Control of crystallization by polymer additives

Understanding how crystallization processes are controlled by polymer additives is relevant for a vastly diverse number of fields, for example in biomineralization, where the morphology of minerals is controlled by proteins or in scale inhibition strategies in industrial plants, in which macromolecules are added to prevent the precipitation of minerals. While numerous investigations have focused on elucidating additive-controlled crystallization, a detailed understanding of the underlying mechanisms is still desired. Herein, based on calcium carbonate as a mineral system, a comprehensive study on the manifold effects of selected polycarboxylate additives on the distinct species along the crystallization pathway is presented. Poly(glutamic acid) and poly(aspartic acid) are chosen as additives, as these polyaminoacids resemble biomineralization-associated peptides, as well as poly(acrylic acid), a commercially used scale inhibitor. Using potentiometric titrations, it is shown that even the basic interaction of polycarboxylates with calcium ions is more complex than commonly assumed. Quantitative determination of the Langmuir parameters of the binding process reveals that higher order effects and contributions arising from the whole polymer chain play a significant role, while the chemistry of the monomer unit constituting the polymer plays a subordinate role. The results put a question mark on whether the binding processes can be accurately described using solely the Langmuir binding model that assumes non-interacting binding sites. The investigation of the following stages of the crystallization pathway reveals that the polymer additives show the largest effect in the stabilization of liquid-like mineral precursors. A key step of this inhibition is the additive-driven binding of bicarbonates. Quantitative evaluation of ion association in the prenucleation regime reveals that more than 20% of bicarbonate species are bound in mineral precursors at pH 9.8, which can also be detected in isolated solid amorphous intermediates. Surprisingly, the protons introduced by bicarbonates are highly mobile, causing the formation of amorphous mineral ion conductors, which opens up possibilities for novel applications of mineral materials. The importance of liquid-like precursors for the mineral formation pathway is still highly debated in the community, and they are often ignored in the explanation of crystal formation. Using a refined gas diffusion method, it is demonstrated that liquid-like precursors show sufficient kinetic stability to be detected, both in presence of polymers and in additive-free systems. Observing the time dependent formation and transformation of the precursors shows that they play an important role in the early stages of crystallization and must be generally considered for the interpretation of gas diffusion experiments. Regarding the technological application of liquid-like minerals, a new and easily scalable synthesis method is presented, which solves existing limitations of the available synthesis methods. The “scalable controlled synthesis and utilization of liquid-like precursors for technological applications” (SCULPT) method effectively allows the isolation of the precursor on a gram scale and to access to the full potential of these mineral precursors for material synthesis. Implementing the gained insights into the current picture of nonclassical mineral formation, which was subject of many advancements in recent years, an updated view on additive-controlled mineralization is presented. The discoveries presented in this work are beneficial for the scientific and industrially-related communities far beyond the field of nucleation and crystallization mechanisms, such as materials chemistry, and improve the understanding of the mechanisms underlying biomineralization and mineral formation in general

Learning Behavior Models for Interpreting and Predicting Traffic Situations

In this thesis, we present Bayesian state estimation and machine learning methods for predicting traffic situations. The cognitive ability to assess situations and behaviors of traffic participants, and to anticipate possible developments is an essential requirement for several applications in the traffic domain, especially for self-driving cars. We present a method for learning behavior models from unlabeled traffic observations and develop improved learning methods for decision trees

Recruitment practices influencing enrollment of four-year undergraduate students who specialize in graphic arts

The purpose of this study was to identify recruitment practices and other selected factors that could be utilized to increase undergraduate student enrollment in three types of graphic arts programs: education, technology, and management. The study involved graphic arts faculty and students in 76 colleges and universities in the United States. Six instruments were used to secure data. These included two preliminary devices, three faculty opinionnaires, and one student opinionnaire. Each faculty opinionnaire focused on one of three graphic arts programs and contained a list of 32 recruitment practices. The student opinionnaire consisted of a similar list, an additional listing of 28 other influential factors, and demographic information. Faculty and students were asked to indicate those recruitment practices they used and experienced and then to rate them for effectiveness. Students also identified and rated other influential factors in their program selection process. Instruments were received from 75 of 76 faculty members each representing one institution with 23 in education, 25 in technology, and 27 in management programs. Opinionnaires were received from 901 students with 112 in education, 244 in technology, and 545 in management programs. Descriptive statistical methods and content analysis were used in studying the data relating to frequencies, percents, means and ranks. The t-test for independent means (two-tailed, p = .05) was used to determine the differences in the perceived effectiveness between faculty and students of 32 recruitment practices used in attracting students into graphic arts. Male students dominate the enrollments in the three graphic arts programs. They represented 79% of education, 55% of technology, and 60% of management students. The education students were the oldest with an average age of 23.6 years and a greater percentage of them were reared in smaller communities than technology and management students. Among the three groups, 57% to 67% of graphic arts students decided to specialize in their programs while in college/university. Seventy-seven percent of education students indicated they most likely would teach after completing baccalaureate degrees. Enrollment in graphic arts education courses has been declining, but it has been stable in technology and increasing in management programs. Significant differences were found between faculty and students concerning their perceptions of effectiveness with recruitment practices.Three differences were found both in education and technology and four in management areas. When combining the recruitment practices experienced by the students and those perceived as being effective by students the following top three practices were found effective: offering related general education courses through the graphic arts or industrial education/technology department, indicating to non-majors in the institution the advantages of graphic arts careers, and recruitment packets distributed to those expressing interest. The most effective influential factor besides direct recruitment in attracting students into graphic arts was their personal interests and hobbies. Work experiences were also a top influence

