Reverse Shifts Research Articles

Mechanistic and Compositional Aspects of Industrial Catalysts for Selective CO2 Hydrogenation Processes

The characteristics of industrial catalysts for conventional water-gas shifts, methanol syntheses, methanation, and Fischer-Tropsch syntheses starting from syngases are reviewed and discussed. The information about catalysts under industrial development for the hydrogenation of captured CO2 is also reported and considered. In particular, the development of catalysts for reverse water-gas shifts, CO2 to methanol, CO2-methanation, and CO2-Fischer-Tropsch is analyzed. The difference between conventional catalysts and those needed for pure CO2 conversion is discussed. The surface chemistry of metals, oxides, and carbides involved in this field, in relation to the adsorption of hydrogen, CO, and CO2, is also briefly reviewed and critically discussed. The mechanistic aspects of the involved reactions and details on catalysts’ composition and structure are critically considered and analyzed.

Stable stadial and interstadial states of the last glacial's climate identified in a combined stable water isotope and dust record from Greenland

Abstract. During the last glacial interval, the Northern Hemisphere climate was punctuated by a series of abrupt changes between two characteristic climate regimes. The existence of stadial (cold) and interstadial (milder) periods is typically attributed to a hypothesised bistability in the glacial North Atlantic climate system, allowing for rapid transitions from the stadial to the interstadial state – the so-called Dansgaard–Oeschger (DO) events – and more gradual yet still fairly abrupt reverse shifts. The physical mechanisms driving these regime transitions remain debated. DO events are characterised by substantial warming over Greenland and a reorganisation of the Northern Hemisphere atmospheric circulation, which are evident from concomitant shifts in the δ18O ratios and dust concentration records from Greenland ice cores. Treating the combined δ18O and dust record obtained by the North Greenland Ice Core Project (NGRIP) as a realisation of a two-dimensional, time-homogeneous, and Markovian stochastic process, we present a reconstruction of its underlying deterministic drift based on the leading-order terms of the Kramers–Moyal equation. The analysis reveals two basins of attraction in the two-dimensional state space that can be identified with the stadial and interstadial regimes. The drift term of the dust exhibits a double-fold bifurcation structure, while – in contrast to prevailing assumptions – the δ18O component of the drift is clearly mono-stable. This suggests that the last glacial's Greenland temperatures should not be regarded as an intrinsically bistable climate variable. Instead, the two-regime nature of the δ18O record is apparently inherited from a coupling to another bistable climate process. In contrast, the bistability evidenced in the dust drift points to the presence of two stable circulation regimes of the last glacial's Northern Hemisphere atmosphere.

Epilithic Bacterial Assemblages on Subtidal Rocky Reefs: Variation Among Alternative Habitats at Ambient and Enhanced Nutrient Levels.

Temperate rocky reefs often support mosaics of alternative habitats such as macroalgal forests, algal turfs and sea urchin barrens. Although the composition of epilithic microbial biofilms (EMBs) is recognized as a major determinant of macroalgal recruitment, their role in regulating the stability of alternative habitats on temperate rocky reefs remains unexplored. On shallow rocky reefs of the Island of Capraia (NW Mediterranean), we compared EMB structure among canopy stands formed by the fucoid Ericaria brachycarpa, algal turfs, and urchin barrens under ambient versus experimentally enhanced nutrient levels. The three habitats shared a core microbial community consisting of 21.6 and 25.3% of total ASVs under ambient and enhanced nutrient conditions, respectively. Although Gammaproteobacteria, Alphaproteobacteria and Flavobacteriia were the most abundant classes across habitats, multivariate analyses at the ASV level showed marked differences in EMB composition among habitats. Enhancing nutrient level had no significant effect on EMBs, although it increased their similarity between macroalgal canopy and turf habitats. At both ambient and enriched nutrient levels, ASVs mostly belonging to Proteobacteria and Bacteroidetes were more abundant in EMBs from macroalgal canopies than barrens. In contrast, ASVs belonging to the phylum of Proteobacteria and, in particular, to the families of Rhodobacteraceae and Flavobacteriaceae at ambient nutrient levels and of Rhodobacteraceae and Bacteriovoracaceae at enhanced nutrient levels were more abundant in turf than canopy habitats. Our results show that primary surfaces from alternative habitats that form mosaics on shallow rocky reefs in oligotrophic areas host distinct microbial communities that are, to some extent, resistant to moderate nutrient enhancement. Understanding the role of EMBs in generating reinforcing feedback under different nutrient loading regimes appears crucial to advance our understanding of the mechanisms underpinning the stability of habitats alternative to macroalgal forests as well as their role in regulating reverse shifts.

