107,767 research outputs found
On Multi-stack Visibly Pushdown Languages
No full textWe contribute to the theory of formal languages of visibly multistack pushdown automata (MVPA). First, we show closure under the main operations and decidability of the main decision problems for the class of MVPA restricted to computations where a symbol can be popped out of a stack S only if it was pushed within the last k contexts of S, for a given k (in a context only one stack can be pushed or popped). In particular, this class turns out to be determinizable. Second, we show the closure under complement of the class of languages accepted by ordered MVPA (where the limitation is that a stack can be popped only if all the lower indexed stacks are empty). This gains decidability of universality, inclusion and equivalence for this class. As a further contribution, we compare the classes of languages accepted by different models of MVPA
DESIGN & DEVELOPMENT OF PLANAR SOLID OXIDE FUEL CELL STACK
No full textIn the present work, planar anode-supported Solid Oxide Fuel Cell short-stacks have been designed, assembled, tested and characterized. The design of the stacks and its components (frame, housing, interconnect, compressive and bonded seals) required a great attention to the materials properties (i.e. thermal expansion coefficient compatibility, durability, strength and oxidation resistance, conductivity and so on), as well as to the fluid-dynamic analysis focused on flow field and gas distribution. Then, a careful analysis was done based on a multidisciplinary approach to select the stack components materials, geometries, and dimensions; in order to assure a high performing stack at elevated temperatures with cost reduction of materials, parts manufacturing and assembly procedure. The materials selected were: Crofer®22APU for the interconnect and the frame; AISI 316L for bolts and housing; Thermiculite® 866 for the compressive seal placed between the frame and the interconnect plate; Flexible Mica Paper for the compressive seal positioned between the interconnect endplate and the housing; SiO2-CaO-Al2O3-Na2O glass-ceramic sealant for the bonded seal to join the frame with the cell. On the other hand, the stack assembly was focused on the implementation of innovative and simple procedures, which allowed power capacity scale-up in accordance to power requirements. In this work, two different stack configurations were produced: with one cell (for initial testing of the materials and fluid-dynamic selected solutions) and with three cells. It must be mentioned that all developed stacks in this research were assembled with commercial cells "ASC3" from H.C. Starck. Also, calculations at ambient temperature and 800°C were done in the stack compression system to determine the proper tightening torque to be applied: this value was 50N. Although this calculation took into consideration the loss of tightening torque at high temperatures, some marks were found in housing and micas during the stack inspection after disassembly. These marks are a clear indicator of gas leakage. Additionally, a study was carried out related to the effect of the protective Mn1.5Co1.5O4 coating deposited on interconnect surface to prevent the cathode Cr poisoning. This experiment was executed in the stack of one cell configuration. No voltage degradation was observed during the galvanostatic experiment of 360 h at 800°
Megan K. Stack, 34th Annual ODU Literary Festival
No full textMegan K. Stack has reported on war, terrorism, and political Islam from the Arab world, the Middle East and Southeast Asia since 2001. During a decade at the Los Angeles Times, she was based in Jerusalem, Cairo, Moscow and finally Beijing. Her first book, Every Man in This Village is a Liar, was drawn from her experiences covering the war on terror, and was one of the five nonfiction finalists for the National Book Award in 2010. For her coverage of Iraq she was awarded the 2007 Overseas Press Club’s Hal Boyle Award for best newspaper reporting from abroad, and was a finalist for the 2007 Pulitzer Prize in international reporting. She lives in Beijing with her husband, and is working on her next book – a novel set in contemporary Moscow
Design improvement of circular molten carbonate fuel cell stack through CFD Analysis
No full textMolten carbonate fuel cell (MCFC) is a promising technology for distributed power generation. The core of an MCFC power generation unit is the stack, where various fuel cells are connected together in series and parallel in order to obtain the desired voltage and power. Stack geometry and configuration are major engineering topics, as inhomogeneous temperature or mass fractions cause inefficient performances of the fuel cells, as efficiency and power smaller than the expected and shorter lifetime. A detailed model is a useful tool to improve stack performances, through design improvements. In this paper, a 3D model of a stack composed of 15 circular MCFC, considering heat, mass and current transfer as well as chemical and electrochemical reactions is presented. The model validation is conducted using some preliminary experimental data obtained for an MCFC stack developed in the Fabbricazioni Nucleari laboratories. These results are examined in order to improve the stack configuration. It is shown that power density may be increased of about 20% through double side feeding. In addition, the average temperature gradients in the axial direction are reduced of more than 70%. Significant reductions in the temperature gradients, especially in transversal direction, can be achieved by adjusting the mass flow rate of cathodic gas supplied to the various cell
Numerical computation for parallel plate thermoacoustic heat exchangers in standing wave oscillatory flow
No full textA simplified computational method for studying the heat transfer characteristics of parallel plate thermoacoustic heat exchangers is presented. The model integrates the thermoacoustic equations of the standard linear theory into an energy balance-based numerical calculus scheme. Details of the time-averaged temperature and heat flux density distributions within a representative domain of the heat exchangers
and adjoining stack are given. The effect of operation conditions and geometrical parameters on the heat exchanger performance is investigated and main conclusions relevant for HX design are drawn as far as fin length, fin spacing, blockage ratio, gas and secondary fluid-side heat transfer coefficients are concerned. Most relevant is that
