V3 Band Research Articles

MIPAS observations of ozone in the middle atmosphere

Abstract. In this paper we describe the stratospheric and mesospheric ozone (version V5r_O3_m22) distributions retrieved from MIPAS observations in the three middle atmosphere modes (MA, NLC, and UA) taken with an unapodized spectral resolution of 0.0625 cm−1 from 2005 until April 2012. O3 is retrieved from microwindows in the 14.8 and 10 µm spectral regions and requires non-local thermodynamic equilibrium (non-LTE) modelling of the O3 v1 and v3 vibrational levels. Ozone is reliably retrieved from 20 km in the MA mode (40 km for UA and NLC) up to ∼ 105 km during dark conditions and up to ∼ 95 km during illuminated conditions. Daytime MIPAS O3 has an average vertical resolution of 3–4 km below 70 km, 6–8 km at 70–80 km, 8–10 km at 80–90, and 5–7 km at the secondary maximum (90–100 km). For nighttime conditions, the vertical resolution is similar below 70 km and better in the upper mesosphere and lower thermosphere: 4–6 km at 70–100 km, 4–5 km at the secondary maximum, and 6–8 km at 100–105 km. The noise error for daytime conditions is typically smaller than 2 % below 50 km, 2–10 % between 50 and 70 km, 10–20 % at 70–90 km, and ∼ 30 % above 95 km. For nighttime, the noise errors are very similar below around 70 km but significantly smaller above, being 10–20 % at 75–95 km, 20–30 % at 95–100 km, and larger than 30 % above 100 km. The additional major O3 errors are the spectroscopic data uncertainties below 50 km (10–12 %) and the non-LTE and temperature errors above 70 km. The validation performed suggests that the spectroscopic errors below 50 km, mainly caused by the O3 air-broadened half-widths of the v2 band, are overestimated. The non-LTE error (including the uncertainty of atomic oxygen in nighttime) is relevant only above ∼ 85 km with values of 15–20 %. The temperature error varies from ∼ 3 % up to 80 km to 15–20 % near 100 km. Between 50 and 70 km, the pointing and spectroscopic errors are the dominant uncertainties. The validation performed in comparisons with SABER, GOMOS, MLS, SMILES, and ACE-FTS shows that MIPAS O3 has an accuracy better than 5 % at and below 50 km, with a positive bias of a few percent. In the 50–75 km region, MIPAS O3 has a positive bias of ≈ 10 %, which is possibly caused in part by O3 spectroscopic errors in the 10 µm region. Between 75 and 90 km, MIPAS nighttime O3 is in agreement with other instruments by 10 %, but for daytime the agreement is slightly larger, ∼ 10–20 %. Above 90 km, MIPAS daytime O3 is in agreement with other instruments by 10 %. At night, however, it shows a positive bias increasing from 10 % at 90 km to 20 % at 95–100 km, the latter of which is attributed to the large atomic oxygen abundance used. We also present MIPAS O3 distributions as function of altitude, latitude, and time, showing the major O3 features in the middle and upper mesosphere. In addition to the rapid diurnal variation due to photochemistry, the data also show apparent signatures of the diurnal migrating tide during both day- and nighttime, as well as the effects of the semi-annual oscillation above ∼ 70 km in the tropics and mid-latitudes. The tropical daytime O3 at 90 km shows a solar signature in phase with the solar cycle.

Temperature-scanning saturation cavity ring-down spectrometry for Doppler-free spectroscopy.

Saturation cavity ring-down spectroscopy (SCRDS) is a powerful Doppler-free spectroscopy means for measuring absolute frequencies of transitions at the ultra-low uncertainties. We report in this paper a simple way to implement it by temperature scanning the cavity length, which circumvents the need for a complex optical cavity-length stabilization system based upon a piezoelectric actuator (PZT). To demonstrate this approach, the absolute frequencies of the two transitions, R6F1 of the 2v3 and Q9A1 of the 2v2 + v3 bands, of 12CH4, are determined to be 182 185 269.362(20) MHz and 182 187 617.543(39) MHz. The accuracy of measurements is improved by about 3-4 orders of magnitude when compared to those obtained with conventional spectroscopic methods.

