Long-term correlations in short,non-stationary time series: An application to international R&D collaborations     

Lorenzo Righetto  Alessandro Spelta  Emanuele Rabosio  Fabio Pammolli 《Journal of Informetrics》2019,13(2):583-592

Within the perimeter of patent collaboration networks, the average distance of collaborations and the number of countries involved per each collaboration have been shown to have increased steadily in time. Less attention, though, has been devoted to assessing whether this growth of cross-country collaborations is stable in time. To address this scientific question we focus on the identification of long-term correlations (i.e. temporal persistence). Our data set consists of time series of yearly average collaboration radii and of cross-border links in the Euro-American subsystem of the global collaboration network for the period 1978–2014. To investigate the fundamental persistence properties of these time series, we use Detrended Fluctuation Analysis, a method that allows us to measure long-term correlations in detrended signals. Also, we devise a general and original procedure to assess the statistical significance of results for short time series. Our results, showing that long-term correlations do exist in the majority of our signals, reinforce the hypothesis of a diminishing role of geographical distance in technological collaborations. Results at national level show that a significant degree of heterogeneity in persistence parameters can be detected within Europe, irrespectively of the efforts towards the set-up of an integrated European Research Area.  相似文献   

A hermeneutic defence of the cognitive autonomy of science     

Fabio Gironi 《Metascience》2013,22(2):461-464

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Venture capital financing and the growth of high-tech start-ups: Disentangling treatment from selection effects   总被引：3，自引：0，他引：3  

Fabio Bertoni  Massimo G. ColomboLuca Grilli 《Research Policy》2011,40(7):1028-1043

The financial and innovation literature generally claims that venture capital (VC) investments spur the growth of new technology-based firms (NTBFs). However, it has proved difficult so far to separate the “treatment” effect of the VC investment from the “selection” effect attributable to the ability of the VC investor to screen high growth NTBFs. The aim of this work is to test whether VC investments have a positive treatment effect on the growth of employment and sales of NTBFs. For this purpose we consider a 10-year longitudinal data set for 538 Italian NTBFs, most of which are privately held. The sample includes both VC-backed and non-VC-backed firms. We estimate Gibrat-law-type dynamic panel-data models augmented with time-varying variables that capture the VC status of firms. To control for the endogeneity of VC investments we use several GMM estimators. The econometric results strongly support the view that VC investments positively influence firm growth. The treatment effect of VC investments is of large economic magnitude, especially on growth of employment. Most of it is obtained immediately after the first round of VC finance. Conversely, the selection effect of VC appears to be negligible in the Italian context.  相似文献   

Modelling the joint torques and loadings during squatting at the Smith machine     

Biscarini A  Benvenuti P  Botti F  Mastrandrea F  Zanuso S 《Journal of sports sciences》2011,29(5):457-469

An analytical biomechanical model was developed to establish the relevant properties of the Smith squat exercise, and the main differences from the free barbell squat. The Smith squat may be largely patterned to modulate the distributions of muscle activities and joint loadings. For a given value of the included knee angle (θ(knee)), bending the trunk forward, moving the feet forward in front of the knees, and displacing the weight distribution towards the forefoot emphasizes hip and lumbosacral torques, while also reducing knee torque and compressive tibiofemoral and patellofemoral forces (and vice versa). The tibiofemoral shear force φ(t) displays more complex trends that strongly depend on θ(knee). Notably, for 180° ≥ θ(knee) ≥ 130°, φ(t) and cruciate ligament strain forces can be suppressed by selecting proper pairs of ankle and hip angles. Loading of the posterior cruciate ligament increases (decreases) in the range 180° ≥ θ(knee) ≥ 150° (θ(knee) ≤ 130°) with knee extension, bending the trunk forward, and moving the feet forward in front of the knees. In the range 150° > θ(knee) > 130°, the behaviour changes depending on the foot weight distribution. The conditions for the development of anterior cruciate ligament strain forces are explained. This work enables careful use of the Smith squat in strengthening and rehabilitation programmes.  相似文献   

Multispectral data cube acquisition of aligned images for document analysis by means of a filter-wheel camera provided with focus control     

Gianfranco Bianco  Fabio Bruno  Maurizio Muzzupappa 《Journal of Cultural Heritage》2013,14(3):190-200

