Browsing by Subject "phase"
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Item Anisotropic Magnetoresistance in Antiferromagnetic Sr2IrO4(2014-11) Wang, C.; Seinige, H.; Cao, G.; Zhou, J. S.; Goodenough, J. B.; Tsoi, M.; Wang, C.; Seinige, H.; Zhou, JS; Goodenough, J. B.; Tsoi, M.We report point-contact measurements of anisotropic magnetoresistance (AMR) in a single crystal of antiferromagnetic Mott insulator Sr2IrO4. The point-contact technique is used here as a local probe of magnetotransport properties on the nanoscale. The measurements at liquid nitrogen temperature reveal negative magnetoresistances (up to 28%) for modest magnetic fields (250 mT) applied within the IrO2 a-b plane and electric currents flowing perpendicular to the plane. The angular dependence of magnetoresistance shows a crossover from fourfold to twofold symmetry in response to an increasing magnetic field with angular variations in resistance from 1% to 14%. We tentatively attribute the fourfold symmetry to the crystalline component of AMR and the field-induced transition to the effects of applied field on the canting of antiferromagnetic-coupled moments in Sr2IrO4. The observed AMR is very large compared to the crystalline AMRs in 3d transition metal alloys or oxides (0.1%-0.5%) and can be associated with the large spin-orbit interactions in this 5d oxide while the transition provides evidence of correlations between electronic transport, magnetic order, and orbital states. The finding of this work opens an entirely new avenue to not only gain a new insight into physics associated with spin-orbit coupling but also to better harness the power of spintronics in a more technically favorable fashion.Item Effect of Laser Additive Manufacturing of Microstructure Evolution of Inoculated Zr47.5Cu45.5Al5Co2 Bulk Metallic Glass Matrix Composites(University of Texas at Austin, 2018) Rafique, Muhammad Musaddique Ali; Brandt, Milan; Easton, Mark; Qiu, Dong; Cole, Ivan; John, SabuBulk metallic glass matrix composites are advocated to be material of future owing to their superior strength, hardness and elastic strain limit. However, they possess poor toughness which makes them unusable in any structural engineering application. Inoculation has been used as an effective means to overcome this problem. Zr47.5Cu45.5Al5Co2 bulk metallic glass matrix composites (BMGMC) inoculated with ZrC have shown considerable refinement in microstructure owing to heterogeneous nucleation. Efforts have also been made to exploit modern laser-based metal additive manufacturing to fabricate BMGMC parts in one step. However, the effect of laser treatment on inoculated material is unknown. In this study, an effort has been made to apply laser based additive manufacturing on untreated and inoculated BMGMC samples. It is observed that laser treatment not only refined the microstructure but resulted in change of size, morphology and dispersion of CuZr B2 phase in base metal, heat affected zone and fusion zone. This effect is documented with back scattered electron imaging. This provides a basis for further research to quantify this phenomenon and full-scale part development.Item Femtosecond Pump-Probe Diagnostics Of Preformed Plasma Channels(2004-12) Zgadzaj, R.; Gaul, E. W.; Matlis, N. H.; Shvets, G.; Debus, A.; Downer, M. C.; Zgadzaj, R.; Gaul, E. W.; Matlis, N. H.; Shvets, G.; Debus, A.; Downer, M. C.We report on recent ultrafast pump-probe experiments 28 in He plasma waveguides using 800 nm, 80 fs pump pulses of 0.2 x 1018 W/cm2 peak guided intensity, and single orthogonally-polarized 800 nm probe pulses with similar to0.1% of pump intensity. The main results are: (1) We observe frequency-domain interference between the probe and a weak, depolarized component of the pump that differs substantially in mode shape from the injected pump pulse; (2) we observe spectral blue-shifts in the transmitted probe that are not evident in the transmitted pump. The evidence indicates that pump depolarization and probe blue-shifts both originate near the channel entrance.Item Frequency-Domain Streak Camera And Tomography For Ultrafast Imaging Of Evolving And Channeled Plasma Accelerator