Nonlinear dynamics of electromagnetic pulses in cold relativistic plasmas

In the present analysis we study the self consistent propagation of nonlinear electromagnetic pulses in a one dimensional relativistic electron-ion plasma, from the perspective of nonlinear dynamics. We show how a series of Hamiltonian bifurcations give rise to the electric fields which are of relevance in the subject of particle acceleration. Connections between these bifurcated solutions and results of earlier analysis are made.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France

Coherence and incoherence in extended broad band triplet interaction

In the present analysis we study the transition from coherent to incoherent dynamics in a nonlinear triplet of broad band combs of waves. Expanding the analysis of previous works, this paper investigates what happens when the band of available modes is much larger than that of the initial narrower combs within which the nonlinear interaction is not subjected to selection rules involving wave momenta. Here selection rules are present and active, and we examine how and when coherence can be defined.Comment: 6 pages, 2 figure

Testing Hu-Sawicki f(R) gravity with the Effective Field Theory approach

We show how to fully map a specific model of modified gravity into the Einstein-Boltzmann solver EFTCAMB. This approach consists in few steps and allows to obtain the cosmological phenomenology of a model with minimal effort. We discuss all these steps, from the solution of the dynamical equations for the cosmological background of the model to the use of the mapping relations to cast the model into the effective field theory language and use the latter to solve for perturbations. We choose the Hu-Sawicki f(R) model of gravity as our working example. After solving the background and performing the mapping, we interface the algorithm with EFTCAMB and take advantage of the effective field theory framework to integrate the full dynamics of linear perturbations, returning all quantities needed to accurately compare the model with observations. We discuss some observational signatures of this model, focusing on the linear growth of cosmic structures. In particular we present the behavior of $f\sigma_8$ and $E_G$ that, unlike the $\Lambda$CDM scenario, are generally scale dependent in addition to redshift dependent. Finally, we study the observational implications of the model by comparing its cosmological predictions to the Planck 2015 data, including CMB lensing, the WiggleZ galaxy survey and the CFHTLenS weak lensing survey measurements. We find that while WiggleZ data favor a non-vanishing value of the Hu-Sawicki model parameter, $\log_{10}(-f^0_{R})$, and consequently a large value of $\sigma_8$, CFHTLenS drags the estimate of $\log_{10}(-f^0_{R})$ back to the $\Lambda$CDM limit.Comment: 13 pages, 8 figure

Wave breaking and particle jets in intense inhomogeneous charged beams

This work analyzes the dynamics of inhomogeneous, magnetically focused high-intensity beams of charged particles. While for homogeneous beams the whole system oscillates with a single frequency, any inhomogeneity leads to propagating transverse density waves which eventually result in a singular density build up, causing wave breaking and jet formation. The theory presented in this paper allows to analytically calculate the time at which the wave breaking takes place. It also gives a good estimate of the time necessary for the beam to relax into the final stationary state consisting of a cold core surrounded by a halo of highly energetic particles.Comment: Accepted in Physics of Plasma Letter

