Jamming is a physical process which is both easy to describe and incredibly difficult to understand. One such difficulty is that mechanical treatments of jamming focus on pressure, force, stress, and strain, which are identically zero below jamming, making it hard to differentiate systems whcih which are near or far from the transition. Instead, I introduce a geometric framework based on the Voronoi tesselation which treats all of phase space on an equal footing. This work will show that the jamming transition can be seen entirely through the geometry of the local environment of particles encoded in the Voronoi tesselation, and it will build the framework for an as yet undefined field theory for jamming.

Spectrum supremacy is a vital part of security in the modern era. In the past 50 years, a great deal of work has been devoted to designing defenses against attacks from malicious nodes (e.g., anti-jamming), while significantly less work has been devoted to the equally important task of designing effective strategies for denying communication between enemy nodes/radios within an area (e.g., jamming). Such denial techniques are especially useful in military applications and intrusion detection systems where untrusted communication must be stopped. In this dissertation, we study these offensive attack procedures, collectively termed as communication denial. The communication denial strategies studied in this dissertation are not only useful in undermining the communication between enemy nodes, but also help in analyzing the vulnerabilities of existing systems. A majority of the works which address communication denial assume that knowledge about the enemy nodes is available a priori. However, recent advances in communication systems creates the potential for dynamic environmental conditions where it is difficult and most likely not even possible to obtain a priori information regarding the environment and the nodes that are present in it. Therefore, it is necessary to have cognitive capabilities that enable the attacker to learn the environment and prevent enemy nodes from accessing valuable spectrum, thereby denying communication. In this regard, we ask the following question in this dissertation ``Can an intelligent attacker learn and adapt to unknown environments in an electronic warfare-type scenario?" Fundamentally speaking, we explore whether existing machine learning techniques can be used to address such cognitive scenarios and, if not, what are the missing pieces that will enable an attacker to achieve spectrum supremacy by denying an enemy the ability to communicate? The first task in achieving spectrum supremacy is to identify the signal of interest before it can be attacked. Thus, we first address signal identification, specifically modulation classification, in practical wireless environments where the interference is often non-Gaussian. Upon identifying the signal of interest, the next step is to effectively attack the victim signals in order to deny communication. We present a rigorous fundamental analysis regarding the attackers performance, in terms of achieving communication denial, in practical communication settings. Furthermore, we develop intelligent approaches for communication denial that employ novel machine learning techniques to attack the victim either at the physical layer, the MAC layer, or the network layer. We rigorously investigate whether or not these learning techniques enable the attacker to approach the fundamental performance limits achievable when an attacker has complete knowledge of the environment. As a result of our work, we debunk several myths about communication denial strategies that were believed to be true mainly because incorrect system models were previously considered and thus the wrong questions were answered. / Ph. D.

The intent of this thesis it to find a correlation between the stiffness of granular jammed particles and the pressure of the vacuum initiating the jamming force. Currently, granular jamming is being used to create palpation simulators for physicians to practice feeling the variety of stiffnesses of organs when healthy or ill. Because granular jamming allows for variable stiffness of any shape, it is an apt phenomenon to simulate the change of rigidity organs like the liver undergoes when diseased. For physicians to correctly identify how stiff the organ must be when using these palpation simulators, there needs to be a way to know how much pressure must be applied to correctly simulate the stiffness of the organ for each specific scenario. This thesis will discuss how pressure affects stiffness by using the three-point bending test. To perform this test, a tubular balloon filled with coffee granules was used to represent the beam. An impact force as well as a hanging force was used to displace the beam. The displacement of the beam is adequate to find the Young's Modulus or stiffness of the beam of granules at different pressures provided by the vacuum. It was found that there is a correlation between stiffness and pressure of a granular jammed system. This will allow for future physicians to accurately and consistently use model organs to practice palpation techniques.

With the increasing volume of wireless traffic that military operations require, the likelihood of transmissions interfering with each other is steadily growing to the point that new techniques need to be employed. Furthermore, to combat remotely operated improvised explosive devices, many ground convoys transmit high-power broadband jamming signals, which block both hostile as well as friendly communications. These wide-band jamming fields pose a serious technical challenge to existing anti-jamming solutions that are currently employed by the Navy and Marine Corps. This thesis examines the feasibility of removing such deterministic jammers from the spectral environment, enabling friendly communications. Anti-jamming solutions in self-jamming environments are rarely considered in the literature, principally due to the non-traditional nature of such jamming techniques. As a result, a combination of approaches are examined which include: Antenna Subset Selection, Spectral Subtraction, and Source Separation. These are combined to reduce environmental interference for reliable transmissions. Specific operational conditions are considered and evaluated, primarily to define the limitations and utility of such a system. A final prototype was constructed using a collection of USRP software defined radios, providing solid conclusions of the overall system performance.

