Revising Abstracts

These are ordered in increasing difficulty: both with respect to the amount of material to be cut to reach 80-90 word limit and to the clarity (or lack of it of) of the prose.

No-nos are (i) future tense and (ii) promissory notes (e.g., will be discussed). To be avoided are (a) passive tense, (b) ill-defined subject (e.g., "this idea" refering to previous sentence with multiple topics), (c) jargon and acronyms, and (d) excessive technical detail.
Incompressible Quantum Liquids and New Conservation Laws

Revised
For quantum liquids, the class of model Hamiltonians can be extended to conserve not only the center-of-mass (CM) momentum but also the center-of-mass position. Regardless of the particle statistics. CM implies the energy spectrum is at least q-fold degenerate when the filling factor is p/q. The simplest Hamiltonian respecting this symmetry encapsulates two novel states of matter: the fractional quantum Hall liquid and the quantum dimer liquid. This Hamiltonian class can also be extended to discriminate possible featureless Mott Insulators.

Original
In this talk I present a class of Hamiltonians which, in addition to the usual center-of-mass (CM) momentum conservation, also have center-of-mass position conservation. I will show that regardless of the particle statistics, as a consequence of CM position conservation, the energy spectrum is at least q-fold degenerate when the filling factor is p/q. the simplest Hamiltonian respecting this type of symmetry encapsulates two prominent examples of novel states of matter, namely the fractional quantum Hall liquid and the quantum dimer liquid. I will discuss the relevance ofthis class of Hamiltonian to the search for featureless Mott Insulators.


This next example had two paragraphs -- another no-no as are references.
DMRG, quantum information, and solving the time dependent Schrodinger equation

Revised
The density matrix renormalization group (DMRG) originally provided a numerical method for solving condensed-matter quantum-lattice systems. Quantum information concepts -- entropy, entanglement, quantum computers -- have recently been connected closely to DMRG. These connections lead to more than a dozen new, numerical DMRG-related techniques. A particularly fruitful one -- the focus today -- is solving the time-dependent, many-particle Schrodinger equation.

Original
The density matrix renormalization group is a numerical method for solving condensed matter quantum lattice systems. Quantum information deals with entanglement, communication using quantum systems, building and using quantum computers, etc. Although these fields seem unrelated, recently a close connection between them has been discovered. In fact, techniques (and people) from quantum information have generated a dozen or so new numerical DMRG-related techniques for solving quantum lattice systems in the last two years.

After discussing the basic ideas of these subjects I will focus on one particularly fruitful area, solving the time dependent Schrodinger equation.


This next example was misleading. When I read it, I thought the speaker had also explained the source of the `negative dc-resistivity' (a long-standing problem). and rewrote the abstract accordingly. That smoked out that he simply assumed it was true and went from there.
Dynamical-symmetry breaking is the origin of the zero-resistance state

Revised
An ultra-pure, two-dimensional electron gas in crossed microwave and magnetic fields shows a zero dc-resistance state (ZRS). A phenomenological theory explains the ZRS in terms of a dynamical instability. The approach relies on the earlier result: microwave radiation slightly above the cyclotron frequency can lead to a negative linear response dc-resistivity. In this case the homogeneous state becomes absolutely unstable. The system develops a current domain pattern with a finite current density such that the differential resistance vanishes.

Original
A novel zero dc-resistance state (ZRS) was recently discovered in a two-dimensional electron gas that is placed in a magnetic field and subjected to microwave radiation. I will review the experimental results and present a phenomenological theory that explains the ZRS in terms of a dynamical instability. If the linear response dc-resistivity turns negative in the presence of the microwave radiation the homogeneous state of the system becomes absolutely unstable. As a result, the system develops a current domain pattern with a finite density, j_0, such that the differential resistance vanishes.


 

This abstract was too long. Worse it seemed to need several ideas to get started. The revision, using a single concept, "drilling holes into material,." managed to drastically shorten it with no loss. The speaker appreciate the work done.
Extraordinary thermal emission from sub-wavelength metallo-dielectric photonic crystals

Revised
Drilling holes in materials can produce surprising results: (i) photonic crystals with bandgaps not in bulk material and (ii) remarkable transmission enhancement in metal sheets. A combined metallo-dielectric photonic crystal exhibits thermal emission so narrow it is being used commercially in (MEMS) gas sensors. A scattering matrix approach can solve the Maxwell's equations in Fourier space. The resulting electromagnetic properties exhibit, in agreement with measurement, sharp resonant absorption and corresponding resonant emission modes with an enormous enhancement of the fields within the sub-wavelength apertures.

Original
A sub-wavelength array of holes in a metal sheet has been known to exhibit a remarkable enhancement of transmission. Such sub-wavelength arrays have been combined with photonic crystals to generate a novel metallo-dielectric photonic crystal by Ion-Optics. When heated this structure exhibits an extraordinary narrow band thermal emission that is being actively used for gas sensing and infrared applications.

