Young Workers, Old Workers, and Convergence

The human capital of young and old workers are imperfect substitutes both in production and in on-the-job training. This helps explain why capital does not flow from rich to poor countries, causing instantaneous convergence of per capita output. If each generation chooses its human capital optimally given that of the previous and succeeding generations, human capital follows a unique rational- expectations path. For moderate substitutability, human capital within each sector oscillates relative to that in other sectors, but aggregate human capital converges to the steady state monotonically, at rates consistent with those observed empirically.

Experience with Ada on the F-18 High Alpha Research Vehicle Flight Test Program

Considerable experience was acquired with Ada at the NASA Dryden Flight Research Facility during the on-going High Alpha Technology Program. In this program, an F-18 aircraft was highly modified by the addition of thrust-vectoring vanes to the airframe. In addition, substantial alteration was made in the original quadruplex flight control system. The result is the High Alpha Research Vehicle. An additional research flight control computer was incorporated in each of the four channels. Software for the research flight control computer was written in Ada. To date, six releases of this software have been flown. This paper provides a detailed description of the modifications to the research flight control system. Efficient ground-testing of the software was accomplished by using simulations that used the Ada for portions of their software. These simulations are also described. Modifying and transferring the Ada for flight software to the software simulation configuration has allowed evaluation of this language. This paper also discusses such significant issues in using Ada as portability, modifiability, and testability as well as documentation requirements

Investigating the role of cAMP in mycobacterial antimicrobial drug tolerance by the discovery of a novel cAMP-phosphodiesterase

M. tuberculosis, the causative agent of Tuberculosis (TB), is an ancient pathogen that has plagued mankind for over 70,000 years. In 2018, TB was responsible globally for 10 million new infections and 1.5 million deaths - more than any other infectious disease. M. tuberculosis bacilli have evolved to thrive in the harsh, nutrient limited environment within the host alveolar macrophage and evade the constant pressure of immune cell mediated killing. This evolution has led to the bacilli developing phenotypic adaptions that concurrently, drastically decrease their susceptibility to many antimicrobials. The basis for phenotypic adaptions is signalling to detect an environmental stimulus and to mediate an appropriate response. To this end, M. tuberculosis and other mycobacteria have evolved a robust cyclic AMP (cAMP) signalling system with multiple cAMP producing and cAMP binding effector proteins. Several of these proteins have already been shown to regulate virulence, carbon metabolism and essential gene expression. However, the link between cAMP signalling and antimicrobial susceptibility in mycobacteria has not previously been investigated. In this project, I identified a new cAMP degrading phosphodiesterase enzyme (Rv1339) and used it as a tool to significantly decrease intrabacterial levels of cAMP in mycobacteria. The effect of this in M. smegmatis mc2155 was to increase antimicrobial susceptibility. By using a combination of metabolomics, RNA-sequencing, antimicrobial susceptibility assays and bioenergetics analysis, I was able to characterise the potential mechanism behind this increased susceptibility. I was also able to begin preliminary work required to investigate this link in M. tuberculosis H37Rv. This work represents a proof-of-concept that targeting cAMP signalling is a promising new avenue for antimicrobial development, and expands our understanding of cAMP signalling in mycobacteria.Open Acces

The time cost of care

Extensive small scale studies have documented that when people assume the role of assisting a person with impairments or an older person, care activities account for a significant portion of their daily routines. Nevertheless, little research has investigated the problem of measuring the time that carers spend in care-related activities. This paper contrasts two different measures of care time – an estimated average weekly hours question in the 1998 Australian Survey of Disability, Ageing and Carers, and diary estimates from the 1997 national Australian Time Use Survey. This study finds that diaries provide information for a more robust estimate, but only after one models the time use patterns in the days of carers to identify care-related activities, which diarists do not necessarily record as care. Such a measure of care time reveals that even people who offer only occasional assistance to a person with impairments tend to spend the equivalent of more than 10 minutes a day providing care. Most caregivers undertake the equivalent of a part-time job to help a friend or family member. Summing the average caregiving time provided by all household members reveals that over a quarter of Australian households caring for an adult or child provide the equivalent of a full-time employee’s labour, and another quarter work between 20 and 39 total weekly hours to provide informal care.Care, unpaid work, time estimation, family and gender roles, informal economic activity

Train-induced dynamic response of railway track and embankments on soft peaty foundations

