Diffusion in heterogeneous systems studied by laser scanning confocal microscopy and fluorescence correlation spectroscopy

Understanding and controlling the mechanism of the diffusion of small molecules, macromolecules and nanoparticles in heterogeneous environments is of paramount fundamental and technological importance. The aim of the thesis is to show, how by studying the tracer diffusion in complex systems, one can obtain information about the tracer itself, and the system where the tracer is diffusing. rnIn the first part of my thesis I will introduce the Fluorescence Correlation Spectroscopy (FCS) which is a powerful tool to investigate the diffusion of fluorescent species in various environments. By using the main advantage of FCS namely the very small probing volume (<1µm3) I was able to track the kinetics of phase separation in polymer blends at late stages by looking on the molecular tracer diffusion in individual domains of the heterogeneous structure of the blend. The phase separation process at intermediate stages was monitored with laser scanning confocal microscopy (LSCM) in real time providing images of droplet coalescence and growth. rnIn a further project described in my thesis I will show that even when the length scale of the heterogeneities becomes smaller than the FCS probing volume one can still obtain important microscopic information by studying small tracer diffusion. To do so, I will introduce a system of star shaped polymer solutions and will demonstrate that the mobility of small molecular tracers on microscopic level is nearly not affected by the transition of the polymer system to a “glassy” macroscopic state. rnIn the last part of the thesis I will introduce and describe a new stimuli responsive system which I have developed, that combines two levels of nanoporosity. The system is based on poly-N-isopropylacrylamide (PNIPAM) and silica inverse opals (iOpals), and allows controlling the diffusion of tracer molecules. rn

Formation and surface exchange of nitrous acid

Die salpetrige Säure (HONO) ist eine der reaktiven Stickstoffkomponenten der Atmosphäre und Pedosphäre. Die genauen Bildungswege von HONO, sowie der gegenseitige Austausch von HONO zwischen Atmosphäre und Pedosphäre sind noch nicht vollständig aufgedeckt. Bei der HONO-Photolyse entsteht das Hydroxylradikal (OH) und Stickstoffmonooxid (NO), was die Bedeutsamkeit von HONO für die atmosphärische Photochemie widerspiegelt.rnUm die genannte Bildung von HONO im Boden und dessen anschließenden Austausch mit der Atmosphäre zu untersuchen, wurden Messungen von Bodenproben mit dynamischen Kammern durchgeführt. Im Labor gemessene Emissionsflüsse von Wasser, NO und HONO zeigen, dass die Emission von HONO in vergleichbarem Umfang und im gleichen Bodenfeuchtebereich wie die für NO (von 6.5 bis 56.0 % WHC) stattfindet. Die Höhe der HONO-Emissionsflüsse bei neutralen bis basischen pH-Werten und die Aktivierungsenergie der HONO-Emissionsflüsse führen zu der Annahme, dass die mikrobielle Nitrifikation die Hauptquelle für die HONO-Emission darstellt. Inhibierungsexperimente mit einer Bodenprobe und die Messung einer Reinkultur von Nitrosomonas europaea bestärkten diese Theorie. Als Schlussfolgerung wurde das konzeptionelle Model der Bodenemission verschiedener Stickstoffkomponenten in Abhängigkeit von dem Wasserhaushalt des Bodens für HONO erweitert.rnIn einem weiteren Versuch wurde zum Spülen der dynamischen Kammer Luft mit erhöhtem Mischungsverhältnis von HONO verwendet. Die Messung einer hervorragend charakterisierten Bodenprobe zeigte bidirektionale Flüsse von HONO. Somit können Böden nicht nur als HONO-Quelle, sondern auch je nach Bedingungen als effektive Senke dienen. rnAußerdem konnte gezeigt werden, dass das Verhältnis von HONO- zu NO-Emissionen mit dem pH-Wert des Bodens korreliert. Grund könnte die erhöhte Reaktivität von HONO bei niedrigem pH-Wert und die längere Aufenthaltsdauer von HONO verursacht durch reduzierte Gasdiffusion im Bodenporenraum sein, da ein niedriger pH-Wert mit erhöhter Bodenfeuchte am Maximum der Emission einhergeht. Es konnte gezeigt werden, dass die effektive Diffusion von Gasen im Bodenporenraum und die effektive Diffusion von Ionen in der Bodenlösung die HONO-Produktion und den Austausch von HONO mit der Atmosphäre begrenzen. rnErgänzend zu den Messungen im Labor wurde HONO während der Messkampagne HUMPPA-COPEC 2010 im borealen Nadelwald simultan in der Höhe von 1 m über dem Boden und 2 bis 3 m über dem Blätterdach gemessen. Die Budgetberechnungen für HONO zeigen, dass für HONO sämtliche bekannte Quellen und Senken in Bezug auf die übermächtige HONO-Photolyserate tagsüber vernachlässigbar sind (< 20%). Weder Bodenemissionen von HONO, noch die Photolyse von an Oberflächen adsorbierter Salpetersäure können die fehlende Quelle erklären. Die lichtinduzierte Reduktion von Stickstoffdioxid (NO2) an Oberflächen konnte nicht ausgeschlossen werden. Es zeigte sich jedoch, dass die fehlende Quelle stärker mit der HONO-Photolyserate korreliert als mit der entsprechenden Photolysefrequenz, die proportional zur Photolysefrequenz von NO2 ist. Somit lässt sich schlussfolgern, dass entweder die Photolyserate von HONO überschätzt wird oder dass immer noch eine unbekannte, HONO-Quelle existiert, die mit der Photolyserate sehr stark korreliert. rn rn

