Surface Chemistry of Vitamin: Pyridoxal 5′‐Phosphate (Vitamin B6) as a Multifunctional Compound for Surface Functionalization

Vitamins are non‐toxic compounds that perform a variety of biological functions and also available in a large quantity. Other than the usage as food supplements, few attempts have been made to use them as functional materials. In this study, we report that vitamin B6, pyridoxal 5′‐phosphate (PLP), is a multi‐functional molecule for oxide surface chemistry. PLP‐immobilized surfaces exhibit superhydrophilicity and even hemophilicity, enhancing proliferation, migration, and differentiation of mammalian cells. Unlike existing molecules used so far in surface modification, PLP has an intrinsic chemical reactivity toward biomacromolecules due to the presence of the aldehyde group. In fact, RGD peptide is covalently tethered onto PLP surfaces directly in one step without any chemical activation. Furthermore, PLP‐functionalized implant device showed rapid bone healing. As vitamin B6 is a FDA approved molecule for human usage, the surface chemistry of vitamin B6 potentially allows a fast route for surface functionalized medical devices into clinic.     

Parallel optical transmitter module using angled fibers and a V-grooved silicon optical bench for VCSEL array

We propose an advanced structure of optical subassembly (OSA) for packaging of the vertical-cavity surface-emitting laser (VCSEL) array, using (111) facet mirror of the V-groove ends formed in a silicon optical bench (SiOB) and angled fiber apertures. The feature of our OSA can provide a low optical crosstalk between neighboring channels, a low feedback reflection, and a large misalignment tolerance along the V-groove. We describe the optimized design of fiber angle, VCSEL position, and fiber position. The fabricated OSA structure consists of 12 channels of angled fiber array, 54.7/spl deg/ V-grooves, Au-coated mirrors on (111) end facet of the V-grooves, and flip-chip-bonded VCSEL array on a SiOB. In this structure, the beam emitted from the VCSEL is deflected at the 54.7/spl deg/ mirror of (111) end facet and propagated into the angled fiber. The angled fiber array was polished by 57/spl deg/. Fabricated OSAs showed a coupling efficiency of 30%-50% that is 25 times larger than that obtained from an OSA with a vertically flat fiber array. Our OSA showed large misalignment tolerance of about 90 /spl mu/m along the longitudinal direction in the V-groove. We fabricated a parallel optical transmitter module using the OSA and demonstrated 12 channels /spl times/2.5 Gb/s data transmission with a clear eye diagram.     

Efficient methods for modelling substrate coupling in mixed-signalintegrated circuits

A key problem in the design of large mixed-signal circuits is the noise caused by the coupling of digital signals into the substrate. This paper describes methods that allow circuit designers to model efficiently such substrate noise in large mixed-signal SPICE designs. In the light of these techniques a new methodology is presented for efficiently modelling the substrate noise caused by current injection and its coupling to analogue signals; this is then extended to provide a real-time modelling capability. The practicality and the numerical efficiency of the methods are demonstrated on several prototype example circuits     

Highly Stretchable and Sensitive Strain Sensors Using Fragmentized Graphene Foam

Stretchable electronics have recently been extensively investigated for the development of highly advanced human‐interactive devices. Here, a highly stretchable and sensitive strain sensor is fabricated based on the composite of fragmentized graphene foam (FGF) and polydimethylsiloxane (PDMS). A graphene foam (GF) is disintegrated into 200–300 μm sized fragments while maintaining its 3D structure by using a vortex mixer, forming a percolation network of the FGFs. The strain sensor shows high sensitivity with a gauge factor of 15 to 29, which is much higher compared to the GF/PDMS strain sensor with a gauge factor of 2.2. It is attributed to the great change in the contact resistance between FGFs over the large contact area, when stretched. In addition to the high sensitivity, the FGF/PDMS strain sensor exhibits high stretchability over 70% and high durability over 10 000 stretching‐releasing cycles. When the sensor is attached to the human body, it functions as a health‐monitoring device by detecting various human motions such as the bending of elbows and fingers in addition to the pulse of radial artery. Finally, by using the FGF, PDMS, and μ‐LEDs, a stretchable touch sensor array is fabricated, thus demonstrating its potential application as an artificial skin.     

