bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Variations in Translucency and Background on Color Differences in CAD/CAM Lithium Disilicate Glass Ceramics
Authors: Al Ben Ali Abdulaziz , Kang Kiho , Finkelman Matthew D. , Zandparsa Roya , Hirayama Hiroshi
Published: July 2013

Purpose

The purpose of this study was to compare the effect of variations in translucency and background on color differences (ΔE) for different shades of computer‐aided design and computer‐aided manufacturing (CAD/CAM) lithium disilicate glass ceramics.

Materials and Methods

A pilot study suggested n = 10 as an appropriate sample size for the number of lithium disilicate glass ceramic cylinders per group. High‐transparency (HT) and low‐transparency (LT) cylinders (diameter, 12 mm; length, 13 mm) were fabricated in three ceramic shades (BL1, A2, C3) using CAD/CAM technology and were cut into specimen disks (thickness, 1.2 mm; diameter, 12 mm) for placement on Natural Die (ND1 and ND4) backgrounds. Four combinations of translucency and background color were evaluated in terms of color differences for the three ceramic shades: group 1 (HT ND1, reference), group 2 (HT ND4), group 3 (LT ND1), and group 4 (LT ND4). A spectrophotometer was used to measure the color differences. Nonparametric tests (Kruskal‐Wallis tests) were used to evaluate the color differences among the tested groups, and Mann‐Whitney U tests with Bonferroni correction were used as post hoc tests. Furthermore, for each ceramic shade, the HT groups were compared to the LT groups using the Mann‐Whitney U test.

Results

Significant differences were present among the tested groups of the same ceramic shade (p < 0.001). The highest ΔE values were observed in the HT ND4 group for BL1, while the lowest ΔE values were found in the LT ND1 group for both A2 and C3. Further, the HT groups and the groups with a darker background (ND4) showed increased ΔE values compared with the other groups (p < 0.001).

Conclusions

Within the limitations of this study, the results suggested that the translucency and background color significantly influenced the lithium disilicate glass ceramic color among the BL1, A2, and C3 ceramic shades. Changing the underlying color from a lighter background to a darker background resulted in increased color differences.
Making Linguistics Matter: Building on the Public's Interest in Language
Authors: Purnell Thomas , Raimy Eric , Salmons Joseph
Published: July 2013

Linguists in the United States are acutely aware of the need to engage the public about their work in new and better ways. We describe here our effort to take up that challenge in Wisconsin by building a set of outreach projects that connect with communities throughout the state and that focus on issues of importance to particular audiences. Through these projects, we have become convinced that outreach, teaching, and research — treated separately and distinctly for academic evaluation — are inextricably linked, often to the point of being indistinguishable in practice.
Creole Speakers and Standard Language Education
Authors: Wigglesworth Gillian , Billington Rosey , Loakes Deborah
Published: July 2013

Speakers of creole languages experience educational disadvantage in schools that teach in the standard language of their region, but there remain many misconceptions about why this is the case and how best to facilitate academic improvement, despite research demonstrating that actively using creoles in the classroom leads to a range of positive outcomes for these students. This paper reviews how attitudes towards creoles influence their place in educational contexts, some of the challenges for research on creoles in education, approaches to teaching creole‐speaking children with particular reference to bilingual programs, and the ramifications of standardized testing for creole‐speaking students.
A metabolic gene cluster in Lotus japonicus discloses novel enzyme functions and products in triterpene biosynthesis
Authors: Krokida Afrodite , Delis Costas , Geisler Katrin , Garagounis Constantine , Tsikou Daniela , Peña‐Rodríguez Luis M. , Katsarou Dimitra , Field Ben , Osbourn Anne E. , Papadopoulou Kalliope K.
Published: July 2013

Genes for triterpene biosynthetic pathways exist as metabolic gene clusters in oat and Arabidopsis thaliana plants. We characterized the presence of an analogous gene cluster in the model legume Lotus japonicus.

In the genomic regions flanking the oxidosqualene cyclase AMY2 gene, genes for two different classes of cytochrome P450 and a gene predicted to encode a reductase were identified. Functional characterization of the cluster genes was pursued by heterologous expression in Nicotiana benthamiana. The gene expression pattern was studied under different developmental and environmental conditions. The physiological role of the gene cluster in nodulation and plant development was studied in knockdown experiments.

A novel triterpene structure, dihydrolupeol, was produced by AMY2. A new plant cytochrome P450, CYP71D353, which catalyses the formation of 20‐hydroxybetulinic acid in a sequential three‐step oxidation of 20‐hydroxylupeol was characterized. The genes within the cluster are highly co‐expressed during root and nodule development, in hormone‐treated plants and under various environmental stresses. A transcriptional gene silencing mechanism that appears to be involved in the regulation of the cluster genes was also revealed.

