bluuebunny/crossref_metadata_2025 huggingface dataset:
The micropolitical orientation of facilitative school principals and its effects on teachers’ sense of empowerment
Authors: Blase Joseph , Blase Jo
Published: July 2002

Describes the everyday micropolitical facilitative strategies and personal characteristics of exemplary school principals who have influenced and enhanced teachers’ sense of empowerment. The data discussed here were drawn from a qualitative study of teachers in 11 schools affiliated with Glickman’s League of Professional Schools in Georgia. An open‐ended questionnaire designed by the researchers, according to general guidelines for grounded theory inquiry, provided teachers with the opportunity to identify and describe in detail characteristics of principals that enhanced their sense of empowerment. Inductive analyses of the data generated a description of facilitative leadership that includes seven major “facilitative” strategies and one set of facilitative personal characteristics that enhanced teacher empowerment. Focuses on the strategies and characteristics teachers identified as facilitative principal leadership. Discusses findings in terms of the relevant empirical and theoretical literature.
Finite element simulation of transient laminar flow past a circular cylinder and two cylinders in tandem – Influence of buoyancy
Authors: Patnaik B.S.V. , Narayana P.A.A. , Seetharamu K.N.
Published: July 2002

Flow past an isolated circular cylinder and two cylinders in tandem is numerically simulated, under the influence of buoyancy aiding and opposing the flow. A modified velocity correction method is employed, which has second order accuracy in both space and time. The influence of buoyancy on the temporal fluid flow patterns is investigated, with respect to streamlines, isotherms and streaklines. Comparisons are made with respect to mean center line velocities, drag coefficients, Strouhal number and streakline patterns. Degeneration of naturally occurring Kármán vortex street into a twin eddy pattern is noticed in the Reynolds number (Re) range of 41‐200, under buoyancy aided convection. On the contrary, buoyancy opposed convection could trigger vortex shedding even at a low Re range of 20‐40, where only twin eddies are found in the natural wake. Temporal evolution of unsteady eddy patterns is visualized by means of numerical particle release (NPR). Zones of vortex shedding and twin vortices are demarcated on a plot of Richardson number against Strouhal number. Root mean square (RMS) lift coefficients (CL,RMS) and average drag coefficient (\overlineCd) are obtained as a function of Richardson number (Ri).
Coupled finite/boundary element solution of magnetothermal problems
Authors: Khodadadi J.M.
Published: July 2002

A computational methodology, based on the coupling of the finite element and boundary element methods, is developed for the solution of magnetothermal problems. The finite element formulation and boundary element formulation, along with their coupling, are discussed. The coupling procedure is also presented, which entails the application of the LU decomposition to eliminate the need for the direct inversion of matrices resulting from FE‐BE formulation, thereby saving computation time and storage space. Corners for both FE‐BE interface and BE regions, where discontinuous fluxes exist, are treated using the double flux concept. Numerical results are presented for three different systems and compared with analytical solutions when available. Numerical experiments suggest that for magnetothermal problems involving small skin depths, a careful mesh distribution is critical for accurate prediction of the field variables of interest. It is found that the accuracy of the temperature distribution is strongly dependent upon that of the magnetic vector potential. A small error in the magnetic vector potential can produce significant errors in the subsequent temperature calculations. Thus, particular attention must be paid to the design of a suitable mesh for the accurate prediction of vector potentials. From all the cases examined, 4‐node linear elements with adequate progressive coarsening of meshes from the surface gave the results with best accuracy.
Natural convection in horizontal annulus filled with an anisotropic porous medium
Authors: Aboubi K. , Robillard L. , Vasseur P.
Published: July 2002

The natural two‐dimensional convection taking place between horizontal concentric cylinders filled with a satured anisotropic porous medium is studied numerically. The anisotropy concerns exclusively the permeability. Isothermal boundary conditions are applied on both inner and outer boundaries, with the outer boundary being warmer. The effects of the anisotropic permeability ratio K*, of the orientation angle of the principal axes defined by γ, and of the Rayleigh number Ra* on the flow and heat transfer are investigated. Results indicate that a net circulating flow around the annulus is generated, except for values of γ that preserve the symmetry of flow conditions with respect to the vertical diameter. It is also shown that the anisotropic part of the resistivity tensor is equivalent to a magnetic resistivity tensor.
Bifurcation in steady laminar mixed convection flow in uniformly heated inclined tubes
Authors: Orfi J. , Galanis N. , Nguyen C.T.
Published: July 2002

