Continuous Separation of Multiple Size Microparticles using Alternating Current Dielectrophoresis in Microfluidic Device with Acupuncture Needle Electrodes

The need to continuously separate multiple microparticles is required for the recent development of lab-on-chip technology. Dielectrophoresis（DEP）-based separation device is extensively used in kinds of microfluidic applications. However, such conventional DEP-based device is relatively complicated and difficult for fabrication. A concise microfluidic device is presented for effective continuous separation of multiple size particle mixtures. A pair of acupuncture needle electrodes are creatively employed and embedded in a PDMS（poly-dimethylsiloxane） hurdle for generating non-uniform electric field thereby achieving a continuous DEP separation. The separation mechanism is that the incoming particle samples with different sizes experience different negative DEP（n DEP） forces and then they can be transported into different downstream outlets. The DEP characterizations of particles are calculated, and their trajectories are numerically predicted by considering the combined action of the incoming laminar flow and the n DEP force field for guiding the separation experiments. The device performance is verified by successfully separating a three-sized particle mixture, including polystyrene microspheres with diameters of 3 μm, 10 μm and 25 μm. The separation purity is below 70% when the flow rate ratio is less than 3.5 or more than 5.1, while the separation purity can be up to more than 90% when the flow rate ratio is between 3.5 and 5.1 and meanwhile ensure the voltage output falls in between 120 V and 150 V. Such simple DEP-based separation device has extensive applications in future microfluidic systems.

Time-resolved characteristics of a nanosecond pulsed multi-hollow needle plate packed bed dielectric barrier discharge

In this paper,self-designed multi-hollow needle electrodes are used as a high-voltage electrode in a packed bed dielectric barrier discharge reactor to facilitate fast gas flow through the active discharge area and achieve large-volume stable discharge.The dynamic characteristics of the plasma,the generated active species,and the energy transfer mechanisms in both positive discharge(PD)and negative discharge(ND)are investigated by using fast-exposure intensified charge coupled device(ICCD)images and time-resolved optical emission spectra.The experimental results show that the discharge intensity,number of discharge channels,and discharge volume are obviously enhanced when the multi-needle electrode is replaced by a multihollow needle electrode.During a single voltage pulse period,PD mainly develops in a streamer mode,which results in a stronger discharge current,luminous intensity,and E/N compared with the diffuse mode observed in ND.In PD,as the gap between dielectric beads changes from 0 to250μm,the discharge between the dielectric bead gap changes from a partial discharge to a standing filamentary micro-discharge,which allows the plasma to leave the local area and is conducive to the propagation of surface streamers.In ND,the discharge only appears as a diffusionlike mode between the gap of dielectric beads,regardless of whether there is a discharge gap.Moreover,the generation of excited states N_(2)^(+)(B^(2)∑_(u)^(+))and N2(C^(3)Π_(u))is mainly observed in PD,which is attributed to the higher E/N in PD than that in ND.However,the generation of the OH(A^(2)∑^(+))radical in ND is higher than in PD.It is not directly dominated by E/N,but mainly by the resonant energy transfer process between metastable N_(2)(A^(3)∑_(u)^(+))and OH(X^(2)Π).Furthermore,both PD and ND demonstrate obvious energy relaxation processes of electron-to-vibration and vibration-to-vibration,and no vibration-to-rotation energy relaxation process is observed.

Quantitating Changes in Jitter and Spike Number Using Concentric Needle Electrodes in Amyotrophic Lateral Sclerosis Patients

Background： Single-fiber electromyography （SFEMG） has been suggested as a quantitative method for supporting chronic partial denervation in amyotrophic lateral sclerosis （ALS） by the revised El Escorial criteria. Although concentric needle （CN） electrodes have been used to assess jitter in myasthenia gravis patients and healthy controls, there are few reports using CN electrodes to assess motor unit instability and denervation in neurogenic diseases. The aim of this study was to determine whether quantitative changes in jitter and spike number using CN electrodes could be used for ALS studies. Methods： Twenty-seven healthy controls and 23 ALS patients were studied using both CN and single-fiber needle （SFN） electrodes on the extensor digitorum communis muscle with an SFEMG program. The SFN-jitter and SFN-fiber density data were measured using SFN electrodes. The CN-jitter and spike number were measured using CN electrodes. Results： The mean CN-j itter was significantly increased in ALS patients （47.3 ±17.0 μs） than in healthy controls （27.4 ± 3.3 las） （P 〈 0.001 ）. Besides, the mean spike number was significantly increased in ALS patients （2.5 ± 0.5） than in healthy controls （1.7 ± 0.3） （P 〈 0.001）. The sensitivity and specificity in the diagnosis of ALS were 82.6% and 92.6% for CN-jitter （cut-offvalue： 32 gs）, and 91.3% and 96.3% for the spike number （cut-off value： 2.0）, respectively. There was no significant difference between the SFN-jitter and CN-jitter in ALS patients; meanwhile, there was no significant difference between the SFN-jitter and CN-jitter in healthy controls. Conclusion： CN-jitter and spike number could be used to quantitatively evaluate changes due to denervation-reinnervation in ALS.

