1,646 research outputs found
Crystal Conner and party
No full textCrystal Conner and partyhttps://mavmatrix.uta.edu/specialcollections_wdsmithphotography/9309/thumbnail.jp
Gel-mediated chemo-mechanical control of calcium carbonate crystal formation
No full textThe production of synthetic crystals with controlled shapes and properties is an enticing prospect, yet, the production of such materials is an ongoing challenge. Here, we present a strategy for chemo-mechanically directing the growth of crystals with non-equilibrium structures using a custom-designed double-diffusion cell. We combine chemical additives (e.g., Mg2+ ions) and mechanical confinement (e.g., hydrogel networks) to modulate the growth of calcium carbonate crystals. Specifically, the combination of Mg2+ ions with a strong agarose gel results in calcitic structures, at the gel-glass slide interface, with distinct fried egg-like morphologies and radial or Maltese-cross extinction patterns. In contrast, precipitation with only Mg2+ or agarose results in aragonite spherulites or squished calcite rhombohedra, respectively. Raman spectroscopy and energy dispersive spectroscopy of the “fried eggs” reveals that they are composed of Mg-calcite, which becomes less disordered over time, and the “egg whites” make this transition before the “yolks”. We propose that the “fried eggs” form due to a spherulitic growth process molded by the crystallization-induced delamination of the gel away from the glass slide at the gel-glass interface. In support of the importance of the gel-glass interface, the “fried eggs” do not form when the glass slide is treated with a hydrophobic silane, suppressing heterogeneous nucleation and weakening the interfacial adhesion between the gel and glass, making it easier for the gel to delaminate, thus reducing the confinement effect. As such, this work highlights the important chemo-mechanical role that gel environments can play in crystal formation.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Materials and Environmen
Investigation of nucleation and crystal growth kinetics of nickel manganese oxalates
No full textThe nucleation and the crystal growth rates of mixed nickel manganese oxalates have been determined from the changes of the ionic concentration of the solution and the crystal size distribution during the precipitation process within a supersaturation range 0–0.1 M. Thermodynamic solubility calculations have been used to identify the different species contributing the precipitation reaction and for estimation of the thermodynamic constant. Experimental data show that the nucleation rate of mixed nickel manganese oxalate in this supersaturation range is consistent with a primary heterogeneous mechanism and was found to obey to an exponential law. The crystal growth rates indicate a surface-integration-controlled mechanism with a first-order law with respect to the supersaturation
Large Scale Fabrication Of Periodical Bowl-Like Micropatterns Of Single Crystal Zno
No full textNanostructured ZnO materials are of great significance for their potential applications in photoelectronic devices, light-emitting displays, catalysis and gas sensors. In this paper, we report a new method to produce large area periodical bowl-like micropatterns of single crystal ZnO through aqueous-phase epitaxial growth on a ZnO single crystal substrate. A self-assembled monolayer of polystyrene microspheres was used as a template to confine the epitaxial growth of single crystal ZnO from the substrate, while the growth morphology was well controlled by citrate anions. Moreover, it was found that the self-assembled monolayer of colloidal spheres plays an important role in reduction of the defect density in the epitaxial ZnO layer. Though the mechanism is still open for further investigation, the present result indicates a new route to suppress the dislocations in the fabrication of single crystal ZnO film. A predicable application of this new method is for the fabrication of two-dimensional photonic crystal structures on light emitting diode surfaces
Resonant Pumping of d-d Crystal Field Electronic Transitions as a Mechanism of Ultrafast Optical Control of the Exchange Interactions in Iron Oxides
No full textThe microscopic origin of ultrafast modification of the ratio between the symmetric (J) and antisymmetric (D) exchange interaction in antiferromagnetic iron oxides is revealed, using femtosecond laser excitation as a pump and terahertz emission spectroscopy as a probe. By tuning the photon energy of the laser pump pulse we show that the effect of light on the D/J ratio in two archetypical iron oxides FeBO3 and ErFeO3 is maximized when the photon energy is in resonance with a spin and parity forbidden d-d transition between the crystal-field split states of Fe3+ ions. The experimental findings are supported by a multielectron model, which accounts for the resonant absorption of photons by Fe3+ ions. Our results reveal the importance of the parity and spin-change forbidden, and therefore often underestimated, d-d transitions in ultrafast optical control of magnetism.QN/Caviglia La
