Prediction of bubble departing diameter in pool boiling of mixtures by ANN using modified ReLU.

In this research, bubble departure diameter in pool boiling have been measured in aqueous amine and ethylene glycol solutions for various concentrations. The experimental data have been compared with major existing predictive correlations. It is shown that the effect and identity of the independent variables on bubble diameter proposed in the previous studies are inconsistent. The predictions of different correlations have on average a deviation of about 40% from the experimental data. This is mainly due to the complicated interactions between bubbles on the heterogeneous boiling medium, which provides a complex condition. This complexity limits any mathematical modelling of the forces acting on the developing bubbles. Particularly in liquid solutions, where mass transfer by back diffusion through micro-sub-layers adds further complexity. In this work, the classical artificial neural network, ANN, with rectified linear unit, ReLU, activating function, AF, has been modified. This modification is based on adding a numerical matrix to each layer to adjust the slope of AF for each neuron independently. The addition of this parameter, together with the adjustment of the bias matrix, makes the activation function more flexible than the classical ReLU. To find the tuning parameters, a genetic algorithm was implemented instead of the back-propagation technique. It is shown that the predictions of the trained ANN with modified ReLU AF agree within an absolute average error of 10%, which is equal to the total uncertainty of the measurements. Prediction of bubble departing diameter in boiling phenomena is a key parameter for accurate design, operation and optimisation in many industrial systems.

Modeling extracellular stimulation of retinal ganglion cells: theoretical and practical aspects.

Objective.Retinal prostheses use electric current to activate inner retinal neurons, providing artificial vision for blind people. Epiretinal stimulation primarily targets retinal ganglion cells (RGCs), which can be modeled with cable equations. Computational models provide a tool to investigate the mechanisms of retinal activation, and improve stimulation paradigms. However, documentation of RGC model structure and parameters is limited, and model implementation can influence model predictions.Approach.We created a functional guide for building a mammalian RGC multi-compartment cable model and applying extracellular stimuli. Next, we investigated how the neuron's three-dimensional shape will influence model predictions. Finally, we tested several strategies to maximize computational efficiency.Main results.We conducted sensitivity analyses to examine how dendrite representation, axon trajectory, and axon diameter influence membrane dynamics and corresponding activation thresholds. We optimized the spatial and temporal discretization of our multi-compartment cable model. We also implemented several simplified threshold prediction theories based on activating function, but these did not match the prediction accuracy achieved by the cable equations.Significance.Through this work, we provide practical guidance for modeling the extracellular stimulation of RGCs to produce reliable and meaningful predictions. Robust computational models lay the groundwork for improving the performance of retinal prostheses.

Improving focality and consistency in micromagnetic stimulation.

The novel micromagnetic stimulation (µMS) technology aims to provide high resolution on neuronal targets. However, consistency of neural activation could be compromised by a lack of surgical accuracy, biological variation, and human errors in operation. We have recently modeled the activation of an unmyelinated axon by a circular micro-coil. Although the coil could activate the axon, its performance sometimes lacked focality and consistency. The site of axonal activation could shift by several experimental factors, including the reversal of the coil current, displacement of the coil, and changes in the intensity of the stimulation. Current clinical practice with transcranial magnetic stimulation (TMS) has suggested that figure-eight coils could provide better performance in magnetic stimulation than circular coils. Here, we estimate the performance of µMS by a figure-eight micro-coil, by exploring the impact of the same experimental factors on its focality and consistency in axonal activation. We derived the analytical expression of the electric field and activating function generated by the figure-eight micro-coil, and estimated the location of axonal activation. Using NEURON modeling of an unmyelinated axon, we found two different types (A and B) of axon activation by the figure-eight micro-coil, mediated by coil currents of reversed direction. Type A activation is triggered by membrane hyperpolarization followed by depolarization; Type B activation is triggered by direct membrane depolarization. Consequently, the two types of stimulation are governed by distinct ion channel mechanisms. In comparison to the circular micro-coil, the figure-eight micro-coil requires significantly less current for axonal activation. Under figure-eight micro-coil stimulation, the site of axonal activation does not change with the reversal of the coil current, displacement of the coil, or changes in the intensity of the stimulation. Ultimately, the figure-eight micro-coil provides a more efficient and consistent site of activation than the circular micro-coil in µMS.

Finding the Location of Axonal Activation by a Miniature Magnetic Coil.

