Category: Sciency things

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Econophysics and oil

Many years ago when I was a lowly undergrad, I heard mumblings about physicists working in the financial and economic fields. They weren’t changing careers, they were applying math and physics concepts to create financial and economic models.

Today I ran into an article (registration required, but it’s free) over on PhysicsWorld about some econophysicists who analyzed recent oil prices using statistical physics methods and came to the conclusion that much of the run-up in oil prices is due to speculation, rather than increased demand.

Abstract:

We present an analysis of oil prices in US$ and in other major currencies that diagnoses unsustainable faster-than-exponential behavior. This provides evidence that the recent oil price run-up has been amplified by speculative behavior of the type found during a bubble-like expansion.

From the paper:

Based on analogies with statistical physics and complexity theory, we have developed in the last decade an approach that diagnoses bubbles as transient superexponential regimes. In a nutshell, our methodology aims at detecting the transient phases where positive feedbacks operating on some markets or asset classes create local unsustainable price run-ups. The mathematical signature of these bubbles is a log-periodic power law (LPPL). The power law models the faster-than-exponential growth culminating in finite time. The log-periodic oscillations reflect hierarchical structures as well as competition between the trading dynamics of fundamental value and momentum investors

In conclusion, the present study supports the hypothesis that the recent oil price run-up, when expressed in any of the major currencies, has been amplified by speculative behavior of the type found during a bubble-like expansion. The underlying positive feedbacks, nucleated by rumors of rising scarcity, may result from one or several of the following factors acting together: (1) protective hedging against future oil price increases and a weakening dollar whose anticipations amplify hedging in a positive self-reinforcing loop; (2) search for a new high return investment, following the collapse of real-estate, the securitization disaster and poor yields of equities, whose expectations endorsed by a growing pool of hedge, pension and sovereign funds will transform it in a self-fulfilling prophecy; (3) the recent development since 2006 of deregulated oil future trading, allowing spot oil price to be actually more and more determined by speculative future markets and thus more and more decoupled from genuine supply-demand equilibrium

A pre-print of their paper, The 2006-2008 Oil Bubble and Beyond, is available from arxiv.org. It’s actually a pretty interesting read.

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The game is tied!

Much buzz abounds about Phoenix‘s successful landing on Mars. There are already plenty of pictures to check out too.

With that landing, the score is tied at 20-20 and Earth’s scoring streak continues!

Although the mission is only scheduled to last 90 days, considering the success of Opportunity and Spirit, I have high hopes that Phoenix’s mission will last longer.

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Journal Club: From Baking a Cake to Solving the Schrödinger Equation

This latest installment of the journal club isn’t exactly medical physics related, but it was something that I thought was interesting more from a topical point of view rather than the actual research itself.

The title of the paper, From Baking a Cake to Solving the Schrödinger Equation, may give the impression of being just another trivial waste of time and a candidate for an Ig Nobel award.

Look a little deeper and it actually turns out to be much more.

Physics is all about developing, describing and modeling systems or processes, which is exactly what this paper is about. Once you have a decent model, you use it to make predictions and design experiments to verify those predictions. The author takes a seemingly trivial process (how changes in cake dimension and volume affect baking time) and attempts to describe the process mathematically using well known equations and experimental results.

Found via Talk Like A Physicist

First comes the initial model. The authors begin with the diffusion equation.

Along with some known initial conditions, the equation can be solved to produce a solution that approximates the cake baking process. In the case of the paper, the solution provides the baking time given the dimensions of the cake.

Once the solutions have been obtained, it’s now possible to visualize the theoretical behaviour of the system. However, this still needs to be correlated to the actual observed behaviour, which is where the experimental part comes in. If the experimental results deviate from the expected theoretical results, it probably means that some of the assumptions in the model were incorrect and need to be modified. Usually it’s possible to figure out how the model needs to be modified by studying the differences between the theoretical and experimental results. With the modified model, a new set of solutions can be created and then verified against experimental results.

With enough iterations, the model becomes accurate enough to make predictions that can be verified experimentally. Often new experiments need to be designed in order to verify any predictions made. Sometimes current technology is insufficient and verifying predictions must wait years or decades before it can be done. If you’re really clever, you notice that the solutions of the model can be applied to other systems, or you notice that the solution or equations resemble a process in a completely unrelated field. In the paper, the author notes the similarity between the diffusion equation and Shrödinger’s equation and analyzes not only what the solutions mean when applied to the Shrödinger equation, but also the limitations of the solutions.

Thus, rather than being an apparently trivial paper, this paper is really a very impressive study of what physics and the process of doing physics is all about.

