bluuebunny/crossref_metadata_2025 huggingface dataset:
The grading of practical examinations in complete denture technology
Authors: Spratley M. H.
Published: May 2009

The problems associated with the grading of practical examinations are discussed and statistical analyses of two gradings are presented. Consideration is given to the difficulties of failing students who may wish to transfer to another faculty and a recommendation is made for the introduction of non‐graded passes.
Some social characteristics and background of first‐year dental students, University of Sydney, 1976–85
Authors: Sivaneswaran Shanti , Barnard P. D.
Published: May 2009

This paper presents some information, derived by questionnaire, on the social characteristics and background of 1148 first‐year dental students at the University of Sydney for the years 1976–1985. Student entry age was 19.4 years; 27 per cent were female; 36 per cent of fathers and 24 per cent of mothers were professionals and 37 per cent of fathers and 11 per cent of mothers had attended university; parents of female students had higher educational levels than parents of male students; 55 per cent had medicine as the course of first preference. Eighty‐five per cent of students entered dentistry from high school with 78 per cent from Sydney.

Characteristics of students showed little change over the period 1976–1985. Some changes noted were an increase in the number of female students with fewer living in their parents' home; increase in number of students from government schools; decrease in foreign students but an increase in students (Australian citizens, or residents) born overseas, and of different ethnic backgrounds.
Microleakage of glass ionomer/composite resin restorations: A laboratory study. 1. The influence of glass ionomer cement
Authors: Smith E. Dell Kingsford , Martin F. Elizabeth
Published: May 2009

Acid‐etching of enamel margins, often combined with bevelling and use of a low viscosity resin, has resulted in improved sealing of composite restorations. When enamel is absent and margins involve dentine or cementum, microleakage is more often observed. The use of glass ionomer cement, as both a restorative material and as a base combined with a veneer of composite resin, has been advocated as a means of minimizing microleakage where margins are placed in dentine or cementum.

Four restorative techniques incorporating glass ionomer cement were used, in vitro, to restore cervical cavities. After thermal cycling, dye penetration was scored along occlusal and gingival margins. In all instances the gingival margin exhibited a less reliable seal than the occlusal margin. The sandwich restorations produced a superior seal at both occlusal and gingival margins when compared with glass ionomer restorative cement.
Dimensional accuracy of small gold alloy castings. Part 3. Gypsum‐bonded investment expansion
Authors: Morey Erica F.
Published: May 2009

The literature on the setting and thermal expansion of investments under both laboratory and practical conditions is reviewed.
Choice of toothbrush: A survey of dentists' personal preferences and recommendations for patients*
Authors: Gotjamanos Theo , Singh Harjinder , Strangio Tony
Published: May 2009

Data on dentists' choice of toothbrush brand/type for personal use and their recommendations for patients were obtained by means of a questionnaire. Seventy‐nine per cent of dentists surveyed received free samples, with Oral‐B comprising 33 per cent of all such samples, followed by Colgate (16 per cent) and Tek (13 per cent). Fifty‐three per cent of dentists surveyed indicated they used all free samples received. Sixty‐two per cent of dentists do not consider that different brushes differ significantly in their plaque‐removing ability. Therefore, while an effective toothbrushing technique is important, selection of the ‘correct toothbrush’ from the wide range available may not be critical. The results of the present investigation provide information that is relevant to dental health education and can be applied at the chairside as well as at the broader community level.
The evolution of the complete denture base. Theories of complete denture retention — A review. Part 1
Authors: Murray Michael D. , Darvell Brian W.
Published: May 2009

The history of denture base materials and the accompanying development of impression techniques are traced from the earliest times to the present day (Part 1) as a prelude to a study (Part 2–4) of the various theories that have been advanced to explain retention of the base without mechanical support. These theories are critically reviewed and tabulated in chronological order. Some areas for further investigation are identified.
Multiple external root resorption. Case report
Authors: Darbar U. R. , Jenkins C. B. G.
Published: May 2009

A case of a patient with multiple external root resorption affecting principally the molars and premolars is described. This case is unusual in that although both right and left molar and premolar teeth are involved, the resorption is worse on the left side and affects only the distal roots of the molars.
Early pulpal involvement in an unusual case of dens in dente. Case report
Authors: Türker Mustafa , Karaca İnci
Published: May 2009

Dens in dente (dens invaginatus, tooth within a tooth, dilated composite odontome) is an abnormal tooth form which occurs most frequently in the permanent maxillary lateral incisor region. Dens in dente may occur, however, in any tooth in the dental arch, although these other forms are comparatively rare. It may appear within both the coronal part of the tooth and the root, although coronal forms are more common.

