Flux Drop Research Articles

PLASMA ENVIRONMENT AROUND COMET 67P/CHURYUMOV–GERASIMENKO AT PERIHELION: MODEL COMPARISON WITHROSETTADATA

The plasma environment near comet 67P/Churyumov–Gerasimenko (67P/CG) is dynamically affected by various factors, including the incident solar wind and outgassing from the nucleus. The Rosetta spacecraft MAGnetometer (MAG) instrument observations near perihelion showed crossing events into a magnetic field-free region at about 170 km from the nucleus in 2015 July at 1.26 au from the Sun. At each crossing, the magnitude of the magnetic field dropped by more than 20 nT to near zero. We compared the Ion and Electron Sensor (IES) electron differential flux energy spectrum inside and outside the crossing boundaries. The IES observations show a modest but consistent drop in electron flux for energies between 40 eV and a few hundred eV at each cavity crossing event. This drop in the electron spectra might be due to the absence or attenuation of solar wind electrons inside the observed diamagnetic regions, which might or might not be a diamagnetic cavity. There is no apparent simple linear correlation between the electron count rate measured by the IES at different energies and the magnitude of the magnetic field, however; at all energies, the highest electron count rates are recorded at the highest magnetic field magnitudes. From model-data comparisons it seems that inside diamagnetic regions, pure coma photoelectrons are not sufficient to explain the observations and that a trapping mechanism and/or infused solar wind electrons are necessary to explain the observed electron fluxes.

Avalanche Statistics Identify Intrinsic Stellar Processes near Criticality in KIC 8462852.

The star KIC8462852 (Tabby's star) has shown anomalous drops in light flux. We perform a statistical analysis of the more numerous smaller dimming events by using methods found useful for avalanches in ferromagnetism and plastic flow. Scaling exponents for avalanche statistics and temporal profiles of the flux during the dimming events are close to mean field predictions. Scaling collapses suggest that this star may be near a nonequilibrium critical point. The large events are interpreted as avalanches marked by modified dynamics, limited by the system size, and not within the scaling regime.

Impacts of the total solar eclipse of 9 March 2016 on meteorological parameters in Ternate

The total solar eclipse on 9th March 2016 has given a unique opportunity to assess impacts of the eclipse on various meteorological parameters in Ternate. A weather transmitter, a net radiometer, and a heat flux plate for measuring soil heat flux in bare soil were deployed during this special observation in Madaha, Ternate (0°51'17.5" N, 127°20'56.8" E). The measured meteorological parameters presented here are net radiation, air temperature, relative humidity, and soil heat flux. The results show that those parameters are significantly affected by the eclipse. The percentage of the observed decrease of net radiation during the eclipse was proportional to the obscuration percentage. The air temperature measured at 1.5 m declined around 1.9 °C with approximately 11 minutes lag between the mid-eclipse and minimum temperature during eclipse. Influences from the surrounding environment in the measurement site minimize the temperature response. As a consequence of temperature decrease, relative humidity increased. A drop in soil heat flux was also detected but its response was slower.

Thermal design and operational limits of two-phase micro-channel heat sinks

While the vast majority of published studies on two-phase micro-channel heat sinks have been focused on determination of pressure drop and heat transfer coefficient, very few studies have addressed the operational limits of these devices. This study provided a comprehensive methodology for thermal design of micro-channel heat sinks with saturated inlet conditions. This includes predictive methods for pressure drop and heat transfer coefficient using universal correlations that rely on large databases amassed from numerous sources, and which encompass many working fluids, and very broad ranges of hydraulic diameter, mass velocity, inlet pressure, and inlet quality. This is followed by predictive tools for thermal limits associated with dryout incipience and premature critical heat flux, as well as two-phase critical flow limit. The three limits are combined to define an envelope for acceptable heat sink performance. Using these tools, a parametric study is performed to determine the variation of maximum heat flux with total volumetric flow rate for different combinations of the channel’s geometrical parameters for three working fluids, HFE-7100, R134a, and water. Then, the values of maximum heat flux are used to assess corresponding variations of pressure drop and maximum bottom wall temperature of the heat sink. It is shown that maximum heat flux is dominated by different limits for different flow rate ranges, and may be increased significantly, while decreasing bottom wall temperature, by using a large number of small channels. Furthermore, using deeper micro-channels is shown to increase maximum heat flux and decrease pressure drop, while producing a relatively weak adverse effect on bottom wall temperature.

