A Robust and Cooperative MAC Protocol for IEEE 802.11a Wireless Networks

In wireless networks, it is well known that the interference of hidden nodes can interrupt frame receptions. Although several solutions have been proposed to alleviate the problem of DATA corruptions at receivers, control frame corruptions at transmitters have not been considered yet. In this paper, we propose an enhanced MAC protocol, called Robust and Cooperative Medium Access Control (RCMAC), to improve the network throughput and fairness by reducing control frame losses at transmitters. RCMAC uses a relay mechanism to allow transmitters of long distance links to receive control frames more robustly by relaying control frames via relay nodes. Furthermore, RCMAC improves the network throughput through fast two-hop DATA transmissions via relay nodes. Our extensive simulation results show that RCMAC has better performance than existing well-known MAC protocols.     

Enhanced efficiency of organic light emitting devices (OLEDs) by control of laser imaging condition

Laser Induced Thermal Imaging (LITI) is a laser addressed thermal patterning technology with unique advantages such as excellent uniformity of transfer film thickness, capability of multilayer stack transfer, high resolution and scalability to large-size mother glass. However, the deterioration of the device performance during imaging process has been an obstacle to use it as a commercial technology. To investigate a possibility of thermal deformation of organic materials as a transfer layer and a receptor layer during imaging process, we executed a preliminary annealing test by using standard green devices at various temperatures. By comparison of these results with those obtained from LITI devices, we found that the main reason of device deterioration could be originated from the mobility change of the organic layers. Hence, we developed the dwell time control technology to suppress the thermal impact during LITI process and we finally obtained current efficiency which is quite equivalent to that obtained from the standard evaporation devices.     

High current conduction with high mobility by non-radiative charge recombination interfaces in organic semiconductor devices

We report a unique non-radiative p-n-p junction structure to provide high current conduction with high mobility in organic semiconductor devices. The current conduction was improved by increasing p-n junctions made with intrinsic p-type hole transport layer and n-type electron transport layer. The excellent hole mobility of 5.3 × 10^?1 cm²/V s in this p-n-p device configuration is measured by the space charge limited current method with an electric field of 0.3 MV/cm. Enhanced current conduction of 248% at 4.0 V was observed in fluorescent blue organic light-emitting diodes with introduction of non-radiative p-n-p-n-p junction interfaces. Thereupon, the power efficiency at 1000 cd/m² was improved by 22% and the driving voltage also was reduced by 17%, compared to that of no interface device. Such high current conduction with high mobility is attributed to the carrier recombination at p-n-p interfaces through coulombic interaction. This non-radiative p-n-p junction structure suggested in this report can be very useful for many practical organic semiconductor device applications.     

Highly Crystalline Soluble Acene Crystal Arrays for Organic Transistors: Mechanism of Crystal Growth During Dip‐Coating

The preparation of uniform large‐area highly crystalline organic semiconductor thin films that show outstanding carrier mobilities remains a challenge in the field of organic electronics, including organic field‐effect transistors. Quantitative control over the drying speed during dip‐coating permits optimization of the organic semiconductor film formation, although the kinetics of crystallization at the air–solution–substrate contact line are still not well understood. Here, we report the facile one‐step growth of self‐aligning, highly crystalline soluble acene crystal arrays that exhibit excellent field‐effect mobilities (up to 1.5 cm V^?1 s^?1) via an optimized dip‐coating process. We discover that optimized acene crystals grew at a particular substrate lifting‐rate in the presence of low boiling point solvents, such as dichloromethane (b.p. of 40.0 °C) or chloroform (b.p. of 60.4 °C). Variable‐temperature dip‐coating experiments using various solvents and lift rates are performed to elucidate the crystallization behavior. This bottom‐up study of soluble acene crystal growth during dip‐coating provides conditions under which one may obtain uniform organic semiconductor crystal arrays with high crystallinity and mobilities over large substrate areas, regardless of the substrate geometry (wafer substrates or cylinder‐shaped substrates).     

