Papers by Isaac Flores Diaz
Bulletin of the American Physical Society, 2016
Submitted for the MAR16 Meeting of The American Physical Society Hierarchical assembly of anisotr... more Submitted for the MAR16 Meeting of The American Physical Society Hierarchical assembly of anisotropic particles in AC electric fields. ISAAC TORRES DIAZ, BRADLEY RUPP, XIAOQING HUA, YUGUANG YANG, MICHAEL A. BEVAN, Johns Hopkins University-Hierarchical microstructures composed of colloids are of great interest for technological applications and advanced materials such as metamaterials and microfluidic devices. The dynamics of spherical colloidal particles has been analyzed previously for several systems, and has led to the control of the formation of perfect crystals using AC electric fields. However, spherical particles do not have a dependence on its orientation as anisotropic particles. Recently, researchers reported experiments showing the capabilities of anisotropic particles to assemble in different configurations, yet a detailed understanding of the mechanism and control is lacking. This work shows both theoretical and experimental results of the control of a colloidal system composed of anisotropic colloidal particles with a tri-axial ellipsoidal shape subjected to a non-uniform electric field close to a planar wall. We show that particles pack into different structures and orientations as a function of the applied electric field amplitude and frequency by taking into account dipole-field, dipole-dipole, and colloidal interactions. This analysis provides a theoretical framework for the equilibrium and non-equilibrium structures that can be formed via field mediated interaction, which are validated by experimental microscopy results, and can ultimately be used to engineer the hierarchical assembly of anisotropic particles.
Bulletin of the American Physical Society, 2018
Plant Ecology and Evolution, 2020
Background and aims – Flowers of Jaltomata quipuscoae (Solanaceae) secrete blood-red nectar that ... more Background and aims – Flowers of Jaltomata quipuscoae (Solanaceae) secrete blood-red nectar that serves as an energy reward and possible attractant to pollinators. The purposes of this study were to determine whether simulated pollinator visits (manual removal of nectar) stimulates replenishment of nectar, and report the pattern of nectar presentation during the lifespan of the flower. Methods – For the nectar replenishment experiments flowers were paired: each pair of flowers was selected to be on the same plant and at the same developmental stage. From all 62 flowers nectar was removed and discarded (not measured) at time zero. Then, over a period of eight hours, the nectar of one flower was measured four times, i.e., every two hours, while nectar of the paired control flower was measured only at the end of the eight-hour period. In the nectar dynamics experiment five sets of flowers received different treatments: flowers were unmanipulated for zero, one, two, three or four days a...
P.P.D.Q. Boletín, 1969
El texto es una compilación de los trabajos de diversos autores que se dieron a la tarea de hace... more El texto es una compilación de los trabajos de diversos autores que se dieron a la tarea de hacer una síntesis de los planteamientos pedagógicos de autores como J. Dewey, F. Ferrer, M. Montessori, O. Decroly, A. Makarenko, A.S. Neill, J. Piaget, L. Vigotsky, B.F. Skinner, C. Freinet, I. Illich, B. Berstein y P. Freire
TED: Tecné, Episteme y Didaxis, 2017
Este artículo de investigación presenta los aportes teóricos al conocimiento especializado del pr... more Este artículo de investigación presenta los aportes teóricos al conocimiento especializado del profesor de matemáticas que se han tenido como elementos bases del desarrollo profesional planteados en la elaboración de la Tesis de Doctorado titulada “Desarrollo profesional del profesor de matemáticas: estudio de caso en el nivel medio de secundaria” . En un primer momento se retoman las definiciones de conocimiento del profesor y conocimiento profesional de Shulman (1986) y Ball, Thames y Phelps (2008) y se justifica el paso a la propuesta del conocimiento especializado de las investigaciones de Muñoz-Catalán y otros (2015) Seguido a lo anterior, se aborda el concepto de desarrollo profesional del profesor y por último se propone una tercera estructura del Conocimiento Especializado del Profesor de Matemáticas con tres componentes: conformación de guiones,; conformación de imágenes y conformación de técnicas concretas, Se concluye que el conocimiento de la experiencia junto con la ref...
