Features of the optical medium of the surface of plant seeds

It was found that the integumentary tissue of plant seeds has the property of enhancing luminescence light. This phenomenon manifests itself in both the time and frequency domain. The gain factor (in power), depending on the type of seed, varies from 1.7 (beans) to 2.6 (rye). To determine it, the optical medium of the plant seed surface was represented as a dynamic link having an input and output. The impulse (time) characteristic of the link was found by the relaxation curve of luminescence. The dependence of the gain on temperature is expressed in the fact that when it decreases from 50 oC to –30 oC, the gain increases from 1.73 to 2.48. This phenomenon can be explained by the fact that at the stage of relaxation of luminescence, the absorption coefficient of the optical medium of the seed surface takes a negative value

Trabecular Meshwork Motion Profile from Pulsatile Pressure Transients: A New Platform to Simulate Transitory Responses in Humans and Nonhuman Primates

Trabecular meshwork (TM) motion abnormality is the leading cause of glaucoma. With technique limitations, how TM moves is still an enigma. This study describes a new laboratory platform to investigate TM motion responses to ocular transients in ex vivo eyes. The anterior segments of human cadaver and primate eyes were mounted in a perfusion system fitting. Perfusion needles were placed to establish mean baseline pressure. A perfusion pump was connected to the posterior chamber and generated an immediate transient pressure elevation. A phase-sensitive optical coherent tomography system imaged and quantified the TM motion. The peak-to-peak TM displacements (ppTMD) were determined, a tissue relaxation curve derived, and a time constant obtained. This study showed that the ppTMD increased with a rise in the pulse amplitude. The ppTMD was highest for the lowest mean pressure of 16 mmHg and decreased with mean pressure increase. The pulse frequency did not significantly change ppTMD. With a fixed pulse amplitude, an increase in mean pressure significantly reduced the time constant of recoil from maximum distension. Our research platform permitted quantitation of TM motion responses to designed pulse transients. Our findings may improve the interpretation of new TM motion measurements in clinic, aiding in understanding mechanisms and management.

Stress relaxation in samples made of acrylonitrile butadiene styrene material manufactured by fused deposition modelling

Increased interest in fused deposition modeling (FDM) resulting, for example, from its use in the production of utility models determines the undertaking of research on mechanical and rheological properties of materials. Mechanical and rheological properties of models made of materials used in FDM technology depend on technological parameters. In this paper, the effect of 0° and 90° print orientation on stress relaxation was analyzed. Additionally, the usefulness of the rheological model to describe the relaxation curve was evaluated. Stress relaxation tests were performed by tensile testing. The five-parameter Maxwell-Wiechert model was used to describe stress relaxation. The tests showed little effect of print orientation on the rheological parameters of the five-parameter model. The Maxwell-Wiechert model showed a very good approximation to the stress relaxation curves.

Loading History Effect on Stress Relaxation of Rock Joints

In this study, a data analysis method for the relaxation test was proposed under step loading by conducting creep and stress relaxation tests of dentate discontinuity poured by cement mortar using biaxial creep machine under step loading and single-stage loading. First, a superposition method for the stress relaxation curve was deduced based on the data processing method of creep test by considering the effect of loading history on the relaxation curve and the characteristic of relaxation was analyzed. Second, this superposition method was verified by testing data under step loading and single-stage loading. Finally, this paper indicate the accurate way for the processing of relaxation test data under step loading. The results show that under the same stress level, the values of relaxation curve after the superposition are different from that under the single-stage loading test. Furthermore, the relaxation curves in the step loading test under different stress levels are similar to those in single-stage loading under the same stress level. Furthermore, creep deformation increase monotonically during the creep, but stress do not exhibit such a trend during relaxation, which is inconsistent with the Boltzmann superposition principle. The relaxation curve in the step loading test under different shear stress could reflect the relaxation properties of the single-stage loading test under the same shear stress, and unlike the data processing method of step loading creep test, superimposition is not needed.

Validation of Fenoterol to Study β2-Adrenoceptor Function in the Rat Urinary Bladder

Fenoterol is a β₂-adrenoceptor (AR)-selective agonist that is commonly used to investigate relaxation responses mediated by β₂-AR in smooth muscle preparations. Some data have questioned this because fenoterol had low potency in the rat urinary bladder when a muscarinic agonist was used as a pre-contraction agent and because some investigators proposed that fenoterol may act in part via β₃-AR. We designed the present study to investigate whether fenoterol is a proper pharmacological tool to study β₂-AR-mediated relaxation responses in the rat urinary bladder. Firstly, we have compared the effect of pre-contraction agents on fenoterol potency and found that fenoterol potency was about 1.5 log units greater against KCl than carbachol (pEC₅₀ 7.19 ± 0.66 and 5.62 ± 1.09 of KCl and of carbachol, respectively). To test the selectivity of fenoterol, we have determined the effects of the β₂-AR antagonist ICI 118,551 and the β₃-AR antagonist L 748,337 on relaxation responses to fenoterol. While 300 nM L 748,337 had little effect on the potency of fenoterol (pEC₅₀ 6.56 ± 0.25 and 6.33 ± 0.61 in the absence and presence of L 748,337, respectively), the relaxation curve for fenoterol was right-shifted in the presence 300 nM ICI 118,551 (pEC₅₀ 5.03 ± 0.18). Thus, we conclude that fenoterol is a proper pharmacological tool to assess β₂-AR-mediated responses in the rat urinary bladder and most likely in other smooth-muscle preparations containing multiple subtypes of the β-AR.

