169,810 research outputs found
Confinamiento de átomos de Cesio por medio de trampas magneto-ópticas
No full textEn este trabajo se estudian los principios físicos y se calculan los parámetros necesarios para implementar una trampa magneto-óptica (MOT) para átomos de cesio. El estudio comienza con la evaluación de la factibilidad de atrapar los átomos mediante campos magnéticos generados por bobinas en configuración anti-Helmholtz. Posteriormente, se analiza el comportamiento del cesio en presencia de dicho campo y se calcula explícitamente el potencial de confinamiento. Se estudia también la interacción de la luz láser con los átomos para entender la fuerza de radiación y el proceso de enfriamiento láser. Se investigan las temperaturas de confinamiento alcanzables y los límites teóricos de enfriamiento, mostrando que es posible llegar a temperaturas del orden de los microKelvin.
Finalmente, se examina cómo la melaza óptica y el campo magnético actúan de forma complementaria para lograr el confinamiento de los átomos de cesio. La dinámica de los átomos en la trampa puede describirse como el de un oscilador sobreamortiguado. Se espera que este trabajo siente las bases para la futura implementación experimental de una MOT para cesio en la universidad.This work studies the physical principles and calculates the parameters required to implement a magneto-optical trap (MOT) for cesium atoms. The study begins with an evaluation of the feasibility of trapping atoms using magnetic fields generated by coils in an anti-Helmholtz configuration. The behavior of cesium in the presence of such a field is then analyzed, and the corresponding confinement potential is explicitly calculated. The interaction between laser light and atoms is also studied to understand the radiation force and the laser cooling process. Confinement temperatures and theoretical cooling limits are explored, showing that it is possible to reach temperatures on the order of microKelvin. Finally, the combined effect of optical molasses and the mag netic field is examined to achieve stable confinement of cesium atoms. The atomic dynamics in the trap can be described as that of an overdamped harmonic oscillator. This work aims to lay the theoretical foundation for the future experimental implementation of a cesium MOT at the university.Pregrad
Estudio teórico y experimental de la sección eficaz de la absorción de dos fotones en átomos de Cesio
No full textEl proceso de absorción de dos fotones, TPA por sus siglas en inglés, ha sido ampliamente estudiado en diferentes átomos y moléculas, con el fin de aplicarlo a diferentes áreas de desarrollo tecnológico y científico. Uno de los parámetros que permite cuantificar la probabilidad de que este proceso ocurra es la sección eficaz de la absorción de dos fotones. Calcularla y medirla es, por lo general, el punto de partida para realizar experimentos que buscan producir este tipo de transiciones multifotónicas usando diferentes tipos de fuentes de luz, como, por ejemplo, una fuente de pares de fotones enredados. Bajo este contexto, el presente trabajo consiste en estudiar la sección eficaz del TPA en átomos de Cesio bajo dos facetas, una teórica y una experimental. La parte teórica se enfoca en el cálculo de la sección eficaz del TPA en átomos de Cesio usando la teoría de perturbaciones dependiente del tiempo a segundo orden para la transición 6S1/2 8S1/2. La parte experimental se centra en la medición de la sección eficaz mediante la técnica de la fluorescencia inducida por TPA (TPIF) en un gas de Cesio, analizando la señal de fluorescencia generada por la interacción del Cesio con luz láser de 822 nmFísicoPregrad
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Mitomycin C in highly myopic eyes - Author reply
No full textOphthalmology. 2005 Feb;112(2):208-18; discussion 219.
Mitomycin C modulation of corneal wound healing after photorefractive keratectomy in highly myopic eyes.
Gambato C, Ghirlando A, Moretto E, Busato F, Midena E.
SourceRefractive Surgery Service and Antimetabolite Therapy Research Unit, Department of Ophthalmology, University of Padova, Padova, Italy.
Abstract
PURPOSE: To evaluate the role of topical mitomycin C in corneal wound healing (CWH) after photorefractive keratectomy (PRK) in highly myopic eyes.
DESIGN: Prospective, double-masked, randomized clinical trial.
PARTICIPANTS: Seventy-two eyes of 36 patients affected by high (>7 diopters) myopia.
