Transition from a filamentary mode to a diffuse one with varying distance from needle to stream of an argon plasma jet

Plasma jet has extensive application potentials in various fields, which normally operates in a diffuse mode when helium is used as the working gas. However, when less expensive argon is used, the plasma jet often operates in a filamentary mode. Compared to the filamentary mode, the diffuse mode is more desirable for applications. Hence, many efforts have been exerted to accomplish the diffuse mode of the argon plasma jet. In this paper, a novel single-needle argon plasma jet is developed to obtain the diffuse mode. It is found that the plasma jet operates in the filamentary mode when the distance from the needle tip to the central line of the argon stream(d) is short. It transits to the diffuse mode with increasing d. For the diffuse mode, there is always one discharge pulse per voltage cycle, which initiates at the rising edge of the positive voltage. For comparison, the number of discharge pulse increases with an increase in the peak voltage for the filamentary mode. Fast photography reveals that the plasma plume in the filamentary mode results from a guided positive streamer,which propagates in the argon stream. However, the plume in the diffuse mode originates from a branched streamer, which propagates in the interfacial layer between the argon stream and the surrounding air. By optical emission spectroscopy,plasma parameters are investigated for the two discharge modes, which show a similar trend with increasing d. The diffuse mode has lower electron temperature, electron density, vibrational temperature, and gas temperature compared to the filamentary mode.

Growth mechanism and characteristics of electron drift instability in Hall thruster with different propellant types

The existence of a significant electron drift instability(EDI) in the Hall thruster is considered as one of the possible causes of the abnormal increase in axial electron mobility near the outlet of the channel. In recent years, extensive simulation research on the characteristics of EDI has been conducted, but the excitation mechanism and growth mechanism of EDI in linear stage and nonlinear stage remain unclear. In this work, a one-dimensional PIC model in the azimuthal direction of the thruster near-exit region is established to gain further insights into the mechanism of the EDI in detail, and the effects of different types of propellants on EDI characteristics are discussed. The changes in axial electron transport caused by EDI under different types of propellants and electromagnetic field strengths are also examined. The results indicate that EDI undergoes a short linear growth phase before transitioning to the nonlinear phase and finally reaching saturation through the ion Landau damping. The EDI drives a significant ion heating in the azimuthal direction through electron–ion friction before entering the quasi-steady state, which increases the axial mobility of the electrons. Using lighter atomic weight propellant can effectively suppress the oscillation amplitude of EDI, but it will increase the linear growth rate, frequency, and phase velocity of EDI. Compared with the classical mobility, the axial electron mobility under the EDI increases by three orders of magnitude, which is consistent with experimental phenomena. The change of propellant type is insufficient to significantly change the axial electron mobility. It is also found that the collisions between electrons and neutral gasescan significantly affect the axial electron mobility under the influence of EDI, and lead the strength of the electric field to increase and the strength of the magnetic field to decrease, thereby both effectively suppressing the axial transport of electrons.

Long-term clinical performance of flapless implant surgery compared to the conventional approach with flap elevation:A systematic review and meta-analysis

BACKGROUND The conventional implant approach involves flap elevation,which may result in increased soft tissue and bone loss and postoperative morbidity.The flapless surgical technique,aided by three-dimensional medical imaging equipment,is regarded as a possible alternative to the conventional approach to alleviate the above issues.Several studies have been performed regarding the role of flapless implant surgery.However,the results are inconsistent and there is no robust synthesis of long-term evidence to better inform surgeons regarding which type of surgical technique is more beneficial to the long-term prognosis of patients in need of implant insertion.AIM To compare the long-term clinical performance after flapless implant surgery to that after the conventional approach with flap elevation.METHODS PubMed,EMBASE,Cochrane Central Register of Controlled Trials,and grey literature databases were searched from inception to 23 September 2019.Randomised controlled trials(RCTs)and cohort studies comparing the long-term clinical performance after flapless implant surgery to that after the conventional approach over a follow-up of three years or more were included.Meta-analyses were conducted to estimate the odds ratios(ORs)or mean differences(MDs)and their 95%confidence intervals(CIs)between the long-term implant survival rate,marginal bone loss,and complication rate of the flapless and conventional groups.Subgroup analyses were carried out to account for the possible effects of the guided or free-hand method during flapless surgery.RESULTS Ten articles,including four RCTs and six cohort studies,satisfied the eligibility criteria and nine of them were included in the meta-analysis.There was no significant difference between the long-term implant survival rate[OR=1.30,95%CI(0.37,4.54),P=0.68],marginal bone loss[MD=0.01,95%CI(-0.42,0.44),P=0.97],and complication rate[OR=1.44,95%CI(0.77,2.68),P=0.25]after flapless implant surgery and the conventional approach.Moreover,subgroup analyses revealed that there was no statistically significant difference between the implant survival rate[guided:OR=1.52,95%CI(0.19,12.35),P=0.70];free-hand:n=1,could not be estimated,marginal bone loss[guided:MD=0.22,95%CI(-0.14,0.59),P=0.23;free-hand:MD=-0.27,95%CI(-1.10,0.57),P=0.53],or complication rate[guided:OR=1.16,95%CI(0.52,2.63),P=0.71;free-hand:OR=1.75,95%CI(0.66,4.63),P=0.26]in the flapless and conventional groups either with use of the surgical guide or by the free-hand method.CONCLUSION The flapless surgery and conventional approach had comparable clinical performance over three years or more.The guided or free-hand technique does not significantly affect the long-term outcomes of flapless surgery.

