Comparison of laser performances of 5at.% Yb : Gd2xY2(1-x)SiO5 crystals between different cutting directions

We investigate the laser actions of 5at.% Yb:Gd2xY2(1-x)SiO5 (Yb:GYSO; x = 0.1) crystals with different cutting directions, parallel and vertical to the growth axis. Our results show that the cutting direction of the sample plays an astonished role in the laser operation. The sample cut vertically to the growth axis possesses the favourable lasing characteristics. Its output power reaches 3.13W at 1060nm with a slope efficiency of 44.68% when the absorbed pump power is 8.9 W. In contrast, the sample cut parallel reaches only 1.65 W at 1044 nm with a slope elLiciency of 33.76% with absorbed pump power of 7.99 W. The absorption and emission spectra of the two samples are examined and the merit factor M is calculated. Our analysis is in agreement well with the experimental results. The wavelength tuning range of the superior sample covers from 1013.68 nm to 1084.82 nm.

Zeitweilige Schillzunahme als Voraussetzung starker Miesmuscheljahrgänge

The sandy and muddy bottom of tbe German Waddensea offers a great diversity of secondary substrates to mussel larvae ready to settle. But every substrate with the exception of dead shell material may result in very small mussel colonies only. Large mussel beds of a size up to many hectares depend on aggregations of molluscan shells covering comparably areas of ground. Such shell aggregations are created by extremely cold winters and during years with extended stormy periods.

Makrelen- und Holzmakrelenfänge stimmen zuversichtlich

In order to determine the abundance of incoming year classes of both mackerel and horse mackerel a couple of research vessels in the frame of ICES investigats waters west of the British Isles, the Gulf of Biscay and areas west of the Iberian Peninsula in the first half of each third year. In 1995, Germany took place in these investigations with R.V. "Walther Herwig III" from March 23 to April 18. A total of 100 plankton stations were made using a Gulf - III - Sampier between Fastnet Rock and the Gironde estuary. In addition, 87 fishing stations were occupied by a GOV net. Though fish indications were not fished on purpose large amounts of especially horse mackerel and mackerel were gained in the half hour tows. Besides, boarfish (Capros aper L.), blue whiting, and sprat were found in considerable quantities and numbers in some areas. The hydrographc situation was as expected: The development of a surfaee thermocline created by radiation indieates the collapse of the vertically homogeneous situation of the winter period.

Extracting material response from simple mechanical tests on hardening-softening-hardening viscoplastic solids

Compliant foams are usually characterized by a wide range of desirable mechanical properties. These properties include viscoelasticity at different temperatures, energy absorption, recoverability under cyclic loading, impact resistance, and thermal, electrical, acoustic and radiation-resistance. Some foams contain nano-sized features and are used in small-scale devices. This implies that the characteristic dimensions of foams span multiple length scales, rendering modeling their mechanical properties difficult. Continuum mechanics-based models capture some salient experimental features like the linear elastic regime, followed by non-linear plateau stress regime. However, they lack mesostructural physical details. This makes them incapable of accurately predicting local peaks in stress and strain distributions, which significantly affect the deformation paths. Atomistic methods are capable of capturing the physical origins of deformation at smaller scales, but suffer from impractical computational intensity. Capturing deformation at the so-called meso-scale, which is capable of describing the phenomenon at a continuum level, but with some physical insights, requires developing new theoretical approaches.

A fundamental question that motivates the modeling of foams is ‘how to extract the intrinsic material response from simple mechanical test data, such as stress vs. strain response?’ A 3D model was developed to simulate the mechanical response of foam-type materials. The novelty of this model includes unique features such as the hardening-softening-hardening material response, strain rate-dependence, and plastically compressible solids with plastic non-normality. Suggestive links from atomistic simulations of foams were borrowed to formulate a physically informed hardening material input function. Motivated by a model that qualitatively captured the response of foam-type vertically aligned carbon nanotube (VACNT) pillars under uniaxial compression [2011,“Analysis of Uniaxial Compression of Vertically Aligned Carbon Nanotubes,” J. Mech.Phys. Solids, 59, pp. 2227–2237, Erratum 60, 1753–1756 (2012)], the property space exploration was advanced to three types of simple mechanical tests: 1) uniaxial compression, 2) uniaxial tension, and 3) nanoindentation with a conical and a flat-punch tip. The simulations attempt to explain some of the salient features in experimental data, like
1) The initial linear elastic response.
2) One or more nonlinear instabilities, yielding, and hardening.

