Rotational symmetry of photonic bound states in the continuum

The bound states in the continuum (BICs) have been investigated by simulating the optical reflectivity of a tri-layer photonic crystal slab. We found that optical BICs can occur in a class of photonic crystal systems with $$c_{1}^{z}$$ c 1 z , $$c_{2}^{z}$$ c 2 z or $$c_{4}^{z}$$ c 4 z rotational symmetries, which are constructed by three identical photonic crystal slabs. By applying the two mode coupled model, we obtain the reflectivity formula to fit the numerical data and evaluate the lifetime of radiation decay. In vicinity of BIC, the lifetime diverges as a power law form, when approaching the BIC point. The infinity life time of $$c_{1}^{z} {\text{ } - \text{ BIC}}$$ c 1 z - BIC in the tri-layer structure indicate that it is a true BIC. The $$c_{1}^{z} {\text{ } - \text{ BIC}}$$ c 1 z - BIC occurs robustly in tri-layer structures, but the resonance frequency of the BICs is dependent on the permittivity of slab, air-hole size and hole shape.

Radiation decay of thaumatin crystals at three X-ray energies

Radiation damage is an unavoidable obstacle in X-ray crystallographic data collection for macromolecular structure determination, so it is important to know how much radiation a sample can endure before being degraded beyond an acceptable limit. In the literature, the threshold at which the average intensity of all recorded reflections decreases to a certain fraction of the initial value is called the `dose limit'. The first estimatedD50dose-limit value, at which the average diffracted intensity was reduced to 50%, was 20 MGy and was derived from observing sample decay in electron-diffraction experiments. A later X-ray study carried out at 100 K on ferritin protein crystals arrived at aD50of 43 MGy, and recommended an intensity reduction of protein reflections to 70%,D70, corresponding to an absorbed dose of 30 MGy, as a more appropriate limit for macromolecular crystallography. In the macromolecular crystallography community, the rate of intensity decay with dose was then assumed to be similar for all protein crystals. A series of diffraction images of cryocooled (100 K) thaumatin crystals at identical small, 2° rotation intervals were recorded at X-ray energies of 6.33 , 12.66 and 19.00 keV. Five crystals were used for each wavelength. The decay in the average diffraction intensity to 70% of the initial value, for data extending to 2.45 Å resolution, was determined to be about 7.5 MGy at 6.33 keV and about 11 MGy at the two higher energies.

XDSAPP: a graphical user interface for the convenient processing of diffraction data usingXDS

XDSAPPis a Tcl/Tk-based graphical user interface for the easy and convenient processing of diffraction data sets usingXDS. It provides easy access to allXDSfunctionalities, automates the data processing and generates graphical plots of various data set statistics provided byXDS. By incorporating additional software, further information on certain features of the data set, such as radiation decay during data collection or the presence of pseudo-translational symmetry and/or twinning, can be obtained. Intensity files suitable forCCP4,CNSandSHELXare generated.