Synthesis and characterization of polypyrrole-polyurethane cationomer composites

Poly(ether urethane) cationomers based on poly(oxytetramethylene), 4,4'-bibenzyldiisocyanate, N-methyldiethanolamine as chain extender, and acrylic acid/poly(acrylic acid) as quaternization agent were synthesized. Pyrrole (15 wt.-%) was polymerized in films of the ionomer containing CuCl2. The films were characterized by dynamic mechanical analysis, thermogravimetry and differential scanning calorimetry. The electric conductivity of the film without polypyrrole is 7.5 . 10(-12) Omega(-1)cm(-1), while incorporation of polypyrrole increases the conductivity to 4.5 . 10(-6) Omega(-1) cm(-1).

纳电子器件制备的单根碳纳米管精确装配与电连接研究

目前,利用单根碳纳米管进行纳电子器件的研制成为纳电子学界研究的前沿与热点,但在纳电子器件研制过程中,如何实现单根碳纳米管与微电极的精确装配与电连接成为关键技术难题之一。为探索实现此关键技术的新方法,本文尝试将介电电泳与具有实时力/视觉反馈的原子力显微镜操作方法相结合,从而结合粗、精两级操作方式,来实现单根碳纳米管的精确装配与电连接。单根多壁碳纳米管的精确装配与电特性测试实验验证了该方法的有效性,从而为装配研制基于单根纳米管/线的纳电子器件提供了一种新颖可行的方法。

Conductive junctions with parallel graphene sheets.

The establishment of conductive graphene-molecule-graphene junction is investigated through first-principles electronic structure calculations and quantum transport calculations. The junction consists of a conjugated molecule connecting two parallel graphene sheets. The effects of molecular electronic states, structure relaxation, and molecule-graphene contact on the conductance of the junction are explored. A conductance as large as 0.38 conductance quantum is found achievable with an appropriately oriented dithiophene bridge. This work elucidates the designing principles of promising nanoelectronic devices based on conductive graphene-molecule-graphene junctions.

Radium and barium removal through blending hydraulic fracturing fluids with acid mine drainage.

Wastewaters generated during hydraulic fracturing of the Marcellus Shale typically contain high concentrations of salts, naturally occurring radioactive material (NORM), and metals, such as barium, that pose environmental and public health risks upon inadequate treatment and disposal. In addition, fresh water scarcity in dry regions or during periods of drought could limit shale gas development. This paper explores the possibility of using alternative water sources and their impact on NORM levels through blending acid mine drainage (AMD) effluent with recycled hydraulic fracturing flowback fluids (HFFFs). We conducted a series of laboratory experiments in which the chemistry and NORM of different mix proportions of AMD and HFFF were examined after reacting for 48 h. The experimental data combined with geochemical modeling and X-ray diffraction analysis suggest that several ions, including sulfate, iron, barium, strontium, and a large portion of radium (60-100%), precipitated into newly formed solids composed mainly of Sr barite within the first ∼ 10 h of mixing. The results imply that blending AMD and HFFF could be an effective management practice for both remediation of the high NORM in the Marcellus HFFF wastewater and beneficial utilization of AMD that is currently contaminating waterways in northeastern U.S.A.

A whole-cell and single-channel study of the voltage-dependent outward potassium current in avian hepatocytes.

Voltage-dependent membrane currents were studied in dissociated hepatocytes from chick, using the patch-clamp technique. All cells had voltage-dependent outward K+ currents; in 10% of the cells, a fast, transient, tetrodotoxin-sensitive Na+ current was identified. None of the cells had voltage-dependent inward Ca2+ currents. The K+ current activated at a membrane potential of about -10 mV, had a sigmoidal time course, and did not inactivate in 500 ms. The maximum outward conductance was 6.6 +/- 2.4 nS in 18 cells. The reversal potential, estimated from tail current measurements, shifted by 50 mV per 10-fold increase in the external K+ concentration. The current traces were fitted by n2 kinetics with voltage-dependent time constants. Omitting Ca2+ from the external bath or buffering the internal Ca2+ with EGTA did not alter the outward current, which shows that Ca2+-activated K+ currents were not present. 1-5 mM 4-aminopyridine, 0.5-2 mM BaCl2, and 0.1-1 mM CdCl2 reversibly inhibited the current. The block caused by Ba was voltage dependent. Single-channel currents were recorded in cell-attached and outside-out patches. The mean unitary conductance was 7 pS, and the channels displayed bursting kinetics. Thus, avian hepatocytes have a single type of K+ channel belonging to the delayed rectifier class of K+ channels.

