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Journal articles on the topic 'Negative charge carrier transport'
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1
Ma, Dongge, M. Aguiar, and I. A. H�mmelgen. "Negative Charge Carrier Transport in Poly(methylmethacrylate-co-9-anthracenyl-methylmethacrylate) Thin Films." physica status solidi (b) 222, no. 1 (November 2000): 179–83. http://dx.doi.org/10.1002/1521-3951(200011)222:1<179::aid-pssb179>3.0.co;2-a.
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WAGNER, P., I. GORDON, A. DAS, J. VANACKEN, V. V. MOSHCHALKOV, and Y. BRUYNSERAEDE. "INTERPLAY BETWEEN TRANSPORT, MAGNETIC-, AND STRUCTURAL PROPERTIES OF MN-PEROVSKITES WITH VARIOUS DOPING LEVEL." International Journal of Modern Physics B 14, no. 29n31 (December 20, 2000): 3735–40. http://dx.doi.org/10.1142/s0217979200004283.
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We performed a comparative study on the colossal negative magnetoresistivity and the Hall effect in thin films of the manganese perovskite La 1-x Ca x MnO 3 with x =0.3 and x =0.67. The underdoped sample ( x =0.3) undergoes a phase transition from a paramagnetic semiconductor to a ferromagnetic quasimetal at the Curie temperature T C =280 K , while the overdoped compound ( x =0.67) stays a paramagnetic semiconductor at all temperatures. Both materials show colossal negative magneto-resistivity, albeit on considerably different temperature- and field scales, depending on the magnetic interactions between neighbouring Mn ions. According to the Hall data, the charge carriers in the underdoped material are hole-type, partially compensated by an electron-type contribution. The overdoped system shows electronic carriers with a thermally activated concentration. The ordinary Hall effect is in both compounds superimposed by an anomalous Hall contribution with a sign opposite to the intrinsic charge-carrier type.
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Kulbachinskii, V. A., and L. Shchurova. "Calculation of Carrier Scattering and Negative Magnetoresistance in Mn-Doped GaAs/InGaAs/GaAs Quantum Well with Ferromagnetism." Solid State Phenomena 152-153 (April 2009): 283–86. http://dx.doi.org/10.4028/www.scientific.net/ssp.152-153.283.
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We have investigated the thermodynamic, transport and magnetotransport properties of free charge carriers in a diluted magnetic semiconductor with a quantum well InGaAs in the GaAs with δ-doped by C and Mn. In order to determine the density of the holes in a quantum well, we carried out thermodynamic calculations of the system of free holes, atoms Mn0 and ions Mn–. We calculated the temperature dependence of resistance and magnetoresistance of holes in the quantum well. The contributions of various scattering mechanisms of holes to the resistance were analyzed. The negative magnetoresistance are explained as the reduction of spin-flip scattering by aligning spins of the magnetic field.
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Lei, X. L., and N. J. M. Horing. "Balance-Equation Approach to Hot-Carrier Transport in Semiconductors." International Journal of Modern Physics B 06, no. 07 (April 10, 1992): 805–936. http://dx.doi.org/10.1142/s0217979292000505.
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The balance-equation approach to nonlinear hot-carrier transport theory, formulated by Lei and Ting (1984), is addressed in this comprehensive review. A central feature is the role of strong electron-electron interactions in promoting rapid thermalization about the drifted transport state and the concomitant substantial simplification of the transport theory. This physical feature is embodied in the initial density matrix chosen to represent the unperturbed carrier system. Force and energy balance equations are formulated for the dc steady state, ac dynamic and transient cases of charge conduction, including memory effects. The scattering mechanisms include impurity and phonon interactions along with dynamic nonlocal screening effects due to carrier-carrier interactions. Both linear and nonlinear resistivities are discussed in the degenerate and nondegenerate statistical regimes. Interesting phenomena such as electron cooling and thermal noise and diffusion are discussed as well. Semiconductor microstructure transport is described for both linear and nonlinear hot carrier conduction. In this connection, quasi-2D-systems, heterojunctions, and quantum well superlattices are treated with attention to steady state, transient and high frequency transport, including, for example, superlattice plasmon resonance structure. Type-II superlattice transport is reviewed as well as type-I, and electron-hole drag is treated in conjunction with negative minority electron mobility in a quantum well. Multivalley semiconductors are discussed in some detail. Furthermore, attention is also focused on the center-of-mass velocity fluctuation, Langevin-type equation and thermal noise and diffusion for microstructures and multivalley systems. A number of particularly important phenomena are examined from the balance-equation point of view, such as nonequilibrium phonons, higher order scattering effects and weak localization, hydrodynamic equations for weakly nonuniform systems, and the intracollisional field effect. Alternative formulations and interpretations of the balance-equation approach are reviewed. The distinction between this many-particle, isothermal, balance-equation theory and the noninteracting (single-particle) adiabatic transport theory is discussed to clarify issues subject to controversy in the literature. Finally, we give a brief review of recent developments in the balance-equation approach: investigation of the distribution function in balance-equation theory, improved calculations for GaAs/AlGaAs heterojunctions, extension of the balance equations to an abitrary energy band and recent work on superlattice miniband transport.
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BASAK, S., and S. K. GHATAK. "DENSITY OF STATES AND TRANSPORT PROPERTIES IN NORMAL STATE OF CUPRATE-SUPERCONDUCTORS." International Journal of Modern Physics B 13, no. 13 (May 30, 1999): 1633–43. http://dx.doi.org/10.1142/s0217979299001612.
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Three-state model for quasi-two dimensional Cu-O layer of oxide superconductor is considered. The density of states and transport properties (resistivity and thermo-electric power) in normal state are calculated for resonance and non-resonance condition of Cu d-level and O p-level. Thermoelectric power can be positive or negative depending on carrier concentration, bare charge transfer gap and transfer integral between d–p and p–p states and its sign changes at higher temperature. The thermo-electric power when positive passes through a maximum with increase in temperature. The value at its maximum and its location moves up with decrease in carrier concentration. The thermal variation of resistivity changes from metallic like (linear in -T) to semiconducting-like as carrier concentration reduces by small amount.
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Torres, A. M., J. V. Rodriguez, G. C. Lunazzi, and C. Tiribelli. "Carrier-mediated transport of tetrabromosulfonephthalein by rat liver plasma membrane vesicles." American Journal of Physiology-Gastrointestinal and Liver Physiology 263, no. 3 (September 1, 1992): G338—G344. http://dx.doi.org/10.1152/ajpgi.1992.263.3.g338.
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To investigate the molecular requirements and mechanisms for the hepatic uptake of phthaleins, the transport of tetrabromosulfonephthalein (TBS) was investigated in basolateral rat liver plasma membrane vesicles. TBS uptake was electrogenic as greatly accelerated by the creation of a positive-inside membrane potential by the addition of valinomycin in the presence of an inwardly directed potassium gradient. No effect was observed when the ionophore was added in the presence of a sodium gradient. The transport occurred into an osmotic-sensitive space and was saturable with an apparent Michaelis constant of 5.32 +/- 0.56 microM and a maximal velocity of 9.23 +/- 0.25 nmol.s-1.mg protein-1 (mean +/- SD, n = 3 experiments). TBS uptake was directly related to the extra-vesicular pH, indicating the deprotonated quinoid negative-charged form of the dye as the transported species. In contrast, TBS uptake was inversely related to the intravesicular pH, suggesting that protonation inside the vesicles may act as an efficient trap in transport process. Addition of polyclonal monospecific anti-bilitranslocase antibody to liver vesicles specifically inhibited TBS uptake rate (3.27 +/- 0.17 vs. 5.82 +/- 0.61 nmol.s-1.mg protein-1, n = 3, P less than 0.001). These data indicate that TBS is electrogenically transported across the liver cell plasma membrane by bilitranslocase. They also indicate that the presence of a negative charged group on the benzenic ring of the ligand is important in accounting for the transport.
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Song, X. M., Z. G. Huang, M. Gao, D. Y. Chen, Z. Fan, and Z. Q. Ma. "Role of Interfacial Oxide Layer in MoOx/n-Si Heterojunction Solar Cells." International Journal of Photoenergy 2021 (April 22, 2021): 1–8. http://dx.doi.org/10.1155/2021/6623150.
