Collective Brownian Motors - Experiments and Models
description
Transcript of Collective Brownian Motors - Experiments and Models
![Page 1: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/1.jpg)
Collective Brownian Motors - Experiments and ModelsErin Craig, Heiner LinkeUniversity of Oregon
Ann Arbor, June 12 2007
Load force
![Page 2: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/2.jpg)
-
+
J. Bader et al,PNAS 96, 13165 (1999)
Ajdari and Prost, C.R. Acad. Sci. Paris II 315, 1635 (1992)
Non-equilibrium+ Asymmetry+ Thermal fluctuations= Transport
Brownian motorsexample: flashing ratchet
ON
OFF
ON
![Page 3: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/3.jpg)
Brownian motors: overview of projects
Experimental ratchets:
Collective Brownian motors: modeling and experimental planning
Computational models of biological molecular motors:
Information feedback Coupled particle ratchet Polymer motor
Self-propelled droplets Quantum ratchets
1D kinesin model 3D myosin V model
Efficient thermoelectrics
e
![Page 4: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/4.jpg)
QuickTime™ and aMPEG-4 Video decompressor
are needed to see this picture.
Self-propelled fluids
![Page 5: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/5.jpg)
Droplet of liquid nitrogen (77 K) onmachined brass surface (300 K).
Filmed at 500 frames per second
15 mm
Slow motion
QuickTime™ and aMicrosoft Video 1 decompressorare needed to see this picture.
![Page 6: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/6.jpg)
Film boiling (Leidenfrost effect)
Vapor layer separates solid and liquid (≈ 10 - 100 µm).
Film boiling point: Water ≈ 200 - 300 °C
Ethanol ≈ 120 °C R134a ≈ 22 °C
0.3 mm
1.5 mm
![Page 7: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/7.jpg)
Film boiling (Leidenfrost effect)
0.3 mm
1.5 mm
QuickTime™ and aMotion JPEG A decompressor
are needed to see this picture.
H. Linke et. al., PRL 96, 154502 (2006).More movies: darkwing.uoregon.edu/~linke/dropletmovies
![Page 8: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/8.jpg)
Brownian motors: overview of projects
Experimental ratchets:
Collective Brownian motors: modeling and experimental planning
Computational models of biological molecular motors:
Information feedback Coupled particle ratchet Polymer motor
Self-propelled droplets Quantum ratchets
1D kinesin model 3D myosin V model
Efficient thermoelectrics
e
![Page 9: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/9.jpg)
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
How to get flux or work out of a thermal system?Open-loop strategy:ex: Brownian ratchet
Closed-loop (feedback) strategy:ex: Maxwell’s demon
• Directionality: spatial asymmetry• Energy input: turning potential on/off
• Directionality: information feedback• Energy input:
collecting informationopen/closing door
![Page 10: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/10.jpg)
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
How to get flux or work out of a thermal system?Open-loop strategy:ex: Brownian ratchet
Closed-loop (feedback) strategy:ex: Maxwell’s demon
• Directionality: spatial asymmetry• Energy input: turning potential on/off
• Directionality: information feedback• Energy input:
collecting informationopen/closing door
Both systems produce net flux w/o applying macroscopic forces directly to particles and w/o violating the 2nd Law of Thermodynamics.
![Page 11: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/11.jpg)
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
How to get flux or work out of a thermal system?Open-loop strategy:ex: Brownian ratchet
Closed-loop (feedback) strategy:ex: Maxwell’s demon
• Directionality: spatial asymmetry• Energy input: turning potential on/off
• Directionality: information feedback• Energy input:
collecting informationopen/closing door
• Do closed-loop strategies always out perform open-loop strategies?
• Fundamental limitations on output of information feedback strategy?
• Experimental realization?
![Page 12: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/12.jpg)
Information feedback in thermal ratchets:
For a system of N particles,
€
ft()=1N Fxi( )i
N∑ , is av e rage
force particles w ou ld fee l if potentia l ONß If
€
f t()≥0, turn potential ONß If
€
f t()<0, turn potential OFF
F. J. Cao et. al., PRL 93, 040603 (2004).
V(x)
x
aL
L
![Page 13: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/13.jpg)
Information feedback in thermal ratchets:
F. J. Cao et. al., PRL 93, 040603 (2004).
optimal periodic switching
V(x)
x
aL
L
![Page 14: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/14.jpg)
Time delay in feedback implementation:
t1 = delay due to computational time(If a measurement is taken at time t, the feedback based on this measurement will occur at
time t + t1.)
t2 = delay due to measurement time(If a measurement is taken at time t, the next measurement will be taken at time t + t2.)
