Conductivity Gradient Research Articles

Electrokinetic instabilities in co-flowing ferrofluid and buffer solutions with matched electric conductivities

Electrokinetic instabilities have been extensively studied in microchannel fluid flows with conductivity or conductivity and permittivity gradients for various microfluidic applications. This work presents an experimental and numerical investigation of the electrokinetic co-flow of ferrofluid and buffer solutions with matched electric conductivities. We find that the ferrofluid and buffer interface becomes unstable with periodic waves if the applied direct-current electric field reaches a threshold value. We develop a two-dimensional numerical model to seek a preliminary understanding of such an electrically originated flow instability. Our model indicates that the observed phenomenon is not a consequence of the electric body force acting on the permittivity gradients between the ferrofluid and buffer solutions. It is instead attributed to the diffusion-induced conductivity gradients that are formed at the ferrofluid and buffer interface due to the mismatching diffusivities of ferrofluid nanoparticles and buffer ions.

Modeling nanoscale temperature gradients and conductivity evolution in pulsed light sintering of silver nanowire networks

Sintering of metal nanowire (NW) networks on transparent polymers is an emerging approach for fabricating transparent conductive electrodes used in multiple devices. Pulsed light sintering is a scalable sintering process in which large-area, broad-spectrum xenon lamp light causes rapid NW fusion to increase network conductivity, while embedding the NWs in the polymer to increase mechanical robustness. This paper develops a multiphysical approach for predicting evolution of conductivity, NW fusion and nanoscale temperature gradients on the substrate during pulsed light sintering of silver NWs on polycarbonate. Model predictions are successfully validated against experimentally measured temperature and electrical resistance evolution. New insight is obtained into the diameter-dependent kinetics of NW fusion and nanoscale temperature gradients on the substrate, which are difficult to obtain experimentally. These observations also lead to the understanding that NW embedding in intense pulsed light sintering (IPL) can occur below the glass transition temperature of the polymer, and to a new differential thermal expansion-based mechanism of NW embedding during IPL. These insights, and the developed model, create a framework for physics-guided choice of NWs, substrate and process parameters to control conductivity and prevent substrate damage during the process.

Predicting the Temperature Distribution in Longitudinal Fins of Various Profiles with Power Law Thermal Properties Using the Variational Iteration Method

In this article, the variational iteration method (VIM) is used to analyze heat transfer in longitudinal fins of various profiles with temperature dependent thermal conductivity and heat transfer coefficient. In order to show the efficiency of the VIM, the results obtained using the VIM are compared with the previously obtained results using the differential transform method (DTM) and Lie group analysis of a fin problem with the rectangular profile. After establishing confidence in VIM, heat transfer is analyzed to determine the temperature profiles in longitudinal fins of various profiles with power law thermal properties. The temperature distribution is compared between various profiles. The effects of some physical parameters such as the thermo-geometric fin parameter and thermal conductivity gradient on temperature distribution are illustrated.

Local and Regional Scale Heterogeneity Drive Bacterial Community Diversity and Composition in a Polar Desert.

The distribution of organisms in an environment is neither uniform nor random but is instead spatially patterned. The factors that control this patterning are complex and the underlying mechanisms are poorly understood. Soil microbes are critical to ecosystem function but exhibit highly complex distributions and community dynamics due in large part to the scale-dependent effects of environmental heterogeneity. To better understand the impact of environmental heterogeneity on the distribution of soil microbes, we sequenced the 16S rRNA gene from bacterial communities in the microbe-dominated polar desert ecosystem of the McMurdo Dry Valleys (MDV), Antarctica. Significant differences in key edaphic variables and alpha diversity were observed among the three lake basins of the Taylor Valley (Kruskal–Wallis; pH: χ2 = 68.89, P < 0.001, conductivity: χ2 = 35.03, P < 0.001, observed species: χ2 = 7.98, P = 0.019 and inverse Simpson: χ2 = 18.52, P < 0.001) and each basin supported distinctive microbial communities (ANOSIM R = 0.466, P = 0.001, random forest ratio of 14.1). However, relationships between community structure and edaphic characteristics were highly variable and contextual, ranging in magnitude and direction across regional, basin, and local scales. Correlations among edaphic factors (pH and soil conductivity) and the relative abundance of specific phyla were most pronounced along local environmental gradients in the Lake Fryxell basin where Acidobacteria, Bacteroidetes, and Proteobacteria declined while Deinococcus–Thermus and Gemmatimonadetes increased with soil conductivity (all P < 0.1). Species richness was most strongly related to the soil conductivity gradient present within this study system. We suggest that the relative importance of pH versus soil conductivity in structuring microbial communities is related to the length of edaphic gradients and the spatial scale of sampling. These results highlight the importance of conducting studies over large ranges of key environmental gradients and across multiple spatial scales to assess the influence of environmental heterogeneity on the composition and diversity of microbial communities.