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Interfacial oxide layer plays a crucial role in a MoOx/ n -Si heterojunction (MSHJ) solar cell; however, the nature of this interfacial layer is not yet clarified. In this study, based on the experimental results, we theoretically analyzed the role of the interfacial oxide layer in the charge carrier transport of the MSHJ device. The interfacial oxide layer is regarded as two layers: a quasi p -type semiconductor interfacial oxide layer (SiOx(Mo))1 in which numerous negatively charged centers existed due to oxygen vacancies and molybdenum–ion-correlated ternary hybrids and a buffer layer (SiOx(Mo))2 in which the quantity of Si-O bonds was dominated by relatively good passivation. The thickness of (SiOx(Mo))1 and the thickness of (SiOx(Mo))2 were about 2.0 nm and 1.5 nm, respectively. The simulation results revealed that the quasi p -type layer behaved as a semiconductor material with a wide band gap of 2.30 eV, facilitating the transport of holes for negatively charged centers. Additionally, the buffer layer with an optical band gap of 1.90 eV played a crucial role in passivation in the MoOx/ n -Si devices. Furthermore, the negative charge centers in the interfacial layer had dual functions in both the field passivation and the tunneling processes. Combined with the experimental results, our model clarifies the interfacial physics and the mechanism of carrier transport for an MSHJ solar cell and provides an effective way to the high efficiency of MSHJ solar cells.
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Pospisil, Jan, Alexander Kovalenko, Veronika Schmiedova, Oldrich Zmeskal, and Martin Vala. "Impedance Spectroscopy Study of Organic Photovoltaic Cells with an Inkjet Printed Hole-Extracting Graphene Oxide Layer." Materials Science Forum 955 (May 2019): 31–36. http://dx.doi.org/10.4028/www.scientific.net/msf.955.31.
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This paper deals with the study of light conversion efficiency of organic photovoltaic cells with an inkjet-printed graphene oxide layer. The graphene oxide is used in this experiment as a hole-extracting, electron blocking layer in bulk heterojunction organic solar cells based on DPP(TBFu)2:PC60BM blend. It is also studied the influence of the GO reduction (chemically, by UV radiation and by annealing) on the final efficiency of photovoltaic conversion. Power conversion efficiency and the transport of charge carriers are evaluated by measuring of current-voltage characteristics and mainly by impedance spectroscopy analysis. In this regard, using of graphene oxide and its reduced form showed negative influence on the device performance caused by an inefficient charge carrier collection at the short-circuit condition.
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Mikubayeva, E. V., N. S. Kobotayeva, and E. E. Sirotkina. "Combined Sensitisation of Benzaldehyde Diphenylhydrazones: Effect of Hydrazone Structure on Sensitization Efficiency." Eurasian Chemico-Technological Journal 6, no. 2 (July 12, 2017): 133. http://dx.doi.org/10.18321/ectj602.
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Injection, spectral and combined (injection-spectral) sensitisations of several benzaldehyde diphenylhydrazones have been studied using the layers of amorphous selenium and complex compounds based on<br />pyril dyes to broaden photosensitivity spectrum of electrophotographic carrier and to study sensitisation mechanism. Two photogeneration mechanisms for charge carriers have been shown to exist at a combined<br />sensitisation, i.e. generation in the injection layer followed by the injection into a transport layer and generation in a transport layer on a dye. The excited dye molecules have been established to create hole strapping sites in a transport layer: it is exhibited in a different nature of photodischarge curves in selenium- and dye-absorbing regions at the negative surface potential. The effect of the substituent in a benzaldehyde fragment on the efficiency of injection, spectral and combined sensitisations of benzaldehyde diphenylhydrazones<br />has been studied. The ionization potentials of hydrazones were determined by the two following methods: according to the charge transfer band of hydrazone-chloranil charge transfer complexes and<br />by means of quantum-chemical calculations of hydrazone molecules to interpret the results obtained. In the course of quantum-chemical calculations the conjugation character was also determined in the molecules of benzaldehyde diphenylhydrazones.
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GRUBIN, H. L., and H. L. CUI. "SPIN DEPENDENT TRANSPORT IN QUANTUM AND CLASSICALLY CONFIGURED DEVICES." International Journal of High Speed Electronics and Systems 16, no. 02 (June 2006): 639–58. http://dx.doi.org/10.1142/s0129156406003904.
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This paper presents of development of quantum transport equations for barrier devices with both electron and hole transport in dilute magnetic semiconductor (DMS) structures. The equations are developed from the time dependent equation of motion of the density matrix equation in the coordinate representation, from which both the spin drift and diffusion and transient Wigner equations are obtained, for a system in which high 'g' factor materials result in significant spin-splitting of the valence and conduction bands. Then for a structure in which the DMS layer is confined to the first barrier solutions to the coupled Poisson's and spin dependent Wigner equations yield the IV and carrier distributions. Negative differential conductance as well as the significant unequal spinup and spin down charge distributions are obtained.
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Bogach, A. V., S. V. Demishev, K. Flachbart, S. Gabani, V. V. Glushkov, A. V. Levchenko, N. Y. Shitsevalova, D. N. Sluchanko, and N. E. Sluchanko. "Magnetic Phase Diagram and Charge Transport in TmB12." Solid State Phenomena 152-153 (April 2009): 45–48. http://dx.doi.org/10.4028/www.scientific.net/ssp.152-153.45.
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High precision measurements of magnetoresistance =f(T,H) and magnetization M(T,H) have been carried out on single crystals of rare earth dodecaboride TmB12 at temperatures 1.8–30 K in magnetic fields up to 80 kOe. The high accuracy measurements and precise temperature stabilization allowed us to perform numerical differentiation and analyze quantitatively a behavior of derivative d()/dH=f(T,H) and magnetic susceptibility (T,H)=dM/dH in paramagnetic and magnetically ordered phases of thulium dodecaboride. It was shown that negative magnetoresistance anomalies observed in present study in paramagnetic state of TmB12 can be consistently interpreted in frameworks of a simple relation between resistivity and magnetization - /M2 proposed by K. Yosida (Phys. Rev., 107, 396 (1957)). A local magnetic susceptibility loc(T,H)=(1/H(d(/)/dH))1/2 was deduced directly from the magnetoresistance measurements and compared with bulk susceptibility (T,H)=dM/dH results of the present study. Moreover, the susceptibility dependences loc(T,H) and (T,H) have been applied to analyze in detail the H-T magnetic phase diagram of TmB12.
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Khrypunov, G., A. Meriuts, H. Klochko, T. Shelest, and A. Khrypunova. "Investigation of Thin Film Solar Cells on CdS/CdTe Base with Different Back Contacts." Advances in Science and Technology 74 (October 2010): 119–23. http://dx.doi.org/10.4028/www.scientific.net/ast.74.119.
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The peculiarities of photo-electric processes in thin film CdS/CdTe solar cells (SC) with different back electrodes (Cu/Au, ITO, Cu/ITO) have been studied. As it was established by capacitance – voltage (C – V) characteristics, the potential barrier heights for CdTe/Cu/Au and CdTe/ITO were 0.3 eV and 2.2 eV, respectively. The concentrations of charge carriers near back contact consisted 91020 m–3 and 21021 m–3, respectively. A high carrier concentration and high potential barrier of the ITO back contact caused the tunnel – recombination mechanism of the charge transport. The investigations of CdS/CdTe/ITO SC spectral photosensitivity testify a negative impact of the developed grain-boundary surface of the base layer on the processes of diffusion and separation of non-equilibrium current carriers generated by short-wave radiation. It is shown that the deposition of Cu nanolayer before the deposition of ITO films give stable efficiency 10 % for bifacial CdS/CdTe solar cells.
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Viglin, N. A., V. V. Ustinov, T. N. Pavlov, and V. M. Tsvelihovskaya. "Quantum Amplifier with Spin-Polarized Electrons Injection." Solid State Phenomena 168-169 (December 2010): 43–46. http://dx.doi.org/10.4028/www.scientific.net/ssp.168-169.43.
