CSM Testbed Development and Large-Scale Structural Applications

A research activity called Computational Structural Mechanics (CSM) conducted at the NASA Langley Research Center is described. This activity is developing advanced structural analysis and computational methods that exploit high-performance computers. Methods are developed in the framework of the CSM Testbed software system and applied to representative complex structural analysis problems from the aerospace industry. An overview of the CSM Testbed methods development environment is presented and some new numerical methods developed on a CRAY-2 are described. Selected application studies performed on the NAS CRAY-2 are also summarized

Game Theoretical Interactions of Moving Agents

Game theory has been one of the most successful quantitative concepts to describe social interactions, their strategical aspects, and outcomes. Among the payoff matrix quantifying the result of a social interaction, the interaction conditions have been varied, such as the number of repeated interactions, the number of interaction partners, the possibility to punish defective behavior etc. While an extension to spatial interactions has been considered early on such as in the "game of life", recent studies have focussed on effects of the structure of social interaction networks. However, the possibility of individuals to move and, thereby, evade areas with a high level of defection, and to seek areas with a high level of cooperation, has not been fully explored so far. This contribution presents a model combining game theoretical interactions with success-driven motion in space, and studies the consequences that this may have for the degree of cooperation and the spatio-temporal dynamics in the population. It is demonstrated that the combination of game theoretical interactions with motion gives rise to many self-organized behavioral patterns on an aggregate level, which can explain a variety of empirically observed social behaviors

Standardization of Postoperative Care Guidelines for Pediatric Cleft Palate Patients

At a large, community-based pediatric hospital in Southern California, a quality improvement project commenced with a goal to improve patient outcomes by decreasing length of stay and pain levels, while increasing toleration of feeds. Implementing a standardized guideline would ensure safe practice across the continuum and allow providers to use a systematic tool for postoperative care, including nursing care interventions and medications. The Root-Cause-Analysis tool was used to assess the microsystem and determine the contributing factors to the identified problem. A SWOT analysis was then performed, followed by a plan to collect data from all pediatric cleft palate procedures performed at the hospital within the last year. The data collected included all necessary actions that took place upon patient’s exit from surgery. Patient exclusion criteria included PICU admits and those with cleft palate repair resulting from injury. The patients that fell within the exclusion criteria were excluded due to the increased risk and complications that these conditions bear. Considerations for care guideline use include: congenital abnormalities of the heart, brain, or gastrointestinal system as well as those with hematology or oncology conditions and developmental delays. Research was then performed on the patient information found from chart audits, in order to verify the best practices following postoperative cleft palate repair. Ultimately, research on the impact of care guidelines on postoperative cleft palate repair versus physician preference yielded a recommendation for the development of standardized care guidelines, however, the results showed that additional steps are needed to evaluate the results of this implementation on length of stay, pain levels, and time of first tolerated feed

Standardization of Postoperative Care Guidelines for Pediatric Cleft Palate Patients

At a large, community-based pediatric hospital in Southern California, a quality improvement project commenced with a goal to improve patient outcomes by decreasing length of stay and pain levels, while increasing toleration of feeds. Implementing a standardized guideline would ensure safe practice across the continuum and allow providers to use a systematic tool for postoperative care, including nursing care interventions and medications. The Root-Cause- Analysis tool was used to assess the microsystem and determine the contributing factors to the identified problem. A SWOT analysis was then performed, followed by a plan to collect data from all pediatric cleft palate procedures performed at the hospital within the last year. The data collected included all necessary actions that took place upon patient’s exit from surgery. Patient exclusion criteria included PICU admits and those with cleft palate repair resulting from injury. The patients that fell within the exclusion criteria were excluded due to the increased risk and complications that these conditions bear. Considerations for care guideline use include: congenital abnormalities of the heart, brain, or gastrointestinal system as well as those with hematology or oncology conditions and developmental delays. Research was then performed on the patient information found from chart audits, in order to verify the best practices following postoperative cleft palate repair. Ultimately, research on the impact of care guidelines on postoperative cleft palate repair versus physician preference yielded a recommendation for the development of standardized care guidelines, however, the results showed that additional steps are needed to evaluate the results of this implementation on length of stay, pain levels, and time of first tolerated feed

A Search for Very Low-mass Stars and Brown Dwarfs in the Young sigma Orionis Cluster

