Revealing the relationship between liquid fragility and medium-range order in silicate glasses.

Despite decades of studies, the nature of the glass transition remains elusive. In particular, the sharpness of the dynamical arrest of a melt at the glass transition is captured by its fragility. Here, we reveal that fragility is governed by the medium-range order structure.

ABINIT: Overview and focus on selected capabilities.

abinit is probably the first electronic-structure package to have been released under an open-source license about 20 years ago. It implements density functional theory, density-functional perturbation theory (DFPT), many-body perturbation theory (GW approximation and Bethe-Salpeter equation), and more specific or advanced formalisms, such as dynamical mean-field theory (DMFT) and the "temperature-dependent effective potential" approach for anharmonic effects. Relying on planewaves for the representation of wavefunctions, density, and other space-dependent quantities, with pseudopotentials or projector-augmented waves (PAWs), it is well suited for the study of periodic materials, although nanostructures and molecules can be treated with the supercell technique.

Simulating rewetting events in intermittent rivers and ephemeral streams: A global analysis of leached nutrients and organic matter.

Climate change and human pressures are changing the global distribution and the extent of intermittent rivers and ephemeral streams (IRES), which comprise half of the global river network area. IRES are characterized by periods of flow cessation, during which channel substrates accumulate and undergo physico-chemical changes (preconditioning), and periods of flow resumption, when these substrates are rewetted and release pulses of dissolved nutrients and organic matter (OM). However, there are no estimates of the amounts and quality of leached substances, nor is there information on the underlying environmental constraints operating at the global scale.

Why Ubiquitin Has Not Evolved.

Ubiquitin, discovered less than 50 years ago, tags thousands of diseased proteins for destruction. It is small (only 76 amino acids), and is found unchanged in mammals, birds, fish, and even worms, indicating that ubiquitin is perfect. Key features of its functionality are identified here using critical point thermodynamic scaling theory.

Dynamics of glass relaxation at room temperature.

The problem of glass relaxation under ambient conditions has intrigued scientists and the general public for centuries, most notably in the legend of flowing cathedral glass windows. Here we report quantitative measurement of glass relaxation at room temperature. We find that Corning® Gorilla® Glass shows measurable and reproducible relaxation at room temperature.

Communication: Resolving the vibrational and configurational contributions to thermal expansion in isobaric glass-forming systems.

A fundamental understanding of isobaric thermal expansion behavior is critical in all areas of glass science and technology. Current models of glass transition and relaxation behavior implicitly assume that the thermal expansion coefficient of glass-forming systems can be expressed as a sum of vibrational and configurational contributions. However, this assumption is made without rigorous theoretical or experimental justification.

Viscosity of glass-forming liquids.

The low-temperature dynamics of ultraviscous liquids hold the key to understanding the nature of glass transition and relaxation phenomena, including the potential existence of an ideal thermodynamic glass transition. Unfortunately, existing viscosity models, such as the Vogel-Fulcher-Tammann (VFT) and Avramov-Milchev (AM) equations, exhibit systematic error when extrapolating to low temperatures. We present a model offering an improved description of the viscosity-temperature relationship for both inorganic and organic liquids using the same number of parameters as VFT and AM.

Excimer-laser-induced densification in binary silica glasses.

We report that the rate of excimer-laser-induced densification is a strong function of composition in the binary metal-oxide-silica system. The pulsed excimer-laser-induced densification rate is shown to increase with metal-oxide content. A good correlation was found between the densification rate and the relative softness of the glass, as indicated by the annealing temperature.

Low-loss hollow-core silica/air photonic bandgap fibre.

Photonic bandgap structures use the principle of interference to reflect radiation. Reflection from photonic bandgap structures has been demonstrated in one, two and three dimensions and various applications have been proposed. Early work in hollow-core photonic bandgap fibre technology used a hexagonal structure surrounding the air core; this fibre was the first demonstration of light guided inside an air core of a photonic bandgap fibre.

Single-Mode Photonic Band Gap Guidance of Light in Air.

The confinement of light within a hollow core (a large air hole) in a silica-air photonic crystal fiber is demonstrated. Only certain wavelength bands are confined and guided down the fiber, each band corresponding to the presence of a full two-dimensional band gap in the photonic crystal cladding. Single-mode vacuum waveguides have a multitude of potential applications from ultrahigh-power transmission to the guiding of cold atoms.

193-nm excimer-laser-induced densification of fused silica.

We report the densification of fused silica as a function of exposure to pulsed 193-nm excimer-laser irradiation. Defining a dose as the number of pulses N times the square of fluence I per pulse, we find that densification follows a universal function of dose, a x (NI(2))(b), where a and b can vary somewhat according to glass preparation. Densification is measured with interferometry and birefringence, interpreted with a finiteelement elastic model.