The fully developed laminar mixed convection flow in inclined tubes subject to axially and circumferentially uniform heat flux has been studied numerically for a Boussinesq fluid. Dual solutions characterized by a two‐ and a four‐vortex secondary flow structure in a cross‐section normal to the tube’s longitudinal axis have been found for different combinations of the Grashof number Gr and of the tube inclination α for all Prandtl numbers between 0.7 and 7. In the two‐parameter space defined by Gr and α dual solutions occur: at a given α, if the Grashof number exceeds a critical value Grℓ (for horizontal tubes Grℓ is approximately 5.5 × 105, 1.7 × 105 and 1.7 × 104 respectively for Pr = 0.7, 7 and 70); at a given Gr, if the tube inclination is below a critical value αc (for Gr = 106 this critical angle is approximately 62.5° and 83.5° respectively for Pr = 0.7 and 7). Numerical experiments carried out for developing flows indicate that the two‐vortex solution is the only stable flow structure.
Contingency plan exercises
Authors: Payne Christopher F.
Published: July 2002

This article highlights the value of close co‐ operation and understanding between those inthe public, private and voluntary sectors who have the responsibility for planning and responding to major incidents. Multi‐agency response and co‐operation can be improved through joint planning and exercises which serve to validate plans, enable staff to familiarise themselves with the arrangements and assist in training. The whole plan or just part of it may be exercised according to need, and may involve participation by one or more agencies. It has to be decided who needs to be exercised and which type of exercise is appropriate, for example paper feed, table‐top, communications‐simulated or live. When staging exercise, it is important to plan, conduct and supervise them in a way which will ensure maximum benefit to all participants, enhance response safely and enable weaknesses in the plans to be revealed and corrected.
From Quality Assessment to Quality Enhancement
Authors: Rippin Ann , White Jeremy , Marsh Peter
Published: July 2002

A practical inquiry into the best way to introduce quality in an
academic context, working through a consultancy approach. Describes the
development and refinement of a framework for a consultancy approach to
teaching and learning quality enhancement. Outlines future developments
and gives an example of a subject area taking on quality for itself and
beginning to take independent quality enhancement initiatives.
What do teachers think about thinking skills?
Authors: Baumfield Vivienne , Oberski Iddo
Published: July 2002

Presents findings from a case study of the implementation of three different thinking skills programmes ‐ Somerset Thinking Skills, Instrumental Enrichment and Philosophy for Children, in year seven of an inner city secondary school. Focuses on the perceptions of the teachers involved and explores the extent to which teacher perceptions affected implementation. An understanding of teachers’ perceptions is important if effective training and support is to be provided and the problem of poor implementation of thinking skills programmes is to be addressed. Analysis of teacher perceptions will also contribute to our understanding of why a particular programme is chosen and the extent to which the needs of the teacher are consistent with its aims. Findings of the study reaffirm the difficulty experienced teachers face when attempting to develop new skills and highlight the problems presented by the lack of immediate, concrete outcomes from a thinking skills lesson. Identifies teachers’ planning and perceptions of what constitutes group work as areas deserving further research and notes the importance of the presentation of thinking skills materials for the teachers using them.
Internet acceptable usage policy for organizations
Authors: Lichtenstein Sharman , Swatman Paula M.C.
Published: July 2002

Explains how, with the Internet increasingly being used for the conduct of electronic commerce, organizations are now cognizant of the need to control their employees’ usage of the Internet. Little research has been conducted to date into this important concern. Suggests that an Internet acceptable usage policy is one vehicle for providing this control, containing guidelines for employees indicating both acceptable and unacceptable Internet usages. The policy aims to control those employee behaviours and actions which contribute to the incidence and severity of internal and external Internet risks, while enabling employees and the organization to gain maximum business value from the Internet connection. Explores the issues to be considered in the development of an organization’s Internet acceptable usage policy. Uses a case study of a large Australian organization to illustrate the issues. Proposes a set of criteria for an effective Internet acceptable usage policy as a result of this research.
Get linked or get lost: marketing strategy for the Internet
Authors: Aldridge Alicia , Forcht Karen , Pierson Joan
Published: July 2002

Develops detailed marketing strategy recommendations for online commerce based on the general popularity of the Internet, the unique nature of doing business there, and how its attributes may be utilized for a successful marketing presence.
Who is going online? Results from the National Capital FreeNet
Authors: Patrick Andrew S. , Black Alex
Published: July 2002

The National Capital FreeNet (NCF) in Ottawa, Canada is one of the largest and most successful community online services in the world. A sample of 1,073 National Capital FreeNet (NCF) users were surveyed about their demographic characteristics, their access methods, and their levels of satisfaction. The results indicate that NCF users are not a specialized group in the community, but are comparable to the local regional population in age, education, and income. NCF users most often connect from home using modems, often using equipment and telephone lines purchased specifically for this service. NCF users connect to the system regularly, and usage of the system was not strongly related to demographic factors. NCF users are very satisfied with the system and satisfaction and donations were not strongly related to demographic factors or use of the system. These results suggest that this community network has a broad appeal and that current and future online services may have significant widespread impacts on individuals and society.
Novel liquid crystal resins for stereolithography – processing parameters and mechanical analysis
Authors: Ullett J.S. , Schultz J.W. , Chartoff R.P.
Published: July 2002