In this paper, a case of extreme dens in dente with pulpal involvement at an early stage of eruption is presented.
The evolution of the complete denture base. Theories of complete denture retention — A review. Part 4
Authors: Murray Michael D. , Darvell Brian W.
Published: May 2009

The history of denture base materials and the accompanying development of impression techniques are traced from the earliest times to the present day (Part 1) as a prelude to a study (Part 2–4) of the various theories that have been advanced to explain retention of the base without mechanical support. These theories are critically reviewed and tabulated in chronological order. Some areas for further investigation are identified.
Acrylic resins reinforced with woven highly drawn linear polyethylene fibres. 3. Mechanical properties and further aspects of denture construction
Authors: Ladizesky N. H. , Pang M. K. M. , Chow T. W. , Ward I. M.
Published: May 2009

Previous work1 has established the feasibility of producing acrylic denture bases reinforced with layers of highly drawn linear polyethylene fibres in a woven form. This paper reports on the mechanical properties of the system, including the effect of water conditioning. It is confirmed that substantial improvements in impact strength can be obtained by the incorporation of the polyethylene fibres in woven form. The fibre/resin integration within the dentures has also been studied by optical microscopy. It was found that delamination may occur during some processing stages and steps are suggested to avoid this problem.
Mandibular central giant cell granuloma associated with sclerosing osteomyelitis of Garrè (periostitis ossificans). Case report
Authors: Toller Melahat Öǧütcen , Karaca Inci
Published: May 2009

Garrè's sclerosing osteomyelitis or periostitis ossificans with a radiographic ‘onion skin’ appearance is a separate clinical entity. The new bone formation underneath the periosteum is a response of periosteum to stimulation by low grade infection. This may occur in a variety of other developmental, metabolic, inflammatory and neoplastic diseases of bone. A case of mandibular giant cell granuloma of a central type associated with Garrè's sclerosing osteomyelitis is presented and the literature is reviewed.
CAD/CAM subperiosteal implants in Australia. Case report
Authors: Fischer James Edward
Published: May 2009

This is the first known report of a subperiosteal implant inserted in Australia using computer assisted design (CAD) and computer assisted manufacture (CAM). A case report is presented describing a method of eliminating first stage surgery in treating fully edentulous patients with subperiosteal implants.
Australian Dental Research Fund Trebitsch Scholarship*
Authors: Lange P. , Walsh L. J. , Savage N. W.
Published: May 2009

Several overseas studies have documented the presence of defects in unused latex and vinyl gloves. Since such defects compromise the barrier protection afforded by gloves, information regarding the frequency and site of defects which occur during manufacture is of direct clinical relevance. This study utilized a four‐stage testing procedure to evaluate defects in 13 brands of gloves which are used commonly in dental practice in Australia. Macropores in unused gloves were a significant problem, with 10 brands containing 1 per cent or more defective gloves. In addition, variations in electrical conductivity, signifying microporosity or inconsistencies in thickness, were also observed. These findings indicate that there is room to improve further the quality of protective gloves.
The modified Le Fort III osteotomy in the correction of mid‐facial deficiency. Case reports
Authors: Heggie Andrew A. C. , Lawry Denise M. , Ruljancich M. Kevin
Published: May 2009

Maxillary hypoplasia is a common diagnosis in the spectrum of dentofacial deformities and is usually corrected by a Le Fort I maxillary advancement osteotomy. The modified Le Fort III osteotomy enables correction of mid‐face hypoplasia where the maxillary hypoplasia is associated with infraorbital and zygomatic deficiency. This procedure is described and illustrated in two case reports. It is considered to be a superior technique to the maxillary osteotomy and onlay procedure and is recommended for use in selected patients.
Incidence of invasive cervical resorption in bleached root‐filled teeth
Authors: Heithersay Geoffrey S. , Dahlstrom Stephen W. , Marin Paul D.
Published: May 2009

Invasive cervical resorption, a form of external root resorption, has been reported to be associated with intra‐coronal bleaching of root‐filled teeth and this has raised concerns about carrying out such bleaching procedures. The purpose of the present study was to examine the incidence of invasive cervical resorption in root‐filled teeth which had been bleached using a standardized technique. Three observers examined records and radiographs from a total of 158 patients, whose bleaching treatment had been carried out in a specialist endodontic practice. The sample comprised 204 teeth with a review period of between 1 and 19 years. One‐hundred‐and‐fifty‐one teeth (77.94 per cent) had an associated history of traumatic injury. All teeth had been treated with a combination of thermocatalytic and ‘walking bleach’ procedures using 30 per cent hydrogen peroxide. In 54.41 per cent of teeth, guttapercha and AH26 root‐fillings were kept at the height of the cemento‐enamel junction while 18.63 per cent were below and 26.96 per cent were above the CEJ. Sealing cement was not placed over the gutta‐percha and AH26 root‐fillings in any of the teeth in the study. It was found that a total of four teeth from the sample group (1.96 per cent) had developed invasive cervical resorption during the review period. All of these teeth had a history of traumatic injury and the level of gutta‐percha was at the CEJ. The incidence of resorption found in this study of root‐filled teeth using a combined thermocatalytic and ‘walking bleach’ technique is lower than previously reported and indicates a relatively low risk of invasive cervical resorption using the technique outlined.
Vitamin K — its essential role in craniofacial development
Authors: Howe Andrew M. , Webster William S.
Published: May 2009

The normal vitamin K status of the human embryo appears to be close to deficiency. Maternal dietary deficiency or use of a number of therapeutic drugs during pregnancy, may result in frank vitamin K deficiency in the embryo. First trimester deficiency results in maxillonasal hypoplasia in the neonate with subsequent facial and orthodontic implications.

