Página 1 dos resultados de 5870 itens digitais encontrados em 0.025 segundos

PLGA nanoparticles containing praziquantel: effect of formulation variables on size distribution

Mainardes, R. M.; Evangelista, R. C.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 137-144
ENG
Relevância na Pesquisa
45.87%
Praziquantel has been shown to be highly effective against all known species of Schistosoma infecting humans. Spherical nanoparticulate drug carriers made of poly(D,L-lactide-co-glycolide) acid with controlled size were designed. Praziquantel, a hydrophobic molecule, was entrapped into the nanoparticles with theoretical loading varying from 10 to 30% (w/w). This investigates the effects of some process variables on the size distribution of nanoparticles prepared by emulsion-solvent evaporation method. The results show that sonication time, PLGA and drug amounts, PVA concentration, ratio between aqueous and organic phases, and the method of solvent evaporation have a significant influence on size distribution of the nanoparticles. (C) 2004 Elsevier B.V. All rights reserved.

Study of ITO@PMMA composites by transmission electron microscopy

Arlindo, Elen P. S.; Orlandi, Marcelo O.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência Formato: 183-188
ENG
Relevância na Pesquisa
45.79%
ITO nanowires were synthesized by carbothermal reduction process, using a co-evaporation method, and have controlled size, shape, and chemical composition. The electrical measurements of nanowires showed they have a resistance of about 102 Ω. In order to produce nanocomposites films, nanowires were dispersed in toluene using an ultrasonic cleaner, so the PMMA polymer was added, and the system was kept under agitation up to obtain a clear suspension. The PMMA polymer was filled with 1, 2, 5 and 10% in weight of nanowires, and the films were done by tape casting. The results showed that the electrical resistance of nanocomposites changed by over 7 orders of magnitude by increasing the amount of filler, and using 5 wt% of filler the composite resistance decreased from 1010 Ω to about 104 Ω, which means that percolation threshold of wires occurred at this concentration. This is an interesting result once for nanocomposites filled with ITO nanoparticles is necessary about 18% in weight to obtain percolation. The addition of filler up to 10 wt% decreased the resistance of the composite to 103 Ω, which is a value close to the resistance of wires. The composites were also analyzed by transmission electron microscopy (TEM), and the TEM results are in agreement with the electrical ones about percolation of nanowires. These results are promising once indicates that is possible to produce conductive and transparent in the visible range films by the addition of ITO nanowires in a polymeric matrix using a simple route. © 2011 Materials Research Society.

Desenvolvimento de sistemas de liberação modificada para herbicidas triazínicos utilizando nanocápsulas poliméricas; Development of controlled release systems for triazine herbicides using polymeric nanocapsules

Renato Grillo
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 19/07/2011 PT
Relevância na Pesquisa
35.85%
Muitas das novas tecnologias desenvolvidas atualmente envolvem a nanobiotecnologia, dentre elas, os sistemas carreadores nanoestruturados poliméricos. Os sistemas nanoestruturados poliméricos (SNP) agem como compartimentos transportadores de substâncias bioativas e apresentam tamanho inferior a 1 ?m. Estes sistemas têm a capacidade de alterar as propriedades físico-químicas dos compostos a eles incorporados, levando a algumas vantagens. Para herbicidas estes sistemas podem ser responsáveis pela redução na quantidade de substância química necessária para o controle de pragas, diminuição no risco de poluição ambiental, redução na quantidade de energia gasta, uma vez que se reduz o número de aplicações necessárias comparadas às formulações convencionais e aumento na segurança das pessoas responsáveis pela aplicação do produto no campo. Neste trabalho pretende-se introduzir esta nova abordagem tecnológica de sistemas de liberação modificada para herbicidas triazínicos, preparando e caracterizando dois tipos de nanocápsulas obtidas do polímero biodegradável poli(_-caprolactona) (PCL). Os herbicidas triazínicos escolhidos foram ametrina, atrazina e simazina devido a sua ampla utilização em plantações de cana-de-açúcar e milho no Brasil. Em uma primeira etapa deste projeto foram preparadas nanocápsulas pelo método deposição interfacial de polímero préformado e analisadas quanto sua eficiência de encapsulação...

