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Structural investigation of B{sup +} ion implantation induced amorphization in polycrystalline Ni thin films

Description: High fluence metalloid ion implantation have been shown to induce amorphous phase formation in transition metals systems. In this study, electron energy loss spectroscopy and energy filtered selective area electron diffraction have been used along with conventional TEM to characterize the structural and electronic changes resulting from B{sup +} ion implantation into polycrystalline Ni thin films.
Date: June 1, 1996
Creator: Liu, P.C.; Zaluzec, N.J.; Okamoto, P.R. & Meshii, M.
Partner: UNT Libraries Government Documents Department

Reactive Separations via a Hydrothermally Stable Hydrogen Selective Membrane. Final Report

Description: In this SBIR Phase I program, we have successfully completed the fabrication of SiC-based hydrogen selective membranes suitable for use as a membrane reactor for steam-methane reforming applications. Hydrothermal stability was performed for selected membrane to demonstrate their stability for appx. 50 hours under the proposed reforming condition. In addition, several mechanistic study was conducted to elucidate the SiC membrane formation mechanism. This understanding will facilitate membrane optimization work to be proposed for the Phase II study. The reaction study was postponed to the Phase II study.
Date: October 29, 2002
Creator: Ciora, R. J. & Liu, P. KT.
Partner: UNT Libraries Government Documents Department

The Madden-Julian Oscillation in the National Center for Atmospheric Research Community Atmospheric Model-2 with the Tiedtke Convective Scheme

Description: The boreal winter Madden-Julian oscillation (MJO) remains very weak and irregular in structure in the National Center for Atmospheric Research (NCAR) Community Atmosphere Model version 2 (CAM2) as in its direct predecessor, the Community Climate Model version 3 (CCM3). The standard version of CAM2 uses the deep convective scheme of Zhang and McFarlane (1995), as in CCM3, with the closure dependent on convective available potential energy (CAPE). Here, sensitivity tests using several versions of the Tiedtke (1989) convective scheme are conducted. Typically, the Tiedtke convection scheme gives an improved mean state, intraseasonal variability, space-time power spectra, and eastward propagation compared to the standard version of the model. Coherent eastward propagation of MJO related precipitation is also much improved, particularly over the Indian-western Pacific Oceans. Sensitivity experiments show that enhanced downdrafts in the Tiedtke scheme reduces the amplitude of the MJO but to a lesser extent than when this scheme is closed on CAPE to represent deep convections. A composite life cycle of the model MJO indicates that over the Indian Ocean wind induced surface heat exchange functions, while over the western/central Pacific Ocean aspects of frictional moisture convergence are evident in the maintenance and eastward propagation of the oscillation.
Date: July 26, 2004
Creator: Liu, P; Wang, B; Sperber, K R; Li, T & Meehl, G A
Partner: UNT Libraries Government Documents Department

Role of C and P Sites on the Chemical Activity of Metal Carbide and Phosphides: From Clusters to Single-Crystal Surfaces

Description: Transition metal carbides and phosphides have shown tremendous potential as highly active catalysts. At a microscopic level, it is not well understood how these new catalysts work. Their high activity is usually attributed to ligand or/and ensemble effects. Here, we review recent studies that examine the chemical activity of metal carbide and phosphides as a function of size, from clusters to extended surfaces, and metal/carbon or metal/phosphorous ratio. These studies reveal that the C and P sites in these compounds cannot be considered as simple spectators. They moderate the reactivity of the metal centers and provide bonding sites for adsorbates.
Date: July 1, 2007
Creator: Rodriguez, J. A.; Vines, F.; Liu, P. & Illas, F.
Partner: UNT Libraries Government Documents Department

Theoretical Studies in Heterogenous Catalysis: Towards a Rational Design of Novel Catalysts for Hydrodesulfurization and Hydrogen Production

