Coherent electron dynamics in a two-dimensional random system with mobility edges

We study numerically the dynamics of a one-electron wavepacket in a two-dimensional random lattice with long-range correlated diagonal disorder in the presence of a uniform electric field. The time-dependent Schrodinger equation is used for this purpose. We find that the wavepacket displays Bloch-like oscillations associated with the appearance of a phase of delocalized states in the strong correlation regime. The amplitude of oscillations directly reflects the bandwidth of the phase and allows us to measure it. The oscillations reveal two main frequencies whose values are determined by the structure of the underlying potential in the vicinity of the wavepacket maximum.

Estudo de efeitos da polarização eletrostática periférica no Tokamak TCABR

Efeitos da polarização eletrostática de eletrodos na periferia de tokamaks têm sido investigados em pequenos tokamaks e mesmo em alguns tokamaks de grande porte. Em geral as experiências são realizadas em condições em que bifurcação do campo elétrico radial é obtida, processo este identificado como modo H de polarização. No Tokamak TCABR, as experiências indicam que o confinamento aumenta para tensões aplicadas até +300 volts, atingindo um máximo de duas vezes o tempo de confinamento do modo L, mas sem bifurcação. Indícios de bifurcação foram notados com +400 V de polarização, mas a descarga termina devido à excitação da atividade MHD, ainda sob investigação. No presente trabalho, a pesquisa é aprofundada com a utilização de uma sonda de Langmuir com 18 pinos dispostos em duas fileiras sob a forma de um ancinho (rake probe) o que permite a medição da temperatura, densidade e flutuação de potencial ao longo do raio menor na periferia do Tokamak. A resolução temporal desse sistema é de cerca de 0,5 ms, para a temperatura, e 5 microssegundos para densidade e potencial flutuante do plasma. Outra sonda eletrostática com 5-pinos na mesma posição radial, mas em diferentes posições poloidal e toroidal foi usada para medições de turbulência e transporte de partículas. Os efeitos da polarização foram investigados e indicam que os níveis de turbulência e transporte começam a diminuir entre +150 e +200 V e para +300 V chegam a atingir uma quase supressão. Nesse mesmo intervalo de tensão a densidade começa a aumentar e para +300 V chega a ser um fator de aproximadamente 2. Quanto ao perfil de temperatura a variação é pouco significativa, mas as incertezas das medidas são maiores. Esses dados são compatíveis com a criação de uma barreira de transporte na região entre o eletrodo em r = 17 cm e o limitador em a = 18 cm. Além disso, o campo elétrico radial mostra forte cisalhamento nessa região. Tomando o início da subida do potencial flutuante como origem de uma escala de tempo, o atraso temporal do início da subida da densidade de elétrons e o atraso do início do decréscimo do transporte de partículas foram medidos. Os resultados são 50 microssegundos para a densidade de elétrons e 60 microssegundos para o transporte de partículas. A questão dos limiares de potência é discutida no texto. Os dados desta experiência indicam que o campo elétrico radial desempenha o papel principal para a melhoria do confinamento.

Ion heating in transitions to CERC in the stellarator TJ-II

In TJ-II stellarator plasmas, in the electron cyclotron heating regime, an increase in the ion temperature is observed, synchronized with that of the electron temperature, during the transition to the core electron-root confinement (CERC) regime. This rise in ion temperature should be attributed to the joint action of the electron–ion energy transfer (which changes slightly during the CERC formation) and an enhancement of the ion confinement. This improvement must be related to the increase in the positive electric field in the core region. In this paper, we confirm this hypothesis by estimating the ion collisional transport in TJ-II under the physical conditions established before and after the transition to CERC. We calculate a large number of ion orbits in the guiding-centre approximation considering the collisions with a background plasma composed of electrons and ions. The ion temperature profile and the thermal flux are calculated in a self-consistent way, so that the change in the ion heat transport can be assessed.

Ion kinetic transport in TJ-II

The ion Drift Kinetic Equation (DKE) which describes the ion coUisional transport is solved for the TJ-II device plasmas. This non-linear equation is computed by peribrming a mean field iterative calculation. In each step of the calculation, a Fokker-Planck equation is solved by means of the Langevin approach: one million particles are followed in a realistic TJ-II magnetic configuration, taking into account collisions and electric field. This allows to avoid the assumptions made in the usual neoclassical approach, namely considering radially narrow particle trajectories, diffusive transport, energy conservation and infinite parallel transport. As a consequence, global features of transport, not present in the customary neoclassical models, appear: non-diffusive transport and asymmetries on the magnetic surfaces.

