Weak Currents Research Articles

Moored Observations of Transport and Variability of Halmahera Sea Currents

AbstractThe ocean currents in the Halmahera Sea are studied using a subsurface mooring deployed in the Jailolo Strait from November 2015 to October 2017. The subtidal currents of the mooring measurements are characterized by a two-layer system, with the current variability below about 200 m in opposite phases to that in the upper layer. The mean along-strait velocity (ASV) is toward the Indonesian seas in the whole water column, producing an estimated mean transport of 2.44 ± 0.42 Sv (1 Sv ≡ 106 m3 s−1). The errors of the transport calculation based on the single mooring measurements are estimated to be less than 15% using simulations of high-resolution ocean models. A weak current is observed to flow northward during 2017 at the bottom of the strait. The ASV variability is found to be dominated by an annual cycle both in the upper and lower layers. The total transport, however, is dominated by semiannual variability because of the cancelation of the annual transports in the upper and lower layers. The variability of the transport is suggested to be driven by the pressure difference between the Pacific Ocean and the Indonesian seas, as evidenced by the agreement between the satellite pressure gradient and the two-layer transports. The transport of the Jailolo Strait during the 2015/16 super El Niño is found to be nearly the same as that during the 2016 La Niña, suggesting that the interannual variability of the transport is much smaller than the seasonal cycle.

Corona Discharge Properties Near Metal and Dielectric Surface

This following research of the properties of a coronary discharge has a serious impact on the study of metallurgy. There are a lot of cases of practical use of the corona discharge functions. An example is the creation of electrostatic precipitators for the purification of industrial gases from solid and liquid particles. Using the corona discharge method, for example, smoke is cleaned in the production of sulfuric acid, air in non-ferrous metal foundries and other harmful industries. Shape of the corona discharge made utilizing cone shaped and round and hollow terminals was examined. The most electrical characteristics of discharge of this type are decided. Corona discharges are characterized by weak currents within the extend of one microampere at voltages on the arrange of 10 kilovolts and adequately week gleam discharge. Electric fluctuations within the discharge current circuit within the extend 1 kHz-120 MHz are enlisted. To think about the oscillatory forms, there were used electric and attractive tests, signals from which were sent to the Tektronix TDS 2024B oscilloscope working within the frequency analyzer mode. The electrical tests were spoken to by metal poles 1-10 cm in length and 4-5 mm in diameter. As magnetic tests, there were used coils (diameter 2-4 mm, number of turns 70-140, wire thickness 0.1 mm) set in protective dielectric walled in areas. These tests were located at a separate of 0.5-1.0 m from the release. Possible waves in plasma are suggested to explain these oscillations.

Assessment of trace metal contamination, total organic carbon and nutrient accumulation in surface sediments of Monastir Bay (Eastern Tunisia, Mediterranean Sea)

Monastir Bay, located on the eastern coast of Tunisia was, a few decades ago, characterized by high marine biodiversity. However, the environmental quality of this coast is affected by several urban and industrial discharges. An evaluation of heavy metal contamination, total organic carbon and nutrient accumulation was undertaken to assess the quality of surface sediments. The geochemical data and statistical approaches show that the coast extending from Khniss to Sayada is a region contaminated with trace metals (Zn, Cu and Ni), with higher contents of TOC, TN, TP and TS and lower values of Eh, suggesting a confined zone with anoxic environmental conditions. The C/N, the S/C and the C/P ratios shows that the sediments of the nearshore zone of Monastir Bay are largely higher (C/N) or lower (S/C and C/P) than the expected ratios in marine sediments suggesting anthropogenic inputs of organic matter. The submarine topography associated with weak hydrodynamic currents acts as physical barriers limiting the exchange with open sea.

