Periods Of High Flux Research Articles

Design of Radially Variant Phase‐Change Material Composites

Phase‐change materials (PCMs) and high‐conductivity elements can be combined to form highly compact and efficient composite heat sinks. However, the design challenge presented by thermal composites composed of PCMs and high‐conductivity elements remains unresolved. Herein, design guidelines are presented for radially varying cylindrical PCM composites. Numerical and analytical techniques are utilized to explore the utility and limits of optimal composite designs selecting for 1) temperature minimization, 2) specific effective heat capacity maximization, and 3) volumetric effective heat capacity maximization. Significant increases in each metric are observed when implementing radially variant designs in cylindrical geometries, especially for metrics of heat capacity. Furthermore, a hybrid approach to variant composite design is presented, allowing for the balancing of different design objectives. The utilization of a variable design under high heat flux (10 ± 1.4 W cm−2) and short melting periods (up to 50 s) is experimentally demonstrated, directly resulted in a 65% decrease in total system mass and a 200% increase in specific heat capacity while maintaining strong temperature dampening performance. In a second case study, a 23% decrease in mass is demonstrated while maintaining strong specific heat performance, emphasizing the broad utility of this approach.

Factors Influencing the Seasonal Flux of the Varved Sediments of Kusai Lake on the Northern Tibetan Plateau During the Last ∼2280 years

The varved sediments of Kusai Lake on the northern Tibetan Plateau are rhythmically laminated with the interaction of dark and light layers formed during winter and summer within a year. This provides opportunities to explore the seasonal fluxes of varves and, thus, assess the potential for annual-resolution climate reconstruction. Here, we define a season index (SI) based on the difference in thickness between the light and dark layers, to evaluate the factors influencing the seasonal flux of varved Kusai Lake sediments. A positive SI represents more summer flux, and a negative SI indicates more winter flux. The results showed that the summer flux was higher than the winter flux in most of the last 2280 years. The summer flux had periodicities of approximately 2.3–2.9, 27, and 99 years at the 99% confidence level and approximately 15–16, 36 and 285 years at the 95% confidence level, indicating that summer flux is affected mainly by solar activity (Gleissberg and 350 unnamed cycle) at centennial scales, by the Pacific Decadal Oscillation (Pacific Decadal Oscillation with a period of 15–25 years) at decadal scales, and by the Quasi-biennial Oscillation (Quasi-biennial Oscillation with a period of 2–3 years) at interannual scales. Noticeable increasing spikes of high winter flux corresponded well to lower solar activity and stronger Siberian high pressure (SH). The periods of high and low winter flux are generally related to the negative and positive phases of the North Atlantic Oscillation and Atlantic Multidecadal Oscillation respectively, during the last 1000 years.

Impact and synergies of GIM error estimates on the VTEC interpolation and single-frequency PPP at low latitude region

The vertical total electron content (VTEC) is one of the key quantities to describe variations of the ionosphere and can be provided to users to correct the ionospheric disturbances for GNSS (Global Navigation Satellite System) positioning. The VTEC values and the corresponding standard deviations are routinely provided in the so-called Global Ionosphere Maps (GIM), with a typical time resolution of 2 h (and up to 15 min) on regular grids with 2.5º resolution in latitude and 5º resolution in longitude. To determine the ionospheric corrections from the GIMs for positioning applications, an interpolation has to be applied to the VTEC grid values, which generally degenerates the final VTEC accuracy. In this context, the typically applied bi-linear interpolation of the VTEC values is calculated by introducing a new weighting scheme by means of the standard deviation maps in the ionospheric domain. In the sequel, the impact of the use of the VTEC uncertainties for the interpolation procedure is applied to the GIMs of different centers and assessed in the ionospheric and in the positioning domain. For the assessment of the GIM in the ionospheric domain, the VTEC values calculated are compared with VTEC directly obtained from the given GIM, i.e., without interpolation. In the positioning domain, the impact of the VTEC uncertainties is analyzed by means of single-frequency precise point positioning (PPP), considering four Brazilian stations in challenging regions. The use of the standard deviation values in positioning provides a significant improvement in periods of high solar flux, especially for stations in the region under more intense ionospheric effect (mean rates of improvements up to 47%).

