Background Pain sensitivity is critical for preventing non-suicidal self-injury(NSSI)behaviours;however,individuals engaging in such behaviours often exhibit decreased pain sensitivity,which may undermine this natural...Background Pain sensitivity is critical for preventing non-suicidal self-injury(NSSI)behaviours;however,individuals engaging in such behaviours often exhibit decreased pain sensitivity,which may undermine this natural safeguard.The dorsolateral prefrontal cortex(DLPFC)is a key region involved in pain regulation,and recent approaches using transcranial direct current stimulation(tDCS)to target the DLPFC have shown potential for modulating pain processing and restoring normal pain perception for individuals engaging in NSSI behaviours.Aims This study aimed to explore the immediate and short-term effects of a single session of tDCS on pain sensitivity in individuals with NSSI,as well as its secondary effects on mood and NSSI-related factors.Methods In this randomised,double-blind,parallel,sham-controlled clinical trial,participants with a history of NSSI were randomly assigned to receive either active or sham tDCS.The intervention consisted of a single 20 min tDCS session targeting the left DLPFC.The primary outcome was pain sensitivity,measured by the pressure pain threshold(PPT)and heat pain score(HPS).Secondary and additional outcomes included NSSI urges,NSSI resistance,self-efficacy in resisting NSSI,mood-related variables and exploratory cognitive-affective processes such as rumination,self-criticism and self-perceived pain sensitivity,assessed at baseline,immediately post-intervention,and at 24 hours,1 week and 2 weeks follow-ups.Results For the primary outcomes,no significant differences between groups were observed for pain sensitivity(PPT,padj=0.812;HPS,padj=0.608).However,an exploratory sensitivity analysis treating each trial as an individual observation revealed a significant effect on HPS(padj=0.036).For the secondary and additional outcomes,although there were initial improvements in joyful feelings and reductions in negative affect at 2 weeks post-intervention,these effects did not remain significant after multiple comparison corrections.Notably,reductions in rumination were statistically significant at both 1-week and 2-week follow-ups(1 week,p_(adj)=0.040;2 weeks,p_(adj)=0.042).There were no significant effects on NSSI urges,NSSI resistance,self-efficacy in resisting NSSI or self-criticism.Conclusions A single session of tDCS over the left DLPFC did not produce significant changes in pain sensitivity in individuals with NSSI.A sensitivity analysis indicated an effect on heat pain sensitivity,possibly reflecting changes in brain activity,warranting confirmation through neuroimaging.These findings suggest that tDCS warrants further investigation for its potential to influence pain-related cognitive-affective processes in individuals with NSSI.展开更多
The integration of large-scale new energy and high-capacity DC transmission leads to a reduction in system inertia.Grid-forming renewable energy sources(GF-RES)has a significant improvement effect on system inertia.Co...The integration of large-scale new energy and high-capacity DC transmission leads to a reduction in system inertia.Grid-forming renewable energy sources(GF-RES)has a significant improvement effect on system inertia.Commutation failure faults may cause a short-term reactive power surplus at the sending end and trigger transient overvoltage,threatening the safe and stable operation of the power grid.However,there is a lack of research on the calculation method of transient overvoltage caused by commutation failure in high-voltage DC transmission systems with grid-forming renewable energy sources integration.Based on the existing equivalent model of highvoltage DC transmission systems at the sending end,this paper proposes to construct a model of the high-voltage DC transmission system at the sending end with grid-forming renewable energy sources.The paper first clarifies the mechanism of overvoltage generation,then considers the reactive power droop control characteristics of GF-RES,and derives the transient voltage calculation model of theDC transmission system with GF-RES integration.It also proposes a calculation method for transient overvoltage at the sending-end converter bus with GF-RES integration.Based on the PSCAD/EMTDC simulation platform,this paper builds an experimental simulation model.By constructing three different experimental scenarios,the accuracy and effectiveness of the proposed transient overvoltage calculation method are verified,with a calculation error within 5%.At the same time,this paper quantitatively analyzes the impact of grid strength,new energy proportion,and rated transmission power on transient overvoltage from three different perspectives.展开更多
Herein,the effect of direct current(DC)attached the mold on refining the microstructure and alleviating the central segregation of a tin–bismuth(Sn–10 wt.%Bi)alloy ingot during the solidification process has been in...Herein,the effect of direct current(DC)attached the mold on refining the microstructure and alleviating the central segregation of a tin–bismuth(Sn–10 wt.%Bi)alloy ingot during the solidification process has been investigated.The experiment used a self-made device,which can achieve the effect of refining the solidified structure and alleviate the segregation of the metal casting.Numerical simulations were performed to calculate the Lorentz force,Joule heating and induced melt vortex flow for the magneto-hydrodynamic case.Our results show that the maximum velocity of the global electro-vortex reached 0.017 m s^(–1).The DC-induced electro-vortex was found to be the primary reason of refining the equiaxed grain and alleviating the segregation of theβ-Sn crystal boundary.The grain refining effect observed in these experiments can be solely attributed to the forced melt flow driven by the Lorentz force.DC field attached the mold can lead to grain refinement and alleviate the segregation of the ingot via a global vortex.The technology can be applied not only to opened molds,but also toward improving the quality in closed molds.展开更多
BACKGROUND Postoperative delirium(POD),an acute neuropsychiatric complication in elderly surgical patients,manifests as attention and cognitive disturbances that may last 24-72 hours after surgery,potentially progress...BACKGROUND Postoperative delirium(POD),an acute neuropsychiatric complication in elderly surgical patients,manifests as attention and cognitive disturbances that may last 24-72 hours after surgery,potentially progressing to dementia.Transcranial direct current stimulation(tDCS),a non-invasive neuromodulation technique,enhances cortical excitability and cognitive function by modulating brain networks and synaptic plasticity.Elderly patients undergoing major laparoscopic surgery face elevated POD risks due to prolonged anesthesia and pneumoperitoneum-induced cerebral hypoperfusion.This study investigates whether pre-anesthesia tDCS can reduce POD incidence in this population.AIM To investigate the effect of preoperative tDCS on reducing the incidence of POD in elderly patients undergoing major laparoscopic surgery.METHODS In this study,we enrolled 220 elderly patients who underwent major laparoscopic surgery between April 2024 and December 2024.Patients were randomly assigned to the active-tDCS(group A)and sham-tDCS(group S)groups.A single session of tDCS or sham stimulation was administered 30 minutes before anesthesia induction.The primary outcome was the incidence of POD during within 3 days postoperatively.RESULTS A total of 201 patients were included in the final analysis,with 100 patients in group A and 101 in group S.The incidence of POD within 3 days postoperatively was 7.0%in group A,which was significantly lower than 22.8%in group S.On postoperative day 1,the Self-Rating Anxiety Scale and Self-Rating Depression Scale scores significantly differed between the two groups,but the pain scores showed no significant difference.CONCLUSION A single session of preoperative tDCS can reduce the incidence of POD in elderly patients undergoing major laparoscopic surgery and can also reduce postoperative anxiety and depression in these patients.展开更多