Resistance gradient polymeric electromagnetic shielding composites: Preparation and Characterization

Based on the principle of Stokes’ law, a series of polyvinyl butyral (PVB)/nickel (Ni) composite films with a resistance gradient were successfully prepared using a suspension casting method with the aid of gravity. Gradient distribution structure, conductive and mechanical properties, and electromagnetic shielding effectiveness (SE) were investigated. Scanning electron microscopy (SEM) observations and energy‐dispersive spectrometer (EDS) detection show that the gradient distribution of Ni particles in the PVB matrix was formed along the thickness‐direction. A surface resistivity difference of 10 orders of magnitude appears between the top surface (PVB‐rich side) and the bottom surface (Ni‐rich side). Percolation transformation occurs in the range of Ni content of 3.0∼4.5 vol% at the Ni‐rich side, which is much lower than that of PVB/Ni composites with homogeneous Ni distribution. The gradient distribution structure grants the composite both good electromagnetic shielding performance and good mechanical properties. When the Ni loading reaches 10.5 vol% in the film, its SE value rises to 30 dB, which is 15 dB higher than that of a homogenous film with the same filler content. It is believed that electrically conductive gradient polymeric composites have potential application value in the field of electromagnetic shielding. POLYM. COMPOS., 40:1842–1849, 2019. © 2018 Society of Plastics Engineers

Alteration in contact line dynamics of fluid-fluid interfaces in narrow confinements through competition between thermocapillary and electrothermal effects

The paper reports the results of our numerical investigation on contact line dynamics of a thermal field assisted flow configuration of two immiscible fluids in a narrow thermofluidic pathway. The surfaces of the channel are wetted with predesigned wettabilities and interdigitated electrodes are mounted on the substrates to generate a non-uniform electric field. In this study, the interplay of thermocapillary and electrothermal forces on interfacial dynamics are considered. The former is caused by temperature-induced surface tension gradients while the latter is originated from the temperature-induced gradients in permittivity and electrical conductivity. Our investigations reveal that the relative strength of interfacial forces and electrothermal forces and their interactions can be effectively used to control the capillary filling time as well as flow dynamics. For the same strength of thermocapillary and electrothermal forces (characterized by individual dimensionless numbers), electrothermal effects dominate over thermocapillary effects. However, interfacial forces dominate over electrothermal forces at certain wettabilities (characterized by the imposed contact angle on the surfaces), and depending on the direction of the interfacial forces, the contact line travels toward the entry or exit of the channel.

Predicting Global Ground Geoelectric Field With Coupled Geospace and Three‐Dimensional Geomagnetic Induction Models

AbstractWe forecast the global effects of space weather on the geoelectric and geomagnetic fields using a novel combination of methods. We use a realistic three‐dimensional (3‐D) model of Earth's electrical conductivity and a realistic representation of magnetospheric and ionospheric current systems. Our scheme involves the following steps: (1) We run a global magnetohydrodynamic model of the magnetosphere coupled to an electrostatic model of the ionosphere. (2) We calculate a global time series of the ground magnetic field resulting from the ionospheric, field‐aligned, and magnetospheric currents of the global magnetohydrodynamic model. (3) We approximate this external field by an equivalent source current flowing in a thin shell above Earth. (4) We calculate a global time series of geoelectric and geomagnetic fields from the equivalent current and a 3‐D conductivity model of Earth that also takes into account the coast effect due to large horizontal conductivity gradient. We verify our implementation by comparing the results against known analytic and numeric solutions, and then apply our scheme to the geomagnetic storm of 14 and 15 December 2006. In particular, we show that accounting for 3‐D structure of Earth's conductivity results in significantly enhanced geoelectric field at large lateral gradients of conductivity, especially in coastal regions, both at middle and high latitudes. In the studied geomagnetic storm the largest values of 3‐D geoelectric field are detected at high latitudes reaching 2.5 V/km and the 3‐D effect extends inland by a few hundred kilometers.

