Dense Wave Research Articles

Grain growth in millimeter wave sintered silicon nitride ceramics

In this paper, to investigate the effect of millimeter wave heating on grain growth behavior in silicon nitride ceramics, specimens doped various rare earth sesquioxides as additives were sintered using a millimeter wave radiation 28 GHz. Comparative studies of densification, phase transformation, grain growth behavior of silicon nitride fabricated by millimeter wave and conventional sintering were carried out. Microstructure of the specimens was analyzed by scanning electron microscopy (SEM) and image analysis. Fully dense millimeter wave sintered silicon nitride presented a bimodal microstructure exhibiting higher values of fracture toughness and fracture strength than materials processed by conventional heating techniques. Results indicate that millimeter wave sintering is more effective in enhancing the grain growth and in producing the bimodal microstructure than conventional heating. It is also confirmed that the localized heating by millimeter wave radiation is taking place within the samples.

Silicon-based optical integrated circuits for terabit-rate optical networks

Dense Wave Guide Division Multiplexing (DWDM), the recent revolutionary technology in optical communication, promises 100-fold transmission rate increase for fiber-optical channels. In this paper we discuss optical Integrated Circuits on SiO 2 based on Ge (SiON)/Si structures (SiOIC) – the basic element of DVDM and spectral optical channel switch devices, details of SiOIC’s manufacturing, e.g. thick-layer PECVD and deep-trench RIE technological processes, and micromechanical technique of the fiber-planar optical waveguide connection. Other important topics under consideration are passive DWDM SiOIC’s, functional principles of the planar optical DWDM and the volume analog, the Array Waveguide Grating (AWG) as a synthesis of the Michelson’s Echelon and the Phased Antenna Array (PHASAR), and spectral selective Add-Drop SiOIC; DWDM optical switches; Waveguide thermooptical modulator and Mach-Zehnder 2×2 switch element, Controlled Add-drop and wavelength selective switch circuits examples, challenge and prospect of optical switch on SiOIC’s, fast optical switches on Silicon-on-Isolator (SOI) structures, and charge-controlled electrooptical modulators of plasma dispersion effect in Si-core waveguides.

Dispersion compensation and crosstalk reduction in a bidirectional dense wavelength division multiplexing cable television system

We propose and demonstrate a bidirectional dense wave- length division multiplexing cable television system that uses large effec- tive area fibers (LEAFs) as transmission fibers and chirped fiber grating (CFG) as a dispersion compensation device to reduce the dispersion and cross-phase modulation (XPM)-induced crosstalk. By comparing the system link with the transmission length of a 50-km single-mode fiber (SMF) without CFG, good performances of carrier-to-noise ratio (CNR) >50 dB, a composite second order (CSO) >69 dB, and a composite triple beat (CTB) >66 dB are obtained in our proposed system over a 50-km LEAF transport. © 2003 Society of Photo-Optical Instrumentation Engineers. (DOI: ORACLE)

Metro Dense Wave Division Multiplexing (DWDM)

Metro Dense Wave Division Multiplexing (DWDM) has been touted by its proponents as the future of optical telecommunications in the metro market. But is it? Its proponents have presented it as a natural extension of long haul DWDM into the metro network. But can Metro DWDM be cost justified and, if so, under what conditions? Whether and to what extent the economics of metro DWDM will change over time are other major questions certain to affect materially the acceptance of metro DWDM and thus the market opportunity for manufacturers of metro DWDM equipment. Finally, questions concerning regional variations in the market opportunity for Metro DWDM equipment must be answered.

THE NEUROPROTECTIVE EFFECTS OF ELECTROACUPUNCTURE ON FOCAL CEREBRAL ISCHEMIA IN MONKEY

The present study was designed to investigate whether the electro-acupuncture (EA) is beneficial to extenuate cerebral ischemic injuries following the middle cerebral artery occlusion (MCAO) in monkey. The results indicated that after MCAO. the EEG was severely inhibited, while the EEG recovery was slow after reperfusion compared with the control group. EA, given between the acupuncture points Baihui Point (GV. 20) and Renzhong Point (GV. 26) with a dense-sparse waveforms,which can be transformed into each other when dense or sparse wave is terminated, facilitated the recovery of EEG after ischema. The local cerebral blood flow (ICBF) in the striatum decreased during MCAO, whereas EA improved the ICBF significantly. The neurological deficit scale significantly decreased after ischemia but increased in EA group. The brain swelling coefficient (right/left) increased significantly in the ischemia group, but EA attenuated this increase. The neuropathological study showed that EA could significantly decrease the infarct area (p<0.05) and increase the percentages of the residual cells in the ipsilateral striatum and cortex (p<0.05 respectively). These results implied that EA is effective to extenuate cerebral ischemic injuries following the transient middle artery occlusion in monkeys.

Cooling Mechanism of Expanding Plasmas Produced by Optical-Field-Induced Ionization

Particle-in-cell simulation is carried out to investigate the cooling process of a multicharged dense plasma produced by optical-field-induced ionization. All coulomb collisions among charged particles are taken into consideration using Nanbu's theory of coulomb collisions and its recent extension to the case when the weight assigned to a simulated particle varies from particle to particle. The effect of coulomb collisions on the expanding plasma is very large. Two cases are considered: expansion of a source plasma 1) into a vacuum and 2) into an ambient cold plasma. The results obtained for the first case agree well with the self-similar hydrodynamic solution. In the second case, the rapid cooling of the multicharged plasma, which is essential for x-ray lasing, is accomplished. The mechanism of this cooling is clarified by the simulation. It is also shown that the expansion is accompanied by a dense wave front. Near the wave front, a double layer of electric charge is formed.