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A promising idea to use the transport of spin-polarized conduction electrons in a magnetic hetero-structure in order to invert population of the charge-carrier spin level in one of its layers, aiming at creation of an active environment for the electromagnetic radiation amplification, has been realized in a number of FMС/SC structures in which FMС is a ferromagnetic conductor and SC is a semiconductor. The n-InSb single crystals, featured by a high mobility of charge carriers, narrow ESR line, and anomalously high absolute value of the negative g-factor (g = −52), were used as SC. The following materials were used as FMC playing a role of spin polarizer: (i) ferromagnetic semiconductors EuO0.98Gd0.02O and HgCr2Se4, (ii) Geisler alloys Co2MnSn, Ni2MnSn and Co2MnSb. We have demonstrated that the spin-polarized electrons injection into the n-InSb semiconductor from the above-mentioned ferromagnetic materials results in a generation of the laser-type electromagnetic radiation.
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Dani, J. A., and G. Eisenman. "Monovalent and divalent cation permeation in acetylcholine receptor channels. Ion transport related to structure." Journal of General Physiology 89, no. 6 (June 1, 1987): 959–83. http://dx.doi.org/10.1085/jgp.89.6.959.
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Single channel patch-clamp techniques were used to study nicotinic acetylcholine receptors in cultured rat myotubes. The single channel conductance in pure cesium and sodium levels off at high concentrations, as if a binding site within the channel were saturating. The conductances at very low concentrations, however, are larger than predicted by the simplest one-site transport model fitted to the high-concentration data. At low concentrations, the current-voltage relations are inwardly rectifying, but they become more ohmic if a small amount of divalent cations is added externally. Magnesium and barium are good permeants that have rather high affinities for the channel. Upon adding low millimolar concentrations of these divalent cations externally to a membrane bathed in pure cesium, the inward current carried by cesium is decreased. As more divalent cations are added, the inward-going currents continued to decrease and the divalent cation replaces cesium as the main current carrier. The ion transport data are described by considering the size, shape, and possible net charge of the channel. In that way, even the complex features of transport are explained in a realistic physical framework. The results are consistent with the channel having long, wide, multiply occupied vestibules that serve as transition zones to the short, selective, singly occupied narrow region of the channel. A small amount of net negative charge within the pore could produce concentration-dependent potentials that provide a simple explanation for the more complicated aspects of the permeation properties.
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Kulanchikov, Yu O., P. S. Vergeles, and E. B. Yakimov. "Low-energy electron beam irradiation effect on Al/SiO2/Si structure voltage-farad characteristics." Izvestiya Vysshikh Uchebnykh Zavedenii. Materialy Elektronnoi Tekhniki = Materials of Electronics Engineering 22, no. 2 (December 10, 2019): 112–17. http://dx.doi.org/10.17073/1609-3577-2019-2-112-117.
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The effect of electron irradiation with energy of 2.5 keV on the MOS structure Al/SiO2/Si capacitance-voltage (C-V) characteristics have been studied. At chosen beam energy the electron penetration depth is lower than the dielectric thickness that allows to reveal the contribution of excess carrier transport to the trap formation on the SiO2/Si interface. It was established that the electron beam irradiation leads to a significant change in the C-V characteristics slope, i.e. to to the trap formation at the interface. A study of effect of bias applied to the investigated structure before and during the electron beam irradiation was carried out. It was established that while the bias applied before irradiation practically did not affect the C-V characteristics of the investigated MOS structure, the positive voltage applied to metallization during irradiation produced a pronounced effect on the C-V curve changes. At the same time the C-V characteristics after irradiation with zero and negative voltage were very similar. The investigation of stability of changes produced by the electron beam irradiation showed that the C-V curves are slowly restored even at room temperature. An applied negative bias was found to slow down the charge relaxation process.
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Singh, Jitendra, R. G. Singh, Subodh K. Gautam, Himanshi Gupta, Sunil Ojha, and Fouran Singh. "Swift heavy ion irradiation induced negative differential resistance and transport of charge carriers in conducting polymer-metal oxide hybrids." Radiation Physics and Chemistry 179 (February 2021): 109211. http://dx.doi.org/10.1016/j.radphyschem.2020.109211.
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Reichel, Andreas, David J. Begley, and N. Joan Abbott. "Carrier-Mediated Delivery of Metabotropic Glutamate Receptor Ligands to the Central Nervous System: Structural Tolerance and Potential of the l-system Amino Acid Transporter at the Blood-Brain Barrier." Journal of Cerebral Blood Flow & Metabolism 20, no. 1 (January 2000): 168–74. http://dx.doi.org/10.1097/00004647-200001000-00021.
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The brain endothelial large neutral amino acid carrier (l-system) is well suited for facilitated drug transport to the brain because of its high transport capacity and relatively broad structural substrate tolerance. The authors have examined the potential of this transporter for central nervous system (CNS) delivery of a new family of compounds derived from the large neutral amino acid phenylglycine. These compounds are highly selective for specific isoforms of metabotropic glutamate receptors (mGluRs) but will only become effective therapeutics for CNS diseases such as ischemic disorders, stroke, and epilepsy if they can effectively cross the blood-brain barrier. Using the immortalized rat brain endothelial cell line RBE4 as in vitro blood-brain barrier model, the authors have studied the interaction of phenylglycine and selected derivatives with the l-system-mediated transport of l-[3H]-histidine. The transport of l-histidine was characteristic of the l-system in vivo with the following kinetic parameters: Km 135 ± 18 μmol/L, Vmax 15.3 ± 1.13 nmol/min/mg protein, and KD 2.38 ± 0.84 μL/min/mg protein. The affinities of the l-system for phenylglycine and the derivatives investigated increased in the order S-4-carboxy-phenylglycine (Ki = 16 mmol/L) < R-phenylglycine (2.2 mmol/L) < S-3-hydroxy-phenylglycine (48 μmol/L) < S-phenylglycine (34 μmol/L), suggesting that a negative charge at the side chain or R-configuration is detrimental for carrier recognition, whereas neutral side chain substituents are well tolerated. The authors have further shown (1) that the mode of interaction with the l-system of S-phenylglycine and S-3-hydroxy-phenylglycine is competitive, and (2) that the transporter carries these two agents into the cell as shown by high-performance liquid chromatography (HPLC) analysis of the RBE4 cell contents. The study provides the first evidence for the potential of S-phenylglycine derivatives for carrier-mediated delivery to the CNS and outlines the substrate specificity of the l-system at the blood-brain barrier for this class of mGluR ligands. As the affinities of S-phenylglycine and S-3-hydroxy-phenylglycine for the l-system carrier are even higher than those of some natural substrates, these agents should efficiently enter CNS via this route. Possible strategies for a synergistic optimization of phenylglycine-derived therapeutics with respect to desired activity at the CNS target combined with carrier-mediated delivery to overcome the blood-brain barrier are discussed.
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SCHLETTWEIN, D., J. P. MEYER, and N. I. JAEGER. "Intermolecular Interactions and Electrical Properties in Thin Films of Tetrapyridotetraazaporphyrinatozinc(II)." Journal of Porphyrins and Phthalocyanines 03, no. 07 (October 1999): 611–19. http://dx.doi.org/10.1002/(sici)1099-1409(199908/10)3:6/7<611::aid-jpp184>3.0.co;2-c.
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Tetrapyridotetraazaporphyrinatozinc ( TPyTAPZn ) can be looked at as a substituted phthalocyanine. Thin films of TPyTAPZn were prepared on quartz glass by physical vapour deposition under high-vacuum conditions. During the deposition, island growth was observed by a characteristic change in the electrical conduction, indicating an increasing number of conduction pathways along the film. Deposition conditions could be optimized to yield an ordered rather than amorphous growth as detected by a characteristic absorption band in the visible range, strongly red-shifted from the absorption of the monomeric molecule in solution. A negative Seebeck coefficient confirmed n-type conduction for TPyTAPZn . In temperature-dependent measurements of the electrical conductivity and thermopower across the samples an activation energy of 0.31 eV was established for the conductivity and of 0.04 eV for charge carrier generation. From this difference it is concluded that a thermally activated charge carrier transport mechanism (hopping) rather than delocalized conduction (band model) is dominant in TPyTAPZn . Photoconduction turned out to be rather small in these samples, although light was absorbed quite efficiently. The time dependence of photoconduction indicated a significant trap density. Interaction with ammonia or triethylamine in the gas phase led to an increase in the conductivity; oxygen or water led to a decrease. The time dependence of these interactions indicated that triethylamine and water were only reacting with the surface region, whereas NH 3 and O 2 were also diffusing into the bulk of the films.
