First-Order Decomposition Trees

Lifting attempts to speed up probabilistic inference by exploiting symmetries in the model. Exact lifted inference methods, like their propositional counterparts, work by recursively decomposing the model and the problem. In the propositional case, there exist formal structures, such as decomposition trees (dtrees), that represent such a decomposition and allow us to determine the complexity of inference a priori. However, there is currently no equivalent structure nor analogous complexity results for lifted inference. In this paper, we introduce FO-dtrees, which upgrade propositional dtrees to the first-order level. We show how these trees can characterize a lifted inference solution for a probabilistic logical model (in terms of a sequence of lifted operations), and make a theoretical analysis of the complexity of lifted inference in terms of the novel notion of lifted width for the tree

Highly Stable Multicrown Heterostructures of Type-II Nanoplatelets for Ultralow Threshold Optical Gain

Solution-processed type-II quantum wells exhibit outstanding optical properties, which make them promising candidates for light-generating applications including lasers and LEDs. However, they may suffer from poor colloidal stability under ambient conditions and show strong tendency to assemble into face-to-face stacks. In this work, to resolve the colloidal stability and uncontrolled stacking issues, we proposed and synthesized CdSe/CdSe1-xTex/CdS core/multicrown hetero-nanoplatelets (NPLs), controlling the amount of Te up to 50% in the crown without changing their thicknesses, which significantly increases their colloidal and photostability under ambient conditions and at the same time preserving their attractive optical properties. Confirming the final lateral growth of CdS sidewalls with X-ray photoelectron spectroscopy, energy-dispersive analysis, and photoelectron excitation spectroscopy, we found that the successful coating of this CdS crown around the periphery of conventional type-II NPLs prevents the unwanted formation of needle-like stacks, which results in reduction of the undesired scattering losses in thin-film samples of these NPLs. Owing to highly efficient exciton funneling from the outmost CdS crown accompanied by the reduced scattering and very low waveguide loss coefficient (similar to 18 cm(-1)), ultralow optical gain thresholds of multicrown type-II NPLs were achieved to be as low as 4.15 mu J/cm(2) and 2.48 mJ/cm(2) under one- and two-photon absorption pumping, respectively. These findings indicate that the strategy of using engineered advanced heterostructures of nanoplatelets provides solutions for improved colloidal stability and enables enhanced photonic performance

Assessment of AFT and Cox Models in Analysis of Factors Influencing the survival of Women with Breast Cancer in Yazd city

BACKGROUND AND OBJECTIVE: Breast cancer is one of the most common cancers in women. The statistical methods in the survival analysis of these patients are accelerated time models and Cox model. The purpose of this study is to evaluate two models in determining the effective factors in the survival of breast cancer. METHODS: The study was an analytical and cohort study of survival analysis. The 538 of the patients referred to Ramezanzade Radiotherapy Center who had breast cancer and recorded survival status as a census from the April 2005 until March 2012 in Yazd. and survived by phone call. The Kaplan-Meier estimate was used to describe the survival of the patients. The research variables included clinical and demographic factors. The choice of final variables in the model was done by the methods of diminishing the dimension and all possible Cox regressions by the acaian criterion. Then, the best accelerated time model was considered Getting different distributions was also determined by the Akayake criteria. FINDINGS: The most effective Cox model among all Cox models was variables including Age, Her2 and Ki67 variables (AIC = 30270). The generalized gamma model was the most optimal accelerated time model (AIC 463.966). Her2 was significant in both accelerated and cox models(p0.05). CONCLUSION: In both accelerated time- Generalized Gamma- models and Cox Models, the Her2 variable was identified as a risk factor for breast cancer and There is a positive impact on the risk of death and reduced survival

