3,562 research outputs found
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
A Structured Hardware/Software Architecture for Embedded Sensor Nodes
No full textOwing to the limited requirement for sensor processing in early networked sensor nodes, embedded software was generally built around the communication stack. Modern sensor nodes have evolved to contain significant on-board functionality in addition to communications, including sensor processing, energy management, actuation and locationing. The embedded software for this functionality, however, is often implemented in the application layer of the communications stack, resulting in an unstructured, top-heavy and complex stack. In this paper, we propose an embedded system architecture to formally specify multiple interfaces on a sensor node. This architecture differs from existing solutions by providing a sensor node with multiple stacks (each stack implements a separate node function), all linked by a shared application layer. This establishes a structured platform for the formal design, specification and implementation of modern sensor and wireless sensor nodes. We describe a practical prototype of an intelligent sensing, energy-aware, sensor node that has been developed using this architecture, implementing stacks for communications, sensing and energy management. The structure and operation of the intelligent sensing and energy management stacks are described in detail. The proposed architecture promotes structured and modular design, allowing for efficient code reuse and being suitable for future generations of sensor nodes featuring interchangeable components
Stężenie radonu w atmosferze w okolicy hałdy fosofgipsów w Wiślince (Pólnocna Polska)
No full textThe measurements of atmospheric radon concentration were carried out for one year
at the turn of 2008/2009, using Kodak LR 115 passive track detectors. The average atmospheric
radon activity near the phosphogypsum stack was 104 Bq m–3. This is below the
level accepted for indoor air. The results indicate that there are strong positive correlations
between radon concentration and temperature (r=0.9) or atmospheric pressure
(r=0.9) and a negative correlation between radon concentration and humidity (r=-0.7) or
wind velocity (r=-0.7). Moreover, for all monitoring points the correlation between radon
atmospheric concentrations measured in four seasons of the year were analyzed. The correlation
coefficients are as follows: winter-summer 0.7, winter-autumn 0.2, winter-spring
0.2. Influence of radon exhalation from the stack was especially distinct in winter when
the background radon activity was low. Spring and autumn farmland cultivation works
increase radon exhalation from the soil, so that the contribution of radon emitted from
the stack was less obvious.Pomiary stężenia radonu w atmosferze przeprowadzono w ciągu jednego roku, na
przełomie lat 2008/2009, z użyciem detektorów Kodak LR-115. średnie stężenie radonu
w atmosferze wynosiło 104 Bq m–3, co jest wartością poniżej dopuszczalnego stężenia tego
gazu w budynkach mieszkalnych. Wykazano silne dodatnie korelacje między stężeniem radonu
i temperaturą (r=0.9), i ciśnieniem atmosferycznym (r=0.9) oraz ujemne korelacje
między stężeniem radonu a wilgotnością powietrza (r=-0.7) oraz prędkością wiatru (r=-0.7).
Ponadto obliczono korelację między stężeniami radonu zarejestrowanymi w wyznaczonych
punktach pomiarowych w poszczególnych sezonach. Współczynniki korelacji w sezonach:
zima – lato, zima – jesień, zima – wiosna wynoszą odpowiednio: 0,7; 0,2; 0,2. Wpływ ekshalacji
radonu z hałdy na stężenie radonu w atmosferze jest szczególnie widoczny w sezonie
zimowym, w którym poza obszarami sąsiadującymi z hałdą rejestruje się najniższe w roku
stężenie tego gazu. Wiosną i jesienią prace rolnicze wpływają na wzrost ekshalacji radonu
z gruntu, przez co udział radonu, który wydostał się z hałdy, staje się mniej wyrazisty
Enumerating the number of admissible stack polygons: An approach using finite automaton
No full textLet R(H, W) be a rectangle with positively integral valued height H and width W. We consider the classes of stack polygons that can be formed inside R(H, W) in such a way that the point of origin and the base of these polygons respectively coincides with the southwest corner and the bottom portion of R(H, W). In this paper, we construct an automaton to enumerate the number of stack polygons that satisfies the above restrictions. Moreover we derive the generating function from this automaton
Deterministic stack automata and the quotient operator
No full textAbstractA stack automaton is a pushdown automaton with the added privilege of scanning the contents of its pushdown tape without erasing. In this paper, the deterministic stack automaton with a one-way input (dsa) is considered.It is shown that if L is a language accepted by a dsa and R is a regular set, then L/R={w| for some x in R, wx is in L}, is accepted by a dsa. As a corollary, end markers are not needed on the input of the dsa. It is also shown that if L is accepted by a dsa, then Max(L)={w|w in L and for no x is wx is wx in L} is accepted by a dsa
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Seismic qualification of ventilation stack
No full textThis paper describes the method to be used to qualify the 105 K ventilation stack at the U.S. Department of Energy`s Hanford Site, near Richland, Washington, under seismic and wind loadings. The stack stands at 175 ft (53.34 m), with a diameter tapering from 22 ft (6.71 m) at the foundation to 12.83 ft (3.91 m) at the top. Although the stack is classified as Safety Class 3 (low hazard), it is treated as a Safety Class 1 (high hazard) component, as failure could damage a Safety Class 1 facility (the irradiated fuel storage basin). The evaluation used U.S. Department of Energy criteria specified in UCRL 15910 (1990). The seismic responses of the stack under earthquake loading were obtained from modal analyses with response spectrum input that used the ANSYS (1989) finite-element computer code. The moments and shear forces from the results of seismic analysis were used to qualify the reinforcement capacity of the stack structure by the ultimate-strength method. The wind forces acting on the stack in both along-wind and crosswind directions were also calculated. Presented are evaluations of the soil bearing pressure, the moment, and the shear capacity of the stack foundation
