Towards the spatial resolution of metalloprotein charge states by detailed modeling of XFEL crystallographic diffraction.

Oxidation states of individual metal atoms within a metalloprotein can be assigned by examining X-ray absorption edges, which shift to higher energy for progressively more positive valence numbers. Indeed, X-ray crystallography is well suited for such a measurement, owing to its ability to spatially resolve the scattering contributions of individual metal atoms that have distinct electronic environments contributing to protein function. However, as the magnitude of the shift is quite small, about +2 eV per valence state for iron, it has only been possible to measure the effect when performed with monochromated X-ray sources at synchrotron facilities with energy resolutions in the range 2-3 × 10-4 (ΔE/E). This paper tests whether X-ray free-electron laser (XFEL) pulses, which have a broader bandpass (ΔE/E = 3 × 10-3) when used without a monochromator, might also be useful for such studies. The program nanoBragg is used to simulate serial femtosecond crystallography (SFX) diffraction images with sufficient granularity to model the XFEL spectrum, the crystal mosaicity and the wavelength-dependent anomalous scattering factors contributed by two differently charged iron centers in the 110-amino-acid protein, ferredoxin. Bayesian methods are then used to deduce, from the simulated data, the most likely X-ray absorption curves for each metal atom in the protein, which agree well with the curves chosen for the simulation. The data analysis relies critically on the ability to measure the incident spectrum for each pulse, and also on the nanoBragg simulator to predict the size, shape and intensity profile of Bragg spots based on an underlying physical model that includes the absorption curves, which are then modified to produce the best agreement with the simulated data. This inference methodology potentially enables the use of SFX diffraction for the study of metalloenzyme mechanisms and, in general, offers a more detailed approach to Bragg spot data reduction

Local pressure-induced metallization of a semiconducting carbon nanotube in a crossed junction

The electronic and vibrational density of states of a semiconducting carbon nanotube in a crossed junction was investigated by elastic and inelastic scanning tunneling spectroscopy. The strong radial compression of the nanotube at the junction induces local metallization spatially confined to a few nm. The local electronic modifications are correlated with the observed changes in the radial breathing and G-band phonon modes, which react very sensitively to local mechanical deformation. In addition, the experiments reveal the crucial contribution of the image charges to the contact potential at nanotube-metal interfaces

Practical Writing: The Expository Essay [9th grade]

This Understanding by Design unit is written to fulfill the requirement of the elective class Practical Writing and accompanying TEKS objectives. The course is structured to strengthen emerging writer\u27s ability to generate, revise, and refine their writing through the consistent use of writer\u27s notebooks, anchor rubrics, and model texts. A heavy emphasis is placed on student ownership of the revision process and self reflection based on progress demonstrated in a student portfolio. The unit culminates in a personal essay collection, illustration, and author page generated by the student and compiled by the teacher into a class essay collection published as a Kindle EBook

Harnessing Science to Strengthen Communication of Scientific Findings

Remembrances of an ACE member who was around when it started to happen

Task Force Proposes Research

The Morrill Act of 1862 created public universities with specific responsibilities to the sons and daughters of the working classes - to provide higher education in agriculture and the mechanic arts

Communicator Roles in Extension

The preamble of the Smith-Lever Act - which created and continues to guide the Cooperative Extension Service - charged the extension organization to disseminate information and encourage its application

The Good Guys Made Me Do It

Kern\u27s remarks at the Awards Banquet, National ACE Conference, where he received the ACE Professional Award

An Approach to Annual Reports By Agricultural Research Departments

Leaders in agricultural research institutions in many developing countries want to publish English-language annual reports. They have few editorial and financial resources. Few have ( 1) analyzed their reasons for reporting, (2) set priorities among audiences, or (3) considered a design that would serve the audience(s). This paper proposes three main audiences for such reports: heads of agencies that use agricultural research findings, agricultural scientists, and some persons interested in agricultural science (but not scientists). An audience-friendly approach is suggested for the design and preparation of annual reports that can be more useful than those written in the usual scientific-report form