Showing papers by "Worcester Polytechnic Institute published in 1990"

Exploring N-dimensional databases

Abstract: The authors present a tool for the display and analysis of N-dimensional data based on a technique called dimensional stacking. This technique is described. The primary goal is to create a tool that enables the user to project data of arbitrary dimensions onto a two-dimensional image. Of equal importance is the ability to control the viewing parameters, so that one can interactively adjust what ranges of values each dimension takes and the form in which the dimensions are displayed. This will allow an intuitive feel for the data to be developed as the database is explored. The system uses dimensional stacking, to collapse and N-dimension space down into a 2-D space and then render the values contained therein. Each value can then be represented as a pixel or rectangular region on a 2-D screen whose intensity corresponds to the data value at that point. >

Measurement and analysis of the indoor radio channel in the frequency domain

Abstract: Using a network analyzer, several experiments for the frequency-domain characterization of the indoor radio channel in the 0.9-1.1-GHz band are performed. In the experiments, the frequency response measurements are taken at spatially distributed locations throughout the test area by fixing the receiver in a central location and moving the transmitter to different locations. The experiments are performed in a high-rise office building and a three-story building with offices and laboratories. For each experiment, the exponent of the power-distance relationship and the statistics of the 3-dB width of the frequency correlation function are determined from the frequency-domain data. The approximation to the impulse response of the channel is obtained from the inverse Fourier transform of the frequency response. An empirical exponential relationship between the 3-dB width of the frequency correlation function and the inverse of the RMS (root mean square) delay spread of the impulse response is derived. >

Method and apparatus for monitoring blood analytes noninvasively by pulsatile photoplethysmography

Abstract: A non-invasive system for measuring the concentration of an analyte, such as glucose, in an absorbing matrix is described. The system directs beams of light at the matrix using an analyte sensitive wavelength and an analyte insensitive wavelength. The principles of photoplethysmography are applied to measure the change in light intensity caused by matrix absorption before and after the blood volume change caused by the systolic phase of the cardiac cycle. The change in light intensity is converted to an electrical signal which is used to adjust the light intensity and as a measure of analyte concentration.

Measurement Of Vibration Patterns Using Electro-Optic Holography

Abstract: This paper describes the use of an Electro-Optic Holography system for measuring vibration patterns on diffusely reflecting objects. The system provides a high-quality display of fringes for identifying modal frequencies and setting vibration levels after which image brightness data can be transferred to a host computer. A bias vibration is introduced into the illumination beam to shift the 0 fringes so that fringe shift algorithms can be used to determine vibration amplitude. Using this approach, high spatial density displacement fields for vibrating objects were obtained directly form the time-average interferograms recorded by the Electro-Optic Holography system. These results show good correlation with the reconstructions from the holograms and with the vibration characteristics predicted by the Finite Element Methods.

Inventory models with cost increases

Abstract: Two of the basic assumptions of economic order quantity models are an infinite horizon and static costs. In this paper, both assumptions are relaxed and results on the form of the optimal inventory policy are developed for both finite and infinite horizon models with changes in any or all costs. These results are used to develop short procedures for the computation of the optimal policy.

Spray casting of steel strip: Process analysis

Abstract: Near-net shape manufacturing (NNSM) of thin steel sections by spray casting eliminates casting as a separate step with attendant improved microstructures and properties and significant energy savings. The process involves atomization of a stream of liquid metal and deposition of droplets in the generated spray on a moving substrate at mass flow rates of 0.25 to 2.5 kg/s. In this paper, NNSM of steel strip by the Osprey spray casting process is investigated by combining numerical simulation and experiments. Critical input parameters for the computation are quantified utilizing existing state-of-the-art mathematical models and specific experiments. Numerical computation of the consolidation of the spray at the substrate during manufacture of thin sections is conducted using bothcontinuum anddiscrete event (“splat solidification”) approaches to predict: (1) variation of strip thickness in the transverse dimension and (2) isotherms and cooling rates across the strip thickness. Predicted geometries of the strip simulated by the continuum model are in good agreement with measurements. Predicted isotherms in narrow strip by the continuum approach are in reasonable agreement with thermocouple measurements for intermediate thicknesses (2 to 5 mm), and the observed microstructure is consistent with predicted cooling rates. The discrete event model predicts significantly higher cooling rates than the continuum model in the basal portion of the strip. This is consistent with the observed grain size in thin strip (

Doppler spread measurements of indoor radio channel

Abstract: The temporal variations caused by human movement or human-induced motion of the communication equipment, on the otherwise static indoor radio channel, are measured. For the reported narrowband measurements, a maximum Doppler spread of 6.1 Hz and a maximum RMS Doppler bandwidth of 0.87 Hz are observed.

