2,816 research outputs found
Shear transfer mechanism in reinforced engineered cementitious composite (ECC) beams: Quantification of Vs and Vc
No full textTo enhance the structural and seismic resistance, as well as durability of concrete structures, an ultra ductile fiber reinforced cementitious composites called Engineered Cementitious Composite (ECC), also known as Strain Hardening Cementitious Composite (SHCC), was developed. ECC has a similar compressive and tensile strength to conventional concrete, but it exhibits a pseudo-strain-hardening behaviour under uniaxial tension with excellent crack control ability. The ultimate tensile strain of ECC can reach 3–12%, which is 300–1200 times higher than that of concrete. It is reported that ECC can also exhibit at least twice as high shear carrying capacity compared to traditional concrete, signifying a potential to use ECC material in shear-resistance elements. However, the shear resisting mechanism of reinforced ECC (R/ECC) members is still not clear. In most existing codes and models, the shear strength of reinforced structural members (Vu) is divided into two parts, i.e., shear resistance coming from the matrix (Vc) and from the transverse reinforcement (Vs). To quantify accurately Vc and Vs and also their development throughout the loading, a well-designed testing method consisting of continuous strain quantification along the stirrups, was used in this research. Six steel reinforced beams incorporating different matrix (ECC, concrete and mortar) were tested under four-point bending. The test results indicated that Vc changed continuously with the propagation of shear crack, whereas the stirrups that crossed the critical shear crack, did not always yield at the ultimate shear resistance.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Concrete Structure
Monte Carlo simulation on ferroelectric response to magnetic field in an elastic lsing spin chain
No full textAuthor name used in this publication: 姚晓燕Author name used in this publication: Veng Cheong Lo, 羅永祥Author name used in this publication: 刘俊明2009-2010 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishedVoR allowe
Market Potential and Operational Scenarios for Virtual Coupling
No full textThis document evaluates the attractiveness of Virtual Coupling (VC) for different market segments (high-speed, main line, regional, urban/suburban, freight) and defines operational scenarios for each of them. A SWOT analysis identifies main strengths and weaknesses of the Virtual Coupling concept and corresponding opportunities and threats to each specific railway market segment. The research relies on a Delphi method with an extensive survey of expert opinions and stated travel preferences assuming VC has been implemented. The survey involved subject matter experts of the wide European railway industry including infrastructure managers, railway undertakings, system suppliers, transport authorities, railway institutions, private consultants and academics. In addition, travel preferences have been collected by interviewing European representatives belonging to other socio professional categories. Results show that the implementation of Virtual Coupling can be attractive to customers of high-speed, main line, regional and especially freight segments. Virtual Coupling has the potential of completely changing the way in which such segments operate and attract a modal shift from other transport modes to railways. Customers are even willing to pay higher fares for more frequent and flexible train services, especially on the regional and freight segments which are currently perceived as not satisfactory. Several operational scenarios have been defined based on the outcomes of the survey, setting market-attractive VC service headways for each market segment as well as specifying characteristics of rolling stock, power supply, traffic, and platform crowd management. Principles to couple/decouple convoys of virtually coupled trains are also provided based on the specific network characteristics of the different market segments.A SWOT analysis is presented which builds on the outcomes of the survey, the operational scenarios and brainstorming sessions with experts of the European railway industry. The main strengths identified for VC are a substantial increase in capacity and reduced operational costs with respect to Moving Block while mitigating delay propagation and improving reliability of ground/train communication. On the other hand, weaknesses of this concept refer to the fact that capacity gains at diverging junctions equipped with current switch technologies might be marginal, since here trains still need to be separated by a full braking distance. Also, the implementation of VC operations would require an investment to upgrade the overhead line