A tightly co‐regulated cluster of functionally related genes is involved in legume triterpene biosynthesis, with a possible role in plant development.
Characterization of the Late Endosomal ESCRT Machinery in Trypanosoma brucei
Authors: Silverman Jason S. , Muratore Katherine A. , Bangs James D.
Published: July 2013

The multivesicular body (MVB) is a specialized Rab7+ late endosome (LE) containing multiple intralumenal vesicles that function in targeting ubiquitinylated cell surface proteins to the lysosome for degradation. African trypanosomes lack a morphologically well‐defined MVB, but contain orthologs of the ESCRT (Endosomal Sorting Complex Required for Transport) machinery that mediates MVB formation. We investigate the role of TbVps23, an early ESCRT component, and TbVps4, the terminal ESCRT ATPase, in lysosomal trafficking in bloodstream form trypanosomes. Both localize to the TbRab7+ LE and RNAi silencing of each rapidly blocks growth. TbVps4 silencing results in approximately threefold accumulation of TbVps23 at the LE, consistent with blocking terminal ESCRT disassembly. Trafficking of endocytic and biosynthetic cargo, but not default lysosomal reporters, is also negatively affected. Others reported that TbVps23 mediates ubiquitin‐dependent lysosomal degradation of invariant surface glycoproteins (ISG65) (Leung et al., Traffic 2008;9:1698–1716). In contrast, we find that TbVps23 ablation does not affect ISG65 turnover, while TbVps4 silencing markedly enhances lysosomal degradation. We propose several models to accommodate these results, including that the ESCRT machinery actually retrieves ISG65 from the LE to earlier endocytic compartments, and in its absence ISG65 traffics more efficiently to the lysosome. Overall, these results confirm that the ESCRT machinery is essential in Trypanosoma brucei and plays important and novel role(s) in LE function in trypanosomes.
Predicting Rough Wall Heat Transfer and Skin Friction in Transitional Boundary Layers—A New Correlation for Bypass Transition Onset
Authors: Lorenz M. , Schulz A. , Bauer H.-J.
Published: July 2013

This paper summarizes the experimental results of a comprehensive study on the heat transfer and aerodynamic losses of a highly loaded turbine blade with surface roughness. A few hundred test cases conducted at several Reynolds numbers, freestream turbulence levels, and different deterministic roughness geometry have been examined. Some of these results have been published in two previous papers, showing a strong effect of roughness on laminar-turbulent bypass transition on the airfoil suction side. Beside roughness height, roughness anisotropy has turned out to be one of the major influencing factors. The airfoil heat transfer distribution of these measurements is used for detecting the transition onset. Additionally, further transition onset data from the literature is reevaluated. Thus, important roughness (geometry) parameters are identified and a new correlation for the transition onset is deduced, including roughness parameters along with freestream turbulence. Moreover, a method to extract the relevant roughness parameters from realistic surface roughness is presented. Additional heat transfer and aerodynamic measurements are conducted for two different real surface roughness types. Calculations with a 2D-boundary layer code on these surfaces are presented in order to validate the new model.
A Spectral Study of a Moderately Loaded Low-Pressure Turbine Airfoil—Part I: Identifying Frequencies Affecting Bypass Transition
Authors: Graveline J. R. S. , Sjolander S. A.
Published: July 2013

A single wire, hot-wire, probe is used to examine the airflow in, and in close vicinity to, the shear layer of a low-pressure turbine (LPT) airfoil. A spectral analysis of the data identifies two sets of wide peaks of turbulent kinetic energy, one near 200 Hz and a second near 1 kHz. A method is developed to identify these peaks based on a combination of empirical relations between the airflow velocity and boundary layer thickness and on the location of the frequency peaks relative to the state of the free shear layer as it transitioned from laminar to turbulent. The method suggests the presence of Tollmien–Schlichting waves and Kelvin–Helmholtz instabilities. The Kelvin–Helmholtz instabilities are shown to pair.
Aeroelasticity at Reversed Flow Conditions—Part III: Reduction of Surge Loads by Means of Intentional Mistuning
Authors: Schoenenborn Harald , de Vries Mirja
Published: July 2013

Compressor surge consists of four phases: (i) pressure rise, (ii) flow breakdown, (iii) blow-down, and (iv) flow recovery. During the blow-down phase reversed flow conditions exist, where a blade may accumulate hundreds of vibration cycles, depending on the surge volume and the vibration frequency. High vibration amplitudes and blade damages were observed in the past. In Part I (GT2011-45034) a compressor cascade was analyzed experimentally and analytically at steady reversed flow conditions. It has been shown that (i) the steady flow field can be predicted well by CFD analysis, (ii) the overall damping coefficient calculated by unsteady CFD compares reasonably well with measurements, and (iii) a blade may become unstable at certain reversed flow conditions. In Part II (GT2011-45035) the analytical procedures used in Part I were applied to the front part of a multistage HPC for reversed flow conditions. It was found that surge loads consist in reality of two physically different phenomena (i) the pressure wave during the flow breakdown leading to rather low blade stresses and (ii) flutter during the blow-down phase which may lead to very high blade stresses and damages during surge for some stages. As it is well known that intentional mistuning is a way to mitigate flutter, intentional mistuning is investigated in Part III of the paper at reversed flow conditions. At first, a CFD study of a single airfoil is presented showing the dependency of aerodynamic damping upon flow angle and pressure ratio over the airfoil at reversed flow conditions, including intentional mistuning studies. Secondly, an investigation is presented which shows experimentally and analytically that surge stresses can be reduced significantly by the use of intentional mistuning. In a multistage compressor test rig, one rotor stage, which experienced very high stresses during surge, was subjected to a cutback on every second blade, leading to significantly reduced surge stresses. Analytically, an aeroelastic eigenvalue analysis showed the same behavior.
Heat Transfer Enhancement in Narrow Diverging Channels
Authors: Lamont Justin , Ramesh Sridharan , Ekkad Srinath V. , Tolpadi Anil , Kaminski Christopher , Salamah Samir
Published: July 2013

