Molecular dynamics study of oxygen diffusion in Pr₂NiO_4+δ

Oxygen transport in tetragonal Pr2NiO4+δ has been investigated using molecular dynamics simulations in conjunction with a set of Born model potentials. Oxygen diffusion in Pr2NiO4+δ is highly anisotropic, occurring almost entirely via an interstitialcy mechanism in the a-b plane. The calculated oxygen diffusivity has a weak dependence upon the concentration of oxygen interstitials, in agreement with experimental observations. In the temperature range 800-1500 K, the activation energy for migration varied between 0.49 and 0.64 eV depending upon the degree of hyperstoichiometry. The present results are compared to previous work on oxygen self-diffusion in related K2NiF4 structure materials

Anisotropic oxygen diffusion in tetragonal La₂NiO_4+δ: molecular dynamics calculations

Molecular dynamics simulations, used in conjunction with a set of Born model potentials, have been employed to study oxygen transport in tetragonal La2NiO4+δ. We predict an interstitialcy mechanism with an activation energy of migration of 0.51 eV in the temperature range 800-1100 K. The simulations are consistent with the most recent experiments. The prevalence of oxygen diffusion in the a-b plane accounts for the anisotropy observed in measurements of diffusivity in tetragonal La2NiO4+δ

Diffusion of Botulinum Toxins

Background: It is generally agreed that diffusion of botulinum toxin occurs, but the extent of the spread and its clinical importance are disputed. Many factors have been suggested to play a role but which have the most clinical relevance is a subject of much discussion. Methods: This review discusses the variables affecting diffusion, including protein composition and molecular size as well as injection factors (e.g., volume, dose, injection method). It also discusses data on diffusion from comparative studies in animal models and human clinical trials that illustrate differences between the available botulinum toxin products (onabotulinumtoxinA, abobotulinumtoxinA, incobotulinumtoxinA, and rimabotulinumtoxinB). Results: Neither molecular weight nor the presence of complexing proteins appears to affect diffusion; however, injection volume, concentration, and dose all play roles and are modifiable. Both animal and human studies show that botulinum toxin products are not interchangeable, and that some products are associated with greater diffusion and higher rates of diffusion-related adverse events than others. Discussion: Each of the botulinum toxins is a unique pharmacologic entity. A working knowledge of the different serotypes is essential to avoid unwanted diffusion-related adverse events. In addition, clinicians should be aware that the factors influencing diffusion may range from properties intrinsic to the drug to accurate muscle selection as well as dilution, volume, and dose injected

Interstitialcy diffusion of oxygen in tetragonal La₂CoO_4+δ

We report on the mechanism and energy barrier for oxygen diffusion in tetragonal La2CoO4+δ. The first principles-based calculations in the Density Functional Theory (DFT) formalism were performed to precisely describe the dominant migration paths for the interstitial oxygen atom in La2CoO4+δ. Atomistic simulations using molecular dynamics (MD) were performed to quantify the temperature dependent collective diffusivity, and to enable a comparison of the diffusion barriers found from the force field-based simulations to those obtained from the first principles-based calculations. Both techniques consistently predict that oxygen migrates dominantly via an interstitialcy mechanism. The single interstitialcy migration path involves the removal of an apical lattice oxygen atom out from the LaO-plane and placing it into the nearest available interstitial site, whilst the original interstitial replaces the displaced apical oxygen on the LaO-plane. The facile migration of the interstitial oxygen in this path is enabled by the cooperative titling-untilting of the CoO6 octahedron. DFT calculations indicate that this process has an activation energy significantly lower than that of the direct interstitial site exchange mechanism. For 800-1000 K, the MD diffusivities are consistent with the available experimental data within one order of magnitude. The DFT- and the MD-predictions suggest that the diffusion barrier for the interstitialcy mechanism is within 0.31-0.80 eV. The identified migration path, activation energies and diffusivities, and the associated uncertainties are discussed in the context of the previous experimental and theoretical results from the related Ruddlesden-Popper structures

Modelling science trustworthiness under publish or perish pressure

Scientific publication is immensely important to the scientific endeavour. There is, however, concern that rewarding scientists chiefly on publication creates a perverse incentive, allowing careless and fraudulent conduct to thrive, compounded by the predisposition of top-tier journals towards novel, positive findings rather than investigations confirming null hypothesis. This potentially compounds a reproducibility crisis in several fields, and risks undermining science and public trust in scientific findings. To date, there has been comparatively little modelling on factors that influence science trustworthiness, despite the importance of quantifying the problem. We present a simple phenomenological model with cohorts of diligent, careless and unethical scientists, with funding allocated by published outputs. This analysis suggests that trustworthiness of published science in a given field is influenced by false positive rate, and pressures for positive results. We find decreasing available funding has negative consequences for resulting trustworthiness, and examine strategies to combat propagation of irreproducible science

