Lower Positive Charge Research Articles

Variation of Atmospheric Temperature with Height in the Phenomena of Lightning Waveforms

The temperature at different height at different places is different, it may depend on various factors. The variation of atmospheric temperature varies as a function of height taken from the sea level. The temperature decreases with height in the troposphere. The location of the charge centre appears to be determined by temperature and not by the height of the cloud above the ground. The main negative charge centre is generally located between the -10°C and -25°C isotherms with the main positive charges some km higher up. Due to the variation of temperature, the ice crystal, super cooled water droplet etc. move updraft and downdraft, forms the charge in the cloud due to which the lightning phenomena occurs. In the cloud, the negative charge lies in the central part of the cloud, positive charge remains on above the negative charge centre in the cloud and small amount of positive charge as a pocket charge remains on the bottom part of the cloud. The positive ground flashes are initiated from the upper positive charge region and the negative ground flashes are initiated from the negative charge region in the thunder-cloud. The lower positive charge also play an important role for determining the different types of lightning.

Theoretical/experimental investigation and antimutagenic effect of the oxidovanadium(IV) baicalin coordination complex

Vanadium is a transition metal with several oxidation states and some of these are represented in its biochemistry. The vanadium(IV) metal ion generally exists as oxidovanadium(IV) ion (VIVO2+) and forms stable complexes with a wide range of ligands. Flavonoids are a large group of polyphenolic compounds ubiquitously present in plants that can coordinate and chelate metal ions due to the presence of oxo and hydroxyl groups. Baicalin is one of the main single active constituents isolated from the dried roots of S. baicalensis. We have previously synthesized and characterized the baicalin coordination complex with the oxidovanadium(IV) cation, Na4[VO(baic)2].6H2O (VIVO(baic)2). Unfortunately, suitable single crystals for X-ray diffraction determinations could not be obtained. In the present work, we carried out a complete study of the geometrical, vibrational and electronic properties of this complex, and the knowledge of its biological properties was also extended. The penta-coordinated VIVO(baic)2 complex has a square pyramidal geometry. The theoretical IR spectrum showed reasonable agreement with the experimental FTIR spectrum. The frontier molecular orbitals (FMO) of the VIVO(baic)2 and [VO(apigenin)(H2O)2]Cl (VIVO(api)) complexes show significant differences. Nevertheless, the FMO on each complex show the same spatial arrangements than those of the free ligands. The VIVO(baic)2 complex shows no alkaline phosphatase inhibitory activity due to the low positive charge on the VO group. This complex shows not only an adequate safety profile (without mutagenic action), but also an enhanced antimutagenic effect (protective effect) compared with the parental flavonoid.

Improved lightning model: Application to discuss the characteristics of upward lightning

A stochastic discharge parameterization scheme of upward lightning is presented and embedded into an existing fine resolution two-dimensional thundercloud electrification and lightning model. At present, our lightning model can simulate not only intra-cloud (IC) lightning and cloud-to-ground (CG) lightning but also upward lightning. By this improved model, 139 upward flashes originating from the tall structures were obtained. Out of these upward flashes, 67 cases occur without any nearby preceding lightning discharges (called self-initiated upward flashes), whereas 72 cases are triggered by the preceding lightning discharges (called nearby-lightning-triggered upward flashes). The relationship between the initiation of self-initiated upward flashes and thundercloud electrical environment parameters is discussed. The results show that the initiation of self-initiated upward flashes is related to the weighted average of the lower charge heights (H) and the average of the lower charge density (D). As D increases, the critical H increases. In addition, the reason for IC lightning or upward lightning triggering upward lightning is investigated. IC lightning discharges or upward lightning discharges neutralize the main negative charge region in the cloud and enhance the influence of the lower positive charge region on the ground electric field.

