Thermal Transport in Chiral Conformal Theories and Hierarchical Quantum Hall States

Chiral conformal field theories are characterized by a ground-state current at finite temperature, that could be observed, e.g. in the edge excitations of the quantum Hall effect. We show that the corresponding thermal conductance is directly proportional to the gravitational anomaly of the conformal theory, upon extending the well-known relation between specific heat and conformal anomaly. The thermal current could signal the elusive neutral edge modes that are expected in the hierarchical Hall states. We then compute the thermal conductance for the Abelian multi-component theory and the W-infinity minimal model, two conformal theories that are good candidates for describing the hierarchical states. Their conductances agree to leading order but differ in the first, universal finite-size correction, that could be used as a selective experimental signature.Comment: Latex, 17 pages, 2 figure

Technology and skill requirements: implications for establishment wage structures

Wages ; Human capital ; Technology ; Income distribution ; Labor market ; Regression analysis

Multipole Expansion in the Quantum Hall Effect

The effective action for low-energy excitations of Laughlin's states is obtained by systematic expansion in inverse powers of the magnetic field. It is based on the W-infinity symmetry of quantum incompressible fluids and the associated higher-spin fields. Besides reproducing the Wen and Wen-Zee actions and the Hall viscosity, this approach further indicates that the low-energy excitations are extended objects with dipolar and multipolar moments.Comment: 29 pages, 5 figures; v2: comments and references adde

On the Trace Anomaly as a Measure of Degrees of Freedom

Recent conjectures of the c-theorem in four and higher dimensions have suggested that the coefficient of the Euler characteristic in the trace anomaly could measure the degrees of freedom in field theory and decrease along the renormalization-group flow. We compute this quantity for free massless scalar, fermion and antisymmetric tensor fields in any dimension, and analyse its dependence on spin and space-time dimension. In the limit of large number of dimensions, where the theories become semiclassical, we find that this quantity does not approach the classical number of field components, but is enhanced for spinful particles. This seemingly strange behaviour is found to be consistent with known renormalization-group patterns and a specific c-theorem conjecture.Comment: Latex, 14 pages, 2 table

A universal conformal field theory approach to the chiral persistent currents in the mesoscopic fractional quantum Hall states

We propose a general and compact scheme for the computation of the periods and amplitudes of the chiral persistent currents, magnetizations and magnetic susceptibilities in mesoscopic fractional quantum Hall disk samples threaded by Aharonov--Bohm magnetic field. This universal approach uses the effective conformal field theory for the edge states in the quantum Hall effect to derive explicit formulas for the corresponding partition functions in presence of flux. We point out the crucial role of a special invariance condition for the partition function, following from the Bloch-Byers-Yang theorem, which represents the Laughlin spectral flow. As an example we apply this procedure to the Z_k parafermion Hall states and show that they have universal non-Fermi liquid behavior without anomalous oscillations. For the analysis of the high-temperature asymptotics of the persistent currents in the parafermion states we derive the modular S-matrices constructed from the S matrices for the u(1) sector and that for the neutral parafermion sector which is realized as a diagonal affine coset.Comment: 45 pages, LaTeX2e, 4 EPS figures, 1 table, for related color figures see http://theo.inrne.bas.bg/~lgeorg/PF_k.htm

Investigation of work function and chemical composition of thin films of borides and nitrides

Thin films of various borides, nitrides, and barium fluorides were tentatively deposited by pulsed laser deposition and by magnetron sputtering in order to develop the components of thermionic-photovoltaic devices for the high-temperature thermal to electrical conversion by solid state. To improve the device performance, the materials characterized by a low work function were selected. In the present work, the chemical composition and work function of obtained films were investigated by X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy techniques. The values of work function were determined from the cut-off in the He I valence band spectra. Different films were compared and estimated on the basis of X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy results

Employee Screening: Theory and Evidence

Arguably the fundamental problem faced by employers is how to elicit effort from employees. Most models suggest that employers meet this challenge by monitoring employees carefully to prevent shirking. But there is another option that relies on heterogeneity across employees, and that is to screen job candidates to find workers with a stronger work ethic who require less monitoring. This should be especially useful in work systems where monitoring by supervisors is more difficult, such as teamwork systems. We analyze the relationship between screening and monitoring in the context of a principal-agent model and test the theoretical results using a national sample of U.S. establishments, which includes information on employee selection. We find that employers screen applicants more intensively for work ethic where they make greater use of systems such as teamwork where monitoring is more difficult. This screening is also associated with higher productivity and higher wages and benefits, as predicted by the theory: The synergies between reduced monitoring costs and high performance work systems enable the firm to pay higher wages to attract and retain such workers. Screening for other attributes, such as cognitive ability, does not produce these results.

2D Superconductivity: Classification of Universality Classes by Infinite Symmetry

I consider superconducting condensates which become incompressible in the infinite gap limit. Classical 2D incompressible fluids possess the dynamical symmetry of area-preserving diffeomorphisms. I show that the corresponding infinite dynamical symmetry of 2D superconducting fluids is the coset ${{W_{1+\infty} \otimes \bar W_{1+\infty}} \over U(1)_{\rm diagonal}}$, with $W_{1+\infty}$ the chiral algebra of quantum area-preserving diffeomorphisms and I derive its minimal models. These define a discrete set of 2D superconductivity universality classes which fall into two main categories: conventional superconductors with their vortex excitations and unconventional superconductors. These are characterized by a broken $U(1)_{\rm vector} \otimes U(1)_{\rm axial}$ symmetry and are labeled by an integer level $m$. They possess neutral spinon excitations of fractional spin and statistics $S = {\theta \over 2\pi} = {{m-1} \over 2m}$ which carry also an $SU(m)$ isospin quantum number; this hidden $SU(m)$ symmetry implies that these anyon excitations are non-Abelian. The simplest unconventional superconductor is realized for $m=2$: in this case the spinon excitations are semions (half-fermions). My results show that spin-charge separation in 2D superconductivity is a universal consequence of the infinite symmetry of the ground state. This infinite symmetry and its superselection rules realize a quantum protectorate in which the neutral spinons can survive even as soft modes on a rigid, spinless charge condensate.Comment: Revised version to appear in Nuclear Physics

The Path to the Top: Changes in the Attributes and Careers of Corporate Executives, 1980-2001

The analyses below compare the career histories and personal characteristics of the executives in the top ranks of the world's largest and most stable business operations, the Fortune 100, between 1980 and 2001. To our knowledge, there have been no prior studies of contemporary changes in the experience or attributes of executives beyond CEOs. In 2001, these executives were younger, more likely to be women, and less likely to have been Ivy League educated. Most important, they got to the executive suite about four years faster than in 1980 and did so by holding fewer jobs on the way to the top. (In particular, women in 2001 got to their executive jobs faster than their male counterparts --there were no women executives in the Fortune 100 in 1980). Executives in 2001 also spent about five years less in their current organization and were more likely to be hired from the outside than in 1980. Interestingly, the most stable firms the 26 that were in the Fortune 100 in both periods had just as much lifetime employment among executives in 2001 as in 1980, although changes in other aspects of careers were similar. Overall, the path to the executive suite and the attributes of the individuals who get there appear to have changed even in the largest and most stable business operations.