有限Abel群的一个特征

本文证明了有限群Ｇ是Ａｂｅｌ群当且仅当Ｇ_ｒ满足下列条件：（Ⅰ） Ｇ有一个幂自同构 ａ使得 ＣＧ（ａ）是一个初等 ＡｂｅｌＺ一群．（Ⅱ）Ｇ没有子群与２－群＜ａ,ｂ｜ａ~２~ｎ＝ｂ~２~ｍ＝１,ａ~ｂ＝ａ~（１＋２）~（ｎ－１）＞同构,其中ｎ≥３,ｎ≥ｍ．利用该结果,作者还证明若有限群Ｇ有一个幂自同构ａ使得Ｃ_Ｇ（ａ）是一个初等Ａｂｅｌ２－群,则Ｇ是幂零群     

Abel群环上的有限生成投射模

本文得到了有限生成投射ＲＧ－模为自由的充要条件，这里Ｂ为遗传环、零维环以及某些幂级数环，Ｇ为有限生成的Ａｂｅｌ群．     

一类3元生成的有限可解群

设Ｇ是个有限可解解，若对Ｇ的每个商群Ｈ，Ｈ的正规Ａｂｅｌ子群都是可以由２元生成的，则称Ｇ为ＡＤ２－群，在本文里，我们证明了：如果Ｇ是个ＡＤ２－群，那么Ｇ是３元生定的，且Ｇ＾（６）＝１。另外，我们举了２个例子，说明这些界都是最好的。     

一类无限的多重循环群

设Ｇ是无限的多重循环群，如果对Ｇ的每个有限商群Ｇ，Ｇ的所有Ａｂｅｌ子群都是３元生成的，那么Ｇ￣（７）＝１且Ｇ是４元生成的．     

分裂扩张的稳定自同构群

本文给出有限群的分裂的Ａｂｅｌ扩张的稳定自同构群的计算．作为应用,给出了循环群的半直积的自同构群的结构,它包括了若干已知结果,如文［１］的全部结果,并解决了［１］提出的问题．     

Gn（K）的极大Abel正规子群与自同构

文献［３］－［５］确定了２是单位的某些环Ｒ上Ｇｎ（Ｒ）的自同构形式。本文确定了任意特征（包括特征２）的除环Ｋ上Ｇｎ（Ｋ）的极大Ａｂｅｌ正规子群中的共轭类。利用这些结果，进而确定了Ｇｎ（Ｋ）的自同构形式。     

关于一个组合常数的注记

本文证明了下面定理．设Ｇ是一个有限Ａｂｅｌ群，ｅ为Ｇ的元之最大阶，则对任一由Ｇ的元构成｜Ｇ｜＋ｅ－１项序列都可找到其中ｅ项和为０.     

Abel子群的阶为连续整数的有限群

本文给出了所有有限群它的Ａｂｅｌ子群的阶为连续整数的分类     

Hyperabelian群的Abel子群

本文利用Ｄｉｒｉｃｈｌｅｔ单位定理证明了：设Ｇ是个Ｈｙｐｅｒａｂｅｌｉａｎ群．若Ｇ的亏数２的次正规Ａｂｅｌ子群都是有限生成的，则Ｇ是个多重循环群，且Ｇ的Ｈｉｒｓｃｈ数ｈ（Ｇ）ｎ２＋ｎ，其中ｎ是Ｇ的亏数２的次正规Ａｂｅｌ子群的最大０－秩．这个定理进一步推广了Ｍａｌｃ＇ｅｖ关于多重循环群的著名工作［５］．     

群环上的幂自由模

本文证明了：设Ｒ为ｃｈａｒＲ≠０，Ｇ为有限生成的Ａｂｅｌ群，则：Ｐ∈Ｆ＝（ＲＧ）当且仅当ｓ＞０，使得Ｐ^ｓ∈Ｆ＝（ＲＧ）．     

Self Extending Rings

A ring R is an IPQ (isomorphic proper quotient)-ring if R ? R/A for every proper ideal A ? R. If every ideal A ? R satisfies: either R ? A or R ? R/A, then R is called an SE (self extending)-ring. It is shown that with one exception, an abelian group G is the additive group of an IPQ-ring if and only if G is the additive group of an SE-ring. The one exception is the infinite cyclic group Z. The zeroring with additive group Z is an SE-ring, but a ring with infinite cyclic additive group is not an IPQ-ring. Since the structure of the additive groups of IPQ-rings is known, the structure of the additive groups of SE-rings is completely determined.     

