Critical Dependence of Polarization Phenomena on Conductivity in Ferroelectric Polymers

Experimentally obtained data on the polarization dynamics in polyvinylidene fluoride, a typical ferroe-lectric polymer, are analyzed during initial poling, short circuiting and polarization switching. Considering a two-component structure of the samples, namely, presence of ferroelectric and non-ferroelectric phases, it is shown that value and stability of the ferroelectric polarization significantly depend on conductivity and space charges. Application of a simple two-layer theoretical model with an explicit conductivity allowed ex-plaining such important features, as slow development and switching of the ferroelectric polarization and a partial back-switching of the already formed polarization after short-circuiting of the sample. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3554

Use of in vivo phage display to engineer novel adenoviruses for targeted delivery to the cardiac vasculature

We performed in vivo phage display in the stroke prone spontaneously hypertensive rat, a cardiovascular disease model, and the normotensive Wistar Kyoto rat to identify cardiac targeting peptides, and then assessed each in the context of viral gene delivery. We identified both common and strain-selective peptides, potentially indicating ubiquitous markers and those found selectively in dysfunctional microvasculature of the heart. We show the utility of the peptide, DDTRHWG, for targeted gene delivery in human cells and rats in vivo when cloned into the fiber protein of subgroup D adenovirus 19p. This study therefore identifies cardiac targeting peptides by in vivo phage display and the potential of a candidate peptide for vector targeting strategies

Self-consistent model of unipolar transport in organic semiconductor diodes: accounting for a realistic density-of-states distribution

A self-consistent, mean-field model of charge-carrier injection and unipolar transport in an organic semiconductor diode is developed utilizing the effective transport energy concept and taking into account a realistic density-of-states distribution as well as the presence of trap states in an organic material. The consequences resulting from the model are discussed exemplarily on the basis of an indium tin oxide/organic semiconductor/metallic conductor structure. A comparison of the theory to experimental data of a unipolar indium tin oxide/poly-3-hexyl-thiophene/Al device is presented.Comment: 6 pages, 2 figures; to be published in Journal of Applied Physic

Self consistent theory of unipolar charge-carrier injection in metal/insulator/metal systems

A consistent device model to describe current-voltage characteristics of metal/insulator/metal systems is developed. In this model the insulator and the metal electrodes are described within the same theoretical framework by using density of states distributions. This approach leads to differential equations for the electric field which have to be solved in a self consistent manner by considering the continuity of the electric displacement and the electrochemical potential in the complete system. The model is capable of describing the current-voltage characteristics of the metal/insulator/metal system in forward and reverse bias for arbitrary values of the metal/ insulator injection barriers. In the case of high injection barriers, approximations are provided offering a tool for comparison with experiments. Numerical calculations are performed exemplary using a simplified model of an organic semiconductor.Comment: 21 pages, 8 figure

Self-consistent analytical solution of a problem of charge-carrier injection at a conductor/insulator interface

We present a closed description of the charge carrier injection process from a conductor into an insulator. Common injection models are based on single electron descriptions, being problematic especially once the amount of charge-carriers injected is large. Accordingly, we developed a model, which incorporates space charge effects in the description of the injection process. The challenge of this task is the problem of self-consistency. The amount of charge-carriers injected per unit time strongly depends on the energy barrier emerging at the contact, while at the same time the electrostatic potential generated by the injected charge- carriers modifies the height of this injection barrier itself. In our model, self-consistency is obtained by assuming continuity of the electric displacement and the electrochemical potential all over the conductor/insulator system. The conductor and the insulator are properly taken into account by means of their respective density of state distributions. The electric field distributions are obtained in a closed analytical form and the resulting current-voltage characteristics show that the theory embraces injection-limited as well as bulk-limited charge-carrier transport. Analytical approximations of these limits are given, revealing physical mechanisms responsible for the particular current-voltage behavior. In addition, the model exhibits the crossover between the two limiting cases and determines the validity of respective approximations. The consequences resulting from our exactly solvable model are discussed on the basis of a simplified indium tin oxide/organic semiconductor system.Comment: 23 pages, 6 figures, accepted to Phys.Rev.

Charge carrier injection into insulating media: single-particle versus mean-field approach

Self-consistent, mean-field description of charge injection into a dielectric medium is modified to account for discreteness of charge carriers. The improved scheme includes both the Schottky barrier lowering due to the individual image charge and the barrier change due to the field penetration into the injecting electrode that ensures validity of the model at both high and low injection rates including the barrier dominated and the space-charge dominated regimes. Comparison of the theory with experiment on an unipolar ITO/PPV/Au-device is presented.Comment: 32 pages, 9 figures; revised version accepted to PR

Identification of novel small molecule inhibitors of adenovirus gene transfer using a high throughput screening approach

Due to many favourable attributes adenoviruses (Ads) are the most extensively used vectors for clinical gene therapy applications. However, following intravascular administration, the safety and efficacy of Ad vectors are hampered by the strong hepatic tropism and induction of a potent immune response. Such effects are determined by a range of complex interactions including those with neutralising antibodies, blood cells and factors, as well as binding to native cellular receptors (coxsackie adenovirus receptor (CAR), integrins). Once in the bloodstream, coagulation factor X (FX) has a pivotal role in determining Ad liver transduction and viral immune recognition. Due to difficulties in generating a vector devoid of multiple receptor binding motifs, we hypothesised that a small molecule inhibitor would be of value. Here, a pharmacological approach was implemented to block adenovirus transduction pathways. We developed a high throughput screening (HTS) platform to identify the small molecule inhibitors of FX-mediated Ad5 gene transfer. Using an in vitro fluorescence and cell-based HTS, we evaluated 10,240 small molecules. Following sequential rounds of screening, three compounds, T5424837, T5550585 and T5660138 were identified that ablated FX-mediated Ad5 transduction with low micromolar potency. The candidate molecules possessed common structural features and formed part of the one pharmacophore model. Focused, mini-libraries were generated with structurally related molecules and in vitro screening revealed novel hits with similar or improved efficacy. The compounds did not interfere with Ad5:FX engagement but acted at a subsequent step by blocking efficient intracellular transport of the virus. In vivo, T5660138 and its closely related analogue T5660136 significantly reduced Ad5 liver transgene expression at 48 h post-intravenous administration of a high viral dose (1 × 10<sup>11</sup> vp/mouse). Therefore, this study identifies novel and potent small molecule inhibitors of the Ad5 transduction which may have applications in the Ad gene therapy setting

