Dissertations / Theses on the topic 'Contact'

On introduit trois types de structures géométriques nouvelles sur des variétés différentiables : formes de contact généralisé, couples de contact et couples contacto-symplectiques. Une forme de contact généralisé sur M est une 2k + 1-forme ω telle que ω∧dω soit une forme volume. Plusieurs exemples sont construits et on donne un critère local qui permet de montrer que tous ces exemples ne sont pas triviaux dans le sens qu'ils ne sont pas de la forme α ∧ dαk (où α est une forme de contact). Un couple de contact sur M est un couple (α, β) de formes de Pfaff de classe constante 2k + 1 et 2h + 1 respectivement et telles que la forme α ∧ dαk ∧ β ∧ dβh soit une forme volume. Chacune de ces formes détermine un feuilletage caractéristique dont les feuilles sont des variétés de contact. Ces feuilletages sont transverses et supplémentaires. La géométrie de tels objets est très riche car on peut naturellement leur associer deux champs de Reeb qui commutent, deux types de courbes de Legendre et deux crochets de Poisson. D'une manière similaire on définit un couple contacto-symplectique. Pour les deux dernières structure on démontre qu'il y a un unique modèle local et on construit plusieurs exemples non triviaux dans les groupes de Lie et dans les fibrés principaux en tores. Comme conséquence de la théorie des couples contacto-symplectiques on construit des exemples de champs de vecteurs (sur des variétés de contact) sans transversale fermée et qui ne sont le champ de Reeb d'aucune forme de contact. Ce qui répond à un célèbre problème de Reeb.

The tangential contact stiffness for ground Ti-6Al-4V surfaces is measured to linearly decrease with the application of tangential load. At the beginning of the application of tangential load, for ground surfaces, the ratio of the tangential contact stiffness to the normal contact stiffness is seen to be approximately half the Mindlin ratio. This is consistent with many other published experimental studies. Measurements of normal contact stiffness for ground surfaces conform to a model that posits a linear relationship between normal contact stiffness and normal load. An equivalent surface roughness parameter is defined for two surfaces in contact; and the normal contact stiffness for ground surfaces is observed to be inversely proportional to this parameter. Single asperity models were constructed to simulate the effect of different frictional laws and plasticity on the tangential displacement of an asperity contact. Further, multi-asperity modelling showed the effect of different normal load distributions on the tangential behaviour of interfaces. In addition, normal contact stiffness was modelled for a grid of asperities taking into account asperity interactions. A receding contact problem for which the required form of the distributed dislocations is bounded-bounded was solved. Then, a fundamental 2D frictional receding contact problem involving a homogeneous linear elastic infinite layer pressed by a line load onto a half-plane of the same material was analysed. This was done by the insertion of preformed distributed dislocations (or eigenstrains), which take into account the correct form of the separation of the interface at points away from the area of loading, along with corrective bounded-bounded distributions. The general method of solution was further refined and adapted to solve three other receding contact problems. The solutions demonstrated the robustness and applicability of this new procedure.

This thesis examines the influence of asperities such as found on the teeth of gears and discs, and failure mechanisms associated with rough surface Elastohydrodynamic Lubrication (EHL). The principal outcomes of the research provide a good insight into fatigue life, residual stress effects, damage prediction and surface contact failures. In particular, the study is intended to provide understanding into the residual stress distribution resulting from plastic deformation of surface asperities in the running in process. The residual stress is then added to the asperity elastic stress distribution and examined in detail to see the effects on fatigue damage and fatigue life. So, a theoretical model has been developed to assist design against the residual stress effect and surface contact fatigue, such as micropitting. The technique used in the study starts with developing an elastic plastic model of the rough surface by using the Abaqus Finite Element analysis software package. This is a nonlinear problem and ranges of applied loads have been applied to the as-manufactured surfaces causing the asperity features to experience varying degrees of plastic deformation. The pre and post running roughness profiles are studied in order to assess the level of plastic deformation actually occurring at significant surface asperity features by aligning the pre and post running profiles. This results in a new technique that has helped to identify the level of plastic deformation occurring in the practice, and also to make a comparison with FEA contact analysis for the same asperity features to identify the appropriate residual stress field. The residual stress field associated with the plastic deformation was extracted and evaluated. The extracted residual stress field was transferred to a form that facilitated IV inclusion in stress evaluation code to obtain the stress history for the material subject to loading in an EHL contact. The research carried out considers surface fatigue analysis with and without a residual stress field, so as to establish the influence of asperity plastic deformation on the fatigue properties of the surface. All the work is based on numerical simulation of surface fatigue failure in EHL situations and carried out numerically. The procedure can be applied quickly and gives the opportunity to apply several models and investigate the influence of all the model parameters on material deformation and fatigue life.

This fiction novel focuses on the Sankofa philosophy that we as human beings must learn from our past to better understand our current existence and future; however, sometimes we choose to ignore or suppress the past because remembering it may be too hurtful. When we forget what happened yesterday our outlook on today and tomorrow becomes distorted. Contact is a novel that attempts to explore how 'living in the now' alone becomes problematic because the past'if not remembered'will come back to haunt you. The erasure of the line between Diasporic Africans and their African past is the primary theme explored. The writer deconstructs how living in the now is indeed living in the past because the past and present, in the life of Tufa, become one. Reincarnation serves as the vehicle to explore this theme. Tufa, known for her aberrant behavior, is the reincarnation Afua Ataa - an Ashanti woman who survived the Maafa, or Transatlantic Slave Trade. Past love, hate, dishonor, rivalry, pain, and hope complicate the 'ordinariness' of Tufa's teenage life. The novel is divided into a prologue and eight chapters. The bulk of each chapter follows Tufa's current life and ends with a vignette told by five African women, one being Afua Ataa. Each vignette paints in broad strokes the landscape and historical moments of the Maafa. The present becomes complicated when traces of the Maafa seep into Tufa's life. Some of these traces are culturally specific rather than unique to Tufa. However, other traces are uniquely shaped by Tufa's former life. People from her past disrupt her current life by their presence. Their disruption takes many forms'some of it brings pain and some of it brings joy. By reading Tufa's story, others may find the strength to confront their past when it makes contact with their present. Like Tufa, we must confront the pain in our past to experience its joy.
M.F.A.
Department of English
Arts and Humanities
Creative Writing MFA

A year after Alyssa Milano’s tweet launched the #MeToo movement, survivors of sexual assault are being called ‘accusers’ in the media, and public opinion is swinging in favor of guilty men. #MeToo raised awareness but not understanding. What is rape? What is consent? As evidenced by the #MeToo movement and the backlash against it, clearly, as a society, we don’t know. Contact is a work of Creative Nonfiction that uses scenes and details from the narrator’s personal experiences to illuminate the micro-negotiations that occur in sex and seduction. In a world where women are still expected to stay small and stay out of the way, where we publicly decry but privately propagate the notion of being 'seen and not heard,' and where to be seen means to be sexualized, this narrator seeks to take up space and make noise. In Contact the personal is political and the political is personal.

A novel method for coupling fluid pressure and crack deformation for the purpose of analysing rolling contact fatigue (RCF) cracks in lubricated, hydrodynamic and elastohydrodynamic, contacts is presented. The model addresses some of the simplifying assumptions applied to existing models presented in the literature such as: (i) using an imposed fluid pressure gradient inside the crack, (ii) using an imposed fluid pressure at the crack mouth, and (iii) adopting a surface contact pressure, Hertzian or EHL, that does not account for the fluid flow in and out of the crack during loading. The model has been used to model the effect of lubricant/crack interaction in various RCF configurations as the rolling element passes over the pre-formed crack; which has direct application to bearings and rail/wheel contacts. The results of the simulations performed with the fully-coupled fluid/solid solver developed by the author suggest that the cracked component/lubricant interaction contributes significantly to accelerate the rate of surface breaking crack growth in rolling element bearings and wheel/rail type contacts. It is shown through simulations that the lubricant works as a catalyst inside the crack to convert the compressive contact load into a crack opening, tensile fatigue mechanism, through the effect of fluid pressurisation inside the crack. The results obtained using such a model suggest that the opening associated with the fluid action within the crack induces large mode I stress intensity factors. This has been shown to be the principal factor that promotes and influences the rate of rolling contact fatigue crack growth in lubricated contacts. In addition to the modelling work, an experimental method of analysing RCF cracks in real time has been developed. The technique is based on laser induced fluorescence that allows the penetration of the fluid within the crack to be observed. Though the method would require development to be used to provide results that could be used for quantitative comparisons with crack models, some encouraging preliminary results have been obtained: the technique has been shown to be suitable for measuring, at least qualitatively, the real time evolution of the film thickness in RCF cracks.