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Albrecht, J. D., P. P. Ruden, and M. G. Ancona. "New Materials-Theory-Based Model for Output Characteristics of AlGaN/GaN Heterostructure Field Effect Transistors." MRS Internet Journal of Nitride Semiconductor Research 5, S1 (2000): 640–46. http://dx.doi.org/10.1557/s1092578300004877.
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A new model is used to examine the DC output characteristics of AlGaN/GaN heterostructure field effect transistors. The model is based on the charge-control/gradual-channel approximation and takes into account the non-linear current vs. voltage characteristics of the ungated AlGaN/GaN heterostructure channel regions. The model also includes thermal effects associated with device self-heating. For the power dissipation levels considered for many applications, the thermal degradation of the carrier drift velocity is shown to cause a negative output conductance in saturation. The temperature is incorporated self-consistently into the model through the field and temperature dependent mobility obtained from Monte Carlo transport simulations for electron transport in GaN. Calculated results presented for the DC output characteristics of several AlGaN/GaN field effect transistors show a strong dependence on the thermal properties of the substrate material. The substrate materials considered in this work are sapphire, SiC, AlN, and GaN.
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Lash, Lawrence H. "Mitochondrial glutathione in toxicology and disease of the kidneys." Toxicology Research 1, no. 1 (May 17, 2012): 39–46. http://dx.doi.org/10.1039/c2tx20021j.
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Abstract The tripeptide glutathione (GSH), comprised of the amino acids l-cysteine, glycine, and l-glutamate, is found in all cells of aerobic organisms and plays numerous, critical roles as an antioxidant and nucleophile in regulating cellular homeostasis and drug metabolism. GSH is synthesized exclusively in the cytoplasm of most cells by two ATP-dependent reactions. Despite this compartmentation, GSH is found in other subcellular compartments, including mitochondria. As the GSH molecule has a net negative charge at physiological pH, it cannot cross cellular membranes by diffusion. Rather, GSH is a substrate for a variety of anion and amino acid transporters. Two organic anion carriers in the inner membrane of renal mitochondria, the dicarboxylate carrier (DIC; Slc25a10) and the 2-oxoglutarate carrier (OGC; Slc25a11), are responsible for most of the transport of GSH from cytoplasm into mitochondrial matrix. Genetic manipulation of DIC and/or OGC expression in renal cell lines demonstrated the ability to produce sustained increases in mitochondrial GSH content, which then protected these cells from cytotoxicity due to several oxidants and mitochondrial toxicants. Several diseases and pathological states are associated with mitochondrial dysfunction and oxidative stress, suggesting that the mitochondrial GSH pool may be a therapeutic target. One such disease that is of particular concern for public health is diabetic nephropathy. Another chronic, pathological state that is associated with bioenergetic and redox changes is compensatory renal hypertrophy that results from reductions in functional renal mass. This review summarizes pathways of mitochondrial GSH transport and discusses studies on its manipulation in toxicological and pathological states.
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SHCHUROVA, LJUDMILA, and VLADIMIR KULBACHINSKII. "THE THERMODYNAMIC, TRANSPORT AND MAGNETOTRANSPORT PROPERTIES OF Mn-DOPED GaAs/InGaAs/GaAs QUANTUM WELL WITH FERROMAGNETISM." International Journal of Modern Physics B 23, no. 17 (July 10, 2009): 3596–601. http://dx.doi.org/10.1142/s0217979209063031.
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We have investigated the thermodynamic, transport and magnetotransport properties of free charge carriers in a diluted magnetic semiconductor with a quantum well In0.17Ga0.83As in GaAs with δ-doped by C and Mn. In order to determine the density of the holes in a quantum well, we carried out thermodynamic calculations of the system of free holes, atoms Mn0 and ions Mn-. We calculated the temperature dependence of resistance and magnetoresistance of holes in the quantum well. The contributions of various scattering mechanisms of holes to the resistance were analyzed. The negative magnetoresistance are explained as the reduction of spin-flip scattering by aligning spins of the magnetic field.
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Schwab, S. J., and M. R. Hammerman. "Electrogenic Na+-independent Pi transport in canine renal basolateral membrane vesicles." American Journal of Physiology-Renal Physiology 250, no. 3 (March 1, 1986): F419—F424. http://dx.doi.org/10.1152/ajprenal.1986.250.3.f419.
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To define the mechanism by which Pi exists from the renal proximal tubular cell across the basolateral membrane, we measured 32Pi uptake in basolateral membrane vesicles from dog kidney in the absence of Na+. Preloading of basolateral vesicles with 2 mM Pi transstimulated 32Pi uptake, which is consistent with counterflow. We used measurements of transstimulation to quantitate the transport component of 32Pi uptake. Transstimulation of 32Pi uptake was inhibited less than 30% by concentrations of probenecid as high as 50 mM. In contrast, transstimulation of 35SO4(2-) uptake by intravesicular SO4(2-) was inhibited 92% by 5 mM probenecid. Preloading basolateral vesicles with SO4(2-) did not result in transstimulation of 32Pi uptake. Accumulation of 32Pi in basolateral vesicles above steady state was driven by a membrane potential (intravesicular positive), consistent with Na+-independent Pi transport being accompanied by the net transfer of negative charge across the membrane. We conclude that carrier-mediated, electrogenic Na+-independent 32Pi transport can be demonstrated in basolateral vesicles from dog kidney. This process appears to be mediated, at least in part, via a mechanism different from that by which SO4(2-) is transported. Electrogenic Na+-independent Pi transport may reflect one means by which Pi reabsorbed across the luminal membrane exists from the proximal tubular cell down an electrochemical gradient.
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SCHLETTWEIN, D., J. P. MEYER, and N. I. JAEGER. "Influence of Mn as a redox-active central metal on the electrical conduction behaviour of phthalocyanine thin films." Journal of Porphyrins and Phthalocyanines 04, no. 01 (January 2000): 23–30. http://dx.doi.org/10.1002/(sici)1099-1409(200001/02)4:1<23::aid-jpp181>3.0.co;2-6.
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Thin films of phthalocyaninatomanganese ( PcMn ) in the thickness range of 100 nm have been prepared by vapour deposition on quartz glass substrates. The films were characterized in situ during film growth and following film deposition by measurements of the electrical conductivity under DC applied electric fields parallel to the substrate surface. The dependence of the conductivity on the average film thickness was determined and the mechanism of film growth is discussed. Without breaking the vacuum, a temperature gradient was established again parallel to the substrate surface and a thermopower was detected. Its dependence on the size of the temperature gradient gave a Seebeck coefficient of –780 μV K-1 at 460 K. From the negative sign it is evident that electrons are the majority carriers in PcMn in a freshly prepared thin film. The temperature dependence of the Seebeck coefficient gave the thermal activation of charge carrier generation as ΔE = 0.19 eV , which is discussed in terms of the position of the Fermi energy in the films. The temperature dependence of the electrical conductivity gave an activation energy EA = 0.38 eV considerably higher, indicating a thermal activation of charge carrier transport and hence supporting a hopping mechanism rather than delocalized transport. Under exposure to oxygen the conductivity showed a fast small increase followed by a slow large decrease, which is discussed considering surface as well as bulk interactions. Hole conduction was measured for the completely oxidized films by a positive Seebeck coefficient. Optical spectroscopy performed ex situ was used to allow further discussion of redox interactions of the films. Evidence was found for the presence of Pc (-2) Mn (+3) O 2(-1) as well as Pc (-2) Mn (+3) O (-2) Mn (+3) Pc (-2) and Pc (-2) Mn (+2) in freshly prepared films. Films exposed to air for as long as several months were completely oxidized to Pc (-2) Mn (+3) O 2(-1).
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Fung, A. W. P., Z. H. Wang, K. Lu, M. S. Dresselhaus, and R. W. Pekala. "Characterization of carbon aerogels by transport measurements." Journal of Materials Research 8, no. 8 (August 1993): 1875–85. http://dx.doi.org/10.1557/jmr.1993.1875.