Maturation of GABAergic Transmission in Cerebellar Purkinje Cells Is Sex Dependent and Altered in the Valproate Model of Autism

Brain development is accompanied by a shift in gamma-aminobutyric acid (GABA) response from depolarizing-excitatory to hyperpolarizing-inhibitory, due to a reduction of intracellular chloride concentration. This sequence is delayed in Autism Spectrum Disorders (ASD). We now report a similar alteration of this shift in the cerebellum, a structure implicated in ASD. Using single GABAA receptor channel recordings in cerebellar Purkinje cells (PCs), we found two conductance levels (18 and 10 pS), the former being dominant in newborns and the latter in young-adults. This conductance shift and the depolarizing/excitatory to hyperpolarizing/inhibitory GABA shift occurred 4 days later in females than males. Our data support a sex-dependent developmental shift of GABA conductance and chloride gradient, leading to different developmental timing in males and females. Because these developmental sequences are altered in ASD, this study further stresses the importance of developmental timing in pathological neurodevelopment.

Five-Membered Cyclic Sulfur Compounds as (Co-)Solvents for Lithium-Ion Battery Electrolytes

Lithium-ion batteries (LIBs) are known for their domination in the market for rechargeable energy storage systems. However, the state-of-the-art non-aqueous aprotic electrolytes, as inevitable components thereof, generally comprising organic carbonates such as ethylene carbonate (EC) and dimethyl carbonate (DMC) with lithium hexafluorophosphate (LiPF6) as conducting salt, still cope with well-known drawbacks and limitations1. In order to realize a substantial improvement, it is of significant importance to tailor new electrolyte formulations and to understand the structural impacts of the electrolyte components, especially solvents, on the electrolyte’s properties. The established organic carbonates, e.g., EC or propylene carbonate (PC), have a structural similarity to five-membered cyclic sulfur compounds. A variation of the oxygen atom number and position leads to five commercially available modifications with constant geometry, i.e., tetrahydrothiophene, tetrahydrothiophene 1-oxide, ethylene sulfite, sulfolane, 1,3-propane sultone and 1, 3, 2- dioxathiolane 2, 2- dioxide. Most of them have already been approved as solid electrolyte interphase (SEI) additives, whereas sulfolane has been used as single or co-solvent, as well2, 3. To reveal the impact of the aforementioned compounds on physicochemical and electrochemical properties of the formulated electrolytes, they were investigated as co-solvents with PC to achieve dissolution of every compound, as 1,3-propane sultone and 1, 3, 2- dioxathiolane 2, 2- dioxide are solid at room temperature. Lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) was used as conducting salt due to its good solubility, thermal and electrochemical stability, and inertness to water4. Viscosity, conductivity, permittivity, Raman and pulsed-field gradient nuclear magnetic resonance (PFG NMR) measurements as well as linear sweep voltammetry (LSV) were conducted to characterize the performance of the formulated electrolytes. It was demonstrated that not the amount of oxygen atoms but the type of functional group (sulfinyl or sulfonyl) plays a decisive role in ionic mobility. Tetrahydrothiophene 1-oxide was selected as promising solvent candidate due to its excellent physicochemical properties. Therefore, the focus for further electrochemical, analytical and spectral characterization was set on this sulfur compound containing electrolytes. The convincing physicochemical properties have a direct impact on the electrochemical behavior, enabling stable galvanostatic cycling of cells containing the PC-based electrolyte. With this in line, interfacial electrochemistry regarding formation, dynamics and also stability of the protective layer was considered, as well. The obtained results pointed out that tetrahydrothiophene 1-oxide as co-solvent in organic carbonate-based electrolytes has a highly positive effect on its ionic mobility as well as on the overall cell performance. S. Hess, M. Wohlfahrt-Mehrens and M. Wachtler, J. Electrochem. Soc., 2015, 162, A3084-A3097.A. Hofmann, M. Schulz, S. Indris, R. Heinzmann and T. Hanemann, Electrochim. Acta, 2014, 147, 704-711.A. Birrozzi, N. Laszczynski, M. Hekmatfar, J. von Zamory, G. A. Giffin and S. Passerini, J. Power Sources, 2016, 325, 525-533.K. Xu, Chem. Rev., 2004, 104, 4303-4417.