Nuclear Spin-Dependent Effects of Parity Nonconservation in Ortho-H2

We report a theoretical treatment of the nuclear spin-dependent spatial parity nonconserving (NSD-PNC) electron–nuclear interaction effect in the diatomic homonuclear ortho-H 2 molecule. The magnetic dipole transition between v = 1 and v = 0 vibrational sublevels of the ground 1 Σ g + state is examined. The orthohydrogen molecule is a unique molecular system where the parity nonconserving (PNC) nuclear spin-dependent interaction due to the neutral weak currents can be directly observed and the corresponding coupling constant can be extracted from the future experiments. The theoretical simulation shows that using the cavity-enhanced scheme in conjunction with the record achievement of the intracavity absorption spectroscopy, the experiment on the observation of the NSD-PNC effect due to the neutral weak current in ortho-H 2 looks feasible.

Stability analysis of deep-water waves on a linear shear current using unsteady conformal mapping

This paper describes linear stability analysis of the two-dimensional steady motion of periodic deep-water waves with symmetric non-overhanging profiles propagating on a linear shear current, namely a vertically sheared current with constant vorticity. In order to investigate numerically with high accuracy the stability of large-amplitude waves, we adopt a formulation using conformal mapping, in which the time-varying water surface is always mapped onto the real axis of a complex plane. This formulation allows us to apply numerical methods developed for large-amplitude irrotational waves without a shear current directly to the present problem, and reduces the linear stability problem to a generalized eigenvalue problem. Numerical solutions describe both super- and sub-harmonic instabilities of the periodic waves for a wide range of wave amplitudes and clarify how the behaviours of dominant eigenvalues change with the strength of the shear current. In particular, it is shown that, even in the presence of a linear shear current, the steady periodic waves lose stability due to superharmonic disturbances at the wave amplitude where the wave energy attains an extremum, similarly to the case of irrotational waves without a shear current. It is also found that re-stabilization with an increase in wave amplitude characterizes subharmonic instability for weak shear currents, but the re-stabilization disappears for strong shear currents.

Double Electric Layer of a Helium Discharge in Modulation Mode

The positive column of a helium gas discharge in modulation mode has been investigated. It has been revealed that the contribution of the stepwise ionization to population of the 31D2 level is low due to small population of metastable levels at weak discharge currents (20–100 mA). With increasing discharge current, the metastable atom population increases and hence, the modulation depth of spectral line intensities of metastable levels also increases. At high currents (>100 mA), the modulation depth of spectral line intensities decreases because of saturation of metastable level population.

Monitoring the mechanical response of early aged cement-mortar specimens using the Pressure Stimulated Currents technique

The time evolution of the electric signals emitted during uniaxial compression of prismatic cement mortar specimens is investigated in this study. The electric signals are recorded in the form of very weak electric currents, and their analysis is achieved in terms of the Pressure Stimulated Currents technique. The study is focused on the quantification of the role of the specimens’ age, i.e., the time interval between the production of the specimens and the implementation of the tests, on the intensity of these electric signals. In this context, four classes of specimens were tested, including specimens of ages equal to 3, 14, 28 and 90 days. It was concluded that for early ages the Pressure Stimulated Currents are quite stronger in comparison with those of mature specimens. There were no detectable differences between the specimens of ages 28 and 90 days, neither concerning the electric activity nor the mechanical response. Moreover, it was indicated that during loading, the electric activity is strongly intensified only after the mechanical response of the specimens abandons linearity, independently of the specimens’ age. Finally, it was concluded that the time evolution of the electric activity provides indicators that can be considered as pre-failure warnings, i.e., signals of upcoming fracture.

Vortex guide under a Lorentz force.

In the present work we study the effect that the metallic quality of the contacts by which an external current is applied, has on the magnetic properties of a superconducting sample. We analyze the magnetization, magnetic susceptibility, Cooper pair density as applied magnetic field function. The contacts are simulated using the

Noninvasive transdermal delivery of liposomes by weak electric current.