We present a CCD-based photometric survey covering 870 sq. arcmin in a young stellar cluster around the young multiple star sigma Orionis. Our survey limiting R, I, and Z magnitudes are 23.2, 21.8, and 21.0, respectively. From our colour-magnitude diagrams, we have selected 49 faint objects, which smoothly extrapolate the photometric sequence defined by more massive known members. Adopting the currently accepted age interval of 2-10 Myr for the Orion 1b association and considering recent evolutionary models, our objects may span a mass range from 0.1 down to 0.02 Msun, well within the substellar regime. Follow-up low-resolution optical spectroscopy (635-920 nm) for eight of our candidates (I=16-19.5) shows that they have spectral types M6-M8.5 which are consistent with the expectations for true members. Compared with their Pleiades counterparts of similar types, Halpha emission is generally stronger, while NaI and KI absorption lines appear weaker, as expected for lower surface gravities and younger ages. Additionally, TiO bands and in particular VO bands appear clearly enhanced in our candidate with the latest spectral type, SOri 45 (M8.5, I=19.5), compared to objects of similar types in older clusters and the field. We have estimated the mass of this candidate at only 0.020-0.040 Msun, hence it is one of the least massive brown dwarfs yet discovered. We also discuss in this paper the potential role of deuterium as a tracer of both substellar nature and age in very young clusters.Comment: Accepted for publication in ApJ Main Journal. 32 pages of text and tables + 9 pages of figures. Figures 3a and 3b (gif format) provided separatel

Learning and innovative elements of strategy adoption rules expand cooperative network topologies

Cooperation plays a key role in the evolution of complex systems. However, the level of cooperation extensively varies with the topology of agent networks in the widely used models of repeated games. Here we show that cooperation remains rather stable by applying the reinforcement learning strategy adoption rule, Q-learning on a variety of random, regular, small-word, scale-free and modular network models in repeated, multi-agent Prisoners Dilemma and Hawk-Dove games. Furthermore, we found that using the above model systems other long-term learning strategy adoption rules also promote cooperation, while introducing a low level of noise (as a model of innovation) to the strategy adoption rules makes the level of cooperation less dependent on the actual network topology. Our results demonstrate that long-term learning and random elements in the strategy adoption rules, when acting together, extend the range of network topologies enabling the development of cooperation at a wider range of costs and temptations. These results suggest that a balanced duo of learning and innovation may help to preserve cooperation during the re-organization of real-world networks, and may play a prominent role in the evolution of self-organizing, complex systems.Comment: 14 pages, 3 Figures + a Supplementary Material with 25 pages, 3 Tables, 12 Figures and 116 reference

Crust-core interactions and the magnetic dipole orientation in neutron stars

We develop an effective model for a neutron star with a magnetosphere. It takes into account the electromagnetic torques acting on the magnetic dipole, the friction forces between the crust and the core, and the gravitational corrections. Anomalous electromagnetic torques, usually neglected in a rigid star model, play here a crucial role for the alignement of the magnetic dipole. The crust-core coupling time implied by the model is consistent with the observational data and other theoretical estimations. This model describes the main features of the behavior of the magnetic dipole during the life of the star, and in particular gives a natural explanation for the n<3 value of the breaking index in a young neutron star.Comment: 23 pages, 1 figur

Anomalous metamagnetism in the low carrier density Kondo lattice YbRh3Si7

We report complex metamagnetic transitions in single crystals of the new low carrier Kondo antiferromagnet YbRh3Si7. Electrical transport, magnetization, and specific heat measurements reveal antiferromagnetic order at T_N = 7.5 K. Neutron diffraction measurements show that the magnetic ground state of YbRh3Si7 is a collinear antiferromagnet where the moments are aligned in the ab plane. With such an ordered state, no metamagnetic transitions are expected when a magnetic field is applied along the c axis. It is therefore surprising that high field magnetization, torque, and resistivity measurements with H||c reveal two metamagnetic transitions at mu_0H_1 = 6.7 T and mu_0H_2 = 21 T. When the field is tilted away from the c axis, towards the ab plane, both metamagnetic transitions are shifted to higher fields. The first metamagnetic transition leads to an abrupt increase in the electrical resistivity, while the second transition is accompanied by a dramatic reduction in the electrical resistivity. Thus, the magnetic and electronic degrees of freedom in YbRh3Si7 are strongly coupled. We discuss the origin of the anomalous metamagnetism and conclude that it is related to competition between crystal electric field anisotropy and anisotropic exchange interactions.Comment: 23 pages and 4 figures in the main text. 7 pages and 5 figures in the supplementary materia

Communication Research

Contains reports on seven research projects.Rockefeller FoundationCarnegie Foundatio