Log Pa Research Articles

The role of deformation on the early crystallization and rheology of basaltic liquids

This study highlights the rheological variation of magmatic systems during the early crystallization stage, which undergoes very different shear stress. Etna basaltic glass, made from natural rock powder, was used as a starting material. Nine shear rate-controlled experiments were conducted at 1150 °C (below liquidus temperature and undercooling degree ΔT ∼ 40 °C) with shear rates (γ˙) of 0.1, 1 and 10 s−1 using wide-gap concentric cylinder viscometry. Three additional experiments were conducted without spinning the melts (no shear, γ˙= 0 s−1). Run-products were collected after 3, 6 and 9 h. The experiment with the highest shear rate (γ˙=10s−1) showed a brittle failure when viscosity reached the value of 2.90 log (Pa·s) and after ca. 1150s. The measured viscosity matches the shear stress at 7244 Pa, corresponding to the brittle failure in our partly crystallised system at these conditions. After 9 h, the response of the partly crystallised Etna basalt to different deformation rates results in decreasing viscosity from 4.89 to 3.83 and 2.90 (log Pa s) as the γ˙ increases from 0.1 to 1 and 10 s−1, respectively. The main outcome of this study relates to the nucleation and growth of minerals with shear deformation. The deformation-free (γ˙ = 0 s−1) runs show the presence of only two phases: glass and Fe-oxides (Fe-ox) with only a few vol% (1–3) of oxides crystals after 3, 6 and 9 h. The deformation-bearing (γ˙ = 0.1, 1 and 10 s−1) runs show different scenarios: after 3 h, we observed only Fe-ox for a γ˙ of 0.1 s−1 (similar to deformation-free ones). As the shear rate increases to 1 s−1 and 10 s−1, solid phases after 3 h experiments are Fe-ox, plagioclase and clinopyroxene. Crystal growth rate depends on the applied shear rate: the highest rate is 1.1 × 10−6 cm/s and was measured for plagioclase after a 3 h experiment for γ˙ = 10 s−1. At γ˙ = 0.1 s−1, the plagioclase growth rate decreases to 2.70 and 1.35 × 10−6 cm/s as experimental time increases from 6 to 9 h, respectively. The vast range of shear stress and the systematic data obtained in this study are fundamental to deciphering crystallization dynamics suffered by magmas in volcanic reservoirs, dikes, conduits and lavas.

Systemic inflammation mediates environmental polycyclic aromatic hydrocarbons to increase chronic obstructive pulmonary disease risk in United States adults: a cross-sectional NHANES study.

This study explored the relationship between environmental polycyclic aromatic hydrocarbons (PAHs) and Chronic obstructive pulmonary disease (COPD), and identified systemic inflammation as a mediator of the increased risk of COPD from PAHs. Data were obtained from 60,936 middle-aged and older Americans recruited in the National Health and Nutrition Examination Survey 2005-2016. Environmental PAHs were measured in terms of urinary concentrations of PAHs metabolites (NAP: 1-hydroxynaphthalene, FLU: 2-hydroxyfluorene, PA: 1-hydroxyphenanthrene, and PYR: 1-hydroxypyrene). We used multifactor logical analysis to figure out the link between PAHs and COPD, and the non-linear relationship was examined using Restricted cubic spline. Spearman correlation analysis was utilized to analyze the connection between PAHs and systemic immune-inflammation index (SII). The results showed that the COPD population had higher NAP (3.550 vs. 3.282, p < 0.001), FLU (2.501 vs. 2.307, p < 0.001), PA (2.155 vs. 2.082, p = 0.005), and PYR (2.013 vs. 1.959, p = 0.008) levels than non-COPD population. In unadjusted logistics analysis, the risk of COPD with log NAP was higher [OR = 1.461, 95% CI (1.258-1.698), p < 0.001]. Upon taking into account, confounders like sex, age, race, and log NAP still increased a possible COPD risk [OR = 1.429, 95% CI (1.224-1.669), p < 0.001]. Similarly, FLU, PA, and PYR significantly increased the risk of COPD (all OR > 1, p < 0.05), both unadjusted and adjusted. Furthermore, Restricted cubic spline demonstrated a strong link between PAHs levels and COPD risk (p < 0.05). Additionally, a Spearman correlation analysis revealed a favorable association between log FLU and log SII (R = 0.43, p = 0.006), while NAP, PA, and PYR levels were not associated with log SII (all p > 0.05). Ultimately, the mediating effect analysis revealed a mediating effect capacity of 5.34% for the SII-mediated association between FLU and COPD. The findings suggest that the risk of COPD is significantly increased when environmental PAHs exposure is at high levels, and that systemic inflammation may be involved in the process.