How emotions and social interaction affect our food experience

The initial intent of this research was to understand whether there were possible interferences between the perception – the sensorial response of the individual when approaching food – and the effective, objective quality of the food Our aim was to investigate whether, at the moment a person is about to experience food, some external factor might influence the individual’s subsequent choice of food. We also wondered whether external factors might render a dish more or less appetizing. Initially we thought about investigating "external factors" such as changes of (exclusively) visual sensory aspects that would directly influence the appeal of food, such as color or size. Later, and during the course of our research, we decided to change our approach and investigate whether there might also be factors unrelated to the food that influence the perception of taste and the subsequent desirability of the food. For a given food, just before its consumption, we asked ourselves which environmental, external human factors might affect the internal subjective representation sufficiently to change the entire food experience. Our approach did not take into consideration a human environment where there was consumption of food, which has already been extensively investigated in numerous studies, but only the interference of the mere sight of an emotion relayed by others’ facial expressions. This research hypothesis is based on the concept of heterosis. We are interested in the method by which to approach a path of heterosis of scientific thought. Starting from the genetic concept of "hybrid vigor", we asked ourselves about the power of a multidisciplinary approach among different scientific disciplines, especially between food science and technology (presence of food), neuroscience (recent discoveries in the field of mirror neurons) and behavioral psychology (changes in food choice). In the field of genetics, heterosis refers to crossbreeding between unrelated individuals. The term heterosis is synonymous with interspecific hybridization, and is the opposite of inbreeding: in the scientific field, according to our approach and idea for the thesis, inbreeding signifies continuing to investigate within the same field of study, without any aperture towards other disciplines, or at least without assessing whether there might be possible interactions of an interdisciplinary nature. The population (gene pool) deriving from heterosis is a genotype which increases the frequency of heterozygosity, which means an increase in the number of loci with different alleles for the gene for the same character. This involves the generation of advantages that improve the fertility and genetics of the species. On the contrary, inbreeding increases the homozygosity, i.e. the presence of identical alleles at the same locus, and this is to the detriment of future genetic improvement. Heterosis is associated with the observed phenomenon known as hybrid vigor, in which the individual is the product of the coupling characteristics of a particularly vigorous phenotype: for example, there is an increase in stature, enhanced fertility, and a stronger resistance to disease. On the other hand, in the case of inbreeding one finds inbreeding depression, in which, among other things, there is an increase in the frequency of genetic diseases and a reduction of vigor and stature. The parallelism that we assumed in the scientific disciplines sees, in the field of interdisciplinary studies, a multiplier effect of discoveries and insights to the benefit of specific individual fields of research. The hybridization of different fields of science can generate new and unexplored fields of research, which may (this is our hypothesis) lead to new disciplines that are the result of the hybridization of such fields. For example: intelligent eating might be a wide new field of research involving neuroscience, psychology, medicine and food science and technology. The underlying theme of this thesis project, supported by comprehensive bibliographic database, is clearly of a hybrid nature, also in the formulation and planning of behavioral experiments. We followed the exploration of such hybridization of science fields without ever going into the specifics of one or the other discipline, but trying to maintain its cross-cutting nature. It is our hope that new fields of research, and even new branches of studies, might result from the heterosis of scientific disciplines, and this effort is intended to be a modest, experimental start whose ambition is to inspire a future in which every field of science has an internal development, specific and specialized, and one or more parallel multidisciplinary developments, each with a precise logic for the development and evolution of the holistic understanding of man.openDottorato di ricerca in Scienze degli alimentiopenRizzato, Matte

Towards a deeper understanding of protein sequence evolution

Most bioinformatic analyses start by building sequence alignments by means of scoring matrices. An implicit approximation on which many scoring matrices are built is that protein sequence evolution is considered a sequence of Point Accepted Mutations (PAM) (Dayhoff et al., 1978), in which each substitution happens independently of the history of the sequence, namely with a probability that depends only on the initial and final amino acids. But different protein sites evolve at a different rate (Echave et al., 2016) and this feature, though included in many phylogenetic reconstruction algorithms, is generally neglected when building or using substitution matrices. Moreover, substitutions at different protein sites are known to be entangled by coevolution (de Juan et al., 2013). This thesis is devoted to the analysis of the consequences of neglecting these effects and to the development of models of protein sequence evolution capable of incorporating them. We introduce a simple procedure that allows including the among-site rate variability in PAM-like scoring matrices through a mean-field-like framework, and we show that rate variability leads to non trivial evolutions when considering whole protein sequences. We also propose a procedure for deriving a substitution rate matrix from Single Nucleotide Polymorphisms (SNPs): we first test the statistical compatibility of frequent genetic variants within a species and substitutions accumulated between species; moreover we show that the matrix built from SNPs faithfully describes substitution rates for short evolutionary times, if rate variability is taken into account. Finally, we present a simple model, inspired by coevolution, capable of predicting at the same time the along-chain correlation of substitutions and the time variability of substitution rates. This model is based on the idea that a mutation at a site enhances the probability of fixing mutations in the other protein sites in its spatial proximity, but only for a certain amount of time

Chaos and Energy Redistribution the Nonlinear Interaction of Two Spatio-Temporal Wave Triplets

In this paper we examine the spatio-temporal dynamics of two nonlinearly coupled wave triplets sharing two common modes. Our basic findings are the following. When spatial dependence is absent, the homogeneous manifold so obtained can be chaotic or regular. If chaotic, it drives energy diffusion from long to small wavelengths as soon as inhomogeneous perturbations are added to the system. If regular, one may yet have two distinct cases: (i) energy diffusion is again present if the inhomogeneous modes are linearly unstable and triplets are effectively coupled; (ii) energy diffusion is absent if the inhomogeneous modes are linearly stable or the triplets are uncoupled.Comment: 21 pages, 5 figures, accepted for publication in Physica D (1997

Dynamic properties of coarse-grained models of linear and circular DNA in nanochannels

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