Beyond the Average: Spatial and Temporal Fluctuations in Oxide Glass-Forming Systems.

Atomic structure dictates the performance of all materials systems; the characteristic of disordered materials is the significance of spatial and temporal fluctuations on composition-structure-property-performance relationships. Glass has a disordered atomic arrangement, which induces localized distributions in physical properties that are conventionally defined by average values. Quantifying these statistical distributions (including variances, fluctuations, and heterogeneities) is necessary to describe the complexity of glass-forming systems. Only recently have rigorous theories been developed to predict heterogeneities to manipulate and optimize glass properties. This article provides a comprehensive review of experimental, computational, and theoretical approaches to characterize and demonstrate the effects of short-, medium-, and long-range statistical fluctuations on physical properties (e.g., thermodynamic, kinetic, mechanical, and optical) and processes (e.g., relaxation, crystallization, and phase separation), focusing primarily on commercially relevant oxide glasses. Rigorous investigations of fluctuations enable researchers to improve the fundamental understanding of the chemistry and physics governing glass-forming systems and optimize structure-property-performance relationships for next-generation technological applications of glass, including damage-resistant electronic displays, safer pharmaceutical vials to store and transport vaccines, and lower-attenuation fiber optics. We invite the reader to join us in exploring what can be discovered by going beyond the average.

Juvenile sparids (Rhabdosargus holubi) consistently select structurally dense vegetated habitat in nursery seascapes.

Seagrass habitats provide structural complexity in coastal estuarine and marine environments, which offer fish optimal foraging grounds and refuge from predation. However, seagrasses are some of the most threatened ecosystems globally, with anthropogenic activities such as population growth and environmental degradation leading to the fragmentation, thinning, and loss of these habitats. Rhabdosargus holubi is one of only a few vegetation-associated marine fish species in South African estuaries. Although field studies have shown a strong association with seagrass over other aquatic vegetation for the juveniles of this species, habitat choice has never been empirically tested. Here, we used artificial vegetation units to test habitat choice (different structural complexities) for this species. We also tested whether habitat choice is influenced by a predatory threat, with fish preferentially selecting dense habitat in the presence of a predator and whether this effect may be more apparent in smaller individuals. We found that R. holubi significantly prefer greater structural complexity over less complex habitats, in both the absence and presence of a predator and for both small and large juveniles, showing that R. holubi actively choose more complex structures and are attracted to the structure per se irrespective of the threat of predation. This study highlights the importance of dense seagrass as nursery areas for this species and demonstrates how the loss of these habitats could impact the nursery function of estuaries.

Extended and Continuous Decline in Effective Population Size Results in Low Genomic Diversity in the World's Rarest Hyena Species, the Brown Hyena.

Hyenas (family Hyaenidae), as the sister group to cats (family Felidae), represent a deeply diverging branch within the cat-like carnivores (Feliformia). With an estimated population size of <10,000 individuals worldwide, the brown hyena (Parahyaena brunnea) represents the rarest of the four extant hyena species and has been listed as Near Threatened by the IUCN. Here, we report a high-coverage genome from a captive bred brown hyena and both mitochondrial and low-coverage nuclear genomes of 14 wild-caught brown hyena individuals from across southern Africa. We find that brown hyena harbor extremely low genetic diversity on both the mitochondrial and nuclear level, most likely resulting from a continuous and ongoing decline in effective population size that started ∼1 Ma and dramatically accelerated towards the end of the Pleistocene. Despite the strikingly low genetic diversity, we find no evidence of inbreeding within the captive bred individual and reveal phylogeographic structure, suggesting the existence of several potential subpopulations within the species.

Catalyst free, base free microwave irradiated synthesis of aryl nitrites from potassium aryltrifluoroborates and bismuth nitrate.

A mixture of bismuth nitrate pentahydrate and potassium aryltrifluoroborate in toluene under microwave heating at 120 °C for 20 min provides an interesting and mild reaction protocol for the synthesis of aryl nitrite. The conversion to aryl nitrites from aryltrifluoroborates without transition metal catalyst and base in high yields is remarkable.

Modeling Oxygen Tricluster Formation in Calcium Aluminosilicate Supercooled Liquids and Glasses.

Calcium aluminosilicate glasses have technological importance for a variety of industrial applications. However, the short-range structure of this glass system remains widely debated regarding the formation of oxygen triclusters. It is argued that triclusters are observed in high percentages within molecular dynamics simulations because of the high melting temperatures and correspondingly high fictive temperatures. This work explores the formation of such structural units by first simulating various compositions at different liquid temperatures to understand thermodynamic factors affecting the formation of such species. Structural results are then implemented into a statistical mechanical model which can predict the formation of triclusters at a given fictive temperature. Results show temperature and composition dependence of these structures, with aluminum charge modification favored in the peraluminous regime. It is concluded that oxygen triclusters are the preferred method of charge compensation even when extrapolating to laboratory fictive temperatures, indicating that triclusters are not a byproduct of simulation timescales.

Assumptions about fence permeability influence density estimates for brown hyaenas across South Africa.

Wildlife population density estimates provide information on the number of individuals in an area and influence conservation management decisions. Thus, accuracy is vital. A dominant feature in many landscapes globally is fencing, yet the implications of fence permeability on density estimation using spatial capture-recapture modelling are seldom considered. We used camera trap data from 15 fenced reserves across South Africa to examine the density of brown hyaenas (Parahyaena brunnea). We estimated density and modelled its relationship with a suite of covariates when fenced reserve boundaries were assumed to be permeable or impermeable to hyaena movements. The best performing models were those that included only the influence of study site on both hyaena density and detection probability, regardless of assumptions of fence permeability. When fences were considered impermeable, densities ranged from 2.55 to 15.06 animals per 100 km2, but when fences were considered permeable, density estimates were on average 9.52 times lower (from 0.17 to 1.59 animals per 100 km2). Fence permeability should therefore be an essential consideration when estimating density, especially since density results can considerably influence wildlife management decisions. In the absence of strong evidence to the contrary, future studies in fenced areas should assume some degree of permeability in order to avoid overestimating population density.

