Structural and electronic properties of extremely long perylene bisimide nanofibers formed through a stoichiometrically mismatched, hydrogen-bonded complexation

Extremely long nanofibers, whose lengths reach the millimeter regime, are generated via co-aggregation of a melamine-appended perylene bisimide semiconductor and a substituted cyanurate, both of which are ditopic triple-hydrogen-bonding building blocks; they co-aggregate in an unexpected stoichiometrically mismatched 1:2 ratio. Various microscopic and X-ray diffraction studies suggest that hydrogen-bonded polymeric chains are formed along the long axis of the nanofibers by the 1:2 complexation of the two components, which further stack along the short axis of the nanofibers. The photocarrier generation mechanism in the nanofibers is investigated by time-of-flight (TOF) experiments under electric and magnetic fields, revealing the birth and efficient recombination of singlet geminate electron-hole pairs. Flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurements revealed intrinsic 1D electron mobilities up to 0.6 cm(2) V(-1) s(-1) within nanofibers.     

High-performance organic field-effect transistors with binary ionic liquids

High-performance rubrene single-crystal field-effect transistors are developed with binary ionic liquid electrolytes used for gating. Inclusion of small amount of inorganic salts in the ionic liquids enhances the degree of dissociation for the organic ions and accelerates formation of the electric-double-layers in response to the gate voltage. High carrier mobility of 2.9 cm²/Vs is achieved in the rubrene single-crystal transistors with the mixture ionic liquid. In addition to the advantage of the low-voltage operation due to concentrated field in ultra-thin electric-double-layers, drastically increased capacitance at above 100 Hz makes the technique of the ionic liquid gating more attractive for fast-switching devices.     

Defective bone remodelling in osteoprotegerin-deficient mice

Previous studies have reported enhanced osteoclastogenesis, increased bone resorption and osteoporosis in osteoprotegerin (OPG)-deficient mice. In the present study, we show that the tibial epiphyses contain abundant, thin trabeculae lined with numerous osteoclasts and cuboidal osteoblasts. The increase in osteoblasts and osteoclasts was associated with a dramatic increase in calcein labelling of the mineralization fronts and replacement of much of the intertrabecular marrow with numerous alkaline phosphatase-positive preosteoblasts. Furthermore, the discrete, linear cement lines seen in wild-type mice were replaced by a randomly oriented meshwork of cement lines that were stained intensely for tartrate-resistant acid phosphatase and osteopontin in the OPG-/- mice. These indices of accelerated bone remodelling in mutant bone were associated with irregular trabecular surfaces, a disorganized collagen matrix interspersed with amorphous ground substance and numerous fissures between old and new bone. In total, these observations indicate that enhanced osteoclastic activity in OPG-/- epiphyses led to a coupled increase in osteoblast differentiation and activity and an increase in bone remodelling. The high bone turnover, disorganized matrix and impaired attachment of new to old bone in the cement lines in OPG-/- mice appear to cause bone fragility.     

Design criteria of 1.3-μm multiple-quantum-well lasers forhigh-temperature operation

We present design criteria for high-temperature operation in 1.3-μm multiple-quantum-well (MQW) lasers from the viewpoint of the light output power penalty, i.e., the change in the light output power at a fixed drive current with increasing temperature. It is shown that not only the characteristic temperature (T₀) but also internal loss dependence on temperature (γ) and threshold current (I_th) are significant parameters for reducing the power penalty. We compare the high-temperature performance of InGaAsP-based and AlGaInAs-based MQW lasers and demonstrate that AlGaInAs-based lasers have more potential in terms of the power penalty. Furthermore, we also demonstrate that the power penalty can be reduced by introducing a buried-heterostructure (BH) structure into AlGaInAs-based lasers. From these results, we conclude that the AlGaInAs-based BH lasers are promising for high-temperature performance     

Design strategy and development of spherical silicon solar cell with semi-concentration reflector system

Structural and economical merits of a spherical silicon solar cell with semi-concentration reflector system have been discussed. The roles of the reflector system have been clarified; the reflector improves short-circuit current density and also open-circuit voltage by 4–6 times concentration to make a light irradiation area comparable to a p–n junction area. We have theoretically demonstrated that the spherical Si solar cell with semi-concentration reflector system can realize a performance comparable to that of conventional Si solar cells, with less amount of silicon material use.     

