查询词典 radio-frequency spectrum

Nowadays the researches of frequency distribution of data are almost limited to normal distribution, while other distributions are seldom studied. Many frequency distributions of data are not normal. This kinds of frequency distribution of data widely exist. Unimodal frequency distribution of data often occurs.

现在绝大多数关于频数资料分布的研究都是基于正态分布的，而对其他类型的分布研究得比较少，实际上频数分布在许多情况下并非呈现正态分布，分布的形态丰富多彩，很多资料都是呈现单峰分布，本研究就是利用数学上常见的八种连续型变量的分布类型去拟合单峰频数资料。

Then the creative research work on ultra-low frequency and large amplitude elcectromagnetic vibrator based on moving magnet is done, improving exciting signal at ultra-low frequency, and, the theoretic analysis and experiment model are studied. Thus, the reference for establishing ultra-low frequency standard vibrator in future is provided. In chapter 5, two control strategies for ultra-low frequency standard vibrator test table waveform are studied.

首先采用机械振动隔振理论，研究设计了机械低通滤波器来滤除噪声信号，并运用等效的小振级信号进行了实验研究，得出了有益的结论；然后为提高超低频时激振信号，作者创造性地提出了动铁型大位移的电动振动台结构，进行了理论分析和实验模型研究，为将来建立大位移的超低频标准振动台提供了参考。

The curve obviously declined from the low frequency to the middle frequency section, and was reduced to zero in the high frequency section, which objectively showed the change in imaging characteristics of the eyes from the low to high frequency areas.

PSF分析系统可直接采用屈光系统MTF曲线表达人眼的成像特征，该曲线MTF值从低频至中频迅速下降，高频趋向缓和至零，定量并客观地表达了人眼成像质量从低频至高频的改变。

The study on the electrical property shows that its dielectric property decreases with the slowly increase of frequency in dry state; in hygrometric state (52.9%), the dielectric property grows obviously and declines swiftly with the increase of frequency; and it tends to be stable when the frequency is over 10^4Hz. The specific resistance decreases linearly with the increase of the frequency. The results indicate that the electric properties of the hot press moulded wheat gluten are subject to the compaction rate of the material structure.

对小麦麸质模压板的电性能研究表明，干态下其介电性能随电场频率增加而下降，但变化小；湿态下其介电性能明显提高，且随频率增加迅速下降，超过10^4Hz后区域变化趋于稳定；热压小麦麸质材料的电阻率随频率的增加呈直线下降；小麦麸质热压材料的电性能主要决定于材料结构的密实程度。

The digital frequency source this paper researched uses high integrated DDS chip AD9851 as frequency sources and signal mirac processors AT89C51 as system control center, it can output 10Hz-20MHz signal with high-precision and high stability frequency. The evenness of signal within the range of 10MHz is low to 0.1dB degree, and the smallest step is low to 10Hz frequency.

本课题研究的数字频率源采用高集成度DDS芯片AD9851作为频率源；以单片机AT89C51作为系统的控制中心，实现了10Hz～20MHz的高精度、高稳定度的频率输出。10MHz内信号幅度的平坦度为0.1dB、频率最小步进为10Hz。

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The findings: with the apparent dominant frequency of the Ricker wavelet rising, the detection SNR will get worse gradually, it is obvious that the variety of the SNR is slower during the portion of high frequency than during the portion of low frequency; in the usual range of seismic prospecting frequency, the SNR of the chaotic oscillator detection system could partially make up the amplitude attenuation aroused by the transmit of the seismic wave; the results could provide help for detecting the event constituted by aberrant wavelets.

本文以Ricker子波模拟地震子波，研究Ricker子波视主频变化的相应检测效果。研究结果：随着Ricker子波视主频的升高，检测SNR逐渐变差，在高频部分SNR的变化明显比低频部分缓慢；在通常地震勘探频率范围内，混沌振子系统检测SNR有可能部分补偿由于地震波传播引起的幅度降低；为检测由畸变子波构成的同相轴提供一定的可能。

This paper bases on frequency-hopped and frequency synthesis theories, and through demonstrating three schemes of frequency synthesis, the paper selects one of these schemes that uses DDS spiriting up PLL and improves on the method according to the practical target and synchronously, the paper analysis the capability of the output signal and the conversion time of the frequency.

本文在对跳频理论及频率合成理论分析的基础上，在讨论三种频率合成方案后，设计完成了一种适于本课题的DDS激励PLL的混合方案，并对频率合成器主要性能中的输出信号的噪声特性和频率转换性能做了研究分析。

According to the field variation with frequency in the test volume, the work frequency of GTEM cell can be divided into three frequency areas, namely, quasi-static area, high frequency area and out of the vertical polarization area.

根据测试区场分布随频率的变化情况，可将GTEM传输室的工作频率分为三个特征频段，即：准静态区、高频区和非垂直极化区。

Taking the development platform of HVDC power transmission for example, the calculation result of impedance-frequency characteristic of traditional line commutated converter and that of FCC are compared. Simulation results show that the impact of impedance-frequency characteristic of converter on the resonance frequency of AC system is not negligible, and FCC can enhance the strength of AC system in a certain extent, improve system stability and effectively reduce AC equivalent impedance under resonance frequency, thus the harmonic instability of HVDC power transmission system can be avoided.

以直流输电开发平台为例，对传统电网换相换流器(line commutated converter，LCC)与FCC的阻抗频率特性计算结果进行对比，仿真结果表明换流器的阻抗频率特性对交流系统的谐振频率有着不可忽略的作用，FCC在一定程度上提高了交流系统强度，改善了系统稳定性，有效降低了系统谐振频率下的交流等值阻抗，从而更好避免直流输电系统谐波不稳定现象的发生。

We got alerted a couple of times while we were down south that HETs were on the way to bring us back up north because things were going to go hot again, but it was just rumors.

南下的途中我们不只一次得到警告说重型装备运输车将拉着我们重新北上，因为局势正在变得重新紧张起来，但这只是谣传。

It's the one where they find the ghost in the salt mine.

这一集是演他们在盐矿找到鬼