A rat model of the vitamin K deficiency embryopathy shows that the facial dysmorphology is preceded by uncontrolled calcification in the normally uncalcified nasal septal cartilage, and decreased longitudinal growth of the cartilage, resulting in maxillonasal hypoplasia. The developing septal cartilage is normally rich in the vitamin K‐dependent protein matrix gla protein (MGP). It is proposed that functional MGP is necessary to maintain growing cartilage in a non‐calcified state.

Developing teeth contain both MGP and a second vitamin K‐dependent protein, bone gla protein (BGP). It has been postulated that these proteins have a functional role in tooth mineralization. As yet this function has not been established and abnormalities in tooth formation have not been observed under conditions where BGP and MGP should be formed in a non‐functional form.
Fixed prosthodontic failure. A review and discussion of important aspects
Authors: Selby Alex
Published: May 2009

In order to justify the time and expense involved in complex restorative treatment there is an expectation of a favourable result and long‐term success. Longevity in fixed prosthodontics is not only dependent upon the precision and skill with which the work is carried out, but also to a large degree upon a proper assessment and diagnosis and the utilization and implementation of valid principles of design. This paper reviews the literature in an attempt to determine the incidence of failure and the reasons for, and types of, failures that occur. There is a consideration of some factors important in preoperative assessment and a detailed discussion of various aspects of design for fixed prosthodontic restorations.
Physiopathology of primary periodontitis associated with plaque. Microbial and host factors. A review. Part 1
Authors: Liébana J. , Castillo A.
Published: May 2009

Microbial factors involved in the genesis of periodontitis include colonization, bacterial penetration of the epithelium, multiplication and invasive‐destructive capacity. Colonization of the gingival sulcus is related, to a certain extent, to supragingival plaque. Bacterial multiplication is induced by nutrients in the gingival fluid, and nutrients produced by degradative and excretory microbial activity. Invasion and destruction are mediated by exotoxins, structural elements of the bacteria, enzymes, metabolites, polyclonal lymphocyte activity, fibroblastic cytotoxicity, and leukocyte chemotactic inhibition.
Differences in the perceptions of HIV risk amongst dental care providers in Western Australian clinics
Authors: Waddell Charles E. , Bennett Colin L. , Davies John L.
Published: May 2009

This paper examines the perceived risk of occupationally contracting HIV among dental care providers. This examination is based upon responses to a mailed questionnaire from all registered dentists (76 per cent response rate, n = 550) and dental therapists (63 per cent response rate, n = 208) in Western Australia during 1992. Results indicate that: 1) dental care providers who perceive a high risk of occupationally contracting HIV report a more conservative, cautious approach to HIV infection than do providers who perceive less risk of contracting the virus; 2) dental therapists are more likely than dentists to report a higher degree of perceived risk of occupationally contracting HIV; and 3) dentists are more likely than dental therapists to perceive compliance with universal precaution guidelines in dental practices in which they work. Reasons are presented for a suspicion that both sets of perceptions may be exaggerated. The need to educate dental therapists on the realistic risks of occupationally contracting HIV and to educate dentists on the value of compliance (and of appearing to comply) with universal precaution guidelines in order to help reduce undue stress and hindrances in the provision of safe and effective dental care in this era of AIDS concludes this paper.
High magnification in situ viewing of wound healing in oral mucosa
Authors: Walsh L. J. , L'Estrange P. R. , Seymour G. J.
Published: May 2009

Microscope endoscopy is a technique which allows high resolution, non‐invasive examination of soft tissues. This study employed microscope endoscopy to examine the process of healing following exposure of the oral mucosa to carbon dioxide laser radiation. On the wound boundaries, cellular debris and the laser‐induced char layer were shed as epithelial migration occurred. Wounds healed by secondary intention, with complete epithelial closure by 72 hours. A marked vascular response was evident from 6 to 48 hours following wounding, a time period coincident with the known pattern of blood vessel activation and infiltration of the wound site by leukocytes. The use of microscope endoscopy as an adjunct to biopsy and other invasive diagnostic methods in the assessment and follow‐up of soft tissue pathology may have value in clinical practice.
The role of adhesion molecules in oral cancer
Authors: Walsh L. J. , Coyne R. M. , Xu L. J. , Savage N. W.
Published: May 2009

Cell‐cell and cell‐matrix interactions are mediated by adhesion molecules. By altering interactions between epithelial cells, extracellular matrix and leukocytes, changes in adhesion molecule expression can influence tumour development and metastasis. This study compared the adhesion molecule profile of oral squamous cell carcinoma (SCC) with normal buccal mucosa. The pattern of expression of adhesion molecules differed between normal epithelial cells and tumour cells, while leukocytes and endothelial cells adjacent to the tumour showed a pattern common to inflammatory sites. Aberrations in cell adhesion receptors on tumour cells may contribute to the unique biologic behaviour of individual tumours.
Epithelial growth fraction and expression of p53 tumour suppressor gene in oral submucous fibrosis
Authors: Cox S. C. , Walker D. M.
Published: May 2009

