Approach for the determination of heat transfer coefficients for filling process of pressure vessels with compressed gaseous media

Paper presented at the 6th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 30 June - 2 July, 2008.For fast and effective simulation of filling processes of pressure vessels with compressed gaseous media the governing equations are derived from a mass balance equation for the gas and from energy balance equations for the gas and the wall of the vessel. For simplicity the gas is considered as a perfectly mixed phase and two heat transfer coefficients are introduced. The first one is the mean heat transfer coefficient between the gas and the inner surface of the pressure vessel and the second one is the heat transfer coefficient between outer surface of the vessel and the surroundings. Although the process is transient, steady-state heat transfer coefficients for free convection are used between outer surface of the vessel and the surroundings. The use of available correlations for steady-state heat transfer coefficients to describe transient processes is common practice, e.g. in the modelling of the transient behaviour of heat exchangers [1]. But no correlations – neither steady-state nor transient – are available for the heat transfer coefficient between inflowing gas and inner surface of the vessel. To solve this problem a CFD tool is used to determine the gas velocities at the vicinity of the inner surface of the vessel for a number of discrete surface elements. The results of a large amount of numerical experiments show that there exists a unique relationship between the tangential fluid velocities at the vicinity of the inner surface of the vessel and the gas velocity at the inlet. Once this unique relationship is known the complete velocity distribution at the vicinity of the inner surface can be easily calculated from the inlet velocity of the gas. The nearwall velocities at the outer limit of the boundary layer are substituted into the heat transfer correlation for external flow over flat plates. The final heat transfer coefficient is the areaweighted mean of all local heat transfer coefficients. The method is applied to the special case of filling a 70 MPa composite vessel for fuel cell vehicles with hydrogen. Because of the heat capacity of the composite wall consisting of an inner aluminium liner wrapped with carbon fibre, heat transfer from the compressed gas to the vessel wall strongly influences the temperature field of the gas which is predicted by the model and confirmed by experiments.vk201

Perception of nonnative tonal contrasts by Mandarin-English and English-Mandarin sequential bilinguals

This study examined the role of acquisition order and crosslinguistic similarity in influencing transfer at the initial stage of perceptually acquiring a tonal third language (L3). Perception of tones in Yoruba and Thai was tested in adult sequential bilinguals representing three different first (L1) and second language (L2) backgrounds: L1 Mandarin-L2 English (MEBs), L1 English-L2 Mandarin (EMBs), and L1 English-L2 intonational/non-tonal (EIBs). MEBs outperformed EMBs and EIBs in discriminating L3 tonal contrasts in both languages, while EMBs showed a small advantage over EIBs on Yoruba. All groups showed better overall discrimination in Thai than Yoruba, but group differences were more robust in Yoruba. MEBs’ and EMBs’ poor discrimination of certain L3 contrasts was further reflected in the L3 tones being perceived as similar to the same Mandarin tone; however, EIBs, with no knowledge of Mandarin, showed many of the same similarity judgments. These findings thus suggest that L1 tonal experience has a particularly facilitative effect in L3 tone perception, but there is also a facilitative effect of L2 tonal experience. Further, crosslinguistic perceptual similarity between L1/L2 and L3 tones, as well as acoustic similarity between different L3 tones, play a significant role at this early stage of L3 tone acquisition.Published versio

Identification and functional analysis of the genes encoding Δ6-desaturase from Ribes nigrum†

Gamma-linolenic acid (γ-linolenic acid, GLA; C18:3 Δ6, 9, 12) belongs to the omega-6 family and exists primarily in several plant oils, such as evening primrose oil, blackcurrant oil, and borage oil. Δ6-desaturase is a key enzyme involved in the synthesis of GLA. There have been no previous reports on the genes encoding Δ6-desaturase in blackcurrant (Ribes nigrum L.). In this research, five nearly identical copies of Δ6-desaturase gene-like sequences, named RnD8A, RnD8B, RnD6C, RnD6D, and RnD6E, were isolated from blackcurrant. Heterologous expression in Saccharomyces cerevisiae and/or Arabidopsis thaliana confirmed that RnD6C/D/E were Δ6-desaturases that could use both α-linolenic acids (ALA; C18:3 Δ9,12,15) and linoleic acid (LA; C18:2 Δ9,12) precursors in vivo, whereas RnD8A/B were Δ8-sphlingolipid desaturases. Expression of GFP tagged with RnD6C/D/E showed that blackcurrant Δ6-desaturases were located in the mitochondrion (MIT) in yeast and the endoplasmic reticulum (ER) in tobacco. GC-MS results showed that blackcurrant accumulated GLA and octadecatetraenoic acids (OTA; C18:4 Δ6,9,12,15) mainly in seeds and a little in other organs and tissues. RT-PCR results showed that RnD6C and RnD6E were expressed in all the tissues at a low level, whereas RnD6D was expressed at a high level only in seeds, leading to the accumulation of GLA and OTA in seeds. This research provides new insights to our understanding of GLA synthesis and accumulation in plants and the evolutionary relationship of this class of desaturases, and new clues as to the amino acid determinants which define precise enzyme activity

L3 acquisition of German adjectival inflection: A generative account

Studies testing the knowledge of syntactic properties have resulted in two potentially contrasting proposals in relation to third language acquisition (TLA); the Cumulative Enhancement Model (Flynn et al., 2004), which proposes that previously learned languages will positively affect the acquisition of a third language (L3); and the ‘second language (L2) status factor’ hypothesis (Bardel and Falk, 2007), which proposes that the primacy of the L2 can block the potential positive effects that may be transferable from the first language (L1). This article attempts to extend these hypotheses to the domain of morphosyntax, in relation to the TLA of the properties of grammatical number and gender concord marking on German attributive adjectives; these properties not present in the L1 of Japanese, or the L2 of English. Two further factors are of interest in the current study; first, the performance of the learners according to their L3 and their L2 proficiency levels, a variable not discussed in the above-mentioned studies; and, second, the role that the type of task has on the performance of these learners. Three groups of Japanese native speakers (matched for proficiency within each German group), but with differing English proficiencies, completed a carefully balanced gap-filling task, together with two oral elicitation tasks in the form of games; both of these elicited tokens of adjectival inflection. Initial results offer partial support for weaker versions of the two hypotheses mentioned above. However, neither of the L3 models tested can fully account for the results obtained, which are more consistent with a feature-based account of the organization of grammar in the domain of morphosyntax, such as that of Distributed Morphology (DM) (Halle and Marantz, 1993). DM is a model for language acquisition which — coupled with a view that the Subset Principle proposed by this account is not observed by non-primary language learners — has recently been proposed to explain the optionality observed in L2 learners’ production (Hawkins et al., 2006). The data presented here suggest that it could be extended to L3 learners’ production. </jats:p