Uncoupled Phase Research Articles

Revealing the effect of phase and time coupling on NMR relaxation rate by random walks in phase space.

Phase-time coupling is a natural process in the phase random walks of a spin system; however, its effect on the nuclear magnetic resonance (NMR) relaxation is a challenge to the established theories such as the second-order quantum perturbation theory. This paper extends the recently developed phase diffusion method to treat the phase-time coupling effect, based on uncoupled phase diffusions, and coupled random walks. The instantaneous projection of the rotating random field is employed to get the accumulated phase of the NMR observable. In the static frame and the rotating frame, the phase diffusion coefficients are derived. The obtained theoretical results show that the phase-time coupling has a significant impact on the NMR relaxation rate: The angular frequency ω in the spectral density is modified to an apparent angular frequency ηω, where η is the phase-time coupling constant. The strongest coupling has η equaling 2, while η equaling 1 corresponds to the traditional results. As an example, the modified relaxation time expressions based on both monoexponential and nonmonoexponential functions can successfully fit the previously reported ^{13}CT_{1} NMR experimental data of polyisobutylene (PIB) in the blend of PIB and head-to-head poly(propylene). In contrast, the traditional relaxation rate expression based on the monoexponential time correlation function cannot fit such experimental data. With the phase-time coupling, the obtained characteristic time of the segmental motion is faster than that from conventional results.

Probabilistic model for determining the failure time of steel-to-timber connections with multiple dowel-type fasteners exposed to fire

There is a lack of knowledge on the structural reliability of dowel-type connections exposed to fire. The objective of this paper is to propose a model for the structural reliability analysis of steel-to-timber connections with multiple dowel-type fasteners two shear planes exposed to standard fire to determine the failure time probabilistically. A thermomechanical model was developed in two uncoupled phases. The phase to calculate the temperature field was based on the finite element method, while the phase to calculate the load carrying capacity was based on Johansen's theory, modified to consider the influence of temperature on the materials thermomechanical properties. The model error was calculated for the failure time of the connections. The structural reliability analysis of the failure time was carried out using Monte Carlo simulations. The analysis indicated that modes I and II, which are influenced by the solicitation rate and the relation between thickness of timber member and dowel diameter, have the largest probability to occur. The structural reliability analysis provided the mean and the 5th and 20th percentiles failure times of probability distributions for 25 connections. A sensitivity analysis through Sobol’ indices showed that the model error is the random variable with the higher relative importance.

Depolarized Mitochondrial Membrane Potential and Protection with Duroquinone in Isolated Perfused Lungs from Rats Exposed to Hyperoxia

ObjectiveDissipation of mitochondrial membrane potential (Δψm) is a hallmark of mitochondrial dysfunction, which plays a key in the pathogenesis of Acute Respiratory Distress Syndrome (ARDS). Our objective was to use a previously developed experimental‐computational approach to estimate tissue Δψm in isolated perfused lungs of rats exposed to hyperoxia as a rat model of human ARDS, and to evaluate the ability of the ubiquinone analog duroquinone (DQ) to reverse any hyperoxia‐induced depolarization of lung Δψm.MethodsRats were exposed to hyperoxia (>95% O2) or normoxia (room air) for 48 hrs, after which lungs were excised and connected to a ventilation‐perfusion system. The experimental protocol consisted of measuring the concentration of the fluorescent dye rhodamine 6G (R6G) during three single‐pass phases: loading, washing, and uncoupling, in which the lungs were perfused with and without R6G, and with the mitochondrial uncoupler FCCP, respectively. For normoxic lungs, the protocol was repeated with 1) rotenone (mitochondrial complex I inhibitor), 2) rotenone and either DQ or its vehicle (DMSO), and 3) rotenone, glutathione (GSH), and either DQ or DMSO added to the perfusate. Hyperoxic lungs were studied with and without DQ and GSH added to the perfusate. A physiologically‐based pharmacokinetic (PBPK) computational model was used to estimate lung Δψm from R6G data.ResultsFigure 1 shows that for hyperoxic lungs, R6G venous effluent concentrations tended to be higher during the loading phase, but significantly lower during the uncoupling phase compared to normoxic lungs, consistent with less uptake of R6G by hyperoxic lungs due to partial depolarization of Δψm. Figure 1 also shows that adding DQ to perfusate during the three phases almost completely reversed differences in R6G concentrations between normoxic and hyperoxic lungs. The PBPK computational model analysis of the R6G data show that exposure to hyperoxia depolarized lung tissue Δψm from ‐140 ± 9 (SE, n = 5) mV to ‐107 ± 9 (n = 5) mV, and complex I inhibition depolarized lung Δψm from ‐140 ± 9 (n = 5) to ‐57 ± 2 (n = 4) mV. Computational model analysis results also demonstrate the efficacy of DQ to fully reverse both rotenone‐induced and hyperoxia‐induced lung Δψm depolarization, consistent with the ability of the lungs to reduce DQ to its hydroquinone form (DQH2), which in turn bypasses mitochondrial complexes I and II to reduce mitochondrial complex III and restores Δψm.ConclusionsThis study demonstrates hyperoxia‐induced Δψm depolarization in isolated perfused lungs, and the utility of this approach for assessing the impact of potential therapies such as exogenous quinones that target mitochondria in isolated perfused lungs.