A new and practical method to obtain grain size measurements in sandy shores based on digital image acquisition and processing

Baptista, Paulo; Cunha, Telmo; Gama, Cristina; Bernardes, Cristina
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
35.87%
Modern methods for the automated evaluation of sediment size in sandy shores relay on digital image processing algorithms as an alternative to time-consuming traditional sieving methodologies. However, the requirements necessary to guarantee that the considered image processing algorithm has a good grain identification success rate impose the need for dedicated hardware setups to capture the sand surface images. Examples are specially designed camera housings that maintain a constant distance between the camera lens and the sand surface, tripods to fix and maintain the camera angle orthogonal to the sand surface, external illumination systems that guarantee the light level necessary for the image processing algorithms, and special lenses and focusing systems for close proximity image capturing. In some cases, controlled image-capturing conditions can make the fieldwork more laborious which incurs in significant costs formonitoring campaigns considering large areas. To circumvent this problem, it is proposed a new automated image-processing algorithm that identifies sand grains in digital images acquired with a standard digital camera without any extra hardware attached to it. The accuracy and robustness of the proposed algorithm are evaluated in this work by means of a laboratory test on previously controlled grain samples...

A new and practical method to obtain grain size measurements in sandy shores based

Baptista, Paulo; Cunha, Telmo; Gama, Cristina; Bernardes, Cristina
Fonte: Sedimentary Geology Publicador: Sedimentary Geology
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
35.87%
Modern methods for the automated evaluation of sediment size in sandy shores relay on digital image processing algorithms as an alternative to time-consuming traditional sieving methodologies. However, the requirements necessary to guarantee that the considered image processing algorithm has a good grain identification success rate impose the need for dedicated hardware setups to capture the sand surface images. Examples are specially designed camera housings that maintain a constant distance between the camera lens and the sand surface, tripods to fix and maintain the camera angle orthogonal to the sand surface, external illumination systems that guarantee the light level necessary for the image processing algorithms, and special lenses and focusing systems for close proximity image capturing. In some cases, controlled image-capturing conditions can make the fieldwork more laborious which incurs in significant costs for monitoring campaigns considering large areas. To circumvent this problem, it is proposed a new automated image-processing algorithm that identifies sand grains in digital images acquired with a standard digital camera without any extra hardware attached to it. The accuracy and robustness of the proposed algorithm are evaluated in this work by means of a laboratory test on previously controlled grain samples...

Embryonic stem cell bioprinting for uniform and controlled size embryoid body formation

Xu, Feng; Sridharan, BanuPriya; Wang, ShuQi; Gurkan, Umut Atakan; Syverud, Brian; Demirci, Utkan
Fonte: American Institute of Physics Publicador: American Institute of Physics
Tipo: Artigo de Revista Científica
Publicado em 29/06/2011 EN
Relevância na Pesquisa
45.87%
Embryonic stem cells (ESCs) are pluripotent with multilineage potential to differentiate into virtually all cell types in the organism and thus hold a great promise for cell therapy and regenerative medicine. In vitro differentiation of ESCs starts with a phase known as embryoid body (EB) formation. EB mimics the early stages of embryogenesis and plays an essential role in ESC differentiation in vitro. EB uniformity and size are critical parameters that directly influence the phenotype expression of ESCs. Various methods have been developed to form EBs, which involve natural aggregation of cells. However, challenges persist to form EBs with controlled size, shape, and uniformity in a reproducible manner. The current hanging-drop methods are labor intensive and time consuming. In this study, we report an approach to form controllable, uniform-sized EBs by integrating bioprinting technologies with the existing hanging-drop method. The approach presented here is simple, robust, and rapid. We present significantly enhanced EB size uniformity compared to the conventional manual hanging-drop method.

