CO2 Oscillations Research Articles

Self-excited oscillation characteristics and mechanisms of supercritical CO2 flowing in a Helmholtz oscillator for enhancing heat transfer

The drastic variations in thermal properties of supercritical CO2 near its pseudo-critical point induce the formation of complex boundary layer structures within pipelines, rendering it susceptible to heat transfer deterioration under the influence of buoyancy forces. The Helmholtz self-excited cavity can generate self-excited pulsating jets, enhancing the intermixing between fluids inside the heat exchanger tubes, disrupting the thermal boundary layer, and suppressing heat transfer deterioration. In this study, the characteristics and mechanisms of self-excited oscillations of supercritical CO2 flowing vertically upward in the Helmholtz self-excited cavity were investigated using the large eddy simulation (LES) method. A detailed analysis of cavitation and vortex evolution within the cavity was conducted, along with an exploration of the influence of inlet pressure and structural parameters on the frequency characteristics of pulsations. The results indicate a close relationship between cavitation and vortex interactions and the pulsation frequency. An increase in inlet pressure leads to a significant cavitation phenomenon near the jet shear layer and an increase in vortex frequency. Dimensionless cavity length (Lc/d1) enlargement results in an increase in outlet pulsation frequency but a decrease in pulsation amplitude. The critical dimensionless ratio of cavity diameter (Dc/d1) plays a crucial role in maintaining the desired pulsation frequency and amplitude. Within the working range outlined in this paper, practical insights for system design and operation are provided by the optimal parameters of Lc/d1 = 3 and Dc/d1 = 10.

Ocean iron cycle feedbacks decouple atmospheric CO2 from meridional overturning circulation changes

The ocean’s Meridional Overturning Circulation (MOC) brings carbon- and nutrient-rich deep waters to the surface around Antarctica. Limited by light and dissolved iron, photosynthetic microbes incompletely consume these nutrients, the extent of which governs the escape of inorganic carbon into the atmosphere. Changes in MOC upwelling may have regulated Southern Ocean outgassing, resulting in glacial-interglacial atmospheric CO2 oscillations. However, numerical models that explore this positive relationship do not typically include a feedback between biological activity and abundance of organic chelating ligands that control dissolved iron availability. Here, I show that incorporating a dynamic ligand parameterization inverts the modelled MOC-atmospheric CO2 relationship: reduced MOC nutrient upwelling decreases biological activity, resulting in scant ligand production, enhanced iron limitation, incomplete nutrient usage, and ocean carbon outgassing, and vice versa. This first-order response suggests iron cycle feedbacks may be a critical driver of the ocean’s response to climate changes, independent of external iron supply.

Phytoplankton responses to dust addition in the Fe–Mn co-limited eastern Pacific sub-Antarctic differ by source region

The seasonal availability of light and micronutrients strongly regulates productivity in the Southern Ocean, restricting biological utilization of macronutrients and CO2 drawdown. Mineral dust flux is a key conduit for micronutrients to the Southern Ocean and a critical mediator of multimillennial-scale atmospheric CO2 oscillations. While the role of dust-borne iron (Fe) in Southern Ocean biogeochemistry has been examined in detail, manganese (Mn) availability is also emerging as a potential driver of past, present, and future Southern Ocean biogeochemistry. Here, we present results from fifteen bioassay experiments along a north-south transect in the undersampled eastern Pacific sub-Antarctic zone. In addition to widespread Fe limitation of phytoplankton photochemical efficiency, we found further responses following the addition of Mn at our southerly stations, supporting the importance of Fe-Mn co-limitation in the Southern Ocean. Moreover, addition of different Patagonian dusts resulted in enhanced photochemical efficiency with differential responses linked to source region dust characteristics in terms of relative Fe/Mn solubility. Changes in the relative magnitude of dust deposition, combined with source region mineralogy, could hence determine whether Fe or Mn limitation control Southern Ocean productivity under future as well as past climate states.