Galactic fountain flows in high-resolution hydrodynamical simulations of galaxy disks

Feedback from the most massive components of a young stellar cluster deeply affects the surrounding ISM driving an expanding over-pressured hot gas cavity in it. In spiral galaxies these structures may have sufficient energy to break the disk and eject large amount of material into the halo. The cycling of this gas, which eventually will fall back onto the disk, is known as galactic fountains. We aim at better understanding the dynamics of such fountain flow in a Galactic context, frame the problem in a more dynamic environment possibly learning about its connection and regulation to the local driving mechanism and understand its role as a metal diffusion channel. The interaction of the fountain with a hot corona is hereby analyzed, trying to understand the properties and evolution of the extraplanar material. We perform high resolution hydrodynamical simulations with the moving-mesh code AREPO to model the multi-phase ISM of a Milky Way type galaxy. A non-equilibrium chemical network is included to self consistently follow the evolution of the main coolants of the ISM. Spiral arm perturbations in the potential are considered so that large molecular gas structures are able to dynamically form here, self shielded from the interstellar radiation field. We model the effect of SN feedback from a new-born stellar cluster inside such a giant molecular cloud, as the driving force of the fountain. Passive Lagrangian tracer particles are used in conjunction to the SN energy deposition to model and study diffusion of freshly synthesized metals. We find that both interactions with hot coronal gas and local ISM properties and motions are equally important in shaping the fountain. We notice a bimodal morphology where most of the ejected gas is in a cold $10^4$ K clumpy state while the majority of the affected volume is occupied by a hot diffuse medium. While only about 20\% of the produced metals stay local, most of them quickly diffuse through this hot regime to great scales.

Estimates of Use of Research-Based Instructional Strategies in Core Electrical or Computer Engineering Courses

Many research-based instruction strategies (RBISs) have been developed; their superior efficacy with respect to student learning has been demonstrated in many studies. Collecting and interpreting evidence about: 1) the extent to which electrical and computer engineering (ECE) faculty members are using RBISs in core, required engineering science courses, and 2) concerns that they express about using them, are important aspects of understanding how engineering education is evolving. The authors surveyed ECE faculty members, asking about their awareness and use of selected RBISs. The survey also asked what concerns ECE faculty members had about using RBISs. Respondent data showed that awareness of RBISs was very high, but estimates of use of RBISs, based on survey data, varied from 10% to 70%, depending on characteristics of the strategy. The most significant concern was the amount of class time that using an RBIS might take; efforts to increase use of RBISs must address this.

