Comparison of ion sites and diffusion paths in glasses obtained by molecular dynamics simulations and bond valence analysis

Based on molecular dynamics simulations of a lithium metasilicate glass we study the potential of bond valence sum calculations to identify sites and diffusion pathways of mobile Li ions in a glassy silicate network. We find that the bond valence method is not well suitable to locate the sites, but allows one to estimate the number of sites. Spatial regions of the glass determined as accessible for the Li ions by the bond valence method can capture up to 90% of the diffusion path. These regions however entail a significant fraction that does not belong to the diffusion path. Because of this low specificity, care must be taken to determine the diffusive motion of particles in amorphous systems based on the bond valence method. The best identification of the diffusion path is achieved by using a modified valence mismatch in the BV analysis that takes into account that a Li ion favors equal partial valences to the neighboring oxygen ions. Using this modified valence mismatch it is possible to replace hard geometric constraints formerly applied in the BV method. Further investigations are necessary to better understand the relation between the complex structure of the host network and the ionic diffusion paths.Comment: 16 pages, 10 figure

Das Auftreten des Late Gadolinium Enhancement in der Magnetresonanztomographie ist assoziiert mit einer erhöhten linksventrikulären Wandspannung und Masse bei Patienten mit dilatativer Kardiomyopathie

Das Auftreten von Late Gadolinium Enhancement (LGE), gemessen mittels kardialer Magnetresonanztomographie, wird häufig bei verschiedenen Herzmuskelerkrankungen gefunden. Bei ischämischen Herzerkrankungen ist es bereits gut charakterisiert und häufig auf postischämische Fibrosierung und Narbenbildung zurückzuführen. Bei nicht-ischämischen Herzerkrankungen sind, mit Ausnahme der HCM, die Ursachen noch unklar. Nach unserer Hypothese ist das Auftreten von LGE bei nicht-ischämischer dilatativer Kardiomyopathie assoziiert mit erhöhter linksventrikulärer (LV) Wandspannung. Für diese Studie haben wir 300 Patienten mit fraglicher nicht-ischämischer dilatativer Kardiomyopathie mittels kardialer MRT untersucht. Dabei wurden LV-Volumen, LV-Masse, LV-Wandspannung und LGE bestimmt. Eine erhöhte LV-enddiastolische Wandspannung (> 4 kPa) wurde bei 112 Patienten (37 %), eine erhöhte LV-endsystolische Wandspannung (> 18 kPa) bei 121 Patienten (40 %) gefunden. Das Auftreten von LGE wurde bei 93 Patienten (31 %) beobachtet. Enddiastolisches (94 ± 43 vs. 79 ± 42 ml/m², p = 0.006) und endsystolisches LV-Volumen (62 ± 44 vs. 44 ± 37 ml/m², p < 0.001) sowie LV-Masse (95 ± 34 vs. 78 ± 31 g/m², p < 0.001) waren bei Patienten, die gleichzeitig LGE aufwiesen, erhöht. Weiterhin war bei diesen Patienten die enddiastolische und endsystolische Wandspannung erhöht (4.5 ± 2.8 kPa vs. 3.6 ± 3.0 kPa, p = 0.025; 19.6 ± 9.1 kPa vs. 17.5 ± 8.2 kPa, p = 0.045). LGE konnte dabei überzufällig häufig bei Patienten mit erhöhter enddiastolischer (39 % vs. 26 %, p = 0.020) und endsystolischer Wandspannung (41 % vs. 24 %, p = 0.002) gefunden werden. Eine normale enddiastolische und endsystolische Wandspannung besaß einen hohen negativ prädiktiven Wert für LGE (75 % bzw. 76 %). Zusammenfassend kann man festhalten, dass das Auftreten von LGE, unabhängig voneinander, assoziiert ist mit erhöhter LV-Wandspannung und erhöhter LV-Masse. Pathophysiologisch dürften dabei verschiedene Ursachen zum vermehrten Auftreten von LGE führen: Zum einen eine erhöhte kapilläre Leckage durch vermehrte myokardiale Dehnung und zum anderen eine erhöhte Kontrastmittel-Umverteilung sowie verlängerte Diffusionsstrecken. Dabei könnten lokale Wandspannungsinhomogenitäten, ähnlich wie in Randzonen beim Myokardinfarkt, zum einen ein magnetresonanztomographisch-nachweisbares LGE unterstützen sowie ein vermehrtes Arrhythmierisiko bei den betroffenen Patienten bedingen. Somit scheint LGE, vermittelt über LV-Masse und LV-Wandspannung, ein potentieller prognostischer Marker für die Progression einer Herzinsuffizienz, für das Auftreten von plötzlichem Herztod sowie zur Risikostratifizierung für die prophylaktische Implantation eines Cardioverter-Defibrillators (ICD) bei Patienten mit DCM zu sein, was durch weitere Studien belegt werden sollte

