Dissertations / Theses on the topic 'Mechanical ablation'
To see the other types of publications on this topic, follow the link: Mechanical ablation.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Mechanical ablation.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Fu, Rui. "Thermo-Mechanical Coupling for Ablation." UKnowledge, 2018. https://uknowledge.uky.edu/me_etds/111.
Abstract:
In order to investigate the thermal stress and expansion as well as the associated strain effect on material properties caused by high temperature and large temperature gradient, a two-way thermo-mechanical coupling solver is developed. This solver integrates a new structural response module to the Kentucky Aerothermodynamics and Thermal response System (KATS) framework. The structural solver uses a finite volume approach to solve either hyperbolic equations for transient solid mechanics, or elliptic equations for static solid mechanics. Then, based on the same framework, a quasi-static approach is used to couple the structural response and thermal response to estimate the thermal expansion and stress within Thermal Protection System (TPS) materials.
To better capture the thermal expansion and study its impacts on material properties such as conductivity and porosity, a moving mesh scheme is also developed and incorporated into the solver. Grid deformation is transferred among different modules in the form of variations of geometric parameters and strain effects. By doing so, a bi-direction information loop is formed to accomplish the two-way strong thermo-mechanical coupling.
Results revealed that the thermal stress experienced during atmospheric re-entry concentrates in a banded area at the edge of the pyrolysis zone and its magnitude can be large enough to cause the failure of the TPS. In addition, thermal expansion causes the whole structure to deform and the changes in material properties. Results also indicated that the impacts coming from structural response should not be ignored in thermal response.
2
Walsh, Conor James. "Image-guided robots for dot-matrix tumor ablation." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/61613.
Abstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 203-208).
Advances in medical imaging now provides detailed images of solid tumors inside the body and miniaturized energy delivery systems enable tumor destruction through local heating powered by a thin electrode. However, the use of thermal ablation as a first line of treatment is limited due to the difficulty in accurately matching a desired treatment and a limited region of active heating around an electrode. The purpose of this research is to identify and quantify the current limitations of image-guided interventional procedures and subsequently develop a procedure and devices to enable accurate and efficient execution of image-based interventional plans and thus ablation of a tumor of any shape with minimal damage to surrounding tissue. Current limitations of probe placement for ablation therapy were determined by a detailed retrospective study of 50 representative CT-guided procedures. On average, 21 CT scans were performed for a given procedure (range 11-38), with the majority devoted to needle orientation and insertion (mean number of scans was 54%) and trajectory planning (mean number of scans was 19%). A regression analysis yielded that smaller and deeper lesions were associated with a higher number of CT scans for needle orientation and insertion; highlighting the difficulty in targeting. Another challenge identified was repositioning the instrument distal tip within tissue. The first robot is a patient-mounted device that aligns an instrument along a desired trajectory via two motor-actuated concentric, crossed, and partially nested hoops. A carriage rides in the hoops and grips and inserts an instrument via a two degree-of-freedom friction drive. An imagebased point-and-click user interface relates appropriate clicks on the medical images to robot commands. Mounting directly on the patient provides a sufficiently stable and safe platform for actuation and eliminates the need to compensate for chest motion; thereby reducing the cost and complexity compared to other devices. Phantom experiments in a realistic clinical setting demonstrated a mean targeting accuracy of 3.5 mm with an average of five CT scans. The second robot is for repositioning the distal tip of a medical instrument to adjacent points within tissue. The steering mechanism is based on the concept of substantially straightening a pre-curved Nitinol stylet by retracting it into a concentric outer cannula, and re-deploying it at different axial and rotational cannula positions. The proximal end of the cannula is attached to the distal end of a screw-spline that enables it to be translated and rotated with respect to the casing. Translation of the stylet relative to the cannula is achieved with a second concentric, nested smaller diameter screw that is constrained to rotate with the cannula. The robot mechanism is compatible with the CT images, light enough to be supported on a patient's chest or attached to standard stereotactic frames. Targeting experiments in a gelatin phantom demonstrated a mean targeting error of 1.8 mm between the stylet tip and that predicted with a kinematic model. Ultimately, these types of systems are envisioned being used together as part of a highly dexterous patient-mounted positioning platform that can accurately perform ablation of large and irregularly shaped tumors inside medical imaging machines - offering the potential to replace expensive and traumatic surgeries with minimally invasive out-patient procedures.
by Conor James Walsh.
Ph.D.
3
Chang, I.-Ta. "Excimer Laser Ablation of Polymer-Clay Nanocomposites." University of Akron / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=akron1333995807.
4
Payne, Barry. "The role of chromophore on pulsed laser ablation of biological tissue." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/43315.
5
Walter, Aaron Joseph. "Approximate Thermal Modeling of Radiofrequency Cardiac Ablation." Diss., CLICK HERE for online access, 2005. http://contentdm.lib.byu.edu/ETD/image/etd1002.pdf.
6
Karim, Nejad Aliabadi Parya. "Development of thermoelectric cooling system for tissue ablation." Thesis, University of Birmingham, 2017. http://etheses.bham.ac.uk//id/eprint/7536/.
Abstract:
There is growing interest in the use of cryosurgical treatment for the ablation of cancerous and diseased tissue. This thesis describes experimental and numerical investigation of the thermoelectric devices to be utilized in development of the cryosurgical probe for generating freezing and rewarming temperature required for tissue ablation. Thermoelectric cooling devices were used in this research due to being compact, noiseless with no moving parts and no circulating refrigerant. A novel three-dimensional model of human living tissue including metabolic heat, perfusion of blood and variation of tissue properties with temperature has been developed to determine thermal behaviour of tissue during cryosurgery process and predict the cooling requirement of the cryosurgical probe using COMSOL Multiphysics 5.2 software. COMSOL Multiphysics was used for the first time to develop three dimensional model of single stage and multistage thermoelectric devices and to predict the temperature difference across the thermoelectric modules at different input of electrical power. It is concluded that three stage thermoelectric module is capable of generating the temperature of the 213 K for cancer tissue ablation. The laboratory prototype of the cryosurgical probe was developed to investigate the performance of three stage thermoelectric device and the minimum temperature of the approximately 240 K were achieved in the experimental test. A circular hollow pin fin with lower thermal resistance was developed in SolidWorks flow simulation 2015 software and introduced as a suitable heat exchanger to be used in the laboratory prototype.
7
Lv, Wener. "A novel means of cardiac catheter guidance for ablation therapy of ventricular tachycardia." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/87978.
Abstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 118-123).
This work presents a system for identifying the site of origin of ventricular tachycardia (VT) and guiding a catheter to that site in order to deliver radio-frequency (RF) ablation therapy. Myocardial infarction (MI), also known as ischemic heart disease, is one of the most common pathophysiologic substrates for the development of ventricular tachycardia (VT). Implantable cardioverter defibrillators (ICDs) have been found to be successful in terminating VT but do not prevent the initiation of the arrhythmia. Alternatively, the radiofrequency (RF) ablation procedure has been recently used as a potentially curative therapy by delivering a high-frequency current at the arrhythmia site in order to disrupt the re-entrant circuit and to prevent the arrhythmia from occurring. However, RF ablation of VT presents a great challenge. The origin of the arrhythmia may be anywhere in the ventricles, and existing techniques used to locate the site require that patients be maintained in VT for 30 to 45 minutes, which leads to blood pressure collapse in 90% of the patients. Recently, we have developed a novel guidance system for the ablative treatment of VT. This system employs an Inverse Solution Guidance Algorithm (ISGA) based upon a single equivalent moving dipole (SEMD) model for the generation of body surface potentials and is able to localize both the arrhythmia site and the ablation catheter in real-time. With the proposed system VT need be induced and maintained for only a few seconds. This system has been shown in our tank experiment and in vivo animal studies to be highly accurate, low cost and reliable. An optimization analysis of the system is also included in this thesis for the purpose of further reducing the cost and surgical risk of the RF ablative therapy.
by Wener Lv.
Ph. D.
8
Simsek, Bugra. "Ablation Modeling Of Thermal Protection Systems Of Blunt-nosed Bodies At Supersonic Flight Speeds." Master's thesis, METU, 2013. http://etd.lib.metu.edu.tr/upload/12615414/index.pdf.
Abstract:
The objective of this thesis is to predict shape change due to ablation and to find temperature distribution of the thermal protection system of a supersonic vehicle under aerodynamic heating by using finite element method. A subliming ablative is used as thermal protection material. Required material properties for the ablation analyses are found by using DSC (Differential Scanning Calorimetry) and TGA (Thermogravimetric Analysis) thermal analysis techniques. DSC is a thermal analysis technique that looks at how a material's specific heat capacity is changed by temperature and TGA is a technique in which the mass of a substance is monitored as a function of temperature. Moreover, oxyacetylene ablation tests are conducted for the subliming ablative specimens and measured recession values are compared with the analytically calculated values. Maximum difference between experimental results and analytical results is observed as 3% as seen in Table 7. For the finite element analyses, ANSYS Software is used. A numerical algorithm is developed by using programming language APDL (ANSYS Parametric Design Language) and element kill feature of ANSYS is used for simulation of ablation process. To see the effect of mesh size and time step on the solution of analyses, oxyacetylene test results are used. Numerical algorithm is also applied to the blunt-nosed section of a supersonic rocket which is made from subliming ablative material. Ablation analyses are performed for the nose section because nose recession is very important for a rocket to follow the desired trajectory and nose temperature is very important for the avionics in the inner side of the nose. By using the developed algorithm, under aerodynamic heating, shape change and temperature distribution of the nose section at the end of the flight are obtained. Moreover, effects of ablation on the trajectory of the rocket and on the flow around the rocket are examined by Missile DATCOM and CFD (computational fluid dynamics) analysis tools.
9
Dilwith, Jason. "Feasibility Study of Laser Ablation using Long Pulsed 300W, CW Single Mode Fiber Laser." NCSU, 2005. http://www.lib.ncsu.edu/theses/available/etd-06132005-191622/.
Abstract:
Many applications now require micro sized holes that are difficult to produce with conventional methods. The entrance of lasers in the industry has brought about a better method for producing these holes. However the ultra-short pulse lasers that are normally used are extremely expensive and require many pulses to remove the material due to the small amount of energy they deposit. The objective of this research is to examine the feasibility of laser ablation using a 300W, CW Single Mode fiber laser which has high continuous power output for each pulse and has excellent beam quality. The results show that laser ablation occurs when a 100mm lens is used with pulse durations at 40 microseconds or below. Using one 18 microsecond pulse, a blind hole of 43.6 microns in diameter and 23.6 microns in depth with an aspect ratio of 0.54 can be created with little heat affected zone. This performance is comparable to nanosecond lasers, but with much higher hole depth per pulse. It was also found that the pulse duration must be short enough so that the ablating effect of the initial spike of an enhanced pulse is not nullified due to melting. At longer pulse durations (50 microseconds or more), raised surfaces are created instead of holes.
10
Ortiz, Luis G. "Design of a chemical sampling and analysis system using excimer laser ablation and quartz microcolumns." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/43422.
11
Buratin, Stefano. "Pulsed laser ablation of silicon : the influence of beam parameters on ablated crater morphology." Thesis, University of Birmingham, 2018. http://etheses.bham.ac.uk//id/eprint/8569/.
