Showing papers by "Hyun-Chul Kim published in 1990"

Fusion cross sections for 46,50Ti+90Zr,93Nb and some systematics of heavy-ion fusion at barrier and subbarrier energies.

Abstract: Measurements of the fusion cross sections in the barrier and subbarrier regions are presented for the four heavy-ion systems $^{46,50}\mathrm{Ti}$${+}^{90}$Zr${,}^{93}$Nb. The measured cross sections varied from 0.04 to 400 mb. The evaporation residues were detected by the use of a velocity filter. Procedures are described for extracting fusion cross sections from such measurements. The observed differences in the subbarrier fusion cross sections for the $^{90}\mathrm{Zr}$ and $^{93}\mathrm{Nb}$ nuclei, both of which have small collectivity, have led us to question the view that excursions of the strong nuclear force due to collective motions of the colliding nuclei are the primary enhancement mechanisms for the observed heavy-ion subbarrier fusion cross sections.A simple formula is presented, based on a flat distribution of barriers, which is applied to the near-barrier region (10--200 mb). This formula states that the quantity (\ensuremath{\sigma}E${)}^{1/2}$ vs E is linear in the near-barrier region with a zero intercept defining a threshold energy for fusion. These threshold values reflect variations in the binding energies of the valence neutrons. We also point out that the far-subbarrier region (10 mb) shows large variations in fusion cross sections and that these variations reflect differences in the collectivities of the colliding nuclei (especially noticeable differences are seen between permanently deformed nuclei and ``vibrational'' nuclei). These systematics of heavy-ion subbarier fusion suggest that neck formation is playing an important role. The barrier for neutron transfer vanishes at distances typically 1.5 fm beyond the typical barrier distance and this distance could vary with the binding energy of the valence neutrons. The presence of neutrons in the region between the nuclei could promote neck formation which provides a force strong enough to overcome the Coulomb force. The collective properties of the colliding nuclei are then interpreted as a modulation of the threshold for neck formation and thereby reflect the large observed differences in the far-subbarrier cross sections. Formulas are presented for ${\mathrm{\ensuremath{\sigma}}}_{\mathit{L}}$ which result from a flat distribution of barriers. These formulas predict a broad bell-shaped spin distribution and are compared to the measured distribution in the subbarrier region for the system $^{64}\mathrm{Ni}$${+}^{100}$Mo.

Thermally stable ohmic contacts to n‐type GaAs. VIII. Sputter‐deposited InAs contacts

Abstract: The electrical properties and microstructure of InAs ohmic contacts to n‐type GaAs, prepared by sputter‐depositing a single target, were studied by measuring the contact resistance (Rc) by the transmission line method and analyzing the interfacial structure by x‐ray diffraction and cross‐sectional transmission electron microscopy. Current‐voltage measurement of an as‐deposited InAs/W contact showed Schottky behavior, where the W layer was used as a cap layer. The InAs layer had an amorphous structure and a uniform oxide layer was observed at the InAs/GaAs interface. Even after annealing at 800 °C, ohmic behavior was not obtained in this contact because the intervening oxide layer prevented the InAs and GaAs interaction. By adding Ni to the InAs/W contacts (where Ni was deposited by an evaporation method), the interaction between the InAs and the GaAs was enhanced. Nickel interacted with As in the InAs layer and formed NiAs phases after annealing at temperature above 600 °C. The excess In in the InAs layer...

Case report 643

Abstract: A 46-year -o ld w o m a n had a pa infu l mass in the left chest wal l for 10 months . Phys ica l e x a m i n a t i o n revea led a p r o t r u d i n g tender t u m o r in the fou r th left in tercos ta l space tha t d id n o t involve the skin. Ches t roen t genog rams and c o m p u t e d t o m o g r a phy (CT) showed a 1 0 c m r o u n d mass wi th mul t ip le i r r egu la r calcifica t ions o f the fou r th and fifth r ibs and the s u r r o u n d i n g in te rcos ta l soft t issues (Fig. 1). Rou t ine b l o o d cell coun t and b l o o d chemist r ies were normal . A b iopsy was p e r f o r m e d and the pa t i en t u n d e r w e n t an opera t ive excision. N o satel l i te nodules or me ta s ta t ic foci in the lungs were detected. The p o s t o p e r a t i v e course was uneventful , a n d the pa t i en t was discha rged on the 20th d a y o f hosp i t a l i za t ion w i thou t fur ther t r ea tmen t .

Performance of self-routing ATM switch under nonuniform traffic pattern

Abstract: An asynchronous transfer model (ATM) switch which has lower hardware complexity than that of the output queuing switch is presented. The reduction in the hardware complexity is obtained without either losing the self-routing property or suffering from performance degradation under nonuniform traffic patterns. The switch consists of shift networks that are interconnected with distributors in two stages. Introducing the distributor between the stages of shift networks allows of packets to be distributed evenly to all the input ports of shift networks in the following stage. Although the switch becomes blocking, it retains the self-routing property and achieves the maximum throughput of 100% with only a small additional delay. >

Measurement of the Faraday effect of a few optical glasses using a direct polarimetric method

Abstract: A new method of measuring the longitudinal magneto‐optic effect has been introduced. This method does not require a modulator; instead, the analyzer is rotated and the intensity of light is collected as a function of the analyzer angle. The Fourier analysis of the intensity date versus the analyzer angle yields the information about the rotation angle and the ellipticity of the transmitted light. This method is simple in design as well as fast and accurate in data acquisition by virtue of computer‐assisted data collection. It was applied to the real samples of the optical glasses of Schott—SF2, F2, SF6, and SF10. The rotation angle was linearly proportional to the magnetic intensity and the Verdet constants showed a normal dispersion versus photon energy. The results were in a good agreement with other published values. Some possible applications of the present technique to the measurement of a very small birefringence have been discussed.

Design of a multistage switching network for ATM

Abstract: The authors propose a switching network that approaches a maximum throughput of 100% as buffering is increased. This self-routing switching network consists of simple 2*2 switching elements, distributors, and buffers located between stages and in the output ports. The switching network requires a speedup factor of two. The switch has log/sub 2/ N stages that move packets in store-and-forward fashion, thus incurring a latency of log/sub 2/ N time periods. The performance analysis of the switch under a uniform traffic pattern shows that the additional delay is small and a maximum throughput of 100% is achieved as buffering is increased. >