Recoverable Stress Research Articles

β-cyclocitral induced rapid cell death of Microcystis aeruginosa

β-cyclocitral (BCC) is an odorous compound that can be produced by bloom-forming cyanobacteria, for example, Microcystis aeruginosa. BCC has been proposed to explain the rapid decline of cyanobacterial blooms in natural water bodies due to its lytic effects on cyanobacteria cells. However, few insights have been gained regarding the mechanisms of its lethality on cyanobacteria. In this study, M. aeruginosa was exposed to 0–300 mg/L BCC, and the physiological responses were comprehensively studied at the cellular, molecular, and transcriptomic levels. The result indicated that the lethal effect was concentration-dependent; 100 mg/L BCC only caused recoverable stress, while 150–300 mg/L BCC caused rapid rupture of cyanobacterial cells. Scanning electron microscope images suggested two typical morphological changes exposed to above 150 mg/LBCC: wrinkled/shrank with limited holes on the surface at 150 and 200 mg/L BCC exposure; no apparent shrinkage at the surface but with cell perforation at 250 and 300 mg/L BCC exposure. BCC can rapidly inhibit the photosynthetic activity of M. aeruginosa cells (40%∼100% decreases for 100–300 mg/L BCC) and significantly down-regulate photosynthetic system Ⅰ-related genes. Also, chlorophyll a (by 30%∼90%) and ATP (by ∼80%) contents severely decreased, suggesting overwhelming pressure on the energy metabolism in cells. Glutathione levels increased significantly, and stress response-related genes were upregulated, indicating the perturbation of intracellular redox homeostasis. Two cell death pathways were proposed to explain the lethal effect: apoptosis-like death as revealed by the upregulation of SOS response genes when exposed to 200 mg/L BCC and mazEF-mediated death as revealed by the upregulation of mazEF system genes when exposed to 300 mg/L BCC. Results of the current work not only provide insights into the potential role of BCC in inducing programmed cell death during bloom demise but also indicate the potential of using BCC for harmful algal control.

Competing and decisive roles of 1D/2D/3D sp2-carbons in controlling the shape switching, contact sliding, and functional properties of polymers

Stimuli-controllable shape-shifting polymers, such as shape memory polyurethane (SMPU), are promising for robotics, aerospace, sensing, automobiles, and many other applications. However, slow actuation or high shape recovery time, low recovery stress, and inadequate understanding of friction and wear characteristics of SMPU limit its widespread practical uses. Further, SMPU has been engineered with diverse foreign materials but inconsistent results and ambiguous underlying mechanisms, especially when SMPU is modified with sp2-carbon materials, are also major concerns. Here we determine and simultaneously cross-compare the role of 1D/2D/3D graphitic carbons, namely carbon nanotubes, multilayer graphene and graphite, in controlling the properties of SMPU. The designed SMPU-composites display 8–15-folds faster shape recovery in different mediums, higher recoverable stress, faster healing of the dents, 2–3-folds lower friction, better wear resistance, and improved thermal, wettability, and dielectric properties than pristine SMPU. Further, while the introduction of 2D/3D graphitic carbons massively degrade the elongation, 1D carbon nanotubes maintains the stretchability of SMPU. Eventually, we develop a novel heat alarm device employing SMPU-composite as a major component that acts as a heat sensor, an actuator, and enables the closure of the circuit. Our results uncover many unknown phenomena of engineered SMPU and pave the way for the development of smart-technologies.

