Computational modelling of polymer-based drug delivery systems

Polymer-based drug delivery systems have fantastic potential in chemotherapy as they can reduce drug side effects, help in patient compliance and provide targeting. Nanoprecipitation is used to encapsulate small drug molecules into polymer nanoparticles to form a drug delivery system. A major obstacle in polymer-based drug delivery systems reaching the clinic is their inability to load sufficient drug molecules. Little is known about the processes involved in the encapsulation of drug molecules into these delivery systems. An insight into the processes that govern the formation of these particles and encapsulation of small drug molecules within them is therefore desirable. We used molecular dynamics to model nanoprecipitation by simulating the dispersion of an acetone drop, containing polymer, into water containing drug. To allow sufficient dispersion of acetone a large amount of water is required, thus coarse-graining becomes mandatory. However, we maintain accuracy for our polymer-drug interactions by using a multiscale force field. Atomistic polymer and drug molecules contain coarse-grain virtual sites which facilitate interactions with the coarse-grain solvent molecules. We also employed fully atomistic reference simulations via resolution transformation to optimise our multiscale force field. This thesis details the theory and design behind this model of nanoprecipitation including how other techniques produced inferior results. Initial simulations with our multiscale model matched an experimental trend and were shown to be accurate relative to atomistic reference simulations. We also analysed a fully atomistic simulation of nanoprecipitation that took several months to complete. This atomistic simulation was used as a reference to update the multiscale force field. The updated force field improved on some aspects of the simulation but there are still areas that need improvement. Insight from the simulations provides an understanding of the experimental results and trends. The transferability of the model should help in designing more efficient polymer-based drug delivery systems in the future. We conclude with future work on modelling polymer-based drug delivery systems including alternate methods to gain understanding of not only drug incorporation but also drug release

Computational modelling of polymer-based drug delivery systems

Polymer-based drug delivery systems have fantastic potential in chemotherapy as they can reduce drug side effects, help in patient compliance and provide targeting. Nanoprecipitation is used to encapsulate small drug molecules into polymer nanoparticles to form a drug delivery system. A major obstacle in polymer-based drug delivery systems reaching the clinic is their inability to load sufficient drug molecules. Little is known about the processes involved in the encapsulation of drug molecules into these delivery systems. An insight into the processes that govern the formation of these particles and encapsulation of small drug molecules within them is therefore desirable. We used molecular dynamics to model nanoprecipitation by simulating the dispersion of an acetone drop, containing polymer, into water containing drug. To allow sufficient dispersion of acetone a large amount of water is required, thus coarse-graining becomes mandatory. However, we maintain accuracy for our polymer-drug interactions by using a multiscale force field. Atomistic polymer and drug molecules contain coarse-grain virtual sites which facilitate interactions with the coarse-grain solvent molecules. We also employed fully atomistic reference simulations via resolution transformation to optimise our multiscale force field. This thesis details the theory and design behind this model of nanoprecipitation including how other techniques produced inferior results. Initial simulations with our multiscale model matched an experimental trend and were shown to be accurate relative to atomistic reference simulations. We also analysed a fully atomistic simulation of nanoprecipitation that took several months to complete. This atomistic simulation was used as a reference to update the multiscale force field. The updated force field improved on some aspects of the simulation but there are still areas that need improvement. Insight from the simulations provides an understanding of the experimental results and trends. The transferability of the model should help in designing more efficient polymer-based drug delivery systems in the future. We conclude with future work on modelling polymer-based drug delivery systems including alternate methods to gain understanding of not only drug incorporation but also drug release

Locations of marine animals revealed by carbon isotopes

Knowing the distribution of marine animals is central to understanding climatic and other environmental influences on population ecology. This information has proven difficult to gain through capture-based methods biased by capture location. Here we show that marine location can be inferred from animal tissues. As the carbon isotope composition of animal tissues varies with sea surface temperature, marine location can be identified by matching time series of carbon isotopes measured in tissues to sea surface temperature records. Applying this technique to populations of Atlantic salmon (Salmo salar L.) produces isotopically-derived maps of oceanic feeding grounds, consistent with the current understanding of salmon migrations, that additionally reveal geographic segregation in feeding grounds between individual philopatric populations and age-classes. Carbon isotope ratios can be used to identify the location of open ocean feeding grounds for any pelagic animals for which tissue archives and matching records of sea surface temperature are available

Law, politics and the governance of English and Scottish joint-stock companies 1600-1850

This article examines the impact of law on corporate governance by means of a case study of joint-stock enterprise in England and Scotland before 1850. Based on a dataset of over 450 company constitutions together with qualitative information on governance practice, it finds little evidence to support the hypothesis that common-law regimes such as England were more supportive of economic growth than civil-law jurisdictions such as Scotland: indeed, levels of shareholder protection were slightly stronger in the civil-law zone. Other factors, such as local political institutions, played a bigger role in shaping organisational forms and business practice

