Profile

Cover photo
David Roberts
Works at University of Adelaide
Lives in Adelaide, Australia
18,963 followers|1,609,695 views
AboutPostsPhotos

Stream

 
Take a rectangular sheet of paper, and glue two opposite sides of the rectangle to each other to make a cylinder. Now glue the other two opposite sides to each other — you'll probably have to crumple or fold the paper to do it, because a round cylinder won't bend around smoothly to let you do this step. The result is a surface with the topology of a torus, but (using distances measured in terms of paths within the surface, not shortcutting through the space around it) the geometry of a flat Euclidean plane everywhere — the points in the middle of the rectangle already started with this Euclidean geometry, but the gluing process made it so that the points that were originally on the boundary of the rectangle look just the same, so they also have flat Euclidean neighborhoods in the torus. You can do the same gluing process with a square, a parallelogram, or a regular hexagon, and in each case get a flat torus.

Flat tori have nice smooth embeddings in four-dimensional space (take the Cartesian product of two perpendicular circles) but some crumpling seems to be required in 3d. Nevertheless, they can be embedded into 3d, and this video shows one way to do it using fractal crumpling rather than folds.

Via https://plus.google.com/+KevinClift/posts/N9Qx8JYRfnZ and https://plus.maths.org/content/abel-prize-2015-all-wrapped which have more on how this sort of embedding problem relates to the recent award of the Abel Prize to John Nash and Louis Nirenberg.
View original post
2
Add a comment...
 
Ho ho ho...
 
Breaking News! LHC Run 2 cancelled, CERN closes doors. The ALICE Control Room will be repurposed into a massive Call of Duty multiplayer facilitiy!
After a three week review CERN Director General, Rolf Dieter Heuer has announced that the LHC will not have another run and that the international laboratory will be closing its doors to science. The revelation follows an intense week of discussion, analysis and rumour mongering.
View original post
5
1
Hayden Roberts's profile photoDomenico Monaco's profile photo
 
Reads title, checks date.

Phew!
Add a comment...

David Roberts

Shared publicly  - 
 
I wonder if they have the term to add to the Lagrangian yet...
 
CERN researchers confirm existence of the Force

Physicists at the European Laboratory for Particle Physics announced today that an invisible Force permeates the universe and binds the galaxy together

http://cern.ch/go/c7dB

Image shows research in the CERN Beams department

(Image credit: Maximilien Brice and Daniel Dominguez © CERN - for terms of use see http://cern.ch/copyright )
86 comments on original post
11
1
Drew Armstrong's profile photoDomenico Monaco's profile photo
 
This would be more plausible if they had already switched the thing on.
Add a comment...

David Roberts

Shared publicly  - 
 
Ingrid has been the president of the International Mathematical Union - the "top job" in mathematics, in a manner of speaking.

#womeninstem  
 
Ingrid Daubechies, Duke University, will present MAA Centennial Lecture 3, "Mathematics for Art Investigation", at MAA MathFest2015 in Washington, D.C.
Abstract: Mathematical tools for image analysis increasingly play a role in helping art historians and art conservators assess the state of conservation of paintings, and probe into the secrets of their history. The talk will review several case studies, Van Gogh, Gauguin, Van Eyck among others.
Register for MAA MathFest at http://bit.ly/MF15-register ‪#‎MAAthFest‬
View original post
3
Add a comment...

David Roberts

Shared publicly  - 
 
Hooray!
 
#‎RestartLHC‬ is back on track!

The LHC should be ready for beam in a few days’ time: http://cern.ch/go/PRD9

Image shows tests carried out last week to identify the cause of the fault detected between a magnet and its diode. Image credit Maximilien Brice/CERN © CERN - for terms of use see http://cern.ch/copyright
56 comments on original post
3
David Roberts's profile photoHayden Roberts's profile photo
3 comments
 
+David Roberts Cross fingers and toes then :P.
Add a comment...
Have him in circles
18,963 people
Marcelene Ellington's profile photo
Ryan Kasprzak's profile photo
Daniel Arther's profile photo
Benjamin Dougherty's profile photo
Donna Aker's profile photo
rocky russ's profile photo
Bin Shao's profile photo
Jasmine Taylor's profile photo
Michael Burt's profile photo
 
RP[+Richard Poynder​] : Based on your experience then, how much would you say its costs to publish an open access journal?