KIC 8462852 FADED THROUGHOUT THE KEPLER MISSION

ABSTRACT KIC 8462852 is a superficially ordinary main sequence F star for which Kepler detected an unusual series of brief dimming events. We obtain accurate relative photometry of KIC 8462852 from the Kepler full-frame images, finding that the brightness of KIC 8462852 monotonically decreased over the four years it was observed by Kepler. Over the first ∼1000 days KIC 8462852 faded approximately linearly at a rate of 0.341 ± 0.041% yr−1, for a total decline of 0.9%. KIC 8462852 then dimmed much more rapidly in the next ∼200 days, with its flux dropping by more than 2%. For the final ∼200 days of Kepler photometry the magnitude remained approximately constant, although the data are also consistent with the decline rate measured for the first 2.7 years. Of a sample of 193 nearby comparison stars and 355 stars with similar stellar parameters, none exhibit the rapid decline by >2% or the cumulative fading by 3% of KIC 8462852. Moreover, of these comparison stars, only one changes brightness as quickly as the 0.341% yr−1 measured for KIC 8462852 during the first three years of the Kepler mission. We examine whether the rapid decline could be caused by a cloud of transiting circumstellar material, finding that while such a cloud could evade detection in submillimeter observations, the transit ingress and duration cannot be explained by a simple cloud model. Moreover, this model cannot account for the observed longer-term dimming. No known or proposed stellar phenomena can fully explain all aspects of the observed light curve.

Plasma detachment study of high density helium plasmas in the Pilot-PSI device

We have investigated plasma detachment phenomena of high-density helium plasmas in the linear plasma device Pilot-PSI, which can realize a relevant ITER SOL/Divertor plasma condition. The experiment clearly indicated plasma detachment features such as drops in the plasma pressure and particle flux along the magnetic field lines that were observed under the condition of high neutral pressure; a feature of flux drop was parameterized using the degree of detachment (DOD) index. Fundamental plasma parameters such as electron temperature (Te) and electron density in the detached recombining plasmas were measured by different methods: reciprocating electrostatic probes, Thomson scattering (TS), and optical emission spectroscopy (OES). The Te measured using single and double probes corresponded to the TS measurement. No anomalies in the single probe I–V characteristics, observed in other linear plasma devices [, , ], appeared under the present condition in the Pilot-PSI device. A possible reason for this difference is discussed by comparing the different linear devices. The OES results are also compared with the simulation results of a collisional radiative (CR) model. Further, we demonstrated more than 90% of parallel particle and heat fluxes were dissipated in a short length of 0.5 m under the high neutral pressure condition in Pilot-PSI.

The Close AGN Reference Survey (CARS)

We report the discovery that the known `changing look' AGN Mrk 1018 has changed spectral type for a second time. New VLT-MUSE data taken in 2015 as part of the Close AGN Reference Survey (CARS) shows that the AGN has returned to its original Seyfert 1.9 classification. The CARS sample is selected to contain only bright type 1 AGN, but Mrk 1018's broad emission lines and continuum, typical of type 1 AGN, have almost entirely disappeared. We use spectral fitting of the MUSE spectrum and previously available spectra to determine the drop in broad line flux and the Balmer decrement. We find that the broad line flux has decreased by a factor of 4.75+/- 0.5 in H{\alpha} since an SDSS spectrum was taken in 2000. The Balmer decrement has not changed significantly implying no enhanced reddening with time, but the remaining broad lines are more asymmetric than those present in the type 1 phase. We posit that the change is due to an intrinsic drop in flux from the accretion disk rather than variable extinction or a tidal disruption event.

