Showing papers by "Worcester Polytechnic Institute published in 1992"

Digital Signal Processing: Principles, Algorithms, and Applications

Abstract: 1. Introduction. 2. Discrete-Time Signals and Systems. 3. The Z-Transform and Its Application to the Analysis of LTI Systems. 4. Frequency Analysis of Signals and Systems. 5. The Discrete Fourier Transform: Its Properties and Applications. 6. Efficient Computation of the DFT: Fast Fourier Transform Algorithms. 7. Implementation of Discrete-Time Systems. 8. Design of Digital Filters. 9. Sampling and Reconstruction of Signals. 10. Multirate Digital Signal Processing. 11. Linear Prediction and Optimum Linear Filters. 12. Power Spectrum Estimation. Appendix A. Random Signals, Correlation Functions, and Power Spectra. Appendix B. Random Numbers Generators. Appendix C. Tables of Transition Coefficients for the Design of Linear-Phase FIR Filters. Appendix D. List of MATLAB Functions. References and Bibliography. Index.

Pulse oximetry: theory and applications for noninvasive monitoring.

Abstract: Noninvasive measurement of arterial oxygen saturation (SaO2) by pulse oximetry is widely acknowledged to be one of the most important technological advances in monitoring clinical patients. Pulse oximeters compute SaO2 by measuring differences in the visible and near infrared absorbances of fully oxygenated and deoxygenated arterial blood. Unlike clinical blood gas analyzers, which require a sample of blood from the patient and can provide only intermittent measurement of patient oxygenation, pulse oximeters provide continuous, safe, and instantaneous measurement of blood oxygenation. Here I review the theoretical background behind this advanced technology, instrumentation requirements, practical instrument calibration, common features of commercial pulse oximeters, specific clinical applications, and performance limitations of pulse oximeters.

Parallel processing in power systems computation

Abstract: The availability of parallel processing hardware and software presents an opportunity and a challenge to apply this new computation technology to solve power system problems. The allure of parallel processing is that this technology has the potential to be cost effectively used on computationally intense problems. The objective of this paper is to define the state of the art and identify what the authors see to be the most fertile grounds for future research in parallel processing as applied to power system computation. As always, such projections are risky in a fast changing field, but the authors hope that this paper will be useful to the researchers and practitioners in this growing area.

Invariant Properties of the Stress in Plane Elasticity and Equivalence Classes of Composites

Abstract: Attention is drawn to the invariance of the stress field in a two-dimensional body loaded at the boundary by fixed forces when the compliance tensor $\scr{G}$($\chi $) is shifted uniformly by $\ell^{\text{I}}$($\lambda $, -$\lambda $), where $\lambda $ is an arbitrary constant and $\scr{G}^{\text{I}}$($\kappa $, $\mu $) is the compliance tensor of a isotropic material with two-dimensional bulk and shear moduli $\kappa $ and $\mu $. This invariance is explained from two simple observations: first, that in two dimensions the tensor $\scr{G}^{\text{I}}$($\frac{1}{2}$, -$\frac{1}{2}$) acts to locally rotate the stress by 90 degrees and the second that this rotated field is the symmetrized gradient of a vector field and therefore can be treated as a strain. For composite materials the invariance of the stress field implies that the effective compliance tensor $\ell^{\ast}$ also gets shifted by $\scr{G}^{\text{I}}$($\lambda $, -$\lambda $) when the constituent moduli are each shifted by $\ell^{\text{I}}$($\lambda $, -$\lambda $). This imposes constraints on the functional dependence of $\ell^{\ast}$ on the material moduli of the components. Applied to an isotropic composite of two isotropic components it implies that when the inverse bulk modulus is shifted by the constant 1/$\lambda $ and the inverse shear modulus is shifted by -1/$\lambda $, then the inverse effective bulk and shear moduli undergo precisely the same shifts. In particular it explains why the effective Young's modulus of a two-dimensional media with holes does not depend on the Poisson's ratio of the matrix material.

Processing-microstructure relationships in compocast magnesium/SiC

Abstract: Compocasting experiments were conducted to investigate the feasibility of the process as applied to the AZ91 D magnesium alloy-SiC particles system. Processing-macro/ microstructure relationships were examined. Three temperature-time processing sequences were investigated: stirring temperature maintained above liquidus; stirring temperature in the semi-solid temperature range; and lastly, an imposed temperature rise above the liquidus after stirring in the mushy zone. Stirring temperature and particle size significantly affect spatial particle distribution and porosity level. The easy incorporation and even dispersion of particles in the matrix suggest good wetting of SiC particles by the magnesium matrix. Impact fracture surfaces show strong bonding at the particle/matrix interface. A reaction takes place at the matrix/particle interface whilst stirring at temperatures above the liquidus. Reaction products have been identified. Finally, the mechanical properties of a compocast ingot which was extruded have been studied and are reported. This work clearly points out that there is a preferred procedure to follow during compocasting to obtain an optimum microstructure. The procedure is to add the reinforcing materials to the semi-solid alloy followed by stirring above the liquidus temperature.

