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Transient magnetization in practical composite superconductors

Description: This paper presents detailed magnetization measurements as well as analysis on typical cryostable NbTi composite conductors (1-mm diameter and Cu/SC ratio of 6:5) with filaments nonuniformly distributed in both circular and rectangular cross sections (aspect ratio approx. 2:1). As a result of the excellent agreement between the measurements and a previously reported transformer model, both transient magnetization and losses incurred in each sample can be described by functions of a unique time constant tau/sub 0/ which depends strongly on the shape of the cross section. Other prominent features of the measurement results such as the deduction of values of J/sub c/ and matrix resistivity are demonstrated. In an exponentially decaying field from 2T to 0, J/sub c/ is 4.5 x 10/sup 9/ A/m/sup 2/ at 1.5T, and the average matrix resistivity is 2.73 x 10/sup -10/ ..cap omega..-m. Saturation effects were also observed for field decaying time constant tau comparable with tau/sub 0/.
Date: January 1, 1979
Creator: Shen, S S
Partner: UNT Libraries Government Documents Department

Determination of the K/sub L/$sup 0$ $Yields$ $pi$$sup -$$mu$$sup +$$nu$/ sub $mu$/ form factor xi(q$sup 2$) by muon polarization measurements

Description: The polarization of the muon in the decay K$sup 0$/sub L/ $Yields$ $pi$$sup -$$mu$$sup +$$nu$/sub $mu$/ was measured as a function of q$sup 2$, the four-momentum transferred to the lepton pair. The kinematic information was used to compute the polarization expected on the basis of various assumed values of the form factor xi(q$sup 2$). By comparing the interpolated curve of the polarization as a function of xi(q$sup 2$) to the experimentally measured polarization, one has determined xi(q$sup 2$) as a function of q$sup 2$. If one parameterizes the q$sup 2$ dependence of xi by xi(q$sup 2$) = xi(0) + $lambda$ q$sup 2$/m$sup 2$/sub $pi$/, then xi(0) = 0.178 +- 0.105 - 3.80 $lambda$. (auth)
Date: September 1, 1975
Creator: Shen, G.
Partner: UNT Libraries Government Documents Department

Substitution chemistry of Ruthenium clusters with the diphosphine ligands: 4,5-Bis(diphenylphosphino)-4-cyclo-penten-1,3-dione (bpcd), (Z)-Ph₂PCH=CHPP₂ and 3,4-Bis(diphenylphosphino)-5-methoxy-2(5H)-furanone (bmf)

Description: This study embarks on a program designed to study the reactivity of polynuclear clusters with redox-active phospines in an effort to prepare new ligand/cluster redox systems. This study aims to prove that such compounds will display superior electron reservoir capabilities, as a result of the cooperative mixing of ligand and cluster orbitals.
Date: May 1997
Creator: Shen, Huafeng
Partner: UNT Libraries

Electromagnetic properties of LCT coils

Description: One of the major objectives of the Large Coil Task (LCT) is to demonstrate that large-scale magnet systems can be operated stably and safely while subjected to external transient disturbances. This paper reviews the design of the conductor and the coil structure of all six LCT coils with special emphasis on their ac loss properties. The function and capability of the test facility and the test scheme are also summarized. Finally, the interpretation of the test results and its relevance to practical large-scale applications are presented.
Date: January 1, 1985
Creator: Shen, S.S.
Partner: UNT Libraries Government Documents Department

Contribution of the two-photon annihilation process in the measurement of sigma/sub t/ (e/sup +/e/sup /minus//. -->. hadrons at PEP)

Description: The possible impact of the 2..gamma.. process e/sup /plus//e/sup/minus// ..-->.. e/sup /plus//e/sup /minus// /plus/ hadrons is evaluated as a source of background for the study of the one photon annihilation process. Two regions of hadron system invariant mass are considered---the resonance region with low invariant mass, and the ''diffractive'' region above 2 GeV hadron invariant mass. In spite of the fact that the 2..gamma.. cross-section rises with the energy of the initial e/sup /plus//e/sup /minus// system, it seems clear that measurements of the total energy of the final hadron system will allow the clean separation of the 2..gamma.. events from the single photon annihilation reaction.
Date: January 1, 1988
Creator: Shen, B.
Partner: UNT Libraries Government Documents Department

Nonlinear optical studies of organic monolayers

Description: Second-order nonlinear optical effects are forbidden in a medium with inversion symmetry, but are necessarily allowed at a surface where the inversion summary is broken. They are often sufficiently strong so that a submonolayer perturbation of the surface can be readily detected. They can therefore be used as effective tools to study monolayers adsorbed at various interfaces. We discuss here a number of recent experiments in which optical second harmonic generation (SHG) and sum-frequency generation (SFG) are employed to probe and characterize organic monolayers. 15 refs., 5 figs.
Date: February 1, 1988
Creator: Shen, Y.R.
Partner: UNT Libraries Government Documents Department