Rolling contacts are utilized in many technical applications, both in bearings and in the contact between gear teeth. These components are often highly loaded, which makes them susceptible to suffer from rolling contact fatigue. This work focuses on the rolling contact fatigue mechanism of pitting. In order to attain a better understanding of why pitting initiates and grows, detailed simulations of rolling contacts have been performed. In particular the contact between two gears in a truck retarder was here used as a case study. The investigated contact experienced elastohydrodynamic lubrication conditions since the load was high enough to causes the surfaces in contact to deform and the viscosity of the lubricant to increase significantly. In Paper A it was investigated if surface irregularities in the size of the surface roughness are large enough to cause surface initiated fatigue. The investigation focused on the pitch line since small surface initiated pits were found here even though there was no slip present. Since there were pits present at the pitch line, it is important that the theories of pitting can explain the development of pits also in the absence of slip. The conclusion of the work was that surface irregularities of the size of normal surface roughness are enough to cause surface initiated fatigue at the pitch line. In Paper B it was investigated why pits are more likely to initiate in the dedendum of pinion gears than in the addendum. In both areas slip is present but in different directions. In the dedendum the friction from slip is against the rolling direction which enhances the risk for pitting. The investigation was performed by studying the effect of the temperature rise in the contact caused by the slip. The conclusion drawn was that the temperature rise in the contact explained why pitting was more common in the dedendum than in the addendum.
Rullande kontakter förekommer i många applikationer, till exempel i lager och mellan kugghjulständer. Både lager och kugghjul utsätts ofta för höga laster vilket gör att dess ytor löper stor risk att utmattas, vilket kallas rullande kontaktutmattning. Denna studie fokuserar på pitting, även kallat spalling, vilket är en typ av rullande kontaktutmattning där en utmattninsspricka växer fram som får delar av ytan att ramla av. För att få en bättre förståelse varför pittingskador uppkommer har noggranna simuleringar utförts av rullande kontakter. Kontakten mellan två tänder på kugghjul i en lastbilsretarder har används som underlag då många pittingskador påträffats på dem.  För att minska friktionen och nötningen i kontakten mellan kuggtänderna användes smörjmedel. De höga lasterna lastbilsretardern utsattes för deformerade kuggarnas ytor elastiskt samtidigt de kraftigt ökade viskositeten hos smörjmedlet. Dessa förhållanden gör att kontakten kallas för elastohydrodynamiskt smord, vilket på engelska förkortas till EHL. I Artikel A undersöktes om små ytojämnheter kan orsaka ytinitierade pittingskador. Eftersom skadan påträffats i friktionslösa kontakter, så som vid rullcirkeln på de undersökta kugghjulen, är det viktigt att teorierna som förklarar uppkomsten inte är beroende av friktion. Undersökningen fokuserade därför på förhållandena vid rullcirkeln.  Slutsatsen från arbetet var att små ytojämnheter, av samma storleksordning som ytojämnheterna på de undersökta kugghjulen, är tillräckligt stora för att orsaka utmattningsskador. I Artikel B undersöktes varför det är vanligare att pitts initieras i dedendum än addendum på drivande kugghjul. Kontakten på båda sidorna om rullcirkeln slirar svagt åt olika håll. Att kontakten slirar skapar friktion som är motriktad rullriktningen i dedendum vilket ökar risken för pittingskador. För att undersöka varför dessa förhållanden ökar risken för skador fördjupades analysen av kontakten genom att inkludera temperaturfältet. Simuleringarna visade att temperaturen ökar genom kontakten vilket orsakar en asymmetrisk spänningsfördelning. Denna asymmetriska spänningsfördelning gör att ytojämnheter i dedendum är troligare att orsaka skador än ytojämnheter i addendum.

QC 20180213

L'objet principal de cette thèse est l'étude locale de structures sous-riemanniennes : étude des petites sphères, du front d'onde, du lieu conjugué et du lieu de coupure. La première partie de cette thèse concerne les structures sous-riemanniennes de quasi-contact. On construit tout d'abord, dans le cas de quasi-contact générique de dimension quelconque, des coordonnées normales, un champ de bases orthonormées canonique et une famille de champs de tenseurs qui sont les analogues d'objets riemanniens classiques. On étudie ensuite, dans le cas de la dimension quatre, l'application exponentielle et nous présentons sa singularité locale qui est un arrangement de singularités lagrangiennes classiques. La seconde partie, en collaboration avec A. Agrachev, J. -P. Gauthier et V. Zakalyukin, traite du cas de contact en dimension trois. La première partie de l'article consiste en la mise en évidence de modules à l'origine des caustiques génériques, dont le premier a une interprétation géométrique simple. La deuxième partie de l'article montre au contraire un résultat de stabilité. Si on considère le front d'onde étendu, où le temps est reparamétré d'une certaine façon, on obtient un objet de dimension trois qui a à nouveau une structure naturelle de front d'onde. La projection de ses singularités n'est autre que le lieu conjugué. On montre que ce grand front d'onde est Legendre-stable.

Spectroscopic and photometric observations of six late-type contact and near-contact binaries are presented, and the results of the analyses discussed. Absolute dimensions have been deduced for three systems: YY Ceti. CX Aquarii and RV Corvi. YY Ceti, which has an orbital period of 0.79 days, is found to be composed of a normal main-sequence star of spectral type A8 and an evolved G-type star which completely fills its Roche lobe. We argue that the system will evolve into contact within approximately 10 9 years, either by the nuclear evolution of the primary component, or by the loss of angular momentum via magnetic braking. We also propose that this may represent a route to the A-type contact binaries which does not involve a passage through the W-type phase. The binary CX Aquarii, which has an orbital period of 0.56 days is found to have a similar configuration to YY Ceti, except that its primary component is a main-sequence star of spectral type F5 with an evolved companion of spectral type G9. We argue that the system should achieve contact by loss of angular momentum via magnetic braking within approximately 108 years if the atmosphere of the primary component is convective, or within approximately 5 x 108 years if the primary possesses a radiative atmosphere. RV Corvi is found to consist of an unevolved F2 primary component with a K-type companion which has a much larger radius and luminosity than expected for its mass. The system has an orbital period of 0.75 days. Although the binary may be semi-detached, with the primary component completely filling its Roche lobe, it is most probably in a state of marginal contact. In order to obtain a solution to the photometric data it was necessary to treat the secondary component albedo as a free parameter, yielding a value greater than unity. This result implies that there is an abnormal distribution of luminosity on the surface of the binary, which may be interpreted either as an excess of light on the facing hemisphere of one or both of the components, or as a deficit of light on the averted hemisphere of the secondary. The three remaining binaries, EZ Hydrae, AD Phoenicis and RS Columbae, were all identified as contact systems: EZ Hydrae as a W-type system of orbital period 0.45 days, AD Phoenicis as an A-type system of period 0.38 days, and RS Columbae as an A-type system with a period of 0 .67 days. Although a value for the mass ratio of EZ Hydrae had been obtained from spectroscopic observations, no photometric solution could found because of severe 'disturbances' in its light curve. From our sample of six systems, AD llioenicis and RS Columbae were the only two for which there were no spectroscopic observations. Although photometric solutions were obtained for both systems, these were very insensitive to the value of mass ratio, which tended toward the physically unrealistic value of unity. The results for YY Ceti, CX Aquarii and RV Corvi are combined with the published masses, radii and luminosities of 21 other contact and near-contact binaries. It is shown that the primary components of all contact and near-contact systems are normal main-sequence stars with radii and luminosities appropriate to their masses. The secondary components of the B-type systems and the W-type systems are all overluminous for their masses, due mostly to the radii being increased by a factor of ~1.7. However, these secondary components are segregated on the H-R diagram, where the W-type secondaries appear to the left of the main sequence band due to luminosity transfer from the primary components. The secondary components of the A-type contact systems all have radii and luminosities substantially larger than expected for their masses.

No presente trabalho foi desenvolvida uma teoria de característica elétrica da estrutura metal-isolante-metal considerando uma camada fina de óxido entre o metal e o isolante, sendo o óxido um outro isolante de banda de energia proibida mais larga. Foi considerada uma distribuição energética uniforme de estados de impurezas à interface óxido-isolante. Estudamos a distribuição real do potencial na região de carga espacial usando a equação de Poisson. Através desta distribuição obtemos a relação entre o potencial de contato e a carga positiva na região de depleção e assim a característica capacitância-voltagem da estrutura. Este tipo de característica é útil para se calcular as características corrente em função do potencial e corrente em função do tempo para um dado potencial e deste modo é importante para o entendimento das estruturas MIM e MOIM.
In this work we have developed a theory of electric characteristic of the metal-oxide-insulator-metal structure, considering a thin film of oxide between metal and insulator; the oxide is another insulator of wider forbidden energy gap. A uniform energy distribution of impurity states at the oxide-insulator interface was considered. W e have studied the actual distribution of potential in the region of spatial charge using the Poisson equation. With this distribution we obtain the relation between the contact potential and the charge in the depletion region and then the characteristic potential - capacitance of t his structure. This type of characteristic is useful to calculate the characteristic current - potential, and current-time at a given potential . In this manner it is important to the understanding of MIM and MOIM structures.

This paper describes a new statistical, model-based approach to building a contact state observer. The observer uses measurements of the contact force and position, and prior information about the task encoded in a graph, to determine the current location of the robot in the task configuration space. Each node represents what the measurements will look like in a small region of configuration space by storing a predictive, statistical, measurement model. This approach assumes that the measurements are statistically block independent conditioned on knowledge of the model, which is a fairly good model of the actual process. Arcs in the graph represent possible transitions between models. Beam Viterbi search is used to match measurement history against possible paths through the model graph in order to estimate the most likely path for the robot. The resulting approach provides a new decision process that can be use as an observer for event driven manipulation programming. The decision procedure is significantly more robust than simple threshold decisions because the measurement history is used to make decisions. The approach can be used to enhance the capabilities of autonomous assembly machines and in quality control applications.

