Harmonic fold back reduction at the N‐path filters

In this paper, a method is proposed to reduce harmonic fold back (HFB) problem of N‐path filters, without increasing the input reference clock (f_CLK ) frequency. The HFB at the N‐path filter is analyzed, and simple expressions are extracted to model this problem. Using the results of the analysis, an M‐of‐N‐path filter has been proposed that behaves like an M × N‐path filter in terms of HFB problem; however, the f_CLK frequency of this structure is the same as an N‐path filter. To demonstrate the feasibility of the proposed idea, a 3‐of‐4‐path filter is designed, and its characteristics are compared with 4‐path and 12‐path filters by simulation. Impacts of different non‐idealities like clock‐phase error, mismatch, and parasitic capacitance are investigated. The transistor‐level implementation of this filter is performed in 0.18 µm Complementary Metal Oxide Semiconductor (CMOS) technology. The simulation results show that the filter has the pass‐band gain of 17 dB, tuning range of 0.2–1.2 GHz, −3 dB bandwidth of 25 MHz, quality factor of 8–48, 18 dB out‐of‐band rejection, 16 dB rejection of the third harmonic of switching frequency (f_s ), and the noise figure of 4.35 dB (using ideal G_m cells) and 6.95 dB (for practical G_m cells). The strongest harmonic folding to the filter pass‐band occurs around 11f_s with the attenuation of 23.8 dB. Each G_m cell draws about 12.4 mA from 1.8 V supply, and the out‐of‐band IIP3 and P _{1 dB,CP} are 17 and 4 dBm, respectively. Copyright © 2016 John Wiley & Sons, Ltd.     

变形率和退火温度对TaW12合金再结晶行为的影响

研究两种不同加工状态下的Ta W12合金在室温下强度、塑性随退火温度变化的规律,采用金相显微镜分析微观组织,确定两种加工状态下合金的再结晶退火温度。结果表明,变形率为85%的Ta W12合金经1 430℃、2 h退火能够发生完全再结晶。变形率增大至95%,再结晶退火温度降低至1 380℃。     

ICP-AES法测定钛酸锂中的13个杂质元素

采用ICP-AES对钛酸锂中的镍、钴、锰、钾、钙、镁、铝、铜、铁、铅、锌、铬、钠13个杂质元素进行测定。对试样的处理方法、仪器的分析参数、分析谱线的选择做了对比研究,并且对基体干扰情况、背景情况进行研究。最终确定了最佳实验条件:将钛酸锂试样用HF-H_2SO_4溶解,加热挥发除去HF,控制硫酸酸度在2.5%~5.0%左右,用ICP-AES直接测定钛酸锂中的镍、钴、锰、钾、钙、镁、铝、铜、铁、铅、锌、铬、钠13个杂质元素。样品加标回收率为97.40%~105.04%,相对标准偏差0.01%~2.51%。方法操作简便、快速、准确。     

球形Li_4Ti_5O_(12)/NC复合材料的制备及性能

以CH_3COOLi为锂源、Ti(OC_4H_9)_4为钛源、聚乙二醇(PEG)1000为碳源、CO(NH_2)_2为氮源,采用溶胶-凝胶法制备球形氮修饰碳(NC)包覆钛酸锂(Li_4Ti_5O_(12))复合材料。用XRD、X射线光电子能谱(XPS)和热重测试分析材料的晶型及元素组成,用SEM和透射电子显微镜测试分析结构。制备的材料呈球形,NC包覆未改变Li_4Ti_5O_(12)的晶型,但会导致烧结过程中部分Ti~(4+)还原成Ti~(3+)。恒流充放电、循环伏安和交流阻抗等测试表明:NC包覆,可提高Li_4Ti_5O_(12)的电化学性能,当NC包覆量为4.11%时,复合材料的循环性能最好,以1 C在0.8~2.5 V循环100次,仍保持103.5 mAh/g的比容量。     

城市轨道交通盾构区间预埋尼龙套管技术研究

通过对盾构管片预埋尼龙套管存在问题进行分析,提出了尼龙套管布置方案,解决了盾构管片旋转带来的定位问题,同时解决了盾构管片制造中尼龙套管的定位难题和管片的吊离问题。     

The sources of the urban wage premium by worker skills: Spatial sorting or agglomeration economies?

