浅析英语语音教学中的/n//l/发音错误

在大学英语教学过程中,有关/n/与/l/的发音错误很常见,原因是没有完全掌握它们的发音规则。/n//l/发音规则的相似性造成了/n//l/不分的情况,而且局部方言中这两个音也不作区分,使得/n//l/混淆的情况更加严重。在教学过程中,可以通过重点讲解区分/n/与/l/的发音规则及其区别来避免/n//l/发音错误。本文同时也分析了含糊/l/音的发音错误,通过对/n/与/l/相关的发音错误分析找出大学英语语音教学行之有效的途径:在完全把握单音的发音规则的基础上,进一步强调语调的掌握,使学生拥有良好的语音。     

一种基于 MXene 的Fe2O3/Nb2O5/Nb4C3Tx 高灵敏丙酮传感器

MXene 具有较大比表面积和优异的导电性, 当与金属氧化物半导体结合时可以抑制片层团聚, 还可以大大提高载流子转移速率, 提高气敏性能。通过简单的水热和煅烧两步法成功合成了Fe₂O₃/Nb₂O₅/Nb₄C₃T_x 三元复合材料。通过表征, Fe₂O₃ 微米球分布在 MXene 纳米片层之间。气敏测试结果表明, 与原始Fe₂O₃相 比, Fe₂O₃/Nb₂O₅/Nb₄C₃T_x 传感器对丙酮的响应能力有明显的提高。传感器灵敏度高, 选择性较好, 对环境中 浓度为 5 ×10^?6 的丙酮响应高 (R_a /R_g = 7.81, 30% RH), 响应和恢复速度快, 具有出色的重复性和长期稳定性。Fe₂O₃/Nb₂O₅/Nb₄C₃T_x 传感器具有良好的气敏性能, 主要因为三元复合材料提供了较大比表面积和丰富的氧空位, 增强了活性位点, 使得气体易于在传感器表面扩散, 为开发丙酮敏感复合材料提供了参考。     

肼类燃料液滴的亚临界——超临界蒸发/分解燃烧理论

对肼、一甲基肼、偏二甲肼的亚临界－－超临界蒸发／分解燃烧进行了研究,计算了肼类燃料滴在不同压力下液滴温度和蒸发速度的变化历程,计算了蒸发常数、传热数和传质数,其结果和实验数据是吻合的。本文不但考虑了肼类燃料滴的亚临界蒸发／分解燃烧,还考虑到了其超临界蒸发／分解燃烧,并对达到超临界工况时的界限参数进行了计算。     

Modification of LiCo1/3Ni1/3Mn1/3O2 cathode material by CeO2-coating

LiCo_1/3Ni_1/3Mn_1/3O₂ was coated by a layer of 1.0 wt% CeO₂ via sol-gel method. The bared and coated LiMn_1/3Co_1/3Ni_1/3O₂ was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammogram (CV) and galvanotactic charge-discharge test. The results show that the coating layer has no effect on the crystal structure, only coating on the surface; the 1.0 wt% CeO₂-coated LiCo_1/3Ni_1/3Mn_1/3O₂ exhibits better discharge capacity and cycling performance than the bared LiCo_1/3Ni_1/3Mn_1/3O₂. The discharge capacity of 1.0 wt% CeO₂-coated cathode is 182.5 mAh·g⁻¹ at a current density of 20 mA·g⁻¹, in contrast to 165.8 mAh·g⁻¹of the bared sample. The discharge capacity retention of 1.0 wt% CeO₂-coated sample after 12 cycles reaches 93.2%, in comparison with 86.6% of the bared sample. CV results show that the CeO₂ coating could suppress phase transitions and prevent the surface of cathode material from direct contact with the electrolyte, thus enhance the electrochemical performance of the coated material.     

