Front cover

NMR imaging of moisture inside heated porous building materials

The design of noise-free, low-pollutant combustion devices requires the understanding and the prediction of the combustion noise. The noise originates from the coupling between perturbations in the heat release rate with the oscillating gas (acoustic velocity). Prediction of combustion noise requires the transfer function (TF) that correlates the variation in the heat release rate of the ame with the perturbation (acoustic velocity). Computational costs prohibit an e??cient calculation of the TF by simulating all combustion phenomena associated with the ame dynamics. Simpli??ed theoretical models, such as the hydrodynamic models, allow a signi??cant reduction of the computation time and capture the main features of the ame front dynamics. The fundamental assumption of the hydrodynamic models is that the Bunsen ame, which is described as a thin layer ( ame front) separating the burnt from the unburnt gas, is attached at the burner rim. Within the thin layer approximation, the computation of the TF requires the ame area and, consequenctly, the time-dependent ame front position. By de??ning the ame front as the zero-level set of a distance function, the evolution of the ame front is described by a level set equation. The existent experiments and theoretic kinematic models based on the thin layer approximation (e.g., the G-equation model) provide contradictory information on the phase of the TF. Experiments suggest a low-pass ??lter behaviour of the gain of the TF and an increase of the TF's phase up to several ?? as the frequency increases. In contrast, most of the theoretical models indicate a saturation of the phase of the TF at the level of ??/2. Although the use of a convective wave model for the ow [80] leads to a better agreement between theory and experiments, the origin of the convective wave remains little understood. The discrepancies between theory and experiments most likely reside in the simpli??cations employed in the theoretical models. To understand the behaviour of the experimental TF, here we extend the theoretical models based on the G-equation approach. In the ??rst step, we extend the models by addressing ames that have an arbitrary cone angle and a burning velocity with variable direction. To carry out this ??rst extension we analyse the evolution of a Bunsen ame in a Poiseuille ow from an initially at pro??le to a stationary conical shape. The analysis leads to the correct derivation of the boundary conditions in the extended model employed for the ame evolution in a perturbed Poiseuille ow. We demonstrate that the new model proposed here improves the description of the front close to the boundary and, hence, the behaviour of the ame response to velocity perturbations. Because recent measurements [52] suggest that a better understanding of the TF's phase behaviour requires a hydrodynamic model that accounts for the moving edge of the ame, in the second step we extend the hydrodynamic model to account for non-attached ames. We model the ame front as an open curve by using two level set functions whose zero-level sets are locally normal at the edge point. The movement of the edge along the ame front is accounted for via a novel model for the edge speed. During computer simulations of the ame kinematics with the new extended model the local orthogonality of the level sets is preserved by employing a novel algorithm. The simulations demonstrate that our extended model qualitatively accounts for the ame stabilisation, the ame front and edge kinematics, and the stand-o?? distance of the ame above the burner rim.

Even though friction affects everyday life in many ways, it is still one of the biggest mysteries of physics. Friction is a truly multi-scale phenomenon with a large variety of processes acting at various length and time scales. In recent years, much attention was paid to the micro- and nano-scale properties of frictional interfaces in order to uncover the origins of friction. The structural aspects of friction at the meso- to macro-scales have, however, often been neglected. This thesis aims at demonstrating that these aspects are key to the frictional response of macroscopic systems and pursues therefore the objective of improving today's knowledge of the rupture-like propagation of slip fronts at frictional interfaces. The mechanics of frictional interfaces is studied with state-of-the-art dynamic finite-element simulations of systems mimicking experimental set-ups. Two and three-dimensional simulations are conducted according to the nature of the studied phenomena. In addition, theoretical models based on fracture mechanics theory are developed and applied to confirm the numerical observations. These models provide insights on the underlying mechanisms of the slip front propagation and reveal the influence of various system, material, and interface parameters. The results presented in this thesis show that the applied numerical models reproduce quantitatively well experimental observations as reported in literature. The studied aspects of frictional slip include, among others, the propagation speed, the arrest position, and the effect of interface heterogeneity. Beyond confirming experimental observations, the simulations and theoretical models further reveal new features of the propagation and arrest of slip fronts. They show, for instance, that the speed of slip fronts depends on the propagation direction and that the arrest position of slip precursors is predictable with linear elastic fracture mechanics theory. Furthermore, simulations of slip fronts at heterogeneous interfaces uncover an interaction between the length scales of the slip front and the heterogeneous pattern.

