21,324 research outputs found

    Curve Shortening and the Rendezvous Problem for Mobile Autonomous Robots

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    If a smooth, closed, and embedded curve is deformed along its normal vector field at a rate proportional to its curvature, it shrinks to a circular point. This curve evolution is called Euclidean curve shortening and the result is known as the Gage-Hamilton-Grayson Theorem. Motivated by the rendezvous problem for mobile autonomous robots, we address the problem of creating a polygon shortening flow. A linear scheme is proposed that exhibits several analogues to Euclidean curve shortening: The polygon shrinks to an elliptical point, convex polygons remain convex, and the perimeter of the polygon is monotonically decreasing.Comment: 15 pages, 18 figure

    Status of the AIAA Modeling and Simulation Format Standard

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    The current draft AIAA Standard for flight simulation models represents an on-going effort to improve the productivity of practitioners of the art of digital flight simulation (one of the original digital computer applications). This initial release provides the capability for the efficient representation and exchange of an aerodynamic model in full fidelity; the DAVE-ML format can be easily imported (with development of site-specific import tools) in an unambiguous way with automatic verification. An attractive feature of the standard is the ability to coexist with existing legacy software or tools. The draft Standard is currently limited in scope to static elements of dynamic flight simulations; however, these static elements represent the bulk of typical flight simulation mathematical models. It is already seeing application within U.S. and Australian government agencies in an effort to improve productivity and reduce model rehosting overhead. An existing tool allows import of DAVE-ML models into a popular simulation modeling and analysis tool, and other community-contributed tools and libraries can simplify the use of DAVE-ML compliant models at compile- or run-time of high-fidelity flight simulation

    Benefits to the Simulation Training Community of a New ANSI Standard for the Exchange of Aero Simulation Models

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    The American Institute of Aeronautics Astronautics (AIAA) Modeling and Simulation Technical Committee is in final preparation of a new standard for the exchange of flight dynamics models. The standard will become an ANSI standard and is under consideration for submission to ISO for acceptance by the international community. The standard has some a spects that should provide benefits to the simulation training community. Use of the new standard by the training simulation community will reduce development, maintenance and technical refresh investment on each device. Furthermore, it will significantly lower the cost of performing model updates to improve fidelity or expand the envelope of the training device. Higher flight fidelity should result in better transfer of training, a direct benefit to the pilots under instruction. Costs of adopting the standard are minimal and should be paid back within the cost of the first use for that training device. The standard achie ves these advantages by making it easier to update the aerodynamic model. It provides a standard format for the model in a custom eXtensible Markup Language (XML) grammar, the Dynamic Aerospace Vehicle Exchange Markup Language (DAVE-ML). It employs an existing XML grammar, MathML, to describe the aerodynamic model in an input data file, eliminating the requirement for actual software compilation. The major components of the aero model become simply an input data file, and updates are simply new XML input files. It includes naming and axis system conventions to further simplify the exchange of information

    Stochastic Dominance in Wheat Variety Development and Release Strategies

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    Variety development and release decisions involve tradeoffs between yields and characteristics valued by end-users, as well as uncertainties about agronomic, quality, and economic variables. In this study, methods are developed to determine the value of varieties to growers and end-users including the effects of variability in economic, agronomic, and quality variables. The application is to hard red spring (HRS) wheat, a class of wheat for which these tradeoffs and risks are particularly apparent. Results indicate two experimental varieties provide improvements in grower and end-user value, relative to incumbents. Stochastic dominance techniques and statistical tests are applied to determine efficient sets and robustness of the results. A risk-adjusted portfolio model, which simultaneously incorporates correlations between grower and end-use characteristics, is also developed to compare the portfolio value of varieties.end-user value, grower value, portfolio value, stochastic dominance, tradeoffs, variety development, wheat, Crop Production/Industries,

    A Discontinuity in the Distribution of Fixed Point Sums

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    The quantity f(n,r)f(n,r), defined as the number of permutations of the set [n]={1,2,...n}[n]=\{1,2,... n\} whose fixed points sum to rr, shows a sharp discontinuity in the neighborhood of r=nr=n. We explain this discontinuity and study the possible existence of other discontinuities in f(n,r)f(n,r) for permutations. We generalize our results to other families of structures that exhibit the same kind of discontinuities, by studying f(n,r)f(n,r) when ``fixed points'' is replaced by ``components of size 1'' in a suitable graph of the structure. Among the objects considered are permutations, all functions and set partitions.Comment: 1 figur

    Relationship between depressive symptom severity and emergency department use among low-income, depressed homebound older adults aged 50 years and older