system, platform lengths (to allow platoons of trains to stop) and possibly the switch technology. An upgrade of the switch technology towards faster and more reliable ones (e.g. Railtaxi and REPOINT) will unleash the full potential of VC operations. Significant opportunities will be brought about Virtual Coupling such as potential increase in the profit of infrastructure managers and operators as well as a deregulation of the current railway market which could be opened also to smaller transport operators due to the increase of available train paths and the decrease of operational costs by full train automation. In addition, the train-to-train communication could lead to the institution of cooperative consortia of railway operators which can be more economically beneficial than the current competitive market model. This would also provide the chance to migrate obsolescent command and control systems towards future-proof digital railway architectures. Possible threats to the introduction of this concept mainly relate to potential increase of train control complexity increasing risks of approval from the railway industry. The need for an initial investment might be not well received by infrastructure managers and local governments. As well as the necessity of partially changing policies, operational procedures and engineering rules currently in place. When overcoming such challenges, Virtual Coupling has potentials to fully revolutionise and improve current train operations so to induce a sustainable shift to railways.Transport and Plannin
INVESTIGATION OF NEGATIVE TRANSIENT CURRENT OF ARGON-IMPLANTED GAAS USING PHOTOINDUCED TRANSIENT-CURRENT SPECTROSCOPY
No full textThe investigation of deep levels of argon-implanted LEC-grown semi-insulating GaAs with implantation dosages ranging from 1 x 10(11) to 1 x 10(15) cm-2 has been performed. Using a photoinduced transient-current spectroscopy (PITCS) it was demonstrated that, for implantation dosages below 1 X 10(13) cm-2, a negative peak or negative transient current (NTC) was observed in the temperature range from 330 to 350 K. The magnitude of this negative peak increased with dosage up to a level of 1 X 10(12) cm-2, beyond which it decreased with dosage. The dosage dependence of the EL3 peak height and the resistance of the specimen have also been investigated. It was observed that the variation of the EL3 peak height with dosage was similar to the variation of the magnitude of the negative peak, that is the EL3 peak height likewise increased with dosage up to 1 X 10(12) cm-2, and then decreased. The resistance of the original high-resistivity specimen dropped abruptly when the dosage reached 1 X 10(12) cm-2. This critical dosage (1 X 10(12) cm-2) was found to be a threshold for the generation of a highly disordered state
Variegated VC Rime Restrictions in Sinitic Languages
No full textIn this study, we consider a non-Markedness-based account for VC rime phonotactics in Sinitic languages, with special reference to Taiwanese Southern Min and Hakka. Rime gaps in Chinese languages have been customarily analyzed as co-occurrence markedness constraints. But analyses along this line not only overgenerate by predicting unattested gaps, but also fail to motivate those phonotactic constraints in a principled fashion. By adopting Hsieh\u27s (2010) duration-based account, we present further phonetic evidence to show that phonotactics of Chinese VC combinations may be attributed to: (i) low perceptibility of coda consonants due to absence of release, and (ii) decreased vowel distinctiveness as a result of vowel reduction. One of the new findings in this study is that the perceptual difficulties are further exacerbated by the relatively shorter duration of Taiwanese checked syllables, if compared with those of Hakka and Cantonese. Also, salient F2 transitions (vowel gliding) may occur to enhance the place of articulation of a stop coda in Taiwanese. Therefore, rime gaps are normally found in contexts whereby (i) VC coarticulation is weak and (ii) vowel distinctiveness cannot be maintained. In sum, the results of our acoustic studies suggest that the duration-based approach offers a more straightforward account for why Taiwanese has more rime gaps than Hakka and Cantonese do
Impact orientation and venture capital financing: The interplay of governmental, social impact and traditional venture capital
No full textIn addition to traditional venture capital (VC), governmental VC and social impact VC investors have emerged as alternatives to fund entrepreneurial ventures, especially start-ups that incor- porate social and/or environmental objectives into commercial operations. Using a sample of 15,510 VC-backed start-ups, we show that impact-oriented ventures are more likely to receive funding from alternative VCs. Both social and environmental orientations increase the chances that a start-up secures funding from impact VCs while social orientation drives results for gov- ernment VCs. Importantly, we also show that impact-oriented ventures are more likely to secure investment from traditional VCs when impact and governmental VCs co-invest