High-resolution GEOS-Chem model for Indian monsoon region: Seasonal cycle and budget of tropospheric CO2

A nested GEOS-Chem atmosphere transport model has been set up for the Indian monsoon region (40° E-110° E & 15° S–45° N at 0.250X0.3125°) spatial resolution to study the variability of the tropospheric CO2 over India and surrounding oceans during 2012–2020. The model has been constrained by the influxes of CO2 at its four lateral boundaries derived from the GEOS-Chem global simulations and surface fluxes of CO2 over the land and oceans based on historical databases. It is initialized from a known state and driven by the GEOS reanalysis's meteorological forcing. Model simulations were evaluated at three in situ measurement locations and with respect to the satellite retrievals from OCO-2 and GOSAT. Model parameters were tuned to have reasonable solutions to resolve observed latitudinal gradient and seasonal and inter-annual variability. Three additional model runs were made to evaluate the role of long-range transport, net terrestrial ecosystem exchange, air-sea fluxes, and regional emissions in controlling seasonal oscillations of tropospheric CO2 over the study region. It revealed that the net terrestrial ecosystem exchanges are responsible for 35% control in the surface layer CO2 seasonal tendency for India and the Bay of Bengal domains, and 10% for the Arabian Sea. The air-sea fluxes have 8% control on the CO2 seasonal tendency for the Arabian Sea and Bay of Bengal and 5% for India. The anthropogenic emissions have 4% control for India and <1% for the Arabian Sea, and 9% for the Bay of Bengal. The long-range transport, as the residual, is responsible for 60% variability in the seasonal cycle of CO2 over India and the Bay of Bengal and 75% for the Arabian Sea domain.

Carbon Fluxes during Dansgaard–Oeschger Events as Simulated by an Earth System Model

Abstract The Community Earth System Model with marine and terrestrial biogeochemistry is configured to simulate glacial climate. The integration shows transitions from warm to cold states—interstadials to stadials—and back. The amplitude of the associated Greenland and Antarctica temperature changes and the atmospheric CO2 signal are consistent with ice-core reconstructions, and so are the time lags between termination of a stadial, Antarctic temperature reversal, and the decline of the atmospheric CO2 concentration (for brevity’s sake simply referred to as CO2 from here on). The present model results stand out because the transitions occur spontaneously (without forcing changes like hosing) and because they reproduce the observed features above in a configuration that uses the same parameterizations as climate simulations for the present day (i.e., no retuning has been done). During stadials, precipitation shifts lead to reduced growth on land, which dominates the CO2 increase; the ocean acts as a minor carbon sink during the stadials. After the end of the stadials, however, the sudden reversal of the stadial anomalies in temperature, wind, and precipitation turns the ocean into a carbon source, which accounts for the continued rise of CO2 for several hundred years into the interstadial. The simulations also provide a novel possible interpretation for the observed correlation between CO2 and Antarctic temperature: rather than both being controlled by Southern Ocean processes, they are both controlled by the North Atlantic Ocean, and most of the extra CO2 may not be of Southern Hemisphere origin. If the stadials are prolonged through North Atlantic hosing, the upper ocean comes to an equilibrium, and the CO2 response is dominated by a single process: reduced export production in the North Atlantic as result of the collapsed overturning circulation. This is in contrast to the unforced simulation where the net ocean carbon flux anomaly is the sum of several regional responses of both signs and similar magnitudes. Reducing the aeolian iron deposition by half, to account for the observed reduction of Southern Hemisphere dust fluxes during stadials, reduces biological productivity and export production so that the Southern Ocean emerges as an important carbon source, at least for the three centuries up until a new equilibrium for the upper ocean is reached. Significance Statement The last ice age featured millennial-scale oscillations in CO2 and temperature, the latter being anticorrelated between Greenland and Antarctica. This is often referred to as the bipolar seesaw. Here, an Earth system model is described that reproduces these signals, and its results are used to explain the observed correlation between temperature and CO2. In contrast to previous idealized studies it is found that all ocean basins and the land each contribute equally to the CO2 signal.