Abstract:
Laser micromachining is one of the principal fields where the laser capability to change the material morphology is frequently applied and silicon is still the element most used in the semiconductor and photovoltaic industries despite the recent studies on new materials. Although various models reported in the literature describe the laser material interaction, the relation between the ablated crater morphology and the laser beam parameters remains unclear or does not give methods and equations that can be applied on the engineering environment. The aim of this thesis is to reduce the knowledge gap of the understanding of three laser parameters (pulse duration, energy beam shape, and polarisation) influence on the ablated crater morphology by providing functions and relations that can be applied in the engineering environment. First, a systematic study on laser pulse duration based on two different functions (i.e. thermal-based and non-thermal based) is carried out, then the impact of the thermal effect on crater morphology of two non-standard energy beam distributions (i.e. round flat-top and square-top) is evaluated, and finally the laser polarisation effects in the non-linear laser ablation regime are explored, providing the engineering environment of new functions and relations between laser beam parameters and crater morphology.
12
Tang, Chen. "Novel Performance Evaluation Method for Electrosurgical Ablation by Monopolar Hot Biopsy Forceps." Ohio University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1461217424.
13
Devarakonda, Surendra B. "Enhanced Thermal Ablation of Biomaterials Using High-Intensity Focused Ultrasound (HIFU) Energized Nano-particles." University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1544001995977567.
14
Aykan, Serap Fatma. "Numerical Analysis Of Ablation Process On A Two Dimensional External Surface." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/2/12606675/index.pdf.
Abstract:
The thermal response analysis of an ablative material on a two dimensional external surface is performed. The method is applied to both rectangular and cylindrical coordinate systems, where rectangular coordinate system is used for comparison with results available in literature. The current study solves the decomposition of the material at high temperatures by using the nth order Arrhenius equation but excludes the removal of char from the surface due to mechanical erosion or phase change and considers that the ablation process takes place in a finite zone. The method considers the whole domain as one computational domain, eliminating the necessity to check the positions of the start and end of decomposition zone. The decomposition of pyrolysis gases and/or char that may occur at high temperatures and the chemical reaction between pyrolysis gases and char is neglected while pyrolysis gases are assumed to behave as ideal gas. The pressure is taken as a constant value on a whole physical domain.
The formulation for one-dimensional case is validated by experimental results obtained from literature. The two-dimensional case in a Cartesian geometry is formulated and an algebraic transformation is used to normalize the region in both directions and transformed at same time into a square computational domain in order to get a solution for the variable thickness domains. The formulation for two-dimensional case is revised for the cylindrical coordinates with finite length in the axial direction. To solve geometries where the outer surface deviates from cylindrical, the formulation is scaled and transformed into a non-dimensional square computational domain. The method is also applied to a two layer material problem in axisymmetric geometry.
In all problems, the radiation and constant heat flux boundary conditions exist on the outer surface while whole domain is initially at a constant temperature.
Case studies are performed to demonstrate the application of the solution method in optimizing the insulation material thickness.
15
Pearson, Stephen Herbert. "Nonlinear Ball Chain Waveguides For Acoustic Emission And Ultrasound Sensing Of Ablation." ScholarWorks @ UVM, 2014. http://scholarworks.uvm.edu/graddis/256.
Abstract:
Harsh environment acoustic emission and ultrasonic wave sensing applications often benefit from placing the sensor in a remote and more benign physical location by using waveguides to transmit elastic waves between the structural location under test and the transducer. Waveguides are normally designed to have high fidelity over broad frequency ranges to minimize distortion - often difficult to achieve in practice. This thesis reports on an examination of using nonlinear ball chain waveguides for the transmission of acoustic emission and ultrasonic waves for the monitoring of thermal protection systems undergoing severe heat loading, leading to ablation and similar processes. Experiments test the nonlinear propagation of solitary, harmonic and mixed harmonic elastic waves through a copper tube filled with steel and elastomer balls and various other waveguides. Triangulation of pencil lead breaks occurs on a steel plate. Data are collected concerning the usage of linear waveguides and a water-cooled linear waveguide. Data are collected from a second water-cooled waveguide monitoring Atmospheric Reentry Materials in UVM's Inductively-Coupled Plasma Torch Facility.
The motion of the particles in the dimer waveguides is linearly modeled with a three ball and spring chain model and the results are compared per particle. A theoretical nonlinear model is presented which is capable of exactly modeling the motion of the dimer chains. The shape of the waveform propagating through the dimer chain is modeled in a sonic vacuum. Mechanical pulses of varying time widths and amplitudes are launched into one end of the ball chain waveguide and observed at the other end in both time and frequency domains. Similarly, harmonic and mixed harmonic mechanical loads are applied to one end of the waveguide. Balls of different materials are analyzed and discriminated into categories. A copper tube packed with six steel particles, nine steel or marble particles and a longer copper tube packed with 17 steel particles are studied with a frequency sweep. The deformation experienced by a single steel particle in the dimer chain is approximated. Steel ball waveguides and steel rods are fitted with piezoelectric sensors to monitor the force at different points inside the waveguide during testing.
The corresponding frequency responses, including intermodulation products, are compared based on amplitude and preloads. A nonlinear mechanical model describes the motion of the dimer chains in a vacuum. Based on the results of these studies it is anticipated that a nonlinear waveguide will be designed, built, and tested as a possible replacement for the high-fidelity waveguides presently being used in an Inductively Coupled Plasma Torch facility for high heat flux thermal protection system testing. The design is intended to accentuate acoustic emission signals of interest, while suppressing other forms of elastic wave noise.
16
Roper, Ryan Todd. "A Study of Radiofrequency Cardiac Ablation Using Analytical and Numerical Techniques." Diss., CLICK HERE for online access, 2003. http://contentdm.lib.byu.edu/ETD/image/etd262.pdf.
17
Mullenix, Nathan J. "A COUPLED GAS DYNAMICS AND HEAT TRANSFER METHOD FOR SIMULATING THE LASER ABLATION PROCESS OF CARBON NANOTUBE PRODUCTION." University of Akron / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=akron1131648970.
18
Journaux-Duclos, Justine. "Ciblage thérapeutique de l'adénocarcinome pancréatique par hyperthermie magnétique ou ablation magnéto-mécanique." Electronic Thesis or Diss., Toulouse 3, 2023. http://www.theses.fr/2023TOU30360.
Abstract:
Grâce à leurs propriétés physico-chimiques et leur biocompatibilité les nanoparticules magnétiques d'oxyde de fer (SPION) offrent de nombreux avantages. Elles répondent à l'application de champs magnétiques en libérant de l'énergie thermique en réponse à l'application d'un champ magnétique alternatif à haute fréquence (AMF), ou générant des forces mécaniques exposées à des champs magnétiques rotatifs à basse fréquence (RMF). Des essais cliniques utilisant le principe de l'hyperthermie magnétique ont été menés sur le glioblastome et le cancer de la prostate en association avec de la radiothérapie. Néanmoins, le bénéfice était négligeable en raison d'effets indésirables sur les tissus sains adjacents. Or, notre équipe a précédemment montré qu'il était possible d'induire spécifiquement la mort de cellules grâce à de faibles concentrations de SPION vectorisées qui s'accumulent spécifiquement dans les lysosomes de cellules ciblées. L'application d'AMF va induire la mort des cellules-cibles par hyperthermie magnétique intra-lysosomale ciblée MILH via la production de ROS dans le lysosome selon la réaction de Fenton qui nécessite des ions Fe et peut être catalysée par un pH acide et une augmentation de la température. Cependant, l'origine des ions Fe impliqués dans la réaction de Fenton n'a pas été élucidée. Une autre stratégie a également été établie dans l'équipe ; elle repose sur l'application de champs RMF qui vont générer des forces mécaniques à partir des SPION et induire la mort des cellules par ablation mécanique intra-lysosomale ciblée. Nous avons choisi comme modèle, l'adénocarcinome pancréatique particulièrement résistant aux thérapies conventionnelles et caractérisé par la présence d'un microenvironnement important et dense. Dans ce microenvionnement, les CAF (Cancer Associated Fibroblast) jouent un rôle clef, notamment par la sécrétion de matrice extracellulaire et de molécules solubles, limitant la pénétration et l'efficacité des traitements et contribuant à l'acquisition de résistance. Les cellules cancéreuses et les CAF peuvent surexprimer le récepteur de type 2 de la cholécystokinine (RCCK2). Ce récepteur membranaire présente la propriété de s'internaliser après fixation de son agoniste spécifique : la gastrine. Afin de cibler spécifiquement ces cellules, l'équipe a développé, des SPION, fonctionnalisées, à haut pouvoir chauffant et vectorisées avec de la gastrine (NF@Gastrine). Ces nanoparticules reconnaissent spécifiquement les cellules pancréatiques humaines MiaPaca2 et de CAF exprimant le récepteur CCK2 et s'accumulent dans leurs lysosomes. L'application d'AMF (275 kHz, 30mT) ou de RMF (1 Hz, 40 mT) induit spécifiquement la mort de ces cellules par MILH ou ablation mécanique intra-lysosomale ciblée. Nous avons comparé les effets de l'hyperthermie magnétique intra-lysosomale induits par des NF@Gastrine à ceux induits par les mêmes nanoparticules recouvertes d'une coque de silice hermétique (NF@SiO2@Gastrine), empêchant la libération de fer sous l'AMF, en présence ou non de Ferristatin-II, un inhibiteur de la capture de fer par la cellule. Cette étude a permis de mettre en évidence que le fer impliqué dans la réaction de Fenton à l'origine de la production de ROS par MILH provenait du pool endogène de la cellule et non de la libération de fer par les SPION soumises à l'AMF. Nous avons ensuite mis en évidence que l'hyperthermie magnétique et l'ablation mécanique intra-lysosomales augmentent l'expression de motifs moléculaires associés aux dégâts (DAMPs) à la surface des cellules MiaPaca2 et des CAF ayant internalisées les NF@Gastrine et stimulent leur phagocytose par des macrophages. Ces deux approches, pourraient donc être deux nouvelles stratégies capables de rétablir une immunité anti tumorale dans l'adénocarcinome pancréatique. Enfin, ces deux stratégies peuvent également modifier le phénotype pro-tumoral des CAF, en inhibant leur migration, diminuant leur sécrétion de collagèneDue to their physico-chemical properties, magnetic iron oxide nanoparticles (SPION) offer many advantages. They are biocompatible and functionalizable and therefore have already been used as a contrast agent for MRI diagnosis. They can respond to the application of magnetic fields: release thermal energy in response to the application of a high frequency alternating magnetic field (AMF), or generate mechanical forces when they are exposed to low frequency rotating magnetic fields (RMF). Clinical trials using magnetic hyperthermia mediated by SPION and AMF fields have been carried out on glioblastoma and prostate cancer in association with radiotherapy. Nevertheless, the benefit on life expectancy was negligible and adverse effects were noted on adjacent healthy tissues. But our team has previously shown that it is possible to specifically induce tumor cells and microenvironment cells death through the use of low concentrations of targeted magnetic nanoparticle that specifically accumulate in the lysosomes of the targeted cells. Then AMF fields specifically induce the death of target cells by targeted intra-lysosomal magnetic hyperthermia MILH. The mechanisms leading to the death of these cells have been characterized and show that it is initiated in the lysosomes by the generation of ROS according to the Fenton reaction which requires Fe ions and can be catalyzed by an acid pH and an increase of temperature (optimal at 40°C). However, the origin of the Fe ions involved in the Fenton reaction has not been elucidated. Another strategy was also established in the team; it is based on the application of RMF fields which will generate mechanical forces from the SPIONs and induce cell death by targeted intra-lysosomal mechanical ablation. We have chosen as a model, the pancreatic adenocarcinoma particularly resistant to conventional therapies and characterized by the presence of a large and dense microenvironment. In this microenvironment, CAFs (Cancer Associated Fibroblasts) play a key role, in particular through the secretion of extracellular matrix and soluble molecules, limiting the penetration and effectiveness of treatments and contributing to the acquisition of resistance. Cancer cells as well as CAF can overexpress the cholecystokinin receptor type 2 (RCCK2). This membrane receptor has the property of internalizing after binding of its specific agonist: the gastrin. The team has developed functionalized nanoparticles with high heating power vectorized with gastrin peptides (NF@Gastrin). These nanoparticles specifically recognize human pancreatic MiaPaca2 cells and CAFs expressing the CCK2 receptor and accumulate in their lysosomes. The application of AMF (275 kHz, 30 mT) or RMF (1 Hz, 40 mT) fields specifically induces the death of these cells by MILH or targeted intra-lysosomal mechanical ablation. First, we compared the effects of MILH induced by NF@Gastrin to those induced by the same nanoparticles covered with a hermetic silica shell (NF@SiO2@Gastrin), preventing the release of iron under the application of AMF field, in the presence or absence of Ferristatin-II, an inhibitor of iron uptake by the cell. This study demonstrate that the iron involved in the Fenton reaction at the origin of ROS production by MILH came from the endogenous pool of the cell and not from the release of iron by the iron oxide nanoparticles submitted to AMF. Then, we demonstrate that MILH and mechanical ablation increase the expression of damage-associated molecular patterns (DAMPs) on the surface of MiaPaca2 cells and CAFs having specifically internalized NF@Gastrin and stimulate their phagocytosis by macrophages. These two approaches, magnetic hyperthermia and mechanical ablation, could therefore be two new strategies to restore anti-tumor immunity in pancreatic adenocarcinoma. Finally, these two strategies can also modify the pro-tumoral phenotype of CAFs, by inhibiting their migration, decreasing their collagen secretion
19
Binti, Mohamad Noor Shafini. "Impact of P2RX7 purinoceptor ablation on the morphometric, mechanical and tissue properties in the murine model of Duchenne muscular dystrophy." Thesis, University of Portsmouth, 2016. https://researchportal.port.ac.uk/portal/en/theses/impact-of-p2rx7-purinoceptor-ablation-on-the-morphometric-mechanical-and-tissue-properties-in-the-murine-model-of-duchenne-muscular-dystrophy(60c82bbf-ce54-4054-aa0e-31a39affbd7c).html.
