Weak Conductors Research Articles

Superprotonic conduction of intrinsically zwitterionic microporous polymers based on easy-to-make squaraine, croconaine and rhodizaine dyes.

Porous organic polymers (POPs) have been prepared via a novel metal free polycondensation between a tritopic indole-based monomer and squaric, croconic and rhodizonic acids. Each of the three POPs exhibited high BET surface areas (331–667 m2 g−1) and zwitterionic structures. Impedance measurements revealed that the intrinsic POPs were relatively weak proton conductors, with a positive correlation between the density of oxo-groups and the proton conduction. Doping the materials with LiCl vastly improved the proton conductivity up to a value of 0.54 S cm−1 at 90 °C and 90% relative humidity.

Dendritic osmosensors modulate activity-induced calcium influx in oxytocinergic magnocellular neurons of the mouse PVN.

Hypothalamic oxytocinergic magnocellular neurons have a fascinating ability to release peptide from both their axon terminals and from their dendrites. Existing data indicates that the relationship between somatic activity and dendritic release is not constant, but the mechanisms through which this relationship can be modulated are not completely understood. Here, we use a combination of electrical and optical recording techniques to quantify activity-induced calcium influx in proximal vs. distal dendrites of oxytocinergic magnocellular neurons located in the paraventricular nucleus of the hypothalamus (OT-MCNs). Results reveal that the dendrites of OT-MCNs are weak conductors of somatic voltage changes; however, activity-induced dendritic calcium influx can be robustly regulated by both osmosensitive and non-osmosensitive ion channels located along the dendritic membrane. Overall, this study reveals that dendritic conductivity is a dynamic and endogenously regulated feature of OT-MCNs that is likely to have substantial functional impact on central oxytocin release.

Reflectionless metasurface with high refractive index in the terahertz waveband.

Terahertz flat optics is a design concept for replacing conventional three-dimensional bulky optical components with two-dimensional ultra-thin optical components. However, high refractive index materials suitable for flat optics are frequently subject to high Fresnel reflections due to the cumbersome control of the relative permeability it requires. Here we experimentally demonstrate a reflectionless metasurface with a high refractive index of 5.88 + j1.57, extremely low reflectance of 1.3%, high relative permittivity of 6.73 + j0.85, and the high relative permeability of 5.03 + j2.11 at 2.97 THz. The super-fine ink-jet printer using silver paste ink fabricates the metasurface consisting of 80,036 pairs of cut metal wires on both the front and back of a 5 μm-thick polyimide film. The findings also demonstrate that weak conductors as well as good conductors can be used in the design of reflectionless metasurfaces with a high refractive index in the terahertz waveband. The presented metasurface can offer an accessible platform for terahertz flat optics in 6G (beyond 5G) wireless communications and imaging.

Disrupted layered lithology can jeopardise airborne electromagnetic interpretation

The majority of airborne electromagnetic (AEM) data is processed using stitched consecutive 1D approximations, from which conductivity depth or CDI sections can be produced. Obtaining calculated variable layer depths from AEM is one of the appealing assets of the method. The current induced by an AEM system in the nearsurface circulates preferentially at a radial distance from the horizontal transmitter (commonly called footprint), the section plotted below the receiver is actually generated from currents induced in the general vicinity and not directly below the reviver-transmitter system. Detection of palaeochannels, faults and other laterally varying structures are common geophysical mapping targets. Caution should be taken when interpreting these horizontally-anisotropic targets; especially if smaller that the system 'Annulus of resolution' or close to edges of discontinuous layering. All AEM systems have different transmitter-receiver geometries, moments, wave forms and others specifics. Forward modelling and conductivity-transforms provide a good method to understand CDI sections and for system comparison. When 2D/3D effects of discontinuities are present, 1D modelling incorrectly predicts weak conductors at depth. Within a conductive layer where conductivity changes with facies or geometrical thickness, 1D approximations work well. 2D processing of 2D data is clearly needed, but existing inversion methods are too slow. 2D/3D structures with abrupt conductivity boundaries resolved with an isotropic layered assumption must always be queried.