The build characteristics of two liquid crystal (LC) reactive monomers were studied using a table‐top stereolithography apparatus (TTSLA). LC materials contain stiff, rod‐like mesogenic segments in their molecules, which can be aligned causing an anisotropy in properties. When cured in the aligned state the anisotropic structure is “locked in” resulting in materials with anisotropic physical and mechanical properties. By varying the alignment of layers, properties such as thermal expansion coefficient can be optimized. High heat distortion (or glass transition) temperatures are possible depending on the monomer chemical structure. Working curves for the LC resins were developed under various conditions. A permanent magnet placed outside the TTSLA vat was used to uniformly align the monomer in the nematic state. Photo‐initiator type and content; alignment of the nematic phase; and operating conditions affected the working curve parameters. Glass transition temperatures of post‐cured parts ranged from 75 to 1488C depending on the resin and processing conditions. Mechanical analysis data revealed a factor of two difference between glassy moduli measured in the molecular alignment versus the transverse alignment directions. Based on these initial studies, more advanced resins with higher glass transitions are being developed at the University of Dayton.
Usage of accuracy models in stereolithography process planning
Authors: Lynn‐Charney Charity , Rosen David W.
Published: July 2002

Determining whether a set of tolerances on a part can be met by a rapid prototyping (RP) machine is often difficult. To achieve a set of tolerances as closely as possible, relationships between part geometry, tolerances, and process variables must be understood quantitatively. This paper presents an empirical model for stereolithography apparatus (SLA) accuracy, as specified by geometric tolerances, and a process planning method based on response surface methodology and multiobjective optimization. Response surfaces are used to capture the relationships among part surfaces, tolerances, and process variables. These response surfaces were generated by extensive design‐of‐experiment studies for a variety of geometries. An annotated STL data format is also presented that enables the inclusion of tolerance and surface information in faceted representations. Application of the accuracy models and process planning method is illustrated on one part.
Effects of processing conditions on short TLCP fiber reinforced FDM parts
Authors: Gray Robert W. , Baird Donald G. , Helge Bøhn Jan
Published: July 2002

Focusses on preliminary studies on developing thermoplastic composite materials suitable for use in fused deposition modeling (FDM). Looks at thermotropic liquid crystalline polymers (TLCPs). Specifically aims to determine the feasibility of post‐processing TLCP composite strands generated by means of the dual extrusion process using FDM to enhance the tensile properties and functionality of prototypes. Describes the experiments and gives in‐depth results which include the finding that final mechanical properties of a composite prototype can be tailored to a specific application by adjusting the laydown pattern to increase the functionality of the prototype, and that these properties can be predicted by composite theory.
Effect of heat‐spreader sizes on the thermal performance of large cavity‐down plastic ball grid array packages ‐ NuCSP
Authors: Lau John , Chen Tony
Published: July 2002

The effect of heat‐spreader sizes on the temperature distribution, thermal resistance, and cooling power of a set of cost‐effective cavity‐down plastic ball grid array (PBGA) packages assembled on an FR‐4 epoxy glass printed circuit board (PCB) is presented. The sizes of these packages are 35 × 35mm and 40 × 40mm and with four and five rows of solder balls.
Macromolecular organization of the Yersinia pestis capsular F1 antigen: Insights from time‐of‐flight mass spectrometry
Authors: Tito Mark A. , Miller Julie , Griffin Kate F. , Williamson E. Diane , Titball Richard W. , Robinson Carol V.
Published: July 2002

Mass spectrometry has been used to examine the subunit interactions in the capsular F1 antigen from Yersinia pestis, the causative agent of the plague. Introducing the sample using nanoflow electrospray from solution conditions in which the protein remains in its native state and applying collisional cooling to minimize the internal energy of the ions, multiple subunit interactions have been maintained. This methodology revealed assemblies of the F1 antigen that correspond in mass to both 7‐mers and 14‐mers, consistent with interaction of two seven‐membered units. The difference between the calculated masses and those measured experimentally for these higher‐order oligomers was found to increase proportionately with the size of the complex. This is consistent with a solvent‐filled central cavity maintained on association of the 7‐mer to the 14‐mer. The charge states of the ions show that an average of one and four surface accessible basic side‐chains are involved in maintaining the interactions between the 7‐mer units and neighboring subunits, respectively. Taken together, these findings provide new information about the stoichiometry and packing of the subunits involved in the assembly of the capsular antigen structure. More generally, the data show that the symmetry and packing of macromolecular complexes can be determined solely from mass spectrometry, without any prior knowledge of higher order structure
HMG‐D complexed to a bulge DNA: An NMR model
Authors: Cerdan Rachel , Payet Dominique , Yang Ji‐Chun , Travers Andrew A. , Neuhaus David
Published: July 2002

