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There is an ongoing debate whether transdiagnostic neural mechanisms are shared by different anxiety-related disorders or whether different disorders show distinct neural correlates. To investigate this issue, studies controlling for design and stimuli across multiple anxiety-related disorders are needed.
The present functional magnetic resonance imaging study investigated neural correlates of visual disorder-related threat processing across unmedicated patients suffering from panic disorder (n = 20), social anxiety disorder (n = 20), dental phobia (n = 16) and post-traumatic stress disorder (n = 11) relative to healthy controls (HC; n = 67). Each patient group and the corresponding HC group saw a tailor-made picture set with 50 disorder-related and 50 neutral scenes.
Across all patients, increased activation to disorder-related v. neutral scenes was found in subregions of the bilateral amygdala. In addition, activation of the lateral amygdala to disorder-related v. neutral scenes correlated positively with subjective anxiety ratings of scenes across patients. Furthermore, whole-brain analysis revealed increased responses to disorder-related threat across the four disorders in middle, medial and superior frontal regions, (para-)limbic regions, such as the insula and thalamus, as well as in the brainstem and occipital lobe. We found no disorder-specific brain responses.
The results suggest that pathologically heightened lateral amygdala activation is linked to experienced anxiety across anxiety disorders and trauma- and stressor-related disorders. Furthermore, the transdiagnostically shared activation network points to a common neural basis of abnormal responses to disorder-related threat stimuli across the four investigated disorders.
Rotationally symmetric annular combustors are of practical importance because they generically resemble combustion chambers in gas turbines, in which thermoacoustically driven oscillations are a major concern. We focus on azimuthal thermoacoustic oscillations and model the fluctuating heat release rate as being dependent only on the local pressure in the combustion chamber. We study the dynamics of the annular combustor with a finite number of compact flames equispaced around the annulus, and characterize the flames’ response with a describing function. We discuss the existence, amplitude and the stability of standing and spinning waves, as a function of: (i) the number of the burners; (ii) the acoustic damping in the chamber; (iii) the flame response. We present the implications for industrial applications and the future direction of investigations. We then present as an example the first theoretical study of thermoacoustic triggering in annular combustors, which shows that rotationally symmetric annular chambers that are thermoacoustically unstable do not experience only stable spinning solutions, but can also experience stable standing solutions. We finally test the theory on one experiment with good agreement.
Monolayers of cobalt phthalocyanine (CoPc) and fluorinated cobalt phthalocyanine (F16CoPc) on silver (111) and on highly (0001) oriented pyrolytic graphite (HOPG) were imaged with a scanning tunneling microscope (STM) at cryogenic temperatures (around 30 K) at Chemnitz University of Technology. Domains of regular arrays with periodicity in two dimensions (2D) and a variety of plane symmetries were observed. Crystallographic image processing (CIP) was used to quantify deviations from the plane symmetry groups and to obtain symmetrized versions of the content of the average unit cells of some of these arrays. Conclusions on the point symmetry of the CoPc and F16CoPc molecules within the arrays were drawn.
Since the crystallographic phase and morphology of many materials changes with the crystal size in the one to hundred nanometer range and the potential technological applications of nanoparticles are enormous, a need arises to determine the crystallography of nanoparticles individually. Direct space high- resolution phase-contrast transmission electron microscopy (TEM) and atomic resolution Z-contrast scanning TEM when combined with goniometry of direct and/or reciprocal lattice vectors offer the possibility of developing dedicated nanocrystallography characterization methods for such small nanoparticles. Although experimentally feasible for cubic nanocrystals with lattice constants larger than 0.4 nm in contemporary high-resolution TEMs with modest tilt range, image-based nanocrystallography by means of transmission electron goniometry has so far only been employed by a few specialists worldwide. This is likely to change in the future with the availability of aberration-corrected TEMs. The reasons why this change is likely to happen are outlined in this paper.
We are of the opinion that students of an introductory materials science and engineering course should gain a thorough understanding of crystallographic core concepts by applying them quasi-experimentally in computer simulation sessions that run parallel to the lectures. Software simulations of goniometry of direct lattice vectors in a transmission electron microscope (TEM) will serve two purposes at once: to introduce students to practical aspects of electron microscopy and support their comprehension of crystallographic core concepts. We use the programming software Matlab and Java (Jmol applets) on a PC platform for the creation of software simulations that demonstrate this methodology and complement already existing software simulations. The newly created software is used in classroom demonstrations of an introductory materials science and engineering course at Portland State University and will become freely accessible over the internet. This software will also support and promote image-based nanocrystallography in TEM.