Comprehensive study of recycling municipal solid waste incineration fly ash in lightweight aggregate with bloating agent: Effects of water washing and bloating mechanism

Recycling into lightweight aggregate (LWA) by sintering is a promising technology for disposal of municipal solid waste incineration fly ash (FA). In this study, FA and washed FA (WFA) were combined with bentonite and SiC (bloating agent) to make LWA. The performance was comprehensively studied by hot-stage microscopy and laboratory preparation experiments. Water washing and increased FA/WFA improved LWA bloating extent, while shorten the bloating temperature range. Water washing also increased the 1 h-water absorption rate of LWA, making it harder to meet the standard. Excessive FA /WFA usage (70 wt%) will prevent LWA from bloating. For the goal of recycling more FA, mixture with 50 wt% WFA could prepare LWA that meet standard GB/T 17431 at 1140–1160 °C. After water washing, the ratio of Pb, Cd, Zn, and Cu stabilized in LWA increased by 279 %, 410 %, 458 %, and 109 % for 30 wt% FA/WFA addition, and 364 %, 554 %, 717 %, and 697 % for 50 wt% FA/WFA addition, respectively. The change of liquid phase content and viscosity at high temperature were determined using the thermodynamic calculations and chemical compositions. The bloating mechanism was further investigated by integrating these two properties. To obtain accurate results of the bloat viscosity range (2.75–4.44 log Pa·s) for high CaO systems, the composition of the liquid phase should be taken into account. The liquid phase viscosity required for bloating start was proportional to the liquid phase content. With temperature increasing, bloating would end when viscosity drops to 2.75 log Pa·s or liquid phase content reach 95 %. These findings provided further understanding of the heavy metal stabilization during LWA production and the bloating mechanism of high CaO content systems, and could contribute to the feasibility and sustainability of recycling FA and other CaO-rich solid wastes into LWA.

Atomic structure and physical properties of peridotite glasses at 1 bar

Earth’s mantle, whose bulk composition is broadly peridotitic, likely experienced periods of extensive melting in its early history that formed magma oceans and led to its differentiation and formation of an atmosphere. However, the physical behaviour of magma oceans is poorly understood, as the high liquidus temperatures and rapid quench rates required to preserve peridotite liquids as glasses have so far limited their investigation. In order to better characterize the atomic structure and estimate the physical properties of such glasses, we examined the Raman spectra of quenched peridotite melts, equilibrated at 1900 °C ± 50 °C at ambient pressure under different oxygen fugacities (fO2), from 1.9 log units below to 6.0 log units above the Iron-Wüstite buffer. Fitting the spectra with Gaussian components assigned to different molecular entities (Q-species) permits extraction of the mean state of polymerisation of the glass. We find that the proportions of Q1 (0.36–0.32), Q2 (0.50–0.43), and Q3 (0.16–0.23) vary with Fe3+/FeTOT (FeTOT = Fe2+ + Fe3+), where increasing Fe3+/FeTOT produces an increase in Q3 at the expense of Q2 at near-constant Q1. To account for the offset between Raman-derived NBO/T (2.06–2.27) with those determined by assuming Fe2+ exists entirely as a network modifier and Fe3+ a network former (2.10–2.44), ∼2/3 of the ferric iron and ∼90% of the ferrous iron in peridotite glasses must behave as network modifiers. We employ a deep neural network model, trained to predict alkali and alkaline-earth aluminosilicate melts properties, to observe how small variations in the atomic structure of peridotite-like melts affect their viscosity. For Fe-free peridotite-like melts, the model yields a viscosity of ∼ −1.75 log Pa s at 2000 °C, similar to experimental determinations for iron-bearing peridotite melts. The model predicts that changes in the peridotite melt atomic structure with Fe3+/FeTOT yield variations in melt viscosity lower than 0.1 log Pa s, barely affecting the Rayleigh number. Therefore, at the high temperatures typical of magma oceans, at least at 1 bar, small changes in melt structure from variations in oxidation state are unlikely to affect magma ocean fluid dynamics.

