The free-piston engine generator(FPEG)is regarded as the next generation of energy conversion system which may replace traditional engines in the future.The effect of key operational parameters like excess air ratio o...The free-piston engine generator(FPEG)is regarded as the next generation of energy conversion system which may replace traditional engines in the future.The effect of key operational parameters like excess air ratio of input mixture and ignition position on the engine performance of a dual-cylinder FPEG was investigated,and their sensitivity was analyzed in this paper.The operating compression ratio of the system is susceptible to changes in excess air ratio and ignition position.At the same time,it decreases from 15.8 to 6.6 when excess air ratio increases from 0.85 to 1.15,but it increases from 6.1 to 13.3 as ignition position increases from 15 mm to 20 mm.The operating frequency and indicated power are more sensitive to changes in excess air ratio than ignition position.But it is the opposite for the indicated thermal efficiency and friction loss.Excess air ratio and ignition position have a quite similar influence on heat transfer.Therefore,from the perspective of system operation and performance,it is preferable to keep excess air coefficient slightly below 1.0.In contrast,when selecting ignition position,it is of great importance to comprehensively consider the risk of structural damage caused by the increase in the compression ratio and in-cylinder gas pressure.展开更多
Petermann Glacier is a marine-terminating outlet glacier that had a 70 km-long floating ice tongue prior to a ～ 270 km2 calving event that was observed from satellite sensors in August 2010,shortening the ice tongue ...Petermann Glacier is a marine-terminating outlet glacier that had a 70 km-long floating ice tongue prior to a ～ 270 km2 calving event that was observed from satellite sensors in August 2010,shortening the ice tongue by ～ 27 km.Further,in July 2012,another 10 km was lost through calving.In order to understand these events in perspective,here the authors perform a long-term data analysis of Petermann Glacier calving-front variability and ice velocity for each year in the 1990s-2000s,supplemented by available observations from the previous three decades.Five major （on the order of 100 krm2） calving events are identified,with ～ 153 km2 calved from 1959 to 1961,～ 168 km2 in 1991,～ 71 km2 in 2001,～ 270 km2 in 2010,and ～ 130 km2 in 2012-as well as ～ 31 k m2 calved in 2008.The increased frequency of major calving events in recent years has left the front terminus position retreated nearly 25 km beyond the range of observed in previous decades.In contrast,stable ice-dynamics are suggested from ice-velocity measurements made each year between 1993-2012,which are on average 1063 m yr-1,with limited interannual variability and no significant trend; moreover,there is no apparent relationship between ice-velocity variability and calving events.The degree to which the massive calving events in 2010 and 2012 represent natural episodic variability or a response to atmospheric and/or oceanic changes remains speculative; however,melt-induced weakening of the floating ice tongue in recent years is strongly suggested.展开更多
Let k, m and n be three positive integers such that 2^m= 1 （mod n） and k ≥ 2. The Bouwer graph, which is denoted by B（k,m,n）, is the graph with vertex set {（a,b） ｜ a ∈Zm, b ∈Zn×…×Zn} k-1 times and...Let k, m and n be three positive integers such that 2^m= 1 （mod n） and k ≥ 2. The Bouwer graph, which is denoted by B（k,m,n）, is the graph with vertex set {（a,b） ｜ a ∈Zm, b ∈Zn×…×Zn} k-1 times and two vertices being adjacent if they can be written as （a,b） and （a＋ 1,c）, where either c ： b or c = （cl,c2 …,ck-1） differs from b = （b1, b2,…, bk-1） in exactly one position, say the jth position, where cj = bj ＋ 2^a. Every B（k, m, n） is a vertex- and edge-transitive graph, and Bouwer proved that B（k, 6, 9） is half-arc-transitive for every k ≥ 2. In 2016, Conder and Zitnik gave the classification of half-arc-transitive Bouwer graphs. In this paper, the full automorphism group of every B（k, m, n） is determined.展开更多
基金Projects(51675043,52005038)supported by the National Natural Science Foundation of China。
文摘The free-piston engine generator(FPEG)is regarded as the next generation of energy conversion system which may replace traditional engines in the future.The effect of key operational parameters like excess air ratio of input mixture and ignition position on the engine performance of a dual-cylinder FPEG was investigated,and their sensitivity was analyzed in this paper.The operating compression ratio of the system is susceptible to changes in excess air ratio and ignition position.At the same time,it decreases from 15.8 to 6.6 when excess air ratio increases from 0.85 to 1.15,but it increases from 6.1 to 13.3 as ignition position increases from 15 mm to 20 mm.The operating frequency and indicated power are more sensitive to changes in excess air ratio than ignition position.But it is the opposite for the indicated thermal efficiency and friction loss.Excess air ratio and ignition position have a quite similar influence on heat transfer.Therefore,from the perspective of system operation and performance,it is preferable to keep excess air coefficient slightly below 1.0.In contrast,when selecting ignition position,it is of great importance to comprehensively consider the risk of structural damage caused by the increase in the compression ratio and in-cylinder gas pressure.
基金supported by the Trond Mohn Donation to the Mohn-Sverdrup Center at the Nansen Center,the Research Council of Norway’s UK/Netherlands/Norway RAPID programthe project AWAKE under the Polish-Norwegian Research Fund(2009–2011)
文摘Petermann Glacier is a marine-terminating outlet glacier that had a 70 km-long floating ice tongue prior to a ～ 270 km2 calving event that was observed from satellite sensors in August 2010,shortening the ice tongue by ～ 27 km.Further,in July 2012,another 10 km was lost through calving.In order to understand these events in perspective,here the authors perform a long-term data analysis of Petermann Glacier calving-front variability and ice velocity for each year in the 1990s-2000s,supplemented by available observations from the previous three decades.Five major （on the order of 100 krm2） calving events are identified,with ～ 153 km2 calved from 1959 to 1961,～ 168 km2 in 1991,～ 71 km2 in 2001,～ 270 km2 in 2010,and ～ 130 km2 in 2012-as well as ～ 31 k m2 calved in 2008.The increased frequency of major calving events in recent years has left the front terminus position retreated nearly 25 km beyond the range of observed in previous decades.In contrast,stable ice-dynamics are suggested from ice-velocity measurements made each year between 1993-2012,which are on average 1063 m yr-1,with limited interannual variability and no significant trend; moreover,there is no apparent relationship between ice-velocity variability and calving events.The degree to which the massive calving events in 2010 and 2012 represent natural episodic variability or a response to atmospheric and/or oceanic changes remains speculative; however,melt-induced weakening of the floating ice tongue in recent years is strongly suggested.
基金This work was partially supported by the National Natural Science Foundation of China （11671030） and the Fundamental Research Funds for the Central Universities （2015JBM110）.
文摘Let k, m and n be three positive integers such that 2^m= 1 （mod n） and k ≥ 2. The Bouwer graph, which is denoted by B（k,m,n）, is the graph with vertex set {（a,b） ｜ a ∈Zm, b ∈Zn×…×Zn} k-1 times and two vertices being adjacent if they can be written as （a,b） and （a＋ 1,c）, where either c ： b or c = （cl,c2 …,ck-1） differs from b = （b1, b2,…, bk-1） in exactly one position, say the jth position, where cj = bj ＋ 2^a. Every B（k, m, n） is a vertex- and edge-transitive graph, and Bouwer proved that B（k, 6, 9） is half-arc-transitive for every k ≥ 2. In 2016, Conder and Zitnik gave the classification of half-arc-transitive Bouwer graphs. In this paper, the full automorphism group of every B（k, m, n） is determined.