Assessment of the zonal asymmetry trend in Antarctic total ozonecolumn using TOMS measurements and CCMVal-2 models

In the paper the seasonal trends in the zonal asymmetry in the quasi-stationary wave pattern of total ozone column (TOC) at southern polar latitudes have been investigated. We evaluated and compared seasonal trends in the zonal TOC asymmetry from modern era satellite measurements using the Total Ozone Mapping Spectrometer data and the second Chemistry Climate Model Validation (CCMVal-2) assessment. The model longitude phase shifts in asymmetry are in general consistent with the eastward phase shifts observed in historical period 1979–2005, however, there are underestimated values in individual seasons. Future trends in zonal asymmetry from the eleven CCMVal-2 models up to 2100 are presented. They demonstrate the appearance of reverse (westward) future phase shifts, mainly in austral summer. The results are in agreement with previous study and highlight that the general eastward/westward phase shift is caused by both greenhouse gases changes and ozone depletion/recovery. The greenhouse gases change drives a basic long-term eastward shift, which is enhanced (decelerates or reverses) in austral spring and summer by ozone depletion (recovery). The trends in the TOC asymmetry are forced by a general strengthening of the stratospheric zonal flow, which is interacting with the asymmetry of the Antarctic continent to displace the quasi-stationary wave-1 pattern and thus influences the TOC distribution. The results will be useful in prediction of seasonal anomalies in ozone hole and long-term changes in the local TOC trends, in ultraviolet radiation influence on the Southern Ocean biological productivity and in regional surface climate affected by the zonally asymmetric ozone hole.

The gap not only closes: Resistance and reverse shifts in the digital divide in Russia

The reduction of the digital divide due to the availability of the Internet and the improvement of skills is accompanied by reverse and resistance trends associated with the influence of socio-demographic and economic characteristics of users. In this paper, we estimate the volume and dynamics of the digital divide in access and use of the Internet in Russia by key social groups according to a longitudinal survey for 2008–2018. We found that along with the reducing of the digital divide, its gaps still remain. The greatest polarization is associated with the income, age, and type of residence of the respondents. The most vulnerable social groups on access to ICTs and Internet use are the low-income, the elderly, citizens with disabilities, and those living in rural areas. The reverse shifts in the digital divide were recorded mainly in relation to the Internet usage by age between the middle-age and youth and by gender. In addition, we pointed out the most resistance social groups to reduce the digital divide in the period under review, in particular, by income and type of residence of the respondents. The findings contribute to an understanding of the dynamics and social consequences of the digital divide and can be taken into account in social policy and measures.

A coupled electro-chemo-mechanical model for all-solid-state thin film Li-ion batteries: The effects of bending on battery performances

All-solid-state thin film Li-ion batteries (TFBs) have broad application prospects in new technology products such as smart cards, power implantable medical devices, and wearable equipment. Recently, the mechanical-related issues in all-solid-state batteries draw considerable attention. Herein, a fully coupled electro-chemo-mechanical theoretical model for TFBs is proposed accounting for species diffusion, interfacial transfer kinetics and mechanical deformation. A TFB with the setup of LiCoO2 cathode, graphite anode and a solid polymer electrolyte is applied to the simulation process for investigating the bending effects. The results indicate that bending the TFB from the anode to the cathode reduces the cell potential, which enables the battery to own a higher lithiation capacity at the given cut-off potential; conversely, the reverse bending-induced potential shifts result in a lower lithiation capacity. The theoretical predictions are consistent with previous experimental results. The bending effects on cell potential are similar to the working principle of a kind of bending energy harvest device. In addition, the interfacial stress drop can be alleviated by bending the TFB properly toward the cathode, thus improving the interfacial mechanical reliability. This model provides an effective way for studying the TFBs with respect to different initial states, materials combination, and structural parameters.

Judging the phase transition pressure of the unknown parent phase if the resulting state is known.

