569 Emergent States of Matter

Term essays Fall 2009

These essays were written by students taking Physics 569 Emergent States of Matter, Fall 2009, at the University of Illinois at Urbana-Champaign. The copyright of each essay is due to the author.

Please acknowledge the essay title, author, and this course in any citation to these articles.

The information, opinions and interpretations expressed are those of the authors, not necessarily those of the instructor.

Author: Minghao Guo

Title:  Herd Behavior and Phase Transition in Financial Market


In this paper, I brief reviewed the herd behavior in financial market. Benerjee model and EZ model are introduced. Phase transition behavior just like in physical systems is found in EZ herding model. Power law distribution of returns with exponential cutoff of bump are studied in EZ model.

Author: Huiming Xu

Title: Emergent Phases in Optical Lattice


Optical lattice formed by counter propagating laser beams provides us a new platform to study condensed matter physics. Cold atoms moving in an optical lattice could be described by Bose-Hubbard Model. By controlling laser intensity, we could change interaction and tunneling strength at will. Thus, different quantum phases could occur in optical lattice. In this review, I will give an overview of different phases (i.e. Superfluid, Mott Insulating) in optical lattice. I will focus on the phase diagram and the characteristics of different phases.

Author: Braden Brinkman

Title: How Many Neurons Does It Take to Make a Mind?


The human race has made great strides in understanding the world around us, but the understanding of why it is we understand eludes us! We know that thought originates in the brain, we know that the brain is a network of billions of cells called neurons, we know that neurons transmit electric signals between one another and we even know how they transmit these signals, but we still do not know how such features combine to form a mind. Understanding how the mind, or consciousness, emerges from a network of neurons has become one of the great problems of modern science.

In this essay I will tell a story (not the story!) of our attempts to understand our own minds. I begin our exposition, as physicists tend to do, with the basic ``fundamental'' element of our system, the neuron. We then increase our cast and investigate how a network of neurons computes and learns, and finally, I end our story with the tale of a most peculiar hypothesis, that a mere network of neurons is not enough - quantum mechanics must play a role in how the brain computes...

Author: Zachary Yoscovits

Title: Memetics: The Evolution of Culture


Evolution is caused by replicators, which make copies of themselves, with occasional errors.  One can model the evolution of culture using the idea of memes.  Memes are the basic unit of culture which is copied from one person to another by imitation.  By modifying genetic algorithms to take into account the difference between memes and genes one can come up the algorithms to describe the evolution of culture.

Author: Tony Hegg

Title: The Silence of Sound: Acoustic Localization in Bubble Water

Abstract: In this essay classical localization is discussed within the context of air bubbles scattering sound waves in water. Analytical theory, computational calculations, and conclusive properties of the localized state are discussed as well as future avenues of research.

Author:  Seo Ho Youn

Title:  Superradiance :  one theory with different faces


Superradiance, originally theorized by Dicke in 1954, is a collective behavior of individual quantum mechanical systems interacting with their common radiation field. In this essay the main features of superradiance are briefly described in a qualitative manner. Then, along with discussion of three systems (two atoms with mirror, Bose-Einstein condensate in coherent motion, and an ensemble of quantum dots), which can be naively seen different, their connection is drawn through superradiance theory.

Author: Maksim Sipos

Title: Emergence of realistic metabolic networks from artificial chemistry


Complex metabolic networks characterize the life of every cell.  In this paper we review how such metabolic networks can emerge from a model that applies optimization pressure to artificial chemistries.  This model can lead to metabolic networks that share many of the features of real networks, such as cycles and hierarchies.

Author: Anatol E. Wegner

Title: The Emergence of Cooperation in Evolutionary Game Theory


Cooperation is a fundamental aspect of biological systems. The evolution of complex organism, intelligence and complex societies all depend on cooperative behavior. Yet it is not clear how cooperation can evolve through natural selection. This essay will review game theoretical models of cooperation following a chronological approach with the final aim to explore their connection to physics.

Author: Samuel O. Skinner

Title: Emergence of the Canonical Genetic Code


I will review literature that expands the theory that the canonical genetic code was not universal in early life.  Instead, the rudimentary genetic code and decoding mechanism were highly ambiguous, in that mistranslations were made and tolerated.  From this early communal state, genetic codes diverged in pools of innovation.  Through the interaction and competition of these pools, the optimization and universality of the canonical genetic code emerged.

Author: Adam Weis

TItle: The Modern Universe As an Emergent State


The early universe was a hot, opaque soup of unbound fundamental particles.  Our current universe is a cool transparent gas of bound atoms.  What happened?  In this paper, I will discuss our universe's cosmological history as a series of spontaneously-broken symmetries, and the resultant universe as an emergent state.  The quark-hadron transition, nucleosynthesis, and recombination are discussed in terms of their thermodynamics and relevant order parameters.  Concepts are compared with observations and experiments where relevant.  I conclude with some (very) brief comments about structure formation.

Author: William R. McGehee

Title: Long-Range Order in the Hubbard Model


This paper begins by analyzing the Fermi-Hubbard Hamiltonian, a hopping model for Fermions on a lattice, and the pathology of the model's extreme cases is discussed. Finally, the usefulness of experiments with ultracold atoms for studying order in these systems is presented.

Author: En Cai

Title: Emergence in Collective Animal Behavior


Nature has presented us a wide variety of fascinating collective behaviors in animals birds flying in flocks, fish swim in shoals and wild horses move in herds. A number of models are proposed in order to understand the origin of collective behavior and reveal the underlining physics. In this paper, two theoretical models are reviewed: the discrete SPP model and the continuum hydrodynamic model. Both model show that long-range ordering arise as a result of local interactions of the system. The results are compared with recent quantitative experimental data and the emergence of ordered collective motion is discussed. 

Author: Jeremy Morales

Title: Charge Density Waves: An Emergent Ground State in the Manganites


This paper reviews selected developments from the last ten years which argue that the stripe phase observed in the manganites is, in fact, an emergent charge density wave ground state.  The paper's main focus is directed towards two recent papers on this subject.  The first is a theoretical treatment using Ginzburg-Landau theory, and the second is an experimental work using resistivity measurements to find evidence for the collective charge transport mode known as charge density wave "sliding."

Author: Yanxin Liu

Title: Modeling language competition


As same as biological species, languages have the life cycle of birth, evolve, and death. There are about 6900 languages currently spoken in the world. Unfortunately, 90% of them are facing extinction in 21st century as a result of language competition. The loss of linguistic diversity means the loss of cultural diversity. The language competition can be modeled as a collective phenomena resulting from the interactions of individual language speakers. Modeling language competition may be helpful in preserving some of the endangered language. I will review three popular models exploring the question at different level of descriptions: The top-down macroscopic model proposed by Adrams and Strogatz (AS model) is based on the differential rate equation; A modified version of AS model incorporating bilingualism; And the bottom-up microscopic model based on computer simulations focusing the individual language speakers and their interactions. Possible applications of each model are suggested.

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