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51.
This study contributes to insights into mechanisms that influence the successes and failures of emerging energy technologies. It is assumed that for an emerging technology to fruitfully develop, it should be fostered by a Technological Innovation System (TIS), which is the network of actors, institutions and technologies in which it is embedded. For an emerging technology a TIS has yet to be built up. This research focuses on the dynamics of this build-up process by mapping the development of seven key activities: so-called system functions. The main contribution revolves around the notion of cumulative causation, or the phenomenon that the build-up of a TIS accelerates due to system functions reinforcing each other over time. As an empirical basis, an analysis is provided of the historical development of the TIS around automotive natural gas technology in the Netherlands (1970–2007). The results show that this TIS undergoes a gradual build-up in the 1970s, followed by a breakdown in the 1980s and, again, a build-up from 2000 to 2007. It is shown that underlying these trends are different forms of cumulative causation, here called motors of innovation. The study provides strategic insights for practitioners that aspire to support such motors of innovation. 相似文献
52.
Rosenbaum David A.; Meulenbroek Ruud J.; Vaughan Jonathan; Jansen Chris 《Canadian Metallurgical Quarterly》2001,108(4):709
This article describes a model of motion planning instantiated for grasping. According to the model, one of the most important aspects of motion planning is establishing a constraint hierarchy—a set of prioritized requirements defining the task to be performed. For grasping, constraints include avoiding collisions with to-be-grasped objects and minimizing movement-related effort. These and other constraints are combined with instance retrieval (recall of stored postures) and instance generation (generation of new postures and movements to them) to simulate flexible prehension. Dynamic deadline setting is used to regulate termination of instance generation, and performance of more than one movement at a time with a single effector is used to permit obstacle avoidance. Old and new data are accounted for with the model. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
53.
Biometrics authentication offers many advantages over conventional authentication systems that rely on possessions or special knowledge. With conventional technology, often the mere possession of an employee ID card is proof of ID, while a password potentially can be used by large groups of colleagues for long times without change. The fact that biometrics authentication is non-repudiable (hard to refute) and, yet, convenient, is among its most important advantages. Biometrics systems, however, suffer from some inherent biometrics-specific security threats. These threats are mainly related to the use of digital signals and the need for additional input devices, though we also discuss brute-force attacks of biometrics systems. There are also problems common to any pattern recognition system. These include “wolves” and “lambs”, and a new group we call “chameleons”. An additional issue with the use of biometrics is the invasion of privacy because the user has to enroll with an image of a body part. We discuss these issues and suggest some methods for mitigating their impact. 相似文献
54.
Generating cancelable fingerprint templates 总被引:5,自引:0,他引:5
Ratha NK Chikkerur S Connell JH Bolle RM 《IEEE transactions on pattern analysis and machine intelligence》2007,29(4):561-572
Biometrics-based authentication systems offer obvious usability advantages over traditional password and token-based authentication schemes. However, biometrics raises several privacy concerns. A biometric is permanently associated with a user and cannot be changed. Hence, if a biometric identifier is compromised, it is lost forever and possibly for every application where the biometric is used. Moreover, if the same biometric is used in multiple applications, a user can potentially be tracked from one application to the next by cross-matching biometric databases. In this paper, we demonstrate several methods to generate multiple cancelable identifiers from fingerprint images to overcome these problems. In essence, a user can be given as many biometric identifiers as needed by issuing a new transformation "key". The identifiers can be cancelled and replaced when compromised. We empirically compare the performance of several algorithms such as Cartesian, polar, and surface folding transformations of the minutiae positions. It is demonstrated through multiple experiments that we can achieve revocability and prevent cross-matching of biometric databases. It is also shown that the transforms are noninvertible by demonstrating that it is computationally as hard to recover the original biometric identifier from a transformed version as by randomly guessing. Based on these empirical results and a theoretical analysis we conclude that feature-level cancelable biometric construction is practicable in large biometric deployments 相似文献
55.
Recent research has revealed that nonconscious activation of desired behavioral states--or behavioral goals--promotes motivational activity to accomplish these states. Six studies demonstrate that this nonconscious operation of behavioral goals emerges if mental representations of specific behavioral states are associated with positive affect. In an evaluative-conditioning paradigm, unobtrusive linking of behavioral states to positive, as compared with neutral or negative, affect increased participants' wanting to accomplish these states. Furthermore, participants worked harder on tasks that were instrumental in attaining behavioral states when these states were implicitly linked to positive affect, thereby mimicking the effects on motivational behavior of preexisting individual wanting and explicit goal instructions to attain the states. Together, these results suggest that positive affect plays a key role in nonconscious goal pursuit. Implications for behavior-priming research are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
56.
