384 research outputs found
Theory and simulation of surface effects on intrinsic dissipation
No full textThe goal of this research is to study the role of surface on intrinsic dissipation in silicon (Si) nanostructures. We look at two different cases namely (i) Si(100) surface with (2x1) reconstruction and (ii) Hydrogen (H) terminated Si surface. We utilize molecular dynamics (MD) simulations and show that the two surfaces play opposing role on intrinsic dissipation. While surface defects always aid in the entropy generation process, the scattering of phonons from rough surfaces can suppress Akhiezer damping. For the case of (2x1) reconstructed silicon surface, the former dominates and the inverse quality factor (Q^-1) is found to increase with the decrease in size. However, different scaling trends are observed in the case of a H-terminated silicon surface with no defects and dimers. Particularly, in the case of a H-terminated silicon, if the resonator is operated with a frequency Ω such that Ωτph < 1, where τph is the phonon relaxation time, Q^-1 is found to decrease with the decrease in size. The opposite scaling is observed for Ωτph. A simplified model, based on two phonon groups (with positive and negative Grüneisen parameters), is considered to explain the observed trend. We show that the equilibration time between the two mode groups decreases with the decrease in size for the H-terminated structure. We also study the scaling of Q factor with frequency for these cases.Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2016-07-07 without embargo termsThe student, Subhadeep De, accepted the attached license on 2016-04-26 at 16:07.The student, Subhadeep De, submitted this Thesis for approval on 2016-04-26 at 16:22.This Thesis was approved for publication on 2016-04-28 at 13:33.DSpace SAF Submission Ingestion Package generated from Vireo submission #9530 on 2016-07-07 at 13:33:36Made available in DSpace on 2016-07-07T19:58:14Z (GMT). No. of bitstreams: 2
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Modeling of mechanical energy dissipation of low-dimensional resonators
No full textNanoelectromechanical systems (NEMS) made from low-dimensional materials based on carbon, transition metal dichalcogenides, and their combinations have opened up new possibilities in high-precision sensing, signal processing, and studies of fundamental physical phenomena. In the heart of the NEMS is a vibrating mechanical element, known as the resonator. The performance of the NEMS critically depends on the mechanical energy dissipated by the resonator. Studies on dissipation are important because an understanding of the loss mechanisms can suggest ways to mitigate it. In most practical scenarios, the resonators suffer from intrinsic dissipation mediated by its inherent atomic thermal motions or phonons and extrinsic dissipation due to a fluid environment. In this context, low-dimensional resonators need special attention because the dissipation cannot be explained using the existing continuum theories. Due to atomic thickness, sub-micron dimension, and mega- to gigahertz frequencies of these resonators, nano-scale physical processes start becoming important. Most macroscale models do not account for these physical processes, warranting the current line of research. In this thesis, we use atomistic simulations and statistical-mechanical theories to understand and formulate the nanoscale physical processes, and integrate them to develop a multiscale model for dissipation.
In the first part of the thesis, we explore fluid coupled resonator systems with an objective to understand different dissipative processes such as phonon-mediated intrinsic dissipation, viscous damping by the fluid, and the cross-interaction between each source of dissipation, i.e., phonons and fluid at a regime of gigahertz frequency, and nanometer length scale. First, we consider a single-walled carbon nanotube (SWCNT) resonator with confined Argon and driven under axial mode. The intrinsic dissipation in the SWCNT at gigahertz frequencies could be explained by Akhiezer theory. We show that intrinsic dissipation, which is conventionally treated as an independent process, can be modified by fluid interactions due to the phonon- fluid coupling. We show that an important consequence of this phonon-fluid coupling is the counter-intuitive inverse scaling of net dissipation with fluid density at low excitation frequencies. Next, we consider flexural vibration of the SWCNT with interior and exterior Argon. When compared with the fluid exterior case, the SWCNT with confined fluid shows a low and anomalous scaling of dissipation with fluid density. We systematically analyzed the sources of dissipation and found that the fluid contributed to the anomalous scaling. A formulation of the fluid response during the flexural motion revealed a viscoelastic nature of the fluid under nano-confinement, which explains the anomalous scaling. Further, we use the framework for dissipation analysis to examine the effect of thermal motion of the resonator atoms on fluid dissipation, demonstrate a frequency dependent dissipation scaling with density, and comment on the mechanism of intrinsic dissipation during flexural resonance of an SWCNT.