Effect of Chloroplast Movement on Laser Speckle Method

HighlightsThis study investigates the use of laser speckle to evaluate chloroplast movement in plant cells.The analysis value of the laser speckle corresponds to chloroplast movement.The run-length matrix analysis that we propose is more sensitive than existing methods.Abstract. Abiotic and biotic stresses change the cytoplasmic streaming in plant cells. In particular, the state of chloroplast movement changes rapidly in response to environmental changes. Thus, detecting chloroplast movement allows us to comprehend the physiological state of plants. This study investigated the applicability of the laser speckle method for evaluating chloroplast movement. Moreover, we propose a new analysis method for sensitively evaluating chloroplast movement. Leaves of Egeria densa were used, and electrical stimulation was applied as recoverable abiotic stress. Laser speckle measurement and light microscopic observation of the same specimen were performed before and after stimulation. The results showed that the laser speckle method can nondestructively evaluate macroscopic and collective chloroplast movement. The proposed method was more sensitive to chloroplast movement than existing methods. Keywords: Chloroplast, Image processing, Laser speckle, Textual analysis.

Suppression of water-bloom cyanobacterium Microcystis aeruginosa by algaecide hydrogen peroxide maximized through programmed cell death

The global expansion and intensification of toxic cyanobacterial blooms require effective algaecides. Algaecides should be selective, effective, fast-acting, and ideally suppress cyanotoxin production. In this study, whether both maximum growth suppression and minimal toxin production can be simultaneously achieved was tested with a selective algaecide H2O2, through its ability to induce apoptosis-like programmed cell death (AL PCD) in a common bloom species Microcystis aeruginosa. Under doses of 1−15 mg L−1, non-monotonic dose-response suppression of H2O2 on M. aeruginosa were observed, where maximal cell death and minimal microcystin production both occurred at a moderate dose of 10 mg L−1 H2O2. Maximal cell death was indeed achieved through AL PCD, as revealed by integrated biochemical, structural, physiological and transcriptional evidence; transcriptional profile suggested AL PCD was mediated by mazEF and lexA systems. Higher H2O2 doses directly led to necrosis in M. aeruginosa, while lower doses only caused recoverable stress. The integrated data showed the choice between the two modes of cell death is determined by the intracellular energy state under stress. A model was proposed for suppressing M. aeruginosa with AL PCD or necrosis. H2O2 was demonstrated to simultaneously maximize the suppression of both growth and microcystin production through triggering AL PCD.

Robust polyimide nano/microfibre aerogels welded by solvent-vapour for environmental applications.

Due to the high porosity, resilience and ultra-low density, polymer nanofibre-derived aerogels (NFAs) have been widely investigated in recent years. However, welding of the fibrous networks of NFAs, which has been proved extremely essential to their structural performance, still remains a major challenge. Herein, electrospun polyimide (PI) nano/microfibres were used as building blocks to construct hierarchically porous aerogels through a solid-templating technique. By further welding the adjacent nano/microfibres at their cross-points in a controllable fashion by solvent-vapour, super elasticity was achieved for the aerogels, with a recoverable ultimate strain of 80%. It is noteworthy that this process is free from cross-linking, heating and significant structure changing (i.e. chemical structure, crystallinity and fibrous network). Additionally, the porous structure of PI nano/microfibre aerogels (PI-N/MFAs) could be tuned by adjusting the organization of microfibres from a disordered/ordered cellular to a uniform structure. The as-obtained aerogels showed ultra-low density (4.81 mg cm−3), high porosity (99.66%), and comparable or higher recoverable compressive strain and stress relative to the other nanofibre-based aerogels. Furthermore, we showed the potential of such an aerogel for particle or aerosol filtration. PI nanofibre aerogels composite filters (PI-NFACFs) manifested excellent performance in PM2.0 filtration (99.6% filtration efficiency with 115 Pa pressure drop). Therefore, this study brought a new perspective on the simple preparation of nanofibre-based aerogels for air filtration.

