3,373 research outputs found

    Branching Avoidance in Kinematic Image Space for Linkage Synthesis

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    We consider a finite position synthesis and branching avoidance of four-bar linkages based on kinematic theory derived from dual quaternions. The branching defect is defined as a situation where all specified task positions are not connected by a continuous motion of the linkage end effector. The workspace of a four-bar linkage is derived to be the intersection of two hyperboloids in the kinematic image space. This is used to develop a fast method to determine branching of a linkage and to find an explicit solution to the end effector trajectory. A new synthesis method is developed where one task position is given a lower priority. Using the new branching analysis method and by synthesizing linkages with various values of one parameter of the linkage, we can determine a range of values for the constrained dimension which will give useful linkages for the four most prioritized task positions. Finally a method to find the closest useful linkage to the last task position is derived.Vi betraktar syntes och grendefekten av fyrlÀnks-mekanismer utifrÄn ett bergÀnsat antal task-positioner, baserat pÄ kinematisk teori hÀrledd frÄn duala kvarternioner. Grendefekten Àr definierad som situationen dÀr alla specificerade task-positionerna inte Àr sammankopplade av en kontinuerlig rörelse av mekanismens end-effector. ArbetsomrÄ det av en fyrlÀnks-mekanism Àr hÀrlett som snittet mellan tvÄ hyperboloider i det kinematiska bildrummet. Detta anvÀnds för att utveckla en snabb metod för att avgöra om grendefekten föreligger för mekanismen, och för att hÀrleda en explicit lösning för mekanismens end effector trajektoria. En ny syntes-metod Àr utvecklad dÀr en av task-positionerna Àr given en lÀgre prioritet. Genom att anvÀnda den nya grendefektsanalys-metoden och berÀkna lÀnk-mekanismer med varierande vÀrden av mekanismens parametrar, kan vi hitta ett intervall av vÀrden pÄ parametern som ger en anvÀndbar mekanism för de första fyra task-positionerna. Slutligen hÀrleder vi en metod för att avgöra vilket vÀrde pÄ parametern som ger den lÀnk-mekanism som nÄr nÀrmast den lÀgre prioriterade task-positionen

    Fast all-optical nuclear spin echo technique based on EIT

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    We demonstrate an all-optical Raman spin echo technique, using Electromagnetically Induced Transparency (EIT) to create the different pulses of the spin echo sequence: initialization, pi-rotation, and readout. The first pulse of the sequence induces coherence directly from a mixed state, and the technique is used to measure the nuclear spin coherence of an inhomogeneously broadened ensemble of rare-earth ions (Pr3+^{3+}). In contrast to previous experiments it does not require any preparatory hole burning pulse sequences, which greatly shortens the total duration of the sequence. The effect of the different pulses is characterized by quantum state tomography and is compared with simulations. We demonstrate two applications of the technique by using the spin echo sequence to accurately compensate a magnetic field across our sample, and to measure the coherence time at high temperatures up to 11 K, where standard preparation techniques are difficult to implement. We explore the potential of the technique and possible applications.Comment: 8 pages, 6 figure

    Considerations in Future Development of the IIASA Forest Sector Project: Model Structure, Product Demand Models, Product Category Definition, Geographical Aggregation, and Data Availability

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    The Forest Sector Project at IIASA has advanced to the stage of producing an embryonic prototype model. The prototype is intended to serve as a guide for development of detailed individual or multi-country models of the forest sector, which is one of the principal objectives of the Forest Sector Project. The current prototype model is intended as a first approximation and therefore lacks detail within any given module. Further, no firm decisions have been made on the procedures to be employed in pursuit of the Project's second major objective, the analysis of global trade in forest products. It is appropriate at this stage, therefore, to begin a more detailed consideration of some of the fundamental decisions which must be made in the future development of the Project. This paper is intended to serve as a stimulus for further discussion, and ultimately decisions, on options for modeling the forest sector at the national and global levels. It addresses four broad topics thought to be crucial at this stage of project development: (1) the overall direction and organization of the Forest Sector Project at IIASA, (2) definitions of product categories and the specific degree of geographical aggregation to be employed in the analysis of global trade, (3) alternatives for modeling the critical elements of demand for forest products in both detailed country and global trade studies, an (4) problems of data availability and consistency which will likely be encountered as work on the Forest Sector Project proceeds

    Real-time precipitation suppression in video streams

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    In surveillance cameras rain and snow can introduce an unwelcome noise to the video stream. The resulting effect of the rain becomes bright streaks in the frames of the video. These streaks can disturb human viewers and image processing algorithms. Rain streaks can be hard to detect and remove as they are a very dynamic phenomenon dependent on camera settings and weather conditions. This thesis aims to research some already invented rain removal algorithms and compare and evaluate them. Surveillance cameras supply video in real-time so it is not possible to access the whole video and perform heavy computations relying on information from the future. Qualities such as level of streak suppression and time required to perform necessary calculations are weighed against each other

    Spectroscopy and level detuning of few-electron spin states in parallel InAs quantum dots

