High pressure vapor-liquid equilibria and critical loci for the HFC125-HFC134a system

We measured vapor-liquid equilibria (VLE) ranging from 303.75 to 363.15 K and the critical locus for the system of pentafluoroethane (HFC125)-1,1,1,2-tetrafluoroethane (HFC134a). The critical locus exhibited type I behavior by van Konynenberg and Sccot. Correlating the VLE data with an extended BWR equation of state, we found the optimum binary interaction parameter for this system 1.0081 and estimated coefficients of performance (C.O.P.) as a mixture refrigerant. As a result of the correlation, we found that the HFC125-HFC134a system is a potential alternative refrigerant when mole fraction of HFC125 is lower than 0.6. Calculations showed a 4.9% saving energy in the cycle compared with chlorodifluoromethane (HCFC22), for a composition of 30 mole percent HFC125. This paper was presented at The 5th International Symposium on Separation Technology-Korea and Japan held at Seoul between August 19 and 21, 1999.     

The future generations of mobile communications based on broadband access technologies

The forthcoming mobile communication systems are expected to provide a wide variety of services, from high-quality voice to high-definition videos, through high data rate wireless channels anywhere in the world. The high data rate requires broad frequency bands, and sufficient broadband can be achieved in higher frequency bands such as microwave, Ka-band, and millimeter-wave. Broadband wireless channels have to be connected to broadband fixed networks such as the Internet and local area networks. The future-generation systems will include not only cellular phones, but also many new types of communication systems such as broadband wireless access systems, millimeter-wave LANs, intelligent transport systems, and high altitude stratospheric platform station systems. Key to the future generations of mobile communications are multimedia communications, wireless access to broadband fixed networks, and seamless roaming among different systems. This article discusses future-generation mobile communication systems.     

Proposal of Asynchronous Time Division Multiple Access Radio Highway Using Chirp Multiplexing Transform

Asynchronous TDMA bus-link systems using chirp multiplexing transform(CMT) are proposed for radio highway networks to provide the flexibleconstruction of fiber-optic radio access networks and thepossibility of the universal use of these networks among future diverseradio services. The CMT equipped at the radio base station performs twofunctions. One is the conversion of FDM multiple radio services intosignals with a TDMA format and the other is the time compression ofthe generated signal in order to allow asynchronous access. As aresult, the proposed systems can realize the unified transmission ofmultiple radio services and the switching of them in the optical stage(photonic routing) in the networks according to the type of radioservice. The realization of such photonic routing of the radio servicewould greatly benefit the goal of a seamless and universalnetwork available to different types of radio service. Therelationship between the pulse-loss probability performance and thecall-blocking probability performance is theoretically analyzed. Theeffect on the performance of traffic partiality in the coveredarea and the way the performance can be improved are theoreticallyinvestigated. Finally, one of the ways to determine the network sizecovered by a bus link and the number of connected radio base stationsis introduced.     

Three-layer organic solar cell with high-power conversion efficiency of 3.5%

To prepare organic solar cells with practical level of energy-conversion efficiency, the following strategies were adopted. By using HD as the photosensitizer, which is heterodimer consisting of a weak electron-donating 5, 10, 15, 20-tetra(2, 5-dimethoxyphenyl)porphyrinatozinc and a weak electron-accepting 5, 10, 15-triphenyl-20-(3-pyridyl)porphyrin, intramolecular photoinduced electron transfer is promoted resulting in effective charge separation. To create an energetically well-arranged system, the HD was placed between an electron-acceptor layer of PV (perylene-3, 4, 9, 10-tetracarboxyl-bis-benzimidazole) and strong electron-donor layer of MC (3-carboxymethyl-5-[(3-ethyl-2(3H)-benzothiazolylidine)ethylidene]-2-thioxo-4-thiazolidinone), where photoinduced intermolecular electron transfer from HD to PV and rapid injection of electrons from MC to HD suppress back electron transfer in the charge-separated HD. As a result of this, the three-layer solar cell Al/PV/HD/MC/Au showed fairly good photovoltaic properties, short-circuit photocurrent quantum yield of 49.2%, open-circuit photovoltage of 0.39 V, fill factor of 0.51, and energy conversion yield of 3.51% when irradiated with 445 nm monochromatic light of 12 μW cm⁻² intensity transmitted through the Al/PV interface. Since the photocurrent hardly decreased with age, the photocurrent observed here is really from energy conversion and not from photocorrosion of Al electrode being occasionally responsible for the photocurrent.     

Measurement of water content distribution in catalyst coated membranes under water permeation conditions by magnetic resonance imaging

The through-plane water content distribution in a polymer electrolyte membrane (PEM) and in catalyst coated membranes (CCMs) and the flux of water through these membranes were determined under water permeation conditions by means of magnetic resonance imaging and dew point measurements. The PEM or CCM was placed in an experimental cell and subjected to water permeation conditions with various water activities across the membrane. A comparison of the water content distribution and the water flux in the various samples showed that the PEM and CCMs have different water transport properties. These differences suggested that diffusion through the membrane and interfacial transport across the membrane-gas interface, which are the rate determining processes for water transport through the membrane, change depending on whether the membrane has a catalyst coating.     