Characteristics of sediment resuspension on a deep abyssal plain in the Eastern Tropical Pacific Ocean

We examined the biogenic and lithogenic particle composition and radiocarbon content of sinking particulate organic carbon to investigate sediment resuspension and its contribution to sinking particles on the deep abyssal plain of the Eastern Tropical Pacific Ocean. Samples were collected using sediment traps from August 2011 to July 2012 at depths of 4500 and 4950 m (50 m above the seafloor); above and within the benthic nepheloid layer (BNL), respectively. Biogenic particles derived from export production were the major source of sinking particles and their flux showed a unimodal temporal distribution, with larger values between February and April. At a depth of 4500 m, the lithogenic material flux was slightly greater than, or similar to, the flux of atmospheric dust deposition. In comparison, lithogenic material and excess Mn consistently showed a greater contribution to resuspended particles at 4950 m. The lithogenic material flux was proportional to the biogenic flux. These observations imply that resuspended particles exist at a background concentration in the BNL throughout the year, and are scavenged by sinking biogenic particles, especially during the high flux period.

High-latitude crochet: solar-flare-induced magnetic disturbance independent from low-latitude crochet

Abstract. A solar-flare-induced, high-latitude (peak at 70–75∘ geographic latitude – GGlat) ionospheric current system was studied. Right after the X9.3 flare on 6 September 2017, magnetic stations at 68–77∘ GGlat near local noon detected northward geomagnetic deviations (ΔB) for more than 3 h, with peak amplitudes of >200 nT without any accompanying substorm activities. From its location, this solar flare effect, or crochet, is different from previously studied ones, namely, the subsolar crochet (seen at lower latitudes), auroral crochet (pre-requires auroral electrojet in sunlight), or cusp crochet (seen only in the cusp). The new crochet is much more intense and longer in duration than the subsolar crochet. The long duration matches with the period of high solar X-ray flux (more than M3-class flare level). Unlike the cusp crochet, the interplanetary magnetic field (IMF) BY is not the driver, with the BY values of only 0–1 nT out of a 3 nT total field. The equivalent ionospheric current flows eastward in a limited latitude range but extended at least 8 h in local time (LT), forming a zonal current region equatorward of the polar cap on the geomagnetic closed region. EISCAT radar measurements, which were conducted over the same region as the most intense ΔB, show enhancements of electron density (and hence of ion-neutral density ratio) at these altitudes (∼100 km) at which strong background ion convection (>100 m s−1) pre-existed in the direction of tidal-driven diurnal solar quiet (Sq0) flow. Therefore, this new zonal current can be related to this Sq0-like convection and the electron density enhancement, for example, by descending the E-region height. However, we have not found why the new crochet is found in a limited latitudinal range, and therefore, the mechanism is still unclear compared to the subsolar crochet that is maintained by a transient redistribution of the electron density. The signature is sometimes seen in the auroral electrojet (AE = AU − AL) index. A quick survey for X-class flares during solar cycle 23 and 24 shows clear increases in AU for about half the > X2 flares during non-substorm time, despite the unfavourable latitudinal coverage of the AE stations for detecting this new crochet. Although some of these AU increases could be the auroral crochet signature, the high-latitude crochet can be a rather common feature for X flares. We found a new type of the solar flare effect on the dayside ionospheric current at high latitudes but equatorward of the cusp during quiet periods. The effect is also seen in the AU index for nearly half of the > X2-class solar flares. A case study suggests that the new crochet is related to the Sq0 (tidal-driven part) current.

High resolution osmium data record three distinct pulses of magmatic activity during cretaceous Oceanic Anoxic Event 2 (OAE-2)

