[Aztlan] Re-Posted; A muon attenuation method to search for hidden chambers in the Pyramid of the Sun at Teotihuacan, Mexico.

[michael ruggeri]

Listeros,

Since James R Van Dyke's forward had an attachment, our system would  
not let it go through so I have copied the paper here,

Mike Ruggeri




A muon attenuation method to search for hidden chambers in the  
Pyramid of the Sun at Teotihuacan, Mexico.
R. Alfaro, E. Belmont-Moreno, A. Cervantes, V. Grabski, J.M. López- 
Robles, L. Manzanilla, A. Martínez-Dávalos, M. Moreno, A. Sandoval,  
and A. Menchaca-Rocha.
Instituto de Física, Universidad Nacional Autónoma de México, A.P.  
20-364, 01000, México D.F., México
One of the most interesting activities in archaeology is the search  
for hidden chambers in historical and prehistorical monuments. When  
large pyramids are the object of such research, and direct excavation  
is not viable, the need to search deeply into the structure severely  
limits the available prospective techniques. In 1970, the Berkeley  
Professor (and Nobel Prize winner) Luis Alvarez was able to solve a  
long-standing speculation about the existence of hidden chambers in  
the Chephren Pyramid at Giza, Egypt. He used a sort of radiographic  
technique in which the attenuation of cosmic rays gives information  
on the internal distribution of matter in that monument. As a result,  
he demonstrated that there are no hidden cavities. Incidentally, the  
method was originally developed by E.P. George in 1955 to measure the  
ice-layer depth of Australian mountains in winter, by installing muon  
detectors in the summer. Hence, this transmission technique requires  
the installation of a detector underneath the investigated volume.  
For this purpose, Alvarez and his group profited from the existence  
of a chamber located at the base of the Chephren Pyramid, near its  
symmetry axis. In Teotihuacan, Mexico, the discovery in 1971 of a 100  
m long tunnel running 8 m below the Pyramid of the Sun, which also  
ends near the symmetry axis, represents an extraordinary opportunity  
to carry out an experiment similar to that of Alvarez in an attempt  
to solve one of the most important enigmas of the Teotihuacan  
culture: what was the purpose of building this great pyramid. The aim  
of this manuscript is to describe the archaeological
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motivation of this work, the physics of the technique, and current  
status of this project.
Figure 1 The Valley of Mexico is located in the region of the Central  
Plateau, within the great cultural area that Paul Kirchhoff  
denominated Mesoamérica. The Valley of Teotihuacan is located 40 km  
to the northeast of what is today Mexico City. The valley has an area  
of 500 km2 with a sea-level elevation of 2300 m. As can be  
appreciated, the Valley of Mexico had a vast amount of water sources  
that allowed the establishment and development of cultures like the  
Teotihuacan and Aztec, among others.
About Teotihuacan we know that it was the most important and  
representative city of the Mexican Central Plateau (Figure 1). Dating  
back to the Classic Period, its great cultural heritage had an  
extended influence over Mesoamerica and north-central Mexico. The  
center of Teotihuacan (Figure 2) is characterized by its two colossal  
monuments, the pyramids of the Sun and of the Moon. Teotihuacan also  
has an administrative and religious building complex known as the  
“Ciudadela”. The site was planned with an urban grid having a main  
north-south axis marked by the “Street of the Dead” along which  
one also finds other buildings and residential complexes.
2
Figure 2. The urban center of Teotihuacan with some of its most  
important structures: the pyramids of the Sun and the Moon and the  
Ciudadela, located along the Street of the Dead, one of the main axes  
defining the city.
The Pyramid of the Sun (Figure 3) is the largest structure in  
Teotihuacan. With a height of 65 m it dominates the entire  
archaeological complex. The square base, 215 m on a side, delimits a  
volume of one million of cubic meters. The exterior of the Pyramid is  
subdivided into 5 bodies and its principal face is oriented towards  
“The Street of the Dead”, having an orientation of 15° 17´ north  
and steeply ascending stairs allowing an easier climb to the top of  
the pyramid. On the same face, and centered on it, there is an  
associated body known as “Plataforma Adosada”, which deviates a  
few degrees west-north from the pyramid’s axis, being better aligned  
with the direction of the sunset. Its height is slightly lower than  
the first body, extending some 17 m away from it, and 38 m along it.  