In high-pressure phase transition experiments, the crystal structure of the intermediate phase in some phase transitions is difficult to successfully measure due to the limitations of the experimental conditions. The absence of crystal structure data for the intermediate phase also makes it difficult to calculate the pressure point from the intermediate phase to the new phase by the traditional thermodynamic criterion in theoretical simulations. The Conch Criterion is employed by us to successfully verify the phase transition points by observing the reverse shifts of the DOS (electron density of states) curves for the new phase of Cu2S, PbS, PbSe and PbTe, which breaks through the constraints of the traditional criterion and realizes tracing the source of the phase transition in theoretical calculations.

Ecological contingency in species shifts: downslope shifts of woody species under warming climate and land-use change

A predicted impact of a warming climate is an upslope shift of montane plant species. These upslope shifts may be amplified by land-use changes or attenuated by forest recoveries at low elevations where historical disturbances were ceased allowing for plant regrowth. Consequently, species may shift downslope back to low elevations where they had been previously harvested. The cessation-driven downslope shifts are hypothesized to dampen or even reverse climate-driven upslope shifts. We tested this hypothesis by a 20 year (1989–2009) forest inventory dataset from five mountainous areas in eastern China. In our study region, intense deforestation occurred mostly at low elevations until 1970, but was then ceased to facilitate natural forest recovery. Based on the analyses of 30 216 woody plants in 609 plots, we found that: (1) forest recovery occurred over the 20 year survey period, and increment rates of both recruitment and basal area increased up to 2004. However, in the last period (2004–2009), increment rates of basal area leveled off and recruitment was close to zero; (2) forest recovery was faster at lower elevations, as indicated by the higher increment rates there; (3) despite rising regional temperatures, the mean elevations of study species showed a downslope shift over the 20 years; and (4) the contribution of forest recovery to elevational shifts was supported by the fact that the species shifts were positively related to elevational changes in the recruitment increment, e.g. the negative (or downslope) shifts occurred in association with higher increments at lower elevations. These results suggest that, the cessation of disturbances and consequent lowland forest recovery had greater effects on the species distributions than did warming climate. In mountain systems that are being allowed to recover from historical disturbances, the effects of forest recovery on species distributions should be explicitly accounted for when assessing and predicting climate change impacts.

Habitat and fishing control grazing potential on coral reefs

Abstract Herbivory is a key process on coral reefs, which, through grazing of algae, can help sustain coral‐dominated states on frequently disturbed reefs and reverse macroalgal regime shifts on degraded ones. Our understanding of herbivory on reefs is largely founded on feeding observations at small spatial scales, yet the biomass and structure of herbivore populations is more closely linked to processes which can be highly variable across large areas, such as benthic habitat turnover and fishing pressure. Though our understanding of spatiotemporal variation in grazer biomass is well developed, equivalent macroscale approaches to understanding bottom‐up and top‐down controls on herbivory are lacking. Here, we integrate underwater survey data of fish abundances from four Indo‐Pacific island regions with herbivore feeding observations to estimate grazing rates for two herbivore functions, cropping (which controls turf algae) and scraping (which promotes coral settlement by clearing benthic substrate), for 72 coral reefs. By including a range of reef states, from coral to algal dominance and heavily fished to remote wilderness areas, we evaluate the influences of benthic habitat and fishing on the grazing rates of fish assemblages. Cropping rates were primarily influenced by benthic condition, with cropping maximized on structurally complex reefs with high substratum availability and low macroalgal cover. Fishing was the primary driver of scraping function, with scraping rates depleted at most reefs relative to remote, unfished reefs, though scraping did increase with substratum availability and structural complexity. Ultimately, benthic and fishing conditions influenced herbivore functioning through their effect on grazer biomass, which was tightly correlated to grazing rates. For a given level of biomass, we show that grazing rates are higher on reefs dominated by small‐bodied fishes, suggesting that grazing pressure is greatest when grazer size structure is truncated. Stressors which cause coral declines and clear substrate for turf algae will likely stimulate increases in cropping rates, in both fished and protected areas. In contrast, scraping functions are already impaired at reefs inhabited by people, particularly where structural complexity has collapsed, indicating that restoration of these key processes will require scraper biomass to be rebuilt towards wilderness levels. A free Plain Language Summary can be found within the Supporting Information of this article.

