38 research outputs found
Degenerate Stars and Gravitational Collapse in AdS/CFT
We construct composite CFT operators from a large number of fermionic primary
fields corresponding to states that are holographically dual to a zero
temperature Fermi gas in AdS space. We identify a large N regime in which the
fermions behave as free particles. In the hydrodynamic limit the Fermi gas
forms a degenerate star with a radius determined by the Fermi level, and a mass
and angular momentum that exactly matches the boundary calculations. Next we
consider an interacting regime, and calculate the effect of the gravitational
back-reaction on the radius and the mass of the star using the
Tolman-Oppenheimer-Volkoff equations. Ignoring other interactions, we determine
the "Chandrasekhar limit" beyond which the degenerate star (presumably)
undergoes gravitational collapse towards a black hole. This is interpreted on
the boundary as a high density phase transition from a cold baryonic phase to a
hot deconfined phase.Comment: 75 page
A soliton menagerie in AdS
We explore the behaviour of charged scalar solitons in asymptotically global
AdS4 spacetimes. This is motivated in part by attempting to identify under what
circumstances such objects can become large relative to the AdS length scale.
We demonstrate that such solitons generically do get large and in fact in the
planar limit smoothly connect up with the zero temperature limit of planar
scalar hair black holes. In particular, for given Lagrangian parameters we
encounter multiple branches of solitons: some which are perturbatively
connected to the AdS vacuum and surprisingly, some which are not. We explore
the phase space of solutions by tuning the charge of the scalar field and
changing scalar boundary conditions at AdS asymptopia, finding intriguing
critical behaviour as a function of these parameters. We demonstrate these
features not only for phenomenologically motivated gravitational Abelian-Higgs
models, but also for models that can be consistently embedded into eleven
dimensional supergravity.Comment: 62 pages, 21 figures. v2: added refs and comments and updated
appendice
Quantitative characterization of metabolism and metabolic shifts during growth of the new human cell line AGE1.HN using time resolved metabolic flux analysis
For the improved production of vaccines and therapeutic proteins, a detailed understanding of the metabolic dynamics during batch or fed-batch production is requested. To study the new human cell line AGE1.HN, a flexible metabolic flux analysis method was developed that is considering dynamic changes in growth and metabolism during cultivation. This method comprises analysis of formation of cellular components as well as conversion of major substrates and products, spline fitting of dynamic data and flux estimation using metabolite balancing. During batch cultivation of AGE1.HN three distinct phases were observed, an initial one with consumption of pyruvate and high glycolytic activity, a second characterized by a highly efficient metabolism with very little energy spilling waste production and a third with glutamine limitation and decreasing viability. Main events triggering changes in cellular metabolism were depletion of pyruvate and glutamine. Potential targets for the improvement identified from the analysis are (i) reduction of overflow metabolism in the beginning of cultivation, e.g. accomplished by reduction of pyruvate content in the medium and (ii) prolongation of phase 2 with its highly efficient energy metabolism applying e.g. specific feeding strategies. The method presented allows fast and reliable metabolic flux analysis during the development of producer cells and production processes from microtiter plate to large scale reactors with moderate analytical and computational effort. It seems well suited to guide media optimization and genetic engineering of producing cell lines
Theorems on existence and global dynamics for the Einstein equations
This article is a guide to theorems on existence and global dynamics of
solutions of the Einstein equations. It draws attention to open questions in
the field. The local-in-time Cauchy problem, which is relatively well
understood, is surveyed. Global results for solutions with various types of
symmetry are discussed. A selection of results from Newtonian theory and
special relativity that offer useful comparisons is presented. Treatments of
global results in the case of small data and results on constructing spacetimes
with prescribed singularity structure or late-time asymptotics are given. A
conjectural picture of the asymptotic behaviour of general cosmological
solutions of the Einstein equations is built up. Some miscellaneous topics
connected with the main theme are collected in a separate section.Comment: Submitted to Living Reviews in Relativity, major update of Living
Rev. Rel. 5 (2002)
A competitive integration model of exogenous and endogenous eye movements
We present a model of the eye movement system in which the programming of an eye movement is the result of the competitive integration of information in the superior colliculi (SC). This brain area receives input from occipital cortex, the frontal eye fields, and the dorsolateral prefrontal cortex, on the basis of which it computes the location of the next saccadic target. Two critical assumptions in the model are that cortical inputs are not only excitatory, but can also inhibit saccades to specific locations, and that the SC continue to influence the trajectory of a saccade while it is being executed. With these assumptions, we account for many neurophysiological and behavioral findings from eye movement research. Interactions within the saccade map are shown to account for effects of distractors on saccadic reaction time (SRT) and saccade trajectory, including the global effect and oculomotor capture. In addition, the model accounts for express saccades, the gap effect, saccadic reaction times for antisaccades, and recorded responses from neurons in the SC and frontal eye fields in these tasks. © The Author(s) 2010
The Einstein-Vlasov System/Kinetic Theory
The main purpose of this article is to provide a guide to theorems on global
properties of solutions to the Einstein--Vlasov system. This system couples
Einstein's equations to a kinetic matter model. Kinetic theory has been an
important field of research during several decades in which the main focus has
been on non-relativistic and special relativistic physics, i.e., to model the
dynamics of neutral gases, plasmas, and Newtonian self-gravitating systems. In
1990, Rendall and Rein initiated a mathematical study of the Einstein--Vlasov
system. Since then many theorems on global properties of solutions to this
system have been established.Comment: Published version http://www.livingreviews.org/lrr-2011-
Methods to study microbial adhesion on abiotic surfaces
Microbial biofilms are a matrix of cells and exopolymeric substances attached to a wet and solid surface and are commonly associated to several problems, such as biofouling and corrosion in industries and infectious diseases in urinary catheters and prosthesis. However, these cells may have several benefits in distinct applications, such as wastewater treatment processes, microbial fuel cells for energy production and biosensors. As microbial adhesion is a key step on biofilm formation, it is very important to understand and characterize microbial adhesion to a surface. This study presents an overview of predictive and experimental methods used for the study of bacterial adhesion. Evaluation of surface physicochemical properties have a limited capacity in describing the complex adhesion process. Regarding the experimental methods, there is no standard method or platform available for the study of microbial adhesion and a wide variety of methods, such as colony forming units counting and microscopy techniques, can be applied for quantification and characterization of the adhesion process.This work was financially supported by: Project UID/EQU/00511/2013-LEPABE, by the FCT/MEC with national funds and co-funded by FEDER in the scope of the P2020 Partnership Agreement; Project NORTE-07-0124-FEDER-000025 - RL2_Environment&Health, by FEDER funds through Programa Operacional Factores de Competitividade-COMPETE, by the Programa Operacional do Norte (ON2) program and by national funds through FCT - Fundacao para a Ciencia e a Tecnologia; European Research Project SusClean (Contract number FP7-KBBE-2011-5, project number: 287514), Scholarships SFRH/BD/52624/2014, SFRH/BD/88799/2012 and SFRH/BD/103810/2014