Regenerative process for desulfurization of high temperature combustion and fuel gases. Progress report No. 13, April 1-September 30, 1979

Description: Various types of portland cement were subjected to sulfation/regeneration cycling for application in fluidized bed combustion (FBC) systems. Among them, Type III was the most reactive sorbent for SO/sub 2/ absorption. Sulfated portland cement is highly superior in its resistance to attrition than sulfated limestone which has serious attrition loss problems in fluidized-bed combustors. An isothermal sulfation/regeneration cycle for portland cement Type III pellets has been evaluated. Sulfation reactivity was optimized as a function of the quantity of carbon and water used in preparing the pellets. The sulfation rate was independent of the type of carbon used. Cement kiln dust, a waste product, was also teated as an absorbent for SO/sub 2/. TGA experiments on the extent of regeneration and SO/sub 2/ concentration in the off-gas under various pressures and temperatures are being conducted. This information is of importance to pressurized fluidized bed (PFC) operations. Cycling of Type III portland cement pellets between sulfation and regeneration conditions indicate good maintenance of capacity with little deterioration after 20 cycles. These cycling experiments are continuing. Experiments are being made with a 3'' rotary kiln to provide information on kiln performance under various operating conditions. Among the variables considered are temperature, residence time, extent of regeneration and SO/sub 2/ concentration in the off gas. The feasibility of an alternative regeneration scheme has been studied.
Date: January 1, 1979
Creator: Shen, M S & Albanese, A S
Partner: UNT Libraries Government Documents Department

Paramagnetic properties of mixed-matrix NbTi conductors

Description: Magnetization measurements are performed up to 4T on a series of samples with different compositions of Cu, CuNi, and superconductors. It is observed that most samples exhibit a strong paramagnetic moment that is in contrast with the inherent hysteretic magnetization associated with superconducting filaments. Chemical analysis results of nickel contents and iron impurities are also reported and correlated with the measured paramagnetic properties. For samples with high contents of nickel (Cu-30% Ni) and iron impurities (greater than or equal to 500 ppM), the saturated paramagnetic magnetization field can be as high as 0.02T.
Date: January 1, 1979
Creator: Shen, S.S.
Partner: UNT Libraries Government Documents Department

Sonic resonator control and method for determining component concentration in multiple-component liquid

Description: This invention teaches a control to be used in smelting aluminum by the electrolysis breakdown of alumina (Al/sub 2/O/sub 3/) in a molten electrolyte heated to approximately 950 to 1000/sup 0/C. The invention provides a sonic resonator and control that can accurately detect the resonant frequency of the resonator in the molten electrolyte. The resonator preferably is made with tubular side wall 1/4 of the sonic wavelength, or is a quarter wave resonator. A wave generator inputs a signal having a range of frequencies that includes the resonant frequency, so that a peak resonant output at the resonant frequency can be detected on an oscilloscope or like detector. This instantaneous resonant frequency is then checked against an accurate data base correlating the resonant frequencies of the resonator in the electrolyte at specific alumina concentrations normally experienced throughout the electrolysis cycle. The electrolysis cycle can thus be controlled and recharged at any predetermined low alumina concentration greater than where the anode effect phase of the cycle normally might begin.
Date: October 29, 1982
Creator: Shen, S.Y.
Partner: UNT Libraries Government Documents Department

Few recent experiments on surface studies by second harmonic generation

Description: Surface second harmonic generation (SHG) is used to monitor adsorption and desorption of molecules on metal and semiconductor surfaces in ultrahigh vacuum. Surface SHG has also been used to study monolayers of molecules at a liquid/air interface. 13 refs., 6 figs. (WRF)
Date: December 1, 1985
Creator: Shen, Y.R.
Partner: UNT Libraries Government Documents Department

Nonlinear optical techniques for surface studies. [Monolayers]

Description: Recent effort in developing nonlinear optical techniques for surface studies is reviewed. Emphasis is on monolayer detection of adsorbed molecules on surfaces. It is shown that surface coherent antiStokes Raman scattering (CARS) with picosecond pulses has the sensitivity of detecting submonolayer of molecules. On the other hand, second harmonic or sum-frequency generation is also sensitive enough to detect molecular monolayers. Surface-enhanced nonlinear optical effects on some rough metal surfaces have been observed. This facilitates the detection of molecular monolayers on such surfaces, and makes the study of molecular adsorption at a liquid-metal interface feasible. Advantages and disadvantages of the nonlinear optical techniques for surface studies are discussed.
Date: September 1, 1981
Creator: Shen, Y.R.
Partner: UNT Libraries Government Documents Department