RDSS/Doppler/GPS/SINS组合导航系统研究

针对双星定位系统(RDSS)存在的定位位置滞后的先天缺陷,根据组合导航定位系统输出速度误差小的特点,给出了一套消除RDSS位置滞后的方案,并对RDSS／SINS组合系统进行了建模,依据联邦滤波器理论,考虑到GPS的实际情况,提出了RDSS／Doppler／GPS／SINS多传感器组合导航系统的设想,仿真结果表明,该组合导航系统具有准确度高、自主性强的特点。     

Transport Properties of Polycrystalline La2/3Ca1/3Mn1-xCuxO3

The infuence of Cu dopant (x) and sintering temperature(Ts) on the troansport propeties of La2/3Ca1/3Mn1-xCuxO3 series samples prepared by Sol-Gel technique was investigated.X-ray diffraction patterns show that all the samples with different Cu dopant and sintering temperatures (Ts) are of single phase without obvious latice distortion.Experimental results indicate that the insulator-metal transition temperature is diectly related to the sintering temperature and Cu dopant x.It is interesting to observe that a proper amount of Cu dompant can substantially improve magnetoresistance effects.     

Low temperature properties of organic-inorganic Ag/ p -CuPc/ n -GaAs/Ag photoelectric sensor

A thin organic film of p-type semiconducting copper phthalocynanine (CuPc) was deposited by vacuum evaporation on an n-type GaAs single-crystal semiconductor substrate. The fabricated Ag/p-CuPc/n-GaAs/Ag sensor was carried through an ageing process to stabilize the parameters. Voltage-current characteristics and photoelectrical response of the sensor were investigated at a wide temperature range of 82 to 350 K. Photoelectric characteristics were measured under nonmodulated filament-lamp illumination. It was observed that such sensor parameters as rectification ratio, threshold voltage, junction, shunt and series resistances, open-circuit voltage and short circuit current are temperature-dependent. It was found that wide-range voltage-current characteristics of the sensor may be described similarly to that of a Schottky barrier diode. Using the experimental data on voltage-current characteristics and absorbance of the CuPc films, the energy-band diagram of the p-CuPc/n-GaAs heterojunction was developed. It was shown that data obtained from simulation of an equivalent circuit of photoelectric sensor agreed with experimental results. Supported by the National Engineering and Scientific Commission of Pakistan     

St/BA/MAA/AA/VAC复合乳液的合成及其应用

采用半连续乳液种子聚合法合成苯乙烯（St）、丙烯酸丁酯（BA）、甲基丙烯酸 （MAA）、丙烯酸（AA）、醋酸乙烯酯 （VAc）的复合乳液.分析了丙烯酸对乳液电解质性能的影响,引发剂对聚合反应转化率的影响及乳化剂含量对乳液粘度的影响.通过正交试验确定组分的适当配比.该共聚乳液的粘度及固体含量符合要求,稳定性好, 性能价格比高.应用表明：用此乳液配制成地毯乳胶,胶膜具有良好的机械性能.     

Reliability of Au/PZT/BIT/p-Si ferroelectric diode

A ferroelectric memory diode that consisted of Au/PZT/BIT/p-Si multilayer configuration was fabricated by pulsed laser deposition (PLD) technique. The reliability issues (I-V characteristics, capacitance retention, fatigue and imprint) were investigated. The I-V curve showed the conventional Schottky diode characteristics with a small current density of - 5.3×10 -10 A/cm2 at a voltage of - 4 V and 6.7×10-8 A/cm2 at a voltage of + 4V, and this characteristic can be maintained below 50℃. The capacitance variety of the ferroelectric diode was only 5 % in 10 hours after withdrawing the applied bias of + 5 V or - 5 V, indicating the diode had good capacitance retention. By applying 100 kHz bipolar pulses of 5 V amplitude, the decay in remanent polarization was only 10% after 109 switching cycles, and meanwhile the increase in coercive field was 12%. After being irradiated for 20 min with a 200 W ultraviolet ray lamp, the remanent polarization and coercive field had both varied, and a voltage shift was obse     

亚锰酸盐La0.7-xYxCa0.3MnO3的电磁特性和磁电阻效应

研究了用固相反应法制备亚锰酸盐多晶样品La0.7-xYxCa0.3MnO3,并研究了Y的不同掺杂(x=0.1,0.2)对样品的晶体结构、电磁特性和磁电阻效应的影响.实验结果表明,随着温度的降低,x=0.1样品的R-T曲线没有出现峰值,而x=0.2样品出现了峰值,显示了复杂的输运特性.两种样品的磁电阻Rm都随着温度的降低而升高,但都没有出现峰值.x=0.2的样品在较宽的温区内,磁电阻效应都很显著,而且Y掺杂由x=0.1提高至x=0.2,磁电阻效应增强.     