Developments in ultrasonic modeling with finite element analysis

Abstract: An overview is given of finite element analysis and its application to the modeling of ultrasonic nondestructive evaluation phenomena. Following a discussion of the underlying weighted residual methodology, a mass-lumping technique is described which results in an efficient computer implementation for 2D geometries. Code predictions are compared with both analytical and experimental results, and data from studies of attenuation, anisotropy, defect interactions, and surface waves are given. Initial results from a full 3D formulation are also shown.

Genes that can be mutated to unmask hidden antigenic determinants in the cuticle of the nematode Caenorhabditis elegans.

Abstract: Rabbit antisera directed against a mixture of proteins solubilized from the wild-type adult Caenorhabditis elegans cuticle were used to isolate mutants, induced by ethyl methanesulfonate treatment, that exhibit alterations in surface antigenicity by immunofluorescence. Genetic mapping and complementation data for four such mutations define two genes, srf-2(I) and srf-3(IV). The mutant phenotypes observed by immunofluorescence appear to result from unmasking of antigenic determinants that are normally hidden in the wild-type cuticle. In support of this hypothesis, surface radioiodination experiments indicate that components labeled on the wild-type surface are missing or less readily labeled on the surface of srf-2 and srf-3 mutants.

Methodologia oeconomiae et systematis dynamis

Abstract: After enduring years of criticism from members of the economics profession, many system dynamicists have concluded that economists do not like system dynamics. This article outlines the methodologies of both neoclassical and institutional economics and demonstrates that the system dynamics modeling process is strikingly similar to the latter. Because a majority of economists trained in the West are neoclassicals, system dynamicists should not be surprised if many economists label system dynamics models unscientific. And since the institutional approach and the system dynamics approach are similar, it is argued, system dynamics should be used to strengthen and extend institutional economics.

A comparison of tests for setar-type non-linearity in time series

Abstract: Tests for SETAR-type non-linearity in time series have recently been proposed by Petruccelli and Davies (1986), W. S. Chan and Tong (1986), Tsay (1987), Luukkonen et al. (1988), Petruccelli (1987) and Moeanaddin and Tong (1988). In this paper we consider the relative performance of thes: tests.

Flows emerging from a nozzle and falling under gravity

Abstract: Steady two-dimensional free-surface flows of an inviscid and incompressible fluid emerging from a nozzle and falling under gravity are calculated numerically. The nozzle is aimed at an angle β above the horizontal. It is shown that there are flows for which the fluid falls down along the underside of the nozzle and other flows which split into two sheets. The latter flows occur for each value of β when the Froude number F is greater than a critical value. Local solutions are constructed to describe the limiting behaviour of the flows as F → 0 and as F → ∞.

Correlation of extrudate infusibility with bulk properties using image analysis

Abstract: Corn meal extrudates were produced using process conditions designed to obtain various product structures. Extrudates were infused with a particle-containing, high melting point lipid suspension, a process used to produce calorically dense components for military rations. Image analysis was used to estimate the degree of particle penetration into the extruded matrices and determine cell size distributions. Infusion uniformity was correlated with structural attributes, such as density, expansion, and average cell size.

The lost-foam casting of aluminum alloy components

Abstract: In the lost-foam casting process, liquid metal is poured directly onto a refractory-coated, foamed polymer pattern which is buried in loose sand. The polymer pattern undergoes thermal degradation and is gradually replaced by the molten metal, which solidifies and produces the casting. The inherent operating advantages of this innovative technique have generated considerable interest among casting manufacturers. Currently, the process is being utilized to manufacture a wide variety of ferrous and nonferrous components catering primarily to the automotive industry. Because the process is relatively new, there is a compelling need to quantify the influence of process parameters on microstructure and mechanical properties. Furthermore, the interaction of the thermal degradation products with the solidifying metal may produce several unique defects in the casting.

Design sensitivity analysis of boundary-element substructures

Abstract: A reduced set of DSA equations is obtained from the implicit differentiation of reduced BEM equations. Relationships for the expansion of the reduced DSA expressions to determine the sensitivities of all condensed quantities that are present in the analysis are also given. The present formulation allows for arbitrary condensing and noncondensing of zones in multiple zone models, and such zones can simultaneously exist in the reduced set of analysis equations. A set of numerical examples for two-dimensional plane and axisymmetric continua are presented

Fracture Toughness of Ceramic Precracked Bend Bars

Abstract: Fracture toughness was measured for four ceramic materials using precracked bend bar specimens. The effect of the precracking parameters, used for the bridge indentation method on fracture toughness values, was determined. Excellent agreement was obtained between fracture toughness values measured by this method and values obtained by other techniques.

