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As reservoirs subject to sedimentation, the dam gradually loses its ability to store water. The identification of the sources of deposited sediments is an effective and efficient means of tackling sedimentation problems. A state-of-the-art Lagrangian stochastic particle tracking model with backward–forward tracking methods is applied to identify the probable source regions of deposited sediments. An influence function is introduced into the models to represent the influence of a particular upstream area on the sediment deposition area. One can then verify if a specific area might be a probable source by cross-checking the values of influence functions calculated backward and forward, respectively. In these models, the probable sources of the deposited sediments are considered to be in a grid instead of at a point for derivation of the values of influence functions. The sediment concentrations in upstream regions must be known a priori to determine the influence functions. In addition, the accuracy of the different types of diffusivity at the water surface is discussed in the study. According to the results of the case study of source identification, the regions with higher sediment concentrations computed by only backward simulations do not necessarily imply a higher likelihood of sources. It is also shown that from the ensemble results when the ensemble mean of the concentration is higher, the ensemble standard deviation of the concentration is also increased.

We classify two types of finite groups with certain normality conditions, namely SSN groups and groups with all noncyclic subgroups normal. These conditions are key ingredients in the study of the multiplicative Jordan decomposition problem for group rings.

In this paper, we complete the classification of those finite 3-groups G whose integral group rings have the multiplicative Jordan decomposition property. If G is abelian, then it is clear that ℤ[G] satisfies the multiplicative Jordan decomposition (MJD). In the nonabelian case, we show that ℤ[G] satisfies MJD if and only if G is one of the two nonabelian groups of order 33 = 27.

If G is a finite group whose integral group ring Z [ G ] has the multiplicative Jordan decomposition property, then it is known that all Wedderburn components of the rational group ring Q [ G ] have degree at most 3. While degree 3 components can occur, we prove here that if they do, then certain central units in Z [ G ] cannot exist. With this, we are able to greatly simplify the argument that characterizes those 3-groups with integral group ring having MJD. Furthermore, we show that if G is a nonabelian semidirect product of the form C p ⋊ C 3 k , with prime p > 7 and with the cyclic 3-group acting like a group of order 3, then Z [ G ] does not have MJD.

Let p be a prime and let G be a finite p -group. We show that if the integral group ring Z [ G ] satisfies the multiplicative Jordan decomposition property, then every noncyclic subgroup of G is normal. This is used to simplify the work of Hales, Passi and Wilson on the classification of integral group rings of finite 2-groups with the multiplicative Jordan decomposition property.

The employees of an organization are usually divided into different security classes to authorize the information retrieval, and the number of leaf classes is substantially larger than the number of non-leaf classes. Additionally, the alternations in leaf classes are more frequent than in non-leaf classes. We proposed a new key assignment scheme for controlling the access right in a large POSET (partially ordered set) hierarchy to reduce the required computation for key generation and derivation with the storage amount of data decreased.

In this paper, we essentially finish the classification of those finite 2, 3-groups G having integral group rings with the multiplicative Jordan decomposition (MJD) property. If G is abelian or a Hamiltonian 2-group, then it is clear that ℤ[G] satisfies MJD. Thus, we need only consider the nonabelian case. Recall that the 2-groups with MJD were completely determined by Hales, Passi and Wilson, while the corresponding 3-groups were almost completely determined by the present authors. Thus, we are concerned here, for the most part, with groups whose order is divisible by 6. As it turns out, there are precisely three nonabelian 2, 3-groups, of order divisible by 6, with ℤ[G] satisfying MJD. These have orders 6, 12, and 24. In view of another result of Hales, Passi and Wilson, this completes a significant portion of the classification of all finite groups with MJD.

Let R be a commutative associative ring with 1 and let Der ( R ) be the Lie ring of all derivations of R. Suppose that D is a Lie subring and an R-submodule of Der ( R ) . When R is D-prime, we give necessary and sufficient conditions for D to be Lie prime. Since results of this nature are already known for rings R of characteristic different from 2, what is really new here is the characteristic 2 case.

Let F be a finite field of characteristic not 2, and S@?F a subset with three elements. Consider the collectionS={S.a+b|a,b@?F,a 0}.Then (F,S) is a simple 2-design and the parameter @l of (F,S) is 1, 2, 3 or 6. We find in this paper the full automorphism group of (F,S). Namely, if we put U={r|{0,1,r}@?S} and K the subfield of F generated by U, then the automorphisms of (F,S) are the maps of the form x@?g(@a(x))+b, x@?F, where b@?F, @a:F->F is a field automorphism fixing U, and g is a linear transformation of F considered as a vector space over K.

Let R be a prime ring and U(R) the group of units of R. We prove that if U(R) generates R and satisfies a group identity,then R is either a domain or a full matrix ring over a finite field.

Let R be a unital ring satisfying a group identity. We prove that if B is a nil subsemigroup of R, then it is locally nilpotent, and is contained in the sum of all nilpotent ideals of R, where the positive integer d is determined by the group identity. Note that the above result for PI-rings is due to Amitsur.

For convenience, a ring with units satisfying a group identity will be called a GI-ring. We show that GI-rings have the following properties which are also properites of PI-rings. (1) Any GI-ring is Dedekind finite (von Neumann finite). (2) Nilpotent elements of a semiprimitive GI-ring have bounded index. (3) The Kurosh problem has a positive answer for GI-algebras, namely, any algebraic GI-algebra is locally finite. We also study Hartley's problem for algebraic GI-algebras.

We study locally finite algebras and twisted group algebras with units satisfying a group identity. As a preliminary result, we obtain a necessary condition for twisted group algebras to satisfy a generalized polynomial identity.

The high peak-to-average power ratio (PAPR) of the output signal for the transmitter is one of the main drawbacks of orthogonal frequency division multiplexing (OFDM) systems. To properly approximate the exact peaks of the continuous-time OFDM signal, L (usually ges 4) times oversampling is generally used for the discrete-time OFDM signal in many PAPR reduction schemes. However, the oversampling process increases the computational complexity. In this paper, we propose a low-complexity PAPR estimation method-peak-search-and- partial-interpolation" (PSPI) scheme-to efficiently estimate the PAPR value for the discrete-time OFDM signal. Instead of doing L times oversampling, the proposed PSPI method interpolates the 2(L-1) neighboring samples of L times oversampling for each searched peak of the original discrete-time OFDM signal. The simulation results illustrate that the proposed PSPI method can achieve well-approximated results as good as those of the scheme with four times oversampling, but with much lower computational complexity.

We prove that an artinian Hopf algebra over a field is finite dimensional. This answers a question of Bergen.

We study units of twisted group algebras. Let G be a finite group and K be a field of characteristic p > 0. Assume that K is not algebraic over a finite field. We determine when units of K t [ G ] do not contain any nonabelian free subgroup. We also discuss what will happen when G is locally finite. For twisted group algebras of locally finite groups over any infinite field of characteristic p > 0, we characterize those twisted group algebras with units satisfying a group identity. Finally, we include a new characterization for twisted group algebras to satisfy a polynomial identity.