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Background: High resolution three-dimensional (3-D) magnetic resonance imaging (MRI) is widely used to predict the neurovascular anatomy within the cerebellopontine angle. Objective: To assess value of 3-D three-dimensional Steady-state free precession imaging (SSFP) and Time-of-flight magnetic resonance angiography (TOF MRA) and in detecting the offending vessels in hemifacial spasm by comparison to intraoperative endoscopic visualization. Methods: 42 patients underwent endoscope-assisted microvascular decompression (MVD). All available preoperative 3-D SSFP and TOF MRA images were checked. Intraoperative videos were captured by a high definition endoscopic camera attached to endoscopes while exploring the area of facial nerve root exit zone (REZ). Evaluation of the 3-D images was performed by two independent groups of observers and compared with the operative findings. Results: 3-D MRI had an average positive predictive value (PPV) of 89.1% in differentiating between simple and complex compression. Mean accuracy of the before mentioned images in detection of the offending vessels was 83.3% and 77% according to the first and second group of observers respectively. Averaged inter-observer agreement between the two groups of observers was substantial with an averaged Kappa coefficient (K) of 0.56. In simple compression group, mean accuracy was 97% and 89.4% according to the first and second group of observers respectively. Averaged K for agreement was substantial (K=0.65). Conclusion: According to endoscopic visualisation, 3-D SSFP and TOF MRA images are accurate in detecting the offending vessels in simple compression of the facial nerve, and in predicting presence of a complex compression with variable sensitivity in identifying all offending vessels.
Urban Green Areas – their functions under a changing lifestyle of local people, the example of Hanoi
(2013)
Hanoi is a rapidly developing city - in terms of area, population and economy. It also has to face social and environmental problems that often accompany the fast development of a city. Increasing environmental pollution leads to a decrease in living conditions, such as clean water, housing, social services, etc., for most of the city’s inhabitants. Other well-known social problems in cities worldwide also occur in Hanoi nowadays, for example inequality, food supply, and unemployment. In addition, the society is altering; lifestyle- change is a permanent process. Today, it seems that the changing process in Asian countries is rather leap-frogging than continuously. Although many research projects concerning to urban green areas in Hanoi have been completed recently, less is known about utilization of parks&gardens in a practical and systematic way. This study aims at contributing to fulfills the gaps with up-to-date facts and figures of parks’ utilization in the inner city of Hanoi. Based on “grounded theory”, triangular methodology was applied to collect empirical data in four main parks in the inner city of Hanoi namely: Thong Nhat, Bach Thao, Hoan Kiem, and Lenin. Scientific observations, visitor countings were done in 2010-2011; including 2143 face-to-face interviews to park users covering the course of the year and a small online-poll of 113 responses. Thirteen interviews with experts have been done in several phases and taken into account for discussing and testing hypotheses. Empirical results have shown that utilization of the parks is in abundance in terms of the use - numbers as well as activities. A comparison between the courses of the day for parks in Berlin and Hanoi shown that the time of using parks in Hanoi is earlier in the day. In details, there is 25% and 1.4% of total daily visitors went to parks in Hanoi and Berlin,, respectively. However, the biggest peak in park-visiting time for both cities is in the afternoon. The findings also clarified that students and retirees are the major users even though there is some different in structures of park user among the four parks. The length of stay depends on how large and interesting a park is. In this aspect, Hanoi parks are very poor in facilities showing by a long list of missing facilities in the parks. However, as there is no alternative, parks in Hanoi still attract a high number of visitors. In general, results from this study have shown a close relationship among socio-economic and political situations in Vietnam with UGAs and its utilization. Influencing factors on parks’ utilization were also indentified, which are social changes, lifestyle changes, economic situation, conflicts in land usage, and maintaining cost for UGAs. Three given hypotheses were confirmed: i) the demand of public UGAs in inner Hanoi will grow mid-term and increase strongly long-term; ii) Hanoi’s residents will claim strongly for more parks in the future; ii) The number of conflicts inside the area of UGAs, among the visitors will occur very soon and require a specific master plan for the development and the management of UGAs. Finally, based on the weaknesses of UGAs in Hanoi recently, two groups of recommendations were also suggested to improve UGAs. Firstly, in terms of quality – quantity: • Retain each square meter of green space as UGA – do not unblock any green space for construction; • The existing UGA have to be well maintained. Secondly, in terms of management – planning: • Elaborate a UGA-masterplan for (inner) Hanoi; • Keep UGA management in the responsibility of public bodies; • Implement participation of affected population defector in the process of planning and management (as it has already been written in planning guidelines); • Be aware of potential conflicts among park user groups; • Establish an UGA monitoring system – involving regular (or even permanent) countings based on up-to-date technology; Realize horizontal partnering structures.
