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1.  Introduction to power-frequency electric and magnetic fields. 
Environmental Health Perspectives  1993;101(Suppl 4):73-81.
This paper introduces the reader to electric and magnetic fields, particularly those fields produced by electric power systems and other sources using frequencies in the power-frequency range. Electric fields are produced by electric charges; a magnetic field also is produced if these charges are in motion. Electric fields exert forces on other charges; if in motion, these charges will experience magnetic forces. Power-frequency electric and magnetic fields induce electric currents in conducting bodies such as living organisms. The current density vector is used to describe the distribution of current within a body. The surface of the human body is an excellent shield for power-frequency electric fields, but power-frequency magnetic fields penetrate without significant attenuation; the electric fields induced inside the body by either exposure are comparable in magnitude. Electric fields induced inside a human by most environmental electric and magnetic fields appear to be small in magnitude compared to levels naturally occurring in living tissues. Detection of such fields thus would seem to require the existence of unknown biological mechanisms. Complete characterization of a power-frequency field requires measurement of the magnitudes and electrical phases of the fundamental and harmonic amplitudes of its three vector components. Most available instrumentation measures only a small subset, or some weighted average, of these quantities. Hand-held survey meters have been used widely to measure power-frequency electric and magnetic fields. Automated data-acquisition systems have come into use more recently to make electric- and magnetic-field recordings, covering periods of hours to days, in residences and other environments.(ABSTRACT TRUNCATED AT 250 WORDS)
PMCID: PMC1519708  PMID: 8206045
2.  The effect of ambient humidity on the electrical properties of graphene oxide films 
Nanoscale Research Letters  2012;7(1):363.
We investigate the effect of water adsorption on the electrical properties of graphene oxide (GO) films using the direct current (DC) measurement and alternating current (AC) complex impedance spectroscopy. GO suspension synthesized by a modified Hummer's method is deposited on Au interdigitated electrodes. The strong electrical interaction of water molecules with GO films was observed through electrical characterizations. The DC measurement results show that the electrical properties of GO films are humidity- and applied voltage amplitude-dependent. The AC complex impedance spectroscopy method is used to analyze the mechanism of electrical interaction between water molecules and GO films in detail. At low humidity, GO films exhibit poor conductivity and can be seen as an insulator. However, at high humidity, the conductivity of GO films increases due to the enhancement of ion conduction. Our systematic research on this effect provides the fundamental supports for the development of graphene devices originating from solution-processed graphene oxide.
PMCID: PMC3467191  PMID: 22748079
Graphene oxide; Humidity sensing; Complex impedance spectroscopy; Nano device
3.  Monitoring Scanning Electrochemical Microscopy Approach Curves with Mid-Infrared Spectroscopy – Towards a Novel Current-Independent Positioning Mode 
Analytical chemistry  2010;82(8):3132-3138.
Single-bounce attenuated total reflection infrared spectroscopy in the 3–20 µm range (MIR) has been combined with scanning electrochemical microscopy (SECM) for in situ spectroscopic detection of electrochemically induced localized surface modifications using an ultramicroelectrode (UME). In this study, a novel current-independent approach for positioning the UME in aqueous electrolyte solution is presented using either changes of IR absorption intensity associated with borosilicate glass (BSG), which is used as shielding material of the UME wire, or by monitoring IR changes of the water spectrum within the penetration depth of the evanescent field due to displacement of water molecules in the volume between the sample surface and the UME within the evanescent field. The experimental results show that the UME penetrates into the exponentially decaying evanescent field in close vicinity (a few µm) to the ATR crystal surface. Hence, the resulting intensity changes of the IR absorption spectra for borosilicate glass (increase) and for water (decrease), can be used to determine the position of the UME relative to the ATR crystal surface independent of the current measured at the UME.
