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Anomalous Fermi-Surface Dependent Pairing in a Self-Doped High-Tc Superconductor

Description: We report the discovery of a self-doped multi-layer high T{sub c} superconductor Ba{sub 2}Ca{sub 3}Cu{sub 4}O{sub 8}F{sub 2} (F0234) which contains distinctly different superconducting gap magnitudes along its two Fermi surface(FS) sheets. While formal valence counting would imply this material to be an undoped insulator, it is a self-doped superconductor with a T{sub c} of 60K, possessing simultaneously both electron- and hole-doped FS sheets. Intriguingly, the FS sheet characterized by the much larger gap is the electron-doped one, which has a shape disfavoring two electronic features considered to be important for the pairing mechanism: the van Hove singularity and the antiferromagnetic ({pi}/a, {pi}/a) scattering.
Date: May 3, 2010
Creator: Chen, Y.
Partner: UNT Libraries Government Documents Department

Single Dirac Cone Topological Surface State and Unusual Thermoelectric Property of Compounds from a New Topological Insulator Family

Description: Angle resolved photoemission spectroscopy (ARPES) study on TlBiTe2 and TlBiSe2 from a Thallium-based III-V-VI2 ternary chalcogenides family revealed a single surface Dirac cone at the center of the Brillouin zone for both compounds. For TlBiSe{sub 2}, the large bulk gap ({approx} 200meV) makes it a topological insulator with better mechanical properties than the previous binary 3D topological insualtor family. For TlBiTe{sub 2}, the observed negative bulk gap indicates it as a semi-metal, rather than a narrow gap semi-conductor as conventionally believed; this semi-metality naturally explains its mysteriously small thermoelectric figure of merit comparing to other compounds in the family. Finally, the unique band structures of TlBiTe{sub 2} also suggests it as a candidate for topological superconductors.
Date: August 18, 2011
Creator: Chen, Y
Partner: UNT Libraries Government Documents Department

Thermal conductivity of irradiated, additively-colored, and deformed MgO

Description: Low-temperature (0.1-100$sup 0$K) thermal conductivity measurements were made on neutron-irradiated, electron-irradiated, additively colored, and deformed MgO. Resonance scattering of phonons occurs at 15 to 20$sup 0$K and is associated with anion vacancies. A resonance also occurs at 1$sup 0$K in neutron- irradiated samples which is attributed to defect aggregates. (DLC)
Date: January 1, 1974
Creator: Hartmann, J.B.; Weinstock, H. & Chen, Y.
Partner: UNT Libraries Government Documents Department

Using Reactive Transport Modeling to Evaluate the Source Term at Yucca Mountain

Description: The conventional approach of source-term evaluation for performance assessment of nuclear waste repositories uses speciation-solubility modeling tools and assumes pure phases of radioelements control their solubility. This assumption may not reflect reality, as most radioelements (except for U) may not form their own pure phases. As a result, solubility limits predicted using the conventional approach are several orders of magnitude higher then the concentrations of radioelements measured in spent fuel dissolution experiments. This paper presents the author's attempt of using a non-conventional approach to evaluate source term of radionuclide release for Yucca Mountain. Based on the general reactive-transport code AREST-CT, a model for spent fuel dissolution and secondary phase precipitation has been constructed. The model accounts for both equilibrium and kinetic reactions. Its predictions have been compared against laboratory experiments and natural analogues. It is found that without calibrations, the simulated results match laboratory and field observations very well in many aspects. More important is the fact that no contradictions between them have been found. This provides confidence in the predictive power of the model. Based on the concept of Np incorporated into uranyl minerals, the model not only predicts a lower Np source-term than that given by conventional Np solubility models, but also produces results which are consistent with laboratory measurements and observations. Moreover, two hypotheses, whether Np enters tertiary uranyl minerals or not, have been tested by comparing model predictions against laboratory observations, the results favor the former. It is concluded that this non-conventional approach of source term evaluation not only eliminates over-conservatism in conventional solubility approach to some extent, but also gives a realistic representation of the system of interest, which is a prerequisite for truly understanding the long-term behavior of the proposed repository. Therefore, it is a very promising alternative approach for source-term evaluation.
Date: December 19, 2001
Creator: Chen, Y.
Partner: UNT Libraries Government Documents Department