Jitter analysis with concentric needle electrodes in the extensor digitorum communis for the diagnosis of myasthenia gravis：a pilot study

Background Single-fiber electromyography is the most sensitive neurophysiological test for the diagnosis of myasthenia gravis （MG）,but its use is limited by the potential risk of transmission of infections.Jitter analysis with disposable concentric needle electrodes （CNEs） is therefore being investigated.This pilot study aimed to evaluate jitter analysis with CNEs for the diagnosis of MG.Methods Forty-two healthy Chinese volunteers and 44 MG patients were prospectively enrolled.MG patients were classified according to the Osserman classification,and acetylcholine receptor antibody titer was measured.Jitter analysis with CNEs in the extensor digitorum communis and repetitive nerve stimulation （RNS） testing were performed.Jitter was expressed as the mean consecutive difference （MCD）,and 20 action potential pairs were analyzed in each subject.The mean MCD in each subject and the mean individual MCD of all action potential pairs were compared between groups.Results The mean MCD and mean individual MCD were higher in MG patients （（42.3±20.0） μs and （42.2±26.0） μs） than in healthy volunteers （（23.0±3.1） μs and （22.8±7.5） μs）.The area under the receiver operating characteristic curve for the mean MCD of MG patients and healthy volunteers combined was 0.85.The mean MCD and mean individual MCDwere higher in generalized MG patients （（64.1±18.5） μs and （63.6±30.0） μs） than in ocular MG patients （（33.1±12.0） μs and （33.2±17.6） μs）,and were higher in MG patients with abnormal RNS results （（57.2±18.3） μs and （57.3±29.2） μs） than in MG patients with normal RNS results （（32.9±14.8） μs and （32.7±18.3） μs）.Abnormal RNS results were observed in 38.60% （17/44） of MG patients and abnormal jitter were observed in 72.70% （32/44） of MG patients.Conclusion Jitter analysis with CNEs is feasible for the diagnosis of MG.

Multi-point discharge model: study on corona discharge of double-ended needle in large space

Corona discharge, as a common means to obtain non-equilibrium plasma, can generally obtain high-concentration plasma by increasing discharge points to meet production needs. However,the existing numerical simulation models used to study multi-point corona discharge are all calculations of small-scale space models, which cannot obtain the distribution characteristics of plasma in large space. Based on our previous research, this paper proposes a hybrid model for studying the distribution of multi-point discharge plasma in large-scale spaces, which divides the computational domain and computes separately with the hydrodynamic model and the ion mobility model. The simulation results are verified by a needle–ball electrode device. Firstly, the electric field distribution and plasma distribution of the needle electrodes with single tip and double tips are compared and discussed. Secondly, the plasma distribution of the needle electrode with the double tip at different voltages is investigated. Both computational and experimental results indicate that the charged particle concentration and current of the needle electrode with double tips are both twice as high as those of the needle electrode with a single tip. This model can extend the computational area of the multi-point corona discharge finite element model to the sub-meter(25 cm) or meter level, which provides an effective means to study the plasma distribution generated by multiple discharge points in large-scale space.

Characteristics of Partial Discharge in Oil-paper Insulated Needle Plate Electrode Model Under Composite AC-DC Voltage

Converter transformers are the core device in ultrahigh voltage direct current(UHVDC)transmission systems,and the oil-paper insulation at its rectifying valve side deals with the composite AC-DC voltage.A detailed investigation of the partial discharge(PD)mechanism in the oil-paper insulation under the composite AC-DC voltage is,therefore,very important.The oilpaper insulated needle plate electrode simulation model for the electric field and charge distribution can be established using hydrodynamic drift-diffusion theory and bipolar charge carrier theory,and the simulation results can reflect the morphological changes of PD.The development characteristics of PD under composite AC-DC voltage are researched.In addition,the effects of simulation time,the AC-DC component proportion,and model parameters on PD are also explored.Results indicate that differences in applied voltage,interface charge,and geometry structure can cause changes in the electric field strength,which consequently influences the PD process in the simulation model.Oil-immersed paperboard is a type of liquid-immersed dielectric(LID).When the LID is arranged in perpendicular,only the positive streamers have narrow channels oriented toward the LID.When the LID is arranged in parallel,the PDs are in the form of creeping discharges and the negative streamers are more dispersed.The development characteristics of PD and its influencing factors reported here may provide theoretical and simulation support to explain the physical mechanism of PD at the rectifying valve side of the converter transformer.