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Abstract

The purpose of the project is to examine the cultural and geologic history of Yosemite

National Park, and then map out areas of interest in the park using Global Positioning equipment.

Yosemite National Park is renowned for its magnificent valley, great granite domes and peaks,

waterfalls, giant sequoias, and spectacular high country. The cultural history of Yosemite

National Park is as intriguing as the natural history of the Park. Starting with the original

inhabitants (Native Americans), to the entrance of Europeans, to the designation of park status,

Yosemite National Park has gone through a number of cultural changes.

After the geologic and cultural histories of the park are examined, the next step in the

project was to map out specific areas of interest in the Park. A Global Positioning System (GPS)

was used to collect raw attribute data in the field. The collected data was then downloaded into a

Geographic Information System (GIS), where a number of GIS functions (reclasses, overlays,

etc.) would be performed to combine the collected data with existing maps of the park.

Unfortunately, no data could be collected in the field using GPS equipment. The towering cliffs

and giant sequoias surrounding the valley caused too much interference with signals being sent

between satellites and the GPS receiver. Since no GPS data could be collected, a final step was

added to this project. The final step of this project was to determine ways, if any, to collect GPS

data in areas of high interference.

1.0 Introduction

Yosemite National Park (YNP) is one of the best-known and most visited parks in the world.

More than 4 million people visit Yosemite each year to admire the parks natural beauty (Mullins,

1998). A magnificent valley, great granite domes and peaks, waterfalls, giant sequoias, and a

spectacular high country make up the natural beauty of the park. But the natural beauty of the

park is not the only intriguing part of Yosemite. The cultural history of Yosemite is just as

exciting. The original inhabitants of Yosemite are thought to have occupied the land for

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Figure 1: Yosemite National Park located near the eastern border of central

California and western Nevada. Inset (highlighted in red) provides a close-up of

YNP and the surrounding area (Mullins, 1998).

thousands of years. It was not until the late 1800�s that Europeans entered Yosemite and saw

what the park had to offer (Mullins, 1998). A quest was started by environmentalists, primarily

John Muir, to designate Yosemite a National Park.

Within YNP are a number of sites to see. The use of global positioning equipment can be

used to map out all the sites. A Global Positioning System (GPS) is a way of collecting

geographic locational data from satellites that orbit the earth. In order to collect data, a sufficient

number of satellites must be visible to the GPS receiver. When trees, mountains, or other

obstructions interfere with signals being sent from the satellite, sufficient data cannot be

collected. When no data can be collected, alternative methods must be taken in order to collect

data in areas of high interference.

The purpose of this paper is to examine YNP, and the use of GPS within the park. First, the

paper will explore the natural and cultural beauty of Yosemite National Park. Second, the paper

will examine how GPS can be used to collect locational data. Third, the paper will look into why

no GPS data can be collected in YNP. Finally, the paper will provide three theories of how GPS

data can be collected in areas of high interference, including SatView, base stations and laser

range finders, and the launching of more satellites into the earth�s atmosphere.

2.0 Yosemite National Park

Yosemite National Park (YNP) is located near the eastern

border of central California and Nevada (Figure 1). The park is

approximately the size of Rhode Island, comprising about

3030.30 square kilometers of Sierra Nevada splendor. Roughly

oval in shape, the park includes 423.25 kilometers of roads;

1351.81 kilometers of hiking trails; about 240 species of birds;

80 species of mammals; and 1,400 species of flowering plants,

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Figure 2: Map of Yosemite National Park showing five major areas in YNP, purple circle represents Yosemite Valley (NPS, 1999)

37 of which are trees. Elevations inside the park range

from 609.60 meters to more than 3962.40 meters. The

park is largely undeveloped, with 94.5 percent of the

park officially designated as wilderness. Today, five

distinct areas attract more than 4 million visitors each

year to YNP (Mullins, 1998). The areas include

Yosemite Valley, Wawona, Hetch Hetchy, Tuolumne

Meadow, and the Mariposa Grove of Giant Sequoias.

Figure 2 provides a good illustration of the five major

areas within YNP.

