1,720,998 research outputs found
Ultra-slow dynamics in low density amorphous ice revealed by deuteron NMR: indication of a glass transition
No full textThe postulated glass-liquid transition of low density amorphous ice (LDA) is investigated with deuteron NMR stimulated echo experiments. Such experiments give access to ultra-slow reorientations of water molecules on time scales expected for structural relaxation of glass formers close to the glass-liquid transition temperature. An involved data analysis is necessary to account for signal contributions originating from a gradual crystallization to cubic ice. Even if some ambiguities remain, our findings support the view that pressure amorphized LDA ices are of glassy nature and undergo a glass-liquid transition before crystallization
Colloquium: Water's controversial glass transitions
No full textWater is the most common and, judged from its numerous anomalous properties, the weirdest of all known liquids and the complexity of its pressure-temperature map is unsurpassed. A major obstacle on the way to a full understanding of water's structure and dynamics is the hard-to-explore territory within this map, colloquially named the no man's land. Many experiments suggest that just before stepping across its low-temperature border, amorphous ices undergo glass-to-liquid transitions while other interpretations emphasize the importance of underlying disordered (nano) crystalline states. Prospects for reconciling the conflicting views regarding the nature of water's glass transitions are discussed
Limits of metastability in amorphous ices: <sup>2</sup>H-NMR relaxation
No full textThe high-frequency reorientation dynamics of O-H-2 bonds is investigated in various amorphous ices including eHDA (expanded high density amorphous ice), LDA-II (low density amorphous ice II) and HGW (hyperquenched glassy water) using H-2-NMR spin-lattice relaxation as a local probe. Both low density forms, HGW and LDA-II, show similar spin-lattice relaxation but differ in the thermal stability with respect to the transition into crystalline cubic ice I-c. HGW already transforms slightly above 135 K whereas LDA-II crystallizes at 150 K. eHDA is distinguishable from other high density amorphous ices in its thermal stability and spin-lattice relaxation. Its relaxation times are much larger compared to those of VHDA (very high density amorphous ice) and uHDA (unrelaxed high density amorphous ice). eHDA does not show annealing effects, transforms sharply into LDA-II above 123 K and provides higher thermal stability as compared to other high density forms.Austrian Science Fund [T463, Y391]; European Research Counci
Limits of metastability in amorphous ices: the neutron scattering Debye–Waller factor
No full textRecently, it became clear that relaxation effects in amorphous ices play a very important role that has previously been overlooked. The thermodynamic history of amorphous samples strongly affects their transition behavior. In particular, well-relaxed samples show higher thermal stability, thereby providing a larger window to investigate their glass transitions. We here present neutron scattering experiments using fixed elastic window scans on relaxed forms of amorphous ice, namely expanded high density amorphous ice (eHDA), a variant of low density amorphous ice (LDA-II) and hyperquenched glassy water (HGW). These amorphous ices are expected to be true glassy counterparts of deeply supercooled liquid water, therefore fast precursor dynamics of structural relaxation are expected to appear below the calorimetric glass transition temperature. The Debye-Waller factor shows a very weak sub-T-g anomaly in some of the samples, which might be the signature of such fast precursor dynamics. However, we cannot find this behavior consistently in all samples at all reciprocal length scales of momentum transfer
Dynamic Contact Angles on Moving Fibers Measured by X-ray Holography
No full textWetting of solid surfaces by a liquid is important for many natural and industrial processes, such as printing, painting, and coating. However, a quantitative description of the dynamic receding and advancing contact angle is still debated, in particular for aqueous solutions. One reason for our lack of quantitative understanding is the limited spatial resolution of currently used optical methods. We therefore present a new approach to access the submicroscopic region. We use X-ray phase contrast imaging to measure the dynamic receding contact angle on a moving glass fiber of 17 μm diameter. The fiber was pulled out of a liquid bath, which was filled with a mixture of glycerol and Milli-Q water. The dynamic receding contact angle decreased with increasing contact line velocity for all mixtures. In the holograms, we achieved a resolution of 50 nm/pixel with a spatial error of 450 nm. This spatial error is due to an extended surface region of the fiber and the liquid surface in the holograms. Our results demonstrate the feasibility of X-ray holography as a method to investigate dynamic contact angle phenomena and thereby open pathways to higher spatial and temporal resolution
Three-phase contact line dynamics on moving fibers measured by X-ray holography
No full textWetting of solid surfaces by a liquid is important for many natural and
industrial processes such as printing, painting and coating. However, a
quantitative description of the dynamic receding and advancing contact angle is
still debated, in particular for aqueous solutions. One reason for our lack of
quantitative understanding is the limited spatial resolution of currently used
optical methods. We therefore present a new approach to access the
sub-microscopic region. We use X-ray phase contrast imaging to measure the
dynamic receding contact angle on a moving glass fiber of 17 um diameter. The
fiber was pulled out of a liquid bath which was filled with a mixture of
glycerol and Milli-Q water. The dynamic receding contact angle decreased with
increasing contact line velocity for all mixtures. In the holograms we achieved
a resolution of 50 nm/pixel with a spatial error of 450 nm. This spatial error
is due to an extended surface region of the fiber and the liquid surface in the
holograms. Our results demonstrate the feasibility of X-ray holography as a
method to investigate dynamic contact angle phenomena and thereby opening
pathways to higher spatial and temporal resolution
Three-phase contact line dynamics on moving fibers measured by X-ray holography
No full textWetting of solid surfaces by a liquid is important for many natural and
industrial processes such as printing, painting and coating. However, a
quantitative description of the dynamic receding and advancing contact angle is
still debated, in particular for aqueous solutions. One reason for our lack of
quantitative understanding is the limited spatial resolution of currently used
optical methods. We therefore present a new approach to access the
sub-microscopic region. We use X-ray phase contrast imaging to measure the
dynamic receding contact angle on a moving glass fiber of 17 um diameter. The
fiber was pulled out of a liquid bath which was filled with a mixture of
glycerol and Milli-Q water. The dynamic receding contact angle decreased with
increasing contact line velocity for all mixtures. In the holograms we achieved
a resolution of 50 nm/pixel with a spatial error of 450 nm. This spatial error
is due to an extended surface region of the fiber and the liquid surface in the
holograms. Our results demonstrate the feasibility of X-ray holography as a
method to investigate dynamic contact angle phenomena and thereby opening
pathways to higher spatial and temporal resolution
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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