1,307 research outputs found

    What is the Jacobian of a Riemann surface with boundary?

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    We define the Jacobian of a Riemann surface with analytically parametrized boundary components. These Jacobians belong to a moduli space of ``open abelian varieties'' which satisfies gluing axioms similar to those of Riemann surfaces, and therefore allows a notion of ``conformal field theory'' to be defined on this space. We further prove that chiral conformal field theories corresponding to even lattices factor through this moduli space of open abelian varieties.Comment: 27 pages. Minor explanation and motivation added

    Laplaza Sets, or How to Select Coherence Diagrams for Pseudo Algebras

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    We define a general concept of pseudo algebras over theories and 2-theories. A more restrictive such notion was introduced by Hu and Kriz, but as noticed by M. Gould, did not capture the desired examples. The approach taken in this paper corrects the mistake by introducing a more general concept, allowing more flexibility in selecting coherence diagrams for pseudo algebras.Comment: 21 pages. To appear in the Advances of Mathematics. Exposition improved, notion of operad with degeneracies removed as a simplification, definition of pseudo algebra improved

    Although the utility of open stack systems has been widely debated, little empirical research relevant to the controversy is available. Using circula- tion, book availability, and search and library-use statistics, major elements of the direct access debate are tested in a six-year study of a library that has recently undergone the transition from closed to open stacks. Direct shelf access, it was found, contributed to an increase in library use and a decrease in c~rculation. Contrary to expectations, book availability perfor- mance also improved significantly during the study period.

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    Citation analysis was used as an aid in collection development in the field of engineering. It was found that for graduate students books are of greater importance than journals. Substantial reductions in the number o f subscrip- tions released funds for the purchase of books within the limitations of a constant dollar budget. Library usefulness appears to have been increased

    Haptic feedback in the training of veterinary students

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    This paper reports on an initial study into the use of haptic (or touch) technology in the training of veterinary students. One major problem faced in veterinary education is that animals can be harmed by inexperienced students who are trying to learn the skills they need. The aim of the work described here is to provide haptic models to simulate internal examinations of horses so that students can learn the basic skills required on computer and then transfer to real animals with much less risk of doing them injury

    The Elliptic curves in gauge theory, string theory, and cohomology

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    Elliptic curves play a natural and important role in elliptic cohomology. In earlier work with I. Kriz, thes elliptic curves were interpreted physically in two ways: as corresponding to the intersection of M2 and M5 in the context of (the reduction of M-theory to) type IIA and as the elliptic fiber leading to F-theory for type IIB. In this paper we elaborate on the physical setting for various generalized cohomology theories, including elliptic cohomology, and we note that the above two seemingly unrelated descriptions can be unified using Sen's picture of the orientifold limit of F-theory compactification on K3, which unifies the Seiberg-Witten curve with the F-theory curve, and through which we naturally explain the constancy of the modulus that emerges from elliptic cohomology. This also clarifies the orbifolding performed in the previous work and justifies the appearance of the w_4 condition in the elliptic refinement of the mod 2 part of the partition function. We comment on the cohomology theory needed for the case when the modular parameter varies in the base of the elliptic fibration.Comment: 23 pages, typos corrected, minor clarification

    Numerical Simulation and Visualization Models of Stress Wave Propagation Graphite/Epoxy Composites

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    Within the last ten years there has been a renewed interest in simulation of stress wave propagation because of the availability of fast supercomputers with large memory capabilities [1,2,3]. Only recently have a few investigators [4,5] applied these simulations to problems where elastic anisotropy was included as a major factor. The massive output of results from these simulations, together with the added complexity of coupled phenomena that uniquely exist for a given anisotropy, defies intuition. To grasp the significance of these simulations requires scientific visualization [6] of these complex physical phenomena. Such visualizations often require a movie format to better understand the physics of particular problems [7]. In this study we simulated the experimental measurement of a shift in the quasi-transverse bulk wave propagation in an off-axis unidirectional graphite/epoxy composite in plane strain [8]. The purpose of the simulation was to aid the nondestructive evaluation engineer in designing an acoustic array to improve the measurement of the shift in the QT wave propagation direction [9]. Previously a finite element model [5] was used to simulate this measurement. In this study we demonstrate the advantages of using a finite difference model to simulate this experiment and, with special visual aids, observe the physics

    A Discipline-Spanning Overview of Action Research and Its Implications for Technology and Innovation Management

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    The iterative and learning character of action research is particularly beneficial for exploring complex socio-technical problems in technology and innovation management (TIM). In this respect, action research allows both rigorous and relevant research due to parallel solving of real-world problems, capability building, and gaining scientific insights. However, the use of action research within TIM research is surprisingly limited. Action research also is not a homogeneous research methodology since each research discipline, such as education and organizational science, has its own action research streams, which are often only loosely linked. A systematic overview of those action research traditions and specific best practices is still missing, which complicates a systematic transfer and use of action research in TIM. This article addresses this essential gap by building a cross-disciplinary overview of action research streams based on a bibliometric analysis using Scopus. The analysis includes relevant disciplines with action research traditions, their development over time, and the most influential journals, authors, institutions, and countries. Along with this discipline-spanning analysis, the article investigates particular TIM benefits and challenges of action research. The two key contributions of this article are: 1) a discipline-spanning overview of action research and its evolution and 2) an analysis of its implications for TIM research. These contributions build the basis for strengthening the use of action research in TIM. In the medium-term, action research has the capacity to link academia and industry more closely and, in doing so, assists important endeavours of translating more of our research outcomes into practice