An NMR model is presented for the structure of HMG‐D, one of the Drosophila counterparts of mammalian HMG1/2 proteins, bound to a particular distorted DNA structure, a dA2 DNA bulge. The complex is in fast to intermediate exchange on the NMR chemical shift time scale and suffers substantial linebroadening for the majority of interfacial resonances. This essentially precludes determination of a high‐resolution structure for the interface based on NMR data alone. However, by introducing a small number of additional constraints based on chemical shift and linewidth footprinting combined with analogies to known structures, an ensemble of model structures was generated using a computational strategy equivalent to that for a conventional NMR structure determination. We find that the base pair adjacent to the dA2 bulge is not formed and that the protein recognizes this feature in forming the complex; intermolecular NOE enhancements are observed from the sidechain of Thr 33 to all four nucleotides of the DNA sequence step adjacent to the bulge. Our results form the first experimental demonstration that when binding to deformed DNA, non‐sequence‐specific HMG proteins recognize the junction between duplex and nonduplex DNA. Similarities and differences of the present structural model relative to other HMG–DNA complex structures are discussed.
Heat capacity changes upon burial of polar and nonpolar groups in proteins
Authors: Loladze Vakhtang V. , Ermolenko Dmitri N. , Makhatadze George I.
Published: July 2002

In this paper we address the question of whether the burial of polar and nonpolar groups in the protein locale is indeed accompanied by the heat capacity changes, ΔCp, that have an opposite sign, negative for nonpolar groups and positive for polar groups. To accomplish this, we introduced amino acid substitutions at four fully buried positions of the ubiquitin molecule (Val5, Val17, Leu67, and Gln41). We substituted Val at positions 5 and 17 and Leu at position 67 with a polar residue, Asn. As a control, Ala was introduced at the same three positions. We also replaced the buried polar Gln41 with Val and Leu, nonpolar residues that have similar size and shape as Gln. As a control, Asn was introduced at Gln41 as well. The effects of these amino acid substitutions on the stability, and in particular, on the heat capacity change upon unfolding were measured using differential scanning calorimetry. The effect of the amino acid substitutions on the structure was also evaluated by comparing the 1H‐15N HSQC spectra of the ubiquitin variants. It was found that the Ala substitutions did not have a considerable effect on the heat capacity change upon unfolding. However, the substitutions of aliphatic side chains (Val or Leu) with a polar residue (Asn) lead to a significant (> 30%) decrease in the heat capacity change upon unfolding. The decrease in heat capacity changes does not appear to be the result of significant structural perturbations as seen from the HSQC spectra of the variants. The substitution of a buried polar residue (Gln41) to a nonpolar residue (Leu or Val) leads to a significant (> 25%) increase in heat capacity change upon unfolding. These results indicate that indeed the heat capacity change of burial of polar and nonpolar groups has an opposite sign. However, the observed changes in ΔCp are several times larger than those predicted, based on the changes in water accessible surface area upon substitution.
CODA: A combined algorithm for predicting the structurally variable regions of protein models
Authors: Deane Charlotte M. , Blundell Tom L.
Published: July 2002

CODA, an algorithm for predicting the variable regions in proteins, combines FREAD a knowledge based approach, and PETRA, which constructs the region ab initio. FREAD selects from a database of protein structure fragments with environmentally constrained substitution tables and other rule‐based filters. FREAD was parameterized and tested on over 3000 loops. The average root mean square deviation ranged from 0.78 Å for three residue loops to 3.5 Å for eight residue loops on a nonhomologous test set. CODA clusters the predictions from the two independent programs and makes a consensus prediction that must pass a set of rule‐based filters. CODA was parameterized and tested on two unrelated separate sets of structures that were nonhomologous to one another and those found in the FREAD database. The average root mean square deviation in the test set ranged from 0.76Å for three residue loops to 3.09 Å for eight residue loops. CODA shows a general improvement in loop prediction over PETRA and FREAD individually. The improvement is far more marked for lengths six and upward, probably as the predictive power of PETRA becomes more important.

CODA was further tested on several model structures to determine its applicability to the modeling situation. A web server of CODA is available at http://www‐cryst.bioc.cam.ac.uk/∼charlotte/Coda/search_coda.html.
Amino‐acid substitutions at the fully exposed P1 site of bovine pancreatic trypsin inhibitor affect its stability
Authors: Krowarsch Daniel , Otlewski Jacek
Published: July 2002

It is widely accepted that solvent‐exposed sites in proteins play only a neglible role in determining protein energetics. In this paper we show that amino acid substitutions at the fully exposed Lys15 in bovine pancreatic trypsin inhibitor (BPTI) influenced the CD‐ and DSC‐monitored stability: The Tden difference between the least (P1 Trp) and the most stable (P1 His) mutant is 11.2°C at pH 2.0. The ΔHden versus Tden plot for all the variants at three pH values (2.0, 2.5, 3.0) is linear (ΔCp,den = 0.41 kcal• mole−1 • K−1; 1 cal = 4.18 J) leading to a ΔGden difference of 2.1 kcal•mole−1. Thermal denaturation of the variants monitored by CD signal at pH 2.0 in the presence of 6 M GdmCl again showed differences in their stability, albeit somewhat smaller (ΔTden =7.1°C). Selective reduction of the Cys14–Cys 38 disulfide bond, which is located in the vicinity of the P1 position did not eliminate the stability differences. A correlation analysis of the P1 stability with different properties of amino acids suggests that two mechanisms may be responsible for the observed stability differences: the reverse hydrophobic effect and amino acid propensities to occur in nonoptimal dihedral angles adopted by the P1 position. The former effect operates at the denatured state level and causes a drop in protein stability for hydrophobic side chains, due to their decreased exposure upon denaturation. The latter factor influences the native state energetics and results from intrinsic properties of amino acids in a way similar to those observed for secondary structure propensities. In conclusion, our results suggest that the protein‐stability‐derived secondary structure propensity scales should be taken with more caution.
Importance of secondary structural specificity determinants in protein folding: Insertion of a native β‐sheet sequence into an α‐helical coiled‐coil
Authors: Kwok Stanley C. , Mant Colin T. , Hodges Robert S.
Published: July 2002