The incidence of squamous cell carcinoma in patients with oral submucous fibrosis (OSF) exceeds 7 per cent. The proliferative cell nuclear antigen (PCNA) is a convenient marker of epithelial cell proliferation and p53 tumour suppressor gene mutations or deletions are frequent in oral cancer. The present study estimated the basal epithelial cell growth fraction using a standard immunohistological method for the detection of nuclear PCNA from 20 Nepalese patients with OSF as 31.8 per cent compared with 7.6 per cent for oral mucosa from 43 normal subjects (p<0.001) and 39.4 per cent for 44 patients with oral cancer. The PCNA growth fraction correlated significantly with that derived by Ki‐67 labelling. There was no correlation between the growth fraction and the severity of epithelial dysplasia found is OSF.

Abnormal expression of p53 protein identified by immunohistochemistry with a panel of antibodies was found in 70 per cent of the OSF specimens, and 21 per cent of mucosal specimens from subjects with clinically normal mouths. PCNA‐positive cells and p53 expression were restricted to the basal epithelial layer in OSF. The unexpected finding of p53 protein in clinically healthy mucosa was confined to subjects aged over 40 years who smoked tobacco, a known risk factor for oral cancer. There was no association between p53 expression and epithelial atypia scores in OSF.

It is concluded that the proportion of actively cycling epithelial cells is increased in OSF and that p53 tumour suppressor gene mutations or deletions may be prevalent. Confirmation by molecular biology techniques of this genetic damage is now needed.
Split‐mouth study of sealant retention with carbon dioxide laser versus acid etch conditioning
Authors: Walsh L. J.
Published: May 2009

A split mouth clinical trial was undertaken to compare the retention of fissure sealants placed using laser or acid conditioning. After a mean follow‐up period of 14.5 months, the retention rate for laser conditioning was greater than that for acid etching (97.9 per cent versus 94.6 per cent, respectively), although this difference was not statistically significant. No adverse effects occurred during or subsequent to laser conditioning procedures. It is concluded that carbon dioxide laser conditioning is a viable alternative to acid etching for fissure sealing.
Experimental and Numerical Study of the Time-Dependent Pressure Response of a Shock Wave Oscillating in a Nozzle
Authors: Ott P. , Bo¨lcs A. , Fransson T. H.
Published: May 2009

Investigations of flutter in transonic turbine cascades have shown that the movement of unsteady normal shocks has an important effect on the excitation of blades. In order to predict this phenomenon correctly, detailed studies concerning the response of unsteady blade pressures versus different parameters of an oscillating shock wave should be performed, if possible isolated from other flow effects in cascades. In the present investigation the correlation between an oscillating normal shock wave and the response of wall-mounted time-dependent pressure transducers was studied experimentally in a nozzle with fluctuating back pressure. Excitation frequencies between 0 Hz and 180 Hz were investigated. For the measurements, various measuring techniques were employed. The determination of the unsteady shock position was made by a line scan camera using the Schlieren flow visualization technique. This allowed the simultaneous use of unsteady pressure transducers to evaluate the behavior of the pressure under the moving shock. A numerical code, based on the fully unsteady Euler equations in conservative form, was developed to simulate the behavior of the shock and the pressures. The main results of this work were: (1) The boundary layer over an unsteady pressure transducer has a quasi-steady behavior with respect to the phase lag. The pressure amplitude depends on the frequency of the back pressure. (2) For the geometry investigated the shock amplitude decreased with increasing excitation frequency. (3) The pressure transducer sensed the arriving shock before the shock had reached the position of the pressure transducer. (4) The computed unsteady phenomena agree well with the results of the measurements.
Heat (Mass) Transfer and Film Cooling Effectiveness With Injection Through Discrete Holes: Part II—On the Exposed Surface
Authors: Cho H. H. , Goldstein R. J.
Published: May 2009

The heat (mass) transfer coefficient and the film cooling effectiveness are obtained from separate tests using pure air and naphthalene-saturated vapor injected through circular holes into a crossflow of air. The experiments indicate that Sherwood numbers around the injection hole are up to four times those on a flat plate (without injection holes) due to the interaction of the jets and the mainstream. The mass transfer around the injection holes is dominated by formations of horseshoe, side, and kidney vortices, which are generated by the jet and crossflow interaction. For an in-line array of holes, the effectiveness is high and uniform in the streamwise direction but has a large variation in the lateral direction. The key parameters, including transfer coefficients on the back surface (Part I), inside the hole (Part I), and on the exposed surfaces, and the effectiveness on the exposed surface, are obtained so that the wall temperature distribution near the injection holes can be determined for a given heat flux condition. This detailed information will also aid the numerical modeling of flow and mass/heat transfer around film cooling holes.
Developing Buoyancy-Modified Turbulent Flow in Ducts Rotating in Orthogonal Mode
Authors: Bo T. , Iacovides H. , Launder B. E.
Published: May 2009