    Customer Relationship Management: Examining the Central Proposition in the Online Context

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    This paper presents a summary of a doctoral dissertation investigating the application of customer relationship management (CRM) theory to the online context. The major finding of this study was to confirm that the central proposition of CRM theory is supported in the online context—that is, while the operational context influences the extent to which effective service enhances the relationships between a firm and its customers, and their resulting perceptions of customer loyalty; there is general support for a mediating relationship in which effective service will enhance the quality of the relationship between a firm and its customer, and increase loyalty perceptions from the customer. The study has also revealed that the service delivery channel has a significant and differential affect on the central proposition and the interactions of the key relationship marketing constructs. Perceptions of financial risk were not observed to significantly affect either service quality or relationship quality perceptions

    Airborne Radar for sUAS Sense and Avoid

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    A primary challenge for the safe integration of small UAS operations into the National Airspace System (NAS) is traffic deconfliction, both from manned and unmanned aircraft. The UAS Traffic Management (UTM) project being conducted at the National Aeronautics and Space Administration (NASA) considers a layered approach to separation provision, ranging from segregation of operations through airspace volumes (geofences) to autonomous sense and avoid (SAA) technologies for higher risk, densely occupied airspace. Cooperative SAA systems, such as Automatic Dependent Surveillance-Broadcast (ADS-B) and/or vehicle-to-vehicle communication systems provide significant additional risk mitigation but they fail to adequately mitigate collision risks for non-cooperative (non-transponder equipped) airborne aircraft. The RAAVIN (Radar on Autonomous Aircraft to Verify ICAROUS Navigation) flight test being conducted by NASA and the Mid-Atlantic Aviation Partnership (MAAP) was designed to investigate the applicability and performance of a prototype, commercially available sUAS radar to detect and track non-cooperative airborne traffic, both manned and unmanned. The radar selected for this research was a Frequency Modulated Continuous Wave (FMCW) radar with 120 degree azimuth and 80 degree elevation field of view operating at 24.55GHz center frequency with a 200 MHz bandwidth. The radar transmits 2 watts of power thru a Metamaterial Electronically Scanning Array antenna in horizontal polarization. When the radar is transmitting, personnel must be at least 1 meter away from the active array to limit nonionizing radiation exposure. The radar physical dimensions are 18.7cm by 12.1cm by 4.1cm and it weighs less than 820 grams making it well suited for installation on small UASs. The onboard, SAA capability, known as ICAROUS, (Independent Configurable Architecture for Reliable Operations of Unmanned Systems), developed by NASA to support sUAS operations, will provide autonomous guidance using the traffic radar tracks from the onboard radar. The RAAVIN set of studies will be conducted in three phases. The first phase included outdoor, ground-based radar evaluations performed at the Virginia Techs Kentland Farm testing range in Blacksburg, VA. The test was designed to measure how well the radar could detect and track a small UAS flying in the radars field of view. The radar was used to monitor 5 test flights consisting of outbound, inbound and crossing routes at different ranges and altitudes. The UAS flown during the ground test was the Inspire 2, a quad copter weighing less than 4250 grams (10 pounds) at maximum payload. The radar was set up to scan and track targets over its full azimuthal field of view from 0 to 40 degrees in elevation. The radar was configured to eliminate tracks generated from any targets located beyond 2000 meters from the radar and moving at velocities under 1.45 meters per second. For subsequent phases of the study the radar will be integrated with a sUAS platform to evaluate its performance in flight for SAA applications ranging from sUAS to manned GA aircraft detections and tracking. Preliminary data analysis from the first outdoor ground tests showed the radar performed well at tracking the vehicle as it flew outbound and repeatedly maintained a track out to 1000 meters (maximum 1387 meters) until the vehicle slowed to a stop to reverse direction to fly inbound. As the Inspire flew inbound tracks from beyond 800 meters, a reacquisition time delay was consistently observed between when the Inspire exceeds a speed of 1.45 meters per second and when the radar indicated an inbound target was present and maintained its track. The time delay varied between 6 seconds to over 37 seconds for the inbound flights examined, and typically resulted in about a 200 meter closure distance before the Inspire track was maintained. The radar performed well at both acquiring and tracking the vehicle as it flew crossing routes out past 400 meters across the azimuthal field of view. The radar and ICAROUS software will be integrated and flown on a BFD-1400-SE8-E UAS during the next phase of the RAAVIN project. The main goal at the conclusion of this effort is to determine if this radar technology can reliably support minimum requirements for SAA applications of sUAS. In particular, the study will measure the range of vehicle detections, lateral and vertical angular errors, false and missed/late detections, and estimated distance at closest point of approach after an avoidance maneuver is executed. This last metric is directly impacted by sensor performance and indicates its suitability for the task
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