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Metal chalcogenides have attracted great attention because of their broad applications. It has been well acknowledged that microstructure can alter the intrinsic properties and performance of metal chalcogenides. The structure–property–performance relationships can be investigated at atomic scale with scanning transmission and transmission electron microscopy (STEM and TEM). Nevertheless, careful specimen preparation is paramount for accurate analyses and interpretations. In this work, we compare the effects of a variety of well-established TEM specimen preparation methods on the observed microstructure of an ingot stoichiometric lead telluride (PbTe). Most importantly, from aberration corrected STEM and first principles calculations, we discovered that argon (Ar) ion milling can lead to surface irradiation damage in the form of Pb vacancy clusters and self-interstitial atom (SIA) clusters. The SIA clusters appear as orthogonal nanoscale features when characterized along the <001> crystal orientation of the rock salt structured PbTe. This obfuscates the interpretation of the intrinsic microstructure of metal chalcogenides, especially lead chalcogenides. We demonstrate that with sufficiently low energy (300 eV) Ar ion cleaning or appropriate high-temperature annealing, the surface damage layer can be properly cleaned and the orthogonal nanoscale features are significantly reduced. This reveals the materials’ intrinsic structure and can be used as the standard protocol for future TEM specimen preparation of lead-based chalcogenide materials.
The Best Practices in Social and Behavioral Research Course was developed to provide instruction on good clinical practice for social and behavioral trials. This study evaluated the new course.
Participants across 4 universities took the course (n=294) and were sent surveys following course completion and 2 months later. Outcomes included relevance, how engaging the course was, and working differently because of the course. Open-ended questions were posed to understand how work was impacted.
Participants rated the course as relevant and engaging (6.4 and 5.8/7 points) and reported working differently (4.7/7 points). Participants with less experience in social and behavioral trials were most likely to report working differently 2 months later.
The course was perceived as relevant and engaging. Participants described actions taken to improve rigor in implementing trials. Future studies with a larger sample and additional participating sites are recommended.
We present spectral descriptions based on high-resolution spectrograms of central stars of planetary nebulae, obtained with the ESO 3,6-m telescope + CASPEC (Cassegrain Echelle Spectrograph). We make preliminary determinations of stellar photospheric metal abundances, using non-LTE model atmospheres and non-LTE line formation calculations.
First results from the 4-6 months observations of the VIRGO experiment (Variability of solar IRradiance and Gravity Oscillations) on the ESA/NASA Mission SOHO (Solar and Heliospheric Observatory) are reported. The time series are evaluated in terms of solar irradiance variability, solar background noise characteristics and p-mode oscillations. The solar irradiance is modulated by the passage of active regions across the disk, but not all of the modulation is straightforwardly explained in terms of sunspot flux blocking and facular enhancement. The observed p-mode frequencies are more-or-less in agreement with earlier measurements, but it is interesting to note that systematic differences seem to exist between the observations in different colours. There is also evidence that magnetic activity plays a significant role in the dynamics of the oscillations beyond its modulation of the resonant frequencies. Moreover, by comparing the amplitudes of different components of p-mode multiplets, each of which are influenced differently by spatial inhomogeneity, we have found that activity enhances excitation.
The results of photometric and spectroscopic observations of dwarf novae are presented. The data were obtained during an international program of multiwavelength observations, held in 1986 February at several observatories, of dwarf novae during the first and subsequent days of outburst. During the campaign numerous dwarf novae were monitored in order to catch them in outburst. Preliminary results and analysis of some objects are reported elsewhere. A total of 30 dwarf novae were observed in the northern and southern hemispheres. Among them 37% were caught in outburst, including 10% on the rise to outburst and 17% in decline. Photometric observations were carried out in the UBVRI system and colour indexes were calculated.
New morphometric data gathered from cross-sections of two Lower Devonian land plants (Rhynia gwynne-vaughanii and Asteroxylon mackiei) are interpreted in terms of the evolution of the function of vascular bundles in early land plants. The following conclusions can be drawn from these new data: (1) The ratio of the cross-sectional area of the xylem (representing the conducting volume supplying the axis with water) to the xylem perimeter (representing the “contact area” between xylem and parenchyma through which water leaves the xylem and enters the parenchyma) is not constant for Rhynia axes, almost constant for Asteroxylon axes, and different between Rhynia and Asteroxylon. Thus, Bowers hypothesis that the ratio of cross-sectional area of the xylem to xylem perimeter is constant during ontogenetic development is true for Asteroxylon. That this ratio is constant during phylogeny, however, is not supported by our data. (2) The ratio between cross-sectional area of xylem to parenchyma is higher in Asteroxylon than in Rhynia. (3) As predicted by previous computer simulations, the ratio of the xylem perimeter to the axis perimeter plays a major role in determining water transport performance of the transpiring axis. This ratio is constant within ontogeny but is different in Asteroxylon and Rhynia. In Asteroxylon axes, this ratio is about twice as large as in Rhynia axes. (4) Contrary to the expectations, the distance between the outermost layer of the xylem and the transpiring surface, which represents the low-conductivity pathway through the parenchyma, appears not to be a limiting factor for the water transport in axes of Rhynia and Asteroxylon. (5) From the analysis of the geometric parameters, it is evident that Rhynia and Asteroxylon with their distinct stelar geometries represent two different constructional types for which no transitional stages are known.