Energetic Radio Emissions and Possible Terrestrial Gamma‐Ray Flashes Associated With Downward Propagating Negative Leaders

AbstractA study of negative polarity energetic in‐cloud pulses (−EIPs) during thunderstorms reveals that −EIPs occur during two distinct stages of downward negative leader development. The first group is observed at the beginning of downward negative leaders, with estimated average source altitude of ~5.9 km between main negative and lower positive charge regions. The second and new group are observed at the very end of downward negative leaders and appear to be produced at low altitudes close to the ground, where image charges amplify the electric field between the leader tip and conducting ground. Negative EIPs appear to occur only in these two scenarios, suggesting that their production require a high background electric field. Their radio emission signatures and occurrence contexts are similar with +EIPs, which are known to be connected to terrestrial gamma‐ray flashes. We thus suggest that these two types of −EIPs may be associated with downward terrestrial gamma ray flashes.

Physically and chemically bound chlorides in hydrated cement pastes: a comparison study of the effects of silica fume and metakaolin

Increasing the chloride binding capacity of hydration products is an effective countermeasure to improve the chloride resistance of cement-based materials. The alumina content of binder is usually adopted to evaluate the chloride binding capacity, in terms of Friedel’s salt. However, the influences of aluminum on the characteristics of C–S–H and finally on physically bound chloride are not taken into account. In the present study, the characteristics of hydration products were widened by introducing silica fume and metakaolin into Portland cement pastes, respectively; then, the consequent chloride binding capacity was followed using Freundlich binding isotherms; chemically and physically bound chlorides were further distinguished. The results show that the chloride binding capacity of cement pastes reduced with the increase of SF addition, but proportionally increased with the increasing MK addition. The amount of chemically bound chloride was doubled by adding 16% MK (15.07 mg/g), which was about 6 times as high as that of cement paste with 16% SF. The chemically bound chloride through formation of Friedel’s salt by ion-exchange mainly related to the monocarboaluminate content, whereas the physically bound chloride was largely depended on the specific surface area of cement pastes. Moreover, MK promoted the substitution of Al3+ for Si4+ in C–S–H, resulting in more sites for chloride binding and then a higher amount of physically bound chloride. In contrast, SF increased the protonation degree of C–S–H, leading to a lower positive charge density on the surface of C–S–H and finally a lower amount of physically bound chloride due to poor electrostatic adsorption.

Numerical Simulation of the Formation of a Large Lower Positive Charge Center in a Tibetan Plateau Thunderstorm

Numerical Simulation of the Formation of a Large Lower Positive Charge Center in a Tibetan Plateau Thunderstorm

Na+ ion migration on the surface of reduced graphene oxide

The increasing demand of sodium ion batteries (SIBs) remarkably accelerates the study of solid-state sodium ion conductors due to their potential application as solid-state electrolytes in SIBs. In the present work, the sodium ion is attached to reduced graphene oxide (rGO) to realize a sodium ion conductor. Tuning the activation energy of migration for Na+ and Li+ ions on rGO surface is investigated by varying the concentration of both ions. The lowest values of activation energies for Na+ and Li+ conduction are found to be 0.28 eV and 0.37 eV, respectively. It is seen that the activation energy of migration of the Na+ ion is smaller than that of the Li+ ion. The lower positive charge density of Na+ compared to Li+ causes this lowering of activation energy in Na+ due to the comparatively weak cation–π interaction between the Na+ ion and the carbon hexagon. From the relaxation study, the relaxation exponent (β) value of the Na+ ion is found to be smaller than that of the Li+ ion. This deviation from Debye-type relaxation behavior of the Na+ ion also agrees well with the decreasing value of activation energy as mentioned above. We hope that this study will aid the design of ion conductors for solid-state SIBs.