In the second part, we develop a multiscale framework to model intrinsic dissipation in two-dimensional (2D) microresonators. The work aims to reveal the fundamental limit of dissipation and enable looking at the isolated effect of various parameters over a wide range, both of which are inaccessible in experiments. The damping of the flexural mode of a 2D microresonator takes place due to the nonlinear coupling with other thermally excited elastic modes. A particular flexural mode can couple with another flexural mode with a wavelength ranging from the size of the resonator to that of the lattice spacing. However, the coupling at these disparate length scales needs different modeling approaches. In the multiscale framework, we model the continuum-scale modes as Langevin oscillators (LOs) with nonlinear coupling terms. The parameters of the LOs are computed using continuum mechanical analysis and atomistic simulations. Using this framework, we study the effect of various parameters of interest such as vibration amplitude, resonator size, temperature, and pre-strain in the case of graphene resonators and draw some important conclusions towards engineering high-quality 2D resonators.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2021-05-01The student, Subhadeep De, accepted the attached license on 2019-02-13 at 12:01.The student, Subhadeep De, submitted this Dissertation for approval on 2019-02-13 at 12:51.This Dissertation was approved for publication on 2019-02-15 at 11:34.DSpace SAF Submission Ingestion Package generated from Vireo submission #13388 on 2019-08-22 at 15:04:21Made available in DSpace on 2019-08-23T20:28:06Z (GMT). No. of bitstreams: 3
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Development and evaluation of smartphone-based ITS applications for vehicular networks
No full text[ES] Una de las áreas de investigación que está recibiendo más atención recientemente es la de vehículos autónomos. Los investigadores están en este momento centrados en el tercer de los cinco niveles de autonomía, los cuales son: asistencia en la conducción, automatización parcial, automatización condicional, alta automatización y automatización completa. A pesar de los rápidos progresos que están habiendo en este campo, la adopción de estas soluciones llevará tiempo no sólo debido a cuestiones legales, sino también por el hecho de que los avances tecnológicos se enfrentan a un lento respaldo por parte de los fabricantes. Además, la baja tasa de renovación de vehículos de carretera, dificulta el despliegue de tecnologías innovadoras, como es el caso de la red vehicular. Ocho años después de la introducción de la norma 802.11p para la comunicación vehicular del Instituto de Ingenieros Eléctricos y Electrónicos (IIEE), los vehículos que se usan a diario todavía carecen de la capacidad de comunicarse entre sí. Este hecho impide el uso de las muchas aplicaciones de seguridad del Sistema de Inteligencia de Transporte (SIT) que aprovecha la red vehicular para el intercambio de datos. La forma obvia de manejar este problema es poner las tecnologías disponibles a la disposición de los usuarios comunes para desarrollar soluciones que se puedan implementar fácilmente y, además, económicas.