the fin length and spacing affect in conjunction the heat exchanger behaviour and have to be simultaneously optimized to minimize thermal losses localized at the HX-stack
junctions. Model predictions fit experimental data found in literature within 36% and 49% respectively at moderate and high acoustic Reynolds numbers
Movement strategies used during fall-related activities by repeat fallers and nonrepeat fallers with Parkinson's Disease (PD) (abstract of paper presented at Society for Research in Rehabilitation, Manchester 2001)
No full textMovement strategies used during fall related activities by repeat fallers and nonrepeat fallers with Parkinson's disease (PD) E Stack, A Ashburn and K JuppBackground: Information about the movement strategies deployed by repeat fallers (RFs) during fall-related activities is limited. The aims of this study were to describe how people with PD naturally turn and reach and compare the movement strategies of RFs with those of nonrepeat fallers (NRFs).Method: Independently mobile people with PD living in the community were recruited through GPs. Their disease severity, self-assessed disability and fall history was assessed at home. How subjects turned, reached high and reached low whilst making a cup of tea was video-recorded and rated blind using a validated, reliable checklist. Results: Seventy-five subjects (48 men), median age 73 years and median Hoehn and Yahr grade III were recruited. Forty-three subjects were RFs: they had greater disease severity and self-assessed disability than NRFs. Falls reported had occurred most frequently when walking (41%) or turning (17%). When turning, forwards stepping (33%) or sideways stepping (32%) movements were common, a median of six steps was taken, 88% demonstrated reduced heel strike and 25% used support. When reaching, 75% of subjects used support, 82% aligned forwards and 69% stood with their feet parallel. RFs and NRFs moved in similar ways, but RFs had a significantly smaller base width between their feet prior to moving (p < 0.001). Increased disease severity was linked with a high number of turning steps and observed instability.Conclusion: Surprisingly, the RFs were not distinguishable from NRFs by the way they moved during common fall-related activities. Rather, the small base area and apparent instability during functional activity should be targeted for intervention
Joshua Davis: Author of Spare Parts
No full textCitation: K-State First (2016). Joshua Davis: Author of Spare Parts [Flier]. Manhattan, Kansas: K-State First.Flyer advertising Joshua Davis's author talk at Kansas State University
How people with Parkinson's disease describe their difficulties in turning
No full textBackground: People with Parkinson’s disease (PD) fall more frequently than healthy elderly people (Nevitt et al,1989). Turning has been identified as an activity frequently associated with falls among people with PD (Stack and Ashburn, 1999). As part of a larger study comparing turning strategies used by repeat fallers and non-repeat fallers, participants were asked a series of questions about falling and turning. The aim of the study was to increase the understanding of the difficulties people with PD experience while turning and how they have attempted to overcome these difficulties.Method: Cross-sectional study of a community sample of 75 people with consultant-diagnosed PD. All subjects were independently mobile and were screened for cognitive impairment using the Middlesex Elderly Assessment of Mental State. Interviews took place in the participants’ own homes. Participants were asked how many times they had fallen in the previous 12 months and on the basis of this answer were categorised as repeat fallers or non-repeat fallers. They were asked to describe their location, activity at the time and suspected cause of each reported fall. In addition, participants were asked whether they experienced difficulty in turning, if they had consciously modified the way they turned and if they believed any modification made was successful. Contents of the interviews were categorised by two researchers.Results: Of the 75 participants, 32 were non-repeat fallers and 43 repeat fallers. Turning was identified as the second most common activity during which a reported fall had occurred (17%) after walking (41%). After loss of balance (21%), turning was identified as the second most common cause of the fall (14%). Difficulty in turning was reported by 45% of non-repeat fallers and 82% of repeat fallers. The most common difficulties experienced while turning were freezing (27%), falling (27%) and loss of balance (25%).32% of non-repeat fallers and 61% of repeat fallers said they had attempted to modify the way they turned. Over 80% of all participants considered their modifications successful. Modifications included slowing down (22%), concentrating (20%) and holding on (17%).Conclusion: As previously shown, people with PD who have fallen frequently report turning as a causative factor. We have highlighted some of the reasons why turning can be difficult for people with PD and the modifications they have made to their movement strategies in an attempt to overcome these difficulties. What remains to be understood is which movement strategies used by people with PD when turning are beneficial stabilising adaptations and which are associated with an increased risk of falling
Steven Johnson Author Talk Poster
No full textK-State Book NetworkA poster advertising an author talk by Steven Johnson at Kansas State University on September 3, 2014. Steven Johnson's book "The Ghost Map" was the 2014-2015 common book
Algorithmic Debugging of Real-World Haskell Programs: Deriving Dependencies from the Cost Centre Stack
No full textExisting algorithmic debuggers for Haskell require a transformation of all modules in a program, even libraries that the user does not want to debug and which may use language features not supported by the debugger. This is a pity, because a promising ap- proach to debugging is therefore not applicable to many real-world programs. We use the cost centre stack from the Glasgow Haskell Compiler profiling environment together with runtime value observations as provided by the Haskell Object Observation Debugger (HOOD) to collect enough information for algorithmic debugging. Program annotations are in suspected modules only. With this technique algorithmic debugging is applicable to a much larger set of Haskell programs. This demonstrates that for functional languages in general a simple stack trace extension is useful to support tasks such as profiling and debugging
- …