The climatologic phenomena of large-scale El Nino and La Ninaare associated with variations in surface temperature of the Pacific Ocean.In the southern Brazil, they are responsible for changing the patterns ofoccurrence and intensity of frontal systems and the events was analyzed tounderstand theirs effects. Three periods were analyzed: June 2004 to May2005, June 2007 to May 2008 and June 2005 to May 2006. These periodscorrespond to El Nino, La Nina and neutral period, respectively. The frontsystem analysis was made using synoptic maps of the Centro de Previsaodo Tempo e Estudos Climaticos (CPTEC). The fronts were counted andclassified according to their intensity, and the linear correlations wereperformed between an index of intensity of ENSO, provided by theNational Oceanic Atmospheric Administration (NOAA), and the intensityof fronts. The results were seasonally grouped. During the El Ninohappened a decrease in the amount of cold fronts at the region in all seasons(autumn excepted), and the biggest difference occurred in the summer(there was 4 fronts in El Nino period and 14 in neutral period). In La Ninaperiod, there was an increase of the number of cold fronts in all seasons,especially in winter (18 front systems); at neutral period occurred 11 frontsystems. However, the intensity of cold fronts was not affected by thephenomenon, except in October. Therefore, the climate of the region insouthern Brazil is influenced by both direct ENSO phenomena analyzedand this is conditioned by the intensity that they present themselves.

The French National Front (FN), currently one of the most successful radical right-wing parties at the electoral booth in Western Europe, has more than doubled its vote share from around 10 per cent in the late 2000s, or the final years of Jean-Marie Le Pen’s presidency, to around 15–25 per cent in the 2010s after Marine Le Pen has taken over the leadership of the party. Aiming to understand the reasons for this increase in the party’s vote and possible differences in the FN voter between Le Pen father and Le Pen daughter, we compare the individual characteristics of the FN voters, as well as the structural conditions in an individual’s surrounding that might influence why somebody votes FN in 2007 and 2012. Except for the fact that the FN electorate became younger in 2012, the core characteristics of the FN voter (for example, low education, dissatisfaction with democracy in France and a working class background) have remained constant. However, what has changed in 2012 is that the FN was more successful in attracting a higher proportion of voters that belong to the socio-demographic strata traditionally, overrepresented within its electorate.

This study aims to explore the practice types and the problem solving practice sequences of a third grade primary mathematics class, where “students at the front” pattern was adopted by the teacher. The fundamental issue of this study is teacher’s mathematics teaching practice approaches. It is also considered that one approach may derive from different beliefs. Therefore “video taping in the classroom” and “video taping of after-class interview” are used to collect data. The source of the study analysis is based on eighteen working transcripts, which were transcribed and edited from the videotapes of six mathematics classes teaching. This study discovers that in order to “understand the students’ learning situation”, “prepare for the follow-up materials”, “adjust the speed of teaching rhythm”, and “gather students’ attention”, the teacher invited the students to come to the front to write answers, explain reasons, draw, receive and dispatch books, clean the blackboard. The teacher might also, depending on the situations, invite those students who usually write correct answers or incorrect answers to write at the front In addition, the teacher applied “student at the front” to implement mathematics problem solving practice sequences with the results as the follows: 1. After student A wrote at the front, the teacher had the whole class find the mistakes by giving hints. The other students corrected the mistakes consequently. 2. The teacher encouraged the students to try to explain a new concept as much as possible. 3. If a student could not explain very explicitly, then came to the front to draw. If he/she couldn’t not draw very well, the teacher helped. 4. The low-level students came first. The high-level students came later. 5. The teacher invited those who probably knew the correct answers to came at front in turns. 6. The teacher continuously hinted those students who had obvious mistakes and waited for them to make corrections. 7. The teacher stopped the laughs at those who wrote wrong answers. 8. The teacher hinted if the drawing could not be completed. Other students substituted if the mark was not clear. 9. The teacher directly spoke out the answers if the break time bell rang. 10. If there was not enough time, the teacher invited high-level students to answer the questions and then explained. According to the content of the sequences, five roles of students are found: “sacrifices of wrong answers”, “pure answer presenters”, “reasons explainers”, “supplement explainers” and “self-correctors”. As to the teacher, three kinds of roles are divided: “a mistake shower and reminder”, “a summary interpreter and” and “an active hinter.”