BACKGROUND Schizophrenia is a chronic psychiatric condition with complex symptomatology,including debilitating auditory hallucinations.Transcranial direct current stimulation(tDCS)has been explored as an adjunctive tr...BACKGROUND Schizophrenia is a chronic psychiatric condition with complex symptomatology,including debilitating auditory hallucinations.Transcranial direct current stimulation(tDCS)has been explored as an adjunctive treatment to alleviate such symptoms.AIM To evaluate the therapeutic efficacy of tDCS in schizophrenia.METHODS Adhering to PRISMA guidelines,we systematically searched PubMed,Embase,Web of Science,and the Cochrane Library on September 19,2023,for randomized controlled trials examining the efficacy of tDCS in schizophrenia,with no language or time restrictions.We included studies that compared tDCS with a control condition and reported clinically relevant outcomes.Data extraction and quality assessments were performed by independent evaluators using the Cochrane Collaboration's risk of bias tool.Statistical heterogeneity was evaluated,and a random-effects model was applied due to moderate heterogeneity(I2=41.3%).RESULTS Nine studies comprising 425 participants(tDCS group:219,control group:206)were included.The meta-analysis demonstrated a significant reduction in auditory hallucination scores following tDCS treatment(weighted mean difference:-2.18,95%confidence interval:-4.0 to-0.29,P<0.01).Sensitivity analysis confirmed the robustness of the results,with no significant influence from individual studies.Additionally,publication bias was not detected,supporting the reliability and generalizability of the findings.These results underscore the efficacy of tDCS as a therapeutic intervention for auditory hallucinations in schizophrenia.CONCLUSION tDCS significantly reduces auditory hallucinations in schizophrenia,suggesting its potential as an effective adjunctive treatment for managing this disabling symptom.The findings highlight the practical significance of tDCS in clinical settings,particularly for patients with treatment-resistant auditory hallucinations.展开更多
Effect of direct current electric field （DCEF） on corrosion behaviour of copper printed circuit board （PCB-Cu）, Cl-ion migration behaviour, dendrites growth under thin electrolyte layer was investigated using pote...Effect of direct current electric field （DCEF） on corrosion behaviour of copper printed circuit board （PCB-Cu）, Cl-ion migration behaviour, dendrites growth under thin electrolyte layer was investigated using potentiodynamic polarization and scanning electron microscopy （SEM） with energy dispersive spectrometer （EDS）. Results indicate that DCEF decreases the corrosion of PCB-Cu;Cl-ions directionally migrate from the negative pole to the positive pole, and enrich on the surface of the positive pole, which causes serious localized corrosion; dendrites grow on the surface of the negative pole, and the rate and scale of dendrite growth become faster and greater with the increase of external voltage and exposure time, respectively.展开更多
The combined effects of direct current pulsed magnetic field （DC-PMF） and inoculation on pure aluminum were investigated, the grain refinement behavior of DC-PMF and inoculation was discussed. The experimental resul...The combined effects of direct current pulsed magnetic field （DC-PMF） and inoculation on pure aluminum were investigated, the grain refinement behavior of DC-PMF and inoculation was discussed. The experimental results indicate that the solidification micro structure of pure aluminum can be greatly refined under DC-PMF. Refinement of pure aluminum is attributed to electromagnetic undercooling and forced convection caused by DC-PMF. With single DC-PMF, the grain size in the equiaxed zone is uneven. However, under DC-PMF, by adding 0.05% （mass fraction） Al5Ti-B, the grain size of the sample is smaller, and the size distribution is more uniform than that of single DC-PMF. Furthermore, under the combination of DC-PMF and inoculation, with the increase of output current, the grain size is further reduced. When the output current increases to 100 A, the average grain size can decrease to 113 μn.展开更多
To deal with the problem of low computational precision at the nodes near the source and satisfy the requirements for computational efficiency in inversion imaging and finite-element numerical simulations of the direc...To deal with the problem of low computational precision at the nodes near the source and satisfy the requirements for computational efficiency in inversion imaging and finite-element numerical simulations of the direct current method, we propose a new mesh refinement and recoarsement method for a two-dimensional point source. We introduce the mesh refinement and mesh recoarsement into the traditional structured mesh subdivision. By refining the horizontal grids, the singularity owing to the point source is minimized and the topography is simulated. By recoarsening the horizontal grids, the number of grid cells is reduced significantly and computational efficiency is improved. Model tests show that the proposed method solves the singularity problem and reduces the number of grid cells by 80% compared to the uniform grid refinement.展开更多
The investigation on bubble behavior in electric field helps to analyze the mechanism of electric enhancement of boiling heat transfer. Experiments were performed to investigate the bubble deformation in direct curre...The investigation on bubble behavior in electric field helps to analyze the mechanism of electric enhancement of boiling heat transfer. Experiments were performed to investigate the bubble deformation in direct current （DC） electric field with bubbles attached to the orifice. The air bubbles were slowly generated in the transformer oil pool at different orifices, so that the effect of flow on bubble shape was eliminated. The results showed that the bubbles were elongated and the departure volume decreased when the electric field was intensified. The major and minor axes, aspect ratio and departure volume increased with increasing the orifice diameter. Both the electric field and orifice size have great influence on bubble behavior. The bubble deformation was also simulated to compare with the experimental results. The numerical and experimental data qualitatively agree with each other.展开更多
Directional solidification experiments were carried out with Al-Pb alloys under the effect of a direct current （DC）. The experimental results show that the DC causes a migration of the minority phase droplets （MPDs...Directional solidification experiments were carried out with Al-Pb alloys under the effect of a direct current （DC）. The experimental results show that the DC causes a migration of the minority phase droplets （MPDs） from the middle part to the surface region of the sample, Samples with either a finely dispersed microstructure or a shell/ core structure were obtained by solidifying the alloy under the effect of the properly selected DC densities, A model was developed to describe the microstructure evolution in an immiscible alloy directionaliy solidified under the effect of the DC. The microstructure formation in the AI-Pb alloys was calculated. The numerical results are in favorable agreement with the experimental ones. They demonstrate that the DC affects the microstructure formation mainly through changing the spatial motions of the MPDs and the temperature field of the melt in front of the solid/liquid interface. The formation mechanisms of the finely dispersed microstructure as well as the shell/core structure were sufficiently clarified.展开更多