Characterization and properties of micro- and nanowires of controlled size, composition, and geometry fabricated by electrodeposition and ion-track technology

Toimil-Molares, Maria Eugenia
Fonte: Beilstein-Institut Publicador: Beilstein-Institut
Tipo: Artigo de Revista Científica
Publicado em 17/12/2012 EN
Relevância na Pesquisa
45.84%
The combination of electrodeposition and polymeric templates created by heavy-ion irradiation followed by chemical track etching provides a large variety of poly- and single-crystalline nanowires of controlled size, geometry, composition, and surface morphology. Recent results obtained by our group on the fabrication, characterization and size-dependent properties of nanowires synthesized by this technique are reviewed, including investigations on electrical resistivity, surface plasmon resonances, and thermal instability.

Kinetic Assembly of Near-IR Active Gold Nanoclusters using Weakly Adsorbing Polymers to Control Size

Tam, Jasmine M.; Murthy, Avinash K.; Ingram, Davis R.; Nguyen, Robin; Sokolov, Konstantin V.; Johnston, Keith P.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/06/2010 EN
Relevância na Pesquisa
35.87%
Clusters of metal nanoparticles with an overall size less than 100 nm and high metal loadings for strong optical functionality, are of interest in various fields including microelectronics, sensors, optoelectronics and biomedical imaging and therapeutics. Herein we assemble ~5 nm gold particles into clusters with controlled size, as small as 30 nm and up to 100 nm, which contain only small amounts of polymeric stabilizers. The assembly is kinetically controlled with weakly adsorbing polymers, PLA(2K)-b-PEG(10K)-b-PLA(2K) or PEG (MW = 3350), by manipulating electrostatic, van der Waals (VDW), steric, and depletion forces. The cluster size and optical properties are tuned as a function of particle volume fractions and polymer/gold ratios to modulate the interparticle interactions. The close spacing between the constituent gold nanoparticles and high gold loadings (80–85% w/w gold) produce a strong absorbance cross section of ~9×10−15 m2 in the NIR at 700 nm. This morphology results from VDW and depletion attractive interactions that exclude the weakly adsorbed polymeric stabilizer from the cluster interior. The generality of this kinetic assembly platform is demonstrated for gold nanoparticles with a range of surface charges from highly negative to neutral...

Growth of arrays of oriented epitaxial platinum nanoparticles with controlled size and shape by natural colloidal lithography

Komanicky, Vladimir; Barbour, Andi; Lackova, Miroslava; Zorko, Milena; Zhu, Chenhui; Pierce, Michael; You, Hoydoo
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Publicado em 05/07/2014 EN
Relevância na Pesquisa
45.93%
We developed a method for production of arrays of platinum nanocrystals of controlled size and shape using templates from ordered silica bead monolayers. Silica beads with nominal sizes of 150 and 450 nm were self-assembled into monolayers over strontium titanate single crystal substrates. The monolayers were used as shadow masks for platinum metal deposition on the substrate using the three-step evaporation technique. Produced arrays of epitaxial platinum islands were transformed into nanocrystals by annealing in a quartz tube in nitrogen flow. The shape of particles is determined by the substrate crystallography, while the size of the particles and their spacing are controlled by the size of the silica beads in the monolayer mask. As a proof of concept, arrays of platinum nanocrystals of cubooctahedral shape were prepared on (100) strontium titanate substrates. The nanocrystal arrays were characterized by atomic force microscopy, scanning electron microscopy, and synchrotron X-ray diffraction techniques.

The impact of group size on software architecture evaluation: a controlled experiment

Ali Babar, Muhammad; Kitchenham, Barbara
Fonte: IEEE Computer Society Publicador: IEEE Computer Society
Tipo: Conference item; all_ul_research; ul_published_reviewed; none
ENG
Relevância na Pesquisa
35.96%
peer-reviewed; Background: An important element in scenario-based architecture evaluation is the development of scenario profiles by stakeholders working in groups. In practice groups can vary in size from 2 to 20 people. Currently, there is no empirical evidence about the impact of group size on the scenario development activity. Goal: Our experimental goal was to investigate the impact of group size on the quality of scenario profiles developed by different sizes of groups. Experimental design: We had 165 subjects, who were randomly assigned to 10 groups of size 3, 13 groups of size 5, and 10 groups of size 7. Participants were asked to develop scenario profiles. After the experiment each participant completed a questionnaire aimed at identifying their opinion of the group activity. Result: The average quality score for group scenario profiles for 3 person groups was 362.4, for groups of 5 person groups was 534.23 and for 7 person groups was. 444.5. The quality of scenario profiles for groups of size 5 was significantly greater than the quality of scenario profiles for groups of size 3 (p=0.025), but there was no difference between the size 3 and size 7 groups. However, participants in groups of size 3 had a significantly better opinion of the group activity outcome and their personal interaction with their group than participants in groups of size 5 or 7. Conclusion: Our results suggest that the quality of the output from a group does not increase linearly with group size. However...