Tuning magnetic and high frequency dielectric behavior in Li-Zn ferrites by Ho doping

In the present study, the impact of holmium (Ho) substitution on structural, spectral, dielectric and magnetic behavior of Li1.2Zn0.4HoxFe2−xO4 (0.00 ≤ x ≤ 0.15) ferrites was investigated. The development of spinel phase and structural changes induced by Ho doping were confirmed by X-ray diffraction. The accommodation of Ho ions into spinel lattice was restricted for x ≥ 0.06 as indicated by ortho phase (HoFeO3) traces. The decrease in lattice parameter (a) was attributed to the segregation of Ho ions on grain boundaries. FTIR spectra featured two intrinsic vibrational bands v1 (617cm−1) and v2 (488cm−1) for x = 0 due to tetrahedral and octahedral vibrations respectively. The compositional dependence of force constants and bond lengths has explained on the basis of cations distribution and oxygen-cation bond distances of respective sites. The addition of Ho ions decreased the saturation magnetization and optimized the coercivity from 59 to 335Oe, proposing these ferrites for magnetic recording media. Dielectric results for the entire range of frequency (1MHz to 3GHz) revealed that ac conductivity increased from 3.5 × 105 to 1.8 × 106 (Ω-cm)−1 up to x = 0.09 and then it decreased slightly for x = 0.12. The effective contribution of grain-interior mechanism to dielectric behavior was confirmed by complex impedance study. The results of dielectric studies displayed that Ho doped lithium ferrites are suitable low loss potential materials for high frequency based applications.

Raman Spectra of Nitrogen, Carbon Dioxide, and Hydrogen in a Methane Environment

Changes in the Raman spectra of N2, H2, and CO2 are studied in the range of 200–3800 cm–1 depending on the concentration of surrounding CH4 molecules at a fixed medium pressure of 25 atm and temperature of 300 K. It has been found that changes in the spectral characteristics of purely rotational H2 lines in a CH4 medium are negligible, while the Q-branches of the v1/2v2 Fermi dyad in СO2 become narrower and wavenumbers of its high-frequency component and v1 band of N2 decrease. In addition, under these conditions, the ratio of intensities of the CO2 Fermi dyad Q-branch varies in proportion to the concentration of surrounding molecules of CH4. The obtained data will be used in diagnosing the composition of natural gas using Raman spectroscopy.

Experimental Study of Broadening Coefficients for the v3 Band of CO by Tunable Diode Laser Spectroscopy

A diode laser sensor based on absorption spectroscopy is developed for measurement of self-broadening coefficients for the three lines of v3 band of CO at high temperature. the spectra of CO at 6390.8152 cm-1, 6393.1767 cm-1 and 6395.4312 cm-1 at temperatures ranging from 323K to 873K with different pressures are recorded. The line widths are acquired by the line shape fittings based on Voigt function, and the collitional broadening coefficients and temperature dependences of the three lines are also derived.

In situ Fourier Transform Infrared Spectroscopy Diagnostic for Characterization and Performance Test of Catalysts

The present work establishes a systematic approach based on the application of in-situ Fourier transform infrared spectroscopy (FTIR) for the investigation of the crystal structure, thermal stability, redox behavior (temperature-programmed reduction/temperature-programmed re-oxidation) as well as the catalytic properties of Co3O4 thin films. The syntheses of Co3O4 were achieved by chemical vapor deposition in the temperature range of 400–500 °C. The structure analysis of the as-prepared material revealed the presence of two prominent IR bands peaking at 544 cm−1 (v1) and 650 cm−1 (v2) respectively, which originate from the stretching vibrations of the Co−O bond, characteristic of the Co3O4 spinel. The lattice stability limit of Co3O4 was estimated to be above 650 °C. The redox properties of the spinel structure were determined by integrating the area under the emission bands v1 and v2 as a function of the temperature. Moreover, Co3O4 has been successfully tested as a catalyst towards complete oxidation of dimethyl ether below 340 °C. The exhaust gas analysis during the catalytic process by in situ absorption FTIR revealed that only CO2 and H2O were detected as the final products in the catalytic reaction. The redox behavior suggests that the oxidation of dimethyl ether over Co3O4 follows a Mars-van Krevelen type mechanism. The comprehensive application of in situ FTIR provides a novel diagnostic tool in characterization and performance test of catalysts.

