Deceleration of probe beam by stage bias potential improves resolution of serial block-face scanning electron microscopic images.

Serial block-face scanning electron microscopy (SBEM) is quickly becoming an important imaging tool to explore three-dimensional biological structure across spatial scales. At probe-beam-electron energies of 2.0 keV or lower, the axial resolution should improve, because there is less primary electron penetration into the block face. More specifically, at these lower energies, the interaction volume is much smaller, and therefore, surface detail is more highly resolved. However, the backscattered electron yield for metal contrast agents and the backscattered electron detector sensitivity are both sub-optimal at these lower energies, thus negating the gain in axial resolution. We found that the application of a negative voltage (reversal potential) applied to a modified SBEM stage creates a tunable electric field at the sample. This field can be used to decrease the probe-beam-landing energy and, at the same time, alter the trajectory of the signal to increase the signal collected by the detector. With decelerated low landing-energy electrons, we observed that the probe-beam-electron-penetration depth was reduced to less than 30 nm in epoxy-embedded biological specimens. Concurrently, a large increase in recorded signal occurred due to the re-acceleration of BSEs in the bias field towards the objective pole piece where the detector is located. By tuning the bias field, we were able to manipulate the trajectories of the  primary and secondary electrons, enabling the spatial discrimination of these signals using an advanced ring-type BSE detector configuration or a standard monolithic BSE detector coupled with a blocking aperture

In-phase and antiphase complete chaotic synchronization in symmetrically coupled discrete maps

We consider in-phase and antiphase synchronization of chaos in a system of coupled cubic maps. Regions of stability and robustness of the regime of in-phase complete synchronization was found. It was demonstrated that the loss of the synchronization is accompanied by bubbling and riddling phenomena. The mechanisms of these phenomena are connected with bifurcations of the main family of periodic orbits and orbits appeared from them. We found that in spite of the in-phase synchronization, the antiphase self-synchronization of chaos is impossible for discrete maps with symmetric diffusive coupling. For achieving antiphase synchronization we used method of controlled synchronization by addition feedback. The region of the controlled antiphase synchronization and phenomena which accompany the loss of the synchronization are presented

Crystal design simulation for a high resolution depth encoding pet tomograph

Position Emission Tomography is a functional imaging modality where positron labeled radiotracers are used to investigate biological processes. The imaging process occurs via simultaneous detection of two 511keV gamma rays originating from positron annihilation. A PET camera is a γ detection apparatus. Reconstruction algorithms are used to reconstruct the original radioactivity source distribution in the camera field of view (FOV) from the simultaneous detection of y rays originating from the same annihilations. PET has been extensively used to investigate function in living organism, especially in human subjects. In order to make the detection process efficient and useful, PET camera designs strive for high detection sensitivity and high resolution. One of the factors influencing the resolution is the size of the detectors. Smaller detectors lead to a better spatial resolution. On the other hand sensitivity is affected by the detector crystal composition and by the solid angle subtended by the detection apparatus. An ideal tomograph design will therefore involve small, efficient detectors placed as close as possible to the object being scanned. The work described in this thesis examines various detector crystal configurations that would lead to an optimum tomograph performance. In order to make the results of this study immediately relevant to the PET community the overall tomograph geometry was constrained to that which is currently being built by a tomograph manufacturing company CTI. This design consists of an octagonal detector configuration where each detector head is built with two layers of detector material. Such a design allows for the identification of the y depth of interaction (DOI) in the detector assembly which in turn allows to minimize the effect of the parallax error and thus contributes to an increased resolution uniformity across the camera FOV. The studies presented here examine the effect of different crystal layer configuration on resolution and sensitivity. Octagonal HRRT geometry was also compared to circular detector geometry. As part of a system design optimization, several novel methods for crystal element identification were investigated: Genetic-algorithm, neural network algorithm and "simple" geometric algorithm were tested and showed relatively equal identification performance in identifying 64x64 crystal elements of each layer. A fuzzy-logic approach for estimation of depth-of-interaction (DOI) was investigated and compared with the decay time discrimination approach. The simulation results were used to generate a Look-Up-Table (LUT) that is accessed during simulated data acquisition for an effective and quick crystal identification. A correct crystal identification also facilitated an improvement of the capability for accurate energy discrimination, since the detector gain and appropriate energy thresholds were considered on an element-by-element basis by accessing energy LUT. The final result of the work presented in this thesis is the determination of the effect of DOI correction on resolution uniformity for different crystal configuration. DOI correction was found to improve the resolution uniformity up to 67%.Science, Faculty ofPhysics and Astronomy, Department ofGraduat

Monitoring the health environment in Ukrainian primary schools

El artículo describe los resultados del monitoreo del ambiente de salud en las escuelas primarias de la región de Jarkiv (Ucrania), realizado en 2017 y 2018. En el estudio respondieron a unas preguntas las directores de 77 escuelas primarias, 42 inspectores de departamentos de educación (el número de distritos administrativos en la región de Jarkiv), 462 maestros y 847 padres de los niños. Mediante un modelo cualitativo construido sobre esta base, se evaluó la implementación del ambiente de salud en las escuelas. El modelo se construyó teniendo en cuenta aspectos organizativos, gerenciales, médicos, metodológicos, pedagógicos y familiares. Los resultados del monitoreo indican que los directores califican el estado del ambiente de salud en las escuelas primarias ligeramente más alto que los funcionarios. Al mismo tiempo, el indicador general se encuentra en los niveles promedio y suficiente. Con el desarrollo general del ambiente de salud, el análisis reveló un deterioro en el desarrollo de los aspectos familiares y pedagógicos (participación de los padres en eventos de salud, trabajo de la escuela de padres jóvenes, etc.). La disminución en el nivel de cooperación con los padres también se confirma por los resultados de las respuestas de los padres. El número más pequeño de participantes en el estudio caracterizó el sistema de monitoreo del ambiente de salud en las escuelas primarias de alto nivel. Reafirmamos la importancia de involucrar a todos los interesados en el contexto de la planificación, implementación, monitoreo y gestión del ambiente de salud