一类可解的（q）－群

有限群Ｇ叫（ｑ）－群，如果Ｇ中每个次正规子群均为拟正规子群，群Ｇ叫Ｅｑ－群，若Ｇ中每个子群在Ｇ中拟正规或自正规，有限群Ｇ叫内Ｅｑ－群，如果Ｇ本身不是Ｅｑ－群，但Ｇ的每个真子群是Ｅｑ－群，本文确定了Ｅｑ－群的结构与内Ｅｑ－群的分类．     

Magnus subgroups of one-relator surface groups

A one-relator surface group is the quotient of an orientable surface group by the normal closure of a single relator. A Magnus subgroup is the fundamental group of a suitable incompressible sub-surface. A number of results are proved about the intersections of such subgroups and their conjugates, analogous to results of Bagherzadeh, Brodski? and Collins in classical one-relator group theory.     

非SM-群的一类rp~3-阶群

称有限群的不可约特征标x为SM-特征标,如果x可由某个次正规子群的线性特征标诱导得到.称有限群为SM-群,如果有限群的所有不可约特征标均为SM-特征标.通过一个例子,将说明rp~3-阶群不一定是SM-群.     

阿贝尔群与极大类p-群的半直积的Coleman自同构

设G=A\×P是阿贝尔群$A$与极大类p -群P的半直积,其中P中的元以幂自同构的方式作用于A. 该文证明了G的每个Coleman自同构都是内自同构.作为该结果的一个直接推论, 作者得到了这样的群$G$有正规化子性质.     

L-模糊正规子群之间的对应定理

群G的一个L-模糊正规子群A的陪集做成的群G／A与群G的一个商群是自然同构的。如果f：G→G’是群的满同态，则G’的L-模糊正规子群做成的群与G的在f的核上取定值的L-模糊正规子群做成的群之间存在一个保序的双射。     

Three examples of pseudocompact quasitopological groups

A quasitopological group is an abstract group with topology in which the inversion and all translations are continuous. We show that a pseudocompact quasitopological group of countable cellularity need not be a Moscow space. Then we present an example of two pseudocompact quasitopological groups whose product fails to be pseudocompact, and of a pseudocompact quasitopological group that contains an infinite discrete subgroup.     

A group ring construction of the [48,24,12] type II linear block code

A new construction of the self-dual, doubly-even and extremal [48, 24, 12] binary linear block code is given. The construction is much like that of a cyclic code from a polynomial. A zero divisor in a group ring with an underlying dihedral group generates the code. A proof that the code is of minimum distance twelve, without need to resort to computation by computer, is outlined. We also prove the code is self-dual, doubly even and that the code is an ideal in the group ring. The underlying group ring structure is used, which offers a number of useful generator matrices for the code. Interestingly, the construction involves unipotent elements within the group ring, and these lead to the creation of weighing matrices.     

Quasi-hopf algebra actions and smash products

A classical result of Magnus asserts that a free group F has a faithful representation in the group of units of a ring of non-commuting formal power series with integral coefficients. We generalize this result to the category of A-groups, where A is an associative ring or an Abelian group. We say that a free A-group F^A has a faithful Magnus representation if there is a ring B containing A as an additive subgroup (or a subring) such that F^A is faithfully represented (exactly as in Magnus' classical result in the case A = Z)in the group of units of the ring of formal power series in non-communting indeterminater over B.The three principal results are: (I) If A is a torsion free Abelian group and F^A is a free A-groupp of Lyndon' type, then F^A has a faithful Magnus representation; (II) If A is an ω‐residually Z ring, then F^A has a faithful Magnus representation;(III) for every nontrivial torsion-free Abelian group A, F^A has a faithful Magnus representation in B[[Y]] for a suitable ring B in and only if F^Q has a faithful Magnus representation in Q[[Y]].     

Effects of group sensitivity on cooperation in N-person snowdrift game with dynamic grouping

In nature and society, individuals are often tempted to exploit free-riding opportunities. Previous studies have shown that, without additional measures like spatially restricted interactions and costly punishment, defection should be more prevalent than cooperation. By incorporating group sensitivity and size adjustable interacting groups into the N-person snowdrift game, we have studied the coevolution of the preferred group sizes and the frequencies of cooperators. It is found that the widespread of cooperation is closely related to the degree of an individual’s group sensitivity. In comparison with a weak or a strong sensitivity, a moderate group sensitivity can greatly promote cooperation. With the rise of the group sensitivity, the step-like changes of the frequencies of cooperators and the average preferred group sizes are found. A theoretical analysis reveals that an individual’s group sensitivity may lead to a decrease in the preferred group size and accordingly an increase in cooperation. A functional relation between the frequencies of cooperators and the average preferred group sizes is found.