نشریه علوم دانشگاه خوارزمی
سال سوم شماره 3 (پاییز 1382)

Let be a set and let be the set of subsets of. The pair in which is a collection of elements of (blocks) is called a design if every element of appears in, times. Is called a symmetric design if. In a symmetric design, each element of appears times in blocks of. A mapping between two designs and is an isomorphism if is a one-to-one correspondence and. Every isomorphism of a design,, to itself is called an automorphism.

Sometimes observations in statistical analysis are not independent and typically are correlated with their spatial locations. In spatial statistics there are some methods to interpolate this kind of data. In this paper some of interpolators for spatial data will be studied. Then they will be evaluated and compared by means of mean square errors criteria. Finally it will be shown that kriging acts better than other methods such as spline, inverse distance, for interpolation of spatial data

In this paper, we purpose a new algorithm for shape-based image indexing and retrieval. This new scheme efficiently extracts the image feature vector without any need to segmentation algorithms and high computation. The feature considers correlation between adjacent edges. Thus it includes information of continuous edges and lines of images and estimates shape of objects in images. With implementation of algorithms on a prototype system and using some evaluation metrics, we show the indexes are invariant relative to translation, image size, color, illumination, and small viewing positions. Experimental results show that averages of precision and recall rates of this new indexing scheme compared to other similar methods are 1.02 to 6.9 and 1.22 to 10.59 times greater respectively.

For a fixed positive integer, we say a ring with identity is n-generalized right principally quasi-Baer, if for any principal right ideal of, the right annihilator of is generated by an idempotent. This class of rings includes the right principally quasi-Baer rings and hence all prime rings. A certain n-generalized principally quasi-Baer subring of the matrix ring are studied, and connections to related classes of rings (e.g., p.q.-Baer rings and n-generalized p.p. rings) are considered1

Quasicrystals are a group of materials with the quasi-periodic structure, and since their discovery in 1980; their specially interesting physical properties have attracted the attention of many researchers. The lack of translational periodicity makes the numerical calculations of their physical properties much more difficult than the crystalline solids. In this work we present a detailed numerical study of the vibrational properties of quasi- periodic systems. For our purpose, we use the forced oscillator method (FOM), which is relatively fast and basically simple, and originally designed for the calculation of the phonon density of states in the disordered solids. The quasi-periodic structure is also produced by the Fibonacci series. In this framework we calculate the vibrational properties of the quasi-periodic structures in one, two, and thee dimensions, which compare well with experimental results. In addition to these, we performs similar calculations for the perfectly ordered and disordered systems. Thus we are provided with a basis for comparison of the vibrational properties of quasi- crystalline materials with the perfect crystals and amorphous materials. We also study the effects of bond and site impurities in vibrational properties of materials.

Energy levels of carriers are calculated for three-dimensional quantum- confinement structures with finite potential barriers using the Effective mass approximation. And systems are considered, and a spatially dependent effective mass is included in effective mass approximation. Calculated values are compared with those obtained earlier by other method.