The model-inherent relationships between the material properties and the overall stress-strain behavior were validated against the available experimental data. The material properties include the gradient in stiffness along the height, plastic and elastic compressibility, and hardening. Each of these tests was evaluated in terms of their efficiency in extracting material properties. The uniaxial simulation results proved to be a combination of structural and material influences. Out of all deformation paths, flat-punch indentation proved to be superior since it is the most sensitive in capturing the material properties.

Magnetic alignment of high-aspect ratio microwires into vertical arrays

Fundamental studies of magnetic alignment of highly anisotropic mesostructures can enable the clean-room-free fabrication of flexible, array-based solar and electronic devices, in which preferential orientation of nano- or microwire-type objects is desired. In this study, ensembles of 100 micron long Si microwires with ferromagnetic Ni and Co coatings are oriented vertically in the presence of magnetic fields. The degree of vertical alignment and threshold field strength depend on geometric factors, such as microwire length and ferromagnetic coating thickness, as well as interfacial interactions, which are modulated by varying solvent and substrate surface chemistry. Microwire ensembles with vertical alignment over 97% within 10 degrees of normal, as measured by X-ray diffraction, are achieved over square cm scale areas and set into flexible polymer films. A force balance model has been developed as a predictive tool for magnetic alignment, incorporating magnetic torque and empirically derived surface adhesion parameters. As supported by these calculations, microwires are shown to detach from the surface and align vertically in the presence of magnetic fields on the order of 100 gauss. Microwires aligned in this manner are set into a polydimethylsiloxane film where they retain their vertical alignment after the field has been removed and can subsequently be used as a flexible solar absorber layer. Finally, these microwires arrays can be protected for use in electrochemical cells by the conformal deposition of a graphene layer.

A multi-scale approach to shaping carbon nanotube structures for hollow microneedles

The concept of a carbon nanotube microneedle array is explored in this thesis from multiple perspectives including microneedle fabrication, physical aspects of transdermal delivery, and in vivo transdermal drug delivery experiments. Starting with standard techniques in carbon nanotube (CNT) fabrication, including catalyst patterning and chemical vapor deposition, vertically-aligned carbon nanotubes are utilized as a scaffold to define the shape of the hollow microneedle. Passive, scalable techniques based on capillary action and unique photolithographic methods are utilized to produce a CNT-polymer composite microneedle. Specific examples of CNT-polyimide and CNT-epoxy microneedles are investigated. Further analysis of the transport properties of polymer resins reveals general requirements for applying arbitrary polymers to the fabrication process.

The bottom-up fabrication approach embodied by vertically-aligned carbon nanotubes allows for more direct construction of complex high-aspect ratio features than standard top-down fabrication approaches, making microneedles an ideal application for CNTs. However, current vertically-aligned CNT fabrication techniques only allow for the production of extruded geometries with a constant cross-sectional area, such as cylinders. To rectify this limitation, isotropic oxygen etching is introduced as a novel fabrication technique to create true 3D CNT geometry. Oxygen etching is utilized to create a conical geometry from a cylindrical CNT structure as well as create complex shape transformations in other CNT geometries.

CNT-polymer composite microneedles are anchored onto a common polymer base less than 50 µm thick, which allows for the microneedles to be incorporated into multiple drug delivery platforms, including modified hypodermic syringes and silicone skin patches. Cylindrical microneedles are fabricated with 100 µm outer diameter and height of 200-250 µm with a central cavity, or lumen, diameter of 30 µm to facilitate liquid drug flow. In vitro delivery experiments in swine skin demonstrate the ability of the microneedles to successfully penetrate the skin and deliver aqueous solutions.

