Multi-phonon scattering and Ti-induced hydrogen dynamics in sodium alanate

We use ab initio methods and neutron inelastic scattering (NIS) to study the structure, energetics, and dynamics of pure and Ti-doped sodium alanate (NaAlH_4), focusing on the possibility of substitutional Ti doping. The NIS spectrum is found to exhibit surprisingly strong and sharp two-phonon features. The calculations reveal that substitutional Ti doping is energetically possible. Ti prefers to substitute for Na and is a powerful hydrogen attractor that facilitates multiple Al--H bond breaking. Our results hint at new ways of improving the hydrogen dynamics and storage capacity of the alanates.Comment: 5 pages, with 4 postscript figures embedded. Uses REVTEX4 and graphicx macro

Interplay of NH4+ and BH4- reorientational dynamics in NH4BH4

The reorientational dynamics of ammonium borohydride (NH4BH4) was studied using quasielastic neutron scattering in the temperature interval from 10 to 240 K, which covers both the dynamically ordered and disordered polymorphs of NH4BH4. In the low-temperature (50 K) ordered polymorph of NH4BH4, analysis of the quasielastic neutron scattering data reveals that no reorientational dynamics is present within the probed timescale region of 0.1 to 100 ps. In the high-temperature (50 K) disordered polymorph, the analysis establishes the onset of NH4+ and BH4- dynamics at around 50 and 125 K, respectively. The relaxation time at 150 K for NH4+ is approximately 1 ps, while around 100 ps for BH4- . The NH4+ dynamics at temperatures below 125 K is associated with preferential tetrahedral tumbling motions, where each of the hydrogen atoms in the NH4+ tetrahedron can visit any of the four hydrogen sites, however, reorientations around a specific axis are more frequently occurring (C-2 or C3). At higher temperatures, the analysis does not exclude a possible evolution of the NH4+ dynamics from tetrahedral tumbling to either cubic tumbling, where the hydrogen atoms can visit any of the eight positions corresponding to the corners of a cube, or isotropic rotational diffusion, where the hydrogen atoms can visit any location on the surface of a sphere. The BH4- dynamics can be described as cubic tumbling. The difference in reorientational dynamics between the two ions is related to the difference of the local environment where the dynamically much slower BH4- anion imposes a noncubic environment on the NH4+ cation

Interplay between the Reorientational Dynamics of the B3H8- Anion and the Structure in KB3H8

The structure and reorientational dynamics of KB3H8 were studied by using quasielastic and inelastic neutron scattering, Raman spectroscopy, first-principles calculations, differential scanning calorimetry, and in situ synchrotron radiation powder X-ray diffraction. The results reveal the existence of a previously unknown polymorph in between the alpha\u27- and beta-polymorphs. Furthermore, it was found that the [B3H8](-) anion undergoes different reorientational motions in the three polymorphs alpha, alpha\u27, and beta. In alpha-KB3H8, the [B3H8](-) anion performs 3-fold rotations in the plane created by the three boron atoms, which changes to a 2-fold rotation around the C-2 symmetry axis of the [B3H8](-) anion upon transitioning to alpha\u27-KB3H8. After transitioning to beta-KB3H8, the [B3H8](-) anion performs 4-fold rotations in the plane created by the three boron atoms, which indicates that the local structure of beta-KB3H8 deviates from the global cubic NaCl-type structure. The results also indicate that the high reorientational mobility of the [B3H8](-) anion facilitates the K+ cation conductivity, since the 2-orders-of-magnitude increase in the anion reorientational mobility observed between 297 and 311 K coincides with a large increase in K+ conductivity

Promoting Persistent Superionic Conductivity in Sodium Monocarba-closo-dodecaborate NaCB11H12 via Confinement within Nanoporous Silica

Superionic phases of bulk anhydrous salts based on large cluster-like polyhedral (carba)borate anions are generally stable only well above room temperature, rendering them unsuitable as solid-state electrolytes in energy-storage devices that typically operate at close to room temperature. To unlock their technological potential, strategies are needed to stabilize these superionic properties down to subambient temperatures. One such strategy involves altering the bulk properties by confinement within nanoporous insulators. In the current study, the unique structural and ion dynamical properties of an exemplary salt, NaCB11H12, nanodispersed within porous, high-surface-area silica via salt-solution infiltration were studied by differential scanning calorimetry, X-ray powder diffraction, neutron vibrational spectroscopy, nuclear magnetic resonance, quasielastic neutron scattering, and impedance spectroscopy. Combined results hint at the formation of a nanoconfined phase that is reminiscent of the high-temperature superionic phase of bulk NaCB11H12, with dynamically disordered CB11H12-anions exhibiting liquid-like reorientational mobilities. However, in contrast to this high-temperature bulk phase, the nanoconfined NaCB11H12 phase with rotationally fluid anions persists down to cryogenic temperatures. Moreover, the high anion mobilities promoted fast-cation diffusion, yielding Na+ superionic conductivities of similar to 0.3 mS/cm at room temperature, with higher values likely attainable via future optimization. It is expected that this successful strategy for conductivity enhancement could be applied as well to other related polyhedral (carba)borate-based salts. Thus, these results present a new route to effectively utilize these types of superionic salts as solid-state electrolytes in future battery applications