Oceanic Anoxic Event 2 (OAE-2) occurred at the Cenomanian-Turonian boundary (∼94.1 Ma) and was a time of profound global changes in ocean chemistry and the carbon cycle. This event was characterized by a positive carbon isotope excursion (CIE) caused by massive organic carbon burial, global greenhouse temperatures, ocean deoxygenation, and changes in ocean life driven by large igneous province (LIP) activity. LIPs throughout the Phanerozoic have had dynamic magma flux, with episodes of major eruptions interspersed with periods of relatively less intense eruptions. A possible trigger for LIP activity throughout the Phanerozoic has been attributed to extraterrestrial impacts because there are multiple contemporaneous occurrences of large craters, LIP activity, and mass extinctions in the geologic record. At the Cenomanian-Turonian boundary, there is a 25 km diameter (rim-to-rim) complex crater in NW Alberta, Canada known as the Steen River impact structure dated at 91 ± 7 Ma (Carrigy and Short, 1968). An alternative explanation for those craters found contemporaneous with LIP activity and mass extinctions is that they were created by large explosive events related to LIP activity. Explosive events associated with mantle plume incubation beneath cratonic lithosphere have been suggested to create geologic features commonly attributed to impacts (e.g., shocked quartz, microspherules, etc.). Currently, the trigger for LIP activity during OAE-2, as well as the duration of LIP activity and the temporal variation and magnitude of eruption rates are not well constrained.To address the issue of LIP eruption rates and the trigger for LIP activity, we examined osmium (Os) abundances and isotopes as well as highly siderophile element (HSE; for this study: Re, Ru, Pd, Os, Ir, Pt) abundance data from a continuous sedimentary section spanning OAE-2. The section is from the Eagle Ford Group in the Iona-1 core, deposited in the Cretaceous Western Interior Seaway (KWIS). We found three high Os concentration intervals with mantle-like initial Osi isotope (initial 187Os/188Os) values of ∼0.16. These intervals are interpreted to reflect high-flux LIP magmatic pulses. Between the pulses, lower Os abundances with more radiogenic Osi values of ∼0.20 are observed, which we interpret as low-flux LIP activity between the high-flux periods. This trend of high-and-low flux Os concentration pulses with mantle-like Osi values during the high flux periods is found in another KWIS core (USGS Portland #1) deposited to the north of Iona-1, and in core Deep Sea Drilling Project (DSDP) Site 530 Hole A (hereafter DSDP 530A; drilled off-shore Namibia in the Angola Basin) deposited in the Southern Hemisphere. Before and throughout the Iona-1 core OAE-2 interval, HSE abundance patterns indicate a mantle source for the unradiogenic Os, and are not consistent with an extraterrestrial impact trigger or contribution to LIP activity during OAE-2.This evidence for multiple high-flux pulses of LIP activity driving ocean deoxygenation has implications for the modern ocean, which is currently experiencing deoxygenation. These results provide new constraints on subsequent high-flux periods that extended the event. The first high-flux period started ∼60 Kyr after our selection of the onset of the CIE. The second and third high-flux periods started ∼270 and ∼400 Kyr after the onset of the CIE, respectively. After the third high-flux period, δ13Corg and Os isotope ratios shifted back to pre-excursion values over ∼585 kyr. In the Iona-1 core, OAE-2 lasted for 1.04 ± 0.12 Myr based on our selection of the CIE.

Midwinter Arctic leads form and dissipate low clouds

Leads are a key feature of the Arctic ice pack during the winter owing to their substantial contribution to the surface energy balance. According to the present understanding, enhanced heat and moisture fluxes from high lead concentrations tend to produce more boundary layer clouds. However, described here in our composite analyses of diverse surface- and satellite-based observations, we find that abundant boundary layer clouds are associated with low lead flux periods, while fewer boundary layer clouds are observed for high lead flux periods. Motivated by these counterintuitive results, we conducted three-dimensional cloud-resolving simulations to investigate the underlying physics. We find that newly frozen leads with large sensible heat flux but low latent heat flux tend to dissipate low clouds. This finding indicates that the observed high lead fractions likely consist of mostly newly frozen leads that reduce any pre-existing low-level cloudiness, which in turn decreases downwelling infrared flux and accelerates the freezing of sea ice.

δ13C and δ15N Values of Sediment-trap Particles in the Japan and Yamato Basins and Comparison with the Core-top Values in the East/Japan Sea

Investigation of sediment-trap deployments in the East/Japan Sea (EJS) showed that distinct seasonal variations in particulate organic carbon (POC) fluxes of intermediate-water sediment-traps clearly corresponded to changes in chlorophyll a concentrations estimated from SeaWiFS data. The prominent high POC flux periods (e.g., March) were strongly correlated with the enhanced surface-water phytoplankton blooms. Deep-water sedimenttraps exhibited similar variation patterns to intermediate-water sediment-traps. However, their total flux and POC flux were higher than those of intermediate-water sediment-traps during some months (e.g., April and May), indicating the lateral delivery of some particles to the deep-water sediment-traps. Distinct seasonal δ13C and δ15N variations in settling particles of the intermediate-water sediment-traps were observed, strongly supporting the notion of seasonal primary production. Seasonal variations in δ13C and δ15N values from the deep-water sediment-traps were similar to those of the intermediate-water sediment-traps. However, the difference in δ13C and δ15N values between the intermediate-water and the deepwater sediment-traps may be attributed to degradation of organic matter as it sank through the water column. Comparison of fluxweighted δ13C and δ15N mean values between the deep-water sediment-traps and the core-top sediments showed that strong selective loss of organic matter components (lipids) depleted in 13C and 15N occurred during sediment burial. Nonetheless, the results of our study indicate that particles in the deep-water sediment-trap deposited as surface sediments on the seafloor preserve the record of surface-water conditions, highlighting the usefulness of sedimentary δ13C and δ15N values as a paleoceanographic application in the EJS.