Collimator design for single photon emission tomography.

Abstract: We discuss recent trends in collimator design and technology, with emphasis on theoretical and practical issues of importance for single photon emission tomography (SPET). The well-known imaging performance parameters of parallel-hole collimators are compared with those of fan-beam collimators, which have enjoyed considerable success in recent years, particularly for brain SPET. We review a simplistic approach to the collimator optimization problem, as well as more sophisticated “task-dependent” treatments and important considerations for SPET collimator design. Practical guidance is offered for understanding trade-offs that must be considered for clinical imaging. Finally, selective comparisons among different SPET systems and collimators are presented for illustrative purposes.

Charge-coupled device detector: performance considerations and potential for small-field mammographic imaging applications.

Abstract: The physical characteristics of a charge‐coupled device(CCD)image detector were evaluated, as well as its potential as a digital imagingdevice for small field mammographic applications such as preoperative needle localization. The detectionsystem is based on a 2048×2048 pixel CCD operated in 1024×1024 mode. The CCD was optically coupled to an intensifying screen via a lens, without intermediate intensification. The thermal noise was suppressed to 0.15 electrons pixel−1s−1 by cooling the CCD with liquid nitrogen. The dominant source of noise was attributed to the on‐chip amplifier during the readout process that was performed at 50 000 pixels s−1. The measured readout noise level was 15 electrons per pixel. The low‐noise characteristics of this CCD prototype detector produced encouraging results under conditions simulating mammography, with a signal level close to one electron per pixel for each detected x ray. The mean glandular dose to the breast, based on the entrance exposure measured from a standard mammographic phantom would be 1.52 mGy (152 mrad). The ultimate spatial resolution of the system was approximately 8 cycles/mm but it was limited to about 5 cycles/mm when operated in the 1024×1024 imaging mode. Other physical characteristics of the system such as optical coupling efficiency, exposure response, and signal‐to‐noise ratio were evaluated. The results of this study suggest that the use of a scientific‐grade CCD allows for very good low‐contrast discrimination and moderate spatial resolution under conditions simulating mammography, but the current prototype is limited to a 9×9‐cm2 field of view. The results of this study suggest that with realistic improvements in the optical coupling via a faster lens or fiberoptic coupling, additional improvements in image quality and dose are feasible.

Fracture Toughness of Advanced Ceramics at Room Temperature.

Abstract: Results of round-robin fracture toughness tests on advanced ceramics are reported. A gas-pressure silicon nitride and a zirconia-toughened alumina were tested using three test methods: indentation fracture, indentation strength, and single-edge precracked beam. The latter two methods have produced consistent results. The interpretation of fracture toughness test results for the zirconia alumina composite is shown to be complicated by R-curve and environmentally assisted crack growth phenomena.

A combined FEM/MoM approach to analyze the plane wave diffraction by arbitrary gratings

Abstract: The diffraction of TE- and TM-polarized plane waves by planar gratings is numerically analyzed using a combined finite-element-method/method-of-moments (FEM/MoM) algorithm based on the generalized network formulation. The interior region, treated using the FEM, is truncated to a single unit cell with the introduction of an exact periodic boundary condition, which is enforced as a natural boundary condition. Using the FEM to compute the fields within the periodic structure allows gratings of arbitrary cross section and material composition to be efficiently modeled. >

Nuclear magnetic resonance properties of rocks at elevated temperatures

Abstract: Although the NMR properties of fluid-saturated rocks have been studied for decades, the temperature dependence of these properties has never been systematically investigated. A hot-air-flow loop has been constructed that can elevate the temperature of a core sample. An algorithm to estimate the distribution of NMR relaxation times from Fast Inversion Recovery/CPMG data has been developed and used to analyze the effects of temperature. Proton magnetic resonance measurements have been made on an assortment of water-saturated sandstones and carbonates and an oil-saturated sandstone at temperatures ranging from 25 to 175°C. The relaxation times of all the water-saturated sandstones and most of the carbonates depend only weakly on temperature. This indicates that the water-saturated rocks studied are in the fast-diffusion limit and the intrinsic surface relaxation strength is independent of temperature. In all the rocks studied the magnitude of the NMR signal, which is proportional to porosity, decreases with increasing temperature in accordance with the Curie Law. Data from oil-saturated sandstone clarify the roles of molecular diffusion, material-specific surface interactions, and bulk fluid relaxation.