A new criterion for the prediction of solid-state phase transition in TMDs.

The classical thermodynamic criterion for phase transition predicts whether the phase transition will occur according to whether the nth derivative of the state parameter is discontinuous, and the continuity verification of multi-order derivatives increases the difficulty and complexity of judgment for phase transition to a certain extent. Based on the reverse shifts of the DOS curves near the Fermi level, we propose a new criterion for solid-state phase transition named Conch Criterion, which has been verified in the TMD system. The new criterion can observe the occurrence of phase transition from another perspective besides the thermodynamic properties while mutually confirming the thermodynamic criterion.

Evolutions of Pressure Fluctuations and Runner Loads During Runaway Processes of a Pump-Turbine

The pressure fluctuations and runner loads on a pump-turbine runner during runaway process are very violent and the corresponding flow evolution is complicated. To study these phenomena and their correlations in depth, the runaway processes of a model pump-turbine at four guide vane openings (GVOs) were simulated by three-dimensional computational fluid dynamics (3D-CFD). The results show that the flow structures around runner inlet have regular development and transition patterns—the reverse flow occurs when the trajectory moves to the turbine-brake region and the main reverse velocity shifts locations among the hub side, the shroud side and the midspan as the trajectory comes forward and backward in the S-shape region. The locally distributed reverse flow vortex structures (RFVS) enhance the local rotor–stator interaction (RSI) and make the pressure fluctuations in vaneless space at the corresponding section stronger than at the rest sections along the spanwise direction. The transitions of RFVS, turning from the hub side to midspan, facilitate the inception and development of rotating stall, which propagates at approximately 45–72% of the runner rotation frequency. The evolving rotating stall induces asymmetrical pressure distribution on the runner blade, resulting in intensive fluctuations of runner torque and radial force. During the runaway process, the changing characteristics of the reactive axial force are dominated by the change rate of flow discharge, and the amplitude of low frequency component of axial force is in proportion to the amplitude of discharge change rate.

Resource partitioning along multiple niche axes drives functional diversity in parrotfishes on Caribbean coral reefs.

The recent loss of key consumers to exploitation and habitat degradation has significantly altered community dynamics and ecosystem function across many ecosystems worldwide. Predicting the impacts of consumer losses requires knowing the level of functional diversity that exists within a consumer assemblage. In this study, we document functional diversity among nine species of parrotfishes on Caribbean coral reefs. Parrotfishes are key herbivores that facilitate the maintenance and recovery of coral-dominated reefs by controlling algae and provisioning space for the recruitment of corals. We observed large functional differences among two genera of parrotfishes that were driven by differences in diet. Fishes in the genus Scarus targeted filamentous algal turf assemblages, crustose coralline algae, and endolithic algae and avoided macroalgae, while fishes in the genus Sparisoma preferentially targeted macroalgae. However, species with similar diets were dissimilar in other attributes, including the habitats they frequented, the types of substrate they fed from, and the spatial scale at which they foraged. These differences indicate that species that appear to be functionally redundant when looking at diet alone exhibit high levels of complementarity when we consider multiple functional traits. By identifying key functional differences among parrotfishes, we provide critical information needed to manage parrotfishes to enhance the resilience of coral-dominated reefs and reverse phase shifts on algal-dominated reefs throughout the wider Caribbean. Further, our study provides a framework for predicting the impacts of consumer losses in other species rich ecosystems.

Characterization and correction of charge-induced pixel shifts in DECam

Interaction of charges in CCDs with the already accumulated charge distribution causes both a flux dependence of the point-spread function (an increase of observed size with flux, also known as the brighter/fatter effect) and pixel-to-pixel correlations of the {Poissonian} noise in flat fields. We describe these effects in the Dark Energy Camera (DECam) with charge dependent shifts of effective pixel borders, i.e. the Antilogus et al. (2014) model, which we fit to measurements of flat-field {Poissonian} noise correlations. The latter fall off approximately as a power-law r−2.5 with pixel separation r, are isotropic except for an asymmetry in the direct neighbors along rows and columns, are stable in time, and are weakly dependent on wavelength. They show variations from chip to chip at the 20% level that correlate with the silicon resistivity. The charge shifts predicted by the model cause biased shape measurements, primarily due to their effect on bright stars, at levels exceeding weak lensing science requirements. We measure the flux dependence of star images and show that the effect can be mitigated by applying the reverse charge shifts at the pixel level during image processing. Differences in stellar size, however, remain significant due to residuals at larger distance from the centroid.

