Steep Shift Research Articles

Dynamic operation of fixed-bed methanation reactors: Yield control by catalyst dilution profile and magnetic induction

Dynamic operation of fixed-bed methanation reactors has been subject to increasing research efforts over the past years, as a consequence of its potential interest for the energy transition (power-to-gas). Due to the reaction exothermicity, the thermal management of a reactor is particularly difficult. In the present work, a model and a software are developed to simulate the behavior of a reactor whose reaction medium contains a mixture of catalytic pellets and induction-sensitive pellets. The study shows that a reactor made-up of two reaction zones of different catalytic fractions can produce a gas of identical steady-state compositions for two different flow rates. A steep shift from the low to the high inflow rate generates a transient drop in the methane yield. Magnetic induction rapidly heats up an appropriate portion of the reaction medium, so that the yield remains nearly constant during both transient and steady state after a flow rate shift. This study constitutes a first step towards the final aim of using induction and catalyst dilution profile to stabilize the yield for any flow rate variation in a given range.

Amelioration of obesity-associated inflammation and insulin resistance in c57bl/6 mice via macrophage polarization by fish oil supplementation

Enormous phenotypic plasticity makes macrophages the target cells in obesity-associated inflammatory diseases. Thus, nutritional components that polarize macrophages toward antiinflammatory phenotype can partially reverse inflammatory diseases like insulin resistance. In the present study, macrophage-polarizing and insulin-sensitizing properties of fish oil (FO) were evaluated in obese insulin-resistant c57bl/6 mice fed high-fat diet (HFD-IR) after oral supplementation with FO (4, 8 or 16mg/kg body weight) and compared to lean and HFD-IR mice. FO-supplemented HFD-IR mice exhibited reduced adiposity index, serum cholesterol and triglycerides and increased insulin sensitization and showed improved adipose tissue physiology under light and transmission electron microscopy. NF-κB/P65 expression showed a downward shift on FO supplementation. The surface marker of M1 macrophages (CD-86) and the TLR-4 expression reduced with the increased supplementation of FO. Expression of arginase 1, an important marker of M2 macrophages, increased in a dose-dependent manner in response to FO dosage, which was observed at protein level by the western blotting and at mRNA level by real-time PCR. The cytokine profile of adipose tissue macrophages showed a steep shift toward antiinflammatory ones (IL-4 and IL-10) from the inflammatory TNF-α, IFN-γ, IL-2 and IL-1β. Thus, macrophage polarization seems to be the plausible mechanism via which FO alleviates obesity-induced inflammation and insulin resistance.

Explaining Pre- and Post-1987 Crash Asset Prices Within a Unified General Equilibrium Framework

The 1987 stock market crash occurred with minimal impact on observable economic variables (e.g., consumption), yet dramatically and permanently changed the shape of the implied volatility curve for equity index options. Here, we propose a general equilibrium model that captures many salient features of the U.S. equity and options markets before, during, and after the crash. The representative agent is endowed with Epstein-Zin preferences and the aggregate dividend and consumption processes are driven by a persistent stochastic growth variable that can jump. In reaction to a market crash, the agent updates her beliefs about the distribution of the jump component. We identify a realistic calibration of the model that matches the prices of short-maturity at-the-money and deep out-of-the-money S&P 500 put options, as well as the prices of individual stock options. Further, the model generates a steep shift in the implied volatility 'smirk' for S&P 500 options after the 1987 crash. This 'regime shift' occurs in spite of a minimal impact on observable macroeconomic fundamentals. Finally, the model's implications are consistent with the empirical properties of dividends, the equity premium, as well as the level and standard deviation of the risk-free rate. Overall, our findings show that it is possible to reconcile the stylized properties of the equity and option markets in the framework of rational expectations, consistent with the notion that these two markets are integrated.

Can Standard Preferences Explain the Prices of Out-of-the-Money S&P 500 Put Options?

The 1987 stock market crash occurred with minimal impact on observable economic variables (e.g., consumption), yet dramatically and permanently changed the shape of the implied volatility curve for equity index options. Here, we propose a general equilibrium model that captures many salient features of the U.S. equity and options markets before, during, and after the crash. The representative agent is endowed with Epstein-Zin preferences and the aggregate dividend and consumption processes are driven by a persistent stochastic growth variable that can jump. In reaction to a market crash, the agent updates her beliefs about the distribution of the jump component. We identify a realistic calibration of the model that matches the prices of shortmaturity at-the-money and deep out-of-the-money S&P 500 put options, as well as the prices of individual stock options. Further, the model generates a steep shift in the implied volatility ‘smirk’ for S&P 500 options after the 1987 crash. This ‘regime shift’ occurs in spite of a minimal impact on observable macroeconomic fundamentals. Finally, the model’s implications are consistent with the empirical properties of dividends, the equity premium, as well as the level and standard deviation of the risk-free rate. Overall, our findings show that it is possible to reconcile the stylized properties of the equity and option markets in the framework of rational expectations, consistent with the notion that these two markets are integrated.

