Techn. Universiẗat, Diss., 2003--Berlin.

The concept of "aggregation-induced emission" (AIE) effect has induced a great deal of attention these days. Now, exploration of new AIE-active molecular system and multiple high technique applications for AIE materials are the two research hotspots. Cyanostilbene, as a classical structural unit in photoelectric functional materials, also exhibited this unique luminescence behavior. The research background was illustrated in Chapter 1, which mainly introduced the development of this subject. In this project, Chapter 2 and Chapter 3 presented two classes of functionalized AIE-active molecules based on cyanostilbene moiety, and their applications were investigated, while Chapter 4 demonstrated a series of donor-acceptor (D-A) molecules with highly emissive unit, and their photophysical properties were studied.;In Chapter 2, four different donor-substituted cyanostilbene-based dipyrrins were synthesized and characterized. The investigation of photophysical properties confirms that these molecules are AIE-active, which should be attributed to the cyanostilbene moiety. The introduction of different donor groups showed little impact on their luminescence. Furthermore, the emission properties of these molecules were found to be sensitive to Zn2+, that is, addition of Zn2+ enormously enhanced its fluorescence in THF. The titration experiments proved they showed good selectivity and sensitivity for Zn2+ detection with relatively low limit of detection. Job's curve and spectral studies of their corresponding zinc complex indicated that the ratio for dipyrrins and Zn2+ is 2:1, which suggested the formation of zinc complex by chelation-enhanced fluorescence (CHEF) effect should be the reason of the enhanced fluorescence. By combining dipyrrin with typical AIE-active moiety tetraphenylethylene (TPE), an AIE-active TPE-based dipyrrin was prepared. The studies of its fluorogenic Zn2+ detection confirmed that the CHEF effect together with AIE effect are responsible for the intense fluorescence, indicating the potential application as a Zn2+ detector in aqueous media.;In Chapter 3, the cyanostilbene backbone was functionalized with a terpyridine unit to construct four terpyridine-based cyanostilbene molecules with different donor substitutents. The investigation of their photophysical properties confirms that they are AIEE-active. With the effect of different electron-donating groups, their solid-state fluorescence color was adjusted from blue to orange-red successfully. According to the calculation results of their frontier molecular orbitals, terpyridine has little impacts on their luminescence, but would influence their solid-state emission obviously owing to its large steric hindrance. This class of molecules displayed higher luminescence efficiency in solid state than in their dissolved state. The twisted molecular conformation in single crystal, which effectively avoids close π-π stacking, was assumed to be responsible for the high luminescence efficiency in solid state. This kind of molecules show distinct switched fluorescence by stimuli of acid/base vapors, and this phenomenon derives from the protonation effect of nitrogen atoms in the terpyridine unit. Moreover, three of these molecules exhibit good electroluminescence properties. Especially, the crystal of non-donor substituted molecule show amplified spontaneous emission (ASE) properties, indicating this blue-emissive material can be used in multiple areas such as chemical sensor, organic light emitting diodes (OLEDs) and organic laser media.

Photovoltaic technology based on solution-processable organic solar cells (OSCs) provides a promising route towards a low-cost strategy to address the sharply increasing energy demands worldwide. However, up to date, the vast majority of solar cell reports have been based on spin-cast BHJ layers. Spin coating is not compatible with high speed and scalable coating processes, such as blade-coating and slot-die coating, which require the nanoscale morphology to be reproduced in scalable coating methods. And tolerance for thicker BHJ films would also facilitate high speed scalable coating. In the first part of this thesis, we investigate how pre-aggregating the conjugated polymer in solution impacts the charge transport in polymer films. We use P3HT in a wide range of molecular weights in different solvents of common use in organic electronics to investigate how they impact the aggregation behavior in the ink and in the solid state. By deliberately disentangling polymer chains via sonication of the solution in the presence of solvophobic driving forces, we show a remarkable ability to tune aggregation, which directly impacts charge transport, as measured in the context of field effect transistors. The second part of this thesis looks at the impact of the solution-coating method and the photovoltaic performance gap when applying modern BHJ inks developed for spin coating to scalable coating methods, namely blade coating. We ascribe this to significant differences in the drying kinetics between the processes. Emulating the drying kinetics of spin-coating was found to result in performance parity as well as morphological parity across several systems, resulting in demonstration of PTB7:PC71BM solar cells with efficiency of 9% and 6.5% PCEs on glass and flexible PET substrates, respectively. The last part of this thesis looks into going beyond performance parity by leveraging the differences of the scalable coating method to enable highly efficient thick solar cells which surpass the performance of spin-cast devices. High-speed wire-bar coating (up to 0.25 m/s) was used to produce OPV devices with power conversion efficiency (PCE) >10% and significantly outperforming devices prepared by spin-coating the BHJ layer for thicknesses >100 nm by maintaining a higher fill factor.

