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  • 1
    Publication Date: 2019-08-28
    Description: The wave representation and scattering matrix of n-ports is discussed. This representation is particularly suited to the treatment of microwave switching.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-TM-77770 , NAS 1.15:77770
    Format: application/pdf
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  • 2
    Publication Date: 2009-01-01
    Description: We have collected high resolution neutron powder diffraction patterns from Na2SO4·10D2O over the temperature range 4.2–300 K following rapid quenching in liquid nitrogen, and over a series of slow warming and cooling cycles. The crystal is monoclinic, space-group P21/c ( Z  = 4) with a  = 11.44214(4) Å, b  = 10.34276(4) Å, c  = 12.75486(6) Å, β = 107.847(1)°, and V  = 1436.794(8) Å3 at 4.2 K (slowly cooled), and a  = 11.51472(6) Å, b  = 10.36495(6) Å, c  = 12.84651(7) Å, β = 107.7543(1)°, V  = 1460.20(1) Å3 at 300 K. Structures were refined to R P (Rietveld powder residual, $$ R{P} = {{sum {left| {I{ ext{obs}} - I{ ext{calc}} } ight|} } mathord{left/ {vphantom {{sum {left| {I{ ext{obs}} - I{ ext{calc}} } ight|} } {sum {I{ ext{obs}} } }}} ight. kern- ulldelimiterspace} {sum {I{ ext{obs}} } }} $$ ) better than 2.5% at 4.2 K (quenched and slow cooled), 150 and 300 K. The sulfate disorder observed previously by Levy and Lisensky (Acta Cryst B34:3502–3510, 1978 ) was not present in our specimen, but we did observe changes with temperature in deuteron occupancies of the orientationally disordered water molecules coordinated to Na. The temperature dependence of the unit-cell volume from 4.2 to 300 K is well represented by a simple polynomial of the form V  = − 4.143(1) × 10−7 T 3 + 0.00047(2) T2 − 0.027(2) T  + 1437.0(1) Å3 ( R 2 = 99.98%). The coefficient of volume thermal expansion, α V , is positive above 40 K, and displays a similar magnitude and temperature dependence to α V in deuterated epsomite and meridianiite. The relationship between the magnitude and orientation of the principal axes of the thermal expansion tensor and the main structural elements are discussed; freezing in of deuteron disorder in the quenched specimen affects the thermal expansion, manifested most obviously as a change in the behaviour of the unit-cell parameter β. ©2008 Springer-Verlag
    Print ISSN: 0342-1791
    Electronic ISSN: 1432-2021
    Topics: Chemistry and Pharmacology , Geosciences , Physics
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  • 3
    Publication Date: 2015-09-12
    Description: Article Quantum wires offer a platform for controlling spin–orbit coupling and therefore creating exotic phases of matter. Here, the authors use high-resolution spin- and angle-resolved photoemission measurements to identify an interaction-induced spin- and orbital-entangled state in atomic lead wires. Nature Communications doi: 10.1038/ncomms9118 Authors: C. Brand, H. Pfnür, G. Landolt, S. Muff, J. H. Dil, Tanmoy Das, Christoph Tegenkamp
    Electronic ISSN: 2041-1723
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General , Physics
    Published by Springer Nature
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  • 4
    Publication Date: 2013-05-09
    Description: Syntheses in acidified hydrothermal (HT) solutions (1 n H 2 SO 4 or stronger) produce monoclinic non-stoichiometric K-jarosites which contain Fe-site vacancies with long-range order. Syntheses in non-acidified HT solutions produce rhombohedral K-jarosites which contain relatively large numbers of Fe-site vacancies with no long-range order. Increasing the [Fe]/[K] ratio, reaction temperature and reaction time in non-acidified solutions promotes the formation of monoclinic jarosites which contain Fe-site vacancies with short-range order. A structural model including details of the ordering of the Fe-site vacancies was obtained by refinement of single-crystal synchrotron data from one of the HT synthesis products; this model was used to refine synchrotron powder X-ray diffraction data from products synthesized at different reaction times, temperatures and [Fe]/[K] ratios. Thermal and chemical analyses are consistent with a model for non-stoichiometry in which domains of stoichiometric jarosite are intergrown with butlerite-like iron-deficient domains with a composition [Fe 2 (SO 4 ) 2 (OH) 2 (H 2 O) 4 ]. It was found that heterogeneous nucleation of monoclinic jarosite on Si disks is preceded by the formation of an oriented film of Maus's Salt, K 5 Fe 3 O(SO 4 ) 6 ·10H 2 O, as a precursor phase, and that this transforms topotactically into oriented jarosite, which contains butlerite-like layers parallel to the disk surface. Structural models for the transformation of Maus's Salt into jarosite are proposed.
