Profile

Cover photo
David Roberts
Works at Home
Lives in Adelaide, Australia
19,326 followers|2,721,986 views
AboutPostsCollectionsPhotos

Stream

David Roberts

Shared publicly  - 
 
Gravitational wave papers now on the arXiv!

Observation of Gravitational Waves from a Binary Black Hole Merger
http://arxiv.org/abs/1602.03837 (the actual paper, published in Phys. Rev. Lett.)

Tests of general relativity with GW150914
http://arxiv.org/abs/1602.03841

Swift follow-up of the Gravitational Wave source GW150914
http://arxiv.org/abs/1602.03868

Astrophysical Implications of the Binary Black-Hole Merger GW150914
http://arxiv.org/abs/1602.03846

The Rate of Binary Black Hole Mergers Inferred from Advanced LIGO Observations Surrounding GW150914
http://arxiv.org/abs/1602.03842

Properties of the binary black hole merger GW150914
http://arxiv.org/abs/1602.03840

GW150914: First results from the search for binary black hole coalescence with Advanced LIGO
http://arxiv.org/abs/1602.03839

GW150914: The Advanced LIGO Detectors in the Era of First Discoveries
http://arxiv.org/abs/1602.03838

Observing gravitational-wave transient GW150914 with minimal assumptions
http://arxiv.org/abs/1602.03843

Characterization of transient noise in Advanced LIGO relevant to gravitational wave signal GW150914
http://arxiv.org/abs/1602.03844

Calibration of the Advanced LIGO detectors for the discovery of the binary black-hole merger GW150914
http://arxiv.org/abs/1602.03845

GW150914: Implications for the stochastic gravitational wave background from binary black holes
http://arxiv.org/abs/1602.03847

Testing Gravity with Gravitational Wave Source Counts
http://arxiv.org/abs/1602.03883

Any that I missed?

#gravitationalWaves  
Abstract: On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of $1.0 ...
3
1
Artem Zvyagintsev's profile photo
Add a comment...

David Roberts

Shared publicly  - 
10
3
Charles Filipponi's profile photoAndrew King (science student)'s profile photoSreekumar Sreekumar's profile photoPeter Waaben's profile photo
 
Pretty cool stuff...
Add a comment...

David Roberts

Shared publicly  - 
 
Observation of Gravitational Waves from a Binary Black Hole Merger (licensed CC-BY)

B. P. Abbott et al. (LIGO Scientific Collaboration and Virgo Collaboration)

Phys. Rev. Lett. *116*, 061102 – Published 11 February 2016


On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10^−21. It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203 000 years, equivalent to a significance greater than 5.1σ. [...snip...] These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.

http://dx.doi.org/10.1103/PhysRevLett.116.061102

#openaccess   #gravitationalWaves  
Gravitational waves emitted by the merger of two black holes have been detected, setting the course for a new era of observational astrophysics.
11
2
Sandy Murguia's profile photoHolger K. von Jouanne-Diedrich's profile photoArtem Zvyagintsev's profile photo
 
So cool and exciting
Add a comment...

David Roberts

Shared publicly  - 
 
Feb 11 is International Day of Women and Girls in Science!
Today is the inaugural International Day of Women and Girls in Science. In December 2015, the United Nations passed a resolution to recognise on February 11 each year women's contributions to the field. The UN's research showed females "continued to be excluded from participating fully in ...
5
Add a comment...

David Roberts

Shared publicly  - 
Has the LIGO experiment seen gravitational waves? New Scientist has probed public observation logs, and here is our exclusive look at where they might be
7
1
Helger Lipmaa's profile photo
Add a comment...

David Roberts

Shared publicly  - 
 
#arXiv  
 
On the relation between continuous and combinatorial
 
F. Marmolejo, M. Menni

Axiomatic Cohesion proposes that the contrast between cohesion and non-cohesion may be expressed by means of a geometric morphism p:→ (between toposes) with certain special properties that allow to effectively use the intuition that the objects of  are `spaces' and those of  are `sets'. Such geometric morphisms are called (pre-)cohesive. We may also say that  is pre-cohesive (over ). In this case, the topos  determines an -enriched `homotopy' category. The purpose of the present paper is to study certain aspects of this homotopy theory. We introduce weakly Kan objects in a pre-cohesive topos, which are analogous to Kan complexes in the topos of simplicial sets. Also, given a geometric morphism g:→ between pre-cohesive toposes  and  (over the same base), we define what it means for g to preserve pieces. We prove that if g preserves pieces then it induces an adjunction between the homotopy categories determined by  and , and that the direct image g∗:→ preserves weakly Kan objects. These and other results support the intuition that the inverse image of g is `geometric realization'. In particular, since Kan complexes are weakly Kan in the pre-cohesive topos of simplicial sets, the result relating g and weakly Kan objects is analogous to the fact that the singular complex of a space is a Kan complex.
View original post
3
2
Mike G's profile photoFernando Yamauti's profile photo
Add a comment...
Have him in circles
19,326 people
Corey Green's profile photo
Ralph Aldredge's profile photo
Crystal Barnhill's profile photo
Albert Siguenza's profile photo
Abiy Kaltiso's profile photo
susan smith's profile photo
kristina repasch's profile photo
Concepcion Gonzalez's profile photo
Jacqueline Smith's profile photo

David Roberts

Shared publicly  - 
 
Another, weaker chirp showed up in the weeks that followed

This is what I want to hear about! What was that??

https://www.quantamagazine.org/20160211-gravitational-waves-discovered-at-long-last/

#gravitationalWaves  
8
Add a comment...

David Roberts

Shared publicly  - 
 
All the main points you need to know.