RALLOC: Stata module to design randomized controlled trials

Ryan, Philip
Fonte: Boston College Department of Economics Publicador: Boston College Department of Economics
Tipo: Software
Publicado em //1997 EN
Relevância na Pesquisa
35.85%
ralloc provides a sequence of treatments randomly permuted in blocks of constant or varying size. If not constant, the size and order of the blocks are also random. Allocation may be stratified by one or more variables. In non-factorial designs, up to 10 treatments may be specified. Randomisation may also proceed simultaneously on 2 factors: 2x2, 2x3, 3x2, 3x3, 2x4, 4x2, 3x4, 4x3 and 4x4 factorial designs are supported, or on 3 factors for 2x2x2, 2x2x3, 2x3x3 and 3x3x3 designs. ralloc will also handle a 2x2 crossover design with or without a supplementary 3rd period as either a "switchback" or "extra period" design (Jones and Kenward 1989). A typical use of ralloc is in a randomised controlled clinical trial (RCT), and, in particular, in a multicentred trial where balance in treatment allocations may be desirable within centre and other defined strata. This is version 3.4.3 of the software, updated from the version published in STB-54. A test data file is included in raltest6.dta.; Philip Ryan

The IDEAL study: investigation of dietary advice and lifestyle for women with borderline gestational diabetes: a randomised controlled trial - study protocol

Crowther, C.; Hague, W.; Middleton, P.; Baghurst, P.; McPhee, A.; Tran, T.; Yelland, L.; Ashwood, P.; Han, S.; Dodd, J.; Robinson, J.
Fonte: BioMed Central Ltd. Publicador: BioMed Central Ltd.
Tipo: Artigo de Revista Científica
Publicado em //2012 EN
Relevância na Pesquisa
35.85%
BACKGROUND: The Australian Carbohydrate Intolerance Study in Pregnant Women (ACHOIS) showed that treatment of pregnant women with mild gestational diabetes mellitus is beneficial for both women and their infants. It is still uncertain whether there are benefits of similar treatment for women with borderline gestational diabetes. This trial aims to assess whether dietary and lifestyle advice and treatment given to pregnant women who screen for borderline gestational diabetes reduces neonatal complications and maternal morbidities. METHODS/DESIGN: Design: Multicentre, randomised controlled trial. Inclusion criteria: Women between 240 and 346 weeks gestation with a singleton pregnancy, a positive oral glucose challenge test (venous plasma glucose ≥7.8 mmol/L) and a normal oral 75 gram glucose tolerance test (fasting venous plasma glucose <5.5 mmol/L and a 2 hour glucose <7.8 mmol/L) with written, informed consent. Trial entry and randomisation: Women with an abnormal oral glucose tolerance test (fasting venous plasma glucose ≥5.5 mmol/L or 2 hour glucose ≥7.8 mmol/L) will not be eligible and will be offered treatment for gestational diabetes, consistent with recommendations based on results of the ACHOIS trial. Eligible women will be randomised into either the ‘Routine Care Group’ or the ‘Intervention Group’. Study groups: Women in the ‘Routine Care Group’ will receive routine obstetric care reflecting current clinical practice in Australian hospitals. Women in the ‘Intervention Group’ will receive obstetric care...