The base of the Pyramid of the Sun is surrounded by a U-shaped  
platform along its north, east and south sides. One of the most  
recent findings was a three meter wide channel surrounding the  
pyramid, as well as astronomical markers on the stucco floor  
corresponding to the last constructive stage of Teotihuacan.
3
Figure 3. The city of Teotihuacan viewed from the top of the Pyramid  
of the Moon. To the center, the great axis marked by the Street of  
the Dead, and on its left lies the Pyramid of the Sun, the highest  
construction of the city,.
Since Colonial times, the “Cronistas” dedicated part of their work  
to Teotihuacan, in particular to the Pyramid of the Sun. Among them  
were Motolinía, Mendieta, Sahagún and Torquemada, and later  
Alexander von Humboldt who wrote in 1803. In the year of 1864 the  
first formal study of Teotihuacan was made by the Scientific  
Commission of Pachuca under the direction of Ramon Almaraz. Their  
reports inform about the orientation of the pyramids, and concerning  
the one of the Sun, they also indicated the existence of the U-shaped  
platform that surrounds it on three of its sides. Yet, it was not  
before 1905 that the official explorations in Teotihuacan began, when  
the President (Porfirio Díaz) designated Leopoldo Batres as  
Archaeological Monument Inspector. The same year, Batres carried out  
the first restoration works in the Pyramid of the Sun, removing the  
soil that covered it, hence revealing its original shape. Years  
later, in 1917, Manuel Gamio was the first archaeologist to carry out  
a multidisciplinary project in Teotihuacan, using artificial  
stratigraphy with the intention to decipher the chronology of the  
Pyramid of the Sun. In 1922, to explore the inside, Gamio decided to  
open a tunnel (Figure 4) starting on the east side of the pyramid and  
ending in the central region. This tunnel penetrated 97 m in the west  
direction from the first platform of the pyramid, which marks the  
division between the first and second bodies (those which are closer  
to the ground level).
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Figure 4. The tunnels in the Pyramid of the Sun. From the bottom up,  
one finds the underground tunnel, then, on the fist body, are the  
tunnels excavated by Gamio and by Noguera. Finally, on the fifth body  
lies the Smith tunnel.
In 1933, Eduardo Noguera and Jose R. Pérez excavated a second tunnel,  
116.5 m long, beginning at the “Plataforma Adosada”, in the west- 
side and meeting with the Gamio tunnel in the central portion of the  
pyramid. The relevant result of both excavations was that no internal  
structure exists that could indicate some type of superposition of  
buildings, as is common to find in other Mesoamerican pyramids.  
Nevertheless, with the excavation of these tunnels, data was obtained  
on the construction technique, while the ceramic material found in  
the pyramid’s volume was analyzed to investigate whether there  
existed two or more cultures at that site.
In 1947, Rémy Bastien made a detailed architectural research of the  
Pyramid of the Sun, and two years later he excavated a 9 m tunnel  
along the south-north direction, in the joining point between the  
Gamio and Noguera tunnels. Unfortunately, the archaeological report  
of these last works was never published. Ten years later, René  
Millon, Bruce Drewitt and James A. Bennyhoff reexamined the Gamio and  
Noguera tunnels’ walls, looking for evidences of possible internal  
structures not mentioned before. However, Millon indicated that the  
previous conclusions concerning the lack of evidence for a  
superimposed configuration could not be contradicted. Hence, the  
pyramid seems to have been constructed in a single operation,.
5
In 1962, Robert Smith excavated another east-west tunnel, 30 m long,  
in the upper part of the pyramid, on the fifth body. Within this  
tunnel Evelyn Rattray in 1968 excavated a prospective pit looking for  
ceramic remains to allow a dating of the upper part of the pyramid.  
There are also reports that archaeologist Ponciano Salazar carried  
excavations (1962-1964) in the north side of the Pyramid of the Sun,  
digging a tunnel north-south on the lower platform, however there is  
no published material on that intervention either.
