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- Cosmicomics: (04 March
1994)
Source: (04 March 1994) - NMR signal
reception:
Virtual
photons and
coherent
spontaneous
emission: Concepts in
Magnetic
Resonance,
Vol. 9, No. 5.
(1997), pp.
277-297.In
portions of
the magnetic
resonance
community,
there is a
misunderstandi
ng of the
process of
nuclear
magnetic
resonance
(NMR) signal
generation and
reception, and
even in
accepted
texts, it is
frequently
described in
terms of
absorption and
emission of
radio waves,
or radiation,
by a two-level
quantum
system. While
this
explanation
can be
refuted, for
those who do
understand
that the NMR
free induction
decay signal
is easily
explained by
Faraday's law
of induction,
reconciling
the presence
of an induced
electromotive
force with an
apparent
absence of
transitions
between
nuclear energy
levels causes
conceptual
problems. This
difficulty is
examined, and
an explanation
of the signal
given whereby
Faraday's law
is explained
simply in
terms of an
exchange of
virtual
photons. The
article thus
attempts to
reconcile the
standard
engineering
approach to
signal
reception with
a quantum
mechanical
description of
the NMR
phenomenon.
Radiation
damping and
its relations
to detection
of the induced
signal and to
signal-to-nois
e ratio are
then
scrutinized,
and the
misleading
nature of the
appellation
noted. In the
process, it is
shown that
while damping
is inherently
necessary for
signal
detection and
the transfer
of energy that
it entails,
the degree of
such damping
depends on the
efficiency of
the
detector - in
other words,
of the
preamplifier
in the NMR
receiver - and
can therefore
be minimized.
Mathematics in
the article is
kept to a
minimum;
proofs of the
Principle of
Reciprocity
description of
Faraday's law
for reception
of both signal
and noise from
a conducting
sample are
given in an
appendix. ©1
997 John Wiley
& Sons,
Inc. Concept
s Magn Reson
9: 277-297,
1997
Source: Concepts in Magnetic Resonance, Vol. 9, No. 5. (1997), pp. 277-297. - The
thermodynamics
of
computation?a
review: International
Journal of
Theoretical
Physics, Vol.
21, No. 12. (1
December
1982), pp.
905-940.
Source: International Journal of Theoretical Physics, Vol. 21, No. 12. (1 December 1982), pp. 905-940. - Designing a
programming-ba
sed approach
for modelling
scientific
phenomena: Journal of
Computer
Assisted
Learning, Vol.
21, No. 2.
(April 2005),
pp. 143-158.We
describe an
iteratively
designed
sequence of
activities
involving the
modelling of
one-dimensiona
l collisions
between moving
objects based
on programming
in ToonTalk.
Students aged
13?14 years in
two settings
(London and
Cyprus)
investigated a
number of
collision
situations,
classified
into six
classes based
on the
relative
velocities and
masses of the
colliding
objects. We
describe
iterations of
the system in
which students
engaged in a
repeating
cycle of
activity for
each collision
class:
prediction of
object
behaviour from
given
collision
conditions,
observation of
a relevant
video clip,
building a
model to
represent the
phenomena,
testing,
validating and
refining their
model, and
publishing it
? together
with comments
? on our
web-based
collaboration
system,
WebReports.
Students were
encouraged to
consider the
limitations of
their current
model, with
the aim that
they would
eventually
appreciate the
benefit of
constructing a
general model
that would
work for all
collision
classes,
rather than a
different
model for each
class. We
describe how
our intention
to engage
students with
the underlying
concepts of
conservation,
closed systems
and system
states was
instantiated
in the
activity
design, and
how the
modelling
activities
afforded an
alternative
representation
al framework
to traditional
algebraic
description.
Source: Journal of Computer Assisted Learning, Vol. 21, No. 2. (April 2005), pp. 143-158. - The Potts
model: Reviews of
Modern
Physics, Vol.
54, No. 1.
(January
1982),
235.This is a
tutorial
review on the
Potts model
aimed at
bringing out
in an
organized
fashion the
essential and
important
properties of
the standard
Potts model.
Emphasis is
placed on
exact and
rigorous
results; but
other aspects
of the problem
are also
described to
achieve a
unified
perspective.
Topics
reviewed
include the
mean-field
theory;
duality
relations;
series
expansions;
critical
properties;
experimental
realizations;
and the
relationship
of the Potts
model with
other
lattice-statis
tical
problems.
Source: Reviews of Modern Physics, Vol. 54, No. 1. (January 1982), 235.
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