United States
Environmental Protection
Agency
Health Effects
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S1-87/002 Aug. 1987
Project Summary
Millimeter-Wave Emissivity of
Cellular Systems
K. H. Illinger
A general analysis is presented of the
millimeter-wave and far-infrared spec-
troscopic properties of in vivo cellular
systems, and of the boson radiative
equilibrium with steady-state nonequili-
brium molecular systems. The frequency
threshhold of spectroscopic properties
associated with such nonequilibrium ef-
fects is (roughly) estimated to be as low
as ~100 GHz, if the Frbhlich vibrational
model can be invoked for cellular-
membrane systems. On this basis, the
rationale for the specific experimental
protocol employed was further to utilize
the fact that in a photosynthetic pre-
paration the onset and disappearance
of the nonequilibrium state can be
switched by modulating the optical-
illumination input. The negative findings
of the present V-band (50-75 GHz)
radiometric study on in vivo chloralla
pyrenoidosa algal cells appear to con-
firm the absence of non-Planckian
emissivity features in the total radio-
metric study on saccharomyces
cerevislae near 42 GHz (3), but does
not negate totally the existence of non-
equilibrium emissivity terms in the
frequency range studied. Limitations of
radiometer sensitivity, in spite of the
S/N enhancement achieved through the
AM-modulation technique, and/or
damping of the non-Planckian emissivity
features may have vitiated their detec-
tion. More fundamentally, the frequency
threshhold for such properties may
indeed lie at higher frequencies, in the
far-infrared region. An order of magni-
tude of refinement in the theoretical
models will be required to serve as a
reliable guide for the prediction of such
frequency threshholds.
This Project Summary was developed
by EPA's Health Effects Research Labo-
ratory, Research Triangle Park, NC, to
announce key findings of the research
project that Is fully documented In a
separate report of the same title (see
Protect Report ordering Information at
back).
Discussion
As a consequence of the existence of
nonequilibrium thermodynamic subsys-
tems in in vivo biological entities, in-
cluding cellular systems, spectroscopic
features may be expected to arise which
differ from those exhibited by ordinary
equilibrium thermodynamic systems. A
detailed theoretical analysis identifies, in
particular, the emissivity function as a
targetable observable in this category.
The emissivity function, t(w), is defined
as the ratio of the aetuat emission in-
tensity of the system under consideration,
at a given frequency, to that of an ideal
blackbody at the same temperature. The
emission intensity is the photon energy
emitted across a unit surface area, per
unit time, into a solid angle of 2?r
steradians, and is proportional to the
value of the generalized distribution func-
tion of photons over frequencies, n(o>), at
the given frequency, characteristic of the
thermodynamic system under considera-
tion. If the system is an ideal blackbody,
n(oj) is the Planck function and e(cu) is
unity and frequency-independent.
A general thermodynamic analysis
shows that nonequilibrium systems
should exhibit frequency-dependent fea-
tures in t(tu). If the Froehlich vibrational
model is applied to cellular systems and
the cellular membrane is identified as
the locus of nonequilibrium thermo-
dynamic processes, a frequency regime
as low as ~ 100 GHz is credible for the
possible existence of non-Planckian fea-
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tures. This study utilized in vivo photo-
synthetic algal cells [chlorellapyrenoidosa
(American Type Culture Collection, in the
form of their strains ATCC 22521, 7516
and 11469)] as the experimental model
system, since the photosynthetic ap-
paratus is located in the cell membrane,
and since photosynthetic processes lend
themselves directly to external modula-
tion. In consequence, the temporal onset
and disappearance of these nonequili-
brium processes are externally control-
lable, and the opportunity is provided to
improve the S/N ratio of measurements
of the contribution of the nonequilibrium
subsystem(s) to the total emissivity func-
tion, the preponderant portion of which
arises from the Planckian background
from the remainder of the system.
Millimeter-wave radiometry systems
usually operate within the frequency
regions encompassed by individual
wavequide systems. This study employed
V-band [WR-15], 50-75 GHz, to roughly
approximate the frequency domain
charted in the application of the Froehlich
model to the photosynthetic chloroplast.
The latter consists of a flat, double-
membraned configuration, with a mem-
brane thickness between 100-200 A, the
site of the photosynthetic apparatus and
the putative locus of longitudinal vibra-
tions invoked in the model. A serious
caveat in any generalization that might
be made from the results of this type of
study arises from the combination of the
crudeness of the frequency-range esti-
mate from theory and the inherent nar-
row-bandedness of microwave and
millimeter-wave waveguide systems.