Quantification of Mitochondrial Membrane Potential in the Isolated Rat Lung Using Rhodamine 6G

Mitochondrial membrane potential (ΔΨm) plays a key role in vital mitochondrial functions, and its dissipation is a hallmark of mitochondrial dysfunction. The objective of this study was to develop an experimental and computational approach for estimating ΔΨm in intact rat lungs using the lipophilic fluorescent cationic dye rhodamine 6G (R6G). Rat lungs were excised and connected to a ventilation‐perfusion system. The experimental protocol consisted of three single‐pass phases: loading, wash, and uncoupling, in which the lungs were perfused with R6G‐containing perfusate, fresh R6G‐free perfusate, or R6G‐free perfusate containing the mitochondrial uncoupler FCCP, respectively. This protocol was carried out with lung perfusate containing verapamil vehicle or verapamil, an inhibitor of the multi‐drug efflux pump P‐glycoprotein (Pgp). Results show that the addition of FCCP resulted in an increase in R6G venous effluent concentration (Figure 1), and that this increase was larger in the presence of verapamil than in its absence. A physiologically‐based pharmacokinetic (PBPK) model for the pulmonary disposition of R6G was developed and used for quantitative interpretation of the kinetic data, including estimating ΔΨm. The estimated value of ΔΨm (−139 ± 21 (SD) mV) was not significantly altered by inhibiting Pgp with verapamil, and is consistent with that estimated previously in cultured pulmonary endothelial cells. These results demonstrate the utility of the proposed approach for quantifying ΔΨm in intact functioning lungs. This approach has potential to provide quantitative assessment of the effect of injurious conditions on lung mitochondrial function, and to evaluate the impact of therapies that target mitochondria.Support or Funding InformationSupported by NIH 2R15HL129209‐02 and VA Merit Review Award BX001681.Solid symbols: R6G venous effluent concentrations during the loading phase, wash phase, and uncoupling phase using FCCP (67 μM). Values are mean ± SE (n = 7 for loading and wash phases, and n = 5 for uncoupling phase). Solid line is PBPK model fit to data.Figure 1

A kinetic sensitivity analysis for the SO2 and NOx removal using the electron beam technology

The mathematical modeling of the phenomena taking place during the electron beam flue gas treatment is a complex endeavor due to the different time scales of the processes occurring as accelerated electrons are bombarding the flue gas. The paper presents a complex kinetic model for these gas phase interactions, consisting of 1034 chemical reactions with the participation of 115 reactive species. The mathematical model couples the complex gas phase kinetics with a liquid phase kinetic model, taking into account the nucleation and condensation phenomena occurring due to the presence of sulfuric acid. The modeling results for both coupled and uncoupled gas phase kinetics are validated against a set of literature experimental data with satisfactory outcome. The work aims to identify the most important chemical reactions influencing the pollutants removal, proposing a sensitivity analysis using the concept of generated entropy. To the best of the authors’ knowledge a sensitivity analysis of this extent has not been performed for the electron beam flue gas treatment. The results of this analysis emphasize the link between the removal efficiencies of NOx and SO2, the importance of hydroxyl radicals and can aid in future model reduction efforts.