Employment needs of the graphic arts industry in Iowa as perceived by Iowa graphic arts manufacturers and Iowa graphic arts educators

Purposes. The two purposes of the research were to determine if differences existed between the perceptions of Iowa graphic arts manufacturers and Iowa graphic arts educators regarding current (1988) and future (1993) employment needs for skilled production workers and management and sales personnel, and to identify selected characteristics of manufacturers and educators in attempting to meet employment needs. The following supporting objectives were established: (1) To identify areas of agreement and disagreement as perceived by manufacturers and educators concerning: (a) current and future demand for skilled workers, management, and sales personnel, (b) comparison of those current and future demands, and (c) selected issues regarding employment and other factors. (2) To identify the anticipated number of skilled workers, management personnel, and sales personnel needed in the industry as perceived by the manufacturers considering current demand and probable future demand. (3) To identify selected characteristics of manufacturing companies plus educators and their programs. Methods and analyses. Usable opinionnaires were returned from 181 manufacturers (72%) and 40 educators (87%). The three parts of objective one were tested against the null hypotheses using appropriate t-tests at the.05 significance level. The other two objectives were addressed in question form

Darstellung intramyokardialer Temperaturphänomene während der Radiofrequenz-Katheterablation mittels Thermografie im In-vitro-Modell

Ziel der Untersuchung war die Entwicklung eines In-vitro-Modells zur Evaluierung von Ablationskathetern für die Therapie von Herzrhythmusstörungen, die durch thermische Prozesse eine Modifikation des Myokards bewirken. Hierzu wurde erstmals die Technik der modernen Thermografie angewandt. Diese ermöglicht während der Ablation eine Online-Registrierung von Temperaturprozessen an jedem beliebigen Ort im Myokardquerschnitt mit einer Auflösung von 0,1mm und einer Messgenauigkeit von 0,1°C. Ebenfalls lassen sich die Temperaturprozesse zweidimensional in Falschfarbenbildern darstellen. Durch die kontaktfreie Technik der Thermografie konnte auf intramyokardiale Temperatursonden verzichtet werden, welche in ihrer Positionierung meist schwierig standardisierbar sind und selbst zu störenden Effekten und somit Messfehlern während der Stromabgabe führen können. Als optisches Medium zwischen Myokard und Thermografiekamera wurde Saphirglas mit einer Transmission von 92% verwendet. Das Modell konnte mit Hilfe eines Schwarzen Strahlers in seiner Messgenauigkeit und Aussagekraft validiert werden. Im zweiten Teil der Studie wurden drei verschiedene Ablationskatheter (4mm-, 8mm- und eine gekühlte 4mm-Elektrodenspitze) mit dem vorgestellten Versuchsmodell auf ihre thermischen Eigenschaften während der Ablation in n=105 Messreihen bei unterschiedlichen Ablationsleistungen untersucht. Neben den bereits in der Literatur beschriebenen Temperaturphänomenen war es mit dem vorgestellten Versuchsmodell erstmals möglich Prozesse nachzuweisen, welche bisher nur in mathematisch-numerischen Modellen postuliert werden konnten (Bsp. Temperaturverteilung im Perfusionsstrom an der Myokardoberfläche). Ebenfalls zeigte sich eine hohe Korrelation zwischen den Temperaturverteilungsmustern und den resultierenden Nekrosezonen im Myokard, was die rein thermische Alteration des Myokards während der Ablation erneut beweisen konnte. Prinzipiell kann mit dem vorgestellten In-vitro-Modell jedes Ablationssystem auf seine Eigenschaften untersucht werden, welches eine thermische Veränderung des Ablationssubstrats bewirkt. Durch eine geringe Kostenintensität und eine gute Reproduzierbarkeit könnte dieses Modell außerdem zu einer Einsparung von Tierversuchen führen

Reproduzierbarkeit duplexsonographischer Strömungsparameter am Beispiel der Arteria mesenterica superior und des Truncus coeliacus