The emissivity of the cellular prepa-
ration was measured using a 50-75 GHz
radiometer, with its detection circuit
phase-locked to the optical illumination
of the sample in the wavelength range
centered at 4900 A (±350 A), AM-
modulated by a precision optical chopper
at 100 Hz, to accomodate the response
time constant of the photosynthetic ap-
paratus of the preparation, and to provide
selectivity and S/N ratio enhancement of
the radiometer signal arising from pro-
cesses associated with the photosynthetic
apparatus. The source of the optical
illumination was a 1000W Xe lamp, fol-
lowed by standard components of an
optical train, including a (distilled-H20)
broadband infrared filter and optical filters
selected to tailor the illumination to the
wavelength response function of the
cellular preparation. Millimeter-wave
emission from the sample was measured
at an angle of 90° to the optical-illumina-
tion axis, with the cell preparation con-
tained in a quartz cuvette, transparent to
both visible light and millimeter-wave
emission. In the context of the present
experiments, the task of the radiometer
was to detect any response, phase-locked
to the optical illumination, within a
primary-illumination ra nge of 200-1OOOW
total (regulated and calibrated) power, of
the cell preparation.
The local-oscillator (LO) arm of the
radiometer originated in a set of three
klystron oscillators spanning the 50-75
GHz range, and was coupled to the sample
arm and the detection-system arm via
broadband (50-75 GHz) ferrite isolators.
The frequency axis of the radiometer
signal was provided by measurement of
the LO frequency by means of a mil-
limeter-wave electronic counter and sub-
sequent conversion of its frequency
output via a digital/analog (D/A) con-
verter to a voltage analog signal to com-
prise the Y-axis of an X/Y recorder output.
Under typical experimental conditions,
frequency resolution thus obtained is
equal to or better than 0.1 MHz, over the
entire V-band frequency range, and
frequency tracking of the LO is automatic.
A separate power-measurement loop
permits determination of the LO relative
power across a given klystron mode, as a
function of LO frequency. The primary
element of the radiometer detection
system is a broadband (50-75 GHz)
harmonic mixer matched to an inter-
mediate-frequency (IF) amplifier, the latter
rejecting IF signals below ~ 500 MHz
and above ~ 1500 MHz. Electronic tuning
of the LO, by means of its reflector
voltage, moves the center of this IF detec-
tion window (bandwidth ~ 1000 MHz)
across the klystron mode. Director moni-
toring of radiometer performance is ac-
complished by feeding the output of the
IF amplifier directly into a (0-2 GHz)
spectrum analyzer. Radiometry of the
sample preparation is achieved by
entering the output of the IF amplifier
into a microwave video detector, thus,
converting that output into a dc voltage.
The phase-lock synchronization loop,
externally synchronized to the precision
optical chopper, is engaged via a phase-
sensitive lock-in amplifier which accepts
the dc radiometer-output signal. Finally,
the radiometer-signal axis, from the out-
put of the lock-in amplifier, is combined
with the frequency axis, from the elec-
tronic counter and D/A converter, to
present the radiometry data on an X/Y
recorder.
The present study failed to detect any
(non-artifactual) frequency-dependent
features m the radiometry signal phase-
locked to the optical illumination of th«
photosynthetic algal-cell preparation
Among the possible explanations for sucf
a finding, two are salient. The centra
modality of the radiometer experimen
(direct AM-modulation of the photosyn
thetic process) may have been vitiated b>
insufficiently favorable S/N ratio char
acteristics of any non-Planckian features
in the emissivity. This would render the
sensitivity of the current radiometei
design incapable of detecting such fea-
tures, in a manner which excludes arti-
facts of millimeter-wave waveguide
circuits. From a mechanistic standpoint,
any of three (heuristic) parameters ma\
have contributed to such a possibility, (a
the low concentration of subsystems
which undergo nonequilibrium processes,
per unit volume, compared to the (bulk;
system near equilibrium; (b) low absolute
emission intensity associated with any
non-Planckian features; and/or (c)
damping of any non-Planckian emissivity
features, with an attendant reduction in
S/N ratio, within a given frequency
interval.
The second case arises from the central
question, to which existing theory is only
a very rough guide, concerning the low-
frequency threshhold, w,, of non-
Planckian features. If (n 01,/«T) -4 1 is
inadmissible as an assumption for cellular
systems, no non-Planckian features are
expected in the frequency range studied,
with Ts300°K, and their absence in the
present study is not inconsistent with the
thermodynamic or the generalized Froeh-
lich model, but would imply that definitive
refinement in the theory is required for
the prediction of their (frequency) range
of existence.
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K. H. Illinger is with Tufts University. Medford, MA 02155.
Jamas R. Rabinowitz is the EPA Project Officer (see below).
The complete report, entitled "Millimeter- Wave Emissivity of Cellular Systems,"
(Order No. PB 87-175 840; Cost: $ 11.95, subject to change) will be available
only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Health Effects Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
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Agency
Center for Environmental Research
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