Paleoatmospheric CO2 oscillations through a cool middle/Late Cretaceous recorded from pedogenic carbonates in Africa

This study presents the first African pedogenic carbonate estimated atmospheric CO2 concentrations for the Early to Late Cretaceous transition. Pedogenic carbonates have been used extensively as proxies to reconstruct past climates, yet few studies have focused on the climatic conditions of Africa during the Mesozoic. The paucity of paleoclimate data from the region represents a significant obstacle in interpreting past climate change, and thus our ability to predict future changes. Paleosol carbonate nodules were sampled from Bk horizons of seven particularly well-exposed and well-characterized paleosols through the Cretaceous Galula Formation, including four from the lower Mtuka Member (Aptian–Cenomanian) and three from the upper Namba Member (Campanian). The Cretaceous Galula Formation is a fossiliferous continental sedimentary succession of braided fluvial deposits that are well exposed in recently incised river drainages of the Rukwa Rift Basin, Tanzania. Oxygen isotope values averaged −5.6‰ and −7.2‰ VPDB for the Mtuka and Namba members, equating to mean annual temperatures of 14.5 °C and 11.2 °C, respectively. Using the stable isotope composition of pedogenic carbonates from the Mtuka Member, an average pCO2 of 1860 ppmv was estimated for the Aptian–Cenomanian, before declining to an average of 520 ppmv in the Namba Member, during the Campanian. Atmospheric pCO2 values fluctuated, but remained above 1000 ppmv through the middle Cretaceous, and correspond to the “cool” greenhouse period that spanned the Aptian–Albian. The gradual decline in pCO2 (550–502 ppmv) recorded in the Namba Member paleosols occurred during Late Cretaceous cooling following the Cretaceous Thermal Maximum.

Impact of lung structure on airway opening index during mechanical versus manual chest compressions in a porcine model of cardiac arrest

ObjectivesThe exhaled CO2 signal provides guidance during cardiopulmonary resuscitation. The Airway opening index (AOI) has been recently used to quantify chest-compression (CC) induced expired CO2 oscillations. We aimed to determine whether levels of intrathoracic pressures developed during CC or parameters related to lung structure may affect AOI. MethodsSecondary analysis of a randomized animal study (n = 12) in a porcine model of cardiac arrest (CA) and cardiopulmonary resuscitation (CPR) during ambulance transport. Animals were randomized to 18-min of manual or mechanical CCs. Changes in AOI and right atrial pressure (ΔRAP) were recorded during CCs in animals undergoing manual (n = 6) or mechanical (n = 6) CCs. Lung CT scan and measurement of the respiratory system compliance (Cpl,rs) were performed immediately after return of spontaneous circulation. ResultsAnimals undergoing mechanical CCs had a lower AOI compared to animals treated with manual CCs (p < 0.001). AOI negatively correlated with the swings of intrathoracic pressure, as measured by the change in ΔRAP (ρ=−0.727, p = 0.007). AOI correlated with the lung density (ρ=−0.818, p = 0.001) and with the Cpl,rs (ρ = 0.676, p = 0.016). Animals with cardiopulmonary resuscitation associated lung edema (CRALE) (i.e. mean CT≥−500 HU) showed lower levels of AOI compared to animals without it (29 ± 12 % versus 50 ± 16 %, p = 0.025). ConclusionsAnimals undergoing mechanical CCs had lower levels of AOI compared to animals undergoing manual CCs. A higher swing of intrathoracic pressure during CC, a denser and a stiffer lung were associated with an impaired CO2 exhalation during CC as observed by a lower AOI.

Breath-hold task induces temporal heterogeneity in electroencephalographic regional field power in healthy subjects.