PMCID: PMC2862910  PMID: 20329757
4.  Spatial variation of permittivity of an electrolyte solution in contact with a charged metal surface: a mini review 
Contact between a charged metal surface and an electrolyte implies a particular ion distribution near the charged surface, i.e. the electrical double layer. In this mini review, different mean-field models of relative (effective) permittivity are described within a simple lattice model, where the orientational ordering of water dipoles in the saturation regime is taken into account. The Langevin-Poisson-Boltzmann (LPB) model of spatial variation of the relative permittivity for point-like ions is described and compared to a more general Langevin-Bikerman (LB) model of spatial variation of permittivity for finite-sized ions. The Bikerman model and the Poisson-Boltzmann model are derived as limiting cases. It is shown that near the charged surface, the relative permittivity decreases due to depletion of water molecules (volume-excluded effect) and orientational ordering of water dipoles (saturation effect). At the end, the LPB and LB models are generalised by also taking into account the cavity field.
PMCID: PMC3664910  PMID: 22263808
charged metal surface; relative permittivity; electric double layer; finite element method; metallic electrode; water ordering; finite-sized ions; saturation effect; excluded volume effect
5.  Fabrication and Characterization of Polyaniline/PVA Humidity Microsensors 
Sensors (Basel, Switzerland)  2011;11(8):8143-8151.
This study presents the fabrication and characterization of a humidity microsensor that consists of interdigitated electrodes and a sensitive film. The area of the humidity microsensor is about 2 mm2. The sensitive film is polyaniline doping polyvinyl alcohol (PVA) that is prepared by the sol-gel method, and the film has nanofiber and porous structures that help increase the sensing reaction. The commercial 0.35 μm Complimentary Metal Oxide Semiconductor (CMOS) process is used to fabricate the humidity microsensor. The sensor needs a post-CMOS process to etch the sacrificial layer and to coat the sensitive film on the interdigitated electrodes. The sensor produces a change in resistance as the polyaniline/PVA film absorbs or desorbs vapor. Experimental results show that the sensitivity of the humidity sensor is about 12.6 kΩ/%RH at 25 °C.
PMCID: PMC3231745  PMID: 22164067
humidity microsensors; polyaniline; polyvinyl alcohol; MEMS
6.  Magnetic Behavior of Surface Nanostructured 50-nm Nickel Thin Films 
Nanoscale Research Letters  2010;5(10):1596-1602.
Thermally evaporated 50-nm nickel thin films coated on borosilicate glass substrates were nanostructured by excimer laser (0.5 J/cm2, single shot), DC electric field (up to 2 kV/cm) and trench-template assisted technique. Nanoparticle arrays (anisotropic growth features) have been observed to form in the direction of electric field for DC electric field treatment case and ruptured thin film (isotropic growth features) growth for excimer laser treatment case. For trench-template assisted technique; nanowires (70–150 nm diameters) have grown along the length of trench template. Coercive field and saturation magnetization are observed to be strongly dependent on nanostructuring techniques.
PMCID: PMC2956046  PMID: 21076670
Magnetic nanostructures; Magnetic properties; Surface treatment
7.  Magnetic Behavior of Surface Nanostructured 50-nm Nickel Thin Films 
Nanoscale Research Letters  2010;5(10):1596-1602.
Thermally evaporated 50-nm nickel thin films coated on borosilicate glass substrates were nanostructured by excimer laser (0.5 J/cm2, single shot), DC electric field (up to 2 kV/cm) and trench-template assisted technique. Nanoparticle arrays (anisotropic growth features) have been observed to form in the direction of electric field for DC electric field treatment case and ruptured thin film (isotropic growth features) growth for excimer laser treatment case. For trench-template assisted technique; nanowires (70–150 nm diameters) have grown along the length of trench template. Coercive field and saturation magnetization are observed to be strongly dependent on nanostructuring techniques.
PMCID: PMC2956046  PMID: 21076670
Magnetic nanostructures; Magnetic properties; Surface treatment
8.  Ultrahigh humidity sensitivity of graphene oxide 
Scientific Reports  2013;3:2714.
Humidity sensors have been extensively used in various fields, and numerous problems are encountered when using humidity sensors, including low sensitivity, long response and recovery times, and narrow humidity detection ranges. Using graphene oxide (G-O) films as humidity sensing materials, we fabricate here a microscale capacitive humidity sensor. Compared with conventional capacitive humidity sensors, the G-O based humidity sensor has a sensitivity of up to 37800% which is more than 10 times higher than that of the best one among conventional sensors at 15%–95% relative humidity. Moreover, our humidity sensor shows a fast response time (less than 1/4 of that of the conventional one) and recovery time (less than 1/2 of that of the conventional one). Therefore, G-O appears to be an ideal material for constructing humidity sensors with ultrahigh sensitivity for widespread applications.
