Change In Transport Mechanism Research Articles

NMR investigation of multi-scale dynamics in ionic liquids containing Li+ and La3+: From vehicular to hopping transport mechanism

The dynamics in mixtures of ionic liquid and monoatomic cations has been studied at different time scales ranging from the nanosecond up to the second. The mixtures were composed of cholinium bis(trifluoromethanesulfonyl)imide ([Chol][TFSI]) and LiTFSI, with LiTFSI mole fraction, ▪, spanning from 0 to 0.5 (saturated solution), and [Chol][TFSI] and ▪ from 0 to 0.12. The translational self-diffusion coefficients of ▪, ▪ and ▪ have been measured, along with NMR their relaxation times at various magnetic fields, in order to decipher the intertwined dynamics between the ions, and to reveal how the local dynamics impact the long range translational diffusion. When the concentrations of lithium and lanthanum are increased in the liquid, the long range dynamics of all the ions drop. In the case of LiTFSI, the self-diffusion coefficient of lithium becomes higher than the one of TFSI at high concentration, revealing a change in lithium transport mechanisms. The NMR relaxation data confirm this change, showing a clearer transition at ▪. It is interpreted as a change from a vehicular transport mechanism of the lithium below ▪ to a hopping mechanism above. A similar crossover seems to occur in the lanthanum solutions. This phenomenon seems correlated to the departure of the hydroxyl group of the organic cation from the lithium solvation shell.

Engineering interfaces to facilitate charge transport pathways in electrospun scaffolds for high-performance, flexible supercapacitors

Understanding and engineering the interface of a polymeric matrix with the ionic conductor offers important insights into the electrochemical charge polarization performance of flexible solid-state supercapacitors. These aspects are captured herewith utilizing chemically identical yet morphologically and interfacially different and distinct non-woven, electrospun polymeric membranes as scaffolds. Three distinct variations achieved through electrospinning namely, bilayered (PU/Ge) and core-shell geometries (PU@Ge and Ge@PU) with polyurethane (PU) and gelatin (Ge) are utilized in both conditions as polymeric electrolyte membranes for flexible supercapacitors. Equally important is the unique graphenic nanoplatelets (GNPs), fabricated through a single-step, template-driven approach, providing synergistic electrode/electrolyte interfaces. We unravel distinct changes in charge transport mechanism brought out by the interplay between surface chemistry and morphology of the electrospun scaffolds. The all-solid-state symmetric supercapacitor devices assembled with GNP@CC electrodes and PU/Ge, PU@Ge or Ge@PU polymeric membrane electrolyte of 1 M H3PO4 or EMIMBF4 are studied.Accordingly, the charge transport is protic and aprotic observed to switch from interfacial driven in the case of PU@Ge with H3PO4 to distinct phase separated ion transport channels in the case of PU/Ge with EMIMBF4. Thereby, a range of energy density (1.03–21.94 Wh kg−1), power density (0.049–99.97 kW kg−1) and scan rate operability (5–10,000 mV s−1) are demonstrated in such devices without any compromise on the cyclability. This study establishes rational design principles for tailoring the ion transport mechanism in a variety of matrices and thereby opens transformative possibilities for realizing high performance energy storage devices.

Activation of Piezo1 Increases Na,K-ATPase-Mediated Ion Transport in Mouse Lens.

