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排序方式: 共有1016条查询结果,搜索用时 15 毫秒
61.
Turrisi Rob; Mastroleo Nadine R.; Mallett Kimberly A.; Larimer Mary E.; Kilmer Jason R. 《Canadian Metallurgical Quarterly》2007,21(4):453
The present study used perspectives from the general literature on college alcohol consumption to examine mediational influences of peer, environmental, and parental variables on heavy drinking for student athlete and nonathlete samples. Eight hundred thirty-five freshmen who differed in organized sports involvement were compared on heavy drinking outcomes, peer norms, environmental influences, and parental communication. College athletes reported significantly more heavy drinking experiences than nonathletes. Peer norms, environmental influences, and parental communication were all significant mediators of the athlete-heavy drinking relationship. Athletes reported a higher perception of peer drinking, peer approval of drinking, higher alcohol availability, and direct drink offers, which, in turn, were related to higher rates of heavy drinking. Parental communication mediated the athlete-heavy drinking relationship differently, depending on the specific topic of conversation. Discussion surrounding the importance of incorporating a variety of interventions aimed at reducing collegiate athlete drinking on the basis of the peer, environmental, and parental influences observed in the present analyses are presented. Limitations and directions for future research are also noted. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
62.
Rob DiMatteo Fred Dimock 《中国电子商情》2007,(11):74-75
现在,电子制造行业必须满足无铅标准,并且已经取得了很大的进展,整个行业正在了解可靠的无铅方案。业内正在生产高性能无铅电路板,并且已经制订出无铅处理的新标准。本文重点介绍无铅焊接处理中的回流焊工艺考虑因素。[第一段] 相似文献
63.
64.
Constantin F. Caruntu Mircea Lazar Rob H. Gielen P.P.J. van den Bosch Stefano Di Cairano 《Control Engineering Practice》2013,21(12):1884-1898
Vehicle drivetrains are characterized by fast dynamics, subject to physical and control constraints, which make controller design for driveline oscillations damping a challenging problem. Furthermore, in current implementations, the connections between the controller and the physical plant are realized using a controller area network (CAN) as the communication medium, which introduces time-varying delays. As such, the goal of this paper is to provide a control design methodology that can cope with all these challenges and limitations and still yield an effective solution. To this end, firstly, a continuous-time model of a vehicle drivetrain is derived. Then, a method for determining a worst case upper bound on the delays that can be introduced by a CAN is presented, which enables the usage of a polytopic approximation technique to obtain a discrete-time model of the closed-loop CAN system. Thirdly, a non-conservative Lyapunov based predictive controller is designed for the resulting model with time-varying delays, polytopic uncertainty and hard constraints. Several tests performed using an industry validated drivetrain model and the Matlab toolbox TrueTime indicate that the proposed design methodology can handle both the performance/physical constraints and the strict limitations on the computational complexity, while effectively coping with time-varying delays. Preliminary real-time results further validate the proposed methodology. 相似文献
65.
Timothy Dube Onisimo Mutanga Elfatih M. Abdel-Rahman Riyad Ismail Rob Slotow 《International journal of remote sensing》2013,34(14):3751-3772
Accurate, reliable, and up-to-date forest stand volume information is a prerequisite for a detailed evaluation of commercial forest resources and their sustainable management. Commercial forest responses to global climate change remain uncertain, and hence the mapping of stand volume as carbon sinks is fundamentally important in understanding the role of forests in stabilizing climate change effects. The aim of this study was to examine the utility of stochastic gradient boosting (SGB) and multi-source data to predict stand volume of a Eucalyptus plantation in South Africa. The SGB ensemble, random forest (RF), and stepwise multiple-linear regression (SMLR) were used to predict Eucalyptus stand volume and other related tree-structural attributes such as mean tree height and mean diameter at breast height (DBH). Multi-source data consisted of SPOT-5 raw spectral features (four bands), 14 spectral vegetation indices, rainfall data, and stand age. When all variables were used, the SGB algorithm showed that stand volume can be accurately estimated (R2 = 0.78 and RMSE = 33.16 m3 ha?1 (23.01% of the mean)). The competing RF ensemble produced an R2 value of 0.76 and a RMSE value of 37.28 m3 ha?1 (38.28% of the mean). SMLR on the other hand, produced an R2 value of 0.65 and an RMSE value of 42.50 m3 ha?1 (42.50% of the mean). Our study further showed that Eucalyptus mean tree height (R2 = 0.83 and RMSE = 1.63 m (9.08% of the mean)) and mean diameter at breast height (R2 = 0.74 and RMSE = 1.06 (7.89% of the mean)) can also be reasonably predicted using SGB and multi-source data. Furthermore, when the most important SGB model-selected variables were used for prediction, the predictive accuracies improved significantly for mean DBH (R2 = 0.81 and RMSE = 1.21 cm (6.12% of the mean)), mean tree height (R2 = 0.86 and RMSE = 1.39 m (7.02% of the mean)), and stand volume (R2 = 0.83 and RMSE = 29.58 m3 ha?1 (17.63% of the mean)). These results underscore the importance of integrating multi-source data with remotely sensed data for predicting Eucalyptus stand volume and related tree-structural attributes. 相似文献
66.
