Programmable group-delay module using binary polarization switching

We demonstrate the first programmable group-delay module based on polarization switching. With a unique binary tuning mechanism, the device can generate any differential group delay value from -45 to +45 ps with a resolution of 1.40 ps, or any true-time-delay value from 0 to 45 ps with a resolution of 0.7 ps. The delay varying speeds for both applications are under 1 ms and can be as fast as 0.1 ms. We evaluate both the dynamic and static performances of the device while paying special attention to its dynamic figures of merit for polarization-mode dispersion emulation and compensation applications. Our experiment shows that the device exhibits a negligible transient-effect induced power penalty (<0.2 dB) in a 10-Gb/s nonreturn-to-zero system.     

Long-wavelength infrared photoinduced switching of a resonanttunneling diode using the intersubband transition

Voltage switching induced by long-wavelength infrared light from a CO₂ laser was observed using a double-barrier resonant tunneling diode (RTD) biased in the bistable region and the intersubband transition (IT) between the quantum confined states. Possible optoelectronic and all-optical switching applications involving hysteresis are proposed and discussed     

Traction-based Completed Adjoint Double Layer Boundary Element Method in elasticity

This paper is concerned with a traction-based Completed Adjoint Double Layer Boundary Element Method to solve for the surface traction of a system of rigid particles embedded in an elastic matrix. The main feature of the method is a single layer representation of the displacement field, which leads to a system of second-kind integral equations for the traction field, the extreme eigenvalue of which could be deflated, allowing iterative solution strategies to be effectively applied. The method is therefore most suitable for large-scale simulations of particulate solids. The method is benchmarked against some known analytic solutions, including the difficult stress singularity problems at sharp edges. The effectiveness of the method in dealing with a large number of inclusions is also demonstrated with an elongational deformation problem involving up to 25 inclusions.Research supported by the Australian Research Council (to NP-T and X-JF) and the National Natural Science Foundation of China (X-JF).     

Powder Deposition in Three Parallel-Oriented Dies of Different Shapes

Uniformity of bulk density distribution during the die filling process is required to minimize quality problems, such as distortion and cracking, for powder compacts. Understanding the die filling process is necessary in ensuring a uniform powder deposition. The second-generation pressure deposition tester (PDT-II) was used to investigate the deposition process and final pressure distribution of powder filling in toroidal, cylindrical, and E-shaped dies. All tests were conducted using a spray-dried free-flowing granular powder. The results indicated that for toroidal dies: (1) the area around 0° orientation (the leeward end) had the highest pressure values (1186.7 to 2498.0 Pa), with the average pressure values of the remaining area 353.7-648.0 Pa; (2) the pressure distribution was symmetrical about the centerline parallel to the feed shoe movement direction; (3) the highest feed shoe speed (500 mm/s) led to the most nonuniform pressure distribution among the three speeds; (4) higher feed shoe speed did not always result in higher final pressure values; and (5) the right die tended to have higher final pressure values (215.0 to 2498.0 Pa) than the center die (95.4 to 2052.5 Pa). For E-shaped dies: (1) the final pressure values of the middle leg (308.9 to 760.7 Pa) were higher than those of the left and the right legs (148.9 to 530.3 Pa); (2) the area along the backside had the highest final pressure value (1054.6 to 1303.8 Pa); (3) the pressure distribution was symmetrical about the centerline parallel to the feed shoe movement direction; and (4) neither the center die nor the right die always had higher pressure values than the other one at all locations. Comparison between cylindrical and toroidal dies indicated that: (1) neither of the two die shapes (cylinder and toroid) led to consistently higher or lower final pressure values at all locations and (2) for all three feed shoe speeds, the toroidal die had higher average final pressure values in the 0° orientation.     

