COMPARISION OF HIGH ACHIEVERS WITH LOW ACHIEVERS: Discussion of Juter’s (2007) article

The use of questionnaires and interviews to compare the responses to a mathematical task of high achievers with low achievers has limitations. The partial information that they have provides a way of comparing high and low achievers. Some references are given here to relevant task formats and theories. An example is given of how examinees’ performance with unusual task formats (specifically, answer-until-correct) may be analysed to throw light on the mathematical description of partial information

Can we improve the identification of cold homes for targeted home energy-efficiency improvements?

Objective: To investigate the extent to which homes with low indoor-temperatures can be identified from dwelling and household characteristics.Design: Analysis of data from a national survey of dwellings, occupied by low-income households, scheduled for home energy-efficiency improvements. Setting: Five urban areas of England: Birmingham, Liverpool, Manchester, Newcastle and Southampton.Methods: Half-hourly living-room temperatures were recorded for two to four weeks in dwellings over the winter periods November to April 2001-2002 and 2002-2003. Regression of indoor on outdoor temperatures was used to identify cold-homes in which standardized daytime living-room and/ or nighttime bedroom-temperatures were < 16 degrees C (when the outdoor temperature was 5 degrees C). Tabulation and logistic regression were used to examine the extent to which these cold-homes can be identified from dwelling and household characteristics.Results: Overall, 21.0% of dwellings had standardized daytime living-room temperatures < 16 degrees C and 46.4% had standardized nighttime bedroom-temperatures below the same temperature. Standardized indoor-temperatures were influenced by a wide range of household and dwelling characteristics, but most strongly by the energy efficiency (SAP) rating and by standardized heating costs. However, even using these variables, along with other dwelling and household characteristics in a multi-variable prediction model, it would be necessary to target more than half of all dwellings in our sample to ensure at least 80% sensitivity for identifying dwellings with cold living-room temperatures. An even higher proportion would have to be targeted to ensure 80% sensitivity for identifying dwellings with cold-bedroom temperatures.Conclusion: Property and household characteristics provide only limited potential for identifying dwellings where winter indoor temperatures are likely to be low, presumably because of the multiple influences on home heating, including personal choice and behaviour. This suggests that the highly selective targeting of energy-efficiency programmes is difficult to achieve if the primary aim is to identify dwellings with cold-indoor-temperatures. (c) 2006 Published by Elsevier Ltd

Comment on "Trivariate statistical analysis of extreme rainfall events via the Plackett family of copulas" by Shih-Chieh Kao and Rao S. Govindaraju: How are trivariate copulas put to use?

T. P. Hutchinso

Summary of the Workshop on Ecological Effects of Hydrocarbon Spills in Alaska

In any study of the effects of the introduction of an organic compound, such as oil, into a particular environment, such as the Arctic we should, at the outset separate two basic responses: the responses of those organisms (largely bacteria and fungi) to whom the oil is a nutrient to be attacked and eventually decomposed, from the responses of those organisms (largely plants and animals) to whom the oil is a physical and chemical agent of potential toxicity to be tolerated with varying degrees of success. ... both groups really function as mixed populations that exhibit dynamic responses to environmental changes, such as oil spills, but our perception of the effects of these changes is largely population-oriented in the decomposers and species-oriented among higher organisms. ... The actual removal of oil from the Arctic environment depends on a combination of physical weathering and microbial decomposition .... Thus a general principle of microbial ecology is sustained here in that the addition of an organic material to a system stimulates the development of a specific microbial population capable of using that material as a nutrient. The rate of this decomposition process is of maximum importance and it obviously depends on the robustness of the initial microbial population and on nutrient limitation. ... One of the special problems of the Arctic is the very slow rate at which these decomposer populations develop significant activities ... and accessory nutrient supplementations may be required to achieve acceptable rates of hydrocarbon decomposition. A very important facet of oil degradation is the relative rates at which the different components of oil are broken down by bacteria and fungi. ... There are many reasons why oil may be toxic to animals .... Oil appears to constitute a fairly general "contact herbicide" whose direct application is most often toxic to plants. ... plants vary in their sensitivity to this "contact herbicide" and sensitivity mapping ... and bioassays of the sensitivity of specific plants under field conditions are very valuable. ... oil exerts direct and immediate toxic effects on certain plants and animals, in both aquatic and terrestrial systems, and ... more subtle toxic effects are often detected only with the passage of time. Whole populations react in the expected manner in that oil-resistant forms proliferate and then lead the recolonization of the system as the toxic hydrocarbons are removed by weathering or by microbial decomposition. The extent of severe ecological damage from oil spills is, therefore, a function both of the oil-sensitivity of the plant and animal populations and of the rates at which oil is removed by human intervention, weathering or microbial decomposition. ... In the decomposition studies perhaps the most promising development is the advent of rate studies which should be extended to cover the major classes of oil constituents and a very wide variety of ecological systems. ... In many cases it is clear that microbial decomposition, aided by fertilizer application ... will reduce the level of hydrocarbons below the toxic level for the indigenous plants and animals at a satisfactory rate. ... This entire program, with its emphasis on rates of microbial decomposition and on differential sensitivity of both species and populations of higher organisms, is basically well designed and offers a scientific basis for the development ... [of] rational oil spill clean-up policies in the sensitive Alaskan ecosystem

