Tungsten nanostructure formation in a magnetron sputtering device

Fuzzy tungsten is a phenomena that could potentially occur in future fusion reactors. There are three conditions for fuzz to form, the existence of He ions impinging on a tungsten sample for a sufficient amount of time, that these ions be of sufficient energy, and that the surface temperature of the tungsten is hot enough. These conditions will likely be fulfilled in ITER, the future flagship fusion reactor. Therefore efforts to understand and characterise the fuzz formation are of importance. A thorough literature review has been provided, bringing together for the first time works from over 100 papers on the area. The history of its discovery is explained and the characteristics of the structure are detailed. The potential for fuzz to occur in ITER is shown, and positive and negative aspects of fuzz for fusion operation are discussed. The current accepted growth mechanisms are explained and a brief summary of the current work on simulating the phenomena is given. Fuzz appearing on other metals is introduced, and evidence of creating fuzz in a tokamak is shown. Methods for removing fuzz are presented should it be deemed necessary to do so in ITER. Results are compiled from many fuzz samples created in the literature spanning four orders of magnitude of fluence. This provided the foundation for a collaboration with the UC San Diego, and lab time at their facilities. Several samples were created to complement the dataset. The compilation provides new insights into the growth equation surrounding fuzz formation. A new addition to the equation is introduced in the form of an incubation fluence, a minimum fluence required before fuzz can develop. The growth model is expanded to fuzz grown in erosive regimes, and a new equation is proposed that encompasses the competition between growth and erosion, giving good predictions for the resulting equilibrium thickness. A new method for creating fuzz has been developed in a cheap and simple way. Conventional methods involve using large scale expensive devices, only available in a select few places worldwide. Magnetrons are apparent in many laboratories around the world and a technique for making fuzz in them has been developed. The three parameters controlling fuzz formation have been studied in the magnetron by making samples at many different conditions. The results provide new insight into early fuzz formation, providing results in a fluence range often over-looked. A cross-over fluence is noted from pre-fuzz to fully formed fuzz, overlapping with the predicted incubation fluence. The results differ slightly from fuzz created in other devices at similar fluence. The most probable cause is due to the unique existence of deposition of metallic particles in a magnetron incident on the samples during the growth of fuzz

Assessment of fetal heart rate variability and velocity variability by Doppler velocimetry of the descending aorta at 10-20 weeks of gestation

Objectives: Determination of gestational age-related modulations in fetal heart rate and descending aorta blood flow velocity in the early human fetus and comparison of aortic variability data with data obtained from the umbilical artery. It is hypothesized that these modulations present in the umbilical artery also occur in the descending aorta. Methods: Doppler studies of descending aorta velocity waveforms were performed at 10-20 weeks in 55 normal pregnant women. In 24 of the 55 women, Doppler recordings from both the descending aorta and the umbilical artery were collected. Absolute values and variability of fetal heart rate, peak systolic and time-averaged velocities were determined from flow velocity waveforms of at least 18 s in duration. Results: From 10 to 20 weeks of gestation, the descending aorta peak systolic and time-averaged velocities increased, whereas the fetal heart rate decreased. The descending aorta peak systolic variability also increased. However, the time-averaged velocity variability and the fetal heart rate variability remained constant during the study period. In the subset of 24 women, the fetal heart rate variability and velocity variability data from the descending aorta and umbilical artery were not significantly different. Conclusions: Reproducible fetal heart rate and velocity variability data can be derived from the descending aorta and umblilical artery. The increase in heart rate variability observed in the umbilical artery was not seen in recordings obtained from the descending aorta. Different fetal activity states may be the underlying mechanism for these heart rate variability discrepancies

Instantons and radial excitations in attractive Bose-Einstein condensates

Imaginary- and real-time versions of an equation for the condensate density are presented which describe dynamics and decay of any spherical Bose-Einstein condensate (BEC) within the mean field appraoch. We obtain quantized energies of collective finite amplitude radial oscillations and exact numerical instanton solutions which describe quantum tunneling from both the metastable and radially excited states of the BEC of 7Li atoms. The mass parameter for the radial motion is found different from the gaussian value assumed hitherto, but the effect of this difference on decay exponents is small. The collective breathing states form slightly compressed harmonic spectrum, n=4 state lying lower than the second Bogolyubov (small amplitude) mode. The decay of these states, if excited, may simulate a shorter than true lifetime of the metastable state. By scaling arguments, results extend to other attractive BEC-s.Comment: 6 pages, 3 figure

Microstructural control of TiC/a-C nanocomposite coatings with pulsed magnetron sputtering