Cylindrical Expansion of a Ultra-High Density Plasma for X-Ray Laser Source. 2nd Report. Rapid Cooling Accomplished by an Ambient Plasma.

Particle-in-cell simulation is carried out for the expansion of a multi-charged dense plasma for X-ray laser systems. All Coulomb collisions among charged particles are taken into consideration. The rapid cooling of the multi-charged plasma, which is essential for X-ray lasing, is accomplished when this plasma is surrounded by a cold ambient plasma. The mechanism of this cooling is clarified by the simulation. The expansion spreads, accompanying with the expanding dense wave front. Existence of a double layer of electric charge at the wave front is confirmed.

Reconstructing transmission networks using ATM and DWDM

TDM transmission and ATM switching have been established as two wide area core network technologies, operating separately but in conjunction with each other at different layers of the protocol stack. History shows that transmission networks have been reconstructed on a regular basis, and the reconstruction, based on fiber, SONET, and DWDM (dense wave division multiplexing), allows TDM transmission capabilities to be integrated with ATM switches, resulting in increased transmission efficiencies, effective bandwidth management, and greatly reduced capital, operational, and maintenance costs.

Optical networking

The author discusses the history of telecommunication networks and the development of fiber networks. The expansion of capacity is considered as is the introduction of DWDM (dense wave division multiplexing).

IP routers: new tool for gigabit networking

IP routing continues to receive much attention from the research and vendor communities. Its primary function-forwarding packets between networks-must keep pace with the demands of the exponentially growing end user population. It must accommodate attachment of gigabit data link technologies such as ATM, packet Sonet, Gigabit Ethernet, and dense wave division multiplexing, and fill those links at full capacity. As network providers introduce new services supporting multicast, QoS, voice, and security, IP routing-and more specifically the IP forwarding function-will be called upon to analyze additional packet information at gigabit rates to determine how each packet should be handled. Performing these new functions while maintaining parity with the advances in available bandwidth will present an interesting challenge for the forwarding capabilities of IP routers. Indeed, for the Internet to scale, we must scale all dimensions of the IP routing process.

An evaluation of different antenna designs for helicon wave excitation in a cylindrical plasma source

A magnetohydrodynamic numerical model, based on the finite element method, is employed to analyze the antenna radiation resistance in a cylindrical helicon wave driven plasma source. The antenna radiation resistances of four commonly used antennas are compared. The effects on antenna radiation resistance of frequency, plasma density, density profile and the system dimensions are investigated. It is confirmed that m=+1 is the most strongly excited mode. It is shown that the plasma density gradient tends to suppress the excitation of negative m-modes. Some wave field patterns are also presented which demonstrate commonly observed features in the experiments such as the beat patterns of copropagating radial modes. The findings highlight the importance of antenna radiation resistance modelling as a first step to a self consistent model of the discharge physics of cool dense helicon wave driven sources.

Geosat data give wind speed and wave height

The Navy has released Geosat radar cross section and significant wave height data from the 18‐month Geodetic Mission for use by the general public. These data, when combined with data from the Exact Repeat Mission, comprise the most dense global wind speed and wave height data set ever archived. The accuracy of the data when compared with NDBC buoys has been shown [Dobson et al., 1987] to be +/− 1.7 m/s for wind speed and +/− 0.5 m for wave height.The Geosat altimeter orbits the Earth at an altitude of 800 km and, during the Geodetic Mission, laid down a ground track which precessed about 100 km every 3 days forming a tight mesh over 72 days which was repeated for three consecutive 72‐day periods. The primary mission of the instrument was to measure the marine geoid, but it also measured radar cross section (RCS) and significant wave height (SWH). RCS is the return signal backscattered from the ocean surface and is proportional to wind speed. SWH is obtained from the slope of radar‐returned pulse. Data are available at a one per second rate with complete global coverage.

Binaural coherence edge pitch

The binaural coherence edge pitch (BICEP) is a dichotic broadband noise pitch effect similar to the binaural edge pitch (BEP). The BICEP stimulus is made by summing spectrally dense sine wave components with random phases. The interaural phase angle is a constant (0 or pi) for components with frequencies below (or above) a chosen edge frequency, and it is a random variable for the remaining components. The chosen edge frequency is a coherence edge because the noises to the two ears are mutually coherent within any band of frequencies on one side of the edge and they are mutually incoherent in any band on the other side. Pitch-matching experiments show that the BICEP exists for coherence edge frequencies between about 300 and 1000 Hz. It is matched by a pure-tone frequency that differs from the edge frequency by 5% to 10%. The matching frequency lies on the incoherent side of the edge, an important result that is consistent with the way that the equalization-cancellation model has been applied to binaural pitch effects, especially the BEP. The results of BICEP experiments depend upon whether the coherent components are presented in 0 or pi interaural phase for some listeners but not for all. The BICEP persists if the noise to one of the ears is delayed, but it becomes weaker and less well matched as the delay increases beyond 2 ms. The BICEP does not depend on whether the component amplitudes are all created equal or are given a Rayleigh distribution. Some reliable pitch sensation exists even when the component amplitudes are entirely independent in the two ears, so long as the phase coherence conditions of the BICEP stimulus are maintained. The existence of the BICEP is a challenge for current models of dichotic pitch because none of them predicts all its features.