M/M/c型与M/M/1型排队系统对比仿真

为了更具体地分析M/M/c和c个M/M/1并联系统在性能上的差异,首先分析了Little公式在应用中可能存在的缺陷,然后通过AnyLogic仿真工具对模型运行过程进行跟踪,最后通过管理系统仿真(general purpose simulation system,GPSS) JAVA仿真获取了2种排队系统中服务台利用率、平均队长、最大队长、平均等待时间等对比指标,并指出了M/M/1并联系统用解析法求解存在的缺陷.仿真结果表明:2种排队系统中服务台利用率几乎相同;M/M/c系统中顾客平均等待时间稍短于c个M/M/1并联系统,对传统排队论中的“与c个M/M/1并联系统相比,M/M/c系统可以显著提高服务效率和减少等待时间”结论进行了修正.此外,M/M/c系统中“短时等待”顾客更多,其“零等待”顾客数和“长时等待”顾客数均显著少于c个M/M/1并联系统.     

铬/氢/空气/氯体系的焚烧动力学分析

对含铬固体废物焚烧体系进行动力学分析是提出控制六价铬化合物排放措施的基础。本文对铬/氢/空气/氯焚烧体系进行了动力学分析,研究了温度、初始氯含量对产物中六价铬化合物含量的影响。研究表明,六价铬化合物主要以CrO2(OH)2的形式出现,最高含量出现在1700K左右;氯的存在没有导致六价铬化合物CrO2Cl2的大量生成;六价铬化合物CrO2(OH)2的含量随初始氯含量的增大略有下降。建议含铬固体废物实际焚烧过程中,避开1700K左右的温度区域,减少六价铬化合物的排放。     

用Cr/Au/Ni/Au制备n-GaN欧姆接触

为了获得n-GaN的低接触电阻的欧姆接触,采用Cr/Au/Ni/Au金属化系统与n—GaN形成欧姆接触,并对其不同温度下的接触电阻率进行了测试分析.室温下Cr/Au/Ni/Au的接触电阻率为0.32mΩ·m2。随着温度的升高,接触电阻率略有增加,在300℃时接触电阻率为0.65mΩ·cm2,因此此欧姆接触适合在高温下使用.     

St/BA/MAA/AA/VAC复合乳液的合成及其应用

采用半连续乳液种子聚合法合成苯乙烯(St)、丙烯酸丁酯(BA)、甲基丙烯酸(MAA)、丙烯酸(AA)、醋酸乙烯酯(VAc)的复合乳液。分析了丙烯酸对乳液电解质性能的影响,引发剂对聚合反应转化率的影响及乳化剂含量对乳液粘度的影响。通过正交试验确定组分的适当配比。该共聚乳液的粘度及固体含量符合要求,稳定性好,性能价格比高。应用表明:用此乳液配制成地毯乳胶,胶膜具有良好的机械性能。     

Synthesis and characterization of Mg3(PO4)2-coated Li1.05Ni1/3Mn1/3Co1/3O2 cathode material for Li-ion battery

Mg₃(PO₄)₂-coated Li_1.05Ni_1/3Mn_1/3Co_1/3O₂ cathode materials were synthesized via co-precipitation method. The morphology, structure, electrochemical performance and thermal stability were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), cyclic voltammetry(CV), electrochemical impedance spectroscopy(EIS), charge/discharge cycling and differential scanning calorimeter (DSC). SEM analysis shows that Mg₃(PO₄)₂-coating changes the morphologies of their particles and increases the grains size. XRD and CV results show that Mg₃(PO₄)₂-coating powder is homogeneous and has better layered structure than the bare one. Mg₃(PO₄)₂-coating improved high rate discharge capacity and cycle-life performance. The reason why the cycling performance of Mg₃(PO₄)₂-coated sample at 55 °C was better than that of room temperature was the increasing of lithium-ion diffusion rate and charge transfer rate with temperature rising. Mg₃(PO₄)₂-coating improved the cathode thermal stability, and the result was consistent with thermal abuse tests using Li-ion cells: the Mg₃(PO₄)₂ coated Li_1.05Ni_1/3Mn_1/3Co_1/3O₂ cathode did not exhibit thermal runaway with smoke and explosion, in contrast to the cells containing the bare Li_1.05Ni_1/3Mn_1/3Co_1/3O₂. Funded by the National Natural Science Foundation of China (No. 20273047)     

