Displacement, asymmetric information and heterogeneous human capital

In a seminal paper Gibbons and Katz (1991; GK) develop and empirically test an asymmetric information model of the labor market. The model predicts that wage losses following displacement should be larger for layoffs than for plant closings, which was borne out by data from the Displaced Workers Survey (DWS). In this paper, we take advantage of many more years of DWS data to examine how the difference in wage losses across plant closing and layoff varies with race and gender. We find that the differences between white males and the other groups are striking and complex. The "lemons" effect of layoff holds for white males as in the GK model, but not for the other three demographic groups (white females, black females, and black males). These three all experience a greater decline in earnings at plant closings than at layoffs. This results from two reinforcing effects. First, plant closings have substantially more negative effects on minorities than on whites. Second, layoffs seem to have more negative consequences for white men than the other groups. These findings suggest that the GK asymmetric information model is not sufficient to explain all of the data. We augment the model with heterogeneous human capital and show that this model can explain the findings. We also provide some additional evidence suggestive that both asymmetric information and heterogeneous human capital are important. In support of both explanations, we demonstrate that the racial and gender effects are surprisingly robust to region, industry and occupation controls. To look at the asymmetric information, we make use of the Civil Rights Act of 1991 which induced employers to lay off "protected" workers in mass layoffs rather than fire them for cause. As a result, relative to whites, a layoff would be a more negative signal for blacks after 1991 than before. If information is important, this would in turn imply that blacks experience a relatively larger loss in earnings at layoffs after 1991 than prior; and that's what we find in the data. In addition, as further evidence for heterogeneous human capital, we document for the first time in the literature that the two types of layoffs reported in the DWS data, namely layoffs due to "slack work" and "position abolished" have very different features when compared to plant closings. Finally, we simulate our model and show that it can match the data.Displaced workers ; Discrimination in employment

Layoffs, Lemons, Race, and Gender

This paper expands on Gibbons and Katz (1991) by looking at how the difference in wage losses across plant closing and layoff varies with race and gender. We find that the differences between white males and the other groups are striking and complex. The lemons effect of layoff holds for white males as in Gibbons and Katz model, but not for the other three demographic groups (white females, black females, and black males). These three all experience a greater decline in earnings at plant closings than at layoffs. This results from two reinforcing effects. First, plant closings have substantially more negative effects on minorities than on whites. Second, layoffs seem to have more negative consequences for white men than the other groups. We also find that the relative wage losses of blacks following layoffs increased after the Civil Rights Act of 1991 which we take as suggestive of an informational effect of layoff as in Gibbons and Katz. The results are suggestive that the large losses that African Americans experience at plant closing could result from heterogeneity in taste discrimination across firms.

Displacement, Asymmetric Information, and Heterogeneous Human Capital

In a seminal paper, Gibbons and Katz (1991) develop and empirically test an asymmetric information model of the labor market. The model predicts that wage losses following displacement should be larger for layoffs than for plant closings, which was borne out by data from the Displaced Workers Survey (DWS). In this paper, we take advantage of many more years of DWS data to examine how the difference in wage losses across plant closings and layoffs varies with race and gender. We find that the differences between white males and the other groups are striking and complex. The “lemons effect” of layoffs holds for white males, as in the Gibbons-Katz model, but not for the other three demographic groups (white females, black females, and black males). These three all experience a greater decline in earnings at plant closings than at layoffs. This results from two reinforcing effects. First, plant closings have substantially more negative effects on minorities than on whites. Second, layoffs seem to have more negative consequences for white men than the other groups. These findings suggest that the Gibbons-Katz asymmetric information model is not sufficient to explain all of the data. We augment the model with heterogeneous human capital and show that this model can explain the findings. We also provide some additional evidence suggestive that both asymmetric information and heterogeneous human capital are important. In support of both explanations, we demonstrate that the racial and gender effects are surprisingly robust to region, industry, and occupation controls. To look at the asymmetric information, we make use of the Civil Rights Act of 1991, which induced employers to lay off “protected” workers in mass layoffs rather than fire them for cause. As a result, relative to whites, a layoff would be a more negative signal for blacks after 1991 than before. If information is important, this would in turn imply that blacks experience a relatively larger loss in earnings at layoffs after 1991 than prior; and that’s what we find in the data. In addition, as further evidence for heterogeneous human capital, we document for the first time in the literature that the two types of layoffs reported in the DWS data, namely layoffs due to “slack work” and “position abolished,” have very different features when compared to plant closings. Finally, we simulate our model and show that it can match the data.human capital, plant closings, layoffs, sex, gender, race