The Effect of Porefill on Pre- and Post-stack Seismic Data in a Dutch Buntsandstein Reservoir
No full textWintershall is operating a number of Buntsandstein fields in the Southern North Sea. It has proven a major exploration challenge in the area to predict the reservoir quality of these fields based on seismic data only. The effect of salt present in the area plugging the pore space leads at first sight to similar seismic responses on post-stack data as for gas filled reservoirs. This study aims to gain better insight into the (subtle) differences in seismic response induced by water-, gas- or salt-fill scenario. The approach adopted is by studying the seismic response at various existing wells in one of the fields and the corresponding seismic responses of the processed 3D seismic survey. First a thorough analysis of the log responses of 13 wells is made and the effect of a.o. depth trends, compaction, diagenesis and facies changes to the seismic response is qualitatively investigated. Then, a match between the log data and the poststack seismic data is established by creating synthetic seismic data. Finally by using fluid substitution and more recent solid substitution theory, subtle changes in seismic response, both pre-stack and post-stack, between the different porefills are predicted. Based on these modeled predictions recommendations are made concerning the type of data analysis that should be carried out to discern the different porefills on the seismic data. The results of this research should lead to an improved characterization of the Buntsandstein reservoirs and as a consequence, to a higher success rate in drilling (i.e. less “dry wells”).Applied Geophysics and PetrophysicsGeotechnologyCivil Engineering and Geoscience
Równoległy pomiar temperatury akumulatorów w pojazdach elektrycznych
No full textA parallel temperature measurement system for monitoring a battery stack in an electric vehicle is presented in the paper. The proposed system utilizes parallel multi-channel temperature measurements with digital temperature sensors operating on separate serial buses. An FPGA device collects data from sensors and translates it into CAN bus frames. The CAN bus is incorporated for communication with car Battery Management System. The described system can parallel measure 8 temperatures but it can be extended in case of additional needs. The structure of the system as well as particular devices are described in the paper. Selected results of experimental investigations which show proper operation of the system are presented as well.W artykule przedstawiono system równoległego pomiaru temperatury zestawu akumulatorów stosowanego w pojazdach elektrycznych EV lub hybrydowych HEV. Podczas ładowania lub rozładowywania akumulatorów Li-ion, może dochodzić do nadmiernego nagrzewania a nawet do pożaru. Aby tego uniknąć stosuje się układy nadzorowania akumulatorów pełniące także funkcje balansowania ładunku. Takie układy potrzebują do działania informacji o temperaturze zewnątrznej poszczególnych akumulatorów. Cyfrowe czujniki temperatury wyposażone w interfejs szeregowy komunikują się z procesorem nadzorującym w sposób sekwencyjny. Przy większej liczbie czujników czas odczytu wszystkich wartości jest nadmiernie wydłużony. W prezentowanym rozwiązaniu zastosowano oddzielne magistrale szeregowe dla każdego czujnika. W związku z tym czas pełnego odczytu nie zależy od liczby czujników. Aby to było możliwe, wykorzystano układ FPGA z zaimplementowanymi interfejsami 1-Wire. Całość jest kontrolowana przez procesor programowy NIOS, który dodatkowo zapewnia komunikację z systemami pojazdu przez magistralę CAN. W artykule przedstawiono strukturę proponowanego systemu oraz zostały przedstawione wybrane wyniki badań laboratoryjnych
Portable size DMFC-stack
No full textS.219-224A small, low temperature, direct methanol fuel cell stack for portable applications has been developed. Several flow field designs were investigated with respect to stable operation and high performance. Due to carbon dioxide and water production on the anode and cathode, respectively, methanol and oxygen access to the electrodes is hindered. During single cell operation the effect of both carbon dioxide evolution and water production on the current output was observed. The difference between parallel and serial feeding of both fuel and oxidant to the DMFC stack was also investigated. It was found that it is very important to remove reaction products from the active cell surface in order to ensure stable stack operation at low temperatures. The maximal power realised with the 12-cell direct methanol fuel cell stack was 30 W.4Nr.
The stack of -zips is a Mori dream space
No full textWe first extend previous results of the author with T. Wedhorn and W.
Goldring regarding the existence of -ordinary Hasse invariants for
Hodge-type Shimura varieties to other automorphic line bundles. We also
determine exactly which line bundles admit nonzero sections on the stack of
-zips of Pink--Wedhorn--Ziegler. Then, we define and study the Cox ring of
the stack of -zips and show that it is always finitely generated. Finally,
beyond the case of line bundles, we define a ring of vector-valued automorphic
forms on the stack of -zips and study its properties. We prove that it is
finitely generated in certain cases
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