17,383 research outputs found
Process engineering and development of post-combustion CO2 separation from fuels using limestone in CaO-looping cycle
No full textGlobal CO2 emissions produced by energy-related processes, mainly power plants, have increased rapidly in recent decades; and are widely accepted as the dominant contributor to the greenhouse gas (GHG) effect and consequent climate changes. Among countermeasures against the emissions, CO2 capture and storage (CCS) is receiving much attention. Capture of CO2 is the core step of CCS as it contributes around 75% of the overall cost, and may increase the production costs of electricity by over 50%. The reduction in capture costs is one of the most challenging issues in application of CCS to the energy industry. Using limestone in CaO-looping cycles is a promising capture technology to provide a cost-effective separation process to remove CO2 content from power plants operations. Limestone has the advantage of being relatively abundant and cheap, and that has already been widely used as a sorbent for sulphur capture. However, this technology suffers from a critical challenge caused by the decay in the sorbent capture capacity during cyclic carbonation/calcination, which results in the need for more sorbent make-up; hence a reduction in cost efficiency of the technology. The performance of sorbent influenced by several operating and reaction conditions. Therefore, much research involves investigation of influencing factors and different methods to reduce the sorbent deactivation. Cont/d
Selective chlorination of CaO from titania slag by CO+Cl-2 mixtures in fluidized bed
No full text
This paper presents a facile approach to selectively decrease the CaO content in titania slag from 1.09 to 0.18 wt.% under a selective chlorination atmosphere of Cl-2 and CO. Thermodynamic analysis indicated that a predominance area exists to selectively chlorinate CaO with a low reduction potential. The intrinsic chlorination kinetics indicated that both the high partial pressure of chlorine and high temperature were advantageous to increase the chlorination selectivity,of CaO. Under the guidance of the thermodynamic and intrinsic kinetics, selective chlorination kinetics of CaO from titania slag were conducted at 1173-1273 K and were represented by the pore-blocking rate law. The present study indicated that a high concentration of reactant gases with a low reduction potential at high temperature could simultaneously overcome the inner mass transfer resistance while maintaining a high chlorination selectivity. The optimized partial pressures of Cl-2 and CO were 0.8 and 0.2 atm, respectively, and the temperature was 1273 K. (C) 2016 Elsevier B.V. All rights reserved.</p
Burmadactylus tenuicerci Fan & Gu & Cao 2023, sp. nov.
No full textBurmadactylus tenuicerci sp. nov. urn:lsid:zoobank.org:act: 0DF8451E-7121-4B2D-9328-64E458B68B8B Material. Holotype, LNU-22, gender unknown, a nearly complete specimen, including the head, prothoracic leg, mesothoracic leg, metathoracic leg and terminal abdomen. The specimen is in fair condition, covered by a large crack from the head to the end of the abdomen. Locality and horizon. Hukawng Valley, Kachin Province, Myanmar; lowermost Cenomanian, Upper Cretaceous. Description. Holotype, LNU-22 (Fig. 1), gender unknown, body 3.12 mm long measured from the head to the abdominal apex; pronotum 0.7 mm long at midline; profemur 0.6 mm long; protibia 0.5 mm long; mesofemur 1.1 mm long; mesotibia1.0 mm long; metafemur 2.1 mm long; metatibia 1.8 mm long. The specimen is in fair condition, covered by a large fissure from the head to the end of the abdomen. Head. Hypognathous, capsulate; compound eyes large and well developed; ocelli invisible; antennae moniliform, 7 segments visible, flagellomere widening towards apex, inserted beneath the lower margin of the compound eyes (Fig. 1A, D). Thorax. The thorax dark brown; pronotum large, shield-like, extending posteriorly to entirely cover the metanotum; posterior margin of pronotum broadly rounded; tegmen and hindwing absent (Fig. 1A, D). Leg. Prothoracic leg brown; profemur slender, distinctly shorter than mesothoracic leg; protibia robust, apex slightly inflated, with a sparse covering of thick setae and four strong teeth; protarsus two-segmented, slender, with second segment longer than first; basitarsus short; apical tarsomere elongate, slightly curved, with two claws. Mesothoracic leg brown; mesofemur slender, curved, over twice as long as the profemur, basally narrow and apically broad, with sparse setae on the ventral margins; mesotibia almost as long as mesofemur, middle inflated, with dorsal and ventral setae; mesotarsus almost identical to the protarsus. Metathoracic leg dark, saltatorial; metafemur slightly longer than abdomen and greatly inflated along its entire length, with prominent dorsal carina; metafemur mostly obscured by cracks, ventral with several