Phased Aligned Passive Bus (PAB) Scheme for ISDN User-Network Interface

This paper proposes an alternative to the passive bus realization of the current CCITT ISDN user-network interface. Our new approach is termed phase aligned passive bus (PAB) scheme. An automatic phase adjusting mechanism using a monitor bit is employed in the terminal equipment. This scheme enables the terminals to operate in complete phase synchronization on a passive bus. The advantages that result from this technique are: 1) Eliminates, in principle, the bus length limitation due to round-trip delay time. If line bit rate of 192 kbit/s is kept, then a practical bus length is about 700 m with no limitation on terminal distribution. 2) Allows various extended bus configurations, such as simple repeatered extention, connection of optical link, and multibranched passive bus. 3) Provides spare bit transmission capability to facilitate intrabus communication and maintenance. As an alternative it keeps the general framework of the current CCITT I-series standard such asB + B + Dchannel structure and LAP-Dprotocol. Experiments realizing long passive buses are shown to confirm the feasibility of the proposed scheme. This concept is also shown to be applicable to a 2-wire full duplex user-network interface, advantageous in the existing office environment, employing time compression transmission.     

Optimised bandwidth of optical filter in optical preamplifier

An optimisation scheme is proposed for the optical-filter bandwidth in an optical preamplifier for a given tolerance in the signal-wavelength and a given filter profile. The optimised bandwidth is 3.46 times the conceivable detuning for a Lorentzian-shaped filter profile. Preamplifiers with optimised bandwidth can operate with the lowest noise figure at maximum detuning.<>     

Comparison of thermal neutron distributions within shield materials obtained by experiments, SN and Monte Carlo code calculations

Benchmark experiments of thermal neutron distributions within the shield materials, graphite pile and pure water, were performed by using 252Cf fission neutrons and gold foil activation detectors, and, to these results, the estimates obtained by using the discrete ordinate code ANISN and the Monte Carlo code MCNP5 with two different cross-section libraries, ENDF/B-VI and the Japanese new version of JENDL-3.3, were compared. The results revealed that the MCNP5 calculations with the two libraries closely agree with the experiments and that there are slight differences between the MCNP5 and the ANISN calculations. The differences are caused mainly by the overestimation of the thermal neutron absorption cross sections constructed in NJOY99. The ANISN calculations with the modified absorption cross sections reproduced the results of the MCNP5 fairly well.     

Micro-CT of Pseudocneorhinus bifasciatus by projection X-ray microscopy

The projection X-ray microscope utilises a very small X-ray source emitted from a thin (0.1-3 microm) target metal film excited by the focused electron beam of a scanning electron microscope. When an object is placed just below the target metal film, the diverging X-rays enlarge the shadow of the object. Because no X-ray optics such as a zone-plate is used, the focal depth is, in principle, infinitely large. We exploited this to apply projection X-ray microscopy to three-dimensional (3-D) structure analysis by means of cone-beam computed tomography. The projection images of a small arthropod (Pseudocneorhinus bifasciatus, 5 mm in length), was recorded at 3 degrees increments over the whole range (360 degrees) of a stepping-motor-controlled sample rotator. A 3-D image was reconstructed from corn-beam projections using a filtered back-projection algorithm. The reconstructed 3-D image showed in detail the internal structure of an opaque object.     

Modulation and demodulation techniques in optical heterodyne PSKtransmission systems

Modulation and demodulation techniques are described for an optical PSK heterodyne transmission system operating at 560 Mb/s and 1.2 Gb/s. Performance limitations affecting the receiver sensitivity in a 1.2-Gb/s DPSK system, such as laser phase noise, phase modulation depth, IF center frequency deviation, and local laser power, are studied. High receiver sensitivities for PSK systems were achieved. The applicability of the Mach-Zehnder modulator as a phase modulator for 1.2-Gb/s DPSK is also demonstrated. A 1.2-Gb/s DPSK transmission of over 100 km, using polarization diversity with novel polarization-insensitive automatic frequency control in an attempt to overcome signal fading caused by polarization fluctuation in the transmitting fiber, is also described. A receiver sensitivity of less than -42.8 dBm and varying within 1.4 dB for all states of polarization was achieved. A multichannel high-definition TV (HDTV) transmission experiment using a DPSK polarization-diversity tunable receiver is described     

The fate of dioxins during green tea manufacture

Dioxin concentrations and homologue profiles were examined in plucked new shoots, crude tea and its hot water extracts, soils and atmosphere in tea orchards. The rate of dry provisions in crude tea has increased 4 times as that of the plucked new shoots. However, dioxin concentrations except O8CDD in crude tea have increased only 2 to 3 times as those of the plucked new shoots. O8CDD concentration increased remarkably during processing. Little dioxins were detected in hot water extracts of crude tea leaves.     

Mechanical properties of zirconia-alumina composite ceramics prepared from Zr-Al metallo-organic compounds

The mixture of a Zr-Al metallo-organic compound and Al₂O₃ powder yields dense ZrO₂-Al₂O₃ composite ceramics. The fraction of the tetragonal ZrO₂ phase in as-sintered ZrO₂-Al₂O₃ ceramics is almost 100% and the ZrO₂ grains at about 500 nm in diameter are dispersed in the matrix. The ceramics have high fracture toughness and bending strength.     

Phase noise cancellation in a carrier recovered optical heterodynereceiver

The performance and application of an optical heterodyne receiver which uses a carrier recovery demodulator are described. Phase sensitive demodulators used in coherent optical transmission are compared, and the suppression of both phase noise and frequency instability of light sources by a carrier recovery (CR-) demodulator is described. A carrier recovered PSK (CR-PSK) demodulator and a phase noise canceling circuit (PNC) for a coherent SCM receiver are introduced as examples of CR-demodulators. The relationship between laser diode spectral linewidths and the delay time difference between the two paths in the CR-PSK demodulator necessary to keep the system performance within a certain power penalty is then derived. In a preliminary experiment using 560-Mb/s CR-PSK transmission, a receiver sensitivity of -51.6 dBm was obtained, and a laser phase noise suppression of about ¹/₂ that of DPSK was confirmed. The results suggest the possibility of constructing a heterodyne receiver which has no AFC-loop. Applications of a CR-demodulator to an optical frequency division multiplexing (OFDM) system and to a multivalue modulation scheme are discussed