Solution-processed quantum dot infrared lasers

(English) Colloidal semiconductors quantum dots (CQDs) have emerged as a promising solutionprocessed gain material that can be engineered via low-cost and scalable chemical techniques. Owing to quantum confinement, their emission wavelengths and optical properties can be tuned from the visible to the infrared. Despite these possible advantages, the realization of lasing action in CQDs is complicated and fundamentally stems from the non-unity degeneracy of the band-edge state. This results in high optical gain thresholds, demanding multiexcitons for achieving lasing action. This, in turn, leads to a very short optical gain lifetime which is caused by Auger recombination. Following the first demonstration of lasing action in CQDs, this field has thus far experienced remarkable development with materials offering emission in the visible showing limited application potential. However, the possibility of lasing in the infrared region would open a new realm of applications for this material platform in optical telecommunications, photonic integrated circuits, and LIDAR applications. To unleash those applications, the demonstration of solution-processed infrared lasers in the eye-safe window between 1.5-1.6 µm operating robustly at room temperature is a prerequisite. Midgap trap states in CQDs limit the performance of optoelectronics devices. In particular, PbS CQDs suffer from a very fast trap-assisted Auger process leading to high lasing thresholds. To suppress this type of Auger process, in this work, we use a binary nanocomposite of PbS CQDs and ZnO nanocrsystals (NCs) where the former serves as the infrared gain medium and the latter as a remote passivant for midgap traps in PbS CQDs. This binary heterostructure drastically suppresses the Auger process and lowers the lasing thresholds. Low threshold infrared CQD-laser has been thought to be not possible because of 8-fold degeneracy of the band-edge state in the infrared-emitting Pb-chalcogenide CQDs. In this Thesis, we demonstrate that using core-alloyed shell heterostructured CQD comprising PbS as core and PbSSe as shell allows suppressing Auger process. Furthermore, by applying doping to specially engineered CQDs, we demonstrate a substantial reduction in lasing threshold down to sub-single exciton level per-dot thanks to the blocking of the ground state absorption. Employing these CQDs has drastically improved the net modal coefficient of the medium and brought it on par with a gain coefficient of epitaxially grown III-V infrared semiconductors. The realization of CQD infrared laser-diodes will have a profound impact in many disciplines. Here, by engineering the electric field distribution in our devices, we show stimulated emission in a record ultra-thin gain media which is beyond the slab waveguide theoretical limit by introducing scatterers implemented by ZnO NCs. We employ this thin gain media as the active layer in a full-stack light emitting diode (LED) device. Also, to overcome the existing challenge underpinned by the optical losses of the metal contacts that have prevented the realization of stimulated emission in a LED, we use an engineered transparent conductive oxide and graphene as anode and cathodeof the LED, respectively. Finally, our proposed LED structure leads us to realize a dual function device showing strong infrared spontaneous- and stimulated-emission under electrical- and optical-pumping, respectively. In summary, we have demonstrated that CQDs can emerge as a robust technology for the realization of infrared lasers. Our proposed CQD systems lead us to achieve high performance laser devices under optical excitation and using CQD heterostructures asan active medium in the proposed LED structure paves the way towards the future development of infrared CQD-laser diodes.(Español) Los puntos cuánticos de semiconductor sintetizados mediante procesos coloidales (CQDs) han resultado ser un prometedor medio de ganancia cuya obtención puede llevarse a cabo mediante técnicas de bajo coste y alta reproducibilidad química. Gracias al efecto del confinamiento cuántico, su longitud de onda puede modularse con precisión desde el visible hasta el infrarrojo. A pesar de todas estas ventajas, conseguir acción láser utilizando estos materiales presenta una gran dificultad, originada fundamentalmente por el alto grado de degeneración de los niveles energéticos más bajos, dando lugar a umbrales ópticos más altos. Esto hace que se requiera de múltiples excitones para conseguir la acción láser, lo que a su vez resulta en tiempos de ganancia muy reducidos por culpa de la recombinación Auger. Tras la primera demostración del láser utilizando CQDs, este campo ha experimentado un importante desarrollo utilizando materiales con emisión en el visible, limitando sus potenciales aplicaciones. La obtención de luz láser en la región infrarroja supondría por tanto un nuevo abanico de posibilidades para tecnologías tales como las telecomunicaciones ópticas, la fotónica integrada, la imagen biomédica o las aplicaciones LIDAR. Para la realización de todas ellas, es requisito fundamental el desarrollo de láseres infrarrojos en el rango 1.5-1.6 ¿m y que puedan operar a temperatura ambiente de forma estable. Las trampas electrónicas dentro de la banda prohibida son factores limitantes en el funcionamiento de los dispositivos optoelectrónicos. En el caso de los CQDs basados en PbS, los procesos Auger debidos a estas trampas dan lugar a altos umbrales de ganancia láser. Para mitigar dichos procesos, empleamos un nanocomposite a base de CQDs de PbS y nanocristales de ZnO, donde los CQDs actúan como medio de ganancia y los nanocristales de ZnO sirven de pasivantes de dichas trampas. Esta heteroestructura binaria suprime drásticamente los procesos Auger y reduce el umbral láser. La fuerte degeneración (8) de los estados energéticos fundamentales de la banda prohibida en los calcogenuros de plomo ha obstaculizado el desarrollo del láser infrarrojo basando en CQDs. En esta tesis, demostramos la supresión de los procesos Auger mediante el uso de CQDs con estructura núcleo (PbS)/corteza (PbSSe). También probamos que, mediante dopaje, es posible reducir el umbral láser a valores por debajo de 1 excitón/CQD gracias a la reducción en la absorción del estado fundamental. El uso de estos CQDs mejora sustancialmente el coeficiente modal neto del medio de ganancia, equiparándose al de los semiconductores infrarrojos del grupo III/V crecidos epitaxia. El uso de diodos láser infrarrojos fabricados mediante procesos en solución supondrá un cambio significativo en múltiples disciplinas. Mostramos que es posible la obtención de emisión estimulada de luz en un medio de ganancia ultrafino con un espesor por debajo del límite teórico para guías de onda planas gracias a la modificación del campo eléctrico mediante la inclusión de nanocristales de ZnO actuando como puntos dispersivos. Empleamos este medio activo para construir un dispositivo LED. Además, para evitar el problema de las pérdidas ópticas debidas a los contactos metálicos que hasta ahora habían dificultado la obtención de emisión estimulada, hemos empleado un óxido conductor transparente y grafeno como ánodo y cátodo de nuestro LED, respectivamente. Nuestra propuesta de LED demuestra que es posible la fabricación de un dispositivo de funcionamiento dual capaz de producir luminiscencia espontánea y estimulada mediante bombeo eléctrico y óptico, respectivamente. En resumen, hemos probado que el uso de CQDs ofrece una alternativa tecnológica para la producción de luz láser. Estos dispositivos basados en CQDs permiten fabricar fuentes láser de alto rendimiento mediante bombeo óptico. Además, su uso como medio activo en un dispositivo LED supone un avance hacia futuros láseres de diodo basados en CQDs

