490 research outputs found
On-chip Microdialysis System with Flow-through Glucose Sensing Capabilities
No full textThe published version of this article is available at http://www.journalofdst.org/May2007/pdf/VOL-1-3-ORG3-HSIEH.pd
Non-Invasive Glucose Monitoring: A Novel Approach
No full textBackground: The main concern in noninvasive (NI) glucose measurement is achieving high accuracy readings, although no blood (or other fluid) is involved in the process. Using methods based on different physical properties of a measured object can ensure the independence of each of the readings and therefore improve the validity of the end result. By using a combination of (three) independent technologies—ultrasonic, electromagnetic, and thermal—GlucoTrack™ presents a unique approach for a real-time, truly NI blood glucose spot measurement. Methods: Clinical trials were performed in two stages. Stage 1 was an initial method validation and performance verification of the device. In this stage, 50 type 1 and 2 diabetic patients, as well as healthy subjects, were evaluated with GlucoTrack against Ascensia Elite® (Bayer). In the second stage, 85 additional diabetic subjects were evaluated in half and full daytime sessions using a GlucoTrack comparison with HemoCue® (Glucose 201+). Results: A total of 135 subjects were tested during the trial period, producing 793 data pairs. Using Clarke error grid analysis, 92% of the readings fell in the clinically acceptable zones A and B, with 50% in the A zone. Mean and median relative absolute differences were 29.9 and 19.9%, respectively. Conclusions: Integrating several modalities for NI assessment of glucose level enables more accurate readings, while a possible aberration in one modality is bypassed by the others. The present generation of GlucoTrack gives promising results; however, further improvement of the accuracy of the device is needed.The published version of this article is available at http://www.journalofdst.org/amember/plugins/protect/new_rewrite/login.php?v=-any&url=/March2009/Articles/VOL-3-2-SYM4-HARMAN-BOEHM.pdf%3
Hieracium murorum subsp. cophogonium Bornm. & Zahn
No full textHieracium murorum subsp. cophogonium Bornm. & Zahn in Zahn (1925: 161). Ind. loc.: “Frontière bâloise-badoise: Hohr[sic!] M i hr près Zell (A. Krafft). Trouvé aussi par Bornmüller à Tr i bsdorf, près Weimar, dans la Thuringe.” Lectotype (designated here by Gottschlich): — GERMANY. Baden-Wuerttemberg: Hohe M i hr, 11 June 1923, A. Krafft (BREG!). — Remaining syntype: GERMANY. Thuringia: Weimar, Tr i bsdorf, westl. bei d. Bahnbrücke, 8 June 1923, J. Bornmüller (B barcode B 10 0460350!). Remarks: —Although Bornmüller is co-author of the taxon, in the protologue the collection of Krafft is cited first and is here selected as lectotype.Published as part of Vogt, Robert & Gottschlich, Günter, 2023, Type material in the Hieracium (Compositae: Cichorieae) collection of Joseph Bornmüller, pp. 81-126 in Phytotaxa 613 (2) on page 102, DOI: 10.11646/phytotaxa.613.2.1, http://zenodo.org/record/834553
European enlargement and the economic crisis : impact and lasting effects
No full textThis working paper by Rebecca Zahn looks at the effects of the economic crisis on the enlarged European Union and the European Social Model. Starting from an analysis of the well-known Viking and Laval decisions of the European Court of Justice from 2007 and 2008, the author of the report sees increasing tensions between EU member states over “social dumping”, austerity packages and growing inequality between workers. This development results in citizens questioning the benefits of further European integration and threatens the very existence of the European social model
Effiziente Ansätze zur Modellierung und Charakterisierung der Selbstorganisation von Nanomaterialien
No full textThe design of innovative materials poses an ongoing challenge to researchers around the world. Nowadays, many disciplines are involved in this process: engineering, physics, chemistry, biology, and computer science, amongst others.
Looking back to the beginning of materials research, in the early eighteenth century, chemists started to classify materials according to their origin. They introduced three different kingdoms: vegetables/plants, animals, and minerals. More criteria were applied to further subdivide these classes into a full taxonomy, such as the mode of extraction and preparation, and what it could be applied for.
