Showing papers by "Hong Kong University of Science and Technology published in 1991"
TL;DR: A recognition of the functional advantages derivable from the post-transcriptional addition of peptide cofactors to RNA apo-catalysts enables the formulation of a theory for the origin of the genetic encoding of protein synthesis by RNA.
Abstract: The difficulty in explaining the origin of genetic coding centres on the need to identify selective advantages that could account for the synthesis of peptidyl-tRNA, the essential intermediate in genetically programmed translation. It is resolved by a recognition of the functional advantages derivable from the post-transcriptional addition of peptide cofactors to RNA apo-catalysts. This enables the formulation of a theory for the origin of the genetic encoding of protein synthesis by RNA.
61 citations
TL;DR: In this article, the authors proposed a more relaxed selection rules compared with IR and Raman, allowing alllR-active vibrational modes are hyper-Raman allowed, and those modes inactive in both IR and RAMAN (i.e., the “silent” modes) may be active in hyper Raman scattering.
Abstract: Hyper-Raman scattering (HRS), first theoretically predicted by Decius and Rauch in 1959 [l] and experimentally demonstrated by Terhune et al. in 1965 [2], is a nonlinear optical process involving two incident photons (ω0) and one emitted photon (ω). The emitted hyper- Raman photon frequencies are Raman-shifted relative to the second harmonic frequency (2ω0) of the incident laser radiation [3–6]. The energy difference (2ω0 – w) corresponds to one of the characteristicvibrational frequencies of the scattering medium or molecule. In Fig. 1 is given a schematic illustration of resonant and nonresonant HRS. The primary advantage of this nonlinear optical technique lies in its more relaxed selection rules compared with IR and Raman [7,8]. AlllR-active vibrational modes are hyper-Raman allowed, and those modes inactive in both IR and Raman (i.e., the “silent” modes) may be active in hyper-Raman scattering.
40 citations
TL;DR: In this article, the use of an efficient and convenient silver substrate in the development of surfaceenhanced near-infrared Fourier transform (FT) Raman scattering as a useful analytical technique that compliments the bulk FT-Raman method is described.
Abstract: This report describes the use of an efficient and convenient silver substrate in the development of surface-enhanced near-infrared Fourier transform (FT) Raman scattering as a useful analytical technique that compliments the bulk FT-Raman method. The SERS-active material, prepared in the form of solid silver powder by means of chemical precipitation, is particularly well suited for surface Raman enhancement in the near-IR region. To demonstrate the unique features of surface-enhanced FT-Raman, a detailed spectroscopic study of the charge-transfer donor molecule tetrathiafulvalene (TTF) adsorbed on the silver powder is also reported. The advantages of near-IR FT-SERS over bulk FT-Raman include the ability to analyze dilute solution samples, the acquisition of Raman spectra for near-IR fluorescent compounds and new vibrational information concerning the mixed-valence behavior of surface-bound TTF molecules.
25 citations
TL;DR: Using the conjugate complex variables formulation, closed-form formulae for the gravity gradient tensors of the gravitational potential due to a homogeneous polyhedral body composed of polygonal facets are derived in this article.
Abstract: Using the conjugate complex variables formulation, closed-form formulae for the gravity gradient tensors of the gravitational potential due to a homogeneous polyhedral body composed of polygonal facets are derived. The treatise considers the cases of the observation point being inside the polyhedron, on the surface of a facet, or outside the polyhedron.
23 citations
01 Jun 1991
TL;DR: It is argued that the learning process takes advantage of the transfer effects of prior learning in constructing large networks from smaller ones, which is a dynamic network construction process which involves adjusting the network weights as well as the topology.
Abstract: Determining the appropriate size of an artificial neural network for a given inductive learning problem at hand has been more of an art than a science. Human intervention through educated guess is often needed in the otherwise automatic learning process. We address this issue by formulating the problem as a systematic search in the space of functions which corresponds to a subclass of multilayer feedforward networks. Learning is thus a dynamic network construction process which involves adjusting the network weights as well as the topology. Adding new hidden units corresponds to extracting new features from the input attributes for reducing the residual classification errors. We argue that the learning process takes advantage of the transfer effects of prior learning in constructing large networks from smaller ones. The paper also includes empirical results of several inductive learning problems.
