Wakefield generation by chirped super-Gaussian laser pulse in inhomogeneous plasma

We study the effect of nonlinearly chirped super-Gaussian （SG） laser pulse on wakefield generation in an inhomogeneous plasma. The different types of nonlinearly chirped pulse are employed, and different kinds of inhomogeneous plasma density are used. The maximum wakefield amplitude as the function of nonlinearly chirped laser pulse and inhomogeneous plasma density in parameter space are obtained. Moreover, the dependence of the maximum wakefield amplitude on the SG laser pulse index is discussed. This shows that a larger wakefield can be obtained when the chirped pulse and inhomogeneous density are in the critical regions. Wakefield generation can be controlled by adjusting the chirped SG pulse and inhomogeneous plasma density parameters. That is, we provide an efficient way for the controlled generation of the wakefield.

Observation on the Anesthesia Effect of Ultrasound-Guided Nerve Block for Elderly Patients with Lower Limb Fractures

Objective:To explore the anesthesia effect of ultrasound-guided nerve block in elderly patients with lower limb fractures.Methods:From November 2017 to November 2020,50 elderly patients with lower limb fractures in our hospital were divided into experimental group(25 cases,general anesthesia+femoral nerve and sciatic nerve block)and control group(25 cases,general body anesthesia).Compare the MAP,HR,anesthesia effect,and adverse reactions between the two groups at each time period.Results:Before induction,the difference in MAP and HR between the two groups of patients did not form,p>0.05;the MAP and HR of the experimental group were compared with the control group at the time of skin incision,1 hour during the operation,and removal of the laryngeal mask,P<0.05;the time of extubation in the experimental group(14.28±3.18)min,awake time(5.57±1.32)min,orientation recovery time(11.89±2.23)min,propofol dosage(191.36±22.48)mg,remifentanil dosage(0.23±0.04)mg,Compared with the control group,P<0.05;the adverse reaction rate of the experimental group(8%,2/25)was lower than that of the control group(32%,8/25),P<0.05.Conclusion:The use of ultrasound-guided femoral nerve and sciatic nerve block for elderly patients with lower limb fractures can enhance the effect of anesthesia,effectively reduce the use of anesthetics,and have fewer adverse reactions.It is worthy of promotion.

Near infrared emissions from both high efficient quantum cutting (173%) and nearly-pure-color upconversion in NaY(WO_(4))_(2):Er^(3+)/Yb^(3+) with thermal management capability for silicon-based solar cells

Raising photoelectric conversion efficiency and enhancing heat management are two critical concerns for siliconbased solar cells.In this work,efficient Yb^(3+) infrared emissions from both quantum cutting and upconversion were demonstrated by adjusting Er^(3+) and Yb^(3+) concentrations,and thermo-manage-applicable temperature sensing based on the luminescence intensity ratio of two super-low thermal quenching levels was discovered in an Er^(3+)/Yb^(3+) codoped tungstate system.The quantum cutting mechanism was clearly decrypted as a two-step energy transfer process from Er^(3+) to Yb^(3+).The two-step energy transfer efficiencies,the radiative and nonradiative transition rates of all interested 4 f levels of Er^(3+) in NaY(WO_(4))_(2) were confirmed in the framework of Föster-Dexter theory,Judd-Ofelt theory,and energy gap law,and based on these obtained efficiencies and rates the quantum cutting efficiency was furthermore determined to be as high as 173%in NaY(WO_(4))_(2):5 mol%Er^(3+)/50 mol%Yb^(3+) sample.Strong and nearly pure infrared upconversion emission of Yb3+under 1550 nm excitation was achieved in Er^(3+)/Yb^(3+)co-doped NaY(WO_(4))_(2) by adjusting Yb^(3+) doping concentrations.The Yb^(3+) induced infrared upconversion emission enhancement was attributed to the efficient energy transfer ^(4)I_(11/2)(Er^(3+))+^(2)F_(7/2)(Yb^(3+))→^(4)I_(15/2)(Er^(3+))+^(2)F_(5/2)(Yb^(3+))and large nonradiative relaxation rate of ^(4)I_(9/2).Analysis on the temperature sensing indicated that the NaY(WO_(4))_(2):Er^(3+)/Yb^(3+)serves well the solar cells as thermos-managing material.Moreover,it was confirmed that the fluorescence thermal quenching of ^(2)H_(11/2)/^(4)S_(3/2) was caused by the nonradiative relaxation of ^(4)S_(3/2).All the obtained results suggest that NaY(WO_(4))_(2):Er^(3+)/Yb^(3+) is an excellent material for silicon-based solar cells to improve photoelectric conversion efficiency and thermal management.

HPMA modified aluminium nitride powder for aqueous tape casting of AlN ceramic substrates

Aluminum nitride(AlN)is considered one of the most desirable materials for integrated circuits and electronic packaging substrates.However,raw AlN powder reacts easily with water,forming Al(OH)3 or AlOOH on the surface and hindering the development of an aqueous tape-casting process for preparing AlN ceramic substrates.In this study,hydrolyzed polymaleic anhydride(HPMA)was used to modify AlN powder,which has good water solubility and dispersibility.The AlN powder was modified with 5 wt%HPMA remained stable in water for at least 90 h under magnetic stirring condition and 24 h under ball milling condition,indicating that HPMA-modified AlN powder has good resistance to hydrolysis.The action mechanism of HPMA is revealed.Firstly,–COOH of the HPMA polymer and the oxide layer on the surface of the AlN powder underwent a dehydration condensation reaction to form a compound.Secondly,long chains of the polymer further coated the surface of the AlN powder,forming an anti-hydration layer with a thickness of about 7.0 nm on the surface of the AlN particles.In addition,AlN green sheets were successfully prepared by aqueous tape casting using the HPMA-modified AlN powder without additional dispersants.Subsequently,AlN ceramic substrates were obtained by sintering at 1750℃for 4 h under an N2 atmosphere with a pressure of 0.2 MPa.The relative density and thermal conductivity were tested to be 97.3%and 122 W/(m·K),respectively.

Effects of Bi^(3+) on down-/up-conversion luminescence,temperature sensing and optical transition properties of Bi^(3+)/Er^(3+)co-doped YNbO_(4) phosphors

A series of YNbO_(4):Bi^(3+) and YNbO_(4):Bi^(3+)/Er^(3+) phosphors were prepared by a conventional high temperature solid-state reaction method.The results of XRD and Rietveld refinement confirm that monoclinic phase YNbO_(4)samples are achieved.The down-/up-conversion luminescence of Er^(3+) ions was investigated under the excitation of ultraviolet light(327 nm)and near infrared light(980 nm).Under 327 nm excitation,broad visible emission band from Bi^(3+) ions and characteristic green emission peaks from Er^(3+) ions are simultaneously observed,while only strong green emissions from Er^(3+) ions are detected upon excitation of 980 nm.Remarkable emission enhancement is observed in down-/up-conversion luminescence processes by introducing Bi^(3+) ions into Er^(3+)-doped YNbO_(4)phosphors.Pumped current versus up-conversion emission intensity study shows that two-photon processes are responsible for both the green and the red up-conversion emissions of Er^(3+)ion.Through the study of the temperature sensing property of Er^(3+) ion,it is affirmed that the temperature sensitivity is sensitive to the doping concentration of Bi^(3+) ions.By comparing the experimental values of the radiative transition rate ratio of the two green emission levels of Er^(3+) ions and the theoretical values calculated by Judd-Ofelt(J-O)theory,it is concluded that the temperature sensing property of Er^(3+) ions is greatly affected by the energy level splitting.