Pattern formation of chevrons in the conduction regime in homeotropically aligned liquid crystals

We report on chevrons (herringbonelike patterns) observed in homeotropically aligned liquid crystals with high electric conductivity. We focus our attention on two types of chevrons observed in the conduction regime. The threshold voltage and the characteristic double periodicity of chevrons (i.e., the short wavelength lambda(1) of the striated rolls and the long wavelength lambda(2) Of the chevron bands) have been measured as functions of the applied electric frequency f. With the aid of a crossed polarizer set, we have, in addition, determined the director field which shows a periodic in-plane rotation for our chevrons (with a wavelength lambda(2)) We arrived at the types of chevrons after qualitatively different bifurcation sequences with increasing voltage. The frequency dependence of lambda(2) also shows a qualitatively different behavior with respect to the two types of chevrons. The experimental results are discussed in terms of recent theoretical investigations.

Large-scale density functional calculations of the surface properties of the Wigner crystal

The surface properties of the jellium model have been investigated by large supercell computations in the density functional theory-local spin-density (DFT-LSD) approach for planar slabs with up to 1000 electrons. A wide interval of densities has been explored, extending into the stability range of the Wigner crystal. Most computations have been carried out on nominally paramagnetic samples with an equal number of spin-up and spin-down electrons. The results show that within DFT-LSD spontaneous spin polarization and charge localization start nearly simultaneously at the surface for r(s) similar to 20, then, with decreasing density, they progress toward the center of the slab. Electrons are fully localized and spin polarized at r(s) = 30. At this density the charge distribution is the superposition of disjoint charge blobs, each corresponding to one electron. The distribution of blobs displays both regularities and disorder, the first being represented by well-defined planes and simple in-plane geometries, and the latter by a variety of surface defects. The surface energy, surface dipole, electric polarisability, and magnetization pattern have been determined as a function of density. All these quantities display characteristic anomalies at the density of the localization transition. The analysis of the low-frequency electric conductivity shows that in the fluid paramagnetic regime the in-plane current preferentially flows in the central region of the slab and the two spin channels are equally conducting. In the charge localized, spin-polarized regime, conductivity is primarily a surface effect, and an apparent asymmetry is observed in the two spin currents.

3D Analysis of Heat Transfer Intensification by Re-Entrance Flow Pin-Fins Microstructures with a Highly Thermal-Conductive Plate

Joule heat-induced hot-spot formation sets severe limits in the operation of continuous annular electrochromatography (CAEC), a new concept for preparative separation as an analog to analytical capillary electrochromatography (CEC). This may lead to eluent flow perturbance, even to boiling, which would massively weaken separation efficiency and may even hamper the stationary phase used for separation. For reasons of system integration and high-efficiency heat transfer, micro flow heat exchangers are considered with a separate coolant flow. A 3D numerical analysis of the heat transfer of water single-phase laminar flow in a square microchannel and different arrays of micro pin-fins was carried out using COMSOL Multiphysics. Several advanced materials with low electric conductivity and at the same time with high heat conductivity were put forward to be used in the CAEC system. As essential design point, it is proposed to constitute the micro heat exchanger from two different parts of the CAEC system, namely a microstructured pin-fins plate and a so-called conductive plate.

The structural response of an oscillating wave surge converter to wave slamming

This paper describes the problems in experimentally obtaining hydrodynamic loads on an oscillating wave surge converter during slamming events, with the aim of furthering understanding of full scale hydrodynamic loads that flap type devices must be designed to withstand. Including how hydro-elastic effects and structural response are linked and why they are essential to the measurement of impulsive hydrodynamic loads. A combined experimental and numerical structural response study carried out on a 40th scale Oyster model drew conclusions on the structural vibration observed in the strain gauge load cell measurement. A further structural response study on a piezo electric load measurement device gave an insight into the advantages it could bring to reducing hydro-elastic effects.