Abstract:
Duchenne muscular dystrophy (DMD) is an inherited, lethal disorder characterised by progressive muscle degeneration and associated bone abnormalities. It has previously demonstrated that P2RX7, a purinergic receptor, contributed to the pathogenesis of DMD, and found that P2RX7 ablation alleviated the severity of the disease. In this work a dystrophic mdx mouse crossed with the global P2RX7 receptor has been used to generate a knockout mouse model (mdx/P2X7-/-), and compared its morphometric, mechanical and tissue properties against those of mdx,a mouse model without the dystrophin protein, as well as a wild type (WT) and aP2RX7 knockout (P2X7-/-). Micro-computed tomography (μCT), three-point bending testing, scanning electron microscopy (SEM) and nanoindentation were utilised in the study. The bones were analysed at approximately 4 weeks of age to examine the impact of P2RX7 ablation on the bone properties during the acute disease phase, before muscle wasting is fully developed. The results show that P2RX7 purinoceptor ablation has produced improvement or significant improvement in some of the morphological, mechanical and tissue properties of the dystrophic bones examined. Specifically, although the ablation produced smaller bones with significantly lower total cross-section area (Tt.Ar) and Second Moment of Area (SMA), significantly higher cortical bone area (Ct.Ar),cortical bone area ratio (Ct.Ar/Tt.Ar) and trabecular bone volume fraction (BV/TV)are found in the mdx/P2X7-/- mice than in any other types. Further, the mdx/P2X7-/- bones have relatively higher average flexural strength, work-to-fracture and significantly higher strain to failure compared with those of mdx, suggesting greater resistance to fracture. Indentation modulus, elasticity and creep are also significantly improved in the knockout cortical bones over those of mdx. These findings seem to suggest that specific pharmacological blockade of P2RX7 may improve dystrophic bones, with a potential for therapeutic application in the treatment of the disease.
20
Sockalingam, Subramani. "Coupling of Fluid Thermal Simulation for Nonablating Hypersonic Reentry Vehicles Using Commercial Codes FLUENT and LS-DYNA." University of Cincinnati / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1218801526.
21
Martin, Nicholas C. "Steady State Simulation of Pyrolysis Gases in an Inductively Coupled Plasma Facility." ScholarWorks @ UVM, 2017. http://scholarworks.uvm.edu/graddis/791.
Abstract:
An important step in the more efficient use of PICA (Phenolic Impregnated Carbon Ablator) as a Thermal Protection System (TPS) material for spacecraft is the understanding of its pyrolysis mechanics. The gases released during pyrolysis and their subsequent interaction with the reactive plasma environment is not yet well understood. The surface recession of PICA as it ablates during testing only makes the study and characterization of the chemical reactions more difficult. To this end, a probe has been designed for this study to simulate, in steady state, the pyrolysis gases within the UVM 30kW Inductively Coupled Plasma (ICP) Torch Facility. This probe, which is an extension of previous work done at UVM, has been used to inject Carbon Dioxide, Hydrogen, and a mixture of the two into pure Argon and dilute Nitrogen, Oxygen, and air plasmas. During testing, spatially resolved, pointwise, line of sight emission measurements were taken in the boundary layer region. These results were then compared to temporally resolved PICA emission data taken in a previous study. After the correct temporal PICA scan was found the data sets closely matched. This indicates that the gas-injection probe is a viable method to simulate pyrolysis in a steady state environment. The key pyrolysis species of CN, NH, OH, Hydrogen Alpha (Hα), and Hydrogen Beta (Hβ) were spatially traced along the stagnation line for the pure Hydrogen and mixture injection cases. These measurements show evidence of spatial relationships between NH and Hα as well as between OH and Hβ. They also show that all of the molecules tend to follow the same general trend spatially. The work done for this study has both reintegrated gas-injection capability into the UVM facility as well as laid the groundwork for future gas-injection testing within the facility. Spatial emission analysis techniques currently being developed at UVM will provide a more resolved picture of the interactions occurring in the boundary layer once completed.
22
Hanich, Maxwell James. "Analysis of Efficiency of Laser Ablation of Aluminum By Modeling of Plume Shielding Effect." University of Akron / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=akron1595509756016075.
23
Mullenix, Nathan Joel. "Fully Coupled Model for High-Temperature Ablation and a Reative-Riemann Solver for its Solution." University of Akron / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=akron1271035105.
24
Wang, Yeqing. "Modeling of lightning-induced thermal ablation damage in anisotropic composite materials and its application to wind turbine blades." Diss., University of Iowa, 2016. https://ir.uiowa.edu/etd/2164.
Abstract:
A primary motivation for this research comes from the need to improve the ability of polymer-matrix composites to withstand lightning strikes. In particular, we are concerned with lightning strike damage in composite wind turbine blades. The direct effects of lightning strike on polymer-matrix composites often include rapid temperature rise, melting or burning at the lightning attachment points, and mechanical damage due to lightning-induced magnetic force and acoustic shock wave. The lightning strike damage accumulation problem is essentially multiphysic. The lightning plasma channel discharges an electric current up to 200 kA, inducing a severe heat flux at the surface of the composite structure, as well as generating Joule heating through the composite structure. The resulting electro-thermo-mechanical response of the composite structure may include matrix degradation and decomposition, delamination, and fiber breakage and sublimation, thus leading to catastrophic failure.
The existing studies related to the lightning strike damage in composites ignored the lightning channel radius expansion during the initial lightning discharge and lacked adequate treatment of material phase transitions. These assumptions significantly simplify the mathematical treatment of the problem and affect the predictive capabilities of the models. Another common feature of these limited studies is that they all focused on carbon-fiber-reinforced polymer-matrix (CFRP) composites, which are electrically conductive.
In the present thesis, the thermal responses and thermal ablations in a non-conductive glass-fiber-reinforced polymer-matrix (GFRP) composite wind turbine blade and in a conductive CFRP composite wind turbine blade are studied, respectively. In the case of non-conductive GFRP composite wind turbine blade, prior to the thermal response and thermal ablation analysis, a finite element analysis is performed to calculate the electric field due to lightning stepped leader to estimate the dielectric breakdown of the non-conductive composite wind turbine blade. The estimation of dielectric breakdown is used to determine whether Joule heating needs to be included in the problem formulation. To predict the thermal response and thermal ablation in the composite structure due to lightning strike, a physics-based model describing surface interaction between the lightning channel and the composite structure has been developed. The model consists of: (i) spatial and temporal evolution of the lightning channel as a function of the electric current waveform; (ii) temporary and spatially non-uniform heat flux and current density (in the case of electrically conductive CFRP composite or if dielectric breakdown occurs in the case of non-conductive GFRP composite) generated at the composite structure; and (iii) nonlinear transient heat transfer problem formulation for layered anisotropic composites that includes the moving boundary of the expanding lightning channel and the phase transition moving boundary associated with instantaneous material removal due to sublimation. The model has been employed to investigate the thermal responses and thermal ablations in a GFRP composite laminated panel used in a Sandia 100-meter all-glass baseline wind turbine blade (SNL 100-00) and a typical CFRP composite laminated panel subjected to lightning strike. The temperature-dependent directional material properties for both the GFRP and CFRP composites have been determined in this thesis using a micromechanics approach based on the experimental data for fibers and resin. An integrated Matlab-ABAQUS numerical procedure features the aforementioned aspects (i), (ii), and (iii) of the developed model. The obtained results include the evolution of temperature fields in the composite laminated panel and the progressive shape change of the composite laminated panel due to thermal ablation. The predictions of thermal ablation in the CFRP composite laminated panel are validated by reported experimental results.
25
Boualleg, Abdelmadjid. "Investigations on post-processing of 3D printed thermoplastic polyurethane (TPU) surface." Thesis, Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:hh:diva-41203.