MB: I’ll need to dodge this question somewhat, as my experience as the editor at BDL was removed from the balance sheets available to BMC. All I knew was that I had a set number of author fee waivers I could grant each year, which I generally used for authors from less-wealthy nations. I relied on the balance of authors to come from institutions that mostly (or ideally, completely) subsidised publication.


Beyond my experience, the reported figures for publishing articles open access vary widely. Outsell’s average cost for a publishing an OA article in 2011 was $660 [1], but during that same year Nature reported that it would cost $30,000-$40,000 per paper to go completely OA. This figure beggars belief, no matter how selective a journal may be.


Less insidious are claims from many publishers that it is hard to isolate the mean cost of publishing an open access paper, as these costs are absorbed within complex business entities and/or cross-sudsidised by other parts of a publishing enterprise (as at PLOS, where PLOS One papers underwrite papers in other journals.)


But even this explanation is unsatisfactory. My view aligns with Andrew Odlyzko’s [2], which is that article publication costs of $400/article should be sufficient. Any figure appreciably higher than that is likely a reflection of a publication’s perceived non-substitutability in the market, and not the actual costs of publication.

[1] http://www.nature.com/news/open-access-the-true-cost-of-science-publishing-1.12676
[2] http://www.dtc.umn.edu/~odlyzko/doc/libpubcomp.

http://poynder.blogspot.co.uk/2015/03/the-life-and-death-of-open-access.html?m=1
2
Add a comment...
 
Whoa; did not see this coming. Just found out about this from +Jan Vitek after his meeting w/ ACM leadership today, in response to his survey.

ACM Enters Publishing Agreement with Elsevier

In a move to unite the two leading publishing arms of computer science, the Association of Computing Machinery [2 Penn Plaza, Suite 701 New York, NY 10121-0701] has entered into an agreement with Elsevier [Radarweg 29, 1043 NX Amsterdam, Netherlands].

With this move, Elsevier will take over the ownership and management of the ACM's existing repository of publication, known as the Digital Library. ACM President Alexander Wolf said that the move is in response to a recent survey taken by SIGPLAN about access to ACM publications. "We have known this for a while, which is why our negotiations have been ongoing, but the recent survey made the situation unambiguous", he said. "The community spoke loud and clear: the ACM Digital Library is poorly organized, hard to search, and simply not fulfilling the needs of the community."

Elsevier CEO Ron Mobed said, "We are excited to put this excellent collection of content under the elsevierconnect label. We already offer excellent access facilities to institutions around the world, all of whom will now have access to even more literature, both classic and modern. This move will open access to the ACM Digital Library to a large number of Elsevier customers at no extra cost."

Recognizing the survey's comments about Open Access, both Mobed and Wolf noted that the move lets the organizations harmonize their Open Access policies, reducing a great deal of confusion for customers.  Mobed expects the introduction of a new Open Access classification, Black, that will cover the combined policies by picking the best rules for each situation.
4 comments on original post
1
Add a comment...
 
#womeninstem (we seem to be on a roll here)
 
Cecile DeWitt-Morette relates the story of her career in relativistic physics starting in post-World War II France
https://t.co/psOtw5M1tB
#historyofphysics  
View original post
4
Add a comment...

David Roberts

Shared publicly  - 
 
 
Teaching how to solve problems... G. Polya is one of the best! 
View original post
7
Add a comment...

David Roberts

Shared publicly  - 
 
I don't know why the below is true, but I've always tried to encourage students of all stripes, but especially so for girls.

#womeninstem  
 
According to #pisa girls feel significantly worse than boys about #maths

Maybe we (teachers) should think what are we doing in the classroom.

