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91.
92.
Semra Pamuk 《代数通讯》2013,41(7):3220-3243
Let G be a finite group and ? be a family of subgroups of G closed under conjugation and taking subgroups. We consider the question whether there exists a periodic relative ?-projective resolution for ? when ? is the family of all subgroups H ≤ G with rk H ≤ rkG ? 1. We answer this question negatively by calculating the relative group cohomology ?H*(G, 𝔽2) where G = ?/2 × ?/2 and ? is the family of cyclic subgroups of G. To do this calculation we first observe that the relative group cohomology ?H*(G, M) can be calculated using the ext-groups over the orbit category of G restricted to the family ?. In second part of the paper, we discuss the construction of a spectral sequence that converges to the cohomology of a group G and whose horizontal line at E 2 page is isomorphic to the relative group cohomology of G. 相似文献
93.
94.
We introduce (n+1)-preprojective algebras of algebras of global dimension n. We show that if an algebra is n-representation-finite then its (n+1)-preprojective algebra is self-injective. In this situation, we show that the stable module category of the (n+1)-preprojective algebra is (n+1)-Calabi–Yau, and, more precisely, it is the (n+1)-Amiot cluster category of the stable n-Auslander algebra of the original algebra. In particular this stable category contains an (n+1)-cluster tilting object. We show that even if the (n+1)-preprojective algebra is not self-injective, under certain assumptions (which are always satisfied for n∈{1,2}) the results above still hold for the stable category of Cohen–Macaulay modules. 相似文献
95.
Ulrich Krause 《Journal of Difference Equations and Applications》2013,19(4):343-356
Sufficient conditions are given under which the higher order difference equation x n+1= f(x n,x n-1,...,xn-k ), n=0,1,2,... generates an order preserving discrete dynamical system with respect to the discrete exponential ordering. It is shown that under the above monotonicity assumption the boundedness of all solutions as well as the local and global stability of an equilibrium hold if and only if they hold for the much simpler first order equation x n+1=h(x n ), where h(x)=f(x,x,…,x). As an application, a second order nonlinear difference equation from macroeconomics and a discrete analogue of a model of haematopoiesis are discussed. 相似文献
96.
AbstractThe structure of Al, Ge, Mo-doped Higher Manganese Silicide (HMS) crystals with the general formulas Mn(Si0.99Ge0.01)1.75, Mn(Si0.995Ge0.005)1.75 and (Mn0.98Mo0.02)[(Si0.98Ge0.02)1.75]0.99Al0.01 was investigated by scanning and transmission electron microscopy, electron diffraction and X-ray energy dispersive spectrometry in a wide scale range from a few mm to several Å. Several secondary phases were identified in the Mn4Si7 matrix: Ge1?xSix (0.1 < x < 0.9) solid solution precipitates with Ge concentration ranging from 5 at. % up to 93 at.%, MoSi2 platelets, MnSi and Mn5Si3 precipitates. Their morphology, structure and crystallographic relationships with the HMS matrix were determined. Mostly local strains in the matrix and precipitates due to lattice misfits at interfaces derived from crystallographic relationships were found two orders of magnitude higher than deformation induced by thermal expansion mismatch. Only a few exceptions of specific relationships were found when the lattice misfit and thermal mismatch have close values. The largest misfit of about 22% was observed between MnSi and Mn4Si7 what led to big and numerous cracks in crystals. Therefore, doping can improve the material performance (1) by preventing the formation of MnSi precipitates with metallic properties and (2) by reduction of cracking and crack propagation because of larger MnSi /Mn4Si7 lattice misfit compared to Ge1?xSix /Mn4Si7 or MoSi2/Mn4Si7 misfits. 相似文献
97.
98.
99.
In this paper we have analyzed the Kaluza-Klein type Robertson Walker (RW) cosmological models by considering three different
forms of variable Λ:
,
and Λ∼ρ. It is found that, the connecting free parameters of the models with cosmic matter and vacuum energy density parameters are
equivalent, in the context of higher dimensional space time. The expression for the look back time, luminosity distance and
angular diameter distance are also derived. This work has thus generalized to higher dimensions the well-known results in
four dimensional space time. It is found that there may be significant difference in principle at least, from the analogous
situation in four dimensional space time. 相似文献
100.
G. S. Khadekar B. Sarada Cenap Ozel 《International Journal of Theoretical Physics》2008,47(6):1542-1551
A homogeneous and isotropic Friedmann-Robertson-Walker (FRW) model with varying gravitational and cosmological constant is
studied in the context of higher dimensional space time. Exact solution of the field equations are obtained by using the “gamma
law” equation of state p=(γ−1)ρ, where γ is adiabatic parameter varies continuously as the universe expands. The functional form γ which is assumed to be the function of scale factor R as proposed by Carvalho (1996) is used to analyse the behavior of scale factor R, cosmological constant Λ and the gravitational constant G for two different phases: inflation and radiation. The various physical aspects of the early cosmological models has also
been discussed in the framework of higher dimensional space time. 相似文献