Abstract:

The primary emphasis of this study has been to explain how modifying a cake recipe by changing either the dimensions of the cake or the amount of cake batter alters the baking time. Restricting our consideration to the génoise, one of the basic cakes of classic French cuisine, we have obtained a semi-empirical formula for its baking time as a function of oven temperature, initial temperature of the cake batter, and dimensions of the unbaked cake. The formula, which is based on the Diffusion equation, has three adjustable parameters whose values are estimated from data obtained by baking génoises in cylindrical pans of various diameters. The resulting formula for the baking time exhibits the scaling behavior typical of diffusion processes, i.e. the baking time is proportional to the (characteristic length scale) of the cake. It also takes account of evaporation of moisture at the top surface of the cake, which appears to be a dominant factor affecting the baking time of a cake. In solving this problem we have obtained solutions of the Diffusion equation which are interpreted naturally and straightforwardly in the context of heat transfer; however, when interpreted in the context of the Schrödinger equation, they are somewhat peculiar. The solutions describe a system whose mass assumes different values in two different regions of space. Furthermore, the solutions exhibit characteristics similar to the evanescent modes associated with light waves propagating in a wave guide. When we consider the Schrödinger equation as a non-relativistic limit of the Klein-Gordon equation so that it includes a mass term, these are no longer solutions.

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Arsenic PET imaging

When most people think of PET imaging, the more commonly used isotopes of 18F, 11C, 15O and 82Rb usually come to mind. When this article on arsenic imaging (free registration required I think) showed up in my feed reader a few days ago, I was a little intrigued. It certainly wouldn’t be the first time a toxic metal was used for imaging purposes. 201Tl has been used as a cardiac imaging agent for years and is still used in a lot of places. Fortunately, the amounts used are way below toxicity levels making it safe to use for imaging.

The article looks at some research being done using 74As tagged to bavituximab (an antibody). So being curious, I looked up the decay scheme for 74As. It produces a β+ 66% of the time and a β– 34% of the time with mean beta energies of 440 and 400 keV respectively. That means it should have good spatial resolution characteristics (travels a shorter distance from the decay point before annihilating). The half life of 17.77 days makes it less than ideal as an imaging agent though, but perfect for research because it allows researchers to follow the imaging characteristics of anything tagged to 74As without having to do repeated injections.

From the article:

A study published in the latest issue of the journal Clinical Cancer Research (14 1377) shows that arsenic behaves as a promising functional imaging agent when linked to a developmental anti-cancer drug called bavituximab, an antibody that homes in on the blood vessels that feed cancerous tumours. The findings, which are based on animal studies, mark the first time that arsenic has been used to label antibodies for the detection of tumours.

Significantly, there appears to be little or no detectable uptake of bavituximab by normal organs, with 22 times as much bavituximab localized to the tumour compared to the liver when measured 72 hours post-injection. The study further showed no specific localization of bavituximab to blood or other tissues, including the heart, kidney, intestine, muscle, bone and brain.

It’s all still in the research phase but it sounds interesting. It will probably be a few years before anything is ready for clinical research on people but it sounds like there’s a lot of potential.


Abstract from the paper:

Purpose: We recently reported that anionic phospholipids, principally phosphatidylserine, become exposed on the external surface of vascular endothelial cells in tumors, probably in response to oxidative stresses present in the tumor microenvironment. In the present study, we tested the hypothesis that a chimeric monoclonal antibody that binds phosphatidylserine could be labeled with radioactive arsenic isotopes and used for molecular imaging of solid tumors in rats.

Experimental Design: Bavituximab was labeled with 74As (β+, T1/2 17.8 days) or 77As (β-, T1/2 1.6 days) using a novel procedure. The radionuclides of arsenic were selected because their long half-lives are consistent with the long biological half lives of antibodies in vivo and because their chemistry permits stable attachment to antibodies. The radiolabeled antibodies were tested for the ability to image subcutaneous Dunning prostate R3227-AT1 tumors in rats.

Results: Clear images of the tumors were obtained using planar {gamma}-scintigraphy and positron emission tomography. Biodistribution studies confirmed the specific localization of bavituximab to the tumors. The tumor-to-liver ratio 72 h after injection was 22 for bavituximab compared with 1.5 for an isotype-matched control chimeric antibody of irrelevant specificity. Immunohistochemical studies showed that the bavituximab was labeling the tumor vascular endothelium.

Conclusions: These results show that radioarsenic-labeled bavituximab has potential as a new tool for imaging the vasculature of solid tumors.