Specific resistivity of dislocations and vacancies for super-pure aluminium at 4.2 K determined in-situ and post-recovery deformation and correlated to flow stress

ABSTRACTThe evolution of dislocations during shape-change of metal forms results from microstructural shear mechanism that is essential to enhance ductility. However, at room temperatures for face-centred cubic metals, this evolution results in the generation of vacancies that tend to form nano-voids, the growth of which leads to ductile failure. The correlated occurrence of dislocations and vacancies may be differentiated using the change of resistivity with plastic strain at 4.2 K, because resistivity is very sensitive to single vacancies compared to the formation of stacking faulted defects and dislocations. In order to assess the microstructure, the specific resistivity of these defect species was measured at 4.2 K, whereby thermal recovery processes are non-existent. The resistivity per dislocation line-length per volume was determined to be 1.87 × 10−25 Ωm3 for super-pure aluminium. The change in resistivity directly correlated to the shear flow stress squared. Vacancy-like defects formed during plastic flow were correlated to the recoverable resistivity after 298 K anneal and the derived volume fraction (CV) from mechanical data. The magnitude could be expressed as 12.9 × 10−9 Ωm per CV in % or as 1.21 × 10−25 Ωm3 in terms of line-length of vacancies per volume. The choice of representation depends on the presumed vacancy distribution. However, the recoverable flow stress upon 298 K anneal only appear to be proportional to √ CV at low strains; that is, at high strains the generated vacancies had transformed to defects that give rise to a small decrease in resistivity but a more notable increase in the flow stress. The possible mechanisms for this transformation are discussed.

Complete Set of Elastic Moduli of a Spin-Crossover Solid: Spin-State Dependence and Mechanical Actuation.

Molecular spin crossover complexes are promising candidates for mechanical actuation purposes. The relationships between their crystal structure and mechanical properties remain, however, not well understood. In this study, combining high pressure synchrotron X-ray diffraction, nuclear inelastic scattering, and micromechanical measurements, we assessed the effective macroscopic bulk modulus ( B = 11.5 ± 1.5 GPa), Young's modulus ( Y = 10.9 ± 1.0 GPa), and Poisson's ratio (ν = 0.34 ± 0.04) of the spin crossover complex [FeII(HB(tz)3)2] (tz = 1,2,4-triazol-1-yl). Crystal structure analysis revealed a pronounced anisotropy of the lattice compressibility, which was correlated with the difference in spacing between the molecules as well as by the distribution of the stiffest C-H···N interactions in different crystallographic directions. Switching the molecules from the low spin to the high spin state leads to a remarkable drop of the Young's modulus to 7.1 ± 0.5 GPa both in bulk and thin film samples. The results highlight the application potential of these films in terms of strain (ε = -0.17 ± 0.05%), recoverable stress (σ = -21 ± 1 MPa), and work density ( W/V = 15 ± 6 mJ/cm3).

Effects of orientation on the shape memory behavior of Ni51Ti49 single crystals

The orientation dependence of the shape memory responses of [001], [011] and [111]-oriented Ni51Ti49 single crystals and Ni50.8Ti49.2 polycrystals are systematically studied in compression. Thermal cycling under constant stress and superelasticity experiments were conducted on both homogenized and aged (1.5h at 500°C) samples to understand the effects of precipitation on their shape memory behavior. It has been found that recoverable strain, temperature and stress hysteresis, Classius-Clapeyron slopes, and critical stress for plastic deformation are highly orientation dependent. The recoverable strains were 3, 2.65 and 2.38% under 400MPa in [001], [011] and [111] orientations, respectively. After aging, the recoverable strains were 3.19, 2.78 and 2.11% under 400MPa in [001], [011] and [111] orientations, respectively. Above 400MPa, irrecoverable strain increased considerably for [011] and [111]-oriented samples. In [001] orientation, very narrow temperature hysteresis of 10°C, recoverable strain of 3.03% and total strain of 3.65% were observed under ultra high compressive stress level of 1500MPa. Moreover, [001] orientation showed perfect superelasticity with total strain of 7% and a large superelastic window (∆T=140°C). The transformation temperatures are lower in homogenized samples than the aged samples due to decreased Ni-concentration in matrix by the formation of Ni-rich precipitates.