PMCID: PMC3776968  PMID: 24048093
9.  Plasmonic and photonic scattering and near fields of nanoparticles 
We theoretically compare the scattering and near field of nanoparticles from different types of materials, each characterized by specific optical properties that determine the interaction with light: metals with their free charge carriers giving rise to plasmon resonances, dielectrics showing zero absorption in wide wavelength ranges, and semiconductors combining the two beforehand mentioned properties plus a band gap. Our simulations are based on Mie theory and on full 3D calculations of Maxwell’s equations with the finite element method. Scattering and absorption cross sections, their division into the different order electric and magnetic modes, electromagnetic near field distributions around the nanoparticles at various wavelengths as well as angular distributions of the scattered light were investigated. The combined information from these calculations will give guidelines for choosing adequate nanoparticles when aiming at certain scattering properties. With a special focus on the integration into thin film solar cells, we will evaluate our results.
PMCID: PMC3915561  PMID: 24475923
Nanoparticles; Plasmonics; Photonics; Scattering; Near field; Mie theory; FEM simulations; Solar cells; 42.70.-a; 78.67.Bf; 73.20.Mf
10.  Integrated Inductors for RF Transmitters in CMOS/MEMS Smart Microsensor Systems 
Sensors (Basel, Switzerland)  2007;7(8):1387-1398.
This paper presents the integration of an inductor by complementary metal-oxide-semiconductor (CMOS) compatible processes for integrated smart microsensor systems that have been developed to monitor the motion and vital signs of humans in various environments. Integration of radio frequency transmitter (RF) technology with complementary metal-oxide-semiconductor/micro electro mechanical systems (CMOS/MEMS) microsensors is required to realize the wireless smart microsensors system. The essential RF components such as a voltage controlled RF-CMOS oscillator (VCO), spiral inductors for an LC resonator and an integrated antenna have been fabricated and evaluated experimentally. The fabricated RF transmitter and integrated antenna were packaged with subminiature series A (SMA) connectors, respectively. For the impedance (50 Ω) matching, a bonding wire type inductor was developed. In this paper, the design and fabrication of the bonding wire inductor for impedance matching is described. Integrated techniques for the RF transmitter by CMOS compatible processes have been successfully developed. After matching by inserting the bonding wire inductor between the on-chip integrated antenna and the VCO output, the measured emission power at distance of 5 m from RF transmitter was -37 dBm (0.2 μW).
PMCID: PMC3814858
Bonding wire inductor; RF transmitter; CMOS/MEMS; CMOS compatible process
11.  Theoretical modeling of relative humidity on contact electrification of sand particles 
Scientific Reports  2014;4:4399.
Contact electrification of identical insulating particles has crucial significance for industrial and environmental science, especially in wind-blown granular systems. At the same time, the experimental phenomena of charge transfer first increased and then decreased with the increase of relative humidity has attracted the interest of many researchers. Humidity can affect the charge transfer has been early observed in the experiment, but the reason always puzzles researchers. In this study, based on trapped high-energy electron transfer mechanism, we introduce the effect of the water film in the charge transfer model and consider the actual situations of the sand particles in the collision process. Furthermore, charge transfer between sand particles in a single collision under different humidity conditions is investigated. The predicted results agree well with the law obtained in existing experiments qualitatively and thereby a possible explanation why humidity can affect the charge transfer is given.
PMCID: PMC3957149  PMID: 24637964
12.  Theoretical Treatment and Numerical Simulation of Potential and Concentration Profiles in Extremely Thin Non-Electroneutral Membranes Used for Ion-Selective Electrodes 
The applicability of extremely thin non-electroneutral membranes for ion-selective electrodes (ISEs) is investigated. A theoretical treatment of potential and concentration profiles in space-charge membranes of << 1 μm thickness is presented. The theory is based on the Nernst-Planck equation for ion fluxes, which reduces to Boltzmann’s formula at equilibrium, and on the Poisson relationship between space-charge density and electric field gradient. A general solution in integral form is obtained for the potential function and the corresponding ion profiles at equilibrium. A series of explicit sub-solutions is derived for particular cases. Membrane systems with up to three different ion species are discussed, including trapped ionic sites and co-extracted ions. Solid-contacted thin membranes (without formation of aqueous films at the inner interface) are shown to exhibit a sub-Nernstian response. The theoretical results are confirmed by numerical simulations using a simplified finite-difference procedure based on the Nernst-Planck-Poisson model, which are shown to be in excellent agreement.
