569 Emergent States of Matter

Term essays Fall 2008

These essays were written by students taking Physics 569 Emergent States of Matter, Fall 2008, 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: Yiruo Lin

Title: Vortices in Superfluid Fermi Gases

I briefly reviewed vortex properties and its formation in ultra-cold Fermi gases. For the problem of vortex structure, I focused on mechanisms of density depletion in the vortex core, which is relevant to experiment.

Author: Nir Friedman

Title: Different approaches to population biology

A brief discussion of the main ideas behind population biology. The basic starting points in modelling populations, and common assumptions are discussed. Possible difficulties in assumptions are also mentioned. Different models are discussed as examples, each using different (progressively less) assumptions.
Finally, the possible dangers in some of these assumptions is discussed.

Author: David Zeb Rocklin

Title: The Physics of Traffic Jams: Emergent Properties of Vehicular Congestion

The application of methodology from statistical physics to the flow of vehicles on public roadways challenges the standard physical notion of a "particle".  However, while the individual driver, is macroscopic, unique, and possessing free will, the character of the overall flow of traffic can be captured by "microscopic" models similar to those standard in physics.  "Car following" models and others such as the cellular automata (CA) and hydrodynamic models can capture both the phenomena observed by traffic engineers and the experience of being in traffic.  These models explore the observed phase transition between free-flowing and congested states of traffic.

Author: Harrison Mebane

Title: The Emergence of Criticality in the Earth's Atmosphere


The theory of self-organized criticality has been shown to have applications to many complex phenomena in nature. This paper will address the emergence of criticality in the Earth's atmosphere as observed in rainfall. Recent observations have shown power-law scaling of rainfall events, a signature of criticality. These results have been reproduced by means of a simple sandpile model which sheds light on the origin of criticality in the atmosphere. A summary of the model and a comparison of its results to observational data will be presented, followed by a discussion of ?ndings and ideas for future research.

Author: Johannes Stroehle

Title: How do pedestrian crowds react when they are in an emergency situation - models and software


This term essay re?ects research made for pedestrian behavior in evacuation situations, using di?erent models and software like for example Exodus. Models used in these calculations consider emergent behavior of pedestrian crowds when panic,close space or a high density of people arise. These simulations play an important role to calculate the time needed to rescue people and help to make new buildings like stadiums or skyscrapers a safer place.

Author: Daniel Sussman

Title: The Replica Approach: Spin and Structural Glasses

A spin glass is a type of magnetic ordering that can emerge, most transparently, when a system is both frustrated and has quenched disorder. This paper will review some of the basics of such systems, and then touch on some of the experimental results that served as a guide for the theory. In exploring the theory it will focus on one particular framework, the replica approach, that has been used to study such systems, and will briefly examine how that framework is being expanded to look not only at spin but also structural glasses.

Author: Gustaf Olson

Title: Emergent Schooling Behavior in Fish


The simple rules that govern individual fish behavior lead to the collective motion of larger fish populations known as schooling. This paper looks at the experimental observations of both individual fish behavior and the schooling behavior that arises within larger populations. The broad features of theoretical models which try to simulate schooling in fish are also discussed.

Author: Richard Turner

Title: Abrupt Climate Change and Multistability of the Thermohaline Circulation


Ice core records suggest that the Earth's climate has undergone rapid, catastrophic shifts on multiple occasions in geologically recent times. The multiplicity of steady states found in fluid convection models has led many to speculate that the changes may have been caused by transitions between different stable modes of ocean current patterns. This paper reviews analytical and numerical modeling of multistability in the thermohaline circulation with particular reference to bifurcation analysis. The relevance of these models to paleoclimate data and contemporary observations is discussed.

Author: Matthias W. Gempel

Title: Oscillons formed by granular matter


This text reports on the emergence of oscillons: Their experimental discovery and three models which try to explain them. Respectively the answer to the question: What causes the existence of oscillons and why are they observed in this particular parameter region is tried to be answerd.

Author: Xiaoqian Chen

Title: Physical Models of Blood Vessel Formation


Understanding the mechanism of blood vessel formation has been an important subject in recent medical research. Various experiments and models have been proposed, yet fully understanding the mechanism has been challenging. This paper is meant to be a brief description of experimental results and methods of modeling the blood vessel formation. Models are compared with experimental data for the process of both vasculogenesis and angiogenesis to discuss how physical assumptions in the models lead to the understanding of biological mechanism.

