups 1 and 3 were maintained on switching from MP to SP (Group 3 scored significantly higher on both systems). Surg-TLX and difficulty scores were also maintained for both groups on switching from MP and SP except for a significant increase in SP camera movement (+7.2, p = 0.03) in Group 1 compared to Group 3 that maintained low scores on both. Group 2 demonstrated significant lower GEARS (-2.9, p = 0.047) and RACE (-5.1, p = 0.011) scores on SP vs MP. On subanalysis, GEARS subscores for force sensitivity and robotic control (-0.7, p = 0.04; -0.9, p = 0.02) and RACE subscores for needle entry, needle driving, and tissue approximation (-0.9, p = 0.01; -1.0, p = 0.02; -1.0, p < 0.01) significantly decreased. GEARS (depth perception, bimanual dexterity, and efficiency) and RACE subscores (needle positioning and suture placement) were maintained. All participants scored significantly lower in knot tying on the SP robot (-1.0, p = 0.03; -1.2, p = 0.02, respectively). Group 2 reported higher Surg-TLX (+13 pts, p = 0.015) and difficulty ratings on SP vs MP (+11.8, p < 0.01; +13.6, p < 0.01; +14 pts, p < 0.01). Conclusions: The partial skill transference across robots raises the question regarding SP-specific training for urologists proficient in MP. Novices maintained difficulty scores and cognitive load across platforms, suggesting that concurrent SP and MP training may be preferred.

Development of a Compact Magnetic Suspension Balance

This article develops a prototype of magnetic suspension balance (MSB) for mass measurement, in which the mass of the sealed sample is transferred to the measuring unit via the magnetically suspended method. Considering that the excitation current decides the magnetic force while the magnetic force balances the gravity of the detected object, a type of compact MSB can be obtained by combining the force sensor unit and the magnetic suspension coupling unit (MSCU). Many efforts are undertaken to improve the performance of the compact MSB. The design parameters of the MSCU are optimized to decrease the sensitivity of the magnetic force to the variation in the suspension height; the magnetic suspension system is regulated by an active disturbance rejection control method to decrease the current fluctuation in the stator coil; the calibration method founded on the least-squares method is used to suppress the data drifts existed in the measuring process. The testing results show that both the resolution and repeatability of the MSB reach <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$500~\mu \mathrm {g}$ </tex-math></inline-formula> , and the measuring uncertainty is less than 1 mg for the weights up to 1 g.

First principles reaction discovery: from the Schrodinger equation to experimental prediction for methane pyrolysis.

Our recent success in exploiting graphical processing units (GPUs) to accelerate quantum chemistry computations led to the development of the ab initio nanoreactor, a computational framework for automatic reaction discovery and kinetic model construction. In this work, we apply the ab initio nanoreactor to methane pyrolysis, from automatic reaction discovery to path refinement and kinetic modeling. Elementary reactions occurring during methane pyrolysis are revealed using GPU-accelerated ab initio molecular dynamics simulations. Subsequently, these reaction paths are refined at a higher level of theory with optimized reactant, product, and transition state geometries. Reaction rate coefficients are calculated by transition state theory based on the optimized reaction paths. The discovered reactions lead to a kinetic model with 53 species and 134 reactions, which is validated against experimental data and simulations using literature kinetic models. We highlight the advantage of leveraging local brute force and Monte Carlo sensitivity analysis approaches for efficient identification of important reactions. Both sensitivity approaches can further improve the accuracy of the methane pyrolysis kinetic model. The results in this work demonstrate the power of the ab initio nanoreactor framework for computationally affordable systematic reaction discovery and accurate kinetic modeling.