Impact of submerged herbaceous vegetation on wind-induced current in shallow water

A combined wind tunnel and water flume experiment was performed to study the effect of an aquatic herbaceous plant patch on the turbulent structure and flow field of wind-induced currents. Eel grass was chosen as the test plant. The plants were settled in patch form. Three-dimensional instantaneous velocities were measured using an acoustic doppler velocimeter (ADV). The results indicate that in the non-eel grass patch flow, turbulent shear stress −u′w′¯has a local minimum near the flow reverse point, turbulent intensity has the tendency to decrease continually from surface to bottom, and the dominant turbulent event is sweeping. In the eel grass patch with wind-induced flow, reverse flow occurs more quickly than in the non-eel grass patch case, and the reverse point shifts downward. Turbulent shear stress −u′w′¯ has two maxima below the canopy. Turbulent intensity u′2¯ decreases generally from water surface to flume bed, but there are maxima below the canopy. The dominant turbulent event is the fourth quadrant event below the canopy, and the two relative contributions of the second and the fourth quadrant event have similar values above the canopy. The mean bias and RMS values at centre of the eel grass patch are almost as two times larger as that at other measuring lines in non-eel grass region. This indicates that not only the shear stress and turbulent intensity become larger, and the vertical variations of the shear stress and turbulent intensity are also larger due to the effect of vegetation. The differences in the effects of submerged herbaceous vegetation on open channel flow and wind-induced flow were discussed in relation to time averaged velocity, turbulent shear stress, turbulent intensity and coherent structure based on the present test data and previous data.

Are regime-shift sources of risk priced in the market?

Abstract In this paper we develop a discrete-time pricing model for European options where the log-return of the underlying asset is subject to discontinuous regime shifts in its mean and/or volatility which follow a Markov chain. The model allows for multiple regime shifts whose risk cannot be hedge out and thus must be priced in option market. The paper provides estimates of the price of regime-shift risk coefficients based on a joint estimation procedure of the Markov regime-switching process of the underlying stock and the suggested option pricing model. The results of the paper indicate that bull-to-bear and bear-to-crash regime shifts carry substantial prices of risk. Risk averse investors in the markets price these regime shifts by assigning higher transition (switching) probabilities to them under the risk neutral probability measure than under the physical. Ignoring these sources of risk will lead to substantial option pricing errors. In addition, the paper shows that investors also price reverse regime shifts, like the crash-to-bear and bear-to-bull ones, by assigning smaller transition probabilities under the risk neutral measure than the physical. Finally, the paper evaluates the pricing performance of the model and indicates that it can be successfully employed, in practice, to price European options.

Sea urchin barrens as alternative stable states of collapsed kelp ecosystems

Sea urchin barrens are benthic communities on rocky subtidal reefs that are dominated by urchins and coralline algae; in the absence of intense herbivory by urchins, these barrens support luxuriant seaweed communities such as kelp beds (or forests). Barrens can extend over 1000s of km of coastline or occur in small patches (10s to 100s of m) within a kelp bed. They are characterized by low primary productivity and low food-web complexity relative to kelp communities and are generally considered a collapsed state of the kelp ecosystem. To assess the stability of sea urchin barrens and potential for return to a kelp-dominated state, we document temporal and spatial patterns of occurrence of barrens along temperate and polar coasts. We examine the various drivers of phase (or regime) shifts in these areas, the threshold levels of urchin abundance that trigger abrupt changes in ecosystem state, and the feedback mechanisms that stabilize each state. Although longitudinal (decadal) studies are limited, we find evidence in several regions that transitions between barrens and kelp beds are characterized by discontinuous phase shifts, with different thresholds for forward (to barrens) and reverse (to kelp beds) shifts, in accordance with alternative stable-state dynamics. In other areas, barrens may reflect regime shifts associated with large-scale oceanographic changes. Accelerating climate change and increasing anthropogenic impacts play important roles in altering alternative stable-state dynamics and triggering phase shifts. Recovery of the kelp state may be possible through management or remediation measures, but this necessitates a clear understanding of the thresholds and stabilizing factors for a given system.