Beiboer Sigrid H.W.; Berg Bert van den; Dekker Niek; Cox Ruud C.; Verheij Hubertus M. 《Protein engineering, design & selection : PEDS》1996,9(4):345-352
The effect of the substitution of the active site histidine48 by the unnatural 1,2,4-triazole-3-alanine (TAA) amino acidanalogue in porcine pancreas phospholipase A2 (PLA2) was studied.TAA was introduced biosynthetically using a his-auxotrophicEscherichia coli strain. To study solely the effect of the substitutionof the active site histidine, two nonessential histidines (i.e.His17 and His 115) were replaced by asparagines, resulting ina fully active mutant enzyme (His-PLA2). In this His-PLA2 thesingle histidine at position 48 was substituted by TAA withan incorporation efficiency of about 90%, giving a mixture ofHis-PLA2 and TAA-PLA2. Based on the charge difference at acidicpH, both forms could be separated by FPLC, allowing for thepurification of TAA-PLA2 free from His-PLA2. At pH 6, TAA-PLA2has a fivefold reduced activity compared with His-PLA2. Thisreduced activity paralells a reduced rate of covalent modificationwith p-nitrophenacyl bromide of TAA-PLA2 compared with His-PLA2.Competitive inhibition gave comparable IC50 values for WT-PLA2,His-PLA2 and TAA-PLA2. These results indicate that the reductionin activity is not caused by a different affinity for the substrate,but more likely results from a reduced kcat value in TAA-PLA2.The enzymatic activities for native and mutant PLA2s were measuredat different pH values. For WT-PLA2 and His-PLA2 the activityis optimal at pH 6 and is strongly deminished at acidic pH,with no observable activity at pH 3. In contrast, TAA-PLA2 isas active at pH 3 as at pH 6. Most likely, the decrease in activityobserved for WT-PLA2 and His-PLA2 is caused by the protonationof the active site His48, which is the general base involvedin the activation of the nucleophilic water molecule. In TAA-PLA2,however, the active site residue TAA48 is unprotonated at bothpH 3 and 6 as a result of the low pKa of TAA compared with histidine. 相似文献
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59.
High-accuracy spectral-slit-function calibration measurements, in situ ambient absorption gas cell measurements for ozone and nitrogen dioxide, and ground-based zenith sky measurements with the Earth Observing System Aura Ozone Monitoring Instrument (OMI) flight instrument are reported and the results discussed. For use of high-spectral-resolution gas absorption cross sections from the literature in trace gas retrieval algorithms, accurate determination of the instrument's spectral slit function is essential. Ground-based measurements of the zenith sky provide a geophysical determination of atmospheric trace gas abundances. When compared with other measurements, they can be used to verify the performance of the OMI flight instrument. We show that the approach of using published high-resolution absolute absorption cross sections convolved with accurately calibrated spectral slit functions for OMI compares well with in situ gas absorption cell measurements made with the flight instrument and that use of these convolved cross sections works well for reduction of zenith sky data taken with the OMI flight instrument for ozone and nitrogen dioxide that are retrieved from measured spectra of the zenith sky with the differential optical absorption spectroscopy technique, the same method to be used for the generation of in-flight data products. Finally, it is demonstrated that the spectral stability and signal-to-noise ratio performance of the OMI flight instrument, as determined from preflight component and full instrument tests, are sufficient to meet OMI mission objectives. 相似文献
60.
Lonneke Driessen Ruud Brekelmans Herbert Hamers Dick den Hertog 《Structural and Multidisciplinary Optimization》2006,31(1):40-48
Various sequential derivative-free optimization algorithms exist for solving black-box optimization problems. Two important
building blocks in these algorithms are the trust region and the geometry improvement. In this paper, we propose to incorporate
the D-optimality criterion, well known in the design of experiments, into these algorithms in two different ways. Firstly,
it is used to define a trust region that adapts its shape to the locations of the points in which the objective function has
been evaluated. Secondly, it is used to determine an optimal geometry-improving point. The proposed trust region and geometry
improvement can both be implemented into existing sequential algorithms. 相似文献