22 citations
01 Aug 1991
TL;DR: A first generation anatomic brain model was developed to estimate strains induced in the brain as a result of typical head impacts sustained in automotive collisions to support the development of an expanded head-injury criteria.
Abstract: This article first describes modeling and analysis of relatively rigid head impacts with upper interior structures and compares results with laboratory test measurements. In addition to demonstrating the capacity of a well defined model to accurately replicate dynamic response and to predict levels of injury mitigation obtainable from structural modification, such models are also capable of estimating physical quantities (e.g. detailed stress/strain patterns) known to affect the functional capacity of brain tissue. Measuring these quantities in a test program would be virtually impossible. To provide estimates of such quantities, a first generation anatomic brain model was developed to estimate strains induced in the brain as a result of typical head impacts sustained in automotive collisions. The latter model is viewed as the first step in a complicated process, leading towards the ability to assess soft tissue injuries, and to the development of an expanded head-injury criteria which addresses specific forms of brain injuries known to result from automobile crashes.
19 citations
TL;DR: A study of lenses of varying age showed that carotenoid incorporation is accelerated as the fish grows older and hence its concentration is highest in the cortex.
17 citations
15 citations
01 Oct 1991
TL;DR: Tasks, which combine data and processing objects into encapsulated units that are easily joined with other tasks, are proposed as an effective knowledge encapsulation technique for organizational support systems.
11 citations
18 Nov 1991
TL;DR: The authors formulating the problem as an automatic search in the space of functions which corresponds to a subclass of multilayer feedforward networks which takes advantage of the transfer effects of prior learning in the construction of large networks from smaller ones.
Abstract: Determining the appropriate size of an artificial neural network for a given supervised learning problem at hand has usually been done through educated guess rather than automated means. The authors address this issue by formulating the problem as an automatic search in the space of functions which corresponds to a subclass of multilayer feedforward networks. Learning is thus a dynamic network construction process which involves adjusting the network weights as well as the topology. Adding new hidden units corresponds to extracting new features from the input attributes for reducing the residual classification errors. It is argued that the process takes advantage of the transfer effects of prior learning in the construction of large networks from smaller ones. Empirical results of some supervised learning experiments are also reported. >
7 citations
TL;DR: In this article, the UV laser ablation of three thermostable polymers, polyimide, polyphenylquinoxaline and Teflon AF of interest for microelectronics is presented.
Abstract: The UV laser ablation of three thermostable polymers, polyimide, polyphenylquinoxaline and Teflon AF of interest for microelectronics is presented. Direct absorption of the laser beam is not possible by Teflon, but a doping technique is described.
18 Nov 1991
TL;DR: The authors present a novel architecture, known as the rotational quadratic function neuron (RQFN), to implement the quadratics function neurons, which possesses some attributes which are unique when compared to QFN, which facilitates VLSI implementation.
Abstract: The authors present a novel architecture, known as the rotational quadratic function neuron (RQFN), to implement the quadratic function neuron (QFN). Although with some loss in the degree of freedom in the boundary formation, RQFN possesses some attributes which are unique when compared to QFN. In particular, the architecture of RQFN is modular, which facilitates VLSI implementation. Moreover, by replacing QFN by RQFN in a multilayer perceptron (MP), the fan-in and the interconnection volume are reduced to that of MP utilizing linear neurons. In terms of learning, RQFN also offers varieties such as the separate learning paradigm and the constrained learning paradigm. Single-layer MP utilizing RQFNs have been demonstrated to form more desirable boundaries than the normal MP. This is essential in the scenario where either the closure of the boundary or boundaries of higher orders are required. >
TL;DR: A duality theory using conjugate functions for mathematical programs that involve the composition of two convex functions was established in this paper, which generalizes our earlier work in quadratic and composite geometric programs.
Abstract: A duality theory using conjugate functions is established for mathematical programs that involve the composition of two convex functions. This generalizes our earlier work in quadratic and composite geometric programs. A specific application to minimax programs is given.