Noninvasive transdermal drug delivery (NTDD) offers an exciting new method of administration relative to conventional routes, but is associated with some challenges. Liposomes are capable of encapsulating transdermally-unfavorable drugs. However, the horny layer of skin is a significant barrier that limits efficient transdermal delivery of liposomes. Iontophoresis using weak electric current (WEC) represents a NTDD technology. WEC treatment of liposomes applied to the skin surface improves transdermal penetration of encapsulated drugs by cooperative effects. In this review, we provide an overview of the application of WEC/liposomes for transdermal delivery of macromolecules and low molecular weight drugs. We compare the transdermal delivery and therapeutic efficiency of the combined system with conventional routes of administration and their individual use. We discuss a novel perspective on the mechanism of WEC-mediated transdermal delivery of liposomes, which suggests that WEC activates the intracellular signaling pathway for transdermal permeation and induces unique endocytosis in skin cells.

Electric and acoustic activity in notched fiber-reinforced concrete beams under three-point bending

An experimental study is presented, aiming to comparatively consider the electric and acoustic activity in fiber-reinforced concrete beams subjected to three-point bending. The study is part of an ongoing project attempting to detect phenomena considered as warning signals of upcoming catastrophic fracture, in case brittle materials are loaded mechanically at levels approaching the critical ones. A mature, well established monitoring tool (Acoustic Emissions) is used, in conjunction with a relatively new sensing technique, which is based on the detection of very weak electric currents (known as Pressure Stimulated Currents) produced during the various damage processes which precede (and lead to) the macroscopic fracture of brittle materials. In this direction, series of three-point bending tests with notched beam-shaped specimens made of concrete (either reinforced with metallic or plastic fibers or without any reinforcing agents) were implemented. It is concluded that, independently of the nature of the reinforcing fibers, both monitoring techniques employed in the experimental protocols (namely, the Acoustic Emissions and the Pressure Stimulated Currents) follow pretty faithfully the respective time evolution of the mechanical quantities and, what is more important, they provide well distinguishable features that can be considered as pre-failure indicators.

Enhancement of phytoplankton biomass leeward of Tahiti as observed by Biogeochemical-Argo floats

Abstract The South Pacific Subtropical Gyre (SPSG) is a vast and remote oceanic system where the variability in phytoplankton biomass and production is still largely uncertain due to the lack of in situ biogeochemical observations. The SPSG is an oligotrophic environment where the ecosystem is controlled predominantly by nutrient depletion in surface waters. However, this dynamic is altered in the vicinity of islands where increased biological activity occurs (i.e. the island mass effect, IME). This study mainly focuses on in situ observations which show evidence of an IME leeward of Tahiti (17.7°S - 149.5°W), French Polynesia. Physical and biogeochemical observations collected with two Biogeochemical-Argo profiling floats are used to investigate the dynamics of phytoplankton biomass. Data from the first float, drifting from April 2015 to November 2016 over >1000 km westward of Tahiti, describe the open ocean conditions. The second float, deployed leeward of Tahiti in October 2015, stayed within 45 km off Tahiti for three months before it stopped communicating. In the oligotrophic central SPSG, our observations show that the deepening of the deep chlorophyll maximum (DCM) from winter to summer is light-driven and that the wintertime increase in chlorophyll a concentration in the upper layer is likely to be due to the process of photoacclimation, consistent with previous observations in oligotrophic environments. In contrast, leeward of Tahiti, the DCM widens toward the surface during late spring in association with a biological enhancement in the upper layer. Using Biogeochemical-Argo data, meteorological data from Tahiti, Hybrid Coordinate Ocean Model outputs and satellite-derived products (i.e., horizontal currents and associated fronts), the physical mechanisms involved in producing this biological enhancement leeward of Tahiti have been investigated. The IME occurs during a period of strong precipitation and in a zone of weak currents downstream of the island. We conjecture that the land drainage induces a significant supply of nitrate in the ocean upper layer (down to ~100 m) while a zone of weak currents in the southwestern zone behind Tahiti allows an accumulation zone to form, hence increasing phytoplankton growth up to 20 km away from the coastlines. A bio-optical-based community index suggests that the composition of the phytoplankton community differs leeward of Tahiti from that in the open ocean area, with more microphytoplankton within the IME, which is associated with an increase in the carbon export to the deeper ocean.