Magnetic stimulation for neural activation is widely used in clinical and lab research. In comparison to electric stimulation using an implanted electrode, stimulation with a large magnetic coil is associated with poor spatial specificity and incapability to stimulate deep brain structures. Recent developments in micromagnetic stimulation (µMS) technology mitigates some of these shortcomings. The sub-millimeter coils can be covered with soft, biocompatible material, and chronically implanted. They can provide highly specific neural stimulation in the deep neural structure. Although the µMS technology is expected to provide a precise location of neural stimulation, the exact site of neural activation is difficult to determine. Furthermore, factors that could cause the shifting of the activation site during µMS have not been fully investigated. To estimate the location of axon activation in µMS, we first derived an analytical expression of the activating function, which predicts the location of membrane depolarization in an unmyelinated axon. Then, we developed a multi-compartment, Hodgkin-Huxley (H-H) type of NEURON model of an unmyelinated axon to test the impact of several important coil parameters on the location of axonal activation. The location of axonal activation was dependent on both the parameters of the stimulus and the biophysics properties of the targeted axon during µMS. The activating function analysis predicted that the location of membrane depolarization and activation could shift due to the reversal of the coil current and the change in the coil-axon distance. The NEURON modeling confirmed these predictions. Interestingly, the NEURON simulation further revealed that the intensity of stimulation played a significant role in the activation location. Moderate or strong coil currents activated the axon at different locations, mediated by two distinct ion channel mechanisms. This study reports several experimental factors that could cause a potential shift in the location of neural activation during µMS, which is essential for further development of this novel technology.

Modeling the Impact of the Variation in Peripheral Nerve Anatomy on Stimulation.

Introduction: The peripheral nervous system has a complex anatomical structure. Stimulation of nerve fibers in the peripheral nervous system depends on the fiber diameter and myelination as well as its location within the nerve, packing fraction and fascicle distribution within the nerve bundle. This paper analyzes the impact of the variation in peripheral nervous system anatomy and the distance of the stimulating electrodes on the probability of generating an action potential. Methods: A mathematical model for effective fascicle conductivity has been developed to capture the variation in the packing fraction and fiber diameter. A linear activating function is utilized to analyze the impact of this effective conductivity and fascicle distribution as an indicator of generating an action potential. Results: Finite element simulations are performed for the nerve-electrode configuration to evaluate the electric field. The simulation results are used to analyze the activating function for different packing fractions and type of nerve fibers. The effect of electrode distance on activating function and the total current through a nerve bundle has also been studied. Discussion: The simulation results indicate that the peripheral nerve anatomy and electrode distance have a significant effect on the action potential generation.

[Identification of active components in Xuefu Zhuyu Decoction based on targets of blood-activating function].

As a classic prescription for promoting blood circulation to remove blood stasis, Xuefu Zhuyu Decoction(XFZYD) is widely used in clinical practice and has notable curative effect. Based on the key targets of activating blood circulation, this study identified the active components of XFZYD to reveal the material basis. The components of XFZYD were collected from Traditional Chinese Medicine Systems Pharmacology Database and Analysis Platform(TCMSP). The molecular docking models were built for the blood-activating targets obtained from the previous study with the components of XFZYD. The top five active components with measurability for each target were selected as the potential blood-activating components in the prescription. The efficacy of the prescription can embody key pharmacological and high-content components. In this study, anti-platelet aggregation activity was used to characterize the effect of activating blood, and the in vivo experiments were conducted to verify the accuracy of the active components. A total of 210 chemical components of XFZYD were screened out from TCMSP and docked with the key targets with the function of activating blood. Ligustrazine, acteoside, naringin, etc. were selected as the potential active components for activating blood in XFZYD. The anti-platelet aggregation activity of the combination of Chuanxiong Rhizoma, Rehmanniae Radix, Aurantii Fructus, Glycyrrhizae Radix et Rhizoma, and Carthami Flos was 9.82%±5.11%. Compared with that in the control group, the platelet aggregation induced by adenosine diphosphate(ADP) was significantly inhibited in the test group(P<0.01), which verified the accuracy of the active components. This study can guide the research on the material basis of XFZYD and provide insights into the development and utilization of the classical prescription.

Identification of active components in Xuefu Zhuyu Decoction based on targets of blood-activating function / 中国中药杂志

As a classic prescription for promoting blood circulation to remove blood stasis, Xuefu Zhuyu Decoction(XFZYD) is widely used in clinical practice and has notable curative effect. Based on the key targets of activating blood circulation, this study identified the active components of XFZYD to reveal the material basis. The components of XFZYD were collected from Traditional Chinese Medicine Systems Pharmacology Database and Analysis Platform(TCMSP). The molecular docking models were built for the blood-activating targets obtained from the previous study with the components of XFZYD. The top five active components with measurability for each target were selected as the potential blood-activating components in the prescription. The efficacy of the prescription can embody key pharmacological and high-content components. In this study, anti-platelet aggregation activity was used to characterize the effect of activating blood, and the in vivo experiments were conducted to verify the accuracy of the active components. A total of 210 chemical components of XFZYD were screened out from TCMSP and docked with the key targets with the function of activating blood. Ligustrazine, acteoside, naringin, etc. were selected as the potential active components for activating blood in XFZYD. The anti-platelet aggregation activity of the combination of Chuanxiong Rhizoma, Rehmanniae Radix, Aurantii Fructus, Glycyrrhizae Radix et Rhizoma, and Carthami Flos was 9.82%±5.11%. Compared with that in the control group, the platelet aggregation induced by adenosine diphosphate(ADP) was significantly inhibited in the test group(P<0.01), which verified the accuracy of the active components. This study can guide the research on the material basis of XFZYD and provide insights into the development and utilization of the classical prescription.

