Host-Parasite Co-evolution and Optimal Mutation Rates for Semi-conservative Quasispecies

In this paper, we extend a model of host-parasite co-evolution to incorporate the semi-conservative nature of DNA replication for both the host and the parasite. We find that the optimal mutation rate for the semi-conservative and conservative hosts converge for realistic genome lengths, thus maintaining the admirable agreement between theory and experiment found previously for the conservative model and justifying the conservative approximation in some cases. We demonstrate that, while the optimal mutation rate for a conservative and semi-conservative parasite interacting with a given immune system is similar to that of a conservative parasite, the properties away from this optimum differ significantly. We suspect that this difference, coupled with the requirement that a parasite optimize survival in a range of viable hosts, may help explain why semi-conservative viruses are known to have significantly lower mutation rates than their conservative counterparts

Exactly Conservative Integrators

Traditional numerical discretizations of conservative systems generically yield an artificial secular drift of any nonlinear invariants. In this work we present an explicit nontraditional algorithm that exactly conserves these invariants. We illustrate the general method by applying it to the three-wave truncation of the Euler equations, the Lotka--Volterra predator--prey model, and the Kepler problem. This method is discussed in the context of symplectic (phase space conserving) integration methods as well as nonsymplectic conservative methods. We comment on the application of our method to general conservative systems.Comment: 30 pages, postscript (1.3MB). Submitted to SIAM J. Sci. Comput

Is surgery more effective than non-surgical treatment for spinal stenosis and which non-surgical treatment is more effective? a systematic review

BACKGROUND: Spinal stenosis can be treated both conservatively and with decompression surgery. OBJECTIVES: To explore the effectiveness of surgery vs conservative treatment, and conservative interventions for spinal stenosis. DATA SOURCES: Medline, CINAHL, AMED, PEDro and Cochrane databases, as well as the reference lists of retrieved studies. STUDY SELECTION: The search included non-English studies, and all conservative interventions were included. STUDY APPRAISAL: The PEDro scale was used to assess quality, and levels of evidence were used to synthesise studies where possible. RESULTS: Thirty-one studies met the inclusion criteria, and 18 were high-quality studies. Decompression surgery was more effective than conservative care in four out of five studies, but only one of these was of high quality. In six high-quality studies, there was strong evidence that steroid epidural injections were not effective; in four out of five studies (two of which were of high quality), there was moderate evidence that calcitonin was not effective. There was no evidence for the effectiveness of all other conservative interventions. LIMITATIONS: Further research is needed to determine if decompression surgery is more effective than conservative care, and which conservative care is most effective. CONCLUSION AND IMPLICATIONS: At present, there is no evidence that favours the effect of any conservative management for spinal stenosis. There is an urgent need to see if any conservative treatment can change pain and functional outcomes in spinal stenosis.</p

Tilting Rightward: C-SPAN's Coverage of Think Tanks

This study's main finding is that C-SPAN coverage of think tanks overwhelmingly favors conservative think tanks while left-of-center think tanks are under-represented. In 2006, conservative think tanks received 43.76 percent of total think tank coverage. Conservative/ libertarian and centrist think tanks received 6.94 percent and 31.76 percent respectively. Center-left and progressive think tanks, on the other hand, only received 12.73 percent and 4.86 percent respectively. Thus, the combined conservative and conservative/libertarian think tanks got an absolute majority of 50.7 percent representation on C-SPAN. Everything left of center got only 17.59 percent, just one third of the coverage received by the Right

Non-Conservative Diffusion and its Application to Social Network Analysis

The random walk is fundamental to modeling dynamic processes on networks. Metrics based on the random walk have been used in many applications from image processing to Web page ranking. However, how appropriate are random walks to modeling and analyzing social networks? We argue that unlike a random walk, which conserves the quantity diffusing on a network, many interesting social phenomena, such as the spread of information or disease on a social network, are fundamentally non-conservative. When an individual infects her neighbor with a virus, the total amount of infection increases. We classify diffusion processes as conservative and non-conservative and show how these differences impact the choice of metrics used for network analysis, as well as our understanding of network structure and behavior. We show that Alpha-Centrality, which mathematically describes non-conservative diffusion, leads to new insights into the behavior of spreading processes on networks. We give a scalable approximate algorithm for computing the Alpha-Centrality in a massive graph. We validate our approach on real-world online social networks of Digg. We show that a non-conservative metric, such as Alpha-Centrality, produces better agreement with empirical measure of influence than conservative metrics, such as PageRank. We hope that our investigation will inspire further exploration into the realms of conservative and non-conservative metrics in social network analysis