Solution-processed quantum dot infrared lasers

(English) Colloidal semiconductors quantum dots (CQDs) have emerged as a promising solutionprocessed gain material that can be engineered via low-cost and scalable chemical techniques. Owing to quantum confinement, their emission wavelengths and optical properties can be tuned from the visible to the infrared. Despite these possible advantages, the realization of lasing action in CQDs is complicated and fundamentally stems from the non-unity degeneracy of the band-edge state. This results in high optical gain thresholds, demanding multiexcitons for achieving lasing action. This, in turn, leads to a very short optical gain lifetime which is caused by Auger recombination. Following the first demonstration of lasing action in CQDs, this field has thus far experienced remarkable development with materials offering emission in the visible showing limited application potential. However, the possibility of lasing in the infrared region would open a new realm of applications for this material platform in optical telecommunications, photonic integrated circuits, and LIDAR applications. To unleash those applications, the demonstration of solution-processed infrared lasers in the eye-safe window between 1.5-1.6 µm operating robustly at room temperature is a prerequisite. Midgap trap states in CQDs limit the performance of optoelectronics devices. In particular, PbS CQDs suffer from a very fast trap-assisted Auger process leading to high lasing thresholds. To suppress this type of Auger process, in this work, we use a binary nanocomposite of PbS CQDs and ZnO nanocrsystals (NCs) where the former serves as the infrared gain medium and the latter as a remote passivant for midgap traps in PbS CQDs. This binary heterostructure drastically suppresses the Auger process and lowers the lasing thresholds. Low threshold infrared CQD-laser has been thought to be not possible because of 8-fold degeneracy of the band-edge state in the infrared-emitting Pb-chalcogenide CQDs. In this Thesis, we demonstrate that using core-alloyed shell heterostructured CQD comprising PbS as core and PbSSe as shell allows suppressing Auger process. Furthermore, by applying doping to specially engineered CQDs, we demonstrate a substantial reduction in lasing threshold down to sub-single exciton level per-dot thanks to the blocking of the ground state absorption. Employing these CQDs has drastically improved the net modal coefficient of the medium and brought it on par with a gain coefficient of epitaxially grown III-V infrared semiconductors. The realization of CQD infrared laser-diodes will have a profound impact in many disciplines. Here, by engineering the electric field distribution in our devices, we show stimulated emission in a record ultra-thin gain media which is beyond the slab waveguide theoretical limit by introducing scatterers implemented by ZnO NCs. We employ this thin gain media as the active layer in a full-stack light emitting diode (LED) device. Also, to overcome the existing challenge underpinned by the optical losses of the metal contacts that have prevented the realization of stimulated emission in a LED, we use an engineered transparent conductive oxide and graphene as anode and cathodeof the LED, respectively. Finally, our proposed LED structure leads us to realize a dual function device showing strong infrared spontaneous- and stimulated-emission under electrical- and optical-pumping, respectively. In summary, we have demonstrated that CQDs can emerge as a robust technology for the realization of infrared lasers. Our proposed CQD systems lead us to achieve high performance laser devices under optical excitation and using CQD heterostructures asan active medium in the proposed LED structure paves the way towards the future development of infrared CQD-laser diodes.