Towards breaking the Omega-bias degeneracy in density--velocity comparisons

I derive a second-order local relation between the REDSHIFT-space mass density field and the REAL-space velocity field. This relation can be useful for comparisons between the cosmic density and peculiar velocity fields, for a number of reasons. First, relating the real-space velocity directly to the redshift-space density enables one to avoid the Omega-dependent reconstruction of the density field in real space. Secondly, the reconstruction of the three-dimensional velocity field in redshift space, questionable because of its vorticity, is also unnecessary. Finally, a similar relation between the GALAXY density field and the velocity field offers a way to break the Omega-bias degeneracy in density--velocity comparisons, when combined with an additional measurement of the redshift-space galaxy skewness. I derive the latter relation under the assumption of nonlinear but local bias; accounting for stochasticity of bias is left for further study.Comment: 13 pages, no figures, uses mn.sty. The calculation properly redone for bias in real space, added references. Accepted by MNRA

Statistical modelling of financial crashes: Rapid growth, illusion of certainty and contagion

We develop a rational expectations model of financial bubbles and study ways in which a generic risk-return interplay is incorporated into prices. We retain the interpretation of the leading Johansen-Ledoit-Sornette model, namely, that the price must rise prior to a crash in order to compensate a representative investor for the level of risk. This is accompanied, in our stochastic model, by an illusion of certainty as described by a decreasing volatility function. The basic model is then extended to incorporate multivariate bubbles and contagion, non-Gaussian models and models based on stochastic volatility. Only in a stochastic volatility model where the mean of the log-returns is fixed does volatility increase prior to a crash.financial crashes; super-exponential growth; illusion of certainty; contagion

Bubbles and contagion in English house prices

Using methods originating from statistical physics we model bubbles in English house prices. It is found that there was a nationwide housing bubble 2002-2007. Typically prices were 30-40% over-valued and fell around 20%. London is atypical in that the level of over-pricing was lower, only around 20%, and experienced a drop in prices of only around 15%. There is some suggestion of contagious effects, with the bubble in London affecting prices in Yorkshire and the North.financial crashes; super-exponential growth; illusion of certainty; contagion; housing-bubble; Enlish house prices

Bubbles and crashes in finance: A phase transition from random to deterministic behaviour in prices.

We develop a rational expectations model of financial bubbles and study ways in which a generic risk-return interplay is incorporated into prices. We retain the interpretation of the leading Johansen-Ledoit-Sornette model, namely, that the price must rise prior to a crash in order to compensate a representative investor for the level of risk. This is accompanied, in our stochastic model, by an illusion of certainty as described by a decreasing volatility function. As the volatility function goes to zero, crashes can be seen to represent a phase transition from stochastic to deterministic behaviour in prices.financial crashes; super-exponential growth; illusion of certainty; housing-bubble

Revolutionary change and structural breaks: A time series analysis of wages and commodity prices in Britain 1264-1913

In this paper we empirically test the hypothesis that economic revolutions are associated with structural breaks in historical economic data. A simple test for structural breaks in economic time series is applied to British wage and price data from the medieval to the modern period. Evidence for structural change is found in nearly half of the series studied -- suggesting that structural breaks are an intrinsic feature of such historic data. Structural changes are most closely linked to the Commercial Revolution followed by the Agricultural Revolution and the Industrial Revolution, with changes linked to an underlying process of price stabilisation as measured by a decrease in the long-term level of volatility.historical economics; economic revolutions; structural breaks; price stabilisation

Risk management and the implementation of the Basel Accord in emerging countries: An application to Pakistan.

This paper addresses an important contemporary issue; namely the implementation of the Basel Accord worldwide. The Basel Accord provides a series of measures to improve the stability of the world’s financial system but its implementation poses a number of challenges for both developing and emerging economies. Pakistan faces a number of unique challenges in this regard due to its recent economic expansion and the fact that the rate at which the Basel Accord is being adopted lags behind that of other countries. This paper throws light on this and a number of related issues due to a combination of the novelty of the survey data from risk managers coupled with a rigorous statistical analysis. Results reflect that the Basel Accord is generally well regarded due to its underlying aims of improved capital standards and a scientific treatment of risk. However, operational risk emerges as a key barrier to implementation in Pakistan. A number of further obstacles are highlighted, which, do seem to have been addressed although only with a partial degree of success. Privately owned banks appear to be more technically competent and more favourably disposed towards implementation than publicly owned banks.Risk Management; Basel Accord; Banking; Financial Regulation; Emerging Markets

Feasibility of V/STOL concepts for short-haul transport aircraft

Feasibility of V/STOL concepts for short-haul transport aircraf

Radiation protection guidelines for space missions

NASA's current radiation protection guidelines date from 1970, when the career limit was set at 400 rem. Today, using the same approach, but with the current risk estimates, a considerably lower career limit would obtain. Also, there is considerably more information about the radiation environments to be experienced in different missions than previously. Since 1970 women have joined the ranks. For these and other reasons it was necessary to reexamine the radiation protection guidelines. This task was undertaken by the National Council on Radiation Protection and Measurements Scientific Committee 75 (NCRP SC 75). Below the magnetosphere the radiation environment varies with altitude and orbit inclination. In outer space missions galactic cosmic rays, with the small but important heavy ion component, determine the radiation environment. The new recommendations for career dose limits, based on lifetime excess risk of cancer mortality, take into account age at first exposure and sex. The career limits range from 100 rem (4.0Sv) for a 24 year old female to 400 rem for a 55 year old male compared to the previous single limit of 400 rem (4.0 Sv). The career limit for the lens of the eye was reduced from 600 to 400 rem (6.0 to 4.0 Sv.