Applying Lambert problem to association of radar-measured orbit tracks of space objects

Thousands of orbit tracks of space objects are collected by a radar each day,and many may be from uncatalogued objects.As such,it is an urgent demand to catalogue the uncatalogued objects,which requires to determine whether two or more un-correlated tracks(UCTs)are from the same object.This paper proposes to apply the Lambert problem to associate two radar-measured orbit tracks of LEO and HEO objects.A novel method of position correction is proposed to correct the secular and short periodic effects caused by the J_2 perturbation,making the Lambert problem applicable to perturbed orbit tracks.After that,an orbit selection method based on the characteristics of residuals solves the multiple-revolution Lambert problem.Extensive experiments with simulated radar measurements of LEO and HEO objects are carried out to assess the performance of the proposed method.It is shown that the semi-major axis can be determined with an error less than 200 m from two tracks separated by 4 days.The true positive(TP)rates for associating two LEO tracks apart by less than 6 days are 94.2%.The TP rate is still at 73.1%even for two tracks apart by 8–9 days.The results demonstrate the strong applicability of the proposed method to associate radar measurements of uncatalogued objects.

Therapeutic potential of Rho-associated kinase inhibitor Y27632 in corneal endothelial dysfunction:an in vitro and in vivo study

AIM:To investigate the effects of a selective inhibitor of Rho-associated kinase(ROCK),Y-27632,on inbred Wuzhishan porcine corneal endothelial cells(PCECs)in vitro and in vivo studies.METHODS:Primary PCECs were trypsinized from Wuzhishan miniature porcine corneal tissues.The optimal concentration of Y-27632 on PCECs was determined through MTT and 5-ethynyl-2'-deoxyuridine(EdU)-labeling assays.Seven New Zealand rabbits were used as a corneal endothelial dysfunction model,and a PCECs suspension supplemented with Y-27632 was injected into the anterior chamber of the rabbits.The progression of rabbit corneal opacity and edema were observed by slit lamp examination.The rabbits were sacrificed,and rabbit globes were enucleated for trypan blue-alizarin red staining,hematoxylineosin staining,and immunofluorescence analysis.RESULTS:Administration of 100μmol/L Y-27632 facilitated PCECs'proliferation obviously.The rabbit corneas injected with PCECs suspension and 100μmol/L Y-27632 were restored to transparency significantly after 14d.CONCLUSION:The 100μmol/L Y-27632 treatment improves PCECs'proliferation significantly.And our results suggest that Y-27632 and PCECs can be used to treat corneal endothelial dysfunction.