A new ionospheric electron precipitation module coupled with RAM‐SCB within the geospace general circulation model

AbstractElectron precipitation down to the atmosphere due to wave‐particle scattering in the magnetosphere contributes significantly to the auroral ionospheric conductivity. In order to obtain the auroral conductivity in global MHD models that are incapable of capturing kinetic physics in the magnetosphere, MHD parameters are often used to estimate electron precipitation flux for the conductivity calculation. Such an MHD approach, however, lacks self‐consistency in representing the magnetosphere‐ionosphere coupling processes. In this study we improve the coupling processes in global models with a more physical method. We calculate the physics‐based electron precipitation from the ring current and map it to the ionospheric altitude for solving the ionospheric electrodynamics. In particular, we use the BATS‐R‐US (Block Adaptive Tree Scheme‐Roe type‐Upstream) MHD model coupled with the kinetic ring current model RAM‐SCB (Ring current‐Atmosphere interaction Model with Self‐Consistent Magnetic field (B)) that solves pitch angle‐dependent electron distribution functions, to study the global circulation dynamics during the 25–26 January 2013 storm event. Since the electron precipitation loss is mostly governed by wave‐particle resonant scattering in the magnetosphere, we further investigate two loss methods of specifying electron precipitation loss associated with wave‐particle interactions: (1) using pitch angle diffusion coefficients Dαα(E,α) determined from the quasi‐linear theory, with wave spectral and plasma density obtained from statistical observations (named as “diffusion coefficient method”) and (2) using electron lifetimes τ(E) independent on pitch angles inferred from the above diffusion coefficients (named as “lifetime method”). We found that both loss methods demonstrate similar temporal evolution of the trapped ring current electrons, indicating that the impact of using different kinds of loss rates is small on the trapped electron population. However, for the precipitated electrons, the lifetime method hardly captures any precipitation in the large L shell (i.e., 4 < L < 6.5) region, while the diffusion coefficient method produces much better agreement with NOAA/POES measurements, including the spatial distribution and temporal evolution of electron precipitation in the region from the premidnight through the dawn to the dayside. Further comparisons of the precipitation energy flux to DMSP observations indicates that the new physics‐based precipitation approach using diffusion coefficients for the ring current electron loss can explain the diffuse electron precipitation in the dawn sector, such as the enhanced precipitation flux at auroral latitudes and flux drop near the subauroral latitudes, but the traditional MHD approach largely overestimates the precipitation flux at lower latitudes.

Hollow fiber membrane lumen modified by polyzwitterionic grafting

In this study, we demonstrate an effective way to modify the lumen of polyetherimide hollow fibers by grafting zwitterionic poly(sulfobetaine) to increase the membrane resistance to fouling. Surface-selective grafting of the protective hydrogel layers has been achieved in a facile two-step process. The first step is the adsorption of a macromolecular redox co-initiator on the lumen-side surface of the membrane, which in the second step, after flushing the lumen of the membrane with a solution comprising monomers and a complementary redox initiator, triggers the in situ cross-linking copolymerization at room temperature. The success of grafting reaction has been verified by the surface elemental analyses using X-ray photoelectron spectroscopy (XPS) and the surface charge evaluation using zeta potential measurements. The hydrophilicity of the grafted porous substrate is improved as indicated by the change of contact angle value from 44° to 30°, due to the hydration layer on the surface produced by the zwitterionic poly(sulfobetaine). Compared to the pristine polyetherimide (PEI) substrate, the poly(sulfobetaine) grafted substrates exhibit high fouling resistance against bovine serum albumin (BSA) adsorption, E. coli attachment and cell growth on the surface. Fouling minimization in the lumen is important for the use of hollow fibers in different processes. For instance, it is needed to preserve power density of pressure-retarded osmosis (PRO). In high-pressure PRO tests, a control membrane based on PEI with an external polyamide selective layer was seriously fouled by BSA, leading to a high water flux drop of 37%. In comparison, the analogous membrane, whose lumen was modified with poly(sulfobetaine), not only had a less water flux decline but also had better flux recovery, up to 87% after cleaning and hydraulic pressure impulsion. Clearly, grafting PRO hollow fiber membranes with zwitterionic polymeric hydrogels as a protective layer potentially sustains PRO performance for power generation.