Dependence of the Head Injury Criterion and Maximum Acceleration on Headform Mass and Initial Velocity in Tests Simulating Pedestrian Impacts With Vehicles

Impact testing of pedestrian headforms is usually conducted at one velocity and with one mass of headform, but real impacts occur at a range of velocities and masses. A method is proposed to predict the Head Injury Criterion (HIC) and similar quantities at other velocities from their values observed under test conditions. A specific assumption is made about acceleration during the impact as related to displacement, its differential (instantaneous velocity), mass of headform, and initial velocity: namely, that it is the product of a power function of displacement (representing a possibly nonlinear spring) and a term that includes a type of damping. This equation is not solved, but some properties of the solution are obtained: HIC, maximum acceleration, and maximum displacement are found to be power functions of mass of headform and initial velocity. Expressions for the exponents are obtained in terms of the nonlinearity parameter of the spring. Simple formulae are obtained for the dependence of HIC, maximum acceleration, and maximum displacement on velocity and mass. These are relevant to many types of impact

Bivariate tt-distribution for transition matrix elements in Breit-Wigner to Gaussian domains of interacting particle systems

Interacting many-particle systems with a mean-field one body part plus a chaos generating random two-body interaction having strength $\lambda$, exhibit Poisson to GOE and Breit-Wigner (BW) to Gaussian transitions in level fluctuations and strength functions with transition points marked by $\lambda=\lambda_c$ and $\lambda=\lambda_F$, respectively; $\lambda_F >> \lambda_c$. For these systems theory for matrix elements of one-body transition operators is available, as valid in the Gaussian domain, with $\lambda > \lambda_F$, in terms of orbitals occupation numbers, level densities and an integral involving a bivariate Gaussian in the initial and final energies. Here we show that, using bivariate $t$-distribution, the theory extends below from the Gaussian regime to the BW regime up to $\lambda=\lambda_c$. This is well tested in numerical calculations for six spinless fermions in twelve single particle states.Comment: 7 pages, 2 figure

Gapless finite-TT theory of collective modes of a trapped gas

We present predictions for the frequencies of collective modes of trapped Bose-condensed $^{87}$Rb atoms at finite temperature. Our treatment includes a self-consistent treatment of the mean-field from finite-$T$ excitations and the anomolous average. This is the first gapless calculation of this type for a trapped Bose-Einstein condensed gas. The corrections quantitatively account for the downward shift in the $m=2$ excitation frequencies observed in recent experiments as the critical temperature is approached.Comment: 4 pages Latex and 2 postscript figure

Verifying raytracing/Fokker-Planck lower-hybrid current drive predictions with self-consistent full-wave/Fokker-Planck simulations

Raytracing/Fokker-Planck (FP) simulations used to model lower-hybrid current drive (LHCD) often fail to reproduce experimental results, particularly when LHCD is weakly damped. A proposed reason for this discrepancy is the lack of "full-wave" effects, such as diffraction and interference, in raytracing simulations and the breakdown of raytracing approximation. Previous studies of LHCD using non-Maxwellian full-wave/FP simulations have been performed, but these simulations were not self-consistent and enforced power conservation between the FP and full-wave code using a numerical rescaling factor. Here we have created a fully-self consistent full-wave/FP model for LHCD that is automatically power conserving. This was accomplished by coupling an overhauled version of the non-Maxwellian TORLH full-wave solver and the CQL3D FP code using the Integrated Plasma Simulator. We performed converged full-wave/FP simulations of Alcator C-Mod discharges and compared them to raytracing. We found that excellent agreement in the power deposition profiles from raytracing and TORLH could be obtained, however, TORLH had somewhat lower current drive efficiency and broader power deposition profiles in some cases. This discrepancy appears to be a result of numerical limitations present in the TORLH model and a small amount of diffractional broadening of the TORLH wave spectrum. Our results suggest full-wave simulation of LHCD is likely not necessary as diffraction and interference represented only a small correction that could not account for the differences between simulations and experiment