The confinement of energy has always been a challenge in magnetic confinement fusion devices. Due to their toroidal shape there exist regions of high and low magnetic field, so that the particles are divided into two classes - trapped ones that are periodically reflected in regions of high magnetic field with a characteristic frequency, and passing particles, whose parallel velocity is high enough that they largely follow a magnetic field line around the torus without being reflected. The radial drift that a particle experiences due to the field inhomogeneity depends strongly on its position, and the net drift therefore depends on the path taken by the particle. While the radial drift is close to zero for passing particles, trapped particles experience a finite radial net drift and are therefore lost in classical stellarators. These losses are described by the so-called neoclassical transport theory. Recent optimised stellarator geometries, however, in which the trapped particles precess around the torus poloidally and do not experience any net drift, promise to reduce the neoclassical transport down to the level of tokamaks. In these optimised stellarators, the neoclassical transport becomes small enough so that turbulent transport may limit the confinement instead. The turbulence is driven by small-scale-instabilities, which tap the free energy of density or temperature gradients in the plasma. Some of these instabilities are driven by the trapped particles and therefore depend strongly on the magnetic geometry, so the question arises how the optimisation affects the stability. In this thesis, collisionless electrostatic microinstabilities are studied both analytically and numerically. Magnetic configurations where the action integral of trapped-particle bounce motion, J, only depends on the radial position in the plasma and where its maximum is in the plasma centre, so-called maximum-J configurations, are of special interest. This condition can be achieved approximately in quasi-isodynamic stellarators, for example Wendelstein 7-X. In such configurations the precessional drift of the trapped particles is in the opposite direction from the direction of propagation of drift waves. Instabilities that are driven by the trapped particles usually rely on a resonance between these two frequencies. Here it is shown analytically by analysing the electrostatic energy transfer between the particles and the instability that, thanks to the absence of the resonance, a particle species draws energy from the mode if the frequency of the mode is well below the charateristic bounce frequency. Due to the low electron mass and the fast bounce motion, electrons are almost always found to be stabilising. Most of the trapped-particle instabilities are therefore predicted to be absent in maximum- J configurations in large parts of parameter space. Analytical theory thus predicts enhanced linear stability of trapped-particle modes in quasi-isodynamic stellarators compared with tokamaks. Moreover, since the electrons are expected to be stabilising, or at least less destabilising, for all instabilities whose frequency lies below the trapped-electron bounce frequency, other modes might benefit from the enhanced stability as well. In reality, however, stellarators are never perfectly quasi-isodynamic, and the question thus arises whether they still benefit from enhanced stability. Here the stability properties of Wendelstein 7-X and a more quasi-isodynamic configuration, QIPC, are investigated numerically and compared with another, non-quasiisodynamic stellarator, the National Compact Stellarator Experiment (NCSX) and a typical tokamak. In gyrokinetic simulations, performed with the gyrokinetic code GENE in the electrostatic and collisionless approximation, several microinstabilities, driven by the density as well as both ion and electron temperature gradients, are studied. Wendelstein 7-X and QIPC exhibit significantly reduced growth rates for all simulations that include kinetic electrons, and the latter are indeed found to be stabilising when the electrostatic energy transfer is analysed. In contrast, if only the ions are treated kinetically but the electrons are taken to be in thermodynamic equilibrium, no such stabilising effect is observed. These results suggest that imperfectly optimised stellarators can retain most of the stabilising properties predicted for perfect maximum-J configurations. Quasi-isodynamic stellarators, in addition to having reduced neoclassical transport, might therefore also show reduced turbulent transport, at least in certain regions of parameter space.