MULTIPULSE – high resolution and high power in one TDEM system

An airborne time domain electromagnetic (TEM) system with high resolution and great depth of exploration is desired for geological mapping as well as for mineral exploration. The MULTIPULSE technology enables an airborne TEM system to transmit a high power pulse (a half-sine, for instance) and one or multiple low power pulse(s) (trapezoid or square) within a half-cycle. The high power pulse ensures good depth of exploration and the low power pulse allows a fast transmitter current turn off and earlier off-time measurement thus providing higher frequency signals, which allows higher near-surface resolution and better sensitivity to weak conductors. The power spectrum of the MULTIPULSE waveform comprising a half-sine and a trapezoid pulse clearly shows increased power in the higher frequency range (> ~2.3 kHz) compared to that of a single half-sine waveform. The addition of the low power trapezoid pulse extends the range of the sensitivity 10-fold towards the weak conductors, expanding the geological conductivity range of a system and increasing the scope of its applications. The MULTIPULSE technology can be applied to standard single-pulse airborne TEM systems on both helicopter and fixed-wing. We field tested the HELITEM MULTIPULSE system over a wire-loop in Iroquois Falls, demonstrating the different sensitivity of the high and low power pulses to the overburden and the wire-loop. We also tested both HELITEM and GEOTEM MULTIPULSE systems over a layered oil sand geologic setting in Fort McMurray, Alberta, Canada. The results show comparable shallow geologic resolution of the MULTIPULSE to that of the RESOLVE system while maintaining superior depth of exploration, confirming the increased geological conductivity range of a system employing MULTIPULSE compared to the standard single-pulse systems.

Billions of Human Brains Immersed Within a Shared Geomagnetic Field: Quantitative Solutions and Implications for Future Adaptations

The implications for adaptation when billions of human cerebrums are considered weak conductors immersed within the same medium, the geomagnetic field, are examined. Quantitative solutions indicated that the intensity of the “transcerebral” field produced from all human brains within the geomagnetic field is the same order of magnitude as the values associated with cognitive processes and altered expressions of proteins within the individual brain. This convergence could meet one of the criteria for a holographic-like phenomenon. The transition from 6 to 8 billion brains would be associated with shared energies within individual cerebral space whose frequencies increase across the visible electromagnetic wavelength from infrared to ultraviolet. Magnetic diffusivity indicates all brains could be influenced within about 10 minutes. Implications for induced ubiquitous genetic changes, shared modifications in protein sequences associated with memory during dream sleep, and limitations upon the proliferation of the species are discussed.

Geophysical imaging of municipal solid waste contaminant pathways

Surface electrical and electromagnetic surveys were conducted on top of a solid waste facility in Unguwan Dosa, Kaduna State, Northwest Nigeria. The aim of the geophysical survey was to detect vertical and subvertical fractures that may provide pathways for groundwater and contaminant transport. Results from the 2D electrical resistivity imaging showed vertical and subvertical contacts overlain by 6–10 m thick overburden. Quantitative interpretation of the VLF-EM data correlates well with the results of the 2D resistivity imaging delineating the vertical and subvertical contacts as good and weak conductors (fractures zones) with resistivity values of 40–220 and 300–420 Ω m, respectively. Azimuthal Schlumberger VES measurements yield apparent anisotropy values ranging from 1.01 to 1.47 for electrode spacings of 1–45 m with the highest value recorded at spacing of 2 m. However, azimuthal variations at large spacings (30–45 m) showed no fracture anisotropy due possibly to the array’s low sensitivity to anisotropy at these spacings. The result of the study showed that pollutants in the leachate can reach and contaminate the groundwater. Therefore, urgency for leachate treatment at this site is recommended to prevent contamination of groundwater.

Delamination strength of YBCO coated conductors under transverse tensile stress**Contribution of NIST, a US Government Agency, not subject to copyright.

We present a new experimental technique to measure the delamination strength under transverse tensilestress of YBa2Cu3O7−δ coated conductors for electric power applications. The delamination strength, defined asthe tensile stress at which the ceramic layers delaminate from one another, is measured at76 K for different sample configurations. The delamination strength is reduced by as muchas 40% when the conductor is slit to smaller width, a standard fabrication process, and thisreduction is due to damage to the ceramic layers near the edges of the conductor. We foundthat the delamination strength of slit coated conductors can be raised significantly byreinforcing the conductor by laminating it with copper strips and adding solder fillets atthe edges. In relatively strong conductors, where the delamination strength is ashigh as 15 MPa, the critical current does not degrade before actual delamination.This fact greatly simplifies sample characterization of practical high-strengthconductors, since only mechanical measurements need to be made. The criticalcurrent does, however, degrade significantly as a function of transverse stress beforedelamination in weak conductors that have relatively low delamination strength below15 MPa. We discuss how a soft metallic layer in YBCO coated conductors may limitthe transverse stress that the superconducting layer experiences in applications.

