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201.
介绍了多小区协作ICI处理技术的最新研究成果,分析了现有方案所面临的挑战,最后对多小区协作ICI处理技术的发展趋势做了展望. 相似文献
202.
为了提高正交频分复用（OFDM）系统中传输数据的可靠性,对抗频率偏差带来的系统信噪比的下降,在OFDM系统接收端引入自适应波束形成。自适应波束形成实现了对期望信号方向的增益接收,同时对干扰信号方向进行有效的抑制。仿真结果表明,文中方法比单纯的OFDM系统具有更低的误码率,即使在有多普勒频移的多径信道下,也能获得更高的传输可靠性。从输入、输出信干噪比的曲线也可以看出,此方法是可行且收敛的。 相似文献
203.
智能天线技术可以在提高移动通信服务容量和质量的同时而不占用更多的频谱资源。文中就一种利用切比雪夫天线阵来实现智能天线下行波束的优化设计进行了详细分析和仿真。理论分析和仿真结果表明，与其它方法相比，该方法具有空间分辨率高，同信道干扰可控，且计算量小，鲁棒性好，用户波束个数不受阵元个数限制的优点。 相似文献
204.
Optical microscopy allows a magnified view of the sample while decreasing the depth of focus. Although the acquired images from limited depth of field have both blurred and focused regions, they can provide depth information. The technique to estimate the depth and 3D shape of an object from the images of the same sample obtained at different focus settings is called shape from focus (SFF). In SFF, the measure of focus–sharpness–is the crucial part for final 3D shape estimation. The conventional methods compute sharpness by applying focus measure operator on each 2D image frame of the image sequence. However, such methods do not reflect the accurate focus levels in an image because the focus levels for curved objects require information from neighboring pixels in the adjacent frames too. To address this issue, we propose a new method based on focus adjustment which takes the values of the neighboring pixels from the adjacent image frames that have approximately the same initial depth as of the center pixel and then it re-adjusts the center value accordingly. Experiments were conducted on synthetic and microscopic objects, and the results show that the proposed technique generates better shape and takes less computation time in comparison with previous SFF methods based on focused image surface (FIS) and dynamic programming. Microsc. Res. Tech., 2009. © 2008 Wiley-Liss, Inc. 相似文献
205.
D. COOPER R. TRUCHE A.C. TWITCHETT-HARRISON† R.E. DUNIN-BORKOWSKI† & P.A. MIDGLEY† 《Journal of microscopy》2009,233(1):102-113
Focused Ion beam (FIB) prepared GaAs p-n junctions have been examined using off-axis electron holography. Initial analysis of the holograms reveals an experimentally determined built-in potential in the junctions that is significantly smaller than predicted from theory. In this paper we show that through combinations of in situ annealing and in situ biasing of the specimens, by varying the intensity of the incident electron beam, and by modifying the FIB operating parameters, we can develop an improved understanding of phenomena such as the electrically 'inactive' thickness and subsequently recover the predicted value of the built-in potential of the junctions.
PACS numbers: 85.30.De 相似文献
PACS numbers: 85.30.De 相似文献
206.
Y. Z. Huang S. Lozano-Perez R. M. Langford J. M. Titchmarsh & M. L. Jenkins 《Journal of microscopy》2002,207(2):129-136
The preparation of transmission electron microscope (TEM) thin foil specimens from metal alloys containing cracks is usually thwarted by the difficulty in preventing preferential erosion of material along the flanks and at the tips of cracks. Recent developments in focused ion beam (FIB) micromachining methods have the potential to overcome this inherent problem. In this article we describe the development of new procedures, one using FIB alone and the other using a combination of FIB with more conventional ion milling to generate TEM specimens that largely retain the microstructural information at stress corrosion cracks in austentic alloys. Examples of corrosion product phase identification and interfacial segregation are included to verify that detailed information is not destroyed by ion bombardment during specimen preparation. 相似文献
207.
