Selectively etched undercut apertures in AlAsSb-based VCSELs

Apertures were formed in single-growth, AsSb-based, long-wavelength (1.55 μm) vertical-cavity surface-emitting lasers by laterally etching the active region. The materials contrast between the AlAsSb-based mirrors and the AlInGaAs-based active region leads to a high selectivity for the etch, allowing long apertures to be formed with minimal etching of the mirrors. Lasers showing reduced threshold currents and increased efficiencies were demonstrated using these apertures     

Fracture and deformation behaviour of melt growth composites at very high temperatures

Unidirectionally solidified Al₂O₃/Y₃Al₅O₁₂ (YAG) or Al₂O₃/Er₃Al₅O₁₂ (EAG) eutectic composites, which are named as Melt Growth Composites (MGCs) has recently been fabricated by unidirectional solidification. The MGCs have a new microstructure, in which continuous networks of single-crystal Al₂O₃ phases and single-crystal oxide compounds (YAG or EAG) interpenetrate without grain boundaries. The MGCs fabricated are thermally stable and has the following properties: 1) the flexural strength at room temperature can be maintained up to 2073 K (just below its melting point), 2) a fracture manner from room temperature to 2073 K is an intergranular fracture different from a transgranular fracture of sintered composite with the same composition, 3) the compressive creep strength at 1873 K and a strain rate of 10^–4/sec is 7–13 times higher than that of sintered composites, 4) the mechanism of creep deformation is based on the dislocation creep models completely different from the Nabarro-Herring or Coble creep models of the sintered composites, and 5) it shows neither weight gain nor grain growth, even upon heating at 1973 K in an air atmosphere for 1000 hours. The above superior high-temperature characteristics are caused by such factor as the MGCs having a single-crystal Al₂O₃/single-cryatal oxide compounds without grain boundaries and colonies, and the formation of the thermodynamically stable and compatible interface without amorphous phase.     

Seismic design method of clamped-free thin cylindrical shells immersed in fluid

We carried out excitation experiments on clamped-free thin cylindrical shells immersed in fluid that represented thermal baffles of a fast breeder reactor. At a certain excitation level, occurred external pressure buckling. We also observed that parametric vibration, which involved high-order circumferential vibration modes, occurred at a certain combination of excitation frequency and excitation level. Concerning seismic design of the thermal baffles, we, therefore, take not only the buckling but also the effect of the parametric vibration into consideration. We adopt buckling eigenvalue analyses to estimate buckling pressure and propose a formula to prevent the buckling. Further, we discuss important factors such as buckling strength reduction caused by initial shape imperfections and interaction between horizontal and vertical seismic response. Concerning the parametric vibration, a significant deformation of cylinders should be prevented. A practical method applying the dynamic stability theory is proposed to obtain the condition, under which the parametric vibration takes place.     

Synthesis of MoSi2-TiSi2 pseudobinary alloys by reactive sintering

MoSi₂-TiSi₂ pseudobinary alloys are synthesized from mixtures of elemental powders of molybdenum, silicon, and titanium by reactive sintering under a pseudoisostatic pressure of 150 MPa. When the titanium content in the alloy increases from 0 to 33 at. pct, the density of the alloy decreases from approximately 6 to 4 g/cm³, while the relative density is more than 95 pct independent of the titanium content. Vickers hardness of the alloy is approximately 800 when the alloy consists of a monophase structure of α-MoSi₂ or β-MoSi₂. However, the hardness increases to approximately 950 when the alloy consists of a dual-phase structure of (α-MoSi₂+β-MoSi₂) or (β-MoSi₂+γ-TiSi₂). The oxidation resistance of the alloy at 773 K is approximately tripled when the titanium content increases from 0 to 1.7 at. pct, but the effect of the titanium content on the oxidation resistance becomes less remarkable as the titanium content increases.     