ACS Applied Materials & Interfaces, 2018
We report a novel approach to directly measure interactions and deposition behavior of functional... more We report a novel approach to directly measure interactions and deposition behavior of functional capsule delivery systems on glass substrates vs. concentration of anionic surfactant sodium lauryl ether sulfate (SLES) and cationic acrylamide-acrylamidopropyltrimonium copolymer (AAC). Analyses of three dimensional optical microscopy trajectories were used to quantify lateral diffusive dynamics, deposition lifetimes, and potentials of mean force for different solution conditions. In the absence of additives, negatively charged capsule surfaces yield electrostatic repulsion with the negatively charged substrate, which inhibits deposition. With increasing SLES concentration below the CMC, capsules-substrate electrostatic repulsion is mediated by the charged surfactant solution that decreases the Debye length. Above the SLES CMC, depletion attraction causes enhanced deposition until eventually depletion repulsion inhibits deposition at concentrations ~10 wt%. Addition of ACC causes deposition via capsulesubstrate bridging at all concentrations; the weakest deposition occurs at intermediate AAC concentrations from a competition of steric repulsion and attraction via a few extended bridges. The novel measurements and models of capsule interactions and deposition on substrates in this work provide a basis to fundamentally understand and rationally design complex rinse-off cleansing formulations with optimal characteristics.
Materials, 2019
Copper oxide nanoparticles (CuO NPs) were synthesized in air by reducing copper (II) sulfate pent... more Copper oxide nanoparticles (CuO NPs) were synthesized in air by reducing copper (II) sulfate pentahydrate salt (CuSO4·5H2O) in the presence of sodium borohydride. The reaction was stabilized with Hexadecyltrimethylammonium bromide (CTAB) in a basic medium and using ultrasound waves. Different molar ratios of CTAB:Cu2+ and NaBH4:Cu2+ were explored, to optimize the synthesis conditions, and to study the stability, size, and Zeta potential of the colloidal suspension. Optimum conditions to generate spherical, stable, and monodispersed nanoparticles with hydrodynamic diameters of 36 ± 1.3 nm were obtained, using 16 mM CTAB and 2 M NaBH4 (molar ratios Cu2+:CTAB:NaBH4 of 1:6:10). X-ray diffraction (XRD) was implemented, and a monoclinic CuO crystal system was formed. This demonstrated a monoclinic crystal system corresponding to CuO. The diffraction peaks were identified and confirmed according to their selected area electron diffraction (SAED) patterns.
Mitochondrial DNA Part B, 2018
Fucus spiralis L. is a broadly distributed monoecious intertidal seaweed. The specific status of ... more Fucus spiralis L. is a broadly distributed monoecious intertidal seaweed. The specific status of F. spiralis however is debatable. Here, we contribute to the bioinformatics and systematics of F. spiralis by analysing the complete mitochondrial and plastid genomes of a specimen from California, U.S.A. The F. spiralis mitogenome is 36,396 base pairs (bp) in length and contains 67 genes, and the plastid genome is 125,066 bp in length and contains 171 genes. The F. spiralis genomes are 99.7% and 99.8% similar in nucleotide sequence to F. vesiculosus, and support the revised classification of F. spiralis to Fucus vesiculosus var. spiralis.
Harvard Deusto Marketing Y Ventas, 2013
Dermatologia Venezolana, 1974
Tdx, Jan 21, 2011
La estructura espinela MIIAl2O4 presenta una serie de propiedades que hacen idonea su utilizacion... more La estructura espinela MIIAl2O4 presenta una serie de propiedades que hacen idonea su utilizacion dentro del sector industrial ceramico, y en concreto como aditivos a los esmaltes vitreos, tradicionalmente empleados en este sector, proporcionandoles unas propiedades opticas y mecanicas que por si mismos no poseen, mediante la generacion de materiales de naturaleza vitrocristalina y vitroceramica. La sintesis de espinela mediante la ruta ceramica tradicional empleada en la industria, presenta una serie de inconvenientes, tales como la necesidad de recurrir a altas temperaturas de sintesis con largos tiempos de retencion, y la introduccion de agentes mineralizadores para disminuir esta temperatura, con la consiguiente problematica medioambiental que lleva asociada el empleo de estos compuestos. La ruta ceramica sigue siendo la unica via de sintesis de compuestos que se realiza en la industria ceramica, si bien cada dia se estan realizando mas trabajos encaminados a la minimizacion de recursos energeticos necesarios asi como a obtener unas nuevas rutas de sintesis acordes con las nuevas legislaciones medioambientales, cada vez mas estrictas con los niveles de emision permitidos. En la presente Tesis Doctoral, se plantea una ruta de sintesis alternativa a la ruta tradicional para