An algorithm for pole-zero system model order estimation

In system identification, estimates of the unknown system model orders are often required. An algorithm for estimating model orders is described that looks at input/output data covariance matrix eigenvectors. When model orders are overestimated, zeros appear in the noise subspace eigenvectors. The number of zeros present can be used to estimate model orders     

A simpler 100-V polysilicon TFT with improved turn-oncharacteristics

An improved polysilicon high-voltage thin-film transistor (HVTFT) structure for eliminating the current-pinching phenomenon often observed in the conventional offset-gate polysilicon HVTFTs is discussed. The device employs, in lieu of implantation, a metal field plate overlapping the entire offset region to control the conductivity of the offset region. By properly biasing the field plate to distribute the drain electric field at both ends, high-voltage operation of up to 100 V, suitable for many large-area applications, is achieved. Good turn-on characteristics without current pinching effects are consistently obtained. The structure also eliminates the lightly doped drain implant required in conventional offset-gate HVTFTs, resulting in a simpler and more reproducible process     

Optimal sampling and range of measurement in displacement-only laser-speckle correlation

A statistical analysis of the subjective laser-speckle pattern is performed with emphasis on its spectral distribution. An optimal sampling resolution of the laser-speckle pattern is obtained using the Shannon sampling theorem. Experiments show that the displacement-only correlation using laser speckles is a reliable measurement as long as the sampling requirement is satisfied. Upper limits of measurement such as accuracy, measurable area and measurable deformation are discussed. A method of changing the measurement capabilities by adjusting the speckle-recording arrangement is also given.Paper was presented at the 1989 SEM Spring Conference on Experimental Mechanics held in Cambridge, MA on May 23–June 1.     

Refractive-index profiling of graded-index planar waveguides fromeffective indexes measured for both mode types and at differentwavelengths

It is well known that, under the WKB approximation, the refractive-index profile of a graded-index planar waveguide can be calculated from the corresponding effective-index function, which can be found approximately by least-squares fitting of a set of measured effective indexes. In the previous work, effective indexes measured for a particular type of modes (the TE or TM modes) at a single wavelength are used. This requires that the waveguide supports at least three modes of the same type. In this paper, techniques of combining the effective indexes measured for both mode types and at different wavelengths are proposed and demonstrated with examples. With these techniques, single-mode and two-mode waveguides can be profiled     

Finite element method for cutoff frequencies of weakly guiding fibres of arbitrary cross-section

A finite element method is presented for directly determining the cutoff frequencies of a weakly guiding fibre, which can be of arbitrary inhomogeneity and cross-sectional shape. Errors of the method are discussed. Simple correction factors are given to improve the accuracy.     

Atomic and electronic processes of switching in amorphous thin films

It is proposed that the conversion of C₃⁰ from C₂⁰ leads to switching. Since C₃⁰ has more connection points, the conductivity of C₃⁰ is higher and large current favours the C₃⁰ species; thus increasing the current increases the C₃⁰ density and less voltage is needed to sustain the same amount of current. This explains the S-shaped negative resistance. The concept is simple and the mathematics for quantitative calculation is manageable.     

Tree multicast strategies in mobile,multihop wireless networks

Tree multicast is a well established concept in wired networks. Two versions, persource tree multicast (e.g., DVMRP) and shared tree multicast (e.g., Core Based Tree), account for the majority of the wireline implementations. In this paper, we extend the tree multicast concept to wireless, mobile, multihop networks for applications ranging from ad hoc networking to disaster recovery and battlefield. The main challenge in wireless, mobile networks is the rapidly changing environment. We address this issue in our design by: (a) using soft state (b) assigning different roles to nodes depending on their mobility (2level mobility model); (c) proposing an adaptive scheme which combines shared tree and persource tree benefits, and (d) dynamically relocating the shared tree Rendezvous Point (RP). A detailed wireless simulation model is used to evaluate various multicast schemes. The results show that persource trees perform better in heavy loads because of the more efficient traffic distribution; while shared trees are more robust to mobility and are more scalable to large network sizes. The adaptive tree multicast scheme, a hybrid between shared tree and persource tree, combines the advantages of both and performs consistently well across all load and mobility scenarios. The main contributions of this study are: the use of a 2level mobility model to improve the stability of the shared tree, the development of a hybrid, adaptive persource and shared tree scheme, and the dynamic relocation of the RP in the shared tree.     

A short,efficient total synthesis of (±) acivicin and (±) bromo-acivicin

A practical approach to the synthesis of (±) acivicin (1) and (±) bromo-acivicin (6) has been developed. It centers on the synthesis of alkene 10 by a thermal [3,3] sigmatropic rearrangement of trichloroimidate 9.