irregularly spaced setae (Fig. 1A, D); metatibia slightly shorter than metafemur, very slender, with tiny spines on the dorsal margins, without setae, lacking swimming plates, with two small subapical spurs and longer apical spurs; metatarsus slightly over twice as long as apical spurs, with a subapical denticular process; metatarsus ventral with sparse setae (Fig. 1C, F). Abdomen. The abdomen dark brown, with sparse and long setae; dorsal of abdomen obscured by cracks; subgenital plate broad, without styli, bearing a marginal fringe of long setae; cercus long, with numerous long setae, two-segmented, the second segment longer and distinctly slender than the first; paraproctal lobe cone-shaped, relatively small, almost the same as the first segment of cercus, covered with sparse setae, one of the setae near the apex thick and long (Fig. 1B, E). Diagnosis. The new species is similar to Burmadactylus grimaldi Heads, 2009. The major differences are listed in Table 1. Etymology. The specific epithet is from the Latin ‘tenui’ and ‘cercus’, used to describe the slender and elongated second segment of cercus in Burmadactylus. Remarks. Owing to the metatarsus of this specimen with a subapical denticular process, it should be assigned in Dentridactylinae Günther, 1979. B. tenuicerci sp. nov. is distinguished from other fossil Dentridactylinae species by presence of small paraproctal lobe which are much longer (as long as the cercus) in other members of the subfamily (Azar & Nel, 2008; Poinar, 2020). This new species can be assigned to Burmadactylus Heads, 2009 by the following characters: paraproctal lobe small, conical shape; swimming plates absent; margin of subgenital plate with long setae; metatarsus slightly over twice as long as apical spurs. The differences between the new species and the type species B. grimaldii Heads, 2009 are demonstrated in the Table 1.Published as part of Fan, Shilv, Gu, Jun-Jie & Cao, Chengquan, 2023, A new species of the genus Burmadactylus Heads, 2009 from mid-Cretaceous amber in north Myanmar (Orthoptera: Caelifera: Tridactyloidea), pp. 595-598 in Zootaxa 5306 (5) on pages 596-597, DOI: 10.11646/zootaxa.5306.5.7, http://zenodo.org/record/807332
Dossier : les 18 plus grandes fortunes Chinoises
No full textYufen Cao, Fan Wang, Jacquet Raphaël. Dossier : les 18 plus grandes fortunes Chinoises. In: Perspectives chinoises, n°7, 1992. pp. 32-34
Querying big data with bounded data access
No full textQuery answering over big data is cost-prohibitive. A linear scan of a dataset D may
take days with a solid state device if D is of PB size and years if D is of EB size. In
other words, polynomial-time (PTIME) algorithms for query evaluation are already
not feasible on big data. To tackle this, we propose querying big data with bounded
data access, such that the cost of query evaluation is independent of the scale of D.
First of all, we propose a class of boundedly evaluable queries. A query Q is boundedly
evaluable under a set A of access constraints if for any dataset D that satisfies
constraints in A, there exists a subset DQ ⊆ D such that (a) Q(DQ) = Q(D), and (b) the
time for identifying DQ from D, and hence the size |DQ| of DQ, are independent of |D|.
That is, we can compute Q(D) by accessing a bounded amount of data no matter how
big D grows.We study the problem of deciding whether a query is boundedly evaluable
under A. It is known that the problem is undecidable for FO without access constraints.
We show that, in the presence of access constraints, it is decidable in 2EXPSPACE for
positive fragments of FO queries, but is already EXPSPACE-hard even for CQ.
To handle the undecidability and high complexity of the analysis, we develop effective
syntax for boundedly evaluable queries under A, referred to as queries covered
by A, such that, (a) any boundedly evaluable query under A is equivalent to a query
covered by A, (b) each covered query is boundedly evaluable, and (c) it is efficient to
decide whether Q is covered by A. On top of DBMS, we develop practical algorithms
for checking whether queries are covered by A, and generating bounded plans if so.
For queries that are not boundedly evaluable, we extend bounded evaluability
to resource-bounded approximation and bounded query rewriting using views.
(1) Resource-bounded approximation is parameterized with a resource ratio a ∈ (0,1],
such that for any query Q and dataset D, it computes approximate answers with an
accuracy bound h by accessing at most a|D| tuples. It is based on extended access constraints
and a new accuracy measure. (2) Bounded query rewriting tackles the problem
by incorporating bounded evaluability with views, such that the queries can be exactly
answered by accessing cached views and a bounded amount of data in D. We study the
problem of deciding whether a query has a bounded rewriting, establish its complexity
bounds, and develop effective syntax for FO queries with a bounded rewriting.