A numerical study of developing flow through a heated duct of square cross section rotating in orthogonal mode is reported. The two main aims are to explore the effects of rotational buoyancy on the flow development and to assess the ability of available turbulence models to predict such flows. Two test cases have been computed corresponding to values of the rotation number, Ro, of 0.12 and 0.24, which are typical of operating conditions in internal cooling passages of gas turbine blades. Computations from three turbulence models are presented: a k–ε eddy viscosity (EVM) model matched to a low-Reynolds-number one-equation EVM in the near-wall region; a low-Re k–ε EVM and a low-Re algebraic stress model (ASM). Additional computations in which the fluid density is assumed to remain constant allow the distinct contributions from buoyancy and Coriolis forces to be separated. It is thus shown that rotational buoyancy can have a substantial influence on the flow development and that, in the case of outward flow, it leads to a considerable increase of the side-averaged heat transfer coefficient. The Coriolis-induced secondary motion leads to an augmentation of the mean heat transfer coefficient on the pressure surface and a reduction on the suction side. The k–ε/one-equation EVM produces a mostly reasonable set of heat transfer predictions, but some deficiencies do emerge at the higher rotation number. In contrast, predictions with the low-Re k–ε EVM return a spectacularly unrealistic behavior while the low-Re ASM thermal predictions are in encouragingly close agreement with available measurements.
Factors Affecting Measured Axial Compressor Tip Clearance Vortex Circulation
Authors: Khalid S. A.
Published: May 2009

The relationship between turbomachinery blade circulation and tip clearance vortex circulation measured experimentally is examined using three-dimensional viscous flow computations. It is shown that the clearance vortex circulation one would measure is dependent on the placement of the fluid contour around which the circulation measurement is taken. Radial transport of vorticity results in the magnitude of the measured clearance vortex circulation generally being less than the blade circulation. For compressors, radial transport of vorticity shed from the blade tip in proximity to the endwall is the principal contributor to the discrepancy between the measured vortex circulation and blade circulation. Further, diffusion of vorticity shed at the blade tip toward the endwall makes it impossible in most practical cases to construct a fluid contour around the vortex that encloses all, and only, the vorticity shed from the blade tip. One should thus not expect agreement between measured tip clearance vortex circulation and circulation around the blade.
Modeling Unsteady Boundary Layer Transition on a Curved Plate Under Periodic Unsteady Flow Conditions: Aerodynamic and Heat Transfer Investigations
Authors: Chakka P. , Schobeiri M. T.
Published: May 2009

A boundary layer transition model is developed that accounts for the effects of periodic unsteady wake flow on the boundary layer transition. To establish the model, comprehensive unsteady boundary layer and heat transfer experimental investigations are conducted. The experiments are performed on a curved plate at zero-streamwise pressure gradient under periodic unsteady wake flow, where the frequency of the periodic unsteady flow is varied. The analysis of the time-dependent velocities, turbulence intensities, and turbulence intermittencies has identified three distinct quantities as primarily responsible for the transition of an unsteady boundary layer. These quantities, which exhibit the basis of the transition model presented in this paper, are: (1) relative intermittency, (2) maximum intermittency, and (3) minimum intermittency. To validate the developed transition model, it is implemented in an existing boundary layer code, and the resulting velocity profiles and the heat transfer coefficients are compared with the experimental data.
Intermittent Flow and Thermal Structures of Accelerating Transitional Boundary Layers: Part 1—Mean Quantities
Authors: Wang T. , Keller F. J.
Published: May 2009

A conditional sampling technique was employed to separate the turbulent and nonturbulent parts of accelerated boundary layers undergoing laminar-turbulent transition on a uniformly heated flat plate. Tests were conducted with zero pressure gradient and two levels of streamwise acceleration parameter: K = 0.07 × 10−6 and 0.16 × 10−6. The conditionally sampled distribution of the skin friction coefficients revealed that the values for Cf in the nonturbulent and turbulent portions deviated significantly from the respective laminar and turbulent correlations. These deviations increased as acceleration increased. Reconstructing the local average Cf values using the laminar and fully turbulent correlations consistently overestimated the unconditioned Cf values. Using the conditionally sampled data for reconstructing Cf values provided better results, but does not necessarily result in the same unconditioned Cf values. The mean velocity profiles from the turbulent portions had the appearance of a low-Reynolds-number turbulent boundary layer with a large wake region. In the late transition region, as acceleration increased, the wake region in the turbulent portion was suppressed relative to the unconditioned result. The integral parameters, δ*, θ, and shape factor, H, were conditionally sampled and analyzed.
Flow and Heat Transfer of Natural Convection in Horizontal Annulus With a Heating Element on Inner Cylinder
Authors: Yang C. S. , Jeng D. Z. , Tang U. H. , Gau C.
Published: June 2009

Experiments have been performed to study natural convection flow and heat transfer in a horizontal annulus when a square heating element is positioned at different locations on the inner insulated cylinder. The annulus is filled with water and has cylinder to cylinder diameter ratio of 3. The square heating element is small and has the width to annulus gap width ratio of 1/6. The range of Rayleigh number studied is approximately from 1.9×106 to 3.3×107. It has been found that the flow pattern, the temperature distribution around the inner cylinder wall, and the local heat transfer rate around the outer cylinder are very sensitive to the location of the heating element. The heating element Nusselt numbers at various locations on the inner cylinder are obtained and well correlated against the Rayleigh number to the 1/3 powers. A maximum in the correlation parameter C is obtained when the heating element is placed 90 deg from the bottom.
Flame Suppression Technique in Arc Tracking of Circuit Boards
Authors: Lu Frank K. , Phonharath Linda , Mitchell Richard R. , Bigdeli Behzad
Published: May 2009

