排序方式： 共有99条查询结果，搜索用时 15 毫秒
91.
Kleinbergs HITS algorithm (Kleinberg 1999), which was originally developed in a Web context, tries to infer the authoritativeness of a Web page in relation to a specific query using the structure of a subgraph of the Web graph, which is obtained considering this specific query. Recent applications of this algorithm in contexts far removed from that of Web searching (Bacchin, Ferro and Melucci 2002, Ng et al. 2001) inspired us to study the algorithm in the abstract, independently of its particular applications, trying to mathematically illuminate its behaviour. In the present paper we detail this theoretical analysis. The original work starts from the definition of a revised and more general version of the algorithm, which includes the classic one as a particular case. We perform an analysis of the structure of two particular matrices, essential to studying the behaviour of the algorithm, and we prove the convergence of the algorithm in the most general case, finding the analytic expression of the vectors to which it converges. Then we study the symmetry of the algorithm and prove the equivalence between the existence of symmetry and the independence from the order of execution of some basic operations on initial vectors. Finally, we expound some interesting consequences of our theoretical results.Supported in part by a grant from the Italian National Research Council (CNR) research project Technologies and Services for Enhanced Content Delivery. 相似文献
92.
In search of complementary assets: The determinants of alliance formation of high-tech start-ups 总被引：2，自引：0，他引：2
Why do new technology-based firms (NTBFs) cooperate? Starting from Teece's [Teece, D.J., 1986. Profiting from technological innovation: implications for integration, collaboration, licensing, and public policy. Research Policy 15, 285-305] conceptual framework and taking advantage of subsequent literature on alliance formation in the resource and competence-based tradition and in the social structure perspective, we derive an empirical model that aims at highlighting the inducements and obstacles that these firms face in alliance formation according to firm-specific characteristics and the nature of the alliance. In particular, a distinction is made between exploitative commercial alliances and explorative technological alliances. The econometric estimates, based on a large sample of Italian young high-tech firms that are observed from 1994 to 2003, provide strong evidence supporting two key intuitions of Teece's work. First, the “combination of specialized complementary assets” appears to be a key driver of the formation of exploitative commercial alliances by NTBFs. More specifically, patent holding affects positively the likelihood to establish commercial alliances, but this propensity is found to rapidly decrease with firm size, suggesting that as long as NTBFs become larger and possess specialized commercial assets their urge for commercial alliances diminishes. Second, following the parallelism set forth by Teece between search for alliance partners and access to external financing, the analysis indicates that potentially beneficial alliances may not take place because of the high transaction costs faced by smaller NTBFs. In this respect, our results clearly support the view that sponsor institutions as public research organizations, venture and corporate venture capitalists may sensibly reduce these costs and that their role crucially depends on both the identity of the sponsor and the type of alliance. 相似文献
93.
Andrea Viggiano Sergio Chieffi Domenico Tafuri Giovanni Messina Marcellino Monda Bruno De Luca 《Journal of sports sciences》2013,31(1):46-62
Vividness and controllability of relaxing and energizing imagery by efficient and less efficient imagers. 相似文献
94.
Several recent reports pointed out how the practice of using a “second screen” while following a television program is becoming an increasingly widespread phenomenon. When the secondary device is used to read or to comment about a watched program, most of the discussion takes place on popular social media such as Facebook and Twitter. Previous research has shown that the analysis of these contents could lead to a better understanding of the behavior of networked publics and of the structure of the show itself. Nevertheless most of the existing research is focused on the content only and focused on a single episode analysis or on big media events. Leveraging this background, this article presents instead a study focused on the relationships between content and users across an entire airing season of a TV program. Through a quantitative network analysis of the tweets produced during 25 episodes of the Italian political talks show Servizio Pubblico, we identified a small loyal group of viewers. Despite the differences in quantity of content produced, the loyal viewers do not show any sign of forming a community-like structure. We also performed a qualitative analysis of the tweets produced during one specific episode and discussed the elements of the TV show that generated the higher level of engagement on Twitter. 相似文献
95.