Enhanced efficiency of organic photovoltaic cells with Sr2SiO4:Eu2+ and SrGa2S4:Eu2+ phosphors

We report the effect of yellow Sr₂SiO₄:Eu²⁺ and green SrGa₂S₄:Eu²⁺ phosphors on the efficiency of organic photovoltaic (OPV) cells. Each phosphor was coated on the back side of indium tin oxide (ITO)/glass substrates by spin coating with poly(methyl methacrylate) (PMMA). The maximum absorption wavelength of the active layer in the OPV cells was ～512 nm. The emission peaks of Sr₂SiO₄:Eu²⁺ and SrGa₂S₄:Eu²⁺ were maximized at 552 nm and 534 nm, respectively. The short circuit current density (J_sc) and power conversion efficiency (PCE) of the OPV cells with Sr₂SiO₄:Eu²⁺ (8.55 mA/cm² and 3.25%) and with SrGa₂S₄:Eu²⁺ (9.29 mA/cm² and 3.3%) were higher than those of the control device without phosphor (7.605 mA/cm² and 3.04%). We concluded that phosphor tuned the wavelength of the incident light to the absorption wavelength of the active layer, thus increasing the J_sc and PCE of the OPV cells.     

Comparison of noise power spectrum methodologies in measurements by using megavoltage X-ray energies

The noise power spectrum (NPS) is one of the most general methods for measuring the noise amplitude and the quality of an image acquired from a uniform radiation field. The purpose of this study was to compare different NPS methodologies by using megavoltage X-ray energies. The NPS evaluation methods in diagnostic radiation were applied to therapy using the International Electrotechnical Commission standard (IEC 62220-1). In order to measure the region of interest (ROI) of the NPS, we used the following five factors: the overlapping impact, the non-overlapping impact, the penumbra, the flatness and different ROI sizes. We used NPS from four different types of detectors, the CR-IP (computed radiography image plate: photo-stimulable phosphor screen), the CR-IP-lead (hexalon lead screen), the CR-IP-back [lanex TM fast back screen: {terbium-doped gadolinium oxysulfide granular phosphor screen (Gd₂O₂S:Tb,133 mg/cm²)} + 1-mm-thick copper plate and the CR-IP-front (lanex TM fast front screen). A Kodak 2000 RT photo-stimulable phosphor-based computed radiographic (CR) system showed that the normalized noise power spectrum (NNPS) curve gradually decreased, in compliance with increasing spatial resolution. In addition, each detector showed a different reactivity of the NPS to megavoltage. The results of multivariate analysis of variance (MANOVA) test (methods × detectors) revealed significant main effects of the methods [F(1, 4) = 53.543, P = 0.001 and of the detectors [F(1, 4) = 17.556, P = 0.001]. The present study revealed that various factors could be employed to produce megavoltage imaging (MVI) of the NPS and as a baseline standard for NPS control in MVI.

     

Design of polydiacetylene-phospholipid supramolecules for enhanced stability and sensitivity

We present polydiacetylene (PDA) liposome assemblies with various phospholipids that have different headgroup charges and phase transition temperatures (T(m)). 10,12-Pentacosadiynoic acid (PCDA)-epoxy was used as a base PDA monomer and the insertion of highly charged phospholipids resulted in notable changes in the size of liposome and reduction of the aggregation of PDA liposome. Among the various phospholipids, the phospholipid with a moderate T(m) demonstrated enhanced stability and sensitivity, as measured by the size and zeta potential over storage time, thermochoromic response, and transmission electron microscopy images. By combining these results, we were able to detect immunologically an antibody of bovine viral diarrhea virus over a wide dynamic range of 0.001 to 100 μg/mL.     

Real hypersurfaces in complex two-plane Grassmannians with certain commuting condition

In this paper, first we introduce a new notion of commuting condition that φφ ₁ A = A φ ₁ φ between the shape operator A and the structure tensors φ and φ ₁ for real hypersurfaces in G ₂(? ^m+2). Suprisingly, real hypersurfaces of type (A), that is, a tube over a totally geodesic G ₂(? ^m+1) in complex two plane Grassmannians G ₂(? ^m+2) satisfy this commuting condition. Next we consider a complete classification of Hopf hypersurfaces in G ₂(? ^m+2) satisfying the commuting condition. Finally we get a characterization of Type (A) in terms of such commuting condition φφ ₁ A = A φ ₁ φ.     

Achiral auxiliary-assisted chiral transfer via microwave-accelerated aza-Claisen rearrangement: a short synthesis of (+)-1-hydroxyquinolizidinone

A short and efficient synthesis of (+)-1-hydroxyquinolizidinone as an advanced core intermediate for the syntheses of (+)-epiquinamide, (+)-homopumiliotoxin, and (+)-lupinine is described. The key feature of our strategy includes a sequential chiral transfer using an achiral phenylsulfide auxiliary via microwave-accelerated aza-Claisen rearrangement of the unexplored N-thiophenoxyacetyl-α-vinyl piperidine substrate and the oxone-induced transannulation.