Monte Carlo simulation of ferroelectricity induced by collinear magnetic order in Ising spin chain
No full textAuthor name used in this publication: Veng Cheong Lo2008-2009 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishedVoR allowe
Combination of bone graft and resorbable membrane for alveolar ridge preservation: A systematic review, meta-analysis, and trial sequential analysis
No full textIntroduction: Alveolar ridge preservation (ARP) techniques aim to reduce resorption after tooth extraction. The combination of a graft material covered with a resorbable membrane represents one of the most common strategies performed in the clinical practice. The aim of this systematic review is to analyze evidence regarding potential benefits of ARP procedures performed with allogenic/xenogenic grafts in combination with a resorbable membrane coverage in comparison with spontaneous healing. Methods: Electronic databases were screened independently to select studies suitable for inclusion in this review. Horizontal ridge width reduction (HRWR) and vertical ridge height reduction (VRHR) were investigated as primary outcomes and volume changes (VC) as a secondary outcome. Meta-analysis was performed using the inverse of variance test with a random effect model. Adjustment for Type I and II errors and analysis of the power of evidence was performed with trial sequential analysis (TSA). Results: Seven studies met the inclusion criteria and were included in the quantitative synthesis. Meta-analysis revealed that the combination therapy resulted in a lower rate of resorption for both HRWR (−2.19 mm, 95% confidence interval [CI]: −2.67 to −1.71 mm) and VRHR (−1.72 mm, 95% CI: −2.14 to −1.30 mm). For VC no meta-analysis was performed due to insufficient data. Analysis of the power of the evidence performed with TSA showed that the number of both studies and sockets analyzed is sufficient to validate such findings, despite the high rate of heterogeneity. Conclusions: Use of bone graft covered by a resorbable membrane can decrease the rate of alveolar ridge horizontal and vertical resorption after tooth extraction. The power and reliability of the evidence is strong enough to confirm the above-mentioned findings, despite the high rate of heterogeneity of included studies.Introduction: Alveolar ridge preservation (ARP) techniques aim to reduce resorption after tooth extraction. The combination of a graft material covered with a resorbable membrane represents one of the most common strategies performed in the clinical practice. The aim of this systematic review is to analyze evidence regarding potential benefits of ARP procedures performed with allogenic/xenogenic grafts in combination with a resorbable membrane coverage in comparison with spontaneous healing.Methods: Electronic databases were screened independently to select studies suitable for inclusion in this review. Horizontal ridge width reduction (HRWR) and vertical ridge height reduction (VRHR) were investigated as primary outcomes and volume changes (VC) as a secondary outcome. Meta-analysis was performed using the inverse of variance test with a random effect model. Adjustment for Type I and II errors and analysis of the power of evidence was performed with trial sequential analysis (TSA).Results: Seven studies met the inclusion criteria and were included in the quantitative synthesis. Meta-analysis revealed that the combination therapy resulted in a lower rate of resorption for both HRWR (-2.19 mm, 95% confidence interval [CI]: -2.67 to -1.71 mm) and VRHR (-1.72 mm, 95% CI: -2.14 to -1.30 mm). For VC no meta-analysis was performed due to insufficient data. Analysis of the power of the evidence performed with TSA showed that the number of both studies and sockets analyzed is sufficient to validate such findings, despite the high rate of heterogeneity.Conclusions: Use of bone graft covered by a resorbable membrane can decrease the rate of alveolar ridge horizontal and vertical resorption after tooth extraction. The power and reliability of the evidence is strong enough to confirmthe above-mentioned findings, despite the high rate of heterogeneity of included studies
Simulation of electromechanical responses of ferroelectric ceramics driven by alternating compressive stress and static electric field
No full textAuthor name used in this publication: Simon Ching-kin Chow2008-2009 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishedVoR allowe
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