Role of M1 transitions in the quasicontinuum

Description: M1 transition rates are strongly structure dependent and may therefore reveal the structure in a quasicontinuum of nuclear excited states. The theoretical interpretations of low-energy stretched dipole bumps are briefly reviewed. Furthermore, it is suggested that there are higher-energy M1 bumps with a signficant unstretched component, and that the related shell effects influence the cooling which feeds the yrast cascade.
Date: January 1, 1982
Creator: Chen, Y.S. & Leander, G.A.
Partner: UNT Libraries Government Documents Department

Compact Proton Accelerator for Cancer Therapy

Description: An investigation is being made into the feasibility of making a compact proton dielectric wall (DWA) accelerator for medical radiation treatment based on the high gradient insulation (HGI) technology. A small plasma device is used for the proton source. Using only electric focusing fields for transporting and focusing the beam on the patient, the compact DWA proton accelerator m system can deliver wide and independent variable ranges of beam currents, energies and spot sizes.
Date: June 12, 2007
Creator: Chen, Y & Paul, A C
Partner: UNT Libraries Government Documents Department

Advanced Accelerator Applications University Participation Program

Description: Our research tasks span the range of technology areas for transmutation, gas-cooled reactor technology, and high temperature heat exchangers, including separation of actinides from spent nuclear fuel, methods of fuel fabrication, reactor-accelerator coupled experiments, corrosion of materials exposed to lead-bismuth eutectic, and special nuclear materials protection and accountability.
Date: July 25, 2007
Creator: Chen, Y. & Hechanova, A.
Partner: UNT Libraries Government Documents Department

High pressure calibration with a new absolute pressure gauge

Description: The simultaneous measurement of length and transit time of a specimen under pressure was used to develop a new way of determining absolute high pressure. The mercury freezing point at 0 deg C was deterinined with this new method at 7571.2 plus or minus 1.6 bars. Accurate high-pressure calibration of secondary pressure gages such as manganin gages is possible with this method. The maximum deviation from linearity of the present gage studied is 11.6 plus or minus 1 bars between atmospheric pressure and the mercury freezing point at 0 deg C. (auth)
Date: January 1, 1973
Creator: Ruoff, A.L.; Lincoln, R.C. & Chen, Y.C.
Partner: UNT Libraries Government Documents Department

New absolute high pressure gauge

Description: A new absolute pressure measurement system based on the simultaneous measurement of length and ultrasonic transit times is described. The system was used to determine the transition pressure of pure mercury at 0 deg C at 7571.2 plus or minus 1.6 bars. It is particularly advantageous to use a device for calibrating secondary gauges such as manganin gauges inasmuch as it gives a highly accurate measurement of nonlinearities in such secondary gages. The gage calibrated in the present study reaches a maximum deviation from linearity of 11.6 bars at a pressure midway between atmospheric pressure and the 0 deg C mercury melting pressure. (auth)
Date: January 1, 1972
Creator: Ruoff, A.L.; Lincoln, R.C. & Chen, Y.C.
Partner: UNT Libraries Government Documents Department

Designs for a high power superconducting delay line

Description: Potential designs for a high power superconducting delay line of approximately 10 microsecs duration are described. The transmitted signal should have low dispersion and little attenuation to recapture the original signal. Such demands cannot be met using conventional metal conductors. This paper outlines a proposal for a new transmission line design using low temperature superconducting material which meets system specifications. The 25 omega line is designed to carry pulsed signals with an approximate rise time of 8 nsec and a maximum voltage magnitude of 25 kV. Predicted electrical design and performance of the line will be presented.
Date: June 26, 1997
Creator: Chen, Y.J. & Caporaso, G.
Partner: UNT Libraries Government Documents Department

