Exploring transmission Kikuchi diffraction using a Timepix detector

Electron backscatter diffraction (EBSD) is a well-established scanning electron microscope (SEM)-based technique [1]. It allows the non-destructive mapping of the crystal structure, texture, crystal phase and strain with a spatial resolution of tens of nanometers. Conventionally this is performed by placing an electron sensitive screen, typically consisting of a phosphor screen combined with a charge coupled device (CCD) camera, in front of a specimen, usually tilted 70° to the normal of the exciting electron beam. Recently, a number of authors have shown that a significant increase in spatial resolution is achievable when Kikuchi diffraction patterns are acquired in transmission geometry; that is when diffraction patterns are generated by electrons transmitted through an electron-transparent, usually thinned, specimen. The resolution of this technique, called transmission Kikuchi diffraction (TKD), has been demonstrated to be better than 10 nm [2,3]. We have recently demonstrated the advantages of a direct electron detector, Timepix [4,5], for the acquisition of standard EBSD patterns [5]. In this article we will discuss the advantages of Timepix to perform TKD and for acquiring spot diffraction patterns and more generally for acquiring scanning transmission electron microscopy micrographs in the SEM. Particularly relevant for TKD, is its very compact size, which allows much more flexibility in the positioning of the detector in the SEM chamber. We will furthermore show recent results using Timepix as a virtual forward scatter detector, and will illustrate the information derivable on producing images through processing of data acquired from different areas of the detector. We will show results from samples ranging from gold nanoparticles to nitride semiconductor nanorods

A Linear Iterative Unfolding Method

A frequently faced task in experimental physics is to measure the probability distribution of some quantity. Often this quantity to be measured is smeared by a non-ideal detector response or by some physical process. The procedure of removing this smearing effect from the measured distribution is called unfolding, and is a delicate problem in signal processing, due to the well-known numerical ill behavior of this task. Various methods were invented which, given some assumptions on the initial probability distribution, try to regularize the unfolding problem. Most of these methods definitely introduce bias into the estimate of the initial probability distribution. We propose a linear iterative method, which has the advantage that no assumptions on the initial probability distribution is needed, and the only regularization parameter is the stopping order of the iteration, which can be used to choose the best compromise between the introduced bias and the propagated statistical and systematic errors. The method is consistent: "binwise" convergence to the initial probability distribution is proved in absence of measurement errors under a quite general condition on the response function. This condition holds for practical applications such as convolutions, calorimeter response functions, momentum reconstruction response functions based on tracking in magnetic field etc. In presence of measurement errors, explicit formulae for the propagation of the three important error terms is provided: bias error, statistical error, and systematic error. A trade-off between these three error terms can be used to define an optimal iteration stopping criterion, and the errors can be estimated there. We provide a numerical C library for the implementation of the method, which incorporates automatic statistical error propagation as well.Comment: Proceedings of ACAT-2011 conference (Uxbridge, United Kingdom), 9 pages, 5 figures, changes of corrigendum include

Robert Edward Gross (1905-1988): ligation of a patent ductus arteriosus and the birth of a specialty.

The early 20th century saw an explosion in surgical expertise. Specialties dedicated to delicate organs such as the heart and vulnerable populations, like children, were in their infancy. Dr. William E. Ladd, the father of pediatric surgery, founded the first dedicated department of pediatric surgery at Boston Children’s Hospital in 1910. At the time, attempts at cardiac surgery almost universally ended in death of the patient. The first successful surgical treatment of the cardiac valves would not occur for another 15 years, and the great vessels would remain out of reach for decades more. Dr. Robert E. Gross, the shy and humble heir to the greats of this epoch, would push these embryonic fields into the modern era and train a generation of surgeons to face countless new challenges (Fig. 1)

Implementation of a Standardized Handoff System for a General Surgery Residency Program

