Protein crystals contain many kinds of disorder, but only a small fraction of these are likely to be important in limiting the diffraction properties of interest to crystallographers. X-ray topography, high-angular-resolution reciprocal space measurements, and standard crystallographic data collection have been used to probe three factors that may produce diffraction-limiting disorder: (1) solu...

Gallium nitride (GaN) is a tetrahedrally coordinated III-V compound semiconductor which has the hexagonal wurtzite structure with a wide band gap of 3.5 eV at 300 K. It is reported that a simple-metal-insulator-n-typeGaN diode produces blue electroluminescence. ' For this reason it has been studied as a material suitable for an effective optoelectronic device such as laser and light emitting di...

An international project was successfully completed which involved two major undertakings: (1) a round-robin to demonstrate the viability of the selected standard and (2) the certification of the lattice parameters of the SRM 1990, a Standard Reference Material(®) for single crystal diffractometer alignment. This SRM is a set of ≈3500 units of Cr-doped Al2O3, or ruby spheres [(0.420.011 mole fr...

The thermosalient effect (crystal jumping on heating) attracts much attention as both an intriguing academic phenomenon and in relation to its potential for the development of molecular actuators but its mechanism remains unclear. 1,2,4,5-Tetrabromobenzene (TBB) is one of the most extensively studied thermosalient compounds that has been shown previously to undergo a phase transition on heating...

Here V is periodic with respect to the crystal lattice Γ ⊂ R, and it models the electric potential generated by the lattice of atoms in the crystal. The potential W is a decreasing perturbation and h a small positive constant. There has been a growing interest in the rigorous study of the spectral properties of Bloch electrons in the presence of slowly varying external perturbations see 1–11 . ...

In those cases where charge-stripe order has been observed in cuprates, the crystal structure is such that the average rotational symmetry of the CuO2 planes is reduced from fourfold to twofold. As a result, one could argue that the reduced lattice symmetry is essential to the existence of stripe order. We use pressure to restore the average fourfold symmetry in a single crystal of La1.875Ba0.1...

We present an effective theory for the Bloch functions of a two-dimensional square lattice near a quadratic degeneracy point. The degeneracy is protected by the symmetries of the crystal, and breaking these symmetries can either open a band gap or split the degeneracy into a pair of linear degeneracies that are continuable to Dirac points. A degeneracy of this type occurs between the second and...

We have studied the photochromic reaction of p-hydroxycinnamic-thiophenyl ester in the microcrystalline state. We attributed the fluorescence spectral evolution of the microcrystal, under UV irradiation, to the photoinduced trans-to-cis isomerization. The photocyclic behavior of the chromophore was demonstrated by cis-to-trans back reaction under a subsequent visible light irradiation. In addit...

The asymmetric unit of the title compound, Na(+)·C(6)H(10)NS(2) (-)·2H(2)O, is composed of a sodium cation, a piperidine-dithio-carbamate anion which exhibits positional disorder, and two lattice water mol-ecules. The atoms of the piperidine ring are divided over two sites with occupancy factors of 0.554 (6) and 0.446 (6). In the crystal, the sodium cation (coordination number of 6) and the pip...

In this study, gene expression programming (GEP), a novel genetic algorithm, is used to developquantitative model as potential screening mechanism for mineral crystal lattice energy for the firsttime. Eight descriptors, including ionic radius, charges, effective nuclear charges and principalquantum number, are selected to establish this model. A nonlinear quantitative structure-...