Secondary generalisation in categorisation: an exemplar-based account

The parallel rule activation and rule synthesis (PRAS) model is a computational model for generalisation in category learning, proposed by Vandierendonck (1995). An important concept underlying the PRAS model is the distinction between primary and secondary generalisation. In Vandierendonck (1995), an empirical study is reported that provides support for the concept of secondary generalisation. In this paper, we re-analyse the data reported by Vandierendonck (1995) by fitting three different variants of the Generalised Context Model (GCM) which do not rely on secondary generalisation. Although some of the GCM variants outperformed the PRAS model in terms of global fit, they all have difficulty in providing a qualitatively good fit of a specific critical pattern

A NOTE ON HIGH DISCOUNT RATES AND DEPLETION OF PRIMARY FORESTS

Conventional wisdom implies that high discount rates accelerate depletion of tropical forests. As shown in this article, this result does not necessarily hold in a two-state variable model that distinguishes between primary and secondary forest stocks. In the context of a fixed concession period and imperfect government control, logging of primary forests may be both accelerated and depressed as discount rates increase.Resource /Energy Economics and Policy,

The Optimal Income Taxation of Couples

This paper analyzes the optimal income tax treatment of couples. Each couple is modelled as a single rational economic agent supplying labor along two dimensions: primary and secondary earnings. We consider fully general joint income tax systems. Separate taxation is never optimal if social welfare depends on total couple incomes. In a model where secondary earners make only a binary work decision (work or not work), we demonstrate that the marginal tax rate of the primary earner is lower when the spouse works. As a result, the tax distortion on the secondary earner decreases with the earnings of the primary earner and actually vanishes to zero asymptotically. Such negative jointness is optimal because redistribution from two-earner toward one-earner couples is more valuable when primary earner income is lower. We also consider a model where both spouses display intensive labor supply responses. In that context, we show that, starting from the optimal separable tax schedules, introducing some negative jointness is always desirable. Numerical simulations suggest that, in that model, it is also optimal for the marginal tax rate on one earner to decrease with the earnings of his/her spouse. We argue that many actual redistribution systems, featuring family-based transfers combined with individually-based taxes, generate schedules with negative jointness.

HMM with auxiliary memory: a new tool for modeling RNA structures

For a long time, proteins have been believed to perform most of the important functions in all cells. However, recent results in genomics have revealed that many RNAs that do not encode proteins play crucial roles in the cell machinery. The so-called ncRNA genes that are transcribed into RNAs but not translated into proteins, frequently conserve their secondary structures more than they conserve their primary sequences. Therefore, in order to identify ncRNA genes, we have to take the secondary structure of RNAs into consideration. Traditional approaches that are mainly based on base-composition statistics cannot be used for modeling and identifying such structures and models with more descriptive power are required. In this paper, we introduce the concept of context-sensitive HMMs, which is capable of describing pairwise interactions between distant symbols. It is demonstrated that the proposed model can efficiently model various RNA secondary structures that are frequently observed

Capitalising the Value of Free Schools: The Impact of Supply Constraints and Uncertainty

There has been a growing literature in both the US (for example Haurin and Brasington 1996, and Black 1999) and the UK (for example Gibbons & Machin, 2001) that estimates the way in which school quality is capitalised into house prices. Cheshire and Sheppard 1995 and 1999 have estimated hedonic models in which the quality of the secondary school to which a household was assigned was a significant variable. This provided evidence that the value of secondary school quality was being capitalised into the price of houses. In contrast Gibbons and Machin concluded that primary schools had an identifiable and significant price associated with their quality but that secondary schools did not. Their study did not have data for individual houses but used post-code sector data and then various techniques to standardised for all but one variable: either the notional primary school catchment area or the notional secondary school catchment area. Each of these analyses is predicated on the assumption that the value of local schools should be reflected in the value of houses. We expect variation in the capitalised price of a given school quality at either primary or secondary level according to the elasticity of supply of ‘school quality’ in the local market. This will vary systematically between and perhaps within cities and this paper explores the sources and the impact of such variations as well as the impact of model specification. Using an hedonic model and data from 1999-2000, we estimate values attached to both secondary school and primary school quality. The results support the conclusion that both secondary and primary school quality is capitalised into the market price of houses and that the capitalisation of school quality is discounted within the context of an urban area that is tightly constrained by land use planning in areas where new construction is concentrated. We also find evidence that appropriate model specification is imperative since bias is evident both when key neighbourhood characteristics are omitted and if the actual allocation of addresses to schools is not included. JEL: D12; H4; I2; R5

A solvable model of the genesis of amino-acid sequences via coupled dynamics of folding and slow genetic variation

We study the coupled dynamics of primary and secondary structure formation (i.e. slow genetic sequence selection and fast folding) in the context of a solvable microscopic model that includes both short-range steric forces and and long-range polarity-driven forces. Our solution is based on the diagonalization of replicated transfer matrices, and leads in the thermodynamic limit to explicit predictions regarding phase transitions and phase diagrams at genetic equilibrium. The predicted phenomenology allows for natural physical interpretations, and finds satisfactory support in numerical simulations.Comment: 51 pages, 13 figures, submitted to J. Phys.

Electromagnetic cascade masquerade: a way to mimic γ\gamma--axion-like particle mixing effects in blazar spectra

Context. Most of the studies on extragalactic {\gamma}-ray propagation performed up to now only accounted for primary gamma-ray absorption and adiabatic losses ("absorption-only model"). However, there is growing evidence that this model is oversimplified and must be modified in some way. In particular, it was found that the intensity extrapolated from the optically-thin energy range of some blazar spectra is insufficient to explain the optically-thick part of these spectra. This effect was interpreted as an indication for {\gamma}-axion-like particle (ALP) oscillation. On the other hand, there are many hints that a secondary component from electromagnetic cascades initiated by primary {\gamma}-rays or nuclei may be observed in the spectra of some blazars. Aims. We study the impact of electromagnetic cascades from primary {\gamma}-rays or protons on the physical interpretation of blazar spectra obtained with imaging Cherenkov telescopes. Methods. We use the publicly-available code ELMAG to compute observable spectra of electromagnetic cascades from primary {\gamma}-rays. For the case of primary proton, we develop a simple, fast and reasonably accurate hybrid method to calculate the observable spectrum. We perform the fitting of the observed spectral energy distributions (SEDs) with various physical models: the absorption-only model, the "electromagnetic cascade model" (for the case of primary {\gamma}-rays), and several versions of the hadronic cascade model (for the case of primary proton). We distinguish the following species of hadronic cascade models: 1) "basic hadronic model", where it is assumed that the proton beam travels undisturbed by extragalactic magnetic field and that all observable {\gamma}-rays are produced by primary protons through photohadronic processes with subsequent development of electromagnetic cascades /abridgedComment: Accepted by A&A. 25 pages, 31 figures. Corrected fig. 5, fig. 7; new explanations for fig. 6--7; several typos fixed wrt v.