Introduction: The I-PASS Handoff Bundle is an evidence based standardized set of educational materials designed to decrease handoff failures in patient care. Two of every three sentinel events , the most serious events reported to the Joint Commission, are due to failures of communication, including miscommunication during patient care handoffs. Implementation of the I-PASS method results in decreased medical errors and preventable adverse events There are few studies that evaluate this validated method in the context of a General Surgery resident program We aim to implement the I-PASS system into the transition of care process for General Surgery residents at our institution, and to analyze of the quality of the handoff process before and after the implementation.https://jdc.jefferson.edu/patientsafetyposters/1047/thumbnail.jp

Combination of measurements and the BLUE method

The most accurate method to combine measurement from different experiments is to build a combined likelihood function and use it to perform the desired inference. This is not always possible for various reasons, hence approximate methods are often convenient. Among those, the best linear unbiased estimator (BLUE) is the most popular, allowing to take into account individual uncertainties and their correlations. The method is unbiased by construction if the true uncertainties and their correlations are known, but it may exhibit a bias if uncertainty estimates are used in place of the true ones, in particular if those estimated uncertainties depend on measured values. In those cases, an iterative application of the BLUE method may reduce the bias of the combined measurement.Comment: 10 pages, 4 figures, proceedings of the XIIth Quark Confinement and Hadron Spectrum conference, 28/8-2/9 2016, Tessaloniki, Greec

Iron Dynamics in a Gas-Water-Sediment Microcosm

Iron dynamics in eutrophic systems were studied in the laboratory utilizing gas-water-Sediment phase sealed microcosms. Sediments from Hyrum Reservoir (2.4 percent iron by weight) were placed in the dark to simulate the hypolimnetic regions of a eutrophic impoundment. Iron both chemically and physically was readily available to microorganisms of the aqueous phase because iron in these systems was soluble. In the light microcosms, which simulated shallow littoral regions of eutrophic impoundments, iron was found in higher aqueous phase concentrations than was predicted chemically and physically; this was rationalized through biological mechanisms. The experiment was conducted in two phases: Phase I lasted 189 days (0 and 0.300 mg NO3–N/1 inputs) and phase II lated 175 days (10mg NO3-N/1 imput). Average light microcosm effluent iron concentrations increased from 0.092 mg FE/1 (Phase I) to 0.246 mg Fe/1 (Phase II) given higher inorganic nitrogen inputs. In Phase II, when nitrogen input into the microcosms ceased (nitrogen perturbations, day 115), aqueous phase iron concentrations in the dark microcosms increased dramatically (0.011 to 0.624 mg Fe/1)

Mapping Exoplanets

The varied surfaces and atmospheres of planets make them interesting places to live, explore, and study from afar. Unfortunately, the great distance to exoplanets makes it impossible to resolve their disk with current or near-term technology. It is still possible, however, to deduce spatial inhomogeneities in exoplanets provided that different regions are visible at different times---this can be due to rotation, orbital motion, and occultations by a star, planet, or moon. Astronomers have so far constructed maps of thermal emission and albedo for short period giant planets. These maps constrain atmospheric dynamics and cloud patterns in exotic atmospheres. In the future, exo-cartography could yield surface maps of terrestrial planets, hinting at the geophysical and geochemical processes that shape them.Comment: Updated chapter for Handbook of Exoplanets, eds. Deeg & Belmonte. 17 pages, including 6 figures and 4 pages of reference

Analysis of optical magnetoelectric effect in GaFeO_3

We study the optical absorption spectra in a polar ferrimagnet GaFeO_3. We consider the E1, E2 and M1 processes on Fe atoms. It is shown that the magnetoelectric effect on the absorption spectra arises from the E1-M1 interference process through the hybridization between the 4p and 3d states in the noncentrosymmetry environment of Fe atoms. We perform a microscopic calculation of the spectra on a cluster model of FeO_6 consisting of an octahedron of O atoms and an Fe atom displaced from the center with reasonable values for Coulomb interaction and hybridization. We obtain the magnetoelectric spectra, which depend on the direction of magnetization, as a function of photon energy in the optical region 1.0-2.5 eV, in agreement with the experiment.Comment: 18 pages, 5 figure