Electron-molecular vibration coupling effect on the Raman spectrum of organic charge transfer salts

Vibrational spectra of dimerized and tetramerized radical clusters have been calculated to understand the features of electron-molecular vibration (EMV) coupling effects for the charge ordered system (CO). The calculated spectra show that the totally in-phase Raman band, which is usually used as a measure of the molecular ionicity, approaches to the frequency corresponding to the average molecular ionicity in the cluster, with increasing the EMV coupling constant. On the other hand, when large charge disproportionation (CD) presents, vibronic bands show steep shift for small variation of the CD ratio. These results suggest that concerning to the normal modes with a large EMV coupling constant, we should focus on the frequency of the vibronic bands instead of the totally in-phase mode to discuss the charge distribution.

Fastigial nucleus activity during different frequencies and orientations of vertical vestibular stimulation in the monkey.

Neurons in the rostral part of the fastigial nucleus (FN) respond to vestibular stimulation but are not related to eye movements. To understand the precise role of these vestibular-only neurons in the central processing of vestibular signals, unit activity in the FN of alert monkeys (Macaca mulatta) was recorded. To induce vestibular stimulation, the monkey was rotated sinusoidally around an earth-fixed horizontal axis at stimulus frequencies between 0.06 (+/-15 degrees) and 1.4 Hz (+/-7.5 degrees). During stimulation head orientation was changed continuously, allowing for roll, pitch, and intermediate planes of orientation. At a frequency of 0.6 Hz, 59% of the neurons had an optimal response orientation (ORO) and a null response (i.e., no modulation) 90 degrees apart. The phase of neuronal response was constant except for a steep shift of 180 degrees around the null response. This group I response is compatible with a semicircular canal input, canal convergence, or a single otolith input. Several other features indicated more complex responses, including spatiotemporal convergence (STC). 1) For 35% of the responses at 0.6 Hz, phase changes were gradual with different orientations. Fifteen percent of these had a null response (group II), and 20% showed only a minimal response but no null response (group III). The remaining responses (6%), classified as group IV, were characterized by a constant sensitivity at different orientations in most instances. 2) For the vast majority of neurons, the stimulus frequency determined the response group, i.e., an individual neuron could show a group I response at one frequency and a group II (III or IV) response at another frequency. 3) ORO changed with frequency by >45 degrees for 44% of the neurons. 4) Although phase changes at different frequencies were close to head velocity (+/-45 degrees ) or head position (+/-45 degrees ) for most neurons, they exceeded 90 degrees for 29% of the neurons between 0.1 and 1.0 Hz. In most cases, this was a phase advance. The change in sensitivity with change in frequency showed a similar pattern for all neurons; the average sensitivity increased from 1.24 imp. s-1. deg-1 at 0.1 Hz to 2.97 imp. s-1. deg-1 at 1.0 Hz. These data demonstrate that only an analysis based on measurements at different frequencies and orientations reveals a number of complex features. They moreover suggest that for the vast majority of neurons several sources of canal and otolith information interact at this central stage of vestibular information processing.

Artificial Ageing of Wood Monitored by DRIFT Spectroscopy and CIE L*a*b* Color Measurements. 1. Effect of UV Light

The effect of UV irradiation up to 200hrs was monitored on five wood species (Picea abies, Pinus sylvestris, Larix decidua, Populus euramericana, Robinia pseudoacacia) by spectro colorimetry and diffuse reflectance infrared Fourier transform (DRIFT) spectrometry. The CIE L * a * b * color calculations exemplified the rapid change of total color difference (ΔE * ) in the first 25 to 50hrs of irradiation. All samples exhibited yellowing, i.e. a pronounced steep shift to positive Δa * values in the Δa * , Δb * coordinate system. Robinia p. showed an additional shift to redness, i.e. towards positive Δb * values. The colored compounds developed could be removed by water extraction only to a moderate extent. Thus it was concluded that the yellow color was mainly due to oligomeric chromophores, arisen probably from leuco chromophores of the lignin moiety of wood. In agreement with the literature, DRIFT measurements revealed the preferred degradation of aromatic structures and the formation of nonconjugated carbonyl and carboxyl groups. The DRIFT spectra indicate dehydration, oxidation to carboxyl groups and the formation of lactones or other esters. It was demonstrated by spectral subtraction that the increasing carbonyl bands consisted in the case of softwoods of two sub-bands with equal intensity at 1763 and 1710 cm -1 . The formation carbonyl bands of the hardwoods obeyed different rules. The formation of conjugated carbonyl groups below 1700 cm -1 was observed only to a limited extent. The carboxyl group containing photodegradation products could easily be removed by water extraction. This was interpreted that the oxidized compounds did not necessarily contribute to the formation of colored compounds. The plots of DRIFT band intensities, derived from baseline corrected and normalized spectra, vs. the irradiation time revealed pronounced intensity changes in the first 50 hrs of irradiation. The coherent intensity profiles were beveling above 100hrs of irradiation.