Kinetic modelling of growth and storage molecule production in microalgae under mixotrophic and autotrophic conditions.

In order to improve algal biofuel production on a commercial-scale, an understanding of algal growth and fuel molecule accumulation is essential. A mathematical model is presented that describes biomass growth and storage molecule (TAG lipid and starch) accumulation in the freshwater microalga Chlorella vulgaris, under mixotrophic and autotrophic conditions. Biomass growth was formulated based on the Droop model, while the storage molecule production was calculated based on the carbon balance within the algal cells incorporating carbon fixation via photosynthesis, organic carbon uptake and functional biomass growth. The model was validated with experimental growth data of C. vulgaris and was found to fit the data well. Sensitivity analysis showed that the model performance was highly sensitive to variations in parameters associated with nutrient factors, photosynthesis and light intensity. The maximum productivity and biomass concentration were achieved under mixotrophic nitrogen sufficient conditions, while the maximum storage content was obtained under mixotrophic nitrogen deficient conditions.

Optical investigations of the effect of solvent and thermal annealing on the optoelectronic properties of Poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) films

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is one of the most promising conducting polymers that can be used as transparent electrode or as buffer layer for organic electronic devices. However, when used as an electrode, its conductivity has to be optimized either by the addition of solvents or by post-deposition processing. In this work, we investigate the effect of the addition of the polar solvent dimethylsulfoxide (DMSO) to an aqueous PEDOT:PSS solution on its optical and electrical properties by the implementation of the Drude model for the analysis of the measured pseudo-dielectric function by Spectroscopic Ellipsometry from the near infrared to the visible-far ultraviolet spectral range. The results show that the addition of DMSO increases significantly the film conductivity, which reaches a maximum value at an optimum DMSO concentration as it has confirmed by experimentally measured conductivity values. The post-deposition thermal annealing has been found to have a smaller effect on the film conductivity. © 2013 Elsevier B.V.

Effects of buffer layer properties and annealing process on bulk heterojunction morphology and organic solar cell performance

The performance of polymer-fullerene bulk heterojunction (BHJ) solar cells is strongly dependent on the vertical distribution of the donor and acceptor regions within the BHJ layer. In this work, we investigate in detail the effect of the hole transport layer (HTL) physical properties and the thermal annealing on the BHJ morphology and the solar cell performance. For this purpose, we have prepared solar cells with four distinct formulations of poly(3,4- ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) buffer layers. The samples were subjected to thermal annealing, applied either before (pre-annealing) or after (post-annealing) the cathode metal deposition. The effect of the HTL and the annealing process on the BHJ ingredient distribution - namely, poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) - has been studied by spectroscopic ellipsometry and atomic force microscopy. The results revealed P3HT segregation at the top region of the films, which had a detrimental effect on all pre-annealed devices, whereas PCBM was found to accumulate at the bottom interface. This demixing process depends on the PEDOT:PSS surface energy; the more hydrophilic the surface the more profound is the vertical phase separation within the BHJ. At the same time those samples suffer from high recombination losses as evident from the analysis of the J-V measurements obtained in the dark. Our results underline the significant effect of the HTL-active and active-ETL (electron transport layer) interfacial composition that should be taken into account during the optimization of all polymer-fullerene solar cells. © 2012 The Royal Society of Chemistry.

Substrate treatment and drying conditions effect on the properties of roll-to-roll gravure printed PEDOT:PSS thin films

The optical, structural and electrical properties of poly(3,4- ethylenedioxythiophene):poly(4-styrenesulfonic acid) (PEDOT:PSS) thin films printed by roll-to-roll gravure have been investigated. Corona treatment has been applied to enhance the adhesion of PEDOT:PSS on PolyEthylene Terephthalate (PET) web. It has been found that there was a stronger in-depth surface modification of PET with the increase of corona efficiency; however, the adhesion of PEDOT:PSS was not actually affected. Also, Spectroscopic Ellipsometry and Atomic Force Microscopy have been used to extract information on the mechanisms that define PEDOT:PSS properties. The increase of the drying temperature of the PEDOT:PSS films has been found to reduce the remaining water inside the films and lead to the decrease of the PEDOT:PSS particles size. © 2011 Elsevier B.V. All rights reserved.