Description: Traditionally, knowledge in heterogeneous catalysis has come through empirical research. Nowadays, there is a clear interest to change this since millions of dollars in products are generated every year in the chemical and petrochemical industries through catalytic processes. To obtain a fundamental knowledge of the factors that determine the activity of heterogeneous catalysts is a challenge for modern science since many of these systems are very complex in nature. In principle, when a molecule adsorbs on the surface of a heterogeneous catalyst, it can interact with a large number of bonding sites. It is known that the chemical properties of these bonding sites depend strongly on the chemical environment around them. Thus, there can be big variations in chemical reactivity when going from one region to another in the surface of a heterogeneous catalyst. A main objective is to understand how the structural and electronic properties of a surface affect the energetics for adsorption processes and the paths for dissociation and chemical reactions. In recent years, advances in instrumentation and experimental procedures have allowed a large series of detailed works on the surface chemistry of heterogeneous catalysts. In many cases, these experimental studies have shown interesting and unique phenomena. Theory is needed to unravel the basic interactions behind these phenomena and to provide a general framework for the interpretation of experimental results. Ideally, theoretical calculations based on density-functional theory have evolved to the point that one should be able to predict patterns in the activity of catalytic surfaces. As in the case of experimental techniques, no single theoretical approach is able to address the large diversity of phenomena occurring on a catalyst. Catalytic surfaces are usually modeled using either a finite cluster or a two-dimensionally periodic slab. Many articles have been published comparing the results of these two approaches. An ...
Date: October 1, 2008
Creator: Rodriguez,J.A. & Liu, P.
Partner: UNT Libraries Government Documents Department

Understanding of catalytic behaviors of TiO2/CuOx catalysts

Description: Aiming to reveal the catalysis at the metal-oxide and oxide-oxide interfaces,1,2 the water-gas shift reaction (WGS, CO + H2O and #61664; CO2 + H2) and CO oxidation (2CO + O2 and #61664; 2CO2) at the interface of the Cu(111) and Cu2O(111) supported TiO2 clusters were studied based on DFT calculations
Date: September 8, 2013
Creator: Y., Kim H. & Liu, P.
Partner: UNT Libraries Government Documents Department

Sensitivity of MJO to the CAPE lapse time in the NCAR CAM3

Description: Weak and irregular boreal winter MJO in the NCAR CAM3 corresponds to very low CAPE background, which is caused by easy-to-occur and over-dominant deep convection indicating the deep convective scheme uses either too low CAPE threshold as triggering function or too large consumption rate of CAPE to close the scheme. Raising the CAPE threshold from default 70 J/kg to ten times large only enhances the CAPE background while fails to noticeably improve the wind mean state and the MJO. However, lengthening the CAPE lapse time from one to eight hours significantly improved the background in CAPE and winds, and salient features of the MJO. Variances, dominant periods and zonal wave numbers, power spectra and coherent propagating structure in winds and convection associated with MJO are ameliorated and comparable to the observations. Lengthening the CAPE lapse time to eight hours reduces dramatically the cloud base mass flux, which prevents effectively the deep convection from occurring prematurely. In this case, partitioning of deep to shallow convection in MJO active area is about 5:4.5 compared to over 9:0.5 in the control run. Latent heat is significantly enhanced below 600 hPa over the central Indian Ocean and the western Pacific. Such partitioning of deep and shallow convection is argued necessary for simulating realistic MJO features. Although the universal eight hours lies in the upper limit of that required by the quasi-equilibrium theory, a local CAPE lapse time for the parameterized cumulus convection will be more realistic.
Date: September 5, 2007
Creator: LIU, P.; Wang, B. & Meehl, Gerald, A.
Partner: UNT Libraries Government Documents Department

High temperature ceramic membrane reactors for coal liquid upgrading. Final report, September 21, 1989--November 20, 1992