la espinela, basada en la descomposicion termica de compuestos con estructura tipo hidrotalcita. Los compuestos tipo hidrotalcita, son hidroxidos dobles laminares, constituidos por capas de hidroxidos de cationes divalentes, en los que cierta cantidad de cation divalente, se ha sustituido por una cation trivalente, generando una descompensacion de cargas. Este exceso de carga positiva, se compensa con la introduccion de aniones en la intercapa que ejercen de puente entre las dos capas de hidroxidos. De esta forma, un tratamiento termico de estos compuestos, provocara una reordenacion cationica, asi como la eliminacion de los aniones de la intercapa, favoreciendo la formacion de otros compuestos cristalinos a baja temperatura. En el caso que nos ocupa, los cationes divalentes estudiados, han sido el Mg, Co, Ni y Zn, mientras que el cation trivalente, ha sido el Al. Se han introducido una serie de variables en el estudio, como el pH de sintesis, relacion inicial MII:Al en los compuestos tipo hidrotalcita, introduccion de un segundo cation trivalente, como es el caso del Cr, etc. Se ha conseguido rebajar la temperatura de sintesis de las espinelas correspondientes a temperaturas inferiores a 1000oC, sin tiempo de retencion a la temperatura maxima de calcinacion, y lo que es mas importante, sin la introduccion de ningun tipo de agentes mineralizadores, con el consiguiente beneficio economico y medioambiental que ello conlleva. La ultima parte de la Tesis Doctoral, ha sido el desarrollo de esmaltes de naturaleza vitroceramica en la que la fase cristalina principal es la espinela MgAl2O4, obteniendo de esta forma esmaltes de elevadas propiedades mecanicas de superficie, adaptados a las nuevas tecnologias de gres porcelanico. En este desarrollo se ha estudiado la composicion idonea de las fritas de partida, para producir el proceso de desvitrifcacion de la espinela durante los ciclos de coccion industriales actualmente en uso.
Reumatología Clínica, 2015
Please cite this article as: Macaya F, Adrover A, Díaz I. Nódulos periarticulares, artritis y nef... more Please cite this article as: Macaya F, Adrover A, Díaz I. Nódulos periarticulares, artritis y nefropatía crónica. Reumatol Clin. 2015;11:401–402. ∗ Corresponding author. E-mail address: [email protected] (F. Macaya). of gouty arthritis, he was treated with colchicine. A few years later, the kidney stones were found to be composed of uric acid and hyperuricemia of approximately 10 mg/dL was detected. The patient was recommended to drink abundant liquids and to take potassium citrate, together with dietary measures and allopurinol.
The Journal of pharmacology and experimental therapeutics, 1987
The effects of altered thyroid function on the levels of histamine, histidine decarboxylase activ... more The effects of altered thyroid function on the levels of histamine, histidine decarboxylase activity and the number of mast cells were studied in the brain of 5-day-old rats. At this age both brain histamine levels and mast cells number are at a maximum. In addition the major portion of the amine is stored in mast cells and upon subcellular fractionation it sediments in the crude nuclear fraction (P1). Treatments with thyroid hormones or thyrotropic hormone up to 5 days of age leads to a decrease in the histamine levels and mast cells number in the brain, whereas administration of the antithyroid agent 6-n-propyl-2-thiouracil increases both parameters. All treatments affected only the histamine in the P1 fraction and failed to alter the levels of neuronal histamine which is located in the supernatant of P1 (S1). These facts suggest that in neonatal rat thyroid hormones could be involved in the regulation of the levels of brain histamine by regulating the number of brain mast cells.
2015 28th IEEE International Conference on Micro Electro Mechanical Systems (MEMS), 2015
This work describes the modeling and experimental characterization of a fabrication method for fo... more This work describes the modeling and experimental characterization of a fabrication method for forming magnetic microstructures using self-assembled iron oxide (Fe3O4) magnetic nanoparticles. This method can potentially be used in roll-to-roll production of magnetic structures patterned onto substrates or optionally lifted off to create free-floating micromagnetic actuators. This article reports: (1) the use of a selective magnetization process to create magnetic microstructures with complex, photolithographically defined shapes, (2) development of multi-physics simulations that model key fabrication steps (selective magnetization and particle assembly), and (3) experimental evaluation of the microstructure features (line width and height) as functions of process variables. The primary accomplishment is obtaining well-defined microstructures with complex shape and demonstrating their magnetic actuation when released as free-floating structures.
