Modular Omni-directional AGV Developmental Platform with Integrated Suspension, Power-plant and Control Systems

The thesis focuses on the development of an industrial automatic guided vehicle (AGV) with omni-directional capabilities. The omni-directional strategy used was the "swerve drive" system, a system whereby a wheel can be rotated about both its y axis (rolling axis) and z axis (vertical axis). Unlike most commonly used swerve drive systems that have swerve capabilities on each wheel attached to the body of the vehicle, this research seeks to reduce cost by only having swerve capabilities on two diagonal wheels. The remaining two wheels will act as castor units. AC drives are used on the system in place of more traditional DC drives, due to their cost vs capability advantage over DC and their prevalence in the industrial environment. Since an AGV is a mobile platform any power source found on it is usually derived from batteries, a DC source. Usage of DC introduces several limitations including difficulty transforming voltage levels for different systems, inability to run AC drives directly from the power source and comparably larger conduction wires. These limitations were overcome by adding a stand-alone power-plant on the AGV in the form of an inverter. The inverter transformed the DC power supplied by a battery bank from 48 volts DC to 230 volts AC. Thus, the primary focus of this research is on the development and validation of a novel two wheel omni-directional drive system that makes use of inexpensive and readily available components that have already been proven to work in industry.Thesis (PhD) -- Faculty of Engineering, the Built Environment, and Technology, 202

Towards an eficient atomic frequency comb quantum memory

We present an efficient photon-echo experiment based on atomic frequency combs [Phys. Rev. A 79, 052329 (2009)]. Echoes containing an energy of up to 35% of that of the input pulse are observed in a Pr3+-doped Y2SiO5 crystal. This material allows for the precise spectral holeburning needed to make a sharp and highly absorbing comb structure. We compare our results with a simple theoretical model with satisfactory agreement. Our results show that atomic frequency combs has the potential for high-efficiency storage of single photons as required in future long-distance communication based on quantum repeaters.Comment: 10 pages, 5 figure

’We do not have a writing culture’: exploring the nature of ‘academic drift’ through a study of lecturer perspectives on student writing in a vocational university

Vocational universities are increasingly becoming susceptible to pressures associated with the phenomenon known as ‘academic drift’. Yet the specific influence of such pressures is experienced differently at various institutional levels and by different stakeholders in such universities. Exploring lecturers’ understanding and perceptions of student academic writing can make visible the ways in which these pressures are realised, for example, in the types of writing given value and writing pedagogies deemed suitable in the context of the vocational university. In this paper, we report on an ethnographically shaped study exploring lecturers’ writing pedagogies and perceptions of students as academic writers at a South African vocational university. The study analytically illustrated how wider socio-political, regulatory and ideological framings of these universities were implicated in lecturers’ writing practices and pedagogies. The study found that lecturers and students were generally constricted by narrow vocationalist agendas, which reinforced negative conceptions of students as academic writers. Our findings suggest that while the explicit impact of academic drift drivers was minimally felt at the undergraduate diploma level of study in our research site, this appeared to close off the potential for writing to act as a means to facilitate students’ epistemic access to their disciplines

Quantifying the burden of stillbirths before 28 weeks of completed gestational age in high-income countries: a population-based study of 19 European countries

Background International comparisons of stillbirth allow assessment of variations in clinical practice to reduce mortality. Currently, such comparisons include only stillbirths from 28 or more completed weeks of gestational age, which underestimates the true burden of stillbirth. With increased registration of early stillbirths in high-income countries, we assessed the reliability of including stillbirths before 28 completed weeks in such comparisons. Methods In this population-based study, we used national cohort data from 19 European countries participating in the Euro-Peristat project on livebirths and stillbirths from 22 completed weeks of gestation in 2004, 2010, and 2015. We excluded countries without national data for stillbirths by gestational age in these periods, or where data available were not comparable between 2004 and 2015. We also excluded those countries with fewer than 10 000 births per year because the proportion of stillbirths at 22 weeks to less than 28 weeks of gestation is small. We calculated pooled stillbirth rates using a random-effects model and changes in rates between 2004 and 2015 using risk ratios (RR) by gestational age and country. Findings Stillbirths at 22 weeks to less than 28 weeks of gestation accounted for 32% of all stillbirths in 2015. The pooled stillbirth rate at 24 weeks to less than 28 weeks declined from 0·97 to 0·70 per 1000 births from 2004 to 2015, a reduction of 25% (RR 0·75, 95% CI 0·65–0·85). The pooled stillbirth rate at 22 weeks to less than 24 weeks of gestation in 2015 was 0·53 per 1000 births and did not significantly changed over time (RR 0·97, 95% CI 0·80–1·16) although changes varied widely between countries (RRs 0·62–2·09). Wide variation in the percentage of all births occurring at 22 weeks to less than 24 weeks of gestation suggest international differences in ascertainment. Interpretation Present definitions used for international comparisons exclude a third of stillbirths. International consistency of reporting stillbirths at 24 weeks to less than 28 weeks suggests these deaths should be included in routinely reported comparisons. This addition would have a major impact, acknowledging the burden of perinatal death to families, and making international assessments more informative for clinical practice and policy. Ascertainment of fetal deaths at 22 weeks to less than 24 weeks should be stabilised so that all stillbirths from 22 completed weeks of gestation onwards can be reliably compared