New evidence for a continental rift tectonic setting of the Neoproterozoic Imorona-Itsindro Suite (central Madagascar)

The Neoproterozoic Imorona-Itsindro Suite of central Madagascar represents one of the crucial petrological records of the supercontinent transformation from Rodinia into Gondwana, whereas its tectonic setting remains open to debate. Here newly reported and existing zircon U/Pb-Hf-O isotope data are used to better understand the tempo-spatial features and petrogenetic mechanisms of this enigmatic suite. The following results are at least more compatible with, if not suggestive of, a continental rift setting than the traditionally accepted continental arc setting. (1) This suite is present throughout central Madagascar, including the Manampotsy-Anaboriana Domain and probably also the Antongil Sub-domain. Particularly, the high-flux magmatic pulse at ∼790 Ma has a width of more than 300 km. (2) This suite is in essence an igneous expression of lithospheric reworking with no asthenosphere contribution being clearly detected. (3) The felsic and mafic end-members of this suite have independent sources and were derived from the crustal basement and lithospheric mantle, respectively. (4) Input of mantle materials (via magma mixing process) into the crust-derived felsic end-member increased at the ∼790 Ma high-flux period, as indicated by a discernible positive zircon εHf(t) excursion. (5) Felsic end-member magma systems may have interacted with meteoric water at a high temperature, as implied by a previously reported zircon low-δ18O signature. Thus, there is perhaps no Neoproterozoic Mozambique Ocean suture across the Archean basement of central Madagascar. The most important implication of this study is that an elongate Andean-type orogenic system assumed in many Neoproterozoic paleogeography maps may not have been developed along the western margin of the supercontinent Rodinia.

Early-Holocene greening of the Afro-Asian dust belt changed sources of mineral dust in West Asia

Production, transport and deposition of mineral dust have significant impacts on different components of the Earth systems through time and space. In modern times, dust plumes are associated with their source region(s) using satellite and land-based measurements and trajectory analysis of air masses through time. Reconstruction of past changes in the sources of mineral dust as related to changes in climate, however, must rely on the knowledge of the geochemical and mineralogical composition of modern and paleo-dust, and that of their potential source origins. In this contribution, we present a 13,000-yr record of variations in radiogenic Sr–Nd–Hf isotopes and Rare Earth Element (REE) anomalies as well as dust grain size from an ombrotrophic (rain fed) peat core in NW Iran as proxies of past changes in the sources of dust over the interior of West Asia. Our data shows that although the grain size of dust varies in a narrow range through the entire record, the geochemical fingerprint of dust particles deposited during the low-flux, early Holocene period (11,700–6,000 yr BP) is distinctly different from aerosols deposited during high dust flux periods of the Younger Dryas and the mid-late Holocene (6,000–present). Our findings indicate that the composition of mineral dust deposited at the study site changed as a function of prevailing atmospheric circulation regimes and land exposure throughout the last deglacial period and the Holocene. Simulations of atmospheric circulation over the region show the Northern Hemisphere Summer Westerly Jet was displaced poleward across the study area during the early Holocene when Northern Hemisphere insolation was higher due to the Earth's orbital configuration. This shift, coupled with lower dust emissions simulated based on greening of the Afro-Asian Dust Belt during the early Holocene likely led to potential sources in Central Asia dominating dust export to West Asia during this period. In contrast, the dominant western and southwest Asian and Eastern African sources have prevailed during the mid-Holocene to modern times.