The two-temperature, 2D hydrodynamic code Hydro–ELectro–IOnization–2–Dimensional (HELIO2D), which takes into account self-consistently the laser energy absorption in a target, ionization, heating, and expansion of the created plasma is elaborated. The wide-range two-temperature equation of state is developed and used to model the metal target dynamics from room temperature to the conditions of weakly coupled plasma. The simulation results are compared and demonstrated a good agreement with experimental data on the Mg target being heated by laser pulses of the nanosecond high-energy laser for heavy ion experiments (NHELIX) at Gesellschaft fur Schwerionenforschung. The importance of using realistic models of matter properties is demonstrated.
At the heart of a flight simulator resides the mathematical representation of aircraft behaviour in response to control inputs, atmospheric disturbances and system inputs including failures and malfunctions. While this mathematical model can never be wholly accurate, its fidelity, in comparison with real world behaviour, underpins the usefulness of the flight simulator. The present paper examines the state of the art achieved in validating mathematical models for helicopter simulators, addressing the strengths and weaknesses of the present European standard for the qualification of helicopter flight simulators, JAR FSTD-H (previously JAR-STD-1H/2H/3H). Essential questions are examined, such as: What is the required model fidelity to guarantee a simulation is sufficiently representative to be fit for purpose? Are the tolerances set in the current standards fine enough that they lead to only minor changes in handling qualities? What is an acceptable tuning process for the simulation? What is the effect of modelling fidelity on the overall pilot control strategy? What is the relationship between the settings of the simulator cueing environment and the behaviour of the pilot? What is the industrial experience on qualification of flight simulators that might usefully inform developments? Many of these questions were addressed in Europe in a previous GARTEUR Action Group (AG) HC/AG-12 the results of which are documented in this paper. Solutions are proposed for improving the current JAR-FSTD standard with respect to validation of mathematical models.
This paper investigates prospects of utilizing a high-power laser-driven target-normal-sheath-acceleration proton beam for the experimental demonstration of the magnetic self-focusing phenomenon in charged particle beams. In the proposed concept, focusing is achieved by propagating a space-charge dominated ion beam through a stack of thin conducting and grounded foils separated by vacuum gaps. As the beam travels through the system, image charges build up at the foils and generate electric field that counteracts the beam's electrostatic self-field — a dominant force responsible for expansion of a high current beam. Once the electrostatic self-field is “neutralized” by the image charges, the beam currents magnetic self-field will do the focusing. The focal spot size and focal length depends on the choice of a number of foils and distance between foils. Considering the typical electrical current level of a target-normal-sheath-acceleration proton beam, we conclude that it is feasible to focus or collimate a beam within tens of millimeters distance, e.g., using 200–1000 Al foils, 0.5 µm thick each, with foil spacing ranging from 25 µm to 100 µm. These requirements are within technical capabilities of modern target fabrication, thus allowing the first possible demonstration of the pinch effect with heavy ion beams.
The effect of positive inotropic agents on circulation and ventricular fibrillation threshold are not fully understood during the influence of metabolic acidosis during circulatory arrest. This is the same case with alkalosis, caused by the over-correction of sodium bicarbonate. Furthermore, the role of calcium during CPR is not clear.
Therefore, we investigated the influence of metabolic acidosis and alkalosis with and without the administration of the positive inotropic substances epinephrine and calcium upon contractility and ventricular fibrillation threshold.
The effect of alternative preparation methods (copper mold casting, melt spinning, and mechanical attrition) on amorphization and properties of Nd57Fe20Co5Al10B8 and Nd40Fe40Co5Al8B7 alloys has been investigated. For all differently prepared samples an amorphous phase is formed upon solidification or solid sate reaction. However, the samples prepared by different processing routes exhibit different transformation behavior in thermal analysis. The cast Nd57Fe20Co5Al10B8 rod exhibits crystallization at 790 K followed by melting at 810 K. Neither appreciable endothermic reaction due to a glass transition nor a supercooled liquid region have been observed. Mechanically alloyed powders and ball-milled prealloys reveal two exothermic DSC peaks in the range of 650-850 K. The J-H hysteresis loops of samples synthesized by different routes show that the unique atomic order responsible for hard magnetic properties can only be accessed at moderate cooling rate of the melt as realized in copper mold casting. Rapidly quenched ribbons, mechanically alloyed powders and ball-milled ingots do not show hard magnetic properties at room temperature. These results indicate that amorphous samples with different local atomic order can be prepared by different processing routes.
