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61.
Abhishek Arun Barry Haddow Philipp Koehn Adam Lopez Chris Dyer Phil Blunsom 《Machine Translation》2010,24(2):103-121
Recent advances in statistical machine translation have used approximate beam search for NP-complete inference within probabilistic
translation models. We present an alternative approach of sampling from the posterior distribution defined by a translation
model. We define a novel Gibbs sampler for sampling translations given a source sentence and show that it effectively explores
this posterior distribution. In doing so we overcome the limitations of heuristic beam search and obtain theoretically sound
solutions to inference problems such as finding the maximum probability translation and minimum risk training and decoding. 相似文献
62.
The objective of the current research is to model trends in video game playing, overall computer use, and communication technology use in a longitudinal sample of youths, aged 11-16 over a 3-year interval. In addition, individual difference characteristics that may be predictive of these trends were included, namely, socio-demographic characteristics (gender, ethnicity, and parental income) and personality characteristics (self-esteem, the Big Five personality factors). Findings suggested that youth increased their overall computer and communication technology use but decreased their videogame playing over time. Many individual differences predicted mean levels of these technologies with fewer predicting slopes. Conclusions, implications, and limitations are discussed. 相似文献
63.
64.
Nikolaus Correll Nikos Arechiga Adrienne Bolger Mario Bollini Ben Charrow Adam Clayton Felipe Dominguez Kenneth Donahue Samuel Dyar Luke Johnson Huan Liu Alexander Patrikalakis Timothy Robertson Jeremy Smith Daniel Soltero Melissa Tanner Lauren White Daniela Rus 《Intelligent Service Robotics》2010,3(4):219-232
This paper describes the architecture and implementation of a distributed autonomous gardening system with applications in urban/indoor precision agriculture. The garden is a mesh network of robots and plants. The gardening robots are mobile manipulators with an eye-in-hand camera. They are capable of locating plants in the garden, watering them, and locating and grasping fruit. The plants are potted cherry tomatoes enhanced with sensors and computation to monitor their well-being (e.g. soil humidity, state of fruits) and with networking to communicate servicing requests to the robots. By embedding sensing, computation, and communication into the pots, task allocation in the system is de-centrally coordinated, which makes the system scalable and robust against the failure of a centralized agent. We describe the architecture of this system and present experimental results for navigation, object recognition, and manipulation as well as challenges that lie ahead toward autonomous precision agriculture with multi-robot teams. 相似文献
65.
In recent years, there has been significant shift from rigid development (RD) toward agile. However, it has also been spotted that agile methodologies are hardly ever followed in their pure form. Hybrid processes as combinations of RD and agile practices emerge. In addition, agile adoption has been reported to result in both benefits and limitations. This exploratory study (a) identifies development models based on RD and agile practice usage by practitioners; (b) identifies agile practice adoption scenarios based on eliciting practice usage over time; (c) prioritizes agile benefits and limitations in relation to (a) and (b). Practitioners provided answers through a questionnaire. The development models are determined using hierarchical cluster analysis. The use of practices over time is captured through an interactive board with practices and time indication sliders. This study uses the extended hierarchical voting analysis framework to investigate benefit and limitation prioritization. Four types of development models and six adoption scenarios have been identified. Overall, 45 practitioners participated in the prioritization study. A common benefit among all models and adoption patterns is knowledge and learning, while high requirements on professional skills were perceived as the main limitation. Furthermore, significant variances in terms of benefits and limitations have been observed between models and adoption patterns. The most significant internal benefit categories from adopting agile are knowledge and learning, employee satisfaction, social skill development, and feedback and confidence. Professional skill-specific demands, scalability, and lack of suitability for specific product domains are the main limitations of agile practice usage. Having a balanced agile process allows to achieve a high number of benefits. With respect to adoption, a big bang transition from RD to agile leads to poor quality in comparison with the alternatives. 相似文献
66.