Timing Analysis of V404 Cyg during Its Brightest Outburst with INTEGRAL/SPI

Abstract The outburst of V404 Cyg during the summer of 2015 reached unparalleled intensities at X-ray and soft gamma-ray energies with fluxes Crab in the 20–50 keV energy band. To date, studies in the hard X-ray/soft gamma-ray energy domain have focused primarily on the energy spectra. In this work, a timing analysis has been performed with INTEGRAL/SPI data in the 20–300 keV energy range for INTEGRAL revolution 1557, which corresponds to the brightest flare of V404 Cyg (on 2015 June 26). The power spectra are fit with broken power-law and multi-Lorentzian models and compared with previously reported results of V404 Cyg flaring activity from 1989 and 2015. Also, we took advantage of the good signal-to-noise ratio obtained above 70 keV to quantify the timing/fast-variability properties of the source as a function of energy. We then point out similarities of V404 Cyg with the black hole transient V4641 Sgr. Like V4641 Sgr, we found that the power spectra of V404 Cyg during high flux periods did not possess the expected flat-top feature typically seen in a hard spectral state. Interpretations are proposed in the framework of the fluctuating-propagation model to explain the observed properties.

Characteristics of nighttime E-region over Arecibo: Dependence on solar flux and geomagnetic variations

Electron concentration (Ne) inferred from Incoherent Scatter Radar (ISR) measurements has been used to determine the influence of solar flux and geomagnetic activity in the ionospheric E-region over Arecibo Observatory (AO). The approach is based on the determination of column integrated Ne, referred to as E-region total electron content (ErTEC) between 80 and 150km altitude regions. The results discussed in this work are for the AO nighttime period. The study reveals higher ErTEC values during the low solar flux periods for all the seasons except for summer period. It is found that the E-region column abundance is higher in equinox periods than in the winter for low solar activity conditions. The column integrated Ne during the post-sunset/pre-sunrise periods always exceeds the midnight minima, independent of season or solar activity. This behavior has been attributed to the variations in the coupling processes from the F-region. The response of ErTEC to the geomagnetic variability is also examined for different solar flux conditions and seasons. During high solar flux periods, changes in Kp cause an ErTEC increase in summer and equinox, while producing a negative storm-like effect during the winter. Variations in ErTEC due to geomagnetic activity during low solar flux periods produce maximum variability in the E-region during equinox periods, while resulting in an increase/decrease in ErTEC before local midnight during the winter/summer periods, respectively.

The supersoft X-ray source in V5116 Sagittarii

Classical novae occur on the surface of an accreting white dwarf in a binary system. After ejection of a fraction of the envelope and when the expanding shell becomes optically thin to X-rays, a bright source of supersoft X-rays arises, powered by residual H burning on the surface of the white dwarf. While the general picture of the nova event is well established, the details and balance of accretion and ejection processes in classical novae are still full of unknowns. The long-term balance of accreted matter is of special interest for massive accreting white dwarfs, which may be promising supernova Ia progenitor candidates. V5116 Sgr was observed as a bright and variable supersoft X-ray source by XMM-Newton 610~days after outburst. The light curve showed a periodicity consistent with the orbital period. During one third of the orbit the luminosity was a factor of seven brighter than during the other two thirds of the orbital period. In the present work we aim to disentangle the X-ray spectral components of V5116 Sgr and their variability. We present the high resolution spectra obtained with XMM-Newton RGS and Chandra LETGS/HRC-S in March and August 2007. The grating spectrum during the periods of high-flux shows a typical hot white dwarf atmosphere dominated by absorption lines of N VI and N VII. During the low-flux periods, the spectrum is dominated by an atmosphere with the same temperature as during the high-flux period, but with several emission features superimposed. Some of the emission lines are well modeled with an optically thin plasma in collisional equilibrium, rich in C and N, which also explains some excess in the spectra of the high-flux period. No velocity shifts are observed in the absorption lines, with an upper limit set by the spectral resolution of 500 km/s, consistent with the expectation of a non-expanding atmosphere so late in the evolution of the post-nova.

Average field‐aligned ion velocity over the EISCAT radars

AbstractLong‐term measurements by the European Incoherent Scatter (EISCAT) radars at Tromsø (69.6°N, 19.2°E) and Svalbard (78.2°N, 16.0°E) are used to determine the climatology of the field‐aligned ion velocity in the F region ionosphere (175–475 km) at high latitudes. The average ion velocity is calculated at various altitudes and times of day. The magnitude of the average field‐aligned ion velocity is on the order of 10 m/s, similar to previous results at middle and low latitudes. The results obtained for the two radars are in good agreement. During daytime the direction of the average field‐aligned ion velocity changes from downward to upward around 350 km, while during nighttime it is upward at all heights. The reversal height of the daytime field‐aligned ion velocity depends on solar activity. It is elevated by more than 100 km during high solar flux periods compared to low solar flux periods. The Thermosphere Ionosphere Electrodynamics General Circulation Model reproduces the main features of the field‐aligned ion velocity climatology. The simulation results suggest that the plasma pressure gradient force and gravity force play a dominant role for the daytime field‐aligned ion motion. The height pattern of the field‐aligned ion velocity tends to be preserved in different solar activity conditions at constant pressure surfaces, but not at constant altitudes, which explains the observed dependence on solar activity. During nighttime, the effect of the neutral wind dominates the field‐aligned ion velocity.

