Download PCR GPS handout

Basic concept of GPS
A GPS receiver calculates its position
by precisely timing the signals sent by
GPS satellites high above the Earth.
Each satellite continually transmits
messages that include 1) the time the
message was transmitted and 2) the
satellite position at time of message
transmission. The receiver uses the
messages it receives to determine the
transit time of each message and
computes the distance to each satellite
using the speed of light. Each of these
distances and satellites' locations define
a sphere. The receiver is on the surface
of each of these spheres when the
distances and the satellites' locations
are correct. These distances and
satellites' locations are used to
compute the location of the receiver
using the navigation equations.
In 1956, the German-American
physicist Friedwardt Winterberg
proposed a test of general relativity
(for time slowing in a strong
gravitational field) using accurate
atomic clocks placed in orbit inside
artificial satellites. (To achieve
accuracy requirements, GPS uses
principles of general relativity to
correct the satellites' atomic clocks.)
Additional inspiration for GPS came
when the Soviet Union launched the
first man-made satellite, Sputnik in
1957. Two American physicists,
William Guier and George
Weiffenbach, at Johns Hopkins's
PCR: Telling Science Stories, October 11, 2012. !
Applied Physics Laboratory (APL),
decided on their own to monitor
Sputnik's radio transmissions. Within
hours they realized that, because of the
Doppler effect, they could pinpoint
where the satellite was along its orbit
from the Doppler shift. The Director of
the APL gave them access to their
UNIVAC to do the heavy calculations
required. When they released the orbit
of Sputnik to the media, the Russians
were dumbfounded to learn how
powerful American computers had
become, as they would not have been
able to calculate the orbit themselves.
The following spring, the deputy
director of the APL asked Guier and
Weiffenbach to look at the inverse
problem where you know the location
of the satellite and you want to find
your own location.
While there were wide needs for
accurate navigation in military and
civilian sectors, almost none of those
were seen as justification for the
billions of dollars it would cost in
research, development, deployment,
and operation for a constellation of
navigation satellites. During the Cold
War arms race, the nuclear threat to
the existence of the United States was
the one need that did justify this cost in
the view of the United States Congress.
Considered vital to the nuclear
deterrence posture, accurate
determination of the US Navy’s
submarine-launched ballistic missiles
launch position was a force multiplier.
Compiled from http://en.wikipedia.org
Nuclear Power
Nuclear power plants provide about
6% of the world's energy and 13–14%
of the world's electricity, with the
U.S.,France, and Japan together
accounting for about 50% of nuclear
generated electricity
Just as many conventional thermal
power stations generate electricity by
harnessing the thermal energy released
from burning fossil fuels, nuclear
power plants convert the energy
released from the nucleus of an atom
via nuclear fission that takes place in a
nuclear reactor. The heat is removed
from the reactor core by a cooling
system that uses the heat to generate
steam, which drives a steam turbine
connected to a generator producing
electricity.
Nuclear fission is either a nuclear
reaction or a radioactive decay process
in which the nucleus of an atom splits
into smaller parts (lighter nuclei), often
producing free neutrons and photons
(in the form of gamma rays), and
releasing a very large amount of
energy.
Uranium is a fairly common element in
the Earth's crust. Uranium is
approximately as common as tin or
germaniumin Earth's crust, and is
about 40 times more common than
silver. Uranium is a constituent of most
rocks, dirt, and of the oceans. The fact
PCR: Telling Science Stories, October 11, 2012. !
that uranium is so spread out is a
problem because mining uranium is
only economically feasible where there
is a large concentration. Still, the
world's present measured resources of
uranium, economically recoverable at a
price of 130 USD/kg, are enough to
last for "at least a century" by some
estimates, or at little at 70 years by
others. This represents a higher level of
assured resources than is normal for
most minerals.
Disposal of nuclear waste is often said
to be the Achilles' heel of the industry.
Presently, waste is mainly stored at
individual reactor sites and there are
over 430 locations around the world
where radioactive material continues to
accumulate. Some experts suggest that
centralized underground repositories
which are well-managed, guarded, and
monitored, would be a vast
improvement. There is an
"international consensus on the
advisability of storing nuclear waste in
Deep geological repository", with
much confidence in the safety of the
method coming from the analysis of
the lack of movement of nuclear waste
in the numerous 2 billion year
oldNatural nuclear fission reactors in
Oklo Gabon. As of 2009 there were no
commercial scale purpose built
underground repositories in operation.