Rapid identification of pearl powder from Hyriopsis cumingii by Tri-step infrared spectroscopy combined with computer vision technology

Pearl powder, an important raw material in cosmetics and Chinese patent medicines, is commonly uneven in quality and frequently adulterated with low-cost shell powder in the market. The aim of this study is to establish an adequate approach based on Tri-step infrared spectroscopy with enhancing resolution combined with chemometrics for qualitative identification of pearl powder originated from three different quality grades of pearls and quantitative prediction of the proportions of shell powder adulterated in pearl powder. Additionally, computer vision technology (E-eyes) can investigate the color difference among different pearl powders and make it traceable to the pearl quality trait–visual color categories. Though the different grades of pearl powder or adulterated pearl powder have almost identical IR spectra, SD-IR peak intensity at about 861cm−1 (v2 band) exhibited regular enhancement with the increasing quality grade of pearls, while the 1082cm−1 (v1 band), 712cm−1 and 699cm−1 (v4 band) were just the reverse. Contrastly, only the peak intensity at 862cm−1 was enhanced regularly with the increasing concentration of shell powder. Thus, the bands in the ranges of (1550–1350cm−1, 730–680cm−1) and (830–880cm−1, 690–725cm−1) could be exclusive ranges to discriminate three distinct pearl powders and identify adulteration, respectively. For massive sample analysis, a qualitative classification model and a quantitative prediction model based on IR spectra was established successfully by principal component analysis (PCA) and partial least squares (PLS), respectively. The developed method demonstrated great potential for pearl powder quality control and authenticity identification in a direct, holistic manner.

Geothermometry and geobarometry of overpressured lower Paleozoic gas shales in the Jiaoshiba field, Central China: Insight from fluid inclusions in fracture cements

The Wufeng-Longmaxi organic-rich shales host the largest shale gas fields of China. This study examines sealed fractures within core samples of the Wufeng-Longmaxi shales in the Jiaoshiba shale gas field in order to understand the development of overpressures (in terms of magnitude, timing and burial) in Wufeng-Longmaxi shales and thus the causes of present-day overpressure in these Paleozoic shale formations as well as in all gas shales. Quartz and calcite fracture cements from the Wufeng-Longmaxi shale intervals in four wells at depth intervals between 2253.89 m and 3046.60 m were investigated, and the fluid composition, temperature, and pressure during natural fracture cementation determined using an integrated approach consisting of petrography, Raman spectroscopy and microthermometry. Many crystals in fracture cements were found to contain methane inclusions only, and aqueous two-phase inclusions were consistently observed alongside methane inclusions in all cement samples, indicating that fluid inclusions trapped during fracture cementation are saturated with a methane hydrocarbon fluid. Homogenization temperatures of methane-saturated aqueous inclusions provide trends in trapping temperatures that Th values concentrate in the range of 198.5 °C–229.9 °C, 196.2 °C-221.7 °C for quartz and calcite, respectively. Pore-fluid pressures of 91.8–139.4 MPa for methane inclusions, calculated using the Raman shift of C-H symmetric stretching (v1) band of methane and equations of state for supercritical methane, indicate fluid inclusions trapped at near-lithostatic pressures. High trapping temperature and overpressure conditions in fluid inclusions represent a state of temperature and overpressure of Wufeng-Longmaxi shales at maximum burial and the early stage of the Yanshanian uplift, which can provide a key evidence for understanding the formation and evolution of overpressure. Our results demonstrate that the main cause of present-day overpressure in shale gas deposits is actually the preservation of moderate-high overpressure developed as a result of gas generation at maximum burial depths.

Structural and Dielectric Properties of Bismuth Doped Cobalt Nano Ferrites Prepared by Sol-Gel Auto Combustion Method

The present study is focused on the preparation of a series of Bismuth doped CoFe2O4 (CFO) nanoparticles and its structural and dielectric properties. The CFO particles having chemical composition CoBixFe2-xO4 (where x = 0.0, 0.1, 0.5) has been synthesized using sol-gel auto combustion method. Phase formation study of the prepared samples is carried out using X -ray diffraction (XRD) technique. It reveals single phase spinel structure having space group Fd3m. The two absorption bands v1 and v2 are observed in Fourier transform infrared spectroscopy (FTIR) spectra corresponding to the tetrahedral and octahedral sites, which show mark of spinel structure of the samples. Morphological study is carried out using Field Emission Scanning Electron Microscope (FESEM) and Transmission Electron Microscopy (TEM) which revealed that the particle size obtained is around 40 nm to 120 nm. In addition, phase formation has been confirmed from the analysis of Raman spectra. Different types of conduction mechanism of the charge carriers have been analysed with DC resistivity and AC impedance measurement at room temperature. Results demonstrate the presence of dielectric relaxation, which is found to be of non-Debye type.