    Print ISSN: 0026-461X
    Electronic ISSN: 1471-8022
    Topics: Geosciences
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  • 5
    Publication Date: 2011-12-01
    Description: Monoclinic, non-stoichiometric natrojarosite–hydroniumjarosite solid solution phases have been synthesized hydrothermally over a range of temperatures, starting compositions and reaction times, and have been characterized using Rietveld refinement of synchrotron X-ray diffraction data, and chemical and thermal analyses. The H atom locations have been obtained from refinement of neutron diffraction data on a deuterated sample. The results confirm a direct relationship between the monoclinic distortion and the ordering of iron site vacancies in one of two independent iron sites. Ordering of iron vacancies gives rise to domains containing butlerite-like 7 Å chains of corner-connected octahedra and tetrahedra. The formation of these chains within (100) planes results in an expansion of the monoclinic a lattice parameter and a contraction of the c parameter relative to stoichiometric jarosites. The results support a recent model for iron deficiency, whereby an iron vacancy is compensated by the replacement of four coordinated OH- ions by H2O molecules, with one of the H2O molecules coming from deprotonation of H3O+. The general formula, based on intergrowth of stoichiometric jarosite and non-stoichiometric, butlerite-like regions, is [(Na,H3O)Fe3(SO4)2(OH)6]1–y[(H2O)Fe2(SO4)2(OH)2(H2O)4]y.
    Print ISSN: 0026-461X
    Electronic ISSN: 1471-8022
    Topics: Geosciences
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  • 6
    Publication Date: 2014-10-22
    Description: Truncating mutations of chromodomain helicase DNA-binding protein 8 (CHD8), and of many other genes with diverse functions, are strong-effect risk factors for autism spectrum disorder (ASD), suggesting multiple mechanisms of pathogenesis. We explored the transcriptional networks that CHD8 regulates in neural progenitor cells (NPCs) by reducing its expression and then...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 7
    Publication Date: 2016-12-01
    Description: Bettertonite, [Al 6 (AsO 4 ) 3 (OH) 9 (H 2 O) 5 ]·11H 2 O and penberthycroftite, [Al 6 (AsO 4 ) 3 (OH) 9 (H 2 O) 5 ]·8H 2 O, two new minerals from the Penberthy Croft mine, Cornwall, have flexible layer structures based on corner-connected heteropolyhedral columns. Their response to dehydration on heating was studied using in situ synchrotron powder X-ray diffraction at temperatures in the range –53 to 157°C. The bettertonite sample transforms to penberthycroftite in a narrow temperature range of 67 to 97°C with a large (8%) contraction of the layer separation and a 6 Å sliding of adjacent layers relative to each other. Above 100°C a second phase transition occurs to a DL (displaced layer) phase, involving another 8% inter-layer contraction combined with a rotation of the columns. On heating the penberthycroftite sample the phase transition to the DL phase occurs at a lower temperature of ~80°C. The DL phase is stable to a temperature of ~120°C. At higher temperatures, increased rotation of the columns is accompanied by a progressive amorphization of the sample. Bettertonite, penberthycroftite and the DL phase exhibit negative thermal expansion (NTE) along all three axes with large NTE coefficients, of the order of –100 x 10 –6 °C –1 .