Apart from the manifold of forms and structures in the inanimate world, in living nature, evolution has created a rich pool of specialized materials. These include functional tissue, serving specific purposes: spider silk is strong but preserves a high elasticity whilst being adhesive to insects; the cornea refracts light whilst being able to bend to focus on objects at varying distances; horn features specific shapes and surfaces, being stiff enough to endure fights in the animal kingdom; bone and teeth are even harder than horn, but nevertheless not too brittle. Besides a very high availability of the resources required for their synthesis, many of these materials feature built-in repair mechanisms.
The appealing properties of biomaterials serve as inspiration for man-made materials. The use of bio-inspired processes and systems for engineering purposes is called biomimetics, or bionics. Naturally, the biological systems have to be well-understood to serve as template for the industry.
The present work aims to establish a new level of understanding of solid materials, their principles of self-organization, along with their intrinsic physicochemical properties. Within chapter 1, a short introduction to the topics and systems under investigation will be given, with references to works published in the respective field by the author. Chapter 2 deals with a novel method of quantitatively and qualitatively analyzing atomistic structures, and applications for rationalizing the evolution of forming crystal nuclei. In chapter 3, we shift to composite materials, and provide insights into two different model systems of high complexity. Chapter 4 describes the modelling of a functionalized ZnO nanoparticle, and methods of analyzing its stabilization in solution. Finally, a summary of the results and gained insights, along with an outlook on future perspectives, is given in chapter 5
Three hundred eighty thousand year long stable isotope and faunal records from the Red Sea : influence of global sea level change on hydrography
No full textStable isotope and faunal records from the central Red Sea show high-amplitude oscillations for the past 380,000 years. Positive δ18O anomalies indicate periods of significant salt buildup during periods of lowered sea level when water mass exchange with the Arabian Sea was reduced due to a reduced geometry of the Bab el Mandeb Strait. Salinities as high as 53‰ and 55‰ are inferred from pteropod and benthic foraminifera δ18O, respectively, for the last glacial maximum. During this period all planktonic foraminifera vanished from this part of the Red Sea. Environmental conditions improved rapidly after 13 ka as salinities decreased due to rising sea level. The foraminiferal fauna started to reappear and was fully reestablished between 9 ka and 8 ka. Spectral analysis of the planktonic δ18O record documents highest variance in the orbital eccentricity, obliquity, and precession bands, indicating a dominant influence of climatically - driven sea level change on environmental conditions in the Red Sea. Variance in the precession band is enhanced compared to the global mean marine climate record (SPECMAP), suggesting an additional influence of the Indian monsoon system on Red Sea climates
Molecular Simulations Study of Silver Precipitation from Aqueous Solution and on Silica Substrate : Control of Shape and Charge via Redox Condition
No full textIn the last decades, nanoparticles became a material of great interest, due to their ap-
plications and properties. One of the possible applications for nanoparticles is for the
creation of self-assembled materials [1, 2, 3]. Nanoparticles can be self-assembled through
chemical reactions [4]. However, in recent years, anisotropic particles have been also used
to produce self-assembled materials. Anisotropic particles are usually made of two or
more materials, those materials differ from each other in physical or mechanical prop-
erties. An example of anisotropic particles is silica nanoparticles covered with a noble
metal (i.e. silver). These silica nanoparticles covered with a metal patch use the metal
cover as a ”glue” to assemble the nanoparticles in complex structures.
In this thesis, the main focus was on the creation of silver patches on silica nanoparticles.
To have a complete understanding of the precipitation process, a smaller study is also
presented on the precipitation in aqueous solution without any substrate.
The formation of silver patches on silica nanoparticles is performed in aqueous solution
through a chemical reaction, which uses a salt (silver nitrate) as a silver source. The silver
is reduced using a reducing agent such as formaldehyde [5, 6]. The understanding of the
precipitation/crystallization process for the formation of the silver patches is crucial to
make the production reliable. This thesis is focused on the understanding of the silver
patch growth process under the effect of different redox potential.