Possibility for albedo estimation of exomoons: Why should we care about M dwarfs?

Occultation light curves of exomoons may give information on their albedo and hence indicate the presence of ice cover on the surface. Icy moons might have subsurface oceans thus these may potentially be habitable. The objective of our paper is to determine whether next generation telescopes will be capable of albedo estimations for icy exomoons using their occultation light curves. The success of the measurements depends on the depth of the moon's occultation in the light curve and on the sensitivity of the used instruments. We applied simple calculations for different stellar masses in the V and J photometric bands, and compared the flux drop caused by the moon's occultation and the estimated photon noise of next generation missions with 5 $\sigma$ confidence. We found that albedo estimation by this method is not feasible for moons of solar-like stars, but small M dwarfs are better candidates for such measurements. Our calculations in the J photometric band show that E-ELT MICADO's photon noise is just about 4 ppm greater than the flux difference caused by a 2 Earth-radii icy satellite in a circular orbit at the snowline of an 0.1 stellar mass star. However, considering only photon noise underestimates the real expected noise, because other noise sources, such as CCD read-out and dark signal become significant in the near infrared measurements. Hence we conclude that occultation measurements with next generation missions are far too challenging, even in the case of large, icy moons at the snowline of small M dwarfs. We also discuss the role of the parameters that were neglected in the calculations, e.g. inclination, eccentricity, orbiting direction of the moon. We predict that the first albedo estimations of exomoons will probably be made for large icy moons around the snowline of M4 -- M9 type main sequence stars.

MBBR followed by microfiltration and reverse osmosis as a compact alternative for advanced treatment of a pesticide‐producing industry wastewater towards reuse

AbstractThe treatment of a chemical industry wastewater with the goal of reuse was evaluated in a three‐step process. First, the industrial waste stream underwent biological treatment in a two‐stage moving‐bed biofilm reactor (MBBR) system, which allowed achieving average effluent chemical oxygen demand (COD), dissolved organic carbon (DOC), ammonium, total nitrogen (TN), and total suspended solids (TSS) concentrations of 45.5, 27.2, 1.0, 34.2, and 210 mg/L, respectively. Salt and TSS concentrations after the MBBR process were still not compatible with the requirements for effluent reuse and the silt density index (SDI15) was found to be > 6.5, making a direct reverse osmosis (RO) application impractical. By employing microfiltration (MF) downstream of the biological treatment, no salt removal was observed, but the SDI15 was reduced to around 2, enabling final RO application. Long‐term RO experiments conducted at different pressures (1.5–3.0 MPa) showed that biofouling became more severe under higher pressures, leading to the enhancement of the permeate flux drop. Rejection of DOC, TN, and salt by RO corresponded to 97.8 %, 89 %, and 99 %, respectively. The combined MBBR/MF/RO process allowed the production of a high‐quality effluent appropriate for direct reuse in the industry as feed water in cooling towers, steam boilers, and general industrial process activities.

OBSERVATION AND SIMULATION OF THE VARIABLE GAMMA-RAY EMISSION FROM PSR J2021+4026

ABSTRACT Pulsars are rapidly spinning and highly magnetized neutron stars, with highly stable rotational periods and a gradual spin-down over a long timescale due to the loss of radiation. Glitches refer to events that suddenly increase the rotational speed of a pulsar. The exact causes of glitches and the resulting processes are not fully understood. It is generally believed that couplings between the normal matter and superfluid components, and starquakes, are the common causes of glitches. In this study, one famous glitching pulsar, PSR J2021+4026, is investigated. PSR J2021+4026 is the first variable gamma-ray pulsar observed by Fermi. From gamma-ray observations, it is found that the pulsar experienced a significant flux drop, an increase in the spin-down rate, a change in the pulse profile and a shift in the spectral cut-off to a lower energy, simultaneously around 2011 October 16. To explain these effects on high-energy emissions by the glitch of PSR J2021+4026, we hypothesized the glitch to be caused by the rearrangement of the surface magnetic field due to crustal plate tectonic activities on the pulsar, which was triggered by a starquake. In this glitch event, the inclination angle of the magnetic dipole axis was slightly shifted. This proposition is then tested by numerical modeling using a three-dimensional two-layer outer gap model. The simulation results indicate that a modification of the inclination angle can affect the pulse profile and the spectral properties, which can explain the observation changes after the glitch.