Growth of transformed roots in a nutrient mist bioreactor: reactor performance and evaluation

Abstract: A nutrient mist bioreactor was modified for culturing transformed roots of Beta vulgaris and Carthamus tinctorius on a nylon support. Culture conditions of misting cycle, inoculum size, batch or continuous operation and sucrose concentration were varied in order to maximize growth over a 1-week period. Root tissue cultured in nutrient mists in a 1.8-1 culture chamber achieved levels of growth equivalent to hairy roots cultured in shake flasks with identical medium. Our results demonstrate the effectiveness of nutrient mist culture as applied to hairy roots, thereby providing an alternative means for successful culture of these tissues.

New magnetic resonance techniques for evaluating cerebrovascular disease

Abstract: Magnetic resonance (MR) imaging of acute stroke has made important contributions to diagnosis. Several novel MR technologies, now in preclinical and clinical development, will contribute to stroke diagnosis and perhaps help to guide therapy. MR angiography is the most clinically advanced new MR technology and offers the clinician a method to image noninvasively the extra- and intracranial vasculature. Diffusion-weighted MR imaging can demonstrate ischemic lesions quantitatively within minutes of onset in experimental stroke models, and human application is proceeding. Perfusion MR studies can reveal the presence or absence of cerebral perfusion in specific arterial territories. MR spectroscopy can assess tissue metabolites in vivo and reveal changes in these metabolites associated with ischemic injury. The combination of these new MR techniques should provide a plethora of information about the extent of ischemic lesions, associated vascular and perfusion deficits, and metabolic consequences. This information will afford the clinician the opportunity to assess and subtype ischemic stroke patients more rapidly and could be used to monitor therapeutic responses.

Axiomatic approach to structural design

Abstract: As civil engineering enters the 21st century, the demands on the profession will move toward complex, interdisciplinary tasks such as infrastructure rehabilitation, environmental cleanup, and the delivery of high-technology facilities (e.g., hospitals, RD particularly since conceptual design decisions determine a significant portion of a project's total cost. Axiomatic design is presented as a systematic framework for structural design because it aids the designer in satisfying multiple design objectives in a homogeneous manner throughout the design process. It is also an effective framework for formalizing and evaluating conceptual design decisions. The design of a structural frame for an innovative mechanical parking system is presented as an illustrative case study. This paper represents an initial effort to apply the principles of axiomatic design to the domain of civil engineering structures.

Excited-state absorption at 980 nm in erbium-doped glass

Abstract: Excited state absorption (ESA) spectra were measured for the 4I11/2? 4F7/2 transition at 980 nm in Er-doped fluoride and fluorophosphate glass, by varying the pump wavelength from a tunable Ti:sapphire laser and monitoring the relative strength of the green upconverted fluorescence. The ESA cross section spectra are the same order of magnitude in strength as the 980 nm ground state absorption, but shifted to shorter wavelength by 4-6 nm. The 980 nm ESA may limit the efficiency of high power erbium-doped fiber amplifiers, and provides a possible pump mechanism for IR upconversion pumped fiber lasers operating in the visible.

A composite micromechanical model for connective tissues: Part II--Application to rat tail tendon and joint capsule.

Abstract: A micromechanical model of fibrous soft tissue has been developed which predicts upper and lower bounds on mechanical properties based on the structure and properties of tissue components by Ault and Hoffman [3, 4]. In this paper, two types of biological tissue are modeled and the results compared to experimental test data. The highly organized structure of rat tail tendon is modeled using the upper bound aggregation rule which predicts uniform strain behavior in the composite material. This model fits the experimental data and results in a correlation coefficient of 0.98. Applied to cat knee joint capsule, the lower bound aggregation rule of the model correlates with the data and predicts uniform stress within this more loosely organized tissue structure. These studies show that the nature of the interactions between the components in tissue differs depending upon its structure and that the biomechanical model is capable of analyzing such differences in structure.

Formation of zeolite membranes from sols

Abstract: The present invention relates to a method of forming a zeolite membrane. The method includes forming an aqueous-based or an alcohol-based sol which can form a zeolite. The sol composition is then disposed on a porous support. The porous support and the sol composition are exposed to an atmosphere and to a temperature sufficient to cause the sol composition to hydrothermally crystallize, thereby forming the zeolite membrane.

