scholarly journals THEORETICAL TOOLS FOR CMB PHYSICS

2005 ◽  
Vol 14 (03n04) ◽  
pp. 363-510 ◽  
Author(s):  
MASSIMO GIOVANNINI
Keyword(s):  
Early Universe ◽  
Large Scale ◽  
Theoretical Models ◽  
Unified Theory ◽  
Open Problems ◽  
Gauge Invariant ◽  
Origin And Evolution ◽  
Consistent Manner ◽  
Stochastic Backgrounds ◽  
Analytical Tools

This review presents, in a self–consistent manner, those analytical tools that are relevant for the analysis of the physics of CMB anisotropies generated in different theoretical models of the early Universe. After introducing the physical foundations of the Sachs–Wolfe effect, the origin and evolution of the scalar, tensor and vector modes of the geometry is treated in both gauge-invariant and gauge-dependent descriptions. Some of the recent progresses in the theory of cosmological perturbations are scrutinized with particular attention to their implications for the adiabatic and isocurvature paradigms, whose description is reviewed both within conventional fluid approaches and within the Einstein–Boltzmann treatment. Open problems and theoretical challenges for a unified theory of the early Universe are outlined in light of their implications for the generation of large-scale anisotropies in the CMB sky and in light of the generation of stochastic backgrounds of relic gravitons between few Hz and the GHz.

Game Theory for Cooperation in Multi-Access Edge Computing

2019 ◽  
pp. 100-149
Author(s):  
Jose Moura ◽  
Rui Neto Marinheiro ◽  
Joao Carlos Silva
Keyword(s):  
Game Theory ◽  
Large Scale ◽  
Network Performance ◽  
Theoretical Models ◽  
Spectrum Utilization ◽  
Open Problems ◽  
Cooperative Strategies ◽  
Complex Interactions ◽  
Management Policies ◽  
Multi Access

Cooperative strategies amongst network players can improve network performance and spectrum utilization in future networking environments. Game Theory is very suitable for these emerging scenarios, since it models high-complex interactions among distributed decision makers. It also finds the more convenient management policies for the diverse players (e.g., content providers, cloud providers, edge providers, brokers, network providers, or users). These management policies optimize the performance of the overall network infrastructure with a fair utilization of their resources. This chapter discusses relevant theoretical models that enable cooperation amongst the players in distinct ways through, namely, pricing or reputation. In addition, the authors highlight open problems, such as the lack of proper models for dynamic and incomplete information scenarios. These upcoming scenarios are associated to computing and storage at the network edge, as well as, the deployment of large-scale IoT systems. The chapter finalizes by discussing a business model for future networks.

scholarly journals Evolution of Neutron Star Magnetic Fields

Universe ◽  
2021 ◽  
Vol 7 (9) ◽  
pp. 351
Author(s):  
Andrei P. Igoshev ◽  
Sergei B. Popov ◽  
Rainer Hollerbach
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Magnetic Fields ◽  
Neutron Stars ◽  
Binary Systems ◽  
Theoretical Models ◽  
Compact Objects ◽  
Open Problems ◽  
Origin And Evolution ◽  
Field Decay

Neutron stars are natural physical laboratories allowing us to study a plethora of phenomena in extreme conditions. In particular, these compact objects can have very strong magnetic fields with non-trivial origin and evolution. In many respects, its magnetic field determines the appearance of a neutron star. Thus, understanding the field properties is important for the interpretation of observational data. Complementing this, observations of diverse kinds of neutron stars enable us to probe parameters of electro-dynamical processes at scales unavailable in terrestrial laboratories. In this review, we first briefly describe theoretical models of the formation and evolution of the magnetic field of neutron stars, paying special attention to field decay processes. Then, we present important observational results related to the field properties of different types of compact objects: magnetars, cooling neutron stars, radio pulsars, and sources in binary systems. After that, we discuss which observations can shed light on the obscure characteristics of neutron star magnetic fields and their behaviour. We end the review with a subjective list of open problems.

Opinion Dynamics Optimization by Varying Susceptibility to Persuasion via Non-Convex Local Search

2021 ◽  
Vol 16 (2) ◽  
pp. 1-34
Author(s):  
Rediet Abebe ◽  
T.-H. HUBERT Chan ◽  
Jon Kleinberg ◽  
Zhibin Liang ◽  
David Parkes ◽  
...  
Keyword(s):  
Local Search ◽  
Objective Function ◽  
Iterative Process ◽  
Large Scale ◽  
Opinion Dynamics ◽  
Theoretical Models ◽  
Global Optimum ◽  
Local Optimum ◽  
Opinion Formation ◽  
Long Line

