Evan Evans
Physics, UBC

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Tuesday,10:30 AM, Sept 9 @ P8445B

Ron Dong, Physics,
Brandon University

"Structure and Dynamics of LC materials: An NMR Prospective"

Abstract:
Nuclear Magnetic Resonance (NMR) spectroscopy is a powerful tool for providing insights on soft condensed matter. Here some recent studies will be highlighted to illustrate nuclear spin relaxation, molecular ordering and structure of liquid crystals (LC), e.g., calimatics, bent-core mesogens etc., and molecular solids. Both deuteron and carbon-13 NMR will be discussed.

Tuesday, Sept 16, 2003 10.30 AM @ P8445B

Evan Evans, Physics, UBC

"Dramatic Weakening of Membranes by Microbial Proteins"

Tuesday,10:30 AM, Oct 7@ P8445B

"Clustering induced by fluctuating potentials"
Mustansir Barma ,Tata Institute of Fundamental Research, Mumbai, India

Abstract:
What happens at long times to a system of particles sliding locally downwards
on a randomly fluctuating surface? This question is of interest in a number
of contexts, ranging from the passive scalar problem in a Burgers fluid to
models of growth of binary films. We find that particles cluster together
on a length scale that grows indefinitely in time. As in conventional phase
ordering processes, the density-density correlation function follows a
scaling law, but with the interesting difference that the scaling function
is singular at small argument, implying a breakdown of the Porod law.

Tuesday Oct 14, 2003 @ 10:30 am P8445b

Eldon Emberly, SFU
Title: Bioinformatics: From proteins to gene regulation

Abstract: In this talk I will present a couple applications of mining biological data to extract functional information. The first part will present a statistical analysis of the protein structure database to learn about two important factors influencing protein structure: namely hydrophobicity and secondary structure flexibility. The second part of the talk will present a method for analyzing genomic sequence to determine regulatory sequences which govern gene transcription. Two experimentally validated applications in fruit fly will be discussed: early embryo development and insulation and silencing.

Tuesday, October 21, 2003.

Molecular Aspects of Proton Mobility in Fuel Cell Membranes
Michael Eikerling, Chemistry Department, SFU

Abstract:
Nowadays, polymer electrolyte fuel cells are considered as the most
promising autonomic energy converters for vehicles and portable devices.
They exhibit high efficiencies, low pollution levels and technological
versatility. These outstanding prospects motivate intensive research in
proton conducting polymer electrolyte membranes (PEM). While the presence
of highly mobile liquid-like water in pores of current PEMs promotes
desirable high rates of proton transfer, it imposes penalties of low
operation temperatures and proper fuel cell water balance. In view of these
restrictions, obtaining high proton conductivities with small amounts of
water, tightly bound to a stable host polymer and, thus, restricted in
mobility, would be a major technological breakthrough. However, this
requires understanding of mechanisms of proton transfer in these systems.
Three types of model calculations of proton transport in PEMs will be
presented. At the molecular level, hydration and dissociation of various
acidic functional units for fuel cell polymers have been studied, using
density functional theory calculations. The results can explain differences
in proton conductivity of distinct fuel cell polymers at low levels of
hydration. At the level of a single water-filled membrane pore, kinetic
parameters of proton transfer were calculated with continuum dielectric
theory. These calculations can rationalize effects of pore sizes, proton
distribution within pores and charge distribution of fixed anions on the
activation energy of proton transfer. Moreover, proton transport in a
trifluoromethane sulfonic (triflic) acid monohydrate solid (TAM) was
studied, expecting that it provides (i) a meaningful reference system for
minimally hydrated sulfonic acid head groups involved in PEM of
Nafion®-type and (ii) an appropriate basis of controlled molecular-scale
calculations. Based on ab-initio molecular dynamics calculations the
picture of a concerted mechanism of proton transfer in the crystalline
environment emerged.

Tuesday November 4, 2003
10:30 am P8445b

Mike Dugdale, SFU Phyiscs

Title: Do Casimir forces play a role in soft-matter physics?

