Showing papers by "Worcester Polytechnic Institute published in 1991"

General procedure for the analysis of Er(3+) cross sections.

Abstract: We have applied the theory of McCumber to the (4)4I(13/2) ? (4)I(15/2) transition of Er(3+) -doped glasses and confirmed its ability to provide both spectra and accurate values of cross sections. For an Al/P-silica fiber, the exact McCumber treatment is within 3% of the measured emission cross section, whereas an Einstein analysis is off by >50%. An approximate treatment that eliminates the McCumber theory's requirement of detailed electronic structure has been developed and found to usually provide more accurate values than an Einstein analysis.

Momentum, pseudomomentum, and wave momentum: Toward resolving the Minkowski-Abraham controversy.

Abstract: We derive the momentum and pseudomomentum conservation laws from a very general nonrelativistic Lagrangian theory of the interaction of the electromagnetic field with a deforming, dispersive dielectric. From the former of these laws, we obtain the momentum density of an electromagnetic wave in matter to be ${\mathrm{\ensuremath{\epsilon}}}_{0}$E\ifmmode\times\else\texttimes\fi{}B, not the Abraham form of ${\mathrm{\ensuremath{\epsilon}}}_{0}$E\ifmmode\times\else\texttimes\fi{}${\mathrm{\ensuremath{\mu}}}_{0}$H. From the latter of these laws, we obtain the electromagnetic pseudomomentum density in the absence of deformation of the matter to be P\ifmmode\times\else\texttimes\fi{}B plus a dispersive term, not the Minkowski form of D\ifmmode\times\else\texttimes\fi{}B as proposed by Blount (unpublished). We show by quantizing the energy of the wave that the sum of momentum and pseudomomentum, which we name wave momentum, corresponds to N\ensuremath{\Elzxh}k (N an integer), the quantity that enters wave-vector conservation or phase-matching relations in wave interactions and that is consistent with the Jones-Richards experiment.

Automatic conversion of triangular finite element meshes to quadrilateral elements

Abstract: A method is presented for the fully automatic conversion of a general finite element mesh containing triangular elements into a mesh composed of exclusively quadrilateral elements. The initial mesh may be constructed of entirely triangular elements or may consist of a mixture of triangular and quadrilateral elements. The technique used employs heuristic procedures and criteria to selectively combine adjacent triangular elements into quadrilaterals based on preestablished criteria for element quality. Additional procedures are included to eliminate isolated triangles. The methods operates completely without user intervention once the nodal co-ordinates and element connectivity of the original mesh are supplied.

Molten metal processing of advanced cast aluminum alloys

Abstract: Premium quality aluminum alloy castings are used extensively in various applications requiring a high strength-to-weight ratio, such as aerospace, automotive and other structural components. The mechanical properties in these structure-sensitive alloys are determined primarily by the secondary dendrite arm spacing and the morphology of interdendritic phases. In addition, the amount of porosity in the casting and the inclusion concentration have a strong influence on fracture, fatigue and impact properties. During the production of the casting, various molten metal processing techniques can be implemented to control these microstructural parameters. These melt treatments include grain refinement with Ti-B, eutectic modification with strontium or sodium, degassing with purge gases and filtration of inclusions. The efficiency of these treatments determines the quality of the cast component.

Analysis of the formation of monodisperse populations by homogeneous nucleation

Abstract: A mathematical analysis of the precipitation of monodisperse populations of particles, governed by homogeneous nucleation from solution, is presented. The model incorporates a “hydrolysis” reaction step, homogeneous nucleation of the population, and size-independent linear growth of the particles once formed. The population balance formalism is used to describe the particulate phase, and material balances are developed to account for changes in the solute concentrations in the precursor phase and the active phase. Any statistical parameters of the particulate population may be predicted. It is shown that the success of forming monodisperse populations depends on the magnitude of the interfacial energy of the solution/particulate system. It is also shown that separating the nucleation and growth steps of the process is not an essential feature in the formation of monodisperse populations; however, the length of time the solution concentration is above the nucleation threshold is important. The rate at which the intermediate active solute species is generated affects the induction time significantly, but has little to do with the success of forming a monodisperse particle population, at least in the cases shown here.

Method and apparatus for measuring the concentration of absorbing substances

Abstract: A non-invasive system for measuring the concentration of an analyte in an absorbing matrix is described. The system directs a beam of radiation at the matrix. The beam consists of a series of successive alternate pulses of electro-magnetic radiation, one of which is highly absorbed by the analyte and the other of which is non-absorbed. The transmitted or reflected beam is optically detected and an electrical signal proportional to beam intensity is used to adjust the beam intensity and as a measure of analyte concentration.