Response to salinity in young olive trees of three Iberian varieties

Soil salinization is a problem in the Mediterranean region. This paper reports a research on the response to salt in two year-old olive trees (Olea europaea L.) of three Iberian varieties: Arbequina, Cobrançosa and Galega Vulgar. Plants were grown in plastic pots containing approximately 9 Kg of a sandy granitic soil, on a greenhouse at the University of Évora since February 2010. The experiment went from February to April 2012. As a rule, plants were watered every other day alternating salt solution (0 mM, 80 mM or 200 mM NaCl) or tap water. After three months irrigation with the different NaCl solutions, soil electric conductivity and soil water content were significantly higher on salt-irrigated pots. Salt also decreased significantly stomatal conductance (gs) and mid-day leaf water potential (), Cobrançosa having in general higher gs and but lower SLA than the two other varieties. Chlorophyll content of leaves was not affected by salt after this three months exposure to NaCl but was significantly higher on Arbequina and lower on Cobrançosa. In general, hyperspectral reflectance indexes did not show significant correlations with salt irrigation, except for the Photochemical Reflectance Index (PRI) which was clearly lower on plants of all three varieties irrigated with salt. Interestingly, Cobrançosa showed frequently vegetation indexes different from the other two varieties.

Hidroquímica e qualidade das águas subterrâneas da Ilha de Santiago - Cabo Verde

A ilha de Santiago, Cabo Verde é uma ilha de origem vulcânica, constituída basicamente por lavas e piroclastos, localizada no Oceano Atlântico ao lado da costa ocidental de África. A ilha é caracterizada por três unidades hidrogeológicas, sendo estas a Formação de Base (semi-confinada), a Formação Intermédia (freática) e a Formação Recente (freática), que apresentam características geológicas e comportamentos hidráulicos que as diferenciam, recebendo recarga directa e/ ou diferida por infiltração das águas de chuva e descarregam ao mar, na rede hidrográfica ou, ainda, em outros níveis aquíferos subjacentes, desde que induzidos por gradientes hidráulicos favoráveis. O clima de Santiago é árido a semi-árido, com precipitações muito escassas e irregulares, condicionadas na sua distribuição pela altitude, ventos e orientação das vertentes, dando por vezes origem a períodos de seca prolongados. Em anos de ‘boa’ chuva, as precipitações propiciam a existência temporária de recursos hídricos superficiais e a recarga dos recursos de água subterrânea. Foi realizado um estudo hidrogeoquímico detalhado da ilha que incluiu a recolha de amostras em 133 pontos de água, entre furos, poços e nascentes. A composição química das águas analisadas na ilha de Santiago apresenta significativas variações em função da geologia e do tempo de residência. Na ausência de episódios de contaminação, as águas subterrâneas têm uma composição do tipo bicarbonatada-sódica (HCO3-Na) nas zonas mais altas da ilha, onde afloram as formações da Unidade Aquífera Intermédia. Nas zonas mais próximas da costa ocorrem águas de composição cloretada-magnesiana (Cl-Mg) ou cloretada-sódica (Cl-Na). Estas últimas predominam nas partes terminais das ribeiras, onde afloram materiais de elevada permeabilidade, e o excesso de bombagem para irrigação tem conduzido a um avanço da cunha de intrusão marinha. A ocorrência da fácies Cl-Na é neste caso o resultado de processos de intercâmbio catiónico que ocorrem durante o processo de intrusão e é concordante com os elevados teores de cloretos e de condutividade eléctrica observados. Os resultados das análises de isótopos estáveis de oxigénio-18 e deutério, realizadas em amostras recolhidas a distintas altitudes, revelam um gradiente negativo com a altitude, que já tinha sido verificado em outras ilhas com declives acentuados, permitindo assim determinar altitudes de recarga de água subterrânea. Os estudos hidrogeoquímicos até agora realizados permitiram caracterizar os principais níveis aquíferos da ilha de Santiago, colocando em evidência a limitada recarga do aquífero e o risco de gradual degradação dos recursos de água subterrânea por fenómenos de intrusão salina e contaminação agrícola. Estes resultados revelam a importância da gestão integrada da qualidade e quantidade dos parcos recursos de água subterrânea na ilha de Santiago.

