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This is a great paper.

As a counterpoint, one place where determinants are incredibly useful is in Hartree-Fock theory, where they effective encode the Pauli exclusion principle (or anti-symmetry requirements) of atomic orbitals.

https://en.wikipedia.org/wiki/Hartree–Fock_method


Also: Cross products.


I'm sure it's out there somewhere, but it would be an appropriate corollary to the OP if there was a "Down with Cross Products", which argues that multivectors and wedge products should be taught instead of cross products in multivariable calculus. Then, determinants are "the wedge product of N linearly independent vectors", and cross products are "the wedge product of 2 vectors in 3 dimensions", which gives a bivector and trivially encodes their pseudovector properties.

(Also, surface normals in integrals are bivectors, the 'i' of complex analysis is the bivector resulting from wedge product x^y, and e^(i theta) is the exponential map applied to the i operator, and (del wedge vector-function f) is the (bivector-valued) curl while (del wedge bivector-function g) is the (scalar valued) divergence (and that's why del(del(f)) = 0).)

(But differential forms should probably be omitted in a first course, because they get hairy quickly and are hard to wrap one's head around. It's enough to know that dxdy in integrals is actually dx^dy, and therefore the Jacobian appears when changing variables because of the factor that appears from dx'^dy' = dx'(x,y)^dy'(x,y).)


Which books would you recommend to learn this wedge product / differential forms approach to linear algebra and complex numbers?


Doesn't Spivak get into them?


Michael Spivak has written multiple books. Which one do you mean?


Calculus on Manifolds. I'd recommend Hubbard and Hubbard over that as it's a little easier read with the same material.


> I'd recommend Hubbard and Hubbard over that as it's a little easier read with the same material.

John Hamal Hubbard, Barbara Burke Hubbard - Vector Calculus, Linear Algebra and Differential Forms: A Unified Approach


Based on this article, I would venture to guess that Axler is also not a fan of the cross product, though, so he wouldn't feel that much is lost. Cross products are practically a vector-calculus hack that lack generality and risk obscuring intuition at the mathematical level.


One problem with cross product, it only exists in three dimensions.


No, it exists in dimension 3 and 7:

> https://en.wikipedia.org/wiki/Seven-dimensional_cross_produc...

EDIT: Nore precisely: A common way to axiomatize the cross product yields a cross products exactly in dimension 3 and 7.


A wedge product exists in all dimensions but only in 3 & 7 is it identifiable with a unique vector.


We are already struggling to make low cost solar panels that have a high efficiency using light absorbed from the visible spectrum (which accounts for most of the sun's spectral irradiation [1]).

Furthermore, you can't just have solar cells that absorb a wide range of the solar spectrum, there is an optimum band gap for these materials of around 1.34 eV [2].

This means that the most popular solar cells in development, namely CIGS and CdTe are already occupying the niche for maximum efficiency. The challenge now is finding new materials that are cheaper to make and show greater efficiencies whilst not relying on the use of rare earth/toxic elements.

(Hint: the real development in this area at the moment is hybrid perovskites [3])

Basically, this is irrelevant cruft.

[1] http://zebu.uoregon.edu/~imamura/122/images/solar_spectrum.p...

[2] http://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limit

[3] http://www.nrel.gov/ncpv/images/efficiency_chart.jpg

(source: currently doing a PhD in a new photovoltaic materials)


You can't make single cells that absorb a wide range, but you can layer cells that absorb different spectras to achieve a much higher absorbtion in aggregate.


This is a great point. We shouldn't ignore other efficiencies though. When used on the building envelope, light energy that would otherwise heat the building is converted into electricity instead. Assuming a reasonable efficiency for the conductors and inverters, this reduces the overall building demand. Even small reductions in demand can have huge price benefits for wholesale electricity buyers during expensive summer months (i.e. large commercial buildings). Hence, even if these panels are less efficient than opaque panels (and really how could they not be?) there may be other ways they can make sense from both energy savings and cost perspectives.


Now your window needs wiring. And an inverter. Would be more effective to coat it or tint it or put up some blinds.


Why couldn't you collect the solar energy from the outside of the window and put up blinds to block the light from the inside of the window? Putting up blinds won't generate any electricity.


What if we could design a solar cell that could shift from transparent to opaque on demand? Instead of putting up blinds, simply move a slider or tap a button or what have you, and suddenly the amount of light coming in is dimmed, and the energy being captured is increased. Seems like a win-win to me, if it were possible.


Solar-panel covered shuttering could do that.


Well blinds would presumably block the light you want in (visual spectrum). Furthermore, anything that isn't reflected back out serves to heat the building. Absorbing the energy in a PV material takes some fraction of energy that would otherwise become heat and turns it into something valuable.

Efficiency is very important but just one-big factor to consider in your application. Less efficient panels can have other benefits that justify their use. Crystalline silicon panels are more efficient than thin film but thin films are lighter and so can be used on roofs that don't support the heavier panels.


Blinds would block the light after the light has already passed through the solar panels. You get the shade plus the electricity.


As they say in the video, even if these are half as efficient as regular solar panels, you could still see them on other types of surfaces where current solar panels can't be used right now: think windows or smartphone screens.

We could also see them on large buildings or rich people's villas whose owners perhaps want to use energy from solar panels, but don't like the "look" of solar panels on those buildings. So then the choice becomes using this or using no other solar panels.


We really don't have a shortage of space to put solar panels. The challenge is making solar panels that are cost effective (e.g. $ per Watt).

In response to your edit: That is a possibility, that yes they may find a niche in the fancy of the rich.

But the point I'm making is that the article is hyperbolic and misleading.

Transparent solar is not the future of utility scale power generation. It is not going to solve any of the problems currently holding back solar power from becoming ubiquitous.


