This paper presents a novel piezoelectric strain sensor for damping and accurate tracking control of a high-speed nanopositioning stage. Piezoelectric sensors have the benefit of simple interface ...circuitry, low cost, high sensitivity, and high bandwidth. Although piezoelectric sensors have been successfully used as vibration sensors in smart structures, complications arise when they are used in a feedback loop for tracking. As piezoelectric strain sensors exhibit a capacitive source impedance, a high-pass filter is created, typically with a cut-off frequency of 1 to 10 Hz. This filter can cause significant errors and destabilize a tracking control system. Here, we overcome this problem by using a low-frequency bypass technique to replace the low-frequency component of the strain measurement with an estimate based on the open-loop system. Once the low-frequency filter is accounted for, any standard control system can be applied. In this paper, an analog integral resonant controller together with an integral tracking controller are implemented on a flexure-guided nanopositioner. The resulting closed-loop bandwidth is experimentally demonstrated to be 1.86 kHz. The nanopositioner is installed in an Atomic Force Microscope to obtain open- and closed-loop images at line rates of 40 and 78 Hz. Images recorded in closed loop show a significant improvement due to the elimination of nonlinearity.
In this article, we combine nonlinear estimation and control methods for precise bending angle control in soft pneumatic actuators driven by a pressure source and single low-cost on / off solenoid ...valve. First, a complete model for the soft actuator is derived, which includes both the motion and pressure dynamics. An unscented Kalman filter (UKF) is used to estimate the velocity state and filter noisy measurements from a pressure sensor and an embedded resistive flex sensor. Then, a feedback linearization approach is used with pole placement and linear quadratic regulator (LQR) controllers for bending angle control. To compensate for model uncertainties and improve reference tracking, integral action is incorporated to both controllers. The closed-loop performance of the nonlinear estimation and control approach is experimentally evaluated with a soft pneumatic network actuator. The simulation and experimental results show that the UKF provides accurate state estimation from noisy sensor measurements. The results demonstrate the effectiveness and robustness of the proposed observer-based nonlinear controllers for bending angle trajectory tracking.
Developing synchronous bilateral Wilms tumor suggests an underlying (epi)genetic predisposition. Here, we evaluate this predisposition in 68 patients using whole exome or genome sequencing (n = 85 ...tumors from 61 patients with matched germline blood DNA), RNA-seq (n = 99 tumors), and DNA methylation analysis (n = 61 peripheral blood, n = 29 non-diseased kidney, n = 99 tumors). We determine the predominant events for bilateral Wilms tumor predisposition: 1)pre-zygotic germline genetic variants readily detectable in blood DNA WT1 (14.8%), NYNRIN (6.6%), TRIM28 (5%), and BRCA-related genes (5%) or 2)post-zygotic epigenetic hypermethylation at 11p15.5 H19/ICR1 that may require analysis of multiple tissue types for diagnosis. Of 99 total tumor specimens, 16 (16.1%) have 11p15.5 normal retention of imprinting, 25 (25.2%) have 11p15.5 copy neutral loss of heterozygosity, and 58 (58.6%) have 11p15.5 H19/ICR1 epigenetic hypermethylation (loss of imprinting). Here, we ascertain the epigenetic and genetic modes of bilateral Wilms tumor predisposition.
It has long been accepted that differential radial thickening of guard cells plays an important role in the turgor-driven shape changes required for stomatal pore opening to occur 1–4. This textbook ...description derives from an original interpretation of structure rather than measurement of mechanical properties. Here we show, using atomic force microscopy, that although mature guard cells display a radial gradient of stiffness, this is not present in immature guard cells, yet young stomata show a normal opening response. Finite element modeling supports the experimental observation that radial stiffening plays a very limited role in stomatal opening. In addition, our analysis reveals an unexpected stiffening of the polar regions of the stomata complexes, both in Arabidopsis and other plants, suggesting a widespread occurrence. Combined experimental data (analysis of guard cell wall epitopes and treatment of tissue with cell wall digesting enzymes, coupled with bioassay of guard cell function) plus modeling lead us to propose that polar stiffening reflects a mechanical, pectin-based pinning down of the guard cell ends, which restricts increase of stomatal complex length during opening. This is predicted to lead to an improved response sensitivity of stomatal aperture movement with respect to change of turgor pressure. Our results provide new insight into the mechanics of stomatal function, both negating an established view of the importance of radial thickening and providing evidence for a significant role for polar stiffening. Improved stomatal performance via altered cell-wall-mediated mechanics is likely to be of evolutionary and agronomic significance.
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•Stomatal poles are stiff and have a distinct cell wall composition•Loss of polar stiffening is associated with decreased degree of stomatal opening•Lack of radial guard cell stiffening does not preclude stomatal opening•A “fix and flex” model predicts more efficient opening of stomata via polar stiffening
Textbooks state that radial stiffening of guard cells is required for stomatal opening. Carter et al. show that this is not the case. They demonstrate that stomatal poles are stiffer than surrounding cells. A new “fix and flex” model is proposed in which polar stiffening leads to more efficient stomata, potentially allowing better water use by plants.
Stomata are formed by a pair of guard cells which have thickened, elastic cell walls to withstand the large increases in turgor pressure that have to be generated to open the pore that they surround. ...We have characterized FOCL1, a guard cell-expressed, secreted protein with homology to Hyp-rich cell wall proteins. FOCL1-GFP localizes to the guard cell outer cuticular ledge and plants lacking FOCL1 produce stomata without a cuticular ledge. Instead the majority of stomatal pores are entirely covered over by a continuous fusion of the cuticle, and consequently plants have decreased levels of transpiration and display drought tolerance. The focl1 guard cells are larger and less able to reduce the aperture of their stomatal pore in response to closure signals suggesting that the flexibility of guard cell walls is impaired. FOCL1 is also expressed in lateral root initials where it aids lateral root emergence. We propose that FOCL1 acts in these highly specialized cells of the stomata and root to impart cell wall strength at high turgor and/or to facilitate interactions between the cell wall and the cuticle.