The thesis explores the dilemmas faced by parents and their representatives in conducting child contact negotiations through letters. These institutional letters are explored using discursive analysis to illustrate the ways in which entiltlement to contact claims by the non resident parent and other family members are worked up and resisted. Features of footing are analysed to show how issues of interest and accountability are managed. A discursive psychological approach is used to explore the notion of "understanding" in language and interaction.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2016.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 127-142).
In this thesis, we seek to plan a robust motion for robot with multiple non-coplanar contact on the environment. When the robot interacts with the environment through contact, it relies on the contact forces to generate the desired acceleration. The contact forces have to satisfy some physical constraints, such as lying within the friction cones. These constraints limit the robot acceleration. The robustness of the motion can be measured as the margin to the boundary of these constraints. By planning motion with a large preserved margin, we enable the robot to withstand large disturbance in the online motion execution. In this thesis, we adopt the notion of contact wrench set to approximate the constraints on the robot dynamics. The margin of such set measures the capability of the motion to perfectly resist external wrench disturbance. We plan robust motion to increase this contact wrench set margin. We present two planners to improve this robustness metric. For the first simple-model planner, we pre-specify the contact locations, and it generates a Center of Mass trajectory and an angular momentum trajectory, by solving a convex optimization problem. We show that this planner has similar output as the widely-used walking pattern generator that relies on Zero Moment Point (ZMP) on flat ground. Moreover, it can plan feasible motion on uneven ground with friction cone limits, while the ZMP planner fails. For the second planner with robot whole-body model, we will search for the contact location and the robot whole-body motion simultaneously. We show that we can improve the robustness metric through certain non-convex optimization techniques. We apply our planner to three problems: 1) force closure grasp optimization, 2) static posture optimization, 3) trajectory optimization, achieving improved performance for all of them.
by Hongkai Dai.
Ph. D.

Accurate determination of surface texture is essential for the manufacturing of mechanical components within design specifications in engineering and materials science disciplines. It is also required for any subsequent modifications to physical properties and functional aspects of the object. A number of methods are available to characterize any surface through the measurement of roughness parameters that can then be used to describe surface texture. These methods may be divided into those in that direct contact is made with the surface and those where such contact is not required. This report describes two methods approach for the surface profiling of a quartz glass substrate for step height, and tungsten substrate for roughness measure. A stylus profilometer (contact method) and vertical scanning interferometer, (VSI) or (non-contact optical method) were used for step height and roughness parameter measurements. A comparison was made with nominal values assigned to the studied surface, and conclusions drawn about the relative merits of the two methods. Those merits were found to differ, depending on the parameters under consideration. The stylus method gave better agreement of step height values for dimensions greater than a micron. Both methods showed excellent accuracy at smaller dimensions. Both methods also provided accurate average roughness values, although the VSI data significantly overestimated 35% above the peak-to-valley parameter. Likely sources and nature of such differences are discussed based on the results presented, as well as on the previous comparison studies reported in the literature. Because of such method-specific differences, the multi-technique approach used in this work for accurate surface profiling appears to be a more rational option than reliance upon a single method. Both contact and non-contact approaches have problems with specific roughness parameters, but a hybrid approach offers the possibility of combining the strengths of both methods and eliminating their individual weaknesses.

Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 61-65).
In order for robots to interact safely and intelligently with their environment they must be able to reliably estimate and localize external contacts. This paper introduces the CPF, the Contact Particle Filter, which is a general algorithm for detecting and localizing external contacts on rigid body robots without the need for external sensing. The CPF finds external contact points that best explain the observed external joint torque, and returns sensible estimates even when the external torque measurement is corrupted with noise. We demonstrate the capability of the CPF in multiple scenarios. We show how it can track multiple external contacts on a simulated Atlas robot, and also perform extensive simulation and hardware experiments on a Kuka iiwa robot arm.
by Lucas Manuelli.
S.M.

Tesis para optar al grado de Magíster en Administración
Alicia Salazar A. [Parte I], Miguel Molina [Parte II] Autores no autorizan acceso a texto completo de su documento
El presente informe contiene el Plan de Negocio relacionado con una nueva empresa de Servicio de Contact Center para las Grandes Empresas del Norte de Chile. La empresa de servicio “Resource Contact Center” entregará valor a sus clientes a través de un servicio diferenciador, con conocimiento en temas de recursos humanos, que se integre a través de una mesa de ayuda para apoyar todas las necesidades de información que tengan los trabajadores de nuestros clientes, mediante atención de consultas telefónicas con llamadas de entradas y salidas, sobre consultas relacionadas con su empresa, adicionalmente sea considerado el apoyo in situ para aquellos empleados que registren emergencias en fallecimientos, accidentes enfermedades, y/o siniestros en sus hogares por catástrofes naturales, otro servicio a entregar es el envío de comunicaciones a través de mailling masivos, con entrega de reportabilidad a nuestros clientes, con esta forma la empresa mandante logrará generar un canal de comunicación fluido, actualizado, oportuno y flexible con su fuerza laboral. Lo anterior es posible realizarlo a través de un equipo de profesionales de amplia experiencia en empresas mineras que conocen el negocio, la demanda y necesidad de los potenciales clientes. A esto se sumará una atención personalizada cuyo objetivo será diseñar cada servicio de acuerdo a la situación de cada cliente. Servicio “Resource Contact Center” se insertará en industrias de crecimiento sostenido y constante, con una alta dotación de personal especializado y con demandas de información permanente. Esto nos lleva a pensar en cubrir dos oportunidades claves: 1. Satisfacer la necesidad de información y solución en línea a temas de Recursos Humanos del personal, que crece constantemente en las empresas. 2. Convertir este servicio en un “valor” para las empresas, que las ayude con los desafíos más importantes que enfrentan, principalmente el de mantener un ambiente de trabajo grato, buscando la fidelización del personal y apoyando en la resolución de conflictos que se dan por falta de información oportuna y de calidad.

Given a desired function for an effector, what is its appropriate shape? This thesis addresses the problem of designing the shape of a rigid end effector to perform a given manipulation task. It presents three main contributions: First, it describes the contact kinematics of an effector as the product of both its shape and its motion, and assumes a fixed motion model to explore the role of shape in satisfying a certain manipulation task. Second, it formulates that manipulation task as a set of constraints on the geometry of contact between the effector and the world. Third, it develops tools to transform those contact constraints into an effector shape for general 1-DOF planar mechanisms and general 1-DOF spatial mechanisms, and discusses the generalization to mechanisms with more than one degree of freedom.

We describe the case studies of designing grippers with invariant grasp geometry, grippers with improved grasp stability, and grippers with extended grasp versatility. We further showcase the techniques with the design of the fingers of the MLab hand, a three-fingered gripper actuated with a single motor, capable of exerting any combination of geometrically correct enveloping or fingertip grasps of spherical, cylindrical, and prismatic objects of varying size.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.
Includes bibliographical references (p. 65-67).
Contact thermal lithography is a method for fabricating microscale patterns using heat transfer. In contrast to photolithography, where the minimum achievable feature size is proportional to the wavelength of light used in the exposure process, thermal lithography is limited by a thermal diffusion length scale and the geometry of the situation. In this thesis the basic principles of thermal lithography are presented. A traditional chrome-glass photomask is brought into contact with a wafer coated with a thermally sensitive polymer. The mask-wafer combination is flashed briefly with high intensity light, causing the chrome features heat up and conduct heat locally to the polymer, transferring a pattern. Analytic and finite element models are presented to analyze the heating process and select appropriate geometries and heating times. In addition, an experimental version of a contact thermal lithography system has been constructed and tested. Early results from this system are presented, along with plans for future development.
by Aaron Jerome Schmidt.
S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2002.
Includes bibliographical references (leaves 113-116).
Full-Contact Poetry is a digital play space for children's poetic expression. It is a software environment in which children can express their poetic thoughts, create their interpretations of writing by others and also share these expressions. The environment combines ideas from literary theory and analysis with constructionism to extend tools for poetic expression. Children can experience poetry by playing with words as objects, experimenting with typographic effects, moving words through space and navigating into and through the text, while also being able to incorporate and reconfigure sound and image. In this thesis, I first describe the Full-Contact Poetry environment then continue with a discussion of a workshop I led for six weeks with a small group of teenagers from Boston. The workshop raised many important issues that fall under the interconnected themes of: finding a voice, creating a language and negotiating context. The experience required negotiations at many levels from our small group. Each member needed to find an individual voice both as part of the group and as a poet. As a group, we needed to develop a language with which we could discuss the work that we were creating since the traditional language regarding poetry, or even workshops, did not quite apply. Finally, we were faced with new contexts. The workshop setting encouraged a classroom feeling, yet it was not a classroom. We were working with technology, but not in the way the children were accustomed-likewise with poetry. The thesis explores the challenges of facilitating an environment to support children's expression and the role that personal models play in shaping that environment.
Anindita Basu.
S.M.

