http://idea.library.drexel.edu/handle/1860/1063 Search the Channel search http://idea.library.drexel.edu/simple-search http://idea.library.drexel.edu/handle/1860/3963 Title: HPDLC Films doped with Carbon Nano-onions to improve its electro optic response <br/> <br/>Authors: Bellingham, Alyssa; Shriyan, Sameet K.; Fontecchio, Adam K. <br/> <br/>Abstract: Holographically-formed Polymer Dispersed Liquid Crystal films (HPDLC) are electro-optical thin films that phase separate upon exposure to an interference pattern to form a Bragg grating composed of alternating layers of liquid crystal droplets and polymer. The Bragg grating allows the film to reflect a preselected wavelength of light. When an electric field is applied to the film , the liquid crystals in the film align in the direction of that field allowing all wavelengths of light to pass through. This switching property makes these films ideal for many applications including displays, biomedical sensors, gas analysis, and Hyperspectral imaging devices. In order to reduce the voltage at which the films switch, materials with high conductivities can be introduced into the polymer regions of the films to slightly increase the overall conductivity of the polymer relative to the liquid crystal. This research focuses on doping the polymer used in the films with carbon nano-onions, which resemble nano-scale buckyballs in structure. They can be functionalized to attach only to the polymer regions during phase separation, which will increase the polymer’s conductivity and lead to a reduction in the voltage needed to switch the samples without hindering the alignment of the liquid crystals. In the mixtures that have been developed so far, there have been aggregates of nano-onions, which reduces the increase in conductivity of the polymer caused by the introduction of nano-onions and decreases transmission through the film. Ideally, the films will retain higher than 80% transmission with the carbon nano-onions, so work is currently being done to reduce the nano-onion aggregates and determine the best ratio of nano-onions to polymer. http://idea.library.drexel.edu/handle/1860/2748 Title: Validation of high gradient magnetic field based drug delivery to magnetizable implants under flow <br/> <br/>Authors: Forbes, Zachary G.; Yellen, Benjamin B.; Halverson, Derek S.; Fridman, Gregory; Barbee, Kenneth A.; Friedman, Gary <br/> <br/>Abstract: The drug-eluting stent’s increasingly frequent occurrence late stage thrombosis have created a need for new strategies for intervention in coronary artery disease. This paper demonstrates further development of our minimally invasive, targeted drug delivery system that uses induced magnetism to administer repeatable and patient specific dosages of therapeutic agents to specific sites in the human body. Our first aim is the use of magnetizable stents for the prevention and treatment of coronary restenosis; however, future applications include the targeting of tumors, vascular defects, and other localized pathologies. Future doses can be administered to the same site by intravenous injection. This implant-based drug delivery system functions by placement of a weakly magnetizable stent or implant at precise locations in the cardiovascular system, followed by the delivery of magnetically susceptible drug carriers. The stents are capable of applying high local magnetic field gradients within the body, while only exposing the body to a modest external field. The local gradients created within the blood vessel create the forces needed to attract and hold drug-containing magnetic nanoparticles at the implant site. Once these particles are captured, they are capable of delivering therapeutic agents such as antineoplastics, radioactivity, or biological cells. http://idea.library.drexel.edu/handle/1860/2720 Title: Distributed linear block coding for cooperative wireless communications <br/> <br/>Authors: Rossi, Pierluigi Salvo; Petropulu, Athina P.; Palmieri, Francesco; Iannello, Giulio <br/> <br/>Abstract: Performance of wireless communications systems is degraded by fading, typically combated via spatial diversity by multiple transmit and receiver antennas. Practical limitations may limit their use; thus, cooperative transmissions have been proposed to introduce diversity without the need for multiple antennas. We propose a novel cooperative scheme that performs distributed coding of user data. It needs each user transmit on one single channel and allows large flexibility between rate and diversity. A trade-off is increased complexity