Chiara Manneschi Paola Fanzio Tapio Ala-Nissila Elena Angeli Luca Repetto Giuseppe Firpo Ugo Valbusa 《Biomicrofluidics》2014,8(6)
There is currently a growing interest in control of stretching of DNA inside nanoconfined regions due to the possibility to analyze and manipulate single biomolecules for applications such as DNA mapping and barcoding, which are based on stretching the DNA in a linear fashion. In the present work, we couple Finite Element Methods and Monte Carlo simulations in order to study the conformation of DNA molecules confined in nanofluidic channels with neutral and charged walls. We find that the electrostatic forces become more and more important when lowering the ionic strength of the solution. The influence of the nanochannel cross section geometry is also studied by evaluating the DNA elongation in square, rectangular, and triangular channels. We demonstrate that coupling electrostatically interacting walls with a triangular geometry is an efficient way to stretch DNA molecules at the scale of hundreds of nanometers. The paper reports experimental observations of λ-DNA molecules in poly(dimethylsiloxane) nanochannels filled with solutions of different ionic strength. The results are in good agreement with the theoretical predictions, confirming the crucial role of the electrostatic repulsion of the constraining walls on the molecule stretching. 相似文献
96.
In this study the authors propose a distinction between two approaches to market information, rooted in the marked-based learning theory. The two approaches are conceptualized and operationalized on the basis of their differences along three processes: generation, dissemination and use of market information. In the retrospective approach, the generation process is based on expressed customer needs and extant market relations; the dissemination is based on formal mechanisms; the use process is more instrumental. In the forward-looking approach, the generation process is based on latent customer needs and on the evolutionary patterns of the future market relations; the dissemination process is more informal; the use of information is more conceptual. A series of hypotheses concerning the relationships between these approaches, product innovativeness and firm performance are tested on a sample of Italian fashion firms. Results suggest that the two approaches are complementary for firm performance, but have opposite effects on product innovativeness: while a forward-looking approach is positively related to product innovativeness, a retrospective approach seems to be negatively related. The results also shed light on how market information approaches and product innovativeness jointly affect firm performance. 相似文献
97.
Luca Oggiano Olga Troynikov Inna Konopov Aleksandar Subic Firoz Alam 《Sports Engineering》2009,12(1):1-12
Wind tunnel testing has been carried out on nine-knitted single jersey fabrics (100% polyester) using cylinder and leg models
to determine its aerodynamic behaviour over a range of speeds (20–80 km/h) representative of sports activities. Strong correlation
between fabric manufacturing (cover factor) and fabric roughness and aerodynamic parameters has been established. Similar
aerodynamic behaviour of fabrics was observed when tested on the cylinder model and on the leg model. 相似文献
98.
Conservation of historical reinforced concrete structures damaged by carbonation induced corrosion by means of electrochemical realkalisation 总被引：1，自引：0，他引：1
Electrochemical realkalisation is a technique aimed at stopping rebar corrosion in carbonated concrete. The alkalinity of the concrete around the rebars is restored, and an environment favourable to the passivation of steel is re-created. The technique is based on the application of a DC current from an anode, placed on the external surface of the concrete, and the rebar. The anode is usually embedded in cellulose pulp soaked with a solution of sodium or potassium carbonate. The rebar and the anode are connected to a DC current feeder, the rebar to the negative terminal and the anode to the positive terminal. The applied current produces alkalinity at the surface of the rebar, while the alkaline electrolyte in which the anode is immersed penetrates from the external surface. In this way the concrete is realkalised, its protective characteristics towards the steel are restored and rebars can return to passive conditions. The treatment is temporary: this feature makes it very attractive in the field of historical buildings and cultural heritage, where the conservation of the original materials and surfaces is often a stringent requirement in the design of the repair. This paper shows the advantages of this technique applied to historical structures by describing the application to a bell tower built in the 1920s. The electrochemical realkalisation treatment was applied to eight columns on the bell tower where a traditional repair (based on the substitution of carbonated concrete with a repair mortar) would have been practically impossible. The application of the treatment followed two steps: initially, a trial was made on two sections of two columns, so as to calibrate the process parameters such as current density, time length and type of anode. Subsequently, the treatment was applied to all the columns. The analyses carried out on the concrete after the application of the treatment showed that the protection to the reinforcement was mainly connected to the alkaline layer produced around the steel, which is expected to prevent further corrosion of the steel. 相似文献
99.