Construit dans le cadre de la mecanique des milieux continus, un modele d'adherence a caractere previsionnel est presente. Une nouvelle variable cinematique, la proportion de liens actifs a l'interface des solides en contact adhesif est introduite. Le modele est fonde sur le principe des puissances virtuelles faisant intervenir la proportion de liens actifs qui donne des equations d'equilibre nouvelles. Les equations aux derives partielles du modele ont ete discretisees par des elements finis en espace et des differences finies implicites en temps. Une methode basee sur la sous-structuration et la condensation a ete developpee. Elle s'est montree efficace pour resoudre ce probleme de type frontiere mobile. Grace a elle on a pu modeliser des materiaux a imperfections de facon economique. Cette methode a par ailleurs ete couplee a des techniques multigrilles. Les moyens de calcul mis au point ont permis d'aborder de facon simple de nombreux exemples de portee pratique. Signalons les structures elastiques bicouche et tricouche, les structures fissurees reparees par injection de colle. Des problemes de fissuration fine ont aussi ete abordes. Des comparaisons avec des experiences de pelage et de rupture ont ete effectuees

Leidenfrost phenomenon has been studied extensively for its role in applications ranging from nuclear reactor cooling, to metals manufacturing, combustion, and other fields. Herein, Leidenfrost phenomenon is pursued towards non-contact distillation processes with hopes of reducing or even eliminating contaminant fouling. In particular, the microgravity environment of a drop tower is exploited to demonstrate the facility with which droplets achieve and sustain the Leidenfrost state. Dynamic Leidenfrost impacts in microgravity are presented for impacts on hydrophilic and superhydrophobic planar substrates, macro-pillar arrays, confined passageways, and others. Nearly ideal elastic non-contact impacts and droplet oscillation modes are observed. Dynamic Leidenfrost impacts in microgravity for uniquely low velocity impacts are investigated analytically and experimentally. We find Leidenfrost vapor layer thicknesses on the order of millimeters for a 1 mL droplet of water with impact velocity 1 mm/s - a 100-fold increase relative to terrestrial vapor layers. Such results are supported by preliminary experimental observations. Further droplet distillation experiments are conducted in a terrestrial gravity environment using a heated tilted rotating hemi-circular track. Droplet evaporation rates and lifetimes are tabulated for the sliding/rolling drops at varying angular velocities and tilt angles. An analytical model for the evaporation rate of a rolling Leidenfrost droplet is developed and compared to the experimental results with good agreement. The empirical and analytical results serve as key design tools for sizing a prototypical non-contact distillation system for terrestrial desalinization or spacecraft water recycling.