Fire performance of single plate shear connections in a composite floor

Purpose This paper aims to present a numerical investigation on the fire performance of a single plate shear connection in a steel-framed composite floor. Large-scale fire experiments show that the tensile membrane action of the concrete slab enhances the fire performance of composite floors. The enhancement in the performance is contributed to large slab deflections. However, these deflections cause significant rotations and tensile force in the single plate connection. Design/methodology/approach A finite element model is constructed, which consists of a secondary steel beam, concrete slab and shear connection components. The interaction between the connection components such as bolts and single plate is defined by contact surfaces. The analysis is conducted in two uncoupled phases: thermal analysis by creating fire boundaries on the composite floor model with convective and radiative heat transfer, and mechanical analysis by considering thermal expansion and changes in the material stiffness and strength due to temperature. Findings The thermo-mechanical analysis of the composite floor finite element model shows that the structure survives the 2-h Standard fire, but the connection fails by bolt shear and buckling of the connection plate. Originality/value This paper investigates the fire performance of a shear connection in a steel-framed concrete slab. Previous work generally focused on the concrete slab behavior only. The originality of the research is that the connection is considered as part of a sub-assembly and is subjected to forces due to concrete and steel beam interaction.

Origin of open recoil curves in L10-A1 FePt exchange coupled nanocomposite thin film

Mixed phase FePt systems with intergranular coupling may be looked upon as natural exchange spring systems. The coupling strength between the soft and hard phase in these systems can be analyzed using recoil curves. However, the origin of open recoil curves depicting the breakdown of exchange coupling or anisotropy variation in hard phase is still an ambiguity and requires an in-depth analysis. In order to investigate this, an analysis of the recoil curves for L10–A1 FePt nanocomposite thin films of varying thickness have been performed. The switching field distribution reveals that the maximum of openness of recoil curve is directly proportional to the amount of uncoupled soft phase present in the system. The coupling between the hard and soft phase is also found to increase with the thickness of the film. Monte Carlo simulations on a model three dimensional array of interacting nanomagnetic grains provide further insight into the effect of inter granular exchange interactions between the soft and hard phases.

FIRE ANALYSIS OF CURVED REINFORCED CONCRETE BEAM

In the present study the fire analysis of a curved reinforced concrete beam exposed to concrete spalling is presented. Due to the complexity of physical and chemical processes in concrete at elevated temperatures, the proposed numerical model is divided into two consecutive mathematically uncoupled phases. In the second phase of the fire analysis a partially coupled numerical model is introduced in order to evaluate the effect of concrete spalling on the behaviour of curved RC beam in fire. In addition, the effect of depth, time development and the length of spalling area on the fire resistance of a curved RC beam is discussed.

Intake ground vortex and computational modelling of foreign object ingestion

AbstractWhen an aero-engine is operating on the ground the formation of a potent inlet ground vortex can arise which has the ability to ingest foreign object debris. The ingestion of foreign objects can cause notable damage to engine components as well as overall performance degradation. The assessment of foreign object ingestion has been conducted using a combination of computational fluid dynamics, analytical modelling and an Euler-Lagrange uncoupled discrete phase particle tracking method. The flow fields for a full-scale aero-engine have been simulated for a range of ground clearances and intake velocity ratios under crosswind conditions. The sensitivity of the debris ingestion thresholds and characteristics to particle size and material density has been evaluated. The characteristics of the ingestion location within the intake are also considered for a range of operating conditions and particle parameters.

Spin-crossover, mesomorphic and thermoelectrical properties of cobalt(ii) complexes with alkylated N3-Schiff bases

Cobalt complexes of alkylated N3-Schiff bases show mesomorphic and spin-crossover behaviours, and high Se values.