To examine how a short secondary structural element derived from a native protein folds when in a different protein environment, we inserted an 11‐residue β‐sheet segment (cassette) from human immunoglobulin fold, Fab new, into an α‐helical coiled‐coil host protein (cassette holder). This de novo design protein model, the structural cassette mutagenesis (SCM) model, allows us to study protein folding principles involving both short‐ and long‐range interactions that affect secondary structure stability and conformation. In this study, we address whether the insertion of this β‐sheet cassette into the α‐helical coiled‐coil protein would result in conformational change nucleated by the long‐range tertiary stabilization of the coiled‐coil, therefore overriding the local propensity of the cassette to form β‐sheet, observed in its native immunoglobulin fold. The results showed that not only did the nucleating helices of the coiled‐coil on either end of the cassette fail to nucleate the β‐sheet cassette to fold with an α‐helical conformation, but also the entire chimeric protein became a random coil. We identified two determinants in this cassette that prevented coiled‐coil formation: (1) a tandem dipeptide NN motif at the N‐terminal of the β‐sheet cassette, and (2) the hydrophilic Ser residue, which would be buried in the hydrophobic core if the coiled‐coil structure were to fold. By amino acid substitution of these helix disruptive residues, that is, either the replacement of the NN motif with high helical propensity Ala residues or the substitution of Ser with Leu to enhance hydrophobicity, we were able to convert the random coil chimeric protein into a fully folded α‐helical coiled‐coil. We hypothesized that this NN motif is a “secondary structural specificity determinant” which is very selective for one type of secondary structure and may prevent neighboring residues from adopting an alternate protein fold. These sequences with secondary structural specificity determinants have very strong local propensity to fold into a specific secondary structure and may affect overall protein folding by acting as a folding initiation site.
Genomic‐scale comparison of sequence‐ and structure‐based methods of function prediction: Does structure provide additional insight?
Authors: Fetrow Jacquelyn S. , Siew Naomi , Di Gennaro Jeannine A. , Martinez‐Yamout Maria , Dyson H. Jane , Skolnick Jeffrey
Published: July 2002

A function annotation method using the sequence‐to‐structure‐to‐function paradigm is applied to the identification of all disulfide oxidoreductases in the Saccharomyces cerevisiae genome. The method identifies 27 sequences as potential disulfide oxidoreductases. All previously known thioredoxins, glutaredoxins, and disulfide isomerases are correctly identified. Three of the 27 predictions are probable false‐positives. Three novel predictions, which subsequently have been experimentally validated, are presented. Two additional novel predictions suggest a disulfide oxidoreductase regulatory mechanism for two subunits (OST3 and OST6) of the yeast oligosaccharyltransferase complex. Based on homology, this prediction can be extended to a potential tumor suppressor gene, N33, in humans, whose biochemical function was not previously known. Attempts to obtain a folded, active N33 construct to test the prediction were unsuccessful. The results show that structure prediction coupled with biochemically relevant structural motifs is a powerful method for the function annotation of genome sequences and can provide more detailed, robust predictions than function prediction methods that rely on sequence comparison alone.
Correlation of NADH and Ca2+ signals in mouse pancreatic acinar cells
Authors: Voronina S. , Sukhomlin T. , Johnson P. R. , Erdemli G. , Petersen O. H. , Tepikin A.
Published: July 2002