Ariel - Volume 8 Number 3

Executive Editor James W. Lockard, Jr. Business Manager Neeraj K. Kanwal University News Richard J . Perry World News Doug Hiller Opinions Elizabeth A. McGuire Features Patrick P. Sokas Sports Desk Shahab S. Minassian Managing Editor Edward H. Jasper Managing Associate Brenda Peterson Photography Editor Robert D. Lehman. Jr. Graphics Christine M. Kuhnl

A bone of contention: A dynamic ultrasound assessment of the role of the radial head in the arthrokinematics of the proximal radioulnar joint

INTRODUCTION: The arthrokinematics of the proximal radioulnar joint (PRUJ) are believed to follow the convex-concave rule, meaning that when the convex radial head articulates with the concave radial notch on the ulna, rolling and gliding occur in opposite directions during forearm pronation and supination. Previous research using helical computerized tomography (CT) identified that the sequence of joint actions is in contrast with this rule, which would indicate a posterior glide of the radius on the ulna during pronation movement and the converse during supination. OBJECTIVES: The aims of this study are to determine the arthrokinematics of the PRUJ while being assessed via ultrasound (US) imaging and to assess the impact the direction of joint mobilization has on active and passive range of motion (ROM) during forearm supination and pronation at the PRUJ. METHODS: A convenience sample of 53 healthy individuals were recruited. The arthrokinematics of the PRUJ were observed via US cine-loops. A linear US transducer was applied in the transverse plane and placed over the radial head during all testing conditions. A metronome standardized the rate of forearm pronation and supination at 1Hz (60 bpm) during US cine-loops acquisition. Radial head motion was assessed in two different elbow positions during US and joint range of motion assessment. The elbow was flexed to 90° with a neutral forearm position and fully extended with a neutral forearm position. The glenohumeral joint was stabilized during all testing conditions. A repeated measures design randomizing joint mobilization direction to the radial head was utilized to assess forearm pronation and supination via inclinometer data measured in degrees. Joint glides were applied to the radial head according to the convex-concave rule to facilitate forearm supination and pronation. An anteromedial glide to facilitate forearm supination and a posterolateral glide to facilitate forearm pronation. A metronome standardized the rate of joint mobilization at a rate 2Hz (120 bpm). A bubble inclinometer assessed active and passive PRUJ ROM at the wrist during all testing conditions. RESULTS:US imaging cine-loops showed the radial head rolled anteromedially during pronation and posterolaterally during supination, with no translation/gliding evident. Multivariate analysis revealed that the direction of joint mobilization had a significant impact on ROM F(1,47.0)= 6.964, p=.011, partial η2 =.129), with anterior mobilization increasing pronation and posterior mobilization increasing supination. Supination ROM was significantly increased F1(1, 47.0) = 78.03, p CONCLUSION: Our findings are in conflict with the convex-concave rule, which is frequently used by physical therapists to improve joint motion. Should we now reconsider applying this rule to improve joint ROM at the PRUJ

Direct detection of Rydberg–Rydberg millimeter-wave transitions in a buffer gas cooled molecular beam

Millimeter-wave transitions between molecular Rydberg states (n ∼ 35) of barium monofluoride are directly detected via Free Induction Decay (FID). Two powerful technologies are used in combination: Chirped-Pulse millimeter-Wave (CPmmW) spectroscopy and a buffer gas cooled molecular beam photoablation source. Hundreds of Rydberg–Rydberg transitions are recorded in 1 h with >10:1 signal:noise ratio and ∼150 kHz resolution. This high resolution, high spectral velocity experiment promises new strategies for rapid measurements of structural and dynamical information, such as the electric structure (multipole moments and polarizabilities) of the molecular ion-core and the strengths and mechanisms of resonances between Rydberg electron and ion-core motions. Direct measurements of Rydberg–Rydberg transitions with kilo-Debye dipole moments support efficient and definitive spectral analysis techniques, such as the Stark demolition and polarization diagnostics, which enable semi-automatic assignments of core-nonpenetrating Rydberg states. In addition, extremely strong radiation-mediated collective effects (superradiance) in a dense Rydberg gas of barium atoms are observed.National Science Foundation (U.S.) (Grant No. CHE-1361865)United States. Department of Defense (National Defence Science & Engineering Graduate Fellowship (NDSEG) Program