I had the good fortune to be working on the Galileo mission during its Mission Design phase. Many of the techniques used by the Cassini mission designers were developed for Galileo. Disclamer: I was not on the mission design team.
First of all, the Voyager encounters with Jupiter and Saturn were always when the spacecraft were moving away from the sun. However, during the Galileo satellite tour the mission designers realized that the Galileo spacecraft could encounter Callisto, Ganymede, and Europa when moving away and moving toward Jupiter. Furthermore, the closest approach ("encounter") could be targeted to be either in front of the moon (with respect its orbit around Jupiter) or behind it. These choices allowed the designers a great deal of freedom to use the moons' gravity to shape the spacecraft's orbit. As I understand it, they did not just plan the current encounter to obtain the next encounter, but also the encounter after that.
The ability to use a moon to shape a spacecraft orbit depends on the ratio of the mass of the planet to the mass of the moon (for all practical purposes the spacecraft is massless.) Only Io, Callisto, Ganymede, and Europa are able to provide gravity assists at Jupiter, and only Titan at Saturn.
I spoke to Bob Mitchell, Cassini Project Manager, a few years ago and asked him about this specifically. He told me that while it was true that having to go back to Titan every time to change the orbit was a constraint, it also provided the freedom to send the spacecraft out of the "plane" where the moons orbited. At Jupiter it was necessary to stay in the plane to make multiple visits to all the moons, but since at Saturn you must visit the same moon to change the spacecraft's orbit every time (Titan) there is fewer reasons to stay in the plane. And, as you can see from the orbit diagrams, Cassini has traveled outside of the plane many times.
In 1980 I met with Joe Weber at the Jet Propulsion Lab.
He had been reducing the noise in his experiment over the decades was still confident that the disturbances he was recording were gravitational waves.
Rather that being bitter about the 20 years of skepticism concerning his experiment, he was upbeat and optimistic. He understood that the theorists claimed that he could not possibly being seeing gravitational waves, but, as he told me, "You are not going to see them if you don't look!"
The reason he was at JPL was that John Anderson, Frank Estabrook, and Hugo Walquist conducted searches for gravitational waves using high precision spacecraft tracking during the 1970s and continue to search to this day.
Re:This is Neal's Best Book Yet
on
Anathem
·
· Score: 1
I think we need to be careful here.
I believe that the ending of the book can be interpreted to include both the many-worlds interpretation of quantum mechanics AND the idea that the cosmos is made up of many universes, each with sightly different values for the fundamental physical constants.
When Prof. Wheeler was at the University of Texas (and probably at Princeton as well) he used to give a penny to any student who found an error in what he had written on the chalkboard in class.
...for going to the effort to implement this idea. IMHO this network's real goal should be to provide rapid warning of an earthquake that is already happening:
I do not see how anyone's privacy is violated if the government monitored the Internet and looked for patterns of computers going off line. An disk shaped pattern expanding at about 5000 m/s would be one pattern to look for.
Ulysses was originally part of the International Solar Polar Mission (ISPM) where two spacecraft were to pass over the North and South poles of the Sun simultaneously. In 1981, NASA backed out. There would only be one ISPM spacecraft. I was at the Jet Propulsion Lab then, and while the NASA scientists and engineers were disappointed, the Europeans were well and truly pissed. Simultaneous polar measurements are what was used to sell the mission to the governments.
ESA built the spacecraft (designed in the 70s), but the launch from the shuttle was delayed until 1990 by the Challenger disaster. A generation of European space scientists who expected to use the (now renamed) Ulysses data lost out.
Let us instead praise ESA and the European space scientists for this mission.
Anyone who has lived in an earthquake zone knows that even a ten second warning of an impending earthquake could save many lives. Dive under a desk, stand in a door frame, get out of an elevator, stop your car, etc.
I wonder if cell phones equipped with GPS and an accelerometer could provide such a warning? Even if only twenty per cent of the accelerometers registered abnormal acceleration, a real time analysis of the data would show the distinctive expanding wave front that could only be caused by a major earthquake. People could then be alerted by cell phone or radio.
