Effect of Surface Charge on Flashover for Oil-Pressboard Insulation under AC-DC Combined Electric Field

For converter transformer, AC-DC combined electric field can trigger space charge accumulation on oil-impregnated pressboard interface. The accumulation of space charge on oil-pressboard interface can result in electric field distortion, trend to trigger surface discharge of barriers. This paper studied the influence of surface charge on flashover voltage of oil-impregnated pressboard under AC-DC combined electric field. The study finds that the flashover voltage of oil-pressboard interface under negative polarity DC superimposed AC electric field is higher than that.of positive DC superimposed AC voltage to form composite electric field. It was found that homopolar surface charge has been accumulated on the interface of oil-pressboard with positive or negative DC voltage through measuring surface potential by the electrostatic capacitive probe. The surface charge produced electric field in the opposite direction, which weakening the synthetic electric field strength. What＇s more, under the same conditions, the negative surface charge density oil-pressboard is much larger than the positive.

Management and outcomes of surgical patients with intestinal Behçet’s disease and Crohn’s disease in southwest China

BACKGROUND Gastrointestinal involvement in Behçet's disease(GIBD)and Crohn’s disease(CD)are inflammatory diseases sharing a considerable number of similarities.However,different from CD,the operative and postoperative management of GIBD remains largely empirical because of the lack of comprehensive treatment guidelines.AIM To compare surgical patients with GIBD and those with CD in a medical center and identify notable clinical features and effective postoperative treatment for surgical patients with GIBD.METHODS We searched patients diagnosed with CD and GIBD who underwent operations for gastrointestinal complications from 2009 to 2015 at West China Hospital of Sichuan University.A total of 10 surgical patients with GIBD and 106 surgical patients with CD were recruited.Information including demographic data,medication,and operative and postoperative parameters were collected and analyzed.As the incidence of surgical GIBD is low,their detailed medical records were reviewed and compared to previous studies.Moreover,the prognoses of CD and GIBD were evaluated respectively between groups treated with biological and non-biological agents.RESULTS Indication for first surgery was often acute intestinal perforation for GIBDpatients (7/10 vs 0/106, P < 0.001), whereas intestinal fistulae (0/10 vs 44/106, P =0.013) and ileus (0/10 vs 40/106, P = 0.015) were the indications for surgical CDpatients. Approximately 40% of patients with GIBD and 23.6% of patients withCD developed postoperative complications, 50% of patients with GIBD and 38.7%of patients with CD had recurrence postoperatively, and 40% (4/10) of patientswith GIBD and 26.4% (28/106) of patients with CD underwent reoperations. Theaverage period of postoperative recurrence was 7.87 mo in patients with Behçet'sdisease (BD) and 10.43 mo in patients with CD, whereas the mean duration fromfirst surgery to reoperation was 5.75 mo in BD patients and 18.04 mo in CDpatients. Surgical patients with GIBD more often used corticosteroids (6/10 vs7/106, P < 0.001) and thalidomide (7/10 vs 9/106, P < 0.001) postoperatively,whereas surgical patients with CD often used infliximab (27/106), azathioprine,or 6-mercaptopurine (74/106) for maintenance therapy.CONCLUSIONPatients suffering GIBD require surgery mostly under emergency situations,which may be more susceptible to recurrence and reoperation and need moreaggressive postoperative treatment than patients with CD.

Generation of visible Raman operation laser by a fiber electro-optical modulator feedback loop

Phase-coherent multi-tone lasers play a critical role in atomic,molecular,and optical physics.Among them,the Raman opeartion laser for manipulating atomic hyperfine qubits requires gigahertz bandwidth and low phase noise to retain long-term coherence.Raman operation lasers generated by directly modulated and frequency-multipled infrared lasers are compact and stable but lack feedback control to actively suppress the phase noise,which limits their performance in practical applications.In this work,we employ a fiber electro-optical modulator driven by a voltage-controlled oscillator(VCO)to modulate a monochromatic laser and employ a second-harmonic generation process to convert it to the visible domain,where the beat note of the Raman operation laser is stabilized by controlling the output frequency of VCO with a digital phase-locked loop(PLL).The low-frequency phase noise is effectively suppressed compared to the scheme without active feedback and it reaches-80 d Bc/Hz@5 k Hz with a 20 k Hz loop bandwidth.Furthermore,this compact and robust scheme effectively reduces the system's complexity and cost,which is promising for extensive application in atomic,molecular,and optical physics.