#gravitationalWaves  
 
Graviational waves

The rumors are true: LIGO has seen gravitational waves! Based on the details of the signal detected, the LIGO team estimates that 1.3 billion years ago. two black holes spiralled into each other and collided. One was 29 times the mass of the Sun, the other 36 times. When they merged, 3 times the mass of the Sun was converted directly to energy and released as gravitational waves.

For a very short time, this event produced over 10 times more power than all the stars in the Universe!

We knew these things happened. We just weren't good enough at detecting gravitational waves to see them - until now.

I'll open comments on this breaking news item so we can all learn more. LIGO now has a page on this event, which is called GW150914 because it was seen on September 14th, 2015:

http://www.ligo.org/science/Publication-GW150914/index.php

You can see the gravitational waveforms here:

https://pbs.twimg.com/media/Ca8dpleUAAALI2n.jpg

At left in blue is the wave detected in Livingston, Louisiana. At right in red is the wave detected in Hanford Washington. The detector in Hanford saw the wave a few milliseconds later, so it must have come from the sky in the Southern hemisphere.

#LIGO #astronomy
50 comments on original post
4
Add a comment...

David Roberts

Shared publicly  - 
 
A treasure trove!
3
2
Helger Lipmaa's profile photoWillie Wong's profile photo
Add a comment...

David Roberts

Shared publicly  - 
 
If you want to see the original paper predicting #gravitationalWaves  , according to Nature News it's this:

A. Einstein, Näherungsweise Integration der Feldgleichungen der Gravitation, Sitzungsberichte der Preussischen Akademie der Wissenschaften zu Berlin, 1 (1916) 688–696,
http://echo.mpiwg-berlin.mpg.de/MPIWG:RA6W5W65

The title in English, as far as Google gets me, is Approximate integration of the field equations of gravitation. The key word to look out for is Gravitationswellen, 'gravitational waves'.
 ·  Translate
8
1
wendy krieger's profile photoUrs Schreiber's profile photoWillie Wong's profile photoJohn “Brian” Peterson's profile photo
16 comments
 
Unfortunately I read that book about 7 years ago and my memory of it is hazy. If I remember I will check when I get home. 
Add a comment...

David Roberts

Shared publicly  - 
 
This is pretty impressive! The important part is that one recovers the other usual p-adic cohomologies: this is what we expect once we have a full theory of motives, but for all (reasonable) cohomologies of schemes.

http://arxiv.org/abs/1602.03148

Title: Integral p-adic Hodge theory

Authors: Bhargav Bhatt, Matthew Morrow, Peter Scholze

Abstract: We construct a new cohomology theory for proper smooth (formal) schemes over the ring of integers of C_p. It takes values in a mixed-characteristic analogue of Dieudonne modules, which was previously defined by Fargues as a version of Breuil-Kisin modules. Notably, this cohomology theory specializes to all other known p-adic cohomology theories, such as crystalline, de Rham and etale cohomology, which allows us to prove strong integral comparison theorems. 
The construction of the cohomology theory relies on Faltings's almost purity theorem, along with a certain functor Lη on the derived category, defined previously by Berthelot-Ogus. On affine pieces, our cohomology theory admits a relation to the theory of de Rham-Witt complexes of Langer-Zink, and can be computed as a q-deformation of de Rham cohomology.

#arXiv  arXiv:1602.03148
Abstract: We construct a new cohomology theory for proper smooth (formal) schemes over the ring of integers of C_p. It takes values in a mixed-characteristic analogue of Dieudonne modules, which was previously defined by Fargues as a version of Breuil-Kisin modules.
3
Add a comment...

David Roberts

Shared publicly  - 
 
Henstock's lectures on Henstock integration

Of course, this notion of integral has many other names, but these notes (~130 page) look to be rather nice

http://arxiv.org/abs/1602.02993

Title: Ralph Henstock's Lectures on the Theory of Integration
Authors: Ralph Henstock, Pat Muldowney

Abstract: These are the class notes of lectures given by Ralph Henstock at the New University of Ulster in 1970-71. The notes deal with the Riemann-complete integral (also known as the generalized Riemann integral, the gauge integral, and the Henstock-Kurzweil integral). They also introduce Henstock's abstract theory of integration.

Comments: Ralph Henstock (d. 2007) is the author of these notes. Pat Muldowney is the note-taker (1970-71) and editor (2015)

#arXiv  
Abstract: These are the class notes of lectures given by Ralph Henstock at the New University of Ulster in 1970-71. The notes deal with the Riemann-complete integral (also known as the generalized Riemann integral, the gauge integral, and the Henstock-Kurzweil integral).
7
5
Mike G's profile photoCharles Filipponi's profile photoAndres Caicedo's profile photoManuel Alzurutt's profile photo
2 comments
 
From Wikipedia: " (also known as the (narrow) Denjoy integral ... Luzin integral or Perron integral, but not to be confused with the more general wide Denjoy integral) " 

They were discussed on the nForum once, and I thought about how one might extend them to spaces other than R (or R^n). I didn't get hugely far, but it was interesting to consider.
Add a comment...
David's Collections
People
Have him in circles
19,326 people
Corey Green's profile photo
Ralph Aldredge's profile photo
Crystal Barnhill's profile photo
Albert Siguenza's profile photo
Abiy Kaltiso's profile photo
susan smith's profile photo
kristina repasch's profile photo
Concepcion Gonzalez's profile photo
Jacqueline Smith's profile photo
Work
Occupation
Househusband and general busybody
Employment
  • Home
    present
  • NCVER
    2015 - 2015
  • University of Adelaide
    2012 - 2015
Basic Information
Gender
Male
Relationship
Married
Story
Tagline
Mathematician, among other things (husband, avid reader, cyclist, Christian,...)
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 am a visiting fellow in the School of Mathematical Sciences at the University of Adelaide.

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