Caracterização elétrica de túnel-FET em estrutura de nanofio com fontes de SiGe e Ge em função da temperatura.

Este trabalho teve como objetivo estudar os transistores de tunelamento por efeito de campo em estruturas de nanofio (NW-TFET), sendo realizado através de analises com base em explicações teóricas, simulações numéricas e medidas experimentais. A fim de avaliar melhorar o desempenho do NW-TFET, este trabalho utilizou dispositivos com diferentes materiais de fonte, sendo eles: Si, liga SiGe e Ge, além da variação da espessura de HfO2 no material do dielétrico de porta. Com o auxílio de simulações numéricas foram obtidos os diagramas de bandas de energia dos dispositivos NW-TFET com fonte de Si0,73Ge0,27 e foi analisada a influência de cada um dos mecanismos de transporte de portadores para diversas condições de polarização, sendo observado a predominância da influência da recombinação e geração Shockley-Read-Hall (SRH) na corrente de desligamento, do tunelamento induzido por armadilhas (TAT) para baixos valores de tensões de porta (0,5V > VGS > 1,5V) e do tunelamento direto de banda para banda (BTBT) para maiores valores tensões de porta (VGS > 1,5V). A predominância de cada um desses mecanismos de transporte foi posteriormente comprovada com a utilização do método de Arrhenius, sendo este método adotado em todas as análises do trabalho. O comportamento relativamente constante da corrente dos NW-TFETs com a temperatura na região de BTBT tem chamado a atenção e por isso foi realizado o estudo dos parâmetros analógicos em função da temperatura. Este estudo foi realizado comparando a influência dos diferentes materiais de fonte. O uso de Ge na fonte, permitiu a melhora na corrente de tunelamento, devido à sua menor banda proibida, aumentando a corrente de funcionamento (ION) e a transcondutância do dispositivo. Porém, devido à forte dependência de BTBT com o campo elétrico, o uso de Ge na fonte resulta em uma maior degradação da condutância de saída. Entretanto, a redução da espessura de HfO2 no dielétrico de porta resultou no melhor acoplamento eletrostático, também aumentando a corrente de tunelamento, fazendo com que o dispositivo com fonte Ge e menor HfO2 apresentasse melhores resultados analógicos quando comparado ao puramente de Si. O uso de diferentes materiais durante o processo de fabricação induz ao aumento de defeitos nas interfaces do dispositivo. Ao longo deste trabalho foi realizado o estudo da influência da densidade de armadilhas de interface na corrente do dispositivo, demonstrando uma relação direta com o TAT e a formação de uma região de platô nas curvas de IDS x VGS, além de uma forte dependência com a temperatura, aumentando a degradação da corrente para temperaturas mais altas. Além disso, o uso de Ge introduziu maior número de impurezas no óxido, e através do estudo de ruído foi observado que o aumento na densidade de armadilhas no óxido resultou no aumento do ruído flicker em baixa frequência, que para o TFET, ocorre devido ao armadilhamento e desarmadilhamento de elétrons na região do óxido. E mais uma vez, o melhor acoplamento eletrostático devido a redução da espessura de HfO2, resultou na redução desse ruído tornando-se melhor quando comparado à um TFET puramente de Si. Neste trabalho foi proposto um modelo de ruído em baixa frequência para o NW-TFET baseado no modelo para MOSFET. Foram realizadas apenas algumas modificações, e assim, obtendo uma boa concordância com os resultados experimentais na região onde o BTBT é o mecanismo de condução predominante.

Enhanced removal of 8-quinolinecarboxylic acid in an activated carbon cloth by electroadsorption in aqueous solution

The effect of the electrochemical treatment (potentiostatic treatment in a filter-press electrochemical cell) on the adsorption capacity of an activated carbon cloth (ACC) was analyzed in relation with the removal of 8-quinolinecarboxylic acid pollutant from water. The adsorption capacity of an ACC is quantitatively improved in the presence of an electric field (electroadsorption process) reaching values of 96% in comparison to 55% in absence of applied potential. In addition, the cathodic treatment results in higher removal efficiencies than the anodic treatment. The enhanced adsorption capacity has been proved to be irreversible, since the removed compound remains adsorbed after switching the applied potential. The kinetics of the adsorption processes is also improved by the presence of an applied potential.