The problem of arc tracking in power electronic enclosures was studied through simple bench-top experiments aimed at understanding the phenomenon. Experiments were performed to isolate the causes of arc tracking on PCB boards with high-powered electrodes subjected to a Solventol/water mixture contamination. These experiments show that a minimum electrode spacing of 1 mm would be susceptible to arc tracking. A larger spacing of 3.2 mm appears to prevent arc tracking. In the event that arc tracking causes combustion, a passive flame suppression method is indicated. This method comprises of four layers of off-the-shelf expanded metal network. Tests show that the flame is quenched in about one minute, with minimum damage to the plastic enclosure.
Vascularized Svelte (Compact) Flow Architectures
Authors: Lorente Sylvie , Bejan Adrian
Published: May 2009

In this paper we describe a new concept for vascularizing the flow architectures of compact devices. Vascularization is achieved by using tree-shaped (dendritic) flow passages on both sides of the heat transfer surface. For each side, we propose to use an architecture that consists of trees that alternate with upside down trees. By evaluating the fluid flow performance we show that dendritic vascularization is superior to the use of parallel microchannels when the tree structures have four or more levels of bifurcation. The local pressure losses that occur at the multiple junctions of each tree structure become negligible when the svelteness of the architecture (Sv) exceeds the order of 10. The svelteness is a global geometric property defined as the external length scale of the architecture divided by the internal length scale (the total flow volume raised to the power 1/3). The combination of fluid architectures and solid constitute a “smart” composite material: the fluids that bathe the volume can be used to provide multiple functions, such as serf-healing, serf-cooling, and variable transport properties. For example, when placed in counterflow, the vascularized hot and cold sides of the surface are a compact heat exchanger. The article shows under what conditions the tree vascularization offers greater flow access than parallel single-scale channels oriented perpendicularly to the parallel lines.
Rendering the Transient Hot Wire Experimental Method to Dual-Phase Applications
Authors: Vadasz Peter
Published: May 2009

The Transient Hot Wire method is well established as the most accurate, reliable and robust technique for evaluating the thermal conductivity of fluids and solids [3, 12, 14, 15, 18]. Unfortunately its direct application to dual-phase systems such as solid suspensions in fluids or porous media cannot be supported by the very principles and methodology underlying this method. The derivation of possible ways of rendering the transient hot wire method to dual-phase applications including the development of validity criteria for such applications is proposed and discussed.
Free Bending Vibrations of a Centrally Bonded Symmetric Double Lap Joint (or Symmetric Double Doubler Joint) With a Gap in Mindlin Plates or Panels
Authors: Yuceoglu U. , Gu¨vendik O. , O¨zerciyes V.
Published: May 2009

In this present study, the “Free Bending Vibrations of a Centrally Bonded Symmetric Double Lap Joint (or Symmetric Double Doubler Joint) with a Gap in Mindlin Plates or Panels” are theoretically analyzed and are numerically solved in some detail. The “plate adherends” and the upper and lower “doubler plates” of the “Bonded Joint” system are considered as dissimilar, orthotropic “Mindlin Plates” joined through the dissimilar upper and lower very thin adhesive layers. There is a symmetrically and centrally located “Gap” between the “plate adherends” of the joint system. In the “adherends” and the “doublers” of the “Bonded Joint” assembly, the transverse shear deformations and the transverse and rotary moments of inertia are included in the analysis. The relatively very thin adhesive layers are assumed to be linearly elastic continua with transverse normal and shear stresses. The “damping effects” in the entire “Bonded Joint” system are neglected. The sets of the dynamic “Mindlin Plate” equations of the “plate adherends”, the “double doubler plates” and the thin adhesive layers are combined together with the orthotropic stress resultant-displacement expressions in a “special form”. This system of equations, after some further manipulations, is eventually reduced to a set of the “Governing System of the First Order Ordinary Differential Equations” in terms of the “state vectors” of the problem. Hence, the final set of the aforementioned “Governing Systems of Equations” together with the “Continuity Conditions” and the “Boundary conditions” facilitate the present solution procedure. This is the “Modified Transfer Matrix Method (MTMM) (with Interpolation Polynomials). The present theoretical formulation and the method of solution are applied to a typical “Bonded Symmetric Double Lap Joint (or Symmetric Double Doubler Joint) with a Gap”. The effects of the relatively stiff (or “hard”) and the relatively flexible (or “soft”) adhesive properties, on the natural frequencies and mode shapes are considered in detail. The very interesting mode shapes with their dimensionless natural frequencies are presented for various sets of boundary conditions. Also, several parametric studies of the dimensionless natural frequencies of the entire system are graphically presented. From the numerical results obtained, some important conclusions are drawn for the “Bonded Joint System” studied here.
Professional and Soft Skills for Engineering Graduate Students
Authors: Barakat Nael
Published: May 2009