TL;DR: In this paper, the authors review the current state of commercial electronic design automation (EDA) tools for the design of multichip modules and discuss the impact of MCM on various aspects of EDA.
Abstract: In this paper we will review the current state of commercial electronic design automation (EDA) tools for the design of multichip modules. MCM can be classified in terms of its substrate technology. The choice of substrate technology has important implications for the selection of design automation tools. A PCB EDA system seems more appropriate for MCMs with stacked via substrate which closely resembles the through-hole printed circuit board (PCB). A chip layout system may be more appropriate for MCMs with low-cost thin-film silicon substrate which typically uses staircase vias. The cofired ceramic substrate MCM which evolved from the hybrid integrated circuit technology may use the specialized hybrid EDA software packages available for the designing of hybrid integrated circuits. Historically, printed circuit board and integrated circuit design automation software evolved separately. There exists a boundary between the printed circuit board and integrated circuit design automation tools in the physical design hierarchy. This boundary can be an important limitation for the repartitioning of the physical design hierarchy within the MCM. We shall discuss in detail the impact of MCM on various aspects of EDA. In the area of physical design, we must face the traditional placement and routing problem for any high speed design. Problems such as system clock skew and tight timing requirements must be considered. As one push clock frequency higher, one also must consider discontinuities due to vias and bends besides the classical transmission line effect due to long wires. Other traditional physical design problems such as ground and power plane generation, physical design verification and mask tooling must be revisited in the context of various MCM substrate technologies. The thermal aspects of MCM design are strongly influenced by the placement of chips on the MCM substrate. Thermal design is especially important for high density MCMs using the flip-chip mounting technology. Here, the heat must be dissipated through the back of the substrate via thermal pillars or bumps. We still need to deal with the traditional coupled transmission line problems. Due to the small cross section, high performance MCM substrate interconnects are resistive and the transmission lines they form are lossy. Noise is another main problem for MCM design. For high speed MCM with many CMOS buffers, the ground bouncing noise resulting from simultaneous switching of a large number of CMOS drivers must be controlled through proper substrate and package design. We will conclude the paper by comparing existing VLSI and PCB EDA tools for MCM design.
TL;DR: In this article, the authors report non-linear properties observed on polymer surfaces caused by excimer laser exposures, like increased hydrophilicity of polymer surfaces, imagewise wetting and metallization, and new metal compound formations on laser exposed polymer films.
Abstract: Surface properties of photoablated thermostable polymers are considerably different from those of original, unexposed ones, and of mercury UV lamp exposed surfaces. They also depend on the laser exposure conditions. This paper reports such non-linear phenomena observed on polymer surfaces, caused by excimer laser exposures, like increased hydrophilicity of polymer surfaces, imagewise wetting and metallizations, and new metal compound formations on laser exposed polymer films. Because these features are limited to polymer films with high glass transition temperature, like polyimides and poly(phenylquinoxaline), photo-mechanical effects may be important. In some cases, new interfacial reactions appear between exposed polymer surfaces and deposited metal films. Swelling of polyimide in pre-photoablation irradiation is discussed.
TL;DR: Complex contour integrals for the computation of vertical gravity and its vertical derivative due to a horizontal 2 1 2 -D mass model with arbitrary cross-sectional area and variable density are developed in this paper.
TL;DR: In this article, the authors carried out photoablation of Teflon AF (a copolymer of tetrafluoroethylene and 2, 2-bis(trifluoromethyl)-4, 5-difluoro-1, 3-dioxolene) at 193 and 248nm.