Properties of lithium under hydrothermal conditions revealed by in situ Raman spectroscopic characterization of Li2O-SO3-H2O (D2O) systems at temperatures up to 420 °C

Lithium (Li) is an important component of hydrothermal fluids, especially submarine hydrothermal fluids. Investigation of the species and ion complexation of Li+ at elevated temperature and pressure can improve our knowledge on the behavior of Li under hydrothermal conditions. In this study, in situ optical and Raman spectroscopic experiments were conducted on the Li2SO4-H2SO4-H2O system and its D2O analogue at temperatures≤420°C. An unexpected liquid-liquid phase separation (immiscibility) was observed at temperatures above 336.5°C; the aqueous phase was separated into a sulfate-rich heavy liquid phase and a sulfate-poor light liquid phase at vapor-saturation pressures. The liquid-liquid phase separation temperature decreased as the Li2SO4 concentration increased in dilute solutions (≤1.25 m), increased as the Li2SO4 concentration increased in concentrated solutions (>1.25 m), and exhibited a lower critical solution temperature (LCST) at ~336.5°C. The presence of excess H2SO4 (or D2SO4) increased the liquid-liquid phase separation temperature at a constant Li2SO4 concentration. Liquid-liquid phase separation is common in organic-bearing solutions, and LCST is considered to be a macro-scale property of polymer solutions, indicating complicated ion pairing between Li+ and SO42− at high temperature. In situ Raman spectra of the v1(SO42−) band indicated the presence of “free” SO42−, LiSO4−, possible Li2SO40 and other poly-ion associations. The Li+-SO42− association increased with increasing temperature at a constant Li2SO4 concentration. These results indicate that Li+ can form contact ion pairs with ligands despite its strong hydration tendency.In submarine hydrothermal systems, various contact ion pairs should be important Li species during the high-temperature leaching of Li from basalts (e.g., >200°C). The formation of strong and various Li+-SO42− pairs can enhance the leaching of Li because the mobility and diffusion of the Li+-SO42− complex has been reported to be stronger than that of “free” ions. During the low-temperature (e.g., <150°C) uptake of Li+ into secondary minerals (e.g., clays), free Li+ and outer-sphere ion pairs are the dominant Li+ species. Contact ion pairs are also important Li species during the hydrothermal alteration/precipitation of Li-rich minerals in pegmatite systems. Moreover, liquid-liquid phase separation was found to play important roles in the formation of low-temperature minerals (e.g., calcite). However, similar crystallization pathways have rarely been documented for inorganic systems under high temperatures. Anhydrous Li2SO4 was observed to precipitate within the dense liquid phase at ≥360°C in 1.5 m Li2SO4, confirming that the immiscible dense liquid phase can serve as a precursor for the crystallization of sulfates and other minerals under hydrothermal conditions. The possible processes for the dense-liquid-based crystallization by particle attachment can be summarized as (1) strong and reversible ion association induces liquid-liquid phase separation, (2) nucleation and crystallization within the dense liquid phase, and (3) continued growth on the surface of early formed solid phase. Submarine hydrothermal fluids often contain low-dielectric components such as methane and other organic components, which lower the dielectric constant of hydrothermal fluids and promote ion association. Therefore, liquid-liquid phase separation may occur in submarine hydrothermal fluids and can play important roles in the precipitation of sulfates and other minerals.

Raman investigation on the behavior of parasibirskite CaHBO3 at high pressure

Knowledge about the stability of hydrous borates and borosilicates at high pressures are of critical importance to our understanding on the boron geochemical cycle. Raman spectroscopic measurements of parasibirskite CaHBO3, containing the [BO2(OH)] groups, have been made to pressures up to 5.4GPa. The Raman data show that a progressive structural evolution from ambient pressure to 5.4GPa can be accounted for by the same monoclinic phase P21/m, where the splitting of several Raman bands observed at some pressures is interpreted as the effect of the complex disordering in the H-bond network that has bifurcated H-bonds and ½–occupied H sites. There is no unambiguous evidence for phase transition to the ordered P21 monoclinic phase predicted by first-principles calculations at T=0K (W. Sun et al., Can. Miner., 2011). On the contrary, the disordering of parasibirskite, evidenced by the widening and attenuating Raman spectra, increases markedly at high pressures above 4.5GPa that results in incipient amorphization.Comparison of theoretical (lattice-dynamical) and experimental Raman spectra allows the reliable interpretation of almost all observed bands. The strongest symmetric B-O stretching band v1 at the wavenumber 908cm−1, which is split into a doublet at high pressures, exhibits a shift rate of 4.22cm−1/GPa for the main component.