Thunderstorm characteristics favouring downward and upward lightning to wind turbines

Meteorological conditions and thunderstorm characteristics related to lightning threats to wind turbines are discussed in this paper. Due to the rotating blades, wind turbines may be regarded peculiar tall objects, more susceptible to lightning strikes than other tall man-made structures. In the present study, Lightning Mapping Array and weather radar observations allowed to draw a clear picture of the thunderstorm characteristics leading to lightning strokes to wind turbines, in a coastal area of the Mediterranean basin. Results showed that lightning threats to wind turbines tend to occur during transitional periods (spring and autumn), although the main thunderstorm activity concentrates in the warm summer months. Thunderstorms with downward strokes to wind turbines presented particular features, like a limited vertical development and a dominant lower positive charge layer. Downward cloud-to-ground strokes hitting wind turbines were mainly of negative polarity and with peak currents above the average. On the other hand, conditions for self-initiated upwards from wind turbines resemble those reported in Japan and the U.S winter thunderstorms, with low-cloud based large electrified stratiform regions. These particular conditions, leading to lightning threats to wind turbines, should be properly included in lightning protection standards.

Kinetics of Phosphorus Release in Soils with Different Textures in Intensive Cultivation Systems

In this study, the effect of loam and Sandy loam textures on Phosphorus (P) release was investigated in greenhouse intensive cultivation soils of Kurdistan, Western Iran. Results showed that the kinetic of P release was higher in soils with sandy loam texture than loam texture soils. It probably was due to low positive charge points and adsorption capacity of sandy loam soils in compare with loam soils. So, more attentions must be conducted in sandy loam textures in cultivation systems because of environmental problems. As well as, according to our results other soil properties like organic matter (OM) and Cation exchange capacity (CEC) showed high correlation in respect to P release.

ZnO Nanoparticle Modification by Polyethylenimine for Biomolecule Conjugation

This study aims to find a way for the creation of polyethyleneimine-modified biofunctionalized zinc oxide (ZnO) nanoparticles, stable in phosphate buffered saline (PBS). Biofunctionalized ZnO nanoparticles are promising for bioanalitycal applications due to a combination of diverse physico-chemical ZnO properties and selectivity of biomolecules. ZnO nanoparticles were synthesized in diethylene glycol media at 150°C. Different strategies were utilized for ZnO nanoparticle modification in order to disclose the role of polyethylenimine (PEI) in stability of colloidal system. Synthesized and modified ZnO nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and infrared spectroscopy measurements, and stability of colloidal system was investigated using DLS data. Finally, ability of ZnO nanoparticles to attach proteins for potential analytical applications was proved using Bradford protein assay. Among different strategies of modification, ZnO nanoparticles modified by trisodium citrate, PEI and glutaraldehyde (GA) have showed the best stability in PBS while preserving low aggregation level and high positive surface charge.

Advanced numerical model of lightning development: Application to studying the role of LPCR in determining lightning type

AbstractAn advanced 3‐D numerical model of lightning development is presented. The key features of the model include the probabilistic branching, bidirectional propagation, nonzero internal electric field, simultaneous growth of multiple branches, physical timing, channel decay, and, for the first time, probabilistic propagation field threshold. The new model can be used for computing electrical parameters of individual branches, including conductivity, current, and longitudinal electric field, each as a function of time, in different parts of the discharge tree. For illustrative purposes, the model was applied to studying the occurrence of lightning flashes of different type depending on the cloud charge structure, with emphasis on the lower positive charge region (LPCR). We demonstrated with the new model that the presence of relatively large (excessive) LPCR can prevent the occurrence of negative CG flashes by “blocking” the progression of descending negative leader from reaching ground. The blocking effect of excessive LPCR was found to occur when the vertical component of electric field near the cloud bottom was negative (downward directed). Further, we showed that significant reduction or absence of LPCR can eliminate the possibility of negative CG flashes and lead to normal‐polarity IC flashes instead. The model predicts the polarity‐asymmetry, which suggests that the amount of collected charge depends not only on the number of branches but also on the dynamics of their conductivity (lifetime) and the local cloud charge density.