Detailed heat transfer coefficient distributions have been obtained for narrow diverging channels with and without enhancement features. The cooling configurations considered include rib turbulators and concavities (or dimples) on the main heat transfer surfaces. All of the measurements are presented at a representative Reynolds number of 28,000. Pressure drop measurements for the overall channel are also presented to evaluate the heat transfer enhancement geometry with respect to the pumping power requirements. The test models were studied for wall heat transfer coefficient measurements using the transient liquid crystal technique. The model wall inner surfaces were sprayed with thermochromic liquid crystals and a transient test was used to obtain the local heat transfer coefficients from the measured color change. An analysis of the results shows that the choice of designs is limited by the available pressure drop, even if the design provides significantly higher heat transfer coefficients. Dimpled surfaces provide appreciably high heat transfer coefficients and a reasonable pressure drop, whereas ribbed ducts provide significantly higher heat transfer coefficients and a higher overall pressure drop.
Optimization of a U-Bend for Minimal Pressure Loss in Internal Cooling Channels—Part II: Experimental Validation
Authors: Coletti Filippo , Verstraete Tom , Bulle Jérémy , Van der Wielen Timothée , Van den Berge Nicolas , Arts Tony
Published: July 2013

This two-part paper addresses the design of a U-bend for serpentine internal cooling channels optimized for minimal pressure loss. The total pressure loss for the flow in a U-bend is a critical design parameter, as it augments the pressure required at the inlet of the cooling system, resulting in a lower global efficiency. In the first part of the paper, the design methodology of the cooling channel was presented. In this second part, the optimized design is validated. The results obtained with the numerical methodology described in Part I are checked against pressure measurements and particle image velocimetry (PIV) measurements. The experimental campaign is carried out on a magnified model of a two-legged cooling channel that reproduces the geometrical and aerodynamical features of its numerical counterpart. Both the original profile and the optimized profile are tested. The latter proves to outperform the original geometry by about 36%, in good agreement with the numerical predictions. Two-dimensional PIV measurements performed in planes parallel to the plane of the bend highlight merits and limits of the computational model. Despite the well-known limits of the employed eddy viscosity model, the overall trends are captured. To assess the impact of the aerodynamic optimization on the heat transfer performance, detailed heat transfer measurements are carried out by means of liquid crystals thermography. The optimized geometry presents overall Nusselt number levels only 6% lower with respect to the standard U-bend. The study demonstrates that the proposed optimization method based on an evolutionary algorithm, a Navier–Stokes solver, and a metamodel of it is a valid design tool to minimize the pressure loss across a U-bend in internal cooling channels without leading to a substantial loss in heat transfer performance.
Nanomanufacturing Methods for the Reduction of Noise in Carbon Nanotube-Based Piezoresistive Sensor Systems
Authors: Cullinan Michael A. , Culpepper Martin L.
Published: July 2013

Carbon nanotube (CNT)-based piezoresistive strain sensors have the potential to outperform traditional silicon-based piezoresistors in MEMS devices due to their high strain sensitivity. However, the resolution of CNT-based piezoresistive sensors is currently limited by excessive 1/f or flicker noise. In this paper, we will demonstrate several nanomanufacturing methods that can be used to decrease noise in the CNT-based sensor system without reducing the sensor's strain sensitivity. First, the CNTs were placed in a parallel resistor network to increase the total number of charge carriers in the sensor system. By carefully selecting the types of CNTs used in the sensor system and by correctly designing the system, it is possible to reduce the noise in the sensor system without reducing sensitivity. The CNTs were also coated with aluminum oxide to help protect the CNTs from environmental effects. Finally, the CNTs were annealed to improve contact resistance and to remove adsorbates from the CNT sidewall. The optimal annealing conditions were determined using a design-of-experiments (DOE). Overall, using these noise mitigation techniques it is possible to reduce the total noise in the sensor system by almost 3 orders of magnitude and increase the dynamic range of the sensors by 48 dB.
Development and Implementation of the Advanced Environmental Burner for the Alstom GT13E2
Authors: Zajadatz Martin , Pennell Douglas , Bernero Stefano , Paikert Bettina , Zoli Raffaele , Döbbeling Klaus
Published: July 2013

