How proxy is a proxy? - Part II

So, I believe that last time I threatened to, for once, have a series of evolving posts that gradually elucidate on a single topic. Henceforth, here is round two.

As a reminder, last time I posed the question:

How accurate are experiments where non-human, proxy cadavers are used?

In particular, I'm considering experiments where we want to use existing acoustic technology to image submerged cadavers.

To start with, lets think about precisely what we're going to be imaging with the acoustic returns. Sounds simple, doesn't it?! Sadly, as with almost everything to do with acoustics, simple questions tend to result in complex answers.

In order to image something using sound, it needs to present a measurable change in acoustic impedance (i.e., basically a measure of the strength to which the material resists the passage the sound wave) to it's immediate surroundings. The human body is generally considered to consist of 60 -70 % water, suggesting that a cadaver sitting on the seabed, lakebed, or riverbed will tend not to offer as strong an acoustic target as, say, the sediments on which it is resting because it closer resembles the water around it than the sediments do.

However, the acoustic backscatter from a target (the sound which travels from the source to the object and is reflected back towards the source again) is the combined response of two processes:

1. Surface scattering: the energy reflected back by the water/cadaver interface.

2. Volume scattering: the energy reflected back from within the target.

Of these, the volume scattering is the one we're particularly interested in. As I said earlier, the surface scattering will not be very strong for a cadaver. The volume scattering, on the other hand, will be. This is because, during decomposition, gas builds up within the tissue and internal cavities of the cadaver. This gas will present a very strong change in acoustic impedance.

So, when we want to acoustically image a cadaver, we would expect the dominant acoustic signature to be from the build up interstitial gas as a result of decomposition.

How proxy is a proxy? - Part I

As I've mentioned in a blog a couple of months ago, Piggy hide and seek, I've recently been looking into the idea of using shallow water marine geophysical techniques in helping Law Enforcement Agencies conduct underwater body searches. Going through the frantic research process involved with writing any kind of research proposal, a particularly interesting thought occurred to me, namely:

How accurate are taphonomic experiments where non-human, proxy cadavers are used?

In certain states of the USA it is possible to use human cadavers when people have donated their body to science, or their body remains unclaimed. This has enabled researchers at the University of Tennessee's Anthropological Research Centre, in Knoxville, to setup their 'Body Farm', where human cadavers are placed in a variety of environmental conditions and their decay monitored over a period of days, weeks, months, and sometimes years. As a result of the ground-breaking research conducted at Tennessee, other body farms have now sprung up in Western Carolina University and Texas State University, although on considerably smaller scales.

The work undertaken by these institutions has been truly astonishing, advancing forensic entomology immensely. Without this work there must be thousands, perhaps hundreds of thousands, of homicides the world over that would never have been solved. However, outside of these specific locations, the vast majority of people trying to undertake research in this, or related, fields have to rely of using proxy cadavers, normally domestic pigs. This leads to the question of how accurately a pig cadaver can imitate a human one? Taphonomically they have been shown to be very, very similar; their skin is close enough to ours for use in skin grafts for burns victims, whilst, also being omnivores, they have much the same gut bacteria, leading to a decomposition progression that very closely mimics our own.

This is all well and good for taphonomic and forensic entomology studies of beetle or fly larvae colonization, etc, but for our purposes, where we want to image the acoustic properties of the cadavers, can we truly say the same?

This is something I'm, hopefully, going to explore in the next few blogs by discussing the physics behind the variety of acoustic profilers that can be used. In this way, it should be possible to see where the potential differences between the different cadavers could result in different observations.

The Obama-wagon...quick, jump!

Firstly, and probably most importantly, congratulations to Senator Obama on his resounding victory Tuesday evening. Secondly, congratulations America!

It was quite a surreal evening for me. I attended my first ever 'Election Party' (I'm not sure what it says about me that it was for an American Election rather than a British one, but...). Throughout the evening there was a lot of talk about how, if Obama got in, people would feel 'proud to be American again', which says a lot for the damage our friend George W. has done to international relations on all levels. However, the best comment of the evening, I think, came when someone said:

'We've really dodged a bullet by avoiding electing Palin as Vice President.'

I couldn't agree more, it's hard to imagine what could be worse that having the gun-toting creationist loitering in the wings, just in case something happened to McCain. I have to admit, though, there is a part of me that feels sorry for Senator McCain. The guy is not a bad politician, and probably wouldn't have made a particularly bad President, but suffered because somehow his party decided Sarah Palin would make a great running-mate!