PXR variants: the impact on drug metabolism and therapeutic responses.

The pregnane X receptor (PXR) plays an important and diverse role in mediating xenobiotic induction of drug-metabolizing enzymes and transporters. Several protein isoforms of PXR exist, and they have differential transcriptional activity upon target genes; transcript variants 3 (PXR3) and 4 (PXR4) do not induce target gene expression, whereas transcript variants 1 (PXR1) and 2 (PXR2) respond to agonist by activating target gene expression. PXR protein variants also display differences in protein-protein interactions; PXR1 interacts with p53, whereas PXR3 does not. Furthermore, the transcript variants of PXR that encode these protein isoforms are differentially regulated by methylation and deletions in the respective promoters of the variants, and their expression differs in various human cancers and also in cancerous tissue compared to adjacent normal tissues. PXR1 and PXR4 mRNA are downregulated by methylation in cancerous tissue and have divergent effects on cellular proliferation when ectopically overexpressed. Additional detailed and comparative mechanistic studies are required to predict the effect of PXR transcript variant expression on carcinogenesis, therapeutic response, and the development of toxicity.

variants: the impact on drug metabolism and therapeutic responses

The pregnane X receptor (PXR) plays an important and diverse role in mediating xenobiotic induction of drug-metabolizing enzymes and transporters. Several protein isoforms of PXR exist, and they have differential transcriptional activity upon target genes; transcript variants 3 (PXR3) and 4 (PXR4) do not induce target gene expression, whereas transcript variants 1 (PXR1) and 2 (PXR2) respond to agonist by activating target gene expression. PXR protein variants also display differences in protein-protein interactions; PXR1 interacts with p53, whereas PXR3 does not. Furthermore, the transcript variants of PXR that encode these protein isoforms are differentially regulated by methylation and deletions in the respective promoters of the variants, and their expression differs in various human cancers and also in cancerous tissue compared to adjacent normal tissues.andmRNA are downregulated by methylation in cancerous tissue and have divergent effects on cellular proliferation when ectopically overexpressed. Additional detailed and comparative mechanistic studies are required to predict the effect of PXR transcript variant expression on carcinogenesis, therapeutic response, and the development of toxicity.

Influence of the sodium channel band on retinal ganglion cell excitation during electric stimulation--a modeling study.

Electric stimulation using retinal implants allows blind people to re-experience a rudimentary kind of vision. The elicited percepts or so called 'phosphenes' are highly inconstant and therefore do not restore vision properly. The better knowledge of how retinal neurons, especially retinal ganglion cells, respond to electric stimulation will help to develop more sophisticated stimulation strategies. Special anatomic and physiologic properties like a band of highly dense sodium channels in retinal ganglion cells may help to achieve a focal activation of target cells and as a result better restoration of vision. A portion of retinal ganglion cell axons, about 40µm from the soma and between 25 and 40µm in length, shows a specific biophysical property. Electrode locations close to a band of highly dense sodium channels which were identified immunochemically show lowest thresholds during electric stimulation. The (modeled) thresholds for this kind of structure result in lowest thresholds as well. The influence on the location where action potentials are generated within the axon is far reaching. When a stimulating electrode is positioned far outside the actual band region the site of spike initiation still remains within the sodium channel band. These findings suggest to further examine the key mechanisms of activation for retinal ganglion cells because focal activation without influencing passing axons of neurons located far away can improve the outcome of electric stimulation and therefore the development of retinal implants.

Simulation analysis of extracellular selective stimulation of optic nerve with new helix electrode / 国际生物医学工程杂志

ObjectiveElectric stimulation of the central nervous system has been served as a treatment method for variety of neurological,psychiatric and sensory disorders.Despite considerable success in some applications,current stimulation techniques offer little control over which neuronal targets are activated by stimulation.This study aimed to present a new shape self-adaptive helix electrode for selective activation of optic nerve.MethodsThe geometric model of optic nerve and new helix electrode was elaborated with COMSOL Multiphysics.The new helix electrodes consist of silicone helix frame,which acted as support and insulation,and platinum contacts embedded within the frame.The activating function (AF) was introduced to characterize the stimulation effects,and the selectivity of activating optic nerve fascicle with new helix electrode was simulated by COMSOL Multiphysics,taking into account the variations of electrode contact locations.ResultsAssuming normalized AF threshold was 0.1 V/m2,the ratio difference of AF over threshold between new helix electrode and traditional electrode was only 1.2410％.With contacts in two ends of helix electrode closer to the middle contact,the small nerve fascicle was first activated and then the large one.ConclusionThe results show that the new helix electrodes have the same stimulation effects as that of traditional cuff electrodes.The new helix electrodes can selectively activate optic nerve fascicle with variations of electrode contact locations.