Sensitivity to electron-to-proton mass ratio variation from 12C2H2 rovibrational transitions to v1 + v3 and v1 + v2 + v4 + v5 interacting levels

Calculations of the sensitivity to a variation of the electron-to-proton mass ratio μ for 12C2H2 transitions of the v1+v3 and v1+v2+v4+v5 bands in the spectral region at 1.5μm are presented. They account for the Fermi and l-type rotation and vibration resonances of the excited states. The frequency splittings between near resonant transitions, arising from a cancellation of effective rotational intervals with frequency shifts associated to the vibrational band origin, the anharmonicity and the rotation-vibration interactions, have sensitivity coefficients to a variation of μ of both signs in the range of 10–103. The measurements of temporal drifts of frequency splittings against the Cs frequency standard have the potential to better constrain a variation of μ comparing to that of other fundamental constants. The systematic frequency shifts for frequency splittings are discussed for experimental setups based on intracavity saturated absorption spectroscopy and the constraint of a measurement of a fractional variation of μ is projected at 10−10 level.

Calculating 14N16O2 spectral line parameters in an infrared range: A comparison of “global” and “local” effective operator methods

Nitrogen dioxide, 14N16O2, line positions and intensities calculated by us based on a “local” effective operator method are compared to the recent results of the “global” calculation. The comparison was made for theoretical absorption coefficients in the spectral range of 600–3700cm−1 using the measured data taken from the Pacific Northwest National Laboratory. In order to conduct the calculations, empirical parameters of the effective rotational Hamiltonian of the twenty-one vibrational states were applied from the most recent experimental works. The second order parameters of the dipole moment function of 14N16O2 were determined for the first time. The “local” line list in this research consists of one hundred and four bands and includes the line intensities of the v1+v2+v3 band of 14N16O2 that have not yet been investigated in the literature. Among these bands, only eleven bands are included in HITRAN2012. The reasons behind the disagreements between the theoretical and measured absorption coefficients of 14N16O2 are discussed.

Visual and in situ Raman spectroscopic observations of the liquid–liquid immiscibility in aqueous uranyl sulfate solutions at temperatures up to 420 °C

The phase behaviors of aqueous UO2SO4 solutions were investigated in situ with a microscope and a Raman spectrometer at temperatures from 25 to 420°C. Results show that aqueous UO2SO4 solution separated into UO2SO4-rich (Urich) and UO2SO4-poor (Upoor) liquid phases coexisted with a vapor phase at ≥285.8±0.5°C. Both visual and Raman spectroscopic investigations suggest that a reversible strong UO22+–SO42− association was responsible for the liquid–liquid immiscibility in aqueous UO2SO4 solutions. Main evidences were summarized as: (1) the liquid–liquid phase separation temperature decreases with increasing UO2SO4 concentration up to 0.54mol/kg, and then increased at greater concentrations, characterizing a lower critical solution temperature (LCST) at 285.8°C±0.5°C. LCST is commonly accepted as a diagnostic feature of polymer solutions; (2) analyses of the shapes of the Raman spectra of v1(UO22+) and v1(SO42−) bands show that the UO22+–SO42− association becomes stronger at elevated temperatures, especially in the immiscible Urich phase; and (3) with increasing temperature, the Urich phase becomes more concentrated, whereas the Upoor phase becomes more dilute, indicating that the hydration of UO22+ and SO42− cannot be maintained in the Urich phase. Destruction of the hydration spheres of UO22+ and SO42− further favors the ion association in the Urich phase. These results are important for describing similar sulfate solutions at elevated temperatures, especially under supercritical conditions.