We demonstrated that changes in CO2 values cause oscillations in the cortical activity in δ-and α-bands. The analysis of the regional field power (RFP) showed evidence that different cortical areas respond with different time delays to CO2 challenges. An opposite behavior was found for the end-tidal O2. We suppose that the different cortical time delays likely expresse specific ascending pathways to the cortex, generated by chemoreceptor nuclei in the brain stem. Although the brain stem is in charge of the automatic control of ventilation, the cortex is involved in the voluntary control of breathing but also receives inputs from the brain stem, which influences the perception of breathing, the arousal state and sleep architecture in conditions of hypoxia/hypercapnia. We evaluated in 11 healthy subjects the effects of breath hold (BH; 30 s of apneas and 30 s of normal breathing) and BH-related CO2/O2 changes on electroencephalogram (EEG) global field power (GFP) and RFP in nine different areas (3 rostrocaudal sections: anterior, central, and posterior; and 3 sagittal sections: left, middle, and right) in the δ- and α-bands by cross correlation analysis. No significant differences were observed in GFP or RFP when comparing free breathing (FB) with the BH task. Within the BH task, the shift from apnea to normal ventilation was accompanied by an increase in the δ-power and a decrease in the α-power. The end-tidal pressure of CO2 ([Formula: see text]) was positively correlated with the δ-band and negatively with the α- band with a positive time shift, whereas an opposite behavior was found for the end-tidal pressure of O2 ([Formula: see text]). Notably, the time shift between [Formula: see text] / [Formula: see text] signals and cortical activity at RFP was heterogenous and seemed to follow a hierarchical activation, with the δ-band responding earlier than the α-band. Overall, these findings suggest that the effect of BH on the cortex may follow specific ascending pathways from the brain stem and be related to chemoreflex stimulation.NEW & NOTEWORTHY We demonstrated that the end tidal CO2 oscillation causes oscillations of delta and alpha bands. The analysis of the regional field power showed that different cortical areas respond with different time delays to CO2 challenges. An opposite behavior was found for the end-tidal O2. We can suppose that the different cortical time delay response likely expresses specific ascending pathways to the cortex generated by chemoreceptor nuclei in the brainstem.

The temperature increase in Greenland has accelerated in the past five years

Abstract Understanding the changes in Greenland's temperature is important for assessing and predicting the mass of the Greenland ice sheet, which plays an important role in sea level rise. In this study, we analyzed the annual and seasonal coastal Greenland's temperatures during the period 1952–2017 (focusing on the period 2013–2017) based on a dataset obtained from the Danish Meteorological Institute (DMI). Overall, the annual coastal Greenland's temperature increased during 1952–2017 at a rate of 0.23 °C decade−1, especially in the southeastern (0.70 °C decade−1) and northern (0.42 °C decade−1) regions of the island. From the changes in the seasonal coastal Greenland's composite temperature (CT), winter exhibited the largest change rate (0.28 °C decade−1), and the summer CT increased by 0.25 °C decade−1, while the spring CT increased by 0.17 °C decade−1 with less variation. The temperature increase accelerated during 2013–2017 according to Mann-Kendall (M-K) tests, especially in the northeastern and northern regions of the island. The seasonal temperature change of the whole island decreased in the following order: annual > autumn > summer > winter > spring. We also analyzed the annual inland temperature change during the period 1997–2017 based on a dataset obtained from the Greenland Climate Network; the results indicated that the inland temperature increased by 0.13 °C decade−1. Pearson correlation analysis was used to determine the teleconnection relationship between the coastal temperatures and large-scale atmosphere-ocean climate indexes, and we found that the Greenland Blocking Index (GBI), Atlantic Multidecadal Oscillation (AMO), Tropical Northern Atlantic Index (TNA), North Tropical Atlantic Index (NTA), Caribbean Index (CAR), Atlantic Meridional Mode (AMM), East Atlantic (EA) and Western Hemisphere warm pool (WHWP) have significant positive correlations with the coastal temperature in most months, except in February and May. However, the North Atlantic Oscillation (NAO), Arctic Oscillation (AO) and Eastern Asia/Western Russia (EAWR) show significant negative correlations with temperature. Overall, there exists a time lag effect between the climate indexes (except for the GBI, AO and NAO) and temperature. From the application of the random forest model, we found that the GBI, NAO, CO2, AMO, N2O, SF6, CH4, and Northern Oscillation Index (NOI) are the most important variables that influenced the CT changes during 1979–2017. Finally, we calculated the contribution rates of the most important variables to temperature change during the period 1979–2017 and showed that the contribution rates of the GBI, CO2 and NOI to temperature change were 47.30%, 35.68%, and 17.02%, respectively.