Degassing, Crystallization and Rheology of Hawaiitic Lava Flows: the Case of the 1669 AD Eruption of Mount Etna (Italy)

Abstract Understanding lava flow dynamics during major effusive events is of paramount importance in volcanic areas characterized by a high risk of lava invasion. Mount Etna volcano (Sicily, Italy) has a long history of eruptions characterized by the emplacement of kilometer-wide lava fields, which have often reached the distal parts of the volcanic edifice, nowadays the location of numerous population centers. The 1669 eruption was one of the volcano’s most important events in historic times due to the low altitude of the eruptive vent and the high volume of emitted products (607 ± 105 × 106 m3), with lava flows that destroyed numerous villages located along their path. The flows reached the city of Catania, at a distance of &amp;gt;16 km from the emission point. In this work, we investigate the products of the 1669 eruption through geochemical, mineralogical, 2D and 3D textural analyses with the aim of reconstructing the degassing, crystallization and rheological history of the magma and lavas in pre- to post-eruptive conditions. Combining geothermobarometric and hygrometric models allowed us to estimate magmatic water content (4.1 wt.%) before the eruption, whereas the syn-eruptive crystal content (10 vol.% at the onset of flowing) was retrieved through the textural analysis of pyroclasts sampled from the near-vent fallout. Finally, crystallization and degassing occurring at surface conditions were reconstructed using the textural and mineralogical analysis of lavas. Results were integrated in a three-phase (melt + crystal + bubble) rheological model indicating that lava viscosity, at the onset of the eruption, was low enough (&amp;lt;3.51 log Pa s) to permit the development of a complex and extensive lava field. Flows reached numerous kilometers in length, thanks to the joint effects of lava tunneling, delayed crystal nucleation and growth, and the presence (up to 21.35 vol.%) of deformed bubbles. The combination of these processes maintained the high fluidity of the melt suspension, allowing the flow to arrive at considerable distances from the vent. Lastly, the results of this study highlight the necessity of an accurate real-time multi-analytical petrological characterization of active lavas during the monitoring of effusive eruptions, essential for reliable viscosity modeling of advancing flow units and therefore vital in predicting the direction of lava flows, especially in densely populated areas such as the southern flank of Mount Etna.

Exact limit theorems for restricted integer partitions

For a set of positive integers A, let pA(n) denote the number of ways to write n as a sum of integers from A, and let p(n) denote the usual partition function. In the early 40s, Erdős extended the classical Hardy–Ramanujan formula for p(n) by showing that A has density α if and only if log⁡pA(n)∼log⁡p(αn). Nathanson asked if Erdős's theorem holds also with respect to A's lower density, namely, whether A has lower-density α if and only if log⁡pA(n)/log⁡p(αn) has lower limit 1. We answer this question negatively by constructing, for every α>0, a set of integers A of lower density α, satisfyinglim infn→∞log⁡pA(n)log⁡p(αn)≥(6π−oα(1))log⁡(1/α). We further show that the above bound is best possible (up to the oα(1) term), thus determining the exact extremal relation between the lower density of a set of integers and the lower limit of its partition function. We also prove an analogous theorem with respect to the upper density of a set of integers, answering another question of Nathanson.

Pharmacological Characterization of GSK573719 (Umeclidinium): A Novel, Long-Acting, Inhaled Antagonist of the Muscarinic Cholinergic Receptors for Treatment of Pulmonary Diseases