According to the Contact Hypothesis, positive encounters with outgroup members have the potential of reducing prejudice toward the whole outgroup (Allport, 1954). Research has widely demonstrated the effectiveness of contact in ameliorating intergroup relations across a variety of situations and cultural contexts (Brown & Hewstone, 2005; Pettigrew & Tropp, 2006); research has further shown that positive contact reduces, besides blatant prejudice, also subtle and implicit forms of prejudice. Recent developments of the Contact Hypothesis investigated the mediators of the contact-reduced prejudice relationship. The recent meta-analysis by Pettigrew and Tropp (2008) underlined that affective mediators, such as reduced intergroup anxiety and increased empathy, have stronger effects than cognitive mediators, such as outgroup knowledge. In four correlational studies, we explored the relationship between different forms of contact and prejudice toward immigrants in Italy. Concerning the mediators of the relationship between contact and prejudice, we considered the affective mediators identified by Pettigrew and Tropp (2008): intergroup anxiety, namely the anticipation of negative psychological or behavioral consequences deriving from intergroup interactions (Stephan & Stephan, 1985), and emotional empathy, namely an other-oriented emotional response, congruent with the perception of her/his welfare (Batson et al., 1997). Besides empathy and anxiety, we considered a more recently proposed mediator, namely outgroup trust. Trust consists in positive expectations about intentions and behaviors of other persons or groups (Kramer & Carnevale, 2001), and is associated to positive attitudes and cooperative behaviors with outgroup members. As regards prejudice, we considered both explicit attitudes toward immigrants, and more indirect prejudice measures, i.e. subtle prejudice and a scale measuring the percentage of crimes in Italy attributed to immigrants. Recent theoretical approaches further studied a very subtle form of prejudice, that consists in attributing more secondary emotions and uniquely human traits to ingroup than to outgroup members (infrahumanization; Leyens, Demoulin, Vaes, Gaunt, & Paladino, 2007). Thus, we also considered humanity attributions to ingroup and outgroup members and hypothesized, consistently with empirical evidence (Brown, Eller, Leeds, & Stace, 2007; Capozza, Trifiletti, Vezzali, & Favara, 2012), that positive intergroup contact could increase the attribution of uniquely human characteristics to outgroup members. In the first study, 174 Italian participants completed a questionnaire including: measures of quantity of meaningful contact with immigrants (Voci & Hewstone, 2003); measures of attitude toward immigrants (Voci & Hewstone, 2003), subtle prejudice (adapted from Pettigrew & Meertens, 1995), attribution of uniquely human and non uniquely human traits to ingroup and outgroup members (Capozza, et al., 2012), estimate of the percentage of crimes in Italy committed by immigrants (Pagotto, Voci, & Maculan, 2010); as emotional processes, measures of intergroup anxiety (adapted from Stephan & Stephan, 1985), emotional empathy (based on Batson et al., 1997), and outgroup trust (Voci, 2006). We used Structural Equation Modelling with latent variables (Lisrel, Jöreskog & Sörbom, 2004) to test the effects of contact; in the model, quantity of contact was the predictor; empathy, anxiety, and trust were the mediators, and attitudes, prejudice, crimes rating, and uniquely human traits attributed to immigrants were the criterion variables. Contact with immigrants led, through reduced intergroup anxiety and increased empathy and trust, to the reduction of prejudice and crimes estimate, to the improvement of outgroup attitudes and to greater attribution of uniquely human traits to immigrants. The first study thus confirmed that meaningful direct contact with outgroup members reduced various forms of prejudice, through affective mediators. Anyway, direct contact with outgroup members is not always attainable and frequent; in highly segregated settings, indeed, people belonging to different groups may not have the chance to develop deep relationships with outgroup members; moreover, even when contact is possible, people may seek friendships among ingroup members, and not form cross-group friendships (see, e.g., Stearns, Buchmann, & Bonneau, 2009). In these situations, indirect forms of contact may have important effects on intergroup attitudes. Wright, Aron, McLaughlin-Volpe and Ropp (1997) proposed that extended contact, namely the knowledge that an ingroup member has an outgroup friend, may reduce prejudice toward the whole outgroup. Experimental and correlational studies demonstrated that extended contact is effective for prejudice reduction toward various outgroups, and has significant effects controlling for direct contact (Turner, Hewstone, Voci, Paolini, & Christ, 2007). Research has also shown that observing cross-group interactions through mass media may affect prejudice and intergroup relationships. Mutz and Goldman (2010), in their review of the effects of exposure to mass media on prejudice, underlined that mass media are the main source of information about outgroups. In Study 2, thus, we investigated, besides direct contact effects, also the effects of extended contact with immigrants and of contact through mass media. Concerning contact through mass media, we chose to consider separately contact through TV news and newspapers and contact through movies and TV series. In the second study, 201 Italian participants completed a questionnaire containing, besides measures included in the questionnaire of Study 1, measures of extended contact (Wright et al., 1997; Turner, Hewstone, Voci, & Vonofakou, 2008), contact through TV news and newspapers, and contact through movies and TV series. We tested a regression model with latent variables; predictors were quantity of the four forms of contact (direct contact, extended contact, contact through TV news and newspapers, contact through movies and TV series); mediators and outcome variables were the same of the model tested in Study 1. Confirming results of Study 1, direct contact ameliorated attitudes, enhanced the attribution of uniquely human traits to immigrants, and reduced prejudice and crimes estimate, through the reduction of intergroup anxiety and the increase of empathy and trust. Extended contact ameliorated outgroup attitudes and reduced prejudice through outgroup trust. Contact through TV news and newspapers instead increased all forms of prejudice, partially via increased intergroup anxiety. Finally, contact through movies and TV series had a positive direct effect on the attribution of uniquely human traits to immigrants. Thus, Study 2 showed that direct contact, extended contact, and contact through movies and TV series were related to lower prejudice, while contact through TV news and newspapers increased prejudice. Recent meta-analysis and theorizations on intergroup contact (Pettigrew, 2008; Pettigrew & Tropp, 2006) underlined the lack of research on the negative episodes of contact, and on comparing the effects of positive and negative contact. Indeed, in most of the published studies, contact measures concerned quantity and quality of contact, and quantity of cross-group friendships; through these procedures, it would not be possible to analyze the role of contact episodes perceived as positive or negative. In the third study, thus, we considered the distinction between positive and negative episodes of the contact forms analyzed in Study 2. Participants were 330 Italian adults and students, who completed a questionnaire containing, besides the prejudice and emotions measures included in the questionnaires of the previous studies, measures of quantity of positive and negative episodes of direct contact with immigrants, quantity of positive and negative episodes of extended contact with immigrants, quantity of positive and negative episodes of contact through TV news and newspapers, quantity of positive and negative episodes of contact through movies and TV series. Preliminary analyses showed that positive direct contact episodes were more frequent than negative ones; we found the same pattern for extended contact and contact through movies and TV series, while negative episodes of contact through TV news and newspapers were far more frequent than positive ones. We tested a regression model with latent variables, where predictors were quantity of positive and negative episodes of the above mentioned forms of contact (eight predictors); mediators were intergroup anxiety, trust, and empathy; the outcome variables were attitudes, subtle prejudice, crimes rating, and uniquely human traits attributed to immigrants. The contact forms which were most influent on prejudice reduction were positive direct contact and positive extended contact; they decreased all the forms of prejudice, and the mediation involved the three emotions (reduced intergroup anxiety, increased empathy and trust). Also contact through TV news and newspapers was very influential: positive contact through TV news and newspapers ameliorated attitudes and increased outgroup humanization, while the negative episodes were related to stronger prejudice, influencing all the outcome measures. It is noteworthy that positive direct contact was related to reduced prejudice more than negative direct contact was related to increased prejudice; the same pattern emerged for extended contact and for contact through movies and TV series, while negative contact through TV news and newspapers was a stronger predictor of prejudice than positive contact through TV news and newspapers of reduced prejudice. In the fourth study we considered, besides variables included in the questionnaire of the third study, implicit attitudes toward immigrants. Participants were 197 Italian adults and students, who completed an online questionnaire, containing the same measures of the questionnaire used in Study 3, followed by a Single Category IAT (SC-IAT, Karpinski & Steinman, 2006). In the SC-IAT score, higher values reflected more positive implicit attitudes; mean score of the SC-IAT was negative, indicating negative implicit attitudes. We applied regression analysis, to test the effects of the contact measures on prejudice indexes. Positive direct contact, positive extended contact, and positive contact through movies and TV series were strong predictors of reduced explicit prejudice; positive direct contact and positive contact through movies were also weakly related to better implicit outgroup attitudes. Negative direct contact and negative contact through TV news were instead related to worse explicit outgroup attitudes. As in Study 3, positive direct contact, positive extended contact, and positive contact through movies and TV series were more influential, respectively, than negative direct contact, negative extended contact, and negative contact through movies and TV series; concerning contact through TV news and newspapers, instead, the negative episodes increased prejudice more than the positive episodes reduced prejudice. Taken together, results of the four studies showed that: 1. All the contact forms we considered (direct contact, extended contact, contact through TV news and newspapers, contact through movies and TV series) have significant effects on prejudice and on intergroup attitudes. The most influent form of contact is direct contact. 2. It is useful to consider separately positive and negative episodes of contact, which have independent effects. 3. Direct contact and extended contact are usually positive, and the positive episodes of these forms of contact have stronger effects on prejudice reduction, compared to the effects of negative episodes on increased prejudice. 4. To improve the relationships between Italians and immigrants, it could be useful to favor meaningful direct contact, given then, when direct contact occurs, positive episodes are more frequent and more influential than negative episodes. 5. Also programs basing on extended contact could be effective: it would thus be useful to favor social networks with individuals belonging to various outgroups; moreover, programs basing on reading romances or tales portraying cross-group friendships could be implemented in schools. 6. Contact through TV news and newspapers is usually negative; only for this contact form, negative episodes are more influential than positive episodes. It would thus be useful to provide guidelines to mass media, to avoid that the conveyed information increase prejudice toward immigrants. 7. Contact through movies and TV series is generally positive, and is mainly related to the perception of immigrants as fully human, and to better implicit attitudes toward immigrants.
Secondo l’ipotesi del contatto, incontri positivi con membri di un gruppo estraneo riducono il pregiudizio verso l’intero gruppo (Allport, 1954). La ricerca ha ampiamente dimostrato l’efficacia del contatto nel migliorare le relazioni intergruppi in una grande varietà di situazioni e contesti culturali (Brown & Hewstone, 2005; Pettigrew & Tropp, 2006); ha inoltre dimostrato che il contatto positivo non solo migliora gli atteggiamenti espliciti verso i gruppi esterni, ma riduce anche forme più sottili e implicite di pregiudizio. Recenti sviluppi dell’ipotesi del contatto hanno indagato i mediatori del contatto, ovvero attraverso quali processi il contatto riduce il pregiudizio. La recente meta-analisi di Pettigrew e Tropp (2008) ha evidenziato che i mediatori affettivi, come riduzione dell’ansia intergruppi ed aumento dell’empatia, hanno effetti più forti dei mediatori cognitivi, come la conoscenza dell’outgroup. In quattro studi correlazionali, abbiamo esplorato la relazione tra diverse forme di contatto ed il pregiudizio verso gli immigrati in Italia. Per quanto riguarda i mediatori della relazione tra contatto e riduzione del pregiudizio, abbiamo considerato i mediatori affettivi identificati da Pettigrew e Tropp (2008): l’ansia intergruppi, ovvero i sentimenti di disagio dovuti all’anticipazione dell’interazione con membri dell’outgroup (Stephan & Stephan, 1985), e l’empatia emotiva, ovvero la risposta emotiva orientata verso l’altro, congruente con la percezione del suo benessere (Batson et al., 1997). Oltre ad empatia ed ansia, abbiamo considerato un mediatore proposto più recentemente, ovvero la fiducia verso l’outgroup. La fiducia consiste nelle aspettative positive riguardo le intenzioni e il comportamento di altre persone o altri gruppi (Kramer & Carnevale, 2001), ed è associata ad atteggiamenti positivi e comportamenti cooperativi con l’outgroup. Come misure di pregiudizio, abbiamo considerato sia l’atteggiamento esplicito verso gli immigrati, sia misure più indirette di pregiudizio, ovvero il pregiudizio sottile ed una scala che misura la percentuale di crimini attribuita agli immigrati. Recenti approcci teorici hanno inoltre studiato una forma molto sottile di pregiudizio, che consiste nell’attribuire ai membri dell’outgroup meno emozioni secondarie e meno caratteristiche unicamente umane che ai membri dell’ingroup (infraumanizzazione; Leyens, Demoulin, Vaes, Gaunt, & Paladino, 2007). Abbiamo quindi considerato anche le percezioni di umanità dell’ingroup e dell’outgroup, ipotizzando, coerentemente con alcune evidenze empiriche (Brown, Eller, Leeds, & Stace, 2007; Capozza, Trifiletti, Vezzali, & Favara, 2012), che il contatto intergruppi positivo potesse aumentare la percezione dell’outgroup come definito da caratteristiche unicamente umane. Nel primo studio, a 174 partecipanti italiani è stato somministrato un questionario contenente misure di quantità del contatto approfondito con immigrati (Voci & Hewstone, 2003); misure di atteggiamento verso l’outgroup (Voci & Hewstone, 2003), pregiudizio sottile (adattamento della scala di Pettigrew & Meertens, 1995), attribuzione di tratti unicamente umani e non unicamente umani all’ingroup e all’outgroup (Capozza, et al., 2012), stima dei crimini commessi da immigrati (Pagotto, Voci, & Maculan, 2010); come processi emotivi legati al contatto, misure di ansia intergruppi (adattamento della scala di Stephan & Stephan, 1985), empatia emotiva (item adattati da Batson et al., 1997) e fiducia verso l’outgroup (Voci, 2006). Abbiamo applicato Modelli di Equazioni Strutturali con variabili latenti (Lisrel, Jöreskog & Sörbom, 2004) per verificare gli effetti del contatto; nel modello, la quantità del contatto era la variabile iniziale, empatia, ansia e fiducia erano i mediatori, e atteggiamento, pregiudizio, stima dei reati commessi dagli immigrati e tratti unicamente umani attribuiti all’outgroup erano le variabili finali. Il contatto con membri del gruppo esterno portava, attraverso la riduzione dell’ansia intergruppi e l’aumento di fiducia ed empatia, alla riduzione del pregiudizio sottile e della stima di reati commessi da immigrati, al miglioramento dell’atteggiamento e a una maggiore attribuzione di tratti unicamente umani agli immigrati. Il primo studio ha quindi confermato che il contatto diretto approfondito con membri dell’outgroup riduceva varie forme di pregiudizio, attraverso mediatori affettivi. Il contatto diretto con membri del gruppo esterno però non è sempre possibile e frequente; in contesti caratterizzati da forte segregazione, infatti, persone che appartengono a gruppi diversi potrebbero non avere occasione di sviluppare conoscenze approfondite; inoltre, anche in casi in cui il contatto è possibile, le persone potrebbero cercare amicizie all’interno dei membri del proprio gruppo, e non avere amici che fanno parte dell’outgroup (si veda, per esempio, Stearns, Buchmann, & Bonneau, 2009). In queste situazioni, forme indirette di contatto possono avere importanti effetti sugli atteggiamenti intergruppi. Wright, Aron, McLaughlin-Volpe e Ropp (1997) hanno proposto che anche il contatto esteso, ovvero la conoscenza che un membro dell’ingroup ha un amico che è un membro dell’outgroup, possa ridurre il pregiudizio verso l’intero outgroup. Ricerche sperimentali e correlazionali hanno dimostrato che il contatto esteso è efficace nella riduzione del pregiudizio verso vari outgroup, e che ha effetti significativi anche considerando simultaneamente gli effetti del contatto diretto (Turner, Hewstone, Voci, Paolini, & Christ, 2007). Recenti teorizzazioni hanno proposto che anche osservare interazioni intergruppi attraverso i mass media possa influenzare il pregiudizio e i rapporti intergruppi. Mutz e Goldman (2010), nella loro review sugli effetti sul pregiudizio dell’esposizione ai mass media, hanno sottolineato che i mass media sono la principale fonte di informazioni degli individui per formarsi impressioni sugli outgroup. Nel secondo studio abbiamo quindi indagato, oltre agli effetti del contatto diretto, anche gli effetti del contatto esteso con gli immigrati e del contatto attraverso i mass media. Per quanto riguarda il contatto attraverso i mass media, abbiamo scelto di considerare separatamente il contatto attraverso telegiornali e quotidiani ed il contatto attraverso film e fiction. Nello specifico, a 201 partecipanti italiani è stato somministrato un questionario, in cui erano inserite, oltre alle misure del questionario dello Studio 1, misure di contatto esteso (Wright et al., 1997, Turner, Hewstone, Voci, & Vonofakou, 2008), di contatto attraverso telegiornali e quotidiani, e di contatto attraverso film, telefilm e fiction. È stato verificato un modello di mediazione con variabili latenti, in cui le variabili iniziali erano i punteggi relativi alla quantità delle quattro forme di contatto (contatto diretto, contatto esteso, contatto attraverso telegiornali e quotidiani, contatto attraverso film e fiction); i mediatori e le variabili finali erano gli stessi del modello verificato nello Studio 1. Confermando i risultati dello Studio 1, il contatto diretto migliorava l’atteggiamento, aumentava l’attribuzione di tratti unicamente umani e diminuiva pregiudizio e stima dei reati, attraverso la mediazione delle tre emozioni verso l’outgroup (diminuzione dell’ansia, aumento di empatia e fiducia). Il contatto esteso migliorava gli atteggiamenti e diminuiva il pregiudizio attraverso la mediazione della fiducia. Il contatto attraverso notiziari e giornali invece aumentava tutte le forme di pregiudizio considerate, in parte attraverso la mediazione dell’ansia. Il contatto attraverso film e fiction, infine, aumentava l’attribuzione di tratti unicamente umani all’outgroup. La Studio 2 ha quindi dimostrato che il contatto diretto, il contatto esteso e il contatto attraverso film e fiction diminuivano il pregiudizio, mentre il contatto attraverso notiziari e giornali lo aumentava. Recenti meta-analisi e teorizzazioni sul contatto intergruppi (Pettigrew, 2008; Pettigrew & Tropp, 2006) hanno evidenziato la mancanza di ricerca sugli episodi negativi di contatto, e sul confronto tra gli effetti del contatto positivo e del contatto negativo. Nella maggior parte degli studi presenti in letteratura, infatti, le misure di contatto intergruppi riguardano quantità e qualità del contatto, o quantità di amicizie intergruppi; tramite tali procedure, risulta difficile analizzare il ruolo di episodi di contatto vissuti come positivi e di episodi di contatto vissuti come negativi. Nel terzo studio abbiamo quindi considerato la distinzione tra gli episodi positivi e negativi delle varie forme di contatto incluse nel secondo studio. A 330 partecipanti italiani è stato somministrato un questionario contenente, oltre alle misure di emozioni e di pregiudizio inserite nei questionari dei due precedenti studi, misure di quantità di episodi positivi e negativi di contatto diretto con immigrati, quantità di episodi positivi e negativi di contatto esteso con immigrati, quantità di episodi positivi e negativi di contatto attraverso telegiornali e quotidiani, quantità di episodi positivi e negativi di contatto attraverso film e fiction. Considerando le medie delle misure di contatto, è emerso che gli episodi di contatto diretto positivo erano più frequenti degli episodi di contatto diretto negativo; abbiamo trovato lo stesso risultato per il contatto esteso e per il contatto attraverso film e fiction; gli episodi negativi di contatto attraverso telegiornali e quotidiani invece erano molto più frequenti degli episodi positivi. È stato verificato un modello di mediazione con variabili latenti; le variabili iniziali del modello erano rappresentate dalla quantità di episodi positivi e negativi delle quattro forme di contatto considerate (otto variabili iniziali); i mediatori erano ansia intergruppi, fiducia ed empatia; le variabili finali erano atteggiamento, pregiudizio sottile, stima dei crimini e tratti unicamente umani attribuiti agli immigrati. Le forme di contatto maggiormente associate alla riduzione del pregiudizio erano il contatto diretto positivo ed il contatto esteso positivo, che diminuivano tutte le forme di pregiudizio, attraverso la mediazione delle tre emozioni intergruppi (diminuzione dell’ansia, aumento di empatia e fiducia). Anche il contatto attraverso notiziari e giornali era molto influente: il contatto positivo attraverso notiziari e giornali migliorava l’atteggiamento e aumentava l’attribuzione di tratti unicamente umani agli immigrati; gli episodi negativi erano invece legati ad un aumento di tutte le forme di pregiudizio. È importante notare che il contatto diretto positivo riduceva il pregiudizio più di quanto il contatto diretto negativo lo aumentasse; gli stessi risultati sono emersi per quanto riguarda il contatto esteso ed il contatto attraverso film e fiction, mentre il contatto negativo attraverso notiziari e giornali aumentava il pregiudizio più di quanto il contatto positivo attraverso notiziari e giornali lo riducesse. Nel quarto studio, abbiamo considerato, oltre alla variabili inserite nel questionario del terzo studio, l’atteggiamento implicito verso gli immigrati. I partecipanti erano 197 adulti e studenti italiani, che hanno completato un questionario contenente le stesse misure del questionario somministrato per lo Studio 3, e un Single Category IAT (SC-IAT, Karpinski & Steinman, 2006). Il punteggio dello SC-IAT è stato calcolato in modo che a valori più alti corrisponda un migliore atteggiamento implicito; il punteggio medio del campione era negativo; i partecipanti avevano quindi un atteggiamento implicito negativo verso gli immigrati. Attraverso l’analisi della regressione, abbiamo verificato gli effetti delle varie forme di contatto sul pregiudizio. Il contatto diretto positivo, il contatto esteso positivo ed il contatto positivo attraverso film e fiction erano fortemente associati a migliori atteggiamenti espliciti verso gli immigrati; il contatto diretto positivo ed il contatto positivo attraverso film e fiction inoltre miglioravano debolmente gli atteggiamenti impliciti verso gli immigrati. Il contatto diretto negativo ed il contatto negativo tramite telegiornali e quotidiani invece aumentavano il pregiudizio. Confermando i risultati dello Studio 3, il contatto diretto positivo, il contatto esteso positivo ed il contatto positivo attraverso film e fiction avevano effetti più forti, rispettivamente, del contatto diretto negativo, del contatto esteso negativo e del contatto negativo attraverso film e fiction; per quanto riguarda il contatto attraverso notiziari e quotidiani, gli episodi negativi aumentavano il pregiudizio più di quanto gli episodi positivo lo diminuissero. Considerando i risultati dei quattro studi insieme, i risultati hanno indicato che: 1. Tutte le quattro tipologie di contatto da noi considerate (contatto diretto, contatto esteso, contatto attraverso telegiornali e quotidiani, contatto attraverso film e fiction) hanno effetti sul pregiudizio e sugli atteggiamenti intergruppi. La forma di contatto che ha effetti più forti, influenzando le emozioni e le variabili finali in tutti gli studi, è il contatto diretto. 2. È utile considerare separatamente episodi positivi e negativi di contatto, che hanno effetti indipendenti. 3. Il contatto diretto ed il contatto esteso sono generalmente positivi, e gli episodi positivi di queste forme di contatto hanno effetti di riduzione del pregiudizio più forti rispetto a quanto gli episodi negativi aumentino il pregiudizio. 4. Per migliorare le relazioni tra italiani e immigrati, potrebbe essere utile favorire il più possibile il contatto diretto approfondito, considerando che, quando il contatto effettivamente avviene, gli episodi positivi sono molto più frequenti e hanno effetti più rilevanti degli episodi negativi. 5. Interventi potrebbero anche essere basati sul contatto esteso: sarebbe quindi utile favorire reti sociali con individui appartenenti a vari outgroup; potrebbero inoltre essere implementati programmi nelle scuole basati su lettura di libri o racconti che presentino storie di amicizia tra membri dell’ingroup e membri dell’outgroup. 6. Il contatto attraverso telegiornali e quotidiani è generalmente negativo; solo per quanto riguarda questa tipologia di contatto, gli episodi negativi hanno effetti più forti degli episodi positivi. Nel contesto analizzato, quindi, sarebbe necessario fornire linee guida ai mezzi di comunicazione, per evitare che le informazioni trasmesse sugli immigrati portino ad un aumento dei pregiudizi verso gli immigrati in generale. 7. Il contatto tramite film e fiction è generalmente positivo, e risulta legato principalmente alla percezione degli immigrati come definiti da tratti unicamente umani, e all’atteggiamento implicito verso gli immigrati.