Relationships between calcium signals and NADH responses were investigated in pancreatic acinar cells stimulated with calcium‐releasing secretagogues. Cytosolic calcium signals were studied using Fura Red or calcium‐sensitive Cl− current. Mitochondrial calcium was measured using Rhod‐2. The highest levels of NADH autofluorescence were found around the secretory granule region. Stimulation of cells with physiological doses of cholecystokinin (CCK) triggered slow oscillations of NADH autofluorescence. NADH oscillations were clearly resolved in the mitochondrial clusters around secretory granules. Very fast apical calcium signals induced by acetylcholine (ACh) produced no detectable changes in NADH; slightly more extended apical (or preferentially apical) calcium transients triggered clear NADH responses. Triple combined recordings of cytosolic calcium, mitochondrial calcium and NADH revealed the sequence of development of individual signals: an increase in cytosolic calcium was accompanied by a slower mitochondrial calcium response followed by a delayed increase in NADH fluorescence. Recovery of cytosolic calcium was faster than recovery of mitochondrial calcium. NADH recovery occurred at elevated mitochondrial calcium levels. During the transient cytosolic calcium oscillations induced by intermediate doses of ACh, there was an initial increase in NADH fluorescence following the first calcium transient; each of the subsequent calcium responses produced biphasic NADH changes comprising an initial small decline followed by restoration to an elevated calcium level. During the higher‐frequency sinusoidal calcium oscillations induced by higher doses of ACh, NADH responses fused into a smooth rise followed by a slow decline. Supramaximal doses of ACh and CCK produced single large NADH transients.
H∞ Preview Control for Discrete-Time Systems
Authors: Choi Chintae , Tsao Tsu-Chin
Published: July 2002

A preview controller to be able to prepare a plant with the future information for external disturbances will guarantee better performance to suppress their effects. A design approach for the optimal H∞ preview controller in the discrete-time domain is given. The preview and feedback controller are simultaneously designed to minimize the worst case RMS value of the regulated variables when the bounded unknown disturbances and the previewable disturbances hit the dynamic plants. Thus, a state feedback controller and the related preview controller are derived in this design, even though problem formulation and solving an algebraic Riccati equation are based on the full-information H∞ controller design scheme. The performance of the proposed preview controller is simulated with a rolling stand of the tandem cold mill in the steel-making works. The objective of the control system for the rolling stand is to minimize thickness error of the exit strip and tension variation between stands simultaneously. The entry strip thickness to the stand and the roll gap variation are considered as previewable disturbances, since they can be measured and estimated. The future informations of these physical variables are utilized in the preview controller to suppress their effects on the exit strip thickness and the inter-stand tension. The simulation results shows that the H∞ preview controller is effective to satisfy the requirements for the thickness and the tension.
Mathematical Analysis of the Entrapment of Solid Spherical Particles in Non-Conformal Contacts
Authors: Nikas George K.
Published: July 2002

The process of entrapment of small spherical particles in both lubricated and dry, line, and point contacts, is mathematically analyzed and a criterion is postulated in order to evaluate the possibility of entrapment. The analysis is generalized for non-conformal contacts, operating under mixed rolling-sliding conditions with emphasis given to elastohydrodynamic contacts. This study aims to provide the methods, suitable for easy computer programming, to evaluate the risks of surface damage from small debris particles in machine element applications and to make the selection of proper filtration more confined.
Debris Effects on EHL Contact
Authors: Kang Young S. , Sadeghi Farshid , Ai Xiaolan
Published: July 2002

A model was developed to study the effects of a rigid debris on elastohydrodynamic lubrication of rolling/sliding contacts. In order to achieve the objectives the time dependent Reynolds equation was modified to include the effects of an ellipsoidal shaped debris. The modified time dependent Reynolds and elasticity equations were simultaneously solved to determine the pressure and film thickness in EHL contacts. The debris force balance equation was solved to determine the debris velocity. The model was then used to obtain results for a variety of loads, speeds, and debris sizes. The results indicate that the debris has a significant effect on the pressure distribution and causes a dent on the rolling/sliding bounding surfaces. Depending on the size and location of the debris the pressure generated within the contact can be high enough to plastically deform the bounding surfaces. Debris smaller than the minimum film thickness do not enter the contact and only large and more spherical debris move toward the contact. [S0742-4787(11)00501-7]
An Experimental Study on Mixed Convection in a Horizontal Rectangular Channel Heated From a Side
Authors: Gau C. , Jeng Y. C. , Liu C. G.
Published: July 2002

Experiments are performed to study the mixed convection flow and heat transfer in a horizontal rectangular channel heated from a side. The channel is made of two vertical parallel plates with one of the plates heated uniformly and the opposite plate well insulated. The gap between the parallel plates is small and the height to gap ratio of the channel cross section is 6.67. Both flow visualization and the heat transfer along the heated wall are measured. The Reynolds number ranges from 317 to 2000, the buoyancy parameter, Gr/Re2, from 0 to 20000 and Pr of the air flow is 0.7. Flow structure inside the channel is visualized by injecting smoke at the inlet flowing along the heated side wall. The heated buoyant flow accumulates in the upper region of the channel, which grows in size as the buoyancy parameter increases. The accumulated flow is thermally stable and has a slower motion which can reduce the heat transfer enhancement by the buoyancy force. The effect of the Reynolds number and the buoyancy parameter on the heat transfer is presented and discussed. Comparisons of the Nusselt numbers with the case of the vertical channel flow and the prediction similar to the case of a horizontal flow through a heated vertical plate are also made. The normalized Nusselt numbers are found in proportion to the buoyancy parameter, correlations of the heat transfer data in terms of this parameter have been very successful. [S0022-1481(00)01404-3]
Thermoelastic Analysis of Thick-Walled Vessels Subjected to Transient Thermal Loading
Authors: Segall A. E.
Published: July 2002

