J.R. (Josh) Gladden
Assistant Professor of Physics
National Center for Physical Acoustics
University of Mississippi
662-915-7428
jgladden@olemiss.edu
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- Research Interests
Resonant Ultrasound
Spectroscopy
RUS is an elegant
experimental method
for determining the full elastic
tensor of a single crystal by measuring the mechanical resonance
spectrum (see animations below) of a sample. Elastic constants are a
measure of the
interaction of the atoms in the crystal lattice and so are sensitive to
phase transitions. We specialize in small sample (sub-millimeter
dimensions) RUS and thin
film RUS in which the elastic constants for a thin film on a substrate
can be obtained. A special cell to handle very small samples as
recently been constructed (see images).
Thin film RUS has
been
used to study collosal magnetoresistance phase transitions and thin
tangled mats of single wall carbon nanotubes on a variety of
substrates.
Additionally, we have the capabilities to make
elastic
constant measurements of materials at temperatures up to 1300 K using
quartz buffer rods to transmit the ultrasonic waves into the sample
and back out. We are currently using these two facilities to
study
such novel materials as:
- aligned and random arrays of carbon nanotubes in
polymer composites
- super hard
diamond films made from C-13
- glass transitions in bulk
metallic glasses
- critical phenomenon in transition metal oxides
- novel piezoelectric materials
- Zintl phase thermoelectrics
More details about
how
RUS works can be found here.
Dynamic problems in continuum
mechanics and soft matter
Ripping Fluids
We have the dynamics
of
how a rigid rod moves through a viscoelastic gel-like material,
including transitions
from fluid-like flow to solid-like tearing. The "fluid" is a
highly concentrated worm-like micelle (WM) solution - a mixture of
water, soap, and salts. In response to a stress, the material
flows like a liquid on long time scales (more than a few seconds), but
tears like a solid on short time scales. As an added benefit, WM
fluids are highly birefringent so that stress fields can be readily
visualized using crossed polarizing plates. This work was
performed with Prof. Andrew Belmonte of Penn
State. More information can
be found here:
- More complete web page on ripping fluids. [ go there ]
- Physical Review Letter reporting our findings [pdf]
- American Institute of Physics News Update (May 21,
2007) [ go
there ]
- Included in "Physics News of 2007" by the American Physical Society [ pdf ]
Dynamics of Buckling
Using high speed video, we have
studied the buckling of a thin rod impacted by a projectile ~ a fancy
way of breaking pasta! The story can be found here and
the Physical Review Letter can be downloaded here. This work was also featured
Science
News [Nov. 12, 2005] and
on an CBC radio "Quirks and Quarks" [Nov. 19, 2005]
interview with one of my co-authors Prof. Andrew Belmonte of Penn
State. The interview can be downloaded
here in MP3 format.
Electromagnetic and mechanical
properties of chiral materials
We have been fabricating and investigating chiral materials - materials
which have internal structures posessing a certain "handedness".
These structures break inversion symmetry and produce interesting
effects when waves (electromagnetic or acoustic) scatter off
them. We've been studying small beryllium-copper springs embedded
in a dielectric wax using a custom designed square cross section wave
guide. These studies are a collaboration with the Electrical
Engineering Dept. at Ole Miss.
- Teaching
Current (Spring 2008)
General Physics - Physics 214
Computational Physics - Physics 503
Previous Semesters
Physics 213, Physics
224 (lab), Physics 107, Physics 510
Other teaching related things
Software Resources for Physics Education
(presented at MAP 2006)
Lecture notes for my Spring 2008 MCAT Physics review session can be downloaded here.
(NOTE: These are copies of the the overhead
slides, written and projected to students in real time,
so there are probably plenty of
typos and misspellings!)
I am also proposing a Computational Science course teaching general
computational tools for students of the physical sciences and
mathematics. More information can be found here.
- Professional History
List of my publications
Full Curriculum Vitae (html, pdf)
2005 - Present: Assistant Professor
Dept. of Physics and National Center for Physical Acoustics, University
of Mississippi
2003-2005: Postdoctoral Fellow
W.G. Pritchard Lab, Dept. of Mathematics, Penn State University with
Prof. Andrew Belmonte
1999-2003: Ph.D. degree: Dept. of Physics, Penn State University with
Prof. Jay Maynard
1991-1994: M.S. degree: Dept. of Physics, University of Montana
1987-1991: B.S. degree: Dept. of Physics, University of the South
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