Use of the yellow fever virus vaccine strain 17D for the study of strategies for the treatment of yellow fever virus infections

We have employed the attenuated vaccine strain 17D of yellow fever virus (YFV) to evaluate the inhibitory effect of a selected series of compounds on YFV in Vero cells. Use of the vaccine strain does not require high-level microbiological containment facilities and should allow extensive screening. In addition, YFV may serve as a model for other flaviviruses including hepatitis C virus (HCV), and thus strategies for the treatment of YFV infections may apply to flavivirus infections in general. In the present study, several compounds belonging to different classes of nucleoside analogues and polyanions were evaluated for their inhibitory effect on the replication of YFV. Compounds that are targeted at: (i) IMP dehydrogenase (ribavirin, EICAR, tiazofurin, selenazofurin and mycophenolic acid), (ii) OMP decarboxylase (pyrazofurin and 6-azauridine), (iii) CTP synthetase (carbodine and cyclopentenyl cytosine), (iv) dihydrofolate reductase (methotrexate) and the (v) sulfated polymers (dextran sulfate and PAVAS) proved inhibitory to the replication of YFV. Mycophenolic acid (EC50: 0.08 microgram/ml). EICAR (EC50: 0.8 microgram/ml) and methotrexate (EC50: 0.07 microgram/ml) were the most effective. The findings that EICAR and mycophenolic acid, despite their potent anti-YFV activity, had little or no effect on the replication of the bunyavirus Punta Toro or herpes simplex virus in Vero cells, indicates that their anti-YFV activity is rather specific and does not merely result from cytotoxicity. Inhibitors of S-adenosylhomocysteine hydrolase (SAH hydrolase) and thymidylate synthase were found to be devoid of anti-YFV activity.     

Preferentially oriented BaTiO3 thin films deposited on silicon with thin intermediate buffer layers

Barium titanate (BaTiO₃) thin films are prepared by conventional 2-methoxy ethanol-based chemical solution deposition. We report highly c-axis-oriented BaTiO₃ thin films grown on silicon substrates, coated with a lanthanum oxynitrate buffer layer of 8.9 nm. The influence of the intermediate buffer layer on the crystallization of BaTiO₃ film is investigated. The annealing temperature and buffer layer sintering conditions are optimized to obtain good crystal growth. X-ray diffraction measurements show the growth of highly oriented BaTiO₃ thin films having a single perovskite phase with tetragonal geometry. The scanning electron microscopy and atomic force microscopy studies indicate the presence of smooth, crack-free, uniform layers, with densely packed crystal grains on the silicon surface. A BaTiO₃ film of 150-nm thickness, deposited on a buffer layer of 7.2 nm, shows a dielectric constant of 270, remnant polarization (2P_r) of 5 μC/cm², and coercive field (E_c) of 60 kV/cm.     

Electrical modeling of interface roughness in thin filmelectroluminescent devices

If two dielectric materials with different permittivities are in contact with each other and the interface between them is rough, then the electric field near this interface will be very inhomogeneous. In thin film electroluminescent devices, light is generated when electrons move back and forth in the phosphor layer under the influence of a strong ac electric field. At high electric fields, the electrons trapped in deep states at the interface between phosphor and insulator layer tunnel into the conduction band of the phosphor. This tunnel process is very sensitive to the electric field at the interface, so for a rough interface the electron flow will be very inhomogeneous. The relation between the interface roughness and the inhomogeneous charge transfer in thin film electroluminescent devices is investigated, based on an analytical flux tube model. The importance of the inhomogeneous current for the use of gray levels and aging is discussed     

Realization of a Four-Electrode Liquid Crystal Device With Full In-Plane Director Rotation

A liquid crystal device with micrometer-scale hexagonal electrodes has been fabricated and characterized. By using weak anchoring at the liquid crystal interfaces, the orientation of the director is completely governed by the applied electric fields. The appropriate voltage waveforms applied to electrodes allow the director in the liquid crystal layer to be rotated in the plane parallel to the substrates over large angles, exceeding 180 deg. This paper is a technological and experimental verification of an earlier proposed device concept     

Polyanion inhibitors of HIV and other viruses. 7. Polyanionic compounds and polyzwitterionic compounds derived from cyclodextrins as inhibitors of HIV transmission