Por esta razón, trasladamos nuestra atención a los dispositivos inteligentes, especialmente a los teléfonos inteligentes, los cuales han recorrido un largo camino desde la primera introducción de teléfonos móviles a finales del siglo XX. Hoy en día casi todos llevan uno en su bolsillo a donde sea que vayan, permitiéndoles no sólo hacer llamadas, sino también medir y controlar diferentes parámetros con la ayuda de los muchos sensores integrados que están disponibles para estos dispositivos compactos pero potentes. Nuestro objetivo es estudiar los efectos de la integración de los teléfonos inteligentes a la red vehicular para desarrollar aplicaciones de seguridad del SIT. La elección de los teléfonos inteligentes aquí no solo está justificada por su amplia disponibilidad y uso, sino también porque están evolucionando hacia terminales de alto rendimiento con microprocesadores de múltiples núcleos cargados dotados de un grupo suficientemente diverso de sensores. En esta tesis proponemos tres diferentes aplicaciones de seguridad SIT para teléfonos inteligentes, diseñados para aprovechar el entorno de red vehicular: una aplicación de generación de advertencia llamada Messiah que alerta a los conductores de la presencia de vehículos de emergencia en las cercanías; una aplicación de Advertencia de Colisión Frontal (ACF) que advierte a los conductores si no se mantiene la distancia de seguridad mínima entre el vehículo que va delante y el que lo sigue; y, por último, una aplicación que tiene como objetivo ayudar a los conductores con asistencia visual durante el adelantamiento, llamada EYES. Todas estas aplicaciones han sido desarrolladas para la plataforma Android, y dependen de la transmisión de datos entre vehículos. Dado que los vehículos que utilizamos día a día no admiten la posibilidad de comunicarse entre sí, también diseñamos GRCBox, que es una unidad integrada de bajo coste que permite la comunicación del Vehículo a Todo (V2X).
A partir de nuestro estudio de aplicaciones para dispositivos móviles diseñados para redes vehiculares, descubrimos que el uso de teléfonos inteligentes proporciona una nueva dirección para la investigación relacionada con SIT y redes vehiculares al permitir la adopción rápida de las soluciones existentes, donde los usuarios pueden descargar y usar las aplicaciones con sólo un clic a un botón. Al mismo tiempo, la portabilidad y compacidad de los dispositivos los hace limitados en términos de velocidad, potencia de procesamiento y precisi[CA] Una de les àrees d'investigació que està rebent més atenció recentment és la de vehicles autònoms. Els investigadores estan en este moment centrats en el tercer dels cinc nivells d'autonomia, els quals són: assistència en la conducció, automatització parcial, automatització condicional, alta automatització i automatització completa. Malgrat els ràpids progressos que s'estan donant en este camp, l'adopció d'estes solucions portarà temps no sols degut a qüestions legals, sinó també pel fet que els avanços tecnològics s'enfronten a un lent recolzament per part dels fabricants. A més a més, la baixa taxa de renovació de vehicles de carretera, dificulta el desplegament de tecnologies innovadores com és el cas de la xarxa vehicular. Huit anys després de la introducció de la norma 802.11p per a la comunicació vehicular de l'Institut d'Enginyers Elèctrics i Electrònics (IEEE), els vehicles que s'utilitzen a diari encara manquen de la capacitat de comunicar-se entre sí. Este fet impedeix l'ús de les moltes aplicacions de seguretat del Sistema d'Intel·ligència de Transport (SIT) que aprofita la xarxa vehicular per a l'intercanvi de dades. La forma òbvia de tractar aquest problema és posar les tecnologies disponibles a la disposició dels usuaris comuns per a desenvolupar solucions que es puguen implementar fàcilment, còmodes d'adoptar i, a més a més, econòmiques.