Author: Lee, Kyung Suk

Title: The emergence of individual species


As universal phylogenetic trees can be inferred from molecular sequence comparison, the root of the trees, the early stage of evolution drew people's attention. According to studies, near (and even before) the root of phylogenetic trees, there was a community of living organisms, but they were too unstable and ephemeral to be classified as species. The communal ancestor, dominated by horizontal gene transfer, achieved miraculously huge evolution within comparatively short time period before it finally underwent "Darwinian transition" from a communal state to individual species. This paper summarizes the new evolutionary theory of the early stage of evolution, followed by my speculations on it.

Author: Michael Murray

Title: Emergent Viscous Phenomena in Ferrofluids


This essay investigates the magnetoviscous properties of ferrofluid flow in both an external magnetic field and in zero field. Zero-field properties of ferrofluids are examined. Phenomena such as the dramatic increase in ferrofluid viscosity in the presensce of a static field as well as negative viscosity for an alternating magnetic field are described.

Author: Reza Vafabakhsh

Title: Spontaneous symmetry breaking shaping flowers and leaves.


In this paper I discuss how simple physics and geometry arguments can explain formation of pattern in flowers and leaves. I will also review results of computer simulations and experiments that verify this hypothesis.

Author: Bing Lu

Title: Emergent Physics at the Vulcanization Transition


The Essay starts with an overview of the percolation approach and classical elasticity theory of the vulcanization transition of rubber, describing their assumptions and their limitations. Thereafter we discuss a third approach, the Vulcanization Theory (VT) which incorporates the effects of thermal fluctuations and quenched random disorder. The VT is an order parameter theory in the true Landau tradition. We discuss the very subtle type of spontaneous symmetry breaking that occurs in the transition from liquids to amorphous solids and we define a suitable order parameter that captures this symmetry breaking. This necessitates the introduction of replica field theory, and we discuss what these replicas represent physically. We also discuss the physical meaning behind the resulting Goldstone modes. We conclude the Essay by describing a few applications of VT.

Author: Qinglei Meng

Title: Magnetic vortex


Direct observations of vortex structure only appear recently; in this essay we will examine these first observations. And then introduce experiments and theory about the dynamics of vortex core; meanwhile we will propose the principle of chirality conservation in vortex; and with this idea we present another explanation in Bussmann's experimental results. Finally, reveal the high possible application of vortex in MRAM.

Title: Colloidal Crystal: emergence of long range order from colloidal fluid

Author: Lanfang Li


Although emergence, or spontaneous symmetry breaking, has been a topic of discussion in physics for decades, they have not entered the set of terminologies for materials scientists, although many phenomena in materials science are of the nature of emergence, especially soft materials. In a typical soft material, colloidal suspension system, a long range order can emerge due to the interaction of a large number of particles. This essay will first introduce interparticle interactions in colloidal systems, and then proceed to discuss the emergence of order, colloidal crystals, and finally provide an example of applications of colloidal crystals in light of conventional molecular crystals.

Author: Umi Yamamoto

Title: Emergent Rigidity in Randomly Cross-Linked System


In a randomly cross-linked macromolecular system, a liquid state undergoes the phase transition to amorphous solid states as one increases the number of cross-links. However, the statistical mechanical formulation of this system has been challenging due to its quenched randomness. In this review, I will outline the technique to describe such a system, and demonstrate how the essential properties of vulcanized matter can be derived.

Author: Zuanyi Li

Title: Unconventional Quantum Hall Effect in Graphene


Graphene is a new two-dimensional material prepared successfully in experiments several years ago. It was predicted theoretically and then observed experimentally to present unconventional quantum Hall effect due to its unique electronic properties which exists quasi-particle excitations that can be described as massless Dirac Fermions. This feature leads to the presence of a Landau level with zero energy in single layer graphene and hence a shift of in the filling factor of the Hall conductivity.

Author: Christopher Maffeo

Title: What the flock is emergent collective motion?

Abstract: Many species of fish, birds and insects exhibit collective motion in the form of schools, flocks and swarms. Attempts to understand the mechanism of their collective motion suggest a many-bodied, local interaction, leading most studies to use a computational approach to study a discrete model of interaction between members of the flock. Here, the essential features from minimalist models of flock behavior are described, and the resulting implications for biological flocks are discussed.

Author: Cassandra R Hunt

Title: The emergence of oscillons in granular media

A vibrating plate of granular material can exhibit unexpected emergent behavior, including the formation of oscillons. Oscillons are stable, localized, particle-like clumps of vibrating material that are capable of drifting across the plate as well as attracting and repelling other oscillons. This paper details the characteristics of these strange particles and the specific circumstances required for their formation.

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