As hundreds of millions of distributed devices appear in every corner of our lives for information collection and transmission in big data era,the biggest challenge is the energy supply for these devices and the signa...As hundreds of millions of distributed devices appear in every corner of our lives for information collection and transmission in big data era,the biggest challenge is the energy supply for these devices and the signal transmission of sensors.Triboelectric nanogenerator(TENG)as a new energy technology meets the increasing demand of today’s distributed energy supply due to its ability to convert the ambient mechanical energy into electric energy.Meanwhile,TENG can also be used as a sensing system.Direct current triboelectric nanogenerator(DC-TENG)can directly supply power to electronic devices without additional rectification.It has been one of the most important developments of TENG in recent years.Herein,we review recent progress in the novel structure designs,working mechanism and corresponding method to improve the output performance for DC-TENGs from the aspect of mechanical rectifier,tribovoltaic effect,phase control,mechanical delay switch and air-discharge.The basic theory of each mode,key merits and potential development are discussed in detail.At last,we provide a guideline for future challenges of DC-TENGs,and a strategy for improving the output performance for commercial applications.展开更多
Transcranial direct current stimulation(tDCS)has been reportedly beneficial for different neurodegenerative disorders.tDCS has been reported as a potential adjunctive or alternative treatment for auditory verbal hallu...Transcranial direct current stimulation(tDCS)has been reportedly beneficial for different neurodegenerative disorders.tDCS has been reported as a potential adjunctive or alternative treatment for auditory verbal hallucination(AVH).This study aims to review the effects of tDCS on AVH in patients with schizophrenia through combining the evidence from randomized clinical trials(RCTs).The databases of PsycINFO(2000–2019),PubMed(2000–2019),EMBASE(2000–2019),CINAHL(2000–2019),Web of Science(2000–2019),and Scopus(2000–2019)were systematically searched.The clinical trials with RCT design were selected for final analysis.A total of nine RCTs were eligible and included in the review.Nine RCTs were included in the final analysis.Among them,six RCTs reported a significant reduction of AVH after repeated sessions of tDCS,whereas three RCTs did not show any advantage of active tDCS over sham tDCS.The current studies showed an overall decrease of approximately 28%of AVH after active tDCS and 10%after sham tDCS.The tDCS protocols targeting the sensorimotor frontal-parietal network showed greater treatment effects compared with the protocols targeting other regions.In this regard,cathodal tDCS over the left temporoparietal area showed inhibitory effects on AVHs.The most effective tDCS protocol on AVHs was twice-daily sessions(2 mA,20-minute duration)over 5 consecutive days(10 sessions)with the anode over the left dorsolateral prefrontal cortex and the cathode over the left temporal area.Some patient-specific and diseasespecific factors such as young age,nonsmoking status,and higher frequencies of AVHs seemed to be the predictors of treatment response.Taken together,the results of tDCS as an alternative treatment option for AVH show controversy among current literatures,since not all studies were positive.However,the studies targeting the same site of the brain showed that the tDCS could be a promising treatment option to reduce AVH.Further RCTs,with larger sample sizes,should be conducted to reach a conclusion on the efficacy of tDCS for AVH and to develop an effective therapeutic protocol for clinical setting.展开更多
Objective:Emerging evidence shows the effectiveness of speech and language therapy(SLT);however,precise therapeutic parameters remain unclear.Evidence for the use of adjunctive transcranial direct current stimulation(...Objective:Emerging evidence shows the effectiveness of speech and language therapy(SLT);however,precise therapeutic parameters remain unclear.Evidence for the use of adjunctive transcranial direct current stimulation(t DCS)to treat post-stroke aphasia(PSA)is promising;however,the utility of combining t DCS and electroacupuncture(EA)has not yet been analyzed.This study assessed the therapeutic consequences of EA and t DCS coupled with SLT in subacute PSA patients who were also undergoing hyperbaric oxygen therapy(HBOT).Methods:A retrospective analysis was conducted on subacute(<6 months)PSA patients who were divided into three groups:patients who received EA plus t DCS(acupuncture group),patients who underwent t DCS(t DCS group),and patients who experienced conventional therapy(HBOT+SLT).All subjects underwent 21 days of treatment and also received conventional treatment.The aphasia battery of Chinese(ABC)was used to score pre-and post-intervention status.Results:The analysis comprised 238 patients.Cerebral infarction was the most frequent stroke type(137[57.6%]),while motor(66[27.7%])and global aphasia(60[25.2%])were the most common types of aphasia.After 21 days of intervention,the ABC scores of all patients were improved.The acupuncture group had the highest ABC scores,but only repetition,naming,and spontaneous speech were statistically improved(P<0.01).Post-hoc tests revealed significant improvement in word retrieval in the acupuncture and t DCS groups(P<0.01,P=0.037),while the acupuncture group had additional significant improvement in spontaneous conversation(P<0.01).Conclusion:Combining acupuncture and t DCS as an adjuvant therapy for subacute PSA led to significant spontaneous speech and word retrieval improvements.Future prospective,multi-ethnic,multi-center trials are warranted.展开更多
Transcranial direct current stimulation(tDCS)is a promising method for altering cortical excitability with clinical implications.It has been increasingly used in neurodevelopmental disorders,especially attention-defic...Transcranial direct current stimulation(tDCS)is a promising method for altering cortical excitability with clinical implications.It has been increasingly used in neurodevelopmental disorders,especially attention-deficit hyperactivity disorder(ADHD),but its efficacy(based on effect size calculations),safety,and stimulation parameters have not been systematically examined.In this systematic review,we aimed to(1)explore the effectiveness of tDCS on the clinical symptoms and neuropsychological deficits of ADHD patients,(2)evaluate the safety of tDCS application,especially in children with ADHD,(3)model the electrical field intensity in the target regions based on the commonly-applied and effective versus less-effective protocols,and(4)discuss and propose advanced tDCS parameters.Using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses approach,a literature search identified 14 empirical experiments investigating tDCS effects in ADHD.Partial improving effects of tDCS on cognitive deficits(response inhibition,working memory,attention,and cognitive flexibility)or clinical symptoms(e.g.,impulsivity and inattention)are reported in10 studies.No serious adverse effects are reported in 747 sessions of tDCS.The left and right dorsolateral prefrontal cortex are the regions most often targeted,and anodal tDCS the protocol most often applied.An intensity of 2 mA induced stronger electrical fields than 1 mA in adults with ADHD and was associated with significant behavioral changes.In ADHD children,however,the electrical field induced by 1 mA,which is likely larger than the electrical field induced by 1 mA in adults due to the smaller head size of children,was sufficient to result in significant behavioral change.Overall,tDCS seems to be a promising method for improving ADHD deficits.However,the clinical utility of tDCS in ADHD cannot yet be concluded and requires further systematic investigation in larger sample sizes.Cortical regions involved in ADHD pathophysiology,stimulation parameters(e.g.intensity,duration,polarity,and electrode size),and types of symptom/deficit are potential determinants of tDCS efficacy in ADHD.Developmental aspects of tDCS in childhood ADHD should be considered as well.展开更多