![Page 15: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/15.jpg)
Time delay in feedback implementation:
• Original scheme: higher current than optimal periodic switching• Delay t1 reduces current because high fluctuations reduce relevance of delayed information
• Original scheme worse than periodic switching• For some values of t1, system settles into steady state that reproduces optimal periodic flashing.
Large N (more deterministic):
Small N (high fluctuations):
0
1
2
3
4
0 0.02 0.04 0.06 0.08 0.1
N=1N=10N=100N=316N=1000N=3162N=10,000N=100,000N=1,000,000
t1t1 / (L
2/D)
0
0.1
0.2
0.3
0 0.02 0.04 0.06 0.08 0.1
t1 / (L
2/D)
E. Craig et. al., to submit (2007).
![Page 16: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/16.jpg)
Time delay in feedback, N=106:
-1
0
1
0 0.1 0.2 0.3 0.4 0.5At / (L
2/D)
0
1
A
0
1
A
b)
-1
0
1
0 0.1 0.2 0.3 0.4 0.5At / (L
2/D)
0
1
a)
0
1
D
A
α( )t
t1 = 0.02 L2/D; t2 = 0 t1 = 0.09 L2/D; t2 = 0
E. Craig et. al., to submit (2007).
![Page 17: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/17.jpg)
Time delay in feedback, N=106:
-1
0
1
0 0.1 0.2 0.3 0.4 0.5At / (L
2/D)
0
1
A
0
1
A
b)
-1
0
1
0 0.1 0.2 0.3 0.4 0.5At / (L
2/D)
0
1
a)
0
1
D
A
α( )t
t1 = 0.02 L2/D; t2 = 0 t1 = 0.09 L2/D; t2 = 0
E. Craig et. al., to submit (2007).
0
0.2
0.4
0 0.05 0.1 0.15 0.2At
1 / (L
2/D)
0.1
0.15
0.2
0.25
0.3
0 0.05 0.1 0.15 0.2
t1 / (L
2/D)
a)
b)
= t1
= t1/2
a
b
![Page 18: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/18.jpg)
Time delay in electrostatic experiment:
Simulated time delay:Experimental time delay:
V(x)for anegativelychargedparticle
+
_Inter Digitated Electrode Array (IDEA): Manufacturedusing lithography to deposit platinum electrodes on toa silicon substrate.
Expose, Readout Image to Computer
Locate Particles Decide voltage Actuate Voltage
Next Exposure
Actuate Voltage(from previous image)
t2
t1
![Page 19: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/19.jpg)
Brownian motors: overview of projects
Experimental ratchets:
Collective Brownian motors: modeling and experimental planning
Computational models of biological molecular motors:
Information feedback Coupled particle ratchet Polymer motor
Self-propelled droplets Quantum ratchets
1D kinesin model 3D myosin V model
Efficient thermoelectrics
e
E. Craig et. al., PRE, 2006
![Page 20: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/20.jpg)
QuickTime™ and aCinepak decompressor
are needed to see this picture.
Artificial single-molecule motor
M. Downton
![Page 21: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/21.jpg)
Average velocity peaks at L ≈ 5 , independent of polymer length N.
Ratchet period L ()
Vel
ocity
(L/
L
ton = toff = 20
M. Downton et. al.,Phys. Rev. E 73, 011909 (2006)
![Page 22: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/22.jpg)
Stall force is proportional to polymer length
Fstall ≈ 1kT/
= 0.04 pNfor 100 nm
≈ pN for 5 nm
L = 5
Sta
ll fo
rce
(kT
/
M. Downton et. al.,Phys. Rev. E 73, 011909 (2006)
![Page 23: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/23.jpg)
Experiment in progress
1 µm
Brian Long, UOJonas Tegenfeldt, Lund
• cycle time ≈ 20 ms ≈ 50 Hz• expected speed ≈ 1 µm/s
![Page 24: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/24.jpg)
10 µm
• High resolution images of DNA• Response to voltage, background drift
• Future: analysis of conformations, fluctuations, trajectories
Brian Long, UOJonas Tegenfeldt, Lund
Experiment in progress
QuickTime™ and aSorenson Video decompressorare needed to see this picture.