Novel design for a high power superconducting delay line

Description: Potential designs for a high power superconducting delay line of approximately 10ms duration are described. The transmitted signal should have low dispersion and little attenuation to recapture the original signal. Such demands cannot be met using conventional metal conductors. This paper outlines a proposal for a new transmission line design using low temperature superconducting material which meets system specifications. The 25W line is designed to carry pulsed signals with an approximate rise time of 8 nsec and a maximum voltage of 25kV. Predicted electrical design and performance of the line is presented.
Date: May 8, 1997
Creator: Chen, Y. J. & Caporaso, G. J.
Partner: UNT Libraries Government Documents Department

The addition of disilanes to cumulenes

Description: The syntheses of silicon-containing compounds and the studies of their rearrangements have been active research areas in the Barton research group. Previously, the addition of disilanes to acetylenes was studied in the group and an intramolecular 2S + 2A mechanism has been proposed. In this thesis, the work is focused on the addition of disilanes to cumulenes. The syntheses of the precursors are discussed and the possible mechanisms for their thermal, photochemical and catalytic rearrangements are proposed. Conjugated organic polymers have been studied in the group since 1985 because of their potential for exhibiting high electroconductivity, photoconductivity, strong non-linear optical response and intense fluorescence. In the second section of this dissertation, the synthesis and property studies of poly(phenylene vinylene) analogues are discussed.
Date: October 8, 1997
Creator: Chen, Y.
Partner: UNT Libraries Government Documents Department

Heat transfer in a two-pass internally ribbed turbine blade coolant channel with cylindrical vortex generators

Description: The effect of vortex generators on the mass (heat) transfer from the ribbed passage of a two pass turbine blade coolant channel is investigated with the intent of optimizing the vortex generator geometry so that significant enhancements in mass/heat transfer can be achieved. In the experimental configuration considered, ribs are mounted on two opposite walls; all four walls along each pass are active and have mass transfer from their surfaces but the ribs are non-participating. Mass transfer measurements, in the form of Sherwood number ratios, are made along the centerline and in selected inter-rib modules. Results are presented for Reynolds number in the range of 5,000 to 40,000, pitch to rib height ratios of 10.5 and 21, and vortex generator-rib spacing to rib height ratios of 0.55, and 1.5. Centerline and spanwise averaged Sherwood number ratios are presented along with contours of the Sherwood number ratios. Results indicate that the vortex generators induce substantial increases in the local mass transfer rates, particularly along the side walls, and modest increases in the average mass transfer rates. The vortex generators have the effect of making the inter-rib profiles along the ribbed walls more uniform. Along the side walls, horse-shoe vortices that characterize the vortex generator wake are associated with significant mass transfer enhancements. The wake effects and the levels of enhancement decrease somewhat with increasing Reynolds number and decreasing pitch.
Date: December 31, 1995
Creator: Hibbs, R.; Acharya, S. & Chen, Y.
Partner: UNT Libraries Government Documents Department

Design of a relativistic klystron two-beam accelerator prototype

Description: We are designing an experiment to study physics, engineering, and costing issues of an extended Relativistic Klystron Two-Beam Accelerator (RK-TBA). The experiment is a prototype for an RK-TBA based microwave power source suitable for driving a 1 TeV linear collider. Major components of the experiment include a 2.5-MV, 1.5-kA electron source, a 11.4-GHz modulator, a bunch compressor, and a 8-m extraction section. The extraction section will be comprised of 4 traveling-wave output structures, each generating about 360 MW of rf power. Induction cells will be used in the extraction section to maintain the average beam energy at 5 MeV. Status of the design is presented.
Date: October 1, 1995
Creator: Westenskow, G.; Caporaso, G. & Chen, Y.
Partner: UNT Libraries Government Documents Department