Unlike the pyramids of the Moon and of the Feathered Serpent, both  
having underlying structures filled with rubble and soil, the Pyramid  
of the Sun seems to be a pile of organic soil with some small  
fragments of volcanic tuff, that come from the Formative agricultural  
plots in the valley. Hypothetically the first step for the  
construction of the Pyramid of the Sun was to delimit the general  
form of the building by walls coarsely formed of stone and mud,  
volcanic tuff, or adobe, which worked as retaining structures. The  
second step was to fill up the empty spaces with loose stones and  
soil. Finally more stones were added, to end on a 40 cm concrete  
cover layer. Architect Ignacio Marquina mentions that all the bodies  
of the pyramid conserved remains of a stucco layer that must have  
covered them totally and perhaps was painted of some color, or was  
ornamented with mural paintings. The land where the pyramid was based  
is humus but underneath that organic earth layer there is another one  
of volcanic tuff to better sustain the great pyramid’s weight.
In 1971 a well, 8 meters deep, filled with stones and gravel, was  
located at the base of the Pyramid of the Sun. When cleaned, old  
stairs leading to a tunnel running right under the pyramid was  
located and investigated by Jorge Acosta and Doris Heyden. Although  
Millon and Heyden considered it to be a natural “lava  
tube” (Figure 4), running along the west-east direction with a  
slight deviation to the north, today it is known that it was  
excavated by the inhabitants of the valley in the geological contact  
between the volcanic tuff and the volcanic scoria and basalt blocks  
under it.
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Figure 5. Underground tunnel. In spite of its wavy shape, the tunnel  
position is fairly well aligned, and centered, with the pyramid. Note  
the 4-lobbed chamber at the end of the tunnel.
Because the entrance coincides with the center of the stairs of the  
pyramid, Heyden considered that the tunnel already existed when the  
Pyramid of the Sun was built. The tunnel is 103 m long and ends in a  
four-lobbed chamber near the symmetry axis of the monument. This 4- 
cavity complex has the shape of a clover. Heyden indicates that the  
tunnel was sectioned by a series of walls blocking the access to the  
final chamber, and also that the ceiling was reinforced in some  
parts. There were also a few polished stone slabs to collect dripping  
water from the tunnel, possibly associated to the cult of that element.
As part of the investigations of the underground tunnel, authors Hugh  
Harleston Jr, George T. Baker and other collaborators proposed a  
hypothetical reconstruction of the tunnel dividing it in 4 sections.  
This work is interesting because of the detailed description of the  
materials found, with topographic data and measurements for each  
section, as well as some construction elements like walls and  
channels. Baker and Harleston located the center of the four lobbed  
chamber in the exact point underneath the fourth body of the pyramid.  
These authors also claimed that along the tunnel there are 19 or 20  
walls, i.e., more than originally proposed by Heyden. There is  
evidence that these walls were broken into by plunderers.
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Heyden speculated that the tunnel underneath the Pyramid of the Sun  
is a representation of a Chicomoztoc, a mythic Mesoamerican site  
represented in some codices as a 7-lobbed cavity complex. The  
Geographic Relation of Teotihuacan also mentions that oracles were  
frequently located within similar cavities. Indeed, the post- 
Teotihuacan occupations in the valley assigned different meanings to  
the tunnel under the Pyramid of the Sun: womb of the earth, place of  
origin, oracle, sacred place where rulership is invested. For  
example, the Xólotl Codex locates an oracle inside a similar chamber  
and includes the Teotihuacan glyph, itself conformed by two pyramids  
located over a cave that contains an oracle (Figure 6). Presumably  
the oracle fulfilled important functions, designating dates,  
activities or types of religious ceremonies. This religious  
significance should have attracted a great number of pilgrims to the  
site.
Figure 6. The existence of oracles that frequently were located in  
caves, suggests that the tunnel underneath the Pyramid of the Sun  
contained one of them, at least on the Early Postclassic times. In  
fact in the Xólotl Codex there is a glyph of Teotihuacan represented  
by two pyramids with an oracle within a cave.
The tunnel has also been thought to have been taken as a divine  
indication to mark the place to build an important monument, or for  
the establishment of a town, or to build a tomb. The clover-like  
appearance of the end chamber suggests that such a flower could have  
been a general motif in Teotihuacan, with a deep religious meaning.  
