BACKGROUND: Biochemical systems are inherently noisy due to the discrete reaction events that occur in a random manner. Although noise is often perceived as a disturbing factor, the system might actually benefit from it. In order to understand the role of noise better, its quality must be studied in a quantitative manner. Computational analysis and modeling play an essential role in this demanding endeavor. RESULTS: We implemented a large nonlinear signal transduction network combining protein kinase C, mitogen-activated protein kinase, phospholipase A2, and β isoform of phospholipase C networks. We simulated the network in 300 different cellular volumes using the exact Gillespie stochastic simulation algorithm and analyzed the results in both the time and frequency domain. In order to perform simulations in a reasonable time, we used modern parallel computing techniques. The analysis revealed that time and frequency domain characteristics depend on the system volume. The simulation results also indicated that there are several kinds of noise processes in the network, all of them representing different kinds of low-frequency fluctuations. In the simulations, the power of noise decreased on all frequencies when the system volume was increased. CONCLUSIONS: We concluded that basic frequency domain techniques can be applied to the analysis of simulation results produced by the Gillespie stochastic simulation algorithm. This approach is suited not only to the study of fluctuations but also to the study of pure noise processes. Noise seems to have an important role in biochemical systems and its properties can be numerically studied by simulating the reacting system in different cellular volumes. Parallel computing techniques make it possible to run massive simulations in hundreds of volumes and, as a result, accurate statistics can be obtained from computational studies.

For checking equivalence of any two word morphisms, restricted on a subset (language), it suffices to do this for a finite subset of the language, the so-called finite test set. A way of effectively obtaining a finite test set for a special class of languages, the so-called iterated morphisms, is presented here together with an explicit upper bound for its size. The method can be extended to free metabelian groups, and to certain other metabelian groups.

The objective of the paper is to follow-up the success of Finnish telemedicine programs identified in 1996 in a nation-wide survey. The methods used are questionnaires sent to those in charge of a total of 40 telemedicine programs identified in 1996. Of the results of the programs responding to the survey (36 out of 40, i.e., 90%), 69% were still operative at the time of the follow-up in 1999. According to the respondents, one-third of the programs were deemed to have had an impact on the working process of the organization. The majority of the programs lacked a clear effect in this respect. In only four cases out of 36, the telemedicine program was deemed to have achieved savings, three of the programs had brought about extra costs, and four were cost neutral. However, in the majority of the cases, the respondents were not able to assess the financial impart of the program. The average duration of the programs still in progress was 4.2 years and those terminated was 2.5 years. The average number of patients treated in the programs still in progress was 370, i.e., approximately 88 patients per year. Of the telemedicine programs identified three years earlier, two-thirds were still in progress during the repeat survey. The average number of patients treated per year in these programs was relatively small, suggesting that telemedicine was not very successful in replacing traditional ways of delivering patient care. In line with this, only a minority of the programs were deemed to have had an effect on the working process of the organization, and cost savings were achieved in only a handful of cases.

Methods are described for reducing the equivalence problem for sequences defined by recurrence equations in various finitely generated groups to polynomial Gröbner basis constructions. The methods are simple enough to allow a straigthforward implemen

After extending two word morphismsfand g to languages, an equationf(X) = g(X) can be written and ItS language soluUons investigated.An elementary characterization of the famdy of all solutions of the equation is ~ven, and it is used to mvesttgate the maximal solution which is the mum subject of this paper.It turns out that going through all propagating morphismsf and g, the family of maximal solutions obtained equals the famdy of complements of recurslvely enumerable languages after intersecting with regular languages and mapping with propagating morphisms.In the general case (of arbitrary morphismsf and g) the corresponding family is larger and includes the full-AFL closure of the family of complements of recursively enumerable languages.