Description: Membrane reactors are today finding extensive applications for gas and vapor phase catalytic reactions (see discussion in the introduction and recent reviews by Armor [92], Hsieh [93] and Tsotsis et al. [941]). There have not been any published reports, however, of their use in high pressure and temperature liquid-phase applications. The idea to apply membrane reactor technology to coal liquid upgrading has resulted from a series of experimental investigations by our group of petroleum and coal asphaltene transport through model membranes. Coal liquids contain polycyclic aromatic compounds, which not only present potential difficulties in upgrading, storage and coprocessing, but are also bioactive. Direct coal liquefaction is perceived today as a two-stage process, which involves a first stage of thermal (or catalytic) dissolution of coal, followed by a second stage, in which the resulting products of the first stage are catalytically upgraded. Even in the presence of hydrogen, the oil products of the second stage are thought to equilibrate with the heavier (asphaltenic and preasphaltenic) components found in the feedstream. The possibility exists for this smaller molecular fraction to recondense with the unreacted heavy components and form even heavier undesirable components like char and coke. One way to diminish these regressive reactions is to selectively remove these smaller molecular weight fractions once they are formed and prior to recondensation. This can, at least in principle, be accomplished through the use of high temperature membrane reactors, using ceramic membranes which are permselective for the desired products of the coal liquid upgrading process. An additional incentive to do so is in order to eliminate the further hydrogenation and hydrocracking of liquid products to undesirable light gases.
Date: December 31, 1992
Creator: Tsotsis, T. T.; Liu, P. K. T. & Webster, I. A.
Partner: UNT Libraries Government Documents Department

Analysis of Contribution from Edge Radiation to Optical Diffraction Radiation

Description: Beam size measurement with near-field optical diffraction radiation (ODR) has been carried out successfully at CEBAF. The ODR station is installed on the Hall-A beam line after eight bending magnets. The ODR images were affected by an unexpected radiation. Some calculations for analyzing the source of the radiation will be presented. Furthermore, two schemes will be proposed to alleviate the contamination.
Date: May 1, 2009
Creator: C. Liu, P. Evtushenko, A. Freyberger, C. Liu, A.H. Lumpkin
Partner: UNT Libraries Government Documents Department

Gas separations using ceramic membranes

Description: Alcoa's commercial membrane with 40[Angstrom] pore diameter has been identified as one of the potential candidates for high temperature gas separations. This asymmetric multiple layer membrane have been well characterized and evaluated. It has excellent thermal stability and acceptably hydrothermal stability at [approximately]650[degree]C or above. Gas separations with this membrane follow Knudsen diffusion. Its selectivity is suitable for bulk separations, or for reduction/elimination of H[sub 2]S and NH[sub 3] via selective removal of hydrogen. An improved separation efficiency with this membrane is highly desirable for applications involving hydrogen separation, and the removal of trace contaminants, such as H[sub 2]S and NH[sub 3]. One of the effective avenues in improving the efficiency of the existing membrane is to narrow its pore size through surface modifications. Thus membranes with a smaller pore size can be readily available through minor modifications of the existing commercial product. In this paper focus is on the morphological characterization and performance evaluation of hydrogen-selective and zeolitic membranes developed from existing commercial membranes.
Date: January 1, 1992
Creator: Liu, P.K.T.; Lin, C.L.; Flowers, D.L.; Wu, J.C.S. & Smith, G.W.
Partner: UNT Libraries Government Documents Department

Recent Advances in Developing Platinum Monolayer Electrocatalysts for the O2 Reduction Reaction

