Improvement of Ultraviolet Digital Image Correlation (UV-DIC) at Extreme Temperatures

Extreme temperature has increasingly played an essential role in design and operation of various engineering applications including spacecraft re-entry, hypersonic flight, next-generation nuclear reactors, and hot-fire rocket testing. To protect instruments against the harsh environments, it is preferable to use non-contacting measurements when monitoring the integrity of those mechanical structures. Digital Image Correlation (DIC) is a popular method which uses digital cameras in order to track motion thanks to images acquired before and after deformation. Displacements and strains are plotted over a full-field region which is conducive to identify highly risky zones. At high temperature, objects emit light which interferes with image acquisition. It is known that the emitted light is considerably suppressed when images are taken at very short wavelengths such as ultraviolet (UV). This dissertation will investigate the importance of exposure time, which is a significant factor when determining the camera sensitivity, on the uncertainty of UV-DIC measurements. Through examining the exposure time, this dissertation is intended to give insights for users when performing DIC at high temperature in both pre-testing conditions and on-going testing. In addition, the dissertation will discuss a specific phenomenon of pattern inversion which is occasionally reported in high temperature DIC measurement. Under this phenomenon, due to differences in emissivity of refractory paint and the background material, portions of the object which appear dark at room temperature instead appear bright at high temperature, and vice versa. The dissertation will explain the physical principle behind pattern inversion and introduce alternative solutions to evade the pattern inversion.With the aforementioned contributions, the dissertation is expected to improve the UV-DIC technique intensively and extensively

"The Effect of Child Health on Schooling: Evidence from Rural Vietnam"

We study the relationship between long term child health and human capital. Child health may suffer if a child is inadequately nourished or is exposed to disease early in life and this may affect subsequent accumulation of human capital. We use data from rural Vietnam to examine the impact of child health on delay in starting school and schooling progress taking into account that choices of families affect children’s health and schooling. Our instrument is early life rainfall shocks that have differential effects arising from regional economic diversity. Our estimates indicate that better child health results in meaningfully improved schooling outcomes.child health, z-score, school entry delay, schooling gap, rainfall shocks, Vietnam

Importance of Exposure Time on Digital Image Correlation (DIC) at Extreme Temperatures

Extreme temperatures have increasingly played an important role in engineering applications, including leading edges during hypersonic flight, spacecraft re-entry, and propulsion systems. In order to design for such thermo-mechanical conditions, materials must be characterized using suitable measurement methods. DIC is a popular and versatile method in full-field measurement. In brief, DIC compares images of a sample between its undeformed and deformed state in order to get displacement and strain field maps. Since the images are acquired from digital cameras, it is important to have high contrast images for meaningful correlation. Exposure time is a pivotal camera setting relating to camera sensitivity. Alteration in exposure time results in variation of image contrast, thereby affecting DIC correlation. Also, it is well known that at extreme temperatures, materials emit light which can saturate DIC camera sensors, but the light can be mitigated using optical bandpass filters. In previous work, many have shown that blue bandpass filters can effectively extend the temperature range of DIC, and our lab has shown that ultraviolet (UV) filters can extend the range further. In this thesis, four different temperatures: room temperature, 1300°C, 1450°C, and 1600°C were tested by rigid-motion experiments. At each temperature level, UV images were acquired in order to examine the variation of DIC error over the whole range of exposure time. UV images were acquired at exposure times ranging from 500μs to 61,000μs, which are the minimum and maximum possible values for the cameras used in this thesis. The results showed that there were higher errors of UV-DIC at extremely dark or bright exposure times where as errors were generally insignificant at intermediate exposure times. In order to perform meaningful DIC up to 1600oC, the exposure time for the camera used in this thesis is suggested to be set between 10,000μs and 40,000μs