Mobile goes global: The effect of cell phones on economic growth and development

This study investigates the effect of cell phones on economic development and growth by performing an econometric analysis using data from the International Telecommunications Union and the Penn World Table. It discusses the various ways cell phones can make markets more efficient and how the diffusion of information andknowledge plays into development. Several approaches (OLS, Fixed Effects, 2SLS) were used to test over 20 econometric models. Overall, the mobile cellular subscriptions rate was found to have a positive and significant impact on countries’ level of real per capitaGDP and GDP growth rate. Furthermore, the study provides policy implications for the use of technology to promote global growth.

Au@Hg nanoalloy formation through direct amalgamation: Structural, spectroscopic, and computational evidence for slow nanoscale diffusion

Dynamic core-shell nanoparticles have received increasing attention in recent years. This paper presents a detailed study of Au-Hg nanoalloys, whose composing elements show a large difference in cohesive energy. A simple method to prepare Au@Hg particles with precise control over the composition up to 15 atom% mercury is introduced, based on reacting a citrate stabilized gold sol with elemental mercury. Transmission electron microscopy shows an increase of particle size with increasing mercury content and, together with X-ray powder diffraction, points towards the presence of a core-shell structure with a gold core surrounded by an Au-Hg solid solution layer. The amalgamation process is described by pseudo-zero-order reaction kinetics, which indicates slow dissolution of mercury in water as the rate determining step, followed by fast scavenging by nanoparticles in solution. Once adsorbed at the surface, slow diffusion of Hg into the particle lattice occurs, to a depth of ca. 3 nm, independent of Hg concentration. Discrete dipole approximation calculations relate the UV-vis spectra to the microscopic details of the nanoalloy structure. Segregation energies and metal distribution in the nanoalloys were modeled by density functional theory calculations. The results indicate slow metal interdiffusion at the nanoscale, which has important implications for synthetic methods aimed at core-shell particles.

Contrast media enhancement of intracranial lesions in magnetic resonance imaging does not reflect histopathologic findings consistently

Certain magnetic resonance (MR) enhancement patterns are often considered to be associated with a specific diagnosis but experience shows that this association is not always consistent. Therefore, it is not clear how reliably contrast enhancement patterns correlate with specific tissue changes. We investigated the detailed histomorphologic findings of intracranial lesions in relation to Gadodiamide contrast enhancement in 55 lesions from 55 patients, nine cats, and 46 dogs. Lesions were divided into areas according to their contrast enhancement; therefore 81 areas resulted from the 55 lesions which were directly compared with histopathology. In 40 of 55 lesions (73%), the histomorphologic features explained the contrast enhancement pattern. In particular, vascular proliferation and dilated vessels occurred significantly more often in areas with enhancement than in areas without enhancement (P = 0.044). In 15 lesions, there was no association between MR images and histologic findings. In particular, contrast enhancement was found within necrotic areas (10 areas) and ring enhancement was seen in lesions without central necrosis (five lesions). These findings imply that necrosis cannot be differentiated reliably from viable tissue based on postcontrast images. Diffusion of contrast medium within lesions and time delays after contrast medium administration probably play important roles in the presence and patterns of contrast enhancement. Thus, histologic features of lesions cannot be predicted solely by contrast enhancement patterns.

High interstitial fluid pressure is associated with low tumour penetration of diagnostic monoclonal antibodies applied for molecular imaging purposes