The mainline railway track between Dublin and Belfast in Northern Ireland was constructed during the 1850's. Substantial lengths of railway embankment were constructed over poor-quality peaty soils. This was accomplished using tree trunk fascines placed directly on the natural ground surface; with poor-quality local peaty soils used as light weight fill.In recent years, Northern Ireland Railways have noticed that these sections of railway track have been deteriorating more rapidly than sections of the track where the foundations are more competent. The magnitudes of displacement of the track under train loading appear to be increasing gradually over time and train speeds have had to be reduced.This thesis is based on the research done to monitor the response of these railway track and embankment structures to dynamic train loading. The displacements were monitored for two different embankments under a variety of loading conditions and for various seasonal conditions. These displacements were recorded using a sensor created for this task. The sensor consisted of a photo-sensitive array mounted on the sleepers and a laser, which was placed outside the area of influence of train loading, and shone on the photo-sensitive array. Analytical (Winkler) modelling was conducted to determine the effects of train speed and the cause of the large train-induced displacements. Analytical and finite element modelling were used to determine the effectiveness of alternative methods of embankment stabilization.The results from the analytical modelling suggest that the deformation of the embankment under train loading was not due to dynamic excitation, but static deformation of the poor-quality fill and soft foundation materials. From both the analytical and finite element modelling of possible remediation techniques, methods that stiffen the embankment and foundation material are shown to be the most effective at reducing the train induced deflection of the embankment

Defective RNAs of Semliki Forest virus

This thesis describes an investigation into the mouse-protecting nucleotide sequences of defective interfering (Dl) Semliki Forest virus (SFV) RNA was extracted from tissue culture preparations of Dl SFV and reverse transcribed Putative Dl SFV cDNA was amplified by the polymerase chain reaction using primers specific for the termini of the virion RNA A number of molecular clones were constructed from the products of amplification and the nucleotide sequences of two of these clones were determined (pSFVDI-6 2146 nts and pSFVDI-19 1244 nts) Both pSFVDI-6 and pSFVDI-19 were derived from three noncontiguous regions of the SFV genome comprising the 5' and 3' termini and part of the nsP2 coding region RNA transcribed from these clones was transfected into SFV-infected BHK-21 cells to produce genetically homogeneous Dl SFV preparations These preparations were stable on serial passage and interfered with virus multiplication m vitro The transfection technique was also used in a preliminary investigation of the regulatory elements of the SFV genome A 388- nucleotide region within the nsP2 gene of SFV was tentatively defined as containing all or part of a packaging signal since Dl SFV clones lacking this region were not propagated as virions. To determine the biological activity of the cloned Dl SFV preparations in vivo they were mixed with 10 LD₁₀, SFV and inoculated into adult mice by the intranasal route The Dl SFV preparation derived from pSFVDI-19 typically conferred 75% protection against the lethal encephalitis that normally follows infection with SFV. whereas the Dl SFV preparation derived from pSFVDI-6 was non-protecting However, it should be noted that the concentration of Dl SFV in these cloned preparations was not standardised Modulation of infection in vivo was independent of the antigenic load and mice were susceptible to subsequent lethal challenge A preliminary experiment suggested that propagation of Dl SFV genomes was cell-specific because genomes derived from pSFVDI-19, but not pSFVDI-6, could be detected in mouse brain tissue following intracerebral coinoculation of SFV with the cloned Dl SFV preparations

Simulated holographic three-dimensional intensity shaping of evanescent-wave fields

The size of bright structures in traveling-wave light fields is limited by diffraction. This in turn limits a number of technologies, for example, optical trapping. One way to beat the diffraction limit is to use evanescent waves instead of traveling waves. Here we apply a holographic algorithm, direct search, to the shaping of complex evanescent-wave fields. We simulate three-dimensional intensity shaping of evanescent-wave fields using this approach, and we investigate some of its limitations. (c) 2008 Optical Society of America.</p

Ultrafast dynamic conductivity and scattering rate saturation of photoexcited charge carriers in silicon investigated with a midinfrared continuum probe

We employ ultra-broadband terahertz-midinfrared probe pulses to characterize the optical response of photoinduced charge-carrier plasmas in high-resistivity silicon in a reflection geometry, over a wide range of excitation densities (10^{15}-10^{19} cm^{-3}) at room temperature. In contrast to conventional terahertz spectroscopy studies, this enables one to directly cover the frequency range encompassing the resultant plasma frequencies. The intensity reflection spectra of the thermalized plasma, measured using sum-frequency (up-conversion) detection of the probe pulses, can be modeled well by a standard Drude model with a density-dependent momentum scattering time of approx. 200 fs at low densities, reaching approx. 20 fs for densities of approx. 10^{19} cm^{-3}, where the increase of the scattering rate saturates. This behavior can be reproduced well with theoretical results based on the generalized Drude approach for the electron-hole scattering rate, where the saturation occurs due to phase-space restrictions as the plasma becomes degenerate. We also study the initial sub-picosecond temporal development of the Drude response, and discuss the observed rise in the scattering time in terms of initial charge-carrier relaxation, as well as the optical response of the photoexcited sample as predicted by finite-difference time-domain simulations.Comment: 9 pages, 4 figure