The chemical reaction that is performed to create silver patches contains ammonia. Am-
monia has two roles, to control the pH of the solution and to form silver-ammonia clusters.
The variation of pH in the solutions affects the silver growth. The silver patches have a
cup-like shape (i.e. uniform cover of the silica surface) when the pH of the solution is
around 11. Reducing the pH, until 9.5, the patches gradually grow more in a dendritic
IVV
way [5]. In the molecular dynamics simulations it is not possible to reproduce directly all
the effects of the pH variation. To simulate the pH effect on silver patch grow the redox
potential was used.
Previous theoretical studies regarding those types of systems are limited and none of
them addressed the formation of patches using atomistic methods. Therefore, this work
focused on the understanding of which factors influence the patch shape and in which
proportion.
Classical molecular dynamics methods can’t predict the shape of a metal cluster under
the effect of different redox potentials. In previous studies by Milek et al. [7, 8] it was
proven that the use of the charge equilibrium method (QEq) and the embedded atom
method (EAM) can simulate both the variation of shape in the metal cluster due to
charge variation and the associated redox potential. The very same approach was used
in the simulations performed in this work.
In the experimental set up, there are several species. All the species have a concentration
in the order of 1-10 mM. The above-described condition can’t be simulated with molecu-
lar dynamics methods. The problem was approached using limiting cases and increasing
the level of complexity.
In the heterogeneous crystallization processes the surface plays a major role, it is, thus,
extremely important to have a model that describes the silica substrate accurately. The
first part of this work was dedicated to the development of the silica surface. Particular
attention was given in the modeling of the pH effect on the silica. The model and the
parameters created to describe the silica surface work in a pH range between 5 and 12.
Another aspect of high importance in the heterogeneous crystallization is the contribu-
tion of the diffusion of the ions on the surface. The parameters created to simulate the
silica surface proved to represent the diffusivity of both ions and small clusters on the
silica substrate. The 2-D diffusivity of the ions and clusters on the surface was calculated
using an algorithm that was developed to calculate the diffusivity on the surface.
The results are divided into three chapters. The first chapter describes the development
and test of the model and the force field parameters for the surface and the silver ions. In
the second chapter, the methods were tested on silver precipitates in aqueous solutionsVI
without substrate. In the last chapter, all the work previously done was combined and
used to investigate the patch formation.
The whole work confirmed that redox potential is the major factor influencing the shape
of the patch but not the only one. The presence of the cations over the surface was proven
to have a strong impact on the patch shape.
The model for the silica surface was used to study the solvation layers over the silica
surface and the diffusivity of the cations and solvent molecules in each solvation layer.
The silica substrate was also used to analyze the diffusivity on the surface of a silver
cluster with different oxidation states.
In the third chapter, a study on silver particles in aqueous solution was performed. The
study confirmed the relation between the redox potential and the silver particle shape.
Using the combination of the QEq and the EAM, the effect of the surface charge on the
calculation of the diffusivity using the Dynamic Light Scattering (DLS) were analyzed.
In this chapter, also a method to calculate the solvation free energy (∆G) was developed.
The method was used to analyze the affinity the silver particles have for different solu-
tions (i.e. pure water or water-ammonia solutions).
The study of the patch formation was made with all the methods previously adopted
or developed, including the Kawzka-Zahn Method (KZM). The results of this chapter
confirmed that the redox potential plays a major role in the growth of silver patches.