Die Duplexsonographie abdomineller Gefäße mit der Bestimmung von Strömungsparametern gehört zu den etablierten sonographischen Untersuchungstechniken. Veränderungen dieser Parameter werden im klinischen Alltag zur Diagnostik und Verlaufskontrolle bei verschiedenen Krankheitsbildern herangezogen. Dabei wird vorausgesetzt, dass diese Messungen valide und reproduzierbar sind. In der vorliegenden Arbeit wurde die Messgenauigkeit des beschriebenen Verfahrens untersucht. Insgesamt wurden duplexsonographisch Messungen an 39 weiblichen und 42 männlichen gesunden Probanden durchgeführt. An der Arteria mesenterica superior und dem Truncus coeliacus wurden folgende Parameter gemessen: Flussrate, Resistant-Index und Pulsatility-Index. Jeder dieser drei Parameter wurde dreimal unmittelbar in Folge gemessen und daraus der Mittelwert gebildet. Diese Mittelwertsbestimmung ermöglicht die Bestimmung des Messfehlers (Standardfehler des Mittelwertes). Um die Stabilität dieser Parameter zu überprüfen, wurden die Messwerte an jedem Probanden unter identischen Bedingungen an zwei aufeinanderfolgenden Tagen erfasst. Als Ergebnis zeigte sich bei den Messwerten aller drei Parameter ein sehr geringer Messfehler (relativer Fehler: 3,5-4,3%) und hohe Korrelationen der Messwerte an beiden aufeinanderfolgenden Tagen (r=0,66-0,86). Der Schallwinkel hatte in dem Bereich, in dem die Messungen erfolgten (25-70°) keinen signifikanten Einfluss auf die Höhe des Messfehlers. Der hier ermittelte Messfehler ist deutlich geringer als die in der Literatur erwähnten Unterschiede zwischen den Messwerten verschiedener Patientengruppen und gesunder Personen. Dies bedeutet, dass eine valide Erfassung der Flussparameter mittels Duplexsonographie bei spezifischen Krankheitsbildern möglich ist. Die hohe Korrelation der Messwerte an verschiedenen Untersuchungstagen belegt außerdem, dass sich duplexsonographische Messungen auch zu Verlaufskontrollen heranziehen lassen

Konzeption und Realisierung einer Mobile Crowdsensing Anwendung zur Unterstützung von Schwangeren

In der heutigen Zeit gehören Smartphones und andere mobile Geräte in großen Teilen der Welt zu den Gegenständen, die alltäglich benutzt werden. Sie werden beruflich und privat zur weltweiten Kommunikation verwendet, sind aber durch die unzähligen verfügbaren mobilen Anwendungen auch zu vielen anderen Zwecken nutzbar. Diese Arbeit beschreibt eine Anwendung die Frauen während ihrer Schwangerschaft begleiten und unterstützen soll. Hierfür wird auf den KINDEX Fragebogen zurückgegriffen, der es ermöglicht, psychosoziale Risikofaktoren für Mutter und Kind zu identifizieren. In dieser Arbeit wird beschrieben, wie der papierbasierte KINDEX Fragebogen als Android App umgesetzt werden kann und dabei verschiedene Nutzergruppen berücksichtigt werden. Dadurch wird es möglich, dass Schwangere, orts- und zeitunabhängig, ein qualifiziertes Feedback und Verhaltensempfehlungen von einem begleitenden Arzt oder einer begleitenden Ärztin erhalten, um ihre Schwangerschaft positiv zu beeinflussen. Die Nutzung einer solchen Anwendung kann zu einem effizienteren Ressourceneinsatz bei der Betreuung von Schwangeren führen und dadurch die möglichen Stressfaktoren während einer Schwangerschaft reduzieren

Atomistic Simulations of Ferroelectric Lead Zirconate Titanate

Ferroelectric materials are of technological importance for many applications and a thorough understanding of the origins of their high piezoelectric and dielectric properties is needed to optimise materials performance. One of the most widely used ferroelectrics is Pb(Zr1 xTix)O3 (PZT), which shows excellent piezoelectric response near its morphotropic phase boundary (MPB). To study PZT in large scale molecular dynamics (MD) simulations, I have developed a shell model force field that reproduces the details of the phase diagram of the PZT solid solution. The developed force field supports the temperature induced phase transitions from cubic to low symmetry phases over the whole composition range and additionally reproduces the composition driven phase transitions. This force field was subsequently used to study a variety of different effects in PZT. First, the polarisation switching in near morphotropic PZT at different temperatures was investigated, where I report a reduction of the saturation polarisation, accompanied by an exponential increase of the coercive field, as the temperature decreased. The simulations further demonstrated that the switching mechanism is fundamentally different at low temperatures, where it occurs via polarisation rotation, than at high temperatures, where domain nucleation dominates. Second, a set of simulations on near morphotropic PZT showed that the response of the local structure to electric fields highly depends on the local B-cation environment. Furthermore, I find that B-cation clustering largely influences the piezoelectric properties of the material. In a third MD study the electrocaloric effect (ECE) in the PZT compound was calculated, finding that PbTiO3 outperforms other compositions with its giant temperature change of 16 K. Lastly, density functional theory (DFT) calculations were performed to study defects and domain walls in the PZT end member PbTiO3, where we show that the presence of a couple donor-acceptor defect pair stabilises charged head-to-head and tail-to-tail 90 domain walls in PbTiO3