Cette thèse s'intéresse à la problématique du contact entre matériaux hétérogènes. L'industrie (automobile, aéronautique, spatiale, ...) s'intéresse de plus en plus à ces types de matériaux. Il s'agira par exemple des alliages métalliques, des matériaux poreux, matériaux composites (composites tissés, interlocks 3D, interlocks 2D), des billes céramiques contenant des impuretés (porosités/précipités),... Dans ce manuscrit, un modèle de contact basé sur les méthodes semi-analytiques a été développé. Un algorithme de gradient conjugué est utilisé afin de résoudre rapidement le problème de contact. Le modèle permet de prendre en compte la présence d'une ou de plusieurs hétérogénéités isotropes/anisotropes dans le problème de contact. Une approche inspirée de la méthode de l'inclusion équivalente proposée par Eshelby est utilisée dans le solveur de contact pour prendre en compte l'effet de ces hétérogénéités. Les méthodes de transformées de Fourier rapides (FFT) permettent d'accélérer les calculs. Une méthode numérique a été mise en œuvre afin de prendre en compte l'interaction entre plusieurs hétérogénéités. Le massif peut être élastique ou viscoélastique. L'approche développée dans la thèse peut résoudre à la fois les problèmes d'indentation, de roulement/glissement ou de fretting en présence de matériaux élastiques hétérogènes, viscoélastiques homogènes ou hétérogènes. Les solutions sont données en termes de champs de pressions, de cisaillements et de contraintes. Dans le cas des matériaux viscoélastiques le code de calcul est capable de fournir le coefficient de frottement apparent ainsi que toutes les variables de contact aussi bien en régime permanent que transitoire. Le modèle a été validé par comparaison avec la méthode des éléments finis classiques en utilisant le logiciel commercial Abaqus v6.11. Le temps de calcul ainsi que l'espace mémoire nécessaire sont considérablement réduits par rapport à la méthode éléments finis. La parallélisation a été introduite dans le code de contact afin de réduire toujours plus le temps de calcul. Il s'agit d'un code robuste, rapide et facilement utilisable en Bureau d'Etudes. Une approche expérimentale originale a été mise en place afin de mesurer les champs de déplacements à l'interface des corps en contact. De bonnes corrélations essais/calculs ont été obtenues. Enfin quelques applications industrielles ont été présentées. Un couplage entre un code éléments finis structurel et le code semi-analytique de résolution de contact a été également réalisé
The present PhD thesis deals with contact problems between heterogeneous materials. Nowadays heterogeneous materials are extensively used in several industrial domains (automotive, aeronautics, aerospace, ...). Heterogeneous materials involve porous materials, aluminum alloys, composites materials (woven composites, interlocks 3D, interlocks 2D), metallic or ceramics materials containing impurities (porosities/precipitates). In this work, a contact model based on semi-analytical method is proposed. A conjugate gradient algorithm is used for a fast resolution of contact equations. The model can account for one or more isotropic/anisotropic inhomogeneities. An approach taking inspiration from the Eshelby equivalent inclusion method is used in the contact solver to account for the effect of inhomogeneities. 2D and 3D Fast Fourier Transforms (FFT) are used to speed up the computation. A numerical method is implemented in order to take into account interactions between many heterogeneities. The semi-infinite space/ matrix can be either elastic or visco-elastic. The model developed in the present PhD thesis can solve indentation, rolling/sliding or fretting contact problems between heterogeneous elastic materials, homogeneous or heterogeneous visco-elactic materials. In the case of visco-elastic materials, the model permits to get the solution in terms of contact pressure distribution, subsurface stresses, apparent friction coefficient, both in the transient and then steady-state regimes. The model has been validated by performing a comparison with the results of a finite element model. The CPU time and memory necessary are greatly reduced in comparison with the classical finite element method. The model developed is fast, robust and extremely easy to use. An original experimental approach was proposed in order to measure the displacement fields at interface of two contacting bodies. A good agreement between experimental results and numerical simulations is obtained. Finally, the model is applied on some industrial applications. A coupling between a finite element model and the semi-analytical code allow to take into account the effects of structure on contact problem