Transcranial alternating current stimulation attenuates BOLD adaptation and increases functional connectivity.

Transcranial alternating current stimulation (tACS) is used as a noninvasive tool for cognitive enhancement and clinical applications. The physiological effects of tACS, however, are complex and poorly understood. Most studies of tACS focus on its ability to entrain brain oscillations, but our behavioral results in humans and extracellular recordings in nonhuman primates support the view that tACS at 10 Hz also affects brain function by reducing sensory adaptation. Our primary goal in the present study is to test this hypothesis using blood oxygen level-dependent (BOLD) imaging in human subjects. Using concurrent functional magnetic resonance imaging (fMRI) and tACS, and a motion adaptation paradigm developed to quantify BOLD adaptation, we show that tACS significantly attenuates adaptation in the human motion area (hMT+). In addition, an exploratory analysis shows that tACS increases functional connectivity of the stimulated hMT+ with the rest of the brain and the dorsal attention network in particular. Based on field estimates from individualized head models, we relate these changes to the strength of tACS-induced electric fields. Specifically, we report that functional connectivity (between hMT+ and any other region of interest) increases in proportion to the field strength in the region of interest. These findings add support for the claim that weak 10-Hz currents applied to the scalp modulate both local and global measures of brain activity.NEW & NOTEWORTHY Concurrent transcranial alternating current stimulation (tACS) and functional MRI show that tACS affects the human brain by attenuating adaptation and increasing functional connectivity in a dose-dependent manner. This work is important for our basic understanding of what tACS does, but also for therapeutic applications, which need insight into the full range of ways in which tACS affects the brain.

Altered allostery of the left flipper domain underlies the weak ATP response of rat P2X5 receptors

Although the extracellular ATP-gated cation channel purinergic receptor P2X5 is widely expressed in heart, skeletal muscle, and immune and nervous systems in mammals, little is known about its functions and channel-gating activities. This lack of knowledge is due to P2X5's weak ATP responses in several mammalian species, such as humans, rats, and mice. WT human P2X5 (hP2X5Δ328-349) does not respond to ATP, whereas a full-length variant, hP2X5 (hP2X5-FL), containing exon 10 encoding the second hP2X5 transmembrane domain (TM2), does. However, although rat P2X5 (rP2X5) has a full-length TM2, ATP induces only weak currents in rP2X5, which prompted us to investigate the mechanism underlying this small ATP response. Here, we show that single replacements of specific rP2X5 residues with the corresponding residues in hP2X5 (S191F or F195H) significantly enhance the current amplitude of rP2X5. Using a combination of engineered disulfide cross-linking, single-channel recording, and molecular modeling, we interrogated the effects of S191F and F195H substitutions on the allostery of the left flipper (LF) domain. On the basis of our findings, we propose that the bound ATP-induced distinct allostery of the LF domain with that of other functional subtypes has caused the weak ATP response of rP2X5 receptors. The findings of our study provide the prerequisite for future transgenic studies on the physiological and pathological functions of P2X5 receptors.

Lateral variability of ichnological content in muddy contourites: Weak bottom currents affecting organisms\u2019 behavior

Although bioturbation is commonly recognized in contourites, only a few studies have analyzed the ichnological content of these deposits in detail. These studies have mainly focused on meso-scale bigradational sequence (a coarsening upward followed by a fining-upward sequence resulting from variations in current velocity). Here we present data from gravitational cores collected along the NW Iberian Margin showing systematic variation in ichnological content across proximal to distal depocenters within a large-scale elongated contourite drift. Data demonstrate that tracemakers’ behavior varies depending on the distance relative to the bottom current core. Trace fossils are already known to be a useful tool for studying of contouritic deposits and are even used as criterion for differentiating associated facies (e.g., turbidites, debrites), though not without controversy. We propose a mechanism by which the distance to the bottom current core exerts tangible influence on specific macro-benthic tracemaker communities in contourite deposits. This parameter itself reflects other bottom current features, such as hydrodynamic energy, grain size, nutrient transport, etc. Ichnological analysis can thus resolve cryptic features of contourite drift depositional settings.