Inhibitory control of movement in motor learning requires the ability to suppress an inappropriate action, a skill needed to stop a planned or ongoing motor response in response to changes in a variety of environments...Inhibitory control of movement in motor learning requires the ability to suppress an inappropriate action, a skill needed to stop a planned or ongoing motor response in response to changes in a variety of environments. This study used a stop-signal task to determine whether transcranial direct-current stimulation over the pre-supplementary motor area alters the reaction time in motor inhibition. Forty healthy subjects were recruited for this study and were randomly assigned to either the transcranial direct-current stimulation condition or a sham-transcranial direct-current stimulation condition. All subjects consecutively performed the stop-signal task before, during, and after the delivery of anodal transcranial direct-current stimulation over the pre-supplementary motor area （pre-transcranial direct-current stimulation phase, transcranial direct-current stimulation phase, and post-transcranial direct-current stimulation phase）. Compared to the sham condition, there were significant reductions in the stop-signal processing times during and after transcranial direct-current stimulation, and change times were significantly greater in the transcranial direct-current stimulation condition. There was no significant change in go processing-times during or after transcranial direct-current stimulation in either condition. Anodal transcranial direct-current stimulation was feasibly coupled to an interactive improvement in inhibitory control. This coupling led to a decrease in the stop-signal process time required for the appropriate responses between motor execution and inhibition. However, there was no transcranial direct-current stimulation effect on the no-signal reaction time during the stop-signal task. Transcranial direct-current stimulation can adjust certain behaviors, and it could be a useful clinical intervention for patients who have difficulties with response inhibition.展开更多
Electrical potentials up to 800 mV can be observed between different metallic dental restorations. These potentials produce fields in the mouth that may interfere with microbial communities. The present study focuses ...Electrical potentials up to 800 mV can be observed between different metallic dental restorations. These potentials produce fields in the mouth that may interfere with microbial communities. The present study focuses on the impact of different electric field strengths （EFS） on the growth of Staphylococcus aureus （ATCC 25923） and Escherichia coil （ATCC 25922） in vitro. Cultures of S. aureus and E. coil in fluid and gel medium were exposed to different EFS. Effects were determined by calculation of viable counts and measurement of inhibition zones. In gel medium, anodic inhibition zones for S. aureuswere larger than those for E. coliat all field strength levels. In fluid medium, the maximum decrease in the viable count of S. aureus cells was at 10 V.m-1. Field-treated S. aureus cells presented ruptured cell walls and disintegrated cytoplasm. Conclusively, S. aureus is more sensitive to increasing electric field strength than E. coll.展开更多
Detecting, real-time monitoring and early warning of underground water-bearing structures are critically important issues in prevention and mitigation of water inrush hazards in underground engineering. Direct current...Detecting, real-time monitoring and early warning of underground water-bearing structures are critically important issues in prevention and mitigation of water inrush hazards in underground engineering. Direct current （DC） resistivity method is a widely used method for routine detection, advanced detection and real-time monitoring of water-bearing structures, due to its high sensitivity to groundwater. In this study, the DC resistivity method applied to underground engineering is reviewed and discussed, including the observation mode, multiple inversions, and real-time monitoring. It is shown that a priori information constrained inversion is desirable to reduce the non-uniqueness of inversion, with which the accuracy of detection can be significantly improved. The focused resistivity method is prospective for advanced detection;with this method, the flanking interference can be reduced and the detection dis-tance is increased subsequently. The time-lapse resistivity inversion method is suitable for the regions with continuous conductivity changes, and it can be used to monitor water inrush in those regions. Based on above-mentioned features of various methods in terms of benefits and limitations, we propose a three-dimensional （3D） induced polarization method characterized with multi-electrode array, and introduce it into tunnels and mines combining with real-time monitoring with time-lapse inversion and cross-hole resistivity method. At last, the prospective applications of DC resistivity method are discussed as follows： （1） available advanced detection technology and instrument in tunnel excavated by tunnel boring machine （TBM）, （2） high-resolution detection method in holes, （3） four-dimensional （4D） monitoring technology for water inrush sources, and （4） estimation of water volume in water-bearing structures.展开更多
Characteristics of a direct current （DC） discharge in atmospheric pressure helium are numerically investigated based on a one-dimensional fluid model. The results indicate that the discharge does not reach its stead...Characteristics of a direct current （DC） discharge in atmospheric pressure helium are numerically investigated based on a one-dimensional fluid model. The results indicate that the discharge does not reach its steady state till it takes a period of time. Moreover, the required time increases and the current density of the steady state decreases with increasing the gap width. Through analyzing the spatial distributions of the electron density, the ion density and the electric field at different discharge moments, it is found that the DC discharge starts with a Townsend regime, then transits to a glow regime. In addition, the discharge operates in a normal glow mode or an abnormal glow one under different parameters, such as the gap width, the ballast resistors, and the secondary electron emission coefficients, judged by its voltage-current characteristics.展开更多
The strategies that minimize the overall solution time of multiple linear systems in 3D finite element method (FEM) modeling of direct current (DC) resistivity were discussed. A global stiff matrix is assembled and st...The strategies that minimize the overall solution time of multiple linear systems in 3D finite element method (FEM) modeling of direct current (DC) resistivity were discussed. A global stiff matrix is assembled and stored in two parts separately. One part is associated with the volume integral and the other is associated with the subsurface boundary integral. The equivalent multiple linear systems with closer right-hand sides than the original systems were constructed. A recycling Krylov subspace technique was employed to solve the multiple linear systems. The solution of the seed system was used as an initial guess for the subsequent systems. The results of two numerical experiments show that the improved algorithm reduces the iterations and CPU time by almost 50%, compared with the classical preconditioned conjugate gradient method.展开更多
The nitrided layers mainly containing TiN dendrites were fabricated by direct current nitrogen arc melting method. The test results show that the layers are harder and more resistant to wear than the titanium substrat...The nitrided layers mainly containing TiN dendrites were fabricated by direct current nitrogen arc melting method. The test results show that the layers are harder and more resistant to wear than the titanium substrate. Arc traveling speeds and arc currents have an effect on both the microstructures and the properties of the layers. Decreasing the arc traveling speed or increasing the arc current can obviously enhance the hardness and the wear resistance of the nitrided layers.展开更多
基金supported by National Natural Science Foundation of China(82471564)YT is supported by National Natural Science Foundation of China(32322035,32171078).
