116 research outputs found
Solar array thermal snap and the characteristics of its effect on UARS
The single solar array on the Upper Atmosphere Research Satellite (UARS) is subjected to a thermal distortion when the spacecraft enters and exits the Earth's shadow. The distortion results in a torque that alters the spacecraft attitude. Due to the sudden nature of the attitude discontinuity, the effect has been termed 'thermal snap'. Thermal snap has also been experienced by Landsats 4 and 5. Analyses by the spacecraft builder addressed the impact of the resultant torque on the onboard control system. This paper discusses the results of comparisons between the predicted effects of thermal snap on UARS and actual attitude solutions from UARS telemetry data. In addition, this paper describes the characteristics of the thermal snap on UARS in terms of maximum displacement, solar beta angle, and solar array drive angle. Comparisons are made between the actual times of thermal snaps and the predicted spacecraft sunrise and sunset times. The effects of the UARS thermal snap are summarized and a general comment is made relating possible effects of thermal snap on other satellites. Also, an analysis of UARS attitude solutions that span periods of thermal snap was performed to determine whether the gyro sampling time of 1/8 second is sufficient to properly model the resulting spacecraft attitude without compromising the accuracy requirements. The results of this analysis are discussed
Gold Nanoparticle Colorants as Traditional Ceramic Glaze Alternatives
Historically, Roman stained glass has been a standard for high‐temperature color stability since biblical times but was not properly characterized as emission from nanoparticle plasmon resonance until the 1990s. The methods under which it was created have been lost, but some efforts have recently been made to recreate these properties using gold nanoparticle inks on glassy surfaces. This body of work employs gold nanoparticle systems ranging from 0.015% to 0.100% (wt/wt), suspended in a clear glaze body. The glazes are fired with traditional ceramic methods—in both gas reduction and electric oxidation kilns—in which nanoparticles are retained and can be imaged via TEM. Various colors intensities are reported in addition to changes in nanoparticle size after application and firing. The nanoparticle glazes are compared to traditional red glazes, highlighting the significantly lower metal loading required (5%‐10% for traditional glazes vs 0.100% for gold (wt/wt)), therein. Finally, proof of concept is provided with a functional gold nanoparticle mug, fired in reduction, that costs roughly 0.98$ USD in gold used
A Conditional Yeast E1 Mutant Blocks the Ubiquitin–Proteasome Pathway and Reveals a Role for Ubiquitin Conjugates in Targeting Rad23 to the Proteasome
E1 ubiquitin activating enzyme catalyzes the initial step in all ubiquitin-dependent processes. We report the isolation of uba1-204, a temperature-sensitive allele of the essential Saccharomyces cerevisiae E1 gene, UBA1. Uba1-204 cells exhibit dramatic inhibition of the ubiquitin–proteasome system, resulting in rapid depletion of cellular ubiquitin conjugates and stabilization of multiple substrates. We have employed the tight phenotype of this mutant to investigate the role ubiquitin conjugates play in the dynamic interaction of the UbL/UBA adaptor proteins Rad23 and Dsk2 with the proteasome. Although proteasomes purified from mutant cells are intact and proteolytically active, they are depleted of ubiquitin conjugates, Rad23, and Dsk2. Binding of Rad23 to these proteasomes in vitro is enhanced by addition of either free or substrate-linked ubiquitin chains. Moreover, association of Rad23 with proteasomes in mutant and wild-type cells is improved upon stabilizing ubiquitin conjugates with proteasome inhibitor. We propose that recognition of polyubiquitin chains by Rad23 promotes its shuttling to the proteasome in vivo
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Experiments on Forming, Compressing and Extracting Electron Rings for the Collective Acceleration of Ions
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Experiments on Forming Intense Rings of Electrons Suitable for the Acceleration of Ions
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Experiments on Forming,Compressing and Extracting Electron Rings for the Collective Acceleration of Ions
In experiments related to the development of the electron-ring accelerator, electrons were injected into a pulsed magnetic field to form rings that were then compressed radially to a small size. The injected beam had a current of about 150 A at an energy of 3.3 MeV with an energy spread of {+-} 0.1% and a pulse length duration of 20 nsec. At low intensity, an increase in the minor radius of the ring and a large loss of electrons was observed to occur during the compression cycle. At high intensity, cooperative phenomena that caused a large increase in the energy spread accompanied by particle loss were observed. Theoretical interpretation of these observations suggests that the primary source of electron loss and enlargement of the axial dimension was the crossing of single-particle resonances during compression in the presence of large magnetic field nonlinearities and perturbations. The cooperative phenomena are interpreted as resulting from a negative mass instability. Despite the large minor radius and small number of electrons, experiments on extracting the ring were performed; under acceleration the ring failed to retain its integrity because of inadequate self-focusing
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Experiments on Forming Intense Rings of Electrons Suitable for the Acceleration of Ions
Electrons were injected from a 3.3-MeV 300-A accelerator into a circular orbit in a pulsed magnetic field. Trapped ring currents of 150 A (4 x 10{sup 12} electrons) were magnetically compressed from 19 cm to 3.5 cm radii and simultaneously accelerated from 3.3 MeV to 18 MeV in energy. The rms dimensions of the cross section of the ring after compression were a = 2.3 {+-} 0.2 mm radially and b = 1.6 {+-} 0.2 mm axially. The lifetime of the ring was typically 5.5 msec, and was determined by the decay of the magnetic field after compression. This lifetime could be decreased by the addition of hydrogen gas, indicating the focusing effect of the trapped positive ions
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