A study of performance degradation of small-cell radio systemscaused by improper antenna positioning

A report is presented on the results of an extensive computer-simulation study of the cochannel interference caused by imprecise antenna locations. Interference problems are investigated for various percentage tolerances (which determine tolerance circles around ideal locations) and spatial distributions (which determine actual antenna location inside the tolerance circles) using the tenth percentile of the S/I distribution of the mature system as a criterion. One result shows that system performance is highly sensitive to large-percentage tolerances in later stages of cell-splitting. After analyzing the results, a method was developed to predict the performance of a general mature system with any number of cell sites, any cell radius, any set of percentage tolerances, and any set of spatial distributions     

DC and AC characteristics of a nonalloyed delta-doped MESFET byatomic layer epitaxy

The growth and fabrication of a nonalloyed delta-doped FET entirely grown by atomic layer epitaxy are reported. The DC and RF performances are shown to be comparable to similar devices fabricated on materials grown by other techniques. FETs having a gate length of 1.5 μm show transconductances as high as 144 mS/mm at a current density of 460 mA/mm. The breakdown voltage for these devices is between 20 and 25 V for a gate-to-drain spacing of 1.6 μm. An f_T and f_max of 13 and 19 GHz were obtained respectively. These values are among the highest values reported for MESFETs with similar geometry     

Mechanical property relationships in glass-filled polyoxymethylene

The dependence of the mechanical properties such as strength, modulus and fracture toughness on the volume fraction of the reinforcing glass fibres and glass beads in polyoxymethylene (POM) matrix was studied. The majority of the measured quantities in tension or flexure tests, seemed to be linear functions of either the volume fraction of the glass fibres or the glass beads. The relationship between some individual mechanical properties seemed to be linear as well. Consequently, many of the mechanical properties of these POM composites (POM/GF and POM/GB) could be estimated from one measured property using the relationships presented. Also, the same property measured for the two composite systems was found to be linearly related. Consequently, the mechanical properties of one composite system, (i.e. POM/GB) could be used to determine that of the other system (i.e. POM/GF) at the same filler concentration.     

High-performance submicrometer gatelength GaInAs/InP compositechannel HEMT's with regrown ohmic contacts

This letter reports DC and RF performance of 0.25 μm gatelength GaInAs/InP composite channel HEMT's with nonalloyed, regrown ohmic contacts by MOCVD. Regrown channel contacts are used to achieve low contact resistance (0.35 Ω-mm) to (50 Å) GaInAs/(150 Å) InP composite channel HEMT's. High transconductance (600 mS/mm), high full channel current (650 mA/mm), and high peak cut-off frequencies (F_t=70 GHz, F_max=170 GHz) are observed. Contact transfer resistance of regrown channel contacts is compared to conventional alloyed contacts for varying GaInAs/InP channel composition     

Fracture from inherent flaws in polymers

Fracture data on polymethyl methacrylate, polyvinyl chloride, polyacetal and polypropylene in both tension and bending are given for a range of temperatures using unnotched specimens. It is concluded that all the failures occur at the gross crazing or yield stress and are thus stress-controlled, and the flaw size has little effect. The propagation behaviour of the flaws under these conditions is discussed in terms of stability criteria.     

Focal-Plane Spatially Oversampling CMOS Image Compression Sensor

Image compression algorithms employ computationally expensive spatial convolutional transforms. The CMOS image sensor performs spatially compressing image quantization on the focal plane yielding digital output at a rate proportional to the mere information rate of the video. A bank of column-parallel first-order incremental DeltaSigma-modulated analog-to-digital converters (ADCs) performs column-wise distributed focal-plane oversampling of up to eight adjacent pixels and concurrent weighted average quantization. Number of samples per pixel and switched-capacitor sampling sequence order set the amplitude and sign of the pixel coefficient, respectively. A simple digital delay and adder loop performs spatial accumulation over up to eight adjacent ADC outputs during readout. This amounts to computing a two-dimensional block matrix transform with up to 8times8-pixel programmable kernel in parallel for all columns. Noise shaping reduces power dissipation below that of a conventional digital imager while the need for a peripheral DSP is eliminated. A 128times128 active pixel array integrated with a bank of 128 DeltaSigma-modulated ADCs was fabricated in a 0.35-mum CMOS technology. The 3.1 mm times 1.9-mm prototype captures 8-bit digital video at 30 frames/s and yields 4 GMACS projected computational throughput when scaled to HDTV 1080i resolution in discrete cosine transform (DCT) compression     

高速ADC输入驱动器应用注释

LMH6555差分放大器经过精心设计，专门用来驱动每秒千兆样（GSPS）模数转换器（ADC）的100W差分输入，效果可高至0．8VP-P，并对端接线有50Ω输入阻抗以达至最高的回波损耗。这款放大器可以被用作一个单端输入到差分输出，又或可直接作为一个差分输入／输出驱动器。然而，最普遍的是使用在直流，耦合（或宽频）的应用中，     

Hierarchical analysis and multi-scale modelling of rat cortical and trabecular bone

The aim of this study was to explore the hierarchical arrangement of structural properties in cortical and trabecular bone and to determine a mathematical model that accurately predicts the tissue''s mechanical properties as a function of these indices. By using a variety of analytical techniques, we were able to characterize the structural and compositional properties of cortical and trabecular bones, as well as to determine the suitable mathematical model to predict the tissue''s mechanical properties using a continuum micromechanics approach. Our hierarchical analysis demonstrated that the differences between cortical and trabecular bone reside mainly at the micro- and ultrastructural levels. By gaining a better appreciation of the similarities and differences between the two bone types, we would be able to provide a better assessment and understanding of their individual roles, as well as their contribution to bone health overall.