METHODS: In each patient, one eye was randomly assigned to PRK with intraoperative topical 0.02% mitomycin C application, and the fellow eye was treated with a placebo. Postoperatively, mitomycin C-treated eyes received artificial tears (3 times daily, tapered in 3 months), whereas the fellow eye was treated with fluorometholone sodium 2% and artificial tears (3 times daily, tapered in 3 months).
MAIN OUTCOME MEASURES: Uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA), contrast sensitivity, manifest refraction, and biomicroscopy. Contrast sensitivity was determined using the Pelli-Robson chart. Corneal confocal microscopy documented CWH.
RESULTS: Mean follow-up was 18 months (range, 12-36). No side effects or toxic effects were documented. At 12-month follow-up examination, UCVAs (logarithm of the minimum angle of resolution) were 0.4+/-0.48 and 0.5+/-0.53 (P = .03) in mitomycin C-treated eyes and corticosteroid-treated eyes, respectively. At 1 year, corneal haze developed in 20% of corticosteroid-treated eyes, versus 0% of mitomycin C-treated eyes. At 12, 24, and 36 months, corneal confocal microscopy showed activated keratocytes and extracellular matrix significantly more evident in untreated eyes (Ps = 0.004, 0.024, and 0.046, respectively).
CONCLUSION: Topical intraoperative application of 0.02% mitomycin C can reduce haze formation in highly myopic eyes undergoing PRK.
Comment in
Ophthalmology. 2006 Feb;113(2):357; author reply 357-8
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
A Multi-Language Comparison of Influences on Author Verification using Character N-Grams
No full textWe create a new multi-language corpus for author verification based on Wikipedia talkpages, and evaluate the influence that differences in topic and time have on character n-gram author profiles. Topic alignment between two texts is found to increase author verification precision, and an authors writing style is found to change over time, but not more significantly after 3 years than after 1 year.Information ArchitectureWISElectrical Engineering, Mathematics and Computer Scienc
A 0.12mm<sup>2</sup> Wien-Bridge Temperature Sensor with 0.1°C (3σ) Inaccuracy from -40°C to 180°C
No full text Resistor-based temperature sensors can achieve much higher resolution and energy efficiency than conventional BJT-based sensors [1], but they typically occupy more area (> 0.25 mm 2 ) and have lower operating temperatures (le 125 {circ} {C}) [2]-[4]. This work describes a 0.12mm 2 resistor-based sensor that uses a Wien-bridge (WB) filter to achieve 0.1 {circ} {C} (3 sigma) inaccuracy from - 40 {circ} {C} to 180 {circ} {C}. Compared to a state-of-the-art WB sensor [4], it occupies 6 × less area and achieves comparable relative accuracy over a 76% wider operating range. Session 10.3 Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic InstrumentationMicroelectronic
Alterações estruturais de Cr-beidelita tratada até 1350 °C em atmosferas de oxigênio ou nitrogênio
No full textBeidellite clay mineral after intercalation of OH-Cr(III) species were thermally analyzed up to 1350 °C in oxygen and nitrogenatmospheres. OH-Cr-beidellite can be used as a pillared clay precursor for catalysis or as adsorbent applications. However, inthis paper beidellite enriched in chromium were analyzed at different thermal treatments up to high temperature for evaluatingstructural changes for possible future ceramic applications. The structural changes were followed by thermal analysis and X-raydiffraction. The thermal treatment of OH-Cr-beidellite in oxygen and nitrogen atmospheres developed different mineralogicalphases up to 1050 °C, but at higher temperatures, the same phases were developed in both atmosphere treatments. Eskolaitephase (Cr2O3) appeared in the sample after heating at 400 °C in oxygen atmosphere, whereas grimaldite (CrO-OH) in nitrogenatmosphere, maintaining the starting phases. At 1000 °C the raw clay minerals disappeared, as it is knew. At 1050 °C in nitrogenatmosphere, grimaldite was absent and eskolaite appeared. At 1350 °C in the samples calcined in both atmospheres, quartz,cristobalite and mullite as the main phases and in lower contents aluminum oxide and aluminum-chromium oxide [(Al,Cr)2O3]were present.O mineral de argila de beidelita após intercalação das espécies OH-Cr(III) foi termicamente analisado até 1350 °C em atmosferas de oxigénio e nitrogênio. A OH-Cr-beidelita pode ser