![Page 25: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/25.jpg)
Brownian motors: overview of projects
Experimental ratchets:
Collective Brownian motors: modeling and experimental planning
Computational models of biological molecular motors:
Information feedback Coupled particle ratchet Polymer motor
Self-propelled droplets Quantum ratchets
1D kinesin model 3D myosin V model
Efficient thermoelectrics
e
![Page 26: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/26.jpg)
Myosin V: hand-over-hand walking molecular motor
A. R. Dunn, J. A. Spudich, Nature SMB 14, 246 (2007).
• Processive motor involved in vesicle and organelle transport• Two part step: lever arm rotation followed by diffusive search?
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
A. Yildiz,..., P. Selvin,Science 300, 2061 (2003).
![Page 27: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/27.jpg)
Myosin V mechanochemical cycle
K.I.
Ska
u, R
.B. H
oyle
, M.S
. Tur
ner,
BP
J 91
, 247
5 (2
006)
.M
. Rie
f.,...
,J. S
pudi
ch, P
NA
S 9
7, 9
482
(200
0).
• Conformational change• Internal coordination• Brownian diffusion
ATP ADP ADP
ATP
ADP·Pi
ADP
ADPADP
ADP
4. 5.
1.
2.
3.
ATP
PiADP
![Page 28: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/28.jpg)
Myosin V mechanochemical cycle
ATP ADP ADP
ATP
ADP·Pi
ADP
ADPADP
ADP
4. 5.
1.
2.
3.
ATP
PiADP
Conformational change creates strain K
.I. S
kau,
R.B
. Hoy
le, M
.S. T
urne
r, B
PJ
91, 2
475
(200
6).
M. R
ief.,
...,J
. Spu
dich
, PN
AS
97,
948
2 (2
000)
.
• Conformational change• Internal coordination• Brownian diffusion
![Page 29: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/29.jpg)
Myosin V mechanochemical cycle
ATP ADP ADP
ATP
ADP·Pi
ADP
ADPADP
ADP
4. 5.
1.
2.
3.
ATP
PiADP
Conformational change creates strain
Strain-dependent coordination of chemical cycle K
.I. S
kau,
R.B
. Hoy
le, M
.S. T
urne
r, B
PJ
91, 2
475
(200
6).
M. R
ief.,
...,J
. Spu
dich
, PN
AS
97,
948
2 (2
000)
.
• Conformational change• Internal coordination• Brownian diffusion
![Page 30: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/30.jpg)
Myosin V mechanochemical cycle
ATP ADP ADP
ATP
ADP·Pi
ADP
ADPADP
ADP
4. 5.
1.
2.
3.
ATP
PiADP
Conformational change creates strain
Release of strain
K.I.
Ska
u, R
.B. H
oyle
, M.S
. Tur
ner,
BP
J 91
, 247
5 (2
006)
.M
. Rie
f.,...
,J. S
pudi
ch, P
NA
S 9
7, 9
482
(200
0).
• Conformational change• Internal coordination• Brownian diffusion
Strain-dependent coordination of chemical cycle
![Page 31: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/31.jpg)
ATP ADP ADP
ATP
ADP·Pi
ADP
ADPADP
ADP
4. 5.
1.
2.
3.
ATP
PiADP
Diffusion
Myosin V mechanochemical cycle
Conformational change creates strain
Release of strain
K.I.
Ska
u, R
.B. H
oyle
, M.S
. Tur
ner,
BP
J 91
, 247
5 (2
006)
.M
. Rie
f.,...
,J. S
pudi
ch, P
NA
S 9
7, 9
482
(200
0).
• Conformational change• Internal coordination• Brownian diffusion
Strain-dependent coordination of chemical cycle
![Page 32: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/32.jpg)
Myosin V: 3D model
pair of IQ motifstreated as rigid element
flexibility at joints
hinge between neck domains
myosin head
harmonic rotation about state-dependent equilibrium angle
neckdomain
![Page 33: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/33.jpg)
Myosin V 3D model: elasticity of neck domains
Neck domain:• 3 rigid segments • flexibility at joints
M. Terrak et. el., PNAS 102, 12718 (2005).M. Doi and S. F. Edwards, “The Theory of Polymer dynamics”, (1986).
Bending energy of semiflexible filaments:
r´3
r1 r´1
r´2r2
r3
r0 r´0
A
i
j
kr0
![Page 34: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/34.jpg)
Myosin V 3D model: rotational states
Post-stroke:Pre-stroke:
ADP-boundEmpty
ATP-bound
B
x
zy
r1
ADP.Pi-bound
A
y
x
z
r1
y
x
r1
“Bird’s eye” view:
![Page 35: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/35.jpg)
Myosin V 3D model: mechanical cycle
ATP ADP ADP
ATP
ADP·Pi
ADP
ADPADP
ADP
4. 5.