We will discuss the physics underlying these phenomena using a rigorous scattering matrix method, which simulates the electromagnetic properties by the solution of Maxwell's equations in Fourier space. Simulations exhibit sharp resonant absorption and corresponding resonant emission modes, in agreement with measurement, with an enormous enhancement of the fields within the sub-wavelength apertures. The role of diffraction and surface plasmons will be discussed.


Fate of the Josephson effect in thin-film superconductors

Revised
The dc Josephson effect probes the nature of the superconducting state. Two superconducting thin films connected by a point contact should exhibit: (1) nearly thermally activated point-contact resistance; (2) energy gap set by (a) the film's superfluid stiffness, (b) angle between the two films and (c) the effective screening of Coulomb interaction between Cooper pairs. These predictions lie in an accessible experimental range of sample size and temperature.

Original
The dc Josephson effect is a probe of the fundamental nature of the superconducting state. In this talk, I will analyze the case of two superconducting thin films connected by a point contact. Remarkably, the Josephson effect is absent at nonzero temperature, even below the K-T transition of the films, and the resistance across the contact is nonzero. Moreover, the point contact resistance is found to vary with temperature in a nearly activated fashion, with a universal energy barrier determined only by the superfluid stiffness characterizing the films, an angle characterizing the geometry, and whether or not the Coulomb interaction between Cooper pairs is screened. As will be shown, this should be testable even in finite systems at a proper range of length-scales and temperatures.

RNA folding and protein misfolding

Revised
The functioning of biopolymers requires their folding to unique 3-dimensional structures. In, for example, ribozymes how do counterions, such as Mg2+, compensate for large negative charge of the phosphate backbone? Recent Xray scattering experiments measure the strength of the effective potential between DNA segments enabling the development of a more realistic model. Current progress suggests that hydrogen-bond formation dominates RNA folding. More broadly, extensions of folding studies may allow understanding of the formation of protein aggregates involved in illnesses (such as Parkinson's) connected with misfolding.

Original
One of the most fundamental properties of functional biopolymers such as enzymes is their ability to fold to a unique 3-dimensional native state. Understanding how this foldability is determined for ribozymes is complicated by the role of counterions, in particular Mg2+, which are needed to compensate for the very large negative charge of the phosphate backbone. We will discuss recent x-ray scattering experiments designed to measure the strength of the effective potential between segments of DNA in a model system and discuss the results in terms of the solution of the Poisson-Boltzmann equation. For the tetrahymena ribozyme we will look at the forces leading to collapse and ultimately to folding to an enzymatically active native state where we find that hydrogen-bond formation appears to be the dominant process in RNA folding.

Self-association of proteins under mildly denaturing conditions to form amyloid polymers is nowadays believed to be a generic property of the peptide backbone. Amyloid deposits are a major manifestation in depository diseases such as Alzheimer's, Parkinson's and BSE (4mad cow!). We will present results of a simulation of the process of amyloid formation for a 7 residue peptide from sup-35, the yeast prion, using a reaction path annealing algorithm based on Onsager and Machlup's path integral for solutions of the overdamped Langevin equation. This approach allows us to identify the principal forces at play in amyloid formation, including those resulting from alignment of backbone dipoles, through gain in entropy from water release and through formation of hydrogen- bond networks in side chains as originally proposed by Perutz.

STOP HERE

Self-association of proteins under mildly denaturing conditions to form amyloid polymers is nowadays believed to be a generic property of the peptide backbone. Amyloid deposits are a major manifestation in depository diseases such as Alzheimer's, Parkinson's and BSE (4mad cow!). We will present results of a simulation of the process of amyloid formation for a 7 residue peptide from sup-35, the yeast prion, using a reaction path annealing algorithm based on Onsager and Machlup's path integral for solutions of the overdamped Langevin equation. This approach allows us to identify the principal forces at play in amyloid formation, including those resulting from alignment of backbone dipoles, through gain in entropy from water release and through formation of hydrogen- bond networks in side chains as originally proposed by Perutz

Virus symmetry affects their assembly process

Revised
The physical structure of viruses raises the continuing question of the relationship between structure and function in biological systems and, more pertinent to this talk, the physical basis of structure in such systems. The two general classes of viruses are rod-like and spherical -- the latter actually having the symmetry of an icosahedron, the twenty-sided Platonic solid. I will discuss recent theoretical investigations on the influences of energetics and other principles on viral assembly and, in particular, on the symmetries exhibited by spherical viruses. As it turns out, simple arguments and models yield outcomes in agreement with experimental results.

RNA folding and protein misfolding

The functioning of biopolymers requires their folding to unique 3-dimensional structures. In, for example, ribozymes how do counterions, such as Mg2+, compensate for large negative charge of the phosphate backbone? Recent Xray scattering experiments measure the strength of the effective potential between DNA segments enabling the development of a more realistic model. Current progress suggests that hydrogen-bond formation dominates RNA folding. More broadly, extensions of folding studies may allow understanding of the formation of protein aggregates involved in illnesses (such as Parkinson's) connected with misfolding.

