Numerical analysis of the warpage problem in TSOP

The reliability and the solderability of thin small outline package (TSOP) are significantly affected by the warpage that is generated after epoxy molding compound (EMC) molding process. This warpage problem mainly results from the mismatch of material properties such as Young's modulus, Poisson's ratio and coefficient of thermal expansion (CTE) and the geometric structure of each component for TSOP. The optimization of both material properties and geometric structures using the numerical analysis is necessary to reduce the warpage of TSOP. However, there are still some limitations for the numerical analysis to obtain proper results consistent with the practical warpage values. In this paper, the numerical analysis is performed under the assumption of elastic behavior for EMC. Furthermore, to solve the limitations, the material properties at the molding temperature and the degree of reaction rate at the end of the molding process of EMC are considered together for the analysis. This numerical analysis gives the higher warpage values than the measured ones, and is applicable to the practical design of the reliable electronic package.     

An Autophagy-Disrupting Small Molecule Promotes Cancer Cell Death via Caspase Activation

A novel autophagy inhibitor, autophazole (Atz), which promoted cancer cell death via caspase activation, is described. This compound was identified from cell-based high-content screening of an imidazole library. The results showed that Atz was internalized into lysosomes of cells where it induced lysosomal membrane permeabilization (LMP). This process generated nonfunctional autolysosomes, thereby inhibiting autophagy. In addition, Atz was found to promote LMP-mediated apoptosis. Specifically, LMP induced by Atz caused release of cathepsins from lysosomes into the cytosol. Cathepsins in the cytosol cleaved Bid to generate tBid, which subsequently activated Bax to induce mitochondrial outer membrane permeabilization (MOMP). This event led to cancer cell death via caspase activation. Overall, the findings suggest that Atz will serve as a new chemical probe in efforts aimed at gaining a better understanding of the autophagic process.     

Real-Time Global Illumination for VR Applications

Real-time global illumination in VR systems enhances scene realism by incorporating soft shadows, reflections of objects in the scene, and color bleeding. The Virtual Light Field (VLF) method enables real-time global illumination rendering in VR. The VLF has been integrated with the Extreme VR system for real-time GPU-based rendering in a Cave Automatic Virtual Environment.     

Performance characterization of a small-capacity thermoacoustic cooler for air-conditioning applications

The performance of a working prototype, operated with and without water flow through the heat exchangers, was measured and found to be in reasonably close agreement to predictions from a simulation code, DELTAE, based on linear thermoacoustic theory. Further analysis and DELTAE simulations showed that the coefficient of performance may be significantly reduced when the stack temperature profile becomes non-linear, i.e. when the system is operated for a temperature span smaller than the optimal value for a given stack length. Guidelines to avoid this condition are provided.     

Analysis of the reservoir effect on electromigration reliability

The reservoir effect on electromigration reliability is analyzed using the normalized vacancy concentration distribution in the reservoir region of multi-level Al–0.5%Cu interconnect structure. With the assumption of steady state for the vacancy concentration and the fact that no current flow conducts in the reservoir region during electromigration test, a simple equation for calculation of the vacancy concentration is induced. Then direct calculation of the equation is carried out utilizing the hydrostatic stress distribution computed from finite element method to estimate the probability of initial void formation in the reservoir region. Finally, three multi-level Al–0.5%Cu interconnect structures with different reservoir lengths are constructed and electromigration lifetime for the structures is measured to clarify these computational results. From the results of this study, we conclude that the normalized vacancy concentration under the assumption of steady state can be regarded as a quantitative parameter to analyze the reservoir effect on electromigration reliability.     

Higher order eigenfields in mode II cracks under elastic-plastic deformation

The explicit formulation of theJ-integral and theM-integral is constructed in terms of the stress intensity factor and the higher order stress coefficients for Mode II cracks under small or large scale yielding. Furthermore, the stress intensity factor and the higher order stress coefficients as well are computed with the aid of the two-stateJ- and theM - integral, which is found to be accurate and efficient. It is found that the contribution from the higher order singularities to theJ - integral is closely related to the configuration of the plastic zone.     