Natural gas discharges like lightning and polar light are spectacular phenomena that have impressed and fascinated people for a long time. During the last two centuries, people have learned how to create their own gas discharges and how to make use of them. Nowadays, man-made gas discharges are commonly used in many applications. Well-known examples include fluorescent lamps, plasma televisions and high intensity lamps used in data projectors. Also in industry, gas discharges are often part of the production process, for instance in the fabrication of computer chips, cleaning of exhaust gases, coating of fabrics and production of solar cells. A gas discharge, or plasma, consists of a variety of different particles like electrons, ions, atoms and molecules in various excited states. These particles not only interact with each other, but also with electric and magnetic fields and with electrode and wall surfaces in the discharge volume. This wide variety of particles and interactions makes a gas discharge a complex system, which is difficult to understand completely and control accurately. To create a gas discharge one generally needs to apply a sufficiently large voltage across a volume of neutral gas. There are many options how to do this, resulting in many different types of gas discharges. Nevertheless, the basic principles involved are the same for all these situations. The electrically insulating, neutral gas is transformed into a conducting, (partially) ionized state by the applied voltage. This evolution from a neutral gas to a selfsustaining discharge is known as plasma breakdown, or plasma ignition, and is the subject of this thesis. Plasma breakdown is a fundamental process in gas discharges; it is a highly transient process that involves particles drifting in electric fields, charge multiplication in electron avalanches and moving ionization fronts. The driving force for these processes is the electric field in the discharge volume. The research in this thesis was aimed at obtaining a better understanding of the fundamental processes involved in plasma breakdown in low-pressure discharges by experimental investigations. Two types of discharges were studied; a pulsed discharge between parabolic, metal electrodes and a parallel-plate, low-pressure dielectric barrier discharge. The breakdown 155 phases of these discharges were investigated using various experimental techniques. Breakdown processes in the low-pressure dielectric barrier discharge were investigated by studying the light emission from the discharge in a spatially, temporally and spectrally resolved way. Additionally, electrode voltages and discharge currents were measured. These investigations, together with the results from a two-dimensional fluid model, showed that the breakdown process in this discharge followed a Townsend-like mechanism in which the effects of the dielectric plates were limited. The pulsed discharge between parabolic, metal electrodes, was firstly studied in a lowpressure argon environment by light emission imaging with an intensified charge-coupled device (ICCD) camera. This relatively simple diagnostic provided time- and space-resolved information on the characteristic features of the breakdown process. Different phases in the breakdown process were identified. Firstly, the build-up of a light emission region in the discharge gap in front of the anode, followed by a light front crossing the electrode gap from anode to cathode and finally, a stable discharge covering the cathode surface. These features were in qualitative agreement with the breakdown process observed in parallelplate discharges at low pressure, which are accurately described by Townsend’s breakdown theory. The ICCD imaging experiments also showed that before the main breakdown process started, a weak flash of light could be observed around the anode. This pre-breakdown light emission occurred during the rise of the applied voltage, but before the breakdown voltage was reached. The origin of this feature was found to be electron avalanches seeded by volume charges left over from previous discharges in combination with the specific discharge geometry used in our experiments. It was concluded that the initial conditions of the discharge influenced the breakdown process. Although the qualitative behaviour of the main breakdown phase did not change for a wide variety of discharge conditions, the details of the process, especially the timing of the different phases were strongly influenced by the initial conditions. Finally, a new diagnostic was developed to measure electric field distributions during the breakdown phase of a discharge. With this diagnostic, electric field strengths were determined by measuring Stark effects in xenon atoms using laser-induced fluorescence-dip spectroscopy. Stark shifts of up to 4.8 cm-1 (160 pm) were observed for ns and nd Rydberg states, with principal quantum numbers ranging from 12 to 18, as a result of electric fields between 250 and 4000 V/cm. Additionally, a theoretical calculation method, based on solving the Schr¨odinger equation for a perturbed Hamiltonian by matrix diagonalization, proved to be very accurate for describing the observed Stark effects in nd Rydberg levels. With this diagnostic we performed measurements of the electric field distribution during the breakdown phase of the discharge between parabolic electrodes in xenon. For the first 156 time, quantitative, direct measurements of the evolution of electric field during breakdown were obtained. Electric fields between 0 and 1600 V/cm were measured with a resolution of 200–400 V/cm, depending on the magnitude of the electric field. These experiments showed that the ionization front, already observed in the ICCD imaging experiments, is sustained by a spatially narrow, rapidly moving region of strong electric field. Additionally, this ionization front did not completely modify the potential distribution in the discharge gap; the discharge continued developing towards a steady-state after the ionization front crossed the gap. In conclusion, the investigations in this thesis show that the fundamental processes involved in plasma breakdown are well understood. However, the details of the process, especially timing of events, depend strongly on the specific discharge geometry and the initial discharge conditions. The electric field diagnostic has proven to be very useful for breakdown studies, identifying a narrow, moving region of high electric field as the cause of the moving ionization fronts . This diagnostic offers the possibility to obtain quantitative, direct information on local electric field strengths with both spatial and temporal resolution. In future research, such electric field measurements can be very valuable not only for investigations on low-pressure breakdown but also for studies on breakdown processes at higher pressures, which are only poorly understood at the moment.