Many persons have implied that not detecting gravitational radiation will somehow invalidate General Relativity. Unless I am mistaken, every theory of gravitation that requires that
1. Forces due to massive bodies (gravity) to propagate at the speed of light, and 2. Energy to be conserved
must also have gravitational radiation. Information propagates at infinite speed in Newton's theory of gravity, so there is no gravitational radiation.
In some places (the southern United States, for example) people cool their homes for six to seven months a year, and every watt used in a home office costs an addition 2 to 4 watts to remove from the house just to maintain a constant temperature. Add to the $90 a year he would save directly an additional $200 in indirect savings for home cooling for these places.
In the book the characters deduce that "human researchers discover a way of modifying the brain to provide conscious control over the process, allowing people to suspend wavefunction collapse at will..." However, there is at least one passage that suggests that this is not the case. What it suggests is that the book is set in a universe where each of these improbable events just happen, and the characters (being in this special universe) infer that they are causing these improbable events.
As a physicist, Greg Egan knows that although these special universes make up only a small portion of the ensemble of all universes, an infinite number of these universes exist, and he chooses to set his novel in one of these special universes.
"Create a non-profit that researches 'orphaned' works for copyright status. A large percentage of works published post-1923 are eligible for public domain status but it requires time and work to track down the copyright holders."
This suggestion is already in the list, and it is far and away the best suggestion I have seen.
I am a professor, and it is not practical to create conditions where no cheating is possible. With an effort you can make it more trouble than it is worth for most students.
Some steps I normally take:
Never using the same problem twice, even years later.
Three versions of the exam: versions for alternate rows and a version for late students.
Walking around and watching the students during a test.
Banning phones, laptops, PDAs, graphing calculators.
No make-up exams.
Grading all the exams personally and looking for similar answers.
And keep in mind that an unproven accusation of cheating can have consequences for the professor as well as the student.
"On one hand we have an established Harvard Phd, who has testified before the U.S. congress, against a game journalist with a bachelors degree in Psychology."
That doesn't prove anything. I have a Ph.D., and I don't know shit!
Slashdot Mirror
Didn't I suggest something similar to this on Slashdot back in 2008?
http://hardware.slashdot.org/comments.pl?sid=440258&cid=22283136
Ever wonder why you cannot buy Kellogg's Heartwise Cereal anymore? Thank the Texas Attorney General's office.
http://www.nytimes.com/1991/04/03/garden/kellogg-files-slander-suit.html
I laughed at the lawsuit at the time because the claims were baseless. Soon I could no longer buy my favorite cereal.
The Gregorian calendar system repeats every 400 years, and the number of Tuesdays is not exactly one-seventh of the total number of days.
I am guessing that this is the key to the answer.
I had the good fortune to be working on the Galileo mission during its Mission Design phase. Many of the techniques used by the Cassini mission designers were developed for Galileo. Disclamer: I was not on the mission design team.
First of all, the Voyager encounters with Jupiter and Saturn were always when the spacecraft were moving away from the sun. However, during the Galileo satellite tour the mission designers realized that the Galileo spacecraft could encounter Callisto, Ganymede, and Europa when moving away and moving toward Jupiter. Furthermore, the closest approach ("encounter") could be targeted to be either in front of the moon (with respect its orbit around Jupiter) or behind it. These choices allowed the designers a great deal of freedom to use the moons' gravity to shape the spacecraft's orbit. As I understand it, they did not just plan the current encounter to obtain the next encounter, but also the encounter after that.
The ability to use a moon to shape a spacecraft orbit depends on the ratio of the mass of the planet to the mass of the moon (for all practical purposes the spacecraft is massless.) Only Io, Callisto, Ganymede, and Europa are able to provide gravity assists at Jupiter, and only Titan at Saturn.