Gravity-Driven Granular Flows of Smooth, Inelastic Spheres Down Bumpy Inclines

Abstract: We employ a kinetic constitutive theory that includes the effects of particle transport and collisions to analyze steady, fully developed, gravity-driven flows of smooth, inelastic spheres down bumpy inclines

A double quantum coherence transfer proton NMR spectroscopy technique for monitoring steady-state tumor lactic acid levels in vivo

Abstract: If proton nuclear magnetic resonance (1H NMR) spectroscopy is to provide a clinically useful modality for monitoring tumor growth and treatment, the technique must be able to unambiguously detect steady-state metabolite concentrations in human tumors and differentiate these from normal tissue levels. To address this problem, a two-dimensional double quantum coherence transfer spectroscopy (2DDQCT) method was developed and tested in a series of tumor cell lines implanted in mice. Lactate-edited proton NMR spectra were determined from a roughly 1-cm3 region of interest in EMT6, RIF-1, and fibroma. In two-dimensional data matrix representations of the 2DDQCT experiments (double quantum frequency on the vertical axis and chemical shift on the horizontal axis) the lactate signal (330 Hz with the transmitter set at the water resonance) was well-resolved from lipid (480 Hz, 600 Hz). The resolution in the double quantum dimension was also sufficient to conclude that a detectable level of alanine, which would reside at 358 Hz, was not present in the three tumor types. Following the NMR experiment, tumors were chemically assayed for lactate giving 8.17, 9.1, and 6.73 μmol/g wet wt for RIF-1, EMT6, and fibroma, respectively. This technique is likely to provide a noninvasive method for monitoring the steady-state lactic acid levels in small tumors before and after therapy, as well as in tissues with impaired oxygen delivery using clinical and research NMR Systems. © 1990 Academic Press, Inc.

Removal of accidental degeneracies in semiconductor quantum wires.

Abstract: We obtain the energy levels of carriers in rectangular GaAs/${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Al}}_{\mathit{x}}$As quantum-wire heterostructures with finite barriers using finite-element analysis. The energy spectra obtained are dramatically different from those determined analytically with use of the infinite-barrier approximation. The infinite-barrier approximation also introduces extra degeneracies in the energy spectra as a consequence of the separability of the potential. These accidental degeneracies are removed when the barrier height corresponding to the band offset of the surrounding medium is used in calculating the energy levels. Group-theory considerations of the square are used to explain the removal of these accidental degeneracies.

Periodic flow at airway bifurcations. II. Flow partitioning.

Abstract: The distribution of flow among parallel pathways is believed to be determined by the balance of downstream mechanical loads or time constants. We studied the influence of upstream flow conditions a...

Boundary-element shape optimization system for aircraft structural components

Abstract: The design sensitivities are obtained economically by implicit differentiation of the boundary integral equations. The mesh generation and regeneration is done using a parametric and auxiliary geometry concept that allows the original mesh to remain adequate for a wide range of subsequent evolving geometries as the optimization proceeds

Essayist literacy and the rhetoric of deproduction

Abstract: sharply and clearly than I had been able the pedagogical problem I want to explore here. He or she noted, with an undisguised exasperation I understood all too well, "God knows, the seniors in my personal essay class still seem to want to read even the best of essays as if the essays belong to [a] 'monological regime of silence and facticity"' (citing one of the phrases that appears below). This comment was

Microscopic theory for dilute quadrupole glasses.

Abstract: The microscopic free energy is derived for dilute, interacting, tunneling elastic quadrupoles (TQ's) randomly distributed in a nonpolar medium. For low TQ concentrations I obtain low-energy excitations very similar to those observed in glasses. The microscopic derivations give glasslike properties in the density of states, in the specific heat, in the thermal conductivity, in the sound absorption and propagation, and in the complex dielectric constant

Combining Pseudoranges from GPS and Loran-C for Air Navigation

Abstract: User equipment that combines pseudoranges from GPS and Loran would be more reliable than an unaided GPS receiver or a Loran-only receiver. It could remove coverage outages caused by satellite shutdowns and/or bad satellite geometry. Similarly, it could remove most of the coverage outages caused by Loran station shutdowns, high atmospheric noise levels, or precipitation static. A hybrid GPS/Loran receiver could also reliably provide self-contained fault detection and isolation (otherwise known as receiver autonomous integrity monitoring, or RAIM). This paper treats position fixing, receiver autonomous fault detection, and receiver autonomous fault isolation as system services, and computes the probability of outage for these three services. Our analysis computes the outage probability for the level of service required for nonprecision approach and en route navigation in the National Airspace System. It assumes that GPS is configured in the Optimal 21 Satellite Constellation, and includes the effects of satellite as well as Loran station shutdowns. Finally, our analysis examines whether it is important to synchronize Loran transmissions to GPS time.