Can contingent valuation measure nonuse values

Abstract: The authors outline how potentially coherent, consistent economic values can be determined by use of contingent valuation measurement (CVM). They use as an example three different CV studies to estimate nonuse values for groundwater. The authors also point out that rapidly changing political preferences can complicate the issues. They feel that the appropriate goal for CVM is to attempt to provide crystallized values for public decisionmaking.

Carbon dioxide improves the growth of hairy roots cultured on solid medium and in nutrient mists

Abstract: The effect of varying CO2 concentrations on the growth of beet and safflower hairy roots was measured for tissues cultured in nutrient mists and on solid media in chambers fed mixtures of humidified air supplemented with different CO2 concentrations. Hairy root tissue grown on solid media in air enriched with CO2 showed increased growth, as measured by dry weight increases vs air-fed controls. Growth increased with CO2 enrichment as much as 2.5 times more than the air-fed control for safflower at 1.0% CO2 and 1.4 times more than the air-fed control for beets at 1.5% CO2 over a 12-day period. Beet hairy root tissue was also cultured aeroponically in nutrient mists. Beet hairy root cultured aeroponically in nutrient mists enriched with 1.0% CO2 showed a 15% increase in biomass over a 7-day period vs tissue cultured in nutrient mists (with ambient air) or in shake flasks. The stimulation of root growth via CO2 enrichment reduced the time required for biomass accumulation.

Process for the preparation of solid state materials and said materials

Abstract: A process for the preparation of solid state materials such as catalysts, electrolytes, piezo electric materials and superconductors is disclosed. The process produces materials with high phase purity. Novel solid state materials having high phase purity are also disclosed.

A composite micromechanical model for connective tissues: Part I--Theory.

Abstract: A micromechanical model has been developed to study and predict the mechanical behavior of fibrous soft tissues. The model uses the theorems of least work and minimum potential energy to predict upper and lower bounds on material behavior based on the structure and properties of tissue components. The basic model consists of a composite of crimped collagen fibers embedded in an elastic glycosaminoglycan matrix. Upper and lower bound aggregation rules predict composite material behavior under the assumptions of uniform strain and uniform stress, respectively. Input parameters consist of the component material properties and the geometric configuration of the fibers. The model may be applied to a variety of connective tissue structures and is valuable in giving insight into material behavior and the nature of interactions between tissue components in various structures. Application of the model to rat tail tendon and cat knee joint capsule is described in a companion paper [2].

Relation between transmission and throughput of slotted ALOHA local packet radio networks

Abstract: A new method for the exact calculation of the throughput of a centralized slotted ALOHA packet radio network over slow Rayleigh-fading channels is presented and the results are compared with the computer simulations. Also, upper and lower bounds on the performance are provided. The effects of capture on the throughput of the system are related to the modulation and coding technique, signal to noise ratio of the received signal, general terminal distribution in the area, and the length of the transmitted packets. The binary phase shift keying (BPSK), coherent and noncoherent binary frequency shift keying (FSK) modulations and BCH coding are considered for the exact calculations. The results of the analysis show that the maximum average throughput of the slotted Aloha packet radio network is around 60% rather than 36% predicted from the simplified analysis. In contrast with some previous reports, it is shown that the throughput of the system is not affected significantly by the use of coding or the change of packet lengths. >

Mixing in Thermals with and without Buoyancy Reversal

Abstract: The mixing characteristics of turbulent thermals were investigated in a water tank via laser-induced fluorescence techniques. The concentration of mixed fluid in the far field of a “classical” thermal is approximately uniform, whereas the near field is dominated by a moderately diluted toroidal core. The effects of atmospheric evaporative cooling on thermals were simulated by using chemicals with nonlinear buoyancy-reversing behavior. Even though the trajectory of an “evaporating” thermal depends strongly on a buoyancy-reversal parameter, the minimum mixing rate is not greatly modified. A simple derivation, based on the self-similar properties of thermals, provides the minimum molecular-scale mixing rate, which agrees with the measurements. These observations may enhance the understanding of cumulus clouds in weakly stratified environments.

Observation of Localized Above-Barrier Excitons in Type-I Superlattices

Abstract: This Letter reports experimental evidence for the existence or localized excitons at above-barrier energies in type-I superlattices. By using magnetoabsorption measurement on a series or Zn 0.86 Cd 0.14 -Se/Zn 0.75 Mn 0.25 Se superlattices, where the subbands localized in nonmagnetic and magnetic layers undergo drastically different Zeeman splittings, we show conclusively that above-barrier excitons are localized in the barrier rather than in the well regions