We estimate the respective importance of spatial sorting and agglomeration economies in explaining the urban wage premium for workers with different sets of skills. Sorting is the main source of the wage premium. Agglomeration economies are in general small, but are larger for workers with skills associated with non‐routine job tasks. They also appear to involve human capital accumulation, as evidenced by the change in the wage of workers moving away from denser regions. For workers with routine jobs, agglomeration economies are virtually non‐existent. Our results provide further evidence of spatial density bringing about productivity advantages primarily in contexts when problem‐solving and interaction with others are important.     

尼龙束捻度对水泥砂浆界面粘结的影响

通过织物拔出试验、抗折强度试验和扫描电镜对水泥基体微观破坏形貌的分析，研究了织物中尼龙束捻度对其增韧水泥砂浆界面粘结的影响。研究结果表明：存在着1个尼龙束捻度范围，在该范围内，捻度的增加有助于复合材料的界面粘结，且界面粘结强度随之提高；超出这一范围，捻度的增加反而不利于复合材料的界面粘结，界面粘结强度随之下降。     

Periodic autoregressive conditional duration

We propose an autoregressive conditional duration (ACD) model with periodic time-varying parameters and multiplicative error form. We name this model periodic autoregressive conditional duration (PACD). First, we study the stability properties and the moment structures of it. Second, we estimate the model parameters, using (profile and two-stage) Gamma quasi-maximum likelihood estimates (QMLEs), the asymptotic properties of which are examined under general regularity conditions. Our estimation method encompasses the exponential QMLE, as a particular case. The proposed methodology is illustrated with simulated data and two empirical applications on forecasting Bitcoin trading volume and realized volatility. We found that the PACD produces better in-sample and out-of-sample forecasts than the standard ACD.     

铕掺杂NASICON结构红色荧光粉制备和发光性能

采用高温固相法在空气气氛中制备了具有NASICON结构的Eu³⁺掺杂Na₃Zr₂Si₂PO₁₂：Eu³⁺红色荧光粉。利用X射线衍射、漫反射光谱、荧光光谱、荧光寿命衰减曲线以及量子效率系统研究了该样品的晶体结构及荧光性能。结果表明,样品XRD图中不含明显的杂峰,表明在实验浓度范围内Eu³⁺的掺杂没有改变基质的晶体结构,样品为单相。合成过程中,需要对样品多次压片烧结,才能获得较好的单相。在近紫外光激发下,样品能发出618 nm红光,荧光强度最大对应的Eu³⁺的掺杂摩尔分数是24%。根据Rexter理论分析,浓度猝灭源于Eu³⁺离子之间的电四极-电四极相互作用。样品在室温下的最高内量子效率和外量子效率分别是61%和15%,荧光衰减的寿命范围在2.08~2.84 ms。样品Na_2.76Zr₂Si₂PO₁₂：0.24 Eu³⁺在150℃时内量子效率约为50%,表明样品具有良好的热稳定性。将样品Na_2.76Zr₂Si₂PO₁₂：0.24 Eu³⁺与394 nm波长的紫外芯片封装成LED灯,显色指数达到75.6.Eu³⁺掺杂Na₃Zr₂Si₂PO₁₂有望作为一种新型红色荧光粉用于近紫外激发白光LED。     

超支化聚酯酰胺的合成及在尼龙加工中的应用

为研究不同代数超支化聚酯酰胺（HBPEA）在尼龙6加工中的影响,以4-甲基六氢苯酐（MHHPA）和二异丙醇胺（DIPA）为原料,通过一步法熔融聚合的方式,制备了2种不同代数的超支化聚聚酯酰胺（HBPEA）,并将其作为加工助剂与尼龙6（PA6）在双螺杆挤出机中共混。通过红外光谱、热失重分析仪、乌式黏度计分析了两种HBPEA的结构和热稳定性。通过对力学性能、流变行为的测试,研究了HBPEA质量分数对PA6的影响。结果表明:两种不同代数HBPEA的添加,都可以提升HBPEA/PA6共混物的流动性能和机械性能,其中,高代数HBPEA/PA6共混物的提升效果更好。当高代数HBPEA质量分数为1%时,高代数HBPEA/PA6共混物拉伸强度和弯曲强度达到最大值,分别为61.3、183.3 MPa。