Palatability of teff grass by horses

Most forages commonly used to feed horses have potential detriments including blister beetles or excessive fiber concentrations. Teff grass (T), a warm-season annual forage, has the potential to be a good alternative for horses because of its lack of observed disorders. Our objective was to compare preference by horses for T harvested under different conditions with that of bermudagrass (B) harvested at two maturities. Six different forages were evaluated: T harvested at the late vegetative stage (TLV), at late bloom but that incurred 33 mm of rainfall between mowing and baling (TLBR), with caryopsis visible (TES), or at soft dough (TSD), and B harvested at late vegetative (BLV) and mid-bloom (BMB) growth stages. Five mature horses were used in a balanced incomplete block design where each horse received a different combination of 4 forages each day for 6 d. The 4 different forages were suspended in hay nets in each corner of each stall, and each hay was offered at 50% of the average daily hay consumption measured during a 12-d adaptation period. Forage preference as measured by individual forage dry matter (DM) consumption (kg and % of total DM consumed across the 4 forages) was greatest (P \u3c 0.05) from TLV followed by BLV. Preference (kg and % of total DM consumed) of BMB was greater (P \u3c 0.05) than that of TMBR, TES, and TSD, which did not differ from each other (P ≥ 0.63). Therefore, within a specific growth stage, horses apparently preferred teff grass, but effects of maturity and rainfall had a more dramatic effect on preference by horses than forage species

Protein sizing with Differential Dynamic Microscopy

Introduced more than fifty years ago, dynamic light scattering is routinely used to determine the size distribution of colloidal suspensions, as well as of macromolecules in solution, such as proteins, nucleic acids, and their complexes. More recently, differential dynamic microscopy has been proposed as a way to perform dynamic light scattering experiments with a microscope, with much less stringent constraints in terms of cleanliness of the optical surfaces, but a potentially lower sensitivity due to the use of camera-based detectors. In this work, we push bright-field differential dynamic microscopy beyond known limits and show it to be sufficiently sensitive to size small macromolecules in diluted solutions. By considering solutions of three different proteins (Bovine Serum Albumin, Lysozyme, and Pepsin), we accurately determine the diffusion coefficient and hydrodynamic radius of both single proteins and small protein aggregates down to concentrations of a few milligrams per milliliter. In addition, we present preliminary results showing unexplored potential for the determination of virial coefficients. Our results are in excellent agreement with the ones obtained in parallel with a state-of-the-art commercial dynamic light scattering setup, showing that differential dynamic microscopy represents a valuable alternative for rapid, label-free protein sizing with an optical microscope

Topological Andr\'e-Quillen homology for cellular commutative SS-algebras

Topological Andr\'e-Quillen homology for commutative $S$-algebras was introduced by Basterra following work of Kriz, and has been intensively studied by several authors. In this paper we discuss it as a homology theory on CW $S$-algebras and apply it to obtain results on minimal atomic $p$-local $S$-algebras which generalise those of Baker and May for $p$-local spectra and simply connected spaces. We exhibit some new examples of minimal atomic $S$-algebras.Comment: Final revision, a version will appear in Abhandlungen aus dem Mathematischen Seminar der Universitaet Hambur