Abstract:
Abstract The reduction of product development cycle time is a major concern in industries to remain competitive in the marketplace. Among various manufacturing technologies, 3D printing technology or also known as additive manufacturing (AM), has shown excellent potential to reduce both the cycle time and cost of the product due to its lower consumption of energy and material usage compared to conventional manufacturing. Fused deposition modeling (FDM) is one of the most popular additive manufacturing technologies for various engineering applications which has the ability to build functional parts having complex geometrical shapes in reasonable build time and can use less expensive equipment and cheaper material. However, the quality of parts produced by FDM has some challenges such as poor surface quality. The focus of this study is improving the surface quality produced by Fused Deposition Modeling. The investigations include 3D printing study samples with optimum parameter settings and post-processing the sample’s surfaces by laser ablation. Taguchi’s design of the experiment is employed to identify the optimum settings of laser ablation the FDM surfaces. Laser power, laser speed and pulse per inch (PPI) are the laser settings considered in the study. Characterization of the samples are done using Dino-lite USB camera images and GFM Mikro-CAD fringe projection microscope is used to measure the surface roughness of the samples. Areal surface parameters are used to characterize and compare the surfaces of as printed and laser ablated. It is observed that the effect of laser ablation varies with respect to surfaces printed at different angles and laser-ablated with different settings. The surface roughness of laser-ablated surfaces is found to be lower than as-printed FDM surfaces.
26
Tillson, Corey. "Investigation of Pyrolysis Gas Chemistry in an Inductively Coupled Plasma Facility." ScholarWorks @ UVM, 2017. http://scholarworks.uvm.edu/graddis/692.
Abstract:
The pyrolysis mechanics of Phenolic Impregnated Carbon Ablators (PICA) makes it a valued material for use in thermal protection systems for spacecraft atmospheric re-entry. The present study of the interaction of pyrolysis gases and char with plasma gases in the boundary layer over PICA and its substrate, FiberForm, extends previous work on this topic that has been done in the UVM 30 kW Inductively Coupled Plasma (ICP) Torch Facility. Exposure of these material samples separately to argon, nitrogen, oxygen, air, and carbon dioxide plasmas, and combinations of said test gases provides insight into the evolution of the pyrolysis gases as they react with the different environments. Measurements done to date include time-resolved absolute emission spectroscopy, location-based temperature response, flow characterization of temperature, enthalpy, and enthalpy flux, and more recently, spatially resolved and high-resolution emission spectroscopy, all of which provide measure of the characteristics of the pyrolysis chemistry and material response. Flow characterization tests construct an general knowledge of the test condition temperature, composition, and enthalpy. Tests with relatively inert argon plasmas established a baseline for the pyrolysis gases that leave the material. Key pyrolysis species such as CN Violet bands, NH, OH and Hydrogen Alpha (Hα) lines were seen with relative repeatability in temporal, spectral, and intensity values. Tests with incremental addition, and static mixtures, of reactive plasmas provided a preliminary image of how the gases interacted with atmospheric flows and other pyrolysis gases. Evidence of a temporal relationship between NH and Hα relating to nitrogen addition is seen, as well as a similar relationship between OH and Hα in oxygen based environments. Temperature analysis highlighted the reaction of the material to various flow conditions and displayed the in depth material response to argon and air/argon plasmas. The development of spatial emission analysis has been started with the hope of better resolving the previously seen pyrolysis behavior in time and space.
27
Bessière, Francis. "Amélioration des techniques d’ablation pour le traitement des arythmies cardiaques : nouvelles modalités diagnostiques et thérapeutiques par ultrasons." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSE1225/document.
Abstract:
A la croisée des chemins entre médecine et physique des ultrasons, ce travail de thèse s’est intéressé à l’apport de solutions diagnostiques et de thérapeutiques novatrices dans le domaine de l’électrophysiologie cardiaque. Un système capable de délivrer des ultrasons focalisés dans le cœur par voie transoesophagienne sous guidage par ultrasons a été développé et testé in vivo chez 6 porcs. Les tirs HIFU ont été délivrés sur les oreillettes et les ventricules. Lors de l'autopsie, une analyse visuelle a démontré la présence de lésions thermiques dans les zones ciblées chez 3 animaux. Ces lésions ont été confirmées par analyse histologique (taille moyenne: 5,5 mm2 x 11 mm2). Aucune lésion thermique œsophagienne n'a été observée. Un animal a présenté une bradycardie due à un bloc auriculo-ventriculaire, ce qui a permis de confirmer une réelle interaction entre les tirs HIFU et le tissu nodal cardiaque. Nous avons cependant observé un manque de précision, principalement lié aux mouvements cardiaques ainsi qu’aux structures anatomiques situées entre les zones ciblées et le transducteur de thérapie. Ces difficultés ont été principalement reliées à l’anatomie du modèle porcin, loin de celle de l’être humain. La recherche d'un meilleur modèle a conduit à des tests d'imagerie concluants sur des babouins.Des expériences supplémentaires ont été conduites afin d'améliorer la cartographie des arythmies ventriculaires et le suivi de la formation de lésions pendant l'ablation.Des expériences ont été menées sur les ventricules gauches de quatre coeurs de porcs en mode travaillant. Le protocole visait à démontrer que différents modèles d'activation mécanique pouvaient être observés, que le ventricule soit en rythme sinusal, stimulé depuis l'épicarde ou l'endocarde. Des acquisitions d’imagerie de déformation électromécanique (EWI) ont été enregistrées sur les faces antérieures, latérales et postérieures du ventricule gauche. Les boucles ont été ensuite analysées à l’aveugle par deux lecteurs indépendants.Les interprétations des séquences EWI étaient correctes dans 89% des cas. Le taux de concordance globale entre les deux lecteurs était de 83%. Dans un ventricule stimulé, l'origine du front d'onde était focale et provenait de l'endocarde ou de l'épicarde stimulé. En rythme sinusal, le front d'onde était activé depuis tout l'endocarde, en direction de l'épicarde, à une vitesse de 1,7 ± 0,28 m.s-1. Les vitesses du front d'onde ont été mesurées respectivement lorsque l'endocarde ou l'épicarde étaient stimulés à une vitesse de 1,1 ± 0,35 m.s -1 et 1,3 ± 0,34 m.s-1 (p = NS). Nous avons aussi démontré sur des échantillons ex-vivo que l'imagerie trans oesophagienne par analyse des ondes de cisaillement (élastographie) pouvait cartographier l'étendue des lésions HIFU. Des tirs HIFU ont été réalisés à l'aide de la sonde trans oesophagienne sur des échantillons de blancs de poulet (n = 3), puis sur un modèle porcin ex vivo d'oreillette (gauche, n = 2) et de ventricule gauche (n = 1). L’élastographie a fourni des cartes de rigidité des tissus avant et après l'ablation. Les zones des lésions ont été obtenues par analyse et quantification des changements de couleur des tissus puis ont été comparées aux images par élastographie. Dans le blanc de poulet, la rigidité est passée en moyenne de 4.8±1.1 kPa à 20.5±10.0 kPa (ratio 5.0±3.2). Dans le ventricule gauche, la rigidité est passée en moyenne de 21.2±3.3kPa à 73.8±13.9kPa (ratio 3.7±1.2). Dans l’oreillette gauche, la rigidité est passée en moyenne de 12.2±4.3 kPa à 30.3±10.3 (ratio 3.2±2.0). En histologie, la taille des lésions variait de 0.1 à 1.5 cm2 dans la zone du plan d'imagerie. Les caractéristiques morphométriques étaient similaires entre histologie et élastographieAt the crossroads of medicine and physics, this work aimed to provide innovative diagnostic and therapeutic tools based on ultrasound, in the field of cardiac electrophysiology. A system capable of delivering HIFU into the heart by a transesophageal route using ultrasound (US) imaging guidance was developed and tested in vivo in six male pigs. HIFU exposures were performed on atria and ventricles. At the time of autopsy, visual inspection identified thermal lesions in the targeted areas in three of the animals. These lesions were confirmed by histologic analysis (mean size: 5.5 mm2 x 11mm2). No esophageal thermal injury was observed. One animal presented with bradycardia due to an atrio-ventricular block, which provides real-time confirmation of an interaction between HIFU and the electrical circuits of the heart. There was still a lack of accuracy, mainly related to cardiac motion, and to anatomical structures in between the targets and the transducer. It was mainly related to the in vivo model and its anatomy, far from the human’s. The search for a better model led to conclusive imaging tests on baboons. Additional experiments were conduced in order to improve the mapping of ventricular arrhythmias and the monitoring of lesion formation during ablation. First, experiments were conducted on left ventricles of four isolated working mode swine hearts. The protocol aimed at demonstrating that different patterns of mechanical activation could be observed whether the ventricle was in sinus rhythm, paced from the epicardium, or from the endocardium. Electromechanical wave imaging (EWI) acquisitions were recorded on the anterior, lateral, and posterior segments of the left ventricle. Loop records were blindly assigned to two readers. EWI sequences interpretations were correct in 89% of cases. The overall agreement rate between the two readers was 83%. When in a paced ventricle, the origin of the wave front was focal and originating from the endocardium or the epicardium. In sinus rhythm, wave front was global and activated within the entire endocardium towards the epicardium at a speed of 1.7±0.28 m.s-1. Wave front speeds were respectively measured when the endocardium or the epicardium were paced at a speed of 1.1 ± 0.35 m.s-1 vs 1.3±0.34 m.s-1 (p=NS). Lastly, we investigated the feasibility of a dual therapy and imaging approach with the same transoesophageal device. We demonstrated on ex-vivo samples that transoesophageal shear wave imaging (SWE) can map the extent of the HIFU lesions. HIFU ablation was performed with the transoesophageal probe on ex-vivo chicken breast samples (n=3), then atrium (left, n=2) and ventricle (left n=1, right n=1) of swine heart tissues. SWE provided stiffness maps of the tissues before and after ablation. Areas of the lesions were obtained by tissue color change with gross pathology and compared to SWE. Shear modulus of the ablated zones increased from 4.8±1.1 kPa to 20.5+/-10.0 kPa (ratio 5.0±3.2) in the chicken breast, from 12.2±4.3 kPa to 30.3±10.3 (ratio 3.2±2.0) in the atria and from 21.2±3.3kPa to 73.8±13.9kPa (ratio 3.7±1.2) in the ventricles. On gross pathology, the size of the lesions ranged from 0.1 to 1.5cm2 in the imaging plane area and morphometric characteristics were fitting with elasticity-estimated depths and widths of the lesions
28
Choi, Hae Woon. "Femtosecond laser material processing for micro-/nano-scale fabrication and biomedical applications." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1184883900.
29
Vesperini, Doriane. "Biomechanical study of cells in microfluidic flow : application to sorting and platelet production." Thesis, Compiègne, 2018. http://www.theses.fr/2018COMP2437/document.
