Task-set switching with natural scenes: Measuring the cost of deploying top-down attention

In many everyday situations, we bias our perception from the top down, based on a task or an agenda. Frequently, this entails shifting attention to a specific attribute of a particular object or scene. To explore the cost of shifting top-down attention to a different stimulus attribute, we adopt the task-set switching paradigm, in which switch trials are contrasted with repeat trials in mixed-task blocks and with single-task blocks. Using two tasks that relate to the content of a natural scene in a gray-level photograph and two tasks that relate to the color of the frame around the image, we were able to distinguish switch costs with and without shifts of attention. We found a significant cost in reaction time of 23–31 ms for switches that require shifting attention to other stimulus attributes, but no significant switch cost for switching the task set within an attribute. We conclude that deploying top-down attention to a different attribute incurs a significant cost in reaction time, but that biasing to a different feature value within the same stimulus attribute is effortless

US-Europe Differences in Technology-Driven Growth: Quantifying the Role of Education

European economic growth has been weak, compared to the US, since the 80s. In previous work (Krueger and Kumar, 2003), we argued that the European focus on specialized, vocational education might have been effective during the 60s and 70s, but resulted in a growth gap relative to the US during the subsequent information age, when new technologies emerged more rapidly. In this paper, we extend our framework to assess the quantitative importance of education policy, when compared to labor market rigidity and product market regulation, other policy differences more commonly suggested to be responsible for US-Europe differences. A assigns a major role to education policy in explaining US-Europe growth differences.

On the Physics of Size Selectivity

We demonstrate that two mechanisms used by biological ion channels to select particles by size are driven by entropy. With uncharged particles in an infinite cylinder, we show that a channel that attracts particles is small-particle selective and that a channel that repels water from the wall is large-particle selective. Comparing against extensive density-functional theory calculations of our model, we find that the main physics can be understood with surprisingly simple bulk models that neglect the confining geometry of the channel completely.Comment: 4 pages, 3 figures, Phys. Rev. Lett. (accepted

Transport properties of a multichannel Kondo dot in a magnetic field

We study the nonequilibrium transport through a multichannel Kondo quantum dot in the presence of a magnetic field. We use the exact solution of the two-loop renormalization group equation to derive analytical results for the g factor, the spin relaxation rates, the magnetization, and the differential conductance. We show that the finite magnetization leads to a coupling between the conduction channels which manifests itself in additional features in the differential conductance.Comment: 4 pages, 4 figure

Agricultural exit problems: Causes and consequences

"Contrary to conventional economic theories, the relationship between income growth and the share of the population within the rural or agricultural sector is extremely diverse, even among regions starting from similar levels of development, such as Asia and Africa. The pattern in developing Asia is characterized by fast growth and slow urbanization, primarily as the result of labor-intensive agricultural growth and strong farm–nonfarm linkages. But for all its success to date, Asia appears to be increasingly vulnerable to rising inequality and jobless growth patterns. Africa presents a divergent pattern of slow growth with rapid urbanization stemming from urban-biased policies, low rural population density, and high rates of population growth. But whereas Africa's path of urbanization without growth presents problems like unemployment, congestion, and food-price inflation, it may also provide new development possibilities through greater political empowerment, lower fertility rates, and agglomeration externalities. The paper concludes with a discussion of how development strategies can address these agricultural exit problems." from authors' abstracteconomic growth, structural change, Urbanization, agricultural exits, rural to urban migration, rural non-farm employment, Inequality, employment, agglomeration externalities,

Is there an attraction between spinons in the Haldane--Shastry model?

While the Bethe Ansatz solution of the Haldane--Shastry model appears to suggest that the spinons represent a free gas of half-fermions, Bernevig, Giuliano, and Laughlin (BGL) (cond-mat/0011069, cond-mat/0011270) have concluded recently that there is an attractive interaction between spinons. We argue that the dressed scattering matrix obtained with the asymptotic Bethe Ansatz is to be interpreted as the true and physical scattering matrix of the excitations, and hence, that the result by BGL is inconsistent with an earlier result by Essler (cond-mat/9406081). We critically re-examine the analysis of BGL, and conclude that there is no interaction between spinons or spinons and holons in the Haldane--Shastry model

Commercial Agriculture in the Western Cape: Macroeconomic Analysis with a Social Accounting Matrix

A social accounting matrix was developed for the Western Cape to meet growing needs for quantitative analysis of the agricultural sector. Twenty-five farm commodities and seven agribusinesses are explicitly included in the model. The coloured and black populations dominate provincial expenditure on fresh and processed farm commodities, suggesting that future demand growth depends on income increases among these household groups. In the aggregate, agriculture’s contributions to job creation, value added and government revenue significantly exceed those of the nonagricultural sectors; agribusiness exceeds other nonagricultural sectors because of their backward links to production agriculture. Within agriculture, horticulture and livestock subsectors make the most significant contributions to the macro economy. Similar patterns are found with respect to generating household incomes, and in the equality with which such incomes are distributed. Household economic behaviour is explicit. Spending by the poor is found to be more labour intensive than spending by the rich, and generates greater impacts on value added (GGP), gross operating surplus and the demand for most farm and non-farm commodities. A composite ranking of macroeconomic contributions to development is constructed. Nine horticultural enterprises and broilers comprise the ten top sectors.Farm Management,

Charge fluctuations in nonlinear heat transport

We show that charge fluctuation processes are crucial for the nonlinear heat conductance through an interacting nanostructure, even far from a resonance. We illustrate this for an Anderson quantum dot accounting for the first two leading orders of the tunneling in a master equation. The often made assumption that off-resonant transport proceeds entirely by virtual occupation of charge states, underlying exchange-scattering models, can fail dramatically for heat transport. The identified energy-transport resonances in the Coulomb blockade regime provide new qualitative information about relaxation processes, for instance by strong negative differential heat conductance relative to the heat current. These can go unnoticed in the charge current, making nonlinear heat-transport spectroscopy with energy-level control a promising experimental tool