Per aquesta raó, traslladem la nostra atenció als dispositius intel·ligents, especialment als telèfons intel·ligents, els quals han recorregut un llarg camí des de la primera introducció de telèfons mòbils a finals del segle XX. Hui en dia quasi tots porten un en la butxaca on siga que vagen, permetent-los no sols fer cridades, sinó també mesurar i controlar diferents paràmetres amb l'ajuda dels molts sensors integrats que estan disponibles per a estos dispositius compactes però potents. El nostre objectiu és estudiar els efectes de la integració dels telèfons intel·ligents a la xarxa vehicular per a desenvolupar aplicacions de seguretat del SIT. L'elecció dels telèfons intel·ligents ací no està sols justificada per la seua àmplia disponibilitat i ús, sinó també perquè estan evolucionant cap a terminals d'alt rendiment amb microprocessadors de múltiples nuclis dotats amb un grup suficientment divers de sensors. En esta tesi proposem tres diferents aplicacions de seguretat SIT per a telèfons intel·ligents, dissenyats per a aprofitar l'entorn de xarxa vehicular: una aplicació de generació d'advertència anomenada Messiah que alerta els conductors de la presència de vehicles d'emergència en les proximitats; una aplicació Advertència de Col·lisió Frontal (ACF) que adverteix els conductors si no mantenen la distància de seguretat mínima entre el vehicle que va davant i el que el segueix; i, per últim, una aplicació que té com objectiu ajudar els conductors amb assistència visual durant l'avançament, anomenat EYES. Totes aquestes aplicacions han sigut desenvolupades per a la plataforma Android, i depenen de la transmissió de dades entre vehicles. Donat que els vehicles que utilitzem a diari no admeten la possibilitat de comunicar-se entre sí, també dissenyem GRCBox, que és una unitat integrada de baix cost que permet la comunicació de Vechicle a Tot (V2X).
A partir del nostre estudi d'aplicacions per a dispositius mòbils dissenyats per a xarxes vehiculars, descobrim que l'ús de telèfons intel·ligents proporciona una nova direcció per a la investigació relacionada amb SIT i xarxes vehiculars al permetre l'adopció ràpida de les solucions existents, on els usuaris poden descarregar i utilitzar les aplicacions amb un sol clic a un botó. Però al mateix temps, la portabilitat i la compacitat dels dispositius els fa limitats en termes de velocitat, potència de processament i precisió del sensor integrat, cosa que afecta al rendiment de les aplicacions.[EN] One of the research areas that is receiving a lot of attention recently is autonomous vehicles. Researchers are currently focused on the third level of autonomy out of the five levels, which are: drive assistance, partial automation, conditional automation, high automation, and full automation. Even though rapid progress is being made in this field, the adoption of these solutions will take time not only due to legal issues, but also due to the fact that technological improvements face slow endorsement by manufacturers. Also, the slow renewal rate of vehicles on road hinders the deployment of novel technologies, as is the case of Vehicular Networks (VNs). Eight years after the introduction of the IEEE 802.11p standard for vehicular communication, vehicles used on a daily basis still lack the capability of communicating with one other. This fact impedes the use of the many ITS safety applications that take advantage of VNs for data exchange. The obvious way to handle this problem is to use the available technologies at the disposal of common users to develop solutions that are easily deployable, effortless to adopt, and moreover, cost effective.
For this reason we shift our attention to smart devices, specially smartphones, which have come a long way since the first introduction of mobile phones in the late 20th century. Nowadays, nearly everyone carries one in their pocket anywhere they go, allowing them to not only make calls, but also to measure and monitor different parameters with the help of the many on-board sensors that are available to these compact yet powerful devices. Our objective is to study the effects of integrating smartphones to vehicular networks, to develop ITS safety applications. The choice of smartphones here is not only justified by their wide availability and use, but also because they are evolving towards high performance terminals with multi-core microprocessors packed with a sufficiently diverse group of sensors. In this thesis we propose three different ITS safety applications for smartphones, designed to take advantage of the vehicular network environment: a warning generation application called Messiah that alerts drivers of the presence of emergency vehicles in close proximity; a FCW application which warns drivers if a minimum safe distance is not maintained between the vehicle ahead and the one following it; and lastly an application that aims to aid drivers with visual assistance while overtaking, named EYES. All these applications have been developed for the Android platform, and are dependent on the data transmission among vehicles. Since vehicles we use on a day to day basis still do not accommodate the possibility to communicate with one another, we also designed the GRCBox, which is a low cost on-board unit that supports V2X communication.