(Español) Los puntos cuánticos de semiconductor sintetizados mediante procesos coloidales (CQDs) han resultado ser un prometedor medio de ganancia cuya obtención puede llevarse a cabo mediante técnicas de bajo coste y alta reproducibilidad química. Gracias al efecto del confinamiento cuántico, su longitud de onda puede modularse con precisión desde el visible hasta el infrarrojo. A pesar de todas estas ventajas, conseguir acción láser utilizando estos materiales presenta una gran dificultad, originada fundamentalmente por el alto grado de degeneración de los niveles energéticos más bajos, dando lugar a umbrales ópticos más altos. Esto hace que se requiera de múltiples excitones para conseguir la acción láser, lo que a su vez resulta en tiempos de ganancia muy reducidos por culpa de la recombinación Auger. Tras la primera demostración del láser utilizando CQDs, este campo ha experimentado un importante desarrollo utilizando materiales con emisión en el visible, limitando sus potenciales aplicaciones. La obtención de luz láser en la región infrarroja supondría por tanto un nuevo abanico de posibilidades para tecnologías tales como las telecomunicaciones ópticas, la fotónica integrada, la imagen biomédica o las aplicaciones LIDAR. Para la realización de todas ellas, es requisito fundamental el desarrollo de láseres infrarrojos en el rango 1.5-1.6 ¿m y que puedan operar a temperatura ambiente de forma estable. Las trampas electrónicas dentro de la banda prohibida son factores limitantes en el funcionamiento de los dispositivos optoelectrónicos. En el caso de los CQDs basados en PbS, los procesos Auger debidos a estas trampas dan lugar a altos umbrales de ganancia láser. Para mitigar dichos procesos, empleamos un nanocomposite a base de CQDs de PbS y nanocristales de ZnO, donde los CQDs actúan como medio de ganancia y los nanocristales de ZnO sirven de pasivantes de dichas trampas. Esta heteroestructura binaria suprime drásticamente los procesos Auger y reduce el umbral láser. La fuerte degeneración (8) de los estados energéticos fundamentales de la banda prohibida en los calcogenuros de plomo ha obstaculizado el desarrollo del láser infrarrojo basando en CQDs. En esta tesis, demostramos la supresión de los procesos Auger mediante el uso de CQDs con estructura núcleo (PbS)/corteza (PbSSe). También probamos que, mediante dopaje, es posible reducir el umbral láser a valores por debajo de 1 excitón/CQD gracias a la reducción en la absorción del estado fundamental. El uso de estos CQDs mejora sustancialmente el coeficiente modal neto del medio de ganancia, equiparándose al de los semiconductores infrarrojos del grupo III/V crecidos epitaxia. El uso de diodos láser infrarrojos fabricados mediante procesos en solución supondrá un cambio significativo en múltiples disciplinas. Mostramos que es posible la obtención de emisión estimulada de luz en un medio de ganancia ultrafino con un espesor por debajo del límite teórico para guías de onda planas gracias a la modificación del campo eléctrico mediante la inclusión de nanocristales de ZnO actuando como puntos dispersivos. Empleamos este medio activo para construir un dispositivo LED. Además, para evitar el problema de las pérdidas ópticas debidas a los contactos metálicos que hasta ahora habían dificultado la obtención de emisión estimulada, hemos empleado un óxido conductor transparente y grafeno como ánodo y cátodo de nuestro LED, respectivamente. Nuestra propuesta de LED demuestra que es posible la fabricación de un dispositivo de funcionamiento dual capaz de producir luminiscencia espontánea y estimulada mediante bombeo eléctrico y óptico, respectivamente. En resumen, hemos probado que el uso de CQDs ofrece una alternativa tecnológica para la producción de luz láser. Estos dispositivos basados en CQDs permiten fabricar fuentes láser de alto rendimiento mediante bombeo óptico. Además, su uso como medio activo en un dispositivo LED supone un avance hacia futuros láseres de diodo basados en CQDs.Postprint (published version