Comparison of drug prescribing before and during the COVID-19 pandemic: A cross-national European study

Purpose: The COVID-19 pandemic had an impact on health care, with disruption to routine clinical care. Our aim was to describe changes in prescription drugs dispensing in the primary and outpatient sectors during the first year of the pandemic across Europe. Methods: We used routine administrative data on dispensed medicines in eight European countries (five whole countries, three represented by one region each) from January 2017 to March 2021 to compare the first year of the COVID-19 pandemic with the preceding 3 years. Results: In the 10 therapeutic subgroups with the highest dispensed volumes across all countries/regions the relative changes between the COVID-19 period and the year before were mostly of a magnitude similar to changes between previous periods. However, for drugs for obstructive airway diseases the changes in the COVID-19 period were stronger in several countries/regions. In all countries/regions a decrease in dispensed DDDs of antibiotics for systemic use (from −39.4% in Romagna to −14.2% in Scotland) and nasal preparations (from −34.4% in Lithuania to −5.7% in Sweden) was observed. We observed a stockpiling effect in the total market in March 2020 in six countries/regions. In Czechia the observed increase was not significant and in Slovenia volumes increased only after the end of the first lockdown. We found an increase in average therapeutic quantity per pack dispensed, which, however, exceeded 5% only in Slovenia, Germany, and Czechia. Conclusions: The findings from this first European cross-national comparison show a substantial decrease in dispensed volumes of antibiotics for systemic use in all countries/regions. The results also indicate that the provision of medicines for common chronic conditions was mostly resilient to challenges faced during the pandemic. However, there were notable differences between the countries/regions for some therapeutic areas

Mathematical Manipulative Models: In Defense of Beanbag Biology

Mathematical manipulative models have had a long history of influence in biological research and in secondary school education, but they are frequently neglected in undergraduate biology education. By linking mathematical manipulative models in a four-step process-1) use of physical manipulatives, 2) interactive exploration of computer simulations, 3) derivation of mathematical relationships from core principles, and 4) analysis of real data sets-we demonstrate a process that we have shared in biological faculty development workshops led by staff from the BioQUEST Curriculum Consortium over the past 24 yr. We built this approach based upon a broad survey of literature in mathematical educational research that has convincingly demonstrated the utility of multiple models that involve physical, kinesthetic learning to actual data and interactive simulations. Two projects that use this approach are introduced: The Biological Excel Simulations and Tools in Exploratory, Experiential Mathematics (ESTEEM) Project (http://bioquest.org/esteem) and Numerical Undergraduate Mathematical Biology Education (NUMB3R5 COUNT; http://bioquest.org/numberscount). Examples here emphasize genetics, ecology, population biology, photosynthesis, cancer, and epidemiology. Mathematical manipulative models help learners break through prior fears to develop an appreciation for how mathematical reasoning informs problem solving, inference, and precise communication in biology and enhance the diversity of quantitative biology education

Learner-Centered Inquiry in Undergraduate Biology: Positive Relationships with Long-Term Student Achievement

We determined short- and long-term correlates of a revised introductory biology curriculum on understanding of biology as a process of inquiry and learning of content. In the original curriculum students completed two traditional lecture-based introductory courses. In the revised curriculum students completed two new learner-centered, inquiry-based courses. The new courses differed significantly from those of the original curriculum through emphases on critical thinking, collaborative work, and/or inquiry-based activities. Assessments were administered to compare student understanding of the process of biological science and content knowledge in the two curricula. More seniors who completed the revised curriculum had high-level profiles on the Views About Science Survey for Biology compared with seniors who completed the original curriculum. Also as seniors, students who completed the revised curriculum scored higher on the standardized Biology Field Test. Our results showed that an intense inquiry-based learner-centered learning experience early in the biology curriculum was associated with long-term improvements in learning. We propose that students learned to learn science in the new courses which, in turn, influenced their learning in subsequent courses. Studies that determine causal effects of learner-centered inquiry-based approaches, rather than correlative relationships, are needed to test our proposed explanation

Behavior and Impact of Zirconium in the Soil–Plant System: Plant Uptake and Phytotoxicity

Because of the large number of sites they pollute, toxic metals that contaminate terrestrial ecosystems are increasingly of environmental and sanitary concern (Uzu et al. 2010, 2011; Shahid et al. 2011a, b, 2012a). Among such metals is zirconium (Zr), which has the atomic number 40 and is a transition metal that resembles titanium in physical and chemical properties (Zaccone et al. 2008). Zr is widely used in many chemical industry processes and in nuclear reactors (Sandoval et al. 2011; Kamal et al. 2011), owing to its useful properties like hardness, corrosion-resistance and permeable to neutrons (Mushtaq 2012). Hence, the recent increased use of Zr by industry, and the occurrence of the Chernobyl and Fukashima catastrophe have enhanced environmental levels in soil and waters (Yirchenko and Agapkina 1993; Mosulishvili et al. 1994 ; Kruglov et al. 1996)