Insulator coated metal nanoparticles with a core/shell geometry exhibit a temperature sensitivity similar to advanced spinels

The preparation of carbon-coated copper nanoparticles with different carbon layers resulted in materials with a highly sensitive pressure and temperature dependent conductivity. The core/shell geometry of these carbon/metal composites afforded two distinctly different electrical behaviors depending on the carbon layer properties. Graphene layers with a predominant sp 2 character showed an ill-defined bandgap structure as evidenced by UV–vis diffuse reflectance spectroscopy. The resulting composites were weak conductors with low sensitivity. Use of predominately insulating carbon layers with a well-defined bandgap of above 1.9 eV resulted in composites with a material constant β of over 4700 K which is comparable to currently used commercial spinels. A theoretical analysis and detailed material characterization by Raman spectroscopy, X-ray diffraction, 13C NMR spectroscopy and thermoanalysis suggested a tunneling based conduction mechanism in these core/shell materials. This interpretation was supported by a good correlation between experimental data and the estimated effects arising from the theoretical analysis of the tunneling effects.

Exploration Techniques at the Thorn Ag‐Au‐Cu High‐Sulfidation Epithermal Prospect, Northern British Columbia, Canada

Abstract. The Thorn prospect is an El Indio‐style high‐sulfidation epithermal prospect in a little‐explored belt of Late Cretaceous subaerial volcanics and subvolcanic intrusions in northwestern British Columbia, Canada. More than 30 massive sulfide (pyrite‐enargite‐tennantite/tetrahedrite) veins, quartz‐sulfide (quartz‐pyrite‐enargite‐tennantite/tetrahedrite) veins and quartz‐vuggy silica‐alunite veins/breccias fill ENE fractures and faults over an area of 1,600 times 1,900 m. They are hosted within a Late Cretaceous feldspar‐quartz‐biotite granodioritic porphyry stock and flanked by alteration envelopes a few meters to tens of meters wide: an inner envelope of intense sericite‐clay‐pyrite and an outer one of weak clay‐sericite‐chlorite. Where several veins are close together, the sericite‐clay‐pyrite alteration envelopes coalesce into zones up to 150 m wide.The most successful exploration techniques have been prospecting, silt and soil geochemistry, airborne magnetic and electromagnetic surveys and diamond drilling. Silt and soil geochemical anomalies for Au, Ag, As, Cu, Pb, Sb and Zn mark the known veins and indicate prospective areas where veins have not yet been discovered. Magnetics and resistivity outline the gross property‐wide structure and lithologies. Most of the sericite‐clay‐pyrite alteration and known veins are outlined by the <264 ohm‐m resistivity contour, which covers an area of 800 times 2,300 m. Weak EM conductors are thought to represent undiscovered massive sulfide and quartz‐sulfide veins, and their flanking sericite‐clay‐pyrite alteration.

Borehole EM and MMR Methods for Weak Conductors – A Project Review

This paper reviews a 3-year research project targetted towards processing and interpretation methodologies for borehole EM methods in the search for weak electrical conductors. Weak conductors are best energised by current-channelling methods, which include both MMR, and inductive loops off-set from the hole collar. The following results have been achieved: Recognition of the importance of using current-channelling energisation of weak conductors; a sphalerite-rich conductor is frequently too poor a conductor to support an inductive EM response of vortex currents, but any conductor showing a conductivity contrast relative to host rock, can produce an EM response from currents channelled through the conductor from the conducting host rock.Recognition of the equivalence of MMR and long-offset TEM data, in terms of information and interpretation of current-channelling energisation of conductors.Comparison of numerical modelling techniques for inductive and current-channelling responses in TEM surveys using state-of-art software (MARCO and LEROI); identification of instabilities in multiple-plate modelling in LEROI.Development of an algorithm for modelling the three-component MMR or current-channelling EM response of multiple 3D conductors.Recognition of the importance of correct modelling of the MMR response of a layered earth as a precursor to stripping background and modelling of residual MMR anomalies.Development of a software package for processing three-component MMR field data (calibration, stripping of wire field and layered-earth background field) and for modelling the data in 3 components, and with multiple 3D conductive bodies.Development of a 3D rotatable screen viewer for an arbitrary number of boreholes, transmitters and dipping tabular conductors (incorporated in the above software package).Numerical modelling of an MMR phase response.A comparison of noise characteristics of different receivers and borehole EM probes.

