Competing with Gaussian linear experts

We study the problem of online regression. We prove a theoretical bound on the square loss of Ridge Regression. We do not make any assumptions about input vectors or outcomes. We also show that Bayesian Ridge Regression can be thought of as an online algorithm competing with all the Gaussian linear experts

Prediction with expert advice for the Brier game

We show that the Brier game of prediction is mixable and find the optimal learning rate and substitution function for it. The resulting prediction algorithm is applied to predict results of football and tennis matches. The theoretical performance guarantee turns out to be rather tight on these data sets, especially in the case of the more extensive tennis data.Comment: 34 pages, 22 figures, 2 tables. The conference version (8 pages) is published in the ICML 2008 Proceeding

Nanoparticles without and with protein corona: van der Waals and hydration interaction

The van der Waals (vdW) interaction between nanoparticles (NPs) in general, and especially between metal NPs, may be appreciable, and may result in nanoparticle aggregation. In biofluids, NPs become rapidly surrounded by a protein corona (PC). Here, the vdW and hydration interaction of NPs with and without PC are compared in detail. The focus is on two widely used types of NPs fabricated of SiO2 and Au and possessing weak and strong vdW interactions, respectively. For SiO2, the presence of PC increases the vdW interaction, but it remains relatively weak and insufficient for aggregation. For Au, the presence of PC decreases the vdW interaction, and in the case of small NPs (≤ 40 nm in diameter) it may become insufficient for aggregation as well while the larger NPs can aggregate

Ionizable lipids in bio-inspired nanocarriers

In applications of bio-inspired nanoparticles (NPs), their composition is often optimised by including ionizable lipids. I use a generic statistical model to describe the charge and potential distributions in lipid nanoparticles (LNPs) containing such lipids. The LNP structure is considered to contain the biophase regions separated by narrow interphase boundaries with water. Ionizable lipids are uniformly distributed at the biophase–water boundaries. The potential is there described at the mean-filed level combining the Langmuir–Stern equation for ionizable lipids and the Poisson–Boltzmann equation for other charges in water. The latter equation is used outside a LNP as well. With physiologically reasonable parameters, the model predicts the scale of the potential in a LNP to be rather low, smaller or about kBT/ e, and to change primarily near the LNP-solution interface or, more precisely, inside an NP near this interface because the charge of ionizable lipids becomes rapidly neutralized along the coordinate towards the center of a LNP. The extent of dissociation-mediated neutralization of ionizable lipids along this coordinate increases but only slightly. Thus, the neutralization is primarily due to the negative and positive ions related to the ionic strength in solution and located inside a LNP

Kinetic aspects of virus targeting by nanoparticles in vivo

One of the suggested ways of the use of nanoparticles in virology implies their association with and subsequent deactivation of virions. The conditions determining the efficiency of this approach in vivo are now not clear. Herein, I propose the first kinetic model describing the corresponding processes and clarifying these conditions. My analysis indicates that nanoparticles can decrease concentration of infected cells by a factor of one order of magnitude, but this decrease itself (without feedback of the immune system) is insufficient for full eradication of infection. It can, however, induce delay in the progress of infection, and this delay can help to form sufficient feedback of the immune system

Kinetics and percolation: coke in heterogeneous catalysts

In the conventional lattice percolation models, bonds or sites are open at random, whereas in reality there is often interplay of percolation and the kinetics under consideration. An interesting and practically important example is hydrocarbon conversion occurring in a reactor containing similar to 1 mm-sized porous pellets with catalytic nanoparticles deposited at walls of the nanopores. Such catalytic heterogeneous reactions are often accompanied by coke formation deactivating catalytic nanoparticles and blocking pores for reactant diffusion, so that one needs to remove coke from time to time e.g. via reaction with oxygen. Herein, I first present generic coarse-grained Monte Carlo simulations of coke formation in a single pellet with the emphasis on the reaction regime influenced by reactant diffusion in pores. Then, the obtained coke distributions are used for similar simulations of coke removal. This combination of the models has allowed me to illustrate qualitatively new spatio-temporal regimes of the processes under consideration. For example, the removal of coke can be slow in the beginning, due to blocking of oxygen diffusion near the external pellet-gas interface and preventing its penetration to the central part of a pellet, and then fast when the pathways for diffusion to the center become to be open

How the partial-slip boundary condition can influence the interpretation of the DLS and NTA data

Dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA) are widely used to determine the size of biological nanoparticles in liquid. In both cases, one first measures the nanoparticle diffusion coefficient and then converts it to the nanoparticle radius via the Stokes-Einstein relation. This relation is based on the no-slip boundary condition. Now, there is evidence that this condition can be violated in biologically relevant cases (e.g., for vesicles) and that in such situations the partial-slip boundary condition is more suitable. I show (i) how the latter condition can be employed in the context of DLS and NTA and (ii) that the use of the former condition may result in underestimation of the nanoparticle radius by about 10 nm compared with the nominal one

Kinetics of Reaction on a Single Catalytic Particle in a Fluidic Nanochannel

One of the frontiers in heterogeneous catalysis is focused on reactions occurring on single catalytic nanoparticles. In this context, a reaction taking place on a single nanoparticle in a fluidic nanochannel is herein described by using the equation similar to that employed for a plug-flow reactor with dispersion. In the literature, one can find various boundary conditions for this equation. In the practically interesting case of a relatively long channel, the Dirichlet boundary conditions are shown to be valid. The corresponding analytical and numerical results illustrate the specifics of the profiles of the reactant concentration along the channel and the dependence of the reaction rate on the parameters. For comparison, the Danckwerts boundary conditions were used as well. [GRAPHICS]

Extracellular interplay of amyloid fibrils and neural cells

Some neurological disorders such e.g. as Alzheimer disease are accompanied by the appearance of amyloid fibrils inside and outside cells. Herein, I present a generic coarse-grained kinetic mean-field model describing at the extracellular level the interplay of fibrils and cells. It includes the formation and degradation of fibrils, activation of healthy cells with respect to the fabrication of fibrils, and death of activated cells. The corresponding analysis indicates that the disease development can occur in two qualitatively different regimes. The first one is controlled primarily by the intrinsic factors resulting in slow increase of fibril production inside cells. The second one implies faster self-promoted growth of the fibril population by analogy with explosion. This prediction reported as a hypothesis is of interest for conceptual understanding of the neurological disorders

Catalytic Conversion of Hydrocarbons and Formation of Carbon Nanofilaments in Porous Pellets

Catalytic conversion of hydrocarbons occurring at metal nanoparticles in porous pellets is often accompanied by the formation of coke in the form of growing heterogeneous film-like aggregates or carbon nanofilaments. The latter processes result in deactivation of metal nanoparticles. The corresponding kinetic models imply the formation and growth of film-like coke aggregates. Herein, I present an alternative generic kinetic model focused on the formation and growth of carbon nanofilaments. These processes are considered to deactivate metal nanoparticles and reduce the rate of reactant diffusion in pores. In this framework, the kinetically limited reaction regime is described by simple analytical expressions. The diffusion-limited regime can be described as well but only numerically. The model presented can be used for interpretation of experimental results. [GRAPHICS]