AFM Force Relaxation Curve Reveals That the Decrease of Membrane Tension Is the Essential Reason for the Softening of Cancer Cells

Differences in stiffness constitute an extremely important aspect of the mechanical differences between cancer cells and normal cells, and atomic force microscopy (AFM) is the most commonly used tool to characterize the difference in stiffness. However, the process of mechanical characterization using AFM has been controversial and the influence of the membrane tension on AFM measurement results was often ignored. Here, a physical model involving a simultaneous consideration of the effects of the cell membrane, cytoskeleton network and cytosol was proposed. We carried out a theoretical analysis of AFM force relaxation curves, and as a result solved many of the remaining controversial issues regarding AFM-based mechanical characterization of cells, and provided a quantitative solution for the membrane tension measured using AFM indentation experiments for the first time. From the results of experiments on cells with different adherent shapes and different pairs of normal cells and cancer cells, we found additional force provided by membrane tension to be the main component of the force applied to the AFM probe, with decreased cell membrane tension being the essential reason for the greater softness of cancer cells than of normal cells. Hence, regulating membrane tension may become an important method for regulating the behavior of cancer cells.

Measurement of dynamic membrane mechanosensation using optical tweezers

Many cellular processes are orchestrated by dynamic changes in the plasma membrane to form membrane projections and endocytic vesicles in response to extracellular environmental changes. Our previous studies show that ARF6-ACAP4-ezrin signaling regulates membrane dynamics and curvature in response to EGF stimulation. However, there is no quantitative measurement to relate molecular organization of membrane cytoskeletal remodeling to stimulus-elicited mechanosensation on the plasma membrane. Optical tweezers is a powerful tool in the study of membrane tension. Comparing to pulling out an entire membrane tether at one time, the step-like method is more efficient because multiple relaxation curves can be obtained from one membrane tether. Fewer models describe relaxation curves to characterize mechanical properties of cell membrane. Here we establish a new method to measure the membrane relaxation curve of HeLa cells judged by the relationship between membrane tether diameter and tensions. We obtained effective viscosities and static tensions by fitting relaxation curves to our model. We noticed the delicate structure of relaxation curves contains information of cytoskeletal remodeling and lateral protein diffusion. Our study established a quantitative measure to characterize the mechanosensation of epithelial cells in response to stimulus-elicited membrane dynamics.

Characterizing mechanics of membrane tether from relaxation curve obtained by optical tweezers

Optical tweezers is a powerful tool in the study of membrane tension. Comparing to pulling out an entire membrane tether at one time, the step-like method is more efficient because multiple relaxation curves can be obtained from one membrane tether. However, there is few proper models that describe relaxation curves to characterize mechanical properties of cell membrane. Here we established a model to describe the relaxation curve of HeLa cells based on the relationship between membrane tether diameter and tensions. We obtained effective viscosities and static tensions by fitting relaxation curves to our model. We noticed the delicate structure of relaxation curves contains information of cell skeleton changes and protein diffusion. Our study paved a novel pathway to characterize the dynamics and mechanics of cell membrane.

Response functions in linear viscoelastic constitutive equations and related fractional operators

This study addresses the stress–strain relaxation functions of solid polymers in the framework of the linear viscoelasticity with aim to establish the adequate fractional operators emerging from the hereditary integrals. The analysis encompasses power-law and non-power-law materials, thus allowing to see the origins of application of the tools of the classical fractional calculus with singular memory kernels and the ideas leading towards fractional operators with non-singular (regular) kernels. A step ahead in modelling with hereditary integrals is the decomposition of non-power-law relaxation curves by Prony series, thus obtaining discrete relaxation kernels with a finite number of terms. This approach allows for seeing the physical background of the newly defined Caputo–Fabrizio time fractional derivative and demonstrates how other constitutive equations could be modified with non-singular fading memories. The non-power-law relaxation curves also allow for approximations by the Mittag–Leffler function of one parameter that leads reasonably into stress–strain hereditary integrals in terms of Atangana–Baleanu fractional derivative of Caputo sense. The main outcomes of the analysis done are the demonstrated distinguishes between the relaxation curve behaviours of different materials and are therefore the adequate modelling with suitable fractional operators.

Antiasthmatic effect of Curcuma aeruginosa extract on isolated organ of the trachea

Background:Asthma is a major health problem worldwide. Antiasthma drugs have side effects and can be expensive. It is important to develop antiasthma drugs from medicinal plants that have fewer side effects and are cheaper. One of the medicinal plants used for antiasthma treatment comes fromCurcuma aeruginosa(Zingiberaceaefamily). The aim of the research is to examine spasmolytic activity of ethanol extract ofC. aeruginosaon isolated guinea pig tracheas to determine the antiasthma effects.Methods:The spasmolytic activity ofC. aeruginosaextracts was tested in separated organs of guinea pig trachea. Guinea pig was sacrificed and its trachea rings were suspended in L-shaped wire loops in organ baths containing the Krebs solution aerated with carbogen. Isometric contractions of tracheal rings were measured by the transducer coupled to the amplifier. The trachea rings were exposed to DMSO as negative control, aminophylline as positive control andC. aeruginosaextracts. The single concentration-relaxation curve was obtained in every preparation.Results:The result showed that the decrease of the spasmolytic activity in the guinea pig tracheal tone due toC. aeruginosaextract was significantly better (p=0.022) when compared to the negative control. Meanwhile, the EC50value of aminophylline (0.019 ± 0.05) was not significantly different (p=0.454) withC. aeruginosa(0.024 ± 0.05).Conclusion:It could be concluded thatC. aeruginosaextracts have the potency to be further developed as a new natural source of the antiasthma agents.