Interpretation of ground VLF-EM data in terms of vertical conductor models

The very-low-frequency electromagnetic (VLF-EM) method has been used extensively for the detection and delineation of weak conductors such as those formed by water and/or clay-filled fracture and shear zones in the Precambrian rocks of the Canadian Shields as part of the Canadian Nuclear Fuel Waste Management Program. However, no satisfactory method of interpreting VLF anomalies over such conductors was available when the field data became available in the early 1980s. A study was undertaken to develop a method for quantitative interpretation of ground VLF-EM data over two-dimensional (2D) sheet-like conductors of low conductance, finite depth and depth extent, embedded in a resistive host rock of finite resistivity, using characteristic curves. Numerical modelling of the VLF response of such conductors revealed that the axes-ratio (inappropriately termed ellipticity in VLF literature) variations are much smaller than the corresponding tilt angle variations, and much less sensitive to the depths of the conductors. Extensive ground VLF-EM surveys over weakly conductive fractures and shear zones at several test areas in Ontario also indicated that the axes-ratio response is not only much smaller than the corresponding tilt angle response, it is often difficult to identify in the field data. An interpretation scheme was devised to determine the conductance, depth and depth extent of such weak vertical conductors located in a host rock of finite resistivity which depends on the peak-to-peak tilt angle response and the horizontal separation between the peaks. A complete interpretation of such conductors requires knowledge of the host rock resistivity and the approximate depth, if the depth extent of the conductor is required. The interpretation method was applied to interpret a VLF anomaly over a complex conductivity structure at East Bull Lake, Ontario which illustrated the limitations of the technique. A ground VLF anomaly from Chalk River, Ontario, was interpreted using the interpretation scheme described, which agrees well with the information from geological mapping and with the numerical forward modelling response.

MAGNETIC WAVETILT MEASUREMENTS FOR GEOLOGICAL FRACTURE MAPPING1

AbstractThe measurement of wavetilt is diagnostic for determining the electrical characteristics of the upper layers of the ground at VLF and LF frequency ranges. Theoretical and field studies have indicated that electric wavetilt using the transverse magnetic (TM) waves detects lateral inhomogeneities virtually instantly as abrupt changes in electrical properties are encountered. Theoretical studies have also indicated that magnetic wavetilt measurements using transverse electric (TE) waves are superior to electric wavetilts for such purposes.An experimental survey was conducted at two locations near Atikokan, Ontario, to verify the theoretical predictions. The survey area, forming a part of a large granitic pluton, was mapped earlier by various geophysical techniques, including the ground VLF‐EM method, to detect weak conductors formed either by the presence of fractures in the bedrock filled with water and/or clay, or overburden filling bedrock depressions.A small, multi‐turn, horizontal loop was used during the survey as the transmitter to generate TE waves at eleven frequencies from 10.7 to 58.5 kHz. The magnetic wavetilt measurements detected all previously known conductors at the two locations. In addition, the survey detected several weak conductors that were missed by the VLF survey. Thus, the survey indicated the usefulness of magnetic wavetilt results for detection of weak conductors at shallow depths, which may have application in engineering geophysical surveys. The multi‐frequency wavetilt data also provided some indications of the depth and depth extent of such conductors.

Experiences with a local loop VLF transmitter for geological studies in the canadian nuclear fuel waste management program

Very low frequency electromagnetic (VLF-EM) methods have been useful for detecting weak conductors such as overburden infilling resistive bedrock valleys or water-filled fractures and shear zones in the highly resistive Precambrian granitic terrain of Canada. Since VLF-EM methods detect conductors only when their strikes are roughly perpendicular to the direction of the primary magnetic field; at least two VLF sources with orthogonal magnetic field directions are required for a total conductor mapping of an area. At several areas in western Ontario and eastern Manitoba such orthogonal sources are not available; the primary magnetic field directions in that region generated by available U.S. Navy VLF stations are generally only north-south. In order to overcome this problem, a portable local loop VLF transmitter was designed and built at the Geological Survey of Canada. Surveys with the portable local loop transmitter proved that this source was a reliable substitute for Navy VLF stations when the survey area was 3–10 km from the loop source. Identical conductor positions were mapped when the local loop was placed in such a way that its primary magnetic field was aligned in the same direction as that from a U.S. Navy VLF station. In areas where orthogonal VLF magnetic fields were not available, the use of the local loop source resulted in the identification of additional conductors, the locations of which agreed well with results from surface geological mapping.