Increasing public awareness and more stringent legislation on pollutants drive gas turbine manufacturers to develop combustion systems with low NOx emissions. In combination with this demand, the gas turbines have to provide a broad range of operational flexibility to cover variations in gas composition and ambient conditions along with varying daily and seasonal energy demands and load profiles. This paper describes the development and implementation of the Alstom AEV (advanced environmental) burner, an evolution of the envorinmental (EV) burner. A continuous fuel supply to two fuel stages at any engine load simplifies the operation and provides a fast and reliable response of the combustion system during transient operation of the gas turbine. Increased turndown with low emissions is an additional advantage of the combustion system upgrade.
Computational Fluid Dynamics Modeling Flow Field and Side-Wall Heat Transfer in Rectangular Rib-Roughened Passages
Authors: Xie Gongnan , Li Shian , Zhang Weihong , Sunden Bengt
Published: July 2013

In order to achieve higher thermal efficiency and power output, the gas turbine inlet temperature of gas turbine engine is continuously increased. However, the increasing temperature may exceed the melting point of the blade material. Rib turbulators are often used in the midsection of internal cooling ducts to augment the heat transfer from blade wall to the coolant. This study uses computational fluid dynamics (CFD) to investigate side-wall heat transfer of a rectangular passage with the leading/trailing walls being roughened by continuous or truncated ribs. The inlet Reynolds number is ranging from 12,000 to 60,000. The detailed three dimensional (3D) fluid flow and heat transfer over the side-wall are presented. The overall performances of ribbed passages are compared. It is suggested that the usage of truncated ribs is a suitable way to augment the side-wall heat transfer and improve the flow structure near the leading edge especially under the critical limitation of pressure drop.
Time Domain Simulation of the Vibration of a Steam Generator Tube Subjected to Fluidelastic Forces Induced by Two-Phase Cross-Flow
Authors: Sawadogo Téguewindé , Mureithi Njuki
Published: July 2013

Having previously verified the quasi-steady model under two-phase flow laboratory conditions, the present work investigates the feasibility of practical application of the model to a prototypical steam generator (SG) tube subjected to a nonuniform two-phase flow. The SG tube vibration response and normal work-rate induced by tube-support interaction are computed for a range of flow conditions. Similar computations are performed using the Connors model as a reference case. In the quasi-steady model, the fluid forces are expressed in terms of the quasi-static drag and lift force coefficients and their derivatives. These forces have been measured in two-phase flow over a wide range of void fractions making it possible to model the effect of void fraction variation along the tube span. A full steam generator tube subjected to a nonuniform two-phase flow was considered in the simulations. The nonuniform flow distribution corresponds to that along a prototypical steam-generator tube based on thermal-hydraulic computations. Computation results show significant and important differences between the Connors model and the two-phase flow based quasi-steady model. While both models predict the occurrence of fluidelastic instability, the predicted pre-instability and post instability behavior is very different in the two models. The Connors model underestimates the flow-induced negative damping in the pre-instability regime and vastly overestimates it in the post instability velocity range. As a result the Connors model is found to underestimate the work-rate used in the fretting wear assessment at normal operating velocities, rendering the model potentially nonconservative under these practically important conditions. Above the critical velocity, this model largely overestimates the work-rate. The quasi-steady model on the other hand predicts a more moderately increasing work-rate with the flow velocity. The work-rates predicted by the model are found to be within the range of experimental results, giving further confidence to the predictive ability of the model. Finally, the two-phase flow based quasi-steady model shows that fluidelastic forces may reduce the effective tube damping in the pre-instability regime, leading to higher than expected work-rates at prototypical operating velocities.
Rotordynamics of a Two-Phase Flow Twin Screw Pump
Authors: Muhammed Ameen R. A. , Childs Dara W.
Published: July 2013

Twin screw pumps are positive displacement machines. Two meshing screws connected by timing gears push the fluid trapped in the screw cavities axially from suction to discharge. Available steady state hydraulic models predict pump performance and axial pressure distribution in the chambers in single- and two-phase flow conditions. However, no model is available for their rotordynamics behavior. Due to the helix angle of the screw, the pressure distribution around the rotor is not balanced, giving rise to both static and dynamic lateral forces. The work presented here introduces a starting point for rotordynamic analysis of twin screw pumps. First, we show that the screw rotor's geometry can be represented by axisymmetric beam elements. Second, we extend the steady state hydraulic model to predict both the static and dynamic lateral forces resulting from the unbalanced pressure field. Finally, hydraulic forces are applied to the rotor to predict static, synchronous, and nonsynchronous responses. Predictions of the dynamic pressure were compared to measurements from the literature and were found to be in good agreement.
The Application of Rotary Vane Expanders in Organic Rankine Cycle Systems—Thermodynamic Description and Experimental Results
Authors: Gnutek Zbigniew , Kolasiński Piotr
Published: July 2013

