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1.
In the context of the simple growth model of two level pyramids consisting of 2D islands, we examine the incipient transition
from 2D to 3D growth. It is shown that the characteristic time of transition to 3D growth can depend nonmonotonically on temperature.
Under high temperatures, the formation of 3D islands is caused by atoms detaching from the edge of a 2D island to its surface.
Under low temperatures, 3D-island formation is caused by adsorbed atom transition from the initial surface over the edge of
a 2D island, without visiting the position in the kink. The last mechanism takes place under the weak migration of the adsorbed
atoms along an island edge, if the Schwoebel barrier and potential well for the adsorbed atom on the 2D-island surface relative
to the initial surface are present. 相似文献
2.
Robert Forchheimer Keping Chen Christer Svensson Anders Ödmark 《Journal of Signal Processing Systems》1993,5(2-3):121-131
The architectures, implementation and applications of two smart sensors, LAPP and PASIC, are described. The basic idea of these two designs is to integrate an image sensor array with a digital processor array in a single chip. The integrated camera-and-processor eliminates the bottleneck of sequential image read-out that characterizes conventional systems. They provide fast, compact and economic solutions for tasks such as industrial inspection, optical character recognition and robot vision. 相似文献
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Aperture extension (interferometry baseline extension) is achieved in this novel ESPRIT-based two-dimensional (2-D) arrival angle estimation scheme using a sparse (a.k.a., thin or thinned) uniform rectangular array of electromagnetic vector sensors spaced much farther apart than a half-wavelength. An electromagnetic vector sensor is composed of six spatially co-located, orthogonally oriented, diversely polarized antennas, distinctly measuring all six electromagnetic-field components of an incident multisource wavefield. Each incident source's direction of arrival (DOA) is estimated from the source's electromagnetic-field vector component and serves as a coarse reference to disambiguate the cyclic phase ambiguities in ESPRIT's eigenvalues when the intervector sensor spacing exceeds a half wavelength. Simulations demonstrate the significant performance gain realizable by this method for radar and wireless mobile fading-channel communications 相似文献
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Two-dimensional (2D) nanomaterials have demonstrated great potential in the field of flexible gas sensing due to their inherent high specific surface areas, unique electronic properties and flexibility property. However, numerous challenges including sensitivity, selectivity, response time, recovery time, and stability have to be addressed before their practical application in gas detection field. Development of graphene-like 2D/2D nanocomposites as an efficient strategy to achieve high-performance 2D gas sensor has been reported recently. This review aims to discuss the latest advancements in the 2D/2D nanocomposites for gas sensors. We first elaborate the gas-sensing mechanisms and the collective benefits of 2D/2D hybridization as sensor materials. Then, we systematically present the current gas-sensing applications based on different categories of 2D/2D nanocomposites. Finally, we conclude the future prospect of 2D/2D nanocomposites in gas sensing applications. 相似文献
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A new two-dimensional (2D) phase-conjugated retrodirective array with star-shaped antenna elements is proposed. The phase conjugators provide high isolation of -48 dB between RF and IF ports when RF/IF signals share the same ports in a balanced hybrid. By on-off keying modulation of the local oscillator (LO), the new 2D phase-conjugated retrodirective array can reflect the signal back to the interrogator with the modulation signal carried on it for information exchange. Experimental results show that this array can achieve 2D retrodirectivity within 120deg angle of wide scan range at arbitrary signal polarisation and injection direction 相似文献
7.
A 2D array implementation of image segmentation by a directed split and merge procedure is proposed. Parallelism is realized on two levels: one within the split and merge operations, where more than one merge (or split) may proceed concurrently, and the second between the split and merge operations, where several splits may be performed in parallel with merges. Both the split and merge operations are based on nearest neighbor communications between the processing elements (PEs), and facilitating low communication costs. The basic arithmetic operations required to perform split and merge are comparison and addition, allowing a simple structure of the PE as well as a hardwired control. A local of 512 bytes is sufficient to hold the interim data associated with each PE. A prototype PE has been constructed using 3 μm double-metal CMOS technology. Scaling up to 0.8 μm, it is possible to incorporate 32 PEs on a 5 cm2 chip. With sufficiently large PE window sizes, image segmentation can be achieved in linear time 相似文献
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Venkatesh Y.V. Ramani K. Nandini R. 《Vision, Image and Signal Processing, IEE Proceedings -》1994,141(5):348-356
A new class of an array of wavelet-like functions, derived from generalised Hermite polynomials and controlled by a scale parameter, has been used to create a multilayered representation for one- and two-dimensional signals. This representation, which is explicitly in terms of an array of coefficients, reminiscent of Fourier series, is stable. Among its other properties, (a) the shape of the resolution cell in the `phase-space' is variable even at a specified scale, depending on the nature of the signal under consideration; and (b) zero crossings at the various scales can be extracted directly from the coefficients. The new representation is illustrated by examples. However, there do remain some basic problems with respect to the new representation 相似文献
10.