Continuous regime of chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU) reactivity of CuO oxygen carriers

Chemical-looping with CuO and CH4 presents an interesting reaction system, in which CuO participates in heterogeneous reduction reactions with the gaseous fuel, as well as oxygen uncoupling and catalytic reactions. Therefore, there exists a temperature dependent competition between the processes typically termed as chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU). The objective of this work is to carry out an assessment of the rates of all the relevant reactions involved at various temperatures and thus to show a continuous regime, where the CLC reactions domination proceeds to CuO oxygen uncoupling dominance, as temperature increases. The possible reactions occurring in CuO-based chemical-looping include heterogeneous reactions with Cu oxides, CuO oxygen uncoupling and Cu-catalyzed reactions. The significance of each individual reaction and the corresponding kinetic parameters are experimentally examined in a bench-scale fixed-bed, alternating-flow chemical-looping reactor at conditions relevant to both CLC and CLOU. In situ XRD characterization is used to determine the phases in which Cu exists during reduction and oxidation and possible interactions with the SiO2 oxygen carrier support. A kinetic scheme is proposed, applicable to the entire regime of CLC and CLOU, which is validated with in-house experiments and experimental data from the literature, at conditions where heterogeneous reduction, oxygen uncoupling, Cu-catalyzed, and gas phase oxidation reactions present significant contributions.

Magnetization reversal in triangular L10-FePt nanoislands

Triangular FePt nano-islands with size ~70 and ~330nm have been prepared by using regular single-layer arrays of nanospheres (173nm) and microspheres (978nm), as deposition masks. The coercivity of the 330nm islands is close to that of the continuous film (11kOe) whereas the 70nm ones have coercivity close to 9kOe and their hysteresis is characterized by the coexistence of an uncoupled soft phase. The switching behavior is characterized by non-zero dM-plots. The lower dM is obtained for the 70nm sample heat-treated at 500°C for 15min and increases for longer times and higher heat-treatment temperatures. 10% of the islands are in multi-domain state. These findings are compared with micromagnetic modeling which shows that for anisotropy values high enough to match the observed coercivity, multidomain islands can result in due to the existence of either a softer part or different anisotropy direction part within each magnetic entity.

A Linear Model of Phase-Dependent Power Correlations in Neuronal Oscillations

Recently, it has been suggested that effective interactions between two neuronal populations are supported by the phase difference between the oscillations in these two populations, a hypothesis referred to as “communication through coherence” (CTC). Experimental work quantified effective interactions by means of the power correlations between the two populations, where power was calculated on the local field potential and/or multi-unit activity. Here, we present a linear model of interacting oscillators that accounts for the phase dependency of the power correlation between the two populations and that can be used as a reference for detecting non-linearities such as gain control. In the experimental analysis, trials were sorted according to the coupled phase difference of the oscillators while the putative interaction between oscillations was taking place. Taking advantage of the modeling, we further studied the dependency of the power correlation on the uncoupled phase difference, connection strength, and topology. Since the uncoupled phase difference, i.e., the phase relation before the effective interaction, is the causal variable in the CTC hypothesis we also describe how power correlations depend on that variable. For uni-directional connectivity we observe that the width of the uncoupled phase dependency is broader than for the coupled phase. Furthermore, the analytical results show that the characteristics of the phase dependency change when a bidirectional connection is assumed. The width of the phase dependency indicates which oscillation frequencies are optimal for a given connection delay distribution. We propose that a certain width enables a stimulus-contrast dependent extent of effective long-range lateral connections.