Circular core polarization-maintaining optical fibers withelliptical stress-induced cladding

The reproducible technology for producing high-birefringence fibers with stress-induced elliptical cladding and circular core is described. The authors have obtained fibers that have a birefringence of about (1-3) 10^-4, a mode coupling parameter of about (2-7) 10 ^-5 m^-1, and loss of less than 0.5 dB/km at 1.6 μm. The authors have found effects restricting the capability of test fibers to maintain the state of linear polarization     

Low cycle fatigue and creep behavior of recrystallized Molybdenum near room termperature

The deformation behavior of pure recrystallized molybdenum under cyclic and static loads was investigated in the temperature range between 30°C and 10O°C, for stress amplitudes between 100 MPa and 250 MPa and for static loads up to 200 MPa. The results show that in spite of the low test temperatures and stress levels the Mo material exhibits considerable plastic strains which depend sensitively on frequenez and small changes in temperature.The activation energy deduced for the static and dynamic deformation is less than 0.98 eV which indicates thermally activated processes, to be explained by a dislocation kink model as described in the literature. The low-temperature fatigue behavior appears strongly influenced by creep-fatigue interaction phenomena.     

Cytokines and PGE2 modulate the phagocytic function of the beta-glucan receptor in macrophages

Under serum-free conditions the beta-glucan receptor of mouse macrophages mediates phagocytosis of beta-1,3-D-glucan-coated microbeads (diameter 2 microns). IFN-gamma increases the phagocytic function of the beta-glucan receptor in a dose-dependent manner, giving the plateau level at 100 U/ml. Maximum activity appears 9 h after addition of IFN-gamma to the cells. The effect disappears within 24 h. The effect of IFN-gamma may be a result of augmented receptor synthesis since treatment with cycloheximide reduces the phagocytosis. IL-1 also increases the phagocytic function of the beta-glucan receptor giving a dose-dependent response and with the plateau level reached at 10 U/ml. Maximum activity is found 4 h after addition of IL-1 to macrophages. The effect disappears within 24 h. TNF does not alter the phagocytic function of the beta-glucan receptor, but TNF together with IL-1 prolongs the effect of IL-1. PGE2 reduces the phagocytic function of the beta-glucan receptor. Maximum reduction is achieved with 8 ng/ml. Time-course studies show the lowest phagocytic activity 9 h after addition of PGE2 to the cells.     

Synthesis and biological studies on analogs of cyclolinopeptide A with a shortened peptide chain

Continuing our work on the immunosuppressive activity of cyclolinopeptide A (CLA), a cyclic nonapeptide of the sequence: c-(-Leu-Ile-Ile-Leu-Val-Pro-Pro-Phe-Phe), we synthesized a series of 6 linear analogs of CLA, successively shortened at the N-terminus of the peptide chain. Immunosuppressive activity of acetates as well as trifluoroacetates of these peptides was investigated using PFC (humoral immunity) and DTH (cellular immunity) tests. It was found that the immunosuppressive potency of the peptides examined diminishes with shortening of the peptide chain. Octapeptide I with the sequence Ile-Ile-Leu-Val-Pro-Pro-Phe-Phe was found to be the most active of the whole series. The immunosuppressive activity increased again for a tripeptide fragment of CLA of the sequence Pro-Phe-Phe. The immunosuppressive activity of octapeptide probably depends on the suppression of IL-1, IL-6 and TNF production by the cells involved in immune and inflammatory response.     

A perceptually motivated three-component image model-part II:applications to image compression

For past I see ibid., vol.4, no.4, p.405 (1995). The use of the image model of Part I is investigated in the context of image compression. The model decomposes the image into a primary component that contains the strong edge information, a smooth component that represents the background slow-intensity variations, and a texture component that contains the textures. The primary component, which is known to be perceptually important, is encoded separately by encoding the intensity and geometric information of the strong edge brim contours. Two alternatives for coding the smooth and texture components are studied: entropy-coded adaptive DCT and entropy-coded subband coding. It is shown via simulations that the proposed schemes, which can be thought of as a hybrid of waveform coding and feature-based coding techniques, result in both subjective and objective performance improvements over several other image coding schemes and, in particular, over the JPEG continuous-tone image compression standard. These improvements are especially noticeable at low bit rates. Furthermore, it is shown that a perceptual tuning based on the contrast-sensitivity of the human visual system can be used in the DCT-based scheme, which in conjunction with the three-component model, leads to additional subjective performance improvements.