A long line of work in social psychology has studied variations in people’s susceptibility to persuasion—the extent to which they are willing to modify their opinions on a topic. This body of literature suggests an interesting perspective on theoretical models of opinion formation by interacting parties in a network: in addition to considering interventions that directly modify people’s intrinsic opinions, it is also natural to consider interventions that modify people’s susceptibility to persuasion. In this work, motivated by this fact, we propose an influence optimization problem. Specifically, we adopt a popular model for social opinion dynamics, where each agent has some fixed innate opinion, and a resistance that measures the importance it places on its innate opinion; agents influence one another’s opinions through an iterative process. Under certain conditions, this iterative process converges to some equilibrium opinion vector. For the unbudgeted variant of the problem, the goal is to modify the resistance of any number of agents (within some given range) such that the sum of the equilibrium opinions is minimized; for the budgeted variant, in addition the algorithm is given upfront a restriction on the number of agents whose resistance may be modified. We prove that the objective function is in general non-convex. Hence, formulating the problem as a convex program as in an early version of this work (Abebe et al., KDD’18) might have potential correctness issues. We instead analyze the structure of the objective function, and show that any local optimum is also a global optimum, which is somehow surprising as the objective function might not be convex. Furthermore, we combine the iterative process and the local search paradigm to design very efficient algorithms that can solve the unbudgeted variant of the problem optimally on large-scale graphs containing millions of nodes. Finally, we propose and evaluate experimentally a family of heuristics for the budgeted variant of the problem.

scholarly journals Relativistic Cosmology with an Introduction to Inflation

Universe ◽  
2021 ◽  
Vol 7 (8) ◽  
pp. 276
Author(s):  
Muhammad Zahid Mughal ◽  
Iftikhar Ahmad ◽  
Juan Luis García Guirao
Keyword(s):  
Standard Model ◽  
Early Universe ◽  
Large Scale ◽  
Initial Conditions ◽  
Big Bang ◽  
Relativistic Cosmology ◽  
The Standard Model ◽  
Big Bang Model ◽  
The Big Bang ◽  
The Universe

In this review article, the study of the development of relativistic cosmology and the introduction of inflation in it as an exponentially expanding early phase of the universe is carried out. We study the properties of the standard cosmological model developed in the framework of relativistic cosmology and the geometric structure of spacetime connected coherently with it. The geometric properties of space and spacetime ingrained into the standard model of cosmology are investigated in addition. The big bang model of the beginning of the universe is based on the standard model which succumbed to failure in explaining the flatness and the large-scale homogeneity of the universe as demonstrated by observational evidence. These cosmological problems were resolved by introducing a brief acceleratedly expanding phase in the very early universe known as inflation. The cosmic inflation by setting the initial conditions of the standard big bang model resolves these problems of the theory. We discuss how the inflationary paradigm solves these problems by proposing the fast expansion period in the early universe. Further inflation and dark energy in fR modified gravity are also reviewed.

Creep of frozen slopes and ice-filled rock joints under temperature variation

2006 ◽  
Vol 33 (6) ◽  
pp. 719-725 ◽  
Author(s):  
Branko Ladanyi
Keyword(s):  
Creep Behavior ◽  
Large Scale ◽  
Variable Temperature ◽  
Theoretical Models ◽  
Rock Joints ◽  
Interface Problems ◽  
Frozen Ground ◽  
Rock Glaciers ◽  
Rock Interface ◽  
Creep Temperature

Owing to climate warming trends, there has been an increasing interest in recent years in the accelerating creep of rock glaciers and frozen slopes. In the field of glaciology, the creep of glaciers has been extensively studied, observed, and analyzed for more than 100 years. Many valuable and detailed theoretical models have been proposed through the years for simulating the creep behavior of glaciers. This synthesis paper has no intention of proposing another one. Its purpose is only to supply to these models a potential geotechnical background, borrowed from the connected fields of frozen ground mechanics, rock mechanics, and the mechanics of mixtures. In particular, this paper attempts to extend some known models of mechanical behavior of unfrozen soil and rock masses to masses containing ice and to apply these models to large-scale creep of ice–rock mixtures and ice–rock interface problems under variable temperature and stress conditions.Key words: ice, rock, mixture, rock joints, slope stability, creep, temperature.

scholarly journals Magnetic Fields in Galaxies

2010 ◽  
Vol 6 (S271) ◽  
pp. 135-144
Author(s):  
Ellen G. Zweibel
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Cosmic Time ◽  
Origin And Evolution ◽  
Cosmological Problem ◽  
Background Turbulence ◽  
Multicomponent Gas ◽  
Magnetic Buoyancy ◽  
Galactic Dynamos