Microstructures and Thermoelectric Properties of Sintered Misfit-Layered Cobalt Oxide

Misfit-layered cobalt oxide Ca₃Co₄O₉ is considered to be a prospective material for thermoelectric conversion. The thermoelectric properties are anisotropic owing to its anisotropic crystal structure. The crystal has preferred thermoelectric properties along the a–b plane. Therefore, the thermoelectric properties are improved and controlled by the degree of orientation of the sintered sample. In the present work, Sr-doped misfit cobalt oxide Ca_2.7Sr_0.3Co₄O₉ was prepared by solid-phase reaction, followed by uniaxial compression molding and sintering at 1173 K. The Seebeck coefficient α, electrical resistivity ρ, and dimensionless figure of merit ZT were measured as a function of the compression pressure applied in the uniaxial molding. α, ρ, and ZT as functions of the degree of orientation and the relative density are experimentally clarified and explained by calculations using the compound model.     

Anomalous Mixing State in Room-Temperature Ionic Liquid-Water Mixtures: <Emphasis Type="Italic">N,N</Emphasis>-diethyl-<Emphasis Type="Italic">N</Emphasis>-methyl-<Emphasis Type="Italic">N</Emphasis>-(2-methoxyethyl) Ammonium Tetrafluoroborate

The mixing states of room-temperature ionic liquid (RTIL) H₂O mixtures (x = 0.0 mol pct to 99.5 mol pct H₂O) were investigated using wide-angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS), and optical absorption in an ultraviolet and visible (UV-vis) region. The RTIL is N, N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium tetrafluoroborate, [DEME][BF₄]. In a “prepeak” region of the WAXS, the scattered intensities increased at 85 mol pct to 95 mol pct. A medium-range order (MRO) in the liquid structure as observed in network-forming materials developed markedly. In the SAXS experiments, we can detect nanoscale fluctuations relating to polar and nonpolar regions. At 65 mol pct to 85 mol pct, the SAXS intensity increased unexpectedly. Furthermore, entirely different optical absorption spectra in the UV-vis region were observed as a macroscopic property from 90 mol pct to 95 mol pct. We suppose that these anomalies relate to the MRO of the liquid structure. All anomalies probably are induced by an intrinsic property in [DEME][BF₄]-H₂O mixtures.     

Rich bioactive phenolic extract production by microbial biotransformation of Brazilian Citrus residues

Flavanones in Citrus are molecules that play an important role in antioxidant activities in nutraceutical products. Recent studies indicate that molecules of the simplest classes of phenolics have higher biological activity and absorption capacity. However, the molecules that have been shown to be very important bioactive compounds of Citrus, such as hesperetin, naringenin and ellagic acid, are found in trace concentrations in the fruit. An interesting environmentally friendly alternative that deserves attention regarding phenolic compound obtaining is the biotransformation of these molecules. The aim of this study was to develop a process of biotransformation of phenolics from Brazilian Citrus residues by solid-state fermentation with the microorganism Paecilomyces variotii. The optimized fermentation conditions were 10 g of Citrus residues (2.0 mm of substrate particle size), 20 mL distilled water, at 32 °C after 48 h of incubation. The development of this process has generated, simultaneously, an increase of 900, 1400 and 1330% of hesperetin, naringenin and ellagic acid concentration, respectively, and an increase of 73% of the antioxidant capacity. These results give strong evidence that microbial biotransformation does not only produce phenolic compounds but also compounds with high biological activity, such as hesperetin and naringenin.     

Muscle activity during gait-like motion provided by MRI compatible lower-extremity motion simulator

This paper describes an evaluation of muscle activity of volunteers while they undergo gait-like motion in their dorsal position supported by our lower-extremity motion simulator (LoMS) that is magnetic resonance imaging (MRI) compatible. Our LoMS is designed to provide gait-like motion for a wearer in his/her dorsal position while a functional MRI measures his/her brain activity. A purpose of providing gait-like motion by LoMS is to enable a wearer in the dorsal posture to move his/her lower extremities like gait. LoMS is controlled with torque control based on predictive control method to convert the gravity effect of the dorsal posture into the caudal posture. The performance providing gait-like motion is evaluated from two viewpoints of muscle activities: bioelectrical potential (BEP) transition and inhibition of musculus soleus during the motion. There were correlation of BEP transition at iliopsoas, quadriceps femoris, musculus tibialis anterior, and musculus soleus. The inhibition during the gait-like motion provided by LoMS was similar to the inhibition during treadmill gait. The inhibition is modulated by a level of cerebellum, brainstem and spinal. Therefore, it is considered that LoMS induces the motor sensation in the level of cerebellum, brainstem, and spinal by providing the gait-like motion.     

Effects of Structural Isomers of Spermine on the Higher-Order Structure of DNA and Gene Expression

Polyamines are involved in various biological functions, including cell proliferation, differentiation, gene regulation, etc. Recently, it was found that polyamines exhibit biphasic effects on gene expression: promotion and inhibition at low and high concentrations, respectively. Here, we compared the effects of three naturally occurring tetravalent polyamines, spermine (SPM), thermospermine (TSPM), and N⁴-aminopropylspermidine (BSPD). Based on the single DNA observation with fluorescence microscopy together with measurements by atomic force microscopy revealed that these polyamines induce shrinkage and then compaction of DNA molecules, at low and high concentrations, respectively. We also performed the observation to evaluate the effects of these polyamine isomers on the activity of gene expression by adapting a cell-free luciferase assay. Interestingly, the potency of their effects on the DNA conformation and also on the inhibition of gene expression activity indicates the highest for TSPM among spermine isomers. A numerical evaluation of the strength of the interaction of these polyamines with negatively charged double-strand DNA revealed that this ordering of the potency corresponds to the order of the strength of the attractive interaction between phosphate groups of DNA and positively charged amino groups of the polyamines.