Hydrogen reduction mechanisms of ilmenite between 823 and 1353 K

Abstract: In situ gravimetric measurements and microscopic examinations were used to determine the mechanisms of oxygen removal from synthetic ilmenite disks between 823 and 1353 K Under a hydrogen atmosphere, iron was observed to form a layer of low porosity on the surface of samples early in the reduction This created diffusion limitations for hydrogen to the reaction front and for the escape of water vapor A shrinking core reduction model, modified to include the growth of this iron film, was capable of predicting the conversion-time relationships of ilmenite samples An activation energy of 432 ± 26 kcal/gmole was determined to be representative of reaction control over the temperature range 823–1023 K

Skin reflectance pulse oximetry: in vivo measurements from the forearm and calf.

Abstract: This study describes the results from a series of human experiments demonstrating the ability to measure arterial hemoglobin oxygen saturation (SaO2) from the forearm and calf using a reflectance pulse oximeter sensor A special optical reflectance sensor that includes a heating element was interfaced to a temperature controller and a commercial Data-scope ACCUSAT pulse oximeter that was adapted for this study to perform as a reflectance pulse oximeter The reflectance pulse oximeter sensor was evaluated in a group of 10 healthy adult volunteers during steady-state hypoxia Hypoxia was induced by gradually lowering the inspired fraction of oxygen in the breathing gas mixture from 100 to 12% Simultaneous SaO2 measurements obtained from the forearm and calf with two identical reflectance pulse oximeters were compared with SaO2 values measured by a finger sensor that was interfaced to a standard Datascope ACCUSAT transmittance pulse oximeter The equations for the best-fitted linear regression lines between the percent reflectance, SpO2(r), and transmittance, SpO2(t), values in the range between 73 and 100% were SpO2(r)=−706+109 SpO2(t) for the forearm (n=91,r=095) and SpO2(r)=778+093 SpO2(t) for the calf (n=93,r=088) The regression analysis of the forearm data revealed a mean ± SD error of 247±166% (SaO2=90−100%), 235±245% (SaO2=80–89%), and 242±120% (SaO2=70–79%) The corresponding regression analysis of the calf data revealed a mean ± SD error of 336±306% (SaO2=90–100%), 345±412% (SaO2=80–89%), and 297±275% (SaO2=70–79%) This preliminary study demonstrated the feasibility of measuring SaO2 from the forearm and calf in healthy subjects with a heated skin reflectance sensor and a pulse oximeter

Output saturation in a 980-nm pumped erbium-doped fiber amplifier

Abstract: A fiber amplifier model is developed which includes a finite lifetime for the pumped level. Pump excited state absorption (ESA) from the pumped level is also included. The model is solved numerically for a erbiumdoped fiber amplifier pumped at 980 nm. The signal output power at 1.5 microm is found to be limited by the finite lifetime of the (4)I(11/2); ESA of the pump from the (4)I(11/2) further limits the signal output. Lifetimes of the (4)I(11/2) were measured for Er(3+) in a series of oxide and fluoride glasses. Output saturation is most important in the fluoride based glasses, where the (4)I(11/2) lifetime is longest.

Altered expression of an L1-specific, O-linked cuticle surface glycoprotein in mutants of the nematode Caenorhabditis elegans.

Abstract: Mouse mAb M38 was used in indirect immunofluorescence experiments to detect a stage-specific antigen on the surface of the first larval stage (L1) of the free-living nematode Caenorhabditis elegans, and to detect alterations in the apparent expression of this antigen in two distinct classes of C. elegans mutants. In previously described srf-2 and srf-3 mutants (Politz S. M., M. T. Philipp, M. Estevez, P.J. O'Brien, and K. J. Chin. 1990. Proc. Natl. Acad. Sci. USA. 87:2901-2905), the antigen is not detected on the surface of any stage. Conversely, in srf-(yj43) and other similar mutants, the antigen is expressed on the surface of the first through the fourth (L4) larval stages. To understand the molecular basis of these alterations, the antigen was characterized in gel immunoblotting experiments. After SDS-PAGE separation and transfer to nitrocellulose, M38 detected a protein antigen in extracts of wild-type L1 populations. The antigen was sensitive to digestion by Pronase and O-glycanase (endo-alpha-N-acetylgalactosaminidase), suggesting that it is an O-linked glycoprotein. This antigen was not detected in corresponding extracts of wild-type L4s or srf-2 or srf-3 L1s, but was detected in extracts of srf-(yj43) L4s. The antigen-defective phenotype of srf-3 was epistatic to the heterochronic mutant phenotype of srf-(yj43) in immunofluorescence tests of the srf-3 srf-(yj43) double mutant, suggesting that srf-(yj43) causes incorrect regulation of a pathway of antigen formation that requires wild-type srf-3 activity.