Compiled from http://en.wikipedia.org
The internet & our brain
The results of four studies suggest that
when faced with difficult questions,
people are primed to think about
computers and that when people
expect to have future access to
information, they have lower rates of
recall of the information itself and
enhanced recall instead for where to
access it. The Internet has become a
primary form of external or transactive
memory, where information is stored
collectively outside ourselves.
(Sciencemag.org)
US-American writer Nicholas Carr
asserts that Internet use reduces the
deep thinking that leads to true
creativity. He also says that hyperlinks
and overstimulation means that the
brain must give most of its attention to
short-term decisions. Carr also states
that the vast availability of information
on the World Wide Web overwhelms
the brain and hurts long-term memory.
He says that the availability of stimuli
leads to a very large cognitive load,
which makes it difficult to remember
anything.
Psychologist Steven Pinker, however,
argues that people have control over
what they do, and that research and
reasoning never came naturally to
people.
h
UCLA professor of psychiatry Gary
Small...used MRI scans on experienced
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web surfers and casual web surfers to
evaluate brain activity. The study
showed that when Internet surfing, the
brain activity of the experienced
Internet users was far more extensive
than that of the novices, particularly in
areas of the prefrontal cortex
associated with problem-solving and
decision making. However, the two
groups had no significant differences in
brain activity when reading blocks of
text. This evidence suggested that the
distinctive neural pathways of
experienced Web users had developed
because of their Web use.
...
Researchers from the University
College London have done a 5-year
study on Internet habits, and have
found that people using the sites
exhibited “a form of skimming
activity.” The report says, "It is clear
that users are not reading online in the
traditional sense; indeed there are signs
that new forms of “reading” are
emerging as users “power browse”
horizontally through titles, contents
pages and abstracts going for quick
wins.”
According to the New York Times,
many scientists say that "people's
ability to focus is being undermined by
bursts of information...the stimulation
[from emails, phone calls, etc.]
provokes excitement — a dopamine
squirt — that researchers say can be
addictive. In its absence, people feel
bored."
Compiled from http://en.wikipedia.org
The discovery of DNA
Griffith's experiment, reported in 1928
by Frederick Griffith, was one of the
first experiments suggesting that
bacteria are capable of transferring
genetic information through a process
known as transformation.
Griffith used two strains of
pneumococcus (Streptococcus
pneumoniae) bacteria which infect
mice – a type III-S (smooth) and type
II-R (rough) strain. The III-S strain
covers itself with a polysaccharide
capsule that protects it from the host's
immune system, resulting in the death
of the host, while the II-R strain
doesn't have that protective capsule
and is defeated by the host's immune
system. A German bacteriologist, Fred
Neufeld, had discovered the three
pneumococcal types (Types I, II, and
III) and discovered the Quellung
reaction to identify them in
vitro. Until Griffith's
experiment, bacteriologists
believed that the types were
fixed and unchangeable,
from one generation to
another.
and live III-S strains of pneumococcus
from the blood of these dead mice.
Griffith concluded that the type II-R
had been "transformed" into the lethal
III-S strain by a "transforming
principle" that was somehow part of
the dead III-S strain bacteria.
Today, we know that the
"transforming principle" Griffith
observed was theDNA of the III-S
strain bacteria. While the bacteria had
been killed, the DNA had survived the
heating process and was taken up by
the II-R strain bacteria. The III-S strain
DNA contains the genes that form the
protective polysaccharide capsule.
Equipped with this gene, the former IIR strain bacteria were now protected
from the host's immune system and
could kill the host. The exact nature of
the transforming principle (DNA) was
verified in the experiments done by
Avery, McLeod and McCarty and by
Hershey and Chase.
In this experiment, bacteria
from the III-S strain were
killed by heat, and their
remains were added to II-R
strain bacteria. While neither
alone harmed the mice, the
combination was able to kill
its host. Griffith was also
able to isolate both live II-R
PCR: Telling Science Stories, October 11, 2012. !
Compiled from http://en.wikipedia.org