Thermal annealing effect on the nanomechanical properties and structure of P3HT:PCBM thin films

Nanostructured polymer-fullerene thin films are among the most prominent materials for application in high efficient polymer solar cells. Specifically, poly(3-hexylthiophene) (P3HT) and fullerene derivatives (PCBM) blends are used as the donor/acceptor materials forming a bulk heterojunction. Although P3HT:PCBM properties have been extensively studied, less light has been set on its nanomechanical properties, which affect the device service life. In this work Atomic Force Acoustic Microscopy (AFAM), Atomic Force Spectroscopy and Nanoindentation were used to study the effect of the fullerene presence and the annealing on the P3HT:PCBM nanomechanical behavior. The P3HT:PCBM thin films were prepared by spin coating on glass substrates and then annealed at 100 °C and 145 °C for 30 min. Large phase separation was identified by optical and Atomic Force Microscopy (AFM) for the annealed samples. Needle-like PCBM crystals were formed and an increase of the polymer crystallinity degree with the increase of the annealing temperature was confirmed by X-ray diffraction. AFAM characterization revealed the presence of aggregates close to stiff PCBM crystals, possibly consisting of amorphous P3HT material. AFM force-distance curves showed a continuous change in stiffness in the vicinity of the PCBM crystals, due to the PCBM depletion near its crystals, and the AFM indentation provided qualitative results about the changes in P3HT nanomechanical response after annealing. © 2011 Elsevier B.V. All rights reserved.

Enhancing the carbonation of MgO cement porous blocks through improved curing conditions

The use of reactive magnesia (MgO) as the binder in porous blocks demonstrated significant advantages due to its low production temperatures and ability to carbonate, leading to significant strengths. This paper investigates the enhancement of the carbonation process through different curing conditions: water to cement ratio (0.6-0.9), CO2 concentration (5-20%), curing duration (1-7 days), relative humidity (55-98%), and wet/dry cycling frequency (every 0-3 days), improving the carbonation potential through increased amounts of CO2 absorbed and enhanced mechanical performance. UCS results were supported with SEM, XRD, and HCl acid digestion analyses. The results show that CO2 concentrations as low as 5% can produce the required strengths after only 1 day. Drier mixes perform better in shorter curing durations, whereas larger w/c ratios are needed for continuous carbonation. Mixes subjected to 78% RH outperformed all the others, also highlighting the benefits of incorporating wet/dry cycling to induce carbonation. © 2014 Elsevier Ltd.

Effects of sand burial on biomass, chlorophyll fluorescence and extracellular polysaccharides of man-made cyanobacterial crusts under experimental conditions

Soil cyanobacterial crusts occur throughout the world, especially in the semiarid and arid regions. It always encounters sand burial, which is an important feature of mobile sand dunes. A greenhouse 41 study was conducted to determine the effects of sand burial on biomass, chlorophyll fluorescence and extracellular polysaccharides of man-made cyanobacterial crusts in six periods of time (0, 5, 10, 15, 20 and 30 d after burying) and at five depths (0, 0.2, 0.5, 1 and 2cm). The results indicated that with the increase of the burial time and burial depth extracellular polysaccharides content and Fv/Fm decreased correspondingly and there were no significant differences between 20 and 30 burial days under different burial depths. The degradation of chlorophyll a content appeared only at 20 and 30 burial days and there was also no significant difference between them under different burial depths. It was also observed a simultaneous decrease of the values of the Fv/Fm and the content of extracellular polysaccharides happened in the crusted cyanobacterium Microcoleus vaginatus Gom. It may suggest that there exists a relationship between extracellular polysaccharides and recovery of the activity of photosystem II (PS II) after rehydration.

The influence of boundary conditions on tip leakage flow

Most of the current understanding of tip leakage flows has been derived from detailed cascade experiments. However, the cascade model is inherently approximate since it is difficult to simulate the boundary conditions present in a real machine, particularly the secondary flows convecting from the upstream stator row and the relative motion of the casing and blade. This problem is further complicated when considering the high pressure turbine rotors of aero engines, where the high Mach numbers must also be matched in order to correctly model the aerodynamics and heat transfer. More realistic tests can be performed on high-speed turbines, but the experimental fidelity and resolution achievable in such set-ups is limited. In order to examine the differences between cascade models and real-engine behavior, the influence of boundary conditions on the tip leakage flow in an unshrouded high pressure turbine rotor is investigated using RANS calculations. This study examines the influence of the rotor inlet condition and relative casing motion. A baseline calculation with a simplified inlet condition and no relative endwall motion exhibits similar behavior to cascade studies. Only minor changes to the leakage flow are induced by introducing either a more realistic inlet condition or relative casing motion. However when both of these conditions are applied simultaneously the pattern of leakage flow is very different, with ingestion of flow over much of the early suction surface. The paper explores the physical processes driving this change and the impact on leakage losses and modeling requirements. Copyright © 2013 by ASME.