文摘Background Pain sensitivity is critical for preventing non-suicidal self-injury(NSSI)behaviours;however,individuals engaging in such behaviours often exhibit decreased pain sensitivity,which may undermine this natural safeguard.The dorsolateral prefrontal cortex(DLPFC)is a key region involved in pain regulation,and recent approaches using transcranial direct current stimulation(tDCS)to target the DLPFC have shown potential for modulating pain processing and restoring normal pain perception for individuals engaging in NSSI behaviours.Aims This study aimed to explore the immediate and short-term effects of a single session of tDCS on pain sensitivity in individuals with NSSI,as well as its secondary effects on mood and NSSI-related factors.Methods In this randomised,double-blind,parallel,sham-controlled clinical trial,participants with a history of NSSI were randomly assigned to receive either active or sham tDCS.The intervention consisted of a single 20 min tDCS session targeting the left DLPFC.The primary outcome was pain sensitivity,measured by the pressure pain threshold(PPT)and heat pain score(HPS).Secondary and additional outcomes included NSSI urges,NSSI resistance,self-efficacy in resisting NSSI,mood-related variables and exploratory cognitive-affective processes such as rumination,self-criticism and self-perceived pain sensitivity,assessed at baseline,immediately post-intervention,and at 24 hours,1 week and 2 weeks follow-ups.Results For the primary outcomes,no significant differences between groups were observed for pain sensitivity(PPT,padj=0.812;HPS,padj=0.608).However,an exploratory sensitivity analysis treating each trial as an individual observation revealed a significant effect on HPS(padj=0.036).For the secondary and additional outcomes,although there were initial improvements in joyful feelings and reductions in negative affect at 2 weeks post-intervention,these effects did not remain significant after multiple comparison corrections.Notably,reductions in rumination were statistically significant at both 1-week and 2-week follow-ups(1 week,p_(adj)=0.040;2 weeks,p_(adj)=0.042).There were no significant effects on NSSI urges,NSSI resistance,self-efficacy in resisting NSSI or self-criticism.Conclusions A single session of tDCS over the left DLPFC did not produce significant changes in pain sensitivity in individuals with NSSI.A sensitivity analysis indicated an effect on heat pain sensitivity,possibly reflecting changes in brain activity,warranting confirmation through neuroimaging.These findings suggest that tDCS warrants further investigation for its potential to influence pain-related cognitive-affective processes in individuals with NSSI.
基金supported by Key Natural Science Research Projects of Colleges and Universities in Anhui Province(2022AH051831).
文摘The integration of large-scale new energy and high-capacity DC transmission leads to a reduction in system inertia.Grid-forming renewable energy sources(GF-RES)has a significant improvement effect on system inertia.Commutation failure faults may cause a short-term reactive power surplus at the sending end and trigger transient overvoltage,threatening the safe and stable operation of the power grid.However,there is a lack of research on the calculation method of transient overvoltage caused by commutation failure in high-voltage DC transmission systems with grid-forming renewable energy sources integration.Based on the existing equivalent model of highvoltage DC transmission systems at the sending end,this paper proposes to construct a model of the high-voltage DC transmission system at the sending end with grid-forming renewable energy sources.The paper first clarifies the mechanism of overvoltage generation,then considers the reactive power droop control characteristics of GF-RES,and derives the transient voltage calculation model of theDC transmission system with GF-RES integration.It also proposes a calculation method for transient overvoltage at the sending-end converter bus with GF-RES integration.Based on the PSCAD/EMTDC simulation platform,this paper builds an experimental simulation model.By constructing three different experimental scenarios,the accuracy and effectiveness of the proposed transient overvoltage calculation method are verified,with a calculation error within 5%.At the same time,this paper quantitatively analyzes the impact of grid strength,new energy proportion,and rated transmission power on transient overvoltage from three different perspectives.
基金the National Natural Science Foundation of China(51974155)the Outstanding Young Scientific and Technological Talents Project of University of Science and Technology Liaoning(2023YQ07)+4 种基金the University of Science and Technology Liaoning Young Foundation(2018QN06)National Natural Science Foundation of China(51774178)the National Key Research and Development Program(2021YFB3702005)the Central Government Guides Local Science and Technology Development Fund Projects(2023JH6/100100046)the Liaoning Provincial Department of Education Basic Research Projects for Universities(JYTQN2023242).
文摘Herein,the effect of direct current(DC)attached the mold on refining the microstructure and alleviating the central segregation of a tin–bismuth(Sn–10 wt.%Bi)alloy ingot during the solidification process has been investigated.The experiment used a self-made device,which can achieve the effect of refining the solidified structure and alleviate the segregation of the metal casting.Numerical simulations were performed to calculate the Lorentz force,Joule heating and induced melt vortex flow for the magneto-hydrodynamic case.Our results show that the maximum velocity of the global electro-vortex reached 0.017 m s^(–1).The DC-induced electro-vortex was found to be the primary reason of refining the equiaxed grain and alleviating the segregation of theβ-Sn crystal boundary.The grain refining effect observed in these experiments can be solely attributed to the forced melt flow driven by the Lorentz force.DC field attached the mold can lead to grain refinement and alleviate the segregation of the ingot via a global vortex.The technology can be applied not only to opened molds,but also toward improving the quality in closed molds.
文摘BACKGROUND Postoperative delirium(POD),an acute neuropsychiatric complication in elderly surgical patients,manifests as attention and cognitive disturbances that may last 24-72 hours after surgery,potentially progressing to dementia.Transcranial direct current stimulation(tDCS),a non-invasive neuromodulation technique,enhances cortical excitability and cognitive function by modulating brain networks and synaptic plasticity.Elderly patients undergoing major laparoscopic surgery face elevated POD risks due to prolonged anesthesia and pneumoperitoneum-induced cerebral hypoperfusion.This study investigates whether pre-anesthesia tDCS can reduce POD incidence in this population.AIM To investigate the effect of preoperative tDCS on reducing the incidence of POD in elderly patients undergoing major laparoscopic surgery.METHODS In this study,we enrolled 220 elderly patients who underwent major laparoscopic surgery between April 2024 and December 2024.Patients were randomly assigned to the active-tDCS(group A)and sham-tDCS(group S)groups.A single session of tDCS or sham stimulation was administered 30 minutes before anesthesia induction.The primary outcome was the incidence of POD during within 3 days postoperatively.RESULTS A total of 201 patients were included in the final analysis,with 100 patients in group A and 101 in group S.The incidence of POD within 3 days postoperatively was 7.0%in group A,which was significantly lower than 22.8%in group S.On postoperative day 1,the Self-Rating Anxiety Scale and Self-Rating Depression Scale scores significantly differed between the two groups,but the pain scores showed no significant difference.CONCLUSION A single session of preoperative tDCS can reduce the incidence of POD in elderly patients undergoing major laparoscopic surgery and can also reduce postoperative anxiety and depression in these patients.