Isolation of  two cell populations from yeast during high-level alcoholic fermentation that resemble quiescent and nonquiescent cells from the stationary phase on glucose

High-level production of bioethanol (140 g L(-1) in 45 h) in aerated fed-batch cultures of Saccharomyces cerevisiae was shown to be linked to the length of a production phase uncoupled to the growth. The induction of this phase was characterized by metabolic and morphologic changes reminiscent of those occurring in the stationary phase of growth on glucose. Global transcriptomic analysis of ethanol-stressed yeast cells in the uncoupling phase harboured features similar to those from stationary-phase cells on glucose. Two distinct cellular populations were isolated by Percoll density-gradient centrifugation in this uncoupling phase. The lower fraction was enriched by yeast cells that were mostly uniform in size and opalescent, containing a large amount of glycogen and trehalose, and exhibiting high respiratory activity. In contrast, the upper fraction was characterized by cells heterogeneous in size, with one to several small buds, which did not contain storage carbohydrates and which exhibited a poor respiratory competence while retaining a high relative glycolytic activity. These results are discussed in terms of a possible induction of a state similar to the quiescence state previously observed from yeast stationary-phase cultures, in response to ethanol toxicity, whose acquisition may be critical for performing high-level alcoholic fermentation.

Local structural, magnetic and magneto-optical properties of Mn-doped SiC films prepared on a 3C–SiC(001) wafer

We report on a systematic study of local structural, magnetic and magneto-optical properties of Mn-doped SiC films synthesized on a 3C–SiC(001) homoepitaxial wafer by an annealing method. A thin Mn layer was deposited on the SiC wafer, and then annealing was performed to diffuse the Mn atoms into the SiC epitaxial layer. Transmission magnetic circular dichroism and magnetization investigations demonstrated ferromagnetic behavior up to 300 K, although the x-ray diffraction studies indicated that the domaint phase of the synthesized layer was antiferromagnetic α-Mn. A detailed extended x-ray-absorption fine structure measurement further revealed that the synthesized sample, in fact, comprises two uncoupled phases: one is the top antiferromagnetic α-Mn layer and the other one is Mn atoms, which may randomly substitute the Si and C atoms in the 3C–SiC lattice. Combining these experimental results with recent theoretical calculations, we strongly propose that the observed room-temperature ferromagnetism was of intrinsic origin, arising from the ‘embedded Mn atoms’ in the 3C–SiC lattice, instead of other magnetic clusters.

Does the Solid−Liquid Crystal Phase Transition Provoke the Spin-State Change in Spin-Crossover Metallomesogens?