Small (10–100 kW) and micro (0.5–10 kW) Organic Rankine Cycle (ORC) power systems are nowadays considered for local and domestic power generation. Especially interesting are micropower applications for heat recovery from dispersed low potential (85–150 °C) waste and renewable heat sources. Designing and implementing an ORC system dedicated to energy recovery from such a source is difficult. A proper working fluid must be selected together with a suitable expander. Volumetric machines can be adopted as a turbine alternative in small-capacity applications under development, like, e.g., domestic cogeneration. Scroll and screw expanders are a common choice. However, scroll and screw expanders are complicated and expensive. Vane expanders are mechanically simple, commercially available and cheap. This paper documents a study providing the preliminary analysis of the possibility of employing vane-expanders in mini-ORC systems. The main objective of this research was therefore a comprehensive analysis of the use of a vane expander for continuous operation with a low-boiling working fluid. A test-stand was designed and set up starting from system models based on thermodynamic analysis. Then, a series of experiments was performed using the test-stand. Results of these experiments are presented here, together with a model of multivane expanders and a thermodynamic-based method to select the working fluid. The analysis presented in this paper indicates that multivane expanders are a cheap and mechanically simple alternative to other expansion devices proposed for small-capacity ORC systems.
Aircraft Propulsion System Flight Test—Analysis and Evaluation Challenges and Integrated Solutions
Authors: Binkley Brian A. , Malloy Donald J. , Patterson Grant T. , Hansen Eric R. , Kidman David S.
Published: July 2013

The paper describes the challenges and solution methodologies associated with the flight test and evaluation of the propulsion system for a twin-engine military legacy aircraft. Recent flight-test programs evaluated the effects of temperature distortion and biased engine inlet total temperature measurement (TT2) on engine scheduling and compressor stability margin. The challenges are associated with the limited instrumentation and the repeatability of the flight-test points. During the test program it was necessary to employ techniques to extend the usefulness of the data beyond that provided by the acquired and reduced data sets to address the challenges associated with flight-test analysis. The challenges were addressed using mathematical models, engine cycle decks, uninstalled ground-test data, computational fluid dynamics, or some combination of these. Several specific challenges and solutions are described in detail in the paper.
A Literature Review of Low Pressure Steam Turbine Exhaust Hood and Diffuser Studies
Authors: Burton Zoe , Ingram Grant L. , Hogg Simon
Published: July 2013

This paper summarizes the findings from research studies carried out over the last 30 years, to better understand the flows in steam turbine low pressure exhaust hoods and diffusers. The work aims to highlight the areas where further study is still required. A detailed description of the flow structure is outlined and the influence of the last turbine stage and the hood geometry on loss coefficient is explored. At present, the key challenge faced is numerically modeling the three-dimensional, unsteady, transonic, wet steam exhaust hood flow given the impractically high computational power requirement. Multiple calculation simplifications to reduce the computational demand have been successfully verified with experimental data, but at present there is no ‘best-practice’ approach to reduce the computational time for routine design exercises. This paper highlights the importance of coupling the exhaust hood to the last stage steam turbine blades to capture the interaction; ensuring the total pressure and swirl angle profiles, along with the tip leakage jet are accurately applied to the diffuser inlet. The nonaxial symmetry of the exhaust hood means it is also important to model the full blade annulus. More studies have emerged modeling the wet steam and unsteady flow effects, but more work is required in this area to fully understand the impact on the flow structure.
A Model-Based Computationally Efficient Method for On-Line Detection of Chatter in Milling
Authors: Ma Lei , Melkote Shreyes N. , Castle James B.
Published: July 2013

This paper presents a model-based computationally efficient method for detecting milling chatter in its incipient stages and for chatter frequency estimation by monitoring the cutting force signals. Based on a complex exponentials model for the dynamic chip thickness, the chip regeneration effect is amplified and isolated from the cutting force signal for early chatter detection. The proposed method is independent of the cutting conditions. With the aid of a one tap adaptive filter, the method is shown to be capable of distinguishing between chatter and the dynamic transients in the cutting forces arising from sudden changes in workpiece geometry and tool entry/exit. To facilitate chatter suppression once the onset of chatter is detected, a time domain algorithm is proposed so that the dominant chatter frequency can be accurately determined without using computationally expensive frequency domain transforms such as the Fourier transform. The proposed method is experimentally validated.
A New Joining Process for Magnesium Alloys: Rotation Friction Drilling Riveting
Authors: Han Gaokun , Wang Mingxing , Liu Zhongxia , Wang Pei-Chung
Published: July 2013

A new joining process for magnesium alloys, rotation friction drilling riveting (RFDR), is proposed in this paper. In RFDR operation, a semitubular rivet with a grip rod and a rivet cap rotating at high speed is brought to contact with the riveted sheets, generating frictional heat between the rivet and riveted sheets, which softens the sheet materials and enables the rivet to be drilled into the sheets under reduced force. While being inserted, the rivet pierces through the top sheet and flares into the bottom sheets due to the action of the cavity die, thereby forming a mechanical interlock between the rivet and riveted sheets. Our studies showed that RFDR of the magnesium alloy sheets could be carried out at room temperature and provided the joints with superior shear strength and fatigue property when compared with self-piercing riveting (SPR). The effects of the operating parameters of the RFDR process on the quality of the joints were also investigated in the study. The results showed that while the rivet rotating speed little affected the shear strength of RFDR joints, the rivet shank length and the downward pressure had a significant influence on the mechanical properties of the RFDR joints. Therefore, it is very important to choose the right rivet shank length and downward pressure for producing RFDR joints with high quality.
Effects of Pulse Duration on Laser Micro Polishing
Authors: Vadali Madhu , Ma Chao , Duffie Neil A. , Li Xiaochun , Pfefferkorn Frank E.
Published: July 2013