Line intensities and temperature-dependent line broadening coefficients of Q-branch transitions in the v2 band of ammonia near 10.4 μm

We report measured line intensities and temperature-dependent broadening coefficients of NH3 with Ar, N2, O2, CO2, H2O, and NH3 for nine sQ(J,K) transitions in the ν2 fundamental band in the frequency range 961.5–967.5cm−1. This spectral region was chosen due to the strong NH3 absorption strength and lack of spectral interference from H2O and CO2 for laser-based sensing applications. Spectroscopic parameters were determined by multi-line fitting using Voigt lineshapes of absorption spectra measured with two quantum cascade lasers in thermodynamically-controlled optical cells. The temperature dependence of broadening was measured over a range of temperatures between 300 and 600K. These measurements aid the development of mid-infrared NH3 sensors for a broad range of gas mixtures and at elevated temperatures.

N2- and (H2+He)-broadened cross sections of benzene (C6H6) in the 7–15 µm region for the Titan and jovian atmospheres

In support of atmospheric remote sensing of Titan and jovian planets, we measured absorption cross sections of benzene (C6H6) in the 7–15µm region at temperatures between 235K and 297K. For this, high-resolution laboratory spectra of C6H6 were obtained using two cold cells (80cm and 2.07cm path length) configured to a high resolution Fourier-transform infrared (FT-IR) spectrometer, Bruker IFS-125HR, at the Jet Propulsion Laboratory (JPL). The spectrum sets include 15 pure and 15 N2-broadened benzene spectra in the 630–1534cm−1 region, along with four additional spectra broadened by an H2(85%) and He(15%) gas mixture for the 630–740cm-1 region. From these spectra, temperature dependent benzene cross sections were obtained for gas phase benzene in the presence of N2 and (H2+He) at ambient pressures and temperatures down to 235K.In addition, we generated two independent sets of pseudolines: one of N2-broadened benzene for Titan and the other of (H2+He)-broadened benzene for jovian planets. It is shown that the benzene pseudolines can reproduce the observed features to ∼ 5% in transmittance, including the continuum-like absorption formed by numerous overlapping weak and hot band transitions. Based on the pseudoline parameters, the integrated band intensities at 296K for the three strongest bands in the region were measured to be 177.0(73), 14.0(10), 27.2(9)×10−17cm−1/(molecule·cm−2) in the region of v4 at 674cm−1, v14 at 1038.267, and v13 at 1483.985cm−1, respectively, from the combined set of pure and N2-broadened benzene spectra. For the (H2+He) mixture-broadened benzene spectra, the integrated band intensity for v4 band in the 630–735cm−1 region was measured to be 168.8(17)×10−17cm−1/(molecule·cm−2) at 296K, which is in agreement with the intensity derived from the N2-broadened benzene spectra within the combined measurement uncertainties. The results from this work show an excellent agreement (2%) with one of the latest experimental studies by Rinsland et al. (2008). Furthermore, additional characteristics carried by the pseudolines approach are discussed. Finally, we provide the two sets of pseudo line list (PLL) as electronic supplements.

Structural and functional connectivity between the lateral posterior-pulvinar complex and primary visual cortex in the ferret.

The role of higher-order thalamic structures in sensory processing remains poorly understood. Here, we used the ferret (Mustela putorius furo) as a novel model species for the study of the lateral posterior (LP)-pulvinar complex and its structural and functional connectivity with area 17 [primary visual cortex (V1)]. We found reciprocal anatomical connections between the lateral part of the LP nucleus of the LP-pulvinar complex (LPl) and V1. In order to investigate the role of this feedback loop between LPl and V1 in shaping network activity, we determined the functional interactions between LPl and the supragranular, granular and infragranular layers of V1 by recording multiunit activity and local field potentials. Coherence was strongest between LPl and the supragranular V1, with the most distinct peaks in the delta and alpha frequency bands. Inter-area interaction measured by spike-phase coupling identified the delta frequency band being dominated by the infragranular V1 and multiple frequency bands that were most pronounced in the supragranular V1. This inter-area coupling was differentially modulated by full-field synthetic and naturalistic visual stimulation. We also found that visual responses in LPl were distinct from those in V1 in terms of their reliability. Together, our data support a model of multiple communication channels between LPl and the layers of V1 that are enabled by oscillations in different frequency bands. This demonstration of anatomical and functional connectivity between LPl and V1 in ferrets provides a roadmap for studying the interaction dynamics during behaviour, and a template for identifying the activity dynamics of other thalamo-cortical feedback loops.