Observation and analysis of electrical structure change and diversity in thunderstorms on the Qinghai-Tibet Plateau

A comprehensive observation on thunderstorms was conducted in the Qinghai area by using a very high frequency three-dimensional lightning mapping system and Doppler radar. The spatio-temporal evolution of the charge structure of the isolated thunderstorm was analyzed according to the developing process of thunderstorm, and the reasons for the change in charge structure diversity were studied. During the initial developing and mature stages of the thunderstorm, the charge structure was a steady negative dipole polarity, i.e., the negative charge region was above the positive charge region. Furthermore, the total number of flashes was lower during these two stages. During the thunderstorm's dissipation stage, the charge structure was varied and complicated, with a positive dipole, negative dipole, and a tripole charge structure changing and coexisting during this stage. This charge structure diversity was primarily caused by the collision and merging of two local thunderstorm cells, leading to a charge rearrangement and distribution and the formation of a new charge structure. The frequency of the negative cloud-to-ground and intracloud flashes increased sharply in the dissipation stage, reaching a maximum value. The increase in frequency of negative cloud-to-ground was mainly caused by the lower positive charge weakening during the dissipation stage. In addition, the relationship between charging regions and temperature layers was analyzed by combining sounding temperature data with the theory of a non-inductive charging mechanism.

Solvent-free protamine nanocapsules as carriers for mucosal delivery of therapeutics

Local delivery of drugs and biopharmaceuticals for the treatment of inflammatory bowel disease remains a challenge. Innovative nanomedicines with appropriate properties raise the possibility of efficient drug targeting. Hence, the overall aim of this study was to develop and characterize a protamine-based nanosystem for topical delivery of therapeutics to inflamed intestinal mucosa following oral administration. Protamine nanocapsules with a new composition were for the first time prepared by a self-emulsifying process, without the use of organic solvents or heat. A model lipophilic anti-inflammatory agent, cyclosporin A (CsA), was encapsulated in the oily core of these nanocarriers. The CsA-loaded formulation was isolated from the free drug by gel filtration and the entrapment efficiency was determined using reverse phase high-performance liquid chromatography (HPLC). Protamine nanocapsules had sizes within the range of 160–180nm, with low polydispersity index (0.2) and positive surface charge, together with high entrapment efficiency (95%) and drug loading capacity (5%). The nanocapsules exhibited good stability in storage both as an aqueous suspension and as a freeze-dried powder. Nanocapsules also preserved their colloidal stability in simulated intestinal media. In vitro studies performed with the Jurkat human T lymphocyte cell line showed that CsA-loaded protamine nanocapsules are more efficient than the commercial Sandimmune Neoral® formulation at reducing IL-2 secretion (γγp<0.01). At the same time, nanocapsules showed no toxic effects on the cells. The results discussed herein indicate the feasibility of the developed nanosystem to serve as a potential carrier for cyclosporin A administration.

Analysis of energetic radiation associated with thunderstorms in the Ebro delta region in Spain

AbstractThe analysis of high‐energy background radiation (0.1–2 MeV) enhancements during eight winter thunderstorms and five summer storms in the Ebro delta region in the northeast of Spain is presented. For the first time, high‐energy radiation counts, precipitation, radar reflectivity, and very high frequency lightning detections to infer charge regions altitude have been analyzed in order to find out what produces the measured background radiation increments associated with storms. The good agreement between radar reflectivity and precipitation with increases in background radiation counts coupled with the spectrum analysis comparing rain/no rain periods suggests that radon‐ion daughters play a major role in the radiation increments reported. No evidence has been found supporting that measured background radiation enhancements can be produced by storm electric fields. Finally, a single case of a high‐energy radiation increase was prior to a cloud‐to‐ground lightning stroke, which reinforces the theory that a lower positive charge layer's existence is important for the production of Terrestrial Ground Enhancements.

A parameterization scheme for upward lightning in the cloud model and a discussion of the initial favorable environmental characteristics in the cloud

