The “greatest lake period” means that the lakes are in the stage of their maximum areas. As the paleo lake shorelines are widely distributed in the lake basins on the Tibetan Plateau, the lake areas during the “gre...The “greatest lake period” means that the lakes are in the stage of their maximum areas. As the paleo lake shorelines are widely distributed in the lake basins on the Tibetan Plateau, the lake areas during the “greatest lake period” may be inferred by the last highest lake shorelines. They are several, even tens times larger than that at present. According to the analyses of tens of lakes on the Plateau, most dating data fell into the range of 40-25 ka BP, some lasted to 20 ka BP. It was corresponded to the stage 3 of marine isotope and interstitial of last glaciation. The occurrence of maximum areas of lakes marked the very humid period on the Plateau and was also related to the stronger summer monsoon during that period.展开更多
On the base of the construction of abundant semigroups with a normal medial idempotent [14], in this paper we consider a class of naturally ordered abundant semigroups which satisfies the regularity condition and cont...On the base of the construction of abundant semigroups with a normal medial idempotent [14], in this paper we consider a class of naturally ordered abundant semigroups which satisfies the regularity condition and contains a greatest idempotent. Furthermore, we give a completely description of the overall structure of such ordered semigroups via the algebraic structure of them, which generalizes known result obtained by Blyth and McFadden[3].展开更多
For nonlinear feedback shift registers （NFSRs）, their greatest common subfamily may be not unique. Given two NFSRs, the authors only consider the case that their greatest common subfamily exists and is unique. If th...For nonlinear feedback shift registers （NFSRs）, their greatest common subfamily may be not unique. Given two NFSRs, the authors only consider the case that their greatest common subfamily exists and is unique. If the greatest common subfamily is exactly the set of all sequences which can be generated by both of them, the authors can determine it by Grobner basis theory. Otherwise, the authors can determine it under some conditions and partly solve the problem.展开更多
In this paper we prove in a new way, the well known result, that Fermat’s equation a<sup>4</sup> + b<sup>4</sup> = c<sup>4</sup>, is not solvable in ℕ , when abc≠0 . To show this ...In this paper we prove in a new way, the well known result, that Fermat’s equation a<sup>4</sup> + b<sup>4</sup> = c<sup>4</sup>, is not solvable in ℕ , when abc≠0 . To show this result, it suffices to prove that: ( F 0 ): a 1 4 + ( 2 s b 1 ) 4 = c 1 4 , is not solvable in ℕ , (where a 1 , b 1 , c 1 ∈2ℕ+1 , pairwise primes, with necessarly 2≤s∈ℕ ). The key idea of our proof is to show that if (F<sub>0</sub>) holds, then there exist α 2 , β 2 , γ 2 ∈2ℕ+1 , such that ( F 1 ): α 2 4 + ( 2 s−1 β 2 ) 4 = γ 2 4 , holds too. From where, one conclude that it is not possible, because if we choose the quantity 2 ≤ s, as minimal in value among all the solutions of ( F 0 ) , then ( α 2 ,2 s−1 β 2 , γ 2 ) is also a solution of Fermat’s type, but with 2≤s−1<s , witch is absurd. To reach such a result, we suppose first that (F<sub>0</sub>) is solvable in ( a 1 ,2 s b 1 , c 1 ) , s ≥ 2 like above;afterwards, proceeding with “Pythagorician divisors”, we creat the notions of “Fermat’s b-absolute divisors”: ( d b , d ′ b ) which it uses hereafter. Then to conclude our proof, we establish the following main theorem: there is an equivalence between (i) and (ii): (i) (F<sub>0</sub>): a 1 4 + ( 2 s b 1 ) 4 = c 1 4 , is solvable in ℕ , with 2≤s∈ℕ , ( a 1 , b 1 , c 1 )∈ ( 2ℕ+1 ) 3 , coprime in