An optimal checkpointing-strategy for real-time control systemsunder transient faults

Real-time computer systems are often used in harsh environments, such as aerospace, and in industry. Such systems are subject to many transient faults while in operation. Checkpointing enables a reduction in the recovery time from a transient fault by saving intermediate states of a task in a reliable storage facility, and then, on detection of a fault, restoring from a previously stored state. The interval between checkpoints affects the execution time of the task. Whereas inserting more checkpoints and reducing the interval between them reduces the reprocessing time after faults, checkpoints have associated execution costs, and inserting extra checkpoints increases the overall task execution time. Thus, a trade-off between the reprocessing time and the checkpointing overhead leads to an optimal checkpoint placement strategy that optimizes certain performance measures. Real-time control systems are characterized by a timely, and correct, execution of iterative tasks within deadlines. The reliability is the probability that a system functions according to its specification over a period of time. This paper reports on the reliability of a checkpointed real-time control system, where any errors are detected at the checkpointing time. The reliability is used as a performance measure to find the optimal checkpointing strategy. For a single-task control system, the reliability equation over a mission time is derived using the Markov model. Detecting errors at the checkpointing time makes reliability jitter with the number of checkpoints. This forces the need to apply other search algorithms to find the optimal number of checkpoints. By considering the properties of the reliability jittering, a simple algorithm is provided to find the optimal checkpoints effectively. Finally, the reliability model is extended to include multiple tasks by a task allocation algorithm     

Luminescence,charge mobility,and optical waveguiding of two-dimensional organic rubrene nanosheets: Comparison with one-dimensional nanorods

Intrinsic characteristics of organic and inorganic nanostructures depend on their physical dimensions (i.e., size and shape) and crystallinity. Here, we compared the nanoscale optical and electrical properties of organic rubrene one-dimensional (1-D) nanorods (NRs) and two-dimensional (2-D) nanosheets (NSs). From high-resolution laser confocal microscope photoluminescence (PL) measurements, the light-emission characteristics of 2-D rubrene NSs varied with the crystalline domain direction, indicating intrinsic PL anisotropy, which was distinguishable from 1-D rubrene single NRs, because of anisotropy π–π stacking molecular arrangements. We also observed the variation of charge carrier mobility depending on the measured directions (i.e., anisotropy of charge transport) in rubrene NS-based field-effect transistors. The optical waveguiding properties of rubrene nanostructures were strongly correlated to the dimensionality of materials and PL anisotropy.     

Anodized Aluminum Oxide/Polydimethylsiloxane Hybrid Mold for Roll‐to‐Roll Nanoimprinting

Two types (hard and soft) of the molds are widely used in nanoimprint lithography for a high throughput over a large area, and high‐resolution parallel patterning. Although hard molds have proven excellent resolutions and can be used at high temperatures, cracks often occur in the mold in addition to the requirement of high imprinting pressure. On the other hand, though soft molds can operate at lower pressures, they give poor pattern resolution. Here, a novel hybrid mold of anodized aluminum oxide (AAO) template attached to a flexible polydimethylsiloxane (PDMS) plate is introduced. Due to the flexible nature of PDMS, various polymer nanostructures are obtained on flat and curved substrates without crack formation on the AAO mold surface. Furthermore, the hybrid mold is successfully used for roll‐to‐roll imprinting for the fabrication of high density array of various shaped polymeric nanostructures over a large area.     

Code scaling

The order of an electromagnetics algorithm or code is defined by the rate at which the CPU time, and memory requirements C_CPU=O(f^α) and C_m=O(f^β ), respectively-grow with frequency. Knowledge of this information helps in the prediction of computer-run times and memory requirements for problems of interest. This paper presents a methodology for determining the computational and memory orders of a code. These results are presented for a finite-volume time-domain (FVTD) code and for a method-of-moments (MoM) code. Computer-resource requirements are plotted for computer runs that calculate the bistatic radar cross section (RCS) for spheres of different electrical sizes, within a set error level from the Mie-series solution. These plots are used to calculate the computational and memory orders of the codes     

Designing a Stable Cathode with Multiple Layers to Improve the Operational Lifetime of Polymer Light‐Emitting Diodes

The short device lifetime of blue polymer light‐emitting diodes (PLEDs) is still a bottleneck for commercialization of self‐emissive full‐color displays. Since the cathode in the device has a dominant influence on the device lifetime, a systematic design of the cathode structure is necessary. The operational lifetime of blue PLEDs can be greatly improved by introducing a three‐layer (BaF₂/Ca/Al) cathode compared with conventional two‐layer cathodes (BaF₂/Al and Ba/Al). Therefore, the roles of the BaF₂ and Ca layers in terms of electron injection, luminous efficiency, and device lifetime are here investigated. For efficient electron injection, the BaF₂ layer should be deposited to the thickness of at least one monolayer (～3 nm). However, it is found that the device lifetime does not show a strong relation with the electron injection or luminous efficiency. In order to prolong the device lifetime, sufficient reaction between BaF₂ and the overlying Ca layer should take place during the deposition where the thickness of each layer is around that of a monolayer.