Measurements Of Potential Gradient Research Articles

Implications of mitochondrial membrane potential gradients on signaling and ATP production analyzed by correlative multi-parameter microscopy

The complex architecture and biochemistry of the inner mitochondrial membrane generate ultra-structures with different phospholipid and protein compositions, shapes, characteristics, and functions. The crista junction (CJ) serves as an important barrier separating the cristae (CM) and inner boundary membranes (IBM). Thereby CJ regulates the movement of ions and ensures distinct electrical potentials across the cristae (ΔΨC) and inner boundary (ΔΨIBM) membranes. We have developed a robust and flexible approach to visualize the CJ permeability with super-resolution microscopy as a readout of local mitochondrial membrane potential (ΔΨmito) fluctuations. This method involves analyzing the distribution of TMRM fluorescence intensity in a model that is restricted to the mitochondrial geometry. We show that mitochondrial Ca2+ elevation hyperpolarizes the CM most likely caused by Ca2+ sensitive increase of mitochondrial tricarboxylic acid cycle (TCA) and subsequent oxidative phosphorylation (OXPHOS) activity in the cristae. Dynamic multi-parameter correlation measurements of spatial mitochondrial membrane potential gradients, ATP levels, and mitochondrial morphometrics revealed a CJ-based membrane potential overflow valve mechanism protecting the mitochondrial integrity during excessive cristae hyperpolarization.

The effect of the Madden–Julian Oscillation on the global electric circuit

The Madden–Julian Oscillation (MJO) is the most dominant component of the climate variability in the tropics on the timescale of tens of days. Occurring irregularly, the MJO consists of an eastward propagation of certain large-scale coupled structures in atmospheric circulation and deep convection. Here we investigate the effect of the MJO on the direct current global electric circuit (GEC), using both numerical simulations and the results of electric field measurements. We have reproduced the atmospheric dynamics for 1980–2020 with the help of the Weather Research and Forecasting model and meteorological reanalysis data; this allowed us to simulate 41 years of the GEC variation by parameterising contributions to the ionospheric potential (IP) in terms of precipitation and convection. Besides, we have analysed the results of surface potential gradient (PG) measurements at the Vostok station in Antarctica during 2006–2020. When averaged over many days, both the simulated IP and measured fair-weather PG show sinewave-like variations with the MJO phase, which manifest a statistically significant correlation with the MJO cycle. A more elaborate investigation involving an application of empirical orthogonal functions shows that the dynamics of contributions to the IP follows the patterns of variability of deep convection typical for the MJO. The variation of the IP on the MJO scale can largely be represented as a superposition of two basic oscillating patterns of convection, one of which is located over the Maritime Continent and its surrounding seas and the other is located over the Indian Ocean and part of South-East Asia. These oscillating patterns together describe the eastward progression of perturbations and can be naturally associated with the two components of the Real-time Multivariate MJO index, widely used to describe the MJO. Together with earlier results about links between the GEC and the El Niño—Southern Oscillation, the results concerning the MJO obtained in this study indicate that the GEC is an important part of the Earth system, which reflects climate variability on different timescales.

Surface Potential Gradients and NEXRAD Radar Reflectivities Before the Onset of Lightning at the KSC‐ER

AbstractMeasurements provided by Next Generation Weather Radar and operational thunderstorm monitoring instruments at the Kennedy Space Center and the Air Force Eastern Range have been examined to determine the initial electrical development of 13 isolated, air mass thunderstorms. The same instruments were used to examine the surface potential gradient prior to and following 13 long, horizontal discharges that propagated into the area. The motivation and primary objective for this work was to evaluate the safety of the existing lightning‐related launch constraints associated with surface potential gradient and precipitation radar measurements. The onset of cloud electrification as seen by a large‐area surface electric field mill network was detected 3.7–14.6 min before the first lightning discharge, with lead‐times that depended on proximity to the storm. In 11 of 13 cases, the first detectable field change was a positive excursion in potential gradient close to the storm, likely indicating initial development of lower positive charge. Lead‐times for the radar‐derived cloud tops (0 dBZ) reaching −20°C were longer than those for early electrification in all but two cases. Surface potential gradients above +500 V/m or below −100 V/m “warning thresholds” were exceeded before the first lightning flash in all cases. Radar reflectivities >35 dBZ above the −10°C level provided 3–14 min of lead time for lightning. Potential gradients just prior to and near long horizontal discharges exceeded 3 kV/m at most sites and were typically positive. Measurements at a single field mill site would not have provided adequate warning.