The optical properties of automatically darkening welding filters based on liquid crystal technology
No full textThis thesis addresses the problem of the poor optical angular properties displayed by the majority of automatically darkening welding filters currently on the market that are based on liquid crystal technology. It is shown that by reducing the twist-angle present in the liquid crystal cell to below that of 90 together with employment of a novel polariser arrangement, an optical shutter design based on a double-cell construction is obtained that boasts a reduced angular transmittance variation when in the activated phase. This gives an optical filter possessing a wide central viewing cone whilst maintaining the remaining optical parameters at a high level. The only point of compromise comes from the voltage increase requirement upon reduction of the twist- angle in order to maintain cell contrast. Although this inflates the power consumption of the system, beneficial effects upon the total light scattering provoked by the device are also observed. The final sections deal with a new mode of operation for a twisted-nematic liquid crystal cell when placed between crossed polarisers together with an interference filter possessing a high optical transmittance over the central part of the visible spectrum. This mode of operation means that the cell is in a dark state when inactivated. Application of a small stimulating voltage transmutes the unit into the light state, where upon further increment of the driving electronics beyond this point reverts the system back into a low transmittance phase. Such a mode of operation for a twisted-nematic cell offers several advantages over that of the normally white mode when considering the optical lens of an automatically darkening welding filter. In particular, a dark, fail-safe state is provided should the controlling electronics malfunction preventing the unit from holding in a potentially hazardous light phase, a property usually associated with the normally black mode of operation, whilst the fast switching speed from the light to the dark state associated with the normally white mode of operation is maintained. It is shown that there are only two cell types that display this phenomenon and the optical properties of these two systems are analysed in some detail with the view of developing an automatically darkening welding filter based on this technology. This thesis is submitted to the University of Durham for the degree of Master of Science. All work contained within this thesis was carried out by the author at Hornell Innovation AB in Sweden. No material contained within has been submitted for a previous degree and the copyright of this thesis rests with the author. No quotation from it should be published without his prior written consent and information derived from it should be acknowledged
Forming Anisotropic Crystal Composites: Assessing the Mechanical Translation of Gel Network Anisotropy to Calcite Crystal Form
No full textThe promise of crystal composites with direction-specific properties is an attractive prospect for diverse applications; however, synthetic strategies for realizing such composites remain elusive. Here, we demonstrate that anisotropic agarose gel networks can mechanically "mold" calcite crystal growth, yielding anisotropically structured, single-crystal composites. Drying and rehydration of agarose gel films result in the affine deformation of their fibrous networks to yield fiber alignment parallel to the drying plane. Precipitation of calcium carbonate within these anisotropic networks results in the formation of calcite crystal composite disks oriented parallel to the fibers. The morphology of the disks, revealed by nanocomputed tomography imaging, evolves with time and can be described by linear-elastic fracture mechanics theory, which depends on the ratio between the length of the crystal and the elastoadhesive length of the gel. Precipitation of calcite in uniaxially deformed agarose gel cylinders results in the formation of rice-grain-shaped crystals, suggesting the broad applicability of the approach. These results demonstrate how the anisotropy of compliant networks can translate into the desired crystal composite morphologies. This work highlights the important role organic matrices can play in mechanically "molding" biominerals and provides an exciting platform for fabricating crystal composites with direction-specific and emergent functional properties.Accepted Author ManuscriptMaterials and EnvironmentBT/Environmental Biotechnolog
Mitochondrial targeting of cyclosporin A enables selective inhibition of cyclophilin-D and enhanced cytoprotection after glucose and oxygen deprivation
