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We report the synthesis of conjugated polymer nanoparticles carrying stable luminescent radical units. These monodisperse conjugated radical nanoparticles can be tuned in their diameter over several hundred nanometers. They are stable in aqueous medium and highly luminescent in the red and near infrared spectrum, representing a powerful future tool for bioimaging. Moreover, the polymer nanoparticles exhibit paramagnetic properties, making them highly suitable for dual-mode optical and magnetic resonance imaging. In this study, we investigate their synthesis, optical and magnetic properties, and use quantum mechanical calculations to elucidate the effect of the conjugated polymer backbone and electron-withdrawing substituents on the electronic properties of the open-shell molecule in the polymer network of the particles.

Conjugated polymers are promising active materials for batteries. Batteries not only need to have high energy density but should also combine safe handling with recyclability or biodegradability after reaching their end-of-life. Here, we develop π-conjugated polyimidazole particles, which we prepare using atom economic direct arylation adapted to a dis-persion polymerization protocol. The synthesis yields polyimidazole nanoparticles with tunable size and narrow dispersi-ty. In addition, the degree of crosslinking of the polymer particles can be controlled. We demonstrate that the polyimid-azole nanoparticles can be processed together with carbon black and biodegradable carboxymethyl cellulose binder as active material for organic battery electrodes. Electrochemical characterization shows that a higher degree of crosslink-ing significantly improves the electrochemical processes and leads to clearer oxidation and reduction signals from the polymer. Polyimidazole as part of the composite electrode shows complete degradation by exposure to composting bac-teria over the course of 72 h.

We report the synthesis of conjugated polymer nanoparticles carrying stable luminescent radical units. These monodisperse conjugated radical nanoparticles can be tuned in their diameter over several hundred nanometers. They are stable in aqueous medium and highly luminescent in the red and near infrared spectrum, representing a powerful future tool for bioimaging. Moreover, the polymer nanoparticles exhibit paramagnetic properties, making them highly suitable for dual-mode optical and magnetic resonance imaging. In this study, we investigate their synthesis, optical and magnetic properties, and use quantum mechanical calculations to elucidate the effect of the conjugated polymer backbone and electron-withdrawing substituents on the electronic properties of the open-shell molecule in the polymer network of the particles.

There is a lack of data supporting cancer surveillance in pediatric Fanconi Anemia patients. We sought to describe the rates of upper aerodigestive lesions and malignancy in this population to augment current management guidelines.A retrospective cohort study of patients with Fanconi Anemia from a quaternary referral center between 2007-2021 was completed for head and neck cancer risk.One hundred and five FA patients were reviewed. Average age at presentation was 11.3 years old and 90.5% of patients underwent hematopoietic stem cell transplant (HSCT). A total of 8.6% of patients had leukoplakia or erythroplakia and 3.8% developed malignancy. The standardized incidence ratio of head and neck malignancy was 483.8. Patients presented with leukoplakia and malignancy at an average age of 14.6 and 25.1 years old, respectively. Malignancies were aggressive and marked by recurrence. There were no premalignant or malignant lesions found on flexible laryngoscopy. This series represents the largest longitudinal series of pediatric FA head and neck lesions.Fanconi Anemia patients should begin screening for head and neck cancer at age 10 or after HSCT.Level 4 Laryngoscope, 2022.

Derivatives of the stable, luminescent tris-2,4,6-trichlorophenylmethyl (TTM) radical exhibit unique doublet spin properties that are of interest for applications in optoelectronics, spintronics, and energy storage. However, poor reactivity of the chlo-ride-moieties limits the yield of functionalization and thus the accessible variety of high performance luminescent radicals. Here, we present a pathway to obtain mixed-bromide and chloride derivatives of TTM by simple Friedel-Crafts alkylation. The re-sulting radical compounds show higher stability and site-specific reactivity in cross-coupling reactions, due to the better leaving group character of the para-bromide. The mixed halide radicals give access to complex, and so far inaccessible luminescent open-shell small molecules, as well as polymers carrying the radical centers in their backbone. The new mixed-halide triphenyl methyl radicals represent a powerful building block for customized design and synthesis of stable luminescent radicals.