流变相法制备LiFe_(1-x)Mg_xPO_4/C正极材料

通过Mg+金属掺杂及流变相制备方法来改善橄榄石结构的LiFePO4的电化学性能.研究了不同掺杂量和不同制备方法对材料结构性能和电化学性能的影响.SEM,XRD,以及电化学测试结果表明,Mg掺杂可以较大程度提高材料电化学性能;0.1 C倍率下首次充电容量达到140.7 mAh/g.利用流变相法制备的材料粒度更小,其电化学性能得到进一步提高,0.1 C时放电比容量达到了147.5 mAh/g.     

无人机组合导航系统信息融合方法研究

针对小型无人机通常采用的无线电导航,综合考虑无人机具体情况以及其它导航方式的特点,提出了一种将无线电导航系统(RP)、全球导航星系统(GN SS)、多普勒导航系统(DN S)、地形辅助导航系统(TAN)和景象匹配导航系统(SMN)组合起来,取长补短,构成基于联邦卡尔曼滤波器的DR/RP/GN SS/DN S/TAN/SMN组合导航系统。仿真结果表明,该方法完全可以满足导航精度的要求。     

Structural and optical characteristics of Al x Ga1- x N/AlN superlattice

AlN/Al_0.3Ga_0.7N superlattices were grown on (0001) sapphire substrate by metal-organic chemical vapor deposition (MOCVD). The superlattice period varies from 6 to 30. The layer thickness of different period stack was designed. GaN or AlGaN template was employed for growing AlN/AlGaN superlattices. Reflectivity, SEM, AFM and XRD data of the Al _x Ga_1-x N/AlN superlattices are presented. It is found that the templates used have an intensive impact on surface roughness and interfacial properties of following AlN/AlGaN superlattices. The result of atomic force microscopy indicates that AlN/AlGaN superlattices grown on GaN template exhibit quasi-two-dimensional growth mode. The resulting superlattice has a smooth surface morphology and distinct interface. No crack is observed in the area of a 2-inch wafer. Supported by the Special Funds for Major State Basic Research Project (973 Project) (Grant No. 2006CB6049), the Hi-tech Research Project (Grant Nos. 2006AA03A103, 2006AA03A118, and 2006AA03A142), the National Natural Science Foundation of China (Grant No. 60676057), and the Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20050284004)     

带有门限的IBP+MMBP/Geo/1/K休假排队系统

建立了基于门限策略的双队列单服务台有限缓存包级休假排队模型IBP+MMBP/Geo/1/K。针对到达分布不同的两种业务各自的特点来定义休假策略,将H2H(Human to human)业务的休假期等效为M2M(Machine to machine)业务的服务期。为了寻求统一的标准来评价休假策略,定义了一个评价业务QoS的效能函数E。同时,研究了不同条件下的M2M业务对休假策略的影响。最后,通过仿真给出各种情况下系统各项性能指标以及效能函数的变化趋势,该研究结果可以用来指导无线资源分配和业务配置等问题。     

Memory characteristics of Au/PZT/BIT/p-Si ferroelectric diode

A ferroelectric memory diode consisting of Au/PZT/BIT/p-Si multilayer configuration has been fabricated by pulsed laser deposition (PLD) technique. The ferroelectric properties and the memory characteristics are investigated. The P-E curve of the PZT/BIT/p-Si films system had an asymmetry saturated hysteresis loop with P, = 15 μC/cm2 and Ec = 48 kV/cm, and the decay in remanent polarization was only 10% after 109 switching cycles, meanwhile the increase in coercive field was 12% . The C-V hysteresis loop and the I-V curve showed a memory effect derived from the ferroelectric polarization of PZT/BIT films, and the current density was 6.7 × 10-8 A/cm2 at a voltage of + 4V. Our diode had nonvolatile and nondestructive memory readout operation. There was a read current disparity of 0.05 μA for logic "1" and logic "0" at a read voltage of + 2V, and the stored logical value ("1" or "0") could be read out in 30 min.