2.1 Cultural History of Yosemite

The first residents of Yosemite Valley, which is located within YNP, were Native Americans

who inhabited the region perhaps as long as 7,000 to 10,000 years ago (Mullins, 1998). By the

time non-Native Americans entered in the mid-19th century, the valley was inhabited by the

Southern Sierra Miwok. The Miwok called Yosemite Valley Ahwahnee, which translates loosely

as �Place of a Gaping Mouth,� and called themselves the Ahwahneechee. They harvested black

oak acorns, hunted, and fished. They traded acorns and other items native to the Valley with the

Mono Lake Paiute people for obsidian, rabbit skins, pine nuts, and insect foods.

Early mention of Yosemite Valley by non-Native explorers began appearing in the 1830�s

and 1840�s. In 1848, the discovery of gold brought scores of outside gold seekers to the Sierra

Nevada. By 1851, thousands of miners had appropriated the Natives land, which quickly resulted

in the Mariposa Indian War. In an attempt to capture a group of Yosemite Indians, the state-

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sanctioned Mariposa Battalion entered Yosemite Valley on March 27, 1851, and proceeded to

secure the land from the Natives (Mullins, 1998).

Word of Yosemite�s beauty gradually spread, and in 1855, the first party of tourists arrived.

Nine years later, a group of influential Californians persuaded the federal government to grant

Yosemite Valley and the Mariposa Grove to the state as the first public preserve (Mullins, 1998).

2.2 National Park Status

The drive for federal protection of the Yosemite region began shortly after the non-Native

American settlers arrived in 1855 and before conservationist John Muir first visited in 1868.

President Abraham Lincoln provided the first protection when he signed the Yosemite Grant on

June 30, 1864 (Mullins, 1998). This grant is considered the foundation upon which national and

state parks were later established. The grant deeded Yosemite Valley and the Mariposa Grove of

Giant Sequoias to the state of California. However, no such protection existed for the vast

wilderness surrounding the valley.

In 1889, John Muir and Robert Underwood Johnson, the editor of Century magazine, found

the high country overrun with flocks of domestic sheep. Although Muir had been absent from the

Yosemite area during the five years preceding this visit, he had written as early as 1869 of the

devastation that the �hoofed locusts� wrought on the land. Muir said that the sheep not only

consumed meadows and wildflowers but also destroyed the soul of the land. Something must be

done, Muir urged Johnson, as they camped together in Tuolumne Meadows. Johnson responded

by using his influence on key citizens and politicians back East to help preserve the region.

Johnson�s resolve became as strong as Muir�s. Together, they planned a campaign to make the

high country surrounding Yosemite Valley into a national park.

While Johnson lobbied for the park back East, Muir spoke and wrote eloquently of the need

for legislation to set the land aside for a national park, as was done when Yellowstone National

Park was established in 1872. Remarkably, their efforts were rewarded in just a year. On

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October 1, 1890, the United States congress set aside more than 1,500 square miles of �reserved

forest lands� soon to be known as Yosemite National Park. It included the area surrounding

Yosemite Valley and the Mariposa Grove of Giant Sequoias. It took a meeting between President

Theodore Roosevelt and John Muir in 1903, and the effective lobbying of railroad magnate

Edward H. Harriman, to have Yosemite Valley and the Mariposa Grove ceded from the state of

California�s control and included in Yosemite National Park in 1906 (Mullins, 1998).

2.3 Geologic History of Yosemite

Although Yosemite�s history as a national park goes back more than 100 years, its geologic

history dates back 500 million years. Table 1 shows the geologic evolution of Yosemite Valley.

The area began with the Sierra Nevada region submerged beneath a sea, until plates collided

forcing magma to the surface cooling to form the huge blocks of granite seen in the area today.

As YNP evolved, rivers and other processes eroded away the huge blocks of granite forming

Yosemite Valley. Today, the same erosional processes are occurring continuing to shape the

landscape of YNP. Table 2 also shows the geologic evolution of YNP, but includes the rock units

involved in shaping the park.