Thermal-hydrodynamic circulations and water fluxes in a tributary bay of the Three Gorges Reservoir

The impoundment of a large riverine reservoir creates a series of tributary bays in its original tributaries. The increase in the water level and decrease in the velocity may result in the degradation of the water quality in the tributary bays. The thermal conditions can also change in the mainstream of the reservoir and tributary bays. Density flow induced by temperature differences often occurs in tributary bays, which likely influences the water exchange between the tributary bays and mainstream of the reservoir and the nutrient concentration in the tributary bays. To examine the seasonal variation in the circulation pattern and water exchange in the tributary bay, a three-dimensional numerical model was established for the lower reach of the Xiangxi River, a tributary of the Three Gorges Reservoir. The model was calibrated and validated using field-measured data and the results indicate that it can be used to simulate the thermal-hydrodynamic circulations in the tributary bay. The model-simulated results show that the water circulation patterns vary depending on the season. The bottom-layer intrusive currents from the Three Gorges Reservoir generally occur in the normal-running period and early discharging period, while surface-layer intrusive currents are dominant in the rest of the year and middle-layer intrusive currents occasionally occur in the flooding period and early impounding period. Based on the model-simulated results, the water fluxes in the cross sections in the tributary bay were calculated and the factors controlling the fluxes were examined. The results show that the thermal conditions in the tributary bay and mainstream of the reservoir are the predominant factors controlling the water exchange between the tributary bay and mainstream of the reservoir. Although the inflow from the tributary is relatively small, the water exchange between the tributary bay and mainstream of the reservoir is significant. The results show that that the water within the intrusion limit is renewed more than five times in an operation period. However, the water exchange in the upper reach of the tributary bay is weak, especially during the discharging period of the Three Gorges Reservoir. This may be due to the combined effects of small inflow from the upper reach of the Xiangxi River and weak intrusive currents from the mainstream of the Three Gorges Reservoir in the upper reach of the tributary bay.

On the Structural Instability of a Nematic in an Alternating Electric Field and Its Connection with Convection and the Flexoelectric Effect

The threshold structural instability arising in the thin layer of a nematic liquid crystal (nematic) along the surface of an electrode during the flow of a weak direct injection current is described. Local, limited in length Lу, nuclei (precursors) of electrohydrodynamic and flexoelectric instabilities are assumed to be in this thin layer. In the case of electrohydrodynamic instability, such precursors have been called “bullets” (solitons) because of their specific appearance, and their length Lу is a measure of local perturbation of the orientational structure of a nematic. In the case of flexoelectric instability, pieces Lу are formed by an irregular system of short polarized flexoelectric domains. Such an instability corresponds to a system consisting of groups of stripes, which are characterized by the opposite motion of “bullets” along these stripes and the average velocity of this movement.

Beamforming Galvanic Coupling Signals for IoMT Implant-to-Relay Communication

Implants are poised to revolutionize personalized healthcare by monitoring and actuating physiological functions. Such implants operate under challenging constraints of the limited battery energy, heterogeneous tissue-dependent channel conditions, and human-safety regulations. To address these issues, we propose a new cross-layer protocol for galvanic coupled implants, wherein the weak electrical currents are used in place of classical radio frequency links. As the first step, we devise a method that allows multiple implants to communicate individual sensed data to each other through code division multiple access, combined with compressive sensing method to lower the transmission time and save energy, as well as delegates the computational burden of dispreading and decoding only to the on-body surface relays. Then, we devise a distributed beamforming approach that allows coordinated transmissions from the implants to the relays by considering the specific tissue path chosen and tissue heating-related safety constraints. We then proceed to implement distributed beamforming on a phantom of human tissue and prove an increase in received signal strength and a decrease in BER due to constructive interference of the signals of each implant. Our contributions are twofold: First, we devise a collision-free protocol that prevents undue interference at neighboring implants, especially for multiple deployments. Second, this is the first application of near-field distributed beamforming in human tissue. Simulation results reveal significant improvement in the network lifetime for implants of up to 79% compared to the galvanic coupled links without beamforming. In addition, the implementation of phantom tissue proves improved communication metrics when beamforming is used.