Description: For Pt, the best single-element catalyst for many reactions, the question of content and loading is exceedingly important because of its price and availability. Using platinum as a fuel-cell catalyst in automotive applications will cause an unquantifiable increase in the demand for this metal. This big obstacle for using fuel cells in electric cars must be solved by decreasing the content of Pt, which is a great challenge of electrocatalysis Over the last several years we inaugurated a new class of electrocatalysts for the oxygen reduction reaction (ORR) based on a monolayer of Pt deposited on metal or alloy carbon-supported nanoparticles. The possibility of decreasing the Pt content in the ORR catalysts down to a monolayer level has a considerable importance because this reaction requires high loadings due to its slow kinetics. The Pt-monolayer approach has several unique features and some of them are: high Pt utilization, enhanced (or decreased) activity, enhanced stability, and direct activity correlations. The synthesis of Pt monolayer (ML) electrocatalysts was facilitated by our new synthesis method which allowed us to deposit a monolayer of Pt on various metals, or alloy nanoparticles [1, 2] for the cathode electrocatalyst. In this synthesis approach Pt is laid down by the galvanically displacing a Cu monolayer, which was deposited at underpotentials in a monolayer-limited reaction on appropriate metal substrate, with Pt after immersing the electrode in a K{sub 2}PtCl{sub 4} solution.
Date: September 15, 2008
Creator: Vukmirovic,M.B.; Sasaki, K.; Zhou, W.-P.; Li, M.; Liu, P.; Wang, J.X. et al.
Partner: UNT Libraries Government Documents Department

Gas separations using ceramic membranes

Description: Alcoa`s commercial membrane with 40{Angstrom} pore diameter has been identified as one of the potential candidates for high temperature gas separations. This asymmetric multiple layer membrane have been well characterized and evaluated. It has excellent thermal stability and acceptably hydrothermal stability at {approximately}650{degree}C or above. Gas separations with this membrane follow Knudsen diffusion. Its selectivity is suitable for bulk separations, or for reduction/elimination of H{sub 2}S and NH{sub 3} via selective removal of hydrogen. An improved separation efficiency with this membrane is highly desirable for applications involving hydrogen separation, and the removal of trace contaminants, such as H{sub 2}S and NH{sub 3}. One of the effective avenues in improving the efficiency of the existing membrane is to narrow its pore size through surface modifications. Thus membranes with a smaller pore size can be readily available through minor modifications of the existing commercial product. In this paper focus is on the morphological characterization and performance evaluation of hydrogen-selective and zeolitic membranes developed from existing commercial membranes.
Date: December 1, 1992
Creator: Liu, P. K. T.; Lin, C. L.; Flowers, D. L.; Wu, J. C. S. & Smith, G. W.
Partner: UNT Libraries Government Documents Department

Gas separations using ceramic membranes. Final report, September 1988--February 1993

Description: This study covers a comprehensive evaluation of existing ceramic membranes for high temperature gas separations. Methodology has been established for microporous characterization stability and gas separation efficiency. A mathematical model was developed to predict gas separations with existing membranes. Silica and zeolitic modifications of existing membranes were pursued to enhance its separation efficiency. Some of which demonstrate unique separations properties. Use of the dense-silica membranes for hydrogen enrichment was identified as a promising candidate for future development. In addition, the decomposition of trace ammonia contaminant via a catalytic membrane reactor appears feasible. A further economic analysis is required to assess its commercial viability.
Date: February 1, 1993
Creator: Lin, C. L.; Wu, J. C. S.; Gallaher, G. R.; Smith, G. W.; Flowers, D. L.; Gerdes, T. E. et al.
Partner: UNT Libraries Government Documents Department