PMCID: PMC3523753  PMID: 23255874
Ion-selective electrodes; Thin membranes; Space charge; Potential; Concentration profiles; Theory; Numerical simulation; Nernst-Planck-Poisson model
13.  Electric field depth–focality tradeoff in transcranial magnetic stimulation: simulation comparison of 50 coil designs 
Brain stimulation  2012;6(1):1-13.
Various transcranial magnetic stimulation (TMS) coil designs are available or have been proposed. However, key coil characteristics such as electric field focality and attenuation in depth have not been adequately compared. Knowledge of the coil focality and depth characteristics can help TMS researchers and clinicians with coil selection and interpretation of TMS studies.
To quantify the electric field focality and depth of penetration of various TMS coils.
The electric field distributions induced by 50 TMS coils were simulated in a spherical human head model using the finite element method. For each coil design, we quantified the electric field penetration by the half-value depth, d1/2, and focality by the tangential spread, S1/2, defined as the half-value volume (V1/2) divided by the half-value depth, S1/2 = V1/2/d1/2.
The 50 TMS coils exhibit a wide range of electric field focality and depth, but all followed a depth–focality tradeoff: coils with larger half-value depth cannot be as focal as more superficial coils. The ranges of achievable d1/2 are similar between coils producing circular and figure-8 electric field patterns, ranging 1.0–3.5 cm and 0.9–3.4 cm, respectively. However, figure-8 field coils are more focal, having S1/2 as low as 5 cm2 compared to 34 cm2 for circular field coils.
For any coil design, the ability to directly stimulate deeper brain structures is obtained at the expense of inducing wider electrical field spread. Novel coil designs should be benchmarked against comparison coils with consistent metrics such as d1/2 and S1/2.
PMCID: PMC3568257  PMID: 22483681
transcranial magnetic stimulation; electric field; depth; focality; simulation
14.  Interface traps and quantum size effects on the retention time in nanoscale memory devices 
Nanoscale Research Letters  2013;8(1):369.
Based on the analysis of Poisson equation, an analytical surface potential model including interface charge density for nanocrystalline (NC) germanium (Ge) memory devices with p-type silicon substrate has been proposed. Thus, the effects of Pb defects at Si(110)/SiO2, Si(111)/SiO2, and Si(100)/SiO2 interfaces on the retention time have been calculated after quantum size effects have been considered. The results show that the interface trap density has a large effect on the electric field across the tunneling oxide layer and leakage current. This letter demonstrates that the retention time firstly increases with the decrease in diameter of NC Ge and then rapidly decreases with the diameter when it is a few nanometers. This implies that the interface defects, its energy distribution, and the NC size should be seriously considered in the aim to improve the retention time from different technological processes. The experimental data reported in the literature support the theoretical expectation.
PMCID: PMC3847579  PMID: 23984827
Interface trap; Nanocrystalline; Quantum-size effect; Memory; Retention time; 85.30.Tv; 85.35.-p; 73.63.-b
15.  Metal-Enhanced Fluorescence from Nanoparticulate Zinc Films 
A detailed study of metal-enhanced fluorescence (MEF) from fluorophores in the blue-to- red spectral region placed in close proximity to thermally evaporated zinc nanostructured films is reported. The zinc nanostructured films were deposited onto glass microscope slides as individual particles and were 1–10 nm in height and 20–100 nm in width, as characterized by Atomic Force Microscopy. The surface plasmon resonance peak of the zinc nanostructured films was ≈ 400 nm. Finite-difference time-domain calculations for single and multiple nanostructures organized in a staggered fashion on a solid support predict, as expected, that the electric fields are concentrated both around and between the nanostructures. Additionally, Mie scattering calculations show that the absorption and scattering components of the extinction spectrum are dominant in the UV and visible spectral ranges, respectively. Enhanced fluorescence emission accompanied by no significant changes in excited state lifetimes of fluorophores with emission wavelengths in the visible blue-to-red spectral range near-to zinc nanostructured films were observed, implying that MEF from zinc nanostructured films is mostly due to an electric field enhancement effect.
