Mono- and Biexponential Luminescence Decays of Individual Single-Walled Carbon Nanotubes

We have studied the exciton recombination dynamics of individual (6,4) and (6,5) single-walled carbon nanotubes embedded in aqueous gels or deposited on glass surfaces. CoMoCat nanotubes systematically display short monoexponential photoluminescence (PL) decays presumably due to defects introduced during their synthesis. In contrast HiPco nanotubes can either display mono- or biexponential PL decays depending on the environmental conditions. Transition from bi- to monoexponential decays can be reproduced by a simple three level model taking into account defect-dependent nonradiative decay mechanisms

Electrochemistry and self-assembly of complex single-walled carbon nanotube (SWNT) nanostructures

This dissertation explores the optical and electrochemical properties of surfactant stabilized and individually---suspended SWNTs in aqueous media via application of various external stimuli. Resulting effects such as nanostructure formation, photocurrent generation, and inherent nanotube electronic and optical properties are then analyzed. The goal is to engineer SWNT systems which can be tuned by understanding the mechanism of the electrochemical and environmental reactions so that applications in nanophotonics, photovoltaics, and electronics can be effectively exploited. A strategy to obtain a surfactant---polymer protective "shell" that improves the stability and luminescence signal of individual SWNTs is presented. We used literature evidence of emission shifts to understand the interactions between polymers and surfactants and show how morphological changes induced by extrinsic factors distort the SWNT luminescence. We developed an in-situ polymerization which creates an outer shell around the SWNT micelle that resulted in suspensions with stable luminescence at all pH, in saline buffers, and on the surface of living cells. Single molecule imaging and time resolved spectroscopy of individual (6,5) SWNTs demonstrated that SWNT luminescence depends strongly on intrinsic and extrinsic factors such as sample preparation, sample inhomogeneities, defects, and tube synthesis conditions. Moreover, we found compelling spectroscopic evidence of substantial differences in chirality distribution and luminescence properties within HiPco batches. Nanoparticle-nanotube Structures (nanoPaNTs) were fabricated by exploiting the electrochemical properties of SWNTs upon activation with alternating electromagnetic fields. The incident field polarizes the SWNTs at the ends, antenna-like-behavior, which readily drives electrochemical reactions. This process is shown to activate redox reactions preferentially with metallic SWNT and proceed at or near diffusion-limited rates. Electrochemical photocathodes with optical rectifying antennae were developed from an array of vertically grown CNT forests. We demonstrated rectification of AC signals by associating anionic surfactant molecules around the CNT and charge separation in the optical regime that generates measurable, wavelength dependent, electrical current. We show that charge separation drives redox reactions with transition metal salts in SWNT suspensions. The results of this research provide key information on the interaction between SWNTs and electromagnetic fields and insight into the extrinsic and intrinsic factors that affect the optical properties

Impurity-Related Nonlinear Optical Absorption in Delta-Doped Quantum Rings

Using a variational procedure within the efective mass approximation, we have calculated the hydrogenic impurity binding energy as well as the impurity-related nonlinear optical absorption in a single quantum ring with axia ln-type delta-doping

Crecimiento y absorción de nitrógeno, fósforo y potasio en cebolla, Allium cepa L.: variedad ocañera.

El objetivo del estudio fue determinar las variaciones en crecimiento y acumulación de materia seca, N, P, K en hojas y bulbos en la cebolla ocañera. Se realizó el estudio durante 80 días utilizando la cebolla de ciclo corto, propagación asexual y altos rendimientos. Las épocas de crecimiento (6) contadas a partir de 30 días después de la siembra y con intervalos de 10 días, fueron los tratamientos (6 y 4 repeticiones, al azar). Los parámetros determinados fueron: número de falsos tallos por planta, número de hojas por falso tallo, número de hojas por planta altura de hojas, peso fresco y seco de hojas y bulbos, porcentajes y gramos de NPK en hojas y bulbos. Los pesos fresco y seco de hojas y bulbos guardaron estrecha relación a través del período vegetativo. Las necesidades de N y K son mayores en las primeras épocas, las de P en todasCebolla de bulbo-Cebolla japonesa

Optimization of treatment with interferon beta in multiple sclerosis. Usefulness of automatic system application criteria

<p>Abstract</p> <p>Background</p> <p>A software based tool has been developed (Optem) to allow automatize the recommendations of the Canadian Multiple Sclerosis Working Group for optimizing MS treatment in order to avoid subjective interpretation.</p> <p>Methods</p> <p>Treatment Optimization Recommendations (TORs) were applied to our database of patients treated with IFN β1a IM. Patient data were assessed during year 1 for disease activity, and patients were assigned to 2 groups according to TOR: "change treatment" (CH) and "no change treatment" (NCH). These assessments were then compared to observed clinical outcomes for disease activity over the following years.</p> <p>Results</p> <p>We have data on 55 patients. The "change treatment" status was assigned to 22 patients, and "no change treatment" to 33 patients. The estimated sensitivity and specificity according to last visit status were 73.9% and 84.4%. During the following years, the Relapse Rate was always higher in the "change treatment" group than in the "no change treatment" group (5 y; CH: 0.7, NCH: 0.07; p < 0.001, 12 m – last visit; CH: 0.536, NCH: 0.34). We obtained the same results with the EDSS (4 y; CH: 3.53, NCH: 2.55, annual progression rate in 12 m – last visit; CH: 0.29, NCH: 0.13).</p> <p>Conclusion</p> <p>Applying TOR at the first year of therapy allowed accurate prediction of continued disease activity in relapses and disability progression.</p