From our study of applications for mobile devices designed for VNs, we found that the use of smartphones provides a new direction to research related to ITS and VNs by allowing a quick adoption of the existing solutions, where users are able to download and use applications just by one click of a button. But at the same time, the portability and compactness of the devices makes them limited in terms of speed, processing power, and accuracy of the on-board sensor, thus affecting the performance of the applications. In our case, the simpler Messiah application performed very well, while the EYES application that is dependent on GPS data, and the FCW application which required heavy processing and use of the camera due to its dependence on plate recognition, were affected by the hardware limitations of the smartphones.Patra, S. (2019). Development and evaluation of smartphone-based ITS applications for vehicular networks [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/124058TESI
Laser cooling and trapping of barium
No full textLaser cooling and trapping of heavy alkaline-earth element barium have been demonstrated for the first time ever. For any possible cycling transition in barium that could provide strong cooling forces, the excited state has a very large branching probability to metastable states. Additional lasers are thus needed to bring the atoms back in to the cooling cycle. In this work barium atoms were efficiently collected in a magneto-optical trap (MOT) by large optical forces from the strong 6s2 1S0 – 6s6p 1P1 transition. Trapping of barium has been achieved using up to seven lasers simultaneously.
The properties of the barium MOT were characterized. The efficiency of capturing an atom from a thermal atomic beam into the MOT is 0.4(1) %. The developed scheme is very efficient for collecting atoms. Loss rate mechanisms from the trap were studied by observing the decay of the trap population. Typical lifetimes of the MOT cloud are on the order of one second and are limited mainly due to insufficient repumping of metastable states. The range of velocities from which barium atoms can be captured into the MOT is about 30 m/s. Different laser transitions were employed for repumping barium atoms from the 6s5d 3D1 and the 6s5d 3D2 states. They lead to similar trap populations and lifetimes. The temperature of the cold atomic barium cloud was determined to about 5 mK. Atomic properties of the 5d2 3F2 state were studied with trapped atoms, in particular it's lifetime was determined as 160(10) s.
This work has shown a possible scheme to trap atoms with a leaky cooling cycle. Since atoms with such properties are the majority of the elements in the periodic table, the number of optically trapable elements can be significantly enlarged. Of particular high interest is radium, which is chemical homologue to barium. The interest in radium stems from it's high sensitivity to possible nuclear and electron permanent electric dipole moments (EDM's). An EDM violates parity as well as time reversal and is therefore of fundamental importance. Searches for such EDM's are among the main research goals of the recently commissioned TRImP facility at KVI.
Propriétés de transport électronique de nanotubes de carbone remplis de particules magnétiques
No full textLes nanotubes de carbone (CNT) à basse température se comportent comme des points quantiques pour lesquelles les niveaux électroniques deviennent quantifiés. Le transport électronique à travers une jonction-CNT est caractérisé par le phénomène de blocage de Coulomb, dont les spécificités dépendent du couplage entre le nanotube et les électrodes métalliques. Le blocage de Coulomb est extrêmement sensible au moindre changement électrostatique, faisant des jonctions-CNT de précis électromètres. Par exemple, si l'on couple un système magnétique à un nanotube, le transport électronique sera influencé par l'état de spin du système magnétique (effet magnéto-Coulomb). Ce projet de thèse présente des mesures de transport électrique sur un système hybride se composant d'un nanotube de carbone rempli de nanoparticules magnétiques (Fe). Ces mesures, réalisées à très basses températures (40 mK), ont permis de mettre en évidence le comportement hystérétique de la conductance en fonction du champ magnétique, et en particulier la présence de saut de conductance à champ magnétique fini. Nous expliquons ces résultats en termes d'effet magnéto-Coulomb : le renversement d'aimantation des particules de fer à champ magnétique fini provoquant une variation de charge effective due à l'effet Zeeman. Ces mesures sont une étape vers l'étude de l'anisotropie magnétique de nanoparticules individuelles.Carbon Nanotubes at low temperature behave as