Three types of interplay/synergy between spin-crossover (SCO) and liquid crystalline (LC) phase transitions can be predicted: (i) systems with coupled phase transitions, where the structural changes associated to the Cr<-->LC phase transition drives the spin-state transition, (ii) systems where both transitions coexist in the same temperature region but are not coupled, and (iii) systems with uncoupled phase transitions. Here we present a new family of Fe(II) metallomesogens based on the ligand tris[3-aza-4-((5-C(n))(6-R)(2-pyridyl))but-3-enyl]amine, with C(n) = hexyloxy, dodecyloxy, hexadecyloxy, octadecyloxy, eicosyloxy, R = hydrogen or methyl (C(n)-trenH or C(n)-trenMe), which affords examples of systems of types i, ii, and iii. Self-assembly of the ligands C(n)-trenH and C(n)-trenMe with Fe(A)2 x xH2O salts have afforded a family of complexes with general formula [Fe(C(n)-trenR)](A)2 x sH2O (s > or = 0), with A = ClO4(-), F-, Cl-, Br- and I-. Single-crystal X-ray diffraction measurements have been performed on two derivatives of this family, named as [Fe(C6-trenH)](ClO4)2 (C(6)-1) and [Fe(C6-trenMe)](ClO4)2 (C(6)-2), at 150 K for C(6)-1 and at 90 and 298 K for C(6)-2. At 150 K, C(6)-1 displays the triclinic space group P, whereas at 90 and at 298 K C(6)-2 adopts the monoclinic P2(1)/c space group. In both compounds the iron atoms adopt a pseudo-octahedral symmetry and are surrounded by six nitrogen atoms belonging to imino groups and pyridines of the ligands C(n)-trenH and C(n)-trenMe. The average Fe(II)-N bonds (1.963(2) A) at 150 K denote that C(6)-1 is in the low-spin (LS) state. For C(6)-2 the average Fe(II)-N bonds (2.007(1) A) at 90 K are characteristic of the LS state, while at 298 K they are typical for the high-spin (HS) state (2.234(3) A). Compound C(6)-1 and [Fe(C18-trenH)](ClO4)2 (C(18)-1) adopts the LS state in the temperature region between 10 and 400 K, while compound C(6)-2 and [Fe(Cn-trenMe)](ClO4)2 (n = 12 (C(12)-2), 18 (C(18)-2)) exhibit spin crossover behavior at T(1/2) centered around 140 K. The thermal spin transition is accompanied by a pronounced change of color from dark red (LS) to orange (HS). The light-induced excited spin state trapping (LIESST) effect has been investigated in compounds C(6)-2, C(12)-2 and C(18)-2. The T(1/2)LIESST is 56 K (C(6)-2), 48 K (C(16)-2), and 56 K (C(18)-2). On the basis of differential scanning calorimetry, optical polarizing microscopy, and X-ray diffraction findings for C(18)-1, C(12)-2, and C(18)-2 at high temperature a smectic mesophase SX has been identified with layered structures similar to C(6)-1 and C(6)-2. The compounds [Fe(C(n)-trenH)](Cl)2 x sH2O (n = 16 (C(16)-3, s = 3.5, C(16)-4, s = 0.5, C(16)-5, s = 0), 18 (C(18)-3, s = 3.5, C(18)-4, s = 0.5, C(18)-5, s = 0), 20 (C(20)-3, s = 3.5, C(20)-4, s = 0.5, C(20)-5, s = 0)) and [Fe(C18-tren)](F)2 x sH2O (C(18)-6, s = 3.5, C(18)-7, s = 0) show a very particular spin-state change, while [Fe(C18-tren)](Br)2 x 3H2O (C(18)-8) together with [Fe(C18-tren)](I)2 (C(18)-9) are in the LS state (10-400 K) and present mesomorphic behavior like that observed for the complexes C(18)-1, C(12)-2, and C(18)-2. In compounds C(n)-3 50% of the Fe(II) ions undergo spin-state change at T(1/2) = 375 K induced by releasing water, and in partially dehydrated compounds (s = 0.5) the Cr-->SA phase transition occurs at 287 K (C(16)-4), 301 K (C(18)-4) and 330 K (C(20)-4). For the fully dehydrated materials C(n)-5 50% of the Fe(II) ions are in the HS state and show paramagnetic behavior between 10 and 400 K. In the partially dehydrated C(n)-4 the spin transition is induced by the change of the aggregate state of matter (solid<-->liquid crystal). For compound C(18)-6 the full dehydration to C(18)-7 provokes the spin-state change of nearly 50% of the Fe(II) ions. The compounds C(n)-3 and C(18)-6 are dark purple in the LS state and become light purple-brown when 50% of the Fe(II) atoms are in the HS state.

Stochastic dynamics of uncoupled neural oscillators: Fokker-Planck studies with the finite element method

We have investigated the effect of the phase response curve on the dynamics of oscillators driven by noise in two limit cases that are especially relevant for neuroscience. Using the finite element method to solve the Fokker-Planck equation we have studied (i) the impact of noise on the regularity of the oscillations quantified as the coefficient of variation, (ii) stochastic synchronization of two uncoupled phase oscillators driven by correlated noise, and (iii) their cross-correlation function. We show that, in general, the limit of type II oscillators is more robust to noise and more efficient at synchronizing by correlated noise than type I.