A New Unidirectional Solidified Ceramic Eutectic with High Strength at High Temperature

New eutectic composites such as Al₂O₃/Er₃Al₅O₁₂ or Al₂O₃/GdAlO₃ have recently been fabricated by unidirectional solidification. The eutectic composite has a new microstructure, in which continuous networks of Al₂O₃ phases and oxide compounds (Er₃Al₅O₁₂ or GdAlO₃) interpenetrate without grain boundaries. The eutectic composite is thermally stable and has the following properties. In case of Al₂O₃/Er₃Al₅O₁₂ composite,

1. The flexural strength at room temperature can be maintained up to 2073 K (just below its melting point of about 2130 K),

2. The compressive flow stress at 1873 K and a strain rate of 10^-4/sec is about 8 times higher than that of sintered composites of the same composition,

3. It shows neither weight gain nor grain growth, even upon heating at 1973 K in an air atmosphere for 500 hours. In case of Al₂O₃/GdAlO₃ composite, and

4. It shows substantial plastic deformation at 1873 K with a flexural yield stress of about 700 MPa. It is found that the plastic deformation occurred by dislocation motion in each phase.     

RF crosstalk in multiple-wavelength vertical-cavitysurface-emitting laser arrays

We present the crosstalk measured in multiple-wavelength vertical-cavity surface-emitting laser (VCSEL) arrays under RF modulation. The array consists of eight bottom-emitting VCSEL's arranged with a “pie”-like configuration within a 60-μm-diameter circle with a 3-μm spacing for coupling into a multimode fiber. The crosstalk is investigated by measuring a cross-modulation response of two VCSEL's in the array using a monochromator in an optical spectrum analyzer as a receiver. Excess crosstalk is minimized by flip-chip mounting the array and introducing a proper bias condition. The crosstalk observed In the adjacent VCSEL's is less than -40 dB at the modulation frequency below 700 MHz and it Increases at 20 dB/decade above this frequency when both VCSEL's are biased at 5.0 mA     

Room-temperature, CW operation of lattice-matched long-wavelengthVCSELs

Continuous-wave operation of vertical-cavity surface-emitting lasers lattice matched to InP and grown with one epitaxial step is presented. These lasers combine highly reflective AlAsSb/AlGaAsSb mirrors with a double-intracavity contacted structure based on thick InP contact layers     

Improvement of the design of 180° rat-race hybrid

An innovative and simple design for a 180° rat-race hybrid is proposed which has a substantially improved phase shift characteristic over a large bandwidth compared with that of a conventional rate-race hybrid. The proposed hybrid has been fabricated with a three-dimensional technology to benefit from a high level of integration. It exhibits a bandwidth of 31% from 28.8 to 39.4 GHz with -15 dB input and output matching, a coupling loss of 4.6 dB with a power dividing balance better than 1.1 dB, and a phase balance better than 2     

Simulation on chemical mechanical polishing using atomic force microscope

A micro-contact model for chemical–mechanical polishing (CMP) of silicon wafer is presented. The model is developed on the basis of the Greenwood-Williamson micro-contact mechanics. The atomic force microscope (AFM) is used as a polishing test apparatus to evaluate the removal rate by a single particle in a CMP slurry. Using this model and AFM, the simulation on polishing of SiO₂ is performed. The model is evaluated by comparing the simulated polishing rate and that experimentally determined by real CMP processes. The simulation result and experiment result are in good agreement. It suggests that the combination of the model and AFM polishing test can be used to estimate the removal rate of SiO2 CMP and may be used to study the effects of different materials, slurry and operating condition on CMP process.     

Effect of pectin enhancement on plasma quercetin and fecal flora in rutin-supplemented mice

ABSTRACT:  Few reports have considered the effects of dietary fiber on plasma quercetin and the intestinal flora. We investigated the effects of pectin on the plasma and fecal flora of mice fed a diet supplemented with the quercetin glycoside rutin. Male mice were randomly divided into 2 groups, which were fed a pectin–rutin (PR) or cellulose–rutin (CR) diet for 14 d. Plasma quercetin and isorhamnetin metabolites were measured by high-performance liquid chromatography. Feces were immediately processed with bacteriological procedures. The fecal flora was investigated. Plasma quercetin and isorhamnetin concentrations were significantly higher in the PR diet group, as was the plasma isorhamnetin/quercetin ratio. The composition of the intestinal flora differed between the 2 dietary groups. The total number of fecal bacteria was significantly larger in the PR group, in which most types of bacteria were more abundant, with the exceptions of bifidobacteria, fusiform-shaped bacteria, and staphylococci. The lower gut seemed to be the major absorption site for rutin. Pectin might thus enhance the bioavailability of quercetin from rutin by altering the metabolic activity of the intestinal flora and/or gut physiological function.