Voyager 1 observations of the termination shock particles in the inner heliosheath at 122 au

The sharp drop in fluxes of the termination shock particles observed by Voyager 1 in the inner heliosheath at distance of about 122 au from the Sun can be explained by factors, which are not related to the heliopause crossing as is now commonly believed. It is shown that the region of the heliosheath occupied by the current sheet can be considered as a reservoir for suprathermal charged particles accelerated at the termination shock. When a spacecraft crosses the boundary of this region in the latitudinal direction, fluxes of the suprathermal particles can vary by several orders of magnitude.

Membrane fouling insight during reverse osmosis purification of pretreated olive mill wastewater

Abstract The chronological sequence and the relative importance of the individual fouling mechanisms were investigated on a polymeric RO membrane used for final purification of secondary-treated olive mill wastewater (OMW2ST). An insight of membrane fouling under different operating conditions is reported. The goodness of the fitting (R2 → 0.99) points for the formation of a cake or gel layer over the membrane as the dominant fouling mechanism in the transient and steady-state operation stages. A non-uniform cake was built-up, as shown in the HR-SEM analysis on the fouled membrane, principally formed by the organic matter (188.7 ± 37.9 mg L−1) and residual iron colloids carried by the OMW2ST feedstream. However, about 39.0% of the initial flux drop could be attributed to concentration polarization on the boundary region of the membrane. Moreover, it is relevant that the partial blocking model describes correctly the incipient fouling formation on the membrane, disregarding the operating conditions. This behavior was attributed to surface defects, more permeable zones of the membrane that may act as pores during the initial and intermediate operation stages, and in particular to the small organic particles (up to 63.3% between 3 and 30 kDa) remaining in the OMW2ST feedstream.

Microfiltration of micro-sized suspensions of boron-selective resin with PVDF membranes

In this paper microfiltration (MF) separation of fractionized ion exchange Amberlite IRA743 resin from aqueous solutions using polyvinylidene fluoride membranes with the pore sizes of 0.1, 0.22 and 0.45μm was studies. The effect of membrane pore size, transmembrane pressure, pH and concentration of the resin suspensions, presence of NaCl, MgCl2 and Na2SO4 salts on permeate flux has been evaluated. It was shown that the dominant membrane fouling mechanism during MF of the resin suspensions is formation of a cake layer from deposited resin on the membrane surface. The flux declines with increasing operating pressure and suspension concentration, while it increases with the presence of inorganic salts and feed pH. Changes in zeta potential of resin particles and the membranes as well as agglomeration and electroviscous effects should be considered while analyzing these findings. It was shown that the resin particles after boron sorption can be efficiently regenerated and reused in combined adsorption-microfiltration (AMF) process of boron removal from water, however a sharp drop in membrane flux during MF separation of the resin suspension should be further addressed to develop the efficient AMF procedure.

The Effect of Module Geometry on Heat and Mass Transfer in Membrane Distillation

Abstract Some features of Direct Contact Membrane Distillation (DCMD), as one of the interesting membrane processes, has been studied in this effort. 3D computational fluid dynamic simulations were carried out to investigate some geometric parameter effects on flat sheet membrane module performance. It is obvious that using of baffles could noticeably improve the performance of the system. Hence, in present work, some baffle configurations were simulated and some parameters like temperature polarization, vapor flux and pressure drop through module length were investigated. The Simulation was performed based on neglecting viscous flow in membrane pores and dusty gas model was applied to predict vapor flux through membrane. Simulation results predicted that by using the new configuration we could have 40–60% vapor flux improvement (depend on inflow velocity) compared to a module without baffle. It was found that the average temperature polarization (TP), as a proper criteria, was higher for baffled one in all situations.