Lens ion homeostasis depends on Na,K-ATPase and NKCC1. TRPV4 and TRPV1 channels, which are mechanosensitive, play important roles in mechanisms that regulate the activity of these transporters. Here, we examined another mechanosensitive channel, piezo1, which is also expressed in the lens. The purpose of the study was to examine piezo1 function. Recognizing that activation of TRPV4 and TRPV1 causes changes in lens ion transport mechanisms, we carried out studies to determine whether piezo1 activation changes either Na,K-ATPase-mediated or NKCC1-mediated ion transport. We also examined channel function of piezo1 by measuring calcium entry. Rb uptake was measured as an index of inwardly directed potassium transport by intact mouse lenses. Intracellular calcium concentration was measured in Fura-2 loaded cells by a ratiometric imaging technique. Piezo1 immunolocalization was most evident in the lens epithelium. Potassium (Rb) uptake was increased in intact lenses as well as in cultured lens epithelium exposed to Yoda1, a piezo1 agonist. The majority of Rb uptake is Na,K-ATPase-dependent, although there also is a significant NKCC-dependent component. In the presence of ouabain, an Na,K-ATPase inhibitor, Yoda1 did not increase Rb uptake. In contrast, Yoda1 increased Rb uptake to a similar degree in the presence or absence of 1 µM bumetanide, an NKCC inhibitor. The Rb uptake response to Yoda1 was inhibited by the selective piezo1 antagonist GsMTx4, and also by the nonselective antagonists ruthenium red and gadolinium. In parallel studies, Yoda1 was observed to increase cytoplasmic calcium concentration in cells loaded with Fura-2. The calcium response to Yoda1 was abolished by gadolinium or ruthenium red. The calcium and Rb uptake responses to Yoda1 were absent in calcium-free bathing solution, consistent with calcium entry when piezo1 is activated. Taken together, these findings point to stimulation of Na,K-ATPase, but not NKCC, when piezo1 is activated. Na,K-ATPase is the principal mechanism responsible for ion and water homeostasis in the lens. The functional role of lens piezo1 is a topic for further study.

Links between defect chemistry, conduction, and lifetime in heavily Nb doped lead zirconate titanate films

Phase pure PbZr0.52Ti0.48O3 (PZT) films with up to 13 mol. % Nb were prepared on Pt-coated Si substrates using chemical solution deposition; charge compensation for Nb was accomplished by reducing the concentration of lead in the film. For high Nb doping levels, (1) superoxidation of the PZT film surface makes the PZT/Pt interface more p-type and, hence reduces electron injection over the Schottky barrier, (2) the bulk charge transport mechanism changes from electron trapping by Ti4+ to hole migration between lead vacancies, and (3) the ionic conductivity due to migration of oxygen vacancies decreases. For ≤6 mol. % Nb, electrical degradation was controlled via field-induced accumulation of oxygen vacancies near the cathode, which, in turn, leads to Schottky barrier lowering and electron trapping by Ti4+. In phase pure 13 mol. % Nb doped PZT films, on the other hand, the increase in the leakage current during electrical degradation was dominated by hole migration between lead vacancies (2[VPb″]∼[h•]). A much lower lifetime and drastic increase in the leakage current upon electrical degradation was observed in mixed phase PNZT films, which was attributed to (1) a more electrically conductive pyrochlore phase and (2) a high concentration of lead vacancies.

Lithium Solvation and Mobility in Asymmetric Cyano(trifuloromethanesulfonyl)Imide Based Ionic Liquid Electrolyte for Li-Metal Battery

The solvation structure and transport properties of Li+ in ionic liquid (IL) electrolytes based on n-methyl-n-butylpyrrolidinium cyano(trifluoromethanesulfonyl)imide [PYR14][CTFSI] and [Li][CTFSI] (0≤ xLi ≤ 0.7) were studied by Raman and Nuclear Magnetic Resonance (NMR) spectroscopy, and molecular dynamics (MD) simulations. Li+-anion coordination is found to be dominated through the cyano group. Coordination through the sulfonyl group is seen only at higher Li-salt concentrations (xLi > 0.3). Such a trend is not observable in the case of the analogous electrolyte composed of the 1:1 mixture of the symmetric anions bis(trifluoromethanesulfonyl)imide ([TFSI]) and dicyanamide ([DCA]) since the Li-salt concentration was limited by its solubility (xLi < 0.05). The calculated ion pair lifetimes of Li+-cyano coordination for [CTFSI] are found to be shorter than that of [DCA] at xLi = 0.05, indicating the competition from the sulfonyl group on [CTFSI] weakens its solvation with Li+. This translated to the higher Li+ transference estimated for the IL electrolyte with [CTFSI] in comparison to [TFSI]:[DCA]. The NMR diffusivity measurements indicated an increase in Li+ diffusivity compared to [CTFSI] as xLi approached 0.7. These findings suggest the Li+ transport mechanism changes in the asymmetric anion at high salt concentrations. In relation to the utility of these electrolytes in energy storage, the Li-LiFePO4 half cells assembled with IL electrolyte were tested at 363 K. The system with xLi=0.7 demonstrated a capacity retention of 61% at 0.1 C-rate and 363 K after 100 cycles; remarkably higher than those of xLi=0.3 and 0.5. This is attributed to the improved electrochemical stability of the IL electrolyte with the asymmetric anion at higher salt concentrations.