A new approach for active-sonar target detection and bearing estimation from a mobile two-dimensional array of sensors operating in a predominantly noisy environment is presented. Sensor-level adaptive noise cancellation featuring an unconventional method for reference-noise estimation is the key preprocessing step in the proposed approach. A signal-subspace algorithm resulting from two-stage optimisation based on a generalised eigendecomposition of the signal plus (residual) noise covariance matrix is employed to estimate the bearing of the detected target. Simulation results conclusively demonstrate that the proposed scheme is capable of performing target detection and the subsequent two-dimensional bearing estimation with a high degree of reliability at signal-to-noise power ratios as low as -70 and -40-dB, respectively. 相似文献
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S. E. Bankov M. D. Duplenkova 《Journal of Communications Technology and Electronics》2017,62(8):827-837
A 2D periodic array of coupled slot transmission lines is considered in the approximation of equivalent boundary conditions. The eigenmode problem for an array operating in the quasi-periodic mode is formulated and solved. The dispersion equation for eigenmode propagation constants and expressions for eigenmode fields are obtained. The behavior of eigenmodes in a frequency band and in a range of values of geometric parameters is analyzed. The orthogonality of eigenmodes is shown. Theoretical results are compared to the results of numerical calculation performed with the use of electromagnetic simulation systems. 相似文献
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Kawai S. Morimoto M. Mutoh N. Teranishi N. 《Electron Devices, IEEE Transactions on》1995,42(4):652-655
Photo response in CCD image sensors with Vertical-Overflow-Drain (VOD) was analyzed in an attempt to discover a way to lessen the photo response rise that accompanies increasing incident light intensity in the saturation region. A photo response analysis based on transistor I-V characteristics revealed that the extent of rise in the saturation region is uniquely determined by the non-ideality factor and temperature. Calculation of the non-ideality factor and its dependence on P-well impurity concentration and layer thickness further revealed that fabrication of P-wells with lower impurity concentrations and thicker layers would be effective in suppressing photo response rise 相似文献
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Sheng Liu Lisheng Yang Dong Li Hailin Cao 《Multidimensional Systems and Signal Processing》2017,28(1):315-327
A subspace extension algorithm for two-dimensional (2D) direction-of-arrival (DOA) estimation with an L-shaped array is proposed. This L-shaped array is comprised of two orthogonal sparse linear arrays (SLAs). Each SLA consists of two different uniform linear arrays. The cross-correlation matrix of received data is used to construct two extended signal subspaces, by which the azimuth angles and elevation angles can be estimated independently. The procedure used to extend signal subspace only needs a small amount of calculation. Then, an effective pair-matching method is addressed to pair the estimated elevation angles and azimuth angles. Although the signal subspaces are extended, the complexity of the proposed 2D DOA estimation algorithm is lower than many similar algorithms. Simulation results indicate the availability of the proposed pairing-matching method and subspace extension algorithm. 相似文献
18.
为明确星敏感器支架受空间环境影响产生的变形对星敏感器定姿精度的影响,对星敏感器支架的结构/热稳定性进行了研究。通过有限元法对星敏感器支架进行刚度分析,将热分析获得的在轨极端工况下的温度数据映射至结构模型上计算得到热变形,利用最小二乘法得到各星敏感器光轴矢量,最后进行试验验证。结果表明:星敏感器组件的结构基频为429 Hz,与分析结果相差不超过2%,试验前后星敏感器光轴与基准坐标系各轴夹角最大变化不超过5;在轨期间星敏感器支架最大温度波动小于2 ℃,星敏感器光轴变化最大为4~5,与分析结果一致。星敏感器支架的结构/热稳定性良好,能够满足星敏感器定姿精度要求。 相似文献
19.
针对现有圆极化平面阵列的扫描角受限和三维宽角扫描阵列体积大的问题,设计了一种基于阵因子方向图和单元因子方向图互补的低剖面宽角扫描圆极化阵列天线.该阵列单元采用新型圆极化正交偶极子天线,并由其组成多个圆环子阵,每一子阵内单元的法向均偏离阵列法向一个固定倾角并等间距排布在"涟漪"状金属地板上.这种阵列排布方式使得在主波束扫描至大角度时天线单元因子增益可以补偿阵因子的增益下降.设计的一个64元阵列天线的实测结果表明:在8~9 GHz工作带宽内,且波束扫描覆盖0°~±62°,各阵元的有源驻波比均小于2.1,中心频点扫描增益起伏小于1.71 dB,扫描波束的圆极化轴比小于2 dB. 相似文献
20.
Sugibayashi T. Takeshima T. Naritake I. Matano T. Takada H. Aimoto Y. Furuta K. Fujita M. Saeki T. Sugawara H. Murotani T. Kasai N. Shibahara K. Nakajima K. Hada H. Hamada T. Aizaki N. Kunio T. Kakehashi E. Masumori K. Tanigawa T. 《Solid-State Circuits, IEEE Journal of》1993,28(11):1092-1098
A 256-Mb DRAM with a multidivided array structure has been developed and fabricated with 0.25-μm CMOS technology. It features 30-ns access time, 16-b I/Os, and a 35-mA operating current at a 60-ns cycle time. Three key circuit technologies were used in its design: a partial cell array activation scheme for reducing power-line voltage bounce and operating current, a selective pull-up data-line architecture to increase I/O width and reduce power dissipation, and a time-sharing refresh scheme to maintain the conventional refresh period without reducing operational margin. Memory cell size was 0.72 μm2. Use of the trench isolated cell transistor and the HSG cylindrical stacked capacitor cells helped reduce chip size to 333 mm2 相似文献