239 research outputs found
Preparation of yttrium metal by reduction of yttrium trifluoride with calcium
The preparation of yttrium metal by the reduction of yttrium trifluoride with calcium is described. Alternate methods employing the formation of a low melting Y-Zn or Y-Mg intermediate alloy are evaluated and data on chemical and microscopic purity of the resulting metal are presented
Studies on the preparation, properties and analysis of high purity yttrium oxide and yttrium metal at the Ames Laboratory
The research and development work carried out at the Ames Laboratory on the chemistry and metallurgy of yttrium is described in detail in this report or companion reports to which references are herein made. Discussions of the separation of yttrium from the rare-earth elements by ion exchange, of comprehensive investigations of the preparation of yttrium fluoride, and of various ways of reducing the fluoride to the metallic state are presented. Chemical and spectrographic methods of analyzing yttrium and its compounds for oxygen and other impurities are described and comparisons made between the different methods.
A pilot plant process for producing tonnage quantities of yttrium metal is presented with detailed descriptions of the equipment and
operating procedures employed. The complete process entails the extraction of an yttrium and rare earth mixture from xenotime sand, separation of the yttrium from this mixture in thirty-inch-diameter columns, hydrofluorination of the resulting oxide and its subsequent reduction to the metal. The basic metal process consists of the reduction of yttrium fluoride with calcium, forming a low melting yttrium-magnesium alloy. The magnesium is subsequently removed by vacuum sublimation, producing a porous yttrium product. This is consolidated by vacuum arc melting into a six-inch-diameter ingot.
Quantities of high purity yttrium metal were prepared by vacuum distillation and by-a sa,lt extraction refining process. Yttrium metal containing 100 to 300 ppm oxygen is soft, ductile and easily fabricated at room temperature
Landscape science: a Russian geographical tradition
The Russian geographical tradition of landscape science (landshaftovedenie) is analyzed with particular reference to its initiator, Lev Semenovich Berg (1876-1950). The differences between prevailing Russian and Western concepts of landscape in geography are discussed, and their common origins in German geographical thought in the late nineteenth and early twentieth centuries are delineated. It is argued that the principal differences are accounted for by a number of factors, of which Russia's own distinctive tradition in environmental science deriving from the work of V. V. Dokuchaev (1846-1903), the activities of certain key individuals (such as Berg and C. O. Sauer), and the very different social and political circumstances in different parts of the world appear to be the most significant. At the same time it is noted that neither in Russia nor in the West have geographers succeeded in specifying an agreed and unproblematic understanding of landscape, or more broadly in promoting a common geographical conception of human-environment relationships. In light of such uncertainties, the latter part of the article argues for closer international links between the variant landscape traditions in geography as an important contribution to the quest for sustainability
Towards good practice guidelines for the contour method of residual stress measurement
Accurate measurement of residual stress in metallic components using the contour method relies on the achievement of a good quality cut, on the appropriate measurement of the deformed cut surface and on the robust analysis of the measured data. There is currently no published standard or code of practice for the contour method. As a first step towards such a standard, this study draws on research investigations addressing the three main steps in the method: how best to cut the specimens; how to measure the deformation contour of the cut surface; and how to analyse the data. Good practice guidance is provided throughout the text accompanied by more detailed observations and advice tabulated in Appendi
Electrical Resistivity of Lanthanum, Praseodymium, Neodymium, and Samarium
The electrical resistivities of polycrystalline samples of La, Pr, Nd, and Sm are reported in the temperature range 1.3 to 300 deg K. La exhibits a superconducting transition at 5.8 deg K. The curve for Pr has slope changes at 61 and 95 deg K. The Nd curve shows small jumps at 5 and 20 deg K. Sm shows slope changes at 14 and 106 deg K. (auth
Decolonial education and geography: Beyond the 2017 Royal Geographical Society with the Institute of British Geographers annual conference
This review is inspired by the recent resurgence of grassroots movements aimed at the decolonisation of education. The departure point of the paper are the numerous, recent academic responses to campaigns such as Rhodes Must Fall, Why is My Curriculum White?, Why Isn't My Professor Black?, and #LiberateMyDegree. Following from there, the narrative is divided into two sections. The first part reviews theoretical approaches to decolonial education, especially those rooted in the modernity/coloniality/decoloniality paradigm. The second part analyses the ways in which geographers have applied these ideas to our discipline. The review pays particular attention to the 2017 Royal Geographical Society with the Institute of British Geographers annual conference, curated under the “Decolonising geographical knowledges” theme. I argue that as geographers, we have to continue reflecting on the meaning of decolonial praxis, especially in relation to geographical education, beyond the recent conference. To these ends, the review concludes with seven specific questions for geographers to consider in the near future
Neurotrophic Effects of a Cyanine Dye via the PI3K-Akt Pathway: Attenuation of Motor Discoordination and Neurodegeneration in an Ataxic Animal Model