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Table 1: Geological Evolution of Yosemite Valley

500 million years The Sierra Nevada region was submerged beneath a sea. Sediments slowly accumulated

on the ocean floor, growing thousands of feet in thickness and compressing the lower

layers into rock

200 million years Part of the Pacific plate slid under the North American plate in a process called

subdivision. Deep within the earth, tremendous heat and pressure caused the Pacific plate

to melt into magma.

80 to 100 million years Magma rose toward the surface and cooled underground into a huge block of granite.

50 million years The land destined to become Yosemite National Park was made up of gentle, rolling hills

and streams, including the slow-moving Merced River. Hardwood forests flourished.

10 million years Over the next 5 million years, the Sierra Nevada, California�s �backbone,� rose. The

Sierran Block uplifted, tilting westward, increasing the Merced River�s flow so it carved

the valley into a canyon. Redwood forests flourished.

3 million years The Merced River carved its canyon as much as 3,000 feet deep, while its tributaries cut

the land more slowly. Forests thinned as the Ice Age approached.

1 million years Until 250,000 years ago, glaciers filled the V-shaped Yosemite Valley, widening,

deepening, and carving it into a U-shape, forming hanging valleys from which waterfalls

now cascade.

30,000 years Yosemite Glacier entered the valley but did little to alter the landscape. Older glaciers had

already excavated 2,000 feet into the bedrock.

10,000 years Temperatures warmed and the last valley glacier melted. Its terminal moraine (rock

debris) dammed the valley, creating Lake Yosemite. Sediment eventually filled the lake,

creating the flat valley floor we see today.

Today The same process of sedimentation continues at Mirror Lake. Soon sediment will

completely fill in the lake creating a meadow. Water and gravity continue to shape

Yosemite�s landscape through events like the Happy Isles rock slide in July 1996 and the

flood of January 1997, both of which were the most dramatic in the recorded history of the

park.

Source: Mullins,1998

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Table 2: Geologic History of Yosemite National Park Including the Rock Units Involved in the

Evolution of the Park

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Figure 3: El Capitan standing 1095.15 meters is believed to be the

largest single block of exposed granite in the world.

Figure 4: Half Dome dominates valley views reaching a height of 2695.04

meters.

2.4 The Sites of Yosemite

An area full of history and geologic marvels, Yosemite has a variety of sites to see. The sites

include towering granite domes and peaks, waterfalls, a magnificent valley, and groves of giant

sequoias. Three of the most recognizable and beautiful sites in Yosemite are El Capitan, Half

Dome, and the Tuolomne Grove of giant sequoias.

El Capitan (Figure 3) is a massive, granite monolith standing

1095.15 meters from base to summit. It is believed to be the largest

single block of exposed granite in the world. From spring to fall,

rock climbers from around the world challenge their abilities, as

they attempt to climb the sheer face of El Capitan.

Half Dome (Figure 4) is Yosemite�s most distinctive monument,

dominating valley views. Standing at the eastern end of Yosemite

Valley, Half Dome rises to an elevation of 2695.04 meters. At 87

million years old, the granite making up the dome is the youngest

plutonic rock in the valley. Half Dome�s other �half� is believed to

have fallen away when the glaciers receded. Succeeding glaciers

deposited some of the debris in moraines along the valley floor.

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Figure 5: Uprooted Sequoia with colleagues Brad Chopp and Rich Hager next to the tree

for scale

Figure 6: Dead Giant, one of three trees remaining in YNP

that one can still walk through.

The Tuolumne Grove of giant sequoias is one of three groves located in the park. Giant

sequoias are the largest of all living things. The immense size of the trees, most towering over

91.44 meters tall, can be seen in Figure 5 (Empire National Nursery, 1999). Sequoias are

wonderfully adapted to fire. The wood and bark are fire-resistant. Black scars on a number of

large trees that are still prospering indicate they have

survived many scorching fires. Sequoia reproduction also

depends on fire. The tiny seeds require minimal soil for

germination, and seedlings need sunlight. Historically,

frequent natural fires opened the

forest, thinned out competing

plant species, and left rich

mineral soil behind. But years of fire suppression have allowed debris,

such as fallen branches, to accumulate, stifling reproduction and

allowing shade-tolerant trees to encroach. The National Park Service

now sets prescribed fires, intended to stimulate natural fires and

improve the health of the forest. The Tuolumne Grove also contains

the Dead Giant, one of the three remaining trees in Yosemite that one

can still walk through (Figure 6).