Cleaning of Free Machining Brass

Description: We have investigated four brightening treatments proposed by two cleaning vendors for cleaning free machining brass. The experimental results showed that none of the proposed brightening treatments passed the swipe test. Thus, we maintain the recommendation of not using the brightening process in the cleaning of free machining brass for NIF application.
Date: December 29, 2005
Creator: Shen, T
Partner: UNT Libraries Government Documents Department

Engineering Specification Document (ESD) of X-ray Vacuum Transport System (XVTS) for LCLS XTOD

Description: The vacuum system of the X-Ray Vacuum Transport System (XVTS) for the Linac Coherent Light Source (LCLS) X-ray Transport, Optics and Diagnostics (XTOD) system has been analyzed and configured by the Lawrence Livermore National Laboratory's New Technologies Engineering Division (NTED) as requested by the SLAC/LCLS program. The preliminary system layout, detailed analyses and suggested selection of the vacuum components for the XTOD tunnel section are presented in the preliminary design report [1]. This document briefly reviews the preliminary design and provides engineering specifications for the system, which can be used as 'design to' specifications for the final design. Also included are the requirements of plans for procurement, mechanical integration, schedule and the cost estimates.
Date: January 25, 2006
Creator: Shen, S
Partner: UNT Libraries Government Documents Department

LCLS XTOD Tunnel Vacuum Transport System (XVTS) Final Design Report

Description: The design of the X-Ray Vacuum Transport System (XVTS) for the Linac Coherent Light Source (LCLS) X-ray Transport, Optics and Diagnostics (XTOD) system has been analyzed and configured by the Lawrence Livermore National Laboratory's New Technologies Engineering Division (NTED) as requested by the SLAC/LCLS program. A preliminary design review was held on 11/14/05 [1][2]. This FDR (Final Design Report) presents system configuration, detailed analyses and selection of the mechanical and electrical components for the XTOD tunnel section, as well as the response to all issues raised in the review committee report. Also included are the plans for procurement, mechanical integration, schedule and the cost estimates. It should be noticed that, after the XVTS PDR, LCLS management has decided to lower the number of beamlines from three to one, and shorten the tunnel length from 212 m to 184 m. [3][4] The final design of XVTS system is completed. The major subjects presented in this report are: (1) Design of the complete system. (2) System analysis results. (3) ES&H issues and plan. (4) Project cost estimates and schedule.
Date: October 16, 2006
Creator: Shen, S
Partner: UNT Libraries Government Documents Department

APT/LEDA RFQ vacuum pumping system

Description: This paper describes the design and fabrication of a vacuum pumping system for the ATP/LEDA (Low Energy Demonstration Accelerator) RFQ (Radio Frequency Quadrupole) linac. Resulted from the lost proton beam, gas streaming from the LEBT (Low Energy Beam Transport) and out-gassing from the surfaces of the RFQ cavity and vacuum plumbing, the total gas load will be on the order of 7.2 x 10{sup -4} Torr-liters/sec, consisting mainly of hydrogen. The system is designed to pump on a continual basis with redundancy to ensure that the minimal operating vacuum level of 1 x 10{sup -6} Torr is maintained even under abnormal conditions. Details of the design, performance analysis and the preliminary test results of the cryogenic pumps are presented.
Date: July 21, 1997
Creator: Shen, S., LLNL
Partner: UNT Libraries Government Documents Department

Transient loss analysis and measurements on normal conductors and composite superconductors

Description: An equivalent-circuit technique is presented for calculation and measurement of eddy-current losses in conductors under transient external fields. It is demonstrated in this paper that such techniques can yield satisfactory results through a much simpler mathematical process than that encountered in the conventional field theory. Experimental techniques and results of transient loss measurements on both normal conductors and superconducting composites are also presented to verify the model and explore its limits.
Date: January 1, 1978
Creator: Shen, S S & Schwall, R E
Partner: UNT Libraries Government Documents Department

High resolution angle-resolved photoemission study of hightemperature superconductors: charge-ordering, bilayer splitting andelectron-phonon coupling

Description: The latest development of angle-resolved photoemission spectroscopy (ARPES) technique has seen extremely high energy resolution and momentum resolution, as well as multiple angle detection. These advancements have led to new findings through efficient Fermi surface mapping, fine electronic structure resolving, and direct determination of electron self-energy. In this paper, we will highlight some recent high resolution ARPES work on high temperature superconductors. These include: (1) charge-ordering and evolution of electronic structure with doping; (2) bilayer splitting and Fermi surface topology of Bi2212; and (3) strong electron phonon coupling and electron electron interaction in high temperature superconductors.
Date: July 7, 2003
Creator: Zhou, Xingjiang; Hussain, Zahid & Shen, Zhi-xun
Partner: UNT Libraries Government Documents Department