Water and ion transport in nylon as studied by NMR

The majority of hotel front desk employees fulfill their job demands in generally similar ways, in terms of workplace conditions. The demanding and hectic nature of this job results in very tangle physical and emotional effects on the employee. Through an analysis of current literature, guidelines on implementing a wellness program suited specifically for hotel front desk employees will be created. Through successful implementation of an employee wellness program, management will be able to provide effective job resources that will result in engaged front desk employees, and consequently, higher levels of customer service, productivity, and profitability.

The construction of the subaqueous delta front is foundational to deltaic land building and field data is needed to validate conceptual models of delta front evolution. The bathymetric change that occurred across the entire delta front (~ 75.9 km2) of the Wax Lake Delta (WLD) in coastal Louisiana was measured between February 2015 and July 2016. Sediment removal (− 9.85 × 106 m3) exceeded sediment accumulation (7.64 × 106 m3), making the delta front net-erosional (− 2.21 × 106 m3) despite the occurrence of a flood. These results factor in an estimated 4.28 cm of subsidence during the survey period. Deposition on the delta front was localized around channels and the northern and eastern flanks of the delta whereas erosion was more spatially uniform. This erosion coincides with an anomalously strong winter storm season that may have exported this sediment offshore and is consistent with a growing body of research that identifies winter storms as a significant mechanism for sediment removal from Atchafalaya Bay. Winter storm erosion is crucial to understanding and predicting volumetric growth of the WLD and has important implications to land building from sediment diversions. Future models of deltaic growth need to account for significant volume export and erosive episodes on the delta front.

Apanteles carposinae, sp. n.♀. Black; the front legs entirely (save for the black feet and for some occasional slight darkening on femora above and below, on tibiae above, and on coxae and tarsi), middle legs entirely (save for the black feet and for femora darkened above and below and for some occasional slight darkening on tibiae and coxae), hind coxae at apex below, hind trochanters and trochantines, hind femora (save above and below extensively), hind tibiae, hind tarsi (save for black feet and some darkening), and palpi, red testaceous; tibial spurs pale; wings infumated evenly throughout and the setae coloured; stigma, metacarp, and all veins, brown; stigma uniformly opaque.♂. Black; front coxae (save at base), front trochanters and trochantines, front femora (save for darkening above and below, which is sometimes strong), front tibiae (save for strong darkening above), front tarsi (save for some darkening and the black feet), middle coxae (save at base or even basal half), middle trochanters and trochantines largely, middle femora (save for extensive strong darkening above and below), hind coxae at apex below to some extent in the lighter but not in the darker examples, hind femora (save for extensive strong darkening above and below), and palpi, red testaceous; the four posterior tibiae and tarsi, and the hind trochanters and trochantines, largely darkened throughout save perhaps in an occasional lighter example; tibial spurs pale; wings infumated evenly throughout and the setae coloured; stigma, metacarp, and all veins, brown; stigma uniformly opaque.

China is a rising power on the world stage with growing economic and political influence. This influence is particularly felt in Australia and in New Zealand. United Front work is a key aspect of Chinese political influence abroad, particularly after Chinese president Xi Jinping’s rise to power. United Front work is difficult to track, and a survey over all countries is extremely challenging, but Chinese economic influence in each and every country can be measured easily using readily available trade and investment data. This paper finds a significant correlation between the economic influence of China and United Front work. It also highlights particular economic influence indicators that can predict particular United Front influence indicators. The paper thus provides a way to systematically predict United Front influence in many countries by analyzing commodity trade and Chinese investment data. More research can be done, however, in broadening the scope of this project and in improving data quality.

