2,410 research outputs found
Wrapper Maintenance: A Machine Learning Approach
The proliferation of online information sources has led to an increased use
of wrappers for extracting data from Web sources. While most of the previous
research has focused on quick and efficient generation of wrappers, the
development of tools for wrapper maintenance has received less attention. This
is an important research problem because Web sources often change in ways that
prevent the wrappers from extracting data correctly. We present an efficient
algorithm that learns structural information about data from positive examples
alone. We describe how this information can be used for two wrapper maintenance
applications: wrapper verification and reinduction. The wrapper verification
system detects when a wrapper is not extracting correct data, usually because
the Web source has changed its format. The reinduction algorithm automatically
recovers from changes in the Web source by identifying data on Web pages so
that a new wrapper may be generated for this source. To validate our approach,
we monitored 27 wrappers over a period of a year. The verification algorithm
correctly discovered 35 of the 37 wrapper changes, and made 16 mistakes,
resulting in precision of 0.73 and recall of 0.95. We validated the reinduction
algorithm on ten Web sources. We were able to successfully reinduce the
wrappers, obtaining precision and recall values of 0.90 and 0.80 on the data
extraction task
Evaluation of the SSRCT engine with a hydrazine as a fuel, phase 1
The performance parameters for the space shuttle reaction control thruster (SSRCT) when the fuel is changed from monomethylhydrazine to hydrazine were predicted. Potential problems are higher chamber wall temperature during steady state operation and explosive events during pulse mode operation. Solutions to the problems are suggested. To conduct the analysis, a more realistic film cooling model was devised which considers that hydrazine based fuels are reactive when used as a film coolant on the walls of the combustion chamber. Hydrazine based fuels can decompose exothermally as a monopropellant and also enter into bipropellant reactions with any excess oxidizer in the combustion chamber. It is concluded that the conversion of the thruster from MMH to hydrazine fuel is feasible but that a number of changes would be required to achieve the same safety margins as the monomethylhydrazine-fueled thruster
Evaluation of the SSRCS engine with hydrazine as a fuel, phase 2
Test firing of the Space Shuttle Reaction Control Thruster (SSRCT) was conducted to determine the characteristic velocity and chamber throat temperatures when the fuel is changed from monomethylhydrazine (MMH) to hydrazine. Thruster performance with hydrazine was essentially as predicted. Characteristic velocity at a mixture ratio of 1.4 (equal volumetric flow) for hydrazine was 5180 feet/second compared with 5110 feet/second at a mixture of 1.6 for MMH. Specific impulse with 22:1 nozzle is calculated to be 280 lbf-sec/lbm. Thermal performance, as measured by chamber throat temperature, was dramatically different (colder) than predicted. Throat temperatures of 2330 F were predicted from a cooling model which assumed a reactive liquid cooling film. Throat temperatures of 800 - 1000 F were measured. An attempt to reconcile the differences between film cooling predictions and the measurements, indicated that an evaporation (nonreactive fluid) model rather than a decomposition (reactive fluid) model best fits the test data at 0/F = 1.4. At higher mixture ratios, a transition to temperatures typical of the reactive fluid model were observed
Prejudice and effective anti-bullying intervention: Evidence from the bullying of "minorities"
The tradition of research into school bullying, and the development of anti-bullying intervention programmes in Norway, has had a significant influence upon similar efforts being made in other countries. However, recent evaluations of the effectiveness of school-based anti-bullying interventions have revealed mixed and most often modest levels of success. This in turn has led to suggestions being made in Norway that rather than to continue support for a direct approach to the issue of school bullying, making improvements in the "learning environment" should be prioritized; however, it is argued here that there is, as yet, no body of direct evidence to directly confirm that position. Instead, it is contended that research into school bullying has been limited to the conceptualization of bullying as being purely a sub-set of aggression, and that anti-bullying intervention has been, consequently, focused largely on purely behaviour management solutions. From recent studies on specific forms of bullying of minority groups (lesbian, gay and bisexual young people, ethnic minorities, people with disabilities or special educational needs and members of alternative sub-cultures), it appears that prejudice is at least influential on specific patterns of bullying behaviour, but has not received sufficient attention in either the conceptualization of bullying or the design of programmes to prevent and counter it. Hence, rather than scaling down direct anti-bullying intervention efforts, it is suggested that subsequent research and programme design could be re-focused in order to give a greater consideration to prejudice as an underlying factor. © 2014 The Editors of Nordic Psychology
Worker injuries involving the interaction of cattle, cattle handlers, and farm structures or equipment