Terahertz Response of Excitons in Nanorod Heterostructures

Quantum-confined systems are one of the most promising ways to enable us to control a material's interactions with light. Nanorods in particular offer the right dimensions for exploring and manipulating the terahertz region of the spectrum. In this thesis, we model excitons confined inside a nanorod using the envelope function approximation. A region-matching transfer matrix method allows us to simulate excitonic states inside arbitrary heterostructures grown along the length of the rod. We apply the method to colloidal CdSe rods 70 nm in length and under 10 nm in diameter, capped with ligands of DDPA and pyridine. We extend past studies on these types of rods by taking into account their dielectric permittivity mismatch. Compared to previous calculations and experimentally measured terahertz absorption, we predict a higher energy main 1S$z$ to 2P$z$ transition peak. This indicates that the rods are likely larger in diameter than previously thought. We also investigate a nanorod with GaAs/Al$_{0.3}$Ga$_{0.7}$As coupled double dots. The excitonic transitions were found to be manipulable by varying the strength of an applied electric field. We employ quasi-static state population distributions to simulate the effects of exciton relaxation from optically active states to dim ground states. A critical value of the applied field, corresponding to the exciton binding energy of ~18 meV, was found to dramatically alter the terahertz absorption due to state mixing. Above this critical field, more nuanced shifts in transition energies were observed, and gain from radiative relaxation to the ground state is predicted.

(Table 1) Air-earth current density investigated during Atlantic Expedition 1973 of METEOR

One main point of our atmospheric-electric measurements over the Atlantic Ocean 1973 was the investigation of the air-earth current density above the sea. In addition to direct measurements at the water surface with a floating net, we calculated the air-earth current density from the electric field and the air conductivity measured simultaneously on board of the ship and during particular ascents in the free atmosphere. During all five ascents the air-earth current density did not change with altitude. For pure maritime air-conditions, the mean air-earth current density was found to be 2.9 pA/m**2. The mean hourly air-earth current density over the Atlantic shows nearly the same 24-hour pattern as measured by Cobb (1977) at the South Pole at the same time. When dust-loaden air masses of African origin reached the ship as well as under continental influence the mean air-earth current density was reduced to 2.1 pA/m**2. The global 24-hour pattern was modified by this continental influences. Finally, it is shown that the values of the air conductivity measured on board R. V. "Meteor" during our earlier expeditions have been influenced by the exhaust of the ship and must therefore be corrected. With this correction, our new mean values of the air-earth current density over the Atlantic are 2.6 pA/m**2 in 1965 and 2.0 pA/m**2 in 1969. From all measurements, the global air-earth current is estimated to be about 1250 A.