RNA folding and protein misfolding -->

Tailoring ferromagnetic semiconductors

Tailoring ferromagnetic semiconductors

If magnetic semiconductors are ever to find wide application in real spintronic devices, their magnetic and electronic properties will require tailoring in much the same way that band gaps are engineered in conventional semiconductors. Unfortunately, no systematic understanding yet exists of how, or even whether, properties such as Curie temperatures and band gaps are related in magnetic semiconductors. We have explored theoretically these and other relationships within 64 members of a single materials class, the Mn-doped II-IV-V2 chalcopyrites, two of which are already known experimentally to be ferromagnetic semiconductors. Our results reveal a variation of magnetic properties across different materials that cannot be explained by either of the two dominant models of ferromagnetism in semiconductors. Based on our results for structural, electronic, and magnetic properties, we identify a small number of new chalcopyrites with excellent prospects for stable ferromagnetism.

Flexibility of Biomolecules: Beyond Molecular Dynamics

Molecular dynamics is challenged to model the confirmation of a half-million molecular complexes such as proteins and viruses. Using Lagrange constraints for covalent bonds, hydrogen bonds, hydrophobic tethers, and van der Waals excluded volumes, Monte Carlo dynamics efficiently treats clusters and the flexible joints between them. The generation a new protein conformation requires about 100 milliseconds CPU time. Specifically, input from a single X-ray crystallographic structure can generate an ensemble of structures remarkably similar to those observed in NMR. Further applications are pathways for ligand docking, misfolding proteins and viral-shell swelling.

lexibility in Biomolecules: Beyond Molecular Dynamics

We describe a novel approach to the calculation of flexibility and mobility in proteins, protein complexes and other large (up to half a million atoms) macromolecular complexes like virus capsids.

Rather than using conventional molecular dynamics, we use the constraint approach of Lagrange, incorporating covalent bonds, hydrogen bonds, and tethers for hydrophobic interactions. The rigid clusters, including the core, are identified as well as the flexible joints between them. This is used as the basis for dynamics, using Monte Carlo approaches that maintain all the original constraints, as well as van der Waals excluded volumes. The generation a new protein conformation requires about 100 millsecs CPU time on a single processor [1]. These techniques can be used on a single X-ray crystallographic structure to generate an ensemble of structures remarkably similar to those observed in NMR.

We also show how this approach can be used to generate multiple protein complexes for use in ligand docking studies. We give examples of the pathways for misfolding proteins, like prions, and also the swelling of viral capsids.

[1] Work done in collaboration with Stephen Wells, Brandon M. Hespenheide and Scott Menor.


Fate of the Josephson effect in thin-film superconductors

The dc Josephson effect is a probe of the fundamental nature of the superconducting state. In this talk, I will analyze the case of two superconducting thin films connected by a point contact. Remarkably, the Josephson effect is absent at nonzero temperature, even below the K-T transition of the films, and the resistance across the contact is nonzero. Moreover, the point contact resistance is found to vary with temperature in a nearly activated fashion, with a universal energy barrier determined only by the superfluid stiffness characterizing the films, an angle characterizing the geometry, and whether or not the Coulomb interaction between Cooper pairs is screened. As will be shown, this should be testable even in finite systems at a proper range of length-scales and temperatures.

Do spin glasses have phase transitions?

The mean field theory of spin glasses predicts that there is a sharp phase transition both in zero magnetic field and in the presence of a field (the AT line). The latter is particularly surprising because this transition to a glassy state occurs without a change of symmetry. In this talk I will use Monte Carlo simulations combined with finite-size scaling to investigate whether these transitions occur in real systems.

Modeling the optical and structural properties of nanoparticle arrays and DNA-linked nanoparticle aggregates

Arrays and aggregates of silver and gold nanoparticles have a variety of interesting optical and structural properties that have only begun to be explored. In this talk I will describe theory and modeling studies of these arrays and aggregates, emphasizing two points: how the electromagnetic coupling of nanoparticles in arrays and aggregates influence optical spectra (extinction and surface enhanced Raman), and how DNA hybridization that produces nanoparticle aggregates leads to materials with unusual structural and thermal melting properties. A key point of our work on the optical properties of nanoparticle arrays is that the dipolar coupling between nanoparticles can in some cases be extremely long range, leading to narrow lineshapes in plasmon resonances, very large electromagnetic enhancements, and the ability to propagate and bend electromagnetic waves. Our work on DNA-linked aggregates has emphasized the narrow melting transitions that have proven important to the use of these materials in DNA sensing. I will discuss recent work in understanding the narrow melting based on cooperative interactions between nearby DNA's.


To cite this page:
Revising Abstracts
<http://www.physics.ohio-state.edu/~wilkins/writing/Handouts/VGs/absrev-jan06.html>
[Thursday, 14-Dec-2017 13:41:54 EST]
Edited by: wilkins@mps.ohio-state.edu on Thursday, 05-Apr-2012 11:15:33 EDT