WIT Transactions on The Built Environment, 2008
Tropical Montane Cloud Forests (TMCF) are a primary source of fresh water in tropical locations a... more Tropical Montane Cloud Forests (TMCF) are a primary source of fresh water in tropical locations and are highly sensitive to changes in vegetation, sea surface temperatures, and global climate, such is the case in the El Yunque Rain Forest, in Northeastern Puerto Rico. Climatological analyses of this TMCF reveal changes in the region's climate reflected in increasing moisture content and surface air temperature. Historical changes in the low lands due to agriculture and urban sprawl are suspected to be a source of the climate variation. The focus of this paper is to quantify the climate impacts of changes in land use close to coastal TMCFs, using El Yunque during the dry season as the test case. To achieve this goal, the research makes use of high-resolution remote sensing information and surface weather stations, combined with the Regional Atmospheric Modeling System (RAMS). The coupled and individual effects of land use and global climate change are investigated in detail by performing an ensemble of numerical simulations that represent past and present land use conditions, and past and present climate. Results indicate significant impacts in increasing air temperatures, reduction in cloud base heights, and increases in precipitation in the highlands and are attributed to increases of sea surface temperatures. Historical forestation tends to mitigate these global warming effects in the low land areas, while urbanization tends to augment them.
Soft Matter, 2014
Ferrofluids are suspensions of magnetic nanoparticles that have the attractive feature of being c... more Ferrofluids are suspensions of magnetic nanoparticles that have the attractive feature of being controlled by applied magnetic fields. Ferrofluids have been studied for decades in an ever growing number of applications that take advantage of their response to applied magnetic fields. Here, we provide a summary of recent advances in established and emerging applications of ferrofluids, including applications in optics, sensors, actuators, seals, lubrication, and static/dynamic magnetically driven assembly of structures.
Molecular Pharmacology, 2005
H 3 autoreceptors provide feedback control of neurotransmitter synthesis in histaminergic neurons... more H 3 autoreceptors provide feedback control of neurotransmitter synthesis in histaminergic neurons, but the transduction pathways involved are poorly understood. In rat brain cortical slices, histamine synthesis can be stimulated by depolarization and inhibited by H 3 agonists. We show that histamine synthesis stimulation by depolarization with 30 mM K ϩ requires extracellular calcium entry, mostly through N-type channels, and subsequent activation of calcium/calmodulin-dependent protein kinase type II. In vitro, this kinase phosphorylated and activated histidine decarboxylase, the histamine-synthesizing enzyme. Inhibition of depolarization-stimulated histamine synthesis by the histamine H 3 receptor agonist imetit was impaired by preincubation with pertussis toxin and by the presence of a myr-istoylated peptide (myristoyl-N-QEHAQEPERQYMHIGTMVE-FAYALVGK) blocking the actions of G-protein ␥ subunits. The stimulation of another G i/o-coupled receptor, adenosine A 1 , also decreased depolarization-stimulated histamine synthesis. In contrast, protein kinase A activation, which is also repressed by H 3 receptors, elicited a depolarization-and calcium/calmodulin-independent stimulation of histamine synthesis. Protein kinase A was able also to phosphorylate and activate histidine decarboxylase in vitro. These results show how depolarization activates histamine synthesis in nerve endings and demonstrate that both pathways modulating neurotransmitter synthesis are controlled by H 3 autoreceptors.
Physics Procedia, 2010
The flow of a ferrofluid in a stationary cylindrical container driven by a rotating magnetic fiel... more The flow of a ferrofluid in a stationary cylindrical container driven by a rotating magnetic field has received considerable attention since the inception of the field of ferrohydrodynamics. Much controversy has resulted regarding the existence, or lack thereof, of bulk flow under conditions of a rotating uniform magnetic field, which can be generated for example, using a two-pole stator winding. The original observations of flow at the interface showed counter-rotation of field and fluid, whereas recent observations of bulk flow using the ultrasound technique have shown co-rotation of field and fluid. Various theories have been advanced over the years to explain the observed phenomena, including the spin diffusion theory of Shliomis and the hypothesis that it is field non-uniformity, generated by non-ideal stator winding distributions, that actually drives the flow, as first proposed by Glazov. We have revisited this problem from an analytical perspective by solving the ferrohydrodynamic and magnetoquasistatic equations self-consistently for the case of ferrofluid in a cylindrical container, with and without an internal co-axial cylinder, and driven by the field generated by a multipole stator winding distribution. In such a winding increasing the number of poles results in increasingly non-uniform fields. It is shown that regardless of the number of poles in the stator winding the ferrohydrodynamic equations do not predict any flow in either geometry as long as the spin viscosity parameter is assumed to be zero. Velocity profiles are obtained for both geometries and arbitrary number of poles for the case of non-zero spin viscosity. It is shown that only for the case of a two-pole stator winding and ferrofluid constrained to the annular space between an inner and outer cylinder do the ferrohydrodynamic equations predict co-rotation of fluid and field close to the outer cylinder and counter-rotation of fluid and field close to the inner cylinder, in qualitative agreement with experimental measurements made using an oil based ferrofluid.
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Papers by Isaac Flores Diaz