Concurrent bandits and cognitive radio networks

We consider the problem of multiple users targeting the arms of a single multi-armed stochastic bandit. The motivation for this problem comes from cognitive radio networks, where selfish users need to coexist without any side communication between them, implicit cooperation or common control. Even the number of users may be unknown and can vary as users join or leave the network. We propose an algorithm that combines an $\epsilon$-greedy learning rule with a collision avoidance mechanism. We analyze its regret with respect to the system-wide optimum and show that sub-linear regret can be obtained in this setting. Experiments show dramatic improvement compared to other algorithms for this setting

Exploring Molecular Simulations of a Plausible Prebiotic Reduced Phospholipid Using Hyperchem Software

How the first cells emerged from the primordial milieu is one of the great questions in science. Biomolecular emergence scenarios abound in the literature, but the lack of bioaccessible phosphate and molecular oxygen on the primordial Earth has posed formidable challenges for deducing emergence pathways. One idea gaining wide acceptance invokes delivery of the phosphide mineral schreibersite ((Fe,Ni)3P) to Earth via meteorite impacts ca. 4.2 billion years ago, whereupon they were corroded to reduced phosphorous oxyacids and phosphonates in primordial aquatic environments. We previously proposed that these reduced phosphorus forms could readily combine with putative geochemical species in shallow mineral-rich alkaline hydrothermal systems to form reduced phospholipid analogs of contemporary phosphate-based phospholipids (Fitch, N.W., K.L. Even, L.J. Leinen and M.O. Gaylor. 2016. Plausible prebiotic assembly of a primitive reduced phospholipid from meteoritic phosphorus on the primordial earth. Proceedings of the South Dakota Academy of. Science 95:176.). Lacking resources to empirically validate this idea, we explored “water box” simulations of the proposed phospholipid structure using the HyperChem software package. Simulation results showed the hydrophobic tails migrating away from water molecules, while hydrophilic heads migrated towards them, resulting in quasistacking behaviors consistent with those of known amphiphiles in water. Inspired by these results, we are now investigating more complex primordial simulation scenarios

Biofilm forming abilities of Salmonella are correlated with persistence in fish meal- and feed factories

<p>Abstract</p> <p>Background</p> <p>Feed contaminated with <it>Salmonella </it>spp. constitutes a risk of <it>Salmonella </it>infections in animals, and subsequently in the consumers of animal products. <it>Salmonella </it>are occasionally isolated from the feed factory environment and some clones of <it>Salmonella </it>persist in the factory environment for several years. One hypothesis is that biofilm formation facilitates persistence by protecting bacteria against environmental stress, e.g. disinfection. The aim of this study was to investigate the biofilm forming potential of <it>Salmonella </it>strains from feed- and fishmeal factories. The study included 111 <it>Salmonella </it>strains isolated from Norwegian feed and fish meal factories in the period 1991–2006 of serovar Agona, serovar Montevideo, serovar Senftenberg and serovar Typhimurium.</p> <p>Results</p> <p>Significant differences were found between serovars regarding the abilities to form biofilm on polystyrene (microtiter plate assay) and in the air-liquid interface of nutrient broth (pellicle assay). Strains of serovar Agona and serovar Montevideo were good biofilm producers. In Norwegian factories, clones of these serovars have been observed to persist for several years. Most serovar Senftenberg clones appear to persist for a shorter period, and strains of this serovar were medium biofilm producers in our test systems. Strains of the serovar Typhimurium were relatively poor biofilm producers. <it>Salmonella </it>ser. Typhimurium clones have not been observed to persist even though this serovar is resident in Norwegian wild life. When classifying strains according to persistence or presumed non-persistence, persistent strains produced more biofilm than presumed non-persisting strains.</p> <p>Conclusion</p> <p>The results indicate a correlation between persistence and biofilm formation which suggests that biofilm forming ability may be an important factor for persistence of <it>Salmonella </it>in the factory environment.</p

Micro ecosystems from feed industry surfaces: a survival and biofilm study of Salmonella versus host resident flora strains

<p>Abstract</p> <p>Background</p> <p>The presence of <it>Salmonella </it>enterica serovars in feed ingredients, products and processing facilities is a well recognized problem worldwide. In Norwegian feed factories, strict control measures are implemented to avoid establishment and spreading of <it>Salmonella </it>throughout the processing chain. There is limited knowledge on the presence and survival of the resident microflora in feed production plants. Information on interactions between <it>Salmonella </it>and other bacteria in feed production plants and how they affect survival and biofilm formation of <it>Salmonella </it>is also limited. The aim of this study was to identify resident microbiota found in feed production environments, and to compare the survival of resident flora strains and <it>Salmonella </it>to stress factors typically found in feed processing environments. Moreover, the role of dominant resident flora strains in the biofilm development of <it>Salmonella </it>was determined.</p> <p>Results</p> <p>Surface microflora characterization from two feed productions plants, by means of 16 S rDNA sequencing, revealed a wide diversity of bacteria. Survival, disinfection and biofilm formation experiments were conducted on selected dominant resident flora strains and <it>Salmonella</it>. Results showed higher survival properties by resident flora isolates for desiccation, and disinfection compared to <it>Salmonella </it>isolates. Dual-species biofilms favored <it>Salmonella </it>growth compared to <it>Salmonella </it>in mono-species biofilms, with biovolume increases of 2.8-fold and 3.2-fold in the presence of <it>Staphylococcus </it>and <it>Pseudomonas</it>, respectively.</p> <p>Conclusions</p> <p>These results offer an overview of the microflora composition found in feed industry processing environments, their survival under relevant stresses and their potential effect on biofilm formation in the presence of <it>Salmonella</it>. Eliminating the establishment of resident flora isolates in feed industry surfaces is therefore of interest for impeding conditions for <it>Salmonella </it>colonization and growth on feed industry surfaces. In-depth investigations are still needed to determine whether resident flora has a definite role in the persistence of <it>Salmonella </it>in feed processing environments.</p

Structure and function in flow networks

Peer reviewedPublisher PD

Finding 2-Edge and 2-Vertex Strongly Connected Components in Quadratic Time

We present faster algorithms for computing the 2-edge and 2-vertex strongly connected components of a directed graph, which are straightforward generalizations of strongly connected components. While in undirected graphs the 2-edge and 2-vertex connected components can be found in linear time, in directed graphs only rather simple $O(m n)$-time algorithms were known. We use a hierarchical sparsification technique to obtain algorithms that run in time $O(n^2)$. For 2-edge strongly connected components our algorithm gives the first running time improvement in 20 years. Additionally we present an $O(m^2 / \log{n})$-time algorithm for 2-edge strongly connected components, and thus improve over the $O(m n)$ running time also when $m = O(n)$. Our approach extends to k-edge and k-vertex strongly connected components for any constant k with a running time of $O(n^2 \log^2 n)$ for edges and $O(n^3)$ for vertices