1,519 research outputs found
A Mesoscopic Approach to the ``Negative'' Viscosity Effect in Ferrofluids
We present a mesoscopic approach to analyze the dynamics of a single magnetic
dipole under the influence of an oscillating magnetic field, based on the
formulation of a Fokker-Planck equation. The dissipated power and the viscosity
of a suspension of such magnetic dipoles are calculated from non-equilibrium
thermodynamics of magnetized systems. By means of this method we have found a
non-monotonous behaviour of the viscosity as a function of the frequency of the
field which has been referred to as the ``negative'' viscosity effect.
Moreover, we have shown that the viscosity depends on the vorticity field thus
exhibiting non-Newtonian behaviour. Our analysis is complemented with numerical
simulations which reproduce the behaviour of the viscosity we have found and
extend the scope of our analytical approach to higher values of the magnetic
field.Comment: 9 pages, 2 eps figures, simulations have been adde
Multiscale modelling of vascular tumour growth in 3D: the roles of domain size & boundary condition
We investigate a three-dimensional multiscale model of vascular tumour growth, which couples blood flow, angiogenesis, vascular remodelling, nutrient/growth factor transport, movement of, and interactions between, normal and tumour cells, and nutrient-dependent cell cycle dynamics within each cell. In particular, we determine how the domain size, aspect ratio and initial vascular network influence the tumour's growth dynamics and its long-time composition. We establish whether it is possible to extrapolate simulation results obtained for small domains to larger ones, by constructing a large simulation domain from a number of identical subdomains, each subsystem initially comprising two parallel parent vessels, with associated cells and diffusible substances. We find that the subsystem is not representative of the full domain and conclude that, for this initial vessel geometry, interactions between adjacent subsystems contribute to the overall growth dynamics. We then show that extrapolation of results from a small subdomain to a larger domain can only be made if the subdomain is sufficiently large and is initialised with a sufficiently complex vascular network. Motivated by these results, we perform simulations to investigate the tumour's response to therapy and show that the probability of tumour elimination in a larger domain can be extrapolated from simulation results on a smaller domain. Finally, we demonstrate how our model may be combined with experimental data, to predict the spatio-temporal evolution of a vascular tumour
No two without three: Modelling dynamics of the trio RNA virus-defective interfering genomes-RNA satellite
Almost all viruses, regardless of their genomic material, produce defective
viral genomes (DVG) as an unavoidable byproduct of their error-prone
replication. Defective interfering (DI) elements are a subgroup of DVGs that
have been shown to interfere with the replication of the wild-type (WT) virus.
Along with DIs, other genetic elements known as satellite RNAs (satRNAs), that
show no genetic relatedness with the WT virus, can co-infect cells with WT
helper viruses and take advantage of viral proteins for their own benefit.
These satRNAs have effects that range from reduced symptom severity to enhanced
virulence. The interference dynamics of DIs over WT viruses has been thoroughly
modelled at within-cell, within-host, and population levels. However, nothing
is known about the dynamics resulting from the nonlinear interactions between
WT viruses and DIs in the presence of satellites, a process that is frequently
seen in plant RNA viruses and in biomedically relevant pathosystems like
hepatitis B virus and its satellite. Here, we look into a
phenomenological mathematical model that describes how a WT virus replicates
and produces DIs in presence of a satRNA at the intra-host level. The WT virus
is subject to mechanisms of complementation, competition, and various levels of
interference from DIs and the satRNA. Examining the dynamics analytically and
numerically reveals three possible stable states: (i) full extinction, (ii)
satellite extinction and virus-DIs coexistence and (iii) full coexistence.