Volume is key. Volume to push price of silicon panels down to have electricity reach grid parity levels. An intesting project (which I think has been ditched or put on hold) is/was DESERTEC. Install thousands of PV pannels in the Sahara dessert, and connect this to energy-hungry Europe thorugh a new HVDC grid connection.

Source: http://en.wikipedia.org/wiki/Desertec


> The challenge is making solar panels that are cost effective (e.g. $ per Watt).

And the other key challenge is nighttime.

If we had relatively low-cost utility-scale electrical energy storage, we would see a much higher rate of solar energy adoption. More so in sunny places, but that would then drive down the cost for everyone.

I keep hoping something like a flow battery will turn out to be practical, where to size up the storage, you just need bigger storage tanks.


i get smartphone screens, but it's not that every other surface has been covered already or that you can't transport electricity from A to B.


He delivered the BBC Reith Lectures this year too, which were fantastic.

http://www.bbc.co.uk/programmes/b00729d9


If you enjoyed those lectures, the EconTalk conversation with Becky Linddicoat on palliative care may also be of interest to you.

http://www.econtalk.org/archives/2014/11/becky_liddicoat.htm...


Gay marriage has this week been legalised in the UK. I'm really not sure what else they can do.


*in England & Wales. There is a bill that will be considered in Scotland once the parliament reconvenes. Northern Ireland has thus far rejected all legislation to change the law there.


> So a person who lays the iPad2 on their chest while napping, or holds one on their chest while reading, could trigger magnet mode.

I think the point the article is trying to make is that holding an iPad close to your chest is both more likely to happen, and less noticeable than holding a magnet to your chest.


I wonder if those quack 'magnetic wrist {pain reliever,travel/seasickness preventer} bracelet' things are strong enough to affect it?


I'm really not sure what this means:

> My brain works a little differently than most people’s. My body doesn't balance chemicals like serotonin, norepinephrine and dopamine well and as a result I get “sick”, my label for my particular mix of anxiety, depression and general mental health issues.

Chemicals like serotonin, norepinephrine and dopamine? So neurotransmitters? And what does balance have to do with it? Do you lack dopaminergic neurons? Do you have an over expression of serotonin? I'm not asking for you to go into detail about your problems but that sounds a little too wishy washy.

A lot of these issues sound exactly like what many other people also suffer from every day. So it's hard to not think that on some level this is psychosomatic.


I was trying to simplify it, admittedly a lot, I was just trying to illustrate that really in the end behaviour and affect is just chemistry, effected by various different stimulus. (i also should've added as a footnote, i studied psychology for several years)

And sure these are all things that people suffer day-to-day, what makes it more is that an episode can go days, weeks and (thankfully not recently for me) months.


OK. I understand what you were trying to put across. But ultimately what you described was a set of symptoms of a disorder that you didn't fully explain, so I found it confusing reading the essay with vague hints of the underlying issue.

I'm just saying this as cognitive scientists spend a lot of effort working out which mechanisms and pathways are malfunctioning for a specific disorder, and a generalised statement listing 3 neurotransmitters didn't sit well with me.

From a neuroscience perspective, there is a major issue with self diagnosis, its very hard to be objective when you're examining yourself and once you begin to notice something, you tend to 'fix' the evidence in your mind. Psychosomatic symptoms are surprisingly common. However I don't want to sound like I'm questioning your diagnosis, so if you are aware of a deficit on a functional level please ignore me.


Oh no no, I completely understand how it could "not sit well" with someone, I over-simplified it for the audience and it was only supposed to be illustrative in the purpose of what I was writing.

(Obviously I'm more a believer/subscriber/fan of cognitive approaches to psychology, and why I wanted to be a psychologist and not a psychiatrist.)


I suggest ignoring experiment0's comments in this thread.

At any rate, your article has convinced me that you're not just engaging in self-fulfilling prophecies or theorizing as he seems to imply when he writes "psychosomatic".

(And experiment0, you can't have gotten far in your study of neuroscience if you think there are just 3 neurotransmitters.)


Why would you suggest to ignore me when I was aiming to promote discussion. I was primarily questioning the science behind the post as there's a lot of questionable reporting on topics like these and so if it looks dubious, then I'm set to promote clarification. As it turns out oliyoung does seem to know what he's talking about, so I guess I needn't have worried.

And the snark at the bottom of your reply is really quite unnecessary.


I suggest ignoring hollerith's comments in this thread.

things got so meta...


> its very hard to be objective when you're examining yourself and once you begin to notice something, you tend to 'fix' the evidence in your mind.

That's the first time I hear a reasonable argument that I can't diagnosis myself.


It still doesn't tell you who it is on the about page though, just that he's on the AppKit team.


I would imagine email address corydoras@ridculousfish.com would give a hint.


So you're saying he is a fish. Interesting.

http://en.wikipedia.org/wiki/Corydoras


So, email corydoras@ridculousfish.com and he'll reply with a hint about his identity?


nah, you'll have to partion the pre @ part using a reg ex into 2 parts, and then take the one that makes the most sense. >c orydoras

>co rydoras

>cory doras

>coryd oras

>corydo ras

>corydor as

>corydora s

I'm going with coryd oras, sounds like a real name.


Why 2 parts?

Cory D Oras.

Obviously.


Hey so did I!

My first programming experience was working on RS2DBase. It was pretty popular back in the day. I met loads of great people through those forums and I don't think I'd have gotten into programming without them.


I've done the same thing, I've customised holmans dotfiles and just replaced the content with my preferences. I really like the rake mechanism for symlinking. Simple and convenient.


Well Lisp is dynamically typed and Javascript, Ruby and Python seem to be doing pretty well.


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