High energy storage efficiency and temperature stability realized in the Ba0.3Sr0.7Zr0.18Ti0.82O3/LaNiO3 heterostructure thin films directly deposited on the conductive Si substrate

A high-performance energy storage capacitor would not display high energy storage density (Ue) but high energy storage efficiency (η). However, during raising the electric field (E) or temperature (T), the η in dielectric thin films often shows an obvious degradation process. The degradation process is closely related to the change of the charge carrier transport mechanism as a function of E or T. Compared with the electric breakdown strength, the relationship between η and the charge carrier transport mechanisms in the dielectric thin films was less concerning. In this work, by increasing the trigger E and T of the space charge limited current mechanism, the beginning of the η degradation process was delayed into higher E and T. Consequently, a high Ue (∼56.6 J/cm3) and η (∼93.9%) were achieved simultaneously in Ba0.3Sr0.7Zr0.18Ti0.82O3/LaNiO3 heterostructure thin films directly deposited on low-cost conductive silicon wafers. Moreover, the temperature stability was greatly improved. This result would also offer a promising approach to improve the electrical properties of the dielectric oxide thin films in a harsh environment of high temperatures by redistributing oxygen vacancies through the heterostructure interface.

Fine-Grained Sediment Characterization and Process Monitoring Using Nuclear Magnetic Resonance (NMR)

Abstract The intrinsic magnetic moment of hydrogen nuclei allows them to interact with externally imposed magnetic fields; then, nuclear magnetic resonance (NMR) can be used to probe the pore space of wet soils using the water molecules in pores. Surface relaxivity at pore walls combines with molecular diffusion to produce a relaxation rate that is inversely proportional to the pore size in saturated specimens or the mean distance to a pore wall in unsaturated soils. We used NMR to nondestructively characterize pore size distribution, monitor changes in pore space during sedimentation, and track the evolution of water conditions during drying and infiltration. Results show that the evolution of relaxation time distribution reflects pore size contraction, water film thickness reduction, and pore water redistribution. In all cases, the mean relaxation time and water content exhibit a unique relationship for both saturated and unsaturated soils; we propose a parallel plate model to interpret this relationship that only depends on surface relaxivity and specific surface area. Finally, we impose a magnetic field gradient to obtain spatially resolved relaxation spectra; this technique shows the evolution of moisture profile with depth and changes in moisture transport mechanisms during 1D drying. The carefully designed experiments demonstrate the potential of NMR spectroscopy as an effective tool to monitor water conditions and characterize the pore space in fine-grained sediments.

Stable Cu Isotope Ratios Show Changes in Cu Uptake and Transport Mechanisms in Vitis vinifera Due to High Cu Exposure.