Few prognostic models have been created in children that receive liver retransplantation (rLT). We examined the SRTR database of 731 children that underwent second liver transplant between 2002 and 2018. Proportional hazards models using backward variable selection were used to identify recipient, donor, and surgical characteristics associated with survival. A simple prognostic scoring system or nomogram (ie, each risk factor was weighted on a five-point scale) was constructed based on the fitted model. Recipient age (P < .001), MELD/PELD (P < .001), recipient ventilated (P = .003), donor cause of death (P = .024), graft type (P = .045), first graft loss due to biliary tract complications (P = .048), and survival time of the first graft (P = .006) were significant predictors of retransplant survival. The bias-corrected Harrell's C-index for the multivariable model was 0.63. Survival was significantly different (P < .001) for those at low risk (0-4 points), medium risk (5-7 points), and high risk (8+ points). Survival was equivalent between low risk pediatric second transplant recipients and pediatric primary liver transplant recipients (P = .67) but significantly worse for medium- (P < .001) and high-risk (P < .001) recipients. With simple clinical characteristics, this scoring tool can modestly discriminate between those children at high risk and those children at low risk of poor outcomes after second liver transplant.

Orthogonal Frequency-Division Multiple Access (OFDMA) enables nodes to exploit spatial diversity in Wireless Mesh Networks (WMNs). As a result, throughput improves significantly. While existing work often considers the physical layer only, using OFDMA in a WMN also affects the link and network layers. In particular, multi-hop forwarding may result in severe bottlenecks since OFDMA resource allocations are typically based on local information only. In this paper, we design a practical system that mitigates such bottlenecks. To this end, we allow for resource allocation based on channel and traffic conditions at the physical layer, per-subcarrier coding at the link layer, and per-subcarrier packet segmentation at the network layer. We implement our approach on software-defined radios and show that it provides significant throughput gains compared to traditional schemes.

In this paper, K bidirectionally communicating node pairs with each node having N antennas and one amplify and forward relay having R antennas are considered. Each node wants to transmit d data streams to its communication partner. Taking into account that each node can perform self interference cancellation, a new scheme called Pair-Aware Interference Alignment is proposed. In this scheme, the transmit precoding matrices and the relay processing matrix are chosen in such a way that at any given receiver all the interfering signals except the self interference are within the interference subspace and the useful signal is in a subspace linearly independent of the interference subspace. If the number of variables is larger than or equal to the number of constraints in the system, the system is classified as proper, else as improper. Through simulations it is shown that for a proper system (2Kd≤2N+R-d), interferences can be perfectly aligned and the useful signals can be decoded interference-free at the receivers. An iterative algorithm to achieve the interference alignment solution is proposed. Also for the proper system fulfilling a certain additional condition, which will be derived in this paper, a closed form solution is proposed.

A wireless Ad Hoc network consisting of a source and multiple receiving nodes is considered. The source wants to transmit a common message throughout the whole network. The message has to be spread in a multi-hop fashion, as the transmit powers at the source and the nodes are limited. The goal of this paper is to find the multi-hop broadcast tree with a minimum energy consumption in the network. To reach this goal, a new decentralized game theoretic approach is proposed which considers the following two aspects jointly for the first time: Firstly, it optimizes the transmit powers at the source and at the individual intermediate nodes. Secondly, it employs maximum ratio combining at the receiving nodes following the fact that a node can receive several copies of the message from different sources in different time slots. The game is modeled such that the nodes are incentivized to forward the message to their neighbors. In terms of the total transmit energy, the results show that the proposed algorithm outperforms other conventional algorithms.

Conventional shortest path routing protocols suffer from short link lifetime and require much effort for route recovery. Corridor-based routing aims at providing a stable support structure for wireless multihop networks, thus enabling high data throughput. The intermediate hops within the corridor contain multiple nodes, which cooperate and forward data jointly to exploit the diversity of links within the corridor. In this work, we propose a cross-layer approach for corridor construction taking the estimated link lifetime into account. Furthermore, a concept for corridor maintenance is introduced which can adapt the corridor to changes of the network caused by node movements. In combination with a novel resource allocation scheme based on OFDMA, corridor-based routing achieves significant throughput gains and higher stability compared to shortest path routing.

Corridor-based Routing widens traditional hop-by-hop paths to enable advanced physical layer mechanisms in Wireless Multihop Networks. The key concept is to let groups of nodes cooperate to jointly forward data. Instead of establishing a path formed by a fixed sequence of nodes, the network layer builds a "corridor" from source to destination to allow for such an approach. The corridor is divided into stages, which consist of the aforementioned groups of nodes. Existing mechanisms for Corridor-based Routing focus on the physical layer and assume a routing protocol that builds the corridor. In this paper, we design a corridor construction algorithm and a practical protocol that implements it. In particular, we address in detail the overhead introduced by our protocol, since this is crucial for performance and an open issue of Corridor-based Routing. We implement our approach both in simulation and practice. We obtain the turning point at which corridors become profitable and show that our protocol builds corridors, which enable throughput gains up to 74%.