An in vivo study was performed to assess the ability of the CNT-polymer microneedles to deliver drugs transdermally. CNT-polymer microneedles are attached to a hand actuated silicone skin patch that holds a liquid reservoir of drugs. Fentanyl, a potent analgesic, was administered to New Zealand White Rabbits through 3 routes of delivery: topical patch, CNT-polymer microneedles, and subcutaneous hypodermic injection. Results demonstrate that the CNT-polymer microneedles have a similar onset of action as the topical patch. CNT-polymer microneedles were also vetted as a painless delivery approach compared to hypodermic injection. Comparative analysis with contemporary microneedle designs demonstrates that the delivery achieved through CNT-polymer microneedles is akin to current hollow microneedle architectures. The inherent advantage of applying a bottom-up fabrication approach alongside similar delivery performance to contemporary microneedle designs demonstrates that the CNT-polymer composite microneedle is a viable architecture in the emerging field of painless transdermal delivery.

Advancing EDL technologies for future space missions : from ground testing facilities to ablative heatshields

Motivated by recent MSL results where the ablation rate of the PICA heatshield was over-predicted, and staying true to the objectives outlined in the NASA Space Technology Roadmaps and Priorities report, this work focuses on advancing EDL technologies for future space missions.

Due to the difficulties in performing flight tests in the hypervelocity regime, a new ground testing facility called the vertical expansion tunnel is proposed. The adverse effects from secondary diaphragm rupture in an expansion tunnel may be reduced or eliminated by orienting the tunnel vertically, matching the test gas pressure and the accelerator gas pressure, and initially separating the test gas from the accelerator gas by density stratification. If some sacrifice of the reservoir conditions can be made, the VET can be utilized in hypervelocity ground testing, without the problems associated with secondary diaphragm rupture.

The performance of different constraints for the Rate-Controlled Constrained-Equilibrium (RCCE) method is investigated in the context of modeling reacting flows characteristic to ground testing facilities, and re-entry conditions. The effectiveness of different constraints are isolated, and new constraints previously unmentioned in the literature are introduced. Three main benefits from the RCCE method were determined: 1) the reduction in number of equations that need to be solved to model a reacting flow; 2) the reduction in stiffness of the system of equations needed to be solved; and 3) the ability to tabulate chemical properties as a function of a constraint once, prior to running a simulation, along with the ability to use the same table for multiple simulations.

Finally, published physical properties of PICA are compiled, and the composition of the pyrolysis gases that form at high temperatures internal to a heatshield is investigated. A necessary link between the composition of the solid resin, and the composition of the pyrolysis gases created is provided. This link, combined with a detailed investigation into a reacting pyrolysis gas mixture, allows a much needed consistent, and thorough description of many of the physical phenomena occurring in a PICA heatshield, and their implications, to be presented.

Through the use of computational fluid mechanics and computational chemistry methods, significant contributions have been made to advancing ground testing facilities, computational methods for reacting flows, and ablation modeling.

Carga de trabalho de enfermeiros: uma análise do Nursing Activities Score (NAS)

