Showing papers by "Xiang Zhang published in 1989"
13 Jun 1989
TL;DR: In this article, the authors investigate the problems associated with the generation of design data over a larger substrate and line parameter range, and obtain numerical results are curve-fit into closed-form formulas to be incorporated into CAD (computer-aided design) packages.
Abstract: The time-domain finite-difference method combined with Fourier transform techniques has recently been shown to be a very effective approach in modeling the dispersive characteristics of microstrip components. Here, the authors investigate the problems associated with the generation of design data over a larger substrate and line parameter range. The obtained numerical results are curve-fit into closed-form formulas to be incorporated into CAD (computer-aided design) packages. >
7 citations
6 citations
01 Apr 1989
TL;DR: In this paper, a fine-grained hodoscope was constructed with two layers of vertical conducting plastic tubes for the X position measurement of showers, which was accomplished by cathode-induced horizontal strips.
Abstract: A fine-grain hodoscope to measure the position of showers in the outer (>52 cm) region of the E-705 electromagnetic calorimeter is described. The hodoscope is constructed with two layers of vertical conducting plastic tubes for the X position measurement of showers. Y position measurement of showers was accomplished by cathode-induced horizontal strips. A 50/50-ethane mixture bubbled through isopropyl alcohol at 0 degrees C was circulated through the tubes in parallel. The tubes were operated at +1.925 kV on the wire (below the region of saturated avalanche) in the limited proportionality mode. The hodoscope is described, and results are presented for the position resolution, shower width, and charge detected as a function of calibration electron energy. >
3 citations
TL;DR: In this paper, the temperature dependence of the molecular tilt angle in a series of ferroelectric liquid crystals is deduced from X-ray diffraction measurement, and the critical exponent β has been estimated from the experimental data.
Abstract: The temperature dependence of the molecular tilt angle in a series of ferroelectric liquid crystals is deduced from X-ray diffraction measurement. The critical exponent β has been estimated from the experimental data. The non-classical value of β for the compounds lies in the range 0.36–0.41.
2 citations
TL;DR: A trigger processor for the selection of events in which photons of large transverse momentum are detected by a lead and scintillating glass calorimeter was designed, constructed, and operated at interaction rates ranging from 2 kHz to 2 MHz as discussed by the authors.
Abstract: A trigger processor for the selection of events in which photons of large transverse momentum are detected by a lead and scintillating glass calorimeter was designed, constructed, and operated at interaction rates ranging from 2 kHz to 2 MHz. The system achieved suppressions of the raw interaction rate of as much as 1*10/sup -5/. Raw distributions of transverse momenta and direct photon event sensitivities are presented for data taken with 300-GeV/c pion and proton beams on a lithium target. >
2 citations
13 Mar 1989
TL;DR: In this paper, the design and performance of a 4.2-radiation-length, lead-sandwich, gas tube hodoscope was discussed and the results reviewed of an analysis of electron calibration data taken during a recent six-month running period are reviewed.
Abstract: The design and performance of a 4.2-radiation-length, lead-sandwich, gas tube hodoscope are discussed. The device, measuring 1*2 m/sup 2/ in area and 12 cm in depth, was used in Fermi National Accelerator Laboratory experiment 705. Multiple samplings of anode wires situated within three-walled aluminum tubes were used to generate an X coordinate; similarly, capacitively coupled copper-clad strips were ganged together to yield a Y coordinate. The results reviewed of an analysis of electron calibration data taken during a recent six-month running period are reviewed. The position resolution (in millimeters) is seen to be 0.8+3.3/ square root E+31/E for the 9.92 mm-spaced wires and 0.6+3.2/ square root E+32 for the 12.5-mm strips, where E represents the electron beam energy in GeV. The correlation between energy as measured by the wires and energy as measured by the strips is fairly tight, with an asymmetry RMS (root mean square) for 30-GeV electrons of about 4%. >
2 citations
01 Jan 1989
TL;DR: A 544-channel low-noise, high-rate precision charge-amplification and ADC (analog/digital converter) system was constructed for the Fermilab Experiment 705 electromagnetic calorimeter, which uses SCG1-C scintillating glass and SF5 lead glass instrumented with photomultiplier tubes as discussed by the authors.
Abstract: A 544-channel low-noise, high-rate precision charge-amplification and ADC (analog/digital converter) system was constructed for the Fermilab Experiment 705 electromagnetic calorimeter, which uses SCG1-C scintillating glass and SF5 lead glass instrumented with photomultiplier tubes. A general discussion of the system is given, and the charge amplification, fast-trigger-pulse generation, and analog/digital conversion aspects of the system are presented in more detail. Performance is evaluated using data from Experiment 705 and from offline tests. Short- and long-term pedestal stability, baseline recovery and rate capability, linearity of response, and crosstalk between channels are discussed. >
2 citations
TL;DR: In this article, a new form of high-temperature isopiestic technique has been developed for measuring isothermal-isobaric compositions of different melts with only one common volatile component.
Abstract: A new form of the high-temperature isopiestic technique has been developed for measuring isothermal–isobaric compositions of different melts with only one common volatile component; this has been applied to mercury–bismuth, mercury–cadmium, mercury–gallium, mercury–indium and mercury–tin binary amalgams at 600 K. The activities of mercury in mercury–bismuth, mercury–gallium, mercury–indium and mercury–tin amalgams have been calculated from the measured isothermal–isobaric data, taking the mercury–cadmium amalgam as a reference system. Using the results the activities of bismuth, gallium, indium and tin in the amalgams have been calculated analytically.
TL;DR: In this paper, the early stages of MBE growth of InSb on GaAs (001) were investigated using both conventional and high-resolution TEM for a study of 3D nucleation and island growth.
Abstract: This investigation focuses attention on the very early stages of MBE growth of InSb on GaAs (001). Both conventional and high resolution TEM have been used for a study of InSb layers varying between 5 and 300 monolayers in average thickness. The observations provide conclusive evidence of 3D nucleation and island growth. Complete lattice relaxation is brought about by a network of 1/2 Lomer dislocations at the InSb/GaAs interface and there is strong evidence for the presence of an additional sphalerite interfacial phase. Threading dislocations and planar defects in the InSb epilayer are mainly introduced during island coalescence.
TL;DR: In this article, three multiwire proportional chambers (MWPCs) with high-rate capability have been constructed for Fermi National Accelerator Laboratory experiment 705 (charmonium and direct photon production by pi /sup +or-/,p and p at 300 GeV/c).
Abstract: Three multiwire proportional chambers (MWPCs) with high-rate capability have been constructed for Fermi National Accelerator Laboratory experiment 705 (charmonium and direct photon production by pi /sup +or-/,p and p at 300 GeV/c). Each chamber, with a sensitive area of 308 cm/sup 2/, consists of three anode planes, wound with 12.5- mu m-diameter gold-plated tungsten/rhenium wire, facing 25- mu m graphite-coated kapton cathode planes at a distance of 3 mm. Wire spacing is 0.75 mm in two of the MWPCs and 1.00 mm in the third one. After a few weeks of running on 'magic gas' with a beam flux of up to approximately 10/sup 7/ particles/cm/sup 2/ s, severe damage occurred to the graphite coating. All cathode planes were replaced by aluminized kapton, and the chambers worked successfully for the next three months until the end of the run, when a 10% efficiency drop was observed after a total accumulated charge of approximately 1 C/cm of sense wire. After the end of the run the chambers were disassembled and inspected. A white deposit with a characteristic wire pattern etched away from the Al coating was observed in the region of the beam spot. >