Activation of muscarinic subtype 3 (M3) muscarinic cholinergic receptors (mAChRs) increases airway tone, whereas its blockade improves lung function and quality of life in patients with pulmonary diseases. The present study evaluated the pharmacological properties of a novel mAChR antagonist, GSK573719 (4-[hydroxy(diphenyl)methyl]-1-{2-[(phenylmethyl)oxy]ethyl}-1-azoniabicyclo[2.2.2]octane; umeclidinium). The affinity (Ki) of GSK573719 for the cloned human M1-M5 mAChRs ranged from 0.05 to 0.16 nM. Dissociation of [(3)H]GSK573719 from the M3 mAChR was slower than that for the M2 mAChR [half-life (t1/2) values: 82 and 9 minutes, respectively]. In Chinese hamster ovary cells transfected with recombinant human M3 mAChRs, GSK573719 demonstrated picomolar potency (-log pA2 = 23.9 pM) in an acetylcholine (Ach)-mediated Ca(2+) mobilization assay. Concentration-response curves indicate competitive antagonism with partial reversibility after drug washout. Using isolated human bronchial strips, GSK573719 was also potent and showed competitive antagonism (-log pA2 = 316 pM) versus carbachol, and was slowly reversible in a concentration-dependent manner (1-100 nM). The time to 50% restoration of contraction at 10 nM was about 381 minutes (versus 413 minutes for tiotropium bromide). In mice, the ED50 value was 0.02 μg/mouse intranasally. In conscious guinea pigs, intratracheal administration of GSK573719 dose dependently blocked Ach-induced bronchoconstriction with long duration of action, and was comparable to tiotropium; 2.5 μg elicited 50% bronchoprotection for >24 hours. Thus, GSK573719 is a potent anticholinergic agent that demonstrates slow functional reversibility at the human M3 mAChR and long duration of action in animal models. This pharmacological profile translated into a 24-hour duration of bronchodilation in vivo, which suggested umeclidinium will be a once-daily inhaled treatment of pulmonary diseases.

Updating existing QSAR models: selection and weighting of new data

Computational chemistry and quantitative structure-activity relationships (QSAR) are foreseen to be extensively used in the implementation of the new REACH regulation for chemicals in Europe. However, for some compound groups the data are too few in number to permit both calibration and testing of a new model. Usage and previously developed or updated models are then viable alternatives.Perfluorocarboxylic acids (PFCAs) and fluoroteleomer alcohols (FTOHs) are two groups of environmentally relevant compounds, with unique physical and chemical properties. The subcooled liquid vapour pressure (pL) is one such property, where experimental determinations are limited and far from consistent [1]. Updating is, however, challenging when the new compounds are far outside of the original calibration domain space. But by carefully selecting and weighting only three new compounds, we have been able to update a previously developed general QSAR model [2], to cover the new domain while maintaining predictive performance for the earlier calibration and test data. The optimal weighting scheme was determined from the sample leverages and residuals in the calibration phase [3].The performance of this re-calibrated model greatly surpassed previous modelling attempts [4], when applied to an external test set of two PFCAs and four FTOHs with pL in the range 0.2-200 Pa; with Q2Ext = 0.994 and RMSEP = 0.190 units of log Pa. The domain coverage also increased from 1% to 51%, for 426 perfluoroalkylated compounds selected from the REACH registration list, the PhysProp database, and the OECD 2006 survey [5]. Selection and weighting of new calibration data can thus facilitate the extension and use of existing QSAR models. This investigation was supported by the EU FP7 project CADASTER (grant agreement no. 212668).

Complete gas-phase proton microaffinity analysis of five linear tetraamines containing two ethylenediamine residues

Density functional theory (DFT) and ab initio (Hartree–Fock) calculations employing the 6-31G∗∗ basis set were used to determine gas-phase proton microaffinities ( PA n,i ) of five linear tetraamines with general formula NH 2(CH 2) 2NH(CH 2) n NH(CH 2) 2NH 2 (where n = 2, 3, 4, 5 and 6). The corresponding proton macroaffinities ( PA ¯ n ) were calculated according to our recently established method with and without considering Boltzmann distribution of microspecies. The results showed that there are good correlations between the calculated proton macroaffinities, PA ¯ n , and proton overallaffinities, log PA ¯ ov , of these tetraamines in the gas phase with corresponding protonation macroconstants, log K n , and overall protonation constants, log β 4 , in solution, respectively.

Clinical Evaluation of The Handling Properties of Photo-activated Composite Resin Pastes

The purpose of this investigation was to examine the relationship between measured values (rheological properties) of composite pastes, such as viscosity coefficient, peeling rate and external force (objective measurements), and a favorable property of such pastes discriminated by touch by dentists (subjective measurements). The rheological properties were examined using a balance beam plastometer. The subjective measurements were performed by eighteen young dentists and repeated four times. The subjective measurements related to four characteristics;hardness of paste (A), retention of shape (B), self-bonding properties (C) and release properties from an instrument for filling (D). There was a significant correlation between the log of the external force (log F) and the log of the peeling rate (logν) in all materials (r=0.950~0.997). A moderate correlation in all materials, except Degufill ultra, Heliomolar, Litefil IIA and Silux plus was also found between the log of the coefficient of viscosity (logη) and logν (r=0.870~0.995). The coefficient of correlation obtained from regression lines between the ratios of favorable properties (log PA, log PB and log PD) in the subjective test and log F or logηshowed a good approximation with a quadratic equation.