Growth and nutrients content of Atriplex canescens across a soil electric conductivity gradient

Atriplex canescens canopy cover, biomass production, and nutrient content were evaluated after four years of livestock grazing exclusion and mechanical shrub removal, except A. canescensin an arid rangeland with a slightly saline soil and with a long history of heavy livestock grazing in the southern Chihuahuan Desert, Mexico (24° N). Twenty 3 × 3 m paddocks were established in terrains with three levels of electric conductivity (EC): &lt;1.4 dS/m (n=7), 1.4–1.6 dS/m (n=7) and &gt;1.6 dS/m. Atriplex canescens canopy cover was higher (49.5%; p&lt;0.01) on paddocks with soil EC &gt;1.6 dS/m than paddocks with soil EC &lt;1.4 and 1.4–1.6 dS/m (32.1 and 22.9%, respectively). Above-ground biomass did not differ between paddocks with soils with EC of &lt;1.4 and 1.4–1.6 dS/m (1309 ± 535 and 1372 ± 180 kg DM/ha), but biomass increased 2.7 times (p&lt;0.01) when soil EC was greater than 1.6 dS/m. The soil EC had no effect on the levels of crude protein (range 13.6 to 14.3%), neutral detergent fiber (range 56.5 to 57.7%) and ash (range 14.5 to 16.4%). In vitro dry matter digestibility (IVDMD) of the foliage of A. canescens was not affected by of soil EC level (range 60.4 to 62.2%). It was concluded that in an arid rangeland with slight saline soil, the increase in salinity favors canopy cover and biomass production of A. canescens without altering nutrient content and IVDMD of this fodder shrub.

Variable number of TMC1-dependent mechanotransducer channels underlie tonotopic conductance gradients in the cochlea

Functional mechanoelectrical transduction (MET) channels of cochlear hair cells require the presence of transmembrane channel-like protein isoforms TMC1 or TMC2. We show that TMCs are required for normal stereociliary bundle development and distinctively influence channel properties. TMC1-dependent channels have larger single-channel conductance and in outer hair cells (OHCs) support a tonotopic apex-to-base conductance gradient. Each MET channel complex exhibits multiple conductance states in ~50 pS increments, basal MET channels having more large-conductance levels. Using mice expressing fluorescently tagged TMCs, we show a three-fold increase in number of TMC1 molecules per stereocilium tip from cochlear apex to base, mirroring the channel conductance gradient in OHCs. Single-molecule photobleaching indicates the number of TMC1 molecules per MET complex changes from ~8 at the apex to ~20 at base. The results suggest there are varying numbers of channels per MET complex, each requiring multiple TMC1 molecules, and together operating in a coordinated or cooperative manner.

Electrothermally actuated moving contact line dynamics over chemically patterned surfaces with resistive heaters

In this paper, we explore the moving contact line dynamics of two Newtonian immiscible fluids over substrates patterned with two different alternative chemical patches. The bulk fluid motion is actuated using electrothermal kinetics where the thermal field is generated by incorporating resistive heaters on the substrate. The electrothermal forces, which arise from the local gradient in electrical conductivity and permittivity, strongly depend on the local temperature and potential distributions. The thermal field and the potential distribution can be modulated by altering the heater characteristics and electrode patterning. The contact line motion and its intricate physics can be effectively tuned by altering the geometrical parameters of the heaters and electrode arrangement. Further, a comparison is executed between conventional electrothermal and heater-assisted electrothermal processes. The interfacial dynamics of the immiscible binary fluids is greatly affected by the present electrothermal mechanism and shows advantages over the conventional electrothermal process. The results presented here are effective for developing various smart devices involving multiphase flow dynamics within an electrokinetic paradigm.