This research considered the efficient transmission of data within a wireless local area network (WLAN) system. A simulation model was developed to study the performance of our protocol, AGG-MAC (aggregated medium access control). AGG-MAC is a simple and elegant medium access control (MAC) protocol designed to improve performance by transmitting a maximal quantity of data with minimal overhead. Our enhancement to IEEE 802.11, AGG-MAC yields dramatic improvements in both local and global throughput. It furthermore reduces jitter in support of real time communications requirements such as voice over IP (VoIP). In support of heterogeneous roaming between Third Generation (3G) Wideband CDMA (WCDMA), specifically Universal Mobile Telecommunications System (UMTS) and WLAN systems, we constructed a simulation environment which allowed the evaluation of AGG-MAC in such a system. We further demonstrated the suitability of AGG-MAC throughout a range of infrastructure and ad hoc based WLAN scenarios. The AGG-MAC protocol enhancement provides significant performance improvements across a range of wireless applications, while interoperating with standard IEEE 802.11 stations. Performance is commensurate to original WLAN MAC performance for applications that do not benefit from packet level aggregation. The key contributions of this research were two-fold. First was the development of an OPNET simulation environment suitable for evaluation of future protocols supporting tightly coupled, heterogeneous WLAN and 3G systems. Secondly was the implementation and testing of the AGG-MAC protocol which aggregates suboptimal size packets together into a single frame, thereby amortizing the overhead. / Ph. D.

In treating cancer, a primary consideration is the target specificity of the treatment. This is a measure of the treatment dose that the cancerous (target) tissue receives compared to the dose that healthy tissue receives. Nanoparticle (NP) based treatments offer many advantages for target specificity compared to other forms of treatment due to their ability to selectively target tumors. One benefit of using magnetic NPs is their ability to release heat, which can both sensitize tumors to other forms of treatment as well as damage the tumor. The work here aims to incorporate a broad range of relevant physics into a comprehensive model. NP aggregation is known to be a large source of uncertainty in these treatments, thus a framework has been developed that can incorporate the effects of aggregation on NP diffusion, NP heat release, temperature rise, and overall thermal damage. To quanitify thermal damage in both healthy tissue and tumor tissue, the Cumulative Equivalent Minutes at 43 textcelsius~model is used. The Pennes bioheat equation is used as the governing equation for the temperature rise and included in it is a source heating term due to the NPs. NP diffusion and aggregation are simulated via a random walk process, with a probability of aggregation determining if nearest neighbor particles aggregate at each time step. Additionally, models are developed that attempt to incorporate aggregation effects into NP heat dissipation, though each proves to only be accurate when there is little aggregation occurring. In this work, verification analyses are done for each of the above areas and, at minimum, qualitatively accurate results have been achieved. Verification results of this work show that aggregation can be neglected at concentrations on the order of $100~nM$ or less. This however only serves as a rough estimation and further work is needed to gain a better quantitative understanding of the effects of NP concentration on aggregation. Using this concentration as a limitation, results are presented for a variety of tumor sizes and concentration distributions. Because this work incorporates a variety of physics and numerical methods into a single encompassing model, depth and physical accuracy in each area (bio-heat transfer, diffusion via random walk, NP energy dissipation, and aggregation) have been somewhat limited. This does however provide a framework in which each of the above areas can be further developed and their effects examined in the overall course of treatment. / Master of Science

Yes / It is against the background of low engagement by SMEs in e-business that this paper seeks to highlight the potential importance of aggregation and of the role of trusted third parties in facilitating higher levels of involvement. The paper is based on an ongoing SME e-business research programme and reports on some recent research on SMEs that were using high complexity e-business applications and explores the extent to which the research findings could address the core concern of low engagement. This qualitative case study based research includes analysis of data collected from 13 community intermediaries, acting as trusted third parties. It concludes that the role of community intermediaries appears to be central to the adoption of critical e-aggregation applications provided by service providers. For policymakers, this important role of critical e-aggregation applications in facilitating e-business engagement by SMEs has emerged as part of this research but there is limited evidence of policy initiatives that reflect this.