An equation for determining methane densities in fluid inclusions with Raman shifts

Raman shift of the C–H symmetric stretching band (v1) of methane can be used to calculate the pressure and density of methane in fluid inclusions. However, previous numerical functions for Raman band shifts and methane density are only suitable for methane with densities lower than 0.3g/cm3. In this study, Raman shifts for pure CH4 were systematically measured at 25°C and pressures up to 150MPa. Parameters of the long range attractive forces were fitted, and Raman shifts of CH4 were calculated with hard sphere model for density up to 0.55g/cm3. Based on experimental data and theoretical calculation, a unified equation was established to calculate the density of methane gas from Raman shifts over a wide density ranges up to 0.55g/cm3:D=vd−vo=211.3ρ4−73.238ρ3+24.477ρ2−29.0632ρwhere ρ represents the density of methane in g/cm3; D(cm-1)is the difference between the measured peak position of methane in the fluid inclusion (vd) and the known peak position of methane at quite low density (vo). The equation will work regardless of which machine the measurements of Raman shifts are done on, as long as the user knows or finds the zero-density peak position.

Shock tube ignition delay times and methane time-histories measurements during excess CO2 diluted oxy-methane combustion

The combustion of methane in air results in large amounts of CO2 and NOX emissions. In order to reduce the NOX emissions, one possible solution is the oxy-methane combustion with large CO2 dilution so that the combustion products can be reduced mainly to CO2 and H2O. However, there are very few studies on the chemical kinetics of oxy-methane combustion in a CO2 diluted environment. In this study, methane time-histories, CH* emission profiles, and pressure time-histories measurements were conducted behind reflected shock waves to gain insight into the effects of CO2 dilution of the gas mixtures on the ignition of methane. The measurements were carried out for mixtures of CH4, CO2 and O2 in argon bath gas at temperatures of 1577–2144 K, pressures of 0.53–4.4 atm, equivalence ratios (Φ) of 0.5, 1, and 2, and CO2 mole fractions (XCO2) of 0, 30, and 60%. The laser absorption measurements were conducted using a continuous wave distributed feedback interband cascade laser (DFB ICL) centered at 3403.4 nm. The results showed the decrease of activation energy and the increase of ignition delay time as the amount of CO2 dilution was increased. However, the changes were minor and within the experimental uncertainties of the measurements. Also, the results were compared to the predictions of two different natural gas mechanisms: GRI 3.0 and AramcoMech 1.3 mechanisms. In general the predictions were reasonable when compared to the experimental data; however, there were discrepancies at some conditions. Three different influences of CO2 addition to the argon bath gas in regards to chemistry, collision efficiencies, and heat capacities were examined. In addition, the present study included experimentally obtained correlations for absorption cross sections of methane for its P(8) line in the v3 band in argon bath gas with and without carbon-dioxide dilutions at temperatures between 1200 < T < 2000 K and pressures between 0.7 < P < 1.2 atm.

Linear Trends and Closures of 10-yr Observations of AIRS Stratospheric Channels

Abstract The Atmospheric Infrared Sounder (AIRS) level-1b radiances have been shown to be well calibrated (~0.3 K or higher) and have little secular drift (~4 mK yr−1) since operation started in September 2002. This paper investigates the linear trends of 10 years (2003–12) of AIRS global-mean radiances in the CO2 v2 band that are sensitive to emissions from the stratosphere (stratospheric channels). AIRS lower-stratospheric channels have a cooling trend of no more than 0.23 K decade−1 whereas the midstratospheric channels consistently show a statistically significant cooling trend as large as 0.58 K decade−1. The 95% confidence interval for the trend is ~±0.20 K decade−1. Two sets of synthetic AIRS radiances are computed using the principal component–based radiative transfer model (PCRTM), one based on a free-running GFDL Atmospheric Model, version 3 (AM3), over the same period and one based on ERA-Interim. The GFDL AM3 simulations overestimate the cooling trends in the mid- to upper-stratospheric channels but slightly underestimate them in the lower-stratospheric channels. The synthetic radiances based on ERA-Interim, however, have statistically significant positive trends at virtually all stratospheric channels. This confirms the challenge to the GCM modeling and reanalysis community to create a better simulation or assimilation of the stratospheric climate. It is shown that the linear trends in AIRS radiances can be reproduced to a large extent by the spectral radiative kernel technique and the trends from the AIRS L2 temperature retrievals and from the change of CO2. This suggests a closure between AIRS L1 radiances and L2 retrievals and the potential merit of AIRS data in studies of stratosphere changes.