BLAST ENERGY MITIGATION IN POROUS ROCKS

Geo-materials are commonly used and sought after for blast mitigation applications due to their wide availability and low cost compared to industry trademarked materials. Characterization of these natural geo-materials such as volcanic rocks is of paramount importance in determining their blast mitigation capabilities. While there is a large amount of information available for materials such as concrete or sand blasts, information on the properties of volcanic rocks is far more scarce. This lack of data is due to the wide range of existing natural volcanic rocks and the variation in the minerals and pore structures of the rocks. In this thesis, silicate volcanic rock samples are characterized both through static and dynamic experimental methods. Initial X-ray powder diffraction scans have been conducted and analyzed to obtain the mineral composition information of the rock samples. Additional tomographic scans under quasi-static loading have been recorded to better understand the internal composition of the material pore structure and the material fracture. For this study, standard compression experiments were conducted at two separate strain rates for ten samples each on a UTM test frame to characterize the behavior of the rock under quasi-static conditions. High strain rate uniaxial compression tests were conducted for three strain rates using a split-Hopkinson pressure bar with pulse shaping to determine the dynamic response of the material. The stress-strain data from the experiments was used to determine the modulus of toughness of the material. Due to the high porosity and heterogeneity of the material, 25 samples were used for dynamic experimentation to attempt to capture and minimize the effects of scatter in the natural material. High speed photography was used to capture the sample deformation during two separate strain rates and to visualize crack propagation and strain rate in the samples. It was found that after an initial yielding, the material is able to withstand a sustained loading which is desirable for materials used in blast loading applications. Another desirable trait that was observed in this material is that higher strain rates provide a higher sustained stress value. Further dynamic experiments on the rock with larger strains are necessary to completely compare the energy absorption capabilities of the material at high strain rates

A double-blind study of the efficacy of apomorphine and its assessment in "off-periods in Parkinson's disease

Five patients with idiopathic Parkinson's disease with severe response fluctuations were selected for a randomized double-blind placebo-controlled study, concerning the clinical effects of subcutaneous apomorphine and its assessment in `off¿-periods. The study was designed as five n = 1 studies, in which every patient was his own control. The effect of apomorphine was studied by using the Columbia rating scale and quantitative assessments, using tapping, walking and pinboard. There was a significant positive effect of apomorphine, in a mean optimal dose of 2.7 mg, with a mean latency of onset of 7.3 min and a mean duration of response of 96 min. After pretreatment with domperidone, no significant adverse effects were observed. Tapping showed the highest correlation with rigidity and bradykinesia. Walking showed a high correlation with stability and gait. Pinboard testing did not give additional information. The first conclusion was that apomorphine proved to be a significantly effective dopamine agonist, proven now also by a double blind placebo-controlled study. Secondly it was concluded that assessment of clinical effect in parkinsonian patients can be performed best by combining the Columbia item tremor with tapping and walking scores

How should ethnic diversity be represented in medical curricula? A plea for systematic training in cultural competence

Ethnic diversity has become a common reality in European societies, including those of Germany and the Netherlands. Given that ethnic minority groups and immigrants are known to be especially vulnerable to inequalities in health, access to services and quality of care, the need for cultural competency training in medical education is widely acknowledged. This paper presents four key issues in providing medical students and physicians with the knowledge, attitudes and skills to adapt medical care to ethnically diverse populations. It then describes two educational programmes delivered by the University of Amsterdam (UvA Academic Medical Centre, the Netherlands) and Giessen University Medical School (Germany), respectively, to illustrate that translating theoretical educational objectives into educational practice can lead to different teaching programmes depending on specific local conditions. In the conclusions, emphasis is placed on the need for systematic approaches that do not limit their focus to patients and groups of specific ethnic or migration backgrounds. Issues of culture, communication and research in relation to ethnically diverse populations are magnifications of general problems in medicine and healthcare. Explicit attention to ethnic diversity thus offers a view through a ‘magnifying glass’ of subjects of much broader importance and can be a means for improving health care in general

Dissipative generation of pure steady states and a gambler's ruin problem

We consider an open quantum system, with dissipation applied only to a part of its degrees of freedom, evolving via a quantum Markov dynamics. We demonstrate that, in the Zeno regime of large dissipation, the relaxation of the quantum system towards a pure quantum state is linked to the evolution of a classical Markov process towards a single absorbing state. The rates of the associated classical Markov process are determined by the original quantum dynamics. Extension of this correspondence to absorbing states with internal structure allows us to establish a general criterion for having a Zeno-limit nonequilibrium stationary state of arbitrary finite rank. An application of this criterion is illustrated in the case of an open XXZ spin-1/2 chain dissipatively coupled at its edges to baths with fixed and different polarizations. For this system, we find exact nonequilibrium steady-state solutions of ranks 1 and 2.Comment: 7 page

Lagrangian dispersion and deformation in submesoscale flows

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Oceanography and Applied Ocean Science and Engineering at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2019.Submesoscale currents, with horizontal length scales of 1-20 km, are an important element of upper ocean dynamics. These currents play a crucial role in the horizontal and vertical redistribution of tracers, the cascade of tracer variance to smaller scales, and in linking the mesoscale circulation with the dissipative scales. This thesis investigates submesoscale flows and their properties using Lagrangian trajectories of observed and modeled drifters. We analyze statistics of observed drifter pairs to characterize turbulent dispersion at submeso-scales. Contrary to theoretical expectations, we find that nonlocal velocity gradients associated with mesoscale eddies dominate the separation of drifters even at the kilometer scale. At submeso-scales, we observe energetic motions, such as near-inertial oscillations, that contribute to the energy spectrum but are inefficient at dispersion. Using trajectories in a model of submesoscale turbulence, we find that, if drifters have a vertical separation, vertical shear dominates the dispersion and conceals horizontal dispersion regimes from drifter observations. Particularly in submesoscale flows, vertical shear is orders of magnitude larger than horizontal gradients in velocity. Since conventional drifters in the ocean are not affected by vertical shear, it is likely that drifter-derived diffusivity underestimates the diffusivity that a tracer would experience. Lastly, we test and apply cluster-based methods, using three or more drifters, to estimate the velocity gradient tensor. Since velocity gradients become large at submesoscales, the divergence, strain, and vorticity control the evolution and deformation of clusters of drifters. Observing the velocity gradients using drifters, enables us to further constrain the governing dynamics and decipher submesoscale motions from inertia-gravity waves. These insights provide a Lagrangian perspective on submesoscale flows that illuminates scales that are challenging to observe from other platforms. We reveal observational and theoretical challenges that need to be overcome in future investigations.My doctoral studies in the WHOI/MIT Joint Program were funded by the National Science Foundation (OCE-I434788) and the Office of Naval Research (N00014-13-1-0451, Grant N00014-16-1-2470)