Thesis (Ph.D.)--Indiana University, School of Optometry, 2007.
Source: Dissertation Abstracts International, Volume: 68-09, Section: B, page: 5877. Adviser: Arthur Bradley. Title from dissertation home page (viewed May 9, 2008).

The effects of repeated mild concussive head injury on professional rugby players were examined. Data were collected for rugby players (n=26) and cricket player controls (n=21) using a comprehensive neuropsychological test battery comprising five modalities (Verbal Memory, Visual Memory, Verbal Fluency, Visuoperccptual Tracking and Hand Motor Dexterity) and a self-report Postconcussive Symptomology Questionnaire. Group statistical comparisons of the percentage of individuals with deficit were carried out for (i) rugby versus cricket; (ii) rugby forwards versus rugby backs; and (iii) rugby forwards versus cricket. Rugby players performed significantly poorer than controls on SA W AIS Digit Symbol Substitution subtest and on the Trail Making Test. On Digits Forward and Digit Symbol Incidental Recall, the results approached significance with the rugby players showing a tendency toward impairment on these tests. Rugby players exhibited impairment in areas of visuoperceptual tracking, speed of information processing and attention, and there are tendencies of impairment in verbal and/or visual memory. Results obtained on the self-report questionnaire strongly reinforced cognitive test results and a significant proportion of rugby players reported difficulties with sustained attention, memory and lowered frustration tolerance as well as symptoms of anxiety and depression. It was consistently noted that players in the more full contact positions (rugby forwards) were most susceptible to impairment, confirming that these players, who are exposed to repeated mild head injuries, are at greater risk of exhibiting postconcussive sequelae
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Wheel-rail contact is an important aspect of railway, the forces transferred between the wheel and rail are the one that guide, brake, or accelerate the train, and that is why the understanding of the contact between wheel and rail is an interesting research topic. In this master thesis wheel-rail contact model named ANALYN is used to see the effect of the different geometrical input, like undeformed distance, relative longitudinal curvature, and relative lateral curvature calculation affect the contact patch estimation formed at the wheel-rail contact.  In the process, a geometrical contact search code is made to find the contact point between wheel and rail for certain lateral displacement, yaw angle, and roll angle of the wheelset. The codes used to calculate the three geometrical inputs are also prepared, with two methods are prepared for each input. The results that generated from combination of the geometrical contact search and geometrical input preparation are used as the input to ANALYN. The results showed that different geometrical input calculations do affect the shape of the contact patch, with the calculation of lateral curvature being the most important since it affects the shape of the contact patch greater than other geometrical inputs. It is also shown that taking yaw angle into account in the contact search will affect the shape of the contact patch.

This thesis documents research carried over the past two years, aimed at studying the tribology of sliding contacts subjected to high densities of current of the order is 422 --917A/mm2. The overall aim was the development of an experimental test bed for evaluating the effect of different solid lubricant conditioners on sliding electrical contacts. The experimental configuration consists of a flat ended copper tip pressed in contact with a flat copper disc. The copper plate is mounted on a spindle of a lathe which is operated at 550rpm, whereas the copper tip is mounted on a shaft which is instrumented with force sensing piezos to measure the forces during the test. A weak spring is used to compensate for wear of the tip during the experiment. The interface is subjected to high current densities of the order of 422 and 917A/mm2 to evaluate the effect of solid conditioner as contrast with the surface behavior when no interface lubrication was used. The key outputs of the experiments are a) Friction coefficient, b) Contact resistance, c) Amount of material transfer, d) number of passes to failure and e) Wear rate. Two types of tests, namely circular and spiral tests were carried out. The current density of 422A/mm2 would result in softening of the interface whereas current density of 917A/mm2 results in melting of the interface. In terms of contact voltages it is noted that Cu-Cu interface softens at 0.12V and melts at 0.43V. It has been noted that pre-application of SLIC leads to increase of contact resistance by approximately 20% when the interface is loaded statically. When the interface is tested for contact resistance, there is a significant effect of oxide layer on the surface of the plates. When contact resistance is measured these oxide layers contribute significantly, and increase the contact resistance substantially.
Thesis (M.S)-- Wichita State University, College of Engineering, Dept. of Industrial and Manufacturing Engineering
"December 2007."

Dans cette thèse, nous présentons et étudions une nouvelle formulation du problème de contact frottant entre deux corps élastiques se basant sur la méthode de Nitsche. Dans cette méthode les conditions de contact sont imposées faiblement, grâce à un terme additionnel consistant et stabilisé par un paramètre gamma. En premier lieu, nous introduisons, l’étude effectuée en petites déformations pour une version non biaisée de la méthode. La non-distinction entre une surface maître et une surface esclave permettera à la méthode d’être plus générique et applicable directement au problème d’auto-contact. Le cadre restrictif des petites déformations nous permet d’obtenir des résultats théoriques sur la stabilité et la convergence de la méthode. Ces résultats sont complétés par une validation numérique. Ensuite, nous introduisons l’extension de la méthode de Nitsche au cadre des grandes déformations qui est d’avantage pertinent pour les applications industrielles et les situations d’auto-contact. La méthode de Nitsche est formulée pour un matériau hyper-élastique avec frottement de Coulomb et se décline en deux versions : biaisée ou non. La formulation est généralisée à travers un paramètre theta pour couvrir toute une famille de méthodes. Chaque variante particulière a des propriétés différentes du point de vue théorique et numérique, en termes de précision et de robustesse. La méthode est testée et validée à travers plusieurs cas tests académiques et industriels. Nous effectuons aussi une étude de l’influence de l’intégration numérique sur la précision et la convergence de la méthode. Cette étude couvre une comparaison entre plusieurs schémas d’intégration proposés dans la littérature pour d’autres méthodes intégrales
In this thesis, we present and study a new formulation of frictional contact between two elastic bodies based on Nitsche’s method. This method aims to treat the interface conditions in a weak sense, thanks to a consistent additional term stabilized with the parameter gamma. At first, we introduce the study carried out in the small strain framwork for an unbiased version of the ethod. The non-distinction between a master surface and a slave one will allow the method to be more generic and directly applicable to the self-contact problem. The restrictive framework of small strain allowed us to obtain theoretical results on the consistency and convergence of the method. Then, we present the extension of the Nitsche method to the large strain case more relevant for industrial applications and situations of self-contact. This Nitsche’s method is formulated for an hyper-elastic material and declines in the two versions: biased and unbiased. We describe a class of methods through a generalisation parameter theta . Particular variants have different properties from a numerical point of view, in terms of accuracy and robustness. To prove the accuracy of the method for large deformations, we provide several academic and industrial tests. We also study the influence of numerical quadrature on the accuarcy and convergence of the method. This study covers a comparison of several integration rules proposed in the literature for other integral methods

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 199-205).
Gas-pressurized spacesuits are necessary for human spaceflight, most notably for extravehicular activity (EVA). Legacy EVA suits have been primarily rigid, and operation in such suits can result in significant metabolic expense, or even injury, for the wearer. To reduce these effects, modern spacesuits are more flexible, through the incorporation of more softgood materials and specially designed joint interfaces such as hip bearings. However, modeling the effects of human-suit interaction for these softgood materials is challenging due to the highly deformable nature of the suit coupled with the deformable nature of the human. To enable improved analysis and design of modern spacesuits, a computational model that can resolve the structural deformations of the suit and human resulting from contact interactions is developed. This thesis details the development and validation of a coupled contact-mechanics solver architecture for use in studying the effects of human-artifact interaction, particularly with respect to pressurized softgood exosuit design. To resolve contact and structural mechanics interactions for a deformable human and artifact, a finite element model is developed. First, the SUMMIT computational framework is employed for resolving the structural deformations of the system, and is coupled to an explicit contact mechanics scheme. The explicit contact scheme is implemented so as to resolve both external- and self-contact problems. Next, the model architecture is integrated to enable parallelization of both the structural deformation and contact systems, and computational scaling investigated. A computational trade study is performed to benchmark the coupled contact-mechanics method against a simpler rigid body model employing a penalty method. Following this, the model is validated against experimental data for various artifact contact problems. The explicit coupled contact-mechanics model is found to effectively capture contact interactions of the experimental data, with improved fidelity for deformable contact interactions. With careful tuning of the system properties, the coupled contact-mechanics model enables an architecture for an integrated human-suit analysis and design model.
by Christopher David King.
S.M.

