Theoretical and measured characteristics of metal(CoSi2)-insulator(CaF2) resonant tunnelingtransistors and the influence of parasitic elements

We report on the theoretical and measured characteristics of triple-barrier metal (CoSi₂)-insulator(CaF₂) (M-I) resonant tunneling transistors (RTT) grown on an n-Si(111) substrate, and the influence of their parasitic elements on the measured characteristics. First, we analyze theoretical characteristics of an M-I RTT, and then show fabrication process and current-voltage (I-V) characteristics obtained at 77 K, in which several degradations are observed: large resonance voltage, low peak-to-valley (P-V) ratios at negative differential resistance (NDR), and reverse base current. Analysis, taking several parasitic elements (e.g., base resistance, substrate resistance and leakage currents connected to the intrinsic transistor) into account, explains observed characteristics well. Finally, we show the first transistor action with large P-V ratios at 300 K, which is achieved by reducing collector-emitter leakage currents     

Hydroxyapatite crystal growth on calcium hydroxyapatite ceramics

Calcium hydroxyapatite (Ca-HAP) ceramics containing tricalcium phosphate (TCP) were soaked in three solutions: phosphate buffer, tris buffer, and simulated body fluid (SBF). Petal-like crystals of Ca-HAP were deposited on the Ca-HAP ceramics when (i) Ca-HAP ceramics contained -TCP, (ii) the soaking solution contained phosphate ion and (iii) the pH of soaking solution was higher than 7.3. These conditions facilitate the presence of HPO ₄ ^2– and Ca²⁺ ions, the latter from dissolution of -TCP. A well-defined X-ray diffraction pattern for the deposited Ca-HAP crystals indicates preferred growth of {002} planes. Slower crystal growth of Ca-HAP was found for SBF (pH=7.5) than in the phosphate buffer, due possibly to the lower phosphate ion content in SBF.     

Mathematical analysis of oxygen transfer through polydimethylsiloxane membrane between double layers of cell culture channel and gas chamber in microfluidic oxygenator

For successful cell culture in microfluidic devices, precise control of the microenvironment, including gas transfer between the cells and the surrounding medium, is exceptionally important. The work is motivated by a polydimethylsiloxane (PDMS) microfluidic oxygenator chip for mammalian cell culture suggesting that the speed of the oxygen transfer may vary depending on the thickness of a PDMS membrane or the height of a fluid channel. In this paper, a model is presented to describe the oxygen transfer dynamics in the PDMS microfluidic oxygenator chip for mammalian cell culture. Theoretical studies were carried out to evaluate the oxygen profile within the multilayer device, consisting of a gas reservoir, a PDMS membrane, a fluid channel containing growth media, and a cell culture layer. The corresponding semi-analytical solution was derived to evaluate dissolved oxygen concentration within the heterogeneous materials, and was found to be in good agreement with the numerical solution. In addition, a separate analytical solution was obtained to investigate the oxygen pressure drop (OPD) along the cell layer due to oxygen uptake of cells, with experimental validation of the OPD model carried out using human umbilical vein endothelial cells cultured in a PDMS microfluidic oxygenator. Within the theoretical framework, the effects of several microfluidic oxygenator design parameters were studied, including cell type and critical device dimensions.     

Optical element converting linear polarization into circular-tangential polarization

A new optical element capable of converting linear polarization into circular-tangential polarization (i.e., the electric vector is along the tangential direction to a circle) is proposed and demonstrated. The conversion characteristics of the fabricated element are evaluated, and the magnitude of aberration produced by the element is shown to be insignificant.     

Fabrication of a concentric-circular focusing grating coupler by a conic-wave-front interference method and light-convergence experiments using the coupler

An interference method utilizing conic-wave-front light for the fabrication of a concentric-circular and chirped grating is proposed. The design method and fabrication of an interference lens that generates conic-wave-front light are also shown. A focusing element is constructed from a concentric-circular grating coupler with a 0.4-mm diameter and a concentric-circular focusing grating coupler with an annular aperture of 2-mm focal length and 2.0-4.0-mm diameter. Light-convergence experiments using the focusing element were able to obtain a focusing spot of 0.5 μm × 0.7 μm at half-intensity widths for a wavelength of 820 nm in combination with liquid-crystal polarization elements.     