Sound radiation in turbulent channel flows

Lighthill’s acoustic analogy is formulated for turbulent channel flow with pressure as the acoustic variable, and integrated over the channel width to produce a two-dimensional inhomogeneous wave equation. The equivalent sources consist of a dipole distribution related to the sum of the viscous shear stresses on the two walls, together with monopole and quadrupole distributions related to the unsteady turbulent dissipation and Reynolds stresses respectively. Using a rigid-boundary Green function, an expression is found for the power spectrum of the far-field pressure radiated per unit channel area. Direct numerical simulations (DNS) of turbulent plane Poiseuille and Couette flow have been performed in large computational domains in order to obtain good resolution of the low-wavenumber source behaviour. Analysis of the DNS databases for all sound radiation sources shows that their wavenumber–frequency spectra have non-zero limits at low wavenumber. The sound power per unit channel area radiated by the dipole distribution is proportional to Mach number squared, while the monopole and quadrupole contributions are proportional to the fourth power of Mach number. Below a particular Mach number determined by the frequency and radiation direction, the dipole radiation due to the wall shear stress dominates the far field. The quadrupole takes over at Mach numbers above about 0.1, while the monopole is always the smallest term. The resultant acoustic field at any point in the channel consists of a statistically diffuse assembly of plane waves, with spectrum limited by damping to a value that is independent of Mach number in the low-M limit

A study of the security implications involved with the use of executable World Wide Web content

Malicious executable code is nothing new. While many consider that the concept of malicious code began in the 1980s when the first PC viruses began to emerge, the concept does in fact date back even earlier. Throughout the history of malicious code, methods of hostile code delivery have mirrored prevailing patterns of code distribution. In the 1980s, file infecting and boot sector viruses were common, mirroring the fact that during this time, executable code was commonly transferred via floppy disks. Since the 1990s email has been a major vector for malicious code attacks. Again, this mirrors the fact that during this period of time email has been a common means of sharing code and documents. This thesis examines another model of executable code distribution. It considers the security risks involved with the use of executable code embedded or attached to World Wide Web pages. In particular, two technologies are examined. Sun Microsystems\u27 Java Programming Language and Microsoft\u27s ActiveX Control Architecture are both technologies that can be used to connect executable program code to World Wide Web pages. This thesis examines the architectures on which these technologies are based, as well as the security and trust models that they implement. In doing so, this thesis aims to assess the level of risk posed by such technologies and to highlight similar risks that might occur with similar future technologies. ()

Quasi-Exact Helical Cone Beam Reconstruction for Micro CT

A cone beam micro-CT system is set up to collect truncated helical cone beam data. This system includes a micro-focal X-ray source, a precision computer-controlled X-Y-Z-theta stage, and an image-intensifier coupled to a large format CCD detector. The helical scanning mode is implemented by rotating and translating the stage while keeping X-ray source and detector stationary. A chunk of bone and a mouse leg are scanned and quasi-exact reconstruction is performed using the approach proposed in J. Hu et al. (2001). This approach introduced the original idea of accessory paths with upper and lower virtual detectors having infinite axial extent. It has a filtered backprojection structure which is desirable in practice and possesses the advantages of being simple to implement and computationally efficient compared to other quasi-exact helical cone beam algorithms for the long object problem

Post-Acquisition Small-Animal Respiratory Gated Imaging Using Micro Cone-Beam CT

On many occasions, it is desirable to image lungs in vivo to perform a pulmonary physiology study. Since the lungs are moving, gating with respect to the ventilatory phase has to be performed in order to minimize motion artifacts. Gating can be done in real time, similar to cardiac imaging in clinical applications, however, there are technical problems that have lead us to investigate different approaches. The problems include breath-to-breath inconsistencies in tidal volume, which makes the precise detection of ventilatory phase difficult, and the relatively high ventilation rates seen in small animals (rats and mice have ventilation rates in the range of a hundred cycles per minute), which challenges the capture rate of many imaging systems (this is particularly true of our system which utilizes cone-beam geometry and a 2 dimensional detector). Instead of pre-capture ventilation gating we implemented a method of post-acquisition gating. We acquire a sequence of projections images at 30 frames per second for each of 360 viewing angles. During each capture sequence the rat undergoes multiple ventilation cycles. Using the sequence of projection images, an automated region of interest algorithm, based on integrated grayscale intensity, tracts the ventilatory phase of the lungs. In the processing of an image sequence, multiple projection images are identified at a particular phase and averaged to improve the signal-to-ratio. The resulting averaged projection images are input to a Feldkamp cone-beam algorithm reconstruction algorithm in order to obtain isotropic image volumes. Minimal motion artifact data sets improve qualitative and quantitative analysis techniques useful in physiologic studies of pulmonary structure and function