Strong Earthquake Motion Estimates for Three Sites on the U.C. Riverside Campus

Description: The approach of the Campus Earthquake Program (CEP) is to combine the substantial expertise that exists within the UC system in geology, seismology, and geotechnical engineering, to estimate the earthquake strong motion exposure of UC facilities. These estimates draw upon recent advances in hazard assessment, seismic wave propagation modeling in rocks and soils, and dynamic soil testing. The UC campuses currently chosen for application of our integrated methodology are Riverside, San Diego, and Santa Barbara. The procedure starts with the identification of possible earthquake sources in the region and the determination of the most critical fault(s) related to earthquake exposure of the campus. Combined geological, geophysical, and geotechnical studies are then conducted to characterize each campus with specific focus on the location of particular target buildings of special interest to the campus administrators. We drill and geophysically log deep boreholes next to the target structure, to provide direct in-situ measurements of subsurface material properties, and to install uphole and downhole 3-component seismic sensors capable of recording both weak and strong motions. The boreholes provide access below the soil layers, to deeper materials that have relatively high seismic shear-wave velocities. Analyses of conjugate downhole and uphole records provide a basis for optimizing the representation of the low-strain response of the sites. Earthquake rupture scenarios of identified causative faults are combined with the earthquake records and with nonlinear soil models to provide site-specific estimates of strong motions at the selected target locations. The predicted ground motions are shared with the UC consultants, so that they can be used as input to the dynamic analysis of the buildings. Thus, for each campus targeted by the CEP project, the strong motion studies consist of two phases, Phase 1--initial source and site characterization, drilling, geophysical logging, installation of the seismic station, and initial seismic monitoring, ...
Date: November 1, 2000
Creator: Archuleta, R.; Elgamal, A.; Heuze, F.; Lai, T.; Lavalle, D.; Lawrence, B. et al.
Partner: UNT Libraries Government Documents Department

High temperature ceramic membrane reactors for coal liquid upgrading

Description: Membrane reactors are today finding extensive applications for gas and vapor phase catalytic reactions (see discussion in the introduction and recent reviews by Armor [92], Hsieh [93] and Tsotsis et al. [941]). There have not been any published reports, however, of their use in high pressure and temperature liquid-phase applications. The idea to apply membrane reactor technology to coal liquid upgrading has resulted from a series of experimental investigations by our group of petroleum and coal asphaltene transport through model membranes. Coal liquids contain polycyclic aromatic compounds, which not only present potential difficulties in upgrading, storage and coprocessing, but are also bioactive. Direct coal liquefaction is perceived today as a two-stage process, which involves a first stage of thermal (or catalytic) dissolution of coal, followed by a second stage, in which the resulting products of the first stage are catalytically upgraded. Even in the presence of hydrogen, the oil products of the second stage are thought to equilibrate with the heavier (asphaltenic and preasphaltenic) components found in the feedstream. The possibility exists for this smaller molecular fraction to recondense with the unreacted heavy components and form even heavier undesirable components like char and coke. One way to diminish these regressive reactions is to selectively remove these smaller molecular weight fractions once they are formed and prior to recondensation. This can, at least in principle, be accomplished through the use of high temperature membrane reactors, using ceramic membranes which are permselective for the desired products of the coal liquid upgrading process. An additional incentive to do so is in order to eliminate the further hydrogenation and hydrocracking of liquid products to undesirable light gases.
Date: January 1, 1992
Creator: Tsotsis, T.T. (University of Southern California, Los Angeles, CA (United States). Dept. of Chemical Engineering); Liu, P.K.T. (Aluminum Co. of America, Pittsburgh, PA (United States)) & Webster, I.A. (Unocal Corp., Los Angeles, CA (United States))
Partner: UNT Libraries Government Documents Department

Seismic Response and Engineering of Cold-formed Steel Framed Buildings

Description: This article discusses a North American effort which formed as part of the NSF Network for Earthquake Engineering Simulation (NEES), known as Enabling Performance-Based Seismic Design of Multi-Story Cold-Formed Steel Structures (CFS-NEES), as it addresses seismic performance-based design for cold-formed steel framed buildings.
Date: March 18, 2016
Creator: Schafer, B. W.; Ayhan, D.; Leng, J.; Liu, P.; Padilla-Llano, D.; Peterman, K. D. et al.
Partner: UNT College of Engineering