The Epidemiology and Control of Human Influenza in Vietnam

Understanding the epidemiology of human influenza in Viet Nam is important for developing local policies and also for understanding the dynamics of influenza in tropical and subtropical southeast Asia. I have analysed an 18 year time-series of influenza-like-illness (ILI) surveillance data, and assessed the relationship of this time-series with climate variables and with sentinel influenza virus surveillance data. I also conducted a study of influenza A/H1N1 transmission within households. ILI notifications in Viet Nam show a latitudinal gradient, with seasonality in the north but no seasonal pattern observed in low lying areas of central and southern Viet Nam. Seasonality is however observed in the elevated provinces of central Viet Nam, suggesting that the seasonal patterns are driven by climate. Principal component analysis finds that temperature and absolute humidity (AH) are positively correlated and together explain around 59% of total climatic variance, and that there is a strong latitudinal gradient in these variables. Regression tree analysis shows that provinces with strong seasonality of AH have strong ILI seasonality. Although virological surveillance data are limited, increases in ILI notifications are associated with an increase in the proportion of upper respiratory tract swabs that are influenza positive. In a prospective study of H1N1/2009 transmission in a household-based cohort, 11 of 59 household contacts were infected, giving a household secondary infection risk of 18.6% (95%CI 10.7-30.4%), but 5 (45%) did not develop symptoms. Virus genetic sequencing indicated that 10 of the 11 secondary cases (91%) were probably infected within the household rather than from the community. This research provides new insights into the seasonality and climatic determinants of ILI and influenza epidemiology in Viet Nam, and on the transmission of influenza within households. The findings are valuable for national influenza control policies and also add to the current state of knowledge of influenza epidemiology

Are all cognitive items equally prone to position effects? Exploring the relationships among item features and position effects

One type of context effect is a position effect, which implies parameters of an item are influenced by the position of the item on the test. Researchers often discuss two types of position effects: negative position effects and positive position effects (e.g., Albano, 2013; Debeer & Janssen, 2013). Items exhibiting negative position effects become harder when placed later on the test, whereas items exhibiting positive position effects become easier when placed later on the test. Researchers have primarily examined the underlying causes of position effects through an item or person perspective (e.g., Bulut, 2015; Kingston & Dorans, 1984; Qian, 2014). Researchers who adopted an examinee perspective on position effects exclusively studied the relationships among person variables and position effects. Researchers who adopted an item perspective on position effects exclusively studied the relationships among item variables and position effects. These two perspectives are limiting because they do not encourage researchers to consider the potential interactions among person variables, item variables, and position effects. In this dissertation, I examined the underlying causes of position effects through an integrated perspective, where I studied the relationships among person variables, item variables, and position effects simultaneously. I conducted a true experiment in which I administered items from two low-stakes assessments in different order to two groups of examinees, examined the presence of position effects, and evaluated the degree to which position effects were moderated by different item (item length, number of response options, mental taxation, and graphic) and person variables (effort, change in effort, and gender). I modeled position effects and their relationships with item and person variables under the generalized linear mixed modeling (GLMM) framework. On both assessments, I found items exhibited significant negative linear position effects on both assessments, with the magnitude of the position effects varying from item to item. Items became harder when placed later on the assessments but the extent to which they became harder differed slightly across items. Additionally, I found the position effects to be moderated by item difficulty and item length but not number of response options, mental taxation, or graphic. Easier and longer items were more prone to position effects than harder and shorter items; however, items varying in mental taxation, items containing a graphic, and items varying in response options were similarly prone to position effects. More so, I found examinee effort levels, change in effort patterns, and genders did not moderate the relationships among position effects and item features. Based on these findings, testing practitioners should be cautious about administering long or easy items in different order across forms and/or administrations