Synthesis, characterization, and structure of a new cobalt(II) Schiff-base complex with quinoxaline- 2-carboxalidine-2-amino-5-methylphenol

The mononuclear cobalt(II) complex [CoL2] H2O (where HL is quinoxaline-2-carboxalidine- 2-amino-5-methylphenol) has been prepared and characterized by elemental analysis, conductivity measurement, IR, UV-Vis spectroscopy, TG-DTA, and X-ray structure determination. The crystallographic study shows that cobalt(II) is distorted octahedral with each tridentate NNO Schiff base in a cis arrangement. The crystal exhibits a 2-D polymeric structure parallel to [010] plane, formed by O-H...N and O-H... O intermolecular hydrogen bonds and pye stacking interactions, as a racemic mixture of optical enantiomers. The ligand is a Schiff base derived from quinoxaline-2-carboxaldehyde

Parity violation in Aharonov-Bohm systems: The spontaneous Hall effect

We show how macroscopic manifestations of P (and T) symmetry breaking can arise in a simple system subject to Aharonov-Bohm interactions. Specifically, we study the conductivity of a gas of charged particles moving through a dilute array of flux tubes. The interaction of the electrons with the flux tubes is taken to be of a purely Aharonov-Bohm type. We find that the system exhibits a nonzero transverse conductivity, i.e., a spontaneous Hall effect. This is in contrast to the fact that the cross sections for both scattering and bremsstrahlung (soft-photon emission) of a single electron from a flux tube are invariant under reflections. We argue that the asymmetry in the conductivity coefficients arises from many-body effects. On the other hand, the transverse conductivity has the same dependence on universal constants that appears in the quantum Hall effect, a result that we relate to the validity of the mean-field approximation.

On conduction mechanism in paramagnetic phase of Gd based manganites

Materials belonging to the family of manganites are technologically important since they exhibit colossal magneto resistance. A proper understanding of the transport properties is very vital in tailoring the properties. A heavy rare earth doped manganite like Gd0·7Sr0·3MnO3 is purported to be exhibiting unusual properties because of smaller ionic radius of Gd. Gd0·7Sr0·3MnO3 is prepared by a wet solid state reaction method. The conduction mechanism in such a compound has been elucidated by subjecting the material to low temperature d.c. conductivity measurement. It has been found that the low band width material follows a variable range hopping (VRH) model followed by a small polaron hopping (SPH) model. The results are presented here

Bacterial ecology of ancient Saharan salt-enrichment ponds at Teguidda-n-Tessoumt

Little is known about the bacterial ecology of evaporative salt-mining sites (salterns) of which Teguidda-n-Tessoumt at the fringe of the West-African Saharan desert in Niger is a spectacular example with its many-centuries-old and very colorful evaporation ponds. During the different enrichment steps of the salt produced as a widely traded feed supplement for cattle, animal manure is added to the crude brine, which is then desiccated and repeatedly crystallized. This study describes the dominant Bacteria and Archaea communites in the brine from the evaporation ponds and the soil from the mine, which were determined by PCR-DGGE of 16S rDNA. Correspondence analysis of the DGGE-community fingerprints revealed a change in community structure of the brine samples during the sequential evaporation steps which was, however, unaffected by the brine's pH and electric conductivity (EC). The Archaea community was dominated by a phylogenetically diverse group of methanogens, while the Bacteria community was dominated by gamma proteobacteria. Microorganisms contained in the purified salt product have the potential to be broadly disseminated and are fed to livestock across the region. In this manner, the salt mines represent an intriguing example of long-term human activity that has contributed to the continual selection, cultivation, and dissemination of cosmopolitan microorganisms.