BACKGROUND: Neurotrophic factors may be future therapeutic agents for neurodegenerative disease. In the screening of biologically active molecules for neurotrophic potency, we found that a photosensitizing cyanine dye, NK-4, had remarkable neurotrophic activities and was a potent radical scavenger. METHODOLOGY/PRINCIPAL FINDINGS: In this study, we evaluated the effect of NK-4 on the protection of neurons against oxidative damage and investigated the associated intracellular signaling pathways. Subsequently, we evaluated the effect of NK-4 in an animal model of neurodegeneration. In vitro, NK-4 showed dose-dependent protection of PC12 cells from toxicity induced by oxidative stress caused by hydrogen peroxide (H(2)O(2)) or 6-hydroxydopamine (6-OHDA). Comparison of extracellular signal-regulated kinase signaling pathways between treatment with NK-4 and nerve growth factor (NGF) using K252a, an inhibitor of the NGF receptor TrkA, revealed that NK-4 activity occurs independently of NGF receptors. LY294002, a phosphatidylinositol 3-kinase (PI3K) inhibitor, blocked the protective effect of NK-4, and NK-4 caused activation of Akt/protein kinase B, a downstream effector of PI3K. These results suggest that the neuroprotective effects of NK-4 are mediated by the PI3K-Akt signaling pathway. NK-4 treatment also attenuated stress-induced activation of SAPK/JNK, which suggests that NK-4 activates a survival signaling pathway and inhibits stress-activated apoptotic pathways independently of the TrkA receptor in neuronal cells. In vivo, administration of NK-4 improved motor coordination in genetic ataxic hamsters, as assessed by rota-rod testing. Histological analysis showed that cerebellar atrophy was significantly attenuated by NK-4 treatment. Notably, the Purkinje cell count in the treated group was threefold higher than that in the vehicle group. CONCLUSIONS/SIGNIFICANCE: These results suggest that NK-4 is a potential agent for therapy for neurodegenerative disorders based on the activation of survival signaling pathways
Neuropsychological predictors of conversion from mild cognitive impairment to Alzheimer’s disease: a feature selection ensemble combining stability and predictability
Background
Predicting progression from Mild Cognitive Impairment (MCI) to Alzheimer’s Disease (AD) is an utmost open issue in AD-related research. Neuropsychological assessment has proven to be useful in identifying MCI patients who are likely to convert to dementia. However, the large battery of neuropsychological tests (NPTs) performed in clinical practice and the limited number of training examples are challenge to machine learning when learning prognostic models. In this context, it is paramount to pursue approaches that effectively seek for reduced sets of relevant features. Subsets of NPTs from which prognostic models can be learnt should not only be good predictors, but also stable, promoting generalizable and explainable models.
Methods
We propose a feature selection (FS) ensemble combining stability and predictability to choose the most relevant NPTs for prognostic prediction in AD. First, we combine the outcome of multiple (filter and embedded) FS methods. Then, we use a wrapper-based approach optimizing both stability and predictability to compute the number of selected features. We use two large prospective studies (ADNI and the Portuguese Cognitive Complaints Cohort, CCC) to evaluate the approach and assess the predictive value of a large number of NPTs. Results
The best subsets of features include approximately 30 and 20 (from the original 79 and 40) features, for ADNI and CCC data, respectively, yielding stability above 0.89 and 0.95, and AUC above 0.87 and 0.82. Most NPTs learnt using the proposed feature selection ensemble have been identified in the literature as strong predictors of conversion from MCI to AD.
Conclusions
The FS ensemble approach was able to 1) identify subsets of stable and relevant predictors from a consensus of multiple FS methods using baseline NPTs and 2) learn reliable prognostic models of conversion from MCI to AD using these subsets of features. The machine learning models learnt from these features outperformed the models trained without FS and achieved competitive results when compared to commonly used FS algorithms. Furthermore, the selected features are derived from a consensus of methods thus being more robust, while releasing users from choosing the most appropriate FS method to be used in their classification task.PTDC/EEI-SII/1937/2014; SFRH/BD/95846/2013; SFRH/BD/118872/2016info:eu-repo/semantics/publishedVersio
Acid-evoked Ca2+ signalling in rat sensory neurones: effects of anoxia and aglycaemia
Ischaemia excites sensory neurones (generating pain) and promotes calcitonin gene-related peptide release from nerve endings. Acidosis is thought to play a key role in mediating excitation via the activation of proton-sensitive cation channels. In this study, we investigated the effects of acidosis upon Ca2+ signalling in sensory neurones from rat dorsal root ganglia. Both hypercapnic (pHo 6.8) and metabolic–hypercapnic (pHo 6.2) acidosis caused a biphasic increase in cytosolic calcium concentration ([Ca2+]i). This comprised a brief Ca2+ transient (half-time approximately 30 s) caused by Ca2+ influx followed by a sustained rise in [Ca2+]i due to Ca2+ release from caffeine and cyclopiazonic acid-sensitive internal stores. Acid-evoked Ca2+ influx was unaffected by voltage-gated Ca2+-channel inhibition with nickel and acid sensing ion channel (ASIC) inhibition with amiloride but was blocked by inhibition of transient receptor potential vanilloid receptors (TRPV1) with (E)-3-(4-t-butylphenyl)-N-(2,3-dihydrobenzo[b][1,4] dioxin-6-yl)acrylamide (AMG 9810; 1 μM) and N-(4-tertiarybutylphenyl)-4-(3-cholorphyridin-2-yl) tetrahydropryazine-1(2H)-carbox-amide (BCTC; 1 μM). Combining acidosis with anoxia and aglycaemia increased the amplitude of both phases of Ca2+ elevation and prolonged the Ca2+ transient. The Ca2+ transient evoked by combined acidosis, aglycaemia and anoxia was also substantially blocked by AMG 9810 and BCTC and, to a lesser extent, by amiloride. In summary, the principle mechanisms mediating increase in [Ca2+]i in response to acidosis are a brief Ca2+ influx through TRPV1 followed by sustained Ca2+ release from internal stores. These effects are potentiated by anoxia and aglycaemia, conditions also prevalent in ischaemia. The effects of anoxia and aglycaemia are suggested to be largely due to the inhibition of Ca2+-clearance mechanisms and possible increase in the role of ASICs
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