New polyanionic compounds were obtained from radical addition of thiomalic acid and mercaptopropionic acid onto perallylated cyclodextrins (CDs) under UV irradiation with a catalytic amount of alpha,alpha'-azobis(isobutyronitrile). All these polyanions, bearing 18-48 carboxylate groups, inhibited human immunodeficiency virus type 1 (HIV-1) strain IIIB replication in MT-4 cells at a 50% inhibitory concentration (IC50) of 0.1-2.9 microM, while not being toxic to the host cells at concentrations up to 62 microM. These compounds were also active against a clinical HIV-1 isolate (HE) at >/=4-fold higher concentrations. Only some compounds showed activity against the two HIV-2 strains (ROD and EHO) but at higher concentrations than those required to inhibit HIV-1 (IIIB and HE) replication. In addition, these compounds were not active against the M-tropic HIV-1 strain BaL but were active against simian immunodeficiency virus [SIV (MAC251)]. These compounds were also inhibitory to the replication of human cytomegalovirus at an IC50 of 1-10 microM, but not herpes simplex virus (type 1 and type 2) or other (picorna-, toga-, reo-, orthomyxo-, paramyxo-, bunya-, rhabdo-, and poxvirus) viruses. Radical addition on perallylated CDs of a protected cysteine gave polyzwitterionic compounds. None of these last compounds proved inhibitory to the replication of HIV-1, HIV-2, or any of the other viruses tested.     

Analysis of a transparent organic photoconductive sensor

The electro-optical performance of transparent photoconductive sensors based on stacks of organic layers is investigated. The photoconductive sensors are composed of interdigitated electrodes covered with a stack of two transparent organic compounds: a hole transport layer 1,3,5-tris[(3-methylphenyl)phenylamino]benzene (m-MTDAB) and an exciton generation layer 3,4,9,10-perylenetetracarboxylic bis-benzimidazole (PTCBI). The photocurrent through the device is measured as a function of the voltage across the electrodes for different illumination levels. Based on the measurements we can explain the working principle of the photoconductive sensor and compare the performance of four different stacks. In order to study the optical sensitivity in more detail, a photoconductive device with two parallel electrodes is manufactured and illuminated by a line-shaped laser beam that covers only a fraction of the gap between the electrodes. The current through the photoconductive sensor is measured as a function of the position of the local illumination for a set of voltages. The experimental results confirm that there is a high-field space charge region near the cathode.     

Modification of the bile salts-Irgasan-brilliant green agar for enumeration of Aeromonas species from food

The present study evaluated the productivity of BIBG medium for the isolation of Aeromonas spp. from food and describes a modification of the BIBG medium (mBIBG) (increased pH (8.7), replacement of xylose by soluble starch as a carbon source, decreased concentration of bile salts) to increase its selectivity and electivity. Using the mBIBG medium, growth of the majority of the Enterobacteriaceae (9/10) was suppressed except for Citrobacter freundii. The mBIBG medium supported growth of Pseudomonas species but a clear distinction between Aeromonas and Pseudomonas colonies could be made. Interpretation of the mBIBG medium should be performed after 24 h of incubation. It was noted that three of the 27 Aeromonas strains tested did not develop on the mBIBG medium. The ability or inability to grow on a selective medium is strain-dependent. Enumeration of Aeromonas species (A. hydrophila LMG 3771, A. caviae LMG 3775, A. veronii biovar veronii LMG 9075, A. veronii biovar sobria LMG 13071) from artificially contaminated foods (shrimp, minced meat (beef/pork), precut leek, and shredded carrots) confirmed that the mBIBG medium is suitable for quantitative recovery of aeromonads (ca. 10(2)-10(7) cfu/g) in the presence of a high background flora (10(5)-10(6) cfu/g). Screening of naturally contaminated foods (vegetables, seafood, meat) for the presence of Aeromonas resulted in three out of 14 food samples showing presumptive Aeromonas colonies on mBIBG.     

Numerical simulation of charge transfer and light emission inSrS:Ce thin-film electroluminescent devices

When an AC voltage is applied to a thin-film electroluminescent device with an SrS:Ce phosphor layer, the current flowing through the phosphor layer and the emitted light can be complex functions of time. In order to explain the observed current and light waveforms, a numerical model has been constructed for the electrical and optical behavior of such a device. This model is based on the tunneling of electrons from the phosphor-insulator interface, multiplication of the electron current and creation of positive space charge in the high field region, recombination of electrons with the positive charges in the low-field region, and a back-flow of electrons from the anodic interface when the field there changes sign. The rather simple model is able to simulate a number of features observed in current and light characteristics quite well. It could serve as a reference for the interpretation of new experimental results     

Simulation and measurement of multiplication in thin-filmelectroluminescent devices with doped probe layers

When a single voltage pulse is applied to an electroluminescent (EL) device after previous illumination, the current through the phosphor layer will normally not be homogeneous, but increase from the cathodic side-where the electrons tunnel from-to the anodic side, due to multiplication. The positive charges that remain after the multiplication process cause a positive space charge that has been observed in various experiments and influences the efficiency. In this paper a simple numerical model is proposed for the calculation of charge transfer and light emission, in the case that multiplication takes place during a voltage pulse after previous illumination