utilizada como um precursor de argila pilarizada para catálise ou para aplicações adsorventes. No entanto, neste trabalho, a beidelita enriquecida em cromo foi analisada em diferentes tratamentos térmicos até alta temperatura para avaliação de mudanças estruturais para possíveis aplicações cerâmicas futuras. As alterações estruturais foram acompanhadas por análise térmica e difração de raios X. O tratamento térmico da OH-Cr-beidelita em atmosferas de oxigênio e nitrogênio desenvolveu diferentes fases mineralógicas até 1050 °C, mas em temperaturas mais altas, as mesmas fases foram desenvolvidas em ambas atmosferas. A fase eskolaita (Cr2 O3 ) apareceu na amostra após aquecimento a 400 °C em atmosfera de oxigênio, enquanto grimaldita (CrO-OH) em atmosfera de nitrogênio, mantendo as fases iniciais. Em 1000 °C, os minerais originais da argila desapareceram, como é conhecido. Em 1050 °C em atmosfera de nitrogênio, a grimaldita estava ausente e apareceu eskolaita. Em amostras calcinadas a 1350 °C em ambas as atmosferas, estavam presentes quartzo, cristobolita e mulita como fases principais e em menores teores óxido de alumínio e óxido de alumínio e cromo [(Al,Cr)2 O3 ].Fil: Santos, H. S.. Universidade de Sao Paulo; BrasilFil: Cesio, Ana Maria. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Tecnología de Recursos Minerales y Cerámica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Tecnología de Recursos Minerales y Cerámica; ArgentinaFil: Gauna, Matias Roberto. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Tecnología de Recursos Minerales y Cerámica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Tecnología de Recursos Minerales y Cerámica; ArgentinaFil: Justo, V. F.. Universidade de Sao Paulo; BrasilFil: Volzone, Cristina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Tecnología de Recursos Minerales y Cerámica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Tecnología de Recursos Minerales y Cerámica; Argentin
A ±25A Versatile Shunt-Based Current Sensor with 10kHz Bandwidth and ±0.25% Gain Error from -40°C to 85°C Using 2-Current Calibration
No full textAccurate current sensing is critical in many industrial applications, such as battery management and motor control. Precise shunt-based current sensors have been reported with gain errors of less than 1% over the industrial temperature range (-40°C to 85°C) [1]–[4]. However, since they are intended for coulomb counting, their bandwidth is limited to a few tens of Hz, making them unsuitable for battery impedance or motor-current sensing. This paper presents a current sensor with a wide (10kHz) bandwidth and a tunable temperature compensation scheme (TCS), which allows it to be flexibly used with different types of shunts while maintaining high accuracy. A low-cost room-temperature calibration scheme is proposed to optimize gain flatness over temperature by exploiting the shunt's self-heating at large currents. Over the industrial temperature range and a ±25A current range, it achieves state-of-the-art gain error (±0.25%) with both low-cost PCB and stable metal-alloy shunts.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic InstrumentationMicroelectronic
Study on ce-doped nonstoichiometric nanosilica for promoting properties of polysulfone membranes
No full textUsing the sol-gel method a series of nonstoichiometric nanosilica doped with the rare earth element Ce (CeSiO, x = 0.0-0.14) were prepared in order to modify the physicochemical properties of the nanosilica surface and to enhance the strength of the Ce-nanosilica/polysulfone composite membranes. The CeSiO samples were characterized by Fourier transform infrared spectra, X-ray diffraction and X-ray photoelectron spectra. The observations from these characterizations suggest that most Ce atoms enter the silica framework to form a Ce-O-Si solid solution while the cubic CeO phase is segregated when x > 0.08. Transmission electron microscopy images show that CeSiO particles are spherical with a uniform size distribution in the range of 30-50nm and contain some inner pores with sizes up to a few nanometers. Specifically, CeSiO-700 calcined at 700 °C shows the biggest surface area, the smallest pore size and the highest hydrophilicity, which makes the CeSiO/polysulfone composite membranes (8.0wt %) exhibit the strongest mechanical strength (3.223MPa), which is enhanced by more than 100% in comparison with the pure polymer membrane
- …