文摘BACKGROUND Schizophrenia is a chronic psychiatric condition with complex symptomatology,including debilitating auditory hallucinations.Transcranial direct current stimulation(tDCS)has been explored as an adjunctive treatment to alleviate such symptoms.AIM To evaluate the therapeutic efficacy of tDCS in schizophrenia.METHODS Adhering to PRISMA guidelines,we systematically searched PubMed,Embase,Web of Science,and the Cochrane Library on September 19,2023,for randomized controlled trials examining the efficacy of tDCS in schizophrenia,with no language or time restrictions.We included studies that compared tDCS with a control condition and reported clinically relevant outcomes.Data extraction and quality assessments were performed by independent evaluators using the Cochrane Collaboration's risk of bias tool.Statistical heterogeneity was evaluated,and a random-effects model was applied due to moderate heterogeneity(I2=41.3%).RESULTS Nine studies comprising 425 participants(tDCS group:219,control group:206)were included.The meta-analysis demonstrated a significant reduction in auditory hallucination scores following tDCS treatment(weighted mean difference:-2.18,95%confidence interval:-4.0 to-0.29,P<0.01).Sensitivity analysis confirmed the robustness of the results,with no significant influence from individual studies.Additionally,publication bias was not detected,supporting the reliability and generalizability of the findings.These results underscore the efficacy of tDCS as a therapeutic intervention for auditory hallucinations in schizophrenia.CONCLUSION tDCS significantly reduces auditory hallucinations in schizophrenia,suggesting its potential as an effective adjunctive treatment for managing this disabling symptom.The findings highlight the practical significance of tDCS in clinical settings,particularly for patients with treatment-resistant auditory hallucinations.
基金Project(50871044)supported by the National Natural Science Foundation of ChinaProject(2012M511207)supported by the Postdoctoral Science Foundation of ChinaProject(10122011)supported by the Science Research Foundation of Wuhan Institute Technology,China
文摘Effect of direct current electric field （DCEF） on corrosion behaviour of copper printed circuit board （PCB-Cu）, Cl-ion migration behaviour, dendrites growth under thin electrolyte layer was investigated using potentiodynamic polarization and scanning electron microscopy （SEM） with energy dispersive spectrometer （EDS）. Results indicate that DCEF decreases the corrosion of PCB-Cu;Cl-ions directionally migrate from the negative pole to the positive pole, and enrich on the surface of the positive pole, which causes serious localized corrosion; dendrites grow on the surface of the negative pole, and the rate and scale of dendrite growth become faster and greater with the increase of external voltage and exposure time, respectively.
基金Projects(51074031,51271042,50874022)supported by the National Natural Science Foundation of ChinaProject(2013M530913)supported by the China Postdoctoral Science FoundationProject(DUT12RC(3)35)supported by the Fundamental Research Funds for the Central Universities of China
文摘The combined effects of direct current pulsed magnetic field （DC-PMF） and inoculation on pure aluminum were investigated, the grain refinement behavior of DC-PMF and inoculation was discussed. The experimental results indicate that the solidification micro structure of pure aluminum can be greatly refined under DC-PMF. Refinement of pure aluminum is attributed to electromagnetic undercooling and forced convection caused by DC-PMF. With single DC-PMF, the grain size in the equiaxed zone is uneven. However, under DC-PMF, by adding 0.05% （mass fraction） Al5Ti-B, the grain size of the sample is smaller, and the size distribution is more uniform than that of single DC-PMF. Furthermore, under the combination of DC-PMF and inoculation, with the increase of output current, the grain size is further reduced. When the output current increases to 100 A, the average grain size can decrease to 113 μn.
基金financially supported by the National Natural Science Foundation of China(No.41574127 and 41174104)the National Key Technology R&D Program for the 13th five-year plan(No.2016ZX05018006-006)
文摘To deal with the problem of low computational precision at the nodes near the source and satisfy the requirements for computational efficiency in inversion imaging and finite-element numerical simulations of the direct current method, we propose a new mesh refinement and recoarsement method for a two-dimensional point source. We introduce the mesh refinement and mesh recoarsement into the traditional structured mesh subdivision. By refining the horizontal grids, the singularity owing to the point source is minimized and the topography is simulated. By recoarsening the horizontal grids, the number of grid cells is reduced significantly and computational efficiency is improved. Model tests show that the proposed method solves the singularity problem and reduces the number of grid cells by 80% compared to the uniform grid refinement.
基金the National Key Basic Research Program of China (G2000026301)Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Tsinghua University, China
文摘The investigation on bubble behavior in electric field helps to analyze the mechanism of electric enhancement of boiling heat transfer. Experiments were performed to investigate the bubble deformation in direct current （DC） electric field with bubbles attached to the orifice. The air bubbles were slowly generated in the transformer oil pool at different orifices, so that the effect of flow on bubble shape was eliminated. The results showed that the bubbles were elongated and the departure volume decreased when the electric field was intensified. The major and minor axes, aspect ratio and departure volume increased with increasing the orifice diameter. Both the electric field and orifice size have great influence on bubble behavior. The bubble deformation was also simulated to compare with the experimental results. The numerical and experimental data qualitatively agree with each other.
基金the financial support from the National Natural Science Foundation of China(Nos. 51071159,51031003,51271185 and u0837601)
文摘Directional solidification experiments were carried out with Al-Pb alloys under the effect of a direct current （DC）. The experimental results show that the DC causes a migration of the minority phase droplets （MPDs） from the middle part to the surface region of the sample, Samples with either a finely dispersed microstructure or a shell/ core structure were obtained by solidifying the alloy under the effect of the properly selected DC densities, A model was developed to describe the microstructure evolution in an immiscible alloy directionaliy solidified under the effect of the DC. The microstructure formation in the AI-Pb alloys was calculated. The numerical results are in favorable agreement with the experimental ones. They demonstrate that the DC affects the microstructure formation mainly through changing the spatial motions of the MPDs and the temperature field of the melt in front of the solid/liquid interface. The formation mechanisms of the finely dispersed microstructure as well as the shell/core structure were sufficiently clarified.