Assuming DIs replicate faster than the satRNA owed to their smaller size drives
to scenario (ii), which implies that DIs could wipe out the satRNA. In
addition, a small region of the parameter space exists wherein the system is
bistable (either scenarios (ii) or (iii) are concurrently stable).Comment: 22 pages, 9 figure
A multiple scale model for tumor growth
We present a physiologically structured lattice model for vascular tumor growth which accounts for blood flow and structural adaptation of the vasculature, transport of oxygen, interaction between cancerous and normal tissue, cell division, apoptosis, vascular endothelial growth factor release, and the coupling between these processes. Simulations of the model are used to investigate the effects of nutrient heterogeneity, growth and invasion of cancerous tissue, and emergent growth laws
Genetic and Molecular Characterization of Temperate and Tropical Forage Maize Inbred Lines
The livestock feeding in the Central highland of Mexico is based on harvest, grazing and annual forage conservation, being forage maize the most important silage crop (Alarcón, 1995). Even though forage maize is extensively bred in Europe, USA and Asia since 1900\u27s, this started in Mexico in the 1960\u27s, and little is known about the genetic diversity in both agronomic and nutritive value traits. Our breeding program goals are to analyze combining ability of biomass and quality predictors and to study the genetic relationship of inbred lines between lowland tropical and temperate races from Mesa Central, by genetic and molecular approaches
Genetic and Molecular Characterization of Temperate and Tropical Forage Maize Inbred Lines
Livestock feeding in the Central highland of Mexico is based on harvest, grazing and annual forage conservation, with forage maize being the most important silage crop (Alarcón, 1995). Even though forage maize is extensively bred in Europe, USA and Asia since the 1900’s, this started in Mexico only in the 1960’s, and little is known about genetic diversity in both agronomic and nutritive value traits. Our breeding program goals are to analyze combining ability of biomass and quality predictors and to study the genetic relationship of inbred lines between lowland tropical and temperate races from Mesa Central, by genetic and molecular approaches
Acute Effects of Two Different Resistance Circuit Training Protocols on Performance and Perceived Exertion in Semiprofessional Basketball Players
Acute effects of two different resistance circuit training protocols on performance and perceived exertion in semiprofessional basketball players. J Strength Cond Res 30(2): 407–414, 2016—This study aimed to investigate the acute effects of two different resistance circuit training protocols on basketball players' physical and technical performance and rating of perceived exertion (RPE). In a repeated-measures, crossover experimental design, 9 semiprofessional basketball players performed a Power Circuit Training (PCT; 45% 1RM) and a High-Resistance Circuit Training (HRC; 6RM), on consecutive weeks. Vertical and horizontal jump performance, 3-points shooting accuracy, repeated-sprint ability (RSA), agility, and upper body power output were measured before and after training. The RPE was assessed 20 minutes after resistance training. One-way repeated-measures analysis of variance showed performance decrements in vertical jump height and peak power, horizontal jump distance, 3-points percentage, bench-press power output, RSA total and ideal time, and agility T-Test at total time following HRC, but not PCT (p <= 0.05). The RPE was higher in HRC compared with PCT. The results of this study indicated that HRC was perceived as being harder and produced higher fatigue levels, which in turn lowered acute performance. However, low-to-moderate intensity loads did not negatively affect performance. Thus, completing a PCT session may be the most appropriate option before a practice or game as it avoids acute–resistance–training-induced performance decrements. However, if the objective of the basketball session is to develop or perfect technical skills during fatiguing conditions, HRC may be the more suitable option.Actividad Física y Deport
Comparing stochastic differential equations and agent-based modelling and simulation for early-stage cancer
There is great potential to be explored regarding the use of agent-based modelling and simulation as an alternative paradigm to investigate early-stage cancer interactions with the immune system. It does not suffer from some limitations of ordinary differential equation models, such as the lack of stochasticity, representation of individual behaviours rather than aggregates and individual memory. In this paper we investigate the potential contribution of agent-based modelling and simulation when contrasted with stochastic versions of ODE models using early-stage cancer examples. We seek answers to the following questions: (1) Does this new stochastic formulation produce similar results to the agent-based version? (2) Can these methods be used interchangeably? (3) Do agent-based models outcomes reveal any benefit when compared to the Gillespie results? To answer these research questions we investigate three well-established mathematical models describing interactions between tumour cells and immune elements. These case studies were re-conceptualised under an agent-based perspective and also converted to the Gillespie algorithm formulation. Our interest in this work, therefore, is to establish a methodological discussion regarding the usability of different simulation approaches, rather than provide further biological insights into the investigated case studies. Our results show that it is possible to obtain equivalent models that implement the same mechanisms; however, the incapacity of the Gillespie algorithm to retain individual memory of past events affects the similarity of some results. Furthermore, the emergent behaviour of ABMS produces extra patters of behaviour in the system, which was not obtained by the Gillespie algorithm
AC-KBO Revisited
Equational theories that contain axioms expressing associativity and
commutativity (AC) of certain operators are ubiquitous. Theorem proving methods
in such theories rely on well-founded orders that are compatible with the AC
axioms. In this paper we consider various definitions of AC-compatible
Knuth-Bendix orders. The orders of Steinbach and of Korovin and Voronkov are
revisited. The former is enhanced to a more powerful version, and we modify the
latter to amend its lack of monotonicity on non-ground terms. We further
present new complexity results. An extension reflecting the recent proposal of
subterm coefficients in standard Knuth-Bendix orders is also given. The various
orders are compared on problems in termination and completion.Comment: 31 pages, To appear in Theory and Practice of Logic Programming
(TPLP) special issue for the 12th International Symposium on Functional and
Logic Programming (FLOPS 2014
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