A randomized controlled trial to assess the clinical and cost effectiveness of a nurse-led Antenatal Asthma Management Service in South Australia (AAMS study)

Grzeskowiak, L.; Dekker, G.; Rivers, K.; Roberts-Thomson, K.; Roy, A.; Davies, M.; Beilby, J.; Wilson, A.; Middleton, P.; Ruffin, R.; Karnon, J.; Clifton, V.
Fonte: BioMed Central Publicador: BioMed Central
Tipo: Artigo de Revista Científica
Publicado em //2014 EN
Relevância na Pesquisa
35.89%
Background: Pregnancy presents a unique situation for the management of asthma as it can alter the course of asthma severity and its treatment, which in turn can affect pregnancy outcomes. Despite awareness of the substantial adverse effects associated with asthma during pregnancy, little has been done to improve its management and reduce associated perinatal morbidity and mortality. The aim of this randomized controlled trial is to evaluate the clinical and cost effectiveness of an Antenatal Asthma Management Service. Methods/design: Design: Multicentre, randomized controlled trial. Inclusion criteria: Women with physician diagnosed asthma, which is not currently in remission, who are less than 20 weeks gestation with a singleton pregnancy and do not have a chronic medical condition. Trial entry and randomization: Eligible women with asthma, stratified by treatment site, disease severity and parity, will be randomized into either the ‘Standard Care Group’ or the ‘Intervention Group’. Study groups: Both groups will be followed prospectively throughout pregnancy. Women in the ‘Standard Care Group’ will receive routine obstetric care reflecting current clinical practice in Australian hospitals. Women in the ‘Intervention Group’ will receive additional care through the nurse-led Antenatal Asthma Management Service...

Stimulation der Wundheilung durch wiederholte lokale Applikation von Insulin-like growth factor-I (IGF-I) unter dem Aspekt unterschiedlicher Applikationsformen; Improvement of steroid induced delayed cutaneous wound healing by controlled topi-cal application of Insulin-like Growth Factor I (IGF-I) in rats

Haack, Sebastian
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
DE_DE
Relevância na Pesquisa
35.9%
Einleitung: Die Wirksamkeit einer lokalen Therapie mit Insulin-like growth factor-I (IGF-I) zur Stimulation der kutanen Wundheilung scheint erheblich vom verwendeten Trägersystem und der damit verbundenen Applikationskinetik abhängig zu sein. Bisher konnte bei lokaler Anwendung nur für die Kombination aus IGF-I und einem seiner Bindungsproteine ein positiver Effekt nachgewiesen werden, während hingegen IGF-I alleine nur in einer unphysiologisch hohen Dosierung eine beschleunigte Heilung induzieren konnte. Wurde IGF-I als Monosubstanz jedoch kontinuierlich lokal appliziert, war wiederum ein schnellerer Wundverschluß zu beobachten. Eine wiederholte lokale Verabreichung von IGF-I ist bisher jedoch noch nicht beforscht worden. Ziel der vorliegenden Arbeit war es daher, im Tiermodell den Effekt von wiederholt lokal appliziertem IGF-I auf die kutane Wundheilung unter dem Aspekt unterschiedlicher Applikationsformen zu untersuchen. Material und Methoden: Es wurden dabei zwei verschiedene Trägersysteme, nämlich ein Hydrogelverband und ein Methylzellulose-Gel, gewählt. Bei 40 männlichen Sprague-Dawley Ratten wurden 8 mm durchmessende Vollhaut-defekte am Rücken induziert. Diese Tiere wurden in zwei Gruppen eingeteilt: die eine Gruppe erhielt zur Induktion einer verzögerten Heilung subkutan ein Depot-Steroidpräparat (Depo-Medrate...