Quantum Dots for which charging processes become quantized, giving rise to Coulomb Blockade depending upon the coupling to the leads. Any small change in the electrostatic environment (tuned by the gate electrode) can induce shift of the stability diagram (so called Coulomb Diamonds) of the device, leading to conductivity variation of the Quantum Dot. A carbon nanotube can therefore be a very accurate electrometer. For example, if a magnetic system is electronically coupled to a nanotube, its electron conduction may be influenced by the spin state of the magnetic system (magneto- Coulomb effect). In this thesis, we report on the electrical transport measurements of such hybrid systems where a carbon nanotube is filled with magnetic nanoparticles such as Iron(Fe). We find that low-temperature (~40mK) current-voltage measurements of such devices can show a hysteretic behaviour in conductance with sharp jumps at certain magnetic fields. We explain the results in terms of the magneto-Coulomb effect where the spin flip of the iron island at non-zero magnetic field causes an effective charge variation in the Nanotube due to the Zeeman energy. Our studies are a step forward towards the study of the magnetic anisotropy of individual nanoparticles. We believe our findings have important implications for sensitive magnetic detectors to study the magnetization reversal of individual magnetic nanoparticle or molecule, even weakly coupled to a carbon nanotube.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF
Modeling of mechanical energy dissipation of low-dimensional resonators
No full textNanoelectromechanical systems (NEMS) made from low-dimensional materials based on carbon, transition metal dichalcogenides, and their combinations have opened up new possibilities in high-precision sensing, signal processing, and studies of fundamental physical phenomena. In the heart of the NEMS is a vibrating mechanical element, known as the resonator. The performance of the NEMS critically depends on the mechanical energy dissipated by the resonator. Studies on dissipation are important because an understanding of the loss mechanisms can suggest ways to mitigate it. In most practical scenarios, the resonators suffer from intrinsic dissipation mediated by its inherent atomic thermal motions or phonons and extrinsic dissipation due to a fluid environment. In this context, low-dimensional resonators need special attention because the dissipation cannot be explained using the existing continuum theories. Due to atomic thickness, sub-micron dimension, and mega- to gigahertz frequencies of these resonators, nano-scale physical processes start becoming important. Most macroscale models do not account for these physical processes, warranting the current line of research. In this thesis, we use atomistic simulations and statistical-mechanical theories to understand and formulate the nanoscale physical processes, and integrate them to develop a multiscale model for dissipation.
In the first part of the thesis, we explore fluid coupled resonator systems with an objective to understand different dissipative processes such as phonon-mediated intrinsic dissipation, viscous damping by the fluid, and the cross-interaction between each source of dissipation, i.e., phonons and fluid at a regime of gigahertz frequency, and nanometer length scale. First, we consider a single-walled carbon nanotube (SWCNT) resonator with confined Argon and driven under axial mode. The intrinsic dissipation in the SWCNT at gigahertz frequencies could be explained by Akhiezer theory. We show that intrinsic dissipation, which is conventionally treated as an independent process, can be modified by fluid interactions due to the phonon- fluid coupling. We show that an important consequence of this phonon-fluid coupling is the counter-intuitive inverse scaling of net dissipation with fluid density at low excitation frequencies. Next, we consider flexural vibration of the SWCNT with interior and exterior Argon. When compared with the fluid exterior case, the SWCNT with confined fluid shows a low and anomalous scaling of dissipation with fluid density. We systematically analyzed the sources of dissipation and found that the fluid contributed to the anomalous scaling. A formulation of the fluid response during the flexural motion revealed a viscoelastic nature of the fluid under nano-confinement, which explains the anomalous scaling. Further, we use the framework for dissipation analysis to examine the effect of thermal motion of the resonator atoms on fluid dissipation, demonstrate a frequency dependent dissipation scaling with density, and comment on the mechanism of intrinsic dissipation during flexural resonance of an SWCNT.