PROTOPLANETARY DISK SHADOWING BY GAS INFALLING ONTO THE YOUNG STAR AK Sco

ABSTRACT Young solar-type stars grow through the accretion of material from the circumstellar disk during pre-main-sequence (PMS) evolution. The ultraviolet radiation generated in this process plays a key role in the chemistry and evolution of young planetary disks. In particular, the hydrogen Lyα line (Lyα) etches the disk surface by driving photoevaporative flows that control disk evolution. Using the Hubble Space Telescope, we have monitored the PMS binary star AK Sco during the periastron passage and have detected a drop of the H2 flux by up to 10% lasting 5.9 hr. We show that the decrease of the H2 flux can be produced by the occultation of the stellar Lyα photons by a gas stream in free fall from 3 R * ?> . Given the high optical depth of the Lyα line, a very low gas column of N H > 5 × 10 17 ?> cm−2 suffices to block the Lyα radiation without producing noticeable effects in the rest of the stellar spectral tracers.

Graphene Oxide Quantum Dots Covalently Functionalized PVDF Membrane with Significantly-Enhanced Bactericidal and Antibiofouling Performances.

Covalent bonding of graphene oxide quantum dots (GOQDs) onto amino modified polyvinylidene fluoride (PVDF) membrane has generated a new type of nano-carbon functionalized membrane with significantly enhanced antibacterial and antibiofouling properties. A continuous filtration test using E. coli containing feedwater shows that the relative flux drop over GOQDs modified PVDF is 23%, which is significantly lower than those over pristine PVDF (86%) and GO-sheet modified PVDF (62%) after 10 h of filtration. The presence of GOQD coating layer effectively inactivates E. coli and S. aureus cells, and prevents the biofilm formation on the membrane surface, producing excellent antimicrobial activity and potentially antibiofouling capability, more superior than those of previously reported two-dimensional GO sheets and one-dimensional CNTs modified membranes. The distinctive antimicrobial and antibiofouling performances could be attributed to the unique structure and uniform dispersion of GOQDs, enabling the exposure of a larger fraction of active edges and facilitating the formation of oxidation stress. Furthermore, GOQDs modified membrane possesses satisfying long-term stability and durability due to the strong covalent interaction between PVDF and GOQDs. This study opens up a new synthetic avenue in the fabrication of efficient surface-functionalized polymer membranes for potential waste water treatment and biomolecules separation.

Assessment of existing two phase heat transfer coefficient and critical heat flux correlations for cryogenic flow boiling in pipe quenching experiments

To enable efficient design and analysis of cryogenic propellant transfer systems, high accuracy models are required for predicting two phase flow boiling and heat transfer at reduced temperatures. The penalty for poor models translates into higher margin, safety factor, and ultimately cost in design. Recently, there has been a drive towards developing universal correlations to cover a broad range of fluids, tube diameters, and thermodynamic conditions for predicting heat flux and pressure drop. These correlations do not, however, cover cryogenic fluids like liquid hydrogen. Therefore the purpose of this paper is to apply popular two phase heat transfer correlations used in commercial codes against available flow boiling data for cryogenic fluids. Specifically, quenching test data for critical heat flux and two phase heat transfer coefficient are compared against the correlations. Results show that existing correlations over-predict heat transfer by as much as 20,000% and that significant model improvements are warranted.

Concentrating underground brine by FO process: Influence of membrane types and spacer on membrane scaling

Forward osmosis (FO) is a low energy process when recovery of the draw solutes is not necessary. This study focused on the performance of the FO process for concentrating underground brine (UGB) with saturated sodium chloride as draw solution (DS) using two membranes: commercialized flat sheet cellulose triacetate (CTA) membrane and tailor-made thin film composite (TFC) FO membrane. Energy dispersive X-ray spectroscopy (EDS) and powder X-ray diffractometry (XRD) analysis indicate that, majority of the scaling components were calcium sulfate and sodium chloride crystals formed both through surface and bulk crystallization. The spacer in the FO test cell also promoted scaling. Without spacer, a sharp flux decline of TFC membrane occurred at a higher concentration factor while no sharp flux drop was observed for CTA membrane. It was hypothesized that the rough TFC membrane surface may initiate nucleation and aggregation of the crystals in the active surface, and eventually resulting in scaling.