Clinical characteristics and outcomes of primary intracranial alveolar soft-part sarcoma: A case report

BACKGROUND Primary intracranial alveolar soft-part sarcoma(PIASPS)is a rare malignancy.We aimed to investigate the clinical profiles and outcomes for PIASPS.CASE SUMMARY We firstly reported five consecutive cases from our institute.Then,the cases from previous studies were pooled and analyzed to delineate the characteristics of this disease.Our cohort included two males and three females.The median age was 21-years-old(range:8-54-years-old).All the patients received surgical treatment.Gross total resection(GTR),radiotherapy,and chemotherapy were administered in 3 patients,4 patients,and 1 patient,respectively.After a median follow-up of 36 mo,tumor progression was noticed in 4 patients;and 3 patients died of the disease.Pooled data(n=14)contained 5 males and 9 females with a median age of 19 years.The log-rank tests showed that GTR(P=0.011)could prolong progression-free survival,and radiotherapy(P<0.001)resulted in longer overall survival.CONCLUSION Patients with PIASPS suffer from poor outcomes.Surgical treatment is the first choice,and GTR should be achieved when the tumor is feasible.Patients with PIASPS benefit from radiotherapy,which should be considered as a part of treatment therapies.

Influence of pontic design of anterior fixed dental prosthesis on speech: A clinical case study

BACKGROUND The pontic design of fixed dental prostheses(FDPs)is strongly associated with the phonetic function,and the phonetic function of anterior FDPs with different pontic designs remains understudied.AIM To investigate the immediate and short-term influence of pontic design of anterior FDPs on Chinese speech in a clinical case using objective acoustic analysis.METHODS Two FDPs with two types of pontic design(saddle pontic and modified ridge lap pontic)were fabricated for one patient with maxillary anterior teeth missing.The acoustic analysis of patient’s articulation was conducted immediately after wearing the FDPs and 1 wk after wearing these FDPs.RESULTS The effect of FDP on Chinese vowels(/a/,/o/,/e/,/i/,/u/,and/ü/)was insignificant,because the recovery of vowel distortion occurred within 1 wk for both FDPs.Three(/f/,/s/,and/sh/)of eight Chinese fricative consonants were found to have obvious distortions,and the/s/sound distortion last for more than 1 wk for the patient wearing FDP with modified ridge lap pontic design.CONCLUSION The influence of anterior FDP on articulation of Chinese vowels is insignificant,while the articulation of Chinese fricative consonants is more susceptible.When fabricating anterior FDPs for patients with speech related professions,saddle pontic design can be an alternative option compared with modified ridge lap pontic design.

Risk assessment of oil and gas investment environment in countries along the Belt and Road Initiative

With the implementation of the Belt and Road Initiative, China is deepening its cooperation in oil and gas resources with countries along the Initiative. In order to better mitigate risks and enhance the safety of investments, it is of significant importance to research the oil and gas investment environment in these countries for China's overseas investment macro-layout. This paper proposes an indicator system including 27 indicators from 6 dimensions. On this basis, game theory models combined with global entropy method and analytic hierarchy process are applied to determine the combined weights, and the TOPSIS-GRA model is utilized to assess the risks of oil and gas investment in 76 countries along the Initiative from 2014 to 2021. Finally, the GM(1,1) model is employed to predict risk values for 2022-2025. In conclusion, oil and gas resources and political factors have the greatest impact on investment environment risk, and 12 countries with greater investment potential are selected through cluster analysis in conjunction with the predicted results. The research findings may provide scientific decisionmaking recommendations for the Chinese government and oil enterprises to strengthen oil and gas investment cooperation with countries along the Belt and Road Initiative.

Effect of AI_(2)O_(3)and MgO on crystallization and structure of Ca0-Si0_(2)-B_(2)0_(3)-based fluorine-free mold flux

The crytallization behavior and melt structure of the CaO-Si0^(2-)B20_(3)-based fluorine-free mold fux were investigated.The results show that the crytallization of the mold fux was first inhibited and then promoted with the increase in Al_(2)0_(3) content from 4 to 12 wt.%.However,it was enhanced by MgO in the range of 2-10 wt.%.The results of Fourier transform infrared spectroscopy and Raman spectroscopy showed that Al_(2)0_(3) worked as a network former in the mold flux melt when its content was in the range of 4-8 wt.%,whereas it worked as the network breaker to provide 0^(2-)when its content was in the range of 8-12 wt.%.In addition,the combined efects from the charge compensation by Mg^(2+)and the network broken by 0^(2-)led to the increase in some typicalT-O-T(AI-O-A1,B-O-B,etc.,)and simpler structural units(Q^(2)(Si),B_^(O-)in the[B0_(2)0^(-)],.etc.)when the MgO content was in the range of 2-6 wt.%.The continuous increase in 0^(2-)provided by the addition of MgO from 6 to 10 wt.%further depolymerized the network of the melt and fnally caused fast crystallizationo.