Even though copper (Cu) is an essential plant nutrient, it can become toxic under certain conditions. Toxic effects do not only depend on soil Cu content, but also on environmental and physiological factors, that are not well understood. In this study, the mechanisms of Cu bioavailability and the homeostasis of Vitis vinifera L. cv. Tannat were investigated under controlled conditions, using stable Cu isotope analysis. We measured Cu concentrations and δ65Cu isotope ratios in soils, soil solutions, roots, and leaves of grapevine plants grown on six different vineyard soils, in a 16-week greenhouse experiment. The mobility of Cu in the soil solutions was controlled by the solubility of soil organic matter. No direct relationship between Cu contents in soils or soil solutions and Cu contents in roots could be established, indicating a partly homeostatic control of Cu uptake. Isotope fractionation between soil solutions and roots shifted from light to heavy with increasing Cu exposure, in line with a shift from active to passive uptake. Passive uptake appears to exceed active uptake for soil solution concentrations higher than 270 μg L–1. Isotope fractionation between roots and leaves was increasingly negative with increasing root Cu contents, even though the leaf Cu contents did not differ significantly. Our results suggest that Cu isotope analysis is a sensitive tool to monitor differences in Cu uptake and translocation pathways even before differences in tissue contents can be observed.

Mechanisms of charge carrier transport in polycrystalline silicon passivating contacts

We use temperature-dependent contact resistivity ( ρ c ) measurements to systematically assess the dominant electron transport mechanism in a large set of poly-Si passivating contacts, fabricated by varying (i) the annealing temperature ( T ann ), (ii) the oxide thickness ( t ox ), (iii) the oxidation method, and (iv) the surface morphology of the Si substrate. The results show that for silicon oxide thicknesses of 1.3–1.5 nm, the dominant transport mechanism changes from tunneling to drift-diffusion via pinholes in the SiO x layer for increasing T ann . This transition occurs for T ann in the range of 850°C-950 °C for a 1.5 nm thick thermal oxide, and 700°C-750 °C for a 1.3 nm thick wet-chemical oxide, which suggests that pinholes appear in wet-chemical oxides after exposure to lower thermal budgets compared to thermal oxides. For SiO x with t ox = 2 nm, grown either thermally or by plasma-enhanced atomic layer deposition, carrier transport is pinhole-dominant for T ann = 1050 °C, whereas no electric current through the SiO x layer could be detected for lower T ann . Remarkably, the dominant transport mechanism is not affected by the substrate surface morphology, although lower values of ρ c were measured on textured wafers compared to planar surfaces. Lifetime measurements suggest that the best carrier selectivity can be achieved by choosing T ann right above the transition range, but not too high, in order to induce pinhole dominant transport while preserving a good passivation quality. • Electron transport mechanisms through the oxide are investigated by temperature-dependent contact resistivity measurements. • A transition from tunneling to pinhole dominant transport was observed at T ann = 900–950°C for a 1.5 nm thick thermal oxide. • For a 1.3 nm thick wet-chemical oxide, the transition was observed at T ann = 700–750°C. • Good passivation quality is preserved even in the pinhole regime, although it degrades at extremely high T ann .

Space-charge limited ionic conductivity enhancement in gel polymer electrolyte capacitors by embedding nanoparticles

In this work, a novel mixture of ionic liquid gel polymer electrolyte (ILGPE), containing 1-butyl-3-methylimidazolium bromide, ammonium acetate and poly(vinyl alcohol), with Si@C and SiO2 embedded nanoparticles is fabricated. The resulting CILGPE is deposited onto interdigitated electrodes. The fabricated electrolytes have been characterised by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) and the resulting capacitors have been characterised by impedance spectroscopy (IS) and linear sweep voltammetry (LSV) and modelled. The specific capacitance for capacitor with ILGPE is 0.042Fcm−3, while for the capacitor with SiO2 and Si@C embedded in ILGPE are 0.072 Fcm−3 and 0.06 Fcm−3, respectively. Therefore, the addition of SiO2 and Si@C nanoparticles improves the capacitance by 71% and 42%, respectively. The results of fitting I-V curves exhibit reductions in both the activation voltage (Vtr) and in the voltage that indicates the traps are filled (VTFL) with the addition of nanoparticles, revealing an increase in charge contribution. We propose that the capacitance enhancement is due to the contribution of nanoparticles to: (i) the creation new effective ion transport pathways, (ii) ion dissociation in the electrolyte and (iii) the crystallinity reduction of ILGPE. This work contributes with new findings about the effect of nanoparticles on the Space-charge-limited-conduction (SCLC) mechanism and how these changes in transport mechanism are related to the series and leakage resistances, capacitance, and physicochemical properties.

