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Plasma"anti-assistance" and"self-assistance" to high power impulse magnetron sputtering (open access)

Plasma"anti-assistance" and"self-assistance" to high power impulse magnetron sputtering

A plasma assistance system was investigated with the goal to operate high power impulse magnetron sputtering (HiPIMS) at lower pressure than usual, thereby to enhance the utilization of the ballistic atoms and ions with high kinetic energy in the film growth process. Gas plasma flow from a constricted plasma source was aimed at the magnetron target. Contrary to initial expectations, such plasma assistance turned out to be contra-productive because it led to the extinction of the magnetron discharge. The effect can be explained by gas rarefaction. A better method of reducing the necessary gas pressure is operation at relatively high pulse repetition rates where the afterglow plasma of one pulse assists in the development of the next pulse. Here we show that this method, known from medium-frequency (MF) pulsed sputtering, is also very important at the much lower pulse repetition rates of HiPIMS. A minimum in the possible operational pressure is found in the frequency region between HiPIMS and MF pulsed sputtering.
Date: January 30, 2009
Creator: Anders, Andre & Yushkov, Georgy Yu.
System: The UNT Digital Library
How did matter gain the upper hand over antimatter? (open access)

How did matter gain the upper hand over antimatter?

Antimatter exists! We routinely make it in laboratories. For every familiar particle type we find a matching antiparticle with opposite charge, but exactly the same mass. For example, a positron with positive charge has the same mass as an electron; an antiproton with negative charge has the same mass as a proton. Antimatter occurs naturally all over the universe wherever high-energy particles collide. The laws of physics for antimatter are very, very similar to those for antimatter--so far we know only one tiny difference in them, a detail of the weak interactions of quarks that earned Makoto Kobayashi and Toshihide Maskawa a share of the 2008 Nobel Prize for Physics. Our understanding of the early Universe also tells us that after inflation ended equal amounts of matter and antimatter were produced. Today there's a lot of matter in the universe, but very little antimatter. This leaves a big question for cosmology. How did matter gain the upper hand over antimatter? It's a question at the root of our existence. Without this excess, there would be no stars, no Earth, and no us! When a particle meets its antiparticle, they annihilate each other in a flash of radiation. This process removed …
Date: January 30, 2009
Creator: Quinn, Helen
System: The UNT Digital Library
Multidimensional profiling of cell surface proteins and nuclear markers (open access)

Multidimensional profiling of cell surface proteins and nuclear markers

Cell membrane proteins play an important role in tissue architecture and cell-cell communication. We hypothesize that segmentation and multidimensional characterization of the distribution of cell membrane proteins, on a cell-by-cell basis, enable improved classification of treatment groups and identify important characteristics that can otherwise be hidden. We have developed a series of computational steps to (i) delineate cell membrane protein signals and associate them with a specific nucleus; (ii) compute a coupled representation of the multiplexed DNA content with membrane proteins; (iii) rank computed features associated with such a multidimensional representation; (iv) visualize selected features for comparative evaluation through heatmaps; and (v) discriminate between treatment groups in an optimal fashion. The novelty of our method is in the segmentation of the membrane signal and the multidimensional representation of phenotypic signature on a cell-by-cell basis. To test the utility of this method, the proposed computational steps were applied to images of cells that have been irradiated with different radiation qualities in the presence and absence of other small molecules. These samples are labeled for their DNA content and E-cadherin membrane proteins. We demonstrate that multidimensional representations of cell-by-cell phenotypes improve predictive and visualization capabilities among different treatment groups, and identify hidden …
Date: January 30, 2009
Creator: Han, Ju; Chang, Hang; Andarawewa, Kumari; Yaswen, Paul; Helen Barcellos-Hoff, Mary & Parvin, Bahram
System: The UNT Digital Library
Evidence for residual elastic strain in deformed natural quartz (open access)

Evidence for residual elastic strain in deformed natural quartz

Residual elastic strain in naturally deformed, quartz-containing rocks can be measured quantitatively in a petrographic thin section with high spatial resolution using Laue microdiffraction with white synchrotron x-rays. The measurements with a resolution of one micrometer allow the quantitative determination of the deviatoric strain tensor as a function of position within the crystal investigated. The observed equivalent strain values of 800-1200 microstrains represent a lower bound of the actual preserved residual strain in the rock, since the stress component perpendicular to the cut sample surface plane is released. The measured equivalent strain translates into an equivalent stress in the order of {approx} 50 MPa.
Date: January 30, 2009
Creator: Kunz, Martin; Chen, Kai; Tamura,Nobumichi & Wenk, Hans-Rudolf
System: The UNT Digital Library
Is the world shrinking or are we getting bigger? (open access)

Is the world shrinking or are we getting bigger?

None
Date: January 30, 2009
Creator: Alexandre, Melanie
System: The UNT Digital Library
Electron exchange-correlation in quantum mechanics (open access)

Electron exchange-correlation in quantum mechanics

It is shown that Fermi-Dirac statistics is guaranteed by the Dirac current, from which spin-dependent quantum velocity fields and spin-dependent quantum trajectories can be inferred. Pauli's exclusion principle is demonstrated using the spin-dependent quantum trajectories. The Dirac current, unlike the Schroedinger current, is nonzero for stationary bound states due to the permanent magnetic moment of the electron. It is of order c{sup 0} in agreement with observation that Fermi-Dirac statistics is independent of electronic velocity. In summary the physical basis for exchange-correlation is found in Dirac's equation, although Schroedinger's equation may be used to evaluate the Dirac current in the nonrelativistic regime of electronic velocity.
Date: January 30, 2009
Creator: Ritchie, Burke
System: The UNT Digital Library