Systematische Untersuchung der kontrollierten Partikelabscheidung aus überkritischem Kohlendioxid und Entwicklung geeigneter Trägersysteme; Systematic enquiry of controlled particle deposition from supercritical carbon dioxide and development of suitable carrier systems

Metzger, Philipp
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
DE_DE
Relevância na Pesquisa
35.91%
Die Verkleinerung von Arzneistoffpartikeln stellt ein gängiges Verfahren zur Verbesserung ihrer Lösungseigenschaften dar. Eine solche Zerkleinerung kann durch die kontrollierte Paritkelabscheidung (controlled particle deposition – CPD) aus überkritischem Kohlendioxid in poröse Träger hinein erreicht werden. Dabei entsteht unmittelbar die fertige Arzneiform. Die Arbeit beinhaltet zum einen die Entwicklung poröser Träger für die kontrollierte Partikelabscheidung, basierend auf Ammoniumcarbonat, Natriumhydrogencarbonat und Natriumchlorid als Porenbildner. Die Träger können dabei durch ihre mechanische Stabilität, Porosität und die Prozessstabilität charakterisiert werden. Außerdem wird ihre Porengrößenverteilung durch eine neue mikroskopische Methode bestimmt. Weiterhin wird der Modellarzneistoff Cumarin in seinen physikochemischen Eigenschaften untersucht. Abschließend werden Beladungsstrategien für diese Trägertypen vorgestellt, und die Eigenschaften der beladenen Träger durch Fluoreszenzmikroskopie, Thermoanalyse, Sorptions-, Gehalts- und Freistetzungsuntersuchungen beschrieben. Insbesondere wird auf die Entwicklung einer Gleichung zur Vorhersage des Gehaltes und die Interaktionen zwischen Trägermaterial und Modellarzneistoff eingegangen.; The reduction of a drugs particle size is a common method of improving its dissolution properties. This can be achieved by the method of controlled particle deposition (CPD) from supercritical carbon dioxide into porous carrier systems. Thereby an applicable dosage form is generated. This work includes the development of carrier systems for controlled particle deposition based on ammoniumcarbonate...

Controlled Radical Polymerization in the Dispersed Phase

Thomson, Mary
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
35.97%
Controlled radical polymerization (CRP) has emerged as a powerful method of creating polymers with tailored molecular architectures under mild reaction conditions. However, production of these polymers efficiently at an industrial scale will likely require them to be synthesized in the dispersed phase. Three types of CRP are explored, Atom Transfer Radical Polymerization (ATRP), Nitroxide Mediated Polymerization (NMP) and Catalytic Chain Transfer (CCT) to elucidate the intricacies of creating these novel polymer colloids. Compartmentalization in an ATRP dispersed phase system is explored theoretically to understand the effects of particle size and catalyst concentration on the polymerization. The results suggest that there is an optimal range of particle sizes where the rate of polymerization is greater than that in an equivalent bulk system while maintaining both a lower PDI (polydispersity index) and higher livingness. All three factors are desirable in ATRP but generally cannot be achieved simultaneously in bulk. Compartmentalization manifests itself differently in CCT dispersed phase systems, where the segregation of the CCT agents into different polymer particles leads to multimodal molecular weight distributions. Control over the particle size is notoriously difficult for nitroxide mediated polymerization...

A reminiscence program intervention to improve the quality of life of long-term care residents with Alzheimer's disease: a randomized controlled trial

Serrani Azcurra,Daniel Jorge Luis
Fonte: Associação Brasileira de Psiquiatria - ABP Publicador: Associação Brasileira de Psiquiatria - ABP
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2012 EN
Relevância na Pesquisa
35.85%
OBJECTIVE: A single-blinded, parallel-groups (intervention, active and passive control groups) randomized controlled trial (RCT) was chosen to investigate whether a specific reminiscence program is associated with higher levels of quality of life in nursing home residents with dementia. METHODS: The intervention used a life-story approach, while the control groups participated in casual discussions. The Social Engagement Scale (SES) and Self Reported Quality of Life Scale (SRQoL) were used as the outcome measures, which were examined at baseline (T0), 12 weeks (T1), and six months (T2) after the intervention. The final sample had 135 subjects (active control group = 45; passive control group = 45; intervention group = 45). RESULTS: The Wilcoxon test showed significant differences in the intervention group between T2 and T0, and between T1 and T0 in the SES, and there were significant differences between T0 and T1 (intervention effect size = 0.267) and T1 and T2 (intervention effect size = 0.450) in the SRQoL. The univariate logistic regression scores showed that predictors of change in the SRQoL were associated with fewer baseline anxiety symptoms and lower depression scores. CONCLUSIONS: The intervention led to significant differences between the three groups over time...

