A regularized integral equation method for the inverse geometry heat conduction problem

This paper addresses a new technique for solving the inverse geometry heat conduction problem of the Laplace equation in a two-dimensional rectangle, which, named regularized integral equation method (RIEM), consists of three parts. First of all, the Fourier series expansion technique is used to calculate the temperature field u(x, y). Second, we consider a Lavrentiev regularization by adding a term αg(x) to obtain a second kind Fredholm integral equation. The termwise separable property of the kernel function allows us to transform the inverse geometry heat conduction problem into a two-point boundary value problem and therefore, an analytical regularized solution is derived in the final part by using orthogonality. Principally, the RIEM possesses the following advantages: it does not need any guess of the initial profile, it does not need any iteration and a regularized closed-form solution can be obtained. The uniform convergence and error estimate of the regularized solution u^α(x, y) are proved and a boundary geometry p(x) is solved by half-interval method. Several numerical examples present the effectiveness of our novel approach in providing excellent estimates of unknown boundary shapes from given data.     

What drives stickiness in location-based AR games? An examination of flow and satisfaction

Although location-based augmented reality (AR) games are popular in recent years, the motivates of the game’s stickiness still need further investigation. The main goal of this research is to investigate the antecedents of the game’s stickiness. This research develops a conceptual model and hypotheses based on the theory of flow and satisfaction to investigate the antecedents. An online questionnaire was developed and distributed on popular websites to collect data, and 1028 usable responses are collected from the players of Pokémon Go in Taiwan. The eleven hypotheses and control variables were validated by using structural equation modeling (SEM) techniques. Among the antecedents of the game’s stickiness in the model, the flow and satisfaction were found to have strong direct effects. The effects of control variables (age, gender, platform, game experience, and in-app expense) on the stickiness were significant as well. Moreover, telepresence, challenge, perceived control, curiosity, and concentration all have direct influences on the flow. Only perceived currency and responsiveness were found to have a direct impact on players’ satisfaction. The model demonstrated good explanatory power for flow and stickiness in the context of location-based AR game. The proposed model can provide insights to location-based AR game developers to design their games and marketing strategies.     

A two-dimensional analytical subthreshold behavior model for short-channel AlGaAs/GaAs HFETs

Based on the minimum heteroface potential through an evanescent-mode analysis of two-dimensional potential distribution, the comprehensive and accurate expressions for the short-channel threshold voltage and subthreshold swing for self-aligned gated AlGaAs/GaAs HFETs are developed. It is found that the 2-D electron gas is strongly affected by the DIBL effect which will significantly influence the subthreshold behavior of the AlGaAs/GaAs HFETs. Besides the doping density, the thickness of the spacer and doped body can aggressively affect the short-channel subthreshold behavior comprising threshold voltage shift and subthreshold swing degradation. This model not only gives physical insights into the short-channel effects in HFETs but also offers basic designing guideline for the small-geometry AlGaAs/GaAs HFETs.     

Buckling‐Based Strong Dry Adhesives Via Interlocking

High‐aspect‐ratio shape‐memory polymer (SMP) pillar arrays are investigated as a new type of dry adhesive based on buckling and interlocking mechanism. When two identical SMP pillar arrays are engaged at 80 °C, above the glass transition temperature at a preload larger than the critical buckling threshold, the pillars are deformed and become interweaved and/or indented with each other. After cooling to room temperature, strong pull‐off forces are observed in the normal and shear directions, both of which are much larger than those from pillar‐to‐flat surface and flat‐to‐flat surface contact. From finite element anaylsis (FEA) and comparison of measured and calculated adhesion values using different contact mechanics models, it is shown that interweaved pillars are the main source that contributes to the pillar‐to‐pillar adhesion and the indented pillars set the lower limit, whereas the probability of interdigitation is very low. Further, it is found that interweaved pillars are primarily responsible for the decreased adhesion strength and increased anisotropy when the pillar spacing became larger. Finally, it is shown that the bonded pillars can be easily separated after reheating to 80 °C due to significant drop of modulus of SMPs.     

Analysis and Design of a Chip Filter With Low Insertion Loss and Two Adjustable Transmission Zeros Using 0.18- $mu{hbox{m}}$ CMOS Technology