Pulsed laser micro polishing (PLμP) has been shown to be an effective method of polishing micro metallic parts whose surface roughness can approach the feature size. Laser pulse duration in the PLμP process is an important parameter that significantly affects the achievable surface finish. This paper describes the influence of laser pulse duration on surface roughness reduction during PLμP. For this purpose, near-infrared laser pulses have been used to polish Ti6Al4V at three different pulse durations: 0.65 μs, 1.91 μs, and 3.60 μs. PLμP at longer pulse durations resulted in dominating Marangoni convective flows, yet significantly higher reductions in the average surface roughness were observed compared to the short pulse duration regime without convection.
Efficient Machining of Microdimples for Friction Reduction
Authors: Denkena B. , Köhler J. , Kästner J. , Göttsching T. , Dinkelacker F. , Ulmer H.
Published: July 2013

In order to improve the tribological properties of thermomechanically highly stressed surfaces such as cylinder liners, microdimples are produced by fly-cutting kinematics along the functional surface. The structures are used to hold back lubricant but also to increase the hydrodynamic pressure, which is built up between the sliding friction partners. For that, machining strategies for the pattern generation in cylindrical components are developed as well as a mathematical model of the microdimple arrangement and distribution. The tribological performance of the machined microdimples is analyzed by means of ring-on-disk experiments. At low sliding speeds the friction coefficient can be decreased clearly by microdimples. This indicates the potential for low-speed or reciprocating tribosystems like cylinder liners. This potential is quantified by motor driven experiments and the comparison between structured and nonstructured cylinder liners. A honed (fine) liner with additional microdimples along the interstice area shows friction losses up to 19% compared to standard honed nonstructured cylinder liner.
A Novel Method for Generating Continuously Surfable Waves—Comparison of Predictions With Experimental Results
Authors: Schmied Steven A. , Binns Jonathan R. , Renilson Martin R. , Thomas Giles A. , Macfarlane Gregor J. , Huijsmans Rene
Published: July 2013

In this paper, a novel idea to produce continuous breaking waves is discussed, whereby a pressure source is rotated within an annular wave pool, with the inner ring of the annulus having a sloping bathymetry to induce wave breaking. In order to refine the technique, work is being conducted to better understand the mechanics of surfable waves generated by moving pressure sources in restricted water. The pool aims to be capable of creating waves suitable for surfers from beginner to expert level, with an added benefit being by providing a safe learning environment, the overall surfing ability of the participants should be improved. The method of approach reported in this paper is the first stage of an experimental investigation of a novel method for generating continuously surfable waves utilizing a moving pressure source. The aim was to measure and assess the waves generated by two parabolic pressure sources and a wedge-shaped wavedozer (Driscoll, A., and Renilson, M. R., 1980, The Wavedozer. A System of Generating Stationary Waves in a Circulating Water Channel, University of Glasgow, Naval Architecture and Ocean Engineering, Glasgow, UK) for their suitability for future development of continuous breaking surfable waves. The tests were conducted at the University of Tasmania (UTas) Australian Maritime College (AMC) 100 m long towing tank. The predictions and experimental results for the wave height (H) at different values of depth Froude number (Frh) are presented in this paper. Finally, the preferred pressure source is determined based on the wave making energy efficiency and the quality of the waves for surfing.
Study of the Enhancement of Cell Performance of Dye Sensitized Solar Cells Sensitized With Nephelium lappaceum (F: Sapindaceae)
Authors: Kumara N. T. R. N. , Ekanayake Piyasiri , Lim Andery , Iskandar Mohammad , Ming Lim Chee
Published: July 2013

We have studied the performance of dye sensitized solar cells sensitized with pigments extracted from the fruit sheath of Nephelium lappaceum (F: Sapindaceae). The pH of the pigment solution used for impregnation was controlled by adding concentrated HCl (50:0.2 v/v). The UV-Vis spectroscopic results revealed that the extract consists of the pigment of Anthocyanin, with an additional absorption peak appearing around 540 nm at a lower pH of the pigment solution. Also the band gap of the pigment was reduced by 1 eV at low pH conditions. The solar cells fabricated with pigment extracted from the fruit sheath of Nephelium lappaceum showed photo-response with the conversion efficiency of 0.26%, with an open-circuit voltage (VOC) of 453 mV, short-circuit current density (ISC) of 1.17 mA cm−2, and fill factor (ff) of 0.48. The conversion efficiency was significantly enhanced when pH of the pigment solution was lowered by adding concentrated HCl. The conversion efficiency of the dye sensitized solar cells (DSSCs) sensitized after HCl treatment of the pigment was increased to 0.56%, with an open-circuit voltage (VOC) of 404 mV, short-circuit current density (ISC) of 2.71 mA cm−2, and fill factor (ff) of 0.35. The HOMO level of the pigment at low pH was shown to be shifted towards more positive values with respect to vacuum level, giving rise to an enhanced DSSC efficiency. The overall efficiency enhancement of the low pH pigment was due to the combined effect of increased UV-Vis absorption and efficient adsorption of dye molecules onto the TiO2 semiconductor surface.
Research on Constant Velocity Extruding Process Control for 36,000-Ton Vertical Extrusion Press
Authors: Li Wanzhou , Sun Tao , Hu Yuechen , Li Wei
Published: July 2013