View original post
2
john iskra's profile photoDavid Roberts's profile photoMarc Harper's profile photoPatricia Ritter's profile photo
6 comments
 
+Marc Harper I have to fish out the papers again (which I can't guarantee I'll find, but I'll try): I think the studies had been done in German schools, from what I can remember. I am by no means very educated in the field, just came across these things years ago, which might mean it is outdated information. From what I remember, both boys and girls greatly benefited from the separation, especially during teenage years. One claim was that without the girls, the boys were under less pressure to "perform" (which, for them, means "clown around", be loud and ostensive even without knowing the answers). While the girls gradually got the courage to speak up more often, ask more questions, actively participate even and especially in the scientific classes. Of course, teachers may have treated them differently also, when no boys were around for them to encourage more... 
I did go to an all girls school myself, from age 11 to 14 more or less, and what I found funny at the time was that, even in the all girls environment, the usual clowns and bullies very quickly defined themselves, being just as loud, foolish or violent as any boys would be. Sociological gaps and niches will be filled, one way or another. But of course one is a lot less intimidated by the rowdy of your own gender, maybe because we find it easier to understand them and shrug them off. Also, quite possibly, I used to feel performance stress more those days: when a teacher asked a question and nobody answered, even with a stupid joke, I often felt like "fine, I'll give it a shot then!" - just to not leave the teacher hanging :D

Having said all that, I do not believe in gender separation at schools: the real world is filled with loud men, girls have to learn to deal with that from the word go - and vice-versa. It should be up to the teacher to help all discriminated groups grow up in a prejudice-free environment, never even getting the time or suspicion that they may be "different" in any way. As long as you don't suspect something is out of your reach, it really might never happen. 


(papers and stats to follow as soon as I find them)
Add a comment...

David Roberts

Shared publicly  - 
 
The ubiquity of π

Doron Zeilberger opines [1]:

Counting problems are done by solving (often obvious) recurrence equations, alias finite difference equations, that come from the combinatorial structure, that in the "limit" turn out to be (often very simple) differential equations. The simplest differential equation is

y'(x)=y(x)   ,   y(0)=1   ,

whose solution, y(x)=exp(x), naturally leads to e:=exp(1), explaining why e is even more ubiquitous than π . The second-simplest differential equation is

y''(x)= -y(x)   ,   y(0)=0, y'(0)=1   ,

whose solution is y(x)=sin(x), and Pi is the smallest positive root of the equation sin(x)=0.

So the reason that both e and Pi are all over the place is that they both arise from finite counting problems, and for the sake of convenience, one replaces Avogardo's number by "infinity" and get "limits", that are really not true "real" numbers (since "real" numbers do not exist), but some equivalence class of sequence-generating algorithms where the equivalence relation is

"converge to the same limit", (or equivalently the sequence of their differences converges to 0)

in analogy with Frege's famous definition of cardinal numbers.

I'm happy to take, in a certain framework, real numbers to be elements of the Bishop set [2] of sequence-generating algorithms, with equality as described above (pace Bishop-Bridges [3]).


[1] http://www.math.rutgers.edu/~zeilberg/Opinion142.html
[2] http://ncatlab.org/nlab/show/Bishop+set
[3] http://link.springer.com/book/10.1007%2F978-3-642-61667-9
Opinion 142: Why Is π So Ubiquitous? By Doron Zeilberger. Written: π day, 2015 (aka 3/14/15). Eugene Wigner starts out his classic essay, about the "The Unreasonable Effectiveness of Mathematics in the Natural Sciences" by narrating a conversation between a statistician and his friend, ...
16
3
Refurio Anachro's profile photoWilliam Rutiser's profile photoNarges Aghamir's profile photoKazimierz Kurz's profile photo
16 comments
 
Thank you, +John Baez, i do appreciate it! Altough now i seem to remember you did mention that Weierstrass elliptic to me once before... I can certainly try a bit harder on it, especially since i do have some complex tori left by some varieties i encountered last week.
Add a comment...
People
Have him in circles
18,963 people
Marcelene Ellington's profile photo
Ryan Kasprzak's profile photo
Daniel Arther's profile photo
Benjamin Dougherty's profile photo
Donna Aker's profile photo
rocky russ's profile photo
Bin Shao's profile photo
Jasmine Taylor's profile photo
Michael Burt's profile photo
Work
Employment
  • University of Adelaide
    present
Basic Information
Gender
Male
Relationship
Married
Story
Tagline
Mathematician, among other things.
Introduction
I live in Adelaide, Australia.

I am a pure mathematician who works on category theory and a smattering of related fields such foundations and higher geometry.

I work as a post-doc at the University of Adelaide in the School of Mathematical Sciences.

My nLab page: http://ncatlab.org/nlab/show/David+Roberts
Places
Map of the places this user has livedMap of the places this user has livedMap of the places this user has lived
Currently
Adelaide, Australia
Links
Contributor to