Optimization of operational conditions in a submerged membrane bioreactor

In this study, optimization of operational conditions of a submerged membrane bioreactor treating municipal waste-water was studied. Mixed liquid suspended solid (MLSS), membrane flux (J(v)), aeration (Q), ratio of pumping, time to break time (t(p)/t(b)), and ratio of up flow area to down flow area (A Ad) were chosen as the easily manipulable parameters to study their effects on removal efficiency and membrane fouling. Totally, 16 different runs were designed to compare and select the best combination of the 5 parameters. The results showed that the optimal operational conditions were MLSS = 7g(.)L(-1), J(v) = 10L(.)m(-2.)h(-1), Q = 6 m(3.)h(-1), t(p)/t(b)= 4 min/1 min, and A(r)/A(d) = 1.7 m(2)/m(2). Under such conditions, the SMBR could achieve a double win of high removal efficiency and low membrane fouling.

Multi-walled carbon nanotube conductivity enhancement and band gap widening via rapid pulsed thermal annealing

Herein we report on the transport characteristics of rapid pulsed vacuum-arc thermally annealed, individual and network multi-walled carbon nanotubes. Substantially reduced defect densities (by at least an order of magnitude), measured by micro-Raman spectroscopy, and were achieved by partial reconstruction of the bamboo-type defects during thermal pulsing compared with more traditional single-pulse thermal annealing. Rapid pulsed annealed processed networks and individual multi-walled nanotubes showed a consistent increase in conductivity (of over a factor of five at room temperature), attributed to the reduced number density of resistive axial interfaces and, in the case of network samples, the possible formation of structural bonds between crossed nanotubes. Compared to the highly defective as-grown nanotubes, the pulsed annealed samples exhibited reduced temperature sensitivity in their transport characteristics signifying the dominance of scattering events from structural defects. Transport measurements in the annealed multi-walled nanotubes deviated from linear Ohmic, typically metallic, behavior to an increasingly semiconducting-like behavior attributed to thermally induced axial strains. Rapid pulsed annealed networks had an estimated band gap of 11.26 meV (as-grown; 6.17 meV), and this observed band gap enhancement was inherently more pronounced for individual nanotubes compared with the networks most likely attributed to mechanical pinning effect of the probing electrodes which possibly amplifies the strain induced band gap. In all instances the estimated room temperature band gaps increased by a factor of two. The gating performance of back-gated thin-film transistor structures verified that the observed weak semiconductivity (p-type) inferred from the transport characteristic at room temperature. © 2014 Copyright Taylor & Francis Group, LLC.

Kinetic modelling of growth and storage molecule production in microalgae under mixotrophic and autotrophic conditions

In order to improve algal biofuel production on a commercial-scale, an understanding of algal growth and fuel molecule accumulation is essential. A mathematical model is presented that describes biomass growth and storage molecule (TAG lipid and starch) accumulation in the freshwater microalga Chlorella vulgaris, under mixotrophic and autotrophic conditions. Biomass growth was formulated based on the Droop model, while the storage molecule production was calculated based on the carbon balance within the algal cells incorporating carbon fixation via photosynthesis, organic carbon uptake and functional biomass growth. The model was validated with experimental growth data of C. vulgaris and was found to fit the data well. Sensitivity analysis showed that the model performance was highly sensitive to variations in parameters associated with nutrient factors, photosynthesis and light intensity. The maximum productivity and biomass concentration were achieved under mixotrophic nitrogen sufficient conditions, while the maximum storage content was obtained under mixotrophic nitrogen deficient conditions. © 2014 Elsevier Ltd.

Phycobilisome-Deficient Strains of Synechocystis sp. PCC 6803 Have Reduced Size and Require Carbon-Limiting Conditions to Exhibit Enhanced Productivity.

