Scholarly Work - Mathematical Sciences
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/8719
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Item Symmetry breaking clusters in soft clustering decoding of neural codes(2010-02) Parker, Albert E.; Dimitrov, Alexander G.; Gedeon, TomasInformation-based distortion methods have been used successfully in the analysis of neural coding problems. These approaches allow the discovery of neural symbols and the corresponding stimulus space of a neuron or neural ensemble quantitatively, while making few assumptions about the nature of either the code or of relevant stimulus features. The neural codebook is derived by quantizing sensory stimuli and neural responses into a small set of clusters, and optimizing the quantization to minimize an information distortion function. The method of annealing has been used to solve the corresponding high-dimensional nonlinear optimization problem. The annealing solutions undergo a series of bifurcations, which we study using bifurcation theory in the presence of symmetries. In this contribution we describe these symmetry breaking bifurcations in detail, and indicate some of the consequences of the form of the bifurcations. In particular, we show that the annealing solutions break symmetry at pitchfork bifurcations, and that subcritical branches can exist. Thus, at a subcritical bifurcation, there are local information distortion solutions which are not found by the method of annealing. Since the annealing procedure is guaranteed to converge to a local solution eventually, the subcritical branch must turn and become optimal at some later saddle-node bifurcation, which we have shown occur generically for this class of problems. This implies that the rate distortion curve, while convex for noninformation-based distortion measures, is not convex for information-based distortion methods.Item Micro-patterned surfaces reduce bacterial colonization and biofilm formation in vitro: Potential for enhancing endotracheal tube designs(2014-04) May, Rhea M.; Hoffman, Matt G.; Sogo, M.; Parker, Albert E.; O'Toole, George A.; Brennan, Anthony B.; Reddy, Shravanthi T.Ventilator-associated pneumonia (VAP) is a leading hospital acquired infection in intensive care units despite improved patient care practices and advancements in endotracheal tube (ETT) designs. The ETT provides a conduit for bacterial access to the lower respiratory tract and a substratum for biofilm formation, both of which lead to VAP. A novel microscopic ordered surface topography, the Sharklet micro-pattern, has been shown to decrease surface attachment of numerous microorganisms, and may provide an alternative strategy for VAP prevention if included on the surface of an ETT. To evaluate the feasibility of this micro-pattern for this application, the microbial range of performance was investigated in addition to biofilm studies with and without a mucin-rich medium to simulate the tracheal environment in vitro.Item Surface micropattern resists bacterial contamination transferred by healthcare practitioners(2014-12) Mann, Ethan E.; Mettetal, M. Ryan; May, Rhea M.; Drinker, M. C.; Stevenson, B. C.; Baiamonte, V. L.; Marso, J. M.; Dannemiller, E. A.; Parker, Albert E.; Reddy, Shravanthi T.; Sande, M. K.Environmental contamination contributes to an estimated 20-40% of all hospitalacquiredinfections (HAI). Infection control practices continue to improve, butmultipronged approaches are necessary to fully combat the diversity of nosocomialpathogens and emerging multidrug resistant organisms. The Sharkletâ„¢ micropattern,inspired from the microtopography of shark skin, was recently shown to significantlyreduce surface contamination but has not been evaluated in a clinical setting. Thefocus of this study was the transfer of bacteria onto micropatterned surfaces comparedto unpatterned surfaces in a clinical simulation environment involving healthcarepractitioners. Physician volunteers were recruited to participate in an emergencymedicine scenario involving a contact-precaution patient with an acute pulmonaryembolism. Prior to scenario initiation, Staphylococcus aureus was inoculated onto theleg of a simulation mannequin and fresh micropatterned and unpatterned surfacefilms were placed on a code cart, cardiac defibrillator shock button, and epinephrinemedication vial. Six physicians interacted with micropatterned surfaces and fivephysicians interacted with unpatterned surfaces in separate scenarios. Bacterial loadloss from the first contact location (control film over the femoral pulse) to subsequentunpatterned or micropatterned surface test locations was quantified as a log reduction(LR) for each surface type.The code cart, cardiac defibrillator button, and medication vial locations withmicropatterned surfaces resulted in LRs that were larger than the unpatternedLRs by 0.64 (p=0.146), 1.14 (p=0.023), and 0.58 (p=0.083) respectively for eachlocation. The geometric mean CFU/RODAC at the first control surface touched at thefemoral pulse pads ranged from 175-250 CFU/RODAC (95% confidence interval).Thus, the micropatterned LRs were consistently greater than the unpatterned LRs,substantiating the micropattern-dependent reduction of microorganism transfer.Principal component analysis showed that the LRs for the code cart and the cardiacdefibrillator button highly covaried. Thus, a single mean LR was calculated fromthese two locations for each surface type; 5.4 times more bacteria attached to theunpatterned surfaces compared to the micropatterned surfaces (p = 0.058). Thesimulated clinical scenario involving healthcare practitioners demonstrated that themicropatterned surface reduced the transfer of bacterial contamination based onthe larger LRs for the micropatterned surface compared to control surfaces. Furtherinvestigation in hospital rooms where patients are receiving care will ultimately revealthe capability of micropatterned surfaces to minimize the incidence of HAIs.