Citation: Fox, S., Ricketts, M., & Minton, J. E. (2015). Worker injuries involving the interaction of cattle, cattle handlers, and farm structures or equipment. Journal of Agricultural Safety and Health, 21(1), 3-12. doi:10.13031/jash.21.10221Cattle have been identified as leading sources of injuries to agricultural workers. The present study focused on worker injuries that involved the interaction of cattle, cattle handlers, and farm structures or equipment. The goal of the study was to identify opportunities for injury prevention. We examined 221 reports of injury to cattle handlers from the Consumer Product Safety Commission's National Electronic Injury Surveillance System (NEISS). Expected interactions led to many of the cattle-handling injuries reported in the NEISS database. In almost 30% of cases, cattle pushed workers into structures such as fences, gates, posts, and walls. In another 16% to 19% of injuries, cattle struck gates and other objects, propelling them at the victims. The present research makes several important contributions to the study of cattle-handling injuries. First, the research supports an increased emphasis on the development of safer gate designs (e.g., gates that are remotely operated or that absorb energy to limit the speed at which they may be propelled by animals). Second, the research suggests a need for additional study of energy-absorbing fence and wall structures. We view these two points to be of significance because gates and associated structures (e.g., posts, fences, and walls) accounted for 45% of the injuries in the dataset, based on the associated injury narrative. Finally, the research identifies a previously unexplored source of agricultural injury data, namely the NEISS database. © 2015 ASABE
Active Learning with Multiple Views
Active learners alleviate the burden of labeling large amounts of data by
detecting and asking the user to label only the most informative examples in
the domain. We focus here on active learning for multi-view domains, in which
there are several disjoint subsets of features (views), each of which is
sufficient to learn the target concept. In this paper we make several
contributions. First, we introduce Co-Testing, which is the first approach to
multi-view active learning. Second, we extend the multi-view learning framework
by also exploiting weak views, which are adequate only for learning a concept
that is more general/specific than the target concept. Finally, we empirically
show that Co-Testing outperforms existing active learners on a variety of real
world domains such as wrapper induction, Web page classification, advertisement
removal, and discourse tree parsing
Gas-Surface Dynamics and Profile Evolution during Etching of Silicon
Scattering of energetic F atoms on a fluorinated Si surface is studied by molecular beam methods. The energy transfer closely follows hard-sphere collision kinematics. Energy and angular distributions of unreacted F atoms suggest significant multiple-bounce scattering in addition to single-bounce scattering and trapping desorption. An empirical model of the atom-surface interaction dynamics is used in a Monte Carlo simulation of topography evolution during neutral beam etching of Si. Model predictions of profile phenomena are validated by experiments
International Space Station ECLSS Technical Task Agreement Summary Report
A summary of work accomplished under Technical Task Agreement by the Marshall Space Flight Center (MSFC) documents activities regarding the Environmental Control and Life Support Systems (ECLSS) of the International Space Station (ISS) program. These MSFC activities were in-line to the designing, the development, the testing, and the flight of ECLSS equipment. MSFC's unique capabilities for performing integrated system testing and analyses, and its ability to perform some tasks cheaper and faster to support ISS program needs are the basis for the Technical Task Agreement activities. Tasks were completed in the Water Recovery Systems, Air Revitalization Systems, and microbiology areas. The results of each task is described in this summary report
A New Approach for Sampling Ordered Parameters in Probabilistic Sensitivity Analysis
Background
Probabilistic sensitivity analysis (PSA) in cost-effectiveness analysis involves sampling a large number of
realisations of an economic model. For some parameters, we may be uncertain around the true mean values of
the variables, but the ordering of the values is known. Typical sampling approaches lack either statistical or
clinical validity. For example, sampling using a common number generator results in extreme dependence and
independent sampling can lead to realisations with incorrect ordering.
Methods
We propose a new sampling approach for ordered parameters, the Difference Method approach, which samples
the parameters of interest via a difference parameter. If the parameters of interest are bounded, it involves
transforming the variables so that they are unbounded and then sampling via the difference parameter. We have
provided an Excel workbook to implement the method. The proposed approach is illustrated with an example
sampling ordered parameters for utility and cost.
Results
The DM approach has a number of advantages when comparing with the typical approaches used in practice.
The DM approach generates PSA samples which have similar summary statistics as the given values in our
examples whilst maintaining the constraint that one value was greater than another. The method also implies
plausible positive correlation between the two ordered variables.
Conclusions
Both clinical and statistical validity should be checked when producing PSA samples. The DM approach should
be considered as a solution to potential problems in generating PSA samples for ordered parameters
- …