Corridor-based Routing enables advanced physical layer schemes in Wireless Multihop Networks (WMNs). It widens paths in order to span multiple nodes per hop. As a result, groups of nodes cooperate locally at each hop to forward packets. Recent theoretical work suggests using Orthogonal Frequency-Division Multiple Access (OFDMA) in combination with Corridor-based Routing to improve throughput in WMNs. However, results focus on achievable capacity and do not consider practical issues such as modulation and coding schemes. In this paper, we study OFDMA for corridors in practice and implement it on software-defined radios. We show that OFDMA corridors provide significantly larger throughput gains when considering realistic modulation and coding, achieving up to 2x throughput gain compared to traditional routing not based on corridors.

DOI: http://dx.doi.org/10.1109/WoWMoM.2014.6918922 Interference alignment(IA)is often considered in the spatial domain in combination with MIMO systems.In contrast, aligning interference in the frequency domain among multiple subcarriers can also benefit single-antenna OFDM-based access networks. It allows for flexible operation on a per-subcarrier basis. We investigate the achievable by frequency IA in practice for a scenario with multiple access points and clients. Previous work is predominantly theoretical and focuses on idealized cases where all nodes have the same average signal-to-noiseratio(SNR). On the contrary, in practical networks, nodes typically have heterogeneous SNRs depending on channel conditions, which might have a significant impact on IA performance. We tackle this problem by designing mechanisms that adaptively choose which nodes shall perform IA on which subcarriers depending on current channel conditions. We implement and validate our approach on software-defined radios. To the best of our knowledge, this is the first practical implementation of IA in the frequency domain. Our measurements show that (1) frequency IA is feasible in practice, and (2) choosing appropriate nodes and subcarriers overcomes the main limitations due to heterogeneous SNRs. Our mechanisms enable IA in scenarios where it would be infeasible otherwise, achieving throughput gains close to the 33% theoretical maximum. TRUE pub

Today, the performance of routing mechanisms in Wireless Multihop Networks (WMNs) is still limited by the lower layers. While recent cross-layer approaches take advantage of the characteristics of the medium, they are often based on traditional physical layers such as OFDM. State-of-the-art techniques used in one-hop scenarios, such as OFDMA or MIMO, pose a significant challenge in practical multihop networks, since typically Channel State Information (CSI) at the transmitter is required. Due to its volatile nature, disseminating timely CSI in the network is often infeasible. We generalize Corridor-based Routing to enable advanced physical layers in WMNs. Instead of routing packets from node to node, we forward them along fully-connected groups of nodes. As a result (1) CSI only needs to be exchanged locally to enable cooperation in a group, and (2) groups can adaptively choose the best physical layer technique according to CSI. We investigate the benefits of Corridor-based Routing and present a protocol design that enables operation of corridors in WMNs.

Wireless sensor networks are able to perform an aggregation of the data generated by sensors. In networks where no gateway or no central sensor is specified, gossiping algorithms are used such that sensors in the whole network can aggregate messages from all other sensors. In the gossiping algorithm, the bias problem limits the quality of the aggregation results and the lack of message identification results in large aggregation time. In this paper, we reveal the possibility of eliminating or reducing the bias at the sensors by using the concept of the divisible functions that are generally applied in a sensor network and by using the memory of the sensors. Furthermore, we show how the aggregation time can be reduced by using different communication strategies for sensors communicating with their neighbors. Simulation results show the reduction of the aggregation bias at sensors as well as a higher speed of the aggregation in the network.

In multi-hop networks, conventional forwarding along a unicast route forces the data transmission to follow a fixed sequence of nodes. In previous works, it has been shown that widening this path to create a corridor of forwarding nodes and applying OFDMA to split and merge the data as it travels through the corridor towards the destination node leads to considerable gains in achievable throughput compared to the case forwarding data along a unicast route. However, the problem of selecting potential nodes to act as forwarding nodes within the corridor has not been addressed in the literature, as in general a rather homogeneous network topology with equally spaced relay clusters per hop between source and destination node has been assumed. In this paper, a more realistic heterogeneous network is considered where the nodes in the area between source and destination are randomly distributed instead of being clustered with equal distance. A node selection scheme is presented which selects the forwarding nodes within the corridor based on a given unicast route between source and destination node. In simulations, it is shown that with the proposed node selection scheme, considerable throughput gains of up to 50 % compared to forwarding along unicast route can be achieved applying corridor-based routing in heterogeneous networks especially in sparse networks.