In many industrial sectors biotechnological production processes have replaced pure chemical methods and allowed new, ecologically friendly and enzyme-based processes. Microorganisms, such as modified Bacillus strains are used in particular for the industrial enzyme synthesis. The two organisms Bacillus licheniformis and Bacillus pumilus are of great industrial importance. B. licheniformis is able to secrete proteins in large amounts, while B. pumilus shows high resistance to oxidative stress. During production processes different conditions can occur that affect the physiology of the production hosts and may result in a quantitative, but also a qualitative impairment of the products. This influence is based on e.g. chemical processes, the setting of temperature, pH, or oxygen availability and can lead to various stress situations for the bacteria. Cells respond to changes in their environment by sensing stressors and initiate a response to the stress, which is usually implemented by an induction or derepression of various regulons. In order to conduct an optimal production process, the metabolism and stress responses of the utilized bacteria should be known exactly. The aim of this study was to analyze of the stress response of B. licheniformis to heat and salt stress, and the stress response of B. licheniformis and B. pumilus to oxidative stress. These analyses were performed at the level of transcriptomics using cDNA microarrays, which is the most direct and global method for the analysis of changes in the physiology of a cell. The identification of stress specific markers genes and their differentiation from the SigB regulated general stress response has been another purpose of this work. Knowledge of these marker genes enables a prompt analysis of the fermentation conditions and thus a possible optimization of the process. The transcriptome analyses of this work show that B. licheniformis responds to heat stress by the induction of heat shock genes belonging to different regulons. These include the htpG gene, the HrcA regulon or the CtsR regulon, encoding chaperones and proteases, which mainly contribute to the protein quality control. The heat stress response of B. licheniformis revealed no fundamental differences to the heat stress response of the Gram-positive model organism Bacillus subtilis. The general stress response (SigB regulon), which is activated by heat stress, could be analyzed in more detail by the study of a ΔsigB mutant of B. licheniformis. Salt stress also provokes a strong induction of the general stress response in B. licheniformis. Genes for the transport and synthesis of compatible solutes were strongly induced, as well as several genes for transport systems with more or less known functions. The synthesis of the osmoprotective metabolites proline and glycine betaine could be verified in more detail by a metabolomics approach. The response to oxidative stress showed differences between both B. licheniformis and B. pumilus, and also to the oxidative stress response of B. subtilis. In B. licheniformis, the genes of the glyoxylate cycle are induced during oxidative stress. An activation of the glyoxylate bypass under oxidative conditions could be confirmed by a metabolome analysis of B. licheniformis. In addition, the PerR regulon of B. licheniformis is extended to include another two genes compared to B. subtilis. In contrast, several genes of the PerR regulon lack in the genome of B. pumilus, such as katA (vegetative catalase) or ahpCF (alkyl hydroperoxide reductase). However, other genes were induced in B. pumilus that were upregulated under oxidative stress conditions neither in B. subtilis nor in B. licheniformis. In addition, known regulons, regulated by e.g. Spx, CtsR or SOS were induced in both organisms. In summary, this dissertation transcriptionally analyzes the stress responses of B. licheniformis to heat, salt and oxidative stress, and in addition the oxidative stress response of B. pumilus. Several stress-specific regulons were identified in both, B. pumilus and B. licheniformis, which also correspond to the stress response of B. subtilis. However, it was possible to additionally assign genes to the stress specific responses of both organisms and to find differences, such as the absence of parts of the PerR regulon of B. pumilus, or the activation of the glyoxylate pathway in B. licheniformis during oxidative stress.