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Carbon aerogels are a special class of low-density microcellular foams. These materials are composed of interconnected carbon particles with diameters of approximately 10 nm. The temperature dependence of the dc electrical resistivity and magnetic susceptibility (χ) from 4 K to room temperature, magnetoresistance (MR) in a magnetic field up to 15 T, and Raman scattering were measured as a function of aerogel density. While Raman scattering measurements are not sensitive to variations in density, the χ data show that there are more free carriers in samples of higher density. Aerogel samples with different densities all show a negative temperature coefficient of resistivity and a positive MR. The less dense samples exhibit a stronger temperature dependence of resistivity and a stronger field dependence of the MR, indicating that with decreasing density and increasing porosity, charge carriers are more localized. Data analysis precludes variable-range hopping in favor of nearest-neighbor hopping and fluctuation-induced tunneling as the most likely conduction mechanisms for carbon aerogels.
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Yang, Shengyi, and Bingsuo Zou. "To observe bidirectional negative differential resistance at room temperature by narrowing transport channels for charge carriers in vertical organic light-emitting transistor." Organic Electronics 14, no. 1 (January 2013): 362–69. http://dx.doi.org/10.1016/j.orgel.2012.10.037.
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Xu, M., G. C. Montanari, D. Fabiani, L. A. Dissado, and A. Krivda. "A New Ultra Fast Conduction Mechanism in Insulating Polymer Nanocomposites." Journal of Nanotechnology 2011 (2011): 1–11. http://dx.doi.org/10.1155/2011/985801.
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A brand new phenomenon, namely, electrical conduction via soliton-like ultra fast space charge pulses, recently identified in unfilled cross-linked polyethylene, is shown for the first time to occur in insulating polymer nanocomposites and its characteristics correlated with the electromechanical properties of nanostructured materials. These charge pulses are observed to cross the insulation under low electrical field in epoxy-based nanocomposites containing nanosilica particles with relative weights of 1%, 5%, 10%, and 20% at speeds orders of magnitude higher than those expected for carriers in insulating polymers. The characteristics of mobility, magnitude and repetition rate for both positive and negative charge pulses are studied in relation to nanofiller concentration. The results show that the ultra fast charge pulses (packets) are affected significantly by the concentration of nanoparticles. An explanation is presented in terms of a new conduction mechanism where the mechanical properties of the polymer and movement of polymer chains play an important role in the injection and transport of charge in the form of pulses. Here, the charge transport is not controlled by traps. Instead, it is driven by the contribution of polarization and the resultant electromechanical compression, which is substantially affected by the introduction of nanoparticles into the base polymer.
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Ramazanov, V. V., A. Yu Semenchenko, and S. V. Rudenko. "RESTORATION OF ERYTHROCYTE MORPHOLOGY AFTER CRYOPRESERVATION." Актуальні проблеми сучасної медицини: Вісник Української медичної стоматологічної академії 21, no. 1 (March 21, 2021): 101–8. http://dx.doi.org/10.31718/2077-1096.21.1.101.
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During the erythrocyte transfusion, a significant part of the cells (~ 25%) is utilized by the spleen and liver in a day due to the deformations and damage to cell membranes that resulted from the hypothermic storage or cryopreservation. An increase in free iron in the blood during the decomposition of red blood cells leads to the stimulation of oxidative stress and inflammation, as well as to dysfunction of the main organs. The primary indicator of damage to the membranes of erythrocytes can be detected through the changes in their morphology. The work investigated the morphological characteristics of erythrocytes after cryopreservation in a medium containing PEG-1500 and 1,2-PD. Erythrocytes washed after thawing and suspended in an isotonic NaCl solution are represented by echinocytes, at the same time, when placed into a solution with albumin, the cells demonstrate the restoration of their discoid shape. According to the well-established concept, the regulation of the shape of erythrocytes is determined by a change in the conformation of the anionic carrier, which is formed by the main integral membrane protein, the protein of band 3. The study has shown that the treatment of erythrocytes with DIDS, which leads to the fixation of the conformation of the carrier with the transport site facing the outer side of the membrane, does not change the morphomodulatory effect of albumin. At the same time, with a decrease in the medium pH, when the albumin charge approaches zero, its effect is eliminated. The results obtained suggest that, upon freezing-thawing of erythrocytes, the deterioration of hydrophobic interactions of transmembrane segments of the protein of band 3 is accompanied by a change in the balance of electrostatic interactions. Probably, the action of albumin is carried out due to the restoration and stabilization of the indicated balance of membranes, charactestic of the typical eruthrocyte discoid shape. Restoration of the morphology of cryopreserved erythrocytes before the transfusion can help reduce cell deformation, improve systemic hemodynamics and prevent the development of negative clinical consequences.
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Madsen, Karen. "Intestinal Absorption of Bile Salts." Canadian Journal of Gastroenterology 4, no. 2 (1990): 79–84. http://dx.doi.org/10.1155/1990/624985.
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Bile acids are secreted from the liver into the duodenum where they aid in the digestion and absorption of dietary lipids. Absorption of bile acids occurs through both ionic and nonionic diffusion in the jejunum and colon and through an active sodium ion-dependent carrier mechanism in the ileum. The prima, y bile acids synthesized in the liver can be converted by intestinal bacteria into secondary and tertiary bile acids. Bile acids may also be conjugated with glycine or taurine which results in an increase in the hydrophilicity and solubility of these compounds at physiological pH. The amount of passive diffusion of bile acids that occurs across the brush border membrane along the length of the entire intestine depends upon the ratio of ionized to nonionized bile acids coupled with the bile salt concentration and the individual permeability coefficients of monomers. Active transport of both conjugated and nonconjugated species of bile acids depends upon the presence of a single negative charge on the side chain. Maximal transport rates for bile acids are related to the number of hydroxyl groups present while the Michaelis-Menten constant for transport is dependent upon whether or not the bile acid is conjugated. Although active uptake of bile acids from the ileum has been considered the major route for bile salt absorption in the small intestine, the mechanism may actually be responsible for only a small proportion of the total bile acid pool absorbed from the lumen.
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Christen, Thomas. "Nonequilibrium Phase Transition and Current Filaments in Extrinsic Semiconductors." Zeitschrift für Naturforschung A 49, no. 9 (September 1, 1994): 851–55. http://dx.doi.org/10.1515/zna-1994-0906.
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Abstract A phenomenological model for charge transport in extrinsic semiconductors is presented. For shallow impurities, large saturated impact-ionization coefficient and sufficiently low lattice temperature, the current-field characteristic is S-shaped (SNDC) due to the interplay between impact ionization and scattering of carriers from acoustic phonons, ionized and neutral impurities. The present model provides and explanation of the experimentally observed disappearance of SNDC above a critical lattice temperature. In the region of negative differential conductivity where a current-controlled uniform state is unstable, current filaments are calculated numerically.
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Chuang, Chiashain, Chieh-Wen Liu, Yanfei Yang, Wei-Ren Syong, Chi-Te Liang, and Randolph Elmquist. "Magnetoresistance of Ultralow-Hole-Density Monolayer Epitaxial Graphene Grown on SiC." Materials 12, no. 17 (August 23, 2019): 2696. http://dx.doi.org/10.3390/ma12172696.
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Silicon carbide (SiC) has already found useful applications in high-power electronic devices and light-emitting diodes (LEDs). Interestingly, SiC is a suitable substrate for growing monolayer epitaxial graphene and GaN-based devices. Therefore, it provides the opportunity for integration of high-power devices, LEDs, atomically thin electronics, and high-frequency devices, all of which can be prepared on the same SiC substrate. In this paper, we concentrate on detailed measurements on ultralow-density p-type monolayer epitaxial graphene, which has yet to be extensively studied. The measured resistivity ρxx shows insulating behavior in the sense that ρxx decreases with increasing temperature T over a wide range of T (1.5 K ≤ T ≤ 300 K). The crossover from negative magnetoresistivity (MR) to positive magnetoresistivity at T = 40 K in the low-field regime is ascribed to a transition from low-T quantum transport to high-T classical transport. For T ≥ 120 K, the measured positive MR ratio [ρxx(B) − ρxx(B = 0)]/ρxx(B = 0) at B = 2 T decreases with increasing T, but the positive MR persists up to room temperature. Our experimental results suggest that the large MR ratio (~100% at B = 9 T) is an intrinsic property of ultralow-charge-density graphene, regardless of the carrier type. This effect may find applications in magnetic sensors and magnetoresistance devices.