The upward lightning (UL) initiated from the top of tall buildings (at least above 100 m) is a type of atmospheric discharge. Currently, we understand the nature of the UL from ground observations, but the corresponding theoretical research is lacking. Based on an existing bidirectional leader stochastic model, a stochastic parameterization scheme for the UL has been built and embedded in an existing two-dimensional thundercloud charge/discharge model. The ULs simulated from the experiments with two-dimensional high resolution agree generally with the observation results. By analyzing the charge structure of thunderstorm clouds, we determined the in-cloud environmental characteristics that favor the initiation of conventional cloud-to-ground (CG) flashes and analyzed the differences and similarities of some characteristics of the positive and the negative UL. Simulation results indicate that the positive ULs are typically other-lightning-triggered ULs (OLTUL) and are usually a discharge phenomenon between the ground and the lower positive charge region appearing below the main middle negative charge region. The effect of the previous in-cloud lightning (IC) process of space electrical field provides favorable conditions for the initiation of a positive UL. Its entire discharge process is limited, and the branches of the leader are fewer in number as its discharge is not sufficient. A negative UL is generally a discharge phenomenon of the dipole charge structure between the ground and the main negative charge region. The lower temperature stratification and the sinking of the hydrometeors typically initiate a negative UL. Negative ULs develop strongly and have more branches. The OLTUL is initiated mainly during the development stage of a thunderstorm, while the self-triggered UL (STUL) is initiated mainly during the dissipation stage of a thunderstorm.

Structural Changes Correlated with Magnetic Spin State Isomorphism in the S2 State of the Mn4CaO5 Cluster in the Oxygen-Evolving Complex of Photosystem II.

The Mn4CaO5 cluster in Photosystem II catalyzes the four-electron redox reaction of water oxidation in natural photosynthesis. This catalytic reaction cycles through four intermediate states (Si, i = 0 to 4), involving changes in the redox state of the four Mn atoms in the cluster. Recent studies suggest the presence and importance of isomorphous structures within the same redox/intermediate S-state. It is highly likely that geometric and electronic structural flexibility play a role in the catalytic mechanism. Among the catalytic intermediates that have been identified experimentally thus far, there is clear evidence of such isomorphism in the S2 state, with a high-spin (5/2) (HS) and a low spin (1/2) (LS) form, identified and characterized by their distinct electron paramagnetic resonance (EPR spectroscopy) signals. We studied these two S2 isomers with Mn extended X-ray absorption fine structure (EXAFS) and absorption and emission spectroscopy (XANES/XES) to characterize the structural and electronic structural properties. The geometric and electronic structure of the HS and LS S2 states are different as determined using Mn EXAFS and XANES/XES, respectively. The Mn K-edge XANES and XES for the HS form are different from the LS and indicate a slightly lower positive charge on the Mn atoms compared to the LS form. Based on the EXAFS results which are clearly different, we propose possible structural differences between the two spin states. Such structural and magnetic redox-isomers if present at room temperature, will likely play a role in the mechanism for water-exchange/oxidation in photosynthesis.

Dramatic Effect of the Electrostatic Parameters on H2 Sorption in an M-MOF-74 Analogue

Simulations of H2 sorption were performed in Cu-MOF-74, a recent addition to the M-MOF-74 series. Electronic structure calculations revealed that the Cu2+ ions exhibit an unusually low partial positive charge distribution in Cu-MOF-74, which is a direct consequence of the Jahn–Teller effect. This is in contrast to the charge environment for the metal ions in some of the other M-MOF-74 variants as determined in previous work [Pham, T.; J. Phys. Chem. C 2015, 119, 1078−1090]. Because of the low magnitude of the partial charges of the Cu2+ ions in Cu-MOF-74, this MOF displays the lowest H2 uptake and Qst values of the M-MOF-74 series, which is consistent with what was observed experimentally for H2 sorption in this series of MOFs. Control simulations of H2 sorption in a nonphysical Cu-MOF-74 variant were performed in which a set of calculated partial charges, appropriate for one of the other M-MOF-74 analogues, were used. These simulations utilize a much higher partial positive charge for the metal ions and,...

Chitosan functionalisation of gold nanoparticles encourages particle uptake and induces cytotoxicity and pro-inflammatory conditions in phagocytic cells, as well as enhancing particle interactions with serum components.