Abstract
Emperor penguins breed during the Antarctic winter and have to endure temperatures as low as −50 °C and wind speeds of up to 200 km h−1. To conserve energy, they form densely packed huddles with a triangular lattice structure. Video recordings from previous studies revealed coordinated movements in regular wave-like patterns within these huddles. It is thought that these waves are triggered by individual penguins that locally disturb the huddle structure, and that the traveling wave serves to remove the lattice defects and restore order. The mechanisms that govern wave propagation are currently unknown, however. Moreover, it is unknown if the waves are always triggered by the same penguin in a huddle. Here, we present a model in which the observed wave patterns emerge from simple rules involving only the interactions between directly neighboring individuals, similar to the interaction rules found in other jammed systems, e.g. between cars in a traffic jam. Our model predicts that a traveling wave can be triggered by a forward step of any individual penguin located within a densely packed huddle. This prediction is confirmed by optical flow velocimetry of the video recordings of emperor penguins in their natural habitat.
The absolute density of the metastable N2(A,v=0) molecule was extensively studied in nitrogen barrier discharges at 500 mbar. For the detection of the metastables laser-induced fluorescence spectroscopy (LIF) was used, at which for the calibration of the absoute metastables density a comparison with Rayleigh scattering was performed. To get the ratio of the LIF signal to the Rayleigh signal it is shown that the LIF signal is the convolution of the Rayleigh signal with an exponential decay. Besides, the different cross sections are calculated and the ratio of the detection sensitivities at the laser and fluorescence wavelength is determined. As a first step on the way to atmospheric pressure barrier discharges, the laser-induced fluorescence spectroscopy was implemented in low pressure capacitively coupled radio-frequency discharges. The determined metastables density in the capacitively coupled radio-frequency discharge is somewhat below 10^12 cm^(-3) at 40 Pa and somewhat below 10^13 cm^(-3) at 1000 Pa. The axial density profiles show a nearly symmetric shape due to the long lifetime of the metastable state. At a pressure of 500 mbar the two discharge modes of the barrier discharge, the filamentary and the diffuse mode, were analysed. The filamentary mode was mainly investigated in an asymmetric discharge configuration. Typical densities in the detection volume are in the range of 10^13 cm^(-3), resulting in maximal densities of up to 10^15 cm^(-3) in the microdischarge channel. Such large densities are in agreement with the fast decay by the pooling reaction after the maximum of the metastables density in the afterglow of the discharge pulse. The time dependent measurements in the afterglow of single microdischarges offer a delay of the metastables production with respect to the discharge current. This delay indicates that the metastables production takes place mostly by cascades from higher triplet states, which are in turn excited by electron impact. The axial density profiles show a maximum in metastables density in front of the anode in agreement with optical emission spectroscopy, but which cannot be clearly identified because of the asymmetric discharge configuration. The measurements for the diffuse discharge mode were performed in a symmetric discharge configuration. The metastables density is in the range of 10^13 cm^(-3). It increases during the current pulse of the discharge and decays afterwards. The maximum of the metastables density is delayed with respect to the maximum of the discharge current. The depletion of metastables in the early discharge afterglow is dominated by the pooling reaction, afterwards quenching by nitrogen atoms becomes important assuming a nitrogen atom density in the order of 10^14 cm^(-3). As for the filamentary mode, the losses by diffusion are negligible for the measurement positions. The measured axial density profiles show an accumulation of metastables in front of the anode, whereas the density in front of the cathode is below the detection limit. To calculate the metastables current density to the dielectrics after the discharge pulse a simulation is developed including the dominant volume processes for the depletion of metastables and the axial diffusion. Starting point for the simulation is the axial metastables density distribution at the end of the discharge pulse. The calculated metastables current density at the dielectrics is in the range of 10^14 cm^(-2)s^(-1). With the use of recently calculated secondary electron emission coefficients a comparison of the secondary electron emission by metastables with the discharge current is done. It is figured out that the secondary electron emission current is large enough to be important during the discharge ignition. To expand the simulation to the whole voltage cycle, the excitation of metastables is assumed to be proportional to the discharge current and electron density. Using this model, the measured time dependences of the metastables density are well reproduced for the investigated parameter variations. This is not the case for the axial profiles, where a metastables loss process is missed to explain the formation of a density plateau in front of the anode during the discharge pulse. The intended calculation of the metastables current density shows that the delay of the metastables production with respect to the discharge current might be responsible for the ignition of microdischarges at the beginning of the discharge pulse.
