720 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
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
"I don’t know": a usage-based approach to familiar collocations in non-fluent aphasia
No full textBackground: Familiar collocations (e.g., “it’s alright”) are an important part of everyday conversation. Such word combinations are often retained in speakers with Broca’s aphasia. However, only few investigations have studied the forms and functions of familiar collocations available to speakers with Broca’s aphasia. //
Aims: We first apply a frequency-based perspective to word combinations produced by speakers with Broca’s aphasia and their conversation partners (CPs), and compare the frequency characteristics of word combinations in dyadic and non-dyadic speech. Second, we investigate the conversational functions of one prominent familiar collocation, “I don’t know” (IDK). //
Methods & Procedures: In the first analysis, speech samples from interactions of nine dyads (each a speaker with Broca’s aphasia and their CP) were examined. Non-dyadic samples were selected from 39 speakers with Broca’s aphasia from AphasiaBank (MacWhinney et al., 2011). The Frequency in Language Analysis Tool (FLAT; Zimmerer & Wibrow, 2015) was used to estimate collocation strength (the degree of association between words in a combination) of well-formed bigrams (two-word combinations) and trigrams (three-word combinations). The second analysis presents a qualitative investigation of uses of IDK in dyadic exchanges. //
Outcomes & Results: Analysis 1 revealed that residual trigrams in Broca’s aphasia were more strongly collocated in comparison to language produced by CPs. There was no difference in frequency-based profiles between dyadic and non-dyadic aphasic speech. Analysis 2 indicated that speakers with Broca’s aphasia and CPs used IDK to achieve a variety of communicative functions. However, patterns specific to each participant group were found. //
Conclusions: These findings highlight that frequency-based analysis is useful in explaining residual, grammatically well-formed word combinations in Broca’s aphasia. This study provides evidence that IDK can aid turn construction in aphasia
Identification vs. Self-Verification in Virtual Communities (VC)
No full textIdentity-related processes have been identified as important in explaining virtual community (VC) member behavior as well as informing system design of VCs. In particular, the two distinct identity processes of self-verification and identification have been identified and investigated separately, portrayed as two distinctive or contradictory identity processes with different practical implications. This chapter compares and reconciles these two theoretical perspectives in explaining VC participation. Based on a critical and comprehensive review of prior literature, the author identifies three major theoretical gaps that suggest how VC research and management can be advanced through an identity perspective. Finally, the chapter is concluded by discussing key implications of applying identity perspectives in VC research and future research agenda.</jats:p
VC valuation and multiples: an exploration of comparable analysis of software start-ups
No full textThis master thesis seeks to better understand the investment valuation procedure followed by software venture capitalists (VC) in the European context. I explain how VCs perform fair value estimations of software start-ups with the emerging comparable analysis technique. Furthermore, this study examines the relative importance of start-up characteristics in determining the multiple and how these factors influence the VC’s valuation behaviour. Additionally, I explore whether this behaviour and the multiples paid can be explained by differences in VC firm experience at a time of historically low interest rates and record-breaking fund inflows. Based on 36 interviews with European VCs, primarily from the Benelux region, I find that all start-up characteristics matter in the determination of the multiple, but the management team a little more. As a result, software VCs are willing to pay higher multiples for stellar management teams than for exceptional business characteristics. In contrast with the other characteristics, poor traction does not necessarily kill the deal, but VCs might rather use it to enforce a lower valuation. Overall, VC firm experience is not a strong predictor of the valuation behaviour and ARR multiples paid for deals. However, I do find that more experienced VCs are willing to pay higher premiums for benchmark-exceeding traction than their less experienced counterparts.Management of Technology (MoT
Almost Linear VC Dimension Bounds for Piecewise Polynomial Networks
No full textWe compute upper and lower bounds on the VC dimension and pseudo dimension of feedforward neural networks composed of piecewise polynomial activation functions. We show that if the number of layers is fixed, then the VC dimension and pseudo-dimension grow as W log W , where W is the number of parameters in the network. This result stands in opposition to the case where the the number of layers is unbounded, in which case the VC dimension and pseudo-dimension grow as W 2 . We combine our results with recently established approximation error rates, and determine error bounds for the problem of regression estimation by piecewise polynomial networks with unbounded weights. 1 Motivation It is a well known result of much recent work, that in order to derive useful performance bounds for classification, regression, and time series prediction, use must be made of both approximation as well as estimation error bounds. Approximation errors result Part of this work was done while the author..