Possibly the four-petal flower on the tunnel has relation with the  
four cardinal points, that is to say, a cosmological sense.
8
The central problem in Teotihuacan today is that there is no real  
evidence of how it was ruled. There is a controversy about the power  
system, between those who propose that it was a uni-personal dynasty  
and the more accepted hypothesis that it was a co-government of  
several persons. In any case, one important hypothesis that stands is  
that the remains of these individuals may be found buried inside the  
two greater structures of the large city. A recent investigation by  
Rubén Cabrera and Saburo Sugiyama in the Pyramid of the Moon  
discovered numerous burials and offerings that helped to corroborate  
the hypothesis of the use of the Teotihuacan pyramids as tombs.  
Still, the Pyramid of the Moon’s structure is quite different from  
the one of the Sun. Hence, it is difficult to say if the important  
recent findings can be generalized to both monuments. It should be  
added that, like in the Pyramid of the Moon, in Teotihuacan it is  
common to find burials in graves filled with soil and having stone  
walls. As we shall see later, this would be more difficult to locate  
by the Alvarez technique, which is more efficient to detect (hollow)  
cavities, than regions of increased density.
In summary, with respect to the current archaeological problem, the  
intention behind the construction of the Pyramid of the Sun by the  
Teotihuacanos remains an enigma that has inspired numerous studies,  
including several excavations that have reinforced the hypothesis  
that the Pyramid of the Sun was conceived as one monument without  
internal substructures, unlike the neighboring Pyramid of the Moon.  
Thus, the lack of an internal structure has left the archaeologists  
without a clue to guide future excavation works. A similar situation  
appeared in Giza, Egypt where, unlike the Pyramid of Cheops, the  
Chephren one did not give indications of containing mortuary chambers  
on its volume, besides a chamber (named “Belzoni”, after its  
discoverer) that is located in its base, near the axis of symmetry.  
That is what motivated Luis Alvarez to propose the use of cosmic ray  
attenuation measurements to solve this riddle, by installing a  
particle detector in the Belzoni chamber. Let us now review the  
physics basis of such a technique.
Muons are very short-lived particles (two millionths of a second).  
The ones that concern us here are produced in interactions between  
“primary cosmic rays” with
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the upper terrestrial atmosphere. The penetrability of these muons is  
such, that a fraction of them is still detectable several kilometers  
underground. Muons have electric charge and interact with the atoms  
of the materials they cross, loosing energy as they penetrate. Thus,  
the attenuation of their flow turns out to be related to the amount  
of matter crossed.
The Earth is bombarded continuously by radiation coming from the  
cosmos. Light and the lowest energy particles are emitted by stars as  
they burn their nuclear fuel. The higher energy particles are  
accelerated in cataclysmic events like supernova explosions or around  
the massive black holes in the centers of many galaxies.
What we know about cosmic rays is that 90% of them are hydrogen  
nuclei (protons), 9% are helium nuclei, and the rest (1%) is composed  
of heavier nuclei and electrons. Life on Earth is possible thanks to  
the fact that we are protected from these “ionizing” particles by  
two important natural shields: the atmosphere and the Earth's  
magnetic field. The combined effect of these shields causes that only  
one small fraction of that radiation reaches the terrestrial surface,  
and that this flow is minimum in the equatorial region, where the  
magnetic field exerts its greater deviating capacity.
One could expect that, as occurs with visible light, the ionizing  
radiations that the Sun produces should be dominant compared with the  
ones from the rest of the stars. However, most of the Sun’s  
radiations lack the energy to overcome our protective shields.  
Therefore the cosmic rays that concern us here are extra-solar.  