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    We use tunneling spectroscopy to study the evolution of few-electron spin states in parallel InAs nanowire double quantum dots (QDs) as a function of level detuning and applied magnetic field. Compared to the much more studied serial configuration, parallel coupling of the QDs to source and drain greatly expands the probing range of excited state transport. Owing to a strong confinement, we can here isolate transport involving only the very first interacting single QD orbital pair. For the (2,0)-(1,1) charge transition, with relevance for spin-based qubits, we investigate the excited (1,1) triplet, and hybridization of the (2,0) and (1,1) singlets. An applied magnetic field splits the (1,1) triplet, and due to spin-orbit induced mixing with the (2,0) singlet, we clearly resolve transport through all triplet states near the avoided singlet-triplet crossings. Transport calculations, based on a simple model with one orbital on each QD, fully replicate the experimental data. Finally, we observe an expected mirrored symmetry between the 1-2 and 2-3 electron transitions resulting from the two-fold spin degeneracy of the orbitals.Comment: 17 pages, 8 figure

    Motion planning in observations space with learned diffeomorphism models

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    We consider the problem of planning motions in observations space, based on learned models of the dynamics that associate to each action a diffeomorphism of the observations domain. For an arbitrary set of diffeomorphisms, this problem must be formulated as a generic search problem. We adapt established algorithms of the graph search family. In this scenario, node expansion is very costly, as each node in the graph is associated to an uncertain diffeomorphism and corresponding predicted observations. We describe several improvements that ameliorate performance: the introduction of better image similarities to use as heuristics; a method to reduce the number of expanded nodes by preliminarily identifying redundant plans; and a method to pre-compute composite actions that make the search efficient in all directions

    Collaboration for Innovation - a study in the Öresund Region

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    We have made a thesis about Collaboration for Innovation in the Öresund region from a Swedish perspective. The thesis is taking both regional and corporate aspects into consideration when studying this subject. The empiric material is based upon several interviews with persons having knowledge about our subject as well as a web survey including 49 companies situated in the Öresund region. We have been able to divide our findings into two kinds of problems: Structure- and Process problems. The analyze is partialy based upon the Triple- and Penta-Helix models

    Farming systems education: Case study of Swedish test pilots

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    We describe and analyze a pedagogical experiment that introduced a broad and holistic perspective on complete farming systems, systemic learning tools, and a participatory learning strategy at an early stage in agronomy education. The paper describes the adventure of three students, who came from a conventional agronomy program at the Swedish University of Agricultural Sciences (SLU), who were frustrated with the lack of integrated approaches to the study of agricultural systems and a strong focus on molecular-level processes in their first year of education. They encountered a narrow focus in most courses and the overall curricula of agricultural education that is a function of specialization and university organization in unique departments that concentrate on small pieces of the large puzzle, that is the production milieu. In the current educational environment, it is difficult for students to make connections, integrate information and theories, and to create relevance to the challenges they observe in the practical world of farming and food systems. The three students agreed to put on pilots’ costumes and climb into an experimental vehicle called experiential learning, one that provides just-in-time education and a very high degree of self-responsibility for the learning process. The paper describes, analyzes, and evaluates the comprehensive and exhausting pedagogical process they followed in one semester in Sweden and Viet Nam, with positive and negative aspects of the program. We provide reflective recommendations from students and advisors for future agronomic education programs with the focus on developing renewable agriculture, selecting students and evaluating performance, and designing practical programs that will motivate highly committed and action-oriented students

    Forest floor bryophyte and lichen diversity in Scots pine and Norway spruce production forests

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    Bryophytes and lichens are two main components of the forest floor vegetation. They provide essential ecosystem services, including nutrient recycling and water regulation. Here, we contrast the species richness, cover and community composition of forest floor bryophytes and lichens in Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) dominated production forests. The study sites were located in the hemiboreal zone of southern Sweden, and represented early-, mid- and late rotation stands. Our aim was to examine the potential consequences for forest floor biodiversity from the decreasing use of Scots pine production forests in this region.Whereas Scots pine and Norway spruce stands did not differ in bryophyte cover, we found a higher cover of lichens in Scots pine stands, and highest in the intermediate aged stands. Also the species richness of lichens was higher in the Scots pine stands, while bryophyte species richness was higher in the Norway spruce stands. Differences in canopy cover and associated light transmittance to the forest floor appears to be important drivers for distinctive different forest floor communities in the Scots pine and Norway spruce stands, as revealed by NonMetric Multidimensional Scaling (NMDS). Mean Ellenberg indicator values for bryophytes and lichens showed that species associated with Scots pine stands were characterized by their tolerance of brighter conditions, higher insolation, and better adaptation to a continental climate. Norway spruce stands instead had a comparably larger proportion of species tolerating lower light, but also indicators of higher available nutrient levels, humidity, and pH. The outcome of the Ellenberg indicator species analysis, as well as the larger cover of lichens,and adaptations to drought found among some mosses, revealed that forest floor communities are shaped by different environmental factors in Scots pine and Norway spruce production stands. These environmental differences, and the quantified shifts in forest floor communities identified in this study, indicate the large shifts in understory bryophyte and lichen species composition and abundance that is likely to occur if Scots pine stands are converted to Norway spruce
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