Subject-based extraction of a latent blog community

In the blogosphere, there exist posts relevant to a particular subject and blogs that show interest in the subject. In this paper, we define a set of such posts and blogs as a blog community and propose a method for extracting the blog community associated with a particular subject. The proposed method is based on the idea that the blogs who have performed actions (e.g., read, comment, trackback, scrap) to the posts of a particular subject are the ones with interest in the subject, and that the posts that have received actions from such blogs are the ones that contain the subject. The proposed method starts with a small number of manually-selected seed posts containing the subject. Then, the method selects the blogs that have performed actions to the seed posts over some threshold and the posts that have received actions over some threshold. Repeating these two steps gradually expands the blog community. This paper presents various techniques to improve the accuracy of the proposed method. The experimental results show that the proposed method exhibits a higher level of accuracy than the methods proposed in prior research. This paper also discusses business applications of the extracted community, such as target marketing, market monitoring, improving search results, finding power bloggers, and revitalization of the blogosphere.     

Optoelectronic and microwave transmission characteristics of indium solder bumps for low-temperature flip-chip applications

This paper describes low-temperature flip-chip bonding for both optical interconnect and microwave applications. Vertical-cavity surface-emitting laser (VCSEL) arrays were flip-chip bonded onto a fused silica substrate to investigate the optoelectronic characteristics. To achieve low-temperature flip-chip bonding, indium solder bumps were used, which had a low melting temperature of 156.7/spl deg/C. The current-voltage (I-V) and light-current (L-I) characteristics of the flip-chip bonded VCSEL arrays were improved by Ag coating on the indium bump. The I-V and L-I curves indicate that optical and electrical performances of Ag-coated indium bumps are superior to those of uncoated indium solder bumps. The microwave characteristics of the solder bumps were investigated by using a flip-chip-bonded coplanar waveguide (CPW) structure and by measuring the scattering parameter with an on-wafer probe station for the frequency range up to 40 GHz. The indium solder bumps, either with or without the Ag coating, provided good microwave characteristics and retained the original characteristic of the CPW signal lines without degradation of the insertion and return losses by the solder bumps.     

Thermoelastic attenuation of circular-cross-sectional micro/nanoring including single-phase-lag time

In this work, the thermoelastic dissipation (TED) for circular-cross-sectional micro/nanoring model is studied including the single-phase-lag (SPL) time based on the non-Fourier heat conduction model. The toroidal solid ring is simple to manufacture and thus the potential is high for future development. Also, the present model is more precise than the 1D or 2D beam or rectangular-cross-sectional ring because the governing equation is established by 3D coordinate system. Moreover, the SPL shows the delay time of heat-flux and is especially important in cryogenic or ultrafast-vibration environments. In this regard, characteristics of the TED is mainly analyzed according to the lagging time, geometrical shape, mode number and temperature, etc. Using the experimental data in literatures, the effectiveness of this work is verified to represent the investigations. The spectra of the TED with the phenomenon of multiple peaks are presented, and then the results can be grouped and compared with previous works. Moreover, the temperature distribution is graphically described to explain the SPL mechanism.

     

Reduction in thermal conductivity of Bi thin films with high-density ordered nanoscopic pores

We prepared two-dimensional Bi thin films with high-density ordered nanoscopic pores by e-beam evaporation of Bi metal. For this structure, we used polystyrene beads ranging from 200 to 750 nm in diameter as an etch mask. The typical hole and neck sizes of the Bi thin films with approximately 50 nm in thickness on SiO₂/Si substrates were in the range of 135 to 490 nm and 65 to 260 nm, respectively. By measuring the thermal characteristics through a 3ω technique, we found that the thermal conductivities of nanoporous Bi thin films are greatly suppressed compared with those of corresponding bulk materials. With a decrease in pore size to approximately 135 nm, the thermal conductivity decreased significantly to approximately 0.46 W/m·K at 300 K.     

Development of a new spindle motor for a hard disk drive

A new spindle motor is developed with a sloped permanent magnet (PM) for a hard disk drive (HDD). In a conventional spindle motor, a pulling plate is installed at the stationary part under the rotating PM to pull down rotating bodies. This axial force is required for stable operation of the spindle motor using a hydrodynamic bearing. However, the pulling plate has considerable iron loss and a negative torque opposing the direction of rotation due to the induced eddy currents. Our proposed model has a sloped PM surface to generate the required axial force as well as torque without the pulling plate. Optimal design is carried out by a response surface methodology, and the new spindle motors are prototyped. The resulting electrical and mechanical performance of the prototyped motors is compared with that of conventional models, showing the possibility of adapting the proposed model for an HDD spindle motor.     