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Fan, Xiangpeng, Yijun Zhang, Guangshu Zhang, and Dong Zheng. "Lightning Characteristics and Electric Charge Structure of a Hail-Producing Thunderstorm on the Eastern Qinghai–Tibetan Plateau." Atmosphere 9, no. 8 (July 29, 2018): 295. http://dx.doi.org/10.3390/atmos9080295.
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An isolated hail-producing thunderstorm that occurred on 20 August 2012, from the Composite Observing Experiment for Lightning project carried out in the Da Tong Region of Qinghai Province, China, was studied. In most stages, the charge structure in the storm showed a positive tripole structure, which resulted in a low positive ground lightning rate for the whole event. In the thunderstorm process, 202 lightning flashes were detected. The peak lightning rate of lightning was 28 times/5 min. The average number of return strokes of negative ground flash was 2.4, and only one return stroke of positive ground lightning occurred. The duration of the in-cloud process prior to the first return stroke was relatively long. Dynamic transport had a considerable influence on the charge structure of the cloud. Before and after hail landing, the ground electric field of several stations showed a consistent trend of reversal.
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Kadam, Abhijit, Md Moniruzzaman, and Sang-Wha Lee. "Dual Functional S-Doped g-C3N4 Pinhole Porous Nanosheets for Selective Fluorescence Sensing of Ag+ and Visible-Light Photocatalysis of Dyes." Molecules 24, no. 3 (January 27, 2019): 450. http://dx.doi.org/10.3390/molecules24030450.
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This study explores the facile, template-free synthesis of S-doped g-C3N4 pinhole nanosheets (SCNPNS) with porous structure for fluorescence sensing of Ag+ ions and visible-light photocatalysis of dyes. As-synthesized SCNPNS samples were characterized by various analytical tools such as XRD, FT-IR, TEM, BET, XPS, and UV–vis spectroscopy. At optimal conditions, the detection linear range for Ag+ was found to be from 0 to 1000 nM, showing the limit of detection (LOD) of 57 nM. The SCNPNS exhibited highly sensitive and selective detection of Ag+ due to a significant fluorescence quenching via photo-induced electron transfer through Ag+–SCNPNS complex. Moreover, the SCNPNS exhibited 90% degradation for cationic methylene blue (MB) dye within 180 min under visible light. The enhanced photocatalytic activity of the SCNPNS was attributed to its negative zeta potential for electrostatic interaction with cationic dyes, and the pinhole porous structure can provide more active sites which can induce faster transport of the charge carrier over the surface. Our SCNPNS is proposed as an environmental safety tool due to several advantages, such as low cost, facile preparation, selective recognition of Ag+ ions, and efficient photocatalytic degradation of cationic dyes under visible light.
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He, Pan, Kyoji Hagiwara, Hui Chong, Hsiao-hua Yu, and Yoshihiro Ito. "Low-Molecular-Weight Polyethyleneimine Grafted Polythiophene for Efficient siRNA Delivery." BioMed Research International 2015 (2015): 1–9. http://dx.doi.org/10.1155/2015/406389.
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Owing to its hydrophilicity, negative charge, small size, and labile degradation by endogenous nucleases, small interfering RNA (siRNA) delivery must be achieved by a carrier system. In this study, cationic copolymers composed of low-molecular-weight polyethylenimine and polythiophenes were synthesized and evaluated as novel self-tracking siRNA delivery vectors. The concept underlying the design of these copolymers is that hydrophobicity and rigidity of polythiophenes should enhance the transport of siRNA across the cell membrane and endosomal membrane. A gel retardation assay showed that the nanosized complexes formed between the copolymers and siRNA were stable even at a molar ratio of 1 : 2. The high cellular uptake (>80%) and localization of the copolymer vectors inside the cells were easily analyzed by tracking the fluorescence of polythiophene using fluorescent microscopy and cytometry. Anin vitroluciferase knockdown (KD) assay in A549-luc cells demonstrated that the siRNA complexes with more hydrophobic copolymers achieved a higher KD efficiency of 52.8% without notable cytotoxicity, indicating protein-specific KD activity rather than solely the cytotoxicity of the materials. Our polythiophene copolymers should serve as novel, efficient, low cell toxicity, and label-free siRNA delivery systems.
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Miyazawa, Satoru, Reina Hosono, Ryota Osuga, Junko Nomura Kondo, and Sayaka Uchida. "Effect of the ammonium ion on proton conduction in porous ionic crystals based on Keggin-type silicododecatungstate." Acta Crystallographica Section C Structural Chemistry 74, no. 11 (October 17, 2018): 1289–94. http://dx.doi.org/10.1107/s2053229618008227.
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Proton conduction in crystalline porous materials has received much attention from basic scientific research through to practical applications. Polyoxometalates (POMs) can efficiently transport protons because of their small superficial negative charge density. A simple method for enhancing proton conductivity is to introduce NH4 + into the crystal structure, because NH4 + can form hydrogen bonds and function as a proton carrier. According to these considerations, NH4 + was introduced into the porous structure of A 2[Cr3O(OOCH)6(etpy)3]2[α-SiW12O40]·nH2O (A = Li, Na, K and Cs; etpy = 4-ethylpyridine) (I-A+ ) via topotactic cation exchange. The resulting compound, diammonium tris(4-ethylpyridine)hexaformatooxidotrichromium α-silicododecatungstate hexahydrate, (NH4)2[Cr3(CHO2)6O(C7H9N)3]2[α-SiW12O40]·6H2O, showed high proton conductivity and low activation energy under high relative humidity (RH), suggesting that protons migrate efficiently via rearrangement of the hydrogen-bonding network formed by the NH4 + cations and the waters of crystallization (Grotthuss mechanism). The proton conductivity and activation energy greatly decreased and increased, respectively, with the decrease in RH, suggesting that protons migrate as NH4 + and/or H3O+ under low RH (vehicle mechanism).
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Zaitsev, Anton D., Petr S. Demchenko, Dmitry V. Zykov, Ekaterina A. Korotina, Elena S. Makarova, Ivan L. Tkhorzhevskiy, Anastasiia S. Tukmakova, et al. "Optical and Galvanomagnetic Properties of Bi1-xSbx Thin Films in the Terahertz Frequency Range." Applied Sciences 10, no. 8 (April 15, 2020): 2724. http://dx.doi.org/10.3390/app10082724.
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We report results of galvanomagnetic and terahertz time-domain spectroscopy measurements on thin films of Bi 1 − x Sb x on polyimide and mica substrates with various antimony concentrations (x from 0 to 15 %) and film thickness (70, 150 nm). The resistivity, Hall coefficient and magnetoresistivity of the films were measured experimentally in the magnetic field of 0.65 T at room temperature. Mobility and concentration of electrons and holes in the film plane were calculated using the transport coefficients. The terahertz time-domain spectroscopy is used to measure the complex conductivity and permittivity of Bi 1 − x Sb x thin films on the dielectric substrates in the frequency range from 0.2 to 1 THz. The plasma frequency, relaxation time, DC conductivity and effective carrier mass were extracted from these data and evaluated as functions of the Sb concentration for different film thickness and substrate. We observed that the film magnetoresistivity decreases with increasing the Sb concentration and for most of the films the Hall coefficient is negative and depends on the external factors insignificantly. We show that the mobility of charge carriers weakly depends on Sb concentration, which confirms the assertion about the scattering of carriers on themselves and not on defects in the structure. It was revealed that film static and dynamic resistivity (conductivity) as well as dielectric permittivity depend on Sb content and the film thickness. The results may be used for development of various thermoelectric, electronic and optical devices, such as THz detectors or components which can control the properties of THz radiation.
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Kulanchikov, Yuriy O., Pavel S. Vergeles, and Eugene B. Yakimov. "Effect of low-energy electron irradiation on voltage-capacity curves of Al/SiO2/Si structure." Modern Electronic Materials 5, no. 4 (December 31, 2019): 175–79. http://dx.doi.org/10.3897/j.moem.5.4.52311.