Atmospheric electricity observations at Lerwick Geophysical Observatory

Abstract. Atmospheric electricity measurements were made at Lerwick Observatory, Shetland, between 1925 and 1984. These principally provide a long series of hourly potential gradient (PG) measurements at an unpolluted site but also include air–Earth current density measurements during the late 1970s and early 1980s. An especially notable aspect was investigating the dramatic atmospheric electrical changes caused by nuclear weapon detonations in the late 1950s and early 1960s, which has parallels with the discovery of the Antarctic ozone hole. The methodology employed at Lerwick to provide the PG measurements is described. There is renewed international interest in such measurements, not least because the Lerwick PG data have been shown to be linked to Pacific Ocean temperature anomalies. The past measurements described have characterised the Lerwick site exceptionally well in atmospheric electrical terms, which also indicate its suitability for future, similar measurements.

Measuring Global Signals in the Potential Gradient at High Latitude Sites

Previous research has shown that the study of the global electrical circuit can be relevant to climate change studies, and this can be done through measurements of the potential gradient near the surface in fair weather conditions. However, potential gradient measurements can be highly variable due to different local effects (e.g., pollution, convective processes). In order to try to minimize these effects, potential gradient measurements can be performed at remote locations where anthropogenic influences are small. In this work we present potential gradient measurements from five stations at high latitudes in the Southern and Northern Hemisphere. This is the first description of new datasets from Halley, Antarctica; and Sodankyla, Finland. The effect of the polar cap ionospheric potential can be significant at some polar stations and detailed analysis performed here demonstrates a negligible effect on the surface potential gradient at Halley and Sodankyla. New criteria for determination of fair weather conditions at snow covered sites is also reported, demonstrating that wind speeds as low as 3 m/s can loft snow particles, and that the fetch of the measurement site is an important factor in determining this threshold wind speed. Daily and seasonal analysis of the potential gradient in fair weather conditions shows great agreement with the “universal” Carnegie curve of the global electric circuit, particularly at Halley. This demonstrates that high latitude sites, at which the magnetic and solar influences can be present, can also provide globally representative measurement sites for study of the global electric circuit.

Electric Mode Excitation in the Atmosphere by Magnetospheric Impulses and ULF Waves

Variations of vertical atmospheric electric field Ez have been attributed mainly to meteorological processes. On the other hand, the theory of electromagnetic waves in the atmosphere, between the bottom ionosphere and earth’s surface, predicts two modes, magnetic H (TE) and electric E (TH) modes, where the E-mode has a vertical electric field component, Ez. Past attempts to find signatures of ULF (periods from fractions to tens of minutes) disturbances in Ez gave contradictory results. Recently, study of ULF disturbances of atmospheric electric field became feasible thanks to project GLOCAEM, which united stations with 1 sec measurements of potential gradient. These data enable us to address the long-standing problem of the coupling between atmospheric electricity and space weather disturbances at ULF time scales. Also, we have reexamined results of earlier balloon-born electric field and ground magnetic field measurements in Antarctica. Transmission of storm sudden commencement (SSC) impulses to lower latitudes was often interpreted as excitation of the electric TH0 mode, instantly propagating along the ionosphere–ground waveguide. According to this theoretical estimate, even a weak magnetic signature of the E-mode ∼1 nT must be accompanied by a burst of Ez well exceeding the atmospheric potential gradient. We have examined simultaneous records of magnetometers and electric field-mills during >50 SSC events in 2007–2019 in search for signatures of E-mode. However, the observed Ez disturbance never exceeded background fluctuations ∼10 V/m, much less than expected for the TH0 mode. We constructed a model of the electromagnetic ULF response to an oscillating magnetospheric field-aligned current incident onto the realistic ionosphere and atmosphere. The model is based on numerical solution of the full-wave equations in the atmospheric-ionospheric collisional plasma, using parameters that were reconstructed using the IRI model. We have calculated the vertical and horizontal distributions of magnetic and electric fields of both H- and E-modes excited by magnetospheric field-aligned currents. The model predicts that the excitation rate of the E-mode by magnetospheric disturbances is low, so only a weak Ez response with a magnitude of ∼several V/m will be produced by ∼100 nT geomagnetic disturbance. However, at balloon heights (∼30 km), electric field of the E-mode becomes dominating. Predicted amplitudes of horizontal electric field in the atmosphere induced by Pc5 pulsations and travelling convection vortices, about tens of mV/m, are in good agreement with balloon electric field and ground magnetometer observations.