Abstract:
Les mégacaryocytes sont des cellules de la moelle osseuse, à l’origine de la production des plaquettes sanguines. Quand elles arrivent à maturité, elles grossissent et émettent des prolongements de cytoplasme à travers la paroi des vaisseaux irriguant la moelle. Dans la circulation sanguine, ces prolongements, soumis aux forces de l’écoulement, s’allongent et se rompent pour former des plaquettes. Des techniques microfluidiques capables de produire des plaquettes in vitro existent et sont une alternative prometteuse au don. Mais le rendement reste à améliorer. Pour cela, il est nécessaire de mieux comprendre la fragmentation des mégacaryocytes en plaquettes. Ce travail de doctorat s’inscrit dans ce contexte et sera développé en deux axes principaux dans ce manuscrit. Dans une première partie nous développons une méthode pour trier des cellules en fonction de leur déformabilité, afin de savoir si les propriétés mécaniques d’un mégacaryocyte sont liées à leur stade de maturité. La méthode a d’abord été mise au point avec des microcapsules. Leurs propriétés mécaniques sont déterminées par analyse inverse à partir de la mesure de leur forme en écoulement dans des constrictions droites. Puis le dispositif utilisé a été miniaturisé pour s’adapter à la taille des cellules. Pour la caractérisation de leurs propriétés mécaniques, deux outils ont été utilisés: l’analyse inverse et la microscopie à force atomique sans pointe. Une deuxième partie porte sur l’étude de l’élongation et de la rupture de mégacaryocytes soumis écoulement. Nous avons quantifié les variations spatiotemporelles du taux d’élongation et développé un protocole d’ablation laser pour étudier les mécanismes de rupture de cellules en élongationWhen they mature in the bone marrow, the precursors of platelets, called megakaryocytes, grow and extend protrusions able to join blood circulation. There these protrusions elongate and break into platelets. Microfluidic techniques for in vitro platelet production represent a promising alternative to donation. In order to enhance platelet production and match the needs of clinical applications such as transfusion, we need to better understand the fragmentation of megakaryocytes into platelets. Our contribution will be described in this manuscript in two main axes. First, in order to know if mechanical properties of megakaryocytes can indicate their maturity stage, we develop a cell sorting method based on deformability. The method is first validated with microcapsules. Their mechanical properties are determined by inverse analysis from their shape under flow in straight microchannels. Then the device is downscaled. The characterization of cell mechanical properties are performed using inverse analysis and tipless atomic force microscopy. Second, we study megakaryocyte elongation and rupture in a microfluidic device. We quantify the spatial and temporal variations of the elongation rate and develop a laser ablation protocol to trigger and study the rupture of elongating cells
30
Vidal, José Tort. "Desenvolvimento de um sistema opto-mecânico para micro usinagem com laser de femtosegundos." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-10082011-150643/.
Abstract:
A usinagem de estruturas micrométricas pode ser feita com pulsos laser de nano, pico ou fentossegundos. Destes, porém, somente os mais curtos podem resultar em uma interação não térmica com a matéria, o que evita a fusão, formação de rebarba e zona afetada pelo calor. Devido à sua baixa potência média, contudo, a sua utilização na produção em massa somente pode ser considerada em casos muito especiais, isto é, quando o processamento não-térmico é essencial. Este é o caso da usinagem de semicondutores, aços elétricos, produção de MEMS (sistemas micro eletro-mecânicos), de micro canais e diversos dispositivos médicos e biológicos. Assim, visando a produção destes tipos de estruturas, uma estação de trabalho foi construída com capacidade de controlar os principais parâmetros de processo necessários para uma usinagem micrométrica com laser de pulsos ultracurtos. Os principais problemas deste tipo de estação são o controle da fluência e do posicionamento do ponto focal. Assim, o controle do diâmetro do feixe (no foco) e da energia devem ser feitos com grande precisão. Além disso, o posicionamento do ponto focal com precisão micrométrica nos três eixos, também é de fundamental importância. O sistema construído neste trabalho apresenta soluções para estes problemas, utilizando diversos sensores e posicionadores controlados simultaneamente por um único programa. A estação de trabalho recebe um feixe vindo de um laser de pulsos ultracurtos localizado em outro laboratório, e manipula este feixe de maneira a focalizá-lo com precisão na superfície da amostra a ser usinada. Os principais parâmetros controlados dinamicamente são a energia, o número de pulsos e o posicionamento individual de cada um deles. A distribuição espacial da intensidade, a polarização e as vibrações também foram medidas e otimizadas. O sistema foi testado e aferido com medidas de limiar de ablação do silício, que é um material bastante estudado neste regime de operação laser. Os resultados, quando confrontados com a literatura, mostram a confiabilidade e a precisão do sistema. A automatização, além de aumentar esta precisão, também aumentou a rapidez na obtenção dos resultados. Medidas de limiar de ablação também foram realizadas para o metal molibdênio, levando a resultados ainda não vistos na literatura. Assim, de acordo com o objetivo inicial, o sistema foi desenvolvido e está pronto para utilização em estudos que levem à produção de estruturas micrométricas.Machining of very small structures has been made with nano, pico and femtosecond pulsed lasers. Among then, only femtosecond lasers may result in nonthermal interaction with matter, avoiding melting, formation of slag and heat affected zone. Mass production with such lasers yet can only be considered in cases where nonthermal effects are of prime importance. This is the case in machining of semiconductors and electric steels, the production of MEMS, microchannels, and many medical and biological devices. Hence, a workstation for production of such kind of microstructures was built with the capability of controlling the main parameters necessary for the machining process. Control of the laser fluence and focus positioning are the main concern in this kind of processing. So, the control of the laser beam diameter (in the focus) and of the pulse energy must be very precise. Positioning of focal point with micrometric precision in the three axes is also fundamental. The system built in this work provides solutions for these problems incorporating several sensors and positioning stages simultaneously controlled by a single software. The workstation receives a laser beam coming from another laboratory and delivers it to the surface of the sample managing with precision the main process parameters. The system can dynamically control the energy, number of pulses and positioning for each individual laser spot. Besides, the spatial distribution of the laser intensity, polarization and vibrations were also measured and optimized. The system was tested and calibrated with threshold ablation measurement for silicon, which is well studied in this regime of laser operation. The results where compared with data found in the literature and attested the reliability and precision of the system. Besides the increase in precision, the automation also turned much faster the data acquisition. Threshold ablation for metallic molybdenum was also obtained and resulted in data not found in the literature yet. Concluding the initial goal, the workstation was developed and is ready to be used in studies that can lead to production of micrometric structures.
31
Bessière, Francis. "Amélioration des techniques d’ablation pour le traitement des arythmies cardiaques : nouvelles modalités diagnostiques et thérapeutiques par ultrasons." Electronic Thesis or Diss., Lyon, 2019. http://www.theses.fr/2019LYSE1225.
Abstract:
A la croisée des chemins entre médecine et physique des ultrasons, ce travail de thèse s’est intéressé à l’apport de solutions diagnostiques et de thérapeutiques novatrices dans le domaine de l’électrophysiologie cardiaque. Un système capable de délivrer des ultrasons focalisés dans le cœur par voie transoesophagienne sous guidage par ultrasons a été développé et testé in vivo chez 6 porcs. Les tirs HIFU ont été délivrés sur les oreillettes et les ventricules. Lors de l'autopsie, une analyse visuelle a démontré la présence de lésions thermiques dans les zones ciblées chez 3 animaux. Ces lésions ont été confirmées par analyse histologique (taille moyenne: 5,5 mm2 x 11 mm2). Aucune lésion thermique œsophagienne n'a été observée. Un animal a présenté une bradycardie due à un bloc auriculo-ventriculaire, ce qui a permis de confirmer une réelle interaction entre les tirs HIFU et le tissu nodal cardiaque. Nous avons cependant observé un manque de précision, principalement lié aux mouvements cardiaques ainsi qu’aux structures anatomiques situées entre les zones ciblées et le transducteur de thérapie. Ces difficultés ont été principalement reliées à l’anatomie du modèle porcin, loin de celle de l’être humain. La recherche d'un meilleur modèle a conduit à des tests d'imagerie concluants sur des babouins.Des expériences supplémentaires ont été conduites afin d'améliorer la cartographie des arythmies ventriculaires et le suivi de la formation de lésions pendant l'ablation.Des expériences ont été menées sur les ventricules gauches de quatre coeurs de porcs en mode travaillant. Le protocole visait à démontrer que différents modèles d'activation mécanique pouvaient être observés, que le ventricule soit en rythme sinusal, stimulé depuis l'épicarde ou l'endocarde. Des acquisitions d’imagerie de déformation électromécanique (EWI) ont été enregistrées sur les faces antérieures, latérales et postérieures du ventricule gauche. Les boucles ont été ensuite analysées à l’aveugle par deux lecteurs indépendants.Les interprétations des séquences EWI étaient correctes dans 89% des cas. Le taux de concordance globale entre les deux lecteurs était de 83%. Dans un ventricule stimulé, l'origine du front d'onde était focale et provenait de l'endocarde ou de l'épicarde stimulé. En rythme sinusal, le front d'onde était activé depuis tout l'endocarde, en direction de l'épicarde, à une vitesse de 1,7 ± 0,28 m.s-1. Les vitesses du front d'onde ont été mesurées respectivement lorsque l'endocarde ou l'épicarde étaient stimulés à une vitesse de 1,1 ± 0,35 m.s -1 et 1,3 ± 0,34 m.s-1 (p = NS). Nous avons aussi démontré sur des échantillons ex-vivo que l'imagerie trans oesophagienne par analyse des ondes de cisaillement (élastographie) pouvait cartographier l'étendue des lésions HIFU. Des tirs HIFU ont été réalisés à l'aide de la sonde trans oesophagienne sur des échantillons de blancs de poulet (n = 3), puis sur un modèle porcin ex vivo d'oreillette (gauche, n = 2) et de ventricule gauche (n = 1). L’élastographie a fourni des cartes de rigidité des tissus avant et après l'ablation. Les zones des lésions ont été obtenues par analyse et quantification des changements de couleur des tissus puis ont été comparées aux images par élastographie. Dans le blanc de poulet, la rigidité est passée en moyenne de 4.8±1.1 kPa à 20.5±10.0 kPa (ratio 5.0±3.2). Dans le ventricule gauche, la rigidité est passée en moyenne de 21.2±3.3kPa à 73.8±13.9kPa (ratio 3.7±1.2). Dans l’oreillette gauche, la rigidité est passée en moyenne de 12.2±4.3 kPa à 30.3±10.3 (ratio 3.2±2.0). En histologie, la taille des lésions variait de 0.1 à 1.5 cm2 dans la zone du plan d'imagerie. Les caractéristiques morphométriques étaient similaires entre histologie et élastographieAt the crossroads of medicine and physics, this work aimed to provide innovative diagnostic and therapeutic tools based on ultrasound, in the field of cardiac electrophysiology. A system capable of delivering HIFU into the heart by a transesophageal route using ultrasound (US) imaging guidance was developed and tested in vivo in six male pigs. HIFU exposures were performed on atria and ventricles. At the time of autopsy, visual inspection identified thermal lesions in the targeted areas in three of the animals. These lesions were confirmed by histologic analysis (mean size: 5.5 mm2 x 11mm2). No esophageal thermal injury was observed. One animal presented with bradycardia due to an atrio-ventricular block, which provides real-time confirmation of an interaction between HIFU and the electrical circuits of the heart. There was still a lack of accuracy, mainly related to cardiac motion, and to anatomical structures in between the targets and the transducer. It was mainly related to the in vivo model and its anatomy, far from the human’s. The search for a better model led to conclusive imaging tests on baboons. Additional experiments were conduced in order to improve the mapping of ventricular arrhythmias and the monitoring of lesion formation during ablation. First, experiments were conducted on left ventricles of four isolated working mode swine hearts. The protocol aimed at demonstrating that different patterns of mechanical activation could be observed whether the ventricle was in sinus rhythm, paced from the epicardium, or from the endocardium. Electromechanical wave imaging (EWI) acquisitions were recorded on the anterior, lateral, and posterior segments of the left ventricle. Loop records were blindly assigned to two readers. EWI sequences interpretations were correct in 89% of cases. The overall agreement rate between the two readers was 83%. When in a paced ventricle, the origin of the wave front was focal and originating from the endocardium or the epicardium. In sinus rhythm, wave front was global and activated within the entire endocardium towards the epicardium at a speed of 1.7±0.28 m.s-1. Wave front speeds were respectively measured when the endocardium or the epicardium were paced at a speed of 1.1 ± 0.35 m.s-1 vs 1.3±0.34 m.s-1 (p=NS). Lastly, we investigated the feasibility of a dual therapy and imaging approach with the same transoesophageal device. We demonstrated on ex-vivo samples that transoesophageal shear wave imaging (SWE) can map the extent of the HIFU lesions. HIFU ablation was performed with the transoesophageal probe on ex-vivo chicken breast samples (n=3), then atrium (left, n=2) and ventricle (left n=1, right n=1) of swine heart tissues. SWE provided stiffness maps of the tissues before and after ablation. Areas of the lesions were obtained by tissue color change with gross pathology and compared to SWE. Shear modulus of the ablated zones increased from 4.8±1.1 kPa to 20.5+/-10.0 kPa (ratio 5.0±3.2) in the chicken breast, from 12.2±4.3 kPa to 30.3±10.3 (ratio 3.2±2.0) in the atria and from 21.2±3.3kPa to 73.8±13.9kPa (ratio 3.7±1.2) in the ventricles. On gross pathology, the size of the lesions ranged from 0.1 to 1.5cm2 in the imaging plane area and morphometric characteristics were fitting with elasticity-estimated depths and widths of the lesions
32
Crocker, Ryan Campbell. "Direct Numerical Simulation Of Ablative Boundaries In Turbulent And Laminar Flows." ScholarWorks @ UVM, 2015. http://scholarworks.uvm.edu/graddis/397.