3.0 Global Positioning Systems

The sites of YNP can be mapped using Global Positioning Systems. Humans have spent

most of their lives trying to figure out where they are, and where they are going? Navigation

and positioning are crucial to so many activities and yet the process has always been quite

burdensome. Over the years, different technologies have been invented to try to simplify the

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Figure 7: Three satellites showing how triangulation

works as they converge on a GPS receiver. (Trimble,

1999)

task. Finally, the U.S. Department of Defense put forth the money ($12 billion) to design a

super precise form of worldwide positioning for the military. The result was the Global

Positioning System (GPS), a system that's changed navigation forever (Hurn, 1989).

3.1 What is GPS?

GPS is a worldwide radio-navigation system formed from a constellation of 24 satellites and

their ground stations. The system uses these satellites as reference points to calculate positions

accurate to a matter of meters. In fact, with advanced forms of GPS one can make measurements

to better than a centimeter. GPS receivers are becoming smaller and more economical, allowing

for uses in a number of applications such as, cars, boats, planes, construction equipment, movie

making gear, and farm machinery. It is predicted that soon GPS will be as common the

telephone.

3.2 How GPS Works

There are five main steps that make GPS work. The basis of GPS is "triangulation" from

satellites. To "triangulate�, a GPS receiver measures distance using the travel time of radio

signals. To measure travel time the GPS needs very accurate timings. Along with distance, the

system needs to know exactly where the satellites are in space. Finally the system must provide

correction for any delays the signal experiences as it travels through the atmosphere (Hurn, 1989).

The first step in understanding how GPS works is triangulation. Triangulation of satellites

allows the user to determine their position based on their distance from

the satellites. Figure 7 shows how the triangulation process works.

Three satellites are enough to narrow down the user position, but four

satellites are needed to determine exact user position. The point where

all four satellite signals cross will be the exact location of the GPS user.

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Figure 8: Pseudo Random Code of GPS showing �on� (when line is at top) and �off� (when line is at bottom) pulses.

(Trimble, 1999)

The second step taken for GPS to work is measuring distance. Distance to a satellite is

determined by measuring how long a radio signal takes to reach a GPS receiver, from a specific

satellite. To make the measurement one must assume that both the satellite and the receiver are

generating the same pseudo-random codes at exactly the same time. The Pseudo Random Code

(PRC), seen in Figure 8, is a fundamental part of GPS. Physically it's a complicated sequence of

"on" and "off" pulses. By comparing how late the satellite's

pseudo-random code appears with respect to the receiver's

code, one can determine how long the signal took to reach the

receiver. Next, if the travel time is multiplied by the speed of

light one can determine the distance that the satellite is from

the receiver.

Timing is the third thing to consider when understanding GPS. Accurate timing is the key to

measuring distance to satellites from the position of the user. Satellites are accurate because they

have atomic clocks on board, but receiver clocks do not, due to the high costs of atomic clocks.

Receiver Clocks do not have to be too accurate though, because an extra satellite (e.g. a fourth

satellite) range measurement can remove errors created by the imperfect sync of the receiver.

Fourth, the location of the satellites has to be considered. To use the satellites as references

for range measurements one needs to know exactly where the satellites are in space. GPS

satellites are so high up; their orbits are very predictable. The high orbit allows the satellites to be

out of range of errors caused from the earth�s atmosphere. The Department of Defense measures

minor variations in the satellite�s orbit. The minor variations in the satellites orbit found by the

Department of Defense are sent to the satellites, to be transmitted along with the timing signals so

the user knows where the satellite(s) are (Hurn, 1989).