Guidelines for Constructing Strain Gradient Plasticity Theories

Issues related to the construction of continuum theories of strain gradient plasticity which have emerged in recent years are reviewed and brought to bear on the formulation of the most basic theories. Elastic loading gaps which can arise at initial yield or under imposition of nonproportional incremental boundary conditions are documented and analytical methods for dealing with them are illustrated. The distinction between unrecoverable (dissipative) and recoverable (energetic) stress quantities is highlighted with respect to elastic loading gaps, and guidelines for eliminating the gaps are presented. An attractive gap-free formulation that generalizes the classical J2 flow theory is identified and illustrated.

Soil water potential and recoverable water stress in drought tolerant and susceptible rice varieties

We conducted a two-year field experiment to determine if water stress could be exploited to recover yield in one drought resistant (Vandana) and three susceptible (IR36, IR72 and Swarna) rice varieties. Stress was induced in active tillering, flowering and grain filling stages by suspending irrigation until the soil became sufficiently dry and plants began to show stress symptoms when irrigation was resumed, such that plants could recover from stress. We observed that terminal soil water potential (SWP) as low as −110kPa in the active tillering stage was less detrimental to relative water content, proline content, and electrolyte leakage. A 27% rise in the level of stress led to ∼8%, 44% and 21% increase in yield in IR36, Vandana and Swarna. The possible causes are 23%, 39% and 10% increase in the corresponding root biomass of the varieties, resulting in higher water uptake in the vegetative stage treatment plots. This was further supported by high correlations between yield and terminal SWP in this treatment. Critical limits of SWP may be identified to exploit the potential of rice varieties to sustain or improve yield under water stress. Results also suggest an opportunity to design a water saving strategy in lowland rice production.

NiTiCu 형상기억합금의 피로특성

Recently, the actuator worked by the driving recovery-force of the thermo elastic martensitic transformation of shape memory alloys(SMA) has been studied. This paper presents a study on the fatigue life of shape memory alloy (SMA) actuators undergoing thermally induced martensitic phase transformation under various stress levels. shape memory recoverable stress and strain of Ti-44.5at.%Ni-8at.%Cu alloys were by means of constant temperature tensile tests. Differential scanning calorimetry (DSC) was employed in order to investigate the transformation characteristics of the alloy before the tests. the results were summarized as follows. The martensite inducing stress incerased with the increasing of the Cu-contents. The fatigue life decreased with the increasing of the test load and the Cu-content. The data acquired will be very useful during the design process of an SMA NiTiCu element as a functional part of an actuator.

Transient abiotic stresses lead to latent defense and reproductive responses over the Brassica rapa life cycle

Plants can alter physiological and developmental trajectories in response to environmental cues by means of phenotypic plasticity. While cases of immediate plastic responses to different environments are well studied, phenotypic changes can also be delayed and occur in later life cycle stages. In this study, we investigated latent phenotypic plasticity in the development and chemical profile of Brassica rapa plants exposed to transient stress as seedlings. Four different stresses were applied to germinating seedlings: salinity, drought, nutrient deficiency, or acidity. Growth, reproduction, and glucosinolate chemical defenses (in leaves and seeds) were measured over the plants’ life cycles after normal conditions were restored. Despite initial stunting, B. rapa individuals recovered in total stem length and seed count compared with unstressed controls. There were, however, latent responses in flowering time, which was delayed in salinity-, drought-, or acid-stressed plants. Reductions in total flower count and total seed pod count were also observed in nutrient-deficiency stressed plants. Strikingly, previously stressed plants also showed latent differences in glucosinolate chemical defenses. Acid-stressed plants had higher concentrations of the plants’ major glucosinolate, gluconapin (3-butenylglucosinolate), in leaves and seeds, while nutrient deficiency-stressed plants had lower seed levels of gluconapin. Our experiments show that, despite outward recovery of growth, previously stressed B. rapa plants alter later defense and reproduction, leading to a plastic response delayed across life cycle stages. Thus, even transient, recoverable stress can have latent consequences for ecologically important chemical traits.