Wireless sensor networks have many sensor devices that send their data to the sink or base station for further processing. This is called direct delivery. But this leads to heavy traffic in the network and as the nodes are limited with energy, this decreases the lifetime of the network. So data aggregation technique is introduced to improve the lifetime. This technique aggregates or merges the multiple incoming packets in to single packet and forwards it to sink. There is different data aggregation techniques based on the topology of the network. This report clearly explains the purpose of data aggregation and gathering in WSN, data aggregation in flat networks and data aggregation in hierarchical networks, different data aggregation techniques in cluster based networks, chain based, tree based and grid based networks. Data aggregation technique can successfully minimize the data traffic and energy consumption only when it is carried out in a secure manner. Part2 of the survey explains the possible attacks that affect data aggregation in wireless sensor network. The secure data aggregation techniques in wireless sensor networks are also discussed in this report.

The increasing demands for biopharmaceuticals to treat different diseases have raised concerns about controlling the quality and efficacy of such pharmaceuticals. The design and formulation of a stable protein or peptide based biopharmaceutical runs into the limitation that at high concentrations (> 100 mg/ml) or during long storage process the drug undergoes aggregation. During synthesis, purification, storage or packaging of these drugs different kinds of stresses like chemical, oxidative, thermal, shear, etc. are encountered. These stresses promote the non-native aggregation of protein and peptide based drugs. Injection or administration of such drugs if contaminated with aggregates causes patient discomfort or development of an antibody which can adversely affect patient’s conditions. This brings out the necessity of finding a way so that such aggregation is avoided. Nanoparticles have been used as vehicles for drug delivery and diagnostic agents in biology for a while. The surface of the nanoparticles is known to adsorb small as well as large molecules with different kinetics and energetics of interaction. I have used nanoparticles to adsorb proteins to protect them against aggregation when they are subjected to denaturing conditions. The effectiveness of the nanoparticles in stopping protein aggregation, recovery of the proteins and reversibility of the adsorption process, the catalytic activity of the proteins before and after adsorption on the surface have all been studied in details. The work described here has been divided in 8 chapters and the contents of each chapter are described below. In Chapter 1 I have provided a brief introduction to the protein aggregation problem. The motivation and scope of the current work has been presented in this chapter. Materials and methods have been described in Chapter 2. Synthesis of gold and silica nanoparticles, their characterization and stability under experimental conditions have been illustrated in this chapter. The spectroscopic assays and techniques which I have used to study the effect of gold and silica nanoparticles on protein aggregation have been discussed at lengths in this chapter. In Chapter 3 I have demonstrated the effect of gold nanoparticles on thermal aggregation of alcohol dehydrogenase (ADH). The size of the nanoparticle was varied in the range of 15-60 nm and the effect was measured by various spectroscopic assays and techniques. I have observed that gold nanoparticles prevent thermal aggregation of ADH and the efficiency is high. Gold nanoparticles in nanomolar or even picomolar concentrations are capable of preventing the aggregation of ADH at micromolar concentrations. In Chapter 4 the role of gold nanoparticles as suppressor of protein aggregation was extended to another protein, insulin. Chemically induced aggregation of insulin using dithiothreitol (DTT) in the presence of gold nanoparticles was studied in the same manner as was done for ADH. Similar prevention property of gold nanoparticles was established by making the observation independent of the method of denaturation or the type of protein used in the prevention experiments. In Chapter 5 huge second harmonic light scattering (SHS) signal from pure gold nanoparticles has been used to measure the free energy of interaction of ADH and insulin with nanoparticles in solution, for the first time. The change in the second harmonic scattered signal was monitored which decreased steadily as a function of added protein concentration to the aqueous solution of gold nanoparticles. The fitting of the second harmonic signal decay was done with a modified Langmuir adsorption isotherm to extract the free energy change in the interaction and the number of protein molecules adsorbed on the surface. In Chapter 6 I have demonstrated a way to recover the adsorbed ADH and insulin from the gold nanoparticle surface and tested the activity of ADH by an assay. The structure of the proteins in the adsorbed state has been probed by CD spectroscopy and described in this chapter. It is found that ADH retains its activity in the adsorbed state. Both the proteins retain the native secondary structures in their adsorbed state. However, the structures change drastically under denaturing conditions. In Chapter 7 the effect silica nanoparticles which are known to have hydrophilic surface has been examined on the aggregation of ADH and insulin in pretty much the same way as was done with gold nanoparticles. The efficiency of silica nanoparticle was found to be lower compared to gold nanoparticles. In addition, the size dependency of prevention efficiency of silica and gold nanoparticles was found to be completely opposite to each other. In Chapter 8 I have presented the overall summary and possible future directions of this work