Self-Synchronized Oscillatory Metabolism of Clostridium pasteurianum in Continuous Culture

By monitoring the real-time gas production (CO2 and H2) and redox potential at high sampling frequency in continuous culture of Clostridium pasteurianum on glycerol as sole carbohydrate, the self-synchronized oscillatory metabolism was revealed and studied. The oscillations in CO2 and H2 production were in sync with each other and with both redox potential and glycerol in the continuous stirred tank reactor (CSTR). There is strong evidence that the mechanism for this is in the regulation of the oxidative pathway of glycerol metabolism, including glycolysis, and points toward complex, concerted cycles of enzyme inhibition and activation by pathway intermediates and/or redox equivalents. The importance of understanding such an “oscillatory metabolism” is for developing a stable and highly productive industrial fermentation process for butanol production, as unstable oscillations are unproductive. It is shown that the oscillatory metabolism can be eradicated and reinstated and that the period of oscillations can be altered by modification of the operating parameters. Synchronized oscillatory metabolism impacted the product profile such that it lowered the selectivity for butanol and increased the selectivity for ethanol. This elucidates a possible cause for the variability in the product profile of C. pasteurianum that has been reported in many previous studies.

Combined spatially resolved operando spectroscopy: New insights into kinetic oscillations of CO oxidation on Pd/γ-Al2O3

Spatially resolved, combined energy dispersive EXAFS (EDE) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements have been performed over a fixed catalyst bed of Pd/γ-Al2O3 during kinetic oscillations of CO oxidation. The kinetic oscillations of CO oxidation over Pd (or for that matter Pt or Rh) catalysts are a complicated phenomenon that require characterisation techniques with high time resolution and spatial resolution in order to make links between catalyst structure and surface reactivity. By measuring the extent of Pd oxidation at the nanoparticle surface, from Pd K-edge EDE, and matching this with the CO coverage, from DRIFTS spectra, at multiple positions of the fixed bed reactor it is found that the majority of the catalyst undergoes a sharp transition from the CO poisoned catalyst to the highly active, oxidised Pd surface. This transition occurs initially at the end of the catalyst bed, nearest the outlet, and propagates upstream with increasing temperature of the reactor. The oscillations in Pd surface oxide formation and CO coverage are observed only in the first ∼1 mm of the bed, which gives rise to oscillations in CO2 and O2 concentrations observed by end-pipe mass spectrometry after the light-off temperature. The catalyst initially exists as less active, CO poisoned metallic Pd nanoparticles before light-off which transition to a highly active state after light-off when the Pd nanoparticle surface becomes dominated by chemisorbed oxygen. Kinetic oscillations only occur at the front of the catalyst bed where there is sufficient concentration of CO in the gas phase to compete with O2 for adsorption sites at the catalyst surface. We demonstrate the complex nature of the evolving catalyst structure and surface reactivity during catalytic operation and the need for spatially resolved operando methods for understanding and optimising catalyst technologies.

Intrathoracic Airway Closure Impacts CO2 Signal and Delivered Ventilation during Cardiopulmonary Resuscitation.

End-tidal CO2 (EtCO2) is used to monitor cardiopulmonary resuscitation (CPR), but it can be affected by intrathoracic airway closure. Chest compressions induce oscillations in expired CO2, and this could reflect variable degrees of airway patency. To understand the impact of airway closure during CPR, and the relationship between the capnogram shape, airway closure, and delivered ventilation. This study had three parts: 1) a clinical study analyzing capnograms after intubation in patients with out-of-hospital cardiac arrest receiving continuous chest compressions, 2) a bench model, and 3) experiments with human cadavers. For 2 and 3, a constant CO2 flow was added in the lung to simulate CO2 production. Capnograms similar to clinical recordings were obtained and different ventilator settings tested. EtCO2 was compared with alveolar CO2 (bench). An airway opening index was used to quantify chest compression-induced expired CO2 oscillations in all three clinical and experimental settings. A total of 89 patients were analyzed (mean age, 69 ± 15 yr; 23% female; 12% of hospital admission survival): capnograms exhibited various degrees of oscillations, quantified by the opening index. CO2 value varied considerably across oscillations related to consecutive chest compressions. In bench and cadavers, similar capnograms were reproduced with different degrees of airway closure. Differences in airway patency were associated with huge changes in delivered ventilation. The opening index and delivered ventilation increased with positive end-expiratory pressure, without affecting intrathoracic pressure. Maximal EtCO2 recorded between ventilator breaths reflected alveolar CO2 (bench). During chest compressions, intrathoracic airway patency greatly affects the delivered ventilation. The expired CO2 signal can reflect CPR effectiveness but is also dependent on airway patency. The maximal EtCO2 recorded between consecutive ventilator breaths best reflects alveolar CO2.