Crystallographic databases for inorganic materials that are freely accessible over the internet are reviewed. The Nano-Crystallography Database project is described. Instructions are given on how to visualize in three dimensions the atomic arrangements of the several thousand entries of the Crystallography Open Database.
Gallium nitride powders and zinc oxide powders were each calcined with a few weight percent of copper oxide and/or magnesium oxide either in air or N2. Powder X-ray diffractometry, transmission electron microscopy, energy dispersive X-ray spectroscopy, and electron energy loss spectroscopy were performed in order to observe calcination induced structural effects on these wurtzite type semiconductors. We note that our earlier magnetic results on Cu doped GaN are qualitatively consistent with recent first principle calculations [Wu et al., Appl. Phys. Lett. 89 (2006) 62505].
It is well known that the crystallographic phase and morphology of many materials changes with the crystal size in the tens of nanometer range and that many nanocrystals possess structural defects in excess of their equilibrium levels. A need to determine the ideal and real structure of individual nanoparticles, therefore, arises. High-resolution phase-contrast transmission electron microscopy (TEM) and atomic resolution Z-contrast scanning TEM (STEM) when combined with transmission electron goniometry offer the opportunity of develop dedicated methods for the crystallographic characterization of nanoparticles in three dimensions. This paper describes tilt strategies for taking data from individual nanocrystals “as found”, so as to provide information on their lattice structure and orientation, as well as on the structure and orientation of their surfaces and structural defects. Internet based java applets that facilitate the application of this technique for cubic crystals with calibrated tilt-rotation and double-tilt holders are mentioned briefly. The enhanced viability of image-based nanocrystallography in future aberration-corrected TEMs and STEMs is illustrated on a nanocrystal model system.
GeSn alloy nanocrystals were formed by implantation of Ge and Sn ions into an amorphous SiO2 matrix and subsequent thermal annealing. High resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy (STEM) with a high angle annular dark field (HAADF) detector were used to show that phase-segregated crystalline bi-lobe nanocrystals were formed. Rapid melting and solidification using a single excimer laser pulse transformed the bi-lobe structure into a homogeneously mixed amorphous structure. Raman spectroscopy was used to monitor the crystalline nature and approximate grain size of the Ge portion of the nanocrystals after each heat treatment, and the Raman spectra were compared with the TEM images.
In Scanning Transmission Electron Microscopy (STEM) the High-Angle Annular Dark-Field (HAADF) signal increases with atomic number and sample thickness, while dynamic scattering effects and sample orientation have little influence on the contrast. The sensitivity of the HAADF detector for a FEI F30 transmission electron microscope has been calibrated. Additionally, a nearly linear relationship of the HAADF signal with the incident electron current is confirmed. Cross sections of multilayered samples for contrast calibration were obtained by focused ion-beam (FIB) preparation. These cross sections contained several layers with known composition. A database with several pure elements and compounds has been compiled, containing experimental data on the fraction of electrons scattered onto the HAADF detector for each nanometer of sample thickness. Contrast simulations are based on the multi-slice formalism and confirm the differences in HAADF-scattering contrast for the elements and compounds. TEM offers high lateral resolution, but contains little or no information on the thickness of samples. Thickness maps in energy-filtered transmission electron microscopy, convergent-beam electron diffraction and tilt series are so far the only methods to determine thicknesses of particles in a transmission electron microscope. We show that the calibrated HAADF contrast can be used to determine the thicknesses of individual nanoparticles deposited on carbon films. With this information the volumes of nanoparticles with known composition were determined.
We demonstrate the applications of several novel techniques in solid-state nuclear magnetic resonance spectroscopy (SSNMR) to the structural studies of mesoporous organic-inorganic hybrid catalytic materials. Most of these latest capabilities of solid-state NMR were made possible by combining fast magic angle spinning (at ≥ 40 kHz) with new multiple RF pulse sequences. Remarkable gains in sensitivity have been achieved in heteronuclear correlation (HETCOR) spectroscopy through the detection of high-λ (1H) rather than low-λ (e.g., 13C, 15N) nuclei. This so-called indirect detection technique can yield through-space 2D 13C-1H HETCOR spectra of surface species under natural abundance within minutes, a result that earlier has been out of reach. The 15N-1H correlation spectra of species bound to a surface can now be acquired, also without isotope enrichment. The first indirectly detected through-bond 2D 13C-1H spectra of solid samples are shown, as well. In the case of 1D and 2D 29Si NMR, the possibility of generating multiple Carr-Purcell-Meiboom-Gill (CPMG) echoes during data acquisition offered time savings by a factor of ten to one hundred. Examples of the studied materials involve mesoporous silica and mixed oxide nanoparticles functionalized with various types of organic groups, where solid-state NMR provides the definitive characterization.