The human epithelial cell adhesion molecule (EpCAM) is highly expressed in a variety of clinical tumour entities. Although an antibody against EpCAM has successfully been used as an adjuvant therapy in colon cancer, this therapy has never gained wide-spread use. We have therefore investigated the possibilities and limitations for EpCAM as possible molecular imaging target using a panel of preclinical cancer models. Twelve human cancer cell lines representing six tumour entities were tested for their EpCAM expression by qPCR, flow cytometry analysis and immunocytochemistry. In addition, EpCAM expression was analyzed in vivo in xenograft models for tumours derived from these cells. Except for melanoma, all cell lines expressed EpCAM mRNA and protein when grown in vitro. Although they exhibited different mRNA levels, all cell lines showed similar EpCAM protein levels upon detection with monoclonal antibodies. When grown in vivo, the EpCAM expression was unaffected compared to in vitro except for the pancreatic carcinoma cell line 5072 which lost its EpCAM expression in vivo. Intravenously applied radio-labelled anti EpCAM MOC31 antibody was enriched in HT29 primary tumour xenografts indicating that EpCAM binding sites are accessible in vivo. However, bound antibody could only be immunohistochemically detected in the vicinity of perfused blood vessels. Investigation of the fine structure of the HT29 tumour blood vessels showed that they were immature and prone for higher fluid flux into the interstitial space. Consistent with this hypothesis, a higher interstitial fluid pressure of about 12 mbar was measured in the HT29 primary tumour via "wick-in-needle" technique which could explain the limited diffusion of the antibody into the tumour observed by immunohistochemistry.

Distribution of radiodense contrast medium after perineural injection of the palmar and palmar metacarpal nerves (low 4-point nerve block): an in vivo and ex vivo study in horses

REASONS FOR PERFORMING STUDY: Evidence-based information is limited on distribution of local anaesthetic solution following perineural analgesia of the palmar (Pa) and palmar metacarpal (PaM) nerves in the distal aspect of the metacarpal (Mc) region ('low 4-point nerve block'). OBJECTIVES: To demonstrate the potential distribution of local anaesthetic solution after a low 4-point nerve block using a radiographic contrast model. METHODS: A radiodense contrast medium was injected subcutaneously over the medial or the lateral Pa nerve at the junction of the proximal three-quarters and distal quarter of the Mc region (Pa injection) and over the ipsilateral PaM nerve immediately distal to the distal aspect of the second or fourth Mc bones (PaM injection) in both forelimbs of 10 mature horses free from lameness. Radiographs were obtained 0, 10 and 20 min after injection and analysed subjectively and objectively. Methylene blue and a radiodense contrast medium were injected in 20 cadaver limbs using the same techniques. Radiographs were obtained and the limbs dissected. RESULTS: After 31/40 (77.5%) Pa injections, the pattern of the contrast medium suggested distribution in the neurovascular bundle. There was significant proximal diffusion with time, but the main contrast medium patch never progressed proximal to the mid-Mc region. The radiological appearance of 2 limbs suggested that contrast medium was present in the digital flexor tendon sheath (DFTS). After PaM injections, the contrast medium was distributed diffusely around the injection site in the majority of the limbs. In cadaver limbs, after Pa injections, the contrast medium and the dye were distributed in the neurovascular bundle in 8/20 (40%) limbs and in the DFTS in 6/20 (30%) of limbs. After PaM injections, the contrast and dye were distributed diffusely around the injection site in 9/20 (45%) limbs and showed diffuse and tubular distribution in 11/20 (55%) limbs. CONCLUSIONS AND POTENTIAL RELEVANCE: Proximal diffusion of local anaesthetic solution after a low 4-point nerve block is unlikely to be responsible for decreasing lameness caused by pain in the proximal Mc region. The DFTS may be penetrated inadvertently when performing a low 4-point nerve block.

Continuous Formation and Separation of Calcium-Alginate Capsules Containing Viable Mammalian Cells in Microfluidic Devices