Efecto de Cuatro Métodos de Separación Seminal sobre la Calidad y la Capacidad Fertilizante in vitro de Espermatozoides Equinos Criopreservados

The aim of this study was to evaluate the effect of four separation methods on seminal quality and in vitro fertilizing capacity of equine cryopreserved spermatozoa. Straws of equine cryopreserved semen were used for sperm separation through the Androcoll, CushionFluid, EquiPure and Percoll methods. A Sperm Class Analyzer (SCA®) system was used to determine total motility, progressive motility, curvilinear velocity, linear velocity and average speed. Also, intact acrosome and sperm vitality were evaluated by fluorescence microscopy. In vitro fertilizing capacity was assessed by in vitro fertilization of bovine oocytes with spermatozoa obtained by each separation method.Cleavage rates were determined after three days of in vitro culture. The results were analyzed using generalized linear models (GLM) and means of the four methods were compared using the Tukey test. The CushionFluid was superior for most parameters of sperm motility as well as for intact acrosome (p&lt;0.05). Higher means of sperm vitality were obtained with EquiPure and Percoll (p&lt;0.05), but no difference were found on cleavage rates between treatments. It was concluded that cryopreserved stallion semen selected by the CushionFluid method had better sperm quality compared to the other three methods; however no difference was evident between them for in vitro fertilizing capacity of spermatozoa.El objetivo del presente estudio fue evaluar el efecto de cuatro métodos de separación seminal sobre la calidad y la capacidad fertilizante in vitro de espermatozoides equinos criopreservados. Se utilizaron pajillas de semen equino criopreservado para la separación espermática a través de los métodos Androcoll, CushionFluid, EquiPure y Percoll. Mediante un sistema analizador de clase (SCA®) se evaluó la motilidad total, motilidad progresiva, velocidad curvilínea, velocidad lineal y velocidad media, y por microscopía de fluorescencia se determinaron los acrosomas intactos y la vitalidad espermática. La evaluación de la capacidad fertilizante in vitro se realizó mediante la fertilización in vitro de oocitos bovinos con espermatozoides obtenidos en cada método de separación. El clivaje se determinó después de tres días de cultivo in vitro. Los resultados se analizaron mediante modelos lineales generalizados (GLM) y las medias para los diferentes métodos se compararon usando la prueba de Tukey. El CushionFluid fue superior para la mayoría de parámetros de movilidad espermática, así como para acrosomas intactos (p&lt;0.05). Se encontraron medias superiores de vitalidad espermática para EquiPure y Percoll (p&lt;0.05), pero no se encontró diferencia entre las medias de clivaje entre tratamientos. Se concluye que el semen equino criopreservado y seleccionado por el método CushionFluid presenta mejores parámetros de calidad espermática respecto a los otros tres métodos; sin embargo, no se evidencia diferencia entre ellos para la capacidad fertilizante in vitro de los espermatozoides

The Unique Origin of Colors of Armchair Carbon Nanotubes

The colors of suspended metallic colloidal particles are determined by their size-dependent plasma resonance, while those of semiconducting colloidal particles are determined by their size-dependent band gap. Here, we present a novel case for armchair carbon nanotubes, suspended in aqueous medium, for which the color depends on their size-dependent excitonic resonance, even though the individual particles are metallic. We observe distinct colors of a series of armchair-enriched nanotube suspensions, highlighting the unique coloration mechanism of these one-dimensional metals.Comment: 4 pages, 3 figure

A New Route to Fluorescent SWNT/Silica Nanocomposites: Balancing Fluorescence Intensity and Environmental Sensitivity

We investigate the relationship between photoluminescence (PL) intensity and environmental sensitivity of surfactant-wrapped single walled carbon nanotubes (SWNTs). SWNTs were studied under a variety of conditions in suspension as well as encapsulated in silica nanocomposites, which were prepared by an efficient chemical vapor into liquids (CViL) sol-gel process. The dramatically improved silica encapsulation process described here has several advantages, including fast preparation and high SWNT loading concentration, over other encapsulation methods used to prepare fluorescent SWNT/silica nanocomposites. Further, addition of glycerol to SWNT suspensions prior to performing the CViL sol-gel process allows for the preparation of freestanding fluorescent silica xerogels, which to the best of our knowledge is the first report of such nanocomposites. Our spectroscopic data on SWNTs suspended in aqueous surfactants or encapsulated in silica show that achieving maximum PL intensity results in decreased sensitivity of SWNT emission response to changes imparted by the local environment. In addition, silica encapsulation can be used to "lock-in" a surfactant micelle structure surrounding SWNTs to minimize interactions between SWNTs and ions/small molecules. Ultimately, our work demonstrates that one should consider a balance between maximum PL intensity and the ability to sense environmental changes when designing new SWNT systems for future sensing applications