The cations deposited on the surface act as obstacles for the silver patch growth. The
simulation also highlighted how the polarity of the solution has a strong effect on the
final patch shape. Changing the ammonia in solution with other amines (Methylamine,
Dimethylamine) causes the silver patch to rearrange in a completely different way. The
silver patch in contact with a solution with ammonia showed a more dendritic behavior,
while with other amines the behavior was completely different. Finally, the simulations
showed how the formaldehyde changes the solubility of the ammonia in solution. The
ammonia present in solution together with formaldehyde shows a strong tendency to
deposit over the silver patches
Bildung, Charakterisierung und Anwendung Selbstorganisierter Monolagen aus Phosphons¨auren auf Aluminiumoxid
No full textComputational methods have helped a great deal in finding explanations for formerly inscrutable observations, as they provide atomic-level resolution. With respect to self-assembled monolayers (SAMs), both density functional theory (DFT) of individual surfactant-surface interactions and force field calculations of nm-scale SAM patches have made significant contributions towards the understanding of SAM formation and their properties. In the present work, we will apply force field based molecular dynamics (MD) simulations to study the system of phosphonic acids/phosphonates on aluminum oxide surfaces. The main advantages of this combination are the cheap materials and the robustness of the resulting SAMs. An overview of this and various other SAM systems is given in chapter 2 along with the state of the art of research on the formation mechanism and properties.
In the first part of the results in chapter 4, the focus is on the self-assembly of phosphonic acids (PAs) on alumina surfaces and the ordering of their alkyl-chain acting as spacers. The main challenge here is the glaring discrepancy between the timescales in SAM formation and MD simulations. In order to obtain well-ordered monolayers, the alumina substrate is typically immersed for several hours due to the slow diffusion of the surfactant molecules towards and on the surface, whereas \ac{MD} simulations usually range on the ns-scale. An iterative approach to overcome this gap using steered molecular dynamics (SMD) is presented in section 4.1 and applied in vacuo. In section 4.2 this method is applied in three solvents of different polarity to study the influence of solvent polarity on the growth mechanism.
To conclude the part on SAM formation, section 4.3 shows that surfactant molecules can also be incorporated into the monolayer in inverted geometry during the monolayer growth. Such inversion defects may have a very long lifetime and affect the quality of the resulting SAM, as they are removed upon proper rinsing of the SAM. A post-assembly treatment with repeated wetting/drying cycles reverses these molecules by a quasi-Langmuir-Blodgett transfer and can thus significantly improve the ordering and/or reduce immersion-time.
Chapter 5 describes properties and applications of the fully-grown SAMs. The self-healing after plastic deformation of a SAM of octadecyl phosphonic acid (ODPA) molecules on alpha-Al2O3 is investigated in section 5.1. Indentation of the SAM with a micro-lens leads to the formation of gauche-defects in the alkyl-chains. After release of pressure, the healing process begins at the fringe area of the disturbance and proceed towards its center. The ion-doping of an oligoethyleneglycol (OEG)-functionalized SAM is studied in 5.2. Here we explore the simulation-based design of SAMs and electronic devices.Rechnergestützte Methoden haben durch ihre inhäret atomare Auflösung bei der Aufklärung vormals rätselhafter Beobachtungen sehr geholfen. Bezogen auf selbstogranisierte Monolagen (SAMs) haben sowohl Rechnungen zur Wechselwirk einzelnder Adsorbtiv-Moleküle mit der Oberfläche mittels Dichtefunktionaltheorie (DFT) als auch Kraftfeldrechnungen auf der Nanometer-Skala einen großen Beitrag zum Verständnis der Bildung und Eigenschaften von SAMs geleistet. In dieser Arbeit werden kraftfeldbasierte Moleküldynamik-Simulationen (MD) angewendet, um SAMs von Phosphonsäuren auf Aluminiumoxid zu untersuchen. Die größten Vorteile dieser Kombination sind die günstigen Ausgangsmaterialien und die hohe Stabilität der entstehenden Monolage. Ein Überblick über dieses und andere SAM-Systeme ist in Kapitel 2 gegegen.
Im ersten Ergebnisteil (Kapitel 4) liegt der Fokus auf der Selbstorganisation der Phosphonsäuren (PAs) auf Aluminiumoxid-Oberflächen und dem Ausordnen der Alkylketten. Die größte Herausforderung bei der Modellierung ist hierbei die große Diskrepanz zwischen den Zeitskalen der SAM-Bildung und den Simulationen. Um wohlgeordnete Monolagen zu erhalten werden die Aluminiumoxid-Substrate aufgrund der langsamen Diffusion der Moleküle zur und auf der Oberfläche in der Regel für mehrere Stunden in eine PA-Lösung getaucht, während typische MD-Simulationen im Bereich von Nanosekunden liegen. Um diese Lücke zu überbrücken wird in Abschnitt 4.1 ein iterativer Ansatz unter Verwendung von Steered MD (SMD) entwickelt und in Vakuum-Simulationen getestet. In Abschnitt 4.2 wird diese Methode auch in drei Lösungsmitteln unterschiedlicher Polarität angewendet, um den Einfluss der Polarität auf das Wachstum zu untersuchen.