Angle-resolved photoemission studies of lattice polaron formation in the cuprate Ca2CuO2Cl2

Description: To elucidate the nature of the single-particle excitations in the undoped parent cuprates, we have performed a detailed study of Ca{sub 2}CuO{sub 2}Cl{sub 2} using photoemission spectroscopy. The photoemission lineshapes of the lower Hubbard band are found to be well-described by a polaron model. By comparing the lineshape and temperature dependence of the lower Hubbard band with additional O 2p and Ca 3p states, we conclude that the dominant broadening mechanism arises from the interaction between the photohole and the lattice. The strength of this interaction was observed to be strongly anisotropic and may have important implications for the momentum dependence of the first doped hole states.
Date: May 3, 2010
Creator: Shen, K.M.
Partner: UNT Libraries Government Documents Department

Angle Resolved Photoemission Spectroscopy Studies of the Mott Insulator to Superconductor Evolution in Ca2-xNaxCuO2Cl2

Description: It is widely believed that many of the exotic physical properties of the high-T{sub c} cuprate superconductors arise from the proximity of these materials to the strongly correlated, antiferromagnetic Mott insulating state. Therefore, one of the fundamental questions in the field of high-temperature superconductivity is to understand the insulator-to-superconductor transition and precisely how the electronic structure of Mott insulator evolves as the first holes are doped into the system. This dissertation presents high-resolution, doping dependent angle-resolved photoemission (ARPES) studies of the cuprate superconductor Ca{sub 2-x}Na{sub x}CuO{sub 2}Cl{sub 2}, spanning from the undoped parent Mott insulator to a high-temperature superconductor with a T{sub c} of 22 K. A phenomenological model is proposed to explain how the spectral lineshape, the quasiparticle band dispersion, and the chemical potential all progress with doping in a logical and self-consistent framework. This model is based on Franck-Condon broadening observed in polaronic systems where strong electron-boson interactions cause the quasiparticle residue, Z, to be vanishingly small. Comparisons of the low-lying states to different electronic states in the valence band strongly suggest that the coupling of the photohole to the lattice (i.e. lattice polaron formation) is the dominant broadening mechanism for the lower Hubbard band states. Combining this polaronic framework with high-resolution ARPES measurements finally provides a resolution to the long-standing controversy over the behavior of the chemical potential in the high-T{sub c} cuprates. This scenario arises from replacing the conventional Fermi liquid quasiparticle interpretation of the features in the Mott insulator by a Franck-Condon model, allowing the reassignment of the position of the quasiparticle pole. As a function of hole doping, the chemical potential shifts smoothly into the valence band while spectral weight is transferred from incoherent weight at high energies to a coherent quasiparticle peak near E{sub F}. The combined shift in the chemical potential and ...
Date: September 2, 2005
Creator: Shen, Kyle Michael
Partner: UNT Libraries Government Documents Department

Doping Dependence of the $(\pi,\pi)$ Shadow Band in La-Based Cuprates Studied by Angle-Resolved Photoemission Spectroscopy

Description: The ({pi},{pi}) shadow band (SB) in La-based cuprate family (La214) was studied by angle-resolved photoemission spectroscopy (ARPES) over a wide doping range from x = 0.01 to x = 0.25. Unlike the well-studied case of the Bi-based cuprate family, an overall strong, monotonic doping dependence of the SB intensity at the Fermi level (E{sub F}) was observed. In contrast to a previous report for the presence of the SB only close to x = 1/8, we found it exists in a wide doping range, associated with a doping-independent ({pi},{pi}) wave vector but strongly doping-dependent intensity: It is the strongest at x {approx} 0.03 and systematically diminishes as the doping increases until it becomes negligible in the overdoped regime. This SB with the observed doping dependence of intensity can in principle be caused by the antiferromagnetic fluctuations or a particular form of low-temperature orthorhombic lattice distortion known to persist up to x {approx} 0.21 in the system, with both being weakened with increasing doping. However, a detailed binding energy dependent analysis of the SB at x = 0.07 does not appear to support the former interpretation, leaving the latter as a more plausible candidate, despite a challenge in quantitatively linking the doping dependences of the SB intensity and the magnitude of the lattice distortion. Our finding highlights the necessity of a careful and global consideration of the inherent structural complications for correctly understanding the cuprate Fermiology and its microscopic implication.
Date: August 15, 2011
Creator: Shen, Z. X.
Partner: UNT Libraries Government Documents Department