Global and Local PLS Regression Models to Predict Vapor Pressure

AbstractThe vapor pressure is a key property in determining the distribution and fate of environmentally relevant compounds, but experimental determinations are only available for a limited number of the chemicals in current commercial use. Despite experimental efforts there is a need for estimation methods. The liquid or subcooled liquid vapor pressures at 298.15 K were collected from the literature for a diverse set of 1340 organic compounds. Theoretical molecular descriptors were derived after optimization to low‐energy conformations and used to investigate the performance of global and local Quantitative Structure–Property Relationships (QSPR). A global PLSR model with ten latent variables was found to be optimal. The predictive performance of this model, within the domain of applicability, was estimated at n=420, Q2Ext=0.980, and RMSEP=0.410 (log Pa). This model can be used in conjunction with other estimation models to assess the potential for a long range atmospheric transport.

Three new defined proton affinities for polybasic molecules in the gas-phase: Proton microaffinity, proton macroaffinity and proton overallaffinity

A theoretical study on complete protonation of a series of tetrabasic molecules with general formula N[(CH 2) n NH 2][(CH 2) m NH 2][(CH 2) p NH 2] (tren, pee, ppe, tpt, epb and ppb) is reported. For first time, three kinds of gas-phase proton affinities for each polybasic molecule are defined as: ‘proton microaffinity (PA n, i )’, ‘proton macroaffinity ( PA ¯ n ) ’ and ‘proton overall affinity ( PA ¯ ov )’. The variations of calculated log PA ¯ n in the series of these molecules is very similar to that of their measured log K n . There is also a good correlation between the calculated gas-phase proton macroaffinities and proton overallaffinities with corresponding equilibrium macroconstants and overall protonation constants in solution.

Preliminary Parallaxes of 40 L and T Dwarfs from the US Naval Observatory Infrared Astrometry Program

We present preliminary trigonometric parallaxes and proper motions for 22 L dwarfs and 18 T dwarfs measured using the ASTROCAM infrared imager on the US naval Observatory (USNO) 1.55 m Strand Astrometric Reflector. The results presented here are based on observations obtained between 2000 September and 2002 November; about half of the objects have an observational time baseline of t 1:3 yr and half t 2:0 yr. Despite these short time baselines, the astrometric quality is sufficient to produce significant new results, especially for the nearer T dwarfs. Seven objects are in common with the USNO optical CCD parallax program for quality control and seven in common with the European Southern Observatory 3.5 m New Technology Telescope parallax program. We compare astrometric quality with both of these programs. Relative to absolute parallax corrections are made by employing Two Micron All Sky Survey and/or Sloan Digital Sky Survey photometry for reference-frame stars. We combine USNO infrared and optical parallaxes with the best available California Institute of Technology (CIT) system photometry to determine MJ , MH, and MK values for 37 L dwarfs between spectral types L0 and L8 and 19 T dwarfs between spectral types T0.5 and T8 and present selected absolute magnitude versus spectral type and color diagrams, based on these results. Luminosities and temperatures are estimated for these objects. Of special interest are the distances of several objects that are at or near the L-T dwarf boundary so that this important transition can be better understood. The previously reported early to mid T dwarf luminosity excess is clearly confirmed and found to be present at J, H, and K. The large number of objects that populate this luminosity-excess region indicate that it cannot be due entirely to selection effects. The T dwarf sequence is extended to MJ 16:9 by 2MASS J041519 0935, which, at d 5:74 pc, is found to be the lluminous LOG (L=L )pa

Asymptotic Density and the Asymptotics of Partition Functions

Let A be a set of positive integers with gcd (A) = 1, and let p A (n) be the partition function of A. Let c 0 = π√2/3. If A has lower asymptotic density α and upper asymptotic density β, then lim inf log p A (n)/c 0 √n ≧ √α and lim sup log p A (n)/c 0 √n ≦ √β. In particular, if A has asymptotic density α > 0, then log p A (n) ∼ c0√αn. Conversely, if α > 0 and log p A (n) ∼ c 0 √αn, then the set A has asymptotic density α.