The final step taken to allow GPS to work effectively is correcting errors in the signals being

transmitted. The earth's ionosphere and atmosphere cause delays in the GPS signal that translate

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Figure 9: A satellite signal being distorted by interference in the

earth�s atmosphere as the signal travels to a GPS receiver.

(Trimble, 1999)

Figure 10: Cross-section profile of Yosemite Valley showing the towering

cliffs of granite that surround the valley.

into position errors. Some errors can be factored out using

modeling such as looking at the relative speeds of two different

signals. The configuration of the satellites in the sky can magnify

other errors. If the signal from a satellite bounces off something

else before it reaches the user the timing and distance can become

distorted. Figure 9 shows how a GPS signal can be distorted.

3.3 GPS Data Could Not Be Collected in Yosemite Valley

Why could no GPS data be collected in Yosemite Valley? The reason no GPS data could be

collected, one must first consider the geology/geography of the park, along with what was

covered in section 3.2 on how GPS works. Towering cliffs of granite, as seen in Figure 10,

surround Yosemite Valley. The cliffs interfere with signals

being sent from satellites to the GPS receiver. The cliffs make

it almost impossible to receive signals from the minimum

number of three satellites that are needed to collect a point.

Similar results occurred when trying to map trails through the

groves of giant sequoias. The towering sequoias and thick

canopy allowed for little if any satellite signals to get through.

4.0 GPS Use in High Interference Areas

Now that we understand how GPS works, and why data is difficult to collect in areas of high

interference, such as Yosemite Valley, it is time to examine how this problem can be solved.

There are three possibilities to solve the GPS interference problem. 1.) The first, and simplest, is

using SatView to determine the position of the satellites in the atmosphere. 2.) The second option

available involves using a base station on top of the valley and a laser range finder to collect data.

3.) The third possibility is based on plans by a joint Taiwan-United States project to launch a

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Figure 11: Skyplot of satellites seen directly

overhead of Eau Claire, WI on 11-5-99 at 3:00p.m.

(Trimble, 1999)

Figure 12: Total-Satellites-in-View in Eau Claire, WI on 11-5-

99 between the times of 15:00 and 21:00 hours. (Trimble, 1999)

large number of satellites in the atmosphere to aid in meteorological, climatic, ionospheric, and

geodetic research as well as for operational weather forecasting and space weather monitoring.

4.1 SatView

SatView is a program offered by Trimble, one of the leading producers of GPS equipment.

Using SatView allows one to determine when the optimal time to plan a GPS mission would be

based on where the satellites are arranged in the sky. By accessing SatView on the Trimble

homepage (www.trimble.com), one can select from a number of options to see the layout of

satellites in the area. The first step is to determine where the GPS mapping will be taking place,

for example Yosemite National Park. Once a location is selected, the next step is to determine

what �plot type� to choose, and what time the GPS mission will be taking place. One �plot type�

option is the �skyplot�. The �skyplot� shows each satellite's path-in-sky during the time period

that your GPS mission will take place. The display of the �skyplot�, seen in Figure 11, is

oriented so that the center represents the sky directly overhead the

location one specified, and the outer ring represents the horizon line.

Intermediate rings represent 15-degree increments. The �skyplot� option

can be used in the field to check whether the signals from any satellites

that are low on the horizon could be blocked by obstructions such as trees

and buildings.

A second �plot type� to choose is �total-in-view�. The total-in-view

plot displays the total number of satellites with

elevation angles that exceed the mask angle one specifies. The mask

angle is the degree off the horizon which satellite signals can be received.

The total-in-view plot, seen in Figure 12, is useful for a quick look at the

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time periods when there are enough satellites available for your receiver to calculate a GPS

position (Trimble, 1999).

4.2 Base Stations & Laser Range Finders

Since no data could be collected in the valley due to the high amount of interference from the

surrounding cliffs and vegetation, an alternative method had to be developed. One idea is to build

base stations on the many towering peaks that surround the valley. The base stations are out of

range of any interference, and have a clear path to receive signals from the satellites. Base stations

allow one to obtain a known reference point based on satellite signals received at the station.