Reducing excessive light harvesting in photosynthetic organisms may increase biomass yields by limiting photoinhibition and increasing light penetration in dense cultures. The cyanobacterium Synechocystis sp. PCC 6803 harvests light via the phycobilisome, which consists of an allophycocyanin core and six radiating rods, each with three phycocyanin (PC) discs. Via targeted gene disruption and alterations to the promoter region, three mutants with two (pcpcT→C) and one (ΔCpcC1C2:pcpcT→C) PC discs per rod or lacking PC (olive) were generated. Photoinhibition and chlorophyll levels decreased upon phycobilisome reduction, although greater penetration of white light was observed only in the PC-deficient mutant. In all strains cultured at high cell densities, most light was absorbed by the first 2 cm of the culture. Photosynthesis and respiration rates were also reduced in the ΔCpcC1C2:pcpcT→C and olive mutants. Cell size was smaller in the pcpcT→C and olive strains. Growth and biomass accumulation were similar between the wild-type and pcpcT→C under a variety of conditions. Growth and biomass accumulation of the olive mutant were poorer in carbon-saturated cultures but improved in carbon-limited cultures at higher light intensities, as they did in the ΔCpcC1C2:pcpcT→C mutant. This study shows that one PC disc per rod is sufficient for maximal light harvesting and biomass accumulation, except under conditions of high light and carbon limitation, and two or more are sufficient for maximal oxygen evolution. To our knowledge, this study is the first to measure light penetration in bulk cultures of cyanobacteria and offers important insights into photobioreactor design.

Influence of turbulence-chemistry interaction for n-heptane spray combustion under diesel engine conditions with emphasis on soot formation and oxidation

The influence of the turbulence-chemistry interaction (TCI) for n-heptane sprays under diesel engine conditions has been investigated by means of computational fluid dynamics (CFD) simulations. The conditional moment closure approach, which has been previously validated thoroughly for such flows, and the homogeneous reactor (i.e. no turbulent combustion model) approach have been compared, in view of the recent resurgence of the latter approaches for diesel engine CFD. Experimental data available from a constant-volume combustion chamber have been used for model validation purposes for a broad range of conditions including variations in ambient oxygen (8-21% by vol.), ambient temperature (900 and 1000 K) and ambient density (14.8 and 30 kg/m3). The results from both numerical approaches have been compared to the experimental values of ignition delay (ID), flame lift-off length (LOL), and soot volume fraction distributions. TCI was found to have a weak influence on ignition delay for the conditions simulated, attributed to the low values of the scalar dissipation relative to the critical value above which auto-ignition does not occur. In contrast, the flame LOL was considerably affected, in particular at low oxygen concentrations. Quasi-steady soot formation was similar; however, pronounced differences in soot oxidation behaviour are reported. The differences were further emphasised for a case with short injection duration: in such conditions, TCI was found to play a major role concerning the soot oxidation behaviour because of the importance of soot-oxidiser structure in mixture fraction space. Neglecting TCI leads to a strong over-estimation of soot oxidation after the end of injection. The results suggest that for some engines, and for some phenomena, the neglect of turbulent fluctuations may lead to predictions of acceptable engineering accuracy, but that a proper turbulent combustion model is needed for more reliable results. © 2014 Taylor & Francis.

Comparative mechanisms of photosynthetic carbon acquisition in Hizikia fusiforme under submersed and emersed conditions

The economic seaweed Hizikia fusiforme (Harv.) Okamura (Sargassaceae, Phaeophyta) usually experiences periodical exposures to air at low tide. Photosynthetic carbon acquisition mechanisms were comparatively studied under submersed and emersed conditions in order to establish a general understanding of its photosynthetic characteristics associated with tidal cycles. When submersed in seawater, H fusiforme was capable of acquiring HCO3- as a source of inorganic carbon (Ci) to drive photosynthesis, while emersed and exposed to air, it used atmospheric CO2 for photosynthesis. The pH changes surrounding the H fusiforme fronds had less influence on the photosynthetic rates under emersed condition than under submersed condition. When the pH was as high as 10.0, emersed H fusiforme could photosynthesize efficiently, but the submersed alga exhibited very poor photosynthesis. Extracellular carbonic anhydrase (CA) played an important role in the photosynthetic acquisitions of exogenous Ci in water as well as in air. Both the concentrations of dissolved inorganic carbon in general seawater and CO2 in air were demonstrated to limit the photosynthesis of H fusiforme, which was sensitive to O-2. It appeared that the exogenous carbon acquisition system, being dependent of external CA activity, operates in a way not enough to raise intracellular CO2 level to prevent photorespiration. The inability of H fusiforme to achieve its maximum photosynthetic rate at the current ambient Ci levels under both submersed and emersed conditions suggested that the yield of aquaculture for this economic species would respond profitably to future increases in CO2 concentration in the sea and air.