Role of O2/Ar mixing ratio on the performances of IZO thin film transistors fabricated using a two-step deposition process

In this study, a simple method of fabricating a thin-film transistor (TFT) with a double-layered channel using indium–zinc-oxide (IZO) films was proposed. Two IZO films used as channel layers were consecutively deposited via sputtering without stopping the vacuum and only by changing the volumetric fraction of the additive O₂ gas during the deposition. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis showed a large difference in the depth profiles of the InO^? and InO₂^? ions between the two IZO layers. Compared to the conventional single-IZO-channel TFT, the double-IZO-channel TFT that was fabricated using the proposed two-step deposition method showed greatly improved electrical characteristics: the on/off-state current ratio was increased from 1.30 × 10⁵ to 1.03 × 10⁶, and the field effect mobility was enhanced from 1.2 to 9.3 cm²/Vs.     

Effects of additive gases and plasma post-treatment on electrical properties and optical transmittance of ZnO thin films

A zinc oxide (ZnO) thin film as a channel layer in an oxide thin film transistor (TFT) has been characterized by investigating the effects of additive gases (such as hydrogen and oxygen) during growth and plasma treatment (using argon or hydrogen) after growth on its electrical, optical, and structural properties. By decreasing the additive gas ratio of O₂/H₂ or by increasing the treatment time of hydrogen plasma, the electrical resistivities of ZnO films were significantly reduced, and their transmittances and optical bandgap energies were blue-shifted in wavelength. These results were considered to be closely related to the passivation of oxygen vacancies as well as the formation of shallow donors that were induced by the injection of hydrogen in ZnO via gas addition and plasma treatment. In addition, the injection of hydrogen-including additive gas resulted in a decrease in grain size and crystallinity of ZnO films, whereas the plasma treatment hardly affected their crystalline structures.     

Two-phase boosted voltage generator for low-voltage DRAMs

A two-phase boosted voltage (V/sub PP/) generator circuit was proposed for use in gigabit DRAMs. It reduced the maximum gate-oxide voltage of pass transistor and the lower limit of supply voltage to V/sub PP/ and V/sub TN/, respectively, while those for the conventional charge-pump circuit are V/sub PP/+V/sub DD/ and 1.5 V/sub TN/ respectively. Also, the pumping current was increased in the new circuit. The newly proposed two-phase V/sub PP/ charge-pump circuit worked successfully at V/sub DD/ down to 0.8 V by eliminating the threshold voltage loss of the control pulse generator and was tested successfully in a 0.16-/spl mu/m test chip using triple-well CMOS technology.     

Degradation of polystyrene in supercritical n-Hexane

Degradation of polystyrene was carried out in supercritical n-hexane under reaction temperature ranging from 330 °C to 390 °C, pressure ranging from 30 bar to 70 bar and reaction duration of 90 min. The conversion of polystyrene increased with rising temperature and pressure. The degradation performance was influenced by the temperature rather than applied pressure. Polystyrene rapidly degraded in 30 min after reaching a prescribed temperature ranging from 350 °C to 390 °C. At a prescribed temperature of 390 °C, the degree of degradation was higher than 90%. The degradation reaction was examined experimentally at a relatively low temperature of 330 °C. The degradation of polystyrene by using supercritical n-hexane has been found to be more effective compared to general pyrolysis (thermal degradation). Among the selectivity of liquid products, that of a single aromatic ring group like styrene at 390 °C increased up to 65% in 90 min. It was found from the analysis by a gel permeation Chromatograph (GPC), that high molecular-weight compounds decreased but oligomers increased with rising temperature.     

Mathematical modeling for chemical vapor deposition in a single-wafer reactor: Application to low-pressure deposition of Tungsten

A mathematical model for low pressure chemical vapor deposition in a single-wafer reactor in stagnation point flow has been developed to investigate the reactor performance. The transient transport equations for a simulated reactor include continuity, momentum, energy, and gaseous species balances. The model equations are simultaneously solved by using a numerical technique of orthogonal collocation on finite element method. Simulation studies have been performed to gain an understanding of tungsten low pressure chemical vapor deposition process. The model is then used to optimize the deposition rate and uniformity on a wafer, and the effects of operating conditions on deposition rate are studied to examine how system responses are affected by changes in process parameters. Deposition rate and uniformity calculated at the steady state are observed to be very sensitive to both temperature and total pressure. In addition, the model predictions for tungsten deposition from hydrogen reduction of tungsten hexafluoride have been compared with available experimental data in order to demonstrate the validity of the model.