Influence of magnetic field on the characteristics of n-type PSi prepared by photo-electro-chemical etching process

The surface uniformity of porous silicon (PSi) morphologies will enhance the overall properties of the PSi layer. In this study, the role of perpendicular magnetic field (MF) on structural, optical, and electrical properties of (PSi) substrates are reported. The (PSi) is prepared with a photo-electrochemical etching process in the front-side illumination pathway with and without a perpendicular magnetic field (MF). The application of (MF) on the path of the electric charge carrier leads to modify the morphologies of PSi surface. The pores shape, sizes, orientation, and homogeneity, and electrical properties will vary with the (MF). The role of (MF) will contribute to an increase in the number of pores and decrease the overlapping process. And also, promotes the orientation of the relatively more defined pores across the Psi surface. The observed noticeable changes in PL spectra, electrical properties, and charge carrier transport mechanisms may be owing to the surface reconstruction process. The influence of (MF) on the characteristics of Au thin layer / PSi/c-Si/Al structures will lead to converting its behavior from the resistor to Schottky-like junction.

Investigation of Ionic Conductive Behavior of SL-Based Gel Polymer Electrolyte and Interfacial Property of Li / Gel Polymer Electrolyte

IntroductionLithium-Sulfur (Li-S) batteries are attracting attention as high energy density rechargeable battery. Elemental sulfur (S8) has high theoretical capacity (1,672 mAhg-1) as positive electrode active material. However, S8 electrode is degraded by redox shuttle effect of lithium-polysulfide (Li2S n ), which are generated during charge-discharge reactions. To solve this problem, many electrolyte designs were proposed. Sulfolane (SL) based high Li salt concentration electrolyte solution was reported as low solubility electrolyte of Li2S n [1]. The aim of this concept is chemically protection of Li2S n dissolution into electrolyte solution. Therefore, we proposed new polymer electrolyte, which protects chemically and physically dissolution and diffusion of Li2S n . In this study, we prepared SL-based solid gel polymer electrolytes (GPEs), ionic conductive property and time dependence of Li/GPEs interfacial resistance were evaluated.ExperimentalSulfolane (SL), LiN(SO2CF3)2 (LiTFSA), and polyether-based P(EO/PO) macromonomer (EO/PO=8/2) were used as electrolyte materials for GPEs. First, electrolyte solution samples were prepared by mixing LiTFSA and SL at each molar ratio of SL : LiTFSA = x : 1 (x=1, 1.5 and 2, respectively). Next, prepared electrolyte solution and P(EO/PO) macromonomer were mixed at weight ratio of electrolyte solution is 70, 80, 90 wt%, respectively, and added DMPA as photo initiator. After that, these materials were radical polymerized by UV irradiation. Temperature dependence of ionic conductivity of prepared GPEs were investigated by AC impedance measurements (353～217 K). Impressed voltages were changed from 100mV to 500 mV under 258 K. Also, [Li | GPE | Li] symmetrical cells were assembled, and impedance measurements of these cells were carried out to investigation of Li/GPE interfacial resistance at 333 K.Results & DiscussionFig.1 shows temperature dependence of ionic conductivity (s) of GPEs. Conventional polyether-based solid electrolyte ([Li]/[O]=0.1: black circle) was showed for comparison. s of all GPEs indicated higher value compared with [Li]/[O]=0.1. s increased with electrolyte solution composition or decrease of Li salt composition. These should be related with mobility of polymer chain or microscopic viscosity of GPEs, like a T gs. Also, s observed at around or less than T gs by changing impressed voltage. At this area, temperature dependence was changed inconsecutively. Therefore, ionic transport mechanism changes with segmental motion of polymer chain might be occurred below T g.Fig.2 shows time dependence of Li/GPE interfacial resistance (R Li) at 333 K. R Li moderately increased over time, which wasn’t stabilized over 1000 h. (Measurement was interrupted temporary at broken line.) R Li of general polyether based solid electrolyte reported as ca. 100 W cm2 [2],[3]. However, R Li indicated quite low values of 30～40 W cm2 at 1000 h. Therefore, favorable SEI formation might be occurred between Li metal and GPE. In presentation, temperature dependence of R Li and lithium cation transport number (t Li+) will be discussed.