Ageing and inter-generational relationships in Vietnam

This thesis investigates the intergenerational relationships of people aged 60 and over in the context of rapid population ageing and social change in Vietnam. The country is experiencing significant economic development and rising incomes while maintaining strongly embedded Confucian values and norms on family relationships, including respect for older people and filial piety. These relationships have been affected by the social disruptions of war, and continue to change with modernisation, urbanisation and other social processes that have contributed to modifying traditional norms and values for intergenerational relationships. Changing forms of the family, notable declines in multigenerational households and the rise of the modified extended family have been extensive over recent decades. This thesis aims to examine the variations and changes in living arrangements and intergenerational support exchange, social relationships (association, affection and consensus) and the life satisfaction of older people. The thesis applies concepts in sociology and multidisciplinary gerontology to a comprehensive set of secondary data that inform different aspects of the thesis topic. These include the Vietnam National Ageing Survey 2011 (VNAS 2011) (n = 2,789), the Vietnam Family Survey 2006 (VFS 2006) (n = 13,689), the WHO-SAGE INDEPTH survey 2006–2007 (WSI 2007) (n = 5,030) and the Regional Ageing Survey 1996–1997 (RAS 1996 – 1997) (n = 1,770). VNAS 2011 was used as the primary data source for the thesis as it was the first nation-wide survey on older people in Vietnam. To examine the living arrangements of older people, VNAS 2011 and RAS 1996–1997 have been analysed to investigate determinants and consequences of living arrangements. A majority of older people were found to be living in multi-generational households in 2011 (45%), but the proportion had declined from 56% in 1996–1997. Conversely, the proportions living alone or living only with a spouse have been rising. These findings reflect declining family size along with growing ‘independence’ among older people as they gain more economic resources and better health. No longer married older people are seen more in multi-generational households, living only with children or living alone than those who are married. Older people living alone or only with a spouse were found more in rural than urban areas. Multi-generational households were reported more in cities, which may be because of housing constraints in these areas. Changes in cultural preferences for living arrangements have been enabled by rising resources of the older and middle generations. The investigation provides support for an intergenerational exchange interpretation as a strong association was found between older people’s resources and vulnerabilities and support exchange with their children. As per traditional patrilineal norms, eldest adult sons were expected to continue living in their ageing parents’ households after marriage while they and their wife provide financial and practical support. Older people who have more resources were found to receive more financial support, but they receive less assistance in care and housework from adult children than older people who have fewer resources. Older people who have more resources also provided more assistance to adult children by doing housework and providing grandparenting, especially among those who live in multigenerational households. Social relationships between generations were reported to be changing rather than weakening. Adult children, regardless of their gender, were reported to pay more direct visits to older parents when they live nearby. When they live far apart, the distance was overcome by remittances and telephone communication as well as occasional visits. Daughters were found to be more frequently in their contact with parents than sons when living in separate households. The findings suggest a gender-basis for emotional relationships between generations within families. This thesis found that life satisfaction in later life is best predicted by older people’s health, economic status and living conditions as well as the social relationships among generations. The thesis also provides evidence on the ongoing importance of affectual solidarity between generations and the importance to older people’s life satisfaction of feeling respected by younger generations and participating in making important decisions in the family. This study is one of the first comprehensive studies of intergenerational relations in Vietnam. It suggests the value of an intergenerational approach for policy development towards older people and family relationships as well as the value of an age-friendly environment for older people, particularly for those who are vulnerable. Caution is required in applying the research findings to future generations of older people, who would have had different life experiences

Characterization of a home-built low temperature scanning probe microscopy system