Este estudo tem como objeto a carga de trabalho de enfermeiros que trabalham em unidades de cuidados semi-intensivos. Seu objetivo geral foi identificar e analisar a percepção dos enfermeiros de uma unidade semi-intensiva acerca do instrumento Nursing Activities Score - NAS, tendo como foco o conceito de carga de trabalho. Os objetivos específicos foram: identificar domínios do NAS considerados pelos enfermeiros como capazes de avaliar a carga de trabalho; identificar os itens que os enfermeiros consideram relevantes e manteriam no instrumento, os itens que excluiriam e os que acrescentariam; identificar itens que os enfermeiros consideram subdimensionados, para os quais aumentariam a pontuação, os superdimensionados, para os quais diminuiriam a pontuação; e, ao final, discutir implicações dessa avaliação para a organização do trabalho e seus impactos na saúde do trabalhador de enfermagem. Estudo de abordagem quantitativa do tipo descritivo exploratória, com breve aporte qualitativo, utilizando a triangulação metodológica. O local de estudo foi uma unidade de média complexidade com 35 leitos em um hospital privado do Rio de Janeiro. Participaram do estudo 28 enfermeiros e os dados foram coletados por meio de um questionário com perguntas fechadas e abertas no período de abril a maio de 2008. O tratamento dos dados foi realizado com apoio do software Excel, utilizando estatística descritiva. O material qualitativo foi organizado em categorias, usando elementos da Análise de Conteúdo Temática. Entre os domínios, verificou-se que os enfermeiros consideram o que mais avalia a carga real de trabalho o Suporte Ventilatório, com 89%, e o domínio que não avalia a carga de trabalho foi o Suporte Neurológico, com 25%. Os três domínios mais citados para serem acrescidos de atividades foram o Suporte Renal, com 25%, seguido Intervenção Especificas, com 21%, e Suporte Metabólico, respectivamente. Quanto à exclusão de atividades, só dois domínios foram mencionados: Suporte Ventilatório, com 25%, e Atividade Básica, com 21%. Os enfermeiros acham que 69% da pontuação era adequada aos itens e 31% acreditam não estar adequada. No grupo, 27% aumentariam a pontuação em alguns itens e 4% diminuiriam a pontuação. Sobre a mensuração da carga de trabalho, acreditam que essa colabora no processo de trabalho, 79%, e 57% acham que mensurar a carga de trabalho através do NAS pode auxiliar na preservação de sua saúde. Concluímos que esse instrumento mensura a carga de trabalho na opinião dos enfermeiros, mas precisa ser adaptado à realidade da unidade onde está sendo aplicada. Além disso, os enfermeiros alteraram mais os itens relacionados à carga física sem identificar a carga psíquica de trabalho como relevante, evidenciando que o trabalho de enfermagem precisa ser mais bem conhecido pelos enfermeiros no que se refere às dimensões de impacto na sua saúde.

Optical levitation measurements with intensity-modulated light beams

Illumination of an optically levitated particle with an intensity-modulated transverse beam induces a transverse vibration of a particle in an optical trap. Based on this, the trapping force of a trap can be measured. Using an intensity-modulated longitudinal levitating beam causes a particle to move vertically, allowing for the determination of some aerodynamic parameters of a particle in air. The principles and the experimental phenomena are described and the initial results are given. (C) 1997 Optical Society of America.

Rate and Microstructure Effects on the Dynamics of Carbon Nanotube Foams

Soft hierarchical materials often present unique functional properties that are sensitive to the geometry and organization of their micro- and nano-structural features across different lengthscales. Carbon Nanotube (CNT) foams are hierarchical materials with fibrous morphology that are known for their remarkable physical, chemical and electrical properties. Their complex microstructure has led them to exhibit intriguing mechanical responses at different length-scales and in different loading regimes. Even though these materials have been studied for mechanical behavior over the past few years, their response at high-rate finite deformations and the influence of their microstructure on bulk mechanical behavior and energy dissipative characteristics remain elusive.

In this dissertation, we study the response of aligned CNT foams at the high strain-rate regime of 10² - 10⁴ s^-1. We investigate their bulk dynamic response and the fundamental deformation mechanisms at different lengthscales, and correlate them to the microstructural characteristics of the foams. We develop an experimental platform, with which to study the mechanics of CNT foams in high-rate deformations, that includes direct measurements of the strain and transmitted forces, and allows for a full field visualization of the sample’s deformation through high-speed microscopy.

We synthesize various CNT foams (e.g., vertically aligned CNT (VACNT) foams, helical CNT foams, micro-architectured VACNT foams and VACNT foams with microscale heterogeneities) and show that the bulk functional properties of these materials are highly tunable either by tailoring their microstructure during synthesis or by designing micro-architectures that exploit the principles of structural mechanics. We also develop numerical models to describe the bulk dynamic response using multiscale mass-spring models and identify the mechanical properties at length scales that are smaller than the sample height.

