Thanks, that would appear to be the case as battery no longer holds charge for any length of time when laptop is disconnected from charger.
The problem is, I can't figure how to get inside the laptop short of resorting to a hammer and chisel!
I don't think I am meant to get inside - built in obsolescence!
P.S. It's still behaving itself at the moment!
Thanks for the interest folks, we'd better get back to topics of a greater gravity than my little problem.
I looked up the function on my still functioning laptop! Next task is a search for repair videos as suggested by @gpauk!
The "sine cardinal" or "sinc" function is also called the "sampling function".
The function is defined to be sinc(x) = sin x/x and is used in sound recording and radio transmission.
https://www.allaboutcircuits.com/te...hy-is-it-important-in-electrical-engineering/
However, I'm a long way from understanding exactly how the function pertains to fields as you say, in particular to the gravitational field.
Today, scientists can produce condensates of much greater numbers of atoms that can last as long as three full minutes, and they continue to glean intriguing new insights into this unusual form of matter. By September 2001, over three dozen other laboratories had replicated the discovery. In 1997, MIT researchers developed an atom laser based on BECs that was able to drip single atoms downward from a micro spout, and in February 1999, a team at Harvard University used a BEC to slow down light to just 38 MPH by shining a laser beam through the condensate. Two years later the team announced that it had briefly brought light to a complete stop.
https://www.aps.org/publications/apsnews/200406/history.cfm
Also thought to exist near some rather high gravity items.
https://www.aps.org/publications/apsnews/200406/history.cfm
Also thought to exist near some rather high gravity items.
Are you suggesting that Bose-Einstein condensates (BECs) could exist near black holes?
I know that a Bose-Einstein condensate has been made in space:
In July 2018, an experiment aboard the International Space Station cooled a cloud of rubidium atoms to ten-millionth of a degree above absolute zero, producing a Bose-Einstein condensate in space.
As Steve would say, curious minds would want to know more about BECs and gravity.
I mounted an expedition to Portsmouth Central Library today.
TBH, the Maths section was useless, scarcely going beyond algebra.
The Physics section had a few good items. Jim Al-Khalili, Stephen Hawking, Lee Smolin. I went for the ones in large print, since things like "An Introduction to Particle Physics" was almost unreadable without a magnifying glass.
These two are both recent:
I have started with Suzie Sheehy book on my favourite of particle Physics. Gripping stuff. As she says, theory is alright, but everything real is found by experiment. Already we have discovered X-rays, radioactivity, electrons and the tiny size of the atomic nucleus! I have a feeling the Higgs will be final chapter.
Gribbin's book has 21 essays on werid and wonderful things in modern Physics, Leading up to gravitational waves and the expanding Universe. There is a chapter called "The Mystery of the Moon"! I wonder what that is. Can't wait!
Now must get back to my book. The photoelectric effect is just about to be explained by Einstein! This means the Quantum!
TBH, the Maths section was useless, scarcely going beyond algebra.
The Physics section had a few good items. Jim Al-Khalili, Stephen Hawking, Lee Smolin. I went for the ones in large print, since things like "An Introduction to Particle Physics" was almost unreadable without a magnifying glass.
These two are both recent:
I have started with Suzie Sheehy book on my favourite of particle Physics. Gripping stuff. As she says, theory is alright, but everything real is found by experiment. Already we have discovered X-rays, radioactivity, electrons and the tiny size of the atomic nucleus! I have a feeling the Higgs will be final chapter.
Gribbin's book has 21 essays on werid and wonderful things in modern Physics, Leading up to gravitational waves and the expanding Universe. There is a chapter called "The Mystery of the Moon"! I wonder what that is. Can't wait!
Now must get back to my book. The photoelectric effect is just about to be explained by Einstein! This means the Quantum!
I'm reminded of dialup BBSs and the popular taglines, specifically: "How do you accelerate a Macintosh? 9.8m/s"
I recall John Gribbin, he wrote many popular science books that I read back in the 1980s. One was "In Search of Schrodinger's Cat" one of many popular books on quantum mechanics around that time. He also wrote "The Jupiter Effect" about how a then-upcoming alignment of the planets was going to be enough to cause large earthquakes and threaten humanity.
I've read so many popular science books I don't remember them all.
I've read so many popular science books I don't remember them all.
I was typing the following as @benb posted (P.S. I liked the laptop acceleration joke!):
John Gribbin, the astrophysicist, has written many books on science, ranging from Discovering Gravitational Waves to On the Origin of Evolution.
He's best known for his 1984 book, In Search of Schrodinger's Cat: Quantum Physics and Reality which has been cited as an example of how to revive an interest in the study of mathematics - so right up your street, Steve!
How did he ever find time to write a biography of Buddy Holly?
P.S. My laptop has remained 100% charged today, ever since I threatened to hit it with a hammer!
The photoelectric effect chapter was interesting. Millikan was the man who confirmed it, taking 12 years to do. He measured Planck's constant to 0.5%, which is impressive.