AbstractThe origin and evolution of magnetic fields in the Universe is a cosmological problem. Although exotic mechanisms for magneotgenesis cannot be ruled out, galactic magnetic fields could have been seeded by magnetic fields from stars and accretion disks, and must be continuously regenerated due to the ongoing replacement of the interstellar medium. Unlike stellar dynamos, galactic dynamos operate in a multicomponent gas at low collisionality and high magnetic Prandtl number. Their background turbulence is highly compressible, the plasma β ~ 1, and there has been time for only a few large exponentiation times at large scale over cosmic time. Points of similarity include the importance of magnetic buoyancy, the large range of turbulent scales and tiny microscopic scales, and the coupling between the magnetic field and certain properties of the flow. Understanding the origin and maintenance of the large scale galactic magnetic field is the most challenging aspect of the problem.

scholarly journals Large Scale Structure of the Universe: Theoretical Problems

1990 ◽  
Vol 43 (2) ◽  
pp. 159
Author(s):  
E Saar
Keyword(s):  
Early Universe ◽  
Present Status ◽  
Large Scale ◽  
Large Scale Structure ◽  
Short Review ◽  
Fractal Model ◽  
Scale Structure ◽  
The Subject ◽  
The Universe

Implications of the observed large scale structure on the physics of the early universe are described. A short review of Soviet work on the subject is given, and the present status of the fractal model of the large scale structure is discussed.

scholarly journals Reference genome assemblies reveal the origin and evolution of allohexaploid oat

2021 ◽  
Author(s):  
Yuanying Peng ◽  
Honghai Yan ◽  
Laichun Guo ◽  
Cao Deng ◽  
Lipeng Kang ◽  
...  
Keyword(s):  
Large Scale ◽  
Molecular Mechanisms ◽  
Higher Plants ◽  
Cereal Crops ◽  
Origin And Evolution ◽  
Avena Species ◽  
Oxford Nanopore ◽  
Reference Quality ◽  
Phylogenomic Analyses ◽  
Reference Genomes

Abstract Common oat (Avena sativa) is one of the most important cereal crops serving as a valuable source of forage and human food. While reference genomes of many important crops have been generated, such work in oat has lagged behind, primarily owing to its large, repeat-rich, polyploid genome. By using Oxford Nanopore ultralong sequencing and Hi-C technologies, we have generated the first reference-quality genome assembly of hulless common oat with a contig N50 of 93 Mb. We also assembled the genomes of diploid and tetraploid Avena ancestors, which enabled us to identify oat subgenome, large-scale structural rearrangements, and preferential gene loss in the C subgenome after hexaploidization. Phylogenomic analyses of cereal crops indicated that the oat lineage descended before wheat, offering oat as a unique window into the early evolution of polyploid plants. The origin and evolution of hexaploid oat is deduced from whole-genome sequencing, plastid genome and transcriptomes assemblies of numerous Avena species. The high-quality reference genomes of Avena species with different ploidies and the studies of their polyploidization history will facilitate the full use of crop gene resources and provide a reference for the molecular mechanisms underlying the polyploidization of higher plants, helping us to overcome food security challenges.

scholarly journals Acoustics of early universe—Lifshitz versus gauge-invariant theories

2001 ◽  
Vol 42 (2) ◽  
pp. 856 ◽  
Author(s):  
Zdzisław A. Golda ◽  
Andrzej Woszczyna
Keyword(s):  
Early Universe ◽  
Gauge Invariant

scholarly journals Chiral Anomaly, Topological Field Theory, and Novel States of Matter

2018 ◽  
Vol 30 (06) ◽  
pp. 1840007 ◽  
Author(s):  
Jürg Fröhlich
Keyword(s):  
Hall Effect ◽  
Quantum Hall Effect ◽  
Time Reversal ◽  
Topological Insulators ◽  
Large Scale ◽  
Quantum Hall ◽  
Chiral Anomaly ◽  
Open Problems ◽  
Spin Currents ◽  
Spin Orbit Interactions

Starting with a description of the motivation underlying the analysis presented in this paper and a brief survey of the chiral anomaly, I proceed to review some basic elements of the theory of the quantum Hall effect in 2D incompressible electron gases in an external magnetic field, (“Hall insulators”). I discuss the origin and role of anomalous chiral edge currents and of anomaly inflow in 2D insulators with explicitly or spontaneously broken time reversal, i.e. in Hall insulators and “Chern insulators”. The topological Chern–Simons action yielding the large-scale response equations for the 2D bulk of such states of matter is displayed. A classification of Hall insulators featuring quasi-particles with abelian braid statistics is sketched. Subsequently, the chiral edge spin currents encountered in some time-reversal invariant 2D topological insulators with spin-orbit interactions and the bulk response equations of such materials are described. A short digression into the theory of 3D topological insulators, including “axionic insulators”, follows next. To conclude, some open problems are described and a problem in cosmology related to axionic insulators is mentioned. As far as the quantum Hall effect and the spin currents in time-reversal invariant 2D topological insulators are concerned, this review is based on extensive work my collaborators and I carried out in the early 1990’s. Dedicated to the memory of Ludvig Dmitrievich Faddeev — a great scientist who will be remembered

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