Modelling transitions in childrens' development by starting with adults

We present a blocks task in which cognitive change is apparent, and propose that computational modelling can help in examining how cognitive change occurs. We initially examine the performance of adults on the task, and use the results of this experiment to build both an adult model and a simulation of the task. Comparisons of the model with the adult data reveal further completion work regarding the models qualitative behaviour. However, when finished, the model will be able to predict how behaviour changes when domain knowledge is removed, and will provide the basis for models of children’s behaviour on the task

Formation of InAs Self-Assembled Quantum Rings on InP

Shape transformations of partially capped self-assembled InAs quantum dots grown on InP are studied. Atomic force microscopy images show large anisotropic redistribution of the island material after coverage by a 1 nm thick InP layer. The anisotropic material redistribution occurs within a few minutes and leads to a change from lens-like to elongated ring-like islands. The shape transformation is not accompanied by dot material compositional change. The formation of InAs/InP quantum rings disagrees with a previous model of InAs/GaAs ring formation that assumes that the driving force for the dot to ring transformation is the difference in surface diffusion velocity of indium and gallium atoms.Comment: 13 pages, including 2 figures and 1 table. Submitted to Appl. Phys. Let

Commitment as investment under uncertainty

An explanation of how irreversible investment and the techniques associated with pricing real options can apply to a broad range of problems in finance, macroeconomics, and trade policy.Economic policy ; Macroeconomics

Dynamic commitment and imperfect policy rules

An examination of the dynamics of commitment, showing that because the decision regarding rules versus discretion occurs in real time, opting for discretion is often the better choice, since it leaves open the possibility of adopting rules later on.Monetary policy

Dynamic commitment and imperfect policy rules

Considering the dynamics of commitment highlights, some neglected features of time inconsistency problems. We modify the standard rules-versus-discretion question in three ways: (1) A government that does not commit today retains the option to do so tomorrow, (2) the government's commitment capability is restricted to a class of simple rules, and (3) the government's ability to make irrevocable commitments is restricted. Three results stand out. First, the option to wait makes the incumbent regime (rules or discretion) relatively more attractive. Second, the option to wait means that increased uncertainly makes the incumbent regime more attractive. Third, because the commitment decision takes place in 'real time,' policy choice displays hysteresis.Monetary policy

Quantum Channels and Representation Theory

In the study of d-dimensional quantum channels $(d \geq 2)$, an assumption which is not very restrictive, and which has a natural physical interpretation, is that the corresponding Kraus operators form a representation of a Lie algebra. Physically, this is a symmetry algebra for the interaction Hamiltonian. This paper begins a systematic study of channels defined by representations; the famous Werner-Holevo channel is one element of this infinite class. We show that the channel derived from the defining representation of SU(n) is a depolarizing channel for all $n$, but for most other representations this is not the case. Since the Bloch sphere is not appropriate here, we develop technology which is a generalization of Bloch's technique. Our method works by representing the density matrix as a polynomial in symmetrized products of Lie algebra generators, with coefficients that are symmetric tensors. Using these tensor methods we prove eleven theorems, derive many explicit formulas and show other interesting properties of quantum channels in various dimensions, with various Lie symmetry algebras. We also derive numerical estimates on the size of a generalized ``Bloch sphere'' for certain channels. There remain many open questions which are indicated at various points through the paper.Comment: 28 pages, 1 figur

Conservation Laws and the Multiplicity Evolution of Spectra at the Relativistic Heavy Ion Collider

Transverse momentum distributions in ultra-relativistic heavy ion collisions carry considerable information about the dynamics of the hot system produced. Direct comparison with the same spectra from $p+p$ collisions has proven invaluable to identify novel features associated with the larger system, in particular, the "jet quenching" at high momentum and apparently much stronger collective flow dominating the spectral shape at low momentum. We point out possible hazards of ignoring conservation laws in the comparison of high- and low-multiplicity final states. We argue that the effects of energy and momentum conservation actually dominate many of the observed systematics, and that $p+p$ collisions may be much more similar to heavy ion collisions than generally thought.Comment: 15 pages, 14 figures, submitted to PRC; Figures 2,4,5,6,12 updated, Tables 1 and 3 added, typo in Tab.V fixed, appendix B partially rephrased, minor typo in Eq.B1 fixed, minor wording; references adde