However, what has grabbed my attention most about the immediate outfall from the election result, is the level of childishly cynical hero worship that has swept around the political world. Nothing describes this better than the pitiful exchange between Gordon Brown and David Cameron in the House of Commons yesterday.

What is more pathetic than two grown men fighting it out to be associated with Senator Obama's victory? Why is it necessary - is the result of the US election really going to influence British voters in their choice of who they will vote for in our forthcoming election? Had the elections happened the other way around (which they might well have), do they really think that Obama and McCain would have reciprocated and been fighting tooth and nail as to whose campaign closest resembled that of the British PM? I think not!

After all the comments on the blog-o-sphere and articles in newspapers and news websites in the UK criticizing American politics over last few years, on the evidence of this we should perhaps be looking a little closer to home!

E-Day is nigh

Sadly, there's been little activity on this blog in recent weeks. I assure you, it's not that I don't have anything to say, simply too much to do. As anyone who's ever done a PhD will tell you, as the deadline looms everything else in life gets pushed aside as the behemoth of a thesis grows (you should see the amount of facial hair I now have)!

Today is an interesting day. As I'm sure everyone is aware, it's US Election Day! Over recent weeks the newspaper, together with quite a few of my favorite blogs, have been discussing this topic ad infinitum:

Cosmic Variance
Lab Lemming
Shores of the Dirac Sea
Michael Berube

Plus, probably a million more that I don't read! So, I'm not going to say anything else on the subject, other that try reading some of the above if you're interested.

Oh, and, "Come on Obama!"

Talking ourselves into a recession

This morning I had an interesting conversation with a work colleague regarding the dubious present state of the financial system over our usual mug of ultra-strong coffee. I have always tried to shy away from writing social criticisms and keep my blog purely science based, but for this I'm going to make an exception. As a vaguely scientific side note, however, our coffee would normally make a good high school science experiment since it behaves more like a glass than a liquid. I'm not sure whether this is purely a factor of the percolation time, or a combined effect with the obscene amounts of sugar vigorously stirred into it, but, either way, this coffee could quite easily go undercover as treacle.

Today's caffeine fueled discussion stemmed from an article published on BBC News yesterday. Entitled 'UK economy already 'in recession'', it is one of the millions of stories being run on news websites and in papers around the world regarding the impact of the present economic crisis on society at large, i.e. levels of unemployment, high-street spending, manufacturing, etc. The point we were talking about was not the comments on rising unemployment, etc (all of which are very valid and supported by statistics from the British Chambers of Commerce), rather that half-way down it proceeded to say 'Technically the UK is not yet in recession...'.

Hang on one cotton-picking minute! First you say we're in a recession, then you say that, according to the guidelines by which economists define recession, we're not - guidelines which have some well founded mathematical basis.

Don't get me wrong, I know full well why headlines such as this are printed. I am all too aware of the way journalists will twist stories to be more dramatic if they think it will result in more sales. The kernel of our discussion this morning revolved around the fact that, normally, the application of such writer's license effects only a limited number of people. Take, football, (soccer to any Americans reading this) for example. The amount of bad press placed on the England football team after a poor performance has many times affected the confidence of the players and therefore their subsequent performances, resulting in the demise of a number of managers in the process. But, this effect is limited to the team and their immediate circle. Although poor performances leading to us not making a major competition has been shown to cause a drop in revenue for sports bars, etc, in general terms this impact is low.

With the economy, the story is a different one. The western economy is closely coupled to the performance of the stock market, when the market is in a period of growth the economy will grow too, and vice versa. The danger of the stock market is that, to a large extent, is is driven by the mood of it's investors. If they get twitchy and start panicking then all hell breaks loose (as was seen with the Northern Rock debacle earlier this year). Unlike football, in this case any fall out from bad press can effect everybody as overly dramatic stories bemoaning the 'almost' recession cause investors to become less pragmatic and the market to plummet and the economy to wobble. As the news article itself pointed out, this then feeds back into the general public with job losses, etc, which then feeds back into the economy with less high-street spending to prop up the markets, i.e. an economic circle of death.

So, in conclusion, I ask the question we talked about over coffee. By printing and talking all this doom and gloom regarding the state of the economy, are we in fact talking ourselves into a recession when otherwise the markets would have dipped but stabilized?