The mechanism of the deformation memory effect and the deformation rate analysis in layered rock in the low stress region

We propose a new mechanism to explain the deformation memory effect based on sliding over pre-existing sliding planes. Sliding resistance can comprise an element of cohesion and an element of frictional resistance. In this model only the cohesion is considered. The mechanism is modelled for a particular case of parallel sliding planes typical for layered rocks. The model consists of a number of identical basic elements comprising two springs, a St. Venant body and a dashpot. The basic elements only differ in their cohesion. The loading regime incorporating the influence of the delay time was modelled with one, two and 500 basic elements. The results showed that the recoverable stress magnitudes were in the range between the minimum and twice the maximum of cohesion. The model demonstrates the experimentally observed memory fading whereby the fidelity of stress reconstruction reduces with the increase in the time delay between the previous load the rock was subjected to and the measuring cycles.

Geometric confinement effects on the metal-insulator transition temperature and stress relaxation in VO2 thin films grown on silicon

VO2 undergoes a sharp metal-insulator transition at ∼67 °C with several orders of change in conductivity and optical transmittance. Understanding and control of the properties of vanadium oxide layers grown on technologically relevant substrates such as Si (100) single crystals is therefore of great interest. In this work, we show tunability of metal-insulator transition temperature as well as recoverable stress in VO2 thin films grown on Si substrate by introducing nanoscale atomic layer deposited HfO2 interfacial layers with no degradation in the resistance ratio. For a confined VO2 film, the metal-insulator transition temperature is suppressed by ∼16 °C and the recoverable stress is 150 MPa, compared to 400 MPa for a bare film. These observations are further correlated with in situ variable temperature measurement of stress changes occurring during the phase transition. Structural and microstructural studies on the various samples have been carried out by x ray diffraction and cross-sectional transmission electron microscopy. The strategy of tuning the metal-insulator transition characteristics by nanoscale interfacial dielectrics is of broader relevance in design of programmable materials and integration into solid state devices for electronics.

Thermoelastic switching with controlled actuation in VO 2 thin films

Reversible stress switching across the thermally triggered phase transition in vanadium dioxide thin films grown on silicon has been investigated using in situ wafer curvature measurements. Stability of the recoverable stress, hysteresis width and the transition temperature over 100 cycles are studied. Fine control over the recoverable stress has been demonstrated by thermal arrest across the phase boundary, exploiting the incomplete martensitic transition. Stability of the fractional stress changes across the martensitic transition is reported at various temperatures.

Proteome analysis of soybean roots subjected to short-term drought stress

Drought is one of the most important constraints on the growth and productivity of many crops, including soybeans. However, as a primary sensing organ, the plant root response to drought has not been well documented at the proteomic level. In the present study, we carried out a proteome analysis in combination with physiological analyses of soybean roots subjected to severe but recoverable drought stress at the seedling stage. Drought stress resulted in the increased accumulation of reactive oxygen species and subsequent lipid peroxidation. The proline content increased in drought-stressed plants and then decreased during the period of recovery. The high-resolution proteome map demonstrated significant variations in about 45 protein spots detected on Comassie briliant blue-stained 2-DE gels. Of these, 28 proteins were identified by mass spectrometry; the levels of 5 protein spots were increased, 21 were decreased and 2 spots were newly detected under drought condition. When the stress was terminated by watering the plants for 4 days, in most cases, the protein levels tended towards the control level. The proteins identified in this study are involved in a variety of cellular functions, including carbohydrate and nitrogen metabolism, cell wall modification, signal transduction, cell defense and programmed cell death, and they contribute to the molecular mechanism of drought tolerance in soybean plants. Analysis of protein expression patterns revealed that proteins associated with osmotic adjustment, defense signaling and programmed cell death play important roles for soybean plant drought adaptation. The identification of these proteins provides new insight that may lead to a better understanding of the molecular basis of the drought stress responses.