Oscillations and hysteresis during hydrocarbon oxidation on a diesel oxidation catalyst: Predictive model

Dodecane oxidation on zeolite beta (BEA) was studied on a diesel oxidation catalyst (DOC) comprising Pt-Pd/Al2O3. Oscillatory CO2 formation under steady-state and transient conditions was studied by spatially-resolved mass spectrometry (SpaciMS) and coherent optical frequency domain reflectometry (c-OFDR) (Peng et al., 2018). The CO2 oscillations were accompanied by local temperature fluctuations during the steady state and temperature-programmed oxidation. The coupling between hydrocarbon sorption and oxidation, the proposed underlying mechanism for the oscillatory behavior, is investigated using a monolith reactor model. Using independently measured dodecane oxidation and sorption kinetics, the model predicts most of the experimental features, including the existence and amplitude of the oscillations. The model also correctly predicts the existence of an observed hysteresis during temperature ramp-up/ramp-down experiments. A non-dimensional map provides a predictive guide for the existence of oscillations. In addition to providing understanding and prediction of the spatiotemporal phenomena, the model analysis suggests a way to decrease the hydrocarbon slip (emissions) during temperature ramp-down.

Search for Trends and Periodicities in Inter-hemispheric Sea Surface Temperature Difference

Understanding the role of coupled solar and internal ocean dynamics on hemispheric climate variability is critical to climate modelling. We have analysed here 165 year long annual northern hemispheric (NH) and southern hemispheric (SH) sea surface temperature (SST) data employing spectral and statistical techniques to identify the imprints of solar and ocean–atmospheric processes, if any. We reconstructed the eigen modes of NH-SST and SH-SST to reveal non-linear oscillations superimposed on the monotonic trend. Our analysis reveals that the first eigen mode of NH-SST and SH-SST representing long-term trend of SST variability accounts for ~ 15–23% variance. Interestingly, these components are matching with first eigen mode (99% variance) of the total solar irradiance (TSI) suggesting possible impact of solar activity on long-term SST variation. Furthermore, spectral analysis of SSA reconstructed signal revealed statistically significant periodicities of ~ 63 ± 5, 22 ± 2, 10 ± 1, 7.6, 6.3, 5.2, 4.7, and 4.2 years in both NH-SST and SH-SST data. The major harmonics centred at ~ 63 ± 5, 22 ± 2, and 10 ± 1 years are similar to solar periodicities and hence may represent solar forcing, while the components peaking at around 7.6, 6.3, 5.2, 4.7, and 4.2 years apparently falls in the frequency bands of El-Nino-Southern Oscillations linked to the oceanic internal processes. Our analyses also suggest evidence for the amplitude modulation of ~ 9–11 and ~ 21–22 year solar cycles, respectively, by 104 and 163 years in northern and southern hemispheric SST data. The absence of the above periodic oscillations in CO2 fails to suggest its role on observed inter-hemispheric SST difference. The cross-plot analysis also revealed strong influence of solar activity on linear trend of NH- and SH-SST in addition to small contribution from CO2. Our study concludes that (1) the long-term trends in northern and southern hemispheric SST variability show considerable synchronicity with cyclic warming and cooling phases and (2) the difference in cyclic forcing and non-linear modulations stemming from solar variability as a possible source of hemispheric SST differences.