In this paper, synthetic fluorapatite–gelatine composite particles are prepared for transmission electron microscopy (TEM) studies using two methods based on focused ion beam (FIB) milling. TEM studies on the FIB‐prepared specimens are compared with TEM observations on samples prepared using an ultramicrotome. The results show that ultramicrotome slicing causes significant cracking of the apatite, whereas the ion beam can be used to make high‐quality, crack‐free specimens with no apparent ion beam‐induced damage. The TEM observations on the FIB‐prepared samples confirm that the fluorapatite composite particles are composed of elongated, preferentially orientated grains and reveal that the grain boundaries contain many small interstices filled with an amorphous phase. 相似文献
208.
Milani M Drobne D Tatti F Batani D Poletti G Orsini F Zullini A Zrimec A 《Scanning》2005,27(5):249-253
A novel focused ion beam-based technique is presented for the read-out of microradiographs of Caenorhabditis elegans nematodes generated by soft x-ray contact microscopy (SXCM). In previous studies, the read-out was performed by atomic force microscopy (AFM), but in our work SXCM microradiographs were imaged by scanning ion microscopy (SIM) in a focused ion beam/scanning electron microscope (FIB/SEM). It allows an ad libitum selection of a sample region for gross morphologic to nanometric investigations, with a sequence of imaging and cutting. The FIB/SEM is less sensitive to height variation of the relief, and sectioning makes it possible to analyse the sample further. The SXCM can be coupled to SIM in a more efficient and faster way than to AFM. Scanning ion microscopy is the method of choice for the read-out of microradiographs of small multicellular organisms. 相似文献
209.
Lucille A. Giannuzzi 《Scanning》2005,27(4):165-169
In addition to the production of secondary electrons and secondary ions, characteristic x‐ray emission may also result from ion/solid interactions and is the basis for the well‐known analysis technique referred to as particle‐induced x‐ray emission. Characteristic x‐rays may be emitted by either bombardment by MeV protons or heavy ions of a few keV. The advantage to heavy ions is that the x‐ray yield is confined to the region near the surface defined by the collision cascade. An advantage of heavy ion‐induced x‐ray emission over electron‐induced x‐ray emission is that the Bremsstrahlung is potentially orders of magnitude lower. Thus, ion‐induced x‐ray spectra may provide for superior peak‐to‐noise ratios, and there‐fore, offers trace element sensitivity compared with elec‐tron‐induced x‐ray emission. In addition, the near surface ion/solid interactions also allow for the possibility of surface analysis or depth profiling. A Dual Beam instrument was used to collect focused ion beam‐induced x‐ray (FIBIX) spectra. The acquisition of characteristic x‐rays from targets via FIBIX is demonstrated and compared with scanning electron microscopy‐induced x‐ray energy dispersive spectroscopy spectra and is consistent with the theory described above. 相似文献
210.
自适应波束形成随着数字信号处理技术的不断发展,已广泛应用于雷达、语音、医疗等领域。然而,当阵列发生扰动时,将会导致干扰偏离零陷位置,甚至会导致算法完全失效。为了解决现有波束形成算法在发生导向矢量失配和干扰位置扰动时波束形成器性能急剧下降的问题,本文提出了一种导向矢量失配条件下多约束鲁棒波束形成算法。本文参照实际情况引入更多约束,增加了双边范数扰动约束以及二次相似性约束,允许了误差产生的范围。此外,本文确保感兴趣信号（Signal Of Interest, SOI）的到达方向（Direction Of Arrival, DOA）远离干扰导向矢量的所有线性组合的DOA区域,保证了最优导向矢量的DOA位于SOI的角扇形区域。首先,以波束形成器输出最大功率为目标,并结合实际环境下的约束条件,建立了最优导向矢量的数学模型。其次,利用定义的干扰范围重构协方差矩阵,以此来展宽零陷,提高系统的抗干扰性能。最后,先用内点法求得替代变量的解,以此求解针对导向矢量的二次不等式约束问题;随后在约束模型中代入替代变量,用交替方向乘子法迭代求解导向矢量,在每一次的迭代中都会得到显示解。同时,本文还对算法的时间复杂度和收敛性进行了分析。实验结果显示,相较于传统的波束形成算法,所提方法加宽了干扰处零陷,使得波束形成器的抗干扰性能得到了一定的提高,且能够很好地校正失配导向矢量。 相似文献