Characterization of Solar Energetic H and He Spectra Measured by the Energetic Particle Telescope (EPT) On-Board PROBA-V During the January 2014 SEP Event

On January 6, 2014 a Solar Energetic Particle (SEP) event started that led to a 1030 cm $^{-2}$ $\text{s}^{-1}$ sr $^{-1}$ peak flux of E > 10 MeV protons on January 9, 2014 at geosynchronous orbit, an event exceeded only by about 15% of all SEP events. Such high flux events contribute the most to solar event-induced radiation effects in space equipment, while being easy to characterize based on data acquired by spectrometers, such as the EPT. The EPT instrument provides fluxes of electrons (0.5–20 MeV), H (9.5–300 MeV) and He (38–1200 MeV) ions. It presently flies on the PROBA-V satellite, launched into a Low Earth Orbit on May 7, 2013. As it has been reported that the He contribution to Total Non-Ionizing Dose (TNID) may be comparable to that of H in representative space environments, a data analysis to identify periods of high He flux as compared to H, and conditions under which both ions must be accounted for during radiation effect analyses, was performed. From the study of the positional variation of solar H and He fluxes, a formulation of the minimum L-value reached by these particles for a given rigidity is provided. The shape of solar H and He energy spectra as well as the H/He fluence ratio and pitch angle distributions are characterized. The contribution of He compared to H for Total Ionizing Dose (TID) and TNID effects is below 5% for devices shielded by >2mm Al.

The Gulf Stream influence on wintertime North Atlantic jet variability

In this article we investigate the influence of the Gulf Stream sea‐surface temperature (SST) front on the North Atlantic eddy‐driven jet and its variability, by analysing the NCEP‐CFSR dataset and a pair of AGCM simulations forced with realistic and smoothed Gulf Stream SST boundary conditions. The Gulf Stream SST front acts to generate stronger meridional eddy heat flux in the lower troposphere and an eddy‐driven jet over the eastern North Atlantic which is located further polewards than in the simulation with smoothed SST. The strong Gulf Stream SST gradient is found to be crucial in more accurately capturing the trimodal distribution of the eddy‐driven jet latitude, with the more poleward climatological jet being the result of the jet occupying the northern jet position more frequently in the simulation forced with observed SSTs. The more frequent occurrence of the northern jet location is associated with periods of high eddy heat flux over the Gulf Stream region. Composite analysis of high eddy heat flux events reveals that the significantly higher heat flux is followed by larger and more persistient poleward jet excursions in the simulations with realistic SSTs than in the simulation with smoothed SSTs, with upper‐tropospheric eddy momentum fluxes acting to maintain the more poleward eddy‐driven jet. Periods of high eddy heat flux over the Gulf Stream region are also shown to be associated with increased blocking frequency over Europe, which are clearly distinct from periods with a northern jet position.

Artificial Photosynthetic Reaction Center Exhibiting Acid-Responsive Regulation of Photoinduced Charge Separation.

Nonphotochemical quenching (NPQ) is a photoprotective regulatory mechanism employed by many photosynthetic organisms to dynamically modulate energy flow within the photosynthetic apparatus in response to fluctuating light conditions. Activated by decreases in lumen pH produced during periods of high photon flux, NPQ induces rapid thermal dissipation of excess excitation energy. As a result, the rate of charge separation (CS) decreases, thereby limiting the accumulation of potentially deleterious reactive intermediates and byproducts. Herein, a molecular triad that functionally mimics the effects of NPQ associated with an artificial photosynthetic reaction center is described. Steady-state absorption and emission, time-resolved fluorescence, and transient absorption spectroscopies have been used to demonstrate a 1 order of magnitude reduction in the CS quantum yield via reversible protonation of an excited-state-quenching molecular switch moiety. As in the natural system, the populations of unquenched and quenched states and therefore the overall yields of CS were found to be dependent on acid concentration.