The continuing advancement of technology is the driving force behind science and fundamental research. Scanning probe instruments still have a major impact in nanoscience and technology, because they provide a link between the macroscopic world and the atomic scale. The key to a reliable performance of experiments at the nanometer scale is the instrumentation, that allows probe positioning ranging from micrometers to Ångstroms with sub atomic precisions. A new type of scanning probe microscopy (SPM) system operating in ultra high vacuum (UHV) and at liquid Helium (LHe) temperature was developed. This offers the advantages that even reactive surfaces remain clean over time periods of several days, permitting long time experiments. Moreover, these experiments this low temperature scanning probe microscopy (LTSPM) system is the implementation of a focussing Fabry Perot interferometer (fFPi) that allows the following features: - Small amplitude operations and stiff cantilevers require sensors with high deflection sensitivity. With the fFPi in this low temperature SPM system, a deflection sensitivity of 4fm/ sqrt(Hz) at 1MHz can be obtained. - Wide detection bandwidth (DC-10MHz) enables the operation of higher flexural oscillation modes as well as the torsional modes of the cantilever. - A laser spot size of 3µm allows the use of ultra small cantilevers with the dimensions 1/10 of conventional cantilevers. - Photothermal excitation of cantilevers avoids undesirable mechanical vibrations near the cantilever resonance frequency. - Simultaneous flexural and torsional force detection provides quantitative studies of frictions and thus, atom manipulations by atomic force microscopy (AFM). - The combination of both types of microscopes (simultaneous AFM/STM) reveals more information than a scanning tunneling microscopy (STM) or AFM alone. A series of measurements on Si(111)7x7, herringbone superstructure of Au(111) and highly oriented pyrolytic graphite (HOPG) provides information regarding imaging performance of the system. Among these performance tests are atomically resolved scans at three different operating temperatures in STM mode. In non-contact atomic force microscopy (nc-AFM) mode, imaging was performed with the cantilever driven at the fundamental and 2nd oscillation mode. Additional measurements were performed with the fFPi in order to quantify the impact of the laser cooling effects (radiation pressure and photothermal effects) on the oscillating cantilever at three different operating temperatures. The aim of this work is the development, implementation and characterization of a new low temperature scanning probe microscope with an ultra sensitive and high bandwidth fFPi deflection sensor, suitable for nc-AFM operations with small, simultaneous flexural and torsional cantilever oscillation modes. Furthermore, expected upgrades will allow simultaneous nc-AFM/STM operations. Keywords: low temperature home-built simultaneous STM/ nc-AFM, tip-sample gap stability, PLL and self-excitation, highly oriented pyrolytic graphite (HOPG), reconstructed Si(111)7x7, herringbone superstructure, focussing Fabry-Perot interferometer, cantilever cooling, radiation pressure and photothermal effects. Der kontinuierliche, technologische Fortschritt ist die treibende Kraft hinter Wissenschaft und Grundlagenforschung. Rasterkraft und -tunnel Instrumente haben immer noch einen bedeutenden Einfluss auf die Nanotechnologie und -wissenschaft, weil sie eine Verbindung zwischen der makroskopischen Welt und den atomaren Massstäben darstellen. Der Schlüssel für eine zuverlässige Ausführung von Experimenten mit Nanometer Massstäben ist die Instrumentierung, die eine Spitzenpositionierung von Mikrometer bis Ångstroms mit subatomarer Präzision erlaubt. Ein neuartiges Rasterspitzen Mikroskop (SPM) System wurde entwickelt, das im Ultra Hoch Vakuum (UHV) und bei flüssig Helium Temperaturen arbeitet. Dies bietet Vorteile weil sogar reaktive Oberflächen über eine Dauer von einigen Tagen sauber bleiben, was eine längere Experimentierphase zulässt. Zusätzlich zeigen diese Experimente bei tiefen Temperaturen weitere Vorteile wie kleine Driftwerte und tiefe Piezo Kriechraten. Der Ansatz bei diesem Tieftemperatur Rasterspitzen Mikroskop System ist die Implementierung eines fokussierenden Fabry Perot Interferometers das die folgenden Eigenschaften vorweist: - Der Betrieb bei kleinen Amplituden und mit steifen Cantilever setzt Sensoren mit einer hohen Ablenkempfindlichkeit voraus. Mit diesem fokussierenden Fabry Perot Interferometer (fFPi) kann eine Ablenkempfindlichkeit von 4fm/ sqrt(Hz) bei 1MHz erreicht werden. - Detektion mit einer grossen Bandbreite (DC-10MHz) erlauben einen Betrieb von Cantilever mit flexuralen und torsionalen Oszillation Modi. - Ein Laser mit einem Brennpunkt von 3µm lässt einen Betrieb mit einem ultra kleinen Cantilever zu, der 1/10 so gross ist wie ein konventioneller Cantilever. - Photothermische Anregung eines Cantilevers vermeidet unerwünschte mechanische Vibrationen rund um die Resonanzfrequenz. - Gleichzeitige flexural und torsional Kraftdetektion erlauben quantitative Untersuchungen von Reibungen und daher atomare Manipulationen mit Rasterkraft Mikroskopie (AFM). - Die Kombination und simultanen Betrieb von beiden Rasterspitzen Mikroskopen (AFM/STM) zeigen mehr Information als ein Raster Tunnel Mikroskop (STM) alleine. Eine Serie von Messungen mit Si(111)7x7, Herringbone Superstrukturen auf Au(111) und Highly Oriented Pyrolytic Graphite (HOPG) geben Information bezüglich der Leistungen des Systems preis. Einige dieser Leistungstests sind atomar aufgelöste Abbildungen bei drei unterschiedlichen Betriebstemperaturen im STM Betriebsart. Im nicht-Kontakt AFM (nc-AFM) Betriebsart, Abbildungen sind ausgeführt worden auf der Grundschwingung und der zweiten Oberschwingung. Zusätzliche Messungen wurden mit dem fFPi ausgeführt um den Einfluss der Laserkühlung auf den oszillierenden Cantilever bei drei unterschiedlichen Betriebstemperaturen zu quantifizieren. Das Ziel dieser Arbeit ist die Entwicklung, Implementation und Charakterisierung eines neuen Tieftemperatur Rasterspitzen Mikroskops mit einem ultra-empfindlichen und Breitband fokussierenden Fabry Perot Interferometer Ablenk Sensor, geeignet für den nicht-Kontakt AFM Betrieb mit kleinen, simultanen flexural und torsional Cantilever Schwingungsmodi. Naheliegende Erweiterungen des Systems gewährleisten einen simultan nc-AFM/STM Betrieb. Schlüsselwörter: Tieftemperatur simultan nc-AFM/STM aus Eigenbau, Spitzen-Probe Spalt Stabilität, PLL und Eigenanregungsbetrieb, Highly Oriented Pyrolytic Graphite (HOPG), reconstrukturiertes Si(111)7x7, Herringbone Superstruktur, fokussierenden Fabry Perot Interferometer, Cantilever Kühlung, Strahlendruck und photothermische Effekte