基金supported by The National Key R&D Project from Minister of Science and Technology(2021YFA1201602)the National Natural Science Foundation of China(U21A20147,52073037).
文摘As hundreds of millions of distributed devices appear in every corner of our lives for information collection and transmission in big data era,the biggest challenge is the energy supply for these devices and the signal transmission of sensors.Triboelectric nanogenerator(TENG)as a new energy technology meets the increasing demand of today’s distributed energy supply due to its ability to convert the ambient mechanical energy into electric energy.Meanwhile,TENG can also be used as a sensing system.Direct current triboelectric nanogenerator(DC-TENG)can directly supply power to electronic devices without additional rectification.It has been one of the most important developments of TENG in recent years.Herein,we review recent progress in the novel structure designs,working mechanism and corresponding method to improve the output performance for DC-TENGs from the aspect of mechanical rectifier,tribovoltaic effect,phase control,mechanical delay switch and air-discharge.The basic theory of each mode,key merits and potential development are discussed in detail.At last,we provide a guideline for future challenges of DC-TENGs,and a strategy for improving the output performance for commercial applications.
文摘Transcranial direct current stimulation(tDCS)has been reportedly beneficial for different neurodegenerative disorders.tDCS has been reported as a potential adjunctive or alternative treatment for auditory verbal hallucination(AVH).This study aims to review the effects of tDCS on AVH in patients with schizophrenia through combining the evidence from randomized clinical trials(RCTs).The databases of PsycINFO(2000–2019),PubMed(2000–2019),EMBASE(2000–2019),CINAHL(2000–2019),Web of Science(2000–2019),and Scopus(2000–2019)were systematically searched.The clinical trials with RCT design were selected for final analysis.A total of nine RCTs were eligible and included in the review.Nine RCTs were included in the final analysis.Among them,six RCTs reported a significant reduction of AVH after repeated sessions of tDCS,whereas three RCTs did not show any advantage of active tDCS over sham tDCS.The current studies showed an overall decrease of approximately 28%of AVH after active tDCS and 10%after sham tDCS.The tDCS protocols targeting the sensorimotor frontal-parietal network showed greater treatment effects compared with the protocols targeting other regions.In this regard,cathodal tDCS over the left temporoparietal area showed inhibitory effects on AVHs.The most effective tDCS protocol on AVHs was twice-daily sessions(2 mA,20-minute duration)over 5 consecutive days(10 sessions)with the anode over the left dorsolateral prefrontal cortex and the cathode over the left temporal area.Some patient-specific and diseasespecific factors such as young age,nonsmoking status,and higher frequencies of AVHs seemed to be the predictors of treatment response.Taken together,the results of tDCS as an alternative treatment option for AVH show controversy among current literatures,since not all studies were positive.However,the studies targeting the same site of the brain showed that the tDCS could be a promising treatment option to reduce AVH.Further RCTs,with larger sample sizes,should be conducted to reach a conclusion on the efficacy of tDCS for AVH and to develop an effective therapeutic protocol for clinical setting.
文摘Objective:Emerging evidence shows the effectiveness of speech and language therapy(SLT);however,precise therapeutic parameters remain unclear.Evidence for the use of adjunctive transcranial direct current stimulation(t DCS)to treat post-stroke aphasia(PSA)is promising;however,the utility of combining t DCS and electroacupuncture(EA)has not yet been analyzed.This study assessed the therapeutic consequences of EA and t DCS coupled with SLT in subacute PSA patients who were also undergoing hyperbaric oxygen therapy(HBOT).Methods:A retrospective analysis was conducted on subacute(<6 months)PSA patients who were divided into three groups:patients who received EA plus t DCS(acupuncture group),patients who underwent t DCS(t DCS group),and patients who experienced conventional therapy(HBOT+SLT).All subjects underwent 21 days of treatment and also received conventional treatment.The aphasia battery of Chinese(ABC)was used to score pre-and post-intervention status.Results:The analysis comprised 238 patients.Cerebral infarction was the most frequent stroke type(137[57.6%]),while motor(66[27.7%])and global aphasia(60[25.2%])were the most common types of aphasia.After 21 days of intervention,the ABC scores of all patients were improved.The acupuncture group had the highest ABC scores,but only repetition,naming,and spontaneous speech were statistically improved(P<0.01).Post-hoc tests revealed significant improvement in word retrieval in the acupuncture and t DCS groups(P<0.01,P=0.037),while the acupuncture group had additional significant improvement in spontaneous conversation(P<0.01).Conclusion:Combining acupuncture and t DCS as an adjuvant therapy for subacute PSA led to significant spontaneous speech and word retrieval improvements.Future prospective,multi-ethnic,multi-center trials are warranted.
基金This review was supported by the Department of Psychology and Neurosciences,Leibniz-Institut fiir Arbeitsforschung Ministry of Science,Research and Technology,Deputy of Scholarship and Students Affairs,Iran(95000171)the German Ministry of Research and Education(German Center for Brain Stimulation grant number 01EE1403C).
文摘Transcranial direct current stimulation(tDCS)is a promising method for altering cortical excitability with clinical implications.It has been increasingly used in neurodevelopmental disorders,especially attention-deficit hyperactivity disorder(ADHD),but its efficacy(based on effect size calculations),safety,and stimulation parameters have not been systematically examined.In this systematic review,we aimed to(1)explore the effectiveness of tDCS on the clinical symptoms and neuropsychological deficits of ADHD patients,(2)evaluate the safety of tDCS application,especially in children with ADHD,(3)model the electrical field intensity in the target regions based on the commonly-applied and effective versus less-effective protocols,and(4)discuss and propose advanced tDCS parameters.Using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses approach,a literature search identified 14 empirical experiments investigating tDCS effects in ADHD.Partial improving effects of tDCS on cognitive deficits(response inhibition,working memory,attention,and cognitive flexibility)or clinical symptoms(e.g.,impulsivity and inattention)are reported in10 studies.No serious adverse effects are reported in 747 sessions of tDCS.The left and right dorsolateral prefrontal cortex are the regions most often targeted,and anodal tDCS the protocol most often applied.An intensity of 2 mA induced stronger electrical fields than 1 mA in adults with ADHD and was associated with significant behavioral changes.In ADHD children,however,the electrical field induced by 1 mA,which is likely larger than the electrical field induced by 1 mA in adults due to the smaller head size of children,was sufficient to result in significant behavioral change.Overall,tDCS seems to be a promising method for improving ADHD deficits.However,the clinical utility of tDCS in ADHD cannot yet be concluded and requires further systematic investigation in larger sample sizes.Cortical regions involved in ADHD pathophysiology,stimulation parameters(e.g.intensity,duration,polarity,and electrode size),and types of symptom/deficit are potential determinants of tDCS efficacy in ADHD.Developmental aspects of tDCS in childhood ADHD should be considered as well.