1.
2.
3.
ATP
PiADP
![Page 36: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/36.jpg)
Myosin V 3D model: mechanical cycle
ATP ADP ADP
ATP
ADP·Pi
ADP
ADPADP
ADP
4. 5.
1.
2.
3.
ATP
PiADP
r1 r´1
A B
I
![Page 37: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/37.jpg)
Myosin V 3D model: mechanical cycle
ATP ADP ADP
ATP
ADP·Pi
ADP
ADPADP
ADP
4. 5.
1.
2.
3.
ATP
PiADP
r1 r´1
A B
I
r1
r´1
A A
II
![Page 38: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/38.jpg)
Myosin V 3D model: mechanical cycle
ATP ADP ADP
ATP
ADP·Pi
ADP
ADPADP
ADP
4. 5.
1.
2.
3.
ATP
PiADP
r1 r´1
A B
I
r1
r´1
A A
II
r´1
A
III
![Page 39: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/39.jpg)
ATP ADP ADP
ATP
ADP·Pi
ADP
ADPADP
ADP
4. 5.
1.
2.
3.
ATP
PiADP
QuickTime™ and aMPEG-4 Video decompressor
are needed to see this picture.
Myosin V 3D model: mechanical cycle
![Page 40: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/40.jpg)
ATP ADP ADP
ATP
ADP·Pi
ADP
ADPADP
ADP
4. 5.
1.
2.
3.
ATP
PiADP
QuickTime™ and aMPEG-4 Video decompressor
are needed to see this picture.
Myosin V 3D model: mechanical cycle
![Page 41: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/41.jpg)
ATP ADP ADP
ATP
ADP·Pi
ADP
ADPADP
ADP
4. 5.
1.
2.
3.
ATP
PiADP
QuickTime™ and aMPEG-4 Video decompressor
are needed to see this picture.
Myosin V 3D model: mechanical cycle
![Page 42: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/42.jpg)
Myosin V 3D model: inputs and outputs
fext
Model Parameters: • Binding sites• Neck domain length• Drag coefficients• Transition rates • Neck domain persistence length• Equilibrium angles• Rotational stiffness • Neck domains: free swivel?
![Page 43: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/43.jpg)
Myosin V 3D model: inputs and outputs
fext
Model Parameters: • Binding sites• Neck domain length• Drag coefficients• Transition rates • Neck domain persistence length• Equilibrium angles• Rotational stiffness • Neck domains: free swivel?
Experimentally measured behavior: • Average step size• Substep (“prestroke”) size, ATP dependence• Step trajectories, cargo• Step trajectories, individual heads• Profile of step average, cargo• Profile of step average, heads• correlation of z-position with steps• correlation of x and z variance with steps• non-Gaussian fluctuations (failed steps?)• positional distribution of detached head• load dependence of velocity and dwell times• Mechanical processivity (steps per contact) • Kinetic processivity (1 step per ATP)• Stepping vs. neck length• Characteristics of backsteps under load
![Page 44: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/44.jpg)
fext
• Mechanics of stepping: what happens during one-head-bound state?
• Role of strain in coordinated walking?
• Backwards steps under load: processive walking?
• Mechanism behind distribution of step sizes for different neck lengths?
Mechanistic model can demonstrate which physical assumptions are consistent with known data. This can help address...
![Page 45: Collective Brownian Motors - Experiments and Models](https://reader036.fdocuments.us/reader036/viewer/2022062309/56815a6f550346895dc7d1a6/html5/thumbnails/45.jpg)
Funding:NSF CAREER, NSF-GK12, NSF IGERT, ONR, Army, Australian Research Council, ONR-Global.
UO Linke lab:
PhD students:Erin CraigEric HoffmanBen LopezBrian LongNate KuwadaPreeti ManiJason Matthews
PostdocAnn Persson
UgradsAdam CaccavanoMike TaorminaTyler HennonSteve BattazzoBenji Aleman (Berkeley)Laura Melling (UCSB)Corey Dow (UCSC)
Collaborations:
Lars Samuelson, Henrik Nilsson, Linus Fröberg (Lund, Sweden)
Martin Zuckermann, Mike Plischke, Matthew Downton, Nancy Forde (Simon Fraser University, B.C.)
Dek Woolfson (Bristol, U.K.)
Tammy Humphrey, Paul Curmi (Sydney)