I spoke to Bob Mitchell, Cassini Project Manager, a few years ago and asked him about this specifically. He told me that while it was true that having to go back to Titan every time to change the orbit was a constraint, it also provided the freedom to send the spacecraft out of the "plane" where the moons orbited. At Jupiter it was necessary to stay in the plane to make multiple visits to all the moons, but since at Saturn you must visit the same moon to change the spacecraft's orbit every time (Titan) there is fewer reasons to stay in the plane. And, as you can see from the orbit diagrams, Cassini has traveled outside of the plane many times.
PRS-300 has two advantages: no WiFi and no touch screen.
Neither Sony nor anyone else can hack in and erase your ebooks.
A touchscreen is makes the characters less crisp, more muddy. I much prefer clear text to the minor advantages of a touchscreen.
And it works well with Linux. Now if Sony did not supply such lame software...
Ecology and Politics: Kim Stanley Robinson "Forty Signs of Rain"
The role of autistic persons in society: Elizabeth Moon "The Speed of Dark"
How persons and societies cope with pandemics: Connie Willis "Doomsday Book"
Revolution: Robert Heinlein "Moon is a Harsh Mistress"
Feminist issues: Connie Willis "Even the Queen"
Responsibility of leaders to exercise justice: Lois Bujold "Mountains of Mourning"
Utopia and Materialism: Ursula K. LeGuin "The Dispossessed"
I believe that any theory of gravity where
1. Energy is conserved
2. Gravitational information propagates at a finite speed (most theories set this speed equal to the speed of light)
will have gravitational waves of some sort.
Is there any physicist who does not believe in both 1 and 2?
Gravitational waves exit. The real problem is detecting them and interpreting the waveforms.
In 1980 I met with Joe Weber at the Jet Propulsion Lab.
He had been reducing the noise in his experiment over the decades was still confident that the disturbances he was recording were gravitational waves.
Rather that being bitter about the 20 years of skepticism concerning his experiment, he was upbeat and optimistic. He understood that the theorists claimed that he could not possibly being seeing gravitational waves, but, as he told me, "You are not going to see them if you don't look!"
The reason he was at JPL was that John Anderson, Frank Estabrook, and Hugo Walquist conducted searches for gravitational waves using high precision spacecraft tracking during the 1970s and continue to search to this day.
I think we need to be careful here.
I believe that the ending of the book can be interpreted to include both the many-worlds interpretation of quantum mechanics AND the idea that the cosmos is made up of many universes, each with sightly different values for the fundamental physical constants.
These two concepts are distinct.
Before rejecting math, engineering, or science perhaps she should talk to someone who works at JPL:
http://www.jpl.nasa.gov/
I certainly enjoyed working there.
Note that MESSENGER used solar sailing to correct its trajectory for this flyby:
http://www.planetary.org/blog/article/00001674/
I think the cover of the book "Einstein Simplified" illustrates this matter:
http://books.google.com/books?hl=en&id=cdtBd8ljWqYC&dq=einstein+simplified&printsec=frontcover&source=web&ots=uAfnTYjoWdsig=9IglIlkNjXdOT36u9CVMBpgrPPw&sa=X&oi=book_result&resnum=3&ct=result
A simple version of LaTex cannot fill my typesetting needs.
When Prof. Wheeler was at the University of Texas (and probably at Princeton as well) he used to give a penny to any student who found an error in what he had written on the chalkboard in class.
I wish I had kept mine.
...for going to the effort to implement this idea. IMHO this network's real goal should be to provide rapid warning of an earthquake that is already happening:
http://slashdot.org/comments.pl?sid=440258&cid=22283136
I do not see how anyone's privacy is violated if the government monitored the Internet and looked for patterns of computers going off line. An disk shaped pattern expanding at about 5000 m/s would be one pattern to look for.
Ulysses is a great success, but let us look at its history a bit before we praise NASA.
http://en.wikipedia.org/wiki/Ulysses_(spacecraft)
Ulysses was originally part of the International Solar Polar Mission (ISPM) where two spacecraft were to pass over the North and South poles of the Sun simultaneously. In 1981, NASA backed out. There would only be one ISPM spacecraft. I was at the Jet Propulsion Lab then, and while the NASA scientists and engineers were disappointed, the Europeans were well and truly pissed. Simultaneous polar measurements are what was used to sell the mission to the governments.
