SYNOPSIS: Because authoritative statements on corporate governance (e.g., the Sarbanes-Oxley Act of 2002) are silent about how frequently audit committees should meet, corporate audit committees have considerable discretion in scheduling meetings. Although prior research shows the frequency of audit committee meetings is an important indicator of the effectiveness of the audit committee, we know very little about the underlying determinants of meeting frequency. In this study, we examine the determinants of the frequency of audit committee meetings in a voluntary governance system, New Zealand. We find that multiple directorships, audit committee independence, and an independent chair of the audit committee are negatively associated with meeting frequency. Other variables negatively associated with meeting frequency include a Big 4 auditor, growth opportunities, and regulated industry. Audit committee meeting frequency is positively associated with the size of the audit committee and the level of institutional and managerial ownership. We also find that financial expertise and board independence are positively associated with meeting frequency when the risk of financial misreporting is higher.

In non-mammalian vertebrates, retinal bipolar cells show center-surround receptive field organization. In mammals, recordings from bipolar cells are rare and have not revealed a clear surround. Here we report center-surround receptive fields of identified cone bipolar cells in the macaque monkey retina. In the peripheral retina, cone bipolar cell nuclei were labeled in vitro with diamidino-phenylindole (DAPI), targeted for recording under microscopic control, and anatomically identified by intracellular staining. Identified cells included 'diffuse' bipolar cells, which contact multiple cones, and 'midget' bipolar cells, which contact a single cone. Responses to flickering spots and annuli revealed a clear surround: both hyperpolarizing (OFF) and depolarizing (ON) cells responded with reversed polarity to annular stimuli. Center and surround dimensions were calculated for 12 bipolar cells from the spatial frequency response to drifting, sinusoidal luminance modulated gratings. The frequency response was bandpass and well fit by a difference of Gaussians receptive field model. Center diameters were all two to three times larger than known dendritic tree diameters for both diffuse and midget bipolar cells in the retinal periphery. In one instance intracellular staining revealed tracer spread between a recorded cell and its nearest neighbors, suggesting that homotypic electrical coupling may contribute to receptive field center size. Surrounds were around ten times larger in diameter than centers and in most cases the ratio of center to surround strength was approximately 1. We suggest that the center-surround receptive fields of the major primate ganglion cell types are established at the bipolar cell, probably by the circuitry of the outer retina.

Summary After fixating on a colored pattern, observers see a similar pattern in complementary colors when the stimulus is removed. Afterimages were important in disproving the theory that visual rays emanate from the eye[1], in demonstrating inter-ocular interactions[2], and in revealing the independence of binocular-vision from eye-movements[3]. Afterimages also prove invaluable in exploring selective attention[4], filling-in[5], and consciousness[6]. Proposed physiological mechanisms for color afterimages range from bleaching of cone photo-pigments[7] to cortical adaptation[4–6, 8, 9], but direct neural measurements have not been reported. We introduce a time-varying method for evoking after-images, which provides precise measurements of adaptation and a direct link between visual percepts and neural responses[10]. We then use in vivo electrophysiological recordings to show that all three classes of primate retinal ganglion cells exhibit subtractive adaptation to prolonged stimuli, with much slower time-constants than those expected of photoreceptors. At the cessation of the stimulus, ganglion cells generate rebound responses that can provide afterimage signals for later neurons. Our results indicate that afterimage signals are generated in the retina, but may be modified like other retinal signals by cortical processes[4–6], so that evidence presented for cortical generation of color afterimages[8, 9] is explainable by spatio-temporal factors that apply to all signals.

This paper develops and analyzes two least-squares methods for the numerical solution of linear, stationary incompressible Newtonian fluid flow in two and three dimensions. Both approaches use the L 2 norm to define least-squares functionals. One is based on the stress-velocity formulation (see section 3.2), and it applies to general boundary conditions. The other is based on an equivalent formulation for the pseudostress and velocity (see section 4.2), and it applies to pure velocity Dirichlet boundary conditions. The velocity gradient and vorticity can be obtained algebraically from this new tensor variable. It is shown that the homogeneous least-squares functionals are elliptic and continuous in the H(div; Ω) d × H 1 (Ω) d norm. This immediately implies optimal error estimates for conforming finite element approximations. As well, it admits optimal multigrid solution methods if Raviart-Thomas finite element spaces are used to approximate the stress or the pseudostress tensor. Introduction.For incompressible Newtonian fluid flow with homogeneous density, the primitive physical equations are the conservation of momentum and the constitutive law. The constitutive law relates the stress tensor to the deformation rate tensor and pressure, and it states the incompressibility condition. It is a first-order partial differential system for the physical variables stress, velocity, and pressure. By differentiating and eliminating the stress, one obtains the well-known secondorder incompressible Navier-Stokes equations in the velocity-pressure formulation. A tremendous amount of computational research has been done on this second-order partial differential system (see, e.g, mathematical books [17,18]), but these equations may still be one of the most challenging problems in computational fluid mechanics and computational mathematics.In recent years there has been substantial interest in the use of least-squares principles for the numerical approximation of Newtonian fluid flow problems (see, e.g., the survey paper [5], the monograph [21], and references therein). In particular, there are many research articles in both the mathematics and engineering communities on least-squares methods for the stationary Stokes equations (see [5]). Specifically, least-squares methods based on five first-order partial differential systems have been proposed, analyzed, implemented, and tested. These five first-order systems are formulations for variables (i) velocity, vorticity, and pressure [5,21], (ii) velocity, pres-