Analysis of Greedy Algorithm for Vertex Covering of Random Graph by Cubes

We study randomly induced subgraphs G of a hypercube. Specifically, we investigate vertex covering of G by cubes. We instantiate a greedy algorithm for this problem from general hypergraph covering algorithm, and estimate the length of vertex covering of G. In order to obtain this result, a number of theoretical parameters of randomly induced subgraph G were estimated

On High-Rate Cryptographic Compression Functions

The security of iterated hash functions relies on the properties of underlying compression functions. We study highly efficient compression functions based on block ciphers. We propose a model for high-rate compression functions, and give an upper bound for the rate of any collision resistant compression function in our model. In addition, we show that natural generalizations of constructions by Preneel, Govaerts, and Vandewalle to the case of rate-2 compression functions are not collision resistant

Comparison of recalculated Dobson and TOMS total ozone at Hradec Kralove, Czechoslovakia, 1978-1990

The reevaluated Dobson total ozone data from Hradec Kralove, Czechoslovakia were compared with independent Total Ozone Mapping Spectrophotometer (TOMS) 'version 6' data set. The comparison was performed by means of the parallel daily averages of ground-based and satellite total ozone pairs of the period November 1978 to December 1990. The comparison showed slight differences between both data series. Their average relative difference is 0.48 percent. The similar results have been reached for subsets of direct sun and zenith types of measurements as well. Their relative differences are 0.61 percent and 0.11 percent respectively. These facts indicate not only good mutual relation of both data sources but also reliability and accuracy of the zenith charts of the spectrophotometer No. 74 used at Hradec Kralove. Preliminary assessment of seasonal MU-dependence of the differences between Dobson and TOMS data was made while using total ozones of winter and summer months representing values of MU=2.70-5.20 and MU = 1.12-1.30 respectively. The results did not show systematic underestimation or overestimation of total ozone due to MU-dependence of the instrument at Hradec Kralove in both seasons