Concerning the actual energy of the maximum flow in the Mexico City  
(and Teotihuacan) latitude (measured as the kinetic energy divided by  
the mass number “A” of the nuclei, and termed “energy per  
nucleon”) is near 8 GeV/A. From this maximum energy, the cosmic ray  
particle flow decreases exponentially as the E/A increases. One GeV  
(or Giga electron Volt) is a billion times larger than the energy of  
a visible light photon. Thus, in the interaction of these nuclei with  
the particles that compose the atmosphere, violent reactions occur in  
which
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particles to do so. very unstable particles (mostly “pions”,  
having a mean life of 10 billionths of a second) are created (see  
Figure 7). The muons that concern us here are the result of the decay  
of those pions. Although the average lifetime of the muons is still  
very short and classically they would decay before reaching the  
surface of the earth, due to relativistic effects, when traveling  
very close to the speed of light their time expands and an important  
fraction of them survive the trip, reaching the terrestrial surface.  
Muons are the most abundant cosmic-ray-related charged
Figure 7. This schematic representation of an “air shower”,  
initiated (upper part) by a primary cosmic ray interacting with an  
atmospheric particle, creating (among others, not shown) a positive  
pion (left) and a neutral pion (right). On the left hand side chain,  
a positive muon is then created which later decays into a positive  
electron (or positron) and two neutrinos. Kinematics, half-life, and  
other considerations determine that muons represent the most abundant  
charged particles reaching the Erath surface.
A popular prescription is that, at sea level, the flow is one muon  
per cm2 per minute. This flow includes positive and negative mouns,  
being the negative ones
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slightly more abundant. At the latitude of the Valley of Mexico,  
those “cosmic” muons (more appropriately called “atmospheric”  
muons) are characterized by having a mean energy of about 2 GeV. Like  
the “primary” cosmic rays that originate them, the flow of  
atmospheric muons of higher energies decreases exponentially. With  
respect to the vertical, the atmospheric muon flow varies little for  
polar angles smaller than 45 degrees, decaying rapidly for greater  
inclinations.
The technique to locate cavities on material volumes using muon  
attenuation is based on two basic concepts. The first it is that the  
rate of energy loss ΔE/ΔX for high energy charged particles is  
fairly constant, approximately 1 GeV per each 2 m of soil crossed.  
Thus, we can see that the 73 meters that the muons most penetrate (65  
m of height of the Pyramid of the Sun, plus the 8 m of depth to the  
tunnel) imply a minimum energy of incidence of 36.5 GeV, if those  
muons are to be detected inside the tunnel under the monument. As the  
flow of these particles decreases exponentially with energy, the  
muons having just enough energy to cross the pyramid are most  
sensitive to small variations in the amount of matter crossed.
The second important concept needed to understand the technicalities  
of the Alvarez method is that muons lose their energy as a result of  
individual (mostly electrical) interactions with the particles that  
compose the pyramid material, each one causing a small deviation to  
the incident rays. Since the mean deviation turns out to be an  
inverse function of the speed, the muons having the smallest  
energies, which (as mentioned above) are the most sensitive to locate  
empty cavities in a volume of material, also turn out to be those  
that accumulate a greater deviation, affecting the spatial  
resolution. This implies that in the design of this type of  
experiments a negotiation between “sensitivity” and the “space  
resolution” is necessary. To locate possible hidden cavities in a  
volume, it is necessary to measure the flow and the direction of the  
muons that arrive at the detector. When these measurements are  
compared with the result of a simulation assuming that the  
investigated volume has a uniform density, the fact
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that in some direction more muons are measured than simulated, is an  
indication that in that direction there is less matter than assumed  
in the simulation, revealing the possible existence of an empty space.
This use of a simulation requires the best possible knowledge of the  
experimental conditions, such as the distribution in energy and  
arrival direction of the incident muons, as well as the external  
geometry and the internal structure of the pyramid (density profile,  
known cavities, etc.) With this information it is possible to  
determine parameters such as the dimensions of the minimum detectable  
cavity and measuring time that the experiment would require.
Figure 8. The muon detector setup has two scintillator planes and 6  
multiwire chambers, arranged to form 3 X,Y pairs.
The previous information helps the design of the muon detector. The  
experimental setup that we considered (Figure 8) is similar to the  
one used by Alvarez, which satisfies the basic requirements of being  
simple and of low cost. In our case, we determine three points along  
the trajectory of the muons, by using six multiwire chambers (MPC)  
with a sensitive area of 1m x 1m. The wires are spanned across the  
chamber with equal spacing between them. When a charged particle  
crosses the chamber, an electrical signal is generated at the wire  
closest to the particle transversal determining its position in one  
direction.