Charge transfer equilibrium in surface barrier discharge: continuous current and negative ion-driven ionisation wave

Sensitive measurements of very weak electrical currents in sinusoidally driven surface barrier discharge in atmospheric air are reported for discharge arrangements with and without liquid covering the top electrode. The transferred charge of the low-power discharge is carefully quantified and it is shown that after the complete voltage period the total charge balance is approaching zero. This rather obvious result is mechanically assumed in the literature, yet it is experimentally not understood in detail. We show that continuous and pulsed micro-ampere currents measured during the negative polarity are responsible for the gradual renewal of the charge transfer equilibrium abruptly distorted by strong electrical pulses caused by positive streamers during the opposite half-period. Using synchronised ICCD imaging we reveal that weak continuous current is caused by slowly expanding surface discharges stemming from previously established cathode spots. The expansion is caused by a surface ionisation wave. Based on the experimental evidence, supported by the theoretical results found in literature, we conclude that an expanding negative ion cloud is responsible for the electric field enhancement at its forefront which is sufficient to ionise the surrounding air.

Accessibility of cortical regions to focal TES: Dependence on spatial position, safety, and practical constraints

Transcranial electric stimulation (TES) can modulate intrinsic neural activity in the brain by injecting weak currents through electrodes attached to the scalp. TES has been widely used as a neuroscience tool to investigate how behavioural and physiological variables of brain function are modulated by electric stimulation of specific brain regions. For an unambiguous interpretation of TES experiments, it is important that the electric fields can be steered towards one or several brain regions-of-interest. However, the conductive proprieties of the human head impose inherent physical limitations on how focal the electric fields in the brain produced by multi-electrode TES can be. As a rule of thumb, it is not feasible to selectively target deep brain areas with TES, although focusing the field in some specific deeper locations might be possible due to favourable conductive properties in the surrounding tissue. In the present study, we first propose a computationally efficient method for the automatic determination of electrode placements and stimulation intensities to optimally affect a given target position. We provide a robust implementation of the optimization procedure that is able to adhere to safety constraints, while explicitly controlling both the number of active electrodes and the angular deviation of the field in the target area relative to the desired field direction. Leveraging the high computational efficiency of our method, we systematically assess the achievable focality of multi-electrode TES for all cortex positions, thereby investigating the dependence on the chosen constraints. Our results provide comprehensive insight into the limitations regarding the achievable TES dose and focality that are imposed by the biophysical constraints and the safety considerations of TES.

Muon capture in nuclei: An ab initio approach based on Green's function Monte Carlo methods

An ab initio quantum Monte Carlo method is introduced for calculating total rates of muon weak capture in light nuclei with mass number $A \leq 12$. As a first application of the method, we perform a calculation of the rate in $^4$He in a dynamical framework based on realistic two- and three-nucleon interactions and realistic nuclear charge-changing weak currents. The currents include one- and two-body terms induced by $\pi$- and $\rho$-meson exchange, and $N$-to-$\Delta$ excitation, and are constrained to reproduce the empirical value of the Gamow-Teller matrix element in tritium. We investigate the sensitivity of theoretical predictions to current parametrizations of the nucleon axial and induced pseudoscalar form factors as well as to two-body contributions in the weak currents. The large uncertainties in the measured values obtained from bubble-chamber experiments (carried out over 50 years ago) prevent us from drawing any definite conclusions.