**Here is my CV.**

**Here is my Ph.D. thesis
in pdf format.**

__Recent Publications:__

`C.D. Santangelo and A.W.C. Lau, Effects
of counterion fluctuations`

`Z. Dogic, J. Zhang, A.W.C. Lau, H. Aranda-Espinoza, P. Dalhaimer,`

**A.W.C. Lau**, B.D. Hoffman, J.C. Crocker, and T.C. Lubensky,__Microrheology, stress fluctuations
and active behavior of living cells,__`Phys. Rev. Lett. 91, 198101 (2003).`

**A.W.C. Lau** and P. Pincus**, **__Counterion
Condensation and Fluctuation-Induced Attraction__**,**`Phys. Rev. E 66,041501 (2002).`

**A.W.C. Lau, **Keng-Hui Lin, and A.G. Yodh,__Entropic interactions in suspensions of
semiflexible rods:____Short-range effects of flexibility__,
Phys. Rev. E **66,** 020401(R) (2002).

**A.W.C. Lau**, D.B. Lukatsky, P. Pincus, and S.A. Safran,__Charge-Fluctuations and Counterion
Condensation__, Phys. Rev. E **65** 051502 (2002).

__A Brief Research Summary:__

My primary
research interest is theoretical soft condensed matter physics, the study
of

materials
characterized by their ease of response to external forces and thermal
fluctuations.

I am particularly
interested in the exciting area of its overlap with cellular biology. Indeed,

the fundamental
building blocks of life - the plasma membrane, the cytoskeleton, microtubule,

DNA, F-actin
- are all soft materials. To date, I have worked on a number of projects
involving

electrostatic,
entropic, and elastic effects in biomolecular systems. My research
interest has

recently
extended to viscoelastic properties of living cells and nematic gels,
a simple model of

actin networks
in cells. Many of these activities, which were inspired by biological
systems,

have stimulated
experimental investigations, which in turn may provide important

physical
insights.

__Correlation effects in electrostatics__

Of all interactions,
electrostatics is arguably the most fundamental for soft systems and it
is

ubiquitous
in biological materials. The standard mean-field approach to charged systems
is

the Poisson-Boltzmann
(PB) theory, or its linearized version, the Debye-H\"{u}ckel theory.

Although
PB theory provides an adequate description for weakly charged systems,
it fails

for highly
charged membranes and biopolymers such as DNA, and in particular, it cannot

account
for the counterion-mediated attractions, which are believed to play a major
role in

DNA condensation.
I have explored this electrostatic attraction in a unified framework,

based on
the Wigner crystal model. In addition, I have worked out the renormalization
of

the bending
constants of a highly charged membrane produced by charge-fluctuations.

It turns
out that, in contradistinction to PB prediction, a highly charged membrane
can

become more
flexible and likely to bend. Moreover, based on a ``two-fluid'' model,
I have

predicted
a novel fluctuation-induced condensation transition, in which a large fraction
of

counterions
is condensed onto a charged plate. A particularly interesting prediction
of this

theory is
that at physiologically relevant temperatures, monovalent and divalent
counterions

exhibit
qualitatively distinct behaviors, as is often observed experimentally.
I have also

extended
this condensation framework to two similarly charged plates, and found
that,

in addition
to attraction, this system may exhibit a first-order binding transition.
My

recent interest
in correlation effects extends to other charged systems and polyelectrolyte

brushes,
in particular.

__Depletion interaction mediated
by semiflexible rods__

Another interaction that is important
in soft matter and particularly in colloidal science is

the depletion attraction.
Its origin is purely entropic: When two spherical particles are

suspended in a solution of order-of-magnitude-smaller
particles, the larger particles attract

because of the gain in the available
volume -- hence entropy -- of the smaller particles

when the larger particles are
close together. A recent experiment which measures the

interaction potential between
two spheres in a solution of semi-flexible rods (fd virus)

did not agree with the ``rigid-rod''
theory which predicts the depletion interaction

mediated by perfectly rigid rods.
To explain this discrepancy, I proposed a simple

bent-rod model, which relies on
the assumption that if the rods are sufficiently stiff,

they might be approximated by
two rods of half the length attached together at a fixed angle.

This model is simple enough for
an analytical treatment and provides an accurate fit of

the measured interaction potential.

__Fluctuations of a bio-polymer
in a nematic background__

The advent of single-molecule manipulation
of biopolymer provides an enormous opportunity

to learn about the dynamics and
statistical properties of biomolecules on a single-molecule level.

While most *in vitro* experiments
are done in an isotropic background, many biopolymers such

as the actin filaments within
the sarcomere and neurofilaments within the axon actually reside

in an anisotropic nematic-like
environment. Together with the experimental group at UPenn, I

have investigated the behaviors
of single semiflexible polymers dissolved in a nematic background

of fd virus. I have contributed
theoretically to explain the experimental observations, and in

particular, constructed a rotationally-invariant
theory for a single semiflexible polymer in a

nematic matrix, and calculated
from it the fluctuation spectrum, which compares well with experiments.

__Microrheology of living cells__

An physical
picture of active behaviors of living cells is crucial for a more complete

understanding
of cellular processes such as intracellular transport of vesicles and organelles.

The molecular
basis of such behaviors are highly specialized protein molecules which

transduce
the chemical energy of a fuel molecule, ATP, to mechanical work and motion.

Together
with J. Crocker and Lubensky, I am presently pursuing the question of whether

microrheology
can be applied to studying active behavior of the cytoskeleton of living
cells.

Microrheology
has recently become a powerful tool to measure elastic moduli of complex
fluids.

Unlike conventional
rheology measurements, it relies on the Brownian (thermal) fluctuations
of

micron-sized
beads dispersed in the sample to assess the viscoelastic response function.

A natural
extension of this novel technique to living cells is to assume that the
beads

are not
driven by thermal noise, instead by a non-thermal noise arising from the
presence

of active
elements (motors). With Tom Lubensky, I have worked out theoretically
that if one

can quantify
the rheology of a cell using a frequency-dependent shear modulus, the power

spectrum
of the non-thermal noise can be sensibly extracted from two-point microrheology

(tracking
two particles simultaneously) experiments. Preliminary experimental
results of

Crocker
show that this power spectrum exhibits power-law behavior over a few decades

in the ten
Hertz regime.