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Each pair of MPC’s are placed with their wires of one chamber  
perpendicular to those of the next one, therefore determining a  
coordinate pair (X,Y), while the vertical location of the MPC’s  
fixes coordinate Z. The passage of muons is signaled by two, 1m x 1m  
x 1cm, plastic scintillator detectors. One of them is placed above  
the three pairs of multiwire chambers, and second one underneath  
them. By requiring temporary coincidence between the signals of both  
scintillators the signals produced by the background (ambient)  
radiation are eliminated. Simulating the performance of the  
instrument allows us to establish important parameters of these  
detectors, like the separation between the wires in the MPC’s.
Comparing the experimental setup used by Alvarez in Giza and the one  
that is being installed at Teotihuacan, one finds that for equal  
observation times, the Mexican project will obtain a similar counting  
with a detector having one fourth of the surface. This is due to the  
fact that the muon flow is more than twice greater at the altitude of  
Teotihuacan, compared to the near sea-level Giza location. In  
addition, the smaller height of the Pyramid of the Sun (half of the  
one of Chephren) implies less attenuation. The sensitivity expected  
of the Mexican experiment should be better than the Egyptian case;  
simply because a cavity of the same dimensions represents a greater  
fraction of the overall height in one case than in the other. Another  
advantage of the Teotihuacan case is that, as already mentioned, the  
Pyramid of the Sun has internal tunnels that serve like calibration  
structures. Nevertheless, the Mexican experiment presents other  
challenges. One of them is that the external form of the pyramid is  
more complex, hence more difficult to simulate than Chephren. Also,  
the internal density has associated a greater uncertainty than in the  
Egyptian case, where the construction materials are better known and,  
judging on what is observed in the walls of the tunnel that leads to  
the Belzoni chamber, the matter in Chephren case is more uniform than  
in the Teotihuacan pyramid. Taking into account the previous  
considerations, we estimate that the experiment of the Pyramid of the  
Sun is able to detect cavities with a minimum height of 75 cm after a  
year of measurements.
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Figure 9. A laboratory environment has been installed in the 4-lobbed  
end of the tunnel of the Pyramid of the Sun.
Finally, to understand in what stage is the project at the moment, it  
is necessary to take into account that muon attenuation measurements  
in the Pyramid of the Sun, contemplates numerous aspects. At the time  
of writing this note, after four years of work, we received the  
necessary permits and the economic support; we carried out the  
detector design, bought some electronic modules and constructed  
others. We tested and installed in situ the two scintillators (Figure  
9), designed and constructed the first multiwire chamber prototype  
[9]. Once we were satisfied with its operation, we constructed six  
new ones, and integrated them with the 2 scintillators, thus  
obtaining the first version of the full detector, which is currently  
being tested in our laboratory at UNAM (Figure 10).
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Figure 10. The final detector being tested at the UNAM laboratory.
We also constructed a viable laboratory environment at the end of the  
tunnel, which is safe, electrified (the nearest electricity outlet  
was located over 1 Km away). We are in the process of installing a  
wireless data transmission line which should allow us to remotely  
control the experiment from UNAM, 60 Km away. Thus, in percentage  
terms, 80% of the work prior to data collecting has been concluded.  
The remaining 20% should be concluded within the next few months.  
This includes detector performance characterization. After that, for  
calibration purposes, a one-month run outside of the pyramid will be  
carried out before transporting and installing the detector in the  
Pyramid of the Sun tunnel. After new tests, we should be ready to  
start taking data what should take, at least one more year. These  
data will be analyzed on line making sure we reproduce the most  
obvious geometrical features of the pyramid, like the gross details  
of its external shape, as well as the existing tunnels.
We would like to conclude by saying that the multidisciplinary  
collaboration (archaeologists, physicists and engineers) that has  
been integrated for the accomplishment of this project, in all its  
stages, has been an enormous and very rewarding challenge for all the  
participants. Beyond the list of authors, there is much anonymous  
work offered by the simple wish to participate. To all these  
volunteers, especially to the graduate students and the technicians,  
we offer our gratitude.
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