This work describes the evolution cf electronic warfare equipment and techniques in the USA, from the first instance of radio jamming in that country in 1901 until the end of World War II in 1945. It begins with a review of early work on telegraph, radio and radar systems throughout the world, and countermeasures used during trials or in combat prior to World War II. Immediately after the USA ertered the conflict in 1941, the Radio Research Laboratory was set up near Boston to develop radio countermeasures equipment for the US armed forces. The organisation rapidly outgrew the capacity of a angle laboratory and in October 1942 Division 15 of the National Defense Research Committee was formed, to co-ordinate US work on countermeasures. The activities of RRL and Division 15 are described in detail, using cortemporary records and accounts from participants. Radar jammers developed by Divison 15 were first used in action in July 1943 during the invason of Sicily, and went on to play important roles in support amphibious landings and strategic bombing operations in the European and Pacific theatres of operations. The jamming devices and tactics employed, the enemy attempts to develop counter-countermeasures and the US moves to counter these counters are all described in detail. Conclusions are drawn on the effectiveness of the various types of jamming, based on post-war interrogation of German and Japanese serving officers and technical personnel. Appendices give technical details of the countermeasures devices produced in the USA during World War II, and the development of radar and radar countermeasures in Germany and Japan.

Diese Arbeit behandelt die Beschreibung des Fließens und des Blockierens von granularer Materie. Granulare Materie kann einen Verfestigungsübergang durchlaufen. Dieser wird Jamming genannt und ist maßgeblich durch vorliegende Spannungen sowie die Packungsdichte der Körner, welche das Granulat bilden, bestimmt. Die Rheologie dichter granularer Medien ist zusätzlich zu Spannung und Packungsdichte stark durch Reibung zwischen den Körnern beeinflusst. Wir zeigen mittels numerischer Simulationen und analytischer Betrachtungen, wie Reibung Jamming qualitativ verändert. Reibungsfreies Jamming ist ein kontinuierlicher Phasenübergang mit einem kritischen Punkt bei verschwindender Spannung. Reibungsbehaftetes Jamming ist ein diskontinuierlicher Phasenübergang mit einem kritischen Punkt bei endlicher Spannung. Der kritische Punkt bei endlicher Spannung führt zu bemerkenswertem Verhalten: Oberhalb der kri- tischen Packungsdichte gibt es ein Intervall an Packungsdichten, innerhalb dessen große oder kleine Spannungen zum Fließen führen, mittlere Spannungen hingegen führen zum Blockieren des Mediums. Das Fließverhalten nahe Jamming ist stark durch die Systemgröße beeinflusst: Es gibt eine kritische Systemgröße, oberhalb derer zeitabhängiger Fluss entsteht. Dieser zeitabhängige Fluss wird durch die Ausbildung von großskaligen Strukturen im Spannungsfeld erklärt. Sowohl die großskaligen Strukuren als auch der damit einhergehende zeitabhängige Fluss sind neuartige Phänomene im Fluss von trockenen Granulaten und durch Rei- bung hervorgerufen.