In Abschnitt 4.3 wird schließlich gezeigt, dass Phosphonsäure-Moleküle während des Wachstums auch in invertierter Geometrie in die SAM gebunden werden können. Solche Inversionsdefekte haben eine hohe Lebensdauer und beeinträchtigen die Qualität der SAM, da sie beim Spülen herausgelöst werden. Eine nachträgliche Behandlung mit wiederholtem Benetzen und Trocknen ist in der Lage diese Moleküle durch einen quasi-Langmuir-Blodgett-Transfer umzuderehen und so die Ordnung in der SAM signifikant zu erhöhen und/oder die Immersionszeit zu reduzieren.
Kapitel 5 beschäftigt sich mit Anwendungen wohlgeordneter SAMs. Die Selbstheilungseigenschaften einer SAM aus Octadecylphosphonsäure (ODPA) auf alpha-Al2O3 nach plastischer Verformung wird in Abschnitt 5.1 thematisiert. Eindrücken der SAM mit eine Mikrolinse führt hier zur Bildung von gauche-Defekten in den Alkylketten. Nach Wegnehmen des Drucks beginnt der Selbstheilungsprozess am Rande des gestörten Bereichs und pflanzt sich zu dessen Zentrum fort. In Abschnitt 5.2 wird das Dotieren einer SAM aus Oligoethylenglycol-funktionalisierten (OEG) Phosphonsäuren mit Ionen untersucht. Ausgehend von den Ergebnissen der MD Simulationen werden zudem elektronische Bauteile entwickelt
Two-step nucleation rather than self-poisoning : an unexpected mechanism of asymmetrical molecular crystal growth
No full textThe identification of two step nucleation mechanisms considerably extended our understanding of crystal nucleation. Here, we report an analogous observation of a two-step mechanism but in 2-D for deposition of molecules to a growing crystal face. Using molecular dynamics simulations connected with the Kawska-Zahn approach, α-resorcinol precipitation from the vapor is treated at the low driving force regime. Growth at the faster growing (01̅1̅) face reveals the deposition of molecules to form a disordered liquid-like layer. Strikingly, this apparently divergent (nonepitaxial) molecular arrangement does not represent self-poisoning which would lower the growth rate of the (01̅1̅) face. On the contrary, more favorable attachment energy along with a disorder–order transition, akin to a two-step nucleation observed in 3-D systems, leads to growth rates that are about 20 times faster than the more standard mode association of molecules at the (011) face where the molecules readily align according to the crystal lattice
Molekulardynamik-Simulationen zur Selbstassemblierung und deren Auswirkungen auf optische Eigenschaften
No full textComputer simulations on the atomic/molecular scale have become a powerful tool for modern research in all fields of chemistry and related subjects such as material science or molecular biology. This progression was facilitated by ongoing improvements of computational capacities and the development of sophisticated algorithms. The great benefit of computational methods is their capability of gathering insights on time- and length-scales, that are experimentally hardly or not at all accessible. On one hand, these insights may help to interpret experimental results and to establish new theoretical concepts. On the other hand, predictions based on computational studies, such as reaction mechanisms or material properties, are
increasingly serving as input for synthetic and analytic strategies. This mutuality makes computer simulations highly suitable for interdisciplinary applications with experimental studies and vice versa.
Most of the computational studies presented in this thesis were carried out in close cooperation with experimentalist, resulting in comprehensive studies of the investigated systems. Altogether, our results enable a deeper understanding of the mechanisms controlling the optical properties of self-assembled systems and represent an important contribution to this field of research
- …