No full textCsA (cyclosporin A) is a hydrophobic undecapeptide that inhibits CyPs (cyclophilins), a family of PPIases (peptidylprolyl cis–trans isomerases). In some experimental models, CsA offers partial protection against lethal cell injury brought about by transient ischaemia; this is believed to reflect inhibition of CyP-D, a mitochondrial isoform that facilitates formation of the permeability transition pore in the mitochondrial inner membrane. To evaluate this further, we have targeted CsA to mitochondria so that it becomes selective for CyP-D in cells. This was achieved by conjugating the inhibitor to the lipophilic triphenylphosphonium cation, enabling its accumulation in mitochondria due to the inner membrane potential. In a cell-free system and in B50 neuroblastoma cells the novel reagent (but not CsA itself) preferentially inhibited CyP-D over extramitochondrial CyP-A. In hippocampal neurons, mitochondrial targeting markedly enhanced the capacity of CsA to prevent cell necrosis brought about by oxygen and glucose deprivation, but largely abolished its capacity to inhibit glutamate-induced cell death. It is concluded that CyP-D has a major pathogenic role in ‘energy failure’, but not in glutamate excitotoxicity, where cytoprotection primarily reflects CsA interaction with extramitochondrial CyPs and calcineurin. Moreover, the therapeutic potential of CsA against ischaemia/reperfusion injuries not involving glutamate may be improved by mitochondrial targeting
An extracellular steric seeding mechanism for Eph-ephrin signaling platform assembly
No full textErythropoetin-producing hepatoma (Eph) receptors are cell-surface protein tyrosine kinases mediating cell-cell communication. Upon activation, they form signaling clusters. We report crystal structures of the full ectodomain of human EphA2 (eEphA2) both alone and in complex with the receptor-binding domain of the ligand ephrinA5 (ephrinA5 RBD). Unliganded eEphA2 forms linear arrays of staggered parallel receptors involving two patches of residues conserved across A-class Ephs. eEphA2-ephrinA5 RBD forms a more elaborate assembly, whose interfaces include the same conserved regions on eEphA2, but rearranged to accommodate ephrinA5 RBD. Cell-surface expression of mutant EphA2s showed that these interfaces are critical for localization at cell-cell contacts and activation-dependent degradation. Our results suggest a 'nucleation' mechanism whereby a limited number of ligand-receptor interactions 'seed' an arrangement of receptors which can propagate into extended signaling arrays
Crystal, D. (2018) Sounds Appealing: The Passionate Story of English Pronunciation. London: Profile Books. 296 pp.
No full textSounds Appealingis the latest of the 100+ books published to this date by the renowned linguist and lecturer, David Crystal. Just as the title claims, it is a story of English pronunciation in all its aspects, related with passion, humour and fascinating insights into its history as well as possible future. It is part of a series of ‘stories’ on the English language which Crystal has published since 2011, namely Making Sense: The Glamorous Story of English Grammar (2017),Making a Point: The Pernickety Story of English Punctuation(2015),Spell it Out: The Singular Story of English Spelling (2012) andThe Story of English in 100 Words (2011).The book contains 31 chapters accompanied by20 panels, nine auditory check tasks (with key) and Appendix with notes on the teaching of pronunciation for teachers of English as a foreign language (EFL). What is perhaps most appealing about the volume is its versatility towards the readers; indeed, those who may enjoy the book range from linguists to members of the general public, students of phonetics as well as lecturers, native speakers along with users of English as a foreign language. Crystal is able to find a perfect balance between the amount of facts, linguistic terminology, references to the doyens in the field of English phonetics, evidence from literary texts, and even popular culture trivia, be it references to films, advertisements, TV shows, singers or politicians.The opening line of the book reads “in the 1980s, I found myself as the ‘voice of language’ on BBC Radio 4” (p. 1), followed by the author’s account of the beginnings of his involvement with the way English is spoken as well as with the BBC. It was the time when numerous local radio stations across Britain started broadcasting and their announcers often spoke in accents that differed from the traditional BBC model; this in return caused a sustained flood of complaints from listeners “expressing concern at what they perceived to be a falling of standards” (ibid.). To help ease the situation and address some of the issues, the BBC approached Crystal, who then wrote a programme called “How dare you talk to me like that” (ibid.), originally planned as a one-off, but which was – eventually – the first of two successive series, running for almost ten years. The one thing the incoming letters from the general public had in common (apart from the actual comments and criticism concerning e.g. the pronunciation of individual