Bioinformatics Analysis of Microbial Abundance and Diversity in Acid Mine Drainage from the Solomon Mine Near Creede, Colorado

This study focused on characterizing the phylotypic composition of acid mine drainage (AMD) communities associated with the Solomon Mine near Creede, Colorado, and its relative diversity compared to microbial communities found in the East Willow Creek (EWC) watershed. AMD from the Solomon Mine adit flows into an existing passive bioremediation wetland system located next to the Solomon Mine adit that currently is ineffective and is under consideration for renovation. We are interested in gaining an understanding of the baseline microbial communities present in AMD/EWC and to monitor them during future wetland renovation. Prokaryotic community profiling was approached using SSU 16S rRNA marker gene amplification coupled with next generation sequencing. Bioinformatics analysis included raw read preprocessing, data visualization, and statistical testing using a combination of USEARCH and QIIME-based scripts. A pH and conductivity gradient were observed for water moving through the currently inefficient wetland system at the Solomon Mine. The EWC microbiomes had statistically significant higher alpha diversity compared to the AMD microbiomes. Beta diversity analysis parsed the sample locations into statistically significant groups including core AMD microbiomes, the wetland Cell 3 microbiome, and EWC microbiomes using multidimensional scaling. Taxa driving beta diversity included the phylum Proteobacteria for the core AMD microbiomes, the phyla Firmicutes and Chloroflexi for the constructed wetland Cell 3, and the phyla Bacteroidetes and Verrucomicrobia for EWC. Our data suggests that the microbial community in constructed wetland Cell 3 is likely where limited sulfate reduction activity is operating at low capacity, which will be further investigated via shotgun metagenomic analysis.

Observation of Ionospheric Alfvén Resonances at 1–30 Hz and Their Superposition With the Schumann Resonances

AbstractLong‐term measurements of the high‐frequency magnetic field (0.1–100 Hz) have been made at Eskdalemuir Observatory in the United Kingdom since September 2012. We analyze five years of dynamic spectrograms to examine the occurrence and behavior of the Schumann and ionospheric Alfvén resonances (IAR) and Pc1 pulsations. The resonances, observed as diffuse bands, arise from reflections of energy both within the Earth‐ionosphere cavity and from the nonlinear conductivity gradient of the ionosphere. Schumann Resonances (SR) occur continuously but IAR are observed to arise at local nighttime in ∼50% of days in the data set. Typically, IAR are found at frequencies of 1–8 Hz, but we find them extending out to 30 Hz and strongly superimposing over the first three Schumann resonances around 9% of the time. These phenomena include constructive and destructive interference, nonlinear frequency changes over the span of several hours, and polarity enhancements. In addition, the magnitude of the IAR does not decline rapidly with frequency as often proposed. We find that the IAR and their superposition with SR are strongly controlled by season and geomagnetic activity. We compare 6 days with the most unusual IAR behavior in the data set to ionosonde measurements of f0F2, a proxy for ionospheric conductivity but find little correlation. We suggest that, as current theoretical modeling does not account for these observations, further work is needed to understand how they arise.

Application of new point measurement device to quantify groundwater-surface water interactions

The streambed point velocity probe (SBPVP) measures in situ groundwater velocities at the groundwater-surface water interface without reliance on hydraulic conductivity, porosity, or hydraulic gradient information. The tool operates on the basis of a mini-tracer test that occurs on the probe surface. The SBPVP was used in a meander of the Grindsted Å (stream), Denmark, to determine the distribution of flow through the streambed. These data were used to calculate the contaminant mass discharge of chlorinated ethenes into the stream. SBPVP data were compared with velocities estimated from hydraulic head and temperature gradient data collected at similar scales. Spatial relationships of water flow through the streambed were found to be similar by all three methods, and indicated a heterogeneous pattern of groundwater-surface water exchange. The magnitudes of estimated flow varied to a greater degree. It was found that pollutants enter the stream in localized regions of high flow which do not always correspond to the locations of highest pollutant concentration. The results show the combined influence of flow and concentration on contaminant discharge and illustrate the advantages of adopting a flux-based approach to risk assessment at the groundwater-surface water interface. Chlorinated ethene mass discharges, expressed in PCE equivalents, were determined to be up to 444 kg/yr (with SBPVP data) which compared well with independent estimates of mass discharge up to 438 kg/yr (with mini-piezometer data from the streambed) and up to 372 kg/yr crossing a control plane on the streambank (as determined in a previous, independent study).