Estimating the Extent of Soil Contamination During a Redevelopment Excavation

From October 2014 to March 2015, I provided excavation oversight services at a property with substantial environmental concerns. The property in question is located near downtown Seattle and was formerly occupied by the Washington’s first coal gasification plant. The plant operated from 1888 to 1908 and produced coal gas for municipal use. A coal tar like substance with a characteristically high benzene concentration was a byproduct of the coal gasification process and heavily contaminated at or below the surface grade of the plant as shown in previous investigations on the property. Once the plant ceased operation in 1908 the property was left vacant until 1955 when the site was filled in and a service station was built on the property. The main goal of the excavation was not to achieve cleanup on the property, but to properly remove what contaminated soil was encountered during the redevelopment excavation. Areas of concern were identified prior to the commencement of the excavation and an estimation of the extent of contamination on the property was developed. “Hot spots” of contaminated soil associated with the fill placed after 1955 were identified as areas of concern. However, the primary contaminant plume below the property was likely sourced from the coal gasification plant, which operated at an approximate elevation of 20 feet. We planned to constrain the extents of the soil contamination below the property as the redevelopment excavation progressed. As the redevelopment excavation was advanced down to an elevation of approximately 20 feet, soil samples were collected to bound the extents of contamination in the upper portion of the site. The hot spots, known pockets of carcinogenic polycyclic aromatic hydrocarbons (cPAH) located above 20 feet elevation, were excavated as part of the redevelopment excavation. Once a hot spot was excavated, soil samples were collected from the north, south, east, west and bottom sidewalls of the hot spot excavation to check for remaining cPAH. Additionally, four underground storage tanks (USTs) associated with the service station were discovered and subsequently removed. Soil samples were also collected from the resulting UST excavation sidewalls to check for remaining petroleum hydrocarbons. Once the excavation reached its final excavation depth of 20 to 16 feet in elevation, bottom of excavation samples were collected on a 35 foot by 35 foot grid to test for concentrations of contaminants remaining onsite. Once the redevelopment excavation was complete, soils observed from borings drilled for either structural elements, geotechnical wells, or environmental wells were checked for any evidence of contamination using field screening techniques. Evidence of contamination was used to identify areas below the final excavation grade which had been impacted by the operation of the coal gasification plant. Samples collected from the excavation extents of hot spots and USTs show that it was unlikely that any contamination traveled from the post-1955 grade down to the pre-1955 grade. Additionally, the lack of benzene in the bottom of excavation samples suggests that a release from the coal gasification plant occurred below the redevelopment excavation final elevations of 20 to 16 feet. Qualitative data collected from borings for shoring elements and wells indicated that the spatial extent of the subsurface contaminant plume was different than initially estimated. Observations of spoils show that soil contamination extends further to the southwest and not as far to the east and north than originally estimated. Redefining the extent of the soil contamination beneath the property will allow further subsurface investigations to focus on collecting quantitative data in areas that still represent data gaps on the property, and passing over areas that have shown little signs of contamination. This information will help with the formation of a remediation plan should the need to clean up the site arise in the future.

In vivo gene expression: DNA electrotransfer

The use of electric pulses to deliver therapeutic molecules to tissues and organs in vivo is a rapidly growing field of research. Electrotransfer can be used to deliver a wide range of potentially therapeutic agents, including drugs, proteins, oligonucleotides, RNA and DNA. Optimization of this approach depends upon a number of parameters such as target organ accessibility, cell turnover, microelectrode design, electric pulsing protocols and the physiological response to the therapeutic agent. Many organs have been successfully transfected by electroporation, including skin, liver, skeletal and cardiac muscle, male and female germ cells, artery, gut, kidney, retinal ganglion cells, cornea, spinal cord, joint synovium and brain. Electrotransfer technology is relevant in a variety of research and clinical settings including cancer therapy, modulation of pathogenic immune reactions, delivery of therapeutic proteins and drugs, and the identification of drug targets by the modulation of normal gene expression. This, together with the capacity to deliver very large DNA constructs, greatly expands the research and clinical applications of in vivo DNA electrotransfer.

Conductivity tomography at two frequencies

We present a new approach for crosshole radio tomography. Conductivity images of the investigated area are reconstructed from the ratio of the electric field intensities measured at two similar frequencies. The method largely avoids assumptions about the radiation pattern and in-situ intensity of the transmitting antenna, which introduce errors in conventional single-frequency crosshole electromagnetic-absorption tomography. Application of the method to field data achieved an improvement in resolution of anomalies over traditional single-frequency absorption tomography. The dual-frequency method is not a universal approach; it is suitable for moderately conductive media (>0.01 S/m) over the approximate frequency range 1-100 MHz.

Adenosine triphosphate acts as both a competitive antagonist and a positive allosteric modulator at recombinant N-methyl-D-aspartate receptors