The impact of the quality of VC financing and monitoring on the survival of IPO firms
No full text
Purpose
The purpose of this paper is to analyze the impact of venture capital (VC) involvement on the survival rate of French initial public offerings (IPOs) during the period 1996-2006. The paper examines the link between the survival rates of IPO companies, and several proxies for the quality of venture capitalist financing and monitoring.
Design/methodology/approach
To analyze the impact of the involvement of VC on both long and short run post-IPO survival, two methods are used: survival analysis (the Cox proportional hazard), and a logit model.
Findings
This paper shows that the quality of venture capitalist monitoring, measured by the duration of their investment before the IPO, is positively correlated with company survival rates. However, the author does not find the expected result when the author considers the experience of venture capitalists measured by their age.
Research limitations/implications
The findings are limited to a sample of VC-backed companies that went public.
Practical implications
The findings have implications for entrepreneurs. When analyzing the advantages and disadvantages linked to the presence of VC firms in the capital of their companies, entrepreneurs should consider that certain types of venture capitalists might be more or less able to be involved in the monitoring and value adding process.
Originality/value
To date, there is no comprehensive study on the French IPO market analyzing both long and short run post-IPO survival of VC-backed companies. This paper fills this gap.
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Preservation of passive constructions in a patient with primary progressive aphasia
No full textResearch into agrammatic comprehension in English has described a pattern of impaired understanding of passives and retained ability on active constructions. Some accounts of this dissociation predict that patients who are unable to comprehend actives will also be impaired in the comprehension of passives. We report the case of a man with primary progressive aphasia (PPA) (WR), whose comprehension was at chance on active sentences, but at ceiling on passives. In a series of reversible sentence comprehension tests WR displayed difficulties with active transitives and truncated actives with an auxiliary. In passive sentences, he displayed sensitivity to the agent marker by, as well as the passive morphology of the verb. This pattern of dissociation challenges current theories of agrammatic comprehension. We explore explanations based on the distinction between morphological and configurational cues, as well as on the semantic and discourse related differences between active and passive constructions
Exploring Demand Trends and Operational Scenarios for Virtual Coupling Railway Signalling Technology
No full textVirtual Coupling (VC) is a newly introduced concept of train-centric signalling technology that conceives trains to run autonomously in radio-connected platoons. These trains move synchronously at a relative braking distance to significantly improve railway capacity and address the forecasted increase in railway demand. The technical feasibility of VC depends on its strengths, weaknesses, opportunities and threats which can introduce radical changes to current train services, technologies and procedures. This paper investigates demand trends and operational scenarios of future train-centric signalling systems. To this end, stated travel preferences have been collected by means of a survey to have more insight on modal shares in the case of future VC applications. In addition, a Delphi method has been applied where another extensive survey has collected expert opinions about benefits and challenges of VC. Results show that VC can be very attractive to customers of high-speed and main line railways and have special benefits to the regional market where a manifest willing to pay more for using a more frequent train service was found. This concept therefore calls for a deeper understanding of possible Virtual Coupling operational scenarios and the impact on the railway industry.Accepted Author ManuscriptTransport and Plannin
Analysis of Safe and Effective Next-Generation Rail Signalling Systems using a FTA-SAN Approach
No full textMoving Block (MB) and Virtual Coupling (VC) rail signalling will change current train operation paradigm by migrating vital equipment from trackside to onboard to reduce train separation and maintenance costs. Their actual deployment is however constrained by the industry’s need to identify configurations of MB and VC signalling equipment which can effectively guarantee safe train movements even under degraded operational conditions involving component faults. In this paper, we analyse the effectivity of MB and VC in safely supervising train separation under nominal and degraded conditions by using an innovative approach which combines Fault Tree Analysis (FTA) and Stochastic Activity Network (SAN). A FTA model of unsafe train movement is defined for both MB and VC capturing functional interactions and cause effect relations among the different signalling components. The FTA is then used as a basis to apportion signalling component failure rates needed to feed the SAN model. Effective MB and VC train supervision is analysed by means of SAN-based simulations in the specific scenario of an error in the Train Position Reporting (TPR) for five rail market segments featuring different traffic characteristics, namely high-speed, mainline, regional, urban and freight. Results show that the overall approach can support infrastructure managers, railway undertakings, and rail system suppliers in investigating effectiveness of MB and VC in safely supervising train movements in scenarios involving different types of degraded conditions and failure events. The proposed method can hence support the railway industry in identifying effective and safe design configurations of next-generation rail signalling systems.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.Transport and Plannin
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