Microfluidic devices can be used for many applications, including the formation of well-controlled emulsions. In this study, the capability to continuously create monodisperse droplets in a microfluidic device was used to form calcium-alginate capsules.Calcium-alginate capsules have many potential uses, such as immunoisolation of cells and microencapsulation of active drug ingredients or bitter agents in food or beverage products. The gelation of calcium-alginate capsules is achieved by crosslinking sodiumalginate with calcium ions. Calcium ions dissociated from calcium carbonate due to diffusion of acetic acid from a sunflower oil phase into an aqueous droplet containing sodium-alginate and calcium carbonate. After gelation, the capsules were separated from the continuous oil phase into an aqueous solution for use in biological applications. Typically, capsules are separated bycentrifugation, which can damage both the capsules and the encapsulated material. A passive method achieves separation without exposing the encapsulated material or the capsules to large mechanical forces, thereby preventing damage. To achieve passiveseparation, the use of a microfluidic device with opposing channel wa hydrophobicity was used to stabilize co-laminar flow of im of hydrophobicity is accomplished by defining one length of the channel with a hydrogel. The chosen hydrogel was poly (ethylene glycol) diacrylate, which adheres to the glass surface through the use of self-assembled monolayer of 3-(trichlorosilyl)-propyl methacrylate. Due to the difference in surface energy within the channel, the aqueous stream is stabilized near a hydrogel and the oil stream is stabilized near the thiolene based optical adhesive defining the opposing length of the channel. Passive separation with co-laminar flow has shown success in continuously separating calcium-alginatecapsules from an oil phase into an aqueous phase. In addition to successful formation and separation of calcium alginate capsules,encapsulation of Latex micro-beads and viable mammalian cells has been achieved. The viability of encapsulated mammalian cells was determined using a live/dead stain. The co-laminar flow device has also been demonstrated as a means of separating liquid-liquidemulsions.

A MICROFLUIDIC METHOD TO MEASURE DIFFUSION IN HYDROGELS

A novel microfluidic method is proposed for studying diffusion of small molecules in a hydrogel. Microfluidic devices were prepared with semi-permeable microchannels defined by crosslinked poly(ethylene glycol) (PEG). Uptake of dye molecules from aqueous solutions flowing through the microchannels was observedoptically and diffusion of the dye into the hydrogel was quantified. To complement the diffusion measurements from the microfluidic studies, nuclear magnetic resonance(NMR) characterization of the diffusion of dye in the PEG hydrogels was performed. The diffusion of small molecules in a hydrogel is relevant to applications such asdrug delivery and modeling transport for tissue-engineering applications. The diffusion of small molecules in a hydrogel is dependent on the extent of crosslinking within the gel, gel structure, and interactions between the diffusive species and the hydrogel network. These effects were studied in a model environment (semi-infinite slab) at the hydrogelfluid boundary in a microfluidic device. The microfluidic devices containing PEG microchannels were fabricated using photolithography. The unsteady diffusion of small molecules (dyes) within the microfluidic device was monitored and recorded using a digital microscope. The information was analyzed with techniques drawn from digital microscopy and image analysis to obtain concentration profiles with time. Using a diffusion model to fit this concentration vs. position data, a diffusion coefficient was obtained. This diffusion coefficient was compared to those from complementary NMR analysis. A pulsed field gradient (PFG) method was used to investigate and quantify small molecule diffusion in gradient (PFG) method was used to investigate and quantify small molecule diffusion in hydrogels. There is good agreement between the diffusion coefficients obtained from the microfluidic methods and those found from the NMR studies. The microfluidic approachused in this research enables the study of diffusion at length scales that approach those of vasculature, facilitating models for studying drug elution from hydrogels in blood-contacting applications.

A Microfluidic Method to Measure Small Molecule Diffusion in Hydrogels

Drug release from a fluid-contacting biomaterial is simulated using a microfluidic device with a channel defined by solute-loaded hydrogel; as water is pumped through the channel, solute transfers from the hydrogel into the water. Optical analysis of in-situ hydrogels, characterization of the microfluidic device effluent, and NMR methods were used to find diffusion coefficients of several dyes (model drugs) in poly( ethylene glycol) diacrylate (PEG-DA) hydrogels. Diffusion coefficients for methylene blue and sulforhodamine 101 in PEG-DA calculated using the three methods are in good agreement; both dyes are mobile in the hydrogel and elute from the hydrogel at the aqueous channel interface. However, the dye acid blue 22 deviates from typical diffusion behavior and does not release as expected from the hydrogel. Importantly, only the microfluidic method is capable of detecting this behavior. Characterizing solute diffusion with a combination of NMR, optical and effluent methods offer greater insight into molecular diffusion in hydrogels than employing each technique individually. The NMR method made precise measurements for solute diffusion in all cases. The microfluidic optical method was effective for visualizing diffusion of the optically active solutes. The optical and effluent methods show potential to be used to screen solutes to determine if they elute from a hydrogel in contact with flowing fluid. Our data suggest that when designing a drug delivery device, analyzing the diffusion from the molecular level to the device level is important to establish a complete picture of drug elution, and microfluidic methods to study such diffusion can play a key role. (C) 2013 Elsevier B.V. All rights reserved.