Boundary conditions for granular flows at randomly fluctuating bumpy boundaries

Abstract: In this paper, we focus attention on the interactions between rapid flows of identical, smooth spheres that interact with bumpy boundaries through inelastic collisions. The boundaries translate with specified mean velocities, and deviate about the mean with specified fluctuation velocities. Based upon Maxwellian velocity distribution functions that describe the velocities of both the flow particles and boundaries, we calculate the rates at which linear momentum and kinetic energy are exchanged between the two. Using these exchange rates, we write down conditions that ensure that both momentum and energy are balanced at bumpy boundaries. Finally, we employ a constitutive theory that is consistent with these conditions to calculate the granular temperature and solid fraction profiles within a granular material confined between two parallel, bumpy surfaces that randomly fluctuate about zero mean velocity.

Process for extracting enhanced amounts of plant secondary metabolites with limited loss of plant viability

Abstract: A process for extracting enhanced amounts of a plant secondary metabolite from plant tissue with limited loss of tissue viability by reversibly permeabilizing the tissue membrane is disclosed.

Weir flows and waterfalls

Abstract: Two-dimensional free-surface flows, which are uniform far upstream in a channel of finite depth that ends suddenly, are computed numerically. The ending is in the form of a vertical wall, which may force the flow upward before it falls down forever as a jet under the effect of gravity. Both subcritical and supercritical solutions are presented. The subcritical solutions are a one-parameter family of solutions, the single parameter being the ratio between the height of the wall and the height of the uniform flow far upstream. On the other hand, the supercritical solutions are a two-parameter family of solutions, the second parameter being the Froude number. Moreover, for some combinations of the parameters, it is shown that the solution is not unique.

Using design history systems for technology transfer

Abstract: This paper presents the concept of a Design History System (DHS), and describes a protoype DHS called the Process Technology Transfer Tool (PTTT) which was designed to aid in transferring process design information between Advanced Development and Manufacturing.

Hierarchical block truncation coding

Abstract: We present a new image coding technique called hierarchical block truncation coding (HBTC). HBTC is a combination of the block truncation coding (BTC) technique and the quadtree segmentation method. Quadtree segmentation is used to decompose an image into homogeneous regions so that the BTC method can exploit the nonstationary characteristics of the image data. The resulting bit rate is lower than that of conventional BTC, depending on the characteristics and complexity of the digital image. We investigated the performance of the encoder on both still and moving images. A small reduction in the bit rate is achievable for still images, but false contours become apparent as the rate declines. The proposed method works well on difference images from a sequence since the moving areas are encoded with greater resolution than the stationary background. A significant bit rate reduction is seen for sequence transmission. The bit rate is reduced from the 1.625 bits per pixel (bpp) required for a conventional BTC implementation down to 1.19 bpp for the least detailed still image. A typical CCITT image sequence was encoded at an average rate of 1.21 bpp. The bit rate was further reduced to an average of 0.39 bpp with a small degradation in the quality of the reconstructed images by transmitting only the most varying portions of the sequence.

A pitfall associated with lactate detection using stimulated-echo proton spectroscopy.

Abstract: At TE values of 136 ms, it has recently been shown that the lactate methyl signal, when obtained with a stimulated-echo (STE) sequence, is modulated at the zero-quantum (ZQ) frequency when TM is varied. Here we describe an additional modulation of the ZQ lactate signal, due to spin-spin coupling, that results in a 10-fold reduction in the lactate signal for TM intervals ranging between 48 and 84 ms (and at multiples of 136 ms thereof). Because of this J-modulation, improper choice of TE and TM intervals may give false negative results for lactate detection by STE spectroscopy.

Multiple quantum NMR spectroscopy methods for measuring the apparent self-diffusion coefficient of in vivo lactic acid.

Abstract: Nuclear magnetic resonance spectroscopy methods are presented for measuring the apparent self-diffusion coefficient of lactic acid in vivo. These techniques incorporate diffusion-sensitive gradients into multiple quantum NMR pulse sequences that are employed for spectral editing. Both diffusion-sensitive zero quantum (ZQ) and double quantum (DQ) spectral editing techniques have been developed and the DQ method has been used to measure the apparent self-diffusion coefficient of in vivo lactic acid in H-MESO-1 human tumor xenografts subcutaneously implanted in athymic mice.