as more users are required to be decoded simultaneously by the base station. We present construction of the distributed code for different choices of rates and diversity orders by means of simple linear block codes, resulting in reduced complexity for decoding operations. Achieved diversity order is bounded by the minimum distance of the implemented distributed code. Performance of the scheme is studied via analytical bounds and numerical simulations. http://idea.library.drexel.edu/handle/1860/2718 Title: Approximation modeling for the online performance management of distributed computing systems <br/> <br/>Authors: Kusic, Dara; Kandasamy, Nagarajan; Jiang, Guofei <br/> <br/>Abstract: This paper develops a hierarchical control framework to solve performance management problems in distributed computing systems. To reduce the control overhead, concepts from approximation theory are used in the construction of the dynamical models that predict system behavior, and in the solution of the associated control equations themselves. Using a dynamic resource provisioning problem as a case study, we show that a computing system managed by the proposed control framework using approximation models realizes profit gains that are, in the best case, within 1% of a controller using an exact parametric model of the system. http://idea.library.drexel.edu/handle/1860/2702 Title: Ad hoc networks: to spread or not to spread? <br/> <br/>Authors: Andrews, Jeffrey G.; Weber, Steven; Haenggi, Martin <br/> <br/>Abstract: Spread spectrum communication — often called code-division multiple access — has been widely adopted over the years for many types of interference-challenged wireless communication systems including cellular and cordless telephones, wireless LANs and PANs, military applications, and global positioning systems. In this article we explore whether CDMA, in either its frequency hopping (FH) or direct sequence (DS) form, is an appropriate design approach for wireless ad hoc, or mesh, networks. One goal of this article is to help provoke a debate by explaining the main advantages and disadvantages of CDMA in the context of ad hoc networks as exposed by recent research. We argue that CDMA does not inherently improve the spectral efficiency of ad hoc networks; on the contrary, its valued interference averaging effect is not appreciable in ad hoc networks due to the irregular distribution of both the transmitters and receivers. On the positive side, both types (FH and DS) of spread spectrum allow for longer hop distances and a reversal of the usual relationship where the desired transmitter must be closer to the receiver than interfering transmitters. These two facts allow for significant advantages over narrowband systems in terms of energy efficiency and end-to-end delay. http://idea.library.drexel.edu/handle/1860/2698 Title: 4x4 MIMO experimental test-bed using COTS at ISM band <br/> <br/>Authors: Spring, Ryan; Zhou, Liming; Gogate, Nikhil; Daryoush, Afshin S. <br/> <br/>Abstract: This paper presents the implementation of a 4x4 multiple input multiple output (MIMO) test-bed that is employed for channel characterization using virtual MIMO indoor channel sounding technique. The 4x4 MIMO operates at ISM frequency of 2.45GHz with 5MHz of bandwidth using low cost commercially available off-the-shelf components (COTS). The system benefits from direct conversion transceiver units, reported before. Channel propagation measurements were performed in a rich multi-path environment by employing a virtual MIMO indoor wireless channel sounding as well as a direction of arrival (DOA) estimation algorithms. The channel sounding technique employs sequential switching of 1x4 Single Input Multiple Output (SIMO) channels to realize a virtual 4x4 MIMO experiments in a stationary channel environment. A hardware calibration method is also developed as a critical part of the MIMO evaluation. The DOA experiment, which employs a linear four-element patch antenna array at the receiver and a single patch antenna at the transmitter, provides a maximum of 15 degrees offset using Bartlett algorithm. The measured channel response matrix is also verified through comparison with other published results. http://idea.library.drexel.edu/handle/1860/2696 Title: The effect of fading, channel inversion, and threshold scheduling on ad hoc networks <br/> <br/>Authors: Weber, Steven; Andrews, Jeffrey G.; Jindal, Nihar <br/> <br/>Abstract: This paper addresses three issues in the field of ad hoc network capacity: the impact of i) channel fading, ii) channel