The next step is to use laser range finders in order to collect data in Yosemite Valley. Laser

range finders would be mounted to the base stations. The laser range finders, most of which work

up to 500 meters, are aimed at points in the valley where data is to be collected (Pacific Survey

Supply, 1999). Known the reference point of the base station, the laser range finder calculates the

distance, angle, and direction of the point of interest with respect to the base station. Figure 13

gives an illustration of how this system would work.

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B a s e S ta t io n

L a s e r R a n g e F in d e r

Figure 13: Shows satellites sending signal to base station located on top of El Capitan. Laser

range finder, which is mounted on base station, is sent into valley to collect data.

4.3 Launching New Satellites

An octet of microsatellites to be launched in 2003 will provide a large amount of useful data

for meteorological, climatic, ionospheric, and geodetic research, as well as for operational weather

monitoring. The joint Taiwan-United States satellite project, known as Constellation Observing

System for Meteorology, Ionosphere, and Climate (COSMIC), makes use of GPS and tracking

signals. The final operational configuration of COSMIC can be seen in Figure 14. Each of the

eight microsatellites in low-Earth-orbit (LEO) can be seen in comparison to the high-altitude GPS

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Figure 14: A model showing what the orbits of satellites will look like when the new satellites are

launched in 2003. The blue lines represent the orbits of the existing satellites, and red lines

represent the orbits of the satellites to be launched.(Kuo, 1999)

orbits. The smaller red circles represent the radio

receiving range for the COSMIC satellites, which

orbit the earth at an altitude of 800 kilometers. The

larger blue circles depict 24 GPS satellites, which

orbit the earth at an altitude of 20,200 kilometers.

While the satellites are primarily planned to be used

for meteorological research, the increased number of

satellites could lead to many advances in GPS

mapping, possibly even in collecting GPS data in

areas with high interference. The lower orbiting

satellites will be closer to their targets and may be

less likely to have their signals blocked by

obstructions.

5.0 Conclusions

Yosemite National Park is one of the most beautiful and popular places on earth. Millions of

people visit the park each year to see it�s great granite domes and peaks, magnificent valley,

spectacular high country, and three groves of giant sequoias. YNP is not only renowned for it�s

natural beauty; it is also full of cultural history. Native Americans occupied the land thousands of

years before the Europeans entered and took the land from the Natives. The Europeans then

started their quest to designate Yosemite a National Park.

A GPS unit was used to try to collect data within Yosemite Valley, but to no success. The

high peaks and domes, along with the thick vegetation, caused too much interference to allow the

GPS receiver to pick up signals being sent out by satellites orbiting the earth. Alternative ideas

are proposed in order to collect data in areas of high interference, such as Yosemite Valley. The

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ideas include the use of SatView, the use of base stations and laser range finders, and the planned

launch of satellites to be sent into the earth�s atmosphere in the year 2003. The above ideas are

all theories, and have not been practiced in the field. It is my hope that future technology and

ideas will allow one to collect data in Yosemite Valley, and other areas of high interference.

6.0 References

Empire National Nursery, 1999. Coastal Redwoods, Giant Sequoias, & The Dawn Redwood Trees. Empire National Nursery, http://www.cdr3.com/redwoods/

Harris, A. and Tuttle, E., 1990. Geology of National Parks. Iowa: Academic, 15p. Hurn, J., 1989. GPS: A Guide to the Next Utility. California: Academic, 55p. Kuo, Y.H., 1999. A Constellation of Microsatellites Promises to Help in a Range of

Geoscience Research. EOS, American Geophysical Union, Vol. 80 pp. 467 & 471. Mullins, M., 1998. Yosemite Magazine. California: American Park Network, pp. 8-51 National Park Service (NPS), 1999. Visit Your National Parks. Park Net,

http://www.nps.gov/ Pacific Survey Supply, 1999. Want Longer Range? Pacific Survey Supply,

http://www.pacificsurvey.com/sc/parse.cgi/?action=view&PID=SIR-00007

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