Structures(2010-11) Li, Z. Y.; Zgadzaj, R.; Wang, X. M.; Reed, S.; Dong, P.; Downer, M. C.; Li, Zhengyan; Zgadzaj, Rafal; Wang, Xiaoming; Reed, Stephen; Dong, Peng; Downer, Michael C.We demonstrate a prototype Frequency Domain Streak Camera (FDSC) that can capture the picosecond time evolution of the plasma accelerator structure in a single shot. In our prototype Frequency-Domain Streak Camera, a probe pulse propagates obliquely to a sub-picosecond pump pulse that creates an evolving nonlinear index >bubble> in fused silica glass, supplementing a conventional Frequency Domain Holographic (FDH) probe-reference pair that co-propagates with the >bubble>. Frequency Domain Tomography (FDT) generalizes Frequency-Domain Streak Camera by probing the >bubble> from multiple angles and reconstructing its morphology and evolution using algorithms similar to those used in medical CAT scans. Multiplexing methods (Temporal Multiplexing and Angular Multiplexing) improve data storage and processing capability, demonstrating a compact Frequency Domain Tomography system with a single spectrometer.Item Graphite Oxide Activated Zeolite NaY: Applications in Alcohol Dehydration(2013) Todd, Alexander D.; Bielawski, Christopher W.; Bielawski, Christopher W.A mixture of graphite oxide (GO) and the zeolite NaY (Si/Al = 5.1) was used to dehydrate various alcohols to their respective olefinic products. Using conditions optimized for 4-heptanol (15 wt% GO-NaY (1:1 wt/wt), 150 degrees C, 30 min), a series of secondary and tertiary aliphatic alcohols were cleanly dehydrated in moderate to excellent conversions (27.5-97.2%). Several primary alcohols were also dehydrated, although higher catalyst loadings (200 wt% GO-NaY (1 : 1) and longer reaction times (3 h) were required. The enhanced dehydration activity was attributed to the ability of GO to convert NaY to an acidic form and without the need for ammonium cation exchange and/or high temperature calcination.Item Modeling Subsurface Biodegradation of Non-Aqueous Phase Liquids: A Literature Review(University of Texas at Austin, 1995-02) de Blanc, P.C.; McKinney, D.C.; Speitel, G.E. JrItem Plasma Channels And Laser Pulse Tailoring For Gev Laser-Plasma Accelerators(2002-12) Downer, M.C.; Chiu, C.; Fomyts'kyi, M.; Gaul, E.W.; Grigsby, F.; Matlis, N.H.; Shim, B.; Smith, P.J.; Zgadzaj, R.; Downer, M.C.; Chiu, C.; Fomyts’kyi, M.; Gaul, E.W.; Grigsby, F.; Matlis, N.H.; Shim, B.; Smith, P.J.; Zgadzaj, R.We have demonstrated distortion-free guiding of I TW pulses at near relativistic intensity (0.2 x 10(18) W/cm(2)) over 60 Rayleigh lengths at 20 Hz repetition rate in a preformed helium plasma channel. As steps toward efficient channeled Laser Wakefield Acceleration up to the dephasing limit, we have upgraded our laser system from I to 4 TW, adapted femtosecond interferometric diagnostics to probe plasma density fluctuations inside the channel, and developed detailed strategies for managing ionization distortions at the channel entrance and exit at the upgraded intensity. We also report simulations, and preliminary experiments, that explore a strategy for Raman-seeding laser pulses to coherently control both unchanneled and channeled LWFA in order to lower the laser energy threshold and increase the repetition rate of election pickup and acceleration.Item Synthesis of 2-Substituted 9-Oxa-Guanines {5-Aminooxazolo 5,4-D Pyrimidin-7(6H)-Ones} and 9-Oxa-2-Thio-Xanthines{5-Mercaptooxazolo 5,4-D Pyrimidin-7(6H)-Ones}(2008-07) Mandal, Subrata; Li, Wen Tai; Bai, Yan; Robertus, Jon D.; Kerwin, Sean M.; Mandal, Subrata; Li, Wen Tai; Bai, Yan; Robertus, Jon D.; Kerwin, Sean M.Oxazolo[5,4-d] pyrimidines can be considered as 9-oxa-purine analogs of naturally occurring nucleic acid bases. Interest in this ring system has increased due to recent reports of biologically active derivatives. In particular, 5-aminooxazolo[5,4-d]pyrimidine-7(6H)-ones (9-oxa-guanines) have been shown to inhibit ricin. The preparation of a series of 2-substituted 5-aminooxazolo[5,4-d] pyrimidin-7(6H)-ones and related 5-thio-oxazolo[5,4-d] pyrimidines is described, including analogs suitable for further elaboration employing "click" chemistry utilizing copper-catalyzed Huisgen 1,3-dipolar cycloadditions. Two of the compounds prepared were found to inhibit ricin with IC(50) ca. 1-3 mM.