ESA built the spacecraft (designed in the 70s), but the launch from the shuttle was delayed until 1990 by the Challenger disaster. A generation of European space scientists who expected to use the (now renamed) Ulysses data lost out.
Let us instead praise ESA and the European space scientists for this mission.
Anyone who has lived in an earthquake zone knows that even a ten second warning of an impending earthquake could save many lives. Dive under a desk, stand in a door frame, get out of an elevator, stop your car, etc.
I wonder if cell phones equipped with GPS and an accelerometer could provide such a warning? Even if only twenty per cent of the accelerometers registered abnormal acceleration, a real time analysis of the data would show the distinctive expanding wave front that could only be caused by a major earthquake. People could then be alerted by cell phone or radio.
Many persons have implied that not detecting gravitational radiation will somehow invalidate General Relativity. Unless I am mistaken, every theory of gravitation that requires that
1. Forces due to massive bodies (gravity) to propagate at the speed of light, and
2. Energy to be conserved
must also have gravitational radiation. Information propagates at infinite speed in Newton's theory of gravity, so there is no gravitational radiation.
The photo of the DNA in the article does not appear knotted to me. Does anyone have a link to a DNA image that is truly knotted?
I have the same problem with the name "sage" as I do with maxima: it is difficult to use google to find out what work other persons have done.
Results 1 - 10 of about 7,660,000 for maxima
Results 1 - 10 of about 8,890,000 for sage
Couldn't they have named it "famkserigj" or something unique? I never have this problem with Ogg Vorbis.
In some places (the southern United States, for example) people cool their homes for six to seven months a year, and every watt used in a home office costs an addition 2 to 4 watts to remove from the house just to maintain a constant temperature. Add to the $90 a year he would save directly an additional $200 in indirect savings for home cooling for these places.
If a sequence was random is there a way to prove it? Apparently not:
Sergio B. Volchan
"What Is a Random Sequence,"
The American Mathematical Monthly, Vol. 109, 2002, pp. 46-63.
http://links.jstor.org/sici?sici=0002-9890(200201)109%3A1%3C46%3AWIARS%3E2.0.CO%3B2-L
This article won a Lester R. Ford Award in 2003 for "expository excellence".
In the book the characters deduce that "human researchers discover a way of modifying the brain to provide conscious control over the process, allowing people to suspend wavefunction collapse at will..." However, there is at least one passage that suggests that this is not the case. What it suggests is that the book is set in a universe where each of these improbable events just happen, and the characters (being in this special universe) infer that they are causing these improbable events.
As a physicist, Greg Egan knows that although these special universes make up only a small portion of the ensemble of all universes, an infinite number of these universes exist, and he chooses to set his novel in one of these special universes.
"Create a non-profit that researches 'orphaned' works for copyright status. A large percentage of works published post-1923 are eligible for public domain status but it requires time and work to track down the copyright holders."
This suggestion is already in the list, and it is far and away the best suggestion I have seen.
"...and no cheating is possible."
I am a professor, and it is not practical to create conditions where no cheating is possible. With an effort you can make it more trouble than it is worth for most students.
Some steps I normally take:
Never using the same problem twice, even years later.
Three versions of the exam: versions for alternate rows and a version for late students.
Walking around and watching the students during a test.
Banning phones, laptops, PDAs, graphing calculators.
No make-up exams.
Grading all the exams personally and looking for similar answers.
And keep in mind that an unproven accusation of cheating can have consequences for the professor as well as the student.
"On one hand we have an established Harvard Phd, who has testified before the U.S. congress, against a game journalist with a bachelors degree in Psychology."
l ?id=11874
That doesn't prove anything. I have a Ph.D., and I don't know shit!
http://genealogy.math.ndsu.nodak.edu/html/id.phtm