Abstract:

Casimir forces occur whenever boundary conditions are placed on a fluctuating field. They are observable in many contexts: from the classic EM-mediated attraction between conducting plates in a vacuum, to the more familiar Van der Walls force. They may also play a role in lipid membrane stabilization; The coupling of the thermodynamic fluctuations of surface density and bulk hydration fields introduces a surface-structure dependent length scale that is consistent with experiment.
This talk will introduce Casimir forces, review some of their more common manifestations, and describe this new model for hydration forces.

Tuesday November 18, 2003
10:30 am P8445b

Andre Marziali, Department of Physics and Astronomy, UBC

Title:
A nano-sensor for trans-membrane capture and identification of single nucleic acid molecules

Abstract:
We present the construction and operation of a self-assembling nanosensor
for sequence specific detection of oligonucleotides across a lipid
membrane. The sensor is composed of the alpha-hemolysin organic nanopore
and a strand of DNA that is electrophoretically inserted and anchored in
the pore. This strand interacts with oligonucleotides on the trans side of
the membrane the pore is formed in, and reports binding events through
electrical obstruction of the pore. Using this sensor, we can uncover the
energy landscape of binding interactions between single DNA molecules on
the trans side of the membrane and the probe strand. This allows us to
detect and identify single base mutations in short oligonucleotide strands
specifically targeted by the sensor probe sequence. The presentation will
include a discussion of the sensor operation and recent experimental results.

Tuesday December 2, 2003

Dave Muraki
Department of Mathematics
Simon Fraser University

Tales of the Nonlinear: a simple illustration of a spectral cascade

The textbook first encounter with nonlinearity in a partial differential
equation (PDE) is the simple kinematic wave equation:
$u_t + u u_x = 0$.
Many are familiar with this equation in the theoretical contexts of
characteristics, wavebreaking, or shock propagation. Another canonical
behaviour contained within this simplest of PDEs is the `spectral cascade'.
The cascade is basically the dynamical exchange of energy between Fourier
modes due to generation of harmonics through the quadratic nonlinearity.
One reason fewer students are acquainted with this aspect of the equation
is due to the lack of a simple exact solution to serve as an introductory
illustration. Surprisingly, buried in a little-known 1964 article by G.W.
Platzman is an elegant example of an exact Fourier series solution
beginning from purely sinusoidal initial conditions. In fact, it is quite
simple to generalize the idea to arbitrary periodic initial conditions.
The spectral cascade is then obtained as the large wavenumber behaviour of
the Fourier coefficients. The entire story retains its introductory value
as the mathematical techniques involved span the basic curriculum of applied
mathematics: characteristics, Fourier series, Bessel functions, integral
representations, contour integration and perturbation theory.
This example recently arose as a simple illustration to explain how a
perturbative approximation could asymptotically characterize the results of
a weak downscale cascade uniformly to high wavenumbers. The idea is used
to explain how weak short-scale waves are generated when density-stratified
air flows over sinusoidal topography.

Tuesday, December 9 10:30 am P8445b

Sarah Veatch
University of Washington

Immiscibility in Model Lipid Membranes: Small and large scale lipid
organization and possible implications for lipid rafts

There is growing evidence that cell plasma membranes are laterally
organized into "raft" regions in which particular lipids and proteins
are concentrated. These domains have submicron dimensions and have
been implicated in vital cell functions. Liquid domains are also
observed in model membranes mimicking cellular lipid compositions, but
unlike their biological counterparts, domains are large (microns) and
readily form in the absence of proteins. The miscibility transition
occurs in a wide variety of ternary lipid mixtures containing high
melting temperature (saturated) lipids, low melting temperature
(usually unsaturated) lipids, and cholesterol. A detailed miscibility
phase diagram has been constructed for membranes of DOPC, DPPC, and
cholesterol and recent NMR experiments have verified the coexistence
of a saturated lipid and cholesterol rich liquid-ordered phase with a
more disordered, unsaturated lipid rich liquid-crystalline phase at
low temperatures. NMR measurements probe significantly smaller
length-scales than microscopy experiments (<100nm vs. >1um), and small
(<50nm) domains are detected by NMR at temperatures just below the
miscibility transition. In this same temperature range, micron-scale
domains are observed by fluorescent microscopy. These results
reemphasize the complex nature of interactions between cholesterol and
saturated phospholipids and may provide insight into how the
miscibility transition relates to lipid rafts in biological membranes.