This paper presents the structure of a high-selectivity bandpass filter that is fabricated on low-resistivity silicon substrate with a commercial CMOS technology. The filter is constructed using crossed coplanar waveguide (CPW) lines and metal–insulator–metal capacitors to ensure that it has the desired passband characteristics. An adjustable capacitor between the input and output ports is employed to form a capacitive cross-coupled path, yielding two transmission zeros in the lower and upper stopbands, respectively. Additionally, the coupling mechanism can be modified by turning on or off the gate of an nMOS transistor to adjust the positions of the transmission zeros by applying an externally controlled voltage. To obtain a low passband loss and to minimize the chip size, high-impedance CPW transmission lines are adopted. Our analysis indicates that the CPW line possesses more advantages than the preferred stacked-ground CPW line for constructing the proposed filter. A very compact $X$ -band experimental prototype with a size of ${hbox{0.88}}times {hbox{0.54}} {hbox{mm}}^{2}$ was designed and fabricated. The measurements reveal an insertion loss of less than 3.2 dB in the passband, which is from 10.6 to 12.7 GHz, and rejection levels greater than 35 dB at the designed frequencies of transmission zeros. Moreover, the lower and upper transmission zeros can be shifted from 5 to 6.5 GHz and from 18 to 21.4 GHz, respectively, by changing the controlled voltage.      

A new compact LTCC bandpass filter using negative coupling

This letter presents the design and realization of a new compact bandpass filter (BPF) fabricated on multilayered ceramic substrates. This BPF features coupled resonators with negative coupling coefficients. A BPF with center frequency 2.45 GHz is designed and fabricated. Its size is only 2.0 mm/spl times/1.8 mm/spl times/0.67 mm when implemented by a standard low temperature co-fired ceramic technology. The size reduction is due to the higher coupling coefficient between the negatively-coupled resonators than the positively-coupled ones, allowing tighter space between the resonators. The measured insertion losses of the previous BPF were less than 3dB and return losses more than 18dB in the passband. The measured result agrees very well with the electromagnetic (EM) designed response.     

Broadband Multiport Dynamic Optical Power Distributor Based on Thermooptic Polymer Waveguide Vertical Couplers

We propose a broadband multiport dynamic optical power distributor, which consists of a series of asymmetric vertical optical waveguide directional couplers with thermooptically tunable splitting ratios. To demonstrate the idea experimentally, we fabricated a five-port optical power distributor with four polymer waveguide vertical couplers. The fabricated device is 9 mm long and allows a practically arbitrary optical power distribution to be achieved with a maximum electric power consumption less than 50 mW in any of the couplers and a response time of ~1 ms. The device operates effectively in the whole C-band without significant variations in performance.     

Scanning electron microscopy study of the cross section of intermetallic compound in the solder ball on the plastic ball grid array package following reliability tests

The 63Sn-37Pb solder ball (φ=300 μm) was attached to gold-nickel-plated plastic ball grid array (PBGA) substrates, with gold and nickel thicknesses of 0.6 μm and 7 μm, respectively. The thickness of the intermetallic compound (IMC) in solder balls was measured following each instance of infrared (IR) reflow (90 sec at 230 °C), level II preconditioning, a pressure cooking test (for 96 h or 168 h), and a temperature cycle test (with 500 or 1,000 cycles). Scanning electron microscopy (SEM) was used to identify the cross-section sites of the solder balls following testing. Following all the reliability tests, the IMC demonstrated that an IMC thickness exceeding 5 μm will reduce the solder ball shear strength owing to diffusion of Ni into the solder balls.     

Purification and Characterization of a Thermostable alpha-Amylase from Bacillus licheniformis

The heat stability of a bacterial α-amylase is important for industrial starch utilization. Although extensive studies have been done on heat stable α-amylase from various bacterial species little is known about the α-amylases of Bacillus licheniformis. In order to get better understanding of thermostable amylases produced by different strains of B. licheniformis and provide information how to utilize the enzyme in starch processing, studies on purification and characterization of a commercial heat stable bacterial α-amylase from B. licheniformis BLM 1777 are reported.     

The effect of surface modified polytetrafluoroethylene on polyacetal/polytetrafluoroethylene blends

Five kinds of blends: polyacetal (POM) and polytetrafluoroethylenes (PTFEs) [pure (PTFE), coupling agent coated (LZ-PTFE), chemical-treated (CPTFE, containing NaF salt), chemical-treated (WPTFE, no NaF salt), coupling agent coated WPTFE(LZ-WPTFE)] were prepared by mechanical blending. The PTFE presented in the blends, had good wear resistance properties. However, the adhesion interaction between the POM and the PTFE was poor, and increasing the PTFE content caused a decrease in the mechanical properties. Using the chemical surface treatment method to etch PTFE could cause treated-PTFE to homogeneously disperse in POM. This result caused the POM/treated-PTFE blends to have higher mechanical properties than those of the POM/PTFE blends. The NaF salt that adsorbed on the CPTFE surface acted as a coupling agent and offered a very strong adhesion interaction between the POM and the CPTFE. The free salt also acted as a nuclei to aid POM in crystallizing. As a result, the POM/CPTFE blends possessed the highest mechanical properties of all the blends and the best wear resistance property of POM/modified-PTFE(LZ-PTFE, LZ-WPTFE, WPTFE, CPTFE) blends. © 1993 John Wiley & Sons, Inc.