A closed-form solution was derived for the transient thermal fields developed in thick-walled vessels subjected to a plausible exponential heating on the internal surface with convection to the surrounding external environment. The resulting series representation of the temperature distribution as a function of time and radial position was then used to derive new relationships for the transient thermoelastic stress states. The derived expressions allow an easy analysis of the significance of the exponential terms and convective coefficient in determining the magnitudes and distribution of the resulting stress states over time. Excellent agreement was seen between the derived temperature and stress relationships and a finite element analysis when the thermophysical and thermoelastic properties were assumed to be independent of temperature.
Multiobjective Optimum Design of Rotor-Bearing Systems With Dynamic Constraints Using Immune-Genetic Algorithm
Authors: Choi B.-K. , Yang B.-S.
Published: July 2002

In this paper, the combined optimization algorithm (immune-genetic algorithm) is proposed for multioptimization problems by introducing the capability of the immune system to the genetic algorithm. The optimizing ability of the proposed combined algorithm is identified by comparing the result of optimization with sharing genetic algorithm for the two-dimensional multipeak function. Also the combined algorithm is applied to minimize the total weight of the shaft and the transmitted forces at the bearings. The results show that the combined algorithm can reduce both the weights of the shaft and the transmitted forces at the bearing with dynamic constraints.
A Segregated SUPG/FEM for THDL Analysis In High Speed Slider Bearings With Injection Effect
Authors: Kumar B. V. Rathish
Published: July 2002

In this study, a segregated Finite Element Method (FEM) in the Petrov Galerkin framework with suitably defined Streamline Upwind Petrov Galerkin (SUPG) weight functions for a non-isothermal flow with temperature dependent density and viscosity in a high speed slider bearing has been proposed. The nonlinear partial differential equations (PDEs) governing the mass, momentum and energy conservations in thermohydrodynamic lubrication (THDL) of a high speed slider bearing with injection effects has been numerically analyzed for temperature, velocity and pressure fields. To assess the influence of the injection boundary condition on load generation and frictional drag in a slider bearing results have been compared with those from a study devoid of injection effects. Further the influence of consideration of fore-region pressure, geometrical configuration of a slider bearing, Peclet Number and thermoviscosity co-efficient in conjunction with oil injection effect on the load carrying capacity has been investigated. Oil injection is observed to bring in not only a gain in load carrying capacity but also a reduction in frictional drag and a reduction in the temperature specially in the vicinity of pad.
Generation of Five-Axis Cutter Paths for Turbomachinery Components
Authors: Tsay D. M. , Yan W. F. , Ho H. C.
Published: July 2002

A simple, yet useful algorithm is developed to generate tool paths with global interference checking for five-axis point milling of turbomachinery components. Based on the projected distance between the surface data and the cutter-axis of a cylindrical ball-end mill, interference between the surface of a workpiece and the cutter can be detected. Given the cutter contact points of the surface and the cutter’s size, it can produce the cutter location data without incurring interference through relatively rotating and tilting the workpiece. Applications of the developed procedure to five-axis machining of centrifugal compressor impellers with 13 and 15 blades are illustrated to demonstrate the usefulness and reliability of the approach.
Solar Upgrading of Fuels for Generation of Electricity
Authors: Tamme Rainer , Buck Reiner , Epstein Michael , Fisher Uriyel , Sugarmen Chemi
Published: July 2002

This paper presents a novel process comprising solar upgrading of hydrocarbons by steam reforming in solar specific receiver-reactors and utilizing the upgraded, hydrogen-rich fuel in high efficiency conversion systems, such as gas turbines or fuel cells. In comparison to conventionally heated processes about 30% of fuel can be saved with respect to the same specific output. Such processes can be used in small scale as a stand-alone system for off-grid markets as well as in large scale to be operated in connection with conventional combined-cycle plants. The complete reforming process will be demonstrated in the SOLASYS project, supported by the European Commission in the JOULE/THERMIE framework. The project has been started in June 1998. The SOLASYS plant is designed for 300 kWel output, it consists of the solar field, the solar reformer and a gas turbine, adjusted to operate with the reformed gas. The SOLASYS plant will be operated at the experimental solar test facility of the Weizmann Institute of Science in Israel. Start-up of the pilot plant is scheduled in April 2001. The midterm goal is to replace fossil fuels by renewable or non-conventional feedstock in order to increase the share of renewable energy and to establish processes with only minor or no CO2 emission. Examples might be upgrading of bio-gas from municipal solid waste as well as upgrading of weak gas resources.
Finite Element Simulation of Bolt-Up Process of Pipe Flange Connections
Authors: Fukuoka Toshimichi , Takaki Tomohiro
Published: July 2002