High on–off current ratio titanium oxynitride write-once-read-many-times memory

In this letter, we demonstrate a titanium oxynitride (TiO x N y ) write-once-read-many-times memory with a high ON/OFF current ratio of 109. The endurance and read-disturb tests both reveal high stability and data nonvolatility of the TiO x N y resistive memory. A Ti metal layer was transformed into TiO x N y using an annealing process in a nitrogen ambient. The XPS analysis shows that the TiO x N y resistive switching (RS) layer possesses few Ti interstitial defects and oxygen deficiencies. A voltage-polarity dependent set process is observed in the Ag/TiO x N y /Ti/n+-Si resistive memory. The residual Ti metal layer provides a good contact with the TiO x N y RS layer, and the electrons can transport from the Ti to the Ag electrode via tunneling processes. In the low voltage region, the conduction current is dominated by the direct tunneling mechanism. When the voltage is beyond a transition voltage of 1.25 V, the carrier transport mechanism changes to Fowler–Nordheim tunneling. The conduction mechanisms are consistent with the finding obtained by the energy band diagram analysis.

Intestinal Transcriptome Analysis Reveals Soy Derivative-Linked Changes in Atlantic Salmon.

Intestinal inflammation in farmed fish is a non-infectious disease that deserves attention because it is a major issue linked to carnivorous fishes. The current norm is to formulate feeds based on plant-derived substances, and the ingredients that have antinutritional factors are known to cause intestinal inflammation in fishes such as Atlantic salmon. Hence, we studied inflammatory responses in the distal intestine of Atlantic salmon that received a feed rich in soybean derivatives, employing histology, transcriptomic and flow cytometry techniques. The fish fed on soy products had altered intestinal morphology as well as upregulated inflammation-associated genes and aberrated ion transport-linked genes. The enriched pathways for the upregulated genes were among others taurine and hypotaurine metabolism, drug metabolism—cytochrome P450 and steroid biosynthesis. The enriched gene ontology terms belonged to transmembrane transporter- and channel-activities. Furthermore, soybean products altered the immune cell counts; lymphocyte-like cell populations were significantly higher in the whole blood of fish fed soy products than those of control fish. Interestingly, the transcriptome of the head kidney did not reveal any differential gene expression, unlike the observations in the distal intestine. The present study demonstrated that soybean derivatives could evoke marked changes in intestinal transport mechanisms and metabolic pathways, and these responses are likely to have a significant impact on the intestine of Atlantic salmon. Hence, soybean-induced enteritis in Atlantic salmon is an ideal model to investigate the inflammatory responses at the cellular and molecular levels.

The effect of thermal loading on negative permittivity in carbon nanofiber/silicone metacomposites

Nanofiller/polymer composites have recently received much attention for their potential as metacomposites. To date, however, work has focused on understanding the relation between manufacturing parameters and negative permittivity rather than achieving in-operation adaptability. Therefore, this work explores the effect of thermal loading on the negative permittivity of carbon nanofiber (CNF)/silicone nanocomposites as a means to actively change the permittivity of post-manufactured metacomposites. It was found that even modest temperature increases markedly affect the magnitude of negative permittivity, the shape of the permittivity-frequency curve, and the frequency at which permittivity transitions into the negative regime. Further, elevated temperatures and higher CNF concentrations cause the permittivity-frequency response to transition from Lorentz-oscillator to Drude model behavior thereby suggesting a temperature and/or CNF content-initiated change in transport mechanisms. These results are a promising first step towards the realization of on-demand control and adaptability of negative permittivity in next-generation polymeric metacomposites.