The ability to control the geometry of microstructural features, and their local interactions, allows the creation of novel hierarchical materials with desired functional properties. The fundamental understanding provided by this work on the key structure-function relations that govern the bulk response of CNT foams can be extended to other fibrous, soft and hierarchical materials. The findings can be used to design materials with tailored properties for different engineering applications, like vibration damping, impact mitigation and packaging.

Análise de unidades de pré-purificação de ar por adsorção

Os principais constituintes do ar, nitrogênio, oxigênio e argônio, estão cada vez mais presentes nas indústrias, onde são empregados nos processos químicos, para o transporte de alimentos e processamento de resíduos. As duas principais tecnologias para a separação dos componentes do ar são a adsorção e a destilação criogênica. Entretanto, para ambos os processos é necessário que os contaminantes do ar, como o gás carbônico, o vapor dágua e hidrocarbonetos, sejam removidos para evitar problemas operacionais e de segurança. Desta forma, o presente trabalho trata do estudo do processo de pré-purificação de ar utilizando adsorção. Neste sistema a corrente de ar flui alternadamente entre dois leitos adsorvedores para produzir ar purificado continuamente. Mais especificamente, o foco da dissertação corresponde à investigação do comportamento de unidades de pré-purificação tipo PSA (pressure swing adsorption), onde a etapa de dessorção é realizada pela redução da pressão. A análise da unidade de pré-purificação parte da modelagem dos leitos de adsorção através de um sistema de equações diferenciais parciais de balanço de massa na corrente gasosa e no leito. Neste modelo, a relação de equilíbrio relativa à adsorção é descrita pela isoterma de Dubinin-Astakhov estendida para misturas multicomponentes. Para a simulação do modelo, as derivadas espaciais são discretizadas via diferenças finitas e o sistema de equações diferenciais ordinárias resultante é resolvido por um solver apropriado (método das linhas). Para a simulação da unidade em operação, este modelo é acoplado a um algoritmo de convergência relativo às quatro etapas do ciclo de operação: adsorção, despressurização, purga e dessorção. O algoritmo em questão deve garantir que as condições finais da última etapa são equivalentes às condições iniciais da primeira etapa (estado estacionário cíclico). Desta forma, a simulação foi implementada na forma de um código computacional baseado no ambiente de programação Scilab (Scilab 5.3.0, 2010), que é um programa de distribuição gratuita. Os algoritmos de simulação de cada etapa individual e do ciclo completo são finalmente utilizados para analisar o comportamento da unidade de pré-purificação, verificando como o seu desempenho é afetado por alterações nas variáveis de projeto ou operacionais. Por exemplo, foi investigado o sistema de carregamento do leito que mostrou que a configuração ideal do leito é de 50% de alumina seguido de 50% de zeólita. Variáveis do processo foram também analisadas, a pressão de adsorção, a vazão de alimentação e o tempo do ciclo de adsorção, mostrando que o aumento da vazão de alimentação leva a perda da especificação que pode ser retomada reduzindo-se o tempo do ciclo de adsorção. Mostrou-se também que uma pressão de adsorção maior leva a uma maior remoção de contaminantes.

Effect of Microstructural Interfaces on the Mechanical Response of Crystalline Metallic Materials