Reverse DC bias stress shifts in organic thin‐film transistors with gate dielectrics using parylene‐C

AbstractWe have systematically investigated the reliability of organic thin‐film transistors (TFTs) using polychloro‐p‐xylylene (parylene‐C) as a gate dielectric material. The fabricated organic TFT devices exhibited positive bias shifts with negative DC gate‐source voltages; however, no hysteresis was observed in the transfer characteristics for the tested TFT devices. Moreover, this tendency was enhanced with increasing annealing temperatures, whereby X‐ray diffraction (XRD) results revealed that the crystallinity of the parylene‐C layers increased with thermal annealing. As a result the total dipole moments normal to the surface of the parylene‐C layers grew, which caused reverse bias shifts in the TFT devices.

Active Vibration Control Using Delay Compensated LMS Algorithm by Modified Gradients

Active vibration control (AVC) based on adaptive finite impulse response (FIR) filters inhere delays in conditional signal dispersion. Reasons for these delays are geometrical arrangements, and computational time in analog digital converters (ADCs) and in digital analog converters (DACs). The delays represent a phase shift in periodic signals. These delays avoid instant feedback of the signals through the least mean square (LMS) algorithm. This can lead to instability and even divergence. This study presents a modification of the LMS algorithm by adjusting the underlying gradient descent algorithm. Using analytic considerations, it shows the conditions of convergence for the stepsize as well as the gradient. The result is that all delays occurring can be compensated entirely. Unlike the delayed LMS algorithm, the introduced method considers possible delays analytically and furnishes the possibility for a perfect delay compensation. Modifications are easy to put into practice and were researched and verified using various simulations. Measurements on a duct in a range from 100 Hz to 1000 Hz confirm the success of adjustment and show an excellent convergence over the whole tested frequency range. Signal manipulation, for example, with a low-pass filter, which allows reverse phase shifts between – π and π, results only in a small frequency range and may be omitted by using the delay compensated LMS algorithm. The analytic mathematical derivation of the required modification can be implemented easily.

Modifications in phytoplankton size structure by environmental constraints induced by regime shifts in an urban lake

Size related changes of phytoplankton biovolume and species composition have been analysed for forward and reverse regime shifts in a shallow, urban, seepage lake. As a consequence of changes in the hydrology, the pelagic switched from a clear water, macrophyte dominated state to a turbid stable phase with an abundant cyanobacterial population. Experimental nutrient reduction forced the system into a recovery phase. Each state change was associated with significant changes in total biovolume, species composition and size structure affecting surface to volume ratios (S/V). Chlorophyll-a content and S/V drastically increased during the early recovering phase due to small cell sized species developing. As expected, state transitions were associated with significant alterations in size structure and composition.

Blockade of cyclic AMP-dependent protein kinase does not prevent the reverse ocular dominance shift in kitten visual cortex.

Monocular deprivation (MD) during the critical period for the development of visual cortex causes a loss of binocular response of neurons and a shift to the open eye, a normal ocular dominance (OD) shift. However, when MD is combined with chronic inactivation of the visual cortex by muscimol, the OD distribution of the neurons shifts to the deprived eye (reverse OD shift). We have previously shown that the normal OD shift is abolished by chronic infusion of the protein kinase A (PKA) inhibitor, 8-chloroadenosine-3', 5'-cyclic monophosphorothioate, Rp-isomer (Rp-8-Cl-cAMPS), into kitten visual cortex. In this study, we investigated the effect of this inhibitor on the reverse OD shift. Combination of MD and muscimol infusion into the visual cortex of 6-wk-old kittens caused a reverse OD shift that was comparable to that seen in previous studies. However, a reverse OD shift was also seen with concurrent infusion of the PKA inhibitor with muscimol. The strongest OD shift was observed in layer IV regardless of the presence or absence of the PKA inhibitor. This suggests that the dissociation of pre- and postsynaptic activities, which occurs mainly at thalamocortical synapses, induces the reverse OD shift and that inhibition of PKA does not prevent it. Presumably, an inhibition of PKA has no effect in silent cortex. We conclude that 1) an activation of PKA is not required for the induction of the reverse OD shift, and 2) the intracellular signaling mechanism underlying MD-induced OD plasticity differs between normal and reverse OD shifts.