Surface and electrode modifications allow the alteration of surface and electrode properties required for certain applications. In the first part of this thesis, a pH sensitive graphite/quinhydrone composite electrode for Flow-Injection-Analysis (FIA) systems was optimized by using polysiloxane as binder material. This allows an easier handling of the electrode. Furthermore, new applications of the FIA system in conjunction with the pH sensitive detection system were developed. The electrode used here in conjunction with a common reference electrode proved to be a very useful potentiometric detector for FIA acid-base titrations of aqueous solutions. Even acid-base titrations in buffered solutions were performed successfully with the FIA system allowing the determination of activities of enzymes, which catalyse reactions with increasing or decreasing proton concentrations. A FIA system was applied to measure calcium and magnesium ions in different water samples by measuring the hydronium ion release during the complexometric reaction between EDTA and calcium or magnesium ions. A method was established to determine sequentially the titratable acidity and the pH of different wine samples. The new FIA method fulfils the official requirements of the "Organisation Internationale de la Vigne et du Vin" with respect to reproducibility and repeatability and can be easily adjusted to the legal requirements in USA and Europe. In summary, the first part of this thesis shows that the FIA system in conjunction with the graphite/quinhydrone/polysiloxane composite electrode is very well suited for simple, rapid and automatic determinations of small sample volumes in the areas of water analysis, food analysis or even biochemical analysis, provided that hydronium ions are involved. For all applications, one and the same measuring device without changing the detection system is used. Only different carrier solutions are necessary, which can be provided by a proper stream selector. The second part of this thesis is focused on the modification of gold surfaces of medical devices by treatment with OH radicals. These investigations are based on previous studies of the impact of OH radicals on mechanically polished gold surfaces resulting in a smoothing of the surface by dissolution of highly reactive gold atoms. In this thesis, the effect of OH radicals, generated either ex vivo by Fenton solutions or in vivo by immune reactions, on gold implants was analysed using atomic force microscopy. It was found that there is an analogy between the exposure of gold to Fenton solutions and the exposure of gold to immune reactions. The pre-treatment of gold implants with OH radicals of Fenton solution prevents surface alterations of the gold implants in vivo. This indicates that the in vivo release of gold from implants can be reduced by exposing the gold implants to Fenton solution before implantation. Finally, the modification of gold surfaces by OH radicals was applied to a medical nanodetector, which is coated with a gold layer and functionalized with antibodies, for isolating circulating tumour cells (CTCs) from the blood stream of cancer patients. By treating the gold layer of the nanodetector with OH radicals generated by Fenton solution or by UV-photolysis of hydrogen peroxide, the cytotoxicity of the gold layer after gamma irradiation was reduced to almost zero. This modification of the gold surface with OH radicals allows applying the nanodetector for in vivo applications.