Graduate studies in engineering have always been a favorable choice for career advancement, in both the practice and the academic sides of the career. Graduate students constitute a significant population of engineering schools, which brings with it a whole spectrum of questions and issues. To verify the quality of students and their preparedness for graduate studies, checks and balances have been installed to filter these students through investigating their academic records. However, the soft and professional side of the skill set that these students have is not of much significance in these filters. These skills include, but are not limited to, communication, logical reasoning, management, autonomy, and ethics and professionalism. Embedded among these skills is also the intellectual and mental graduation of school. With most students realizing the importance of continuous education and life long learning, many of them are seeking graduate studies. The highly diverse background of these students creates an obvious differential in their ability to meet expectation at that level of academics. This has resulted in many issues arising in graduate schools about the preparedness of the incoming students. To better identify and treat these deficiencies, strategies and applications are being sought. In this paper, a list of the expected soft and professional skills in graduate engineers is provided. A discussion of the most common issues related to this skill set in incoming graduate students is presented. In addition, a strategy that has been designed and applied through a mandatory course in an existing graduate engineering curriculum, at Grand Valley State University (GVSU) School of Engineering (SOE), dealing with these issues, is included. Reflections on the course outcomes and evaluations are also provided.
Controlled Cavitation and Sonoporation in Microfluidics
Authors: Ohl Claus-Dieter , Le Gac Se´verine , Zwaan Ed , Tsuji Kinko , van den Berg Albert
Published: May 2009

Cavitation – the growth and collapse of mostly empty bubbles — is commonly attributed to large scale or very rapid flows, e.g. at ship propellors or at fuel injection nozzles. Cavitation is very aggressive to materials and one reason is its ability to focus fluid flows to very small scales; the bubbles concentrate the energy from the fluid during their shrinkage. Only recently the attention from largely free cavitation bubbles has shifted towards the study of more confined bubbles [1–5]. Here we report on an experiment to exploit cavitation in microfluidic systems or so called lab-on-a-chip devices for flow handling and biological cell manipulation. In microfluidics generally due to the small scales low Reynolds number flows are observed. Yet, cavitation bubble-induced flows allow to reach a high Reynolds number regime also on these small scales. By exploiting this rarely studied flow regime new techniques for liquid and cell handling become feasible. Here, we will report first on the effect of a channel wall on the bubble dynamics and then present an application for cell handling and membrane poration.
Thermal Proximity Effects of Packaged RF High Power Amplifier Discretes
Authors: Comber Brian , Rightley Michael J. , Fleischer Amy
Published: May 2009

This paper analyzes the thermal design of an RF High Power amplifier. The device, with a maximum dimension of only .4 mm, has a high power density, dissipating up to 4 W. There is concern about the impacts of device proximity on thermal performance due to desired packaging density. The devices are numerically modeled and the effects of device proximity, heat spreader dimensions, material conductivity, and die bond layer thickness and substrate thickness on device operating temperature are quantified.
Characterizations of Ball Impact Responses of Tin-Silver-Copper Solder Joints Doped With Nickel or Germanium
Authors: Lai Yi-Shao , Song Jenn-Ming , Chang Hsiao-Chuan , Chiu Ying-Ta
Published: May 2009

The ball impact test (BIT) was developed based on the demand of a package-level measure of the board-level reliability of solder joints in the sense that it leads to brittle intermetallic fracturing, similar to that from a board-level drop test. The BIT itself stands alone as a unique and novel test methodology in characterizing strengths of solder joints under a high-speed shearing load. In this work, we present BIT results conducted at an impact velocity of 500 mm/s on Sn-4Ag-0.5Cu, Sn-1Ag-0.5Cu, Sn-1Ag-0.5Cu-0.05Ni, Sn-1.2Ag-0.5Cu-0.05Ni, and Sn-1Ag-0.5Cu-0.05Ge package-level solder joints, bonded on substrate pads of immersion tin (IT) and direct solder on pad (DSOP) surface finishes. Differences of BIT results with respect to multi-reflow are also reported.
Design of a Multi-Directional Variable Stiffness Leg for Dynamic Running
Authors: Galloway Kevin C. , Clark Jonathan E. , Koditschek Daniel E.
Published: May 2009

Recent developments in dynamic legged locomotion have focused on encoding a substantial component of leg intelligence into passive compliant mechanisms. One of the limitations of this approach is reduced adaptability: the final leg mechanism usually performs optimally for a small range of conditions (i.e. a certain robot weight, terrain, speed, gait, and so forth). For many situations in which a small locomotion system experiences a change in any of these conditions, it is desirable to have a variable stiffness leg to tune the natural frequency of the system for effective gait control. In this paper, we present an overview of variable stiffness leg spring designs, and introduce a new approach specifically for autonomous dynamic legged locomotion. We introduce a simple leg model that captures the spatial compliance of the tunable leg in three dimensions. Lastly, we present the design and manufacture of the multi-directional variable stiffness legs, and experimentally validate their correspondence to the proposed model.
Numerical Investigations of the Jet Breakup Regime of Electrospray Ionization Using a Carbon Fiber Emitter
Authors: Sen A. K. , Darabi J.
Published: May 2009