Abstract:
Rapid surface ablation by a turbulent flow creates complex flow and surface phenomena arising from the evolving boundary topography and its interaction with a turbulent flow that transports the ablative agent onto the surface. The dynamic nature of ablative flow boundaries generate unsteady flow dynamics and thermodynamics occurring over a wide range of scales. The non-equilibrium nature of these phenomena pose a major challenge to the current fundamental understanding of turbulence, which is mostly derived from equilibrium flows, and to Computational Fluid Dynamics (CFD). The simulation of moving boundaries is a necessary tradeoff between computational speed and accuracy. The most accurate methods use surface-conforming grids, forcing the grid to move and deform in time at a high computational cost. The technique used in this study, immersed boundary methods, removes the need for a surface-conforming grid, typically at the expense of numerical accuracy. The objectives of the present study are (i) to develop an Energy Immersed Boundary Method (EIBM) to simulate conjugate heat transfer and phase change with a spatial order of accuracy larger than one, and (ii) use the EIBM to study the dynamics of ablative flows.
A generalized finite volume (FV) flow solver with second-order accuracy in time and space and energy conserving schemes is the basis of the EIBM algorithm development. The EIBM com- bines level-set method for the definition and transport of the fluid/solid interface with an immersed boundary method, i.e. a modification of the transport equation to enforce the proper boundary conditions at the solid surface. The proposed algorithm is shown to be second order accurate in space in the simulation of conjugate heat transfer flows. The validation also included comparison with phase-change (melting) experiments where it was shown to correlate very well to previous ex- periments of a rectangular slab of gallium melted from one side. As well as showing second order convergence for the mass loss and the ablated shape of a cylinder in a melting cross flow.
The EIBM is applied to an investigation of the interactions between turbulence and an erodible surface. The study first focuses on the response of a turbulent flow over a receding wall, with constant recession velocity. It is found that wall recession velocities, near the small scale, the Kolmorgorov microscale, velocity of the buffer layer, produce minute shear free layers near the wall which both enhanced and stretched out the low and high velocity streaks near the wall. The larger streak area produced larger turbulent intensities on the dynamic boundary side of the channel, and far more semi-streamwise vortices. In the Second study the EIBM is applied to the ablation of a generic slab in a turbulent channel heated from one side in the absence of gravity. The study focuses on the characterization of the surface topography in relation to the evolution of coherent structures in the flow as ablation proceeds. The produced surface topology is linked to the flow topology and the turbulent generating and dissipating forces inside the turbulent flow. It is shown that the streaks for stefan numbers producing average ablation velocities slightly smaller than the Kolmorgorov microscale create groves in which the high speed buffer layer streaks sit, and their sinus motion in the spanwise direction is reduced.
33
VIDAL, JOSE T. "Desenvolvimento de um sistema opto-mecanico para micro usinagem com laser de fentossegundos." reponame:Repositório Institucional do IPEN, 2010. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9563.
Abstract:
Made available in DSpace on 2014-10-09T12:28:05Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T14:01:23Z (GMT). No. of bitstreams: 0
Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
34
Benchikh, Épouse Sbaï Nadia. "Couches minces nanostructurées de carbone amorphe dopées ou alliées : Elaboration par ablation laser femtoseconde et Caractérisations." Phd thesis, Université Jean Monnet - Saint-Etienne, 2005. http://tel.archives-ouvertes.fr/tel-00142211.
Abstract:
Amélioration des propriétés des couches minces de carbone amorphe (appelé Diamond Like Carbon, DLC) et recherche de nouvelles fonctionnalités pour ce type de couches minces en dopant les films DLC par des métaux comme le nickel et le tantale.L'ablation laser en régime femtoseconde est la technique utilisée pour la synthèse des couches minces de DLC dopées ou alliées. Ce sujet met également en évidence l'apport de cette technique sur les propriétés morpho-structurales et physiques des DLC dopés ou alliés.
35
O'Brien, Daniel. "Ablation Laser de microparticules de Terfenol-D (Tb0.3Dy0.7Fe1.92) en aérosol etdépôt supersonique des nanoparticules en résultant pour la fabrication defilms magnétostrictifs épais." Phd thesis, Ecole Centrale de Lille, 2007. http://tel.archives-ouvertes.fr/tel-00137712.
Abstract:
Cette thèse décrit la fabrication de couches épaisses nanostructurées magnétostrictives par dépôt supersonique de nanoparticules sur un substrat ; ces nanoparticules étant obtenues par le procédé d'Ablation Laser de Microparticules de Terfenol-D en aérosol. Un bloc solide de Terfenol-D a été réduit en poudre de microparticules de 0,3 à 3 µm de diamètre. Ces microparticules ont ensuite été injectées dans un aérosol s'écoulant en continu et ablaté par un laser ultraviolet KrF pulsé. Puis, les nanoparticules formées après l'ablation ont été accélérées par leur passage dans un micro-orifice. Le jet supersonique de nanoparticules en découlant a été utilisé pour déposer une couche épaisse sur un substrat à température ambiante. Les nanoparticules étaient amorphes, comme l'ont montré les analyses de diffraction aux rayons X des couches et les mesures de microscopie électronique à transmission (TEM) effectuées sur des particules individuelles. La distribution des tailles des nanoparticules était typique du procédé LAM : entre 3 et 20 nm de diamètre avec une moyenne de moins de 10 nm.Les couches déposées ont été caractérisées par la méthode des poutres pour déterminer le module élastique et le niveau de magnétostriction. Les couches étant poreuses en raison de leur nature granulée, leur module élastique était réduit à environ 15 GPa. Le niveau de magnétostriction des couches était d'environ 15 ppm ; cette magnétostriction réduite (1/30 de celui des couches fines) étant dû à un problème d'oxydation. Une analyse spectroscopique du plasma produit par l'ablation a permit la détermination de la source d'oxydation. L'étendue de l'oxydation des couches est apparue directement dépendante de la taille des microparticules utilisées initialement pour fabriquer les nanoparticules. Après calculs théoriques, pour des densités typiques d'aérosol utilisées dans le procédé LAM, il a été démontré que les nanoparticules fabriquées à partir de microparticules de plus de 3 µm de diamètre n'étaient pas affectées de façon significative par les impuretés présentes dans le gaz ou par l'oxydation de surface des microparticules. En revanche, les nanoparticules fabriquées à partir de microparticules de 0,3 µm de diamètre ou moins étaient, elles, oxydées et les couches en résultant l'étaient aussi. Experimentalement le diamètre des microparticules injectées en aérosol était présumé être entre ces deux cas.
36
Schroeder, Olivia. "Verification and Validation Studies for the KATS Aerothermodynamics and Material Response Solver." UKnowledge, 2018. https://uknowledge.uky.edu/me_etds/122.
Abstract:
Modeling the atmospheric entry of spacecraft is challenging because of the large number of physical phenomena that occur during the process. In order to study thermal protection systems, engineers rely on high fidelity solvers to provide accurate predictions of both the thermochemical environment surrounding the heat shield, and its material response. Therefore, it is necessary to guarantee that the numerical models are correctly implemented and thoroughly validated. In recent years, a high-fidelity modeling tool has been developed at the University of Kentucky for the purpose of studying atmospheric entry. The objective of this work is to verify and validate this code. The verification consists of the development of an automated regression testing utility. It is intended to both aid code developers in the debugging process, as well as verify the correct implementation of the numerical models as these are developed. The validation process will be performed through comparison to relevant ablation experiments, namely arc-jet tests. Two modules of the code are used: fluid dynamics, and material response. First the fluid dynamics module is verified against both computational and experimental data on two distinct arc-jet tests. The material response module is then validated against arc-jet test data using PICA.
37
Helvey, Jacob. "Experimental Investigation of Wall Shear Stress Modifications due to Turbulent Flow over an Ablative Thermal Protection System Analog Surface." UKnowledge, 2015. http://uknowledge.uky.edu/me_etds/57.
Abstract:
Modifications were made to the turbulent channel flow facility to allow for fully developed rough quasi-2D Poiseuille flow with flow injection through one surface and flow suction through the opposing surface. The combination of roughness and flow injection is designed to be analogous to the flow field over a thermal protection system which produces ablative pyrolysis gases during ablation. It was found that the additional momentum through the surface acted to reduce skin friction to a point below smooth-wall behavior. This effect was less significant with increasing Reynolds number. It was also found that the momentum injection modified the wake region of the flow.
38
Clark, Ian Gauld. "Aerodynamic design, analysis, and validation of a supersonic inflatable decelerator." Diss., Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/34708.
Abstract:
Since the 1970's, NASA has relied on the use of rigid aeroshells and supersonic parachutes to enable robotic mission to Mars. These technologies are constrained by size and deployment condition limitations that limit the payload they can deliver to the surface of Mars. One candidate technology envisioned to replace the supersonic parachute is the supersonic inflatable aerodynamic decelerator (IAD). This dissertation presents an overview of work performed in maturing a particular type of IAD, the tension cone. The tension cone concept consists of a flexible shell of revolution that is shaped so as to remain under tension and resist deformation. Systems analyses that evaluated trajectory impacts of a supersonic IAD demonstrated several key advantages including increases in delivered payload capability of over 40%, significant gains in landing site surface elevation, and the ability to accommodate growth in the entry mass of a spacecraft. A series of supersonic wind tunnel tests conducted at the NASA Glenn and Langley Research Centers tested both rigid and flexible tension cone models. Testing of rigid force and moment models and pressure models demonstrated the new design to have favorable performance including drag coefficients between 1.4 and 1.5 and static stability at angles of attack from 0º to 20º. A separate round of tests conducted on flexible tension cone models showed the system to be free of aeroelastic instability. Deployment tests conducted on an inflatable model demonstrated rapid, stable inflation in a supersonic environment. Structural modifications incorporated on the models were seen to reduce inflation pressure requirements by a factor of nearly two. Through this test program, this new tension cone IAD design was shown to be a credible option for a future flight system. Validation of CFD analyses for predicting aerodynamic IAD performance was also completed and the results are presented. Inviscid CFD analyses are seen to provide drag predictions accurate to within 6%. Viscous analyses performed show excellent agreement with measured pressure distributions and flow field characteristics. Comparisons between laminar and turbulent solutions indicate the likelihood of a turbulent boundary layer at high supersonic Mach numbers and large angles of attack.