PMCID: PMC2676115  PMID: 19946356
Metal-Enhanced Fluorescence; Plasmon-Enhanced Fluorescence; Surface-Enhanced Fluorescence; Plasmonics; Radiative Decay Engineering; Zinc Oxide Nanostructures; Silver Island Films; Metallic Nanostructures; Plasmonic Nanostructures; Aluminum Nanostructures; Fluorophores
16.  Image Charge Method for Reaction Fields in a Hybrid Ion-Channel Model 
A multiple-image method is proposed to approximate the reaction-field potential of a source charge inside a finite length cylinder due to the electric polarization of the surrounding membrane and bulk water. When applied to a hybrid ion-channel model, this method allows a fast and accurate treatment of the electrostatic interactions of protein with membrane and solvent. To treat the channel/membrane interface boundary conditions of the electric potential, an optimization approach is used to derive image charges by fitting the reaction-field potential expressed in terms of cylindric harmonics. Meanwhile, additional image charges are introduced to satisfy the boundary conditions at the planar membrane interfaces. In the end, we convert the electrostatic interaction problem in a complex inhomogeneous system of ion channel/membrane/water into one in a homogeneous free space embedded with discrete charges (the source charge and image charges). The accuracy of this method is then validated numerically in calculating the solvation self-energy of a point charge.
PMCID: PMC3596020  PMID: 23504509
Ion channels; image charges; cylindrical harmonics; electrostatic interactions
17.  Ionic Size Effects: Generalized Boltzmann Distributions, Counterion Stratification, and Modified Debye Length 
Nonlinearity  2013;26(10):2899-2922.
Near a charged surface, counterions of different valences and sizes cluster; and their concentration profiles stratify. At a distance from such a surface larger than the Debye length, the electric field is screened by counterions. Recent studies by a variational mean-field approach that includes ionic size effects and by Monte Carlo simulations both suggest that the counterion stratification is determined by the ionic valence-to-volume ratios. Central in the mean-field approach is a free-energy functional of ionic concentrations in which the ionic size effects are included through the entropic effect of solvent molecules. The corresponding equilibrium conditions define the generalized Boltzmann distributions relating the ionic concentrations to the electrostatic potential. This paper presents a detailed analysis and numerical calculations of such a free-energy functional to understand the dependence of the ionic charge density on the electrostatic potential through the generalized Boltzmann distributions, the role of ionic valence-to-volume ratios in the counterion stratification, and the modification of Debye length due to the effect of ionic sizes.
PMCID: PMC3899944  PMID: 24465094
18.  Real-Time Remote Monitoring of Temperature and Humidity Within a Proton Exchange Membrane Fuel Cell Using Flexible Sensors 
Sensors (Basel, Switzerland)  2011;11(9):8674-8684.
This study developed portable, non-invasive flexible humidity and temperature microsensors and an in situ wireless sensing system for a proton exchange membrane fuel cell (PEMFC). The system integrated three parts: a flexible capacitive humidity microsensor, a flexible resistive temperature microsensor, and a radio frequency (RF) module for signal transmission. The results show that the capacitive humidity microsensor has a high sensitivity of 0.83 pF%RH−1 and the resistive temperature microsensor also exhibits a high sensitivity of 2.94 × 10−3 °C−1. The established RF module transmits the signals from the two microsensors. The transmission distance can reach 4 m and the response time is less than 0.25 s. The performance measurements demonstrate that the maximum power density of the fuel cell with and without these microsensors are 14.76 mW·cm−2 and 15.90 mW·cm−2, with only 7.17% power loss.
PMCID: PMC3231505  PMID: 22164099
flexible humidity microsensor; flexible temperature microsensor; radio frequency module; power density
19.  Quantifying electric field gradient fluctuations over polymers using ultrasensitive cantilevers 
Nano letters  2009;9(6):2273-2279.