Cyclotron effective masses in layered metals

Many layered metals such as quasi-two-dimensional organic molecular crystals show properties consistent with a Fermi liquid description at low temperatures. The effective masses extracted from the temperature dependence of the magnetic oscillations observed in these materials are in the range, m^*_c/m_e \sim 1-7, suggesting that these systems are strongly correlated. However, the ratio m^*_c/m_e contains both the renormalization due to the electron-electron interaction and the periodic potential of the lattice. We show that for any quasi-two-dimensional band structure, the cyclotron mass is proportional to the density of states at the Fermi energy. Due to Luttinger's theorem, this result is also valid in the presence of interactions. We then evaluate m_c for several model band structures for the \beta, \kappa, and \theta families of (BEDT-TTF)_2X, where BEDT-TTF is bis-(ethylenedithia-tetrathiafulvalene) and X is an anion. We find that for \kappa-(BEDT-TTF)_2X, the cyclotron mass of the \beta-orbit, m^{*\beta}_c, is close to 2 m^{*\alpha}_c, where m^{*\alpha}_c is the effective mass of the \alpha- orbit. This result is fairly insensitive to the band structure details. For a wide range of materials we compare values of the cyclotron mass deduced from band structure calculations to values deduced from measurements of magnetic oscillations and the specific heat coefficient.Comment: 12 pages, 3 eps figure

Transport properties of strongly correlated metals:a dynamical mean-field approach

The temperature dependence of the transport properties of the metallic phase of a frustrated Hubbard model on the hypercubic lattice at half-filling are calculated. Dynamical mean-field theory, which maps the Hubbard model onto a single impurity Anderson model that is solved self-consistently, and becomes exact in the limit of large dimensionality, is used. As the temperature increases there is a smooth crossover from coherent Fermi liquid excitations at low temperatures to incoherent excitations at high temperatures. This crossover leads to a non-monotonic temperature dependence for the resistance, thermopower, and Hall coefficient, unlike in conventional metals. The resistance smoothly increases from a quadratic temperature dependence at low temperatures to large values which can exceed the Mott-Ioffe-Regel value, hbar a/e^2 (where "a" is a lattice constant) associated with mean-free paths less than a lattice constant. Further signatures of the thermal destruction of quasiparticle excitations are a peak in the thermopower and the absence of a Drude peak in the optical conductivity. The results presented here are relevant to a wide range of strongly correlated metals, including transition metal oxides, strontium ruthenates, and organic metals.Comment: 19 pages, 9 eps figure

Holographic mesons in various dimensions

We calculate the spectrum of fluctuations of a probe Dk-brane in the background of N Dp-branes, for k=p,p+2,p+4 and p< 5. The result corresponds to the mesonic spectrum of a (p+1)-dimensional super-Yang-Mills (SYM) theory coupled to `dynamical quarks', i.e., fields in the fundamental representation -- the latter are confined to a defect for k=p and p+2. We find a universal behaviour where the spectrum is discrete and the mesons are deeply bound. The mass gap and spectrum are set by the scale M ~ m_q/g_{eff}(m_q), where m_q is the mass of the fundamental fields and g_{eff}(m_q) is the effective coupling evaluated at the quark mass, i.e. g_{eff}^2(m_q)=g_{ym}^2 N m_q^{p-3}. We consider the evolution of the meson spectra into the far infrared of three-dimensional SYM, where the gravity dual lifts to M-theory. We also argue that the mass scale appearing in the meson spectra is dictated by holography.Comment: 44 pages, 2 figures; v2: typos corrected, references adde

Avanços recentes em nutrição de larvas de peixes

Os requisitos nutricionais de larvas de peixes são ainda mal compreendidos, o que leva a altas mortalidades e problemas de qualidade no seu cultivo. Este trabalho pretende fazer uma revisão de novas metodologias de investigação, tais como estudos com marcadores, genómica populacional, programação nutricional, génomica e proteómica funcionais, e fornecer ainda alguns exemplos das utilizações presentes e perspectivas futuras em estudos de nutrição de larvas de peixes

Spatially heterogeneous ages in glassy dynamics

We construct a framework for the study of fluctuations in the nonequilibrium relaxation of glassy systems with and without quenched disorder. We study two types of two-time local correlators with the aim of characterizing the heterogeneous evolution: in one case we average the local correlators over histories of the thermal noise, in the other case we simply coarse-grain the local correlators. We explain why the former describe the fingerprint of quenched disorder when it exists, while the latter are linked to noise-induced mesoscopic fluctuations. We predict constraints on the pdfs of the fluctuations of the coarse-grained quantities. We show that locally defined correlations and responses are connected by a generalized local out-of-equilibrium fluctuation-dissipation relation. We argue that large-size heterogeneities in the age of the system survive in the long-time limit. The invariance of the theory under reparametrizations of time underlies these results. We relate the pdfs of local coarse-grained quantities and the theory of dynamic random manifolds. We define a two-time dependent correlation length from the spatial decay of the fluctuations in the two-time local functions. We present numerical tests performed on disordered spin models in finite and infinite dimensions. Finally, we explain how these ideas can be applied to the analysis of the dynamics of other glassy systems that can be either spin models without disorder or atomic and molecular glassy systems.Comment: 47 pages, 60 Fig