Finally, we extend bounded evaluability to graph pattern queries, by extending
access constraints to graph data. We characterize bounded evaluability for subgraph
and simulation patterns and develop practical algorithms for associated problems
Effect of CaO content in raw material on the mineral composition of ferric-rich sulfoaluminate clinker
No full textFerric-rich calcium sulfoaluminate (FR-CSA) cement is an eco-friendly cement. Fe2O3 exists in different minerals of FR-CSA clinker, e.g., Ca4Al2Fe2O10 (C4AF), Ca2Fe2O5 (C2F), and Ca4Al6-2xFe2xSO16 (C4A3-xFxS-). The mineral composition depends on the chemical composition of the raw materials and significantly determines the reactivity of FR-CSA cement. To optimize the phase composition of the FR-CSA clinker, chemical reagent raw mixtures with different amounts of CaO were used to prepare the FR-CSA clinker. X-ray diffraction (XRD) analysis, Rietveld quantitative phase analysis (RQPA), Fourier Transform Infrared spectroscopy (FT-IR), and scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS) were used to identify the mineralogical conditions of the FR-CSA clinker. The results indicated that the amounts of CaO in raw materials greatly affected the iron-bearing phase formation in the FR-CSA clinker. With decreasing CaO content involved in calcination reaction, the amounts of Fe2O3 incorporated in C4A3-xFxS- increased up to 17.72 wt% (where x = 0.36). The findings make it possible to optimize the mineral composition of the FR-CSA clinker by changing the CaO content in raw materials. Furthermore, low CaO content in the raw material is beneficial to the formation of C4A3-xFxS-, which enables the use of solid wastes containing low calcium for producing FR-CSA cement.Accepted author manuscriptMaterials and Environmen
Computational study of aero- and acoustic performance of a small axial-flow fan
No full textThis study aims to predict the overall aerodynamic performance, unsteady forces and the tonal noise radiation from a small axial flow fan. The computation is divided into two stages: (a) the computation of the unsteady flow field at design and off-design working conditions, and (b) detailed analysis of the acoustic field. A dual-time scheme for dealing with rotor-stator or wakestruts interactions in turbomachinery environments by introducing a pseudo-time to represent the time variation of source terms and the finite volume control method are applied for the unsteady solutions involving the whole flow passages of the axial flow fan, and the pressure rise against volume flow rate is obtained and shown to be in good agreement with experimental data. The interaction of the rotor wake and the downstream struts has been simulated by investigating the effects of source distribution over the whole blades. And the tonal noise is then predicted based on Lowson’s theory. The unsteady force is divided into thrust in the rotational axis direction and drag in the rotational direction for the rotor and struts. It is demonstrated that the unsteady forces acting on the rotor and struts are produced by the interaction between them, and has a close relationship with the rotor wake structure and the strut alignment. In the rotor near wake, both the viscous and potential flow is dominant not only to aerodynamic forces but also to interaction noise. The present study shows that the higher lean angle of struts can gain about 4 dB reduction of overall sound power level compared to the smallest one
Sediment fan from culvert discharge
No full textCaption: "[WS] 694. CAO [C. A. Ohlander]. Beaver Creek. Sediment fan below campground stream at upper corner.
Dossier : les 18 plus grandes fortunes chinoises
No full textYufen Cao, Fan Wang, Zhen Xu, Chaudière Hélène. Dossier : les 18 plus grandes fortunes chinoises. In: Perspectives chinoises, n°8-9, 1992. pp. 59-61
A 40 Gb/s indoor optical wireless system enabled by a cyclically arranged optical beamsteering receiver
No full textIndoor optical wireless communication with optical beamsteering capability is currently attracting a lot of attention. One major two-dimensional (2D) optical beamsteering scheme is realized by 2D grating or its active counterpart, which is usually based on a spatial light modulator (SLM). However, there is a fundamental trade-off between the field of view (FoV) and power efficiency due to the inherent feature of gratings. In this Letter, we propose a new class of 2D beamsteering, named cyclically arranged optical beamsteering (CAO-BS), which can break that trade-off. Traditional 2D gratings extend the optical beam in the Cartesian coordinates (1D grating in horizontal + 1D grating in vertical), while CAO-BS extends the optical beam in the polar coordinates (1D grating + angular rotation). Since only 1D grating is engaged, the power efficiency increases with the number of grating lobes reduced. In the polar coordinates, the angle rotation tuning in a SLM is quasi-continuous in a full 2휋2π range. The CAO-BS is demonstrated at the receiving end in an indoor experimental system. The FoV is 18° by 360° in polar coordinates without any additional mechanical parts. Based on the CAO-BS, 40 Gbit/s on-off keying data is also successfully transmitted over 1 km single-mode fiber and 0.5 m free space
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