Advances in nano-scale mechanical testing have brought about progress in the understanding of physical phenomena in materials and a measure of control in the fabrication of novel materials. In contrast to bulk materials that display size-invariant mechanical properties, sub-micron metallic samples show a critical dependence on sample size. The strength of nano-scale single crystalline metals is well-described by a power-law function, σαD^-n, where D is a critical sample size and n is a experimentally-fit positive exponent. This relationship is attributed to source-driven plasticity and demonstrates a strengthening as the decreasing sample size begins to limit the size and number of dislocation sources. A full understanding of this size-dependence is complicated by the presence of microstructural features such as interfaces that can compete with the dominant dislocation-based deformation mechanisms. In this thesis, the effects of microstructural features such as grain boundaries and anisotropic crystallinity on nano-scale metals are investigated through uniaxial compression testing. We find that nano-sized Cu covered by a hard coating displays a Bauschinger effect and the emergence of this behavior can be explained through a simple dislocation-based analytic model. Al nano-pillars containing a single vertically-oriented coincident site lattice grain boundary are found to show similar deformation to single-crystalline nano-pillars with slip traces passing through the grain boundary. With increasing tilt angle of the grain boundary from the pillar axis, we observe a transition from dislocation-dominated deformation to grain boundary sliding. Crystallites are observed to shear along the grain boundary and molecular dynamics simulations reveal a mechanism of atomic migration that accommodates boundary sliding. We conclude with an analysis of the effects of inherent crystal anisotropy and alloying on the mechanical behavior of the Mg alloy, AZ31. Through comparison to pure Mg, we show that the size effect dominates the strength of samples below 10 μm, that differences in the size effect between hexagonal slip systems is due to the inherent crystal anisotropy, suggesting that the fundamental mechanism of the size effect in these slip systems is the same.

Geology of the Pacoima Area, Los Angeles County, California

The Pacoima area is located on an isolated hill in the northeast section of the San Fernando, the northeast portion of the Pacoima Quadrangle, Los Angeles County, California. Within it are exposed more than 2300 feet of Tertiary rocks, which comprise three units of Middle Miocene (?) age, and approximately 950 feet of Jurassic (?) granite basement. The formations are characterized by their mode of occurrence, marine and terrestial origin, diverse lithology, and structural features.

The basement complex is composed of intrusive granite, small masses of granodiorite and a granodiorite gneiss with the development of schistosity in sections. During the long period of erosion of the metamorphics, the granitic rocks were exposed and may have provided clastic constituents for the overlying formations.

As a result of rapid sedimentation in a transitional environment, the Middle Miocene Twin Peaks formation was laid down unconformably on the granite. This formation is essentially a large thinning bed of gray to buff pebble and cobble conglomerate grading to coarse yellow sandstone. The contact of conglomerate and granite is characterized by its faulted and depositional nature.

Beds of extrusive andesite, basalt porphyry, compact vesicular amygdaloidal basalts, andesite breccia, interbedded feldspathic sands and clays of terrestial origin, and mudflow breccia comprise the Pacoima formation which overlies the Twin Peaks formation unconformably. A transgressing shallow sea accompanied settling of the region and initiated deposition of fine clastic sediments.

The marine Topanga (?) formation is composed of brown to gray coarse sandstone grading into interbedded buff sandstones and gray shales. Intrusions of rhyolitedacite and ash beds mark continued but sporatic volcanism during this period.

The area mapped represents an arch in the Tertiary sediments. Forces that produced the uplift of the granite structural high created stresses that were relieved by jointing and faulting. Vertical and horizontal movement along these faults has displaced beds, offset contacts and complicated their structure. Uplift and erosion have exposed the present sequence of beds which dip gently to the northeast. The isolated hill is believed to be in an early stage of maturity.

Zooplankton - fish interaction in the littoral zone of Nyanza Gulf, Lake Victoria

The zooplankton community of the littoral zone of Nyanza Gulf, Lake Victoria, was studied between June 1998 and June 1999 to identify and quantify various zooplankton groups, and investigate the interactions that occur between them and the littoral fish through the food chain. Zooplankton samples were collected from five stations using a 83 micro-m mesh size plankton net hauled vertically through the water column. Fish samples were obtained by beach seine, except at Gingra (May 1999), where trawl samples were used. Gut/stomach analysis was carried out on the three major commercial species, Lates niloticus (L.), Oreochromis niloticus (L.) and Rastrineobola argentea (Pellegrin).

Bathymetric surveys and lake deposits

A progress report on the bathymetric survey of Windereme undertaken in June 1937 by the Hydrographic Department of the Admiralty. The brief article outlines the background of the surveying process as well as the initial effectiveness of the survey work. There is a brief background to the geomorphological processes which were involved in shaping the Lake District topography, as well as some explanation of previous studies undertaken in the area. The report includes a figure showing the cross sections of lake beds and a figure detailing a core from the bottom deposits of Windermere.