Diatoms as tools for inferring ecotone boundaries in a coastal freshwater wetland threatened by saltwater intrusion

Species sorting mechanisms often control community assembly patterns across environmentally heterogeneous landscapes, particularly within microbial communities that respond quickly to environmental variability and are not dispersal-limited on intermediate time scales. In this study, we describe the spatial and seasonal patterns of two key environmental drivers, porewater (PW) conductivity and total phosphorus (TP), in the southern Everglades, FL., USA where saltwater intrusion, caused by rising sea level and hydrologic management, are transforming the natural environmental gradients of this ecological stressor and limiting nutrient. We surveyed diatom assemblages along transects capturing PW conductivity and TP gradients and searched for spatial boundaries in diatom assemblages along each transect. We also determined diatom assemblage thresholds to PW conductivity and TP, and identified significant indicator taxa with either negative (declining) or positive (increasing) relationships to each driver and their individual thresholds. We demonstrate that the southern Everglades exhibits spatially-structured gradients of conductivity and P that are oriented in two dimensions (i.e., with distance from the coast and from west to east) and are often, but not always, positively correlated. Our results show that these gradients drive spatial patterns of compositional similarity among our sampling sites. We found the location of greatest dissimilarity in diatom assemblages for each transect coincided with the upper boundary of the “white zone” – the visible ecotone between freshwater and coastal marshes. We did not detect seasonal differences in the position of the diatom-inferred ecotone as expected, nor did we detect significant differences in PW conductivity or TP between wet and dry seasons. Diatom assemblages were highly sensitive to both PW conductivity, with freshwater indicator assemblages declining above 2 mS cm−1 and becoming replaced by a brackish water assemblage at around 20 mS cm−1, and periphyton TP, with thresholds at 82 and 285 µg g−1 for negatively- and positively responding taxa, respectively. Our study highlights that small increases in PW conductivity and TP are sufficient to cause shifts in the diatom assemblages of the Everglades. As saltwater continues to encroach into this area, compositional changes in this important primary producer assemblage are expected to cascade through the ecosystem and influence the food web. The diatom indicator taxa and assemblage thresholds presented here offer a sensitive tool that should continue to be developed and applied to management strategies for saltwater intrusion while its effects can still be mitigated.

On the Nocturnal Downward and Westward Equatorial Ionospheric Plasma Drifts During the 17 March 2015 Geomagnetic Storm

AbstractDuring quiet period, the nocturnal equatorial ionospheric plasma drifts eastward in the zonal direction and downward in the vertical direction. This quiet time drift pattern could be understood through dynamo processes in the nighttime equatorial ionosphere. The present case study reports the nocturnal simultaneous occurrence of the vertically downward and zonally westward plasma drifts over the Indian latitudes during the geomagnetic storm of 17 March 2015. After ~17:00 UT (~22:10 local time), the vertical plasma drift became downward and coincided with the westward zonal drift, a rarely observed feature of low latitude plasma drifts. The vertical drift turned upward after ~18:00 UT, while the zonal drift became eastward. We mainly emphasize here the distinct bipolar type variations of vertical and zonal plasma drifts observed around 18:00 UT. We explain the vertical plasma drift in terms of the competing effects between the storm time prompt penetration and disturbance dynamo electric fields. Whereas, the westward drift is attributed to the storm time local electrodynamical changes mainly through the disturbance dynamo field in addition to the vertical Pedersen current arising from the spatial (longitudinal) gradient of the field aligned Pedersen conductivity.

