31 research outputs found
Do Directors Have a Use-By Date? Examining the Impact of Board Tenure on Firm Performance
Corporate boards serve the dual important functions of monitoring and advising management. We examine whether corporate boards consisting of longer-serving independent directors are better able to fulfill these functions due to firm-specific knowledge accumulation, or whether director performance suffers due to declining effectiveness in monitoring managers and/or overall staleness of board capital (board value to shareholders). Using a broad sample of up to 3,800 firms over a 20-year period, our evidence suggests that board tenure is positively related to forward-looking measures of market value and stock returns, with the relationship reversing after about nine years on average. The detrimental effect of longer average board tenure on market value (after an initial period of positive effects) is stronger for high growth firms, which is consistent with the deterioration of the board membersâ ability to perform their advisory function
Unstable decay and state selection II
The decay of unstable states when several metastable states are available for
occupation is investigated using path-integral techniques. Specifically, a
method is described which allows the probabilities with which the metastable
states are occupied to be calculated by finding optimal paths, and fluctuations
about them, in the weak noise limit. The method is illustrated on a system
described by two coupled Langevin equations, which are found in the study of
instabilities in fluid dynamics and superconductivity. The problem involves a
subtle interplay between non-linearities and noise, and a naive approximation
scheme which does not take this into account is shown to be unsatisfactory. The
use of optimal paths is briefly reviewed and then applied to finding the
conditional probability of ending up in one of the metastable states, having
begun in the unstable state. There are several aspects of the calculation which
distinguish it from most others involving optimal paths: (i) the paths do not
begin and end on an attractor, and moreover, the final point is to a large
extent arbitrary, (ii) the interplay between the fluctuations and the leading
order contribution are at the heart of the method, and (iii) the final result
involves quantities which are not exponentially small in the noise strength.
This final result, which gives the probability of a particular state being
selected in terms of the parameters of the dynamics, is remarkably simple and
agrees well with the results of numerical simulations. The method should be
applicable to similar problems in a number of other areas such as state
selection in lasers, activationless chemical reactions and population dynamics
in fluctuating environments.Comment: 28 pages, 6 figures. Accepted for publication in Phys. Rev.
Instabilities and resistance fluctuations in thin accelerated superconducting rings
The non-equilibrium properties of a driven quasi-one dimensional
superconducting ring subjected to a constant electromotive force ({\it emf}) is
studied. The {\it emf} accelerates the superconducting electrons until the
critical current is reached and a dissipative phase slip occurs that lowers the
current. The phase slip phenomena is examined as a function of the strength of
the {\it emf}, thermal noise, and normal state resistivity. Numerical and
analytic methods are used to make detailed predictions for the magnitude of
phase slips and subsequent dissipation.Comment: Some movies are available here at http://www.lce.hut.fi/~karttune/S
Dynamic transitions between metastable states in a superconducting ring
Applying the time-dependent Ginzburg-Landau equations, transitions between
metastable states of a superconducting ring are investigated in the presence of
an external magnetic field. It is shown that if the ring exhibits several
metastable states at a particular magnetic field, the transition from one
metastable state to another one is governed by both the relaxation time of the
absolute value of the order parameter tau_{|psi|} and the relaxation time of
the phase of the order parameter tau_{phi}. We found that the larger the ratio
tau_{|psi|}tau_{phi} the closer the final state will be to the absolute minimum
of the free energy, i.e. the thermodynamic equilibrium. The transition to the
final state occurs through a subsequent set of single phase slips at a
particular point along the ring.Comment: 7 pages, 6 figures, Revtex 4.0 styl
Functional determinants for general Sturm-Liouville problems
Simple and analytically tractable expressions for functional determinants are
known to exist for many cases of interest. We extend the range of situations
for which these hold to cover systems of self-adjoint operators of the
Sturm-Liouville type with arbitrary linear boundary conditions. The results
hold whether or not the operators have negative eigenvalues. The physically
important case of functional determinants of operators with a zero mode, but
where that mode has been extracted, is studied in detail for the same range of
situations as when no zero mode exists. The method of proof uses the properties
of generalised zeta-functions. The general form of the final results are the
same for the entire range of problems considered.Comment: 28 pages, LaTe
Functional determinants by contour integration methods
We present a simple and accessible method which uses contour integration
methods to derive formulae for functional determinants. To make the
presentation as clear as possible, the general idea is first illustrated on the
simplest case: a second order differential operator with Dirichlet boundary
conditions. The method is applicable to more general situations, and we discuss
the way in which the formalism has to be developed to cover these cases. In
particular, we also show that simple and elegant formulae exist for the
physically important case of determinants where zero modes exist, but have been
excluded.Comment: 29 page
Multiply-connected Bose-Einstein condensed alkali gases: Current-carrying states and their decay
The ability to support metastable current-carrying states in
multiply-connected settings is one of the prime signatures of superfluidity.
Such states are investigated theoretically for the case of trapped Bose
condensed alkali gases, particularly with regard to the rate at which they
decay via thermal fluctuations. The lifetimes of metastable currents can be
either longer or shorter than experimental time-scales. A scheme for the
experimental detection of metastable states is sketched.Comment: 4 pages, including 1 figure (REVTEX
Flux transitions in a superconducting ring
We perform a numeric study of the flux transitions in a superconducting ring
at fixed temperature, while the applied field is swept at an ideally slow rate.
The current around the ring and its free energy are evaluated. We partially
explain some of the known experimental features, and predict a considerably
large new feature: in the vicinity of a critical field, giant jumps are
expected