Archive for the Uncategorized Category

Bayesian weak lensing tomography: Reconstructing the 3D large-scale distribution of matter with a lognormal prior [CEA]

Posted in Uncategorized on January 11, 2017 by telescoper

Bayesian and Lognormal! How could I resist a reblog of this arXiver post?

arXiver

http://arxiv.org/abs/1701.01886

We present a Bayesian reconstruction algorithm that infers the three-dimensional large-scale matter distribution from the weak gravitational lensing effects measured in the image shapes of galaxies. The algorithm assumes that the prior probability distribution of the matter density is lognormal, in contrast to many existing methods that assume normal (Gaussian) distributed density fields. We compare the reconstruction results for both priors in a suite of increasingly realistic tests on mock data. We find that in cases of high noise levels (i.e. for low source galaxy densities and/or high shape measurement uncertainties), both normal and lognormal priors lead to reconstructions of comparable quality. In the low-noise regime, however, the lognormal model produces significantly better reconstructions than the normal model: The lognormal model 1) enforces non-negative densities, while negative densities are present when a normal prior is employed, 2) better traces the extremal values and the skewness of the true underlying…

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R.I.P. Dick Fong 

Posted in Uncategorized on January 5, 2017 by telescoper

Just a quick post to pass on the very sad news that physicist and cosmologist Dr Richard Fong  – known to all his friends and colleagues as Dick Fong – died yesterday, on 4th January 2017.

Dick’s scientific background was in theoretical physics but he played a major part in the late 1970s and early 1980s in setting up and developing a group in cosmology and extragalactic astronomy in the Physics Department at Durham University. Dick was self-effacing about his own research but he was clearly an expert talent-spotter, bringing such luminaries as Tom Shanks, Richard Ellis and Carlos Frenk to work there. This initiative was extremely successful and Durham is now, and has been for many years, one of the world’s leading centres for cosmology research. Dick retired about fifteen years ago, but kept in touch with developments in the field. He leaves quite a legacy.

My own clearest memory of Dick was that he was on the panel that interviewed me for a research fellowship in 1992, just before the Science and Engineering Research Council (SERC) split up and spawned PPARC and STFC. Dick led the questions after my talk which I struggled mightily to answer, at least partly because I couldn’t really work out what he was asking! He was always a bit cryptic when talking about physics. Despite this I was awarded the Advanced Fellowship, which really established my own academic career and led to my first faculty position.

As well as that  very personal reason for remembering Dick, there is another which I’m sure will be shared by those who knew him and worked with him: he was a kindly and charming man who was always generous and helpful to others. He will be greatly missed by his friends and family, to whom I send heartfelt condolences.

R I.P. Richard Fong (1936-2017)

The problem with experts

Posted in Uncategorized on January 1, 2017 by telescoper

A thoughtful piece, well worth a reblog. Especially for the quote from Swift:

“Reasoning will never make a man correct an ill opinion, which by reasoning he never acquired.”

Waiting for Godot

Among my New Year’s Eve companions was a bow-tied academic sociologist specialising in game theory.

The fun we had.

He told me about his use of the Monty Hall problem with his students. You probably know it but (from wikipedia):

Suppose you’re on a game show, and you’re given the choice of three doors: Behind one door is a car; behind the others, goats. You pick a door, say No. 1, and the host, who knows what’s behind the doors, opens another door, say No. 3, which has a goat. He then says to you, “Do you want to pick door No. 2?” Is it to your advantage to switch your choice?

The answer, for those who don’t know the problem, is that by switching you double your chances of winning the car. And you can prove it mathematically.

When Marilyn vos Savant, who originally publicised the problem, gave that answer he was beseiged…

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My 2016 Review of the Year

Posted in Uncategorized on December 30, 2016 by telescoper

Butetown’s Baltic Missions

Posted in Uncategorized on December 29, 2016 by telescoper

More on Cardiff history, this time the Baltic connections..

History On The Dole

German Seamen's Pastors, 1906. Julius Jungclaussen is in the front row, fourth from the right (with the full white beard). German Seamen’s Pastors, 1906. Julius Jungclaussen is in the front row, fourth from the right (with the full white beard).

With today’s blog, the next in the current series looking at the overseas Seamen’s Missions in Cardiff in the late-nineteenth and early twentieth centuries, I want to turn my attention to some of the more hidden and unknown aspects of this rich organisational-religious culture in the port. The Norwegian Church and the Greek Orthodox Church, both of which still stand, and in the case of the latter still serves the community as a religious building, are well-known. Their history, if often misreported in certain details, is at least known about by those familiar with Cardiff’s multicultural past. Less well-known, and in some cases perhaps almost completely unknown, are the missions that served the Dutch, Estonian, Finnish, German, and Latvian, communities that settled in the port and were bolstered by regular…

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A Nordic Beacon

Posted in Uncategorized on December 29, 2016 by telescoper

Cardiff’s Norwegian connection. The Norwegian Church in Cardiff Bay is still an important landmark.

History On The Dole

The Norwegian Church, Cardiff. Courtesy of Cardiff Local Studies Library. The Norwegian Church, Cardiff. Courtesy of Cardiff Local Studies Library.

Since the end of the Second World War, the people of Norway have made an annual gift of Christmas trees to London and other maritime port towns across the United Kingdom in honour of the close ties of friendship that exists between the two countries. The gift of a tree to Cardiff is particularly poignant because, in 1905, Norway gained its independence from Sweden and Cardiff was granted city status – the first (and really only) modern city in Wales. Along with Hull and Liverpool, Cardiff has always had a Scandinavian minority in its population, with most involved directly or indirectly in maritime trade. Two facets of this heritage are now especially visible: the Norwegian Church, a beautiful, brilliantly white wooden building that since 1992 has stood overlooking the Cardiff quayside, having been removed from its original position at Bute…

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The Eastern Cross

Posted in Uncategorized on December 29, 2016 by telescoper

Fascinating insight into Cardiff’s international heritage..

History On The Dole

St Nicholas Greek Orthodox Church, Greek Church Street, Cardiff. Courtesy of Cardiff Local Studies Library. St Nicholas Greek Orthodox Church, Greek Church Street, Cardiff. Courtesy of Cardiff Local Studies Library.

Not far from the Islamic Centre on Alice Street, Butetown, in a long-since demolished terrace, there once stood Cardiff’s original Greek Orthodox church. Opened at 31 Patrick Street on 18 December 1873, the then Feast Day of St Nicholas in the Orthodox tradition, this was another of the town’s new buildings for its growing religious minorities, although because of the formal rules of the Church it was in practice a set of rooms set aside for worship rather than a formal religious building. As explored in this post, the Norwegian Church had opened just a few years earlier catering for the Lutheran population, and Cardiff already had its synagogue – opened at East Terrace, off Bute Street, in 1858 – and Roman Catholic churches. This was all symptomatic of a town that was cosmopolitan…

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