Virus‐Templated Self‐Mineralization of Ligand‐Free Colloidal Palladium Nanostructures for High Surface Activity and Stability

In solution‐based synthesis of colloidal nanostructures, additions of ligands, stabilizers, and redox reagents are generally required to obtain desirable structures, though ligands and stabilizers on the surface of nanostructures can substantially affect the surface‐related activity. Accordingly, an extensive rinsing process is usually required to remove residual reagents and stabilizers. This study reports a spontaneous self‐biomineralization of palladium (Pd) ions on a filamentous virus to form ligand‐free Pd nanowires under ambient conditions. No reducing reagents or additional surface stabilizers are used; the genetically modified virus alone supports the polycrystalline Pd nanowires within the nanostructure, maintaining the clean surface even without a rinsing process. The advantage of the ligand‐free Pd nanowires is found in the Suzuki‐coupling reaction, in which the nanowire catalytic activity is maintained after repeated reactions, while conventional Pd colloids undergo surface contamination by the stabilizer and lose their catalytic activity during repeated uses. The ligand‐free surface, high electronic connectivity, and structural stability of the Pd nanowires also allow high sensitivity and selectivity in hydrogen gas sensing analysis. This work emphasizes the importance of the ligand‐free surface of biotemplated nanostructures in maintaining functionalities without surface contamination.     

Expanding an existing multiple choice test with a mixed format test: simulation study on sample size and item recovery in concurrent calibration

When a new set of mixed format items is augmented with a previous old multiple-choice (MC) test, those mixed format items should be linked to the existing old MC test. This study used simulation to investigate sample size effect on recovery of known item parameter from the concurrent calibration in the context of horizontal equating, where the new mixed format tests are equated to the existing MC test which acts as the common linking items. In the partial credit model following the Andrich style parameterization, item location and item step parameters were differentially affected by the sample size. Item location parameters were recovered better than item step parameters at the individual item, the sub-test, and the total test level. This study also shows the outward bias for the item location parameter estimated by the maximum likelihood estimator.     

Amyloid Formation in Nanoliter Droplets

Processes that monitor the nucleation of amyloids and characterize the formation of amyloid fibrils are vital to medicine and pharmacology. In this study, we observe the nucleation and formation of lysozyme amyloid fibrils using a facile microfluidic system to generate nanoliter droplets that can control the flow rate and movement of monomer-in-oil emulsion droplets in a T-junction microchannel. Using a fluorescence assay, we monitor the nucleation and growth process of amyloids based on the volume of droplets. Using the microfluidic system, we demonstrate that the lag phase, which is vital to amyloid nucleation and growth, is reduced at a lower droplet volume. Furthermore, we report a peculiar phenomenon of high amyloid formation at the edge of a bullet-shaped droplet, which is likely due to the high local monomer concentration. Moreover, we discovered that amyloid fibrils synthesized in the nanoliter droplets are shorter and thicker than fibrils synthesized from a bulk solution via the conventional heating method. Herein, a facile procedure to observe and characterize the nucleation and growth of amyloid fibrils using nanoliter droplets is presented, which is beneficial for investigating new features of amyloid fibril formation as an unconventional synthetic method for amyloid fibrils.     

Highly Efficient Nonvolatile Magnetization Switching and Multi-Level States by Current in Single Van der Waals Topological Ferromagnet Fe3GeTe2

Robust multi-level spin memory with the ability to write information electrically is a long-sought capability in spintronics, with great promise for applications. Here, nonvolatile and highly energy-efficient magnetization switching is achieved in a single-material device formed of van-der-Waals (vdW) topological ferromagnet Fe₃GeTe₂, whose magnetic information can be readily controlled by a tiny current. Furthermore, the switching current density and power dissipation are about 400 and 4000 times smaller than those of the existing spin-orbit-torque magnetic random access memory based on conventional magnet/heavy-metal systems. Most importantly, multi-level states, switched by electrical current are also demonstrated, which can dramatically enhance the information capacity density and reduce computing costs. Thus, the observations combine both high energy efficiency and large information capacity density in one device, showcasing the potential applications of the emerging field of vdW magnets in the field of spin memory and spintronics.