基金supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology of Korea of Republic, No. 2012R1A1B4003477
文摘Inhibitory control of movement in motor learning requires the ability to suppress an inappropriate action, a skill needed to stop a planned or ongoing motor response in response to changes in a variety of environments. This study used a stop-signal task to determine whether transcranial direct-current stimulation over the pre-supplementary motor area alters the reaction time in motor inhibition. Forty healthy subjects were recruited for this study and were randomly assigned to either the transcranial direct-current stimulation condition or a sham-transcranial direct-current stimulation condition. All subjects consecutively performed the stop-signal task before, during, and after the delivery of anodal transcranial direct-current stimulation over the pre-supplementary motor area （pre-transcranial direct-current stimulation phase, transcranial direct-current stimulation phase, and post-transcranial direct-current stimulation phase）. Compared to the sham condition, there were significant reductions in the stop-signal processing times during and after transcranial direct-current stimulation, and change times were significantly greater in the transcranial direct-current stimulation condition. There was no significant change in go processing-times during or after transcranial direct-current stimulation in either condition. Anodal transcranial direct-current stimulation was feasibly coupled to an interactive improvement in inhibitory control. This coupling led to a decrease in the stop-signal process time required for the appropriate responses between motor execution and inhibition. However, there was no transcranial direct-current stimulation effect on the no-signal reaction time during the stop-signal task. Transcranial direct-current stimulation can adjust certain behaviors, and it could be a useful clinical intervention for patients who have difficulties with response inhibition.
文摘Electrical potentials up to 800 mV can be observed between different metallic dental restorations. These potentials produce fields in the mouth that may interfere with microbial communities. The present study focuses on the impact of different electric field strengths （EFS） on the growth of Staphylococcus aureus （ATCC 25923） and Escherichia coil （ATCC 25922） in vitro. Cultures of S. aureus and E. coil in fluid and gel medium were exposed to different EFS. Effects were determined by calculation of viable counts and measurement of inhibition zones. In gel medium, anodic inhibition zones for S. aureuswere larger than those for E. coliat all field strength levels. In fluid medium, the maximum decrease in the viable count of S. aureus cells was at 10 V.m-1. Field-treated S. aureus cells presented ruptured cell walls and disintegrated cytoplasm. Conclusively, S. aureus is more sensitive to increasing electric field strength than E. coll.
基金supported by the National Program on Key Basic Research Project of China (973 Program) (Nos. 2013CB036002 and 2014CB046901)the National Key Technology R&D Program of the Ministry of Science and Technology of China (No. 2013BAK06B01)the National Natural Science Foundation of China (No. 51139004)
文摘Detecting, real-time monitoring and early warning of underground water-bearing structures are critically important issues in prevention and mitigation of water inrush hazards in underground engineering. Direct current （DC） resistivity method is a widely used method for routine detection, advanced detection and real-time monitoring of water-bearing structures, due to its high sensitivity to groundwater. In this study, the DC resistivity method applied to underground engineering is reviewed and discussed, including the observation mode, multiple inversions, and real-time monitoring. It is shown that a priori information constrained inversion is desirable to reduce the non-uniqueness of inversion, with which the accuracy of detection can be significantly improved. The focused resistivity method is prospective for advanced detection;with this method, the flanking interference can be reduced and the detection dis-tance is increased subsequently. The time-lapse resistivity inversion method is suitable for the regions with continuous conductivity changes, and it can be used to monitor water inrush in those regions. Based on above-mentioned features of various methods in terms of benefits and limitations, we propose a three-dimensional （3D） induced polarization method characterized with multi-electrode array, and introduce it into tunnels and mines combining with real-time monitoring with time-lapse inversion and cross-hole resistivity method. At last, the prospective applications of DC resistivity method are discussed as follows： （1） available advanced detection technology and instrument in tunnel excavated by tunnel boring machine （TBM）, （2） high-resolution detection method in holes, （3） four-dimensional （4D） monitoring technology for water inrush sources, and （4） estimation of water volume in water-bearing structures.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11575050 and 10805013)the Midwest Universities Comprehensive Strength Promotion Project+1 种基金the Natural Science Foundation of Hebei Province,China(Grant Nos.A2016201042 and A2015201092)the Research Foundation of Education Bureau of Hebei Province,China(Grant No.LJRC011)
文摘Characteristics of a direct current （DC） discharge in atmospheric pressure helium are numerically investigated based on a one-dimensional fluid model. The results indicate that the discharge does not reach its steady state till it takes a period of time. Moreover, the required time increases and the current density of the steady state decreases with increasing the gap width. Through analyzing the spatial distributions of the electron density, the ion density and the electric field at different discharge moments, it is found that the DC discharge starts with a Townsend regime, then transits to a glow regime. In addition, the discharge operates in a normal glow mode or an abnormal glow one under different parameters, such as the gap width, the ballast resistors, and the secondary electron emission coefficients, judged by its voltage-current characteristics.
基金Projects(40974077,41164004)supported by the National Natural Science Foundation of ChinaProject(2007AA06Z134)supported by the National High Technology Research and Development Program of China+2 种基金Projects(2011GXNSFA018003,0832263)supported by the Natural Science Foundation of Guangxi Province,ChinaProject supported by Program for Excellent Talents in Guangxi Higher Education Institution,ChinaProject supported by the Foundation of Guilin University of Technology,China
文摘The strategies that minimize the overall solution time of multiple linear systems in 3D finite element method (FEM) modeling of direct current (DC) resistivity were discussed. A global stiff matrix is assembled and stored in two parts separately. One part is associated with the volume integral and the other is associated with the subsurface boundary integral. The equivalent multiple linear systems with closer right-hand sides than the original systems were constructed. A recycling Krylov subspace technique was employed to solve the multiple linear systems. The solution of the seed system was used as an initial guess for the subsequent systems. The results of two numerical experiments show that the improved algorithm reduces the iterations and CPU time by almost 50%, compared with the classical preconditioned conjugate gradient method.
文摘The nitrided layers mainly containing TiN dendrites were fabricated by direct current nitrogen arc melting method. The test results show that the layers are harder and more resistant to wear than the titanium substrate. Arc traveling speeds and arc currents have an effect on both the microstructures and the properties of the layers. Decreasing the arc traveling speed or increasing the arc current can obviously enhance the hardness and the wear resistance of the nitrided layers.