First observation of atmospheric electric field at Kashmir valley North Western Himalayas, Srinagar (India)

Preliminary results from the measurement of potential gradient (PG) for the period of March 2018–February 2019 at the University of Kashmir, Srinagar, (34° 03′ N, 74° 51’ E, 1585 m amsl) India is reported. The annual mean diurnal variation of PG represents typical double-maxima pattern with the primary maximum at 0900–1000 LT and the secondary maximum at 1900–2000 LT which is in accordance with the measurements at different continental stations. The primary maximum of PG and its extended duration is explained by the sunrise effect due to increasing surface temperature, the development of surface convection and hence the boundary layer probably favour the uplifting of the surface aerosols. The higher PG values measured at Kashmir valley were explained with the height of the measurement from the surface and the role of mountain-valley winds circulation. Monthly mean PG showed the higher value during December and minimum in June and the amplitude variations were attributed to the local PM concentrations. PG is found to be highly influenced by PM2.5 compared to PM10, due to the high suspension duration in the ambient air. Measurement of PM2.5 to Srinagar showed higher values in December followed by the November and January under the strong inversion layer formation in Kashmir valley with the westerly winds apart from an increase in the local tourist activity. The measured PG values and its observed variations are explained considering the role of aerosol concentration, atmospheric mixing and mountain-valley wind circulations. The present results are comparable with measurements of PG at different continental stations. The level of aerosols and site location shows variation in amplitude as well as temporal shift.

Behind the curve: a comparison of historical sources for the Carnegie curve of the global atmospheric electric circuit

Abstract. The “Carnegie curve” describes the diurnal variation of the global atmospheric electric circuit. It was originally found from atmospheric electric potential gradient (PG) measurements made on the Carnegie, effectively a floating atmospheric electrical observatory, which undertook global cruises between 1915 and 1929. These measurements confirmed that the single diurnal cycle PG variation, previously obtained in both polar regions, was global in extent. The averaged diurnal PG variation, represented by derived harmonic fits, provides a characteristic variation known as the “Carnegie curve”, against which modern measurements are still compared. The ocean air PG measurements were extensively described in reports of the Carnegie Institution of Washington (CIW) but widely used secondary sources of the Carnegie curve contain small differences, arising through approximations and transcription errors. Investigations using the historical CIW data show that the original harmonic fit coefficients are reproducible. Despite the inconsistencies, the secondary sources nevertheless mostly yield diurnal variations which fall within the variability of the original historical data.

The relationship between aerosol concentration and atmospheric potential gradient in urban environments.

Urban aerosol is a growing concern for people living within cities; aerosol have been implicated in many ill health conditions, including that of the lung and of the heart. Atmospheric potential gradient is a consequence of charge carried to the ionosphere through thunderstorms, and its value depends on highly electrically mobile ion concentrations, hence local conductivity of the air. Ions attach to aerosol in the atmosphere, reducing their mobility and therefore increasing the potential gradient, and so potential gradient measurements have been suggested as a proxy for aerosol measurements. Particle number count, size distribution and potential gradient were measured for two campaigns in Manchester, U.K., and one campaign in Bristol, U.K. Using a factor based on size distribution to account for preferential attachment at larger sizes provided the best relationship with potential gradient, but particle count alone showed a weaker, but similar relationship. The increase in particle count caused by annual bonfire and fireworks celebrations (November) was evidenced in both potential gradient and particle numbers. Daily regression or correlation did not show a consistent relationship. In the larger Bristol data set, increasing humidity led to a reduction of potential gradient, while increasing particle number led to an increase.