Effect of operation parameters on the mass transfer and fouling in submerged vacuum membrane distillation crystallization (VMDC) for inland brine water treatment

Membrane distillation-crystallization process has great potential to recover high quality water and valuable precipitates from inland brine water. Incorporation of submerging membrane in a feed tank with agitation provides opportunity to reduce temperature and concentration polarization and energy consumption. This study evaluated membrane transverse vibration and feed aeration on the mass transfer of water vapor, crystallization and fouling in a submerged vacuum membrane distillation and crystallization for inland brine water. At selected vibration frequency, more than 700h of high desalination performance was achieved. However, at elevated initial feed conductivity, the operation time was significantly reduced due to severe fouling.With accelerated tests with extreme feed concentration, both transverse vibration and aeration were able to increase the initial flux by reducing boundary layer thickness on the membrane surface. However, with transverse vibration, rapid reduction of flux occurred earlier due to the enhanced CaCO3precipitation on the membrane surface. The aeration of feed improved productivity with longer period of high flux with the increased nucleation in the bulk feed solution. Thermal water softening procedure prolonged the operation time by increased calcium precipitation in the feed solution and slower CaCO3 nucleation on the membrane surface.

Enhanced nighttime gas emissions from a lake

Methane (CH4) and carbon dioxide (CO2) are two important greenhouse gases. Previous studies have shown that lakes can be important natural sources of atmospheric CH4 and CO2. It is therefore important to monitor the fluxes of these gases between lakes and the atmosphere in order to understand the processes that govern the exchange. Most previous lake flux studies are based on chamber measurements, by using the eddy covariance method, the resolution in time and in space of the fluxes is increased, which gives more information on the governing processes. Eddy covariance measurements at a Swedish lake show that both methane fluxes (FCH4) and carbon dioxide fluxes (FCO2) experience high nighttime fluxes for a large part of the data set (largest median FCH4night ≈ 13 nmol m2 s-1 and smallest median FCH4day ≈ 4.0 nmol m-2 s-1, largest median FCO2night ≈ 0.2 μmol m2 s-1 and smallest median FCO2day ≈ 0.02 μmol m-2 s-1, with larger variability during night). For the diel cycle of the CH4 fluxes it is suggested that water side convection could enhance the transfer velocity, transport CH4 rich water to the surface, as well as trigger ebullition. The high nighttime CO2 fluxes could to a large extent be explained with enhanced transfer velocities due to water side convection. If gas fluxes are not measured during nighttime, when water side convection normally is generated, periods of potential high gas flux might be missed and estimations of the total amount of gas released from lakes to the atmosphere will be biased.

Concentrations and abundance ratios of long-chain alkenones and glycerol dialkyl glycerol tetraethers in sinking particles south of Java

In this study, we obtained concentrations and abundance ratios of long-chain alkenones and glycerol dialkyl glycerol tetraethers (GDGTs) in a one-year time-series of sinking particles collected with a sediment trap moored from December 2001 to November 2002 at 2200m water depth south of Java in the eastern Indian Ocean. We investigate the seasonality of alkenone and GDGT fluxes as well as the potential habitat depth of the Thaumarchaeota producing the GDGTs entrained in sinking particles. The alkenone flux shows a pronounced seasonality and ranges from 1µgm−2d−1 to 35µgm−2d−1. The highest alkenone flux is observed in late September during the Southeast monsoon, coincident with high total organic carbon fluxes as well as high net primary productivity. Flux-weighted mean temperature for the high flux period using the alkenone-based sea-surface temperature (SST) index U37K′ is 26.7°C, which is similar to satellite-derived Southeast (SE) monsoon SST (26.4°C). The GDGT flux displays a weaker seasonality than that of the alkenones. It is elevated during the SE monsoon period compared to the Northwest (NW) monsoon and intermonsoon periods (approximately 2.5 times), which is probably related to seasonal variation of the abundance of Thaumarchaeota, or to enhanced export of GDGTs by aggregation with sinking phytoplankton detritus. Flux-weighted mean temperature inferred from the GDGT-based TEX86H index is 26.2°C, which is 1.8°C lower than mean annual (ma) SST but similar to SE monsoon SST. As the time series of TEX86H temperature estimates, however, does not record a strong seasonal amplitude, we infer that TEX86H reflects ma upper thermocline temperature at approximately 50m water depth.