The objective of this thesis was to increase our understanding of two-phase geophysical flows (e.g. debris flows) by providing velocity profiles in idealized laboratory avalanches. To that end, we developed a new experimental platform made up of an inclined flume coupled to an imaging system to measure velocity in granular suspension. The inclined flume was 3.5 m long and 10 cm wide and could be inclined from 0 to 35°. A reservoir with the capacity for 10 l of fluid was located in the upper part of the flume and closed with a pneumatic controlled gate. Velocity profiles were obtained using Particle Image Velocimetry (PIV) and index-of-refraction matching of the solid and liquid phases. We used transparent PMMA beads with mean diameters of 200 µm and the interstitial fluid was composed of a mixture of three fluids. The interstitial fluid was adapted in order to match the refraction index and the density of the solid phase. Using pulsed laser and a high speed camera we were able to measure velocity profiles at frequencies up to 1000 Hz with very good precision. Two additional cameras tracked the front position along the flume with a frequency of 30 Hz and a spatial resolution of 1 mm. Prior to acquiring data on the granular suspension, we tested our system on Newtonian fluids. Eight flow configurations were selected with different fluids (glycerol and triton X100), different slopes and different released masses. Velocity profiles were found to be parabolic far from the front as well as very close to the contact line. However, near the front, quantitative theoretical predictions given by lubrication theory diverged from experimental results. Velocities were significantly overestimated (∼ 400%) by the theory at low Reynolds numbers (Re < 2) and slightly underestimated (∼ 10%) at high Reynolds numbers (Re > 8). Very good agreement with theory far from the front indicated that the accuracy of the setup was good (reliable calibration procedure and image processing methods). Experiments on granular suspensions revealed a variety of behaviors depending on the particle concentration, the slope and the mass released. At solid fractions up to 45%, suspensions behaved as homogeneous viscous fluids. For the duration of the experiment, it was not possible to detect any inhomogeneity due to migration or sedimentation. In the range of shear rate tested and with the precision allowed by the setup no shear thickening or shear thinning was observed since velocity profiles remained perfectly Newtonian. For slightly more concentrated suspensions (up to 55%), we found that the flow dynamics at the bulk scale could still be described using a viscous theory. However, at the local scale, migration gave rise to concentration inhomogeneities producing a blunted velocity profile. The shape of the blunted profile was well described by the Mills and Snabre migration model coupled to a Krieger-Dougherty effective viscosity. However, magnitudes of the velocities were largely overestimated, most probably because we fitted the effective viscosity at higher shear rates. Above 55%, small released masses with high solid fractions stopped after a finite time and separation between fluid and solid phases occurred. The solid frame stayed at rest while the fluid seeped through the granular media eroding the front. For larger released masses, we observed successions of different regimes: After an inertial regime and a pseudo-viscous regime, the flow slowed down, corresponding to a new regime in which the shearing was localized in a thin layer at bottom and there was no shearing of the front. At the same time, we observed that the free surface deformed and became wavy. Fractures developed on the top of the flow and, if they grew sufficiently, modified the local velocity field substantially. Finally, at longer time (≥ 4 min) an intermittent motion (stick-slip) was observed with phases during which the suspension was flowing in a quasi-steady regime and phases during which the suspension was at a halt.

First Page

Unmanned tractors, even though it uses global positioning system (GPS) technology to identify the working path, still require an ability to recognize the environment in front of it in order to avoid obstacles thatmay exist. A device that can be used to recognize the environment in front of the tractor and avoid obstacles that may exist, is the camera. However, images captured by the camera need to be processed to detect possible obstacles at the front of the tractor. This study aimed to develop image processing algorithms to detect the possible presence of obstacles on the path to be traversed by an unmanned tractor, and directed the tractor to a safe path by giving the new coordinates when there are obstacles in front of it. Several mage processing techniques such as edge detection, opening and closing, marking free area, and the determination of the coordinates were used for the purpose of directing the path in front of the tractor when there are obstacles that must be avoided. Keywords: image processing, obstacles, unmanned tractor, algorithms Diterima: 19 April 2010; Disetujui: 18 Oktober 2010