Sustained concentration and temperature oscillations in a diesel oxidation catalyst

A diesel oxidation catalyst (DOC) comprising an alumina-based washcoat of Platinum (Pt) and Palladium (Pd) is used to catalyze the oxidation of a diesel exhaust containing hydrocarbons (HCs) with sufficiently high conversion. A large-pore zeolite such as Beta (BEA) is added to the DOC to trap diesel exhaust hydrocarbons during the cold start. There is a need to gain insight on how BEA affects the performance of the HC light-off and of the transient HC oxidation. We conducted steady-state and transient trapping experiments involving the n-dodecane in order to enable improved trap design and operating strategy. Simultaneous spatio-temporal measurements of concentration and temperature, respectively by spatially-resolved mass spectrometry and coherent optical frequency domain reflectometer, provide detailed insight into the reactor dynamics. Steady-state experiments reveal unexpected periodic oscillations of CO2 and temperature in a feed temperature range (142–181 °C). The oscillatory amplitude increases with decreasing space velocity. Temperature programmed oxidation experiments reveal unusual multi-peak CO2 generation and temperature excursion behavior. A lower ramp-rate increases the number of the additional peaks. In addition, at a low heating/cooling rate of ±1 °C/min, a counter-clockwise hysteresis behavior exists. The oscillations and multi-peak behavior indicates coupling between HC trapping and oxidation. Analysis of the behavior during the hysteresis suggests that HC trapping and oxidation dominate in different regions along the length of the monolith. Since the downstream is much hotter than the upstream, the HC is re-trapped by the upstream BEA and is oxidized downstream. This study provides insight into the spatiotemporal features of the transient HC trapping and oxidation of BEA/DOC catalysts. To our knowledge, it is the first report of oscillations in a hydrocarbon trap.

Tunable CO2 laser system with subnanosecond-pulse-train output

A CO2 laser system has been demonstrated that generates a train of subnanosecond pulses tunable over the P and R branches of the CO2 laser spectrum at 9–11µm. It utilizes optical free induction decay to generate a single ~100-ps laser pulse from a tunable transverse-excited-atmospheric CO2 laser. This laser pulse is injection-seeded into a high-pressure CO2 oscillator whose output consists of a train of amplified ~100-ps pulses with maximum pulse energy of 30mJ, corresponding to a peak power of 300MW. The ~100-ps, tunable, infrared laser pulses are needed for a new technique to remotely detect atmospheric gaseous molecules, which relies on the train of CO2 laser pulses selectively exciting the target molecules whose presence is then revealed using a separate terahertz probe beam.

Novel cardiac pacemaker-based human model of periodic breathing to develop real-time, pre-emptive technology for carbon dioxide stabilisation

BackgroundConstant flow and concentration CO2 has previously been efficacious in attenuating ventilatory oscillations in periodic breathing (PB) where oscillations in CO2 drive ventilatory oscillations. However, it has the undesirable effect...

Is late Quaternary climate change governed by self-sustained oscillations in atmospheric CO2?

A simple earth system model is developed to simulate global carbon and phosphorus cycling over the late Quaternary. It is focused on the geological cycling of C and P via continental weathering, volcanic and metamorphic degassing, hydrothermal processes and burial at the seabed. A simple ocean model is embedded in this geological model where the global ocean is represented by surface water, thermocline and deep water boxes. Concentrations of dissolved phosphorus, dissolved inorganic carbon, and total alkalinity are calculated for each box. The partial pressure of CO2 in the atmosphere (pCO2A) is determined by exchange processes with the surface ocean and the continents. It serves as key prognostic model variable and is assumed to govern surface temperatures and global sea-level. The model is formulated as autonomous system, in which the governing equations have no explicit time-dependence. For certain parameter values, the model does not converge towards a steady-state but develops stable self-sustained oscillations. These free oscillations feature pCO2A minima and maxima consistent with the ice-core record when vertical mixing in the ocean is allowed to vary in response to pCO2A-controlled temperature change. A stable 100-kyr cycle with a rapid transition from glacial to interglacial conditions is obtained when additional non-linear equations are applied to calculate deep ocean mixing, iron fertilization and the depth of organic matter degradation as function of pCO2A-controlled surface temperature. The δ13C value of carbon in the ocean/atmosphere system calculated in these model runs is consistent with the benthic δ13C record. However, the simulated 13C depletion in the glacial ocean is not driven by the decline in terrestrial carbon stocks but by sea-level change controlling the rates of organic carbon burial and weathering at continental margins. The pCO2A- and δ13C oscillations develop without any form of external Milankovitch forcing. They are induced and maintained by sea-level change generating persistent imbalances in the marine carbon and phosphorus budgets. Stable oscillations are also obtained when sea-level change is allowed to lag temperature with a realistic time scale for ice-sheet adjustment.

