Position sensors with nanometer resolution are a key component of many precision imaging and fabrication machines. Since the sensor characteristics can define the linearity, resolution and speed of ...the machine, the sensor performance is a foremost consideration. The first goal of this article is to define concise performance metrics and to provide exact and approximate expressions for error sources including non-linearity, drift and noise. The second goal is to review current position sensor technologies and to compare their performance. The sensors considered include: resistive, piezoelectric and piezoresistive strain sensors; capacitive sensors; electrothermal sensors; eddy current sensors; linear variable displacement transformers; interferometers; and linear encoders.
The quantitative and spatial coordination of stomatal pores in the epidermis and airspaces in the underlying mesophyll tissue is vital for efficient gas exchange in the leaf. The mechanisms that ...determine the distribution of stomata in the epidermis have been studied extensively, but how this relates to the regulation of mesophyll airspace configuration is poorly understood. Recent studies have investigated how development is coordinated between these tissue layers. The evidence suggests that multiple mechanisms are likely to work concurrently to coordinate stomatal and mesophyll development for optimal leaf gas exchange, and that both genetic and physiological factors contribute to this regulation. Such advances in our understanding of leaf development have important implications for potential improvement of crop water use efficiency.
Stomatal opening and closure depends on changes in turgor pressure acting within guard cells to alter cell shape 1. The extent of these shape changes is limited by the mechanical properties of the ...cells, which will be largely dependent on the structure of the cell walls. Although it has long been observed that guard cells are anisotropic due to differential thickening and the orientation of cellulose microfibrils 2, our understanding of the composition of the cell wall that allows them to undergo repeated swelling and deflation remains surprisingly poor. Here, we show that the walls of guard cells are rich in un-esterified pectins. We identify a pectin methylesterase gene, PME6, which is highly expressed in guard cells and required for stomatal function. pme6-1 mutant guard cells have walls enriched in methyl-esterified pectin and show a decreased dynamic range in response to triggers of stomatal opening/closure, including elevated osmoticum, suggesting that abrogation of stomatal function reflects a mechanical change in the guard cell wall. Altered stomatal function leads to increased conductance and evaporative cooling, as well as decreased plant growth. The growth defect of the pme6-1 mutant is rescued by maintaining the plants in elevated CO2, substantiating gas exchange analyses, indicating that the mutant stomata can bestow an improved assimilation rate. Restoration of PME6 rescues guard cell wall pectin methyl-esterification status, stomatal function, and plant growth. Our results establish a link between gene expression in guard cells and their cell wall properties, with a corresponding effect on stomatal function and plant physiology.
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•The guard cell wall is distinguished by a relatively low level of methylated pectin•Increased methyl pectin leads to stomata with a smaller dynamic range of movement•These plants show increased evaporative cooling and decreased growth under drought•Elevated CO2 restores mutant plant growth to normal
Guard cell wall mechanics must play a role in setting the dynamics of stomatal movement. Amsbury et al. show that the degree of pectin methylation in the wall sets the range of cell swelling, with consequences for plant water use and growth being dependent on CO2 level. Stomatal mechanics are likely to influence plant response to climate change.
Wheat is a staple crop, frequently cultivated in water-restricted environments. Improving crop water-use efficiency would be desirable if grain yield can be maintained. We investigated whether a ...decrease in wheat stomatal density via the manipulation of epidermal patterning factor (EPF) gene expression could improve water-use efficiency. Our results show that severe reductions in stomatal density in EPF-overexpressing wheat plants have a detrimental outcome on yields. However, wheat plants with a more moderate reduction in stomatal density (i.e. <50% reduction in stomatal density on leaves prior to tillering) had yields indistinguishable from controls, coupled with an increase in intrinsic water-use efficiency. Yields of these moderately reduced stomatal density plants were also comparable with those of control plants under conditions of drought and elevated CO2. Our data demonstrate that EPF-mediated control of wheat stomatal development follows that observed in other grasses, and we identify the potential of stomatal density as a tool for breeding wheat plants that are better able to withstand water-restricted environments without yield loss.
Many soft robots are composed of soft fluidic actuators that are fabricated from silicone rubbers and use hydraulic or pneumatic actuation. The strong nonlinearities and complex geometries of soft ...actuators hinder the development of analytical models to describe their motion. Finite element modeling provides an effective solution to this issue and allows the user to predict performance and optimize soft actuator designs. Herein, the literature on a finite element analysis of soft actuators is reviewed. First, the required nonlinear elasticity concepts are introduced with a focus on the relevant models for soft robotics. In particular, the procedure for determining material constants for the hyperelastic models from material testing and curve fitting is explored. Then, a comprehensive review of constitutive model parameters for the most widely used silicone rubbers in the literature is provided. An overview of the procedure is provided for three commercially available software packages (Abaqus, Ansys, and COMSOL). The combination of modeling procedures, material properties, and design guidelines presented in this article can be used as a starting point for soft robotic actuator design.
Herein, the literature on finite element modeling of soft fluidic actuators is reviewed. The combination of modeling procedures with commercial software packages, hyperelastic material parameters, and design guidelines presented in this article can be used as a starting point for soft robotic actuator design, while saving fabrication cost and time.