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Charging of dielectric targets by electron irradiation is a well-known phenomenon which should be taken into account in characterization of dielectric materials and coatings with electron microscopy, in electron beam lithography, in development of dielectric coatings for spacecrafts and other fields of science and engineering. Charging kinetics is strongly affected by spatial distribution of electrons and holes formed by irradiation. At the experimental electron beam energy electron penetration depth is smaller than dielectric thickness and this allows identifying the contribution of excess carrier transport to trap formation at the SiO2/Si interface. Low-energy electron beams have been shown to substantially affect C–V curve slope, i.e., to form traps at the interface. We have studied the effect of bias applied to the test structure before and after electron beam irradiation. The experiment has shown that bias of either polarity applied to the test MOS structure before low-energy electron beam irradiation practically does not affect the C–V curves of the test structure. Positive bias applied to the metallization layer during low-energy electron beam irradiation has a strong effect on the C–V curve pattern while negative bias affects the C–V curves but slightly. Study of the stability of the changes caused by electron beam irradiation has shown that the C–V curves of the test structure restore slowly even at room temperature. Application of negative bias decelerated charge relaxation.
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Schneider, Sabine, Katherine H. Sharp, Paul D. Barker, and Max Paoli. "An Induced Fit Conformational Change Underlies the Binding Mechanism of the Heme Transport Proteobacteria-Protein HemS." Journal of Biological Chemistry 281, no. 43 (August 30, 2006): 32606–10. http://dx.doi.org/10.1074/jbc.m607516200.
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Bacteria rely on their environment and/or host to acquire iron and have evolved specialized systems to sequester and transport heme. The heme uptake system HemRSTUV is common to proteobacteria, and a major challenge is to understand the molecular mechanism of heme binding and transfer between the protein molecules that underlie this heme transport relay process. In the Gram-negative pathogen Yersinia enterocolitica, the HemRSTUV system culminates with the cytoplasmic recipient HemS, which stores and delivers heme for cellular needs. HemS belongs to a family of proteins essential and unique to proteobacteria. Here we report on the binding mechanism of HemS based on structural data from its apo- and ligand-loaded forms. This heme carrier protein associates with its cargo through a novel, partly preformed binding pocket, formed between a large β-sheet dome and a three-helix subdomain. In addition to a histidine interacting with the iron, the complex is stabilized by a distal non-coordinating arginine that packs along the porphyrin plane and extensive electrostatic contacts that firmly anchor the heme propionate groups within the protein. Comparison of apo- and ligand-bound HemS crystal structures reveals striking conformational changes that underlie a “heme-induced fit” binding mechanism. Local shifts in amino acid positions combine with global, rigid body-like domain movements, and together, these bring about a switch from an open, apo-form to a closed, bound state. This is the first report in which both liganded and unliganded forms of a heme transport protein are described, thus providing penetrating insights into its mechanism of heme binding and release.
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AGRAWAL (GARG), NEETU, SANKALPA GHOSH, and MANISH SHARMA. "ELECTRON OPTICS WITH DIRAC FERMIONS: ELECTRON TRANSPORT IN MONOLAYER AND BILAYER GRAPHENE THROUGH MAGNETIC BARRIER AND THEIR SUPERLATTICES." International Journal of Modern Physics B 27, no. 10 (April 20, 2013): 1341003. http://dx.doi.org/10.1142/s0217979213410038.
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In this review article we discuss the recent progress in studying ballistic transport for charge carriers in graphene through highly inhomogeneous magnetic field known as magnetic barrier in combination with gate voltage induced electrostatic potential. Starting with cases for a single or double magnetic barrier we also review the progress in understanding electron transport through the superlattices created out of such electromagnetic potential barriers and discuss the possibility of experimental realization of such systems. The emphasis is particularly on the analogy of such transport with propagation of light wave through medium with alternating dielectric constant. In that direction we discuss electron analogue of optical phenomena like Fabry–Perot resonances, negative refraction, Goos–Hänchen effect, beam collimation in such systems and explain how such analogy is going to be useful for device generation. The resulting modification of band structure of Dirac fermions, the emergence of additional Dirac points was also discussed accompanied by brief section on the interconvertibility of electric and magnetic field for relativistic Dirac fermions. We also discuss the effect of such electromagnetic potential barrier on bilayer graphene (BLG) in a similar framework.
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Qi, Yanjiao, Yaming Zhao, Xiaoe Wang, Huining Lu, and Nengzhi Jin. "Comparative analysis of interactions between the hydropyridine dicarboxylate derivatives and different proteins by molecular docking and charge density analysis." Journal of Theoretical and Computational Chemistry 15, no. 06 (September 2016): 1650050. http://dx.doi.org/10.1142/s0219633616500504.
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Molecular docking and charge density analysis were carried out to understand the geometry, charge density distribution and electrostatic properties of one of newly synthesized 4-substituted-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylates (PDE), which is regarded as the best [Formula: see text]-Glucosidase inhibitor among the hydropyridine dicarboxylate derivatives. The different bonding models of the PDE molecule in the active sites of proteins Human serum albumin (HSA) and Saccharomyces cerevisiae [Formula: see text]-glucosidase (SAG) are firstly compared, which is important to understand the different intermolecular interactions between drug-transport protein and drug-target protein. The deformation density maps suggest that the electron densities of the PDE molecule are redistributed when it presents in the active sites. When the molecule presents in the active site of the SAG, it is evident to find that the negative region does not appear at the vicinity of the oxygen atoms on one of the carboxylic acid dimethyl ester group. Frontier molecular orbital density distributions for the PDE molecule are similar in all forms. The highest occupied molecular orbital (HOMO) and lowest occupied molecular orbital (LUMO) energy gaps in the active sites are higher than that of the molecule in pure solution phase. It is generally noticed that all of the orientations of the dipole moment vectors are reoriented in both active sites. These fine details at electronic level allow to better understand the exact drug-transport protein and drug-target protein interactions.
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Prapan, Ausanai, Nittiya Suwannasom, Chiraphat Kloypan, Saranya Chaiwaree, Axel Steffen, Yu Xiong, Ijad Kao, Axel Pruß, Radostina Georgieva, and Hans Bäumler. "Surface Modification of Hemoglobin-Based Oxygen Carriers Reduces Recognition by Haptoglobin, Immunoglobulin, and Hemoglobin Antibodies." Coatings 9, no. 7 (July 21, 2019): 454. http://dx.doi.org/10.3390/coatings9070454.
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Hemoglobin-based oxygen carriers (HBOCs) represent a propitious type of blood substitute to transport oxygen throughout the body while acting as a carrier in biomedical applications. However, HBOCs in blood are recognized and rapidly scavenged by the body’s innate immune systems. To overcome this problem, HBOCs require a surface modification that provides protection against detection and elimination in order to prolong their circulation time after administration. In this study, we investigated different surface modifications of hemoglobin submicron particles (HbMPs) by double/triple precipitation, as well as by adsorption of human serum albumin (HSA), hyaluronic acid (HA), and pluronic (Plu) to discover how diverse surface modifications influence the oxygen binding capacity and the binding of anti-hemoglobin (Hb) antibodies, immunoglobulin G (IgG), and haptoglobin (HP) to HbMPs. The particle size and zeta potential of the six types of HbMP modifications were analyzed by zeta sizer, confocal laser scanning microscopy, and transmission electron microscopy (TEM), and were compared to the unmodified HbMPs. The results revealed that all surface-modified HbMPs had a submicron size with a negative charge. A slight decrease in the oxygen binding capacity was noticed. The specific binding of anti-Hb antibodies, IgG, and HP to all surface-modified HbMPs was reduced. This indicates a coating design able to protect the particles from detection and elimination processes by the immune system, and should lead to a delayed clearance and the required and essential increase in half-life in circulation of these particles in order to fulfill their purpose. Our surface modification method reflects a promising strategy for submicron particle design, and can lead the way toward novel biomedical applications.
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Khan, Fasihullah, Waqar Khan, and Sam-Dong Kim. "High-Performance Ultraviolet Light Detection Using Nano-Scale-Fin Isolation AlGaN/GaN Heterostructures with ZnO Nanorods." Nanomaterials 9, no. 3 (March 15, 2019): 440. http://dx.doi.org/10.3390/nano9030440.