An ultrasensitive cantilever, oscillating parallel to a surface in vacuum, is used to probe weak thermal electric field gradient fluctuations over thin polymer films. We measure the power spectrum of cantilever frequency fluctuations as a function of cantilever height and voltage over polymers of various compositions and thicknesses. The data are well described by a linear-response theory that calculates stochastic electric fields arising from thermally-driven dielectric fluctuations.
PMCID: PMC2838734  PMID: 19435337
20.  Electric field and grain size dependence of Meyer–Neldel energy in C60 films 
Synthetic Metals  2011;161(17-18):1987-1990.
► Electric field dependence of Meyer–Neldel energy in OFETs. ► A more accurate procedure for evaluation of energetic disorder. ► Agreement with theoretical calculation of Effective Medium Approximation model. ► Film morphology dependence of observed phenomenon.
Meyer–Neldel rule for charge carrier mobility measured in C60-based organic field-effect transistors (OFETs) at different applied source drain voltages and at different morphologies of semiconducting fullerene films was systematically studied. A decrease in the Meyer–Neldel energy EMN from 36 meV to 32 meV was observed with changing electric field in the channel. Concomitantly a decrease from 34 meV to 21 meV was observed too by increasing the grain size and the crystallinity of the active C60 layer in the device. These empiric findings are in agreement with the hopping-transport model for the temperature dependent charge carrier mobility in organic semiconductors with a Gaussian density of states (DOS). Experimental results along with theoretical descriptions are presented.
PMCID: PMC3174423  PMID: 21966084
Organic field effect transistors; Charge carrier mobility; Meyer–Neldel rule; Charge transport; Film morphology; Grain size
21.  Synthesis and Characterization of Carbon Nitride Films for Micro Humidity Sensors 
Sensors (Basel, Switzerland)  2008;8(3):1508-1518.
Nano-structured carbon nitride (CNx) films were synthesized by a reactive RF magnetron sputtering system with a DC bias under various deposition conditions, and their physical and electrical properties were investigated with a view to using them for micro humidity sensors. The FTIR spectra of the deposited films showed a C=N stretching band in the range of 1600∼1700 cm-1, depending on the amount of nitrogen incorporation. The carbon nitride films deposited on the Si substrate had a nano-structured surface morphology with a grain size of about 20 nm, and their deposition rate was 1.5 μm/hr. The synthesized films had a high electrical resistivity in the range of 108 to 109 Ω·cm, depending on the deposition conditions. The micro humidity sensors showed a good linearity and low hysteresis between 5 ∼ 95 %RH.
PMCID: PMC3663008
nano-structure; carbon nitride film; humidity sensors; sputtering system
22.  A Humidity Sensing Organic-Inorganic Composite for Environmental Monitoring 
Sensors (Basel, Switzerland)  2013;13(3):3615-3624.
In this paper, we present the effect of varying humidity levels on the electrical parameters and the multi frequency response of the electrical parameters of an organic-inorganic composite (PEPC+NiPc+Cu2O)-based humidity sensor. Silver thin films (thickness ∼200 nm) were primarily deposited on plasma cleaned glass substrates by the physical vapor deposition (PVD) technique. A pair of rectangular silver electrodes was formed by patterning silver film through standard optical lithography technique. An active layer of organic-inorganic composite for humidity sensing was later spun coated to cover the separation between the silver electrodes. The electrical characterization of the sensor was performed as a function of relative humidity levels and frequency of the AC input signal. The sensor showed reversible changes in its capacitance with variations in humidity level. The maximum sensitivity ∼31.6 pF/%RH at 100 Hz in capacitive mode of operation has been attained. The aim of this study was to increase the sensitivity of the previously reported humidity sensors using PEPC and NiPc, which has been successfully achieved.
PMCID: PMC3658764  PMID: 23493124
composite film; humidity sensor; physical vapor deposition; scanning electron micrograph
23.  Surface Modifications by Field Induced Diffusion 
PLoS ONE  2012;7(1):e30106.