Seismcity in the vicinity of Yucca Mountain, Nevada, for the period October 1, 2000 to September 30, 2001

Starting on October 1, 1995, the monitoring of seismicity within the southern Great Basin near Yucca Mountain was performed with a new digital network. This network features three-component recording with 24-bit A/D conversion in the field. Continuous data are collected at 20 sps, and event triggered windows are collected at 100 sps. A seismic bulletin of events is made by automatically associating triggers among stations, classifying the local earthquake events, and locating the earthquakes and computing their magnitudes with conventional methods. This report covers the operational and seismic results of the sixth full year (FY01) of the improved, digitally based, monitoring. The FY01 earthquake bulletin includes nearly 2000 events within about 65 km of Yucca Mountain. The two largest events in FYO1, both having magnitude (ML) of 3.4, are relatively small compared to the largest events in each of the past 8 years of monitoring by the Nevada Seismological Laboratory. Nearly one-half of the FYO 1 earthquakes are concentrated in the aftershock zone of the 1992 Little Skull Mountain (LSM) earthquake. Hypocentral depths of the aftershocks are largely concentrated in the range of 8-12 km, consistent with previous years. Earthquakes not in the LSM aftershock zone are largely in the 4-12 km range. The observed minimum detection thresholds for earthquakes within the network range in ML from -0.3 to 0.5 or greater, with the lower threshold achieved for earthquakes in the LSM and Yucca Mountain areas where the network is most dense. From the FY01 earthquakes, 37 new short-period first-motion focal mechanisms were reliably determined. These, and the nearly 300 from the previous five years, show a consistent picture of the overall stress field in the region of the digital network. The mean tensional axis is oriented at roughly 60° west of north, at shallow dip, and the pressure axis at roughly 30° east of north, with greater variability in the dip direction accounting for a range of both strike-slip and dip-slip faulting within NW-SE extension. In FY01 three additional small earthquakes occurred within 10 km of the ESF, all with magnitudes \u3c 0.6. A first-motion focal mechanism was determined for one of them — its tensional axis was nearly identical to the mean of the entire set in the last six years. In addition, five small earthquakes were located in the southern part of the Yucca Mountain block, more than 10 km from the ESF. In the Death Valley region, an M 4.3 earthquake occurred in the zone of the Eureka Valley earthquake aftershocks, and five other earthquakes measured M \u3e 3 within the park boundaries. Little of the observed seismicity in the Death Valley region can be related to the two large faults there: Furnace Creek and Death Valley. During FY01 only two local earthquakes provided usable strong-motion recordings. Accelerations were all below l%g for these recordings

Temperature dependence of the drift mobility of poly(9,9'-dioctylfluorene-co-benzothiadiazole)-based thin-films devices

Charge transport in spin coated thin films of poly(9,9′-dioctylfluorene-co-benzothiadiazole) (F8BT) was studied using the Photo-Current Extraction by the Linear Increasing Voltage (Photo-CELIV) method in the temperature range of 120 to 420 K. A continuous change in the slope of a lnμ versus T-2 plot was detected at 205 K with a very weak temperature dependence of the mobility at lower temperatures. According to the Gaussian Disorder Model (GDM), this behavior can be attributed to a progressive decrease in the dispersiveness of the charge transport. In this sense, the weak temperature dependence of the mobility at low temperatures arises from the nonequilibrium condition between thermal released and trapped charges, so the transport becomes trap controlled at low temperature. Furthermore, another change in the mobility behavior was observed at about 360 K, which was related to the glass transitions of the material. This indicates that even for thin films the drift mobility can be significantly affected by a variation in the dynamics and local packing of the polymer chains, which can be detected by Photo-CELIV experiments.FAPESP (08/01935-5; 09/18354-8; 07/08688-0)DAAD (A/09/72945; ref 415)CNPqMCTI/INCT-INE

Properties of Foreshocks and Aftershocks of the Non-Conservative SOC Olami-Feder-Christensen Model: Triggered or Critical Earthquakes?

Following Hergarten and Neugebauer [2002] who discovered aftershock and foreshock sequences in the Olami-Feder-Christensen (OFC) discrete block-spring earthquake model, we investigate to what degree the simple toppling mechanism of this model is sufficient to account for the properties of earthquake clustering in time and space. Our main finding is that synthetic catalogs generated by the OFC model share practically all properties of real seismicity at a qualitative level, with however significant quantitative differences. We find that OFC catalogs can be in large part described by the concept of triggered seismicity but the properties of foreshocks depend on the mainshock magnitude, in qualitative agreement with the critical earthquake model and in disagreement with simple models of triggered seismicity such as the Epidemic Type Aftershock Sequence (ETAS) model [Ogata, 1988]. Many other features of OFC catalogs can be reproduced with the ETAS model with a weaker clustering than real seismicity, i.e. for a very small average number of triggered earthquakes of first generation per mother-earthquake.Comment: revtex, 19 pages, 8 eps figure