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    Namkee G. Choi, and C. Nathan Marti are with The University of Texas at Austin, Austin, TX, USA. -- Martha L. Bruce is with the Weill Cornell Medical College, White Plains, NY, USA. -- Mark E. Kunik is with the VA HSRD Houston Center of Excellence, Michael E. DeBakey VA Medical Center, Houston, TX, USA, and Baylor College of Medicine, Houston, TX, USA, and VA South Central Mental Illness Research, Education and Clinical Center, Houston, TX, USA.Background: Previous research found a high prevalence of depression, along with chronic illnesses and disabilities, among older ED patients. This study examined the relationship between depressive symptom severity and the number of ED visits among low-income homebound older adults who participated in a randomized controlled trial of telehealth problem-solving therapy (PST). Methods: The number of and reasons for ED visits were collected from the study participants (n=121 at baseline) at all assessment points—baseline and 12- and 24-week follow-ups. Depressive symptoms were measured with the 24-item Hamilton Rating Scale for Depression (HAMD). All multivariable analyses examining the relationships between ED visits and depressive symptoms were conducted using zero-inflated Poisson regression models. Results: Of the participants, 67.7% used the ED at least once and 61% of the visitors made at least one return visit during the approximately 12-month period. Body pain (not from fall injury and not including chest pain) was the most common reason. The ED visit frequency at baseline and at follow-up was significantly positively associated with the HAMD scores at the assessment points. The ED visit frequency at follow-up, controlling for the ED visits at baseline, was also significantly associated with the HAMD score change since baseline. Conclusions: The ED visit rate was much higher than those reported in other studies. Better education on self-management of chronic conditions, depression screening by primary care physicians and ED, and depression treatment that includes symptom management and problem-solving skills may be important to reduce ED visits among medically ill, low-income homebound adults. Trial registration ClinicalTrials.gov Identifier: NCT00903019Psycholog

    Progress Toward a Format Standard for Flight Dynamics Models

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    In the beginning, there was FORTRAN, and it was... not so good. But it was universal, and all flight simulator equations of motion were coded with it. Then came ACSL, C, Ada, C++, C#, Java, FORTRAN-90, Matlab/Simulink, and a number of other programming languages. Since the halcyon punch card days of 1968, models of aircraft flight dynamics have proliferated in training devices, desktop engineering and development computers, and control design textbooks. With the rise of industry teaming and increased reliance on simulation for procurement decisions, aircraft and missile simulation models are created, updated, and exchanged with increasing frequency. However, there is no real lingua franca to facilitate the exchange of models from one simulation user to another. The current state-of-the-art is such that several staff-months if not staff-years are required to 'rehost' each release of a flight dynamics model from one simulation environment to another one. If a standard data package or exchange format were to be universally adopted, the cost and time of sharing and updating aerodynamics, control laws, mass and inertia, and other flight dynamic components of the equations of motion of an aircraft or spacecraft simulation could be drastically reduced. A 2002 paper estimated over $ 6 million in savings could be realized for one military aircraft type alone. This paper describes the efforts of the American Institute of Aeronautics and Astronautics (AIAA) to develop a standard flight dynamic model exchange standard based on XML and HDF-5 data formats

    National Transonic Facility status

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    The National Transonic Facility (NTF) was operational in a combined checkout and test mode for about 3 years. During this time there were many challenges associated with movement of mechanical components, operation of instrumentation systems, and drying of insulation in the cryogenic environment. Most of these challenges were met to date along with completion of a basic flow calibration and aerodynamic tests of a number of configurations. Some of the major challenges resulting from cryogenic environment are reviewed with regard to hardware systems and data quality. Reynolds number effects on several configurations are also discussed

    ESTIMATING CORN YIELD RESPONSE MODELS TO PREDICT IMPACTS OF CLIMATE CHANGE

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    Projections of the impacts of climate change on agriculture require flexible and accurate yield response models. Typically, estimated yield response models have used fixed calendar intervals to measure weather variables and omitted observations on solar radiation, an essential determinant of crop yield. A corn yield response model for Illinois crop reporting districts is estimated using field data. Weather variables are time to crop growth stages to allow use of the model if climate change shifts dates of the crop growing season. Solar radiation is included. Results show this model is superior to conventionally specified models in explaining yield variation in Illinois corn.Crop Production/Industries,

    Higher Education Collaboratives for Community Engagement and Improvement

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    Our society is in a period of dramatic change with the transition from an industrial-based to a knowledge-based economy, as well as technological advances, fiscal challenges of higher education, and cultural shifts in society as a whole. Increasing collaborations between communities and universities in order to influence the public good becomes paramount during this time of dramatic change. As frustratingly slow as the movement to strengthen the relationship between higher education and society sometimes seems to be, few social institutions are better situated than colleges and universities to stimulate significant community improvement. Individually and collectively, institutions of higher education possess considerable resources—human, fiscal, organizational, and intellectual— which are critical to addressing significant social issues. Additionally, these institutions are physically rooted in their communities. Therefore, investing in the betterment of their immediate environments is good for both the community and the institution. However, it is recognized that higher education institutions often fall short of making a real impact in their home communities. Therefore, a conference was convened to examine the current and evolving role of higher education institutions, particularly those operating within the context of coalitions, consortia and state systems, to catalyze change on issues affecting communities and society as a whole. Specifically, the focus of the conference was to develop and strengthen an understanding of how higher education might work more effectively with communities and we believe that consortia or collaboratives of higher education institutions, along with community partners, can learn from one another. Cooperation between efforts is important. The papers offered in this monograph are the result of the Wingspread Conference on Higher Education Collaboratives for Community Engagement and Improvement, conducted on October 27-29, 2004, in Racine, Wisconsin. The conference, the second of a three-part series, was sponsored by the National Forum on Higher Education for the Public Good at the University of Michigan School of Education, the Johnson Foundation, Atlantic Philanthropies, and the W.K. Kellogg Foundation. The first conference in the series held in October 2003 and titled Public Understanding, Public Support and Public Policy focused on higher education’s role in society and the concluding conference will be held in the fall of 2005
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