Dynamic Power Integrity Control of ATE for Eliminating Overkills and Underkills in Device Testing

This paper proposes a power integrity control technique for dynamically controlling power supply voltage fluctuations for a device under test (DUT), and demonstrates its effectiveness for eliminating the overkills/underkills due to the difference of power supply impedance between an automatic test equipment (ATE) and a practical operating environment of the DUT. The proposed method injects compensation currents into the power supply nodes on the ATE system in a feed-forward manner such that the ATE power supply waveform matches with the one on the customer’s operating environment of the DUT. A method for calculating the compensation current is also described. Experimental results show that the proposed method can emulate the power supply voltage waveform under a customer’s operating condition and eliminate 95 % of overkills/underkills in the maximum operating frequency testing with 105 real silicon devices. Limitations and applications of the proposed method are also discussed.     

Space–time interface-tracking with topology change (ST-TC)

To address the computational challenges associated with contact between moving interfaces, such as those in cardiovascular fluid–structure interaction (FSI), parachute FSI, and flapping-wing aerodynamics, we introduce a space–time (ST) interface-tracking method that can deal with topology change (TC). In cardiovascular FSI, our primary target is heart valves. The method is a new version of the deforming-spatial-domain/stabilized space–time (DSD/SST) method, and we call it ST-TC. It includes a master–slave system that maintains the connectivity of the “parent” mesh when there is contact between the moving interfaces. It is an efficient, practical alternative to using unstructured ST meshes, but without giving up on the accurate representation of the interface or consistent representation of the interface motion. We explain the method with conceptual examples and present 2D test computations with models representative of the classes of problems we are targeting.     

Neuroelectric Mechanisms of Delayed Cerebral Ischemia after Aneurysmal Subarachnoid Hemorrhage

Delayed cerebral ischemia (DCI) remains a challenging but very important condition, because DCI is preventable and treatable for improving functional outcomes after aneurysmal subarachnoid hemorrhage (SAH). The pathologies underlying DCI are multifactorial. Classical approaches to DCI focus exclusively on preventing and treating the reduction of blood flow supply. However, recently, glutamate-mediated neuroelectric disruptions, such as excitotoxicity, cortical spreading depolarization and seizures, and epileptiform discharges, have been reported to occur in high frequencies in association with DCI development after SAH. Each of the neuroelectric disruptions can trigger the other, which augments metabolic demand. If increased metabolic demand exceeds the impaired blood supply, the mismatch leads to relative ischemia, resulting in DCI. The neuroelectric disruption also induces inverted vasoconstrictive neurovascular coupling in compromised brain tissues after SAH, causing DCI. Although glutamates and the receptors may play central roles in the development of excitotoxicity, cortical spreading ischemia and epileptic activity-related events, more studies are needed to clarify the pathophysiology and to develop novel therapeutic strategies for preventing or treating neuroelectric disruption-related DCI after SAH. This article reviews the recent advancement in research on neuroelectric disruption after SAH.     

Structure and properties of biaxially stretched poly(ethylene terephthalate) sheets

Huge numbers of PET (poly[ethylene terephthalate]) bottles are produced in the world. Especially in Japan, the number of hot-fillable PET bottles used is extremely large and is still increasing. This type of bottle is generally manufactured by the heat-set method using hot molds after stretch-blow molding. Herein, we examined how the PET sheet stretching condition affects the PET heat-shrinkage behavior at 85°C, which is the hot-filling temperature. Sheets stretched at a higher temperature and higher speed had higher thermal stability for a wider range of draw ratios. This is because those sheets have a higher crystallinity and relaxed amorphous regions. The higher stretch speed gives the sheet a higher crystallinity with self heat generation during rapid deformation. A higher stretch temperature makes the molecular segments relaxed.     

Entrapment of Rhodobacter sphaeroides RV in cationic polymer/agar gels for hydrogen production in the presence of NH4+

Cationic polyelectrolytes (chitosan, poly-L-lysine (PLL), polyethyleneimine (PEI) and trimethylammonium glycol chitosan iodide (TGCI)) were used to entrap anoxygenic phototrophic bacteria in order to prevent the inhibitory effect of NH4+ on hydrogen production. When combined with agar gel, chitosan and PLL demonstrated no obvious repressive effect on hydrogen production by Rhodobacter sphaeroides under light-anaerobic conditions with lactate and glutamate as the carbon and nitrogen sources, respectively. On the other hand, both PEI and TGCI exerted a detrimental effect on hydrogen production under these conditions. Hydrogen production in the presence of NH4+ by the bacteria entrapped in the complex gel containing chitosan and agar improved considerably compared to that in the control containing only agar. Evidence shows that chitosan improves the hydrogen production via various effects. Diffusion tests demonstrated that the addition of chitosan increased to some extent the resistance to the diffusion of positively charged NH4+, but had no effect on negatively charged lactate. A buffer effect in the complex gels was also revealed.