In the second part, we develop a multiscale framework to model intrinsic dissipation in two-dimensional (2D) microresonators. The work aims to reveal the fundamental limit of dissipation and enable looking at the isolated effect of various parameters over a wide range, both of which are inaccessible in experiments. The damping of the flexural mode of a 2D microresonator takes place due to the nonlinear coupling with other thermally excited elastic modes. A particular flexural mode can couple with another flexural mode with a wavelength ranging from the size of the resonator to that of the lattice spacing. However, the coupling at these disparate length scales needs different modeling approaches. In the multiscale framework, we model the continuum-scale modes as Langevin oscillators (LOs) with nonlinear coupling terms. The parameters of the LOs are computed using continuum mechanical analysis and atomistic simulations. Using this framework, we study the effect of various parameters of interest such as vibration amplitude, resonator size, temperature, and pre-strain in the case of graphene resonators and draw some important conclusions towards engineering high-quality 2D resonators.U of I OnlyAuthor requested U of Illinois access only (OA after 2yrs) in Vireo ETD syste
Laser cooling and trapping of barium
No full textLaser cooling and trapping of heavy alkaline-earth element barium have been demonstrated for the first time ever. For any possible cycling transition in barium that could provide strong cooling forces, the excited state has a very large branching probability to metastable states. Additional lasers are thus needed to bring the atoms back in to the cooling cycle. In this work barium atoms were efficiently collected in a magneto-optical trap (MOT) by large optical forces from the strong 6s2 1S0 – 6s6p 1P1 transition. Trapping of barium has been achieved using up to seven lasers simultaneously. The properties of the barium MOT were characterized. The efficiency of capturing an atom from a thermal atomic beam into the MOT is 0.4(1) %. The developed scheme is very efficient for collecting atoms. Loss rate mechanisms from the trap were studied by observing the decay of the trap population. Typical lifetimes of the MOT cloud are on the order of one second and are limited mainly due to insufficient repumping of metastable states. The range of velocities from which barium atoms can be captured into the MOT is about 30 m/s. Different laser transitions were employed for repumping barium atoms from the 6s5d 3D1 and the 6s5d 3D2 states. They lead to similar trap populations and lifetimes. The temperature of the cold atomic barium cloud was determined to about 5 mK. Atomic properties of the 5d2 3F2 state were studied with trapped atoms, in particular it's lifetime was determined as 160(10) s. This work has shown a possible scheme to trap atoms with a leaky cooling cycle. Since atoms with such properties are the majority of the elements in the periodic table, the number of optically trapable elements can be significantly enlarged. Of particular high interest is radium, which is chemical homologue to barium. The interest in radium stems from it's high sensitivity to possible nuclear and electron permanent electric dipole moments (EDM's). An EDM violates parity as well as time reversal and is therefore of fundamental importance. Searches for such EDM's are among the main research goals of the recently commissioned TRImP facility at KVI
Laser cooling and trapping of barium
No full textLaser cooling and trapping of heavy alkaline-earth element barium have been demonstrated for the first time ever. For any possible cycling transition in barium that could provide strong cooling forces, the excited state has a very large branching probability to metastable states. Additional lasers are thus needed to bring the atoms back in to the cooling cycle. In this work barium atoms were efficiently collected in a magneto-optical trap (MOT) by large optical forces from the strong 6s2 1S0 – 6s6p 1P1 transition. Trapping of barium has been achieved using up to seven lasers simultaneously. The properties of the barium MOT were characterized. The efficiency of capturing an atom from a thermal atomic beam into the MOT is 0.4(1) %. The developed scheme is very efficient for collecting atoms. Loss rate mechanisms from the trap were studied by observing the decay of the trap population. Typical lifetimes of the MOT cloud are on the order of one second and are limited mainly due to insufficient repumping of metastable states. The range of velocities from which barium atoms can be captured into the MOT is about 30 m/s. Different laser transitions were employed for repumping barium atoms from the 6s5d 3D1 and the 6s5d 3D2 states. They lead to similar trap populations and lifetimes. The temperature of the cold atomic barium