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Owing to their intrinsic wide bandgap properties ZnO and GaN materials are widely used for fabricating passive-type visible-blind ultraviolet (UV) photodetectors (PDs). However, most of these PDs have a very low spectral responsivity R, which is not sufficient for detecting very low-level UV signals. We demonstrate an active type UV PD with a ZnO nanorod (NR) structure for the floating gate of AlGaN/GaN high electron mobility transistor (HEMT), where the AlGaN/GaN epitaxial layers are isolated by the nano-scale fins (NFIs) of two different fin widths (70 and 80 nm). In the dark condition, oxygen adsorbed at the surface of the ZnO NRs generates negative gate potential. Upon UV light illumination, the negative charge on the ZnO NRs is reduced due to desorption of oxygen, and this reversible process controls the source-drain carrier transport property of HEMT based PDs. The NFI PDs of a 70 nm fin width show the highest R of a ~3.2 × 107 A/W at 340 nm wavelength among the solid-state UV PDs reported to date. We also compare the performances of NFI PDs with those of conventional mesa isolation (MI, 40 × 100 µm2). NFI devices show ~100 times enhanced R and on-off current ratio than those of MI devices. Due to the volume effect of the small active region, a much faster response speed (rise-up and fall-off times of 0.21 and 1.05 s) is also obtained from the NFI PDs with a 70 nm fin width upon the UV on-off transient.
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Tyutnev, Andrey P., Vladimir S. Saenko, Evgenii D. Pozhidaev, and Vladislav A. Kolesnikov. "Charge carrier transport in polyvinylcarbazole." Journal of Physics: Condensed Matter 18, no. 27 (June 23, 2006): 6365–77. http://dx.doi.org/10.1088/0953-8984/18/27/019.
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Kanai, N., R. Lu, Y. Bao, A. W. Wolkoff, M. Vore, and V. L. Schuster. "Estradiol 17 beta-D-glucuronide is a high-affinity substrate for oatp organic anion transporter." American Journal of Physiology-Renal Physiology 270, no. 2 (February 1, 1996): F326—F331. http://dx.doi.org/10.1152/ajprenal.1996.270.2.f326.
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Although substantial evidence indicates that estradiol-17 beta (E2) is conjugated to the glucuronide in the kidney and then excreted by a direct tubular secretory route and that the liver transports E2 glucuronides via carrier-mediated mechanisms, the transporters involved in these processes have not been identified. The so-called "organic anion-transporting polypeptide" (i.e., oatp) has a number of known substrates, including bromosulfophthalein (BSP) and taurocholic acid (TCA) (E. Jacquemin, B. Hagenbuch, B. Stieger, A. W. Wolkoff, and P. J. Meier. Proc. Natl. Acad. Sci. USA 91: 133-137, 1994). In a companion study, we determined that steroid hormones represent a class of hormones that interact strongly with oatp when the latter is transiently expressed in vitro. Here, we studied more extensively steroids and steroid anion conjugates as candidate oatp substrates. In HeLa cell monolayers transfected with a full-length oatp cDNA, [3H]estradiol 17 beta-D-glucuronide ([3H]E2-17G) was transported with a signal-to-noise ratio of 15:1 over that of monolayers transfected with a control plasmid. The affinity of oatp for [3H]E2-17G was significantly higher than that for TCA (K(m) of 3 microM vs. 27 microM, respectively). In contrast to E2-17G, unconjugated estradiol (E2) was not significantly transported by oatp. Several unconjugated steroids and anionic steroid conjugates were tested for their ability to compete with tracer E2-17G for oatp-mediated transport. Conjugation at the 17 or 3 position with the anion of a strong acid (sulfate) resulted in a greater degree of inhibition of tracer E2-17G transport than did conjugation at the 17 or 3 position with an uncharged group (acetate), suggesting that the strength of the negative charge at these positions is an important determinant of the affinity of a given steroid conjugate for oatp. We conclude that the preferred substrates for oatp are steroids with a strong 17- or 3-position anionic group. Since steroid sulfotransferases and glucuronosyltransferases are expressed in the proximal tubule, as is oatp, the transporter may serve as an apical exit pathway for steroids following their conjugation within the tubule cell.
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Fischer, Thorben, Inga Winter, Robert Drumm, and Marc Schneider. "Cylindrical Microparticles Composed of Mesoporous Silica Nanoparticles for the Targeted Delivery of a Small Molecule and a Macromolecular Drug to the Lungs: Exemplified with Curcumin and siRNA." Pharmaceutics 13, no. 6 (June 7, 2021): 844. http://dx.doi.org/10.3390/pharmaceutics13060844.
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The transport of macromolecular drugs such as oligonucleotides into the lungs has become increasingly relevant in recent years due to their high potency. However, the chemical structure of this group of drugs poses a hurdle to their delivery, caused by the negative charge, membrane impermeability and instability. For example, siRNA to reduce tumour necrosis factor alpha (TNF-α) secretion to reduce inflammatory signals has been successfully delivered by inhalation. In order to increase the effect of the treatment, a co-transport of another anti-inflammatory ingredient was applied. Combining curcumin-loaded mesoporous silica nanoparticles in nanostructured cylindrical microparticles stabilized by the layer-by-layer technique using polyanionic siRNA against TNF-α was used for demonstration. This system showed aerodynamic properties suited for lung deposition (mass median aerodynamic diameter of 2.85 ± 0.44 µm). Furthermore, these inhalable carriers showed no acute in vitro toxicity tested in both alveolar epithelial cells and macrophages up to 48 h incubation. Ultimately, TNF-α release was significantly reduced by the particles, showing an improved activity co-delivering both drugs using such a drug-delivery system for specific inhibition of TNF-α in the lungs.
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Moddel, Garret, Ayendra Weerakkody, David Doroski, and Dylan Bartusiak. "Optical-Cavity-Induced Current." Symmetry 13, no. 3 (March 22, 2021): 517. http://dx.doi.org/10.3390/sym13030517.
Full textAbstract:
The formation of a submicron optical cavity on one side of a metal–insulator–metal (MIM) tunneling device induces a measurable electrical current between the two metal layers with no applied voltage. Reducing the cavity thickness increases the measured current. Eight types of tests were carried out to determine whether the output could be due to experimental artifacts. All gave negative results, supporting the conclusion that the observed electrical output is genuinely produced by the device. We interpret the results as being due to the suppression of vacuum optical modes by the optical cavity on one side of the MIM device, which upsets a balance in the injection of electrons excited by zero-point fluctuations. This interpretation is in accord with observed changes in the electrical output as other device parameters are varied. A feature of the MIM devices is their femtosecond-fast transport and scattering times for hot charge carriers. The fast capture in these devices is consistent with a model in which an energy ∆E may be accessed from zero-point fluctuations for a time ∆t, following a ∆E∆t uncertainty-principle-like relation governing the process.
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Juška, G., K. Arlauskas, K. Genevičius, and J. Kočka. "Charge Carrier Transport in μc-Si:H." Materials Science Forum 297-298 (December 1998): 327–32. http://dx.doi.org/10.4028/www.scientific.net/msf.297-298.327.
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Hanna, Jun-ichi, Akira Ohno, and Hiroaki Iino. "Charge carrier transport in liquid crystals." Thin Solid Films 554 (March 2014): 58–63. http://dx.doi.org/10.1016/j.tsf.2013.10.051.
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Karl, N. "Charge carrier transport in organic semiconductors." Synthetic Metals 133-134 (March 2003): 649–57. http://dx.doi.org/10.1016/s0379-6779(02)00398-3.
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Nespurek, Stanislav, Julinz Sworakowski, Andrey Kadashchuk, and Petr Toman. "Polysilylenes: charge carrier transport and photogeneration." Journal of Organometallic Chemistry 685, no. 1-2 (November 2003): 269–79. http://dx.doi.org/10.1016/s0022-328x(03)00648-x.
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Novikov, S. V. "Charge-carrier transport in disordered polymers." Journal of Polymer Science Part B: Polymer Physics 41, no. 21 (October 8, 2003): 2584–94. http://dx.doi.org/10.1002/polb.10643.
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