Tourism is booming on global level since many decades and developing countries often capture tourism as a lever to push up their economy. Many regions in Vietnam invest lots of money in this development hoping to change the traditional economic structure. Located in the North Central Vietnam, about 170 km from Ha Noi capital to the south at the coastline, Sam Son is known as an ideal location for holiday makers. Currently the number of tourist has been counted to millions. Realizing its potential, the local authorities decided to enlarge and improve tourism to become the biggest tourism center in the North Central part of Vietnam. As many mass tourism destinations, Sam Son is facing several hidden drawbacks, which are generated by a (too) fast growth. Thats why unexpected problems may occur very soon. One path to mitigate weaknesses and to strengthen the positive impacts of tourism is to develop tourism in a more sustainable manner. As the very first step Sam Son needs to delineate a proper strategy and to establish a powerful "Destination Management System". Although several studies have been conducted already, the destination lacks reliable empirical data. This research intends to fill the gap by supplying concrete information with specific focus on “making tourism more sustainable”. In the study methodological triangulation has been applied to collect data and information. Besides literature review and secondary data analysis, two surveys - statistically well secured - have been conducted: A household survey with more than one thousand questionnaires to record the situation and opinion of local people and a visitor survey with 1139 face-to-face interviews to collect structural data about current guests in Sam Son as well as to explore their behaviour. Moreover expert and stakeholder interviews were included to supplement the information basis. As the research acquired the information directly from local people and from tourists by face-to-face interviews several weaknesses could be unveiled which official statistical data cannot show. There are three facets out of balance in terms of economic benefit: Compared with the political awareness and the financial support the tourism sector does not ensure the livelihood of an adequate number of people; the economic benefits from tourism are very unequally distributed and also the spatial dimension indicates a strong imbalance - only people living directly in the core area of tourism participate in tourism sector, the positive impact of tourism does not reach till the outskirts. In addition social and environmental problems are recognized by a majority of local people as consequences of tourism in the region. Regarding the touristic demand side a very low level of satisfaction has been detected: A small variety and low quality of touristic offers are the main reasons of dissatisfaction. The most exiting finding is that tourists treasure environment in the destination, whereas this aspect is underestimated in the locals view. In addition, tourists are really willing to pay for an improvement of environmental and touristic quality! Even if the amount of voluntary payments is very low, the total sum can enable the local government to develop the destination in a very proper way. Although this is a case study the results deliver valuable information and furthermore a concrete delineated roadmap for all destinations, which are in the same situation as Sam Son today. It is an example how to analyze and evaluate the present condition and how to continue in a proper way towards a more sustainable tourism development.
The concept of the electron surface layer introduced in this thesis provides a framework for the description of the microphysics of the surplus electrons immediately at the wall and thereby complements the modelling of the plasma sheath. In this work we have considered from a surface physics perspective the distribution and build-up of an electron adsorbate on the wall as well as the effect of the negative charge on the scattering of light by a spherical particle immersed in a plasma. In our electron surface layer model we treat the wall-bound electrons as a wall-thermalised electron distribution minimising the grand canonical potential and satisfying Poissons equation. The boundary between the electron surface layer and the plasma sheath is determined by a force balance between the attractive image potential and the repulsive sheath potential and lies in front of the crystallographic interface. Depending on the electron affinity x, that is the offset of the conduction band minimum to the potential in front of the surface, two scenarios for the wall-bound electrons are realised. For x<0 electrons do not penetrate into the solid but are trapped in the image states in front of the surface where they form a quasi two-dimensional electron gas. For x>0 electrons penetrate into the conduction band where they form an extended space charge. These different scenarios are also reflected in the electron kinetics at the wall which control the sticking coefficient and the desorption time. If x<0 electrons from the plasma cannot penetrate into the solid. They are trapped in the image states in front of the surface. The transitions between unbound and bound states are due to surface vibrations. Trapping of electrons is mediated by one-phonon transitions and takes place in the upper bound states. Owing to the large binding energy of the lowest bound state transitions from the upper bound states to the lowest bound state are due to multi-phonon processes. For low surface temperatures relaxation to the lowest bound state takes place while for higher temperature a relaxation bottleneck emerges. Desorption occurs in cascades for systems without relaxation bottleneck and as a one-way process in systems with a relaxation bottleneck. From the perspective of plasma physics the most important result is that the sticking coefficient for electrons is relatively small, typically on the order of 0.001. For x>0 electron physisorption takes place in the conduction band. For this case sticking coefficients and desorption times have not been calculated yet but in view of the more efficient scattering with bulk phonons, responsible for electron energy relaxation in this case, we expect them to be larger than for the case of x<0. Finally, we have studied the effects of surplus electrons on the scattering of light by a spherical particle. For x<0 the electrons form a spherical electron gas around the particle and their electrical conductivity modifies the boundary condition for the magnetic field. For x>0 the electrons in the bulk of the particle modify the refractive index through their bulk electrical conductivity. In both cases the conductivity is limited by scattering with surface or bulk phonons. Surplus electrons lead to an increase of absorption at low frequencies and, most notably, to a blue-shift of an extinction resonance in the infrared. This shift is proportional to the charge and is strongest for submicron-sized particles. The particle charge is also revealed in a blue-shift of the rapid variation of one of the two polarisation angles of the reflected light. From our work we conclude that the electron affinity is an important parameter of the surface which should affect the charge distribution as well as the charge-up. Therefore, we encourage experimentalists to study the charging of surfaces or dust particles as a function of x. Interesting in this respect is also if or under what conditions the electron affinity of a surface exposed to a plasma remains stable. Moreover, we suggest to use the charge signatures in Mie scattering to measure the particle charge optically. This would allow a charge measurement independent of the plasma parameters and could be applied to nano-dust where conventional methods cannot be applied.