Atmospheric Potential Gradient Measurements from a Rooftop in Bangkok

Atmospheric potential gradient measurements at 1 Hz (averaged to 1 minute samples) were taken on the roof of a 6th floor building, approximately 100 m from a busy toll road in Lak Si, northern Bangkok. The measurement period covered the transition from hot season into rainy season. The heavy monsoon rains and heavy traffic can both be significant disruptors of the fair weather atmospheric potential gradient. Heavy traffic increased potential gradient due to aerosol loading, while rain storms increased the magnitude, but also changed the sign of the field due to charge processes within clouds. Increasing relative humidity led to a decrease in potential gradient, implying a lack of hygroscopic growth. Cross correlations of aerosol number in different size fractions showed that aerosols with a D50 value of 155 nm had the strongest correlation. A strong diurnal signal is present in frequency domain analysis of potential gradient.

Fair-weather potential gradient and its coupling with ionospheric potential from three Antarctic stations: Case studies

Simultaneous measurements of potential gradient (PG) from Antarctica stations, Vostok (78° 27′ S, 106° 52′ E), Dome C (75° 06′ S, 123° 20′ E) and Maitri (70° 45′ S, 11°44′ E) during magnetically disturbed days under fair-weather conditions are discussed. An attempt has been made to study the influence of solar wind-magnetosphere interaction on PG. During magnetic daytime (0600–1800 UT), linear relation between ΔPG and associated ionospheric potential from Dome C and Vostok are observed. The liner response is poor during the magnetic night time (1800-0600 UT). This trend has been addressed by the sun-aligned two-cell plasma convection flow and its differential motion over the stations. It is found that linear relation decreased when negative convection pattern moves towards, overhead and away from the stations under dawnward motion of plasma (IMF By < 0). In addition, the ionospheric potential at dusk sector modulated the PG if the plasma flow remained stable for more than 1 h. The results further showed that the scale size factor between ionospheric potential and PG may influence up to some extent in coupling efficiency. Month-wise Fair-weather PG pattern effectively accounts the ambient PG variation.

Urban and rural measurements of atmospheric potential gradient

Atmospheric potential gradient was measured at three sites within the Bristol area of the UK between 19th May and 24th June 2016. Two sites were on rooftops within the city of Bristol, 800 m apart from each other, while the third was in a rural location 17 km to the south. Potential gradient measurements at the two rooftop urban sites showed great temporal similarity, implying that a rooftop measurement may be assumed to represent the local urban area. Frequency domain analysis indicated a half-day cycle in the urban sites that was not observed in the rural site, consistent with other studies showing the effect of traffic aerosol on potential gradient measurements. The correlation between the two urban sites was not affected by an increase in aerosol concentration. Removal of data during rainfall, as well as one hour before and after rain, removed some of the larger changes in potential gradient typical of disturbed weather. However, large changes of potential gradient still existed, showing that rainfall alone should not be relied upon as an indicator of a non-fair weather potential gradient.

Saharan dust electrification perceived by a triangle of atmospheric electricity stations in Southern Portugal

Atmospheric Electric Potential Gradient (PG) measurements were carried out in three sites forming a triangular array in Southern Portugal. The campaign was performed during the summer, characterized by Saharan dust outbreaks; 16th–17th July 2014 dust event is considered. Short time-scale oscillations of the PG at two of the stations and a mid time-scale suppression of the PG in the three stations are found. Results are interpreted as evidencing long-range dust electrification; attributed to the air-Earth electrical current creating a bipolar charge distribution inside of the dust layer. The relevance of using arrays of sensors, instead of single sited, is highlighted.

Diamond nanoparticles as a way to improve electron transfer in sol–gel l-lactate biosensing platforms

In the present work, we have included for the first time diamond nanoparticles (DNPs) in a sol–gel matrix derived from (3-mercaptopropyl)-trimethoxysilane (MPTS) in order to improve electron transfer in a lactate oxidase (LOx) based electrochemical biosensing platform. Firstly, an exhaustive AFM study, including topographical, surface potential (KFM) and capacitance gradient (CG) measurements, of each step involved in the biosensing platform development was performed. The platform is based on gold electrodes (Au) modified with the sol–gel matrix (Au/MPTS) in which diamond nanoparticles (Au/MPTS/DNPs) and lactate oxidase (Au/MPTS/DNPs/LOx) have been included. For the sake of comparison, we have also characterized a gold electrode directly modified with DNPs (Au/DNPs). Secondly, the electrochemical behavior of a redox mediator (hydroxymethyl-ferrocene, HMF) was evaluated at the platforms mentioned above. The response of Au/MPTS/DNPs/LOx towards lactate was obtained. A linear concentration range from 0.053 mM to 1.6 mM, a sensitivity of 2.6 μA mM−1 and a detection limit of 16 μM were obtained. These analytical properties are comparable to other biosensors, presenting also as advantages that DNPs are inexpensive, environment-friendly and easy-handled nanomaterials. Finally, the developed biosensor was applied for lactate determination in wine samples.