By applying a voltage pulse to a scanning tunneling microscope tip the surface under the tip will be modified. We have in this paper taken a closer look at the model of electric field induced surface diffusion of adatoms including the van der Waals force as a contribution in formations of a mound on a surface. The dipole moment of an adatom is the sum of the surface induced dipole moment (which is constant) and the dipole moment due to electric field polarisation which depends on the strength and polarity of the electric field. The electric field is analytically modelled by a point charge over an infinite conducting flat surface. From this we calculate the force that cause adatoms to migrate. The calculated force is small for voltage used, typical 1 pN, but due to thermal vibration adatoms are hopping on the surface and even a small net force can be significant in the drift of adatoms. In this way we obtain a novel formula for a polarity dependent threshold voltage for mound formation on the surface for positive tip. Knowing the voltage of the pulse we then can calculate the radius of the formed mound. A threshold electric field for mound formation of about 2 V/nm is calculated. In addition, we found that van der Waals force is of importance for shorter distances and its contribution to the radial force on the adatoms has to be considered for distances smaller than 1.5 nm for commonly used voltages.
PMCID: PMC3258261  PMID: 22253894
24.  Simulated Effects of Soil Temperature and Salinity on Capacitance Sensor Measurements 
Sensors (Basel, Switzerland)  2007;7(4):548-577.
Dielectric measurement techniques are used widely for estimation of water content in environmental media. However, factors such as temperature and salinity affecting the readings require further quantitative investigation and explanation. Theoretical sensitivities of capacitance sensors to liquid salinity and temperature of porous media were derived and computed using a revised electrical circuit analogue model in conjunction with a dielectric mixing model and a finite element model of Maxwell's equation to compute electrical field distributions. The mixing model estimates the bulk effective complex permittivities of solid-water-air media. The real part of the permittivity values were used in electric field simulations, from which different components of capacitance were calculated via numerical integration for input to the electrical circuit analogue. Circuit resistances representing the dielectric losses were calculated from the complex permittivity of the bulk soil and from the modeled fields. Resonant frequencies from the circuit analogue were used to update frequency-dependent variables in an iterative manner. Simulated resonant frequencies of the capacitance sensor display sensitivities to both temperature and salinity. The gradients in normalized frequency with temperature ranged from negative to positive values as salinity increased from 0 to 10 g L-1. The model development and analyses improved our understanding of processes affecting the temperature and salinity sensitivities of capacitance sensors in general. This study provides a foundation for further work on inference of soil water content under field conditions.
PMCID: PMC3800364
soil water content; capacitance; permittivity; electrical conductivity; resonant frequency
The Journal of General Physiology  1933;16(3):457-474.
1. The electrophoretic velocities of gelatin-, egg-albumin-, and gliadin-covered quartz particles in various alcohol-water solutions are, within the limits employed in usual experimental procedures, proportional to the field strength. 2. The electrophoretic mobilities of small, irregularly shaped quartz particles covered with an adsorbed film of protein in alcohol-water solutions are equal to the electroosmotic mobilities of the liquid past similarly coated flat surfaces. Hence the size and shape of such particles does not influence their mobilities, which depend entirely on the protein film. 3. The corrected mobility and hence presumably the charge of gelatin-covered quartz particles in solutions containing 35 per cent ethyl alcohol is proportional to the combining power of the gelatin; therefore the gelatin is adsorbed with the active groups oriented toward the liquid. The same is true in 60 per cent alcohol. 4. The charge calculated by means of the Debye-Henry approximation from the mobility of gelatin in solutions containing up to 35 per cent ethyl alcohol is, in the neighborhood of the isoelectric point, proportional to the combining power of the gelatin. Therefore the dielectric constant and the viscosity of the bulk of the medium may be used in the Debye-Henry approximation Q = 6 π η r vm (1 + κ r) to predict changes in charge from mobility. 5. In the neighborhood of the isoelectric point gelatin is probably completely ionized in buffered ethyl alcohol-water mixtures up to 60 per cent alcohol. 6. In the presence of ethyl alcohol the isoelectric point of gelatin is shifted toward smaller hydrogen ion activities. This shift, like that caused by alcohol in the isoelectric points of certain amino acids, is approximately linearly related to the dielectric constant of the medium.
PMCID: PMC2141220  PMID: 19872717

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