This paper analyzes multicast (MC) as an efficient approach in transmitting the same information to multiple receivers (RXs). In each transmission time slot (TS), based on the channel realizations and on the specific MC strategy, a subset of RXs to be served is selected. The members of the served subset may change in the next TS. We assume that the channels from the transmitter (TX) to the RXs are independent and identically distributed (i.i.d.). This makes it possible for each RX to get, on average, the same amount of information. Herein, we find a closed form solution regarding the throughput of the Opportunistic Multicast strategy with fixed group size (OppMC-FS) [1] and present a new variant of this strategy called OppMC with optimal group size (OppMC-OS), providing an analytical solution regarding its throughput. Both variants, OppMC-FS and OppMC-OS, require instantaneous channel state information (CSI) at the TX. In addition, we also propose a new MC strategy, named MC based on statistical channel knowledge (StCSI-MC), and find the throughput of this strategy in a closed form. Results show that our strategies outperform broadcast or unicast and also that a good MC strategy can be found without the need of instantaneous CSI.

In this article, a hybrid multi-user OFDMA scheme which considers different user demands regarding channel access and user-specific imperfect channel quality information (CQI) is analytically described and evaluated. The considered hybrid scheme offers two possible modes to serve the user: firstly, via a non-adaptive mode which applies a discrete Fourier transform precoding to exploit frequency diversity and, thus, does not require any CQI at the transmitter. Secondly, via an adaptive mode which performs an adaptive resource allocation and link adaptation. Since this adaptation to the channel is done based on CQI, the adaptive mode is prone to imperfect CQI which results from estimation errors or time delays. Hence, in case of user-specific imperfect CQI, the question arises which user shall be served adaptively or non-adaptively and which resource shall be allocated to which user such that the system data rate is maximized while fulfilling a certain target bit error rate (BER) and minimum required user data rate. Analytical expressions of the system performance considering imperfect CQI and different user demands are derived. Based on these expressions, algorithms determining which user is served adaptively or non-adaptively subject to the BER and minimum data rate constraints are developed. Simulations show the superiority of the hybrid OFDMA scheme in terms of achievable data rate and user satisfaction compared to conventional pure adaptive and non-adaptive OFDMA schemes in the presence of user-specific imperfect CQI.

Recent work in wireless sensor networks implies possibilities of concurrent support of multiple applications. In this paper, we discuss a novel scheme called hybrid computation in two-way relaying, which introduces cooperation of three sensor nodes to support bi-directional communications of two applications. Applications in wireless sensor networks require different computations and forms of aggregation. In the proposed scheme, different computations at the intermediate node are integrated in a two-way relaying scheme. For computations and transmissions in the proposed scheme, data from all three nodes are considered. We propose a superposition coding protocol and a time division protocol to handle the transmission of the messages from the intermediate node. The problem of maximizing the sum rate is discussed. The results show that the superposition coding protocol outperforms the time division protocol. TRUE pub

Dissertation, RWTH Aachen University, 2019; Aachen 1 Online-Ressource (IX, 98 Seiten) : Illustrationen (2019). = Dissertation, RWTH Aachen University, 2019, Inspired by colloidal photonic crystals found in nature, the production of monodisperse particles, which spontaneously self-assemble into artificial colloidal crystals, has always been an inspiring challenge for scientists. Such colloidal crystals have been prepared from a wide variety of dielectric materials and find application in fields, ranging from sensors and fibre optical components to jewelry. In this work, I present novel dispersion polymerization approaches for the production of monodisperse nanoparticles consisting of semiconducting conjugated polymers. These conjugated polymer particles can self-assemble into photonic crystals without elaborate and costly nanofabrication methods. In the first part, I generate monodisperse hard sphere conjugated polymer nanoparticles (CPNs) via palladium catalyzed Heck cross-coupling dispersion polymerization. These particles self-assemble into photonic crystals and are applied as a gain medium and resonator in an organic laser. However, the Pd-catalyzed cross-coupling reaction produces metal residues as an inevitable by-product within the synthesized particles. These are disadvantageous for optical applications. In the following chapters of this thesis, I therefore rigorously focus on metal-free approaches. Using metal-free Knoevenagel dispersion polymerization I create hybrid particles by seeding the particle nucleation with dielectric SiO2 particles, enabling the generation of silica-core conjugated-polymer-shell particles. These hybrid particles act as whispering gallery mode resonators (WGM) and show emission of laser light. Finally, the Horner-Wadsworth-Emmons reaction is investigated as a metal-free dispersion polymerization, offering shape tunable conjugated CPNs. The shape can be controlled between highly monodisperse amorphous CPNs to crystalline platelet-like particles and porous conjugated organic framework particles. This method does not only proceed without any metal catalyst but also takes place at room temperature. Moreover, I investigate the kinetics of particle formation for all aforementioned step growth dispersion polymerizations. This data helps to understand, under which conditions monodisperse particles can be obtained using step growth polycondensation applied to a dispersion polymerization protocol. This work opens up pathways for tailor-made synthesis of CPN and their application in optoelectronic devices or in bio-imaging experiments in the near future., Published by Aachen