pairs. (ii) ∃( a 1 , b 1 , c 1 )∈ ( 2ℕ+1 ) 3 , coprime in pairs, for wich: ∃( b ′ 2 , b 2 , b ″ 2 )∈ ( 2ℕ+1 ) 3 coprime in pairs, and 2≤s∈ℕ , checking b 1 = b ′ 2 b 2 b ″ 2 , and such that for notations: S=s−λ( s−1 ) , with λ∈{ 0,1 } defined by c 1 − a 1 2 ≡λ( mod2 ) , d b =gcd( 2 s b 1 , c 1 − a 1 )= 2 S b 2 and d ′ b = 2 s−S b ′ 2 = 2 s B 2 d b , where ( 2 s B 2 ) 2 =gcd( b 1 2 , c 1 2 − a 1 2 ) , the following system is checked: { c 1 − a 1 = d b 4 2 2+λ = 2 2−λ ( 2 S−1 b 2 ) 4 c 1 + a 1 = 2 1+λ d ′ b 4 = 2 1+λ ( 2 s−S b ′ 2 ) 4 c 1 2 + a 1 2 =2 b ″ 2 4;and this system implies: ( b 1−λ,2 4 ) 2 + ( 2 4s−3 b λ,2 4 ) 2 = ( b ″ 2 2 ) 2;where: ( b 1−λ,2 , b λ,2 , b ″ 2 )={ ( b ′ 2 , b 2 , b ″ 2 ) if λ=0 ( b 2 , b ′ 2 , b ″ 2 ) if λ=1;From where, it is quite easy to conclude, following the method explained above, and which thus closes, part I, of this article. .展开更多
高强度螺栓发生氢脆(hydrogen embrittlement,HE)和应力腐蚀(stress corrosion,SCC)事件直接威胁核电厂安全运行。该文介绍国内核电厂高强度螺栓HE和SCC问题现状,分析了失效机理、规律和控制难点,给出对策建议。在2015—2019这5年时间里...高强度螺栓发生氢脆(hydrogen embrittlement,HE)和应力腐蚀(stress corrosion,SCC)事件直接威胁核电厂安全运行。该文介绍国内核电厂高强度螺栓HE和SCC问题现状,分析了失效机理、规律和控制难点,给出对策建议。在2015—2019这5年时间里,国内核电厂共发生了 22起高强度螺栓HE和SCC事件,其中,内氢脆(internal hydrogenembrittlement,IHE)、阳极溶解型应力腐蚀(anode dissolution type of stress corrosion cracking,AD-SCC)和氢脆型应力腐蚀(hydrogen embrittlement type of stress corrosion cracking,HE-SCC)事件分别占比18%、27%和55%,与强度过高有关的事件占比55%。HE和SCC问题与时间高度关联,具有明显的慢性、偶发和随机性特征,已经成为国内核电厂高强度螺栓安全服役的主要威胁,应引起监管部门关注。长远看,建立针对高强度螺栓HE和SCC问题的行业标准、研究和使用可以有效阻断腐蚀介质到达螺栓表面的新方法、开发新型抗HE和SCC的高强度螺栓,是治理该问题的长久之策。展开更多
提出了一种RS码的快速盲识别方法。该方法基于RS码的等效二进制分组码的循环移位特性,通过欧几里德算法计算循环移位前后码字的最大公约式,根据最大公约式指数的相关性来估计码长,并快速剔除含错码字,进而利用伽罗华域的傅里叶变换(Galo...提出了一种RS码的快速盲识别方法。该方法基于RS码的等效二进制分组码的循环移位特性,通过欧几里德算法计算循环移位前后码字的最大公约式,根据最大公约式指数的相关性来估计码长,并快速剔除含错码字,进而利用伽罗华域的傅里叶变换(Galois Field Fourier Transform,GFFT)实现RS码的本原多项式和生成多项式的识别。仿真结果表明,该算法复杂度低,计算量小,在误码率为10-3的情况下,对RS码的识别概率高于90%。展开更多
基金National Key Project for Basic Research, G19980408 CAS's Project (KZ951-A1-204, KZ95T-06) for Tibetan Research IGSNRR Project
文摘The “greatest lake period” means that the lakes are in the stage of their maximum areas. As the paleo lake shorelines are widely distributed in the lake basins on the Tibetan Plateau, the lake areas during the “greatest lake period” may be inferred by the last highest lake shorelines. They are several, even tens times larger than that at present. According to the analyses of tens of lakes on the Plateau, most dating data fell into the range of 40-25 ka BP, some lasted to 20 ka BP. It was corresponded to the stage 3 of marine isotope and interstitial of last glaciation. The occurrence of maximum areas of lakes marked the very humid period on the Plateau and was also related to the stronger summer monsoon during that period.
文摘On the base of the construction of abundant semigroups with a normal medial idempotent [14], in this paper we consider a class of naturally ordered abundant semigroups which satisfies the regularity condition and contains a greatest idempotent. Furthermore, we give a completely description of the overall structure of such ordered semigroups via the algebraic structure of them, which generalizes known result obtained by Blyth and McFadden[3].
基金supported by the Natural Science Foundation of China under Grant Nos.61272042,61100202and 61170235
文摘For nonlinear feedback shift registers （NFSRs）, their greatest common subfamily may be not unique. Given two NFSRs, the authors only consider the case that their greatest common subfamily exists and is unique. If the greatest common subfamily is exactly the set of all sequences which can be generated by both of them, the authors can determine it by Grobner basis theory. Otherwise, the authors can determine it under some conditions and partly solve the problem.