Wind variability over the northern Indian Ocean during the past 4 million years – Insights from coarse aeolian dust (IODP exp. 359, site U1467, Maldives)

The lithogenic fraction of carbonate drift sediments from IODP Exp. 359 Site U1467 (Maldives) provides a unique record of atmospheric dust transport over the northern Indian Ocean during the past 4 Myr. Grain-size data provide proxies for dust flux (controlled by source area aridity) as well as wind transport capacity (wind speed). Entrainment and long-range transport of dust in the medium to coarse silt size range is linked to the strength of the Arabian Shamal winds and the occurrence of convective storms which prolong dust transport. Dust flux and the size of dust particles increased between 4.0 and 3.3 Ma, corresponding to the closure of the Indonesian seaway and the intensification of the South Asian Monsoon. There is no clear trend in dust flux between 3.3 and 1.6 Ma, whereas wind transport capacity decreased. Between 1.6 Ma and the Recent, dust flux increased and shows higher variability, especially during the last 500 kyr. Transport capacity increased between 1.2 and 0.5 Ma and slightly decreased since then. Frequency analysis shows that dust transport varies on orbital timescales, with eccentricity control being the most prominent (400 kyr throughout the record, 100 kyr between 2.0 and 1.3 Ma, and since 1.0 Ma). Higher frequency cycles (obliquity and precession) are more pronounced in wind transport capacity than in the amount of dust. This indicates that the amount of coarse dust in sediments from the Maldives as a far-field site is more prone to changes in transport mechanisms than to changes in dust source-area aridity.

Large-scale pollen distribution in marine surface sediments from the Bohai Sea, China: Insights into pollen provenance, transport, deposition, and coastal-shelf paleoenvironment

To elucidate the mechanisms responsible for pollen and spore transportation and deposition in the Bohai Sea, fully covered seafloor-surface sediment samples were collected for palynological and grain size analysis. The results reveal that the pollen and spore concentrations were higher in the head of Liaodong Bay and in the muddy area of the Bohai Sea. The Yellow River was the main source of pollen and spores in the Bohai Sea. The sediments with relatively high pollen concentrations consisted mainly of clay and fine silt, whereas sediment with lower pollen concentrations was mostly fine sand. In addition, the percentages of Pinus pollen and pteridophyte spores increased with increasing sea water depth, while other arboreal (excluding Pinus) and herbaceous pollen generally decreased with increasing distance from the shore. The relationship between the pollen taxa and the water depth of the sampling points shows that the fluvial water plays a predominant role in pollen transmission within 20 m of water depth, while the wind is the main driving force for pollen transmission when the water depth exceeds 20 m. Although Pinus pollen and pteridophyte spores were over-represented, there was good correlation between marine pollen signals and terrestrial vegetation. Apart from the influence of rivers and wind on pollen and spore deposition, the tidal currents and circulation were also main force responsible for transporting sediment and determining the differentiation of pollen and spores in the Bohai Sea. The comparison of pollen and spore percentages between surface sediment and fossil records from sedimentary cores made it possible to identify changes in pollen sources and transport mechanisms. Meanwhile, the percentage fluctuations of fossil Pinus and herbaceous pollen revealed concomitant changes of the sea level and climate. These findings are of paramount importance to the interpretation of Quaternary marine pollen data from the Bohai Sea, China.

Pressure-Induced Ionic-Electronic Transition in BiVO4**Supported by the National Natural Science Foundation of China under Grant Nos 11774126, 11774174 and 11404133.