This paper assesses two patterns in transition processes for using them as strategies towards a sustainable energy system, i.e., niche accumulation and hybridisation. Both play important but different roles in transitions. The expected success of these strategies depends on the innovation's history and the innovation context. The different strategies are illustrated with several examples from the energy domain. 相似文献
67.
v. Schröder Karl Boresch K. Dirr R. Ammon Diemair Griebel Schwaibold G. Mall Felicitas Rolleri Kanitz O. Windhausen K. Felix von Querner W. Ludorff E. Fischbach W. Sutthoff Frey-Wyssling Schormüller A. Pirson J. Großfeld E. Chytrek Koelitz Hans Hawelka W. Schreiber Brüning Estler Pawletta W. Wodsak Jesser H. J. Steinbeck Seuss Schmitz Lars Erlandsen W. Hämmerle Masch A. Bäurle W. Leithe Rudolj Abderhalden Haevecker Fr. Bartschat Garber G. Stamm Gertraude Körner-Hennig G. Steinhoff Johannes Wolf Rob Jungkunz Schönfeld Ed. Rentz Klinc K. Höll 《European Food Research and Technology》1940,79(6):568-608
68.
Schormüller J. Großfeld H. Mohler Carls Kanitz Griebel Rudolf Abderhalden W. Schreiber W. Hämmerle Brüning W. Ludorff Pawletta W. Bartels Fr. Bartschat M. Gordienko L. W. Jirak O. Windhausen H. -A. Oelkers I. Stahn J. Ph. Bruno Roßmann Lars Erlandsen Lintzel Flößner Bäurle Reschke Haevecker W. Sutthoff H. Schanderl Masling H. Süllmann v. Noël Reichard E. Dinslage G. Steinhoff Jesser Rob Jungkunz C. Pyriki W. Preiβ K. Müller L. Klinc Zacher Beckel K. Höll 《European Food Research and Technology》1939,78(6):480-496
69.
Illuminance data were collected from 18 UK dwellings during 1-week periods in spring 2007, to establish when luminaires were used and to calculate electricity consumption for lighting. Householders were also interviewed about lighting use and choices. The potential for reducing lighting electricity consumption by replacing incandescent bulbs with compact fluorescent lamps (CFLs) is assessed. Mean weekly electricity consumption for lighting was 3.756 kW h and mean proportion of total electricity consumption used for lighting was 6.55%. It is notable, however, that participants generally expressed high levels of environmental awareness and that electricity consumption figures for less environmentally-aware households may differ. On average, households could have reduced lighting electricity consumption by 50.9% if all incandescent bulbs were replaced with CFLs. Even householders making extensive use of efficient lighting technologies expressed concerns about these technologies’ performance, but seemed willing to tolerate perceived shortcomings for environmental reasons. However, the study raises questions about whether people without strong environmental motivations can be convinced that efficient lighting technologies will meet their needs. It also raises questions about the effectiveness of policies phasing out general lighting service incandescent bulbs, as there is a risk that householders may switch to tungsten halogen bulbs rather than low-energy options. 相似文献
70.
Rob J. Hyndman Roman A. Ahmed George Athanasopoulos Han Lin Shang 《Computational statistics & data analysis》2011,55(9):2579-2589
In many applications, there are multiple time series that are hierarchically organized and can be aggregated at several different levels in groups based on products, geography or some other features. We call these “hierarchical time series”. They are commonly forecast using either a “bottom-up” or a “top-down” method.In this paper we propose a new approach to hierarchical forecasting which provides optimal forecasts that are better than forecasts produced by either a top-down or a bottom-up approach. Our method is based on independently forecasting all series at all levels of the hierarchy and then using a regression model to optimally combine and reconcile these forecasts. The resulting revised forecasts add up appropriately across the hierarchy, are unbiased and have minimum variance amongst all combination forecasts under some simple assumptions.We show in a simulation study that our method performs well compared to the top-down approach and the bottom-up method. We demonstrate our proposed method by forecasting Australian tourism demand where the data are disaggregated by purpose of travel and geographical region. 相似文献