Predicting Ionic Diffusion in Glass from Its Relaxation Behavior.

In low-viscosity liquids, diffusion is inversely related to viscosity via the Stokes-Einstein relation. However, the Stokes-Einstein relation breaks down near the glass transition as the supercooled liquid transitions into the non-ergodic glassy state. The nonequilibrium viscosity of glass is governed by the liquid-state viscous properties, namely, the glass transition temperature and the fragility. Here, a model is derived to predict the ionic diffusivity of a glass from its nonequilibrium viscosity, accounting for the compositional dependence of the glass. The free energy activation barrier for diffusion is related to the activation enthalpy for viscous flow using the Mauro-Allan-Potuzak model of nonequilibrium viscosity [Mauro, J. C.; Allan, D. C.; Potuzak, M. Nonequilibrium Viscosity of Glass. Phys. Rev. B 2009, 80, 094204]. These insights allow for accurate prediction of activation barriers for diffusion of alkali ions. The model is supported by experimental results and nudged-elastic band calculations applied to sodium silicate and borate glasses.

Topological Origins of the Mixed Alkali Effect in Glass.

The mixed alkali effect, the deviation from expected linear property changes when alkali ions are mixed in a glass, remains a point of contention in the glass community. While several earlier models have been proposed to explain mixed alkali effects on ionic motion, models based on or containing discussion of structural aspects of mixed-alkali glasses remain rare by comparison. However, the transition-range viscosity depression effect is many orders in magnitude for mixed-alkali glasses, and the original observation of the effect (then known as the Thermometer Effect) concerned the highly anomalous temperature dependence of stress and structural relaxation time constants. With this in mind, a new structural model based on topological constraint theory is proposed herein which elucidates the origin of the mixed alkali effect as a consequence of network strain due to differing cation radii. Discussion of literature models and data alongside new molecular dynamics simulations and experimental data are presented in support of the model, with good agreement.

A long-term comparison of plication configurations for endoluminal gastroplication: circumferential versus helical.

GOALS: To determine the long-term efficacy of endoluminal gastroplication (ELGP) and the most effective plication configuration. BACKGROUND: Endoluminal gastroplication is an intriguing therapy for gastroesophageal reflux disease. We conducted a retrospective review of a prospective experience of patient cohorts comparing outcomes of the circumferential and helical plication patterns. STUDY: Twenty patients underwent ELGP, with 9 receiving the circumferential (Group 1) and 11 the helical pattern (Group 2). Manometry, endoscopy, and 24-hour pH monitoring were performed at baseline and at 6 months. Symptom scores and medication usage were assessed at baseline, 1, 3, 6, 12, and 18 months. RESULTS: Both groups did not differ significantly from each other with respect to symptom improvement, medication usage, or other variables measured. At 6 months, symptom scores, histamine-2 receptor antagonist (H2RA), proton pump inhibitor usage, and hernia size decreased significantly. No other parameter showed a significant change. At the 18-month follow-up, symptom scores and H2RA usage decreased significantly. CONCLUSION: ELGP improves heartburn and regurgitation scores at 18 months. Our study suggests that there is no benefit to additional plications when using the helical pattern.

Symptom predictability of reflux-induced respiratory disease.

Gastroesophageal reflux disease (GERD) often is associated with pulmonary problems such as asthma as well as recurrent and nocturnal cough. Dual-probe 24-hr pH monitoring may assist in establishing a correlation between these symptoms and GERD-related symptoms. To determine if any specific symptom was predictive of aspiration, this study was undertaken. Ambulatory dual-probe esophageal pH monitoring was performed on 133 patients who had upper airway and additional symptoms for GERD. All patients had esophageal manometric studies of the lower esophageal sphincter (LES), the upper esophageal sphincter (UES), and the esophageal body before dual-probe pH monitoring was performed. Using two assembled glass probes, the distal and the proximal sensors were placed 5 cm above the proximal border of the LES and 1 cm below the lower border of the UES, respectively. Patients were classified into three groups: proximal and distal probe positive (group I), proximal probe negative and distal probe positive (group II) and proximal and distal probe negative (Group III) Upper airway and additional symptoms plus manometry results of the LES, body and UES study were compared between groups. In addition, positive distal probe patients (groups I and II) were compared for distal fraction of time at pH < 4 and number of reflux episodes at each probe position. A positive distal probe result was defined as an abnormal DeMeester score (> 14.8). A proximal probe test result was considered positive if percent time pH < 4.0 was > 1.1 for total, 1.7 for upright, and 0.6 for supine positions. The ages of the subjects ranged from 18 to 83 years (mean age: 50.5 +/- 1.5 years). Groups I, II, and III included 16 patients, 38 patients, and 79 patients, respectively. Group I had a significantly higher incidence of nocturnal cough than the other two groups. (P < 0.05). The manometric data revealed between groups that LES pressure (LESP) for groups I and II was significantly lower than LESP for group III (P = 0.003). Cricoid pressure, pharyngeal pressure, length, and relaxation of UES were not different between groups. Fraction of reflux time for group I was significantly higher than for group II in the supine position and at mealtime (P < 0.05). The number of reflux episodes for group I was significantly higher at meal time (P < 0.01). In conclusion, nocturnal cough is strongly predictive of proximal esophageal reflux. Proximal reflux episodes are significantly more frequent in the supine position and correlate well with the high predictive value of nocturnal cough.