Electrical transport properties of bismuth vanadate (BiVO4) are studied under high pressures with electrochemical impedance spectroscopy. A pressure-induced ionic-electronic transition is found in BiVO4. Below 3.0 GPa, BiVO4 has ionic conduction behavior. The ionic resistance decreases under high pressures due to the increasing migration rate of O2− ions. Above 3.0 GPa the channels for ion migration are closed. Transport mechanism changes from the ionic to the electronic behavior. First-principles calculations show that bandgap width narrows under high pressures, causing the continuous decrease of electrical resistance of BiVO4.

Inter-cluster separation induced change in charge transport mechanism in Ni40Pd60 nanoclusters

Nanoclusters offer a fascinating possibility of studying the evolution of properties of a physical system by varying the number, size and inter-cluster separation of a given cluster to go from one limit to another. By systematically varying the inter-cluster separation in a nanocluster assembly of Ni40Pd60 alloy, that is known to be a metal in bulk, we observe an unusual and hitherto unreported, spatial dimension change as well as a change in the transport mechanism. In the nanocluster form, the temperature dependent resistance shows an activated behavior for virtually all inter-cluster separations, contrary to, the bulk metallic behaviour. At large average inter-cluster separation, the transport happens via three dimensional Efros-Shklovskii hopping, due to the opening of a Coulomb gap at the Fermi surface. With a reduction in the inter-cluster separation, the transport mechanism changes from three dimensional Efros-Shklovskii hopping to that of a three dimensional Mott variable range hopping (VRH) due to the closing up of the gap. With a further reduction in average inter-cluster separation, the three dimensional Mott VRH changes to that of a two dimensional Mott VRH with additional signatures of an insulator to a weak metal-like transition in this particular assembly. So, nanoclusters offer a paradigm for studying the important problem of evolution of charge transport in physical systems with the possibility of directly tuning the average inter-cluster separation enabling the system to go from insulating to metallic limit via intermediate changes in the charge transport mechanism.

Benthic fluxes from hypoxia-influenced Gulf of Mexico sediments: Impact on bottom water acidification

Benthic fluxes are reported from 8 sites on the shelf and slope of the Gulf of Mexico (GoM) in the region near the Mississippi River delta. Benthic landers, with the capability to incubate 3 chambers simultaneously, were deployed in August 2011 to establish the rate of phosphate, nitrate, ammonium, dissolved Si, Dissolved Inorganic Carbon (DIC) and alkalinity concentration change vs. incubation time (7–50 h) thereby providing flux estimates for these parameters. Stations located within 350 km of the Mississippi River mouth have nutrient and DIC fluxes that vary by a factor of 10 but show no longitudinal trends. Chambers deployed in low oxygen bottom water (<4 μM) do not have different flux values compared to chambers deployed in settings with higher bottom water oxygen (160 μM). At some stations, ammonium shows a change in flux with incubation time, yet no other species shows this change; hence neither a change in transport mechanism or reaction rate can explain the non-steady state behavior of ammonium. A positive correlation (r2 = 0.91) between the fluxes of dissolved Si and DIC imply a linkage between the diagenesis of biogenic Si and organic C throughout this region. The efflux of DIC and alkalinity in a ratio > 1 drives GoM bottom waters to a lower calcite and aragonite saturation state. Carbon isotopes of the DIC were measured on chamber waters and the calculated δ13C of the DIC source at 4 stations was similar, between −14 to −17‰ compared to typical δ13C values of bulk organic carbon in the GoM of −22‰. At a fifth station, the DIC added was calculated to have an isotope value of −31‰. Dissolved inorganic carbon isotope compositions that are significantly heavier or lighter than particulate organic carbon are unexpected and may be explained by a combination of inputs: the oxidation of average marine organic carbon and calcium carbonate dissolution, methanogenesis, and/or from oxidation of terrestrial lignin fractions.