I was investigating the Gravity Probe-B mission recently:
It was an amazing bit of kit. Had liquid helium cooled superconducting gyroscopes and used the star IM Pegasi and nearby Quasars to keep precisely aligned. It successfully demonstrated General Relativity frame-dragging:
https://einstein.stanford.edu/index.html
Especially interesting to me is that it incorporated my favourite, the (rectified or squared) Sinc Function in its star guidance system:
In fact, it seems we can demonstrate the idea of frame-dragging at home!
No, I didn't understand that either! But looks like something a child of ten (or cumbb) can try with help from mummy.
I have most of the parts though. Just need some honey and a paper plate and some food colouring now.
I was investigating the Gravity Probe-B mission recently:
It was an amazing bit of kit. Had liquid helium cooled superconducting gyroscopes and used the star IM Pegasi and nearby Quasars to keep precisely aligned. It successfully demonstrated General Relativity frame-dragging:
https://einstein.stanford.edu/index.html
Especially interesting to me is that it incorporated my favourite, the (rectified or squared) Sinc Function in its star guidance system:
In fact, it seems we can demonstrate the idea of frame-dragging at home!
No, I didn't understand that either! But looks like something a child of ten (or cumbb) can try with help from mummy.
I have most of the parts though. Just need some honey and a paper plate and some food colouring now.
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Not really. The light pattern relates to the Airy disk which can be described by a the sinc function
http://electron9.phys.utk.edu/optics421/modules/m5/Diffraction.htm
The picture is just a stylised image of that.
However how perfectly it is formed relates to wavefront errors and optical aberrations. Hubble for instance was manufactured to have a wavefront error of 1/10wave. It was but unfortunately the kit used to measure the main mirror was incorrectly constructed. Rayleigh came up with a "sensible" limit of 1/4wave but even that has an effect on contrast as does the usual secondary mirrors used in many types of reflecting telescopes. Rayleigh sets a limit for the ability to resolve double stars but is not so good on extended objects. Perfect Airy disk - in terms of telescopes it's not really possible to produce one. The bigger they are the harder it gets.
The Strehl ratio is sometimes used as a metric. It relates to light in the rings that should be in the peak if the image was perfect.
Yes, I regarded the light distribution shown in Steve's guide star diagram to be that of a single slit diffraction pattern - but Airy disc would be the more accurate description.
I read that the sinc function squared, mentioned by Steve, is the Fourier transform of the triangle function - not that it aids my understanding!
I read that the sinc function squared, mentioned by Steve, is the Fourier transform of the triangle function - not that it aids my understanding!
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Steve has said elsewhere that the Airy disc is related to the regular sinc function, which is the Fourier transform of a rectangle function - this would seem to be more on the ball than invoking the sinc function squared.
For those not familiar with the Airy disc:
It's often put down to Fraunhofer. There is link to the equations and a more general run down here
https://en.wikipedia.org/wiki/Fraunhofer_diffraction_equation
Forgetting refraction telescopes it's easier to stick to reflective ones. A parabola produces perfect image of an on axis point source at infinity. A secondary mirror can be added retaining the same characteristics. Main reason is it results in a shorter telescope. Off axis the image deteriorates. A perfect on axis image was the driving force of telescope design before more use was made of photography.
Well ahead of their time 2 people had a different idea. Ritchey and Chretien. Idea probably Richey and maths the other. The mirror shapes were distorted in order to obtain the smallest circles of confusion over the entire field of view meaning the axial image wont be as good as it can be - it wont produce a perfect Airy disk but light from all stars in the view is collected into small spots of light rather than being spread out more and more towards the edge of the field of view. Just about all modern large telescopes use the same idea often with a refractive element to improve things further. This shows a comparison
https://www.researchgate.net/profil...angle-for-both-a-classical-Cassegrain-and.png
A refractive corrector can flatten the field and improve things even further.
Refractive telescopes have the same problem. A diagram like this ideally shows the diffraction spot size as a circle.
https://takahashi-europe.com/catalog/refractors/triplets/toa-150/toa-150b?lang=en
https://en.wikipedia.org/wiki/Fraunhofer_diffraction_equation
Forgetting refraction telescopes it's easier to stick to reflective ones. A parabola produces perfect image of an on axis point source at infinity. A secondary mirror can be added retaining the same characteristics. Main reason is it results in a shorter telescope. Off axis the image deteriorates. A perfect on axis image was the driving force of telescope design before more use was made of photography.
Well ahead of their time 2 people had a different idea. Ritchey and Chretien. Idea probably Richey and maths the other. The mirror shapes were distorted in order to obtain the smallest circles of confusion over the entire field of view meaning the axial image wont be as good as it can be - it wont produce a perfect Airy disk but light from all stars in the view is collected into small spots of light rather than being spread out more and more towards the edge of the field of view. Just about all modern large telescopes use the same idea often with a refractive element to improve things further. This shows a comparison
https://www.researchgate.net/profil...angle-for-both-a-classical-Cassegrain-and.png
A refractive corrector can flatten the field and improve things even further.
Refractive telescopes have the same problem. A diagram like this ideally shows the diffraction spot size as a circle.
https://takahashi-europe.com/catalog/refractors/triplets/toa-150/toa-150b?lang=en