Damien Sulla-Menashe Mark A. Friedl Olga N. Krankina Alessandro Baccini Curtis E. Woodcock Adam Sibley Guoqing Sun Viacheslav Kharuk Vladimir Elsakov 《Remote sensing of environment》2011,115(2):392-403
The Northern Eurasian land mass encompasses a diverse array of land cover types including tundra, boreal forest, wetlands, semi-arid steppe, and agricultural land use. Despite the well-established importance of Northern Eurasia in the global carbon and climate system, the distribution and properties of land cover in this region are not well characterized. To address this knowledge and data gap, a hierarchical mapping approach was developed that encompasses the study area for the Northern Eurasia Earth System Partnership Initiative (NEESPI). The Northern Eurasia Land Cover (NELC) database developed in this study follows the FAO-Land Cover Classification System and provides nested groupings of land cover characteristics, with separate layers for land use, wetlands, and tundra. The database implementation is substantially different from other large-scale land cover datasets that provide maps based on a single set of discrete classes. By providing a database consisting of nested maps and complementary layers, the NELC database provides a flexible framework that allows users to tailor maps to suit their needs. The methods used to create the database combine empirically derived climate–vegetation relationships with results from supervised classifications based on Moderate Resolution Imaging Spectroradiometer (MODIS) data. The hierarchical approach provides an effective framework for integrating climate–vegetation relationships with remote sensing-based classifications, and also allows sources of error to be characterized and attributed to specific levels in the hierarchy. The cross-validated accuracy was 73% for the land cover map and 73% and 91% for the agriculture and wetland classifications, respectively. These results support the use of hierarchical classification and climate–vegetation relationships for mapping land cover at continental scales. 相似文献
67.
Adam C. Woodbury Jason F. Shepherd Matthew L. Staten Steven E. Benzley 《Engineering with Computers》2011,27(1):95-104
Finite element mesh adaptation methods can be used to improve the efficiency and accuracy of solutions to computational modeling
problems. In many applications involving hexahedral meshes, localized modifications which preserve a conforming all-hexahedral
mesh are desired. Effective hexahedral refinement methods that satisfy these criteria have recently become available; however,
due to hexahedral mesh topology constraints, little progress has been made in the area of hexahedral coarsening. This paper
presents a new method to locally coarsen conforming all-hexahedral meshes. The method works on both structured and unstructured
meshes and is not based on undoing previous refinement. Building upon recent developments in quadrilateral coarsening, the
method utilizes hexahedral sheet and column operations, including pillowing, column collapsing, and sheet extraction. A general
algorithm for automated coarsening is presented and examples of models that have been coarsened with this new algorithm are
shown. While results are promising, further work is needed to improve the automated process. 相似文献
68.
The reduction of Langmuir triple and quadruple probe data, i.e., the determination of the electron temperature T(e) from the measured voltages and currents, requires the solution of an implicit transcendental equation in T(e), at every point in time. Random errors and noise in the measurements occasionally precludes solution of the equation, resulting in an indeterminate temperature at those times. We present a method for overcoming this problem that uses the method of maximum likelihood. The experimental uncertainties, assumed to be normally distributed, are used in solving the implicit equation in T(e). At every point in time, a likelihood function is calculated, and the temperature which maximizes this function is taken to be the solution T(e). The uncertainty in the resulting measurement is taken to be the width of the likelihood function. Examples of this technique are shown. 相似文献
69.
Fatigue is a serious issue for the rail industry, increasing inefficiency and accident risk. The performance of 20 train drivers in a rail simulator was investigated at low, moderate and high fatigue levels. Psychomotor vigilance (PVT), self-rated performance and subjective alertness were also assessed. Alertness, PVT reaction times, extreme speed violations (>25% above the limit) and penalty brake applications increased with increasing fatigue level. In contrast, fuel use, draft (stretch) forces and braking errors were highest at moderate fatigue levels. Thus, at high fatigue levels, errors involving a failure to act (errors of omission) increased, whereas incorrect responses (errors of commission) decreased. The differential effect of fatigue on error types can be explained through a cognitive disengagement with the virtual train at high fatigue levels. Interaction with the train reduced dramatically, and accident risk increased. Awareness of fatigue-related performance changes was moderate at best. These findings are of operational concern. 相似文献
70.
We prove new lower bounds for learning intersections of halfspaces, one of the most important concept classes in computational learning theory. Our main result is that any statistical-query algorithm for learning the intersection of $\sqrt{n}$ halfspaces in n dimensions must make $2^{\varOmega (\sqrt{n})}$ queries. This is the first non-trivial lower bound on the statistical query dimension for this concept class (the previous best lower bound was n Ω(log?n)). Our lower bound holds even for intersections of low-weight halfspaces. In the latter case, it is nearly tight. We also show that the intersection of two majorities (low-weight halfspaces) cannot be computed by a polynomial threshold function (PTF) with fewer than n Ω(log?n/log?log?n) monomials. This is the first super-polynomial lower bound on the PTF length of this concept class, and is nearly optimal. For intersections of k=ω(log?n) low-weight halfspaces, we improve our lower bound to $\min\{2^{\varOmega (\sqrt{n})},n^{\varOmega (k/\log k)}\},$ which too is nearly optimal. As a consequence, intersections of even two halfspaces are not computable by polynomial-weight PTFs, the most expressive class of functions known to be efficiently learnable via Jackson’s Harmonic Sieve algorithm. Finally, we report our progress on the weak learnability of intersections of halfspaces under the uniform distribution. 相似文献