An experimental study on bubble growth within a narrow space under an interference‐piece

An experimental study was performed on the nucleate boiling of water in the narrow space formed between an interference piece and the heating surface of heat‐proof glass. A past study analyzed the bubble growth due to the conduction of heat through the thinner liquid layer under a growing bubble; however, the thickness of the liquid layer was not shown experimentally. This study investigates the thickness of this thinner layer by the interference method. Almost no change was found on the thickness of the liquid layer under both the interference‐piece and on the heating surface. The experimental results indicate the great contribution of superheating of the test liquid to bubble growth. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(2): 165–177, 2006; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/htj.20100     

Study on creep-fatigue evaluation procedures for high-chromium steels—Part I: Test results and life prediction based on measured stress relaxation

Strong demand for improving thermal efficiency of power generation plants promoted the use of high-chromium steels, which have high creep strength and corrosion resistance. Aiming at cost reduction for future nuclear power plants, these materials are also regarded as candidates for structural materials, being favoured for lower thermal expansion rate compared with austenitic stainless steels. In structural design and life management of these plants, failure due to the combination of fatigue and creep damages has been considered as an important phenomenon to be evaluated, in addition to simple creep failure under sustained loading such as inner pressure. The author has been conducting a series of creep-fatigue tests for three types of high-chromium steels used in fossil power plants and the applicability of life prediction methods has been studied. It was found that the time fraction rule gives a relatively small amount of creep damage and overpredicts the failure life, whereas a simple ductility exhaustion method provides very large creep damage which leads to too conservative prediction of failure lives. A modified ductility exhaustion method developed on the re-definition of creep damage as a ductility consumer gave a moderate amount of creep damage and provided reasonable life predictability. Moreover, an empirical formula was derived which can represent the life reduction in compressive hold tests as a function of pure fatigue life and hold time.     

Practical Controller Design of Hybrid Experimental System for Seismic Tests

A hybrid experimental system is one of the powerful tools to perform various seismic tests for unknown and/or huge structures, where an actuator-excited experimental vibratory system and a computational response analysis are simultaneously combined and implemented. This paper presents a control methodology for high-performance hybrid experimental systems. A 2-DOF control framework is applied from the viewpoint of control techniques, where a feedback compensator is designed according to the system stabilization analysis, and a feedforward (FF) compensator is designed to achieve the desired servo characteristics. In the FF compensator design, an iterative learning control approach is particularly adopted to eliminate the response delays in the hydraulic actuator. The proposed compensation algorithm has been verified using a laboratory hybrid experimental set up with two-mass structure as a load mechanism.     

Sliding window protocol with selective-repeat ARQ: performance modeling and analysis

A sliding window mechanism is well known to be a convenient way to integrate cumulative acknowledgement and flow control functions in a simple manner. Hence, widely used reliable data-transfer protocols such as TCP-SACK and RLC utilize this sliding window mechanism in conjunction with a selective-repeat ARQ (automatic repeat request) function, namely, the selective-repeat sliding window protocol (SR-SWP). We demonstrate that SR-SWP yields a throughput restraint effect (TORE) in particular situations when packet losses occur. We propose an analytical performance model to represent the TORE in the case of heavy traffic. Using this model, we derive explicit forms of goodput and mean resequencing delay, which are fundamental qualities of service parameters. From numerical results, we demonstrate that the impact of TORE on the performance is not negligible for high packet-loss probabilities. Furthermore, we show that the SR-SWP model exhibits the lower goodput and the smaller mean resequencing delay than those obtained from the traditional SR-ARQ protocol model.     

SrCaO Protective Layer for High-Efficiency PDPs

The sustain pulse voltage of the panel for 66-kPa Ne + Xe (5%-30%) is 20%-40% lower with a Sr_0.62Ca_0.38O protective layer than with a MgO protective layer. At a normal sustain voltage of 160-200 V, the luminous efficiency of the panel with the Sr_0.62 Ca_0.38O protective layer for Xe (30%) is about twice as high as with the MgO protective layer for Xe (10%). The luminances of these panels are almost the same. This high efficiency at normal sustain pulse voltage and normal luminance is obtained through the combined use of the Sr_0.62Ca_0.38O protective layer and high Xe content. With regard to ion bombardment, the Sr_0.62Ca_0.38O film has a 4.5 times longer life than SrO film and nearly 80% of the life of MgO film. We also calculated the values of theoretical secondary electron emission yield gamma_imin of MgO, SrO, and CaO without energy bands in the band gap for rare gas ions and found that [ gamma_imin of MgO] les [gamma_imin of CaO] < [gamma_imin of SrO] except for the one case with He. The breakdown voltage decreases with higher gamma_imin values. As expected, the discharge voltage of the panel is much lower with the SrO protective layer than with the MgO protective layer. The discharge voltages of the panels with Sr_0.62Ca_0.38O and SrO protective layers are almost the same. These findings show that the life of the SrO protective layer can be made 4.5 times longer without any increase in the discharge voltage by adding CaO (40 at.%)