This article describes a method for estimating the temperature of high-power piezoelectric actuators when a direct temperature measurement is impractical. The heat flow is estimated from the real ...component of the electrical power; then, the temperature is estimated by a transfer function that approximates the thermal response of the system. The transfer function can be derived analytically from a lumped-element approximation or calibrated experimentally by using a system identification method. The proposed method is demonstrated on a piezoelectric stack actuator used in a high-speed nanopositioning device. A second-order transfer function estimates the temperature to within 3 <inline-formula><tex-math notation="LaTeX">^{\circ }</tex-math></inline-formula>C of a reference measurement for a range of operating conditions. The proposed method is suitable for protecting piezoelectric actuators in applications where direct temperature measurement is impractical, for example, due to space or wiring constraints.
This paper describes the design of a charge drive for reducing the hysteresis exhibited by a piezoelectric bimorph bender. Existing charge drive circuits cannot be directly applied to bimorph benders ...since they share a common electrode. In this paper, a new charge drive circuit and electrical configuration are implemented that allows commonly available piezoelectric bimorphs to be linearized. This circuit consists of four major components, including, a high voltage amplifier, a differential amplifier, a piezoelectric load, and a PI feedback controller. An isolation amplifier was used to achieve a differential amplifier with a high common-mode rejection ratio. The charge drive was tested by driving a series poled three layer bimorph bender. The experiment showed a significant improvement to the hysteresis of the bender when compared to a typical voltage drive. This paper has identified an alternative Feedback method to improve the ac hysteresis performance of a piezoelectric bender by using a charge drive.
Background
Patients with unstable cervical spine (C-spine) fractures are at a significant risk of respiratory failure. There is no consensus on the optimal timing of tracheostomy in the setting of ...recent operative cervical fixation (OCF). This study evaluated the impact of tracheostomy timing on surgical site infections (SSIs) in patients undergoing OCF and tracheostomy.
Methods
Trauma Quality Improvement Program (TQIP) was used to identify patients with isolated cervical spine injuries who underwent OCF and tracheostomy between 2017 and 2019. Early tracheostomy (<7 days from OCF) was compared with delayed tracheostomy (≥7 days from OCF). Logistic regressions identified variables associated with SSI, morbidity, and mortality. Pearson correlations evaluated time to tracheostomy and length of stay (LOS).
Results
Of 1438 patients included, 20 had SSI (1.4%). There was no difference in SSI between early vs delayed tracheostomy (1.6% vs 1.2%, P = .5077). Delayed tracheostomy was associated with increased ICU LOS (23.0 vs 17.0 days, P < .0001), ventilator days (19.0 vs 15.0, P < .0001), and hospital LOS (29.0 vs 22.0 days, P < .0001). Increased ICU LOS was associated with SSI (OR 1.017; CI 0.999-1.032; P = .0273). Increased time to tracheostomy was associated with increased morbidity (OR 1.003; CI 1.002-1.004; P < .0001) on multivariable analysis. Time from OCF to tracheostomy correlated with ICU LOS (r (1354) = .35, P < .0001), ventilator days (r (1312) = .25, P < .0001), and hospital LOS (r (1355) = .25, P < .0001).
Conclusion
In this TQIP study, delayed tracheostomy after OCF was associated with longer ICU LOS and increased morbidity without increased SSI. This supports the TQIP best practice guidelines recommending that tracheostomy should not be delayed for concern of increased SSI risk.
Stomata regulate plant water use and photosynthesis by controlling leaf gas exchange. They do this by reversibly opening the pore formed by two adjacent guard cells, with the limits of this movement ...ultimately set by the mechanical properties of the guard cell walls and surrounding epidermis.1,2 A body of evidence demonstrates that the methylation status and cellular patterning of pectin wall polymers play a core role in setting the guard cell mechanical properties, with disruption of the system leading to poorer stomatal performance.3,4,5,6 Here we present genetic and biochemical data showing that wall arabinans modulate guard cell flexibility and can be used to engineer stomata with improved performance. Specifically, we show that a short-chain linear arabinan epitope associated with the presence of rhamnogalacturonan I in the guard cell wall is required for full opening of the stomatal pore. Manipulations leading to the novel accumulation of longer-chain arabinan epitopes in guard cell walls led to an increase in the maximal pore aperture. Using computational modeling combined with atomic force microscopy, we show that this phenotype reflected a decrease in wall matrix stiffness and, consequently, increased flexing of the guard cells under turgor pressure, generating larger, rounder stomatal pores. Our results provide theoretical and experimental support for the conclusion that arabinan side chains of pectin modulate guard cell wall stiffness, setting the limits for cell flexing and, consequently, pore aperture, gas exchange, and photosynthetic assimilation.
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•Cell walls in stomata have a distinct composition of arabinans•Increasing the level of a specific arabinan makes the walls more flexible•Stomata with more flexible walls can open wider•Under high CO2, more flexible, wider stomata increase carbon assimilation rate
The degree of stomatal opening is set by the mechanical properties of the guard cell walls. Carroll et al. show that wall flexibility is set by the arabinan composition, and that by manipulating arabinan polymers it is possible to engineer stomata with increased opening under elevated CO2, leading to increased carbon assimilation.
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