Development of a Fiber Bragg Grating-Based Force Sensor for Minimally Invasive Surgery–Case Study of Ex-Vivo Tissue Palpation

In this paper, a one-dimensional distal force sensor design is proposed for minimally invasive surgery based on fiber Bragg grating (FBG) sensing principle. The sensor is made with a miniaturized force-sensitive flexure within which an optical fiber is embedded. The former includes a spiral elastomer utilized for high axial force sensitivity, while the fiber includes dual FBGs that are tightly suspended around the distal parts of the flexure and along elastomer’s centerline, respectively. Theoretical model of the flexure was derived based on its components and a design approach for decoupling strain and temperature cross-effects during sensor usage. In addition, design parameters of the flexure were analyzed on physics-based model optimization using fmincon function, while the static and dynamic properties were analyzed in-silico using finite element method. Further experiments were also carried out to analyze the sensor’s performance, and the data obtained was used for calibration study. The latter was done by training a feed-forward neural network designed for predicting the force vs. wavelength-shift relationship. The experimental results show the designed force sensor design can sense force values in a range of 1N with an average relative error less than 2% of full scale. Ex-vivo tissue palpation experiments were further done on pig liver organs to verify the effectiveness and applicability of the proposed sensor design in minimally invasive surgery.

Ultrathin, Graphene‐in‐Polyimide Strain Sensor via Laser‐Induced Interfacial Ablation of Polyimide

AbstractLaser‐induced graphene sensors have attracted considerable interest in various fields; however, the low sensitivity and conformability limit their further applications in measuring soft, large deformable structures. Here, an innovative method of interface ablation is presented to convert the interfacial polyimide into graphene by nanosecond ultraviolet laser (308 nm). Significantly different from the traditional laser surface ablation, interface ablation demonstrates its unique capacity to produce high‐quality graphene with limited ablation depth, which benefits from the combined effect of highly concentrated temperature distribution, the confinement of reaction product, and a unique ablation mode dominated by heat conduction. Using this method, an ultrathin (8 µm), graphene‐in‐polyimide (GiP) strain sensor is obtained, which is six times thinner than that prepared by the traditional surface ablation. The ultrathin GiP sensors exhibit excellent conformability (small bending radius of 400 µm), high strain sensitivity (24.8), and high force sensitivity (4.2 N−1). Demonstrations of this GiP strain sensor in the deformation measurement of the morphing aircraft (e.g., bending, twisting, and impact) illustrate its powerful abilities in the health monitoring of equipment, thus providing engineering opportunities for smart devices requiring accurate deformation measurement.

Resonance characteristics and energy losses of an ultra-high frequency ZnO nanowire resonator

An ultra-high frequency (UHF, 300 MHz∼3 GHz) nano mechanical resonator based on defect-free zinc oxide nanowire (ZnO NW) was fabricated through a top-down processing method. Using UHF detection technology based on a lock-in amplifier, through optimized measurement of high-performance equipment, it was detected at room temperature that the ZnO NW resonator could operate at a resonance frequency of nearly 650 MHz and a quality factor Q ≈ 1000∼2500, and its force sensitivity could reach 1 f N·Hz−1/2. The deformation, driving force and first-order resonance frequency of the resonator were calculated using the continuum model and compared with the experimental data. The resonance characteristics of ZnO NW resonators under piezoelectric excitation were analyzed and compared with that under electromagnetic excitation. The effects of various loss factors on the resonance characteristics were analyzed, with emphasis on the generation mechanism of piezoelectric loss, clamping loss and eddy current loss and their effects on quality factor and force sensitivity. The ZnO NWs used in this paper have piezoelectric effect, which is rare in other NWs, and are difficult to be fabricated in a bottom-up manner. And experiments show that for ZnO NWs resonators, piezoelectric excitation has obvious advantages in Q value compared with electromagnetic excitation. Unlike the bottom-up wet etch processing method, the resonant beam structure is well protected by the top-down processing method to reduce internal defects, and the top-down fabrication method is easier to integrate into the fabrication process of integrated circuits, which provides great potential for the applications of NW resonators, such as quantum electromechanical systems and high-frequency signal processing.