Near-surface lithogeochemical halo as an aid to discovery of deeply buried unconformity-type uranium deposits, Athabasca Basin, Canada

Unconformity-type U deposits are being found to depths of more than 400 m where graphitic rocks underlie the Proterozoic sandstone unconformity. Exploration to date involves drilling weak electromagnetic conductors that reflect the graphitic basement. The deposits are believed to have formed through circulation of heated formation waters which discharged essentially vertically above the deposits. Geochemically detectable zones of alteration are reported for cross-sections through the Deilmann, Midwest, and McClean deposits. Information on the areal dimensions of near-surface haloes was required to justify the drilling of grids of shallow holes along conductors or favourable structures as a cost-effective exploration alternative to deep holes, and to define grid spacings. Orientation surveys were undertaken by sampling the uppermost 10 m of sandstone in a selection of holes from the Cigar Lake, Dawn Lake, and Wolf Lake areas where the deposits are, respectively, 400–430 m, 100–160 m, and 180–210 m below surface. The first two deposits have published reserves of 385 and 30–40 million pounds U 3O 8, respectively, while Wolf Lake is much smaller. Well-developed anomalies lie vertically above the richest portion of the Cigar Lake deposit in an area 150 × 600 m and a weak anomaly in many elements continues over the 1800-m length that was sampled. Total and leachable U are 13 to 8 times background with maximum values of 53 and 26 ppm, respectively. Anomalies of 14 to 8 times background are also present for V, Na 2O and Zn, and 5 to 3 times background for Sr, Y, Pb, Th, As, and P. Of the four Dawn Lake mineralized zones, only the 11B Zone was studied, with partial coverage of the 11A Zone. Anomalies 50–100 m by 250–600 m in size are often displaced up to 100 m northeast of the 11B Zone. B, MgO, Pb and both total and leachable U anomalies are 16 to 8 times background with Y, V and As 7 to 5 times background. By contrast, at the Wolf Lake deposit, only irregular variations occur for most of these elements. The unusual patterns may reflect post-alteration tectonism of the sandstone overlying the deposit as regional thrust faulting occurs nearby. Detection of near-surface lithogeochemical haloes using grids of shallow holes would facilitate discovery of deep deposits and reduce expensive, deep drilling.

Polymere Dimethyl-und Diphenylglyoximatokomplexe des Cobalts und Eisens mit 4.4′ -Bipyridin als Brückenligand. Die Kristallstruktur des Bis(dimethylglyoximato)4.4′-bipyridincobalt(II)*/ Polymeric Dimethyl-and Diphenylglyoximato Complexes of Cobalt and Iron with 4,4′-Bipyridine as a Bridging Ligand. The Crystal Structure of Bis(dimethylglyoximato)4,4′-bipyridine Cobalt(II)

Polymeric bis(dimethyl- and diphenylglyoximato)-complexes of Fe(II) and Co(II) with 4,4′-bipyridine as a bridging ligand have been synthesized from the glyoximato metal complexes and 4,4′-bipyridine in ethanol. The Co(II) compounds are paramagnetic and surprisingly stable against oxidation. The iron complexes are weak electrical conductors with approximately 10-9 Ω-1cm-1 . Bis(dimethylglyoximato)-4,4′-bipyridine cobalt(II) crystallizes triclinic in the space group PT with Z=1. The crystal structure is built up by linear chains of alternating Co(II) glyoximato complexes and axial bonded 4,4′-bipyridine bridges. The compound is characterized by strong Co-N-bonds of 189 pm within the glyoximato moiety and weak bonds of 228 pm to the bipyridine ligand. The two heterocycles of the bipyridine are coplanar, therefore the local symmetry of the complex is D2h.

Reduction in the aciduric properties of the oral bacterium Streptococcus mutans GS-5 by fluoride

Plaque bacteria tend to be aciduric; they can carry out glycolysis even when the environmental pH is low. These bacteria expend energy to maintain their cytoplasm at pH values above that of their environment, commonly by proton extrusion and subsequent proton exclusion by the cell membrane. Any reagent that would compromise the insulating capacity of the membrane would decrease net proton extrusion and thereby may enhance acid sensitivity. Recent studies have indicated that bacterial fluoride uptake is dependent on pH and the concentration of HF rather than F − so the molecular species taken up, then, is probably HF. Therefore, fluoride uptake is probably accompanied by proton uptake as well. In this study, weak acids and ionophores were used to test the hypothesis that a reduction in net proton extrusion would enhance the acid sensitivity of streptococcal glycolysis and discharge a transmembrane proton gradient. Lightly buffered Streptococcus mutans cells were incubated with glucose and the pH was monitored over a 4 h period to assess the rate and extent of metabolic acid production. Transmembrane pH gradients were estimated from the ratio of intracellular to extracellular concentrations of radiolabelled acetate. Fluoride appeared to have an action on Strep. mutans similar to that of weak acids or proton conductors in that it reduced the aciduric property of glycolysis and discharged a pH gradient across the bacterial cell membrane.