39
Avrit, Antoine. "Étude du comportement d’ablation d’une structure solide par un jet liquide chaud." Electronic Thesis or Diss., Université de Lorraine, 2023. http://www.theses.fr/2023LORR0281.
Abstract:
Les études de sureté pour les réacteurs à neutrons rapides à caloporteur sodium (RNR-Na) ont donné lieu au développement de nouveaux systèmes de mitigation des accidents graves. Lors d'un scénario d'accident grave, une partie plus ou moins importante du cœur du réacteur entre en fusion, formant du corium. Ce corium doit être évacué du cœur afin d'éviter des problèmes de criticité. Des tubes de déchargement ("DCS-M-TT") ont donc été intégrés au design des RNR-Na, afin de transférer le cœur fondu vers un récupérateur de corium. En sortant des tubes de déchargement, le corium forme un jet et s'étale sur le récupérateur ce qui permet de le refroidir plus efficacement. Le jet de corium en sortie des tubes de déchargement étant extrêmement chaud (~ 2000 - 3000 K) lorsqu'il impacte le récupérateur, il peut provoquer son ablation thermique. Il faut donc dimensionner le récupérateur pour qu'il ne soit pas percé par le jet. Des expériences ont été réalisées dans une précédente thèse pour améliorer la compréhension du phénomène d'ablation par un jet à surface libre, avec l'installation HAnSoLO (Hot AblatioN of a SOlid by a Liquid - Observations). De nouveaux résultats ont également été obtenus pour traiter des phénoménologies plus variées dans cette thèse. Ainsi, on s'est intéressé à l'ablation d'un solide par un jet immergé, problème qui présente une phénoménologie différente de celle du cas étudié précédemment. L'effet de la rugosité du solide impacté a également été traité et il a été mis en évidence que la prise en compte de la rugosité est importante pour le dimensionnement du récupérateur. L'ensemble de ces résultats ont été utilisés pour valider un code CFD. Les simulations numériques ont notamment permis d'obtenir des résultats d'ablation très similaires aux résultats expérimentaux pour le cas du jet immergé. Les simulations et expériences devront être complétées à l'avenir pour permettre de traiter numériquement l'ablation d'un solide par un jet de corium dans les conditions du réacteurSafety studies for fast neutron reactors with sodium led to the development of mitigation systems for severe accidents. During a hypothetical severe accident, at least part of the reactor's core melts, leading to the formation of corium. The corium has to be relocated to prevent any criticality problems. Therefore, transfer tubes were integrated to the design of the core to relocate the corium from the core to a core-catcher. A jet of corium exits the transfer tubes and spreads on the core-catcher, allowing a better cooling of the corium. However, thermal ablation of the core-catcher will occur as the temperature of the corium is very high (~ 2000 - 3000 K). Thus, the core-catcher has to be dimensioned to prevent any breach due to the ablation. Experiments were performed during a previous thesis to improve understanding of the phenomenon of ablation by a free-surface jet, with a bench called HAnSoLO (Hot AblatioN of a SOlid by a Liquid - Observations). New results were obtained in the present work to address additional phenomenologies. For instance, the ablation of a solid by an immersed jet was studied. This is another situation that could occur in the real case. The effect of the roughness of the impacted solid was also addressed, and it was shown that taking roughness into account is important to design the core-catcher. All these results were used to validate a CFD code. In particular, the ablation result obtained through the numerical simulations were very similar to the experimental results for the immersed jet case. The simulations and experiments will be completed in the future to numerically treat the ablation of a metallic solid by a corium jet under reactor conditions
40
Davuluri, Raghava Sai Chaitanya. "Modeling of spallation phenomenon in an arc-jet environment." UKnowledge, 2015. https://uknowledge.uky.edu/me_etds/63.
Abstract:
Space vehicles, while entering the planetary atmosphere, experience high loads of heat. Ablative materials are commonly used for a thermal protection system, which undergo mass removal mechanisms to counter the heat rates. Spallation is one of the ablative processes, which is characterized by the ejection of solid particles from the material into the flow. Numerical codes that are used in designing the heat shields ignore this phenomenon. Hence, to evaluate the effectiveness of spallation phenomenon, a numerical model is developed to compute the dynamics and chemistry of the particles. The code is one-way coupled to a CFD code that models high enthalpy flow field around a lightweight ablative material. A parametric study is carried out to examine the variations in trajectories with respect to ejection parameters. Numerical results are presented for argon and air flow fields, and their effect on the particle behavior is studied. The spallation code is loosely coupled with the CFD code to evaluate the impact of a particle on the flow field, and a numerical study is conducted.
41
Löffler, Markus. "Nanomanipulation and In-situ Transport Measurements on Carbon Nanotubes." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-33242.
Abstract:
With the advent of microelectronics and micromechanical systems, the benefits of miniaturized technology became evident. With the discovery of carbon nanotubes by Iijima in 1991, a material has been found that offers superior porperties such as high tensile strength, excellent electrical and heat conductivity while being lightweight, flexible and tunable by the specific atomic arrangement in its structure. The first part of this thesis deals with a new synthesis approach, which combines the known routes of chemical vapour deposition and laser ablation. The results concerning diameter and yield fit well within an established model for the nucleation and growth of carbon nanotubes and extend it by considering a larger parameter space. Furthermore, conventional laser ablation has been used to synthesize C-13 augmented carbon nanotubes, whose diameters depend among the usual synthesis parameters also on the C-13 content, an influence which is in line with the changed thermal conductivities of isotope mixtures. Manipulation of carbon nanotubes inside a transmission electron microscope forms the second part of this thesis. With the help of an in-situ nanomanipulator, several experiments involving the mechanical and electrical properties of carbon nanotubes have been performed. Two-probe resistances of individual nanotubes have been measured and the observation of individual shell failures allowed for the determination of current limits per carbon shell. With the help of electrical current, a nanotube was modified in its electrical characteristics by reshaping its structure. By application of DC-currents or square current pulses, the filling of iron- or cementite-filled multi-wall carbon nanotubes has been found to move in a polarity-defined direction guided by the nanotube walls. Depending on the current, nanotube shape, and composition of the filling different regimes of material transport have been identified, including the reworking of the inner nanotube shells. The application of a high driving current leads to a complete reworking of the host nanotube and the current-induced growth of carbonaceous nanostructures of changed morphology. Utilizing the obtained results, a transport mechanism involving momentum transfer from the electron wind to the filling atoms and a solid filling core during transport is developed and discussed. Finally, measurements of mechanical properties using electrically induced resonant or non-resonant vibrations inside the transmission electron microscope have been observed and important mechanical parameters have been determined with the help of a modified Euler-Bernoulli-beam approachMit dem Aufkommen von Mikroelektronik und mikromechanischen Systemen wurden die Vorteile miniaturisierter Geräte augenscheinlich. Mit der Entdeckung von Kohlenstoff-Nanoröhren durch Iijima 1991 wurde ein Material gefunden, welches überlegene Eigenschaften wie hohe Festigkeit, exzellente elektrische und Wärmeleitfähigkeit zeigt, während es zeitgleich leicht und flexibel ist. Diese Eigentschaften können durch eine Änderung der spezifischen atomaren Anordnung in der Nanoröhrenhülle beeinflusst werden. Der erste Teil dieser Dissertationsschrift behandelt einen neuartigen Syntheseansatz, welche die bekannten Syntheserouten der chemischen Gasphasenabscheidung und Laserablation kombiniert. Die Ergebnisse bezüglich des Durchmessers und der Ausbeute lassen sich gut mit einem etablierten Modell der Nukleation und des Wachstums von Kohlenstoff-Nanoröhren beschreiben - sie erweitern es, indem sie einen größeren Parameterraum berücksichtigen. Des Weiteren wurde konventionelle Laserablation benutzt, um C-13 angereicherte Kohlenstoff-Nanoröhren herzustellen, deren Durchmesser nicht nur von den üblichen Parametern, sondern auch vom C-13 Anteil abhängt. Diese Abhängigkeit geht mit der veränderten thermischen Leitfähigkeit von Isotopenmischungen einher. Die Manipulation von Kohlenstoff-Nanoröhren in einem Transmission-Elektronenmikroskop formt den zweiten Teil der Dissertationschrift. Mit Hilfe eines in-situ Manipulators wurden vielfältige Experimente durchgeführt, um die mechanischen und elektrischen Eigenschaften der Kohlenstoff-Nanoröhren zu bestimmen. Zweipunktmessungen des Widerstands einzelner Nanoröhren und die Beobachtung des Versagens einzelner Kohlenstoffschichten erlaubte die Bestimmung der Stromtragfähigkeit einzelner Hüllen. Mit Hilfe eines elektrischen Stromes konnte eine Nanoröhre durch die veränderung der Struktur in ihren elektrischen Eigenschaften verändert werden. Unter Verwendung dauerhaften oder gepulsten Gleichstroms konnte die Eisen- oder Zementit-Füllung der Kohlenstoff-Nanoröhren in eine polaritätsabhängige Richtung bewegt werden. Die Füllung wurde dabei durch die Wände der Nanoröhre geführt. Abhängig von Strom, Form der Nanoröhre und Zusammensetzung der Füllung ließen sich verschiedene Bereiche des Materialtransports identifizieren, u.a. das Umarbeiten einiger innerer Kohlenstoffschichten. Ein hoher Strom hingegen bewirkt eine Umarbeitung der kompletten Nanoröhre und strominduziertes Wachstum von Kohlenstoff-Nanostrukturen mit veränderter Morphologie. Mit Hilfe der gewonnenen Resultate wurde ein Transportmodell entwickelt, welches den Impulstransfer von Elektronen an Füllungsatome sowie einen festen Füllungskern während des Transports diskutiert. Messungen der mechanischen Eigenschaften, welche mit Hilfe von resonanter oder nicht-resonanter elektrischer Anregung von Schwingungen im Transmissions-Elektronenmikroskop durchgeführt wurden bilden den Abschluss der Arbeit. Durch die Beobachtungen konnten mit einem modifizierten Euler-Bernoulli-Balkenmodell wichtige mechanische Eigenschaften bestimmt werden
42
Arnal, Bastien. "Elastographie pour le suivi des thérapies par ultrasons focalisés et nouveau concept de cavité à retournement temporel pour l'histotripsie." Phd thesis, Université Paris-Diderot - Paris VII, 2013. http://pastel.archives-ouvertes.fr/pastel-00786523.
