Search results for "lcsh:Science"
showing 10 items of 2187 documents
Halogen bonding and host–guest chemistry between N-alkylammonium resorcinarene halides, diiodoperfluorobutane and neutral guests
2019
Single crystal X-ray structures of halogen-bonded assemblies formed between host N-hexylammonium resorcinarene bromide (1) or N-cyclohexylammonium resorcinarene chloride (2), and 1,4-diiodooctafluorobutane and accompanying small solvent guests (methanol, acetonitrile and water) are presented. The guests’ inclusion affects the geometry of the cavity of the receptors 1 and 2, while the divalent halogen bond donor 1,4-diiodooctafluorobutane determines the overall nature of the halogen bond assembly. The crystal lattice of 1 contains two structurally different dimeric assemblies A and B, formally resulting in the mixture of a capsular dimer and a dimeric pseudo-capsule. 1H and 19F NMR analyses …
Novel supramolecular affinity materials based on (−)-isosteviol as molecular templates
2013
The readily available ex-chiral-pool building block (−)-isosteviol was combined with the C3-symmetric platforms hexahydroxytriphenylene and hexaaminotriptycene providing large and rigid molecular architectures. Because of the persistent cavities these scaffolds are very potent supramolecular affinity materials for head space analysis by quartz crystal microbalances. The scaffolds serve in particular as templates for tracing air-borne arenes at low concentration. The affinities of the synthesized materials towards different air-borne arenes were determined by 200 MHz quartz crystal microbalances.
Validation of a set of reference genes to study response to herbicide stress in grasses
2012
Abstract Background Non-target-site based resistance to herbicides is a major threat to the chemical control of agronomically noxious weeds. This adaptive trait is endowed by differences in the expression of a number of genes in plants that are resistant or sensitive to herbicides. Quantification of the expression of such genes requires normalising qPCR data using reference genes with stable expression in the system studied as internal standards. The aim of this study was to validate reference genes in Alopecurus myosuroides, a grass (Poaceae) weed of economic and agronomic importance with no genomic resources. Results The stability of 11 candidate reference genes was assessed in plants res…
Fluorination of some highly functionalized cycloalkanes: chemoselectivity and substrate dependence.
2017
A study exploring the chemical behavior of some dihydroxylated β-amino ester stereo- and regioisomers, derived from unsaturated cyclic β-amino acids is described. The nucleophilic fluorinations involving hydroxy–fluorine exchange of some highly functionalized alicyclic diol derivatives have been carried out in view of selective fluorination, investigating substrate dependence, neighboring group assistance and chemodifferentiation.
Osallistava ja tutkimuksellinen kemian opiskelu luokanopettajien koulutuksessa
2015
Luokanopettajat ovat avainasemassa lasten innostuksen herättämisessä sekä kemian tietojen ja taitojen kasvun tukemisessa alakoulussa. Tämän tutkimuksen päätavoitteeksi asetettiin kehittää luokanopettajan perus- ja täydennyskoulutukseen osallistava koulutusmalli, joka tarjoaa sekä sisällöllisiä että menetelmällisiä työkaluja kemian opettamiseen tutkimuksellisuutta korostaen. Opetus- ja opiskelukäytäntöjä kehitettäessä tukeuduttiin kemiaan luonnontieteenä, erityisesti sen kokeellisuuteen ja tutkimuksellisuuteen, sekä osallistavaa ja ammatillista kehittymistä tukevaa opettajankoulutusta käsitteleviin teoreettisiin lähtökohtiin. Koulutusmallia olivat tutkijan ja kouluttajien kanssa yhteisöllise…
X-Ray Nanotomography of Individual Pulp Fibre Bonds Reveals the Effect of Wall Thickness on Contact Area
2019
Fibre bonds play an essential role in various properties of paper. Much research has focused on their strength, but the determination of the actual contact area also provides a challenge. Many of the research methods rely on optical tools, which are restricted by the wavelength of light that is utilised. Novel X-ray computed tomography devices utilise X-rays in studying the inner structure of materials, and surpass the optical methods in terms of resolution, allowing detection of even smaller details and variations in distance between the fibres in the bond intersection area. X-ray nanotomography was used to image 26 individual cellulose fibre bonds made of springwood and summerwood fibres …
Antipredatory function of head shape for vipers and their mimics.
2011
Most research into the adaptive significance of warning signals has focused on the colouration and patterns of prey animals. However, behaviour, odour and body shape can also have signal functions and thereby reduce predators' willingness to attack defended prey. European vipers all have a distinctive triangular head shape; and they are all venomous. Several non-venomous snakes, including the subfamily Natricinae, commonly flatten their heads (also known as head triangulation) when disturbed. The adaptive significance of this potential behavioural mimicry has never been investigated. We experimentally tested if the triangular head shape typical of vipers offers protection against predation.…
Recurrence time distribution and temporal clustering properties of a cellular automaton modelling landslide events
2018
Abstract. Reasonable prediction of landslide occurrences in a given area requires the choice of an appropriate probability distribution of recurrence time intervals. Although landslides are widespread and frequent in many parts of the world, complete databases of landslide occurrences over large periods are missing and often such natural disasters are treated as processes uncorrelated in time and, therefore, Poisson distributed. In this paper, we examine the recurrence time statistics of landslide events simulated by a cellular automaton model that reproduces well the actual frequency-size statistics of landslide catalogues. The complex time series are analysed by varying both the threshold…
Cambio de percepción de los niños de preescolar sobre su ambiente, mediante una intervención educativa con enfoque local.
2015
La investigación se desarrolla con 300 infantes de doce centros escolares de preescolar en cinco comunidades aledañas a los Manglares y Humedales de Tuxpan. El objetivo fue determinar si una intervención educativa cambia la percepción sobre su medio. Se realiza un diagnóstico solicitando a los pequeños que elaboraran un dibujo bajo el título ¿Cómo es mi medio ambiente?. Se diseña e implementa una intervención educativa pertinente al contexto y alineada con el currículum Programa de Estudios 2011/ Preescolar, específicamente con el campo formativo de Exploración y Conocimiento del mundo, fomentando una actitud reflexiva sobre la importancia del aprovechamiento adecuado de los recursos natura…
OBSTÁCULOS AL APRENDIZAJE DEL CONCEPTO ESTRUCTURANTE EVOLUCIÓN BIOLÓGICA
2014
Se contrastaron los obstáculos en el aprendizaje del concepto evolución biológica reportados en publicaciones especializadas en la enseñanza de las ciencias, con losen la implementación de un juego para enseñar evolución por selección natural. Lo anterior, se realizó mediante la revisión de antecedentes que permitieron identificar los obstáculos encontrados por otros investigadores y la puesta en marcha de la propuesta didáctica que posibilitó identificar y superar algunos de los mismos. Existen múltiples factores que dificultan la comprensión de la evolución biológica, componentes culturales, iconografía inapropiada, insuficiente preparación de los profesores, estrategias didácticas inade…