Background Gold nanoparticles (AuNPs) are a popular choice for use in medical and biomedical research applications. With suitable functionalisation AuNPs can be applied in drug delivery systems, or can aid in disease diagnosis. One such functionalisation is with chitosan, which enables efficient interaction and permeation of cellular membranes, providing an effective adjuvant. As both AuNPs and chitosan have been shown to have low toxicity and high biocompatibility their proposed use in nanomedicine, either individually or combined, is expanding. However, further toxicological and immunological assessments of AuNP-chitosan conjugates are still needed. Therefore, we have evaluated how AuNP functionalisation with chitosan can affect uptake, cytotoxicity, and immunological responses within mononuclear cells, and influence the interaction of AuNPs with biomolecules within a complex biofluid. The AuNPs used were negatively charged through citrate-coating, or presented either low or high positive charge through chitosan-functionalisation. Uptake by THP-1 cells was assessed via transmission electron microscopy and electron energy loss spectroscopy, pro-inflammatory responses by ELISA and qRT-PCR, and cell death and viability via lactate dehydrogenase release and mitochondrial activity, respectively. Interactions of AuNPs with protein components of a frequently used in vitro cell culture medium supplement, foetal calf serum, were investigated using mass spectrometry.ResultsAlthough cells internalised all AuNPs, uptake rates and specific routes of intracellular trafficking were dependent upon chitosan-functionalisation. Accordingly, an enhanced immune response was found to be chitosan-functionalisation-dependent, in the form of CCL2, IL-1β, TNF-α and IL-6 secretion, and expression of IL-1β and NLRP3 mRNA. A corresponding increase in cytotoxicity was found in response to chitosan-coated AuNPs. Furthermore, chitosan-functionalisation was shown to induce an increase in unique proteins associating with these highly charged AuNPs.ConclusionsIt can be concluded that functionalisation of AuNPs with the perceived non-toxic biocompatible molecule chitosan at a high density can elicit functionalisation-dependent intracellular trafficking mechanisms and provoke strong pro-inflammatory conditions, and that a high affinity of these NP-conjugates for biomolecules may be implicit in these cellular responses.Electronic supplementary materialThe online version of this article (doi:10.1186/s12951-015-0146-9) contains supplementary material, which is available to authorized users.

Lp...π Interactions involving π-systems with different degrees of electron density delocalization: uracil and isocyanurate

A comparative analysis of non-covalent interactions in the crystals of uracil and isocyanurate derivatives was performed. Most of interactions involving the uracil moiety are formed via π...π-type overlap, but Lp...π-type interactions also occur in some crystals. A comparison of the lone pair—π-system interactions showed that the energy of these interactions in uracil derivatives is lower than that in isocyanurate derivatives, which is attributed to a lower positive charge on the uracil moiety.

Effect of under-dosing coagulant on coagulation–ultrafiltration process for treatment of humic-rich water with divalent calcium ion

The strategy of under-dosing coagulant was firstly applied in a coagulation–ultrafiltration (UF) process for treatment of humic-rich water in this study. When polyaluminum chloride (PACl) dosage was set as 0.025mM (as alum), the removal efficiency of organic matter and residual turbidity were slightly inferior to 0.1mM (as alum), but four times dosage lowered than the optimal-dosing. Although permeate flux of ultrafiltration membrane was larger at the optimal-doing than that of under-dosing, the less proportion of irreversible fouling and large proportion of reversible fouling were proved that under-dosing strategy has more meaningful engineering application value for deep investigation. The impacts of Ca2+ on coagulation and ultrafiltration performance are also investigated under different coagulant doses. Removal of humic-like substance, floc size and incompactness were appreciably enhanced at under-dose with increasing Ca2+ concentration, but did not distinctly change at the optimal-dosing. Besides, lower positive charge of flocs produced at under-dosing hindered the foulants transport to membrane surface. The interactions between humic substance, positively-charged coagulants, and structure of cake layer firstly systemically investigated the impacts on the performance of ultrafiltration in our study. The results shown that the technology of under-dosing with addition of Ca2+ has dramatically increased the UV254 removal efficiency, formed loose and porous flocs still outside of the critical electrostatic distance of membrane surface, which significantly remit the membrane fouling and improve the reversibility of membrane fouling.