Bicontinuous Pickering emulsions (or bijels) are a relatively new class of novel soft material with many potential industrial applications, including microfluidics, tissue engineering and catalysis. They are typically formed by initiating the spinodal decomposition of a binary liquid mixture in the presence of neutrally-wetting colloidal particles. The particles attach at the liquid-liquid interface and arrest the phase separation by jamming when the concentration of particles approaches the 2D close-packing limit. Predicted by simulations in 2005 and realized in the laboratory in 2007, many aspects of the bijels complex behaviour and properties have remained unexplored. This thesis expands the knowledge of the bijels structural and dynamical properties, while focusing specifically on the role of particle size. The bijels porosity (average interfacial separation L) according to simulations can be controlled by varying the size r and volume fraction ϕ of particles in the system (L ∝ r/ϕ). The inverse scaling of L with ϕ has been verified for one size of particle, but to access smaller values of L (to allow the structure to be used for a wider range of industrial applications) the scaling with r must be tested. Chapter 3 presents the first systematic study of reducing particle size in bijels made with the liquid pair water/lutidine (W/L).We find that a five-fold reduction in r only requires moderate modification to preparation methods (concentrations of reactants during particle synthesis and increased particle sonication time) and in principle allows L values of between 1 & 10 μm to be accessed in the W/L system, where previously 10 μm was the limit. We demonstrate that this reduced lower bound of L can be translated into a lower bound for polymerized bijels also. Unfortunately, reducing particle size even further (in the same way) reveals a law of diminishing returns, as the uptake fraction of particles to the interface also reduces as we reduce particle size. Hence, to reduce lengthscale even further, a new bijel fabrication paradigm is required. Unexpectedly, we find that the temperature quench rate becomes less important for smaller particles (which constitutes a direct material synthesis advantage) and develop a new theoretical framework to take account of this observation. Large particles promote domain pinch-off during the coarsening (due to a larger driving force towards spontaneous curvature) resulting in bijel failure when slow rates are used because the time required to jam is greater than the time required for depercolation. To further probe the bijels structure as a function of particle size and quench rate, and to account for the success/failure scenarios which seem not to depend on L, in Chapter 4 we quantitatively characterize the morphology by measuring distributions of interfacial curvatures. By computing area-averaged quantities to make valid comparisons, we find that smaller particles and faster quench rates produce bijels with greater hyperbolic `open' character, aligning with our understanding of bijel formation gained from Chapter 3. We compare to simulated bijel data and an estimate of the hyperbolicity of the bare liquids undergoing spinodal decomposition, validating the results. In addition, we uncover a time-dependent `mutation' of the curvature distributions when large particles are used, but not when smaller particles or a different liquid pair is used. The mutation appears to correlate with the propensity of the interfacial particles to form a 'monogel', whereby the interfacial particles develop permanent bonds and remain as a 3D percolating network after the interface is removed, although the precise mechanism of the mutation is still to be verified. Following the results from Chapters 3 & 4 it is clear that there are potentially microscopic phenomena in the bijel which result in macroscopic aging and/or a determination of macroscopic structural properties. To investigate further, we use diffusing-wave spectroscopy (a form of light scattering) to probe the microscopic dynamics of the interfacial particles and/or the particle-laden liquid-liquid (L-L) interface. We find that bijel dynamics show two-step (fast/slow) decay behaviour, with the dynamics slowing as the system ages. The two-step decay is very similar to that observed in colloidal gels formed by diffusion-limited cluster aggregation (DLCA), with the initial (fast) decay due to thermally-activated modes of the gel network, and the later (slow) decay due to the relaxation of internal stresses induced by gel syneresis. For a bijel, the internal stresses could be due to syneresis, but could also be due to the jamming transition and/or the monogelation process and/or the forces acting on the L-L interface by the particle layer. In terms of the aging, if the system does not form a monogel, the correlation functions can be (almost) rescaled on to a master curve, indicating the property of universal aging. If the system does monogel, the functions cannot be superimposed, implicating the monogelation process as a potential cause for a different kind of aging in this system. Due to the interesting differences found when changing the size of the stabilizing particles in a bijel, in Chapter 6 we combine large and small particles (making `bimodal' bijels) and look for evidence of particle segregation by size, quantitatively estimate the ratio of particle uptake fractions and measure kinetics. Larger particles are found to adsorb to the interface in twice the quantity as smaller particles, and we find evidence to suggest the preference of larger particles for interfaces curved in only one direction, corroborating results from previous Chapters. Bimodal bijels take longer to jam than an equivalent monomodal (standard) bijel, which is backed up by simulations and highlights the increased ability of the bimodal particles to reorganise at the interface before arriving at the jammed metastable state. Finally, we also observe that the lengthscale of a bimodal bijel can heavily depend on the quench rate used during the preparation, suggesting that quench rate could be used (as well as particle size, volume fraction and contact angle) as a lengthscale control parameter. This thesis adds to the bijel literature, building on previous experimental studies and verifying/contradicting simulations. Particle size is shown to be a pivotal parameter for bijel formation in the W/L system, with particles of size r = 63 nm proving more versatile (markedly less sensitive to quench rate) than particles of size r ≈ 300 nm. However, even-smaller particles (of the same type) do not provide any additional advantage. We also show how the particle size can not only control bijel porosity (according to L ∝ r/ϕ as predicted by simulations) but can control bijel topology (smaller particles result in structures with greater hyperbolic character). By monitoring the bijel structure over time (topology and dynamics) we have shown that the bijel (in some cases) continues to age for at least c. 1 hr (topology) and in all cases c. 1 day (dynamics). For the first time experimentally, we have used a bimodal dispersion of particles to stabilize a W/L bijel and have uncovered a potentially useful new way to produce samples with different porosities from the same starting mixture, by changing the quench rate. The knowledge of the interplay between particle size and quench rate along with the effect on bijel topology will both assist in the scaling up of processes for industrial-level production and inform future strategies for tailoring the structure for specific applications. Future research should focus on several remaining open questions. The volume fraction of r = 63 nm particles in the W/L system should be increased towards 10% and sonication procedures improved to allow good redispersion to test the lower bound of L, which we expect to be around 1 μm. Also, a new W/L fabrication paradigm should be devised which uses sterically-stabilized particles, to continue the reduction of r towards the value used in simulations (5 nm) in order to test the fundamental physics of bijel formation, specifically what value of interfacial attachment energy is needed for long-term stability. Bijel dynamics can be further probed by using a technique which allows a variation in the probe lengthscale (e.g. / differential dynamic microscopy, DDM), as well as developing a better theoretical model for (multiple) light scattering in a bijel system to arrive at the mechanisms responsible for the anomalous aging, and compare to the predictions of monogelation. Finally, higher magnification/resolution microscopy should be used to look for particle segregation on the liquid-liquid interface (as seen in simulations) and to identify in real-space the locations of the changes in Gaussian curvature over time as measured in Chapter 4.