Metal extrusion is one of the most significant methods in the field of plastic deformation. The 36,000-ton vertical extrusion press uses one-piece hot extrusion molding method to produce high-pressure, large-diameter, thick-walled, seamless, alloy-steel pipe, which is required by ultrasupercritical power generator units and the third generation of nuclear power plants. The main table (extruding platform) is driven by 36,000-ton thrust. The extrusion process is a typical nonlinear multivariable strong-coupling finite-time system. In this paper, we analyze and solve the large-scaled engineering control problems, including (1) discussion of the mechanical structure of the controlled object and the feature of multivariable strongly coupling for large-scaled parallel-driving hydraulic system, (2) research on the engineering practical simplified control algorithm for multivariable system and propose a way to solve the coupling problem of the hydraulic system, and (3) design of double closed-loop control of velocity and pressure for the new technology of constant velocity extrusion. In our paper, we have proven through practice that the traditional proportional intergral (PI) controlling method, with proper controlling strategy, is still the most efficient and practicable way for a large-dimension complex object in industry.
Trends and Opportunities in Direct-Absorption Solar Thermal Collectors
Authors: Phelan Patrick , Otanicar Todd , Taylor Robert , Tyagi Himanshu
Published: July 2013

Efficient conversion of sunlight into useful heat or work is of increasing global interest. Solar-to-thermal energy conversion, as opposed to solar-to-electricity, is enabled by solar thermal collectors that convert sunlight into heat at some useful temperature. We review here recent developments in solar thermal energy conversion. Our emphasis is on “direct-absorption” solar thermal collectors, in which incident sunlight is absorbed directly by a working fluid. This contrasts with conventional solar thermal collectors where the sunlight strikes and is absorbed by a solid receiver, which then transfers heat to the working fluid. Both liquid-based and gas-based direct-absorption collectors are described, although liquid-based systems are emphasized. We propose that if “direct-absorption” technologies could be developed further, it would open up a number of emerging opportunities, including applications exploiting thermochemical and photocatalytic reactions and direct absorption of a binary fluid for absorption refrigeration.
Finite-Time Input-to-State Stability and Optimization of Switched Nonlinear Systems
Authors: Wang Xiaoli , Shao Chuntao
Published: July 2013

In this paper, we address the (uniform) finite-time input-to-state stability problem for switched nonlinear systems. We prove that a switched nonlinear system has a useful finite-time input-to-state stability property under average dwell-time switching signals if each constituent subsystem has finite-time input-to-state stability. Moreover, we prove the equivalence between the optimal costs for the switched nonlinear systems and for the relaxed differential inclusion.
A Novel in Field Method for Determining the Flow Rate Characteristics of Pneumatic Servo Axes
Authors: Righettini Paolo , Giberti Hermes , Strada Roberto
Published: July 2013

Several strategies, in order to improve an actuator's control and to increase the bandwidth, consider the relationship between the valve's driving signal and the air flow rate. Such an approach to the control strategy takes advantage of the evaluation of the valve's characteristic parameter, known as sonic conductance. The sonic conductance can be measured following the procedure stated by the standard ISO 6358. Nevertheless, the measurement carried out according to this standard is very expensive in terms of time and air consumption. In this paper, an alternative method to evaluate the sonic conductance is presented. The method is based on a new practical approach: the sonic conductance is evaluated leaving the valve mounted on the actuator and using only the piston's position transducer. The steady state piston's motion allows us to determine the sonic conductance. The new approach allows us to get the conductance in a very short time, without the need to use a proper test bench and pressure transducers. Moreover, performing the measurements directly on the pneumatic axis allows us to characterize not only the valve but the duct connecting the valve to the actuator's chamber too.
On the Coincidence of the Acoustical and Mechanical Natural Frequencies of a Pressure Vessel
Authors: Moussou Pierre
Published: July 2013

A widespread conception among field engineers is that the coincidence of the structure and of the acoustic frequencies of a pressure vessel triggers a dramatic increase in the vibration level, leading to fatigue failure. The physics of fluid-structure interaction are revisited in order to clarify this effect, and a simple model of inertial coupling is proposed on the basis of one structure mode and one acoustic mode. It is shown that even if the uncoupled natural frequencies coincide, the coupled frequencies are split apart by an amount depending on the ratio of the fluid density and of the structure density, and on the spatial correlation of the fluid field. As a consequence, a large increase of the vibration level is more likely to occur in a gas system than in a liquid system. Illustrations based on dispersion equations are provided for cylindrical structures filled with vapor and water.
Analytical Model to Estimate the Drag Forces for Microhole Coiled Tubing Drilling
Authors: Zhang Yuan , Hao Ye , Samuel Robello
Published: July 2013