Producing valid statistics when legislation, culture, and medical practices differ for births at or before the threshold of survival: Report of a European workshop

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Measurement of the Bˉ→Dℓνˉ\bar{B}\to D\ell\bar{\nu} Partila Width and Form Factor Parameters

We have studied the decay $\bar{B} \to D\ell\bar{\nu}$, where $\ell=e or \mu$. From a fit to the differential decay rate $d\Gamma/dw$ we measure the rate normalization ${\cal F}_D(1)|V_{cb}|$ and form factor slope $\hat{\rho}^2_D$, and, using measured values of $\tau_B$, find $\Gamma(\bar{B} \to D\ell\bar{\nu}) = (12.0 \pm 0.9 \pm 2.1) ns^{-1}$. The resulting branching fractions are ${\cal B}(\bar{B}^0 \to D^+\ell^-\bar{\nu})=(1.87 \pm 0.15 \pm 0.32)$ and ${\cal B}(B^- \to D^0\ell^-\bar{\nu})=(1.94 \pm 0.15 \pm 0.34)$. The form factor parameters are in agreement with those measured in $\bar{B} \to D^*\ell\bar{\nu}$ decays, as predicted by heavy quark effective theory.Comment: 11 pages, postscript file also available through http://w4.lns.cornell.edu/public/CLN

Study of Gluon versus Quark Fragmentation in Υ→ggγ\Upsilon\to gg\gamma and e+e−→qqˉγe^{+}e^{-}\to q\bar{q}\gamma Events at \sqrt{s}=10 GeV

Using data collected with the CLEO II detector at the Cornell Electron Storage Ring, we determine the ratio R(chrg) for the mean charged multiplicity observed in Upsilon(1S)->gggamma events, to the mean charged multiplicity observed in e+e- -> qqbar gamma events. We find R(chrg)=1.04+/-0.02+/-0.05 for jet-jet masses less than 7 GeV.Comment: 15 pages, postscript file also available through http://w4.lns.cornell.edu/public/CLN

Determination of the Michel Parameters and the tau Neutrino Helicity in tau Decay

Using the CLEO II detector at the $e^+e^-$ storage ring CESR, we have determined the Michel parameters $\rho$, $\xi$, and $\delta$ in $\tau^\mp \to l^\mp\nu\bar{\nu}$ decay as well as the tau neutrino helicity parameter $h_{\nu_\tau}$ in $\tau^\mp \to \pi^\mp\pi^0\nu$ decay. From a data sample of $3.02\times 10^6$ tau pairs produced at $\sqrt{s}=10.6 GeV$, using events of the topology $e^+e^- \to \tau^+\tau^- \to (l^\pm\nu\bar{\nu}) (\pi^\mp\pi^0\nu)$ and $e^+e^- \to \tau^+\tau^- \to (\pi^\pm\pi^0\bar{\nu}) (\pi^\mp\pi^0\nu)$, and the determined sign of $h_{\nu_\tau}$, the combined result of the three samples is: $\rho = 0.747\pm 0.010\pm 0.006$, $\xi = 1.007\pm 0.040\pm 0.015$, $\xi\delta = 0.745\pm 0.026\pm 0.009$, and $h_{\nu_\tau} = -0.995\pm 0.010\pm 0.003$. The results are in agreement with the Standard Model V-A interaction.Comment: 18 page postscript file, postscript file also available through http://w4.lns.cornell.edu/public/CLN

Search for the Decay τ−→4pi−3π+(π0)ντ\tau^{-}\to 4pi^{-}3\pi^{+}(\pi^{0})\nu_{\tau}

We have searched for the decay of the tau lepton into seven charged particles and zero or one pi0. The data used in the search were collected with the CLEO II detector at the Cornell Electron Storage Ring (CESR) and correspond to an integrated luminosity of 4.61 fb^(-1). No evidence for a signal is found. Assuming all the charged particles are pions, we set an upper limit on the branching fraction, B(tau- -> 4pi- 3pi+ (pi0) nu_tau) < 2.4 x 10^(-6) at the 90% confidence level. This limit represents a significant improvement over the previous limit.Comment: 9 page postscript file, postscript file also available through http://w4.lns.cornell.edu/public/CLN