Cette thèse, au sein du département Micro Nano Sciences et Systèmes du laboratoire FEMTO-ST, s'inscrit dans le développement de la microscopie thermique. Nous avons proposé d'étudier la mesure locale par thermocouple intrinsèque en modes contact et non contact. L'originalité de ces méthodes est qu'elles font intervenir l'échantillon conducteur comme l'un des éléments du couple thermoélectrique. La première partie de ces travaux a consisté à concevoir, réaliser et mesurer des étalons thermiques indispensables au développement d'un principe de mesure thermique. La seconde partie de cette thèse a été consacrée à la conception et à la réalisation de sondes locales spécifiquement dédiées à la mesure par thermocouple intrinsèque. Plusieurs architectures différentes ont été proposées et nous avons montré les résultats de caractérisation obtenus ainsi que les limitations de cette méthode intrinsèque. Enfin, la dernière partie de ces travaux a été dédiée à la mise en place d'un microscope à forces électrostatiques. Celui-ci permet la quantification de la Différence de Potentiel de Contact sans contact entre la sonde et l'échantillon de test. Celui-ci a permis de présenter les premières mesures de la variation de l'énergie de surface en fonction de la température
This thesis has been carried out at the department MN2S of the laboratory FEMTO-ST. It has been devoted to the study of thermal microscopy. We have investigated local measurement methods by intrinsic thermocouple in contact mode and non contact mode. The originality of these methods is the fact that the conductive device under test acts as an element of the thermoelectric couple. The first part of this work was to design, implement and calibrate thermal standards necessary in order to develop a thermal metrology principle. The second part of this thesis was dedicated to design and fabricate special probes to investigate the intrinsic thermocouple method. We have proposed different probe designs and complete measurement results, as well as the limitations of this intrinsic method. Eventually, the third part has dealt with assembling an electrostatic force microscope. This microscope allows the quantification of the Contact Potential Difference without contact between the probe and the device under test. The first experimental results are described showing the temperature dependence of the surface energy

Depuis l'utilisation des boulons au XVème siècle pour assembler deux pièces, les assemblages boulonnés posent des questions quant à la compréhension de leur fonctionnement et de leurs défaillances, telles que la variation de la tension de serrage entrainant, le desserrage, le dévissage, la perte d'étanchéité, l'initialisation de fissures, ... Pour comprendre leur fonctionnement, une méthodologie d'analyse tribologique a été mise en place, permettant de démonter un assemblage boulonné sans le desserrer, afin de ne pas modifier les conditions de contact lors du desserrage. Ainsi, toutes les interfaces d'assemblages (‘‘filets’’ écrou/vis et ‘‘autres que filets’’) formant des triplets tribologiques, ont été étudiées durant les trois phases de leur cycle de vie (fabrication, serrage, service) par le biais de cas-tests de matériaux différents. Un dialogue interactif entre les expérimentations (corrélations d'images, expertises) et la simulation numérique (Eléments Finis, Eléments Discrets) a permis de dégager des interprétations, notamment concernant les trois phases. Lors de la fabrication, le roulage des vis engendre des transformations tribologiques superficielles au niveau des sous-surfaces des filets formés. Le cœur des vis (noyau) restant non-déformé, ce procédé crée ainsi une différence de microstructure au sein de ces vis, ce qui est une source d'altération de leurs propriétés en fatigue. Lors du serrage, il se forme à l'interface ‘‘filets’’ une mixture de troisièmes corps ‘‘sec-solide’’, accommodant la vitesse entre la vis et l'écrou. Cette mixture résulte d'une réactivité entre une graisse utilisée pour le serrage et des particules, détachées d'un revêtement appliqué sur les filets d'écrous et/ou de vis. En fin de serrage, une partie de la mixture reste piégée entre les filets, jouant le rôle de maintien de la tension de serrage. Dans ces conditions, il apparaît que le frottement varie en fonction de la rhéologie de la mixture, conditionnant la variation de la tension de serrage. En service, des instabilités de contact (glissement, décollement, ...) ont été identifiées au niveau des interfaces. Ces instabilités engendrent dans les interfaces ‘‘autres que filets’’ la formation d'un troisième corps oxydé. Ce dernier constitue un surplus de matière qui peut entrainer l'augmentation des contraintes mécaniques dans les assemblages. A l'interface ‘‘filets’’ écrou/vis, il a été constaté que si la mixture de troisièmes corps piégée en serrage n'est pas cohésive, elle est extrudée des contacts, initialisant la perte de la tension de serrage. A partir de ces interprétations, des interactions entre plusieurs circuits tribologiques conduisent à converger vers un scénario de fonctionnement des assemblages boulonnés, permettant de solutionner leurs défaillances par la re-conception (mise en place de gorge de décharge, ...)
Since the use of bolts in the fifteenth century to assemble two parts, the bolted assemblies have the interrogations according to the understanding of their operating and failures occurring, such as the variation of the clamping force leading to, self-loosening, loss of sealing performance, cracks initialization, ... In order to understand their operating, a methodology focused on tribological approach was established, enabling to disassemble a bolted assembly without loosen its, allowing to not change the contact conditions during loosening. So, all the bolted assemblies interfaces (nut/screw ‘‘threads’’ and ‘‘others than threads’’) constituting tribological triplets, have been studied according to the three stages of their full life-cycle (manufacturing, tightening and service) using configurations of different materials. An interactive dialogue between the experiments (fields measuring by digital images correlation, tribological analysis) and the numerical simulation (Finite Element Method, Discrete Element Method) has led to interpretations about the three stages. During the manufacturing, the rolling of screws generates tribological superficial transformations in subsurfaces of machined threads. Contrariwise, inside the volume of these machined screws, there is no tribological transformation. So, this manufacturing process creates a difference of microstructure in these screws, that could be a source of their fatigue properties destruction. During the tightening, it produces at ‘‘threads’’ interface a ‘‘dry-solid’’ mixture of third bodies, accommodating the speed jump between the screw and the nut. This mixture is the result of a reactivity between a grease used for bolted tightening and the particles, detached by plastic flow from a coating initially applied on the threads of nuts and/or bolts. At the end of the process, a part of the mixture remains trapped in the threads, playing the role of maintaining the clamping force. In these conditions, it appears that the friction varies depending of the rheology of the mixture, conditioning the variation of the clamping force. In service, contact instabilities (slip, peeling off, ...) have been identified in the interfaces. These instabilities lead to the formation of an oxidized third body in ‘‘others than threads’’ interfaces. This oxidized third body represents a surplus of material and can increase mechanical stresses in the assemblies. In the nut/screw ‘‘threads’’ interface, it was found that if the mixture of third bodies trapped during the tightening stage is not cohesive, it is extruded, initializing the loss of clamping force. Based on the findings, the interactions between multiple tribological circuits lead to converge to a scenario of bolted assemblies operating, allowing to solve their failures by re-designing (create discharge grooves, ...)

L'ambiente di questa tesi è quello del Delay and Disruption Tolerant Networks (DTN), un'architettura di rete di telecomunicazioni avente come obiettivo le comunicazioni tra nodi di reti dette “challenged”, le quali devono affrontare problemi come tempi di propagazione elevati, alto tasso di errore e periodi di perdita delle connessioni. Il Bunde layer, un nuovo livello inserito tra trasporto e applicazione nell’architettura ISO/OSI, ed il protocollo ad esso associato, il Bundle Protocol (BP), sono stati progettati per rendere possibili le comunicazioni in queste reti. A volte fra la ricezione e l’invio può trascorrere un lungo periodo di tempo, a causa della indisponibilità del collegamento successivo; in questo periodo il bundle resta memorizzato in un database locale. Esistono varie implementazioni dell'architettura DTN come DTN2, implementazione di riferimento, e ION (Interplanetary Overlay Network), sviluppata da NASA JPL, per utilizzo in applicazioni spaziali; in esse i contatti tra i nodi sono deterministici, a differenza delle reti terrestri nelle quali i contatti sono generalmente opportunistici (non noti a priori). Per questo motivo all’interno di ION è presente un algoritmo di routing, detto CGR (Contact Graph Routing), progettato per operare in ambienti con connettività deterministica. È in fase di ricerca un algoritmo che opera in ambienti non deterministici, OCGR (Opportunistic Contact Graph Routing), che estende CGR. L’obiettivo di questa tesi è quello di fornire una descrizione dettagliata del funzionamento di OCGR, partendo necessariamente da CGR sul quale è basato, eseguire dei test preliminari, richiesti da NASA JPL, ed analizzarne i risultati per verificare la possibilità di utilizzo e miglioramento dell’algoritmo. Sarà inoltre descritto l’ambiente DTN e i principali algoritmi di routing per ambienti opportunistici. Nella parte conclusiva sarà presentato il simulatore DTN “The ONE” e l’integrazione di CGR e OCGR al suo interno.

As a result, in this thesis we provide a complete implementation of a manipulation system that can operate in unstructured environments. However, there is room for improvement in all the components presented and many unsolved questions that should be addressed in the future remain
Como resultado del trabajo presentado en esta tesis, se proporciona una implementación completa de un sistema de manipulación que puede funcionar en entornos no estructurados. Sin embargo, hay margen de mejora en todos los componentes y quedan muchas preguntas sin resolver que deberían ser abordadas en el futuro.