Made available in DSpace on 2016-04-29T14:22:49Z (GMT). No. of bitstreams: 1 Juana Ribeiro Diniz.pdf: 1256050 bytes, checksum: 71675c4524e8ec274f886cf92c419cc6 (MD5) Previous issue date: 2010-09-24 / This work has as its study object the culture jamming, a form of contemporary activism which, through practices that blend various art techniques and a boyish trick spirit, subverts advertising messages and leads to situations that criticize media culture and the branding process that this culture helps to produce. The question more frequently discussed about jammer performances regards its revolutionary efficacy. Thus, this research intends to make an analysis of the possibilities that the cyberspace opens, as a new format, to the jammer creation. It begins delineating a panorama of jammer performance, using as major references the analyses of the following authors: Kalle Lasn, Mark Dery and Naomi Klein. The next chapter contextualizes the culture jamming in the cyberspace, using André Lemos', Lúcia Santaella's and Pierre Lévy's theories on such matter. Supported by studies about the aesthetics of technology, it was possible to draw a profile of the jammer aesthetic in the cyberspace and, in this way, to analyze some examples in order to compare their approach in the real space and the virtual one. For this topic, Derrick Kerckhove's, Lúcia Santaella's and Pierre Lévy's theories were used. The examples were chosen regarding the necessity to analyze both their diversity as their repercussion. So, the comparative analyses lead us to remark that the jammer creation in the cyberspace is still coy and not completely aware of the full possibilities offered by it. And because of the complex and dynamic aspects of the web environment, it is difficult to foresee or indicate the entire range of possibilities that the cyberspace has to offer to jammer creation. However, this research leads to believe that the better source to increase and explore the creativity inside the cyberspace is in the paths that have been opened by the cyberart. It is a longtime bet, but everything indicates that the more familiar the jammers get with the virtual space, more capable they will become to explore all the creative aspects granted by the cyberspace / O trabalho proposto aqui tem como objeto de pesquisa a culture jamming que pode ser compreendida como uma forma de ativismo contemporâneo que, através de práticas que misturam diversas técnicas artísticas e o espírito de molecagem, subvertem mensagens publicitárias e criam situações que resultam em uma crítica à cultura midiatizada e às imagens das marcas que esta ajuda a construir. A questão em debate mais recorrente sobre a atuação jammer se refere à sua eficiência revolucionária. Na busca por pistas que contribuam e, juntamente com outros estudos, indiquem uma resposta mais confiável para tal debate, este trabalho se propôs a realizar uma análise do potencial que o ciberespaço abre, como um novo formato, para a criação jammer. Com este objetivo, inicialmente foi traçado um panorama da atuação jammer, utilizando como principais referências as descrições dos seguintes autores: Kalle Lasn, Mark Dery e Naomi Klein. Em seguida, um capítulo foi dedicado à contextualização da culture jamming no ciberespaço, utilizando como embasamento teórico André Lemos, Lúcia Santaella e Pierre Lévy nas considerações referentes ao ciberespaço. Através dos estudos sobre a estética tecnológica, foi possível se traçar um perfil da estética jammer dentro do ciberespaço e assim analisar alguns exemplos de forma comparativa, confrontando a sua abordagem no espaço presencial e no virtual. Os pressupostos teóricos para tanto vieram principalmente das leituras de Derrick Kerckhove, Lúcia Santaella e Pierre Lévy. A escolha das amostras levou em consideração a necessidade de analisar exemplos diversificados tanto em formato, quanto em graus de repercussão. Com as observações encontradas nessa análise comparativa foi possível identificar que a criação jammer no ciberespaço ainda se mostra tímida e não totalmente familiarizada com as novas possibilidades estéticas oferecidas pelo mesmo. Pelo próprio caráter complexo e dinâmico dos caminhos rizomáticos do ambiente em questão fica difícil prever ou mapear toda a gama de possibilidades que o ciberespaço tem a oferecer para a criatividade jammer. No entanto, o observado nesta pesquisa leva a crer que a fonte mais indicada para ampliar e melhor explorar a criatividade dentro do ciberespaço está nos caminhos que estão sendo abertos pela ciberarte. A aposta deste trabalho está no decorrer do tempo. Quanto mais íntimos os jammers estiverem do espaço virtual, maior será a sua capacidade de explorar o aspecto criativo da prática dentro do ciberespaço