A novel approach for fabrication of functionally graded W/Cu composites via microwave processing

Functionally graded materials (FGM) are a group of promising materials but demand efficient and reliable manufacturing approaches. We report a novel method utilizing microwave (MW) processing to fabricate functionally graded W/Cu composites. In the present work, the MW sintering set-up was designed to allow a potent heat flux and significant thermal gradient during the sintering. W skeletons with porosity gradient were synthesized first by using MW selective sintering. The W skeletons were subsequently infiltrated with Cu and W-Cu compositional graded composites were obtained. Corresponding to the compositional gradient, the composites showed gradients in hardness and electric conductivity. In addition, the graded microstructure and composition can be tailored by adding sintering activator such as Ni. This route provides an effective fabrication method of both porosity-gradient and compositional graded materials W/Cu composite.

Probing Growth-Induced Anisotropic Thermal Transport in High-Quality CVD Diamond Membranes by Multifrequency and Multiple-Spot-Size Time-Domain Thermoreflectance.

The maximum output power of GaN-based high-electron mobility transistors is limited by high channel temperature induced by localized self-heating, which degrades device performance and reliability. Chemical vapor deposition (CVD) diamond is an attractive candidate to aid in the extraction of this heat and in minimizing the peak operating temperatures of high-power electronics. Owing to its inhomogeneous structure, the thermal conductivity of CVD diamond varies along the growth direction and can differ between the in-plane and out-of-plane directions, resulting in a complex three-dimensional (3D) distribution. Depending on the thickness of the diamond and size of the electronic device, this 3D distribution may impact the effectiveness of CVD diamond in device thermal management. In this work, time-domain thermoreflectance is used to measure the anisotropic thermal conductivity of an 11.8 μm-thick high-quality CVD diamond membrane from its nucleation side. Starting with a spot-size diameter larger than the thickness of the membrane, measurements are made at various modulation frequencies from 1.2 to 11.6 MHz to tune the heat penetration depth and sample the variation in thermal conductivity. We then analyze the data by creating a model with the membrane divided into ten sublayers and assume isotropic thermal conductivity in each sublayer. From this, we observe a two-dimensional gradient of the depth-dependent thermal conductivity for this membrane. The local thermal conductivity goes beyond 1000 W/(m K) when the distance from the nucleation interface only reaches 3 μm. Additionally, by measuring the same region with a smaller spot size at multiple frequencies, the in-plane and cross-plane thermal conductivities are extracted. Through this use of multiple spot sizes and modulation frequencies, the 3D anisotropic thermal conductivity of CVD diamond membrane is experimentally obtained by fitting the experimental data to a thermal model. This work provides an improved understanding of thermal conductivity inhomogeneity in high-quality CVD polycrystalline diamond that is important for applications in the thermal management of high-power electronics.

Conductivity gradients as inferred by electromagnetic-induction meter (EM38) readings within a salt-affected wetland in Saskatchewan, Canada

The change from deep-rooted grass and shrub vegetation to annual-cropping dryland farming has contributed to serious soil salinization challenges on the semi-arid North American Great Plains. In some cases, cultivation of the Great Plains has increased the availability of water, causing dominant sulfate salts to travel from the uphill areas to depressions where it will surface when water evaporates at the soil surface. A potential solution could include the replanting of the native deep-rooted vegetation, which requires knowledge of the spatial distribution of soil salinity. This study tested the soil factors influencing electromagnetic-induction meter (EM38) readings of soil salinity distribution around wetlands. The objectives were to: (1) predict growth and survival of Salix dasyclados Wimm. (cv. ‘India’) along a salinity gradient in a small wetland, and (2) investigate whether newly established willows affected water-table fluctuations, which would indicate their phreatophytic nature or their ability to obtain their water supply from the zone of saturation. Results indicated significantly lower salinity values for sampling points with EM38 readings above 175 and 250 mS m−1 for height and survival, respectively. In addition, diurnal fluxes of the water table in areas of good willow growth and lower salinity indicated that cultivar ‘India’ was phreatophytic in these areas and therefore has great potential for being used to combat saline seeps.