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Background: Cerebrospinal fluid (CSF) flow in disease has been investigated with two‐dimensional (2D) phase‐contrast magnetic resonance imaging (PC‐MRI) in humans. Despite similar diseases occurring in dogs, PC‐MRI is not routinely performed and CSF flow and its association with diseases is poorly understood. Objectives: To adapt 2D and four‐dimensional (4D) PC‐MRI to dogs and to apply them in a group of neurologically healthy dogs. Animals Six adult Beagle dogs of a research colony. Methods: Prospective, experimental study. Sequences were first optimized on a phantom mimicking small CSF spaces and low velocity flow. Then, 4D PC‐MRI and 2D PC‐MRI at the level of the mesencephalic aqueduct, foramen magnum (FM), and cervical spine were performed. Results: CSF displayed a bidirectional flow pattern on 2D PC‐MRI at each location. Mean peak velocity (and range) in cm/s was 0.92 (0.51‐2.08) within the mesencephalic aqueduct, 1.84 (0.89‐2.73) and 1.17 (0.75‐1.8) in the ventral and dorsal subarachnoid space (SAS) at the FM, and 2.03 (range 1.1‐3.0) and 1.27 (range 0.96‐1.82) within the ventral and dorsal SAS of the cervical spine. With 4D PC‐MRI, flow velocities of >3 cm/s were visualized in the phantom, but no flow data were obtained in dogs. Conclusion: Peak flow velocities were measured with 2D PC‐MRI at all 3 locations and slower velocities were recorded in healthy Beagle dogs compared to humans. These values serve as baseline for future applications. The current technical settings did not allow measurement of CSF flow in Beagle dogs by 4D PC‐MRI. [ABSTRACT FROM AUTHOR]

After the discovery of C60, a large family of fullerene molecules was also identified. Among them, elongated fullerenes are formed by the tubular assembly of carbon atoms. The van der Waals bonds between fullerene molecules are due to the correlations between fluctuating charge densities inside the molecules. The interaction is then dominated by collective excitations which are sensitive to the shape of the molecules. Therefore, van der Waals attraction is expected to be modified when considering successively spherical C60, C70 and more elongated fullerenes (tubules). This paper presents self-consistent computations of the van der Waals interaction between a (111) diamond probe tip and various fullerene molecules adsorbed on a gold surface. Relative to spherical C60, the dependence law of the force experienced by the probe tip as a function of the tip-sample distance decreased when approaching fullerene tubules. Simulations of scanning force microscope scans of carbon tubules next to C60 molecules show that the shape of the molecules affects the interpretation of scanning force microscopy imaging. Particularly, information about the height of the various molecules deposited on the surface must be considered with some care since carbon tubules with the same radius as C60 interact more strongly with the probe tip. © 1994 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) have high surface areas and excellent mechanical, electrical, and chemical properties, thus they can be useful in applications related to extraction and conversion of energy. They can be readily produced from hydrocarbon feedstocks. In this work, ethylene, the most voluminously produced hydrocarbon, was used as a CNT feedstock. It was pyrolytically decomposed at elevated temperatures (984-1130 K) to generate CNTs, by catalytic chemical vapor deposition (CVD) on stainless steel substrates. To explore possible utilization of carbon dioxide, a typical combustion byproduct, the ethylene gas was introduced to a preheated CVD reactor at the presence of various amounts of CO2, in a balance of inert nitrogen gas. The ethylene pyrolyzates were assessed at the presence/absence of catalysts and CO2 to identify the gaseous carbon growth agents. Experimental findings were also contrasted to predictions of a detailed chemical kinetic model. It was found that whereas decomposition of ethylene was somewhat inhibited by CO2 at the presence of the catalyst support, its conversion to CNTs was promoted. CNTs consistently formed at 5% CO2. Maximum yields of CNTs occurred at 1130 K, whereas highest CNT quality was achieved at 1080 K. Hydrogen and 1,3-butadiene (C4H6) were experimentally found to be the most abundant species of ethylene thermal decomposition. This was in agreement with the model, which also highlighted the importance of unimolecular hydrogen elimination. [ABSTRACT FROM AUTHOR]

Due to slowing or even inhibition of postmortem processes, freezing may make an estimation of the time-since-death very difficult. This is also true in previously frozen and subsequently thawed bodies. Knowledge of prior freezing is important, as it may lead to a different assessment of the time since death. Twelve pig heads were frozen at -20 °C, and 6 heads were either kept at room temperature (approximately 20 °C) or in a cooling cell (approximately 5 °C). The frozen brains and cadavers were thawed at either room temperature or in a cooling cell. All specimens underwent repeated CT and MRI scanning until the brains were sampled for histological examination. Two radiologists assessed the images and two pathologists reviewed the histological slides with regard to thawing artifacts and putrefaction. All raters were blinded regarding whether the samples had been frozen, for how long and how they had been thawed. Imaging revealed distinct, tiny bubble-like artifacts only in previously frozen specimens. Histology also revealed artifacts only seen in such cases, namely very distinct, columnar bubbles in the cerebral cortex. All raters successfully identified previously unfrozen brains (100%specificity) and nearly all previously frozen brains. Our results suggest that initial postmortem imaging can be of enormous importance in everyday forensic practice by identifying possible cases of previous freezing -- cases that would therefore warrant closer scrutiny and thus raise caution regarding the time of death. [ABSTRACT FROM AUTHOR]