Les émulsions de type huile-dans-eau jouent un rôle important lors des opérations de ré-injection des eaux de production (PWRI). Ce travail s'intéresse à l'écoulement /rétention de ce type d'émulsions en milieux poreux et à leur impact sur l'injectivité. Deux mécanismes fondamentaux sont distingué selon la valeur du Jamming ratio Jr (taille des restrictions /taille des gouttes): le dépôt dit de surface aux forts Jr et le «straining» (blocage, par le forces capillaires, d'une ou plusieurs gouttes à l'amont d'une restriction) aux faibles Jr.Ce document traite, d'abord, de la physicochimie du dépôt de surface. L'étude en fonction de différents paramètres, tels que la salinité et le débit, permis de décrire la structure et la cinétique du dépôt. Nous avons notamment mis en évidence la formation d'une monocouche compacte é gouttelettes individuelles et montré que la cinétique du dépôt vérifie les lois d'échelle développées pour les colloïdes. L'ensemble de nos résulta conforte la similarité de comportement entre les émulsions stables et diluées et les systèmes colloïdaux.Ensuite, le «straining» est mis en évidence et discuté en fonction des distributions en taille -des restrictions et des gouttes- et des valeurs du nombi capillaire.Enfin, nous avons établi que l'endommagement associé au dépôt de surface peut être très significatif et que les pertes d'injectivité sont prédictibles par une loi de Poiseuille modifiée. Pour le «straining», l'impact est encore plus sévère mais sa vitesse de propagation est plus lente.En conclusion, l'effet de ce type d'émulsion doit être pris en compte pour minimiser les risques et optimiser le schéma de réinjection. / The O/W emulsions are major actors in the operations of produced water reinjection (PWRI). This work focuses on the flow/retention of these specific emulsions in porous media and their impact on injectivity. Two fundamental mechanisms are considered according to the jamming ration Jr, that is to say the pore throat to droplet size ratio. At high Jr, surface retention is operative, whereas at small ones, it is the "straining" which describes the upstream clogging of a pore throat by one or more droplets because of the capillary forces.This report firstly targets the physicochemistry of the surface deposit. Several parameters were checked, such as salinity and flow rate, and allow us to descrïbe the deposit structure and the deposition kinetics. We evidenced the formation of a dense monolayer of individual oil droplets and showed that the deposition kinetïcs follows the scaling power laws initially developed for colloids. It clearly underlines the similar behaviour of stable emulsion anc other colloidal systems.Then, the straining was observed and discussed according to size distributions of botte droplets and pore throats and also according to the capillary number.Finally, we established that the injectivity losses caused by surface retention can be very significant and that they are predictable through a modified Poiseuille's law. Concerning the "straining", the impact is even more severe but its propagation rate is far smaller.To conclude, the effects of these emulsions have to be taken into account to minimise the risks and optimise the reinjection scheme.

Bats using their biosonar while flying in dense swarms may face significant bioacoustic challenges, in particular mutual sonar jamming. While possible solutions to the jamming problem have been investigated multiple times in literature, the severity of this problem has received far less attention. To characterize the acoustics of bat swarms, a simple model of the acoustically relevant properties of a bat swarm has been set up and evaluated. The model contains only four parameters: bat spacial density, biosonar beamwidth, duty cycle, and a scalar measure for the smoothness of the flight trajectories. In addition, a threshold to define substantial jamming was set relative to the emission level. The simulations results show that all four model parameters can have a major impact on jamming probability. Depending on the combination of parameter values, situations with or without substantial jamming probabilities could be produced within reasonable ranges of all model parameters. Hence, the model suggests that not every bat swarm does necessarily impose grave jamming problem. A fitting process was introduced to describe the relationship between the four parameters and jamming probability, hence produce a function with jamming probability as output and four parameters as input. Since the model parameters should be comparatively easy to estimate for actual bat swarms, the simulation results could give researchers a way to assess the acoustic environment of actual bat swarms and determine cases where a study of biosonar jamming could be worthwhile. / Master of Science