Magnetic field quality analysis using ANSYS

Description: The design of superconducting magnets for particles accelerators requires a high quality of the magnetic field. This paper presents an ANSYS 4.4A Post 1 macro that computes the field quality performing a Fourier analysis of the magnetic field. The results show that the ANSYS solution converges toward the analytical solution and that the error on the multipole coefficients depends linearly on the square of the mesh size. This shows the good accuracy of ANSYS in computing the multipole coefficients. 2 refs., 16 figs., 4 tabs.
Date: March 1, 1991
Creator: Dell'Orco, D. & Chen, Y.
Partner: UNT Libraries Government Documents Department

High-frequency microinstabilities in hot-electron plasmas

Description: Instabilities with frequencies in the neighborhood of the electron cyclotron frequency are of interest in determining stable operating regimes of hot-electron plasmas in EBT devices and in tandem mirrors. Previous work used model distributions significantly different than those suggested by recent Fokker-Planck studies. We use much more realistic model distributions in a computer code that solves the full electromagnetic dispersion relation governing longitudinal and transverse waves in a uniform plasma. We allow for an arbitrary direction of wave propagation. Results for the whistler and upper-hybrid loss-cone instabilities are presented.
Date: November 24, 1981
Creator: Chen, Y.J.; Nevins, W.M. & Smith, G.R.
Partner: UNT Libraries Government Documents Department

New concepts for drift pumping a thermal barrier with rf

Description: Pump neutral beams, which are directed into the loss cone of the TMX-U plugs, are normally used to pump ions from the thermal barriers. Because these neutral beams introduce cold gas that reduces pumping efficiency, and require a straight line entrance and exit from the plug, alternate methods are being investigated to provide barrier pumping. To maintain the thermal barrier, either of two classes of particles can be pumped. First, the collisionally trapped ions can be pumped directly. In this case, the most promising selection criterion is the azimuthal drift frequency. Second, the excess sloshing-ion density can be removed, allowing the use of increased sloshing-beam density to pump the trapped ions. The selection mechanism in this case is the Doppler-shifted ion-cyclotron resonance of the high-energy sloshing-ions (3 keV less than or equal to U/sub parallel/ less than or equal to 10 keV).
Date: May 9, 1985
Creator: Barter, J.D.; Baldwin, D.; Chen, Y. & Poulsen, P.
Partner: UNT Libraries Government Documents Department

Similarity-Guided Streamline Placement with Error Evaluation

Description: Most streamline generation algorithms either provide a particular density of streamlines across the domain or explicitly detect features, such as critical points, and follow customized rules to emphasize those features. However, the former generally includes many redundant streamlines, and the latter requires Boolean decisions on which points are features (and may thus suffer from robustness problems for real-world data). We take a new approach to adaptive streamline placement for steady vector fields in 2D and 3D. We define a metric for local similarity among streamlines and use this metric to grow streamlines from a dense set of candidate seed points. The metric considers not only Euclidean distance, but also a simple statistical measure of shape and directional similarity. Without explicit feature detection, our method produces streamlines that naturally accentuate regions of geometric interest. In conjunction with this method, we also propose a quantitative error metric for evaluating a streamline representation based on how well it preserves the information from the original vector field. This error metric reconstructs a vector field from points on the streamline representation and computes a difference of the reconstruction from the original vector field.
Date: August 15, 2007
Creator: Chen, Y.; Cohen, J. D. & Krolik, J. H.
Partner: UNT Libraries Government Documents Department

Use of a Moving Heat Conductor Mesh to Perform Reflood Calculations with RELAP4/MOD6

Description: RELAP4 is a computer code which can be used for the transient therm~l hydraulic analysis of light water reactors and related systems .. Various versions of the RELAP4 code are widely used throughout the world for experimental system analysis, reactor design,and nuclear system safety studies. RELAP4/MOD6 includes many new analytical models which were developed primarily for the analysis of the reflood phase of a PWR loss-of-coolant accident (LOCA) transient. The key feature forming the basis for the MOD6 reflood calculation is a unique moving finite differenced heat conductor. This paper will describe the development and application of the moving heat conductor mesh for use in reflood analysis.
Date: May 6, 1979
Creator: Fischer, S R; Ellis, L V & Chen, Y S
Partner: UNT Libraries Government Documents Department