On the angular anisotropy of the randomly averaged magnetic neutron scattering cross section of nanoparticles

The magnetic small-angle neutron scattering (SANS) cross section of dilute ensembles of uniformly magnetized and randomly oriented Stoner–Wohlfarth particles is calculated using the Landau–Lifshitz equation. The focus of this study is on the angular anisotropy of the magnetic SANS signal as it can be seen on a two-dimensional position-sensitive detector. Depending on the symmetry of the magnetic anisotropy of the particles (e.g. uniaxial, cubic), an anisotropic magnetic SANS pattern may result, even in the remanent state or at the coercive field. The case of inhomogeneously magnetized particles and the effects of a particle-size distribution and interparticle correlations are also discussed

Fingerprint of vortex-like flux closure in isotropic Nd-Fe-B bulk magnet

Taking advantage of recent progress in neutron instrumentation and in the understanding of magnetic-field-dependent small-angle neutron scattering, here, we study the three-dimensional magnetization distribution within an isotropic Nd-Fe-B bulk magnet. The magnetic neutron scattering cross section of this system features the so-called spike anisotropy, which points towards the presence of a strong magnetodipolar interaction. This experimental result combined with a damped oscillatory behavior of the corresponding correlation function and recent micromagnetic simulation results on spherical nanoparticles suggest an interpretation of the neutron data in terms of vortex-like flux closure patterns. The field-dependent correlation length is very well reproduced by a power-law model used to describe the London penetration depth in the vortex state of type-II superconductors and suggests the 'pairing' (interaction) of magnetic vortices.Comment: 14 pages, 5 figure

Micromagnetic simulation of neutron scattering from spherical nanoparticles: Effect of pore-type defects

We employ micromagnetic simulations to model the effect of pore-type microstructural defects on the magnetic small-angle neutron scattering cross section and the related pair-distance distribution function of spherical magnetic nanoparticles. Our expression for the magnetic energy takes into account the isotropic exchange interaction, the magnetocrystalline anisotropy, the dipolar interaction, and an externally applied magnetic field. The signatures of the defects and the role of the dipolar energy are highlighted and the effect of a particle-size distribution is studied. The results serve as a guideline to the experimentalist.Comment: arXiv admin note: text overlap with arXiv:2205.0755

Dopaminergic basis for signalling belief updates, but not surprise, and the link to paranoia

Distinguishing between meaningful and meaningless sensory information is fundamental to forming accurate representations of the world. Dopamine is thought to play a central role in processing the meaningful information content of observations, which motivates an agent to update their beliefs about the environment. However, direct evidence for dopamine’s role in human belief updating is lacking. We addressed this question in healthy volunteers who performed a model-based functional magnetic resonance imaging (fMRI) task designed to separate the neural processing of meaningful and meaningless sensory information. We modelled participant behaviour using a normative Bayesian observer model, and used the magnitude of the model-derived belief update following an observation to quantify its meaningful information content. We also acquired positron emission tomography (PET) imaging measures of dopamine function in the same subjects. We show that the magnitude of belief updates about task structure (meaningful information), but not pure sensory surprise (meaningless information), are encoded in midbrain and ventral striatum activity. Using PET we show that the neural encoding of meaningful information is negatively related to dopamine-2/3 receptor availability in the midbrain and dexamphetamine-induced dopamine release capacity in the striatum. Trial-by-trial analysis of task performance indicated that subclinical paranoid ideation is negatively related to behavioural sensitivity to observations carrying meaningful information about the task structure. The findings provide direct evidence implicating dopamine in model-based belief updating in humans, and have implications for understating the pathophysiology of psychotic disorders where dopamine function is disrupted