Abstract:
L'émission d'ultrasons focalisés à forte puissance peut être utilisée pour réaliser l'ablation non-invasive de zones pathogènes, de type cancéreuses par exemple. On distingue deux régimes d'ablations : ablation thermique appelée HIFU (" High Intensity Focused Ultrasound ") et ablation mécanique appelée histotripsie utilisant des ondes de chocs focalisées. Au cours de ma thèse, nous avons développé des méthodes de suivi ultrasonore en temps réel à partir d'une technique d'élastographie quantitative (Supersonic Shear wave Imaging). Nous montrerons que des mesures précises des changements d'élasticité au cours des traitements fournissent un suivi et un guidage avec une robustesse aux mouvements du patient. En effet, l'élastographie nous a permis d'une part de cartographier la température et d'autre part de suivre la formation de lésion en temps réel qu'elle soit de type thermique (HIFU) ou mécanique (histotripsie). Nous aborderons aussi une technique d'inversion totale du front d'onde appliquée à SSI qui améliore la sensibilité à la perte d'information due au bruit et à l'hypoéchogénicité existante dans certaines lésions. Enfin, nous présenterons un nouveau concept de cavité à retournement temporel " réglable " pour l'émission d'impulsions de très fortes pressions à partir d'un nombre limité de transducteurs. Notre prototype a permis de générer des ondes de chocs focalisées au sein d'une étendue considérable et de multiplier par 17 la pression d'une sonde d'imagerie conventionnelle. Ainsi, à partir d'électroniques basse-puissance à faible coût, ce dispositif thérapeutique pourrait avoir de nombreuses applications thérapeutiques limitées actuellement par des contraintes géométriques.
43
Zhang, Lijun. "Thermal and mechanical phenomena in laser-material interaction." 2008. http://proquest.umi.com/pqdweb?did=1622196481&sid=6&Fmt=2&clientId=14215&RQT=309&VName=PQD.
Abstract:
Thesis (Ph.D.)--University of Nebraska-Lincoln, 2008.Title from title screen (site viewed Mar. 5, 2009). PDF text: 97 p. : ill. (some col.) ; 3.12 Mb. UMI publication number: AAT 3331445. Includes bibliographical references. Also available in microfilm and microfiche formats.
44
Kurzawski, Andrew Joseph. "Ablation and ignition by impinging jet flows." Thesis, 2013. http://hdl.handle.net/2152/23684.
Abstract:
Two separate heat transfer problems that involve jet flows impinging on a reacting target are studied through modeling and experimentation. The first system is an ablating carbon-carbon specimen exposed to high heat fluxes from an oxy-acetylene torch which has applications in atmospheric re-entry vehicles. The second system involves the penetration of hot gases into the void space in a compartment. The fire protection stands to benefit from knowledge of this system, both in building component design and informing firefighting personnel. Both problems can be modeled as a jet flow impinging on a flat surface where hot gases from the jet lead to primarily convective heat transfer.
Ablation experiments are outlined and a theoretical framework is developed. A serial inversion technique is tested for predicting the recession rate observed in the experiments. A novel inversion technique that takes advantage of parallel computing is developed to circumvent the shortcomings of the serial technique. These techniques are then compared to synthetically generated and experimental data for different data streams and error signals.
Compartment-scale experiments were conducted to test hot gas penetration into void spaces. Anecdotal evidence was observed outside of the intended test section prompting further investigation into the mechanics of ignition in void spaces. A theoretical framework is established to predict possibility of ignition under varied environmental factors. A leakage-scale experiment is constructed to gain insight into conditions that result in ignition of materials in void spaces.text
45
Barr, Benjamin Witten. "Investigation and modeling of coupled thermochemical and thermomechanical erosion in thermally degrading systems." Thesis, 2012. http://hdl.handle.net/2152/ETD-UT-2012-05-5554.
Abstract:
The coupled effects of thermochemical and thermomechanical erosion are investigated. A quasi-steady ablation model with finite rate surface chemistry is developed and applied to a solid carbon combustion scenario to investigate the system’s behavior in situations in which surface reactions are not in equilibrium. It is found that in this regime, the system can be described effectively in terms of the B number and the Damkohler number, and a useful algebraic relationship between these parameters is determined for nonequilibrium behavior.
The thermochemical ablation model is then expanded by considering mechanical removal of thermochemically weakened material from the ablating surface. A model is developed for a randomly oriented carbon fiber preform material, like that used in the production of phenolic impregnated carbon ablator (PICA), and this model is incorporated into the previously developed ablation code. It is found that for PICA in realistic reentry scenarios, the removal of individual fibers from the ablating surface by mechanical erosion is not an important mass loss mechanism, although hypothetical situations exist where this mechanism for mechanical removal of material is non-negligible.
The thermo-chemo-mechanical erosion mechanism is then extended to address brand generation in wildland fire scenarios. A model is developed to predict the size and number distribution of embers generated from a tree with fractal geometry. This model is coupled to a simple plume and propagation model similar to those existing in the literature, and a case study is performed for a realistic wildfire scenario. The presence of an optimal branch diameter for brand propagation is identified, and areas for future work in thermo-chemo-mechanical degradation are discussed.text
46
Wang, Xiaoliang. "Ultra-short pulsed laser surface processing and decontamination." 2008. http://hdl.rutgers.edu/1782.2/rucore10001600001.ETD.000050472.
47
(10726149), Weirong Yuan. "PHASE CHANGE AND ABLATION STUDY OF METALS BY FEMTOSECOND LASER IRRADIATION USING HYBRID TTM/MD SIMULATIONS." Thesis, 2021.
Abstract:
The interactions of femtosecond lasers with gold targets were investigated with a numerical method combining molecular dynamics (MD) and the two-temperature model (TTM). Previous works using MD-TTM method did not consider all the thermodynamic parameters and the interatomic potential dependent of the electron temperature simultaneously. Therefore, we developed a LAMMPS function to achieve this. To accurately capture the physics behind the interactions, we also included the electron blast force from free electron pressure and the modified Fourier law with steep electron temperature gradient in our model. For bulk materials, a stress non-reflecting and heat conducting boundary is added between the atomistic and the continuum parts. The modified boundary force in our study greatly reduces the reflectivity of the atomistic-continuum boundary compared with its original form. Our model is the first to consider all these factors simultaneously and manage to predict four femtosecond laser ablation phenomena observed in the experiments.
In this dissertation, the thermodynamic parameters in the two-temperature model were extensively explored. We considered three different approaches to calculate these parameters: namely interpolation, ab initio calculation, and analytical expression. We found that simple interpolation between solid state and plasma state could lead to high level of inaccuracy, especially for electron thermal conductivity. Therefore, ab initio calculation and analytical expression were used for the calculation of the thermodynamic parameters in more advanced studies. The effects of electron thermal conductivity and electron-phonon coupling factor on electron and lattice temperatures were analyzed.
Our studies considered electron temperature dependent (ETD) and electron temperature independent (ETI) interatomic potentials. The ETI interatomic potential is easier to implement and therefore it is used in our phase change study to investigate the effects of target thickness on melting. Homogeneous melting occurred for thin films, while melting can be observed through the movement of the solid-liquid interface in thick or bulk materials. However, the ETI potential overestimated the bond strength at high temperatures. Therefore, ablation process was studied with the ETD potential. Three ablation mechanisms were found in our simulations at different laser fluences. Short nonthermal ablation was only observed at the ablation threshold. With increasing laser fluence, spallation was then seen. In high laser fluence regime, phase explosion occurred on the surface and coexisted with spallation.
Lastly, we researched on the effects of the delay time between two femtosecond laser pulses. Various delay times did not have much influence on melting depth. In low laser fluence regime, with increasing delay time, the target went through nonthermal ablation, to spallation and to no ablation. In high laser fluence regime, longer delay time encouraged phase explosion while suppressed spallation.
48
Cloutier, Martin. "Healing of Calvarial Wounds Created by Er:YAG Laser Irradiation in Comparison with Conventional Mechanical and Femtosecond Laser Ablation in Presence or Absence of BMPs." Thesis, 2009. http://hdl.handle.net/1807/18264.
Abstract:
The Er:YAG laser and the USPL are the most promising when considering the previous study results and their physical characteristics. This investigation compared the healing of various laser ablation units versus conventional mechanical cutting to explore the future applications for bone surgery and the effects when combined with rhBMP-7. A full-thickness circular defect was created on the parietal bones of mice for all the groups. Hard tissue healing was assessed using a microcomputerized tomography. Wound closure analyses suggested that the femtosecond laser created wounds displayed slightly healing delay in closure over the healing period when compared to mechanical instrumentation. The Er:YAG laser showed a healing rate similar to that of the mechanically ablated groups. In summary, femtosecond and Er:YAG lasers are two modalities suitable for bone ablation comparable to mechanical instrumentation.
49
(10725372), Rajan Nitish Jain. "Intrinsic Self-Sensing of Pulsed Laser Ablation in Carbon Nanofiber-Modified Glass Fiber/Epoxy Laminates." Thesis, 2021.
Abstract:
Laser-to-composite interactions are becoming increasingly common in diverse applications such as diagnostics, fabrication and machining, and weapons systems. Lasers are capable of not only performing non-contact diagnostics, but also inducing seemingly imperceptible structural damage to materials. In safety-critical venues like aerospace, automotive, and civil infrastructure where composites are playing an increasingly prominent role, it is desirable to have means of sensing laser exposure on a composite material. Self-sensing materials may be a powerful method of addressing this need. Herein, we present an exploratory study on the potential of using changes in electrical measurements as a way of detecting laser exposure to a carbon nanofiber (CNF)-modified glass fiber/epoxy laminate. CNFs were dispersed in liquid epoxy resin prior to laminate fabrication via hand layup. The dispersed CNFs form a three-dimensional conductive network which allows for electrical measurements to be taken from the traditionally insulating glass fiber/epoxy material system. It is expected that damage to the network will disrupt the electrical pathways, thereby causing the material to exhibit slightly higher resistance. To test laser sensing capabilities, a resistance baseline of the CNF-modified glass fiber/epoxy specimens was first established before laser exposure. These specimens were then exposed to an infra-red laser operating at 1064 nm, 35 kHz, and pulse duration of 8 ns. The specimens were irradiated for a total of 20 seconds (4 exposures each at 5 seconds). The resistances of the specimens were then measured again post-ablation. In this study, it was found that for 1.0 wt.% CNF by weight the average resistance increased by about 18 percent. However, this values varied for specimens with different weight fractions. This established that the laser was indeed causing damage to the specimen sufficient to evoke a change in electrical properties. In order to expand on this result, electrical impedance tomography (EIT) was employed for localization of laser exposures of 1, 3, and 5 seconds on a larger specimen, a 3.25” square plate. EIT was used to measure the changes in conductivity after each exposure. EIT was not only successful in detecting damage that was virtually imperceptible to the human-eye, but it also accurately localized the exposure sites. The post-ablation conductivity of the exposure sites decreased in a manner that was comparable to the resistance increase obtained during prior testing. Based on this preliminary study, this research could lead to the development of a real-time exposure detection and tracking system for the measurement, fabrication, and defense industries.
50
Scharf, Thorsten. "Depositionsmechanismen, Struktur und mechanische Eigenschaften laserdeponierter Poly(methyl methacrylat)-Filme." Doctoral thesis, 2007. http://hdl.handle.net/11858/00-1735-0000-0006-B44E-9.