文摘In this paper we prove in a new way, the well known result, that Fermat’s equation a<sup>4</sup> + b<sup>4</sup> = c<sup>4</sup>, is not solvable in ℕ , when abc≠0 . To show this result, it suffices to prove that: ( F 0 ): a 1 4 + ( 2 s b 1 ) 4 = c 1 4 , is not solvable in ℕ , (where a 1 , b 1 , c 1 ∈2ℕ+1 , pairwise primes, with necessarly 2≤s∈ℕ ). The key idea of our proof is to show that if (F<sub>0</sub>) holds, then there exist α 2 , β 2 , γ 2 ∈2ℕ+1 , such that ( F 1 ): α 2 4 + ( 2 s−1 β 2 ) 4 = γ 2 4 , holds too. From where, one conclude that it is not possible, because if we choose the quantity 2 ≤ s, as minimal in value among all the solutions of ( F 0 ) , then ( α 2 ,2 s−1 β 2 , γ 2 ) is also a solution of Fermat’s type, but with 2≤s−1<s , witch is absurd. To reach such a result, we suppose first that (F<sub>0</sub>) is solvable in ( a 1 ,2 s b 1 , c 1 ) , s ≥ 2 like above;afterwards, proceeding with “Pythagorician divisors”, we creat the notions of “Fermat’s b-absolute divisors”: ( d b , d ′ b ) which it uses hereafter. Then to conclude our proof, we establish the following main theorem: there is an equivalence between (i) and (ii): (i) (F<sub>0</sub>): a 1 4 + ( 2 s b 1 ) 4 = c 1 4 , is solvable in ℕ , with 2≤s∈ℕ , ( a 1 , b 1 , c 1 )∈ ( 2ℕ+1 ) 3 , coprime in pairs. (ii) ∃( a 1 , b 1 , c 1 )∈ ( 2ℕ+1 ) 3 , coprime in pairs, for wich: ∃( b ′ 2 , b 2 , b ″ 2 )∈ ( 2ℕ+1 ) 3 coprime in pairs, and 2≤s∈ℕ , checking b 1 = b ′ 2 b 2 b ″ 2 , and such that for notations: S=s−λ( s−1 ) , with λ∈{ 0,1 } defined by c 1 − a 1 2 ≡λ( mod2 ) , d b =gcd( 2 s b 1 , c 1 − a 1 )= 2 S b 2 and d ′ b = 2 s−S b ′ 2 = 2 s B 2 d b , where ( 2 s B 2 ) 2 =gcd( b 1 2 , c 1 2 − a 1 2 ) , the following system is checked: { c 1 − a 1 = d b 4 2 2+λ = 2 2−λ ( 2 S−1 b 2 ) 4 c 1 + a 1 = 2 1+λ d ′ b 4 = 2 1+λ ( 2 s−S b ′ 2 ) 4 c 1 2 + a 1 2 =2 b ″ 2 4;and this system implies: ( b 1−λ,2 4 ) 2 + ( 2 4s−3 b λ,2 4 ) 2 = ( b ″ 2 2 ) 2;where: ( b 1−λ,2 , b λ,2 , b ″ 2 )={ ( b ′ 2 , b 2 , b ″ 2 ) if λ=0 ( b 2 , b ′ 2 , b ″ 2 ) if λ=1;From where, it is quite easy to conclude, following the method explained above, and which thus closes, part I, of this article. .
文摘高强度螺栓发生氢脆(hydrogen embrittlement,HE)和应力腐蚀(stress corrosion,SCC)事件直接威胁核电厂安全运行。该文介绍国内核电厂高强度螺栓HE和SCC问题现状,分析了失效机理、规律和控制难点,给出对策建议。在2015—2019这5年时间里,国内核电厂共发生了 22起高强度螺栓HE和SCC事件,其中,内氢脆(internal hydrogenembrittlement,IHE)、阳极溶解型应力腐蚀(anode dissolution type of stress corrosion cracking,AD-SCC)和氢脆型应力腐蚀(hydrogen embrittlement type of stress corrosion cracking,HE-SCC)事件分别占比18%、27%和55%,与强度过高有关的事件占比55%。HE和SCC问题与时间高度关联,具有明显的慢性、偶发和随机性特征,已经成为国内核电厂高强度螺栓安全服役的主要威胁,应引起监管部门关注。长远看,建立针对高强度螺栓HE和SCC问题的行业标准、研究和使用可以有效阻断腐蚀介质到达螺栓表面的新方法、开发新型抗HE和SCC的高强度螺栓,是治理该问题的长久之策。
文摘提出了一种RS码的快速盲识别方法。该方法基于RS码的等效二进制分组码的循环移位特性,通过欧几里德算法计算循环移位前后码字的最大公约式,根据最大公约式指数的相关性来估计码长,并快速剔除含错码字,进而利用伽罗华域的傅里叶变换(Galois Field Fourier Transform,GFFT)实现RS码的本原多项式和生成多项式的识别。仿真结果表明,该算法复杂度低,计算量小,在误码率为10-3的情况下,对RS码的识别概率高于90%。