    Print ISSN: 0026-461X
    Electronic ISSN: 1471-8022
    Topics: Geosciences
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  • 8
    Publication Date: 2018-12-14
    Description: Whole-genome sequencing (WGS) has facilitated the first genome-wide evaluations of the contribution of de novo noncoding mutations to complex disorders. Using WGS, we identified 255,106 de novo mutations among sample genomes from members of 1902 quartet families in which one child, but not a sibling or their parents, was affected by autism spectrum disorder (ASD). In contrast to coding mutations, no noncoding functional annotation category, analyzed in isolation, was significantly associated with ASD. Casting noncoding variation in the context of a de novo risk score across multiple annotation categories, however, did demonstrate association with mutations localized to promoter regions. We found that the strongest driver of this promoter signal emanates from evolutionarily conserved transcription factor binding sites distal to the transcription start site. These data suggest that de novo mutations in promoter regions, characterized by evolutionary and functional signatures, contribute to ASD.
    Keywords: Development, Genetics, Neuroscience, Online Only
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 9
    ISSN: 1432-0878
    Keywords: Peptidergic neurotransmission ; Lymnaea stagnalis ; Immunocytochemistry ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Three neuronal systems of the pond snail Lymnaea stagnalis were immunocytochemically investigated at the ultrastructural level with the unlabeled peroxidase-antiperoxidase technique. Preliminary electrophysiological and cell-filling investigations have shown that a cluster of neurons which reacts positively with an antiserum against the molluscan cardio-active peptide FMRFamide, sends axons to the penis retractor muscle. In this muscle anti-FMRF-amide (aFM) positive axons form neuro-muscular synapses with (smooth) muscle fibers. The morphological observations suggest the aFM immunoreactive system to be involved in peptidergic neurotransmission. In the right parietal ganglion a large neuron (LYAC) is penetrated by aFM positive axons which form synapse-like structures (SLS) with the LYAC. The assumption that the SLS represent the morphological basis for peptidergic transmission is sustained by the observation that iontophoretical application of synthetic FMRFamide depolarizes the LYAC. The axons of a group of pedal anti-vasopressin (aVP) positive cells run in close vicinity to the cerebral ovulation (neuro-)-hormone producing cell system (CDC system) Synapses or SLS between the two systems were not observed. The fact that (bath) application of arg-vasopressin induces bursting in the CDC, may indicate that the vasopressin-like substance of the aVP cells is released non-synaptically.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0392-6737
    Keywords: Experimental determinations of smectic, nematic, cholesteric, and lyotropic structures ; Specialized material fabrications and fabrication techniques ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Pattern formation at phase boundaries moving in a temperature gradient is one of the major areas of nonequilibrium physics attracting considerable attention. While most of the early work concentrated on the moving solid-liquid interface, now the focus has changed to phase transitions characterized by broken continuous symmetry. Most recently we investigated consequences to interfacial patterns of a chirality-induced equilibrium length. Here we study patterns at another chiral interface where one of the phases has a chirality-induced defect lattice, the twist grain boundary (TGB) phase. The TGB state is analogous to the vortex lattice in Type-II superconductors predicted by the Gennes’ analogy between the nematic (N)-smectic A (A) transition and the normal-superconducting transition. In this analogy, a cholesteric A transition is analogous to the normal-superconducting transition in an external magnetic field and a theory has been developed for its analogous vortex lattice, the TGB phase, when this transition is Type II. We study patterns formed at the traveling TGB-A phase boundary. Different patterns are observed depending on whether TGB grows into A or A into TGB. Indeed, this maybe the first time a steady-state pattern is observed in directional melting (i.e. TGB growing into A). As these patterns have a broad band of wavelengths, they are difficult to characterize physically. Thus, we introduced a novel analysis (most simply but not rigorously described as) measuring the fractal dimension of the patterns at these traveling interfaces. Two lengths emerged from this analysis: a longer one set by sample thickness and a shorter one set by the smallest TGB unit that can grow into an oriented smectic A phase. We invoke our old dynamic arguments to account for why TGB cannot propagate at a second-order TGB-cholesteric phase transition so it is eventually squeezed out leaving behind a direct cholesteric-A transition.
    Type of Medium: Electronic Resource
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