First results of atmospheric electricity measurements by CS110 electric field meter at Paratunka observatory, Kamchatka

The results of continuous measurements of AEF potential gradient by CS110 fluxmeter at Paratunka observatory are presented.

Measurements of the atmospheric electric field under high-mountain conditions in the vicinity of Mt. Elbrus

The measurements of the atmospheric electric field potential gradient are analyzed simultaneously at the two high-mountain stations in the vicinity of Mt. Elbrus: Cheget Peak and Terskol Peak, as well as the Kyzburun mountain station located at the end of the Baksan ravine. A global component in the diurnal variation in the electric field is revealed: the morning minimum (01-04 UT) and the evening maximum (19-21 UT), which conforms to the unitary variation in the ionospheric potential, as well as the daylight maximum (08-12 UT) caused by the action of the local generators in the surface layer. The features of the seasonal variation in the electric field are studied.

Preliminary results on soil-emitted gamma radiation and its relation with the local atmospheric electric field at Amieira (Portugal)

The atmospheric electric field near the Earth's surface is dominated by atmospheric pollutants and natural radioactivity, with the latter directly linked to radon (222Rn) gas. For a better comprehension on the temporal variability of both the atmospheric electric field and the radon concentration and its relation with local atmospheric variables, simultaneous measurements of soil-emitted gamma radiation and potential gradient (defined from the vertical component of the atmospheric electric field) were taken every minute, along with local meteorological parameters (e.g., temperature, atmospheric pressure, relative humidity and daily solar radiation). The study region is Amieira, part of the Alqueva lake in Alentejo Portugal, where an interdisciplinary meteorological campaign, ALEX2014, took place from June to August 2014. Soil gamma radiation is more sensitive to small concentrations of radon as compared with alpha particles measurements, for that reason it is more suited for sites with low radon levels, as expected in this case. Preliminary results are presented here: statistical and spectral analysis show that i) the potential gradient has a stronger daily cycle as compared with the gamma radiation, ii) most of the energy of the gamma signal is concentrated in the low frequencies (close to 0), contrary to the potential gradient that has most of the energy in frequency 1 (daily cycle) and iii) a short-term relation between gamma radiation and the potential gradient has not been found. Future work and plans are also discussed.

Simulations of the Global Electrical Circuit coupled to local Potential Gradient measurements

There are several models describing the Global Electric Circuit of the Earth's atmosphere. Here it is used the common model and parameters of Global Electric Circuit to couple it with a local circuit less studied in literature. The first objective is to test different voltage sources describing thunderstorm activity and compare the output, Potential Gradient, with the known Carnegie Curve. Two sets of parameters are used, the first one from values found in literature and the second one from values tweaked to get the best agreement between the simulated Potential Gradient and the Carnegie Curve. This study is a first step in simulations regarding the coupling of the Global Electric Circuit (primary) to local electric circuit (secondary). One of the main objectives is to estimate the aerosol load on the local resistor in case of aerosol events, e.g. fires.

Atomic force microscopy characterization of printed dots

Functional atomic force microscopy (AFM) techniques are proposed as a high resolution tool to understand relevant physical properties of colorants and printing substrates at nanoscale. In this work, we present an exploratory AFM study of colorants used by three digital printing technologies: LaserJet, Indigo, inkjet and two printing substrates: white paper and transparent media. Surface morphology and phase-contrast imaging are performed using amplitude-modulation (AM) AFM and measurements of surface potential and capacitance gradient are measured through 2nd harmonic Kelvin Probe Force microscopy (KPFM). Compositional mapping contrast is analyzed using both techniques. Non-homogeneous mechanical properties are clearly evident in the AM-AFM images while the variations of local electrical properties are apparent from the KPFM studies.

Comparisons of ground level measurements of ion concentration and potential gradient upwind and downwind of HV power lines in corona

Abstract Simultaneous ion concentration and potential gradient measurements were made at AC high voltage power lines using ion mobility spectrometers and electric field mills. A significant ( p