Structural, magnetic, and magnetotransport properties of Mn-Si films synthesized on a4H−SiC(0001)wafer

We present a comprehensive study of the structural, magnetic, and magnetotransport properties of Mn-Si films synthesized on a $4H\text{\ensuremath{-}}\mathrm{Si}\mathrm{C}(0001)$ wafer by an annealing method. Magnetic- and fluorescence-extended x-ray-absorption fine-structure measurements reveal that the sample comprises two uncoupled magnetic phases: one is the top synthesized Mn-Si layer, which displays a Curie temperature around $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and magnetic anisotropy; the other one is Mn atoms, which solely incorporate on the interstitial site in the $4H\text{\ensuremath{-}}\mathrm{Si}\mathrm{C}$ lattice in the interface and show superparamagnetismlike behavior with a blocking temperature below $2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The magnetoresistance (MR) exhibits an interesting temperature- and field-dependent behavior. At temperatures above $100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the sample only exhibits a positive MR. At temperatures below $100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, a negative MR prevails. Interestingly, at intermediate temperature of $100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, with increasing magnetic field, a sign inversion of the MR from negative to positive is observed. The possible origin of the positive and negative MR is discussed. Furthermore, we found that the Hall effect is dominated by an anomalous Hall effect (AHE) due to side jumps at temperatures between $2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and $100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. However, at temperatures higher than $100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the AHE cannot be described with either a skew scattering or side jumps mechanism.

Physiological behaviour of Saccharomyces cerevisiae in aerated fed-batch fermentation for high level production of bioethanol

Saccharomyces cerevisiae was able to produce 20% (v/v) of ethanol in 45 h in a fully aerated fed-batch process recently developed in our laboratory. A notable feature of this process was a production phase uncoupled to growth, the extent of which was critical for high-level ethanol production. As the level of production was found to be highly variable, we investigated on this high variability by means of a detailed physiological analysis of yeast cells in two fed-batch fermentations showing the most extreme behaviour. We found a massive leakage of intracellular metabolites into the growth medium which correlated with the drop of cell viability. The loss of viability was also found to be proportional to the reduction of plasma membrane phospholipids. Finally, the fed-batch processes with the longest uncoupling phase were characterized by induction of storage carbohydrates at the onset of this phase, whereas this metabolic event was not seen in processes with a short uncoupling phase. Taken together, our results suggested that reproducible high-level bioethanol production in aerated fed-batch processes may be linked to the ability of yeast cells to impede ethanol toxicity by triggering a metabolic remodelling reminiscent to that of cells entering a quiescent GO/G1 state.

Hepatic damage during acute pancreatitis in the rat

We studied the alterations in the metabolism of liver mitochondria in rats with acute pancreatitis. Male Wistar rats were allocated to a control group (group I) and to five other groups corresponding to 2, 4, 12, 24 and 48 h after the induction of acute pancreatitis by the injection of 5% sodium taurocholate into the pancreatic duct. Sham-operated animals were submitted to the same surgical steps except for the induction of acute pancreatitis. Mitochondrial oxidation and phosphorylation were measured polarographically by determining oxygen consumption without ADP (basal respiration, state 4) and in the presence of ADP (activated respiration, state 3). Serum amylase, transaminases (ALT and AST) and protein were also determined. Ascitic fluid, contents of amylase, trypsin and total protein were also determined and arterial blood pressure was measured in all groups. In ascitic fluid, trypsin and amylase increased reaching a maximum at 2 and 4 h, respectively. Serum amylase increased at 2 h reaching a maximum at 4 h. Serum transaminase levels increased at 12 and 24 h. After 2 h (and also 4 h) there was an increase in state 4 respiration (45.65 +/- 1.79 vs 28.96 +/- 1.50) and a decrease in respiration control rate (3.53 +/- 0.09 vs 4.45 +/- 0.08) and in the ADP/O ratio (1.77 +/- 0.02 vs 1.91 +/- 0.01) compared to controls (P < 0.05). These results indicate a disruption of mitochondrial function, which recovered after 12 h. In the 48-h groups there was mitochondrial damage similar to that occurring in ischemic lesion. Beat-to-beat analysis (30 min) showed that arterial blood pressure remained normal up to 24 h (111 +/- 3 mmHg) while a significant decrease occurred in the 48-h group (91 +/- 4 mmHg). These data suggest biphasic damage in mitochondrial function in acute pancreatitis: an initial uncoupled phase, possibly secondary to enzyme activity, followed by a temporary recovery and then a late and final dysfunction, associated with arterial hypotension, possibly related to ischemic damage.