In this study, the actuator load force of a nanopositioning stage is utilized as a feedback variable to achieve both tracking and damping. The transfer function from the applied actuator voltage to ...the measured load force exhibits a zero-pole ordering that greatly simplifies the design and implementation of a tracking and damping controller. Exceptional tracking and damping performance can be achieved with a simple integral controller. Other outstanding characteristics include guaranteed stability and insensitivity to changes in resonance frequency. Experimental results on a high-speed nanopositioner demonstrate an increase in the closed-loop bandwidth from 210 Hz (with an integral controller) to 2.07 kHz (with a force-feedback control). Gain margin is simultaneously improved from 5 dB to infinity.
An increasing proportion of cognitive difficulties are recognized to have a functional cause, the chief clinical indicator of which is internal inconsistency. When these symptoms are impairing or ...distressing, and not better explained by other disorders, this can be conceptualized as a cognitive variant of functional neurological disorder, termed functional cognitive disorder (FCD). FCD is likely very common in clinical practice but may be under-diagnosed. Clinicians in many settings make liberal use of the descriptive term mild cognitive impairment (MCI) for those with cognitive difficulties not impairing enough to qualify as dementia. However, MCI is an aetiology-neutral description, which therefore includes patients with a wide range of underlying causes. Consequently, a proportion of MCI cases are due to non-neurodegenerative processes, including FCD. Indeed, significant numbers of patients diagnosed with MCI do not 'convert' to dementia. The lack of diagnostic specificity for MCI 'non-progressors' is a weakness inherent in framing MCI primarily within a deterministic neurodegenerative pathway. It is recognized that depression, anxiety and behavioural changes can represent a prodrome to neurodegeneration; empirical data are required to explore whether the same might hold for subsets of individuals with FCD. Clinicians and researchers can improve study efficacy and patient outcomes by viewing MCI as a descriptive term with a wide differential diagnosis, including potentially reversible components such as FCD. We present a preliminary definition of functional neurological disorder-cognitive subtype, explain its position in relation to other cognitive diagnoses and emerging biomarkers, highlight clinical features that can lead to positive diagnosis (as opposed to a diagnosis of exclusion), and red flags that should prompt consideration of alternative diagnoses. In the research setting, positive identifiers of FCD will enhance our recognition of individuals who are not in a neurodegenerative prodrome, while greater use of this diagnosis in clinical practice will facilitate personalized interventions.
The formation of stomata and leaf mesophyll airspace must be coordinated to establish an efficient and robust network that facilitates gas exchange for photosynthesis, however the mechanism by which ...this coordinated development occurs remains unclear. Here, we combine microCT and gas exchange analyses with measures of stomatal size and patterning in a range of wild, domesticated and transgenic lines of wheat and Arabidopsis to show that mesophyll airspace formation is linked to stomatal function in both monocots and eudicots. Our results support the hypothesis that gas flux via stomatal pores influences the degree and spatial patterning of mesophyll airspace formation, and indicate that this relationship has been selected for during the evolution of modern wheat. We propose that the coordination of stomata and mesophyll airspace pattern underpins water use efficiency in crops, providing a target for future improvement.
Summary
After entering the leaf, CO2 faces an intricate pathway to the site of photosynthetic fixation embedded within the chloroplasts. The efficiency of CO2 flux is hindered by a number of ...structural and biochemical barriers which, together, define the ease of flow of the gas within the leaf, termed mesophyll conductance. Previous authors have identified the key elements of this pathway, raising the prospect of engineering the system to improve CO2 flux and, thus, to increase leaf photosynthetic efficiency. In this review, we provide a perspective on the potential for improving the individual elements that contribute to this complex parameter. We lay particular emphasis on generation of the cellular architecture of the leaf which sets the initial boundaries of a number of mesophyll conductance parameters, incorporating an overview of the molecular transport processes which have been proposed as major facilitators of CO2 flux across structural boundaries along the pathway. The review highlights the research areas where future effort might be invested to increase our fundamental understanding of mesophyll conductance and leaf function and, consequently, to enable translation of these findings to improve the efficiency of crop photosynthesis.
Significance Statement
Increasing CO2 flux has been identified as an element of leaf structure/function which could significantly improve photosynthetic efficiency and, thus, crop yield. This review highlights the challenges and opportunities of achieving this aim, bringing into focus our ignorance of some fundamental aspects of leaf developmental physiology, and identifying areas where future research investment could yield improved knowledge, understanding, and impact.
Many popular modes of scanning probe microscopy require a vertical feedback system to regulate the tip-sample interaction. Examples include constant-current scanning tunneling microscopy and ...constant-force atomic force microscopy. Due to the control of tip-sample interaction, these modes of microscopy provide precise topographic information and result in drastically reduced sample damage, hence their popularity. Unfortunately the vertical feedback controller also imposes a severe limit on the scan-speed of scanning probe microscopes. In this paper, the foremost bandwidth limitation is identified to be the low-frequency mechanical resonances of the scanner. To overcome this limitation, a dual-stage vertical positioner is proposed. This comprises the original scanner, plus an additional high-speed stage. The improved bandwidth provided by the high-speed stage allows a vast improvement in feedback gain and bandwidth. In this work, the bandwidth is increased from 83 Hz to 2.7 kHz. This improvement allows image quality to be retained with a speed increase of 33 times, or alternatively, feedback error can be reduced by 33 times if scan speed is not increased. The techniques proposed are mechanically and electrically simple and can be retrofitted to any scanning probe microscope.
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