Solid-state seeded nano-second pulse CO2 oscillator for extreme ultraviolet lithography

This Letter describes in some detail a novel, solid-state seeded, nano-second pulse, multi-line CO2 oscillator designed and built for the extreme ultraviolet (EUV) laser-produced-plasma (LPP) source. The oscillator employed quantum cascade laser (QCL) seeders, a spectral beam combiner and a diffusion-cooled, radio-frequency-discharge excited, slab-waveguide CO2 amplifier in a multi-pass and compact regenerative amplifier configuration. The output spectrum consisted of individually controlled laser lines of 0001-1000 band of a CO2 molecule, P18, P20 and P22 with a target 4-line operation (P18-P24). The resistance to self-seeding of more than 40dB and to the parasitic back-seeding of more than 55dB was realized. The oscillator produced up to 20W of average output power at repetition rate of 100kHz in a near-diffraction limited beam of M2 lower than 1.3 and RMS pointing stability below 50 microradians. Full Text: PDF References V. Bakshi, "EUV lithography", vol. 178 (SPIE Press, 2009). T. Ohta, K. M. Nowak, T. Suganuma, H. Kameda, M. Moriya, T. Yokoduka, Y. Kawasuji, J. Fujimoto, and H. Mizoguchi, "Development of the reliable high power pulsed carbon dioxide laser system for LPP EUV light source", Proc. SPIE 8322, 832220 (2012) CrossRef D. C. Brandt, I. V. Fomenkov, M. J. Lercel, B. M. La Fontaine, D. W. Myers, D. J. Brown, et al. "Laser produced plasma EUV sources for device development and HVM", Proc. SPIE 8322, 832246 (2012) CrossRef K. M. Nowak, T. Ohta, T. Suganuma, J. Fujimoto, H. Mizoguchi, and A. Sumitani, "CO2 laser drives extreme ultraviolet nano-lithography ? second life of mature laser technology", Opto-Electronics Review 21, 52 (2013). DirectLink K. M. Nowak, T. Ohta, T. Suganuma, J. Fujimoto, and H. Mizoguchi, "Multiline short-pulse solid-state seeded carbon dioxide laser for extreme ultraviolet employing multipass radio frequency excited slab amplifier", Opt. Lett. 38, 881 (2013). CrossRef K. M. Nowak, T. Ohta, T. Suganuma, T. Yokotsuka, J. Fujimoto, H. Mizoguchi, and A. Endo, "Spectral characteristics of quantum-cascade laser operating at 10.6 ?m wavelength for a seed application in laser-produced-plasma extreme UV source", Opt. Lett. 37, 4765 (2012). CrossRef K. M. Nowak, T. Ohta, T. Suganuma, T. Yokotsuka, J. Fujimoto, and H. Mizoguchi, "Wavefront measurement of single-mode quantum cascade laser beam for seed application in laser-produced plasma extreme ultraviolet system", Opt. Lett. 37, 4886 (2012). CrossRef

Frequency response of microcantilevers immersed in gaseous, liquid, and supercritical carbon dioxide

The frequency response of ferromagnetic nickel microcantilevers with lengths ranging between 200μm and 400μm immersed in gaseous, liquid and supercritical carbon dioxide (CO2) was investigated. The resonant frequency and the quality factor of the cantilever oscillations in CO2 were measured for each cantilever length in the temperature range between 298K and 323K and the pressure range between 0.1MPa and 20.7MPa. At a constant temperature, both the resonant frequency and the quality factor were found to decrease with increasing pressure as a result of the increasing CO2 density and viscosity. Very good agreement was found between the measured cantilever resonant frequencies and predictions of a model based on simplified hydrodynamic function of a cantilever oscillating harmonically in a viscous fluid valid for Reynolds numbers in the range of [1;1000] (average deviation of 2.40%). At high pressures of CO2, the experimental Q-factors agreed well with the predicted ones. At low CO2 pressures, additional internal mechanisms of the cantilever oscillation damping caused lowering of the measured Q-factor with respect to the hydrodynamic model predictions.