sounds and their regional variants, omission of sounds, misplaced word stress or intrusive ‘r’) was the language in which they were written: it was passionate. And so questions like “What is it about pronunciation that produces such a response? Why does pronunciation get to people in a way that other aspects of speech don’t?” (p. 3) are some of those the book is trying to answer.The first chapter deals with the nature of pronunciation and the history of phonetics studies, while Chapter 2 presents the basic concepts and definitions, for instance, phonetic notation, phonemes, minimal pairs and others (pp. 12-16) and introduces some of the most prominent linguists in this field such as Henry Sweet, Paul Passy or Daniel Jones, to name just a few.The segmental level of phonetics is covered in Chapters 3 and 4 (titled The Basic Systemand How Sounds are Made, respectively) where Crystal first explains the division of sounds into vowels and consonants, their numbers in English, the IPA symbol for each of them, etc., and goes on to describe the processes of articulation; to do so he sometimes uses a personal observation or an anecdote, and sometimes a metaphor (such as that about the tongue and lips: “They seem to be performing a beautifully choreographed dance.” (p. 28)), or he provides a tip for YouTube videos. Individual sounds are then dealt with separately, i.e. vowels in Chapters 11-15 and consonants in Chapters 16-20 (each chapter covering one family of consonants according to the manner of their articulation). The treatment of vowels is very thorough, as the author combines the description of their individual properties (i.e. quality, quantity, tongue position and lip movement) and their equivalents in various regional accents across the globe. The reader is thus presented with a much more colourful picture and quite possibly may find an explanation for some peculiar pronunciation they noticed in films, on the Internet or while travelling. The examples are plentiful, with some using puns or playing on humour, such as the case of diphthong substitution in “Devon’s two crame tays” (p. 90) standing for “two cream teas”. Last but not least, Crystal often demonstrates different sound qualities (whether on the articulation or perception level) by quoting from works of literature; we learn that the auditory contrast between close and open vowels is frequently used in nursery rhymes (Jack and Jill), brand names (Kit Kat), or even Shakespeare (pibble-pabble, snip-snap) (all p. 108), that the contrast between close front and close back vowels sounds good in names of characters, cf. /ɑː/ and /i:/ (Charlie Weasley) or /ɪ / and /ʊ / (Lilliput) (p. 109), or that “writers often rely on plosives to give their characters names that are sometimes humorous and sometimes menacing” (p. 123), for instance Dickens’s Jack Bamber, Peggottyor Pip(ibid.). Such details will be most certainly appreciated by many a literature lover.Stress, rhythm, intonation, pauses or speech rate, in other words features of suprasegmental phonology, are introduced in Chapters 5-10, followed by Chapter 21 about the syllable and Chapter 23 about connecting words and linking. Most of these sections of the book are accompanied by panels (inserted text, photographs, copies of newspaper clippings and others), for example, on p. 49 we find a short entry called Uptalk? to complement Chapter 6 on intonation, or the section on word stress is followed up by Laboratory or lavatory? (pp. 60-62), which is a copy of a document from the year 1929, Broadcast English: Recommendations to announcers regarding certain words of doubtful pronunciation, containing 333 words and published by the BBC for its employees.As mentioned previously, accents and regional varieties are referred to in individual chapters dealing with both vowels and consonants, but they are also treated separately in Chapter 24 Accents Welcomeand Chapter 25 Being Accommodating; the former is supplemented with a delightful panel Myths about Accents, wherewe find corrections of various media stories, such as that “the Liverpool accent is the result of mists and fog in the River Mersey […], causing colds and nasal catarrh, which led to its characteristic adenoidal twang” (p. 202) or that “the Australian accent arose because the first convict settlers were regularly drunk, resulting in many so-called ‘lazy’ diphthongs, such as the /aɪ/ sound in words like day” (pp. 202-203). As Crystal puts it, “such explanations spread because they are simple and easy to understand. But none of them stand up to examination” (p. 203).To conclude, Sounds Appealingwill definitely sound appealing to a great number of readers, whatever their academic or linguistic backgrounds, and has proved yet again that David Crystal – apart from being a linguist, writer, editor, lecturer and broadcaster – is an indefatigable campaigner for the popularization of English language studies. Irena Headlandová Kalischov
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