Microhole coiled tubing drilling is a new technology that provides many added advantages but at the same time poses numerous operational challenges. This manifests itself in a number of ways, all of which adversely affect the efficiency of the drilling process. These problems include increased wellbore friction, poor hole-cleaning, tubular failures, and associated problems during tripping operations. Presently conventional torque and drag models are used to calculate drag forces and surface loads during microhole coiled tubing drilling. However, these estimates might be under conservative. Therefore, an improved model and more comprehensive analysis are required. Conditions expected during microhole coiled tubing drilling are completely different from those encountered during conventional drilling. Further complexity is added when the wellbore is undulated. This paper describes a new analytical model for estimating drag forces by assuming that pipe in the horizontal portion follows a sine function wave due to residual bends and snubbing force. In addition, the model takes into account when the wellbore is also tortuous. Fluid viscosity (an important force in the microhole) is also included so we can calculate appropriate surface loads in addition to drag. This study concludes that besides wellbore inclination, curvature, and wellbore torsion, parameters such as wavelength and contact area also influence the results. This paper documents the comparison between the predicted mathematical simulation results with actual data from wells describing the accuracy and applicability of the model. The analysis results and comparison are presented along with three examples (Zhang et al., 2013, “Analytical Model to Estimate the Drag Forces for Microhole Coiled Tubing Drilling,” Society of Petroleum Engineers, Paper No. SPE 163480.).
Simulation and Experimental Study of the Effects of Process Factors on the Uniformity of the Residual Layer Thickness in Hot Embossing
Authors: Omar F. , Kolew A. , Brousseau E. B. , Hirshy H.
Published: July 2013

Hot embossing replica are characterized by the quality of the molded structures and the uniformity of the residual layer. In particular, the even distribution of the residual layer thickness (RLT) is an important issue in hot embossing and the related process of thermal nanoimprint lithography, as variations in the RLT may affect the functionality or further processing of replicated parts. In this context, the paper presents an experimental and simulation study on the influence of three process factors, namely the molding temperature, the embossing force, and the holding time, on the residual layer homogeneity achieved when processing 2 mm thick PMMA sheets with hot embossing. The uniformity of the RLT was assessed for different experimental conditions by calculating the standard deviation of thickness measurements at different set locations over the surface of each embossed sample. It was observed that the selected values of the studied parameters have an effect on the resulting RLT of the PMMA replica. In particular, the difference between the largest and lowest RLT standard deviation between samples was 18 μm, which was higher than the accuracy of the instrument used to carry out the thickness measurements. In addition, the comparison between the obtained experimental and simulation results suggests that approximately 12% of the RLT uniformity was affected by the local deflections of the mold. Besides, polymer expansion after release of the embossing load was estimated to contribute to 8% of the RLT nonuniformity. It is essential to understand the effects of the process parameters on the resulting homogeneity of the residual layer in hot embossing. In this research, the best RLT uniformity could be reached by using the highest considered settings for the temperature and holding time and the lowest studied value of embossing force. Finally, the analysis of the obtained results also shows that, across the range of processing values studied, the considered three parameters have a relatively equal influence on the RLT distribution. However, when examining narrower ranges of processing values, it is apparent that the most influential process parameter depends on the levels considered. In particular, the holding time had the most effect on the RLT uniformity when embossing with the lower values of process parameters while, with higher processing settings, the molding temperature became the most influential factor.
Geometric Optimization of C-Shaped Cavities According to Bejan's Theory: General Review and Comparative Study
Authors: Lorenzini G. , Biserni C. , Rocha L. A. O.
Published: July 2013

The aim of this paper is to consider, by means of the numerical investigation, the geometric optimization of a cavity that intrudes into a solid with internal heat generation. The objective is to minimize the maximal dimensionless excess of temperature between the solid and the cavity. The cavity is rectangular, with fixed volume and variable aspect ratio. The cavity shape is optimized for two sets of boundary conditions: isothermal cavity and cavity cooled by convection heat transfer. The optimal cavity is the one that penetrates almost completely the conducting wall and proved to be practically independent of the boundary thermal conditions, for the external ratio of the solid wall smaller than 2. As for the convective cavity, it is worthy to know that for values of H/L greater than 2, the best shape is no longer the one that penetrates completely into the solid wall, but the one that presents the largest cavity aspect ratio H0/L0. Finally, when compared with the optimal cavity ratio calculated for the isothermal C-shaped square cavity, the cavities cooled by convection highlight almost the same optimal shape for values of the dimensionless group λ ≤ 0.01. Both cavities, isothermal and cooled by convection, also present similar optimal shapes for ϕ0 < 0.3 and ϕ0 > 0.7. However, in the range 0.3 ≤ ϕ0 ≤ 0.7, the ratio (H0/L0)opt calculated for the cavities cooled by convection is greater than the one presented by isothermal cavities. This difference is approximately 17% when λ = 0.1 and ϕ0 = 0.7, and 20% for λ = 1 and ϕ0 = 0.5.