Multispectral imaging techniques are widely used to analyse and restore digital images of ancient documents degraded over time. In particular, acquisitions in infrared and ultraviolet bands can reveal information invisible by naked eye, which is not captured by conventional RGB imaging. Multispectral acquisitions are usually performed with filter-wheel cameras that mount a series of interference filters in front of the sensor to select the spectral band in which the document has to be acquired. Due to the use of different filters, the focus of the lens changes and it is necessary to adjust it manually for each filter, because such imaging systems are devoid of automatic focusing. Thus the acquired images may not be perfectly in-focus and have misalignments. In this work we present an automatic solution to acquire a multispectral data cube of aligned images that can be used in document analysis to extract and/or separate information through enhancement techniques. A custom-made motorized autofocus system controlled by software has been installed on a filter-wheel camera, which allows us to acquire in-focus images automatically at each filter changing, and a registration method based on Fourier-Mellin transform aligns these images. A preliminary calibration is performed to set the focusing of each filter with the working distance. As a result, the camera can capture images independently from the contrast of the scene, also in presence of documents with homogeneous texture. The proposed solution reduces considerably the acquisition time and offers a tool to acquire automatically the data cube to be used in further image analysis techniques. The results of experimentations are hereby presented and discussed.  相似文献   

Education for Integrated Rural Development: transformative learning in a complex and uncertain world     

Arjen E.J. Wals  Fabio Caporali  Paul Pace  Bill Slee  Nadarajah Sriskandarajah  Martyn Warren 《The Journal of Agricultural Education and Extension》2013,19(2):89-100

A key question addressed in this article is: How does the increased pressure for expertise in IRD translate itself into the demand for educational services and the design of appropriate curricula on a European-wide basis? This article examines these issues and generates a number of stepping stones for the development of Education and Training for Integrated Rural Development (ETIRD) in tertiary education, based on a two-year inter-institutional curriculum development project carried out under the umbrella of the AFANetⁱ.  相似文献   

A taxonomy of computer media in distance education     

Fabio Chacón 《Open Learning》2013,28(1):12-27

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Does soccer cleat design influence the rotational interaction with the playing surface?     

Fabio Galbusera  Davide Zai Tornese  Federica Anasetti  Simone Bersini  Piero Volpi  Luigi La Barbera 《Sports biomechanics / International Society of Biomechanics in Sports》2013,12(3):293-301

Non-contact injuries in soccer players may be related to the interplay between cleat type and playing surface, and bladed shoes were often blamed for non-contact injuries with no research support. The aim of this study was to compare the rotational resistance (stiffness and peak sustainable torque) among three types of soccer cleats (metal studs, molded rubber studs, and bladed) in a controlled laboratory environment. The shoes were tested on both natural and artificial turfs under a compressive preload of 1000 N and with internal and external rotations. The three shoe models showed comparable performances with a good repeatability for each individual test on both playing surfaces. A less stiff behavior was observed for the natural turf. A tendency toward highest peak torque was observed in the studded model on natural surface. The bladed cleats provided peak torque and rotational stiffness comparable to the other models. Studded and bladed cleats did not significantly differ in their interaction with the playing surface. Therefore, soccer shoes with bladed cleats should not be banned in the context of presumed higher risk for non-contact injuries.  相似文献   

Government Grants to Private Cultural Institutions–The Effects of a Change in the Italian Legislation     

Bruno Bises  Fabio Padovano 《Journal of Cultural Economics》2004,28(4):303-315

In Italy, the Regular Grant is the most important subsidy to private cultural institutions. Since 1996, law 534/96 has regulated its provision. This law greatly improves on the previous legislation, as it redefines the prerequisites to become a recipient and specifies performance indicators to which the size of the grant must be tied. This paper examines the effects of the introduction of the new law, the characteristics of the government choice process and the redistribution profile of these grants using a variety of estimating techniques on official data gathered for the purpose.  相似文献   

The memory of science: Inflation,myopia, and the knowledge network     

Raj K. Pan  Alexander M. Petersen  Fabio Pammolli  Santo Fortunato 《Journal of Informetrics》2018,12(3):656-678

Scientific production is steadily growing, exhibiting 4% annual growth in publications and 1.8% annual growth in the number of references per publication, together producing a 12-year doubling period in the total supply of references, i.e. links in the science citation network. This growth has far-reaching implications for how academic knowledge is connected, accessed and evaluated. Against this background, we analyzed a citation network comprised of 837 million references produced by 32.6 million publications over the period 1965–2012, allowing for a detailed analysis of the ‘attention economy’ in science. Our results show how growth relates to ‘citation inflation’, increased connectivity in the citation network resulting from decreased levels of uncitedness, and a narrowing range of attention – as both very classic and very recent literature are being cited increasingly less. The decreasing attention to recent literature published within the last 6 years suggests that science has become stifled by a publication deluge destabilizing the balance between production and consumption. To better understand these patterns together, we developed a generative model of the citation network, featuring exponential growth, the redirection of scientific attention via publications’ reference lists, and the crowding out of old literature by the new. We validate our model against several empirical benchmarks, and then use perturbation analysis to measure the impact of shifts in citing behavior on the synthetic system's properties, thereby providing insights into the functionality of the science citation network as an infrastructure supporting the memory of science.  相似文献