This paper presents numerical investigations of jet breakup in electrospray ionization using a carbon fiber emitter. The emitter has a pointed carbon fiber located coaxial with a fused silica capillary of 360μm OD and 75μm ID, with its tip extending 30 micron beyond the capillary exit. The model employs leaky-dielectric formulations to solve electrodynamics and volume-of-fluid technique for tracking the interface. The existing leaky-dielectric model is modified to consider presence of free charges both in the bulk of the liquid as well as on the interface. A velocity perturbation is used at the capillary inlet to emulate the naturally occurring disturbance necessary for the jet breakup. The model is first validated by comparing the model predictions with experimental results for a conventional emitter. Then, it is used to simulate electrospray performance of the carbon fiber emitter, including the Taylor cone and jet breakup processes. The influence of emitter geometry and operating conditions are thoroughly investigated. The droplet diameter and velocity are correlated with flow rate and the correlation results are compared with that reported in literature.
Linking Research and Teaching: Two Design Courses Orchestrated Around a Rotary Diesel Engine Patent
Authors: Schaefer Dirk , Panchal Jitesh H.
Published: May 2009

It is well known and widely accepted that the integration of research and teaching in a problem-based setting helps to foster deep learning among students. In this paper, we describe how a patent of a rotary diesel engine, that had failed to work in practice, was used to link undergraduate research and teaching activities by orchestrating two design courses around this patent. Learning outcomes, course goals, content as well as assignments and projects were defined based on constructive alignment. Students’ performance was assessed using so-called assessment rubrics based on Bloom’s taxonomy, which were specifically developed for both courses. After introducing the educational framework for this approach to enhancing student learning, we explain how both courses were designed and delivered in order to meet the higher level educational outcomes envisaged. The paper closes with an overview of both our experiences and those of our students.
Design and Implementation of Actively Cooled Panels for Scramjets
Authors: Vermaak Natasha , Valdevit Lorenzo , Zok Frank W. , Evans Anthony G.
Published: May 2009

The operating conditions of scramjet engines demand designs that include active cooling by the fuel and the use of lightweight materials that withstand extreme heat fluxes and structural loads. An optimization tool has previously been introduced to direct the development of advanced materials that outperform existing high temperature alloys and compete with ceramic matrix composites. This analysis presents verification and accretion of the analytical design tool through a combination of numerical and experimental techniques. Selected computational fluid dynamics (CFD) analyses have been performed to verify critical thermal assumptions. A high-power CO2 laser provides heat fluxes representative of hypersonic flight conditions.
Prediction of Stress on Pump Blade by One-Way Coupled Method of Fluid and Structure Simulation
Authors: Kobayashi Katsutoshi , Ono Shigeyoshi , Harada Ichiro , Chiba Yoshimasa
Published: May 2009

The stress of a mixed flow pump with open type blades was measured and predicted by a one-way coupled simulation to evaluate the reliability of pump strength. The mechanism generating a large stress was investigated by numerical results. The stress became maximum at 70%Q flow rate of the off design point in both experimental and numerical results. Although the shaft power and total head became maximum at 0%Q flow rate of the shut off point, these did not relate to cause the largest stress. The pressure distribution on the surface of blade was investigated by simulated flow field. The flow separation at 0%Q flow rate occurred near the hub side on the suction surface of blade and loads became largest on the stream line of hub side among the all flow rates. On the other hand, the flow separation at 70%Q flow rate occurred over the whole area through the leading edge and loads became largest on the stream line of tip side among the all flow rates. It was found that the stress could be determined from the location where the flow separation was generated and the area size of it.
Hydrogen-Methane Blend Fuelling of a Heavy-Duty, Direct-Injection Engine
Authors: McTaggart-Cowan G. P. , Munshi S. R. , Rogak S. N. , Hill P. G. , Bushe W. K.
Published: May 2009

Combining hydrogen with natural gas as a fuel for internal combustion engines provides an early opportunity to introduce hydrogen into transportation applications. This study investigates the effects of fuelling a heavy-duty engine with a mixture of hydrogen and natural gas injected directly into the combustion chamber. The combustion system is unmodified from that developed for natural gas fuelling. The results demonstrate that hydrogen can have a significant beneficial effect in reducing emissions without affecting efficiency or requiring significant engine modifications. Combustion stability is enhanced through the higher reactivity of the hydrogen, resulting in reduced emissions of unburned methane. The fuel’s lower carbon-energy ratio also reduces CO2 emissions. These results combine to significantly reduce tailpipe greenhouse gas (GHG) emissions. However, the effect on net GHG’s, including both tailpipe and fuel-production emissions, depends on the source of the hydrogen. Cleaner sources, such as electrolysis based on renewables and hydro-electric power, generate a significant net reduction in GHG emissions. Hydrogen generated by steam-methane reforming is essentially GHG neutral, while electrolysis using electricity from fossil-fuel power plants significantly increases net GHG emissions compared to conventional natural gas fuelling.