The aim of this thesis is to investigate and better understand the mechanisms of protein self-assembly. Specifically, I study three protein systems which form morphologically and structurally distinct brillar protein aggregates. The first of these studies is concerned with the self-assembly of amyloid brils formed from bovine insulin. Amyloid brils are associated with human diseases such as Alzheimers Disease and type-2 diabetes, and are also garnering interest in biomaterial applications. Fragmentation-dominated models for the self-assembly of amyloid brils have had important successes in explaining the kinetics of amyloid bril formation but predict bril length distributions that do not match experimental observations. Here I resolve this inconsistency using a combination of experimental kinetic measurements and computer simulations. I provide evidence for a structural transition demarcated by a critical bril mass concentration, or CFC, above which fragmentation of the brils is suppressed. Our simulations predict the formation of distinct bril length distributions above and below the CFC, which I confirm by electron microscopy. These results point to a new picture of amyloid bril growth in which structural transitions that occur during self-assembly have strong effects on the final population of aggregate species with small, and potentially cytotoxic, oligomers dominating for long periods of time at protein concentrations below the CFC. I further show that the CFC can be modulated by environmental conditions, pointing to possible in vivo strategies for controlling cytotoxicity. I probe the structural nature of the transition by performing small angle neutron scattering. Secondly, I study the formation of amyloid-like brils from the protein ovalbumin. I undertake kinetic experiments of self-assembly and find two key features emerge: the lack of a lag time and the existence of a slow growth regime in the long-time limit. I observe, using TEM, that these brils are worm-like in nature and form closed-loops. I find the growth kinetics are intimately connected to this particular morphology. I present a simple kinetic model which captures the features of the kinetics found in experiments by incorporating end-to-end association of brils. I comment on the ramifications this type of amyloid bril assembly may have on oligomeric toxicity. Thirdly, the DNA-mimic protein ocr is highly charged (-56e at pH 8) and forms non-amyloid brillar assemblies at very high ammonium sulphate concentrations (3.2M). The fact that ocr forms translucent brillar gels at such high salt concentrations is extremely unique. Typically under such high salt conditions, non-specific amorphous aggregates are formed. In order to better understand the mechanism of why ocr forms specific bril aggregates, I used variants of the wile-type protein in which extensive regions of surface have been removed or modified. The structural characteristics of gels formed from the variants were probed using microrheological techniques. I find that non-specific electrostatic charge screening plays an important role in ocr aggregation. However, I also locate a potentially important α-helical region which may play a part in establishing specific interactions so that ocr may form ordered brillar assemblies.

News aggregation is a developing form of professional journalism practice, one uniquely adapted to contemporary communication realities. News companies have always gathered content from a variety of sources when producing their products. However, the sheer volume of information, number of participants and speed of consumption online requires news workers to adopt new routines of collecting and disseminating information. These routines, some argue, fundamentally differ from the beat structure of traditional journalism. As recent ethnographic work has found, online news workers might value a sense of audience and newsworthiness over and above norms like objectivity and getting a good story (Anderson, 2013; Agarwal & Barthel, 2013). As economic pressures continue to strain resources and shrink the number of reporters on staff, news aggregation, both as a practice and a digital filtering tool, is becoming a staple of modern newsrooms. Few researchers have explored the impact of these divergent routines on content. Through a secondary data analysis of the Pew Research Center’s 2012 News Coverage Index, this thesis examines the topics and news-drivers in 12 US news websites. The analysis finds that in-house, so-called “original reporting” tends to rely on institutional actors and hard news topics. When stories are aggregated from a third-party source, soft news topics and celebrity stories are preferred. Finally, different professional practices seem to be favored depending on the type of online news organization. The findings suggest scholars, and those interested in journalism education, think of organizational pressures and professional norms as fluid online, particularly when connecting theories of news work to output in terms of content. / text