Mechanical properties of TiN thin films investigated using biaxial tensile testing

Mechanical properties of TiN thin films were investigated using bulge test measurements performed on square freestanding membranes. For this purpose, both sides of n type Si(1OO) wafers were first coated by a layer of low stress SiN thin films (thickness t = 465 nm). The square windows of side 2a = 4 mm were then made using standard micromachining techniques to obtain freestanding SiN membranes. The edges of the windows were usually aligned with the [110] directions of the underlying Si wafer in order to make perfect squares bounded by (111) planes. These specimens were then coated by a layer of TiNx (0·84 < x < 1·3), using the rf magnetron sputtering method. Bulge testing was first conducted on an SiN film to determine its proper residual stress and Youngs modulus, which were found to be (σi = 227 ± 15 MPa and E = 225 ± lO GPa respectively. Then the composite membrane made of TiNx together with underlying SiNy was bulged and the related load-displacement variation was measured. Finally, using a simple rule of mixtures formula, the elastic mechanical properties of TiNx coatings were determined. Both the Young s modulus and residual stress increased with bias voltage, N/Ti ratio, and coating density. In contrast, the effect of substrate temperature below 600°C was found to be less significant than that of other parameters. Scanning electron microscopy of cross-sectioned specimens showed that coating growth occurs by the formation of equiaxial nanocrystallites, 10-30 nm in size, leading to columnar morphology beyond a thickness of 100-150 nm. The columns are nearly perpendicular to the film surface. The bulge test results are discussed in terms of coating microstructure and chemical composition determined by means of electron probe microscopy.

Thermochemistry of metal-rich manganese telluride and its role in fuel-clad interactions

Vaporisation of Mn-Te alloys was studied by Knudsen-effusion mass spectrometry. The partial pressures of Te(g) over the two-phase field, Mn-MnTe, were determined in the temperature range 1120–1250 K. Two samples of initial composition of 29.1 and 40.1 at% Te were used in the experiments. The vapour phase consists of Mn(g) and Te(g). Partial pressure-temperature relations for Te(g) were found to follow the equation log( (p) Pa ) = − (16099±285) T(K) +(10.525±0.240) . Mn-rich phase boundary of MnTe was determined from continuous vaporisation experiments starting with a sample from two-phase field Mn + MnTe. The boundary composition was found to be 44.3 ± 0.5 at% Te in the temperature range 1205–1280 K. Enthalpy of the following reactions was obtained: MnTe 0.8( s) / ai Mn( s) + 0.8 Te( g), MnTe 0.8( s) / ai Mn( g) + 0.8 Te( g) and Mn( s) / ai Mn( g). The standard molar enthalpy and Gibbs energy of formation of MnTe 0.8 were arrived at. The tellurium potential which would be required for the formation of MnTe 0.8 in AISI 316 stainless steel was calculated and the possibility of such a telluride formation in the fuel-cladding gap of a mixed-oxide fuel pin is discussed.

Probe-Solute Study of Mesomorphic Polysiloxane (Mepsil) Solvents. Discontinuities in Family Retention Plots That Traverse Phase Transitions

Abstract The GLC method of measurement of activity coefficients γ∞A Liquid-gas partition coefficients KR ο specific retention volumes Vg ο, capacity factors k', and excess thermodynamic properties of mixing of solutes at effective infinite dilution in polymeric solvents is considered. It is argued that while van't Hoff plots of any of the retention parameters can reveal subtle phase transitions exhibited by the solvent (the solutes are used as probes of the state of polymer aggregation), it is impractical to make measurements of most of these variables from the standpoints of both theory and experiment. A new method of characterizing the behavior of probe-solutes with polymeric solvents that is based upon evaluation of the slopes of family plots of log Vg ο against log PA ο is therefore described; where Pg ο is the solute vapor pressure at the column temperature. The ideal slope of such plots is -1, deviations from this value being a measure of departure from solution ideality. Results obtained for plots ...

The effect of small changes in arterial carbon dioxide tension on carotid chemoreceptor activity in the cat.