Lifted Probabilistic Inference by Variable Elimination (Gelifte probabilistische inferentie door variabele eliminatie)

Representing, learning, and reasoning about knowledge are central to artificial intelligence (AI). A long standing goal of AI is unifying logic and probability, to benefit from the strengths of both formalisms. Probability theory allows us to represent and reason in uncertain domains, while first-order logic allows us to represent and reason about structured, relational domains. Many real-world problems exhibit both uncertainty and structure, and thus can be more naturally represented with a combination of probabilistic and logical knowledge. This observation has led to the development of probabilistic logical models (PLMs), which combine probabilistic models with elements of first-order logic, to succinctly capture uncertainty in structured, relational domains, e.g., social networks, citation graphs, etc. While PLMs provide expressive representation formalisms, efficient inference is still a major challenge in these models, as they typically involve a large number of objects and interactions among them. Among the various efforts to address this problem, a promising line of work is lifted probabilistic inference. Lifting attempts to improve the efficiency of inference by exploiting the symmetries in the model. The basic principle of lifting is to perform an inference operation once for a whole group of interchangeable objects, instead of once per individual in the group. Researchers have proposed lifted versions of various (propositional) probabilistic inference algorithms, and shown large speedups achieved by the lifted algorithms over their propositional counterparts. In this dissertation, we make a number of novel contributions to lifted inference, mainly focusing on lifted variable elimination (LVE). First, we focus on constraint processing, which is an integral part of lifted inference. Lifted inference algorithms are commonly tightly coupled to a specific constraint language. We bring more insight in LVE, by decoupling the operators from the used constraint language. We define lifted inference operations so that they operate on the semantic level rather than on the syntactic level, making them language independent. Further, we show how this flexibility allows us to improve the efficiency of inference, by enhancing LVE with a more powerful constraint representation. Second, we generalize the `lifting' tools used by LVE, by introducing a number of novel lifted operators in this algorithm. We show how these operations allow LVE to exploit a broader range of symmetries, and thus expand the range of problems it can solve in a lifted way. Third, we advance our theoretical understanding of lifted inference by providing the first completeness result for LVE. We prove that LVE is complete---always has a lifted solution---for the fragment of 2-logvar models, a model class that can represent many useful relations in PLMs, such as (anti-)symmetry and homophily. This result also shows the importance of our contributions to LVE, as we prove they are sufficient and necessary for LVE to achieve completeness. Fourth, we propose the structure of first-order decomposition trees (FO-dtrees), as a tool for symbolically analyzing lifted inference solutions. We show how FO-dtrees can be used to characterize an LVE solution, in terms of a sequence of lifted operations. We further make a theoretical analysis of the complexity of lifted inference based on a corresponding FO-dtree, which is valuable for finding and selecting among different lifted solutions. Finally, we present a pre-processing method for speeding up (lifted) inference. Our goal with this method is to speed up inference in PLMs by restricting the computations to the requisite part of the model. For this, we build on the Bayes-ball algorithm that identifies the requisite variables in a ground Bayesian network. We present a lifted version of Bayes-ball, which works with first-order Bayesian networks, and show how it applies to lifted inference.nrpages: xvii + 251status: publishe

Generalized counting for lifted variable elimination

Lifted probabilistic inference methods exploit symmetries in the structure of probabilistic models to perform inference more efficiently. In lifted variable elimination the symmetry among a group of interchangeable random variables is captured by counting formulas, and exploited by operations that handle such formulas. In this paper we generalize the structure of counting formulas and present a set of inference operators that introduce and eliminate these formulas from the model. This generalization expands the range of problems that can be solved in a lifted way. Our work is closely related to the recently introduced method of joint conversion. Due to its more fine grained formulation, however, our approach can provide more efficient solutions than joint conversion.status: publishe