ATP and glutamate are fast excitatory neurotransmitters in the central nervous system acting primarily on ionotropic P2X and glutamate [N-methyl-D-aspartate (NMDA) and non-NMDA] receptors, respectively. Both neurotransmitters regulate synaptic plasticity and long-term potentiation in hippocampal neurons. NMDA receptors are responsible primarily for the modulatory action of glutamate, but the mechanism underlying the modulatory effect of ATP remains uncertain. In the present study, the effect of ATP on recombinant NR1a + 2A, NR1a + 2B, and NR1a + 2C NMDA receptors expressed in Xenopus laevis oocytes was investigated. ATP inhibited NR1a + 2A and NR1a + 2B receptor currents evoked by low concentrations of glutamate but potentiated currents evoked by saturating glutamate concentrations. In contrast, ATP potentiated NR1a + 2C receptor currents evoked by nonsaturating glutamate concentrations. ATP shifted the glutamate concentration-response curve to the right, indicating a competitive interaction at the agonist binding site. ATP inhibition and potentiation of glutamate-evoked currents was voltage-independent, indicating that ATP acts outside the membrane electric field. Other nucleotides, including ADP, GTP, CTP, and UTP, inhibited glutamate-evoked currents with different potencies, revealing that the inhibition is dependent on both the phosphate chain and nucleotide ring structure. At high concentrations, glutamate outcompetes ATP at the agonist binding site, revealing a potentiation of the current. This effect must be caused by ATP binding at a separate site, where it acts as a positive allosteric modulator of channel gating. A simple model of the NMDA receptor, with ATP acting both as a competitive antagonist at the glutamate binding site and as a positive allosteric modulator at a separate site, reproduced the main features of the data.

Effects of potential models in the vapor-liquid equilibria and adsorption of simple gases on graphitized thermal carbon black

In this paper, we investigate the effects of various potential models in the description of vapor–liquid equilibria (VLE) and adsorption of simple gases on highly graphitized thermal carbon black. It is found that some potential models proposed in the literature are not suitable for the description of VLE (saturated gas and liquid densities and the vapor pressure with temperature). Simple gases, such as neon, argon, krypton, xenon, nitrogen, and methane are studied in this paper. To describe the isotherms on graphitized thermal carbon black correctly, the surface mediation damping factor introduced in our recent publication should be used to calculate correctly the fluid–fluid interaction energy between particles close to the surface. It is found that the damping constant for the noble gases family is linearly dependent on the polarizability, suggesting that the electric field of the graphite surface has a direct induction effect on the induced dipole of these molecules. As a result of this polarization by the graphite surface, the fluid–fluid interaction energy is reduced whenever two particles are near the surface. In the case of methane, we found that the damping constant is less than that of a noble gas having the similar polarizability, while in the case of nitrogen the damping factor is much greater and this could most likely be due to the quadrupolar nature of nitrogen.

Determination of crystal orientation from micrographs using a MATLAB program

Crys.m is a MATLAB routine that combines a micrograph of a crystal with a scaleable, rotatable three-dimensional cage structure to determine the orientation of the crystal axes. The example presented here uses the morphology of tetragonal lysozyme. Rotation of the cage until it aligns with the crystal in the image yields the orientation of the c axis of the crystal relative to the image normal. This analysis can be used for quantitative determination of crystal orientation effects induced by electric, magnetic and/or gravitational fields.

Voltage-dependent inhibition of recombinant NMDA receptor-mediated currents by 5-hydroxytryptamine

1 The effect of 5-HT and related indolealkylamines on heteromeric recombinant NMDA receptors expressed in Xenopus oocytes was investigated using the two-electrode voltage-clamp recording technique. 2 In the absence of external Mg2+ ions, 5-HT inhibited NMDA receptor-mediated currents in a concentration-dependent manner. The inhibitory effect of 5-HT was independent of the NR1a and NR2 subunit combination. 3 The inhibition of glutamate-evoked currents by 5-HT was use- and voltage-dependent. The voltage sensitivity of inhibition for NR1a+NR2 subunit combinations by 5-HT was similar, exhibiting an e-fold change per similar to20 mV, indicating that 5-HT binds to a site deep within the membrane electric field. 4 The inhibition of the open NMDA receptor by external Mg2+ and 5-HT was not additive, suggesting competition between Mg2+ and 5-HT for a binding site in the NMDA receptor channel. The concentration-dependence curves for 5-HT and 5-methoxytryptamine (5-MeOT) inhibition of NMDA receptor-mediated currents are shifted to the right in the presence of external Mg2+. 5 The related indolealkylamines inhibited glutamate-evoked currents with the following order of inhibitory potency: 5-MeOT = 5-methyltryptamine > tryptamine > 7-methyltryptamine > 5-HTmuch greater than tryptophan melatonin. 6 Taken together, these data suggest that 5-HT and related compounds can attenuate glutamate-mediated excitatory synaptic responses and may provide a basis for drug treatment of excitoxic neurodegeneration.