In this paper, we report some striking results on the microstructural control of TiC/a-C nanocomposite coatings with pulsed direct current (DC) magnetron sputtering. The interface morphology and microstructure evolution as a function of pulse frequency and duty cycle were scrutinized using atomic force microscopy, scanning electron microscopy and high-resolution transmission electron microscopy techniques. It is shown that, with increasing pulse frequency, the nanocomposite coatings exhibit evolutions in morphology of the growing interface from rough to smooth and in the microstructure from strongly columnar to fully columnar-free. In addition, the smoothly growing interface favors the formation of a tailor-made multilayered nanocomposite structure. The fundamental mechanisms are analyzed with the assistance of plasma diagnostic experiments. Ion mass/energy spectrometry measurements reveal that, depending on the frequency and duty cycle of DC pulses, pulsing of the magnetrons can control the flux and energy distribution of Ar+ ions over a very broad range for concurrent impingement on the growing interface of deposited coatings, in comparison with DC sputtering. The significantly enhanced energy flux density is thought to be responsible for the "adatom transfer" in interface smoothening and thus the restraint of columnar growth. (C) 2007 Acta Materialia, Inc. Published by Elsevier Ltd. All rights reserved.</p

Plasma polymerization of isopentyl nitrite at atmospheric pressure: gas phase analysis and surface chemistry

Nitric oxide (NO)-releasing coatings have promising potential for biomedical applications notably in implant safety and wound dressing by promoting healing and reducing bacterial growth. Yet, the production of NO-films remains difficult through classic approaches. In this study, plasma polymerized NO-coatings are produced using a helium-isopentyl nitrite mixture under two power settings and deposited on aluminum samples. Analyses of the plasma phase by mass spectroscopy reveal the presence of nitrosoxy groups (O–N═O) in monomer and quasi-monomer at low power, and a higher fragmentation rate at high power. Static and no-static samples are made and analyzed by X-ray photoelectron spectroscopy showing the presence of these group for both power conditions, with a better retention on the sample's center for the latest

Plasma polymerization of (2,2,6,6-tetramethylpiperidin-1-yl)oxyl in a collisional, capacitively coupled radio frequency discharge

Plasma polymerization of (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) yields thin films containing stable nitroxide radicals that have properties analogous to that of nitric oxide (NO) without short lifetimes. This property gives TEMPO films a wide variety of potential applications. Typically, control of the final film chemistry is difficult and the plasma discharge conditions must be tailored to in order to maximize the retention of these nitroxide groups during the polymerization and deposition process. In this study, plasma diagnostics and surface analysis of the deposited films were carried out to determine the optimal plasma conditions for the retention of nitroxide groups. These techniques included energy-resolved mass spectrometry, heated planar probe ion current measurements, deposition rate measurements, and x-ray photoelectron spectroscopy (XPS). Results show that operating the plasma with a combination of low input powers and high pressures produces a collisional discharge in which fragmentation of the TEMPO molecule is suppressed, leading to good retention of nitroxide groups. Ion energy distribution functions and quartz crystal microbalance measurements support the soft landing theory of ion deposition on the substrate within this γ-mode, in which the flux of low energy, soft landed ions form the primary contribution to film growth. XPS analysis of deposited polymers shows 75.7% retention of N - O groups in the polymer films deposited in a 25 Pa 5 W discharge. © 2020 Author(s)

Length of the weaning period affects postweaning growth, health, and carcass merit of ranch-direct beef calves weaned during the fall

Bovine respiratory disease (BRD) is the most economically devastating feedlot disease. Risk factors associated with incidence of BRD include (1) stress associated with maternal separation, (2) stress associated with introduction to an unfamiliar environment, (3) poor intake associated with introduction of novel feedstuffs into the animal\u27s diet, (4) exposure to novel pathogens upon transport to a feeding facility and commingling with unfamiliar cattle, (5) inappropriately administered respiratory disease vaccination programs, and (6) poor response to respiratory disease vaccination programs. Management practices that are collectively referred to as preconditioning are thought to minimize damage to the beef carcass from the BRD complex. Preconditioning management reduces the aforementioned risk factors for respiratory disease by (1) using a relatively long ranch-of-origin weaning period following maternal separation, (2) exposing calves to concentrate-type feedstuffs, and (3) producing heightened resistance to respiratory disease-causing organisms through a preweaning vaccination program. The effectiveness of such programs for preserving animal performance is highly touted by certain segments of the beef industry. Ranch-of-origin weaning periods of up to 60 days are suggested for preconditioning beef calves prior to sale; however, optimal length of the ranch-of-origin weaning period has not been determined experimentally. The objective of this study was to test the validity of beef industry assumptions about appropriate length of ranch-of-origin weaning periods for calves aged 160 to 220 days and weaned during the fall

Photon-axion conversion in intergalactic magnetic fields and cosmological consequences

Photon-axion conversion induced by intergalactic magnetic fields causes an apparent dimming of distant sources, notably of cosmic standard candles such as supernovae of type Ia (SNe Ia). We review the impact of this mechanism on the luminosity-redshift relation of SNe Ia, on the dispersion of quasar spectra, and on the spectrum of the cosmic microwave background. The original idea of explaining the apparent dimming of distant SNe Ia without cosmic acceleration is strongly constrained by these arguments. However, the cosmic equation of state extracted from the SN Ia luminosity-redshift relation remains sensitive to this mechanism. For example, it can mimic phantom energy.Comment: (14 pages, 9 eps figures) Contribution to appear in a volume of Lecture Notes in Physics (Springer-Verlag) on Axion