Abstract: KrF excimer laser lithography is a major candidate for sub-half micron VLSI technology, although it has many problems. The main topics of the present paper is not the excimer laser lithography, but a lithographic application of excimer laser photoablation, and surface modifications of polymer films, including silylation and metallization induced by excimer laser irradiation. Because the main application of excimer laser ablation is contact hole fabrication, photoablation of Teflon or Teflon like materials is important. We carried out photoablation of Teflon AF (a copolymer of tetrafluoroethylene and 2, 2-bis(trifluoromethyl)-4, 5-difluoro-1, 3-dioxolene) using a dopant at 193 and 248nm. High temperature resistant polymers like polyimides and polyphenylquinoxaline show imagewise wetting after excimer laser exposure in air, giving rise to direct surface silylation of these materials. Although we have not carried out image transfer experiments yet, XPS data clearly showed silicon incorporation. Imagewise metallization of these polymer surfaces after ArF excimer laser exposure in air showed some interfacial compound formations between exposed polymer surfaces and metal deposited. The XPS data of gold on PPQ exposed in air will be discussed.Effects of excimer laser exposures on polymer surfaces are repoorted, which include photoablation of Teflon AF by ArF and KrF excimer laser pulses, and surface modifications of some unsolved questions of the nature of interactions between deposited metals and laser exposed polymer surfaces. The study on these problems are in progress.
01 May 1991
TL;DR: In this paper, the authors describe the application of two recently developed spectroscopic techniques surfaceenhanced hyper-Raman and near-JR-excited Fourier transform (FT)-Raman in the structural characterization of biological molecules.
Abstract: This report describes the application of two recently developed spectroscopic techniques surfaceenhanced hyper-Raman and near-JR-excited Fourier transform (FT)-Raman in the structural characterization of biological molecules. Surface-enhanced hyper-Raman scattering (SEHRS) exhibits selection rules that are different from those of normal Raman resonance Raman and JR absorption and it is thus capable of providing new vibrational information unobtainable through existing methodologies. The technique of near-JR-excited FT-Raman almost completely eliminates fluorescence interference and photolytic sample decomposition problems that are frequently encountered in laser Raman studies of biological samples. The recent advent of FT-Raman has thus opened up many exciting opportunities in the vibrational investigation of biological molecules especially those that are highly fluorescent or unstable upon visible laser excitation. Presented as highlights in this report are: (1) a surface hyper-Raman study of an ocular lens chromophore (3- hydroxykynurenine) and copper chlorophyllin (2) an FT-Raman study of three groups of photolabile biomolecules cobalamins bacteriorhodopsin and chiorophylls and (3) near-JR FT-Raman spectra of cytochrome c and model porphyrins.
TL;DR: In this paper, the authors exemplified the use of MACSYMA in solving second order ordinary differential equations and demonstrated the role of MAC SYMA in the enhancement of teaching of an introductory ODE course.
Abstract: It has been becoming more popular to incorporate symbolic computation to supplement college calculus and differential courses. This paper exemplifies the use of MACSYMA in solving second order ordinary differential equations and demonstrates the role of MACSYMA in the enhancement of teaching of an introductory ordinary differential equations course.
TL;DR: In this paper, a two-level six-point finite difference of Pade type for the numerical solution of the quantum mechanical equation of motion is presented, and a family of second order accurate Pade schemes is obtained and the stability properties are analysed by the von Neumann and matrix methods.
Abstract: A systematic approach is presented to search for a two-level six-point finite difference of Pade type for the numerical solution of the quantum mechanical equation of motion. A family of second order accurate Pade schemes is obtained and the stability properties are analysed by the von Neumann and matrix methods. Also, a similar stability analysis is also performed for a family of two-level first order accurate upwinding difference schemes by the von Neumann and matrix methods. Discrepancies between the stability results obtained by the von Neumann and matrix methods are observed.
TL;DR: A method of analysis of both time complexity and space complexity for algorithms using conventional general purpose pipeline architectures is proposed and applied to an algorithm schema for local window operations satisfying a property the authors define as decomposability.
Abstract: Recently a number of machine vision systems have been successfully implemented using pipeline architectures and various new algorithms have been proposed. In this paper we propose a method of analysis of both time complexity and space complexity for algorithms using conventional general purpose pipeline architectures. We illustrate our method by applying it to an algorithm schema for local window operations satisfying a property we define as decomposability. It is shown that the proposed algorithm schema and its analysis generalize previous published results. We further analyse algorithms implementing operators that are not decomposable. In particular the complexities of several median-type operations are compared and the implication on algorithm choice is discussed. We conclude with discussions on space-time trade-offs and implementation issues.