Achieving uniform bolt preload is difficult when tightening a pipe flange with a number of bolts. Several bolt-tightening strategies have been proposed so far for achieving uniform bolt preloads. It seems, however, that effective guidelines for tightening pipe flange connections have not been established. In this study, a numerical approach is presented for estimating the scatter in bolt preloads and achieving the uniform bolt preloads when tightening each bolt one by one in an arbitrary order. Numerical analyses are conducted using three-dimensional FEM as an elastic contact problem. The analytical objects are pipe flanges specified in JIS B 2238 with an aluminum gasket inserted. The validity of the numerical procedures proposed here is ascertained by experiment.
Scattering of Guided Waves by Circumferential Cracks in Steel Pipes
Authors: Bai H. , Shah A. H. , Popplewell N. , Datta S. K.
Published: July 2002

A novel numerical procedure is presented in this paper to study wave scattering problem by circumferential cracks in steel pipes. The study is motivated by the need to develop a quantitative ultrasonic technique to characterize properties of cracks in pipes. By employing wave function expansion in axial direction and decomposing the problem into a symmetry problem and an antisymmetry problem, a three-dimensional wave scattering problem is then reduced into two quasi-one-dimensional problems. This simplification greatly reduces the computational time. Numerical results for reflection and transmission coefficients of different incident wave modes are presented here for a steel pipe with cracks (may have arbitrary circumferential crack length and radial crack depth) and they are shown to agree quite closely with available but limited experimental data.
Structural Health Monitoring With Piezoelectric Active Sensors
Authors: Winston H. A. , Sun F. , Annigeri B. S.
Published: July 2002

A technology for non-intrusive real-time structural health monitoring using piezoelectric active sensors is presented. The approach is based on monitoring variations of the coupled electromechanical impedance of piezoelectric patches bonded to metallic structures in high-frequency bands. In each of these applications, a single piezoelectric element is used as both an actuator and a sensor. The resulting electromechanical coupling makes the frequency-dependent electric impedance spectrum of the PZT sensor a good mapping of the underlying structure’s acoustic signature. Moreover, incipient structural damage can be indicated by deviations of this signature from its original baseline pattern. Unique features of this technology include its high sensitivity to structural damage, non-intrusiveness to the host structure, and low cost of implementation. These features have potential for enabling on-board damage monitoring of critical or inaccessible aerospace structures and components, such as aircraft wing joints, and both internal and external jet engine components. Several exploratory applications will be discussed.
Chaotic Motion of a Symmetric Gyro Subjected to a Harmonic Base Excitation
Authors: Tong X. , Mrad N.
Published: July 2002

Chaotic motion of a symmetric gyro subjected to a harmonic base excitation is investigated in this note. The Melnikov method is applied to show that the system possesses a Smale horse when it is subjected to small excitation. The transition from regular motion to chaotic motion is investigated through numerical integration in conjunction with Poincare´ map. It is shown that as the spin velocity increases, the chaotic motion turns into a regular motion.
Statistical Investigation on Resistance Spot Welding Quality Using a Two-State, Sliding-Level Experiment
Authors: Li Wei , Cheng Shaowei , Hu S. Jack , Shriver Justin
Published: July 2002

Quality variation in resistance spot welding is a major concern in the automotive industry. The relationship between weld quality and various process conditions, including abnormal process conditions, has not yet been systematically studied. This paper investigates this relationship using a newly developed two-stage, sliding-level experiment. In the experiment, welding current is treated as a “slid factor” whose settings are determined based on those of other process variables. Engineering knowledge is applied in statistical model selection. From the analysis, it is found that abnormal process conditions, such as axial misalignment, angular misalignment, poor fitup, edge weld, and electrode wear, significantly affect weld size and thus cause large variation in the weld quality. Although they may help increase the weld size in some cases, abnormal process conditions generally lead to a less robust process. In order to minimize the effects of the abnormal process conditions, a robust parameter design is formulated using the statistical models developed from the experimental data. The analysis suggests that high current and large electrodes should be used for reducing the weld quality variation. Developed in this study, the new experimental design and analysis procedures can also be applied to other processes, where the process variables are inter-dependent.
Self-Sensing in Fault Tolerant Magnetic Bearings
Authors: Montie D. , Maslen E.
Published: July 2002

Several schemes have recently been proposed for achieving either fault tolerance or self-sensing in magnetic bearings. The present work describes the fundamental connection between ability to actuate and ability to sense in a partially failed magnetic bearing system. This relationship is then exploited to construct a self-sensing scheme which operates in the presence of detectable actuator or amplifier faults. Such an approach is advantageous in fault tolerant systems because it reduces or eliminates the need to address potential independent failure mechanisms in sensors and actuators. Based on a model reference parameter estimation mechanism, the self-sensing scheme is shown to provide acceptable position measurement accuracy and bandwidth under various actuator/amplifier faults which are actuator tolerable. Estimates of increase in noise floor and loss of bandwidth under fault conditions are provided. The issue of estimator convergence under fault conditions is examined in detail with comments on implementation complexity arising from scheduling convergence control on fault state.