The hypothesis that the fluctuations in carotid chemoreceptor discharge represent more than a simple proportional response to respiratory oscillations of Pa, CO2 has been examined. Simultaneous recordings of the activity in few- or multi-fibre chemoreceptor preparations of the cut carotid sinus nerve and oscillations of carotid arterial pH have been made in four anaesthetized cats which were paralysed and artificially ventilated at constant frequency. Chemoreceptor activity was averaged over a minimum of twenty consecutive pH cycles and the amplitude of the fluctuations in discharge frequency determined. Using the mean Pa, CO2 obtained from blood-gas analysis and the slope of the relationship between log Pa, CO2 and pH obtained in each cat, the amplitude of the pH oscillations was converted to Pa, CO2 amplitude. This amplitude relative to the mean Pa, CO2 has been compared with the amplitude of the corresponding fluctuation in the chemoreceptor discharge frequency recorded from the carotid sinus nerve (e.s.n.d. amplitude) relative to its mean level. Whereas the Pa, CO2 amplitude was always less than 8% of the mean Pa, CO2, the c.s.n.d. amplitude ranged from 40 to 186% of the mean discharge frequency. C.s.n.d. amplitude was divided by the corresponding Pa, CO2 amplitude to give an index of the sensitivity of the chemoreceptors to Pa, CO2. This sensitivity has been compared with that determined from the mean discharge frequency produced in response to changes in mean Pa, CO2 comparable in magnitude to the Pa, CO2 amplitude. The former sensitivity was usually at least 3 times greater than the latter. Examination of the fluctuations in chemoreceptor discharge frequency in relation to the corresponding pH oscillations revealed that whereas the minimum discharge frequency coincided with the alkaline peak of the pH oscillation (trough of the Pa, CO2 oscillation), the maximum discharge frequency did not invariably coincide with the acid trough of the pH oscillation (peak of the Pa, CO2 oscillation). On 30% of occasions, the maximum discharge frequency was associated with the region of maximum rate of fall of pH (maximum rate of rise of Pa, CO2). It was concluded that fluctuations in the discharge of carotid chemoreceptors cannot be accounted for on the basis of a simple proportional relationship to Pa, CO2. They contain a large rate of change component.

Hypoxic pulmonary vasoconstriction in isolated rat lungs perfused with perfluorocarbon emulsion.

Eight rat lungs were perfused in an in vitro circuit with a blood-PS solution and then with a perfluorocarbon emulsion (perfluorotributylamine, FC-43). With perfusion flow constant, the hypoxic pulmonary vasoconstrictor (HPV) response was measured as changes in pulmonary artery pressure when F1,O2 was changed to 0.1, 0.06, 0.04, 0.03, 0.02 and zero with FI,CO2 of 0.05. The hypoxic response to an FI,O2 of 0.03, with the blood-PSS perfusate, was an increase from baseline pressure of 93.5 +/- 18% and, with the perfluorocarbon perfusate was 67.5 +/- 18%; these values were not significantly different (P greater than 0.2). A stimulus-response relationship was obtained with the FC-43 perfusate by plotting the response as a percentage of the maximum response (R%max) against the logarithm of the alveolar oxygen tension. The equation for the linear portion of the response was R%max = 257.9-140.2 X log (10) PA,O2 and r = 0.78. The PA,O2 corresponding to half of the maximum response (ED50) was 30.4 mmHg. The present study demonstrated that HPV is maintained in isolated rat lungs perfused with an FC-43 emulsion. The stimulus-response relationship as well as the ED50 with the FC-43 is similar to earlier results with blood perfusate. Lung oedema was not found after perfusion with the FC-43 emulsion.

Effect of temperature on the intracellular CO 2 dissociation curve and pH

Mean whole body pH i and pH e were determined at different arterial CO 2 tensions in two groups of dogs maintained at a body temperature of 41.6 and 27.1 °C. From the data HCO − 3, total CO 2 and buffer capacity were calculated for the extracellular and intracellular fluid. The mean regression equations obtained for the hyperthermic group were pH e = −0.792 log Pa CO 2 + 8.531 and pH i = −0.759 log Pa CO 2 + 8.123. For the hypothermic group the following regression equations were obtained: pH e = −0.792 log Pa CO 2 + 8.610 and pH i = −0.759 log Pa CO 2 + 8.308. Total CO 2 and HCO − 3 were appreciably higher in the hypothermic group than in the hyperthermic group. The temperature effect was about 1 % CO 2 content at constant P CO 2 per °C for the ECF and 3 % CO 2 content at constant P CO 2 per °C for the ICF. At a constant CO 2 content ΔpH/Δt was −0.020 for the ECF and −0.037 for the ICF. It was shown that the effect of temperature on the relative alkalinity of the ICF expressed as the OH −/H + ratio would be minimal when the temperature change is done at a constant pH e rather than at a constant total CO 2.