Bending in VO2-coated microcantilevers suitable for thermally activated actuators

The curvature of VO2-coated silicon microcantilevers was measured as the temperature was cycled through the coating’s insulator-to-metal transition (IMT), which drives the curvature change mainly through the strain generated during this reversible structural transformation. The films were grown by pulsed laser deposition (PLD) on heated substrates. Cantilever tip displacement was measured for a 130 μm long cantilever as the temperature was changed by recording the deflection of a laser beam, and the curvature change and estimated film stress were calculated from this data. A change in curvature of over 2000 m−1 was observed through the narrow temperature range of the IMT, with a maximum rate of ∼485 m−1 per degree. Estimated recoverable stress was ∼1 GPa through the transition region. These results suggest applications in actuator devices with reduced dimensions, including submicron lengths, multifunctional capabilities, and possibly with higher operational frequencies than other thermally actuated devices.

Hydraulic failure defines the recovery and point of death in water-stressed conifers.

This study combines existing hydraulic principles with recently developed methods for probing leaf hydraulic function to determine whether xylem physiology can explain the dynamic response of gas exchange both during drought and in the recovery phase after rewatering. Four conifer species from wet and dry forests were exposed to a range of water stresses by withholding water and then rewatering to observe the recovery process. During both phases midday transpiration and leaf water potential (Psileaf) were monitored. Stomatal responses to Psileaf were established for each species and these relationships used to evaluate whether the recovery of gas exchange after drought was limited by postembolism hydraulic repair in leaves. Furthermore, the timing of gas-exchange recovery was used to determine the maximum survivable water stress for each species and this index compared with data for both leaf and stem vulnerability to water-stress-induced dysfunction measured for each species. Recovery of gas exchange after water stress took between 1 and >100 d and during this period all species showed strong 1:1 conformity to a combined hydraulic-stomatal limitation model (r2 = 0.70 across all plants). Gas-exchange recovery time showed two distinct phases, a rapid overnight recovery in plants stressed to <50% loss of leaf hydraulic conductance (Kleaf) and a highly Psileaf-dependent phase in plants stressed to >50% loss of Kleaf. Maximum recoverable water stress (Psimin) corresponded to a 95% loss of Kleaf. Thus, we conclude that xylem hydraulics represents a direct limit to the drought tolerance of these conifer species.

A recoverable stress testing algorithm for compression and encryption cards

This study proposes a recoverable stress testing algorithm (RSTA) for such special devices as compression/decompression card and encryption/decryption card. It uses a chaos function to generate a random sequence, and then, according to the random sequence, generates an effective command sequence. The dispatch of command obeys a special schedule strategy we designed for such devices, i.e., the commands are sent according to the command sequence, and the complete commands are put in a buffer for further result check. RSTA is used to test the HIFN compression acceleration card SAICHI-1000. Test results show that RSTA can make the card work continuously and adequately.

Rubisco and some chaperone protein responses to water stress and rewatering at early seedling growth of drought sensitive and tolerant wheat varieties

Four wheat varieties differing in their drought tolerance were subjected to severe but recoverable water stress at seedling stage. Growth parameters, leaf water deficit (WD) and electrolyte leakage (EL) were used to evaluate the stress intensity and the extent of recovery. The physiological response of the varieties was quite similar under severe drought. Leaf protein patterns and levels of some individual proteins relevant to ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) maintenance were studied in control, stressed and recovering plants by electrophoresis and immunoblotting. The bands representing Rubisco large subunit (RLS), N- and C-terminus of RLS, Rubisco activase (RA) and Rubisco binding protein (RBP, cpn 60), as well as the chaperone and proteolytic subunits of the Clp protease complex were identified using polyclonal antibodies. Under drought conditions RLS, Clp proteases and especially RBP were enhanced, whereas the RA band was only slightly affected. The drought tolerant varieties had higher RBP content in the controls and drought treated plants. Its concentration could be a potential marker for drought tolerance.