On Bakhvalov-type meshes for a linear convection-diffusion problem in 2D

For singularly perturbed two-dimensional linear convection-diffusion problems, although optimal error estimates of an upwind finite difference scheme on Bakhvalov-type meshes are widely known, the analysis remains unanswered (Roos and Stynes in Comput. Meth. Appl. Math. 15 (2015), 531--550). In this short communication, by means of a new truncation error and barrier function based analysis, we address this open question for a generalization of Bakhvalov-type meshes in the sense of Boglaev and Kopteva. We prove that the upwind scheme on these mesh modifications is optimal first-order convergence, uniformly with respect to the perturbation parameter, in the discrete maximum norm. Furthermore, we derive a sufficient condition on the transition point choices to guarantee that our modified meshes can preserve the favorable properties of the original Bakhvalov mesh

Adaptive backstepping control for ship nonlinear active fin system based on disturbance observer and neural network

Adaptive backstepping control based on disturbance observer and neural network for ship nonlinear active fin system is proposed. One disturbance observer is given to observe the disturbances of the system, by this way, the response time is shorten and the negative impact of disturbance and uncertain elements of the system is reduced. In addition, radial basic function neural network (RBFNN) is proposed to approach the unknown elements in the ship nonlinear active fin system, therefor the system can obtain good roll reduction effectiveness and overcome the uncertainties of the model, the designed controller can maintain the ship roll angle at desired value. Finally, the simulation results are given for a supply vessel to verify the successfulness of the proposed controller