Surfactant effects in monodisperse magnetite nanoparticles of controlled size

Guardia, P.; Batlle-Brugal, B.; Roca, A. G.; Iglesias, Oscar; Morales, M. P.; Serna, C. J.; Labarta, A.; Batlle, X.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 15/09/2006
Relevância na Pesquisa
45.79%
Monodisperse magnetite Fe3O4 nanoparticles of controlled size within 6 and 20 nm in diameter were synthesized by thermal decomposition of an iron organic precursor in an organic medium. Particles were coated with oleic acid. For all samples studied, saturation magnetization Ms reaches the expected value for bulk magnetite, in contrast to results in small particle systems for which Ms is usually much smaller due to surface spin disorder. The coercive field for the 6 nm particles is also similar to that of bulk magnetite. Both results suggest that the oleic acid molecules covalently bonded to the nanoparticle surface yield a strong reduction in the surface spin disorder. However, although the saturated state may be similar, the approach to saturation is different and, in particular, the high-field differential susceptibility is one order of magnitude larger than in bulk materials. The relevance of these results in biomedical applications is discussed.; Comment: 3 pages, 3 figures. Presented at JEMS 2006 (San Sebastian, Spain). Submitted to JMMM

The Role of Threshold Size in Insect Metamorphosis and Body Size Regulation

Preuss, Kevin Michael
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Dissertação Formato: 620250 bytes; application/pdf
Publicado em //2010 EN_US
Relevância na Pesquisa
35.86%

The initiation of metamorphosis causes the cessation of the larval growth period which determines the final body size of adult insects. Because larval growth is roughly exponential, differences in timing the initiation of metamorphosis can cause large differences body size. Although many of the processes involved in metamorphosis have been well characterized, little is known about how the timing of the initiation of metamorphosis is determined.

Using different strains from Tribolium castaneum, Tribolium freemani, and Manduca sexta and varied nutritional conditions, I was able to document the existence of a threshold size, which determines when the larva becomes competent to metamorphose. Threshold size, however, does not dictate the exact timing of initiation. The exact timing for the initiation of metamorphosis is determined by a pulse of the molting hormone, ecdysone, but only after threshold size has been reached. Ecdysone pulses before the larva attains threshold size only cause the larva to molt to another larval instar. These results indicate the timing of metamorphosis initiation is controlled by two factors: (1) attainment of threshold size, at which the larva becomes competent to initiate metamorphosis and (2) the timing of an ecdysone pulse after attaining threshold size.

I hypothesize the attainment of threshold size...

Control of the grain size distribution of the raw material mixture in the production of iron sinter

Lwamba,E.; Garbers-Craig,A.M.
Fonte: Journal of the Southern African Institute of Mining and Metallurgy Publicador: Journal of the Southern African Institute of Mining and Metallurgy
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/05/2008 EN
Relevância na Pesquisa
35.99%
The aim of this study was to examine the effect of grain size distribution control of the raw material mixture on the permeability of the green sinter bed and the properties of the produced sinter. This was achieved by evaluating the granulation characteristics of the sinter mixture (moisture content, ranulation time and mean granule diameter) in terms of its green bed permeability, and evaluating the productivity of the sinter bed, the coke rate, tumble index (TI), abrasion index (AI), reduction disintegration index (RDI) and reducibility (RI) of the produced sinter. The raw sinter mixtures contained combinations of Thabazimbi iron ore, Sishen iron ore, coke, lime and return fines. The grain size distributions were controlled by removing the -0.5 mm size fractions of the return fines and coke, and the -1 mm size fraction of lime. Of the examined mixtures, a mixture of 20 mass% Thabazimbi iron ore, 80 mass% Sishen iron ore and fluxes where the coke, lime and return fines were all sized had the highest granulation effectiveness and permeability. The sintering properties of the mixtures in which the grain size distributions were controlled, were very similar for all the mixtures, but superior to the base case mixture in which the grain size distribution was not controlled.