Graphite intercalation compounds (GIC's) are metal-semimetal superlattices which exhibit crystalline order, and have atomically perfect interfaces between the layers of the constituent species. From the standpoint of superconductivity, the KHg-GIC's are particularly interesting. The preparation and properties of these compounds are described, along with a series of recent experiments with hydrogen doping which have helped to elucidate their electronic properties. A density of states model suggested by the results of the hydrogen–doping experiments is presented and used to explain the variation of the superconducting transition temperature in these materials.
The effects of intentionally introduced impurities on the crystallization time, nucleation rate and crystallite growth velocity during solid phase random crystallization of amorphous Si thin films have been determined. Films deposited in UHV onto oxidized Si wafers were subjected to multiple energy ion implantation to introduce uniform distributions of P, B, As, O or F at 0.1–1.0 at.%. Crystallization times and growth velocities were determined over the temperature range 650 to 850°C from time-resolved reflectivity measurements, and nucleation rates were determined from these data using a classical, steady state nucleation and growth model. Strong impurity effects are observed: P, B and As all decrease the nucleation rate but accelerate the growth of crystallites, whereas both 0 and F retard growth while enhancing nucleation. The largest effects are for P, which reduces the nucleation rate more than 100 times at 1% concentration, and F, which increases the rate by roughly the same amount.
Measurements of the competition beween solid phase epitaxy, solid phase random nucleation, and melting in amorphous Si on a microsecond time scale are reported. We find that the behavior of amorphous Si under microsecond pulsed dye laser irradiation depends strongly on film thickness and temperature. In “thin” (≲1000 Å) films solid phase epitaxy is observed at temperatures up to and exceeding 1300°C with random nucleation dominating at T>1330° C; however, melting of amorphous Si does not occur. In contrast, in “thick” (2600 Å) amorphous films melting is observed at T˜1190°C. These results are discussed with respect to measurements obtained previously in the nanosecond time regime using Q-switched laser heating and in the 0.1–1 millisecond regime using “chopped beam” cw laser heating.
This paper discusses the intrusion of H into a-Si layers during solid phase epitaxy and the effect of this H on the growth kinetics. We show that during annealing in the presence of water vapor, H is continuously generated at the oxidizing a-Si surface and diffuses into the amorphous layer, where it causes a reduction in the epitaxial growth rate. The measured variation of growth rate with the depth of the amorphous/crystal interface is correlated with the concentration of H at the interface. The diffusion coefficient for H in a-Si is determined by comparing measured depth profiles with calculated values. Hydrogen intrusion is observed even in layers annealed in vacuum and in inert gas ambients. Thin (<;5000 Åthick) a-Si layers are especially susceptible to this effect, but we show that in spite of the presence of H the activation energy for SPE derived earlier from thin-layer data is in good agreement with the intrinsic value obtained from thick, hydrogen-free layers.
The spectral emissivity of a semi-transparent thin film on a heated substrate varies with film thickness due to optical interference within the layer. This leads to oscillations in the emitted blackbody radiation intensity when the film thickness changes with time. We show how measurements of these oscillations have been used to determine the crystallization kinetics and optical constants of ion-implanted amorphous Si and Ge layers undergoing solid phase epitaxial crystallization. A comparision of emission and reflectivity data illustrates that the emission behavior can be understood in terms of a straightforward optical model.
The use of band-edge reflection spectroscopy (BRS) to determine the substrate temperature during MBE is reviewed. Data are presented for Si, GaAs, InP and CdZnTe substrates, and the use of BRS during the growth of ZnTe on Si is demonstrated. We discuss complications that arise due to optical interference in the epitaxial layers, and methods to compensate for the effects of interference are described.
Ag+ was implanted in silica glass and beta alumina crystal and studied using particle backscattering and optical absorption. We found that Ag aggregates into colloidal metallic particles and when annealed diffuses toward the surface. The activation energy for diffusion is 0.14 eV in silica glass and 0.16 eV in beta alumina. Computer simulations indicate fast Ag+ diffusion is due to large concentrations of vacancies deposited along the track of the implanted ion. The high ionic conductivity of beta alumina promotes uniform spreading of the implanted layer.