Structural and functional diversity of connexin genes in the mouse and human genome

Gap junctions are clustered channels between contacting cells through which direct intercellular communication via diffusion of ions and metabolites can occur. Two hemichannels, each built up of six connexin protein subunits in the plasma membrane of adjacent cells, can dock to each other to form conduits between cells. We have recently screened mouse and human genomic data bases and have found 19 connexin (Cx) genes in the mouse genome and 20 connexin genes in the human genome. One mouse connexin gene and two human connexin genes do not appear to have orthologs in the other genome. With three exceptions, the characterized connexin genes comprise two exons whereby the complete reading frame is located on the second exon. Targeted ablation of eleven mouse connexin genes revealed basic insights into the functional diversity of the connexin gene family. In addition, the phenotypes of human genetic disorders caused by mutated connexin genes further complement our understanding of connexin functions in the human organism. In this review we compare currently identified connexin genes in both the mouse and human genome and discuss the functions of gap junctions deduced from targeted mouse mutants and human genetic disorders.

Three dimensional finite element simulation of polymer melting and flow in a single-screw extruder : optimization of screw channel geometry

Single-screw extrusion is one of the widely used processing methods in plastics industry, which was the third largest manufacturing industry in the United States in 2007 [5]. In order to optimize the single-screw extrusion process, tremendous efforts have been devoted for development of accurate models in the last fifty years, especially for polymer melting in screw extruders. This has led to a good qualitative understanding of the melting process; however, quantitative predictions of melting from various models often have a large error in comparison to the experimental data. Thus, even nowadays, process parameters and the geometry of the extruder channel for the single-screw extrusion are determined by trial and error. Since new polymers are developed frequently, finding the optimum parameters to extrude these polymers by trial and error is costly and time consuming. In order to reduce the time and experimental work required for optimizing the process parameters and the geometry of the extruder channel for a given polymer, the main goal of this research was to perform a coordinated experimental and numerical investigation of melting in screw extrusion. In this work, a full three-dimensional finite element simulation of the two-phase flow in the melting and metering zones of a single-screw extruder was performed by solving the conservation equations for mass, momentum, and energy. The only attempt for such a three-dimensional simulation of melting in screw extruder was more than twenty years back. However, that work had only a limited success because of the capability of computers and mathematical algorithms available at that time. The dramatic improvement of computational power and mathematical knowledge now make it possible to run full 3-D simulations of two-phase flow in single-screw extruders on a desktop PC. In order to verify the numerical predictions from the full 3-D simulations of two-phase flow in single-screw extruders, a detailed experimental study was performed. This experimental study included Maddock screw-freezing experiments, Screw Simulator experiments and material characterization experiments. Maddock screw-freezing experiments were performed in order to visualize the melting profile along the single-screw extruder channel with different screw geometry configurations. These melting profiles were compared with the simulation results. Screw Simulator experiments were performed to collect the shear stress and melting flux data for various polymers. Cone and plate viscometer experiments were performed to obtain the shear viscosity data which is needed in the simulations. An optimization code was developed to optimize two screw geometry parameters, namely, screw lead (pitch) and depth in the metering section of a single-screw extruder, such that the output rate of the extruder was maximized without exceeding the maximum temperature value specified at the exit of the extruder. This optimization code used a mesh partitioning technique in order to obtain the flow domain. The simulations in this flow domain was performed using the code developed to simulate the two-phase flow in single-screw extruders.