The aim of this work is to further analyze the nature of the TiO2 passivation layer regarding structure, hydrophilicity and adsorption behavior, starting with the question how far metal and oxide properties are affected by the contact, regarding structural relaxation, atomic charges and work function. This determines how far the influence of metal has to be considered in simulations of TiO2 passivation layers. Mimicking the initial phases of implant contact with the biological environment, the adsorption of the inorganic ions on titanium oxides is to be investigated next, especially the influence of Ca2+ and HnPO4n-3 on the surface properties. Finally, biomolecule adsorption on TiO2 surfaces is investigated for understanding and improving their bioactivity.
Titanium and Titanium Dioxide
The properties of sharp interfaces formed between metallic titanium and a titanium dioxide layer with rutile or anatase structure and four different surface terminations were investigated. In all cases the work of separation is higher than the sum of surface energies, indicating the formation of an energetically very favorable interface region that glues the two phases together. The interface energy is negative, which means that for Ti and TiO2 bulk phases, mixing is energetically favorable.
The influence of the metal on the atomic and electronic structure of the oxide is limited to a few atomic layers. Depending on its modification, a passivation layer may give rise to up- (rutile) or downshift (anatase) of the work function of the underlying titanium metal.
Calcium and Phosphate
First principles molecular dynamics simulations in vacuum revealed stable bonds between Ca2+ and HnPO4n-3 ions and the investigated TiO2 surfaces. Ca2+ ions bind to 2–4 surface oxygen atoms, preferring peripheral positions as found on both rutile surfaces where adsorption energies reach 9 eV per ion. In solution the hydration energy drastically reduces these values.
Phosphate adsorbs to the TiO2 surface, but the adsorption energy is much lower than that of Ca2+ ions. The approach of phosphate is highly orientation dependent and hampered by the terminal oxygen atoms.
Both ab initio and force field simulations indicate enrichment of Ca2+ ions close to the surface, most of them directly bound to it, which results in a net positive charge. As the adsorption of phosphate takes longer and is strongly reinforced by adsorbed Ca2+ ions, it has become obvious that Ca2+ ions initiate the adsorption of calcium phosphate clusters to titania surfaces. However, the TiO2 surface does not necessarily act as a nucleation site for calcium phosphate crystallization, as adsorbed Ca2+ ions show reduced affinity towards phosphate compared to free ions in solution.
Collagen and Mechanical Stress
Coinciding force distance relations have been obtained for a variety of restraint force constants, expansion rates and environments. The resulting Young’s moduli are in the range of experimental values both at low and high strain ranges. For low strains the calculated Young’s modulus of about 2 GPa is comparable to experimental values between 3 and 5 GPa. For high strains it reaches 10 GPa. The Young’s moduli can be assigned to three different mechanisms of stretching, affecting the macroscopic linearity, the torsional angles and the bond lengths.
Chondroitin Sulfate (CS) and Hyaluronic Acid (HA)
A force field model for CS and HA could be established that reproduced experimental torsion angles and showed the same free energy surface (FES) as an ab initio model. Hydration affects the overall FES, but does not alter the position of the energetic minima. Stabilization of the conformation via bridging water molecules as suggested by other works is not necessary.
Both glycosaminoglycans adsorb to a hydroxylated rutile (100) surfaces despite the negative net charge both on surface and adsorbate. The presence of Na + ions is enough to compensate for the negative surface charge and to allow for adsorption. Ca2+ ions form additional bridges between negative groups on the surface and in the adsorbate.