cloud was determined to about 5 mK. Atomic properties of the 5d2 3F2 state were studied with trapped atoms, in particular it's lifetime was determined as 160(10) s. This work has shown a possible scheme to trap atoms with a leaky cooling cycle. Since atoms with such properties are the majority of the elements in the periodic table, the number of optically trapable elements can be significantly enlarged. Of particular high interest is radium, which is chemical homologue to barium. The interest in radium stems from it's high sensitivity to possible nuclear and electron permanent electric dipole moments (EDM's). An EDM violates parity as well as time reversal and is therefore of fundamental importance. Searches for such EDM's are among the main research goals of the recently commissioned TRImP facility at KVI
Laser cooling and trapping of barium
No full textLaser cooling and trapping of heavy alkaline-earth element barium have been demonstrated for the first time ever. For any possible cycling transition in barium that could provide strong cooling forces, the excited state has a very large branching probability to metastable states. Additional lasers are thus needed to bring the atoms back in to the cooling cycle. In this work barium atoms were efficiently collected in a magneto-optical trap (MOT) by large optical forces from the strong 6s2 1S0 – 6s6p 1P1 transition. Trapping of barium has been achieved using up to seven lasers simultaneously. The properties of the barium MOT were characterized. The efficiency of capturing an atom from a thermal atomic beam into the MOT is 0.4(1) %. The developed scheme is very efficient for collecting atoms. Loss rate mechanisms from the trap were studied by observing the decay of the trap population. Typical lifetimes of the MOT cloud are on the order of one second and are limited mainly due to insufficient repumping of metastable states. The range of velocities from which barium atoms can be captured into the MOT is about 30 m/s. Different laser transitions were employed for repumping barium atoms from the 6s5d 3D1 and the 6s5d 3D2 states. They lead to similar trap populations and lifetimes. The temperature of the cold atomic barium cloud was determined to about 5 mK. Atomic properties of the 5d2 3F2 state were studied with trapped atoms, in particular it's lifetime was determined as 160(10) s. This work has shown a possible scheme to trap atoms with a leaky cooling cycle. Since atoms with such properties are the majority of the elements in the periodic table, the number of optically trapable elements can be significantly enlarged. Of particular high interest is radium, which is chemical homologue to barium. The interest in radium stems from it's high sensitivity to possible nuclear and electron permanent electric dipole moments (EDM's). An EDM violates parity as well as time reversal and is therefore of fundamental importance. Searches for such EDM's are among the main research goals of the recently commissioned TRImP facility at KVI
EXPERIMENTAL INVESTIGATIONS ON THE SURFACE-DRIVEN CAPILLARY FLOW OF AQUEOUS MICROPARTICLE SUSPENSIONS IN THE MICROFLUIDIC LABORATORY-ON-A-CHIP SYSTEMS
No full textIn this work, total 1592 individual leakage-free polymethylmethacrylate (PMMA) microfluidic devices as laboratory-on-a-chip systems are fabricated by maskless lithography, hot embossing lithography, and direct bonding technique. Total 1094 individual Audio Video Interleave Files as experimental outputs related to the surface-driven capillary flow have been recorded and analyzed. The influence of effective viscosity, effect of surface wettability, effect of channel aspect ratio, and effect of centrifugal force on the surface-driven microfluidic flow of aqueous microparticle suspensions have been successfully and individually investigated in these laboratory-on-a-chip systems. Also, 5 micron polystyrene particles have been separated from the aqueous microparticle suspensions in the microfluidic lab-on-a-chip systems of modified design with 98% separation efficiency, and 10 micron polystyrene particles have been separated with 100% separation efficiency. About the novelty of this work, the experimental investigations have been performed on the surface-driven microfluidic flow of aqueous microparticle suspensions with the investigations on the separation time in particle-size based separation mechanism to control these suspensions in the microfluidic lab-on-a-chip systems. This research work contains a total of 10,112 individual experimental outputs obtained using total 30 individual instruments by author’s own hands-on completely during more than three years continuously. Author has performed the experimental investigations on both the fluid statics and fluid dynamics to develop an automated fluid machine.</jats:p
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