inversion power control, and iii) threshold–based scheduling on capacity. Channel inversion and threshold scheduling may be viewed as simple ways to exploit channel state information (CSI) without requiring cooperation across transmitters.We use the transmission capacity (TC) as our metric, defined as the maximum spatial intensity of successful simultaneous transmissions subject to a constraint on the outage probability (OP). By assuming the nodes are located on the infinite plane according to a Poisson process, we are able to employ tools from stochastic geometry to obtain asymptotically tight bounds on the distribution of the signal-to-interference (SIR) level, yielding in turn tight bounds on the OP (relative to a given SIR threshold) and the TC. We demonstrate that in the absence of CSI, fading can significantly reduce the TC and somewhat surprisingly, channel inversion only makes matters worse. We develop a threshold-based transmission rule where transmitters are active only if the channel to their receiver is acceptably strong, obtain expressions for the optimal threshold, and show that this simple, fully distributed scheme can significantly reduce the effect of fading. http://idea.library.drexel.edu/handle/1860/2670 Title: PARAFAC-based blind estimation of possibly underdetermined convolutive MIMO systems <br/> <br/>Authors: Yu, Yuanning; Petropulu, Athina P. <br/> <br/>Abstract: In this paper, we consider the problem of blind identification of a convolutive multiple-input–multiple-output (MIMO) system with No outputs and Ni inputs. While many methods have been proposed to blindly identify convolutive MIMO systems with Nq>/=Ni (overdetermined), very scarce results exist for the case of (underdetermined), all of which refer to systems that either have some special structure or special No and Ni values. In this paper, we show that, as long as min(No,Ni)>/= 2, independent of whether the system is overdetermined or underdetermined, we can always find the appropriate order of statistics that guarantees identifiability of the system response within trivial ambiguities. We also propose an algorithm to reach the solution, that consists of parallel factorization (PARAFAC) of a K-way tensor containing Kth-order statistics of the system outputs, followed by an iterative scheme. For a certain order of statistics K , we provide the description of the class of identifiable MIMO systems. We also show that this class can be expanded by applying PARAFAC decomposition to a pair of tensors instead of one tensor. The proposed approach constitutes a novel scheme for estimation of underdetermined systems, and improves over existing approaches for overdetermined systems. http://idea.library.drexel.edu/handle/1860/2631 Title: Liquid crystal polymer composite films for reconfigurable photomasking applications <br/> <br/>Authors: Fox, Anna E.; Fontecchio, Adam K. <br/> <br/>Abstract: We show proof of concept of a real-time reconfigurable photomask fabricated from holographically formed polymer-dispersed liquid crystal !H-PDLC" reflection gratings on etched indium tin oxide patterned electrodes. H-PDLC films were formed using a thiolene based polymer to have a reflection wavelength that modulates 440 nm, the peak sensitivity wavelength of Shipley 1800 series positive photoresist. A working prototype of this adaptable photomask device is shown by comparing patterns formed using the H-PDLC mask and similar patterns formed using a static contact photomask showing that H-PDLC films have the ability to modulate 440 nm light and control the exposure dose of photoresist. http://idea.library.drexel.edu/handle/1860/2627 Title: RTS/CTS data link abstractions for mobile ad hoc networks <br/> <br/>Authors: Wildman, Jeffrey; Willman, Bryan J.; Kirkpatrick, Michael; Weber, Steven P. <br/> <br/>Abstract: The running time for high fidelity simulation of large-scale mobile ad hoc networks can be prohibitively high. The execution time of physical effects calculations for a single transmission alone can grow unmanageable to account for all potential receivers. Discrete event simulators can also suffer from excessive generation and processing of events, both due to network size and model complexity. In this paper, we present three levels of abstracting the IEEE 802.11 RTS/CTS channel access mechanism. In the process of assessing their ability to mitigate runtime-cost while retaining comparable results to that of a commercially available simulator, OPNET, we found that the abstractions were better suited to collecting one metric over another.