Ion-Exchange Processes and Mechanisms in Glasses

Description: Leaching of alkalis from glass is widely recognized as an important mechanism in the initial stages of glass-water interactions. Pioneering experimental studies [1-3] nearly thirty-five years ago established that alkali (designated as M{sup +}) are lost to solution more rapidly than network-forming cations. The overall chemical reaction describing the process can be written as: {triple_bond}Si-O-M + H{sup +} {yields} {triple_bond}Si-OH + M{sup +} (1) or {triple_bond}Si-O-M + H{sub 3}O{sup +} {yields} {triple_bond}Si-OH + M{sup +} + H{sub 2}O. (2) Doremus and coworkers [4-7] fashioned a quantitative model where M{sup +} ions in the glass are exchanged for counter-diffusing H{sub 3}O{sup +} or H{sup +}. Subsequent investigations [8], which have relied heavily on reaction layer analysis, recognized the role of H{sub 2}O molecules in the alkali-exchange process, without minimizing the importance of charged hydrogen species. Beginning in the 1980s, however, interest in M{sup +}-H{sup +} exchange reactions in silicate glasses diminished considerably because important experimental observations showed that network hydrolysis and dissolution rates were principally controlled by the chemical potential difference between the glass and solution (chemical affinity) [9]. For nuclear waste glasses, formation of alteration products or secondary phases that remove important elements from solution, particularly Si, was found to have very large impacts on glass dissolution rates [10,11]. Consequently, recent work on glass/water interactions has focused on understanding this process and incorporating it into models [12]. The ion-exchange process has been largely ignored because it has been thought to be a short duration, secondary or tertiary process that had little or no bearing on long-term corrosion or radionuclide release rates from glasses [13]. The only significant effect identified in the literature that is attributed to alkali ion exchange is an increase in solution pH in static laboratory tests conducted at high surface area-to-volume ratios [14,15]. Renewed interest in alkali ...
Date: December 2001
Creator: McGrail, B. P.; Icenhower, J. P.; Darab, J. G.; Shuh, D. K.; Baer, D. R.; Shutthanandan, V. et al.
Partner: UNT Libraries Government Documents Department

Science Overview Document Indirect and Semi-Direct Aerosol Campaign (ISDAC) April 2008

Description: The ARM Climate Research Facility’s (ACRF) Aerial Vehicle Program (AVP) will deploy an intensive cloud and aerosol observing system to the ARM North Slope of Alaska (NSA) locale for a five week Indirect and Semi-Direct Aerosol Campaign (ISDAC) during period 29 March through 30 April 2008. The deployment period is within the International Polar Year, thus contributing to and benefiting from the many ancillary observing systems collecting data synergistically. We will deploy the Canadian National Research Council Convair 580 aircraft to measure temperature, humidity, total particle number, aerosol size distribution, single particle composition, concentrations of cloud condensation nuclei and ice nuclei, optical scattering and absorption, updraft velocity, cloud liquid water and ice contents, cloud droplet and crystal size distributions, cloud particle shape, and cloud extinction. In addition to these aircraft measurements, ISDAC will deploy two instruments at the ARM site in Barrow: a spectroradiometer to retrieve cloud optical depth and effective radius, and a tandem differential mobility analyzer to measure the aerosol size distribution and hygroscopicity. By using many of the same instruments used during Mixed-Phase Arctic Cloud Experiment (M-PACE), conducted in October 2004, we will be able to contrast the arctic aerosol and cloud properties during the fall and spring transitions. The aerosol measurements can be used in cloud models driven by objectively analyzed boundary conditions to test whether the cloud models can simulate the aerosol influence on the clouds. The influence of aerosol and boundary conditions on the simulated clouds can be separated by running the cloud models with all four combinations of M-PACE and ISDAC aerosol and boundary conditions: M-PACE aerosol and boundary conditions, M-PACE aerosol and ISDAC boundary conditions, ISDAC aerosol and M-PACE boundary conditions, and ISDAC aerosol and boundary conditions. ISDAC and M-PACE boundary conditions are likely to be very different because of the much ...
Date: November 1, 2007
Creator: Ghan, SJ; Schmid, B; Hubbe, JM; Flynn, CJ; Laskin, A; Zelenyuk, AA et al.
Partner: UNT Libraries Government Documents Department